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  2. 2. ACKNOWLEDGEMENT The completion of this undertaking could not have been possible without the assistance of so many people whose names may not all be enumerated. Their contributions are sincerely appreciated and gratefully acknowledged. However, I would like to express my deep appreciation and indebtedness particularly to the following: Mr.Subramani.K & Mr.Ramesh ,R&D dept., for their guidance throughout the programme. Mr.P.S.Manian , for his endless support throughout the training programme. SSN College of Engineering, for giving me the opportunity to undertake the training. To all relatives, friends, and others who in one way or another shared their support, either morally financially and physically, thank you. Above all, the Great Almighty, the author of knowledge and wisdom, for his countless love. Thank you, Avneesh.S.Manian
  5. 5. ABOUT THE COMPANY (TENNECO AUTOMOTIVES INDIA,HOSUR) As a global leader in Ride Performance products , customers look to Tenneco to provide advanced suspension technologies that deliver performance , comfort and the power to differentiate vehicles . The company strives towards achieving a smoother, quieter and safer transportation and it currently holds the  #1 position for aftermarket ride performance products in North America, Europe, and South America.  manufactures 90+ million shocks and struts manufactured globally  $2.5 billion revenue. Markets served: 1. Commercial vehicles 2. Agricultural 3. Construction 4. Passenger car 5. Bus 6. Specialty 7. Military HISTORY Tenneco is one of the world’s largest designers, manufacturers, and marketers of clean air and ride performance product and systems for the automotive, commercial truck and off-highway original equipment and large engine markets, as well as the aftermarket. The company’s history as a stand-alone entity began in 1999, when it emerged from a conglomerate formerly consisting of six businesses -- shipbuilding, packaging, farm and construction equipment, gas transmission, automotive and chemicals. Through various public offerings, sales, spin-offs and mergers beginning in the 1980s, the company divested all of its businesses, leaving Tenneco Automotive as the remaining part of the original company. The automotive entities that remained showcase a rich history that defines Tenneco today. Its earliest business, the predecessor to the Walker emission control business, began in 1888, while the Monroe ride control operations trace back to 1916. With the 1999 spin-off, these venerable businesses took on new life as Tenneco Automotive. In 2005, the company rebranded its name to Tenneco, to better represent the expanding number of markets the company serves. In 2013, the company aligned along its Clean Air and Ride Performance product lines,
  6. 6. creating a distinct strategic approach for each and further supporting the company’s long-term growth. Since 1999, Tenneco has grown significantly, driven primarily by product and geographic expansion. In addition to its automotive original equipment and aftermarket segments, Tenneco now serves customers in the commercial truck and off-highway equipment markets, as well as large engines used in marine and stationary power applications. To support the growth of light vehicle production as well as these new market segments, Tenneco has significantly expanded its global footprint over the last 15 years. Tenneco was one of the first automotive suppliers to establish operations in China and has significantly enhanced its engineering and manufacturing operations throughout the world. Advanced technology is another key driver that has contributed to the company’s growth. Tenneco is a leader in developing clean air solutions that help its customers meet stringent emissions control regulations throughout the world. It was the first company to commercialize diesel particulate filters (DPFs) in Europe in 2000, and today continues to lead the industry with important aftertreatment technologies for gasoline and diesel engines including selective catalytic reduction, advanced mixing technologies, gasoline particulate filters and hot and cold-end exhaust systems. Tenneco’s advanced ride performance technologies deliver comfort, performance and control to differentiate its customers’ vehicles. The company’s portfolio of advanced electronic suspension technologies – known as Monroe Intelligent Suspension – includes both adaptive and semi-active suspension systems. The company’s suite of elastomer products has also experienced significant growth in both the light and commercial vehicle markets.
  7. 7. With the strong heritage of the Monroe and Walker brands, Tenneco’s global aftermarket business is a significant growth driver as well. Tenneco’s aftermarket brands enjoy leading positions in the world’s large and established automotive regions and the company is expanding aggressively in fast-growing markets such as China and India. Fig.2 Global Footprint Map Ride Performance: Tenneco’s Ride Performance productline meets the increasing demand for advanced suspension technologies that enhance vehicle performance.  Productcostleadership  Superior functionality  Advanced technology  Vehicle dynamics/integrated systems expertise  NVH solutions provider
  8. 8. CUSTOMERS Fig .3 Global customers SHOCK ABSORBERS – A GENERAL OVERVIEW WHAT IS RIDE CONTROL? Many things affect vehicles in motion. Weight, weight distribution, speed, road conditions and wind are some of the of the factors that affect how a car rolls down a highway. Under all these variables, however, the vehicles suspension system must continue to provide steering stability with good handling characteristics. And at the same time maximise passenger comfort. Steering stability and passenger comfort are what we mean by a “good ride control”. For a good ride control, the suspension system including the shocks, struts and springs – must all be in good condition. Worn suspension components may reduce vehicle stability and passenger comfort. They may also accelerate wear on other suspension system components, Including tyres. Wear at regular intervals If a car’s tyres are wearing unevenly, or small areas of heavy wear at regular intervals around the tyre (called “cupping”)are evident, worn shock absorbers are probably the cause. Cupping is caused by the tyre bouncing on and off the road as it rolls.
  9. 9. Worn shocks also increase body roll during cornering. This causes rapid wear on the outer edge of the tyre and affects the over steer and under steer handling characteristics of the vehicle. Another cause of tyre wear is incorrect wheel alignment resulting from loose or worn suspension components. Shocks and struts are the key components of the suspension system. Replacing worn or inadequate shocks and struts and thoroughly inspecting the entire suspension system will maintain god vehicle rid control, which provides customer with:  Improved steering stability and passenger comfort  Reduced wear on suspension components and tyres  Improved cornering, ride and predictable handling. WHY ARE SHOCK ABSORBERS IMPORTANT ? Shock absorbers play an important role and often underestimated role in vehicle safety. They optimise vehicle handling, while providing positive steering response and safe braking. As the wheels hit the bumps in the road, energy is transferred into the springs of a car’s suspension. With the worn shock absorbers, this energy causes the spring to oscillate. These oscillations cause the tyre to break their grip on the road, bouncing on and off the road for some time after hitting the initial bump. Tests have shown that if just one shock absorber is worn, a car may need 2 extra metres to stop. This could be the difference between stopping safely and crashing. When braking in an emergency, worn shock absorbers cause the front of the car to nose dive, transferring the weight to the front of the car from the rear. This reduces the tyres grip on the road, causing them to skid, increasing the braking distance. At the same time, the front tyres may momentarily break their grip on the road causing them to yaw and swerve under brake conditions. Both situations greatly increase the possibility of the driver losing control, particularly in wet conditions. The function of a shock absorber is to dampen spring oscillations, maintaining the tyres’ contact with the road, irrespective of the road’s surface. Shock absorbers literally convert the energy of the suspension movement to heat, which is then dissipated into the air through radiation.
  10. 10. Fig. 4 Monroe safety triangle
  11. 11. A BRIEF HISTORY OF SHOCK ABSORBERS The fitting of damping devices to vehicle suspensions followed rapidly on the heels of the arrival of the motor car itself. Since those early days the damper has passed through a century of evolution, the basic stages of which may perhaps be considered as: (1) dry friction (snubbers); (2) blow-off hydraulics; (3) progressive hydraulics; (4) adjustables (manual alteration); (5) slow adaptives (automatic alteration); (6) fast adaptives (‘semi-active’); (7) electrofluidic, e.g. magnetorheological. Historically, the zeitgeist regarding dampers has changed considerably over the years, in roughly the following periods: (1) Up to 1910 dampers were hardly used at all. In 1913, Rolls Royce actually discontinued rear dampers on the Silver Ghost, illustrating just how different the situation was in the early years. (2) From 1910 to 1925 mostly dry snubbers were used. (3) From 1925 to 1980 there was a long period of dominance by simple hydraulics, initially simply constant-force blow-off, then through progressive development to a more proportional characteristic, then adjustables, leading to a mature modern product. (4) From 1980 to 1985 there was excitement about the possibilities for active suspension, which could effectively eliminate the ordinary damper, but little has come of this commercially in practice so far Because of the cost. (5) From 1985 it became increasingly apparent that a good deal of the benefit of active suspension could be obtained much more cheaply by fast auto-adjusting dampers, and the damper suddenly became an interesting, developing, component again. (6) From about 2000, the introduction, on high-price vehicles at least, of controllable magneto rheological dampers. Development of the adaptive damper has occurred rapidly. Although there will continue to be differences between commercial units, such systems are now effective and can be considered to be mature products. Fully active suspension offers some performance advantages, but is not very cost effective for passenger cars. Further developments can then be expected to be restricted to rather slow detail refinement of design, control strategies and production costs. Fast acting control, requiring extra sensors and controls, will continue to be more expensive,
  12. 12. so simple fixed dampers, adjustables and slow adaptive types will probably continue to dominate the market numerically for the foreseeable future. Damper types, which are explained fully later, can be initially classified as (a) dry friction with solid elements; (i) scissor; (ii) snubber; (b) hydraulic with fluid elements; (i) lever-arm; (ii) telescopic. Only the hydraulic type is in use in modern times. The friction type came originally as sliding discs operated by two arms, with a scissoraction, and later as a belt wrapped around blocks, the ‘snubber’. Thebasic hydraulic varieties are lever-arm and telescopic. The lever-arm type uses a lever to operate a vane,
  13. 13. now extinct, or a pair of pistons. Telescopics, now mostcommon, are either double-tube or gas pressurisedsingle-tube.
  14. 14. The early development timetable of dampers thus ran roughly as follows: 1901: Horock patents a telescopic hydraulic unit, laying the foundations of the modern type. 1902: Mors actually builds a vehicle with simple hydraulic pot dampers. 1905: Renault patents an opposed piston hydraulic type, and also patents improvements to Horock’s telescopic, establishing substantially the design used today. 1906: Renault uses the piston type on his Grand Prix racing cars, but not on his production cars. Houdaille starts to develop his vane- type. 1907: Caille proposes the single-lever parallel-piston variety. 1909: A single-acting Houdaille vane type is fitted as original equipment, but this is an isolated success for the hydraulic type, the friction disc type remaining dominant. 1910: Oil damped undercarriages come into use on aircraft. 1915: Foster invents the belt ‘snubber’ which had great commercial success in the USA. 1919: Lovejoy lever-arm hydraulic produced in the USA. 1924: Lancia introduces the double-acting hydraulic unit, incorporated in the front independent pillar suspension of the Lambda. The Grand Prix Bugatti uses preloaded nonadjustable drum brake type. 1928: Hydraulic dampers are first supplied as standard equipment in the USA. 1930: Armstrong patents the telescopic type. 1933: Cadillac ‘Ride Regulator’ driver-adjustable five-position on dashboard. 1934: Monroe begins manufacture of telescopics. 1947: Koning introduces the adjustable telescopic. 1950: Gas-pressurised single-tube telescopic is invented and manufactured by de Carbon. 2001: Magnetorheological high-speed adjustables introduced (Bentley, Cadillac). The modern success of hydraulics over dry friction is due to a combination of factors, including: (1) Superior performance of hydraulics, due to the detrimental effect of dry Coulomb friction which is especially noticeable on modern smooth roads. (2) Damper life has been improved by better seals and higher quality finish on wearing surfaces. (3) Performance is now generally more consistent because of better quality control. (4) Cost is less critical than of old, and is in any case controlled by mass production on modern machine tools.
  15. 15. WHAT ARE SHOCK ABSORBERS? Shock absorbers are as vital a component as your vehicle’s steering system, tyres and brakes, all of which do not function properly when driving with worn shock absorbers. In their simplest form, shock absorbers are hydraulic (oil) pump like devices that help to control the impact and rebound movement of your vehicle’s springs and suspension. Along with smoothening out bumps and vibrations, the key role of the shock absorber is to ensure that the vehicle’s tyres remain in contact with the road surface at all times, which ensures the safest control and braking response from the car. WHAT DO SHOCK ABSORBERS DO? Essentially, shock absorbers do two things. Apart from controlling the movement of springs and suspension, shock absorbers also keep your tyres in contact with the ground at all times. At rest or in motion, the bottom surface of your tyres is the only part of your vehicle in contact with the road. Any time that a tyre's contact with the ground is broken or reduced, your ability to drive, steer and brake is severely compromised. Despite popular belief, shock absorbers do not support the weight of a vehicle.
  16. 16. GAS CHARGED SHOCKS, STRUTS, & REPLACEMENT CARTRIDGES The development of gas charged shock absorbers was a major advance in ride control technology. The advance was to solve ride control problems, which occurred due to an increasing number of vehicles using unibody construction, shorter wheelbases and the increased use of higher tire pressures. COMFORT VS. CONTROL In the past, ride comfort or vehicle control were compromised by the design limits of conventional hydraulics. A shock absorber or strut can provide either a more comfortable ride or greater vehicle control, but not the optimum of both in the same unit. A shock or strut damps excessive vehicle spring motion by the controlled movement of fluid under pressure. Fluid provides the resistance to movement and valving controls the amount of that resistance. Before Monroe gas charged shocks and struts, valve orifices could not be enlarged to increase riding comfort without losing damping effectiveness. So valving was compromised in one of two directions: soft or hard valving.
  17. 17. With soft valving, fluid flows more easily. The result is a smooth ride, but with poor handling - and a lot of roll and sway. When valving is hard, fluid flows less easily. Handling is improved, but the ride can become rough. In the past, ride engineers had to choose between soft or hard valving. And, either comfort or control was compromised. In addition, fluid inside the shock absorber could mix with air and turn into foam. Engineers called this aeration. Because foam compresses, the amount of resistance provided by the fluid was hard to predict. Before the development of Monroe gas charged shocks and struts, other ways to solve these problems had been tried, but had not been totally successful. The gas cell is one solution. It is a plastic envelope of hexasulphafluoride gas, which is installed between the reserve tube and the pressure tube of a two-stage shock absorber. The gas cell fills the air space to reduce aeration. High-pressure gas charged shocks are mono-tube shocks, with fluid and gas in separate chambers in most designs. The gas can be charged to 360 psi. The advanced design of Monroe two-tube gas charged shocks solves many of today's ride control problems by adding a low-pressure charge of nitrogen gas in the reserve tube. With the shock fluid under pressure, aeration is greatly reduced. The gas pressure also provides resistance to fluid entering the reserve tube. This, combined with the large piston bore design on Monroe shocks, provides the extra working capacity needed for lower spring rate suspensions. With Monroe gas charged shocks and struts, you and your customers can enjoy a better ride - plus improved handling. HOW THEY WORK The pressure of the nitrogen in the reserve tube of a Monroe gas charged shock varies from 100 to 150 psi, depending on the amount of fluid in the reserve tube. The gas serves several important functions to improve the ride control characteristics of the shock. One function is to increase the resistance of fluid flow into the reserve tube. This improves valving performance during the compression stroke and also prevents "dumping" into the reserve tube. Another function is to minimize aeration of the unit's hydraulic fluid. The pressure of the nitrogen gas prevents air bubbles or foam from weakening the hydraulic effectiveness of fluid flow through both the piston and base valve systems. Foam affects performance - foam compresses, fluid does not.
  18. 18. A third important function of the gas is to allow Monroe engineers greater flexibility in valving design. In the past, such factors as dumping and aeration forced compromises in design. GAS CHARGING BENEFITS Here are some of the advantages provided by the advanced technology that Monroe gas charged shocks represent. Improved handling When turning a corner or a sharp curve, a vehicle's body tends to lean away from the direction of the turn and then rebounds. This motion is called roll. Excessive roll may cause a loss of control. With gas charged shocks, roll is reduced. Reduced excessive vibration As tires bounce up and down, road roughness is transmitted to the vehicle's body and cargo, causing them to vibrate. Excessive vibration may increase a truck's cost per mile by increasing downtime, reducing tire mileage, reducing vehicle life and lowering resale value. Gas charged shocks control tire motion better than non-gas units, so vibration is reduced. Wider range of control Because gas charged shocks reduce aeration and dumping, they can provide improved performance levels over a wider variety of road conditions. Reduced Aeration Reduced aeration means greater valving range for improved control and a reduction in excessive vibration. Reduced Fade Shocks can lose damping capabilities as they heat up during use, a process called fade'. Gas charged shocks can prevent this loss of performance.
  19. 19. INSPECTING SHOCKS AND STRUTS Car Park Test First check the vehicle's mileage. When a vehicle has just 20,000 km or more, there could be some internal wear and new shocks and struts may be needed. Also, check the manufacturer's recommended service interval in the owner's manual. Remember, a shock absorber provides resistance to bounce, roll or sway, brake dive, and acceleration squat. This means that the shock needs to be checked for each of these -- and the best way to do this is while driving the vehicle. Take the vehicle for a short drive around the parking lot and do a mini-test. You should still be able to tell if there's excessive brake dive, acceleration squat, or roll or sway. Once inside the vehicle, put on the seat belt and begin. Note any excessive vehicle squat as you accelerate: the vehicle should remain fairly stable. Next, apply the brakes and note any dive. Again, the vehicle should remain fairly stable. Try a couple of sharp turns, noting any excessive roll or sway of the vehicle. If you noticed any excessive bounce, roll and sway, brake dive or acceleration squat this could be an indication of shock or strut control loss. This causes excessive suspension movement that could lead to handling problems and premature wear on other suspension components. Tyres - Front and Rear Check for any unusual wear patterns. Indication of uneven tread wear, such as cupping, can be a result of worn shocks and struts. Check Tyres for any physical problems:  Ply separation  Dry rot  Nails Check Tyre size and construction type:  Same size side to side  Same brand and tread pattern  Mix of radial-ply and bias-ply Tyres
  20. 20. Check the Tyre pressure on all four Tyres and adjust to the doorpost specifications or the specifications listed in the owner's manual. The Tyre pressure established by the vehicle manufacturer will provide the best overall vehicle control and comfort. Check the wheels for physical damage. Upper Strut Mount Inspection If the upper strut mount is defective, it may cause noise, steering binding, or allow the upper end of the strut to change position, affecting wheel alignment angles.  Strut mount inspection should start with a road test checking for unusual noise, pulling, or steering binding.  With the vehicle in the shop and the weight on the wheels, rotate the steering wheel from stop to stop while listening for noises or binding. Noise or binding could indicate a defective bearing. Also inspect the rubber portions of the strut mount for cracks or separation of the rubber from the steel. Before raising the vehicle on a hoist, note the position of the strut piston rod. Raise the vehicle and note any change in the position of the mount assembly. A slight downward movement is normal, but any side-to-side movement could indicate a defective mount.  With the wheels off the ground, grip the coil spring as close to the upper strut mount as possible. Push in and out on the strut and spring while watching for movement of the upper end of the strut piston rod. There should be no free movement. If there is excessive movement, the upper strut mount should be replaced. If the visual inspection reveals separation of the rubber portions from the steel strut mount, it should be replaced.
  21. 21.  Complete the inspection after removal of the upper strut mount from the strut assembly. The steering pivot bearing should be checked to ensure smooth and free (but not sloppy) rotation. Again, check the rubber portion to ensure there is no excessive cracking or breakage. Visual Test Along with the road test, be sure to perform a visual test during the inspection. When the vehicle is in the shop, first check the shocks or struts for leakage. This is indicated by oil outside the units. It's important to remember that shocks and struts are hydraulic systems; any leakage indicates the possible need for replacement. Replace All Four Units When you determine that the vehicle has worn or inadequate shocks or struts, recommend that they be replaced. Also, for the best possible ride, recommend they replace all four units at the same time for a balanced ride. Special Needs Units Some drivers may want a better ride or need a special shock because of the way they use their vehicle. So even if a shock is operating properly, it may not meet your needs. Comparison Test Ride Take a comparison test ride.
  22. 22. WHAT SHOCK ABSORBERS DO Let's start our discussion of shock absorbers with one very important point: Despite what many people think, conventional shock absorbers do not support vehicle weight. Instead, the primary purpose of the shock absorber is to control spring and suspension movement. Shock absorbers are basically oil pumps. As shown in Fig. 1, a piston is attached to the end of a piston rod and works against hydraulic fluid in the pressure tube. As the suspension travels through jounce and rebound, the hydraulic fluid is forced through tiny holes - orifices - inside the piston. However, the orifices let only a small amount of fluid through the piston. This slows down the piston, which in turn slows down spring and suspension movement. The amount of resistance a shock absorber develops depends on the speed of the suspension and the number and size of the orifices in the piston. Shock absorbers are velocity sensitive hydraulic damping devices, meaning the faster the suspension moves, the more resistance the shock absorbers provide. Because of this feature, shock absorbers adjust to road conditions. As a result, shock absorbers reduce:  Bounce  Roll or sway  Brake dive  Acceleration squat
  23. 23. Shock absorbers work on the principal of fluid displacement on both the compression and extension cycle. A typical car or light truck will have more resistance during its extension cycle than its compression cycle. This is because the extension cycle controls the motions of the vehicle sprung weight. The compression cycle controls the motions of the lighter unsprung weight. COMPRESSION CYCLE During the compression stroke or downward movement, some fluid flows through the piston from Chamber B to Chamber A, and some through the compression valve into the reservoir, Chamber C. To control the flow, there are three valving stages in the piston and in the compression valves. At the piston, oil flows through the oil ports, and at slow piston speeds, the first stage opens. This allows fluid to flow from Chamber B to Chamber A. At faster piston speeds, the increase in fluid pressure below the piston in Chamber B causes the second stage piston valve to open. At high speed, the limits of the second stage phase into the third stage orifice restrictions. At the bottom of Chamber B, oil that is displaced by the piston rod is passed through the three-stage compression valve into Chamber C. At slow speeds, the oil flows through an orifice in the compression valve. As the piston speed increases, the fluid pressure increases, causing the disc to open up away from the valve seat. Again, at high speeds the orifice restriction becomes effective.
  24. 24. Compression control, then, is the force that results from the higher pressure present in Chamber B, which acts on the bottom of the piston and the piston rod area. EXTENSION CYCLE As the piston and rod move upward toward the top of the pressure tube, the volume of Chamber A is reduced, and thus is at a higher pressure than Chamber B. Because of this higher pressure, fluid flows down through the piston's three-stage extension valve into Chamber B. However, the piston rod volume has been withdrawn from Chamber B, greatly increasing its volume. Thus, the volume of fluid from Chamber A is insufficient to fill Chamber B. The pressure in Chamber C is now greater than that in Chamber B, forcing the compression intake valve to unseat. Fluid then flows from Chamber C into Chamber B, keeping the pressure tube full. Extension control, then, is the force present as a result of the higher pressure in Chamber A, acting on the top side of the piston area. SHOCK ABSORBER DESIGN There are two basic shock absorberdesigns in use today: the two-tube design and the mono-tube design. The conventional shockabsorberis illustrated in Fig. 2. Notice that it has two tubes. The inner tube is known as the pressure or working cylinder, while the outer tube is known as the reserve tube. The outer tube is used to store excess fluid. The upper mount of the shockabsorberconnects to the vehicle frame. This upper mount is called the piston rod, and at the bottom is the piston. Notice that this piston rod passes through a bushing and a seal at the upper end of the pressure tube. The bushing keeps the rod in line with the pressure tube and allows the piston to move freely inside. The seal keeps the hydraulic oil inside and contamination out. It's usually of a multi-lip design made of neoprene or silicone rubber. The base valve located at the bottomof the pressure tube is called a compression valve. It controls fluid movement during the compressioncycle. The outside of the reserve tube forms the lower mounting of the shock.
  25. 25. Mono-Tube Design Now let's take a look at the mono-tube shockabsorberdesign. These are high- pressure gas shocks with only one tube, the pressure tube. If you look at Fig. 3, you'll see that inside the pressure tube there are two pistons - one dividing piston and one working piston. The working piston and rod are very similar to the double tube shockdesign. The difference is that a mono-tube shock absorbercan be mounted upside down or right side up and it will work either way. *NOTE A conventional two-tube shockabsorbermust be mounted somewhat vertically. Another difference you might notice is that the mono-tube shock absorberdoes not have a base valve. Instead, all of the control during compressionand extension takes place at the piston. Actually, the shockbodyof the mono-tube design is much larger than needed to allow for suspensiontravel. A free floating diving piston travels in the lower end of the pressure tube, separating the gas charge and the oil. The area below the dividing piston is pressurized to about 360 psi with nitrogen gas. This gas pressure tends to keep the rod extended. The oil is located in the area above the dividing piston.
  26. 26. * A mono-tube shockabsorberimproves unsprung mass when mounted upside down. Bore Size Bore size is the diameter of the piston and the inside of the pressure tube. Generally, the larger the unit, the higher the potential controllevels becauseof the larger piston displacements and pressure areas. The larger the piston area, the lower the internal operating pressures and temperatures. This provides higher damping capabilities.
  27. 27. TELESCOPIC HYDRAULIC SHOCK ABSORBER The telescopic hydraulic shock absorber made its appearance in 193on the Lancia lambda vehicle. In the post war years, coil springs and softer rides were favoured and as a result the shock absorbers of telescopic form became popular. Shock absorber fits most conveniently into a coil spring. Also a softer spring with longer suspension travel require a damper unit with considerable operating length. The manufacturing length also caught up, with the design requirements by this item. The all welded, sealed hydraulic shock absorbers were available in the market by1949. A shock absorber achieves control of suspension movements by forcing oil through a series of orifices and valves. The pressure drop due to the fluid flow across these orifices reflects as the damping force on the suspension components . In most passenger car applications, the ratio of compression and expansion(rebound) of shock absorbers is of the order 1:3. Generally the design of a shock absorber takes into account the variations of the road surface vehicle speed and vehicle load. The simplest hydraulic unit is velocity sensitive because resistance to fluid flow through an orifice increases as the square of flow velocity. Because of the actual relationship between flow velocity and the resistance to flow, a gien size of
  28. 28. orifice will not usually meet the needs of a suspension system on all kinds of roads. A relatively smaller orifice might be all right for a smooth road but it may provide excessive damping on bumps or pot holes. A relatively larger orifice will be more suitable for roads with bumps and pot holes but it will give an unsatisfactory ride on other roads. The situation was improved by using multiple valves both on compression and expansion. When the plunger moves slowly the oil is forced through the low speed orifices to achieve the damping force. A medium sped blow-off valve which is spring loaded opens gradually in response to higher velocity plunger movement. CONSTRUCTION The cylinder contains the plunger assembly which is carried on a plunger rod assembly. The cylinder is closed at the bottom end by the foot valve body and at its top end by the plunger rod guide and seal assembly. The entire cylinder assembly is placed full of oil on both sides of the plunger. As the plunger rod is pushed in(compression stroke) oil is displaced through the foot valve into the reservoir tube. Similarly when the rod is pulled out , ( rebound) oil is drawn back into the cylinder through the foot valve. On each stroke oil passes through the plunger in the required direction to ensure that the cylinder remains completely full of oil. PRINCIPLE OF OPERATION The object of the shock absorber is to dampen the movement of the road spring and is achieved by the transfer of oil through small bled valves between both the upper and lower parts of the cylinder and the cylinder of the reservoir. On the compression stroke oil is transferred from the lower to the upper cylinder to the plunger head recuperation valve and also the reservoir through the bleed valve in the foot valve assembly. As the pressure increases, the main compression valve in the foot valve assembly blows off to release a larger quantity of oil into the reservoir. On the rebound stroke, oil transfer from upper to lower cylinder through the plunger head bleed valve and also recuperates from the reservoir cylinder through the recuperation cylinder in the foot valve assembly. As pressure increases the main rebound valve in the plunger head blows off to release a larger flow of oil from the upper to lower cylinder. The rate at which oil is transferred is determined by the valve spring selections called “SETTINGS”.
  29. 29. OTHER TYPES OF SHOCK ABSORBERS Strut type shock absorbers: While their primary function is identical to conventional telescopic shocks, struts are used as a suspension unit and are more ruggedly built to cope with higher suspension loads and lateral (sideways) forces. They eliminate the need for several suspension components like upper control arms, ball joints and more elaborate cross members. This saves weight and valuable engine compartment and luggage space. While struts are used almost exclusively for the front and rear suspension of small and medium-size cars, the trend is for larger vehicles to also be built with struts. MacPherson strut cartridges and sealed struts: Struts are presently manufactured in two types, sealed and repairable units. The shock absorber of are pairable MacPherson strut is replaced by fitting a factory sealed MacPherson strut cartridge to the original strut housing. The cartridge is held securely in position with a lock ring screwed into the top of the strut housing. Sealed or non-repairable struts, as the name suggests, are sealed during manufacture and are sold as a complete unit. Otherwise the design is similar to the repairable struts. The current trend in strut suspension is that vehicle manufacturers are swinging away from repairable struts to sealed struts. Initially restricted to small and medium size vehicles, even large vehicles are now beginning to use struts. Spring seat shocks are also becoming very common. Examples of the spring seat design can be found on the front suspension of BA Ford Falcons and the rear suspension fitted to Mitsubishi Magna sedans. Spring seat shocks: This type of suspension is similar to both struts and telescopic shock designs. Like struts, a spring seat shock is a suspension unit and a damping device in one assembly. However, unlike struts, this type of suspension is not subjected to high side loads. Spring seat shocks are sealed "throw away" units and are built using similar components to conventional telescopic shocks. DAMPER CHARECTERSTICS The damper is characterised by: (1) general dimensional data; (2) force characteristics; (3) other factors. Dimensional data include the stroke, the minimum and maximum length between mountings, diameters, mounting method, etc. Force characteristics indicate how
  30. 30. the force varies with compression and extension velocities, production tolerances on these forces, any effect of position, and so on. Other factors include limitations on operating temperature, power dissipation, cooling requirements, etc. ADJUSTABLES IN A DAMPER Suspensions may be classified by type and speed of response as: (1) Passive – slow (manual adjustment) (2) Adaptive – slow (roughness and speed) – fast (individual bumps) (3) Active – very slow (load levelling) – slow (roughness and speed) – fast (individual bumps) The fast adaptive type of damper is sometimes called ‘semi-active’ but this is a misleading term. An active suspension requires a large power input from a pump. An adaptive suspension requires power for the valves only. The basic purposes of adjustment are: (1) To optimise damper characteristics for varying conditions of road roughness and driving style, (2) To compensate for wear. Various forms of damper adjustment are possible: (1) manual after removal from the car, (2) manual in situ, (3) remote manual from the driving seat, (4) automatic (adaptive). SPECIFYING A DAMPER The full specification of a damper can be immensely complex, covering all the dimensional data, plus solid material specifications, manufacturing methods, liquid specifications, gas pressurisation, and performance specifications with tolerances. However, for a normal damper many of these are fairly standard and may be taken for granted. Essentially, the damper must be connected to the vehicle and exert the desired forces. Hence the primary specification features may be considered to be: (1) end fitting design; (2) length range; (3) F(V) curve. This is a functional specification. That specification may be achieved in a variety of ways, but to guarantee the performance over a range of conditions, the method of achieving it may also be specified. Hence the specification may well include: (4) configuration; (5) diameter;
  31. 31. (6) oil properties. The question of the life of a damper, that is wear rate and maintenance of an acceptable F(V) over a long period of use, is a difficult one. Durability tests, both bench and field, will normally be required. To help to achieve durability, the specification may include information on: (7) seals; (8) surface finish; (9) corrosion resistance. According to the particular case, any other technical details may be added, as required. Finally, last and by no means least, there is (10) cost. End Fittings The end fittings are dictated by the vehicle. Usually the lower end of the damper will use a transverse eye with rubber bush fixed onto a stud protruding from a suspension arm. The actual specification will therefore be the type of fitting and the dimensions, i.e. tube material, inner diameter to accept the bush, wall thickness as length (usually equal to the bush length). In more detail there will be a tolerance on the accuracy of the end tube position, plus a method of attachment, e.g. welding, and a minimum strength. The bush itself needs to be specified too, in particular the dimensions, but also the stiffness of the rubber. In practice, this will frequently be done indirectly by indicating a standard part number. If the upper end is connected directly into the top of the wheel arch, then the protruding rod diameter, length and thread must be stated, plus the size and hardness of the rubber pads and the supporting metal plates. Length Range The range of suspension motion is normally limited by separate bump stops and droop stops, so the maximum spacing of the damper mounting points is known. It is essential that the damper should be able to span this entire range, in order to prevent damage to the damper or unpredictable handling because of improper restriction of suspension motion. Hence the damper has: (1) a minimum maximum length, i.e. a minimum fully extended length; (2) a maximum minimum length, i.e. a maximum fully compressed length. The actual points between which the lengths are measured must, of course, be clear. In the case of transverse eyes then the eye centres will probably be used; this must not be confused with the overall length. With an axial end fixing rod, the measuring point must also be defined. Obviously the damper stroke must
  32. 32. normally exceed the full range of relative motion of the connection points. However, this alone is not sufficient. The exception to the above is when the damper is intended to act as the bump or droop stop, and designed appropriately to do so, often with the incorporation of bump and droop rubbers. F(V) Curve The F(V) curve, over the appropriate range of compression and extension velocities, is the essence of the damper specification, usually expressed as forces at discrete velocities. In practice there must be some tolerance to allow for manufacturing variation, the width of which will depend upon the quality of the damper. The tolerance is not well specified by only a force or only a percentage tolerance, so a combination of these may be given, e.g. _20 N _10% of nominal force. Alternatively, maximum and minimum acceptable forces may be presented in graphical form. Tolerances will also be placed on the gas force, and on the effect of temperature As described earlier, the actual desired force curve for the damper must take into account the desired damping for the vehicle and the effect of the installation motion ratio. Configuration According to the application, some particular configuration of damper will generally be preferred, and required. Hence the damper will be required to be a single-tube or double-tube type, possibly with a floating gas-separator piston, possibly with a remote reservoir and so on. Diameter The required forces may be achievable by a high pressure on a small piston. However such a design will be very sensitive to leaks, and hence to wear. Also a small diameter will have poorer cooling. Therefore a minimum or actual nominal diameter for the piston may be specified, and also perhaps the rod diameter and, for a double-tube type, the diameter of the outer tube. Oil Properties According to the particular application, the oil type, and viscosity and density at standard temperature, may be specified. Usually a standard damper mineral oil will simply be defined by a manufacturer’s reference number. For more difficult cases, a low-viscosity-index synthetic oil may be required, but again indicated by a manufacturer and oil type number.
  33. 33. Life The useful life of a damper is difficult to predict because of variations in conditions of use, i.e. of driving styles and local road roughness, and is difficult to test because the life is usually measured in tens of thousands of kilometres on normal roads. The useful life is normally limited by leakage due to rod seal wear or piston seal wear. Hence the life is enhanced by careful choice of seal design and materials with a very good finish on the hard rubbing surfaces of rod and cylinder, all of which need to be specified. A large piston diameter, giving larger liquid displacement volumes and lower operating pressures, improves the tolerance to leakage. Cost The importance of the manufacturing cost of a damper may seem to be too obvious to require discussion. However, the significance of the price will vary considerably with the application. For a high-grade racing car or rally car the accuracy and predictable of the F(V) curve, and the life reliability, may be so important that a high price is not problematic. On the other hand, for an economy passenger car, which is price sensitive, less critical on exact damping level and produced in large quantities, the dampers will have to be a much lower price. Of course, the cost is not so much a part of the technical specification as the result of it. The technical specification must not be higher than is appropriate to the vehicle, or the price will be adversely influenced. VALVE DESIGN Valves are fitted into the piston and the body of the damper—the piston valves and foot valves respectively. For a given speed of damper action, fluid is displaced through a valve at volumetric flow rate Q. The valve resistance to flow requires a pressure difference across the valve to produce this flow rate. This pressure, acting on the piston annulus area or rod cross sectional area, will create a force resisting damper motion. Hence the F(V), force–velocity, characteristic of the damper is intimately related to the P(Q), pressure–flow rate, characteristic of the valves. In ride quality studies, using analytical or computer simulations of complete vehicles, the dampers are usually modelled as linear, implying a linear valve characteristic. This can be achieved by a valve with a viscous pressure drop, such as a simple tube. However, viscous losses are too temperature sensitive, so more elaborate valves with dynamic losses are used. This also allows the P(Q) characteristic to be controlled to a desired nonlinear form, within limits.
  34. 34. Practical dampers, then, are based on using energy dissipation primarily by turbulence, usually by allowing the liquid to pass through a small hole, giving a turbulent exit jet which dissipates in a bulk of liquid. Viscosity continues to have some effect, as seen in the dependence of the discharge coefficient on Reynolds number, but the viscosity sensitivity is much reduced from that of laminar flow. With the dynamic loss kind of valve, the pressure loss for a given volumetric flow is more dependent upon the fluid density than on viscosity. However, the density is also dependent on temperature, so although the temperature sensitivity is reduced, it is certainly not eliminated. The dynamic loss type of valve introduces a new problem: the pressure loss is now dependent upon the square of the exit velocity. This means that for a simple orifice of fixed area the pressure loss depends on the square of the volumetric flow rate, which will give a damper force proportional to damper velocity squared. This is completely unacceptable. However, unlike the problem of viscosity variation with temperature for flow through a tube, this has an entirely practical solution—the valve area can be made to vary to produce a desired characteristic. All dampers have this area variation in a passive form, with a larger pressure difference forcing the valve to open to a larger area, giving a moderated fluid exit speed. Nowadays some dampers also have area variation by manual intervention (i.e. adjustable) or by automatic control. Valve Types Valves can be arranged to be responsive to many factors. The obvious ones are: (1) position; (2) velocity; (3) acceleration. The damper is essentially a device for dissipating energy and as such the velocity sensitivity is the basic one, i.e. the damper relationship F(V) and the corresponding valve relationship P(Q). All other valve sensitivities are just variations on the basic theme. Other designs, described below, include pressure rate sensitivity, stroke length sensitivity, and so on, and particular other non mechanical methods of implementation, e.g. piezoelectrically operated valves. Basic mechanical damper valves may be classified conveniently by the design configuration used in the variability of area. There are numerous possible forms, but the three basic ones are: (1) disc valve; (2) rod valve; (3) spool valve; (3) shim valve. These are illustrated in Figure 6.2.1. The photographic plates also illustrate some of the valves to be found in passenger car dampers, e.g. plate pages 8 and 9. Shim disc valves are convenient for dampers that need to have their characteristics changed, and are therefore usually favoured for racing, whereas the spoolvalve type and rigid disc with coil spring are more common on passenger cars.
  35. 35. Disc Valves The simple disc with coil spring, Figure 6.3.1(a), is obvious in operation, being sealed until an opening pressure difference is reached, depending upon the active pressure area and the preload force of the coil spring. The active pressure area, that is the effective area of the disc within the seal, may be much larger than the cross-sectional area of the flow passage. The flow area is the circumference of the seal times the lift. If the coil spring is of low stiffness (but not necessarily of low preload force) then further opening can occur easily, and large flow areas and flow rates will be possible with little increase of pressure difference. Alternatively, a stiff spring with low preload will give a more gradual increase of
  36. 36. area. In practice, because the required flow area is only a few square millimetres, even a small lift of this kind of valve tends to give a ‘large’ area, so it is difficult to make this type truly progressive. Rather, it acts as a simple blow-off valve with a constant pressure characteristic. Nevertheless, this type may be suitable in some cases, particularly for a low-preload valve to constrain flow to one direction only with quite a low forward pressure drop, as in a foot valve. Unless the disc is guided, it will probably open asymmetrically because of imperfect symmetry of the spring, which may actually make the individual valve more progressive, although possibly inconsistent one to another. Also, production tolerances make it difficult to achieve consistent preload. Variations of the disc valve include one using a conical spiral spring, Figure 6.3.1(b). This may have several flow holes disposed circumferentially. This is conveniently compact axially, and suitable for low preloads, so it is a likely choice for a foot valve. In a third variation, Figure 6.3.1(c), the mobile disc with a sleeve slides on the guiding rod, restrained by a coil spring. If a disc with coil spring is used on both sides of the piston, the total length may be disadvantageous, Figure 6.3.2. Shim Valves The third main type of valve is the shim valve with basic principle as shown in Figure 6.2.1(d). In practice a pack of shims is used with varying diameters, a system particularly common on racing dampers, partially because the characteristics can be changed easily, Figure 6.6.1. On passenger cars, the shim
  37. 37. valve shows to advantage because it is relatively easy to set up accurately with consistent results. This is because the flat shims sit naturally on the piston without problems of manufacturing dimensional inconsistencies affecting the preload. Figure 6.6.1 shows the usual configuration of one pack on each side of the piston, which will typically contain six holes, three for fluid motion in each direction. Sometimes six holes are used for compression. Hole A is one of the three holes for compression flow, with free entry, and the exit limited by the upper pack of shims. In extension, hole B is one of three active holes, with the lower pack providing resistance. The shim thickness is 0.2–0.5 mm, and the piston surface is sometimes coned at 0.5–2_ to give a preload, possibly just to prevent a leakage path. Generally, there is also a small parallel hole. The shim pack comprises up to six shims of reducing diameter. This gives a controllable stiffness, with greater strength where the bending moment is large, and adds some shim-on-shim friction which may help to prevent valve flutter. The valve opening height is only a fraction of a millimetre, so the flow path is roughly twodimensional. With three holes of diameter 6 mm, the exit circumference is nominally 57 mm, so an exit area of 3 mm2 requires a mean lift of only about 0.05 mm. Here the discharge coefficient will be sensitive to Reynolds number, and also to radiusing or chamfering of the corner at the entry below the shims. There does not seem to be any published information on detailed investigations of flow through such geometry, although Mughal (1979) has reported discharge coefficients for reed type valves. Because of the small valve lift, the characteristics are rather sensitive to burring or small damage at the valve seat, caused by foreign particles being forced through the valve at low lifts. Of course, a very small piece of foreign matter jammed beneath a valve can cause a considerable reduction of resistance.
  38. 38. In a more complex variant of the shim pack valve, further support is provided by one or more supplementary shims in a way that makes the preload force adjustable. Also, the shims may be spaced by small diameter discs, so that support and extra stiffness is introduced progressively with increasing deflection. Even a thin shim is very stiff against compound curvature, so it prefers to bend with planar curvature. This means that there is a limit to the bendable distance available, governed by the number of bending sections on the shim, as in Figure 6.6.2. In part (a), the shim has a small central support, and can bend in two wings, each over a distance D/2. With a solid central support up to D/2, (D cos 60_), there are still two wings, as in (b), forming shorter cantilevers that are stiffer. At this point there is a transition, and a three-wing mode becomes possible for a support diameter exceeding D/2, as in (c). Although a two-wing mode is still possible, the mode that will occur depends on the fluid hole positions. At a support radius 0.71 D (D cos 45_), bending with four wings is possible, as in Figure 6.6.2(e). For consistent and predictable valve behaviour, the number and position of flow holes must be compatible with the preferred bending mode of the shim and its support. For example, with a rigid support of diameter 0.4 D, two- wing bending will be more compliant and more likely than three-wing bending which would be based away from the support, so using three fluid holes could be problematic in such a case. Figure 6.6.3 shows the typical designs used in practice, with three holes, or six holes in three pairs, for fluid flow. The design intent is for a three-wing bending mode. A support smaller than 0.5 D in diameter would make the wings fight each other for space, and permit the more compliant two-wing bending, with possibly erratic results.
  39. 39. When shim valves are to be used for large volume flows (not dampers), radial slots are used in the shim to facilitate greater bending, e.g. 10 or 12 sections, with a small rigid central support to give a long cantilever length. These are called petal valves. Valve Characteristics Some mention has been made of the overall valve area–pressure relationship, and the pressure–flow rate relationship, but this is not the only important aspect of the valve. In fact the following qualities, inter alia, are important: (1) steady state pressure–flow rate; (2) friction and hysteresis; (3) transient response (flutter, overshoot); (4) temperature sensitivity; (5) cavitation; (6) wear; (7) fatigue; (8) consistency in production; (9) required precision of manufacture; (10) economy of manufacture. In a complete valve, the variable-area component above will normally be combined with an orifice in parallel to give some flow even with the valve fully closed. Also, the valve will be limited in its maximum area, or there will be a series orifice to control the flow at very high pressure. These various factors, being the areas of series and parallel holes, the maximum area and the valve pressure–area characteristic, are all juggled to obtain the desired, or at least best available, complete valve characteristic. These valve characteristics may be studied to a useful extent by analysing a basic valve model with variable area, without concern for the actual physical implementation.
  40. 40. Ride engineers select valving values for a particular vehicle to achieve optimum ride characteristics of balance and stability under a wide variety of driving conditions. Their selection of valve springs and orifices control fluid flow within the unit, which determines the "feel" and handling of the vehicle. Full Displaced vs. Rod Displaced Valving Full displaced valving is a significant advance in shock absorber design and construction. It reduces internal operating pressures and aeration for greater damping capabilities. Full displaced valving also provides greater latitude in engineering how a shock will perform on a specific vehicle. A typical rod displaced shock has a total of eight valving stages: A three-stage piston valve A three-stage base valve Two stages as the fluid passes through the piston Full-displaced design allows ten stages by adding a blow-off valve and a dual rate piston replenishing spring. In a rod-displaced shock absorber, control is generated with the fluid displaced by the rod, which goes through the base valve during compression. Fluid moving upward past the piston during the compression cycle does no significant work. When a shock absorber with full displaced valving goes into a compression cycle, the fluid forced up through the piston is performing significant work - it's a much more efficient shock absorber.
  41. 41. Full Displaced Base Valving A. At slow piston rod speeds, fluid passes through a predetermined orifice area in the valve seat. B. At medium rod speeds, fluid is controlled by discs, which act as flat blow-off springs. C. At high speeds, fluid is controlled by the orifice slot areas in the valve plate. Piston Valve During Compression A. At slow piston rod speeds, an orifice controls fluid flow. B. At progressively faster rod speeds, the exclusive patented Monroe dual rate disc system provides two valving stages. C. At very high piston rod speeds, orifice restriction controls fluid flow. Piston Valve During Extension Cycle A. At slow piston rod speeds, fluid is regulated by an orifice in the piston valve seat. B. At medium rod speeds, fluid is controlled by the spring and thickness of steel
  42. 42. discs. C. At high speeds, inner passage restriction provides control.
  43. 43. STRUT DESIGN Before discussing spring design, it is important to understand sprung and unsprung weight. Sprung weight is the weight supported by the springs. For example, the vehicle's body, frame, motor, and transmission would be sprung weight. Unsprung weight is the weight that is not carried by the springs, such as the tyres, wheels and brake assemblies. The springs allow the frame and vehicle to ride undisturbed and the suspension and tyres to follow the road surface. Reduced unsprung weight will provide less road shock. A high sprung weight along with a low unsprung weight provides improved ride and also improved tyre traction. There are four major spring designs in use today: coil, leaf, torsion bar, and air. The most commonly used spring is the coil spring. The coil spring is a length of round spring steel rod that is wound into a coil. Unlike leaf springs, conventional coil springs do not develop inter-leaf friction. Therefore, they provide a smoother ride.
  44. 44. Coil spring strength, or rate, is determined by the length and diameter of the rod. Decreasing the diameter of the rod, the number of turns, and the tightness of the turns increases the strength of the spring. Increasing the rod diameter or the number of turns, or increasing the space between turns reduces spring strength. Spring rate, sometimes referred to as deflection rate, is used to measure spring strength. It is the amount of weight that is required to compress the spring one inch. For example: if it takes 100 pounds to compress a spring one inch, it would take 200 pounds to compress the spring two inches. Some coil springs are made with a variable rate. This variable rate is accomplished by either constructing the spring from material having different thicknesses, or by winding the spring so the coils will progressively bottom out. Variable rate springs provide a lower spring rate under unloaded conditions offering a smoother ride, and a higher spring rate under loaded conditions, resulting in more support and control. Coil springs require no adjustment and for the most part are trouble-free. The most common failure is spring sag. Springs that have sagged below vehicle design height will change the alignment geometry. This can create tyre wear, handling problems, and wear on other suspension components. During suspension service it is very important that vehicle ride height be measured. Ride height measurements not meeting manufacturer's specifications require replacement of the springs.
  45. 45. Leaf springs are designed two ways: multileaf and mono leaf. The multileaf spring is made of several steel plates of different lengths stacked together and held by clips. During operation, the spring compresses to absorb road shock. The spring plates bend and slide on each other allowing movement. The mono leaf spring is an example of a tapered leaf spring. The leaf is thick in the middle and tapers outward to the two ends. Some vehicle manufacturers will use a transverse, or side-to-side, leaf spring. Normally, a transverse spring can be a steel multileaf or a composite mono-leaf. Composite springs are also used in longitudinal, or front-to-back, leaf spring applications. Another type of spring is the torsion bar. The torsion bar is a straight or L-shaped bar of spring steel. Most torsion bars are mounted solidly to the frame, with the other end connected to the suspension. During suspension movement, the torsion bar will twist providing spring action.
  46. 46. The air spring is another type of spring that is becoming more popular on passenger cars, light trucks, and heavy trucks. The air spring is a rubber cylinder filled with compressed air. A piston attached to the lower control arm moves up and down with the lower control arm. This causes the compressed air to provide spring action. If the vehicle load changes, a valve at the top of the air bag opens to add or release air from the air spring. An on-board air compressor supplies air. An often overlooked spring is the tyre. Tyres are air springs that support the total weight of the vehicle. The spring action of the tyre is very important to the ride quality and safe handling of the vehicle. As a matter of fact, tyres may be viewed as the number one ride control component. Tyre size, construction, compound and inflation are very important to the ride quality of the vehicle. The spring rate of a tyre is determined by the air pressure. An over-inflated tyre will have a higher spring rate and will produce excessive road shock. Over-inflated tyres will transmit road shock rather than reduce it. Over- or under- inflation also affects handling and tyre wear.
  47. 47. When adjusting tyre pressure always refer to the vehicle manufacturer's specifications, not the specifications on the side of the tyre. The air pressure specified by the vehicle manufacturer will provide safe operation and ride quality of the vehicle. The tyre pressure stamped on the side is the maximum pressure that the tyre is designed to hold at a specific load and speed. SMART SUSPENSIONS Today, more and more passenger cars are utilizing an active suspension system, or a "smart" suspension. A smart suspension is similar to a traditional, or passive, suspension system since many of the same components are found in each. Shock absorbers or struts, bushings and suspension components all work together to provide good handling and a comfortable ride in both systems. However, in a smart suspension system coil springs are replaced by air bags, which support the weight of the vehicle. These air bags, and usually the shocks or struts, are electronically controlled to respond to changing load and driving
  48. 48. conditions. Most often the driver can also select a firmer or softer ride control setting to adapt to driving conditions. In many systems, the suspension is air operated and controlled by a computer. This computer provides automatic front and rear load levelling by means of air springs. An air compressor supplies the air to the system and airflow is controlled by the interaction of the compressor, solenoids, height sensors, and the control module or computer. In addition to air springs, many systems also use dual-stage struts capable of changing their internal valving by means of a stepper motor. The manufacturer for each individual model recommends specific maintenance and servicing procedures. Typically, diagnosis of these systems involves interpreting trouble codes from the vehicle's computer and electronically measuring the many motors and sensors in the system BASICS OF SUSPENSION To begin this training program, you need to know some basic information. First, you should know that the tyres and wheels make vehicle motion possible. The chassis connects the tyres and wheels to the vehicle's body. The chassis consists of the frame, suspension system, steering system, tyres and wheels. When discussing a vehicle's chassis, the side-to-side distance between the centreline of the tyres on an axle is called track. The distance between the centre of the front and rear tyres is called wheelbase. If the vehicle is in proper alignment, the wheels will roll in a line that is parallel with the vehicle's geometric centreline. Vehicle geometry, suspension, and steering design all affect the "handling" of a vehicle. To better understand the term handling, we can address the following fundamentals that contribute to good handling: ROAD ISOLATION – is the vehicle's ability to absorb or isolate road shock from the passenger compartment. DIRECTIONAL STABILITY – is the ability of the vehicle to maintain a directed path. RETURNABILITY – is the ability of the vehicle to return the front wheels to straight ahead after turning. TRACKING – is the path taken by the front and rear wheels. CORNERING – is the ability of the vehicle to travel a curved path. So, to a great extent, handling depends on optimising the vehicle's suspension dynamics, or dynamic control. This means that when a vehicle is in motion, all the components in the suspension system work together effectively to provide tyre-to-road contact. The amount of this traction force between the tyres and the
  49. 49. road is the major factor in how well a vehicle can manoeuvre through corners, or as it stops and accelerates. The components of the suspension system perform six basic functions: 1. Maintain correct vehicle ride height 2. Reduce the effect of shock forces 3. Maintain correct wheel alignment 4. Support vehicle weight 5. Keep the tyres in contact with the road 6. Control the vehicle's direction of travel. However, in order for this to happen, all of the suspension components, both front and rear, must be in good working condition. COMFORT AND SAFETY The suspensionsystem allows the vehicle bodyto ride relatively undisturbed while travelling over rough roads. It also allows the vehicle to corner with minimum roll or sway, stop with a minimum of brake dive, and accelerate with a minimum of acceleration squat. This dynamic control will keep the tyres in contact with the road. Shocks and Struts ARE Safety Equipment Most people believe that shocks and struts are only necessary for improving a vehicle's riding comfortand handling. In truth, they do much more than that; their job is to help keep tyres on the road. A vehicle riding on worn shocks and struts may be unsafe not only to the driver and passengers, but also to other vehicles on
  50. 50. the road. By replacing your worn shocks and struts, you're providing yourself with a safer, more secure vehicle. Tyre Force Variation: "Downward Force on Tyres" It's important to understand that a vehicle's ability to steer, brake and accelerate depends first and foremost on the adhesion, or friction, between the tyres and the road. This adhesion is also referred to as the roadholding capability of the vehicle. "Tyre ForceVariation" is a measure of the roadholding capability of the vehicle, and is directly influenced by shock absorberor strut performance. Shock absorbers and struts help maintain vertical loads placed on the tyres by providing resistance to vehicle bounce, roll and sway. They also help reduce brake dive along with acceleration squat to achieve a balanced ride. Worn shocks and struts can allow excessive vehicle weight transfer from side to side and front to rear...and that reduces the tyre's ability to grip the road. Because of this variation in tyre-to-road contact, a vehicle's handling and braking performance can be reduced. This may affect the safe operation of the vehicle and the safety of those riding inside. Therefore, shocks and struts ARE SAFETY COMPONENTS.
  51. 51. What controls tyre force are the shocks or struts on that vehicle? Tyre loading changes as a vehicle accelerates, decelerates, and turns corners; the size of the four circles of traction at the tyres is also changing with the changes in tyre load. As a vehicle turns a corner, centrifugal force causes weight to transfer from the tyres on the inside of the turn to the tyres on the outside. As a vehicle brakes, inertia will cause weight to transfer from the rear tyres to the front tyres; weight will transfer from the front to the back during acceleration.
  52. 52. FRONT SUSPENSIONS There are two major types of conventional front suspensions. They are dependent and independent. Dependent Front Suspensions The dependent front suspension uses a solid axle. This design consists of one steel or aluminium beam extending the width of the vehicle. This beam is held in place by leaf springs. Notice that this design also uses king pins and bushings to attach the wheels outboard of the axle. Because of its load carrying ability, the solid axle is only used on heavy trucks, and off-road vehicles. It is not suitable for use on modern passenger cars for three important reasons: Transfer of Road Shock. There is transfer of road shock from one wheel to the other due to the way the wheels are connected to the axle. This causes a rough ride and could result in loss of traction. Unsprung Weight. Because the solid axle has a lot of unsprung weight, it needs more spring and shock control to keep the tyres in contact with the road. Wheel Alignment. The solid axle design makes no provisions for alignment. Independent Front Suspensions The independent front suspension was developed in the 1930's to improve vehicle ride control and riding comfort. With the independent design, each wheel is mounted on its own axle. This allows the wheels to respond individually to road conditions. Also, with independent front suspension the sprung weight is reduced, creating a smoother ride.
  53. 53. Twin I-Beam The twin I-beam is one type of independent front suspension. Although it is similar to the solid axle in many ways, it was designed to improve ride and handling. Because of its load carrying ability, it is used on pickups, vans and four-wheel drive vehicles. The twin I-beam consists of two short I-beams supported by coil springs, and the steering knuckles, which are connected by, king pins or ball joints. The inner end of the axle connects to the vehicle frame through a rubber bushing. There is a radius arm connected to the frame through rubber bushings. This arm controls wheelbase and caster. While the twin I-beam design was an improvement over the solid axle, it still has some flaws. For example, with the twin I-beam the camber and track change as the wheels move up and down creating tyre wear. Type 1 Coil Spring Now, let's look at the coil spring suspension, another example of an independent front suspension. Notice that it is made up of the following components:  two upper control arms  two lower control arms  two steering knuckles  two spindles  two upper ball joints  two lower ball joints
  54. 54.  bushings  coil springs  shock absorbers Notice that the control arms are of unequal length, with the upper arm shorter than the lower arm. This design is known as the short-arm/long-arm, or the parallel arm design. Using control arms of unequal length causes a slight camber change as the vehicle travels through jounce and rebound. While this may sound bad, it actually is not. If both arms were the same length, a track change would occur causing the
  55. 55. tyre to travel sideways. The tyres would then scrub the pavement, causing tyre wear and handling problems. Notice that the shock and spring are positioned between the frame and the lower control arm. You can see that the bottom of the spring rests on the lower control arm, while the top of the spring is connected to the vehicle's frame. The outer end of the control arm is connected to the steering knuckle with ball joints. Ball joints are simple connectors, which consist of a ball and socket. The ball and socket assembly forms the steering axis for the suspension system. One ball joint is called the load carrier, meaning it carries the load of the vehicle or the force of the spring. The other ball joint is called the follower. The follower does not carry any weight; it just provides a pivot point and stabilizes the steering system. Typically, the location of the lower spring seat determines which ball joint is the load carrier and which is the follower. If the lower ball joint is the load carrier. The upper ball joint is then the follower. The control arms act as locators because they hold the position of the suspension in relation to the vehicle. They're attached to the vehicle frame with rubber torsilastic bushings. Rubber bushings are preferred because they do not require lubrication, and will reduce minor road noise and vibrations. Torsilastic refers to the elastic nature of rubber to allow movement of the bushing in a twisting plane. Movement is allowed by twisting of the rubber. The other sleeve of the bushing is press fit into the control arm, while the inner sleeve is locked to the control arm pivot shaft. The rubber must twist to allow movement of the control arm. This twisting action of the rubber will provide resistance to movement. Some sources state that "10% of the resistance to body roll comes from the rubber bushings." Control Arm Design It is important to know that control arm design is matched with spring size. This produces an exact control arm position, allowing for travel over bumps. For this reason, the lower control arm must be horizontal or slightly lower at the ball joint end. If you find that the ball joint end is higher than the inner control bushing, the springs may be weak and sagging. Weak or sagging springs may cause a track change, and can create tyre wear and handling problems. If you find this type of problem during an inspection, measure the vehicle's ride height to confirm the condition of the springs.
  56. 56. Type 2 Coil Spring Type 2 coil spring suspension, the coil spring is mounted on the upper control arm, and the top of the spring is attached to the frame. In this type of design, the upper ball joint receives the weight of the vehicle and the force of the coil spring. This makes it the load carrier. But the upper ball joint isn't the only component supporting the vehicle weight. In the type 2 coil spring suspension, the coil spring also supports the weight of the vehicle. And the movement of the coil spring is controlled by the shock absorber. Notice that in both Type 1 and Type 2 designs, the weight of the vehicle is transmitted through the spring to the control arm at its bottom, and then through the control to the ball joint. You should know that the load carrying ball joints carry approximately one half of the total vehicle weight. This makes them subject to severe wear. Stabilisers Another important component of the suspension system is the stabilizer. This device is used along with the shock absorbers to provide additional stability.
  57. 57. One example of a stabilizer is the sway bar, also known as the anti-sway bar. The sway bar is simply a metal rod connected to both of the lower control arms. When the suspensionat one wheel moves up and down, the sway bar transfers the movement to the other wheel. For example, if the right wheel drops into a dip, the sway bar transfers the movement to the opposite wheel. In this way, the sway bar creates a more level ride and reduces vehicle sway or lean during cornering. Depending on the sway bar thickness and design, it can provide as much as 15% resistance to vehicle roll or sway during cornering. Torsion Bar The torsion bar suspension is one more example of an independent front suspension. With the torsion bar suspension, there are no coil or leaf springs. Instead, a torsion bar supports the vehicle weight and absorbs the road shock. Actually the torsion bar performs the same function as a coil spring: it supports the vehicle's weight. The difference is that a coil spring compresses to allow the tyre and wheel to follow the road and absorb shock, while a torsion bar uses a
  58. 58. twisting action. Other than this difference, however, the two types of suspension construction are much the same. The torsion bar connects to the upper or lower control arm at one end, and at the other end connects to the frame. It can be mounted longitudinally, front to rear, or transversely, side to side. Unlike coil springs and leaf springs, torsion bars can be used to adjust suspension ride height. Keep in mind, however, that torsion bars are not normally interchangeable from side to side. This is because the direction of the twisting or torsion is not the same on the left and right sides. Because the torsion bar is connected to the lower control arm, the lower ball joint is the load carrier. This makes the upper ball joint the follower. Notice that in this type of suspension the shock absorber is connected between the lower control arm and the vehicle frame. This allows it to control the twisting motion of the torsion bar. Double Wishbone The double wishbone is another type of strut suspension that is becoming more common. It combines the space saving benefits of a strut suspension system with the ability of the parallel arm suspension to ride low to the ground. This allows for a more aerodynamic hoodline. With this design, the lower portion of the strut forms a wishbone shape where it attaches to the lower control arm. Unlike other struts, the double wishbone does not rotate when the wheels turn. Instead, the entire spindle assembly rotates on the upper and lower ball joints much like a parallel arm suspension. Since the strut does not rotate, the upper mount does not need a bearing. Instead, a hard rubber bushing replaces the bearing and helps isolate road shock.
  59. 59. MAIN COMPONENTS At this point it's easy to understand that the main components of a moving vehicle's suspension system are the struts, shock absorbers, springs, and tyres. Struts are a major structural member, while shock absorbers are a major component. The struts and shock absorbers control, or damp, excessive spring and suspension movement.
  60. 60. The springs support the weight of the vehicle, maintain ride height, and absorb road shock. Springs are the flexible link that allows the frame and body to ride relatively undisturbed while the tyres and suspension follow the bumps in the road. Springs are the compressible link between the frame and the body. When additional load is placed on the springs, or the vehicle meets a bump in the road, the springs will absorb the load by compressing. The springs are a very important component of the suspension system that provides ride comfort. Shocks and struts help control how fast the suspension is allowed to move which is important in keeping the tyres in firm contact with the road. During the study of springs, the term bounce refers to the vertical (up and down) movement of the suspension system. The upward suspension travel that compresses the spring and shock absorber is called jounce, or compression. The downward travel of the tyre and wheel that extends the spring and shock absorber is called rebound, or extension. When a spring is deflected, it absorbs energy. Without shocks or struts, the spring will extend and release this energy at an uncontrolled rate. The spring's inertia causes it to bounce and over-extend itself. Then it re-compresses, but will again travel too far. The spring continues to bounce at its natural frequency until all the energy originally put into the spring is used up by friction. If the struts or shock absorbers are worn and the vehicle meets a bump in the road, the vehicle will bounce at a frequency of the suspension until the energy of the bump is used up. This may allow the tyres to lose contact with the road. Struts and shock absorbers that are in good condition will allow the suspension to oscillate only through one or two diminishing cycles, limiting or damping excessive vibration. By controlling spring and suspension movement, components such as ball joints and tie rods will operate within their design range and, while the vehicle is in motion, dynamic alignment will be maintained.
  61. 61. MANUFACTURE OF SHOCK ABSORBERS BASE ASSEMBLY MANUFACTURE At every stage of the manufacturing process, care is taken to avoid scrap pieces and contamination which includes accumulated dust, material burr (sheared, accumulated portions of metal in unnecessary locations ), hence preventive measures are taken in order to avoid wastage of products. The base assembly manufacture can be divided into the manufacture of struts (is used as the front assembly in cars), semi-strut(used as both front and rear assembly), and shocks which are used in the rear of the vehicles. PRODUCTION PROCESS FLOW OF STRUT RESERVE TUBE ASSEMBLY ShockAbsorbers DamperAssembly Chrome platingof pistonrods Base Assembly (Manufature of strut, semi strutand shocks) CHILD PART WASHING NAME ROLLING BASE CUP PRESSING KNUCKLE BRACKET PRESSING BASE CUP WELDING SPRINGSEAT TAG WELDING KNUCKLE BRACKET WELDING SPRINGSEAT WELDING KB HOLE PIERCINGAND COINING MANUAL BRACKET WELDING X 4 SEMI AUTO BRACKET WELDING WELD LEAK TESTING FIRE WALL INSPECTION
  62. 62. The first process includes the washing of the reserve tube in a chemical medium to get rid of all the contamination and extra material present on it. This is followed by the name rolling process in which the details of the company, manufacturing date and other required specifications are mentioned. The next step is the base cup pressing in which the base cup is placed inside a mandrel and is hydraulically pressed onto the reserve tube. Now a crude structure of the knuckle bracket is placed on the other end of the reserve tube and is pressed sideways so that it stays in position. Next, the knuckle bracket is welded around its circumference using a MIG welding machine which rotates and welds simultaneously about its axis. This is followed by the spring seat welding in which a spring seat is placed around the reserve tube and is welded in 3 spots using GTAW about its axis to keep it in position and is then circumferentially welded using MIG to seal it ; followed by the base cup welding, also circumferentially to seal the base cup. this is followed by the Knuckle bracket coining in which 4 holes are punched onto the arms of the bracket for attaching the screws and this piece is manually welded on other spots to seal the joints. Now this is made to undergo a leak test to ensure that the all the joints have been sealed properly without any leaks which is then passed onto the firewall inspection counter where it is visually checked for burr and broken areas. PRODUCTION PROCESS FLOW FOR SEMI STRUT RESERVE TUBE ASSEMBLY This process is similar to the strut manufacture except for the structure of the components and a few processes. Here, the name rolling process is followed by CHILD PART WASHING NAME ROLLING SWAGING AND FLARING BASE CUP PRESSING BASE CUP SEAM WELDING LOOP PROJECTION WELDING LOOP MAG WELDING SPRING SEAT TAG WELDING SPRING SEAT WELDING MANUAL BRACKET WELDING X 2 WELD LEAK TESTING FIREWALL INSPECTION
  63. 63. the swaging and flaring in which a mandrel of a diameter larger than the reserve tube is inserted into the reserve tube using a hydraulic press which results in a flared component of larger diameter in order to fit in the base cup. Then a loop like structure is welded onto the base cup to provide space for the bushings. PRODUCTION PROCES FLOW FOR SHOCKS RESERVE TUBE ASSEMBLY CHILD PART WASHING NAME ROLLING SWAGING AND FLARING BASE CUP PRESSING BASE CUP SEAM WELDING LOOP PROJECTION WELDING LOOP LINEAR MAG WELDING LOOP ROTARY MAG WELDING WELD LEAK TESTING FIREWALL INSPECTION
  64. 64. DAMPER ASSEMBLY The damper is the most important part of the shock absorber which affects the performance of the shock absorber if anything goes wrong. This process starts with the washing of the pressure tube followed by the washing of the materials to be used in the CV and PV assembly to avoid any kind of contamination which may retard the performance of the product. The CV assembly is also called the foot valve or the base valve as it is fit on to the base of the pressure tube. The CV assembly takes place inside a clean room in which the workers wear head gear and foot covering before entering the room to avoid any kind of dust or hair follicles inside the room. In this process, the cylinder end is placed at the bottom onto which the first set of valving assembly is placed in a certain order and is riveted in a circular manner to obtain a part hemispherical shape; followed by the 2nd stage of valving for the reverse flow of oil followed by riveting once again to hold the valves in place. This is followed by the PV assembly(also takes place in a clean room) in which the valving discs and springs are placed on the piston post of the piston rod and is held in place using a nut which is mechanically tightened in the nut tightening. The assembly is held in place and is pressed together using the stacking machine. Now the piston assembly is placed inside the pressure tube assembly and is filled with oil of a predetermined volume and is sent to the DF testing unit in which the damper assembly is placed in a DF testing machine and is made to run 2 cycles using which a potato curve is plotted and is sent to the next stage if the curve is within a specific range. After this stage a seal is placed OTA WASHING MATERIAL WASHING CV 1ST STAGE RIVETING CV ASSEMBLY CV 2ND STAGE RIVETING PV ASSEMBLY NUT TIGHTENING STACKING INNER PRESSING OIL FILLING DF TESTING SEALING DATA CODE PUNCHING GAS FILLING BUMP CAP PRESSING NOISETESTING ROD PLAY CHECKING RING GUAGE CHECKING ALIGNMENT GUAGE CHECKING FINAL INSPECTION MARKING FIREWALL CHECKING TIE DOWN CLAMPING PACKING
  65. 65. over the piston rod and is sealed using a roller machine. Require data is punched onto the damper. In this stage the damper assembly has already been placed within the strut or shox assembly before the oil filling takes place. Now Nitrogen gas is filled in the reserve tube in a controlled environment. Then finally the Bump cap is clamped onto the shock absorber. Before it goes to any other inspection it is made to undergo a Noise test in which the worker operates the shock absorber and checks for a squealing noise, which indicates the presence of burr .Then it finally under goes a series of inspections before the shock absorber is pushed to the minimum position and is tied down in place using a rod clamp. Then it is sent for packing following the fire wall inspection. CHROME PLATING OF PISTON RODS CLEANING THE MACHINED RODS INDUCTION HARDENING ROUGH ROD GRINDING ANNEALING CHROMEPLATING FINEROD GRINDING SUPERFINISHING INSPECTION FINISHROD SUPERMARKET