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Hydraulics in Automotives


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Hydraulics in Automotives

  3. 3. What is power steering? It is a hydraulic system which assists the driver in reducing the steering effort on vehicles. It utilizes hydraulic pressure in turning the front wheels of the automobile(car). The system usually consists of a hydraulic pump and fluid reservoir, a power-actuating mechanism such as a power cylinder, a control valve arrangement, and a series of flexible hydraulic hoses and couplings to route the hydraulic fluid under pressure.
  4. 4. Types of power steering systems: The five main types of power steering system in cars are:  Integral  Rack and pinion  Hydro-boost  Linkage or booster  Remote reservoir
  5. 5. Integral system In integral system, the power cylinder and the control valve functions are combined into one unit located in the steering gearbox at the steering column’s end. Here, a pressure flow director valve senses steering wheel movement and directs the fluid pressure to either side of a rack piston, which is directly geared to the pitman arm shaft. As the rack piston travels up or down under fluid pressure, the pitman shaft rotates, applying the needed boost to turn the wheels. The spent fluid is then re-circulated back to the pump reservoir. The pressure line must withstand pressures ranging from 800 to 1300 psi. The return line normally kept less than 50 psi.
  6. 6. Integral system
  7. 7. Rack and pinion system In rack and pinion type, the gear on the steering column’s end is similar to the pinion gear in the differential: cut on an angle, and meshed with a steel bar (the rack) toothed on one side. The rack is mounted parallel to the front axle and as the steering wheel turns, it operates directly on the tie rods without the use of a pitman arm, idler or intermediate (or relay) rod. Adding a power assist to this type of steering is quite simple. The power piston is actually part of the rack, and the rack housing acts as the cylinder. The control valve is located in the pinion housing. Rotation of the steering shaft and pinion turns the valve to direct hydraulic pressure to either end of the rack piston.
  8. 8. Rack and pinion system
  9. 9. The Linkage (booster) system In the linkage system, the pump supplies hydraulic pressure to a control valve assembly attached to the pitman arm and intermediate rod. This control valve senses, by mechanical means, the steering wheel movement in either direction. The valve then directs the proper amount of hydraulic pressure to the power cylinder attached to the car’s frame on one end and to the intermediate rod on the other. As fluid pressure is applied to either end of the power cylinder, it pushes or pulls the intermediate rod to affect the steering boost. The fluid is then re-directed back to the pump reservoir via the return hose line. The pressure and cylinder lines must withstand pressure ranging from 800 to 1,100 psi. The return line normally carries up to 40 psi.
  10. 10. The Linkage (booster) system
  12. 12. Torque Converter The torque converter in an automatic transmission serves the same purpose as the clutch in a manual transmission. A torque converter is a fluid coupling that is used to transfer rotating power from a prime mover, such as an IC engine or electric motor, to a rotating driven load. As a more advanced form of fluid coupling, however, a torque converter is able to multiply torque when there is a substantial difference between input and output rotational speed, thus providing the equivalent of a reduction gear.
  13. 13. Parts of a torque converter: There are four components inside the very strong housing of the torque converter:  Pump (Impeller) Turbine Stator Transmission fluid
  15. 15. Working of Torque converter
  16. 16. Impeller (Pump) The housing of the torque converter is bolted to the flywheel of the engine, so it turns at whatever speed the engine is running at. The fins that make up the pump of the torque converter are attached to the housing, so they also turn at the same speed as the engine. The pump inside a torque converter is a type of centrifugal pump. As it spins, fluid is flung to the outside, much as the spin cycle of a washing machine flings water and clothes to the outside of the wash tub. As fluid is flung to the outside, a vacuum is created that draws more fluid in at the center.
  17. 17. Impeller (Pump)
  18. 18. Turbine The fluid then enters the blades of the turbine, which is connected to the transmission. The turbine causes the transmission to spin, which basically moves your car. The blades of the turbine are curved. This means that the fluid, which enters the turbine from the outside, has to change direction before it exits the center of the turbine. It is this directional change that causes the turbine to spin. So as the turbine causes the fluid to change direction, the fluid causes the turbine to spin. The fluid exits the turbine at the center, moving in a different direction than when it entered. It is seen that the fluid exits the turbine moving opposite the direction that the pump (and engine) are turning. If the fluid were allowed to hit the pump, it would slow the engine down, wasting power. This is why a torque converter has a stator.
  19. 19. Turbine
  20. 20. Stator The stator resides in the very center of the torque converter. Its job is to redirect the fluid returning from the turbine before it hits the pump again. This dramatically increases the efficiency of the torque converter. The stator has a very aggressive blade design that almost completely reverses the direction of the fluid. A one-way clutch (inside the stator) connects the stator to a fixed shaft in the transmission (the direction that the clutch allows the stator to spin). Because of this arrangement, the stator cannot spin with the fluid -- it can spin only in the opposite direction, forcing the fluid to change direction as it hits the stator blades.
  21. 21. Stator
  22. 22. Advantages: Noise insulation Good fuel consumption Less wear on the transmission Better starting dynamics and more driving pleasure when engine power remains the same.
  23. 23. Hydropneumatic suspension • Introduced by Citroën in 1954 • Commonly used by Mercedes- Benz,RR,Peugeot. • Purpose To provide soft,comfortable yet well controlled ride quality
  24. 24. Setup • N2 filled chambers called ‘spheres’ • One sphere per wheel with one main accumulator • Hollow metal ball with desmopan rubber membrane • Nitrogen pressure-75 bar
  25. 25. Layout
  26. 26. Working Pump powered by engine fills and pressurizes the accumulator-150 to 180 bars Powers the front brakes first Next the bottom of the spheres are filled with oil Suspension works by means of compacting the nitrogen in the spheres by means of the rods that push the LHM into the spheres
  27. 27. • Ride height controlled by means of height corrector • Spheres may need recharging after 60000 plus kms
  28. 28. Advantages • Hydropneumatic is naturally a progressive spring-rate suspension • Better control then suspension with steel springs • less endogenous friction than steel • Inexpensive in mass production
  29. 29. Disadvantages • Service sometimes requires a specifically trained mechanic. • Hydropneumatic suspension systems can be expensive to repair or replace, if poorly maintained or contaminated with incompatible fluids. • Failure of the hydraulic system will cause a drop in ride height and braking power will decrease. However, an acute failure will not lead to acute brake failure as the accumulator sphere holds enough reserve pressure to ensure safe braking far beyond that needed to bring a vehicle with a failed system to a standstill.
  30. 30. Hydrostatic Regenerative Braking • Energy from braking is used to power the vehicle. • Kinetic energy is converted to potential energy • Hydraulic hybrid producers: Bosch Rexroth Eaton corp. Parker haniffin Design types: Series and Parallel
  31. 31. Bosch Rexroth’s design • Parallel system • A hydraulic system serves as an auxiliary drivetrain and supplements a traditional one. This design typically uses the hydraulic drive when frequent stops and starts occur. • Basic parts are: axial piston unit with gearbox, accumulator, block control valve, ECU,PRV.
  32. 32. Storing braking energy The hydraulic axial piston unit is coupled to the drive train through a gearbox. When braking ,the axial piston unit uses the kinetic energy to charge the accumulator Conventional brakes kick in after the accumulator is filled.
  33. 33. Releasing the stored energy • Pressurized fluid in the accumulator now drives the axial piston unit that behaves like a motor • The motor in turn drives the mechanical drive train • Hrb unit is engaged until the accumulator discharges • Valve control block controls the filling of the accumulator
  34. 34. Parker’s series system • Runwise advanced series hybrid drive system • Series design • The system is comprised of an engine, primary pump, secondary drive pump and/or motors, accumulators, and Parker’s Power Drive Unit (PDU). A two-speed hydrostatic drive (low speed for 0-25 mph driving and high speed at 26-45 mph) for urban driving is combined with a mechanical direct drive for efficient operation at high speeds (45+ mph)
  35. 35. Hydraulic brakes • Braking mechanism which uses brake fluid to transfer pressure from the controlling unit • Fluid used is mostly ethylene glycol
  36. 36. Components • Brake pedal • Push rod (actuator rod). • A master cylinder assembly containing a piston assembly (made up of either one or two pistons, a return spring, a series of gaskets/ O rings and a fluid reservoir) • Reinforced hydraulic lines • Brake caliper assembly
  37. 37. Operation Brake pedal is pressed, a pushrod exerts force on the piston causing fluid from the brake fluid reservoir to flow into a pressure chamber through a compensating port This forces fluid through the hydraulic lines toward one or more calipers