PrefaceDear Sir,This project is for commercial vehicles which uses compressed air for braking and other systems. In this project I have mentioned about two things, 1) Compressor Suction Line Modification, and 2) Compressor Cut off System. In the compressor cut off system I have designed a mechanical system, but an electric clutch can also be used as in case of AC compressor to cut in or cut off as and when required.I hope you will like project which contains detailed construction andworking of both the above mentioned systems with self explanatory CAD drawings and sketch.And I also hope that these systems will be used by your company, for your future projects.
Index1. Introduction.2. Conventional Compressor Suction Line (Fig A)3. Modified Compressor Suction Line (Separate Air Filter (Fig B).4. Construction of Compressor Cut off System.5. Sketch of Compressor Cut off System (Fig C).6. CAD Diagram of Compressor Cut off System (Fig C).7. Working of Compressor Cut off System.8. Compressor Drive Engaged (Fig D).9. Compressor Drive Disengaged (Fig E).10. Power Consumption of Air Compressor.11. Scope of Compressor Cut off System.
Introduction Almost all the trucks and busses in automobile industryuses compressed air for braking, therefore, an on board aircompressor is used in it. This compressor gets drive from the engine.Thus some amount of power is consumed to run the compressor, andthis power comes from the fuel of the truck (Diesel or CNG). Thecompressed air is stored in the air tanks. After the air tanks are filledwith desired pressure the unloader valve releases the excess amountof air produced by the air compressor there onwards. The aircompressor runs continuously and the excess amount of air producedare released in the atmosphere through unloader valve. Thus thepower required to run the compressor is wasted, along with the fuel. In “Compressor Cut Off system” the drive to the compressorgets cut off automatically ones the air tanks are full and hence nopower is required to drive the compressor and no fuel is wasted. One may think that the compressor will take very littleamount of power to operate. And the compressor will take even lesspower to operate when the unloader valve is opened when nosignificant compression of air is done in the compressor. But the factis that the compressor consumes more power of the engine duringsuction stroke than in compression stroke. And the losses increaseseven further as the inlet for the air compressor already has a negativepressure of air in it. Which makes it difficult for the air compressor to
suck the air inside the compressor and more power is consumed, asshown below in (FIG A). Conventional Compressor Suction Line ENGINE Atmospheric Pressure LOW PRESSURE IN BOOST PRESSURE OUT EXHAUST GASSES TURBO CHARGER COMPRESSED AIR AIR AIR COMPRESSOR FILTERFigure A
In turbo diesel engines the negative pressure at thehose pipe between air filter and turbo charger inlet is directlyproportional to the speed of the engine (R.P.M.). New generation trucks are equipped with viscous faninstead of normal radiator fan just to save around 2% of the totalengine power. The viscous fan also cuts off when not required, henceit saves power. The power consumed by the air compressor will bedefinitely higher than the power consumed by the radiator fan. Thepower consumed by trucks air compressor will be definitely higherthan the power consumed by a portable air compressor of similarcapacity, size, pressure, and in similar R.P.M., because the truckscompressor sucks air from the pipe which connects the air filter to theinlet manifold, which already has a negative pressure of air in it. Toincrease the efficiency of the compressor a separate air filter shouldbe fitted to the air compressor, as shown below in FIG (B).
SEPARATE AIR FILTER FOR THE COMPRESSOR COMPRESSOR SUCTION LINE MODIFIED ENGINE Atmospheric Pressure LOW PRESSURE IN BOOST PRESSURE OUT EXHAUST GASSES TURBO CHARGER COMPRESSED AIR AIR SEPARATE COMPRESSOR AIR AIR FILTER FILTERFigure B
Construction of Compressor Cut off System Usually in Trucks the air compressor is driven continuouslyby the engine, therefore the air compressor crankshaft is directlyconnected to the engine through a gear or pulley. But in this case thatis in “Compressor Cut off System”, two additional shafts are used. 1) Clutch Plate Shaft. 2) Pressure Plate Shaft.1) Clutch Plate Shaft. The clutch plate shaft is used in between thedrive gear or pulley and the pressure plate shaft. The pressure plateshaft is connected to the crankshaft of the air compressor as shown inthe figure. The clutch shaft will be connected to the drive gear orpulley by flange and nut bolt assembly or by single axial threadedjoint with key. This shaft will rotate freely on two taper rollerbearings to overcome axial thrust imparted by pressure plate on theclutch plate. One the taper roller bearing will be fitted on the timinggear housing and the second bearing will be fitted on the clutchhousing as shown in the figure. On the other side of the clutch shaftthe clutch plate will be fitted by flange and nut bolt assembly or bysingle axial threaded joint with key. Compressor Cut off System Diagram.
Click the blank page if the figure is not visible FIG C2) Pressure Plate Shaft.
Both sides of the pressure plate shaft aresplined. The front portion of the shaft is splined so that the pressureplate can slide on it freely. The splines on the other end of the shaftare used to couple the pressure plate shaft with the crankshaft of theair compressor, with the help of a splined coupling. The coupling willhave internal splines where as the pressure plate shaft and crankshaftwill have external splines. The coupling will be held in position bytwo circlip. In the figure (a), I have shown that the pressure plateshaft will rotate on a single ball bearing, this is possible only whenthe splined coupling is fitted snugly (tightly). There should be no orvery less backlash and play between the coupling and the splinedshafts, otherwise it will create an imbalance while rotating. If this is not possible then the pressure plate shaft hasto be supported by second bearing. This bearing will be called pilotbearing, which will be housed inside the clutch shaft, O/D of thebearing will be fitted inside the clutch shaft and the diameter of thepressure plate shaft has to be reduced from the front side so that itwill fit inside the I/D of the bearing. For the clutch shaft to house theO/D of the pilot bearing, the diameter of the shaft from end should bemore. The pressure plate will be fitted with a sleeve on which the forkwill be fitted as shown in figure. The fork will be pivoted on theclutch housing and the other end of the clutch shaft is fitted to thepiston rod/ diaphragm rod. The piston / diaphragm reciprocate in thecylinder according to the condition. The left side inside cut offchamber is fitted with as spring.CAD DIAGRAM OFF COMPRESSOR CUT OFF SYSTEM
SEPERATE AIR FILTER AIR CUT OFF CHAMBER COMPRESSOR AIR NON RETURN VALVE INLET CLAMP COUPLING CLUTCH PRESSURE CRANK SENSING PLATE PLATE SHAFT TANK AIR TANK GEAR OR PULLEY AIR TANK SYSTEM PROTECTION VALVEFigure CIn this system there is no need of unloader valve, only a non-returnvalve is used in its place. The non-return valve is fitted before thesensing tank as shown in the figure. After the sensing tank the systemremains unchanged, that is, the air from the sensing tank goes insidethe system protection valve and from it the air fills in the tank. Theclutch and pressure plate assembly can be covered by housing.
List of parts for “Compressor Cut off System” are as follows: 1. Cut off chamber (Spring loaded pneumatic cylinder with piston Or diaphragm) 2. Clutch plate & Pressure plate 3. Pressure Plate shifting fork and sleeve. 4. Clutch plate shaft & Pressure plate shaft. 5. Splined coupling or flanged coupling. 6. Clutch Housing. 7. A Separate Small Air Filter for the Air Compressor.The clutch plate and pressure plate need not to have any sort ofsprings, because the spring inside the cut off chamber acts as apressure plate spring, which pushes the pressure plate against theclutch plate to transmit the drive to the air compressor. The clampingforce for the pressure plate should be high so that even if the clutchplate are fully worn out the drive should be easily transmitted to thecompressor.
Working In normal trucks when the air tanks are filled withdesired pressure of air, then the excess amount of air is released to theatmosphere through an unloader valve. The unloader valve has a builtin non return valve so that the air ones filled in the tank will notreturn in the compressor. In “Compressor Cut off System”, theunloader valve is not used instead of that a cut off chamber is used. The cut off chamber consists of a cylinder in which aspring loaded piston or diaphragm with a piston rod as shown in thefigure. In normal operation when the air pressure in the tanks is lessat that time the piston or diaphragm along with piston rod is movedtowards the right side and this makes the pressure plate fork to movetowards the left the fork slides the pressure plate towards the left onthe splines. As shown in Fig (D).When the pressure plate is slid towards left side the pressure plate ispressed against the clutch plate. The clutch plate always rotates dueto the clutch shaft which gets the drive from the engine through agear or pulley. As the clutch and pressure plate is in contact withcertain amount of pressure, the clutch plate will rotate the pressureplate. The pressure plate will in turn rotate the pressure plate shaft.The pressure plate shaft will rotate the air compressor crankshaftthrough a splined coupling or a flanged coupling. And hence the aircompressor will run, there by compressing the air into the air tanks.
COMPRESSOR DRIVE ENGAGED AIR CUT OFF CHAMBER COMPRESSOR SEPERATE AIR FILTER AIR NON RETURN VALVE CLUTCH INLET FORK = LOW PRESSURE CLAMP COUPLING CLUTCH PRESSURE CRANK PLATE PLATE SHAFT SENSING TANKGEAR AIR TANK ORPULLEY SYSTEM AIR TANK PROTECTION VALVEFigure DThe air compressor will continue working till the desired air pressurereaches.
As shown in the fig (E). Once the air pressure reaches the desiredlevel the air pressure will push the piston/diaphragm towards left sideof the cylinder and the clutch is disengaged by the clutch fork whichis pivoted to the clutch housing and hence the drive to the compressoris stopped, and the compressor stops rotating.As the compressor is not rotating unnecessarily therefore noadditional fuel is consumed hence the fuel efficiency will increaseand emissions will reduce.
COMPRESSOR DRIVE DISENGAGED AIR CUT OFF CHAMBER SEPERATE COMPRESSOR AIR FILTER CLUTCH AIR NON RETURN VALVE FORK INLET = CUT OFF PRESSURE (HIGH PRESSURE) CLAMP COUPLING CLUTCH PRESSURE CRANK PLATE PLATE SHAFT SENSING TANK AIR TANK GEAR OR PULLEY SYSTEM AIR TANK PROTECTION VALVEFigure EThe Compressor Cut off System is used not only to save the lossesdue to friction, compression etc but also to avoid losses due to thesuction of Air Compressor (Pumping losses).
The fact is that the compressor consumes considerable amount ofpower from the engine during its suction stroke. And the lossesincreases even further as the inlet for the air compressor already has anegative pressure of air in it. Which makes it difficult for the aircompressor to suck the air inside the compressor and more power isconsumed.Therefore to increase the efficiency of the compressor a separate airfilter should be fitted to the air compressor, as shown in Figure (B). Power Consumption of the Air Compressor
This is a very interesting topic. Before proceeding further itis very important for us to know the actual power consumed by theair compressor.The actual power consumed by the air compressor can be calculatedby two ways.1) Theoretical Power consumption.2) Actual Power consumption.1) Theoretical Power consumption.To find the power consumed by the air compressor theoretical thefollowing data’s should be known: • Working pressure of the compressor. • Pressure at which the unloader opens. • Suction pressure of the air compressor. • RPM of Air Compressor. • Inlet air temperature of the Air Compressor. • Friction losses etc.As so many factors are involved in finding the theoretical powerconsumption of the air compressor chances are that the value whichwe get may not be accurate.So it will be better to find the actual power consumption of aircompressor.2) Actual Power consumption.
To measure the actual power consumption of the air compressor 3to 4reading have to be taken around various RPM range of the engine.To get accurate readings it is advisable to perform the test in thevehicle itself. • The inlet and out let pipes of the air compressor should not be changed i.e. it should be connected in it respective places. • We must know the reduction ratio of the trucks air compressor (around 2:1 depending upon the model). • The engine should be started and kept running at a constant RPM at which we have to take the reading. • The compressor should be rotated independently of the engine with the help of a dynamometer or with the help of a electric motor of known HP.The relation between the RPM of the truck’s engine and the aircompressor should be kept according to the reduction ratio of the aircompressor. For example if the reduction ratio of the truckscompressor is 2:1, and if the engine is rotated at a constant speed of2500r.p.m then the compressor should be rotated at 2500/2=1250R.P.M.By performing the above steps we can get the actual power consumedby the air compressor of the truck at a definite RPM range of theengine.
The power consumed by the air compressor is different at differentengine RPM. So it is very important to find the power consumptionof the air compressor at various engine RPM. And once we havedifferent readings of the power consumption of air compressor wecan plot a graph on engine rpm and power consumption of aircompressor.The power consumption of the air compressor will be different in thefollowing 2 cases: 1) When the compressor is working in its maximum pressure. • In this stage the compressor has to overcome greater compression losses than suction losses. 2) When the unloader valve is opened. • In this stage the compressor has to overcome greater Suction losses than compression. Scope The compressor cut off system has tremendous scope in thecoming future. As we know that fossil fuels are becoming scarce
nowadays and the fuel prices are touching the skies, moreover thepollution level due to automobiles are also increasing day by day.The “compressor cut off system” is my small contribution towardsMother Nature, as it reduces small amount of pollution and improvesfuel efficiency of trucks and buses. This system is suitable for longdistance trucks and busses as well as off road trucks. Along with the “compressor cut off system” if we install a separateair filter for the compressor then the torque required to drive thecompressor will further decrease and more C.F.M. of air will beproduced hence more fuel saving will be done.The design which I have shown is mechanical one. We can also use aelectromagnetic clutch to engage and disengage the clutch as in caseof air conditioner compressor of car A/C.Some of trucks like Ashok Leyland trucks (e.g. cargo model) usewater cooled air compressor. As in “compressor cut off system”the air compressor does not run continuously hence it will runcooler, hence the amount of water circulated in the aircompressor can be reduced or it can be converted to air cooledcompressors, thereby reducing the work done by the water pumpand hence some more amount of fuel can be saved.Dear Sir, If you find any difficulty in understanding any topic inthis project you may contact me under the following address.
Mantody Nikhil Saseendran,Phone no 02642 248915.Mobile no 09427464213.E Mail Id- email@example.comA-2, New Rachna Nagar,Behind G.E.B,Bharuch – 392002,Gujarat,India.