Preface

Dear 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 and working 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.

Index

1. 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 industry uses compressed air for braking, therefore, an on board air compressor is used in it. This compressor gets drive from the engine. Thus some amount of power is consumed to run the compressor, and this power comes from the fuel of the truck (Diesel or CNG). The compressed air is stored in the air tanks. After the air tanks are filled with desired pressure the unloader valve releases the excess amount of air produced by the air compressor there onwards. The air compressor runs continuously and the excess amount of air produced are released in the atmosphere through unloader valve. Thus the power required to run the compressor is wasted, along with the fuel.

In “Compressor Cut Off system” the drive to the compressor gets cut off automatically ones the air tanks are full and hence no power is required to drive the compressor and no fuel is wasted.

One may think that the compressor will take very little amount of power to operate. And the compressor will take even less power to operate when the unloader valve is opened when no significant compression of air is done in the compressor. But the fact is that the compressor consumes more power of the engine during suction stroke than in compression stroke. And the losses increases even further as the inlet for the air compressor already has a negative pressure of air in it. Which makes it difficult for the air compressor to

suck the air inside the compressor and more power is consumed, as shown below in (FIG A).

Figure A

In turbo diesel engines the negative pressure at the hose pipe between air filter and turbo charger inlet is directly proportional to the speed of the engine (R.P.M.).

New generation trucks are equipped with viscous fan instead of normal radiator fan just to save around 2% of the total engine power. The viscous fan also cuts off when not required, hence it saves power. The power consumed by the air compressor will be definitely higher than the power consumed by the radiator fan. The power consumed by trucks air compressor will be definitely higher than the power consumed by a portable air compressor of similar capacity, size, pressure, and in similar R.P.M., because the trucks compressor sucks air from the pipe which connects the air filter to the inlet manifold, which already has a negative pressure of air in it. To increase the efficiency of the compressor a separate air filter should be fitted to the air compressor, as shown below in FIG (B).

SEPARATE AIR FILTER FOR THE COMPRESSOR

Figure B

Construction of Compressor Cut off System

Usually in Trucks the air compressor is driven continuously by the engine, therefore the air compressor crankshaft is directly connected to the engine through a gear or pulley. But in this case that is 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 the drive gear or pulley and the pressure plate shaft. The pressure plate shaft is connected to the crankshaft of the air compressor as shown in the figure. The clutch shaft will be connected to the drive gear or pulley by flange and nut bolt assembly or by single axial threaded joint with key. This shaft will rotate freely on two taper roller bearings to overcome axial thrust imparted by pressure plate on the clutch plate. One the taper roller bearing will be fitted on the timing gear housing and the second bearing will be fitted on the clutch housing as shown in the figure. On the other side of the clutch shaft the clutch plate will be fitted by flange and nut bolt assembly or by single axial threaded joint with key.

Compressor Cut off System Diagram.

Click the blank page if the figure is not visible FIG C

2) Pressure Plate Shaft.

Both sides of the pressure plate shaft are splined. The front portion of the shaft is splined so that the pressure plate can slide on it freely. The splines on the other end of the shaft are used to couple the pressure plate shaft with the crankshaft of the air compressor, with the help of a splined coupling. The coupling will have internal splines where as the pressure plate shaft and crankshaft will have external splines. The coupling will be held in position by two circlip. In the figure (a), I have shown that the pressure plate shaft will rotate on a single ball bearing, this is possible only when the splined coupling is fitted snugly (tightly). There should be no or very less backlash and play between the coupling and the splined shafts, otherwise it will create an imbalance while rotating. If this is not possible then the pressure plate shaft has to be supported by second bearing. This bearing will be called pilot bearing, which will be housed inside the clutch shaft, O/D of the bearing will be fitted inside the clutch shaft and the diameter of the pressure plate shaft has to be reduced from the front side so that it will fit inside the I/D of the bearing. For the clutch shaft to house the O/D of the pilot bearing, the diameter of the shaft from end should be more.

The pressure plate will be fitted with a sleeve on which the fork will be fitted as shown in figure. The fork will be pivoted on the clutch housing and the other end of the clutch shaft is fitted to the piston rod/ diaphragm rod. The piston / diaphragm reciprocate in the cylinder according to the condition. The left side inside cut off chamber is fitted with as spring. CAD DIAGRAM OFF COMPRESSOR CUT OFF SYSTEM

Figure C

In this system there is no need of unloader valve, only a non-return valve is used in its place. The non-return valve is fitted before the sensing tank as shown in the figure. After the sensing tank the system remains unchanged, that is, the air from the sensing tank goes inside the system protection valve and from it the air fills in the tank. The clutch 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 plate3. 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 of springs, because the spring inside the cut off chamber acts as a pressure plate spring, which pushes the pressure plate against the clutch plate to transmit the drive to the air compressor. The clamping force for the pressure plate should be high so that even if the clutch plate are fully worn out the drive should be easily transmitted to the compressor.

Working

In normal trucks when the air tanks are filled with desired pressure of air, then the excess amount of air is released to the atmosphere through an unloader valve. The unloader valve has a built in non return valve so that the air ones filled in the tank will not return in the compressor. In “Compressor Cut off System”, the unloader valve is not used instead of that a cut off chamber is used.

The cut off chamber consists of a cylinder in which a spring loaded piston or diaphragm with a piston rod as shown in the figure. In normal operation when the air pressure in the tanks is less at that time the piston or diaphragm along with piston rod is moved towards the right side and this makes the pressure plate fork to move towards the left the fork slides the pressure plate towards the left on the splines. As shown in Fig (D).

When the pressure plate is slid towards left side the pressure plate is pressed against the clutch plate. The clutch plate always rotates due to the clutch shaft which gets the drive from the engine through a gear or pulley. As the clutch and pressure plate is in contact with certain amount of pressure, the clutch plate will rotate the pressure plate. The pressure plate will in turn rotate the pressure plate shaft. The pressure plate shaft will rotate the air compressor crankshaft through a splined coupling or a flanged coupling. And hence the air compressor will run, there by compressing the air into the air tanks.

Figure D

The air compressor will continue working till the desired air pressure reaches.

As shown in the fig (E). Once the air pressure reaches the desired level the air pressure will push the piston/diaphragm towards left side of the cylinder and the clutch is disengaged by the clutch fork which is pivoted to the clutch housing and hence the drive to the compressor is stopped, and the compressor stops rotating.

As the compressor is not rotating unnecessarily therefore no additional fuel is consumed hence the fuel efficiency will increase and emissions will reduce.

Figure E

The Compressor Cut off System is used not only to save the losses due to friction, compression etc but also to avoid losses due to the suction of Air Compressor (Pumping losses).

The fact is that the compressor consumes considerable amount of power from the engine during its suction stroke. And the losses increases even further as the inlet for the air compressor already has a negative pressure of air in it. Which makes it difficult for the air compressor to suck the air inside the compressor and more power is consumed.

Therefore to increase the efficiency of the compressor a separate air filter 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 it is very important for us to know the actual power consumed by the air compressor.

The actual power consumed by the air compressor can be calculated by two ways.

1) Theoretical Power consumption.2) Actual Power consumption.

1) Theoretical Power consumption.

To find the power consumed by the air compressor theoretical the following 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 power consumption of the air compressor chances are that the value which we get may not be accurate.So it will be better to find the actual power consumption of air compressor.

2) Actual Power consumption.

To measure the actual power consumption of the air compressor 3to 4 reading have to be taken around various RPM range of the engine.

To get accurate readings it is advisable to perform the test in the vehicle 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 air compressor should be kept according to the reduction ratio of the air compressor. For example if the reduction ratio of the trucks compressor is 2:1, and if the engine is rotated at a constant speed of 2500r.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 consumed by the air compressor of the truck at a definite RPM range of the engine.

The power consumed by the air compressor is different at different engine RPM. So it is very important to find the power consumption of the air compressor at various engine RPM. And once we have different readings of the power consumption of air compressor we can plot a graph on engine rpm and power consumption of air compressor.

The power consumption of the air compressor will be different in the following 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 the coming future. As we know that fossil fuels are becoming scarce

nowadays and the fuel prices are touching the skies, moreover the pollution level due to automobiles are also increasing day by day. The “compressor cut off system” is my small contribution towards Mother Nature, as it reduces small amount of pollution and improves fuel efficiency of trucks and buses. This system is suitable for long distance trucks and busses as well as off road trucks.

Along with the “compressor cut off system” if we install a separate air filter for the compressor then the torque required to drive the compressor will further decrease and more C.F.M. of air will be produced hence more fuel saving will be done.

The design which I have shown is mechanical one. We can also use a electromagnetic clutch to engage and disengage the clutch as in case of air conditioner compressor of car A/C.

Some of trucks like Ashok Leyland trucks (e.g. cargo model) use water cooled air compressor. As in “compressor cut off system” the air compressor does not run continuously hence it will run cooler, hence the amount of water circulated in the air compressor can be reduced or it can be converted to air cooled compressors, thereby reducing the work done by the water pump and hence some more amount of fuel can be saved.

Dear Sir,

If you find any difficulty in understanding any topic in this project you may contact me under the following address.

Mantody Nikhil Saseendran,

Phone no 02642 248915.Mobile no 09427464213.

E Mail Id- nikhilauto2010@yahoo.com

A-2, New Rachna Nagar,Behind G.E.B,Bharuch – 392002,Gujarat, India.