Unit-IV

Unit-IV:Vehicle systems 

Introduction of chassis layouts, steering system, suspension system, braking system, cooling system and fuel injection system and fuel supply system. Study of Electric and Hybrid Vehicle systems. Study of power transmission system, clutch, gear box (Simple Numerical), propeller shaft, universal joint, differential gearbox and axles. Vehicle active and passive safety arrangements: seat, seat belts, airbags and antilock brake system.

The automobile can be considered to consist of five basic components : 

(a) The Engine or Power Plant : It is source of power. 

(b) The Frame and Chassis : It supports the engine, wheels, body, braking system, steering, etc. 

(c) The transmission which transmits power from the engine to the car wheels. It consists of clutch, transmission, shaft, axles and differential.

 (d) The body fitted on chassis. 

(e) Accessories including light, air conditioner/hearer, stereo, wiper, etc. 

Introduction of chassis layouts

Conventional frame:

 Integral Frame

 Semi - Integral Frame:

Suspension System

Introduction: The automobile frame and body are mounted on the front and rear axle not directly but through the springs and shock absorbers. The assembly of parts, which perform the isolation of parts from the road shocks, may be in the forms of bounce, pitch and roll is called suspension system.

Functions of suspension system:

1. It prevents the vehicle body and frame from road shocks.

2. It gives stability of the vehicle.

3. It safeguards the passengers and goods from road shocks.

4. It gives the good road holding while driving, cornering and braking.

5. It gives cushioning effect.

6. It provides comfort.

Requirements of suspension system:

1. There should be minimum deflection.

2. It should be of low initial cost.

3. It should be of minimum weight.

4. It should have low maintenance and low operating cost.

5. It should have minimum tyre wear.

Components of Suspension system: Coil springs, Leaf springs, shock absorbers, Spring shackles, stabilizer Independent suspension system: The independent suspension system means any arrangement that connects road wheels to the frame in which raise or fall of the wheel has no direct effect on the other wheel. It eliminates wheel wobbling.

Sprung Weight: It is weight of all the parts supported by the spring including weight of the spring.

Un sprung weight: It is the weight of all the parts between the spring and rod and the portion of spring weight it self.

Basic suspension movements:

1. Bouncing: The vertical movement of the complete body.

2. Pitching: The rotating movement of all the parts between the spring and road and the portion of spring weight itself.

3. Rolling: The movement about longitudinal axis produced by the centrifugal force during cornering.

Types of front Independent suspension system: 

There are three types:

1. Wish bone Type

2. Vertical guide type

3. Trailing Link Type

Wish bone Type of Front Independent suspension system:

In this type of suspension system coil springs are mostly used between the two suspension arms and are controlled with frame and at the open ends of the upper and lower wishbones which are connected to the chassis frame. The upper arm is shorter than lower one. This keeps the wheel track constant. The closed ends of the both arms are connected with steering knuckle, supported by means of kingpin. A coil spring is placed in between the lower suspension arm and frame.

Types of suspension springs:

1. Steel Springs : a. Leaf Springs   b. Coil Springs   c. Torsion bar Springs

2. Rubber Springs: a. Compression Springs   b. Progressive Springs

3. Plastic Srings

4. Air Springs: a. Bellow Type   b. Pestoon Type

5. Hydraulic Type

Construction and working of Leaf Springs:

Leaf springs are formed by bending. They are made of long strips of steel. Each strip is named as Leaf. The long leaf is called Master Leaf, and it consists of eyes at its both ends. One end is fixed to the chassis frame, the other end is fixed to the shackle spring. The spring will get elongated during expansion and shortened during compression. This change in length of spring is compensated by the shackle. The U-bolt and clamps are located at the intermediate position of the spring. The bronze or rubber bushes are provided on both eyes on the master leaf.

Types of Leaf Springs: There are five types of leaf springs

1. Full – elliptic type

2. Semi – elliptic type

3. Three Quarter – elliptic type

4. Transverse Spring type

5. Helper Spring type

1. Full elliptic :

The advantage of this type is the elimination of shackle and spring. The lubrication and wear frequently which are on of the main draw back of this type of springs.

2. Semi – elliptic :This type is more popular for rear suspension are used in 75% of cars.

3.Three – Quarter – elliptic type:

This type is rarely used in now-a-days. It gives resistance, but occupies more space than other types.

4. Transverse Type:

This type of spring is arrange transversely across the car instead of longitudinal direction. The transverse spring for front axle as shown in figure

5.Helper Springs:

The helper springs are used in heavy vehicles for rear suspension. When vehicle fully loaded the main sp[ring as well as helper spring to come in action and absorb the road shocks. When the load of the vehicle is less the helper spring will not act and the main spring only absorb the road shocks. Need of Shock Absorber: If the suspension springs are rigid enough, they will not absorb road shocks efficiently, and if they are flexible enough, they will continue to vibrate for longer time even after the bump has passed. Therefore, the springing device must be compromise flexibility and stiffness a shock absorber needed in Automobile Suspension system.

Braking System

INTRODUCTION:

Braking is the mechanism in the motor vehicle which is used to slowing down and stopping the vehicle to rest in the shortest possible distance.

Principle of Braking system: While operating the braking system the KINETIC ENERGY of moving vehicle is converted in to HEAT ENERGY.

Functions of Brakes: Brakes have the following functions.

1.It is used to stop the vehicle.

2.It is used to control the speed where and when required.

3.It is used to control the vehicle while descending along the slope.

4.To park the vehicle and held it in stationary position without the presence of Driver.

Requirements of Automobile Brakes:

1.It should work efficiently irrespective of road condition and quality.

2.The retardation must be uniform throughout its application.

3.The pedal effort must be within the convenient capacity of the driver.

4.It must be reliable and should not be effected by heat water and dust.

5.It should be in minimum weight.

6.It should have long life.

7.It should be easy to maintain and adjust.

8.Noise and vibrations are to be minimum.

9.There should be provision for secondary brake or parking brake.

Classification of Brakes: The following are the classifications of Brakes:

1.By method of power

a) Mechanical brakes

b) Hydraulic brakes

c) Vacuum brakes

d) Air brakes

e) Electrical brakes

f) Magnetic brakes

g) Air assisted hydraulic brakes

2.By method of application:

a) Service or foot brakes

b)Parking or hand brakes

3.By method of operation:

a) Manual

b) Servo

c) Power operation

4.By method of Braking contact

a. Internal Expanding Brakes

b.External Contracting Brakes

5.By Method of Applying Brake force:

a. Single Acting Brakes.

b. Double Acting Brakes.

Types of Mechanical Brakes:

a. Drum Brakes (Internal Expanding or External Contracting)

b. Disc Brakes (Single or Two caliper)

Drum Brakes:

Construction: The main components of drum brakes are

1. Brake drum

2. Back plate

3. Brake shoes

4. Brake Liners

5. Retaining Springs

6. Cam

7. Brake Linkages

In this system the wheel is attached to drum. There are brake shoes used to contact the rotating drum for braking operation. The shoes provide lining on their outer surface. The cam is used to lift the brake shoes at one end, other

end is connected by some method so as to make as the brake sleeve come into contact in the brake drum. The retaining spring is provided for bringing the brake shoes back to its original position, after releasing the brake pedal.

All these parts are fitted in the back plate and enclosed with brake drum. This system .

Working: When the pedal is pressed the cam moves the shoes outwards through linkages, there by coming in frictional contact with the rotating drum. As soon as the brake pedal is released the retaining springs help the brake shoes to brought back and release the brakes.

2. Disc brakes: There are two types of disc brakes:

1. Spot Type

a. Swinging Caliper Type

b. Sliding caliper type

2. Clutch Type

Construction: The discs are made of gray cast Iron. The brake pressure in case of disc brakes have to be much lighter than the drum brakes. It consists of rotating disc and two friction pads which are actuated by the four hydraulic wheel pistons contain in two halves of an assembly is called a caliper. The caliper assembly is secured to the steering knuckle in a front wheel brakes. The road wheel is fashioned to the outer surface of the disc.The friction pads rides freely on each side of the discs. They are in position being the hydraulic systems.

Working:When the brakes is applied hydraulic pressure is supply to the fluid inlet tube, due to which the wheel cylinder piston force the friction pads against the rotating disc. In the released piston, the spring hold the piston pads so that they maintain contact with disc surface.

cooling system 

A system, which controls the engine temperature, is known as a cooling system.

 NECESSITY OF COOLING SYSTEM The cooling system is provided in the IC engine for the following reasons: 

• The temperature of the burning gases in the engine cylinder reaches up to 1500 to 2000°C, which is above the melting point of the material of the cylinder body and head of the engine. (Platinum, a metal which has one of the highest melting points, melts at 1750 °C, iron at 1530°C and aluminium at 657°C.) Therefore, if the heat is not dissipated, it would result in the failure of the cylinder material. 

• Due to very high temperatures, the film of the lubricating oil will get oxidized, thus producing carbon deposits on the surface. This will result in piston seizure. • Due to overheating, large temperature differences may lead to a distortion of the engine components due to the thermal stresses set up. This makes it necessary for, the temperature variation to be kept to a minimum. 

• Higher temperatures also lower the volumetric efficiency of the engine. 

REQUIREMENTS OF EFFICIENT COOLING SYSTEM 

The two main requirements of an efficient cooling system are:

 1. It must be capable of removing only about 30% of the heat generated in the combustion chamber. Too much removal of heat lowers the thermal efficiency of the engine.

 2. It should remove heat at a fast rate when the engine is hot. During the starting of the engine, the cooling should be very slow so that the different working parts reach their operating temperatures in a short time.

 TYPES OF COOLING SYSTEM There are two types of cooling systems: 

(i) Air cooling system and (ii) Water-cooling system. 

AIR COOLING SYSTEM :

In this type of cooling system, the heat, which is conducted to the outer parts of the engine, is radiated and conducted away by the stream of air, which is obtained from the atmosphere. In order to have efficient cooling by means of air, providing fins around the cylinder and cylinder head increases the contact area. The fins are metallic ridges, which are formed during the casting of the cylinder and cylinder head The amount of heat carried off by the air-cooling depends upon the following factors:

 (i) The total area of the fin surfaces, 

(ii) The velocity and amount of the cooling air and

 (iii) The temperature of the fins and of the cooling air. 

Air-cooling is mostly tractors of less horsepower, motorcycles, scooters, small cars and small aircraft engines where the forward motion of the machine gives good velocity to cool the engine. Air-cooling is also provided in some small industrial engines. In this system, individual cylinders are generally employed to provide ample cooling area by providing fins. A blower is used to provide air. 

Advantages of Air Cooled Engines Air cooled engines have the following advantages:

 1. Its design of air-cooled engine is simple.

 2. It is lighter in weight than water-cooled engines due to the absence of water jackets, radiator, circulating pump and the weight of the cooling water. 

3. It is cheaper to manufacture. 

4. It needs less care and maintenance. 

5. This system of cooling is particularly advantageous where there are extreme climatic conditions in the arctic or where there is scarcity of water as in deserts. 

6. No risk of damage from frost, such as cracking of cylinder jackets or radiator water tubes. 

WATER COOLING SYSTEM It serves two purposes in the working of an engine: 

a) It takes away the excessive heat generated in the engine and saves it from over heating. 

b) It keeps the engine at working temperature for efficient and economical working. 

Parts of Liquid Cooling System The main parts in the water-cooling system are: (i) water pump, (ii) fan, (iii) radiator and pressure cap, (iv) fan belt (v) water jacket, (vi) thermostat valve, (vii) temperature gauge and (viii) hose pipes. 

Water Pump:This is a centrifugal type pump. It is centrally mounted at the front of the cylinder block and is usually driven by means of a belt. This type of pump consists of the following parts: (i) body or casing, (ii) impeller (rotor), (iii) shaft, (iv) bearings, or bush, (v) water pump seal and (vi) pulley. The bottom of the radiator is connected to the suction side of the pump. The power is transmitted to the pump spindle from a pulley mounted at the end of the crankshaft. Seals of various designs are incorporated in the pump to prevent loss of coolant from the system. 

Fan: The fan is generally mounted on the water pump pulley, although on some engines it is attached directly to the crankshaft. It serves two purposes in the cooling system of a engine. 

(a) It draws atmospheric air through the radiator and thus increases the efficiency of the radiator in cooling hot water. 

(b) It throws fresh air over the outer surface of the engine, which takes away the heat conducted by the engine parts and thus increases the efficiency of the entire cooling system. 

Radiator :The purpose of the radiator is to cool down the water received from the engine. The radiator consists of three main parts: (i) upper tank, (ii) lower tank and (iii) tubes. Hot water from the upper tank, which comes from the engine, flows downwards through the tubes. The heat contained in the hot water is conducted to the copper fins provided around the tubes. An overflow pipe, connected to the upper1 tank, permits excess water or steam to escape. There are three types of radiators: (i) gilled tube radiator, (ii) tubular radiator  and (iii) honey comb or cellular radiator 

fuel injection system and fuel supply system

The fuel supply system of spark ignition engine consists of: (i) Fuel tank (ii) Fuel filter (iii) Sediment bowl (iv) Fuel lift pump (v) Carburettor (vi) Fuel pipes (vii) Inlet manifold

 In some spark ignition engine, the fuel tank is placed above the level of the carburettor. The fuel flows from the fuel tank to the carburettor under the action of gravity. There are one or two filters between the fuel tank and the carburettor. A transparent sediment bowl is also provided to hold the dust and dirt of the fuel. If the tank is below the level of the carburettor, a lift pump is provided in between the tank and the carburettor for forcing fuel from the tank to the carburettor of the engine. The fuel comes from the fuel tank to the sediment bowl and then to the lift pump. From there the fuel goes to the carburettor through suitable pipe. From the carburettor, the fuel goes to the engine cylinder, through the inlet manifold of the engine. 

CARBURETTOR: The process of preparing an air-fuel mixture away from the cylinders of an engine is called carburetion and the device in which this process take place is called carburettor.

 Principle of carburettor: The basic principle of all carburettor design that when air flows over the end of a narrow tube or jet containing liquid, some liquid is drawn into the air stream. The quantity of liquid drawn into the air stream increases as the speed of air flow over the jet increases and also the quantity is greater if the jet is made larger. 

In practice, the fuel level in the jet is maintained by a float chamber. The fuel levels in the jet and in the float chamber are always the same. As the fuel is consumed, the level in the float chamber goes down. The float in the float chamber also goes down and the needle valve comes off its seat allowing more fuel into the chamber from the fuel tank. When the fuel level rises to its correct level, the float presses the needle valve back to its seat and cuts off the fuel flow. The velocity of the air flowing over the jet is increased by a constriction in the induction pipe known as venturi. A throttle butterfly valve provides an adjustable obstruction in the induction pipe. It is used to control the flow of air-fuel mixture to the engine. As the butterfly valve is turned into the accelerate position, the airflow over the jet increases and more fuel is drawn out into the air stream, keeping the mixture strength constant. 

A second butterfly valve called choke is used to provide a richer mixture for the engine to start in cold condition. The choke controls the volume of air entering into the venturi. A second jet is fitted near the throttle butterfly, which is used when the engine is idling. 

Fuel is delivered to the float chamber through fuel pipe either by gravity or by a pump. The float chamber is connected with the mixing chamber (venturi) via fuel nozzle equipped with fuel jet. 

Function of Carburettor: The main functions of the carburettor are: 

(i) To mix the air and fuel thoroughly 

(ii) To atomise the fuel 

(iii) To regulate the air-fuel ratio at different speeds and loads and 

(iv) To supply correct amount of mixture at different speeds and loads. 

FUEL SYSTEM OF DIESEL ENGINE 

During engine operation, the fuel is supplied by gravity from fuel tank to the primary filter where coarse impurities are removed. From the primary filter, the fuel is drawn by fuel transfer pump and is delivered to fuel injection pump through second fuel filter. The fuel injection pump supplies fuel under high pressure to the injectors through high pressure pipes. The injectors atomise the fuel and inject it into the combustion chamber of the engine. The fuel injection pump is fed with fuel in abundance. The excess fuel is by-passed to the intake side of the fuel transfer pump through a relief valve. 

The main components of the fuel system in diesel engine are: (1) fuel filter (2) fuel lift pump (3) fuel injection pump (4) atomisers and (5) high pressure pipe. 

Two conditions are essential for efficient operation of fuel system: (i) The fuel oil should be clean, free from water, suspended dirt, sand or other foreign matter, (ii) The fuel injection pump should create proper pressure, so that diesel fuel may be perfectly atomised by injectors and be injected in proper time and in proper quantity in the engine cylinder. Fuel should be filtered before filling the tank also. If these precautions are followed, ninety per cent of diesel engine troubles are eliminated. 

FUEL LIFT PUMP (FEED PUMP OR TRANSFER PUMP) :It is a pump, which transfers fuel from the fuel line to the fuel injection pump. It is mounted on the body of fuel injection pump. It delivers adequate amount of fuel to the injection pump. The pump consists of: (I) body (2) piston (3) inlet valve and (4) pressure valve. The valves are tightly pressed against their seats by springs. The piston is free to slide in the bore. The fuel contained in the space below the piston is forced to flow through secondary fuel filter to the injection pump. At the same time downward movement of the piston creates a depression in the space above the piston which, causes the fuel to be drawn in the transfer pump from the fuel tank through the inlet valve and the primary filter. 

FUEL INJECTING PUMP :It is a pump, which delivers metered quantity of fuel to each cylinder at appropriate time under high pressure. Tractor engines may use two types of fuel injection pump: (i) Multi-element pump and (ii) Distributor (Rotary) type pump. 

Fuel Injector: It is the component, which delivers finely atomised fuel under high pressure to the combustion chamber of the engine. Modern tractor engines use fuel injectors, which have multiple holes. Main parts of injector are: nozzle body and needle valve. The nozzle body and needle valve are fabricated from alloy steel. The needle valve is pressed against a conical seat in the nozzle body by a spring. The injection pressure is adjusted by adjusting the screw. 

FUEL INJECTION SYSTEM: Diesel fuel is injected in diesel engine through injectors with the help of fuel injection pump. The system using injectors, fuel injection pump, fuel filter, and fuel lines is called fuel injection system. 

The main functions of fuel injection system are:

 (i) To measure the correct amount of fuel required by engine speed and load, 

(ii) To maintain correct timing for beginning and end of injection, 

(iii) To inject the fuel into the combustion space against high compression pressure.

 (iv) To atomise the fuel for quick ignition. 

Process of fuel injection in diesel engine is of two types: (i) Air injection (ii) Solid injection. 

Air injection: In this process, the engine uses compressed air to force the fuel into the cylinder. It is a bulky system and hence it is not considered very suitable for vehicles and tractors. It is mostly used on heavy-duty stationary engines. 

Solid injection: A high-pressure pump is used for forcing the fuel into the combustion chamber. 

Study of Electric and Hybrid Vehicle systems

Need Electric and Hybrid vehicles

 Over dependence on petrol/diesel

 Rising petrol/diesel prices

 Pollution and the resultant global warming

 Noise in conventional vehicles

 Need for alternate power sources

 Need for Eco friendly vehicles

 EV, HEV - The solution

Electric vehicles

 An Electric vehicle is an automobile that is propelled by one or more electric motors, using electrical energy stored

in energy storage device.

 The primary components are motor, controller, power source, and transmission.

Advantages

 No Gas Required

 No Emissions

 Cost Effective

 Low Maintenance

 Pay back period

 Low noise

Disadvantages

 High Initial Cost- Many times that of conventional vehicles

 Short Driving Range- Range anxiety

 Recharging takes much longer time than refueling gasoline lack of charging infrastructure

 Battery pack takes space and weight of the vehicle which otherwise is available to the people

Concept of hybridization

 Multiple sources of power

 Making ICE work in most efficient range

 Sizing of motor and ICE lower compared to conventional vehicles and EV

Hybrid Vehicles

 The term hybrid vehicles in general usage refer to vehicles with two or three different type of sources delivering power to the wheels for propulsion.

 The most common hybrid vehicles have an IC engine and one or more electric machines for vehicle propulsion.

 The IC engine can be used to generate electric energy ‘on board’ to power the machines.

Classification

 Based on the path of energy flow

 Mechanical power transmission path (MPTP)

 Electrical power transmission path (EPTP)

 Combination of MPTP and EPTP

 Based on architecture

 Series

 Parallel

 Series-Parallel

Based on degree of hybridization

 Mild

 Power

 Energy

Charge depleting

Charge sustaining

Challenges

 Time of battery changing is long

 Batteries are heavy (100kg extra weight consumes 2L/100km more)

 Batteries are expensive

 Low performance in hot or cold temperatures also may damage the battery

 Very sensitive to overcharge/undercharge(Battery life reduces dramatically)

 Contain toxic heavy metals, disposal issue

Advantages of a Hybrid Car

 Environment friendly

 Financial benefits

 Less dependence on fossil fuels

 Regenerative braking system

 Built from lighter materials

Disadvantages of a Hybrid car

 Less power

 Expensive

 Poor handling

 Higher maintenance cost

Study of power transmission system

Introduction to Transmission System : 

The transmission system is the system utilizing which power developed by the engine is transmitted to road wheels to propel the vehicle. In automobiles, the power is developed by the engine which is used to turn wheels. Therefore, the engine is to be connected to the transmission systems for transmitting power to wheels. Also, there should be a system utilizing which engine could be engaged and disengaged with the transmission system smoothly and without shock so that the vehicle mechanism is not damaged and passengers do not feel inconvenience. A clutch is employed in automobiles for this purpose. 

• The engines employed in automobiles are of very high speed. Hence, a speed reduction is necessary to reduce the speed to moderate level as well as to get the required high torque while moving from rest. For this purpose, a gearbox is employed in automobiles.

• The figure shows the general arrangement of a power transmission system of an automobile.

• The motion of the crankshaft is transmitted to the gearbox through the clutch. The gearbox consists of a set of gears to change the speed according to the requirement. The motion is then transmitted to the propeller shaft from the gearbox through a universal joint. The purpose of the universal joint is to connect two shafts at an angle for power transmission.

• The power is transmitted to the differential unit through another universal joint. Finally, the power is transmitted from the differential to wheels through the rear end. The differential unit is used to provide the relative motion between two-run wheels while the vehicle is taking a turn.

Definition Of Transmission System : The mechanism that transmits the power developed by the engine of automobile to the engine to the driving wheels is called the TRANSMISSION SYSTEM (or POWER TRAIN).

It is composed of –  Clutch  The gear box  Propeller shaft  Universal joints  Rear axle  Wheel  Tyres 

Requirements Of Transmission System :-

  Provide means of connection and disconnection of engine with rest of power train without shock and smoothly.

  Provide a varied leverage between the engine and the drive wheels 

 Provide means to transfer power in opposite direction.

  Enable power transmission at varied angles and varied lengths. 

 Enable speed reduction between engine and the drive wheels in the ratio of 5:1.

  Enable diversion of power flow at right angles. 

 Provide means to drive the driving wheels at different speeds when required. 

 Bear the effect of torque reaction , driving thrust and braking effort effectively 

The above requirements are fulfilled by the following main units of transmission system :-  Clutch  Gear Box  Transfer Case  Propeller Shaft and Universal Joints.  Final Drive  Differential  Torque Tube  Road Wheel 

clutch

A clutch is a mechanism which enables the rotary motion of one shaft to be transmitted at will to second shaft ,whose axis is coincident with that of first. 

 Clutch is located between engine and gear box. When the clutch is engaged, the power flows from the engine to the rear wheels through the transmission system and the vehicle moves . when the clutch is disengaged ,the power is not transmitted to the rear wheels and the vehicle stops, while the engine is still running. 

 Clutch is disengaged when a) Starting the engine, b) Shifting the gears, c) Idling the engine 

clutch is engaged only when the vehicle is to move and is kept engaged when the vehicle is moving. 

Function Of a Clutch :- 

a) To permit engagement or disengagement of a gear when the vehicle is stationary and the engine is running

 b) To transmit the engine power to the road wheels smoothly without shock to the transmission system while setting the wheel in motion. 

c) To permit the engaging of gears when the vehicle is in motion without damaging the gear wheels 

Principle Of Operation Of a Clutch :-  The clutch principle is based on friction . when two friction surface are brought in contact with each other and pressed they are united due to friction between them. If one is revolved the other will also revolve . The friction between the two surfaces depends upon 

i. Area of the surface, 

ii. Pressure applied upon them, 

iii. Coefficient of friction of the surface materials

 Here , One surface is considered as driving member and the other as driven member. 

The driving member of a clutch is the flywheel mounted on the crankshaft, the driven member is the pressure plate mounted on the transmission shaft . Friction surfaces (clutch plates ) are between the two members (driving and driven). On the engagement of the clutch, the engine is connected to the transmission (gear box) and the power flows from the engine to the rear wheels through the transmission system . when the clutch is disengaged by pressing a clutch pedal, the engine is disconnected from the transmission and consequently the power does not flow to the rear wheels while the engine is still running. 

Principles of Operation of Friction Clutch

• The clutch works on the principle of friction. In Figure, the driving shaft A with flange C is rotating at ‘N’ rpm, and shaft B with the flange 0 is keyed to the driven shaft which is in stationary position when the clutch is not engaged.

• Now, an external force is applied to the flange D so that it comes in contact with flange C.

• As soon as the contact is made, they are united due to friction between them and the flange D starts rotating with flange C. The rotational speed of flange D depends on the friction between surfaces C and D which in turn proportional to the external force applied.

• Functions of a Clutch:

The torque developed b the engine at the starting speed is very low. Therefore, it is not possible to start the engine under load. This requires that the transmission system should provide a means of connecting and disconnecting the engine from the rest of the transmission system. Such an operation must be smooth and without shock to the occupants of the vehicle.

Thus the two main functions of a clutch are:

1. To engage and disengage the transmission from engine to the remaining parts of the transmission. (To allow the engine to be separated from rest of the transmission system) This is required when:

(a) Starting and running the engine at a sufficiently high speed lo generate sufficient power necessary for moving the vehicle from rest.

(b) Shifting the gears so that damage to gear teeth can be avoided.

(c) Stopping the vehicle after applying brakes.

2. The second function of the clutch is to allow the engine to take up the driving load of the vehicle gradually and without shock.

Requirements of clutch:

The main requirements of a clutch are as follows:

• It should be able to transmit the maximum torque of the engine.

• It should engage gradually to avoid sudden jerks.

• It should be able to dissipate a large amount of heat generated during clutch operation.

• It should be dynamically balanced, particularly in the case of high-speed engine clutches.

• It should have a suitable mechanism to damp vibrations and to eliminate noise produced during power transmission.

• It should be as small as possible so that it will occupy minimum space.

• It should be easy to operate requiring as little exertion as possible on the part of the driver.

• It should be made as light as possible so that it will continue to rotate for any length of time after the clutch has been disengaged.

• It must be trouble-free and have longer life.

• It must be easy to inspect, adjust, and repair.

Clutch Friction Lining material and their Necessity : 

The materials for clutch lining are:

1. Leather

2. Cork

3. Fabric

4. Asbestos

5. Raybestos and Ferodo

6. Non- asbestos clutch lining material.

Necessity of clutch lining: 

1. To transmit maximum power from engine flywheel transmission without jerk

2. To dissipate the heat and able to withstand higher heat generated

3. It should have a higher coefficient of friction

4. It should be cheap and easy to manufacture.

Main parts of Clutch : 

It consists of

(a) a driving member,

•  The driving members consists of a flywheel which is mounted on the engine crankshaft

• The flywheel is bolted to a cover which carries pressure plate, pressure springs, and release levers.

• As the flywheel is bolted to the cover assembly, thus, the entire assembly of the flywheel and the cover rotate all the time.

• The clutch housing and cover provided with openings so that the heat produced during the function dissipates easily

(b) a driven member, and

• The driven members consist of a disc or plate called a clutch plate.

• The clutch is free to slide on the splines of the clutch shaft.

• It carries friction materials on both of its surfaces.

• When the clutch plate is gripped between the flywheel and the pressure plate, it rotates the clutch shaft through splines.

(c) an operating member.

The operating member consists of a pedal or lever which can be pressed to disengage the driving and driven plate.

Types Of Clutch :

Some types of clutches used in vehicles are given below :

The classification of clutch

1)Positive clutch

Dog clutch or spline clutch (In and Out clutch)

2) Gradual engagement Clutch

a) Electromagnetic clutch

b) Vacuum operated clutch

c)Hydraulic clutch

d) Fluid clutch or Fluid flywheel clutch

e) Friction clutch

i) Cone clutch (Internal and External)

ii)Disc Plate clutch (Single plate and Multi-Plate)

iii) Semi centrifugal clutch

iv) Diaphragm or conical spring clutch (Taper finger and crown spring)

v) Centrifugal clutch

Single plate Clutch : 

A single disc or plate clutch as shown in the figure consists of a clutch plate whose sides are faced with the friction material (usually ferrodo). It is mounted on the hub which is free to move axially along the splines of the driven shaft. The pressure plate is mounted inside the clutch body which is bolted to the flywheel. Both the pressure plate and the flywheel rotate with the engine crankshaft or the driving shaft. The pressure plate pushes the clutch plate towards the flywheel by a set of strong spring which is arranged radially inside the body. The three levers (also known as release levers or fingers) are carried on the pivots suspended from the case of the body. These are arranged in such a manner so that the pressure plate moves away from the flywheel by the inward movement of a thrust bearing. The bearing is mounted upon the forked shaft and moves forward when the clutch pedal is pressed.

Necessity of Single plate clutch

1) To transmit a large amount of torque single plate clutch required

2) Response time to operate is very less compared to the multi-plate clutch.

3) It generates low heat so no need of cooling media required.

4) It should be dynamically balanced and easy to operate.

Working:

Disengaging the clutch:

When the clutch pedal is pressed down, it’s linkage forces the thrust bearing to move towards the flywheels and pressing the pressure plate away from the flywheel thereby the compression springs are compressed. This action removes the pressure from the clutch plate and the driving shaft comes to a stationary position.

Engaging the clutch:

On the other hand when the foot is taken off from the clutch pedal, the thrust bearing moves back by levers this action allows the springs to extend, and thus pressure plate pushes the clutch plate back towards the flywheel. The clutch is engaged and power is transmitted from engine to gearbox.

Application of Single plate clutch:

1. Most commonly used in cars.

2. Used in Light commercial vehicles and heavy transport vehicles.

Multi-Plate (Dry) Clutch:

It is the extension of a single plate clutch. It consists of several clutch (friction) as well as pressure plates. As the number of plates increased, the friction surfaces also increase. The increase in the number of friction surfaces increases the capacity of the clutch to transmit torque. The plates are alternately fitted to the engine shaft and gearbox shaft. They are firmly pressed by strong coil springs and assembled in a cover assembly. Each alternate plate has inner and outer splines, this each of the alternate plate slides on the splines on the pressure plate.

Working of Multi-Plate Clutch:

The pressure plates are used to apply the pressure on friction plates and the inside diameter of the pressure plate is splined while making the inside diameter splined, the rotating motion of the pressure plate is restricted. The pressure plate moves on the driven shaft axially. When we apply the pedal the pressure plates and the friction plates come in contact with each other and the speed or power is transmitted from the engine shaft to the transmission shaft.

Applications Of Multi-Plate Clutch :This type of clutch is used in Scooters and Motor Cycles, where space availability is limited. Besides, this finds the application in some Heavy Transport Vehicles and Racing Cars where high torque is to be transmitted. 

Diaphragm clutch:

Clutch remains usually in the engaged condition. It is required to depress the clutch pedal to disengage the clutch. When a driver or an operator drives a vehicle he is required to engage clutch by depressing clutch pedal. As the driver depresses the clutch pedal, the effort applied gets transmitted either through level or cable to clutch release fork. The fork pushes clutch release bearing towards the engine side due to which clutch release levels shown in figure get displaced getting pressure plate in the backward direction. This action creates clearance between drive and driven members resulting in disengagement of the clutch. As the driver leaves the clutch pedal it returns to its original position due to which pressure plate put thrust on the clutch plate from one side and flywheel on the other. This is how the clutch gets engaged.

Centrifugal clutch

• When the engine is started, the speed of the driving shaft is less, so the centrifugal force is also less. Therefore, shoes (flyweights) do not move outwards and torque is not transmitted to the rear wheel. As the speed of the engine increases, the centrifugal force also increases.

• At certain engine speed, the shoes fly off outwards due to increased centrifugal force and they come in contact with the driven member. Now both the driving and driven members rotate together and the clutch is said to be engaged.

• Thus the engine torque is transmitted to the rear wheel.

• When the engine speed decreases, the centrifugal force also decreases. Now the shoes return to their original position due to spring force which results in a disengagement of the clutch and torque is not transmitted to the rear wheel.

Application of Centrifugal Clutch : 

1. Used in Automatic transmission vehicles like mopeds and two-wheelers without gear.

2. Used in semi-automatic transmission vehicles like some modern cars.

Cone Clutch:

Cone clutch consists of friction surfaces in the form of a cone. The engine shaft consists of the female cone. The male cone is mounted on the splined clutch shaft. It has friction surfaces on the conical portion. The male cone can slide on the clutch shaft. Hen the clutch is engaged the friction surfaces of the male cone are in contact with that of the female cone due to force of the spring. When the clutch pedal is pressed, the male cone slides against the spring force, and the clutch is disengaged.

The only advantage of the cone clutch is that the normal force acting on the friction surfaces is greater than the axial force, as compared to the single-plate clutch in which the normal force acting on the friction surfaces is equal to the axial force. The disadvantage in the cone clutch is that if the angle of the cone is made smaller than 200 the male cone tends to bind in the female cone and it becomes difficult to disengage the clutch. Cone clutches are generally now only used in low peripheral speed applications although they were once common in automobiles and other combustion engine transmissions. They are usually now confined to very specialist transmissions in racing, rallying, or in extreme off-road vehicles, although they are common in powerboats. Small cone clutches are used in synchronizer mechanisms in manual transmissions. 

Dog & Spline Clutch:

• This type of clutch is used to lock two shafts together or to lock a gear to a shaft. It consists of a sleeve having two sets of internal splines. It slides on a splined shaft with the smallest diameter splines. The bigger diameter splines match with the external dog clutch teeth on the driving shaft. When the sleeve is made to slide on the splined shaft, its teeth match with the dog clutch teeth of the driving shaft. Thus the sleeve turns the splined shaft with the driving shaft.

• The clutch is said to be engaged. To disengage the clutch, the sleeve is moved back on the splined shaft to have no contact with the driving shaft. This type of clutch does not tend to slip. The driven shaft revolves exactly at the same speed of the driving shaft, as soon as the clutch is engaged. This is also known as a positive clutch.

propeller shaft

The propeller shaft connects the transmission shaft to the pinion shaft at the wheel axle. The propeller shaft is also called driveline shaft or drive shaft. 

The propeller shaft carries the power from the engine, clutch and transmission unit to the driving wheels of the vehicle, through the final drive and differential unit.

Functions of the propeller shaft

In most of the automotive vehicles, the engine is located at the front and the rear wheels of the vehicle are being driven. This arrangement stipulates a longer propeller shaft to be used. In some arrangements two or three propeller shafts are used to make up the length.

In some vehicles, the engine is kept at the front and the front wheels of the vehicle are being driven. In some other vehicles, the engine is at the rear and the rear wheels are being driven. For such arrangements a short propeller shaft is used to drive each wheel.

The engine and the transmission unit are attached to the vehicle frame with some flexible mounting. The rear axle housing with differential and wheels are attached to the vehicle frame by suspension springs.

universal joint

Universal Joints

Universal joints are capable of transmitting torque and rotational motion from one shaft to another when their axes are inclined to each other by some angle, which may constantly vary under working conditions. Universal joints are incorporated in the of vehicle’s transmission system to perform three basic applications :

(a) Propeller shaft end joints between longitudinally front mounted gearbox and rear final drive axle.

(b) Rear axle drive shaft end joints between the sprung final drive and the unsprung rear wheel stub axle.

(c) Front axle drive shaft end joints between the sprung front mounted final drive and the unsprung front wheel steered stub axle.

Universal joints have movement only in the vertical plane when they are used for lon­gitudinally mounted propeller shafts and transverse rear mounted drive shafts. When these joints have been used for front outer drive shaft they have to move in both the vertical and horizontal plane to accommodate both vertical suspension deflection and the swivel pin angular movement to steer the front road wheels. The compounding of angular working movement of the outer drive shaft steering joint in two planes imposes large and varying working angles even when the torque is being transmitted to the stub axle. Due to the severe working conditions, special universal joints known as constant velocity joints are employed. These joints have been designed to absorb torque and speed fluctuations and to operate reliably with very little noise and wear having long life.

Types Of Universal Joint :

Three types of universal joints are commonly used. These are listed below:

(a) Cross or spider joint (variable velocity joint).

(b) Ball and trunnion joint (variable velocity joint).

(c) Constant velocity joints.

Cross Type Universal Joint (B and C)

• It consists of two Y-shaped yokes and a cross piece (spider). One yoke is connected to driving shaft and other is connected to driven shaft. The cross-piece has four-arms which are known as trunnions and are attached to the ends of yokes. Four needle bearings are provided – one for each arm of cross-piece. These bearings allow the yoke to swing around the trunnion when driving and driven shaft remove together at an angle.

Ball and Trunnion Joint:

• This type of joint consists of a ball type head which is fastened to one end of the propeller shaft. A pin is also pressed through this end of shaft. Two steel balls are fitted at the end of this pin. The joint facilitates rotary motion through ball and pin. The balls can also move axially.

• Ball and trunnion joint is also a variable velocity joint.

Constant Velocity Universal Joint

• This type of joint permits movement of both driving and driven shafts at constant velocity. Because, two joints in this case operate at same angles. These joints are generally used when the automobile in a front wheel (axle) drive. Because speed variation between driving and driven shaft will introduce difficulty in steering and excessive tire wear.

Backbone chasis

• Monoque chassis: Monocoque is a type of chassis construction in which the body of the vehicle serves as the main structural component, rather than relying on a separate frame. The term "monocoque" is derived from the French words "mono," meaning "single," and "coque," meaning "shell."

• In a monocoque design, the body panels are designed to bear the loads and stresses of the vehicle, rather than relying on a separate frame to provide structural support. This results in a lighter and stronger structure, and can also improve aerodynamics and reduce the overall size of the vehicle.

• Monocoque construction is commonly used in automobiles, aircraft, and some high-performance racing vehicles. However, it can be more expensive and challenging to manufacture than other types of chassis construction, and may not be suitable for larger or heavier vehicles.

• Overall, monocoque chassis construction offers a number of advantages and disadvantages, and the choice of design is often based on the specific needs and intended use of the vehicle.