GEARBOX(Transmission System)

Functions of transmission•The main purpose of the transmission is to provide a means to vary the leverage or torque ratio between the engine and the road wheels as required.
•The transmission also provides a neutral position so that the engine and the road wheels are disconnected even with the clutch in the engaged position.
•A means to back the vehicle by reversing the direction of rotation of the drive is also provided by the transmission.

Resistances to the vehicle motion•Resistance due to wind – proportional to the square of the vehicle speed
•Resistance due to gradient – remains constant at all speed.
•Miscellaneous – type of road, tyre friction, etc.

Types of gearbox•Sliding mesh gearbox

•Constant mesh gearbox

•Synchromesh gearbox

•Automatic transmission

Sliding mesh gearbox

        • Main components are clutch shaft, splined main shaft, lay shaft and gears having different sizes.
•  In order to mesh gears on the splined main shaft with appropriate gears on the lay shaft for obtaining different speeds they are moved to the right or to the left. It derives it name from the fact that the mashing of the gears takes place by sliding of gears on each other.

Constant mesh gearbox•All the gears on main shaft are in constant mesh with the corresponding gears on the counter shaft.
•Helical gears are employed for quite operation in this gearbox
•Gear shifting is done by shifting dog clutch to the left or right.

Synchromesh gearbox•In constant mesh gearbox there is a difficulty of double declutching.
•In this type of gear box synchromesh device is provided which avoids the necessity of double declutching.
•The parts which ultimately are to be engaged are first brought into the frictional contact which equalizes their speed, after which these may be engaged smoothly.

Gear selector mechanismTypes of mechanism (two types)
•Mechanism with gear selector lever on the top of the transmission case.
•It consists of gear lever, selector sleeve, selector fork, selector rods.
•Interlocking mechanism is provided to ensures that only one gear can be engaged at a time.

Automatic transmission•Three basic parts of an automatic transmission are
–A torque converter
–A gear train that usually has one or more planetary gear sets.
– a hydraulic system

Torque converter•Torque converter increases the torque in a ratio of 2:1 to 3:1
•It consists of three main parts,
–The impeller or the driving member
–The turbine or the driven member
–The stator

Planetary gear set

 •A simple gear set has a sun gear, about which planet pinions turn around.•These planet pinions are carried by a carrier and a shaft and are also in mesh with a ring gear, which is also called annulus or internal gear.
•The simple gear set is shown in figure can provide any one of the five conditions. It can,
•Increase speed an decrease torque (overdrive)•Decrease speed and increase torque (reduction)•Reverse the direction of rotation (reverse)•Acts as solid shaft  (direct drive)•Disconnect the driving shaft from the driven shaft (neutral)•If one member is held stationary and another is turned, there is a speed increase, a speed reduction, or reverse.
•If two members are locked together, the gear set acts like a solid shaft (direct drive or top gear).
•If no members are locked, no power is transmitted through the gear set (Neutral)Hydramatic transmission•Consists of three sets of planetary gears to obtain four forward speeds and one reverse speed
•It also consist of brake band and set of clutch to obtain different gear ratios

Clutch System

Why is CLUTCH Required?

IC engines develop low torque at starting speed and as the speed increases, develop enough torque to pick up the load.

Clutch components and clutch linkages

According to Clutch linkages clutches are classified as,

I.      Mechanically Actuated Clutch: 

II.      Hydraulically Operated Clutch:

         III.      Electromagnetically Operated Clutch:                IV.      Pneumatically Operated Clutch:

         V.      Vacuum Operated Clutch:

Mechanically Linkages and Operation:

Clutch linkage transfers the clutch pedal movement to the release bearing. Mechanical clutch linkage uses shafts, levers, or a cable.

Clutch Pedal Play: It means free movement of the pedal without causing any motion to the linkages.

Clutch fee play is provided in four wheeler= 5 to 25 mm; For two wheeler= 2 to 5mm.

Hydraulically actuated clutch:

It is basically a subassembly which contains:

1.   Central steel plate with splined hub.

2.   Friction Facings or linings mounted on outer rings.

3.   Rivets for attaching friction linings on both sides of steel plates.

4.   Cushioning springs: These springs are segmental in shape and wavy in profile. It is attached to steel plate at equal intervals on its periphery.

It is provided for smoother engagement of a clutch. Thus uniform heat generation over entire friction surface and increase friction surface life.

5.   Torsional springs: While transmitting torque produced at engine shaft to gearbox, undesirable torsional vibrations are introduced in the clutch plates.

The torsional springs are helically coiled springs which absorb torsional vibration by compressing themselves. They 3, 4, 6 or 8 in numbers depending upon the size of clutch.

•   Clutch Facing or Friction Facing:

Suitable Selection of clutch facing is an important aspect because torque transmission is

depends upon the frictional surface.

Basic requirement of Friction Facing:

1.   Good wear resistance

2.   High coefficient of friction

3.   High heat resistance

4.   Light in weight

5.   Longer life

6.   Homogeneous binding

Clutch Facing materials:

1.   Asbestos  2. Reybestos          3. Fabric         4.Leather        5. Cork

6. Organic fiber composites         7.Sintered Metals       8.Ceramic

Pressure Plate Assembly

–  Squeezes clutch disc onto flywheel.

–  Can be engaged or disengaged.

–  Acts like a spring-loaded clamp.

–  Two common types, the coil spring and diaphragm (Belleville) spring design.

Release Levers:

They are used to push release bearing for clutch engagements when driver’s effort is

applied on them through clutch pedal. They are manufactured from alloy steel by forging. They are also called fork lever.

Release bearings

Acted on by clutch fork - acting on pressure plate.

•    Moves toward flywheel when pedal pushed.

•    Slides on front portion of transmission called bearing retainer.

•    Normally not in contact with pressure plate until pedal pushed.

Pivot Bearing:

-The  purpose  of  the  pilot  bushing  or  bearing  is  to  support  the  outer  end  of  the

transmission’s input shaft.

-Allows the input shaft to rotate in the crankshaft.

What is the advantage of diaphragm clutch over spring clutch?

diaphragm clutch is small in size as compare to spring clutch
and it transmits more torque as diaphragm exerts more force as compare to springs......therefore it is advantageous to use diaphragm clutch instead of spring clutch...

more compact means of storing energy. thus compact design results in smaller clutch housing......... less affected by centrifugal force..can withstand higher rotational speeds...

diaphragm acts as both clamping spring and release levers..therefore many extra parts like struts, eye bolts, levers etc can be eliminated....

Advantages of a disc clutch over the Cone clutch?

I assume that we are talking about marine transmissions in which case both types of clutches will be operated "wet". The chief problem with the cone clutch is that when it fails the parts are going to be "captive" and very costly. Disc clutches however can have the friction plates reconditioned by having new material bonded on just like motorcycle clutches. Some Italian fishing boat engines in the 7 to 20 HP range had engines with a dry car type clutch between the engine and gearbox. This avoided wear on the gearbox clutches. For some reason this design has left the marketplace.

What are 3 advantages of a diaphragm spring type clutch compared to a multi coil spring clutch?

diaphragm clutch is small in size as compare to spring clutch and it transmits more torque as diaphragm exerts more force as compare to springs...... therefore it is advantageous to use diaphragm...

Why single plate clutch is used in trucks & Cars  while multi-plate clutch is used in bikes?

In Trucks & Cars use a single plate clutch as there is enough space to use the correct diameter plate to create the right amount of torque while motorbikes use multi-plate clutches as they have  limited room and need to create more friction surfaces to produce the required torque.

Frequently asked questions for Braking System of an automobile

Q. 1. What is the purpose of brake shoe adjustor?

Ans. The purpose of adjustor is to compensate the wear of brake leather due to regular use of vehicle.

Q. 2. Define servo Brakes?

Ans. Mechanism which assist the driver’s effort for applying brakes is called servo mechanism. Servo means self energization. Servo Brakes generally used when vehicle load is above 3 tonnes.

Q. 3. What are different mechanism of Brake actuation.

Ans. Generally following are the actuation methods:

(a) Mechanical brakes

(b) Hydraulic brakes

(c) Electric brakes

(d) Vacuum brakes

(e) Air brakes.

Q. 4. What is fading of Brakes?

Ans. Fading of brakes means that friction is decreased between brake drum and brake lining due to regular use of brake.

Q. 5. What do you mean by bleeding of Brakes?

Ans. Bleeding means to drive out air from braking system. Because if air is entered into braking system their is no actuation of brakes.

Q. 6. What are the basic requirement for braking fluid?

Ans.

1. It should have high boiling temperature.

2. Viscosity of braking fluid should be less.

3. Brake fluid should not act as corrode agent to component which comes into contact.

Q. 7. Comparison between drum and disk brake.

Ans.

1. Drum brakes are heavier than disk brake.

2. Less fading of brake lining takes place in disk brake as compared to drum brakes.

3. In disk brakes uniform wear of friction lining as compared to drum brakes.

4. Disk brakes are more efficient than drum brakes.

 Q. 8. What is the locking of wheel during braking?

Ans. When the braking force is more than force of adhesion then wheel is stopped and start slipping on the road. The stopping of wheel by braking is called locking.

Q. 9. Which factors generally effect braking.

Ans.

1. Radius of brake drum and diameter of wheel.

2. Area of brake lining and amount of pressure applied.

3. Coefficient of friction.

Q. 10. Write few advantages of hydraulic system of braking.

Ans

1. There is less friction in hydraulic system of braking because there are less joints as compared to mechanical brakes.

2. System is self lubricating.

3. In hydraulic system equal pressure is in every circuit.

4. System is more flexible than mechanical system.

Q. 11. What is a leading shoe?

Ans. A leading shoe is that whose tip is dragged along the drum even when their is no brake force. Due to this reason leading shoe fade more than trailing shoe.

Q. 12. What is the function of brake value?

Ans. Function of the brake value is to control the intensity of the braking system in air brakes. It is operated by either foot treadle or by push rods linkage.

Q. 13. What do you understand by brake chamber?

Ans. It is a chamber installed on each wheel to connect pressure energy of compressed air into useful mechanical energy for proper application of brakes.

Q. 14. What are the trouble shooting in brake system?

Ans.

1. Loss of efficiency in braking:

(a) Brake lining does not work properly if oil is entered into brake drum.

(b) Due to defective master cylinder, which need overhauling.

(c) If air enters into braking system, braking application does not work properly.

(d) Brake lining are fade due to regular use or worn out friction lining.

2. Brakes overheating: Overheating of brakes occur while we drive a vehicle ascending down the hill or due to faulty binding material used for brakes binding.

Q. 15. Write short note on disc brake.

Ans. Disc brake consist of cast Iron disc bolted on the hole of wheel and it is housed in stationary housing called caliper. The caliper is connected to stationary part of the vehicle, like the stub axle and is cast in two parts, each part have a piston. In disc brake each piston and disc there is friction, pad held in position by retaining pairs, spring plate etc. There are passage for fluid to enter or leave each housing. This passage is also connected for bleeding when brakes are applied friction pads.

Q.16. What are the basic characteristics of brake fluid?

Ans.

1. Oil point: Due to high temperature during the braking applications brake

fluid should have high boiling point, to avoid vapour formation. Boiling point should be generally around 25O-3OOC.

2. Viscosity: Due to variations in weather conditions from very cold to hot it becomes imperative that the viscosity of the brake fluid should vary little with temperature to keep optimum flow conditions. So viscosity should be such that, flow occur in pipes easily without any temperature variations.

3. Lubrications properties : Brake fluid should have good lubrication properties so that proper lubrications of braking components (e.g. master cylinder) is done.

Q. 17. How can you classify the brakes ? Explain in details hydraulic brake system with neat diagram?

Ans. Brakes can be classified according to following considering the points:

(a) Purpose

(b) Location

(c) Construction

(d) Method of actuation

(e) Enter braking effort

(a) Purpose : Brakes can be applied to following ways to vehicle while in motion or in steady condition, mean during running condition if we applied brakes are called service brakes. But if we applied during parking or hold the vehicle in slop way are called packing brakes.

(b) Location : Brakes can be applied either at transmission or at the wheels. Wheel brakes are good in heat dissipation because energy wheel has separate brake drum which increases surface area and also quick heat dissipation. In automobiles wheel brakes are generally used.

(c) Construction : Generally two types of brakes are used. One is drum brakes and another is disk brakes.

(d) Method of actuation : Following are the ways of actuation.

(a) Mechanical brakes

(b) Hydraulic brakes

(c) Vacuum brakes

(d) Electric brakes

(e) Air brakes.

(e) Enter braking effort Some times due to heavy loaded vehicles are provided with outside power for application of brakes which are helpful for drivers to apply brakes are called servo brakes or power assisted brakes.

Hydraulic brakes : Most of the cars today use hydraulic brake system on all the wheels with additional hand brake to stop rear wheel movement. Main part of hydraulic system is a master cylinder which contains a braking fluid. It is well connected with four wheels by steels pipes, unions and flexible houses. Take the example of Ambassador car in which both front wheel has separate cylinders. On each brake shoe, whereas in rear wheels. There is only one cylinder which

operate both shoes. In hydraulic brake system is so designed that a small pressure of 50 kPa is maintained in all pipes times. So that cups of wheel cylinder are expanded always. This system prevents air entering into wheel cylinders while releasing the brake.

Master cylinder: It is called heart of hydraulic base system. It contains two main chambers, fluid reservoir and another is compression chamber in which piston operates. Fluid chamber which provides the fluid for braking when we apply the brakes with foot pedal. Fluid chamber compensate the fluid volume in pipeline due to any leakage or any temperature variation. To prevent leakage there are two rubber seals on both end of the piston in compression chamber. A rubber boot is provided at one end of push rod to present any dirt entering into cylinder. In brake line there is a fluid check value with rubber cup inside in the compression chamber, Main purpose of fluid check value is to maintained residual pressure in brake lines even when brakes are released. In primary seal side there are number of holes on the piston head. Two holes are connected to reservoir to the compression chamber. Size of smaller holes is about 7mm and it is also called compensation part/Byepars second hail is called recuperation port! intake. To keep fluid at atmospheric pressure their is a vent in the cap. When push rod is operated with links it actuate the piston and further pressure is directed toward pressure lines which apply brakes on the wheels when brakes pedal is released spring pressure in master cylinder push the piston in extreme position. This pressure of spring some times delay the return fluid from lines into compression chamber again. This condition cutes vacuum in compression chamber but is destroyed immediately by intake port in master cylinder which forces fluid into piston which deflects the rubber cup and enters the compression chamber destroying the vacuum.

Q. 18. What are the problems occurring in Braking system and what are their remedies?

Ans.

1. Brakes binding:

(a) To avoid brakes binding anchor pin should be lubricated at regular interval.

(b) Brake shoe retracting spring should be replaced with new one after regular interval.

(c) In hydraulic brakes by-pass port should be proper cleaned with compressed air and fresh fluid is filled in master cylinder, it should never be cleaned with wire drill.

(d) A hole on the master cylinder is to be cleaned.

(e) Brake shoe of vehicle for particular wheel may be adjusted so that dragging of vehicle is avoided.

2. Brake judder: It may take place due to wrong brake adjustment which may be corrected by proper fitting of brake lining by replacing old loose rivets with new one. In general conditions whole brake lining is replaced.

3. Hand brake Ineffective : This problem occurs when starching of operating cable is not properly adjusted. This arrangement comes with nut at one end which cause switching of wire.

4. Vehicle pulling one side:

(a) Some time dissimilar lining of brake shoe is fitted with different wheels. This problem is avoided by replacing with similar lining on all wheels.

(b) Some times dust enters into the brake drum, this also cause pulling of vehicle into one side. This problem is avoided by cleaning the drum.

(c) Some times oil or grease enters the brake drum which puts more load on clean linings. This problem is rectified by replacing greasy lining with dry lining.

5. Graffing brakes : When brakes are to sensitive, following types of problem occur due to reasons.

(a) Back plate may be loose, which should be tightened.

(b) Some time brake lining is greasy due to oil leakage should be replaced.

(c) If brake shoes- are not properly adjusted it should be adjusted after regular interval of time.

(d) Some time brake drum have a problem, it should be replaced with new brake drum.