Automotive Transmission

Clutch and Gear boxMohan Krishna D

Transmission System

• Transmission system in a car helps to transmit mechanical power from the car engine to give kinetic energy to the wheels. It is an interconnected system of gears, shafts, and other electrical gadgets that form a bridge to transfer power and energy from the engine to the wheels. The complete set up of the system helps to maintain the cruising speed of the car without any disturbance to the car’s performance. The oldest variant of the transmission system in India is the manual transmission that has undergone various modifications and alterations to form the present day automatic transmission.

Clutches

• Clutches are useful in devices that have two rotating shafts. In these devices, one of the shafts is typically driven by a motor or pulley, and the other shaft drives another device. In a drill, for instance, one shaft is driven by a motor and the other drives a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed, or be decoupled and spin at different speeds.• In a car, you need a clutch because the engine spins all the time, but

the car's wheels do not. In order for a car to stop without killing the engine, the wheels need to be disconnected from the engine somehow. The clutch allows us to smoothly engage a spinning engine to a non-spinning transmission by controlling the slippage between them.

Types of Clutches :-

• 1) Positive Clutch (Dog Clutch)• 2) Friction Clutch• Cone Clutch• Single Plate Clutch• Multi Plate Clutch• Diaphragm Clutch• 3) Hydraulic Clutch• Fluid Coupling • Hydraulic Torque Converter

1. Positive clutch (Dog clutch):

In the positive clutch, grooves are cut either into the driving member or into the driven member and some extracted parts are situated into both driving and driven member. When the driver releases clutch pedal then these extracted parts insert into grooves and both driving and driven shaft revolve together. When he push the clutch pedal these extracted parts come out from grooves and the engine shaft revolve itself without revolving transmission shaft.

Merits and Demerits

Advantages• a)No slip operation

b)Develop very little heat since they do not depend on frictionc)Generally lighter and less costly than a friction clutch of similar torque capacity

Disadvantages• a)Cannot be engaged at high

speedsb)Shock accompanies engagement at any speedc)When both driven and drive shafts are at rest, some relative motion may be required to engage.

2. Friction clutch:

In this type of clutches, friction force is used to engage and disengage the clutch. A friction plate is inserted between the driving member and the driven member of clutch. When the driver releases the clutch pedal, the driven member and driving member of clutch, comes in contact with each other. A friction force works between these two parts. So when the driving member revolves, it makes revolve the driven member of clutch and the clutch is in engage position. This type of clutch is subdivided into four types according to the design of the clutch

Merits and Demerits

Merits Demerits

A.) Cone clutch:

It is a friction type of clutch. As the name, this type of clutch consist a cone mounted on the driven member and the shape of the sides of the flywheel is also shaped as the conical. The surfaces of contact are lined with the friction lining. The cone can be engage and disengage form flywheel by the clutch pedal.

B.) Single plate clutch:

In the single plate clutch a flywheel is fixed to the engine shaft and a pressure plate is attached to the gear box shaft. This pressure plate is free to move on the spindle of the shaft. A friction plate is situated between the flywheel and pressure plate. Some springs are inserted into compressed position between these plates. When the clutch pedal releases then the pressure plate exerts a force on the friction plate due to spring action. So clutch is in engage position. When the driver pushes the clutch pedal it due to mechanism it serves as the disengagement of clutch.

C.) Multi-plate clutch:

Multi-plate clutch is same as the single plate clutch but there are two or more clutch plates inserted between the flywheel and pressure plate. This clutch is compact than single plate clutch for same transmission of torque.

D.) Diaphragm clutch:

This clutch is similar to the single plate clutch except a diaphragm spring is used instead of coil springs for exerting pressure on the pressure plate . In the coil springs, one big problem occurs when these springs do not distribute the spring force uniformly. To eliminate this problem, diaphragm springs are used into clutches. This clutch is known as diaphragm clutch.

3) Hydraulic Clutch

A.) Fluid coupling:It is a hydraulic unit that replaces a clutch in a semi or fully automatic clutch. In this type of clutch there is no mechanical connection between driving member and driven member. A pump impeller is bolted on a driving member and a turbine runner is bolted on the driven member. Both the above units are enclosed in a single housing filled with a liquid. This liquid serves as a torque transmitter form the impeller to the turbine.

B.) Hydraulic torque converter:Hydraulic torque converter is same as the electric transformer. The main purpose of the torque converter is to engage the driving member to driven member and increase the torque of driven member. In the torque converter, an impeller is bolted on the driving member, a turbine is bolted on the driven member and a stationary guide vanes are placed between these two members. These all parts are enclosed in a single housing which is filled with a hydraulic liquid.

Gear Box

A gearbox is a mechanical method of transferring energy from one device to another and is used to increase torque while reducing speed. Torque is the power generated through the bending or twisting of a solid material.

In a situation where multiple speeds are needed, a transmission with multiple gears can be used to increase torque while slowing down the output speed.

How to Determine Gear Ratio

• In mechanical engineering, a gear ratio is a direct measure of the ratio of the rotational speeds of two or more interlocking gears. As a general rule, when dealing with two gears, if the driving gear (the one directly receiving rotational force from the engine, motor, etc.) is bigger than the driven gear, the latter will turn more quickly, and vice versa. We can express this basic concept with the formula Gear ratio = T2/T1, where T1 is the number of teeth on the first gear and T2 is the number of teeth on the second.

• 1)Start with a two-gear train. To be able to determine a gear ratio, you must have at least two gears attached to each other — this is called a "gear train." Usually, the first gear is a "drive gear" attached to the motor shaft and the second is a "driven gear" attached to the load shaft. There may also be any number of gears between these two to transmit power from the drive gear to the driven gear: these are called "idler gears.“• 2) Count the number of teeth on the drive gear. One simple way

to find the gear ratio between two interlocking gears is to compare the number of teeth (the little peg-like protrusions at the edge of the wheel) that they both have. Start by determining how many teeth are on the drive gear. You can do this by counting manually or, sometimes, by checking for this information labeled on the gear itself.

• 3) Count the number of teeth on the driven gear. Next, determine how many teeth are on the driven gear exactly as you did before for the drive gear.• 4) Divide one teeth count by the other. Now that you know how many

teeth are on each gear, you can find the gear ratio relatively simply. Divide the driven gear teeth by the drive gear teeth. Depending on your assignment, you may write your answer as a decimal, a fraction, or in ratio form (i.e., x : y).

Main types of Gear Box

• An automobile requires high torque when climbing hills and when starting, even though they are performed at low speeds. On other hand, when running at high speeds on level roads, high torque is not required because of momentum. So requirement of a device is occur, which can change the vehicle’s torque and its speed according to road condition or when the driver need. This device is known as transmission box.• In an automobile various type of gear boxes are used which allow the

vehicle to obtain different torque and speed combination. Today I am going to tell you about the types of gear boxes.

1) Manual Gear Box

In this type of gear box different speed ratio or gear ratio is selected by the driver manually. Some special skill of driving is required to operate this type of gear box. According to their design, this type of gear box is subdivided into three types.

--- a) Sliding mesh gear box:

It is that gear box in which gears on the splined main shaft are moved right or left for meshing them with appropriate gears on the counter shaft for obtaining different speed. This type of gear box derives its name from the fact that the gears are meshed by sliding. One disadvantage of this type of gear box is that, special skill is required to operate this gear box

Click icon to add picture(B.) Constant mesh gear box:It is that gearbox in which all the gears are in constant mesh with each other all the time. The gear on the main shaft rotates freely without rotating the main shaft. Three gear transmission constant mesh gear box consist two dog clutches. These clutches are provided on the main shaft, one between the clutch gear and the second gear and the other between the first gear and reverse gear. When the left side dog clutch is made to slide left by means of gearshift lever, it meshes with the clutch gear and the vehicle runs on top speed. If this clutch slide right and mesh with second gear, than the vehicle runs on second gear speed. So in constant mesh gear box we can change the gear ratio by shifting the dog clutch. This type of gear box is more popular than sliding mesh because it creates low noise and less wear of gears.

C) Synchromesh Gear Box

One big problem occur in constant mesh gear box is that when the driver engage the dog clutch, the main shaft and gear to be meshed running at different speed. So when engage this gear cause wear and tear of dog clutch. This problem is solved by a synchromesh gear box. This gear box is same as the constant mesh gear box except dog clutch is replaced by synchromesh devices.Synchromesh gear devices works on the principle that two gears to be engaged are first brought into frictional contact which equalizes their speed after which they are engaged readily and smoothly. The synchromesh looks like as the cone clutch where the outer surface of cone consist the frictional surface. This type of gear box is widely used in automobile.

2. Automatic Gear box :

A transmission in which various speeds are obtained automatically is known as automatic transmission.. In this type of gear box driver merely selects the general car condition such as forward or reverse. The selection, timing and engagement of gear for the required gear speed are accomplished automatically when the accelerator is pressed or depressed. Automatic transmission needs no gear change lever and clutch pedal since clutch and transmission is a combined unit and works automatically.Automatic transmission is generally subdivided into two types:1) Epicycle Gear Box.2) Hydraulic Torque Converter

A)Epicycle Gear Box:

This type of gear box uses no sliding dogs or gears to engage but different gear speeds are obtained by merely tightening brake bands on gear drum. It consists of a ring gear annular wheel, sun gear and planet gears with carrier. In order to obtain different speeds any one of these units can be held from rotation by means of brake bond. The ring gear contains teeth on its inner circumference and it is surrounded by a brake band. The brake band is operated by a gear stick or lever to grip the ring gear and hold its movement. The sun gear is attached to the clutch shaft thus moves along with the movement of engine crankshaft. The planet gears are in constant mesh with both the sun gear and ring gear and are free to rotate on their axes carried by the carrier frame which in turn is connected to the driver shaft.

B) Hydraulic torque converter:

Hydraulic torque converter is same as the electric transformer. The main purpose of the torque converter is to engage the driving member to driven member and increase the torque of driven member. In the torque converter, an impeller is bolted on the riving member, a turbine is bolted on the driven member and stationary guide vanes are placed between these two members. This all parts are enclosed into single housing filled with hydraulic liquid. The impeller rotates with the driven member and it through the liquid outward by centrifugal action. This liquid flowing from the impeller to turbine runner exerts a torque on the stationary guide vanes which change the direction of liquid, thereby making possible the transformation of torque and speed. The difference of torque between impeller and turbine depends upon these stationary guide vanes. This serves as the function of both gear box and clutch.

10 Most common Transmission Problems :-

• 1) Lack of Response• 2) Whining, Clunking & Humming• 3) Leaking/Low fluid• 4) Grinding or Shaking• 5) Burning Smell• 6) Refuses to go into gear• 7) Check Engine Light• 8) Transmission Noisy in Neutral• 9) Gear Slipping• 10) Dragging Clutch