INTRODUCTION
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 setup 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.
A transmission or gearbox provides speed and torque conversions from a rotating power source to another device using gear ratios. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. A transmission will have multiple gear ratios ( or simply "gears") with the ability to switch between them as speed varies. This switching may be done manually (by operator), or automatically. Directional (forward and reverse) control may also be provided.
In motor vehicle applications, the transmission will generally be connected to the crankshaft of the engine. The output of the transmission is transmitted via drive shaft to one or more differentials, which in turn drive the wheels. More modern gearboxes are used to increase torque while reducing the speed of a prime motor output shaft (e.g a motor crankshaft). This means that the output shaft of a gearbox will rotate at slower rate than the input shaft, and this reduction in speed will produce a mechanical advantage, causing an increase in torque.
TYPES OF TRANSMISSION SYSTEM
1. Manual Transmission
2. Automatic Transmission
3. Semi-automatic Transmission
a) Dual-clutch Transmission
b) Sequential Transmission
4. Continuously Variable Transmission.
1. Manual Transmission: In this type of transmission system, the driver has to manually select and engage the gear ratios.
b) Clutch slips: The clutch slips is the point that vary between being fully depressed and released. The clutch slip is used to start the vehicle from a stand still. It then allows the engine rotation to adjust to the newly selected gear ratio gradually. It is recommended not to slip the clutch for a long period of time because a lot of heat is generated resulting in energy wastage.
c) Clutch fully released: The clutch is fully engaged when the pedal is fully released. All the engine torque will be transmitted to the transmission. This results in the power being transmitted to the wheels with minimum loss.
WORKING OF MANUAL TRANSMISSION
When you start a manual transmission car, before you turn the key, you disengage the clutch by pressing down on the clutch pedal. This disconnects power flow between the engine's input shaft and transmission. This allows your engine to run without delivering power to the rest of the vehicle.
With the clutch disengaged, you move the gearshift into first gear. This causes a shifting rod in your transmission gearbox to move the shifting fork towards first gear, which is mounted to the output shaft via ball bearings.
This first gear on the output shaft is enmeshed with a gear that is connected to a countershaft. The countershaft connects the engine input shaft via a gear and spins at the same speed as the engine input shafts.
Attached to the shifting fork is a synchronizer collar. The synchronizer collar does two things:
1. It firmly mounts the driving gear to the output shaft so that the gear can deliver power to the output shaft.
2. It ensures that the gear syncs up with the speed of the output shaft.
Once the synchronizer collar is enmeshed with the first gear, the gear is firmly connected to the output shaft, and the vehicle is now in gear. The first gear is large, it causes the output shaft to spin more slowly than the engine input shaft, but deliver more power to the rest of the drivetrain. This is thanks to the wonders of gear ratios.
To increase the speed of the output shaft, we need to shift up to second gear. So we step on the clutch to disconnect power between the engine and transmission gearbox and shift into second gear. This moves the shifting rod that has a shift fork and synchronizer collar towards second gear. The synchronizer collar syncs up the second gear speed with the output shaft and firmly mounts it to the output shaft. The output shaft can now spin faster without the engine input shaft spinning furiously to produce the power the car needs. For the rest of the five gears, it rinse, wash and repeat.
2. Automatic Transmission: Automatic transmission system is the most advanced system in which drives mechanical efforts are reduced very much and different speeds are obtained automatically. This system is generally also called hydramatic transmission. It contain epicyclic gear arrangement, fluid coupling and torque converter. In this planetary gears sets are placed in series to provide transmission. This type of transmission are used by Skoda, Toyota, Lexus ,e.t.c.
Epicyclic gearing (planetary gearing): It is a gear system consisting of one or more outer gears, or planets gears, revolving about the central gears. By using epicyclic gear, different torque speed ratio can be obtained. It also compact the size of the gearbox.
Stages of automatic transmission
a) Park (P): Selecting the park mode will lock the transmission, thus restricting the vehicle from moving.
b) Reverse (R): Selecting the reverse mode puts the car into reverse gear, allowing the vehicle to move backwards.
c) Neutral (N): Selecting neutral mode disconnects the transmission from the wheel.
d) Low (L): Selecting the low mode will allow you to lower the speed to move on hilly and middy areas with ease.
e) Drive (D): Selecting the drive mode allows the vehicle to move and accelerates through a range of gears thereby increasing the speeds rapidly.
WORKING OF AUTOMATIC TRANSMISSION
An automatic transmission is a motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears. In this transmission system the gears are never physically moved and are always engaged to the same gears. Automatic transmissions contain mechanical systems, hydraulic systems, electrical systems and computer controls, all working together in perfect harmony manually.
Main Components Of An Automatic Transmission
1. Planetary Gear sets
2. Clutches and Bands
3. Torque converter
4. Valve Body
An automatic transmission uses sensors to determine when it should shift gears , and changes them using internal oil pressure. While there are numerous components stuffed into the transmission, and their actual operation is a bit more complicated than the simplified version presented here, the key components are the torque converter and planetary gearsets.
In order to shift gears, the transmission must be temporarily disconnected from the engine. On a manual transmission the driver does that by pushing in the clutch pedal, but on an automatic , it handled by the torque converter.
There are two fan-shaped components inside the torque converter, which is filled with transmission fluid: an impeller, which is attached to the engine crankshaft and a turbine attached to the transmission input shafts. As the engine turns the impeller, its blades move the fluid , which in turn causes the turbine to turn. The fluid moves in a closed loop. A third fan-shaped component, the stator, sits between the impeller and turbine and helps direct the fluid movement. As you push the throttle to speed up, the fluid moves the turbine faster to send more power through the transmission. As you slow down, the fluid movement slows, the turbine stop spinning and the engine can sit and idle without stalling.
The turbine and impeller aren't permanently attached, and the impeller always spin faster. Most vehicle use a lock up converter which has a mechanical clutch that temporarily connects the two components at higher speeds to help improve fuel economy.
Once that power has been transferred to the transmission input shaft, it is time for the planetary gears to do their thing. The name comes from the way they are arranged. A central gear is called the sun gear, while smaller planet gears revolve around it, held in a ring called a planet carrier. A large toothed ring gear surrounds them all and is meshed with the planetary gears in their carrier. Rather than using a separate gear wheel for the gear, the transmission various speeds are achieved through the combinations of gears. the sun, planetary and ring gears are meshed in various combinations such as the outer ring gear turning while the inner sun gear stays stationery. this is achieved with small friction clutches, which engage the gears for turning, and bands which hold them out of the way so they don't turn. The clutches and bands are operated by pins and valves that are activated by pressurized transmission fluid.
ADVANTAGES OF MANUAL TRANSMISSION
1. It is easier to build a strong manual transmission than an automatic one. This is because a manual system has one clutch to operate, whereas an automatic system has a number of clutch packs that function in harmony with each other.
2. Manual transmission normally do not require active cooling, because not much power is dissipated as heat through the transmission.
3. Manual gearshifts are more fuel efficient as compared to their automatic counterpart. Torque converter used to engage and disengage automatic gears may lose power and reduce acceleration as well as fuel economy.
4. Manual transmission generally require require less maintenance than automatic transmissions. An automatic transmission is made up of several components and a breakdown of even a single component can stall the car completely.
ADVANTAGES OF AUTOMATIC TRANSMISSION
1. The manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission; the same set of gears produces all of the different gear ratios. The planetary gear set is the device that makes this possible in an automatic transmission.
2. Automatic cars are easier to use, especially for the inexperienced drivers. manual system require better driving skills, whereas with an automatic , the clever system does it all on its own. This holds a greater advantage for new and inexperienced drivers and also helps during congested traffic situations where it becomes difficult to change gears every seconds.
3. Automatic transmission requires less attention and concentration from the driver because the automatic gears start functioning as soon as the system feels the need of a gear change. For cars with manual gear shifts, the driver has to be more alert while driving and better coordinated.
4. There is no clutch pedal and gear shift in an automatic transmission car. Once you put the transmission into drive (D), everything else is automatic.
5. Automatic cars have better ability to control traction when approaching steep hills or engine braking during descents. Manual gears are difficult to operate on steep climbs.
REQUIREMENTS OF TRANSMISSION SYSTEM
1. Provide means of connection and disconnection of engine with rest of power train without shock and smoothly.
2. provide a varied leverage between the engine and the drive wheels.
3. provide means to transfer power in opposite direction.
4. Enable power transmission at varied angles and varied lengths.
5. Enable speed reduction between the engine and the drive wheels in the ratio of 5:1
6. Enable diversions of power flow at right angles.
7. Provide means to drive the driving wheels at different speed when required.
8. Bear the effect of torque reaction, driving thrust and baking effort effectively.
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