AUTOMOBILE TRANSMISSION

An automobile transmission main function is to allow the engine to operate in a narrow range of speeds, while providing a wide range of output speeds to the road wheels. To do this it employs a transmission system comprising of the following components; the clutch for manual transmission or the torque converter for automatic transmission, gear box, propeller shaft, differentials, axles and the wheels.

Power transmission from the engine to the road wheel is a tricky affair, since the engine output fluctuates or varies about a mean speed or torque. To address this shortcoming a flywheel is attached to the output rotor or shaft of the engine to reduce this variation by storing and releasing energy periodically. Also the transmitted power to the road wheel is expected to operate over a wide range of speeds. Thus a gearing system which allows for this is placed in between the engine and the rest of the transmission components except the clutch or the torque converter which is integrated with the gear box. Speed and torque are inversely related thus it may be desirous to start a car from rest with a low gear with high torque but low speed, conversely when in motion higher gears can be engaged with higher speeds at lower torques without significant loss of momentum.

The clutch for manual transmission and the torque converter for automatic transmission connect and disconnect the engine from the transmission, allowing for smooth gear changes. The clutch is a friction device that connects and disconnects the engine from a manual transmission. Whereas the torque converter is a fluid coupling that connects and disconnects an engine from an automatic transmission.

The difference between a manual and automatic transmission is that different set of gears are engaged and disengaged manually to produce different set of gear ratio in a manual transmission, while the automatic transmission the same set of gear ratios are obtained automatically using a planetary gear set. A planetary gear set is a complex gear set that uses planetary gears, sun gears and ring gears to provide various gear ratios.

The propeller shaft or the drive shaft transmits power from the gear box or transmission to the differentials. The propeller shaft is a long cylindrical rod made of steel or aluminum with universal joints at each end to accommodate movements and vibrations. The propeller shaft rotates at speeds proportional to the engine speed, transmitting power or torque to the differential.

The differential is essentially a gear box that splits the power transmitted by the propeller shaft into two separate wheel axles, one for each wheel. The differential consists of a housing, gears and bearings. The gears are designed to allow the wheels to rotate at different speeds while maintaining traction thus enabling the vehicle to turn smoothly and maintain traction on uneven surfaces.

The axles are rods that connect the differential to the wheel hub, transmitting power from the differentials to the wheel.

The wheel supports the weight of the vehicle, provide traction and enable the vehicle to move. The wheel consists of a rim, tire and hub. The rim is a metal ring that supports the tire, while the hub is the central component that connects the wheel to the axle.

The major advantages of automobile transmission are that it enables smooth power delivery from the engine to the wheels, thus improving the vehicle performance and stability. Modern transmissions optimize gear ratios to reduce fuel consumption and emissions. Moreover transmissions enable vehicles to operate in various driving conditions both in the cities and open rugged country roads.

The obvious disadvantages of automobile transmissions are its complexity and cost, its added weight and space requirement may result in more drag forces and hence more power to keep it in motion resulting in more fuel consumption. Transmission can be difficult to troubleshoot and expensive to repair or replace.

Transmissions find applications in all moving machines and equipment whether as automobile vehicles, hybrid or electric vehicles and factory machinery.

The future of automobile transmission depends on the following trends and developments; increased adoption of electric vehicle will drive the development of new kind of transmission technologies such as e-axles and multispeed transmission. Also the development and use of autonomous vehicles will require advanced transmission systems that can integrate with autonomous driving technologies. The use of advanced materials in their design and construction such as carbon fiber and Nano materials will result in lighter and more efficient transmissions. The development  and the use of more efficient transmission such as continuously variable transmission (CVT) and dual clutch transmission (DCT) is expected to be common place in the near future. Also the integration of the transmission with other vehicle systems will go a long way in improving the transmission response time and efficiency.

 

 

SOURCES:

• Automobile transmissions: fundamentals, selection, design and applications by Harald Naunheimer, Bernd Bertsche, Joachim Rybor and Wolfgang Novak.
• Automobile transmission systems by Robert F. Steyr.
• Transmission systems: Design, analysis and applicatons by M. Azizur Rahman.
• Automotive engineering: Power train, chasis system and vehicle body by David A. Crolla.
• Transmission control for hybrid electric vehicles by Huayu Li.