Manual transmission
A manual transmission (also known as a stick shift or standard transmission) is a type of transmission used in automotive applications. Other types of transmission in mainstream automotive use are the automatic transmission, very common in the United States and Canada, and the still-rare continuously variable transmission.
Vehicles with manual transmissions always feature a driver-operated clutch and gear selector.
Overview
Manual transmissions are most commonly selected for sports cars, since they are typically more efficient than automatics, thus allowing a greater proportion of the engine's power to be used, and because they give drivers the greatest possible degree of control over the operation of the vehicle's power train. To reduce costs, and also to compensate for smaller engines, manual transmissions are also commonly chosen for compact cars.
While no longer common in the United States or Canada, manual transmissions are still very popular in Europe, where they are fitted on most cars, including most rental cars. Because of high fuel costs, European cars typically have less powerful engines, and using automatic transmissions, which are less efficient, especially in earlier models, would result in a lack of acceleration and an increase in fuel costs.
Currently (2004), the vast majority of cars equipped with manual transmissions employ a five-speed gearbox, although six-speed units are becoming more common on performance-oriented cars.
Most automatic transmissions also allow drivers to influence the transmission's gear position by setting a maximum gear (e.g. by shifting from "D" to "3" to disable fourth gear). A few give drivers the ability to fully control the transmission's gear position, as in the Porsche/Audi "Tiptronic™" transmission and the "AutoStick™" found in some recent American vehicles.
History
In the United States and Canada, even though they are frequently no longer available even as options on many cars and trucks, manual transmissions are still commonly referred to as "standard" transmissions.
Traditionally, vehicles with manual transmissions have been able to achieve better fuel economy than those equipped with automatics, but the gap has narrowed substantially with the increasing sophistication of automatic transmission control systems.
All current manual transmissions employ a centrally located, floor- or dash-mounted shift lever. In the past the term "three on the tree" was used to refer to a manual shift lever located on the steering column, where many automatic gear selectors are now found. By analogy, the term "four on the floor" was coined, referring to a four-speed version of today's common configuration.
Theory of operation
In a vehicle with a manual transmission, the engine and transmission are separated by a clutch, controlled by a pedal on the left hand side of the driver's footwell that modulates the transfer of power between the two subsystems:
- When the clutch pedal is fully depressed, the clutch is fully disengaged, and no torque is transferred from the engine to the transmission, and by extension to the drive wheels.
- When the clutch pedal is fully released, the clutch is fully engaged, and essentially all of the engine's torque is transferred.
- In between these extremes, the clutch "slips" to varying degrees.
After the clutch, the transmission employs a variety of gear ratios, selected by the driver, in converting the engine's power into usable torque for moving the vehicle.
The top gear in both manual and automatic transmissions is usually an overdrive gear, indicating that its ratio of input to output speed is less than 1.0.
Driving technique
See Manual transmission driving technique.
Maintenance
Because clutches use changes in friction to modulate the transfer of torque between engine and transmission, they are subject to wear in everyday use. A very good clutch, when used by an expert driver, can last hundreds of thousands of kilometres, whereas weak clutches or inexperienced drivers can lead to more frequent repair or replacement.
Manual transmissions are lubricated with gear oil, which must be changed periodically, although not as frequently as the automatic transmission fluid in a vehicle so equipped.
