Manual transmission

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Manual transmission for a four-wheel-drive vehicle- viewed from the engine side M5OD transmission.jpg
Manual transmission for a four-wheel-drive vehicle- viewed from the engine side
Internals of a manual transmission for a front-wheel-drive vehicle Getrag282internals.jpg
Internals of a manual transmission for a front-wheel-drive vehicle

A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom, and the United States), or stick shift (in the United States), is a multi-speed motor vehicle transmission system, where gear changes require the driver to manually select the gears by operating a gear stick and clutch (which is usually a foot pedal for cars or a hand lever for motorcycles).

Contents

Early automobiles used sliding-mesh manual transmissions with up to three forward gear ratios. Since the 1950s, constant-mesh manual transmissions have become increasingly commonplace and the number of forward ratios has increased to 5-speed and 6-speed manual transmissions for current vehicles.

The alternative to a manual transmission is an automatic transmission; common types of automatic transmissions are the hydraulic automatic transmission (AT), and the continuously variable transmission (CVT), whereas the automated manual transmission (AMT) and dual-clutch transmission (DCT) are internally similar to a conventional manual transmission, but are shifted automatically.

Alternately, there are transmissions which facilitate automatic clutch operation, but the driver's input is still required to manually change gears; namely semi-automatic transmissions. These systems are based on the design of a conventional manual transmission, with a gear shifter, and are mechanically similar to a conventional manual transmission, with the driver's control and input still required for manually changing gears (like with a standard manual transmission), but the clutch system is completely automated, and the mechanical linkage for the clutch pedal is completely replaced by an actuator, servo, or solenoid and sensors, which operate the clutch system automatically, when the driver touches or moves the gearshift. This removes the need for a physical clutch pedal.

Overview

A manual transmission requires the driver to operate the gear stick and clutch in order to change gears (unlike an automatic transmission or semi-automatic transmission, where one (typically the clutch) or both of these functions are automated). Most manual transmissions for cars allow the driver to select any gear ratio at any time, for example shifting from 2nd to 4th gear, or 5th to 3rd gear. However, sequential manual transmissions, which are commonly used in motorcycles and racing cars, only allow the driver to select the next-higher or next-lower gear.

In a vehicle with a manual transmission, the flywheel is attached to the engine's crankshaft, therefore rotating at engine speed. A clutch sits between the flywheel and the transmission input shaft, controlling whether the transmission is connected to the engine (clutch engaged- the clutch pedal is not being pressed) or not connected to the engine (clutch disengaged- the clutch pedal is being pressed down). When the engine is running and the clutch is engaged (i.e., clutch pedal up), the flywheel spins the clutch plate and hence the transmission.

The design of most manual transmissions for cars is that gear ratios are selected by locking selected gear pairs to the output shaft inside the transmission. This is a fundamental difference compared with a typical hydraulic automatic transmission, which uses an epicyclic (planetary) design, and a hydraulic torque converter. An automatic transmission that allows the driver to control the gear selection (such as shift paddles or "+/-" positions on the gear selector) is called a manumatic transmission, and is not considered a manual transmission. Some automatic transmissions are based on the mechanical build and internal design of a manual transmission but have added components (such as computer-controlled actuators and sensors) which automatically control the timing and speed of the gear shifts and clutch; this design is typically called an automated manual transmission (or sometimes a clutchless manual transmission).

Contemporary manual transmissions for cars typically use five or six forward gears ratios and one reverse gear, however, transmissions with between two and seven gears have been produced at times. Transmissions for trucks and other heavy equipment often have between eight and twenty-five gears,[ citation needed ] in order to keep the engine speed within the optimal power band for all typical road speeds. Operating such transmissions often uses the same pattern of shifter movement with a single or multiple switches to engage the next sequence of gears.

History

1890s to 1940s

Cherrier two speed gear, circa 1900 PSM V57 D608 Cherrier two speed gear.png
Cherrier two speed gear, circa 1900

Many of the first automobiles were rear-engined, with a simple belt-drive functioning as a single-speed transmission. The 1891 Panhard et Levassor is considered a significant advance in automotive transmissions since it used a three-speed manual transmission. [2] [3] This transmission, along with many similar designs that it inspired, was a non-synchronous (also called sliding-mesh) design where gear changes involved sliding the gears along their shafts so that the desired cogs became meshed. The driver was therefore required to use careful timing and throttle manipulation when shifting, so the gears would be spinning at roughly the same speed when engaged; otherwise, the teeth would refuse to mesh. This was difficult to achieve, so gear changes were often accompanied by grinding or crunching sounds, resulting in the gearboxes being nicknamed "crash boxes". [4] Even after passenger cars had switched to synchronous transmissions (i.e. with synchronizers), many transmissions for heavy trucks, motorcycles and racing cars remained non-synchronous, in order to withstand the forces required or provide a faster shift time.

1950s to 1980s

Top and side view of a typical manual transmission, in this case, a Ford Toploader, used in vehicles with external floor shifters. Ford Design 3-speed OD Transmission w. Hurst Shifter.jpg
Top and side view of a typical manual transmission, in this case, a Ford Toploader, used in vehicles with external floor shifters.

The first car to use a manual transmission with synchromesh was the 1929 Cadillac, [5] however most cars continued to use non-synchronous transmissions until at least the 1950s. In 1947, Porsche patented the split ring synchromesh system, which went on the become the most common design for passenger cars. [6] The 1952 Porsche 356 was the first car to use a transmission with synchromesh on all forward gears. [7] [8] In the early 1950s, most cars only had synchromesh for the shift from third gear to second gear (drivers' manuals in vehicles suggested that if the driver needed to shift from second to first, it was best to come to a complete stop beforehand).

Up until the late 1970s, most transmissions had three or four forward gear ratios, although five-speed manual transmissions were occasionally used in sports cars such as the 1948 Ferrari 166 Inter and the 1953 Alfa Romeo 1900 Super Sprint. Five-speed transmissions became widespread during the 1980s, as did the use of synchromesh on all forward gears.

1990s to present

Six-speed manual transmissions started to emerge in high-performance vehicles in the early 1990s, such as the 1990 BMW 850i and the 1992 Ferrari 456. The first 6-speed manual transmission was introduced in the 1967 Alfa Romeo 33 Stradale. The first 7-speed manual transmission was introduced in the 2012 Porsche 911 (991). [9]

In 2008, 75.2% of vehicles produced in Western Europe were equipped with manual transmission, versus 16.1% with automatic and 8.7% with other. [10]

Internals

16-speed (2x4x2) ZF 16S181 - opened transmission housing (2x4x2) ZF-16S181-transmission-hous.jpg
16-speed (2×4×2) ZF 16S181 – opened transmission housing (2x4×2)
16S181 -- opened planetary range housing (2x4x2) ZF-16S181-range.jpg
16S181 — opened planetary range housing (2×4×2)

Shafts

A manual transmission has several shafts with various gears and other components attached to them. Most modern passenger cars use 'constant-mesh' transmissions consisting of three shafts: an input shaft, a countershaft (also called a layshaft) and an output shaft. [11]

The input shaft is connected to the engine and spins at engine speed whenever the clutch is engaged. [12] The countershaft has gears of various sizes, which are permanently meshed with the corresponding gear on the input shaft. [13] The gears on the output shaft are also permanently meshed with a corresponding gear on the countershaft, however, the output shaft gears are able to rotate independently of the output shaft itself (through the use of bearings located between the gears and the shaft). [14] Through the use of collars (operated using the shift rods), the speed of the output shaft becomes temporarily locked to the speed of the selected gear. [15] Some transmission designs—such as in the Volvo 850 and S70—have two countershafts, both driving an output pinion meshing with the front-wheel-drive transaxle's ring gear. This allows for a narrower transmission since the length of each countershaft is halved compared with one that contains four gears and two shifters.

The fixed and free gears can be mounted on either the input or output shaft or both. For example, a five-speed transmission might have the first-to-second selectors on the countershaft, but the third-to-fourth selector and the fifth selector on the main shaft. This means that when the vehicle is stopped and idling in neutral with the clutch engaged and the input shaft spinning, the third-, fourth-, and fifth-gear pairs do not rotate.

When neutral is selected, none of the gears on the output shaft are locked to the shaft, allowing the input and output shafts to rotate independently. For reverse gear, an idler gear is used to reverse the direction in which the output shaft rotates. In many transmissions, the input and output shafts can be directly locked together (bypassing the countershaft) to create a 1:1 gear ratio which is referred to as direct-drive.

In a transmission for longitudinal engined vehicles (e.g. most rear-wheel-drive cars), it is common for the input shaft and output shaft to be located on the same axis, since this reduces the torsional forces to which the transmission casing must withstand. The assembly consisting of both the input and output shafts is referred to as the main shaft (although sometimes this term refers to just the input shaft or output shaft). Independent rotation of the input and output shafts is made possibly by one shaft being located inside the hollow bore of the other shaft, with a bearing located between the two shafts.

In a transmission for transverse engined vehicles (e.g., front-wheel-drive cars), there are usually only two shafts: input and countershaft (sometimes called input and output). The input shaft runs the whole length of the gearbox, and there is no separate input pinion. These transmissions also have an integral differential unit, which is connected via a pinion gear at the end of the counter/output shaft.

Dog clutch

In a modern 'constant-mesh' manual transmission, the gear teeth are permanently in contact with each other, and dog clutches (sometimes called dog teeth) are used to select the gear ratio for the transmission. When the dog clutches for all gears are disengaged (i.e. when the transmission is in neutral), all of the gears are able to spin freely around the output shaft. When the driver selects a gear, the dog clutch for that gear is engaged (via the gear selector rods), locking the transmission's output shaft to a particular gear set. This means the output shaft rotates at the same speed as the selected gear, thus determining the gear ratio of the transmission. [16]

The dog clutch is a sliding selector mechanism that sits around the output shaft. It has teeth to fit into the splines on the shaft, forcing that shaft to rotate at the same speed as the gear hub. However, the clutch can move back and forth on the shaft, to either engage or disengage the splines. This movement is controlled by a selector fork that is linked to the gear lever. The fork does not rotate, so it is attached to a collar bearing on the selector. The selector is typically symmetric: it slides between two gears and has a synchromesh and teeth on each side in order to lock either gear to the shaft. Unlike some other types of clutches (such as the foot-operated clutch of a manual-transmission car), a dog clutch provides non-slip coupling and is not suited to intentional slipping.

Synchromesh

Synchronizer rings Sincronizzatore.jpg
Synchronizer rings

In order to provide smooth gearshifts without requiring the driver to manually match the engine revs for each gearshift, most modern passenger car transmissions use 'synchromesh' (also called 'synchronizer rings') on the forward gears. These devices automatically match the speed of the input shaft with that of the gear being selected, thus removing the need for the driver to use techniques such as double-clutching. The synchromesh transmission was invented in 1919 by Earl Avery Thompson and first used on production cars by Cadillac in 1928. [17]

The need for synchromesh in a constant-mesh transmission is that the dog clutches require the input shaft speed to match that of the gear being selected; otherwise, the dog teeth will fail to engage and a loud grinding sound will be heard as they clatter together. Therefore, to speed up or slow down the input shaft as required, cone-shaped brass synchronizer rings are attached to each gear. When the driver moves the gearshift lever towards the next gear, these synchronizer rings press on the cone-shaped sleeve on the dog collar so that the friction forces can reduce the difference in rotational speeds. [18] Once these speeds are equalized, the dog clutch can engage, and thus the new gear is now in use. In a modern gearbox, the action of all of these components is so smooth and fast it is hardly noticed. Many transmissions do not include synchromesh on the reverse gear (see Reverse gear section below).

The synchromesh system must also prevent the collar from bridging the locking rings while the speeds are still being synchronized. This is achieved through 'blocker rings' (also called 'baulk rings'). The synchro ring rotates slightly because of the frictional torque from the cone clutch. In this position, the dog clutch is prevented from engaging. Once the speeds are synchronized, friction on the blocker ring is relieved and the blocker ring twists slightly, bringing into alignment certain grooves or notches that allow the dog clutch to fall into the engagement.

Common metals for synchronizer rings are brass and steel, and are produced either by forging or sheet metal shaping. The latter involves stamping the piece out of a sheet metal strip and then machining to obtain the exact shape required. The rings are sometimes coated with anti-wear linings (also called 'friction linings') made from molybdenum, iron, bronze or carbon (with the latter usually reserved for high-performance transmissions due to their high cost). [19]

Mechanical wear of the synchronizer rings and sleeves can cause the synchromesh system to become ineffective over time. These rings and sleeves have to overcome the momentum of the entire input shaft and clutch disk during each gearshift (and also the momentum and power of the engine, if the driver attempts a gearshift without fully disengaging the clutch). Larger differences in speed between the input shaft and the gear require higher friction forces from the synchromesh components, potentially increasing their wear rate.

Reverse gear

Even in modern transmissions where all of the forward gears are in a constant-mesh configuration, often the reverse gear uses the older sliding-mesh ("crash box") configuration. This means that moving the gearshift lever into reverse results in gears moving to mesh together. Another unique aspect of the reverse gear is that it consists of two gears—an idler gear on the countershaft and another gear on the output shaft—and both of these are directly fixed to the shaft (i.e. they are always rotating at the same speed as the shaft). These gears are usually spur gears with straight-cut teeth which—unlike the helical teeth used for forward gear—results in a whining sound as the vehicle moves in reverse.

When reverse gear is selected, the idler gear is physically moved to mesh with the corresponding gears on the input and output shafts. To avoid grinding as the gears begin to the mesh, they need to be stationary. Since the input shaft is often still spinning due to momentum (even after the car has stopped), a mechanism is needed to stop the input shaft, such as using the synchronizer rings for 5th gear. However, some vehicles do employ a synchromesh system for the reverse gear, thus preventing possible crunching if reverse gear is selected while the input shaft is still spinning. [20]

Most transmissions include a lockout mechanism to prevent reverse gear from being accidentally selected while the car is moving forwards. This can take the form of a collar underneath the gear knob which needs to be lifted or requiring extra force to push the gearshift lever into the plane of reverse gear.

Non-synchronous transmission

3-speed non-synchronous "crash" gearbox; used in automobiles pre-1950s and semi-trailer trucks Crash gearbox 3gears and reverse.gif
3-speed non-synchronous "crash" gearbox; used in automobiles pre-1950s and semi-trailer trucks

Another design of transmission that is used in older cars, trucks, and tractors, is a non-synchronous transmission (also known as a crash gearbox). Non-synchronous transmissions use a sliding-mesh (or constant-mesh, in later years) design and have the nickname "crash" because the difficulty in changing gears can lead to gear shifts accompanied by crashing/crunching noises.

Clutch

Exploded view of a flywheel, friction disk, and clutch kit Tuning World Bodensee 2018, Friedrichshafen (OW1A1318).jpg
Exploded view of a flywheel, friction disk, and clutch kit

Vehicles with manual transmissions use a clutch to manage the linkage between the engine and the transmission, and decouple the transmission from the engine during gearshifts and when the vehicle is stationary. Without a clutch, the engine would stall any time the vehicle stopped, and changing gears would be difficult (deselecting a gear while the transmission requires the driver to adjust the throttle so that the transmission is not under load, and selecting a gear requires the engine RPM to be at the exact speed that matches the road speed for the gear being selected).

Most motor vehicles use a pedal to operate the clutch; except for motorcycles, which usually have a clutch lever on the left handlebar.

Gear stick

Floor-mounted gear stick in a passenger car Shift stick.jpg
Floor-mounted gear stick in a passenger car
Common shift pattern for a 5-speed transmission Manual Layout.svg
Common shift pattern for a 5-speed transmission

In most vehicles with a manual transmission, the driver selects gears by manipulating a lever called a gear stick (also called a gearshift, gear lever or shifter). In most automobiles, the gear stick is located on the floor between the driver and front passenger, but some cars have a gear stick that is mounted to the steering column or center console.

The movement of the gear stick is transferred (via solid linkages or cables) to the selector forks within the transmission.

Motorcycles typically employ sequential manual transmissions, although the shift pattern is modified slightly for safety reasons. Gear selection is usually via the left-foot (or, on older motorcycles; right-foot) shift lever with a layout of 1–N–2–3–4–5–6.

External overdrive

In the 1950s, 1960s, and 1970s, fuel-efficient highway cruising with low engine speed was in some cases enabled on vehicles equipped with 3- or 4-speed transmissions by means of a separate overdrive unit in or behind the rear housing of the transmission. This was actuated either manually while in high gear by throwing a switch or pressing a button on the gearshift knob or on the steering column, or automatically by momentarily lifting the foot from the accelerator with the vehicle traveling above a certain road speed. Automatic overdrives were disengaged by flooring the accelerator, and a lockout control was provided to enable the driver to disable overdrive and operate the transmission as a normal (non-overdrive) transmission. [21]

The term 'overdrive' is also used to describe a gear with a ratio of less than one (e.g., if the top gear of the transmission has a ratio of 0.8:1).

Push starting

Vehicles with a manual transmission can often be push started when the starter motor is not operational, such as when the car has a dead battery.

When push-starting, the energy generated by the wheels moving on the road is transferred to the driveshaft, then the transmission, and eventually the crankshaft. When the crankshaft spins as a result of the energy generated by the rolling of the vehicle, the motor is cranked over. This simulates what the starter is intended for and operates in a similar way to crank handles on very old cars from the early 20th century, with the cranking motion being replaced by the pushing of the car.

Driving techniques

Recently, many automatic transmissions have included more gear ratios than their manual counterparts. [22] [23]

Driving a vehicle with a manual transmission is more difficult than an automatic transmission for several reasons. Firstly, the clutch pedal is an extra control mechanism to operate and in some cases, a "heavy clutch" requires significant force to be operated (this can also preclude some people with injuries or impairments from driving manual transmission vehicles). The operation of the gearstick — another function that is not required on automatic transmission cars — means that the driver must take one hand off the steering wheel while changing gears (unless paddle shift is used). Another challenge is that smooth driving requires co-ordinated timing of the clutch, accelerator, and gearshift inputs. Lastly, a car with an automatic transmission obviously does not require the driver to make any decisions about which gear to use at any given time. On the other hand, being able to choose a specific gear and engine rpm setting manually gives the driver full control of the torque applied by the tires, a critical ability for racing, and important for driving on ice, snow, mud or sand and for spirited driving. Some automatic transmissions have a mode where gears can be manually shifted for such uses.

In some countries, a driving license issued for vehicles with an automatic transmission is not valid for driving vehicles with a manual transmission, but a license for manual transmissions covers both. [24]

Hill starts

Starting from a stationary position in a manual transmission vehicle requires extra torque to accelerate the vehicle up the hill, with the potential for the vehicle to roll backward in the time it takes to move the driver's foot from the brake pedal to the accelerator pedal (to increase the engine RPM before letting out the clutch). The traditional method of hill starts in a manual transmission car is to use the parking brake (also called "handbrake", "emergency brake", or "e-brake") to hold the vehicle stationary. This means that the driver's right foot is not needed to operate the brake pedal, freeing it up to be used on the accelerator pedal instead. Once the required engine RPM is obtained, the driver can release the clutch, also releasing the parking brake as the clutch engages.

A device called the hill-holder was introduced on the 1936 Studebaker. Many modern vehicles use an electronically actuated parking brake, which often includes a hill-holder feature whereby the parking brake is automatically released as the driven wheels start to receive power from the engine. [25]

Other driving techniques

Synchronized downshift rev-matching system

The synchronized down shift rev-matching system is a computer-controlled technology that mimics the manual rev-matching technique.

Truck transmissions

Some trucks have transmissions that look and behave like ordinary consumer vehicle transmissions—these transmissions are used on lighter trucks, typically have up to 6 gears, and usually have synchromesh.

For trucks needing more gears, the standard "H" pattern can be complicated for some truck drivers, so additional controls are used to select additional gears. The "H" pattern is retained, then an additional control selects among alternatives. In older trucks, the control is often a separate lever mounted on the floor or more recently a pneumatic switch mounted on the "H" lever; in newer trucks, the control is often an electrical switch mounted on the "H" lever. Multi-control transmissions are built in much higher power ratings but rarely use synchromesh.

There are several common alternatives for the shifting pattern. The standard types are:

Although there are many gear positions, shifting through gears usually follows a regular pattern. For example, a series of up shifts might use "move to splitter direct; move to splitter overdrive; move the shift lever to No. 2 and move splitter to underdrive; move splitter to direct; move splitter to overdrive; move the shifter to No. 3 and move splitter to underdrive"; and so on. In older trucks using floor-mounted levers, a bigger problem is common gear shifts require the drivers to move their hands between shift levers in a single shift, and without synchromesh, shifts must be carefully timed or the transmission will not engage. For this reason, some splitter transmissions have an additional "under under" range, so when the splitter is already in "under" it can be quickly downshifted again, without the delay of a double shift.

Modern truck transmissions are most commonly "range-splitter". The most common 13-speed has a standard H pattern, and the pattern from the left upper corner is as follows: R, down to L, over and up to 1, down to 2, up and over to 3, down to 4. The "butterfly" range lever in the center front of the knob is flipped up to high range while in 4th, then shifted back to 1. The 1 through 4 positions of the knob is repeated. Also, each can be split using the thumb-actuated under-overdrive lever on the left side of the knob while in high range. The "thumb" lever is not available in low range, except in 18 speeds; 1 through 4 in the low range can be split using the thumb lever and L can be split with the "Butterfly" lever. L cannot be split using the thumb lever in either the 13- or 18-speed. The 9-speed transmission is like a 13-speed without the under-overdrive thumb lever.

Truck transmissions use many physical layouts. For example, the output of an N-speed transmission may drive an M-speed secondary transmission, giving a total of N*M gear combinations. Transmissions may be in separate cases with a shaft in between; in separate cases bolted together; or all in one case, using the same lubricating oil. The second transmission is often called a "Brownie" or "Brownie box" after a popular brand. With a third transmission, gears are multiplied yet again, giving greater range or closer spacing. Some trucks thus have dozens of gear positions, although most are duplicates. Sometimes a secondary transmission is integrated with the differential in the rear axle, called a "two-speed rear end". Two-speed differentials are always splitters. In newer transmissions, there may be two counter shafts, so each main shaft gear can be driven from one or the other countershaft; this allows construction with short and robust countershafts, while still allowing many gear combinations inside a single gear case.

Heavy-duty transmissions are mostly non-synchromesh. Sometimes synchromesh adds weight that could be payload, and is one more thing to fail, and drivers spend thousands of hours driving so can take the time to learn to drive efficiently with a non-synchromesh transmission. Float shifting (also called "floating gears") is changing gears without disengaging the clutch, usually on a non-synchronized transmission used by large trucks. Since the clutch is not used, it is easy to mismatch speeds of gears, and the driver can quickly cause major (and expensive) damage to the gears and the transmission.

Heavy trucks are usually powered with diesel engines. Diesel truck engines from the 1970s and earlier tend to have a narrow power band, so they need many close-spaced gears. Starting with the 1968 Maxidyne, diesel truck engines have increasingly used turbochargers and electronic controls that widen the power band, allowing fewer and fewer gear ratios. As of 2021, fleet operators often use 9, 10, 13, or 18-speed transmissions, but automated manual transmissions are becoming more common on heavy vehicles, as they can improve efficiency and drivability, reduce the barrier to entry for new drivers, and may improve safety by allowing the driver to concentrate on road conditions. [ citation needed ]

Lubrication

Manual transmissions are lubricated with gear oil (or engine oil in some vehicles) which must be changed periodically in some vehicles, although not as frequently as the fluid in an automatic transmission. Gear oil has a characteristic aroma because it contains added sulfur-bearing anti-wear compounds. These compounds are used to reduce the high sliding friction by the helical gear cut of the teeth (this cut eliminates the characteristic whine of straight-cut spur gears). On motorcycles with "wet" clutches (clutch is bathed in engine oil), there is usually nothing separating the lower part of the engine from the transmission, so the same oil lubricates both the engine and transmission.

See also

Related Research Articles

Clutch Mechanical device that connects and disconnects two rotating shafts or other moving parts

A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts. In these devices, one shaft is typically attached to an engine or other power unit, while the other shaft provides output power for work. Typically the motions involved are rotary, but linear clutches also exist.

Double-clutching is a method of shifting gears used primarily for vehicles with an unsynchronized manual transmission, such as commercial trucks and specialty vehicles. While double clutching is not necessary in a vehicle that has a synchronized manual transmission, the technique can be advantageous for smoothly upshifting in order to accelerate and, when done correctly, it prevents wear on the synchronizers which normally equalize transmission input and output speeds to allow downshifting.

Automatic transmission Type of motor vehicle transmission that automatically changes gear ratio as the vehicle moves

An automatic transmission is a multi-speed transmission used in internal combustion engine-based motor vehicles that does not require any driver input to change forward gears under normal driving conditions. It typically includes a transmission, axle, and differential in one integrated assembly, thus technically becoming a transaxle.

Overdrive (mechanics) Operation of an automobile cruising at sustained speed with reduced engine revolutions

Overdrive is the operation of an automobile cruising at sustained speed with reduced engine revolutions per minute (RPM), leading to better fuel consumption, lower noise, and lower wear. The term is ambiguous. The most fundamental meaning is that of an overall gear ratio between engine and wheels, such that the car is over-geared, and cannot reach its potential top speed, i.e. the car could travel faster if it were in a lower gear, with the engine turning at higher RPM.

Propulsion transmission Drivetrain transmitting propulsion power

Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term transmission properly refers to the whole drivetrain, including clutch, gearbox, prop shaft, differential, and final drive shafts. In the United States the term is sometimes used in casual speech to refer more specifically to the gearbox alone, and detailed usage differs. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also used on pedal bicycles, fixed machines, and where different rotational speeds and torques are adapted.

Freewheel Mechanism which disconnects a driveshaft from a faster-rotating driven shaft

In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated.

A semi-automatic transmission is a multiple-speed transmission where part of its operation is automated, but the driver's input is still required to launch the vehicle from a standstill and to manually change gears. Most semi-automatic transmissions used in cars and motorcycles are based on conventional manual transmissions or sequential manual transmissions, but use an automatic clutch system. However, some semi-automatic transmissions have also been based on standard hydraulic automatic transmissions with torque converters and planetary gearsets.

Hydramatic Automatic transmission by General Motors

Hydramatic is an automatic transmission developed by both General Motors' Cadillac and Oldsmobile divisions. Introduced in 1939 for the 1940 model year vehicles, the Hydramatic was the first mass-produced fully-automatic transmission developed for passenger automobile use.

Direct-shift gearbox Type of dual-clutch transmission

A direct-shift gearbox is an electronically-controlled, dual-clutch, multiple-shaft, automatic gearbox, in either a transaxle or traditional transmission layout, with automated clutch operation, and with fully-automatic or semi-manual gear selection. The first dual-clutch transmissions were derived from Porsche in-house development for the Porsche 962 in the 1980s.

Preselector gearbox Type of manual transmission

A preselector gearbox is a type of manual transmission mostly used on passenger cars and racing cars in the 1930s, in buses from 1940-1960 and in armoured vehicles from the 1930s to the 1970s. The defining characteristic of a preselector gearbox is that the gear shift lever allowed the driver to "pre-select" the next gear, usually with the transmission remaining in the current gear until the driver pressed the "gear change pedal" at the desired time.

Automated manual transmission Type of multi-speed motor vehicle transmission system

The automated manual transmission (AMT) is a type of transmission for motor vehicles. It is essentially a conventional manual transmission but uses automatic actuation to operate the clutch and/or shift between gears.

A transmission control unit (TCU), also known as a transmission control module (TCM), or a gearbox control unit (GCU), is a type of automotive ECU that is used to control electronic automatic transmissions. Similar systems are used in conjunction with various semi-automatic transmissions, purely for clutch automation and actuation. A TCU in a modern automatic transmission generally uses sensors from the vehicle, as well as data provided by the engine control unit (ECU), to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality.

Gear stick Lever used for shifting gears manually

A gear stick, gear lever, gearshift or shifter, more formally known as a transmission lever, is a metal lever attached to the transmission of an automobile. The term gear stick mostly refers to the shift lever of a manual transmission, while in an automatic transmission, a similar lever is known as a gear selector. A gear stick will normally be used to change gear whilst depressing the clutch pedal with the left foot to disengage the engine from the drivetrain and wheels. Automatic transmission vehicles, including hydraulic automatic transmissions, automated manual and older semi-automatic transmissions, like VW Autostick, and those with continuously variable transmissions, do not require a physical clutch pedal.

Sequential manual transmission Motor transmission

A sequential manual transmission, also known as a sequential gearbox, or a sequential transmission, is a type of non-synchronous manual transmission used mostly for motorcycles and racing cars. It produces faster shift times than traditional synchronized manual transmissions, and restricts the driver to selecting either the next or previous gear, in a successive order.

Corvair Powerglide

Chevrolet Corvair Powerglide is a two-speed automatic transmission designed specially for the then all-new 1960 Chevrolet Corvair compact car that emerged in the fall of 1959 as Chevrolet's competitor in the then booming small car market. The Corvair was powered by a rear-mounted Chevrolet Turbo-Air 6 engine that necessitated a specially designed transaxle. Corvair Powerglide took the principles of the standard Chevrolet Powerglide and modified them to suit the rear-mounted powertrain location of the new Corvair. The Corvair used the Powerglide for all 10 years it was produced; from 1961 to 1963, Pontiac used a modified version of Corvair Powerglide it called 'TempesTorque' for its front-engine, rear-transaxle Tempest, LeMans and Tempest LeMans cars.

Non-synchronous transmission Form of manual transmission

A non-synchronous transmission, also called a crash gearbox, is a form of manual transmission based on gears that do not use synchronizing mechanisms. They require the driver to manually synchronize the transmission's input speed and output speed.

Motorcycle transmission Transmission for motorcycle applications

A motorcycle transmission is a transmission created specifically for motorcycle applications. They may also be found in use on other light vehicles such as motor tricycles and quadbikes, go-karts, offroad buggies, auto rickshaws, mowers, and other utility vehicles, microcars, and even some superlight racing cars.

9G-Tronic is Mercedes-Benz's trademark name for its nine-speed automatic transmission, starting off with the W9A 700 as core model.

Layshaft

A layshaft is an intermediate shaft within a gearbox that carries gears, but does not transfer the primary drive of the gearbox either in or out of the gearbox. Layshafts are best known through their use in car gearboxes, where they were a ubiquitous part of the rear-wheel drive layout. With the shift to front-wheel drive, the use of layshafts is now rarer.

Car controls Car parts used to control the vehicle

Car controls are the components in automobiles and other powered road vehicles, such as trucks and buses, used for driving and parking.

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