Gear Transmission

Manual transmission Type

1. Sequential transmission

2. Non-synchronous transmission

3. Preselector 

Introduction 

A manual transmission, also known as a manual gearbox or standard transmission (informally, a manual, 5 speed, or the number of forward gears said with the word speed following ie: 4 speed with overdrive, 4 speed, 5 speed, 6 speed or standard, stick-shift, straight shift, or straight, (U.S.)) is a type of transmission used in motor vehicle applications. It generally uses a driver-operated clutch, typically operated by a foot pedal (automobile) or hand lever (motorcycle), for regulating torque transfer from the internal combustion engine to the transmission; and a gear stick, either operated by foot (as in a motorcycle) or by hand (as on an automobile).

A conventional manual transmission is frequently the base equipment in a car; other options include automated transmissions such as an automatic transmission (often a manumatic), a semi-automatic transmission, or a continuously variable transmission (CVT).

1. Sequential transmission

A sequential manual transmission (or sequential manual gearbox) is a type of manual transmission used on motorcycles and high-performance cars for auto racing, where gears are selected in order, and direct access to specific gears is not possible.

With traditional manual transmissions, the driver can move from gear to gear, by moving the shifter to the appropriate position. This type of transmission is often referred to as a H-pattern because of the path that the shift lever takes as it selects the various gears. A clutch must be disengaged before the new gear is selected, to disengage the running engine from the transmission, thus stopping all torque transfer. In auto racing, this process is slow and prone to human error; hence the development of the sequential transmission. A true sequential transmission will very often use dog clutch engagement rather than the more usual synchromesh as fitted to a normal H-pattern road car gearbox. Engagement using dogs only requires a very brief interruption of engine torque to complete a shift into any adjacent gear. This allows shifting between gears without the use of the clutch. The clutch would normally be used only for standing starts.

Benefits

Beyond the ease of use from a driver's standpoint, an additional benefit of sequential manual gearboxes is that use of the clutch via foot pedal or hand control can be minimized or completely obviated, with the clutch only used for starting from a complete stop. Formula One cars of the 1990s made the most high-profile debut of this technology in motor sports, and enhanced variations on this theme are still in use in many forms of road racing and drag racing today. The simple push-pull action of the shift mechanism also lends itself to semi-automatic control using either hydraulic or pneumatic actuators—a system often referred to as paddle-shift. Instead of a manual gear lever, the driver is provided with (usually) a pair of flipper paddles on the steering wheel, rally cars often utilize just a double-acting single paddle. Pulling on the right-hand paddle makes an up-shift and pulling on the left-hand paddle makes a down-shift. The paddle-shift system will use a sophisticated electronic control unit to provide the necessary logic to operate the shift mechanism. This type of paddle-shift system fitted to race and rally cars should not be confused with most of the current crop of so-called paddle-shift systems fitted to some high-end road cars. More often than not, these systems are nothing more than conventional automatic transmissions which allow driver input to select the gears. The Mercedes Smart Car is an example of a Sequential manual transmission.

2.Non-synchronous transmission

A non-synchronous transmission is a form of transmission based on gears that do not use synchronizing mechanisms. They are found primarily in various types of agricultural, and commercial vehicles. Because the gear boxes are engineered without "cone and collar" synchronizing technology, the non-synchronous transmission type requires an understanding of gear range, torque, engine power, range selector, multi-functional clutch, and shifter functions. Engineered to pull tremendous loads, often equal to or exceeding 40 tons, some vehicles may also use a combination of transmissions for different mechanisms. An example would be a PTO.

How non-synchronization works

Non-synchronous transmissions are engineered with the understanding that a trained operator will be shifting gears in a known coordination of timing. Commercial vehicle operators use a double-clutching technique that is taught in driver's trade schools. The most skillful drivers can shift these transmissions without using the clutch by bringing the engine to exactly the right rpm in neutral before attempting to complete a shift, a technique called "float-shifting." With payloads of cargo ranging in commercial freight of 80,000 lbs (40 tons (short) or 36.3 tonnes) or more, some heavy haulers have over 24 gears that an operator will shift through before reaching a top cruising speed of 70 mph (113 km/h). Many low-low (creeper) gears are used in farm equipment to plow, till, or harvest. Also see Engineering vehicle. An inexperienced operator would suddenly find a piece of heavy equipment stuck in gear under full power, or even worse unable to shift into gear a runaway vehicle in neutral headed down a steep slope, unless he understood the synchronizing skill, and torque issues in non-synchronous transmissions. Many mountain roads require heavy equipment operators to remain in gear and not shift while passing down a steep grade. For more details about steep grade operation see either jake brake, or engine brake. Many other circumstances face operators of non-synchronous transmissions. Safety and operator skills need to be learned before operating any of these types of vehicles.

Comparison of transmissions

Non-synchronous transmissions are designed to depend upon an operator experienced in changing gears. The operators must understand how to shift the transmission into and out of gear. Many learn how to do this in certifying schools.

All automatic transmissions have synchronizing mechanisms. Most manual transmissions also have synchronizers. But there are still other types of transmissions used mostly in commercial applications that are non-synchronous.

Fully synchronous, hydrau-pneumatic systems are designed to change gears based on engine performance and other velocity indicators, delivering torque to drive wheels. These transmissions have synchronizing mechanisms (called cone and collar synchronizers) that are designed to keep gear dog-teeth from being broken off.

Heavy equipment for industrial, military, or farm use have different torque and load issues. They have unique stress from massive horsepower that would make converter faces shear. For the reasons of engineering a dependable, longer-life piece of equipment, these machines often use non-synchronous transmissions.

Any transmission that requires the operator to manually synchronize engine crank-shaft revolutions (RPM) with drive-shaft revolutions is non-synchronous.

3.Preselector 

A preselector or self-changing gearbox is a type of manual gearbox (US: transmission) used on a variety of vehicles, most commonly in the 1930s. The defining characteristic of a preselector gearbox is that the manual shift lever is used to "pre-select" the next gear to be used, then a separate control (a foot pedal) is used to engage this in one single operation, without needing to work a manual clutch.

Most pre-selector transmissions avoid a driver-controlled clutch entirely. Some use one solely for starting off.

Preselector gearboxes are not automatic gearboxes, although they may have internal similarities. A fully automatic gearbox is able to select the ratio used, with a preselector gearbox this remains the driver's decision.

There are several radically different mechanical designs of preselector gearbox. The best known is the Wilson design . Some gearboxes, such as the Cotal, shift gear immediately the control is moved, without requiring the separate pedal action. These are termed 'self-changing' gearboxes, but were considered under the same overall heading. In recent years, a similar role is carried out by the increasing number of 'Tiptronic' or 'paddle shift' gearboxes, using manual selection and immediate automated changing.

Advantages of preselector gearboxes

For the driver, there are two advantages:

• Fast shifting, with only a single operation. This requires less skill to learn than techniques like double declutching and it offers faster shifts when racing.
• Ability to handle far more engine power, with a lighter mechanism.

In engineering terms, some designs of pre-selector gearbox may offer particular advantages. The Wilson gearbox offers these, although they're also shared by some of the other designs, even though the designs are quite different:

• Their friction components are brakes, rather than clutches. These are simpler to engineer, as the wear components can be arranged to not also be rotating parts.
• The friction wear components can be mounted on the outside of the mechanism, rather than buried within it. This makes maintenance and regular adjustment easier.

They were common on Daimler cars and commercial vehicles, Maybach, Alvis, Talbot-Lago, and Armstrong Siddeley cars as well as on many London buses. They have also been used in racing cars, such as the 1935 ERA R4D, and hillclimbing cars such as Auto Union "Silver Arrows". Military applications began in 1929 included tanks such as the German Tiger I and Tiger II in World War II, through to the current tanks such as Challenger 2.