A non-synchronous transmission, also called a crash gearbox, is a form of

manual transmission 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 (mechanics), transmission ...

based on gears that do not use synchronizing mechanisms. They require the driver to manually synchronize the transmission's input speed (engine RPM) and output speed (driveshaft speed). Non-synchronous transmissions are found primarily in various types of

industrial machinery The following outline is provided as an overview of and topical guide to industrial machinery: Essence of industrial machinery * Heavy equipment * Hardware * Industrial process * Machine * Machine tool * Tool Industrial machines * Agricul ...

; such as

tractor A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most common ...

s and semi-tractors. Non-synchronous

s are also found on

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...

s, in the form of constant-mesh

sequential manual 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 ...

s. Prior to the 1950s and 1960s, most cars used constant-mesh (and also sliding-mesh) but non-synchronous transmissions.

History

Most early automobiles were rear-engined, using a single-speed transmission and belt-drive to power the rear wheels. In 1891, the French

Panhard et Levassor Panhard was a French motor vehicle manufacturer that began as one of the first makers of automobiles. It was a manufacturer of light tactical and military vehicles. Its final incarnation, now owned by Renault Trucks Defense, was formed b ...

automobile used a three-speed manual transmission and is considered to have set the template for multi-speed manual transmissions in motor vehicles. This transmission used a sliding-gear design without any form of speed synchronization, causing frequent grinding of the gear teeth during gear shifts. The Panhard design was refined over the years by other manufacturers to include "constant-mesh" gears (instead of sliding gears). The first usage of synchromesh was by

Cadillac The Cadillac Motor Car Division () is a division of the American automobile manufacturer General Motors (GM) that designs and builds luxury vehicles. Its major markets are the United States, Canada, and China. Cadillac models are distributed i ...

in 1928.

Driving techniques

Trained drivers of vehicles with non-synchronous transmissions sometimes use the techniques listed below. If improperly implemented, these techniques can cause damage to the vehicle or the loss of control of the vehicle. * Double-clutching: releasing the clutch in neutral to synchronize the speeds of the shafts within the transmission *

Float shifting Float shifting or floating gears, also called "slip shifting", "dead sticking" or "bang shifting", is the process of changing gears, in typically a non-synchronous transmission, without depressing the clutch. Shifting in this manner is also used wi ...

: shifting without using the clutch In big rigs and semi-trucks, the driver may have to complete 24 or more gear changes when accelerating from a standstill to .

Clutch brake

Unlike any other type of transmission, non-synchronous transmissions often have a ''clutch brake'' mechanism, which is usually activated by pressing the clutch pedal all the way to the floor or pressing a button on the top of the gear lever. The purpose of the clutch brake is to slow down (or stop) the rotation of the transmission's input shaft, which assists in shifting the transmission into neutral or first gear when the vehicle is at a standstill. The clutch brake not only slows or stops the idle gear axis but can also prevent shifting into gear until the clutch pedal is released a few centimetres (or inches) off the floor. In order to shift into gear, the clutch must be halfway off the floor, otherwise, the clutch brake will prevent the transmission from being shifted into or out of gear.

Comparison of transmissions

Any transmission that requires the driver to manually synchronize the engine speed with the speed of the driveshaft is non-synchronous. Non-synchronous transmissions are mostly used in semi-trucks, large industrial machines, older agricultural tractors (eg Massey ferguson 135) and

power take-off A power take-off or power takeoff (PTO) is one of several methods for taking power from a power source, such as a running engine, and transmitting it to an application such as an attached implement or separate machine. Most commonly, it is a sp ...

Sequential manual 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 ...

s, which are commonly used in

s, ATVs, and

racecars Auto racing (also known as car racing, motor racing, or automobile racing) is a motorsport involving the racing of automobiles for competition. Auto racing has existed since the invention of the automobile. Races of various sorts were organise ...

, are a type of non-synchronous (unsynchronized) manual transmission, where gear ratios must be selected in succession (order), hence direct access to a specific gear ratio is not possible. Most manual transmissions in modern passenger vehicles are fitted with

synchromesh 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 ...

to equalize the shaft speeds within the transmission, so they are synchronous transmissions. All

automatic transmission An automatic transmission (sometimes abbreviated to auto or AT) is a multi-speed transmission used in internal combustion engine-based motor vehicles that does not require any input from the driver to change forward gears under normal driving c ...

s have synchronizing mechanisms, and

semi-automatic transmission A semi-automatic transmission is a "theoretical" multiple-speed transmission where part of its operation is automated (typically the actuation of the clutch), but the driver's input would be required to launch the vehicle from a standstill and to ...

s that use

dog clutch A dog clutch (also known as a positive clutch or dog gears) is a type of clutch that couples two rotating shafts or other rotating components by engagement of interlocking teeth or dogs rather than by friction. The two parts of the clutch are d ...

es typically have cone-and-collar synchronizing mechanisms.

References

{{DEFAULTSORT:Non-Synchronous Transmission Automotive transmission technologies Gears

History

Driving techniques

Clutch brake

Comparison of transmissions

See also

References