Sprag clutch

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One-way bearing combining sprags and bearing rollers in one race Sprag one-way bearing labeled.png
One-way bearing combining sprags and bearing rollers in one race
Sprags jam when driven and slide when in reverse Sprag clutch.png
Sprags jam when driven and slide when in reverse

A sprag clutch is a one-way freewheel clutch. It resembles a roller bearing but, instead of cylindrical rollers, non-revolving asymmetric figure-eight shaped sprags, or other elements allowing single direction rotation, are used. When the unit rotates in one direction the rollers slip or free-wheel, but when a torque is applied in the opposite direction, the sprags tilt slightly, producing a wedging action and binding because of friction.

Contents

Applications

Automatic transmissions

A sprag clutch is used in some automatic transmissions as a method of allowing the transmission to change gears smoothly under load. Various models of General Motors' Turbo-Hydramatic transmission have used this system as well as many transmissions from Ford, such as the Ford C6 transmission.

A sprag clutch is used in most older automatic transmissions and some newer ones for shifts which require the synchronized engagement of one clutch with the disengagement of another. Using an overrunning clutch instead of a hydraulically actuated one makes this synchronization automatic. The sprag clutch simply "lets go" once the reaction force it provides is no longer needed.

In a Simpson planetary gearset, common to many automatic transmissions, this happens on the 1-2 shift, and reverses on the 2-1 downshift. The 2-3 shift is done by engaging a single clutch, and nothing is released. Some newer electronically controlled transmissions make "clutch to clutch" shifts, without any sprags.

This can also be used exclusively in first gear (transmission shift lever in D, but auto valve body or management selecting 1st) on some autos. That way it will automatically provide forward drive, but will not provide any engine braking. This is done not so much to avoid engine braking per se, but rather to allow a low throttle opening 2-1 downshift as a car decelerates, to avoid a loud (and potentially abrupt) and unnerving jolt as a result of the downshift. On transmissions so equipped, manual selection of 1st gear typically engages an additional band that grips the same section as the one way clutch would engage, and thus allows for engine braking.

Turbine Starter

A sprag clutch may be used in the starting turbine of a turbojet engine, so that the running main engine does not keep the starter engaged at high speeds. [1]

Helicopters

A sprag clutch is used in many helicopter designs to transfer power from the engine to the main rotor. In the event of an engine failure, the sprag clutch allows the main rotor to continue rotating faster than the engines so that the helicopter can enter autorotation. [2]

Motorcycle applications

Starters

A sprag clutch is used in the electric starter motors of modern motorcycle engines to replace the Bendix gear common to automobile starters.

Primary drive

Many modern sport and racing motorcycles use sprag clutches in the primary drive between the engine and transmission. This prevents the rear wheel from losing traction during rapid downshifts when the engine speed is not matched to road speed. If a sprag clutch is not present, much greater care is required when downshifting, because losing rear wheel traction can cause dangerous highside accidents.

Conveyors

On conveyor drives, a sprag clutch is used for indexing and anti-runback.

Overrunning

Overrunning occurs when two or more motors can be used to drive the same machine, including through the same shaft. A typical setup is as follows. The service drive, or prime mover, provides a combination of high speed and high power for normal operation. The secondary drive, or pony drive, can be run at low speed and low power, usually to position the conveyor for maintenance.

The overrunning clutch allows the secondary drive to remain stationary during normal high speed operation of the conveyor drive.

Indexing

An indexing motion provides for accuracy in the drive system. A link is installed between the prime mover and one race of the sprag clutch. The reciprocating motion of the prime mover is converted to an indexing movement on the other race of the sprag clutch.

Backstopping

Backstopping prevents a loaded inclined conveyor from running back when the drive system is stopped. The outer race of the sprag clutch is fixed to the machine frame, usually via a torque arm. The inner race rotates freely in the forward direction of the conveyor drive. When the machine tries to run backward, the sprag clutch prevents this motion. In this application the sprag clutch is often called a "backstop" or "holdback".

Hoist load brake

A hoist load brake is used as a secondary brake to prevent industrial hoists from catastrophically dropping their loads in the event of mechanical failure.

Pumping systems

A sprag clutch is used in some pumping systems where a standby prime mover is required in case of a failure by the main drive. An example is a pump with a single rotating shaft through the unit connected at one end by an electric motor and the other by a standby diesel engine isolated by a spray clutch.

Lubrication

Sprag clutches may be oil or grease lubricated. Most sprag clutch manufacturers don't allow the use of lubricants containing extreme pressure additives.

See also

Related Research Articles

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A clutch is a mechanical device that allows the output shaft to be disconnected from the rotating input shaft. The clutch's input shaft is typically attached to a motor, while the clutch's output shaft is connected to the mechanism that does the work.

<span class="mw-page-title-main">Starter (engine)</span> Device used to start an internal combustion engine

A starter is a device used to rotate (crank) an internal-combustion engine so as to initiate the engine's operation under its own power. Starters can be electric, pneumatic, or hydraulic. The starter can also be another internal-combustion engine in the case, for instance, of very large engines, or diesel engines in agricultural or excavation applications.

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 downshifting 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.

<span class="mw-page-title-main">Automatic transmission</span> Type of motor vehicle transmission that automatically changes gear ratio as the vehicle moves

An automatic transmission is a multi-speed transmission used in motor vehicles that does not require any input from the driver to change forward gears under normal driving conditions. Vehicles with internal combustion engines, unlike electric vehicles, require the engine to operate in a narrow range of rates of rotation, requiring a gearbox, operated manually or automatically, to drive the wheels over a wide range of speeds.

<span class="mw-page-title-main">Torque converter</span> Fluid coupling that transfers rotating power from a prime mover to a rotating driven load

A torque converter is a device, usually implemented as a type of fluid coupling, that transfers rotating power from a prime mover, like an internal combustion engine, to a rotating driven load. In a vehicle with an automatic transmission, the torque converter connects the prime mover to the automatic gear train, which then drives the load. It is thus usually located between the engine's flexplate and the transmission. The equivalent device in a manual transmission is the mechanical clutch.

<span class="mw-page-title-main">Transmission (mechanical device)</span> Drivetrain transmitting propulsion power

A transmission is a mechanical device which uses gears to change the speed or direction of rotation in a machine. Many transmissions have multiple gear ratios, but there are also transmissions that use a single fixed gear ratio.

<span class="mw-page-title-main">Manual transmission</span> Motor vehicle manual gearbox; stick shift

A manual transmission (MT), also known as manual gearbox, standard transmission, or stick shift, 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.

<span class="mw-page-title-main">Freewheel</span> 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. Semi-automatic transmissions were almost exclusively used in motorcycles and are based on conventional manual transmissions or sequential manual transmissions, but use an automatic clutch system. But some semi-automatic transmissions have also been based on standard hydraulic automatic transmissions with torque converters and planetary gearsets.

<span class="mw-page-title-main">Hydramatic</span> Automatic transmission

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.

<span class="mw-page-title-main">Direct-shift gearbox</span> 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.

<span class="mw-page-title-main">Mercedes-Benz 7G-Tronic transmission</span> Motor vehicle component

7G-Tronic is Mercedes-Benz's trademark name for its seven-speed automatic transmission, starting off with the W7A 700 and W7A 400 as core models.

A slipper clutch(also known as a back-torque limiter) is a specialized clutch with an integrated freewheel mechanism, developed for performance-oriented motorcycles to mitigate the effects of engine braking when riders decelerate.

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.

<span class="mw-page-title-main">Corvair Powerglide</span> Automatic transmission

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.

<span class="mw-page-title-main">Non-synchronous transmission</span> 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.

<span class="mw-page-title-main">Ravigneaux planetary gearset</span>

The Ravigneaux gearset is a double planetary gear set, invented by Pol Ravigneaux, who filed a patent application on July 28, 1949, in Neuilly-sur-Seine France. This planetary gear set, commonly used in automatic transmissions, is constructed from two gear pairs, ring–planet and planet–planet.

A MultiMode manual transmission is a type of automated manual transmission offered by Toyota. It uses a traditional manual gearbox with a computer-controlled clutch actuated by permanent magnet motors. Multimode Manual Transmission is available in the Aygo, Yaris, Corolla, Corolla Verso, Mark X and Auris in Europe, and should not be confused with Multimode Automatic Transmission, which is offered in the North American market by Toyota.

<span class="mw-page-title-main">Motorcycle transmission</span> 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.

<span class="mw-page-title-main">Drivetrain</span> Group of components that deliver power to the driving wheels

A drivetrain is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the drivetrain is the components of a motor vehicle that deliver power to the drive wheels. This excludes the engine or motor that generates the power. In marine applications, the drive shaft will drive a propeller, thruster, or waterjet rather than a drive axle, while the actual engine might be similar to an automotive engine. Other machinery, equipment and vehicles may also use a drivetrain to deliver power from the engine(s) to the driven components.

References

  1. "Inside a Planetary Reduction Drive". Youtube. October 4, 2011. Archived from the original on 2021-04-15. Retrieved 2021-07-18.
  2. Federal Aviation Administration, Flight Standards Service (2007). Rotorcraft Flying Handbook (Illustrated ed.). Skyhorse Publishing. pp. 5–4. ISBN   978-1-60239-060-7.