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Freewheel mechanism

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. On a bicycle, the cassette or the freewheel is the set of rear sprockets that attaches to a hub on the rear wheel. ... This is a file from the Wikimedia Commons, a repository of free content hosted by the Wikimedia Foundation. ... This is a file from the Wikimedia Commons, a repository of free content hosted by the Wikimedia Foundation. ... Mechanical Engineering is an engineering discipline that involves the application of principles of physics for analysis, design, manufacturing, and maintenance of mechanical systems. ... Automotive engineering is a branch of Vehicle engineering, incorporating elements of mechanical, electrical, electronic, software and safety engineering as applied to the design, manufacture and operation of automobiles, buses and trucks and their respective engineering subsystems. ... Gearbox redirects here. ... This article is about the mechanical device. ... An overdrive is sometimes a separate unit that fits into the back of a gearbox, as with this Fairey unit. ...

The condition of a driven shaft spinning faster than its driveshaft exists in a bicycle going downhill when the rider holds his or her feet still, no longer pushing the pedals. Without a freewheel the rear wheel would drive the pedals around. For other uses, see Bicycle (disambiguation). ... Note: This page needs to be cleaned up to be brought into conformance with the Manual of Style. ...

An analogous condition exists in an automobile with a manual transmission going down hill or any situation where the driver takes his foot off the gas pedal, closing the throttle; the wheels want to drive the engine, possibly at a higher RPM. In a two-stroke engine this is a lethal situation: as the engine depends on fuel for lubrication, a shortage of fuel to the engine would result in a shortage of oil in the cylinders, and the pistons would seize after a very short time causing extensive engine damage. Saab automobiles used a freewheel system in the two stroke models for this reason and maintained it in the Saab 96 V4 and early Saab 99 for better fuel efficiency. Car redirects here. ... A manual transmission (also known as a stick shift, straight drive, or standard transmission) is a type of transmission used in automotive applications. ... Petrol redirects here. ... In an engine, the throttle is the mechanism by which the engines power is increased or decreased. ... The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle by having only two strokes (linear movements of the piston) instead of four, although the same four operations (intake, compression, power, exhaust) still occur. ... A colored automobile engine The internal combustion engine is an engine in which the combustion of fuel and an oxidizer (typically air) occurs in a confined space called a combustion chamber. ... For other uses, see Fuel (disambiguation). ... Lubrication occurs when opposing surfaces are separated by a lubricant film. ... Cylinder with piston in a steam engine A cylinder in the central working part of a reciprocating engine, the space in which a piston travels. ... For the American composer, see Walter Piston. ... Saab Automobile AB is automobile manufacturing company in Sweden, and is currently a wholly-owned subsidiary of the General Motors Corporation. ... Saab 96 The Saab 96 is an automobile made by Saab. ... 1700 cc High Compression Ford Taurus V4 A V4 is an engine in V configuration, with 4 cylinders. ... The 99 was an automobile produced by Saab from 1969 to 1984. ... Fuel efficiency, in its basic sense, is the same as thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. ...

Mechanics

The simplest freewheel device consists of two saw-toothed, spring-loaded discs pressing against each other with the toothed sides together, somewhat like a ratchet. Rotating in one direction, the saw teeth of the drive disc lock with the teeth of the driven disc, making it rotate at the same speed. If the drive disc slows down or stops rotating, the teeth of the driven disc slip over the drive disc teeth and continue rotating. For other uses, see Spring. ... A ratchet lever hoist. ...

A more sophisticated and rugged design has spring-loaded steel rollers inside a driven cylinder. Rotating in one direction, the rollers lock with the cylinder making it rotate in unison. Rotating slower, or in the other direction, the steel rollers just slip inside the cylinder. Roller may mean: In biology: Roller, family of brightly coloured near passerine birds in the genera Coracias and Eurystomus In industry: Roller (machine part), a cylindrical machine component or a component of a roller bearing Roller (agricultural tool), an agricultural or gardening implement for levelling ground Road roller (also called...

Most bicycle freewheels use an internally step-toothed drum with two or more spring-loaded, hardened steel pawls to transmit the load. More pawls help spread the wear and give greater reliability although, unless the device is made to tolerances not normally found in bicycle components, simultaneous engagement of more than two pawls is rarely achieved. Pawl was a Formula One constructor (Indy 500 only) in 1951, 1954 and 1955. ...

Benefits

By its nature, a freewheel acts as an automatic clutch, making it possible to change gears in a manual gearbox, either up- or downshifting, without depressing the clutch pedal, limiting the use of the clutch to starting from standstill or stopping. For other uses, see Clutch (disambiguation). ... A gearbox is an assembly of gears allowing the rotational speed of an input shaft to be changed to a different speed. ...

A freewheel also produces slightly better fuel efficiency and less wear on the clutch, but leads to more wear on the brakes as there is no longer any ability to perform engine braking. Fuel efficiency, in its basic sense, is the same as thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. ... This article is about the vehicle component. ... It has been suggested that Exhaust brake be merged into this article or section. ...

Uses

In agricultural equipment an overrunning clutch is typically used on hay balers and other equipment with a high inertial load, particularly when used in conjunction with a tractor without a live power take-off (PTO). Without a live PTO, a high inertial load can cause the tractor to continue to move forward even when the foot clutch is depressed, creating an unsafe condition. By disconnecting the load from the PTO under these conditions, the overrunning clutch improves safety. Similarly, many unpowered 'push' cylinder lawnmowers use a freewheel to drive the blades: these are geared or chain-driven to rotate at high speed and the freewheel prevents their momentum being transferred in the reverse direction through the drive when the machine is halted. A Round Baler A baler is a piece of farm machinery that is used to compress a cut, raked, crop (such as hay or straw) into bales and bind the bales with twine. ... This article is about inertia as it applies to local motion. ... A tractor PTO A power take-off (PTO) is a splined driveshaft, usually on a tractor or truck that can be used to provide power to an attachment or separate machine. ... A lawn mower (often spelled as one word—lawnmower) is a machine (electric or mechnical) used to cut grass to an even length. ... This box:      This gyroscope remains upright while spinning due to its angular momentum. ...

A freewheel assembly is also widely used on engine starters as a kind of protective device. Starter motors usually need to spin at 3,000 RPM to get the engine to turn over. When the key is turned to the start position for any amount of time after the engine has already turned over, the starter can not spin fast enough to keep up with the flywheel. Because of the extreme gear ratio between starter gear and flywheel (about 15 or 20:1) it would spin the starter armature at dangerously high speeds, causing an explosion when the centrifugal force acting on the copper coils wound in the armature can no longer resist the outward g-forces acting on them. In starters without the freewheel or overrun clutch this would be a major problem because, with the flywheel spinning at about 1,000 RPM at idle, the starter, if engaged with the flywheel, would be forced to spin between 15,000 and 20,000 RPM. Once the engine has turned over and is running, the overrun clutch will release the starter from the flywheel and prevent the gears from re-meshing (as in an accidental turning of the ignition key) while the engine is running. A freewheel clutch is now used in many motorcycles with an electric starter motor. It is used as a replacement for the Bendix drive used on most auto starters because it reduces the electrical needs of the starting system. Gears on a piece of farm equipment, gear ratio 1:1. ... For the real outward-acting force that can be found in circular motion, see Reactive centrifugal force. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ... Spoked flywheel Flywheel from stationary engine. ... An automobile self-starter is an electric motor that initiates piston motion in a cars internal combustion engine before it can power itself. ... Vincent Hugo Bendix (December 12, 1892 – March 27, 1945) was an American inventor and industrialist. ...

In addition to the automotive uses listed above (i.e. in two-stroke engines vehicles), freewheels were used in some luxury or up-market conventional cars (such as Rovers) from the 1930s into the 1960s. The freewheel meant that the engine returned to its idle speed on the overrun, thus greatly reducing noise from both the engine and gearbox. The mechanism could usually be locked to provide engine braking if needed. A freewheel was also used in the original Land Rover vehicle from 1948 to 1951. The freewheel controlled drive from the gearbox to the front axle, which disengaged on the overrun. This allowed the vehicle to have a permanent 4 wheel drive system by avoiding 'wind-up' forces in the transmission. This system worked, but produced unpredictable handling, especially in slippery conditions or when towing, and was replaced by a conventional selectable 4WD system. Rover may refer to, A stereotyped name for a dog Rover bicycle, originating in 1885, that is usually described as the first recognizably modern bicycle Rover (car), a car marque, and historically a car company, Rover Ltd. ... It has been suggested that Exhaust brake be merged into this article or section. ... The Land Rover Series I, II, and III are off-road vehicles produced by the British manufacturer Land Rover. ... An axle is a central shaft for a rotating wheel or gear. ... Four wheel drive or 4x4, is a type of four wheeled vehicle drivetrain configuration that enables all four wheels to receive power from the engine simultaneously in order to provide maximum traction. ...

In the older style of bicycle, where the freewheel mechanism is included in the gear assembly, the system is called a freewheel, whereas the newer style, in which the freewheel mechanism is in the hub, is called a freehub. An earlier design of a cogset. ... A Shimano Dura-Ace freehub A freehub is a bicycle rear axle assembly that incorporates a ratcheting mechanism. ...

History

The friction freewheel was a part of the Torpedo bicycle gear hub invented by Ernst Sachs in 1903.

The freewheel is sometimes known as the "Stieber Clutch" named after its German developer Ortwin Stieber.