Locking differential

A locking differential is designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft. This forces both wheels to turn in unison, regardless of the traction (or lack thereof) available to either wheel individually. When the differential is unlocked (open differential), it allows each wheel to rotate at different speeds (such as when negotiating a turn), thus avoiding tire scuffing. An open (or unlocked) differential always provides the same torque (rotational force) to each of the two wheels, on that axle. So although the wheels can rotate at different speeds, they apply the same rotational force, even if one is entirely stationary, and the other spinning. (Equal torque, unequal rotational speed). By contrast, a locked differential forces both left and right wheels on the same axle to rotate at the same speed under nearly all circumstances, without regard to tractional differences seen at either wheel. Therefore, each wheel can apply as much rotational force as the traction under it will allow, and the torques on each side-shaft will be unequal. (Unequal torque, equal rotational speeds). Exceptions apply to automatic lockers, discussed below. A locked differential can provide a significant traction advantage over an open differential, but only when the traction under each wheel differs significantly. All the above comments apply to central differentials as well as to those in each axle: full-time four-wheel-drive (often called "All Wheel Drive") vehicles have three differentials, one in each axle, and a central one between the front and rear axles (transfer case). Types Automatic lockers Automatic lockers lock and unlock automatically with no direct input from the driver. Some automatic locking differential designs ensure that engine power is always transmitted to both wheels, regardless of traction conditions, and will "unlock" only when one wheel is required to spin faster than the other during cornering. These would be more correctly termed "automatic unlocking" differentials, because their at-rest position is locked. They will never allow either wheel to spin slower than the differential carrier or axle as a whole, but will permit a wheel to be over-driven faster than the carrier speed. The most common example of this type would be the famous "Detroit Locker," made by Eaton Corporation, also known as the "Detroit No-Spin," which replaces the entire differential carrier assembly. Others, sometimes referred to as "lunchbox lockers," employ the stock differential carrier and replace only the internal...

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Drive wheel

A drive wheel is a wheel of a motor vehicle that transmits force, transforming torque into tractive force from the tires to the road, causing the vehicle to move. The powertrain delivers enough torque to the wheel to overcome stationary forces, resulting in the vehicle moving forwards or backwards. A two-wheel drive vehicle has two driven wheels, typically both at the front or back, while a four-wheel drive has four. A steering wheel is a wheel that turns to change the direction of a vehicle. A trailer wheel is one that is neither a drive wheel, nor a steer wheel. Front-wheel drive vehicles typically have the rear wheels as trailer wheels. The rear driven wheels of a racing car throwing gravel Differentials and drive shafts deliver torque to the front and rear wheels of a four-wheel drive truck Drive wheel configurations Front-wheel drive Front-wheel drive (FWD) vehicles' engines drive the front wheels. Using the front wheels for delivery of power as well as steering allows the driving force to act in the same direction as the wheel is pointing. This layout is commonly used in modern passenger cars. Opperman Motocart A rare example of front wheel drive was the Opperman Motocart. This slow-speed agricultural and light freight vehicle was a tricycle with the front wheel carrying a large tractor tyre. The wheel was powered by a small single cylinder Douglas engine carried on the front mono fork that formed the steering gear. Rear-wheel drive Rear-wheel drive (RWD) typically places the engine in the front of the vehicle, with a driveshaft running the length of the vehicle to the differential transmission. However, mid engine and rear engine layouts can also used. It was a common layout used in automobiles throughout the 20th century. At this time, FWD designs were not practical due to complexity (in FWD, engine power and steering must both be combined in the front axle). Rear-wheel Two-wheel Four-wheel Six-wheel Eight-wheel Twelve-wheel Two-wheel drive For four-wheeled vehicles, two-wheel drive describes vehicles that transmit torque to at most two road wheels, referred to as either front- or rear-wheel drive. The term 4x2 is also used, to indicate four total road-wheels with two being driven. For vehicles that have partial four-wheel drive, the term two-wheel drive refers to the mode when four-wheel drive is deactivated and torque is applied to only two wheels. All-wheel drive Four-wheel drive This configuration allows all four road wheels to receive torque from the power plant simultaneously. It is often used in rally racing on mostly paved roads. Four-wheel drive is common in off-road vehicles because powering all four wheels provides better control on loose and slippery surfaces. Four-wheel drive manufacturers have different systems such as "High Range 4WD" and "Low Range 4WD". These systems may...

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Coupling

A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. By careful selection, installation and maintenance of couplings, substantial savings can be made in reduced maintenance costs and downtime. In a more general context, a coupling can also be a mechanical device that serves to connect the ends of adjacent parts or objects. Rotating coupling An improvised flexible coupling made of car tire pieces connects the drive shafts of an engine and a water pump. This one is used to cancel out misalignment and vibrations. Uses Shaft couplings are used in machinery for several purposes. The most common of which are the following. To transfer power from one end to another end.(ex: motor transfer power to pump through coupling) Primary function. To provide for the connection of shafts of units that are manufactured separately such as a motor and generator and to provide for disconnection for repairs or alterations. To provide for misalignment of the shafts or to introduce mechanical flexibility. To reduce the transmission of shock loads from one shaft to another. To introduce protection against overloads. To alter the vibration characteristics of rotating units. To connect driving and the driven part slips when overload occurs Types Clamped or compression rigid couplings come in two parts and fit together around the shafts to form a sleeve. They offer more flexibility than sleeved models, and can be used on shafts that are fixed in place. They generally are large enough so that screws can pass all the way through the coupling and into the second half to ensure a secure hold. Flanged rigid couplings are designed for heavy loads or industrial equipment. They consist of short sleeves surrounded by a perpendicular flange. One coupling is placed on each shaft so the two flanges line up face to face. A series of screws or bolts can then be installed in the flanges to hold them together. Because of their size and durability, flanged units can be used to bring shafts into alignment before they are joined together. Rigid couplings are used when precise shaft alignment is required; shaft misalignment will affect the...

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Torque converter

A torque converter is a type of fluid coupling which 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 power source to the load. It is usually located between the engine's flexplate and the transmission. The equivalent location in a manual transmission would be the mechanical clutch. The key characteristic of a torque converter is its ability to multiply torque when the output rotational speed is so low that it allows the fluid coming off the curved vanes of the turbine to be deflected off the stator while it is locked against its one-way clutch, thus providing the equivalent of a reduction gear. This is a feature beyond that of the simple fluid coupling, which can match rotational speed but does not multiply torque, thus reduces power. Some of these devices are also equipped with a "lockup" mechanism which rigidly binds the engine to the transmission when their speeds are nearly equal, to avoid slippage and a resulting loss of efficiency. ZF torque converter cut-away A cut-away model of a torque converter Hydraulic systems By far the most common form of torque converter in automobile transmissions is the hydrokinetic device described in this article. There are also hydrostatic systems which are widely used in small machines such as compact excavators. Mechanical systems There are also mechanical designs for continuously variable transmissions and these also have the ability to multiply torque. They include the pendulum-based Constantinesco torque converter, the Lambert friction gearing disk drive transmission and the Variomatic with expanding pulleys and a belt drive. Usage Automatic transmissions on automobiles, such as cars, buses, and on/off highway trucks. Forwarders and other heavy duty vehicles. Marine propulsion systems. Industrial power transmission such as conveyor drives, almost all modern forklifts, winches, drilling rigs, construction equipment, and railway locomotives. Function Theory of Operation Torque converter equations of motion are dominated by Leonhard Euler's eighteenth century turbomachine equation: The equation expands to include the fifth power of radius; as a result, torque converter properties are very dependent on the size of the device. Torque converter elements A fluid coupling is a two element drive that is incapable of multiplying torque, while a torque converter has at least one extra element—the stator—which alters the drive's characteristics during periods of high slippage, producing an increase in output torque. In a torque converter there are at least three rotating elements: the impeller, which is mechanically driven by the prime mover; the turbine, which drives the load; and the stator, which is interposed between the impeller and turbine so that it can alter oil flow returning from the turbine to the impeller. The classic torque converter...

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Freewheel

In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaftfrom the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated. The condition of a driven shaft spinning faster than its driveshaft exists in most bicycles when the rider holds his or her feet still, no longer pushing the pedals. In a fixed-gear bicycle, without a freewheel, the rear wheel would drive the pedals around. An analogous condition exists in an automobile with a manual transmission going downhill, or any situation where the driver takes his or her 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 can be a catastrophic situation: as many two stroke engines depend on a fuel/oil mixture 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 used a freewheel system in their two-stroke models for this reason and maintained it in the Saab 96 V4 and early Saab 99 for better fuel efficiency. Freewheel mechanism Ratcheting freewheel mechanism (van Anden, 1869) 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, producing a characteristic clicking sound proportionate to the speed difference of the driven gear relative to that of the (slower) driving gear. 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. 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. Advantages and disadvantages By its nature, a freewheel mechanism 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 manual clutch to starting from standstill or stopping....

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Preselector gearbox

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, gear selection 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 gears immediately as 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. Auto Union Type D Hillclimb car with preselector gearbox Bugatti Type 51 cockpit, with Wilson preselector gearbox 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, Lagonda Rapier 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 and later included tanks such as the German Tiger I and Tiger II in World War II, through to current tanks such as the Challenger 2. Gearbox designs Epicyclic gearboxes Many pre-selector designs made use of a series of epicyclic gearboxes. Viratelle gearbox The Viratelle epicyclic pre-selector gearbox is the first one known designed and used from 1906, used on Viratelle motorcycles with 3 speeds but also on cyclecarswith 3 forward speeds...

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Transmission (mechanics)

A transmission is a machine in a power transmission system, which provides controlled application of the power. Often the term transmission refers simply to the gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device. In British English, the term transmission refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive), differential, and final drive shafts. In AmericanEnglish, however, the term refers more specifically to the gearbox alone, and detailed usage differs. The most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. Such engines need to operate at a relatively high rotational speed, which is inappropriate for starting, stopping, and slower travel. 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. Often, a transmission has multiple gear ratios (or simply "gears") with the ability to switch between them as speed varies. This switching may be done manually (by the operator) or automatically. Directional (forward and reverse) control may also be provided. Single-ratio transmissions also exist, which simply change the speed and torque (and sometimes direction) of motor output. In motor vehicles, the transmission generally is connected to the engine crankshaft via a flywheel or clutch or fluid coupling, partly because internal combustion engines cannot run below a particular speed. The output of the transmission is transmitted via the driveshaft to one or more differentials, which drives the wheels. While a differential may also provide gear reduction, its primary purpose is to permit the wheels at either end of an axle to rotate at different speeds (essential to avoid wheel slippage on turns) as it changes the direction of rotation. Conventional gear/belt transmissions are not the only mechanism for speed/torque adaptation. Alternative mechanisms include torque converters and power transformation (e.g. diesel-electric transmission and hydraulic drive system). Hybrid configurations also exist. Automatic transmissions use a valve body to shift gears using fluid pressures in response to speed and throttle input. Single stage gear reducer. Explanation Interior view of Pantigo Windmill, looking up into cap from floor—cap rack, brake wheel, brake and wallower. Pantigo Windmill is located on James Lane, East Hampton, Suffolk County, Long Island, New York. Early transmissions included the right-angle drives and other gearing in windmills, horse-powered devices, and steam engines, in support of pumping, milling, and hoisting. Most modern gearboxes are used to increase torque while reducing the speed of a prime mover output shaft (e.g. a motor crankshaft). This means that the output shaft of a gearbox rotates at a slower rate...

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