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39-536: An all-wheel drive vehicle ( AWD vehicle ) is one with a powertrain capable of providing power to all its wheels, whether full-time or on-demand. The most common forms of all-wheel drive are: Vehicles may be either part-time all-wheel drive or full-time: Particularly in North America for several decades, the designation AWD has been used and marketed – distinctly from 4×4 and 4WD – to apply to vehicles with drive train systems that have permanent drive,

78-539: A differential between the front and rear drive shafts, and active management of torque transfer, especially following the advent of the anti-lock braking system (ABS). However, the designations AWD and all-wheel drive long predated the trend, with Associated Equipment Company (AEC) producing AWD trucks in 1929 in conjunction with the British subsidiary of the pioneering American firm Four Wheel Drive Auto Company . Additionally, General Motors began manufacturing

117-401: A propeller shaft or tailshaft ) which transmits the rotational force to a drive axle at the rear of the vehicle. The drive axle may be a live axle , but modern rear-wheel drive automobiles generally use a split axle with a differential. In this case, one half-axle or half-shaft connects the differential with the left rear wheel, a second half-shaft does the same with the right rear wheel; thus

156-416: A bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type of axle is referred to as a spindle . On cars and trucks, several senses of the word axle occur in casual usage, referring to the shaft itself, its housing, or simply any transverse pair of wheels. Strictly speaking, a shaft that rotates with

195-429: A differential (kart racing). However, other go-karts have two rear drive wheels too. Some dump trucks and trailers may be configured with a lift axle (also known as an airlift axle or drop axle ), which may be mechanically raised or lowered. The axle is lowered to increase the weight capacity, or to distribute the weight of the cargo over more wheels, for example, to cross a weight-restricted bridge. When not needed,

234-693: A line as "all-wheel drive" as early as the late 1930s. This distinction in terminology is not generally used outside North America. In the context of hybrid and electric vehicles , the North American designation of 'all-wheel-drive' may differ. In some hybrid vehicles, the combustion engine is only mechanically connected to the front wheels, while the rear wheels are powered independently by an electric motor; this may be marketed as eAWD . Furthermore, many electric vehicles have individual, unconnected motors powering each axle, or even each individual wheel, also without any center differential. When tire grip

273-413: A protruding hub to which the axle shaft flange is bolted. The semi-floating axle setup is commonly used on half-ton and lighter 4×4 trucks in the rear. This setup allows the axle shaft to be the means of propulsion, and also support the weight of the vehicle. The main difference between the full- and semi-floating axle setups is the number of bearings. The semi-floating axle features only one bearing, while

312-400: A single unit called a transaxle . The drive axle is a split axle with a differential and universal joints between the two half axles. Each half axle connects to the wheel by use of a constant velocity (CV) joint which allows the wheel assembly to move freely vertically as well as to pivot when making turns. In rear-wheel drive cars and trucks, the engine turns a driveshaft (also called

351-453: A solid, "live-axle" suspension system, the rotating inner axle cores (or half-shafts) serve to transmit driving torque to the wheels at each end, while the rigid outer tube maintains the position of the wheels at fixed angles relative to the axle, and controls the angle of the axle and wheels assembly to the vehicle body. The solid axles (housings) in this system must also bear the weight of the vehicle plus any cargo. A non-driving axle, such as

390-427: A turn at all. Several manufacturers offer computer-controlled airlifts so that the dead axles are automatically lowered when the main axle reaches its weight limit. The dead axles can still be lifted by the press of a button if needed, for better maneuverability. Lift axles were in use in the early 1940s. Initially, the axle was lifted by a mechanical device. Soon hydraulics replaced the mechanical lift system. One of

429-475: A wheel on the left side of the vehicle to a wheel on the right side. The axis of rotation fixed by the axle is common to both wheels. Such a design can keep the wheel positions steady under heavy stress, and can therefore support heavy loads. Straight axles are used on trains (that is, locomotives and railway wagons), for the rear axles of commercial trucks, and on heavy-duty off-road vehicles. The axle can optionally be protected and further reinforced by enclosing

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468-551: A wider sense, the powertrain includes all of the components used to transform stored (chemical, solar, nuclear, kinetic, potential, etc.) energy into kinetic energy for propulsion purposes. This includes the utilization of multiple power-sources and non–wheel-based vehicles. The most recent developments in powertrain are driven by the electrification of it in multiple components. Electrical energy needs to be provided, usually this leads to larger batteries. Electric motors can be found as isolated component or as part of other elements, e.g.

507-500: Is a single bearing at the end of the axle housing that carries the load from the axle and that the axle rotates through. To be "semi-floating" the axle shafts must be able to "float" in the housing, bearings and seals, and not subject to axial "thrust" and/or bearing preload. Needle bearings and separate lip seals are used in semi-floating axles with axle retained in the housing at their inner ends typically with circlips which are 3¾-round hardened washers that slide into grooves machined at

546-595: Is achieved through metrology technology applied to all of the steps in powertrain manufacturing processes. In automotive manufacturing, the frame plus the "running gear" makes the chassis . Later, a body (sometimes referred to as " coachwork "), which is usually not necessary for integrity of the structure, is built on the chassis to complete the vehicle . Commercial vehicle manufacturers may have "chassis only" and "cowl and chassis" versions that can be outfitted with specialized bodies. These include buses , motor homes , fire engines , ambulances , etc. The frame plus

585-406: Is good during road driving, a differential is used between the axles to avoid driveline windup . This is not required off-road, as the limited grip allows the tires to slip. All-wheel drive vehicles designed for extensive off-road use may not have such a differential, and so they suffer from wind-up when used on-road. Selectable 4WD also avoids this problem and requires only a simple dog clutch in

624-733: Is important to industry, including the automotive and other vehicle sectors. Competitiveness drives companies to engineer and produce powertrain systems that over time are more economical to manufacture, higher in product quality and reliability, higher in performance, more fuel efficient, less polluting, and longer in life expectancy. In turn these requirements have led to designs involving higher internal pressures, greater instantaneous forces, and increased complexity of design and mechanical operation. The resulting designs in turn impose significantly more severe requirements on parts shape and dimension; and material surface flatness , waviness , roughness , and porosity . Quality control over these parameters

663-445: Is known as " carbon steel ". The primary differences between the two are that chrome-moly steel is significantly more resistant to bending or breaking, and is very difficult to weld with tools normally found outside a professional welding shop. An axle that is driven by the engine or prime mover is called a drive axle . Modern front-wheel drive cars typically combine the transmission (gearbox and differential) and front axle into

702-642: The British Rail Class 03 and British Rail Class 04 diesel shunting locomotives. This section uses infographics to show a unified model with variations, the green wheels denote no traction, and the angled wheels denote steering. 6X4 means 6 wheel ends and 4 positions distribute power (power divider installed) 6X2 means 6 wheel ends and 2 positions distribute power (single axle drive) 4X0 means 4 wheel ends no power (Trailer axle) 4x2 means 4 Wheel ends, 2 Positions to distribute power The 6 wheel ends can either be wide base singles or duals. Its about

741-492: The axle . In hybrid powertrains the torque generated by the combustion engine and the electric motor have to be brought together and distributed to the wheels. The control of this process can be quite involved but the rewards are greatly improved acceleration and much lower emissions. Powertrain development for diesel engines involves the following: exhaust gas recirculation (EGR), and advanced combustion. Spark ignition engine development include: fuel injection , including

780-642: The gasoline direct injection variant, as well as improving volumetric efficiency by using multi-valves per cylinder, variable valve timing , variable length intake manifolds , and turbocharging . Changes also include new fuel qualities (no sulphur or aromates ) to allow new combustion concepts. So-called "combined combustion systems" (CCV) or "diesotto" cycles are based on synthetic fuels (synthetic diesel, biomass to liquid (BTL) or gas to liquid (GTL)). BEVs , FCEVs and PHEV powertrains are expected to reach cost parity with ICE powertrains in 2025. The manufacturing of powertrain components and systems

819-410: The transfer case , rather than a differential. For this reason, most early off-road vehicles used that system; e.g., Jeep , Land Rover . As vehicles became more sophisticated and tires gave better winter performance in the 1960s, there was an interest in giving the benefits of all-wheel drive to conventional cars: not for off-road use but for winter use in snow or on wet roads. Exotic vehicles such as

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858-485: The automobile turns, improving traction and extending tire life. A tandem axle is a group of two or more axles situated close together. Truck designs use such a configuration to provide a greater weight capacity than a single axle. Semi-trailers usually have a tandem axle at the rear. Axles are typically made from SAE grade 41xx steel or SAE grade 10xx steel. SAE grade 41xx steel is commonly known as " chrome-molybdenum steel " (or "chrome-moly") while SAE grade 10xx steel

897-400: The axle is lifted off the ground to save wear on the tires and axle, and to increase traction in the remaining wheels, and to decrease fuel consumption. Lifting an axle also alleviates lateral scrubbing of the additional axle in very tight turns, allowing the vehicle to turn more readily. In some situations, the removal of pressure from the additional axle is necessary for the vehicle to complete

936-458: The axles by the function of the suspension system. This is typical of the independent suspensions found on most newer cars, and even SUVs, and on the front of many light trucks. An exception to this rule is the independent (rear) swing axle suspension, wherein the half-axles are also load-bearing suspension arms. Independent drive-trains still need differentials (or diffs), but without fixed axle-housing tubes attached. The diff may be attached to

975-426: The bearings, housings, and only a short section of the shaft itself, that also carries all radial loads. The full-floating design is typically used in most ¾- and 1-ton light trucks, medium-duty trucks, and heavy-duty trucks. The overall assembly can carry more weight than a semi-floating or non-floating axle assembly because the hubs have two bearings riding on a fixed spindle. A full-floating axle can be identified by

1014-502: The body makes a glider (a vehicle without a powertrain). The final drive is the last in the set of components which delivers torque to the drive wheels . In a road vehicle, it incorporates the differential . In a railway vehicle, it sometimes incorporates the reversing gear. Examples include the Self-Changing Gears RF 28 (used in many first-generation diesel multiple units of British Railways ) and RF 11 used in

1053-461: The early manufacturers was Zetterbergs, located in Östervåla, Sweden. Their brand was Zeta-lyften. The liftable tandem drive axle was invented in 1957 by the Finnish truck manufacturer Vanajan Autotehdas , a company sharing history with Sisu Auto . A full-floating axle carries the vehicle's weight on the axle casing, not the half-shafts; they serve only to transmit torque from the differential to

1092-408: The front beam axle in heavy-duty trucks and some two-wheel drive light trucks and vans, will have no shaft, and serves only as a suspension and steering component. Conversely, many front-wheel drive cars have a one-piece rear beam axle. In other types of suspension systems, the axles serve only to transmit driving torque to the wheels: the position and angle of the wheel hubs is made independent from

1131-508: The full-floating assembly has bearings on both the inside and outside of the wheel hub. The other difference is axle removal. To remove the semi-floating axle, the wheel must be removed first; if such an axle breaks, the wheel is most likely to come off the vehicle. The semi-floating design is found under most ½-ton and lighter trucks, as well as in SUVs and rear-wheel-drive passenger cars, usually being smaller or less expensive models. A benefit of

1170-581: The high-powered Jensen FF followed by the AMC Eagle , Subaru Leone and Audi Quattro series were the first to offer all-wheel drive in a high-speed road-based car. These, particularly the Quattro, would extensively develop this drivetrain with the use of viscous couplings and differentials to provide a safe and drivable car. The first off-road / on-road hybrids such as the Range Rover also chose

1209-461: The inner end of the shafts and retained in/by recesses in the differential carrier side gears which are themselves retained by the differential pinion gear (or "spider gear") shaft. A true semi-floating axle assembly places no side loads on the axle housing tubes or axle shafts. Axles that are pressed into ball or tapered roller bearings, which are in turn retained in the axle housings with flanges, bolts, and nuts do not "float" and place axial loads on

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1248-444: The length of the axle in a housing. In split-axle designs, the wheel on each side is attached to a separate shaft. Modern passenger cars have split-drive axles. In some designs, this allows independent suspension of the left and right wheels, and therefore a smoother ride. Even when the suspension is not independent, split axles permit the use of a differential, allowing the left and right drive wheels to be driven at different speeds as

1287-401: The outside of the wheels. Axle An axle or axletree is a central shaft for a rotating wheel or gear . On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case,

1326-409: The permanent all-wheel-drive system rather than manual selection. Powertrain A motor vehicle's driveline or drivetrain consists of the parts of the powertrain excluding the engine. It is the portion of a vehicle, after the prime mover , that changes depending on whether a vehicle is front-wheel , rear-wheel , or four-wheel drive , or less-common six-wheel or eight-wheel drive . In

1365-458: The two half-axles and the differential constitute the rear axle. The front drive axle is providing the force to drive the truck. In fact, only one wheel of that axle is actually moving the truck and trailer down the road. Some simple vehicle designs, such as leisure go-karts, may have a single driven wheel where the drive axle is a split axle with only one of the two shafts driven by the engine, or else have both wheels connected to one shaft without

1404-413: The vehicle frame or body, and/or be integrated with the transmission (or gearbox) in a combined transaxle unit. The axle (half-)shafts then transmit driving torque to the wheels, usually via constant-velocity joints . Like a full floating axle system, the drive shafts in a front-wheel-drive independent suspension system do not support any vehicle weight. A straight axle is a single rigid shaft connecting

1443-456: The vehicle frame or body. Thus, transverse pairs of wheels in an independent suspension may be called an axle in some contexts. This very loose definition of "axle" is often used in assessing toll roads or vehicle taxes , and is taken as a rough proxy for the overall weight-bearing capacity of a vehicle, and its potential for causing wear or damage to roadway surfaces. Axles are an integral component of most practical wheeled vehicles. In

1482-434: The wheel, being either bolted or splined in fixed relation to it, is called an axle or axle shaft . However, in looser usage, an entire assembly including the surrounding axle housing (typically a casting ) is also called an axle . An even broader (somewhat figurative) sense of the word refers to every pair of parallel wheels on opposite sides of a vehicle, regardless of their mechanical connection to each other and to

1521-400: The wheels. They "float" inside an assembly that carries the vehicle's weight. Thus the only stress it must endure is torque (not lateral bending force). Full-floating axle shafts are retained by a flange bolted to the hub , while the hub and bearings are retained on the spindle by a large nut. In contrast, a semi-floating design carries the weight of the vehicle on the axle shaft itself; there

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