The powertrain layout of a motorised vehicle such as a car is often defined by the location of the engine or motors and the drive wheels.
Layouts can roughly be divided into three categories: front-wheel drive (FWD), rear-wheel drive (RWD) and four-wheel drive (4WD). Many different combinations of engine location and driven wheels are found in practice, and the location of each is dependent on the application for which the vehicle will be used.
The front-engine, front-wheel-drive layout (abbreviated as FF layout) places both the internal combustion engine and driven wheels at the front of the vehicle. This is the most common layout for cars since the late 20th century. [1] [2]
Some early front-wheel drive cars from the 1930s had the engine located in the middle of the car.
A rear-engine, front-wheel-drive layout is one in which the engine is between or behind the rear wheels, and drives the front wheels via a driveshaft, the complete reverse of a conventional front-engine, rear-wheel-drive vehicle layout. This layout has only been used on prototype and concept cars.
The front-engine, rear-wheel drive layout (abbreviated as FR layout) is one where the engine is located at the front of the vehicle and driven wheels are located at the rear. [3] This was the traditional automobile layout for most of the 20th century, and remains the most common layout for rear-wheel drive vehicles. [4]
The mid-engine, rear-wheel drive layout (abbreviated as MR layout) is one where the rear wheels are driven by an engine placed just in front of them, behind the passenger compartment. In contrast to the rear-engined RR layout, the center of mass of the engine is in front of the rear axle. This layout is typically chosen for its low moment of inertia and relatively favorable weight distribution.
The rear-engine, rear-wheel drive layout (abbreviated as RR layout) places both the engine and drive wheels at the rear of the vehicle. In contrast to the MR layout, the center of mass of the engine is between the rear axle and the rear bumper. Although common in electric cars, [5] and in transit buses and coaches due to the elimination of the drive shaft with low-floor bus, this layout has become increasingly rare in fossil-fuelled passenger cars. The Porsche 911 is notable for its continuous use of the RR layout since 1963.
Drivetrains where power can be sent to all four wheels are referred to as either four-wheel drive (4WD) or all-wheel drive (AWD). [6]
The front-engine, four-wheel drive layout (abbreviated as F4 layout) places the engine at the front of the vehicle and drives all four roadwheels. This layout is typically chosen for better control on many surfaces, and is an important part of rally racing as well as off-road driving.
Most four-wheel-drive layouts are front-engined and are derivatives of earlier front-engine, rear-wheel-drive designs.
The mid-engine, four-wheel drive layout (abbreviated as M4 layout) places the engine in the middle of the vehicle, between both axles and drives all four road wheels.
Although the term "mid-engine" can mean the engine is placed anywhere in the vehicle such that the centre of gravity of the engine lies between the front and rear axles, it is usually used for sports cars and racing cars where the engine is behind the passenger compartment. The motive output is then sent down a shaft to a differential in the centre of the car, which in the case of an M4 layout, distributes power to both front and rear axles.
The rear-engine, four-wheel drive layout (abbreviated as R4) places the engine at the rear of the vehicle, and drives all four wheels.
This layout is typically chosen to improve the traction or the handling of existing vehicle designs using the rear-engine, rear-wheel-drive layout (RR). For example, the Porsche 911 added all-wheel drive to the existing line-up of rear-wheel drive models in 1989.
In automotive design, dual-motor, four-wheel-drive layout is mainly used by battery electric vehicles by placing electric motors on both front and rear axles and drives all four roadwheels, creating a four-wheel drive layout. This layout is made possible by the small size of electric motors compared to internal combustion engines, allowing it to be placed in multiple locations. It also eliminates the need of a drive shaft that are commonly used by conventional four-wheel drive vehicles to create space for batteries that are commonly mounted on the floor of electric vehicles. [7]
The layout is also beneficial to distribute available electrical horsepower to maximize torque and power in response to road grip conditions and weight transfer in the vehicle. For example, during hard acceleration, the front motor must reduce torque and power in order to prevent the front wheels from spinning as weight transfers to the rear of the vehicle. The excess power is transferred to the rear motor where it can be used immediately. The opposite applies when braking, when the front motor can accept more regenerative braking torque and power. [8] However dual motors usually have less range. [9]
In addition, electric vehicles may be equipped with more than two electric motors to achieve greater power output and superior handling. The first mass-produced triple-motor layout was introduced on the Audi e-tron in 2020, which consists of one motor at the front and two motors at the rear. [10] [11]Four-wheel drive, also called 4×4 or 4WD, refers to a two-axled vehicle drivetrain capable of providing torque to all of its wheels simultaneously. It may be full-time or on-demand, and is typically linked via a transfer case providing an additional output drive shaft and, in many instances, additional gear ranges.
The Audi TT is a production front-engine, 2-door, 2+2 sports coupé and roadster, manufactured and marketed by Audi from 1998 to 2023 across three generations.
Quattro is the trademark used by the automotive brand Audi to indicate that all-wheel drive (AWD) technologies or systems are used on specific models of its automobiles.
In automotive design, a front-engine, front-wheel-drive (FWD) layout, or FF layout, places both the internal combustion engine and driven roadwheels at the front of the vehicle.
In automotive design, an RR, or rear-engine, rear-wheel-drive layout places both the engine and drive wheels at the rear of the vehicle. In contrast to the RMR layout, the center of mass of the engine is between the rear axle and the rear bumper. Although very common in transit buses and coaches due to the elimination of the drive shaft with low-floor buses, this layout has become increasingly rare in passenger cars.
A transfer case is a part of the drivetrain of four-wheel-drive, all-wheel-drive, and other multiple powered axle vehicles. The transfer case transfers power from the transmission to the front and rear axles by means of drive shafts. It also synchronizes the difference between the rotation of the front and rear wheels(only high-speed 4wd-Awd systems), and may contain one or more sets of low range gears for off-road use.
A transaxle is a single mechanical device which combines the functions of an automobile's transmission, axle, and differential into one integrated assembly. It can be produced in both manual and automatic versions.
In automotive engineering, a mid-engine layout describes the placement of an automobile engine in front of the rear-wheel axles, but behind the front axle.
A drive shaft, driveshaft, driving shaft, tailshaft, propeller shaft, or Cardan shaft is a component for transmitting mechanical power and torque and rotation, usually used to connect other components of a drivetrain that cannot be connected directly because of distance or the need to allow for relative movement between them.
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.
Torque steer is the unintended influence of engine torque on the steering, especially in front-wheel-drive vehicles. For example, during heavy acceleration, the steering may pull to one side, which may be disturbing to the driver. The effect is manifested either as a tugging sensation in the steering wheel, or a veering of the vehicle from the intended path. Torque steer is directly related to differences in the forces in the contact patches of the left and right drive wheels. The effect becomes more evident when high torques are applied to the drive wheels because of a high overall reduction ratio between the engine and wheels, high engine torque, or some combination of the two. Torque steer is distinct from steering kickback.
ATTESA is a four-wheel drive system used in some automobiles produced by the Japanese automaker Nissan, including some models under its luxury marque Infiniti.
Super Handling-All Wheel Drive (SH-AWD) is a full-time, fully automatic, all-wheel drive traction and handling system, which combines front-rear torque distribution control with independently regulated torque distribution to the left and right rear wheels. This way the system freely distributes the optimum amount of torque to all four wheels according to the driving conditions. The system was announced in April 2004, and was introduced in the North American market in the second generation 2005 model year Acura RL, and in Japan as the fourth generation Honda Legend.
The following outline is provided as an overview of and topical guide to automobiles:
In automotive design, an F4, or front-engine, four-wheel drive (4WD) layout places the internal combustion engine at the front of the vehicle and drives all four roadwheels. This layout is typically chosen for better control on many surfaces, and is an important part of rally racing, as well as off-road driving. In terms of racing purposes, whether it be on-road or off-road, can be described as follows,
A team that pursues the Weak LS4WD architecture will minimize the development cost of the front-wheel drive system at the expense of having a larger rear powertrain. The Weak architecture produces a vehicle with a large powersplit between the front and rear powertrains, while the Strong architecture recommends a vehicle with more similar power and torque requirements for the front and rear.
Audi hybrid vehicles are hybrid electric vehicles created by the German carmaker, Audi. Some vehicles listed were concept vehicles, which utilised an internal combustion engine and an electric motor, and were used for research and development (R&D) for potential future use of the technology into possible series production. Audi launched its first hybrid concept car in 1989 called the Audi Duo, and was the first European company to sell a hybrid in 1997, though only in very small numbers.
In automotive design, an M4, or Mid-engine, Four-wheel-drive layout places the internal combustion engine in the middle of the vehicle, between both axles and drives all four road wheels.
Torque vectoring is a technology employed in automobile differentials that has the ability to vary the torque to each half-shaft with an electronic system; or in rail vehicles which achieve the same using individually motored wheels. This method of power transfer has recently become popular in all-wheel drive vehicles. Some newer front-wheel drive vehicles also have a basic torque vectoring differential. As technology in the automotive industry improves, more vehicles are equipped with torque vectoring differentials. This allows for the wheels to grip the road for better launch and handling.
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.
In automotive design, dual-motor, four-wheel-drive layout is mainly used by battery electric vehicles by placing electric motors on both front and rear axles and drives all four roadwheels, creating a four-wheel drive layout. This layout is made possible by the small size of electric motors compared to internal combustion engines, allowing it to be placed in multiple locations. It also eliminates the need of a drive shaft that are commonly used by conventional four-wheel drive vehicles to create space for batteries that are commonly mounted on the floor of electric vehicles.
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