Mid-engine design

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A mid-engine layout describes the placement of an automobile engine in front of the rear-wheel axles, but behind the front axle.

Contents

History

The mid-engine, rear-wheel-drive format can be considered the original layout of automobiles.[ citation needed ] A 1901 Autocar was the first gasoline-powered automobile to use a drive shaft and placed the engine under the seat. This pioneering vehicle is now in the collection of the Smithsonian Institution. [1]

Benefits

The Lotus Europa S1 was based on a prototype built to compete for Henry Ford II's contract to build a Le Mans race car in the early 1960s. Lotus Europe series 1 1967.jpg
The Lotus Europa S1 was based on a prototype built to compete for Henry Ford II's contract to build a Le Mans race car in the early 1960s.

Mounting the engine in the middle instead of the front of the vehicle puts more weight over the rear tires, so they have more traction and provide more assistance to the front tires in braking the vehicle, with less chance of rear-wheel lockup and less chance of a skid or spin out. If the mid-engine vehicle is also rear-drive the added weight on the rear tires can also improve acceleration on slippery surfaces, providing much of the benefit of all-wheel-drive without the added weight and expense of all-wheel-drive components. The mid-engine layout makes ABS brakes and traction control systems work better, by providing them more traction to control. The mid-engine layout may make a vehicle safer since an accident can occur if a vehicle cannot stay in its own lane around a curve or is unable to stop quickly enough. Mid-engine design is also a way to provide additional empty crush space in the front of the automobile between the bumper and the windshield, which can then be designed to absorb more of the impact force in a frontal collision in order to minimize penetration into the passenger compartment of the vehicle.

In most automobiles, and in sports cars especially, ideal car handling requires balanced traction between the front and rear wheels when cornering, in order to maximize the possible speed around curves without sliding out. This balance is harder to achieve when the heavy weight of the engine is located far to the front or far to the rear of the vehicle. Some automobile designs strive to balance the fore and aft weight distribution by other means, such as putting the engine in the front and the gearbox and battery in the rear of the vehicle.

Another benefit comes when the heavy mass of the engine is located close to the back of the seats. It makes it easier for the suspension to absorb the force of bumps so the riders feel a smoother ride. But in sports cars, the engine position is once again used to increase performance and the potentially smoother ride is usually more than offset by stiffer shock absorbers.

This layout also allows the motor, gearbox, and differential to be bolted together as a single unit. Together with independent suspension on the driven wheels, this removes the need for the chassis to transfer engine torque reaction.

Drawbacks

Underfloor mid-engine in a historical Hanomag truck chassis. Unterflurmotor Hanomag.jpg
Underfloor mid-engine in a historical Hanomag truck chassis.

The largest drawback of mid-engine cars is restricted rear passenger space; consequently, most mid-engine vehicles are two-seat vehicles. The engine in effect pushes the rear passenger seats forward towards the front axle (if the engine is behind the driver). Exceptions typically involve larger vehicles of unusual length or height in which the passengers can share space between the axles with the engine, which can be between them or below them, as in some vans, large trucks, and buses. The mid-engine layout (with a horizontal engine) was common in single-decker buses in the 1950s and 1960s, e.g. the AEC Reliance. The Ferrari Mondial is to date the only successful example of a true mid-engined convertible with seating for 4 and sports car/supercar performance. A version of the Lotus Evora with a removable roof panel is anticipated but no definite date is known.

Like any layout where the engine is not front-mounted and facing the wind, the traditional "engine-behind-the-passengers" layout makes engine cooling more difficult. This has been a problem in some cars,[ citation needed ] but this issue seems to have been largely solved in newer designs. For example, the Saleen S7 employs large engine-compartment vents on the sides and rear of the bodywork to help dissipate heat from its very high-output engine.

Mid-engined cars are more dangerous than front-engined cars if the driver loses control - although this may be initially harder to provoke due to the superior balance - and the car begins to spin. The moment of inertia about the center of gravity is low due to the concentration of mass between the axles (similar to standing in the middle of a playground roundabout, rather than at the edge) and the spin will occur suddenly, the car will rotate faster and it will be harder to recover from. Conversely, a front-engined car is more likely to break away in a progressive and controllable manner as the tires lose traction.

Variations

Super, sport, and race cars frequently have a mid-engined layout, as these vehicles' handling characteristics are more important than other requirements, such as usable space. In dedicated sports cars, a weight distribution of about 50% front and rear is frequently pursued, to optimise the vehicle's driving dynamics – a target that is typically only achievable by placing the engine somewhere between the front and rear axles.
Usually, the term "mid-engine" has been primarily applied to cars having the engine located between the driver and the rear drive axles. This layout is referred to as rear mid-engine, rear-wheel drive, (or RMR) layout. The mechanical layout and packaging of an RMR car are substantially different from that of a front-engine or rear-engine car.

When the engine is in front of the driver, but fully behind the front axle line, the layout is sometimes called a front mid-engine, rear-wheel-drive, or FMR layout instead of the less-specific term front-engine; and can be considered a subset of the latter. In-vehicle layout, FMR is substantially the same as FR, but handling differs as a result of the difference in weight distribution.

Some vehicles could be classified as FR or FMR depending on the factory-installed engine (I4 vs I6). Historically most classical FR cars such as the Ford Models T and A would qualify as an FMR engine car. Additionally, the distinction between FR and FMR is a fluid one, depending on the degree of engine protrusion in front of the front axle line, as manufacturers mount engines as far back in the chassis as possible. Not all manufacturers use the Front-Mid designation.

Examples

FMR layout – Front Mid-engine / Rear-wheel drive

Front mid-engine position / Rear-wheel drive Automotive diagrams 03 En.png
Front mid-engine position / Rear-wheel drive
Front mid-engine position / Rear-wheel drive 1929 Bentley front 34 right.jpg
Front mid-engine position / Rear-wheel drive

These cars are RWD cars with the engine placed between the driver and the front axle.

FM4 layout – Front Mid-engine / Four-wheel drive

This layout, similar to the above FMR layout, with the engine between driver and behind the front axle, adds front-wheel drive to become a four-wheel drive. An engineering challenge with this layout is getting the power to the front wheels past the engine - this would normally involve raising the engine to allow a propshaft to pass under the engine, or in the case of the Ferrari FF taking power from both ends of the crankshaft with two separate gearboxes.

RMR layout – Rear Mid-engine / Rear-wheel drive

Rear mid-engine position / Rear-wheel drive Automotive diagrams 04 En.png
Rear mid-engine position / Rear-wheel drive

These cars use a traditional engine layout between driver and rear drive axle. Typically, they're simply called MR; for mid-rear (engined), or mid-engine, rear-wheel-drive layout cars.

M4 layout – Rear Mid-engine / Four-wheel drive

These cars use mid-ship, four-wheel-drive, with an engine between the axles.

MF layout – Mid-engine / Front-wheel drive

Front mid-engine position / Front-wheel drive Automotive diagrams 07 En.png
Front mid-engine position / Front-wheel drive

These cars are "mid-ship engined" vehicles, but they use front-wheel drive, with the engine in front of the driver. It is still treated as an FF layout, though, due to the engine's placement still being in the front of the car, contrary to the popular belief that the engine is placed in front of the rear axle with power transferred to the front wheels (an RMF layout). In most examples, the engine is longitudinally mounted rather than transversely as is common with FF cars.

Related Research Articles

Sports car Performance-oriented car class, generally small or light-weight with good handling

A sports car is a car designed with an emphasis on dynamic performance, such as handling, acceleration, top speed, or thrill of driving. Sports cars originated in Europe in the early 1900s and are currently produced by many manufacturers around the world.

Steering System of components that allows vehicles to follow the desired course

Steering is a system of components, linkages, etc. that allows a vehicle to follow a desired course. An exception is the case of rail transport, by which rail tracks combined with railroad switches provide the steering function. The primary purpose of the steering system is to allow the driver to guide the vehicle.

Four-wheel drive Type of drivetrain with four driven wheels

Four-wheel drive, also called 4x4 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.

Toyota MR2 Japanese car model

The Toyota MR2 is a line of two-seat, mid-engined, rear-wheel-drive sports cars manufactured in Japan and marketed globally by Toyota from 1984 to 2007 over three generations: W10 (1984–1989), W20 (1990–1999) and W30 (2000–2007). It is Japan's first rear mid-engined production car.

Front-wheel drive

Front-wheel drive (FWD) is a form of engine and transmission layout used in motor vehicles, where the engine drives the front wheels only. Most modern front-wheel-drive vehicles feature a transverse engine, rather than the conventional longitudinal engine arrangement generally found in rear-wheel-drive and four-wheel drive vehicles.

Front-engine, front-wheel-drive layout Term used in automotive technology

In automotive design, an FF, or front-engine, front-wheel-drive (FWD) layout places both the internal combustion engine and driven roadwheels at the front of the vehicle.

Rear-engine, rear-wheel-drive layout

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.

Rear mid-engine, rear-wheel-drive layout Car layout in automotive design

In automotive design, an RMR, or rear mid-engine, rear-wheel-drive layout, is one in which 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 layout has a tendency toward being heavier in the rear than the front, which allows for best balance to be achieved under braking. However, since there is little weight over the front wheels, under acceleration, the front of the car is prone to lift and cause understeer. Most rear-engine layouts have historically been used in smaller vehicles, because the weight of the engine at the rear has an adverse effect on a larger car's handling, making it 'tail-heavy'. It is felt that the low polar inertia is crucial in selection of this layout. The mid-engined layout also uses up central space, making it impractical for any but two-seater sports cars. However, some microvans use this layout, with a small, low engine beneath the loading area. This makes it possible to move the driver right to the front of the vehicle, thus increasing the loading area at the expense of slightly reduced load depth.

Front-engine, rear-wheel-drive layout Automobile layout

In automotive design, a FR, or front-engine, rear-wheel-drive layout is one where the engine is located at the front of the vehicle and driven wheels are located at the rear via a drive shaft. This was the traditional automobile layout for most of the 20th century. Modern designs commonly use the front-engine, front-wheel-drive layout (FF). It is also used in high-floor buses and school buses.

Rear-wheel drive (RWD) is a form of engine and transmission layout used in motor vehicles, where the engine drives the rear wheels only. Until the late 20th century, rear-wheel drive was the most common configuration for cars. Most rear-wheel drive vehicles feature a longitudinally-mounted engine at the front of the car.

Transaxle Combined transmission, axle and differential in one assembly.

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.

Drive shaft Mechanical component for transmitting torque and rotation

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.

Super GT Auto racing championship in Japan

Super GT is a grand touring car racing series that began in 1993. Originally titled as the Zen Nihon GT Senshuken (全日本GT選手権), generally referred to as either the JGTC or the All Japan Grand Touring Car Championship, the series was renamed to Super GT in 2005. It is the top level of sports car racing in Japan.

Torsen

Torsen Torque-Sensing is a type of limited-slip differential used in automobiles.

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.

Front mid-engine, front-wheel-drive layout

In automotive design, a Front Mid-engine, Front-wheel-drive layout is one in which the front road wheels are driven by an internal-combustion engine placed just behind them, in front of the passenger compartment. In contrast to the Front-engine, front-wheel-drive layout (FF), the center of mass of the engine is behind the front axle. This layout is typically chosen for its better weight distribution. Since the differences between the FF and MF layouts are minor, most people consider the MF layout to be the same as the FF layout.

Rear-engine design

In automobile design, a rear-engine design layout places the engine at the rear of the vehicle. The center of gravity of the engine itself is behind the rear axle. This is not to be confused with the center of gravity of the whole vehicle, as an imbalance of such proportions would make it impossible to keep the front wheels on the ground.

The layout of a motorised vehicle such as a car is often defined by the location of the engine and drive wheels.

Front-engine, four-wheel-drive layout

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 followed, "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."

Ferrari Roma Grand touring sports car designed and manufactured by Ferrari

The Ferrari Roma is a grand touring, high performance Italian sports car created by automobile manufacturer Ferrari. It is a mid-size, two-door, 2+2 hardtop coupé. It has a front mid-engine, rear-wheel-drive layout. Based on the Ferrari Portofino, the car is an ultra high performance turbocharged V8 model placed between the Portofino and the F8 Tributo in Ferrari's range of sports cars. The Roma name comes directly from ancient Roman mythology. The vehicle was christened in honor of Italy's capital city and was originally introduced online on November 13, 2019. Official public unveil of the car took place the next day in Rome.

References

  1. "America on the Move". 2016-11-02.