Mid-engine design

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Formula One cars use rear-mid engine rear wheel drive design. Haryanto Bahrain 2016.jpg
Formula One cars use rear-mid engine rear wheel drive design.

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.

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 or front (in the case of front-mid layouts) 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

Front mid-engine position / Four-wheel drive Covered Willy's jeep Wings Over Wine Country 2007.JPG
Front mid-engine position / Four-wheel drive

This layout, similar to the above FMR layout, with the engine between driver and 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.

FMF layout – Front 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.

See also

Related Research Articles

<span class="mw-page-title-main">Sports car</span> Performance-oriented car class, generally small or light-weight with good handling

A sports car is a type of car that is designed with an emphasis on dynamic performance, such as handling, acceleration, top speed, the thrill of driving, and racing capability. Sports cars originated in Europe in the early 1910s and are currently produced by many manufacturers around the world.

<span class="mw-page-title-main">Four-wheel drive</span> Type of drivetrain with four driven wheels

A four-wheel drive, also called 4×4 or 4WD, is 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.

<span class="mw-page-title-main">Ferrari Enzo</span> Italian flagship sports car

The Ferrari Enzo, officially marketed as Enzo Ferrari, is a mid-engine sports car manufactured by Italian automobile manufacturer Ferrari and named after the company's founder, Enzo Ferrari. It was developed in 2002 using Formula One technology, such as a carbon-fibre body, Formula One-style automated-shift manual transmission, and carbon fibre-reinforced silicon carbide (C/SiC) ceramic composite disc brakes, as well as technologies not allowed in Formula One, such as active aerodynamics. The Enzo's F140 B V12 engine was also the first of a new generation for Ferrari. The Enzo generates substantial amounts of downforce through its front underbody flaps, small adjustable rear spoiler and rear diffuser, which work in conjunction to produce 343 kilograms (756 lb) of downforce at 200 km/h (124 mph) and 775 kilograms (1,709 lb) of downforce at 300 km/h (186 mph), before decreasing to 585 kilograms (1,290 lb) at top speed.

<span class="mw-page-title-main">Front-wheel drive</span> Automotive transmission where the engine drives the front wheels only

Front-wheel drive (FWD) is a form of engine and transmission layout used in motor vehicles, in which 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.

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<span class="mw-page-title-main">Front-engine, front-wheel-drive layout</span> Term used in automotive technology

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.

<span class="mw-page-title-main">Rear-engine, rear-wheel-drive layout</span> Automotive design

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.

<span class="mw-page-title-main">Rear mid-engine, rear-wheel-drive layout</span> 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 with its center of gravity in front of the rear axle, and thus right behind the passenger compartment. Nowadays more frequently called 'RMR', to acknowledge that certain sporty or performance focused front-engined cars are also "mid-engined", by having the main engine mass behind the front axle, RMR layout cars were previously just called MR, or mid-engine, rear-wheel-drive layout), because the nuance between distinctly front-engined vs. front mid-engined cars often remained undiscussed.

<span class="mw-page-title-main">Front-engine, rear-wheel-drive layout</span> Automobile layout

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Rear-wheel drive (RWD) is a form of engine and transmission layout used in motor vehicles, in which 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.

<span class="mw-page-title-main">Transaxle</span> 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.

<span class="mw-page-title-main">De Dion suspension</span> Type of automobile suspension

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<span class="mw-page-title-main">Torsen</span> Type of limited-slip differential used in automobiles

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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.

<span class="mw-page-title-main">Front-mid-engine, front-wheel-drive layout</span>

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.

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.

<span class="mw-page-title-main">Front-engine, four-wheel-drive layout</span> Automotive configuration

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.

<span class="mw-page-title-main">Mid-engine, four-wheel-drive layout</span>

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.

<span class="mw-page-title-main">Mercedes-Benz SLS AMG</span> 2-seater frond mid-engine sports car developed by Mercedes-AMG

The Mercedes-Benz SLS AMG is a front mid-engine, 2-seater, limited production sports car developed by the Mercedes-AMG division of German automotive manufacturer Mercedes-Benz, with the assistance of David Coulthard. The car is the successor to the Mercedes-Benz SLR McLaren and was described by Mercedes-Benz as a spiritual successor to the Mercedes-Benz 300SL Gullwing, mainly because it was inspired by the latter. SLS stands for "Super Leicht Sport".

<span class="mw-page-title-main">Mercedes-AMG GT</span> Sports car manufactured by Mercedes-AMG as a successor to the SLS AMG

The Mercedes-AMG GT is a series of 2-door sports cars produced by German automobile manufacturer Mercedes-AMG. The car was introduced on 9 September 2014 and was officially unveiled to the public in October 2014 at the Paris Motor Show. While not directly replacing the SLS AMG, it is the second sports car developed entirely in-house by Mercedes-AMG. The Mercedes-AMG GT went on sale in two variants in March 2015, while a GT3 racing variant of the car was introduced in 2015. A high performance variant called the GT R was introduced in 2016. A GT4 racing variant, targeted at semi-professional drivers and based on the GT R variant, was introduced in 2017. In 2021, a new variant called the AMG GT Black Series was released. All variants are assembled at the Mercedes-Benz plant in Sindelfingen, Germany.

References

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