In
automotive engineering the electronic differential is a form of
differential, which provides the required
torque
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
for each driving wheel and allows different wheel speeds. It is used in place of the mechanical differential in multi-drive systems. When cornering, the inner and outer wheels rotate at different speeds, because the inner wheels describe a smaller turning radius. The electronic differential uses the
steering wheel command signal and the
motor
An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.
Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...
speed signals to control the power to each wheel so that all wheels are supplied with the torque they need.
Functional description
The classical
automobile
A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods.
The year 1886 is regarde ...
drivetrain
A drivetrain (also frequently spelled as drive train or sometimes drive-train) 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 o ...
is composed by a single
Internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
providing torque to one or more driving wheels. The most common solution is to use a mechanical device to distribute torque to the wheels. This
mechanical differential allows different wheel speeds when cornering. With the emergence of
electric vehicles new drive train configurations are possible. Multi-drive systems become easy to implement due to the large power density of
electric motor
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
s. These systems, usually with one motor per driving wheel, need an additional top level controller which performs the same task as a mechanical differential.
The ED scheme has several advantages over a mechanical differential:
* simplicity - it avoids additional mechanical parts such as a
gearbox
Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differe ...
or
clutch;
* independent torque for each wheel allows additional capabilities (e.g.,
traction control
A traction control system (TCS), also known as ASR (from german: Antriebsschlupfregelung, lit=drive slippage regulation), is typically (but not necessarily) a secondary function of the electronic stability control (ESC) on production motor vehicle ...
,
stability control
Electronic stability control (ESC), also referred to as electronic stability program (ESP) or dynamic stability control (DSC), is a computerized technology that improves a vehicle's stability by detecting and reducing loss of traction ( skiddi ...
);
* reconfigurable - it is reprogrammable in order to include new features or tuned according to the driver’s preferences;
* allows distributed
regenerative braking
Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy into a form that can be either used immediately or stored until needed. In this mechanism, the electric traction mo ...
;
* the torque is not limited by the wheel with least traction, as it is with a mechanical differential.
* faster response times;
* accurate knowledge of traction torque per wheel.
Applications
Several applications of this technology have proven successful and have increased vehicle performance. The application range is wide and includes the huge
T 282B from
Liebherr
Liebherr is a German-Swiss multinational equipment manufacturer based in Bulle, Switzerland, with its main production facilities and origins in Germany.
Liebherr consists of over 130 companies organized into 11 divisions: earthmoving, mining, ...
which is considered the world largest truck. This earth-hauling
truck
A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame constructi ...
is driven by an electric propulsion system composed by two independent electric motors. These motors providing a maximum power of 2700 kW are controlled in order to adjust their speeds when cornering, thus increasing traction and reducing
tire wear
A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...
.
The
Eliica
The Eliica (or the Electric Lithium-Ion Car) is a battery electric vehicle prototype or concept car first shown in 2004 and designed by a team at Keio University in Tokyo, led by Professor Hiroshi Shimizu. The car runs on a lithium-ion battery ...
is also equipped with electronic differential; this eight-wheeled electric vehicle is capable of driving up to 370 km/h whilst maintaining perfect torque control on each wheel. Smaller vehicles for traction purposes and
System on Chip controllers for generic vehicular applications are also available.
References
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Automotive transmission technologies
Vehicle technology
Mechanical power control