Vehicle Safety Features, ABS, Traction Control, ESP

Traction control system (TCS), on current production vehicles, are typically (but not necessarily) electro-hydraulic systems designed to prevent loss of traction (and therefore the control of the vehicle) when excessive throttle or steering is applied by the driver.

Although similar to Electronic Stability Control systems, Traction Control systems do not have the same goal.

The intervention can consist of any, or all, of the following:

Retard or suppress the spark to one or more cylinders
Reduce fuel supply to one or more cylinders
Brake one or more wheels
Close the throttle, if the vehicle is fitted with drive by wire throttle.
In turbo-charged vehicles, the boost control solenoid can be actuated to reduce boost and therefore engine power.
Typically, the Traction Control system shares the brake actuator and the wheel speed sensors with the anti-lock braking system

ESP – Electronic Traction Control

Electronic Stability Control (ESC) is the generic term for systems designed to improve a vehicle's handling, particularly at the limits where the driver might lose control of the vehicle.

Robert Bosch GmbH and Mercedes Benz co-developed the first ESC system called Elektronisches Stabilitätsprogramm (ESP®) that was used by Mercedes-Benz in their flagship S-Class. Mercedes Benz licensed this for use to other car manufacturers at no cost, including BMW with their 7 Series in 1995.

ESP first came to general notice when the original Mercedes-Benz A-Class (without ESC) failed the moose test (sudden swerving to avoid an obstacle); since Mercedes-Benz has built their reputation on safety, they did not want to be seen to be marketing unsafe vehicles, so at great expense every A-Class was retrofitted with ESC. Mercedes-Benz also became the first manufacturer to make ESC standard across its model range in 1999, with BMW following suit in 2000.

ESP was introduced to the mass market by Mercedes-Benz/Bosch, Continental Automotive Systems, Delphi and TRW, usually under the broader name of Electronic Stability Control, which is the more common term recognized by the Society of Automotive Engineers, although individual car manufacturers use a range of different marketing names (see below).

ESC compares the driver's intended direction in steering and braking inputs, to the vehicle's response, via lateral acceleration, rotation (yaw) and individual wheel speeds. ESC then brakes individual front or rear wheels and/or reduces excess engine power as needed to help correct understeer (plowing) or oversteer (fishtailing). ESC also integrates all-speed traction control, which senses drive-wheel slip under acceleration and individually brakes the slipping wheel or wheels, and/or reduces excess engine power, until control is regained. ESC cannot override a car's physical limits. If a driver pushes the possibilities of the car's chassis and ESC too far, ESC cannot prevent a crash. It is a tool to help the driver maintain control.

ESC combines anti-lock brakes, traction control and yaw control (yaw is rotation around the vertical axis).

ABS – Antilock Braking System

An anti-lock braking system (ABS) (translated from German, Antiblockiersystem) is a system on motor vehicles which prevents the wheels from locking while braking. The purpose of this is to allow the driver to maintain steering control under heavy braking and, in some situations, to shorten braking distances (by allowing the driver to hit the brake fully without the fear of skidding or loss of control). Disadvantages of the system include increased braking distances under certain conditions and the creation of a "false sense of security" among drivers who do not understand the operation and limitations of ABS.
Since it came into widespread use in production cars (with "version 2" in 1978), ABS has made considerable progress. Recent versions not only handle the ABS function itself (i.e. preventing wheel locking) but also traction control, brake assist, and electronic stability control, amongst others. Not only that, but its version 8.0 system now weighs less than 1.5 kilograms, compared with 6.3 kg of version 2.0 in 1978.

The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake).

A typical ABS is composed of a central electronic unit, four speed sensors (one for each wheel), and two or more hydraulic valves on the brake circuit. The electronic unit constantly monitors the rotation speed of each wheel. When it senses that any number of wheels are rotating considerably slower than the others (a condition that will bring it to lock) it moves the valves to decrease the pressure on the braking circuit, effectively reducing the braking force on that wheel. The wheel(s) then turn faster and when they turn too fast, the force is reapplied. This process is repeated continuously, and this causes the characteristic pulsing feel through the brake pedal. A typical anti-lock system can apply and release braking pressure up to 20 times a second.

The sensors can become contaminated with metallic dust and fail to detect wheel slip; this is not always picked up by the internal ABS controller diagnostic.

One step beyond ABS are modern ESC systems. Here, two more sensors are added to help the system work: these are a wheel angle sensor, and a gyroscopic sensor. The theory of operation is simple: when the gyroscopic sensor detects that the direction taken by the car doesn't agree with what the wheel sensor says, the ESC software will brake the necessary wheel(s) (up to three with the most sophisticated systems) so that the car goes the way the driver intends. The wheel sensor also helps in the operation of CBC, since this will tell the ABS that wheels on the outside of the curve should brake more than wheels on the inside, and by how much.