Electronic brakeforce distribution
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 | This article's factual accuracy is disputed. (April 2008) |
Electronic brakeforce distribution or EBD is an automobile brake technology that automatically varies the amount of force applied to each of a vehicle's brakes, based on road conditions, speed, loading, etc. Always coupled with anti-lock braking systems, EBD can apply more or less braking pressure to each wheel in order to maximize stopping power whilst maintaining vehicular control.
How ABS works
When a rotating wheel is subjected to excessive heavy braking, it is prone to lock-up. In motor vehicles, the anti-lock braking system (ABS) works to prevent this by monitoring wheel speeds and taking action in the form of releasing pressure on the braking circuit, when a rapid deceleration occurs in any of the wheels to ensure steering and vehicular control is maintained during heavy or emergency braking. Modern ABS has four separate channels - one for each tire - as different amounts of braking pressure are required to lock a rotating wheel on different surfaces. For example, less braking pressure would be needed to lock a wheel which was in contact with ice than a wheel which was in contact with an asphalt road.
In a situation where the wheels of a vehicle are on different surfaces (for example the two left wheels are on a concrete road and the two right wheels were on snow), during an emergency stop ABS would detect the two right wheels about to lock and would activate. Less braking force is sent to the right wheels, which would otherwise lock and not slow the car down.
How EBFD works
As per SAE technical paper #920646 - Buschmann et al. "The job of the EBD as a subsystem of the ABS system is to control the effective adhesion utilization by the rear wheels. The pressure of the rear wheels is approximated to the ideal brake force distribution in a partial braking operation. To do so, the conventional brake design is modified in the direction of rear axle overbraking, and the components of the ABS are used. EBD reduces the strain on the hydraulic brake force proportioning valve in the vehicle. EBD optimizes the brake design with regard to: adhesion utilization; driving stability; wear; temperature stress; and pedal force."
EBFD works in conjunction with ABS to minimize yaw accelerations during turns. It compares steering wheel angle to a yaw sensor. "Yaw" is the vehicle's rotation about its center of gravity (imagine a car spinning out of control). If the yaw sensor detects more/less yaw than the steering wheel angle should create - the car is understeering or oversteering - EBFD activates one of the rear brakes to rotate the car back into its intended course. The sensors are so sensitive, and the actuation is so quick that the driver doesn't notice it working - or how close he/she was to spinning out and hitting something!
For example, if a car is making a left turn, and begins to understeer (the car veers to the outside of the turn) EBFD activates the left rear brake, which will turn the car and make the car point left.
See also
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