Electronic Brake Force Distribution

Electronic Brake Force Distribution:

Electronic Brake Force Distribution

EBD is based on the principle that the weight being supported by the wheels of your car isn't evenly distributed. Some wheels carry a heavier load than others and will require more brake force in order to bring the car to a stop without it going out of control. Furthermore, the amount of weight being supported by a wheel shifts during the braking process, so the amount of force necessary at each wheel can change rapidly. An EBD system can not only detect how much weight is being supported by each wheel, but change the amount of braking power sent to each wheel on an instant-by-instant basis.

It's important for driving safety to maintain the friction between the tire and the road, yet there are a number of conditions under which this friction can be lost. One is acceleration on icy roads, as mentioned above, but friction can also be lost if you brake too hard. The forward momentum of the car can keep it moving at a speed significantly greater than the speed at which the tires are spinning. This is called wheel lock and it's a common cause of driving accidents. Once it happens, the tires no longer grip the pavement and the car continues to travel in the direction it was heading when the skid started.

The key to avoiding a skid is the slip ratio, the difference between the speed at which the car is moving and the speed at which the tire is rotating. Antilock braking systems (ABS) can sense the slip ratio of the individual tires and modulate the brake force applied to each tire so that the slip ratio remains within a safe range, thereby avoiding a skid.

With EBD, a computer called an electronic control unit (ECU) determines the slip ratio of each of the tires individually. If the ECU notices that the rear wheels are in danger of slipping, it applies less force to them while maintaining (or, if necessary, increasing) the force applied to the front wheels. EBD is also useful when the car is braking while driving around a corner. While turning, the outer wheels of the car rotate more quickly than the inside wheels. If too much brake force is applied to the inner wheels they can lock, causing the car to oversteer and go out of control. EBD can sense the slippage of the inner wheels and reduce the brake force on those wheels without reducing the force on the outer wheels.

EBD system needs two pieces of information: the speed at which the wheel is rotating and the speed of the car. If the speed at which the wheel is rotating is slower than the speed at which the car is moving, then the wheel is slipping and a skid can result. A sensor is placed at each wheel to determine wheel speed. There is no specific sensor to measure the forward motion of the car. Instead, the speed measurements from all four wheels are averaged to create an estimate of the vehicle's overall speed.

Brake force modulators: Brake force is applied to the wheels hydraulically, with brake fluid pumped into brake lines in such a way as to pneumatically activate the brake cylinders. The EBD system can modulate the amount of brake fluid going to each wheel through electrically actuated valves.

Electronic Control Unit (ECU): The ECU is a small computer embedded in the antilock braking system. It receives input from the speed sensors, calculates the slip ratio of the wheels, and uses the brake force modulators to apply an appropriate amount of force to keep the slip ratio of each wheel within a reasonable range.

Benefits of EBD:

Imagine that you're driving on an icy surface or a road slick with rainwater. Under these conditions it's really easy for your car to go into a skid. And although EBD cannot detect road conditions directly, it can deduce them from the slip ratio of the wheels and compensate accordingly. If conditions are different for each wheel -- for instance, if one wheel is on a patch of ice and the other is not -- this can be detected through the slip ratio. Although there's no magic solution to the problem of stopping a car under bad road conditions, EBD can make emergency braking under these conditions as safe as possible.

Watch the video to understand the working: