Electronic Brake Force Distribution (EBD)

Electronic brake force distribution (EBD)
The EBD system (Electronic Brake Force Distribution) is a part of the ABS system and is designed to control the brake force applied to the rear wheels.
The EBD System enhances the efficiency of the ABS system by controlling the slip of the rear wheels in partial braking situations. By doing this, the brake force is moved closer to the optimum range and is still controlled electronically. As a result, there is no need for a proportioning valve on the Rio equipped with ABS.
The reason for this is that the proportioning valve, being a mechanical device, has limitations in achieving ideal brake force distribution to the rear wheels. Additionally, a proportioning valve cannot utilize flexible brake force distribution when there are changes in vehicle load or increased vehicle weight.





The EBD System is controlled by the ABS Control Module. The ABS Control Module calculates the slip ratio of each wheels. If the EBD fails, the EBD warning lamp (Parking Brake Lamp) will illuminate.

Brake force distribution of front & rear
The proportioning valve operates by allowing full hydraulic pressure to the rear wheels up to a set point called the valves split point. Beyond this split point, the proportioning valve reduces the amount hydraulic pressure to the rear brakes according to a certain ratio. Therefore, on light brake pedal applications, the proportioning valve allows about the same hydraulic pressure to be applied to both the front and rear brakes. On heavier brake pedal stops, the proportioning valve will control hydraulic pressure to the rear brakes, so that hydraulic pressure at the rear brakes will be lower than that at the front brakes. However, this kind of a mechanical valve does not consider the load condition or weight of the vehicle The EBD System on the other hand, detects and compares the wheel speed of front and rear, and controls the rear wheel brake pressure electronically according to the braking conditions.

Principal of EBD operation





EBD operating (Non-ABS braking)
If a rear wheel slip ratio exceeds a front wheel slip ratio, EBD system begins to operate to stop increasing the brake pressure of the rear wheel. During EBD operation, inlet valve (NO) of the rear wheel is closed (Hold mode) to stop the pressure increase. If closing the inlet valve is not enough, then outlet valve (NC) is open to release the pressure. This time, ABS motor does not operate.





EBD failure

ABS and EBD warning lamp
The ABS and EBD warning lamp in the instrument panel illuminates for 2 seconds after ignition key is turned ON.
If the warning lamp does not turn off, or turns on intermittently, there is a malfunction in ABS or EBD.
When a malfunction of ABS or EBD occurs, the ABS or EBD will not operate and the brakes will operate as a standard brake system.
Location: Inside left right wheel cover





Cluster