Electronic Brake Force Distribution (EBD)
EBD (ELECTRONIC BRAKE-FORCE DISTRIBUTION) CONTROLNecessity
1. Because accident can arise due to generation of spin in vehicle by preceding locking of rear wheel to front wheel owing to drift of vehicle weight at time of sudden braking during running, the preceding locking of rear wheel has been prevented by decreasing the braking pressure of rear wheel in comparison with front wheel, having furnished with P-valve (proportioning valve-passenger car) or LCRV, LSPV (load conscious reducing valve, load sensing proportioning valve-small business car) as a countermeasure to that problem.
2. But these are all mechanical equipments and did not realize ideal rear brake force distribution.
3. Especially, though LCRV and LSPV applied in small business cars distributed rear brake force according to vehicle load to a certain degree, P-valve applied in passenger cars could not perform brake force distribution to weight increase, so inferiority in brake force has been viewed as problem.
4. And the required liquid pressure distribution curves for ideal braking differ by respective wheels according as the brake forces generated at respective wheels differ from one another depending on friction material dispersion in brake lining and pad; but ideal braking could not be achieved as only a certain constant liquid pressure distribution curve is maintained if only with mechanical P-valve, LCRV or LSPV.
5. Driver cannot know symptom at trouble time of P-valve, LCRV, LSPV etc.; and vehicle body spin may arise at time of sudden braking during period of faulty trouble.
6. Wherefore ABS ECU controls so that rear wheel may be locked at same time of later than front wheel to solve the above problem matters, which is called EBD (electronic brake-force distribution) control.
Principle
1. The principle is approximate control of brake force near the required liquid pressure distribution curve (ideal braking distribution curve) by way of adding a logic to ABS ECU instead of the existing P-valve.
2. Rear liquid pressure is controlled so that rear slip ratio will always be less than or same as that of front, having calculated the slip ratio from each wheel speed sensor at braking time.
3. Therefore rear wheel locking does not precede that of front wheel.
4. Consequently brake force improves as rear brake liquid pressure can be enlarged in amount of parts of as shown by deceleration liquid pressure in the figure.
5. And eventually whole brake force improvement is realized as brake force can be controlled by liquid pressure distribution curves required of wheel according to friction material dispersion.
EBD operation
1. Just before rear wheel is locked preceding to front wheel, ABS ECU lets NC valve of wheel side about to be locked be ON (OPEN) so that the brake oil pressure of wheel about to be locked be decreased and the locking be prevented.
2. If then wheel rotates as brake force is decreased, ABS ECU again lets NC valve be OFF (CLOSE) so that the brake pressure applied at NC be transmitted to clipper.
3. Motor pump does not act at this time.
Effect
1. Brake distance is decreased as rear brake force is enhanced in comparison with existing P-valve.
2. Stability is secured at time of rotating braking because as right and left rear wheel liquid pressures may be controlled independently from each other.
3. Brake pedal force decreases.
4. Stable braking effect can be achieved because front brake pad abrasion and temperature rise etc. are decreased as braking effect of rear brake is increased at braking time.
5. P-valve can be eliminated.
EBD type
Safety
1. Failure trouble ratio decreases than with ABS because EBD continues to control even in the following cases among ABS failure causes.
1 One wheel speed sensor failure.
2 Motor pump failure.
3 Failure by low voltage of battery.
2. Though there is no alarm instrument for P-valve by which driver may always be informed so that drive cannot know whether or not of failure trouble, in which case body spin may be generated if taken a sudden braking under condition of failure situation; in case of EBD failure trouble, the existing parking brake lamp is lighted to alarm EBD failure situation to driver so that driver can repair.
3. EBD fail-safe