Abstract
A vacuum brake booster, which assists the braking power using an engine vacuum, is normally used for an automotive brake system. On the other hand, a brake system, which uses no engine vacuum or less engine vacuum, has been expected. A hydraulic brake booster needs no engine vacuum since it uses the high-pressure generated by the pump and motor to boost the braking power. We have developed and manufactured the hydraulic brake booster integrated with the power supply and control valve units. For packaging improvement, it has been necessary to integrate the ECU to the hydraulic brake booster. Thus, the development target is to be an equal size to a vacuum brake booster for a new hydraulic brake booster with the ECU integration.
The following three technologies are described for downsizing the hydraulic brake booster. First, a high-pressure accumulator that uses a metal bellows is adopted. The gas chamber volume can be decreased comparing with the floating piston used for the conventional model since the metal bellows doesn't have the gas leak. Second, the hydraulic passage where the master cylinder and the wheel cylinders are switched is reviewed. Because 2-port valves replace 3-port valves, a width of the valve block body can be reduced. Finally, the ECU integration is achieved with the complete waterproof seal of the ECU housing. The ECU chamber is completely waterproofed by the double lip seal while the ECU chamber was conventionally isolated with the partition. Because the waterproof partition is abolished, the width of the ECU housing can be decreased. Using these technologies, the ECU-integrated hydraulic brake booster, which has an equal size and mass to the vacuum brake booster, has been developed.
One of the advantages for the hydraulic brake booster is the fast brake pressure build-up since it has the high-pressure accumulator for the power source. The vehicle performance improvement due to the fast pressure response is introduced using the developed hydraulic brake booster.
The hydraulic brake booster has the high response of the brake pressure build-up due to the driver's brake pedal input. Since the time to reach the brake pressure, in which the ABS control is activated, is shortened comparing with the vacuum brake booster, the stopping distance can be reduced. In addition, the active brake response is also high for the hydraulic brake booster. Therefore, not only the yaw stability but also the roll stability can be improved especially for the high cg (center of gravity) vehicle.
Keywords - Hydraulic Brake Booster, Downsize, Metal Bellows Accumulator, Double-Lip Seal, Pressure Build-up Response, Electronic Stability Control, Vehicle Stability