Brake booster for vehicles

摘要

A brake booster for a vehicle comprises first and second control pistons operated by hydraulic pressure from a master cylinder, and a power piston pneumatically actuated in response to movement of the control pistons to increase braking pressure applied to the wheel brake cylinders of the vehicle. To control the increasing ratio of the braking pressure in accordance with the changes of the vehicle weight, under unloaded condition of the vehicle only the first control piston is operated by the master cylinder pressure to actuate the power piston and under loaded condition of the vehicle the second control piston co-operates with the first control piston by the master cylinder pressure to accelerate the actuation of the power piston.