Patent ID: 6945610

Claim:
A hydraulically operated braking system comprising: a brake operating member operable by an operator; a master cylinder including a pressurizing piston operatively connected to said brake operating member and partially defining a pressurizing chamber, said pressurizing piston being moved by said brake operating member to pressurize a fluid in said pressurizing chamber; a brake cylinder actuated by the pressurized fluid received from said master cylinder; a sensing device for detecting a brake operating condition quantity indicative of an operating condition of said brake operating member; and an assisting device for applying to said pressurizing piston an assisting drive force which is different than a primary drive force to be applied to said pressurizing piston on the basis of a brake operating force acting on said brake operating member, said assisting device applying said assisting drive force to said pressurizing piston in a first direction in which said primary drive force is applied to said pressurizing piston, without application of a force to said brake operating member in a direction opposite to a second direction in which said brake operating force acts on said brake operating member, and wherein said assisting device comprises an assisting drive force control device electrically operable to control said assisting drive force on the basis of said brake operating condition quantity detected by said sensing device, said assisting drive force control device including changing means for changing a relationship between said assisting drive force and at least one of an operating force and an operating stroke of said brake operating member, detected at least as a part of said brake operating condition quantity, said relationship being in a normal operation of the braking system with an operation of said brake operating member, said changing means including pressure-reducing means for reducing a pressure of the fluid in said brake cylinder for a given value of said brake operating force, by reducing said assisting drive force to be applied to said pressurizing piston in said first direction, without reducing said primary drive force applied to said pressurizing piston on the basis of said brake operating force.