Braking pressure control apparatus capable of switching between two brake operating states using power-operated and manually operated pressure sources, respectively

A braking pressure control apparatus for controlling a pressure of a working fluid in a brake cylinder of a hydraulically operated brake in a hydraulically operated braking system for a vehicle, said braking pressure control apparatus comprising:

• a first hydraulic pressure source including a power-operated pressurizing device for pressurizing the fluid;
• a second hydraulic pressure source operable by an operation of a manually operable brake operating member, to pressurize the fluid to a pressure higher than a level corresponding to an operating force acting on said brake operating member;
• a switching device for selectively placing the braking system in a first operating state in which said brake cylinder is operated with the pressurized fluid delivered from said first hydraulic pressure source while said brake cylinder is disconnected from said second hydraulic pressure source, and a second operating state in which said brake cylinder is operated with the pressurized fluid delivered from said second hydraulic pressure source while said brake cylinder is disconnected from said first hydraulic pressure source;
• and
• at least one of (a) a change restricting means operable upon a switching of the braking system between said first and second operating states by said switching device, to restrict at least one of a change of an operating state of said brake operating member and a change of the fluid pressure in said brake cylinder, which changes take place due to said switching, and (b) a switching control device operable to control said switching device on the basis of a running condition of said vehicle, wherein said running condition of the vehicle is represented by at least one value selected from the group consisting of:
• a value indicating a slipping state of said wheel;
• a yaw rate of the vehicle;
• a steering angle of the vehicle;
• a running speed of the vehicle;
• a deceleration value of the vehicle;
• a value indicating a running environment of the vehicle external to the vehicle;
• and a value indicating a state of operation by a vehicle operator of a manually operable member provided on the vehicle, and wherein said switching control device includes a diagnosing device operable to determine whether the braking system is normal or not, said switching control device controlling said switching device on the basis of said running condition of the vehicle only when said diagnosing device determines that the braking system is normal.