Apparatus and method of operation for a vehicle anti-lock brake system

An anti-lock brake system for a motor vehicle having a master cylinder which is connected with a brake fluid reservoir and which can be activated by means of a brake pedal in order to deliver brake fluid through a connecting line into at least one wheel brake cylinder, the anti-lock system comprising:

• an electromagnetic valve arranged in the connecting line between the master cylinder and the wheel brake cylinder in order to establish or interrupt the connection;
• an electronic control unit connected to said electromagnetic valve, said electronic control unit operable to cause said valve to establish or to interrupt said connection;
• and
• a fluid pump arranged in parallel to said electromagnetic valve in order to remove brake fluid from said wheel brake cylinder, with said fluid pump being adapted to deliver in only one direction and to shut off in the other direction, said fluid pump connected to said electronic control unit, said electronic control unit being operable to selectively actuate said fluid pump and said electronic valve, said electronic control unit having a first controlled pressure build-up mode of operation during which the brake pedal is actuated to supply pressurized brake fluid from the master cylinder and said control unit is operative to actuate said electromagnetic valve to allow a portion of said pressurized brake fluid to the brake cylinder and a second controlled pressure build-up mode of operation during which said fluid pump is activated to short circuit said flow of pressurized brake fluid to the brake cylinder, said electronic control mode also having a controlled pressure holding mode of operation during which said electromagnetic valve is closed and said fluid pump is not activated so that no brake fluid can flow between the master cylinder and said brake cylinder.