Control device for vehicle brake system

A control device for a vehicle brake system having:

• a master cylinder for building up a brake hydraulic pressure depending on the manipulation of a brake manipulation member;
• a vacuum booster for boosting the manipulation force of the brake manipulation member by utilizing a pressure difference between a vacuum pressure chamber supplied with a vacuum pressure and a variable pressure chamber adjoining the vacuum pressure chamber through a diaphragm, to output the boosted manipulation force to the master cylinder;
• wheel cylinders for applying a brake force to respective wheels of a vehicle upon receipt of the brake hydraulic pressure supplied from the master cylinder;
• a hydraulic pump connected to fluid passages connecting the master cylinder to the wheel cylinders for building up a brake hydraulic pressure by being driven by an output of an electric motor and for supplying the wheel cylinders with the brake hydraulic pressure independently of the master cylinder;
• a vacuum pressure sensor for detecting the vacuum pressure in the vacuum pressure chamber of the vacuum booster;
• and
• a master cylinder pressure sensor for detecting the pressure in the master cylinder;
• wherein the control device comprises:
• vacuum pressure acquisition means for acquiring the vacuum pressure in the vacuum pressure chamber of the vacuum booster from the vacuum pressure sensor;
• master cylinder pressure acquisition means for acquiring the pressure in the master cylinder from the master cylinder pressure sensor;
• first storage means for storing a vacuum-boosting limit pressure map representing a relation between various vacuum pressures in the vacuum pressure chamber of the vacuum booster and various boosting limit pressures being pressures in the master cylinder which respectively correspond to various boosting limits of the vacuum booster at the various vacuum pressures;
• boosting limit judgment pressure calculation means for calculating as the boosting limit judgment pressure a boosting limit pressure which is calculated from a vacuum pressure acquired by the vacuum pressure acquisition means and the vacuum-boosting limit pressure map stored in the first storage means;
• boost control means for executing a boost control that if the master cylinder pressure acquired by the master cylinder pressure acquisition means is equal to or higher than the boosting limit judgment pressure calculated by the boosting limit judgment pressure calculation means, the boost control means drives the hydraulic pump to build up a brake hydraulic pressure and supplies the wheel cylinders with a resultant hydraulic pressure which is made by adding the pump-built hydraulic pressure to a master cylinder pressure built up in dependence on the manipulation of the brake manipulation member and that if the master cylinder pressure is lower than the boosting limit judgment pressure, the boost control means stops the driving of the hydraulic pump;
• first judgment value derivation and storage means for deriving and storing as first judgment value a boosting limit judgment pressure which, if a predetermined condition is satisfied during the driving of the hydraulic pump by the boost control means, the boosting limit judgment pressure calculation means calculates at the time when the predetermined conditions is satisfied;
• and
• returning start judgment means for judging whether the returning of the brake manipulation member is started or not;
• wherein the boost control means executes the boost control using as the boosting limit judgment pressure the first judgment value stored in the first judgment value derivation and storage means when the returning start judgment means judges during the driving of the pump that the returning of the brake manipulation member is started.