The invention is based on a hydraulic pump unit for a slip controlled hydraulic brake system for a motor vehicle.
The hydraulic pump unit is provided as a return feed pump for a motor vehicle for a slip-controlled hydraulic brake system. A hydraulic pump unit of this kind has been disclosed by EP 0 699 836 A2. The known hydraulic pump unit has an electric drive motor with a drive shaft whose one shaft end has an eccentric pin that is of one piece with it and is for driving a piston pump whose pistons are disposed radial to the drive shaft. The drive shaft is supported at three points, namely on both sides of an armature of the electric motor and at an end of the eccentric pin remote from the motor. The piston pump is embodied as a radial piston pump having one or a number of pistons disposed in a star pattern radial to the drive shaft; the end faces of these pistons rest against the eccentric pin and are thus driven to a reciprocating stroke motion with the rotation of the drive shaft.
The so-called three point support of the drive shaft has the disadvantage that it is not statically defined, i.e. the three bearings must be exactly in alignment in order to permit a low friction rotation of the drive shaft without its being elastically flexed with every rotation. The drive shaft with its three bearing seats must therefore be manufactured with a high degree of precision. Furthermore, three bearing seats in a motor housing and a pump housing must be manufactured very precisely and must be aligned exactly flush with one another when assembling the motor housing and the pump housing; the manufacturing and assembly costs of the known hydraulic pump unit are therefore high.
Moreover, the eccentric pin must be manufactured of one piece with the drive shaft, which further increases the manufacturing cost of the drive shaft. To reduce the friction between the pump piston and the eccentric pin, a roller bearing is provided on the eccentric pin. For a sufficiently smooth surface for the rolling of the bearing rollers, the eccentric pin must be ground, which additionally increases the manufacturing cost.