Piston pump assembly for a hydraulic power vehicle braking system

A piston pump assembly for a hydraulic power vehicle braking system including an electric motor, a planetary gear set, a helical gear, and a piston which is displaceable in a cylinder. To prevent the piston from rotating in the cylinder, cylinder pins are situated in grooves at an inner side of the cylinder and engage with the recesses in a flange of the piston. Due to reshaping, the grooves are closed at one end, so that the cylinder pins are axially secured.

CROSS REFERENCE

The present application claims the benefit under 35 U.S.C. § 119 of German Patent Application No. DE 102017211873.3 filed on Jul. 12, 2017, which is expressly incorporated herein by reference in its entirety.

BACKGROUND INFORMATION

The present invention relates to a piston pump assembly for a hydraulic power vehicle braking system.

In hydraulic power vehicle braking systems, piston pumps are used to generate a hydraulic brake pressure for a service braking through external power and/or in slip-controlled vehicle braking systems, they are also used to generate a brake pressure and to convey brake fluid from wheel brakes back to the wheel brakes following a pressure drop, for the purpose of again increasing the wheel brake pressures, or back in the direction of a main brake cylinder during a slip regulation.

SUMMARY

The piston pump assembly according to the present invention is provided to generate a brake pressure and/or to convey brake fluid in a hydraulic power and/or slip-controlled vehicle braking system. It includes an electric motor as the drive, a helical gear, for example a spindle drive, which converts a rotary driving motion of the electric motor into a translatory motion, and a piston/cylinder unit whose piston is displaceable in the cylinder with the aid of the helical gear. In this case, a relative movement between piston and cylinder is involved; the cylinder may also be displaced on the piston. A reduction gear unit, for example a planetary gear set, may be interconnected between the electric motor and the helical gear.

To prevent the piston from rotating in the cylinder, the cylinder includes on the inside and/or the piston includes on the outside a groove which runs in a displacement direction of the piston in the cylinder and with which a torque support element engages which is established at the piston and/or in the cylinder in the circumferential direction. At one end, the groove has a constriction, so that the torque support element is not able to axially exit. For example, the groove is closed by a reshaping of the material surrounding that end. If the groove is located inside the cylinder, the torque support element is established at the piston in the circumferential direction and vice versa. In the circumferential direction, the torque support element may also be established displaceably in the displacement direction of the piston in the cylinder and include a groove, for example, with which the torque support element also engages, i.e., include two opposite grooves, one inside the cylinder and one at the outside of the piston.

The present invention prevents the torque support element from exiting the groove and, for example, from entering an adjoining reduction gear unit or the helical gear.

The groove may run in the displacement direction or at an angle to the displacement direction of the piston in the cylinder. Its profile includes a component in the displacement direction and potentially an additional component in a circumferential direction, for example. For example, the groove runs in a straight line and axially parallel or in a helical manner.

To be able to insert the torque support element into the groove in the displacement direction of the piston in the cylinder, the constriction may be applied subsequently, for example by reshaping the material. In this embodiment of the present invention, the torque support element may be inserted into the groove in the displacement direction of the piston in the cylinder without the constriction or prior to forming the constriction. This simplifies or facilitates an assembly of the piston and the cylinder.

Advantageous embodiments and refinements of the present invention are described herein.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Piston pump assembly1according to the present invention and illustrated in the figures is provided to generate pressure in a hydraulic power vehicle braking system and/or to generate pressure and to convey brake fluid in a slip-controlled hydraulic vehicle braking system during a slip regulation. Such slip regulations are, for example, anti-lock braking systems, traction control systems, electronic stability control systems and electronic stability programs, for which the abbreviations ABS, TCS, ESC and ESP are commonly used.

For driving, piston pump assembly1according to the present invention includes an electric motor2with the aid of which a planetary gear set3is drivable. Planetary gear set3rotatably drives a helical gear4which converts the rotary motion into a displacement for the purpose of displacing a piston5of a piston/cylinder unit6in a cylinder7. Piston5is axially displaceable in cylinder7, i.e., a displacement direction of piston5in cylinder7is axial or axially parallel. In the described and elucidated specific embodiment of the present invention, helical gear4is a ball screw gear. Planetary gear set3rotatably drives a nut8of helical gear4and nut8displaces a spindle9of helical gear4. Deviating therefrom, it is also possible that spindle9is rotatably driven and nut8is displaced together with piston5. An end of spindle9, which is distant from planetary gear set3and electric motor2, is connected through a journal10, which is designed in one piece with spindle9and is pressed into a blind hole in a piston base11of piston5, to piston5so that piston5is displaced together with spindle9. Piston5is designed as a hollow piston which is closed in one piece by its piston base11at the end distant from planetary gear set3and electric motor2and which encloses nut8of helical gear4in cylinder7of piston/cylinder unit6. The above-described components of piston pump assembly1, i.e., electric motor2, planetary gear set3which is situated between electric motor2and helical gear4, helical gear4, piston5, and cylinder7are coaxial.

To prevent piston5from rotating in cylinder7, cylinder7includes on its inside three axially parallel grooves12which are distributed across a circumference, have semicircular cross sections and in which cylinder pins13are inserted which may in general also be understood as torque support elements14. The rotation prevention device of piston5in cylinder7is illustrated inFIG. 2in an enlarged manner, where only one of cylinder pins13, a fragment of piston5, and a fragment of cylinder7are drawn in the area of one of grooves12. At an end distant from planetary gear set3, grooves12transition at a ring stage16inside cylinder7into blind holes15in which the ends of cylinder pins13are accommodated. At its end close to planetary gear set3, piston5includes a radially outward-positioned flange17having three semicircular recesses which form receptacles18for cylinder pins13. Cylinder pins13are established at piston5in receptacles18in a circumferential direction. Receptacles18guide piston5axially displaceably and rotatably fixedly along cylinder pins13and in cylinder7. In the exemplary embodiment, grooves12are evenly distributed across the circumference. An uneven distribution and/or a number of grooves12other than three and three cylinder pins13as torque support elements14are also possible. In principle, one groove12and one cylinder pin13are sufficient, but it is also possible to have two, three or more grooves12and cylinder pins13. Other torque support elements14are also possible instead of cylinder pins13. In particular, torque support elements14are straight profile elements having a constant cross section across their lengths. For example, the torque support elements may have a rectangular cross section (not illustrated).

To prevent cylinder pins13which form torque support elements14from exiting grooves12in the direction of planetary gear set3during the up and down movement of piston5in cylinder7, the ends of grooves12facing planetary gear set3are closed.

To close grooves12, cylinder7has at a front end facing planetary gear set3a circumferential groove19whose inner groove flank is reshaped towards the inside at least in the area of axially parallel grooves12, so that the ends of grooves12facing planetary gear set3are closed. The reshaping of grooves12towards the inside may be in general also understood as a constriction20of grooves12which prevents cylinder pins13from exiting axially from grooves12. The inner groove flank of circumferential groove19at the front end of cylinder7is not reshaped towards the inside to form constriction20until piston5is inserted into cylinder7and cylinder pins13are inserted into grooves12, blind holes15, and receptacles18.

Piston pump assembly1according to the present invention is situated at a hydraulic block21of a slip regulation of a hydraulic power vehicle braking system, which is not illustrated, piston pump assembly1being part of the slip regulation. Such slip regulations and hydraulic blocks21are conventional to those skilled in the art and are not explained here in greater detail. Hydraulic block21is used to mechanically fasten and hydraulically interconnect hydraulic, electrohydraulic, and electronic components of the slip regulation which include, in addition to piston pump assembly1, solenoid valves, check valves, hydraulic accumulators, and damping chambers which are situated in and at hydraulic block21and which are hydraulically interconnected with one another through a bore of hydraulic block21. Hydraulic block21which is equipped with piston pump assembly1and the other components of the slip regulation forms a hydraulic assembly which is an integral part or a main item of the slip regulation. During a service braking, a brake pressure of the vehicle braking system is generated through external power using piston pump assembly1according to the present invention.