Piston pump for a hydraulic vehicle braking system

Abstract

Piston pump for a hydraulic vehicle brake system, with a stepped piston (2), wherein the stepped piston (2) has a circular effective pressure-side piston area (3) at a larger diameter end and a perforated disc-shaped effective suction-side piston area (4) facing away from the pressure-side piston area (3) at a diameter step, such that the stepped piston (2) has a smaller effective piston area (4) on a suction side of the piston pump (1) than on a pressure side, and with a suction chamber (9) which is bounded by the effective piston area (4) on the suction side of the stepped piston (2), such that a volume of the suction chamber (9) changes during a stroke movement of the stepped piston (2), such that during a suction stroke fluid is displaced from the decreasing suction chamber (9) into an increasing pumping chamber (8) of the piston pump (1), which is bounded by the effective piston area (3) on the pressure side of the stepped piston (2),wherein the piston pump (1) has an inlet valve (11) that controls an inflow into the suction chamber (9) of the piston pump (1), and wherein the piston pump (1) has a pressure relief valve (13) that connects the pump chamber (8) to the suction chamber (9) when an opening pressure is exceeded, characterized in that the piston pump (1) has a combined control valve (12) that controls a flow direction through the piston pump (1) and a pressure relief valve (13), and that the pressure relief valve (13) is a plate valve (22) with a plate-shaped shut-off element (21) or the control valve (12) is a dome valve with a dome-shaped shut-off element (34).

Description

[0001] The invention relates to a piston pump for a hydraulic vehicle brake system with the features of the preamble of claim 1. The piston pump is intended in particular for building up brake pressure in wheel brakes or for returning brake fluid to a master brake cylinder in slip-controlled hydraulic vehicle brake systems, where such pumps are also referred to as return pumps. The piston pump according to the invention can also be used for building up brake pressure in a hydraulic power-driven vehicle brake system, whereby it can be used here not only for building up brake pressure during service braking but also for slip control. The piston pump can also be understood as a pump element of a piston pump, in particular a multi-piston pump. State of the art

[0002] Such a piston pump is known from published patent application DE 198 12 043 A1. The known piston pump has a stepped piston, i.e., a pump piston with different sized effective piston areas on a suction side and on a pressure side. The effective piston area is defined as the area that causes or contributes to the pumping of brake fluid or fluid in general during a reciprocating stroke of the stepped piston. The effective piston area is also referred to below as the piston area for short. The stepped piston of the known piston pump has a smaller effective piston area on a suction side than on a pressure side.During a delivery stroke, in which the stepped piston reduces the volume of a pumping chamber of the piston pump and displaces brake fluid from the pumping chamber, the piston area on the suction side of the stepped piston increases the volume of a suction chamber of the piston pump, whereby the piston pump sucks in brake fluid or fluid in general. During an opposite suction stroke, the stepped piston enlarges the pumping chamber and reduces the suction chamber. Because of the larger piston area on the delivery side, the increase in the pumping chamber predominates, so that the piston pump sucks in brake fluid or fluid in general even during the suction stroke. Due to its design as a stepped piston pump with a stepped piston, the known piston pump sucks in brake fluid or a fluid in general not only during the suction stroke, but also during the delivery stroke, which results in a more even and less pulsating brake fluid or fluid flow on the suction side or in a pump inlet.

[0003] A piston pump of this type is known from published patent application DE 10 2014 207 538 A1. Further piston pumps are known from published patent applications DE 10 2013 222 949 A1, DE 100 49 909 A1, and DE 37 28 310 A1. Disclosure of the invention

[0004] The piston pump according to the invention with the features of claim 1 is a stepped piston pump with a stepped piston. It has an inlet valve that controls the inflow into the suction chamber of the piston pump. The inlet valve is in particular a check valve, but it can also be a controlled valve, for example. The inlet valve allows the inflow of brake fluid or fluid in general into the suction chamber of the piston pump and prevents brake fluid or fluid in general from flowing back out of the suction chamber of the piston pump through a pump inlet.

[0005] Furthermore, the piston pump according to the invention has a pressure relief valve which, when an opening pressure is exceeded (which can also be referred to as a threshold pressure, for example), connects the pump chamber to the suction chamber of the piston pump. As a result, the pressure relief valve limits the maximum delivery pressure of the piston pump, which also limits the maximum force or maximum torque for driving the stepped piston. Brake fluid or fluid which flows through the open pressure relief valve from the pump chamber into the suction chamber is under pressure and acts on the piston surface on the suction side of the stepped piston in the suction chamber. The pressurization of the piston surface on the suction side of the stepped piston creates a force on the stepped piston in the direction of the delivery stroke and thus supports the displacement of brake fluid or fluid in general from the pump chamber through a pump outlet of the piston pump.The pressurization of the piston surface on the suction side of the stepped piston of the piston pump according to the invention by the pressure relief valve when its opening pressure is exceeded thus supports the delivery of brake fluid or fluid in general with the piston pump according to the invention. The force or torque required to drive the stepped piston during the delivery stroke is reduced. The invention thus has the advantage of a limited or even reduced drive force or drive torque, which allows a less powerful motor to drive the piston pump and limits or reduces maximum power consumption. A further advantage of the invention is that the piston pump has its full delivery volume until the opening pressure of the pressure relief valve is reached, thus enabling rapid pressure buildup.A rapid pressure buildup within a few milliseconds is necessary, for example, for automatic braking to avoid an accident or for vehicle dynamics / skid control systems. The piston pump according to the invention fulfills two essentially opposing requirements: rapid pressure buildup with limited drive force and drive torque of the piston pump.

[0006] The subclaims relate to advantageous embodiments and further developments of the invention defined in claim 1.

[0007] The invention also relates to a hydraulic vehicle brake system with a stepped piston pump of the type explained. Short description of the drawing

[0008] The invention is explained in more detail below with reference to embodiments illustrated in the drawings. They show: Fig. 1 is a schematic representation of a piston pump according to the invention; Fig. 2 is an axial sectional view of a second embodiment of a piston pump according to the invention; and Fig. 3 a detailed view of a modified embodiment of a piston pump according to the invention according to rectangle III in Fig. 2. Embodiments of the invention

[0009] The Fig. The piston pump 1 according to the invention shown in Figure 1 is a stepped piston pump with a diameter-stepped stepped piston 2 as the pump piston. The stepped piston 2 has a circular pressure-side piston surface 3 at a larger diameter end and a perforated disc-shaped suction-side piston surface 4 at a diameter step, which faces away from the pressure-side piston surface 3. The two piston surfaces 3, 4 can also be referred to as effective piston surfaces 3, 4. A piston spring 5 is arranged on the pressure side, which urges a smaller diameter end of the stepped piston 2 against a circumference of a rotationally drivable eccentric 6. A rotary drive of the eccentric 6 drives the stepped piston 2 to perform a reciprocating stroke in a cylinder 7, which, like the stepped piston 2, has a diameter-stepped stepped piston and in which the stepped piston 2 is accommodated for axial displacement. The pressure-side piston surface 3 defines a cylindrical pump chamber 8 in the cylinder 7.The suction-side perforated disc-shaped piston surface 4 delimits an annular suction chamber 9 in the cylinder 7, which encloses a smaller diameter section of the stepped piston 2.

[0010] During a delivery stroke directed away from the eccentric 6, the stepped piston 2 reduces the volume of the pump chamber 8 and increases the volume of the suction chamber 9; during an opposite suction stroke, the situation is reversed. The ratio of the volume changes in the pump chamber 8 and the suction chamber 9 during the stroke of the stepped piston 2 corresponds to the ratio of the effective piston areas 3, 4. During a delivery stroke, the pressure-side piston area 3 displaces fluid from the pump chamber 8 through an outlet valve 10. In this embodiment, the fluid is brake fluid and the outlet valve 10 is a check valve. At the same time, due to the increasing volume of the suction chamber 9 during the delivery stroke, the piston pump 1 draws brake fluid into the suction chamber 9 through an inlet valve 11. In this embodiment, the inlet valve 11 is also a check valve.During a suction stroke, the volume of the pump chamber 8 increases and the volume of the suction chamber 9 decreases, so that brake fluid flows from the suction chamber 9 into the pump chamber 8 through a control valve 12 integrated into the stepped piston 2. In this embodiment, the control valve 12 is a check valve. Valve designs other than check valves are possible for the outlet valve 10, the inlet valve 11, and the control valve 12. The control valve 12 allows brake fluid to flow from the suction chamber 9 into the pump chamber 8 and blocks flow in the opposite direction. Because the increase in volume of the pump chamber 8 during the suction stroke is greater than the decrease in volume of the suction chamber 9, the piston pump 1 also sucks in brake fluid through the inlet valve 11 during the suction stroke.

[0011] The stepped piston pump 1 according to the invention has a pressure relief valve 13 which opens at a specific opening pressure and connects the pump chamber 8 to the suction chamber 9. The pressure relief valve 13 limits a maximum delivery pressure of the piston pump 1 to the opening pressure of the pressure relief valve 13. When the pressure relief valve 13 is open, the suction chamber 9 and thus the suction-side piston surface 4 are pressurized with the pressure prevailing in the pump chamber 8, possibly reduced by a pressure drop at the pressure relief valve 13. The pressurization of the suction-side piston surface 4 causes a force in the direction of the delivery stroke on the stepped piston 2, which assists the delivery stroke and reduces an axial force required to drive the stepped piston 2 or a drive torque of the eccentric 6.Below the opening pressure of the pressure relief valve 13, the piston pump 1 quickly builds up a brake pressure because it delivers with the entire effective pressure-side piston area 3 without brake fluid flowing back towards the suction chamber 9.

[0012] In the Fig. In the embodiment of the invention shown in Figure 1, the pressure relief valve 13 is pressure-controlled, it is opened by the pressure prevailing in the pump chamber 8 when this pressure exceeds the opening pressure of the pressure relief valve 13. It is also possible to use a spring-loaded check valve, as shown in Figure 1. Fig. 2, which allows flow in the direction from the pump chamber 8 to the suction chamber 9. However, a spring-loaded check valve has a greater pressure drop, which reduces the support of the delivery stroke by pressurizing the suction-side piston surface 4. Furthermore, externally controlled valves can be used as pressure relief valves, for example, a mechanically actuated valve, a solenoid valve, or a pneumatically or hydraulically externally pressure-controlled valve (not shown). This list is exemplary and not exhaustive.

[0013] In the following explanation of the Fig. 2 are for with Fig. 1 identical reference numbers are used for matching components. The piston pump 1 from Fig. 2 is also a stepped piston pump with a diameter-stepped stepped piston 2 as the pump piston. As in Fig. 1, the stepped piston 2 is Fig. 2 has a circular effective pressure-side piston surface 3 and a perforated disc-shaped effective suction-side piston surface 4 at a diameter step facing away from the pressure-side piston surface 3. At one pressure-side end, a sealing ring 14 is placed on the stepped piston 2, which seals the stepped piston 2 in a cylinder hole, referred to here as cylinder 7, in which the stepped piston 2 is accommodated in an axially displaceable manner. At its smaller diameter section, the stepped piston 2 is sealed with a sealing ring 15 in the cylinder 7 to the eccentric 6, against the circumference of which a piston spring 5 acts on the stepped piston 2, so that the stepped piston 2, as already Fig. 1, when the eccentric 6 is driven by a rotary actuator, it performs an axial reciprocating stroke in the cylinder 7. Suction and displacement or delivery of brake fluid are carried out in the same way by both piston pumps 1; due to the stepped piston 2, the piston pump 1 sucks Fig. 2 as well as the piston pump 1 from Fig. 1 draws brake fluid through an inlet 16 into a suction chamber 9 both during the suction stroke and during the delivery stroke. The suction chamber 9 is annular and encloses a smaller-diameter section of the stepped piston 2 between the sealing ring 15 and the diameter step of the stepped piston 2. The inlet 16 opens radially into the suction chamber 9. An inlet valve 11 is arranged in the inlet 16, which in the embodiment is designed as a check valve, which, as mentioned, is not essential for the invention. The inlet valve 11 prevents brake fluid from being displaced from the suction chamber 9 through the pump inlet 16 when the volume of the suction chamber 9 decreases during a suction stroke.

[0014] A pump outlet 17 opens axially into the pump chamber 8, in which an outlet valve 10 is arranged. This is also designed as a check valve, although this is not essential for the invention.

[0015] At the level of the suction chamber 9, the stepped piston 2 has intersecting radial holes 18, which intersect one end of an axial blind hole 19, which leads in the stepped piston 2 toward the pump chamber 8, i.e., toward the pressure side. A tubular valve housing 20 of a pressure relief valve 13 is mounted on the pressure-side end of the stepped piston 2. Fig. 2, the pressure relief valve 13 of the piston pump 1 is a spring-loaded check valve with a plate-shaped shut-off body 21. Due to the plate shape of the shut-off body 21, the pressure relief valve 13 can also be referred to as a plate valve 22. The shut-off body 21 of the pressure relief valve 13 interacts with a perforated disc-shaped valve seat 23, which is formed by a diametrical step on the inside of the tubular valve housing 20. The valve seat 23 faces away from the pump chamber 8. The pressure relief valve 13 has a disc spring as the valve spring 24, which is supported in a cavity on the stepped piston 2 and acts on the shut-off body 21 against the valve seat 23. A pressure in the pump chamber 8 acts on the shut-off body 21 of the pressure relief valve 13 on a side facing the valve seat 23.On the opposite side, the pressure from the suction chamber 9 acts on the shut-off body through the radial holes 18 and the blind hole 19 in the stepped piston 2. If a pressure difference between the pump chamber 8 and the suction chamber 9 exceeds a spring force that the valve spring 24 exerts on the shut-off body 21, the shut-off body 21 is lifted from the valve seat 23 so that the pressure relief valve 13 is opened and connects the pump chamber 8 to the suction chamber 9. The pressure difference required to open the pressure relief valve 13 is the opening pressure of the pressure relief valve 13. The pressure from the pump chamber 8 reduced by the opening pressure of the pressure relief valve 13 acts in the suction chamber 9 on the piston surface 4 of the stepped piston 2 on the suction chamber side and creates as shown in . Fig. 1 illustrates an axial force in the direction of the delivery stroke on the stepped piston 2, which reduces the force required to drive the stepped piston 2 in the direction of the delivery stroke. As shown in Fig. 1 also limited in Fig. 2 the pressure relief valve 13 the maximum delivery pressure of the piston pump 1. The design of the pressure relief valve 13 as a plate valve 22 with a plate-shaped shut-off body 21 is not mandatory for the invention.

[0016] The shut-off body 21 of the pressure relief valve 13 has a continuous central hole 25, the opening of which, facing the pump chamber 8, is conically designed as a valve seat 26 of a control valve 12 of the piston pump 1. Fig. 2 is formed. The control valve 12 controls a flow direction of the piston pump 1 or its stepped piston 2; from the direction of the suction chamber 9, brake fluid can flow through the radial holes 18 and the blind hole 19 in the stepped piston 2 and the control valve 12, which is arranged at the pump chamber-side end of the stepped piston 2, into the pump chamber 8. The control valve 12 blocks any backflow of brake fluid from the pump chamber 8 into the suction chamber 9. In the embodiment, the control valve 12 is again a check valve with a valve ball as a shut-off body 27, which is urged against the valve seat 26 by a helical compression spring as a valve spring 28. The valve spring 28 and the shut-off body 27 of the control valve 12 are accommodated in a hood-shaped valve housing 29, which is integral with the shut-off body 21 of the pressure relief valve 13. The valve housing 29 has holes to allow flow.The valve spring 28 can be omitted in embodiments of the invention. In the piston pump 1 of . Fig. 2, the pressure relief valve 13 and the control valve 12 are combined and arranged on the pressure-side end of the pump piston 2, ie the end facing the pump chamber 8.

[0017] The piston pump 1 from Fig. 2 is, as already mentioned, identically designed and functions in the same way as the piston pump 1 from Fig. 1. In addition, to explain the Fig. 2 the explanations of the Fig. 1 is referred to.

[0018] Fig. 3 shows a piston pump 1 according to the invention, in which, in comparison with the piston pump 1 of Fig. 2 the control valve 12 and the pressure relief valve 13 are designed differently. Otherwise, the piston pumps 1 from Fig. 2 and Fig. 3 and function in the same way. As in Fig. 2 are in Fig. 3, the control valve 12 and the pressure relief valve 13 are arranged at the pump-chamber end of the stepped piston 2. The pressure relief valve 13 is a spring-loaded check valve with a helical compression spring as the valve spring 30 and a ball as the shut-off body 31. The valve spring 30 urges the shut-off body 31 against a conical valve seat 32, which is formed on the pump-chamber side of the shut-off body 31 in a hollow cylindrical valve housing 33 of the pressure relief valve 13. Other designs are possible for both the shut-off body 31 and the valve spring 30, for example, a disc spring as the valve spring (not shown).

[0019] The pressure relief valve 13 is arranged in a shut-off body 34 of the control valve 12, which is designed as a hollow body for this purpose. The shut-off body 34 of the control valve 12 has the shape of a hemisphere with a seamlessly adjoining hollow cylinder, into which the valve housing 33 of the pressure relief valve 13 is pressed. The hemisphere of the shut-off body 34 of the control valve 12 faces the suction chamber 9 of the piston pump 1. A helical compression spring acting as the valve spring 35 of the control valve 12 urges the shut-off body 34 of the control valve 12 with the hemisphere against a conical valve seat 36 formed at an opening of the axial blind hole 19 at the pump-chamber-side end of the stepped piston 2.

[0020] The control valve 12, with the pressure relief valve 13 housed in its shut-off body 34, is arranged in a valve cage 37 located at the pump-chamber end of the stepped piston 2. The valve spring 35 of the control valve 12 is supported in the valve cage 37. Other designs of the valve spring 35 and the shut-off body 34 are also possible for the control valve 12 (not shown). Due to the hemispherical shape of the shut-off body 34, which can also be understood as a spherical shape, the control valve 12 can also be referred to as a spherical valve. The arrangement of the pressure relief valve 13 in the shut-off body 34 of the control valve 12 enables compact and space-saving accommodation of these two valves 12, 13. Furthermore, this design enables a control valve 12 with a large diameter and consequently a large flow cross-section.A small flow cross-section of the pressure relief valve 13 is normally not a problem because the pressure relief valve 13 only opens at high pressure, which ensures a large flow and because a flow rate is small, at least smaller than a flow rate through the control valve 12.

[0021] The piston pump 1 from Fig. 3 is also designed and functions in the same way as the piston pump 1 from Fig. 1 and Fig. 2. In addition, to explain the Fig. 3 the explanations of the Fig. 1 and Fig. 2 is referred to.

[0022] The piston pumps 1 from Fig. 1 to 3 are intended for brake pressure buildup in a hydraulic vehicle brake system (not shown). The pumped fluid is therefore brake fluid. The piston pumps 1 serve to build up brake pressure and to return brake fluid during slip control. The piston pumps 1 enable brake pressure buildup within a few milliseconds, which is sufficiently fast, for example, for automatic braking to avoid an accident and for vehicle dynamics / skid protection control. The pressure limitation of the piston pumps 1 from Fig. 1 to 3 limits a drive force required for the delivery stroke of the stepped piston 2 and a drive torque of the eccentric 6, which are reduced when, when the opening pressure of the pressure relief valve 13 is exceeded, the pressure prevailing in the pump chamber 8 acts through the open pressure relief valve 13 back onto the suction chamber 9 and there acts on the suction-side piston surface 4.

Claims

[1] Piston pump for a hydraulic vehicle brake system, with a stepped piston (2), wherein the stepped piston (2) has a circular effective pressure-side piston surface (3) at a larger-diameter end and a perforated disc-shaped effective suction-side piston surface (4) facing away from the pressure-side piston surface (3) at a diameter step, so that the stepped piston (2) has a smaller effective piston surface (4) on a suction side of the piston pump (1) than on a pressure side, and with a suction chamber (9) which is delimited by the effective piston surface (4) on the suction side of the stepped piston (2), so that a volume of the suction chamber (9) changes during a stroke movement of the stepped piston (2), such that during a suction stroke, fluid is displaced from the decreasing suction chamber (9) into an increasing pump chamber (8) of the piston pump (1), which is delimited by the effective piston surface (3) on the pressure side of the stepped piston (2).wherein the piston pump (1) has an inlet valve (11) which controls an inflow into the suction chamber (9) of the piston pump (1), and wherein the piston pump (1) has a pressure relief valve (13) which connects the pump chamber (8) to the suction chamber (9) when an opening pressure is exceeded, , characterized by that the piston pump (1) has a combined control valve (12) which controls a flow direction of the piston pump (1), and a pressure relief valve (13), and that the pressure relief valve (13) is a plate valve (22) with a plate-shaped shut-off body (21) or the control valve (12) is a spherical valve with a spherical shut-off body (34). [2] Piston pump according to claim 1, characterized by that the pressure relief valve (13) is pressure controlled. [3] Piston pump according to claim 1, characterized by that the control valve (12) is arranged on a shut-off body (21) of the pressure relief valve (13). [4] Piston pump according to claim 1, characterized by that the pressure relief valve (13) is arranged in a shut-off body (21) of the control valve (12). [5] Piston pump according to claim 1, characterized by that a shut-off body (21) of the pressure relief valve (13) has a valve seat (26) for a shut-off body (27) of the control valve (12).

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