Piston Pump having an Inlet Valve

Abstract

A piston pump includes a piston, a sealing element sealing the piston radially with respect to a cylinder, and an inlet valve arranged on the piston. The inlet valve includes a valve cage holding a closing member. The sealing element is integrally designed with the valve cage.

Description

PRIOR ART

The invention relates to a piston pump comprising a piston, a sealing element on the piston sealing radially with respect to a cylinder, and an inlet valve arranged on the piston, said inlet valve being designed with a valve cage holding a closing member. In addition, the invention relates to a vehicle brake system comprising a piston pump of this type.

In known vehicle brake systems, the “hydraulic power unit” is a fixed component. It is used to meter the brake pressure and, to this end, has a pump, which is generally a piston pump, in which a piston is displaceable in a cylinder. The piston is displaced in a two-cycle operation. In a first cycle, a fluid to be conveyed, for example brake fluid, is sucked up through an inlet valve. In a second cycle, the fluid is discharged through an outlet valve. The piston is sealed with respect to the inner surface of the cylinder by means of a sealing element and is also guided in the cylinder during its stroke movement by said sealing element. A piston pump of this type is known for example from DE 10 2005 017 131 A1.

The object of the invention is to create a vehicle brake system comprising a piston pump, in which the seal between the piston and the cylinder is designed so as to be permanently reliable whilst, at the same time, creating an arrangement which is particularly cost-effective on the whole.

DISCLOSURE OF THE INVENTION

In accordance with the invention, a piston pump comprising a piston, a sealing element sealing the piston radially with respect to a cylinder, and an inlet valve arranged on the piston is created, said inlet valve being designed with a valve cage holding a closing member. The sealing element and the valve cage are designed in one piece.

With the solution according to the invention, the one-piece component formed from the sealing element and valve cage of the inlet valve can be produced in a more cost-effective manner compared to two individual components. In addition however, the solution according to the invention affords further surprising advantages. In particular, the assembly of the sealing element is also simplified considerably with this solution, because the sealing element is additionally stabilized in terms of shape by means of the valve cage. In addition, the valve cage can be used in an automatic assembly device as a position recognition means for the sealing element. Lastly, the one-piece component can be held particularly easily on the respective piston by a respective return spring and can thus be fastened to said piston in a very simple and cost-effective manner. This will be explained in greater detail hereinafter as a development of the solution according to the invention.

In accordance with a first advantageous development of the piston pump according to the invention, the sealing element and the valve cage are produced from plastic.

Due to the selective choice of a plastic which is sufficiently dimensionally stable for the valve cage and also sufficiently resilient for the sealing element, it is possible to produce the one-piece component according to the invention in only a single manufacturing process.

In accordance with a second advantageous development of the piston pump according to the invention, a spring support for a return spring supporting the piston relative to the cylinder is formed on the sealing element.

The spring support designed in such a way enables a particularly space-saving arrangement of the return spring, wherein said return spring may, at the same time, be selected to be particularly long and large in diameter. The return spring can therefore develop high restoring forces with a small installation space.

In accordance with a third advantageous development of the piston pump according to the invention, the sealing element has a sealing lip resting against the cylinder, said sealing lip ending in an axially set-back manner relative to the spring support on the side facing away from the return spring.

The spring support axially set back in such a way compared to the effective surface of the return spring prevents the respective sealing lip from being damaged due to the applied return spring and the restoring forces thereof.

In accordance with a fourth advantageous development of the piston pump according to the invention, the sealing element is designed with an axial groove, which is open towards the high-pressure area of the piston/cylinder arrangement.

During operation of the piston pump, in the axial groove open in such a way towards the high-pressure area of the piston/cylinder arrangement, the pressure prevailing in the high-pressure area may infiltrate the axial groove and thus expand it. At the same time, the radially outer part of the sealing element, that is to say the part which lies radially outwardly beside the axial groove, is then pressed against the adjacent inner wall of the cylinder. With increasing pressure in the high-pressure area, a reinforcement of the support of the sealing element against the cylinder also thus develops, and therefore an improved seal. At the same time, the leakage behavior in the piston and also the guidance of the piston in the cylinder are improved.

In accordance with a fifth advantageous development of the piston pump according to the invention, the sealing element is designed in a stepped manner on its side facing the piston.

The stepped design of the sealing element leads to a comparatively large contact area between the piston and the sealing element. This large contact area improves the fastening of the sealing element. In particular, the sealing element can be fixed by being pressed on against the axially extending flanks of the step(s). At the same time, the sealing element is centered at these flanks relative to the piston. The radially directed flanks of the step(s) are used to support the sealing element with respect to the piston, which is particularly advantageous when the piston is reset by means of the above-mentioned return spring.

In accordance with a sixth advantageous development of the piston pump according to the invention, the sealing element surrounds the piston.

The sealing element surrounds a portion of the piston in this manner in particular at a step, a groove or a phase of the piston in such a way that the sealing element hooks behind the piston in the axial direction by means of a pawl, which is peripheral or peripheral over portions. A positive-fit connection between the piston and sealing element is thus created, which can be easily produced or pre-assembled, even in an automatic manufacturing process, due to the above-mentioned slightly resilient property of the material of the sealing element.

In accordance with a seventh advantageous development of the piston pump according to the invention, the piston is designed in two parts with a first part turned towards a drive and a second part turned towards the sealing element.

The individual parts of the piston thus designed in two parts can be assigned specific functions. The first part is thus used to transfer the thrust generated at the drive to the second part, which in turn ensures the flow of fluid, in particular brake fluid, into the inlet valve. The high-pressure area inside the cylinder is then defined by means of the sealing element and sealed with respect to the low-pressure area. The second part pushes the sealing element into the cylinder and is in turn pushed by the first part. The piston is reset starting from the return spring by transferring the restoring thrust forces via the sealing element and the second part onto the first part. The individual parts can be optimized in a simpler manner in view of the material selection and possible production methods, as would be the case with a one-part piston.

In accordance with an eighth advantageous development of the piston pump according to the invention, the first part is designed as a solid cylinder and the second part is designed as a hollow cylinder.

The first part designed as a solid cylinder can be produced in a very cost-effective manner and, in particular, can transfer high thrust forces. It is advantageously produced from plastic, to which reinforcing fibers are preferably added. The second part designed as a hollow cylinder may advantageously already be formed as a blank with a cylindrical hollow chamber. The second part is preferably produced from metal and in particular is designed as a sinter cast part or as a deep-drawn part. In a part of this type, merely at least one radial opening is to be formed, through which the fluid to be sucked up can then flow radially from the outside in, in the direction of the inlet valve during operation of the piston pump.

The above-mentioned object is furthermore also achieved by a vehicle brake system comprising a piston pump of this type according to the invention, wherein corresponding advantages are achieved, as already described above for the piston pump.

An exemplary embodiment of the solution according to the invention will be explained in greater detail hereinafter on the basis of the accompanying schematic drawings, in which:

FIG. 1 shows a longitudinal section of a piston pump according to the prior art,

FIG. 2 shows the detail II in FIG. 1 in an enlarged scale,

FIG. 3 shows a longitudinal section of a first exemplary embodiment of a piston pump according to the invention,

FIG. 4 shows the detail IV in FIG. 3 in an enlarged scale,

FIG. 5 shows a longitudinal section of a second exemplary embodiment of a piston pump according to the invention, and

FIG. 6 shows the detail VI in FIG. 5 in an enlarged scale.

A piston pump 10 according to the prior art is illustrated in FIGS. 1 and 2 and comprises, inter alia, a piston arrangement 12, which is formed from a cylinder 14 and a piston 16 mounted displaceably therein. The piston arrangement 12 further comprises an inlet valve 18 and an outlet valve 20. These valves 18 and 20 are provided so that, during its stroke movement in the cylinder 14, the piston 16 can suck a fluid through an inlet 22 into a high-pressure chamber or high-pressure area 24 inside the cylinder 14 and can discharge this fluid again, under pressure, from the high-pressure area 24 through an outlet 26. The fluid is a brake fluid in the present case.

The piston 16 is biased resiliently in the axial direction by means of a return spring 28 located in the high-pressure area 24. On the basis of FIG. 1, the return spring 28 is supported at its left end against the end face of the cylinder 14 and presses at its right end against a spring support 30. The spring support 30 is coupled fixedly to the piston 16 so that the return spring 28 presses accordingly against the piston 16 via the spring support 30.

A sealing element 32 is also arranged between the piston 16 and the cylinder 14 and seals the high-pressure area 24 in the cylinder 14. The sealing element 32 is annular and surrounds the piston 16 at the outer surface thereof. The sealing element 32 is held fixedly on this outer surface by means of a valve cage or valve housing 34 of the inlet valve 18, said valve cage or valve housing being slid over the piston 16. At the valve housing 34, the spring support 30 is also shaped in the form of a shoulder. The sealing element 32 retained in such a way lies radially inwardly against the inner surface of the cylinder 14, so as to slide along and seal said inner surface of the cylinder.

The valve housing 34 is designed in a beaker-shaped manner as a cage, in the interior of which a screw-shaped return spring 36 is located and presses against a spherical closing member 38. The closing member 38 thus lies (in the operating state illustrated in FIGS. 1 and 2) against a valve seat 40, which is formed on the end face of the piston 16. The closing member 38 is lifted from this valve seat 40, against the force of the return spring 36, when the piston 16 is withdrawn to the right from the cylinder 14, based on FIG. 1. With this movement, the inlet valve 18 is thus opened and fluid is sucked into the high-pressure area 24.

The sealing element 32 according to FIGS. 1 and 2 has a main body 42, which is basically square in cross-section and on which a sealing lip 44 facing the high-pressure area 24 is formed.

FIGS. 3 and 4 show a piston pump 10 according to the invention. This piston pump likewise has a piston arrangement 12 comprising a cylinder 14 and a piston 16 displaceable therein. Furthermore, an inlet valve 18 and an outlet valve 20 are likewise provided. The piston 16 is biased resiliently by a return spring 28 located in a high-pressure area 24, said return spring pressing against a spring support 46 according to the invention coupled fixedly to the piston 16.

A sealing element 48 according to the invention is also located between the piston 16 and the cylinder 14, said sealing element being retained fixedly on the piston 16 and being able to slide along the inner surface of the cylinder 14. This sealing element 48 is formed in one piece with a valve housing 50 according to the invention, in such a way that the spring support 46 and the sealing element 48 are also designed in one piece. The one-piece design of the spring support 46 and sealing element 48 enables an axially very short, more compact design with a smaller dead space volume. The sealing element 48 can additionally be biased by the return spring 28. A radially very wide support surface is also provided for the return spring 28 at the spring support 46.

As can be seen in FIG. 4, the sealing element 48 is designed with an axial groove 52, which is open in the direction of the high-pressure area 24. The pressurized fluid located in the high-pressure area 24 accordingly also infiltrates this axial groove 52. The two inner, mutually opposed side faces or flanks 54 and 56 of the axial groove 52 are pressed radially away from one another by this fluid. In particular, the lip-shaped part or portion 58 of the sealing element 48 located radially outwardly from the axial groove 52 and which can also be referred to as a sealing lip is pressed radially outwardly and therefore against the inner surface of the cylinder 14. As the pressure increases in the high-pressure area 24, this portion 58 of the sealing element 48 thus also rests more heavily against the cylinder 14, where it thus provides an improved seal. In addition, the guidance of the piston 16 in the cylinder 14 is improved.

FIGS. 5 and 6 illustrate an exemplary embodiment of a sealing element 48, in which the end of the lip-shaped portion 58 or the sealing lip of the sealing element 48 is set back axially towards the side facing away from the return spring 28, relative to the radially directed plane of the spring support 46. A distance from the return spring 28 is thus also produced axially, so that the return spring 28 cannot damage the lip-shaped portion 58. The return spring 28 also presses the core of the sealing element 48 axially together, however, so that it is pressed radially outwardly.

In both exemplary embodiments shown in FIGS. 3 to 6, the piston 16 is formed in two parts from a first part 60 and a second part 62. The first part 60 is a solid cylindrical, rod-shaped structure, which is injection molded from plastic and is specifically adapted to transfer axially directed shear forces from an eccentric drive (not illustrated) to the second part 62 and thus to the sealing element 48. The second part 62 is a hollow cylindrical sinter cast part, which has a shoulder or a step 64 and 66 at each of its two ends. The step 64 encompasses the first part 60 radially outwardly at the end region thereof, wherein the first part 60 is fixed non-positively in the interior of the step 64 by means of a press fit. The step 66 is located adjacent to the sealing element 48 and is surrounded thereby radially outwardly in the axial direction. A portion 68 of the sealing element 48, which forms the core thereof, rests radially outwardly against the step 66 and forms a press fit therewith. A further portion 70 of the sealing element 48, which is located radially completely outwardly, surrounds the step 66 of the second part 62 completely in the form of a type of arm or sleeve. A plurality of pawls 72 is formed peripherally on this portion 70, said pawls hooking behind the radially outer region of the step 66 and thus producing a positive-fit connection to the second part 62 in the axial direction.

Furthermore, an annular chamber 74 widened in the radial direction is created in the border area between the sealing element 48 and the valve cage or valve housing 34 thus formed in one piece. This annular chamber 74 enables fluid to flow off temporarily, said fluid passing through the gap formed between the valve seat 40 and the closing member 38 when the inlet valve is opened. The annular chamber 74 receives this fluid and thus reduces the pressure surges which would otherwise occur. It thus acts in a damping manner in terms of the pressure impulses produced. An undercut in the valve housing 34 is not necessary for the annular chamber 74, but is created merely by a stepped recess in the valve housing 34 in cooperation with the adjacent second part 62 of the piston 16, which is particularly favorable in terms of manufacture.

Claims

1. A piston pump comprising:

a piston;

a sealing element configured to seal the piston radially with respect to a cylinder; and

an inlet valve arranged on the piston, said inlet valve including a valve cage holding a closing member,

wherein the sealing element and the valve cage are one piece.

2. The piston pump as claimed in claim 1, wherein the sealing element and the valve cage are produced from plastic.

3. The piston pump as claimed in claim 1, wherein a spring support for a return spring supporting the piston relative to the cylinder is formed on the sealing element.

4. The piston pump as claimed in claim 3, wherein:

the sealing element includes a sealing lip resting against the cylinder, and

said sealing lip ends in an axially set-back manner relative to the spring support on the side facing away from the return spring.

5. The piston pump as claimed in claim 1, wherein:

the sealing element includes an axial groove, and

the axial groove is open towards the high-pressure area of the piston/cylinder arrangement.

6. The piston pump as claimed in claim 1, wherein the sealing element is configured in a stepped manner on its side facing the piston.

7. The piston pump as claimed in claim 1, wherein the sealing element surrounds the piston.

8. The piston pump as claimed in claim 1, wherein the piston is designed in two parts with a first part turned towards a drive and a second part turned towards the sealing element.

9. The piston pump as claimed in claim 8, wherein:

the first part is a solid cylinder, and

the second part is a hollow cylinder.

10. A vehicle brake system comprising:

a piston pump including (i) a piston, (ii) a sealing element configured to seal the piston radially with respect to a cylinder, and (iii) an inlet valve arranged on the piston, said inlet valve including a valve cage holding a closing member,

wherein the sealing element and the valve cage are one piece.