EP0935711A1

EP0935711A1 - Valve cap for the reduction of the clearance volume in radial piston pumps for motor vehicle brake systems

Info

Publication number: EP0935711A1
Application number: EP98943656A
Authority: EP
Inventors: Heinz Siegel; Dieter Merklein; Joachim Ehrlich; Andreas Weh; Michael Hellebrandt; Tobias Fluck; Michael Schlitzkus
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-07-30
Filing date: 1998-07-08
Publication date: 1999-08-18
Also published as: WO1999006704A1; DE19747850A1; JP2001501282A; US20010002978A1

Abstract

The invention relates to a piston pump (34) especially for a hydraulic slip regulating device of a motor vehicle braking system. In order to reduce the clearance volume of the piston pump (34), the invention provides a displacement body (104) fastened by means of a retaining device (98) onto the piston (66). The displacement body (104) is projected into the interior area of a valve closing spring (92) configured in the form of a coil of the inlet valve (88) that is integrated within the piston (66). The rectangular shaped coil cross section construction of the valve closing spring (92) and of the piston return spring (72) serves to reduce the clearance volume of the piston pump (34). The reduction of the clearance volume increases the efficiency of the piston pump (34).

Description

VALVE ADAPTER FOR REDUCING THE DEAD SPACE IN RADIAL PISTON PUMPS FOR VEHICLE BRAKE SYSTEMS

State of the art

The invention relates to a piston pump according to the type of the main claim, which is provided in particular for a hydraulic vehicle brake system with a slip control device.

Such a piston pump is known for example from DE 44 07 978 A1. The known piston pump has a piston which can be driven to a reciprocating stroke movement. During its stroke movement, the piston reduces and increases a volume of a displacement space of the piston pump. When the volume of the displacement space is reduced, fluid is displaced; this is a delivery stroke of the piston pump. When the volume of the displacement space is increased, fluid is sucked in; this is a suction stroke of the piston pump.

Advantages of the invention

The piston pump according to the invention with the features of the main claim has a displacement body which is arranged in the displacement space. This displacement body reduces an available volume of the displacement space, it is in particular designed so that a residual or dead volume remaining at the end of the delivery stroke is as small as possible. This improves the efficiency of the piston pump according to the invention.

The piston pump is provided in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS or ASR or FDR or EHB are used for such brake systems. In the brake system, the pump is used, for example, to return brake fluid from a wheel brake cylinder or from several wheel brake cylinders to a master brake cylinder (ABS) and / or to convey brake fluid from a reservoir into a wheel brake cylinder or into several wheel brake cylinders (ASR or FDR or EHB) . The pump is required, for example, in a brake system with wheel slip control (ABS or ASR) and / or in a brake system (FDR) serving as a steering aid and / or in an electro-hydraulic brake system (EHB). With the

Wheel slip control (ABS or ASR) can, for example, prevent the wheels of the vehicle from locking during braking when the brake pedal (ABS) is pressed hard and / or the driven wheels of the vehicle are spinning when the accelerator pedal (ASR) is pressed hard. In the case of a brake system serving as a steering aid (FDR), brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or accelerator pedal, for example in order to prevent the vehicle from breaking out of the lane desired by the driver. The pump can also be used in an electrohydraulic brake system (EMS) in which the pump delivers the brake fluid into the wheel brake cylinder or in the wheel brake cylinders when an electric brake pedal sensor detects an actuation of the brake pedal or in which the pump for filling a memory of the brake system serves.

The subclaims relate to advantageous refinements and developments of the invention specified in the main claim.

drawing The invention is explained below with reference to two exemplary embodiments shown in the drawing. 1 and 2 show axial sections of two exemplary embodiments of piston pumps according to the invention, FIG. 3 shows an end view of a holding part of the piston pump shown in FIG. 2 and FIG. 4 shows a modification of the piston pump shown in FIG.

Description of the first embodiment

The piston pump according to the invention shown in FIG. 1, designated overall by 10, has a pin-shaped piston 12 which is axially displaceably guided in a plastic bushing 14. The liner 14 is inserted into a hydraulic block of a hydraulic vehicle brake system, which is not otherwise shown, which forms a pump housing 16. In the hydraulic block, of which only one fragment surrounding the piston pump 10 is shown in the drawing, further hydraulic components, such as solenoid valves (not shown) are inserted and hydraulically connected to one another and to the piston pump 10.

An end face of the liner 14 is closed with a disk-shaped closure element 18, which by caulking 20

Pump housing 16 is fixed in this. The liner 14, the piston 12 and the closure element 18 enclose a displacement space 22 of the piston pump 10. In the displacement space 22, a helical compression spring is arranged as a piston return spring 24, which is supported on the closure element 18 and which supports the piston 12 against a peripheral surface of an eccentric 26 which can be driven by an electric motor presses, by means of which the piston 12 can be driven in a manner known per se to a reciprocating stroke movement in the liner 14.

Two spring-loaded check valves 28 are provided as inlet and outlet valves outside of the liner 14, in the hydraulic block forming the pump housing 16, which are shown symbolically in FIG. The check valves 28 communicate with the displacement space 22 via a radial bore 30 in the liner 14. In the interior of the piston return spring 24 there is a displacement body 32 which largely fills the interior of the piston return spring 24. The displacement body 32 is pin-like, it protrudes in one piece from the closure element 18. The displacement body 32 reduces the volume available in the displacement space 22 for fluid that can be pumped with the piston pump 10, in particular the volume available at the end of a delivery stroke when the piston 12 is in its most inserted position in the sleeve 14, the so-called residual volume available in the displacement chamber 22, the so-called Dead space to a minimum. This improves the efficiency of the piston pump 10. It also serves to minimize the dead space that the wire of the piston return spring has a rectangular winding cross section. Instead of a rectangular winding cross section, other cross sections, for example parallelogram or roof-shaped winding cross sections, whose facing winding surfaces are approximately complementary, can be selected in order to reduce a gap between the spring windings and thus the dead space when the piston return spring 24 is compressed. The piston return spring 24 largely fills an annular space between the displacement body 32 and the liner 14. The displacement body 32 can also be provided as a peg-like extension on the piston 12 and extend into the interior of the piston return spring 24 (not shown).

Description of the second embodiment

The piston pump 34 according to the invention shown in FIG. 2 is inserted into a pump housing 36 which is formed by a hydraulic block of a hydraulic vehicle brake system, which is otherwise not shown. In the hydraulic block, of which only a fragment surrounding piston pump 10 is shown in the drawing for the sake of clarity, further hydraulic components, such as solenoid valves and the like, are inserted and hydraulically connected to one another and to piston pump 34. The piston pump 34 has a liner 38 with a liner base 40 which is integral with it and which is pressed into a cylinder bore 42. A cylindrical sealing plug 46 is attached to the liner bottom 40 by means of a Bördeis 44. The plug 46 is fixed in the pump housing 36 by caulking 48 and closes one end of the cylinder bore 42 pressure tight. In a blind hole 50 of the plug 46, a check valve is used as an outlet valve 52, which has a valve ball 54 as a valve closing body, which is pressed by a helical compression spring as a valve closing spring 56 against a conical valve seat 58, which is formed at an opening of an axial through hole 60 in the liner bottom 40 is. An outlet is through a radial outlet bore 62 in the plug 46 which communicates with an outlet bore 64 in the pump housing 36.

A piston 66 of the piston pump 34 according to the invention is designed as a composite part with a steel core 68, which is overmolded on its circumference with a sliding jacket 70 made of plastic. A suitable plastic for the sliding jacket is, for example, a fiber plastic with about 15% carbon fibers and with Teflon components, which give the sliding jacket 70 good sliding properties. With its sliding jacket 70, the piston 66 is slidably guided in the axial direction in the cylinder bore 42 or in the liner 40.

An end face of the steel core 68 of the piston 66 facing away from the liner bottom 40, which protrudes from the liner 38, is exposed, i. H. it is not covered by the sliding jacket 70. This end face of the steel core 68 forms a sliding surface 72, with which the piston 66 is pressed by a piston return spring 74 against a circumference of an eccentric 76 which can be driven by an electric motor and with which the piston 40 can be driven to a reciprocating stroke movement in the axial direction. The sliding surface 72 is designed to be low-wear by using a low-wear material for the steel core 68 or by hardening the steel core 68.

The steel core 68 is an essentially cylindrical part that is very easy to produce in terms of shape. The sliding jacket 70 surrounds the circumference of the steel core 68 with a hollow cylindrical section 78, it extends on an end face of the steel core 68 facing away from the eccentric 76, the steel core 68 or the piston 66 extending into the bushing 38. The section 80 of the sliding jacket 70 which extends the piston 66 has a transverse hole 82 which penetrates an axial blind hole 84 which is likewise provided in the section 80 of the sliding jacket 70 which extends the piston 66. The blind hole 84 widens to form a conical valve seat 86 and opens at one of the Liner bottom 40 facing end of the piston 66. In the enlarged part of the blind hole 84, a check valve is used as the inlet valve 88, which has a valve ball 90 as a valve closing body, which is pressed by a helical compression spring as a valve closing spring 92 against the valve seat 86. The transverse hole 82 in the piston 66 communicates through a cylindrical filter screen 94, which is attached to an open end face of the bush 38, with an inlet channel 96, which is attached radially to the piston pump 34 in the pump housing 36. The valve closing spring 92 is supported on a holding part 98 which is attached to the end face of the piston 66 facing the liner bottom 40. The holding part 98 has a perforated disk-shaped edge 100 which is pressed by the piston return spring 74 against the end face of the piston 66 facing it, as a result of which the holding part 98 is held on the piston 66. The holding part 98 is shown in front view from the direction of the piston 66 in FIG. 3. Four angled retaining webs 102 protrude from a side facing away from the piston 66 and are integral with the perforated disk-shaped edge 100. The holding webs 102 hold a cylindrical displacement body 104 which is integral with them and which stands coaxially through the perforated disk-shaped edge 100 of the holding part 98. There is an annular space between the displacement body 104 and the perforated disk-shaped edge 100, so that fluid flowing through the inlet valve 88 into the piston pump 34 can flow through the perforated disk-shaped edge 100 and between the holding webs 102 into a displacement space 106 of the piston pump 34.

The valve closing spring 92, which is supported on the holding webs 102 of the holding part 98, has, like the piston return spring 74, a rectangular winding cross section. The rectangular winding cross section of these two springs 74, 92, like the displacement body 104, serves to reduce the volume of the displacement space 106 of the piston pump 34, which is available to a fluid that can be pumped by the piston pump 34.

In particular, the dead volume of the displacement space 106, which remains with the piston 66 pushed farthest into the liner 38, is reduced by the displacement body 104 and the springs 74, 92 with their rectangular winding cross sections, thereby increasing the efficiency of the piston pump 34 according to the invention. The displacer 104 of the in The piston pump 34 shown in FIG. 2, like the displacement body 32 of the piston pump 10 shown in FIG. /, Can be designed such that it largely fills the dead volume in the displacement space 106, thereby reducing the dead volume to a minimum and increasing the efficiency of the piston pump 34.

In the extension of the holding webs 102, the holding part 98 has four integral parts which protrude from its perforated disk-shaped edge 100 into the blind hole 84

Centering fingers 108, which hold the holding part 98 coaxially on the piston 66. In the illustrated embodiment, the centering fingers 108 have an interference fit in the blind hole 84, i. H. the holding part 98 is by a

Clamping connection frictionally connected to the piston 66. The connection of the holding part 98 to the piston 66 serves to hold the holding part 98 against the force of the valve closing spring 92 on the piston 66 until it is inserted into the bushing 38 and the holding part 98 is held on the piston 66 by the piston return spring 74. The connection of the holding part 98 to the piston 66 can, for example, also take place in a form-fitting manner by means of a snap-in or snap-in connection which is not shown, known per se, or integrally, for example by gluing.

The displacement body 104 limits an opening stroke of the valve ball 90 of the inlet valve 88, it forms a valve stroke limitation. This valve stroke limitation reduces the force with which the valve ball 90 strikes the valve seat 86 when the inlet valve 88 closes and thereby reduces wear on the valve seat 86. This is particularly important if the valve seat 86 is formed from a soft material. As a result, a long service life is achieved in the case of a valve seat 86 which is molded from plastic, as in the exemplary embodiment shown. Since the displacement body 104 forming the valve stroke limiter is made of plastic, the valve stroke limiter can be produced with a more precise measure than a valve stroke limiter manufactured, for example, as a sheet metal deep-drawn part.

Since the centering fingers 108 align the holding part 98 exactly in alignment with the blind hole 84 and the valve seat 86 in the piston 66 and the holding part 98 centers the valve closing spring 92, the valve ball 90 is also guided in alignment with the valve seat 86 when the inlet valve 88 is open. The holding part 98 also forms a guide and sealing element for the piston 66 of the piston pump 34 according to the invention: The holding part 98 has a low, hollow-cylindrical edge 110 which, in one piece from the perforated disk-shaped edge 100 on the circumference of the piston 66, a short distance into an annular space between the piston 66 and the sleeve 38 protrudes. This hollow cylindrical edge 110 and a peripheral edge of the perforated disk-shaped edge 100 of the holding part 98 guide the piston 66 in the liner 38.

On the other side, like the hollow cylindrical edge 110, ie away from the piston 66, a circumferential sealing lip 112 protrudes in one piece from the perforated disk-shaped edge 100 of the holding part 98. The sealing lip 112 is also in one piece with the holding part 98. An expansion ring 114 with a conical expansion surface 116 on its circumference lies between the piston return spring 74 and the sealing lip 112 of the holding part 98. The expanding ring 114 is pressed in the axial direction by the piston return spring 74 against an approximately hollow-conical inner surface 118 of the sealing lip 112, in this way spreads the sealing lip 112 radially and presses it in sealing contact against an inner wall of the bushing 38 the piston return spring 74 ensures a permanently elastic expansion behavior of the sealing lip 112 and thus a permanently reliable sealing of the piston 66 in the liner 38. The spreading force with which the sealing lip 112 is pressed against the inner wall of the bushing 38 can be set via the cone angles of the expanding surface 116 of the expanding ring 114 and the inner surface 118 of the sealing lip 112. The holding part 98 is made of the same plastic as the sliding jacket 70, it is low-wear and has good sliding properties. The plastic holding part 98 is inexpensive to manufacture.

Another advantage of the holding part 98 attached to an end face of the piston 66 is that it protects this end face of the piston against damage before and during the insertion of the piston 66 into the liner 38.

The piston pump 120 shown in FIG. 4 is a modification of the piston pump 34 shown in FIG. 2 according to the invention. The holding part 98 of FIG The piston pump 120 shown in FIG. 4 has no sealing lip and no hollow cylindrical edge for piston guidance. The piston 66 is guided in the liner 38 directly on the outer circumference 122 of the piston 66. To seal the piston 66 in the liner 38, a rubber sealing ring 124 is placed on an annular step 126 of the piston 66, with which the piston 66 engages on it tapered end located in the liner 38. The perforated disk-shaped edge 100 of the holding part 98 holds the sealing ring 124 axially on the piston 66. The sealing ring 124 can be pushed onto the ring step 126 before the holding part 98 is connected to the piston 66. This makes it much easier to attach the sealing ring 124 to the piston 66. Otherwise, the piston pump 120 shown in FIG. 4 is of the same design and functions in the same way as the piston pump 34 shown in FIG. 2. To avoid repetition, the comments on FIG. 2 are referred to in this respect. The same components are labeled with the same reference numbers.

Claims

claims

1. Piston pump with a piston which can be driven to a reciprocating stroke movement, and with a displacement space, the volume of which is reduced and enlarged during the stroke movement of the piston, characterized in that the piston pump (10; 34; 120) has a displacement body (32; 104), which is arranged in the displacement space (22; 106).

2. Piston pump according to claim 1, characterized in that the piston pump (10; 34; 120) has a coil spring (24; 74, 92), in the interior of which the displacement body (32; 104) is arranged.

3. Piston pump according to claim 2, characterized in that the helical spring (24; 74, 92) has spring windings, the mutually facing wind ungsf are essentially complementary to each other.

4. Piston pump according to claim 3, characterized in that the spring windings have a rectangular cross section.

5. Piston pump according to claim 2, characterized in that the coil spring is a piston return spring (24; 74).

6. Piston pump according to claim 2, characterized in that the

Piston pump has a check valve (88) and that the coil spring is a valve closing spring (92) of the check valve (88).

7. Piston pump according to claim 1, characterized in that the piston (66) has a check valve (88), the valve closing body (90) of a αm piston (66) attached holding part (98) on the piston (66) is held, and that Holding part (98) has the displacement body (104).

8. Piston pump according to claim 7, characterized in that the displacement body (104) limits an opening stroke of the valve closing body (90).

9. Piston pump according to claim 5 or 6, characterized in that the holding part (98) centers the coil spring (74, 92).

10. Piston pump according to one of claims 7 to 9, characterized in that the holding part (98) has a centering device (108) which engages in a hole (84) in the piston (66) and the holding part (98) on the piston (66 ) aligns.

11. Piston pump according to claim 10, characterized in that the holding part (98) via its centering device (108) is non-positively, positively and / or cohesively connected to the piston (66).

12. Piston pump according to claim 7, characterized in that the holding part (98) is designed as a guide element which guides the piston (66) in a cylinder bore of the piston pump (34).

13. Piston pump according to claim 7, characterized in that the holding part (98) is designed as a sealing element which seals the piston (66) on a wall of the cylinder bore.

14. Piston pump according to claim 7, characterized in that the holding part (98) is a plastic part.