EP0932764A1

EP0932764A1 - Piston pump

Info

Publication number: EP0932764A1
Application number: EP98933502A
Authority: EP
Inventors: Heinz Siegel; Norbert Alaze
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-07-30
Filing date: 1998-05-12
Publication date: 1999-08-04
Also published as: WO1999006702A1; US20010048884A1; JP2001501274A

Abstract

The invention concerns a piston pump (10) for a vehicle antiskid hydraulic brake system. It aims at ensuring tightness and guidance of the pump (10) piston (20) in a packing (12). To this end, is provided a rigid plastic sealing element (76), with a spacing surface (80) in the form of an inner cone, against which is pressed a piston return spring (54) directly or via a spacer ring (82) having a corresponding conical surface (84). The sealing element (76) is thus sealingly pressed against the packing (12). The advantage of the invention lies in the fact that it is not necessary to resort to separate guide and sealing ring, thereby reducing friction and wear.

Description

Piston pump

State of the art

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

Piston pumps of this type are known per se. They have a piston which is received in an axially displaceable manner in a cylinder bore in a pump housing. A liner can be inserted into the pump housing or the piston can be accommodated directly in the pump housing. By means of an eccentric drive, the piston can be driven to perform a reciprocating stroke movement in the axial direction. In the known piston pumps, a sealing ring made of soft, rubber-like plastic, often an O-ring, is used for sealing between the piston and the cylinder bore in a piston groove or in a cylinder bore groove. The circumference of the piston can be guided directly in the cylinder bore. It is also known to guide the piston in the cylinder bore with a guide ring which, together with the sealing ring, is inserted into the piston groove or into the cylinder bore groove. The guide ring, which usually consists of a dimensionally stable plastic, has the advantage that it reduces friction and wear of the piston and the cylinder bore wall. Another advantage of a guide ring is that the piston and / or Cylinder bore with a larger diameter tolerance and lower surface quality can be produced.

With the seal, it is important that there is always sufficient elasticity so that the seal is always sufficiently biased against the sliding surface regardless of dimensional and shape tolerances and regardless of wear.

Because seals made of a material with sufficient elasticity of their own can only bridge very small gaps at elevated pressures, overall very tight dimensional and shape tolerances must be observed, which means that the effort to manufacture the piston pump is quite high. Often, a support ring is also required to ensure that the seal is not squeezed into the gap. The support ring also increases the manufacturing costs considerably.

The known piston pumps have the disadvantage that in addition to the sealing ring, an additional support ring and / or an additional plastic guide ring is required. Piston pumps without the guide ring have the disadvantage of greater piston friction, greater wear, tighter manufacturing tolerances of piston and cylinder bore diameters and a necessary, higher surface quality of the piston peripheral surface and the cylinder bore surface, which usually requires grinding or flaring of these surfaces.

Advantages of the invention

The piston pump according to the invention with the features of claim 1 has the advantage that because of the spring element biasing the seal against the sliding surface for the seal, a relatively stiff, little inherent elasticity, but particularly low friction and low wear material can be used. The fact that a very stiff and relatively inelastic material can be selected for the seal gives the advantage that even relatively large gaps can be permitted even at high pressures. As a result, relatively coarse dimensional and shape tolerances can be permitted even without the use of a separate support ring, which advantageously reduces the manufacturing outlay considerably. With the possibility of using a material with low friction and consequently low piston friction and low wear, the advantage of an improvement in the delivery rate and extension of the service life of the piston pump according to the invention is achieved without the need for a separate guide ring. The seal is elastically biased in the radial direction against a sliding surface by the spring element. Depending on the design, the seal is elastically expanded in the radial direction by the spring element and thereby pressed in sealing contact against a cylinder bore wall if the seal is axially immovable on the piston and axially displaceable together with the piston in the cylinder bore, or the seal is removed from the The spring element is compressed radially elastically, so that the seal lies sealingly on a piston circumferential surface when it is axially immovably mounted in the cylinder bore and the piston moves axially relative to the seal during its stroke movement. By using the spring element, which presses the seal in sealing contact with the sliding surface, it is possible to use a seal made of relatively stiff plastic, i.e. a material from which guide rings are otherwise made and which has low friction and low wear . A relatively soft, rubber-like plastic, as is usually used for sealing rings, is not suitable as a guide ring. A relatively rigid plastic is in itself not suitable for sealing, since it does not guarantee adequate sealing due to a lack of elasticity or insufficient elasticity, at least in the long run. A guide ring made of rigid plastic loses its sealing effect at the latest at a higher temperature or when there is a change in temperature. This problem is overcome with the aid of the spring element used according to the invention.

The spring element ensures that the seal is sufficiently resiliently biased against the sliding surface under all operating conditions. This gives the advantage of good tightness under all operating conditions, even when the hydraulic pressure is low and also when the seal is made of a relatively rigid material. As a result, the piston pump is advantageously also suitable for very different operating conditions; at low hydraulic pressure, the spring element ensures sufficient Preloading the seal against the sliding surface and for high hydraulic pressure, the material of the seal can be chosen to be sufficiently rigid.

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

In the case of a piston pump, a piston return spring, which is provided in a high-pressure working chamber of the piston pump and acts in the axial direction, presses the piston of the piston pump into constant contact against an eccentric. This acting in the axial direction piston return spring can be the task of

Take over the seal in the radial direction of the spring element. By appropriately selecting the inclination of the spreading surface, the desired force acting in the radial direction can be very easily matched to the force generated by the piston return spring and acting in the axial direction. The fact that the piston return spring can take over the task of the spring element gives the advantage that, overall, few components are required. Because the force of the piston return spring usually does not change during the entire service life of the piston pump, the force acting on the seal in the radial direction advantageously also remains constant, regardless of any wear between the seal and the

Sliding surface. As the preferred selected exemplary embodiments show, to provide the force acting on the seal against the sliding surface, no further spring element is advantageously required in addition to the piston back spring which is usually present anyway.

When the piston of the piston pump is fully retracted, the pressure in the high pressure working space of the piston pump is usually the highest, and when the piston is fully extended, the pressure in the high pressure working space is usually the lowest. When the piston is retracted, the force of the piston return spring is slightly greater than when the piston is extended. Because the force generated by the piston return spring is greatest when the pressure in the high-pressure working space is also greatest, the advantage of a good sealing effect is obtained even at high pressure and less wear at low pressure. In one embodiment of the invention, the seal has an expansion surface inclined to a radial direction, for example a conical ring surface, which is acted upon directly or indirectly by a force acting in the axial direction by a spring element, that is to say, for example, a helical compression spring. Due to the radially outward or inward inclination of the expansion surface, the axial force of the spring element is converted into a radial force which expands or compresses the seal radially and thereby holds it in sealing contact with the sliding surface, i.e. depending on the design on the cylinder bore wall or the piston circumference 4). The inclination of the expansion surface, which can change in the radial direction of the expansion surface, determines the ratio in which the axial force of the spring element is converted into a radial force sealing the seal against the sliding surface, so that the choice of the inclination of the expansion surface increases the the radial force exerted on the seal can be influenced in a targeted manner.

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

drawing

The invention is explained in more detail below on the basis of preferably selected exemplary embodiments shown in the drawing. The three figures show axial sections of three piston pumps according to the invention.

Description of the embodiments

The piston pump according to the invention shown in FIG. 1, generally designated 10, has a liner 12 which is inserted into a stepped pump bore 14 of a hydraulic block, which forms a pump housing 16. The hydraulic block, of which only a fragment surrounding piston pump 10 is shown in the drawing, is part of a slip-controlled hydraulic vehicle brake system, which is otherwise not shown. In addition to the piston pump 10, further hydraulic components such as solenoid valves and hydraulic accumulators are used in it and a master brake cylinder and wheel brake cylinder are connected. The hydraulic components are hydraulically interconnected by means of the hydraulic block.

A pin-shaped piston 20 is received in the liner 12 and protrudes a short distance from the liner 12 on one side. The end of the piston 20 protruding from the liner 12 is axially displaceably guided in the pump bore 14 in the pump housing 16 by means of a guide ring 22 and sealed with an O-ring 24 in the pump housing 16. For the fluid inlet, the piston 20 is provided with an axial blind bore 26 from its end located in the liner 12, which is crossed by transverse bores 28 near its base approximately in the longitudinal center of the piston 20. A nominal diameter of the piston 20 corresponds to an inner diameter of the liner 12, with a clearance fit between the piston 20 and the liner 12, ie the piston 20 has an undersize in relation to the liner 12 on, which ensures the axial displacement of the piston 20. The undersize of the piston 20 creates a circumferential gap between the piston 20 and the bushing 12. So that the bushing 12 does not touch even with unfavorable dimensional and shape tolerances of the piston 20, the gap must be of a sufficiently large size. The blind bore 26 and transverse bores 28 communicate through a wide groove 30 in the circumference of the piston 20 and radial bores 32 in the liner 12 with an inlet bore 34 which is radially attached to the piston pump in the pump housing 16 and opens into the pump bore 14 into which the liner 12 is inserted is.

As the inlet valve 36, the piston pump 10 according to the invention has a spring-loaded check valve which is attached to the end of the piston 20 located in the liner 12. An opening of the blind bore 26 is designed as a conical valve seat 38, against which a valve ball 40 as a valve closing body by a helical compression spring

Valve closing spring 42 is pressed. The valve closing spring 42 is supported against a bottom of a cup-shaped valve cage 44, which is made of sheet metal as a deep-drawn part and has passages 46. On its open side, the valve cage 44 has a circumferential ring step 48, with which it rests on the end face of the piston 20 located in the liner 12. An inwardly formed, free edge 50 of the valve cage 44 engages in the manner of a clip connection in a groove pierced into the piston 20, as a result of which the valve cage 44 is fastened to the piston 20. Valve ball 40 and valve closing spring 42 are received in valve cage 44.

To drive the piston 20 to a reciprocating movement in the axial direction, the piston pump 10 according to the invention has an eccentric 52 which can be driven by an electric motor, against the circumference of which the piston 20 is pressed by a piston return spring 54 which is designed as a helical compression spring and in the bushing 12 is arranged and is supported on the liner bottom 18.

A cylindrical closure element 56 is placed on the liner bottom 18 and connected to the liner 12 with a flange 58. The caulking element 59 closes the closure element 56 by caulking 59 of the pump housing 16 the pump bore 14 is pressure-tight and fixes the liner 12 in the pump housing 16. An outlet valve 60 in the form of a spring-loaded check valve is accommodated in the closure element 56: The closure element 56 has a coaxial blind bore 62 into which a helical compression spring as a valve closing spring 64 and a valve ball 66 as a valve closing spring are used. The valve ball 66 interacts with a conical valve seat 68, which is attached to an opening of a central bore 70, which axially penetrates the bushing base 18. The valve seat 68 is shaped and solidified by stamping. The fluid is discharged through radial channels 72 between the liner bottom 18 and the closure element 56 into an outlet bore 74 in the pump housing 16.

The free volume in the area of the groove 30 and the radial bore 32 serves as a low-pressure chamber 75 of the piston pump 10. Between the inlet valve 36 and the outlet valve 60 there is a high-pressure working chamber 77 of the piston pump 10. Enlarged or reduced in accordance with the extension and retraction movements of the piston 20 the volume of the high-pressure working space 77. For sealing the high-pressure working space 77 from the low-pressure space

75, the piston 20 has an annular, circumferential seal 76 which is placed on the end of the piston 20 located in the bushing 12 at an annular step 78, at which the piston 20 tapers towards its end located in the bushing 12. The seal 76 consists of a relatively rigid plastic, for example of PTFE (polytetrafluoroethylene), which has a low coefficient of friction. The seal 76 also serves to guide the piston 20 in the liner 12. In the selected embodiment, the seal can

76 are therefore also referred to as sealing and guide rings. Because the seal 76 can be made from a relatively rigid, dimensionally stable plastic, it can also bridge a relatively large gap between the piston 20 and the liner 12. This ensures good tightness and durability, even at high pressures. To turn on at high pressures

To prevent the seal from being pushed into the gap, a support ring has frequently been provided up to now. Such a support ring is not required in the piston pump 10 proposed here. The seal 76 shown by way of example has an almost rectangular ring cross section, an end face facing the bushing base 18 being conical as an expanding surface 80, or more precisely forming an inner cone, ie imaginary straight lines perpendicular to the expanding surface 80 run obliquely inwards. The piston return spring 54 presses a ring 82 inserted between it and the seal 76 in the axial direction against the seal 76 and via the ring step 78 of the piston 20 the piston 20 in contact with the circumference of the eccentric 52. The ring 82 serves as an expansion ring. The ring 82 is designed as a conical perforated disk with the same cone angle as the spreading surface 80. An end face of the ring 82 which bears against the spreading surface 80 of the seal 76 forms a counter surface 84 to the spreading surface 80. The piston return spring 54 presses the seal 76 radially via the ring 82 with the conical counter surface 84 which bears against the conical spreading surface 80 of the seal 76 apart in sealing contact with the liner 12. In the preferred embodiment selected, the inner circumference of the liner 12 serves as a sliding surface 85. During the stroke movements of the piston 20, the seal 76 slides on the sliding surface 85. An angle of inclination of the counter surface 84 and the expanding surface 80 to a radial direction Together with the friction between the ring 82 and the seal 76, determines the pressing force of the seal 76 on the bushing 12 in relation to the spring force of the piston return spring 54. The stiffness of the seal 76 is also determined, this stiffness depending on the material stiffness and the cross-sectional area of the seal 76 depends on the Kr aft, with which the seal 76 is pressed against the sliding surface 85. In order to use a sufficiently large, low-wear material for the seal 76 that presses the seal 76 against the sliding surface 85 even when using a stiff, low-wear material

To obtain radial force, the spreading surface 80 can be correspondingly more inclined with respect to the radial direction. The piston return spring 54 at the same time forms a spring element which expands the seal 76 radially and thereby ensures the seal towards the ^" liner 12. The seal 76 seals off the piston 20 by contacting the ring step 78 of the piston 20.

The counter surface 84 and the expansion surface 80 do not have to have the same inclination to the radial direction, in particular the counter surface and / or expansion surface can also be spherical or hollow, for example. The ring 82 serving as an expanding ring can, for example, also have a circular or semicircular ring cross section find use (not shown). The piston return spring 54 can also press directly against the expansion surface 80 of the seal 76 without the interposition of a ring.

In the exemplary embodiment of the invention shown in FIG. 2, the same seal 76 as in the piston pump 10 shown in FIG. 1 is used. However, the conical expansion surface 80 of the seal 76 faces the annular step 78 of the piston 20, which is conical as a counter surface 88 for the expansion surface 80. Via the interposed ring 82, the piston return spring 54 presses the annular circumferential seal 76 against the inclined counter surface 88, as a result of which the seal 76 is pressed radially apart from one another in sealing contact against the sliding surface 85 provided on the bushing 12. The ring 82 ensures that the seal 76 is not damaged by the piston return spring 54. Because a fairly rigid material can be used for the seal 76, the ring 82 can optionally also be dispensed with without the direct contact of the piston return spring 54 with the seal 76 causing damage to the seal 76.

Otherwise, the piston pump 10 shown in FIG. 2 corresponds to the piston pump 10 shown in FIG. 1. To avoid repetition, reference is made to the corresponding explanations for FIG. 1. The same components are provided with the same reference numbers.

In the first exemplary embodiment (FIG. 1), the end face of the seal 76 facing the ring 82 or the piston return spring 54 is inclined conically with respect to the radial direction. In the second exemplary embodiment (FIG. 2), that end of the seal 76 which faces away from the piston return spring 54, together with the ring step 78 of the piston 20, is conically inclined with respect to the radial direction. The piston pump 10 can also be modified such that both the end face of the seal 76 facing the ring 82 or the piston return spring 54 and the end face of the seal 76 facing the ring step 78 are conically inclined. In this case, the direction of inclination of the end face facing the ring 82 or the piston return spring 54 runs as shown in FIG. 1, and the direction of inclination of the end face of the seal 76 facing the ring step 78 is inclined as shown in FIG. 2. In this case, both serve End faces of the seal 76 as an expansion surface, whereby the inclination of the two expansion surfaces with respect to the radial direction can be quite small. As a result, a relatively strong loading of the seal 76 against the sliding surface 85 can be achieved even with a slight inclination of the two end faces of the seal 76.

In the exemplary embodiments shown in FIGS. 1 and 2, the piston 20 consists essentially of metal, and the seal 76, which can also serve as a guide for the piston 20 in the bushing 12 or directly in the pump housing 16, is a separate component on the Piston 20 attached. However, it is also possible to produce the piston 20 partially or entirely from plastic, and it is also possible to form the seal 76 in one piece on the piston 20 or on the part of the piston 20 made of plastic. FIG. 3 shows an embodiment in which the piston 20 essentially consists of a first piston part 20a and a second piston part 20b. Any sealing compound (not shown) applied between the two piston parts 20a, 20b ensures a good seal between these two parts. The first piston part 20a facing the eccentric 52 is made of metal, and the second pump part 20b accommodated in the liner 12 is made of plastic, preferably of a rigid, dimensionally stable plastic. In this embodiment, the seal 76 is integrally formed on the piston part 20b of the piston 20. The end face of the seal 76 facing the piston return spring 54 or the ring 82 is inclined conically or conically. The spreading surface 80 is located on this end face. As FIG. 3 shows, the inclination of the surface of the ring 82 lying against the spreading surface 80 of the seal 76 is adapted to the inclination of the spreading surface 80. The piston return spring 54 acts on the piston 20 in the axial direction, the force of the piston return spring 54 acting in the axial direction on the piston 20 due to the inclination of the expansion surface e 80 causing a force component acting on the seal 76 in the radial direction outward. In the exemplary embodiment shown in FIG. 3, the piston part 20b essentially only presses the area which is directly acted upon by the piston return spring 54 in the radial direction outward against the sliding surface 85, so that this area of the piston 20 performs the function of the seal 76 in an outstanding manner takes over, even if the piston 20 or the piston part 20b consists of a fairly stiff material with little inherent elasticity. The fact that the high pressure Work area 77 facing region of the piston 20 is biased in the radial direction elastically outwards against the sliding surface 85, there is an excellent seal of the high pressure work space 77 with respect to the low pressure space 75 and the low-pressure chamber 75 and for the guidance of the piston 20 within the bushing 12 and within the pump housing 16, no two separate components are required. Here too, a separate support ring protecting the seal 76 is not required even at high pressures.

In the piston pumps 10 according to the invention shown in the drawing, the end of the piston 20 protruding from the liner 12 can be made in the same way with a plastic seal, not shown, which is held by a spring element in sealing contact with the sliding surface instead of with a separate sealing ring 24 and the guide ring 22 must be sealed and guided, like the end of the piston 20 (not shown) located in the liner 12. This embodiment variant, not shown, has a seal that is permanently assigned to the pump housing 16 and is acted upon by the spring element in the radial direction against the sliding surface provided on an outer circumference of the piston.

Claims

claims

1. Piston pump, with a piston which can be driven to a reciprocating stroke movement and is axially displaceably guided in a cylinder bore, and with a seal which seals on a sliding surface, characterized in that the seal (76) is supported by a spring element (54 ) is applied radially against the sliding surface.

2. Piston pump according to claim 1, characterized in that the piston pump (10) has a piston return spring (54) which also forms the spring element.

3. Piston pump according to claim 1 or 2, characterized in that the seal (76) serves to guide the piston (20).

4. Piston pump according to one of claims 1 to 3, characterized in that the seal (76) has an expansion surface (80) with an inclination to a radial direction, and that the spring element (54) acts on the expansion surface (80) in the axial direction, so that the seal (76) is acted upon in the radial direction.

5. Piston pump according to one of claims 1 to 4, characterized in that the piston pump (10) has a counter surface (84, 88) to the expansion surface (80)

Gasket (76), the counter surface (84, 88) facing the expansion surface (80) and one of the inclination of the expansion surface (80) opposite Oriented inclination to a radial direction, and that the seal (76) with its expansion surface (80) is pressed by the spring element (54) against the counter surface (82, 84), so that the seal (76) is acted upon in the radial direction.

6. Piston pump according to claim 5, characterized in that the counter surface (84) is formed on a ring (82).

7. Piston pump according to claim 5, characterized in that the counter surface (88) is formed on the piston (20).

8. Piston pump according to claim 5, characterized in that the counter surface (88) is formed in the cylinder bore of the pump housing (16).

9. Piston pump according to claim 1, characterized in that the seal (76) is a plastic ring.

10. Piston pump according to one of the preceding claims, characterized in that the seal (76) is integrally formed on the piston (20).

11. Piston pump according to claim 9, characterized in that the seal (76) consists of PTFE (polytetrafiourethylene).