Piston Pump

PRIOR ART

The invention relates to a piston pump for a hydraulic vehicle brake system having a slip control system, the brake system having the features of the preamble of claim 1. Slip control systems for vehicle brake systems are known and they are generally implemented as antilock (brake), traction control and/or vehicle dynamics or antiskid control systems. Customary abbreviations are ABS, ASR, FDR and ESP. The piston pumps are used to build up a hydraulic pressure for slip control and are often referred to as return pumps. The piston pump can also be used to build up a hydraulic pressure in a vehicle brake system which employs an independent hydraulic energy source.

Piston pumps for slip-controlled vehicle brake systems are known. They have a cylinder and a piston, which can be moved axially in the cylinder and can be driven so as to perform an axially reciprocating stroke motion in the cylinder. In many cases, the cylinder or cylinders of piston pumps for slip control systems of vehicle brake systems are designed as cylindrical bores in a “hydraulic block”, which, in addition to the piston pump, contains further hydraulic components for slip control, such as solenoid valves, hydraulic accumulators and check valves, and connects them hydraulically. In many cases, the stroke motion is imparted to the piston of such piston pumps by an eccentric, which can be driven in rotation by means of an electric motor and on the circumference of which the piston rests by means of an end face. A piston return spring, which is arranged at an end of the piston facing away from the eccentric, holds the piston end face that faces the eccentric in contact with a circumference of the eccentric.

The pistons of known piston pumps are sealed off in the cylinder by means of a sealing ring, which is supported axially on a side facing away from a pump chamber by a support ring. The pump chamber is a space in the cylinder, the volume of which is increased and reduced alternately during the reciprocating stroke motion of the piston in order alternately to draw in and displace brake fluid, i.e. to deliver brake fluid. The pump chamber is situated at the end of the piston facing away from the eccentric. The sealing ring is generally composed of a rubber-elastic material, while the support ring is composed of a rigid plastic, the intention being that it should be deformed only slightly, if at all, when subjected to pressure. The function of the support ring is to provide axial support for the sealing ring, preferably over as large an area as possible, in order to avoid extrusion of the sealing ring into a gap when subjected to pressure. In piston pumps for slip control in hydraulic vehicle brake systems, pressures of up to 280 bar, for example, can occur and act on the sealing ring. Extrusion into a gap means flowing, i.e. plastic, deformation of the sealing ring into a gap between the piston and the cylinder. The sealing ring is subjected to pressure on the side facing the pump chamber, and the sealing ring is supported by the support ring on the opposite side, i.e. the side facing away from the pump chamber.

DISCLOSURE OF THE INVENTION

According to the invention, the support ring has at least one longitudinal passage for fluid, i.e. for brake fluid. By means of the longitudinal passage, the side of the support ring facing the sealing ring communicates with the side thereof facing away from the sealing ring. As a result, a pressure buildup between the sealing ring and the support ring is avoided, with a pressure between the sealing ring and the support ring being relieved via the longitudinal passage. A pressure between the sealing ring and the support ring can arise as a “drag pressure” when there is drag leakage between the sealing ring and the cylinder during the stroke motion of the piston in the cylinder. A pressure buildup between the sealing ring and the support ring would shift the sealing ring away from the support ring and, as already explained, is avoided by means of the at least one longitudinal passage in the support ring.

The sealing ring and the support ring are usually arranged on the piston, i.e. move with the piston. The opposite situation, in which the sealing ring and the support ring are arranged in the cylinder and are stationary with the latter, is also conceivable.

The advantage of the invention is the possibility of relatively large-area axial support of the sealing ring by the support ring over an annular area with an outside diameter which corresponds to an inside diameter of the cylinder and with an inside diameter which corresponds to an outside diameter of the piston, in each case at the location where the sealing ring and the support ring are situated. Only the cross section of the at least one longitudinal passage, at the mouth thereof facing the sealing ring, does not participate in the supporting cross-sectional area.

The dependent claims relate to advantageous embodiments and developments of the invention indicated in claim 1.

The design of the longitudinal passage as a longitudinal groove on an outer or inner circumference of the support ring as claimed in claim 2 has the advantage that the support ring is simple to produce in comparison, for example, with a through hole through the support ring, which would likewise be possible as a longitudinal passage.

Claim 3 provides the support ring according to the invention on a “compensating piston”. Said piston is driven like a pump piston by means of an eccentric, in particular by means of the same eccentric as the pump piston or pistons, but said compensating piston and the cylinder thereof do not have any fluid control, i.e. in particular, do not have either inlet or outlet valves. The compensating piston communicates with the pump piston or pistons of the piston pump and reduces the pressure pulsation thereof. With its cylinder, it can be understood as a hydraulic accumulator, the volume of which varies in synchronism with the stroke motion of the pump piston or pump pistons. The compensating piston and the cylinder thereof do not require a separate inlet and outlet, one connection being sufficient, although separate inlets and outlets are not excluded.

Claim 4 provides an encircling bead on an outside and/or inside of the sealing ring, the crest of which bead rests in a sealing manner on the cylinder and/or the piston.

The word “crest” refers to the “highest” part of the bead, i.e. the part of the bead which runs around at a point radially furthest toward the outside or furthest toward the inside, and, according to claim 5, the encircling bead is preferably formed on a sealing ring with an otherwise quadrilateral ring cross section. The quadrilateral basic shape of the ring cross section makes it possible to achieve high resistance to pressure by the sealing ring, with the sealing ring being comparatively massive. The design of the sealing region of the sealing ring as a bead likewise allows relatively massive design and hence high resistance to pressure. The importance of resistance to pressure, especially of the sealing region of the sealing ring, is not exclusively in avoiding destruction of the sealing ring but also in keeping deformation of the sealing region to such a low level, when pressure is imposed from one side, that the sealing effect is as far as possible unimpaired. Another advantage of the sealing ring designed in accordance with the invention is the pressure activation thereof: when subjected to pressure, the sealing ring is compressed axially and expands radially outward and/or inward, resulting in an increase in a contact force on the cylinder and/or the piston. A good sealing effect, both at low pressure and high pressure is thus achieved, and it is possible for the contact force at low pressure to be low in order to reduce friction and wear.

Claim 6 provides a cylinder closed at one end. This has the advantage that the end of the cylinder does not have to be closed by means of a separate component.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in greater detail below with reference to an embodiment illustrated in the drawing, in which:

FIG. 1 shows a piston and a cylinder in accordance with the invention in an axially sectioned view;

FIG. 2 shows a support ring according to the invention for the piston in FIG. 1 in a perspective view;

FIG. 3 shows a sealing ring according to the invention for the piston from FIG. 1 in a perspective half section; and

FIG. 4 shows a schematic of a piston pump according to the invention.

EMBODIMENT OF THE INVENTION

The piston 1 illustrated in FIG. 1 is accommodated in an axially movable manner in a cylinder 2. At one end, the piston 1 protrudes from the cylinder 2, while the other end of the cylinder 2 is of closed design by virtue of a base 3, which is an integral part of the cylinder 2. The piston 1 encloses an accumulator chamber 4 in the cylinder 2 between it and the base 3.

The piston 1 can be driven by means of an eccentric 5, which can be driven in rotation about an eccentric axis of rotation by means of an electric motor (not shown), so as to perform an axially reciprocating stroke motion in the cylinder 2. During the reciprocating stroke motion, the piston 1 alternately increases and reduces a volume of the accumulator chamber 4, with the result that fluid is alternately taken up and discharged.

Arranged in the accumulator chamber 4 is a piston return spring 6, which is supported on the base 3 of the cylinder 2 and presses against the piston 1 in the axial direction via a spring holder 7 and holds the end of the piston which protrudes from the cylinder 2 in contact with a circumference of the eccentric 5. The spring holder 7 is a deep drawn part made of sheet metal, which is in the form of a shallow dish and has a broad flange-like rim 8, against which the piston return spring 6 presses. The spring holder 7 is mounted on a coaxial extension 9 of reduced diameter of the piston 1, said extension being an integral part of the piston 1. A sealing ring 11 and a support ring 12 are mounted on the extension 9 of the piston 1 between the rim 8 of the spring holder 7 and an annular shoulder 10 of the piston 1 at the transition to the extension 9. The sealing ring 11 is arranged on a side of the support ring 12 which faces the accumulator chamber 4.

The support ring 12 illustrated in FIG. 2 has a square ring cross section with chamfers 13 on an inner side of the support ring 12. On the outer circumference, the support ring 12 has three longitudinal grooves 14 as longitudinal passages for fluid. On the outside, the support ring 12 rests against the cylinder 2 and, on the inside, rests against the extension 9 of the piston 1. It is composed of a rigid material, e.g. of a PTFE (polytetrafluoroethylene) or a polyamide, such as PA 6.6, and can contain carbon.

As can be seen in FIG. 3, the sealing ring 11 has a rectangular ring cross section, likewise with chamfers 15 on the inside, and an encircling bead 16 on the outer circumference. A crest 17 of the bead 16 rests in a sealing manner on the cylinder 2. The crest 17 is that region of the bead 16 which is furthest out radially and, in the embodiment illustrated, the crest 17 is rounded. The crest 17 is an encircling feature, like the bead 16. The sealing ring 11 is composed of a flexible material, e.g. an elastomer such as EPDM (ethylene propylene diene rubber).

FIG. 4 shows, in schematic form, a multi-piston pump 18 according to the invention, which has the piston 1 and the cylinder 2 from FIG. 1. The multi-piston pump 18 is intended for hydraulic vehicle brake systems, e.g. as a return pump in a vehicle brake system with an antilock, traction control and/or vehicle dynamics or antiskid control system. Customary abbreviations for such control systems are ABS, ASR, FDR and/or ESP. Another possible use for the multi-piston pump 18 is in electro-hydraulic vehicle brake systems (abbreviated to EHB). These are power brake systems, in which the service brake pressure required for braking is produced by means of a piston pump which is part of an independent energy supply device. The multi-piston pump 18 is provided for a brake circuit.

The multi-piston pump 18 has three pistons 1, 19, which are arranged in a star shape around the eccentric 5, part of which is also shown in FIG. 1. The pistons 1, 19 are accommodated in an axially movable manner in cylinders 2, 20, which are inserted into pump bores in a hydraulic block (not shown). In addition to the cylinders 2, 20, the hydraulic block contains further hydraulic components, such as hydraulic accumulators and solenoid valves of a slip control system, which are connected hydraulically by bores, which form brake fluid lines. The hydraulic block is not shown in the drawing; it is a known feature of slip control devices of this kind. The piston 1 and the cylinder 2 from FIG. 1 are illustrated schematically at the bottom in FIG. 4.

The eccentric 5 can be driven in rotation by means of an electric motor (not shown in the drawing) about an axis of rotation 22, with respect to which the eccentric 5 is eccentric. When driven in rotation, the eccentric 5 moves on an orbital path around the axis of rotation 22. The axis of rotation 22 is located at a point of intersection between imaginary longitudinal axes of the pistons 1, 19.

Piston return springs 6, 23, which hold the pistons 1, 19 in contact with the circumference of the eccentric 5, are arranged in the cylinders 2, 20, at the ends of the pistons 1, 19 facing away from the eccentric 5. When driven in rotation, the eccentric 5 drives the pistons 1, 19 so that they perform reciprocating stroke motions in the cylinders 2, 20.

The two pistons 19 illustrated at the top in FIG. 4 have a fluid control system, which comprises an inlet valve 24 and an outlet valve 25. The inlet valves 24 are integrated into the pistons 19, although this is not absolutely essential. The valves 24, 25 are designed as check valves and control the direction of flow of brake fluid. Brake fluid flows radially through a transverse hole into the pistons 19 and then through an axial hole through the inlet valve 24, which is integrated into the pistons 19, into a pump chamber in the cylinder 20. The brake fluid flows out of the pump chamber through the outlet valve 25. The flow and delivery of brake fluid in piston pumps is known. The two pump pistons 19 which have the fluid control system comprising the inlet valves 24 and the outlet valves 25 are referred to below as pump pistons 19. The inlets 26 thereof are interconnected, as are the outlets thereof, which form a common outlet 27 of the multi-piston pump 18.

Both pump pistons 19 are arranged in a V arrangement with an angular offset of, for example, 90°. This results in a phase shift in the delivery flows of the two pump pistons 19, likewise of 90°, and a pulsating flow of brake fluid in the outlet 27.

The third piston 1, which corresponds to the piston 1 from FIG. 1, is referred to below as compensating piston 1, and it has no valves and no fluid control system. It is arranged on an angle bisector of the two pump pistons 19 and is arranged opposite the two pump pistons 19, relative to the eccentric 5, resulting overall in the star arrangement of the pistons 1, 19. By virtue of the arrangement on the angle bisector, opposite the two pump pistons 19, the compensating piston 1 pumps in phase opposition to the common delivery flow of the two pump pistons 19. The compensating piston 1 has just one connection 28, which is connected to the outlet 27, i.e. the compensating piston 1 communicates with the two pump pistons 19. The connection 28 is routed through intersecting radial holes 29 in the cylinder 2 of the compensating piston 1 (cf. FIG. 1). During its stroke motion, the compensating piston 1 alternately draws in brake fluid from the outlet 27 and then displaces the brake fluid volume drawn in back into the outlet 27. Since the compensating piston 1 is driven in phase opposition to the two pump pistons 19, the compensating piston 1 draws in brake fluid when the delivery flow of the pump pistons 19 is large. When the pump pistons 19 are not delivering any brake fluid during their return stroke, the compensating piston 1 displaces brake fluid, with the result that the multi-piston pump 18 according to the invention has a delivery flow at the outlet 27 even when the two pump pistons 19 are not delivering during the return stroke. The compensating piston 1 thus reduces the maximum delivery flow of the pump pistons 19 and increases or brings about a delivery flow when the two pump pistons 19 are delivering little or nothing. A pressure pulsation of the multi-piston pump 18 is reduced and is approximately equal to a pressure pulsation of a comparable multi-piston pump which has four pump pistons with fluid control.

For the same stroke, a piston area of the pump pistons 19 is larger by a factor of √2 than a piston area of the compensating piston 1. The same stroke is obtained by driving all the pistons 1, 19 with the common eccentric 5.

The longitudinal grooves 14 of the support ring 12 avoid a pressure buildup between the sealing ring 11 and the support ring 12 due to “drag leakage” past the sealing ring 11 during a stroke motion of the piston 1. Drag leakage is caused by brake fluid which adheres to the cylinder 2 as a lubricating film and, during the stroke of the piston 1 in the direction of the accumulator chamber 4, is overridden by the sealing ring 11 and by the support ring 12, and a small part of which is scraped off during a return stroke in the opposite direction. The encircling bead 16 with the encircling crest 17 resting in a sealing manner on the cylinder 2 leads to a good sealing effect. The comparatively massive encircling bead 16 imparts a comparatively high stability to the sealing ring 11, which is composed of a flexible material, thus ensuring that the sealing ring 11 withstands even the high pressures which are produced with the multi-piston pump 18 in a hydraulic vehicle brake system.

Like the compensating piston 1, the pump pistons 19 can have an extension 2, on which a sealing ring 11 and a support ring 12 are arranged, as illustrated in FIGS. 1 to 3 and explained above with reference to said figures. The space enclosed in the cylinders 2, 20 by the pistons 1, 19 is referred to as a pump chamber in the case of the pump pistons 19 and as an accumulator chamber 4 in the case of the compensating piston 1.

Piston Pump

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