DE19747850A1 - Piston pump - Google Patents

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

State of the art

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

Such a piston pump is known for example from DE 44 07 978 A1. The known piston pump has a reciprocating Stroke driven piston. Reduced during its lifting movement and the piston increases a volume of a displacement space of the piston pump. When the volume of the displacement space is reduced, fluid becomes displaced, this is a delivery stroke of the piston pump. When enlarging the Volume of the displacement space is sucked in fluid, this is a suction stroke 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, it is particularly designed so that at the end of the Remaining or dead volume is as small as possible.  

This makes an efficiency of the piston pump according to the invention improved.

The piston pump is in particular a pump in a brake system Vehicle is provided and is used in controlling the pressure in wheel brake cylinders used. Depending on the type of brake system, the brake systems for such Abbreviations ABS or ASR or FDR or EHB are used. In the The brake system is used, for example, to return the pump Brake fluid from a wheel brake cylinder or from several Wheel brake cylinders in a master brake cylinder (ABS) and / or for conveying of brake fluid from a reservoir into a wheel brake cylinder or in several wheel brake cylinders (ASR or FDR or EHB). The pump will for example in a brake system with wheel slip control (ABS or ASR) and / or with a braking system (FDR) serving as a steering aid and / or required for an electro-hydraulic brake system (EMS). With the Wheel slip control (ABS or ASR) can, for example, block the Wheels of the vehicle during braking when the pressure is high Brake pedal (ABS) and / or a spinning of the driven wheels of the Vehicle with strong pressure on the accelerator pedal (ASR) can be prevented. At a brake system serving as a steering aid (FDR) becomes independent of one Actuation of the brake pedal or accelerator pedal a brake pressure in or in several wheel brake cylinders built, for example, to break out of the Prevent vehicle from the lane desired by the driver. The pump can also be used with an electro-hydraulic brake system (EMS) in which the pump the brake fluid in the wheel brake cylinder or in the Wheel brake cylinder promotes when an electric brake pedal sensor Actuation of the brake pedal detected or at which the pump to fill a Memory of the brake system is used.

The subclaims have advantageous refinements and developments of in the main claim invention to the subject.

drawing

The invention is explained below with reference to two exemplary embodiments shown in the drawing. In the drawings Fig. 1 and 2 axial sections of two embodiments of inventive piston pumps, Fig. 3 is an end view of a holding portion of a modification of the piston pump shown in Fig. 2 in Fig. 2 and illustrated piston pump Fig. 4.

Description of the first embodiment

The piston pump according to the invention shown in FIG. 1, generally designated 10 , has a pin-shaped piston 12 which is guided axially displaceably 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 piston pump 10 is shown in the drawing, further hydraulic components such as solenoid valves (not shown) are inserted and are hydraulically connected to one another and to piston pump 10 .

An end face of the liner 14 is closed with a disk-shaped closure element 18 which is fixed in the pump housing 16 by caulking 20 . 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 presses the piston 12 against a peripheral surface of an eccentric 26 which can be driven by an electric motor and by means of which the piston 12 moves in a manner known per se towards one in the liner 14 - And coming stroke movement is drivable.

Two spring-loaded check valves 28 are provided as inlet and outlet valves outside the liner 14 , in the hydraulic block forming the pump housing 16 , which are shown symbolically in FIG. 1. 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 conveyable for the piston pump 10 fluid in the displacement chamber 22 available volume, in particular at the end of a pumping stroke when the piston 12 assumes its inserted in the bushing 14 at the furthest position, standing in the displacement space 22 available residual volume, 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 can be selected, for example, parallelogram or roof-shaped winding cross sections, the mutually facing winding surfaces of which are approximately complementary in order to reduce a gap width 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 flange 44 . The sealing plug 46 is fixed in the pump housing 36 by caulking 48 and closes one end of the cylinder bore 42 in a pressure-tight manner. 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, ie 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 the steel core 68 or the piston 66 into the sleeve 38 on an end face of the steel core 68 facing away from the eccentric 76 . The section 80 of the sliding jacket 70 which extends the piston 66 has a transverse hole 82 which passes through 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 an end face of the piston 66 facing the liner bottom 40 . In the enlarged part of the blind hole 84 , a check valve is used as the inlet valve 88 and has a valve ball 90 as the valve closing body, which is pressed against the valve seat 86 by a helical compression spring as the valve closing spring 92 . 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 liner 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 an end view from the direction of the piston 66 in FIG. 3. Four angled holding webs 102 , which are integral with the perforated disk-shaped edge 100, protrude from a side facing away from the piston 66 . 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 when the piston 66 is pushed farthest into the bushing 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 displacement body 104 of the piston pump 34 shown in FIG. 2, like the displacement body 32 of the piston pump 10 shown in FIG. 1, 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 reducing the efficiency of the piston pump 34 increased.

In extension of the retaining fins 102, the holding part 98 four integral with it, protruding from its washer-shaped edge 100 in the blind hole 84 in centering fingers 108 which hold the retaining member 98 coaxially with the piston 66th In the exemplary embodiment shown, the centering fingers 108 have an interference fit in the blind hole 84 , ie the holding part 98 is connected to the piston 66 in a frictional manner by means of a clamping connection. 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 is closed, and thereby reduces wear on the valve seat 86 . This is particularly important when the valve seat 86 is molded 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 limitation is made of plastic, the valve stroke limitation can be produced with a more precise measure than a valve stroke limitation 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 . Via the expansion ring 114 , 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 according to the invention of the piston pump 34 shown in FIG. 2. The holding part 98 of the piston pump 120 shown in FIG. 4 has no sealing lip and no hollow cylindrical edge for guiding the piston. 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 tapers at its 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 has 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. The same components are labeled with the same reference numbers.

Claims (14)

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 winding surfaces are substantially complementary to each other. 4. Piston pump according to claim 3, characterized in that the Spring coils 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 piston ( 66 ) attached holding part ( 98 ) on the piston ( 66 ) is held, and that the 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.