WO2000031415A1

WO2000031415A1 - Piston pump

Info

Publication number: WO2000031415A1
Application number: PCT/EP1999/008600
Authority: WO
Inventors: Peter Volz
Original assignee: Continental Teves Ag & Co. Ohg
Priority date: 1998-11-26
Filing date: 1999-11-10
Publication date: 2000-06-02
Also published as: DE19854716B4; DE19854716A1

Abstract

The invention relates to a piston pump for conveying hydraulic fluid, especially for automotive braking systems, comprising a step piston (12) that can be axially displaced inside a pump chamber (11), whereby a section of the piston (12) sub-divides the pump chamber (11) into a low pressure chamber (33) and a high pressure chamber (26) with a variable volume. The section (16) of the step piston (12) has a shoulder (22) that faces the high pressure chamber (26) and holds a seal (19) to maintain tightness between the low pressure chamber (33) and the high pressure chamber (26). Said pump also comprises a piston spring (13) arranged in the high pressure chamber (26). The invention is characterized in that the pump spring (13) is supported on the seal (19).

Description

Piston pump

The invention relates to a piston pump for conveying hydraulic fluid, in particular for vehicle brake systems, with a step piston which is axially displaceable in a pump chamber and which divides the pump chamber into a low pressure chamber and into a high pressure chamber with a variable chamber volume with a piston section, the step piston having a section with one of the high pressure chamber facing shoulder which holds a seal sealing the high pressure chamber against the low pressure chamber and with a pump spring arranged in the high pressure chamber.

Piston pumps are used in brake systems. They pump the brake fluid into the brake circuits of wheel brakes. The pressure in the brake circuits increases until a brake intervention occurs on the wheels of a vehicle.

The piston divides the pump chamber into two separate pump chambers. One pump chamber is connected to a pump inlet via a suction channel and the other pump chamber is connected to a pump outlet via a pressure channel. One pump chamber is hereinafter referred to as the low-pressure chamber and the other pump chamber is referred to below as the high-pressure chamber.

Piston pumps of the type in question are described in DE 43 16 986 AI. In this known piston pump, the stepped piston is manufactured as a one-piece rotating part, in which several annular grooves are inserted for the realization of pump chambers and for receiving seals. Such punctures do not allow an effective grading of the stepped piston due to the critical cross section. In WO 98/12434, therefore, a bushing is arranged on a shoulder of the stepped piston facing the high-pressure chamber a seal that seals the high pressure chamber against the low pressure chamber.

The pump spring returning the stepped piston after it has reached its top dead center position acts on the end face of the piston via a suction valve cup receiving a suction valve. For this purpose, the suction valve cup has a step-shaped base with a circular support surrounding the end face of the step piston, on which the pump spring is supported. Between the support and the bushing, the seal is arranged without pretension so that a gap remains between the seal and the support. When the piston pump is operating, the suction valve is in the closed position when the stepped piston is off. bottom dead center position from hydraulic fluid in the high pressure chamber is compressed until a pressure valve shutting off the high pressure chamber opens and releases a pump outlet. At the same time, the volume in the low-pressure chamber increases during the piston movement to the top dead center position. As soon as the stepped piston moves back from the top dead center position to the bottom dead center position under the action of the pump spring, the hydraulic fluid located in the low pressure chamber is pre-compressed during the suction stroke taking place in the high pressure chamber and is displaced into the high pressure chamber after overcoming the effective spring opening force of the suction valve. At the beginning of the compression stroke, the pressure of up to 250 bar in the high-pressure chamber causes the seal to be subjected to a sealing pressure by the hydraulic fluid, since the pressure in the high-pressure chamber is significantly higher than in the low-pressure chamber. The pressure difference evenly presses the seal against the socket and holds the seal in the specified position on the socket. With the suction stroke that occurs in the high pressure chamber under the action of the pump spring, however, the gap between the pump wall and the bushing compress the hydraulic fluid to a pressure which acts on the seal and can cause it to move in the direction of the support of the suction valve cup. During the subsequent compression stroke, the seal is pressed against the bush again. This creates a continuous flexing movement that significantly reduces the service life of the seal.

A positionally stable arrangement of the seal is disclosed in EP 0 637 690 A1, which supports the suction valve cup on a shoulder of the piston in such a way that a circumferential annular groove is formed between the support for the pump spring and a shoulder of the piston.

This design, modeled on a puncture for ring seals, reduces the possible flexing work of the seal, because the movement space of the seal is reduced and the seal can only be moved axially by pressing. However, it requires the formation of an additional shoulder on the piston, which increases the cost of production and the complexity of the manufacturing process. The invention has for its object to provide a step piston that can be manufactured inexpensively and on which the seal that seals the high-pressure chamber against the low-pressure chamber can be held in a simple manner on the step piston.

This object is achieved by the features of claim 1.

The invention is based on the basic idea that an additional prestressing force that keeps the seal in a predetermined position compared to the variable compression forces acting on the seal. The function of the existing pump spring is used to preload the seal by placing the suction valve cup on the Seal rests, the pump spring supported on the support prestressing the seal. The preload leads to a sealing pressure of the seal, which is held in the predetermined position at the same time by the sealing pressure.

According to one embodiment of the invention, a foot of a suction valve cup surrounding the section of the stepped piston is arranged between the seal and the pump spring, said foot being slidably connected to the stepped piston via a holding element. An embodiment variant provides for this purpose a projecting holding element arranged on the suction valve cup or stepped piston, which engages in a correspondingly arranged recess in the suction valve cup or stepped piston. The holding element can be in the form of a section of the foot, which extends radially to the interior of the suction valve cup, which engages behind a collar of the stepped piston, or a pin fastened to the suction valve cup or stepped piston, which engages in a corresponding longitudinal groove of the component opposite the pin - stepped piston or suction valve cup . With this design, the stepped piston is connected to the suction valve cup. The suction valve cup receiving the suction valve lies against the wall of the collar or the recess or the longitudinal groove of the stepped piston via the valve spring. The stepped piston and the suction valve cup with suction valve form an independently manageable unit that can be used as a pre-assembled assembly in the pump room. The axial movement of the suction valve cup by the pump spring can be limited by appropriate design of the holding element and / or the recess or the longitudinal groove, since the displacement path of the suction valve cup is determined from the position of the holding element to the limits of the recess or the longitudinal groove.

Other non-positive and / or positive connections between the suction valve cup and the stepped piston, which fulfill the same function, are also encompassed by the invention. According to claim 3, between the seal and the pump spring, a portion of the stepped piston is arranged which has a stop arranged at a predetermined distance from the end face of the stepped piston to limit the suction valve cup movement. This advantageous design limits the pretensioning of the seal to a predetermined pump spring force, since the suction valve cup is supported by the stop on the stepped piston during the stroke movement of the stepped piston after a predetermined change in position and thus limits the sealing pressure of the seal. This limitation of the prestressing of the seal prevents the seal from being crushed during the compression stroke, but ensures a sufficiently high sealing pressure during the suction stroke.

An embodiment of the invention is shown in the drawing and will be described in more detail below.

Show it:

1 a section of a longitudinal section of a piston pump for a vehicle brake system,

2 is an enlarged view of section A in Fig. 1, with the limitation for the movement of the suction valve pot,

Fig. 3 is an enlarged view of section A in Fig.l, with the slidable attachment of the suction valve cup

The piston pump shown in detail in longitudinal section in FIG. 1 for conveying hydraulic fluid is provided in particular as a pump in a brake system of a vehicle and is used in controlling the pressure in wheel brake cylinders. Depending on the type of brake system, the Abbreviations ABS or ASR and the like are used. The piston pump has a pump body 10 in which a cylindrical pump chamber 11 is formed. A stepped piston 12 is axially displaceably guided in the pump chamber 11 and is driven by a driven eccentric, not shown in detail, against the restoring force of a pump spring 13 in a reciprocating stroke movement. The stepped piston 12 consists of a cylindrical piston shaft 14 and a support disk 15 held on the piston shaft 14. The cylindrical piston shaft 14 has a smaller-diameter cylinder section 16 and a larger-diameter cylinder section 17, at the transition of which a radially extending shoulder 18 is formed. The support disk 15 is pressed onto the smaller-diameter cylinder section 16 and is supported on the shoulder 18. An elastomer seal 19 likewise pushed onto the cylinder section 16 seals the stepped piston 12 against the cylinder wall 20 of the pump chamber 11. A back ring is arranged between the support disk 15 and the seal 19, which causes a reduction in wear of the seal 19.

1 shows a coaxial series connection of the suction valve 22 and the pressure valve 23 within the pump chamber 11 and thus within the pump body 10. The suction valve 10 is pressed due to the action of a valve spring 24 in the direction of the valve seat arranged on the stepped piston 12. Another pump spring 13 arranged parallel to the first compression spring within the compression space 26 contacts the radially extending foot 27 of a suction valve cup 28 in which the suction valve with the valve spring 24 is arranged for the purpose of piston return. The valve spring 24 is supported on the bottom 29 of the suction valve cup 28 and the pump spring 13 with its opposite winding ends on the valve seat body 30 of the pressure valve 23. The foot 27 of the suction valve cup 28 is acted upon by the pump spring 13 and presses the elastomer seal 19, the back ring 21 and the support disk 15 against the shoulder 18 of the piston skirt 14 and thus resets the stepped piston 12.

The pump spring 13, which resets the stepped piston 12 after it has reached its top dead center position, acts on the elastomer seal 19 via the stepped foot 27 with its circular support 31 surrounding the end face of the stepped piston 12.

When the piston pump is operating, the suction valve 22 is in the closed position when the stepped piston 12 compresses hydraulic fluid in the high-pressure chamber 26 from its bottom dead center position until the pressure valve 23 opens and releases the pump outlet 32. At the same time, the volume in the low-pressure chamber 33 increases during the piston movement to the top dead center position. As soon as the stepped piston 12 moves back from the top dead center position to the bottom dead center position under the action of the pump spring 13, the suction stroke taking place in the high pressure chamber 26 becomes that in the low pressure chamber 33 located hydraulic fluid pre-compressed and displaced into the high pressure chamber 26 after overcoming the effective spring opening force of the suction valve 22. At the beginning of the compression stroke due to the pressures in the high-pressure chamber 26 up to 250 bar, the seal 19 is subjected to a sealing pressure by the hydraulic fluid, since the pressure in the high-pressure chamber 26 is significantly greater than in the low-pressure chamber 33. The pressure difference acts against the seal 19 the support disc 15 and holds it in a predetermined position. When the suction stroke to the bottom dead center position occurs under the action of the pump spring 13, the relaxing pump spring 13 effects a sealing pressure on the elastomer seal 19 and thus replaces the sealing pressure with the hydraulic fluid in the grain. compression stroke. A pressure that builds up during the pre-compression of the hydraulic fluid in the low pressure chamber 33 to overcome the spring opening force of the valve spring 24 does not lead to leaks between the pump wall and the support disk 15. The pump spring 13 acting on the seal 19 presses the seal during the pre-compression phase and holds it Seal in the specified position. As FIG. 2 shows, the suction valve cup 28 has a limit or a stop 34 to avoid overstressing the seal 19 during the compression stroke. The stop 34 limits the pressing path 35 of the foot 27 in that a section of the suction valve cup running radially around the pressing path 35 extends over the end face 36 of the stepped piston 12 and thus limits the sealing pressure of the seal 19 by the pump spring 13. If the stepped piston 12 moves in the compression stroke to its top dead center position, the seal 19 is subjected to a sealing pressure by the spring-loaded support 31 until the stop 34 sits on the end face 36 and maintains the pressing process at constant pressure. By limiting the sealing pressure of the seal 19, the friction between the seal 19 and the cylinder wall 20 is limited to a predetermined level, which on the one hand maintains the sealing function when the hydraulic fluid in the low-pressure chamber 33 is pre-compressed and on the other hand prevents damage to the seal 19.

A further embodiment of section A of FIG. 1 is shown schematically in FIG. 3, in which, in contrast to FIG. An embodiment variant provides for this purpose a protruding holding element 50 which is arranged on the suction valve cup 28 or step piston 12 and which engages in a correspondingly arranged recess 52 in the suction valve cup or step piston. The holding element 50 can be used as a section 53 of the foot 27, which extends radially to the interior 51 of the suction valve cup, which engages behind a collar 54 of the stepped piston 12, or a pin fastened to the suction valve pot or stepped piston, which engages in a corresponding longitudinal groove of the component opposite the pin — stepped piston or suction valve pot . The suction valve cup 28 receiving the suction valve 22, 24 bears against the wall of the collar 54 or the recess 53 or the longitudinal groove of the stepped piston 12 via the valve spring 24. The stepped piston and the suction valve cup with suction valve form an independently manageable unit that can be used as a pre-assembled assembly in the pump room. The axial movement of the suction valve cup 28 by the pump spring 13 can be limited by appropriate design of the holding element 50 and / or the recess 53 or the longitudinal groove, since the displacement of the suction valve cup 28 from the position of the holding element to the limits of the recess or Longitudinal groove is determined.

The cylindrical piston shaft 14 is sealed in the low-pressure chamber with an annular seal 38 arranged on the shoulder 37 of the pump body 10 with respect to the eccentric space, which is not shown in detail. An elastic means, preferably designed as a spring 39, holds the seal

38 in the axial direction on the shoulder 37, the spring

39 prestresses the seal 38. The spring 39 is supported against the support disk 15 of the stepped piston 12 in such a way that a spring force acts in the direction of the shoulder with each stroke movement. A filter 41 is arranged between the spring 39 and the seal 38 in the region of the pump inlet 40. The suctioned hydraulic fluid can thus be filtered off in the suction area. The filter 41 is preferably provided with two support rings 42, 43, which are arranged between the spring and the filter or between the seal and the filter. By designing the filter 41 with the support rings , 43 as a structural unit, the number of parts is reduced and assembly is made considerably easier.

Claims

claims

1. Piston pump for conveying hydraulic fluid, in particular for vehicle brake systems, with a stepped piston which is axially displaceable in a pump chamber and which divides the pump chamber into a low-pressure chamber and into a high-pressure chamber with a variable chamber volume with a piston section, the stepped piston having a section with a shoulder facing the high-pressure chamber comprises a seal which seals the high pressure chamber against the low pressure chamber and a pump spring arranged in the high pressure chamber, characterized in that the pump spring (13) is supported on the seal (19).

2. Piston pump according to claim 1, characterized in that between the seal (19) and the pump spring (13) a section (16) of the stepped piston (12) surrounding the foot (27) of a suction valve pot (28) is arranged, which via a Holding element (50, 54) is slidably connected to the stepped piston (12).

3. Piston pump according to claim 1 or 2, characterized in that between the seal (19) and the pump spring (13) a section (16) of the stepped piston (12) surrounding the foot (27) of a suction valve cup (28) is arranged a limiting means (34) for the suction valve cup movement arranged at a predetermined distance (35) from the end face (36).

4. Piston pump according to one of claims 1 to 3, characterized in that the limiting means (34) is integrally connected to the suction valve cup (28).

5. Piston pump according to one of claims 1 to 4, characterized in that a back ring (21) is arranged between the support disc (15) and the seal (19).