Hydraulic reciprocating piston pump for brake installations of motor vehicles with an ABS system

An improve the pump including a reciprocal piston pump having a pump piston, guided longitudinally displaceable in a displacement chamber. An outlet valve for the admission of pressure means and a valve for the outflow of pressure means is associated with the displacement chamber. The outlet valve is embodied as a cup-shaped sleeve, having on the outflow side a sealing lip of an elastomeric material, which cooperates with a cylindrical sealing face. The outlet valve is distinguished by low opening pressure, reduced noise when closing and reduced machining effort. The reciprocating piston pump (10) is intended for use in hydraulic brake installations of motor vehicles with ABS systems.

BACKGROUND OF THE INVENTION 
The invention relates to a hydraulic piston pump as set forth hereinafter. 
Such reciprocating piston pumps for generating a relatively high pressure 
are already known from German Published, Non-Examined Patent Application 
DE-OS 32 36 536. During operation in the ABS system mode, a pump of this 
type is intended to return pressure medium taken from a wheel brake 
cylinder during a brake pressure reduction phase back to the main brake 
cylinder of a brake installation of a motor vehicle with an ABS system, 
such as known from U.S. Pat. No. 4,861,116. Pump pressures of up to 
approximately 200 bar can occur in the course of this operation. The 
reciprocating piston pump has an inlet valve and an outlet valve in the 
form of one-way valves. These valves have a conical valve seat of great 
precision and a hardened steel ball as a closing body, which is pressed 
against the valve seat by means of a helical pressure spring. While a 
spring with a relatively low closing force is assigned to the inlet valve, 
the outlet valve has a spring with a great closing force in order to 
diminish the bounce of the ball, which causes noise during closing of the 
valve. 
Furthermore, very high demands are made on the tightness of particularly 
the outlet valve in order to prevent, on the one hand, the flow-off of 
pressure medium from the brake line into a pressure medium reservoir 
disposed at the inlet side of the pump during braking. The reservoir is 
intended for the intermediate storage of a pressure medium during the 
pressure reduction phases in the course of ABS operation, so that it can 
be transported by the pump. On the other hand, the tightness of the valves 
also prevents the automatic emptying of the pressure medium reservoir into 
the main brake cylinder, if during braking without ABS operation, pressure 
medium is incorrectly collected in the reservoir. However, this disrupts 
quick brake pressure reduction in the course of an anti-blocking 
operation. 
OBJECT AND SUMMARY OF THE INVENTION 
In contrast to the above, the reciprocating piston pump has an advantage 
that the outlet valve allows lower opening pressure and, if the 
operational pressure of a pressure medium reservoir provided at the inlet 
is higher than the opening pressure of the inlet valve as well as the 
outlet valve of the pump, automatic emptying of the incorrectly filled 
reservoir via the pump to the main brake cylinder of the brake 
installation. Furthermore, the operating noise of the reciprocating piston 
pump is considerably reduced by use of a sleeve as the resilient closing 
member of the outlet valve. Finally, the sure sealing of the outlet valve 
can be achieved with less effort in connection with the machining of the 
sealing face forming the valve seat, because the sealing lip can 
compensate for tolerances. 
Advantageous further embodiments and improvements of the reciprocating 
piston pump recited in the main claim are possible by means of the steps 
described herein. 
The embodiment of the reciporating piston pump recited is primarily used to 
support the cup sleeve, which is subjected to the pressure medium flow fed 
in pulses and is therefore subjected to great stresses, mechanically as 
well as to protect it from damage, in particular in the opening position 
and the closing position. Additionally, the pressure medium flow is 
steered through the annular gap between the sealing face and the sealing 
lip. 
An axially directed flow to the sealing lip and thus reduced flow-through 
resistance is achieved by means of the further embodiment of the 
reciprocal piston pump. 
The invention will be better understood and further objects and advantages 
thereof will become more apparent from the ensuing detailed description of 
a preferred embodiment taken in conjunction with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The hydraulic reciprocating piston pump 10 shown in FIG. 1 has a pump 
cylinder 11, which is received in a stepped bore 12 of a housing 13. A 
pump piston 14 is guided in a longitudinally displaceable manner in the 
pump cylinder 11. The pump piston 14 can be driven by an eccentric 15. The 
volume of a displacement chamber 16 in the pump cylinder 11 can be changed 
by means of the longitudinal displacement of the pump piston 14. A 
restoring spring 17, by means of which the pump piston 14 is supported on 
the eccentric 15, is disposed in the displacement chamber 16 equiaxially 
with the pump piston 14. 
The displacement chamber 16 is connected with a supply line 20 of the 
housing 13. A connecting bore 21, extending in axially alignment with the 
pump cylinder 11, starts at the outlet side of the displacement chamber 
16. It terminates on the flow-off side in a cylindrical recess 22 of the 
pump cylinder 11 and has a bottom 23 extending at right angles in respect 
to the longitudinal axis of the pump cylinder 11. 
A closure screw 25, by means of which the pump cylinder 11 is fixed in the 
stepped bore 12, follows the pump cylinder 11, with a plate-shaped support 
body 24 interposed. The closure screw 25 contains a blind bore damping 
chamber 26, from which a throttle bore 27 extends to a flow-off line 28 of 
the housing 13. 
A valve 31 for the admission of a pressure medium and a valve 32 for the 
outflow of pressure medium into the damping chamber 26 is associated with 
the displacement chamber 16 of the pump cylinder 11. The inlet valve 31 
opens during the suction stroke of the pump piston 14; during the working 
stroke, the outlet valve 32 opens the connection from the displacement 
chamber 16 to the damping chamber 26. 
The inlet valve 31 has a ball 33 as a closing member, which is supported on 
a conical valve seat 35 of the pump piston 14 by the action of a 
relatively weak closure spring 34 located in the displacement chamber 16. 
The outlet valve 32 has a cup sleeve 36 of an elastomeric material for a 
closing member. The cup sleeve 36 has a disk-shaped body 37 at the 
peripheral extending axially in respect to the damping chamber 26 (FIG. 
2). In the closed position of the outlet valve 32 illustrated in FIG. 1, 
the sealing lip 38 cooperates with the interior peripheral surface of the 
recess 22 used as a sealing face 39. 
On the side of the connecting bore 21, the sleeve 36 is supported by means 
of its body 37 on a flat disk 40 having nearly the diameter of the recess 
22. In the closed position of the outlet valve 32, the disk 40 is seated 
on the bottom 23 of the recess 22 because of the pressure of the pressure 
medium contained in the damping chamber 26. The edge of the disk 40 is 
provided with perforations 41, preferably evenly distributed over the 
periphery, for the flow-through of the pressure medium (FIG. 4). The 
perforations 41 may have the shape illustrated; but they may also be 
formed, for example, in the shape of triangles or circles and in numbers 
differing from the exemplary embodiment. The disk 40 protects the body 37 
of the cup sleeve 36 against wear by the pressure medium which is ejected 
pulse-like from the displacement chamber 16 through the connecting bore 21 
in the course of the operation of the reciprocating piston pump 10. 
Additionally, the disk 40 prevents the body 37 of the sleeve 36 from being 
pulled into the connecting bore 21 because of the effect of the pressure 
in the damping chamber 26. For this reason the perforations 41 of the disk 
40 end in a radial direction in front of the connecting bore 21. 
The support body 24 has a cup-shaped collar 44 extending coaxially in 
respect to the cylindrical recess 22 and directed towards its bottom 23. 
This collar 44 is adapted to the interior contour of the cup sleeve 36. A 
plurality of flow-through openings 45 for the pressure medium, preferably 
disposed at even distances, is provided adjoining the collar 44. In this 
case the cross section of the flow-through openings 45 is located 
predominantly within the cross section of the cylindrical recess 22. 
The shape of the cup-shaped collar 44 is such that, with the cup sleeve 36 
and the disk 40 inserted in the cylindrical recess 22, axial play for the 
disk- shaped body 37 and radial play for the sealing lip 39 of the sleeve 
result. Thus, the sleeve 36 is capable of performing a valve lift from its 
closed position in FIG. 1 into the open position illustrated in FIG. 2, 
during which the sleeve nestles with its interior contour against the 
cup-shaped collar 44 of the support body 24. In this open position the 
sealing lip 38 has been lifted, making use of the radial play, from the 
sealing face 39 of the recess 22. Pressure medium ejected by the pump 
piston 14 from the displacement chamber 16 thus flows in an axial 
direction through the perforations 41 of the disk 40 along the interior 
periphery of the recess 22. The flow is guided by means of longitudinal 
ribs 48 of the sleeve 36, which extend in an even distribution along its 
exterior periphery and end juxtaposed the sealing lip 39, forming flow 
channels 49 (FIG. 3). The pressure means overcoming the sealing lip 39 
enters the damping chamber 26 through the flow- through openings 45 of the 
support body 24. The support body 24, which limits the lift of the cup 
sleeve 36, in the open position of the outlet valve 32 receives the flow 
force of the pressure medium acting on the sleeve 36. 
The foregoing relates to a preferred exemplary embodiment of the invention, 
it being understood that other variants and embodiments thereof are 
possible within the spirit and scope of the invention, the latter being 
defined by the appended claims.