Pressure control valve slip-controlled hydraulic brake systems

A pressure control valve is disclosed comprising a valve tappet (1) guided in a valve housing (3) and accommodating a compression spring (4), with a valve closure member (10) on one end of the valve tappet (1) and mating with a valve seat (9) establishing a connection between a pressure supply port (11) that emanates from a pressure fluid source and a pressure return channels (12) once the pressure attains a specific preset desired valve. In order to diminish noise, at least one friction element (2) is engagement with the valve tappet (1) movable to abut on radial friction surfaces of the valve housing (3) and/or the valve tappet (1).

BACKGROUND OF THE INVENTION 
The present invention relates to a pressure control valve, in particular 
for the pressure fluid control in slip-controlled hydraulic brake systems. 
Conventional pressure control valves for the flow control of fluids in 
slip-controlled hydraulic brake systems are in wide use. 
Pressure control valves are known, such as described in patent application 
P 39 30 757.3 for example, which have a valve tappet guided in a valve 
housing acted upon by a compression spring. The valve tappet end remote 
from the compression spring is formed as a spherical closure cooperating 
with a valve seat in order to interrupt the pressure fluid connection 
between the fluid supply and return in a leak-free manner when the valve 
is in its closed position. 
In order to diminish the occurrence of noise and particularly the 
solid-borne sound during the stroke movement of the valve tappet, axially 
extending recesses are arranged unsymmetrically around the periphery of 
the valve tappet which bring about a radial pressure force resultant 
depending on the rate of flow and thereby an attenuation of the vibration. 
To manufacture such a shaped valve tappet, however, additional 
sophisticated machining steps are required. 
It is therefore an object of this invention to improve upon a pressure 
control valve of the type referred to in such a manner as to achieve a 
major reduction in noise during the valve control phase with simple 
cost-efficient means, while the operational reliability is safeguarded at 
the same time. 
SUMMARY OF THE INVENTION 
According to the present invention, the object set forth is achieved by the 
arrangement of a friction element whose radial friction surfaces are 
effective during the movement of the valve tappet in order to attenuate 
the mechanical vibrations of the valve tappet in such a manner that, on 
the one hand, the audible operating noises of the valve tappet are avoided 
and, on the other hand, possibly occurring compressional vibrations can be 
reduced. 
The friction element can advantageously take the form of a friction ring 
clamped in between the inner end wall of the valve housing and the 
compression spring on the side of the valve tappet which ring having a 
bore which receives and frictionally engages the outside of the valve 
tappet. Upon initiation of the valve stroke movement, the engagement of 
the bore of the friction ring diminishes the vibrations. Likewise, as an 
alternative of the frictional engagement of the bore, the outside diameter 
of the friction ring can be in frictional engagement with the inside wall 
of the valve housing, a considerably larger peripheral effective surface 
thereby being in frictional contact as a result so that good static 
friction properties can be realized on start-up of the stroke movement on 
the tappet side. 
Both design variants permit a relatively simple attachment of the friction 
ring in that the friction ring, preferably constructed as an elastomeric 
friction element, is held in proper position by the compression spring. 
In order to maximize use of available space, it is particularly expedient 
to use a compression spring which itself generates friction forces acting 
in an axial direction. The compression spring may be clamped in between 
the internal end surface of the valve housing and an axial stop of the 
valve tappet, with its spring coils in frictional contact with the radial 
inside wall of the valve housing. It is hence possible by selecting a 
suitable compression spring to control the friction forces generated. 
The frictional contact between the compression spring and the valve housing 
may be brought about by a slope of a spring abutting surface, effective 
transversely to the spring's longitudinal axis, on which slope one end of 
the compression spring is abutting. Buckling of the compression spring may 
thus be initiated, dependent on the spring preloading force. Hence, the 
frictional contact on the valve housing permits an attenuation of the 
vibrations which depend on the valve stroke. 
Major reduction in the manufacturing costs while maintaining adequate 
frictional effectiveness of the compression spring can be realized in a 
surprisingly simple fashion by using a compression spring with an integral 
number of spring coils, since the oppositely disposed, equally long spring 
ends form spring abutment points offset from the line of effect of the 
spring force. This forces a lateral buckling of the compression spring, 
and hence results in abutment of one or more turns on the valve housing in 
frictional engagement therewith. 
The buckling of the compression spring can also be effected by the 
arrangement of a slope in the end portion of the compression spring. 
The present invention shall be explained in more detail in the following by 
way of several embodiments.

DETAILED DESCRIPTION 
FIG. 1 shows a pressure control valve suited for pressure fluid control in 
slip-controlled hydraulic brake systems, with an elongated valve tappet 1 
which is movably guided in a valve housing 3 and receives a compression 
spring 4. A valve closure member 10 is formed on one end of the valve 
tappet 1 shaped to be fit to a valve seat 9. The valve closure member 10 
moves off the valve seat 9 to establish a connection between a pressure 
supply port 11 adapted to be connected to a pressure fluid source and 
pressure return channels 12, once the pressure reaches a specific preset 
desired value. 
The valve tappet 1 is arranged centrally symmetrically in a bore in the 
valve housing 3, designed as a hollow cylinder. To guide the valve tappet 
1, the stem of the valve tappet 1 in the area of the valve seat 9 is 
surrounded by a cage 13 inserted into the opening of the valve housing 3. 
On the side remote from the valve seat, the valve tappet 1 is guided in a 
concentric bore which extends through the inner end wall of the valve 
housing 3. 
Extending tangentially into the opening of the valve housing 3, are 
channels of pressure return 12, which are diametrally arranged and 
establish a connection to the pressure supply port 11 when the valve 
closure member 10 is opened. 
Disposed in an annular groove recessed in the peripheral surface of the 
valve housing 3 is a ring seal 14 which pressure-fluid-tightly closes the 
contact surfaces on the housing side in relation to a valve block (not 
shown). 
To attenuate any noise developing, a friction element, configured as a 
friction ring 2 is held against the inner end wall of the valve housing 3 
by one end of the spring 4, the other end abutting on the axial stops 5 of 
the valve tappet 1. The friction ring 2 is an elastomeric element and has 
an internal bore frictionally gripping the valve tappet 1, so that as the 
valve tappet 1 moves, frictional scrubbing against the internal bore takes 
place. 
Alternatively, FIG. 2 shows the arrangement of the friction ring 2 between 
the two axial stops 5, 6 mounted approximately at the midpoint of the 
valve tappet 1, which stops have the friction ring 2 clamped therebetween 
under the action of the compression spring 4. Thus, the friction ring 2 is 
carried by the valve tappet 1 will slide with its external diameter 
scrubbing on the valve housing wall to be in frictional engagement 
therewith. 
FIG. 3 shows a slope 8 disposed on an axial stop 5 of the valve tappet 1, 
which slope 8 presents a tilted abutment surface exerting an uneven axial 
compression of the helical spring 4. The uneven axial compression causes 
lateral buckling of the helical compression spring 4 which here comprises 
the friction element. Due to this lateral buckling, and the respective 
dimensions of the housing bore, the inside and outside diameter of the 
helical spring 4, and the stem of the valve tappet is such that the 
outside of one or more coils of the helical spring 4 will move into 
frictional abutment on the inside wall of the valve housing 3. At the same 
time, as shown in FIG. 3, inner surfaces of the coils 7 may also scrub on 
the outside stem of the valve tappet 1. 
The embodiment according to FIG. 4 shows a laterally directed elastic 
buckling deformation of the compression spring 4 which can be effected in 
a surprisingly straightforward manner. The helical spring 4 is compressed 
in between the axial stop 5 of the valve tappet 1 and the inner end wall 
of the valve housing 3 and is designed with an integral number of coils 7. 
This design also creates uneven axial compression of the spring 4, which 
automatically causes lateral buckling of the compression spring 4, since 
the contact of the opposite spring ends are on the same side. The lateral 
backing causes frictional engagement of the outside of one or more coils 7 
with the inside wall of the housing 3. In dependence on the spring's 
dimensioning, this results, in the extreme case, in a partial frictional 
contacting of individual inner coil surfaces on the stem of the valve 
tappet 1.