Valve assembly

A valve assembly for a discharge device, in particular a steering pump, including a flow control valve for controlling flow from the discharge device to an actuator, and a pressure-limiting valve, wherein both valves form separate components of the valve assembly and are located in one and the same cavity of the discharge device.

BACKGROUND OF THE INVENTION 
The present invention relates to a valve assembly for a hydraulic discharge 
device, in particular, a steering pump, comprising a flow control valve 
and a pressure-limiting valve. 
In such valve assembly, the flow control valve serves for providing a 
predetermined fluid flow from the discharge device to an actuator. For 
example, when the valve assembly is used for controlling fluid flow from a 
steering pump to a steering gear, the fluid control valve is designed for 
limiting the fluid flow to the actuator to, e.g., no more than 8 1/min. 
The pressure-limiting valve serves for maintaining a predetermined 
pressure in the system, e.g., for preventing the pressure rise above 
100.div.110 bar. 
In known valve assemblies of this type, the flow control and 
pressure-limiting valves are structurally connected with each other, that 
is, both valves are combined in a single structural piece, with the 
pressure-limiting valve being located in the piston of the flow-control 
valve. The drawback of such a structure consists in that it manufacture 
and assembly are very expensive. 
In other known valve assemblies of this type, the flow-control valve and 
the pressure-limiting valve are separate elements located in different 
cavities formed in the discharge device housing. In this case, additional 
channels need be formed in the housing to connect the two valves with each 
other. This also results in increased production cost of the valve 
assembly. 
Accordingly, the object of the invention is a valve assembly of the 
above-mentioned type which can be produced easily and inexpensively, and 
which would have a high functional reliability. 
SUMMARY OF THE INVENTION 
This, and other objects of the invention which will become apparent 
hereinafter, are achieved by providing a valve assembly having separate 
flow-control and pressure-limiting valves located in one and the same 
cavity of the discharge device housing, which significantly simplifies the 
production of the valve assembly and substantially reduces the cost of 
production. The simplification of production and the reduction of costs 
results from having a simplified structure of each valve, and in an 
elimination of the need to provide additional channels in the housing. At 
that, the both valves are directly connected with each other 
hydraulically, because they are located in one and the same cavity of the 
housing. Further, the very simplicity of the valve structures insures 
their high functional reliability. 
According to one of the embodiments of the inventive valve assembly, the 
cavity, in which the two valves are located, is formed as a blind bore, 
with the pressure-limiting valve being at least partially located in a 
pocket formed in the blind bore bottom. 
According to another embodiment of the inventive valve assembly, the cavity 
is formed as a through bore, with the pressure-limiting valve being 
located in a plug, which closes one end of the bore. 
In preferred embodiments of the invention, the pressure-limiting valve 
communicates with the pressure or discharge side of the discharge device 
through a channel extending through the flow control valve. This permits 
to eliminate the need for additional channels in the housing for 
communicating the discharge pressure or the inlet pressure of the actuator 
to the pressure-limiting valve.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The valve assembly 1, which is shown in FIG. 1, comprises a flow-control 
valve 3 and a pressure-limiting valve 5. Both valves 3 and 5 of the valve 
assembly 1 are arranged in the same cavity 7 formed in a housing 9 of a 
hydraulic discharge device. Below, the hydraulic discharge device will be 
referred to, by way of example, as a steering pump of a motor vehicle. 
However, it should be emphasized that the referred to valve assembly is 
equally suitable for use with any type of hydraulic machine, that is, any 
pump or motor. 
In the assembly shown in FIG. 1, the cavity 7 is formed as a blind bore 11. 
A pocket 15 is formed in the bottom 13 of the blind bore 11. The pocket 15 
is designed for receiving the pressure-limiting valve 5. 
The mouth of the bore 11 is closed with a connecting plug 17 which is 
secured there by suitable means, e.g., a thread 19. The connection plug 17 
has a projection 21 extending into the cavity 7. The projection 21 can 
have, for example, a cylindrical shape. An opening 25 is provided in the 
bottom 23 of the projection 21. A stem 27, which projects from a body of a 
piston 29 of the flow-control valve 3, extends through the opening 25 into 
the interior of the projection 21. 
The stem 27 has a through channel 31, which is provided at an end thereof 
located in the interior of the projection 21, with an orifice 33 having a 
cross-section which is smaller than the cross-section of the channel 31. 
The piston 29 is biased, from left to right against a stop 37, with a 
resilient member, e.g., a helical spring 35 in the embodiment shown in 
FIG. 1. The stop 37 is formed by a retaining ring located in a groove 
formed in the wall of the bore 11 and projecting into the bore 11. The 
piston 29 can be made hollow so that the spring 35 projects into the 
piston interior and abuts, with its opposite ends, the bottom 13 of the 
bore 11 and the bottom of the piston 29. 
The outer diameter of the stem 27 is smaller than that of the piston 29, 
whereby a first pressure space 39 is formed in the bore 9. A channel 41, 
which is connected with a pressure space, e.g., discharge side of a 
hydraulic discharge device, for instance, a steering pump, has its mouth 
opening into the first pressure space 39. 
The opening 25 connects the first pressure space 39 with an interior 43 of 
the connection plug 17 which communicates with an actuator of the 
hydraulic discharge device, in the present case, with the steering gear of 
a motor vehicle. The pressure oil from the steering pump can thus flow 
through the channel 41 into the first pressure space 39 and, therefrom, 
through the opening 25 and the interior 43 of the connection plug 17 to 
the steering gear. The pressure oil simultaneously flows through the 
orifice 33 and the channel 31 into an interior 45 of the hollow piston 29. 
The interior 45 of the piston 29 opens into a second pressure space 47 
which is formed between the piston 29 and the bottom 13 of the bore 11. 
Thereby, the pressure prevailing in the interior 43 of the connection plug 
17 is communicated to the second pressure space 47. 
The pressure-limiting valve 5 has, e.g., a cylindrical body formed as a 
sleeve 49 extending in the second pressure space 47. The length of the 
sleeve 49 is so selected that its outer opening 51 is located in the 
interior 45 of the piston 29. A spring, for example, a helical spring 55 
which abuts at its one end the bottom 53 of the sleeve 49, biases an 
abutment 57 from left to right. The abutment 57 applies a pressure force 
to a body 59 for closing a channel 63 formed in a drain plug 61 located in 
the interior of the sleeve 49. 
The closing body 59 can, under the action of the spring 55 sealingly engage 
the mouth of the channel 63 which, at the end thereof lying opposite the 
closing body, opens into the interior 45 and, thus, communicates with the 
second pressure space 47. 
The abutment 57 can freely move in the interior of the sleeve 49 so that 
the pressure medium, which flows into the interior of sleeve 49 through 
the channel 63, can flow past the abutment 57. The bottom of the sleeve 49 
and the drain plug 61 define together an inner space 65 into which opens a 
channel 67, which extends through the housing 9 and communicates, for 
instance, with a reservoir or a suction side of the discharge device. The 
inner space 65 defines a third pressure space with an orifice 69 into 
which the channel 67 opens. 
The valve assembly 100 which is shown in FIG. 2, is basically similar to 
that shown in FIG. 1, with the elements of the valve assembly 100, 
identical to those of the valve assembly 1 in FIG. 1, being designated 
with the same reference numerals. 
The pressure-limiting valve 105 only slightly differs from the 
pressure-limiting valve 5 of the valve assembly 1 shown in FIG. 1. The 
pressure-limiting valve 105 is formed as a plug which closes, from the 
left, the cavity 7 formed in this embodiment as a through bore 110. The 
right side of the bore 110 is closed with the connection plug 17, as in 
FIG. 1. 
In the embodiment of the valve assembly 100 shown in FIG. 2, the helical 
spring 35 which biases the piston 29 of the flow-control valve 3 from left 
to right, abuts not a bottom of a blind opening as in FIG. 1, but the body 
of the closing plug 71. As in FIG. 1, the piston 29 is biased against the 
stop 37. 
The constructive difference between the valve assemblies shown in FIGS. 1 
and 2, consists in that the helical spring 35, which biases the piston 29 
against the stop 37, is located in FIG. 2, not in the interior 45 of the 
piston 29 as is the case of FIG. 1, but is supported on a support shoulder 
of the plug 71. With regard to functioning, there are no differences 
between the embodiments of the inventive valve assembly shown in FIGS. 1 
and 2. 
The sleeve 49 forms a continuation of the base body of the 
pressure-limiting valve 105, and extends in the second pressure space 47 
and into the interior 45 of the piston 29. The interior of the 
pressure-limiting valve 105 defines the third pressure space 65 which is 
connected with the channel 67 by a branch channel 169. The channel 67 
here, as in the embodiment of FIG. 1, leads to a reservoir or a suction 
side of a steering pump. 
The embodiments of the inventive valve assembly, shown in FIGS. 1 and 2, 
have the following common constructive features: 
The connection plug 17, which closes the bore 11 (110), has a projection 21 
extending into the first pressure space to such an extent that the channel 
41, which opens into the first pressure space 39, is not blocked in any 
way. The diameter of the stem 27, which extends in the first pressure 
space 39 along the axis 73, is so selected that a sufficiently large space 
remains between the outer surface of the stem 27 and the inner surface of 
the cavity 7. This insures that the pressure oil, which flows into the 
first pressure space 39 through channel 41, can pass through the opening 
25 without any hindrance into the interior 43 of the connection plug 17. 
The length of the stem 27 is so selected that it extends through the 
opening 25 in the rightmost position of the piston 29 of the flow-control 
valve 3 when the piston 29 abuts the stop 37. In its right end region, the 
stem 27 has a shape such that its outer diameter increases from left to 
right, but the largest diameter of the stem 27 in its right end region 
remains smaller than the diameter of the opening 25. Thus, when the piston 
29 of the flow-control valve 3 is displaced, against the biasing force of 
the spring 35, to the left, the cross-section of the stem 27, which 
intersects the opening 25, increases. This results in decreasing of the 
free annular space between the outer surface of the stem 27 and the inner 
surface of the opening 25, with the displacement of the piston 29 to the 
left. This means that the cross-section of the free space between the 
outer surface of the stem 27 and the inner surface of the opening 25 is 
reduced upon displacement of the piston 29 of the flow-control valve 3 
from the positions shown in FIGS. 1 and 2. 
The stop 37 is arranged so that the piston 29, when abutting the stop 37 
under the action of spring 35, does not obstruct the channel 41, and the 
flow through the channel 41 into the first pressure space 39 passes 
without any hindrance. The outer diameter of the piston 29 corresponds to 
the inner diameter of the cavity 7, and the outer surface of the piston 29 
sealingly engages the inner surface of the cavity, and there is no fluid 
flow therebetween. Thus, the piston 29 acts as a sliding valve. 
In the region of the housing 9 in which the outer surface of the piston 29 
sealingly engages the inner surface of the cavity 7 when the piston 29 
abuts the stop 37, there is provided a channel 75 leading to a suction 
side of a discharge device, e.g., a vane pump. 
In both FIG. 1 and FIG. 2 it is shown that the piston 29 has a sealing 
region which is located between the channels 41 and 75. At that, the 
length of the sealing surface of the piston 29 is so selected that, in 
positions of the piston 29 shown in FIGS. 1 and 2, the channel 75 is 
sealed from the second pressure space 47. 
Both the pressure-limiting valve 5 of FIG. 1 and the pressure-limiting 
valve 105 of FIG. 2 are so made that the opening 55 of the sleeve 49 is 
located in the region of the interior 45 of the piston 29. To this end, 
the sleeve 49 is provided with an outer diameter which is smaller than the 
inner diameter of piston 29 in the region of its interior 45, whereby the 
interior of the sleeve 49, both in FIG. 1 and FIG. 2, communicates with 
the second pressure space 47 when the sleeve 49 projects into the interior 
45 of the piston 29. The sleeve 49 projects only a small distance into the 
interior 45, so that the piston 29 can be displaced to the left against 
the biasing force of the spring 35, without the bottom 77 of the piston 29 
engaging the end surface 79 of the sleeve 49. 
As soon as the piston 29 is displaced against the biasing force of the 
spring 35 a predetermined amount, the sealing region of the piston 29 
unblocks the channel 75 whereby fluid communication is established between 
the channels 41 and 75. 
In both embodiments of the inventive valve assembly, the pressure, 
prevailing in the second pressure space 47, acts on the closing body 59 
through the channel 63 formed in the closing plug 61. When the pressure in 
the second pressure space 47 and thus, in the interior 45 of the piston 29 
increases to an extent that it exceeds the biasing force of the spring 55, 
which biases the abutment 57 and the closing body 59 against the mouth of 
the channel 63, the channel 63 opens, and the oil flows from the second 
pressure space 47 through the channel 63 past the abutment 57 into the 
third pressure space 65. From the third pressure space 65, the oil flows 
through the branch channel 169 into the channel 67 and then into the 
reservoir or to the suction side of the discharge device. 
Functionally, the described valve assembly operates as a conventional valve 
assembly. The flow control valve serves for limiting the fluid flow to the 
actuator, here, to the steering gear, to, for example, 8 1/min, when the 
pressure in the channel 41 and, thus, in the first pressure space 39 
increases. The pressure increases when the rotational speed of the 
internal combustion engine which drives the hydraulic discharge device, 
the steering pump, increases, whereby the fluid flow from the driven pump 
also increases. 
The increase of the rotational speed of the internal combustion engine 
takes place when a steering force, applied to the steering wheel, 
increases. The increased pressure in the first pressure space 39 leads to 
the displacement of the piston 29 to the left, against the biasing force 
of the spring 35, from its initial position shown in FIGS. 1 and 2. This 
results in the displacement of the sealing surface of the piston 29 to the 
left, which provides for fluid communication between the first pressure 
space 39 and the channel 75. 
The displacement of the piston 29 to the left also results in the reduction 
of the free cross-section of the opening 25 because the cross-section of 
the stem 27, which intersects the opening 25, increases. Thereby, with 
increase of pressure in the first pressure space 39, the channel through 
which oil flows into the interior 43 of the connection plug 17 narrows, 
and the fluid flow changes from, for instance, about 8 l/min to 4 l/min. 
Thus, the increase in pressure leads to an increase feel of the steering. 
The pressure in the interior 43 of the connection plug 17 is transmitted 
through the orifice 33 and the channel 31 in the stem 27 to the second 
pressure chamber 47. When the pressure in the second pressure chamber 
exceeds a predetermined amount, e.g., 100.div.110 bar, the closing body, 
under the pressure, moves against the biasing force of the spring 55, 
unblocking the channel 63, and a fluid communication establishes between 
the second and third pressure spaces and, thus, between the areas of high 
and low pressures, the low pressure area being the reservoir or the 
suction side of the discharge device, for example, steering pump. 
This communication leads to the reduction of the pressure acting on the 
piston 29 and the piston 29, when the pressure increases further in the 
system, in particular in the actuator, here, the steering gear, moves to 
the left. Further movement of the piston 29 to the left results in the 
increase of an open area of the channel 75, so that more oil can flow from 
the first pressure space 39 into the channel 75. However, the reduction of 
the free area of the opening 25 leads to reduced flow into the interior 43 
and thereby, to the reduction of flow from the interior 43 of the 
connecting plug 17 into the second pressure space 47. This, together with 
actuation of the pressure-limiting valve 5 (105) leads to pressure 
equilibrium in the first and second pressure spaces, and the position of 
the piston 29 is thereby stabilized. If the pressure in the system 
increases further, the piston 29 is displaced further to the left, and 
more oil flows into the channel 75 which limits any further increase in 
the system pressure. 
Because the pressure-limiting valve 5 or 105 which effects pressure 
control, communicates with the interior 43 of the connection plug 17 and, 
thus, with the actuator, through the piston 29, the channel 31 in the stem 
27, the pressure, supplied by the discharge device, can be controlled in 
an optimal manner without a need to provide additional channels in the 
housing 9 of the discharge device. In this way, a direct pressure 
connection with the pressure-limiting valve is realized in a simple and 
economical manner, with the valves 5 (105) and 3 being very compact. 
The piston 29 of the flow-control valve 3 is acted upon, at one side 
thereof, with a first pressure corresponding to the pressure in the first 
pressure space 39, and at the other side thereof, with a second lower 
pressure corresponding to the pressure in a second pressure space 47, that 
is, with pressure prevailing in the interior 45 of the piston 29, with the 
pressure in the second pressure space 47 able to increase, if needed. 
The increased pressure in the second pressure space 47 can directly act on 
the pressure-limiting valve 5 (105), without a need to provide in the 
housing 9 additional high-pressure channels. Through the pressure-limiting 
valve, a communication with a third pressure, which is reduced in 
comparison with the second pressure, can be established, e.g., with the 
reservoir or the suction side of the discharge device. 
The valve assembly can be produced in a simple and very economical way. By 
the separation of two components of the valve assembly 1 or 100, there is 
provided a simple basic structure and, at the same time, a functional 
reliability is insured with the valve assembly requiring little space. 
It is especially advantageous that, by separating the pressure-limiting and 
flow control valves, a very simple structure of the flow control valve can 
be achieved. On the other hand, the separation of the pressure-limiting 
and flow control valves, with the both valves being located in the same 
cavity of the discharge device housing, permits to provide a simple 
structure of the valve assembly and of the discharge device, in which the 
valve assembly is used. From the manufacturing point of view, it is of no 
importance whether the pressure-limiting valve is located in the pocket of 
a blind bore, as in the embodiment of Fig. 1, or is located in a closing 
plug 71 which closes an end of a through bore, as in the embodiment of 
FIG. 2. 
While the present invention was shown and described with reference to the 
preferred embodiments, various modifications thereof will be apparent to 
those skilled in the art, and it is not intended that the invention be 
limited to the disclosed embodiments or details thereof, and departures 
may be made therefrom within the spirit and scope of the appended claims.