Power steering pump

A power steering pump having a cam with an internal cam surface defining pumping arcs, a rotor in said cam, pumping elements preferably in the form of slippers carried by the periphery of the rotor in sliding engagement with the pumping arcs, flow control valve means having a movable valve element responsive to both static pressure and velocity pressure of the displaced fluid on the high pressure side of the pump wherein provision is made for decreasing the volume of fluid delivered by the pump at high pressure upon an increase in the speed of the rotor, and means for equalizing the pressure between the volume of fluid between two adjacent pumping elements located at a high pressure outlet port and a corresponding volume of fluid between two other adjacent slippers located at a low pressure inlet port as the pumping elements pass through their respective pump cycles.

BRIEF DESCRIPTION OF THE INVENTION 
My invention relates to improvements in power steering pumps such as 
slipper pumps of the kind disclosed in U.S. Pat. Nos. 3,614,266 and 
3,645,647 as well as in pending patent application Ser. No. 885,912, filed 
Mar. 13, 1978, said patents and said application being assigned to the 
assignee of this invention. 
The pump of my invention comprises a cam that surrounds a rotor. The cam 
has two pumping arcs situated 180.degree. out of position with respect to 
each other. The rotor carries multiple pumping elements or slippers which 
engage the cam surface surrounding the rotor. End plates are situated on 
either side of the cam and rotor, and these plates are provided with ports 
which admit fluid to each of the two pumping chambers defined by the cam 
and the rotor. 
The fluid is displaced by the pumping elements or slippers as they traverse 
the pumping arc from the inlet port to the outlet port. After adjacent 
pairs of pumping elements traverse the outlet high pressure port, the 
volume of fluid in the cavity located between those two slippers is 
pressurized at the pressure value of the outlet pressure. Normally in a 
pump of this kind the volume of fluid trapped between the two adjacent 
slippers is exhausted to the inlet port as the pumping elements further 
progress upon rotation of the rotor. 
At the instant that two adjacent pumping elements traverse the outlet port, 
two other adjacent pumping elements are traversing the inlet port. They 
too define a volume of fluid therebetween that is equal in pressure to the 
inlet pressure of the pump. Upon further rotation of those two adjacent 
slippers, the low pressure fluid in the trapped volume between them is 
brought into communication with the outlet port. Thus there are two rapid 
changes in pressure of trapped volumes of fluid between adjacent slippers 
during each pumping cycle. There are two pumping cycles for each 
revolution of the rotor. This condition establishes pressure pulsations 
which may cause pump noise and which reduce pumping efficiency. 
According to a feature of my invention I have made provision for equalizing 
the pressures between the two trapped volumes of fluid so that the trapped 
volume of fluid adjacent the pump outlet port is reduced and the trapped 
volume fluid adjacent the inlet port is increased. This is done by 
providing suitable pressure equalization channels in either or both of the 
pressure plates located adjacent the rotor in the cam. Some of the 
potential energy of the pressurized volume of fluid trapped between two 
adjacent pumping elements near the outlet port is recovered as the high 
pressure in that trapped volume is distributed to the low pressure volume 
trapped between two adjacent pumping elements near the inlet port. 
According to another feature of my invention I have provided a flow control 
valve for controlling the pressure and flow whereby the pressure of the 
fluid displaced by the pump increases at a relatively fast rate upon an 
increase in rotor speed during low and intermediate speed operation and 
wherein the rate of fluid delivery by the pump at high speeds is 
relatively constant upon a further increase in the rotor speed. This 
reduces the effective horsepower required to drive the pump at high speeds 
and avoids excessive fluid delivery in pump applications such as vehicle 
power steering systems for automotive vehicles where the rotor is 
connected drivably to the vehicle engine and the pump normally tends to 
deliver an excessive amount of fluid to accomplish steering functions 
during high speed operation. 
Another feature of my invention is a strategic porting of the flow control 
valve described in the foregoing paragraphs which causes a supercharger 
effect as fluid is returned to the pump circuit from the reservoir for the 
pump to the flow control valve. The direction of the flow from the 
reservoir to the flow control valve is such that the velocity pressure 
developed by the flow augments the pressure at the pump inlet port.

TICULAR DESCRIPTION OF THE INVENTION 
In FIG. 1 numeral 10 designates a pump housing which may be formed of cast 
aluminum or other suitable material. It is provided with a pump cavity 12, 
the left hand end of which is closed by housing wall 14. The right hand 
end of the cavity 12 is closed by end cover 16 which is in the form of a 
plate received in the opening 12 and held in place by a snap ring 18. A 
fluid reservoir 20 formed of fiberglass or some other suitable material is 
situated with its margin surrounding the margin 22 of the housing 10. It 
encloses the end cover plate 16, the latter forming a valve housing for 
the valve assembly indicated generally by reference numeral 24. 
The interior of the reservoir 20 communicates with return flow passage 26, 
which communicates with the low pressure side of a fluid pressure operated 
mechanism such as a power steering gear for an automobile. 
A pump cam 28 is situated in the housing opening 12. As best seen in FIG. 
10, cam 28 defines a pair of pumping arcs 30 and 32 which are joined 
together by two sealing arcs 34 and 36 to define a continuous cam surface 
of irregular shape. The periphery of the rotor 38 is provided with 
multiple recesses 40 each of which receives a fluid pumping element such 
as slipper 42. In the embodiment disclosed each recess is provided with a 
radial opening that receives a spring 44 which urges the associated 
pumping element or slipper radially outward into camming engagement with 
the internal cam surface. 
A lower pressure plate 46 is situated on the left hand side of the rotor 38 
as seen in FIG. 1, and an upper pressure plate 48 is located on the right 
hand side of the rotor 48. End plate 16, which forms the valve body for 
the flow control and pressure relief valve assembly 24, is received within 
the opening 12 in the pump housing and is situated directly adjacent the 
upper pressure plate 48. The lower pressure plate 46, the rotor 38, the 
upper pressure plate 48 and the end plate 16 are held in axially stacked 
relationship and are urged into sealing engagement, one with respect to 
the other, by fluid pressure in the inner pressure chamber 50 at the base 
of the opening 12. Snap ring 18 provides the force reaction for the 
pressure force developed by the pressure in the pressure chamber 50. One 
or more pilot pins 52 received through the cam 28 and the two pressure 
plates as well as the end plate to hold the assembly in proper angular 
registry. 
The lower pressure plate 46 is seen in the detailed views of FIGS. 6 and 7. 
The right hand surface of the pressure plate 48 is seen in FIG. 6 at 52. 
It is formed with low pressure ports 54 and 56 and with high pressure 
ports 58 and 60. Low pressure ports 54 and 56 communicate respectively 
with low pressure ports 62 and 64 in the cam 28. The low pressure ports 
communicate with the inlet portion of the pumping chamber defined by the 
cam ring and the pump rotor. The spaces located between two adjacent 
pumping elements or slippers communicate with the inlet ports as they move 
through the pumping arc and expand in volume. The spaces between the same 
two adjacent pumping elements or slippers, as they decrease in volume upon 
continued rotation of the rotor through the pumping cycle, communicate 
with high pressure ports 58 and 60. They communicate also with high 
pressure ports 66 and 68 located in upper pressure plate 48. The inlet 
ports in the upper pressure plate 48 corresponding to the inlet ports 54 
and 56, respectively, in the lower pressure plate 46, are shown at 70 and 
72. 
The high pressure ports communicate with pump outlet passage 74 as seen in 
FIG. 2 and the low pressure ports communicate with low pressure return 
passage 76, also seen in FIG. 2. These passages are located in the end 
plate 16 which contains the valve assembly 24. This can best be seen by 
referring to FIG. 5 which shows the passages in the face of the end plate 
16 that engages the upper pressure plate 48. 
The cam ring 28, which is received within the opening 12 of the housing, 
defines with the housing a low pressure chamber 78. That space is in fluid 
communication with the seal chamber 80 seen in FIG. 1, suitable internal 
porting 81, as shown in FIG. 4, being formed in the housing 10 for that 
purpose. 
Drive shaft 82 for the rotor 38 extends through an opening 84 formed in the 
housing 10 and is journalled in that opening by a suitable bushing as 
shown. Shaft 82 is splined at 86 to an internally splined opening formed 
in the rotor 38. 
The high pressure passage 74 is in communication with venturi throat 88 
formed in the venturi flow control element 90. That element is threaded at 
92 within a threaded portion of the valve opening 94. The other end of the 
venturi passage 88 communicates with outlet passage 96 formed in a venturi 
element 90. 
Element 90 is provided with a shoulder 98 which registers with an opening 
formed in the reservoir 20 to hold the reservoir fast against the end 
plate 16. That connection and the registry of the margin of the reservoir 
20 with the outer periphery of the housing 10 provides stability for the 
reservoir. The margin of the reservoir 20 is provided with an O ring or 
other seal 100. 
Venturi pressure passage 102 is formed in the venturi element 90, and it is 
in communication with the throat 88. Internal passages formed in the end 
plate 16 connect the passage 102 with the right hand end 104 of the valve 
opening 94. Valve spool 106, having spaced valve lands 108 and 110, is 
slidably positioned in the valve opening 94. Valve spring 113 is situated 
at the end 104 of the opening 94 and urges the valve element 106 in a left 
hand direction as seen in FIG. 2. The outlet pressure in passage 74 tends 
to urge the valve element 106 in a left hand direction against the 
opposing force of the spring 113. As it does this, land 108 uncovers port 
76 thereby bypassing the pumped fluid to the low pressure side of the 
pump. The fluid that is not bypassed is distributed through the venturi 
throat 88 to the outlet passage 96. As the pump speed increases, the flow 
through the venturi throat increases, thereby establishing a reduced 
venturi pressure which is transmitted to the end 104 thereby causing a 
reduced pressure at that point that causes the spool valve to move to a 
more fully opened position thereby bypassing more fluid and reducing the 
effective outlet flow. Conversely, a decrease in pump speed will result in 
a build-up in pressure in the end 104 thereby augmenting the spring force 
and causing a decreased bypass flow. 
A pressure relief valve 112 registers with a relief orifice 114 in the 
valve element 106. It is normally closed by valve spring 116. Upon an 
excessive pressure buildup the pressure transmitted to the right hand side 
of the valve opening will cause the valve 112 to become unseated thereby 
bypassing fluid to the inlet side of the pump and relieving the excessive 
pressure. 
FIGS. 11A and 11B show in generally schematic fashion the valve structure 
of FIG. 2 and reference will be made to it to explain the operation of the 
valve. FIG. 11A shows a low-speed, high-pressure condition of the valve, 
and FIG. 11B shows the high speed condition where part of the outlet flow 
of the pump is bypassed. 
In the valve of FIGS. 11B and 11B fluid is bypassed from the pump outlet 
pressure passage 74 to low pressure port 76 when the valve land 108 
uncovers the port 76. Any fluid not bypassed through port 76 will be 
transmitted to the outlet passage 96, thereby creating a venturi pressure 
which is distributed to internal passage 118 from the throat 102 to the 
opposite side of the valve element 106. After the pump speed increases 
above a predetermined value, a second control port 120 becomes uncovered 
by land 110. This port 120 communicates with the passage 118. When the 
port 120 is uncovered, the low pressure area that communicates with port 
122 is brought into communication with passage 118. Port 122, in turn, 
communicates with the reservoir and fluid is returned from the reservoir 
to the valve assembly through it. As soon as passage 118 becomes subjected 
to lower pressure, valve element 106 will be caused to shift further away 
from the venturi throat thereby increasing the bypass flow from port 74 to 
port 76 and decreasing the outlet flow through the passage 96. Thus a 
decrease in the rate of pressure build up upon increase in pump speed 
occurs and this causes a so-called "drooper" effect. A drooper effect is 
achieved in other ways in other prior art constructions, such as those 
shown in U.S. Pat. Nos. 3,253,607 and 3,349,714. The drooper effect in the 
'607 patent is achieved by using a pair of flow metering orifices and 
controlling the effectiveness of one of the orifices as flow across the 
mouth of the orifice increases. The drooper effect of the '714 patent is 
achieved by having a variable geometry metering pin register with an 
orifice in the outlet flow circuit of the pump. The drooper effect of my 
instant invention is achieved in a much simpler fashion, and it is 
characterized by improved reliability. 
FIG. 11B shows the valve element 106 in a position where the 1 and 110 
uncovers the port 120, which corresponds to the high speed condition. 
Upper pressure plate 48 as well as the lower pressure plate 46 is provided 
with pressure equalizer passages. Each pressure plate has a pair of 
passages, one corresponding to each of the pumping chambers of the pump. 
Equalizer passages for the upper pressure plate 48 are shown at 124 and 
126, which span the inlet ports 70 and 72 respectively. They are arcuate 
in form, and their ends are located close to the cutoff and opening edges 
of the ports to which they are adjacent. The equalizer pressure passages 
for the lower pressure plate 46 are shown at 128 and 130. As in the case 
of the equalizer pressure passages for the upper pressure plate, passages 
128 and 130 span the inlet ports 54 and 56; and they terminate a location 
adjacent the individual edges of these ports. 
In order to explain the operation of the equalizer pressure passages, 
reference will be made to FIG. 12 where I have shown in schematic fashion 
a cam and rotor assembly. I have identified the equalizer pressure 
passages by reference characters 128' and 130' which correspond to the 
passages 128 and 130 of FIG 7. The direction of rotor rotation is 
illustrated by the rotational vector 132. The two low pressure oil inlet 
ports are identified in the schematic sketch of FIG. 12 by reference 
characters 134 and 136. The two outlet high pressure ports are identified 
in the schematic sketch of FIG. 12 by reference numerals 138 and 140. The 
rotor 142, which corresponds to the rotor 38 in the embodiment of FIGS. 1 
through 9, carries slippers 144 located in radial pockets 146. The 
equalizer pressure passage 128' of the rotor 142 is positioned as shown in 
FIG. 12 establishing communication between the pockets located at the 1:30 
o'clock position and the 10:00 o'clock position. The fluid cavity located 
between two adjacent slippers at the 11:30 o'clock and the 1:30 o'clock 
positions becomes trapped after the second of the pair of slippers passes 
the cutoff edge 148 of the high pressure outlet port 138. At the same 
instant the slipper at the 10:00 o'clock position has just passed the 
cutoff edge 150 of the oil inlet port 134. Thus the fluid trapped in the 
cavity between the slippers at the 10:00 o'clock position and the 8:30 
o'clock position is equal in pressure to the pressure at the inlet port 
134. Conversely, the pressure that exists in the trapped volume of fluid 
between the slippers at the 11:30 o'clock position and the 1:30 o'clock 
position is at the high pressure that exists in the outlet port 138. 
It should be noted that the leading edge of each slipper pocket 146 is 
provided with an angular slot 147 which permits the pocket 146 to 
communicate with the pumping chamber between that slipper and the next 
adjacent preceding slipper. Corresponding notches are shown also in FIG. 
10 at 41. 
The pressure equalizer passage 128' will cause a higher pressure to be 
distributed to the trapped volume of fluid at the lower pressure, thereby 
tending to equalize the pressures and permitting a recovery of some of the 
potential energy of the fluid. When the trapped volume of high pressure 
reaches the oil inlet port 134 upon continued rotation of the rotor, the 
pressure change that occurs is less severe and pressure pulsations tend to 
be modified or reduced. The same is true for the trapped volume of fluid 
at the lower pressure port as it is brought into communication with the 
high pressure outlet port 140 upon continued rotation of the rotor. The 
pressure difference between that trapped volume of fluid and the pressure 
at the outlet port 140 is reduced. This pressure equalization improves the 
pumping efficiency and reduces pump noise due to large pressure 
pulsations. 
Equalizer pressure passage 130' functions in a similar fashion on the 
opposite side of the pump as fluid is transferred from the inlet port 136 
and to the outlet port 138.