Note: Descriptions are shown in the official language in which they were submitted.
I ! ~
~066950
Background of the Invention
The present invention relates to pumps, and particu-
larly to power-steering pumps for use in vehicle steering
systems and controls ~herefor. Power-steering pumps for use
i~ veh~cle steering systems are well known and there are a
plu~ality of power-steering pump constructions. Such pumps
have associated therewith some means of controlling the flow
of fluid to the steering system in response to a pressure
demand for steering fluid. Further, normally some means of
controlling the output flow from the pump is provided so
that an excessive amount of flow at high vehicle speeds is
not d~rected to the system.
Typically, and as shown in U.S. Patent No. 3,200,752,
the above-noted functions are provided by a bypass valve which
responds to pressures acting thereon and bypasses output pump
~low to the pump inlet. By controlling the output flow to the
syste~ b~ a b~pass valve, the pump output is controlled and
ma~ntained so that a proper ~low of fluid to the system in order
to handle steering demand is provided and excessive flow to the
system at high vehicle speeds is prevented. In the type of
s~stems diclosed in U.S. Patent No. 3,200,752, the bypass valve
must bypass substantial volumes of fluid in order to provide for
the proper operation of the pump in the system. For example,
the amount of fluid bypassed at extremely high speeds may be
~n the order o$ 25 gallons per minute, which, of course, require s
substantially la~ge valve for purposes of bypassing such flow.
.".'
B ~
.~ .. - ~ ` .
: 1(:~66950
Recently, as disclosed in U.S. Patent No. 3,822,965,
a substantial breakthrough in power-steering pumps was achieved.
In patent 3,822,965, a bypass valve, as conventionally had been
used in power-steering pumps, was eliminated. Rather than the
use of a bypass valve for purposes of bypassing excessive flow
of fluid from the pump, a pUMp construction and control was
developed whereln the pump was unloaded due to movement of a
cheek plate, which defined part of the pumping chamber in which
the pump displacement structure operates. When the cheek plate ~
moves, the pumping chambers connected with the inlet and the ;
pumping chambers connected with the outlet are directly communi-
cated to provide flow f~om the outlet to the inlet of the pump
across the pump displacement structure and across a face of
the cheek plate.
In patent 3,822,965, the cheek plate is moved due to
fluid pressures acting thereon, and specifically a fluid pres-
sure chamber is provided on the side of the cheek plate opposite
the side facing the displacement mechanism. A control valve
is provided in the system and which controls the pressure in
the chamber or cavity. The control valve which controls the
pressure in the cavity is a relatively small valve as compared
to the bypass valve heretofore referred to and, of course, does
not function as the main bypass forfluid, the main bypass being
across the face of the cheek plate.
.~ . ' .
~' .
' .
~ -2-
1066950 ``
' !``
Summary of the Present Invention :
The present invention relates to the type of system
disclosed in U~S. Patent No. 3,822,965 and which utilizes a ~'
cheek plate unloading feature in a pump for purposes of by-
passing fluid directly from the inlet to the outlet of the ':
pump a,nd thereby controlling the flow of fluid to the system
supplied by the pump to modulate and maintain the flow of .
fluid to the system as desired. The cheek plate moves in ~
response to a variation of pressures acting on the cheek plate, ~,
which variation in pressures is controlled by a suitable con-
trol valve which responds to a variety of different conditions ;
including excessive flow or high pressures in the system. , --.
Specifically, the present invention i.s directed to the ~.
problem of stabilizing the control valve which controls the
pressure in the cavity to control the position of the cheek ,'
plate. The distance through which the control valve is moved ''
to cause the cheek plate to move to a full open position is rela- ::
tively small. For example, the total distance through which the : -
valve is moved may be 0.06 inches. Therefore, any instability
which tends to even slightly affect the posltion of the control ~
valve will affect the pressure in the cheek plate cavity and in ...
turn affect the position of the cheek plate and thereby aEfect
performance. Therefore, for uniform and accurate control of the
pressure in the cheek plate cavity, it is desirable, if not essen- :,
tial, to maintain the control valve in a stable position and not
have it subject to extraneous forces which would tend to cause
the valve to move.
. .
-
.
. : , . .
,~
~ 1066950
plicant recognlzes that a varlety or clfferent con- j
structions can be utilized for stabilizing the control valve
which controls the pressure acting on the cheek plate. How-
ever, in the preferred embodiment herein a small stabilizing
flow of fluid is provided which is directed past the control
valve and which causes or effects a stabilization of the control
valve.
In the present invention, when the control valve moves to
a position venting the cheek plate cavity for purposes of con-
trolling movement of the cheek plate, the valve will first .
move to open and communicate the cheek plate cavity to initiate
venting of the pressure in the cavity, and thereafter a small
stabilizing flow of fluid is provided from the pump outlet
across the control valv2 and which stabilizing flow functions
to stabilize the valve. This stabilizing 10w is in the nature
of a small leakage flow, and the bulk bypassing of fluid from
the system occurs across the cheek plate. It is essential
that it be understood that the flow for purposes of valve ,
stabilization in this case is merely a leakacJe flow and is not
a bypass flow of the nature in the prior art for purposes of
maintaining flow to the system at a proper level.
Description of the Figures
Further features and advantages of the present inventionw111 ce me apparent to those skille~ in the art to wh1ch lt
,,
'
'' .
~-~ 1066950
. . . :
. ::
relates upon consideration of the desc~ption of the preferred
embodiment made with reference to the accompanying drawings ; -
in which:
Fig. 1 is an axial sec-tional view of a power-steering
pump embodying the present invention but with parts omitted;
Fig. 2 is a sectional view of a portion of the pump of
Fig. 1 on an enlarged scale;
Figs. 3 and 4 are further sectlonal views of a portion
of the pump of Fig. 2 and showing parts in different positions;
Figs. 5-7 are graphs illustrating operating characteris-
tics of prior art pumps; and
Fig. 8 is a graph illustrating operating characteristics
of the pump of the present lnvention.
Description of a Preferred Embodiment
The present invention is preferably embodied in a power-
steering pump 10. The power-steering pump 10 includes an
assembly 11 made up of a member 12 and an outer shell 13 which
is threadedly engaged with the member 12 at 14. The assembly 11
in part defines a pumping chamber 15 in which are located the
:' . '':
,
~`` ` '
I ~066950
pumping elements of pump displacement mechanism 16 for effect-
ing the pumping of the fluid.
The pump displacement mechanism may be of any conven-
tional construction and as shown herein includes a cam ring 20
which is suitably radially located rela-tive to the member 12 of t} e
~- assembly 11 by the dowels 21. The cam ring 2Q has an internal bo: e
and a series of slippers 22 are mounted for rotation in the bore.
The slippers are mounted in slots located in a rotor 23. The
rotor 23 is rotated or driven by an input shaft 24 which has
a driving spline connecti~n with the inner diameter of the
rotor 23, such as shown at 25. The slippers 22 are biased
outwardly into engagement with the inner periphery of the cam
ring 20 by a series of springs 26. Adjacent slippers define
pumping pockets which expand and contract as the rotor rotates
due to the cam ring configuration~ This specific type of
pump is known as a slipper pump, and since the construction
~ is known, a detailed description will not be made herein.
; It should be apparent, of course, that UpOII rotation
of tlle input shaEt 2~, the rotor 23 is rotated and carries
- the slippers 22 around the inner periphery of the cam ring 20.
As the slippers move around the inner periphery of the cam
ring 20, they cooperate with inlet and outlet ports, not
; shown, formed in a port plate 29. As the slippers move
past the inlet and outlet ports, the pumping pockets defined
between two slippers are either expanding or contracting. ,
", . '":
11 -6-
. . . . . __ _ ... _ .. _ _. ._ . .. .. _
- ~L066950 ~:-
. ,-
Fluid is drawn into the pumping pockets which are expanding
and fluid is forced from the pockets which are contracting. ;
The inlet and outlet port configurations do not speci-
fically form a part of the present invention, and accordingly ~
are not shown in detail herein. Preferably, the pump is of -
a double-lobed construction and has two inlet ports and two
outlet ports. Further, the specific passages connecting the
inlet ports with a fluid supply are not shown, nor are the -
complete outlet passages shown which communicate with the ~ ~,
outlet ports.
The pump 10, like U.S. Patent 3,822,965, has a cheek
plate unloading feature. Specifically, the pump 10 includes a
cheek plate 30 which defines a part of the pumping chamber 15
in which the pumping action occurs. The cheek plate 30 is
made up of a plurality of stamped metal plates, the details
of which will not be described herein. The cheek plate 30 is
biased by a spring 31 into engagement with the pump dls-
placement mechanism. The axial face 32 of the cheelc
plate 30 engages the adjacent axial face oE the cam ring
and rotor and functions to seal or block flow of fluid from
pumping pockets which are communicating with the inlet to pump-
ing pockets which are communicating with the outlet. Accordingly,
when the cheek plate 20 is in the position shown in Fig. l, total
output f the pump lS translated to the steering gear because ther¦
' . , ' ~
,, , '~: ~
~ . .. ,, . . ,
. .
-. 1066gSO
is no bypass of fluid between the inlet and outlet pumping pockets .
However, it should be apparent that if the cheek plate 30 would
move to the right from the position shown in Fig. 1, fluid can th~ n
flow in the space between the cheek plate 30 and the rotor 23 so
that fluid would be directly communicated from the pump outlet
to the pump inlet. This would greatly reduce any flow of fluid
to the system supplied by the pump. Of course, the greater the
amount of movement of the cheek plate 30, the greater the amount
of fluid bypassed. Accordingly, it should be clear that by
accurately controlling the position of the cheek plate 30, a
precise control of flow to the system can be achieved.
In order to provide for accurate positioning of the
cheek plate, the pump 10 includes a pressure cavity, generally
designated 35, located on the right side of the cheek plate 30
(as viewed in~the drawing). It should be apparent that any
pressure in the cavity 35 biases the cheek plate 30 into en-
gagement with the pump displacement mechanism 16 and tends to
move the cheek plate to the left to increase flow from the
pump. Fluid pressure in the chamber 35 is çommunicated to the
chamber 35 by a suitable passage means 40 in the cheek plate. The
passage 40 communicates with the outlet of the pump. Accordingly,
pressure is communicated to the cavity 35 to urge the cheek plate
into t position shown in Fi~
-8-
'
I '~
, . . . . _ ._ ._ _ _.. __ _ , _ . .. . .. , . . . _
` 11 .
` ~06695Q ~
'~
The cheek plate is provided with a seal in the form of
an O-ring 48 encircling the cheek plate. The O-ring 48 is
structured so as to maintain a sealing relationship between
the outer periphery of the cheek plate and the inner periphery
of the m~mber 13 in assembly 11. Accordingly, there is no
leakage of fluid between the part 13 and the outer periphery
of the cheek plate 30. Accordingly, the only fluid flow into
the chamber 35 is through orifice 40, the size of which must
be accurately determined, as will be apparent from the descrip-
tion below.
Of course, it should be apparent from the above that the
forces acting on the cheek plate 30 include the output pressure
of the pump which acts on the face 32 of the cheek plate 30
tending to move the cheek pla-te 30 to the right and the forces
acting to move the cheek plate 30 to the left include the
spring 31 and the pressure in the cavity 35. It should be
further apparent that by controlling the pressure in the
cavity 35, it is possible to control the posi.tion of the
cheek plate.
The pump 10 specifically includes a control valve
mechanism, generally designated 50, for controlling the
pressure in the cavity 35. The valve mechanism 50 is located
in a bore 51 in the pump housing member 12. The bore 51 and
,;
'~ .
',:; . .
Il` 1066~50
the valve mechanism 50 are communicated with the cavity 35
through a passage 52 in the housing member 12 and a hollo~
dowel pin 53. The dowel pin 53 is connected with the member 12
of the housing and extends through the port plate 29, the cam
ring 20 and into the cheek plate 30. It should be apparent that
the hoIlow dowel 53 communicates at one end with the passage 52
and at its other end with the chamber 35. It should further
be apparent that the dowel pin guides axial movement of the
cheek plate 30. Further, it should be apparent that the cheek
plate is nonrotatable, the dowel pin assisting in preventing -
any rotatlon.
The valve mechanism 50 responds in one case to instantaneous
increases in fluid pressure demands and reduced flow to the
system. In that~ case, the valve mechanism 50 provides for an
increase in pressure in the chamber 35 and therefore movement
of the cheek plate toward the left in order to increase the ,
output of the pump in order to meet the pressure and flow de-
mand by the system. Further, the valve mechanism 50 functions
in the case of excessive flow to the system, such as at high
pump speeds, to reduce tlle pre~qsure in t.he chamber 35 and thereby
enable the cheek plate 30 to move under forces acting on the
surface 32 thereof, to bypass fluid flow from the system.
Accordingly, it should be clear that the pump lO,including the
valve mechanism 50,operates in order to modulate the flow of
fluid to the power-steering system, much in the manner described
and disclosed in ~.S. Patent No. 3,822,965.
... . ~
,
: : : . - :
`: 1066950 ~
. ` .
The valve mechanism 50 comprises a spool valve member 60 :
(see Fig. 2j. The spool valve member 60 is mounted in a sleeve .
member 61, which sleeve member is located in the bore 51. The
sleeve-member 61 has a plurality of lands which are designated
62, 63 and 63a. The lands are spaced axially along the sleeve
member 61 and define therebetween and with the bore 51 a pair
of circumferentially extending yrooves or fluid passages 64, 65.
At its right end, the sleeve member 61 abuts a shoulder 70 on
the housing member 12. At the left end of the sleeve member 61, ~
as shown in Fig. 2, the sleeve member engages a screen 71 (shown :
schematically),whlch screen is interposed between the left end
of the sleeve member 61 and a pressed-in plug member 73 which has .
an opening 74 for flow of fluid therethrough to the system. :
A high pressure relie~ valve assembly 80 is suitably
carried at the rignt end of the sleeve member 61. The relief
valve assembly is preferably as shown in V.S. Patent 3,822,965 :
and will not be described herein. A spring member 81 acts
between the relief valve assembly 80 and tilC valve spool 60,
biasing the valve spool toward the leEt, as shown in the drawings.
The valve spool 60 has an annular land member 82 which engages
a snap ring 83 carried on the inner periphery of the sleeve .
member 61 against which the land member 82 is biased by the
spring 81, as shown in Fig. 2.
The passage or chamber 64 communicates with the
inlet of the pump via a passageway 95, and the chamber 65
~06695~
communicates with the passage 52 and therehy communicates with
the chamber 35.
The valve spool 60 has a projection ;00 which projects
through the passage 74. An orifice 91 is defined between
the.outer surface of the projection 100 and the member 73.
The outlet of the pump is shown schematically at 90 in Fig. 2
and the flo.~ from the outlet of the pump flows through the . ~:~
screen 71 through the orifice 91, through passage 74 to the : .
power-steering gear. ~ .
The valve spool 60 further has a passageway 101 ..
extending therethrough and which co~nunicates at the outer
end of the projection 100 with the outlet conduit or system,
and at its inner end communicates with the chamber 81a in .~ :
which the spring 81 is located. Accordingly, it should be
apparent that in the position shown in Fig. 2, fluid pressures
act on the outer surface 110 of the projection 100, as well ::
as on the surface 111 of the land 82, and which pressures
will tend to act to move the spool valve 60 toward the riyht,
in the view shown in Fig. 2. Further it should be apparent that t he
spring 81 and the pressure in the chamber 81a acting on the
end surface 112 of the spool tend to move the valve spool to
the left, in the view shown in Fig. 2.
Prior to start-up of the pump, of course, the cheek
plate 30 is in position illustrated in Fig. 1, biased thereto ..
by spring 31. As rotor 23 is initially turned, fluld is ~-
' . .
~ -12- ~ -
~ ~'
~0669S0
drawn into the pump and forced out of the pump through the
outlet 90, orlfice 91, passage 74, and to the system. In
the event that the system is an open-center system, as is
common, the fluid will be returned to reservoir and from the
reservoir back into the pump, as is known. Of course, prior
to start-up, the valve spool 60 is in the position shown in
Fig. 2 (which corresponds to the position shown in Fig. 3) in
which the body of the valve spool or land area, designated 120,
COVers an opening 121 in the sleeve member 61. The opening 121
communicates the groove 65 with the internal bore of the sleeve
member 61. When the land 120 blocks communication between groove
65 and the internal passage of sleeve 61, the cheek plate <
cavity 35 is blocked by the spool valve and pressure increases
in the cheek plate cavity 35 due to the flow of fluid into the
cavity 35 through the orifice 40a. When the parts are in this
position, i.e., positions of Figs. 1 and 3, as pump speed
increases, output flow increases proportionally. This
proportionate flow occurs through a first or relatively
low pump speed range.
~owever, as pump speed increases with flow increasing
to the system, the pressures acting on the surfaces of the
valve spool 60 act to move the valve spool toward the right.
Of course, it should be apparent that the pressure acting on
the surface area 111 is higher (outlet pump pressure) than the
pressure acting on the surfaces 110, 112 due to the pressure
drop created by flow through the orifice 91. These surfaces ~
are sized to cause the valve spool to move to the right from ;
the position shown in Fiy. 3 to the position shown in Fig. 4
. ~ ~ ..... . .
~066~50`
when pum~ speed reaches a second range above the relatively
low first speed range.
When the valve spool moves to the right to the position
shown in Figure 4, the land area 120 moves to a position un-
blockine the passage 121 and fluid can thereby flow from the
area 65 through the passage 121 and into the bore surroundine
the sleeve 61. Further, in view of the tapered configuration
of the portion 120 of the valve spool, modulated flow control
is provided. The fluid, of course, will flow through passage-
way 121 into the interior of the valve sleeve 61, through pas-
sageway 131, area 64 and passage 95 to the inlet of the pump.
This, of course, vents the cheek plate cavity 35 with the
result that the pressure acting on the surface 32 of the cheek
plate 30 will cause the cheek plate to move to the rieht, as
shown in Figure 1, bypasæing fluid directly from the outlet to the
inelt of the pump across the sur~ace 32 of the cheek plate.
. .
As a result, flow to the system will be controlled.
When the valve spool 60 moves to the position shown
in Figure 4, the land 82 on the valve spool moves to a position,
as shown in Figure 4, where some fluid flow, as indicated by the
arrows 135, can leak past the land 82 through a passage 136
and into the area 64. This Yluid flow may be rererred to QS
a stabllizing flow and comprises a very slight fluid flow,
the function of which iB to provide stabilization of the valve
spool 60. This rlow only slightly reduces the flow of fluid
to the syste=.
'.
,.
- 14 -
l ~ ' `
~66950
The flow designated 135 for purposes of stabili.zation :~
is achieved after the cheek plate cavity 35 is vented due
to the passage of the land 120 past passageway 121. In this con- :
nection, the distance between the line 140 and the line 141 in
the drawings is greater than the distance between the left-
wardmost edge of the ports 136 and 121. As a result, the ;
land 120 opens port 121, while the land 82 still blocks port . :
136, and it is not until after the cheek plate cavity begins /
venting (line 140 passes left edge of port 121) that the . .
establishment of the stabilizing flow is achieved.
It should be clear that when the valve spool 60 is
in the position of Flg. 4, there is a flow through the passage :~
121 and passage 131, indicated by the arrow 150. In addition,
there is a flow,indicated by the arrowS151, to the outlet of
the system. These flows, as is well known, create forces
acting on the valve spool 60 in the nature of pressure forces,
as well as flow forces. Further, the valve ~pool 60 is
subject to vibration forces, etc., all of which have a ten-
dency to cause the valve spool 60 to be unstable. It has
been found that the stabilizing flow, i.ndicated by the arrows
135, provide a stabilizing effect on the valve spool 60 and
is extremely important in terms of providing a stable valve
spool for purposes of accurate control of the cheek plate
position and thereby accurate control of the flow to the
system.
. .
: . .
.. , . . ,.. __ . ... ,... ~ _ _ _ . , _, _____ . _
~ ~ " ' `
1~66950
After the valve spool has been moved to the position
shown in Fig. 4, the valve spool can move or modulate about
that position in order to control flow of fluid to the system ;
during the relatively high pump speeds. For example, if for
some reason the fluid pressure in the system increases, there
would be an instantaneous reduction in flow through the orifice
91. As a result,the differential in pressure between the pres-
sure acting on the surface }11, on the one hand, and the sur-
faces 110, 112, on the other hand, would reduce and thus the -
valve would tend to move toward the left, as viewed in Fig. 2,
causing a reduction in ven~tlng of the cheek plate cavity. This
would result in the pressure increasing in the cheek plate cavity
35 with the result that the cheek plate 30 would move into a
position closer to the pump displacement mechanism 116 and
cause an instantaneous increase in flow to the system.
Further, in the event of vehicle speed increasing
with a corresponding increase in pump speed, an instantaneous
increase in flow through orifice 91 would result, and an
increase in the pressure drop across the ori~ice 91 would occur.
As a result, the differential in pressures acting on surface 111,
on the one hand, and surfaces 110, 112, on the other hand,
would increase and the valve spool would move to the right
increasing venting of the cavity 35 with the result -that
the pressure acting on surface 32 of the cheek plate
. . ~ . . . _ .
L,
1(~669SO
. ..
would cause movement of the cheek plate 30 toward the
right.
It should be apparent that any movement of the valve
spool 60 toward the left from the position shown in Fig. 4
would be in a direction tending to cut in-to the fluid flow
indicated by the arrows 135. Fur-ther, any movement of the
valve spool 60 toward the riyht would be in opposition to the
spring 81 and any fluid pressure acting in chamber 81a. As
a result, it should be apparent that there is some resistance
to movement of the valve spool in either direction from the
position shown in Fig. 4 and this resistance, in effect, acts
as a dampener and does function to provide for accurate move-
ment of the valve, as well as stabilization of the valve when
in any position.
The characteristics of the operation of the present
system should be apparent from the above. However, for purposes
of a complete understandiny of the inventon and how it compares
to the prior art lcnown to applicant, the graplls of output
flow to pump speed shown in Fiys. 5-7 are provided. Refer-
ring, for example, to Fig. 5, it is well known that as the
speed of the pump increases, the output flow to the system
supplied by the pump will increase in proportion to increases
in the speed of the pump. If there is no flow control on
the pump, the total area defined in the triangle shown in
Fig. 5 would be the area representative of the flow to the
, . . .~ _
1~66950 1 -
system in accordance with increasing of pump speed. As noted
above, it is well recognized that a continuing increase of flow
to the system as pump speed increases is unsuitable for power-
steering pumps and that flow control must be provided to min-
mize flow of fluid to the system at high speeds.
The diagram of Fig. 5 is somewhat representative of the
structure and operation of a system, such as shown in Dudley
U.S. Patent No. 2,923,244. Without going into all of the de-
tails of the Dudley patent, the Dudley patent does disclose a
system where rotatable cylinder blocks are moved in order to
bypass fluid. The cylinder blocks are loaded by pressure in `
a chamber between the cylinder blocks, and the flow into the
chamber occurs due to leakage around the cylinder blocks and
between the pistons in the cylinder blocks. As shown in Fig. 5,
the area A represents the volume of flow that does not go to -
the system due to unloading of the cylinder blocks, i.e.,
movement relative to a port plate. The area B represents
the volume of flow which does not go to the system due to
leakage flow that occurs around the cylinder block and ~he
area C is the flow that does not go to the system due to
leakage around the pistons, a point in the line defining the area
D represents the flow to the system at a given speed. It should
be clear upon careful analysis of the Dudley patent that the
area C cannot be finely controlled due to the fact that leakage
which is uncontrolled provides the pressure within the leakage
. . '~:''
. . ';'~
1 -18- ~
- ,, ,,,,
.', ~
` 1066950
between cylinder blocks. Further, it should be clear that all
of these flows which are reductions from the flow to the system
occur simultaneously and, in fact, the bypass ilow and piston
leakage flow occur immediately upon operation of the pump.
- Fig. 6 is a somewhat representative graph of the operating
characteristics of U.S. Patent 2,839,003 to Thrap. This patent o )e-
rates somewhat similarly to the Dudley principle; however, in the
Thrap patent there is a bypass valve which provides a bypass
flow which occurs prior to the unloading of the cheek plate. The
bypass flow is the main flow ~hich controls the output and
cylinder block unloading is a safety feature. The area B in the
Thrap patent represents the area of fluid which is bypassed
by the bypass valve which is a substantial area. The area A
represents the portion of the flow of fluid which is bypassed
due to unloading of the cylinder blocks due to movement of
the cylinder blocks; and the ~ea C represents the area of flow
reduction to the system due to piStOll leakage and leakage
around the cylinder blocks. It should be ~p~arent that there
is a timing differential in the Thrap system and that the
bypass valve opens to bypass fluid from the outlet prior to
unloading of the cylinder blocks and that the unloading of
the cvlinder blocks is merely for purposes of control at very
high speeds.
.` .
,.: . -19-
,
- _
l ~
I'.,.,
~066~S0
The graph of Fig. 7 illustrate~ the operation of U.S.
Patent No. 3,822,965. In this patent there is accurate control
of the fluid pressure in the cheek plate cavity. The area B
is the area of flow reduction to the system which is a slight
metered flow of fluid out of the cheek plate cavity. The area
A is the excess flow above the area B which is provided by
unloading of the cheek plate. The line defining the area D
represents the modulated flow of fluid to the system. The area -
D is defined by a sharp "knee" in the curve at X as opposed to
the smooth curve provided in Figs. S and 6. This, of course,
results in optimum sharp control and is due to precise cheek
plate unloading.
Fig. 8 is a graph of the characteristics of the operation
of the present invention. The area represented by C is the
area of flow out of the cheek plate cavity 35. The area
designated B is the stabilizing flow. The area A is the area
of flow which is bypassed due to unloading of the cheek plate
and movement of the cheek plate. It should be clear that the
stabilizing flow area B is a very small flow and begins at a
time after cheek plate unloading begins. Further, the sharp
"knee" in the curve at X is provided which in part is due to the
establishment o~ cheek plate unloading prior to creaticnof the
stabilizing flow.
Further in accordance with the present invention, tests
have been run on the amount of fluid flow which is utilized
for purposes of stabilization. The amount of stabilizing flow
or precentage of stabilizing flow at various rpm's and for
different types of pump constructions will vary. In certain
'I
-20-
.
.... . ~ -
.; ..........
I 10669~0
pump constructions, the percentage of s-tabilizing flow to
total pump displacement at 7,000 rpm's has been approximately
9.8% and 6.6%. These percentages are higher than they need
to be for stabilization because of mechanical dimensions to
permit ease of machining. However, it should be apparent that
the amount of stabilizing flow is only a very small percentage
of the total pump output and provides for effective results,
as should be obvious to those skilLed in the art.
__
