Note: Descriptions are shown in the official language in which they were submitted.
:;~;lS~ 7
BACKGROUND AND SU~I~tARY OE: TIIE tNVENT~ON
This application is a division of applic~tlon No. 313~058 iled
on October 11, 1978.
This invention relates generally to hydraulic apparatus for control-
ling fluid flow to a hydraulic motor. In particular, it relates to a hydraulic
system for controlling fluid flow to a rotary motor which drives a cooling
fan associated with a vehicle cooling system, and to a pilot-operated pressure-
compensated valve which is used in the system.
The cooling fan for a vehicle engine has been driven mechanically
from the engine crankshaft, either directly or through a friction clutch.
Automotive engineers have recognized for some time that there are problems in-
volved with driving cooling fans in such a manner. In particular the problems
involve excessive use of fuel and excessive noise. One attempt at solving
these problems has been through the use of viscous fluid drives for driving
the fan. However, viscous fluid drives also have presented significant
engineering problems. Fan drive systems and the problems relating to the
design thereof are disclosed and discussed at length in the article "Fan Clutch
a Must for Heavy Trucks", Automotive Engineering Magazine, April 1975.
Another suggested solution to the fan drive problem centers around
driving the fan with a hydraulic motor and controlling the hydraulic motor so
that the fan is not driven when fan cooling is unnecessary, such as at high
vehicle speeds. United States patents 3,650,567; 3~942,4g6; 3,217,697 and
2,769,394 disclose systems having hydraulic motors for driving a fan.
The present invention provides an improved fan drive system utiliz-
ing a hydraulic motor for driving the fan. In particular, the present invention
provides a hydraulic system which includes a pilot-operated pressure-compensated
control valve for controlling flow from a fluid source to the fan motor. The
St;9~
valve has a valve element Eor controlling -~low be-tween an :inlet port, an outlet
port in fluid communication with the fan motor, and a bypass port in Eluid
communication with a reservoir. Tlle valve clement is biased to a Eull open
position to direct -Elow of Eluid to the fan motor. The valve element is moved
toward a closed position to divert flow to the reservoir i.n response to a p:ilot
pressure signal. The pilo-t pressure signal is controlled by engine coolant
temperature. The pi}ot pressure signal controls the valve element to divert
flow to the reservoir when coolant temperature is below a predetermined minimum.
Thus, when fan cooling of the engine is unnecessary, the fan motor is not driven.
The pilot-operated pressure-compensated control valve is designed
to respond to pressure spikes or surges in the system to divert fluid from the
outlet port to the bypass port. As a result of this construction, the valve
provides a protection for the hydraulic motor. This constitutes a substantial
improvement over prior art fan drive systems which have not included a pilot-
operated valve having such functions.
Further, the pilot-operated pressure-compensated control valve is
constructed so that it always allows at least a predetermined minimum flow from
the source to the hydraulic fan motor. Thus, there is always a pressure main-
tained on the fan motor. The fan is therefore free to rotate due to the ram
air impacting thereon and such rotation of the fan can occur without cavltation
occuring in the hydraulic fan motor. Further, when it is desired to drive the
fan by the hydraulic motor lower inertia forces need be overcome as compared
to a system where the fan is stopped.
Accordingly, the present invention provides a pilot-operated
pressure-compensated control valve which functions (1) to control the flow of
fluid to the hydraulic fan motor in response to coolant temperature, ~2) to
respond to pressure spikes or surges in the system to divert fluid from the
-- 2 --
llydraulic fall motor, and (3) to maintain at least a minimum level of fluid flow
from a fluid source to the hydraulic fan motor when the fan motor is not
driving the fan.
As noted above, the pilot-operated pressure-compensated control valve
has significant advantages when used to control flow to a fan motor. It may
also be used in other fluid systems where the need arises.
Further, the present invention provides a combined steering and fan
drive system in which fluid flow from a fixed displacement supply pump is
directed to independent steering and fan motor drive systems under the control
of a priority flow divider valve. The priority flow divider valve insures a
predetermined amount of flow to the steering systems and excess flow to the fan
drive system. Flow from the priority valve to the fan motor drive system is
directed to the pilot operated pressure-compensated valve discussed above.
According to a broad aspect of the present invention, there is
provided apparatus for controlling fluid flow in a hydrauliG system. The
; apparatus comprises a housing having an axially extending bore, an inlet port,
an outlet port, a pilot port and a bypass port. A valve element movable in
the bore controls fluid flow between the inlet port, and outlet port, and the
bypass port. A pilot fluid pressure actuated device is connected with the
valve element for moving the valve element in one axial direction. A spring
moves the valve element in the opposite axial direction. The pilot pressure
actuated device is in fluid con~unication with the pilot port. The valve ele-
ment is axially movable in opposite directions between a first position estab-
; lishing predetermined flow paths between the inlet port, the outlet port and
the bypass port, and a second position establishing at least a predetermined
flow path between the inlet port and the outlet port. Fluid reaction surface
means is connected with th~ valve element and disposed in Eluid com~unication
:~l5~g(37
with the flu:id flowing through the valve element. The :fluid renction swrface
means is designed so that 1u:id pressure acting against it produces a resultantforce on the valve element urging the element toward the first position.
~lore specific aspects of the prese~t :invention are defined in the
claims appendecl to the disclosure~
BRI~F DESCRIPTION OF TIIE D~AW~NGS
The features and advantages of the present lnvention will become
further apparent from the following detailed description taken with reference
to the accompanying drawings wherein:
Figure 1 is a schematic representation of a hydraulic system con-
structed in accordance with the principles of the present invention;
Figure 2 is a sectional view of a fixed displacement pump having a
- priority flow divider valve integral therewith for use in a system accord:ing to
; the preferred embodiment;
Figure 3 is an end view of the pump of Figure 2 as indicated by the
line 3-3 in Figure 2 with portions of the housing broken away to show a portion
of the priority flow divider valve;
Figures 4, 5 and 6 are longitudinal sectional views of the priority
flow divider valve, illustrated in certain of its operating positions;
Figure 7 is a longitudinal sectional view of the pilot-operated
; pressure-compensated~ flow control valve constructed according to the present
invention, illustrated in one of its operating positions;
Figure 8 is a fragmentary sectional view of the pilot-operated
pressure-compensated flow control valve in another of its operating positions;
Figure 9 is a schematic illustration of the priority flow divider
pump circuitry according to the preferred embodiment of the invention; and
Figure 10 is a longitudinal sectional view of an alternative pilot-
-- 4 --
~ :L5~ 7
operated pressure-compensated flow control valve which has been suggested -for
use in a system accorcling to the invention.
DETAILED DESCRIPTION OF TIIE
PREFEIRRED EhlBOD:lMENT OF Tl`IE INVENl'ION
As noted above, the present invention relates to hydraulic apparatus
for controlling operation of a hydraulic motor and in particular for control-
ling operation of a fan motor for a vehicle cooling system. As shown in
Figure 1~ a vehicle cooling system lncludes an engine driven pump 10 which
draws coolant fluid from a reservoir 11 and circulates the coolant fluid through; the engine E. The coolant fluid is directed through the radiator 12 under the
control of thermostatic control means 13 of known construction.
The cooling fan F is disposed adjacent the racliator 12. In opera-
tion, the fan F draws air across the radiator 12 to assist in effecting cooling
of the fluid in the cooling system. The fan F is driven by the rotary output
shaft of a fan motor FM. The fan motor F~t is pre~erably a uni-directional
rotary hydraulic gear motor of known construction.
Referring to Figures 1 and 9, the fan motor FM is provided with
fluid flow from a priority flow divider pump PP. The pump PP includes a fixed
displacement gear pump P which draws low pressure fluid from a reservoir R
; and delivers high pressure fluid to outlet ports A, B under the control of a
priority flow control valve 14. Flow through port A is directed to a conduit
15 of a vehicle power steering system 16. The power steering system 16 may be
of different types, such as an integral power steering gear type or it may be
a hydrostatic type steering system. It is shown herein as an integral power
steering gear system. Flow through port B is directed to conduit 19 of a fan
motor system 20 for driving the cooling fan F.
In accordance with the invention, a pilot-operated pressure-
compensated control valve PCV operates to control fluid flow from outlet port B
~ - 5 -
`~:
of the pump to thc fan motor F~l. When fan cooling is unnecessary the valve PCV
is actuated by a pilot fluid pressure to a condition diverting flow in excess
of a predetermined minimum away from the fan motor so that the fan is not driven
whell fan cooling is unnecessary. When fan cooling is needed, the valve is
actuated by the pilot :Eluid pressure to increase flow to the fan motor to
drive the fan. The valve is further constructed to compensate for pressure
surges in the fan motor system to divert fluid away from the fan motor to pro-
tect the fan motor.
The power steering system 16 includes an integral power steering
gear SG. The steering gear includes an input shaft 13 connected to the vehicle
steering wheel SW, and further includes a mechanism of known construction
connected with the input shafts 13. The mechanism responds to rotation of input
shaft 13 to operate a steering arm 21. The steering arm 21 is connected to
the vehicle wheels 22 by linkage L of known construction.
The steering gear S~ includes a fluid inlet 24 for receiving fluid
from conduit 15 and a fluid outlet 26 for returning fluid to the reservoir R.
The steering gear also includes a valve for directing pressure fluid at inlet
24 to a fluid motor for providing a power assist for operating the steering arm
21, as is well known. Thus, rotation of the steering wheel SW directs fluid
in the steering system in a manner which assists in effecting movement of the
vehicle wheels 22.
The priority flow divider valve 14, described more fully hereinafter,
insures that all flow from the pump up to a predetermined flow rate is directed
to the steering system 16. Flow above the predetermined rate is directed to
the fan motor system 20. Low pressure fluid discharged from both the fan
motor and the steering gear is returned to the reservoir R while bypassing the
motor of the other system. Thus, steering system 16 and fan motor system 20
.
~'
.
~L5~(37
are independent ~Luid systems.
Priority Plow Divider ~
Referring to Figure 2~ the priority flow divider pùmp PP includes a
fixed displacement gear pump P. The gear pump P includes a~pair of housing
members 30, 32 forming a pumping chamber 33. A first pair of axially aligned
bushings 34~ 36 rotatably support a driven shaft 38 having a first gear 40
integral therewith. A second pair of axially aligned bushings 42, 44 rotatably
support a shaft 45 having a driven gear 46 integral therew;th which meshes with
the gear 40. The gears 40, 46 are located in the pumping chamber 33.
The pumping chamber 33 communicates with a pump inlet 48 ~Figure 2)
by passages not shown. Inlet 48 is connected to reservoir R. Rotation of gear
members 40~ 46 draws low pressure fluid through inlet port 48 and directs
high pressure :fluid to a high pressure discharge chamber 50 (Figure 3).
Ret'erring to Figures 3-6, the priority flow divider valve 14 in-
cludes a housing portion 52 disposed in the pump housing 30. The housing por-
tion 52 includes an axially extending bore 54. A valve spool 56 is axially
movable in the bore 54. The spool 56 is biased in one axial direction (right-
wardly as seen in Figures 4-6) by means of spring 58.
The valve housing portion 52 includes one or more radially directed
inlet passages 60 which communicate with the pump discharge chamber 50. The
valve housing portion 52 further includes a plurality of radially directed
passages 62 communicating with bore 54. Passages 62 communicate w:ith a fluid
passage 6~ connected to outlet port B.
Still :Eurther, the valve housing 52 includes radial passages 66 which
communicate with the valve bore 54. Passages 66 also communicate with the inlet
side of the pump ~by means not shown). Additionally the valve includes radial
passages 68 which communicate with a chamber 70 at one end of the valve spool 56.
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~'' .
~ \ furthcr series o~ radial passages 72 are formed in the housing
portion 52. Raclial passages 72 communicate with valve bore 54 and with the up-
stream side of a Eixccl oriEice 74 ~Figure 3) of predetermined size. The down-
stream side of orifice 74 is connected with conduit 76 which directs fluid to
outlet port A.
Orifice 74 is sized to produce a predetermined pressure drop there-
across. A passage 77 ~shown in dashed lines in Figures 4-6) communicates fluid
pressure from conduit 76 with radial passages 68 and thereby with chamber 70.
Pressure upstream of the orifice 74 acts against end surfaces 78, 80 of the
valve spool 56.
The valve spool 56 includes annular fluid passageways 82, 84 and 86.
The valve spool 56 also includes a central bore 88. A plug 90 is disposed in
bore 88~ and includes an axial passageway 92 extending therethrough. A ball 94
is seated in a member 96 which is biased by spring 98 in a direction urging
the ball 94 into sealing engagement with one axial end of the fluid passage 92.
A radial passageway 100 in the valve spool connects the central bore 88 with
the annular passageway 84 formed in the valve spool.
The valve spool 56 is biased in one axial direction toward the posi-
tion shown in Figure 4 by means of the spring 58. In this position annular
~ 20 groove 82 connects high pressure discharge passage 60 with passages 72, and
- radial passages 62 are bloc~ed. All flow from the high pressure side of the
pump is thus directed to port A through the fixed orifice 74 and the conduit 76.
This is the valve position shown at I in Figure 9.
Flow through the orifice 74 creates a pressure differential across
the valve spool 56. Pluid pressure upstream of the orifice 74 acts against
valve end surfaces 78, 80 to urge the spool in one axial direction. Fluid
pressure downstream of the orifice 74 is communicated with chamber 70 and acts
- 8 -
S~i~07
on thc valvc spool to urge thc valve spool in an opposite direction. The
prCSS-lre differellticll procluces 1 resultant -force on the spool 56 acting against
the force oE spring 58. When the flow rate is above a predetermined amount
the pressure clifferential across the valve spool 56 shifts the valve spool from
its Figure 4 position toward a pos:ition such as shown in t'igure 5. In the
position shown in ligure 5, the almular passage 82 commun:icates passage 60 with
passages 62 and 72 thus directing Eluid to both ports A and B. This condition
is illustrated at II in Figure 9.
If fluid pressure downstream of orifice 74 becomes high enough, the
ball check valve 94, may be unseated. The chamber 7Q would then be vented
through passageways 100, 84 and 66 to the low pressure inlet side of the pump.
This results in a rapid drop in pressure ln the chamber 70 and thereby results
in leftward movement of the valve spool 56 to the position of Figure 6. In
this position the amount of flow directed to port A is substQntially reduced and
the amount of Elow directed to port B is substantially increased.
As should be apparent from the above the :Eoregoing valve construction
operates to direct all pump flow to the steering system port A until a predeter-
mined flow rate through the orifice 74 is obtained. Thereafter, the valve
maintains a substantially constant flow rate to the steering system port A and
directs all flow above the constant rate to the fan motor system.
Pilot-Operated Pressure-Compensated Control Valve
Referring to Figure 7, the pilot control valve PCV includes a housing
108. Housing 108 includes an inlet port 110, an outlet port 112 and an bypass
port 114. Housing 108 also includes a pilot port 116. Inlet port 110 communi-
cates with passageway 118 in the housing. Outlet port 112 and bypass port 114
communicate, respectively, with passageways 120 and 122 in the housing.
A valve spool 140 is movable between various positions in which it
_ g _
(37
clirects fluid from the inlet port 110 to the outlet port 112 ~and thereby to
the fan motor), or diverts flow from the inlet port 110 to the bypass port 114
when driving of the fan is unnecessary. The valve spool 140 furtller moves to
restrict Elow to the outlet port 112 in order to avoid pressure surges ac-ting
on the fan motor ~M.
Referring to Figures 7 and 8, the control valve housing 108 includes
an axially extending bore 124. The axially extending bore 124 is in fluicl
communication with inlet passageway 118, outlet passage 120 and bypass passage-
way 122. The passageways 118, 120, 122 communicate with inlet port 110, outlet
port 112 and bypass port 114, respectively. A plug 126 is fixed to housing 108
and forms a closure member which seals one axial end of the bore 124. Another
plug 128 is fixed to the housing 108 and includes a portion 130 which forms
another closure member which extends into the other axial end of the bore 124.
The plug 128 includes a central bore 132 closed at one end by a metal disc 134
and a snap ring 136.
The valve spool 140 is axially slidable in the bore 124. The outer
periphery of valve spool 140 includes an axially extending fluid passageway 142
which directs fluid between the passages 118, 120 and 122. Fluid passageway
142 is formed by a groove extending circumferentially around the spool and in-
cluding an axial surface 133 connecting a pair of radial surfaces 135, 137.
Valve spool 140 also includes radial surfaces 143 and 144 at one axial end
(the right end in ~'igure 7), and radial surfaces 146 and 148 at the other axial
end.
Additionally, valve spool 140 includes a central bore 150 extending
axially therethrough, and a radially extending fluid passageway 154 extending
between axial surface 133 and central bore 150.
An axially extending shaft 160 extends through the central bore 150.
- 10 --
3~3~
The valve spool :is sliclable on the sha~-t 160. Shaft 160 is slidable in an
axial bushiTIg 161 clisposecl in a bore 162 :in the closure member 130. Sealing
members 157 and 159 disposecl between the bore 162 ancl the shaft 160 on opposite
sides of the busll:ing 161 form a space 163 therebetween. A radial passage 167
in closure member 130 communicates space 163 with atmosphere.
Shaft 160 includes an enlarged head 164 at one axial end. The other
axial end of the shaft 160 has a piston 165 fixed thereto. Piston 165 is slid-
able in the bore :L32 in the plug 128. Piston 165 is preferably formed by a
dynamic sealing member 166 disposed between a pair of metal plates 168, 170.
10 One end of a helical spring 172 acts against end surface 146 of the
valve spool. The other end of the spring acts against a member 173 abutting
the fixed closure member 130. The spring 172 continuously urges valve spool
140 against the enlarged head 164 and thus continuously urges the shaft 160
and piston 165 toward the right as viewed in ~igure 7. The piston 165 in fact
is urged into abutment with the closure member 130 in the ~igure 7 position.
~luid reaction chambers are formed at each axial end of the valve
spool. One reaction chamber 180 is defined by the closure member 126, the valve
end surface 144, a portion of valve end surface 143, and the enlarged head 164.
Another fluid reaction chamber 182 is formed at the other axial end of the
valvo spool. The fluid chamber 182 is deined by the axial end surfaces 146,
` 148 of the valve spool, and the closure member 130.
Both axially spaced fluid chambers 180, 182 are in continuous fluid
communication with fluid flowing through axial passageway 142 in the valve spool.
This is achieved by providing sufficient clea.rance (not shown) between the shaft
160 and the bore 150 in the valve spool to establish fluid communication be-
tween passageway 154 in the valve spool and the fluid chambers 180, 182.
The fluid pressure in chambers 180, 182 produces a force differential
- 1 1 -
~S~ 3'7
across vnlve syool l40. Speci~ically, as seen in Figure 7, the ~`luid pressure
in chamber 182 ac-ts aga.inst surfaces having an annular area. The cmnular area
extends from the outer periphery o~ the spool to the central bore lS0 as sllown
at ~1 in Figure 7. The fluid pressure in chamber 180 acts against surfaces
having an e.Efective area which extends the entire diameter of the valve spool,
as shown at A2. Since sha:Et 160 extends through the chamber 182, the area
extending the distance A2 is greater than the area extending the distance A
by an amolmt determined by the cross sectional area of the bore 150. Thus,
fluid pressure communicatecl to the chambers 180, 182 produces a resultant force
- 10 on the valve spool 140 tending to urge the valve spool 140 to the left in Fig-
ures 7, 8. The spring 172, of course, cont1nuously biases the valve spool 140
in opposition to the resultant force.
The pilot controlled valve PCV is thus pressure-compensated to auto-
matically control fluid flow in response to pressure surges or spikes in the
system. In response to a pressure surge of a predetermined magnitude through
the valve spool passage 142, a sharply increased pressure is commlmicated to
the chambers 180, 182. This pressure acts on the unequal reaction surface areas
andsharply increases the resultant force acting on the valve spool 140. The
resultant force, if sufficient, moves the valve spool 140, the shaft 160, and
piston 165 axially against the bias of the spring 172 to divert flow from the
outlet port to the bypass port to compensate for the pressure surge. For ex-
ample, when the valve spool is in the Figure 7 position, a pressure surge of .
sufficient magnitude in the system would move the valve spool 140 leftwardly,
restricting flow to the outlet port 112 and increasing flow to the bypass port
:~ 114.
The foregoing valve construction also results in the valve spool be-
ing viseous damped. ~luid pressure .n ;he chsmbers 180, 182, at the ends of the
:
~5~ 7
~alve spool resists movement of the spool in either direction, thus serving to
damp the valve spool against oscillation.
The valve PCV, as noted, is pilot-operated. Specifically, the valve
spool 140 may be moved to block flow to the fan motor under certain conditions.
To this end a pilot fluid pressllre chamber 190 is formed between the housing
108, the closure member 130 and one side of the piston 165. The other side of the
piston 165 communicates with atmosphere through leakage paths formed between
the snap ring 136 and metal washer 134. The pilot fluid pressure chamber 190
communicates with pilot port 116 through passage 183 in the housing 108. An
0-ring 191 between the closure portion 130 and the housing 108 forms a static
seal between part of the pilot fluid pressure chamber 190 and the fluid chamber
182. Fluid from chamber 190 which leaks through seal 157 into space 163 is
vented to atmosphere through passage 167. Thus, pilot-pressure chamber 190
is sealed against leakage to chamber 182. Fluid pressure in pilot chamber 190
urges the piston, and thereby the valve spool 140, in an axlal direction against
the continuous bias of spring 172.
, ~
As noted above, the spring 172 continuously biases the valve spool
140 toward the position of Figure 7. In that position, all flow at the inlet
port 110 is directed through groove 142 to the outlet port 112 and then to the
; 20 fan motor. Flow through bypass port 114 is blocked. That valve position is
also shown at IV in Figure 1.
In response to an increased pressure in the pilot fluid pressure
;. i
chamber 190 the piston 165 and the valve spool 140 are moved axially from the
position of Figure 7 toward the position of Figure 8. Such movement of the
valve spool restricts fluid flow from the inlet port 110 to the outlet port 112,
and diverts fluid flow to the bypass port 114. If the valve spool is moved to
the Figure 8 position, it diverts most fluid flow to bypass port 114~ but
- 13 -
.
:~
PQ7
insures a minimulll predeterminecl amount o-f flow to outlet port 112. This condi-
tion is also sllo~l at V in ~igure 1. Pilot controlled movement of the valve
spool to positions between the extreme positions of Figures 7 and 8 would meter
fluid flow to both the ou-tlet por* L12 and the bypass port 114.
System Operation
In the system shown in Figures 1 and 9, the priority valve 14 directs
all flow below a predetermined flow rate to the steering system through port A,
and flow in excess of the predetermlned rate to the fan drive system through
port B. The pump P is sized to provide adequate flow for both the steering
system and the fan drive system at minimum engine speed.
The inlet port 110 of the pilot-operated pressure-compensated control
valve PCV is connected to the valve port B through conduit 19. Conduit 150
connects the outlet port 112 of the valve PCV to the high pressure inlet 152 of
fan motor FM. The bypass port 114 of the valve PCV is connected to the pump
inlet.
The spring 172 biases the pilot-operated pressure-compensated control
valve PCV toward the condition of Figure 7 ~position IV in Figure 1), in which
it directs all flow from the inlet port 110 to the outlet port 112, and flow
to the bypass port 114 is blocked.
The pressure in the pilot fluid pressure chamber 190 is controlled
by a fluid system separate from the fan motor system. One end of a pilot con-
duit 155 is connected with pilot port 116 of the pilot-operated pressure-
compensated control valve PCV. Thus, fluid pressure in the conduit 155 is com-
municated to the pilot fluid pressure chamber 190 and acts against piston 165.
In the preferred embodiment, vehicle air pressure is used to provide
the pilot pressure signal. A valve SV of known construction is biased to a
wide open condition establishing maximum fluid communication of air from the
- 14 -
:~S'~
vehlcle compressor C with the conduit 155, and thereby with pilot port 116 oE
valve PCV. Sucll a valve is commercially sold by companies such as Standard
Thomson Corp. 152 Grove St. Watham, rlass., and Kysor of Cadillac, 1100 Wright
St., Cadillac, P~lich. (a Kysor ~ 10~3-36~00-29. StlUTTERSTAT valve may be used).
The air pressure due to valve SV being open biases pilot control
valve PCV toward the Figure 8 position (the position V in Figure 1) in which
most fluid is diverted to the bypass port, but at least a minimum predetermined
flow is directed to the fan motor. When the temperature of the engine coolan-t
is low enough, and fan motor operation is not necessary, the pilot pressure
places the pilot-operated pressure-compensated control valve PCV in the fore-
going condition. The minimum predetermined flow directed to the fan motor
insures a positive pressure on the motor, and the fan may rotate essentially due
to the effect of ram air thereon without cavitation.
When fan operation is necessary, the valve SV is closed under the
control of a thermal sensor T of known construction. The sensor T is positioned
to continuously sense the temperature of the coolant fluid. The thermal sensor
T preferably comprises a conventional wax motor which expands and contracts in
response to the temperature of the coolant fluid. In the preferred embodiment,
the thermal sensor T is integrally connected with the valve SV. When the
temperature of the coolant fluid rises to a predetermined level, the wax motor
expands and closes the valve SV, thus shutting off fluid communication of
pressurized a1r to the conduit 155. An atmospheric vent in the valve SV allows
air to slowly bleed from the pilot conduit 155, thereby allowing spring 172 to
slowly move the pilot-operated pressure-compensated control valve toward the
Figure 7 position. This results in a gradual increase in the flow to the
rotary fan motor FM.
When the temperature of the coolant fluid drops below a predetermined
- 15 -
level the eontraction o~ the wcax motor of thermal sensor T results in the a~mos-
phere vent closing, and the valve SV thercafter moving toward the wide open
condition to increase air pressure in the conduit 155. 'I'his increases pressure
in the pilot chamber 190 to shift pilot-operated pressure-compensated control
valve PCV towarcl tlle ~:igure 8 position in which it diverts most fluid flow to
the bypass port J but maintains at least a minimwn predetermlned flow of fluid
to the fan motor.
Alternative Pilot-Operated Pressure-~ompensated Valve
Suggested ~or Use In The System According To The Invention
An alternat.ive pressure compensated, pilot operated valve has been
suggested for use in a system according to thc invention. The alternative
construction is shown in Pigure 10. The valve includes a spool 200 having an
annular fluid passageway 202. The spool is axially slidable in a stepped bore
204 formed in a housing 206. A sprirhg 208 urges the spool 200 toward the posi-
tion shown in Figure 10 directing all fluid from an i.nlet port 210 to an outlet
port 212~ and blocking flow to a bypass port 214.
The valve spool 200 includes an integral extension 216 having a
smaller diameter than the valve spool. The extension 216 abuts one side of a
pilot piston 218. A pilot pressure chamber 220 on the other side of the pilot
piston communicates with a pilot pressure port 222. ~ressure in the pilot
`~ 20 chamber 220 urges the pilot piston 218 against the valve spool extension 216 to
urge the valve spool against the bias of the spring 214.
A seal 224 is d.isposed between the outer surface of the valve spool
extension 216 and a wall of the stepped bore 20~. A seal 226 is disposed be-
tween the pilot piston 218 and another wall of the stepped bore 204. The space
230 between the seals 226~ 228 communicates with atmosphere through a passage
232 in the housing.
Because the valve spool extension 216 has a smaller diameter than
- 16 -
the valve spool, an annular radially directed sureace 234 is formed at an end
of tlle valve spool. lhe seal 224 helps Eorrll a Eluid chamber 235 which includes
annular surface 235 at the one end of the spool. There is fluid communication
between the passageway 202 and the chamber 235 through clearances betwecn the
spool and the bore 204. The space at the other end of the spool communicates
with the bypass port through a passage 238 in the housing. In response to a
pressure surge in the system~ increased pressure in chamber 235 acts against the
amlular reaction surface 234 to urge the valve spool against ~he bias of the
spring (i.e. leftwardly in Figure 10) to divert flow from the inlet port to
the bypass port.
The valve construction shown in ~igure 10 has been suggested by
Snap-Tite, Inc., Union City, Pa. 16~38 as an alternative valve construction for
the applicant~s valve disclosed above, particularly for use in a system accord-
ing to the present invention.
In summary, the hydraulic system described above includes a fixed
displacemcnt pump for drawing low pressure fluid from a fluid source and for
discharging high pressure fluid to the independent steering and fan motor systems
under the control of a priority flow control valve which insures flow to the
steering system up to a predetermined flow rate and excess flow to the fan motor
system. A pilot-operated pressure-compensated flow control valve upstream of
the fan motor includes an inlet port connected with the discharge side of the
pump (through the priority flow control valve), an outlet port connected with
the fan fluid motor and a bypass port. The pilot-operated pressure-compensated
valve is continuously biased toward a predetermined flow control condition. A
pilot fluid pressure acts against the continuous bias to move the valve member
for controlling fluid flow between the inlet port the outlet port and the bypass
port. The magnitude of the pilot fluid pressure is varied in response to the
- 17 -
temperature of the vehicle cooling system. The valve also responds to pressure
surges in -the fan motor systen~ to control the tlow of fluicl to the :Ean motor.
Tl~s, according to the foregoing detailed description, applicant
has provided what is believed to be improved hydraulic apparatus for controlling
fluid flow, particularly in a -Ean lllotor circuit.
