Power steering system with speed responsive force transmitting control

A power steering control valve including relatively rotatable inner and outer valve members. A power steering resistance control system resists relative rotation between the inner and outer valve members with a force which varies as a function of variations in vehicle speed and steering demand. The power steering resistance control system includes a force transmitting member which is disposed adjacent to one end of the outer valve member. A spring force is applied against the force transmitting member urging it in a first direction along the axis of rotation of the valve members. Fluid pressure is applied against the force transmitting member to urge it in the first direction. A valve is operable to vary the fluid pressure applied against the force transmitting member. A solenoid valve controls the position of the valve as a function of vehicle speed and steering demand.

BACKGROUND OF THE INVENTION 
The present invention relates to a vehicle power steering system, and more 
specifically to a hydraulic vehicle power steering system in which the 
resistance to actuation of a power steering control valve increases with 
increasing vehicle speed and steering demand. 
A known rotary power steering control valve shown in U.S. Pat. No. 
5,046,574 has an inner valve member which is coaxial with and rotatable 
relative to an outer valve member or sleeve. To effect actuation of the 
power steering motor to turn steerable vehicle wheels, the inner valve 
member is rotated relative to the outer valve member. A fluid pressure 
reaction chamber is provided to regulate the torque required to rotate the 
inner valve member relative to the outer valve member. The fluid pressure 
in the reaction chamber increases as vehicle speed increases to increase 
the resistance felt by an operator of the vehicle to rotation of the inner 
valve member relative to the outer valve member. 
SUMMARY OF THE INVENTION 
The present invention provides a new and improved apparatus for controlling 
the operation of a hydraulic power steering motor of a vehicle. The 
apparatus includes a manually actuated hydraulic, rotary, directional 
control valve having inner and outer relatively rotatable valve members. 
The relative rotation of the valve members provides flow and pressure 
control of the hydraulic fluid from the pump to the steering motor and its 
return to reservoir. 
A speed responsive control unit is connected in fluid communication with 
the control valve by a conduit through which hydraulic fluid from the 
control valve is returned to a reservoir. The speed responsive control 
unit is programmed to increasingly restrict fluid flow to the reservoir as 
vehicle speed increases and steering demand increases to increase the 
pressure in a fluid pressure chamber that regulates the torque required to 
displace the inner valve member relative to the outer valve member. 
As the pressure in the fluid pressure chamber increases, the resistance to 
relative rotation between the inner and outer valve members is increased 
and to the vehicle operator the steering feels more manual while still 
having power assisted steering. In neutral, the control valve is in an 
open center condition and hydraulic fluid is circulated at low pressure 
from the pump to the reservoir. Thus, the power steering pump does not 
have to act against high pressure when there is no steering and energy can 
be saved. 
A force transmitting member rotatable with the inner valve member is 
pressed toward the outer valve member by a biasing spring with a small 
spring constant and the fluid pressure in the fluid pressure chamber. The 
force transmitting member provides resistance to relative rotation between 
the inner and outer valve members that increases as pressure in the fluid 
pressure chamber increases. The speed responsive control unit includes an 
orifice that varies the pressure in the fluid pressure chamber. A speed 
responsive valve controls the size of the orifice as a function of 
steering demand and vehicle speed. The orifice is maintained open to vent 
the fluid pressure chamber to reservoir pressure when there is no steering 
demand or when the vehicle speed is low. The orifice is restricted or 
closed in response to increasing hydraulic fluid pressure due to a 
steering demand and increasing vehicle speed. Thus, the pump does not have 
to pump against an increasing pressure in the fluid pressure chamber as 
vehicle speed increases when there is no steering demand.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the present invention, a vehicle power steering system 12 (FIG. 1A) is 
operable to turn steerable vehicle wheels (not shown) upon rotation of a 
steering wheel 18 by an operator of the vehicle. Rotation of the steering 
wheel 18 actuates a hydraulic power steering directional control valve 22 
to port hydraulic fluid from an engine driven pump 24 and supply conduit 
26 to either one of a pair of motor conduits 28 and 30. The high pressure 
fluid conducted from the supply conduit 26 through one of the motor 
conduits 28 or 30 effects operation of a power steering motor 31 to turn 
the steerable vehicle wheels in one or another direction. Simultaneously, 
fluid is conducted from the motor 31 to a reservoir 32 through the other 
one of the motor conduits 28 or 30, the control valve 22, return conduits 
34 and 36, and a speed responsive control unit 38 (FIG. 1B). 
The points marked A, B and C in FIG. 1A correspond to the points marked A, 
B and C in FIG. 1B. Thus, return conduit 36 conducts fluid from the 
steering valve 22 to the speed responsive control unit 38. Return conduit 
34 conducts fluid from the steering valve 22 and the speed responsive 
control unit 38 to the reservoir 32. Conduit 248 conducts fluid from the 
pump 24 to the speed responsive control unit 38 and will be described in 
detail hereinafter. 
The control valve 22 (FIG. 1A) includes an inner rotary valve member 40 and 
an outer rotary valve member or sleeve 42. The outer valve member 42 
encloses the inner valve member 40. The inner valve member 40 and outer 
valve member 42 are rotatable relative to (a) each other and (b) a housing 
44 about a common central axis 46. 
The inner valve member 40 is formed on a part of a cylindrical input member 
or valve stem 50 which is connected with the steering wheel 18. Bearings 
52 support the inner valve member 40 and the valve stem 50 for rotation 
relative to the housing 44. The bearings 52 also maintain the axial 
position of the inner valve member 40 relative to the outer valve member 
42. There is no torsion bar interconnecting the inner and outer valve 
members 40 and 42. 
The outer valve member 42 is connected with a follow-up member 54 by a pin 
56. The follow-up member 54 is rotatably supported in the housing 44 by 
bearings 58 and 60. The follow-up member 54 has a pinion gear portion 64 
which is in meshing engagement with the toothed portion of a rack 66. The 
rack 66 is drivingly connected with the power steering motor 31 and 
steerable vehicle wheels as is well known in the art. 
The outer valve member 42 is fixed against rotation relative to the 
follow-up member 54 by pin 56. The input member 50 and the inner valve 
member 40 can be rotated slightly with respect to the follow-up member 54 
and the outer valve member 42. This relative rotation between the inner 
valve member 40 and the outer valve member 42 is used to control the flow 
of hydraulic fluid from the pump 24 to the steering motor 31. 
The pump 24 is a fixed positive displacement pump. The control valve 22 
(FIG. 1A) is of the open-center type. Therefore, when the control valve 22 
is in an initial or unactuated neutral condition, that is when there is no 
steering demand, fluid flow from the pump 24 is directed by the control 
valve 22 to the return conduits 34 and 36 and reservoir 32. Hence, fluid 
is circulated at low pressure, by the pump 24 through the valve 22 and 
back to the reservoir 32. 
Upon rotation of the steering wheel 18 and rotation of the valve stem 50, 
the inner valve member 40, if there is sufficient resistance to 
displacement of the rack 66 caused by frictional engagement of the vehicle 
tires with the ground or road surface, will be rotated about the axis 46 
relative to the outer valve member 42. This relative rotation moves 
valving edges on the inner valve member 40 relative to valving edges on 
the sleeve 42, creates, in a known manner, a demand for higher pressure 
fluid from the pump 24, and directs the higher pressure fluid from the 
pump 24 to one of the motor conduits 28 or 30 and directs fluid from the 
other motor conduit to the reservoir 32. 
For example, rotation of the inner valve member 40 in one direction 
relative to the outer valve member 42 will reduce the flow area 
communicating the motor conduit 28 with the reservoir 32 and increase the 
flow area communicating the motor conduit 28 with the pump 24. The 
relative rotation between the inner valve member 40 and outer valve member 
42 also increases the flow area communicating the motor conduit 30 with 
the reservoir 32 and reduces the flow area communicating the motor conduit 
30 with the pump 24. The result is higher pressure fluid generated by the 
pump 24 which is conducted to the motor cylinder chamber 72. This higher 
pressure fluid will move the piston 76 toward the right, as viewed in FIG. 
1A. As the piston 76 moves toward the right, fluid is forced from the 
chamber 74 through the motor conduit 30, the control valve 22, the return 
conduits 34 and 36, and the speed responsive control unit 38 to the 
reservoir 32. 
As the power steering motor 31 operates, the rack 66, which is also the rod 
for the motor 31, rotates the pinion 64 and follow-up member 54. This 
rotation of the follow-up member 54 rotates the outer valve member 42 
relative to the inner valve member 40 tending to return the valve 22 to 
its open center, neutral position. When the motor 31 is operated to turn 
the steerable vehicle wheels to an extent corresponding to the extent of 
rotation of the inner valve member 40, the feedback of the rotation of the 
follow-up member 54, caused by movement of the rack 66, rotates the pinion 
64 through a distance sufficient to move the outer valve member 42 to its 
initial position relative to the inner valve member. When this occurs, the 
fluid pressure in the motor cylinder chambers 72 and 74 falls and 
equalizes and the motor 31 stops operating. 
Pressurized fluid from the pump 24 is conducted to an annular central 
groove 80 formed in the outer valve member 42. Fluid flows to the inside 
of the outer valve member 42 through a pair of diametrically opposite 
passages 82 and 84. The inner and outer valve members 40 and 42 may have 
the same construction and cooperate with each other in the same manner as 
described in U.S. Pat. No. 4,276,812 issued Jul. 7, 1981 and entitled 
"Power Steering Valve and Method of Making Same". However, the inner and 
outer valve members 40 and 42 could have a different construction if 
desired. 
The control valve 22 may be a "four land" type valve. The inner valve 
member 40 has a generally square cross-sectional configuration with 
rounded corners which form the four valving lands that cooperate with the 
edges of four axially extending grooves formed inside the outer valve 
member 42 to control the flow of fluid to and from the motor 31. The ends 
of one pair of diametrically opposite grooves on the inside of the outer 
valve member 42 are connected in fluid communication with an annular outer 
groove 88 connected with the motor conduit 28. A second pair of 
diametrically opposite and axially extending grooves on the inside of the 
outer valve member 42 are connected in fluid communication with an annular 
outer groove 90 formed in the outer valve member and connected with the 
motor conduit 30. 
In accordance with the present invention, the torque required to actuate 
the control valve 22 increases as steering demand and vehicle speed 
increase. At relatively low vehicle speeds or no steering demand, relative 
rotation of the inner and outer valve members 40 and 42 requires a 
relatively small torque to actuate the hydraulic assist motor 31 making 
the steering feel less manual. At higher vehicle speeds and high steering 
demand, the control unit 38 causes fluid pressure to act on a slidable, 
annular force transmitting member 116 drivingly connected to the input 
member 50, a cam assembly 120, and outer valve member 42 to require a 
larger torque to rotate the inner valve member 40 relative to the outer 
valve member 42 making the steering feel more manual. 
The force transmitting member or slider 116 (FIG. 1A) is disposed in the 
power steering control valve housing 44. The force transmitting member 116 
rotates about its central axis 46 with the inner valve member 40 and the 
valve stem 50 and is movable axially along the valve stem 50. 
The force transmitting member 116 is connected with the outer valve member 
42 by a cam assembly 120. The cam assembly 120 includes a plurality of 
downwardly facing (as viewed in FIG. 1A) cam surfaces 122 on the force 
transmitting member 116, a plurality of upwardly facing (as viewed in FIG. 
1A) cam surfaces 124 on the outer valve member 42, and a plurality of 
balls or spherical cam elements 126 located between the cam surfaces 122 
and 124, preferably four of each. However, a greater or lesser number of 
cam elements 126 and cam surfaces 122 and 124 could be used if desired. 
The force transmitting member 116 is urged axially toward the outer valve 
member 42 by a spring 130 acting between a collar 232 connected to the 
valve stem 50 and the slidable force transmitting member 116. The force 
applied against the force transmitting member 116 by the spring 130 urges 
the cam surfaces 122 and 124 against opposite sides of the balls 126 and 
maintains and centers the balls on the cam surfaces 122 and 124. 
Annular upper surface 142 and annular lower surface 144 of the force 
transmitting member 116 cooperate with a cylindrical inner side surface 
134 of the housing 44 and the cylindrical outer surface 135 of the valve 
stem 50 to partially define a chamber 98 and an annular pressure chamber 
136 on axially opposite sides of the force transmitting member 116. A pair 
of diametrically opposite openings 94 in the inner valve member 40 extend 
radially inward to an axially extending central passage in the inner valve 
member 40 which is used to conduct hydraulic fluid to the chamber 136 
through opening 138 extending radially outwardly from the axially 
extending central passage. 
The pressure chamber 136 is connected to the reservoir 32 by the return 
conduits 36 and 34 and the speed responsive control unit 38. From the 
pressure chamber 136 the fluid is conducted to the speed responsive 
control unit 38 by the return conduit 36 and from the speed responsive 
control unit 38 to the reservoir 32 by the return conduit 34. 
The force transmitting member 116 has a generally fluid tight fit with the 
inner side surface 134 of the housing 44. The chamber 98 is connected in 
fluid communication with the reservoir 32 by return conduit 34. Any fluid 
which leaks from the pressure chamber 136 into the chamber 98 is thus 
conducted back to the reservoir 32. 
Although the preferred embodiment of the present invention is shown with 
the spring 130 located in chamber 136, the spring 130 may not be needed. 
If there is no spring, a torsion bar interconnecting the linear and outer 
valve members 40 and 42, as is well known in the art is needed and the 
length of the steering control valve housing 44 can be reduced by reducing 
the axial length of the chamber 136. 
Rotation of the valve stem 50 and inner valve member 40 relative to the 
housing 44 and outer valve member 42 is resisted by a force which is 
related to the axial force on the force transmitting member 116 by spring 
130 and the fluid pressure force applied against the annular surface 142. 
The balls 126 act as driving connections between the force transmitting 
member 116 and the outer valve member 42. Upon rotation of the inner valve 
member 40, the cam surfaces 122 and 124 in the force transmitting member 
116 and outer valve member 42 create axial and tangential forces on the 
balls 126 with respect to the force transmitting member 116 and the outer 
valve member 42. These forces translate into (a) additional torque in the 
steering column felt by the operator of the vehicle, and (b) resistance to 
relative rotation of the inner and outer valve members 40 and 42. 
Relative rotation between the inner valve member 40 and the outer valve 
member 42 causes the spherical elements 126 to tend to roll on the cam 
surfaces 122 and 124 and therefore to move the force transmitting member 
116 axially away from an end 146 of the outer valve member 42. Obviously, 
the force required to move the force transmitting member 116 axially away 
from the outer valve member 42 varies as a function of the net force 
urging the force transmitting member 116 toward the outer valve member 42. 
Thus, the greater the net force pressing the force transmitting member 116 
against the balls 126, the greater is the force required to rotate the 
valve stem 50 and inner valve member 40 relative to the outer valve member 
42. 
The speed responsive control unit 38 (FIG. 1B) responds to steering 
activity and vehicle speed to control the fluid pressure in the chamber 
136. The speed responsive control unit 38 is connected in fluid 
communication with the chamber 136 in the housing 44 by the return conduit 
36. 
The speed responsive control unit 38 includes a housing 180 which is 
connected hydraulically in series between the return conduit 36 and the 
return conduit 34. First and second control valves 182 and 184 in the 
housing 180 regulate the fluid pressure in the chamber 136 of the steering 
control valve 22. The valve 182 conducts fluid from the chamber 136 to the 
return conduit 34 and reservoir 32. The valve 184 is responsive to an 
electrical signal from an electronic control unit (ECU) which is 
indicative of the speed of the vehicle as measured by a speed sensor (SS). 
The valve 184 controls the valve 182. 
The housing 180 has an inlet 186 in fluid communication with the valve 182 
and the chamber 136 through return conduit 36. The housing 180 includes an 
outlet 188 in fluid communication with chamber 98, valve 182 and return 
conduit 34. Fluid from the chamber 136 flows through the return conduit 36 
to the valve housing 180 and from the housing 180 to the return conduit 34 
and to the reservoir 32. 
The valve 182 includes a valve body 194 and a valve seat 196. When the 
valve body 194 is open, spaced from the seat 196, the valve body and seat 
define an orifice 198. The valve body 194 includes a main body portion 
202, an insert 204 in the valve body, and a pin 206 fixedly connected to 
the valve body. The pin 206 is received in a bore 210 in the housing 180 
and is exposed to fluid pressure in a passageway 212. The pressure in the 
passageway 212 urges the pin 206 and therefore, the valve body 194 toward 
the valve seat 196. An annular end of a plug 216 in the housing 180 
defines the valve seat 196. The plug 216 includes an axially extending 
passage 218 for conducting fluid from the inlet 186 to the orifice 198. 
A spring 220, schematically illustrated in FIG. 1B, located in a bore 222 
in the main body portion 202 of the valve body 194 urges a ball 224 
against the insert 204 to block an axial bore 225 in the insert. The 
spring 220 has an end engaging the pin 206 and the other end engaging the 
ball 224. The insert 204, ball 224, and spring 220 act as a relief valve 
to limit the maximum pressure in the chamber 136. The main body portion 
202 of the valve body 194 has radially extending openings 226 for 
conducting fluid from the bore 222 to the outlet 188 and to reservoir 32. 
The valve 184 is a solenoid operated valve and comprises a spring 236 which 
urges a spool 238 downward as viewed in FIG. 1B. A plug 239 is threadably 
received in the housing 180 and has an end engaging the spring 236. The 
axial position of the plug 239 is adjusted to vary the load that the 
spring 236 applies to the spool 238. 
The spool 238 has a first land 240 for controlling the flow of fluid from a 
passageway 242 in the housing 180 to the passageway 212. The spool 238 has 
a second land 244 for controlling the flow of fluid from the passageway 
212 to a passageway 246 in the housing 180. A conduit 248 conducts fluid 
pressure generated by the pump 24, in response to steering demand, from 
the pump to the passageway 242 and to an orifice 256 (FIG. 2) defined by 
the land 240 and passageway 242. The passageway 246 conducts fluid from an 
orifice 258 (FIG. 1B) defined by the land 244 and passageway 246, around 
the valve 182 and to the outlet 188 and reservoir 32. The orifice 256 
controls the flow of fluid from the pump 24 to the passageway 212. The 
orifice 258 controls the flow of fluid from the passageway 212 to 
reservoir 32. Therefore, the orifices 256 and 258 control the pressure in 
passageway 212 and therefore, the pressure applied to the valve body 194 
and the size of orifice 198. 
A solenoid 268 of the valve 184 controls the position of the spool 238 as a 
function of vehicle speed. An electronic control unit, ECU, can be 
programmed to provide a signal to solenoid 268 which positions the spool 
238 as a function of vehicle speed. At engine idle and lower vehicle 
speeds, for example, less than 15 mph, solenoid 268 is energized to move 
the spool 238 against the bias of the spring 236 and fully open orifice 
258 and close orifice 256, as seen in FIG. 1B. Therefore, passageway 212 
is open to reservoir 32 and a small pressure is exerted on the valve body 
194. At relatively high vehicle speeds, for example, above 35 mph, the 
solenoid 268 is deenergized allowing the spring 236 to urge the spool 238 
downward, as viewed in FIG. 2, and open orifice 256 while closing or 
restricting orifice 258. At intermediate vehicle speeds, for example, 
between 15 mph and 35 mph, the solenoid 268 controls the size of the 
orifices 256 and 258. The solenoid 268 controls the size of the orifice 
256 from a smaller size orifice 256 at vehicle speeds near 15 mph to a 
larger size orifice 256 at vehicle speeds near 35 mph and controls the 
size of the orifice 258 from a larger size orifice 258 at vehicle speeds 
near 15 mph to a smaller size orifice 258 at vehicle speeds near 35 mph to 
modulate the pressure in passageway 212. 
At engine idle and relatively low vehicle speeds (FIG. 1B), the solenoid 
268 is energized to vent the passageway 212 to reservoir, and the pressure 
in passageway 212 is relatively low. The orifice 198 is open and allows 
fluid from the chamber 136 to flow freely to the reservoir 32. A 
relatively low fluid pressure is present in the return conduit 36 and in 
the chamber 136. At engine idle and low vehicle speeds, the force of the 
spring 130 and the low fluid pressure in chamber 136 urge the force 
transmitting member 116 toward the cam elements 126. 
Upon rotation of the steering wheel 18 and valve stem 50 at engine idle and 
relatively low vehicle speeds, the pressure in conduit 248 increases. The 
orifice 256 is closed and the fluid pressure in conduit 248 cannot act 
against the valve body 194 to close or restrict the orifice 198 and the 
low pressure in chamber 136 is maintained. When there is steering 
activity, a torque is created between the valve stem 50 and the outer 
valve member 42, the cam elements 126 exert a force on the force 
transmitting member 116. The resultant force tends to move the force 
transmitting member 116 axially away from the outer valve member 42 
against the force of the spring 130 and the low pressure in chamber 136. 
As this occurs, the spring 130 is compressed against the collar 232 of the 
valve stem 50. 
At relatively high speeds of the vehicle (FIG. 2), the solenoid 268 is 
deenergized and the orifice 256 is open while the orifice 258 is closed or 
restricted. During a steering maneuver at relatively high speeds, the pump 
24 conducts fluid through conduit 248 and to passageway 212 to apply fluid 
pressure against the valve body 194 and close or restrict the orifice 198. 
Thus, the pressure in chamber 136 is at a maximum and there is maximum 
resistance to relative rotation between the inner valve member 40 and the 
outer valve member 42 and less hydraulic assist is provided and the 
steering feels more manual. 
The maximum pressure in chamber 136 is limited by the spring 220 and ball 
224 acting as a relief valve. Pressure in chamber 136 can overcome the 
bias of the spring 220 and push the ball 224 away from the valve insert 
204 to limit the pressure in the chamber 136. Thus, by changing the 
biasing force of the spring 220, the maximum pressure in the chamber 136 
can be changed and therefore, the resistance to relative rotation between 
the inner and outer valve members 40 and 42 can be tailored to specific 
requirements. 
At high vehicle speeds and no steering, the pump 24 conducts low pressure 
fluid to the passageway 212. A low pressure is applied to the valve body 
194 and orifice 198 is open. The fluid pressure in chamber 136 is low and 
there is a relatively free flow of fluid from the pump 24, through the 
control valve 22, and to reservoir 32. 
It should be apparent to those skilled in the art that certain 
modifications, changes and adaptations may be made in the present 
invention and that it is intended to cover such modifications, changes and 
adaptations coming within the scope of appended claims.