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Claims  |
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Having described the invention, the following is claimed:
1. An apparatus for use in a power steering system, said apparatus
comprising:
first and second members which are rotatable relative to each other to
control operation of a power steering motor,
a torsion-tension spring interconnecting said first and second members,
means for applying torque to said torsion-tension spring to effect
increasing torsional deformation of said torsion-tension spring upon
relative rotation between said members in a first direction, and
means for applying tensile force to said torsion-tension spring to effect
increasing axial deformation of said torsion-tension spring upon relative
rotation between said members in the first direction, said means for
applying tensile force to said torsion-tension spring including means for
varying the tension applied to the torsion-tension spring by a first
amount upon relative rotation between said members in a first direction
through a first incremental angular distance and for varying the tension
applied to said torsion-tension spring by a second amount which is
different than the first amount upon relative rotation between said
members in the first direction through a second incremental angular
distance which is the same as and is offset from the first incremental
angular distance,
said means for applying tensile force to said torsion-tension spring
includes cam surface means for transmitting force to effect axial
deformation of said torsion-tension spring, said cam surface means having
a first portion which has a first slope and a second portion which has a
second slope which is less than said first slope, said first portion of
said cam surface means being effective to apply tensile force to said
torsion-tension spring during relative rotation between said members
through the first incremental angular distance, said second portion of
said cam surface means being effective to apply tensile force to the
torsion-tension spring during relative rotation between said members
through the second incremental distance.
2. An apparatus as set forth in claim 1 wherein said means for applying
tensile force to said torsion-tension spring includes an annular array of
rollers, said cam surface means including a first annular array of cam
surfaces disposed in engagement with a first side of said annular array of
rollers and a second annular array of cam surfaces disposed in engagement
with a second side of said annular array of rollers.
3. An apparatus as set forth in claim 1 wherein said first and second
members are first and second valve members which cooperate to control a
flow of fluid to the power steering motor, said means for applying tensile
force to said torsion-tension spring includes an annular array of rollers
having an open central portion through which said torsion-tension spring
extends, said cam surface means including a first annular array of cam
surfaces fixedly connected with one end portion of said first valve member
and disposed in engagement with a first side of said annular array of
rollers and a second annular array of cam surfaces fixedly connected with
said second valve member and disposed in engagement with a second side of
said annular array of rollers.
4. An apparatus as set forth in claim 1 wherein said first and second
members are rotatable relative to each other in opposite directions from
an initial position, said means for applying torque to said
torsion-tension spring including means for increasing torsional
deformation of said torsion-tension spring upon relative rotation between
said members in a first direction from the initial position and for
increasing torsional deformation of said torsion-tension spring upon
relative rotation between said members in a second direction opposite to
the first direction, said means for applying tensile force to said
torsion-tension spring including means cooperating with said cam surface
means for maintaining said torsion-tension spring in an axially deformed
condition under the influence of tensile force when said members are in
the initial position to enable said torsion-tension spring to provide a
force which biases said first and second members to the initial position.
5. An apparatus as set forth in claim 1 wherein said torsion-tension spring
has first and second end portions, said first member being fixedly
connected with said first end portion of said torsion-tension spring, said
second member being fixedly connected with said second end portion of said
torsion-tension spring, said means for applying tensile force to said
torsion-tension spring being disposed between said first and second end
portions of said torsion-tension spring and being connected with said
first and second end portions of said torsion-tension spring by rigid
bodies which transmit tensile forces between said first and second end
portions of said torsion-tension spring and said means for applying
tensile force without significant deformation.
6. An apparatus for use in a power steering system, said apparatus
comprising:
first and second members which are rotatable relative to each other to
control operation of a power steering motor,
a torsion-tension spring interconnecting said first and second members,
means for applying torque to said torsion-tension spring to effect
increasing torsional deformation of said torsion-tension spring upon
relative rotation between said members in a first direction, and
means for applying tensile force to said torsion-tension spring to effect
increasing axial deformation of said torsion-tension spring upon relative
rotation between said members in the first direction, said means for
applying tensile force to said torsion-tension spring including means for
decreasing the extent of axial deformation of said torsion-tension spring
during each increment of a plurality of equal increments of relative
rotation between said first and second members in the first direction,
said means for applying tensile force to said torsion-tension spring
includes cam surface means for transmitting force to effect axial
deformation of said torsion-tension spring, said cam surface means having
a first portion which is fixedly connected with one of said members and
has a first slope, said cam surface means having a second portion which is
fixedly connected with said one of said members and has a second slope
which is less than said first slope, said first portion of said cam
surface means being effective to apply tensile force to said
torsion-tension spring during a first one of the plurality of equal
increments of relative rotation between said first and second members,
said second portion of said cam surface means being effective to apply
tensile force to the torsion-tension spring during a second one of the
plurality of equal increments of relative rotation between said first and
second members, said first one of the plurality of equal increments of
relative rotation preceding said second one of the plurality of increments
of relative rotation during relative rotation between the first and second
members in the first direction.
7. An apparatus as set forth in claim 6 wherein said means for applying
tensile force to said torsion-tension spring includes an annular array of
rollers, a first annular array of cam surfaces disposed in engagement with
a first side of said annular array of rollers, a second annular array of
cam surfaces disposed in engagement with a second side of said annular
array of rollers, and means for maintaining a constant spatial
relationship between rollers of said annular array of rollers during
relative rotation between said first and second members.
8. An apparatus as set forth in claim 6 wherein said first and second
members are first and second valve members which cooperate to control a
flow of fluid to the power steering motor, said means for applying tensile
force to said torsion-tension spring includes an annular array of rollers
having an open central portion through which said torsion-tension spring
extends, means for maintaining the size of said annular array of rollers
constant during relative rotation between said first and second members, a
first annular array of cam surfaces fixedly connected with one end portion
of said first valve member and disposed in engagement with a first side of
said annular array of rollers, and a second annular array of cam surfaces
fixedly connected with said second valve member and disposed in engagement
with a second side of said annular array of rollers.
9. An apparatus for use in a power steering system, said apparatus
comprising:
first and second members which are rotatable relative to each other to
control operation of a power steering motor,
a torsion-tension spring interconnecting said first and second members,
means for applying torque to said torsion-tension spring to effect
increasing torsional deformation of said torsion-tension spring upon
relative rotation between said members in a first direction, and
means for applying tensile force to said torsion-tension spring to effect
increasing axial deformation of said torsion-tension spring upon relative
rotation between said members in the first direction, said means for
applying tensile force to said torsion-tension spring including a first
cam surface which is fixedly connected with a first end portion of said
torsion-tension spring and a second cam surface which is fixedly connected
with a second end portion of said torsion-tension spring,
said means for applying tensile force to said torsion-tension spring
includes a plurality of members which are disposed between said first and
second cam surfaces and which apply force against said first and second
cam surfaces to increase the distance between said first and second cam
surfaces upon relative rotation between said first and second members in
the first direction, said torsion-tension spring being deformed in tension
in an axial direction by an amount which is the same as the increase in
the distance between said first and second cam surfaces upon relative
rotation between said first and second members in the first direction.
10. An apparatus set forth in claim 9 wherein said first and second members
are first and second valve members which cooperate to control a flow of
fluid to the power steering motor, said first cam surface being fixedly
connected with said first valve member and said second cam surface being
fixedly connected with said second valve member.
11. An apparatus as set forth in claim 9 further including means for
maintaining the spatial relationship between members of said plurality of
members constant during relative rotation between said first and second
members.
12. An apparatus as set forth in claim 9 wherein each of the members of
said plurality of members is a roller having a cylindrical side surface
which is disposed in abutting engagement with said first and second cam
surfaces, each of said rollers having a longitudinal central axis which
extends transversely to a longitudinal central axis of said
torsion-tension spring.
13. An apparatus for use in a power steering system, said apparatus
comprising:
first and second members which are rotatable relative to each other to
control operation of a power steering motor,
a torsion-tension spring interconnecting said first and second members,
means for applying torque to said torsion-tension spring to effect
increasing torsional deformation of said torsion-tension spring upon
relative rotation between said members in a first direction, and
means for applying tensile force to said torsion-tension spring to effect
increasing axial deformation of said torsion-tension spring upon relative
rotation between said members in the first direction, said means for
applying tensile force to said torsion-tension spring includes an annular
array of rollers, a first annular array of cam surfaces disposed in
engagement with a first side of said annular array of rollers, a second
annular array of cam surfaces disposed in engagement with a second side of
said annular array of rollers, and means for maintaining a constant
spatial relationship between rollers of said annular array of rollers
during relative rotation between said first and second members.
14. An apparatus as set forth in claim 13 wherein each of the rollers of
said annular array of rollers has a cylindrical outer side surface which
applies force against said first and second annular arrays of cam surfaces
to increase the distance between said first and second annular arrays of
cam surfaces in an axial direction, said torsion-tension spring being
deformed in tension and an axial direction by an amount which is the same
as the increase in the distance between said first and second annular
arrays of cam surfaces upon relative rotation between said first and
second members. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a new and improved hydraulic control valve
for a hydraulic power steering system and more specifically to a hydraulic
control valve having a torsion-tension spring that resists relative
rotation between a pair of valve members.
In a known power steering system, a torsion bar is utilized to interconnect
a pair of relatively rotatable hydraulic valve members. When a steering
maneuver is made, the torsion bar is subjected to torsional, elastic
deformation. As the torsion bar is elastically deformed, the valve members
are rotated relative to each other. Relative rotation between the valve
members allows pressurized hydraulic fluid flow from a pump to a hydraulic
power steering motor connected between the frame of the vehicle and the
steerable wheels to effect operation of the power steering motor and
steering of the vehicle. Power steering systems in which a torsion bar is
subjected to torsional deformation, are disclosed in U.S. Pat. Nos.
3,709,099; 4,557,342 and 4,598,787.
During operation of a vehicle, it is desirable to have a force which biases
the hydraulic valve of a steering system to a neutral, non-steering
condition when operator input steering torque is low or nonexistent. It is
also desirable to have the amount of manual input torque required to turn
the steerable vehicle wheels to be comparable whether a parking maneuver
is made when the vehicle is stationary or operating at very low speeds or
in a lane change maneuver at 55 miles per hour. However, the amount of
torque which a driver of a vehicle must input to the steering system is
approximately 240% greater during steering in a parking maneuver than
during a lane change maneuver when a vehicle is moving at 55 miles per
hour. Torsion bar springs have essentially linear spring rates, and
provide a torque biasing the hydraulic control valve toward an on center
condition which is the product of angular displacement multiplied times
the spring rate. It is desirable to provide a preload to prevent angular
displacement of the torsion bar until the input torque reaches a
predetermined minimum level.
SUMMARY OF THE INVENTION
The present invention relates to a new and improved torsion-tension spring
apparatus for use in a hydraulic power steering system. The apparatus
includes a pair of hydraulic valve members which are rotatable relative to
each other to control operation of a power steering motor. A
torsion-tension spring resiliently interconnects the hydraulic valve
members.
Upon initiation of a steering operation, torque is applied to the
torsion-tension spring to effect torsional and axial deformation of the
torsion-tension spring. In order to require a similar amount of effort to
effect either a parking maneuver or a relatively high speed lane change,
the incremental axial deformation of the torsion-tension spring with each
increment of relative rotation between the valve members decreases as the
extent of angular displacement of the torsion-tension spring increases
throughout at least a portion of the range of relative rotation between
the members.
A tensile force is applied to the torsion-tension spring by cam surfaces
which engage opposite sides of bearing elements. Relative rotation between
the cam surfaces results in the transmission of tensile forces through
rigid bodies to opposite end portions of the torsion-tension spring to
effect axial elongation of the torsion-tension spring. The cam surfaces
have a configuration such that during at least a portion of the relative
rotation between the cam surfaces, each succeeding increment of relative
rotation results in the torsion-tension spring being axially deformed to a
lesser extent than on the preceding increment of relative rotation between
the cam surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other features of the present invention will become
apparent to one skilled in the art to which the present invention relates
upon consideration of the following description of the invention with
reference to the accompanying drawings, wherein:
FIG. 1 is a sectional view of a power steering system constructed in
accordance with the present invention;
FIG. 2 is an enlarged fragmentary sectional view of a portion of the power
steering system of FIG. 1;
FIG. 3 is an exploded view of some of the components of the apparatus of
FIG. 2;
FIG. 4 is a sectional view, taken generally along the line 4--4 of FIG. 2;
FIG. 5 is a sectional view, taken generally along the line 5--5 of FIG. 2;
FIG. 6 is an enlarged fragmentary view of a portion of a thrust bearing
assembly used in the apparatus of FIGS. 1 and 2;
FIG. 7 is an enlarged fragmentary sectional view of a portion of a roller
in the thrust bearing assembly of FIG. 6 and a portion of a cam surface;
FIG. 8 is a highly schematicized illustration depicting the manner in which
lines of engagement of a bearing with the cam surface changes due to
changing slope of the cam surface; and
FIG. 9 is a graph illustrating the manner in which steering effort varies.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
General Description
A power steering system 10 (FIG. 1) is used to turn steerable wheels (not
shown) of a vehicle. The power steering system 10 includes the elements
required to convert a pressurized hydraulic fluid energy into a mechanical
output torque. One of the elements is a hydraulic power steering motor 12.
The power steering motor 12 includes a housing 14 having a cylindrical
inner surface 16 defining a chamber 18. A piston 20 divides the chamber 18
into left and right (as viewed in FIG. 1) end portions 22 and 24.
A plurality of rack teeth 26 are formed on the piston 20. The rack teeth 26
mesh with sector gear teeth 28. The sector gear teeth 28 are disposed on
an output shaft 32 which is connected with the steerable vehicle wheels by
a suitable steering linkage (not shown). Movement of the piston 20 in the
chamber 18 rotates the output shaft 32 to operate the steering linkage in
a known manner.
The housing 14 has a fluid inlet port 34 connected with a pump or other
source of hydraulic fluid under pressure. The housing 14 also has an
outlet port 36 which is connected with reservoir.
A directional control valve assembly 40, constructed in accordance with the
present invention, controls the direction of operation of the power
steering motor 12. The directional control valve assembly 40 includes a
valve core or member 42 connected with a rotatable input shaft 44. The
input shaft 44 is rotated by manual rotation of a vehicle steering wheel.
The valve core 42 is telescopically received in a valve sleeve or member
46. The valve sleeve 46 is connected with an externally threaded follow-up
shaft 48. The follow-up shaft 48 is connected with the piston 20 by a ball
nut 50.
The valve core 42 and valve sleeve 46 are interconnected by a
torsion-tension spring 52. An inner end portion 56 of the torsion-tension
spring 52 is connected with the valve sleeve 46 by a pin 58. An outer end
portion 60 of the torsion-tension spring 52 is connected with the valve
core 42 by a pin 62. The torsion-tension spring 52 has a configuration
corresponding to the configuration of a known torsion bar.
An outlet passage 66 formed in the valve sleeve 46 connects the interior of
the valve sleeve 46 in fluid communication with the left end portion 22 of
the power steering motor chamber 18. Another passage (not shown) formed in
the valve sleeve 46 connects the interior of the valve sleeve in fluid
communication with the right end portion of the motor cylinder chamber 18
through a housing passage 70.
The power steering system 10 has the same construction as is disclosed in
U.S. Pat. No. 4,942,803. However, the power steering system could have a
construction which is different from the construction illustrated in FIG.
1. For example, the power steering system may be of the rack and pinion
type disclosed in U.S. Pat. No. 3,709,099. If desired, electrically
actuated valves may be utilized to control fluid flow to a power steering
motor in the manner disclosed in U.S. Pat. No. 4,557,342. Alternatively,
the power steering system could include an electrical steering assist
motor in the manner disclosed in U.S. Pat. No. 4,598,787.
Torsion and Tensile Force Applicator Assembly
In accordance with a feature of the present invention, a torsion and
tensile force applicator assembly 74 (FIG. 2) is utilized to apply tensile
force to the torsion-tension spring 52. The assembly 74 is connected with
the inner and outer end portions 56 and 60 of the torsion-tension spring
52 through rigid metal bodies. Thus, the assembly 74 is connected with the
inner end portion 56 of the torsion-tension spring by a metal clip 76 and
by the rigid metal valve sleeve 46. The valve sleeve 46 is connected with
the inner end portion 56 of the torsion-tension spring 52 by the rigid
metal pin 58. The assembly 74 is connected with the outer end portion 60
of the torsion-tension spring 52 through the rigid valve core 42 and rigid
metal pin 62 (FIG. 2).
The torsion and tensile force applicator assembly 74 includes an annular
thrust bearing assembly 80. The thrust bearing assembly 80 is disposed
between an annular outer array 84 (FIG. 3 and 4) of identical cam surfaces
86. The cam surfaces 86 are separated by flat radially extending lands 88.
In the illustrated embodiment of the invention, the cam surfaces 86 are
formed on the axially inner end portion of the rigid metal valve core 42.
However, if desired, the cam surfaces 86 and lands 88 could be formed on
an annular member or washer which is fixedly secured to the inner end
portion of the valve core 42.
An inner annular array 92 of identical cam surfaces 94 is formed on an
annular contour washer 98 (FIGS. 3 and 5). The cylindrical cam surfaces 94
in the annular array 92 are separated by flat radially extending lands 96
(FIG. 5). The cam surfaces 94 (FIG. 5) have the same configuration as the
cam surfaces 86 (FIG. 4).
The contour washer 98 is fixedly secured to a rigid annular metal support
ring 102 (FIG. 2 and 3). Thus, the support ring 102 has a cylindrical
central portion 104 (FIG. 2) which has an interference fit with the inside
diameter of the contour washer 98. The inner support ring 102 also has an
interference fit with the cylindrical end portion 56 of the
torsion-tension spring 52. The axially inner end of the support ring 102
is disposed in abutting engagement with the annular clip 76.
Force is transmitted from the support ring 102 to the inner end portion 56
of the torsion-tension spring 52 by the interference fit between the
support ring and the inner end portion of the torsion-tension spring. In
addition, force is transmitted from the support ring 102 to the inner end
portion of the torsion-tension spring 52 by the clip 76. The thrust
bearing assembly 80 (FIGS. 2 and 6) includes a plurality of cylindrical
rollers 110 which are disposed in an annular array 112. The rollers 110
are held in an evenly spaced relationship by an annular retainer ring 114
(FIG. 6). Although the thrust bearing assembly 80 could have many
different constructions, in one specific embodiment of the invention, the
thrust bearing assembly 80 was an INA TC-1018 thrust bearing.
The number of rollers 110 in the thrust bearing assembly 80 is equal to the
number of cam surfaces in the annular array 84 (FIG. 4) of cam surfaces 86
and the number of cam surfaces in the annular array 92 (FIG. 5) of cam
surfaces 94. A cam surface 86 in the array 84 of cam surfaces and a cam
surface 94 in the array 92 of cam surfaces abuttingly engage opposite
sides of each of the rollers 110. The retainer 114 (FIG. 6) spans the
lands 88 between the cam surfaces 86 and the lands 96 between the cam
surfaces 94 to interconnect the rollers 110. In one specific embodiment of
the invention, the thrust bearing assembly 80 included twenty rollers 110
which engage twenty cam surfaces 86 in the array 84 of cam surfaces and
twenty cam surfaces 94 in the array 92 of cam surfaces.
The relationship between one of the rollers 110 and a cam surface 94 in the
array 92 of cam surfaces is illustrated in FIG. 7. The cam surface 94 has
a central trough or depression 122 upon which a roller 110 rests when the
annular array 112 of rollers is in an on-center position corresponding to
straight ahead movement of a vehicle. The cam surface 94 has a pair of
side portions 124 and 126 which slope gradually upwardly (as viewed in
FIG. 7) to the lands 96. The side portions 124 and 126 are connected with
the trough 122 by transition portions 128 and 130.
The trough 122 has relatively steep side surfaces. The side portions 124
and 126 of the cam surface 94 have a much more gradual upward slope. The
steeply sloping side surfaces of the trough 122 are connected with the
gently sloping side portions 124 and 126 by transition portions 128 and
130. A central axis 134 of the cam surface 94 is disposed midway between
intersections of the side portions 124 and 126 with the lands 96. When the
steering system is in the on-center condition, the central axis of roller
110 is disposed on the central axis 134 of the cam surface 94.
In one specific embodiment of the invention, a portion of the cam surface
94 to one side of the axis 134, for example, the right side as view in
FIG. 7, was constructed in accordance with Chart I (Page 12). It should be
understood that the construction of the cam surface 94 is the same on both
sides of the center line 134. In Chart I, the angle is measured from a
first or base radian 138 (FIG. 5) which extends through the center of the
cam surface 94 and intersects the vertical (as viewed in FIG. 7) axis 134.
The angle is measured to a second radian 140 (FIG. 5). The angle is
indicated at 142 in FIG. 5.
The angle 142 is considered to be 0.degree. when both of the radians 138
and 140 (FIG. 5) extend through the center of the cam surface 94. As the
angle increases in a counterclockwise direction (as viewed in FIG. 5), the
radian 140 separates more and more from the radian 138 and the angle 142
becomes larger.
In Chart I (Page 12), the depth of the cam surface is considered to be the
vertical (as viewed in FIG. 7) distance from the land surface 96 to the
intersection of the radian 140 with the cam surface 94. Thus, the depth of
the cam surface 94 is measured vertically downwardly (as viewed in FIG. 7)
from the land 96 to the level where the radian 140 intersects the cam
surface 94.
When the angle 142 (FIG. 5) is 0.degree., the depth of the cam surface 94
in the specific embodiment of the invention corresponding to Chart I, is
0.00200 inches. When the angle 142 is increased to 1.degree., the depth of
the cam surface 94 is 0.00161 inches. Similarly, when the angle 142 (FIG.
5) has increased to 2.degree. the depth of the cam surface 94 is 0.00136.
The cam surface 94 has a configuration such that it is generated by
radians from the center of the array 92 of cam surfaces. Thus, radians
from the center of the array 92 of cam surfaces are tangent to cam
surfaces 94 throughout the extent of the cam surfaces.
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CHART I
ANGLE DEPTH
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0.00 0.00200
0.25 0.00183
0.50 0.00172
0.75 0.00166
1.00 0.00161
1.25 0.00155
1.50 0.00149
1.75 0.00142
2.00 0.00136
2.25 0.00129
2.50 0.00122
2.75 0.00115
3.00 0.00109
3.25 0.00102
3.50 0.00096
3.75 0.00090
4.00 0.00084
4.25 0.00078
4.50 0.00073
4.75 0.00067
5.00 0.00062
5.25 0.00057
5.50 0.00052
5.75 0.00047
6.00 0.00042
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The extent to which the cam surface 94 rises (as viewed in FIG. 7) with
each increment of the angle 142 varies. Thus, for each increment that the
angle 142 increases close to the center of the cam surface 94, that is, in
the area of the trough 122, there is a relatively large decrease in the
depth of the cam surface. At the gently sloping outer portion 126 of the
cam surface 94, there is a relatively small change in the depth of the
recess 94 with each incremental increase in the angle 142. In the
transition portion 130, the depth of the cam surface changes at a
decreasing rate with each incremental increase in the angle 142.
The cam surfaces 86 and 94 in the two arrays 84 and 92 (FIGS. 4 and 5) of
cam surfaces have the same configuration. A roller 110 engages one of the
cam surfaces 86 in the array 84 of cam surfaces and one of the cam
surfaces 94 in the array 92 of cam surfaces. Therefore, each incremental
increase in the angle 142 results in arrays 84 and 92 of cam surfaces
moving apart by a distance which is twice as great as the distance
indicated in Chart I. For example, if the angle 142 increases from one
degree to two degrees, the arrays 84 and 92 of cam surfaces move apart by
a distance of 0.00050 inches or twice the 0.00025 inch change in the depth
of one of the recesses.
The array 84 of cam surfaces is connected with the outer end portion 60 of
the torsion-tension spring by the rigid valve core 42 and pin 62. The
inner array 92 of cam surfaces is connected with the inner end portion 56
of the torsion-tension spring by the rigid support ring 102 and clip 76.
Therefore, the length of the torsion-tension spring 52 resiliently
increases as the arrays 84 and 82 of cam surfaces move apart.
As a roller 110 (FIG. 7) rolls along the cam surface 94, the slope of the
portion of the cam surface engaged by the roller changes. Thus, when the
roller 110 is in the on-center position corresponding to straight-ahead
movement of a vehicle, the roller engages the relatively steeply sloping
side surfaces of the trough 122. As the roller 110 is displaced from the
on-center position, for example, toward the right as viewed in FIG. 7, the
roller moves into engagement with the more gently sloping transition
portion 130 of the cam surface 94. As the slope of the portion of the cam
surface engaged by the roller changes, the line along which the cam
surface engages the roller also changes.
When the roller 110 (FIG. 8) is in engagement with a relatively steeply
sloping portion, indicated schematically at 144 in FIG. 8, of the cam
surface 94, the roller will have a first line 145 of engagement with the
cam surface 94. When the roller 110 moves upwardly (as viewed in FIGS. 7
and 8) into engagement with a less steeply sloping portion 146 of the cam
surface 94, the roller will have a second line 147 of engagement with the
cam surface 94. It should be understood that the change in the slope of
the portions 144 and 146 of the cam surface 94 has been exaggerated for
purposes of clarity of illustration in FIG. 8 and is greater than would
actually occur.
Since the cam surfaces 94 and 86 have the same configuration, the slope of
the cam surface 86 will change from the slope indicated by the line 148 in
FIG. 8 to the slope indicated by the line 149. This results in the line of
engagement of the roller 110 with the cam surface 86 changing from the
line indicated at 151 in FIG. 8 to the line indicated at 153 in FIG. 8.
The radial distance which the line of engagement of the cam surface 94 with
the roller 110 moves radially outwardly (downwardly as viewed in FIG. 8),
when the slope changes from the line indicated at 144 to the line
indicated at 146, has been designated as the distance X/2 in FIG. 8.
Similarly, the radial distance which the line of engagement of the cam
surface 86 with the roller 110 moves radially outwardly (upwardly as
viewed in FIG. 8), when the slope changes from the line indicated at 148
to the line indicated at 149, has also been designated as the distance
X/2. Thus, the combined radial distance which the lines of engagement of
the roller 110 with the cam surfaces 86 and 94 change is equal to X.
The extent to which the line of engagement of the roller 110 with the cam
surfaces 86 and 94 changes, that is, the distance X, is set forth in Chart
II (Page 16) for each increment of the angle 142 (FIG. 5). For each
increment that the angle 142 changes, the elongation of the
torsion-tension spring 52 changes by an amount which is equal to the sum
of the change due to variations in the depth of the cam surfaces 86 and 94
and variations in the line of engagement of the cam surfaces with the
surface of the rollers 110.
If the angle 142 increases from one degree to two degrees, the change in
the axial length of the torsion-tension spring results from the change in
the depth of the cam surface 86, the change in the depth of the cam
surface 94 and the change in the lines of engagement of the rollers 110
with the cam surfaces. For example, if the angle 142 increases from one
degree to two degrees, the arrays 84 and 92 of cam surfaces move apart by
a distance of 0.00050 inches or twice the 0.00025 inch depth change in one
of the cam surfaces. In addition, the arrays of cam surfaces move apart by
a distance equal to the sum of the distances X set forth in Chart II or
0.00037 inches (0.00014+0.00010+0.00007+0.00006). This results in the
total axial elongation of the torsion-tension spring 52 being 0.00087
inches as a result of a change in the angle 142 from one degree to two
degrees.
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CHART II
ANGLE DEPTH
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0.000
0.25
0.50 0.00011
0.75 0.00020
1.00 0.00018
1.25 0.00014
1.50 0.00010
1.75 0.00007
2.00 0.00006
2.25 0.00005
2.50 0.00004
2.75 0.00003
3.00 0.00003
3.25 0.00002
3.50 0.00002
3.75 0.00002
4.00 0.00001
4.25 0.00001
4.50 0.00001
4.75 0.00001
5.00 0.00001
5.25 0.00001
5.50 0.00001
5.75 0.00001
6.00 0.00001
______________________________________
Operation
When a vehicle is moving straight ahead, the annular arrays 84 and 92 of
cam surfaces 86 and 94 are axially aligned with each other. At this time,
the rollers 110 engage troughs 122 in the cam surfaces 86 and 94. The
torsion-tension spring 52 is axially strained in tension by a preload
force. This results in the torsion-tension spring 52 pressing the cam
surfaces 86 and 94 against opposite sides of the thrust bearing assembly
80.
Until the vehicle steering wheel is rotated, the initial preload force
causes the valve core 42 and valve sleeve 46 to remain in an on-center
position in which the power steering motor 12 is inactive. Upon initiation
of a turning maneuver, the input shaft 44 and valve core 42 rotate
relative to the valve sleeve 46.
Relative rotation between the valve core 42 and valve sleeve 46 ports
pressure fluid to either the left end portion 22 or the right end portion
24 of the power steering motor chamber 18. The other chamber of the power
steering motor is connected with reservoir. This results in turning
movement of the steerable vehicle wheels.
As the valve core 42 rotates relative to the valve sleeve 46, the inner and
outer arrays 84 and 92 of cam surfaces are offset relative to each other.
Thus, the angle 142 (FIG. 5) increases. As the angle 142 increases, the
roller 110 (FIG. 7) rolls along the cam surface 94 away from the trough
122, for example, toward the right (as viewed in FIG. 7).
The portion of the cam surface 94 forming the trough 122 has a relatively
steep slope so that there is a relatively large change in the depth of the
cam surface 94 for each increment of relative movement between the valve
core 42 and valve sleeve 46. Thus, as the angle 142 increases from zero
degrees to one degree of angle, the depth of the portion of the cam
surface 94 engaged by the roller decreases from 0.00200 inches to 0.00161
inches (see Chart I). In addition, the depth of the cam surface 86 which
engages the opposite side of the roller also decreases from 0.00200 inches
to 0.00161 inches. This results in a total change of 0.00078 inches in the
cam surfaces.
As the rollers 110 roll along the cam surfaces 86 and 94, the line of
engagement of the rollers with the cam surfaces changes in an axial
direction relative to the arrays 84 and 92 of cam surfaces by amounts
indicated at X in Chart II. Thus, as the angle 142 increases from zero
degrees to one degree of angle, the axial change in the point of
engagement of the rollers will shift by 0.00049 inches
(0.00011+0.00020+0.00018). The combined or total change in the length of
the torsion-tension spring 52 is t | | |
