Method of assembling a power steering control valve

A power steering control valve (22) has an inner valve member (40) which is connected with a follow-up member (54) by a torsion bar (102). An outer valve member (42) is fixedly connected with the follow-up member (54) by indentations (56). Before the outer valve member (42) is fixedly connected with the follow-up member (54) by the indentations (56), the inner and outer valve members (40 and 42) are moved relative to each other to determine a hydraulically centered condition. When the power steering control valve (22) is in the hydraulically centered condition, equal fluid pressures are conducted to a power steering motor (31) in response to equal clockwise or counterclockwise actuation of the valve members (40 and 42) relative to each other. The outer valve member (42) is then fixedly connected with the follow-up member (54) with the power steering control valve (22) in the hydraulically centered condition.

BACKGROUND OF THE INVENTION 
The present invention relates to a new and improved method of assembling a 
power steering control valve and, more specifically to a method of 
assembling a power steering control valve which is hydraulically centered. 
A power steering control valve is hydraulically centered when equal fluid 
pressures are conducted to a power steering motor in response to equal 
clockwise and counterclockwise actuation of the power steering control 
valve. 
A method of hydraulically centering a power steering control valve is 
disclosed in U.S. Pat. No. 5,230,273. In this patent, an outer valve 
member and follow-up member are connected with one end of a torsion bar. 
An inner valve member is positioned within the outer valve member. When a 
hydraulically centered condition has been determined for the power 
steering control valve, a hole is drilled in the inner valve member and an 
end portion of the torsion bar. A pin is inserted into this hole to 
interconnect the inner valve member and the torsion bar. 
It has also been suggested that a hydraulically centered condition may be 
obtained for a power steering control valve by first interconnecting the 
follow-up member, torsion bar and inner valve member. An outer valve 
member is then moved relative to the inner valve member. When a 
hydraulically centered condition has been ascertained for the outer valve 
member, the follow-up member is pressed into the outer valve member. This 
method of assembling a power steering control valve is disclosed in U.S. 
patent application Ser. No. 08/496,766 filed Jun. 29, 1995 and entitled 
"Method and Device for Assembling a Servo Valve." 
SUMMARY OF THE INVENTION 
The present invention provides a new and improved method of assembling a 
power steering control valve. The power steering control valve has an 
inner valve member which is connected with a follow-up member by a torsion 
bar. An outer valve member at least partially encloses the inner valve 
member. In accordance with a feature of the present invention, the outer 
valve member is connected with the follow-up member by an indentation 
formed by plastically deforming the outer valve member. 
During assembly, the inner and outer valve members are moved relative to 
each other to determine when they are in a hydraulically centered 
condition relative to each other. The outer valve member and the follow-up 
member are then fixedly interconnected by plastically deforming the outer 
valve member to grip the follow-up member.

DESCRIPTION OF ONE SPECIFIC PREFERRED EMBODIMENT OF THE INVENTION 
A vehicle power steering system 12 (FIG. 1) is operable to turn steerable 
vehicle wheels (not shown) upon rotation of a steering wheel (not shown) 
by an operator of a vehicle. Rotation of the steering wheel actuates a 
power steering control valve 22 to port 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 a known manner. Fluid is 
conducted from the motor 31 to a reservoir 32 through the other one of the 
motor conduits 28 or 30, the power steering control valve 22, and return 
conduit 34. 
The power steering control valve 22 includes a first or inner valve member 
40 and a second or outer valve member 42. The outer valve member 42 is 
cylindrical and encloses the inner valve member 40. The inner valve member 
40 and the outer valve member 42 are rotatable relative to each other and 
to a housing 44 about a common central axis 46. 
The inner valve member 40 is formed as one piece with a cylindrical input 
member or valve stem 50 (FIG. 1) which is connected with the steering 
wheel. The one piece outer valve member 42 is fixedly connected with a 
follow-up member 54 by indentations 56. The follow-up member 54 is 
rotatably supported in the housing 44 by bearings 58 and 60. A pinion gear 
64 is formed on the follow-up member 54. The pinion gear 64 is disposed in 
meshing engagement with a rack 66. The rack 66 is connected with the power 
steering motor 31 and steerable vehicle wheels. 
The power steering control valve 22 is of the known open-center type. 
Therefore, when the power steering control valve is in an unactuated 
position, fluid pressure from the pump 24 is conducted through the motor 
conduits 28 and 30 to motor cylinder chambers 72 and 74 on opposite sides 
of a piston 76 in the power steering motor 31. Fluid flow is conducted 
from the power steering control valve 22 to the reservoir 32 through the 
return conduit 34. 
The power steering control valve 22 is hydraulically centered. Therefore, 
equal fluid pressures are present in the motor cylinder chambers 72 and 74 
when the power steering control valve 22 is in an unactuated position. 
Upon rotation of the steering wheel (not shown) and rotation of the valve 
stem 50, the inner valve member 40 is rotated about the axis 46 relative 
to the housing 44 and outer valve member 42. This directs high 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. Since the power 
steering control valve 22 is hydraulically centered, equal amounts of 
rotation of the steering wheel in opposite directions from the initial 
position results in the same relatively high fluid pressure being 
conducted through the motor conduits 28 and 30 to motor cylinder chambers 
72 and 74, respectively. 
Rotation of the inner valve member 40 in one direction relative to the 
outer valve member 42 will reduce the extent of communication of the motor 
conduit 28 with the reservoir 32 and increase the extent of communication 
of the motor conduit 28 with the pump 24. This results in high pressure 
fluid from the pump 24 being conducted to the motor cylinder chamber 72. 
This high fluid pressure moves the piston 76 toward the right (as viewed 
in FIG. 1). As the piston 76 moves toward the right, fluid discharged from 
the chamber 74 is conducted to the reservoir 32 through the motor conduit 
30 and return conduit 34. 
Similarly, rotation of the inner valve member 40 through the same distance 
in the opposite direction relative to the outer valve member 42 will 
reduce the extent of communication of the motor conduit 30 with the 
reservoir 32 and increase the extent of communication of the motor conduit 
30 with the pump 24. This results in the same relatively high fluid 
pressure being conducted from the pump 24 to the motor cylinder chamber 74 
as was previously conducted to the motor cylinder chamber 72 upon rotation 
of the steering wheel in the other direction. The relatively high fluid 
pressure in the motor cylinder chamber 74 moves the piston 76 toward the 
left (as viewed in FIG. 1). As the piston 76 moves toward the left, fluid 
discharged from the chamber 72 is conducted to the reservoir 32 through 
the motor conduit 28 and return conduit 34. 
As the power steering motor 31 operates, the rack 66 rotates the pinion 
gear 64 and follow-up member 54. This rotates the outer valve member 42 
relative to the inner valve member 40. As the power steering 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 rack 66 
rotates the pinion 64 through a distance sufficient to move the outer 
valve member 42 to its central position relative to the inner valve 
member. When this occurs, the fluid pressure in the motor cylinder 
chambers 72 and 74 equalizes and the motor 31 stops operating. 
When the power steering control valve 22 is in the initial position, fluid 
pressure from the pump 24 is conducted to an annular central groove 80 
(FIGS. 1 and 2) formed in the outer valve member 42. Fluid flows from the 
groove 80 to the inside of the cylindrical outer valve member 42 through 
three passages 82 (FIG. 2) spaced equal distances apart about the 
circumference of the groove 80. The inner valve member 40 has axially 
extending grooves 86 and lands 87 (FIG. 2) which cooperate with axially 
extending grooves 89 and lands formed inside the outer valve member 42 in 
a known manner. One set of grooves on the inside of the outer valve member 
42 is connected in fluid communication with an annular outer groove 88 
connected with the motor conduit 28. A second set of axially extending 
grooves on the inside of the outer valve member 42 is connected in fluid 
communication with an annular outer groove 90 formed in the outer valve 
member and connected with the motor conduit 30. 
Openings 94 (FIG. 2) extend radially inwardly on alternate grooves 86 
formed in the inner valve member 40 to an axially extending central 
passage in the inner valve member. The central passage is connected in 
fluid communication with a chamber 98 at the lower end of the outer valve 
member 42. The chamber 98 is connected in fluid communication with the 
reservoir 32 (FIG. 1) through the return conduit 34. 
A torsion bar 102 is disposed in the axially extending fluid return passage 
formed on the central axis 46 of the inner valve member. The upper end of 
the torsion bar 102 is fixedly connected to the valve stem 50 and the 
lower end of the torsion bar is fixedly connected to the follow-up member 
54. The torsion bar 102 twists to enable relative rotation to occur 
between the inner and outer valve members 40 and 42. When rotational force 
is no longer applied to the steering wheel and inner valve member 40, the 
torsion bar urges the inner and outer valve members 40 and 42 to their 
initial positions. 
The power steering control valve 22 is hydraulically centered. Therefore, 
when the inner and outer valve members 40 and 42 are in their initial or 
unactuated positions, the fluid pressure conducted through the motor 
conduits 28 and 30 to the power steering motor 31 are equal. Upon rotation 
of the inner valve member 40 relative to the outer valve member 42 through 
a first distance in a clockwise direction from the initial or unactuated 
position, a first fluid pressure is conducted through one of the motor 
conduits 28 or 30 to the power steering motor 31. Similarly, upon rotation 
of the inner valve member 40 relative to the outer valve member 42 through 
the same distance in the counterclockwise direction, the same fluid 
pressure is conducted through the other motor conduit 28 or 30 to the 
power steering motor 31. 
Even though the inner and outer valve members 40 and 42 are accurately 
made, even small tolerance variations in the location and/or configuration 
of the lands 87 and grooves 86 on the outside of the inner valve member 
and the lands and grooves 89 on the inside of the outer valve member 42 
can effect exactly where the inner and outer valve members 40 and 42 are 
relative to each other in the pressure balanced, hydraulically centered 
condition. As a practical matter, the hydraulically centered condition of 
the inner and outer valve members 40 and 42 is ascertained by assembling 
the valve members and checking the fluid pressures obtained. 
When the inner and outer valve members 40 and 42 are in the initial or 
unactuated position, a relatively small amount of relative movement 
between the valve members effects little or no change in the fluid 
pressure conducted to the power steering motor 31. However, as the extent 
of the relative movement between the inner and outer valve members 
increases, the extent of the change in pressure with an increment of 
relative movement increases. 
To determine the hydraulically centered position of the inner and outer 
valve members 40 and 42, the lower end of the torsion spring 102 is 
fixedly connected with the follow-up member 54 and pinion 64. The inner 
valve member 40 is positioned on the follow-up member 54 (FIG. 4) with the 
torsion spring 102 extending through a central axial passage in the inner 
valve member. The upper end portion of the torsion spring 102 is fixedly 
connected with the inner valve member 40. 
The outer valve member 42 is then telescoped over the inner valve member 
40. The follow-up member 54, torsion spring 102, and inner valve member 40 
form an assembled unit and are rotatable together relative to the outer 
valve member 42. The outer valve member 42 has not yet been connected to 
the follow-up member 54. 
The inner and outer valve members 40 and 42 are then positioned in a 
fixture 166 (FIG. 3). Hydraulic fluid is conducted through a passage 170 
in the fixture 166 to the central groove 80 in the outer valve member 42. 
The hydraulic fluid flows through passages in the inner and outer valve 
members 40 and 42 to passages 172 and 174 in the fixture 166. The passages 
172 and 174 correspond to the motor conduits 28 and 30 of FIG. 1. 
The outer valve member 42 is then rotated to locate a preliminary initial 
position in which substantially equal fluid pressures are present at the 
passages 172 and 174. The outer valve member 42 is then rotated from the 
preliminary initial position to a first actuated position. When the outer 
valve member 42 is in the first actuated position, a relatively high 
predetermined fluid pressure is present at the passage 172. Although many 
different fluid pressures could be selected, in one specific instance, a 
fluid pressure of 100 psi was selected. When the fluid pressure of 100 psi 
was obtained at the passage 172, the relative positions of the inner and 
outer valve members 40 and 42 were noted and will be referred to herein as 
the first actuated position. 
The outer valve member 42 is then rotated in the opposite direction 
relative to the stationary inner valve member 40 until the same 
predetermined fluid pressure is obtained at the passage 174. Thus, in the 
example, the outer valve 42 is rotated in the opposite direction until a 
fluid pressure of 100 psi is obtained at the passage 174. The relative 
position of the inner and outer valve members 40 and 42 is then noted. 
This position is referred to herein as the second actuated position. 
The outer valve member 42 is then rotated back to a central position half 
way between the first and second actuated positions. Thus, the arcuate 
distance which the outer valve member 42 rotates from the central position 
to the first actuated position is equal to the arcuate distance through 
which the outer valve member 42 rotates from the central position to the 
second actuated position. The control valve 22 is in a hydraulically 
centered condition when the outer valve member 42 is in the central 
position midway between the first and second actuated positions. Although 
it is preferred to rotate the outer valve member 42 relative to the inner 
valve member 40 to locate the central position, the inner valve member 
could be rotated relative to the outer valve member if desired. 
When the outer valve member 42 is in the central position relative to the 
inner valve member 40, the outer valve member 42 is fixedly connected to 
the follow-up member 54. The outer valve member 42 is fixedly connected 
with the follow-up member 54 by plastically deforming the outer valve 
member 42 inward toward the longitudinal central axis 46 of the power 
steering control valve 22. The material of the outer valve member 42 then 
grips the follow-up member 54 to hold the outer valve member against 
movement relative to the follow-up member. 
To plastically deform the outer valve member 42, a pair of punches or tools 
184 and 186 (FIG. 4) are moved diametrically inward toward opposite sides 
of the outer valve member 42. The tools 184 and 186 are effective to form 
a pair of indentations 56 (FIG. 2) by plastically deforming the material 
of the outer valve member 42 into a pair of hemispherical recesses 188 and 
190 formed at diametrically opposite portions of the follow-up member 54. 
The two tools 184 and 186 (FIG. 4) apply pressure against diametrically 
opposite areas on the cylindrical outer valve member 42 to plastically 
deform the material of the outer valve member into the recesses 188 and 
190 in the upper (as viewed in FIG. 2) end of the follow-up member 54. 
This results in the outer valve member 42 being fixedly connected with the 
follow-up member 54. At this time, the inner valve member 40 is in a 
hydraulically centered position relative to the outer valve member 42. The 
outer valve member 42 is fixedly connected with the follow-up member 54. 
The outer valve member 42 is connected with the inner valve member 40 
through the follow-up member 54 and the torsion bar 102. 
Upon initiation of a power steering operation, the valve stem 50 of the 
power steering control valve 22 is rotated under the influence of force 
transmitted from the vehicle steering wheel. This force resiliently 
deflects the torsion bar 102 and moves the inner valve member 40 relative 
to the outer valve member 42. Hydraulic fluid is then directed to one of 
the motor conduits 28 or 30 to effect operation of the power steering 
motor 31 in the manner previously explained. As the power steering motor 
31 is operated, the rack 66 rotates the pinion gear 64 on the follow-up 
member 54. Rotation of the follow-up member 54 rotates the outer valve 
member 42 back toward the initial or unactuated position relative to the 
inner valve member 40. When the inner and outer valve members 40 and 42 
reach their initial or unactuated positions, operation of the power 
steering motor 31 is interrupted. 
From the above description of the invention, those skilled in the art will 
perceive improvements, changes and modifications. Such improvements, 
changes and modifications within the skill of the art are intended to be 
covered by the appended claims.