Steering apparatus

A vehicle steering apparatus (10) for turning steerable wheels (14, 16) of a vehicle includes a member (44) movable linearly in opposite directions to turn the steerable wheels in opposite directions. A housing (40) has a chamber (42) into which the member (44) extends. A piston (46) secured to the member (44) is located in the chamber (42). The piston (46) divides the chamber (42) into first and second chamber portions (48, 50). Fluid pressure in the first chamber portion (48) acts on a first area (116) of the piston (46) to cause Linear movement of the member (44) in one direction. Fluid pressure in the second chamber portion (50) acts on a second area (118) of the piston (46) to cause linear movement of the member (44) in a second direction opposite the one direction. The second area (118) of the piston (46) is less than the first area (116) of the piston. A spring (122) acts to urge the member (44) in the second direction. The spring (122) applies a force to the member (44) to balance the forces acting on the member to move the member when the pressure in the first chamber portion (48) equals the pressure in the second chamber portion (50).

FIELD OF THE INVENTION
 The present invention relates to an apparatus for use in turning steerable
 vehicle wheels.
 BACKGROUND OF THE INVENTION
 A known apparatus for use in turning steerable vehicle wheels includes a
 housing which encloses a piston. A hollow piston rod extends from the
 piston and projects outward from one end of the housing. The piston rod is
 connected with a vehicle steering linkage. A compensator chamber is
 provided in the hollow piston rod to enable the working areas on opposite
 sides of the piston to be equalized.
 SUMMARY OF THE INVENTION
 The present invention provides a vehicle steering apparatus for turning
 steerable wheels of a vehicle. The apparatus includes a member movable
 linearly in opposite directions to turn the steerable wheels in opposite
 directions. A housing has a chamber into which the member extends. A
 piston secured to the member is located in the chamber.
 The piston divides the chamber into first and second chamber portions.
 Fluid pressure in the first chamber portion acts on a first area of the
 piston to cause linear movement of the member in one direction. Fluid
 pressure in the second chamber portion acts on a second area of the piston
 to cause linear movement of the member in a second direction opposite the
 one direction. The second area of the piston is less than the first area
 of the piston. A spring acts to urge the member in the second direction.
 The spring applies a force to the member to balance the forces acting on
 the member to move the member when the pressure in the first chamber
 portion equals the pressure in the second chamber portion.

DESCRIPTION OF A PREFERRED EMBODIMENT
 A power steering apparatus 10 constructed in accordance with the present
 invention is illustrated schematically in FIG. 1. The power steering
 apparatus 10 includes a power steering motor 12 which is connected with
 steerable vehicle wheels 14 and 16 by a steering linkage 18. A power
 steering control valve 22 is connected to the power steering motor 12 by
 conduits 24 and 26. Rotation of a vehicle steering wheel 30 operates the
 power steering control valve 22 to direct high pressure hydraulic fluid
 from a pump 32 to the power steering motor 12 and to direct fluid from the
 power steering motor to reservoir 34.
 The power steering control valve 22 is of a known open-center type.
 Therefore, when the power steering control valve 22 is in an unactuated
 neutral condition, illustrated schematically in FIG. 1, opposite ends of
 the power steering motor 12 are connected in fluid communication with each
 other, with the pump 32 and with the reservoir 34. When the control valve
 22 is in the neutral condition, no steering is occurring.
 The power steering motor 12 (FIGS. 1 and 2) includes a housing 40 having a
 chamber 42 into which a member 44 extends. A piston 46 is secured to the
 member 44 and is located in the chamber 42. The piston 46 divides the
 chamber 42 into first and second chamber portions 48 and 50.
 Upon rotation of the steering wheel 30 (FIG. 1) in one direction, the power
 steering control valve 22 is moved toward the right (as viewed in FIG. 1).
 This results in high pressure fluid from the pump 32 being directed to the
 chamber portion 50 of the power steering motor 12. At the same time, the
 chamber portion 48 of the power steering motor 12 is connected with the
 reservoir 34 through the power steering control valve 22.
 The high fluid pressure in the chamber portion 50 of the power steering
 motor 12 results in linear movement of the member 44 and the piston 46
 toward the left (as viewed in FIG. 1) in the housing 40. As the piston 46
 moves toward the left (as viewed in FIG. 1), the steering linkage 18 is
 actuated to turn the steerable vehicle wheels 14 and 16, in a known
 manner, to turn the vehicle in a first direction. As the steerable vehicle
 wheels 14 and 16 are turned, a feedback mechanism 54 is actuated to move
 the power steering control valve 22 toward its neutral or unactuated
 condition.
 Upon rotation of the steering wheel 30 in the opposite direction, the power
 steering control valve 22 is moved toward the left (as viewed in FIG. 1).
 Movement of the power steering control valve 22 to the left results in
 high pressure fluid from the pump 32 being conducted to the chamber
 portion 48 of the power steering motor 12. At the same time, the chamber
 portion 50 of power steering motor 12 is connected with the reservoir 34
 through the conduit 24. This results in the piston 46 being moved toward
 the right (as viewed in FIG. 1). As the piston 46 moves toward the right,
 the steering linkage 18 turns the steerable vehicle wheels 14 and 16 in a
 second direction opposite to the direction in which they are turned as the
 piston moves toward the left. When the steerable vehicle wheels 14 and 16
 have been turned to an extent corresponding to the extent of rotation of
 the steering wheel 30, the feedback mechanism 54 affects operation of the
 power steering control valve 22 back to the unactuated condition.
 The steering linkage 18 (FIG. 2) is connected with the member 44 of the
 power steering motor 12 at a location to the right of the chamber portion
 50. The steering linkage 18 includes ball joint assemblies 60 and 62 which
 connect the steerable wheels 14 and 16 with the power steering motor 12.
 The ball joint assemblies 60 and 62 are secured to a connector section 66
 of the power steering motor 12. The connector section 66 is connected with
 the member 44.
 The connector section 66 extends through a linear slot 70, formed in the
 housing 40. The slot 70 has a length sufficient to enable the ball joint
 assemblies 60 and 62 to move toward either the left or the right (as
 viewed in FIG. 2) through a full operating range of the power steering
 motor 12. The linear slot 70 is disposed in a central portion of the
 housing 40.
 In the illustrated embodiment of the invention, the feedback mechanism 54
 has a screw and nut construction. However, the feedback mechanism 54 could
 have a different construction if desired. The feedback mechanism 54
 includes a rotatable screw member 74 and a nut 76. The nut 76 is fixedly
 connected with the connector section 66. In the illustrated embodiment of
 the invention, the nut 76 is of the recirculating ball type. During axial
 movement of the nut 76 relative to the screw member 74, spherical balls
 (not shown) in the nut cooperate with a helical external thread
 convolution 78 on the screw member to rotate the screw member relative to
 the housing 70. Upon movement of the piston 46 toward the right (as viewed
 in FIG. 2), the screw member 74 is rotated in one direction about its
 longitudinal central axis. Upon movement of the piston 46 toward the left,
 the screw member 74 is rotated in the opposite direction about its
 longitudinal axis. Other known types of nuts could be used in place of the
 recirculating ball type nut 76 if desired.
 In addition, the feedback mechanism 54 includes a gear assembly (not shown)
 which connects the rotatable screw member 74 with the power steering
 control valve 22. Although the screw member 74 is rotatable relative to
 the housing 40, the screw member is held against axial movement relative
 to the housing. Therefore, upon movement of the piston 46 and the member
 44, the screw member 74 is rotated relative to the housing 40 by the
 interaction between the nut 76 and the screw member. This rotational
 motion is transmitted through the gear assembly to the power steering
 control valve 22.
 A cylindrical sleeve 80 interconnects the nut 76 and the connector section
 66. One end of the sleeve 80 is connected with the nut 76. The opposite
 end of the sleeve is connected with the connector section 66. Accordingly,
 the connector section 66 moves linearly with the nut 76 relative to the
 screw member 74. The screw member 74 extends telescopically into the
 sleeve 80.
 The member 44 includes a tubular member 84 with an axially extending
 passage 85. The tubular member 84 interconnects the connector section 66
 and the piston 46. The tubular member 84 has one end connected with the
 connector section 66 and an opposite end connected with the piston 46.
 Accordingly, the connector section 66, the sleeve 80, and the nut 76 move
 with the piston 46 relative to the housing 40.
 The housing 40 has a cylindrical side wall 90. The side wall 90 has a
 longitudinal central axis 92 which is coincident with the longitudinal
 central axis of the piston 46, the screw member 74, and the tubular member
 84.
 The housing 40 has a right (as viewed in FIG. 2) end section 96 with
 bearings 98 which rotatably support the screw member 74. The end section
 96 and the bearings 98 retain the screw member 74 against axial movement.
 An end wall 102 is connected with the opposite or left end of the side wall
 90. The end wall 102 cooperates with the side wall 90 to define the
 chamber 42. The chamber 42 has a central axis which is coincident with the
 central axis 96 of the housing 40.
 A wall 106 extends radially inwardly from the side wall 90 to define a
 right end of the chamber 42. The tubular member 84 extends through the
 wall 106 to the piston 46. A seal member 108 engages the tubular member 84
 and is connected to the wall 106 to prevent leakage of hydraulic fluid
 from the chamber portion 50 along the outside of the tubular member. A
 seal 110 connected to the piston 46 engages the side wall 90 to prevent
 leakage of hydraulic fluid between the chamber portions 48 and 50.
 The end wall 102 cooperates with the side wall 90 and the piston 46 to
 define the chamber portion 48. The wall 106 and seal member 108 cooperate
 with the side wall 90 and the piston 46 to define the chamber portion 50.
 The chamber portion 48 may be in fluid communication with the power
 steering control valve 22 through the passage 85 in the tubular member 84.
 Alternatively, the chamber portion 48 may be in fluid communication with
 the control valve 22 through an external conduit. The chamber portion 50
 may be in fluid communication with the power steering control valve 22
 through an external conduit (not shown).
 Fluid pressure in the chamber portion 48 acts on a first area 116 of the
 piston 46 to cause the member 44 to move to the right, as viewed in FIG.
 2. Fluid pressure in the chamber portion 50 acts on a second area 118 of
 the piston 46 to cause movement of the member 44 to the left, as viewed in
 FIG. 2. The annular area 118 of the piston 46 is less than the area 116 of
 the piston.
 A conical spring 122 is located in the chamber portion 50 and extends
 between the wall 106 and the piston 46. Alternatively, a cylindrical
 spring may extend between the wall 106 and the piston 46. The conical
 spring 122 urges the piston to the left, as viewed in FIG. 2. The spring
 122 applies a force to the piston 46 to balance the forces acting on the
 piston to move the piston and the member 44 when the pressure in the
 chamber portions 48 and 50 are equal.
 The member 44 and piston 46 have an unactuated position corresponding to
 the unactuated conditions of the steering wheel 30 and the control valve
 22, as shown in FIG. 2, when no steering is occurring. The spring 122
 applies a predetermined force to the piston 46 and member 44 when the
 member and piston are in their unactuated positions. The predetermined
 force applied by the spring 122 is equal to the pressure in the pressure
 chamber 48 times the difference between the first and second areas of the
 piston 46.
 Upon operation of the power steering control valve 22, the piston 46 and
 the member 44 move together relative to the side wall 90 of the housing
 40. Movement of the piston 46 varies the volumes of the chamber portions
 48 and 50. This movement of the piston 46 operates the steering linkage 18
 to turn the steerable vehicle wheels 14 and 16.
 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.