WO2019164879A1

WO2019164879A1 - Electric power steering system of a rack and pinion type for a vehicle and method for producing the same

Info

Publication number: WO2019164879A1
Application number: PCT/US2019/018684
Authority: WO
Inventors: John SANTORI; Brian Urbach
Original assignee: Trw Automotive U.S. Llc
Priority date: 2018-02-20
Filing date: 2019-02-20
Publication date: 2019-08-29

Abstract

A vehicle steering system has an electric power steering system, first and second steerable wheels, a steering linkage, and a solid axle. The electric power steering system is of a rack and pinion type and has a member that is a single take off point for the electric power steering system. The first steerable wheel is moved by the member. The steering linkage connects the first steerable wheel to the second steerable wheel and moves the second steerable wheel. The axle is a solid axle connecting the first and second steerable wheels.

Description

TITLE

ELECTRIC POWER STEERING SYSTEM OF A RACK AND PINION TYPE FOR A VEHICLE AND METHOD FOR PRODUCING THE SAME

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to, and the benefit of, U.S. Provisional Application Serial No. 62/632,553, filed February 20, 2018, the full disclosure of which is incorporated herein by reference in entirety.

BACKGROUND OF INVENTION

[0002] This invention relates in general to vehicle steering systems and in particular to an improved electric power steering system and related components thereof and method for producing the same.

[0003] Automotive vehicles typically include a steering system to convert rotational movement of a steering wheel into linear movement that effects turning of steerable wheels. Typically, power steering assistance is provided for the steering system. The power steering may be a hydraulic or electric system. The hydraulic power steering systems use a hydraulic pump, driven by an engine of the vehicle, to supplement a manual force applied to the steering system at the steering wheel by a driver of the vehicle. In contrast, the electric power steering systems use an electric motor to supplement the manual force applied by the driver. By not requiring the hydraulic pump driven by the engine, the electric power steering systems result in improved fuel economy for the vehicle.

[0004] Some vehicles have a solid front axle for robustness. The vehicles with a solid front axle typically use recirculating ball type steering systems. This is because the recirculating ball type steering systems avoid undesirable steering wheel feedback - i.e., bump steer - that results when rack and pinion type steering systems are used with a solid front axle. The electric power steering systems may be used with the recirculating ball type steering systems. However, the recirculating ball type steering systems with the electric power steering systems may not produce sufficient steering torque for the vehicles with a solid front axle.

[0005] Alternatively, the electric power steering systems may be used with the rack and pinion type steering systems for the vehicles with solid front axles. The rack and pinion type steering systems with the electric power steering systems produce greater steering torque than the recirculating ball type steering systems with the electric power steering systems. However, the rack and pinion type steering systems with the electric power steering systems still result in the undesirable steering wheel feedback. Thus, it would be desirable to have an electric power steering system for a vehicle with a solid front axle that produces greater steering torque while improving fuel economy for the vehicle and avoiding undesirable steering wheel feedback.

SUMMARY OF INVENTION

[0006] This invention relates to an electric power steering system of a rack and pinion type for vehicles preferably having a solid front axle.

[0007] According to one embodiment, a vehicle steering system may comprise, individually and/or in combination, one or more of the following features: an electric power steering system of a rack and pinion type and having a member that is a single take off point for the electric power steering system, a first steerable wheel moved by the member, a steering linkage connecting the first steerable wheel to a second steerable wheel, and a solid axle connecting the first and second steerable wheels.

[0008] According to this embodiment, a connection point for the member is vertically aligned with a support point at which a vehicle having the vehicle steering system is supported on the axle.

[0009] According to this embodiment, the connection point is vertically aligned perpendicular to the axle.

[0010] According to this embodiment, the member is a tie rod.

[0011] According to this embodiment, the steering linkage is of a cross steer type, a Haltenberger type, or a center steer type.

[0012] According to this embodiment, the vehicle steering system may further comprise a steering knuckle of the first steerable wheel. The member is connected to a top surface of the steering knuckle. A drag link of the steering linkage connects the first steerable wheel to the second steerable wheel. The drag link is connected to a bottom surface of the steering knuckle.

[0013] According to this embodiment, the connection between the member and the steering knuckle is vertically aligned with the connection between the drag link and the steering knuckle.

[0014] According to this embodiment, the vehicle steering system may further comprise a first connection between the member and the first steerable wheel and a second connection between the steering linkage and the first steerable wheel. The first and second connections are vertically aligned.

[0015] According to this embodiment, the vehicle steering system may further comprise a center link of the steering linkage connecting the electric power steering system and the first steerable wheel and a drag link of the steering linkage connecting the center link to the second steerable wheel.

[0016] According to this embodiment, the vehicle steering system may further comprise a link connection on the center link between the center link and the drag link.

[0017] According to this embodiment, a connection point between the member and the center link is also at the link connection.

[0018] According to this embodiment, the vehicle steering system may further comprise a center link of the steering linkage connected to the electric power steering system, a first tie rod of the steering linkage connecting the center link to the first steerable wheel, and a second tie rod of the steering linkage connecting the center link to the second steerable wheel.

[0019] According to this embodiment, the center link is connected to a rack portion of the electric power steering system.

[0020] According to this embodiment, the center link is connected to a midpoint of the rack portion.

[0021] According to this embodiment, the center link is aligned with a first roll axis of a vehicle having the vehicle steering system and a second roll axis of the axle.

[0022] According to this embodiment, the vehicle steering system may further comprise a rack portion of the electric power steering system, a center link of the steering linkage rigidly connected to a midpoint of the rack portion, wherein the center link is aligned with a first roll axis of a vehicle having the vehicle steering system and a second roll axis of the axle, a first tie rod of the steering linkage connecting the center link to the first steerable wheel, and a second tie rod of the steering linkage connecting the center link to the second steerable wheel.

[0023] According to another embodiment, a method for retrofitting a vehicle steering system to a vehicle comprises the steps of removing the existing recirculating ball type steering system from the vehicle, installing a new electric power steering system on the vehicle in place of the removed existing recirculating ball type steering system, and connecting the new electric power steering system with an existing steering linkage on the vehicle. The vehicle has a solid front axle and was factory assembled with the existing recirculating ball type steering system.

[0024] According to this embodiment, the existing steering linkage is of a cross steer type, a Haltenberger type, or a center steer type.

[0025] According to this embodiment, the existing recirculating ball type steering system is removed by removing a steering gearbox and a pitman arm of the recirculating ball type steering system.

[0026] According to this embodiment, the vehicle has been designed for the existing recirculating ball type steering system.

[0027] One or more advantages of an embodiment of the invention is an electric power steering system for a vehicle with a solid front axle that improves fuel economy for the vehicle and produces greater steering torque while avoiding undesirable steering wheel feedback. Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0028] FIG. 1 is a schematic view of a first embodiment of a vehicle steering system in accordance with the present invention.

[0029] FIG. 2 is a schematic view of a vehicle with a solid front axle having a prior art recirculating bah steering system.

[0030] FIG. 3 is a flow chart of a method for retrofitting the vehicle of FIG. 2 with the vehicle steering system of FIG 1.

[0031] FIG. 4 is a perspective view of an electric power steering system for the vehicle steering system of FIG. 1 mounted to a vehicle.

[0032] FIG. 5 is a schematic view of a second embodiment of a vehicle steering system in accordance with the present invention.

[0033] FIG. 6 is a perspective view of an application of the vehicle steering system of FIG. 5.

[0034] FIG. 7 is a schematic view of a third embodiment of a vehicle steering system in accordance with the present invention.

[0035] FIG. 8 is a perspective view of an application of the vehicle steering system of FIG. 7. [0036] FIG. 9 is a schematic view of a fourth embodiment of a vehicle steering system in accordance with the present invention.

[0037] FIG. 10 is a first perspective view of an application of the vehicle steering system of FIG. 9.

[0038] FIG. 11 is a second perspective view of an application of the vehicle steering system of FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Referring now to FIG. 1, there is schematically illustrated a portion of a vehicle steering system, indicated generally at 100, in accordance with an embodiment of the present invention. The vehicle steering system 100 includes an electric power steering (EPS) system, indicated generally at 102, that is a rack and pinion type steering system with electric power steering assistance.

[0040] The general structure and operation of the EPS system 102 is conventional in the art. For example, the general structure and operation of the EPS system 102 may be as disclosed by U.S. Patent No. 7,055,646 to Bugosh, the disclosure of which is hereby incorporated by reference in entirety herein. Thus, only those portions of the EPS system 102 which are necessary for a full understanding of this invention will be explained and illustrated in detail.

[0041] Although this invention will be described and illustrated in connection with the particular EPS system 102 disclosed herein, it will be appreciated that this invention may be used in connection with other vehicle power steering systems, including other electric or otherwise powered power steering systems known to those skilled in the art.

[0042] The vehicle steering system 100 also includes a steering linkage, indicated generally at 104, that connects the EPS system 102 to first and second steerable wheels 106A and 106B, respectively, of a vehicle and includes a rotatable input shaft 108. A vehicle steering wheel 110 is operatively coupled to the input shaft 108 for rotation therewith about a steering axis XI. A torque sensor 112 is located within a steering housing 114 and encircles the input shaft 108. The torque sensor 112 generates signals in response to rotation of the input shaft 108. The signals are transmitted over a data network 116 to an electronic control unit (ECU) 118.

A torsion bar 120 connects the input shaft 108 to a pinion 122 located inside the steering housing 114. When the torsion bar 120 twists, relative rotation occurs between the input shaft 108 and the pinion 122.

[0043] A linearly moveable steering member 124 is at least partially in, and extends axially through, the steering housing 114. The steering member 124 is linearly (or axially) moveable along a rack axis X2. A rack portion 126 of the steering member 124 is provided with a series of rack teeth which engage gear teeth provided on the pinion 122 in a meshing manner to operatively connect the pinion 122 and rack portion 126. The steering member 124 further includes a screw portion 128 having an external screw thread convolution.

[0044] As previously discussed, the illustrated EPS system 102 has a single take off point. This differs from a typical EPS system which has two take off points, one for each of the steerable wheels. Specifically, the steering member 124 is connected to the steering linkage 104 by a member 130 that is the single take off point for the EPS system 102. As illustrated, the member 130 is a tie rod. Alternatively, and as will be discussed specifically with reference to FIGS. 9-11, the member 130 may be other than a tie rod. The steering member 124 and the member 130 are movable relative to the steering housing 114.

[0045] As discussed, the steering linkage 104 connects the EPS system 102 to the first and second steerable wheels 106A and 106B, respectively.

The steering linkage 104 also connects the first and second steerable wheels 106A and 106B, respectively, to each other. The steering linkage 104 transfers the linear movement of the steering member 124 along the rack axis X2 to and between the first and second steerable wheels 106 A and 106B, respectively, to result in steering movement of the first and second steerable wheels 106 A and 106B, respectively. Movement of the steering member 124 is transferred to the steering linkage 104 through the member 130 - i.e., the member 130 moves the first and second steerable wheels 106A and 106B, respectively. The transfer of linear movement by the steering linkage 104 will be discussed in greater detail with FIGS. 5-11.

[0046] The EPS system 102 further includes an electric motor 132 drivably connected to a ball nut 134 housed in the steering housing 114. The ECU 118 controls the electric motor 132 in accordance with the signals received from the torque sensor 112. Control signals for the electric motor 132 are transmitted from the ECU 118 to the electric motor 132 via the data network 116. The electric motor 132 and the ball nut 134 are operatively connected by a pulley assembly 136 that includes a belt transmitting rotational power between an output of the electric motor 132 and the ball nut 134. Alternatively, the electric motor 132 may be operatively connected to the ball nut 134 by a force transmission means other than the pulley assembly 136. Preferably, a planetary gearing is provided for the electric motor 132.

[0047] The ball nut 134 is operatively connected with the screw portion 128 of the steering member 124 in a known manner. The ball nut 134 effects the linear movement of the steering member 124 upon rotation of the steering wheel 110. As discussed, the electric motor 132 is operated in response to rotation of the steering wheel 110 and the ball nut 134 is driven by the electric motor 132 via the pulley assembly 136. When the ball nut 134 is driven, the ball nut 134 rotates and, because the ball nut 134 is linearly fixed in position on the rack axis X2, the steering member 124 moves linearly. The linear movement of the steering member 124, through the steering linkage 104, effects steering movement of the first and second steerable wheels 106 A and 106B, respectively, of the vehicle. The electric motor 132 thus provides power steering assistance in response to the applied steering torque.

[0048] In the event of the inability of the electric motor 132 to effect the linear movement of the steering member 124, a mechanical connection between the gear teeth on the pinion 122 and the rack teeth on the rack portion 126 of the steering member 124 permits manual steering of the vehicle. The pinion 122 and the rack portion 126 cooperate to convert rotation of the steering wheel 110 around the steering axis XI into linear movement of the steering member 124 along the rack axis X2.

[0049] Further shown in FIG. 1 is a solid axle 138 connecting the first and second steerable wheels 106A and 106B, respectively. When the first and second steerable wheels 106 A and 106B, respectively, are the front wheels of the vehicle, then the axle 138 is a solid front axle. As such, the first and second steerable wheels 106 A and 106B, respectively, and the axle 138 move together as a single assembly or other unit. The vehicle is supported on the axle 138 at first and second support points 140 A and 140B, respectively.

[0050] When the vehicle 100 is driven, the axle 138 rotates about the first or second support points 140 A or 140B, respectively, in a plane defined by a page upon which FIG. 1 is drawn. As non-limiting examples, the axle 138 may rotate because of dynamic force(s) acting on the vehicle 100 while it is being driven or because the vehicle 100 is driven over an uneven surface - e.g., a pothole or speed bump. The axle 138 rotating in these examples is because, as discussed, the illustrated axle 138 is a solid front axle.

Alternatively, the vehicle steering system 100 may be used with a vehicle wherein the axle 138 is other than a solid axle. As a non-limiting example, the vehicle steering system 100 may be used with a vehicle having an independent front suspension or other type of suspension.

[0051] Preferably, and as illustrated, a connection point 142 between the member 130 and the steering linkage 104 is vertically aligned above the first support point 140A (as indicated by dashed line 144). As illustrated, the vertical alignment is preferably perpendicular to the axle 138 when the axle 138 is not rotated. When the axle 138 rotates, the steering linkage 104 and the solid front axle 138 rotate or otherwise displace together and feedback through the steering wheel 110 is reduced. Alternatively, the connection point 142 may be aligned vertically with the second support point 140B.

[0052] Referring now to FIG. 2, there is illustrated a vehicle, indicated generally at 98, having an existing recirculating ball (RCB) steering system 102'. The existing RCB steering system 102' is connected by an existing steering linkage 104' to first and second steerable wheels 106A' and 106B', respectively. The vehicle 98 further has a solid front axle 138'.

[0053] Referring now to FIG. 3, there is illustrated a method, illustrated generally at 146, for retrofitting the vehicle steering system 100 on the vehicle 98 in FIG. 2. Specifically, the vehicle 98 has been configured or otherwise designed to use the existing RCB steering system 102'. Typically, the vehicle 98 being retrofitted according to the method 146 will have been factory assembled with the existing RCB steering system 102'. The vehicle steering system 100 may be retrofitted while maintaining or otherwise reusing the existing steering linkage 104' on the vehicle 98 being retrofitted.

[0054] First, in a step Sl, the existing RCB steering system 102' is removed or otherwise disabled. Preferably, the step S 1 includes removal of the existing RCB steering system 102'. As a non-limiting example, the removal of the existing RCB steering system 102' includes removal of the steering gearbox and/or pitman arm of the existing RCB steering system 102'. Alternatively, the step S 1 may include simply disconnecting the existing RCB steering system 102' and otherwise leaving it installed on the vehicle 98 being retrofitted.

[0055] Then, in a step S2, the EPS system 102 is installed in place of the removed, existing RCB steering system 102'. As a non-limiting example, the EPS system 102 may be bolted to the vehicle 98 being retrofitted.

Alternatively, the EPS system 102 may be installed to replace the existing RCB steering system 102' without the existing RCB steering system 102' being fully removed from the vehicle 98 being retrofitted.

[0056] Last, in a step S3, the new EPS system 102 is connected with an existing steering linkage 104' on the vehicle 98 being retrofitted by connecting the member 130 to the existing steering linkage 104'. As non limiting examples, the existing steering linkage 104' may be of a cross steer type, a Haltenberger type, or a center steer type.

[0057] Referring now to FIG. 4, there is illustrated a non-limiting example of the EPS system 102 mounted to a vehicle frame 148. As shown in FIG. 4, the EPS system 102 is mounted to a cross member 150 of the vehicle frame 148. Alternatively, the EPS system 102 may be mounted other than as shown in FIG. 4 to the vehicle. Alternatively, the EPS system 102 may be mounted to a vehicle or vehicle type other than the vehicle shown in FIG. 4. As a non-limiting example, the EPS system 102 may be mounted to a vehicle having a unibody.

[0058] Referring now to FIG. 5, there is schematically illustrated a second embodiment of a vehicle steering system, indicated generally at 200, in accordance with the present invention. The vehicle steering system 200 is a variation of the vehicle steering system 100 of FIGS. 1-4. As such, like reference numerals, increased by 100, designate corresponding parts in the drawings and detailed description thereof will be omitted. The vehicle steering system 200 includes a steering linkage 204 that is of a cross steer type.

[0059] An EPS system 202 is connected, via a member 230 (shown in FIG. 6 as a tie rod), to a first steering knuckle 252 A of a first steerable wheel 206A. Preferably, the EPS system 202 is connected to a top surface 254 of the first steering knuckle 252A. The steering linkage 204 includes a drag link 256. The drag link 256 connects the first steerable wheel 206 A to a second steerable wheel 206B. Preferably, the drag link 256 is connected to a bottom surface 258 of the first steering knuckle 252 A and a corresponding bottom surface 260 of a second steering knuckle 252B of the second steerable wheel 206B. As such, the EPS system 202 directly moves a first steerable wheel 206A, via the member 230, and the drag link 256 moves a second steerable wheel 206B.

[0060] Specifically, the EPS system 202 is connected to the top surface 254 of the first steering knuckle 252A at a first connection 262 and the drag link 256 is connected to the bottom surface 258 of the first steering knuckle 252A at a second connection 264. Preferably, the first and second connection points 262 and 264 are vertically aligned. As a result, the steering linkage 204 and a solid axle 238 may rotate or otherwise displace together such that feedback through a steering wheel 210 is reduced. As the first and second connection points 262 and 264 become more vertically aligned, the feedback through the steering wheel 210 is reduced.

[0061] Referring now to FIG. 6, there is illustrated a perspective view of the vehicle steering system 200. As shown therein, a damper 266 connects the drag link 256 to the axle 238.

[0062] Referring now to FIG. 7, there is schematically illustrated a third embodiment of a vehicle steering system, indicated generally at 300, in accordance with the present invention. The vehicle system 300 is a variation of the vehicle steering system 100 of FIGS. 1-4. As such, like reference numerals, increased by 200, designate corresponding parts in the drawings and detailed description thereof will be omitted. The vehicle steering system 300 includes a steering linkage 304 that is of a Haltenberger type.

[0063] The steering linkage 304 includes a center link 368 and a drag link 370. The center link 368 connects an EPS system 302 to a first steerable wheel 306A. Specifically, the EPS system 302 is connected to the center link 368 by a member 330 (shown in FIG. 8 as a tie rod). The drag link 370 connects a second steerable wheel 306B to the center link 368. Specifically, the drag link 370 is connected to the center link 368 at a link connection 372 on the center link 368. As such, the EPS system 302 moves the first steerable wheel 306A, via the member 330 and the center link 368, and the drag link 370 moves the second steerable wheel 306B. The EPS system 302 may connect to the center link 368 at the link connection 372.

[0064] As illustrated, there is a connection point 342 between the EPS system 302 and the center link 368. The connection point 342 is positioned between the EPS system 302 and the link connection 372. Alternatively, the connection point 342 may be at the link connection 372. As a non-limiting example, the connection point 242 and the link connection 372 may be a single connection between the EPS system 302, the center link 368, and the drag link 370.

[0065] The center link 368 is connected to the first steerable wheel 306A by a wheel connection 374. As the link connection 372 is positioned closer to the first steerable wheel 306A, the link connection 372 becomes more vertically aligned with the wheel connection 374. As the link

connection 372 and the wheel connection 374 become more vertically aligned, feedback through a steering wheel 310 from an axle 338 rotating is reduced.

[0066] Referring now to FIG. 8, there is illustrated a perspective view of the vehicle steering system 300 applied to a vehicle 376. The perspective view in FIG. 8 is a portion of an undercarriage of the vehicle 376.

[0067] Referring now to FIG. 9, there is schematically illustrated a fourth embodiment of a vehicle steering system, indicated generally at 400, in accordance with the present invention. The vehicle system 400 is a variation of the vehicle steering system 100 of FIGS. 1-4. As such, like reference numerals, increased by 300, designate corresponding parts in the drawings and detailed description thereof will be omitted, unless otherwise noted. The vehicle steering system 400 includes a steering linkage 404 that is of a center steer type.

[0068] An EPS system 402 has a member 430 that is a center link (not a tie rod). The member 430 is preferably connected to a midpoint, indicated generally at 478 (shown in FIGS. 10 and 11), of a rack portion 426 of the EPS system 402. Preferably, the member 430 has a rigid connection to the EPS system 402. As a non-limiting example, the member 430 may be connected to the rack portion 426 by a rigid connection. As a non-limiting example, the rigid connection between the member 430 and the hrack portion 426 may be a bolted connection.

[0069] The member 430 connects to first and second tie rods 480A and 480B, respectively, of the steering gear 404. In turn, the first tie rod 480A is connected to a first steerable wheel 406A and the second tie rod 480B is connected to a second steerable wheel 406B. Preferably, the member 430 is centered or otherwise aligned with a first roll axis 482 of the vehicle having the vehicle steering system 400 and a second roll axis 484 of an axle 438 (as illustrated, the first roll axis 482 and the second roll axis 484 coincide). Both the first roll axis 482 and the second roll axis 484 are shown by dashed lines in FIG. 9. When the member 430 is aligned with both the first roll axis 482 and the second roll axis 484, feedback through a steering wheel 410 is reduced when an axle 438 rotates.

[0070] Referring now to FIG. 10 and 11, there is illustrated a perspective view of the vehicle steering system 400. The vehicle steering system 400 is illustrated with a first steering knuckle 486A to which the first tie rod 480A is attached. A corresponding second steering knuckle to which the second tie rod 480B is attached is not shown.

[0071] In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been described and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Claims

What is claimed is:

1. A vehicle steering system comprising:

an electric power steering system having a member that is a single take off point for the electric power steering system, wherein the electric power steering system is of a rack and pinion type;

a first steerable wheel moved by the member;

a steering linkage connecting the first steerable wheel to a second steerable wheel; and

a solid axle connecting the first and second steerable wheels.

2. The vehicle steering system of Claim 1 wherein a connection point for the member is vertically aligned with a support point at which a vehicle having the vehicle steering system is supported on the axle.

3. The vehicle steering system of Claim 2 wherein the connection point is vertically aligned perpendicular to the axle.

4. The vehicle steering system of Claim 1 wherein the member is a tie rod.

5. The vehicle steering system of Claim 1 wherein the steering linkage is of a cross steer type, a Haltenberger type, or a center steer type.

6. The vehicle steering system of Claim 1 further comprising:

a steering knuckle of the first steerable wheel, wherein the member is connected to a top surface of the steering knuckle; and

a drag link of the steering linkage connecting the first steerable wheel to the second steerable wheel, wherein the drag link is connected to a bottom surface of the steering knuckle.

7. The vehicle steering system of Claim 6 wherein the connection between the member and the steering knuckle is vertically aligned with the connection between drag link and the steering knuckle.

8. The vehicle steering system of Claim 1 further comprising:

a first connection between the member and the first steerable wheel; and

a second connection between the steering linkage and the first steerable wheel, wherein the first and second connections are vertically aligned.

9. The vehicle steering system of Claim 1 further comprising:

a center link of the steering linkage connecting the electric power steering system and the first steerable wheel; and

a drag link of the steering linkage connecting the center link to the second steerable wheel.

10. The vehicle steering system of Claim 9 further comprising:

a link connection on the center link between the center link and the drag link.

11. The vehicle steering system of Claim 10 wherein a connection point between the member and the center link is also at the link connection.

12. The vehicle steering system of Claim 1 further comprising:

a center link of the steering linkage connected to the electric power steering system;

a first tie rod of the steering linkage connecting the center link to the first steerable wheel; and

a second tie rod of the steering linkage connecting the center link to the second steerable wheel.

13. The vehicle steering system of Claim 12 wherein the center link is connected to a rack portion of the electric power steering system.

14. The vehicle steering system of Claim 13 wherein the center link is connected to a midpoint of the rack portion.

15. The vehicle steering system of Claim 12 wherein the center link is aligned with a first roll axis of a vehicle having the vehicle steering system and a second roll axis of the axle.

16. The vehicle steering system of Claim 1 further comprising:

a rack portion of the electric power steering system;

a center link of the steering linkage rigidly connected to a midpoint of the rack portion, wherein the center link is aligned with a first roll axis of a vehicle having the vehicle steering system and a second roll axis of the axle; a first tie rod of the steering linkage connecting the center link to the first steerable wheel; and

17. A method for retrofitting a vehicle steering system to a vehicle, the method comprising the steps of:

removing the existing recirculating ball type steering system from the vehicle, wherein the vehicle has a solid front axle and was factory assembled with the existing recirculating ball type steering system;

installing a new electric power steering system on the vehicle in place of the removed existing recirculating ball type steering system; and

connecting the new electric power steering system with an existing steering linkage on the vehicle.

18. The method of Claim 17 wherein the existing steering linkage is of a cross steer type, a Haltenberger type, or a center steer type.

19. The method of Claim 17 wherein the existing recirculating ball type steering system is removed by removing a steering gearbox and a pitman arm of the recirculating ball type steering system.

20. The method of Claim 17 wherein the vehicle has been designed for the existing recirculating ball type steering system.