Multi-groove ball screw anti-rotation mechanism for steer-by-wire road wheel actuator

Abstract

The present disclosure provides a steer-by-wire road wheel actuator multi-groove ball screw anti-rotation mechanism. A steer-by-wire steering system for a vehicle includes a rod extending from a first end to a second end, the rod defining a first groove and a second groove within an outer surface of the rod. The steer-by-wire steering system also includes an anti-rotation barrel including a sleeve including a separate wear plate in which a plurality of ball bearings roll, where a first end of the sleeve includes a sleeve groove and a window feature, an inner surface of the sleeve includes a V-shaped groove in which the wear plate is disposed.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of priority of U.S. Provisional Application Serial No. 63 / 438,158, filed on January 10, 2023, and this application is a partial continuation application of U.S. Patent Application Serial No. 18 / 457,594, filed on August 29, 2023, which claims the benefit of priority of U.S. Provisional Patent Application Serial No. 63 / 402,620, filed on August 31, 2022, U.S. Provisional Patent Application Serial No. 63 / 417,223, filed on October 18, 2022, and U.S. Provisional Application Serial No. 63 / 429,517, filed on December 1, 2022. The disclosures of these patent applications are hereby incorporated by reference in their entireties. Technical field

[0003] The disclosure of the present application relates to an electric power steering (EPS) system, and more particularly to a road wheel actuator anti - rotation mechanism for such an EPS system. Background art

[0004] Various electric power steering systems have been developed to assist an operator in steering a vehicle. One type of EPS system is known as a rack - electric power steering (REPS) system. Some examples of steer - by - wire (SbW) road wheel actuators (RWAs) are simple ball - screw - based rack - electric power steering systems without an input shaft. In this configuration, the pinion shaft still engages the rack teeth cut into the ball - screw rack bar. This gear engagement provides two main functions. First, it provides a convenient rotating member for ball - screw position sensing. Second, an anti - rotation feature for preventing the rotation of the ball screw emerges. If a steer - by - wire road wheel actuator is designed for a large vehicle, it may be necessary to use two ball nuts on the same ball screw to achieve the required output force. Adding rack - and - pinion engagement to this type of system will result in over - constraint conditions because the center of the ball circuit in each ball nut defines the axis of the ball screw. Over - constraint is undesirable because if there is misalignment of parts, over - constraint will cause friction variations.

[0005] As steer - by - wire road wheel actuator systems with ball - screw actuation evolve, these systems may move away from traditional rack - and - pinion designs because gear engagement is no longer required to receive driver input from a handwheel.

[0006] The existing design is very complex and requires many high-precision surfaces to function correctly. In addition to the complexity of its design, due to the presence of the pinion tower and the rack bearing axis, the system occupies a large amount of packaging space in the vehicle. Summary of the Invention

[0007] According to one aspect of the present disclosure, a steer-by-wire steering system for a vehicle includes a rod extending from a first end to a second end, the rod defining a first groove and a second groove within an outer surface of the rod. The steer-by-wire steering system further includes an anti-rotation cartridge that includes a sleeve containing individual wear plates, a plurality of ball bearings rolling within the wear plates, wherein a first end of the sleeve includes a sleeve groove and a window feature, and an inner surface of the sleeve includes a V-shaped groove in which the wear plates are disposed.

[0008] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. Brief Description of the Drawings

[0009] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of this specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0010] Figure 1 A steering assembly having a rack electric power steering system is shown;

[0011] Figure 2 A dual-motor rack electric power steering system is schematically shown;

[0012] Figure 3 is a perspective view of an anti-rotation mechanism for a rack electric power steering system disposed within a housing;

[0013] Figure 4 is Figure 3 a cross-sectional view of the anti-rotation mechanism;

[0014] Figure 5A is a perspective view of an anti-rotation mechanism according to one aspect of the present disclosure;

[0015] Figure 5B is a perspective view of an anti-rotation mechanism according to another aspect of the present disclosure;

[0016] Figure 6 is a perspective view of an anti-rotation mechanism according to another aspect of the present disclosure;

[0017] Figure 7 is a perspective view of an anti-rotation mechanism according to another aspect of the present disclosure;

[0018] Figure 8 is a perspective view of an anti-rotation mechanism according to another aspect of the present disclosure;

[0019] Figure 9 is Figure 8 another perspective view of the anti-rotation mechanism;

[0020] Figure 10 is Figure 8 a front view of the anti-rotation mechanism;

[0021] Figure 11 is Figure 8 a sectional view of the anti-rotation mechanism;

[0022] Figures 12 to 14 shows another embodiment of the anti-rotation mechanism;

[0023] Figure 15 shows the sleeve and flange of the anti-rotation mechanism as separate components operatively coupled together;

[0024] Figure 16 and Figure 17 shows the sleeve and flange of the anti-rotation mechanism welded together;

[0025] Figure 18 shows the sleeve and the bent tab of the anti-rotation mechanism;

[0026] Figure 19 and Figure 20 shows a sleeve according to another aspect of the present disclosure; and

[0027] Figure 21 and Figure 22 shows a travel stop of the anti-rotation mechanism according to one aspect of the present disclosure. DETAILED DESCRIPTION

[0028] Referring now to the drawings, the embodiments described herein are used in combination with a steering assembly of a vehicle, such as a car, truck, sport utility vehicle, crossover vehicle, minivan, ship, aircraft, all-terrain vehicle, recreational vehicle, or other suitable vehicle. As discussed herein, an electric power steering (EPS) system (e.g., including a steer-by-wire steering system) includes an anti-rotation device in which a pinion is not used in the steering system. The anti-rotation device resists the rotation of a ball screw, a rack, etc. Such rotation is caused by the loading of the threads of a ball nut.

[0029] As used herein, the terms screw, ball screw, and rack define longitudinal members that are translated when another member (e.g., such as a ball nut) rotates. It should be understood that components may be used in various embodiments of the present disclosure and do not limit other components that may be translated to perform a steering maneuver.

[0030] First, referring to Figure 1 , a power steering system 20 is generally schematically illustrated. The power steering system 20 can be configured as a driver interface steering system, an autonomous driving system, or a system that allows both driver interface and autonomous steering. The steering system 20 can include an input device 22 (such as a steering wheel), where the driver can mechanically provide a steering input by turning the steering wheel. The steering column 26 extends along an axis from the input device 22 to an output assembly 28. The steering column 26 can include two or more axially adjustable sections and / or rake adjustable sections, such as a first section 30 and a second section 32 that are axially adjustable relative to each other. However, in some embodiments, there may be only a single section. The embodiments disclosed herein are for a steering system where the output assembly 28 is in operative communication with an actuator 34 that is coupled to a rack, such as a ball screw rack 1 having a lead screw / linear rack configuration. The output assembly 28 is in operative communication with the actuator 34, such as a wired communication 36 (e.g., a steer-by-wire configuration). The translation of the rack 1 can adjust the road wheels 47 for a steering maneuver.

[0031] As Figure 2 illustrated, by way of example and not limitation, the rack 1 translates with at least one actuator and possibly two or more actuators 34. Each actuator 34 includes an electric motor 21 and a ball nut 31, and is configured to drive the rack 1 to translate along a rack axis A1. The rack 1 is radially surrounded by a housing denoted by H.

[0032] Now referring to Figure 3 and Figure 4 , an embodiment of the rack 1 and an anti-rotation mechanism 10 for the rack 1 are shown as being disposed within the housing H. As disclosed herein, the anti-rotation mechanism 10 resists rotation of the rack 1 during operation.

[0033] Figure 5A and Figure 5BShows a view of the anti-rotation mechanism 10 according to an embodiment disclosed herein. The anti-rotation mechanism 10 includes a pair of running plates 3 positioned in the holes of the housing H. The running plates 3 can be formed of any suitable material, such as metal. For example, in some embodiments, the running plates 3 are formed of steel. Although a pair of running plates 3 are shown, it should be understood that in some embodiments, more or fewer running plates 3 may be provided. Each running plate 3 has a plurality of balls 6 disposed between the inner surface of the running plate 3 and the rack 1. Specifically, each set of balls 6 is positioned within a groove 5 defined along the outer surface of the rack 1. Each groove 5 extends in the longitudinal direction of the rack 1 to allow the rack 1 to translate relative to the anti-rotation mechanism 10, which remains relatively stationary within the housing H. The balls 6 react against the running plates 3 and the grooves 5 of the rack 1.

[0034] In Figure 5A the illustrated embodiment, the running plates 3 are axially, radially, and circumferentially retained in the assembly by spring members 4. Specifically, each spring member 4 includes a pair of end legs fixed to the housing H. The connecting portions of the spring members 4 couple the running plates 3 to each other. In another embodiment, as Figure 5B shown, snap fingers 60 positioned at the end regions of each running plate 3 facilitate retaining the running plates 3. The snap fingers 60 are resilient members that are capable of deflecting to insert and retain within the retaining features of the housing H.

[0035] Now referring to Figure 6 , the anti-rotation mechanism 10 includes a bracket 7 that holds the balls 6 in the anti-rotation mechanism 10 to ensure smooth movement and simplicity of the rack 1 relative to the anti-rotation mechanism 10. The bracket 7 includes a body portion 70 that extends around a portion of the outer diameter of the rack 1. In some embodiments, the bracket 7 is generally C-shaped and extends around the outer surface of the rack 1 by approximately 180 degrees. A plurality of fingers 72 are formed at the ends of the body portion 70. The plurality of fingers 72 are arranged to at least partially hold the balls 6 within the anti-rotation mechanism 10. Specifically, adjacent fingers among the plurality of fingers 72 accommodate the corresponding balls 6 therebetween.

[0036] Referring to Figure 7, another embodiment of the carriage is shown and designated as 7a. The carriage 7a includes a body portion 80 that extends around a portion of the outer diameter of the rack 1. In some embodiments, the carriage 7a is generally C-shaped and extends around the outer surface of the rack 1 by approximately 180 degrees. A plurality of fingers 82 are formed at the ends of the body portion 80. The plurality of fingers 82 are arranged to hold the balls 6 at least partially within the anti-rotation mechanism 10. Specifically, adjacent fingers of the plurality of fingers 82 receive a respective ball 6 therebetween. The carriage 7a includes a lateral edge region 84 that projects in the axial direction of the rack 1 and away from the plurality of fingers 82. The lateral edge region 84 provides added material at the ends of the carriage 7a to limit travel relative to the rack 1 based on the presence of a wall 86 created by at least one shoulder 8 defined at the ends of the groove 5. For example, a machined flat surface located on the rack 1 at the ends of the groove 5 can be used as a travel limiter, but other structural features can be provided in other embodiments for interaction with the lateral edge region 84.

[0037] Reference Figures 8 to 11 , another embodiment of the anti-rotation mechanism 10 is shown. The carriage in the illustrated embodiment is designated as 7b and can be similar or even identical to the carriage 7 discussed above. The carriage 7b is supported against rotation about the rack axis A1 and can be fixed relative to the housing H in some embodiments. The carriage 7b is shown as generally C-shaped and has ball retainers in the form of a plurality of fingers 90 on diametrically opposite sides of the rack 1 for rolling reception of the balls 6 therein and for rolling reception of the balls 6 in the grooves 5 of the rack or screw 1 that extend generally parallel to the rack axis A1 along diametrically opposite sides of the rack 1. A travel limiting mechanism 92 is provided for limiting travel of the carriage 7b relative to the rack 1. The travel limiting mechanism 92 may exist in pairs, with each travel limiting mechanism being disposed at the ends of the groove 5.

[0038] A cover 96 is used to assist in assembling the anti-rotation mechanism 10 into the center of the housing H. A sealing joint (e.g., RTV, PIP seal, etc.) can be provided along with fasteners (e.g., screws) to attach the cover 96 to the housing H. Optionally, the cover 96 can also incorporate a travel limiter 9. In some embodiments, the use of a colored carriage 7b can be used to easily identify different ball sizes.

[0039] Regardless of which embodiment is used, when a torsional load is applied to the rack or screw 1, the load is transmitted through the groove 5 to the balls 6, into the extension plate 3, and into the housing H, thereby preventing the rotation of the rack or screw 1. The balls 6 allow for low-friction translation in the axial direction along the groove 5. The size of the balls 6 or the stiffness of the extension plate 3 can be adjusted to accommodate the compliance required for noise and friction characteristics. The number of grooves 5 and the number of balls 6 can also be adjusted based on the system's requirements for friction and torque and to minimize the overconstraint of the system.

[0040] The embodiments disclosed herein provide several structural features and benefits, including but not limited to: ball and groove mechanization for resisting torque in a road wheel actuator steering system; a steel extension surface plate held by using spring members; balls held by a bracket for assembly and performing functions; one or more groove and ball combinations for resisting rotational torque of internal or external members; a bracket that also serves as a travel limiter; a ball screw having features (similar to the mechanization shown using shoulders) that help limit the travel of the bracket; and a side cover for assembling the mechanization and incorporating the attached or combined travel limiter into the cover.

[0041] Now referring to Figures 12 to 14 , the steel rod 101 has two grooves 102 machined into the steel rod at the end opposite the ball screw. The grooves 102 are opposite each other on the rod and parallel to the axis of the rod. A set of ball bearings 103 equally spaced by a ball bracket 104 extends in the grooves 102. The ball bracket 104 is in the shape of a C 105 such that the ball bracket can be assembled from the side of the rod 101 and snapped into the grooves 102. The anti-rotation cylinder 106 includes a sleeve 107, a flange 108, two wear plates 109, a retaining clip 110, a travel stop 111, a radial support bushing 112, and a plurality of bolts 113. The sleeve 107 contains the wear plates 109 in which a plurality of ball bearings roll. The sleeve 107 contains groove and window features at a first end, and the inner surface of the sleeve 107 contains V-shaped grooves in which the wear plates 9 are disposed.

[0042] Referring to Figure 15 , in the embodiment shown, the sleeve 107 and the flange 108 are separate steel pieces having interlocking features 114 to allow torque to be transmitted from the sleeve 107 to the flange 108. During assembly, the flange 108 will be swaged onto the sleeve 107 to axially lock the flange in place and allow a non-bundled joint. However, in some embodiments, as Figure 16 and Figure 17 shown, the sleeve 107 is connected to the flange 108 via a welded joint 115. In other embodiments, as Figure 18 shown, the flange 108 is replaced by an integrated bending tab 116.

[0043] Reference Figure 19 and Figure 20 and

[0043] , there is a window 117 at one end of the sleeve 107 that allows the retaining clip 110 to pass through the sleeve 107 and engage the slot 118 in the wear plate 109. The retaining clip 110 is shaped such that it presses the wear plate 109 radially outward in the sleeve to hold the wear plate in place during assembly. The wear plate 109 includes tabs 119 that slide over the ends of the sleeve 107 to hold the sleeve radially and axially during assembly.

[0044] Now refer to Figure 21 and Figure 22 Figure 21 and Figure 22 , the travel stop 111 includes a radial support bushing 112 that serves as the primary radial support for the steel rod 101 on this side of the steering system. The travel stop 111 can be designed such that the same bolt 113 that clamps the flange 108 to the housing can simultaneously clamp the travel stop 111 in place via the through-hole 120. Due to the tight fit of the radial support bushing 112 with the steel rod 101, an air passage 121 is formed in the travel stop to allow air to flow from one side of the steering system to the other, preventing a pressure differential from forming within the steering system.

[0045] The wear plate includes hook-like features at the first end to hold the wear plate radially and axially to the sleeve. The wear plate includes a slot at the second end opposite the first end to allow engagement by the retaining clip. The retaining clip passes through the wear plate slot and the window feature, and in some embodiments, the retaining clip is made of wire. The retaining clip serves as a biasing member to push the wear plate radially outward against a groove in the sleeve. The retaining clip also engages the sides of the sleeve window feature to provide axial retention of the wear plate to the sleeve. The sleeve has features such as a separate flange with a hole pattern or an integrated tab to allow the sleeve to be fastened to the housing. In some embodiments, the flange is made of steel and joined to the sleeve by welding or forging. If the sleeve is formed of steel, the integrated tab can be bent perpendicular to the axis of the sleeve to provide a mounting surface. The travel stop is provided with an integrated radial support bushing and an air passage to convey air from one side of the steering system to the other, and the conveyance of air prevents high or low pressure conditions within the tie-rod boot during actuation of the steering system. In some embodiments, the travel stop is made of aluminum or zinc by a high-pressure die casting process. In other embodiments, the travel stop is made of iron by a powder metal process. In some embodiments, the radial support surface of the travel stop is made of a multi-layer bushing material or injection molded plastic. The travel stop includes a hole pattern that matches the hole pattern of the flange or tab such that in some embodiments the same bolt used to fasten the flange or tab is used to fasten the travel stop to the housing.

[0046] The embodiments disclosed herein are for a REPS system having only a single ball nut rather than two or more ball nuts. Further, the wear plates disclosed herein are housed in a cartridge sub-assembly that slides into the end of the housing and is bolted in place.

[0047] Although the invention has been described in detail with reference to only a limited number of embodiments, it should be readily understood that the invention is not limited to these disclosed embodiments. On the contrary, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it should be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention should not be regarded as limited by the foregoing description.

Claims

1. A steer-by-wire steering system for a vehicle, comprising: a rod extending from a first end to a second end, the rod defining a first groove and a second groove within an outer surface of the rod; and an anti-rotation cylinder including a sleeve containing individual wear plates, a plurality of ball bearings rolling within the wear plates.

2. The steer-by-wire steering system according to claim 1, wherein an inner surface of the sleeve includes a V-shaped groove, and the wear plates are disposed within the V-shaped groove.

3. The steer-by-wire steering system according to claim 1, further comprising: a flange mechanically fastened to the second end of the sleeve; and a travel stop ring operatively coupled to the flange.

4. The steer-by-wire steering system according to claim 1, further comprising: a flange welded to the second end of the sleeve; and a travel stop ring operatively coupled to the flange.

5. The steer-by-wire steering system according to claim 1, further comprising: a pair of bent tabs extending from the second end of the sleeve; and a travel stop ring operatively coupled to the pair of bent tabs.

6. The steer-by-wire steering system according to claim 1, further comprising a set of ball bearings, the set of ball bearings being spaced apart from each other by a ball carrier, the ball carrier operatively coupled to the rod.

7. The steer-by-wire steering system according to claim 6, wherein the ball carrier is C-shaped and has a first end and a second end, wherein the first end snaps into the first groove of the rod, and wherein the second end snaps into the second groove of the rod.

8. The steer-by-wire steering system according to claim 1, further comprising a travel stop operatively coupled to the sleeve, the travel stop including a radial support bushing to radially support the rod.

9. The steer-by-wire steering system according to claim 1, wherein the rod is formed of steel.

10. The steer-by-wire steering system according to claim 1, wherein a first end of the sleeve defines a sleeve groove and a window, and a retaining clip passes through the sleeve groove and the window of the sleeve to engage at least one slot in the wear plate.

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