STEER-BY-WIRE ROAD WHEEL ACTUATOR MULTI-GROUND BALL SCREW ANTI-TURN MECHANISM

Abstract

A steer-by-wire steering system for a vehicle, comprising: a rod (101) extending from a first end to a second end, the rod (101) defining a first groove (102) and a second groove (102) within an outer surface of the rod (101); and an anti-rotation cartridge (106) comprising a sleeve (107) containing separate wear plates (109) in which a plurality of balls rolls, characterized by a movement stop (111) functionally coupled to the sleeve (107), the movement stop (111) comprising a radial support bushing (112) to radially support the rod (101).

Description

FIELD OF THE INVENTIONThe disclosure of this application relates to electric power steering (EPS) systems, and more particularly to a road wheel actuator anti-rotation mechanism for such EPS systems.BACKGROUNDVarious electric power steering systems have been developed to assist an operator in vehicle steering. One type of EPS system is referred to as a rack and pinion electric power steering (REPS) system. Some examples of steer-by-wire (SbW) road wheel actuators (RWAs) are simply ball-screw based electric rack and pinion servo steering systems without input shafts. In this configuration, a pinion shaft still meshes with rack teeth cut in the ball screw rack. This gear meshing provides two major functions. First, a suitable rotary element is provided for sensing ball screw position. Second, an anti-rotation feature for preventing rotation of the ball screw from occurring. If a steer-by-wire road wheel actuator is designed for a large vehicle, the use of two ball nuts on the same ball screw may be required to achieve the required output force. Adding rack and pinion meshing to this type of system would result in an over-constraint condition because the center of the ball circles in each ball nut defines the axis of the ball screw. The over-constraint is undesirable because it results in frictional variations when parts are not aligned.As ball screw operated steer-by-wire road wheel actuator systems develop, these systems can move away from the conventional rack and pinion design because gear meshing is no longer required to receive driver inputs from the hand wheel.Previous designs are very complex and require many high precision surfaces to function properly. In addition to the complexity of its design, the system occupies a significant packaging space in the vehicle due to the presence of the pinion tower and rack bearing axle.DE 10 2010 052 917 A1 discloses a steer-by-wire steering system for a vehicle according to the preamble of claim 1.DE 10 2017 103 975 A1 teaches 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. A plurality of balls roll in the grooves, which balls are mounted in clamping rings which are prestressed by means of screws and clamping bolts.DE 10 2009 009 031 A1 discloses a rack and pinion steering system in which the rack has a stop ring for mechanical stroke limitation. The stop ring is fastened to the hub via a piece of wire received in an inner circumferential groove of the stop ring. One end of the wire is anchored in a bore in the outer periphery of the hub and the other end of the wire is inserted in a slot in the stop ring.It is the object of the present invention to provide an improved steer-by-wire steering system for a vehicle.This object is achieved by a steer-by-wire steering system for a vehicle having the features of claim 1.Advantageous embodiments are given in the dependent claims.BRIEF DESCRIPTION OF THE DRAWINGSThe following are shown: FIG. 1 illustrates a steering assembly with a rack and pinion electric power steering system; FIG. 2 schematically illustrates a two-motor rack and pinion electric power steering system; FIG. 3 is a perspective view of an anti-rotation mechanism for the electric rack and pinion power steering system disposed in a housing (not in accordance with the invention); FIG. 4 is a cross-sectional view of the anti-rotation mechanism of FIG. 3 (not in accordance with the invention); FIG. 5A is a perspective view of the anti-rotation mechanism according to an aspect of the disclosure (not according to the invention); FIG. 5B is a perspective view of the anti-rotation mechanism according to another aspect of the disclosure (not according to the invention); FIG. 6 is a perspective view of the anti-rotation mechanism according to another aspect of the disclosure (not according to the invention); FIG. 7 is a perspective view of the anti-rotation mechanism according to another aspect of the disclosure (not according to the invention); FIG. 8 is a perspective view of the anti-rotation mechanism according to another aspect of the disclosure (not according to the invention); FIG. 9 is another perspective view of the anti-rotation mechanism of FIG. 8 (not in accordance with the invention); FIG. 10 is an elevational view of the anti-rotation mechanism of FIG. 8 (not in accordance with the invention); FIG. 11 is a sectional view of the anti-rotation mechanism of FIG. 8 (not according to the invention); FIGS. 12-14 illustrate an anti-rotation mechanism (according to the invention); FIG. 15 illustrates a sleeve and flange of the anti-rotation mechanism as separate components operatively coupled together (in accordance with the invention); FIGS. 16 and 17 illustrate a sleeve and flange of the anti-rotation mechanism welded together (according to the invention); FIG. 18 illustrates a sleeve and a curved tab of the anti-rotation mechanism (according to the invention); FIGS. 19 and 20 illustrate the sleeve according to another aspect of the disclosure (according to the invention); and FIGS. 21 and 22 illustrate a movement stop of the anti-rotation mechanism according to an aspect of the disclosure (according to the invention).DETAILED DESCRIPTIONReferring now to the figures, the embodiments described herein are used in connection with a steering arrangement of a vehicle, such as a car, truck, SUV, crossover, minivan, watercraft, aircraft, off-road vehicle, recreational vehicle, or other suitable vehicles. As discussed herein, an electric power steering (EPS) system, for example, including a steer-by-wire system, includes an anti-rotation device in which no pinion gear is used in the steering system. The anti-rotation device resists rotation of a ball screw, a rack or the like. Such rotation is induced by the load on the thread of a ball nut.As used herein, the terms spindle, ball screw, and rack define a longitudinal member that is displaced upon rotation of another member, such as a ball nut. It should be appreciated that the components may be used in various embodiments of the disclosure and do not limit other components that may be moved to perform steering maneuvers.Referring initially to FIG. 1, a power steering system 20 is generally schematically illustrated. The power steering system 20 may be configured as a driver interface steering system, an autonomous driving system, or a system that enables both a driver interface and an autonomous steering. The steering system 20 may include an input device 22, such as a steering wheel, wherein a driver may mechanically provide steering input by turning the steering wheel. A steering column 26 extends along an axis from the input device 22 to an output assembly 28. However, in some embodiments, only a single portion may be present. The embodiments disclosed herein are used in steering systems where the output assembly 28 is operatively connected to an actuator 34 coupled to a rack, such as a ball screw rack 1 having a helical screw / linear rack configuration. The output assembly 28 is operatively connected, such as a wired connection 36 (e.g., steer-by-wire configuration) to the actuator 34.As illustrated in FIG. 2, the rack 1 is displaced by way of example and without limitation with at least one actuator and possibly two or more actuators 34. Each actuator 34 includes a motor 21 and a ball nut 31 configured to drive the rack 1 to be displaced along a rack axis A 1. The rack 1 is radially surrounded by a housing, which is denoted by H.Referring now to Figures 3 and 4 (not according to the invention), the rack 1 and an anti-rotation mechanism 10 for the rack 1 are shown arranged in the housing H. The anti-rotation mechanism 10 resists rotation of the rack 1 during operation, as disclosed herein.FIGS. 5A and 5B (not according to the invention) illustrate views of an anti-rotation mechanism 10. The running plates 3 may 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 runner plates 3 are shown, it should be appreciated that in some embodiments more or fewer runner plates 3 may be provided. Each running plate 3 has a plurality of balls 6 disposed between an inner surface of the running plate 3 and the rack 1. In particular, each set of balls 6 is positioned within a groove 5 defined along an outer surface of the rack 1. Each groove 5 extends in the longitudinal direction of the rack 1 to allow the rack 1 to slide relative to the anti-rotation mechanism 10 which remains relatively stationary within the housing H. The balls 6 react against the running plate 3 and the groove 5 of the rack 1.According to FIG. 5A (not according to the invention), the running plates 3 are held in the arrangement axially, radially and circumferentially by spring elements 4. More specifically, the spring members 4 each include a pair of end legs fixed to the housing H. A connecting portion of the spring elements 4 couples the running plates 3 to one another. In another embodiment, the retention of the running plates 3 is facilitated by snap fingers 60 located at end portions of each running plate 3, as shown in FIG. 5B. The snap fingers 60 are resilient members that can be deflected to be inserted and retained in a retaining feature of the housing H.Referring now to Figure 6 (not according to the invention), the anti-rotation mechanism 10 comprises a support 7 which retains the balls 6 in the anti-rotation mechanism 10 to ensure smooth movement and ease of the rack 1 relative to the anti-rotation mechanism 10. The carrier 7 comprises a main portion 70 which extends around a portion of the outer diameter of the rack 1. In some embodiments, the carrier 7 is substantially C-shaped and extends about 180 degrees around the outer surface of the rack 1. The plurality of fingers 72 are provided to at least partially retain the balls 6 within the anti-rotation mechanism 10. Specifically, adjacent fingers of the plurality of fingers 72 include a respective ball 6 therebetween.Referring to Figure 7 (not according to the invention), another support is shown and designated 7a. The carrier 7a comprises a main portion 80 which extends around a portion of the outer diameter of the rack 1. In some embodiments, the carrier 7a is substantially C-shaped and extends about 180 degrees around the outer surface of the rack 1. The plurality of fingers 82 are provided to at least partially retain the balls 6 within the anti-rotation mechanism 10. In particular, adjacent fingers of the plurality of fingers 82 include a respective ball 6 therebetween. The carrier 7 aincludes side edge portions 84 protruding in the axial direction of the rack 1 and away from the plurality of fingers 82. The lateral edge portions 84 provide additional material at the ends of the carrier 7a to limit movement relative to the rack 1 based on the presence of a wall 86 created by at least one shoulder 8 defined at an end of the groove 5. For example, a machined flat surface on the rack 1 at one end of the groove 5 may be used as the travel limiting means, but other structural features may be provided for interaction with the lateral edge regions 84 in other embodiments.Referring to Figures 8-11 (not according to the invention), another anti-rotation mechanism 10 is illustrated. The carrier in the illustrated embodiment is denoted by 7 b, but may be similar or even identical to the carrier 7 discussed above. The carrier 7 bis supported against rotation about the rack axis A 1 and may be fixed relative to the housing H in some embodiments. The carrier 7b is shown as generally C-shaped, having ball holders in the form of a plurality of fingers 90 on diametrically opposite sides of the rack 1 for rollingly receiving the balls 6 therein and for rollingly receiving the balls 6 in the grooves 5 of the rack or spindle 1 extending substantially parallel to the rack axis A1 along diametrically opposite sides of the rack 1. A movement limiting mechanism 92 is used to limit the movement of the carrier 7b relative to the rack 1. The movement limiting mechanism 92 may be in the form of a pair, one at each end of the grooves 5.A cover 96 is used to aid in mounting the anti-rotation mechanism 10 in the center of the housing H. A seal connection (e.g., RTV, PIP seal, etc.) may be provided along with fasteners (e.g., screws) to secure the cover 96 to the housing H. The cover 96 may also include movement restricting means 9, as required. The use of colored supports 7b may be used in some embodiments for easy identification of different ball sizes.Regardless of which of the above apparatuses not according to the present invention are used when a torsional load is applied from the rack or spindle 1, the load is transmitted through the groove 5 to the balls 6 in the running plate 3 and the housing H, thereby preventing the rack or spindle 1 from rotating. The balls 6 allow low friction displacement in an axial direction along the groove 5. The number of grooves 5 and the number of balls 6 may also be adjusted based on the system requirements for friction and torque as well as to minimize over-limiting of the system.The non-inventive devices disclosed thus far provide several structural features and advantages, including, but not limited to: ball and groove mechanization to resist torque in a road wheel actuator steering system; steel tread plates held by the use of a spring member; balls held by a carrier for assembly and function; one or more groove and ball combinations to resist torque by the inner or outer member; a carrier also acting as a motion limiting device; a ball screw having a feature that helps limit the movement of the carrier similar to the mechanization shown using a shoulder, and a side cover for assembling the mechanization and the inclusion of motion limiting devices attached to or included in the cover.Referring now to Figures 12-14 (in accordance with the invention), a steel rod 101 is provided with two grooves 102 machined at the end opposite the ball screw. The grooves 102 are opposed to each other on the rod and are parallel to the axis of the rod. Running in the grooves 102 are a set of ball bearings 103 which are evenly spaced by a ball carrier 104. The ball carrier 104 is C-shaped 105 so that it can be installed and snap-fitted into the grooves 102 from the side of the rod 101. The anti-rotation cartridge 106 includes a sleeve 107, a flange 108, two wear plates 109, a retaining clip 110, a movement 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 includes a groove and window features at a first end, and the inner surface of the sleeve 107 includes V-shaped grooves in which the wear plates 9 are disposed.Referring to FIG. 15 (according to the invention), in the illustrated embodiment, the sleeve 107 and flange 108 are separate steel pieces that have locking features 114 to enable the transmission of torque from the sleeve 107 to the flange 108. During assembly, flange 108 would be swaged onto sleeve 107 to lock it axially and allow for a clearance free connection. However, in some embodiments, the sleeve 107 is connected to the flange 108 via a welded joint 115, as shown in FIGS. 16 and 17. In other embodiments, flange 108 is replaced with an integral curved tab 116, as shown in FIG. 18.Referring to Figures 19 and 20 (in accordance with the invention), at one end of the sleeve 107 is a window 117 which allows the retainer clip 110 to pass through the sleeve 107 and engage the slots 118 in the wear plates 109. The retainer clip 110 is configured to urge the wear plates 109 radially outward in the sleeve to hold them in place during assembly. The wear plates 109 include tabs 119 which slide over the end of the sleeve 107 to retain them both radially and axially during assembly.Referring now to Figures 21 and 22 (in accordance with the invention), the travel stop 111 includes a radial support bushing 112 which acts as a primary radial support for the steel rod 101 on that side of the steering system. The travel stop 111 may be configured such that the same bolts 113 clamping the flange 108 to the housing may simultaneously clamp the travel stop 111 in place via through holes 120. Due to the close fit of the radial support bushing 112 to the steel rod 101, air passages 121 are formed in the travel stop to allow air flow from one side of the steering system to the other to prevent a pressure differential from forming in the steering system.The wear plates include hook-like features at a first end to radially and axially retain the wear plates to the sleeve. The wear plates include slots at a second end, opposite the first end, to enable engagement by a retaining clip. A retaining clip passes through the wear plate slots and the window features, the retaining clip being made of steel wire in some embodiments. The retainer clip acts as a biasing member to urge the wear plates radially outward against the grooves in the sleeve. The retaining clip also engages the side of the sleeve window feature to provide axial retention of the wear plates to the sleeve. The sleeve has features such as a separate flange or integral tabs with a hole pattern to allow the sleeve to be secured to the housing. The flange is made of steel in some embodiments and is joined to the sleeve by either welding or swaging. If the sleeve is formed of steel, integral tabs may be bent perpendicular to the axis of the sleeve to provide the mounting surface. A travel stop is provided with an integral radial support bushing and air passages for conveying air from one side of the steering system to the other, wherein the conveyance of air prevents high or low pressure conditions in the tie rod shoes during operation of the steering system. The movement stop is made of aluminum or zinc in some embodiments by a high-pressure die casting process. The movement stop is manufactured in other embodiments with a driven metal method using iron. The radial support surface of the travel stop is made of a multi-layered bushing material or an injection molded plastic in some embodiments. The travel stop includes a hole pattern that matches the flange or tabs, such that in some embodiments the travel stop is secured to the housing using the same bolts as what secures the flange or tabs.The embodiments of the invention disclosed herein are for REPS systems that have only a single ball nut instead of two or more. In addition, the wear plates disclosed herein are housed in a cartridge subassembly that slides into the end of the housing and is bolted in place.

Claims

A steer-by-wire steering system for a vehicle, comprising: a rod (101) extending from a first end to a second end, the rod (101) defining a first groove (102) and a second groove (102) within an outer surface of the rod (101); and a anti-rotation cartridge (106) comprising a sleeve (107) including separate wear plates (109) in which a plurality of balls roll, characterized a movement stop (111) operatively coupled to the sleeve (107), the movement stop (111) including a radial support bushing (112) for radially supporting the rod (101).The steer-by-wire steering system of claim 1, wherein the inner surface of the sleeve (107) includes V-shaped grooves in which the wear plates (109) are disposed.The steer-by-wire steering system of claim 1, further comprising: a flange (108) mechanically secured to the second end of the sleeve (107); wherein the travel stop (111) is operatively coupled to the flange (108).The steer-by-wire steering system of claim 1, further comprising: a flange (108) welded to the second end of the sleeve (107); wherein the travel stop (111) is operatively coupled to the flange (108).The steer-by-wire steering system of claim 1, further comprising: a pair of bent tabs (116) extending from the second end of the sleeve (107); wherein the travel stop (111) is operatively coupled to the pair of bent tabs (116).The steer-by-wire steering system of claim 1, further comprising a set of ball bearings (103) spaced apart from one another by a ball carrier (104) operatively coupled to the rod (101).The steer-by-wire steering system of claim 6, wherein the ball carrier (104) is C-shaped (105) and has a first end and a second end, wherein the first end snaps into the first groove (102) of the rod (101) and wherein the second end snaps into the second groove (102) of the rod (101).The steer-by-wire steering system of claim 1, wherein the rod (101) is formed of steel.The steer-by-wire steering system of claim 1, wherein a first end of the sleeve (107) defines a sleeve groove and a window (117), wherein a retaining clip (110) passes through the sleeve groove and the window (117) of the sleeve (107) to engage at least one slot in the wear plates (109).

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