Abstract:
In one exemplary embodiment of the present invention, a torque transmitting assembly is provided. The assembly includes a motor having a motor shaft rotatable about a first axis, a component having a housing and a component shaft, the component shaft translatable along a second axis, and a belt frictionally coupled to the motor shaft and the component shaft to transfer a force therebetween. The first axis is oriented at an angle with respect to the second axis.

Description:
FIELD OF THE INVENTION 
       [0001]    The following description relates to a torque transmitting assembly, and in particular, to a rack electric power steering system. 
       BACKGROUND 
       [0002]    Electrically actuated or electrically assisted steering systems, including rotary-to-linear mechanisms such as ball-screw assemblies, provide power assist to a steering assembly. For example, a nut may surround and threadably engage a screw portion of a rack such that rotation of the nut by a motor imparts axially directed force to the rack, thereby assisting the driver in steering the vehicle. A belt assembled onto the motor and nut transfers rotary motion from the motor shaft to the nut. However, tensioning of the belt during installation may cause the motor shaft to bend with respect to the rack axis, which may cause uneven belt tension resulting in accelerated belt wear. 
         [0003]    Some known systems use larger, stiffer components at added cost to avoid unacceptable bending of the motor shaft. However, such systems may be cost prohibitive and require too much space for space-limited designs. Accordingly, it is desirable to provide an assisted steering system which reduces or eliminates belt wear and uneven belt tension without increased system size and cost. 
       SUMMARY OF THE INVENTION 
       [0004]    In one exemplary embodiment of the present invention, a torque transmitting assembly is provided. The assembly includes a motor having a motor shaft rotatable about a first axis, a component having a housing and a component shaft, the component shaft translatable along a second axis, and a belt frictionally coupled to the motor shaft and the component shaft to transfer a force therebetween. The first axis is oriented at an angle with respect to the second axis. 
         [0005]    In another exemplary embodiment of the present invention, a steering system is provided. The steering system includes a motor having a shaft rotatable about a first axis, a rack housing having a rack therein translatable along a second axis, and a belt frictionally coupled to the shaft and the rack to transfer a force therebetween. The first axis is oriented at an angle with respect to the second axis. 
         [0006]    In yet another exemplary embodiment of the present invention, a method of assembling a steering system is provided. The method includes providing a motor having a shaft rotatable about a first axis, providing a rack housing having a rack therein translatable along a second axis, and providing a belt to frictionally couple the shaft and the rack to transfer a force therebetween. The method further includes determining an angle that the shaft will deflect when the belt is tensioned to a predetermined tension, and orienting the motor such that the first axis is oriented with respect to the second axis at the determined angle. 
         [0007]    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 
         [0008]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the 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: 
           [0009]      FIG. 1  is a schematic illustration of a steering system according to an exemplary embodiment of the present invention; 
           [0010]      FIG. 2  is a schematic illustration of a portion of the steering system shown in  FIGS. 1 ; and 
           [0011]      FIG. 3  is a cross-sectional view of an exemplary electric power steering system that may be used with the steering system shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same,  FIGS. 1 and 2  illustrate an electric power steering (EPS) system  10  for use in a vehicle (not shown). Steering system  10  allows the operator of the vehicle to control the direction of the vehicle through the manipulation of a steering column  12 , which is mechanically connected to road wheels  14  (only one shown). 
         [0013]    Steering column  12  includes an upper steering shaft  16  and a lower steering shaft  18 . A hand wheel  20  is disposed at upper steering shaft  16  and is positioned so that the operator can apply a rotational force to steering column  12 . A torque sensor  22  and a position sensor  24  are located at upper steering column shaft  16  to detect the turning angle of hand wheel  20 . In the exemplary embodiment, torque sensor  22  and position sensor  24  are in electronic communication with a controller  26 . A column universal joint  28  couples upper steering column shaft  16  to lower steering column shaft  18 , which is secured at one end to column universal joint  28 , and to a steering gear assembly  30  at the other end. Gear assembly  30  includes an elongate rack  32  having longitudinal axis ‘A’ along which it linearly translates. The opposed axial ends of rack  32  are coupled to the vehicle&#39;s road wheels  14  through steering linkage that includes tie rods  34  (only one shown) each secured to rack  32  at one end, and to one of a pair of steering knuckles  36  (only one shown) at the other end. 
         [0014]    Steering gear assembly  30  further includes a pinion gear  38  in mechanical connection with rack  32 . Pinion gear  38  is positioned to make contact with a matching toothed portion  40  of rack  32  that extends along a segment of rack  32 . Pinion gear  38  has teeth that are engaged with teeth of matching toothed portion  40 . Pinion gear  38 , in combination with matching toothed portion  40 , form a rack and pinion gear set  42 . Rack  32  also includes an axially extending segment along which is provided generally cylindrical ball screw portion  44  centered about axis ‘A’. Toothed portion  40  and ball screw portion  44  are integrated into rack  32 , and ball screw  44  is in mechanical communication with a reversible servomotor  46 . Ball screw  44  and motor  46  may be located axially along rack  32  on either first side  200  or opposite second side  202  of toothed portion  40 . In addition, motor  46  may be located radially either on top side  204  or bottom side  206  of rack  32 . Actuation of motor  46  is controlled by controller  26 . 
         [0015]    When the vehicle operator turns hand wheel  20 , a rotational force is applied to steering column  12  and pinion gear  38  is accordingly rotated. The movement of pinion gear  38  causes axial movement of rack  32  in the direction of arrows  52 , which in turn manipulates tie rods  34  and knuckles  36  in order to reposition road wheels  14 . Accordingly, when hand wheel  20  is turned, pinion gear  38  and matching tooth portion  40  convert rotary motion of hand wheel  20  into linear motion of rack  32 . In order to assist the operator-applied force to steering system  10 , motor  46  is energized and provides power assist to the movement of rack  32  through ball screw  44 , thereby aiding in the steering of the vehicle. 
         [0016]    Referring to  FIG. 3 , an exemplary embodiment of steering system  10  is illustrated. Motor  46  is in operable communication with ball screw  44  through a ball nut assembly  48  rotatably disposed about ball screw  44 . A shaft  50  having an axis ‘B’ extends from motor  46  and is rotated in one of two opposite angular directions when motor  46  is energized. A driving pulley  54  is rotatably fixed to shaft  50 . A flexible, endless drive belt  58  is wrapped around driving pulley  54  such that a belt inner surface  60  is in frictional contact with pulley  54 . Belt  58  also wraps around a driven pulley  62  defining the outer circumference of ball nut assembly  48  such that belt inner surface  60  is in frictional contact with driven pulley  62 . Driven pulley  62  is radially centered about axis ‘A’ and includes the radially outer surface of a generally cylindrical ball nut  66 . When motor  46  is actuated, movement of belt  58  linking pulleys  54  and  62  causes ball nut  66  to rotate about axis ‘A’ and ball screw  44  to translate rack  32 . 
         [0017]    Typically, shaft  50  is oriented in parallel with rack  32  (i.e., rack axis ‘A’ and shaft axis ‘B’ are parallel). In some situations, belt  58  is tensioned during installation, for example, to prevent belt skip (i.e., when a belt jumps a tooth on the pulley). Such tensioning may skew or slant motor shaft  50  and/or rack  32  (and their associated components) toward each other, thereby causing shaft  50  and/or rack  32  to slant and such that the shaft and/or rack axis is no longer parallel to the original shaft and/or rack axis before the tensioning. Due to such slanting, tension at a first edge  70  of belt  58  will be unequal to the tension at a second edge  72  of belt  58 , which may cause accelerated belt wear. 
         [0018]    However, in the exemplary embodiment shown in  FIG. 3 , a housing  74  of motor  46  is oriented angularly with respect to a rack housing  76  such that motor shaft axis ‘B’ is oriented at an angle ‘α’ with respect to rack axis ‘A’. When belt  58  is subsequently installed over pulleys  54 ,  62  and tensioned as described above, the cantilevered end  51  of motor shaft  50  is deflected, bent, or slanted bend (elastically or plastically) into parallel alignment with rack  32 . As such, the tension at first and second belt edges  70 ,  72  is equal or substantially equal, thereby facilitating reducing or preventing accelerated belt wear. In addition, tilted motor  46  may account for any angle deviation due to bearing lash, manufacturing tolerance in the bearing bore, and dimensional stackup. 
         [0019]    In the exemplary embodiment, angle ‘α’ is between an angle greater 0° and 2°. In another embodiment, angle ‘α’ is between an angle greater than approximately 0° and approximately 2°. In other embodiments, angle ‘α’ is between an angle greater than 0° and 1°, between an angle greater than approximately 0° and approximately 1°, between ¼° and ¾°, or between approximately ¼° and approximately ¾°. However, angle ‘α’ may be variable depending on the tension force, and motor shaft axis ‘B’ may be oriented at any suitable angle with respect to rack axis ‘A’ that enables system  10  to function as described herein when belt  58  is tensioned. 
         [0020]    As shown in  FIG. 3 , rack housing  76  includes a motor receiving surface  78 , and motor housing  74  includes a front surface  80  configured to position against motor receiving surface  78 . In the exemplary embodiment, motor receiving surface  78  is oriented at an angle ‘α’ with respect to an axis ‘C’ that is orthogonal to rack axis ‘A’ or is substantially orthogonal to rack axis ‘A’, thereby causing motor shaft axis ‘B’ to be oriented at angle ‘α’ with respect to rack axis ‘A’. Alternatively, motor housing front surface  80  may be oriented at angle ‘α’ with respect to axis ‘C’, or an insert (not shown) may be positioned between motor receiving surface  78  and front surface  80  to orient axis B′ at angle ‘α’ with respect to axis ‘A’. 
         [0021]    In the exemplary embodiment, angle ‘α’ may be determined by first determining the angle at which motor shaft  50  and/or rack  32  will be deflected or slanted due to a predetermined tensioning of belt  58  when motor shaft  50  and rack  32  are oriented in parallel. For example, the distance of driving pulley  54  from the nearest motor bearing  82  and the width of driving pulley  54  may facilitate determining where a tension force is applied in relation to its support when belt  58  is installed. The magnitude and location of the force may then facilitate determining tilt angle ‘α’ of motor shaft  50  when that force is applied. Motor receiving surface  78  and/or front surface  80  may then be formed (e.g., machined) to orient shaft axis ‘B’ at angle ‘α’ with respect to rack axis ‘A’ to fully or substantially take-up the angle of deflection caused by the tensioning. As such, after tensioning, belt  58  rotates about a shaft axis ‘B’ that is parallel or substantially parallel to rack axis ‘A’. 
         [0022]    A method of assembling a system  10  includes providing rack housing  76  having rack  32  extending along rack axis ‘A’, providing motor  46  having shaft  50  extending along shaft axis ‘B’, and coupling motor  46  to rack housing  76  such that shaft axis ‘B’ is not parallel to rack axis ‘A’. The method may further include forming at least one of motor receiving surface  78  and front surface  80  to be oriented at an angle ‘α’ with respect to axis ‘C’ such that shaft axis ‘B’ is oriented at angle ‘α’ with respect to rack axis ‘A’. 
         [0023]    Described herein are systems and methods providing an EPS motor tilted or angled with respect to a rack axis to facilitate even distribution of tension across a belt transferring torque between the motor and a rack. The angle of tilt may be varied depending on the belt tension required to prevent belt skip or other conditions when the belt is installed. The motor mounting face may then be tilted by the same angle that the motor shaft bends under load, but in the opposite direction. When the load is applied, the motor shaft bends to be parallel or substantially parallel to the rack axis. As such, tension is evenly distributed across the width of the belt, thereby reducing belt wear. 
         [0024]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, 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 is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.