Abstract:
A mechanical clutch coupling back-up system for use with a steer-by-wire arrangement in a vehicle is disclosed. The system includes an input shaft, an output shaft, a clutch assembly, and an actuator assembly. In the event of vehicle power failure, the actuator assembly permits the clutch assembly to provide a mechanical coupling of the input shaft and the output shaft thereby allowing the operator to drive the vehicle without the steer-by-wire system. The actuator assembly includes an actuator and the clutch assembly includes a movable clutch collar which is movable between a disengaged position when vehicle power is present and an engaged position when vehicle power is absent.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to a back-up for electric steering systems. More particularly, the present invention relates to a clutch mechanism to be used as a back-up arrangement for a steer-by-wire system in a vehicle.  
         [0002]     Traditional vehicle steering systems include a steering wheel, a steering column, and an axle with steerable wheels which utilize a rack-and-pinion steering rack arrangement or a steering gear box. According to known arrangements, rotational motion introduced by the driver at the steering wheel is mechanically transmitted directly to the steering mechanism via the steering column. In the early days of vehicles the steering column was little more than an elongated steering shaft with a steering wheel attached at one end and a steering arm attached at the other end for operative engagement with the steerable wheels. Developments in automotive technology enabled designers to modify the early single, straight shaft into an array of linked shafts, thus allowing flexibility in packaging and steering column placement. Such mechanical steering mechanisms have generally been power assisted by hydraulic or electrical assist units.  
         [0003]     Regardless of the design, traditional mechanical steering arrangements suffer from limitations in design flexibility because of the necessity of a direct mechanical linkage. To overcome limitations presented by known mechanical steering arrangements, steer-by-wire systems have been developed which eliminate the direct mechanical connection between the steering wheel and the steering mechanism by replacing the mechanical shaft connections with electrical or wire connections. In addition to offering increased design flexibility, the steer-by-wire system offers weight reduction by eliminating the large mechanical linkage conventionally associated with known mechanical steering systems. This savings in weight produces a lighter, more fuel-efficient vehicle.  
         [0004]     The steer-by-wire system uses electrical actuators connected to the steerable wheels of the vehicle and a control unit to turn the wheels and to control the angle to which the wheels are turned. Electronic components and electronic systems are also added to the steer-by-wire system to enable communication between steering components.  
         [0005]     While removal of the direct mechanical link traditionally associated with mechanical steering systems creates new design flexibility, this absence of such a link presents safety concerns in the event of the failure of the power system of the vehicle. In order to overcome this concern, a mechanical back-up system is required that senses electrical failure and responds in such a way that a mechanical linkage is created to thereby enable the driver to maintain some level of steering control over the vehicle even in the event of electrical failure. There have been proposals to provide a mechanical back-up for the steer-by-wire system yet there remains opportunity for improvement of known systems.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides a mechanical back-up arrangement for use with a steer-by-wire system that provides improvements over known systems. The arrangement of the present invention generally includes, in conjunction with a steer-by-wire system, a steering column assembly that includes an input shaft and an output shaft. The input shaft is connected to the vehicle steering wheel and is thus rotatable by a vehicle operator. The output shaft is mechanically coupled to the steerable axle of the vehicle. The arrangement also includes a clutch assembly that is movable between a disengaged mode when the steer-by-wire system is active or is powered and a disengaged mode when the steer-by-wire system is inactive because of the loss of vehicle power. An actuator assembly is provided that responds to the power status of the vehicle and moves the clutch assembly, via a linkage, accordingly. If power is directed to the actuator assembly, the clutch assembly is maintained in its disengaged mode, whereby no mechanical linkage exists between the input shaft and the output shaft and the driver may rely on the vehicle&#39;s steer-by-wire system to control vehicle direction. If there is a general power failure in the vehicle, the actuator releases the clutch assembly from its disengaged position and the input shaft and the output shaft are mechanically linked.  
         [0007]     The clutch assembly of the present invention includes a clutch collar that is axially movable between disengaged and engaged positions. The movement of the clutch collar is dictated by the actuator assembly, which responds to the presence or absence of vehicle electrical power. A biasing element is provided in conjunction with the clutch assembly and acts upon the clutch collar to move it into its engaged position in the event that vehicle power loss releases the actuator assembly.  
         [0008]     The arrangement of the present invention offers a positive mechanical back-up for a steer-by-wire system that is efficient, is of relatively low weight, and demonstrates relatively low maintenance. The back-up arrangement of the present invention is also relatively compact, thus providing packaging advantages over known arrangements.  
         [0009]     Further scope of the applicability of the present invention will become apparent from the following detailed description, claims and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given for illustrative purposes only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will become more fully understood from the detailed description given here below, in the appended claims, and in the accompanying drawings in which:  
         [0011]      FIG. 1  is a perspective view of a steer-by-wire steering column and steering gear arrangement and including a back-up arrangement according to the present invention;  
         [0012]      FIG. 2  is a perspective view of a first embodiment of the clutch assembly for a steer-by-wire system of the present invention illustrating the clutch coupling and actuator assembly;  
         [0013]      FIG. 3  is a side elevational and partially sectional view of the first embodiment of the present invention shown in  FIG. 2  with the clutch assembly in its disengaged position;  
         [0014]      FIG. 4  is a side elevational view of the first embodiment of the present invention similar to the view shown in  FIG. 3  but without the clutch lever and actuator;  
         [0015]      FIG. 5  is a view of the first embodiment of the present invention similar to that of  FIG. 3  but showing the clutch assembly in its engaged position;  
         [0016]      FIG. 6  is a sectional view of a second embodiment of the clutch assembly for a steer-by-wire system of the present invention illustrating the clutch assembly in its disengaged position;  
         [0017]      FIG. 7  is a view of the second embodiment of the present invention similar to that of  FIG. 6  but showing the clutch assembly in its engaged position;  
         [0018]      FIG. 8  is a partially sectional view of a third embodiment of the clutch assembly for a steer-by-wire system of the present invention illustrating the clutch assembly in its disengaged position;  
         [0019]      FIG. 9  is an exploded view of the clutch components of the third embodiment of the present invention;  
         [0020]      FIG. 10  is a view of the third embodiment of the present invention similar to that of  FIG. 8  but showing the clutch assembly in its engaged position;  
         [0021]      FIG. 11  is an end view of the clutch assembly of the third embodiment of the present invention shown in  FIGS. 8 through 10  taken along lines  11 - 11  of  FIG. 8 ;  
         [0022]      FIG. 12  is a side elevational, partially shadowed illustration of a fourth embodiment of the present invention illustrating the clutch assembly in its disengaged position; and  
         [0023]      FIG. 13  is a view of the fourth embodiment of the present invention similar to that of  FIG. 12  but showing the clutch assembly in its engaged position.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     The drawings disclose the preferred embodiment of the present invention. While the configurations according to the illustrated embodiment are preferred, it is envisioned that alternate configurations of the present invention may be adopted without deviating from the invention as portrayed. The preferred embodiments are discussed hereafter.  
         [0025]     In general, the present invention relates to back-up arrangements for steer-by-wire systems for vehicles. Four embodiments of the present invention are contemplated, as set forth below. While each of these embodiments offers certain distinct design features, each of the embodiments is nevertheless consistent with the overall teaching of the present invention which is to offer improvements over the prior art in terms of reduced weight, low production and maintenance costs, and high reliability. In addition, each of the embodiments provides an efficient system that is characterized in having significant mechanical advantage which results in the need for only upon slight movement of the clutching assembly to accomplish engagement of the mechanical steering back-up through clutch coupling.  
         [0026]     With reference to  FIG. 1 , this view illustrates a perspective view of the steer-by-wire steering column and steering gear assembly according to the present invention, generally illustrated as  10 . The assembly  10  includes a clutch coupling  12 , an associated steering wheel  14 , a mechanical steering linkage and steering gear assembly  16 , and a road wheel steering assembly  18 . An electronic control unit  20  is provided to turn the wheels in response to the steer-by-wheel system.  
         [0027]     A sensor  22  is provided in electrical contact with the clutch coupling system  12  and in connection with a power source  24  comprised of the power supply and the alternator. The sensor  22  responds to the presence of electrical power in the vehicle system and transmits this information to the clutch coupling system  12  which maintains the clutch in a disengaged position so long as power is present. If no power is directed to the sensor  22  then no power can be transmitted to the clutch coupling system  12  and a mechanical engagement occurs as a back-up to the steer-by-wire system. It is to be noted that the arrangement presented in  FIG. 1  is only exemplary and that other connective mechanical and electronic arrangements may be made.  
         [0028]      FIGS. 2 through 13  illustrate various approaches to resolution of the problems associated with known clutch back-up arrangements for steer-by-wire systems. There are four embodiments presented and discussed herein. In brief,  FIGS. 2 through 5  illustrate a first embodiment of the present invention;  FIGS. 6 and 7  illustrate a second embodiment of the present invention;  FIGS. 8 through 11  illustrate a third embodiment of the present invention; and  FIGS. 12 and 13  illustrate a fourth embodiment of the present invention. While having some different features, the four embodiments shown and discussed all illustrate an improved, light-weight, well-packaged, and readily manufactured arrangement that includes an actuator (in the form of a solenoid or a hydraulically- or pneumatically-operated piston) which is ordinarily engaged when the vehicle power system is operating and a mechanical clutch that is engaged when the power system fails.  
       First Preferred Embodiment  
       [0029]     With respect to the first embodiment shown in  FIGS. 2 through 5 , a clutch arrangement, generally illustrated as  100 , is shown. The arrangement  100  includes an input shaft  102  connected with a steering wheel (not shown), an output shaft  104  mechanically linked to the vehicle&#39;s steering column shaft (not shown), an actuator  106 , and a clutch assembly  108 . Both the input shaft  102  and the output shaft  104  are axially fixed.  
         [0030]     The input shaft  102  is mechanically and directly connected with the steering wheel in a known manner. Rotational movement from the steering wheel directly and at all times effects an equal degree of rotational movement of the input shaft  102 . As illustrated in  FIGS. 3, 4  and  5 , the input shaft  102  includes a splined portion  110 . Formed on the splined portion  110  is a pair of sets of external spaced-apart splines  112 ,  114 . A gap  116  exists between the sets of external splines  112 ,  114 .  
         [0031]     The output shaft  104  is mechanically and directly connected with the vehicle&#39;s steering column shaft. The output shaft  104  includes a splined portion  118 . Formed on the splined portion  118  is a pair of sets of spaced-apart external splines  120 ,  122 . A gap  124  exists between the sets of splines  120 ,  122 . An engagement biasing element or spring  125  is provided approximately about the set of splines  122  and provides a biasing force as will be described below.  
         [0032]     The clutch assembly  108  consists of a tubular clutch collar  126  and a clutch lever  128 . The tubular clutch collar  126  has a long axis which is axially aligned with the long axes of the input shaft  102  and the output shaft  104 . The clutch collar  126  includes a pair of spaced-apart internal splines  130 ,  132 . The spacing of the sets of internal splines  130 ,  132  is roughly equal to the spacing between the sets of external splines  112 ,  120 . The clutch lever  128  includes a clutch lever body  134  having a pivot end  136  and an actuator end  138 . The pivot end  136  is pivotably attachable to a fixed point on the vehicle. The actuator end  138  is operably attached to the actuator  106  by way of a linkage  140 . The actuator  106  includes a return spring  107 .  
         [0033]     As shown in  FIG. 4 , a peripheral groove  141  is defined in the clutch collar  126 . A ring  142  is rotatably fitted in the peripheral groove  141 . The clutch lever  128  is operably attached to the ring  142  by a fastener  143  which is shown in  FIG. 2 . This fastening arrangement allows the clutch collar  126  to rotate with the input shaft  102  and the output shaft  104  when the clutch is engaged as described below while still supporting the clutch lever  128 .  
         [0034]     As previously noted, the actuator  106  may be a solenoid or may be a hydraulically- or pneumatically-operated piston. The preferred embodiment, which is not intended to be a limiting embodiment, is that of a solenoid, and the present invention will be described accordingly. The hydraulically- or pneumatically-operated piston configuration, while not described in detail, may be designed as needed consistent with the objects of the present invention.  
         [0035]      FIG. 3  illustrates the clutch assembly  108  in its disengaged position. The actuator  106  is in the activated mode, that is, if a solenoid, vehicle power is present and is working to activate the solenoid in a known manner. In its activated mode, the linkage  140  is in its compressed position, thus positioning the clutch collar  126  approximately mid-way over the splined portions  110 ,  118  and the sets of internal splines  130 ,  132 . In this position the clutch assembly  108  is in its neutral or resting position such that the set of internal splines  130  is generally disposed in the gap  116  formed on the splined portion  110  of the input shaft  102  and the set of internal splines  132  is generally disposed in the gap  124  formed on the splined portion  118  of the output shaft  104 . Thus positioned, the input shaft  102  is allowed to freely rotate independent of the output shaft  104  and the vehicle may be operated by its steer-by-wire system.  
         [0036]     In the event that the there is a power loss in the vehicle or if the actuator  106  is otherwise deactivated, force is removed from the linkage  104  and the biasing force of the spring  125  acts on the clutch assembly  108  by moving the clutch collar  126  to its engaged position illustrated in  FIG. 5 . In this position the set of internal splines  130  is moved into engagement with the set of external splines  112  and the set of internal splines  132  is simultaneously moved into engagement with the set of set of external splines  120 . Once the actuator  106  is reactivated the clutch assembly  108  is returned to its disengaged position as shown in  FIG. 3 .  
       Second Preferred Embodiment  
       [0037]      FIGS. 6 and 7  illustrate a second embodiment of the clutch arrangement of the present invention, generally illustrated as  200 . The arrangement  200  includes an input assembly  202  connected with a steering wheel  204 , an output shaft  206  mechanically linked to the vehicle&#39;s steering column shaft (not shown), an actuator  208 , and a clutch assembly  210 . The input assembly  202  and the output shaft  206  are not axially movable with respect to each other.  
         [0038]     The input assembly  202  includes a shaft  210  that is mechanically and directly connected with the steering wheel  204 . Rotational movement from the steering wheel  204  directly and at all times effects an equal degree of rotational movement of the input assembly  202 . The input assembly  202  further includes a clutch coupler  212  having a closed end  214  fixed to the shaft  210  and an open end  216 . Formed within the open end  216  is a set of internal splines  218 . An engagement biasing element or spring  219  within the clutch coupler  212  and provides a biasing force as will be described below.  
         [0039]     The output shaft  206  is mechanically and directly connected with the vehicle&#39;s steering column shaft The output shaft  206  includes a supporting end  220  and further includes a set of external splines  222 . A bearing element  224  is mounted on the supporting end  220 . The bearing element  224  may be a roller bearing.  
         [0040]     The clutch assembly  210  consists of a tubular clutch collar  226 . The tubular clutch collar  226  has a long axis which is axially aligned with the long axes of the input assembly  202  and the output shaft  206 . The clutch collar  226  includes a set of external splines  228  and a set of internal splines  230 . A bearing surface  232  is formed on the inner wall of one end of the tubular clutch collar  226 . The space between the set of internal splines  218  and the set of external splines  222  is substantially equivalent to the space between the external splines  228  and the internal splines  230 . The set of external splines  228  are in constant engagement with the set of internal splines  218  of the clutch coupler  212  regardless of whether the clutch assembly  210  is engaged or disengaged as will be discussed below.  
         [0041]     The actuator  208  of the second embodiment illustrated in  FIGS. 6 and 7  is of the solenoid type and includes a pair of actuators  234 ,  234 ′ and an annular ring  236 . A pair of engagement pins  238 ,  238 ′ extend from the top side and bottom side of the tubular clutch collar  226 . The engagement pins  238 ,  238 ′ engage an internal annular slot  240  formed within the annular ring  236 . The configuration of the internal annular slot  240  permit the engagement pins  238 ,  238 ′ to move readily therein. Because the clutch collar  226  is in continuous engagement with the clutch coupler  212  it exhibits the same rotational movement as the steering wheel  204 . The free movement of the engagement pins  238 ,  238 ′ within the internal annular slot  240  enables the free rotation of the collar  226  relative to the annular ring  236 .  
         [0042]     The solenoids  234 ,  234 ′ are linked respectively to the annular ring  236  by a pair of linkages  242 ,  242 ′.  
         [0043]      FIG. 6  illustrates the clutch assembly  210  in its disengaged position. The actuators  234 ,  234  (which, according to the preferred arrangement, are solenoids, although a piston arrangement may be usable as well) are shown in their activated mode in which vehicle power is present. In the activated mode, the linkages  242 ,  242 ′ are drawn into the actuators  234 ,  234 ′ respectively, thus drawing the collar  226  toward and substantially into the clutch coupler  212 . The set of internal splines  218  of the clutch coupler  212  are in operative engagement with the set of external splines  228  of the clutch collar  226 . However, the set of internal splines  230  of the clutch collar  226  are out of engagement with the set of external splines  222  of the output shaft  206 . The bearing element  224  is in continuous engagement with the bearing surface  232  of the clutch coupler  212  and provides for constant axial alignment of the output shaft  206  relative to the clutch collar  226 . In this position the clutch assembly  210  is in its neutral or resting position. Thus positioned, the input assembly  202  is allowed to freely rotate independent of the output shaft  206  and the vehicle may be readily operated by its steer-by-wire system.  
         [0044]     Should the vehicle&#39;s power system fail or if the actuators  234 ,  234 ′ are otherwise deactivated, force is removed from the linkages  242 ,  242 ′ and the biasing force of the spring  219  acts on the clutch assembly  210  by forcing the clutch collar  226  to its engaged position as illustrated in  FIG. 7 . In this position the set of internal splines  230  of the clutch collar  226  is moved into engagement with the set of external splines  222  formed on the output shaft  206  and a continuous mechanical connection between the input assembly  202  and the output shaft  206  and the vehicle may be readily operated through mechanical steering. Once the actuators  234 ,  234 ′ are reactivated the clutch assembly  210  is returned to its disengaged position as shown in  FIG. 6 .  
       Third Preferred Embodiment  
       [0045]     The third embodiment of the clutch assembly for use as a back-up system in a steer-by-wire steering system according to the present invention is illustrated in  FIGS. 8 through 11 . With respect to the third embodiment shown in these figures, a clutch arrangement, generally shown as  300 , is shown. The arrangement  300  includes an input shaft  302  connected with a steering wheel (not shown), an output shaft  304  mechanically linked to the vehicle&#39;s steering column shaft (not shown), an actuator assembly  306 , and a clutch assembly  308 . Both the input shaft  302  and the output shaft  304  are axially fixed.  
         [0046]     The input shaft  302  is mechanically and directly connected with the steering wheel in a known manner. Rotational movement of the steering wheel directly and at all times effects an equal degree of rotational movement of the input shaft  302 . As illustrated in  FIGS. 8 through 10 , the input shaft  302  includes a shaft portion  310  that is connected to the steering wheel, a spring support plate  312 , and a tubular output shaft receptacle  314  which is formed so as to operatively receive a portion of the output shaft  304 . The output shaft receptacle  314  includes a snap-ring groove  316  formed in its distal end and at least a pair of bearing slots  318  defined through the output shaft receptacle  314 . The bearing slots  318  are formed between the snap-ring groove  316  and the spring support plate  312 .  
         [0047]     The output shaft  304  is mechanically and directly connected with the vehicle&#39;s steering column shaft. The output shaft  304  includes a steering column shaft end  320  and a bearing receiving end  322 . The bearing receiving end  322  includes a series of relatively wide and cupped splines  324  formed thereon.  
         [0048]     The clutch assembly  306  includes a clutch collar  326  that includes an annular actuator stop plate  328 , an annular body  330 , and an annular stop ring  332 . The annular stop ring  332  includes a bearing lip  334 . The annular body  330  and the annular stop ring  332  could be made from powder metal as two separate pieces which are then fastened by means such as brazing.  
         [0049]     The internal juncture between the annular body  330  and the annular stop ring  332 , generally illustrated as bearing housing  336 , is defined by a conical wall  338  formed within the annular body  330 , the bearing lip  334 , and an intermediate wall  340  generally formed between the conical wall  338  and the bearing lip  334 . An annular bearing engagement wall  341  is formed between the conical wall  338  and the actuator stop plate  328 . The clutch collar  326  is capable of axial movement on the output shaft receptacle  314  of the input shaft  302 . A snap ring  342  is fitted in a known manner in the snap-ring groove  316  of the input shaft  302  to limit axial movement of the clutch collar  326  on the output shaft receptacle  314 . An engagement biasing element or spring  344  is provided between the spring support plate  312  of the input shaft  302  and the annular actuator stop plate  328  of the clutch assembly  306 . The spring  344  provides a biasing force as will be described below. Ball bearings  346  are movably disposed within the bearing region  336 . While it is shown that there are two ball bearings  346  situated within the bearing housing  336  it is to be understood that a greater number of bearing may be disposed therein.  
         [0050]     As previously noted with respect to the embodiments illustrated in  FIGS. 2 through 7 , the actuator  306  may be a solenoid or may be a hydraulically- or pneumatically-operated piston. The preferred and illustrated embodiment, which is not intended to be a limiting embodiment, is that of a solenoid, and the present invention will be described accordingly. The hydraulically- or pneumatically-operated piston configuration, while not described in detail, may be designed as needed consistent with the objects of the present invention as with the previously-mentioned embodiments of the present invention.  
         [0051]     The actuator  306  includes an annular electro-magnetic coil  348 . The electromagnetic coil  348 , when activated, attracts the annular actuator stop plate  328  of the clutch collar  326 . The operations of activation and deactivation and the resulting and respective mechanical clutch disengagement and engagement will now be described with respect to  FIGS. 8, 10  and  11 .  
         [0052]      FIG. 8  illustrates the clutch assembly  308  in its disengaged position. The actuator  306  is in the activated mode, that is, if a solenoid, vehicle power is present and is working to activate the solenoid in a known manner. In its activated mode, and according to the illustrated configuration, the electromagnetic coil  348  has attracted the annular actuator stop plate  328  of the clutch collar  326  such that the stop plate  328  effectively abuts the annular electro-magnetic coil  348 . In this disengaged position, the ball bearings  346  are moved well into the bearing housing  336  and are well spaced-apart from the cupped splines  324  of the bearing receiving end  322  of the output shaft  304 . This situation is clearly shown in  FIG. 11  which is a sectional view of the clutch arrangement  300  taken along lines  11 - 11  of  FIG. 8 . Travel of the ball bearings  346  within the bearing housing  336  is limited by the conical wall  338 , the intermediate wall  340 , and the bearing lip  334 . With the ball bearings  346  thus disengaged from the cupped splines  324 , the input shaft  302  may be freely rotated independent of the output shaft  304  and the vehicle may be operated by its steer-by-wire system.  
         [0053]     In the event that there is a power loss in the vehicle or if the actuator  306  is otherwise deactivated, force is removed from the actuator  306  and the biasing force of the spring  344  acts on the clutch assembly  308  by moving the clutch collar  326  to its engaged position shown in  FIG. 10 . As the clutch collar  326  is moved to its engagement position, the ball bearings  346  are forced to ramp inward toward the cupped splines  324  of the output shaft  304 , into the bearing slots  318 , and are effectively locked into position against the cupped splines  324  by the bearing engagement wall  341  as shown in  FIG. 10  and in shadow lines in  FIG. 11 . Thus engaged, rotation of the input shaft  302  effects simultaneous mechanical rotation of the output shaft  304 . Once the actuator  306  is reactivated the clutch assembly  308  is returned to its disengaged position as shown in  FIG. 8 .  
       Fourth Preferred Embodiment  
       [0054]     The fourth embodiment of the clutch assembly for use as a back-up system in a steer-by-wire steering system according to the present invention is illustrated in  FIGS. 12 and 13  in which a clutch arrangement, generally illustrated as  400 , is shown. The arrangement  400  includes an input shaft  402  connected with a steering wheel (not shown), an output shaft  404  mechanically linked to the vehicle&#39;s steering column (not shown), an actuator  406 , and a clutch assembly  408 . Both the input shaft  402  and the output shaft  404  are axially fixed.  
         [0055]     The input shaft  402  is mechanically and directly connected with the steering wheel in a known manner. Rotational movement from the steering wheel directly and at all times effects an equal degree of rotational movement of the input shaft  402 . The input shaft  402  is rotationally supported by a support member  410  which is provided to attach the clutch arrangement  400  to the vehicle. As illustrated in shadow lines in  FIG. 12  and in shadow lines and bold lines in  FIG. 13 , the input shaft  402  includes a set of external splines  412 .  
         [0056]     The output shaft  404  is mechanically and directly connected with the vehicle&#39;s steering column shaft. The output shaft  404  is rotationally supported by a support member  414  which, as with the support member  410 , is provided to attach the clutch arrangement  400  to the vehicle. A bearing  416  is shown in shadow lines and provides a rotational arrangement between the support member  414  and the output shaft  404 . The combination of the support member  410  and the support member  414  provide axial alignment to the input shaft  402  and the output shaft  404 . The output shaft  404  further includes a coupling end  418  and a driving end  420 . The coupling end  418  is an element of the clutch assembly  408  and includes a face  422  which includes a series of spaced-apart teeth  424  formed thereon. The driving end  420  is mechanically connected with the steering shaft of the vehicle.  
         [0057]     In addition to the coupling end  418  of the output shaft  404 , the clutch assembly  408  includes a clutch collar  426 . The clutch collar  426  includes a driven end  428  and a coupling end  430 . A set of internal splines  432 , shown in shadow lines in  FIGS. 12 and 13 , is formed internally in the driven end  428  of the clutch collar  426 . The set of internal splines  428  of the clutch collar  426  are formed to mate with the set of external splines  412  of the input shaft  402  such that the clutch collar  426  is able to slide axially substantially on the input shaft  402 .  
         [0058]     The coupling end  430  of the clutch collar  428  further includes a face  434 . The face  434  includes a series of spaced-apart teeth  436  formed thereon. The teeth  436  are positioned so as to be selectively matable with the teeth  424  of the face  422  of the output shaft  404 .  
         [0059]     The clutch assembly  408  further includes a clutch lever  438 . The clutch lever  438  includes a clutch lever body  440  having a pivot end  442  and an actuator end  444 . The pivot end  442  is attachable to the support member  410  or may be attached to another fixed point on the vehicle. The actuator end  444  is operably attached to the actuator  406  by way of a linkage  446 .  
         [0060]     As shown in shadow lines, a peripheral groove  448  is defined in the clutch collar  426 . A ring  450 , also shown in shadow lines, is fitted in the peripheral groove  448 . The clutch lever  438  is operably attached to the ring  450  by a fastener  452 . This fastening arrangement allows the clutch collar  426  to rotate with the input shaft  402 .  
         [0061]     As previously noted, the actuator  406  may be a solenoid or may be a hydraulically- or pneumatically-operated piston. The preferred embodiment, which is not intended to be a limiting embodiment, is that of a solenoid, and the present invention will be described accordingly.  
         [0062]      FIG. 12  illustrates the clutch assembly  408  in its disengaged position. The actuator  406  is in the activated mode, that is, if a solenoid, vehicle power is present and is working to activate the solenoid in a known manner. In its activated mode, the linkage  446  is in its retracted position, thus positioning the clutch collar  426  in its disengaged position or substantially in abutment with the support member  410 . In this position the clutch assembly  408  is in its neutral or teeth  436  of the clutch collar  426  are spaced apart from and are thus disengaged from the teeth  424  of the output shaft  404 . Thus situated, the input shaft  402  is allowed to freely rotate independent of the output shaft  404  and the vehicle may be operated by its steer-by-wire system.  
         [0063]     In the event that the there is a power loss in the vehicle or if the actuator  406  is otherwise deactivated, force is removed from the linkage  446  and the biasing force of a spring  447  fitted to the input shaft  402  and positioned within a bore defined within the clutch collar  426  acts on the clutch assembly  408  by moving the clutch collar  428  to its engaged position illustrated in  FIG. 13 . In this position the teeth  436  of the clutch collar  426  are engaged with the teeth  424  of the output shaft  404 , thus providing a direct mechanical linkage between the input shaft  402  and the output shaft  404 . Once the actuator  106  is reactivated the clutch assembly  408  is returned to its disengaged position as shown in  FIG. 12 .  
         [0064]     The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.