Abstract:
A retractable step assist for a vehicle comprises a step, an actuator, an optical fiber sensor, and a safety. The step is movable between a retracted position and a deployed position that is downward and outboard from the retracted position. The actuator is mechanically connected to the step to position the step. The optical fiber sensor has an output that varies when pressure is applied to the optical fiber sensor. The safety is triggered by this output from the optical fiber sensor. The safety is configured to terminate retraction of the step when the optical fiber sensor senses pressure from an object pinched by the step deck.

Description:
RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/510,194, filed Oct. 10, 2003, titled RETRACTABLE VEHICLE STEP WITH INLINE MOTOR; and of U.S. Provisional Patent Application Ser. No. 60/525,074, filed Nov. 25, 2003, titled RETRACTABLE VEHICLE STEP WITH INLINE MOTOR; and of U.S. Provisional Patent Application Ser. No. 60/601,525, filed Aug. 13, 2004, titled DRIVE SYSTEMS FOR RETRACTABLE VEHICLE STEP. The entire contents of each of the above-mentioned provisional patent applications are hereby incorporated by reference herein and made a part of this specification. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to drive systems usable with stepping assists for motor vehicles. 
   2. Description of the Related Art 
   It is commonly known to add a retractable running board or stepping assist to the side of a motor vehicle, especially to a vehicle with a relatively high ground clearance. A variety of drive systems have been developed for these retractable stepping assists, for moving a step member between retracted and deployed positions. However, the drive systems are often unreliable, inefficient, too heavy, and/or too bulky. Accordingly, a drive system which overcomes one or more of these problems is desired. 
   SUMMARY OF THE INVENTION 
   In accordance with one embodiment, there is provided a drive system for use with a retractable vehicle step having (i) a first arm with an upper portion rotatably mountable with respect to an underside of a vehicle so as to be rotatable about a first axis of rotation oriented generally parallel to the ground and (ii) a step member rotatably connected to the first arm so as to be movable generally along an inboard-outboard axis between a retracted position and an extended position. The drive system comprises an electric motor having an armature configured to rotate about an armature axis generally parallel to the first axis, and a pinion gear drivingly connected with respect to the motor. The pinion gear has a first outside diameter. The drive system further comprises an output gear in meshing engagement with the pinion gear. The output gear has a second outside diameter. The pinion gear and the output gear achieve a gear reduction of at least 3:1, and the larger of the first outside diameter and the second outside diameter is no more than 3.0 times the smaller of the first outside diameter and the second outside diameter. 
   In accordance with another embodiment, there is provided a drive system for use with a retractable vehicle step. The drive system comprises an electric motor having an armature configured to rotate about an armature axis, and a pinion gear drivingly connected with respect to the motor. The pinion gear has a first outside diameter. The drive system further comprises an output gear in meshing engagement with the pinion gear. The output gear has a second outside diameter. The drive system further comprises an output shaft having a drive end configured for driving engagement with the retractable vehicle step. The output gear is mounted on the output shaft and the output shaft is configured to rotate about an output shaft axis which is generally parallel to the armature axis. The pinion gear and the output gear achieve a gear reduction of at least 3:1, and the larger of the first outside diameter and the second outside diameter is no more than 3.0 times the smaller of the first outside diameter and the second outside diameter. 
   In accordance with another embodiment, there is provided a drive system for use with a retractable vehicle step having (i) a first arm with an upper portion rotatably mountable with respect to an underside of a vehicle so as to be rotatable about a first axis of rotation oriented generally parallel to the ground and (ii) a step member rotatably connected to the first arm so as to be movable generally along an inboard-outboard axis between a retracted position and an extended position. The drive system comprises an electric motor having an armature configured to rotate about an armature axis generally parallel to the first axis, a pinion gear drivingly connected with respect to the motor, an output gear in meshing engagement with the pinion gear, and an output shaft having a drive end configured for driving engagement with the retractable vehicle step. The output gear is mounted on the output shaft, and the output shaft is configured to rotate about an output shaft axis. The drive system further comprises a breakaway member connecting the output gear to the output shaft. The breakaway member prevents relative angular motion of the output gear and the output shaft, except in response to application of a breakaway torque to one of the output gear and the output shaft. 
   In accordance with another embodiment there is provided a drive system for use with a retractable vehicle step having (i) a first arm with an upper portion rotatably mountable with respect to an underside of a vehicle so as to be rotatable about a first axis of rotation oriented generally parallel to the ground and (ii) a step member rotatably connected to the first arm so as to be movable generally along an inboard-outboard axis between a retracted position and an extended position. The drive system comprises an electric motor having an armature configured to rotate about an armature axis generally parallel to the first axis. The electric motor comprises a standard automotive window-lift unit. 
   In accordance with another embodiment, there is provided a drive system for use with a retractable vehicle step. The drive system comprises an electric motor having an armature configured to rotate about an armature axis, and a pinion gear drivingly connected with respect to the motor. The pinion gear has a first outside diameter. The drive system further comprises an output gear in meshing engagement with the pinion gear. The output gear has a second outside diameter. The drive system further comprises an output shaft having a drive end configured for driving engagement with the retractable vehicle step. The output gear is mounted on the output shaft, and the output shaft is configured to rotate about an output shaft axis generally parallel to the armature axis. The pinion gear and the output gear comprise helical gears, and the larger of the first outside diameter and the second outside diameter is no more than 3.0 times the smaller of the first outside diameter and the second outside diameter. 
   In accordance with another embodiment, there is provided a drive system for use with a retractable vehicle step. The drive system comprises a motor assembly having a drive shaft extending therefrom, a pinion gear connected to the drive shaft and configured to rotate about a pinion axis, and a pinion housing at least partially surrounding the pinion gear. The pinion housing extends generally along the pinion axis. The drive system further comprises a pinion bearing rotatably connecting the pinion gear to the pinion housing. An inner portion of the pinion bearing is coupled to the pinion gear and an outer portion of the pinion bearing is coupled to the pinion housing. The pinion bearing is configured to bear radial loads transmitted through the pinion gear and oriented generally perpendicular to the pinion axis, and isolate the motor assembly from the radial loads. The drive system further comprises an output gear in meshing engagement with the pinion gear. The pinion gear and the output gear comprise crossed helical gears achieving a gear reduction of at least 3:1. 
   In accordance with another embodiment, there is provided a drive system for use with a retractable vehicle step having (i) a first arm with an upper portion rotatably mountable with respect to an underside of a vehicle so as to be rotatable about a first axis of rotation oriented generally parallel to the ground and (ii) a step member rotatably connected to the first arm so as to be movable generally along an inboard-outboard axis between a retracted position and an extended position. The drive system comprises a motor assembly comprising a motor and a drive shaft connected with respect to the motor. The motor assembly is configured to rotate the drive shaft at about 40-160 RPM when unloaded. The drive system further comprises a pinion gear drivingly connected with respect to the drive shaft. The pinion gear has a first outside diameter. The drive system further comprises an output gear in meshing engagement with the pinion gear. The output gear has a second outside diameter. The pinion gear and the output gear achieve a gear reduction, and the larger of the first outside diameter and the second outside diameter is no more than 3.0 times the smaller of the first outside diameter and the second outside diameter. 
   In accordance with another embodiment, there is provided a drive system for use with a retractable vehicle step having (i) a first arm with an upper portion rotatably mountable with respect to an underside of a vehicle so as to be rotatable about a first axis of rotation oriented generally parallel to the ground and (ii) a step member rotatably connected to the first arm so as to be movable generally along an inboard-outboard axis between a retracted position and an extended position. The drive system comprises a motor and a drive shaft connected with respect to the motor, and a pinion gear drivingly connected with respect to the drive shaft. The pinion gear has a first outside diameter. The drive system further comprises an output gear in meshing engagement with the pinion gear. The output gear has a second outside diameter. The output gear is drivingly connected with respect to the first arm. The pinion gear and the output gear achieve a gear reduction, and the larger of the first outside diameter and the second outside diameter is no more than 3.0 times the smaller of the first outside diameter and the second outside diameter. The motor is configured to rotate the first arm at about 7-22 RPM when the drive system is moving the step member toward the deployed position. 
   In accordance with another embodiment, there is provided a drive system for a retractable vehicle step which is configured for attachment to a vehicle. The drive system comprises a frame configured for attachment to the vehicle. The frame is further configured for rotatable connection of a first pivot arm to the frame so that the first pivot arm is rotatable about a first axis of rotation. The drive system further comprises a motor mount removably attached to the frame. The motor mount comprises a motor mounting surface located opposite the frame. The drive system further comprises a motor assembly removably connected to the motor mount at the motor mounting surface. The motor mount spaces the motor assembly from the frame to form a first lateral space between the motor assembly and the frame. The drive system further comprises an output gear located in the first lateral space, the output gear in driving engagement with the motor assembly, the output gear rotatable with respect to the frame about an output axis oriented generally parallel to the first axis of rotation. 
   In accordance with another embodiment, there is provided a retractable vehicle step for use with a vehicle. The retractable vehicle step comprises a first frame configured for attachment to the vehicle. The first frame is further configured for rotatable connection of a first pivot arm to the first frame so that the first pivot arm is rotatable about a first axis of rotation. The retractable step further comprises a second frame configured for attachment to the vehicle. The second frame is further configured for rotatable connection of a second pivot arm to the second frame so that the second pivot arm is rotatable about the first axis of rotation. The retractable step further comprises a motor mount removably attached to the first frame. The motor mount comprises a motor mounting surface located opposite the frame. The retractable step further comprises a motor assembly removably connected to the motor mount at the mounting surface. The motor mount spaces the motor assembly from the first frame to form a first lateral space between the motor assembly and the first frame. The retractable step further comprises an output gear located in the first lateral space. The output gear is in driving engagement with the motor assembly, and the output gear is rotatable with respect to the first frame about an output axis oriented generally parallel to the first axis of rotation. The retractable step further comprises a stepping deck moveably connected with respect to the first frame and the second frame. The stepping deck is moveable between a retracted position and a deployed position under power delivered by the motor assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic plan view of a retractable vehicle step system. 
       FIG. 2  is a perspective view of the retractable vehicle step system of  FIG. 1 , with the step member in the retracted position. 
       FIG. 3  is a perspective view of the retractable vehicle step system of  FIG. 1 , with the step member in the deployed position. 
       FIG. 4  is a side view of one embodiment of one embodiment of a retractable vehicle step. 
       FIG. 5  is an exploded perspective view of one embodiment of a drive system for use with the step system of  FIGS. 1-3  and/or the retractable vehicle step of  FIG. 4 . 
       FIG. 6  is a second perspective view of the drive system of  FIG. 5 , with the gearbox thereof removed for clarity. 
       FIG. 7  is a detail view of the drive system of  FIG. 5 . 
       FIG. 8  is a second detail view of the drive system of  FIG. 5 . 
       FIG. 9  is a third perspective view of the drive system of  FIG. 5 . 
       FIG. 10  is a detail view of the gearbox of the drive system of  FIG. 5 . 
       FIG. 11  is an exploded view of the retractable vehicle step of  FIG. 4 , connected to the drive system of  FIG. 5 . 
       FIG. 12  is a partial sectional view of a motor assembly for use with the drive system of  FIG. 5 . 
       FIG. 13  is a sectional view of the drive system of  FIG. 5 , taken along the line  13 - 13  shown in  FIG. 9 . 
       FIG. 14  is a detail view of the sectional view of  FIG. 13 . 
       FIG. 15  is a perspective view of a retractable vehicle step system. 
       FIG. 16  is a side elevation view of a powered step mechanism of the system of  FIG. 15 . 
       FIG. 17  is another side elevation view of the powered step mechanism of the system of  FIG. 15 . 
       FIG. 18  is an exploded perspective view of the powered step mechanism and a drive system of the retractable vehicle step system of  FIG. 15 . 
       FIG. 19  is a perspective view of another embodiment of a retractable vehicle step system. 
       FIG. 20  is a side elevation view of a powered step mechanism and a drive system of the retractable vehicle step system of  FIG. 19 . 
       FIG. 21  is another side elevation view of the powered step mechanism and the drive system of the retractable vehicle step system of  FIG. 19 . 
       FIG. 22  is an exploded perspective view of the powered step mechanism and the drive system of the retractable vehicle step system of  FIG. 19 . 
       FIG. 22A  is another exploded perspective view of the powered step mechanism and the drive system of the retractable vehicle step system of  FIG. 19 . 
       FIG. 23  is a perspective view of a motor mount and gearbox cover usable with the system of  FIG. 19 . 
       FIG. 24  is another perspective view of the motor mount and gearbox cover of  FIG. 23 . 
       FIG. 25  is a side elevation view of the motor mount of  FIG. 23 . 
       FIG. 26  is an end view of the motor mount of  FIG. 23 . 
       FIG. 27  is a top view of the motor mount of  FIG. 23 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-3  depict one embodiment of a retractable vehicle step system  100 , which may generally comprise a retractable vehicle step  200  mounted adjacent an outboard edge  300  of a vehicle  310 . A drive system  400  may be connected to the vehicle step  200  to provide powered movement of a step member  210  of the vehicle step  200  between a retracted position RP and a deployed position DP. In the depicted embodiment, the step member  210  is movable, under power delivered by the drive system  400 , generally along an inboard-outboard direction between the retracted position RP, in which the step member  210  is partially or completely inboard of the outboard edge, and the deployed position DP, in which the step member  210  is partially or completely outboard of the edge  300 . Accordingly, the step member  210  may serve as a step assist for entering the vehicle when in the deployed position DP. 
   The outboard edge  300  may comprise, for example, a lower outboard edge of the vehicle  310 , such as a lower side edge, lower rear edge, or lower forward edge, depending on the mounting location of the retractable vehicle step  200 . Where the edge  300  comprises a lower side edge, the edge  300  is oriented generally parallel to a direction of travel of the vehicle  310 , and the inboard-outboard direction depicted in  FIG. 1  is oriented generally perpendicular to the direction of travel. The direction of travel is typically parallel to the longitudinal axis of the vehicle  310 . Where the edge  300  comprises a lower rear edge or lower forward edge of the vehicle  310 , the edge  300  is oriented generally perpendicular to the direction of travel of the vehicle, and the inboard-outboard direction depicted in  FIG. 1  is oriented generally parallel to the direction of travel. 
   The retractable vehicle step  200  may comprise any suitable retractable vehicle step mechanism, of which there are many presently known in the relevant arts. Of course, any suitable later-developed mechanism may also be employed as the retractable vehicle step  200 . In some embodiments, the retractable vehicle step  200  may comprise any of the retractable-step mechanisms disclosed in U.S. Pat. No. 6,641,158, issued Nov. 4, 2003, titled RETRACTABLE VEHICLE STEP; or U.S. Patent Application Publication No. US 2003/0184040 A1 (application Ser. No. 10/274,418), published Oct. 2, 2003, titled RETRACTABLE VEHICLE STEP. The entire contents of each of the above-mentioned patent applications and publications are hereby incorporated by reference herein and made a part of this specification. 
     FIG. 4  depicts one mechanism that may be employed as the retractable vehicle step  200 . This embodiment of the retractable vehicle step  200  includes a first arm  202  and a second arm  204 , each of which is pivotably connectable via, e.g., a frame  206 , with respect to the underside of the vehicle  310 . (Alternatively, the first and second arms  202 ,  204  may be directly coupled to the underside of the vehicle  310 .) The first and second arms  202 ,  204  are therefore pivotable with respect to the underside of the vehicle about generally parallel first and second axes A-A, B-B, respectively. Each of the first and second axes A-A, B-B is oriented generally parallel to the ground. The step member  210 , which may comprise a stepping deck  212  rigidly connected to a support bracket  214 , is connected to the first and second arms  202 ,  204  so as to be rotatable about third and fourth axes C-C, D-D, respectively. Thus, upon rotation of the first and second arms  202 ,  204  about the first and second axes A-A, B-B, the step member  210  moves between the retracted position RP and the deployed position DP. 
   It should be noted that the designation of the outboard arm as the “first arm” and the inboard arm as the “second arm,” and the designation of the various axes as the first through fourth axes is for convenience only, and any of the arms or axes may be considered a first arm, second arm, first axis, second axis, etc. where these terms are used in the appended claims. 
     FIGS. 5-10  depict one embodiment of a drive system  400 . The depicted drive system generally comprises a motor assembly  402  which drives a pinion gear  404 , which in turn meshes with an output gear  406 . The output gear  406  is mounted on and turns an output shaft  408 , which forms a drive end  410  for connecting the drive system  400  to the retractable vehicle step  200 . The pinion gear  404  rotates about a pinion axis F-F and the output gear  406  and output shaft  408  rotate about an output axis G-G. 
   In some embodiments, the motor assembly  402  comprises an electric motor  412  which in turn comprises an armature (see  FIG. 12 ) which, when energized, rotates about an armature axis E-E. In certain such embodiments, the internal gearing of the motor assembly  402  is configured to orient a drive shaft  414  (as well as the pinion axis F-F, about which the drive shaft  414  rotates as well) of the motor assembly  402  generally perpendicular to the armature axis E-E. One suitable type of electric motor assembly  402  is a standard automotive window-lift motor, such as those available from Siemens AG of Munich, Germany. Such motors are particularly useful because of their ready availability, low cost, low weight and high reliability. Alternatively, any other suitable type of electric motor may be employed, or a pneumatic or hydraulic motor, or a hand crank may be employed to provide power for the drive system  400 . 
   Whether the motor assembly  402  comprises a window-lift motor as discussed above, or some other type of electric or non-electric motor, the speed of the motor  412  itself (e.g. the armature speed where an electric motor is employed) may, in various embodiments, be (i) about 4,500-6,000 RPM, or about 5,000-5,500 RPM, or about 5,300 RPM when unloaded (e.g., with no drive load coupled to the drive shaft  414 ); (ii) about 3,500-5,500 RPM, or 4,000-5,000 RPM, or about 4,500 RPM when deploying a retractable vehicle step (e.g. the step  200  depicted herein) connected with respect to the output gear  406  or output shaft  408 ; and/or (iii) about 2,500-4,500 RPM, or about 3,000-4,000 RPM, or about 3,500 RPM when retracting such a retractable vehicle step connected with respect to the output gear  406  or output shaft  408 . Similarly, the speed of the drive shaft  414  may, in various embodiments, be (i) about 40-160 RPM, or about 75-125 RPM, or about 90 RPM when unloaded (e.g., with no drive load coupled to the drive shaft  414 ); (ii) about 30-150 RPM, or about 60-120 RPM, or about 75 RPM when deploying a retractable vehicle step (e.g. the step  200  depicted herein) connected with respect to the output gear  406  or output shaft  408 ; and/or (iii) about 15-140 RPM, or about 40-120 RPM, or about 60 RPM when retracting such a retractable vehicle step connected with respect to the output gear  406  or output shaft  408 . 
   Where the drive system  400  is employed with a retractable vehicle step similar to that shown in  FIG. 4 , the output shaft  408  may be connected to the upper end of the first arm  202  (see  FIG. 11 ) or the second arm  204 , to drive the arm under power delivered by the motor assembly  402 , and cause it to rotate about the first axis A-A or second axis B-B, thereby moving the step member  210  between the retracted and deployed positions. With the drive system  400  so connected to the retractable vehicle step  200 , the output axis G-G will be substantially coincident with the first axis A-A or the second axis B-B, depending on whether the first arm  202  or the second arm  204  is driven by the drive system. 
   Moreover, where the drive system  400  is so connected to a retractable vehicle step  200  of the type shown in  FIG. 4 , and a motor assembly  402  of the type shown in  FIG. 5  is employed, the armature axis E-E will extend generally parallel to the outboard edge  300  of the vehicle. This arrangement is advantageous because in some vehicles more room is available for mounting the retractable vehicle step in the lateral (i.e. generally parallel to the outboard edge  300 ) direction than in the inboard-outboard direction, or in the vertical direction. Accordingly, packaging is improved by mounting the motor assembly  402  such that its armature axis E-E (or, more generally, the long/largest dimension of the motor assembly  402 ) extends laterally (rather than inboard) from the retractable vehicle step  200 . 
   In some embodiments, the pinion gear  404  and output gear  406  each comprise helical gears and form a right-angle helical drive. In certain such embodiments, the pinion gear  404  may comprise a 5-tooth helical gear with teeth arranged at a 75-degree helix angle, and/or the output gear  406  may comprise 25-tooth helical gear with a helix angle of 15 degrees. This arrangement facilitates a relatively high gear reduction (5:1) while permitting the gears  404 ,  406  to be of comparable outside diameter (the larger of the two preferably having an outside diameter no more than about 3.0, 2.0, 1.5, 1.2 or 1.1 times that of the smaller). In turn, the output gear  406  may be reduced in size, while preserving a relatively high gear reduction, without requiring an overly small (and weak) pinion gear  404 . Accordingly, in various embodiments, the output gear has outside diameters of less than about 50 mm, less than about 40 mm, or less than about 35 mm. In still another embodiment, the output gear has an outside diameter of about 35 mm. 
   Use of a relatively small output gear  406  is beneficial in terms of packaging of the drive system  400 , particularly where the system  400  is connected to a retractable vehicle step  200  of the type depicted in  FIG. 4 , such that the output axis G-G is substantially coincident with the second axis B-B. In such an installation of the system  400 , minimizing the outside diameter of the output gear  406  can minimize the overall inboard protrusion of the retractable step  200 -drive system  400  assembly, or at the very least minimize the inboard protrusion of the upper portions of the step-drive system assembly, nearest the underside of the vehicle  310 , where the available space for installation of these components tends to be most restricted. Moreover, whether the drive system  400  is connected such that the output axis G-G is substantially coincident with the second axis B-B or the first axis A-A, a relatively small output gear  406  improves packaging because of the general scarcity of space in the inboard-outboard and vertical directions. 
   Accordingly, in one embodiment the entire drive system  400  fits within a three-dimensional box-shaped space or “package” (with sides oriented at right angles to each other) of about 7.5 inches, or about 7-9 inches (measured along the axis E-E) by about 3 inches, or about 3-4 inches (along the axis F-F) by about 4 inches, or about 4-5.5 inches (along an axis orthogonal to both axes E-E, F-F). In another embodiment, the entire drive system  400  fits within a two-dimensional rectangular “profile” of about 3 inches, or about 3-4 inches (measured along the axis F-F) by about 4 inches, or about 4-5.5 inches (measured perpendicular to the axis F-F). In still another embodiment, the drive system  400  less the motor assembly  402  (in other words, the gearbox  430  with all components connected thereto or installed therein) fits within such a three-dimensional box-shaped space or “package” of about 4 inches, or about 4-5.5 inches (measured along the axis E-E) by about 2 inches, or about 2-3 inches (along the axis F-F) by about 3.5 inches, or about 3.5-5 inches (along an axis orthogonal to both axes E-E, F-F). In yet another embodiment, the drive system  400  less the motor assembly  402  fits within a two-dimensional rectangular “profile” of about 2 inches, or about 2-3 inches (measured along the axis F-F) by about 3.5 inches, or about 3.5-5 inches (measured perpendicular to the axis F-F). 
   The gear parameters specified above may be varied in other embodiments. For example, the pinion gear  404  may alternatively have 1, 2, 3, 4, 6, 7, 8 or more teeth, and the number of teeth on the output gear correspondingly varied to achieve the desired gear reduction, which may be 2:1, 3:1, 4:1, 6:1, 7:1 or more. The helix angle of the pinion gear  404  may be varied from the 75-degree angle specified above (as one example, any suitable angle from 45-85 degrees may be employed; other suitable ranges include 60-85 degrees or 70-80 degrees), and the helix angle of the output gear  406  may be selected to complement that of the pinion gear  404 . In still other embodiments, the pinion gear  404  and output gear  406  may comprise bevel gears, standard (non-helical) spur gears, a worm-and-worm-gear arrangement, etc., rather than the right-angle helical drive discussed above. 
   In some embodiments, the drive system  400  is configured to have an output speed (the speed of the output gear  406 /output shaft  408 ) of about 10-25 RPM, or about 15-22 RPM, or about 17.8 RPM when unloaded (e.g., without a retractable vehicle step connected with respect to the output gear  406  or output shaft  408 ). In other embodiments, the drive system  400  is configured to have an output speed of about 7-22 RPM, about 12-19 RPM or about 15 RPM when deploying a retractable vehicle step (e.g. the step  200  depicted herein) connected with respect to the output gear  406  or output shaft  408 . In still other embodiments, the drive system  400  is configured to have an output speed of about 4-19 RPM, about 9-16 RPM or about 11.7 RPM when retracting a retractable vehicle step (e.g. the step  200  depicted herein) connected with respect to the output gear  406  or output shaft  408 . Note that when retracting or deploying a retractable vehicle step similar to the step  200  depicted herein, the output speed of the drive system  400  will be equivalent to the angular speed of the first arm  202  and/or second arm  204  as the step  200  deploys or retracts. 
   In some embodiments, the drive system  400  is configured to move a retractable vehicle step (such as, without limitation, retractable step similar to the step  200  disclosed herein) from the retracted position RP to the deployed position DP in about 0.3-2.0 seconds, or about 0.5-1.0 seconds. In still other embodiments, the drive system  400  is configured to move a retractable vehicle step (such as, without limitation, retractable step similar to the step  200  disclosed herein) from the deployed position DP to the retracted position RP in about 0.6-1.8 seconds, or about 0.8-1.5 seconds, instead of or in addition to the deployment-time capabilities mentioned above. 
   With further reference to  FIGS. 5-10 , the drive system  400  may further comprise a rigid gearbox  430 , which in turn may further comprise a pinion housing  432  connected to (or integrally formed with) an output housing  434 . The pinion housing  432  has a generally cylindrical interior that is substantially centered on and extends along the pinion axis F-F, and the output housing  434  has a generally cylindrical interior that is substantially centered on and extends along the output axis G-G. The pinion and output housings  432 ,  434  intersect in a manner that permits meshing engagement of the pinion and output gears  404 ,  406 , contained therein, respectively. 
   The pinion gear  404  is mounted on the drive shaft  414  of the motor assembly and, in the depicted embodiment, forms a number of locking teeth  436  which are received in matching pockets  438  which rotate in concert with the drive shaft  414  under the power of the motor  412 . The teeth  436  and pockets  438  coact to substantially prevent relative rotation of the drive shaft  414  and pinion gear  404  when the drive system  400  is in operation. Alternatively, any suitable structure, such as a spline, keyway, etc. may be employed instead of the teeth  436  and pockets  438  to prevent such relative rotation. 
   At its end opposite the motor assembly  402 , the pinion housing  432  forms a bearing pocket  440  (see  FIG. 5 ; in addition,  FIGS. 13-14  will facilitate quicker understanding of this structure) which receives an outer race  442   a  of a pinion bearing  442 , while a snap ring  444  retains the bearing  442  in the pocket  440 . An inner race  442   b  of the pinion bearing  442  fits over an axle stub  446  formed on the pinion gear  404 , and is secured thereto with a bearing screw  448 . A dust cap  450  may be employed to prevent debris from entering the pinion housing  432 . In one embodiment, the pinion bearing  442  comprises a radial bearing. 
   Accordingly, the pinion bearing  442  journals the pinion gear  404  with respect to the pinion housing  432 , and coacts with the bearing pocket  440 , snap ring  444  and screw  448  to bear any radial (or thrust) loads transmitted through the pinion gear  404  perpendicular to (or along) the pinion axis F-F. The pinion bearing  442 , etc. therefore substantially isolate the motor assembly  402  from such radial or thrust loads and reduce the potential for damaging the motor assembly thereby. 
   In one embodiment, the pinion bearing  442  is configured to bear thrust loads acting in either direction generally along the pinion axis F-F (i.e. towards or away from the motor assembly  402 ). Such a bearing eliminates a possible need for a second bearing, located at an opposite end of the pinion housing  432 , to journal the pinion gear  404  with respect to the housing  432 . This in turn eliminates alignment and tolerance issues that can arise with the use of multiple bearings and cause premature wear of one or both bearings. 
   The output shaft  408  is journalled to the output housing  434  via first and second output bushings  460 ,  462 , with the first output bushing  460  received in an output opening  464  formed in an end plate  466  connected to the end of the output housing  434 . The second output bushing  462  may be received in a similar opening (not shown) at an opposite end of the output housing  434 . 
   In one embodiment, a breakaway member  470  is employed to connect the output gear  406  to the output shaft  408 . In the depicted embodiment, the breakaway member  470  comprises a tolerance ring. The breakaway member  470  is disposed between the outside diameter of the output shaft  408  and the inside diameter of the output gear  406 , and prevents relative angular motion of the output gear  406  and the output shaft  408 , except in response to the application of a breakaway torque to the output gear or the output shaft. Such a breakaway torque may be applied when an obstruction blocks movement of the retractable step  200  while the motor assembly  402  is energized and turning, or when an external force is applied to the retractable vehicle step  200  to urge it toward the retracted or deployed position while the motor assembly  402  is stationary. 
     FIG. 8  depicts one embodiment of the breakaway member  470  in greater detail. The depicted breakaway member  470  comprises a generally cylindrical spring member which forms a number of longitudinally-extending ridges  472  on its surface. Preferably, the ridges are oriented such that their peaks contact the inside diameter of the output gear  406 ; more generally, the peaks may be oriented such that they contact whichever of the output gear and output shaft is constructed of a softer material. The inherent resilience of the ridges  472  allows the breakaway member  470  to act as a friction coupling between the output gear  406  and the output shaft  408 . Preferably, the breakaway member  470  allows relative rotation of the output gear  406  and the output shaft  408  upon application of a breakaway torque of about 40 foot-pounds to the output gear or the output shaft. One preferred product for use as the breakaway member  470  is a tolerance ring model no. BN, available from USA Tolerance Rings of West Trenton, N.J. 
     FIG. 12  depicts one embodiment of the motor assembly  402  in greater detail. The motor  412  comprises an armature  480  rotatably disposed in a space between magnets  482 . A worm  484  extends from one end of the armature  480 , and when energized the armature  480  rotates the worm  484  about the armature axis E-E at the same angular speed as the armature  480  itself. The worm  484  meshes with a worm gear  486 , which rotates about the pinion axis F-F in concert with the drive shaft  414 , which is coupled to the worm gear  486 . The drive shaft  414  delivers power to the downstream portions of the drive system  400 , as described above. Various embodiments of the motor assembly  402  (including without limitation the embodiment depicted in  FIG. 12 ) may employ a gear reduction of about 20:1-180:1, or about 40:1-80:1, or about 80:1, or about 60:1 between the motor  412  itself (e.g., the armature where the motor  412  comprises an electric motor) and the drive shaft  414  of the motor assembly  402 . Accordingly, in the embodiment depicted in  FIG. 12  the worm  484  and worm gear  486  achieve a gear reduction as specified above. 
     FIGS. 15-18  depict a retractable vehicle step system  500  which is prior art to the system shown in  FIGS. 19-27 . The retractable vehicle step system  500  generally comprises a powered step mechanism  600  and an idler step mechanism  700 , both of which are connected to a stepping deck  612 . Under power delivered by a drive system  800  drivingly connected to the powered step mechanism  600 , the powered and idler mechanisms  600 ,  700  move the stepping deck  612  between a retracted position (e.g., the retracted position RP shown in  FIG. 1 ) and the deployed position depicted in  FIG. 15 . The deployed position is located downward and outboard of the retracted position. 
   Each of the powered step mechanism  600  and idler step mechanism  700  comprises a four-bar linkage which functions in a manner generally similar to the mechanism  200  depicted in  FIG. 4 . Thus, the powered step mechanism  600  includes a first arm  602  and a second arm  604 , each of which is pivotably connected to a generally rigid frame  606 . The frame  606  is configured to be secured to a vehicle (not shown), particularly the underside thereof, via a mounting flange  608 . The first and second arms  602 ,  604  are therefore pivotable with respect to frame  606  about generally parallel first and second axes A-A, B-B, respectively. When the retractable vehicle step system  500  is mounted on a vehicle, each of the first and second axes A-A, B-B is oriented generally parallel to the ground. A support bracket  614  is rigidly connected to the stepping deck  612 , and is connected to the first and second arms  602 ,  604  so as to be rotatable about third and fourth axes C-C, D-D, respectively. Thus, upon rotation of the first and second arms  602 ,  604  about the first and second axes A-A, B-B, the stepping deck  612  moves between the retracted position and the deployed position. 
   Similarly, the idler step mechanism  700  includes a first arm  702  and a second arm  704 , each of which is pivotably connected to a generally rigid frame  706 . The frame  706  is configured to be secured to the vehicle alongside the powered frame  606  via a mounting flange  708 . The first and second arms  702 ,  704  are therefore pivotable with respect to frame  706  about the first and second axes A-A, B-B, respectively. A support bracket  714  is rigidly connected to the stepping deck  612 , and is connected to the first and second arms  702 ,  704  so as to be rotatable about the third and fourth axes C-C, D-D, respectively. Thus, upon rotation of the first and second arms  602 ,  604 ,  702 ,  704  about the first and second axes A-A, B-B, the stepping deck  612  moves between the retracted position and the deployed position. 
     FIGS. 16-18  depict the powered step mechanism  600  and the drive system  800  in greater detail. The drive system  800  generally comprises a motor assembly  802  which drives a pinion gear (not shown, but generally similar to the pinion gear  1204  discussed below), which in turn meshes with an output gear  806 . The output gear  806  is mounted on and turns an output shaft  808 , which drivingly engages the second link  604 . Thus, the output gear  806  and output shaft  808  rotate about an output axis which is coincident with the second axis B-B. 
   The drive system  800  further comprises first and second gearbox halves  820 ,  822  which join at their respective edges and enclose the pinion and output gears. The output shaft  808  passes through an output opening  824  formed in the gearbox half  822 , while a pinion opening  826  accommodates the pinion gear during assembly of the drive system  800 . 
   To secure the motor assembly  802  to the frame  606 , a vertical flange  630  and columns  632  are integrally formed as part of the frame  606 . A mounting boss  634  is formed at the end of each of the columns  632 , and the motor assembly  802  is secured to the columns  632 , over the bosses  634 , via screws  636 . The columns  632  have sufficient length in the lateral direction (i.e. in a direction generally parallel to any of the axes A-A, B-B, C-C, D-D) to provide a lateral space for accommodating the output gear  806  and the gearbox  820 ,  822  between the motor assembly  802  and the frame  606 . 
   On the vertical flange  630  is also formed a pinion bearing  640  having an inner bore  642 . The inner bore  642  is coaxial with the pinion gear and receives an axle stub (not shown, but generally similar to the axle stub  1205  discussed below) which extends laterally from the pinion gear into the inner bore  642 . With the axle stub of the pinion gear thus journalled to the pinion bearing  640 , the pinion gear is less likely to deflect off-axis under loads or torques imparted by the output gear  806  or the motor assembly  802 . 
   The integral formation of the columns  632 , mounting bosses  634  and pinion bearing  640  with the overall frame  606  ensures a very strong, secure connection of the motor assembly  802  (and the drive system  800  in general) to the frame  606 . This advantageously minimizes any tendency of the motor assembly to move or flex with respect to the frame as the motor drives the retractable step. This may occur, for example, when sudden or heavier-than-usual loads or torques are transmitted through the output gear  808 . Such movement or flexure could result in disengagement of the pinion and output gears and damage to the drive system  800  or retractable step  500 . 
     FIGS. 19-27  depict another embodiment of a retractable vehicle step system  900 . The depicted retractable vehicle step system  900  generally comprises a powered step mechanism  1000  and an idler step mechanism  1100 , both of which are connected to a stepping deck  912 . Under power delivered by a drive system  1200  drivingly connected to the powered step mechanism  1000 , the powered and idler mechanisms  1000 ,  1100  move the stepping deck  912  between a retracted position (e.g., the retracted position RP shown in  FIG. 1 ) and the deployed position depicted in  FIG. 19 . The deployed position is located downward and outboard of the retracted position. 
   In other embodiments, two powered step mechanisms  1000  may be employed in place of the combination of powered and idler mechanisms  1000 ,  1100  depicted in  FIG. 19 , or only a single powered step mechanism  1000  (and no idler mechanism  1100  at all) may be employed to support and move the stepping deck  912 . In still other embodiments, two or more idler mechanisms  1100  may be employed in combination with one or more powered mechanisms  1000  to support and move the stepping deck  912 . 
   Each of the powered step mechanism  1000  and idler step mechanism  1100  comprises a four-bar linkage which functions in a manner generally similar to the mechanism  200  depicted in  FIG. 4 . Thus, the powered step mechanism  1000  includes a first arm  1002  and a second arm  1004 , each of which is pivotably connected to a generally rigid frame  1006 . The frame  1006  is configured to be secured to a vehicle (not shown), particularly the underside thereof, via a mounting flange  1008 . The first and second arms  1002 ,  1004  are therefore pivotable with respect to frame  1006  about generally parallel first and second axes A-A, B-B, respectively. When the retractable vehicle step system  900  is mounted on a vehicle, each of the first and second axes A-A, B-B is oriented generally parallel to the ground. A support bracket  1014  is rigidly connected to the stepping deck  912 , and is connected to the first and second arms  1002 ,  1004  so as to be rotatable about third and fourth axes C-C, D-D, respectively. Thus, upon rotation of the first and second arms  1002 ,  1004  about the first and second axes A-A, B-B, the stepping deck  912  moves between the retracted position and the deployed position. 
   Similarly, the idler step mechanism  1100  includes a first arm  1102  and a second arm  1104 , each of which is pivotably connected to a generally rigid frame  1106 . The frame  1106  is configured to be secured to the vehicle alongside the powered frame  1006  via a mounting flange  1108 . The first and second arms  1102 ,  1104  are therefore pivotable with respect to frame  1106  about the first and second axes A-A, B-B, respectively. A support bracket  1114  is rigidly connected to the stepping deck  912 , and is connected to the first and second arms  1102 ,  1104  so as to be rotatable about the third and fourth axes C-C, D-D, respectively. Thus, upon rotation of the first and second arms  1002 ,  1004 ,  1102 ,  1104  about the first and second axes A-A, B-B, the stepping deck  912  moves between the retracted position and the deployed position. 
   Either of the powered step mechanism  1000  or the idler step mechanism  1100  may comprise any suitable retractable vehicle step mechanism, of which there are many presently known in the relevant arts. Of course, any suitable later-developed mechanism may also be employed as either of the powered and idler mechanisms  1000 ,  1100 . In some embodiments, either of the powered and idler mechanisms  1000 ,  1100  may comprise any of the retractable-step mechanisms disclosed in U.S. Pat. No. 6,641,158, issued Nov. 4, 2003, titled RETRACTABLE VEHICLE STEP; or U.S. Patent Application Publication No. US 2003/0184040 A1 (application Ser. No. 10/274,418), published Oct. 2, 2003, titled RETRACTABLE VEHICLE STEP. The entire contents of each of the above-mentioned patent, patent application and publication are hereby incorporated by reference herein and made a part of this specification. 
     FIGS. 20-22A  depict the powered step mechanism  1000  and the drive system  1200  in greater detail. The drive system  1200  generally comprises a motor assembly  1202  which drives a pinion gear  1204 , which in turn meshes with an output gear  1206 . The output gear  1206  is mounted on and turns an output shaft  1208 , which drivingly engages the second link  1004 . Thus, the output gear  1206  and output shaft  1208  rotate about an output axis which is coincident with the second axis B-B. Alternatively, the output shaft can drivingly engage the first link  1002 , in which circumstance the output gear and output shaft would desirably rotate about an output axis which is coincident with the first axis A-A. The pinion gear  1204  rotates about a pinion axis (not shown) which is generally parallel to the output axis. 
   In the depicted embodiment, the output shaft  1208  forms a flat  1209  (see  FIGS. 22 ,  22 A) that engages a wedge (not shown) in the second link  1004 , to facilitate the driving engagement of the second link  1004  by the output shaft  1208 . During assembly of this embodiment, the output shaft  1208  is inserted into the second link  1004  and frame  1006 . After insertion of the shaft  1208  into the second link  1004  and frame  1006 , the wedge of the second link  1004  is drawn against and into engagement with the flat  1209  by turning a set screw  1005  (see  FIG. 21 ) located on the inboard side of the second link  1004 . 
   One suitable type of electric motor assembly  1202  is a standard automotive window-lift motor, such as those available from Siemens AG of Munich, Germany. Such motors are particularly useful because of their ready availability, low cost, low weight and high reliability. Alternatively, any other suitable type of electric motor may be employed, or a pneumatic or hydraulic motor, or a hand crank may be employed to provide power for the drive system  1200 . 
   The drive system  1200  further comprises a motor mount  1250  and a gearbox cover  1252 . The motor mount  1250  is removably connected to the frame  1006  via screws  1254 , and forms mounting bosses  1256  and columns  1258  which underlie the mounting bosses  1256 . The motor assembly  1202  is secured to the columns  1258 , over the bosses  1256 , via screws  1260 . 
   The motor mount  1250  is shown in greater detail in  FIGS. 23-27 . In the depicted embodiment, the motor mount  1250  comprises a single, monolithic piece of material, such as molded plastic or cast/forged/machined metal. Thus the mounting bosses  1256  and columns  1258  are interconnected by a generally rigid body  1270 . In the embodiment shown in  FIGS. 23-27 , the body  1270  forms a number of stiffening ribs  1270   a  which connect the columns  1258  to each other and/or to other portions of the motor mount  1250 . In other embodiments, the body  1270  may instead comprise a solid, slab-like member which is not subdivided into individual ribs, or the body may comprise any suitable rigid member having sufficient strength to hold the columns  1258  together when used in a retractable step of the type depicted herein. 
   The mounting bosses  1256  and the adjacent portions of the body  1270  collectively comprise a motor mounting surface MS of the motor mount  1250 . More generally, the motor mounting surface MS comprises those areas of the motor mount  1250  which contact the motor assembly  1202  (whether through direct contact as shown, or through intervening member(s) such as washers, gaskets, seals, etc.) The motor mounting surface of the depicted embodiment is desirably adapted for mounting the depicted motor assembly  1202 , which employs three cylindrical connection members which fit over the bosses  1256  and contact the adjacent portions of the body  1270 . While this configuration provides a number of advantages, in other embodiments the motor mounting surface may be configured however necessary to fit the motor assembly employed with the motor mount  1250 . Accordingly, the motor mounting surface may comprise simply a single flat surface, or a plurality of separate flat surfaces (whether coplanar or non-coplanar), or one or more non-flat surfaces, or any other configuration suitable for use with the selected motor assembly. It will be appreciated, therefore, that the bosses  1256  and columns  1258 , and the depicted configuration of the body  1270 , are optional, and may be replaced or supplemented in various embodiments by structure suitable for securing the chosen motor assembly  1202  to the motor mount  1250 . 
   The depicted motor mount  1250  also forms a gearbox  1272 , and a rim  1274  which surrounds the gearbox  1272 . The rim  1274  mates with a corresponding rim  1276  of the gearbox cover  1252  to seal the gearbox  1272  from dust and other contaminants. Although the gearbox  1272  is depicted in  FIGS. 23-27  as an integrally-formed part of the motor mount  1250 , in other embodiments the gearbox may be provided as a component separate from the motor mount  1250 , or omitted altogether. 
   As best seen in  FIG. 24 , each of the columns  1258  may form a hex pocket  1278  for securely receiving a nut  1280  (see  FIG. 22 ) which engages a corresponding screw  1260  to secure the motor assembly  1202  to the motor mount  1250 . However, instead of or in addition to the pockets  1278  and nuts  1280 , each of the columns  1258  may form a threaded inner bore for threadingly engaging the screws  1260 . As shown the motor mount  1250  may also form an alignment rim  1282  and tab  1284  which are configured to engage corresponding depressions (not shown) formed on the frame  1006  and force a desired alignment of the mount  1250  with respect to the frame  1006 . The alignment rim  1282  surrounds an output opening  1286  through which the output shaft  1208  passes. 
   As best seen in  FIGS. 23 and 25 , the gearbox  1272  includes a pinion portion  1272   a  which houses the pinion gear  1204 , and an output portion  1272   b  which houses the output gear  1206 . A rigid gearbox wall  1272   c  surrounds both the pinion and output portions  1272   a ,  1272   b , and extends laterally to an inner surface  1272   d  of the gearbox  1272 . 
   On the inner surface  1272   d  of the pinion portion  1272   a  is formed a pinion bearing  1288  having an inner bore  1290 . The inner bore  1290  is coaxial with the pinion gear  1204  and receives an axle stub  1205  which extends laterally from the pinion gear  1204  into the inner bore  1290 . With the axle stub  1205  of the pinion gear  1204  thus journalled to the pinion bearing  1288 , the pinion gear is less likely to deflect off-axis under loads or torques imparted by the output gear  1206  or the motor assembly  1202 . Preferably, a number of stiffening ribs  1272   e  extend radially outward from the pinion bearing  1288 , to the gearbox wall  1272   c , and stiffen both the pinion bearing  1288  and the motor mount  1250  in general. 
   One of the stiffening ribs  1272   e  extends from the pinion bearing  1288  to an annular inner wall  1292  formed in the inner surface  1272   d  of the output portion  1272   b . Still further stiffening ribs  1272   e  extend radially outward from the annular inner wall  1292  to the gearbox wall  1272   c . Arranged in a circular pattern around the annular inner wall  1292  are a number of thinned circular portions  1272   f , any one or more of which may be drilled-out to create an opening for receiving one of the screws  1254  for attaching the motor mount  1250  to the frame  1006 . 
   As best seen in  FIGS. 23-24  and  26 - 27 , the motor mount  1250  has sufficient length in the lateral direction (i.e. in a direction generally parallel to any of the axes A-A, B-B, C-C, D-D) to provide a lateral space for accommodating the output gear  1206  and the gearbox  1272  between the motor assembly  1202  and the frame  1006 . 
   Advantageously, the motor mount  1250  facilitates use of a substantially identical component for both the powered frame  1006  and the idler frame  1106  (see  FIG. 19 ). Use of the motor mount  1250  thus eliminates the need to produce one component to serve as the powered frame  1006  and another, different component to serve as the idler frame  1106 . Instead, two substantially identical frames can be employed as both the powered frame and the idler frame, with the motor mount  1250  (and the rest of the drive system  1200 ) connected to the frame designated to serve as the driven frame  1006 . The retractable vehicle step system  900  depicted in  FIG. 19  is configured in this manner. 
   Although certain embodiments and examples have been described herein, it will be understood by those skilled in the art that many aspects of the devices shown and described in the present disclosure may be differently combined and/or modified to form still further embodiments. Such alternative embodiments of the devices described above and obvious modifications and equivalents thereof are intended to be within the scope of the present disclosure. Thus, it is intended that the scope of the present invention should not be limited by the particular embodiments described above, but should be determined only by a fair reading of the claims that follow.