WO1992004208A1

WO1992004208A1 - Step assembly for vehicles

Info

Publication number: WO1992004208A1
Application number: PCT/US1991/006163
Authority: WO
Inventors: Samuel Kofele Martin
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-09-04
Filing date: 1991-09-03
Publication date: 1992-03-19
Anticipated expiration: 1993-03-04
Also published as: EP0547113A4; AU8518891A; JPH06503772A; EP0547113A1

Abstract

A step assembly (38, 38', 38''', 38''''), for vehicles having either a hinged door (26) or a sliding door (26'), includes two step supporting members (44) attached to the underside of the vehicle for adjustably supporting at least one step (42). The proximal ends of the step supporting members (44) are longitudinally spaced apart. At least one step supporting member (44) pivots about a lateral axis, extending the step vertically downward. The step is extended downwardly when the door is opened. A cable (64) has a first end attached to the locking end of the door and a second end attached to the one step supporting member (44), thus interconnecting the opening of the door and the extending of the step; or a switch (112), responsive to the position of the door, actuates a motor (110) for extending the step.

Description

STEP ASSEMBLY FOR VEHICLES

BACKGROUND 1.^' Field of Invention

This invention pertains to a step apparatus for vehicles and particularly to a step apparatus which is automatically operated upon the opening of a vehicle door.

2. Prior Art and Other Considerations

In recent years recreational vehicles (RVs) and light trucks have been sold in increasing numbers. These vehicles are now being used not just for light hauling and off-road trips, but also for commuting and general transportation purposes.

One of the primary features of these vehicles is their high road clearance. The purpose of the high road clearance is to facilitate off-road driving on rough and uneven terrain. The drawback of having such high road clearance is that embarking and disembarking the vehicle presents difficulty for certain passengers most notably the elderly, the infirm, children, and women wearing tight fitting skirts or gowns. Previous attempts to overcome this problem fall into two basic categories; permanent steps and retractable steps. The first type of step has limited effectiveness since the closer the step gets to the ground the more the vehicle road clearance is compromised. The second type of step, the retractable step, also has certain drawbacks. An example of a retractable step is shown in U.S. Patent No. 3,751,068 to Green, wherei the step extends down and out by a cable attached to the hinged end of a door. In the above regard, the Green patent does not disclose any way of adjusting the height or the number of steps. Furthermore, since the device patented by Green can only be used with vehicles which have hinged doors, it is not possible to use the device with sliding door vehicles. Finally, by attaching the cable to the hinged end of the door, the Green device has only limited energy available for extending the step since the distance of displacement of the cable is minimal. U.S. Patent No. 3,608,957 (Maneck) shows a horizontal running board for vehicles with sliding doors. The Maneck running board extends outwardly horizontally by the movement of the door. The Maneck device cannot be readily adapted for use with hinged doors. Maneck also does not disclose any way of adjusting the number and height of the steps.

US Patent 3,572,753 to Claassen shows a sole outwardly-angled arm which has an oblique orientation which is approximately 45° to a horizontal frame bar. US Patent 4,062,582 to Youmans discloses spaced support arms which are not provided in spaced relation along the longitudinal horizontal axis of a vehicle.

Accordingly, it is an object of the present invention to provide an improved step for boarding vehicles. An advantage of the present invention is to provide an improved step for boarding vehicles which can be used with both sliding door vehicles as well as with vehicles which have hinged doors.

A further advantage of the present invention is ^' the provision of an improved step apparatus where the number and height of the steps are adjustable.

A further advantage of the present invention is the provision of embodiments of an improved retractable step assembly which translates energy used or produced in the act of opening and/or closing a vehicle door into energy for operating the retractable step assembly.

A further advantage of the present invention is the provision of embodiments of an improved retractable ste assembly which uses an electric motor for operation.

SUMMARY

A step apparatus is provided for vehicles having either a hinged door or a sliding door. The apparatus includes two step supporting members pivotally attached to the^' underside of the vehicle for adjustably supporting a step or plurality of steps. The proximal ends of the step supporting members are spaced apart along a longitudinal vehicle axis 36. At least one of the step supporting members is pivotal about a horizontal axis which is perpendicular to vehicle axis. Opening the vehicle door causes the step assembly to pivot about an axis perpendicular to the longitudinal horizontal axis of the vehicle, thereby extending the step assembly for facilitating easy boarding of the vehicle.

In some embodiments, transmission means include a cable has a first end attached to the locking end of the door and a second end attached to a front one of the supporting members. The cable is at least partially disposed within a hollow cord which extends through portions of the vehicle frame.

In another embodiment, a cable has a first end attached to an electric motor and a second end attached to one of the supporting members. A switch, responsive to the position of the door, actuates the motor for extension and retraction of the step assembly.

In some embodiments, a biasing member is used to bias the supporting members and attached step to a retracted position beneath the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Fig. 1 is a side view of a hinged door vehicle having a step assembly of a first embodiment of the invention mounted thereon.

Fig. 2 is an isometric side view of the step assembly of Fig. 1 in an extended position. Fig. 3 is an isometric side view of the step assembly of Fig. 1 in a retracted position.

Fig. 4 is a front view of the step assembly of Fig. 2.

Fig. 5 is a side view of a sliding door vehicle having a step assembly of a second embodiment of the invention mounted thereon.

Fig. 6 is a side view of a hinged door vehicle having a step assembly of a third embodiment of the invention mounted thereon. Fig. 7 is a side view of a hinged door vehicle having a step assembly of a fourth embodiment of the invention mounted thereon.

Fig. 8 is a side view of a step assembly according to a fifth embodiment of the invention. Fig. 9 is a front view of the step assembly of

Fig. 8. DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a recreational vehicle 20 having a vehicle body 22 and a vehicle undercarriage 24. The vehicl body ^•includes a door 26 hinged to the body 22 by hinges 28. Around the vehicle door 26, the vehicle body 22 further includes a windshield post 30; a top 32; and, a center post 34. The vehicle 20 has a longitudinal horizontal axis from its front to its rear, which axis is depicted by the arrow 36. A step assembly 38 of the embodiment of Fig. 1 includes a mounting bracket 40; a step or platform 42; step supporting members 44 or rails pivotally attached to the mounting bracket 40; step assembly biasing means 46; and, transmission means including cable assembly 48. The mounting bracket 40 is a rectangular plate which is secured to the vehicle under carriage 24. The mounting bracket 40 can be secured to vehicle undercarriage 24 by any suitable means such as welding, fastening, or clamping. In the illustrated embodiment, apertures 41 are provided for fastening the bracket 40 to the vehicle undercarriage 24.

The underside of mounting bracket 40 has two pair of depending semi-circular rings 50 formed therebeneath. The pairs of rings 50 are displaced from one another along the direction of axis 36 by a distance which is on the orde of the length of the step 42. Within each pair of rings 50, an outer ring 50a is positioned closer to the step 42 in th sense of the width of the bracket 40 (e.g., in the sense of a transverse or width axis 51 of the vehicle 20) , as seen i Fig. 4.

Two step supporting members 44 are provided. The step supporting members 44 each have proximal ends which bear projections 52. In this regard, the proximal end of each step supporting member has a first projection 52a which extends transversely toward the step 42 and second projection 52b which extends toward a centerline of the vehicle 20. A bearing sleeve or other friction reducing means is provided in each ring 50 to provide smooth pivoting action about axis 51. Accordingly, the step supporting members 44 pivotally depend about the rings 50 on mounting bracket 40.

The proximal ends of the step supporting members 44 are thus spaced apart (i.e., are in spaced relation) along the axis 36. Each step supporting member 44 is pivotal about a horizontal axis 51 which is perpendicular to axis 36. The axis 51 about which each step supporting member pivots extends through the projections 52 provided at the proximal ends of the members 44. The step supporting members 44 also have a plurality of evenly spaced apertures 54 for securing at least one step 42 to the step supporting members 44. The apertures 54 are provided so that the height of the step 42 relative to the ground is adjustable. In addition, the apertures 54 permit the inclusion of further steps should such be desirable.

The step 42 lies in an essentially horizontal plane. The step 42 has a pair of cylindrical support arms 56 attached to the underside thereof. The support arms are spaced apart relative to the length of the step (e.g., in the sense of arrow 36) at a distance on the order of the separation between centerlines of the supporting members 44. Each support arm 56 has an end adapted for insertion into a selected one of the apertures 54 provided in its corresponding step supporting member 44. In this respect, apertures 54 are provided with bearing sleeves or other friction reducing means so that the support arms 56 can rotate within the apertures 54. -1-

The support arms 56 also have a plurality of apertures 58 extending diametrically therethrough. A selected one of the apertures 58 receives a fastener 60 which extends through the step 42 for securing the step 42 to the support arm 56. The provision of a plurality of apertures 58 facilitates positional adjustment of the step 42 relative to width of the vehicle body (e.g., transverse to the direction of arrow 36) . Thus, the user can adjust the step 42 so as to provide a desired clearance from the vehicle.

The step assembly biasing means 46 is securely fastened to the mounting bracket 40. The biasing means 46 includes a tightly coiled spring, a first end of which is anchored to the mounting bracket 40 and a second end of which is connected to a first length of cable 62. The coiled spring is located in a housing 63.

The first length of cable 62 is connected to a distal portion of the rear step supporting member 44. As will be seen below, the biasing means 46 urges the step supporting members 44 to a retracted position (shown in Fig. 3) beneath the vehicle body 22 by causing the step supporting members 44 to pivot about an axis which is perpendicular to the longitudinal axis 36 of the vehicle 20. Referring again to Fig. 1, the transmission cable assembly 48 includes a second length of cable 64- which has a first end attached to the front step supporting member 44. The cable 64 travels through an aperture in the vehicle body 22 to and around a first pulley 68. The first pulley 68 changes the orientation of the cable 64 so that cable 64 acquires an essentially vertical orientation. After the cable 64 passes over the first pulley 68, it is threaded through a hollow cord 70. The hollow cord 70 is secured to or within the vehicle body 22 so as to remain stationary relative to the cable 64. The cable 64 travels substantially vertically past the vehicle door 26 through the windshield post 30 to a second pulley 72. The second pulley 72 changes the orientation of the cable 64 so that cable 64 now acquires an essentially horizontal orientation along the top 32 of the vehicle 20. The cable 64 is horizontally disposed along or within the vehicle top 32 until it passes through an aperture 74 in the vehicle top. The second end of the cable 64, which extends through the aperture 74, is attached to the non-hinged edge of the vehicle door 26, i.e., the end of the door which engages the vehicle centerpost 34.

The step assembly 38' of the embodiment of Fig. 5 differs from the embodiment of Fig. 1 in the manner in which the transmission cable assembly is positioned relative to the vehicle. In this regard, Fig. 5 shows a sliding door vehicle 20' having a sliding door 26¹. A cable 64' is attached to the step supporting member 44 ' which is nearest the front of the vehicle 20'. The cable 64' passes over a first pulley 68'; travels through hollow cord 70'; and passes over a second pulley 72'. The cable passes through aperture 74' and is connected to the vehicle door 26'.

The step assembly 38" of the embodiment of Fig. 6 also differs from the embodiment of Fig. 1 in the manner in which the transmission cable assembly is positioned relative to the vehicle. In this regard, Fig. 6 also shows a hinged door 26" of a vehicle 20". The step assembly 38" of the embodiment of Fig. 6 has its biasing means 46" positioned beneath a front portion of the mounting bracket 40", rather than beneath a rear portion thereof as occurs in Fig. 1. The first length of cable 62" is connected from the biasing means 46" to the front supporting member 44". The rear supporting member 44" has a first end of the second length of cable 64" connected thereto. The second length of cable 64" extends about pulley 68" up through the center post 34" of the vehicle 20"; about' pulley 74"; and, has its second end connected to the top corner of the locking end of the door 26". Portions of the cable 68" extend through a hollo cord 70". The step assembly 38"' of the embodiment of Fig. differs from the embodiment of Fig. 6 in the manner in whic the force is produced to extend the step assembly 38"'. In this regard, Fig. 7 also shows a hinged door vehicle 20"'. The embodiment of Fig. 7 obviates the extension of a transmission cable through the body of the vehicle 22V ', an instead connects the cable 64"* to an electric motor 110 or other force generating device attached to the rear portion of the mounting bracket 40"'. The electric motor 110 can contain its own battery, be connected to the battery of the^* vehicle 20"', or be otherwise powered.

The electric motor 110 or other force producing device is securely fastened to the mounting bracket 40"'. One end of the cable 64"' is coupled to the output shaft of the motor 110 and the other end of cable 64"' is coupled to the rear step supporting member 44"'.

A switch 112 is attached to the center post 34"' of the vehicle 22"'. In the illustrated embodiment, the ■switch 112 is positioned so that closure of the door 26"' causes the switch to be held in an "off" position for deactivating or reversing the motor 110. Switch 112 is connected to motor 110 by electrical wires 116. It should be understood that the motor-driven embodiment of the step assembly 38"' can be employed with a sliding door vehicle as well as with a swinging or hinged door vehicle. The step assembly 38"" of the embodiment of Figs.

8 and 9 can be used with either a hinged or sliding door vehicle. Like the embodiment of Fig. 7, the step assembly 38"" of Figs. 8 and 9 is electrically actuated. Figs. 8 and 9 do not show vehicle structure except for a vehicle undercarriage 224 and a floorboard 225. In this regard, it is .understood in Figs. 8 and 9 that the vehicle has a longitudinal axis depicted by arrow 236 (perpendicular to the plane of the sheet of Fig. 9) and a width axis depicted by arrow 251 (perpendicular to the plane of the sheet of Fig. 8) .

The step assembly 38"" has a mounting bracket means which includes an undercarriage mounting bracket 240 and an floorboard mounting bracket 241. The undercarriage mounting bracket 240 has an essentially U-shaped channel cross section (see Fig. 9) facing upwardly to the underside of the floorboard 225. The undercarriage mounting bracket 240 and the floorboard mounting bracket 241 are welded or otherwise affixed to the undercarriage 224 and underside of the floorboard 225, respectively. In addition, the floorboard mounting bracket 241 is mounted by an inverted brace 280 to the underside of the floorboard 225. The brace 280 is secured to the underside of the floorboard by_. fasteners 281.

The undercarriage mounting bracket 240 carries transmission means and force producing means in its channel. In this respect, the undercarriage mounting bracket 240 carries an electrical actuator 284 (which includes an electric motor 210) and a first end of transmission shaft 286. The electric motor 210 is connected by electrical wiring 287 to a door switch, such as door switch 112 of a previously described embodiment.

The electrical actuator 284 is mounted on the undercarriage mounting bracket 240 by an actuator support 290 (see Fig. 9) . The electrical actuator 284 includes an extendable piston 292. Fig. 8 shows the piston 292 both in its retracted and extended (phantom) positions. The undercarriage mounting bracket 240 also carries a pillow block bearing 300 through which a first en of the transmission shaft 286 rotatably extends. The first end of the transmission shaft 286 extends just slightly beyond the pillow block 300, and is connected to the extendable piston 292 of actuator 284 by a yoked crank 302. The floorboard mounting bracket 241 has a flanged bracket 310 depending therefrom. A bearing 312 is mounted to the rear of the bracket 310. The bracket 310 has an aperture provided therein so that the second end of the transmission shaft 286 rotatably extends through the bearin 312 and the bracket 310.

A step supporting member 320 is attached to the second end of the transmission shaft 286 protruding from th floorboard mounting bracket. The step supporting member 32 is crooked to have a configuration of three angled segments, particularly proximate segment 322, intermediate segment 324, and distal segment 326. At its distal extremity, the distal segment 326 of the step supporting member 320 has tw spaced-apart ears 328 which carry a pivot rod 330 therebetwee .

The floorboard mounting bracket 241 also carries another step supporting member, particularly step supportin member 350. The step supporting member 350 is in the form of a slide. A proximal end of the step supporting member

350 is pivotally attached to the floorboard mounting bracket 241 so that the member 350 pivots about axis 352 (which is perpendicular to the longitudinal axis 236) .

The step supporting member 350 is elongated and slightly arcuate in shape. The step supporting member 350 has an elongated arcuate aperture 354 centrally provided therein. A shaft 360 extends with sliding clearance through the aperture 354 in an orientation whereby the axis of shaft 360 is parallel to the axis 352. Two washers 362 provided on shaft 360 trap the step supporting member 350 therebetween. A hex nut 364 is also provided on the shaft 360.

The step assembly 38"" has a step 242 which lies in an essentially horizontal plane. Near a front portion thereof, an underside of the step 242 has the shaft 360 welded thereto. In describing the step 242, the "front" is toward the front of the vehicle (e.g., to the right of Fig. 8) . A rear portion of the step 242 is supported by a crest 370 formed on the distal segment 326 of the step supporting member 320.

Near an intermediate portion of its underside, the step 242 has two inverted, triangularly-shaped brackets 372 depending therefrom. The brackets 372 are spaced apart and carry a pivot pin 374 therebetween.

A step-attachment bar 380 connects the step 242 to the step supporting member 320. The step-attachment bar 380 has pivot pin 374 extending through a front aperture and the pivot rod 330 carried by the step supporting member 320 extending through a rear aperture thereof.

It should be understood that the mounting bracket means acquires different configurations depending on the particular vehicle with which the step assembly 38"" is employed. Thus, in another embodiment the mounting bracket means is of unitary construction, rather than two separate members.

OPERATION In operation, as the door 26 of vehicle 20 of Fig. 1 is pivoted to its opened position, the cable 64, having its second end connected to the door 26, is pulled in the direction shown by arrows 90. As the cable 64 is pulled in the direction of arrows 90, the force on the cable 64 overcomes the tension of biasing means 46 and causes the step supporting members 44 to pivot in the counterclockwise sense (shown by arrow 92 in Fig. 1) for extension to an essentially perpendicularly depending position as shown in Figs. -. an»u 4. n overcoming iε c-ension θj- --.laslng means 46, the cable 64 passes over first pulley 68 through the vehicle body 22 via hollow cord 70 along the windshield post 30 to the second pulley 72 through the horizontal section of hollow cord 70 along the top 32 of the vehicle body 22 to aperture 74 and out to the point on the vehicle door 26 where the cable 64 is attached.

The first pulley 68 thus acts to translate essentially horizontal motion of the transmission means into essentially vertical motion. The second pulley 72 operates to translate essentially vertical motion into essentially horizontal motion. The distal ends of the step supporting members 44 thereby descend in a vertical direction (i.g. below the vehicle 20) when in the extended vertical position.

When the vehicle door 26 is pivoted to the closed position, the force formerly applied by cable 64 is relaxed, permitting biasing means 46 to exert its biasing force on step supporting members 44, thereby rotating the step supporting members 44 about axis 51 (which is perpendicular to the longitudinal axis of the vehicle 20) in the clockwise sense as shown by arrow 94 in Fig. 3. The plane. of the step thus translates vertically between the retracted and extended positions.

The step assembly 38" of the embodiment of Fig. 6 operates in a similar manner as the embodiment of Fig. 1. However, the biasing means 46" exerts a counterclockwise force on the step assembly 38". Upon the opening of the door 26, the cable 64" has forces exerted thereon in the direction of arrows 90" to apply a clockwise rotational force on the step assembly 38". When the door 26' of the vehicle 20' of the embodiment of Fig. 5 is slid to its opened position, the cable 64 ' pulls the step supporting members 44 ' to the extended position against the tension of the biasing means 46'. The cable 64' passes over first pulley 68' through the vehicle body 22' via hollow cord 70' along the windshield post 30' to the second pulley 72' to aperture 74' and out to the point on the vehicle door 26' where the cable 64' is attached. When the vehicle door 26* is slid, moved, pushed, or swung to the closed position, biasing means 46' causes step supporting members 44 ' to rotate about an axis which is perpendicular to the longitudinal horizontal axis 36' of the vehicle 20 ' .

For doors which open as sliding doors along a track, it is easier to convert the sliding motion to energy for extending the step assembly. Factors enhancing ease of operation include the fact that people generally use two hands when opening a sliding door, and the fact that the entire force applied to displace the door can be utilized instead of a vectorial component thereof. Hence, a sliding door can be easily coupled to translate the door's movement along the horizontal axis to the step assembly's pivoting about an axis which is perpendicular to the horizontal longitudinal axis of the vehicle. Thus it is seen the present invention provides a retractable step assembly which is connected to the locking end of a door, as opposed to a hinged end of a door, to ensure that the maximum amount of energy available from opening the door will be used to operate the extension. In addition, the step assembly pivots about an axis which is perpendicular to the longitudinal horizontal axis of the vehicle.

When the door 26"' of the embodiment of Fig. 7 is pivoted to the open position, switch 112 will be in an "on" position, thereby causing activation of the electric motor 110. Activation of the motor 110 causes the cable 64"' to be wound or otherwise pulled about the output shaft of the motor 110, overcoming the bias of biasing means 46"', and thereby pulling the cable 64"' (and thus the step supporting members 44"') in the direction of arrow 90"' until the step assembly 38"' is pivoted to the extended position.

When the vehicle door 26"' is pivoted to the closed position, the output shaft of the electric motor 110 is relaxed or reversed, depending on the type of motor 110 employed, with the result that the biasing means 46"' successfully exerts its biasing force on the step supporting members 44"' to urge the step supporting members 44"' into _* the retracted position. Again, it should be understood that the embodiment of the step assembly 38"' of the embodiment of Fig. 7 works in the same manner on a sliding door vehicle as on a hinged door vehicle. Moreover, it should also be understood that the relation of the switch 112 and motor 110 components of the step assembly 38"' can easily be reversed so that, if opening the door 26"' turns off the switch 112, the motor 110 can be made to be responsive to the "off" position of the switch 112 to extend the step assembly 38".

For the embodiment of Fig. 7, the extension and retraction of the step assembly is related to the opening and closing of the vehicle door but does not directly depend upon energy exertion of the user. Hence, no additional energy is ^"required to open a door with the step assembly 38"', the assembly 38"' being automatic. For the embodiment of Figs. 8 and 9, when the vehicle door is opened, switch 112 is opened causing the piston 292 of electric motor 210 to retract. Retraction of piston 292 pivots shaft 286 and the step supporting member 320 in the clockwise direction about the axis of shaft 286. Consequently, the step supporting member 320 is vertically extended. As the step supporting member 320 is vertically extended (e.g., lowered), the step-attachment bar 380 pulls the step 242 into a vertically lowered position shown by solid lines in Fig. 8.

When the vehicle door is closed, the switch 112 is closed causing the piston 292 of the electric motor 210 to extend. Extension of piston 292 pivots shaft 286 and the step supporting member 320 in the counterclockwise direction about the axis of shaft 286. Consequently, the step supporting member 320 is verticall retracted to assume the position shown by phantom lines in Fig. 8. As the step supporting member 320 is vertically retracted (e.g. , raised) , the step 242 is pushed upwardly. The upward force caused by the vertical elevation of the step supporting member 320 causes the shaft 360 to slide up the aperture 354 provided in the other step supporting member 350.

It should be understood that the embodiment of Figs. 8 and 9 can also be installed for a rear opening door of a vehicle. In such a configuration, the axes about which the step supporting members 320 and 350 pivot are parallel to the longitudinal axis of the vehicle.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various alterations in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A step apparatus for a vehicle having a door frame and an entrance door hinged in said door frame, said door havin a hinged end about which said door pivots between an open and a closed position and a locking end, the apparatus comprising: mounting bracket means for attachment beneath the vehicle; at least one step lying in an essentially horizontal plane; two step supporting members having proximal ends attached to said mounting bracket means and distal ends, at least one of said step supporting members having pivotal movement between a retracted position beneath said vehicle and an extended vertical position subjacent to said vehicle said pivotal movement of said step supporting member occurring about a horizontal axis which is perpendicular to a longitudinal horizontal axis of said vehicle, said step supporting members being attached to said mounting bracket means at attachment points which are spaced apart along the longitudinal horizontal axis of said vehicle; transmission means responsive to the position of said door for causing said step supporting member to acquir the extended position when the door is in the open position; and wherein the plane of the step translates vertically between the retracted and extended positions.

2. A step apparatus for a vehicle having a door frame and an entrance door hinged in said door frame, said door having a hinged end about which said door pivots between an open and a closed position and a locking end, the apparatus comprising: mounting bracket means for attachment beneath the vehicle; two step supporting members having proximal ends pivotally. attached to said mounting bracket means and distal ends, each of said step supporting members having pivotal movement between a retracted position beneath said vehicle and an extended vertical position subjacent to said vehicle, said pivotal movement of each of said step supporting members occurring about horizontal axes which are perpendicular to a longitudinal horizontal axis of said vehicle, said step supporting members being attached to said mounting bracket at attachment points which are spaced apart along the longitudinal horizontal axis of said vehicle; at least one step attached to said step supporting members, the step lying in an essentially horizontal plane; biasing means attached beneath said vehicle and connected to at least one of said step supporting members for urging said step supporting members to the retracted position beneath said vehicle; transmission means responsive to the position of said door for causing said step supporting members to acquire the extended position when the door is in the open position; and wherein the plane of the step translates vertically between the retracted and extended positions.

3. The apparatus of claims 1 or 2, wherein said step is adjustably attached to said step supporting members.

4. The apparatus of claim 2, wherein said step supporting members comprise two parallel rails, each of said rails having a plurality of evenly spaced apertures, said step having step support arms which extend through selected ones of said apertures.

5. The apparatus of claims 1 or 2, wherein said transmission means has first and second ends, the first end of said transmission means being connected to one of said step supporting members and the second end of said transmission means connected to force producing means, said force producing means being actuatable in response to the position of said door.

6. The apparatus of claims 1 or 2 , further comprising: door position detection means; and, force producing means responsive to said door position detection means, said force producing means being adapted to exert a force on said transmission means to overcome said biasing means.

7. The apparatus of claims 5 or 6, wherein said force producing means is an electric motor.

8. The apparatus of claim 2, wherein said transmission means has first and second ends, the first end of said transmission means being connected to one of said step supporting members and the second end of said transmission means connected to the locking end of said entrance door.

9. The apparatus of claim 8, wherein said transmission means comprises a cable slidably disposed within a hollow cord.

10. The apparatus of claim 9, wherein said hollow cord is mounted within said door frame, and said transmission means further comprises first and second pulleys, the first pulley acting to translate essentially horizontal motion of the transmission means into essentially vertical motion, the second pulley operating to translate essentially vertical motion into essentially horizontal motion.