Externally stowed wheelchair lift

The present invention provides a robust, highly stable and vertically compact when folded-up wheelchair lift suitable for placement on a variety of vehicles such as vans and mini-vans. The lift has an elongate horizontal support member that is pivotally attached to a post fixed to the undercarriage of a vehicle. The horizontal support member supports the lifting mechanism and the wheelchair platform and is powered to swing the platform and lifting mechanism between a use position and a storage position. The lifting mechanism uses a pair of connecting links spaced lengthwise on the support member and connecting to the wheelchair platform in a four bar linkage arrangement generally in the form of a parallelogram. Both connecting links are rotated by bell cranks both of which are powered by the same hydraulic cylinder.

BACKGROUND OF THE INVENTION
 This invention relates to lifts. More particularly, it relates to wheel
 chair lifts for vehicles.
 Lift mechanisms which enable large and/or unwieldy articles to be
 transferred into and out of vehicles have been in existence for some time.
 A number of lifts have been adapted for passenger vehicles to provide
 access for people with handicaps. Most of the prior art wheelchair lifts
 which are stowable on the exterior of vehicles require relatively
 extensive track systems or support structures on the undercarriage of the
 vehicles. These extensive tracks and support systems add weight to the
 vehicle and take up substantial amounts of space which limits their usage
 to certain full size vans or other large vehicles.
 The prior art wheelchair lifts, which do not utilize the track systems or
 extensive support structures will typically provide attachment points that
 are quite close to each other on the wheelchair platform. This can cause
 stability problems and extreme stress in the areas of attachment between
 the platform and the lifting links. Attempts to increase the stability and
 rigidity such as by providing reinforcing structure on the platform will
 necessarily increase the weight which will be raised and lowered requiring
 more power and thus stronger and heavier structures for supporting the up
 and down drive lifting means. Examples of prior art lifts follows.
 U.S. Pat. No. 3,263,835 to Lugash discloses a lift that is rotatably
 attached to an undercarriage of a truck. The lift comprises a platform
 which is raised or lowered by two sets of rotatable "pantographic" arms
 located at the sides of the platform and which are concurrently actuated
 by a hydraulic cylinder. This lift takes up a substantial amount of
 vertical space and thus would be difficult to use as a wheelchair lift
 mounted below the undercarriage on modern mini-vans.
 U.S. Pat. No. 4,711,613 to Fretwell discloses a wheelchair lift rotatably
 attached to an undercarriage of a vehicle. The lift comprises a platform
 which is raised or lowered by a pair of adjacent parallel links located at
 one side of the platform. Power to the parallel links is provided by a
 hydraulic cylinder one end of which is attached to one of the parallel
 links, the other end of which is attached to the rotational support
 assembly. The platform is attached to the links at a centrally positioned
 region at two points quite close to each other on the side of the
 platform. This may cause operating difficulty or instability, particularly
 when the weight of the wheelchair is forward or rearward on the platform.
 Another lift which is rotatably attached to a vehicle is disclosed in U.S.
 Pat. No. 4,026,387 to Abreu. In Abreu, a platform is attached at one
 corner to a dual purpose mechanism which is attached to an exterior side
 of a vehicle adjacent a door opening. The dual purpose mechanism raises
 and lowers the platform by means of powered telescoping shafts which serve
 to raise and lower the platform. The dual purpose mechanism also permits
 the platform to be rotated between operative and storage position. When
 the platform is in its stored position, the top surface of the platform
 abuts the undercarriage of the vehicle and frictionally retains the lift
 in its storage position. Again, the closely spaced attachment points of
 the lift mechanism to the platform can create operating and stability
 problems particularly when the weight of the wheelchair is distally
 positioned on the platform.
 Another type of lift is disclosed in U.S. Pat. No. 4,134,504 to Salas. In
 Salas, a lift is attached to an undercarriage of a vehicle and is
 horizontally extended and retracted between operative and storage
 positions by a somewhat complex cable system. The lift comprises a
 platform which is raised or lowered by two sets of parallel arms located
 at the sides of the platform, and which are concurrently actuated by a
 hydraulic cylinder. Only one of the parallel arms of each set is powered.
 Yet another type of lift is disclosed in U.S. Pat. No. 5,556,250 to
 Fretwell. The Fretwell '250 is similar to the Salas lift mechanism in that
 Fretwell '250 provides two sets of parallel arms located at the sides of a
 platform, the parallel arms are concurrently actuated by a hydraulic
 cylinder, and the lift mechanism is linearly extended and retracted
 between operative and storage positions by a complex gear and chain driven
 track system. Fretwell '250 also discloses an enclosure, attachable to the
 undercarriage of a vehicle into which the lift mechanism is positioned for
 storage.
 SUMMARY OF THE INVENTION
 The present invention provides a robust, highly stable and compact
 wheelchair lift suitable for placement on a variety of vehicles such as
 vans and mini-vans. The lift has an elongate horizontal support member
 that is pivotally attached to a post on the underside of a vehicle. The
 horizontal support member supports the lifting mechanism and the
 wheelchair platform and is powered to swing the platform and lifting
 mechanism between a use position and a storage position. The lifting
 mechanism uses a pair of connecting links spaced lengthwise on the support
 member and connecting to the wheelchair platform in a four bar linkage
 arrangement generally in the form of a parallelogram. Both connecting
 links are rotated by bell cranks both of which are powered by the same
 hydraulic cylinder.
 A feature and advantage of the invention is that the horizontal support
 member extends along a substantial length of the platform and the
 connecting links are spaced lengthwise on the platform to provide a
 robust, stable, and compact design.
 A further object of the invention is to utilize a four bar linkage
 arrangement in which the two pivot points on the wheelchair platform are
 substantially in horizontal alignment and the two pivot points on the
 horizontal support member are in substantial horizontal alignment.
 Moreover, when the platform is in its storage position all of the pivot
 points are in substantial horizontal alignment to facilitate a vertically
 compact configuration.
 An object of the present invention is to provide a lift which can be easily
 attached to an undercarriage of a vehicle in its own enclosure.
 Another object of the present invention is to provide a lift which can be
 easily moved between storage and operative positions.
 Another object of the present invention is to provide a platform which can
 be easily raised and lowered through a large range of motion.
 Another object of the present invention is to provide a lift mechanism
 which is easily assembled and maintained.
 Another object of the present invention is to provide a lift mechanism
 which is compact and thus highly versatile and may be installed in a wide
 range of vehicle types.
 Yet another object of the present invention is to provide an enclosure into
 which the lift is housed to protect the lift from the elements.
 These and other objects of the present invention will be apparent from a
 reading of the specification and claims.

DETAILED SPECIFICATION
 In FIGS. 1A-1D, a vehicle A is illustrated with a lift 10 and an attachment
 structure configured as an enclosure 300 mounted to the undercarriage of
 the vehicle. The various component parts as described below may be readily
 fabricated from steel stock by conventional means. The enclosure 300 is
 mounted such that an opening 304 in the enclosure is adjacent an entryway
 C and floor D of vehicle A. While the lift 10 and the enclosure 300 are
 depicted as being attached for use with the passenger side of a vehicle,
 it is understood that the lift and the enclosure 300 may be attached
 adjacent any other suitable entryway of a vehicle. Additionally, it is
 noted that the lift 10 may be attached directly to the undercarriage of a
 vehicle without the enclosure 300, if desired. Further note that the lift
 10 may be operated while the door B of an entryway C is either open or
 closed. For purpose of clarification throughout the specification, the
 following terms are defined as follows. The term "operative position" is
 construed to be the state from which loading and unloading of the platform
 in the raised and lowered positions takes place. In the "operative
 position" the horizontal support is generally perpendicular to the
 entryway of a vehicle. The term "storage position" is construed to be the
 state where the lift is effectively positioned beneath an undercarriage of
 a vehicle. The term "actuator" is construed to mean a device which capable
 of movement and may comprise linear motors, hydraulics, pneumatics, or
 mechanical devices such as threaded screws or linkages, all of which may
 be manually operated or powered.
 Turning to the individual figures, in FIG. 1A, the lift 10 has been swung
 about a vertical pivot pin (not shown in this view) from a stowed storage
 position to an operative position by a first actuator (not shown in this
 view) wherein a horizontal support 20 extends generally perpendicularly
 from an entryway C of a vehicle A. Here, a lift mechanism attached to a
 lift mechanism side of the horizontal support (not shown in this view) has
 been rotated in a clockwise direction (viewed from the platform side) by a
 second actuator (not shown in this view), causing first and second
 connecting links 50, 60 attached to the lift mechanism, to simultaneously
 rotate, thus lowering a platform support 70 and platform 80 to a lowered
 position adjacent a loading surface. As will be later shown and described
 in additional figures, the first and second connecting links 50, 60 are
 attached to the lift mechanism by first and second attachment pins which
 are rotatably received by first and second apertures in the horizontal
 support 20. Note that when platform 80 contacts a loading surface, a
 safety roll-off plate 87 is rotated from a generally vertical position to
 a generally horizontal position, thereby facilitating loading.
 In FIG. 1B, the lift 10 is again in the operative position wherein the
 horizontal support 20 extends generally perpendicularly from an entryway C
 of a vehicle A. Here, the lift mechanism attached to a lift mechanism side
 of the horizontal support (not shown in this view) has been rotated in a
 counterclockwise direction viewed from the platform side by the second
 actuator (not shown in this view), causing the first and second connecting
 links attached to the lift mechanism, to simultaneously rotate, thus
 raising the platform support 70 and platform 80 to a raised position
 adjacent the entryway C and floor D of the vehicle A. As will be later
 shown and described in additional figures, the first and second connecting
 links are attached to the lift mechanism by first and second attachment
 pins which are rotatably received by first and second apertures in the
 horizontal support 20. Note that when the platform 80 is not in contact
 with a loading surface, the safety roll-off plate 87 is biased in a
 generally vertical position, thereby preventing accidental unloading.
 In FIG. 1C, the lift 10 is at an intermediate position midway between
 storage and operative positions as depicted in FIGS. 1D and 1A,
 respectively. Note that the platform 80, has been positioned such that it
 is generally coextensive with the plane of the horizontal support 20. The
 horizontal support 20, along with the lift mechanism 200, platform support
 70 and platform 80 are then rotated about a vertical pivot pin (not shown
 in this view). As shown in the figure, vehicle A has been equipped with an
 enclosure 300, and the lift 10 is swung into an opening 304 in the
 enclosure 300 to the storage position beneath the undercarriage of the
 vehicle A.
 In FIG. 1D, the lift is in the storage position. Note that in the storage
 position, only the lift mechanism side 22 of the horizontal support 20 and
 the lift mechanism 200 are visible.
 The enclosure 300, as depicted in FIG. 2, comprises a top plate 301 and a
 bottom plate (not shown in this view) which are parallel to each other and
 similarly shaped. The top and bottom plates are attached to, and spaced
 apart from each other by a sidewall 303 along a portion of their
 perimeters. The sidewall 303 does not extend entirely around the
 perimeters of the top and bottom plates of the enclosure. Rather, a
 segment of the top and bottom plates is not attached to the sidewall thus
 forming an opening 304 which is sized to accept passage of the lift. An
 aperture 305 is located in the top plate adjacent to one side of the
 opening 304 and a corresponding aperture 302 is located in the bottom
 plate adjacent to one side of the opening, to receive a vertical pivot pin
 320 which supports the lift. The interior of the enclosure includes a
 projection or structure which serves as an attachment for a first end of a
 first actuator. The enclosure 300 comprises an attachment structure may be
 fixedly attached to an undercarriage of a vehicle by any suitable means,
 such as bolts, rivets, welds, etc. While it is understood that the lift
 may be used with or without the attachment structure configured as an
 enclosure 300, it is preferred to use the lift in conjunction with such an
 enclosure because the structure provides support for the vertical pivot
 pin 320 and also protects the lift from the elements. Alternatively, a
 bracket could support the pivot pin 320 and be attached to the vehicles
 undercarriage.
 The arrangement of the lift 10 in relation to the horizontal support 20 can
 be better appreciated in FIG. 3. In FIG. 3, the lift 10 has been rotated
 about the vertical pivot pin (not shown in this view) from the storage
 position (denoted by dashed lines which form the outline of the enclosure)
 to the operative position by the first actuator 40. The first actuator 40
 has a first end 41 which is attached to the attachment or some other
 appropriate anchor point structure and a second end 42 which is attached
 by flanges 31 for example, near the inboard end 23 of the horizontal
 support 20, on the connecting link side 21. As shown in the figure, the
 platform 80 has been lowered so that it is adjacent to a loading surface.
 Briefly, the platform 80 includes a platform support 70 which in turn is
 movably connected to the horizontal support 20 by first and second
 connecting links 50, 60. In more detail, the platform 80 comprises a
 generally rectangularly shaped deck 81 having an inboard end 82, an
 outboard end 83, and opposing sides 84, 85. A side rail 86 is fixedly
 attached to one side 84 of the deck 81, and the platform support 70 is
 fixedly attached to the opposing side 85 of the deck 81. A safety roll-off
 plate 87 is hingedly attached to the outboard end 83 of the deck and
 provides a transition between the deck 81 and a loading surface. As will
 be later shown and described in additional figures, the platform support
 70 and the horizontal support 20 each have been provided with a pair of
 parallel, horizontally oriented first and second apertures which are sized
 to rotatably receive attachment pins which are affixed to and project from
 the first and second connecting links. The horizontal support 20 and the
 platform support 70 may be provided with friction reducing elements such
 as grease fittings, or bearings to reduce friction between the attachment
 pins as they rotate within the horizontally oriented first and second
 apertures of the platform support and the horizontal support,
 respectively. The first and second connecting links attach to the
 horizontal support at a first pair 90 of pivot points. A second pair 91 of
 pivot points connect the wheelchair platform to the connecting links. The
 platform, the horizontal support, and the platform support form a
 parallelogram. Such an arrangement enables the platform to remain parallel
 to the horizontal support as it is raised and lowered. It is understood,
 however, that the lengths of the linkages may be varied as desired to
 permit other lifting and lowering motions.
 The entire lift may be better appreciated in FIG. 4. This is a top view
 showing the lift as it appears in the storage position within the
 enclosure 300 (depicted in dashed lines). Initially, one can observe that
 the first actuator 40 is in an extended mode. In the extended mode, the
 first actuator 40 pushes against the flanges 31 of the horizontal support
 20 and rotates the horizontal support 20 about a vertical pivot pin 320.
 In this figure, the horizontal support 20 is parallel with an entryway of
 a vehicle to which it is attached. Different views of the lift 10 as it
 appears in the operative position can be seen in FIGS. 5 and 6. Referring
 back to FIG. 4, and the lift itself, it can be seen that one side of the
 platform 80 is attached to the platform support 70 and that the platform
 support 70 is attached to the first and second connecting links 50, 60 by
 attachment pins 54, 64, respectively. It can also be seen that a first and
 second attachment pins 53, 63 are attached to the first and second
 connecting links and extend through first and second A apertures of the
 horizontal support from the connecting link side 21 to a lift mechanism
 side 22, where they are attached to a lift mechanism 200. The lift
 mechanism 200 comprises a first bell crank 210, a second bell crank 220, a
 rod 260 and a second actuator 250. The first bell crank 210 is adjustably
 affixed to the first attachment pin 53. The first bell crank comprises an
 attachment collar 211, a first arm 212 which extends radially from the
 attachment collar, a spacer 214 which extends orthogonally from the first
 arm and a second arm 215 which extends orthogonally from the spacer such
 that the first and second arms are parallel and coincident with each
 other. Each of the first and second arms are provided with an aperture,
 sized to receive a fifth attachment pin 230.
 The second bell crank 220 is adjustably affixed to the second attachment
 pin. The second bell crank comprises an attachment collar 221 and a first
 arm 222 which extends radially from the attachment collar. The first arm
 of the second bell crank is provided with an aperture, sized to receive a
 sixth attachment pin 240. A rod 260, with first and second apertures 261,
 262, is rotatably attached to ends of the fifth and sixth attachment pins,
 respectively so that power may be transmitted from the first bell crank
 210 to the second bell crank 220. Power to rotate the first bell crank is
 supplied by a second actuator 250. The second actuator has a first end 251
 and a second end 252, with the first end positioned between the first and
 second arms 211, 215 of the first bell crank 210, and rotatably connected
 to the fifth attachment pin 230, and the second end 252 of the second
 actuator 250 is connected to a mounting bracket 30 on the lift mechanism
 side of the horizontal support 20. In the preferred embodiment, the
 longitudinal axis of the first and second bell cranks are offset from the
 longitudinal axis of the first and second connecting links by about 50
 degrees to avoid having the second actuator and the first and second bell
 cranks line up at top dead center. It is understood, however, that the
 amount of offset may be varied without departing from the spirit and scope
 of the invention.
 The various components of the lift mechanism along with the horizontal
 support, first and second connecting links and the platform support can be
 seen from a different perspective in FIG. 5. Starting with the connecting
 links, the first and second connecting links 50, 60 have first and second
 ends, with the first ends 51, 61 of the first and second connecting links
 having first and second attachment pins 53, 63, respectively, which
 project orthogonally from the longitudinal axis of the first and second
 connecting links 50, 60 in one direction, and the second ends 52, 62 of
 the first and second connecting links 50, 60 having third and fourth
 attachment pins 54, 64, respectively, which project orthogonally from the
 longitudinal axis of the first and second connecting links in a direction
 opposite from the direction of the first and second attachment pins 53, 63
 at the first ends 51, 61 of the first and second connecting links 50, 60.
 To assemble the connecting links to the horizontal support and the
 platform support, the first and second attachment pins 53, 63 are inserted
 into the first and second apertures 25, 26 of the horizontal support 20
 from the connecting link side of the horizontal support 21, and that the
 third and fourth attachment pins 54, 64 are inserted into the first and
 second apertures of the platform support 73, 74 from a connecting link
 side 71 toward the platform facing side 72. The third and fourth
 attachment pins are rotatably retained in the first and second apertures
 of the platform support in a conventional manner, such as circlips,
 washers and nuts, or the like (not shown).
 As described earlier, the first and the second attachment pins 53, 63
 project through the first and second apertures 25, 26 of the horizontal
 support where they are adjustably affixed to first and second bell cranks
 210, 220 which form part of the lift mechanism 200. The lift mechanism 200
 comprises a first bell crank 210, a second bell crank 220, a rod 260 and a
 second actuator 250. The first bell crank 210 is adjustably affixed to the
 first attachment pin 53. The first bell crank comprises an attachment
 collar 211, a first arm 212 which extends radially from the attachment
 collar, a spacer 214 which extends orthogonally from the first arm and a
 second arm 215 which extends orthogonally from the spacer such that the
 first and second arms are parallel and coincident with each other. Each of
 the first and second arms are provided with an aperture 213, 216, sized to
 receive a fifth attachment pin 230. The second bell crank 220 is
 adjustably affixed to the second attachment pin. The second bell crank
 comprises an attachment collar 221 and a first arm 222 which extends
 radially from the attachment collar. The first arm of the second bell
 crank is provided with an aperture 223, sized to receive a sixth
 attachment pin 240. A rod 260, with first and second apertures 261, 262,
 is rotatably attached to ends of the fifth and sixth attachment pins,
 respectively so that power may be transmitted from the first bell crank
 210 to the second bell crank 220. Power to rotate the first bell crank is
 supplied by a second actuator 250. The second actuator has a first end 251
 and a second end 252, with the first end positioned between the first and
 second arms 211, 215 of the first bell crank 210, and rotatably connected
 to the fifth attachment pin 230, and the second end 252 of the second
 actuator 250 is connected to a mounting bracket 30 on the lift mechanism
 side of the horizontal support 20. The offset angle between the first and
 second bell cranks and the first and second connecting links can be seen
 wherein the offset angle is approximately 50 degrees.
 The lift mechanism side 22 of the horizontal support includes a first stop
 28 and a second stop 29 located on either side of the first aperture 25,
 wherein the first and second stops limit the rotational motion of the
 first bell crank 210 by coming into contact with the first arm 212 of the
 first bell crank. The horizontal support 20 is provided with a vertical
 aperture 27 near the inboard end 23, which is sized to rotatably receive a
 vertical pivot pin 320. The horizontal support 20 is rotatably attached to
 the vertical pivot pin 320 in a conventional manner such as a thrust
 bearing or washer attached onto the bottom of the vertical pivot pin.
 FIG. 6. shows the lift viewed from the lift mechanism side 22 of the
 horizontal support 20 while the lift is in the operational position. From
 this position, the lift may be raised, lowered, or rotated between the
 operative and the storage positions. The lift mechanism 200 depicted shows
 the first bell crank 210, the second bell crank 220, the second actuator
 250 and the rod 260 which is rotatably attached to the first and second
 bell cranks as shown and described earlier in FIGS. 4 and 5. Returning to
 FIG. 6, the offset angle between the longitudinal axis of the second
 connecting link and the longitudinal axis of the second bell crank can be
 seen. Although the preferred offset angle is around 50 degrees, it can be
 varied without departing from the spirit and scope of the invention. FIG.
 6 also shows the first and second stops 28, 29 as they are positioned on
 the lift mechanism side of the horizontal support on either side of the
 first aperture. The purpose of the first and second stops is to limit the
 motion of the first bell crank 210, and thus limiting the motion of the
 lift mechanism 200. In operation, the stops 28, 29 come into contact with
 the first arm 212 of the first bell crank 210 as the first bell crank is
 rotated by the second actuator 250. It is understood that the first and
 second stops may be positioned on either side of the first aperture to
 provide various ranges of motion for the lift mechanism, and subsequently
 the platform attached thereto.
 As can be seen the horizontal support member is approximately the length of
 the platform. Although, the length is not critical it should be at least
 one third the length of the platform to allow for sufficient spacing of
 the pivot points on the horizontal support member and the platform.
 The operation of the lift as it translates from a raised to a lowered
 position while in the operative position is illustrated in FIGS. 7A, B7,
 and 7C. These figures do not show the second bell crank or the rod which
 is rotatably connected between the first and second bell cranks as shown
 in FIG. 6. They do serve, however, to illustrate the range of motion which
 may be achieved with the lift mechanism of the present invention.
 In FIG. 7A, the lift is in an elevated position where the deck of the
 platform (not shown) is adjacent the floor of a vehicle. To elevate the
 lift, the first 251 and the second end 252 of the second actuator 250 are
 extended away from each other, thus rotating the lift mechanism in a
 clockwise direction when viewed from the lift mechanism side 22 of the
 horizontal support 20. Although the first arm 212 of the first bell crank
 210 is depicted as being in contact with the first stop 28, it is clear
 that rotation of the first bell crank can be stopped before the first arm
 212 comes into contact with the first stop.
 In FIG. 7B, the lift is midway between the raised position and the lowered
 position wherein the lift is in the same plane as the horizontal support
 20. To lower the lift, the first and second ends 251, 252 of the second
 actuator 250 are drawn towards each other, thereby rotating the lift
 mechanism in a counter clockwise direction when viewed from the lift
 mechanism side of the horizontal support. Note that the first arm 212 of
 the first bell crank is between the first and second stops 28, 29.
 In FIG. 7C, the lift is in a lowered position where the deck of the
 platform (not shown) is adjacent a loading surface 400. To position the
 platform so that it is adjacent a loading surface, the first and second
 ends 251, 252 of the second actuator 250 are drawn further towards each
 other, as depicted in FIG. 7B, thereby further rotating the lift mechanism
 in a counter clockwise direction when viewed from the lift mechanism side
 22 of the horizontal support 20. Note that the safety roll-off plate 87,
 when in contact with a loading surface, is rotated to a generally
 horizontal position to facilitate loading.
 The general operation of a lift in accordance with the embodiment of the
 present invention illustrated in FIGS. 1A, 1B, 1C, and 1D will now be
 described. Starting from the storage position as shown in FIG. 1D, to
 utilize the lift while outside a vehicle, a person will perform the
 following steps. First, the lift will be rotated about the vertical pivot
 pin to the operative position. Then the platform will be lowered adjacent
 to a loading surface. The object to be transported is loaded onto the deck
 of the platform. The platform is then elevated until the surface of the
 deck is level with the floor of the vehicle. The object is then moved into
 the vehicle. The lift is then lowered until the platform is in the same
 horizontal plane as the horizontal support. From here, the lift is rotated
 about the vertical pivot pin into the storage position. To remove and
 object from the, the steps are reversed.
 The present invention may be embodied in other specific forms without
 departing from the spirit or essential attributes thereof, and it is
 therefore desired that the present embodiment be considered in all
 respects as illustrative and not restrictive, reference being made to the
 appended claims rather than to the foregoing description to indicate the
 scope of the invention.