Note: Descriptions are shown in the official language in which they were submitted.
CA 022261S6 1997-12-30
W~FF.I C~HAIR LIET Wll~I W~;~;LCHAIR BARRIER GROUND
INTERLOCK MEC~ANISM
Field of the Invention
The present invention relates to wheelGh~ir lifts, and more particularly, to
5 platform type wheP1Ghqir lifts that include platforms that extend out from the side or
back of a vehicle and move b~ ,el~ a lowered position and a raised position.
Background of the Invention
WhePlch~ir lifts of the type installed in the stairwells of transit vehicles, such
as city buses, are well-known. One type of whePlch~ir lift commonly referred to as a
"step lift,U is illustrated in U.S. Patent No. 4,466,771 to Thorleyet al. (the '771
patent). Another type of whePl~h~ir li~, commonly referred to as a "platform lift," is
illustrated in U.S. Patent No. 4,058,228 to Hall (the '228 patent).
Both whePl~h~ir step lifts and platform lifts typically include a wheelch~ir
platform that is movable from a lowered position in which the wheelchair platform lies
15 adj~cpnt the sidewalk or ground to a raised position in which the whePlchqir platform
lies in the same plane as the aisle way of the bus, train, or other vehicle on which the
lift is mounted. A wheplch~ir is loaded onto the wheelchair platform when it is in the
lowered or raised position at which time the platform is moved to the opposite
position in order to allow the wheelch~ir to be moved into or out of the bus or other
20 vehicle on which the whePlch~ir lift is mounted. In order to decrease storage space
and improve usability, a number of platform-type wheelc.h~ir lifts such as that
described in the '228 patent include wheelch~ir platforms that retract under the bottom
of the bus or other vehicle on which the li~ is mounted. In some wheelch~ir li~s such
CA 02226156 1997-12-30
as that di~rlosed in the '228 patent, the wheelçhsir platforrn forms the lower step of
the vehicle e.llly~,a~,r.
A number of wheelchsir lifts incorporate outer and sometimps inner (with
respect to the vehicle) foldable barriers that help to ..~ sin a wheelrhsir on the
5 wheelchs;~ pl~lr~ . In a l~litiotl~ some wheelchsir lifls include fixed side barriers to
help ...~ the whpelch-s-ir on the wheelch-s-ir platforrn. It would be beneficial if
h~ oved outer and inner barriers could be developed to ensure that a wheelchair
cannot move off the ~I~GeIrh~ ~ platform during operation of the wheelGhsir lift. It
would also be bPnefi~irs~i to provide some type of electrical and/or me~hqnical
10 mecl-~ .. to prevent the whePIrhsir barriers and the whePlrhq-ir lift from opelaling in
an il.,proper manner.
As can be seen from the discussion above, there exists a need in the industry
for whPPIchsir lifts having improved whePIchrsir barriers. The present invention is
directed toward fi)lfilling this need.
Summary of the Invention
The present invention is a whee1rh-s-ir lift that in~.ludes foldable outer and/or
inner wheelrhsir barriers that help to prevent a wheelchair from moving off of the
ends of the whePlrhqir platforrn. In one embodiment, the wheelchair lift includee a
wheelr.hqir plalr~llll that is moveable between a raised position and a lowered
20 position. The wheelchLsir plalr""" in~llldPe at least one wheelchqir barrier pivotally
~stta~.hed to one end of the whePlchqir platforrn. The wheelchsir barrier is moveable
between an P.Ytçn~ed position in which the wheelchair barrier extends outward from
the end of the whePIchqir platform in an upright position in which the wheelch-q-ir
platform extends upward from the surface of the wheelchair platform, and thus
25 prevents an article located on the wl.eclcll~ir platform from moving offthe end of the
wheelchqir plalrollll. The wheelrhqir lift also includes a ground interlock mechqniem
The ground interlock ...ech~lie~m is moveable between an unlocked position in which
the wheelchqir barrier is free to move between an upright position and the e~rtPnded
position and a locked position in which the ground interlock mechqniem meçh~nically
30 prevents the wheelrhqir barrier from moving from the upright position to the eYtended
position.
In accordance with other features of the invention, the ground interlock
me~hqniem Itlllains in the locked position as the wheelGhqir platform moves between
the raised position and the lowered position. The ground interlock mechqni~rn moves
35 from the locked position to the unlocked position when the wheelchqir platform
contacts the ground.
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In accordance with still other aspects of the invention, the wheelch-q-ir barrier is
also moveable to a rel~-cted position in which the wheelchqir barrier lies adj~qcent the
upper surface of the whe~lçh~q,ir platform. Movement of the wheelçhqir barrier to the
retracted position depresses a stow latch on the ground interlock meçhqnism that5 moves the interlock ",eC~ from the locked position to an unlocked and stowed
position.
In accG,dance with still other aspects of the invention, the wheelçhqir barrier
inrhldes a hinge ~eçll~n c.,~ that moves the wheelchq-ir barrier between the eYtçnded
and upright pos;tion~ The ground interlock meçhqnism includes an interlock pin that
10 mer.hqn:cqlly prevents the movement of the hinge mechqniem toward the ~oYt~nded
position when the interlock mer.hq,niem is in the locked position. The ground
interlock mPrhqnism also in~ludes a four-bar linkage includine an input leaf, a coupler
leaf, an output leaf and an interlock leaf. When the ground interlock is moved to the
locked position, the input leaf moves the interlock pin to prevent movement of the
15 hinge m~çhqni5m thus preventing the wheçlchqir barrier from moving from the
upright position to the eYtrnded position.
In accoldance with further aspects of the invention, the ground interlock
mrçh~n.~... includes a biasing meshqnism that biases it into the locked position. The
ground interlock mer.h~nism also includes an electrical sensor that detects the position
20 of the ground interlock mrrl~ ... The electrical sensor provides a control signal
indicative of the position of the ground interlock merhqniem to the wheelçh-q-ir lift's
control system.
In accordance with yet other aspects of the invention, the wheçlcAh-qir lift also
incl~ldes a plalfo"" interlock mechqniem The platform interlock mech~ni~m
25 meçhqnically prevents movement of the wheçlchqir barrier from the upright position
to the retracted position when an article is located on the platform interlock
meçhqniem The plalru-", interlock .lleçh~ em prevents the wheelchair barrier from
moving from the upright position to the retracted position by mech-qn:cqlly preventing
movement of the hinge ...eçh~niem when the platform interlock meçhqniem is in the
30 locked position.
The wheelcl~ lift of the invention helps to reduce or çlimin~te a number of
the plebl~ms aesori~ted with prior art wh~Pl~h~ir lifts. The invention's use of an inner
barrier to form a bridge between the wheçlch~ir platform and the steps of a vehicle on
which the lift is ~o~ ed allows the invention to be used on di~rel-t vehicles with
35 only minor çh~ng~s The same wheelchair lift may be used on d,~elelll vehicles by
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,~dj.~tin~ the height to which the whP,~Içh~ir platform raises and the length of the inner
barner.
The foldable outer and iMer barriers also help prevent a wheelchair from
moving offthe whe~lch~ir platform. The ground interlock meçh~ni~m and platform
5 interlock mec~ also provide redllnd~ncy to ensure that the barriers do not move
in an in"~lopel manner.
Brief Description of the Drawings
The folegoing aspects and many of the attPnd~nt advantages of this invention
will beco~.lc more readily apl,r~cialed as the same becomes better understood byreference to the following det~iled description, when taken in conjunction with the
acco,npan~ing drawings, wherein:
FIGURE lis a perspective view of a wheelch~ir lift according to the present
invention mollnted within the ellll~way of a bus;
FIGURE 2is a pe,~e~ e view of a wheeleh~ir lift of the present invention
showing the wheelrhsir platform retracted within the frame of the whePvlch~ir lift;
FIGURE 3is a perspective view of the wheelch~ir lift of FIGURE 2 showing
the wheelch~ir plalr~""~ in an e~tçnded and a lowered position;
FIGURE 4 is a side elevational view of the whePlGh~ir lift of FIGURE 2
illusl,aliilg the v~l~eplcl~;r platform in a lowered and a raised position;
FIGURE Sis a sGhen~tic re~,esel"alion of the outer whePIr.h~ir barrier of the
wheP1rh~ir lift of FIGURE 2 showing the various operational positions of the barrier;
FIGURE 6Ais a side partial cutaway view of an alternate whe~PIch~ir platform
according to the present invention;
FIGURE 6B is a side partial cutaway view of the wheelch~ir platform of
FIGURE 6A in a depressed position;
FIGURE 7Ais a side partial cutaway view of the outer wheelch~ir barrier and
ground interlock ~.~eçh~ni~." of the whe~P,Irh~ir platforrn of FIGURE 6A;
FIGURE 7B is a side partial cutaway view of the outer wheel~h~ir barrier and
ground interlock illustrated with the plalru"., lifted off the ground;
FIGURE 8Ais a side partial cutaway view of the outer wheelch~ir barrier and
ground interlock in the eYt-Pn~ied position;
FIGURE 8B is another side partial cutaway view of the outer whe~PIc.h~ir
barrier and ground interlock in the ~ n~led position;
FIGURE 9Ais a side partial cutaway view of the outer wheelch~ir barrier and
ground interlock in the retracted position;
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CA 022261~6 1997-12-30
FIGURE 9B is another side partial cutaway view of the outer whePlr.hqir
barrier and ground interlock in the retracted position;
FIGUR~ lOA is an enlarged partial cutaway view of the middle section of the
whe~lrhqir lift plalru.,.. of FIGURE 6A;
FIGURE lOB is an enlal~,ed partial cutaway view of the outer section of the
whcelc~ lift platform of FIGURE 6A in an unlocked position;
FIGURE lOC is an enlarged partial cutaway view of the inner section of the
whe~lGhqir lift plalru..n of FIGURE 6A in an unlocked position;
FIGURE 1 lA is an enlar~ed partial cutaway view of the middle section of the
10 whe~lçhqir lift plalro.... of FIGURE 6B in a depressed position;
FIGURE 1 lB is an enlarged partial cutaway view of the outer section of the
whe~lçh~: Iift platform of FIGURE 6B in a locked position;
FIGURE 1 lC is an enlarged partial cutaway view of the inner section of the
wheelchqir lift plalrû..., of FIGURE 6B in a locked position; and
FIGURE 12 is a top partial vul~ay view of the wheelr.h~ir lift platform of
FIGURE 6A.
Detailed Desc,iL.Iion ofthe Preferred Embodiment
A plalru-----type wheelchqir lift generally dçsi~l ~ted 20 constructed accordingto the present invention is illustrated in FIGURES 1-3. The wLcf~lçl~qir lift20
incl~dçs a generally re.ilq-~lg~ q-r stationary frame 22 that is mounted to the underside
of a vehicle such as a bus or train. A wheelchair platform frame generally
desi~nated 24 (FIGURE 3) is slidably mounted within the stationary frame 22 so that
the platform frame may move between a first or retracted position (FIGURE 2) in
which the plalrull,l frame is retracted underneath the floor of the vehicle to a second
25 or eYtended position (PIGURE 3) in which the platform frame 24 extends outward
from the vehicle on which the wh~e1çh~ir lift is mollnted A whe~lçh~ir platform 26is
mounted within the plalro"" frame 24 through the use of outer platform arms 28 and
inner platform arms 30 so that the wheelch~ir platform may be moved from a lowered
position as best seen in phantom in FIGU~ES 3 and 4 to a raised position as shown in
30 FIGURE 4.
When the platform frame 24 is fully extended and the wheelçh~ir platform 26
is in the lowered position (shown in phantom in FIGURES 3 and 4), a whe~lçh~ir
occupant may maneuver a wheelçh~ir onto or off of the wheçlch~ir platforrn 26. The
whcclr.~ p1alro".l 26 is then moved to its raised position (FIGURE 4), at which
35 time the wheelçh~ir occ~lp~nt may maneuver the wheelchair into or out of the interior
of the bus or other vehicle, as described in more detail below.
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CA 022261~6 1997-12-30
The plall'ol,l, frame 24 is moved between the PYtPn-led and retracted positions
by a belt drive tnech~n~ dçci~qted 32. The belt drive meçhqnism 32 is attqched to
the plal~llu frame 24 be~ outer and iMer cross members 34 and 36 that extend
across the width of the platform frame. The belt drive mechqni~m 32 extends and
S retracts the plalrullll frame 24 by moving the platform frame along a primary belt 38
that extends bcl~,en an outer cross mPmher 40 and an inner cross member 42 of the
stationary frame 22 as best illustrated in FIGURES 2 and 3 and as described in more
detail below.
The v~l.e~lch~;l pldlfollll 26 is raised and lowered through the use of the outer
10 and iMer arrns28 and30. The arms28 and 30 are attached at one end to the
wl.cclch~;r platform 26 and at the other end to two platform frame arms 44 that form
the opposing sides of the pldl~ll.l frame 24. The outer and inner arms 28 and 30 are
rotated around pivots on the platform frame arms 44 through the use of opposing
pairs of parallel drive links 46. Each drive link 46 ~IGU~E 4) is rotatably -q-ttr~hed
to an e1ong~ted end of the iMer arms 28 and 30 (as best seen in FIGURE 4) as
described in more detail below. As the drive links 46 are moved outward or inward
with respect to the platform frame arms 44, they cause the outer and inner arms 28
and 30 to rotate with respect to the platform frame arms. Each drive link 46 and thus
outer and iMer arm 28 and 30 is driven by hydraulic actuator 48. Each hydraulic
actu~qtQr 48 is att, ~e~ at the, ctuqtor end to the inner end of the platform frame
arms 44 and at the rod end to the inner end of the drive links 46 as best illustrated in
FIGURE 2 and as described in more detail below.
The wheçlchsir platform 26 includes a foldable outer wheelc.hsir barrier 50,
and a fo~dqhle whePlrhqir platform extension and inner wheçlchqir barrier 52, asshown in FIGURE 4. The outer and inner barriers 50 and 52 help to ensure that a
whPPlchqir and wheel~hqir occupqnt remain on the wheelr.hq-ir platform 26 duringoperation of the wheelchqir lift20. The de.t~qiled structure and operation of the
whePlchair platform and the foldable barriers will be described in more detail below.
The leclq~y~lqr stationary frame 22 includes two opposing side mçmhers 56
(FIGURE 2) that are separated by and joined together by the outer cross member 40,
a middle cross member 58, and the inner cross member 42. The three cross
mçmhPrs 40, 58, and 42 are located above the frame side members 56 and are joined
to the frame side mPmhPrs at each end by angle pieces 60 that are welded or
otherwise fq-~tçned to the frame side members 56 and the cross mçmhP.rs 40, 58, and
42. The angle pieces 60 also serve as mounting brackets to attach the stationary
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CA 022261~6 1997-12-30
frame 22 to the underside of a vehicle or other structure by bolting, welding, or other
suitable f~tçni~ methnd
Each frame side n.f~...her 56 incllldes upper and lower inwardly eYten~ling
f~long~ted rails 62 and 64 as inf~ic~ted in FIGURES 2 and 3. The platform frame 24 is
5 slidably mounted within the stationary frame 22 through the use of a series of slide
bearings 65 molmted along the length of the platform frame arms 44. Each slide
- bearing 65 extends oul~ald from the outer surface of the respective plalru,~n frame
arm 44 into a slot formed by the upper and lower rails 62 and 64. It is advantageous
to form the upper and lower rails 62 and 64 of wear resistant stainless steel or other
10 material which does not corrode or pit and the slide bearings 65 out of a low friction
material such as nylon, Teflon, or another suitable low friction bearing material.
The platrùll,, frame 24 is formed of the opposing side platform frame arms 44
that are joined together by the outer cross member 34 (FIGURE 3) and the inner
cross member 36. The inner cross mçn hPr 36 is located approxil"ately adjacçnt to
15 the inner end of the platform frame arms 44 while the outer cross member 34 extends
between a midpoint of the platform frame arrns. The cross members 34 and 36 are
~ttaçlled to the platform arms44 by welding, bolting, or other suitable f~tf~ning
method. As described briefly above, the platform frame 24 is moved between its
eYtçnded and retracted positions as shown in FIGURES 2 and 3 by the belt drive
20 mecl.sn:s... 32.
The belt drive ~.,çr.l~ m 32 includes two opposing parallel support plates 66
that are spaced apart and joined at opposite ends to the outer cross mf~mhf r 34 and
inner cross member 36 by welding, bolting, or other suitable f~tening method. A
drive motor 68 is mounted on one of the plates 66 such that the shaft of the drive
25 motor extends through one of the plates 66.
A drive reduction belt 76 extends around a drive pulley (not shown) on the
shaft of the drive motor 68 and around a larger secondary pulley 78. The larger
secondary pulley 78 is rotatably mounted on a drive axle that is connected to a smaller
secondary drive pulley 80. The secondary pulley 78 serves as a reduction pulley to
30 decrease the speed and increase the torque from the drive mo~or 68.
A p.i~.a y belt38 (FIGURES 2 and 3) extends over the secondary drive
pulley 80 and an inner idler pulley 82 and an outer idler pulley 84 that are mounted on
either side of the smaller secondary drive pulley 80. The inner end of the p.ima-y
belt 38 is att~ched to the lower surface of the inner cross memher 42 by a quick35 release clamp 86 ~IGURE 3) that is bolted or otherwise releasably ~tt~ ed to the
rear cross ~--f ~--he- 42 of the stationary frame 22. The outer end of the plh~aly
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07/lS/ff S 38 PU
CA 022261~6 1997-12-30
belt 38 is similarly Att~lGhed to the outer cross member 40 of the stationary frame 22
by a quick release clamp 90.
As the shaft of the drive motor68 rotates counterclockwise, the large
secondary pulley 78 and small second~ry drive pulley 80 rotate counterclockwise.5 The counterclockwise movement of the small secondary drive pulley 80 causes the
belt drive 32 and thus platform frame 24 to move outward along the length of thep~;m~ belt 38, thus eYtending the platform frame. Similarly, as the shaft of the drive
motor 68 is rotated clockwise the platform frame 24 moves inward along the length of
the p,i",a,~ belt 38, thus retracting the platform frame. The movement of the drive
10 motor 68 and thus platform frame 24 is controlled by a control system (not shown)
that is connected to the drive motor 68.
As ~liccussed briefly above, the wheelchAir platform26 is ~ttached to the
platform frame arms 44 by outer arms 28 and inner arms 30 that form a parallelogram
linkage b~lween the plalro,l,. frame arms and the wheel~hsir platform. The
15 parallelogram linkage keeps the plalro,frame arms 44 and wheelchAir platform 26
parallel throughout the movement o'f the wheelchAir platform from a lowered position
to a raised position and vice versa. The ends of the arms 28 and 30 Attarhed to the
platform frame arms44 are elongated (FIGURES 3 and 4) and include laterally
spaced apart pivots that are ~tt~hed to the platform frame arms 44 and the drivelinks 46. As best seen in FIGURE 4, the lower portion of the elon~ted portion of the
arms 28 and 30 is pivotally att~hed to the platform frame arms 44 at pivots 100
and 102, respecti~/ely. The upper portion of the elongate portion of each arm 28and 30 is attached to a drive link 46 at pivots 104 and 106, respectively. As the drive
links 46 are moved outward or inward with respect to the platform arms 44 as best
seen in FIGURE4, the outer and iMer arms28 and 30 pivot about pivots 100
and 102, l.,spe~ ely, thus lowering or raising the platform 26.
The iMer end of each drive link46 is attached to the rod of one of the
hydraulic ar,tllAtors 48 at a pivot 108 as best seen in FIGURES 2 and 3. The inner
arms 30 are also joined together at the pivot points 102 by a torque tube 110 that is
welded or otherwise f~ct~ned to the inner surfaces of the inner arms 30. The torque
tube 110 ensures that the iMer arms 30 move in unison and thus ~ Ain the same
orientation with respect to each other. The torque tube 110 allows the two hydraulic
~ctu~tors 48 to work to~ether and also ensures that if there is a mAlfi~nction in the
wheelGh~ir lift the platform 26 is mA;l~lAined at the same elevation on both sides and
does not cant or lean, possibly causing harm to the wheelchair occupant.
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The drive links 46 are moved outward or inward with respect to the platform
frame arms 44 by the PYtçnQ;on or retraction of the rods of the hydraulic actuators 48.
The hydraulic actuators 48 are ~qtt~q~çhçd to the drive links 46 at pivots 108 at one end
and are pivotally att~-hed to the platform frame arms 44 at pivot points 112 at the
other end as best seen in FIGURE 3.
In order to assist the platform 26 in clearing the stairs 124 (FIGURES 1, 2 and
4) of the bus or similar vehicle on which the wheelchair lift 20 is mol~ntefl, the
ends 120 and 122 of the arrns 28 and 30, respecli~rely, are bent upward or inward as
shown in FIGURE 4. Configuring the whe~lçh-q-ir lift as shown with arms 28 and 30
10 having elongated portions ~qttqçhPd at the upper end to a drive link 46 and at the
lower end to a platform frame arm 44 and inwardly bent ends 120 and 122 helps the
whçPlchqir platform 26 to clear the stairs 124 (FIGURE 4) without requiring an
excessive eYt~nsiQn ofthe plalro~ frame 24 out from underneath the stairs 124.
As best seen in FIGURE 4, the outer and inner wheelchqir barriers 50 and 52
lS are rotatably ~tt~~hçd to the front edge of the wheelçhvir platform 26 and the rear
edge of the wheP1çh~ir plalrollll re3pecli~ely~ The rear edge of the outer barrier S0 is
rotatably att~~-hed to the front edge of the wheelch~qir platform 26 over its length by
hinge 146 (FIGURE 3). The outer barrier rotates about the hinge 146 such that it is
movable from a fully folded position as illustrated in FIGURE 2, to a fully ~,Yten~ed
20 position as illustrated in phantom in FIGURE 4. The inner barrier 52 (FIGURE 4) is
rotatably mollnted to the inner edge of the platform 26 using a hinge 184. The inner
barrier 52 is movable b~ ,en a fully retracted position in which the upper surface of
the inner barrier 52 lies adiaeent to the upper surface of the whcelc~ platform 26, as
illustrated in phantom in position 256, to an upright position illustrated in phantom in
25 position 188, to a fully eYtçnded position 186 in which the upper surface of the inner
barrier 52 forms an çYtPn~ion of the upper surface of the wheP1ch~ir platform 26 as
shown in FIGURE 4.
The structure and operation of the outer and inner wheelchair barriers 50 and
52, ~es~,c~ ,ly, will now be described by reference to FIGURES S and 12. The rear
30 edge of the outer barrier S0 is rotatably ~tt~ched to the front edge of the wheçlrh~ir
platform 26 over its width by the hinge 146 as seen in FIGURE SA. As illustrated in
FIGURE 5, the outer barrier S0 rotates around the hinge 146 such that the barrier is
movable from a fully retracted position 172 in which it is in an overlapping
relationship with the wheP1~hqir platform 26, to a fully çYtçnfled position 176 in which
35 barrier S0 extends in approxiately the same plane as the wheelch~ir platform.
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-10-
As shown in FIGURE 5, in the fully retracted position 172, the lower
surface 148 of the outer barrier 50 faces upward and forms the bottom stair step 124
of the vehicle in which the wheelch~ir lift 20 is mounted (see phantom steps in
FIGURE 2), while the upper surface 150 of the outer barrier lies adjacent the upper
surface of the platform 26. In its fully eYtçnded position 176, the outer barrier 50
extends ou~ d from the end of the wheelçh~ir platform 26. The upper surface 150
of the outer barrier 50 slants upward to form a tri~n~ r shape such that in its
PYtPn~ed position 176 the outer barrier forrns a ramp that helps a wheelch~ir occu
to move a whePlrhsir up the ramp and onto the wheçlçh~ir platform 26.
As shown in FIGURE 12, the barrier 50 is moved between its PYtçn~ed and
retracted positions by a hydraulic cylinder 152 that is mounted on opposing spaced-
apart support frames 154 and 156 that run the length of the whePl~h~ir platform 26.
The hydraulic cylinder 152 incllldçs a rod 158 that is mollnted to a hinge
...ecl~ni~ 160 at its free end. The hydraulic cylinder 152 is ct nnected to a hydraulic
control system (not shown) through hydraulic lines 164 and 166.
The prerelled çmhor~inlPnt of the hinge meçhsnism 160 is described in more
detail below. In alternate embo~ nPnts, the hinge meçh~ni~m 160 could be any
suitable hinge ...eçl-~ni~m capable of moving the outer barrier 50 through
apploxi...~tPly 180~ of movement so that the outer barrier may be moved between its
20 PYtPnded and retracted positions. One suitable hinge meçh~ni~m is described in
United States Patent No. 5,284,418 to Kempf, the disclosure of which is hereby
speçifirslly incorporated by reference.
In a1dition to serving as a ramp, the outer barrier50 also serves as a
whePlchsir barrier to prevent a wheçlch~ir located on the wheelçh~ir platform 26 from
25 moving off the outer edge of the whePlch~ir platform. The various positions of the
outer barrier 50 are best illustrated in FIGURE 5. From the fully retracted
position 172, the barrier 50 can move upward, pivoting on hinge 146 to an unl~tc.hed
position 174. When the barrier 50 is in the unlatched position 174, the platformframe 24 can be moved between its eYtçnded and retracted positions, as described30 above. Once the plalrullll frame 24 is in its extended position, the outer barrier 50
moves from the l~nlstched position 174 to the approx,..,ately upright position 180.
When the platform 26 is lowered to the ground, the barrier 50 moves from the upright
position 180 to the fully PYsPnded position 176 in which the outer barrier serves as a
ramp between the ground and the platform. Once a wheelchair is located on the
platform 26, the outer barrier 50 moves back to the upright position 180 in which it
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CA 022261~6 1997-12-30
acts to prevent a whPPlçh~ir from moving off of the front of the whP,el~hqir
platform 26.
The outer barrier in its upright position 180 can also act as an energy-
al-s~ ption, energy-~lic~;p~tioll safety barrier to absorb or discip~te some of the energy
5 of an impact with a whePlr.h~ir located on the whePlçh~ir platform 26. In order to
absorb and diccipate the energy of collision, the control system 237 (FIGllRE S) that
controls the hydraulic cylinder 152 can include a pressure relief valve 239 that is set at
a predetermined pressure. When a whee~ch~ir rolls into the outer barrier 50, the outer
barrier moves from the fully upright position 180 to a partially lowered position 182
10 as the hydraulic fluid plesa.-le in the hydraulic cylinder 152 is relieved by the press.~le
relief valve239. The movcl"elll of the outer barrierS0 between the upright
position 180 and partially lowered position 182 allows the outer barrier to absorb and
r~iCcipqte part of the energy of collision between a wheelch~ir and the outer barrier,
thus helping to reduce any injury to the whePlr.h~ir occ~lp~nt or damage to the
15 whePlr-hqir or lift.
The control system 237 detects the various positions of the outer barrier 50
through the use of two prox~lluly sensors 236 and 238 (FIGURES 5 and 12) and a
p-o~ uly plate 240 ~IGURES 5 and 12). The proximity sensors 236 and 238 are
mounted on the support frame 156 while the proximity plate 240 is mollnted on the
20 rod 158 such that it moves outward and inward along with the rod. The proxil~uly
sensors 236 and 238 are used to provide a digital indication of the various positions of
the outer barrier 50. Each sensor 236 and 238 provides a "0" or "1" signal depending
on whether part of the ploAilluly plate 240 which is formed from a target material is
located in front ofthe sensor. A "1" signal is given from a sensor which has the target
25 material in front of it. The h~ alion from the sensors is thus digital in nature.
As shown in FIGURE 5, when the outer barrier 50 is in its fully e~Pnded
position 176, the p-o~illlily plate 240, which moves with the rod 158, is in front of
both of the pro~i....ly sensors 236 and 238 and thus provides the control system with
a (1,1) position signal indication. The (1,1) signal is comprised of the signal from the
sensor 236 as the first digit, and the signal from the sensor 238 as the second digit.
The signals co--c~ponding to each range of positions are shown sçhem~tirelly above
the various positions of the outer barrier 50 in FIGURE 5. When the outer barrier 50
reaches the fully upright position 180, the plo~h~ y plate 240 has moved inward to a
point where a cut-out section of the plate 240 is in front of sensor 236 and a lower
eYten~ed part of the plate 240 is in front of the sensor 238, thus providing the control
system 237 with a position in~1ication of (0,1). As the outer barrier 50 moves slightly
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CA 022261~6 1997-12-30
past the upright position 180 towards the retracted position 174, the cut-out section
of the p~o~i" ily plate 240 is in front of both of the sensors 236 and 238, which thus
provides the control system with a position indication of (0,0). When the rod 158 has
moved inward to the point that the outer barrier 50 is in the lmlntçhed position 174,
5 an upper PYtçnded portion ofthe plo~illlily plate 240 is in front ofthe sensor 236, and
the cut-out section is in front of the sensor 238, thus providing a position indication of
(1,0). The position indication of (1,0) is provided to the control system throughout
the outer barrie~s movement from the l~nl~qtched position 174 to the stowed and
latched position 172.
Failure of the sensors 236 and 238 can cause the control system to receive
erroneous signals as to the outer barrier's position. For example, if the sensor 236
were to fail low, it would output a conslanl "0" signal regardless of the position of the
plate 240. The outer barrier 50 is dçsigned to make the lift safer with regard to the
motion of the outer barrier 50 should sensor failure occur. Safety during the period
when the barrier 50 is moving from the ~Ytçnded position 176 to the upright
position 180 is illlpo,l~,lt because a paCcenger may be on the lift. The dangers during
outer barrier movement are that due to sensor failure the barrier 50 will fail to move
far enough upwards towards the upright position 180 to properly protect the
pqCse~r~ or that the barrier 50 will move past the upright position 180 and trap or
crush a person or object between the barrier 50 and the wheelchair platform 26. Such
dangers are avoided using the sensors 236 and 238.
The following example helps illustrate how the sensors 236 and 238 are used
to increase barrier safety. Once a passenger has boarded the platform 26, the lift is
dçciered to move the outer barrier 50 from the extended position 176 (FIGURE 5B)to a position just pa~t the upright position 180 and then immedi~q~tçly back to the
upright position again. Thus, using the above binaly design~qtions, the control system
begins rolaling the barrier clockwise from the ramp (1,1) position and continuesrotating it until it receives a (0,0) sensor signal, which will occur immerliqtely afler the
normal upright (0,1) position. The control system then rotates the barrier 50
counterclockwise back toward the eYtPn-led position 176 until it receives a (0,1)
sensor signal which occurs almost immedi~tely.
When a sensor failure occurs, it outputs a constant '0' reading regardless of
whether or not the sensor plate 240 is in front of the sensor. There are three possible
sensor failures which can occur and hinder the normal operation of the barrier 50.
First, the sensor 236 can fail by itself, second, the sensor 238 can fail by itself, and
third, both sensors can fail at the same time.
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If only one of the two sensors 236 or 238 fails while the barrier 50 is moving
clockwise from the eYt~nded position 176 to the upright position 180, the control
system will receive either a (0,1) signal or a (1,0) signal, (dep~-nrline on which sensor
failed). The control system waits for a (0,0) signal before it stops moving the
5 barrier 50 during this seqll~ne~, so it continues to move the barrier 50 even when this
type of sensor failure occurs. Thus the danger of the control system prel~alurely
stopping the barrier50 from leaGhing the upright positionl80, and inco,,eclly
inte,l,reli~,g that it had in fact reached the upright position is avoided.
If under these cir.;~ . t~-ces the sensor238 failed, then when the control
system moves the barrier 50 to the upright position 180, the usual (0,1) signal will
instead register as a (0,0). As a result, the control system will incorrectly interpret
that it has reached a position just past the upright position 180 and will stop the
barrier 50. Once the (0,0) signal is received, the control system moves the barrier 50
counterclockwise, looking for a (0,1) signal. In this case, sensor 238 has failed, so a
15 (0,1) signal will not occur and the barrier 50 will continue to move all the way back to
the eYtetlded position 176. The control system, having not ever received the proper
(0,1) signal, will not allow the platform to be raised.
If instead the sensor 236 fails, the control system will still receive the correct
(0,1) signal at the upright position 180, and will move the barrier 50 to the position
20 just past the upright position 180, where the control system receives a (0,0) signal and
stops the barrier 50. The control system then moves the barrier 50 counterclockwise
until it receives a (0,1) signal, stopping the barrier in the upright position 180.
In the event that both sensors 236 and 238 fail during movement of the barrier
from e~ nded position 176 to upright position 180, the control system will stop
25 barrier 50 at whatever point the double failure occurs, since it will receive a (0,0)
signal. The control system then moves the barrier 50 back the other way searching
for the (0,1) sensor signal, which will not occur. Thus the barrier50 will move
counterclockwise back to the e~nrled position 176. The control system, having not
ever received the proper (0,1) signal, will not allow the platform to be raised. Thus,
30 in all three possible cases of sensor failure, the control system prevents the barrier 50
from ll~ping or crushing a person or object located on the platform.
As mentioned above, the wheelcll~ir platform 26 also includ~s a movable inner
barrier 52, as illusllaled in FIGURES 4 and 12. The outer edge of the inner barrier 52
is rotatably mounted to the inner edge of the platform 26 using the hinge 184. As was
35 illustrated in FIGI~RE4, the inner barrier52 is movable from a fully retracted
position 256, to an upright position 188, to a fully extended position 186. In its fully
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upright position 188, the inner barrier 52 prevents a wheelchair from moving off the
inner edge of the WheC'lrllAi~ platform 26. In its fully PYtended position 186, the iMer
barrier 52 forms a bridge between the wheelchsir platform 26 and the stairs 124 of the
bus on which the lift 20 is mounted so that a wheelchsir may exit the wheelçhsir lift
5 and enter the interior ofthe bus 124b or other vehicle.
As shown in FIGURE 12, the inner barrier 52 is actu~sted using a hydraulic
cylinder 190 that is connected to the control mer.hsni~m by hydraulic lines 192
and 194. The rod 196 of the hydraulic cylinder 190 is connected to a hinge
".ech~nic.~ 198 that aetuvtes the inner barrier 52. The hinge me~.hsni~m 198 may be
similar to the hinge .. eçh~ m 160 used to actuate the outer barrier 50. In a manner
similar to that used on the outer barrier 50, it may be advantageous for the control
system to include a pr~,s;,.J.~ relief valve (not shown) that allows the inner barrier 52
to absorb part of the energy of a collision between a wheelchs-ir and the inner
barrier 52.
In a manner similar to that described with respect to the outer barrier 50, the
inner barrier 52 includes a positiQnsl indication system consisting of two pro~-imily
sensors244 and 246 (one sensor is shown in FIGURE 12, the other sensor is
mol~nted directly bPn~th sensor 244) and mounted on the support frame 156, and apro~in~ly plate 242 mounted on the rod 196 such that the plate 242 moves oulu,dld
and inward along with the rod 196. The two proximity sensors 244 and 246 and
proxi~...ly plate 242 function in a manner similar to the proximity sensors 236 and 238
and proxil...ly plate 240 described above with respect to the outer barrier 50 and are
used to provide a digital indic~tiQn of the various positions of the inner barrier 52.
Each sensor 244 or 246 provides a "0" or "1" signal depending on whether part of the
25 pro~i----ly plate 242 which is formed from a target material is located in front of the
sensor. A " 1 " signal is given from a sensor which has the target material in front of it.
The h~...,alion from the sensors is thus digital in nature.
In addition to the folcl~sble barriers 50 and 52, the wheelchs-ir platform 26 also
incl~des opposing hand rails 250 (FIGURE 2) that extend upward from the opposing30 edges of the wl.e~lr~ platform. The hand rails 250 may be placed within one of
rnultiple recesses 252 located on the side of the wheelchair platform 26. The multip'c
ecesses 252 allow the position ofthe hand rails 250 to be adjusted. This adjllstmçnt
allows the wheçlchsir lift 20 to be used in di~len~ vehicles while still allowing the
hand rails 250 to be positioned so that they do not interfere with the steps or doors of
35 the vehicle. The hand rails 250 are secured within the recesses 252 by pins that
extend through the hand rails 252 and holes 260 (FIGVRE 4) in the walls of the
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recesses The hand rails 250 could also be secured within the recesses by other
suitable fqctçning methods
The general operation of the whPPl~h~ir lift 20 will now be described. During
standard operation of the bus or other vehicle on which the whePlçhsir lift 20 is
S mounted, the whçPlçhqir lift20 is ~ ed in its stowed position (FIGIJRE2)
underneath the bus. When the vehicle stops in order to load a wheçlçh-q-ir onto the
vehicle, the whePl~hqir lift 20 moves as follows. First, the pla~r~"", frame 24 is moved
to its fully eYtPnded posi~ion by the belt drive meçhqnism 32. Once eYtP~n~e~1, the
outer and inner barriers 50 and 52 are moved to upright positions by hydraulic
achlstors 152 and 190 (FIGURE 12). As shown in phantom in FIGURE 4, the
platform 26 is then lowered into contact with the ground by arms 28 and 30 which are
a~lste~ by drive links 46 (FIGURE 3) which are ~ctu~ted by hydraulic actuators 48.
As the outer edge of a wheelchqir platform26 nears the sidewalk wheels258
(FIGURE 4) located at the front edge of the wheçlc.hqir platform 26 contact the
15 ground and allow the wheelchsir plalro""26 to move in and out on the ground
slightly as the vehicle tilts or rolls due to vehicle suspension movement duringoperation of the whePlçhqir lift. Once the wheelchair platforrn 26 contacts the
ground, the control system stops the downward movement of the WhP,Plchqir
plalrc,...~ 26. The outer barrier 50 is then moved to its fully eYt~nded position 176 as
illustrated in FIGVRE 5.
Once the whe~plçhqir lift is fully deployed, a wheelch~ir occupant moves his or
her wheçlçhq-ir up the ramp formed by the outer barrier 50 onto the whP,Plchsir
platforrn26. Af~er the wheelchsir is on the wheelchair platform26, the outer
barrier 50 moves to its upright position 180, as shown in FIGURE 5. As shown in
FIGURE 4, the v~he~lc~ plall~llll 26 is then raised to its fully raised position by the
arms 28 and 30 and drive links 46 and hydraulic actuators 48. Once the upper surface
of the wheelGhsir platform26 lies in the same plane as the upper surface of the
stairs 124b (shown in ph~ntom in FIGURE 4), the inner barrier 52 moves to its fully
e~tçnded position 186 such that the inner barrier 52 bridges the gap between thewheelçh~ir plalfo"" 26 and the stairs 124b. The wheelchair occupant may then move
the whe~lç~ into the interior of the bus or other vehicle over the inner barrier 52.
In order for a whe.o~lGh~ir to be lowered from the interior of the bus to the sidewalk
the whe.olchsir lift operates in reverse order. A~er loading or unloading a wheçlçh~ir,
the whçelçhsir plal~"~ 26, barriers 50 and 52, and platform frame 24, move to their
fully retracted and stowed position, as illustrated in FIGURE 2.
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The wheelch~ir platform26 is constructed with electrical and me~h~nical
barrier interlocks that prevent the inner or outer wheelc.h~ir barriers 50 and 52 from
op~.alin~ in ways which could alter the barriers to fold inward onto an occup~-l or
other item located on the wheelch~ir platform. The prefe~red embodiment of the
5 wheelrhqir pldtru~ 26 is illustrated in FIGURES 6-12. As seen in FIGURE 6A, the
wheelrh~i~ plalru~..26 inrludes a structure frame generally design~ted as 304, adeck 307, the outer barrier 50, iMer barrier 52, outer and inner hinge me.ch~l-is...~ 160
and 198, the hydraulic cylinders 152 and 190, and the rods 158 and 196, along with
ground interlock ~e~ icm 440 (FIGURE 7A), and a movable deck plalru.l..
10 interlock ,..~rh~l~ic... 502.
In the p-er~..ed embo~lim~nt the outer barrier linkage utilizes a plurality of
flat bar linlages incllldine co....e~;~;ne links 344, control links 352, and floating
links 354 to disl~ilJule the loads unilaterally throughout the lin~ee. Although the
prer~l.ed embodiment of the hinge mecl-~ni~n, 160 is described below, the hinge
15 ,eçh~l-is could be any suitable hinge me~h~nicm capable of moving the outer
barrier 50 through applo~iln~lely 180~ of movement so that the outer barrier may be
moved from bel~een its eYtended and retracted positions.
As de3_,il,ed above, the outer barrier 50 is actu~ted by the outer hinge
meçh~rlic~ 160 and hydraulic cylinder 152. The outer end of the rod 158 of the
hydraulic cylinder 152 is mounted to the inner end of a clevis 340 (FIGI~RE 12) by a
cylinder nut 342. The outer end of the clevis 340 is rotatably ~ttached to the inner
end of four cQnnectine links 344 ~IGURES 7B and 12) using a clevis pin 360.
Plastic self lubricating bl~hingc are used in the connecting links 344 to provide low
friction and to serve as a dielectric to .~ini~ni7e corrosion between the connectine
links 344 and the clevis pin 360. The outer ends of the connectine links 344 arerotatably ~ttll-hed ~FIGURES 7A and 12) to four control links 352 near their outer
ends using a pivot pin 362 (FIGURES 7A and 12).
As the cylinder rod 158 (FIGllRE 16) moves inward from its outermost
position, the barrier linkage 160 moves the outer barrier 50 from a fully eYtPnded
position, as shown in FIGURES 8A and 8B, to an upright position, as shown in
FIGURES 7A and 8B, to a fully retracted position, as shown in FIGURES 9A and
9B. As seen in FIGURES 7B and 12, the four control links 352 are also rotatably
~tt~hed on their outer ends to the inner ends of the four floating links 354 using a
pivot pin 364 (FIGURE 8B). As illustrated in FIGURE 8B, the outer ends of the four
control links 352 are rotatably attached to the outer ends of the four connecting
links 344 inward from the att~chment point of the floating links 354 at pivot pin 362.
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CA 022261~6 1997-12-30
The inner ends of the control links 352 are rotatably q.~t~qçhed to a frame lug 358
located on the outer end of the wheell hqir platform 26 using pivot pin 368. Snap
rings (not shown) on the ends each of the pivot pins 362, 364, and 368 are used to
n.~ P;.~ the pivot pins and respective control links in place. Bushings or other types
S of bearing are used in the various links to minimize the friction between the links and
the pivot pins.
The outer ends of the four floating links 354 are rotatably attnched to a
midpoint of the outer barrier 50 at a pivot block356 (FIGURE 9B) by a pivot
pin 366. The pivot block 356 is releasably f~tçned to the outer barrier 50 usingcapscrews 357 that extend through the upper surface 334 of the outer barrier and are
received in the pivot block 356. ~ttn~.hing the pivot block 356 to the outer barrier 50
using Ca~Js~ilt;~,.i~ 357 allows the pivot block to be removed or replaced easily. After
removing the capscr~ws, the pivot block356 may be removed from barrier50
through an opening (not shown) in the inner end of the outer barrier 50. Removing
the pivot block 356 through the opening in the end of the barrier allows the pivot
block356 to be removed without removing a step tread359 covering the lower
surface 332 of the outer barrier 50. This configuration helps to prevent possible
damage to the step tread 359 and also eases ~ s~mbly of the outer barrier 50 andlinkage 160.
The att~hmPnt between the c-~nnecting links 344 and the structure frame 304
will now be di~cussed in more detail in reference to FIGURES 7B and 12. Clevis
rollers 326 are rotatably attllched to the outer ends of the clevis pin 360. The clevis
rollers326 are captured within and roll in upper and lower tracks328 and 330
(FIGURE llB) which are fixed to and extend inward from both of the parallel
frames 154 and 156. As diccussed above, the frames 154 and 156 are located on
either side of the pivot pin 360 and control links 344 and extend over the length of the
wheP~lchqir platform. The tracks 328 and 330 guide the clevis rollers 326 in and out
as the rod 158 moves the clevis 340 and clevis pin 360 inward and outward.
As ~ cu~ed above, the whpplçh~ir platform 26 also includes a movable inner
barrier 52, as seen in FIGURES 6A and B. The outer edge of inner barrier 52 is
rotatably mounted to the inner edge of the deck 307 over its width by the hinge 184
(FIGURE lOC). The inner barrier 52 is movable between a fully eYt~nded position
(FIGURE 4), to an upright position, to a fully retracted position.
As shown in FIGURE 12, the inner barrier 52 is ~ctll~ted similarly to the outer
barrier 50 using the hydraulic cylinder 190 which is connected to the control
meçl~ ... by hydraulic lines 192 and 194. The inner end of the rod 196 is connected
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to the outer end of a clevis 380 using a cylinder nut 382. The inner end of the end of
the clevis 380 is rotatably att~~hed to the outer end of the hinge .~.ech~ 198 using
a clevis pin 400 ~FIGURE 10C). The hinge merh,q,nism 198 is mec.hqnicslly sirnilar to
and operates in a similar manner to the barrier linkage 160 used to actuate the outer
5 barrier 50.
As shown in FIGURES 10C and 12, the hinge mechqni~m 198 inrh1(1es four
parallel connectine links 384, four control links 392, four floating links 394 and a
releasable pivot block (not shown). The connectine links 384, control links 392,floating links 394 and pivot block are assembled and operate in a similar manner as
10 previously described with respect to the barrier linkage 160. Thus, the outer ends of
the connectine links 384 are rotatably ~q~tt~q~rhed to the inner end ofthe clevis 380 using
a clevis pin 400. The inner ends of the connecting links 384 are rotatably ~qttr~hed to
the control links 392 near their inner ends using a pivot pin 402 (FIGllRE 10C). The
inner ends of the control links 392, oul~ard from the ~qttqrhmPnt points at which the
connectine links 384 attach at pivot pin 402, are also rotatably attqrhed to the outer
ends of the flo. tine links 394 using a pivot pin 404. The outer ends of the control
links 392 are rolalably att;lched to a frame lug 398 using a pivot pin 408. The frame
lug 398 is ~ttached to the inner end of the wheelçh~ir platforrn 26. The inner ends of
the floating links 394 are rotatably att~ched to the inner barrier 52 at the pivot block
20 using a pivot pin 406.
Clevis rollers412 are rotatably attached to the outer ends of the clevis
pin 400. The clevis rollers are captured within and roll in upper and lower tracks 414
and 416 which are fixed to and extend inward from the parallel frames 154 and 156
located on either side ofthe clevis pin 400 and hinge mech~ni~m 198. The upper and
25 lower tracks 414 and 416 capture and guide the clevis rollers 412 in and out as the
rod 196 (PIGURE 12) moves in and out.
As described above, it is impol lanl that the wheelchair lift incorporate features
to prevent the inner and outer whPelchqir barriers 50 and 52 from eYten~line or
retracting ~I.lprop~lly. The p.er~"ed embodiment of the wheelchqir lift incorporates
30 the electronic position control system, namely the respective ploxilnily plates 240 and
242 and proxil~uly sensors 236, 238, 244, and 246 in order to provide the control
system data ,egarding the position ofthe outer and inner barriers 50 and 52.
In ~ditiQn to electronic controls features, the prere~led embodiment also
includes a ground interlock mech~ .. 440 (FIGURES 7-9) and a platform interlock
~.. ech~n ~.. 502 ~IGURES 6-12). The ground interlock mec.hqni~m 440 and platform
interlock mechqni~m 502 are also provided to mechanically limit improper movement
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- -19-
of the outer and inner barriers 50 and 52. The ground interlock mech~niem 340 and
plalrol,l, interlock mec.l-Al~is... 502 are used to prevent the inner and outer barriers 50
and 52 from moving to their fully eYt~nded or fully retracted positions at an improper
time. For eY~mple, it is ill-pOll~ll that the outer barrier 50 not move to its fully
eYtended position while a wheelcll~ir is on the platform and the platform is in motion.
As shown in FIGURES 7A and 7B, the ground interlock .~ecl~niem 440
in~ des a skid bar 442, an input leaf 444, a coupler leaf 446, an interlock leaf 448, an
output leaf450, a fixed leaf452, a stow lever454, return springs456, and an
interlock pin 466. Skid bar 442, input leaf 444, coupler leaf 446, interlock leaf 448,
output leaf450 and fixed leaf452 are generally planar and extend partially across the
width of the whePleh~ir plalr~." 26. The input leaf 444 is rotatably mounted on its
outer edge to the outer edge ofthe wheelçh~ir platform 26 using a pivot pin 460. The
inner edge of the input leaf 444 is rotatably attached to the outer edge of the coupler
leaf446 using a pivot pin462. The wear resistant skid bar442 is mollnted to the
bottom surface of the input leaf444 using fasteners such as rivets (not shown). As
tliscueee~ below, the skid bar442 contacts the ground during operation of the
wheelch~i~ lift and serves as a protective cover for the bottom of the input leaf 444.
The inner edge of the coupler leaf 446 is rotatably ~tt~clle(l to both the inneredge of the interlock leaf448 and the outer edge of the output leaf450 using a pivot
pin 464. The upper edge of output leaf 450 is rotatably ~ttaclled to the upper edge of
the fixed leaf 452 using a pivot pin 470. The outer edge of the interlock leaf 448 is
rotatably att~ched to the interlock pin 466. The interlock pin 466 is slidably mollnted
within interlock slots 458. The interlock slots 458 extend through the frames 154
and 156 on which the rails co~ g the clevis rollers 326 are mounted
The slots 458 extend at an angle such that the outer edges of the slots are
higher than the inner edges of the slots. As shown in FIGURE 7B, the outer edge of
each slot 458 is positioned so that when the interlock pin 466 is slid all the way to the
outer edge of the slot 458, it is moved upward into the path of the clevis rollers 326,
thus preventing the clevis rollers from moving outward past the interlock pin 466. As
illustrated in FIGURE 8B, when the interlock pin 466 is slid inward to the inner edge
of the slot 458, it moves dow..~drd and is positioned below the clevis rollers 326,
thus allowing the clevis rollers, and thus connecting links 344, to move outward past
the interlock pin 466.
As illustrated in FIGURE 7A, a lower spring keeper 474 seats on the hinge
pin462 co--~-ec~ P. the input leaf444 and the coupler leaf446. An upper spring
keeper 476 is connected to a pivot pin 468 that is connected to the frame of the
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wheelçhsir platrol,.. 26. The return springs 456 are connected between the upper and
lower spring keepers 476 and 474 and provide a biasing force which biases the pivot
pin 462 do~.. a~d, as illustrated in FIGURE 7A. In the prerelled embo~linnent three
return springs 456 are placed as shown over the width of the whe~lch-qir platform 26
S (FIGURE 16).
In the prer~--ed embodiment, the skid bar 442, input leaf444, coupler
leaf 446, and output leaf 450 extend over the majority of the width of the whe~lçhqir
plalro-.,~ 26 to both sides of the hinge meçhqni~m 160 (FIGURE 16). The interlock
leaf448 (FIGURE 16) is actually two separate parts that extend over central areas of
10 the whce1cl-q;~ pl&lrollll 26 in front of the forward frame 156 and in back of the rear
frame 154. The interlock pins466 extend slightly beyond the edges of interlock
leaves 448 into the respective interlock slots 458 in the frames 156 and 159.
As illustrated in FIGURES 7-9, the pivot pins 460 and 470 are fixed to the
frames 154 and 156 and the fo.~d.J and rear edge of the wheelchqir platform 26.
15 This confi~ration causes the ground interlock me~hqni~m 440 to act as a four bar
linkage col..hil-ed with a slider crank. As illustrated in FIGIJRES 7A and 7B, when
the wl.f~,lcl-qil plàlr~ .. 26 is not to~lçhing the ground, the ground interlock...cçh~nis-~ 440 is in an llnl ~rl~ed state in which the return springs 456 bias the pivot
pin 462 dO~ 4ald away from the pivot pin 468 as illustrated by arrow 469 (FIGURE7A). In its unlocked state the biasing action of the return springs 456 causes the
lower end ofthe output leaf450 to be biased outward by the dow--wal-l movement of
the coupler leaf446. This in turn moves the interlock leaves 448 and thus interlock
pins 466 outward and upward so that the interlock pins 466 are moved upward to the
outer edge of the interlock slots 458. When the interlock pins 466 are located at the
outer edges ofthe interlock slots 458, they prevent the clevis rollers 326 from moving
outward past the interlock pins 466, as shown in FIGURE 7B. The ground interlockmecl-~ni5.~. 440 thus prevents the outer barrier 50 from moving beyond an upright
position (FIGURE 7B) when the wheelch-qi~ platform 26 is not cont<qcting the ground.
Thus, the ground interlock ...Cch~ .. 440 prevents a wheelchair from moving off of
30 the outer end of the wheelch-q-i~ platform 26 when the wheelchair platform is not
co~t~qcting the ground.
As the whee1chqir pldl~.-.. 26 moves downward to where the skidbar 442
contn~ts the ground (FIGURES 8A and 8B), the skidbar442 is pressed upward,
causing the input leaf444 to pivot counterclockwise about hinge pin460. The
35 counterclockwise rotation of the input leaf444 causes the inner end of the input
leaf 444, and thus the outer end of the coupler leaf 446 and pivot pin 462, to move
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upward against the biasing force of the return springs 456. As the pivot pin 462moves upward, it causes the inner end of the coupler leaf446 and pivot pin 464 to
move inward, as illustrated in FIGURE 8A. The inward ",ove",enl of the pivot
pin 464 causes the interlock leaves 448 to move inward, thus sliding the interlock
5 pins 466 (FIGURE 8B) downward and inward to the inner edges of the interlock
slots 458. As the interlock pins 466 move downward, the ground interlock
merl-~niL-.. 440 moves to its unlocked position in which the interlock pins 466 are
moved out of the way of the clevis rollers 326, thus allowing the outer barrier 50 to
be moved to its fully eYt~n~ed position, as illustrated in FIGURES 8A and 8B.
10In ad~itiQn to ~--n'--- cally blocking the clevis rollers 326 and connectine
links 344, when the ground interlock me~h~ni~m 440 is in the locked position, the
interlock ...cch~nis-.. also in- ludes an electronic sensor 478 (FIGURES 7B and 8B).
The elecll~ sensor 478 sends a signal to the control system to prevent extension of
the outer barrier 50 until the interlock mech~ni~m 440 has contacted the ground. As
15shown in FIGURES 7B and 8B, the electronic sensor 478 is mounted to the fixed
leaf 452 and faces the inner side of the output leaf 450. The sensor 478 operates such
that when the output leaf450 rotates counterclockwise about the pivot pin470
toward the fixed leaf and sensor 478, the sensor 478 detects the position of the output
leaf450 and sends a signal to the control system. The signal provides the control
20 system an in-lir.~tion that it is allowed to move the outer barrier 50 to the eYtended
position. Until the sensor 478 provides the control system a proper signal, the control
system is both ~h~ lly and electrically prevented from moving the outer
barrier 50 to the fully eYtçnded position.
As illustrated in FIGURES 7A and 7B, when the wheelch~ir platform 26 is not
25 cont~cting the ground, part of the ground interlock mecll~ni~m 440 hangs below the
lower surface of the whPPlch~ir plalro~,l,. It is desirable when the wheçlch~ir
platform 26 is to be stowed under the bus, to make the ground interlock
meçh~l~iG-.. 440 as co",~act as possible to save space and help prevent damage to the
interlock ...~,h~ni~n~ 440 during retraction of the platform. Thus, it is beneficial to
30 move the interlock ...çch~ni~m 440 to its locked position in which it folds
appro~i~n~lely flat with the lower surface of the wheelchair platform 26
(FIGURES 9A and 9B) when the platform is being stored. The ground interlock
n~ecl-Ani~m 444 incllldes a stow level 454 to move the interlock meçh~ni~m to its
locked position when the outer barrier is folded flat and the wheelch~ir platform is
35 retracted.
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The stow lever 454 is alt~~hed to the outer surface of the output leaf450.
The stow lever454 extends Oul~a~d and upward from the output leaf450 such that
the outer end of the stow lever extends slightly above the upper surface of the
whe~lc~ plalrollll 26 when the interlock mech~nism 440 is in its locked position, as
S illustrated in FIGURES 7A and 7B. As illustrated in FIGURES 9A and 9B, when the
outer barrier 50 is moved into the fully retracted/stowed position for plepa-~lion of
the wheelch~ir plalr~ l being stored under the bus, the top of the stow lever 4S4 is
contacted by and pushed downward by the upper surface of the outer barrier 50. As
the top of the stow lever 454 is pushed dOwll~àid by the outer barrier 50, the output
leaf 450 rotates counterclockwise about pivot pin 470 as shown by arrow 471. Therotation of the counterclockwise output leaf 450 moves the coupler leaf 446 and input
leaf444 inward, causing the outer end of the coupler leaf446 to hinge upwards
clockwise about pivot pin 462, and also causing the inner end of the input leaf 444 to
hinge up~4ards counterclockwise about fixed pivot pin 460, against the biasing force
of the return springs 456. Thus, the ground interlock mech~nicm 440 is placed in the
folded, unlocked position in which interlock mech~nicm 440 is most compact and
least susceptible to d~mage.
In a1~lition to the ground interlock meçh~nicm 440, the p-ere-led embodiment
of the wheelch~ir plalro.... 26 also inchldes the platform interlock meçh~nicm 502 to
20 prevent the outer and inner barriers 50 and 52 from moving/folding toward their
retracted positions onto a pacsçneer or other article located on the wheelGh~ir
platform. The operation of the plalro.... interlock mech~nicm 502 is shown with
reference to FIGURES 6-12. The platform interlock mecll~niSm 502 includes a
floating deck plate 308 (FIGUl~E 6A), outer and inner interlock links 504 and 506,
25 outer and inner interlock pins 518 and 522 (FIGURES IOB and lOC), outer and inner
control levers 510 and 514, return springs 508 and an electronic sensor 534.
The platform interlock ...ech~nism 502 operates in a manner similar to the
ground interlock mer.h~nic... 440 in that it uses outer and inner interlock pins 518 and
522 (FIGURES lOB and lOC) to block the path of the clevis rollers 326 and 412 and
connectirg links 344 and 384 so that the inner and outer barriers 50 and 52 are
m~ ni~lly prevented from moving/folding toward their retracted positions onto a
paCce-~er~ as described in detail below.
As shown in FIGURES 6A and 6B, the floating deck plate 308 is formed with
a slight upward camber, which allows the deck plate 308 to act as a large leaf spring
that is rotatably att~c-hed along its opposing ends wheelch~ir to the inner and outer
ends of the plalro~ 26 by an outer pivot pin 542 (FIGURE 10B), and on the inner
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end to the upper edge of a pin leaf 52 using a pivot pin 544 (PIGURE 10C). The
lower end of the pin leaf 552 is rotatably connected to the wheelc.h~ir plalrulm frarne
using a pivot pin S48. The use of the cambered deck plate 308 pivoted at the outer
and iMer ends allows the deck plate to deflect downward when a weight is placed on
the deck plate as deselil.ed in more detail below.
The center of the deck plate is supported by inner and outer interlock
links 504 and 506. A pair of inner and a pair of outer interlock links 504 and 506 are
mounted below the deck plate and move upward or downward and inward and
outward as the deck plate deflects upward or downward as described below. As
10 shown in FIGURE 10A, the control levers 510 and 514 are positioned underneath the
deck plate308 near the center of the wheelchair platform26. As shown in
FIGURES 10A and 12, the upper ends of a pair of outer control levers 510 are
pivotally connected to the inner ends of each outer interlock link 504 and the upper
ends of a pair of inner control levers 514 are pivotably connected to the outer end of
15 each inner interlock link 506. One control lever 510 or 514 is located on either side
of each interlock link 504 and 506, respectively. The lower ends of the outer control
levers510 are pivotably connected to the platform frame26 using pivot pins512
while the lower ends of the inner control levers 514 are pivotably connected to the
platforrn frame26 using pivot pinsS16. The upper ends of the outer control
20 levers 510 are rotatably connected to the inner ends of the outer interlock links 504
using pivot pins 520. The upper ends of the inner control levers 514 are pivotally
conl-r,cled to the outer ends ofthe inner interlock links 506 using pivot pins 524.
A return spring 508 is connected between the inner end of each outer interlock
link 504 and the outer end of each m~tçlling inner interlock link 506 using outer and
25 iMer spring retainers528 and 530, respectively (FIGURE 10). The spring
retainers 528 and 530 are c-~nnected to walls that extend downward from the
respective ends of the inner and outer interlock links 504 and 506. The return
springs 508 bias the inner and outer interlock links 504 and 506 apart, thus biasing the
upper ends of the control links 510 and 514 upward against the lower surface of the
30 deck plate 308.
As illustrated in FIGURE 10B, the outer ends of the outer interlock links 504
are connected to the interlock pins 518. The interlock pins 518 are slidably mounted
within slots 526 that extend through the platform frames 154 and 156 (FIGURE 12)on which the rails 328 and 330 col.~ g the clevis rollers 326 are mounted. The
35 slots 526 (FIGURE 10B) extend at an angle such that the outer edge of each slot is
higher than the inner edge of each slot. As shown in FIGURES 10B and 1 lB, the
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inner edge of each slot 506 is positioned so that when the interlock pin 518 is slid
dow"wdrd all the way to the inner edge of the slot 526, the outer interlock pin 518
prevents the clevis rollers326 from moving inward past the interlock pin518.
However, as illustrated in FIGURE lOB, when the outer interlock pins 518 are slid
ouLwàld and upward to the outer edge of the slot 526, the outer interlock pins 518
are pos;tion~d above the clevis roller 326, thus allowing the clevis rollers, and thus
connP,cting links 344, to move inward past the outer interlock pins 518.
As illustrated in FIGURE lOC, the inner end of each inner interlock link 506 is
conl-e~iled to an interlock pin 522. Each inner interlock pin 522 is slidably mounted
10 within a slot 532 that extends through one of the platform frames 154 and 156(FIGURE 12) on which the rails 414 and 416 co~ il,;ng the clevis rollers 412 aremounted. Each slot 532 extends at an angle such that the inner edge of the slot is
higher than the outer edge of the slot. As shown in FIGURE 11 C, the outer edge of
the slot 532 is positioned so that when the interlock pin 522 is slid outward and
15 downward to the outer edge ofthe slot 532, the interlock pin 522 prevents the clevis
rollers 412 from moving oulwald past the interlock pin 522. However, as illustrated
in FIGURE lOC, when the interlock pin 522 is slid inward and upward to the inneredge of the slot 532, the interlock pin 522 is positioned above the clevis rollers 412,
thus allowing the clevis rollers 412 and the connecting links 384 to move outward
20 past the interlock pin 522.
FIGURES lOA-lOC show the platform interlock meçh~nicm 502 with no
psCsçnger on the plàlrollll deck plate 308 and the interlock mech~nism in an unlocked
state, and FIGURES llA-llC show the platform interlock meçh~ni~m 502 when a
p~csçnger has moved onto the deck plate 308 and the platform interlock mer.h~nism in
25 a locked state. As a p~Cserleer moves onto the deck plate 308 of the wheçlch~ir
platform, the leaf spring action of the deck plate 308 causes its center to deflect
downward. The dc,wnward movement of the deck plate 308 presses the upper ends
of the control levers 510 and 514 downwards, thus causing the control levers to
rotate downward about fixed pivot pins 512 and 516, respectively. As the ends of the
control levers 510 and 514 rotate dow.. w~rd, as illustrated by arrows 555
(FIGURE lOA), the inner and outer ends of the interlock links 504 and 506,
respectively, are pulled towards the center of the platform 307. As the interlock
links 504 and 506 are pulled toward the center of the platform, spring retainers 528
and 530 are also moved inwards and compress the return springs 508. As the
35 interlock links are pulled toward the center, the outer end of the outer interlock
link 504 and the inner end of the inner interlock link 506 also move toward the center
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of the pl~lrol.ll, causing the interlock pins 518 to move from the outer edge ofslots 526 ~FIGURE 10B) to the inner edge of slots 526 (PIGURE 1 lB), and causingthe interlock pins 522 to move from the inner edge of slots 532 (FIGURE 10C) to the
outer edge of slots 532 (FIGURE 11C). Thus, the platform interlock mec.h~nis... 507
5 is moved into its locked state. In the locked state, the interlock pins 518 block the
path of the clevis rollers 326 and connecting links 344 from moving further inward,
and the interlock pins 522 blocks the path of the clevis rollers 412 and connecting
links 384 from moving further outward, thus preventing the outer and inner
barriers 50 and 52, respectively, from moving/folding toward their retracted positions.
In addition to the mer.hsnical locking provided by the interlock pins 518 and
522, the psCseng~r interlock ~ncchsl)icm 502 also includes an electronic lockingfeature to prevent the outer and inner barriers 50 and 52 from moving/folding toward
their retracted positions when a paCsp~nger is on the deck plate 308. As the deck
plate 308 is pressed dow~ ald by a ps~spnger moving onto the wheel~hsir platform, a
target plate 536 (FIGURE 10A), which is fixed perpendiculsr to the deck plate 308,
also moves dOwllwald in front of an electronic sensor 534 that is molmted on theframel54 (PIGURE12). When the sensor534 senses the target plate536, it
provides a signal to the control system in-licflting that a passenger or other article is
on the wheelchsir platform. As long as the control system receives a signal indicating
that a paCcpn~er or other article is on the wheelch~ir platform, it electronically
prevents the control system from moving the outer or inner barriers 50 and 52 toward
their retracted positions.
Once a psCseneP~r moves off of the wheel~hsir platform 26, the platform
interlock rnP,çhs~ni~m 502 returns to the unlocked position shown in FIGURES 10A-
10C through the force of the return springs 508 and the preset camber spring force of
the deck plate 308. The return springs 508 and camber spring force of the deck
plate 308 are used to offset the weight of the deck plate 308 and the friction of the
pac~PngPr interlock system 502 in returning the system to its normal, unlocked state.
The whePlçhsir lift 20 of the present invention reduces or e~ ec a number
of the problems s-csoçisted with prior art wheelchair lifts. The use of an innerbarrier 52 to form a bridge between the wheelchair platforrn 26 and the steps 124b of
the bus allows the whePl~h-s-ir li~ to be used on di~elenl vehicles with only rninor
r.hsnges The same design wheelçh-s-ir lift 20 may be used in di~renl vehicles byadjusting the height to which the wheelchair platform 26 is raised and the length of the
inner barrier or bridge 52.
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The whePlGhoir lift 20 also incorporates a number of features to prevent or
reduce the pGs~ y of improper operation of the wheelchair lift. Such fealules
include fold-'ole outer . nd inner barriers 50, 52 to prevent a whP,PI~hqir from moving
off of the wheelçhqir plalro"" 26. The electronic control system that controls the
5 whP~PIGhsir barriers is designed to prevent the barriers and lift from operating in ways
and at times which could allow the barriers to fold inward onto a whePlçhqir,
whePIchqir occupqnt or other item located on the wheçlrhqir platform, even if sensor
failure occurs.
The whçplchqir life inchldçs redl.nd~nt merh~niçql and electronic locking
10 ...eçh~ c."~ A ground interlock mPçhqnicm 440 also both merh~qnically and
electrically p,e~e.,ls the outer barrier 50 from moving to its fully eYten.led position
while the whçelçhqir plalru,m 26 is not touching the ground.
The ground interlock meçhoni~m 440 incllldes a stow lever 454 which serves
to fold-up the ground interlock mec.honicm 306 for storage.
While the plere"ed embodiment of the invention has been illustrated and
described, it will be appre~idled that various changes can be made therein without
departing from the spirit and scope of the invention.
LIUI\9~PI DOC
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