Dual hydraulic, parallelogram arm wheelchair lift

In a dual-arm parallelogram wheelchair lift, having a platform connected to spaced, dual parallelogram arm lifting assemblies pivotably mounted to speed base members, a base plate to which base members carrying said arm assemblies are attached, and a generally rectangular bridgeplate for spanning a gap between an inboard end of the lift platform and an outboard edge of said base plate, said lifting assemblies moving said platform from a first lowered level to an intermediate higher transfer level, and thence rotating said platform to a generally vertical stowed position, and back, the improvement which comprises in operative combination therewith;

• a) said base plate is generally rectangular, and has an outboard edge, an inboard edge and two side edges;
• b) said bridgeplate includes means for pivotally attaching said bridgeplate to said base members adjacent said inboard edge above said base plate so that said base plate pivots upwardly upon the stowage motion of said platform;
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• c) said pivotal attachment is disposed so that upon said bridgeplate pivoting upwardly a gap is provided between the now-raised inboard edge of said bridgeplate and said base plate so that debris is easily clearable from the area between the bridgeplate and the base plate.

In a dual-arm hydraulic parallelogram wheelchair lift, having a platform connected to spaced, dual parallelogram arm lifting assemblies pivotally connected to spaced base members, a base plate to which said base members carrying said arm assemblies are attached, and which includes at least one hydraulic cylinder oriented diagonally across said parallelogram arm assemblies, said lifting assemblies moving said platform from a first lowered level to an intermediate higher transfer level, and thence rotating said platform to a generally vertical stowed position, and back, the improvement which comprises in operative combination therewith;

• a) said hydraulic cylinder has a longitudinal axis along which the hydraulic cylinder rod reciprocates, a base cylinder end, and a projecting rod having an external end;
• b) said base cylinder end and said external end of said rod each have a transverse bearing sleeve, and each of said sleeves have a central aperture therein for engaging a fixed pin so that said rod end and cylinder end pivots on said pins;
• c) a pair of pin members mounted in association with a parallelogram arm assembly, each pin member receivingly engaged in said bearing sleeves at the external end of said rod and at said cylinder end respectively, said pins being non-rotatably fixed with respect to the arms of said parallelogram assembly to which they are mounted;
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• d) said fixed pin providing extended bearing surface to said bearing sleeve to reduce channel hole elongation from extended use under load.

Method of lifting a wheelchair user with a hydraulic dual parallelogram arm wheelchair lift having a platform pivotally attached at an inboard end to a pair of spaced-apart parallelogram arm lifting assemblies, each of said assemblies including a base member, an end link and a pair of spaced arms forming with said end link and said base member generally a parallelogram, at least one of said lifting assemblies being hydraulically actuated from a first lowered level to an intermediate higher transfer level and thence rotatable to a generally vertical stowed position and back, comprising the steps of:

• a) actuating said hydraulic cylinder to pull while lifting said platform upwardly from said lowered position by fluid pressure on a shaft side of said hydraulic cylinder so that a shaft of said cylinder is substantially withdrawn into said cylinder when said lift is in its generally vertical stowed position;
• b) purging air in said hydraulic fluid which accumulates in said hydraulic cylinder upon gravity down operation of said lift during each cycle from its stowed and transfer levels to the transfer and lower levels, respectively;
• c) spreading the rotational and pulling forces from said hydraulic cylinder across large surfaces of fixed pins in the arms of said arm assemblies;
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• d) said pull, purging and force spreading steps improving synchronization, reducing drift and/or spongy operation, and reducing arm misalignment binding, said loading and parallelogram arm pivot pin bushing elongation.

In a wheelchair lift having dual parallelogram-type arm lifting assemblies including a base member, an end link and a pair of spaced arms each of which is pivotally connected to said base member and said end link at the ends of said arm to form generally a parallelogram, a platform connected to said lifting assemblies moveable thereby from a first lowered level to an intermediate higher transfer level and thence rotatable to a generally vertical stowed position, and back, the improvement comprising in operative combination therewith:

• a) a microswitch trigger assembly is provided to at least one inboard end of one of said arms forming said parallelogram;
• b) said microswitch trigger assembly follows the lifting movement of said parallelogram linkages and triggeringly engages a plurality of microswitches, each at different predetermined platform positions during said lifting and stowage movements;
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• c) said microswitch trigger assembly includes means for positioning adjustment of each of said microswitches, both along an arcuate path and at an angle of inclination with respect to a horizontal adjustment setting for each of said microswitches.

In a wheelchair lift having a dual, parallelogram-type arm lifting assembly, a platform connected to said lifting assembly moveable thereby from a first lowered level to an intermediate higher transfer level and thence rotatable to a generally vertical stowed position, and back, at least one hydraulic cylinder assembly actuating each said lifting assembly for movement between said first lowered level, said intermediate transfer level and said vertically stowed position, and a base assembly for mounting said lifting assembly to a vehicle floor to which is mounted said lifting assembly by pivotal connections, the improvements comprising in operative combination therewith:

• a) each of said parallelogram assemblies includes a base member, an end link, and a pair of arms, each of which arm pairs is pivotally connected to said base member and said end link at opposing ends of each of said arms, said arms forming with said end link and said base member generally a parallelogram;
• b) each pair of arms and end link of said parallelogram comprise U-channel members having spaced side walls sized for receiving a hydraulic cylinder nestable therewithin;
• c) said hydraulic cylinder assembly comprises a cylinder having a base end mounted to an upper, inboard pivot connection of said parallelogram and a rod end mounted to a diagonally opposite lower, outboard pivot connection of said parallelogram, and said cylinder assembly is single-acting and is oriented substantially parallel to a diagonal axis across the parallelogram of at least one lifting assembly, said axis being a long axis when the lift is in its first lowered level and a short axis when the lift is in its stowed position;
• d) each said hydraulic cylinder assembly is connected with a fluid power source to pull while lifting said platform upwardly from said lowered position by fluid pressure on a rod side of the hydraulic cylinder, and to operate gravity down;
• e) said hydraulic cylinder is oriented in the platform stowed position with the rod retracted into the cylinder and the cylinder is oriented base-end down;
• f) a hydraulic fluid inlet-outlet of said cylinder is located adjacent an upper rod inlet end of said hydraulic cylinder assembly to provide purging of air accumulating inside said cylinder upon each gravity down portion of an operational cycle;
• g) said pivotal connections of said parallelogram arm lifting assemblies include fixed pin and sleeve means for reducing elongation of pivot bushings associated with said pivotal connections;
• h) said fixed pin and sleeve means are removably secured within the various components of said parallelogram assemblies to permit convenient replacement of said pivot bushings;
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• i) said orientation and linkage of said hydraulic cylinder improves synchronization, reduces drift and/or spongy operation, and reduces arm misalignment binding, side loading and parallelogram arm pivot pin bushing elongation.