Lift device with variable speed actuation

A lift device of the type appended to a vehicle such as a tailgate lift or wheelchair lift. The lift includes a platform movable between a lower or ground position, an upper or load position and stowed position. The platform assumes a horizontal orientation in the ground and load positions and is pivotable to a vertical orientation when stowed for vehicle movement. The platform is connected to a lever arm assembly and further includes hydraulic apparatus to move the platform between ground, load and stowed positions. The hydraulic apparatus is actuated by a pump and motor assembly which includes an electric motor for actuation of the pump and hydraulic apparatus. By varying the speed of the motor, the speed of the platform between various platform orientations can be varied.

DETAILED DESCRIPTION OF THE INVENTION The present disclosure does not depict a wheelchair lift apparatus other than that shown as prior art in FIG. 1 for the actual wheelchair lift apparatus in the form of a platform, parallelogram linkage and hydraulic cylinder do not change from structures shown in the prior art incorporating the present invention. Specifically, the present invention continues to employ mobile platform 12 , hydraulic system 14 and parallelogram mechanism 13 . As in the prior art, the operation of the lift involves hydraulic ram or cylinder 38 which operates in the upper parallelogram structure 17 to open and close the parallelogram. Lower parallelogram structure 19 retains an open configuration during the transporting or raising-lowering motion patterns but collapses or closes during the storage motion pattern as a result of its engagement with upper parallelogram structure 17 . In addition to the use of a pump assembly such as assembly 36 of the prior art affixed to the outside of rear armature bracket 28 for support, the present invention also includes the equivalent of pump 40 to actuate cylinders 38 and a motor 42 to drive the pump and reservoir 44 to supply and accept fluid to and from hydraulic drive system 14 . Where the present invention differs from the prior art is the use of variable speed motor 42 in order to accurately control the speed of pump 40 and therefore the pressure of hydraulic fluid within hydraulic cylinders 38 . Through the use of variable speed motor 42 , the moving orifice of FIG. 3 and hydraulic lines of varying dimension can be eliminated thus significantly simplifying actuation of platform 12 between its different orientations eliminating the need for a very costly valve component. In further detail, an electrical schematic of one embodiment of the present invention is shown in FIG. 4 . In this embodiment, the electric motor 42 is a standard DC motor. The operation of the lift is controlled by two switches SW 1 and SW 2 . By design, only one of these switches can be in the “ON” position at a given time. Switch SW 1 operates to raise or lower the lift, and switch SW 2 folds and unfolds the lift. Three position switches LS 1 , LS 2 and LS 3 operate to enable or disable the various possible movements of the lift, depending upon the position of the lift. The position switches also control the speed of the electric motor. For example, if switch SW 1 is “ON” and the lift is in the maximum “UP” position, then the position switches LS 1 and LS 2 operate to apply appropriate control signals to the two solenoid valves SV 1 and SV 2 to lower the lift. Similarly, if the lift is completely folded, and switch SW 2 is selected, the position switches LS 1 and LS 2 operate to apply the appropriate signals to the two solenoid valves SV 1 and SV 2 to “unfold” the lift. The effective electric motor speed is controlled by a combination of two switches SS 1 , SS 2 and a resistance R. The two speed switches SS 1 and SS 2 are, in turn, controlled by the position switches LS 2 and LS 3 . If switch SS 1 is enabled by the position switch LS 3 , a DC voltage from the battery 200 is reduced by the series resistance R, thereby reducing the speed of the motor 42 This slow speed is used when the lift is being folded. However, if switch SS 2 is enabled by the position switch LS 2 , the battery 200 is directly connected to the motor 42 , resulting in a higher speed of operation. The higher speed is used to raise or lower the lift to and from ground level. Thus, the electrical controls provide two different operational speeds, depending upon the relative position of the lift. FIG. 5 is a schematic of the hydraulic system according to the present invention. However, instead of having complicated valving to control the speed of the lift, the valves are of a fixed design, and the speed is controlled by controlling the speed of the motor pumping the hydraulic fluid. Specifically, the electric motor 42 connects to a gear pump to pump the hydraulic fluid in the system. The hydraulic cylinder connection to the lift is as depicted in the prior art. As noted previously, the present invention is also adaptable for use in a folding tailgate lift system of the type shown in Maxon Industries' U.S. Pat. No. 4,836,736, the disclosure of which is incorporated by reference. The application of the variable speed motor to a typical tailgate lift mirrors that of the wheelchair lift previously discussed. This is because a tailgate lift goes through the same operational movements of stow/deploy and up and down as does a wheelchair lift. Also, as previously noted, the variable speed motor discussed above can also be employed in an automobile lift assembly of the type found in garages for under chassis work. Such lifts, as shown in FIG. 6 , move only along a single vertical axis 101 , but it is oftentimes desirable to vary the speed of lifting and collapse for safety reasons. This can be accomplished through the use of the present invention without need for complex plumbing or restricted orifices. Specifically, vehicle 200 is caused to be supported on foldable support brace 201 . Support brace 201 moves along channel 202 located within each upright frame member 300 . Movement of support brace 201 within channel 202 can be done by use of hydraulic cylinders (not shown) located within each upright frame member 300 . The present variable speed motor can cause support brace 201 to, for example, lift vehicle 200 faster than the vehicle is lowered for safety reasons.