VEHICLE SCISSOR LIFT

Abstract: The scissor lift has two parallel sets of legs (12, 14). Each set has one end of an outer leg (12) pivoted on a base (10) and the other end slideable on the elevating platform (22) One end of the inner leg (24) of each set is pivotally connected to the platform (12) while the other end slides on the base (10). The mid portion of the legs (12, 24) are pivotally connected on a pin (32) which also supports a crank (34) which can rotate about 90° between a first generally horizontal position in which the actuated end (36, 42) of the crank (34) is eccentric to an imaginary line connecting the pivot pin (32) and the pivot (41) of a ram (40) which actuates the end of the crank. Initial actuation of the crank 90° raises the pivot pin (32) and the actuated end (36, 42) of the crank (34) to increase the mechanical advantage of the ram (40). The angle of the ram (40) now has adequate uplift to be as effective as the prior art while requiring about 1/2 the storage height. A stop bar (43) is pivoted on the pivot pin (42) and has a free end (54) or tail slideable along the base (10) as the pivot pin (32) rises. A plurality of spaced stops (56) are welded on the base and are engaged by the stop bar (43) as the lift is lowered due to pressure loss or failure to actuate a control cable to lift the lock bar (43) over the stops (56).

Description: This invention relates to automotive service lifts of the type mounted on the floor in service garages and more particularly to service lifts including scissor type linkages for raising a vehicle according to the features of the preamble of claim 1. Scissor lifts of the type mounted on the floor of a service area project above the surface, even when fully collapsed. Typically, such lift arrangements when fully collapsed have a height of at least six inches above the floor and in many cases, more than that. When the service lifts are not in use, they present an obstacle to people working in the area and they obstruct movement of vehicles and equipment in the service area. Accordingly, in many cases, scissor lifts are recessed into the floor, and installation of the lift is expensive because of the work reqired in forming a recess in the floor for housing the service lift. A lift of the type described in the preamble of claim 1 which allows a relatively flat arrangement of the lift in the fully collapsed state is known from US-A-4526346. Furthermore, GB-A-975154 describes a lift which simplifies the initial lifting procedure. Another lift is known from GB-A-981991. It is an object of the present invention, to simplify the intitial lifting procedure with a lift which has a substantially reduced height or thickness when the lift is collapsed. This object is solved by the feature of claim 1. In the scissor lift embodying the invention, a hydraulic ram is connected to the pivot of the pairs of scissors of the scissor lift by a crank and roller assembley. The crank and roller assembley is caused to pivot by initial elongation of the hydraulic ram and functions to elevate the scissors pivot point while at the same time increasing the effective angle of the ram with respect to horizontal to thereby increase the mechanical advantage of the hydraulic ram. This results in providing a means for initiating upward movement of the scissor arrangement and also for rapidly increasing the mechanical advantage of the hydraulic ram during the initial stage of scissor movement. The scissor lift embodying the invention can have a height which is one-half the height of the prior art scissor lifts and yet does not sacrifice mechanical advantage. Another feature of the scissor lift embodying the invention is that it includes a lock bar pivoted on the pivot pin interconnecting the scissor legs and having a lower end which can engage successive spaced stops on the base. The lock bar and spaced stops function as a ratchet or rack and pawl arrangement as the lift is raised and if pressure in the hydraulic ram is lost, the end of the lock bar engages a stop to prevent dropping the load. To lower the scissor lift, the lower end of the lock bar can be raised to lift the lower end of the bar over the stops. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a scissor lift embodying the invention in a raised position. Fig. 2 is a side elevation of the scissor lift shown in Fig. 1. Fig. 3 is a plan view of the lift shown in Fig. 1 in a collapsed position. Fig. 4 is a side elevation of the scissor lift shown in Fig. 3, and showing the lift in a fully collapsed position in phantom. Fig. 5 is a detailed elevation view of the crank assembly which imparts the initial upward movement to the scissor lift shown in Figs. 1-4. Fig. 6 is an enlarged partial view of the lifting ram and crank assembly of the scissor lift shown in Figs. 1-4. Fig. 7 is an enlarged view of a locking bar assembly included in the scissor lift shown in Figs. 1-4. Fig. 8 is a cross section view taken along line 8-8 in Fig. 3. Fig. 9 is a cross-section view taken along line 9-9 in Fig. 8. DETAILED DESCRIPTION OF THE DRAWINGS Illustrated in Fig. 1 is a vehicle scissor lift embodying the invention and including a base 10 supporting a set of inner scissor legs 24 and a pair of outer scissor legs 12. Each outer leg 12 includes one end pivotally supported on the base by a pivot pin 14 in turn supported by a bracket or block 16. The other end of each leg 12 is provided with a pivoted slider block 18 which slides in and is restrained in a guide track 20 fixed to the elevating platform 22. While the elevating platform 22 could have other constructions, in the illustrated arrangement it includes a frame comprised of a pair of side bars 21 joined by end bars 23. The opposite ends of the frame 22 each support a plurality of pivoting arms 25, in turn, each supporting a support pad 27 adapted to be positioned under the frame of a vehicle for lifting the vehicle. Each inner leg 24 includes one end pivotally joined to the platform 22 by a pivot pin 26, and an opposite end of each inner leg 24 is pivotally connected by a pin 29 (Fig. 6) to a slider block 28 which is housed in a slider block guide bracket 30 fixed to the base 10 and supported by the guide bracket 30 for limited linear reciprocal movement. The medial portions of the legs 12 and 24 are pivotally interconnected by a pivot pin 32. The pivot pin 32 also supports and serves as a pivot or fulcrum for a pivot bar or crank 34 positioned between the two pairs of legs 12 and 24. The pivot bar 34 constitutes a double ended crank having its mid-portion pivoted on pin 32. Each end of the pivot bar includes spaced apart ears 36, and the space between the ears 36 is adapted to house an end of a piston rod 38 of a hydraulic ram 40. A pivot pin 42 extends through all the ears 36 and through the ends of pairs of piston rods 38. The opposite ends of the hydraulic rams 40 are pivotally connected to the base 10 by brackets 39 fixed to the base 10 and pivot pins 41 extending through the brackets 39 and through ends of the hydraulic cylinders 40. The opposite "end" of the pivot bar or crank 34 includes two more pairs of spaced ears 44 (Fig. 3) which support pivot shafts 46 on which rollers 48 are mounted. In the fully collapsed position of the scissor lift, (as shown in phantom in Fig. 4) the rollers 48 engage the upper surface of the floor of the base 10, and the crank 34 is generally horizontally disposed but with pivot pin 42 slightly above the axis of the main pivot pin 32 and above the pivot pin 41 supporting the lower end of the ram 40. Thus, as best shown in Figs. 5 and 6, when the scissor lift is in the fully lowered position and when the ram is then extended, the ram 40 will apply a torque on the crank 34 about the main pivot pin 32 in a counterclockwise direction, as seen in Fig. 5, and force the crank 34 to pivot on pin 32. This causes the roller 48 to roll on the base 10. As the crank 32 rotates in the counterclockwise direction, the pivot 32 is raised by the crank, and the pivot pin 42 connecting the end of the crank to piston end 38 also moves upwardly to now give the ram 40 an increased vertical angle and increased leverage. The crank 34 pivots about pin 32 approximately 90° to the position shown in Fig. 6 wherein a stop surface 50 of the crank 34 engages the edge of a stop plate 52 which interconnects and is fixed between the inner legs 24. Once the crank 34 has pivoted to the generally vertical position, the point of engagement of the ram 40 with the crank 34 is at a position of maximum advantage and continued extension of the ram 40 will cause the scissor legs 12 and 24 to pivot about the anchor pivots 14 and 26 thereby causing the platform 22 to be elevated. In the illustrated arrangement the scissor lift also includes a lock bar 43 having one end pivotally joined to the crank 34 by pivot pin 42. As the platform 22 rises, a lower end 54 (Fig. 7) of the lock bar 43 will drag along the base and will ride over spaced stops 56 fixed to the base 10. In order to lower the scissor lift, the lower end 54 of stop bar 42 has to be raised over the stops 56. When the scissor lift embodying the invention is in the lowered or retracted position, it has a very low profile. Because the scissor lift has a low profile, it can be installed in a garage or service area on the existing floor, and modification of the floor to recess the scissor lift into the floor is not required. Additionally, because the scissor lift can be readily installed, it can be moved from one service area to another at minimal expense. The low profile of the scissor lift is permitted by the provision of the crank arrangement 34 and provides means for initiating upward movement of the scissor lift when the hydraulic ram is in a nearly horizontal position, and the moment arm of the force generated by the hydraulic ram would be otherwise insufficient to cause lifting movement of the lift arms of the scissor lift. Various features of the invention are set forth in the following claims.

Claims: A hydraulically operated scissor lift comprising: a base (10) a platform (22) supported for vertical movement between a fully collapsed position and a raised position; a first leg (12) having opposite ends, one end (14) pivotally connected to the base (10) and the other end (18) slideably connected to the platform; a second leg (24) having opposite ends, one end (26) of the second leg (24) being pivotally connected to the platform (22) and the opposite end (28) of the second leg (24) being slideably connected to the base (10); a pivot (32) interconnecting the mid portion of the first leg (12) to the mid portion of the second leg (24); an initial lifting assembly avoiding unlimited forces, which assembly comprises a crank (34) that is pivotally mounted to the pivot (32) for pivotal movement between a first position where the crank (34) is generally horizontal and a second position where the crank (34) is generally vertical; a hydraulic ram (40) having opposite ends, one end (38) of the hydraulic ram (40) being connected to the crank (34) and being adapted to cause pivotal movement of the crank (34) between the first position and the second position, the said second position being defined by a stop surface (50) and a stop plate (52) cooperating to limit rotation of the crank (34); characterized in that the crank (34) is pivotally mounted to the pivot (32) and has two opposite ends, one end (42) of the crank (34) being pivotally connected to the ram (40), and the other end (44) of the crank (34) rotatably supporting a roller (48); the roller (48) is adapted to contact the base (10) when the platform (22) is in the fully collapsed position; and the three pivot points (32, 42, 44) of the crank are in a non-linear arrangement such that when the platform (22) is in the fully collapsed position the pivot point (42) to the ram (40) is elevated, with respect to the base (10), above a line including the roller axis (44) and the pivot axis (32). A scissor lift as set forth in claim 1 including a third leg (12) parallel to said first leg (12), said third leg (12) having opposite ends, one end (14) of the third leg (12) pivotally connected to the base (10) and the other end (18) of the third leg (12) slideably connected to the platform (22), and a fourth leg (24) parallel to the second leg (24) and having opposite ends, one end (26) of the fourth leg (24) being pivotally connected to the platform (22) and the opposite end (28) of the fourth leg (24) being slideably connected to the base (10), and the third leg (12) and the fourth leg (24) being pivotally joined together by the pivot (32). A scissor lift as set forth in claim 1 or 2 and further including means for locking the platform (22) in a raised position. A scissor lift as set forth in claim 3 wherein the locking means including a lock bar (43) pivoted on said crank (34) and having an end (54) biased into engagement with said base (10), spaced stops (56) fixed on said base (10) along the path of movement of said bar (43), said end (54) of said bar (43) engaging the next adjacent stop (56) to prevent the lowering of said platform (22) if hydraulic pressure in the hydraulic ram (40) is lost. A scissor lift as set forth in claim 4 wherein said lock bar (43) being pivoted on said one end (42) of said crank (34) which is opposite to said roller (48).

Inventors: CRAIG, THOMAS A.
Applicants: HEIN-WERNER CORPORATION
Application year: 1989
Main classification: B66F7
IPC codes: B66F7