GB2108924A

GB2108924A - Hydraulic Trolley Jack

Info

Publication number: GB2108924A
Application number: GB08132937A
Authority: GB
Inventors: Hung Michael Mao-Hsiung
Original assignee: SHINN FU AUTO SUPPLY Co L
Current assignee: SHINN FU AUTO SUPPLY Co L
Priority date: 1981-11-02
Filing date: 1981-11-02
Publication date: 1983-05-25

Abstract

A hydraulic trolley jack comprises a base frame (3, 32), a load carrying mechanism including a support arm (1) pivotally mounted to said frame and provided at one end with a load platform (9) for contacting a load, and a hydraulic piston-in-cylinder actuator (6, 7) operably connected between said base frame and support arm through an articulating inter- connecting link mechanism e.g. (2, 2a) and operable to articulate or pivot the support arm relatively to the base for elevation and retraction of said load platform. <IMAGE>

Description

SPECIFICATION Hydraulic trolley jack This invention relates to hydraulic jacks and is particularly concerned with a so-called hydraulic trolley jack, of compact overall design, in particular utilising a configuration of hydraulic actuator which achieves savings in overall size and weight particularly desirable for a portable trolley jack, such as may readily be carried, say, aboard a motor vehicle for occasional use.

The term trolley jack is used generally to cover a jack in which an elevating platform is mounted on a moveable base. Generally the base incorporates wheels to facilitate movement and commonly a wheeled carriage comprising two spaced pairs of wheels at opposite ends of an elongate base is employed.

Hitherto, such trolley jacks have been typically large and cumbersome and have been restricted to professional garage use in view of their bulk and weight and indeed their attendant complication and expense.

Another category of jacks, namely bottle jacks, in which an upright, direct-acting, piston-incylinder hydraulic actuator is employed, do not have the stability and ease of movement or indeed, except in very restricted or cramped conditions, the facility for location/installation that is afforded by a trolley jack, aithough such bottle jacks have had the portability suitable for amateur or domestic use.

More recently, more compact, lighter-weight trolley jack designs, suitable for amateur or domestic use and more readily portable, have evolved, but these have typically suffered from reduced overall lift necessitated by compact overall dimensions in the context of a conventional design configuration.

Generally, trolley jacks have employed a horizontallySisposed, piston-in-cylinder hydraulic actuator operating directly upon a pivoted support arm disposed in tandem or in series with the actuator within a base frame. As a result, the overall length of the jack has generally been increased and the length of the support arm and thus the maximum elevation achievable has been restricted for given overall base frarhe length, without making the base frame unduly long and cumbersome. It is desirable to achieve maximum lift with attendant stability, in particular the relative configuration of the lifting pivot and ground engaging points, for safety and freedom from tipping about one end of the jack during load bearing operation.Various geometries of jack have been proposed hitherto, but without achieving a compact overall design in which the operating length of the support arm and thus the elevation height is a substantial proportion of the overall base length of the jack.

Another problem is that, by directly interconnecting the hydraulic piston-in-cylinder actuator and the support arm, the actuator must pivot with the support arm during pumping or priming the cylinder for actuation thereof to elevate the support arm and also during exhaustion of the cylinder, by releasing a pressure release valve in the body thereof for piston retraction and lowering of the support arm. The relative movement between the support arm and the piston and the base frame Imposes lateral loads on the piston, directly reflecting the load being lifted, often at a 'mechanical disadvantage, in order to achieve a high velocity ratio for rapid elevation and retraction of the support arm with respect to the base frame, particularly prior to and after an actual lifting operation.

According to the invention a hydraulic trolley jack comprises a base frame, a load carrying mechanism comprising a support arm pivotally mounted to said frame and provided at one end with a support platform for contacting a load, and a hydraulic piston-in-cylinder actuator operably connected between said base frame and said support arm through an articulating interconnecting link mechanism and operable to articulate or pivot the support arm relatively to the base for elevation and restriction of said load platform This trolley jack configuration enables the piston-in-cylinder hydraulic actuator to be accomodated entirely within the length of the base frame and in particular to occupy In its extended position substantially the entire length of the base frame, so as to achieve the longest possible operating stroke thereof and the maximum elevation of the interconnected support arm for a given number of priming or pumping operations of hydraulic fluid with respect to the cylinder.

Similarly, the support arm itself can occupy a substantial length of the base frame and indeed can overlie the hydraulic piston-in-cylinder actuator, to achieve a reduction In overall length, without sacrifice in the maximum degree of elevation and retraction, that is the lifting height of the support arm with respect to the base frame.

Moreover, if as is usual, the support arm is hollow inverted 'U' as section it can receive the actuator with that section in its retracted condition without unduly increasing the overall depth of the jack, in particular the base frame, over and above that required for the necessary frame strength and rigidity.

The indirect articulating link arrangement of the present invention enables the load applied to the jack to be evenly distributed between the various operating parts thereof and in particular concentrated pressure upon the hydraulic piston in-cylinder actuator is obviated.

Moreover, the range of movement of the support arm, and in particular articulation or pivotal movement thereof with respect to the base frame, is not such as to put the various parts of the jack in a position whereby the jack tends to tip during load-bearing operations.

The dimensions of the various parts of the jack enable a deep-walled side member configuration to be employed, in which maximum strength is achieved for sheet metal material by employing a fianged plate or girder like configuration of channel steel, with a sectional bending moment or moment of interia calculated by the formula:

where Mi=moment of the inertia of the channel steel b=width of the flange of mechanical steel d=height of depth of the channel steel q=slope of the flange of the channel steel h=maximum height of depth between two (opposite) flanges of the channel steel (excluding the thickness of the material) I=minimum height of depth between two (opposite) flanges of the channel steel (excluding the thickness of the material).

From this formula it can be appreciatea that a deep base frame may increase the frame bending resistance or stiffness and thus the material thickness can be reduced, with significant attendant weight saving.

There now follows a description of some specific embodiments of the invention, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a general perspective view of a trolley jack; Figure 2 shows an upper plan view of Figure 1; Figure 3 shows a diagrammatic or schematic representation of the mechanical linkage and leverage action of the jack shown in Figures 1 and 2; Figure 4 shows a transverse sectional view of the hydraulic mounting block of the jack shown in Figures 1 and 2; Figure 5 shows a longitudinal section taken along the line A in Figure 4; Figure 6 shows a longitudinal section taken along the line B in Figure 4; Figure 7 shows a part transverse section view from above taken along line C in Figure 4; Figure 8 shows a longitudinal section of the hydraulic actuator of the jack shown in Figures 1 and 2;; Figure 9 shows a schematic or diagrammatic representation of the mechanical and geometrical operational clearance characteristics of the hydraulic actuator shown in Figure 8; Figures 10 and 11 show respectively rear and front perspective views of another embodiment of trolley jack to that shown in Figure 1; Figures 12 and 13 show respectively diagrammatic, part sectional side elevational and underside plan views of the jack shown in Figures 10 and 11; Figures 14 and 15 shows respectively front and rear perspective views of a further embodiment of trolley jack to that shown in Figures 10 and 11, and indeed Figures 1 and 2;; and Figures 16 and 1 7 show respectively diagrammatic, part-sectional side elevations and underside plan views of the jack shown in Figures 14and 15.

The alternative jack designs shows in Figures 10 to 1 7 represent detail modifications of the basic Figure 1 design and as such their various features should be generally self-explanatory by reference to the corresponding features now described with reference to Figures 1 to 9, but will not be described further than that.

Referring now to Figures 1 and 2, there is shown a trolley jack comprising two arms 1 having an hydraulic cylinder 6 and a piston stem 7 therebetween, a pulling stem 2, pulling arms 2a coupling stem 2 to arms 1, a middle spindle 4, and a frame 3 having an upper flange 31 and a lower flange 32 which design configuration produces a smaller bending stress and larger moment of intertia and as a result require a thinner frame. Arms 1 each include two portions 102 and 103. The middle spindle 4 is fixed onto arms 1 and at the junction of portions 102 and 103 and is attached to the frame 3 by means of a bushing 5 soldered to said frame 3 so as to allow the middle spindle 4 to rotate between the bushing 5 and said frame 3, and consequently the bending stress is considerably reduced and the safety factor of said middle spindle 4 in withstanding the shear stress is greatly increased.

The hydraulic cylinder 6 and the piston stem 7 are disposed within the length of and concealed under the pulling arms 2a and the arms 1.

Referring to Figures 1 to 3, one end of the piston stem 7 is connected with and driven by a piston 8 and the other end of the piston stem 7 is attached to the pulling stem 2 at point 'C'. End 'A' of the pulling stem 2 is attached via arms 2a to said arms 1 composed of movable arm portions 102 and 103, which are fixed to each other at a certain angle at 'O'. The other end 'B' of the movable arm 103 is a specially shaped load contacting or support platform 9.When the piston 8 moves from D to D, one end of the said piston stem 7 moves from C to C and brings said pulling stem arms 2a and said arms 1 (including the movable arms 102, 103) from AOB to A'OB'; and when CC is the greatest stroke of said piston 8, B will be the highest rising point of the load platform 9, and B will be the lowest falling point of the load platform 9.

The piston 8 incorporated in the hydraulic cylinder 6 actuates the pulling stem 2 to raise said arms 1 composed of movable arms 102 and 103 which form a fixed angle so as to indirectly lift a load in an indirect-acting articulating link action. A mounting base 10 of the hydraulic cylinder 6 is rigidly secured to said frame 3 and will not be tilted or tipped over by the load carrying mechanism.

Figures 4 to 7 show an oil way system provided in the base 10. A channel 1001 communicating to said base 10 is provided with a pump piston or plunger 1101 which is driven through hinged links by a pivoted pump handle 11. The channel 1001 also communicates with an oil way, whose oil intake 1002 communicates with an oil storage chamber 61 of the hydraulic cylinder 6. When the piston 1101 is pulled/drawn upwardly by the handle 11, oil flows out of the oil storage chamber 61 through the oil way, one-way openings 1005, 1006 and an oil outlet 1003 into the hydraulic cylinder 6 to drive the piston mechanism.Another oil way (not shown) exists between the openings 1005, 1006 and incorporates a safety means 1004 including a one-way opening 10041, a spring device 10042 and an adjusting nut 10043, wherein the opening 10041 being compressed by the spring device 10042 and such compression can be adjusted by the adjusting nut 10043 which is covered by one wheel and can be adjusted by a screw-driver.

After the oil enters the oil way, it will flow through said one-way openings 1005, 1006 and the outlet 1003 into said cylinder 6 to actuate the piston mechanism by which a load is lifted. When a load imposed upon the load-carrying mechanism exceeds a certain limit, the pressure in the oil way between the one-way opening 1006 and the cylinder 6 will be increased to a certain value. If the piston 1001 actuated by the swing handle 11 continues to pump oil from the oil storage chamber 61 into the oil way, the oil will pass by the one-way opening 1005 to open the one-way opening 10041 of the safety means 1004 and through a reverse flow opening 10044 into said oil storage chamber 61. In other words, the spring device 10042 of said safety means 1004 will limit the load of the jack.

Also provided in the oil way is a releasing device 1007 communicating with a point between the one-way opening 1006 and the hydraulic cylinder 6. The releasing device 1007 is exposed on the outer surface of said base 10 and connected with a lateral oil way for communicating with the oil storage chamber 61.

When the releasing device 1007 is screwed or loosened, the lateral oil way will be closed or opened so as to control the pressure between the one-way opening 1006 and the storage chamber 61.

Referring to Figure 8, there is shown an annular cavity provided between the piston stem 7 and the piston head 8. The underside of the piston 8 is tightly connected with a back-up ring 81 which is made of synthetic plastics material by injection moulding, and an oil seal means composed of an 0 type ring 82 made of thermal resistant materials, an annular packing 83 and a working ring 84. The upper portion of the said piston stem 7 forms a sliding fit with the upper portion of the hydraulic cylinder 6.

Figure 9 shows how to determine the smallest clearance c between the piston stem 7 and the piston 8 by means of the following equation

where c=smallest width of the room between the piston and the piston stem L=maximum distance between the sliding fit and the piston a=maximum deviating displacement that may be caused by the load-carrying mechanism of the jack upon the sliding fit length of the sliding fit In operation, arm 2a can exert a force on stem 7 transverse to its direction of movement (that Is, in direction 'a' or Figure 9). The annular cavity having a width c between stem 7 and piston 8 permits the stem to react to the aforementioned traverse force without damage to the inner wall of cylinder 6.

Provided on inner wall of said cylinder 6 approaching to the extreme outward point of the stroke of said piston 8 is a screw groove 62 having a reverse flow opening 63 therein for leading the oil to said oil storage chamber 61 so as to permit the flow of oil by way of a lateral oil way to said oil storage chamber 61 and to release the pressure when said piston 8 reaches the predetermined highest point of its stroke.

Claims

1. A hydraulic trolley jack comprising a base frame, a load carrying mechanism including a support arm pivotally mounted to said frame and provided at one end with a load platform for contacting a load, and a hydraulic piston-incylinder actuator operably connected between said base frame and said support arm through an articulating interconnecting link mechanism and operable to articulate or pivot the support arm relatively to the base for elevation and retraction of said load platform.

2. A hydraulic trolley jack as claimed in Claim 1, wherein said articulating link comprises a first link member rigidly attached at one end of said support arm and in a fixed angular relationship thereto and provided at its other end, remote from said fixing point of attachment to said support arm, with a pivotal connection to a link member itself pivotally connected at its other end to an outward end of the piston of the piston-incylinder hydraulic actuator.

3. A hydraulic trolley jack as claimed in Claim 2, wherein the piston-in-cylinder hydraulic actuator is rigidly mounted on the base frame and is restrained from pivoting or relative rotational movement thereto.

4. A hydraulic trolley jack as claimed in Claim 3, wherein said piston-in-cylinder hydraulic actuator occupies in the extended position, substantially the entire length of the base frame and is mounted internally thereof and enclosed between the side walls thereof and said articulated support arm extended over a substantial length of the base frame and may be articulated into an elevated condition with respect to said base frame and into which the load platform is raised through a distance substantially of the order of the length of the support arm and thus a substantial proportion of the length of the base frame.

5. A hydraulic trolley jack as claimed in Claim 4, wherein an ancillary link is provided between the base frame and said load platform, which is in tum pivotally mounted upon one end of the support arm, the link arrangement being such that the load platform is tilted during Its elevating movement by articulation of said support arm relative to said base frame to maintain a constant orientation with respect to the base frame.

6. A hydraulic trolley jack as claimed in Claim 5, wherein a retracting spring is operably connected between the remote end of the piston and the fixed end of the cylinder or the base frame, for assisting in retraction of the piston with respect to the cylinder and thus retraction of the support arm.

7. A hydraulic trolley jack as claimed in Claim 6, wherein the cylinder is mounted on a cylinder mounting block fixedly or rigidly attached to the base frame and the cylinder mounting block incorporates a pumping and release chamber with associated oil-ways for charging the cylinder with hydraulic fluid and releasing the same therefrom in order to respectively extend and retract the piston relative to the cylinder and thereby respectively elevate and retract the support arm with respect to the base frame.

8. A hydraulic trolley jack as claimed in Claim 7, wherein the cylinder mounting block incorporates a pressure release value for releasing the hydraulic pressure from the cylinder once a predetermined value is exceeded, thereby preventing overloading of the hydraulic actuator when excessive loading is applied to the jack through the support arm.

9. A hydraulic trolley jack as claimed in Claim 8, wherein the base frame is provided with running wheels.

10. A hydraulic trolley jack as claimed in Claim 9, wherein a pair of said running wheels are mounted for swivel action.

11. A hydraulic trolley jack as claimed in any of the preceding Claims, wherein an annular clearance is defined between the piston and the outward end of the cylinder for accomodating lateral displacement of the piston under loads applied thereto by the pressurising of the cylinder and the loading of the support arm connected thereto.

12. A hydraulic trolley as claimed in any of the preceding Claims, wherein the base frame comprises two upright side frame members spaced by spacing struts, one of which defines the pivot for the support arm, another of which defines a mounting pin for the hydraulic cylinder actuator base plate or the like and a further of which defines an axle for running wheels.

13. A hydraulic trolley jack as claimed In Claim 12, wherein the support arm comprises spaced side plates with flanges, separated by a flanged spacer member and combined spacer and pivot pins respectively for said pivotal interconnection with the base frame and with said articulating llnk and said pivoting support platform.

14. A hydraulic trolley jack substantially as hereinbefore described with reference to and as shown in the accompanying drawings.