GB2275910A - Vehicle jack - Google Patents

Abstract

A vehicle jack comprises two members (3, 5) pivoted together at (11) and respectively having lever arms (3A, 3B, 5A, 5B) the free ends of which extend adjacent the ground when the jack is in the fully lowered position. The member (5) is in the form of a bell crank lever whose shorter arm is mounted on an axle 10 bearing a pair of wheels (7), and extends downwardly with reference to the pivot (11). In use, a hydraulic tension cylinder actuating means (1) controlled by pump handle (2) exerts tension between the one member (3) and the axle (10) to cause relative pivoting movement of the two members (3, 5). As shown the jack comprise a single hydraulic cylinder (1) disposed between two bell crank levers (5) each of which is of inverted-U section and encloses a respective one member (3). A foot (4) joining the free extremities of the one members (3) rests flat on the ground whilst the wheels (7) on the other members (5) permit horizontal movement thereof with reference to the ground enabling a lifting arm palm (6) joining the other ends of said other members to lift a vehicle. <IMAGE>

Description

VEHICLE JACK This invention concerns improvements in and relating to vehicle jacks and, more especially to a wheeled jack that is adapted to allow the lifting of vehicles having a relatively low ground clearance.

From EP 0 295 066 there is known a vehicle jack comprising two relatively pivoted elongate members respectively having lever arms the free ends of which extend adjacent the ground when the jack is in the fully lowered position, actuating means being provided for causing relative pivoting movement of the two members whereby the free extremity of one member is caused to bear on the ground whilst the free extremity of the other provides lift for a vehicle, the said other member being wheeled at a point remote from the said free extremity, whereby during lifting action the horizontal position of the jack is maintained by the free extremity of said one member in contact with the ground, whilst the wheels on the other member permit horizontal movement thereof with reference to the ground during pivotal action of the jack.

Such a known arrangement has the advantage in comparison with conventional trolley jacks that it can provide lift for vehicles with relatively low ground clearance whilst being capable of providing vertical lift without substantial displacement of the load in a horizontal direction relatively to the free extremity of the said one member. The known arrangement has the disadvantage, however, that the area of contact between the said extremity of the one member is relatively small because the said extremity is required to have an arcuate contact surface to accommodate angular movement during operation of the jack. The maximum lift capable of being provided in the vertical direction is also relatively small in comparison to the overall horizontal length of the jack.

It is accordingly an object of the invention to overcome, or at least reduce the disadvantages of the known arrangement.

In accordance with the invention, a jack of the kind initially referred to is characterised in that the said other member is in the form of a bell crank lever of which the shorter lever arm, in the normal position of use of the jack, extends downwardly with reference to the pivot about which the said two members are relatively rotatable, that the said actuating means comprises means for exerting tension between the said one member and an anchorage in the region of the extremity of said shorter arm of the bell crank lever, and that said other member is wheeled for contact with the ground in the region of the said extremity of the shorter arm of the bell crank lever.

An arrangement in accordance with the invention has the advantage that it can provide a relatively high vertical lift in relation to the horizontal dimension of the jack, since the pivot point between the two relatively pivoted members is located near one horizontal end of the jack. Furthermore, since the shorter bell crank lever arm of the other member extends downwardly and is supported from the ground by wheels, the angular movement of the said one member during lifting action of the jack is substantially reduced, and thus the extremity of said one member that makes contact with the ground can be flatter than in the known arrangement and can provide a greater area of contact with the ground.Moreover, the arc of movement of the extremity of said other member can be so arranged that the lifting point of the jack is more closely centred on the area of pressure of the extremity of the one member against the ground during the full range of lifting movement, at least in circumstance where the nature of the load allows a vertical lift.

The invention is illustrated by way of example in the accompanying drawings, in which Fig.1 is a side elevation of one embodiment of wheeled jack in accordance with the invention, Fig.2 is plan view of the jack shown in Fig.1, and Fig.3 is an end elevation of the jack of Fig.1, taken in the direction of the arrow III of Fig.l.

Referring to the drawings, the wheeled jack illustrated is a hydraulic jack based upon a so-called hydraulic tension cylinder 1 having a piston rod 1A and an integral hydraulic pump that is actuated by means of a return spring-loaded plunger 1B. The plunger 1B can be actuated by means of a pump handle 2 that is pivoted relatively to a bracket 8 of the cylinder 1 at 2A, and since the cylinder 1 is a tension cylinder, the action is such that when the plunger 1B is actuated, the piston rod 1A is retracted relatively to the body of the cylinder 1. In known manner, the cylinder 1 is provided with a hydraulic pressure release valve, not shown, that enables the piston rod 1A to extend relatively to the body of the cylinder 1, for example under return spring-loading not shown.

The body of the cylinder 1 carries an axle 10 upon which are mounted a pair of wheels 7 that serve for transportation of the jack and are also effective during lifting operation of the jack as described below.

Also mounted on the axle 10 is a lifting arm assembly 5 that is generally in the form of a bell crank lever and comprises two lateral arms 5A and 5B between the free extremities of which is secured a lifting arm palm 6.

The upper sections of the lateral arms 5A and 5B are of channel section and housed therein is a compression strut assembly 3 comprising two lateral arms 3A and 3B of rectangular section metal tube, the free ends of which are connected by a foot 4 formed from a flat metal plate welded between stubs located at the ends of the compression strut arms 3A and 3B.

The compression strut assembly 3 is pivoted with respect to the lifting arm assembly 5 by means of a pivot shaft 11 extending through both sets of arms and anchored in place by means not shown. The compression strut assembly 3 is also linked to the piston rod 1A by means of a pivot shaft 12 extending through a head portion of the piston rod 1A and the compression strut arms 3A and 3B, via bosses 3C secured to the latter and serving to support the shaft 12 against bending forces applied thereto via the hydraulic cylinder 1.

The operation of the jack illustrated is generally as follows.

With the jack in the lowered condition illustrated in the drawings the jack can be transported on the wheels 7, the weight of the jack forward of the wheels 7 being counterbalanced by manual pressure exerted on the pump handle 2. The jack can thus be manoeuvred to locate the compression strut foot 4 and the lifting arm palm 6 below a vehicle or other load to be lifted.

It will be appreciated that the configuration of the jack allows insertion thereof under an element having very low ground clearance, as can be seen from the side elevation of the jack in Fig.l.

After closing the hydraulic pressure release valve, not shown, the pump handle 2 is now actuated to depress the pump plunger 1B repeatedly, thus causing the piston rod 1A to be retracted relatively to the body of the cylinder 1. Tension is thus applied between the shafts 10 and 12, causing the bell crank lever assembly 5 to be rotated counter-clockwise relatively to the compression strut assembly 3, as viewed in Fig.1. Thus, whilst the compression strut foot 4 rests flat upon the ground, the lifting arm palm 6 is raised vertically to lift the load.

Once the lifting arm palm 6 engages under the load and reaction pressure is transmitted to the compression strut foot 4, the horizontal position of the latter is fixed by friction against the ground, and thus further pivoting movement of the lifting arm assembly 5 is accommodated by the wheels 7 which allow the shaft 10 to move horizontally relatively to the ground in a direction towards the compression strut foot 4. In some circumstances the wheels 7 may be lifted from the ground when the nature of the load requires that the jack should tilt.

It will be appreciated that since the arc of movement of the shorter arm of the bell crank lever assembly 5 that links pivot shafts 10 and 11 extends in a direction towards the point at which the arc becomes tangential to the horizontal plane, during the major part of the lifting movement, the vertical position of the pivot shaft 11 is moved only very slightly, and thus effective contact with the ground can be maintained over substantially the full area of the compression strut foot 4 when the jack is lifting vertically. The geometry is also such that there is a substantially uniform load on the pressure cylinder 1 during the lifting operation.

To return the jack to its idle condition and to lower the load, the aforementioned hydraulic release valve is actuated in the conventional manner.

From the above disclosure it will be seen that a hydraulic jack in accordance with the invention provides a novel and mechanically simple construction of jack that is of relatively small horizontal and vertical dimension in relation to the vertical lift provided, which enables the lifting of loads having a very small ground clearance, with minimal horizontal movement of the load during lifting, with minimal load on any wheels of the jack that are required to move during the lifting operation, and with a substantially uniform load on the pressure cylinder.

Claims (7)

1. A vehicle jack comprising two relatively pivoted members respectively having lever arms the free ends of which extend adjacent the ground when the jack is in the fully lowered position, actuating means being provided for causing relative pivoting movement of the two members whereby the free extremity of one member is caused to bear on the ground whilst the free extremity of the other provides lift for a vehicle, the said other member being in the form of a bell crank lever of which the shorter arm, in the normal position of use of the jack, extends downwardly with reference to the pivot about which the said two members are relatively rotatable, the shorter arm being wheeled in the region of the extremity of said shorter arm at a point remote from the said other free extremity, wherein said actuating means is arranged for exerting tension between said one member and an anchorage in said region of the other member so that during lifting action the horizontal position of the jack is maintained by the free extremity of said one member in contact with the ground, whilst the wheels on the other member permit horizontal movement thereof with reference to the ground during pivotal action of the jack.

2. A jack as claimed in Claim 1, wherein the means for exerting tension is provided by a hydraulic tension cylinder including a piston, the body of which carries an axle providing the said anchorage on which is mounted the said other member and a pair of wheels.

3. A jack as claimed in Claim 2, wherein the hydraulic tension cylinder has an integral hydraulic pump actuable by means of a return spring-loaded plunger.

4. A jack as claimed in Claim 2 or Claim 3, wherein said piston free end is pivotally connected to said one member proximate its free extremity.

5. A jack as claimed in any preceding Claim, wherein the lever arms of the other member are arranged to accommodate the lever arms of the one member.

6. A jack as claimed in any preceding Claim, wherein the free extremity of said one member is provided with a foot of substantially flat metal plate for stability and load distribution.

7. A vehicle jack substantially as hereinbefore described with reference to the accompanying drawings.