Jacks

Abstract

 A load-lifting jack has pairs of upper and lower arms (10, 6) connected by pivots (8, 9) and, respectively, pivotted on a head (14) and base (2) to provide a parallel linkage. Rotation of a lead screw (16) extending between the pivots (8, 9) raises or lowers the head (14) relative to the base (2). A crown gear (22) secured coaxially to the lead screw (16) meshes with a pinion (28) adapted for connection to a handle (34) whereby rotation of the pinion (28) by the handle (34) turns the screw (16) through the gear (22). The gear ratio provides a mechanical advantage for the gear (22). Preferably the axis of the pinion (28) is angled upwardly, outwardly relative to the axis of the lead screw (16).

Description

[0001] This invention is concerned with load-lifting jacks having a pair of upper arms supporting a load-engaging head and a pair of lower arms supported on a base member, the upper and lower arms being pivotally interconnected to form the sides of a parallelogram, and a lead screw extending between the pivot points of the opposite pairs of the upper and lower arms so that rotation of the lead screw raises or lowers the load-engaging head relative to the base. Such a jack is referred to hereinafter as "a jack of the type defined".

[0002] Jacks of the type defined are known, see for example Patent Specification No. 1369186. In this Patent Specification the jack is shown in Figure 1 in a partly extended condition. When the jack is, however, in a retracted condition, both the load-engaging head and the base member are closely adjacent the lead screw and close to one another. While such jacks operate reasonably satisfactorily and have been used extensively, the applicants have found that such jacks can be difficult for a relatively weak person to operate from a fully closed position (with the load-engaging head and base in close proximity) especially when jacking a heavy vehicle. In addition, the disposition of the handle mounting close to the ground in the fully-closed position with the handle necessarily extending generally coaxially with the lead screw, has been found to often lead to the hands of the operator striking the ground when operating the jack and also, as the handle is close to the ground, may result in back injury.

[0003] One of the various objects of the present invention is to provide an improved jack of the type defined.

[0004] In one aspect, the invention provides a load-lifting jack having a pair of upper arms supporting a load-­engaging head and a pair of lower arms supported on a base member, the upper and lower arms being pivotally interconnected to form the sides of a parallelogram, a lead screw extending between the pivot points of the opposite pairs of the upper and lower arms so that rotation of the lead screw raises or lowers the load-­engaging head relative to the base, and means for rotating the lead screw characterised in that the jack comprises a first gear secured to the lead screw in axial alignment therewith and a second gear mounted in mesh with the first gear and adapted for connection to a handle so that rotation of the second gear by a handle turns the lead screw by means of the first gear, the gear ratio providing a mechanical advantage for rotating the first gear.

[0005] Preferably in a jack in accordance with the invention the axis of the second gear is angled relative to the axis of the lead screw in an upward direction away from the jack, in the operative position of the jack. Thus a handle which may be connected to the drive means to rotate the second gear is inclined upwardly at a convenient angle for operation by a motorist without stooping unduly.

[0006] Preferably a jack in accordance with the invention comprises a housing through which the lead screw passes having bearing means which support the lead screw, and the second gear is mounted for rotation on the housing.

[0007] Conveniently, the first gear is a crown gear, suitably pressed from metal sheet and secured to a suitably shaped end portion of the lead screw keying in a correspondingly shaped hole in the gear. Suitably the gear is retained on the lead screw by heading an end portion of the lead screw.

[0008] Conveniently the gear ratio between the first and second gears is such that the second gear is rotated by the drive means through between 1.5 and 2.0 revolutions, preferably about 1.75 revolutions, for each revolution of the crown wheel (and thus the lead screw).

[0009] The second gear is suitably a pinion gear made by any convenient means, for example sintering metal, cutting the gear from a suitable single piece of metal and any of the other known gear forming techniques.

[0010] There now follows a detailed description to be read with reference to the accompanying drawing of a jack of the type defined embodying the invention.

[0011] The accompanying drawing is a side view of a jack embodying the invention in a partially opened condition.

[0012] The jack shown in the drawing comprises a base member 2 on which are pivotted by pins 4 two lower arms 6. The lower arms 6 are pivotally connected by pivots 8, 9 to upper arms 10, which are themselves connected by pivots 12 to a load-engaging member 14. The upper and lower arms 6, 10, thus form a parallelogram and provide a type of parallel linkage. A lead screw 16 extends between the two pivots 8, 9. The lead screw 16 is mounted for rotation by bearing means. 20 and is threaded into a screw threaded bore in the pivot 9 in a manner similar to that known in jacks of the type defined, for example as described in Patent Specification No. 1369186. The base member 2, arms 6, 10 and load-engaging member 14 are conveniently pressed from metal sheets in known manner.

[0013] A housing 18, also conveniently made of a formed metal sheet, is also mounted on the pivot 8 and supports the bearing means 20 in which the lead screw rotates and which mounts for rotation a crown gear 22 secured to the lead screw 16 by a headed end portion 24. Thus, as the crown gear rotates, the lead screw 16 rotates with it. The housing 18 is, in plan, generally of U-shaped configuration and comprises an upwardly projecting bracket 26. An axle on which a second gear, namely a pinion 28, is mounted for rotation is secured to the bracket 26. Drive means comprising a U-shaped bracket 30 is secured to the pinion 28 by any suitable means for example welding. The U-shaped bracket 30 comprises two arms projecting outwardly from the pinion having aligned holes 32 in which a driving member or handle 34 may be engaged. A suitable handle 34 is shown in dash line in the drawing and comprises a hooked end portion 36 adapted to be engaged in the aligned holes 32 and a shaft portion 38 extending upwardly at an angle. By rotation of the shaft portion 38 in the operation of the jack, the U-shaped bracket 30 may be rotated thereby rotating the pinion 28 and the crown gear 22 with which the pinion 28 is in meshing engagement. Rotation of the crown gear 22 is effective to rotate the lead screw 16 and thus to raise or lower the load-engaging member 14. The base member 2 is placed on a suitable surface for example a surface of the road 40 and the lead screw 16 is disposed generally parallel with the surface of the road 40. Because the axis of the pinion 28 is inclined at an angle relative to the axis of rotation of the lead screw 16, the drive shaft 38 is inclined upwardly thus providing a convenient means for the motorist to operate the jack without stooping.

[0014] The gear ratio between the second gear i.e. pinion 28, and the first, crown gear 22 is chosen to give a suitable mechanical advantage so that the initial opening movement of the jack from its fully closed position when the load-engaging member 14 and the base member 2 are both in close proximity to one another and to the lead screw does not require undue effort from the motorist. Once the jack has been opened to a reasonable extent, the necessary operating force is in any event, reduced because of the operating characteristics of this type of parallel linkage. Suitably, the gear ratio between the pinion 28 and the crown gear 22 is chosen to be such that for each complete revolution of the crown gear 22, the pinion rotates between 1.5 and 2 times, suitably 1.75 times.

[0015] Although a U-shaped bracket 30 is shown for rotating the pinion 28, other connection means may be provided to enable the motorist to make a suitable connection to rotate the pinion 28. Whereas in the illustrative jack shown in the drawing the first gear is a crown gear 22 and the second gear is a pinion mounted for rotation about an axis inclined relative to the axis of the lead screw, a mechanical advantage may be provided by two meshing gears rotating about parallel axes; however, this latter arrangement is not preferred because in that event, the operator of the jack would have to stoop whilst operating the jack.

Claims

1. A load-lifting jack having a pair of upper arms (10) supporting a load-engaging head (14) and a pair of lower arms (6) supported on a base member (2), the upper and lower arms being pivotally interconnected to form the sides of a parallelogram, a lead screw (16) extending between the pivot points (8, 9) of the opposite pairs of the upper and lower arms (10, 6 ) so that rotation of the lead screw (16) raises or lowers the load-engaging head (14) relative to the base, and means (30) for rotating the lead screw characterized in that the jack comprises a first gear (22) secured to the lead screw (16) in axial alignment therewith and a second gear (28) mounted in mesh with the first gear (22) and adapted for connection to a handle (34) so that rotation of the second gear (28) by a handle (34) turns the lead screw (16) by means of the first gear (22), the gear ratio providing a mechanical advantage for rotating the first gear (22).

2. A jack according to Claim 1 characterized in that it comprises a housing (18) through which the lead screw (16) passes having bearing means (20) which support the lead screw (16) and in that the second gear (28) is mounted for rotation on the housing (18).

3. A jack according to either one of the preceding claims characterized in that the axis of the second gear (28) is angled relative to the axis of the lead screw (16) in an upward direction away from the jack.

4. A jack according to any one of the preceding claims characterized in that the gear ratio between the first and second gears (22, 28) is such that the second gear (28) is rotated through between 1.5 and 2.0 revolutions for each revolution of the first gear (22).

5. A jack according to any one of the preceding claims characterized in that the first gear (22) is a crown gear (22) and the second gear (28) is a pinion gear (28).

Drawing