GB2028762A - Scissors-type vehicle lifting jack - Google Patents

Abstract

In a scissors-type lifting jack comprising lever arms 1, pivots 5, 9, nut 8, threaded spindle 11 and thrust member 12, the forces in the lever arms 1 extending from opposite sides of the head and base portions 6 and 7 are balanced by toothed wheels 2 or equivalent ribbed plates 10, Figure 6 engaging toothed formations on the arms. <IMAGE>

Description

SPECIFICATION Scissors-type vehicle lifting jack This invention relates to a scissors-type lifting jack.

Scissors-type vehicle lifting jacks are used as means for lifting vehicles, in particular passenger cars and small goods vehicles. Under certain conditions, scissors-type vehicle lifting jacks can be used as auxiliary equipment for other purposes, for example in industrial assemblies for the aligning of components or instead of known pressureproducing means.

Known scissors-type vehicle lifting jacks comprise four members of substantially U-shaped crosssection, which each have bores at their respective ends and which are joined together to form a variable quadrilateral. Members of U-shaped crosssection or members of a closed cross-section, besides inherent stability, suffer from the disadvantage that the scissors jack is heavy and difficult to handle.

The members, which are of the same dimension in order to avoid weak points, cannot be joined together at the pivot points, so that six to eight pivot points are required. A screw-threaded spindle with a spindle nut and a thrust support member is arranged diagonally, parallel to the supporting surface, for the purposes of adjusting the jack lifting height. So that the four arm members of a scissors-type lifting jack are moved uniformly, the ends thereof are provided with teeth which mate with each other during the jack movement, in the region of the base and head portions of the jack.

Scissors-type lifting jacks of this kind suffer from the disadvantage that not all the toothed segments are subjected to equal loading, due to production tolerances. Consequently, some toothed segments are overloaded, resulting in deformation, a severe degree of wear or damage to the teeth. In known scissors-type vehicle lifting jacks with six to eight pivots, because they are arranged in pairs, very high tipping moments occur in the spindle mounting and in particular in the toothed segments of the head and base portions of the jack, during the lifting operation, due to the low degree of elasticity of the system and due to its being connected to the vehicle to be lifted.

Due to the movement of the vehicle when it is lifted on the jack, the head portion of the jack does not move vertically but moves in a circular arc upwardly so that additional moments are applied to the pivot system, which moments generally result in damage to or destruction of the jack.

According to the present invention there is provided a scissors-type lifting jack comprising four lever arms which are pivotably interconnected at pivot points, and a spindle and nut drive means, in which the lever arms are provided with teeth engaged by a toothed or apertured member in a head portion and in a base portion and the spindle nut is mounted on a pivot pin which is provided with a transverse screw-th readed bore.

The pivot pin which is usual in a four-pivot scissors-type vehicle lifting jack and which is provided with a motion screw-thread is replaced by a pivot pin with a spindle nut let therein. For the purposes of transmitting high spindle forces, the spindle nut may be made from a material with good anti-friction properties and of suitable length.

According to a feature of the invention, the pivot pin has a motion screw-thread with a greater degree of screw-threaded backlash. The thread of the pivot pin only comes to carry the loading, if the screw-thread of the spindle nut fitted therein is worn due to frequent use. Subsequently, the spindle forces are carried by the spindle nut and the pivot pin and the scissors-type jack can be used over a substantially longer period of time. For the purposes of transmitting the spindle traction forces and uniform loading of all four lever arms, a toothed wheel or a toothed disc are preferably fitted in the head and base portions of the jack. The lever arms which are toothed on one side are each engaged with the respective toothed wheel and carry the proportionate loading which is produced by the load to be lifted and the eccentrically applied forces.The teeth of the lever arms are properly guided laterally by the toothed wheel, so that the known phenomenon of bending of the teeth is avoided. So that the vehicle lifting jack can be brought into a suitable starting position, in the unloaded condition, the toothed wheel also has to carry out a holding function.

According to an embodiment of the invention, a spring segment is also suitable for providing the holding function. The spring segment may be fitted instead of the toothed wheels, in the head or base portion of the jack, and is directly connected to the teeth of the lever arm. This form of the. jack is preferably used for vehicles in regard to which the head portion of the jack is connected to the vehicle by being hung in place or inserted into position.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a general side view of the scissorstype vehicle lifting jack, Figure 2 shows the four lever arms with a toothed wheel, in the opened extend condition, Figure 3 shows a view in cross-section through the head portion provided with the toothed wheel, Figure 4 shows the head portion with an oval opening for receiving the bearing pin, Figure 5 shows a spring segment which can be used instead of a toothed wheel, Figure 6shows a cross-section through the base portion provided with a spring segment, and Figure 7showsthe pivot with spindle nut.

The scissors-type vehicle lifting jack shown in Figure 1 comprises four lever arms 1 which are joined together in the form of a pantograph. Toothed wheels 2 are rotatably mounted in a head portion 6 and in a base portion 7, on bearing pins 3 mounted in a rubber member 4. A thrust support member 12 and a spindle nut 8 are connected horizontally by a spindle 11. The thrust support member 12 and the spindle nut 8 are secured in position by pivot pins 5 between each two lever arms 1. The lever arms 1 which are offset at one side carry a tooth arrangement. The toothed wheel 2 shown in Figure 2 provides a form-locking connection between the toothed portions of the lever arms 1. A rivet 9 acting as a connecting member connects the lever arms 1 to the head portion 6 and to the base portion 7 respectively.Figure 3 shows the co-operation of the arm members and wheel 2 in the region of the head portion 6. The toothed wheel 2 is rotatably secured on a bearing pin 3, mounted in a rubber member 4.

An oval opening is provided in the head portion 6 and the base portion 7, for receiving the rubber member 4. Instead of having a toothed wheel 2 a spring segment 10 as shown in Figure 5 can be used.

The segment 10 has a bore in the centre, and a raised portion at both ends. As can be seen from Figure 6, the spring segment 10 is fixedly connected to the head portion 6 and the base portion 7 respectively.

Whenever it has passed over one tooth of an arm 1, the raised portion of the spring segment 10 moves into the next following gap between the teeth, and catches therein. Figure 7 shows the members at the pivot point of the spindle nut 8. Two lever arms 1 are held together by a pivot pin 5. The distance between the ends of the lever arms 1 is filled by the spindle nut 8. The spindle nut 8 is mounted movably on the pivot pin 5. The screw-thread length of the spindle nut 8 is determined by calculation, in consideration of the maximum lifting force. Unlike the spindle nut 8, the pivot pin 5 has a transverse spindle screwthreaded bore with increased flank clearance or backlash.

Claims (8)

1. A scissors-type lifting jack comprising four lever arms which are pivotably interconnected at pivot points, and a spindle and nut drive means, in which the lever arms are provided with teeth engaged by a toothed or apertured member in a head portion and in a base portion and the spindle nut is mounted on a pivot pin which is provided with a transverse screw-threaded bore.

2. A jack as claimed in claim 1, in which one side of the lever arms are offset in the region of the head and base portions and at one end, and they are provided at the end of the offset side with a tooth formation, in the centre of which is provided a bore for a pivot.

3. Ajack as claimed in claim 1, in which the toothed or apertured member comprises a disc which is provided with apertures therethrough, or a shaped member which is bent to form teeth our a toothed wheel.

4. A jack as claimed in any preceding claim, in which the toothed or apertured member is rotatably mounted on a bearing pin mounted in a rubber member received in an oval opening provided in the head and base portion.

5. A jack as claimed in any of claims 1 to 3, in which the toothed member comprises a vertically flexible, shaped spring segment which is in engagement with the teeth of the lever arms and is provided in the head and base portions.

6. A jack as claimed in claim 2, in which the ends of the lever arms which are possibly offset, are of greater radii, in order to receive the tooth arrangement.

7. Ajack as claimed in any preceding claim, in which the pivot pin which is associated with the spindle nut also has a motion screw-thread whose flank clearance is greater than that of the spindle nut.

8. A scissors-type lifting jack substantially as herein before described with reference to and as illustrated in the accompanying drawings.