GB2070560A - Vehicle lifting jack - Google Patents

Abstract

In a vehicle lifting jack comprising a supporting leg (10) and a carrier arm (23) mounted pivotally on the leg for movement about a fixed horizontal axis, a threaded spindle (17) is adjustable in a spindle nut (18) which is of plastics material and which is mounted hingedly on the leg or on the arm. In order to improve the stability and safety of the jack and the load- bearing capacity of its plastics spindle nut, the thread flank width of the thread (30) of the spindle is made less than the thread flank width of the thread (29) of the plastics nut. <IMAGE>

Description

SPECIFICATION Vehicle lifting jack This invention relates to a vehicle lifting jack comprising a supporting leg, a carrier arm pivotally movable relative to the leg about a fixed horizontal axis, a threaded spindle by means of which the carrier arm is moved and which is actuated by a crank arm, a spindle nut on the one hand and bearing means on the other hand hingedly connecting the threaded spindle to the supporting leg and to the carrier arm, in which the threaded spindle is of metal and the spindle nut is of plastics material and has a greater length for a given loading than a metal nut.

The spindle nut of plastics material replaces the nut of cast metal at present generally used in vehicle lifting jacks of this type. The spindle nut of plastics material, as compared with a spindle nut of cast metal, is lighter and thus reduces the manual force needed in order to operate the jack.

A small manual force means not only a reductio in the strength needed by the user, but above all gives an increase in the stability of the vehicle lifting jack. This is because with the exertion of a large manual force there is always the danger that the vehicle lifting jack, if for example it is not fully loaded and/or is slightly askew, could become dislodged with high crank forces so that the load take-up point of the jack would then no longer lie within the friction cone of the load take-up point of the jack, with the result that sliding away of the jack is possible or might actually take place.

However, the use of a spindle nut of plastics material has the disadvantage that it must be substantially larger than the usual nut of cast metal because of the lesser strength of the plastics material. In relation to this it is known to increase the length of the plastics material nut and to lengthen the meshing thread portion. However, this leads to a partial compensation in the reduction of the manual force required. Moreover the additional manufacturing expense is undesirable. Also, it has been shown that the known spindle nuts of plastics material do not have sufficient load-bearing capacity in certain overload cases, such that the plastics material threads shear off.

It is an object of the present invention to provide a vehicle lifting jack of the type first referred to above which is improved in such a way that the aforesaid disadvantages in particular are no longer encountered. On the contrary, the stability and utility as well as the load-bearing capacity of its spindle nut of plastics material are improved.

This is achieved in accordance with the present invention in that the flank width of the thread of the threaded spindle at half thread depth is made smaller than the flank width of the thread of the spindle nut at half thread depth. The length of the spindle nut may be shortened compared to its length for spindle and nut threads of equal flank width, the shortening being at most proportional to the reduction in the flank width of the thread of the threaded spindle.

While with the known spindle nuts of plastics material the thread flank width is equal to the thread flank width of the threaded spindle, the thread flank width of the threaded spindle of the present invention is smaller than the thread flank width of the spindle nut of plastics material. A reduction in the thread flank width of the threaded spindle when using a spindle nut of plastics material is possible, since a metallic threaded spindle with the same size flank width of threaded spindle and spindle nut of plastics material is oversized. This applied both in respect of the loadbearing capacity and also in respect of the frictional resistance, which with a metal/plastics material interface is comparatively small.

Corresponding to this reduction in the flank width of the thread of the threaded spindie, the flank width of the thread of the spindle nut of plastics material can be increased, so that this maintains a correspondingly greater load-bearing capacity. If such an increase in the load-bearing capacity of the spindle nut of plastics material is not wanted, then this may be shortened at most in proportion to the reduction in the flank width of the thread of the threaded spindle, i.e. because of the increased load capacity as a result of the greater thread flank width of the spindle nut of plastics material the length of the threaded section or the length overall of the spindle nut can be reduced.

Preferably, the increase in the thread flank width of the spindle nut is equal to the reduction in the thread flank width of the threaded spindle.

By this means one achieves the greatest possible increase in load-bearing capacity of the spindle nut of plastics material without changing the flank angles of the meshing threads.

The minimum structural expenditure with unchanged load-bearing capacity of the jack is achieved if the thread flank width of the spindle nut and the thread flank width of the threaded spindle bear a dimensional relationship one to the other such that they each have the same loadbearing capacity. Preferably, the thread flank width of the spindle nut is approximately twice the thread flank width of the threaded spindle.

An embodiment of jack in accordance with the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a schematic side view of a vehicle lifting jack in accordance with the invention; Fig. 2 is a sectional view of the vehicle lifting jack of Fig. 1 in the region of the spindle nut, the section being taken longitudinally through the threaded spindle; and, Fig. 3 is a sectional view on an enlarged scale showing the threaded connection between spindle nut and threaded spindle.

The vehicle lifting jack comprises a supporting leg 10, at the lower end of which a tilting foot 11 is fixedly connected. The vehicle lifting jack is set in place on the ground 13 upon a take-up or locating plate 12 when the jack is to be applied to the vehicle. In addition, the tilting foot 11 includes a stand plate 14 which is set at an angle to the take-up plate 12. The tilting foot 11 is provided at the free ends of its two plates and at the junction 1 5 of the two plates with detents 1 6 engageable with the ground 13 in order to increase the antiskid resistance of the foot to sliding on the ground.

At the upper end of the supporting leg 10, which is of U-shaped cross-section, a threaded spindle 17 is pivotally mounted by means of a spindle nut 18. The spindle nut 18 is provided with pins 19 which engage in slots 20 in the side webs of the U-shaped supporting leg 10. At the upper end of the threaded spindle 17 there is secured an articulated joint 21 to which a crank arm 22 is undetachably connected. By means of the crank arm 22 the threaded spindle 1 7 can be rotated in an advancing or retracting sense within the spindle nut 18, possibly with an accompanying change in the tilt orientation of the crank arm 22.

At the other end of the threaded spindle 1 7 a carrier arm 23, which is U-shaped in cross section, is hingedly connected by means of a spindle counterpressure bearing 24 which is not shown in detail and which may comprise for example a roller bearing. One bearing plate of the bearing takes the thrust of the threaded spindle 1 7 while the other bearing plate carries pins 24' which engage in the side webs of the U-shaped carrier arm 23.

The carrier arm 23 is hingedly connected to the supporting leg 10 at the end adjacent to the supporting leg by means of a hinge pin 25, and executes pivotal movements relative to the supporting leg 10 about the pin 25 corresponding to the drive imparted by the threaded spindle 17.

At the end of the carrier arm 23 remote from the supporting leg there is provided a load head in the form of a carrier plate 26 which is capable of limited tilting movement and by means of which the lifting jack is set into place against the underside of the vehicle to be lifted. The carrier plate 26 is provided with a recess 28 which serves to receive a weld seam of the vehicle bodywork.

The spindle nut 18, shown on an enlarged scale in Fig. 2, has an internal thread 29 which meshes with a thread 30 on the threaded spindle 17. In contrast to the known thread pairs, in which the thread of the spindle nut 1 8 of plastics material is the same size as the thread of the threaded spindle 1 7 which is of metal, the two threads 29, 30 are here made different. This is more clearly seen from Fig. 3 in which the profile 29' of the thread 29 of the spindle nut 1 8 of plastics material and the profile 30' of the thread 30 of the threaded spindle 1 7 of metal are shown on an enlarged scale.Thus H2 represents the depth of the thread profile 30' of the threaded spindle 17 and FdS represents the thread flank width of the threaded spindle measured at half the thread depth H2/2, while FdM represents the thread flank width of the profile 29' of the spindle nut 1 8, again measured at half its thread depth.

The dotted lines indicate the unaltered, i.e.

conventional, profile of the threaded spindle and of the spindle nut. In comparison thereto it can be seen that the flank width FdS of the threaded spindle 1 7 has been reduced and that the flank width FdM of the spindle nut 1 8 has been increased. In proportion to this reduction in the flank width FdS of the threaded spindle 17 and the increase of the flank width FdM of the spindle nut 18, the length of the spindle nut 18 can be reduced, so that this then has the shape shown in solid outline in Fig. 2, compared with the unreduced length shown in dotted outline for the case where one has the same flank width dimension for both spindle nut and threaded spindle.

From Fig. 3 it can also be seen that the increase in the dimension of the flank width FdM of the spindle nut 1 8 is the same as the reduction in the dimension of the flank width FdS of the threaded spindle 17, and also that the threads 29, 30 of the threaded spindle 1 7 and of the spindle nut 1 8 with their different flank widths FdM and FdS are each trapezoidal in cross-section.

If a corresponding reduction in length of the spindle nut 1 8 is not wanted, then this keeps its original length indicated in Fig. 2 by the dotted lines, with the result that such a spindle nut has a correspondingly greater load-bearing strength, since it meshes with about two additional thread turns, in order to transfer the load which is imparted to the carrier plate 26 and transmitted by way of the threaded spindle 17, via its pins 1 9 to the supporting leg 10.

The maximum reduction in the length of the spindle nut 18 is possible when the flank width FdM of the thread of the spindle nut 1 8 and the flank width FdS of the thread of the threaded spindle 17 bear a dimensional relationship one to the other such that they each have the same load-bearing capacity.

In practice, the flank width Fdm of the nut 1 8 is approximately twice the flank width FdS of the threaded spindle 17, as shown in Fig. 3.

Although in the preferred embodiment described above the spindle nut is shown at the upper end of the spindle and is mounted on the supporting leg, it could alternatively be mounted so as to be hingedly connected to the carrier arm.

Claims (7)

1. A vehicle lifting jack comprising a supporting leg, a carrier arm pivotally connected to the leg for movement about a fixed horizontal axis, a threaded spindle which is actuated by means of a crank arm and by means of which the carrier arm is moved, a spindle nut on the one hand and bearing means on the other hand hingedly connecting the threaded spindle to the supporting leg and to the carrier arm, in which the threaded spindle is of metal and the spindle nut is of plastics material and has a greater length for a given loading than a metal nut, and in which the flank width of the thread of the threaded spindle at half thread depth is smaller than the flank width of the thread of the spindle nut at half thread depth.

2. A vehicle lifting jack according to claim 1, in which the length of the spindle nut is shortened compared to its length for spindle and nut threads of equal flank width, the shortening being at most proportional to the reduction in the flank width of the thread of the threaded spindle.

3. A vehicle lifting jack according to claim 1 or 2, in which, compared with an arrangement in which the flank width of each element of the thread pair is the same, the increase in the flank width of the thread of the spindle nut is equal to the reduction in the flank width of the thread of the threaded spindle.

4. A vehicle lifting jack according to any preceding claim, in which the flank width of the thread of the spindle nut and the flank width of the thread of the threaded spindle bear a dimensional relationship one to the other such that they each have the same load-bearing capacity.

5. A vehicle lifting jack according to any preceding claim, in which the flank width of the thread of the spindle nut is approximately twice the flank width of the thread of the threaded spindle.

6. A vehicle lifting jack according to any preceding claim, in which the thread of the threaded spindle and the thread of the spindle nut are each trapezoidal in cross-section.

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