Car jack

A car jack having a stand column secured at its lower end to a plate-like base and pivotally supporting an arm having a head for engaging a vehicle and adapted to be pivoted by a threaded spindle rotated by a hand crank, in which the base has relatively angularly disposed front and rear portions forming a transverse edge on which the jack tilts when raising, a car with a major portion of the front base portion underlying the stand column with the front base portion having a central supporting zone projecting downwardly below side zones with means at the side zones connecting the base to the stand column.

The invention relates to a car jack. 
In the known car jacks, the supporting arm and the base consist of steel 
profiles. 
Continued attempts have been made to reduce the weight of such car jacks, 
which, among other means, was achieved to a substantial extent by 
appropriate profiling of the arms of the metal profiles in longitudinal 
direction. This made it possible to reduce the wall thicknesses of the 
metal profiles correspondingly. 
However, new requirements have been raised in motor vehicle construction 
with regard to weight reduction, which cannot be achieved with the 
hitherto employed steel profiles. It has therefore already been attempted 
to obtain the required, greatly reduced maximum weight of such car jacks 
by the use of other materials, namely light metal, in which rather 
favourable results have been achieved. It was found however in the course 
of these attempts that a simple substitution of construction materials 
whilst retaining the conventional structural embodiment is not sufficient 
to achieve an adequate inherent and torsional rigidity, not even by 
substantially increasing for this purpose the wall thicknesses of the 
metal profiles 
The weak point of such a structure was found to be the base. The latter, 
even with an appropriate material thickness and profiling, remains 
elastically yielding under extreme loadings owing to its relatively low 
strength to such an extent, that the shanks of the stand column, as viewed 
in their longitudinal direction, can be displaced under certain 
circumstances by as much as several millimeters due to twisting of the 
stand column relative to each other. Such a case can occur when a raised 
vehicle stands on a slightly sloping road. In this case, such a jointed 
lever must be applied to the car body in such a manner, that its stand 
column comes to be located substantially in a plane perpendicular to the 
ground surface. If then the vehicle is raised and forces oriented in 
longitudinal direction of the vehicle appear, which may be caused by the 
action of the wind or by a person leaning against the car body, the stand 
column, owing to the elasticity of the light metal, will correspondingly 
incline in the direction of the force, although the base will 
substantially retain its plane position on the ground surface. From this 
obliqueness of the stand column there results a mutual displacement of its 
profile members in longitudinal direction, which also brings about a 
corresponding displacement of the transverse pivot axle of the supporting 
arm and thus a torsion of the latter, because its load head is fast on the 
vehicle body while under load. This twisting of the stand column relative 
to the base and the torsion of the supporting arm is unacceptable for 
safety reasons, although these parts, when free of load, can return in 
their original positions. 
The purpose underlying the invention therefore is one of providing a car 
jack having a structural embodiment, the construction of which makes it 
possible to manufacture it from light metal with a weight which is 
substantially reduced by comparison with the conventional car jacks, in 
which the stand column and the supporting arm cannot undergo twisting and 
torsion, respectively, in the load-bearing state and when its stand column 
is inclined under the effects of a force in a direction parallel to the 
longitudinal direction of the vehicle. 
In such a car jack, its base, in the raised state of a vehicle, contacts 
the supporting ground surface only with its raised portion, so that the 
base, when forces displacing the vehicle body appear, can tilt in their 
direction. This ensures, that in any relative position of the stand column 
to the ground surface, the base will retain its original position relative 
to the stand column under any condition of loading of the car jack, so 
that no bending forces capable of twisting the stand column can appear at 
the points of connection between these two parts. 
The raised portion of the base can be constituted by a pressing having for 
example circular cross-section. It can furthermore be embodied in the form 
of a pressed longitudinal bead extending in the plane of the supporting 
arm and stand column. In this case, it is advantageous if the raised 
portion has a greater resistance to pressure than the remainder of the 
positioning surface of the base. Such a partial increase of pressure 
resistance on the positioning surface can be obtained in a simple manner. 
A preferred form of embodiment of the car jack base is that, owing to which 
the position of the tiltable base plate on the ground surface can be 
rendered particularly secure against slipping.

The hinged jack shown in FIGS. 1 and 2 is intended to illustrate, for the 
purpose of better understanding, that a hinged car jack in light metal 
construction and identical in embodiment to a steel car jack does not have 
the torsional strength of such a hinged car jack, even if its profiles for 
the stand column and the supporting arm are given correspondly stronger 
dimensions. 
The illustrated hinged jack has a stand column 10 of U-shaped 
cross-section, which carries at its lower end for example a tiltable base 
plate 12, which in known manner has a rear bearing surface 14 and, at an 
obtuse angle to the latter, a frontal supporting surface 16. 
At approximately mid-point of the stand column, one end of a supporting arm 
referenced 17 is mounted pivotable about a transverse pivot axle 18, the 
free lever end of which has in a known manner a load head 20, by means of 
which the supporting arm 17 can be applied to the underside of the body of 
a vehicle to be raised 21, indicated in composite lines. 
The load head 20, which is constituted for example of a heavy plastic 
moulding, has e.g. on its load-bearing face a groove-like recess 22, 
extending perpendicularly to the plane of the drawing and located in the 
centre of the load head, which serves for accommodating a web of the car 
body constituted by a tie seam. 
The transverse pivot axle 18 is disposed in the arms referenced 28 and 30 
of stand column 10 at a distance from a tie referenced 32 which 
interconnects the two sections of the stand column. 
The supporting arm 17 is pivotable about the transverse pivot axle 18 with 
the aid of a threaded spindle 34, which pierces with one of its end-pieces 
the load head 20 and is mounted therein rotatable but undisplaceable in 
axial direction, whilst when the supporting arm 17 is swung upwards, the 
threaded spindle 34 is supported on a thrust bearing 36. 
The axial movement of the threaded spindle 34 required for pivoting the 
supporting arm 17 is provided by a threaded nut 38, which is located in a 
bushing fitted on the upper end of stand column 10. Reference 44 
designates a hand crank, preferably a tumbling-action crank secured for 
rotation to the upper end of the threaded spindle 34, for effecting the 
rotation of the latter. 
The supporting arm 17 also has a profile of U-shaped cross-section, the two 
shanks of which are disposed at such a distance from each other, that the 
supporting arm can be mounted with slight lateral play between the shanks 
28, 30 of the stand column on the transverse pivot axle 18. In its lower 
starting position the supporting arm extends over the major portion of its 
length between the shanks 28, 30 of the stand column. 
The stand column 10 and the tiltable base plate 12 are made fast to each 
other by welding. 
The sole difference between this hinged jack embodied in light construction 
and a known hinged jack in steel construction consists in that the stand 
column, the supporting arm and the tiltable base plate are made of 
corresponding aluminium sections or aluminium sheet instead of steel 
sections or steel sheet. Such a substitution of materials makes possible a 
substantial reduction in weight in such hinged jacks. However, it was 
found in the course of experiments that the high torsional strength of 
hinged jacks made of steel, with regard to the mutual disposition of stand 
column and tiltable base plate, cannot be achieved even when the base or 
the shanks of the base plate are given a profiled embodiment instead of a 
plane construction. On the other hand, for reasons of the desired weight 
reduction, the wall thicknesses of stand column and tiltable base plate 
cannot be increased at will. 
FIG. 2 illustrates that a mere substitution of materials, namely the use of 
aluminium instead of steel, does not by itself suffice to provide a hinged 
jack of adequate torsional strength with substantially reduced weight. 
With regard to the illustration according to FIG. 2, let it be assumed for 
example that forces oriented in its longitudinal direction come to act on 
the raised vehicle 21, be it by the influence of wind, or by the 
positioning of the vehicle on a sloping road. As was determined by 
exhaustive tests, under the effect of such forces the stand column 10 
positions itself to a considerable extent obliquely to the base plate, 
whilst its positioning surface 16, even under the influence of the 
absorbed load, substantially retains its position relative to the ground 
surface. Apart from the fact, that this yielding between stand column and 
base plate can cause the car jack to fall ever as the action of the forces 
is intensified, the stand column is thereby twisted to such an extent, 
that its shanks, in the longitudinal direction, are displaced 
correspondingly relative to each other. This in turn causes a 
corresponding displacement of the transverse pivot axle 18 and thereby a 
torsion of the supporting arm, since the load head 20 is fixed in position 
on the vehicle body. 
By the embodiment of the base according to the invention, for example in 
the form of a tiltable base plate, as will be described in the following 
with reference to FIGS. 3 to 5, it can be achieved, that the relative 
disposition of base and stand column, in spite of the elasticity inherent 
to the use of the material, is preserved in the region of their mutual 
connection should a displacement of the load-bearing point occur, and thus 
the occurrence of damaging bending and torsional moments at the point of 
connection between stand column and base is effectively prevented. 
For this purpose, the positioning surface 16 of the tiltable base plate 12 
has spaced one behind the other for example, two protrusions formed 
preferably by steel rivets 46, 48 disposed in the tiltable base plate, 
which are arranged symmetrical to a plane a-a in which the longitudinal 
axes of stand column 10 and supporting arm 17 are located. The protrusions 
formed by the two rivets are bounded relative to the extension of the 
positioning surface 16 to both sides of this plane. They thus define 
bearing points which ensure that in a position of the stand column which 
deviates from the perpendicular to the ground surface when the vehicle is 
raised and, alternatively, in the case of a non-plane ground surface, 
there is still a centric force engagement is established on the 
positioning surface of the tiltable base plate, so that only small 
unilateral load couples can occur on the tiltable base plate. This 
prevents a twisting of the hinged jack in the region of the tiltable base 
plate in the manner illustrated in FIG. 2, with a corresponding torsion of 
the stand column. 
Even in the case where the vehicle is to be raised on a sloping road, as 
shown for example in FIG. 6, a load acceptance symmetrical to the 
above-mentioned plane a-a is ensured. Should it happen in this case that a 
longitudinal edge portion of the positioning surface comes into contact 
with the ground surface, then an elastic deformation will occur, but to 
such insignificant extent only that no detrimental changes can occur on 
the stand column. In addition, in this case the strength of the material 
will effect, that after discharge of the load the relative displacement of 
tiltale base plate and stand column is again compensated. 
Instead of the two rivets 46, 48 it is also possible to provide a single 
protrusion constituted by a corresponding pressing in the base plate. 
Further, the protrusion can be formed by a longitudinal corrugation 
extending in the plane a-a. 
By the use of steel rivets 46, 48 which, to avoid electrolytic corrosion, 
are to be disposed insulated in the tiltable base plate preferably made of 
aluminium, additionally a high resistance to slipping of the hinged jack 
on the ground surface will be achieved. 
In the example of embodiment shown, the positioning surface 14 and 
supporting surface 16 of the tiltable base plate are moreover provided 
with spaced steel rivets 50 forming anchoring claws, of which those in the 
supporting surface 16 are correspondingly set back in height relative to 
those steel rivets 46, 48 which are located in the plane a-a of supporting 
arm and stand column. With this end in view, in the present example of 
embodiment, the supporting surface 16 for example is convexly arched 
outward transverse to the longitudinal direction of the base plate. Here, 
the disposition of the two median steel rivets 46, 48 on the supporting 
surface is such, that the rear steel rivet 48 is located approximately in 
the plane of the two outer steel rivets 50. In addition, the two steel 
rivets 50 serve at the same time for fastening the base plate 12 to the 
stand column 10, in that they are riveted to the base plate with 
corresponding side flanges 52, 54 and 56, 58 respectively. 
As FIG. 7 shows, the supporting surface 16 can also be provided with only 
the steel rivet 46. Further, the lateral rivets 50 may be at a smaller 
distance from the plane a-a than the rivets 50 provided on the positioning 
surface 14. By such an arrangement of the rivets, the degree of freedom of 
the supporting surface 16 relative to the ground surface can be further 
substantially increased. 
It is obvious, that the construction of the tiltable base plate, for 
satisfying the purpose underlying the invention, can be modified in many 
different ways; the only essential point is that the construction 
according to the invention ensures, in case of the stand column assuming 
an oblique position or being positioned obliquely to the ground surface, 
that the load bearing point of the supporting surface is not displaced or 
only insignificantly so in lateral direction relative to the plane a-a.