Abstract:
A support device for a mobile lifting machine, in particular a vehicle crane, comprises a carrier support coupled to the vehicle chassis, a piston rod coupled to the carrier support and movable relative to the carrier support, and a support disc coupled to the piston rod, wherein the support device is configured such that it allows a movement of the support disc relative to the carrier support in a direction perpendicular to the longitudinal axis (L) of the piston rod.

Description:
RELATED APPLICATIONS 
     The present patent document claims the benefit of priority to German Patent Application No. 10 2012 208 058.9, filed May 14, 2012, and entitled “Transverse Force-Reducing Support Device,” the entire contents of each of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a support device such as is used in mobile lifting machines, in particular in vehicle cranes, in order to support them during operation. The present invention also relates to a mobile lifting machine, in particular a vehicle crane, comprising at least one such support device. 
     2. Background Information 
     Modern mobile cranes are used for lifting increasingly heavier loads to ever greater heights. The demand for using an efficient mobile crane which exhibits as low an inherent weight as possible, in order to reduce logistical costs, is increasing in the same way. A particular aim is to provide a mobile crane which exhibits as high a bearing load as possible on as few axles as possible, without exceeding the permissible axial loads. This has a favourable effect on the maneuverability of the mobile crane during transport on the one hand, and a lowering effect on the overall costs of the crane on the other. This stated object can also be transposed, unchanged, to other mobile lifting machines, for example movable working platforms or hydraulic rescue vehicles, which are supported by means of support devices during operation. 
     Such support devices consist substantially of a carrier support which can be extended or pivoted out of the vehicle chassis, and a support cylinder which is arranged in the region of the end of the carrier support pointing away from the vehicle chassis. The support cylinder in turn comprises a hydraulic cylinder and a piston rod which can be extended out of the hydraulic cylinder. In order to support the lifting machine, the piston rod is extended out of the carrier support, such that the lifting machine comprising a plurality of support devices is ultimately raised together with the carrier supports. Due to the design, the carrier supports are deformed during the support procedure by the application of force by the support cylinders. The resultant sagging at the outer end of the carrier support generates a transverse force that causes the piston rod to be deformed. The transverse force has to be accommodated by the piston rod as an additional load, which increases the calculated total force that has to be accommodated by the piston rod and taken into account when designing the piston rod. 
     BRIEF SUMMARY 
     The present invention is based on the object of overcoming the described disadvantages of the prior art. In particular, the intention is to reduce the inherent weight of the support device and therefore the inherent weight of the lifting machine and/or vehicle crane as a whole. 
     This object is solved by the subject-matter of co-ordinated patent claims  1  and  10 , wherein the sub-claims define preferred embodiments of the present invention. 
     The support device in accordance with the invention comprises: a carrier support which is coupled to the vehicle chassis; a piston rod which is coupled to the carrier support and can be moved relative to the carrier support; 
     a support disc which is coupled to the piston rod, 
     wherein the support device is configured such that it allows a movement of the support disc, directed perpendicular to the longitudinal axis of the piston rod, relative to the carrier support. 
     In other words, the support disc is given the option during support of being moved and/or aligned relative to the carrier support and perpendicular to the longitudinal axis of the piston rod. If a crane is being supported on the ground, this movement is performed in a substantially horizontal plane or direction, respectively, since the longitudinal axis of the piston rod extends substantially vertically in this case. 
     In this way, the support device in accordance with the invention forms a sort of loose bearing which compensates for the deformation in the carrier supports. As noted, the deformation is caused by the application of a force by the support cylinders onto the carrier supports, which ultimately causes the transverse force that acts on the piston rods. Eliminating the transverse force acting on the piston rod enables the piston rod to be given smaller dimensions, such that it is lighter and consequently has a positive effect on the overall weight of the support device and therefore the overall weight of the lifting machine. Eliminating the transverse force likewise prevents the distorting effect of the transverse force on any support pressure indicator, which improves the accuracy measured by the support pressure indicator. With the aid of a support pressure indicator, it is possible to ascertain whether a crane is being properly supported. The supporting force is deduced from the pressure of the hydraulic oil for the hydraulically operated support cylinders, The transverse forces mentioned likewise have to be taken into account because they can distort the actual supporting force indicated because some of the supporting force is dissipated as a frictional force via the guide for the support cylinder. 
     The movement of the support disc which is directed perpendicular to the longitudinal axis of the support cylinder can then comprise rotational and/or translational components. All that is important is that the support disc is given a certain degree of freedom relative to the carrier support in order to prevent or at least reduce the transverse forces acting on the support cylinder. 
     In accordance with a preferred embodiment of the present invention, the support disc automatically moves into a base position when the support device is not being used. In other words, the support disc is always situated in the same base position before the support procedure so that it can be moved out of its base position during the support procedure, i.e. as soon as elastic deformation of the carrier support sets in. 
     In accordance with another preferred embodiment of the present invention, the movement of the support disc relative to the carrier support is allowed either by means of the coupling between the piston rod and the hydraulic cylinder or carrier support, respectively, or the coupling between the support disc and the piston rod or by a combination of the two couplings. It is therefore precisely the couplings and/or interfaces between the individual components of the support device which would enable the movement of the support disc relative to the support cylinder. In principle, however, it is likewise conceivable to provide devices, which individually or together enable the support disc to move relative to the carrier support as described above, outside of the couplings and/or interfaces on the components themselves, for example the support disc or the support cylinder. 
     In accordance with one preferred embodiment, the coupling between the support disc and the support cylinder allows a rotational movement of the support disc relative to the support cylinder, wherein in accordance with another preferred embodiment, only such a rotational movement is allowed. In this way, the support disc can adapt to uneven ground, without causing transverse forces which act on the piston rod. A spherical bearing is particularly preferred as the coupling between the support disc and the piston rod. 
     In accordance with another preferred embodiment, the piston rod is moved and/or operated hydraulically. A hydraulic cylinder can be provided in the carrier support for this purpose, in which the piston rod is guided as a piston and extended by means of hydraulic fluid introduced into the cylinder space or retracted by means of hydraulic fluid expelled from the cylinder space, respectively. The piston rod can however also comprise a separate piston which assumes the guiding and sealing function within the cylinder and is coupled to the piston rod. 
     In accordance with another preferred embodiment, the coupling between the piston rod and the hydraulic cylinder or carrier support, respectively, allows the piston rod to rotate about its central longitudinal axis within the hydraulic cylinder. This function can be performed very well by means of a hydraulic cylinder piston rod pairing which exhibits a circular cross-section. The piston rod and/or its piston can then be rotated within the hydraulic cylinder of the carrier support, which enables a crucial advantage which is described further below. 
     In accordance with another preferred embodiment, the spherical bearing is spaced from the longitudinal axis of the piston rod in a projection along said longitudinal axis. In other words, the spherical bearing is arranged eccentrically with respect to the central longitudinal axis of the piston rod. 
     The eccentric arrangement of the spherical bearing, together with the rotational freedom of the piston rod about its central longitudinal axis, enables a movement of the spherical bearing perpendicular to the longitudinal axis of the piston rod. The support disc, which is coupled to the piston rod by means of the spherical bearing, can therefore also follow this movement and therefore obtains a degree of freedom perpendicular to the longitudinal axis of the piston rod. A support device configured in this way can therefore assume the function of a loose bearing which compensates for the load-induced deformation of the carrier support and therefore prevents the associated transverse force on the piston rod. 
     In accordance with another preferred embodiment, the piston rod is connected to the piston and rotationally fixed about its longitudinal axis, wherein the base of the piston in particular comprises a cavity into which a corresponding protrusion in the region of the base of the hydraulic cylinder—which surrounds the piston—can move. The cavity and the protrusion are configured such that when the protrusion moves into the cavity the piston rod rotates about its longitudinal axis into a base position. If the piston rod does not comprise a piston and/or itself assumes the sealing and guiding function within the hydraulic cylinder of the carrier support, then it can comprise such a cavity itself instead of the piston. The configuration of the cavity and the protrusion provides the function of automatically resetting the support disc into a base position. It is however likewise conceivable to provide other elements which assume the resetting function, for example one or more spring elements which are tensed when the support disc is moved out of its base position and which, when discharged, move the support disc back into its base position again. 
     Another aspect of the present invention relates to a mobile lifting machine, in particular a vehicle crane, comprising at least one and preferably precisely one support device such as has been described above for each pair of support devices, where support devices are arranged in pairs on both sides of the lifting machine and opposite each other. In a vehicle crane comprising four support devices arranged in pairs in the front and rear region on both sides of the vehicle crane, one “loose bearing” support device in accordance with the invention can preferably be provided for each pair of support devices, while the other support device in each of the two pairs is a conventional support device which exhibits the function of a fixed bearing. 
     A particularly preferred embodiment of the present invention is explained in more detail on the basis of the enclosed figures. The invention can comprise any of the features described here, individually and in any expedient combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  to  1   c  illustrates a conventional support device in its unburdened and burdened state, and a conventional spherical bearing. 
         FIG. 2   a  illustrates the support device in accordance with the invention in its burdened state. 
         FIG. 2   b  illustrates the coupling between the piston rod and the hydraulic cylinder or carrier support, respectively, in accordance with the invention. 
         FIG. 2   c  illustrates the coupling between the support disc and the piston rod in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1   a  shows the vehicle chassis  1  of a vehicle crane  10 , out of which the carrier support  2  of a support device  15  has been extended. The piston rod  3  is also shown, which can be extended vertically downwards out of the hydraulic cylinder  5  of the carrier support  2  and is situated at the end of the carrier support  2  pointing away from the vehicle chassis  1 . The lower end of the piston rod  3  is connected to a support disc  4  via a spherical bearing  6 , wherein the spherical bearing  6  allows rotational degrees of freedom of the support disc  4  relative to the piston rod  3 . The piston rod  3  is mounted in a hydraulic cylinder  5  of the carrier support  2 . 
     As shown in  FIG. 1   b , the carrier support  2  and ultimately also the vehicle chassis  1  is raised by extending the piston rod  3 , wherein the occurring weight forces deform the carrier support  2 . Since the support disc  4  remains at its position on the ground, the piston rod  3  is deformed due to the occurring transverse forces. The consequence of this is in turn that the piston rod  3  has to be dimensioned such that the occurring transverse forces can be accommodated. The transverse forces affect the accuracy of the measurement of the supporting force, an affect that typically cannot be prevented. 
       FIG. 1   c  shows the spherical cap of a conventional spherical bearing which is arranged in the lower region of the piston rod  3 . 
       FIG. 2   a  shows a vehicle chassis  22  that includes a support device  25  in accordance with the invention in its burdened state. A spherical bearing  30  which is fastened to the piston rod  35  is arranged eccentrically with respect to the longitudinal axis L of the piston rod  35 , such that a transverse force which is transmitted onto the piston rod  35  by the support disc  40  causes a rotational movement of the piston rod  35 . Once the support disc  40  has touched the ground during the support procedure, the carrier support  45  begins to be raised within its clearance towards the crane  50 . In accordance with the invention, the application of the transverse force turns the piston rod  35 , wherein the eccentric spherical bearing  30  remains on the resting support disc  40  and merely completes a rotational movement in the corresponding receptacle of the support disc  40 , such that the piston rod  35  yields on a circular trajectory as viewed from the support disc  40 . The piston rod  35  can thus equalise the lateral offset caused by the elastic deformation of the carrier support  45  by turning within the hydraulic cylinder  55  of the carrier support  45  so that the piston rod  35  can effectively be prevented from being deformed. 
       FIG. 2   b  shows the coupling between the piston rod  35  and the carrier support  45  in accordance with the invention, which generates an automatic resetting movement of the piston rod  35  into a base position when the piston rod  35  is retracted. To this end, the piston  8  arranged at the upper end of the piston rod  35  comprises a cavity  9  into which the protrusion  10  on the upper base of the hydraulic cylinder  55  can move in order to cause the piston  8  to turn together with the piston rod  35  within the hydraulic cylinder  55  of the carrier support  45 . 
       FIG. 2   c  shows the coupling between the support disc  40  (not shown) and the piston rod  35 , wherein only the upper joint portion  7 , i.e. the spherical cap  7 , of the spherical joint or bearing  30  is shown. The eccentricity of the spherical joint or bearing  30  relative to the longitudinal axis L of the piston rod  35  can also be seen, which together with the rotational degree of freedom of the piston  8  or support cylinder  35 , respectively, within the hydraulic cylinder  55  of the carrier support  45  allows a movement of the support disc  40  relative to the carrier support  45 . 
     The support procedure using the support device  25  in accordance with the invention progresses in the following order. The mobile crane  50  is initially resting on its wheels, wherein the piston rods  35  are retracted into the hydraulic cylinders  55  and the support discs  40  are suspended via the spherical joints or bearings  30  on the piston rods  35 . The spherical joints or bearings  30  are initially still situated in their base position. The piston rods  35  are extended until the support discs  40  touch the ground, wherein the carrier supports  45  are lifted as soon as the piston rods  35  are extended further, which create a lateral offset between the support disc  40  and the piston rods  35 . The transverse force thus created causes the piston rods  35  to turn within the hydraulic cylinders  55 , wherein this effect increases until the wheels of the crane  50  disengage from the ground. 
     The takedown procedure correspondingly progresses in the reverse order. The mobile crane  50  is resting on its carrier supports  45 , wherein the wheels are not touching the ground. The spherical joints or bearings  30  on the piston rods  35  are situated in their turned position, which prevents transverse forces on the piston rod  35 . When the piston rods  35  are retracted, the carrier supports  45  are lowered at the outer end as soon as the wheels touch the ground due to the abating elastic deformation of the carrier supports  45 , wherein a lateral offset between the support disc  40  and the piston rod  35  is created. The transverse force thus created causes the piston rod  35  to rotate back. When the piston rods  35  are retracted further until they abut, they are rotated back into their base position together with the spherical joints  7  and the support discs  40  by the cavity  9  in the base of the piston  8  and the protrusion  10  in the upper base of the hydraulic cylinder  55 .