Abstract:
A drive unit is provided for the coaxial twisting movement of two stabilizer halves of a motor vehicle axle stabilizer with a tubular housing. Two housing halves are provided having an interior of which a hydraulically movable actuating piston is arranged displaceably in relation to the longitudinal axis of the housing. The longitudinal displacement of the piston is converted by an intercalated cam drive into a rotary movement of the housing halves around their common longitudinal axis. The housing halves are fixed with their respective free ends facing away from one another at a stabilizer halve. A hydraulically actuated releasing piston is pretensioned against a spring element and arranged at each opposite flat sides of the actuating piston, wherein the releasing pistons make possible the displacing movement of the central actuating piston in the pretensioned position and fix the actuating piston in its middle position in the released position.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This is a continuation of and claims the benefit (35 U.S.C. §120 and 365(c)) of copending International Application PCT/DE 03/03047 of Sep. 12, 2003, which designated inter alia the United States and which claims the priority of German Application DE 102 42 724.0 of Sep. 13, 2002. The entire contents of each application is hereby incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention pertains to a hydraulic drive unit for the coaxial twisting movement of two stabilizer halves of a motor vehicle axle stabilizer with a tubular housing, which comprises two housing halves and in the interior of which a hydraulically movable actuating piston is arranged displaceably in relation to the longitudinal axis of the housing, wherein the longitudinal displacement is converted by means of an intercalated cam drive into a rotary movement of the housing halves around their common longitudinal axis, and wherein the housing halves are fixed with their respective free ends facing away from one another at one of the respective stabilizer halves each. 
   BACKGROUND OF THE INVENTION 
   Axle stabilizers, for which the drive unit of this type is designed, are used, in general, to reduce or even fully compensate rolling movements of the body around the longitudinal axis of the vehicle, which occur because of the lateral acceleration during travel in curves. The wheel carriers, which usually belong to the same axle of the vehicle, are connected with one another via a split axle stabilizer bar, and the axle stabilizer parts are fixed at the same time rotatably at the vehicle body by means of separate bearing elements. The ends of the stabilizer halves, which are located opposite each other and are not fixed to the wheel carrier, are coupled by means of an intercalated rotary drive. The drive unit arranged between the two stabilizer halves as a part of the rotary drive is used to twist the axle stabilizer ends in relation to one another, which may markedly increase the stability of the vehicle against rolling. 
   When such hydraulic drive units are used, it shall be guaranteed for safety reasons that no uncontrolled adjustment of the rotary drive and consequently no unintended change in the properties of the axle stabilizer are brought about in case of failure of the corresponding hydraulic circuit or in case of errors in the electrical system of the motor vehicle. The hydraulic drive units known from the state of the art are equipped for this purpose with expensive and bulky pressure reservoirs with valve systems belonging to them. 
   Moreover, automatic adjustment of the rotary drive into a predefined neutral position, in which the axle stabilizer assembly unit has a medium torsional rigidity, is desirable in case of the above-described failures of the hydraulic and electrical systems of the motor vehicle. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is therefore to provide a drive unit of the type described in the introduction with a safety means that ensures the fixing of the stabilizer adjustment in a predefined neutral position in case of failure of the system in a simple and inexpensive manner. 
   According to the invention, a drive unit is provided for the coaxial twisting movement of two stabilizer halves of a motor vehicle axle stabilizer. The drive unit has a tubular housing, which comprises two housing halves. In the interior a hydraulically movable actuating piston is arranged displaceably in relation to the longitudinal axis of the housing. The longitudinal displacement is converted by means of a intercalated cam drive into a rotary movement of the housing halves around their common longitudinal axis. The housing halves are fixed with their respective free ends facing away from one another at a stabilizer half each. Hydraulically actuated releasing pistons, which can be pretensioned against a spring element, may be arranged at the opposite flat sides of the actuating piston, and the respective releasing pistons make possible the displacing movement of the actuating piston in the pretensioned position and fix the actuating piston in its middle position in the released position. 
   The design embodiment makes possible a compact design and is used to utilize the hydraulically generated pretension of the releasing piston for the longitudinal adjustment of the actuating piston bringing about the twisting of the stabilizer arrangement in case of failure of the electrical, pneumatic or hydraulic system. The spring force for the displacement of the actuating piston may be advantageously ensured by a pneumatic spring; moreover, the use of coil springs is also conceivable due to the compact dimensions of these springs. 
   Corresponding to an advantageous variant of the subject of the present invention, the drive unit may be a hydraulic drive unit, and it is especially advantageous in view of the compact dimensions of the entire stabilizer adjustment unit if the releasing piston and the actuating piston are arranged concentrically with the longitudinal axis of the hydraulic drive unit. 
   To avoid needless loads on the hydraulic pump responsible for the hydraulic circulation, it may, moreover, be expedient to embody the control of the releasing pistons and the stopping of the latter in their pretensioned position by an electrically actuated seat valve. When hydraulics is mentioned here, it is, of course, also possible in the sense of the present invention to use other medias or energies (pneumatic energy, electricity, etc.) to operate the system or parts thereof. An exemplary embodiment of the subject of the present invention will be explained in greater detail below on the basis of the drawings attached. 
   The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a half section through a hydraulic drive unit for twisting the ends of two stabilizer halves of a motor vehicle axle stabilizer in relation to one another; 
       FIG. 2  is a partial sectional view of the exemplary embodiment from  FIG. 1  in the operating state of stabilizer halves twisted in relation to one another; 
       FIG. 3  is a partial sectional view of the exemplary embodiment according to  FIGS. 1 and 2  in the operating position in case of failure of the connected hydraulic network; and 
       FIG. 4  is a partial sectional view through another embodiment variant similar to the exemplary embodiment according to  FIGS. 1 through 3 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The hydraulic drive unit shown in  FIGS. 1 through 3  is part of a rotary drive, which is used to twist the ends of two stabilizer halves  1 ,  2 . The stabilizer halves  1 ,  2  are parts of a motor vehicle axle stabilizer, which is not shown here specifically. The other ends of the stabilizer halves  1  and  2 , which are not shown here, are fixed at the wheel suspension of a respective wheel of a motor vehicle axle and are used to reduce rolling movements of the body around the longitudinal axis of the vehicle, which occur because of the lateral acceleration during the travel of a motor vehicle in curves. 
   The hydraulic drive unit according to the present invention is part of the rotary drive, which comprises essentially two housing halves  3  and  4 , which are twistable in relation to one another and are connected via a flange  5 ,  6  each arranged at each housing half  3 ,  4  with the stabilizer ends  1  and  2 , rotating in unison with them. 
   A thrust ball bearing  7 , which makes possible the twisting movement of the housing halves  3  and  4  in relation to one another, is arranged in the middle between the two housing halves. The housing halves  3  and  4  are braced against each other via a central threaded pin  8 . A fixed partition  9 , which is arranged in the interior of an actuating piston  13  formed by two side walls and a cylindrical connection web  12 , is located centrally in the middle of the rotary drive formed by the two housing halves  3  and  4 . Two piston spaces  14  and  15 , to which oil pressure can be admitted through connections  16  located in the side walls  10  and  11 , are created due to the design of the actuating piston  13  in conjunction with the partition  9 . 
   The connection  16  for the piston space  15  is shown in all  FIGS. 1 through 4 , and a connection of the same type for the piston space  14  is located in the side wall  10  of the actuating piston  13 , radially offset and not visible in the figures. Besides the connections  16  for the oil supply, three cams  17  protruding above the circumference of the side walls are located in the side walls  10  and  11 , distributed over the circumference, and they are arranged distributed by 120° over the circumference of the cylindrical side walls  10  and  11 . The cams  17  are provided in their area projecting above the circumference of the side walls  10  with a needle bearing  18  each, which are recessed in elongated hole-like openings  19  in the outer walls of the cylindrical housing halves  3  and  4 . 
   The cams arranged in the side walls  10  and  11  form, together with the openings  19  distributed over the circumference of the housing walls  20 , a cam drive, which converts a translational motion of the actuating piston  13  in the direction of the arrows P 1  and P 2  into a rotary movement corresponding to the arrows Q 1 , Q 2  for the housing half  3  and S 1 , S 2  for the housing half  4 . 
   To explain the mode of operation of the rotary drive, the operating state will be described on the basis of  FIG. 2 , in which oil is admitted under pressure into the piston space  14  via one of the connections  16  by a hydraulic pump  21 . The piston space  14  is enlarged due to this measure, causing a translational displacement of the actuating piston  13  in the direction of arrow P 1 . The cams  17  arranged in the side walls  10  and  11  move simultaneously with the actuating piston  13  due to this displacement. Since the housing halves  3  and  4  and the openings  19  are restrictedly guided by the cams  17 , twisting of the housing halves  3  in the direction of arrow P 1  is brought about at the same time by the movement of the actuating piston  13  in the direction of arrow P 1 , whereas the housing half  4  is twisted by the movement of the actuating piston  13  in the direction of arrow S 2  in the opposite direction. Thus, the admission of a certain amount of oil under pressure to the piston space  14  corresponds to a corresponding twisting of the ends of the stabilizer halves  1  and  2  in relation to one another. 
   Should a line rupture occur in the connected hydraulic circuit or should the hydraulic pump fail to pump because of a defect in the electrical system of the motor vehicle, no pressure is inherently admitted into the piston space  14 , so that an uncontrolled displacement of the actuating piston  13  would be impossible. 
   The solution offered by the present invention is a further improvement of the rotary drive described such that an uncontrolled translational motion of the actuating piston  13  is ruled out in case of failure of the hydraulic or electrical system of the motor vehicle. 
   A respective, hydraulically actuated releasing piston  22  and  23 , which can be pretensioned against a spring force, is located for this purpose within the housing halves  3  and  4  on the outside of the actuating piston facing away from the piston spaces  14  and  15 . Oil is admitted under pressure into the releasing pistons  22  and  23  into the piston spaces  24  and  25 , which are defined between the releasing piston  22  and  23  and the housing wall, and to which oil is admitted under pressure by the hydraulic pump  21  via the connections  26  and  27 , respectively. On the side of the releasing pistons  22  and  23  facing away from the piston spaces  24  and  25 , there is a compressed air cushion  28  and  29  each, which are compressed in the views shown in  FIGS. 1 and 2  because of the displacement of the releasing pistons  22  and  23  in the direction of the arrows T 1  and T 2 , which displacement is brought about by the admission of oil into the piston spaces  24  and  25  under pressure. The compression of the pressurized medium contained in the compressed air cushion spaces  28  and  29  produces a spring force, which is in equilibrium with the pressure oil located within the piston spaces  24  and  25  during the normal operating state of the hydraulic drive unit. This state is maintained by means of the electrically actuated seat valve  30 . 
   The view in  FIG. 3  illustrates how the operating state shown in  FIGS. 1 and 2  changes as soon as an error develops within the hydraulic or electrical system of the motor vehicle. It can be recognized from  FIG. 3  that the lack of admission of oil under pressure into the entire device makes possible, as was already described in the introduction, a displacement of the actuating piston  13  and a displacement of the releasing pistons  22  and  23  is brought about at the same time as a consequence of the expansion of the air within the compression air cushions  28  and  29  because of the lack of admission of oil under pressure into the piston spaces  24  and  25 . The stored spring forces of the compressed air cushions push the releasing pistons  22  and  23  in the direction of the actuating piston  13  until the front surface of the releasing pistons comes into contact with the outsides of the side walls  10  and  11  of the actuating piston  13 . Due to the symmetrical design of the releasing pistons  22  and  23 , the actuating piston  13  is pushed into the middle position shown in  FIG. 1  if it was displaced, for example, in the direction of arrow P 1  corresponding to  FIG. 2 . The actuating piston  13  is then fixed in the middle position, so that a neutral position of the entire axle stabilizer arrangement is guaranteed. 
   It shall be noted in this connection that the pretension of the releasing pistons  22  and  23  is usually brought about in the piston spaces  24  and  25  in less than 1 sec in case of intact hydraulic and electrical systems when the vehicle is put into operation as a consequence of the build-up of the oil pressure of the hydraulic pump  21 . The seat valve  30  then fixes the above-mentioned state of the releasing pistons  22  and  23 , so that the entire axle stabilizer system is ready to operate. The readiness to operate means that the releasing pistons are in the outer position shown in  FIGS. 1 and 2 , so that the operating piston  13  can be displaced in the direction of the arrows P 1  and P 2 . 
   The view in  FIG. 4  shows another embodiment variant of the subject of the present invention, which differs from the exemplary embodiment shown in  FIGS. 1 through 3  essentially by the manner in which the spring pretension is generated. 
   Therefore, the individual parts of the exemplary embodiment according to the present invention will not be described again. It is essential that the spring pretension is provided in the exemplary embodiment shown in  FIG. 4  by a coil spring  31 . The view in  FIG. 4  shows the normal operating state of the hydraulic drive unit, in which the releasing pistons  22  and  23  are in the spring pretension position. The actuating piston  13  is able in this position to be displaced in the direction of the ends of the stabilizer halves  1  and  2  depending on the admission of oil under pressure into the piston spaces  14  and  15 . 
   Other spring variants, for example, plate springs, are also conceivable for providing the spring pretensioning forces. It is essential for the present invention that displacement of the actuating piston  13  into its middle neutral position is brought about in case of failure of the hydraulic system or the electrical system of the motor vehicle in question due to the release of the spring pretensioning forces as a consequence of the return movement of the releasing pistons  22  and  23 , and the housing halves  3  and  4 , which are coupled with the actuating piston  13  by means of the cams  19 , are moved at the same time back into the neutral position from their twisted position. 
   While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. 
   APPENDIX 
   List of Reference Numbers:
       1  Stabilizer half     2  Stabilizer half     3  Housing half     4  Housing half     5  Flange     6  Flange     7  Thrust ball bearing     8  Threaded pin     9  Partition     10  Side wall     11  Side wall     12  Connecting web     13  Actuating piston     14  Piston space     15  Piston space     16  Connection     17  Cam     18  Needle bearing     19  Opening     20  Housing wall     21  Hydraulic pump     22  Releasing piston     23  Releasing piston     24  Piston space     25  Piston space     26  Connection     27  Connection     28  Compressed air cushion     29  Compressed air cushion     30  Seat valve     31  Coil spring