Abstract:
A motor vehicle is provided with a vehicle body ( 2 ) and with a steering arrangement ( 15 ), which is connected to the vehicle body ( 2 ) and by means of which the motor vehicle ( 1 ) can be steered. At least two wheels ( 3, 4 ) are spring-mounted at the vehicle body ( 2 ) and are each connected to the vehicle body ( 2 ) via a hydraulic actuator. A switching unit ( 31 ) is coupled with the hydraulic actuators ( 7, 8 ) and by which the hydraulic actuators ( 7, 8 ) can be controlled or connected hydraulically in different ways. A control unit ( 23 ) is coupled hydraulically with the switching unit ( 31 ) and has an adjusting element ( 25 ), which is connected to the steering ( 15 ), can be moved by same and by which the switching unit ( 31 ) coupled hydraulically with the actuators ( 7, 8 ) is or can be hydraulically actuated for controlling or connecting the actuators ( 7, 8 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase application of International Application PCT/DE2006/001310 and claims the benefit of priority under 35 U.S.C. § 119 of German Patent Application DE 10 2005 037 661.4 filed Aug. 5, 2005, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains to a motor vehicle with a vehicle body; with a steering connected to the vehicle body, by means of which the motor vehicle can be steered; with at least two wheels, which are spring-mounted on the vehicle body and which are connected to the vehicle body via a hydraulic actuator each; and with a switching unit, which is coupled with the hydraulic actuators and by means of which the hydraulic actuators can be steered or connected hydraulically in different ways. 
       BACKGROUND OF THE INVENTION 
       [0003]    Motor vehicles, which have assembly units for the roll stabilization of the motor vehicle, are known from the state of the art. Conventional roll stabilizers connect, e.g., the two wheels of one axle. This leads to copying motions of the body during straight travel as a consequence of excitations from the road surface and impairs driving smoothness as a result. The cross-country mobility of off-road vehicles is limited because of a permanently acting roll stabilizer. In particular, the lack of torsional flexing may lead to losses of traction. Furthermore, systems for switchable uncoupling (switchable rocker pendulums, shifting claws in the stabilizer back) may be used, which use, e.g., a hydraulic unit for uncoupling the stabilizer. However, an electronic unit and a function software are used for this, which makes the system more expensive. 
         [0004]    An absorption control device for a stabilizing bar is known from DE 196 54 562 A1, wherein an electronically controlled shock absorber is fastened to a suspension arm located under it and holds an end section of the stabilizing bar and exerts a force, which corresponds to a voltage applied, between the stabilizing bar and the suspension arm. An electronic control unit receives output signals from a vehicle velocity sensor as well as a steering angle sensor and actuates the shock absorber via the intermediary of a voltage amplifier. 
         [0005]    A suspension system, in which a stabilizer, which is formed by a torsion bar, is connected to a left and right suspension arm each at its ends via an actuating member, is known from DE 199 40 420 A1. The apparent torsional rigidity of the stabilizer can be changed by the actuating member being provided at least on the left or right side of the stabilizer, so that it can extend or withdraw depending on the needs. A drive control for the actuating member has an electronic control unit, which receives output variables of a plurality of sensors, one of which is a steering angle sensor. The extent of tightness of a curve, in which the vehicle is traveling, is determined by detecting the transverse acceleration, but this can also be determined by calculating the transverse acceleration and the yaw rate from the steering angle and the velocity of the wheel or the vehicle. An electromagnetic linear actuating member of the type of a linear motor, a rotating electromagnetic actuating member or a conventional hydraulic component may be used as the actuating member. 
       SUMMARY OF THE INVENTION 
       [0006]    Based on this state of the art, the basic object of the present invention is to perfect a motor vehicle of the type mentioned in the introduction such that control of the actuators can be achieved without or with only a slight electronic effort. 
         [0007]    The motor vehicle according to the present invention has a vehicle body; a steering, which is connected to the vehicle body and by means of which the vehicle can be steered; at least two wheels, which are spring-mounted on the vehicle body and which are connected to the vehicle body via a hydraulic actuator each; and a switching unit, which is coupled with the hydraulic actuators and by means of which the hydraulic actuators can be controlled or connected hydraulically in different ways. A switching unit is hydraulically coupled with the switching unit and has an adjusting element, which is connected to the steering, can be moved by the steering arrangement and by means of which the switching unit coupled hydraulically with the actuators can be or is hydraulically actuated for controlling or connecting the actuators. 
         [0008]    An adjusting element connected to the steering is used in the motor vehicle according to the present invention to control the actuators or the characteristics thereof. The adjusting element, which is connected to the steering especially mechanically, acts hydraulically on the switching unit and actuates same to vary the actuator characteristics. Controlling of the actuators or changing their characteristics can thus be achieved purely mechanically and hydraulically, so that a complicated electronic control with sensors can be done away with. Controlling of the actuators or the characteristics thereof preferably takes place by the actuators being able to be connected or being connected hydraulically in different ways by means of the switching unit. Each wheel is mounted, in particular, movably, preferably pivotably via the corresponding actuator on the vehicle body. In particular, the spring rate for the spring-mounted wheels can be influenced by means of the actuators. Since the roll stabilization characteristics or roll characteristics of the motor vehicle can also be influenced via the characteristics of the actuators, controlled roll stabilization can also be achieved with the motor vehicle according to the present invention without a complicated electronic control. The actuators, the switching unit as well as the control unit with the adjusting element form a hydraulic actuator unit of the motor vehicle, which is coupled with the steering and is controlled or actuated by the latter. 
         [0009]    The hydraulic coupling of the control unit with the switching unit is preferably uncoupled via the switching unit against feedback from the hydraulic couplings of the actuators with the switching unit, so that the control unit is coupled with the actuators without feedback. As a result, the influence of the actuators on the steering can be avoided or reduced. In particular, a plurality of hydraulic circuits can be embodied, the first hydraulic circuit coupling the control unit with the switching unit being separated by means of the switching unit from the other hydraulic circuits coupling the actuator or actuators with the switching unit in such a way that a hydraulic fluid present in the first hydraulic circuit cannot mix with a hydraulic fluid present in the other hydraulic circuit or hydraulic circuits. A hydraulic liquid is preferably used as the hydraulic fluid. 
         [0010]    Depending on the control unit, the switching unit may assume different switching states, and the characteristics of the actuators can be varied between at least two different operating states. The two actuators are preferably separated for this from each other hydraulically in a first of the switching states by means of the switching unit and the two actuators are hydraulically coupled with one another via the intermediary of the switching unit in a second of the switching states. Hydraulic coupling of the two actuators with one another leads to different characteristics than when the two actuators are hydraulically uncoupled from each other. In particular, the two actuators mutually influence each other hydraulically in the second switching state and are hydraulically connected together hydraulically such that, e.g., rebound of one of the wheels also forces the other wheel to rebound and, e.g., inward deflection of one of the wheels also forces the other to perform an inward deflection. A wheel performing inward deflection or rebound actuates the actuator (e.g., as a hydraulic pump) connected to that wheel, which actuator drives the other actuator (as a final control element or motor), which will then cause the other wheel connected to same to perform an inward deflection or a rebound. Such a mutual hydraulic influence of the actuators on each other is prevented in the first switching state. 
         [0011]    A hydraulic throttle each, which is coupled with the switching unit and via which the respective actuator is hydraulically short-circuited in the first switching state via the intermediary of the switching unit, is preferably connected to the actuators. It is possible by means of the throttles to set the absorption characteristics in the first switching state, a different absorption characteristic being able to be achieved especially for the pulling and pushing stage of each wheel. The term “pushing stage” is defined here as the inward deflection and the term “pulling stage” as the rebound of the corresponding wheel in relation to the vehicle body. In particular, absorption is greater in the pulling stage than the absorption in the pushing stage. For example, an approximately 30% greater absorption can be embodied for the pulling stage than in the pushing stage. 
         [0012]    However, the actuators may also be short-circuited via the switching element without the intermediary of throttles in the first switching state. Furthermore, it is possible to completely stop the feed or removal of hydraulic fluid into or from each actuator. The actuators can form only a rigid connection between the wheels and the vehicle body in this case, which may, however, have a negative effect on driving smoothness. The actuators may also be coupled with one another without or via the intermediary of the throttles in the second switching state. 
         [0013]    The switching unit preferably has a switching chamber, in which a control piston, which can be brought into different positions by the control unit, is mounted movably or guided displaceably, and which control piston hydraulically separates the actuators from each other in the first switching state and forms a hydraulic connection of the two actuators with one another or forms at least part of this connection in the second switching state. The control piston may be provided with a plurality of recesses or channels, the hydraulic fluid flowing through different channels depending on the switching state. Furthermore, the control piston forms especially a hydraulic connection (or a part thereof) between the respective throttle and the respective actuator in the first switching state, so that the two actuators are hydraulically short-circuited via the intermediary of the control piston and optionally of the respective throttle. Additional recesses or channels may be provided in the control piston for this connection. 
         [0014]    The control unit preferably has a hydraulic chamber, which is filled especially with hydraulic fluid and in which a hydraulic piston forming the adjusting element is mounted movably or guided displaceably. The hydraulic chamber is preferably connected hydraulically to the switching unit or the control piston. Two hydraulic spaces, which are hydraulically coupled especially with the front sides of the control piston, may be formed between the hydraulic piston and the closed front sides of the hydraulic chamber. 
         [0015]    The actuators may be designed as hydraulic linear actuators, e.g., as hydraulic linear absorbers and/or hydraulic linear motors. However, the actuators are preferably hydraulic rotary actuators, e.g., rotation absorbers and/or hydraulic swivel motors, which have a flat shape, contrary to linear actuators. The actuators may form hydraulic absorbers or pumps, which can preferably also be operated as hydraulic drives (motors) or final control elements. The actuator unit forms an absorber unit or an absorber-motor unit in this case. The absorption characteristics of the hydraulic actuators can now be varied by means of the switching unit, which is or can be hydraulically actuated or controlled by the adjusting element for this purpose. 
         [0016]    To compensate temperature-related changes in the volume of the hydraulic fluid and/or losses due to leakage, at least one hydraulic reservoir may be hydraulically coupled with one of the actuators. However, both actuators are preferably connected hydraulically to a hydraulic reservoir each. The reservoirs can, furthermore, reduce or absorb hydraulic pressure peaks, especially when the two actuators or wheels are coupled with one another by the switching unit and thus act like a hydraulic capacity. The hydraulic fluid in the reservoir or reservoirs is especially under pressure. Furthermore, hydraulic pumps may be provided, which maintain the hydraulic fluid in the reservoir or reservoirs under pressure or feed hydraulic fluid to the reservoirs under pressure. The hydraulic pumps may be driven by the throttles or supplied with energy by same. It is also possible for the throttles themselves to have a pumping action or to be designed as pumps and especially to prestress the reservoir or the reservoirs especially automatically. 
         [0017]    The control unit is preferably coupled hydraulically with the switching unit via a switchable hydraulic valve. The control unit can thus be hydraulically separated from the switching unit when needed. In particular, the coupling of the two actuators or wheels can be prevented by the hydraulic valve. This is utilized, e.g., when the steering is in the zero position and the vehicle is being operated off the road. 
         [0018]    The two wheels are preferably connected to the vehicle body via a spring each, so that the wheels can be maintained at spaced locations from the vehicle body. Furthermore, the two wheels can be mounted pivotably at the vehicle body, especially by means of or via the intermediary of the actuators. 
         [0019]    The two wheels are preferably provided on a common vehicle axle of the motor vehicle, which axle forms especially a steerable vehicle axle. The two wheels are or can be pivoted in this case by means of the steering in relation to the vehicle body. However, it is also possible that the two wheels are provided at a common, non-steerable vehicle axle. The motor vehicle preferably has in this case at least one additional, steerable vehicle axle, whose wheels are pivotable, especially in relation to the vehicle body, by means of the steering. Furthermore, it is possible to provide a plurality of vehicle axles of the motor vehicle with the actuator unit according to the present invention, of which especially at least one vehicle axle forms a steerable vehicle axle. 
         [0020]    A torsion bar as a roll stabilizer can be done away with in the motor vehicle according to the present invention, because the actuator unit makes possible a roll stabilization controlled by the steering. The spring rate for the spring-mounted wheels can thus be reduced (by the dimension of the stabilizer spring), especially during straight travel or even permanently during off-road operation. Yet, it is possible to provide a torsion bar as an additional roll stabilizer, which preferably has soft spring characteristics. 
         [0021]    Thus, the present invention describes a motor vehicle, which has an assembly unit or actuator unit, which is suitable for the roll stabilization of the motor vehicle. The actuator unit is characterized especially in that the conventional roll stabilizer has no effect during straight travel. The undesired copying is thus avoided. A rigidity can be switched on additionally during travel in curves in order to counteract rolling motions. The connection takes place especially via the hydraulic piston, which is preferably connected directly to the steering and drives or actuates the switching unit. It can be predetermined by the design of the switching unit that the additional rigidity will begin to act only beginning from a predetermined steering angle value or steering angle from the zero position, so that a hysteresis or hysteresis range can be obtained. This predetermined steering angle or steering angle value can especially be set and equals, e.g., ±3°. Furthermore, the zero position preferably represents a position of the steering wheel during straight travel of the motor vehicle. Within the hysteresis range, the wheels of the vehicle axle are guided independently from one another via the two throttles or a throttle package, with which the coordination of the absorber can be embodied for the pulling stage and the pushing stage for straight travel. 
         [0022]    If the additional rigidity becomes necessary for compensating the rolling motion during travel in a curve (the steering angle being greater than the hysteresis), the actuators of one vehicle axle are coupled with one another. The respective reservoir can then be stressed further due to the slope of the vehicle during travel in a curve. If no reservoir is present, the system is nevertheless prestressed in the tubes or in the hydraulic lines. An elasticity is, in particular, always present, so that one can also speak of an “oil spring” or “hydraulic spring.” By contrast, absorption is preferably brought about via the throttles during straight travel. 
         [0023]    In particular, the following advantages can be achieved with the present invention: A conventional roll stabilizer can be eliminated, as a result of which the design of the wheel suspension can be simplified. Furthermore, conventional linear actuators can be replaced by rotary actuators, which can be embodied with a flat design. Control arms and actuators may also be designed as one component. No sensor system and electronic system is necessary, unless a hydraulic valve is present or integrated and is switched electrically (e.g., in case of permanent uncoupling). Furthermore, permanent uncoupling of the wheels of one axle is possible (integrated off-road functionality). 
         [0024]    The present invention will be described below on the basis of preferred embodiments with reference to the drawings. 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 
         [0025]    In the drawings: 
           [0026]      FIG. 1  is a schematic view of the motor vehicle according to the present invention according to a first embodiment; 
           [0027]      FIG. 2  is a schematic sectional view of the switching unit from  FIG. 1  in a coupled state of the actuators; 
           [0028]      FIG. 3  is a schematic sectional view of the switching unit from  FIG. 1  in another coupled state of the actuators; 
           [0029]      FIG. 4  is a schematic sectional view of the switching unit from  FIG. 1  in an uncoupled state of the actuators; 
           [0030]      FIG. 5  is a schematic sectional view of the control unit from  FIG. 1 ; 
           [0031]      FIG. 6  is a schematic view of an alternative, switchable valve; and 
           [0032]      FIG. 7  is a schematic view of the motor vehicle according to the present invention according to a second embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Referring to the drawings in particular,  FIG. 1  shows a schematic view of a first embodiment of the motor vehicle according to the present invention, which is designated as a whole by  1 . Two wheels  3 ,  4  are connected to a vehicle body  2  of the motor vehicle  1  via a respective spring  5 ,  6  each. Furthermore, two hydraulic rotary actuators  7 ,  8 , which have each a housing  9 ,  10  and an inner part  11 ,  12  arranged therein, are fastened to the vehicle body  2 . The inner parts  11 ,  12  are connected to the vehicle body  2  in such a way that they rotate in unison, whereas the housings  9 ,  10  are connected to a suspension arm  13 ,  14  in such a way that they rotate in unison. The inner parts  11 ,  12  are mounted rotatably in the respective housing  9 ,  10  and have a plurality of (e.g., four) radial wings each, between which chambers filled with hydraulic fluid are formed. The design of the actuators  7 ,  8  resembles, in particular, the design of a hydraulic swivel motor. Furthermore, the suspension arm  13  is articulated to wheel  3  and the suspension arm  14  to wheel  4 . 
         [0034]    A steering arrangement  15  connected to the vehicle body  2  has a steering wheel  16  and a steering gear  17 , which is coupled with the steering wheel  16  via a steering shaft  18 . A rack and pinion  19 , which protrudes from a housing of the steering gear  17  on both sides and is displaceable in its longitudinal direction by means of a rotary motion of the steering wheel  16 , is arranged in the steering gear  17 . The rack and pinion  19  is connected to the wheel  3  by means of a track rod  20  and to the wheel  4  by means of a track rod  21 , so that the two wheels  3 ,  4  are pivotable in relation to the vehicle body  2  by means of a rotary motion of the steering wheel  16 . The two wheels  3 ,  4  are thus part of a steerable front axle  22  of the motor vehicle  1 . 
         [0035]    Even though the steering arrangement  15  is described here on the basis of a rack-and-pinion steering, it is, however, also possible to use another type of steering arrangement. The rack and pinion steering arrangement  15  is replaced in this case by a component that is movable by the steering wheel  16  or steering gear  17  and is connected to the wheels  3 ,  4  for pivoting the wheels  3 ,  4 . 
         [0036]    A control unit  23  has a hydraulic chamber  24 , which is fastened to the housing of the steering gear  17  and in which a hydraulic piston  25  is guided displaceably. The hydraulic piston  25  is mechanically connected to the rack and pinion  19  by means of a mechanical connection, especially via a linkage  26  or another pull-push mechanism. The hydraulic chamber  24  is filled with a hydraulic fluid and is closed on the front side, the linkage  26  being guided displaceably through one of the front sides of the hydraulic chamber  24  and sealed against the front side (see  FIG. 5 ). The piston  25  is sealingly in contact with the inner wall of the hydraulic chamber  24 , so that hydraulic spaces  27 ,  28  filled with hydraulic fluid are formed between the piston  25  and the two front sides of the hydraulic chamber  24 . The hydraulic space  27  is hydraulically connected via a hydraulic line  29  to a hydraulic space  30  in a switching unit  31 . Furthermore, the hydraulic space  28  is hydraulically connected to a valve  33  via a hydraulic line  32 . Valve  33  is connected via a hydraulic line  34  to a hydraulic space  35  in the switching unit  31 . Furthermore, valve  33  is connected to the hydraulic line  29  via a hydraulic line  36 . 
         [0037]    The switching unit  31  has a switching chamber  37 , in which a control piston  38  is guided displaceably. The switching chamber  37  is closed on the front side, so that the two hydraulic spaces  30  and  35  are formed between the front sides of the control piston  38  and the front sides of the switching chamber  37  (see  FIG. 4 ). 
         [0038]    The control piston  38  has a plurality of through holes  39 , which are separated from one another by walls  40  and may be designed as holes, the walls  40  being formed by the material of the control piston  38 . Furthermore, the holes  39  are separated from the hydraulic spaces  30  and  35  via the front sides of the control piston  38 . As an alternative, the holes  39  may, however, also be completely or partially replaced by grooves in the outer circumferential surface of the control piston  38 . 
         [0039]    The actuator  7  or one of the chambers in the actuator  7  is connected to the switching unit  31  via a hydraulic line  41 . Furthermore, the actuator  7  or another one of the chambers in the actuator  7  is connected to a hydraulic line  43  and to a hydraulic line  44  via a hydraulic line  42 , the two hydraulic lines  43  and  44  being connected to the switching unit  31 . 
         [0040]    The actuator  8  or one of the chambers in the actuator  8  is connected to the switching unit  31  via a hydraulic line  45 . Furthermore, the actuator  8  or another one of the chambers in the actuator  8  is connected via a hydraulic line  46  to a hydraulic line  47  and to a hydraulic line  48 , the two hydraulic lines  47  and  48  being connected to the switching unit  31 . 
         [0041]    The hydraulic line  42  is connected, furthermore, to a hydraulic line  50 , which is connected to the switching unit  31  via the intermediary of a hydraulic throttle  51 . Furthermore, the hydraulic line  46  is connected to a hydraulic line  52 , which is connected to the switching unit  31  via the intermediary of a hydraulic throttle  53 . 
         [0042]    The control lines  41 ,  43 ,  44 ,  45 ,  47 ,  48 ,  50  and  52  are connected to the interior space of the switching chamber  37  at different points via through holes  49  provided in the wall of the switching chamber  37 . 
         [0043]    The control unit  23 , the valve  33 , as well as the hydraulic lines  29 ,  32 ,  34  and  36  form a first hydraulic circuit with the hydraulic spaces  30  and  35  via the intermediary of the control piston  38 , the valve  33  being connected such that the hydraulic line  32  is connected to the hydraulic line  34  and the hydraulic line  36  is closed by the valve  33 . If the steering wheel  16  is rotated in one direction, so that the rack and pinion  19  is moving together with the piston  25  in the direction of arrow P, hydraulic fluid is pressed out of the hydraulic space  27  and through the hydraulic line  29  into the hydraulic space  30 . As a result, the control piston  38  is displaced in the direction of arrow Q, so that hydraulic fluid flows out of the hydraulic space  35  into the hydraulic space  28  through the hydraulic line  34 , through the valve  33  and through the hydraulic line  32 . If the steering wheel  16  is rotated in the opposite direction, so that the rack and pinion  19  and the hydraulic piston  25  are moving in a direction opposite arrow P, the control piston  38  is displaced in a direction opposite the direction indicated by arrow Q. The displacement of the control piston  38  always takes place relative to the switching chamber  37 . 
         [0044]    The first hydraulic circuit is uncoupled from the actuators  7 ,  8  via the switching unit  31  in such a way that hydraulic fluid of the first hydraulic circuit cannot exchange or mix with hydraulic fluid of the actuators  7 ,  8 . Furthermore, the switching unit  31  prevents feedback from the actuators  7 ,  8  to the first hydraulic circuit, because the hydraulic fluid of the actuators  7 ,  8  cannot displace the control piston  38 . This is achieved especially by the hydraulic fluid of the actuator  7 ,  8  flowing at right angles to the direction of motion of the control piston  38  into and out of the switching chamber  37 . 
         [0045]    In the position of the control piston  38  shown in  FIG. 1 , the actuator  7  is hydraulically short-circuited via the hydraulic lines  41 ,  50  and  42  via the intermediary of throttle  51 . The hydraulic line  50  or the throttle  51  is in connection now with the hydraulic line  41  via one of the holes  39  in the control piston  38 . Furthermore, the actuator  8  is hydraulically short-circuited via the hydraulic lines  45 ,  52  and  46  via the intermediary of throttle  53 , the hydraulic line  52  or the throttle  53  being in connection with the hydraulic line  45  via another one of the holes  39  of the control piston  38 . These two actuators  7  and  8  are thus hydraulically uncoupled from one another. 
         [0046]      FIG. 2  shows a schematic view of the switching unit  31  in a coupled state of the actuators  7 ,  8 , wherein the control piston  38  is displaced in the direction of arrow Q. The hydraulic line  41  is connected in this case to the hydraulic line  47  via one of the holes  39 . Furthermore, the hydraulic line  45  is connected to the hydraulic line  43  via another one of the holes  39 , so that the two actuators  7 ,  8  are hydraulically coupled with one another. This hydraulic coupling of the two actuators  7 ,  8  is preferably carried out such that roll stabilization or stabilization of the yaw characteristic of the motor vehicle  1  is achieved. 
         [0047]      FIG. 3  shows a schematic view of the switching unit  31  in another coupled state of the actuators  7 ,  8 , where the control piston  38  is displaced in a direction opposite the direction of arrow Q. The hydraulic line  41  is connected in this case to the hydraulic line  48  via one of the holes  39 . Furthermore, the hydraulic line  45  is connected to the hydraulic line  44  via another one of the holes  39 , so that the two actuators  7 ,  8  are hydraulically coupled with one another. This hydraulic coupling of the two actuators  7 ,  8  is preferably brought about such that roll stabilization or stabilization of the roll angle of the motor vehicle  1  is achieved. 
         [0048]      FIG. 4  shows a schematic view of the switching unit  31  in an uncoupled state of the actuators  7  and  8 , which corresponds to the state of the switching unit  31  shown in  FIG. 1 . Furthermore,  FIG. 5  shows a schematic view of the control unit  23 . 
         [0049]    Valve  33  in  FIG. 1  can be actuated via a switch  54  and it can thus be switched over. The hydraulic line  32  is connected to the hydraulic line  36  in the switched-over state, whereas the hydraulic line  34  is closed by valve  33 . The control piston  38  of the switching unit  31  cannot be adjusted by the control unit  23  any longer in this state. The switched-over state can now be switched on preferably only if the two actuators  7 ,  8  are uncoupled from one another. Relative to the embodiment, this means that the switched-over state can be switched on especially only when the control piston  38  is in the position according to  FIG. 1  or  4 . 
         [0050]      FIG. 6  shows an alternative embodiment of valve  33 , wherein the hydraulic line  29  connected to the hydraulic space  30  is connected hydraulically to the hydraulic space  27  via the intermediary of valve  33  and a hydraulic line  57 . Valve  33  can be switched over by means of switch  54  such that the two hydraulic lines  32  and  57  and hence also the two hydraulic spaces  27  and  28  are connected hydraulically to one another, whereas the two lines  29  and  34  are closed by valve  33 . 
         [0051]      FIG. 7  shows a schematic view of a second embodiment of the motor vehicle according to the present invention, wherein identical or similar features are designated by the same reference numbers as in the first embodiment. The second embodiment differs from the first embodiment only in that the hydraulic throttles  51  and  53  are connected into the hydraulic lines  41  and  46  rather than into the hydraulic lines  50  and  52 . The actuators  7 ,  8  are thus coupled with one another in the coupled state via the intermediary of the throttles  51 ,  53 , so that the flow of hydraulic fluid (oil flow) is also throttled during travel in a curve. 
         [0052]    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.