Abstract:
A stabilizer assembly unit for a motor vehicle, having a first fluid pressure actuator and a second fluid pressure actuator which are associated with opposite ends of an antiroll bar, characterized in that exactly one pressure fluid connection is provided on each of the fluid pressure actuators.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/EP2006/007154 filed Jul. 20, 2006, the disclosures of which are incorporated herein by reference in their entirety, and which claimed priority to German Patent Application No. 20 2005 014 926.8 filed Sep. 21, 2005, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a stabilizer assembly unit for a motor vehicle, including a first fluid pressure actuator and a second fluid pressure actuator which are associated with opposite ends of an antiroll bar. 
     Such stabilizer assembly units are used in active chassis for suppressing or controlling the roll movements of the vehicle body in cornering. In these arrangements the use of an antiroll bar that is passive when taken by itself has been known for a long time. Such an antiroll bar is comprised of an elastic middle section that is rotatably attached to the vehicle body, and two levers that are connected to the wheel suspensions. Now if the vertical distance between the vehicle axle with which the antiroll bar is associated and the vehicle body changes on one vehicle side as compared to the other vehicle side, the antiroll bar is increasingly elastically tensioned as the change in distance increases. This results in a roll torque which attempts to urge the vehicle body into a position in which both ends of the vehicle axle have the same distance to the vehicle body. 
     A basic disadvantage of the sole use of such antiroll bars is that the latter impede cushioning movements of the axle on one side, which are for example necessary in the case of an uneven road on one side. 
     The active chassis already mentioned serve to solve this problem. In these active chassis, the chassis characteristics are changed with the aid of actuators in response to vehicle parameters and a particular traffic situation by, for example, pretensioning or relieving antiroll bars. This results in an improved adaptation of the vehicle to the respective traffic situation, such as an improved road grip when cornering. 
     DE 44 43 809 A1 discloses, for example, a stabilizer assembly unit including an antiroll bar that is configured in two parts and the ends of which may be tensioned with respect to one another by means of a hydraulic rotary drive. Such rotary drives have to be produced with close tolerances and sealed in a complicated manner. Therefore, they are expensive. They are, moreover, relatively maintenance-intensive and susceptible to faults in operation. 
     The generic document WO 02/083439 A1, and corresponding U.S. Pat. No. 7,055,832 B2, both of which are incorporated by reference herein, shows a stabilizer assembly unit including an antiroll bar which may be connected to the wheels via two linear hydraulic actuators. Each of the hydraulic actuators configured as a piston/cylinder unit disposes of two pressure connections via which the two cylinder chambers existing in each actuator may be acted upon with pressure. Provided for this purpose are one or several control valves, a plurality of hydraulic lines, and a hydraulic pump having a reservoir associated therewith, these components forming a comparatively complicated arrangement with a space requirement that should not be neglected. 
     BRIEF SUMMARY OF THE INVENTION 
     In contrast to the above prior art stabilizer assembly units, the present invention provides a stabilizer assembly unit that is distinguished by a simple construction and a considerably reduced space and may therefore be implemented at a particularly favorable price. 
     In a stabilizer assembly unit of the present invention, exactly one pressure fluid connection is provided on each of the fluid pressure actuators. In this manner a system is provided which is considerably simplified as compared to the prior art and may therefore be manufactured at low cost, and which is less susceptible to failure. 
     Preferably, the fluid pressure actuator is a linear fluid pressure actuator which is distinguished by a simple construction and therefore operates particularly reliably. 
     According to a preferred embodiment, the fluid pressure actuator is a hydraulic cylinder and the pressure fluid connection is a hydraulic connection. Hydraulic cylinders are standard components which are available at low cost. 
     Advantageously, the hydraulic cylinder has a return element that is disposed in an interior space of the hydraulic cylinder. Such an arrangement offers the advantage of a particularly small space required. 
     Preferably, the hydraulic cylinder includes a piston which is urged into a neutral position by the return element. Therefore, only one hydraulic connection is required to move the piston into an extended position, since the piston may be returned to the neutral position by the return element. Since, moreover, the neutral position is not restricted to a central position of the piston, as customary with hydraulic cylinders in other arrangements, it is possible to obtain a hydraulic cylinder that is distinguished by a particularly small axial dimension by appropriately selecting the piston neutral position. 
     Advantageously, the piston divides the interior space of the hydraulic cylinder into a first chamber and a second chamber, the first chamber being connected to a source via the hydraulic connection, and the second chamber being under atmospheric pressure. Thus, when the hydraulic cylinder is suitably configured, with the piston rod extending in and out of the second chamber, a sealing arrangement around the piston rod is not required, which renders the production of the hydraulic cylinder particularly simple and cost-effective. 
     The return element may be disposed in the first chamber. In this manner the second chamber may completely be used for the piston travel. 
     According to a preferred embodiment, the return element is a helical spring which is a reliable, almost maintenance-free but still low-priced component. 
     Preferably, a valve is provided for actuating both fluid pressure actuators, the valve being arranged between a pressure source and the pressure fluid connections. Thus, a hydraulic system of a particularly simple construction is obtained, which has a minimum of components and in which the single valve provided controls the entire system. 
     Advantageously, the valve has a neutral position and two actuating positions, one fluid pressure actuator each being actuated in each actuating position. Thereby, an uncomplicated arrangement materializes, whose susceptibility to failure is low. 
     According to a preferred embodiment, in the neutral position of the valve, both fluid pressure actuators are connected to a reservoir of the pressure source. This allows an exchange of pressure of the fluid pressure actuators both with the reservoir and among each other, whereby the mechanical antiroll bar is bridged in the neutral position. 
     Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic representation of a stabilizer assembly unit in accordance with the invention in a neutral position; and 
         FIG. 2  shows a schematic representation of the stabilizer assembly unit of  FIG. 1  in an actuating position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  schematically shows a stabilizer assembly unit  10  having an antiroll bar  12  for a vehicle axle. The antiroll bar  12  includes a lever arm  14  on the left in the figure, a lever arm  16  on the right in the figure, and a middle section  18 . The middle section  18  is mounted so as to be rotatable about its longitudinal axis in two bearings  20  and  22  on the vehicle body, whilst the two lever arms  14  and  16  are connected to one linear fluid pressure actuator each in the form of a hydraulic cylinder  24  and  26 , respectively. 
     Each hydraulic cylinder  24  and  26  comprises a piston  28  and  30 , respectively, and a cylinder body  32  and  34 , respectively, the pistons  28  and  30  being attached to the lever arms  14  and  16 , respectively, of the antiroll bar  12 , and the cylinder bodies  32  and  34  being connectable to the respective wheel suspension. Thus, the hydraulic cylinders  24  and  26  replace the connecting rods which are normally provided and which connect the lever arms  14  and  16  of the antiroll bar  12  to the wheel suspensions of the vehicle. The wheels, not illustrated, are thus connected to fastening points  35 . 
     By means of the pistons  28  and  30  the interior spaces of the cylinder bodies  32  and  34  are each divided into a first chamber  36  or  38  and a second chamber  40  or  42 . Disposed in the first chambers  36  and  38  is a return element in the form of a helical spring  44  and  46 , respectively, which couples the respective piston  28  or  30  to the associated cylinder body  32  or  34 . 
     In this arrangement, the second chambers  40  and  42 , in which rod sections  48  and  50 , respectively, of the pistons  28  and  30 , respectively, extend, are not sealed with respect to the atmosphere, and are consequently under atmospheric pressure. The first chambers  36  and  38 , on the other hand, are sealed by the pistons  28  and  30 , respectively, and communicate with a pressure source  60  via pressure fluid connections, more precisely via hydraulic connections  52  and  54 , respectively, and associated hydraulic lines  56  and  58 , respectively. 
     The pressure source  60  comprises a hydraulic pump  62  and a pressureless reservoir  64 . A valve  66  for controlling the stabilizer assembly unit  10  is provided between the hydraulic cylinders  24  and  26  and the pressure source  60 . The valve  66 , which may for example be a solenoid valve, has a neutral position II and two actuating positions I and III. In the neutral position II, both hydraulic cylinders  24  and  26  are connected to the reservoir  64 . 
     In the state of the stabilizer assembly unit  10  shown in  FIG. 1 , both the valve  66  and the two hydraulic cylinders  24  and  26  are in the neutral position. The neutral position of the pistons  28  and  30  is determined by the springs  44  and  46 , respectively, the neutral position of the pistons  28  and  30  being selected in the embodiment shown such that in the neutral position the first chambers  36  and  38  are of considerably smaller dimensions than the second chambers  40  and  42 . Thereby, the pistons  28  and  30  dispose of almost twice the stroke length than would be the case with a conventional linear actuator in which in the neutral position the piston is arranged in the center, the overall size of the hydraulic cylinders  24  and  26  being the same. 
     Now if a situation arises in which an increase in the distance between the vehicle body and the wheel associated with the lever arm  14 , on the left in the figure, of the antiroll bar  12  is required, the valve  66  is switched to the actuating position I shown in  FIG. 2 . Thereby, the first chamber  36  of the hydraulic cylinder  24  on the left in the figure is acted upon with pressure via the hydraulic connection  52 , whereby the piston  28  shifts downwards against the atmospheric pressure prevailing in the second chamber  40 , whereas the hydraulic cylinder  26  on the right in the figure is blocked in its neutral position. In so doing, the pressurized hydraulic cylinder  24  rotates the antiroll bar  12 , which permits to provide a controlled roll torque to the vehicle body. 
     The hydraulic cylinder  26  on the right in the figures may analogously be actuated by switching the valve  66  to the actuating position III, the left hydraulic cylinder  24  being then blocked in its neutral position. 
     Upon switching the valve  66  to the neutral position II, the respective piston  28  or  30  displaced is returned on account of the return force of the spring  44  or  46  and the forces acting on the vehicle from the outside. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of the invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.