Abstract:
Apparatus for the active stabilization of the rolling of a vehicle that has at least two axles that each have at least two wheels. The axles are each equipped with a transverse stabilizer that is hydraulically actuated by a directional control valve. The transverse stabilizers are operated by respective hydraulic motors. A pressure supply pump applies different hydraulic pressure levels through respective pressure limiting valves. The directional control valve is actuated hydraulically by a directly controlled control valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a continuation of International application Ser. No. PCT/DE2006/000520, with an international filing date of Mar. 24, 2006, and designating the United States, the entire contents of which are hereby incorporated by reference to the same extent as if fully rewritten. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to apparatus for active roll stabilization of a motor vehicle having at least two axles, which each have at least two wheels and are each equipped with a transverse stabilizer, whereby the transverse stabilizers can be activated using a direction-switching valve device using hydraulic devices, which can be acted upon by a pressure supply unit, such as a pump, through axle pressure-limiting valves with varying pressure levels. 
   2. Description of the Related Art 
   Roll stabilization devices are also designated as anti-roll systems or roll stabilization systems.  FIG. 1  shows a hydraulic diagram of a conventional roll stabilization device. 
   An object of the present invention is to provide a device for the active roll stabilization of a motor vehicle having at least two axles, which respectively have at least two wheels and are respectively equipped with a transverse stabilizer, whereby the transverse stabilizers can be activated using a direction-switching valve device using hydraulic devices, on which a pressure supply unit, such as a pump, can apply different pressure levels via axle pressure-limiting valves, which is more cost effective to manufacture than conventional roll stabilization devices. 
   SUMMARY OF THE INVENTION 
   The object is achieved in a device for active roll stabilization of a motor vehicle having at least two axles, which respectively have at least two wheels and are respectively equipped with a transverse stabilizer, whereby the transverse stabilizers can be activated using a direction-switching valve device through hydraulic devices, on which a pressure supply unit, such as a pump, can apply different pressure levels via axle pressure-limiting valves, in that the direction-switching valve device is actuated hydraulically by means of a directly actuated control valve device. Within the scope of the present invention, it was found that the cost of the magnetic coil used in conventional anti-roll systems for direct actuation of the direction-switching valve device is not negligible. In contrast, the present invention provides the advantage that a commercially available, economical, directly actuated control valve can be used. Compared to the pilot control of the axle pressure-limiting valves via a separate pilot control circuit with a pressure regulator connected downstream from the pump, the roll stabilization device of the invention advantageously provides a simple design without a pilot control circuit. Besides, the pressure regulator can be dispensed with in any case, thus minimizing system leakage. 
   A preferred embodiment of the roll stabilization device is characterized in that the control valve device includes a valve spool or valve plunger, which interacts with a proportional magnet. The valve spool produces the pressure for the hydraulic actuation of the direction-switching valve device, which pressure is proportional to the strength of the proportional magnet. 
   A further preferred embodiment of the roll stabilization device is characterized in that the control valve device is formed by a control pressure-limiting valve, which is connected in parallel to the axle pressure-limiting valves. The control pressure-limiting valve raises the system pressure to a system pressure required for a desired switch combination. The axle pressure-limiting valves then only need to adjust the remaining pressure differentials to the required axle pressures in each case. 
   A further preferred embodiment of the roll stabilization device is characterized in that the control valve device is formed by a control pressure valve, which is connected in series to the pressure supply unit. In the deenergized state of the control pressure-reducing valve, the hydraulic actuator spaces of the direction-switching valve device and, if necessary, a fail-safe valve are selectively held at the tank pressure level. That should ensure that the direction-switching valve and, if necessary, the fail-safe valve, remain at their normal positions. In order to adjust the control pressure, a minimum pressure, e.g. 2.5 bar, is set by means of one of the axle pressure-limiting valves. 
   A further preferred embodiment of the roll stabilization device is characterized in that the control valve device is acted upon by the pressure from a tank, from which the pressure supply unit is fed. In that way, it is ensured that a change in the tank pressure level, e.g. by temperature influence, does not lead to a change in the switch points at the direction-switching valve device. 
   A further preferred embodiment of the roll stabilization device is characterized in that the axle pressure-limiting valves are acted upon by the pressure from a tank that supplies the pressure supply unit. The axle pressure-limiting valves feature a plunger chamber and a spring chamber that each are specifically acted upon by the tank pressure level. That has the advantage that the magnets used in the axle pressure-limiting valves need not be designed to be pressure-resistant. 
   A further preferred embodiment of the roll stabilization device is characterized in that the direction-switching valve device includes a 7/2 directional control valve. The 7/2 directional control valve is intended for direction-switching of the hydraulic devices and is actuated hydraulically via the control valve device. 
   A further preferred embodiment of the roll stabilization device is characterized in that a hydraulically actuated fail-safe valve is connected between the direction-switching valve device and one of the hydraulic devices. Both the direction-switching valve device and the fail-safe valve are controlled by one and the same control valve device. In this way, the manufacturing costs of the roll stabilization device in accordance with the present invention can be reduced. 
   A further preferred embodiment of the roll stabilization device is characterized in that the fail-safe valve is acted upon by the pressure from a tank from which the pressure supply unit is fed. In that way, it is ensured that a change in the tank pressure level, e.g. by the influence of temperature, does not lead to a change in the switch points at the fail-safe valve. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages, characteristics, and details of the present invention will become apparent from the following description in which embodiments of the invention are explained in more detail with reference to the drawings. The features mentioned in the claims and description can each be fundamental to the present invention as such, or in any combination thereof. In the drawings: 
       FIG. 1  is a hydraulic circuit diagram of a conventional roll stabilization device; 
       FIG. 2  is a hydraulic circuit diagram of an embodiment of a roll stabilization device in accordance with the present invention with a control pressure-limiting valve and 
       FIG. 3  is a hydraulic circuit diagram of a second embodiment of a roll stabilization device in accordance with the present invention with a control pressure-limiting valve. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows the actual state of a standard system. The pressure supply unit is a suction-throttled radial piston pump  21 , which provides two different pressure levels via a series connection using two proportional pressure-limiting valves  22  and  28  designated as axle pressure-limiting valves and switched as differential pressure valves. The pressure levels are monitored by pressure sensors  23  and  27 . Those different pressure levels are for a rotary motor  37  at the front axle stabilizer  35  for the right side and  34  for the left side, respectively, and correspondingly for a rotary motor  36  at the rear axle stabilizer  33  and  32 . The pressure at the rear axle must always be lower than or equal to the pressure at the front axle. Those two pressure levels are reduced and/or increased by means of a 7/2 directional control valve  24 , also designated as a direction-switching valve, which, depending upon the direction of turning, is switched to the right or left, so that the pressure in the rotary motors is either reduced or increased on the right or left side of the motor vehicle, respectively, at constant velocity. The operation of the direction-switching valve  24  is monitored by means of a control position detection sensor  26 . 
   In addition, a fail-safe valve  25  is arranged on the front axle, which in a fail-safe case blocks the rotary motor  37  of the front axle and depressurizes the rotary motor  36  of the rear axle when a valve is jammed and/or there is a power failure. Additionally, two feeder valves  29  and  30  are installed that can connect the pressure branches  35  and  34  of the rotary motor  37  at the front axle with a tank  31  via a tank line, and namely in such a way that throttled unrestricted oscillation of the rotary motor  37  over the leakage points in the rotary motor can take place without cavitation problems even by resuctioning the volumetric flow. 
   The basic approach of the present invention is that cost intensive elements are dispensed with. That relates particularly to the reduction of electromagnets of directly controlled valves. In accordance with the present invention, the operation of different valve spools can in part be combined. In accordance with a further aspect of the present invention, a directly controlled hydraulic concept is created, which is simple to construct and cost effective to manufacture. An essential characteristic of the present invention is that both switch magnets of the direction-switching valve  24  and of the fail-safe valve  25  can be replaced by one proportional magnet of a control valve. 
   In accordance with the embodiment illustrated in  FIG. 2 , the desired result is achieved by connecting an additional pressure-limiting valve  61  in series with the proportional pressure-limiting valves  42  and  48 , which are also designated as axle-pressure-limiting valves. The additional pressure-limiting valve  61 , which is also designated as a control-pressure-limiting valve, is used for hydraulically actuating the 7/2 directional control valve  44  and fail-safe valve  45 . Alternatively, in accordance with the embodiment illustrated in  FIG. 3 , an additional pressure-limiting valve  81 , which is also designated as a control pressure-limiting valve, can be connected parallel to the pump pressure for the pressure supply to the rotary motors, and for the pressure supply to the 7/2 directional control valve  44  and fail-safe valve  45 . In accordance with a further aspect of the present invention, instead of the pressure-limiting valves  22  and  28 , pressure-limiting valves  42 ,  48  having tank pressure compensation are used. 
     FIG. 2  illustrates a hydraulic diagram similar to that shown in  FIG. 1  and in accordance with a first embodiment of the present invention. The pressure supply unit is a suction-throttled radial piston pump  41 , which provides two different pressure levels via a series connection by means of two proportional pressure-limiting valves  42  and  48 . Both proportional pressure-limiting valves  42  and  48  are also designated as axle-pressure-limiting valves. Unlike the known roll stabilization device illustrated in  FIG. 1 , the axle-pressure valves are not differential pressure-limiting valves but normal pressure-limiting valves. The spool and spring spaces of the axle-pressure-limiting valves  42  and  48  are each connected specifically with the tank  51  pressure level via a relief line  71 ,  72 . The pressure levels provided by the axle-pressure-limiting valves  42  and  48  are monitored by pressure sensors  43  and  47 . 
   As in the conventional roll stabilization device shown in  FIG. 1 , the pressure levels or pressure ranges for a rotary motor  57  on the front axle stabilizer are designated by  55  for the right side and by  54  for the left side, respectively, and correspondingly by  53  and by  52  for a rotary motor  56  on the rear axle stabilizer. The pressure at the rear axle must always be lower than or equal to the pressure at the front axle. On rounding a curve, both pressure levels are switched to the right or left, depending upon the turning direction, by means of 7/2 directional control valve  44 , also designated as a direction-switching valve, so that the pressures in the rotary motors are either reduced or increased, respectively, on the right or left side of the motor vehicle at constant velocity. The operation of the directional control valve  44  is monitored by means of a control position detection sensor  46 . 
   In addition, a fail-safe valve  45  is arranged on the front axle, which in a fail-safe case blocks the rotary motor of the front axle  57  and depressurizes the rotary motor of the rear axle  56  when a valve is jammed and/or there is a power failure. Additionally, two feeder valves  49  and  50  are installed that can connect the pressure branches  55  and  54  of the rotary motor  57  at the front axle with a tank line and a tank  51  in such a way that throttled unrestricted oscillation of the rotary motor  57  over the leakage points in the rotary motor can take place without cavitation problems even by resuctioning the volumetric flow. 
   In the embodiment illustrated in  FIG. 2 , the directional control valve  44  and fail-safe valve  45  are provided with valve spools and not with switch magnets like the roll stabilization device shown in  FIG. 1 . Instead, the end surfaces of the valve spools of the directional control valve  44  and fail-safe valve  45  are specifically acted upon with pressure. In the embodiment illustrated in  FIG. 2 , that pressure is provided via a control-pressure-limiting valve  61 , which is connected in series with the proportional pressure-limiting valve  48 , into a line  60  originating at the proportional pressure-limiting valve  48 . The control-pressure-limiting valve  61  is preferably a spool valve and includes a valve spool that provides a control pressure proportional to the strength of a proportional magnet  62 . The control pressure is led to both directional control valve  44  and fail-safe valve  45  via a line  64  and lines  66  and  67 . 
   The directional control valve  44  is biased by a spring  68  to the switch position illustrated in  FIG. 2 . Similarly, the fail-safe valve  45  is biased by a spring  69  to the switch position illustrated in  FIG. 2 . The springs  68  and  69  of the directional control valve  44  and fail-safe valve  45  are designed such that the fail-safe valve  45  switches at a control pressure of, e.g., 2.5 bar, and the directional control valve  44  still remains at its normal position. At a control pressure of, e.g., 5 bar, the directional control valve  44  will then switch as well. In such a case, the fail-safe valve  45  will remain switched as well. 
   During operation of the roll stabilization device illustrated in  FIG. 2 , the control-pressure-limiting valve  61  connected in series with the axle-pressure-limiting valves  42  and  48  increases the system pressure by the control pressure required for the desired switch combination. The axle pressure-limiting valve  48  for the rear axle then only needs to regulate the remaining differential pressure for the required rear axle pressure. The same applies to the subsequent pressure series with the axle-pressure-limiting valve  42  for the front axle. 
   The pressure relief lines  75  and  76  originate at the directional control valve  44  and fail-safe valve  45 , by which the tank pressure from tank  51  is applied to the actuator spaces of the directional control valve  44  and fail-safe valve  45 . That ensures that a change in the tank pressure level, e.g. by the influence of temperature, does not lead to a distortion of the switch points at the directional control valve  44  and fail-safe valve  45 . 
   In  FIG. 3 , a hydraulic diagram similar to the hydraulic diagram illustrated in  FIG. 2  is shown. The same reference numerals are used to designate similar parts. For the description of those parts, reference is made to the preceding description of  FIG. 2 . The following description will basically address the differences between the embodiments illustrated in  FIGS. 2 and 3 . 
   In the embodiment illustrated in  FIG. 3 , the control pressure is provided by a control-pressure-limiting valve  81 , which is provided by a line  82  originating at a connection line  83  that connects the pump  41  to the axle pressure-limiting valve  42 , and which is connected in series with the pump  41  and parallel to the axle-pressure-limiting valves  42 ,  48 . Hence, pump pressure is applied to the control-pressure-limiting valve  81 . The control-pressure-limiting valve  81  having a proportional magnet  85 , like the control-pressure-limiting valve  61  in  FIG. 2 , serves to provide control pressure to the directional control valve  44  and fail-safe valve  45 . For that purpose, the control-pressure-limiting valve  81  is connected to the directional control valve  44  and fail-safe valve  45  via a line  84  and lines  86  and  87 . 
   In the deenergized state, the hydraulic actuator spaces of the directional control valve  44  and fail-safe valve  45  are applied specifically on the tank pressure level of tank  51  by means of the control-pressure-limiting valve  81  through a pressure relief line  89 , so that the directional control valve  44  and fail-safe valve  45  remain firmly at their normal positions. In order to adjust the control pressure, a minimum pressure of, e.g., 2.5 bar is preferably set by means of the axle-pressure-limiting valve  48 . 
   As in the embodiment illustrated in  FIG. 2 , in the embodiment in accordance with  FIG. 3 , the axle-pressure-limiting valves  42  and  48  are also connected to the tank pressure level of tank  51  via lines  91  and  92 . Likewise, the actuator spaces of the directional control valve  44  and fail-safe valve  45  are connected to the tank pressure level of tank  51  via the pressure relief lines  95  and  96  by a line  98 .