Abstract:
A hydraulic control system for high flow applications in motor vehicles, in particular for active wheel suspensions and active steering arrangements, includes at least one passive high flow valve which is controlled hydraulically by at least one low flow valve.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a national stage of International Application No. PCT/EP2005/009524 filed Sep. 5, 2005, the disclosures of which are incorporated herein by reference, and which claimed priority to German Patent Application No. DE 20 2004 013 836.0 filed Sep. 6, 2004, the disclosures of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a hydraulic control system for high flow applications in motor vehicles. 
     For the hydraulic actuation of actuators which are used in motor vehicles with active wheel suspension (active chassis) and/or active steering, special high flow valves are used because of the high oil flow requirements. On the other hand, in control systems for brake regulation applications such as ABS (anti-blocking system), ESP (electronic stability program) or EHB (electro-hydraulic brake system), valves are used which, owing to the broad distribution of the said applications (partially already standard equipment in many vehicles) are able to be produced in large numbers and hence at a favourable price. Such brake regulation valves are, however, not designed for high oil flows and are therefore not suitable for high flow applications. 
     It is an object of the invention to provide a possibility for designing hydraulic control systems for high flow applications in motor vehicles at a more favourable cost. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the invention, a hydraulic control system for high flow applications in motor vehicles, in particular for active wheel suspensions and active steering arrangements, includes at least one passive high flow valve which is controlled hydraulically by at least one low flow valve. Through the use of low flow valves, in accordance with the invention, as pilot valves with which passive high flow valves are controlled, the costs for a control system for high flow applications, in particular for active chassis, can be distinctly reduced. The invention makes use of the fact that low flow valves are offered at a favourable cost as a “package” with integrated control apparatus (e.g. for brake regulation applications). The low flow valves are coupled magnetically and/or electrically to the control apparatus. Such a package can be extended according to the invention in a simple manner by the passive high flow valves, in that the latter are coupled hydraulically to the low flow valves. On the basis of such a structure in accordance with the invention, various tasks of a hydraulic control arrangement can be realized. 
     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 the logic structure of a hydraulic control system for high flow applications according to the invention; 
         FIG. 2  shows an example application for the control system according to the invention; and 
         FIG. 3  shows a hydraulic pressure regulating device for an active chassis regulating system with a hydraulic control system according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The structure illustrated in  FIG. 1  shows the structure of a hydraulic control system  10  according to the invention. A control apparatus  12  and low flow valves  14  coupled thereto represent a package  16  for brake regulating applications. This package  16  with two levels is extended by a third level, namely the passive high flow valves  18 . The passive high flow valves  18  are coupled hydraulically to the low flow valves  14 , so that the passive high flow valves  18  can be controlled hydraulically by the low flow valves  14 . The low flow valves  14  therefore serve as pilot valves for the passive high flow valves  18 . The extended package  16  in accordance with the invention is therefore basically able to be used for active high flow applications. 
       FIG. 2  shows how, for example, an oil flow can be controlled with the control system  10  according to the invention. The oil flow is adjusted by means of a passive high flow valve in the form of a slide valve  20 . The passive slide valve  20  is controlled by means of two low flow valves. The low flow valves are two 2/2-way valves  22 ,  24 , which are otherwise used as ABS valves. The first valve is a “normally closed” valve, which is arranged in a pressure line in which a system pressure p P  prevails. The second valve  24  is a “normally open” valve, which is arranged in a return line to a tank in which a tank pressure p T  prevails. By means of a control apparatus (not illustrated here) the two 2/2-way valves  22 ,  24  can be set simultaneously into the respectively other switching state. Through this pre-control, the control surface of the passive slide valve  20  can therefore be acted upon by means of the two 2/2-way valves either with the system pressure p P  or with the tank pressure p T . This control can be applied to any n/2-way slide valves. Through an extending to four 2/2-way valves, in addition n/3-way slider functions can be realized. 
     A control system  10  according to the invention can also be used for regulating a pressure. Thus, for example, a proportionally acting brake regulating valve (proportional brake regulating valve), as is known from EHB- or ESP applications, can control a passive proportional pressure control valve or a proportional pressure reducing valve. In this case, the pressure control valve or the pressure reducing valve is in equilibrium with the brake regulating valve. For regulating a pressure circuit, an active proportional brake regulating valve with a passive proportional pressure control valve is necessary. For the regulating of n pressure circuits, an active proportional brake regulating valve with a passive proportional pressure limiting valve and n active proportional brake regulating valves with n passive proportional pressure reducing valves are necessary. 
     Through combination of the functions achievable with a control system  10  according to the invention, in particular the pressure regulation and the controlling of passive high flow valves, also complex device controls can be realized. In  FIG. 3 , as a further example application, a hydraulic pressure regulating device  26  is illustrated, with which front and rear actuators  28  and  30 , respectively, of a vehicle chassis can be actuated. The pressure regulating device  26  comprises a motor-driven pump  32  which conveys hydraulic oil from a tank  34 , and a hydraulic control system  10  according to the invention with respectively two connections A 1 , A 2  and B 1 , B 2  for each actuator  28 ,  30  and also a return line to the tank  34 . A control apparatus  36  of the control system  10  controls a proportional pressure control valve  38  and a proportional pressure reducing valve  40  and also two 2/2-way valves  42 ,  44 . The two 2/2-way valves  42 ,  44  serve as pre-control valves for a direction control valve arrangement  46 , with which the direction of the actuator movement is established, and for a blocking valve arrangement  48 , with which the front actuator  28  can be blocked. Both the proportional valves  38 ,  40  and also the 2/2-way valves  42 ,  44  are active low flow valves, whereas the direction control valve arrangement  46  and the blocking valve arrangement  48 , which can also be replaced by a similar valve arrangement, are formed from passive high flow valves. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this 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.