Abstract:
A hydraulic system for a motor vehicle having a convertible top ( 2 ) which can be folded back has a convertible-top control system ( 1 ) and further hydraulic control devices ( 3, 4 ) which can be activated by a common hydraulic pump ( 6 ). In hydraulic lines ( 8, 9 ) leading to the convertible-top control system ( 1 ) there are arranged hydraulic valves ( 13, 14 ) which enable optional operation of the convertible-top control system ( 1 ) or of the further control devices ( 3, 4 ). Because of this, the hydraulic system turns out to be particularly simple structurally.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a hydraulic system for a motor vehicle having a convertible top which can be folded back, with a convertible-top control system which can be operated by a hydraulic pump. 
     Hydraulic systems of this type are frequently used in modern motor vehicles described as convertibles and are known from practical experience. For safety reasons the convertible top can only be opened or closed when the motor vehicle is at a standstill or when traveling at a low speed, for example of less than 10 km/h. The other control devices which are arranged in the motor vehicle serve, for example, for the activation of adjustable spring struts, a transmission control system or an additional steering system for a rear axle. In known motor vehicles these hydraulic control devices are activated via their own hydraulic circuits and via hydraulic pumps or pressure accumulators additionally arranged in the motor vehicle. 
     SUMMARY OF THE INVENTION 
     The invention is based on the problem of providing a hydraulic system of the type mentioned at the beginning in such a manner that it is constructed as simply as possible and can be produced cost-effectively. 
     According to the invention, this problem is solved in that in a hydraulic line, which leads to the convertible-top control system, there is arranged a controllable hydraulic valve for the activation of a further hydraulic control device for operating a further functional unit of the motor vehicle. 
     In one refinement the convertible-top control system and the further hydraulic control device are switched on at the same time, there being a clear distinction between the power consumption of the convertible-top control system and the control device as an alternative to this, the further hydraulic control device can be activated only with the convertible-top control system switched off. 
     This enables the hydraulic system according to the invention to be used for the activation of the further hydraulic control devices when the convertible-top control system is not in use. Since the two devices have approximately the same power requirement, the hydraulic pump does not need to be adapted for the system according to the invention. Because of this, the hydraulic system according to the invention is of particularly simple construction and can be produced cost-effectively. Since, thanks to the invention, in each case either the convertible-top control system or one of the further hydraulic devices can be activated, pressure fluctuations do not arise in the hydraulic lines. Therefore, only a small pressure accumulator or none at all is needed as a buffer for operation of the further control devices. This results in a further reduction in the structural design of the system according to the invention. 
     The system according to the invention requires a particularly small structural design if a control electronics unit of the hydraulic pump is provided for the activation of the hydraulic valve. Furthermore, a designated pressure level can be produced for each of the hydraulic control devices by the simultaneous activation of the hydraulic pump and of the hydraulic valve. 
     According to another advantageous development of the invention, mutual interference of two further control devices can be avoided if the hydraulic pump is designed for the conveying of hydraulic oil in both directions, and a hydraulic valve is arranged in each of the hydraulic lines leading to the convertible-top control system. 
     According to another advantageous development of the invention, a multiplicity of hydraulic control devices can be operated in a simple manner with particularly low outlay if a plurality of branches to the hydraulic control devices are arranged in one of the hydraulic lines leading to the convertible-top control system. If certain hydraulic control devices are only to be activated separately, this can be achieved via further hydraulic valves which can be controlled by the control electronics unit. 
     In the case of hydraulic control devices which can be activated in parallel, a drop in pressure in one of the hydraulic control devices when a further hydraulic device is switched on can be avoided in a simple manner if a nonreturn valve is in each case arranged between the branches and the control devices. Because of the nonreturn valves, discharging of the hydraulic oil from the hydraulic control device activated first is reliably avoided. 
     According to another advantageous development of the invention, a plurality of hydraulic control devices, which require the same volume flow of hydraulic oil at essentially the same time, can be operated with a small number of hydraulic lines if one hydraulic line is designed as a return line of one of the hydraulic control devices and as a supply line of a further hydraulic control device. 
     According to another advantageous development of the invention, a multiplicity of hydraulic control devices can be operated without mutual interference if a plurality of hydraulic valves, which in each case activate hydraulic control devices, are arranged in series in one of the hydraulic lines, each of the hydraulic valves being formed as a shuttle valve. By means of this design, when one hydraulic control device arranged close to the hydraulic pump is activated, all of the hydraulic control devices arranged further away are automatically switched off. Each of the hydraulic control devices is hereby assigned a priority. The convertible-top control system can therefore be arranged next to the hydraulic pump and, for example, the hydraulic control device for the rear-wheel steering system can be arranged in second place. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention permits numerous embodiments. To further clarify its basic principle a plurality of these are represented in the drawings and are described in the following. The drawings show in 
     FIG. 1 a schematic representation of a hydraulic system according to the invention with a convertible-top control system and two control devices, and 
     FIGS. 2-5 further embodiments of the hydraulic system according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a hydraulic system according to the invention with a convertible-top control system  1  for opening and closing a convertible top  2  of a motor vehicle, and with two further hydraulic control devices  3 ,  4 . The hydraulic system has a hydraulic pump  6 , which can be driven in both directions by an electric motor  5 , and a control electronics unit  7 . With the control electronics unit  7 , the conveying direction and the conveying volume of the hydraulic pump  6  can be controlled. Two hydraulic lines  5 ,  9  lead from the hydraulic pump  6  to the convertible-top control system  1 . The convertible-top control system  1  has a hydraulic cylinder  10  which is coupled to the convertible top  2  of the motor vehicle. To simplify the drawing, a single hydraulic cylinder  10  is shown. Arranged in the hydraulic lines  8 ,  9  are hydraulic valves  11 ,  12  which can in each case be controlled electrically by the control electronics unit  7  and with which the hydraulic control devices  3 ,  4  can be activated. Furthermore, FIG. 1 shows that pressure control valves  13 ,  14 , which are connected to a common reservoir  15 , are arranged in the hydraulic lines  8 ,  9 . Return lines  16 - 18  lead in each case from the convertible-top control system  1  and the hydraulic control devices  3 ,  4  into the reservoir  15 . 
     The hydraulic valves  11 ,  12  are designed as shuttle valves and in the basic position shown are preloaded into a position which enables the convertible top  2  to be activated. Since the hydraulic control devices  3 ,  4  are in each case connected to one of the hydraulic lines  8 ,  9 , in each case only one of the hydraulic control devices  3 ,  4  can be activated, corresponding to the conveying direction of the hydraulic pump  6 . Electric signal lines  19  lead from the control electronics unit  7  to switches and measuring devices which are not shown. The measuring devices may, for example, be a motor-vehicle speedometer. It is thereby possible, for example above a designated motor-vehicle speed, to block the convertible-top control system  1  by the control electronics unit  7 . 
     The hydraulic control devices  3 ,  4  may, for example, be a level adjustment of spring struts of the motor vehicle. By this means, with the system according to the invention compensation for the spring travel or a difference in wheel load when loading, or the raising and lowering of the motor vehicle, for example as a function of the speed thereof, may be undertaken. 
     FIG. 2 shows a further embodiment of the hydraulic system according to the invention with a convertible-top control system  1  and with a hydraulic control device  2  for a rear-wheel steering system of the motor vehicle. The system according to the invention has a hydraulic pump  22  which draws in hydraulic oil from a reservoir  23  and conveys it via a hydraulic line  24  to a controllable hydraulic valve  25 . The hydraulic valve  25  has two switching positions for the optional activation of the convertible-top control system(  20  and op the control device  21  for the rear-wheel steering system. Nonreturn valves  26 ,  27  are in each case arranged between the hydraulic valve  25  and the convertible-top control system  20  and also the control device  21  for the rear-wheel steering system. The nonreturn valves  26 ,  27  prevent hydraulic oil from flowing back via the hydraulic pump  22  into the reservoir  23 . The hydraulic control device  21  of the rear-wheel steering system has a double action differential cylinder  28  which can be activated via two electrically controllable valves  29 ,  30 . The convertible-top control system  20  has two hydraulic cylinders  31 ,  32  which can in each case be activated by means of controllable valves  33 ,  34  and nonreturn valves  35 ,  36 . Furthermore, FIG. 2 shows that the convertible-top control system  20  and the control device  21  for the rear-wheel steering system are in each case connected to the reservoir  23  via return line  37 ,  38 . 
     FIG. 3 shows a further embodiment of the hydraulic system according to the invention with a convertible-top control system  39  and two further control devices  40 ,  41 . The convertible-top control system  39  is connected via a hydraulic line  42  to a hydraulic pump  44  conveying hydraulic oil from a reservoir  43 . A plurality of branches  45 ,  46  for the control device s  40 ,  41  are arranged in the hydraulic line  42 . Hydraulic valves  48 ,  49 , which can be activated by a common control electronics unit  47 , and in each case one nonreturn valve  50 ,  51  are arranged between the control devices  40 ,  41  and t he branches  45 ,  46 . The convertible-top control system  39  likewise has a nonreturn valve  52  and an activatable hydraulic valve  53 . The control electronics unit  47  serves to switch the hydraulic valves  48 ,  49 ,  53  in such a manner that the convertible-top control system  39  and the two control devices  40 ,  41  can be operated at the same time. The control devices  40 ,  41  may, for example, be an adjustable differential of the driving axle of the motor vehicle or a hydraulic boost for a manually-operated transmission (not shown). Furthermore, the control devices  40 ,  41  can be designed for the hydraulic boosting of a motor-vehicle clutch (not shown). Such control devices  40 ,  41  require a low volume flow of hydraulic oil, so that there is no risk of mutual interference between the two control devices  40 ,  41  when they are operated at the same time. 
     FIG. 4 shows a further embodiment of the hydraulic system according to the invention, with a convertible top control system  54  and two further control devices  55 ,  56 . The system according to the invention has a hydraulic pump  57  and a plurality of hydraulic valves  59 - 61  arranged in series in a hydraulic line  58 . The hydraulic valves  59 - 61  are in each case designed as a shuttle (changeover) valve having two switching positions, so that either the control device  55 ,  5  and the convertible-top control system  54 , which are connected to the respective hydraulic valve  59 - 61 , or the following hydraulic valve  59 - 61  is connected to the hydraulic pump  57 . As a result, by corresponding switching of the hydraulic valves  59 ,  61  in each case only the convertible-top control system  54  or only one of the control devices  55 ,  56  can be operated. 
     The control devices  55 ,  56  may, for example, be designed for adjusting aerodynamic components of the motor vehicle as a function of the motor-vehicle speed, or for adjusting a radiator or air-flow apertures for the motor-vehicle radiator as a function of the cooling-air requirements. The control devices  55 ,  56  may furthermore serve for adjusting vehicle seats or for locking vehicle doors or for activating a parking brake. 
     FIG. 5 shows a further embodiment of the hydraulic system according to the invention, with a convertible-top control system  62  and a hydraulic control device  63 . A hydraulic line  64  is designed in this case as a return line of the convertible-top control system  62  and at the same time as a supply line of the control device  63 . Furthermore, the hydraulic system has two hydraulic valves  65 ,  66  by means of which the control device  63  and the convertible-top control system  62  can in each case be activated or bypassed. 
     The control device  63  is, for example, a control device for head restraints, which control device only builds up a slight difference in pressure.