Abstract:
An electronic compressed-air system includes a compressed-air supply part having a compressor and a consumer part having load circuits. The load circuits are supplied with compressed-air via solenoid valves. At least one load circuit is provided with a pressure reservoir. The pressure in the load circuits is monitored by pressure sensors, whose signals are evaluated by an ECU that controls the solenoid valves. The load circuits include service-brake circuits having a compressed-air reservoir, secondary load circuits and a high-pressure circuit, wherein the solenoid valves of the service-brake circuits and the solenoid valves of the secondary load circuits are open in a de-energized normal state and the solenoid valve of the high-pressure circuit is closed in the de-energized normal state.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electronic compressed-air system for vehicles. 
     WO 98/47751 A1 describes a pneumatic vehicle brake system provided with a compressor, at least one air-load circuit, such as service-brake circuits, a parking-brake circuit, a low-pressure auxiliary circuit and a high-pressure circuit, wherein the circuits are provided with compressed-air reservoirs and demand valves. Between the compressor and the at least one load circuit, there are disposed first electrically actuatable valves, which are closed in the de-energized normal state, and, between the compressor and the auxiliary circuit, there is disposed a second electrically actuatable valve, which is open in the de-energized normal state. The valves are actuated by an electronic control unit. The outlet ports of the first valves of the air-load circuits are in communication via check valves with the outlet port of the second valve, which is open in the de-energized normal state. If a compressed-air demand exists in one of the load circuits, for example due to too-low reservoir pressure, the corresponding valve is activated by the control unit, whereby the air demand is covered by the compressor, while at the same time the second valve of the auxiliary circuit is closed. Failure of the compressor leads to a pressure drop, which is detected by the control unit, which closes the valves or keeps them closed, whereby the pressure in the circuits is maintained. A pressure-regulating valve determines the pressure level. In the event of failure of the pressure-regulating valve, overpressure is relieved via an overpressure valve. Pressure sensors monitor the circuits. The circuits are supplied with air via the second, normally open valve and via the check valves connected upstream from the circuits. If the electrical system fails, all valves go to normal state. Nevertheless, the compressor continues to run and supplies the circuits with air via the second, normally open valve of the auxiliary circuit, the system pressure being determined by a low-pressure relief valve of the auxiliary circuit. If one valve fails, the associated circuit can be supplied with air via the valve of the auxiliary circuit and the check valve. The known system is complex, since each load circuit is equipped with its own compressed-air reservoir. 
     SUMMARY OF THE INVENTION 
     Generally speaking, in accordance with the present invention an improved compressed-air system is constructed and arranged in such a way that the need for compressed-air reservoirs can be very largely eliminated. 
     By virtue of the inventively designed compressed-air system there are achieved cost savings, because all compressed-air reservoirs with the exception of the reservoirs for the service-brake circuits can be dispensed with. Nevertheless, several pressure levels can be achieved. 
     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
     The present invention accordingly comprises the features of construction, combination of elements, and arrangements of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in more detail hereinafter on the basis of the accompanying drawing, in which: 
         FIG. 1  shows a compressed-air system according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , where pressurized-fluid lines are represented by solid lines and electrical lines by broken lines, there is shown a compressed-air system  2  with a compressed-air supply part  4  and a consumer part  6 . Compressed-air supply part  4  comprises a compressor  7 , a compressor control device  8  and an air-dryer part  10 . 
     Consumer part  6  is provided with a compressed-air distributor line  14 , a plurality of electrically actuatable valves, preferably solenoid valves  16 ,  18 ,  20 ,  22 ,  24  with restoring springs and a plurality of load circuits  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38  supplied with compressed-air via the solenoid valves. 
     From compressor  7 , a compressed-air supply line  40  leads via a filter  42 , an air dryer  44  and a check valve  46  to distributor line  14 , from which there are branched off lines  48 ,  50 ,  52 ,  54 ,  56  leading to the solenoid valves. From the solenoid valves, compressed-air lines  58 ,  60 ,  62 ,  64 ,  66  lead to the load circuits. Line  62  splits into lines  62 ′ and  62 ″ leading to circuits  30  and  32 , a check valve  68  also being disposed in line  62 ″. A pressure limiter  70  is disposed in supply line  52 . Line  54 , which leads to solenoid valve  22 , branches off downstream from pressure limiter  70 . Line  64  splits into lines  64 ′ and  64 ″ leading to circuits  34  and  36 . 
     Pressure sensors  72 ,  74 ,  76 ,  78 ,  80 ,  82  monitor the pressure in the load circuits and in distributor line  14 , and transmit the respective pressure as a pressure signal to electronic control unit  84 , which controls the solenoid valves. 
     Load circuits  26 ,  28  can be, for example, service-brake circuits. Load circuit  30  can be a trailer-brake circuit, in which case normally two lines, a supply line and a brake line, lead to the trailer. Load circuit  32  can be a parking-brake circuit with spring accumulator. Load circuits  34  and  36  can be secondary load circuits, such as operator&#39;s cab suspension, door controller, etc., in other words, all components that have nothing to do with the brake circuits. Load circuit  38  can be a high-pressure circuit. 
     Service-brake circuits  26 ,  28  are provided with compressed-air reservoirs  90 ,  92  in conformity with EU Directive  98 / 12 . 
     The inventive compressed-air system makes it possible to dispense with compressed-air reservoirs in circuits  30 ,  32 ,  34 ,  36  and also in high-pressure circuit  38 . As an example, it is permissible to supply other load circuits from the service-brake circuits (circuits  26  and  28 ), provided the braking function or braking action of service-brake circuits  26  and  28  is not impaired. 
     Via a line  40 ′, compressor  7  is mechanically (pneumatically) controlled by compressor controller  8 . Compressor controller  8  comprises a solenoid valve  94  of small nominal width that can be switched by electronic control unit  84 . In the de-energized normal state it is vented, as illustrated, whereby compressor  7  is turned on. If compressor  7  is to be turned off, for example because all load circuits are filled with compressed-air, control unit  84  changes over solenoid valve  94  so that the pressure-actuatable compressor is turned off via line  40 ′. If solenoid valve  94  is switched to de-energized condition, for example because a load circuit needs compressed-air after filling, solenoid valve  94  is again switched to the normal state illustrated in the drawing, whereby line  40 ′ is vented and in this way compressor  7  is turned on. 
     Air-dryer part  10  comprises a solenoid valve  100  with small nominal width, whose inlet  102  is in communication with distributor line  14  and via whose outlet  104  there is pneumatically switched a shutoff valve  106 , which is in communication with supply line  40  of compressor  7  and serves for venting of the air dryer. 
     When solenoid valve  100  is switched to passing condition, compressor  7  no longer discharges into the load circuits but instead discharges via valve  106  to the atmosphere. At the same time, dry air flows from distributor line  14  (out of reservoirs  90 ,  92  of the service-brake circuits) via solenoid valve  100 , throttle  108  and a check valve  110  through air dryer  44  for regeneration of its desiccant and further via filter  42  and valve  106  to the atmosphere. 
     Reference numeral  112  denotes an overpressure valve. 
     Solenoid valves  16 ,  18 ,  20 ,  22 ,  24  are controlled by control unit  84 , solenoid valves  16  to  22  of load circuits  26  to  34  being open in de-energized normal state, while solenoid valve  24  of the high-pressure circuit is closed in de-energized normal state. Pilot-controlled solenoid valves can also be used. The pressure in the circuits is directly monitored at the solenoid valves by pressure sensors  72 ,  74 ,  76 ,  78 ,  80 . 
     If the pressure were to drop in a load circuit while the solenoid valves were not actuated, for example in circuit  30  (trailer-brake circuit), the compressed-air supply by service-brake circuits  26  and  28  takes place from their compressed-air reservoirs  90 ,  92  via open solenoid valves  16 ,  18 ,  20 . In this way it is possible to do without pressure reservoirs in the load circuits (except in the service-brake circuits). Moreover, the switching frequency of the solenoid valves is also reduced. The pressure in load circuits  30  to  36  is adjusted by pressure limiter  70  to a lower level, such as 8.5 bar, than the pressure level of, for example, 10.5 bar in the service-brake circuits. 
     High-pressure circuit  38  is shut off and therefore is not in communication with the other circuits. The high-pressure circuit usually has a higher pressure than the other load circuits, for example 12.5 bar. 
     If the reservoir in high-pressure circuit  38  is dispensed with, as described hereinabove, only the reservoir volumes of the service-brake circuits and a small dead volume in the other secondary consumers exist. If a small leak then occurs in the high-pressure circuit, frequent regulation via solenoid valve  24  would normally be required. Because the nominal width of solenoid valve  24  is usually large, the corresponding regulation algorithm is complicated, and so it would be desirable to open the solenoid valve only when the high-pressure circuit actually needs compressed-air. This information about the compressed-air demand of the high-pressure valve sensed by pressure sensor  80  could be transmitted via a CAN data line to control unit  84 , which then activates valve  24  and turns on compressor  7  via solenoid valve  94  in order to supply compressed-air to high-pressure circuit  38  from brake circuits  26 ,  28  and by compressor  7 . 
     High-pressure circuit  38  has a different pressure level than do the further load circuits; nevertheless, it has to be refilled with compressed-air relatively infrequently, and therefore is usually shut off by solenoid valve  24 , which is closed in the de-energized normal state. In the event of a demand, it also does not need its compressed-air within a very short time (msec or fractions of seconds), and so, a certain dead time can be tolerated for communication with the control unit and for control of solenoid valve  24 . According to the present invention, therefore, the high-pressure circuit is normally kept closed. Circuits  30 ,  32 ,  34 ,  36  are supplied from reservoirs  90  and  92  of service-brake circuits  26  and  28  via valves  16 ,  18 ,  20 ,  22 , which are open in de-energized condition during normal driving. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.