Abstract:
An electronic compressed air system for vehicles includes a compressed air supply part having a compressor, a compressed air consumer part having load circuits forming an air-suspension circuit, and service-brake circuits having reservoirs. The load circuits are supplied with compressed air via solenoid valves. The pressure in the load circuits is monitored by pressure sensors whose signals are evaluated by an ECU that controls the solenoid valves. The solenoid valve of the air-suspension circuit does not include reservoirs and is closed in the de-energized normal state. The solenoid valves of other load circuits, especially of the service-brake circuits are open in the de-energized normal state. With a pressure demand of the air-suspension circuit, the associated solenoid valve is switched by the ECU to open position to establish communication with the compressed air supply part and/or with the service-brake circuits or with the reservoirs thereof, to refill the air-suspension circuit.

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 for 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 a compressed air reservoir. 
     DE 10004091 C2 describes a compressed air supply device for vehicle compressed air systems with a multi-circuit protective valve, a pressure regulator, a supply line for supplying the circuits of the multi-circuit protective valve with compressed air, and a compressor, which can be switched by means of a pneumatic switching device, a pilot valve for controlling the pressure regulator and the switching device being provided, and a throttle being interposed between the pilot valve and the switching device. Each circuit is provided with a compressed air reservoir. The pilot valve is controlled and/or regulated by an electronic control and/or regulation unit. Pressure sensors monitor the pressure in the circuits and in the supply line. 
     In vehicles with a compressed air brake system, it is known that the EU Brake Directive can be satisfied by providing separate compressed air reservoirs for the front-axle and rear-axle brake circuits. Additional compressed air reservoirs are used for other compressed air consumers, such as an air-suspension circuit, to ensure that the functionality of the brake system is not negatively influenced by the operation of such further compressed air consumers. Such known compressed air systems with separate compressed air reservoirs for a plurality of compressed air load circuits are quite costly. 
     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—with the exception of the brake circuits—the need for compressed air reservoirs for further compressed air load circuits, such as air-suspension circuits, can be very largely eliminated, without having to fear negative consequences for the brake circuits. 
     The present invention provides electrically actuatable valves, preferably solenoid valves, for the individual load circuits. By virtue of the inventively designed compressed air system there are achieved cost savings, because there is no need for compressed air reservoirs for further compressed air consumers, especially for the air-suspension circuit including the associated components. The reservoirs for the service-brake circuits are not dispensed with. By virtue of the inventive design, the costs for the overall system can be reduced. The installation complexity is less. In the case of pressure demand, the further compressed air consumers, especially the air-suspension circuit, can be filled primarily by the service-brake circuits as long as the brake pressures of the brake circuits are in conformity with applicable legal regulations, for which purpose it is merely necessary to open the normally closed solenoid valve of the air-suspension circuit, since the solenoid valves of the service-brake circuits are normally open, or in other words in de-energized normal state. In the compressed air suspension-circuit without compressed air reservoir, the switching frequency of the normally closed solenoid valve is reduced, since actuation takes place only in the case of a request for compressed air from the electronically controlled air-suspension system (ECAS). The system safety and system availability are improved. Because the solenoid valve is closed during normal operation, no reactions due to the air-suspension circuit are felt in the brake circuits. 
     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 an air-processing system according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the FIGURE, where compressed air 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 compressed air consumer part  6 . Compressed air supply part  4  comprises a compressor  7 , a compressor control device  8  and an air-dryer part  10 . 
     Compressed air consumer part  6  is provided with a compressed air distributor line  14 , a plurality of electrically actuatable solenoid valves  16 ,  18 ,  20 ,  22 ,  24  with restoring springs and a plurality of compressed air 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 consumer loops and in distributor line  14 , and transmit the respective pressure as a pressure signal to electronic control unit  84 , which directly controls the solenoid valves. 
     Load circuits  26 ,  28  can be, for example, service-brake circuits, and 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, and 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  is designed as a high-pressure circuit for an air-suspension system (represented as an air bellows). An air-suspension system normally requires high pressure, because the air-suspension bellows exhibit large volumes and relatively high pressures. 
     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 particularly in air-suspension circuit  38 . As an example, it is permissible to supply other compressed air 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, 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 air-suspension circuit  38  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 . Air-suspension circuit  38  is electronically controlled by a control device  120  (also known as ECAS), which is connected to electronic control unit  84  via a data line  122 . 
     If the pressure were to drop in a load circuit, for example in circuit  30  (trailer-brake circuit), the compressed air supply by the service-brake circuits also takes place via the open solenoid valves, the pressure in secondary load circuits  30  to  36  being 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 service-brake circuits  26  and  28 . Air-suspension circuit  38  is shut off by solenoid valve  24  and therefore is not in communication with the other circuits. It frequently has a higher pressure level, such as 12.5 bar. 
     If the reservoir in air-suspension circuit  38  is dispensed with, as described hereinabove, and as is made possible by the specially described arrangement and construction of the solenoid valves, only the reservoir volumes of the service-brake circuits and a small dead volume up to the load circuits exist. If a small leak occurs in an air-suspension system without compressed air reservoir, frequent regulation via solenoid valve  24  would normally be required. Because of the large nominal width of solenoid valve  24 , the corresponding regulation algorithm is extremely complicated, and so it would be desirable to open the solenoid valve only when the air-suspension circuit actually needs compressed air. In this way it is possible to dispense with the pressure regulation described hereinabove. 
     In the event of a compressed air demand, for example because of a level-regulation function, control device  120 , which is connected via data line  122  to electronic control unit  84 , sends a compressed air request signal via the data line to electronic control unit  84 . This checks whether the pressures (or flow rate, air mass or energy) in brake circuits  26  and  28  are in conformity with the specified index values. If this is the case, control unit  84  switches solenoid valve  24  from the closed normal position to the open position, whereby communication with reservoirs  90 ,  92  of the service-brake circuits is established via normally open solenoid valves  16 ,  18 . Air-suspension circuit  38  is then filled from compressed air reservoirs  90 ,  92  of brake circuits  26 ,  28  via open solenoid valves  16 ,  18  thereof. If the pressure in the brake circuits, measured by pressure sensors  72 ,  74 , drops below the specified value, this is detected by electronic control unit  84 , which thereupon closes solenoid valve  24  of air-suspension circuit  38  and turns on compressor  7  via compressor control device  8  by changing over solenoid valve  94 . The compressor discharges into the brake circuits. When the index pressure has been restored in the brake circuits, electronic control unit  84  switches solenoid valve  24  of air-suspension circuit to open position once again, so that the air-suspension circuit continues to be filled by the brake circuits or by compressed air reservoirs  90 ,  92  thereof. This cyclic filling by the brake circuits is continued until the index pressure is reached in air-suspension circuit  38 . The pressure-request signal disappears, solenoid valve  24  is closed once again and the brake circuits are filled once again. Thereafter, solenoid valve  94  is switched to the vented normal state once again in order to turn off compressor  7  and to vent line  40 ′. 
     The compressor normally discharges only into brake circuits  26 ,  28 . If necessary, it can also discharge into the air-suspension circuit, in which case, depending on the air pressure in the brake circuits, solenoid valves  16 ,  18  of the brake circuits can be closed. 
     Solenoid valves  20  and  22  of the secondary load circuits remain open, since the pressure in associated load circuits  30  to  36  is limited by pressure limiter  70 . 
     As discussed above, air-suspension circuit  38  usually has a higher pressure level than the other circuits; nevertheless, it needs pressure relatively infrequently, and so, according to the present invention, it is closed in de-energized condition. 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 electronic control unit  84 ; the air-suspension circuit is therefore normally closed. Circuits  30  to  36  are supplied from reservoirs  90  and  92  of service-brake circuits  26  and  28 , and so valves  16 ,  18 ,  20  and  22  thereof are open in de-energized condition during normal driving. 
     As an alternative to the pressure, it is also possible to monitor other variables of state, such as air flow rate, air mass and energy, in the load circuits and distributor line. 
     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.