Abstract:
To detect a defect or failure of a compressed air load circuit in a compressed air system for vehicles, pressure is measured in compressed air load circuits and evaluated in an electronic control unit, which briefly shuts off the compressed air load circuits, measures pressure values and/or determines pressure gradients during the shutoff time and compares the pressure values and/or the determined pressure gradients with a respective threshold value, identifies defective circuits and definitively shuts off circuits detected as defective if the results are below the threshold value.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a method and system for detecting a defect or failure of a compressed air load circuit in an electronic compressed air system for vehicles.  
         [0002]     Conventional multi-circuit protective valves divide energy supply into several mutually independent load circuits and, in the event of failure of one load circuit, for example by line rupture, maintain a minimum pressure in the intact circuits. If a defect allowing more air to be lost than can be resupplied by the compressor occurs in a service-brake circuit, the pressure in the service-brake circuit drops until the pressure reaches the closing pressure of the valve. The pressure in the defective circuit continues to drop, whereas the closing pressure is maintained in the intact circuit. While the pressure in the defective circuit continues to drop, the circuit that is still intact can be refilled by the compressor until the opening pressure of the defective circuit is reached. There is established a dynamic equilibrium, in which the delivered compressed air can supply the circuits that are still intact (as well as secondary load circuits), although at the same time air is being lost via the defect. A disadvantage of conventional multi-circuit protective valves is that the maximum pressure in the brake system is equal to the opening pressure of the defective circuit when it breaks. Another disadvantage is that the pressure momentarily drops to the closing pressure of the defective circuit. Yet another disadvantage in particular is the relatively large energy loss in the event of a circuit failure, because defective circuits are detected and shut off at a relatively late stage.  
       SUMMARY OF THE INVENTION  
       [0003]     Generally speaking, in connection with the present invention, a method and system are provided which overcome the disadvantages associated with conventional methods and systems and which provide the capability to detect a defect or failure of a compressed air load circuit at an early stage and to shut off such defective or failed circuit at an early stage, minimizing energy loss. It will be appreciated that vehicle safety is substantially increased.  
         [0004]     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.  
         [0005]     The present invention accordingly comprises the various steps and the relation of one or more of such steps with respect to each of the others, and embodies features of construction, combinations of elements, and arrangements of parts which are adapted to effect such steps, all as exemplified in the construction herein set forth, and the scope of the invention will be indicated in the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The present invention will be described in more detail hereinafter on the basis of the accompanying drawings, in which:  
         [0007]      FIG. 1  shows a compressed air system according to a preferred embodiment of the present invention; and  
         [0008]      FIGS. 2 and 3  are graphical representations illustrating aspects of a method for detecting the defect or failure of a load circuit according to preferred embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0009]     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 .  
         [0010]     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.  
         [0011]     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 .  
         [0012]     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 controls the solenoid valves.  
         [0013]     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.  
         [0014]     Service-brake circuits  26 ,  28  are provided with compressed air reservoirs  90 ,  92  in conformity with EU Directive  98 / 12 .  
         [0015]     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 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.  
         [0016]     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  FIG. 1 , whereby line  40 ′ is vented and in this way compressor  7  is turned on.  
         [0017]     Air-dryer part  10  comprises a solenoid valve  100  with small nominal width, whose inlet  102  is in communication with distributor line  14  and whose outlet  104  is in communication with a shutoff valve  106 , which, in turn, is in communication with supply line  40  of compressor  7  and serves for venting of the air dryer.  
         [0018]     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.  
         [0019]     Reference numeral  112  denotes an overpressure valve.  
         [0020]     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 .  
         [0021]     If the pressure were to drop in a load circuit, for example in circuit  30  (trailer-brake circuit), the compressed air supply also takes place by service-brake circuits  26  and  28 , 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 the service-brake circuit (see hereinafter). 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, such as 12.5 bar.  
         [0022]     The inventive method will now be explained in more detail on the basis of  FIGS. 2 and 3 .  
         [0023]     As explained above, the pressure in a load circuit  26  to  38  can be measured by pressure sensors  72  to  80 . Because of the location of these pressure sensors shown in  FIG. 1 , however, such a pressure sensor does not directly measure the pressure in the respective load circuit. Instead it measures the pressure at the inlet of pressure-supply line  58  to  66  to the load circuit, or in other words at the outlet of the respective associated solenoid valve  16  to  24 .  
         [0024]     The pressure recorded by a pressure sensor  72  to  80  is therefore equal to the pressure in associated load circuit  26  to  38  itself only in the pressure-equalized condition. Otherwise, it is different, when repressurization via a pressure line  48  to  66  is taking place because of compressed air consumption in the circuit and supply air is flowing through the pressure line. A dynamic pressure difference, by which the pressure in the circuit is lower than the pressure measured at the solenoid valve, develops across the pressure line. This pressure loss is greatest during a failure of the load circuit (for example, due to a line break), namely when, because of the break, atmospheric pressure is present at the port of pressure-supply line  58  to  64  directed toward the circuit, and the pressure in connecting line  14 , measured at the pressure-sensor measurement point, is reduced by the pressure drop at the solenoid valve.  
         [0025]     Because of the very high air flows in the case of such a break (on the order of magnitude of 5000 l/m), the pneumatically coupled pressure chambers are also vented, meaning that the pressure in connecting line  14 , for example, also drops sharply.  
         [0026]     In a state characterized by such powerful venting flows, a reliable overall state that permits unambiguous detection of the failed compressed air circuit can be reconstructed only with difficulty from the measured values of pressure sensors  72  to  80  themselves.  
         [0027]     According to a preferred embodiment of the present invention, the defective compressed air load circuit can be detected by determining how the venting flow affects a circuit when venting is momentarily turned off. Only in the defective circuit does the pressure continue to drop, while in all other circuits either no influence is detectable or a pressure rise occurs, because, as a result of the lack of venting via the defective circuit, the pressure can be raised again by the air present in the compressed air reservoirs. This is schematically illustrated in  FIG. 2 .  
         [0028]     In load circuits in which the pressure drops due to a defect or due to brake actuation (see line A in  FIG. 2 ) and goes below a pressure threshold, such as point P, or in which the negative pressure gradient (pressure drop versus time) decreases below a threshold value, normally open solenoid valves or all such valves are momentarily shut off by electronic control unit  84  and the pressure variation after shutoff is tracked by the control unit. If the pressure continues to drop despite shutoff, as indicated by line B, this is an indication of a genuine defect, for example due to line rupture or line break, which is detected by electronic control unit  84  on the basis of the pressure signals of the pressure sensors. The control unit then turns off the solenoid valve associated with the defective load circuit and thereby shuts off the defective circuit as a whole, so that the intact circuits can continue to operate properly without being influenced by defective circuits.  
         [0029]     If the pressure in the shut-off circuit does not change after shutoff instant P (line C), as is the case for an intact circuit without compressed air reservoir, or if the pressure even rises to a higher value than at instant P (line D), as is the case for an intact circuit with compressed air reservoir, although pressure fluctuations E can still occur at first, this is an indication of an intact circuit. In this case, no measures are taken by control unit  84 .  
         [0030]     Pressures below the threshold values can also be caused by dynamic pressure surges in the air-suspension system or by other dynamic pressure overshoots or dynamic pressure changes in the load circuits, and can be interpreted as defects by control unit  84  even though they do not represent actual defects. To ensure that load circuits will not be shut off in such cases that are erroneously detected as defective circuits, it is provided according to an advantageous embodiment of the present invention that momentary shutoff will be applied several times in succession, in pulsed manner, so to speak, and that each momentary shutoff will be followed by a brief observation time, such as 0.4 sec. Only if the pressure has dropped further after several pulsed shutoffs have been applied will the corresponding load circuit be definitively shut off. The definitively shut-off load circuit will continue to be monitored thereafter to determine whether it is actually not defective or no longer defective.  
         [0031]     An example of detection of failure of brake circuit  26  will now be explained in more detail on the basis of  FIG. 3 .  
         [0032]     With failure of brake circuit  26  due to line break at instant  120  according to  FIG. 3 , the pressure value measured by pressure sensor  72  drops very rapidly. As a consequence, and as already explained, the pressure in brake circuit  28  (see curve  74  in  FIG. 3 ), which is in pneumatic communication, and in connecting line  14  also drops rapidly (not illustrated in  FIG. 3 ). The pressure drop in connecting line  14  has the consequence that solenoid valve  94 , which turns on the compressor, is actuated at instant  121 . By virtue of the now detected pressure drop in circuit  26 , a test pulse of 0.2 seconds, for example, is transmitted to the control input of solenoid valve  16  at instant  122 , thus blocking the solenoid valve for this time interval. Solenoid valve  16  is selected, since a line break is to be suspected there first because of the greater pressure drop than in circuit  28 .  
         [0033]     As a consequence of this blockage, the pressure at pressure sensor  74  in unaffected brake circuit  28  rises momentarily, because compressed air reservoir  92  can supply air to intact circuit  28  once again when venting is interrupted by defective circuit  26 . With respect to defective circuit  26 , however, a faster pressure drop takes place at pressure sensor  72  during the time of valve blockage because repressurization by the intact circuits is interrupted. The pressure at pressure sensors  76 ,  78  of circuits  30 ,  36  is unchanged during the test pulse. The pressure in these circuits undergoes little change in any case during the entire venting operation, because pressure limiter  70  ensures that the pressure sensors will be decoupled from distribution line  14 . Because the pressure drops more rapidly only in circuit  26  during the test pulse, the suspicion that this circuit is defective is strengthened. In order to be certain whether this conclusion is correct, this testing can be repeated by turning off valve  16  several times in pulsed manner. In the practical example, this is done a second and last time at instant  123 . The pressure again drops more rapidly in circuit  26 , and it is now definitively established that circuit  26  is the defective circuit, after which it is kept permanently blocked.  
         [0034]     To resupply intact brake circuit  28  with air, solenoid valve  24  of high-pressure circuit  38  is switched to open condition at instant  124 , so that intact circuit  28  and if necessary circuits  30  and  36 , which are in pneumatic communication therewith and are also intact, can be rapidly resupplied with air. To ensure that resupply with air can be achieved in the desired manner, high-pressure circuit  38  is provided with a compressed air reservoir (not illustrated). The pressure drop in the high-pressure circuit during this rapid resupply with air can be detected at pressure sensor  80 , as shown by the drop at instant  124 . After resupply with air has been achieved, circuit  28  is shut off for a certain time, beginning at instant  125 . During this time, the high-pressure circuit is refilled via the compressor, which is running. On completion of this refilling (no longer illustrated in  FIG. 3 ), the control signals for solenoid valves  94  and  18  are reset once again.  
         [0035]     Instead of test shutoff of the solenoid valve of the supposedly defective circuit with the rapid pressure drop in the manner explained, it is also possible to shut off several other or even all solenoid valves. A similar pressure variation is then obtained, specifically because each blockage of this type is capable of preventing repressurization of the defective circuit via connecting line  14 .  
         [0036]     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 compressed air load circuits.  
         [0037]     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 drawings shall be interpreted as illustrative and not in a limiting sense.  
         [0038]     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.