Abstract:
A method and system is provided for refilling vehicle operational brake circuits after a large consumption of compressed air. The operational brake circuits are compressed air consumer circuits of a consumer part of a vehicle compressed air system. The operational brake circuits also include at least one additional compressed air consumer circuit provided with a compressed air reservoir. The actual pressure values in the operational brake circuits and in the additional compressed air consumer circuit are continuously determined and compared against a lower threshold value. If the values are below the threshold value, the identified operational brake circuits are blocked as defective and communication is established between the additional compressed air consumer circuits and the intact operational brake circuits in order to refill the operational brake circuits from the compressed air reservoirs of the additional compressed air consumer circuits.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and system for refilling brake circuits after rapid compressed air consumption. 
     Multi-circuit protective valves are known that divide an-energy supply into several mutually independent consumer circuits and, in the event of failure of a 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 refilled by the compressor occurs in a service-brake circuit, the pressure in the service-brake circuits drops mutually until the closing pressure of the valve is reached. The pressure in the defective circuit continues to drop, whereas the closing pressure is maintained in the intact circuits. While the pressure in the defective circuit continues to drop, the circuits that are still intact can be refilled by the compressor until the opening pressure of the defective circuit is reached. A dynamic equilibrium is established in which the delivered compressed air can supply the circuits that are still intact (as well as secondary consumer circuits), although at the same time air is being lost via the defect. A disadvantage of such known multi-circuit protective valves is that refilling by the compressor takes a relatively long time because the compressor has only a relatively small delivery capacity, approximately 200 to 400 liters per minute. Accordingly, the nominal energy in the brake system is restored slowly—representing a disadvantage with respect to system safety. 
     SUMMARY OF THE INVENTION 
     Generally speaking, in accordance with the present invention, a method and system are provided whereby the air pressure in vehicle brake circuits can be restored rapidly after rapid compressed air consumption. 
     In accordance with the present invention, the brake circuits are filled, after rapid air consumption, from a high-pressure consumer circuit in addition to the compressor. Since a high-pressure circuit can usually deliver a much larger air flow per unit time (up to several thousand liter/min.) than a compressor (approximately 200 to 400 liter/min.), the intact brake circuits are refilled much faster than merely by means of the compressor. As a result, the nominal energy in the brake system, possibly reduced by a defective circuit, can be restored in a very short time. This is particularly important after a circuit break. System safety is substantially improved by distributing the energy between the circuits. This is achieved according to the present invention by providing, for the high-pressure circuit, an electrically actuatable valve that is closed in the de-energized normal state, preferably a solenoid valve (alternatively, a pilot-controlled valve can be used), and, for the other consumer circuits, including the brake circuits, electrically actuatable valves that are open in the normal state, preferably solenoid valves. All solenoid valves are in communication with one another via a common distributor line. To fill the brake system, the solenoid valve of the high-pressure circuit is switched to open position in order to allow compressed air to flow out of the high-pressure circuit in which the pressure or the energy has been conserved via the open solenoid valves into the intact 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 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 
       The present invention will be described in more detail hereinafter on the basis of the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a compressed air system according to an embodiment of the present invention; and 
         FIG. 2  is a graphical representation showing pressure variations during an operation of refilling of a brake system in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , 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 consumer part  6 . Compressed air supply part  4  includes 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 solenoid valves  16 ,  18 ,  20 ,  22 ,  24  with restoring springs and a plurality of compressed air consumer 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 consumer 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 compressed air consumer 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. 
     As an alternative to pressure, it is also possible to monitor other variables of state, such as air flow rate, air mass and energy, in the consumer circuits and in the connecting line. 
     Compressed air consumer circuits  26 ,  28  can be, for example, service-brake circuits. Compressed air consumer 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. Compressed air consumer circuit  32  can be a parking-brake circuit with spring accumulator. Compressed air consumer circuits  34  and  36  can be secondary consumer 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. Compressed air consumer 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. High-pressure circuit  38  is provided with a compressed air reservoir  39 . 
     The inventive compressed air system makes it possible to dispense with compressed air reservoirs in circuits  30 ,  32 ,  34 ,  36 . As an example, it is permissible to supply other compressed air consumer 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  includes 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 compressed air consumer 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 compressed air consumer circuit needs compressed air, solenoid valve  94  is again switched to the normal state illustrated in the drawing, whereby line  40 ′ is vented and compressor  7  is turned on. 
     Air-dryer part  10  includes a solenoid valve  100  with small nominal width. An inlet  102  is in communication with distributor line  14 . A shutoff valve  106 , which is in communication with supply line  40  of compressor  7  and is used for venting of the air dryer, is pneumatically switched via an outlet  104 . 
     When solenoid valve  100  is switched to passing condition, compressor  7  no longer discharges into the consumer circuits but instead discharges to the atmosphere via valve  106 . At the same time, dry air flows from distributor line  14  (out of reservoirs  90 ,  92  of the service-brake circuits) to the atmosphere 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 . 
     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 compressed air consumer circuits  26  to  34  being open in de-energized normal state, while solenoid valve  24  of high-pressure 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 . 
     If the pressure were to drop in a compressed air consumer circuit, for example in circuit  30  (trailer-brake circuit), the supply of compressed air also is effected by the service-brake circuits  26  and  28  via the open solenoid valves, the pressure in secondary compressed air consumer circuits  30  to  36  being adjusted by pressure limiter  70  to a lower level, such as, for example, 8.5 bar, than the pressure level of, for example, 10.5 bar in service-brake circuits  26  and  28 . High-pressure circuit  38  is normally shut off by solenoid valve  24 , and therefore is not in communication with the other circuits. The high-pressure circuit usually has a higher pressure than the other compressed air consumer circuits, such as, for example 12.5 bar. 
     In the inventive compressed air system, the pressure in compressed air consumer circuits  26  to  38  is measured by means of pressure sensors  72  to  80 , which transmit electrical pressure signals to electronic control device  84  for evaluation. The control device compares the measured pressure values with a lower threshold value, which corresponds to the pressure to be adjusted in the respective compressed air consumer circuit. If the pressure of the brake circuits drops below this threshold value due to rapid air consumption or to line rupture or break, the control device switches solenoid valve  24  of high-pressure circuit  38  to open position so that the high-pressure circuit is in communication with brake circuits  26  and  28  via connecting line  14  and open solenoid valves  16  and  18  and the energy stored in the high-pressure circuit is directed into the intact brake circuits and the intact brake circuits are refilled. At the same time, control device  84  shuts off the defective circuits by switching their solenoid valves to closed position; and compressor  7  also delivers into the intact brake circuits. 
     Refilling takes place very rapidly because the high-pressure circuit delivers a greater air flow per unit time into the brake circuits (up to several thousand liter/min.) than the compressor (approximately 200 to 400 liter/min.). 
     When the control device senses that the pressure in the high-pressure circuit and the pressure in the filled brake circuits are equal or that the index pressure value has been reached in the brake circuits, the control device closes solenoid valve  24  once again to interrupt the communication with the brake circuits. 
     It should be appreciated that the inventive method ensures distribution of energy between the consumer circuits, the salutary result being safe vehicle operating conditions. 
     Referring now to  FIG. 2 , the pressure variations during a brake-circuit failure due, for example, to a line break in brake circuit  26  at instant  120 , and during refilling of intact brake circuit  28  at instant  124 , are shown. In addition to the pressure drop in circuit  26  (see curve  72 ), the pressure in brake circuit  28  (see curve  74 ), which is in pneumatic communication, and in connecting line  14  (not illustrated) also drops. The pressure drop in connecting line  14  results in solenoid valve  94 , which turns on the compressor, being actuated at instant  121 . To resupply intact brake circuit  28  with air, solenoid valve  24  of high-pressure circuit  38  is switched to the open state at instant  124 , and defective brake circuit  26  is closed approximately at the same time by the closing of solenoid valve  16 , so that intact circuit  28 , and if necessary pneumatically coupled circuits  30  and  36 , which are also intact, can be rapidly resupplied with air. The pressure in circuits  30  and  36  undergoes little change during the entire venting operation since pressure limiter  70  ensures decoupling of the pressure sensors from distribution line  14  (see broken pressure curves  76 ,  78 ). 
     In  FIG. 2 , the closing of solenoid valve  16  is illustrated at an instant  123 , which occurs shortly before instant  124 ; this is explained in greater detail hereinafter. With the opening of solenoid valve  24  of high-pressure circuit  38  and the closing of defective brake circuit  26  at instant  124 , the pressure in brake circuit  28  rises very rapidly, until the pressure of the high-pressure circuit and the pressure of the brake circuit become equal or until the index pressure of the brake circuit is reached. The pressure drop in the high-pressure circuit during this rapid resupply with air can be detected at pressure sensor  80  (see drop of pressure curve  80  of high-pressure circuit  38  at instant  124 ). After it has been resupplied with air, circuit  28  is shut off for a certain time by switching solenoid valve  18  to blocked state at instant  125 . During this time, the high-pressure circuit is refilled via the compressor, which has been switched on since the actuation of solenoid valve  94  at instant  121 . To complete this refilling operation (instant  126 ), the control signals for solenoid valves  94  and  24  are reset once again, which means that solenoid valve  94  is electrically energized and solenoid valve  24  is switched to the closed normal state once again. Thereafter, the control signal for brake circuit  28  is also reset (instant  127 ), which means that solenoid valve  18  is switched to open normal state once again. 
     Reference numerals  122  and  123  denote two brief test blocking pulses with a duration of 0.2 sec., for example, transmitted to the control input of solenoid valve  16  before instant  124  of definitive blocking of defective circuit  26 . Such test blocking pulses can be used for safe detection of the failure of a circuit (circuit  26  in this case). The test blocking pulse at instant  122  blocks solenoid valve  16  for the indicated time interval of 0.2 sec. As a consequence of this blockage, the pressure at pressure sensor  74  in unaffected brake circuit  28  rises momentarily; because pressure 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 , a faster pressure drop takes place at pressure sensor  72  during the time of the test blocking pulse-since repressurization by the intact circuits is interrupted. Since the pressure drops more rapidly only in circuit  26  during the test blocking pulse, the suspicion that this circuit is defective is strengthened. In order to be certain whether this conclusion is correct, this test can be repeated by turning off valve  16  several times in pulsed manner. In the example illustrated in  FIG. 2 , this is done a second and third time at instant  123 . The pressure again drops more rapidly in circuit  26 . It is now definitively established that circuit  26  is the defective circuit. Thereafter, beginning at instant  124 , circuit  26  is kept blocked. 
     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. 
     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.