Abstract:
A testing system and method are provided for an electronically controlled braking system to determine whether the solenoids of each of the modulators are properly wired. According to the test, each modulator is tested in sequence. The exhaust solenoid of a modulator is actuated multiple times and the hold solenoid of a modulator is actuated once. Discrete signals will evidence whether the modulator solenoids have been properly wired.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to monitoring and testing of a vehicle braking system, and more particularly to monitoring and testing an electronically controlled braking system for an automotive vehicle equipped with pneumatically actuated brakes to determine if there is a mis-wired brake system modulator. Although the present invention may be used with adaptive braking systems, it is also intended for use with other electronically controlled braking systems, such as electropneumatic braking systems. 
     Generally, it is necessary for a driver to be sure that a vehicle braking system is working properly at all times. Accordingly, it is common to provide a series of checks upon starting the vehicle to assure that the electronically controlled braking system is operating properly. one check relates to the solenoids associated with a brake pressure modulator and the associated electrical circuits which operate the valves and selectively control communication with the vehicle brakes. For example, it is important to discern whether the solenoids are either electrically open or shorted. if it is determined that an electrically open or shorted condition exists in the solenoid circuit, the braking system is shut down and the vehicle driver is provided a suitable warning signal. 
     Typically, the brake pressure modulator includes an inlet or hold valve, which controls communication with a pressure source, and an exhaust valve which is selectively actuated to exhaust braking pressure to atmosphere. If the exhaust valve is actuated, the inlet or hold valve must also be actuated to preclude dumping the air supplied to the modulator from the pressure source to atmosphere. 
     The braking system further includes an electronic control unit (ECU), which receives inputs from speed sensors which measure speeds of the vehicle wheels. The ECU processes these wheel speed signals to determine if one or more of the vehicle wheels is about to lock up. If an incipient lock-up condition is sensed, the ECU actuates the inlet or hold solenoid valve, which blocks communication between the pressure source and the brake actuator to thereby hold the pressure level then existing in the actuator. Pressure in the brake actuator is dumped to atmosphere by simultaneously actuating both the hold and exhaust valves. 
     Three wires connect the ECU with each modulator. One wire is a source wire that supplies power to both solenoids. A second wire provides a ground to the inlet or hold valve if a hold function is desired. Finally, a third wire supplies a ground to the exhaust valve if an exhaust function is desired. On occasion the hold and exhaust wires are reversed. Since the resistance of both of the solenoids is the same, the ECU cannot easily detect the reversed condition of the wires. 
     In U.S. Pat. No. 5,327,781 miswiring is detected based on the difference in the exhaust sound generated by a correctly wired modulator versus an incorrectly wired modulator. Particularly, when properly wired, the hold solenoid is actuated for ten milliseconds compared to an incorrectly wired modulator which provides an exhaust pulse on the order of thirty milliseconds. This time difference or difference in exhaust sound is not sufficient to consistently identify an incorrectly wired modulator during testing. 
     When modulators have been incorrectly wired by the original equipment manufacturers or by a mechanic, extended stopping distances of vehicles may be encountered or excessive system pressure may be exhausted during a traction control or ABS event. 
     The present invention contemplates a new and improved apparatus and method which overcomes the above referenced problems and others and provides a consistent and efficient detection method to determine if a modulator has been miswired. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an improved apparatus and method for testing an electronically controlled braking system. According to another aspect of the invention, the apparatus and method includes determining if exhaust and hold solenoid valves in a modulator controlling a brake sub-system of at least one wheel on a vehicle are properly wired. First, a brake pedal in a vehicle is depressed. Then, an ignition of the vehicle is turned on to power the vehicle and ECU. The system uses the ECU to determine if at least one of the exhaust and the hold solenoid valves is open or short circuited. If the determination is positive, present information of the vehicle is stored in a storage device in the ECU and testing is aborted. If the determination is negative, the test apparatus and method pauses for a predetermined period of time. As an example, the system then energizes a first one of the hold solenoid valves at least twice, and then energizes one of the exhaust solenoid valves once. Finally, the system determines whether there are two or more signals generated from the energizing step. If there are two or more signals, e.g. audible signals, the solenoid valves are mis-wired. 
     According to another limited aspect of the present invention, the system serially performs the pausing and valve energizing for the modulator for a plurality of the wheels. 
     An advantage of this invention is that the miswiring of solenoid valves in a modulator can be more consistently detected. 
     Another advantage of the invention is that the prospects for miswiring solenoids is reduced. 
     Still other benefits and advantages of the invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention. 
     FIG. 1 is a schematic illustration of a partial air brake system for an automotive vehicle which is equipped with an adaptive braking system to control wheel lock; 
     FIG. 2 is a cross-sectional view of a modulating valve of the type used in the system of FIG. 1; 
     FIG. 3 shows a modulator circuit schematic for the preferred embodiment; and, 
     FIG. 4 is a flow block diagram illustrating the manner in which the electronic control unit of the system illustrated in FIG. 1 performs the testing function of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, an air brake system, generally indicated by numeral  10 , includes right front wheel  12  and associated brake actuator  14 , left front wheel  16  and associated brake actuator  18 , and a double rear axle assembly comprising right rear wheels  20 ,  22 , left rear wheels  24 ,  26  and associated tandem brake actuators  28 ,  30 ,  32 , and  34 , respectively. The system  10  further includes an operator actuated, brake valve  36  having a treadle  38  actuated by the vehicle operator. When the treadle  38  is actuated the valve  36  allows communication between inlet port  40  and outlet port  42  and simultaneously communicates inlet port  44  with outlet port  46  in a manner well known to those skilled in the art. The system  10  further includes a source of air pressure, such as reservoir  48 , which is charged by an air compressor operated by the vehicle engine (not shown). The port  44  communicates with the pressure source  48 , but for clarity these communication lines have been omitted from the drawing. Outlet port  46  is communicated to the right and left wheel actuators  14 ,  18  through a conventional quick release valve  50  and right and left front wheel modulators  52 ,  54 . Outlet port  42  of brake valve  36  is connected to control port  56  of a conventional relay valve generally indicated by the numeral  58 . Supply port  60  of relay valve  58  communicates with the pressure source  48  and outlet ports  62 ,  64  of relay valve  58  are connected respectively to the right rear wheel actuators  28 ,  30  and left rear wheel brake actuators  32 ,  34  through right rear wheel brake modulator  66  and left rear wheel modulator  68 . The modulators  52 ,  54 ,  66 , and  68  will be described in greater detail below with reference to FIG.  2 . 
     Traditionally, the electronic control unit (ECU) for the braking system which controls the modulators  52 ,  54 ,  66 , and  68  is housed in the cover of the relay valve  58 . Accordingly, the ECU is indicated generally by the numeral  70 . Speed sensors  72 A-F associated with selected ones of the wheels sense the speed of the associated wheel and generate signals which are transmitted to the ECU  70  via the lines indicated on the drawing. Similarly, actuating signals generated by the ECU  70  when, for example, an incipient skidding condition of one of the wheels is detected are transmitted to the modulators  52 ,  54 ,  66 , and  68  through the leads connecting the ECU  70  and the corresponding modulators as illustrated in FIG.  1 . 
     Referring now to FIG. 2, the representative modulator  52  will now be described in detail, it being understood that modulators  54 ,  66 , and  68  are structurally and functionally identical unless specifically noted to the contrary. Modulator  52  includes an inlet or supply port generally indicated by  74 , and outlet or delivery port  76 , which communicates with the corresponding brake actuator, and an exhaust port  78  which communicates with ambient atmosphere. 
     An exhaust diaphragm  80  is moveable within an exhaust cavity  82  and urged into sealing engagement with exhaust seat  84  by a spring  86  and by air pressure communicating against the upper surface of the diaphragm  80  through passage  88 . Passage  88  is normally connected through passage  90  with supply port  74  when the exhaust solenoid valve indicated by the numeral  92  is in its normally open position. In the normally open position, valve  92  allows communication between passages  88  and  90  and closes communication through passage  94 , which communicates with exhaust chamber  82 . Accordingly, upon energizing exhaust solenoid  92 , passage  90  is sealed off and passage  88  is communicated to  94 , whereupon higher pressure air at outlet port  76  lifts the exhaust diaphragm  80  off the seat  84  to permit venting of the pressure level at outlet delivery port  76  through exhaust port  78 . 
     Similarly, a supply or hold diaphragm  96  is interposed in the communication path between the supply or inlet port  74  and the outlet or delivery port  76  and is normally closed as illustrated in FIG.  2 . Supply diaphragm  96  is controlled by a hold or supply solenoid valve  98 . When in its normally closed position illustrated in FIG. 2, the hold diaphragm closes off passage  100  which communicates with the supply port  74  and vents passage  102  to exhaust port  78 . More particularly, passage  102  allows communication between the control surface of the hold diaphragm  96  and passage  104  which communicates with exhaust port  78  through the exhaust chamber  82  when valve  98  is in its normally closed condition. Upon energizing of the valve  98 , the passage  104  is closed off and passage  100  communicates with passage  102  thereby admitting supply air from inlet port  74  to the control surface of diaphragm  96 . Control pressure acting on diaphragm  96  is supplemented by spring  106  to urge the diaphragm  96  into sealing engagement with valve surface  108 , thereby closing off communication between the supply inlet port  74  and the outlet or delivery port  76 . As discussed above, the supply or hold valve  98  would also be actuated upon actuation of the exhaust solenoid valve  92 , to prevent pressure at the supply or inlet port  74  from exhausting to an atmosphere through exhaust port  78 . It will be appreciated that the modulator valve  52  shown and described is merely representative of this type of valve. The present invention, however, can be used with other modulator valves that, although structurally different, provide the same features and benefits as described above. 
     Referring now to FIG. 3, there is shown a modulator circuit with an exhaust coil and a hold coil and a three pin connection to the solenoids of the modulator valve. Node A of the exhaust coil side of the modulator circuit is connected to the exhaust solenoid  92 , node B in the modulator is the common connection for both the exhaust solenoid  92  and the hold solenoid  98 , and node C is the connection for the hold solenoid coil and hold solenoid  98 . As indicated above, if the connections at nodes A and C are inadvertently interchanged, the ECU may not detect the incorrectly wired modulator. Accordingly, the following test procedure was developed to analyze and verify proper wiring of the solenoids. 
     Turning now to FIG. 4, a subroutine programmed within the ECU  70  in order to perform the wiring test is illustrated schematically. The test is initiated at  110  and requires that the treadle  38 , or brake pedal, is depressed while the ignition key is turned on, as indicated at  114 . This also powers the ECU  70 . The test then proceeds to interrogate each of the solenoids and each of the modulators for an open or shorted condition, as indicated at  116 . As is known in the art, testing of the solenoids includes and audible clicking or popping associated with actuating the solenoid (sometimes referred to as a “Chuff” test). An observer listens for the actuating noises of the modulator solenoids in a predetermined pattern established by test protocol. As indicated at  118 , the results of the test made at  116  are processed. If any of the solenoids are electronically opened or shorted, the wiring test according to the present invention is aborted as indicated at  120  and an update of the current fault and fault history is stored in the memory of ECU  70 . A corresponding warning light (not shown) is actuated to provide a visual notification of the fault. 
     Assuming that there are no open or shorted solenoids, there is a short wait state between solenoid tests. As indicated at  122 , the ECU  70  then recognizes the right front modulator where multiple solenoid actuation tests are performed by energizing, for example, the hold solenoid multiple times and the exhaust solenoid once. This will produce a distinct difference from the exhaust sound if the modulator is wired incorrectly, as is indicated at  124 . After this is done, the program imposes another wait state between solenoid actuation tests as indicated at step  126  and then energizes the left front modulator using the same multiple solenoid actuation tests by energizing the hold and exhaust solenoids multiple times. Again, if the modulator is wired incorrectly as indicated at  128  a distinct audible signal will be heard. After still another wait state between solenoid actuations, as indicated at  130 , the solenoids of the right rear modulator  66  are actuated for a test procedure and the program then executes another wait state, as indicated at  134 . The solenoids of the left rear modulator  68  are then monitored as indicated at  136 , thus completing all four modulators of the brake system. 
     As indicated at step  138 , the program determines next if this is the first or second time that this test has been performed. If it is determined that this is the second time the test has been performed, the solenoid actuated testing is terminated as indicated at  146 . If this is the first time that this test has been performed, the test is repeated as indicated at  142  by starting at step  140  and running through steps  132 - 138  for a second time. The program will end once the second time is completed at  146 . 
     The process described above in which each hold solenoid of the modulator is actuated multiple times and the exhaust solenoid is actuated once produces a distinct, audible signal to the test operator/observer. If the modulator is improperly wired the modulator will exhaust multiple times. On the other hand, if the connector is properly wired, the modulator will exhaust once. By interrogating each solenoid of each modulator through this routine, an effective test of the wire connection is achieved. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the proceeding detailed description of the preferred embodiment. It is intended that the invention be construed as including all such alterations and modifications insofar as a they fall within the scope of the appended claims with the equivalents thereof.