Testing rotary movement-electrical signal transducer system, particularly for vehicle wheel anti-block transducer systems
Cross reference to related U.S. Pat. Nos. 3,907,380; 3,874,743, 3,874,741, 3,822,920 and 3,866,980, all assigned to the assignee of the present application. 
     The present invention relates to testing of a signal transducer, and more particularly to the testing of rotary-electrical signal transducers for use in automatic wheel anti-block systems for automotive vehicles, and especially to methods and systems to carry out such tests. 
     Transducers used in automotive wheel anti-block systems provide pulses representative of rotation of the wheel. It is particularly important to supervise the proper function of the anti-block transducers continuously, and during operation. If one of the transducers should fail and provide an output signal which simulates blocking of a wheel -- that is, no sequential pulses -- then the usual anti-block system would vent the brake line to that particular wheel. Thus, the wheel cannot be braked if desired. A defect in the transducer, therefore, interferes with operating reliability of the vehicle. 
     It has previously been proposed to check the operation of the transducers by passing a test current therethrough. A test current was applied to one terminal of the transducer and the other terminal was connected to a check element which tested if the particular test current was present, or not. This system permits testing for an interruption in the transducer supply line as well to test the continuity of the transducer, but requires substantial equipment and components. Additionally, some malfunction effects cannot be checked by this method; for example, short circuits with a medium resistance short-circuiting junction, or other interferences in the supply lines to the transducers similar to short circuits are not checked by this method; intermittent or imperfectly-making contacts also cannot be tested thereby. Further, the system does not permit additional supervision of the wave-shaping stages usually associated with the transducers themselves. 
     It is an object of the present invention to provide a method and system to easily and simply check operability of the transducer system while recognizing as many malfunction effects as possible, and at least those usually encountered. 
     SUBJECT MATTER OF THE PRESENT INVENTION 
     Briefly, the period or pulse time of the pulses is measured; the sensed or measured value is compared with a reference time which has a limit with respect to its final time duration; upon exceeding this limit, the malfunction or evaluation signal is derived. 
     The invention proceeds from the basic concept that malfunction with respect to normal operation increases the pulse period of the pulses. In those applications in which the transducer should sense a region of speed range which is limited towards slow speed, the slowest possible speed which the transducer is to sense can be used as a reference value from which the longest period of time for the pulses, and hence the limiting value of the time period can be determined. If the pulse time of the pulse period is longer, an error evaluation or malfunction signal is derived. In this manner, shortcircuits, breaks in connecting lines, malfunction in the waveshaping circuit, as well as intermittently operating contacts or connections can be sensed, if the interruptions due to the intermittent contacts or terminals result in pulses which are longer than the time period determined by the limiting time value. 
     Many wheel anti-block systems sense very slow wheel speeds, that is, wheel speeds of close to zero (wheel stopped). The last pulse, just before the wheel stops, will become quite long. A limiting time cannot be readily determined therefor. When applied to wheel anti-block systems, however, acceleration (and its negative, deceleration) is also sensed; thus, not only the extent of time of a pulse can be used to derive an evaluation signal; in accordance with a feature of the invention, the system is additionally so arranged that, during normal operation, a certain maximum acceleration (or, rather, deceleration) is determined. By use of change in length of pulses between sequential pulses, the time periods of the last pulses which arise before the wheel will stop can be determined, particularly by calculation. The limiting value is then selected to be longer than the time period of the next to the last pulse before the wheel has stopped. If the last wheel transducer pulse only is used as the basis to derive a malfunction signal, its time period can be longer than that so computed limiting value. Yet, the anti-block system may function properly with such a longer time period. Thus, that very last signal must be disabled from indicating a malfunction. In accordance with a feature of the invention, therefore, the pulse period not of only one pulse, but of succeeding pulses, for example two succeeding pulses, is measured. The time limit duration of the next to the last pulse is compared with a time limit duration which is shorter than the time limit duration for the last pulse. If this next to the last pulse has a time period which is longer than the second limit (which second limit, it must be remembered, represents a shorter time than the final limit), then a blocking signal is derived which inhibits further propagation of the error, or malfunction evaluation signal. 
     The second time period -- also set with respect to longtime duration -- is determined to be somewhat shorter than the duration of the period of the penultimate pulse, upon maximum deceleration of the wheel. Thus, the method and the system operating in accordance with this embodiment ensure that malfunction signals are not indicated if the time period of the penultimate pulse is longer than this second period. In other words, an evaluation signal is used to indicate malfunction if the sequences of periods of two preferably sequential transducer pulses fall in different time ranges beyond a time interval which is longer than the maximum possible change of periods of time in ordinary, normal operation. 
     In accordance with a feature of the invention, a system to carry out the method is provided which has a device to measure the time period of the transducer pulses by using a counter which is set by the flanks of the output signal from the transducer, a clock generator to provide a time base, and two decoding circuits connected to the output of the counter to derive, respectively, a malfunction signal and a malfunction output inhibiting signal. A memory is provided to store the malfunction inhibit signal, the output of the memory being connected to a logic gate to which the malfunction signal, as well as the inhibiting signal is applied to logically either propagate the malfunction signal, or not. 
     The system can readily be constructed in digital technology using a minimum of standard commercially available digital units; it can easily be integrated in existing digital wheel anti-block systems. Other constructions are possible, particularly those based on analog technology. 
     The invention will be described by way of example with reference to the accompanying drawings, wherein the single figure is a schematic block diagram of the system in accordance with the present invention, showing also the basis for the method. 
     A transducer system 10 includes a tachometer generator 11 which provides an a-c output voltage having a frequency proportional to speed of a vehicle wheel, indicated as W schematically only. A wave-shaping stage 12 is connected to the output of the transducer 11 and converts the output signal from the transducer to a square wave. 
     A counter 20 has two inputs; count input 21 connected to a clock pulse generator 22, and reset terminal 23 connected to the output of wave-shaping circuit 12. Counter 20 has a group of count stage outputs 24, numbered 24a to 24i. 
     The time period of the pulses derived from the wave-shaping circuit 12 are measured by using like flanks, for example the rising or leading flanks of each pulse from the wave-shaping circuit 12 to reset the counter 20, and counting the number of pulses derived from clock source 22 during a pulse period. The count state then will be proportional to the time period of the measured pulses. 
     The count state is available at the outputs 24 of the counter. The value of the count state increases from a to i. This output may be in binary-digital form and the binary-sequential or decimal decoding of the output of counter 20 is not shown separately, since this is a well-known logic process for which standard commercial items are available, already incorporated in counters. The outputs from the counter 20 are connected to two decoding elements 30, 31. The output signal from the decoding element 30 changes when the count state of the counter exceeds a predetermined value, namely when the output signal corresponding to count state g becomes a 1-signal. During ordinary operation, the counter will not reach the count state of g, and the output of decoding element 30, which is a NOR-gate, will have a 1-signal appear thereat. The output of decoding element 30 will change to a 0-signal only if the count state of counter 20 exceeds that of stage g. The presence of such a long signal might indicate malfunction; but could also be due to deceleration of a wheel just before stopping. 
     The output signal of decoding element 31 changes as soon as the count state of counter 20 exceeds a second, and shorter limit, which is shorter than the limiting value assigned to NOR-gate 30. Thus, element 31, which is an OR-gate, will provide a 1-signal when the output of counter 20 has a 1-signal at its e terminal. This 1-signal from the output of OR-gate 31 is used as a blocking, or inhibiting, or suppression signal, which is stored in a memory 40 formed as a flip-flop. It is stored for the duration of the period of the then existing pulse, and reset upon occurrence of the next subsequent pulse. Blocking gate 50 then will have appear at its input approximately simultaneously digital signals of which the one from input 51 is derived from the first occurring transducer pulse, and that at input 52 from the next subsequent transducer pulse. Blocking gate 50, which is a NOR-gate, will have a 1-signal appear at its output only if neither of the two inputs has a 1-signal thereon. This is the case only if the count state, upon measuring of the first occurring pulse, has not exceeded the time period assigned to the count of the counter to reach the stage e and, further, the count state of the next subsequent pulse has exceeded the time period assigned to the limiting duration of stage g. The output from gate 50 is then connected to a warning lamp 60 and can additionally be used to disconnected the wheel anti-block system 70, or to change over operation of the anti-block system to a different mode. This output signal from gate 50 is derived if, and only if, the time duration of the penultimate signal does not exceed a predetermined second time limit, whereas the time duration of the subsequent last signal being counted exceeds the longer predetermined time duration. The reset pulse to memory 40 can be derived, for example, from the trailing flank of the pulse wave-shaping circuit 12 so that the output from circuit 40 will be timed with the next subsequent pulse applied to its SET input. 
     Various changes and modifications may be made within the scope of the inventive concept.