STEERING WHEEL OPERATION STATE DETECTOR OF VEHICLE

Abstract: A steering wheel operation state detector of a vehicle in accordance with the present invention includes position detection means and a pulse generator which produce outputs in the interlocking arrangement with the steering wheel operation of a vehicle, and a microcomputer which compares the output change value of the position detection means due to the steering wheel operation with the generated number of pulses of the pulse generator at a predetermined sample cycle and judges that either the position detection means or the pulse generator is out of order when a proportional relationship is not established between the compared values. The microcomputer compares the output change value of the position detection means due to the steering wheel operation with the generated number of pulses of the pulse generator at the predetermined sample cycle, and judges that the position detection means or the pulse generator is out of order when the proportional relationship is not established by utilizing the fact that the output change value and the generated number of pulses have the proportional relationship.

Description: TECHNICAL FIELD This invention relates to a vehicular steering condition detecting apparatus according to the preamble of claim 1. BACKGROUND ART Such a vehicular steering condition detecting apparatus is known from JP-A-59 102 103. This document discloses a position sensor in the form of an angle sensor comprising a resolver, a potentiometer or the like, and a pulse generator in the form of a pulse sensor, for sensing a rotational position of a crankshaft operatively connected therewith for synchronized rotation. The angle sensor generates an output signal representative of an angular or rotational position of the crankshaft of an internal combustion engine. The output signal is fed through a converter such as an A/D converter to a D terminal of each of a pair of latch circuits. The output signal from the pulse sensor is waveform shaped by a converter and then fed to a CK terminal of a latch through an inverter, whereby the digitized output signal from the angle sensor is held by the latch circuit upon occurrence of a rising edge of the waveform-shaped output signal of the pulse sensor, and also by the other latch circuit upon occurrence of a falling edge of the waveform-shaped output signal of the pulse sensor. Output signals of the latch circuits are then fed to an adder wherein they are added to each other to provide an average signal S. This average signal S is fed to a comparator where it is compared with a reference signal F indicative of a predetermined angular position, which is supplied thereto from a reference signal generator. If a difference between the average signal S and the reference signal F is greater than a predetermined value, the comparator generates a high-level output, thus indicating an abnormality of the angle sensor. As apparent from the above explanation, the output signal of the pulse generator is used as a trigger signal for making the latch circuits hold the output signal of the angle sensor at a predetermined angular or rotational position. From the WO-A-89 10865 (= EP-A-0 418 258) a control unit for steering the rear wheels of a road service vehicle is known. According to this document, two position sensors of the same kind and construction are employed so that a failure or malfunction of one of these sensors is detected by comparing the output signals therefrom. Such a measure of failure detection is very popular and well known, but it is disadvantageous from the point of view of cost reduction because the position sensors, which are required to accurately detect the angular position of the steering wheel of a vehicle are rather expensive and hence use of two positon sensors (i.e., a normal and an additional position sensor for exclusive use with failure detection) is much costly, thus increasing the manufacturing cost of an entire steering condition detecting apparatus employing the two position sensors. Fig. 4 is a block diagram showing the construction of a known vehicular steering condition detecting apparatus. In Fig. 4, reference numeral 1 designates a steering wheel connected to a steering shaft 2 which is mounted on a front wheel steering mechanism 3. The front wheel steering mechanism 3 is connected with a tie rod 4 to which a front wheel 5 is mounted. A variable resistor 6 constituting a position sensor is connected to the steering shaft 2 so that the resistance thereof varies in accordance with the rotation of the steering shaft 2. The variable resistor 6 is connected to an unillustrated power source so as to generate an output voltage which is proportional to the resistance thereof which varies with the rotation of the steering shaft 2. The output voltage of the variable resistor 6 is input to an analog/digital converter 7 (which is hereinafter referred to as an A/D converter). The A/D converter 7 converts the output voltage of the variable resistor 6 into a digital value which is then output to a microcomputer 8. The operation of the above apparatus will now be described. In accordance with the rotation of the steering wheel 1, the steering shaft 2 is thereby caused to rotate so that the resistance of the variable resistor 6 is accordingly varied. The variable resistor 6 generates an output voltage proportional to the varied resistance thereof to the A/D converter 7 where it is converted into a digital value. The output of the A/D converter 7 is fed to the microcomputer 8 which calculates, based thereon, the absolute value of the steering angle and the angular velocity of the steering wheel 1, which are utilized as steering condition data for controlling various aspects of the operation of the vehicle. With the known vehicular steering condition detecting apparatus as constructed above, a failure in the variable resistor 6 or a failure in the A/D converter 7 directly results in the destruction of the steering condition data prepared by the microcomputer 8. In addition, it is sometimes impossible to detect such a failure, thus providing the drawback that the control of the vehicle is seriously affected. It is an object of the present invention to provide a vehicular steering wheel condition detecting apparatus which can detect a failure or malfunction of position sensor or an A/D converter in a precise manner to thereby prevent improper or faulty control of a vehicle based on the erroneous data indicative of a position and an angular velocity of a steering wheel of the vehicle, having a simple construction at low cost. This object is solved by a vehicular steering wheel condition detecting apparatus of the initially defined type which is characterized by a microcomputer for comparing between a change in the output of the position sensor due to the operation of the steering wheel by the driver and the number of pulses generated by the pulse generator for every sampling period of a predetermined length, the microcomputer being operable to determine that a failue in the position sensor or the pulse generator occurred, if there exists no proportional relationship therebetween. A preferred embodiment is listed in dependent claim 2. The present invention proposes to employ the one position sensor, which accurately detects the rotational or steering angle of a steering wheel, and one pulse generator, which generates pulses for sensing or representing the angular velocity of the steering wheel. The microcomputer of the present invention operates to make a comparison between a change in the output of the position sensor due to the operation of the steering wheel by the driver and the number of pulses generated by the pulse generator for every sampling period of a predetermined length, and determines, by utilizing the fact that there is a proportional relationship between the change in the position sensor output and the number of output pulses of the pulse generator when the position sensor and the pulse generator are normal, that a failure in the position sensor or the pulse generator occurred if there no longer exists a proportional relationship therebetween. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the construction of a vehicular steering condition detecting apparatus in accordance with one embodiment of the present invention; Fig. 2 is a wave form diagram showing the output signal of a pulse generator of the embodiment of Fig. 1; Fig. 3 is an explanatory view showing the relationship between the steering condition of a steering wheel and a microcomputer for an explanation of the operation of the above embodiment; and Fig. 4 is a block diagram of the construction of a conventional vehicular steering condition detecting apparatus. In the following, an embodiment of a vehicular steering condition detecting apparatus according to the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a block diagram showing the construction of this embodiment. In Fig. 1, for the purpose of explaining the construction of the embodiment, the same components as those of Fig. 4 are identified by the same symbols so as to avoid an unnecessary duplicate explanation thereof. As clearly seen from a comparison between Figs. 1 and 4, those portions which are identified by reference numerals 1 through 8 in Fig. 1 are the same as those in Fig. 4, excepting that a pulse generator, which is designated by reference numeral 9, is added to the construction of Fig. 4. Similar to the variable resistor 6 constituting a position sensor, the pulse generator 9 is connected to the steering shaft 2 so that it generates output pulses in conjunction with the operation of the steering wheel 1. The pulse generator 9 sends to the microcomputer 8 an output signal which contains two kinds of pulses comprising a series of pulses of phase A and a series of pulses of phase B, which are 90 degrees out of phase with respect to each other, as shown in Figs. 2(A) and 2(B). The microcomputer 8 receives the output signal of the A/D converter 7 and the phase A pulses and the phase B pulses of the pulse generator 9, and makes, based thereon, a comparison between a change in the output of the variable resistor 6 due to the driver's steering operation and the number of pulses generated by the pulse generator 9 for every sampling period of a predetermined length, so that it can detect a failure in the A/D converter 7 or a failure in the variable resistor 6 or a failure in the pulse generator 9 by checking, on the basis of the fact that there is a proportional relation between the change in the variable resistor output and the number of the generated pulses when the A/D converter 7 and the pulse generator 9 are normal, whether there is a proportional relation therebetween. The construction of this embodiment other than the above is the same as that of Fig. 4. The operation of this embodiment will now be described in detail. When the driver turns the steering wheel 1, the variable resistor 6, forming a position sensor, and the pulse generator 9, which are connected to the steering shaft 2, are caused to rotate in accordance with the turning of the steering wheel 1, so that the variable resistor 6 generates an output signal which is input to the A/D converter 7 where it is converted into a digital value which is in turn output to the microcomputer 8 so as to be utilized therein for detecting the absolute position of the steering wheel 1. Also, the pulse generator 9 generates an output signal which is directly input to the microcomputer 8 which can identify, based thereon, the steering direction of the steering wheel 1 and detect the absolute position thereof by counting the number of pulses contained therein. Further, the microcomputer 8 can calculate the angular velocity of the steering wheel 1 by differentiating the number of pulses thus counted with respect to time. According to the present invention, these signals are utilized for readily detecting a failure in the variable resistor 6 and a failure in the pulse generator 9. Fig. 3 is a view for explaining this situation, in which the abscissa represents the steering condition of the steering wheel 1 and the ordinate represents data in the microcomputer 8. In Fig. 3, reference numeral 101 designates the absolute value of the steering angle representative of the position of the steering wheel 1 which is the output signal of the variable resistor 6 converted into a digital value by the A/D converter 7 and transmitted therefrom to the microcomputer 8. Reference numeral 102 designates the output signal of the pulse generator 9 representative of the relative position of the steering wheel 1. The microcomputer 8 is programmed in advance in such a manner that it can detect the absolute value 101 of the steering wheel position and the relative position 102 of the steering wheel 1 for every sampling period of a predetermined length. Here, let us assume that the time at which an arbitrary first sampling is performed is point A1 and the absolute value of the position of the steering wheel 1 at that time is point A2. Further, assuming that the subsequent sampling time after the steering wheel 1 has once been turned is point B1, and that the absolute value of the position of the steering wheel 1 is point B2, a change in the absolute value of the position of the steering wheel 1 during the time from the first sampling point A1 to the second sampling point B1 is the distance between B2 and A2. Similarly, the change in the relative position of the steering angle of the steering wheel 1 can be determined by the number of pulses generated by the pulse generator 9 during the time from point A1 to point B1. There exists a proportional relationship between the change (B2 - A2) in the absolute value of the steering wheel position and the number of output pulses of the pulse generator 9 which corresponds to the change in the relative position of the steering wheel 1. Therefore, by detecting, upon every arbitrary sampling, whether there exists a proportional relationship therebetween, it is possible to confirm whether the output signals of the position sensor and the pulse generator 9 are normal. INDUSTRIAL APPLICABILITY As described in the foregoing, according to the present invention, the fact that there exists a proportional relation between a change in the output signal of the steering-angle sensing position sensor which is digitized by the A/D converter and a change in the number of pulses generated by the pulse generator is utilized for detecting a failure in the output signals of the position sensor and the pulse generator by checking the changes in these signals for every sampling period. Thus, by detecting a discrepancy in these signals, it is possible to detect a failure in the position sensor and the pulse generator in a simple manner, thus preventing in advance the control of the vehicle from being seriously endangered.

Claims: A vehicular steering condition detecting appartus comprising a single position sensor (6) for generating, in conjunction with an operation of a steering wheel (1) of a vehicle, an output signal which is proportional to the steering angle of the steering wheel (1), and a pulse generator (9) for generating pulses in conjunction with an operation of the steering wheel (1) for sensing the angular velocity of the steering wheel (1), an analog/digital converter (7) for converting the output signal of the position sensor (6) into a digital value, characterized by a microcomputer (8) for comparing between a change in the output of the position sensor (6) due to the operation of the steering wheel (1) by the driver and the number of pulses generated by the pulse generator (9) for every sampling period of a predetermined length, the microcomputer (8) being operable to determine that a failure in the position sensor (6) or the pulse generator (9) occurred, if there exists no proportional relationship therebetween. A vehicular steering condition detecting appartus according to claim 1, wherein said pulse genarator (9) generates a series of first pulses and a series of second pulses, said first and second pulses being out of phase from each other by 90 degrees, and the microcomputer (8) identifies, based thereon, the steering direction and absolute position of the steering wheel (1).

Inventors: KASHIHARA MASANOBU MITSUBISHI, KASHIHARA, MASANOBU; MITSUBISHI DENKI KABUSHIKI
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: G01B21
IPC codes: G01D5, B62D5, G01B21, B62D15