Rear wheel steering angle detection device for a vehicle

Abstract: The rear wheel steering angle detection device to which this invention relates is connected to a rear wheel steering apparatus, and provided with an absolute type rotary encoder (13) that detects the steering angle of a rear wheel and a control device that fractionizes the rear wheel steering angle by fractionizing the output of the absolute type rotary encoder (13) with the output of a pulse generator (12), and detects the rear wheel steering angle with high resolution by fractionizing the steering angle of the rear wheel detected by the absolute type rotary encoder (13) with the pulse of the pulse generator (12) for speed detection.

Description: TECHNICAL FIELD The present invention relates to a rear-wheel steering angle detecting apparatus for a vehicle capable of detecting the steering angle of the rear wheels of a vehicle with a high degree of resolution. PRIOR ART In a conventional rear-wheel steering angle detecting apparatus for a vehicle, a variable resistor is connected with a rear-wheel steering mechanism so that the output voltage of the variable resistor is input to an analog/digital converter (hereinafter referred to as an AD converter) where it is converted into a digital value which is then transmitted to a microcomputer. In the following, the operation of the above conventional apparatus will be described. In accordance with the operation of the rear-wheel steering mechanism, the resistance of the variable resistor changes, and the output voltage of the variable resistor, varying according to such changes, is input to the AD converter where it is converted into a digital value. The digital value thus converted is input to the microcomputer for detection of the rear-wheel steering angle. With the conventional rear-wheel steering angle detecting apparatus as constructed above, it is necessary to detect the rear-wheel steering angle with a high degree of resolution and at the correct positions of the rear wheels. In order to perform the detection of the rear-wheel steering angle with a high resolution, however, an AD converter having a multi-bit output is required. This poses a problem that such an AD converter with a multi-bit output is expensive. JP-A-60 171 417 discloses a circuit for detecting speed and frequency using a low-frequency false sine wave for speed detection while a high-frequency probe signal is generated for position detection from the false sine wave. This arrangement suffers from similar problems. The present invention is intended to obviate the above-described problem, and has for its object the provision of a rear-wheel steering angle detecting apparatus for a vehicle which is able to perform the detection of the rear-wheel steering angle with a high degree of resolution at low costs. DISCLOSURE OF THE INVENTION According to the present invention there is provided a rear-wheel steering angle detecting apparatus according to Claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the construction of a rear-wheel steering angle detecting apparatus for a vehicle in accordance with one embodiment of the present invention, and Fig. 2 is an explanatory view for showing the relationship between the rear-wheel steering angle and the rear-wheel angular signal for describing the operation of the above embodiment. PREFERRED EMBODIMENTS OF THE INVENTION In the following, a preferred embodiment in accordance with a rear-wheel steering angle detecting apparatus of the present invention will be described in detail with reference to the drawings. Fig. 1 is a block diagram of the construction of the embodiment. In Fig. 1, reference numeral 1 designates a steering wheel in accordance with the steering operation of which front wheels 6 of a vehicle are steered through the intermediary of a steering shaft 2 and a front-wheel steering mechanism 5. Connected with the steering wheel 2 is a steering angle sensor 3. The steering angle sensor 3 generates a steering angle signal 3S for the front wheels 6 to a controller 14. Similarly, connected with the steering wheel 2 is a steering speed sensor 4 which serves to generate a steering speed signal 4S for the front wheels 6 to the controller 14. The controller -14 is input with a vehicle speed signal 16S, the steering angle signal 3S and the steering speed signal 4S, calculates and determines, based thereon, target steering positions of the rear wheels 7 in relation to the steering of the front wheels 6, and generates a DC motor drive signal 11S to a DC motor 11 so as to control it. Operatively connected with the DC motor 11, which constitutes a rear-wheel steering drive mechanism, is a worm gear 10 which is in meshing engagement with a rear-wheel steering rack and pinion mechanism 8. The worm gear 10 and the rear-wheel steering rack and pinion mechanism 8 together constitute a rear-wheel steering mechanism. The rear-wheel steering rack and pinion mechanism 8 is connected with the rear wheels 7 through tie rods 9. Further, mounted to the DC rotor 11 is a pulse generator 12 which generates a pulse corresponding to the number of revolutions per minute of the DC motor 11. The pulse generator output signal 12S is input to the controller 14 so as to feed back thereto the number of revolutions per minute of the DC motor 11. In addition, connected with the worm gear 10 is an absolute type rotary encoder 13 which serves to detect the steering positions of the rear wheels 7 and generate an output signal 13S to the controller 14. Reference 15S designates an engine rotation signal which is input to the controller 14. The operation of the above embodiment will now be described. When the steering wheel 1 is turned for steering, the front wheels 6 is steered to accordingly turn through the intermediary of the steering wheel 2 and the front-wheel steering mechanism 5. At this time, the steering angle sensor 3 operatively connected with the steering wheel 2 detects the steering angle of the front wheels 6 and generates a steering signal 3S for the front wheels 6 to the controller 14. Simultaneous with this, the steering speed sensor 4 detects the steering speed of the front wheels 6 and generates a steering speed signal 4S for the front wheels 6 to the controller 14. The controller 14 receives the steering angle signal 3S, the steering speed signal 4S and the vehicle speed signal 16S, calculates and determines, based thereon, target steering positions for the rear wheels 7, and generates a DC motor drive signal 11S to the DC motor 11. With this, the DC motor 11 is controllably driven to operate so that the rear wheels 7 are steered to the target steering positions through the action of the worm gear 10, the rear-wheel steering rack and pinion mechanism 8 and the tie rods 9. In addition, the pulse generator 12 generates pulses in accordance with the number of revolutions per minute of the DC motor 11, so that the number of revolutions per minute of the DC motor 11 is fed back to the controller 14 from the pulse generator 12, thus steering the rear wheels 7 in a speed-controlled manner. Further, the absolute type rotary encoder 13 is operatively connected with the worm gear 10 so that it detects the positions of the rear wheels 7 through the operation of the worm gear 10 and generates an output signal 13S to the controller 14. As a result, the controller 14 controllably drives the DC motor 11 in such a manner as to make the detected steering positions of the rear wheels 7 approach to the target steering positions, thereby steering the rear wheels 7. Next, the process for detecting the steering of the rear wheels 7 will be described while referring to Fig. 2. In Fig. 2, the abscissa represents the steering angle of the rear wheels 7 and the ordinate the rear-wheel steering signal inside the controller 14. The absolute rotary encoder 13 is in the form of 5 bits, has a structure, mechanical strength and size suitable and sufficient for the mounting thereof on a vehicle, and is inexpensive to manufacture. The output signal 13S of the absolute rotary encoder 13, being in the form of a 5-bits signal, has a resolution capacity of dividing the total steering angle of the rear wheels 7 into 32 angle sections. In the illustrated example, the encoder 13 provides a resolution of 0.1 degrees. On the other hand, the output signal 12S of the pulse generator 12 is to be used for controlling the rotational speed of the DC motor 11, as described above, and it is a signal representing the steering amount of the rear wheels 7 in a very fine manner. Accordingly, by adding or subtracting the output signal of the pulse generator 12 to or from the point of change of the output signal 135 of the absolute rotary encoder 13 in accordance with the rotational direction of the DC motor 11, the steering positions of the rear wheels 7 can be detected with absolute values in a very fine manner. In this manner, the combination of the output signal 138 of the inexpensive absolute rotary encoder 13 and the output signal 12S of the pulse generator 12 can be employed as a high-resolution position detector. INDUSTRIAL APPLICABILITIES As described in the foregoing, according to the present invention, the rear-wheel steering angle as detected by the absolute rotary encoder is finely divided by a pulse which is generated by the pulse generator which is used for detecting the rotational speed of the DC motor. This construction provides the advantage that it is possible to detect the positions of the rear wheels with a high degree of resolution at low costs.

Claims: A rear-wheel steering angle detecting apparatus for a vehicle comprising: a rear-wheel steering mechanism (8,10); a rear-wheel steering drive mechanism (11) for driving the rear-wheel steering mechanism (8,10); an absolute rotary encoder (13) operatively connected with the rear-wheel steering mechanism (8,10) for detecting the steering angle of the rear wheels (7) of a vehicle; a pulse generator (12) for generating pulses in accordance with the number of revolutions per time unit of the rear-wheel steering drive mechanism (11); and a controller (14) for adding or subtracting the output signal (12s) of the pulse generator (12) to or from the point of change of an output signal (13s) of the absolute rotary encoder (13) in accordance with the rotational direction of the rear-wheel steering drive mechanism (11) so as to detect the rear-wheel steering angle with a high degree of resolution.

Inventors: KASHIHARA MASANOBU C O MITSUBI, ONISHI MASAYOSHI C O MITSUBISH, OZAWA HIROMASA C O MITSUBISHI, KASHIHARA, MASANOBU, C/O MITSUBISHI DENKI K.K., ONISHI, MASAYOSHI, C/O MITSUBISHI DENKI K.K., OZAWA, HIROMASA, C/O MITSUBISHI DENKI K.K
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: G01B21
IPC codes: B62D7, G01B21, G01D5