Rear-wheel steering angle detecting apparatus for a vehicle

A rear-wheel steering angle detecting apparatus according to the present invention includes an absolute value type rotary encoder (13) operatively connected with a rear-wheel steering mechanism for detecting the steering angle of the rear wheels of a vehicle, and a controller for finely dividing the output of the rotary encoder by the output of a pulse generator (12) for fine division of the rear-wheel steering angle. By finely dividing the rear-wheel steering angle, as detected by the rotary encoder, by the number of pulses generated by the pulse generator, which is used for speed detection, the rear-wheel steering angle is detected with a high degree of resolution.

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 coventional 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. 
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 aable to perform the detection 
of the rear-wheel steering angle with a high degree of resolution at low 
costs. 
DISCLOSURE OF THE INVENTION 
The rear-wheel steering angle detecting apparatus for a vehicle according 
to the present invention includes an absolute value type rotary encoder 
operatively connected with a rear-wheel steering mechanism for detecting 
the steering angle of the rear wheels of a vehicle, a pulse generator for 
detecting the speed of a rear-wheel steering drive mechanism, and a 
controller for finely dividing the output of the absolute type rotary 
encoder by the output of the pulse generator for fine division of the 
rear-wheel steering angle. 
The controller of the invention detects the rear-wheel steering angle with 
a high degree of resolution by dividing the rear-wheel steering angle, as 
detected by the rotary encoder, by the number of pulses generated by the 
pulse generator.

THE BEST MODE FOR IMPLEMENTING THE INVENTION 
In the following, a preferred embodiment in accordance with a rear-wheel 
steering angle detecting apparatus of the present inveniton 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 vehicle speed signal 16S, the steeing 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 B. 
The worm gear 10 and the rear-wheel steering rack and pinion mechanism B 
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 motor 11 is a pulse generator 12 which generates 
pulses 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 a digital or 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 are 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 accordnace 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 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 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 rotary encoder 13 is a 5 bit device, and 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 rotary encoder 13, being in the form of a 
5-bit 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 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 13S of 
the 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 13S of the inexpensive 
absolute value rotary encoder 13 and the output signal 12S of the pulse 
generator 12 can be employed a 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 value rotary encoder 
is finely divided by a pules 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 
.