JPS61153518A - Detecting circuit for quantity of steering - Google Patents

Abstract

PURPOSE:To calculate the actual quantity of steering with a simple structure by adding a rotational angle signal corresponding to the rotational position of a steering wheel to an offset signal generated on the basis of the variation state of the rotational angle signal. CONSTITUTION:Offset quantity generating circuits 12a and 13a and gate circuits 12b and 13b constitute offset output circuits 12 and 13. The circuits 12a and 13a send out signals indicating a -256 and a +256 offset. An accumulating circuit 14a, an absolute value circuit 14c, and a steering angle arithmetic circuit 14 constitute a steering angle arithmetic circuit 14. The circuit 14a accumulates an offset signal sent out of the offset output circuit 12 or 13 every time a high edge detecting circuit 10 or low edge detecting circuit 11 generates a signal. Thus, the quantity of an offset at the time of steering is added to the quantity of steering within a range of a clockwise or counterclockwise half turn of the steering wheel to calculate the actual quantity of steering.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a steering amount detection circuit that detects the amount of steering when a steering wheel is used for steering.

[Conventional technology]

Generally, the steering force of an automobile tends to increase as the vehicle speed decreases. Therefore, with power steering that provides auxiliary power according to the steering force, there is a problem that if it is set to provide a light steering force at low speeds, it will be too light at high speeds.
In order to solve this problem, various methods have been proposed in which the ratio of the output to the input of the auxiliary power increases as the vehicle speed increases.

By using such a power steering device, it is possible to perform steering that is sufficiently light at low speeds and not too light even at high speeds.

Furthermore, in recent years, power steering devices have been proposed that take into account the amount of steering in addition to the vehicle speed, and the larger the amount of steering, the greater the steering force. In this case, the steering amount is determined from the rotation of the steering wheel.

[Problem that the invention seeks to solve]

However, since the steering wheel rotates more than 360 degrees in either the right or left direction, it is not enough to simply detect the rotation angle of the steering wheel; it is also necessary to detect the state in which it is in order to determine the amount of steering. For this reason, in the past, a complicated mechanism had to be used, resulting in poor economic efficiency and reliability.

[Means for solving problems]

This invention aims to solve these drawbacks.

When the rotation angle of the steering wheel increases, the rotation angle signal that is output according to the rotation position is generated repeatedly between the minimum value and the maximum value. The originally generated offset signal is added.

[Effect]

The offset amount at the time of steering is added to the amount of steering within the range in which the steering wheel has turned half a turn in the right or left direction to determine the amount of actual steering.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a schematic diagram of a power steering device using the device shown in FIG. In FIG. 2, C0NT is the control device shown in FIG. 1, cv is a controller, 1& is a vehicle speed sensor, and 2m is a steering sensor that generates a steering angle signal. Among these, the control device C0NT determines the characteristics of the control pulp CVIfC shown in FIG. 3 based on the steering angle determined based on the signal generated from the steering sensor 2a and the signal corresponding to the vehicle speed V generated from the vehicle speed sensor 1m. It is designed to supply a current l. The control valve CV controls the magnitude of the steering force in accordance with the supplied current, and is configured such that the greater the current value, the greater the steering force. Therefore, in this device, when the vehicle speed is low, the steering force is small and the amount of change in current with respect to a change in steering angle is also small, so the amount of change in steering force with respect to a change in steering angle is small. but.

The structure is such that the amount of change in steering force with respect to change in steering angle increases as the speed increases.

Therefore, a larger steering force is required at high speeds than at low speeds, and this steering force has a characteristic that it suddenly increases as the steering angle increases. This prevents excessive steering at high speeds, makes it possible to clearly recognize straight-ahead driving conditions, and provides a comfortable steering feel.

Next, a process in which the characteristics shown in FIG. 3 are controlled by the apparatus shown in FIG. 1 will be explained. In FIG. 1, 1 is a vehicle speed pulse generation circuit, which is composed of a reed switch 1a that is repeatedly turned on and off by a magnet (not shown) that is rotationally driven by a transmission output shaft, a resistor 1b, and a waveform shaping circuit 1C. is adapted to send out a short vehicle speed pulse at the timing when the reed switch 1a is turned off. Reference numeral 2 designates a rotation angle signal generation circuit, which includes a potentiometer 2a which is a steering sensor, a converter for converting the value from the lowest pupil to the highest pupil of the analog signal output from the potentiometer 2& into a digital signal expressed by O to 255. It consists of As shown in Figure 4, the potentiometer used here consists of a main body consisting of a slip ring SL and a resistor R attached to the steering column, and a slider C that rotates together with the steering shaft. . Since the slider C rotates while contacting the slip ring SL and the resistor R, the resistance value of this potentiometer is! As shown in FIG. 5, when the steering wheel is rotated half a turn in the positive or negative direction from the straight-ahead state, the steering wheel takes a value between the minimum value and the maximum value corresponding to the rotation angle. The same resistance value change is repeated each time the steering wheel rotates once.

Reference numeral 3 designates an instantaneous vehicle speed signal generation circuit, which is composed of a counter 3a and a register 3b.
In addition to counting the clock signal CLI supplied every s, when a vehicle speed pulse is generated from the vehicle speed pulse generating circuit 1, the counting result of the counting register 3a is taken into the register 3b, and then the counting result is reset. It looks like this. Therefore, the instantaneous vehicle speed signal generating circuit 3 sends out a larger output signal as the vehicle speed is lower, and the data is updated every time a vehicle speed pulse is generated.

4 is an average vehicle speed signal generation circuit, which is a mono multivibrator 4! L, an AND circuit 4b, a counter 4c, and a register 4d. The mono multi-vibrator 4a is used to prevent vehicle deceleration or stopping due to red lights, etc. from affecting the calculation of average vehicle speed, and does not count vehicle speed pulses of 5 km/h or less with the kawanta 4c. That's what I do. For example, when four vehicle speed pulses are generated per one rotation of the axle, the operating period of the mono-multivibrator 4a is selected to be approximately 282 m5, and the vehicle speed generated by the vehicle speed pulses supplied within this period, that is, the vehicle speed of 5 km/h or more. The pulses are supplied to the counter 4c, but because the period of the pulses generated by a vehicle speed lower than 5 km/IH is longer than 282 m5, the pulses are not supplied to the counter 4c. The counter 4C counts vehicle speed pulses, is supplied with a clock signal generated every 30 seconds, and is reset after the count result is taken into the register 4d.

Reference numeral 5 designates an average steering amount generation circuit, which includes a delay circuit 5m that delays the input signal by 10 mg and outputs it, a subtraction circuit 5b that subtracts the input signal and the output of the delay circuit every 10 mII, an absolute value conversion circuit 5c, a counter 5d, and a register. The counter 5d and the register 5e are configured to generate an average steering amount signal for 30 seconds in the same manner as the average vehicle speed signal generating circuit 4 in response to a clock signal CL4 supplied every 30 seconds.

Reference numeral 6 denotes a pattern memory, in which data representing three types of driving conditions, Mode A to Mode B, are written, as shown in FIG. 6, and this data is read out using the average steering amount signal and the average vehicle speed signal. It's starting to look like this. Mode A in FIG. 6 represents a state where the average vehicle speed is low and the average steering amount is large, such as when driving in a city area, and mode B represents driving in a suburban area.

Mode C represents highway driving.

7at7b and 7c are pattern memories, as shown in FIG.
).

As shown in (b) + (0)K, the vehicle speed-sensitive instruction value (signal that determines the amount of power steering at the time of starting steering) for the instantaneous vehicle speed is written.
) is suitable for driving in suburban areas, and (C) is suitable for driving on expressways.

8 is a selection circuit, which includes a decoder 8m and a selection switch 8b.
, AND circuits 8c to 8e, OR circuits 8f to 8h, gate circuits 81 to 8, and light emitting diodes 8J to 8n. Here, the decoder 8a decodes whether the data read from the pattern memory 6 is in mode A-C, and the selection switch 8b switches modes A-C manually or depending on the vehicle speed and steering amount. There is a switch to select whether to automatically switch between modes A and C.

9 is a steering angle control judgment circuit; game) 9a, decoder 9;
b, 9c, OR circuit 9d, 9a, 9f, NAND circuit 9
It consists of a gT 9h, a 15 second timer 9M, and an 8 second timer 9j. The decoder 9b sends out the signals shown in Table 1 in response to the instantaneous vehicle speed signal, and the decoder 9C sends out the signals shown in Table 2 in response to the rotation angle signal output from the rotation angle signal generation circuit 2. It has become.

Table 1, Table 2, and Table 10 show high edge detection circuits, and reference signal generation circuit 1.
0a, 10b, a delay circuit 10a that delays the input signal by 1 ms and sends it out, a comparator IQd, 10e, and an AND circuit 10f. Reference numeral 11 is a low edge detection circuit. It consists of a delay circuit 11c which delays the signal by 1 ms and sends it out, comparators 11d and 11e, and an AND circuit 11f.

12.13 is an offset output circuit, which includes offset amount generation circuits 12a, 13m, gate circuit 12b, and
The offset amount generating circuit 12& sends out a signal representing an offset amount of -256, and the offset amount generating circuit 13a sends out a signal representing an offset amount of +256.

Reference numeral 14 denotes a steering angle calculation circuit, which is composed of an accumulation circuit 14a, an addition circuit 14b, and an absolute value conversion circuit 14c. The offset signals sent from the offset output circuit 12 or the offset output circuit 13 are accumulated.

Reference numeral 15 denotes a pattern memory in which, as shown in FIG. 8, a correction value for correcting the vehicle speed sensitive instruction value read out from the pattern memories 78 to 7C is written, and this correction value is based on the instantaneous vehicle speed and steering. It is determined by the angle, and is written with the steering angle as a variable and the instantaneous vehicle speed as a parameter. In addition,
9 is the correction characteristic at the highest speed, e is the correction characteristic at the lowest speed, b
-d is the characteristic at intermediate vehicle speed.

Reference numeral 16 denotes a drive circuit including adder circuits 16a, 16e, register 16b, timer 16d, and transistor 16e.

It is composed of a k-level converter 16f, a comparator 16g, an edge down counter 16t, and a reference current memory 16h. The timer 16d generates a signal that is turned on for a time corresponding to the output of the adder circuit 16c at cycle 2 of the clock signal CL3.
This occurs every 0 m5, and when the output of the adder circuit 16e is zero, the transistor 16e does not turn on.

17 is a clock signal generation circuit, 1 millisecond (ms)
, 10m5, 20m5. It is designed to send out four types of clock signals that repeat at a cycle of 30 seconds.

Before explaining the systematic operation of the device configured in this way, the operation of the main circuits and the applications of the circuits will be explained.

(IL) Steering Angle Control Determination Circuit 9 When the power is turned on, the one rotation angle signal generation circuit 9 generates a rotation angle signal corresponding to the rotation angle of the steering wheel. However, as shown in Figure 5, this value is the same every time the steering wheel rotates, and at this time, it is difficult to determine whether the tires are turning to the right or to the left. I don't know. Correct steering angle control cannot be performed in this state.

Therefore, the steering angle control judgment circuit 9 assumes two cases that are unlikely to occur at the beginning of driving, and when the situation is not in such a state,
When the right direction is a positive angle and the left direction is a negative angle, it is determined that the steering wheel satisfies the initial condition within ±180 degrees.

The first example of a situation that cannot normally occur is when driving at r 50 km/h or higher, the steering wheel moves to the right or left (several turns +150) (steering amount is ±21
0) or more, and the condition continues for more than 8 seconds without causing vomiting." When the vehicle is traveling at a speed of 50 km/h or more, the decoder 9b sends out a "1" level output signal from the terminal a.

At this time, if the steering wheel turns 15 degrees to the right or left,
If it is generated more than 0 times, the terminal a of the decoder 9c
, b, and e all send out output signals of "0" level as shown in Table 2. For this reason, the NAND circuit 9h sends out an output signal at the "1" level, so the 8-second timer 9j is reset and its output signal remains at the "0" level. As long as this state continues, the 8-second timer 9j is The output signal continues to be at rOJ level.

However, since it is unlikely that the vehicle will continue to drive with this condition continuing from the beginning of driving, the steering wheel should eventually reach a state where the steering wheel is operated within 150 degrees to the right or left. be. At this time, terminals a and b of the decoder 9c.

According to the second rule, a level "1" should be sent out from one of the circuits C and 1, and in that case, both inputs to the AND circuit 9h will be at the level 11. As a result, the 8-second timer 9j is released from reset, and if this state continues for 8 seconds or more, it sends out a "1" level output signal. 8 second timer 9
j If such a "1" level signal is sent out even once, its state is stored in the OR circuit 9f. In other words, the recognition of the initial conditions is stored. The output signal of the OR circuit 9f is supplied to the gate circuit 9a, which is turned on, so that the one rotation angle signal is supplied to the next stage, and the steering angle is controlled by that signal. The circuit that receives the rotation angle signal may perform steering angle control assuming that the current steering angle is within ±150 degrees.

The second example of a condition that does not normally occur is [20Km/I(
When driving at a speed greater than or equal to
390) and the state will not continue for more than 15 seconds."

If the vehicle speed is 20 Km/H or more, the OR circuit 9d is
If the operating angle of the steering wheel is less than 130 degrees, the decoder 9C sends out a "1" level output signal from the terminal, so the NAND circuit 9g outputs a "0" level output signal. Send a signal. and,
If this state continues for 15 seconds or more, the 15 second timer 91 will
A 1'' level output signal is generated, which is stored in the NOR circuit 9f, and the fact that the initial condition has been recognized is also stored.

In this way, when either the first or twelfth initial condition is recognized, the steering wheel should be within ±180 degrees, assuming 0 degrees when the vehicle is traveling straight. Therefore, the rotation angle signal sent from the rotation angle signal generation circuit 2 may be handled in this manner.

(b) Low edge detection circuit 11. Offset output circuit 13, steering amount calculation circuit 14 When the initial condition g is recognized, the one rotation angle signal is handled as if the steering wheel is within ±180 degrees, but
At this time, one rotation angle signal generating circuit from two companies sends out the rotation angle of the steering wheel in the form of a digital signal having a number of 0 to 255. In other words, as shown in Figure 9, +180 degrees sends out a digital signal representing the number 255, and when the steering wheel is turned slightly further to the right, a digital signal representing the number O is sent out. I come to do it. At this time, the signal output from the rotation angle signal generation circuit 2 represents O, which is a state in which the number has increased by one from 255, that is, 25.
It may also be expressed as 6. To do this, once the amount reaches a high value and then becomes O, the rotation angle signal generation circuit 2
It is sufficient to add the offset signal 256 to the output signal of . If you perform this operation, the rotation angle signal generated when you rotate the steering wheel to the right and cross +180 degrees will be 0.

O of the rotation angle signal generated when crossing 1180 degrees in the left direction can be identified as being different even though the rotation angle signal itself is the same. Do the same.

Furthermore, when the steering wheel is rotated to the right and the rotation angle signal becomes 0 again, the number that was previously handled is 25 again.
Just add 6. That is, from the initial state, 512
This means that we have added

Therefore, as shown by arrow A in FIG. 10, the edge where the value of the rotation angle signal reaches the maximum value and then becomes the lowest value is defined as a low edge, and the low edge detection circuit 11 detects this state. That is, the rotation angle signal is delayed by 1 ms, which is the repetition period of the clock signal CLI, by the delay circuit 11C, and the comparator 11d determines whether or not this signal power matches 255. Right steering is performed, +1
If the angle crosses 80 degrees, the input terminal signal of the comparator 11d becomes the same value, and the comparator 11d generates an output signal of the rlJ level. On the other hand, since the rotation angle signal has crossed +180 degrees, the rotation angle signal becomes O, and the comparator 11e sends out a signal at the "1" level. As a result, the AND circuit 11f sends out a "1" level signal as a low edge detection signal.

Goo due to the generation of low edge detection signal)
13b is on) and offset signal generation circuit 13m
The offset signal 255 generated in the accumulator circuit 14a
Since the offset signal is supplied to the accumulator 14m, the offset signal is taken in and stored in the accumulator circuit 14m. The signal of the accumulator circuit 14a is added to the rotation angle signal supplied from the gate circuit 9a, and becomes a steering angle signal representing the steering angle at that time. When the steering wheel is further rotated, the a-edge signal is generated again, the offset signal 256 is accumulated again, and the value obtained by adding 512 to the rotation angle signal becomes the steering angle signal.

(,) High edge detection circuit 10, offset output circuit 12 When the steering wheel is operated to the right and has crossed +180 degrees, when the steering wheel is operated to the left this time, a one rotation angle signal is generated as shown by arrow B in Fig. 10. gradually decreases and reaches 0, and then becomes 255. Therefore, an edge where the value of the rotation angle signal reaches the maximum value after reaching the minimum value is defined as a high edge, and the high edge detection circuit 10 detects this state. In other words, the state 1ms ago was O, and the current state is 2.
55, the AND circuit 10f is sending out a high edge signal of "1" level. Then, when a high edge signal is generated, the offset signal output circuit 12 sends out an offset signal of Ruru minus 256. This is good.

The accumulator circuit 14m subtracts 256 from the value stored so far.

In this way, the high edge detection circuit 10, the low edge detection circuit 11. The offset output circuits 12 and 13 and the steering angle calculation circuit 14 calculate the current steering angle by adding an offset signal ±256 to the rotation angle signal that changes between θ and 255.

(d) Instantaneous vehicle speed signal generation circuit 3, average vehicle speed signal generation circuit 4, average steering amount generation circuit 5 These circuits calculate the nine vehicle speed pulse periods for each pulse and calculate the instantaneous vehicle speed, and the total number of vehicle speed pulses determined every 30 seconds. Alternatively, the total steering view is set as the average vehicle speed or the average steering amount.

(e) Pattern memory 6, pattern memo IJ7. ~7c
, selection circuit 8 The steering force of an automobile is large at low speeds and small at high speeds. For this reason, power steering generally increases the output of auxiliary power at low speeds and decreases the output of auxiliary power at high speeds so that a substantially constant steering force can be obtained regardless of the vehicle speed.

However, when steering is required frequently even at low speeds, such as in urban areas, it is better to use less steering force to reduce driver fatigue, but when driving on a highway, even at the same low speed, it is better to use less steering force. Since there are very few opportunities to do this, it is uneconomical to use a small steering force even at such times. In this way, even if the vehicle speed is the same, it is more economical to determine the power steering characteristics depending on the driving conditions. There are countless possible driving conditions depending on the combination of vehicle speed and steering amount, but
As shown in Fig. 7, if three types of characteristics are prepared and one of these three types of characteristics is selected according to the values taken by the average vehicle speed and average steering amount, there will be no practical problem with the actual vehicle. Confirmed by driving. Based on this idea, the pattern memory 6 is written with data indicating which of the three types of characteristics the combination of the average steering amount and the average vehicle speed is in, and the pattern memories 71 to 7C are as shown in FIG. (a)～(
The selection circuit 8 is a circuit that decodes the data read from the pattern memory 6 with a decoder 8a and selects any one of the pattern memories 7a to 7C. However, if the input signal to the OR circuits 8f to 8h is selected from among the selection switches 8b by the driver's will, priority is given to this selection.

(f) Pattern Memory 15 The data written in the pattern memories 7a to IC is the steering force required when steering is started in a straight-ahead state. As described above, this steering force needs to be corrected as shown in FIG. 8 based on the instantaneous vehicle speed and steering angle. Correction data for this purpose is written in the pattern memory 5.

(g) By adding the data read from any of the drive circuit pattern memories 71 to 7c and the correction value read from the pattern memory 15, and driving the control pulp CV using this value, the desired steering force can be obtained. However, the current flowing through the control valve coil is not necessarily a stable constant value. For this reason.

Reference current memory 16 for the current flowing through the control valve
By comparing the current of the solenoid pulp with the reference value read from h and correcting it with the amplifier down counter 161, the current flowing through the control valve Cv can be made to a more stable value depending on the excess or deficiency.

The above is the operation of the main circuits and the purpose of use of the circuits. Next, the payment operation of this device will be explained. First, when the power is turned on, the steering angle control determination circuit 9 determines whether or not to perform steering angle control, and when one of the two initial conditions described above is recognized, a 1 rotation angle signal is generated. The rotation angle signal generated by the circuit 2 is supplied to the steering angle calculation circuit 14.

Then, an offset signal is added depending on the amount of rotation of the steering wheel. This offset signal is 256 in O1 range B in range A in FIG. 9, 512 in range C,
In range S, -256 is selected, and in range C, -512 is selected.

Once the steering angle is determined, the average steering amount is determined based on this, the average vehicle speed is determined based on the vehicle speed signal, and a signal representing the driving state is read out from the pattern memory 6 based on these signals. be done. and.

The pattern memory 17 is selected by the selection circuit 8 according to the read signal.
A vehicle speed sensitive instruction value is read from any one pattern memory among 7a to IC.

On the other hand, a correction signal for correcting the vehicle speed sensitive instruction value is read out from the pattern memory 15 based on a signal obtained by converting the steering angle into an absolute value and an instantaneous vehicle speed signal, and this correction signal and the vehicle speed sensitive instruction value are added in the drive circuit 16. , the control valve Cv is controlled according to the addition result. As a result,
The characteristic indicated by symbol a in FIG. 11 is obtained. Note that the characteristics already indicated by the symbols apply only to vehicle speed sensitive control.

By performing such control, as shown in Fig. 3, the current supplied to the control pulp Cv when the steering angle is zero, that is, at the start of steering, is determined in accordance with the vehicle speed, and the current supplied to the control pulp Cv when the steering starts is determined next. This value is corrected to the optimum value according to the steering angle. As a result, as shown in FIG. 3, at low speeds, the vehicle can be steered with a small steering force over a wide range of steering amounts, and the range that can be steered with this small steering force becomes narrower as the vehicle speed increases. This prevents the steering wheel from turning sharply even if you have to turn the steering wheel suddenly at high speed.
Furthermore, even when returning the steering wheel from this state, the straight ahead position can be clearly recognized, which prevents the steering wheel from being returned too far.

FIG. 11 is a flowchart showing the procedure for controlling this device by a microcomputer. In the figure, each step and the block of FIG. 1 correspond as shown in Table 3.

Table 3 [Effects of the Invention] As explained above, the present invention adds the rotation angle signal corresponding to the rotation position of the steering wheel and the offset signal generated based on the change state of the rotation angle signal. Because of this, the actual steering amount can be determined using a steering sensor with a simple structure, and there is no need to use a complicated mechanism as in the past, which has the effect of improving economy and reliability. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a schematic diagram showing an embodiment of a power rudder augmentation device using the device of the present invention, and FIG. 3 is a steering angle diagram of the device of the present invention. Graph showing the output current characteristics, Figure 4 is an exploded perspective view showing the state when the potentiometer is installed on the steering wheel, Figure 5 is a graph showing the resistance value change characteristics of the potentiometer, and Figure 6 is written in the pattern memory 6. Figure 7 is a graph showing the characteristics of the vehicle speed sensitive instruction value, and Figure 8 is a graph showing the correction value characteristics of the vehicle speed sensitive instruction value determined in response to the steering angle and instantaneous vehicle speed. , FIG. 9 is a graph showing changes in offset amount, FIG. 10 is a graph for explaining high edge and low edge,
FIG. 11 is a graph showing the change characteristics of the steering angle and steering force, and FIG. 12 is a flowchart showing the procedure when implementing the present invention on a microcomputer. 1...Vehicle speed pulse generation circuit, 2...Rotation angle signal generation circuit, 3...Instantaneous vehicle speed signal generation circuit, 4...
- Average vehicle speed signal generation circuit, 5... Average steering amount generation circuit, 6, 7a, 7b, γC215... Pattern memory, 8... Selection circuit, 9... Rudder angle control determination circuit , 10... High edge detection circuit, 11... Low edge detection circuit. 12.13...Offset output circuit, 14...
Steering angle calculation circuit, 16... Drive circuit, 17...
Cronk signal generation circuit. Patent Applicant: Automotive Equipment Co., Ltd. Agent Masaki Yamakawa (2 people for fυ) Figure 2 C0NT Figure 5 Rudder Angle Figure 6 (0) (b) (
c) Shun Kano Hat Shun 11
Todatsu Figure 8

Claims (1)

[Claims] In a steering amount detection circuit using a steering sensor in which a rotation angle signal output according to the rotational position of the steering wheel repeatedly changes between a minimum value and a maximum value in response to monotonous changes in the rotation angle of the steering wheel, means for outputting a first offset signal when the rotation angle signal crosses a maximum value from an increasing direction; means for generating a second offset signal when the rotation angle signal crosses a minimum value from a decreasing direction; A steering amount that makes it possible to grasp the entire steering range by providing means for accumulating offset signals every time the first and second offset signals are generated and adding the accumulated value and the rotation angle signal. detection circuit.