JPH0240517A - Torque sensor - Google Patents

Abstract

PURPOSE:To detect torque caused by steering high accurately by a constitution wherein the torque is detected from the peak value of an AC voltage outputted from a peak detecting circuit. CONSTITUTION:In a torque sensor part TS, the following parts are provided: an oscillating circuit 13; a temperature compensating circuit 15 wherein a temperature compensating coil L1 and a capacitor C1 are connected in parallel; a torque detecting circuit 16 wherein a torque detecting coil L2 and capacitor C2 are connected in parallel; clamping circuits 17 and 22; peak detecting circuits 18 and 23; a differential amplifier 21; a reference voltage circuit 19; a comparing circuit 20; an offset voltage output part 14; a power source stabilizing part 12; voltage-current converter circuits 24 and 25; and a connector CN1. An AC voltage which is induced by magnetic coupling corresponding to torque caused by steering force is imparted to the circuits 17 and 22. The circuits 17 and 22 impart bias voltages which make the given AC voltages at a zero level to be the value at the negative maximum level so as to cause clamping. The peak detecting circuits 18 and 23 detect the peak values of the AC voltages which are imparted from the circuits 17 and 22.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a torque sensor, and in particular provides a torque sensor suitable for an electric power steering device of an automobile.

[Conventional technology]

2. Description of the Related Art Electric power steering devices are being developed that assist the power to operate the steering wheels of automobiles. This has a structure in which the torque acting on the steering wheels is detected, and an electric motor provided in the steering mechanism is rotated in accordance with the detected torque.

By the way, a torque sensor that detects torque acting on a steered wheel has a structure shown in FIG. 2, for example. Two cylinders 2^ and 2B made of magnetic material and facing each other with inclined edges separated by an appropriate length are separately fitted onto two shafts (not shown) connected via a torsion bar 1. are doing. These cylinders 2A and 2B are torsion bars 1
When twisted in one direction, the opposing gap between the inclined edges expands, and when twisted in the other direction, the opposing gap narrows. And on the sides of cylinders 2A and 2B,
Cylinder 2A.

A ring-shaped sensor core 3 having an inner flange with dimensions that can span 2B is disposed, and a torque detection coil 4 with a required number of turns is wound around the inner circumference of the sensor core 3. A series circuit including a resistor 5, an oscillator 6, and a power source 7 consisting of a battery is connected to the torque detection coil 4.
The negative electrode of the power source 7 is grounded. Further, both ends of the resistor 5 are connected to AC input terminals 8a and 8b of the rectifying bridge 8. A positive DC output terminal 8c of the rectifier bridge 8 is connected to an input side 9a of an amplifier 9. The output side 9b and the negative side DC output terminal 8d of the amplifier 9 are respectively connected to a control section (not shown).

In this torque sensor, when the oscillation output of the oscillator 6 is applied to the torque detection coil 4, an alternating current voltage corresponding to the magnetic coupling between the cylinders 2A and 2B is induced in the torque detection coil 4.
The divided voltage is generated across the resistor 5. The voltage generated across the resistor 5 is full-wave rectified by a rectifier bridge 8, and the rectified DC voltage is amplified by an amplifier 9. Then, the torque acting on the torsion bar 1 is detected from the output of the amplifier 9.

[Problem to be solved by the invention]

When using the conventional torque sensor described above in an electric power steering system for a car, the negative terminal of the oscillator 6 is connected to the body ground because the car's power source is a battery (single power supply) whose negative terminal is grounded to the body of the car. However, if this is done, waveform distortion will occur near the zero-crossing of the oscillation output waveform of the oscillator 6, and the waveform of the AC voltage induced in the torque detection coil will become distorted, resulting in an increase in the detection error of the detected torque. .From such a point of view,
A DC voltage is obtained by full-wave rectification of an AC voltage, but since the negative terminals of the oscillator 6 and the rectifier bridge 8 are not common, the midpoint A of the oscillation output waveform and the induced AC voltage as shown in Figure 3. are different from the midpoint B. Therefore, as shown in FIG. 4, the voltage level L of the DC voltage obtained by full-wave rectification pulsates, and there is a problem that the detected torque cannot be detected with high accuracy even if the induced voltage is full-wave rectified.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome these problems and to provide a highly reliable torque sensor that can accurately detect the torque applied during steering even when used in an electric power steering system for an automobile.

[Means to solve the problem]

The torque sensor according to the present invention obtains a magnetic coupling state related to torque applied by a steering force and detects torque by an alternating current voltage induced in relation to the magnetic coupling. A clamp circuit that provides a bias, and a peak detection circuit that receives an AC voltage from the clamp circuit and detects its peak, and detects the torque based on the peak value of the AC voltage output by the peak detection circuit. It is characterized by

C action] An AC voltage induced by magnetic coupling corresponding to the torque applied by the steering force is applied to the clamp circuit. The clamp circuit applies a bias that makes the 0 level of the applied AC voltage to the negative maximum level and clamps it. The peak detection circuit detects the peak value of the AC voltage applied from the clamp circuit.

The detected torque is obtained from the peak value of the AC voltage detected by the peak detection circuit.

Thereby, the detected torque can be obtained with high accuracy.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof.

FIG. 1 is a block diagram of a torque sensor according to the present invention. The output voltage of the power supply stabilizing section 12 is applied to an oscillation circuit 13 of the torque sensor section TS, and also to an offset voltage output section 14 consisting of a resistive voltage divider circuit. The torque sensor section TS includes an oscillation circuit 13 and a temperature compensation coil L1.
and a temperature compensation circuit 15 in which a capacitor CI is connected in parallel, a torque detection circuit 16 in which a torque detection coil L2 and a capacitor C2 are connected in parallel, clamp circuits i17 and 22, a peak detection circuit 18.23, and a differential amplifier circuit 21. and,
It includes a reference voltage circuit 19, a comparison circuit 20, an offset voltage output section 14, a power supply stabilization section 12, voltage-current conversion circuits 24 and 25, and a connector CNI.

The controller CTR of the electric power steering device is
It includes a connector CN2, current-voltage converters 26 and 27, a microcomputer 28, and a power supply stabilizing section 29.

The temperature compensation coil changes its magnetic coupling state in relation to the ambient temperature and its inductance changes, and the torque detection coils I and t change in relation to the torque applied to a column shaft (not shown) due to steering force and the ambient temperature. The state of magnetic coupling changes, and the inductance changes. The oscillation output of the oscillation circuit 13 is applied to one side of the temperature compensation circuit 15 and the torque detection circuit 16 through respective resistors R, , Ih. The other sides are each grounded.

The AC voltage, which is the resonance voltage of the temperature compensation circuit 15, is applied to the clamp circuit 17, and the clamp circuit 17 has a bias that changes the level of the applied AC voltage waveform to the positive voltage side so that the maximum value on the negative side of the applied AC voltage waveform becomes OV. It is designed to be clamped by giving

The AC voltage output from the clamp circuit 17 is applied to a peak detection circuit 18, and the peak detection circuit 18 detects the peak value of the applied AC voltage. Peak detection circuit 18
The output voltage is applied to a comparison circuit 20 and a differential amplifier circuit 21, which provide a reference voltage output from the reference voltage circuit 19. The comparison circuit 20 is configured to output a voltage when the output voltage of the peak detection circuit 18 becomes less than or equal to a reference voltage.

Further, the resonance voltage of the torque detection circuit 16 is applied to a clamp circuit 22, and the output voltage of the clamp circuit 22 is applied to a peak detection circuit 23. The clamp circuit 22 and peak detection circuit 23 operate in the same manner as the clamp circuit 17 and peak detection circuit 18.

The output voltage of the peak detection circuit 23 is given to the differential amplifier circuit 21. The offset voltage of the offset voltage output section 14 is obtained by dividing the output voltage of the power supply stabilizing section 12, and is set to be output as a required value when the torque sensor section TS does not detect torque. . The offset voltage is applied to the differential amplifier circuit 21 and the voltage-current conversion circuit 25. Further, the output voltage of the differential amplifier circuit 21 is applied to a voltage-current conversion circuit 24. The differential amplifier circuit 21 determines the difference between the output voltages of the peak detection circuits 18 and 23, and outputs an output voltage obtained by adding an offset voltage to the determined difference voltage, that is, a voltage corresponding to the detected torque.

The output voltage of the differential amplifier circuit 24 is converted into a current by the voltage-current conversion circuit 24 and inputted to the current-voltage conversion section 26 of the controller CTR via the connectors CNI and CN2, and the output thereof is inputted to the microcomputer 28. Ru.

Further, an off-cent voltage is input, and the off-cent voltage is converted into a current by the voltage-current conversion circuit 24 to connect the connector CN.
It is input to the current-voltage converter 27 of the controller CTR via I and CN2, and its output is input to the microcomputer 28. The output voltage of the comparator circuit 20 is sent to the controller CT via connectors CNI and CN2.
It is input to the microcomputer 28 of H. The voltage of an external power supply 30 is supplied to the power supply stabilizing section 29 of the controller CTH via a key switch or connector CN2, and the output voltage of this power supply stabilizing section 29 is applied to the circuit inside the controller CTR. and connector CN2.
Power supply stabilization unit 1 of torque sensor unit TS via CNI
2 and an electronic circuit (not shown) in the torque sensor section TS.

Note that the grounding parts E and E of the controller CTR and the torque sensor part TS are connected to the connector CN1. They are commonly connected via CN2. Also, the external ground point E0 is connected to the connector CN.
It is connected to the grounding part E of the controller CTR via 2.

Next, the torque detection operation of the torque sensor configured as described above will be explained with reference to FIG.

When the key switch S is closed and the power supply 30 is turned on, the output voltage of the power supply stabilization section 29 is given to the power supply stabilization section 12, and the output voltage of the power supply stabilization section 12 is applied to the oscillation circuit 13 and the offset voltage output section 14. are given to each.

As a result, the oscillation circuit 13 operates in oscillation, and the offset voltage output section 14 outputs an offset voltage.

The oscillation output of the oscillation circuit 13 is provided to a temperature compensation circuit 15 and a torque detection circuit 16, respectively. The alternating voltage generated by the resonance of the temperature compensation circuit 15 is obtained in relation to the ambient temperature and is applied to the clamp circuit 17. Further, the alternating voltage generated by the resonance of the torque detection circuit 16 is obtained in relation to the torque applied by the operation of the steering wheel and the ambient temperature, and the alternating current voltage is applied to the clamp circuit 22. The clamp circuits 17 and 22 clamp the AC voltage by applying a bias to change the level of the waveform toward a positive voltage so that the maximum negative value of the applied AC voltage becomes 0v. Then, the output voltage of the clamp circuit 17.22 is applied to the peak detection circuit 18.22.
23 separately. The peak detection circuits 1B, 23 sequentially detect the peak values of the applied AC voltage. Thereby, the peak detection circuit 18 detects the AC voltage related to the ambient temperature at its peak value, and the peak detection circuit 23 detects the AC voltage related to the torque and the ambient temperature at its peak value.

Therefore, even if the AC voltage obtained by the temperature compensation circuit 15 and the torque detection circuit 16 has waveform distortion near the zero cross, or the midpoint of the oscillation output waveform and the midpoint of the AC voltage waveform obtained by resonance are inconsistent with each other. Even if there are differences, the sensor output of the torque sensor section TS can be stably obtained with high precision without being influenced by those problems at all. Each output voltage of these peak detection circuits 18.23 is given to a differential amplifier circuit 21 together with the offset voltage of the offset voltage output section 14, and the differential amplifier circuit 21 receives each output voltage of the peak detection circuit 18.23. In addition to finding the difference, an offset voltage is added to the output voltage of the difference. Therefore, the output voltage of the differential amplifier circuit 21 is such that the output voltages related to the ambient temperature of the temperature compensation circuit 15 and the torque detection circuit 16 are canceled out, and only the output voltage related to the acting torque is applied to the differential amplifier circuit 21. You will get it from 21.

Note that when the torque sensor unit TS does not detect torque, the output voltage of the differential amplifier circuit 21 becomes an offset voltage, and when torque is detected, the output voltage is determined based on the offset voltage depending on the rotation direction of the steering wheel. When the voltage changes in the positive or negative direction, the output voltage of the power supply stabilizing section 12 and the oscillation circuit 1
Even if there is a difference between the input voltage and the specified input voltage of No. 3, an appropriate detected torque can be obtained. The output voltage related to the torque of the differential amplifier circuit 21 is inputted to the microcomputer 28 of the controller CTR via the connectors CNI and CN2, and controls an electric motor (not shown) that assists the steering force in relation to the detected torque. become. Also, the offset voltage of the offset voltage output section 14 is determined by the connector CNICN2.
Through the controller CTR microcomputer 2
8, the offset voltage when the power supply 30 is turned on is stored in the microcomputer 28, and then the difference between the offset voltage and the offset voltage given from the differential amplifier circuit 21 is determined to detect a failure of the power supply stabilizing unit 12. Can be detected.

Furthermore, if the oscillation circuit 13 fails and the oscillation output disappears, the output voltages of the temperature compensation circuit 15 and the torque detection circuit 16 disappear. Therefore, the output voltage of the peak detection circuit 18 is no longer given to the comparison circuit i2Q, and only the reference voltage given from the reference voltage circuit 19 is given to the comparison circuit 20, and the comparison circuit 20 outputs the voltage and transfers the voltage to the controller CTR. Since the signal is sent to the microcomputer 28 of the oscillation circuit 13, a failure of the oscillation circuit 13 can be detected.

Therefore, when a failure of the power supply stabilizing unit 12 or the oscillation circuit 13 is detected, the safety of the power steering device can be improved by, for example, prohibiting control of the electric motor that assists the steering force.

Although the torque sensor of the present invention is used in an electric power steering device for an automobile, it is of course applicable to simply detecting torque in a vehicle other than an automobile.

〔Effect of the invention〕

As described in detail above, the torque sensor of the present invention is provided with an AC voltage induced in relation to the magnetic coupling state corresponding to the torque applied by the steering force, and a predetermined bias and voltage applied thereto.
A clamp circuit that gives the AC voltage and an AC voltage clamped by the clamp circuit are provided, and a peak detection circuit that detects the peak value of the AC voltage is provided, and the detected torque is obtained based on the peak value of the AC voltage. It is completely free from the effects of waveform distortion caused near the zero cross of the induced voltage due to the automobile battery and the difference between the midpoint of the oscillation output waveform and the midpoint of the DC voltage waveform obtained by rectifying the induced voltage.

Therefore, according to the present invention, a torque sensor that can detect changes in torque with high accuracy, has high reliability, and is particularly suitable for an electric power steering device of an automobile can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a torque sensor according to the present invention, Fig. 2 is a block diagram of a torque sensor according to the present invention;
The figure is a circuit diagram of the main part of a conventional torque sensor, Figure 3 is a waveform diagram comparing the midpoint of the oscillation output waveform and the midpoint of the induced AC voltage, and Figure 4 is the full-wave rectified waveform of the AC voltage. FIG. 11... Power supply (battery) 13... Oscillation circuit 14
... Offset voltage output section 15 ... Temperature compensation circuit 16 ... Torque detection circuit 17 ... Clamp circuit 18 ... Peak detection circuit 21 ... Differential amplifier circuit 22 ... Clamp circuit 23.・Peak detection circuit
24.25...Voltage-current conversion circuit 28...Microcomputer TS...Torque sensor section CTR...
・Controller patent Applicant Koyo Seiko Co., Ltd. Agent Patent attorney Noboru Kono

Claims (1)

[Claims] 1. A torque sensor that obtains a magnetic coupling state related to torque applied by a steering force and detects torque by an alternating current voltage induced in relation to the magnetic coupling, comprising: a clamp circuit to which the alternating current voltage is applied and applies a predetermined bias to it; A torque sensor comprising: a peak detection circuit configured to receive an AC voltage of the clamp circuit and detect its peak; and detect the torque based on the peak value of the AC voltage output by the peak detection circuit. .