JP2000028449A - Torque detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a torque detector in which a decision is made that a failure has occurred on the occurrence of a failure at any one point in the coil or detection circuit and steering assist is not performed in power steering control when a decision is made that a failure has occurred. SOLUTION: The torque detector comprises a passive shaft 1 having a stress sensitive section where the magnetic characteristics varies depending on the torque, and a plurality of coils 5a, 5b wound forward around the passive shaft 1. The torque detector further comprises a first detection circuit 100a for detecting flux generated from the coil 5a, 5b as torque output, and a second detection circuit 100b having a single coil 5c wound around the passive shaft 1 and detecting flux generated from the coil 5c as torque output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque detecting device for detecting a torque applied to a rotatable passive shaft in an electric power steering mechanism of an automobile or the like.

[0002]

2. Description of the Related Art Generally, in an electric power steering mechanism of an automobile, it is necessary to detect a torque applied to a handle shaft which is a passive shaft. As a torque detecting device for this purpose, for example, there is a magnetostrictive torque detecting device disclosed in JP-A-1-94230. The structure of this device will be described with reference to FIG. In the figure, 1 is a passive shaft which is a rotating shaft, 7
Reference numerals a and 7b denote bearings rotatably supporting the passive shaft 1, and reference numeral 3 denotes a bobbin supported by the bearings 7a and 7b. First and second magnetostrictive elements 2 serving as first and second stress-sensing portions spaced apart in the axial direction on the outer peripheral surface of passive shaft 1
a and 2b are fixed. The first magnetostrictive element 2a is in the direction of an angle θ = 45 ° with respect to the central axis, and the second magnetostrictive element 2b is in the direction of θ.
= A plurality of strips are formed in a strip shape in the direction of 145 °. Each bobbin 3 has a magnetostrictive element 2.
The first and second coils 5a and 5b, and the first and second yokes 4a and 4b are arranged corresponding to a and 2b.
The first and second yokes 4a and 4b are members for preventing magnetic flux from spreading outside. Reference numeral 101 denotes a drive circuit for supplying an AC exciting current to the coils 5a and 5b. 100 detects a voltage generated in the first and second coils 5a and 5b by the AC exciting current to output a torque output corresponding to the stress. It is a detection circuit.

Next, the operation will be described. When an external torque is applied to the passive shaft 1, θ
= ± 45 °, and the magnetostrictive elements 2a, 2a
Tensile stress is generated in one of b and compressive stress is generated in the other. When this stress occurs, the magnetic permeability of the magnetostrictive elements 2a and 2b changes,
The magnetic permeability changes in the opposite direction depending on the tensile stress and the compressive stress. Due to the change in the magnetic permeability, the inductances of the first and second coils 5a and 5b change in opposite directions. When an AC exciting current is applied to these coils by the drive circuit 101, a voltage corresponding to the inductance is generated at both ends of each coil. Therefore, the detection circuit 100 detects this voltage to obtain the torque. The magnetic permeability of the magnetostrictive elements 2a and 2b varies not only with the stress caused by the torque but also with the temperature. However, the change in magnetic permeability due to temperature occurs in the same direction and to the same extent in both magnetostrictive elements 2a and 2b.
By detecting 0, the voltages generated in the coils 5a and 5b are detected and differentially amplified to obtain a temperature-compensated torque output.

[0004]

Since the conventional torque detecting device is constructed as described above, the detecting circuit 1 includes the coils 5a and 5b and the coils 5a and 5b.
The output changes when a failure such as a slight short circuit or poor contact occurs at any one of the four coil wires connected to 00 or any part of the detection circuit. The output change is caused by torque. It could not be distinguished whether it was due to a failure, or a temperature change. For this reason,
If the output is used as it is for important control such as electric power steering, there is a problem in that if a failure occurs even at one location, steering assist contrary to the driver's will is caused.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has a configuration in which if a failure occurs in any one of a coil and a detection circuit, the failure can be recognized. In power steering control, an object is to obtain a torque detection device that can perform control such as not performing steering assist when it is determined that a failure has occurred.

[0006]

According to a first aspect of the present invention, there is provided a torque detecting device comprising: a passive shaft having a stress sensitive portion whose magnetic characteristics change according to torque; and a winding wound around the passive shaft in order. First detecting means having a plurality of coils, and detecting a magnetic flux generated by the coils as a torque output;
It has a single coil wound around the passive shaft, and has a second detecting means for detecting a magnetic flux generated by the coil as a torque output.

According to a second aspect of the present invention, there is provided a torque detecting device.
In the invention of claim 1, the first detecting means has first and second coils as the plurality of coils, and the second detecting means has a third coil as a single coil. Things.

[0008] According to a third aspect of the present invention, there is provided a torque detecting device.
The invention according to claim 1 or 2, further comprising a disconnection detecting circuit for detecting disconnection of the third coil.

According to a fourth aspect of the present invention, there is provided a torque detecting device comprising:
According to any one of the first to third aspects of the present invention, a temperature compensating unit whose magnetic characteristics change according to temperature and whose magnetic characteristics do not change depending on torque is used in combination with the stress sensitive unit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a torque detecting device according to an embodiment of the present invention will be described with reference to the drawings. Embodiment 1 FIG. FIG. 1 is a configuration diagram showing a first embodiment of the present invention. Here, a case where the torque detection device according to the present embodiment is used in an electric power steering system is shown. Parts corresponding to those in FIG. 3 will be described with the same reference numerals. In the figure, 1 is a passive shaft which is a rotating shaft,
Reference numerals 2a and 2b denote a plurality of elongated strip-shaped magnetostrictive elements fixed on the passive shaft 1 and oriented in the + 45 ° direction and the 145 ° direction with respect to the central axis, respectively, and are the first and second stress-sensitive elements. Functions as a unit. 5a, 5b, and 5c are first, second, and third coils, respectively, 101 is a drive circuit that supplies an AC exciting current to the first and second coils 5a and 5b that are connected in series, and 100a is a first drive circuit. And a first detection circuit connected to the second coils 5a and 5b, and the first and second coils, the drive circuit, and the first detection circuit constitute a first detection means. 100c is the second coil connected to the third coil 5c.
The third coil and the second detection circuit constitute second detection means. 201 is a motor that performs steering assist, and 202 is an ECU that controls the motor 201 based on the output of the torque detection device.

Next, the operation will be described. Since the first detecting means includes all the same components as in the conventional example, the same operation as in the conventional example is performed, and a temperature-compensated first torque output is obtained. A torque is applied to the passive shaft 1 and, for example, the inductance of the first coil 5a changes to the value of the second coil 5b.
1, the magnetic flux generated by the first coil 5a by the AC exciting current i becomes larger than the magnetic flux generated by the second coil 5b, as shown in FIG. When the magnetic flux having a magnitude corresponding to the torque passes through the second coil 5c, an electromotive force is generated in the third coil 5c. A torque output is obtained. That is, it operates as a so-called differential transformer. When the torque detecting device is operating normally, the first torque output and the second torque output are configured to be substantially the same, so that the difference between the first torque output and the second torque output is obtained. Is smaller, the ECU 202 determines that the torque detection device is normal, and controls the motor 201 so as to perform steering assist with a force corresponding to the torque output.

When a disconnection occurs in the first coil 5a or the second coil 5b, the impedance of one of the coils becomes infinite, so that the first torque output swings to either side, but the exciting current is reduced. Does not flow, no voltage is induced in the third coil 5c, and the second torque output outputs zero torque. Therefore, the first and second torque outputs are different, and the ECU 202 determines that a failure has occurred in the torque detection device. When the third coil 5c is disconnected,
Is zero, the first torque output is completely independent of the circuit that generates the second torque output. For this reason, when torque is applied to the passive shaft 1, a discrepancy occurs between the first torque output and the second torque output. If the ECU 202 monitors this, it is determined that the torque detection device has failed. can do.

[0013] Even if a failure occurs in either the first detection circuit 100a or the second detection circuit 100b, the first torque output differs from the second torque output.
If this is monitored, it is possible to determine the failure of the torque detecting device. Even when a slight contact failure or short-circuit occurs in any of the coils 5a, 5b, 5c, the ECU 2 cannot control the first torque output and the second torque output.
If this is monitored in 02, a failure of the torque detecting device can be determined. When the drive circuit 101 fails and no drive voltage is generated, no AC excitation current flows, so that no induced voltage is generated in all the coils, and therefore, regardless of the torque actually applied. ,
Both the first output and the second output output zero torque. This is a malfunction of the torque sensor, but the assist of the electric power steering system is not performed. As a result, the control on the normal side is performed.

As described above, in the present embodiment, the first and second coils and the first detecting circuit perform the same operation as the conventional torque detecting device to generate the first output. Since the second output is generated by detecting a change in magnetic flux generated from the coils of the first and second coils by the third coil and the second detection circuit, an ECU that controls a motor or the like according to the output of the torque sensor Now, the first output and the second
When there is a large discrepancy in the output of the motor, it is determined that a failure has occurred in the torque detector, and control can be performed so that the motor or the like is not driven.
When a failure occurs in a location, it is known that a failure has occurred. For example, in power steering control, if it is determined that a failure has occurred, control such as not performing steering assist can be performed.

Embodiment 2 FIG. 2 is a configuration diagram showing a second embodiment of the present invention. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and the other parts are the same as those in the first embodiment, and thus description thereof is omitted here. In the first embodiment, a failure such as a disconnection is determined only by comparing the first torque output and the second torque output. However, as shown in the figure, a disconnection detection circuit 300 is provided in the third coil 5c. You may.

In the figure, both 301 and 302 are 1M
Resistors having a high resistance value of about Ω, and 303 and 304 are decoupling capacitors. Since the resistance value of the third coil 5c is smaller than the resistances of the resistors 301 and 302, if there is no disconnection in the third coil 5c, the DC potential at the upper end of the resistor 302 becomes approximately half the power supply potential Vcc. Become. Third
When the disconnection occurs in the coil 5c, the DC potential at the upper end of the resistor 302 falls to the ground, so that the disconnection is detected, and when the disconnection occurs, the detection circuit 100b
Sets the second torque output to a value outside the normal output range. The ECU 202 receives the signal and the third coil 5
It is determined that there is a disconnection in c, and the motor 201 is controlled based only on the first torque output signal. Therefore, even when the third coil 5c is disconnected, a normal steering assist operation can be performed.

As described above, according to the present embodiment, when the third coil wire is disconnected, the disconnection detecting circuit detects the E coil.
The CU can know the failure of the third coil, and thereby can perform control so as not to drive the motor or the like, or perform control of the motor or the like using only the first output. Also, even when the third coil is disconnected, a normal steering assist operation can be performed based only on the first torque output.

Embodiment 3 In the above-described embodiment, the magnetostrictive element is used as the stress-sensitive part. May be used. Further, in the above-described embodiment, a pair of stress-sensitive sections whose magnetic properties change in the opposite direction according to the torque are used. However, one stress-sensitive section whose magnetic properties change according to the torque,
A combination of temperature compensating units may be used in which the magnetic characteristics change only in accordance with the temperature in the same manner as in the stress sensitive unit, and the magnetic characteristics do not change depending on the torque. As a result, a torque output with temperature compensation can be obtained, and torque detection with high detection accuracy corresponding to the environmental temperature can be performed.

[0019]

As described above, according to the present invention, a passive shaft having a stress sensitive portion whose magnetic characteristics change according to torque, and a plurality of coils wound sequentially around the passive shaft. A first detecting means for detecting a magnetic flux generated by the coil as a torque output, and a single coil wound around the passive shaft to detect a magnetic flux generated by the coil. Since the second detection means for detecting the torque output is provided, if a failure occurs in any one of the detection means, it is known that the failure has occurred. For example, in power steering control, it is determined that the failure has occurred. In this case, there is an effect that control such as not performing steering assist can be performed.

Further, according to the present invention, since the disconnection detecting circuit for detecting the disconnection of the third coil is provided, even when the disconnection occurs in the third coil, the disconnection is detected based on only the first torque output. There is an effect that a normal steering assist operation can be performed.

According to the present invention, since the temperature compensating portion whose magnetic characteristics change according to the temperature and the magnetic characteristics do not change depending on the torque is used in combination with the stress sensitive portion, a temperature compensated torque output can be obtained. In addition, there is an effect that torque detection with high detection accuracy corresponding to the environmental temperature can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram illustrating a conventional torque detection device.

[Explanation of symbols]

Reference Signs List 1 passive axis, 2a, 2b magnetostrictive element, 5a first coil, 5b second coil, 5c third coil, 100a first detection circuit, 100b second detection circuit, 101 drive circuit, 300 disconnection detection circuit .

Claims (4)

[Claims] 1. A passive shaft having a stress sensitive portion whose magnetic characteristics change in accordance with a torque, and a plurality of coils wound sequentially around the passive shaft, wherein a magnetic flux generated by the coil is provided. First detection means for detecting as a torque output, and second detection means having a single coil wound around the passive shaft and detecting a magnetic flux generated by the coil as a torque output. A torque detecting device comprising: 2. The method according to claim 1, wherein the first detecting means has first and second coils as the plurality of coils, and the second detecting means has a third coil as the single coil. The torque detecting device according to claim 1, wherein: 3. The torque detecting device according to claim 1, further comprising a disconnection detecting circuit for detecting disconnection of the third coil. 4. A temperature-compensating part whose magnetic characteristics change according to temperature and whose magnetic characteristics do not change depending on torque is used in combination with said stress-sensitive part.
4. The torque detection device according to any one of claims 1 to 3.