JPH1137865A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost and the heat generation by making a torque sensor have a configuration wherein torque is detected based on a transient voltage being generated between a coil and an electric resistance when a voltage having square waveform is supplied to the coil. SOLUTION: An input shaft 2 and an output shaft 3 arranged coaxially while being coupled through a torsion bar 102 are supported rotatably. The input shaft 2 is secured integrally in the rotational direction with a tubular member 104 while surrounding the outer circumferential surface of the output shaft 3. An axial groove 3B is made in the part of the output shaft 3 surrounded by the tubular member 104 which is provided with windows 104a, 104b such that the superposition on the groove 3B is varied depending on the relative position to the output shaft 3. The tubular member 104 is surrounded by a yoke 112 applied with coils 110, 111 surrounding the windows 104a, 104b. An electric resistance is arranged in series with the coils 110, 111 and a torque to be generated on a rotary shaft 23 is detected based on a transient voltage being across the electric resistor upon application of a voltage having square waveform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque sensor for detecting, in a non-contact manner, a steering torque generated on a rotating shaft of a steering wheel of a vehicle, and more particularly to a torque sensor whose impedance changes according to the generated steering torque. In addition to easily correcting the neutral output voltage deviation caused by errors, assembly errors, output errors of electronic parts, etc., when the torque is not detected, the failure of each part is detected by a different operation from the detection. And a torque sensor having improved reliability.

[0002]

2. Description of the Related Art A steering device for an automobile or a vehicle is mounted on a motor.
An electric power steering apparatus for urging an auxiliary load by the rotational force of a motor is such that a driving force of a motor is urged to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt through a speed reducer. It has become. here,
The configuration of a general electric power steering device will be described with reference to FIG. The shaft 2 of the steering handle 1 is a reduction gear 3
A, universal joints 4a and 4b, and a pinion rack mechanism 5 are connected to a tie rod 6 of a steered wheel. The shaft 2 is provided with a torque sensor 100 for detecting the steering torque of the steering wheel 1. A motor 20 for assisting the steering force of the steering wheel 1 is connected to the shaft 2 via a clutch 21 and a reduction gear 3A. Is joined to. Electric power is supplied from a battery 14 through an ignition key 11 to a control unit 200 for controlling the power steering device. The control unit 200 is connected to a steering torque T detected by a torque sensor 100 and a vehicle speed sensor 12.
The steering assist command value I of the assist command is calculated on the basis of the vehicle speed V detected by
Is controlled based on the current. The clutch 21 is turned on / off by the control unit 200.
It is controlled and is ON (coupled) in a normal operation state. In the control unit 200, the clutch 21 is turned off (disconnected) when it is determined that the power steering device has failed, and when the power of the battery 14 is turned off by the ignition key 11.

The control unit 200 is mainly composed of C
FIG. 12 shows a general function executed by a program inside the CPU, which is constituted by a PU. The steering torque T detected and input by the torque sensor 100 is used by the phase compensator 2 to improve the stability of the steering system.
01, and the phase-compensated steering torque TA is input to the steering assist command value calculator 202. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 202. The steering assist command value calculator 202 is
A steering assist command value I, which is a control target value of a current supplied to the motor 20, is determined based on the input steering torque TA and the vehicle speed V.
03 is attached. The memory 203 stores the steering assist command value I corresponding to the steering torque using the vehicle speed V as a parameter, and is used for calculating the steering assist command value I by the steering assist command value calculator 202. The steering assist command value I is input to a subtractor 200A, and is also input to a feedforward type differential compensator 204 for increasing the response speed. The deviation (Ii) of the subtractor 200A is calculated by a proportional calculator. 20
5, and the proportional output is input to the adder 200B and also to the integration calculator 206 for improving the characteristics of the feedback system. The outputs of the differential compensator 204 and the integration calculator 206 are also added to the adder 200B, and the current control value E that is the result of the addition in the adder 200B is added.
Is input to the motor drive circuit 207 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 208, and the motor current value i is subtracted by the subtractor 200.
Feedback is made to A.

As the torque sensor 100 of the power steering device described above, for example, Japanese Patent Publication No. 63-455
No. 28 is disclosed. In this torque sensor, two cylindrical bodies are coaxially fitted so as to rotate relatively in accordance with a torque generated on a shaft, and an axially long groove and teeth are formed on an outer peripheral surface of an inner cylindrical body. The outer cylinders are formed alternately, and cutouts are formed in the outer cylinder so that the degree of overlap with the groove changes according to the relative rotation between the cylinders, and a coil is arranged so as to surround the outer cylinder. Has been established. When the relative rotation position of the two cylinders changes and the degree of overlap with the notch in the groove changes, the impedance of the coil changes. Therefore, the torque generated on the shaft is measured by measuring the impedance of the coil. Is to be detected.

[0005]

With the conventional torque sensor described above, it is possible to detect the torque generated on the shaft based on the change in the impedance of the coil. However, since the current for driving the coil is a high-frequency AC current, an oscillation power supply unit for supplying an accurate sine-wave AC current is required for a high-precision torque sensor. For this reason, a large number of electronic components are required, and the individual electronic components themselves are required to have high accuracy, resulting in a problem that the cost increases. In addition, the coil is driven by a sine-wave alternating current. In addition, in order to keep the current direction constant (single power supply drive), the coil is driven by adding an offset voltage, and power consumption is reduced. However, there is also a problem that the heat generation is very large and uneconomical, and the amount of heat generated is large due to the large current consumption. Furthermore, since the impedance change of the coil is not so rapid, there is a problem that the sensor sensitivity is not so good.

On the other hand, in the conventional torque sensor, the output voltage at the time of zero input torque deviates from the predetermined neutral voltage of the controller due to an assembly error of a sensor component such as a shaft or a tolerance of each electronic part for signal processing. Therefore, the output voltage must always be adjusted. However, this voltage adjustment is performed by adjusting the position of the torque sensor, etc., which is not only troublesome, but also depends on the reliability of the fixing method. . Also, there is a tolerance in the reference voltage such as A / D which determines the predetermined voltage of the controller. Even if the neutral voltage of the torque sensor is accurately adjusted to the predetermined value, it is recognized that the controller is shifted. In some cases. For example, in Japanese Patent Application Laid-Open No. HEI 1-173843, a memory is provided for a magnetostrictive sensor, and the initial neutral deviation of the sensor is corrected by balancing two coils, but an abnormal state cannot be detected. And
Conventionally, when improving the reliability of a torque sensor, a plurality of identical sensors are arranged, and the detection values of the plurality of sensors are constantly compared to detect an abnormal state or prevent malfunction due to a change in the difference. Was. Arranging a plurality of sensors increases costs and disadvantageously complicates the detection system.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to eliminate the need for troublesome neutral adjustment by a position adjusting mechanism or the like, and to reduce costs, reduce heat generation, and the like. Another object of the present invention is to provide a torque sensor which has a small size, saves space, improves reliability, and can be configured by a single detection circuit.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a torque sensor, and an object of the present invention is to provide a control operation unit for varying a drive timing of a coil for detecting a torque and a sample-hold timing, and an initial value of each sensor unit. A storage unit for storing the torque, based on the sampling of the transient voltage of the coil, to detect the torque, during the interval between the sample and hold that does not perform the torque detection, by comparing with the initial value of the storage unit, This is achieved by detecting a failure in each part of the sensor. Further, the present invention provides an electric power steering which detects a steering torque of a steering wheel and applies an auxiliary load by a motor to a steering shaft provided integrally with the steering wheel according to the steering torque. It relates to the torque sensor of the device,
It is an object of the present invention to detect the torque based on sampling of a transient voltage of a coil, to provide a control operation unit capable of changing a drive timing of the coil and a timing of a sample hold, and to store an initial value. This is achieved by providing a storage unit for performing the operation, and detecting a failure of each unit by comparing with the initial value between sample hold periods where the steering torque is not detected. That is, based on the A / D value after the sample hold in which the coil is not driven, the failure of the coil voltage, the differential amplifier and the sample hold circuit is detected, and the A / D after the neutral voltage switching is performed. On the basis of the D value, the failure of the neutral voltage section of the differential amplifier and the failure of the sample hold section of the sample hold circuit are detected.

The torque sensor of the present invention has a structure in which first and second rotating shafts arranged coaxially are connected via a torsion bar and made of a conductive and non-magnetic material. The second cylindrical member is integrated with the second rotating shaft in a rotating direction so as to surround the outer peripheral surface of the first rotating shaft, and the cylindrical member is surrounded by at least the cylindrical member of the first rotating shaft. Part is formed of a magnetic material, a groove extending in the axial direction is formed in the enclosed part, and the degree of overlap with the groove changes in the cylindrical member according to a relative rotation position with respect to the first rotation shaft. Forming a window so as to surround the portion of the cylindrical member where the window is formed, arranging an electric resistor in series with the coil, and changing the coil in a square wave shape. Transient generated between the coil and the electric resistance when voltage is supplied Based on the pressure, and detects the torque generated in the first and second rotating shafts.
Here, the non-magnetic material is a paramagnetic material and some diamagnetic materials, and the magnetic material is a ferromagnetic material. The magnetic permeability of a non-magnetic material is about the same as that of air, and is smaller than the magnetic permeability of a magnetic material. The transient voltage is a final voltage that changes when a voltage that changes in the form of a square wave is supplied. In the present invention, the coil is driven by a square wave voltage. The supply interval of the wave voltage is synchronized with the sampling clock of the controller to which the output of the torque sensor is supplied. For this reason, the time during which the current is actually flowing through the coil is greatly reduced, the power consumption is reduced, and the heat generation is also reduced. Further, a square wave has an advantage that it can be easily and accurately generated with a smaller number of electronic components than a sine wave.

Further, in the present invention, a drive mode is adopted in which the coil has different states of a steady state and a transient state, and the coil drive timing and the sample hold timing are varied so that the torque is not detected (torque). During the time between signal sampling times), an operation different from that at the time of torque signal detection is performed, and a failure of each unit is detected by comparing with an initial assembly value stored in the storage unit. In addition, one circuit system is realized by confirming all circuit units by a combination of drive timings of the respective units.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 3 show a torque sensor 1 according to the present invention.
00 is shown as an example of a structure applied to an electric power steering device for a vehicle, and FIG.
The input shaft 2 (see FIG. 11) and the output shaft 3 (corresponding to the shaft of the reduction gear 3A in FIG. 11) connected via a torsion bar 102 have bearings 103a and 103, respectively.
3b rotatably supported. The input shaft 2, the output shaft 3 and the torsion bar 102 are coaxially arranged, and the input shaft 2 and the torsion bar 102 are connected via a sleeve 2A whose ends are spline-coupled.
The other end of the torsion bar 102 is spline-coupled to a position deeply entering the output shaft 3. The input shaft 2 and the output shaft 3 are formed of a magnetic material such as iron. A steering handle 1 (see FIG. 11) is integrally mounted on the right end of the input shaft 2 in the rotational direction, and a reduction gear 3 and universal joints 4a and 4b are provided on the left end of the output shaft 3.
It is connected to a tie rod 6 via a pinion rack mechanism 5 (see FIG. 11). Therefore, the steering force generated by the driver steering the steering wheel 1 is transmitted to the steered wheels via the input shaft 2, the torsion bar 102, the output shaft 3, and the steering device.

A sleeve 2A fixed to the end of the input shaft 2
Has a length that surrounds the outer peripheral surface of the end of the output shaft 3, and the inner peripheral surface of the portion of the sleeve 2A that surrounds the outer peripheral surface of the end of the output shaft 3 has a plurality of axially long portions. A plurality of convex portions 2a are formed, and a plurality of grooves 3a (the same number as the number of convex portions 2a) that are long in the axial direction are formed on the outer peripheral surface of the output shaft 3 facing these convex portions 2a. The projection 2a and the groove 3a are fitted with a margin in the circumferential direction, thereby preventing the relative rotation between the input shaft 2 and the output shaft 3 over a predetermined range (for example, about ± 5 degrees). A worm wheel 103 coaxially and integrally rotating with the output shaft 3 is externally fitted to the output shaft 3.
a meshes with a worm 20b formed on the outer peripheral surface of the output shaft 20a of the motor 20. Therefore, Mo
The rotation force of 0 is transmitted to the output shaft 3 via the output shaft 20a, the worm 20b, and the worm wheel 103, and by appropriately switching the rotation direction of the motor 20, a steering assist torque in an arbitrary direction is applied to the output shaft 3. It has become so.

Further, a thin cylindrical member 104 is integrally fixed in the rotation direction to the sleeve 2A integrated with the input shaft 2 so as to be close to and surround the outer peripheral surface of the output shaft 3. I have. That is, the cylindrical member 104 is formed of a conductive and non-magnetic material (for example, aluminum). As shown in FIG. 2, the portion of the cylindrical member 104 surrounding the output shaft 3 is located on the side near the sleeve 2A. , A plurality of rectangular windows 104a,...
4a is formed, and on the side remote from the sleeve 2A, a window 10a is formed.
A plurality of rectangular windows (same shape as the window 104a) 104b,..., 104b are formed at regular intervals in the circumferential direction so as to be 180 ° out of phase with each other. I have. A plurality of grooves 3B having a substantially rectangular cross section extending in the axial direction are formed on the outer peripheral surface of a portion of the output shaft 3 surrounded by the cylindrical member 104.

More specifically, as shown in FIGS. 3 and 4, an angle obtained by dividing the circumferential surface of the cylindrical member 104 into N equal parts in the circumferential direction (N = 9 in this example) is defined as one cycle angle θ (= 360 / N, θ = 40 degrees in this example) and the sleeve 2A of the cylindrical member 104.
, 104a are windows 104a,..., 104a from one end of one cycle angle θ, and the remaining b degrees (= θ−a) are closed. Window 104
.., 104a are shifted by a half cycle (θ / 2) from the other end of the one-cycle angle θ at a portion of the cylindrical member 104 farther from the sleeve 2A. Part is window 10
4b,..., 104b, and the remaining b degrees (= θ−a)
Part is blocked. .., 3B, the circumferential width of the convex portion 3C having a convex cross section is c degrees, and the grooves 3B,.
The circumferential width of 3B is d degrees, and the relative rotatable range between the cylindrical member 104 and the output shaft 3 (between the input shaft 2 and the output shaft 3) is e degrees. However, when the torsion bar 102 is not twisted (steering torque is zero), for example, when c = 20 degrees, as shown in FIG. 3, one of the center of the circumferential width of the window 104a and the circumferential direction of the groove 3B. (One edge of the convex portion 3C), and as shown in FIG. 4, the central portion in the circumferential direction of the window 104b and the other circumferential end of the groove 3B (the other edge of the convex portion 3C). Part) overlap with each other. Therefore, the overlapping state of the window 104a and the groove 3B,
The overlapping state of the groove b and the groove 3B is reversed in the circumferential direction, and the center of the circumferential width of the windows 104a and 104b and the center of the groove 3B in the circumferential direction are shifted by θ / 4.
In this embodiment, b> a, d> c, and e <θ / 4.

The cylindrical member 104 is surrounded by a yoke 112 around which coils 110 and 111 of the same standard are wound. That is, the coils 110 and 111 are arranged coaxially with the cylindrical member 104, and the coil 110 is
, 104a are wound around the yoke 112 so as to surround the portion where the window 104a is formed.
, 104b is wound around the yoke 112 so as to surround the portion where the yoke 112 is formed, and the yoke 112 is fixed to the housing 101. The housing 101
A space in which the worm wheel 103 is disposed;
The space between the yoke 112 and the space where the yoke 112 is provided is separated by an oil seal 113 so that lubricating oil supplied to the meshing portion between the worm wheel 103 and the worm 20b does not enter the yoke 112 side. I have.

The coils 110 and 111 are connected to a control unit 200 (including a motor control circuit) formed on a control board 210 in the sensor case 114.
It is connected to the. As shown in FIG. 5, the motor control circuit includes a torque detection unit 220 and a calculation unit 230. The motor control circuit includes two resistors Ro having the same resistance and connected in series with the coils 110 and 111. R
A bridge circuit is formed by o and Ro. In this bridge circuit, the connection between the coils 110 and 111 is grounded via a coil driving unit 221 composed of a PNP transistor Tr, and the connection between the electric resistances Ro is an arithmetic unit (MPU or A / D converter). , A D / A converter, etc.) and a reference voltage V of 230
2 are connected. The connection between the coils 110 and 111 is connected to the output port 1 of the arithmetic unit 230 via a diode 222 that regenerates a current when a reverse electromotive force is generated in the coils 110 and 111. . The control voltage Vl is supplied from the arithmetic unit 230 to the gate of the transistor Tr of the coil driving unit 221. The control voltage Vl is a square wave voltage as shown in FIG. 6A, and the output interval of the square wave is synchronized with the sampling clock of the arithmetic unit 230. In addition, the control voltage V1 is determined by the fact that the transistor Tr of the coil driving
Since the transistor Tr is an NP type, it falls from a logical value “1” to “0” when the transistor Tr is turned on, and the logical value “0” when the transistor Tr is turned off.
Is a negative logic voltage that rises to "1". Then, the reference voltage V2 supplied from the resistor Ro and the coils 110 and 111 to the coil driving unit 221 becomes a square wave voltage as shown in FIG. 6B synchronized with the ON / OFF of the transistor Tr. That is, the voltage V2 is a square wave obtained by inverting the control voltage Vl.

Further, one output voltage V3 of the bridge circuit, which is the voltage between the coil 110 and the resistor Ro, and the coil 1
11 and the other output voltage V4 of the bridge circuit, which is a voltage between the resistor Ro, is input to the differential amplifier 223 and input to the A / D1 terminal and A / D2 terminal for A / D of the arithmetic unit 230, respectively. Have been. The differential amplifier 22
3 is supplied with the neutral voltage Vr supplied from the neutral voltage switching unit 224, and the differential amplifier 223 outputs an output voltage V5 represented by the following equation (1), where G is an amplification factor.

V5 = G × (V3−V4) + Vr (1) The output voltage V5 of the differential amplifier 223 is A / A of the arithmetic unit 230.
While being input to the D2 terminal,
Sampled and held by the sample and hold circuit 225 in accordance with the hold signal Vs, and the output voltage Vo at the time of predetermined sampling.
Is input to the A / D1 terminal of the arithmetic unit 230. Arithmetic unit 2
Reference numeral 30 indicates to the sample-and-hold circuit 225 a short-pulse-like hold signal Vs as shown in FIG. 7C, which rises at the same time as the fall of the control voltage Vl and falls after a lapse of a predetermined time.
, And the sample-and-hold circuit 225 outputs the voltage V5 at the falling point of the hold signal Vs to the output voltage Vo.
The voltage Vo is A / D converted by the arithmetic unit 230. The arithmetic unit 230 is connected to a neutral signal storage unit 240 for storing a neutral signal after assembling, and to store the neutral signal after assembly.
A write signal communication unit (serial communication port or general-purpose input / output port) 241 for receiving a write signal to be stored in 0 is connected.

The falling timing of the hold signal Vs is during the time when the output voltages V3 and V4 in the transient state are being supplied to the differential amplifier 223. More specifically, from the time when the control voltage Vl falls, the coil 11
The point in time when a time constant τ determined by the inductance Ro and the resistance Ro elapses is defined as evening when the hold signal Vs falls. The reason for using the time constant τ is to hold the output voltage V5 when the difference between the output voltages V3 and V4 is largest. Therefore, if the hold signal Vs is varied up to the time constant τ, the gain of the torque sensor output can be adjusted. Further, the neutral signal storage unit 240 may be a memory having a built-in backup power supply such as a battery.

The calculating section 230 calculates the direction and magnitude of the relative rotational displacement of the input shaft 2 and the cylindrical member 104 based on the voltage Vo input from the sample hold circuit 225, and calculates a proportional constant to the calculation result. The motor drive circuit 207 is multiplied to obtain the steering torque generated in the steering system, and the motor drive circuit 207 is controlled so that the drive current I for generating the steering assist torque is supplied to the motor 20 based on the calculation. FIG. 8 shows the timing of such a normal operation, FIG. 8A shows the timing of the control voltage V1 for driving the coil, time T1 is the coil non-drive time, and FIG. It shows a coil voltage corresponding to the input control voltage V1. FIG. 8 (c) shows the operation of the sample hold circuit 225, in which the hold time T2 is used for CPU operation time, motor control time, etc., and at time t1.
A / D-convert the sensor output. The calculation unit 230 receives the vehicle speed V from the vehicle speed sensor 12 and determines whether or not the vehicle is traveling at a high speed based on the vehicle speed V. During the high-speed traveling, no steering assist torque is required. Therefore, control of the motor drive circuit 207 is prohibited.

Next, the operation of this embodiment will be described.

When the steering system is in a straight running state and the steering torque is zero, no relative rotation occurs between the input shaft 2 and the output shaft 3, and the relative rotation also occurs between the output shaft 3 and the cylindrical member 104. No rotation occurs. On the other hand, when the steering wheel 1 is steered to generate a torque on the input shaft 2, the torque is applied to the torsion bar-1.
02 to the output shaft 3. At this time, a resistance force is generated on the output shaft 3 in accordance with the frictional force between the steered wheels and the road surface and the frictional force such as the meshing of the gears of the steering device of the output shaft 3. When the torsion bar 102 is twisted, a relative rotation occurs in which the output shaft 3 is delayed, and a relative rotation also occurs between the output shaft 3 and the cylindrical member 104. When the cylindrical member 104 has no window, the cylindrical member 104 is made of a conductive and non-magnetic material. Therefore, when an alternating current is applied to the coil to generate an alternating magnetic field inside the coil, the outer peripheral surface of the cylindrical member 104 An eddy current is generated in the opposite direction to the coil current. When the magnetic field due to the eddy current and the magnetic field due to the coil are superimposed, the cylindrical member 104
The magnetic fields inside are canceled.

When the windows 104a and 104b are provided on the cylindrical member 104, the eddy current generated on the outer peripheral surface of the cylindrical member 104 cannot go around the outer peripheral surface by the windows 104a and 104b. Member 10
4, a loop is formed which flows in the same direction as the coil current on the inner peripheral surface and returns to the outer peripheral surface along the end surfaces of the adjacent windows 104a and 104b. That is, an eddy current loop is periodically formed in the circumferential direction inside the coil (θ = 360 /
N). The magnetic field generated by the coil current and the eddy current are superimposed, and a magnetic field having periodic strength in the circumferential direction and having a gradient that becomes smaller toward the center is formed inside and outside the cylindrical member 104. The strength of the circumferential magnetic field is
Windows 104a, 104 strongly affected by adjacent eddy currents
It is strong at the center of b, and weak at a half cycle (θ / 2) shift from it. A shaft 3 made of a magnetic material is coaxially disposed inside the cylindrical member 104, and a protrusion 3B and a recess 3C are formed on the shaft 3 at the same period as the windows 104a and 104b. A magnetic substance placed in a magnetic field is magnetized to generate spontaneous magnetization (magnetic flux), but the amount increases according to the strength of the magnetic field until saturation is reached.

For this reason, the spontaneous magnetization of the shaft 3 is increased or decreased by the relative phase with the cylindrical member 104 due to the magnetic field having the periodic periodic strength and the radial gradient generated by the cylindrical member 104.

The phase at which the spontaneous magnetization is maximum is determined by the window 104.
In this state, the centers of a and 104b coincide with the centers of the protrusions, and the inductance of the coil increases and decreases according to the increase and decrease in spontaneous magnetization. The change is almost a sine wave. When no torque is applied, the phase is shifted by 列 period (θ / 4) from the phase at which the spontaneous magnetization (inductance) is maximized, and the window row on the side closer to the sleeve 2A and the other window are arranged. The phase with the row is a phase difference of 周期 cycle (θ / 2).

For this reason, when a phase difference occurs between the cylindrical member 104 and the shaft 3 due to the torque, the two coils 110 and 111
On the one hand increases and the other decreases at the same rate. When the steering system is in the neutral position and the steering torque is zero, the inductance of the coils 110 and 111 is equal because the inductances of the coils 110 and 111 are equal, and the self-induced electromotive force of the coils 110 and 111 is equal. In this state, the calculation unit 230 sends the coil driving unit 221
6A is supplied to the coils 110 and 111 as shown in FIG. 6A, and a square wave voltage V2 as shown in FIG. 6B obtained by inverting the control voltage V1 is supplied to the coils 110 and 111. , The output voltages V3 and V4 of the bridge circuit also have the same values during the transition as shown in (1)-(a) of FIG. Since the difference is zero, the output voltage V5 of the differential amplifier 223 becomes the neutral voltage Vr as shown in (1)-(b) of FIG.
Therefore, even if the hold signal Vs as shown in (1)-(c) of FIG. 7 is output, the output voltage Vo of the sample and hold circuit 225 becomes as shown in (1)-(d) of FIG. It remains at the neutral voltage Vr. As a result, the operation unit 230
Detects that the steering torque of the steering system is zero,
The drive current I is not particularly output from the motor drive circuit 207, and unnecessary steering assist torque is not generated in the steering system.

On the other hand, when the right steering torque is generated, the inductance of the coil 110 increases as the right steering torque increases, as compared with the case where the steering torque is zero.
Is reduced. Conversely, as the left steering torque increases, the inductance of the coil 110 decreases and the inductance of the coil 111 increases. If the inductances of the coils 110 and 111 change as described above, the impedances of the coils 110 and 111 change in the same manner, and the self-induced electromotive forces of the coils 110 and 111 change in the same manner. For this reason, when the right steering torque is generated, the output voltage V3 rises more steeply than the output voltage V4 as shown in (2)-(a) of FIG. 7, so that as shown in FIG. 7 (2)-(b). Output voltage V3
A difference occurs in the transition period between V1 and V4, and the difference (V5) increases as the generated steering torque increases. Conversely, when the left steering torque is generated, (3)-
Since the output voltage V4 rises more steeply than the output voltage V3 as shown in (a), a difference similarly occurs in the transition period of the output voltages V3 and V4 as shown in FIGS. The difference (V5) increases as the generated steering torque increases.

As described above, the output voltage V5 of the differential amplifier 223 depends on the direction and magnitude of the generated steering torque as shown in (2)-(b) and (3)-(b) of FIG. It changes greatly from the neutral voltage Vr. Accordingly, the hold signal Vs is applied to the sample hold circuit 225 at the timings shown in (2)-(c) and (3)-(c) of FIG.
And the voltage V5 is held, when the right steering torque is generated, a hold value of the output voltage Vo larger than the neutral voltage Vr is obtained as shown in (2)-(d) of FIG. When the steering torque is generated, a hold value of the output voltage Vo smaller than the neutral voltage is obtained as shown in (3)-(d) of FIG.

The arithmetic unit 230 calculates a steering torque based on the input output voltage Vo and the like, and inputs the steering torque to the motor drive circuit 207. The motor drive circuit 207 generates a drive current I in accordance with the direction and magnitude of the steering torque. Is supplied to the motor 20. Thereby, the motor 20 generates a rotational force according to the direction and magnitude of the steering torque generated in the steering system,
The rotational force is transmitted to the output shaft 3 via the worm 20b and the like, and a steering assist torque is applied to the output shaft 3 to reduce the burden on the operator.

As described above, even in the configuration in which the square wave voltage V2 is supplied to the coils 110 and 111, the difference between the transient voltages of the output voltages V3 and V4 is determined by the differential amplifier 223 and the sample hold circuit 225. Hold and
The output voltage Vo is input to the arithmetic unit 230. For this reason, the direction and the magnitude of the steering torque generated in the steering system can be grasped, and the steering assist torque corresponding to the direction can be generated. When the coils 110 and 111 are driven by the square wave voltage V2, the coils 110 and 111 are driven.
Since the current flows to 1 only while the voltage V2 is rising, if the duty ratio of the waveform of the voltage V2 is made sufficiently small, the current consumption can be greatly reduced. In the configuration of the present embodiment, what is necessary for detecting the steering torque is the output voltage Vo when the difference between the output voltages V3 and V4 is sufficiently generated in the transition period, and for that purpose, the output voltage V1 is lowered. It is sufficient that the voltage V2 rises until the time constant τ elapses from the time point. Therefore, in consideration of the safety factor, the transistor Tr only needs to be turned on for a time slightly longer than the time constant τ, so that the duty ratio of the voltage V2 can be made very small (for example, about 5%). As a result, the time during which the current flows through the coils 110 and 111 becomes very short, so that the power consumption is reduced, which is economical, and the amount of generated heat is also reduced. If the amount of generated heat is reduced, a reduction in the rate of failure occurrence can be expected. The operation unit 2
The coils 110 and 111 can be driven by the square-wave voltage V2 only by supplying the control voltage Vl controlled on / off by the transistor 30 to the transistor Tr. The number is reduced, and the accuracy required for each electronic component is low. For this reason,
Cost reduction can also be expected.

On the other hand, in the present invention, the neutral signal storage unit 240 is connected to the arithmetic unit 230, and the assembly initial values are stored in the neutral signal storage unit 240 via the write signal communication unit 241 after the assembly is completed. After the assembly is completed, when the input torque is zero ((1) in FIG. 7), the sample hold circuit 22 is turned off.
5, the output voltage Vo should be a neutral voltage value Vr (2.5 V which is the median value of A / D). However, in actuality, as shown in FIG. The output voltage Vo becomes (2.5 ± α) V, where α is the initial deviation, due to the angle error, the component tolerance of the torque detector 220, and the like.
There is a possibility that the deviation range ± α due to the initial deviation α may deviate beyond the operating voltage range. In this state, as shown in FIG.
A signal for operating the neutral switching unit 224 is transmitted from the output port 3 so that the arithmetic unit 230 enters a predetermined software adjustable range by external communication, and a signal within the predetermined software adjustable range is provided. A storage command for storing the output voltage (2.5 ± α1) V at the time of entering as an offset value is sent via the write signal communication unit 241, and in response to the storage command, the arithmetic unit 230 causes the neutral signal storage unit 240 The initial value of the assembly is stored as a neutral signal. Thereafter, when the function of the external signal communication unit 241 is removed and the system is operated, thereafter, the initial value stored in the neutral signal storage unit 240 is always set to the neutral value (correction of ± α1) of the differential amplifier 223, and the drive current I is calculated. I do. As described above, the system can be operated without troublesome mechanical neutral adjustment without being affected by the neutral deviation (± α) due to the initial assembly tolerance.

Further, in the present invention, each output voltage and data of the switching section are also stored in the neutral signal storage section 240, and are used for judging a failure of each section. That is, as shown in FIG. 9, the timing of torque detection based on the transient voltage change is determined by the calculation unit 23.
0 is performed at a constant cycle (several milliseconds) as needed, but the coil is driven for several tens of microseconds, and most of the time is the time T1 during which the coil is not driven.
It has become. During the coil non-drive time T1 during which this coil is not driven, as shown in FIG.
And at the interval of T4, and at the time t1 during the time T3, the hold value is A / D converted to obtain a torque output, and at the time t2 after the next sampling, the A / D conversion of each part is obtained. , Is compared with the initial value stored in the neutral signal storage unit 240. And the coil voltage V3
And V4 are different from the initial values, it is determined that the coil ground fault or the coil driving transistor is conductive, and the differential amplifier 22
If the output voltage V5 is different from the initial value, it is determined that there is a neutral voltage abnormality, a differential amplifier abnormality, or an A / D conversion unit abnormality. If the output voltage Vo of the sample hold circuit 225 is different from the initial value, it is determined that the sample hold circuit is abnormal or the A / D converter is abnormal.

Further, the neutral voltage is switched by the neutral voltage switching unit 224 at the subsequent time t3, and the A / D value of each unit at the subsequent time t4 is compared with the A / D value of each unit at the time t2. If the output voltage V5 of the differential amplifier 223 is not a normal value (initial value + offset voltage due to switching), it is determined that the neutral voltage section 224 is abnormal, and the output voltage Vo of the sample hold circuit 225 is If it is not a normal value (initial value + output voltage Vo at time t2), it is determined that the sample hold circuit 225 is abnormal.

In the above embodiment, the case where the torque sensor is applied to the electric power steering device for a vehicle has been described, but the application of the present invention is not limited to this.

[0036]

As described above, according to the torque sensor of the present invention, the torque is determined based on the transient voltage generated between the coil and the electric resistance when the voltage that changes in a square wave is supplied to the coil. Since the detection is performed, the time during which the current flows through the coil is extremely short, the power consumption is reduced, the cost is low, and the amount of heat generated is reduced. In addition, the number of required electronic components is reduced, and the accuracy required for each electronic component can be reduced, so that there is an effect that the manufacturing cost is reduced. In addition, since the initial assembly value is stored and the initial deviation is corrected, the reliability is improved, and the initial value is compared with the initial value during a sample hold period in which the steering torque is not detected. Since the failure of each part is detected, one system of the circuit can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of an electric power steering device to which a torque sensor according to the present invention is applied.

FIG. 2 is a perspective view of a cylindrical member and its periphery.

FIG. 3 is a cross-sectional view of a cylindrical member and an output shaft taken along line AA of FIG.

FIG. 4 is a sectional view of the cylindrical member and the output shaft taken along line BB of FIG.

FIG. 5 is a circuit diagram illustrating an example of a motor control circuit.

FIG. 6 is a diagram for explaining the operation of the square wave drive.

FIG. 7 is a timing chart showing the operation timing of the present invention.

FIG. 8 is a timing chart showing an example of a normal operation;

FIG. 9 is a timing chart showing an operation example when a failure is detected.

FIG. 10 is a waveform chart for explaining the operation of the present invention.

FIG. 11 is a configuration diagram showing a general configuration of an electric power steering device.

FIG. 12 is a block diagram showing an example of a control unit of the electric power steering device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering handle 6 Tie rod 12 Vehicle speed sensor 100 Torque sensor 102 Torsion bar 104 Cylindrical member 110,111 Coil 200 Control unit 203 Memory 220 Torque detection unit 223 Differential amplifier 224 Neutral voltage switching unit 225 Sample hold circuit 230 Operation unit (MPU) 240 neutral signal storage

Claims (4)

[Claims] 1. A control operation unit for varying a drive timing and a sample hold timing of a coil for detecting a torque, and a storage unit for storing initial values of respective units of a sensor, wherein sampling of a transient voltage of the coil is performed. While detecting the torque based on the torque, and between the sample and hold where the torque detection is not performed, a failure of each part of the sensor is detected by comparing with the initial value of the storage unit. Torque sensor. 2. An electric power steering apparatus which detects a steering torque of a steering wheel and applies an auxiliary load by a motor to a steering shaft provided integrally with the steering wheel in accordance with the steering torque. In the torque sensor of the present invention, the steering torque is detected based on sampling of a transient voltage of a coil, and a control operation unit capable of changing a drive timing of the coil and a timing of a sample hold is provided. A storage unit for storing the initial values of the above, and between the sample hold in which the steering torque is not detected, a failure of each of the units is detected by comparing with the initial values. Torque sensor. 3. A failure in a coil voltage, a differential amplifier and a hold amplifier is detected based on an A / D value after the sample hold at a timing when the coil is not driven. 3. The torque sensor according to 2. 4. The apparatus according to claim 3, wherein a fault in the neutral voltage section of the differential amplifier and a failure in the sample hold section of the hold amplifier are detected based on the A / D value after the neutral voltage switching. 2. The torque sensor according to 1.