JP4024130B2 - Torque sensor temperature compensation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a temperature compensation device in a torque sensor that detects torque based on an inductance change of a pair of coils connected to an AC power supply.
[0002]
[Prior art]
In such a torque sensor, the coil itself has temperature characteristics, and a temperature displacement due to thermal expansion of a component of the torque sensor, such as a housing of the coil holding portion, affects the torque sensor detection output, thereby preventing accurate torque detection. ing.
[0003]
Therefore, there is an example in which a temperature sensor dedicated to temperature detection such as a thermistor is attached to the torque sensor (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP 2002-148128 A (paragraph [0024])
[0005]
In Patent Document 1, a thermistor is inserted into one of a pair of coils and a pair of resistors constituting a bridge circuit, and at least only a temperature change of the bridge circuit is compensated.
[0006]
In the case of Patent Document 1, an oscillation output terminal of a control board is connected to a pair of coils so that alternating current is supplied from an alternating current power source, but the specific structure is not clear.
[0007]
[Problems to be solved by the invention]
If this AC power supply is not stable with respect to temperature, highly accurate torque cannot be detected even if temperature compensation on the circuit is performed.
[0008]
The present invention has been made in view of such a point, and the purpose of the present invention is to compensate the temperature of a torque sensor that allows an AC power supply to detect a highly accurate torque by supplying a stable AC voltage with respect to temperature. The point is to provide the device.
[0009]
[Means for solving the problems and effects]
In order to achieve the above-mentioned object, the invention according to claim 1 includes a pair of coils connected to an AC power source through a transistor and having inductances that change in opposite directions according to torque, and each inductance of the pair of coils. A torque sensor comprising a torque detection means for obtaining a voltage difference between the first and second voltages output via the smoothing circuit based on the change and outputting the difference as a torque detection voltage. Another pair of rectification conversion circuits that respectively output a first correction voltage and a second correction voltage based on the above, an adding means for adding the first correction voltage and the second correction voltage to obtain a temperature correction voltage, Correction means for correcting the torque detection voltage based on the temperature correction voltage output from the addition means, and an emitter terminal connected to the pair of coils. Kuta terminal connected to the emitter terminal of the PNP transistor with the DC power supply to the base terminal of an NPN transistor connected to a DC power source and a temperature compensating device of a torque sensor connected to AC power supply to the base terminal of the PNP-type transistor.
[0010]
Each inductance of the pair of coils of the torque sensor has a temperature characteristic. Since the voltage difference between the first voltage and the second voltage according to the induced electromotive force of each coil is used as the torque detection voltage, each coil The temperature change is substantially canceled and does not affect the torque detection voltage.
[0011]
The temperature displacement due to thermal expansion of the components of the torque sensor, for example, the housing of the coil holding part, etc. is compensated by correcting the torque detection voltage based on the temperature correction voltage by the correction means, but the AC power supply is not stable The temperature correction voltage itself is affected and accurate correction cannot be made.
[0012]
Therefore, the temperature characteristics of the voltage in an AC power supply with only an NPN transistor are combined into a PNP transistor in a cascade to provide an AC power supply that can supply a stable voltage that is not affected by temperature, and the torque detection voltage is accurately corrected to a high level. Accurate torque can be detected.
[0013]
According to a second aspect of the present invention, in the temperature compensation device for a torque sensor according to the first aspect, the rectification conversion circuit is a smoothing circuit that smoothes an alternating voltage.
[0014]
The first and second correction voltages obtained by smoothing the AC voltage with a simple smoothing circuit can be easily obtained.
[0015]
According to a third aspect of the present invention, in the temperature compensation device for a torque sensor according to the first aspect, the rectification conversion circuit is a filter circuit that extracts a direct current component from an alternating current voltage.
[0016]
The first and second correction voltages obtained by extracting the DC component from the AC voltage can be easily obtained by a simple filter circuit.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.
The torque sensor 1 according to the present embodiment is applied to a vehicle power steering apparatus, and its schematic structure is shown in FIG.
[0018]
An input shaft 3 and an output shaft 4 that are rotatably supported on the housing 2 via bearings 5 and 6 and are coaxially connected to each other are connected to each other by a torsion bar 7.
A cylindrical core 8 is serrated to the outer peripheral surface of the large-diameter end portion 4 a of the output shaft 4, is slidable only in the axial direction with respect to the output shaft 4, and is a slider protruding from the input shaft 3 The pin 9 is engaged with the spiral groove 8a of the core 8 through a long hole extending in the circumferential direction of the large-diameter end 4a.
[0019]
Two torque detection coils 11 and 12 supported inside the housing 2 are provided on the outer periphery of a cylindrical core 8 that slides in the axial direction via a gap.
The two coils 11 and 12 are arranged on opposite sides with respect to the axial movement center of the core 8.
[0020]
When a torsional force acts on the input shaft 3, a rotational force is transmitted to the output shaft 4 through the torsion bar 7, but the torsion bar 7 is elastically deformed and rotates between the input shaft 3 and the output shaft 4. A relative displacement in direction occurs.
The relative displacement in the rotational direction causes the core 8 to slide in the axial direction through the engagement between the slider pin 9 and the spiral groove 8a.
[0021]
When the core 8 moves in the axial direction, the area surrounding the core 8 of each of the coils 11 and 12 changes, and when one area increases, the other area decreases.
When the area surrounding the core 8 increases, the magnetic loss increases and the inductance of the coil decreases. Conversely, when the area surrounding the core 8 decreases, the magnetic loss decreases and the inductance of the coil increases.
[0022]
Therefore, when the torque that moves the core 8 toward the coil 11 acts, the inductance L1 of the coil 11 decreases, the inductance L2 of the coil 12 increases, and conversely, the torque that moves the core 8 toward the coil 12 acts. When the inductance L1 of the coil 11 increases, the inductance L2 of the coil 12 decreases.
[0023]
An electric circuit for detecting torque based on changes in the inductances L1 and L2 of the coils 11 and 12 of the torque sensor 1 is shown in FIG. 2 as a schematic configuration diagram.
The coils 11 and 12 are connected at one end to each other, signal lines extend from the connection ends and the other ends, and are connected to a connection terminal of a torque detection circuit 20 provided in the electronic control unit ECU.
[0024]
In the torque detection circuit 20, the connection ends of the coils 11 and 12 are grounded, and the other ends are connected to the emitter terminal of the NPN transistor 51 of the AC power supply circuit 50 via the resistors 13 and 14, respectively.
[0025]
The AC power supply circuit 50 has a configuration in which a PNP transistor 52 is further connected in series with an NPN transistor 51.
That is, in the NPN transistor 51, a constant voltage is applied to the collector terminal, and the emitter terminal of the PNP transistor 52 whose collector is grounded is connected to the base terminal via the resistor 53.
[0026]
A constant voltage is applied to the emitter terminal of the PNP transistor 52 via the resistor 54, and an AC voltage is input to the base terminal.
The NPN transistor 51 and the PNP transistor 52 have the characteristics that the temperature characteristics of the output voltage are opposite to each other, and the output voltage of the PNP transistor 52 tends to decrease with increasing temperature, whereas the NPN transistor 51 output voltage is increasing.
[0027]
Therefore, by using the NPN transistor 51 and the PNP transistor 52 connected in series, the temperature characteristics of the AC power supply circuit 50 can be compensated with the temperature characteristic of the final stage output voltage constant.
[0028]
The voltage signal line 16 extending from the connection portion of the resistor 13 and the coil 11 to which the output voltage of the AC power supply circuit 50 is applied is connected to the smoothing circuit 23 via the capacitor 21 and extends from the connection portion of the coil 12 and the resistor 14. The voltage signal line 17 is connected to the smoothing circuit 24 via the capacitor 22.
[0029]
That is, a bridge circuit is constituted by the coils 11 and 12 and the resistors 13 and 14, an oscillation voltage is input to the bridge circuit, an output voltage thereof is input to the smoothing circuits 23 and 24, and is smoothed to obtain the first and second voltages V. is output as _{1, V 2.}
[0030]
The first and second voltages V ₁ and V ₂ are input to the inverting input terminal and the non-inverting input terminal of a differential amplifier 27, which is an operational amplifier, via resistors 25 and 26, respectively.
The differential amplifier 27 is negatively fed back by a resistor 28 to function as a differential amplifier, and its output is input to the CPU 30 as a torque detection voltage Vt.
The bias voltage V ₀ is input to the non-inverting input terminal of the differential amplifier 27.
[0031]
Therefore the differential amplifier 27, the first voltages V ₁ and multiplied by the amplification degree A second difference between the voltage V _2, and outputs a voltage obtained by adding a bias voltage V ₀ as the torque detection voltage Vt.
That is, the torque detection voltage Vt is
Vt = (V ₂ −V ₁ ) · A + V ₀
It is.
[0032]
The neutral torque detection voltage Vt that is not biased to either the right steering torque (right torsion torque) or the left steering torque (left torsion torque) is referred to as a neutral point voltage. the voltage V ₀ becomes a neutral point voltage.
[0033]
The torque sensor 1 has a schematic circuit configuration as described above, and its operation will be described below with reference to FIG. 3 showing the states of the first and second voltages V ₁ and V ₂ and the torque detection voltage Vt.
In the coordinates shown in FIG. 3, the vertical axis is voltage, the horizontal axis right direction is right steering torque, and the horizontal axis left direction is left steering torque, and the origin 0 is a neutral point.
[0034]
FIG. 3 shows the torque sensor 1 operating normally. When the right steering torque increases, the core 8 moves to the coil 11 side due to the relative rotation of the input shaft 3 and the output shaft 4, and the inductance of the coil 12. L2 increases and the larger the induced electromotive force, so to reduce the induced electromotive force by reducing the inductance L1 of the coil 11 in the opposite, second voltage V ₂ increases, the first voltage V ₁ is smaller (See Fig. 3 (1)).
[0035]
In the case where the left steering torque is increased, the second voltage V ₂ is reduced contrary to the first voltage V ₁ is increased (see ▼ FIG 3 ▲ 1).
Therefore, the torque detection voltage Vt, which is the output of the differential amplifier 27 obtained by multiplying the difference between the two by A and adding the bias voltage, is a slope that rises to the right passing through the bias voltage V ₀ at the neutral point as shown in FIG. Become a line.
[0036]
The steering torque to the left and right can be detected from the torque detection voltage Vt based on the slope line of the torque detection voltage Vt shown in the graph of FIG.
[0037]
The CPU 30 outputs a motor control instruction signal to the motor driver 31 based on the torque detection voltage Vt, and the motor 32 that assists steering is driven by the motor driver 31.
Therefore, the assist of the motor 32 corresponding to the steering torque is obtained in the steering operation.
[0038]
In the power steering control mechanism as described above, the influence of the temperature of the torque sensor 1 is inevitable.
Since the torque detection voltage Vt is obtained from the voltage difference between the first voltage V ₁ and the second voltage V ₂ , the temperature changes of the coils 11 and 12 themselves cancel each other and almost affect the torque detection voltage Vt. Although the distortion due to the thermal expansion of the structural parts such as the core 8 and the slider pin 9 of the torque sensor 1 and the housing 2 affects the first and second voltages V ₁ and V ₂ separately, the torque detection voltage Vt is It fluctuates and accurate torque cannot be obtained.
[0039]
Therefore, a temperature compensation circuit 40 is attached to the torque sensor 1.
As shown in FIG. 2, the voltage signal lines 41 and 42 branched from the voltage signal lines 16 and 17 are connected to the smoothing circuits 43 and 44, respectively, and the smoothing circuits 43 and 44 are connected to each other through the resistors 45 and 46, respectively. The connection point is connected to the non-inverting input terminal of the adder 47 which is an operational amplifier.
[0040]
The inverting input terminal of the adder 47 is connected to the output terminal via the resistor 48 and grounded via the resistor 49, and the adder 47 receives the first and second correction voltages U ₁ and U ₂ that are input voltages. The sum U ₁ + U ₂ is output to the CPU 30 as the temperature correction voltage Vs.
[0041]
The temperature correction voltage Vs which is the sum U ₁ + U ₂ of the first and second correction voltages U ₁ and U ₂ of the temperature compensation circuit 40 shows a substantially constant value regardless of the steering torque if the temperature is constant.
[0042]
The temperature correction voltage Vs, which is the output of the adder 47, varies depending on the temperature.
Assume that the temperature characteristics of the temperature correction voltage Vs when the left and right steering are in a neutral state are as shown in FIG.
[0043]
However, the temperature characteristic of the temperature correction voltage Vs is a characteristic determined when the output value of the AC power supply voltage is stable at a constant value. When the AC power supply voltage itself changes with temperature, the temperature characteristic curve of FIG. Therefore, although the temperature cannot be accurately detected and dealt with from the temperature correction voltage Vs, the AC power supply circuit 50 has the NPN transistor 51 and the PNP transistor 52 connected in series as described above. By using it, the temperature characteristic of the final stage output voltage is kept at a substantially constant value, so that an accurate temperature can be obtained based on the temperature characteristic of the temperature correction voltage Vs detected by the temperature compensation circuit 40. I can do it.
[0044]
On the other hand the left and right steering even for torque detection voltage Vt temperature characteristic of the torque detection voltage Vt ₀ at a neutral state, and was as shown in FIG. 5, for example.
A normal voltage in the neutral state of the torque detection voltage Vt is a constant value at the bias voltage V ₀ , but shows a temperature characteristic curve (substantially straight line) that is inclined due to the influence of the temperature of the torque sensor constituent member and the like. .
[0045]
In FIG. 5, a voltage difference ΔV (= Vt ₀ −V ₀ ) between the torque detection voltage Vt ₀ and the bias voltage V ₀ at a certain temperature is a temperature correction value at that temperature.
[0046]
Therefore, the temperature t can be detected from the temperature correction voltage Vs by the temperature characteristic of FIG. 4 and the temperature correction value ΔV can be derived from the detected temperature t by the temperature characteristic curve of FIG. By changing the temperature, the correspondence between the temperature correction voltage Vs and the temperature correction value ΔV is directly measured and recorded in the memory 33.
[0047]
FIG. 6 shows the correspondence between the temperature correction voltage Vs measured in advance and recorded in the memory 33 and the temperature correction value ΔV.
The corresponding temperature correction value ΔV is directly extracted from the temperature correction voltage Vs by collating with this correspondence.
[0048]
The torque detection voltage Vt actually detected by the torque detection circuit 20 is corrected to Vt + ΔV by adding the temperature correction value ΔV.
The actual steering torque is detected from the corrected torque detection voltage Vt + ΔV based on FIG.
[0049]
Therefore, when the temperature correction voltage Vs detected from the temperature compensation circuit 40 is input to the CPU 30, the CPU 30 checks the correspondence relationship between the temperature correction voltage Vs recorded in the memory 33 and the temperature correction value ΔV. The temperature correction value ΔV to be extracted is extracted, the torque detection voltage Vt input separately by the temperature correction value ΔV is corrected, the temperature change depending on other components other than the temperature change of the coil itself, and the AC power supply circuit 50 Accurate steering torque that is not affected by temperature changes can be detected and used to drive the motor 32.
[0050]
The temperature compensation device of the torque sensor 1 according to the present embodiment is configured as described above, and the temperature compensation circuit 40 may be disposed in the electronic control unit ECU or the like, and need not be attached to the torque sensor.
[0051]
This eliminates the need for special substrates and holding parts, and reduces the number of parts, thereby reducing costs.
In addition, since a temperature sensor such as a thermistor dedicated to temperature detection is not used, the cost can be further reduced.
[0052]
If only the correspondence between the temperature correction voltage Vs and the temperature correction value ΔV is recorded, the temperature characteristic of the temperature correction voltage Vs (FIG. 4) and the temperature characteristic of the torque detection voltage Vt ₀ (FIG. 5) are measured. There is no need to record them, the control procedure is simplified, and errors are less likely to occur.
[0053]
The temperature correction value ΔV is directly calculated from the temperature correction voltage Vs detected from the temperature compensation circuit 40 by the calculation means based on the correspondence between the temperature correction voltage Vs recorded in the memory 33 and the temperature correction value ΔV. It can also be calculated.
[0054]
In the above embodiment, the temperature correction voltage Vs is input to the CPU 30. However, the temperature correction voltage Vs is appropriately changed to directly apply to the non-inverting input terminal of the differential amplifier 27 of the torque detection circuit 20. As a bias voltage, the torque detection voltage Vt may always be in a fixed relation to the steering torque (see (2) in FIG. 3) regardless of the temperature.
[0055]
In the temperature compensation circuit 40 in the above embodiment, the voltage signal lines 41 and 42 extend from the pair of coils 11 and 12, respectively, and are connected to the smoothing circuits 43 and 44. It is also possible to remove the line so that only the other smoothing circuit is used, and the output of the smoothing circuit is the temperature correction voltage Vs.
[0056]
In that case, the correspondence between the temperature correction voltage Vs and the temperature correction value ΔV of the smoothing circuit remaining by changing the temperature in advance is directly measured and recorded in the memory 33, so that this correspondence can be verified. The corresponding temperature correction value ΔV is directly extracted from the temperature correction voltage Vs, and the torque detection voltage Vt can be corrected by this temperature correction value ΔV to compensate the temperature.
[0057]
The first and second correction voltages U ₁ and U ₂ input to the non-inverting input terminal of the adder 47 of the temperature compensation circuit 40 may be input from the outputs of the smoothing circuits 23 and 24 of the torque detection circuit 20. (In this case, the capacitors 21 and 22 are omitted). By doing so, the smoothing circuits 43 and 44 of the temperature compensation circuit 40 can be omitted, and the number of components can be further reduced.
[0058]
In the temperature compensation circuit 40, the AC voltage is smoothed by the smoothing circuits 43 and 44 to obtain the first and second correction voltages U ₁ and U ₂ , but the DC component is extracted from the AC voltage by a pair of filter circuits. The first and second correction voltages may be used.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a mechanical part of a torque sensor according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of an electric circuit of the torque sensor.
FIG. 3 is a diagram illustrating a state of first and second voltages and a torque detection voltage at a normal time.
FIG. 4 is a diagram illustrating an example of a temperature characteristic of a temperature detection voltage.
FIG. 5 is a diagram illustrating an example of a temperature characteristic of a torque detection voltage in a neutral state.
FIG. 6 is a diagram showing a correspondence relationship between a temperature correction voltage Vs measured in advance and recorded in a memory, and a temperature correction value ΔV.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Torque sensor, 2 ... Housing, 3 ... Input shaft, 4 ... Output shaft, 5, 6 ... Bearing, 7 ... Torsion bar, 8 ... Core, 9 ... Slider pin,
11,12 ... coil, 13,14 ... resistor, 16,17 ... voltage signal line,
20 ... Torque detection circuit, 21, 22 ... Capacitor, 23, 24 ... Smoothing circuit, 25, 26 ... Resistance, 27 ... Differential amplifier, 28 ... Resistance,
30 ... CPU, 31 ... motor driver, 32 ... motor, 33 ... memory,
40 ... temperature compensation circuit, 41, 42 ... voltage signal line, 43, 44 ... smoothing circuit, 45, 46 ... resistor, 47 ... adder, 48, 49 ... resistor.
50 ... AC power supply circuit, 51 ... NPN transistor, 52 ... PNP transistor, 53, 54 ... resistor.

Claims (3)

A pair of coils connected to an AC power source via a transistor and having inductances that change in opposite directions according to torque;
A torque sensor comprising torque detecting means for obtaining a voltage difference between the first and second voltages output via the smoothing circuit based on each inductance change of the pair of coils and outputting as a torque detection voltage,
Another pair of rectification conversion circuits that respectively output a first correction voltage and a second correction voltage based on respective inductance changes of the pair of coils;
Adding means for adding the first correction voltage and the second correction voltage to obtain a temperature correction voltage;
Correction means for correcting the torque detection voltage based on the temperature correction voltage output from the addition means,
Connecting the emitter terminal of the PNP transistor together with the DC power source to the base terminal of the NPN transistor having the emitter terminal connected to the pair of coils and the collector terminal connected to the DC power source;
A temperature compensation device for a torque sensor, wherein an AC power supply is connected to a base terminal of the PNP transistor. 2. The temperature compensation device for a torque sensor according to claim 1, wherein the rectification conversion circuit is a smoothing circuit for smoothing an AC voltage. The temperature compensation device for a torque sensor according to claim 1, wherein the rectification conversion circuit is a filter circuit that extracts a direct current component from an alternating voltage.

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