JP2001281081A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a torque sensor wherein the abnormal torque signal is processed with no load on a microcomputer. SOLUTION: A torque sensor is provided which comprises a coil L where an inductance changes according to the change of torque acting on an object and detects the torque based on the inductance. Here, there are provided oscillation circuits 22 and 23 which detect the inductance of the coil and oscillate a torque signal having a cycle corresponding to the inductance, a torque calculating means for calculating the torque from the torque signal oscillated by the oscillation circuit, a torque signal counting means for counting the torque signal oscillated by the oscillation circuit, a torque signal checking means for checking abnormality of the torque signal by a first timer whose cycle is longer than that of the torque signal, and a torque signal abnormality processing means for processing abnormality of the torque signal by a second timer whose cycle is longer than that of the first timer.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque sensor usable for electric power steering and the like.

[Prior art]

Conventionally, as a torque sensor, for example, FIG.
There is known a steering mechanism shown in FIG. The steering mechanism 10 includes a hollow shaft 11 connected to a steering handle of a vehicle (not shown), and a lower portion of the shaft 11 is inserted into an upper portion 12 a of the housing 12. A shaft 1 is provided on a lower portion 12b of the housing 12.
An upper portion of the shaft 3 is inserted, and a pinion 14 that meshes with the rack R is provided at a lower portion of the shaft 13. A rack (not shown) for assisting the steering force is provided on the rack R.
Data is provided.

[0002] A torsion bar 1 is provided inside a shaft 11.
5 is accommodated, and the upper end of the torsion bar 15 is connected to the shaft 11 by a pin 16. The lower end of the torsion bar 15 is spline-engaged with the inside of the shaft 13.

[0003] Further, inside the housing 12,
The sensor ring 17 made of a magnetic material is used for the shaft 1.
1, a sensor ring 18 made of a magnetic material is provided on the shaft 13. A coil 19 is provided at a position facing the outer peripheral surface of the sensor rings 17 and 18 with a predetermined gap from each of the sensor rings 17 and 18.

[0004] The coil 19 is connected to an interface circuit (hereinafter, referred to as an I / F circuit) 80.
The F circuit 80 is a microcomputer (not shown)
It is called a microcomputer. )It is connected to the.

In this steering mechanism 10, when torque is transmitted to the shaft 11 by operating the steering wheel, the torsion bar 15 is twisted, so that the shaft 11 and the shaft 1 are rotated.
3, a relative displacement occurs. As a result, the circumferential overlapping amounts of the sensor rings 17 and 18 are displaced, and the inductance of the coil 19 changes. This change in inductance is input to the microcomputer via the I / F circuit 80 shown in FIG.

[0006] The coil 19, a DC power supply 81 and an A / D conversion circuit 91 are connected to the I / F circuit 80. Also,
The I / F circuit 80 includes a filter circuit 82, a regulator circuit 83, a transmission circuit 84, a DC cut circuit 85, a detection circuit 86, a subtraction circuit 87, a temperature compensation circuit 88, a scaling circuit 89, and an output amplifier circuit 90. .

[0007] The DC current supplied from the DC power supply 81 is:
An excess harmonic component is removed by the filter circuit 82 and sent to the regulator circuit 83. The regulator circuit 83 generates a reference voltage.
4 and a scaling circuit 89. Transmission circuit 8
4 generates a sine wave signal based on the reference voltage, and the sine wave signal is applied to the coil 19. As a result, a sine wave voltage proportional to the inductance of the coil 19 is generated at both ends of the coil 19.

The sine wave voltage generated at both ends of the coil 19 is input to a DC cut circuit 85. The DC cut circuit 85 extracts an AC component of the sine wave voltage, and the AC component is input to the detection circuit 86. The detection circuit 86 converts the AC component into a signal having a DC voltage proportional to the amplitude of the AC component, and outputs this signal to the subtraction circuit 87.

The sine wave voltage generated at both ends of the coil 19 is also input to a temperature compensation circuit 88. The temperature compensation circuit 88 extracts a temperature drift signal indicating the amount by which the inductance of the coil 19 drifts under the influence of the temperature, based on the sine wave voltage. Then, this temperature drift signal is output to the subtraction circuit 87.

[0010] Then, a subtraction circuit 87 extracts a difference between the signal output from the detection circuit 86 and the temperature drift signal output from the temperature compensation circuit 88. That is, a torque component signal of only the torque component in which the temperature drift component is canceled is generated. This torque component signal is input to the scaling circuit 89. In the scaling circuit 89,
The gain of the torque component signal is converted, and the converted torque component signal is amplified by the output amplifier circuit 90. This torque component signal is input to the A / D conversion circuit 91 as a torque signal. In the A / D conversion circuit 91, the torque signal is converted from an analog signal to a digital signal, and the converted torque signal is input to a microcomputer provided in the vehicle.

The microcomputer calculates an assist amount of the steering mechanism 10 based on the magnitude of the input torque signal, and outputs a drive signal corresponding to the assist amount to a motor drive circuit (not shown). The motor drive circuit rotates a motor (not shown) based on the commanded drive signal. Thus, the steering mechanism 10 is assisted.

[0012]

However, in the above-mentioned conventional torque sensor, the oscillation circuit 84 for applying a sine wave signal to the coil 19, the DC cut circuit 85 for detecting the inductance of the coil 19 as torque, and the detection circuit Since many circuits such as the circuit 86 are required, it hinders the improvement of the reliability of the torque sensor. Further, since the torque signal output from the output amplifier circuit 90 is an analog signal, even if a voltage drop occurs, the torque cannot be detected unless the operating voltage of the microcomputer does not become lower. Therefore, there is a problem that a DC power supply 81 for supplying a voltage (for example, 8 V) higher than the operating voltage (for example, 5 V) of the microcomputer to the oscillation circuit 84 must be separately provided.

[0013] In this respect, Japanese Patent Application No.
As in -263988, a torque sensor that directly inputs a torque signal to a microcomputer using an LR oscillation circuit or the like can be considered. In this torque sensor, since the inductance of the coil that changes in response to the change in torque is used, an oscillation circuit for applying a sine wave to the coil is not required, and the circuit configuration can be simplified.
Further, since a signal oscillated from the LR oscillation circuit of the I / F circuit can be directly input to the microcomputer via the pulse shaping circuit, an A / D conversion circuit is not required, which can also simplify the circuit configuration. . On the other hand, by providing an intermediate tap in the coil and providing a rare short detection circuit in the I / F circuit, a rare short in the coil can be detected. From these facts, according to this torque sensor, the reliability of the torque sensor can be improved and the manufacturing cost can be reduced.

However, even with a torque sensor that directly inputs such a torque signal to a microcomputer using an LR oscillation circuit or the like, there may be cases where the processing of the microcomputer is not appropriate due to abnormal processing. That is, if the microcomputer performs the abnormality check processing every time the microcomputer takes in the torque signal, the torque signal is generated at a high speed, and this processing alone occupies much of the execution capability of the microcomputer. In particular, when a part of the coil is short-circuited or a rare short-circuit occurs, the torque signal is generated at a higher speed. For this reason, a situation in which the microcomputer can hardly perform any processing other than the torque signal may occur. When such a situation occurs, a pulse signal is not output to the watchdog timer circuit (see Japanese Patent Application Laid-Open No. H08-211909), and the microcomputer is reset. As a result, various services provided by the microcomputer to the driver are stopped, and comfortable steering is not ensured.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a torque sensor capable of performing abnormal processing of a torque signal without applying a load to a microcomputer. I have.

[0016]

According to the present invention, there is provided a torque sensor having a coil whose inductance changes in response to a change in torque acting on an object, and detecting the torque based on the inductance. An oscillation circuit that detects an inductance of the coil and oscillates a torque signal having a cycle corresponding to the inductance;
Torque calculating means for calculating the torque based on the torque signal oscillated by the oscillating circuit; torque signal counting means for counting the torque signal oscillated by the oscillating circuit; A torque signal checking unit for checking an abnormality of the torque signal by a first timer, and a torque signal abnormality processing unit for performing an abnormal process of a torque signal by a second timer having a period longer than the period of the first timer. It is characterized by.

In the torque sensor according to the present invention, the torque signal checking means checks the abnormality of the torque signal by the first timer having a cycle longer than the cycle of the torque signal. Further, the torque signal abnormality processing means performs the abnormality processing of the torque signal by the second timer having a cycle longer than the cycle of the first timer. Therefore, the microcomputer cannot occupy much of its execution ability for processing the torque signal. Therefore, according to the torque sensor of the present invention, abnormal processing of the torque signal can be performed without applying a load to the microcomputer. For this reason,
If this torque sensor is used for a steering mechanism,
The steering performance can be made comfortable.

In the torque sensor according to the present invention, it is preferable that the torque signal abnormality processing means has a security means for stopping the torque calculation means and the torque signal counting means based on the torque signal. In this case, the microcomputer is not reset even if an abnormality occurs such that the frequency of the torque signal becomes extremely high.

Further, in the torque sensor of the present invention, the detection range of the inductance is divided into a plurality of parts by taps on the coil, and a signal detected from one of the divided ranges is provided by:
It is also possible to have a comparing means for comparing a signal detected from another divided range, and a rare short detecting means for detecting a rare short of the coil based on a comparison result of the comparing means. This allows water to enter the circuit,
Rare shorts caused by wiring deterioration, wiring scratches, and the like can be detected. For this reason, if it is used for a steering mechanism, the driver can quickly grasp the situation of the vehicle.

Further, the torque sensor of the present invention comprises: a DC component detecting means for detecting a DC component of the coil; and a temperature compensating means for temperature-compensating the torque based on the DC component detected by the DC component detecting means. It can also have. Thus, it is not necessary to provide a coil for temperature compensation, so that the size and cost of the torque sensor can be reduced. Further, since the DC component of the coil is used, the temperature of the torque can be compensated without being affected by the signal fluctuation generated in the coil.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. As shown in FIG. 1, the torque sensor according to the present embodiment includes a sensor unit 32, an I / F circuit 20 connected to the sensor unit 32, and a microcomputer 31 connected to the I / F circuit 20. Is done. The external configurations of the sensor unit 32 and the I / F circuit 20 are the same as those shown in FIG.

In the sensor section 32, an intermediate tap P is provided at a position where the coil L is bisected, and the coil L is divided into two by the intermediate tap P into a coil L1 and a coil L2.

The I / F circuit 20 comprises a torque detecting circuit 21 for detecting torque and a fail detecting circuit 25 for detecting a rare short of the coil L. The torque detection circuit 21 has an LR oscillation circuit 22, a pulse shaping circuit 23, and a temperature detection circuit 24. Where L
The R oscillation circuit 22 and the pulse shaping circuit 23 are oscillation circuits, and the temperature detection circuit 24 is DC component detection means. The fail detecting circuit 25 is a rare short detecting circuit 30.
And a differential amplifier circuit 29. Here, the rare short detection circuit 30 and the differential amplifier circuit 29 are comparison means. The microcomputer 31 has a watchdog timer circuit 40. Here, the watchdog timer circuit 40 is a security means.

LR oscillation circuit 22 of torque detection circuit 21
Is the inductance of the coil L, as shown in FIG.
This is an application of a hysteresis comparator operation that oscillates a signal based on the resistance R1 of the LR oscillation circuit 22.
The resistors R2 and R3 are bias circuits for establishing oscillation, and the resistors R4 and R5 determine a threshold voltage. The signal oscillated by the oscillation circuit 22 is output from the comparator 22a.

As shown in FIG. 1, the pulse shaping circuit 23
The microcomputer 31 shapes the waveform of the signal output from the LR oscillation circuit 22 and uses the shaped signal as a torque signal.
To the timer input 31a. This torque signal is used by the microcomputer 31 to calculate the steering torque.

The temperature detecting circuit 24 extracts a DC component from the AC / DC superimposed signal generated in the coil L, adds necessary scaling to the extracted DC component, and outputs a signal obtained by adding this scaling to a temperature characteristic signal (hereinafter, referred to as a temperature characteristic signal). , A temperature characteristic signal) to the A / D input 31b of the microcomputer 31. The temperature characteristic signal is used by the microcomputer 31 as temperature compensation when calculating the steering torque.

As shown in FIG. 3, the rare short detecting circuit 30 of the fail detecting circuit 25 extracts the DC components of the AC / DC superimposed signal generated in the entire coil L and the intermediate tap P, and outputs the DC components via the amplifiers 30a and 30b. , To the differential amplifier circuit 29 shown in FIG. That is, as shown in FIG. 3, a DC component of the AC / DC superimposed signal generated from one end of the coil L is extracted by the resistor R6 and the capacitor C1, and the extracted DC component is passed through the amplifier 30a to the differential amplifier circuit. 29. A DC component of the AC / DC superimposed signal generated from the intermediate tap P is extracted by the resistor R7 and the capacitor C2, and the extracted DC component is amplified twice by the amplifier 30b, and the amplified DC component is The signal is output to the differential amplifier circuit 29.

Also, as shown in FIG.
9 differentially amplifies the signal output from the rare short detection circuit 30, and outputs the differentially amplified signal to the A / D input 31d of the microcomputer 31 as a monitor signal.

The microcomputer 31 periodically outputs a pulse from the WDT output 31e to the watchdog timer circuit 40. When the pulse output from the WDT output 31e stops for a predetermined time or more, the watchdog timer circuit 40
When it is determined that an abnormality has occurred in the microcomputer 31, the microcomputer 3
A reset signal is output to one reset input 31f. Then, the microcomputer 31 is forcibly returned to the initial state by the reset signal. In this way, runaway of the microcomputer is avoided, and the safety of the entire system is ensured.

Next, the contents of the torque calculation processing of the microcomputer 31 will be described.

First, when the steering wheel of the vehicle is operated, a relative displacement occurs between the shaft 11 and the shaft 13 shown in FIG. 9, and the displacement causes the coil L shown in FIG.
Changes in inductance. Then, the changed inductance is applied to the LR oscillation circuit 22 of the torque detection circuit 21.
The LR oscillation circuit 22 oscillates a signal having a period proportional to the inductance. This signal is waveform-shaped by the pulse shaping circuit 23 and input to the timer input 31a of the microcomputer 31 as a torque signal.

In the torque calculation process of the microcomputer 31, as shown in FIG. 4, first, in step S40, a cycle T of the torque signal is calculated. That is, as shown in FIG. 1, the torque signal from the I / F circuit 20 is
From the timer input 31a. Then, a cycle T of the torque signal is calculated based on the input torque signal.

In step S41, as shown in FIG.
The temperature characteristic signal from the I / F circuit 20 is the A / D of the microcomputer 31
It is input from input 31b. Then, the digital value of the A / D converted temperature characteristic signal is set to V1. Here, step S41 is the temperature compensating means.

In step S42, the period T of the torque signal
Then, the temperature-compensated torque is calculated based on the temperature characteristic signal V1. The calculation of this torque is performed as follows. First, a first table in which the cycle T of the torque signal is associated with the torque and a second table in which the temperature characteristic signal V1 is associated with the temperature compensation torque are stored in the memory in advance. Then, the temperature-compensated torque is obtained by adding the torque obtained from the first table based on the period T of the torque signal and the temperature compensation torque obtained from the second table based on the temperature characteristic signal V1. Here, steps S40 and S42
Is a torque calculating means.

Next, the contents of the abnormality processing of the microcomputer 31 will be described with reference to FIGS.

As shown in FIG. 5, a torque signal from the I / F circuit 20 is input from a timer input 31a of the microcomputer 31. This torque signal is normal during t1, t
Between two, it is indicated that there is an abnormality. That is, when an abnormality such as short-circuit of the intermediate tap P occurs in the coil L, the oscillation frequency of the LR oscillation circuit 22 shown in FIGS. 1 and 2 increases. Since the cycle of the torque signal is shortened accordingly,
During t2, the torque signal becomes abnormal.

When the torque signal is input to the microcomputer 31, a torque signal interrupt occurs due to the rise and fall of the torque signal as shown in FIG. When a torque signal interruption occurs, a torque signal interruption process shown in FIG. 6 is performed. In the torque signal interruption processing, only the torque counter TCT is incremented in step S10. Here, step S10 is a torque signal counting means.

Next, as shown in FIG. 5, a timer 1 interrupt is generated by software at intervals longer than the cycle of the torque signal. When the timer 1 interrupt occurs, the timer 1 interrupt processing shown in FIG. 7 is performed. In the timer 1 interrupt processing, a torque counter TCT indicating the value of the torque signal counted in the torque signal interrupt processing is checked.

That is, if the value of the torque counter TCT is 3 or less at step S20 (YES), the process proceeds to step S20-1 to check whether the value of the torque counter TCT is not abnormally long. Here, when the value of the torque counter TCT is 2 or more (NO), it is determined that the torque signal is normal, and the process proceeds to step S22. When the value of the torque counter TCT is smaller than 2 (YES)
Since the number of interrupts is abnormally small, it is determined that the oscillation frequency is excessive due to disconnection, failure of the resistor, and the like, and the torque signal is abnormal, and the process proceeds to step S21.

In step S21, a torque abnormality flag TFL indicating abnormality of the coil L is set (TFL = 1), and the routine proceeds to step S22. Here, steps S20 to S2
2 is a torque signal checking means.

In step S22, a torque counter TCT indicating the value of the torque signal is cleared. The value of the torque counter TCT for determining that the torque signal is abnormal (3 in the present embodiment) differs depending on the setting of the timer 1 interrupt cycle.

Here, the functions of the torque counter TCT and the torque abnormality flag TFL will be described with reference to FIG. First,
The torque counter TCT counts a torque signal within an interval of a timer 1 interrupt. That is, the torque signal is counted until it is cleared by the timer 1 interrupt and until it is cleared by the next timer 1 interrupt. At this time, when an abnormality such as a short circuit occurs in the intermediate tap P of the coil L, the oscillation frequency of the LR oscillation circuit 22 shown in FIGS. 1 and 2 increases. Accordingly, the cycle of the torque signal is shortened, and the torque signal interrupt frequently occurs. Then, in the timer 1 interrupt processing, the torque counter T
If it is determined by checking CT that a torque signal abnormality has occurred, a torque abnormality flag TFL is set. Therefore, the torque abnormality flag TFL indicates whether the torque signal is normal or abnormal.

Next, a timer 2 interrupt is also generated by software at an interval longer than the period of the timer 1 interrupt. When the timer 2 interrupt occurs, the timer 2 interrupt processing shown in FIG. 8 is performed. In timer 2 interrupt processing, torque signal abnormality processing and rare short detection,
Perform processing.

First, in step S30, a torque abnormality flag TFL indicating whether the torque signal is normal or abnormal is checked. That is, when the torque abnormality flag TFL is 0 (YES), the torque signal is normal, and step S31 is performed.
Proceed to. If the torque abnormality flag TFL is not 0 (NO), the torque signal is abnormal, and the process proceeds to step S33.

In step S31, a monitor signal from the I / F circuit 20 is input from the A / D input 31d of the microcomputer 31, as shown in FIG. The digital value of the A / D converted monitor signal is set to V2.

In step S32, it is checked whether V2 is within a normal range. That is, when V2 is within the normal range (YES), it is determined that no rare short has occurred in the coil L, and the process proceeds to step S35. If V2 is not within the normal range (NO), it is determined that a rare short has occurred in the coil L, and step S34 is performed.
Proceed to. Here, steps S31 and S32 are rare short detecting means.

In step S33, a torque abnormality process is performed. That is, the warning lamp is turned on to call the driver's attention, and the torque signal interruption is prohibited. Then, the process proceeds to step S35. Here, steps S30 and S33 are torque signal abnormality processing means.

In step S34, a rare short process is performed. That is, the warning lamp is turned on to call the driver's attention. At this time, the inhibition of the torque signal interruption is not performed. Then, the process proceeds to step S35.

In step S35, a pulse is output to the watchdog timer circuit 40 shown in FIG. As a result, the reset output is not output from the watchdog timer circuit 40, and the microcomputer 31 can continue normal processing.

Therefore, according to the torque sensor of the present embodiment, the abnormality check processing of the torque signal is not performed by the torque signal interruption, so that much of the execution ability of the microcomputer is occupied by the torque signal interruption processing. Absent.

When an abnormality such as an increase in the frequency of the torque signal occurs, the interruption of the torque signal is prohibited, so that the microcomputer 31 is not occupied solely by the torque signal interruption processing. It is possible to avoid a situation in which resetting is performed. That is, when an abnormality occurs in the torque signal, the microcomputer 3
By performing the abnormal processing of the torque signal without resetting 1, it is possible to ensure comfortable steering.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a main electrical configuration of a torque sensor according to an embodiment.

FIG. 2 is a circuit diagram of an LR oscillation circuit according to the torque sensor of the embodiment.

FIG. 3 is a circuit diagram of a rare short detection circuit according to the torque sensor of the embodiment.

FIG. 4 is a flowchart of a torque calculation process according to the torque sensor of the embodiment.

FIG. 5 is a timing chart according to the torque sensor of the embodiment.

FIG. 6 is a flowchart of a torque signal interruption process according to the torque sensor of the embodiment.

FIG. 7 is a flowchart of a timer 1 interrupt process according to the torque sensor of the embodiment.

FIG. 8 is a flowchart of a timer 2 interrupt process according to the torque sensor of the embodiment.

FIG. 9 is a longitudinal sectional view of a steering mechanism of the vehicle.

FIG. 10 is a block diagram showing a main electrical configuration of a conventional torque sensor.

[Explanation of symbols]

L: coil 22, 23: oscillation circuit (22: LR oscillation circuit, 23: pulse shaping circuit) S40, S42: torque calculating means S10: torque signal counting means S20, S21, S22: torque signal checking means S30, S33: torque Signal abnormality processing means 40 ... security means (watchdog timer circuit) P ... tap (intermediate tap) 30, 29 ... comparison means (30 ... rare short detection circuit,
29: Differential amplifier circuit) S31, S32: Rare short detecting means 24: DC component detecting means (temperature detecting circuit) S41: Temperature compensating means

Claims (4)

[Claims] 1. A torque sensor having a coil whose inductance changes in response to a change in torque acting on an object, wherein the torque sensor detects the torque based on the inductance. An oscillating circuit for oscillating a torque signal having a corresponding cycle, a torque calculating means for calculating the torque based on the torque signal oscillated by the oscillating circuit, and a torque signal for counting the torque signal oscillated by the oscillating circuit Counting means, torque signal checking means for checking abnormality of the torque signal by a first timer having a cycle longer than the cycle of the torque signal, and torque signal checking means by a second timer having a cycle longer than the cycle of the first timer. And a torque signal abnormality processing means for performing abnormality processing. Sa. 2. The torque sensor according to claim 1, wherein the torque signal abnormality processing means includes a guarantee means for stopping the torque calculation means based on the torque signal and the torque signal counting means. 3. A detection means for dividing an inductance detection range into a plurality of parts by taps on a coil, and comparing a signal detected from one divided range with a signal detected from another divided range. 3. The torque sensor according to claim 1, further comprising: a rare short detecting unit configured to detect a rare short of the coil based on a comparison result of the comparing unit. 4. A DC component detecting means for detecting a DC component of a coil, and a temperature compensating means for temperature-compensating torque based on the DC component detected by the DC component detecting means. Item 3. The torque sensor according to item 1, 2 or 3.