JP3387337B2 - Torque sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque sensor for detecting a torque generated on a rotating shaft, and more particularly, to a torque sensor having a coil whose impedance changes according to the generated torque. In a torque sensor that detects a torque based on a change in impedance of the coil, the torque detection accuracy is further improved. [0002] As a conventional torque sensor, for example,
There is one disclosed in Japanese Utility Model Laid-Open No. 2-89338.
That is, in this conventional torque sensor, the torque acting on the rotating shaft is reflected on a change in the impedance of the coil, and the torque is detected by detecting the change in the impedance. In other words, the coil is arranged so as to surround the rotating shaft, and the impedance of the coil is changed according to the torque of the rotating shaft. Therefore, the impedance change is measured by measuring the terminal voltage of the coil. By doing so, the torque generated on the rotating shaft can be detected. [0004] In the above-described conventional torque sensor, the coil wound around the bobbin has an outer peripheral surface and both end surfaces made of iron so that magnetic flux does not leak. Is covered with a yoke member. However, since the end of the coil must be drawn out of the yoke member, a cutout is formed in the yoke member for drawing out the coil end. [0005] Then, the notch causes the magnetic field inside the coil to be non-uniform in the circumferential direction, so that the number of magnetic fluxes interlinking with the coil changes due to the phase difference between the coil and the rotating shaft. As a result, the impedance of the coil changes irrespective of the torque, and the detection accuracy of the torque is reduced accordingly. As in the torque sensor described in the above publication, two coils are provided so that the impedances change in opposite directions according to the torque, and a bridge circuit including the two coils is formed. If the torque is detected based on the difference between the two outputs, even if the impedance change due to a temperature change or the like can be canceled out by the differential, the impedance change due to the above notch will be amplified in reverse, and the torque detection will be performed. It is included in the value. SUMMARY OF THE INVENTION The present invention has been made in view of such unresolved problems of the prior art, and is capable of improving the torque detection accuracy by reducing the impedance change due to the notch as described above. It is intended to provide a sensor. [0008] In order to achieve the above object, a torque sensor according to the present invention connects first and second rotating shafts arranged coaxially through a torsion bar. A cylindrical member made of a conductive and non-magnetic material is integrally formed with the second rotating shaft in a rotating direction so as to surround an outer peripheral surface of the first rotating shaft; At least an enclosed portion surrounded by the cylindrical member is formed of a magnetic material; an axially extending groove is formed in the enclosed portion; and the cylindrical member has a relative rotational position with respect to the first rotation axis. A window is formed so that the degree of overlap with the groove changes in accordance with, a coil is disposed so as to surround a portion of the cylindrical member where the window is formed, and the coil is arranged based on a change in impedance of the coil. The torque generated on the first and second rotating shafts In a torque sensor for detecting a torque, a first notch is provided on an outer periphery of a yoke member that holds the coil inside, and a first notch for pulling out an end of the coil to the outside of the yoke member. Forming at least one or more second notches, and the first and second notches
Are formed due to the impedance change of the coil caused by the non-uniformity of the magnetic field inside the coil caused by the first notch and the non-uniformity of the magnetic field inside the coil caused by the second notch. The position where the impedance change of the coil is reduced to each other. Here, the non-magnetic material in the present invention refers to a paramagnetic material and some diamagnetic materials, and the magnetic material refers to a ferromagnetic material. The magnetic permeability of the non-magnetic material is substantially equal to that of air, and is smaller than the magnetic permeability of the magnetic material. Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 4 show an embodiment of the present invention. In this embodiment, a torque sensor according to the present invention is applied to an electric power steering device of a vehicle. First, the construction will be described. In the housing 1, an input shaft 2 and an output shaft 3 connected via a torsion bar 4 are rotatably supported by bearings 5a, 5b and 5c. The input shaft 2, the output shaft 3 and the torsion bar 4 are coaxially arranged, and the input shaft 2 and the torsion bar 4 are integrated in the rotational direction by spline coupling. The other end of the torsion bar 4 is connected to the output shaft. At the position where it is deeply inserted into the inside 3, it is connected by a pin 3 a and is integrated in the rotation direction. The input shaft 2 and the output shaft 3 are made of a magnetic material such as iron. A steering wheel is integrally mounted in the rotation direction on the right end (not shown) of the input shaft 2 in FIG. 1, and a known rack is mounted on the left end of the output shaft 3 (not shown) in FIG. A pinion shaft constituting the AND pinion type steering device is connected. Therefore, the steering force generated by the steering of the steering wheel by the driver is applied to the input shaft 2, the torsion bar 4,
The power is transmitted to steered wheels (not shown) via the output shaft 3 and the rack-and-pinion type steering device. The end of the input shaft 2 surrounds the outer peripheral surface of the end of the output shaft 3, and the inner peripheral surface of the portion surrounding the outer peripheral surface of the end of the output shaft 3 of the input shaft 2 has a plurality of axially long convexes. A plurality of grooves 3a (same number as the number of the protrusions 2a) are formed in the outer peripheral surface of the output shaft 3 facing the protrusions 2a, and the protrusions 2a and the grooves 3a are formed in the circumferential direction. To prevent relative rotation between the input shaft 2 and the output shaft 3 beyond a predetermined range (for example, about ± 5 degrees). A worm wheel 6 that coaxially and integrally rotates with the output shaft 3 is externally fitted to the output shaft 3. The worm wheel 6 is formed on a resin meshing portion 6 a of the worm wheel 6 and on an outer peripheral surface of the output shaft 7 a of the electric motor 7. The formed worm 7b is engaged. Accordingly, the torque of the electric motor 7 is transmitted to the output shaft 3 via the output shaft 7a, the worm 7b and the worm wheel 6, and the electric motor 7
By appropriately switching the rotation direction, a steering assist torque in an arbitrary direction is applied to the output shaft 3. Further, a thin cylindrical member 8 is integrally fixed in the rotation direction at the end of the input shaft 2 on the output shaft 3 side so as to approach and surround the outer peripheral surface of the output shaft 3. I have. That is, the cylindrical member 8 is formed of a conductive and non-magnetic material (for example, aluminum), and as shown in FIG. 2 which is a perspective view of the cylindrical member 8 and its surroundings,
Of the cylindrical member 8 surrounding the output shaft 3, the input shaft 2
On the side near the end, a plurality of (eight in this embodiment) windows 8a,..., 8a are formed at regular intervals in the circumferential direction, and on the side far from the end of the input shaft 2 are windows. 8a, ..., 8a
, 8b (in this embodiment, eight) are formed in a rectangular shape (having the same shape as the window 8a) which is equally spaced in the circumferential direction so that the phase is shifted by 180 degrees. On the outer peripheral surface of a portion of the output shaft 3 surrounded by the cylindrical member 8, a plurality of grooves (same in number as the windows 8a and 8b, that is, eight in this example) extending in the axial direction and having a substantially rectangular cross section are provided. 3A is formed. The cylindrical member 8 has a coil bobbin 9
A, two coils 10 of the same standard wound around 9B
And 11. That is, coils 10 and 11
Are arranged coaxially with the cylindrical member 8, and the coil 10 surrounds the portion where the windows 8a,.
Numeral 1 surrounds the portion where the windows 8b,..., 8b are formed. Further, the outer peripheral surfaces and both end surfaces of the coils 10 and 11 are covered with iron yoke members 13 and 14, respectively. Since the configurations of the yoke members 13 and 14 are the same, the following description will be made with respect to the yoke member 14. That is, FIG. 3A is a sectional view of the yoke member 14, and FIG. 3B is a front view of the yoke member 14. Note that FIG. 3A corresponds to a cross-sectional view taken along the line AA of FIG. As shown in FIGS. 3A and 3B, the yoke member 14 includes a ring member 14A having an L-shaped cross section that covers the outer peripheral surface and one end surface of the coil 11, and a rectangular cross section that covers the other end surface of the coil 11. And the ring member 14B. The portion of the ring member 14A that covers the outer peripheral surface of the coil 11 also covers the outer peripheral surface of the ring member 14B, whereby the entire outer peripheral surface and both end surfaces of the coil 11 are covered with the yoke member 14. It has become. However, the ring member 1 of the ring member 14A
In the portion covering 4B, three notches 16A, 16B and 16C are formed at equal intervals in the circumferential direction (ie, at 120 ° intervals). Each of the notches 16A to 16C is formed to have a size that slightly overlaps with the outer peripheral surface of the coil 11, and a plastic or the like is formed on the outer peripheral surface of the ring member 14B so as to fit into one of the notches 16A. Is fixed. Then, on the surface of the terminal holding member 17 facing outward in the radial direction,
Two terminals 17A and 17B are fixed with their distal ends facing radially outward, the proximal end of one terminal 17A is connected to one end of the coil 11, and the proximal end of the other terminal 17B is It is connected to the other end of the coil 11. With this configuration, both ends of the coil 11 are drawn out of the yoke member 14. The notches 16B and 16C have the same dimensions as the notch 16A, but in particular, the notches 16B and 16C have the same dimensions.
No terminal holding member or the like is provided corresponding to 16C.
Therefore, in the portion where the notches 16B and 16C are formed, a part of the coil bobbins 9A and 9B is exposed. The other yoke member 13 has the same structure as the yoke member 14, and the two yoke members 13 and 14B abut on each other and the terminal holding members 17A overlap each other, as shown in FIG. It is arranged in the housing 1 in such a state that it abuts. Further, the tips of a total of four terminals 17A and 17B penetrate the housing 1 and reach the inside of the sensor case 18, and the coils 10 and 11 are connected to the terminals 17A and 17B.
Control board 1 in sensor case 18 via A and 17B
9 is connected to the motor control circuit. As shown in FIG. 4, for example, the motor control circuit includes an oscillating unit 21 for supplying an alternating current of a predetermined frequency to the coils 10 and 11 via a constant current unit 20, and rectifying and smoothing the terminal voltage of the coil 10. And output rectifying / smoothing circuit 22
And a rectifying / smoothing circuit 23 for rectifying and smoothing the terminal voltage of the coil 11 and outputting the same, and differential amplifiers 24A and 24B for amplifying and outputting the difference between the output of the rectifying / smoothing circuit 22 and the output of the rectifying / smoothing circuit 23. And a noise removal filter 25A for removing high frequency noise components from the output of the differential amplifier 24A
A noise removal filter 25B for removing high-frequency noise components from the output of the differential amplifier 24B, and the direction of the relative rotational displacement of the input shaft 2 and the cylindrical member 8 based on, for example, an average value of the outputs of the noise removal filters 25A and 25B. And a magnitude, and multiplies the result by, for example, a predetermined proportionality constant to obtain a steering torque generated in the steering system; and a steering that reduces the steering torque based on the calculation result of the torque calculation unit 26. And a motor drive unit 27 that supplies a drive current I that generates an auxiliary torque to the electric motor 7. Next, the operation of this embodiment will be described.
Now, assuming that 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. Therefore, no relative rotation occurs between the output shaft 3 and the cylindrical member 8. On the other hand, when the steering wheel is steered to generate a torque on the input shaft 2, the torque is transmitted to the output shaft 3 via the torsion bar 4. At this time, a resistance force corresponding to a frictional force between the steered wheels and the road surface and a frictional force such as meshing of gears of a rack and pinion type steering device formed on the left end side (not shown) of the output shaft 3 are applied to the output shaft 3. Therefore, the relative rotation of the output shaft 3 is delayed between the input shaft 2 and the output shaft 3 due to the torsion bar 4 being twisted, and the relative rotation is also generated between the output shaft 3 and the cylindrical member 8. When the cylindrical member 8 has no window, the cylindrical member 8 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 cylindrical member 8 is An eddy current is generated on the outer peripheral surface in a direction opposite to the coil current. When the magnetic field due to the eddy current and the magnetic field due to the coil are superimposed, the magnetic field inside the cylindrical member 8 is canceled. When the windows 8a and 8b are provided in the cylindrical member 8, the eddy current generated on the outer peripheral surface of the cylindrical member 8 cannot go around the outer peripheral surface by the windows 8a and 8b, so that the cylindrical member 8 extends along the end surfaces of the windows 8a and 8b. , Flows in the same direction as the coil current in the inner circumferential surface, and returns to the outer circumferential surface along the end surfaces of the adjacent windows 8a and 8b to form a loop. That is, an eddy current loop is periodically arranged in the circumferential direction (θ = 360 / N) inside the coil. The magnetic field generated by the coil current and the eddy current are superimposed, and a magnetic field having a periodic strength in the circumferential direction and a magnetic field having a gradient that becomes smaller toward the center are formed inside and outside the cylindrical member 8. The strength of the magnetic field in the circumferential direction is strong at the central portions of the windows 8a and 8b which are strongly affected by the adjacent eddy currents, and weakens at a position shifted by half a period (θ / 2) therefrom. The output shaft 3 made of a magnetic material is provided inside the cylindrical member 8.
Are arranged coaxially, and the output shaft 3 has a groove 3A formed with a protrusion and a recess having the same period as the windows 8a and 8b, but the magnetic material placed in the magnetic field is magnetized. , And generates 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 output shaft 3 is increased or decreased by the relative phase with the cylindrical member 8 by the magnetic field having the periodic periodic strength and the radial gradient generated by the cylindrical member 8. The phase at which the spontaneous magnetization is maximized is a state in which the centers of the windows 8a and 8b coincide with the centers of the protrusions. Then, the inductance of the coils 10 and 11 also increases and decreases according to the increase and decrease of the spontaneous magnetization, and the change becomes substantially sinusoidal. When no torque is applied, the phase is shifted by 1/4 cycle (θ / 4) from the phase at which the spontaneous magnetization (inductance) is maximized, and the window row on the side closer to the end of the input shaft 2 And the other window row have a phase difference of 1/2 cycle (θ / 2) as described above. Therefore, when a phase difference occurs between the cylindrical member 8 and the output shaft 3 due to the torque, one of the inductances of the two coils 10 and 11 increases and the other decreases at the same rate. If the inductance changes in this manner, the impedance of the coils 10 and 11 changes in a similar tendency under the condition that the frequency of the current supplied from the current amplifying unit 26 is constant, and the self-induction of the coils 10 and 11 occurs. Electric power also changes in a similar tendency. Therefore, the outputs of the differential amplifiers 24A and 24B that determine the difference between the terminal voltages of the coils 10 and 11 change according to the direction and magnitude of the steering torque. Further, since the difference between the rectifying / smoothing circuits 22 and 23 is obtained in the differential amplifiers 24A and 24B, a change in self-inductance due to temperature or the like is canceled. The torque calculator 26 calculates the average value of the outputs of the differential amplifiers 24A and 24B supplied via the noise removing filters 25A and 25B, and multiplies the average value by, for example, a predetermined proportional constant to perform steering. The torque is obtained, and the result is supplied to the motor drive unit 27. The motor drive unit 27
A drive current I according to the direction and magnitude of the steering torque is supplied to the electric motor 7. Then, a torque corresponding to the direction and magnitude of the steering torque generated in the steering system is generated in the electric motor 7, and the torque is output to the output shaft 3 via a worm gear or the like.
, The steering assist torque is applied to the output shaft 3, the steering torque decreases, and the burden on the driver is reduced. Further, in the present embodiment, the yoke members 13 and 14 that hold the coils 10 and 11 inside,
In addition to the notch 16A for taking out the terminals of the coils 10 and 11 to the outside, notches 16B and 16C are formed, and the positions of the notches 16A to 16C are shifted from each other by 120 degrees in the circumferential direction. , Each notch 16A
The impedance change of each of the coils 10 and 11 due to the non-uniformity of the magnetic field inside the coils 10 and 11 caused by １６16C is reduced. That is, in the present embodiment, as described above, the impedance of the coils 10 and 11 is changed by changing the degree of overlap between the groove 3A and the windows 8a and 8b. Since there are eight pairs of the coils 8a and 8b in the circumferential direction, for example, the coil 1
Due to the non-uniformity of the magnetic flux inside 0,11, each time the output shaft 3 makes one rotation, a torque-independent impedance change appears as eight waves. However, the impedance change unrelated to the torque due to the non-uniformity of the magnetic flux inside the coils 10 and 11 is as follows.
It is caused by the notch 16B and also by the notch 16C. For this reason, the impedance change unrelated to the torque due to each of the notches 16A to 16C can be strengthened or weakened by appropriately selecting the number and formation position of the notches 16A to 16C. Or Assuming that the notches 1 are provided in the yoke members 13 and 14,
If only one notch of the same size is formed at a position shifted by 180 degrees from the groove 3A, the groove 3A and the windows 8a, 8a
Since eight combinations with b exist at equal intervals in the circumferential direction, impedance changes due to these two notches occur at the same timing. For this reason, the impedance changes reinforce each other. On the other hand, when three notches 16A to 16C are formed as in the present embodiment, eight combinations of the groove 3A and the windows 8a and 8b are present at equal intervals in the circumferential direction. Therefore, for example, the positional relationship between the notch 16B and each groove 3A is 2 with respect to the positional relationship between the notch 16A and each groove 3A.
The phase is delayed by π / 3, and the positional relationship between the notch 16C and each groove 3A is delayed by 4π / 3. For this reason, the impedance changes irrespective of the torque due to the notches 16A to 16C are weakened with each other.
As a result, the impedance change is greatly reduced. FIG. 5 shows a measurement result of the impedance change rate of the coil 10 when the input shaft 2 and the output shaft 3 are rotated once while the torque is set to zero with the same configuration as that of the present embodiment. I have. According to this, the impedance includes:
Changes in low frequency (one cycle per revolution) with small amplitude,
A change in high frequency (eight cycles per rotation) of extremely small amplitude is recognized. The change in low frequency is caused by the groove 3A or the cylindrical member 8
If the differential amplifiers 24A and 24B as shown in FIG. 4 perform differential operation, the rate of change of the output voltage becomes extremely small as shown in FIG. Only high-frequency changes enable extremely high-precision torque detection. Therefore, accurate steering assist torque can be applied to the steering system. Incidentally, like the conventional torque sensor,
When the notches 16A are formed but the notches 16B and 16C are not formed, even if the torque is zero, as shown in FIG. A change in one cycle per rotation) and a change in high frequency (eight cycles per rotation) having a large amplitude occur. Also, as shown in FIG. 8, the impedance of the coil 11 has a change in low frequency (one cycle per rotation) with a small amplitude and a change in high frequency (eight cycles per rotation) with a large amplitude. However, since there is a 180 degree phase difference between the windows 8a,..., 8a and the windows 8b,. The phase is shifted by 180 degrees with respect to the component. For this reason, even if the differential amplifiers 24A and 24B take the differential, the low-frequency change component can be canceled, but the high-frequency component is amplified in reverse. Therefore, the output voltages of the differential amplifiers 24A and 24B greatly change regardless of the torque as shown in FIG.
As a result, the detection accuracy of the torque is reduced, which hinders the execution of good steering assist torque control. In this embodiment, the input shaft 2 corresponds to the second rotating shaft, the output shaft 3 corresponds to the first rotating shaft, and the portion of the output shaft 3 surrounded by the cylindrical member 8. Corresponds to the surrounding portion, the notch 16A corresponds to the first notch, and the notches 16B and 16C correspond to the second notch. In the above embodiment, the groove 3A and the window 8
Since there are eight combinations of a and 8b in the circumferential direction, three notches 16A to 16C are formed at equal intervals in the circumferential direction to shift the impedance change phases so as to weaken each other. The number and position of the notches formed in the yoke members 13 and 14 are not limited to those in the above-described embodiment, but may be determined according to the number of sets of structures that change the impedance according to the torque of the grooves 3A and the windows 8a and 8b. May be set appropriately. In short, the notches for pulling out the ends of the coils 10 and 11 to the outside of the yoke members 13 and 14 and the impedance changes caused by other notches are reduced so that the impedance changes caused by the other notches are mutually reduced. May be formed. In the above embodiment, the case where the torque sensor according to the present invention is applied to an electric power steering device for a vehicle has been described. However, the present invention is not limited to this. Even if there is, it is applicable. As described above, according to the present invention,
A first notch for drawing out an end of the coil to the outside and at least one or more second notches other than the first notch are formed in the yoke member, and the first notch is formed. Because the impedance change of the coil due to the non-uniformity of the magnetic field inside the coil caused by the notch and the impedance change of the coil due to the non-uniformity of the magnetic field inside the coil caused by the second notch are reduced mutually. Thus, there is an effect that highly accurate torque detection can be performed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall sectional view showing an embodiment of the present invention. FIG. 2 is a perspective view showing a coil and a structure around the coil. FIG. 3 is a diagram showing a configuration of a yoke member. FIG. 4 is a circuit diagram illustrating an example of a motor control circuit. FIG. 5 is a waveform chart showing an impedance change rate in the embodiment. FIG. 6 is a waveform chart showing an output voltage change rate of the differential amplifier according to the embodiment. FIG. 7 is a waveform diagram showing an impedance change rate of one coil in a conventional torque sensor. FIG. 8 is a waveform diagram showing an impedance change rate of the other coil in the conventional torque sensor. FIG. 9 is a waveform diagram showing an output voltage change rate when the results of FIGS. 7 and 8 are input to a differential amplifier. [Description of Signs] 1 Housing 2 Input shaft (second rotating shaft) 3 Output shaft (first rotating shaft) 3A Groove 4 Torsion bar 8 Cylindrical member 8a, 8b Window 9A, 9B Coil bobbin 10, 11 Coil 13, 14 Yoke member 16A Notch (first notch) 16B, 16C Notch (second notch) 20 Constant current unit 21 Oscillator 22, 23 Rectifier / smoothing circuit 24A, 24B Differential amplifier 25A, 25B Noise removal filter 26 Torque calculation unit 27 Motor drive circuit

Claims (1)

(57) [Claim 1] A cylindrical member made of a conductive and non-magnetic material while connecting a first and a second rotating shaft arranged coaxially through a torsion bar. Is integrated with the second rotating shaft in the rotating direction so as to surround the outer peripheral surface of the first rotating shaft, and the enclosed portion of the first rotating shaft surrounded by at least the cylindrical member is made of magnetic material. It is formed of a material, a groove extending in the axial direction is formed in the enclosed portion, 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. A window is formed, a coil is disposed so as to surround a portion of the cylindrical member where the window is formed, and a torque generated in the first and second rotating shafts is detected based on a change in impedance of the coil. In the torque sensor, the coil is held inside A first notch on the outer periphery of the yoke member for drawing out an end of the coil to the outside of the yoke member, and at least one or more second notches different from the first notch; Forming the first and second
The position of the notch 2 is determined by the impedance change of the coil due to the non-uniformity of the magnetic field inside the coil caused by the first notch , and the position of the magnetic field inside the coil caused by the second notch. The torque sensor according to claim 1, wherein a change in impedance of said coil due to uniformity is at a position where they are reduced to each other.