JPH0961263A - Torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce heat generation of a detection circuit or the like by increasing impedance of a coil to suppress power consumption with a simple constitution. SOLUTION: A plurality of grooves 3A which are long in an axial direction are formed on an output axis 3 made of a magnetic material, while a thin cylindrical member 8 made of a conductive and non-magnetic material is made into a single body with an input axis in a rotation direction so that a part formed with the grooves 3A is surrounded. Aplurality of windows 8a, 8b are formed on the cylindrical member 8 so that an overlapping state varies according to a relative rotational position between the cylindrical member 8 and the output axis 3, and a peripheral width of the windows 8a, 8b is wider than a peripheral width of a protrusion 3B between the grooves 3A. A part formed with the window 8a of the cylindrical member 8 is surrounded by a coil 10, while a part formed with the window 8b is surrounded by a coil 11, wherein torque is obtained from a change in impedance of the coils 10, 11.

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 a torque generated on a rotating shaft, and more particularly to a torque sensor having a coil whose impedance changes in accordance with the generated torque, in which the impedance of the coil is simple. It is possible to reduce the heat generation of the detection circuit and the like by increasing the power consumption.

[0002]

2. Description of the Related Art For example, by providing a torsion bar which is elastically deformable in a twisting direction in a part of a steering system of a vehicle,
The steering torque can be detected by generating a relative rotation proportional to the steering torque between the shafts connected via the torsion bar, and measuring the relative rotation. The steering assist torque can be detected according to the detected torque. There is a power steering device that reduces the burden on the driver by generating Then, as a torque sensor of a type that measures such relative rotation, conventionally, there is one that changes the impedance of the coil according to the torque and detects the torque by measuring the impedance of the coil (for example, See JP-A-2-102428, etc.).

[0003]

In the power steering device for a vehicle as described above, there is a large restriction on the installation space, so that it is desired to reduce the size of each constituent member. There is also a demand for miniaturization of the torque sensor. If semiconductors such as transistors and resistors provided on the substrate for the torque sensor are miniaturized, the upper limit of power consumption and countermeasures for heat generation become problems, so that the impedance of the coil is reduced so that the amount of current is reduced. It is necessary to raise. However, if the impedance of the coil is simply increased, the number of turns of the coil is increased, which goes against the demand for miniaturization.

The present invention has been made in view of the above-mentioned unsolved problems of the conventional technique, and provides a torque sensor capable of increasing the impedance of a coil without causing an increase in size. Is intended.

[0005]

In order to achieve the above object, a torque sensor according to the present invention has a first and a second rotating shafts, which are coaxially arranged, connected to each other via a torsion bar and has a conductive property. A cylindrical member made of a magnetic and non-magnetic material is integrated with the second rotary shaft in the rotation direction so as to surround the outer peripheral surface of the first rotary shaft, and at least the first rotary shaft of the first rotary shaft is formed. A surrounding member surrounded by a cylindrical member is formed of a magnetic material, a groove extending in an axial direction is formed in the surrounding member, and a circumferential width of the cylindrical member is larger than a non-groove portion of the surrounding member. A wide window is formed, and the positional relationship between the groove and the window is set such that the circumferential center portion of the window and the circumferential end portion of the groove overlap each other when the torsion bar is not twisted, And a portion of the cylindrical member in which the window is formed Disposed coil to surround,
The torque generated on the first and second rotating shafts is detected based on the change in the impedance of the coil.

Here, the non-magnetic material in the present invention means a paramagnetic material and a part of diamagnetic material, and the magnetic material means 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.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an overall configuration of an embodiment of the present invention, which is an example in which a torque sensor according to the present invention is applied to an electric power steering device for a vehicle.

First, the structure will be described. Inside the housing 1, an input shaft 2 and an output shaft 3 connected via a torsion bar 4 are rotatably supported by bearings 5a and 5b. The input shaft 2, the output shaft 3 and the torsion bar 4 are coaxially arranged. The input shaft 2 and the torsion bar 4 are connected to each other via a sleeve 2A whose ends are spline-coupled. The other end of 4 is spline-coupled to a position in the output shaft 3 that goes deeply. 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 side of the input shaft 2 (not shown) in FIG. 1, and a known rack is mounted on the left end side of the output shaft 3 (not shown) in FIG. A pinion shaft that constitutes 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.

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. A plurality of projections 2 long in the axial direction are provided on the inner peripheral surface of the portion surrounding the outer peripheral surface of the end portion of the output shaft 3 of the sleeve 2A.
are formed on the outer peripheral surface of the output shaft 3 opposed to these convex portions 2a.
Are formed, and the projections 2a and the grooves 3a are fitted with a margin in the circumferential direction, whereby relative rotation between the input shaft 2 and the output shaft 3 over a predetermined range (for example, about ± 5 degrees) or more is achieved. Preventing.

A worm wheel 6 that rotates coaxially and integrally with the output shaft 3 is externally fitted to the output shaft 3, and a resin meshing portion 6a of the worm wheel 6 and an outer peripheral surface of the output shaft 7a of the electric motor 7 are provided. It meshes with the formed worm 7b. 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 rotational direction to the sleeve 2A which is integral with the input shaft 2 so as to surround and surround the outer peripheral surface of the output shaft 3. There is. That is, the cylindrical member 8 is made 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, the output of the cylindrical member 8 is reduced. Of the part surrounding the shaft 3,
On the side close to the sleeve 2A, a plurality of (nine in this embodiment) rectangular windows 8a,.
a is formed, and windows 8a, 8a,
, 8a are formed (in this embodiment, nine) of windows 8b,..., 8b which are equally spaced in the circumferential direction so as to be 180 ° out of phase with each other.

On the outer peripheral surface of the portion of the output shaft 3 surrounded by the cylindrical member 8, a plurality of grooves (having the same number as the windows 8a and 8b, and thus nine in this example) extending in the axial direction have a substantially rectangular cross section. 3A is formed. More specifically, AA in FIG.
3 is a cross-sectional view of the cylindrical member 8 and the output shaft 3 taken along the line of FIG.
And, as shown in FIG. 4 which is a cross-sectional view of the cylindrical member 8 and the output shaft 3 taken along the line BB of FIG. 1, the circumferential surface of the cylindrical member 8 is equally divided into N (N = 9 in this example) in the circumferential direction. One cycle angle θ (= 360 / N, θ = 40 degrees in this example)
In the portion of the cylindrical member 8 on the side close to the sleeve 2A, the portion a degrees from one end of the one cycle angle θ is the window 8a ,.
a, and the remaining (θ-a) degree part is blocked,
, 8a are shifted by 180 degrees, the portion of the cylindrical member 8 on the side far from the sleeve 2A has a portion a degrees away from the other end of the one cycle angle θ of the windows 8b ,.
b, and the remaining (θ-a) degree portion is blocked.
It should be noted that the circumferential width of the convex portion 3B having a convex cross-section between the grooves 3A, ..., 3A is b degrees, and is between the cylindrical member 8 and the output shaft 3 (input shaft 2
And the relative rotatable range (between the output shaft 3) is c degrees.

However, when the torsion bar 4 is not twisted (when the steering torque is zero), as shown in FIG. 3, the central portion of the circumferential width of the window 8a and one of the grooves 3A in the circumferential direction are arranged. The end portion (one edge portion of the convex portion 3B) overlaps,
As shown in FIG. 4, the circumferential width center portion of the window 8b and the groove 3A
The other end portion (the other edge portion of the convex portion 3B) in the circumferential direction of is overlapped. Therefore, the overlapping state of the window 8a and the groove 3A and the overlapping state of the window 8b and the groove 3A are opposite in the circumferential direction.

In the present embodiment, the relationship between the angles is as follows: a> b (1) a ≦ 2 (θ-c-b) (2) The condition of the equation (1) is for increasing the impedance of the coil described later,
The condition of the expression (2) is to prevent the convex portion 3B from completely protruding from the windows 8a and 8b. That is, when the torsion bar 4 is not twisted, the edge portion of the convex portion 3 </ b> B inside the closed portion between the windows 8 a and 8 a causes the torsion bar 4 to be twisted and the edge portion between the cylindrical member 8 and the output shaft 3. In order to prevent it from being located inside the windows 8a and 8b even if relative rotation occurs, it suffices to satisfy the condition b−a / 2 + c ≦ θ−a (3), and therefore (3) Rearranging the equations for a gives the above equation (2).

The cylindrical member 8 is surrounded by a yoke 9 around which coils 10 and 11 of the same standard are wound. That is, the coils 10 and 11 are arranged coaxially with the cylindrical member 8, and the coil 10 is wound around the yoke 9 so as to surround the portion where the windows 8a,.
The coil 11 is wound around the yoke 9 so as to surround the portion where the windows 8b,..., 8b are formed, and the yoke 9 is fixed to the housing 1. The space in the housing 1 where the worm wheel 6 is disposed and the yoke 9
Is separated by an oil seal 12 so that lubricating oil supplied to the meshing portion of the worm wheel 6 and the worm 7 does not enter the yoke 9 side. .

The coils 10 and 11 are connected to a motor control circuit formed on a control board 14 in the sensor case 13. The motor control circuit, as shown in FIG.
An oscillating unit 21 for supplying to the coils 10 and 11 via a rectifying / smoothing circuit 22 for rectifying and smoothing the self-induced electromotive force of the coil 10, and outputting the rectified and smoothed self-induced electromotive force of the coil 11. A high-frequency noise component is output from the rectifying / smoothing circuit 23 that outputs, the differential amplifiers 24A and 24B that amplify and output the difference between the output of the rectifying / smoothing circuit 22 and the output of the rectifying / smoothing circuit 23, and the output of the differential amplifier 24A. A noise removal filter 25A for removal and a noise removal filter 25 for removing high frequency noise components from the output of the differential amplifier 24B.
B and the direction and magnitude of the relative rotational displacement of the input shaft 2 and the cylindrical member 8 are calculated based on, for example, an average value of the outputs of the noise removal filters 25A and 25B, and the result is multiplied by, for example, a predetermined proportional constant to perform steering. A torque calculation unit 26 that obtains a steering torque generated in the system, and a motor that supplies a drive current I to the electric motor 7 such that a steering assist torque that reduces the steering torque based on the calculation result of the torque calculation unit 26 is generated. And a drive unit 27.

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 rotational force on the input shaft 2, the rotational force is transmitted to the output shaft 3 via the torsion bar 4. At this time, the output shaft 3 receives a frictional force between the steered wheels and the road surface and a resistance force corresponding to a frictional force such as gear engagement of the rack-and-pinion type steering device configured on the left end side (not shown) of the output shaft 3. Since the torsion bar 4 is twisted between the input shaft 2 and the output shaft 3,
Relative rotation occurs, and relative rotation also occurs between the output shaft 3 and the cylindrical member 8.

Here, for example, when the right steering torque (steering torque generated during steering in the right rotation direction) is generated, the cylindrical member 8 rotates counterclockwise in FIGS. 3 and 4, so that the steering torque is zero. Compared with the above, the overlapping area of the window 8a and the convex portion 3B becomes large, and the overlapping area of the window 8b and the convex portion 3B becomes small. On the contrary, when the left steering torque (the steering torque generated during the steering in the left rotation direction) is generated, the cylindrical member 8 rotates clockwise in FIGS. 3 and 4, and therefore, compared with the case where the steering torque is zero,
The overlapping area of the window 8a and the convex portion 3B is small, whereas the overlapping area of the window 8b and the convex portion 3B is large.

Since the cylindrical member 8 is made of a conductive and non-magnetic material having a property of making it difficult for magnetic flux to pass due to the eddy current effect, and the convex portion 3A is made of a magnetic material, the window 8a, the convex portion 3B, and the window 8b are formed. Since the increase and decrease of the overlapping portion of the convex portions 3B are synonymous with the increase and decrease of the region occupied by the magnetic material inside the coils 10 and 11, based on the induction principle, the convex portions 3B exposed through the windows 8a and 8b The larger the surface area, the larger the inductance L of the coils 10 and 11, and conversely, the smaller the surface area of the convex portion 3B exposed through the windows 8a and 8b, the smaller the inductance L of the coils 10 and 11. .

That is, as shown in FIG. 6, the inductance L _{10 of the} coil 10 increases as the right steering torque increases.
Increases, the inductance L _{11 of the} coil 11 decreases, and as the left steering torque increases, the inductance L ₁₀ of the coil ₁₀ decreases and the inductance L _{11 of the} coil 11 increases. Note that FIG. 6 also shows the relationship between the relative rotation angle between the cylindrical member 8 and the output shaft 3 and the steering torque. According to this, from the position where the steering torque is 0 to the right steering torque or In the range in which the relative angle changes by the angle (ba−2 + c) in the direction in which the left steering torque increases, the overlapping area of the windows 8a and 8b and the convex portion 3B changes in only one direction, and thus the inductance L ₁₀ and L ₁₁ changes substantially linearly, but beyond that, the overlapping area of the windows 8a and 8b and the convex portion 3B changes in the opposite direction, so that the inductances L ₁₀ and L ₁₁ also change in the opposite direction. . Therefore, as described above, the relative rotation range is limited to the range of ± c degrees.

If the inductances L ₁₀ and L ₁₁ change as shown in FIG. 6, the impedances of the coils 10 and 11 are also as shown in FIG. 6 under the condition that the frequency ω of the current supplied from the oscillator 21 is constant. The inductances L ₁₀ and L ₁₁ change with the same tendency, and the self-induced electromotive forces of the coils 10 and 11 also change with the same tendency. Therefore, the outputs of the differential amplifiers 24A and 24B, which determine the difference between the self-induced electromotive forces of the coils 10 and 11, change linearly according to the direction and magnitude of the steering torque. In the differential amplifiers 24A and 24B, the rectifying / smoothing circuit 22,
Since the difference of 23 is obtained, the change of the 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 through the noise removal filters 25A and 25B, and multiplies the average value by a predetermined proportional constant, for example, and steers the steering wheel. The torque is obtained and the result is supplied to the motor drive unit 27. The motor drive unit 27 is
A drive current I according to the direction and magnitude of the steering torque is supplied to the electric motor 7.

Then, a rotating force is generated in the electric motor 7 according to the direction and magnitude of the steering torque generated in the steering system, and the rotating force is transmitted through the worm gear or the like to the output shaft 3
, The steering assist torque is applied to the output shaft 3, the steering torque decreases, and the burden on the driver is reduced. Here, in the detection circuit as shown in FIG. 5, between the resistance value of the resistor R connected in series with the coils 10 and 11 and the value of the inductance L of the coils 10 and 11, the coil Although there is a desirable ratio that the output voltage of 10 and 11 tends to be different, the collector loss of the transistor Tr in the constant current unit 20 causes the coils 10 and 11 to be different.
The maximum value of the current flowing through is limited, and its collector loss also depends on the temperature. Considering automobile parts whose temperature rises, it is desirable to reduce the current flowing through the coils 10 and 11. In addition, considering the heat dissipation effect, it is necessary to increase the surface area of the control board 14, but this leads to an increase in the size of the entire apparatus.

In consideration of such various conditions, in the present embodiment, the coil 10 and the coil 10 are provided in order to realize the desired ratio and suppress the current flowing through the coils 10 and 11.
Without increasing the number of turns of the coil 11, etc.
An increase in impedance of 1 is achieved. Specifically, the angle a that is the circumferential width of the windows 8a and 8b and the convex portion 3B
The impedance of the coils 10 and 11 is increased by setting the relationship with the angle b, which is the width in the circumferential direction of the coil, as in the above equation (1).

That is, considering the case where the circumferential widths of the windows 8a, 8b, the groove 3A, and the convex portion 3B are all equal in the relationship of angles shown in FIGS. 3 and 4, a = (θ-a ) = B = (θ−b) = θ / 2 and N = 9, so θ / 2 = 20 degrees.

Then, the impedance was measured by changing the angles a and (θ-a) around 20 degrees while fixing b = (θ-b) = 20 degrees.
The results shown in FIG. 7 were obtained. That is, when the angle a is made larger than the angle θ / 2 (= 20 degrees), the impedance becomes large, and conversely, the angle a is made the angle θ / 2 (= 20 degrees).
The impedance becomes smaller when the angle is smaller than (degrees), and when the relationship is rewritten for the relationship between the angle a and the angle b, the relationship shown in the above equation (1) is obtained.

That is, if there is a relation of the above expression (1) between the angles a and b, the relative rotation angle between the cylindrical member 8 and the output shaft 3 and the specifications of the output shaft 3 (dimensions of the groove 3A, the convex portion 3B, etc.). ) Is the same, the convex portion 3 exposed through the windows 8a and 8b
Since the surface area of B becomes large, the inductances L ₁₀ and L ₁₁ shown in FIG. 6 are offset to the upper side, and as a result, the impedance is increased.

Then, the coil 10,
If the impedance of 11 can be increased, the current amount of the coils 10 and 11 can be reduced, and the transistors and resistors in the detection circuit can be downsized. Further, if the amount of current in the coils 10 and 11 is reduced, the amount of heat generated is also suppressed, so there is no need to increase the size of the control board 14 or the like to improve its heat dissipation effect, which also reduces the size of the entire device. Be done. Further, the advantage that the configuration of the torque sensor can be made smaller than the conventional one is particularly advantageous for the device applied to the vehicle having a small space margin as in the present embodiment.

In this embodiment, the input shaft 2 corresponds to the second rotary shaft, the output shaft 3 corresponds to the first rotary shaft, the convex portion 3B corresponds to the non-groove portion, and the output The portion of the shaft 3 surrounded by the cylindrical member 8 corresponds to the enclosed portion.

[0031]

As described above, according to the present invention,
A window is formed in a cylindrical member made of a conductive and non-magnetic material that rotates integrally with the first rotating shaft, and an enclosed portion surrounded by at least the cylindrical member of the second rotating shaft is formed of a magnetic material. A groove extending in the axial direction is formed in the enclosed portion, the circumferential width of the window is made wider than the circumferential width of the non-groove portion of the enclosed portion, and the overlapping condition of the window and the groove is increased. Change is measured based on the electromotive force of the coil, and the torque generated in the first and second rotating shafts is detected based on the measurement result. There is an effect that the electric power can be suppressed and the heat generation of the detection circuit can be reduced.

[Brief description of drawings]

FIG. 1 is a front sectional view showing the configuration of an embodiment of the present invention.

FIG. 2 is a perspective view of a main part of the embodiment.

3 is a sectional view of the cylindrical member and the output shaft taken along the line AA in FIG.

FIG. 4 is a cross-sectional view of a cylindrical member and an output shaft taken along line BB in FIG.

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

FIG. 6 is a graph showing the relationship between steering torque and coil inductance.

FIG. 7 is a graph showing the relationship between the angle a and the impedance when the steering torque is zero.

[Explanation of symbols]

 2 Input shaft (second rotary shaft) 3 Output shaft (first rotary shaft) 3A groove 3B convex portion (non-groove portion) 4 torsion bar 8 cylindrical member 8a, 8b window 10, 11 coil 20 constant current portion 21 oscillation Part 22, 23 Rectification / smoothing circuit 24A, 24B Differential amplifier 25A, 25B Noise removal filter 26 Torque calculation part 27 Motor drive circuit

Claims (1)

[Claims] 1. A first and a second rotating shafts, which are coaxially arranged, are connected via a torsion bar, and a cylindrical member made of a conductive and non-magnetic material is attached to the first rotating shaft. The surrounding portion is integrally formed with the second rotating shaft in the rotation direction so as to surround the outer peripheral surface, and the surrounding portion surrounded by at least the cylindrical member of the first rotating shaft is formed of a magnetic material. A groove extending in the axial direction is formed in the cylindrical member, a window having a circumferential width wider than the non-groove portion of the enclosed portion is formed in the cylindrical member, and the positional relationship between the groove and the window is the torsion bar. It is set so that the circumferential center portion of the window and the circumferential end portion of the groove overlap each other when no twist is generated, and a coil is provided so as to surround the portion of the cylindrical member in which the window is formed. Based on the impedance change of the coil And a torque sensor for detecting torque generated on the first and second rotating shafts.