JPH0989692A - Steering torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a cost by improving mass productivity of a steering torque sensor. SOLUTION: A lower end face of front and rear legs 21a, 21b of a sensor module 21 is made to be a recessed face having a curvature equal to that of an outer peripheral face of a torsion bar 7, the lower end face of the legs 21a, 21b is integrally fixed to the front and the rear in an axial direction of the torsion bar, and thin film strain gage elements 25a, 25b, 25c, 25d are formed respectively four positions which are line-symmetrical and also point-symmetrical with respect to a symmetry axis parallel to the axial direction of the torsion bar on a surface of a body 21e coupling between the front and rear legs 21a, 21b of the sensor module 21. A wheatstone bridge circuit is assembled so that each of the four thin film strain gage elements 25a to 25d provides a resistor on each side, thereby forming a steering torque sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering torque sensor used for measuring a steering torque of a steering column of an automobile.

[0002]

2. Description of the Related Art As a means for measuring the torque applied to a steering column of an automobile, a foil strain gauge is conventionally adhered to a surface of a torsion bar that joins a lower shaft and an upper shaft of the steering column. A steering torque sensor is known in which a Wheatstone bridge circuit is assembled so that the strain gauge forms a resistance element on each side, and the steering torque is obtained from the resistance change of the foil strain gauge.

However, in a steering torque sensor using such a foil strain gauge, since a synthetic resin film is used as the material of the strain gauge foil together with an inorganic substance which constitutes an actual electric resistance element, it is applied to the torsion bar. The resistance change caused by the torque is small, and it is difficult to detect the torque with high accuracy.

A thin film strain gauge element is directly formed on a torsion bar as a steering torque sensor which can solve the problems of the steering torque sensor using the foil strain gauge element and can detect the torque with high accuracy, and the thin film strain gauge element is formed. A steering torque sensor that obtains a steering torque from the change in resistance is disclosed in, for example, JP-A-63-823.
No. 31 is disclosed.

This conventional steering torque sensor is
The thin film strain gauge element made of an inorganic material is formed directly on the torsion bar, and a Wheatstone bridge circuit is assembled so that they form resistance elements on each side, and the torque applied to the torsion bar is detected.

However, in such a conventional steering torque sensor, a thin film strain gauge element is directly formed at a predetermined position on the surface of the torsion bar by a vacuum vapor deposition method. Therefore, in manufacturing the same, the torsion bar is evacuated. The thin film strain gauge element has to be formed in a predetermined location by placing it in a vapor deposition kettle, and the number is limited because the torsion bar is accommodated in the vapor deposition kettle of a limited volume. However, there is a problem that the manufacturing cost is high because the number of products is small.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and by using a thin film strain gauge element, highly accurate torque detection can be achieved.
Moreover, it is an object of the present invention to provide a steering torque sensor that can reduce the manufacturing cost.

[0008]

According to a first aspect of the present invention, a sensor module is integrally attached to a circumferential surface of a torsion bar that joins a lower shaft and an upper shaft of a steering column shaft, and a torque applied to the torsion bar is applied. A steering torque sensor for detecting,
The lower end surfaces of the front and rear legs of the sensor module are concave surfaces having the same curvature as the curvature of the outer peripheral surface of the torsion bar, and the lower end surfaces of these legs are integrally fixed to the front and rear in the axial direction of the torsion bar. , Four positions that are line-symmetrical and point-symmetrical with respect to the axis of symmetry parallel to the axial direction of the torsion bar on the surface of the body that connects the front and rear legs of the sensor module. A thin film strain gauge element is formed on each of them, and a Wheatstone bridge circuit is assembled so that each of the four thin film strain gauge elements constitutes a resistance on each side.

Thus, in manufacturing the steering torque sensor, the sensor module is manufactured separately from the torsion bar, and the thin film strain gauge element is formed on the surface of the body of the sensor module by an appropriate method. Since the thin film strain gauge element is formed on the sensor module that is smaller in size than the torsion bar, the thin film strain gauge element can be formed on many modules at the same time in the same manufacturing space. The work can be performed, and the manufacturing cost can be reduced.

According to a second aspect of the present invention, in the steering torque sensor according to the first aspect, the surface of the body of the sensor module is a flat surface parallel to the axis of the torsion bar. The gauge element can be easily formed.

According to a third aspect of the present invention, in the steering torque sensor according to the first aspect, the lower end surfaces of the front and rear legs of the sensor module are welded to the peripheral surface of the torsion bar by an electron beam welding method to be integrated. As a result, the steering torque sensor can be attached without forming a recess so that stress concentration occurs on the torsion bar side, and the steering torque applied to it can be maintained without compromising the mechanical strength of the steering column. Can detect.

According to a fourth aspect of the present invention, in the steering torque sensor according to any of the first to third aspects, the thin film strain gauge element is composed of a resistance element made of a polycrystalline silicon material formed by a plasma chemical vapor deposition method. It was done.

As a result, a larger number of materials can be manufactured at a time in the same equipment volume as compared with the case where the thin film strain gauge element is directly formed on the torsion bar, and the manufacturing cost can be reduced.

According to a fifth aspect of the present invention, in the steering torque sensor according to any of the first to third aspects, the thin film strain gauge element is composed of a resistance element made of a nickel chrome material formed by a sputtering method.

As a result, a larger number of materials can be manufactured at a time in the same equipment volume as compared with the case where the thin film strain gauge element is directly formed on the torsion bar, and the manufacturing cost can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows the structure of a steering column shaft assembly 1 of an automobile. The steering torque sensor 2 of the present invention is built inside column covers 4a and 4b below a combination switch 3 of the steering column shaft assembly 1. .

As shown in FIG. 2, a torsion bar 7 is arranged between the lower shaft 5 and the upper shaft 6 of the steering column shaft assembly 1 so as to connect them, and the steering torque sensor 2 is arranged on the torsion bar 7. Is attached. The entire structure is covered with the jacket tube 8.

As shown in FIG. 3, the steering torque sensor 2 includes a sensor module 21 integrally attached to the circumferential surface of a cylindrical torsion bar 7, and a predetermined voltage applied to the sensor module 21. A sensor circuit 22 that amplifies a signal output from the sensor module 21 to detect torque, a wire harness 23 connected to the sensor circuit 22, and a sensor cover 24 that covers sensor components.
It is composed of

Next, the mounting structure of the sensor module 21 of the steering torque sensor 2 to the torsion bar 7 will be described with reference to FIGS. The sensor module 21 is manufactured by cold forging, powder sintering, or cutting of a stainless steel material, and the lower end faces of the leg portions 21a and 21b on both front and rear sides of the torsion bar 7 in the direction of the axis 7c are the torsion bar 7. It becomes a concave surface having the same curvature as the peripheral surface, and is closely adhered to the peripheral surface of the torsion bar 7 and is integrated by a welding method such as an electron beam welding method. This integration method is the torsion bar 7
This is a method in which the lower end portions 21c and 21d of the leg portions 21a and 21b of the sensor module 21 are welded to the circumferential surface of the torsion bar 7 without providing grooves or depressions on the side where stress concentration occurs.

The front and rear legs 21 of the sensor module 21
The body 21e for connecting between a and 21b is a torsion bar 7
It has a flat plate shape parallel to the axis 7c of
Thin film strain gauge elements 25a, 25b, 25c, 25 at the locations
d is formed. As shown in FIGS. 5 and 6, the four thin film strain gauge elements 25a, 25b, 25c, 25
d has the same resistance value so as to form the resistance elements R1, R2, R3, R4 on each side of the Wheatstone bridge circuit 26, and has a symmetry axis A parallel to the axis line 7c of the torsion bar 7, and It is set so as to be located at a point-symmetrical position with respect to one point B on the axis of symmetry A.

On the body 21e of the actual sensor module 21, an internal wiring pattern surrounded by the alternate long and short dash line 28 shown in FIG. 6 is formed, and the external wiring pattern of the alternate long and short dash line 28 is on the sensor circuit 22 side. And the circuit elements of both the sensor module 21 and the sensor circuit 22 form a Wheatstone bridge circuit 26. Further, the thin film resistance element Ri and the resistance elements Ra and Rb shown in FIG. 6 are to be attached later for circuit balance adjustment, and are unnecessary if there is no manufacturing error.

4 to 6, the right side of the paper surface is the front side, the left side is the rear side, the front side of the torsion bar 7 is the fixed side, and the rear side is the twisting side, which is counterclockwise when viewed from the twisting side. When a torque is applied, a tensile stress is generated in the direction connecting the thin film strain gauge elements 25a and 25c, and a compressive stress is generated in the direction connecting the thin film strain gauge elements 25b and 25d, as shown in FIG. Conversely, when a torque is applied clockwise to the twisting side, a compressive stress is generated in the direction connecting the thin film strain gauge elements 25a and 25c, and the thin film strain gauge elements 25b and 25b
Tensile stress is generated in the direction connecting the 25d.

The thin film strain gauge elements 25a, 25b, 25c, which form the resistance elements R1, R2, R3, R4, respectively.
Each of 25d shows resistance value change characteristics in which the resistance value increases due to tensile stress and the resistance value decreases due to compressive stress. Therefore, when a counterclockwise torque is applied to the torsion side of the torsion bar 7, as shown in the Wheatstone bridge circuit 26 of FIG. 6, the resistance elements R1 and R3 exhibiting resistance value changes in the same direction with respect to a certain torque. Of the resistance elements R1, R2 and R4 associated with the action of torque by connecting the pair of resistance elements R2 and R4 to the two opposite sides.
The bridge circuit 26 becomes unbalanced due to the change ΔR in the resistance value of each of R3 and R4, and the output voltage Δ
Vout is generated.

[0024]

[Equation 1] The sensor circuit 22 detects this output voltage and outputs it to the outside through the wire harness 23. The direction of the torque is determined by the positive / negative of this output voltage ΔVout.

Next, a manufacturing procedure of a polycrystalline silicon strain gauge type torque sensor as the steering torque sensor 2 will be described with reference to FIGS. 7 and 8. The sensor module 21 is manufactured into a predetermined shape as shown in FIG. 4 by cold forging of stainless steel, powder sintering, or cutting, and the surface is polished (steps S1 and S2).

Next, the body portion 2 of the sensor module 21.
An insulating film of SiO2 is formed on the surface of 1e by plasma enhanced chemical vapor deposition (P-CVD) (step S3).
Subsequently, a gauge film of polycrystalline silicon is formed by P-CVD, and a gauge pattern is formed by photolithography so that the gauge elements 25a, 25b, 25c, 25d remain at predetermined four places (steps S4 and S5). Subsequently, an Au electrode pattern is formed by electron beam PVD, and a Si-Nx protective film is further formed by P-CVD (steps S6 and S7).

Thus, the body portion 21 of the sensor module 21
When the thin film strain gauge elements 25a, 25b, 25c, 25d of polycrystalline silicon are formed at four predetermined positions on the surface of e and the electrode patterns are also formed, next, zero point adjustment in the sensor module 21 is performed. Is performed, and the thin-film correction resistance element Ri is added on the bridge circuit to correct the temperature characteristic under no load (step S8).

Subsequently, the leg portion 21 of the sensor module 21
The a and 21b are placed on the circumferential surface of the torsion bar 7 and welded by the electron beam welding method to be integrated with the torsion bar 7 (step S9). Then, in order to remove the residual strain that may have occurred during welding, an excessive torque is applied to the torsion bar 7 to remove the residual strain (step S).
10). According to this electron beam welding method, the legs 21a,
The lower ends 21c and 21d of the respective 21b are irradiated with an electron beam to locally melt the bonding portion in a short time and bond the surface to the torsion bar 7. Therefore, the stress applied at the time of joining tends to remain in the joint portion, and after removing the stress, the sensor module 21 is welded to the torsion bar 7 and then excessive torque is applied to the torsion bar 7 to force the joint portion to remain. The stress is removed.

After that, the sensor module 21 is connected to the sensor circuit 22, and a predetermined torque is actually applied to the torsion bar 7 in order to correct the temperature characteristic of sensitivity, and the sensitivity is adjusted. The correction resistance elements Ra and Rb are additionally connected to the Wheatstone bridge circuit 26 (steps S11 and S12). When the adjustment is completed in this way, the sensor cover 24 is assembled and the steering torque sensor 2 is completed (steps S13 and S1).
4).

Next, a procedure for manufacturing a metal thin film strain gauge type torque sensor as the steering torque sensor 2 will be described with reference to FIGS. 9 and 8. The sensor module 21 is manufactured into a predetermined shape as shown in FIG. 4 by cold forging of stainless steel, powder sintering, or cutting, and the surface is polished (steps S21 and S22).

Next, the body portion 2 of the sensor module 21.
An insulating film of SiO2 is formed on the surface of 1e by the sputtering method (step S23). Then, a Ni-Cr gauge film is formed by a sputtering method, and the gauge elements 25a, 2 are formed at predetermined four locations by photolithography.
A gauge pattern is formed so that 5b, 25c, and 25d remain (steps S24 and S25). Then, an Au electrode film is formed by a vacuum evaporation method, and an electrode pattern is further formed by photolithography (steps S26, S).
27). After that, Si-Nx is formed by a sputtering method.
Forming a protective film (step S28).

Thus, the body portion 21 of the sensor module 21
When the thin film strain gauge elements 25a, 25b, 25c, 25d of Ni-Cr metal are formed at four predetermined positions on the surface of e and the electrode pattern is also formed, the polycrystalline silicon thin film strain gauge type torque sensor will be described below. Same as the manufacturing procedure
Finally, the steering torque sensor 2 using the polycrystalline silicon thin film strain gauge type torque sensor is obtained according to the procedure shown in FIG.

Thus, according to this embodiment, the thin film strain gauge elements 25a, 25b, 25c and 25d are formed on the surface of the flat body portion 21e of the sensor module 21, and the leg portions 21a and 21b of the sensor module 21 are formed. Since the steering torque sensor is constructed by welding and integrally forming it on the circumferential surface of the torsion bar 7, the thin film strain gauge element is directly formed on the surface of the torsion bar 7 by the vacuum deposition method in the conventional manufacturing process. Sensor module 2 which is smaller in size than the torsion bar 7
Since a thin film strain gauge element may be formed at a predetermined position of No. 1 by a plasma chemical vapor deposition method or a sputtering method, and this may be welded to a predetermined position of the torsion bar 7, a thin film strain gauge element may be formed once. A large number of materials can be manufactured at the same time, and the manufacturing cost can be reduced.

In this embodiment, the front and rear legs 21a and 21b of the sensor module 21 are made concave so as to be aligned with the peripheral surface of the torsion bar 7 and welded by the electron beam welding method. Groove that causes metal fatigue due to stress concentration on the peripheral surface of 7.
There are no notches or dents, and the strength is not impaired.

Furthermore, according to this embodiment, since the torsion bar 7 and the sensor module 21 which is a separate body are integrated, the surface of the body portion 21e of the sensor module 21 against the torque acting on the torsion bar 7 is integrated. The amount of strain generated can be adjusted by changing the wall thickness and the notch shape, and a large strain amount can be obtained for the same torque, and the sensor sensitivity can be improved.

[0036]

As described above, according to the invention of claim 1,
In manufacturing the sensor module, the sensor module may be manufactured separately from the torsion bar, the thin film strain gauge element may be formed on the surface of the body of the sensor module by an appropriate method, and the sensor bar may be integrated with the torsion bar. You can
Since the thin film strain gauge element is formed on the sensor module that is smaller in size than the torsion bar, it is possible to perform the work of forming the thin film strain gauge element for many modules at the same time in the same manufacturing space, and the manufacturing cost is low. Can be converted.

Further, the sensitivity of the thin film strain gauge element with respect to the torque acting on the torsion bar can be adjusted by adjusting the shape and thickness of the sensor module, and a torque sensor having appropriate sensitivity can be easily manufactured according to the application. You can

According to the second aspect of the invention, the surface of the body of the sensor module is a flat surface parallel to the axis of the torsion bar, which facilitates formation of a thin film strain gauge element. .

According to the invention of claim 3, since the lower end surfaces of the front and rear legs of the sensor module are welded to the circumferential surface of the torsion bar by an electron beam welding method to be integrated, stress is applied to the torsion bar side. The steering torque sensor can be mounted without forming a stress concentration portion such as a groove, notch, or dent that causes concentration, and the steering torque applied to the steering torque sensor without impairing the mechanical strength of the steering column. Can be detected.

According to the invention of claim 4, since the thin film strain gauge element is constituted by the resistance element made of the polycrystalline silicon material formed by the plasma chemical vapor deposition method, the thin film strain gauge element is directly formed on the torsion bar. Than if you
A larger number of materials can be manufactured at the same time in the same equipment volume, and the manufacturing cost can be reduced.

According to the invention of claim 5, since the thin film strain gauge element is constituted by the resistance element made of the nickel chrome material formed by the sputtering method, it is possible to form the thin film strain gauge element directly on the torsion bar. A larger number of materials can be manufactured at the same time in the same equipment volume, and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a steering column shaft to which a steering torque sensor according to an embodiment of the present invention is attached.

FIG. 2 is a partially cutaway front view showing a mounting state of the above embodiment.

FIG. 3 is a cross-sectional view of the above embodiment.

FIG. 4 is a perspective view of the above embodiment.

FIG. 5 is a plan view of the sensor module according to the above embodiment.

FIG. 6 is a circuit diagram of a Wheatstone bridge circuit assembled according to the above embodiment.

FIG. 7 is a flowchart showing the first half of an example of the manufacturing method according to the embodiment.

FIG. 8 is a flowchart showing the latter half of an example of the manufacturing method according to the above embodiment.

FIG. 9 is a flowchart showing the first half of another example of the manufacturing method according to the embodiment.

[Explanation of symbols]

 1 Steering Column Shaft Assembly 2 Steering Torque Sensor 5 Lower Shaft 6 Upper Shaft 7 Torsion Bar 21 Sensor Module 21a, 21b Leg 21c, 21d Lower End 21e Body 22 Sensor Circuit 23 Wire Harness 24 Sensor Cover 25a, 25b, 25c, 25d Thin film strain gauge element R1, R2, R3, R4 resistance element Ri correction thin film resistance element Ra, Rb correction resistance element

Claims (5)

[Claims] 1. A steering torque sensor for integrally mounting a sensor module on a peripheral surface of a torsion bar that joins a lower shaft and an upper shaft of a steering column shaft, and detecting a torque applied to the torsion bar. The lower end surfaces of the front and rear legs of the module are concave surfaces having the same curvature as the curvature of the outer peripheral surface of the torsion bar, and the lower end surfaces of these legs are integrally fixed to the front and rear in the axial direction of the torsion bar, On the surface of the body that connects the front and rear legs of the sensor module, at each of four positions that are line-symmetrical and point-symmetrical with respect to the axis of symmetry parallel to the axial direction of the torsion bar. A thin film strain gauge element is formed, and a Wheatstone bridge circuit is formed so that each of the four thin film strain gauge elements constitutes a resistance on each side. A steering torque sensor made up of roads. 2. The steering torque sensor according to claim 1, wherein the surface of the body of the sensor module is a flat surface parallel to the axis of the torsion bar. 3. The lower end surfaces of the front and rear legs of the sensor module are welded and integrated with the peripheral surface of the torsion bar by an electron beam welding method.
The steering torque sensor described. 4. The steering torque according to claim 1, wherein the thin film strain gauge element is composed of a resistance element made of a polycrystalline silicon material formed by a plasma chemical vapor deposition method. Sensor. 5. The steering torque sensor according to claim 1, wherein the thin film strain gauge element is composed of a resistance element made of a nickel chrome material formed by a sputtering method.