JP2018036118A - Thrust sensor for electric brake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress variation of strain output due to positional deviation and angular deviation between a piston and a thrust sensor to which thrust is applied from the piston.SOLUTION: In a thrust sensor 1, a strain sensor 11 (strain sensors 11a, 11b) is mounted on a pressure receiving frame 12 at which an inclination part 15 is formed, and deformation of the pressure receiving frame 12 is directly transmitted to the strain sensors 11a, 11b. The strain sensor 11a and the strain sensor 11b are mounted along an X-axis direction of the pressure receiving frame 12 at an equal interval, so as to output ideally the same strain by thrust via a piston 2. A curved surface 16 is formed at a tip of the piston 2, and the piston 2 and the thrust sensor 1 contact with each other via the curved surface 16 and the inclination part 15.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a thrust sensor used in an electric brake device.

  In an electric brake device that brakes a vehicle using an electric motor as a driving source, as shown in Patent Document 1, a slip including a current ripple and grease viscosity of a machine part that is operated by the current motor is generated from a current that drives the electric motor. Thrust is estimated and controlled by calculating the so-called thrust-contributing current that contributes only to the generation of the brake pad pressing force (hereinafter referred to as thrust) from which the dynamic resistance current (viscosity / friction torque component current) is removed. It is carried out.

  In the electric brake control technique described above, the accuracy of the estimated value of the thrust may be inaccurate due to a change in the mechanical portion over time. If such a state occurs in the left and right wheels, the vehicle stability during braking may be reduced.

  Therefore, conventionally, methods for calculating a detailed thrust have been studied, and braking of the vehicle is ensured for a long time by measuring the thrust with a thrust sensor or the like. As a thrust sensor, a thrust sensor as in Patent Document 2 that measures a thrust (load) acting in a uniaxial direction (for example, a Z direction in an orthogonal coordinate system) has been conventionally known. The thrust sensor described in Patent Document 2 is a thrust sensor that measures thrust by pushing a sensing unit through a piston, and includes a piston that transmits a load in a uniaxial direction, and a strain gauge that measures the load through the piston. When there is a support case and stopper that protects the strain gauge, the thrust is measured using the strain gauge within the allowable measurement range of the strain gauge, and the load applied to the strain gauge exceeds the allowable measurement range. Has a structure that stops at the stopper and does not deform the strain gauge excessively. Further, the periphery of the piston is covered with a piston guide so that thrust is applied in one axial direction.

JP 2003-106355 A Japanese Patent Application No. 2015-1111084

  In the configuration of the thrust sensor described in Patent Document 2 described above, the piston is covered with the piston guide so that thrust is applied in a uniaxial direction, and it is necessary to process the piston and the piston guide with high accuracy. Becomes larger.

  In addition, since the tip of the piston has a conical shape to push the center of the strain gauge, stress is concentrated at one point on the top of the cone when a large thrust is applied. Unsuitable.

  An object of the present invention is to provide a low-cost thrust sensor that can accurately measure a large thrust acting in a uniaxial direction. It is another object of the present invention to provide a thrust sensor that enables position correction when the thrust application position is shifted.

  In order to solve the above-described problem, a thrust sensor according to a first aspect of the present invention includes a piston that transmits a load in a uniaxial direction, a pressure receiving frame that receives the thrust through the piston, and a thrust through the pressure receiving frame. A pressure receiving plate that receives the pressure sensor, and a strain sensor that receives thrust through the pressure receiving plate, wherein the pressure receiving frame has an inclined portion, the inclined portion and the piston are in contact with each other, and the piston A portion in contact with the inclined portion is a curved surface.

  ADVANTAGE OF THE INVENTION According to this invention, the thrust sensor which reduced the distortion output dispersion | variation accompanying the position shift and angle shift | offset | difference of a piston and a thrust sensor can be provided.

  Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is sectional drawing which shows the structure of the electric brake using the thrust sensor of this invention. It is sectional drawing which shows the structure of the thrust sensor of 1st Example of this invention. It is explanatory drawing which showed the example of the bridge circuit. It is sectional drawing which shows the structure of the thrust sensor of 2nd Example of this invention. It is the graph which showed the output variation at the time of each angle shift | offset | difference at the time of the inclination part from the thrust sensor of 1st Example of this invention, and a curved surface from a piston.

  Hereinafter, examples will be described with reference to the drawings.

FIG. 1 is a sectional view showing the structure of an electric brake using a thrust sensor of the present invention. The electric brake 7 is mainly composed of a thrust sensor 1, a piston 2, a motor 3, a rotation-linear motion conversion mechanism 4, a pad 5, a disk 6, and the like. When the driver steps on the brake, the rotational torque of the motor 3 is converted from a rotational motion to a translational motion by the rotation-linear motion conversion mechanism 4, and the piston 2 moves in the direction of the motor rotation axis. By this movement, a thrust, which is a force in the direction of the motor rotation axis, is applied to the thrust sensor 1 that is in contact with the piston 2. At the same time, by pushing the pad 5 through the piston 2, the disc 6 is sandwiched between the pads 5 on both sides and the brake is applied. FIG. 2 shows a cross-sectional view and a plan view of the thrust sensor 1 of this embodiment. The thrust sensor 1 has a configuration in which a pressure receiving plate 13 for mounting the strain sensor 11 is mounted on a pressure receiving frame 12 in which an inclined portion 15 is formed via a connection pin 14. The pressure receiving plate 13 and the pressure receiving frame 12 are connected by welding the connection pin 14 and the pressure receiving plate outer peripheral portion 18, and deformation of the pressure receiving frame 12 is detected via the connection pin 14 and the pressure receiving frame outer peripheral portion 18. , 11b. The pressure receiving plate 13 has a thin beam structure that can be easily deformed so as not to prevent deformation of the pressure receiving frame 12. On the pressure receiving plate 13, square strain sensors 11a and 11b are joined via joining layers 17a and 17b. The strain sensor 11a and the strain sensor 11b are mounted along the X-axis direction of the pressure receiving plate 13 and symmetrically with respect to the connection pin 14, and ideally the same strain is caused by the thrust through the piston 2. Is output.

  The contact portion between the piston 2 and the inclined portion 15 is a curved surface 16, and the piston 2 and the thrust sensor 1 are in contact with each other at the curved surface 16 and the inclined portion 15.

  FIG. 3 shows the configuration of the Wheatstone bridge circuit of the strain sensor 11. The strain sensor 11 has a gauge region 22 at the center of the surface not joined to the pressure receiving plate 13, and has four strain gauges 21 (first to fourth strain gauges 21 a to 21 d) in the gauge region 22. The four strain gauges 21 are connected by wiring not shown. The gauge region 22 is disposed on the central portion of the strain sensor 11, and the first strain gauge 21a and the second strain gauge 21b have strain in the X-axis direction of the pressure receiving plate 13, and the third strain gauge 21c and the fourth strain gauge 21d. Are arranged so that the strain in the Y-axis direction of the pressure receiving plate 13 can be measured. In the thrust sensor 1, the pressure receiving frame 12 and the pressure receiving plate 13 are deformed with respect to the thrust applied via the piston 2, and the stress of the strain gauge 21 changes, and the resistance of the strain gauge 21 changes accordingly. As a differential output of the bridge circuit, an output proportional to the pressure is obtained.

  The pressure receiving frame 12 and the pressure receiving plate 13 are made of metal such as stainless steel. The pressure receiving frame 12 has a structure in which a circular tube is formed on a circular plate. As the processing method, cutting, electric discharge machining, press working, or the like can be used. An inclined portion 15 is formed on the pressure receiving frame outer peripheral portion 18 which is an end portion of the surface processed into a circular tube shape, and the pressure receiving plate 13 is attached by welding.

  The strain sensor 11 is manufactured using a single crystal silicon substrate as a material, and the strain gauge 21 is a p-type silicon piezoresistive gauge manufactured by impurity diffusion. A silicon substrate having a crystal plane (100) is used so that the X-axis and the Y-axis coincide with <110> of the silicon crystal axis. Accordingly, the first to fourth strain gauges 21a to 21d are all piezoresistive gauges in the p-type silicon <110> direction.

  Au / Sn solder or glass is used for the adhesive layer 17. The bonding process is performed, for example, by forming a Ni / Au film on the bonding surface of the strain sensor 11 by sputtering, and forming an Sn film on the bonding area of the strain sensor 11 of the pressure receiving plate 13 by plating. Alignment is performed with Au / Sn sandwiched, and bonding is performed by heating to melt Au / Sn.

  The thrust sensor 1 of the present invention is characterized in that the contact portion between the piston 2 of the piston 2 and the inclined portion 15 is a curved surface 16.

  Due to the mounting error of the thrust sensor 1, there is a possibility that a positional shift in which the centers of the thrust sensor 1 and the piston 2 are shifted as seen in a plan view may occur. Assuming that a thrust is applied in a state in which the displacement has occurred, the inclined portion 15 formed on the pressure receiving frame 12 and the curved surface 16 of the piston 2 are slid together to correct the position of the piston 2, and the center of the thrust sensor 1 And the center of the piston 2 substantially coincide. As a result, the position of the thrust applied to the pressure receiving frame 12 via the piston 2 is substantially the same as the position to which the thrust is applied when there is no displacement, and the output is close to the output when there is no displacement. That is, the variation in distortion output can be reduced with respect to the positional deviation.

  Further, due to mounting error of the thrust sensor 1, there is a possibility that an angle shift in which the angles of the thrust sensor 1 and the piston 2 are shifted occurs. Assuming that thrust is applied in a state where angular deviation has occurred, the curved surface 16 of the piston 2 is pressed against the inclined portion 15 formed on the pressure receiving frame 12. Since the tip of the piston 2 is the curved surface 16, the place where it comes into contact is almost the same as the ideal state with no angular deviation, and the output is close to the output when there is no angular deviation. That is, the variation in distortion output can be reduced with respect to the angular deviation.

  In addition, the thrust sensor 1 of the present invention has two strain sensors 11 mounted at equal intervals from the connection pin along the pressure receiving plate 13, and the same strain is obtained in an ideal state where no positional deviation or angular deviation occurs. Generate output. Therefore, even when a failure of the strain sensor 11 occurs, for example, when one of the bonding layers 17 between the strain sensor 11 and the pressure receiving plate 13 is cracked due to deterioration with time, the output of the other strain sensor 11 is not output. It has a fail-safe function that makes it possible to control the electric brake.

  Furthermore, ideally, since two strain sensors 11 that output the same output are mounted, it is possible to predict the positional deviation and the angular deviation and calculate the ideal output by taking the difference between the outputs of the strain sensors 11. .

  The strain sensor 11 can include not only a bridge circuit but also peripheral circuits such as an output amplifier, a current source, an A / D conversion, an output correction circuit, a memory for storing correction values, and a temperature sensor. By having the signal processing circuit as described above in the strain sensor, output signal amplification, temperature correction, zero point correction, and the like can be performed, and the accuracy of the output signal can be increased. In the temperature correction, since the strain gauge 21 and the temperature sensor can be formed on the same strain sensor 11, the temperature of the strain gauge 21 can be accurately measured, and the temperature correction can be performed with high accuracy.

  In the present embodiment, since the pressure receiving frame 12 and the pressure receiving plate 13 that receive thrust are made of stainless steel, the material has a high yield strength, and it is easy to configure a sensor with a high pressure measurement range. It can also be used when the liquid or gas to be measured is highly corrosive. The material of the stainless steel can be selected by selecting a precipitation hardening type stainless steel such as SUS630 when importance is attached to the proof stress and selecting a stainless steel having high corrosion resistance such as SUS316 when importance is attached to the corrosion resistance. Further, the material is not limited to stainless steel, and various steel types can be selected in consideration of proof stress, corrosion resistance, difference in linear expansion coefficient from silicon, and the like.

  Further, the material of the bonding layer 17 and the bonding process are not limited to the materials and processes described above. As the bonding layer 17, for example, glass, Au / Ge solder, or Au / Si solder is used, so that the creep deformation of the bonding layer 17 can be further reduced. Moreover, although it is easy to carry out creep deformation | transformation, if it is a use which accept | permits it, various adhesive agents can be used. As for the bonding process, there is a method in which Au / Sn is directly formed on the rear surface of the diaphragm or sensor chip by plating or the like in addition to the method using the Au / Su pellet.

  FIG. 4 shows a cross-sectional view and a plan view of a second embodiment of the thrust sensor 1 of the present invention. In the thrust sensor 1, the strain sensor 11 is mounted on the pressure receiving frame 12 in which the inclined portion 15 is formed, and the deformation of the pressure receiving frame 12 is directly transmitted to the strain sensors 11a and 11b. The strain sensor 11 a and the strain sensor 11 b are mounted at equal intervals along the X-axis direction of the pressure receiving frame 12, and ideally the same strain is output by the thrust through the piston 2. Cost reduction can be achieved by not using the pressure receiving plate 13.

  The thrust sensor 1 of the present invention is characterized in that the contact portion between the piston 2 of the piston 2 and the inclined portion 15 is a curved surface 16.

  Due to the mounting error of the thrust sensor 1, there is a possibility that a positional shift in which the centers of the thrust sensor 1 and the piston 2 are shifted as seen in a plan view may occur. Assuming that a thrust is applied in a state in which the displacement has occurred, the inclined portion 15 formed on the pressure receiving frame 12 and the curved surface 16 of the piston 2 are slid together to correct the position of the piston 2, and the center of the thrust sensor 1 And the center of the piston 2 substantially coincide. As a result, the position of the thrust applied to the pressure receiving frame 12 via the piston 2 is substantially the same as the position to which the thrust is applied when there is no displacement, and the output is close to the output when there is no displacement. That is, the variation in distortion output can be reduced with respect to the positional deviation.

  Further, due to mounting error of the thrust sensor 1, there is a possibility that an angle shift in which the angles of the thrust sensor 1 and the piston 2 are shifted occurs. Assuming that thrust is applied in a state where angular deviation has occurred, the curved surface 16 of the piston 2 is pressed against the inclined portion 15 formed on the pressure receiving frame 12. Since the tip of the piston 2 is the curved surface 16, the place where it comes into contact is almost the same as the ideal state with no angular deviation, and the output is close to the output when there is no angular deviation. That is, the variation in distortion output can be reduced with respect to the angular deviation.

  Hereinafter, the result of verifying the effect obtained by the present invention will be described.

  In order to confirm the effect of reducing the influence of the angular deviation of the piston 2 of the present invention, a numerical analysis using a finite element method (FEM) was performed. The structure of FIG. 2 was used for the model of the present invention, and a structure without the inclined portion 15 of the pressure receiving frame 12 and the curved surface 16 of the piston 2 was used as a comparative structure. The calculation was performed assuming that the diameter of the pressure receiving frame 12 was 30 mm, the depth of the inclined portion 15 of the pressure receiving frame 12 was 1 mm, the angle of the inclined portion 15 was 45 °, the diameter of the piston 2 was 15 mm, and the R of the curved surface 16 was 15 mm.

  A method for calculating the output of the thrust sensor from the stress generated in the strain gauge is described below.

In the thrust sensor of the present invention, the same stress acts on the first strain gauge 21a and the second strain gauge 21b arranged along the X axis, and it can be considered that the resistance change is equal. Similarly, the third strain gauge 21c and the fourth strain gauge 21d have the same resistance change. Assuming that the initial resistance R ₀ is the same for all strain gauges, the resistance of each strain gauge is expressed by the following equation.

The voltage change rate V _out / V _cc obtained by the bridge circuit of FIG.

Resistance changes ΔR1 and ΔR3 are obtained as follows. When the stress component in the X direction is σ _x and the stress component in the Y direction is σ _{y in} the stress generated in the first and second strain gauges, the resistance change ΔR ₁ is the longitudinal piezoresistance coefficient of the strain gauge π _l , Where the transverse piezoresistance coefficient is π _t

It is expressed. On the other hand, the same stress is generated in the third and fourth strain gauges, but since the gauges are arranged along the Y direction, the stress in the current direction is σ _y , and the stress component in the direction perpendicular thereto is σ _x . , Resistance change △ R ₃ is

It is expressed as The stress in the Z direction was ignored because it was almost zero.
In equation (3), if the change in resistance is sufficiently small with respect to the initial resistance (2R ₀ << ΔR ₁ + ΔR ₃ ), substituting equations (4) and (5) gives the following.

Note that in the p-type silicon <110> direction, π _l and π _t are opposite in sign and have almost the same value.

It is. Assuming that the Young's modulus of the strain sensor 11 is E, the stress difference σ _x -σ _y is E (ε _x -ε _y ). The strain in the current direction is ε _y , and the strain component in the direction perpendicular thereto is ε _x .

From the above, the output change rate of the thrust sensor, that is, the sensitivity is proportional to the strain difference ε _x -ε _y acting on the strain gauge in the X direction and the Y direction.

FIG. 5 shows the result of analysis for applying a thrust of 10 kN to the piston 2 in the structure of the present invention and the comparative structure. The strain difference ε _x -ε _y when a thrust of 10 kN was applied in the ideal state was displayed, and the strain difference when the angle deviation occurred was compared.

  From the results, it was found that the distortion difference output variation due to the angular deviation, which had a great influence on the comparative structure, can suppress the influence of the angular deviation in the structure of the present invention.

DESCRIPTION OF SYMBOLS 1 Thrust sensor 2 Piston 3 Motor 4 Rotation-linear motion mechanism 5 Pad 6 Disk 7 Electric brake 11 Strain sensor 12 Pressure receiving frame 13 Pressure receiving plate 14 Connection pin 15 Inclination part 16 Curved surface 17 Bonding layer 18 Pressure receiving frame outer peripheral part 21 Strain gauge 22 Gauge region

Claims (5)

  A piston that transmits a load in a uniaxial direction; a pressure receiving frame that receives thrust through the piston; and a strain sensor that receives thrust; and the pressure receiving frame has an inclined portion, and the inclined portion and the piston Are in contact with each other, and the portion of the piston in contact with the inclined portion is a curved surface.   2. The thrust sensor according to claim 1, wherein a piston that transmits a load in a uniaxial direction, a pressure receiving frame that receives the thrust via the piston, a pressure receiving plate that receives the thrust via the pressure receiving frame, and the pressure receiving plate A strain sensor that receives thrust, and an inclined portion is formed on the pressure receiving frame, the inclined portion and the piston are in contact with each other, and a portion of the piston that is in contact with the inclined portion is curved. It is characterized by becoming.   3. The thrust sensor according to claim 1, wherein two strain sensors are mounted at a constant interval, and outputs when the thrust is applied are the same. 4.     4. The thrust sensor according to claim 3, wherein the pressure receiving frame and the pressure receiving plate are connected at a central portion.     5. The thrust sensor according to claim 1, wherein the four strain gauges are made of p-type single crystal silicon and are formed along a <110> crystal orientation of silicon. .

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