LOAD DETECTION DEVICE AND GAIN ADJUSTMENT METHOD FOR LOAD DETECTION DEVICE

Abstract

The present invention provides: a load detection device that, even when a load cell has a wide output range, keeps a measurement value of a load detection device within a prescribed measurement range and is capable of detecting a load with high accuracy; and a gain adjustment method for a load detection device. The load detection device detects a load on the basis of a differential signal output from a load cell and comprises: an excitation-side differential amplification circuit that amplifies an excitation signal which is transmitted to the load cell; a measurement-side differential amplification circuit that amplifies a first differential signal output from the load cell; and a control device that controls the excitation-side differential amplification circuit and the measurement-side differential amplification circuit. The control device executes a gain adjustment process for adjusting output gain by adjusting excitation-side gain of the excitation-side differential amplification circuit and / or measurement-side gain of the measurement-side differential amplification circuit such that a measurement value, which is measured on the basis of a second differential signal output from the measurement-side differential amplification circuit, is within a prescribed range.

Description

[Technical field]

[0001] The present disclosure relates to a load detection device that detects a load applied to a measurement object based on a differential signal output from a load cell, and a gain adjustment method for the load detection device. [Background technology]

[0002] Load cells using strain gauges, whose resistance changes with strain caused by a load, are widely used. For example, a load cell is known in which a strain gauge is incorporated in a bridge circuit, which is a conversion circuit that converts the change in the resistance value of the strain gauge caused by a load into an electrical signal, and the change in resistance value is output as a differential signal. When measuring a load using such a load cell, an amplifier may be used to amplify the output differential signal.

[0003] For example, Patent Document 1 discloses a detection device capable of detecting the output voltage of a bridge circuit with high accuracy. Specifically, the detection device of Patent Document 1 includes a bridge circuit, a power supply that applies a voltage to the bridge circuit, an instrumentation amplifier that receives the output voltage of the bridge circuit from a high-impedance input terminal and amplifies and outputs the input output voltage, and a physical quantity calculation unit that receives the output voltage amplified by the instrumentation amplifier and calculates a physical quantity based on the output voltage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-39871 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, a force detection sensor, such as a load cell mounted on a vehicle, which is attached to an axle and detects the load applied to a wheel, has a wide output range, and therefore it is necessary to set the gain appropriately according to the output from the load cell. For example, if the gain is set small even though the output from the load cell is small, the load detection accuracy may decrease. On the other hand, if the gain is set large even though the output from the load cell is large, the measurement range of the detection device may be exceeded.

[0006] The present disclosure has been made in consideration of the above problems, and an object of the present disclosure is to provide a load detection device and a gain adjustment method for a load detection device that can keep the measurement value of the load detection device within a predetermined measurement range and detect loads with high accuracy, even when the output range of the load cell is wide. [Means for solving the problem]

[0007] In order to solve the above problem, according to one aspect of the present disclosure, A load detection device that detects a load applied to a measurement object based on a differential signal output from a load cell having a bridge circuit to which a strain gauge is connected, comprising: an excitation side differential amplifier circuit that amplifies an excitation signal to be transmitted to the load cell; a measurement-side differential amplifier circuit that amplifies a first differential signal output from the load cell; a control device for controlling the excitation side differential amplifier circuit and the measurement side differential amplifier circuit, The control device includes: There is provided a load detection device that executes a gain adjustment process to adjust an output gain by adjusting at least one of an excitation side gain by the excitation side differential amplifier circuit and a measurement side gain by the measurement side differential amplifier circuit so that a measurement value measured based on a second differential signal output from the measurement side differential amplifier circuit falls within a predetermined range.

[0008] In order to solve the above problems, according to another aspect of the present disclosure, A gain adjustment method for adjusting a gain of a load detection device that detects a load applied to a measurement object based on a differential signal output from a load cell having a bridge circuit to which a strain gauge is connected, comprising the steps of: amplifying an excitation signal to be transmitted to the load cell by an excitation side differential amplifier circuit; amplifying a first differential signal output from the load cell by a measurement side differential amplifier circuit; and adjusting an output gain by adjusting at least one of an excitation side gain by the excitation side differential amplifier circuit and a measurement side gain by the measurement side differential amplifier circuit so that a measurement value measured based on a second differential signal output from the measurement side differential amplifier circuit falls within a predetermined range. Effect of the Invention

[0009] As described above, according to the present disclosure, even if the output range of the load cell is wide, the measurement value of the load detection device can be set within a predetermined measurement range, and the load can be detected with high accuracy. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view showing a configuration example of a load cell (six-component force detector). [Diagram 2] FIG. 2 is a schematic diagram showing the arrangement of strain gauges in a load cell. [Diagram 3] FIG. 2 is an explanatory diagram showing a configuration example of a bridge circuit of a load cell. [Figure 4] 1 is a block diagram showing a configuration example of a load detection device according to an embodiment of the present disclosure. [Diagram 5] 5 is a flowchart showing a presetting process in the gain adjustment method for the load detection device according to the embodiment; [Figure 6] 5 is a flowchart showing a gain feedback adjustment process by the gain adjustment method for the load detection device according to the embodiment. [Figure 7]5 is a flowchart showing a process of setting an excitation-side gain and a measurement-side gain in the gain adjustment method for the load detection device according to the embodiment. [Figure 8] 10 is a flowchart showing a modified example of the gain feedback adjustment process in the gain adjustment method for the load detection device according to the embodiment. [Figure 9] FIG. 13 is an explanatory diagram showing basic measurement values ​​when the output gain is fixed and no gain adjustment is performed. [Figure 10] 11 is an explanatory diagram showing measurement values ​​when the output gain of the load detection device according to the embodiment is increased. FIG. [Figure 11] FIG. 13 is an explanatory diagram showing basic measurement values ​​when the output gain is fixed and no gain adjustment is performed. [Figure 12] 10 is an explanatory diagram showing measurement values ​​when the output gain of the load detection device according to the embodiment is reduced. FIG. [Figure 13] 11 is an explanatory diagram showing an example of adjustment of an output gain by adjusting an excitation-side gain and a measurement-side gain in the load detection device according to the embodiment. FIG. [Figure 14] 5 is a flowchart showing a gain feedforward adjustment process by the gain adjustment method for the load detection device according to the embodiment. [Figure 15] 5 is a flowchart showing a zero point offset process in the gain adjustment method for the load detection device according to the embodiment. [Figure 16] 11 is an explanatory diagram showing measurement values ​​when output gain adjustment and zero point offset processing are performed by the load detection device according to the embodiment. FIG. [Figure 17] FIG. 13 is a schematic diagram showing the arrangement of strain gauges in a six-component force detector of a modified example. [Figure 18] FIG. 2 is an explanatory diagram showing a gauge pattern of a biaxial shear strain gauge. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are denoted by the same reference numerals, and redundant description will be omitted.

[0012] <<1. Overview of the embodiments of the present disclosure>> <1-1. Detailed Description of the Background of the Present Disclosure> First, the background to the creation of the technology of the present disclosure will be described. Note that the background described below merely shows one aspect of the configuration of a load cell to which the technology of the present disclosure can be applied, and the load cell to which the present disclosure can be applied is not limited to the load cell having the configuration exemplified below.

[0013] There is known a six-component force detector that detects loads (Fx, Fy, Fz) applied to the wheels of a vehicle such as an automobile in the longitudinal direction (hereinafter also referred to as the "x-axis direction"), the width direction (hereinafter also referred to as the "y-axis direction"), and the height direction (hereinafter also referred to as the "z-axis direction") of the vehicle, as well as moments (Mx, My, Mz) about the x-axis, y-axis, and z-axis, respectively. In such a six-component force detector, the sensitivity of the strain gauge is likely to vary depending on the direction of the component force.

[0014] In addition, because the maximum load applied to the wheel is large, the six-component force detector uses a strain gauge with a large output. For this reason, the output range of the six-component force detector is wide and may exceed the measurement range of the load detection device. To deal with this, it is necessary to reduce the gain that amplifies the output of the load cell, but simply setting the gain to a small value will result in a decrease in measurement accuracy when the output from the six-component force detector is small. Conversely, if the gain is set to a large value to match the small output from the six-component force detector, the output from the six-component force detector will exceed the measurement range of the load detection device when it is large.

[0015] Against this background, the technology disclosed herein provides a load detection device and a gain adjustment method for a load detection device that can automatically set a gain according to the output of a load cell even when the output range of the load cell is wide, and can accurately detect a load within the measurement range of the load detection device, as well as a recording medium having a computer program recorded thereon.

[0016] <1-2. Features of the embodiment of the present disclosure> (1-2-1) The embodiment of the present disclosure is A load detection device that detects a load applied to a measurement object based on a differential signal output from a load cell having a bridge circuit to which a strain gauge is connected, comprising: an excitation side differential amplifier circuit that amplifies an excitation signal to be transmitted to the load cell; a measurement-side differential amplifier circuit that amplifies a first differential signal output from the load cell; a control device for controlling the excitation side differential amplifier circuit and the measurement side differential amplifier circuit, The control device includes: The present invention has a configuration in which a gain adjustment process is executed to adjust at least one of the excitation side gain by the excitation side differential amplifier circuit and the measurement side gain by the measurement side differential amplifier circuit, thereby adjusting the output gain, so that a measurement value measured based on the second differential signal output from the measurement side differential amplifier circuit falls within a predetermined range.

[0017] In addition, the embodiments of the present disclosure can also be realized as a gain adjustment method for a load detection device that automatically sets a gain in accordance with the output of a load cell, a computer program that causes a control device to execute such a gain adjustment process, and a recording medium having the computer program recorded thereon.

[0018] With this configuration, the output gain can be decreased when the measurement value by the load detection device increases, and increased when the measurement value by the load detection device decreases, and the output gain can be adjusted automatically without adjustment by a user, etc. In particular, by adjusting at least one of the excitation side gain and the measurement side gain to adjust the output gain, it is possible to adjust the resolution of the load being measured while adjusting the measurement value to a predetermined range. Therefore, even when a load cell with a wide output range is used, the detection accuracy of the load can be improved.

[0019] The "excitation side gain" refers to the gain by the excitation side differential amplifier circuit, the "measurement side gain" refers to the gain by the measurement side differential amplifier circuit, and the "output gain" refers to the total gain obtained by multiplying the "excitation side gain" by the "measurement side gain."

[0020] In this specification, the values ​​of the excitation-side gain and the measurement-side gain set by the control device are referred to as the "excitation-side gain setting value" and the "measurement-side gain setting value", respectively. Furthermore, the total gain obtained by multiplying the "excitation-side gain setting value" and the "measurement-side gain setting value" is referred to as the "output gain setting value".

[0021] Additionally, an "excitation signal," a "first differential signal," and a "second differential signal" each indicate a voltage signal, and a "measurement value" indicates a voltage value.

[0022] (1-2-2) In addition, in the embodiment of the present disclosure, The control device includes: In the gain adjustment process, the excitation side gain and the measurement side gain may be selected from a plurality of excitation side gain candidate values ​​set at a predetermined interval as the excitation side gain and a plurality of measurement side gain candidate values ​​set at a predetermined interval as the measurement side gain, respectively, to set the output gain.

[0023] With this configuration, an output gain for amplifying the output from the bridge circuit is set by a combination of preset excitation-side gain candidate values ​​and measurement-side gain candidate values, and the load on the control device for adjusting the output gain can be reduced. Also, by adjusting the excitation-side gain and the measurement-side gain, respectively, the output gain can be adjusted while balancing the range of the measurement value and the resolution of the load to be measured.

[0024] The "excitation-side gain candidate value" refers to a candidate for a preset excitation-side gain setting value, and the "measurement-side gain candidate value" refers to a candidate for a preset measurement-side gain setting value. The "output gain candidate value" refers to a total gain value obtained by multiplying the "excitation-side gain candidate value" and the "measurement-side gain candidate value."

[0025] (1-2-3) In addition, in the embodiment of the present disclosure, The load detection device detects a plurality of component forces acting on a tire of a vehicle, The control device includes: In the gain adjustment process, The vehicle is in a traveling state within a predetermined period before the current time, and the maximum measurement value, which is the maximum value of the measurement values ​​within the predetermined period, is equal to or greater than the load. detection If the device is below the specified maximum measurable value, determining whether a first ratio, which is a ratio of the maximum measurement value to a maximum allowable measurement value at which the measurement value can be guaranteed and which is determined according to the currently set output gain, is smaller than a second ratio, which is a ratio of the output gain that is one step smaller than the currently set output gain; The output gain may be increased when a state in which the first ratio is smaller than the second ratio continues for a predetermined first time period or longer.

[0026] With this configuration, even if the output gain is increased, the most recent maximum measurement value does not exceed the maximum allowable measurement value. No. 1If the load continues for more than this time, the output gain is increased, reducing the risk of the measurement value exceeding the maximum allowable measurement value. This amplifies the output from the bridge circuit within a range in which the measurement value does not exceed the maximum allowable measurement value, improving the load detection accuracy.

[0027] The "maximum measurable value" refers to the maximum measurement value that can guarantee measurement accuracy, which is determined from the characteristics of the devices and elements included in the load detection device. The "maximum allowable measurement value" refers to the maximum measurement value that is arbitrarily determined according to the set output gain.

[0028] (1-2-4) In addition, in the embodiment of the present disclosure, The control device includes: Even before the state in which the first ratio is smaller than the second ratio continues for the predetermined first time or more, The output gain may be increased when the vehicle is in a decelerating state and a state in which either or both of a value obtained by multiplying the acceleration acting on the vehicle in a predetermined direction by the weight of the vehicle, or a value obtained by summing the component forces acting on each of the tires in the predetermined direction, is less than a first threshold value based on gravitational acceleration continues for the predetermined period of time.

[0029] With this configuration, even if the state where the most recent maximum measurement value does not exceed the allowable maximum measurement value even if the output gain is increased has not continued for a predetermined first time or more, if it is determined from the vehicle's running state that the measurement value will not exceed the allowable maximum measurement value, the output gain can be quickly increased. This amplifies the output from the bridge circuit within a range where the measurement value does not exceed the allowable maximum measurement value, thereby improving the load detection accuracy.

[0030] The "first threshold based on the gravitational acceleration" is a value obtained by multiplying the gravitational acceleration by a coefficient set arbitrarily, and is a calculated value that simply indicates that the vehicle is not traveling close to the tire's limit in terms of vehicle motion. For example, if the coefficient of friction between the tire and the road surface can be estimated, or if the road surface condition can be estimated in advance, it may be possible to estimate the vehicle's limit of slippage from moment to moment, but by dynamically calculating the coefficient based on the load (N) at that time, it becomes possible to estimate the vehicle's limit of slippage.

[0031] (1-2-5) In addition, in the embodiment of the present disclosure, The control device includes: Even before the state in which the first ratio is smaller than the second ratio continues for the predetermined first time or more, The output gain may be increased when the vehicle is in a decelerating state and a state in which either or both of a value obtained by multiplying the sum of the lateral acceleration and the centrifugal acceleration acting in a vehicle width direction on the vehicle by the weight of the vehicle, or a value of the sum of the component forces acting on each of the tires in the vehicle width direction, is less than the first threshold value for the specified period of time continues.

[0032] With this configuration, the output gain can be increased quickly when the vehicle is traveling in a state in which lateral acceleration occurs.

[0033] (1-2-6) In addition, in the embodiment of the present disclosure, The control device includes: Even before the state in which the first ratio is smaller than the second ratio continues for the predetermined first time or more, The vehicle is in a decelerating state when traveling straight ahead, The output gain may be increased when a state in which either or both of a value obtained by multiplying an absolute value of longitudinal acceleration acting on the vehicle in the longitudinal direction by the weight of the vehicle, or a value obtained by summing component forces acting on each of the tires in the longitudinal direction, is less than the first threshold value for the specified period of time continues.

[0034] With this configuration, the output gain can be increased quickly when the vehicle is running in a state in which longitudinal acceleration occurs.

[0035] (1-2-7) In addition, in the embodiment of the present disclosure, The control device includes: In the gain adjustment process, The output gain may be reduced when the vehicle is in a traveling state within the predetermined period and the maximum measurement value within the predetermined period is equal to or greater than the predetermined measurable maximum value.

[0036] With this configuration, the output gain is reduced when the most recent maximum measurement value is equal to or greater than the maximum allowable measurement value, so that the output gain is maintained high while there is little risk that the measurement value will exceed the maximum allowable measurement value, thereby improving the accuracy of load detection.

[0037] (1-2-8) In addition, in the embodiment of the present disclosure, The control device includes: In the gain adjustment process, before The output gain may be reduced when a state in which either or both of a value obtained by multiplying the acceleration acting on the vehicle in a predetermined direction by the weight of the vehicle, or a value of the sum of the component forces acting on each of the tires in the predetermined direction, exceeds a second threshold value based on gravitational acceleration continues for the predetermined period of time.

[0038] With this configuration, when it is determined that the vehicle is in a state where there is a high possibility that the measured value will exceed the maximum allowable value, the output gain can be quickly reduced, thereby adjusting the output gain so that the measured value does not exceed the maximum allowable value, thereby improving the load detection accuracy.

[0039] The "second threshold based on gravitational acceleration" is a value obtained by multiplying the gravitational acceleration by an arbitrarily set coefficient, and is a calculated value that simply indicates that the vehicle is traveling close to the tire's limit in terms of vehicle motion. For example, if the coefficient of friction between the tire and the road surface can be estimated, or if the road surface condition can be estimated in advance, it may be possible to estimate the vehicle's limit of slippage from moment to moment, but by dynamically calculating the coefficient based on the load (N) at that time, it becomes possible to estimate the vehicle's limit of slippage.

[0040] (1-2-9) In addition, in the embodiment of the present disclosure, The control device includes: A value obtained by multiplying the sum of the lateral acceleration and the centrifugal acceleration acting on the vehicle in a vehicle width direction when the vehicle is accelerating by the weight of the vehicle, or Each the sum of the lateral forces acting on the tire in the vehicle width direction, or In front When the state in which the second threshold is exceeded continues for the predetermined period of time, the output gain may be reduced.

[0041] With this configuration, the output gain can be reduced quickly when the vehicle is traveling in a state in which lateral acceleration is occurring.

[0042] (1-2-10) In addition, in the embodiment of the present disclosure, The control device includes: When the vehicle continues to travel straight, the output gain may be reduced if a state in which either or both of a value obtained by multiplying the absolute value of the longitudinal acceleration acting on the vehicle in the longitudinal direction by the weight of the vehicle, or a value obtained by summing the component forces acting on each of the tires in the longitudinal direction, exceeds the second threshold value continues for the specified period of time.

[0043] With this configuration, when the vehicle is running in a state in which longitudinal acceleration occurs, the output gain can be reduced quickly.

[0044] (1-2-11) In addition, in the embodiment of the present disclosure, The control device includes: In the gain adjustment process, determining whether the pumping side gain can be increased; When the excitation-side gain can be increased, the excitation-side gain may be increased preferentially over the measurement-side gain.

[0045] This configuration makes it possible to amplify the output of the bridge circuit without reducing the resolution of the load being measured, thereby increasing the output of the bridge circuit without reducing the load detection accuracy.

[0046] (1-2-12) In addition, in the embodiment of the present disclosure, The control device includes: determining whether or not the strain gauge is not under load and is held in a proper position; When no load is applied to the strain gauge and the strain gauge is held in a proper position, a zero point offset process of the measurement value may be executed.

[0047] With this configuration, when the control device determines that no load is being applied to the strain gauge, zero point offset processing of the measurement value is automatically performed, further improving the load detection accuracy.

[0048] <<2. Details of the embodiment of the present disclosure>> <2-1. Example of load cell (6-component force detector) configuration> Next, a configuration example of a load cell to which the load detection device according to the embodiment of the present disclosure can be applied will be described.

[0049] In this embodiment, an example will be described in which the technology of the present disclosure is applied to a six-component force detector capable of detecting six-component forces (Fx, Fy, Fz, Mx, My, Mz) applied to a wheel of a vehicle, as one aspect of a load cell. The load cell according to this embodiment is a six-component force detector that detects six-component forces applied to a wheel, and is incorporated in a hub bearing unit that is attached to a suspension device and rotatably supports the wheel of a vehicle such as an automobile.

[0050] Fig. 1 shows a cross-sectional view of a hub bearing unit including a six-component force detector, cut along a plane including the axle. In Fig. 1, the right side shows the outer side in the vehicle width direction, and the left side shows the inner side in the vehicle width direction. Note that the configuration of the hub bearing unit shown in Fig. 1 is merely an example, and is not limited to the configuration shown in Fig. 1.

[0051] The hub bearing unit 100 is configured to include a hub 110, an outer cylinder 120, an inner cylinder 130, rolling elements 140, a base 150, and a six-component force detector 1. The hub 110 is a member to which a rim disc portion of a wheel (not shown) consisting of a rim and a tire is fastened. The hub 110 is configured by integrally forming a cylindrical portion 111, a flange portion 112, a collar portion 113, etc.

[0052] The cylindrical portion 111 is formed in a cylindrical shape concentric with the rotation axis (axle) of the wheel. The cylindrical portion 111 is inserted into the inner diameter side of the inner tube 130, the sensor 10, and the base portion 150. A spline hole 111a that fits with a spline shaft portion of a drive shaft (not shown) is formed in the vehicle width direction outer region of the inner peripheral surface portion of the cylindrical portion 111. The flange portion 112 is a disk-shaped portion formed by protruding from the end portion of the cylindrical portion 111 on the vehicle width direction outer side in a brim-like shape to the outer diameter side. The surface portion of the flange portion 112 on the vehicle width direction outer side functions as a base portion to which the rim disc is fastened. The flange portion 112 has openings 112a into which hub bolts are inserted, for example, about five openings 112a are formed on a predetermined pitch circle diameter at equal intervals in the circumferential direction. The collar portion 113 is a cylindrical portion concentric with the axle protruding from the surface portion of the flange portion 112 on the vehicle width direction outer side. The collar portion 113 fits into a center bore, which is a circular opening formed in the center of the rim disc, and improves the mounting accuracy of the wheel.

[0053] The outer cylinder 120, the inner cylinder 130, and the rolling elements 140 cooperate to form a rolling bearing (hub bearing) that rotatably supports the wheel. The outer cylinder 120 is formed by integrally forming a tubular portion 121, a flange portion 122, etc. The tubular portion 121 is a cylindrical portion that is concentric with the axle. A raceway surface that guides the rolling elements 140 is formed on the inner peripheral surface of the tubular portion 121. The inner end of the tubular portion 121 on the vehicle width direction is formed to protrude inward in the vehicle width direction with respect to the inner end of the tubular portion 131 of the inner cylinder 130 on the vehicle width direction.

[0054] The flange portion 122 is formed so as to protrude radially outward from the end portion of the cylindrical portion 121 on the outer side in the vehicle width direction in a brim-like shape. The flange portion 122 is a portion to which the flange portion 112 of the hub 110 is fastened. An outer surface portion of the flange portion 122 in the vehicle width direction abuts against an inner surface portion of the flange portion 112 of the hub 110 in the vehicle width direction. The flange portion 122 has a screw hole 122a formed concentrically with the opening 112a of the hub 110. A hub bolt (not shown) used to secure the wheel is fastened to the screw hole 122a.

[0055] The inner cylinder 130 is configured by integrally forming a cylindrical portion 131, a flange portion 132, and the like. The cylindrical portion 131 is a cylindrical member concentric with the axle, and is inserted into the inner diameter side of the cylindrical portion 121 of the outer cylinder 120. A predetermined gap is provided between the outer peripheral surface of the cylindrical portion 131 and the inner peripheral surface of the cylindrical portion 121 of the outer cylinder 120. A raceway surface that guides the rolling element 140 is formed on the outer peripheral surface of the cylindrical portion 131. The flange portion 132 is formed by protruding from the outer end of the cylindrical portion 131 in the vehicle width direction to the inner diameter side. The flange portion 132 holds the outer end of the first flange 12 of the sensor 10 in the vehicle width direction. The rolling element 140 is a bearing incorporated between the raceway surfaces of the outer cylinder 120 and the inner cylinder 130. The rolling element 140 is incorporated between the outer cylinder 120 and the inner cylinder 130 together with a retainer 141 and a retainer 142 that position the rolling element 140 between the outer cylinder 120 and the inner cylinder 130 .

[0056] The base 150 is a portion that fastens and fixes the hub bearing unit 100 to an upright (hub knuckle) (not shown) of a suspension device. The base 150 is configured by integrally forming a tubular portion 151, a flange portion 152, a recess 153, a protrusion 154, etc. The tubular portion 151 is a cylindrical member that is concentric with the axle, and an end portion on the inside in the vehicle width direction of the tubular portion 111 of the hub 110 is inserted into the tubular portion 151. The outer peripheral surface of the tubular portion 111 of the hub 110 is disposed opposite the inner peripheral surface of the tubular portion 151 at a predetermined radial distance.

[0057] The flange portion 152 is formed by projecting outwardly from the end portion on the outer side in the vehicle width direction of the cylindrical portion 151 in a brim-like shape. The flange portion 152 is a fastening surface portion for fastening the base portion 150 to an upright (not shown). A plurality of bolts used for fastening to the upright are inserted into the flange portion 152. Not shown Open Mouth A plurality of through holes 152b are formed in the flange portion 152 and are distributed in the circumferential direction. The through holes 152b are formed inside the flange portion 152, from the inside of the space in which the outer peripheral surface of the cylindrical portion 11 of the sensing body 10 is disposed to the outer peripheral edge of the flange portion 152, in which wiring connected to the strain gauges and the like are disposed.

[0058] The recess 153 is a portion formed by stepwise expanding the inner diameter of a region of the inner circumferential surface of the base 150 that corresponds to the flange portion 152 in the axial direction. The recess 153 is a portion that holds the second flange 13 of the sensor 10. The protruding portion 154 is a cylindrical portion formed protruding outward in the vehicle width direction from a radially intermediate portion of the flange portion 152. The outer circumferential surface of the protruding portion 154 is disposed opposite to, and spaced apart from, the inner circumferential surface of the tubular portion 121 of the outer cylinder 120 at the end portion on the inner side in the vehicle width direction.

[0059] The six-component force detector 1 is a load cell capable of detecting loads acting on a wheel in three orthogonal axial directions and moments around the three orthogonal axes. The six-component force detector 1 is configured with a sensing body 10 formed substantially in a cylindrical shape, a plurality of strain gauges provided on the sensing body 10, and a bridge circuit including the strain gauges.

[0060] The sensing body (sensor core) 10 is formed to have a cylindrical portion 11, a first flange 12, a second flange 13, etc. The cylindrical portion 11 is a cylindrical portion having substantially constant inner and outer diameters over a predetermined axial length, and is a portion to which a plurality of strain gauges, described below, are attached (bonded). The first flange 12 is provided at the outer end of the cylindrical portion 11 in the vehicle width direction, and is a portion formed to protrude both on the outer diameter side and the inner diameter side with respect to the cylindrical portion 11. The first flange 12 has an outer peripheral surface that is in contact with the inner cylinder. 130 The inner circumferential surface of the inner circumferential surface of the tubular portion 131 is in contact with the outer end of the tubular portion 131 in the vehicle width direction, and the end surface of the inner circumferential surface of the flange portion 132 is in contact with the inner circumferential surface of the inner circumferential surface of the flange portion 132 in the vehicle width direction. 130 is fixed at.

[0061] The second flange 13 is provided at the end of the cylindrical portion 11 on the inner side in the vehicle width direction, and is formed to protrude radially outward and radially inward from the cylindrical portion 11. The second flange 13 is fixed to the base portion 150 with its outer peripheral surface and end surface fitted into the recess 153 of the base portion 150. With this configuration, substantially all of the force acting on the wheel is transmitted between the base portion 150 and the sensing body 10 via the sensing body 10.

[0062] The six-component force detector 1 has an Fx detection system, an Fy detection system, an Fz detection system, an Mx detection system, a My detection system, and an Mz detection system, each having a bridge circuit including a strain gauge provided on the cylindrical portion 11 of the sensing body 10 described above. The Fx detection system detects a radial force Fx (x-axis direction) acting on the cylindrical portion 11 of the sensing body 10. The Fz detection system detects a radial force Fz (z-axis direction) acting on the cylindrical portion 11 of the sensing body 10 in a direction perpendicular to the x-axis direction. The Fy detection system detects an axial force Fy (y-axis direction) acting on the cylindrical portion 11 of the sensing body 10. The Mx detection system detects a moment Mx about the x-axis acting on the cylindrical portion 11 of the sensing body 10. The Mz detection system detects a moment Mz about the z-axis acting on the cylindrical portion 11 of the sensing body 10. The My detection system detects the moment My acting on the cylindrical portion 11 of the sensor 10 about the y-axis.

[0063] The above-mentioned Fx detection system, Fy detection system, Fz detection system, Mx detection system, My detection system, and Mz detection system are each configured with a bridge circuit including four strain gauges. Fig. 2 is a schematic diagram showing the arrangement of strain gauges in the six-component force detector 1. Fig. 3 is a diagram showing the arrangement of strain gauges in the Fx detection system and the configuration of the bridge circuit in the six-component force detector 1, and shows a representative example of the arrangement of strain gauges and the configuration of the bridge circuit in each force detection system (Fx detection system, Fy detection system, Fz detection system) and each moment detection system (Mx detection system, My detection system, Mz detection system).

[0064] As shown in Figs. 2 and 3, the Fx detection system is configured to include strain gauges 21 to 24. The strain gauges 21 to 24 are single-axis strain gauges, and are attached to the outer circumferential surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis direction of the cylindrical portion 11. The strain gauge 21 is attached to the area of ​​the outer circumferential surface of the cylindrical portion 11 on the first flange 12 side. In the region The strain gauge 22 is disposed on a straight line that passes through the strain gauge 21 and is parallel to the axial direction of the cylindrical portion 11, and is disposed on the outer peripheral surface of the cylindrical portion 11 on the second flange 13 side. In the regionThe strain gauge 23 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 when viewed from the strain gauge 22 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 22). The strain gauge 24 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 when viewed from the strain gauge 21 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 21).

[0065] As shown in FIG. 3, the bridge circuit of the Fx detection system is configured as a Wheatstone bridge circuit, in which the strain gauges 21 to 24 are connected in sequence in a loop shape, and the positive and negative poles of a power supply are connected between the strain gauges 22 and 23, and between the strain gauges 21 and 24, respectively. Terminal , and between the strain gauge 23 and the strain gauge 24 Terminal The potential difference is extracted as the output. The configuration of the bridge circuit will be explained in detail later.

[0066] The Fy detection system includes strain gauges 41 to 44. The strain gauges 41 to 44 are single-axis strain gauges and are attached to the outer circumferential surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis direction of the cylindrical portion 11. The strain gauge 41 is disposed between the strain gauges 21 and 22 of the Fx detection system. The strain gauges 42, 43, and 44 are disposed at positions where their phases around the central axis of the cylindrical portion 11 are shifted by 90 degrees, 180 degrees, and 270 degrees, respectively, from the strain gauge 41. The bridge circuit of the Fy detection system has the same configuration as that of the Fx detection system except that the strain gauges 21 to 24 of the Fx detection diameter shown in FIG. 3 are replaced with the strain gauges 41 to 44.

[0067] The Fz detection system is configured with strain gauges 31 to 34. The strain gauges 31 to 34 are single-axis strain gauges, and are attached to the outer circumferential surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis direction of the cylindrical portion 11. The strain gauge 31 is disposed at a 90° offset around the central axis of the cylindrical portion 11 with respect to the strain gauge 21 of the Fx detection system. The strain gauge 32 is disposed at a 90° offset around the central axis of the cylindrical portion 11 with respect to the strain gauge 22 of the Fx detection system. The strain gauges 31 and 32 are disposed on the same straight line parallel to the axial direction of the cylindrical portion 11. The strain gauge 33 is disposed at a position offset 180° around the central axis of the cylindrical portion 11 from the strain gauge 32 (a position symmetrical to the strain gauge 32 with respect to the central axis of the cylindrical portion 11). The strain gauge 34 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 from the strain gauge 31 (at a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 31). The bridge circuit of the Fz detection system is the same as that of the Fx detection system shown in FIG. system The configuration is the same as that of the first embodiment except that the strain gauges 21 to 24 are replaced with strain gauges 31 to 34.

[0068] The Mx detection system is configured with strain gauges 51 to 54. The strain gauges 51 to 54 are single-axis strain gauges and are attached to the outer circumferential surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis direction of the cylindrical portion 11. The strain gauge 51 is disposed adjacent to the strain gauge 31 of the Fz detection system in the central axis direction of the cylindrical portion 11. The strain gauge 52 is disposed adjacent to the strain gauge 32 of the Fz detection system in the central axis direction of the cylindrical portion 11. The strain gauges 51 and 52 are disposed on the same straight line parallel to the axial direction of the cylindrical portion 11. The strain gauge 53 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 from the strain gauge 52 (a position symmetrical to the strain gauge 52 with respect to the central axis of the cylindrical portion 11). The strain gauge 54 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 as viewed from the strain gauge 51 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 51). The bridge circuit of the Mx detection system is the same as that of the Fx detection system shown in FIG. systemThe configuration is the same as that of the first embodiment except that the strain gauges 21 to 24 are replaced with strain gauges 51 to 54.

[0069] The My detection system is configured with strain gauges 71-74. The strain gauges 71-74 are shear type strain gauges, and are attached to the outer circumferential surface of the cylindrical portion 11 so that their detection direction is the circumferential direction of the cylindrical portion 11. The strain gauge 71 is disposed midway between the strain gauges 41 and 42 of the Fy detection system. The strain gauge 72 is disposed midway between the strain gauges 42 and 44 of the Fy detection system. The strain gauges 73 and 74 are disposed at positions symmetrical with respect to the central axis of the cylindrical portion 11 with respect to the strain gauges 72 and 71, respectively. The bridge circuit of the My detection system is the same as the Fx detection circuit shown in FIG. 3. system Strain gauges 21 to 24 71~74 It has the same configuration except for replacing

[0070] The Mz detection system is configured with strain gauges 61 to 64. The strain gauges 61 to 64 are single-axis strain gauges, and are attached to the outer circumferential surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis direction of the cylindrical portion 11. The strain gauge 61 is disposed adjacent to the strain gauge 21 of the Fx detection system in the central axis direction of the cylindrical portion 11. The strain gauge 62 is disposed adjacent to the strain gauge 22 of the Fx detection system in the central axis direction of the cylindrical portion 11. The strain gauge 61 and the strain gauge 62 are disposed on the same straight line parallel to the axial direction of the cylindrical portion 11. The strain gauge 63 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 from the strain gauge 62 (a position symmetrical to the strain gauge 62 with respect to the central axis of the cylindrical portion 11). The strain gauge 64 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 from the strain gauge 61 (at a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 61). The bridge circuit of the Mz detection system is the same as that of the Fx detection system shown in FIG. system The configuration is the same as that of the first embodiment except that the strain gauges 21 to 24 are replaced with strain gauges 61 to 64.

[0071] <2-2. Bridge circuit> Next, taking the bridge circuit of the Fx detection system shown in FIG. 3 as an example, configuration examples of the bridge circuits of each force detection system and each moment detection system will be specifically described.

[0072] The bridge circuit 80 of the Fx detection system shown in Fig. 3 has four terminals, namely a first terminal 81, a second terminal 82, a third terminal 83 and a fourth terminal 84, and four strain gauges 21, 22, 23 and 24. Strain gauge 22 is provided between the first terminal 81 and the second terminal 82, and is a strain gauge 21 is provided between the second terminal 82 and the fourth terminal 84. 23 is provided between the first terminal 81 and the third terminal 83, and is a strain gauge 24 is provided between the third terminal 83 and the fourth terminal 84. A current path passing through the first terminal 81, the strain gauge 21, the second terminal 82, the strain gauge 22, and the fourth terminal 84 constitutes a first path 86. Further, a current path passing through the first terminal 81, the strain gauge 24, the third terminal 83, the strain gauge 23, and the fourth terminal 84 constitutes a second path 87.

[0073] The strain gauges 21, 22, 23, and 24 are resistive elements whose resistance value changes according to the amount of strain. In this embodiment, the strain gauges are made of a material with a gauge factor of 4 or more. For example, the strain gauges may be made of a Cr-N thin film. If the gauge factor of the strain gauge is 4 or more, it is possible to obtain an output that is desired for a six-component force detector 1 that detects a load applied to a wheel. However, the strain gauge is not limited to a Cr-N thin film.

[0074] In the bridge circuit 80, when a load is applied to the strain body, a strain is generated in each of the strain gauges 21, 22, 23, and 24, and the resistance value of each of the strain gauges 21, 22, 23, and 24 changes according to the amount of strain. The bridge circuit 80 outputs a differential signal (first differential signal) according to the potential difference between the second terminal 82 of the first path 86 and the third terminal 83 of the second path 87.

[0075] In addition, a resistive element for adjusting the deviation of the initial balance of the resistance values ​​of the bridge circuit 80 or a resistive element for compensating for temperature characteristics may be connected to any position of the bridge circuit 80.

[0076] <2-3. Details of the embodiment of the load detection device> Next, the load detection device according to the present embodiment will be described in detail. In the following description, the first to fourth terminals of the bridge circuits of each force detection system and each moment detection system of the load cell 1 will be represented as a first terminal 81, a second terminal 82, a third terminal 83, and a fourth terminal 84 of a bridge circuit 80 shown in FIG.

[0077] FIG. 4 is a block diagram functionally illustrating an example of the configuration of the load detection device of this embodiment. The load detection device 200 of this embodiment includes a load cell (six-component force detector) 1, a measurement circuit 160, and a CAN (Controller Area Network) communication driver 183. 160 may be connected to each other via a connector.

[0078] The measurement circuit 160 includes an excitation side differential amplifier circuit 161, a measurement side differential amplifier circuit 163, a lock-in amplifier 165, and a control device 180. The control device 180 is connected, via a CAN communication driver 183, to a CAN bus 191, which is a communication bus to which multiple control devices mounted on a vehicle are connected.

[0079] The excitation side differential amplifier circuit 161 has a function of generating an excitation signal, amplifying the excitation signal, and transmitting the amplified excitation signal to the load cell 1. The excitation side differential amplifier circuit 161 is configured to include, for example, a conventionally known sine wave oscillator, a gain switching differential amplifier, and an excitation driver differential amplifier. The excitation side differential amplifier circuit 161 is controlled by the control device 180 to generate a sine wave electric signal (excitation signal) of a predetermined frequency, phase, and amplitude, amplify the excitation signal by a set gain (excitation side gain), and transmit the excitation signal to the first terminal 81 and the fourth terminal 84 of each bridge circuit 80 of the load cell 1.

[0080] The measurement side differential amplifier circuit 163 has a function of acquiring a first differential signal output from the load cell 1, amplifying the first differential signal, and outputting the amplified signal. The measurement side differential amplifier circuit 163 is configured to include, for example, a conventionally known differential instrumentation amplifier, a gain switching differential amplifier, an A / D converter, and the like. The measurement side differential amplifier circuit 163 is controlled by the control device 180, amplifies the acquired first differential signal with a set gain (measurement side gain), and outputs a second differential signal to the lock-in amplifier 165.

[0081] The configuration of the excitation side differential amplifier circuit 161 is not particularly limited as long as it is configured to generate an excitation signal to be transmitted to the bridge circuit in accordance with a drive command from the control device 180 and amplify the excitation signal. Similarly, the configuration of the measurement side differential amplifier circuit 163 is not particularly limited as long as it is configured to amplify a first differential signal output from the bridge circuit in accordance with a drive command from the control device 180. Furthermore, either or both of the excitation side differential amplifier circuit 161 and the measurement side differential amplifier circuit 163 may be provided with various elements having a function of correcting the frequency, phase, amplitude, etc. of a signal.

[0082] The lock-in amplifier 165 extracts a signal corresponding to the frequency and phase of the excitation signal from the second differential signal output from the measurement side differential amplifier circuit 163. The extracted signal is output to the control device 180 as data indicating a measurement value. The lock-in amplifier 165 may also be configured by a conventionally known lock-in amplifier.

[0083] The control device 180 includes one or more processors and one or more memories communicably connected to the processors, and executes control of the measurement circuit 160. The control device 180 also calculates the load applied to the load cell 1 based on the measurement value input from the lock-in amplifier 165 and the output gain. The control device 180 outputs command signals to the excitation side differential amplifier circuit 161 and the measurement side differential amplifier circuit 163. In this embodiment, the control device 180 sets the excitation side gain and the measurement side gain, and adjusts the output gain so that the measurement value input from the lock-in amplifier 165 does not exceed the maximum allowable measurement value.

[0084] In particular, the control device 180 executes a process (gain feedback adjustment process) of adjusting at least one of the excitation side gain and the measurement side gain so that the measurement value falls below the maximum allowable measurement value based on the history of the measurement value input from the lock-in amplifier 165. The control device 180 also acquires information on the vehicle's running state via the CAN communication driver 183, and executes a process (gain feedforward adjustment process) of adjusting the output gain so that the measurement value falls below the maximum allowable measurement value based on the acquired information on the running state.

[0085] In this embodiment, a plurality of gain candidate values ​​are set at a predetermined interval for each of the excitation side gain and the measurement side gain, and the control device 180 determines the gain setting value for each of the excitation side gain and the measurement side gain, and adjusts the output gain. For example, if the excitation side gain can be set up to 5 times (amplification rate of 500%) and the measurement side gain can be set up to 4 times (amplification rate of 400%), the output gain can be adjusted up to 20 times (amplification rate of 2,000%).

[0086] Since the output gain can be adjusted by the excitation side gain and the measurement side gain, the resolution of the measured load can be optimized while adjusting the measured value to a desired range. For example, if there is a load detection device whose full range is 0-100mV and which can measure with an accuracy of 0.1mV by calculation, when detecting a physical quantity of 0-5000N, comparing the case where an output of 0-10mV is measured with the case where an output of 0-100mV is measured, the former allows the load to be detected in increments of 50N, and the latter allows the load to be measured in increments of 5N. Therefore, the maximum measured value can be adjusted to a more optimal resolution while approaching the maximum allowable measured value according to the set value of the output gain.

[0087] More specifically, when the gain is adjusted on the excitation side, the output of the bridge circuit is doubled by doubling the excitation side gain. However, when the excitation side gain is doubled, the output of the bridge circuit is doubled but the resolution of the measured load does not decrease. On the other hand, when the gain is adjusted on the measurement side, the resolution of the measured load itself can be adjusted by amplifying the first differential signal by a factor of two or four. For example, when the measurement side gain is doubled, the output of the second differential signal is doubled compared to the first differential signal, while the resolution of the measured load is halved. Therefore, by configuring the output gain to be adjustable with the excitation side gain and the measurement side gain, the resolution of the measured load can be optimized while adjusting the measurement value to a desired range.

[0088] In this embodiment, the control device 180 is configured to acquire information on the vehicle's running state via the CAN communication driver 183, and execute zero-point offset processing of the load cell 1 when a predetermined offset processing condition is satisfied. In the case of the load cell 1 mounted on a vehicle, such as the six-component force detector described above, the offset amount, which is the difference between the actual measurement value and the measurement value that should be measured for the applied load, can always change due to thermal history, mechanical stress history, and the like. In order to prevent such an offset amount from becoming excessive, the control device 180 determines whether or not an offset processing condition that allows the zero-point offset processing to be executed is satisfied from the information on the vehicle's running state, and executes the zero-point offset processing when the zero-point offset processing condition is satisfied. This can further improve the detection accuracy of the load.

[0089] <2-4. Operation of the load detection device> Next, an example of the operation of the load detection device according to this embodiment will be described by taking as an example a load detection device that detects component forces applied to tires of a vehicle using a six-component force detector 1.

[0090] (2-4-1. Pre-setting process) The control device 180 executes a presetting process for setting conditions required for executing a gain adjustment process and a zero point offset process. The presetting process is basically executed before the load detection device 200 is used for the first time, but may be executed again when the load cell 1 or the measurement circuit 160 is repaired, inspected, or replaced.

[0091] FIG. 5 is a flowchart showing the presetting process. In the presetting process, the control device 180 refers to data indicating the specifications of the load detection device 200 (step S1), and sets the maximum output gain Gain_max, the maximum measurable value S_max_sys, and the maximum allowable measurement value S_max_def(gain_x) based on the specifications of each element constituting the measurement circuit 160 (step S3). The specification data may be a data sheet also called a TEDS (Transducer Electronic Data Sheet).

[0092] A plurality of settable excitation-side gain and measurement-side gain values ​​(excitation-side gain candidate values ​​and measurement-side gain candidate values) are set in advance at a predetermined interval, and the control device 180 calculates and records the maximum settable output gain value Gain_max. The control device 180 also reads and records data on the maximum value measurable by the measurement circuit 160 (maximum measurable value) S_max_sys. The control device 180 also reads and records data on the maximum allowable measurement value S_max_def(gain_x), which is the maximum measurement value for which the measurement circuit 160 guarantees measurement accuracy according to the output gain Gain.

[0093] (2-4-2. Gain feedback adjustment process) 6 is a flowchart showing a gain adjustment process (gain feedback adjustment process) based on a history of measured values. The gain feedback adjustment process may be executed at all times while the vehicle system is running, but may be configured to be executed during execution of a specific control using a component force applied to a tire.

[0094] First, the control device 180 acquires vehicle state information via the CAN communication driver 183 (step S11). The vehicle state information includes information that can determine whether the vehicle is traveling and the acceleration / deceleration and yaw rate of the vehicle. The vehicle state information may include information on the vehicle speed, acceleration / deceleration, accelerator operation amount, and brake operation amount, but is not limited to these. For example, the vehicle state information may include status information indicating that the vehicle is traveling.

[0095] Next, the control device 180 judges whether the vehicle was in a traveling state from a time T seconds before the current time t to the current time t based on the vehicle state information (step S13). For example, the control device 180 judges that the vehicle was in a traveling state from a time T seconds before the current time t to the current time t when at least one of the following conditions is satisfied during the period: the vehicle speed is a positive value exceeding 0 km / h, the acceleration / deceleration is not 0, or the accelerator operation amount is a positive value. The value of T seconds may be set arbitrarily within a range of, for example, 5 to 20 seconds.

[0096] If the vehicle was not in a running state between the time T seconds before the current time t and the current time t (S13 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S25). Specifically, the control device 180 maintains the excitation side gain and the measurement side gain at the current excitation side gain setting value and the measurement side gain setting value, respectively. In this case, since the vehicle is in a stopped state and there is no change in the component force applied to the tire as the vehicle runs, the process of this routine ends without adjusting the output gain Gain, and returns to step S11.

[0097] On the other hand, if the vehicle has been in a traveling state from a time T seconds before the current time t to the current time t (S13 / Yes), the control device 180 acquires the maximum measurement value S_max_t from a time T seconds before the current time t to the current time t (tT to t) (step S15). That is, the control device 180 acquires the maximum value (maximum measurement value) S_max_t of the measurement values ​​S measured during a predetermined period that has already passed.

[0098] Next, the control device 180 judges whether the acquired maximum measurement value S_max_t is less than the maximum measurable value S_max_sys (step S17). That is, the control device 180 judges whether the maximum measurement value S_max_t measured within a predetermined period in which the vehicle was in a traveling state is less than the maximum measurable value S_max_sys. If the maximum measurement value S_max_t is equal to or greater than the maximum measurable value S_max_sys (S17 / No), the control device 180 sets the output gain Gain to a value Gain_now-1 that is one step smaller than the current output gain setting value Gain_now (step S27).

[0099] Specifically, the control device 180 reduces either the excitation side gain or the measurement side gain by one step, and reduces the output gain Gain. This brings the measured maximum measurement value S_max_t closer to the measurable maximum value S_max_sys, and the measurement value S measured when the same running state continues becomes the measurable maximum value S_max_sys. x In particular, by maintaining the excitation side gain and decreasing the measurement side gain, the range of the measurement value S can be narrowed and the resolution of the measured load can be increased.

[0100] On the other hand, if the maximum measurement value S_max_t is less than the maximum measurable value S_max_sys (S17 / Yes), the control device 180 judges whether or not a first ratio, which is a ratio of the maximum measurement value S_max_t to the maximum allowable measurement value S_max_def(gain_now) determined according to the currently set output gain Gain, is smaller than a second ratio, which is a ratio of the output gain Gain_now, which is one step smaller, to the currently set output gain Gain_now (step S19). In this step S19, it is judged whether or not the measured maximum measurement value S_max_t does not exceed the maximum allowable measurement value S_max_def(gain_now) even if the output gain is increased by one step, that is, whether or not there is a margin for increasing the output gain by one step. In order to set this margin as a design value, the set value maximum allowable measurement value S_max_def(gain_x) of each output gain Gain is set in advance.

[0101] The gain feedforward adjustment process based on vehicle state information, which will be described later, is performed for each vehicle, but the comparison between the maximum measurement value S_max_t and the allowable maximum measurement value S_max_def(gain_x) is performed for each component force of the vehicle.

[0102] If the determination in step S19 is negative (S19 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S25). In this case, if the output gain Gain is increased, there is a risk that the measured value S will exceed the maximum allowable measured value S_max_def(gain_x) according to the output gain. Therefore, the process of this routine ends without adjusting the output gain Gain, and the process returns to step S11.

[0103] On the other hand, if the determination in step S19 is affirmative (S19 / Yes), the control device 180 performs the following procedure once the condition in step S19 is satisfied. 2nd It is determined whether the state has been maintained for one time N1 (seconds) (step S21). The first time N1 may be set to any time that can be determined as a stable continuation of a state in which there is room to increase the output gain by one step. Note that information indicating that the condition in step S19 is satisfied is used in the gain feedforward adjustment process described below. For this reason, a flag indicating that the condition in step S19 is satisfied is set so that it can be referenced.

[0104] If the first time N1 has not been maintained since the condition in step S19 was satisfied (S21 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S25). In this case, since it cannot be determined that there is no risk that the measured value S will exceed the maximum allowable measured value S_max_def(gain_x) corresponding to the output gain even if the output gain Gain is increased, the process of this routine ends without adjusting the output gain Gain, and returns to step S11.

[0105] On the other hand, if the state in step S19 is satisfied and the state is maintained for the first time N1 (S21 / Yes), the control device 180 sets the output gain Gain to a value Gain_now+1, which is one step larger than the current output gain setting value Gain_now (step S23).

[0106] Specifically, the control device 180 increases either the excitation side gain or the measurement side gain by one step to increase the output gain Gain. This makes it possible to increase the measurement value S so that the measurement value S does not exceed the maximum allowable measurement value S_max_def(gain_x) corresponding to the adjusted output gain (Gain_now+1). At this time, the excitation side gain may be increased preferentially.

[0107] FIG. 7 is a flowchart showing a process for setting the excitation-side gain and the measurement-side gain when increasing the output gain Gain. The control device 180 reads out the currently set excitation-side gain setting value, and judges whether the excitation-side gain can be increased (step S31). Specifically, the control device 180 judges whether the currently set excitation-side gain setting value is the maximum value of a plurality of excitation-side gain candidate values ​​set in advance at a predetermined interval, and judges that the excitation-side gain can be increased if the excitation-side gain setting value is not the maximum value of the excitation-side gain candidate values.

[0108] If it is determined that the excitation side gain can be increased (S31 / Yes), the control device 180 increases the output gain Gain by increasing the excitation side gain preferentially (step S33). On the other hand, if it is not determined that the excitation side gain can be increased (S31 / No), the control device 180 increases the output gain Gain by increasing the measurement side gain (step S35). In this way, by increasing the excitation side gain preferentially, the measurement value S can be increased without reducing the resolution of the load being measured.

[0109] The control device 180 repeatedly executes the processing of each step described above at a predetermined sampling period. Even if the output range from the bridge circuit of the load cell 1 is wide, the control device 180 sets the output gain Gain based on the history of the actual measurement value S so that the measured maximum measurement value S_max_t falls below the maximum measurable value S_max_sys and the maximum allowable measurement value S_max_def(gain_now). This amplifies the output of the bridge circuit so that the measurement value S does not exceed the maximum measurable value S_max_sys and the maximum allowable measurement value S_max_def(gain_x), thereby improving the measurement accuracy of the load.

[0110] (2-4-3. Modification of Gain Feedback Adjustment Process) In the gain feedback adjustment process according to the modified example, the method of setting the output gain Gain when increasing the output gain Gain is different from the example of the gain feedback adjustment process shown in FIG.

[0111] Fig. 8 is a flowchart showing a modified example of the gain feedback adjustment process. In the flowchart shown in Fig. 8, the processes of steps S19 to S21 in the flowchart shown in Fig. 6 are replaced with processes of steps S18 to S22.

[0112] In the modified example, if it is determined in step S17 that the maximum measurement value S_max_t is less than the maximum measurable value S_max_sys (S17 / Yes), the control device 180 calculates a basic measurement value ms_max_ori corresponding to the maximum measurement value S_max_t when the output gain Gain is not adjusted (Gain=1) (step S18). Specifically, the control device 180 calculates the basic measurement value ms_max_ori by dividing the maximum measurement value S_max_t by the currently set output gain setting value Gain_now.

[0113] Next, the control device 180 calculates the maximum output gain Gain_M from among the output gain candidate values ​​such that the value S_max obtained by multiplying the basic measurement value ms_max_ori by the output gain Gain_x is less than the maximum allowable measurement value S_max_def(gain_x) according to the output gain Gain (step S20).

[0114] Next, the control device 180 judges whether the obtained output gain Gain_M is smaller than the currently set output gain setting value Gain_now (step S22). If it is not judged that the output gain Gain_M is smaller than the output gain setting value Gain_now (S22 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S25). In this case, since the output gain Gain cannot be increased, the process of this routine ends without adjusting the output gain Gain, and the process returns to step S11.

[0115] On the other hand, if it is determined that the output gain Gain_M is smaller than the output gain setting value Gain_now (S22 / Yes), the control device 180 sets the output gain Gain to a value Gain_now+1, which is one step larger than the current output gain setting value Gain_now (step S23). At this time, the control device 180 may increase the output gain Gain by more than one step, but if the increase rate of the output gain Gain is too large, there is a risk that the measured value S will easily exceed the maximum allowable measured value S_max_def(gain_x) when the running state of the vehicle changes and the load applied to the tires suddenly increases. For this reason, it is preferable to increase the output gain Gain little by little, such as by one or two steps at a time.

[0116] Even in the gain feedback adjustment process according to the modified example described above, it is possible to obtain the same effects as those of the above-described gain feedback adjustment process.

[0117] (2-4-4. Function of Gain Feedback Adjustment Processing) 9 and 10 are explanatory diagrams showing an example of increasing the output gain by gain feedback adjustment processing. Both Fig. 9 and Fig. 10 show the measurement value of the component force Fy in the vehicle width direction applied to the tires of a vehicle going around a curve. Fig. 9 shows the measurement value (basic measurement value) ms when the output gain Gain is fixed at 2 and no gain adjustment is made to the output of the bridge circuit. Fig. 10 shows the measurement value S when the gain adjustment is made to the output of the bridge circuit. In this example, the maximum measurable value S_max_sys is assumed to be 1.50 mV.

[0118] In the example shown in Fig. 9, when no gain adjustment is performed, the basic measurement value ms fluctuates between 0.00-0.05mV in the period from the start of measurement to 8 seconds (first period). In addition, the basic measurement value ms fluctuates between 0.00-0.20mV in the period from 8 seconds to 23 seconds after the start of measurement (second period). In addition, the basic measurement value ms fluctuates between 0.00-0.70mV in the period after 23 seconds (third period). This indicates that the vehicle's running condition changes in each period, and the load applied to the tires changes.

[0119] If the gain is not adjusted, the basic measurement value ms is significantly lower than the maximum measurable value S_max_sys and the maximum allowable measurement value S_max_def(gain_x). Therefore, by amplifying the output of the bridge circuit, the range of the measurement value S can be shifted to the larger side, thereby making it possible to improve the load detection accuracy.

[0120] 10, the output gain Gain is set to 5 at the start of measurement, and the measurement value S fluctuates between 0.00-0.10 mV in the first period. The measurement value S in the first period is significantly below the maximum measurable value S_max_sys, and continues to be below the maximum allowable measurement value S_max_def(gain_5) according to the output gain Gain. Therefore, the control device 180 doubles the output gain Gain.

[0121] Therefore, the measurement value S in the second period is amplified and fluctuates between 0.00-0.25 mV. Although the basic measurement value ms in the second period fluctuates more widely than in the first period due to changes in the vehicle's running state, the measurement value S in the second period falls significantly below the maximum measurable value S_max_sys and continues to be below the maximum allowable measurement value S_max_def(gain_10) according to the output gain Gain. Therefore, the control device 180 further doubles the output gain Gain.

[0122] Therefore, the measurement value S in the third period is further amplified and fluctuates between 0.00-1.40 mV. The basic measurement value ms in the third period fluctuates more widely compared to the second period due to changes in the vehicle's running state, and the maximum value of the measurement value S in the second period approaches the maximum measurable value S_max_sys. This makes it possible to detect the load based on the larger measurement value S, thereby improving the load detection accuracy.

[0123] Fig. 11 and Fig. 12 are explanatory diagrams showing an example of reducing the output gain by gain feedback adjustment processing. Fig. 11 and Fig. 12 both show the measurement value of the component force Fx in the vehicle longitudinal direction applied to the tire when the vehicle decelerates. Fig. 11 shows the measurement value (basic measurement value) ms when the output gain Gain is fixed at 10 and no gain adjustment of the bridge circuit output is made, and Fig. 12 shows the measurement value S when the gain adjustment of the bridge circuit output is made. In this example, the maximum measurable value S_max_sys is assumed to be 1.50 mV.

[0124] In the example shown in Fig. 11, when no gain adjustment is performed, the basic measurement value ms fluctuates between 0.05-0.35mV in the period from the start of measurement to 8 seconds (first period). In addition, the basic measurement value ms fluctuates between 0.20-1.10mV in the period from 8 seconds to 23 seconds after the start of measurement (second period). In addition, the basic measurement value ms fluctuates between 0.20-1.80mV in the period after 23 seconds (third period). This indicates that the vehicle's running condition changes in each period, and the load applied to the tires changes.

[0125] When no gain adjustment is performed, the basic measurement value ms increases over time, exceeds the maximum allowable measurement value S_max_def(gain_10) in the second period, and exceeds the maximum measurable value S_max_sys 32 seconds after the start of measurement.

[0126] 12, the output gain Gain is set to 20 at the start of measurement, and the measurement value S fluctuates between 0.10-0.75 mV in the first period. The measurement value S in the first period is significantly lower than the maximum measurable value S_max_sys, but exceeds the maximum allowable measurement value S_max_def(gain_20) according to the output gain Gain. Therefore, the control device 180 multiplies the output gain Gain by 0.5, making it the same as the output gain Gain in the case of FIG.

[0127] Therefore, the measurement value S in the second period fluctuates between 0.20 and 1.10 mV. However, the basic measurement value ms About In the second period, the range of the measured value S is larger than that in the first period due to a change in the running state of the vehicle, so although the output gain Gain is reduced, the measured value S exceeds the maximum allowable measured value S_max_def(gain_10) according to the output gain Gain. Therefore, the control device 180 further increases the output gain Gain by 0.5.

[0128] For this reason, the measurement value S in the third period is kept small, fluctuating between 0.10-0.75 mV. The basic measurement value ms in the third period exceeded the maximum measurable value S_max_sys and the maximum allowable measurement value S_max_def(gain_5), but by reducing the output gain Gain, it is now below the maximum measurable value S_max_sys and the maximum allowable measurement value S_max_def(gain_5). This ensures the accuracy of the measurement value S, and makes it possible to improve measurement accuracy.

[0129] (2-4-5. Adjustment of output gain by excitation side gain and measurement side gain) Figure 13 shows the pump side gain and measurement side13 is an explanatory diagram showing adjustment of the output gain by adjusting the gain. Fig. 13 shows an output gain Gain determined by an excitation-side gain Gain_u and a measurement-side gain Gain_d, and a measurement value S obtained by amplifying a basic measurement value ms by the output gain Gain, and a measurement value S of a component force Fy in the vehicle width direction applied to a tire of a vehicle traveling on an uneven road.

[0130] In the period from the start of measurement to 8 seconds later, both the excitation side gain Gain_u and the measurement side gain Gain_d are set to 1, and the total output gain Gain is set to 1. In addition, in the period from 8 seconds later to 13 seconds later, the measurement side gain Gain_d is maintained at 1, while the excitation side gain Gain_u is increased to 2.5, and the total output gain Gain is increased to 2.5. In addition, in the period from 13 seconds later to 22 seconds later, the excitation side gain Gain_u is maintained at 2.5, while the measurement side gain Gain_d is increased to 4, and the total output gain Gain is increased to 10. Furthermore, in the period after 22 seconds, the excitation side gain Gain_u is increased to 5, while the excitation side gain Gain_u is decreased to 2, and the total output gain Gain is maintained at 10. As a result, the basic measurement value ms is amplified according to the setting of the output gain Gain, and the range of the measurement value S is changed.

[0131] In the six-component force detector 1, differential signals are output from the bridge circuits of the three force detection systems (Fx, Fy, Fz) and the three moment detection systems (Mx, My, Mz). If there is a force component that causes insufficient output from the bridge circuit, noise components and allowable Yong Sai large measurement In order to adjust the value, it is effective to adjust the excitation side gain and the measurement side gain. In this case, even if the total output gain Gain is the same, if there is room to increase the excitation side gain Gain_u, it is possible to obtain an output gain Gain that reduces the decrease in the resolution of the measured load while keeping the range of the measurement value S within a targeted range by increasing the excitation side gain Gain_u rather than the measurement side gain Gain_d.

[0132] 13, 22 seconds after the start of measurement, the control device 180 increases the excitation side gain Gain_u to 5 while maintaining the total output gain Gain at 10, and decreases the excitation side gain Gain_u to 2. This makes it possible to increase the resolution of the measured load while maintaining the range of the measurement value S.

[0133] (2-4-6. Gain feedforward adjustment process) 14 is a flowchart showing a gain adjustment process (gain feedforward adjustment process) based on information on the vehicle's running state. The gain feedforward adjustment process may be executed at all times while the vehicle system is running, but may be configured to be executed during execution of a specific control using a component force applied to a tire. The gain feedforward adjustment process described below is executed using information used in the gain feedback adjustment process, and is executed in parallel with the gain feedback adjustment process.

[0134] First, the control device 180 acquires vehicle state information via the CAN communication driver 183 (step S41). The process content of this step S41 is the same as step S11 of the gain feedback adjustment process described above, and step S11 and step S41 may be one process.

[0135] Next, the control device 180 determines whether the vehicle was in a decelerating state between the time T seconds before the current time t and the current time t based on the vehicle state information (step S43). For example, the control device 180 determines that the vehicle was in a decelerating state when the vehicle acceleration included in the vehicle state information is a negative value. However, the method of determining that the vehicle was in a decelerating state is not limited to the above example.

[0136] If the vehicle was not in a decelerating state between the time T seconds before the current time t and the current time t (S43 / No), it is determined whether the vehicle was in an accelerating state between the time T seconds before the current time t and the current time t (step S55). For example, the control device 180 determines that the vehicle was in an accelerating state when the vehicle acceleration included in the vehicle state information is a positive value. However, the method of determining that the vehicle was in an accelerating state is not limited to the above example.

[0137] vinegar If step S43 is a positive determination (S43 / Yes), the control device 180 executes a process of determining whether or not to increase the output gain Gain (steps S45 to S49). On the other hand, if step S55 is a positive determination (S55 / Yes), the control device 180 executes a process of determining whether or not to decrease the output gain Gain (steps S57 to S59). On the other hand, if both steps S43 and S55 are negative determinations (S43 / No and S55 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S53). Specifically, the control device 180 maintains the excitation side gain and measurement side gain at the current excitation side gain setting value and measurement side gain setting value, respectively. In this case, since it is difficult to adjust the output gain Gain by the gain feedforward adjustment process, the process of this routine is terminated, and step S41 Return to.

[0138] If step S43 is judged as positive (S43 / Yes), the control device 180 judges whether or not either one or both of the value obtained by multiplying the acceleration acting on the vehicle in a predetermined direction by the vehicle weight, or the value of the sum of the component forces acting on each tire in a predetermined direction, is less than a first threshold value based on the gravitational acceleration (step S45). Step S45 is a process for determining whether or not the vehicle is in a traveling state in which the load applied to the tires is small, and is executed in order to predict that the basic measurement value ms in a state in which the gain adjustment is not performed will be a small value.

[0139] In step S45 of the flowchart shown in FIG. 14, in a traveling state in which acceleration in the vehicle width direction may occur to the vehicle, the control device 180 calculates the absolute value abs[M*(G_lat+v*ω) ] or the absolute value abs(ΣFy) of the sum ΣFy of the component forces Fy acting on each tire in the vehicle width direction is less than a first threshold kmin*M*g based on the gravitational acceleration g. This is a process for determining whether the load applied to the tire in the vehicle width direction is small in a situation where a load is applied to the tire in the vehicle width direction.

[0140] Whether or not the vehicle is in a driving state in which acceleration in the vehicle width direction may occur can be determined based on, for example, steering angle information detected by a steering angle sensor. Furthermore, the lateral acceleration G_lat and the centrifugal acceleration v*ω are determined based on sensor value information from an acceleration sensor and a yaw rate sensor, respectively. The coefficient kmin of the first threshold kmin*M*g is a positive setting value that is preset in the range of 0 to 1 in order to simply determine that the vehicle is not driving close to the tire limit in terms of vehicle motion. Furthermore, the vehicle weight M may also be acquired together with the vehicle state information. The absolute value abs[M*(G_lat+v*ω) of the sum of the lateral acceleration G_lat and the centrifugal acceleration v*ω multiplied by the vehicle weight M is calculated. ] Alternatively, it may be determined whether either of the absolute value abs(ΣFy) of the sum ΣFy of the component forces Fy acting on each tire in the vehicle width direction is less than the first threshold kmin*M*g. However, by determining whether both are less than the first threshold kmin*M*g, the reliability of the determination result can be increased.

[0141] When the vehicle is traveling straight, the tire is not subjected to a load in the vehicle width direction. In this case, the control device 180 may determine whether the load applied to the tire in the front-rear direction is small or not. Specifically, when the vehicle is traveling straight and decelerating, the control device 180 determines whether or not either one or both of the value abs[M*G_longi] obtained by multiplying the absolute value abs(G_longi) of the front-rear acceleration G_longi acting on the vehicle in the front-rear direction by the vehicle weight M, or the absolute value abs(ΣFx) of the sum ΣFx of the component forces Fx acting on each tire in the front-rear direction is less than a first threshold kmin*M*g based on the gravitational acceleration.

[0142] Whether the vehicle is traveling straight or not can be determined based on steering angle information detected by a steering angle sensor, for example. The longitudinal acceleration G_longi is calculated based on sensor value information from an acceleration sensor. The first threshold kmin*M*g for determining the load applied to the tire in the longitudinal direction and the first threshold kmin*M*g for determining the load applied to the tire in the vehicle width direction may be the same or different. The longitudinal acceleration G_long i The absolute value of the value obtained by multiplying by the vehicle weight M is abs[M *G _longi ] Alternatively, it may be determined whether either of the absolute value abs(ΣFx) of the sum ΣFx of the component forces Fx acting on each tire in the front-rear direction is less than the first threshold kmin*M*g. However, by determining whether both are less than the first threshold kmin*M*g, the reliability of the determination result can be increased.

[0143] If the determination in step S45 is negative (S45 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S53). In this case, since it cannot be determined that there is no risk that the measured value S will exceed the maximum allowable measured value S_max_def(gain_x) corresponding to the output gain if the output gain Gain is increased, the process of this routine is terminated without adjusting the output gain Gain, and the process returns to step S41.

[0144] On the other hand, if the determination at step S45 is positive (S45 / Yes), the control device 180 determines whether or not a second time N2 (seconds) has been maintained since the condition at step S45 was satisfied (step S47). The value of the second time N2 is set to a value smaller than the value of the first time N1 used at step S21 of the gain feedback adjustment process. If the second time N2 has not been maintained since the condition at step S45 was satisfied (S47 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S53). Even in this case, since it cannot be determined that there is no risk that the measured value S will exceed the maximum allowable measured value S_max_def(gain_x) according to the output gain even if the output gain Gain is increased, the process of this routine is terminated without adjusting the output gain Gain, and the process returns to step S41.

[0145] On the other hand, if the condition in step S45 is satisfied and then the second time N2 is maintained (S47 / Yes), the control device 180 determines whether the condition in step S19 of the gain feedback adjustment process is satisfied (whether step S19 is judged to be positive) (step S49). For example, the control device 180 determines whether a flag indicating that the condition in step S19 is satisfied is set.

[0146] If the condition of step S19 is not satisfied (S49 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S53). Even in this case, since it cannot be determined that there is no risk that the measured value S will exceed the maximum allowable measured value S_max_def(gain_x) corresponding to the output gain even if the output gain Gain is increased, the process of this routine is terminated without adjusting the output gain Gain, and the process returns to step S41.

[0147] On the other hand, if the condition of step S19 is satisfied (S49 / Yes), the control device 180 sets the output gain Gain to a value Gain_now+1, which is one step larger than the current output gain setting value Gain_now (step S51). Specifically, the control device 180 increases either the excitation side gain or the measurement side gain by one step to increase the output gain Gain. At this time, as shown in FIG. 7, the excitation side gain may be increased preferentially. Since the second time N2 used in step S47 is set shorter than the first time N1 used in step S21, even before the condition of step S19, that is, the first ratio is smaller than the second ratio, continues for the first time N1 or more, if it is determined from the running state of the vehicle that the measurement value does not exceed the maximum allowable measurement value, the output gain can be increased quickly.

[0148] On the other hand, if the above step S55 is judged as positive (S55 / Yes), the control device 180 judges whether or not either or both of the value obtained by multiplying the acceleration acting on the vehicle in a predetermined direction by the vehicle weight, or the value of the sum of the component forces acting on each tire in a predetermined direction, exceed a second threshold value based on the gravitational acceleration (step S57). Step S57 is a process for determining whether or not the vehicle is in a driving state in which the load applied to the tires is large, and is executed in order to predict that the basic measurement value ms in a state in which the gain adjustment is not performed will be large.

[0149] In step S57 of the flowchart shown in FIG. 14, in a traveling state in which acceleration in the vehicle width direction may occur to the vehicle, the control device 180 calculates the absolute value abs[M*(G_lat+v*ω) ]or the absolute value abs(ΣFy) of the sum ΣFy of the component forces Fy acting on each tire in the vehicle width direction exceeds a second threshold kmax*M*g based on the gravitational acceleration g. This is a process for determining whether the load applied to the tire in the vehicle width direction is large in a situation where a load is applied to the tire in the vehicle width direction.

[0150] Second threshold kmax * M * The coefficient kmax of g is a positive value preset in the range of 0 to 1 to easily determine whether the vehicle is traveling close to the tire limit in terms of vehicle motion. The absolute value of the sum of the lateral acceleration G_lat and the centrifugal acceleration v*ω multiplied by the vehicle weight M, abs[M*(G_lat+v*ω) ] Alternatively, it may be determined whether either of the absolute value abs(ΣFy) of the sum ΣFy of the component forces Fy acting on each tire in the vehicle width direction exceeds the second threshold kmax*M*g. However, by determining whether both exceed the second threshold kmax*M*g, the reliability of the determination result can be increased.

[0151] When the vehicle is traveling straight, the tire is not subjected to a load in the vehicle width direction. In this case, the control device 180 may determine whether or not the load applied to the tire in the front-rear direction is large. Specifically, when the vehicle is traveling straight and accelerating, the control device 180 determines whether or not either one or both of the value abs[M*G_longi] obtained by multiplying the absolute value abs(G_longi) of the front-rear acceleration G_longi acting on the vehicle in the front-rear direction by the vehicle weight M, or the absolute value abs(ΣFx) of the sum ΣFx of the component forces Fx acting on each tire in the front-rear direction, exceeds a second threshold kmax*M*g based on the gravitational acceleration.

[0152] The second threshold kmax*M*g for determining the load applied to the tire in the longitudinal direction and the second threshold kmax*M*g for determining the load applied to the tire in the vehicle width direction may be the same or different. i The absolute value of the value obtained by multiplying by the vehicle weight M is abs[M *G _longi ] Alternatively, it may be determined whether or not either of the absolute value abs(ΣFx) of the sum ΣFx of the component forces Fx acting on each tire in the front-rear direction exceeds the second threshold kmax*M*g. However, it is also possible to determine whether or not both of the absolute value abs(ΣFx) of the component forces Fx acting on each tire in the front-rear direction exceed the second threshold kmax*M*g. Is it more than By determining whether or not the determination result is correct, the reliability of the determination result can be increased.

[0153] If the determination in step S57 is negative (S57 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S53). In this case, since it cannot be determined that there is no risk that the measured value S will exceed the maximum allowable measured value S_max_def(gain_x) corresponding to the output gain if the output gain Gain is increased, the process of this routine is terminated without adjusting the output gain Gain, and the process returns to step S41.

[0154] On the other hand, if the determination in step S57 is positive (S57 / Yes), the control device 180 determines whether or not a second time N2 (seconds) has been maintained since the condition in step S57 was satisfied (step S59). The value of the second time N2 is set to a value smaller than the value of the first time N1 used in step S21 of the gain feedback adjustment process. If the second time N2 has not been maintained since the condition in step S57 was satisfied (S59 / No), the control device 180 maintains the output gain Gain at the current output gain setting value Gain_now (step S53). Even in this case, since it cannot be determined that there is no risk that the measured value S will exceed the maximum allowable measured value S_max_def(gain_x) according to the output gain even if the output gain Gain is increased, the process of this routine is terminated without adjusting the output gain Gain, and the process returns to step S41.

[0155] On the other hand, if the second time N2 has been maintained after the condition of step S57 has been satisfied (S59 / Yes), the control device 180 sets the output gain Gain to a value Gain_now-1 that is one step smaller than the current output gain setting value Gain_now (step S61). Note that the second time N2 used in step S47 and the second time N2 used in step S59 may be different.

[0156] Specifically, the control device 180 reduces either the excitation side gain or the measurement side gain by one step, and reduces the output gain Gain. This brings the measured maximum measurement value S_max_t closer to the measurable maximum value S_max_sys, and the measurement value S measured when the same running state continues becomes the measurable maximum value S_max_sys. x In particular, by maintaining the excitation side gain and decreasing the measurement side gain, the range of the measurement value S can be narrowed and the resolution of the measured load can be increased.

[0157] The control device 180 repeatedly executes the processing of each step described above at a predetermined sampling period. Even if the output range from the bridge circuit of the load cell 1 is wide, the control device 180 sets the output gain Gain based on the vehicle's running state so that the measured maximum measurement value S_max_t falls below the maximum measurable value S_max_sys and the maximum allowable measurement value S_max_def(gain_now). This amplifies the output of the bridge circuit so that the measurement value S does not exceed the maximum measurable value S_max_sys and the maximum allowable measurement value S_max_def(gain_x), thereby improving the measurement accuracy of the load.

[0158] (2-4-7. Zero point offset processing) 15 is a flowchart showing an example of the zero point offset process. The zero point offset process may be executed at all times while the vehicle system is running, but may be configured to be executed during execution of a specific control using a component force applied to a tire.

[0159] First, the control device 180 acquires vehicle state information via the CAN communication driver 183 (step S 71 The processing content of this step S51 is the same as that of step S11 of the gain feedback adjustment processing or step S41 of the gain feedforward adjustment processing described above, and steps S11, S41, and S51 may be one process.

[0160] Next, the control device 180 determines whether or not an offset processing condition that allows the zero point offset processing to be executed is satisfied based on the acquired vehicle state information (step S 73 ). The offset processing condition is a condition for determining a state in which no load is applied to the load cell 1, and it is sufficient if it can be determined that no acceleration is occurring in the longitudinal direction and in the width direction of the vehicle. Specifically, the control device 180 may determine that the offset processing condition is satisfied when the vehicle is stopped and is not tilted. Whether the vehicle is stopped can be determined based on information on the sensor value of the vehicle speed sensor, or status information indicating the stopped state of the vehicle. Also, whether the vehicle is not tilted can be determined based on information on the sensor value of the inclination sensor.

[0161] If the offset processing conditions are not met (S 73 If no, the control device 180 ends this routine and returns to step S 71 On the other hand, if the offset processing condition is satisfied (S 73 / Yes), the control device 180 executes the zero point offset process (step S 75 ). The zero-point offset process may be performed by a conventionally known method. For example, a measurement value detected when the offset process conditions are met is multiplied by minus 1 and recorded as an offset correction value. The offset correction value is added to the measurement value S input from the lock-in amplifier 165, and the measurement value S is corrected by an amount equivalent to the offset amount. Note that the contents of the zero-point offset process are not limited to the above example.

[0162] (2-4-8. Effects of zero point offset processing) FIG. 16 shows an example in which the measurement value (basic measurement value) ms (dashed line) shown in FIG. 11 when no gain adjustment is made to the output of the bridge circuit is performed in the same pattern as the example shown in FIG. 12, with zero-point offset processing being performed midway through the gain adjustment.

[0163] In the example shown in Fig. 16, the output gain Gain is set to 20 at the start of measurement, and the measurement value S fluctuates between 0.10-0.75 mV in the first period. The measurement value S in the first period is significantly lower than the maximum measurable value S_max_sys, but exceeds the maximum allowable measurement value S_max_def(gain_20) according to the output gain Gain. Therefore, the control device 180 multiplies the output gain Gain by 0.5, making it the same as the output gain Gain in Fig. 11. Therefore, the measurement value S changes in the same manner as in Fig. 12 from 8 seconds after the start of measurement to 12 seconds after the start of measurement.

[0164] However, in the example shown in FIG. 16, the zero point offset process is executed 13 seconds after the start of measurement, and the measurement value S at that time is set to zero. rear, Measurements S is The measured value S is shifted to a value that is smaller by the offset correction value than the measured value S when the output gain Gain is adjusted as shown in Fig. 12. In this way, by executing the zero-point offset process, the accuracy of the measured value S is further guaranteed, and the measurement accuracy can be further improved.

[0165] Although the preferred embodiment of the present disclosure has been described in detail above with reference to the accompanying drawings, the present disclosure is not limited to such examples. It is clear that a person having ordinary knowledge in the technical field to which the present disclosure belongs can conceive of various modified or amended examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally belong to the technical scope of the present disclosure.

[0166] For example, in the above embodiment, an example of a load cell using a single-axis strain gauge has been described, but the load cell to which the technology of the present disclosure can be applied is not limited to such an example. For example, the technology of the present disclosure can be applied to a load cell using a biaxial shear strain gauge as shown in Figs. 17 and 18.

[0167] Specifically, Fig. 17 is a schematic diagram showing the arrangement of strain gauges in a six-component force detector of a modified example, and Fig. 18 is an explanatory diagram showing the gauge pattern of a biaxial shear strain gauge. The six-component force detector shown in Fig. 17 is provided with shear strain gauges 271, 272 of the Fx detection system and shear strain gauges 275, 277 of the Fz detection system, which will be described below, instead of the above-mentioned strain gauges 21-24 of the Fx detection system and the strain gauges 31-34 of the Fz detection system. Fig. 18 shows the shear strain gauge 271 as an example, but the shear strain gauges 272, 275, 277 also have substantially the same gauge pattern.

[0168] The shear strain gauge 271 is configured as a so-called arrow-shaped two-axis (two-pole). The shear strain gauge 271 has a first detection part 271a and a second detection part 271b made of a Cr-N thin film or the like formed on a common insulating layer 271c, which is a thin film of an insulating material. 271 Each of the first and second detection sections 271a and 271b is configured by sequentially connecting in series a plurality of straight sections arranged in parallel along the detection direction. The first and second detection sections 271a and 271b are set so that the electrical resistance is likely to change according to the strain in the direction in which the straight sections expand and contract (detection direction). The detection directions of the first and second detection sections 271a and 271b are arranged to be substantially perpendicular to each other. The shear strain gauge 271 is attached to the outer circumferential surface of the cylindrical section 250 so that the detection directions of the first and second detection sections 271a and 271b are inclined at 45° in opposite directions with respect to the central axis direction of the cylindrical section 250. The shear strain gauges 272, 275, and 277 are also attached to the outer circumferential surface of the cylindrical section 250 in a similar manner.

[0169] As shown in Fig. 17, shear strain gauges 271, 272, 275, and 277 are attached to the outer circumferential surface of the central portion in the central axis direction of cylindrical portion 250. Fx detection system shear strain gauge 271 is disposed midway between Mx detection system strain gauges 251 and 252. Fx detection system shear strain gauge 272 is disposed midway between Mx detection system strain gauges 253 and 254 (at a position symmetrical about the central axis with shear strain gauge 271). Fz detection system shear strain gauge 275 is disposed midway between Mz detection system strain gauges 261 and 262. Fz detection system shear strain gauge 277 is disposed midway between Mz detection system strain gauges 263 and 264 (at a position symmetrical about the central axis with shear strain gauge 275).

[0170] Further, the Fy detection system strain gauges 281-284 and the My detection system strain gauges 291-294 are arranged at positions shifted around the central axis to avoid interference with the Fx detection system strain gauges 271, 272 and the Fz detection system strain gauges 275, 277. For example, as shown in Fig. 17, the shear strain gauge 271, the strain gauge 282, the strain gauge 292, the shear strain gauge 277, the strain gauge 284, the strain gauge 294, the shear strain gauge 272, the strain gauge 283, the strain gauge 293, the shear strain gauge 275, the strain gauge 281 and the strain gauge 291 may be arranged sequentially at positions shifted at intervals of 30° around the central axis along the circumferential direction of the cylindrical portion 250.

[0171] The first and second detection parts of the shear strain gauges 271 and 272 of the Fx detection system constitute a bridge circuit similar to the bridge circuit shown in FIG. Cylindrical Part 250 generates an output according to the Fx direction component force input to the shear strain gauge 275. Similarly, the first and second detection parts of the shear strain gauges 275 and 277 of the Fz detection system form a bridge circuit similar to the bridge circuit shown in FIG. Cylindrical Part It generates an output according to the Fz direction force component input to 250.

[0172] The technology of the present disclosure can be applied to a load cell using a biaxial shear strain gauge configured in this manner, and the effects obtained by the above embodiment can be achieved. [Explanation of symbols]

[0173] 1: load cell, 21, 22, 23, 24: strain gauge, 80: bridge circuit, 81: first terminal, 82: second terminal, 83: third terminal, 84: fourth terminal, 160: measurement circuit, 161: excitation side differential amplifier circuit, 163: measurement side differential amplifier circuit, 165: lock-in amplifier, 180: control device, 183: CAN communication driver, 191: CAN bus, 200: load detection device

Claims

1. A load detection device that detects a load applied to a measurement object based on a differential signal output from a load cell having a bridge circuit to which a strain gauge is connected, comprising: an excitation side differential amplifier circuit that amplifies an excitation signal to be transmitted to the load cell; a measurement-side differential amplifier circuit that amplifies a first differential signal output from the load cell; a control device for controlling the excitation side differential amplifier circuit and the measurement side differential amplifier circuit, The control device includes: a gain adjustment process is executed to select the excitation-side gain and the measurement-side gain from a plurality of excitation-side gain candidate values ​​set at predetermined intervals as the excitation-side gain by the excitation-side differential amplifier circuit and a plurality of measurement-side gain candidate values ​​set at predetermined intervals as the measurement-side gain by the measurement-side differential amplifier circuit, and adjust the output gain, so that a measurement value measured based on the second differential signal output from the measurement-side differential amplifier circuit falls within a predetermined range. Load detection device.

2. The load detection device detects a plurality of component forces acting on a tire of a vehicle, The control device includes: In the gain adjustment process, When the vehicle is in a traveling state within a predetermined period prior to the current time, and a maximum measurement value that is a maximum value of the measurement values ​​within the predetermined period is less than a predetermined maximum measurable value that can be measured by the load detection device, determining whether a first ratio, which is a ratio of the maximum measurement value to a maximum allowable measurement value at which the measurement value can be guaranteed and which is determined according to the currently set output gain, is smaller than a second ratio, which is a ratio of the output gain that is one step smaller than the currently set output gain; increasing the output gain when a state in which the first ratio is smaller than the second ratio continues for a predetermined first time period or longer; The load detection device according to claim 1 .

3. The control device includes: Even before the state in which the first ratio is smaller than the second ratio continues for the predetermined first time or more, increasing the output gain when the vehicle is in a decelerating state and a state in which either or both of a value obtained by multiplying an acceleration acting on the vehicle in a predetermined direction by a weight of the vehicle, or a value of a sum of component forces acting on each of the tires in the predetermined direction, is less than a first threshold value based on gravitational acceleration continues for the predetermined period. The load detection device according to claim 2 .

4. The control device includes: Even before the state in which the first ratio is smaller than the second ratio continues for the predetermined first time or more, increasing the output gain when the vehicle is in a decelerating state and a value obtained by multiplying a sum of lateral acceleration and centrifugal acceleration acting in a vehicle width direction on the vehicle by a weight of the vehicle, or a value of a sum of component forces acting on each of the tires in the vehicle width direction, is less than the first threshold value for the predetermined period of time. The load detection device according to claim 3 .

5. The control device includes: Even before the state in which the first ratio is smaller than the second ratio continues for the predetermined first time or more, increasing the output gain when the vehicle is decelerating while traveling straight ahead and either or both of a value obtained by multiplying an absolute value of longitudinal acceleration acting on the vehicle in the longitudinal direction by a weight of the vehicle, or a value of a sum of component forces acting on each of the tires in the longitudinal direction, are less than the first threshold value for the predetermined period of time; The load detection device according to claim 3 .

6. The control device includes: In the gain adjustment process, reducing the output gain when the vehicle is in a traveling state within the predetermined period and the maximum measurement value within the predetermined period is equal to or greater than the predetermined measurable maximum value; The load detection device according to claim 2 .

7. The control device includes: In the gain adjustment process, reducing the output gain when a state in which either or both of a value obtained by multiplying an acceleration acting on the vehicle in a predetermined direction by a weight of the vehicle or a value of a sum of component forces acting on each of the tires in the predetermined direction exceeds a second threshold value based on gravitational acceleration continues for the predetermined period of time; The load detection device according to claim 2 .

8. The control device includes: reducing the output gain when the vehicle is in an accelerating state and a state in which either or both of a sum of a lateral acceleration and a centrifugal acceleration acting in a vehicle width direction on the vehicle and a weight of the vehicle are multiplied, or a sum of component forces acting in the vehicle width direction on each of the tires, exceeds the second threshold value, continues for the predetermined period of time; The load detection device according to claim 7.

9. The control device includes: When the vehicle continues to travel straight, if a state in which either or both of a value obtained by multiplying an absolute value of a longitudinal acceleration acting on the vehicle in the longitudinal direction by a weight of the vehicle, or a value of a sum of component forces acting on each of the tires in the longitudinal direction, exceeds the second threshold value continues for the predetermined period, the output gain is reduced. The load detection device according to claim 7.

10. The control device includes: In the gain adjustment process, determining whether the pumping side gain can be increased; When the excitation-side gain can be increased, the excitation-side gain is increased preferentially over the measurement-side gain. The load detection device according to claim 1 .

11. The control device includes: determining whether or not the strain gauge is not under load and is held in a proper position; When no load is applied to the strain gauge and the strain gauge is held in a proper posture, a zero point offset process is performed on the measurement value. The load detection device according to claim 1 .

12. A gain adjustment method for adjusting a gain of a load detection device that detects a load applied to a measurement object based on a differential signal output from a load cell having a bridge circuit to which a strain gauge is connected, comprising the steps of: amplifying an excitation signal to be transmitted to the load cell by an excitation side differential amplifier circuit; amplifying a first differential signal output from the load cell by a measurement-side differential amplifier circuit; selecting the excitation-side gain and the measurement-side gain from among a plurality of excitation-side gain candidate values ​​set at predetermined intervals as the excitation-side gain by the excitation-side differential amplifier circuit and a plurality of measurement-side gain candidate values ​​set at predetermined intervals as the measurement-side gain by the measurement-side differential amplifier circuit, and adjusting an output gain, so that a measurement value measured based on a second differential signal output from the measurement-side differential amplifier circuit falls within a predetermined range; A method for adjusting a gain of a load detection device, comprising:

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