LOAD DETECTION DEVICE AND LOAD DETECTION DEVICE AMPLIFICATION PROCEDURES

Abstract

A load detection device and a gain adjustment procedure for the load detection device are specified. Even if the output range of a load cell is large, a measured value from the load detection device can fall within a predetermined measuring range, and a load can be accurately detected. The load detection device is designed to detect a load based on a differential signal output by the load cell. The load detection device comprises an excitation-side differential amplifier circuit, a measurement-side differential amplifier circuit, and a control unit. The excitation-side differential amplifier circuit is designed to amplify an excitation signal sent to the load cell. The measurement-side differential amplifier circuit is designed to amplify an initial differential signal output by the load cell. The control unit is designed to control both the excitation-side and measurement-side differential amplifier circuits.The control device is designed to perform a gain adjustment process for setting an output gain by adjusting one or more of an excitation-side gain by the excitation-side differential amplifier circuit and a measurement-side gain by the measurement-side differential amplifier circuit such that a measured value, which is measured on the basis of a second differential signal output by the measurement-side differential amplifier circuit, falls within a predetermined range.

Description

Technical area

[0001] The present invention 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 of the load detection device. State of the art

[0002] In widely used load cells, a change in the resistance value of a strain gauge occurs due to a deformation caused by a load. For example, known load cells are designed as described below. A strain gauge is arranged in a bridge circuit, which is a converter circuit for converting a change in the resistance value of the strain gauge due to a load into an electrical signal, and the change in the resistance value is thus output as a differential signal. When a load is measured using such a load cell, an amplifier can be used to amplify the output differential signal.

[0003] For example, PTL 1 discloses a detection device that can accurately detect the output voltage of a bridge circuit. For example, the detection device according to PTL 1 includes a bridge circuit, a power source, an instrumentation amplifier, and a physical quantity calculator. The power source applies a voltage to the bridge circuit.

[0004] The instrumentation amplifier receives the output voltage of the bridge circuit from a high-impedance input terminal, amplifies the received output voltage, and outputs it. The physical quantity calculator receives the output voltage amplified by the instrumentation amplifier and calculates a physical quantity based on the output voltage. Literature listPatent literature

[0005] PTL 1: Unexamined Japanese Patent Application Publication JP 2019- 39 871 A Brief description of the inventionTechnical problem

[0006] However, a force detection sensor, such as a load cell mounted on a vehicle axle to detect a load applied to a wheel, has a large output range. Therefore, it is necessary to set a suitable gain according to the load cell output. For example, if the specified gain is small despite a small load cell output, the load detection accuracy may decrease. Conversely, if the specified gain is large despite a large load cell output, the detection device's measuring range may be exceeded.

[0007] The present invention was conceived in view of the problems described above. The object of the present invention is to provide a load detection device and a gain adjustment method of the load detection device. Thus, a measured value of the load detection device can fall within a predetermined measurement range even when the output range of a load cell is large, and a load can be detected accurately. Solution to the problem

[0008] In order to solve the above-mentioned problems, according to one aspect of the present invention, a load detection device is provided.

[0009] The load detection device is designed to detect a load applied to a measurement object based on a differential signal output by a load cell with a bridge circuit to which a strain gauge is connected. The load detection device comprises: an excitation-side differential amplifier circuit configured to amplify an excitation signal to be sent to the load cell; a measurement-side differential amplifier circuit configured to amplify a first differential signal output by the load cell; and a control device configured to control the excitation-side differential amplifier circuit and the measurement-side differential amplifier circuit.

[0010] The control device is designed to a gain adjustment process for adjusting an output gain by adjusting one or more 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 difference signal output from the measurement-side differential amplifier circuit falls within a predetermined range.

[0011] Furthermore, to solve the above-mentioned problems, according to another aspect of the present invention, a gain adjustment method of a load detection device is provided for adjusting a gain of a load detection device. The load detection device is configured to detect 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. The gain adjustment method includes the following measures: Amplifying an excitation signal to be sent to the load cell by an excitation-side differential amplifier circuit; Amplifying a first differential signal output by the load cell by a measurement-side differential amplifier circuit; and Adjusting an output gain by adjusting one or more 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 measured value measured based on a second difference signal output from the measurement-side differential amplifier circuit falls within a predetermined range. Advantageous effects of the invention

[0012] As described above, according to the present invention, even if the output range of the load cell is large, the measured value of the load detecting device can fall within the predetermined measuring range, and the load can be accurately detected. Short description of the drawings

[0013] The drawings show in: Fig. 1 a cross-sectional view of a configuration example for a load cell (six-component force detector). Fig. 2 a schematic representation of an arrangement of strain gauges in the load cell. Fig. 3 an explanatory diagram of a configuration example for a bridge circuit of the load cell. Fig. 4 is a block diagram illustrating a configuration example of a load detection device according to an embodiment of the present invention. Fig. 5 is a flowchart illustrating a setting process by a gain adjustment method of the load detection device according to the embodiment. Fig. 6 is a flowchart illustrating a gain feedback adjustment process by the gain adjustment method of the load detection device according to the embodiment. Fig. 7 is a flowchart illustrating a setting process of an excitation-side gain and a measurement-side gain by the gain setting method of the load detection device according to this embodiment. Fig. 8 is a flowchart illustrating a modification of the gain feedback adjustment process by the gain adjustment method of the load detection device according to the embodiment. Fig. 9 is an explanatory diagram of a base measurement value when an output gain is fixed and no gain adjustment is performed. Fig. 10 is an explanatory diagram of measured values ​​when the output gain is increased by the load detection device according to the embodiment. Fig. 11 is an explanatory diagram of the base measurement value when the output gain is fixed and no gain adjustment is performed. Fig. 12 is an explanatory diagram of the measured values ​​when the output gain of the load detection device according to the embodiment is reduced. Fig. 13 is an explanatory diagram showing an example in which the output gain is adjusted by adjusting the excitation-side gain and the measurement-side gain by the load detection device according to the embodiment. Fig. 14 is a flowchart illustrating a gain feedforward adjustment process by the gain adjustment method of the load detection device according to the embodiment. Fig. 15 is a flowchart illustrating a zero point shift process by the gain adjustment method of the load detection device according to the embodiment. Fig. 16 is an explanatory diagram of the measured values ​​when the output gain is adjusted and the zero shift process is performed by the load detection device according to the embodiment. Fig. 17 is a schematic diagram showing the arrangement of strain gauges in the six-component force detector according to a modification. Fig. 18 is an explanatory diagram of a strain measurement pattern of a biaxial shear strain gauge. Description of the embodiments

[0014] A preferred embodiment of the invention will be described in detail below with reference to the accompanying drawings. In the description and the drawings, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant descriptions thereof will be omitted. 1. Summary of the Embodiment of the Present Invention 1.1. Detailed Description of the Background of the Present Invention

[0015] First, the background for the creation of the technology of the present invention will be described. Note that the background described below represents only one aspect of the configuration of a load cell to which the technology of the present invention can be applied. The load cell to which the present invention can be applied is not limited to a load cell having the configuration exemplified below.

[0016] Known six-component force detectors detect, as loads applied to a wheel of a vehicle such as a car, loads (Fx, Fy, and Fz) applied in the longitudinal direction (hereinafter also referred to as the "x-axis direction"), the vehicle 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. The six-component force detector also detects moments (Mx, My, and Mz) about the x-axis, y-axis, and z-axis. In such a six-component force detector, the sensitivity of a strain gauge tends to vary depending on the direction of a component force.

[0017] Furthermore, since the maximum value of the load applied to the wheel can be large, the aforementioned six-component force detector uses a strain gauge with a large output. Thus, the output range of the six-component force detector is large and may exceed the measuring range of a load detection device. To handle this, it is necessary to reduce the gain for amplifying the load cell output.

[0018] However, if the gain is simply specified as a small gain, the measurement accuracy will be reduced when the output from the six-component force detector is small. In contrast, if the gain is specified as a large gain in a case where the output from the six-component force detector is small, the measurement range of the load detection device will be exceeded when the output from the six-component force detector is large.

[0019] Against this background, the technology of the present invention provides a load detection device, a gain adjustment method of the load detection device, and a recording medium on which a computer program is recorded. The load detection device can automatically set a gain according to the output of the load cell and accurately detect a load within a measuring range of the load detection device, even when the output range of a load cell is large. 1.2. Features of the embodiment of the present invention

[0020] 1.2.1 In the embodiment of the present invention, a load detection device configured to detect a load applied to a measurement object based on a differential signal output by a load cell having a bridge circuit to which a strain gauge is connected, comprising: an excitation-side differential amplifier circuit configured to amplify an excitation signal to be sent to the load cell; a measurement-side differential amplifier circuit configured to amplify a first differential signal output by the load cell; and a control device designed to control the excitation-side differential amplifier circuit and the measurement-side differential amplifier circuit, wherein the control device is designed to a gain adjustment process for adjusting an output gain by adjusting one or more 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 difference signal output from the measurement-side differential amplifier circuit falls within a predetermined range.

[0021] Note that the embodiment of the present invention can also be implemented as a gain adjustment method of a load detection device for automatically setting a gain according to the output from the load cell. The embodiment of the present invention can also be implemented as a computer program for causing a control device to execute such a gain adjustment process, and as a recording medium on which the computer program is recorded.

[0022] According to this configuration, it is possible to decrease the output gain as the measured value obtained by the load detection device increases, and increase the output gain as the measured value obtained by the load detection device decreases. It is also possible to automatically adjust the output gain without user adjustment or the like. For example, by adjusting the output gain by adjusting one or both of the excitation-side gain and the measurement-side gain, it is possible to adjust the resolution of the load to be measured within the predetermined range while adjusting the measured value. Thus, the accuracy of load detection can be increased even when a load cell with a wide output range is used.

[0023] The "excitation-side gain" refers to the gain provided by the excitation-side differential amplifier circuit, and the "measurement-side gain" refers to the gain provided by the measurement-side differential amplifier circuit. The "output gain" is the total gain obtained by multiplying the "excitation-side gain" by the "measurement-side gain."

[0024] The values ​​of the excitation-side gain and the measurement-side gain specified by the control device are referred to as the "excitation-side gain default value" and the "measurement-side gain default value," respectively. Furthermore, the total gain obtained by multiplying the "excitation-side gain default value" by the "measurement-side gain default value" is referred to as the "output gain default value."

[0025] Furthermore, the “excitation signal”, the “first difference signal” and the “second difference signal” each indicate a voltage signal, and the “measured value” indicates a voltage value.

[0026] 1.2.2 Furthermore, in the embodiment of the present invention, the control device in the gain setting process, select the excitation-side gain and the measurement-side gain from candidate values ​​for the excitation-side gain specified at predetermined intervals as the excitation-side gain and candidate values ​​for the measurement-side gain specified at predetermined intervals as the measurement-side gain, respectively, and specify the output gain.

[0027] With this configuration, the output gain for amplifying the output from the bridge circuit is set by a combination of the excitation-side gain candidate value and the measurement-side gain candidate value, which are set in advance. Furthermore, the load on the control device for adjusting the output gain can be reduced. Furthermore, the output gain can be adjusted by adjusting each of the excitation-side gain and the measurement-side gain while maintaining a balance between the measurement range and resolution of the load to be measured.

[0028] The "excitation-side gain candidate value" indicates a candidate for a predefined preset value for the excitation-side gain, and the "measurement-side gain candidate value" indicates a candidate for a predefined preset value for the measurement-side gain. Furthermore, an "output gain candidate value" is a total gain value obtained by multiplying the "excitation-side gain candidate value" by the "measurement-side gain candidate value."

[0029] 1.2.3 Furthermore, in the embodiment of the present invention, the load detection device is a device designed to detect component forces acting on one of the tires of a vehicle, and it can control the control device in the gain adjustment process, when the vehicle is in a driving state within a predetermined period before a current time and a maximum measured value, which is a maximum value of the measured value within the predetermined period, is smaller than a predetermined measurable maximum value that is measurable by the load detection device, determine whether a first ratio is smaller than a second ratio, wherein the first ratio is a ratio of the maximum measured value to a permissible maximum measured value up to which the measured value can be guaranteed and which is determined according to the currently specified output gain, wherein the second ratio is a ratio of the output gain lower by one level to the currently specified output gain, and increase the output gain when a condition in which the first ratio is smaller than the second ratio persists for a predetermined first time or longer.

[0030] With this configuration, since the output gain is increased in a case where a state where the latest maximum measured value does not exceed the allowable maximum measured value persists even if the output gain is increased for the predetermined initial time or longer, the possibility of the measured value exceeding the allowable maximum measured value can be reduced. Thus, the output from the bridge circuit is amplified in a range where the measured value does not exceed the allowable maximum measured value, and the accuracy of load detection can be improved.

[0031] It should be noted that the "measurable maximum value" indicates the maximum value of the measured value up to which measurement accuracy can be guaranteed, which is determined based on the characteristics of the devices and elements arranged in the load detection device. Furthermore, the "permissible maximum measured value" indicates the maximum value of the measured value that is determined to be suitable according to the specified output gain.

[0032] 1.2.4 Furthermore, in the embodiment of the present invention the control device, even before the condition in which the first ratio is smaller than the second ratio lasts for the predetermined first time or longer, increase the output gain when the vehicle is in a deceleration state and when one or both of a value obtained by multiplying an acceleration acting on the vehicle in a predetermined direction by a weight of the vehicle and a value of a sum of component forces acting on the respective tires in the predetermined direction are continuously smaller than a first threshold value based on a gravitational acceleration for the predetermined period.

[0033] With this configuration, the output gain can be quickly increased even before the state where the latest maximum measured value does not exceed the allowable maximum measured value persists, even if the output gain is increased for the predetermined initial time or longer. The output gain is increased when it can be determined from the vehicle's driving condition that the measured value does not exceed the allowable maximum measured value. Thus, the output from the bridge circuit is amplified within the range where the measured value does not exceed the allowable maximum measured value, and the accuracy of load detection can be increased.

[0034] The “gravity acceleration-based first threshold” is a value obtained by multiplying the gravity acceleration by a coefficient preset as appropriate and is a calculated value that simply indicates that the vehicle is driving in such a way that the tires are not close to their limits in terms of vehicle dynamics.

[0035] For example, if a friction coefficient between the tires and the road surface can be estimated, or the road surface condition can be estimated in advance, the threshold at which the vehicle skids can be estimated moment by moment. However, by dynamically calculating the coefficient based on the load (N) at that time, the threshold at which the vehicle skids can be estimated.

[0036] 1.2.5 Furthermore, in the embodiment of the present invention the control device, even before the condition in which the first ratio is smaller than the second ratio lasts for the predetermined first time or longer, increase the output gain when the vehicle is in the deceleration state and when one or both of a value obtained by multiplying a sum of a lateral acceleration acting on the vehicle in the vehicle width direction and a centrifugal acceleration by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the vehicle width direction are continuously smaller than the first threshold value for the predetermined period.

[0037] With this configuration, the output gain can be quickly increased in a driving condition where lateral acceleration is applied to the vehicle.

[0038] 1.2-6 Furthermore, in the embodiment of the present invention the control device, even before the condition in which the first ratio is smaller than the second ratio lasts for the predetermined first time or longer, increase the output gain when the vehicle is in the deceleration state while the vehicle is traveling straight, and one or both of a value obtained by multiplying an absolute value of a longitudinal acceleration acting on the vehicle in the longitudinal direction by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the longitudinal direction are continuously smaller than the first threshold value for the predetermined period.

[0039] With this configuration, the output gain can be quickly increased in a driving condition where longitudinal acceleration is applied to the vehicle.

[0040] 1.2.7 Furthermore, in the embodiment of the present invention the control device in the gain adjustment process reduce the output gain when the vehicle is in the driving state within the predetermined period and the maximum measured value within the predetermined period is the predetermined measurable maximum value or more.

[0041] With this configuration, since the output gain is reduced when the latest maximum measured value is the allowable maximum measured value or more, it is possible to maintain the output gain while there is a low probability that the measured value exceeds the allowable maximum measured value and increase the accuracy of load detection.

[0042] 1.2.8 Furthermore, in the embodiment of the present invention the control device in the gain adjustment process reduce the output gain when one or both of a value obtained by multiplying an acceleration acting on the vehicle in a predetermined direction by a weight of the vehicle and a value of a sum of component forces acting on the respective tires in the predetermined direction continuously exceed a second threshold value based on a gravitational acceleration for the predetermined period.

[0043] With this configuration, the output gain can be quickly reduced if the vehicle's driving condition indicates that the measured value is likely to exceed the maximum permissible value. Thus, the output gain is adjusted so that the measured value does not exceed the maximum permissible value, and the accuracy of load detection can be increased.

[0044] The "gravity acceleration-based second threshold" is a value obtained by multiplying the gravity acceleration by a suitably predetermined coefficient and is a calculated value that simply indicates that the vehicle is traveling with the tires close to their limits in terms of vehicle dynamics. For example, if a friction coefficient between the tires and the road surface can be estimated, or the road surface condition can be estimated in advance, the limit at which the vehicle skids can be estimated moment by moment. However, by dynamically calculating the coefficient based on the load (N) at that time, the limit at which the vehicle skids can be estimated.

[0045] 1.2.9 Furthermore, in the embodiment of the present invention the control device reduce the output gain when the vehicle is in an acceleration state and when one or both of a value obtained by multiplying a sum of a lateral acceleration acting on the vehicle in the vehicle width direction and a centrifugal acceleration by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the vehicle width direction continuously exceed the second threshold value for the predetermined period.

[0046] With this configuration, the output gain can be quickly reduced in the driving state where lateral acceleration is applied to the vehicle.

[0047] 1.2.10 Furthermore, in the embodiment of the present invention the control device reduce the output gain when the vehicle is continuously traveling straight and when one or both of a value obtained by multiplying an absolute value of a longitudinal acceleration acting on the vehicle in the longitudinal direction by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the longitudinal direction continuously exceed the second threshold value for the predetermined period.

[0048] With this configuration, the output gain can be quickly reduced in the driving state where the longitudinal acceleration is applied to the vehicle.

[0049] 1.2.11 Furthermore, in the embodiment of the present invention the control device in the gain adjustment process determine whether it is possible to increase the excitation-side gain, and If it is possible to increase the excitation-side gain, increase the excitation-side gain preferentially over the measurement-side gain.

[0050] With this configuration, the output of the bridge circuit can be amplified without reducing the resolution of the load being measured. Thus, the output of the bridge circuit can be increased without reducing the accuracy of load detection.

[0051] 1.2.12 Furthermore, in the embodiment of the present invention the control device determine whether no load is applied to the strain gauge and whether a suitable posture is maintained, and When no load is applied to the strain gauge and the appropriate posture is maintained, perform a zero shift process of the measured value.

[0052] With this configuration, when the controller determines that no load is applied to the strain gauge, the zero shift process of the measured value is automatically executed, and the accuracy of load detection can be further increased. 2. Details of the Embodiment of the Present Invention 2.1. Configuration Example of a Load Cell (Six-Component Force Detector)

[0053] Next, a configuration example of a load cell to which a load detection device according to the embodiment of the present invention can be applied will be described.

[0054] In the embodiment, an example is described. In the example, the technology of the present invention is used as one aspect of the load cell for a six-component force detector that can detect six component forces (Fx, Fy, Fz, Mx, My, and Mz) applied to a wheel of a vehicle. The load cell according to this embodiment is a six-component force detector that detects six component forces applied to the wheel. The load cell is arranged in a hub bearing unit attached to a suspension device and on which the wheel of the vehicle, such as a car, is rotatably supported.

[0055] Fig. Figure 1 is a cross-sectional view of the hub bearing assembly incorporating the six-component force detector, taken along a plane containing a wheel axis. Fig. 1, the right side indicates the outside in the vehicle width direction, and the left side indicates the inside in the vehicle width direction. It should be noted that the Fig. 1 shown configuration of the hub bearing unit is only an example and does not refer to the configuration shown in Fig. 1 shown configuration is limited.

[0056] A hub bearing unit 100 includes a hub 110, an outer cylinder 120, an inner cylinder 130, a rolling element 140, a base 150, and a six-component force detector 1. The hub 110 is a member to which a rim disk of a wheel (not shown) is attached, which includes a rim and a tire. The hub 110 is formed by permanently attaching a cylinder 111, a flange 112, a collar 113, and the like.

[0057] The cylinder 111 is formed in a cylindrical shape concentric with the rotational center axis (wheel axis) of the wheel. The cylinder 111 is inserted into the inner diameter side of the inner cylinder 130, a detection unit 10, and the base 150. A splined hole 111a, into which a splined shaft of a drive shaft (not shown) is to be inserted, is formed in a region on the outer side of the inner peripheral surface of the cylinder 111 in the vehicle width direction.

[0058] The flange 112 is shaped like a disc and is formed to protrude from one end on the outer side of the cylinder 111 in the vehicle width direction toward the outer diameter side in the shape of a handguard. A surface on the outer side of the flange 112 in the vehicle width direction serves as a base to which the rim disc is to be attached.

[0059] In the flange 112, for example, approximately five openings 112a are formed at equal intervals along a predetermined pitch circle diameter in the circumferential direction, into which hub bolts are to be inserted.

[0060] The collar 113 has a cylindrical shape that protrudes from the outer surface of the flange 112 in the vehicle width direction and is concentric with the wheel axis. The collar 113 is fitted into a center hole, which is a circular opening formed in the center of the rim disc, and improves the mounting accuracy of the wheel.

[0061] The outer cylinder 120, the inner cylinder 130, and the rolling element 140 together form a rolling bearing (hub bearing) on ​​which the wheel is rotatably mounted. The outer cylinder 120 is formed by the permanent attachment of a cylinder 121, a flange 122, and the like. The cylinder 121 has a cylindrical shape concentric with the wheel axis.

[0062] A raceway surface for guiding the rolling element 140 is formed on the inner peripheral surface of the cylinder 121. An end on the inner side of the cylinder 121 in the vehicle width direction is formed to protrude toward the inner side in the vehicle width direction with respect to an end on the inner side of a cylinder 131 of the inner cylinder 130 in the vehicle width direction.

[0063] The flange 122 is formed to protrude in the shape of a handguard from one end on the outer side of the cylinder 121 in the vehicle width direction toward the outer diameter side. The flange 112 of the hub 110 is attached and fixed to the flange 122. A surface on the outer side of the flange 122 in the vehicle width direction abuts against a surface on the inner side of the flange 112 of the hub 110 in the vehicle width direction. The flange 122 has bolt holes 122a formed concentrically with the openings 112a of the hub 110. A hub bolt (not shown) used for fastening the wheel is to be fastened into the bolt holes 122a.

[0064] The inner cylinder 130 is formed by permanently attaching the cylinder 131, a flange 132, and the like. The cylinder 131 is a cylindrical member concentric with the wheel axis and is inserted into the inner diameter side of the cylinder 121 of the outer cylinder 120. A predetermined clearance is formed between the outer peripheral surface of the cylinder 131 and the inner peripheral surface of the cylinder 121 of the outer cylinder 120.

[0065] The raceway surface for guiding the rolling element 140 is formed on the outer peripheral surface of the cylinder 131. The flange 132 is formed to protrude from one end on the outer side of the cylinder 131 in the vehicle width direction toward the inner diameter side. The flange 132 supports one end on the outer side of a first flange 12 of the detection unit 10 in the vehicle width direction.

[0066] The rolling element 140 is a bearing disposed between the raceway surfaces of the outer cylinder 120 and the inner cylinder 130. The rolling element 140 is disposed between the outer cylinder 120 and the inner cylinder 130, along with a cage 141 and a cage 142 for positioning the rolling element 140 between the outer cylinder 120 and the inner cylinder 130.

[0067] The base 150 fastens and fixes the hub bearing unit 100 to a support (a hub knuckle) (not shown) of the suspension device. The base 150 is formed by permanently attaching a cylinder 151, a flange 152, a recess 153, a projection 154, and the like. The cylinder 151 is a cylindrical member concentric with the wheel axis, and one end on the inner side of the cylinder 111 of the hub 110 in the vehicle width direction is inserted therein. The outer peripheral surface of the cylinder 111 of the hub 110 is arranged to face the inner peripheral surface of the cylinder 151 with a predetermined distance therebetween in the radial direction.

[0068] The flange 152 is formed so as to protrude in the shape of a handguard from one end on the outer side of the cylinder 151 in the vehicle width direction toward the outer diameter side. The flange 152 is a fastening surface that fastens the base 150 to the bracket (not shown). Holes into which bolts for fastening to the bracket are inserted are formed in the flange 152 at a distance distributed in the circumferential direction. A through hole 152b is formed in the flange 152 from the inside of a space in which the outer peripheral surface of a cylinder 11 of the detection unit 10 is arranged to the outer peripheral edge of the flange 152. Wiring connected to, for example, a strain gauge is arranged in the through hole 152b.

[0069] The recess 153 is formed by gradually expanding the inner diameter of a portion corresponding to the flange 152 in the axial direction in the inner peripheral surface of the base 150. The recess 153 holds a second flange 13 of the detection unit 10. The projection 154 has a cylindrical shape formed to protrude from a central portion of the flange 152 in the radial direction toward the outside of the vehicle width direction.

[0070] The outer peripheral surface of the projection 154 is arranged to face the inner peripheral surface at one end on the inside of the cylinder 121 of the outer cylinder 120 in the vehicle width direction, with a space formed therebetween in the radial direction.

[0071] The six-component force detector 1 is a load cell capable of detecting loads in three orthogonal axes and moments around the three orthogonal axes acting on the wheel. The six-component force detector 1 includes the substantially cylindrical detection unit 10, strain gauges formed on the detection unit 10, and a bridge circuit including the strain gauges.

[0072] The detection unit (sensor core) 10 includes the cylinder 11, the first flange 12, the second flange 13, and the like. The cylinder 11 is formed in a cylindrical shape with which the inner diameter and outer diameter are substantially constant over a predetermined length in the axial direction, and the strain gauges described later are attached (adhered) to the cylinder 11. The first flange 12 is attached to one end on the outer side of the cylinder 11 in the vehicle width direction and formed to protrude toward the outer diameter side and the inner diameter side with respect to the cylinder 11.

[0073] The first flange 12 is fixed to the inner cylinder 130 in a state where the outer peripheral surface abuts against the inner peripheral surface near an end on the outside of the cylinder 131 of the inner cylinder 130 in the vehicle width direction and an end surface abuts against a surface on the inside of the flange 132 in the vehicle width direction.

[0074] The second flange 13 is mounted at one end on the inner side of the cylinder 11 in the vehicle width direction and is formed to protrude toward the outer diameter side and the inner diameter side with respect to the cylinder 11. The second flange 13 is fixed to the base 150 in a state where the outer peripheral surface and the end surface thereof are inserted into the recess 153 of the base 150. With such a configuration, substantially all forces acting on the wheel are transmitted to and from the base 150 via the detection unit 10.

[0075] The six-component force detector 1 includes 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 of which includes a bridge circuit comprising the strain gauges formed on the cylinder 11 of the above-described detection unit 10. The Fx detection system detects a force Fx acting in the radial direction (x-axis direction) on the cylinder 11 of the detection unit 10.

[0076] The Fz detection system detects a force Fz acting on the cylinder 11 of the detection unit 10 in the radial direction (z-axis direction) orthogonal to the x-axis direction. The Fy detection system detects a force Fy acting on the cylinder 11 of the detection unit 10 in the axial direction (y-axis direction). The Mx detection system detects a moment Mx acting on the cylinder 11 of the detection unit 10 about the x-axis. The Mz detection system detects a moment Mz acting on the cylinder 11 of the detection unit 10 about the z-axis. The My detection system detects a moment My acting on the cylinder 11 of the detection unit 10 about the y-axis.

[0077] Each of the above-described Fx detection system, Fy detection system, Fz detection system, Mx detection system, My detection system and Mz detection system has a bridge circuit having four strain gauges. Fig. Figure 2 is a schematic diagram of an arrangement of strain gauges in the six-component force detector 1. Fig. Figure 3 is a diagram showing the arrangement of strain gauges of the Fx detection system and the configuration of the bridge circuit in the six-component force detector 1.

[0078] Fig. 3 shows an illustrative example of the arrangement of the strain gauges of each force detection system (the Fx detection system, the Fy detection system, and the Fz detection system) and each moment detection system (the Mx detection system, the My detection system, and the Mz detection system), as well as the configuration of the bridge circuit.

[0079] As in Fig. 2 and Fig. As shown in Figure 3, the Fx detection system includes strain gauges 21 to 24. The strain gauges 21 to 24 are uniaxial strain gauges. The strain gauges 21 to 24 are mounted on the outer peripheral surface of the cylinder 11 so that their detection directions are parallel to the central axis direction of the cylinder 11.

[0080] The strain gauge 21 is arranged in a region on the first flange 12 side of the outer peripheral surface of the cylinder 11. The strain gauge 22 is arranged on a straight line passing through the strain gauge 21 and parallel to the axial direction of the cylinder 11, and is arranged in a region on the second flange 13 side of the outer peripheral surface of the cylinder 11.

[0081] The strain gauge 23 is arranged at a position offset by 180° from the strain gauge 22 around the central axis of the cylinder 11 (position symmetrical to the strain gauge 22 with respect to the central axis of the cylinder 11).

[0082] The strain gauge 24 is arranged at a position offset from the strain gauge 21 by 180° around the central axis of the cylinder 11 (position which is symmetrical to the strain gauge 21 with respect to the central axis of the cylinder 11). As shown in Fig. As shown in Figure 3, the bridge circuit of the Fx detection system is formed as a Wheatstone bridge circuit. Strain gauges 21 to 24 are arranged in a circular pattern in the circuit. A positive electrode and a negative electrode of a power source are arranged between strain gauge 22 and strain gauge 23, and between strain gauge 21 and strain gauge 24, respectively.

[0083] The bridge circuit extracts a potential difference between a terminal between strain gauge 21 and strain gauge 22 and a terminal between strain gauge 23 and strain gauge 24 as output. The configuration of the bridge circuit will be described in detail later.

[0084] The Fy detection system has strain gauges 41 to 44.

[0085] Strain gauges 41 to 44 are uniaxial strain gauges. Strain gauges 41 to 44 are mounted on the outer peripheral surface of cylinder 11 so that their detection directions are parallel to the central axis of cylinder 11. Strain gauge 41 is located midway between strain gauges 21 and 22 of the Fx detection system.

[0086] The strain gauges 42, 43 and 44 are arranged at positions where phases are shifted around the central axis of the cylinder 11 by 90°, 180° and 270°, respectively, with respect to the strain gauge 41. The bridge circuit of the Fy detection system has the same configuration except that the strain gauges 21 to 24 of the Fig. 3 are replaced by the strain gauges 41 to 44.

[0087] The Fz detection system includes strain gauges 31 to 34. The strain gauges 31 to 34 are uniaxial strain gauges. The strain gauges 31 to 34 are mounted on the outer peripheral surface of the cylinder 11 such that their detection directions are parallel to the central axis of the cylinder 11. The strain gauge 31 is arranged offset by 90° around the central axis of the cylinder 11 with respect to the strain gauge 21 of the Fx detection system.

[0088] The strain gauge 32 is arranged offset by 90° around the central axis of the cylinder 11 with respect to the strain gauge 22 of the Fx detection system. The strain gauges 31 and 32 are arranged on the same straight line parallel to the axial direction of the cylinder 11. The strain gauge 33 is arranged at a position offset by 180° around the central axis of the cylinder 11 from the strain gauge 32 (a position symmetrical to the strain gauge 32 with respect to the central axis of the cylinder 11).

[0089] The strain gauge 34 is arranged at a position offset by 180° from the strain gauge 31 around the central axis of the cylinder 11 (position symmetrical to the strain gauge 31 with respect to the central axis of the cylinder 11). The bridge circuit of the Fz detection system has the same configuration, except that the strain gauges 21 to 24 of the Fig. 3 are replaced by the strain gauges 31 to 34.

[0090] The Mx detection system includes strain gauges 51 to 54. The strain gauges 51 to 54 are uniaxial strain gauges. The strain gauges 51 to 54 are mounted on the outer peripheral surface of the cylinder 11 so that their detection directions are parallel to the central axis direction of the cylinder 11. The strain gauge 51 is arranged so that it is adjacent to the strain gauge 31 of the Fz detection system in the central axis direction of the cylinder 11.

[0091] The strain gauge 52 is arranged so that it is adjacent to the strain gauge 32 of the vehicle detection system in the central axis direction of the cylinder 11. The strain gauges 51 and 52 are arranged on the same straight line parallel to the axis direction of the cylinder 11. The strain gauge 53 is arranged at a position offset by 180° from the strain gauge 52 around the central axis of the cylinder 11 (a position that is symmetrical to the strain gauge 52 with respect to the central axis of the cylinder 11).

[0092] The strain gauge 54 is arranged at a position offset by 180° from the strain gauge 51 around the central axis of the cylinder 11 (position symmetrical to the strain gauge 51 with respect to the central axis of the cylinder 11). The bridge circuit of the Mx detection system has the same configuration, except that the strain gauges 21 to 24 of the Fig. 3 are replaced by the strain gauges 51 to 54.

[0093] The Fy detection system includes strain gauges 71 to 74. The strain gauges 71 to 74 are shear strain gauges. The strain gauges 71 to 74 are mounted on the outer peripheral surface of the cylinder 11 so that their detection directions are the circumferential direction of the cylinder 11. The strain gauge 71 is arranged midway between the strain gauges 41 and 42 of the Fy detection system. The strain gauge 72 is arranged midway between the strain gauges 42 and 44 of the Fy detection system.

[0094] The strain gauges 73 and 74 are arranged at positions symmetrical to the strain gauges 72 and 71, respectively, with respect to the central axis of the cylinder 11. The bridge circuit of the My detection system has the same configuration, except that the strain gauges 21 to 24 of the Fig. 3 are replaced by the strain gauges 71 to 74.

[0095] The Mz detection system includes strain gauges 61 to 64. The strain gauges 61 to 64 are uniaxial strain gauges. The strain gauges 61 to 64 are mounted on the outer peripheral surface of the cylinder 11 so that their detection directions are parallel to the central axis direction of the cylinder 11. The strain gauge 61 is arranged so that it is adjacent to the strain gauge 21 of the Fx detection system in the central axis direction of the cylinder 11.

[0096] The strain gauge 62 is arranged so that it is adjacent to the strain gauge 22 of the Fx detection system in the central axis direction of the cylinder 11. The strain gauges 61 and 62 are arranged on the same straight line parallel to the axis direction of the cylinder 11. The strain gauge 63 is arranged at a position offset by 180° from the strain gauge 62 around the central axis of the cylinder 11 (a position symmetrical to the strain gauge 62 with respect to the central axis of the cylinder 11).

[0097] The strain gauge 64 is arranged at a position offset by 180° from the strain gauge 61 around the central axis of the cylinder 11 (position symmetrical to the strain gauge 61 with respect to the central axis of the cylinder 11). The bridge circuit of the Mz detection system has the same configuration, except that the strain gauges 21 to 24 of the Fig. 3 are replaced by the strain gauges 61 to 64. 2.2. Bridge circuit

[0098] Next, the example of the bridge circuit of the Fig. 3, a configuration example for the bridge circuit of each force detection system and each moment detection system is described.

[0099] A bridge circuit 80 of the Fig. The Fx detection system shown in Figure 3 has four terminals, the first, second, third, and fourth terminals 81, 82, 83, and 84, as well as four strain gauges 21, 22, 23, and 24. The strain gauge 22 is arranged between the first terminal 81 and the second terminal 82, and the strain gauge 21 is arranged between the second terminal 82 and the fourth terminal 84.

[0100] The strain gauge 23 is arranged between the first terminal 81 and the third terminal 83, and the strain gauge 24 is arranged 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 forms a first path 86. 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 forms a second path 87.

[0101] The strain gauges 21, 22, 23, and 24 are resistance elements whose resistance changes depending on the degree of deformation. In this embodiment, the strain gauge comprises a material with a strain factor of 4 or more. The strain gauge may, for example, comprise a Cr-N thin film. When the strain gauge has a strain factor of 4 or more, an output can be obtained that is desirable for the six-component force detector 1 for detecting the load applied to the wheel. However, the strain gauge is not limited to the Cr-N thin film.

[0102] When a load is applied to a strain-generating body in the bridge circuit 80, 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) corresponding to a potential difference between the second terminal 82 of the first path 86 and the third terminal 83 of the second path 87.

[0103] It should be noted that a resistance element for adjusting the deviation from the initial equilibrium of the resistance value of the bridge circuit 80 or a resistance element for compensating the temperature characteristics may be connected to a given position of the bridge circuit 80. 2.3. Details of the design of the load detection device

[0104] Next, an embodiment of the load detection device according to the present embodiment will be described in detail. In the following description, the first terminal to the fourth terminal of the bridge circuit of each force detection system and each moment detection system of the load cell 1 will be referred to as the first terminal 81, the second terminal 82, the third terminal 83, and the fourth terminal 84 of the Fig. 3 shown bridge circuit 80.

[0105] Fig. 4 is a block diagram functionally illustrating a configuration example of a load detection device according to the present embodiment.

[0106] A load detection device 200 according to the present embodiment includes a load cell (six-component force detector) 1, a measuring circuit 160, and a controller area network (CAN) communication driver 183. The bridge circuit 80 and the measuring circuit 160 of each force detection system and each moment detection system of the load cell 1 can be connected via a connector.

[0107] 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 controller 180. The controller 180 is connected via the CAN communication driver 183 to a CAN bus 191, which is a communication bus to which control devices mounted in the vehicle are connected.

[0108] The excitation-side differential amplifier circuit 161 has the function of generating an excitation signal, amplifying the excitation signal, and sending the amplified signal to the load cell 1. The excitation-side differential amplifier circuit 161 includes, for example, a sine wave oscillator, a gain circuit differential amplifier, an excitation driver differential amplifier, and the like, as are known in the art.

[0109] The control of the excitation-side differential amplifier circuit 161 is controlled by the controller 180. The excitation-side differential amplifier circuit 161 generates an electrical sine wave signal (excitation signal) with a predetermined frequency, phase, and amplitude. The excitation-side differential amplifier circuit 161 further amplifies the excitation signal with a predetermined gain (excitation-side gain) and sends the excitation signal to the first terminal 81 and the fourth terminal 84 of each bridge circuit 80 of the load cell 1.

[0110] The measurement-side differential amplifier circuit 163 has a function of detecting the first differential signal output from the load cell 1, amplifying the differential signal, and outputting the amplified signal. The measurement-side differential amplifier circuit 163 includes, for example, an instrumentation differential amplifier, an amplification circuit differential amplifier, an A / D converter, and the like, which are known in the art.

[0111] The control of the measurement-side differential amplifier circuit 163 is controlled by the control device 180, and the measurement-side differential amplifier circuit 163 amplifies the detected first differential signal with a predetermined gain (measurement-side gain) and outputs a second differential signal to the lock-in amplifier 165.

[0112] The configuration of the excitation-side differential amplifier circuit 161 is not limited as long as the configuration can generate an excitation signal to be sent to the bridge circuit according to a drive command from the controller 180 and amplify the excitation signal. Similarly, the configuration of the measurement-side differential amplifier circuit 163 is not limited as long as the configuration can amplify the first differential signal output from the bridge circuit according to a drive command from the controller 180. Furthermore, one or both of the excitation-side differential amplifier circuit 161 and the measurement-side differential amplifier circuit 163 may include various elements that have a function of correcting the frequency, phase, amplitude, or the like of the signal.

[0113] The lock-in amplifier 165 extracts a signal corresponding to the frequency and phase of the excitation signal from the second differential signal output by the measurement-side differential amplifier circuit 163. The extracted signal is output to the control device 180 as data indicating the measured value. The lock-in amplifier 165 can also be implemented using a lock-in amplifier known in the art.

[0114] The controller 180 includes one or more processors and one or more memories communicatively connected to the one or more processors, and executes the control of the measuring circuit 160. Furthermore, the controller 180 calculates the load applied to the load cell 1 based on the measured value input from the lock-in amplifier 165 and an output gain.

[0115] The controller 180 outputs a command signal to the excitation-side differential amplifier circuit 161 and the measurement-side differential amplifier circuit 163. In the present embodiment, the controller 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 a permissible maximum measurement value.

[0116] For example, the controller 180 executes a process (gain feedback adjustment process) to adjust one or more of the excitation-side gain and the measurement-side gain so that the measured value falls below the allowable maximum measured value. The controller 180 executes the process based on the history of the measured values ​​input from the lock-in amplifier 165.

[0117] Furthermore, the controller 180 acquires information about a driving state of the vehicle via the CAN communication driver 183. The controller 180 executes a process (gain feedforward adjustment process) to adjust the output gain based on the acquired driving state information so that the measured value falls below the allowable maximum measured value.

[0118] In the present embodiment, candidate gain values ​​are set for each of the excitation-side gain and the measurement-side gain at predetermined intervals. The controller 180 determines a gain set value for each of the excitation-side gain and the measurement-side gain and sets the output gain. For example, if the excitation-side gain can be set up to 5 times (500% gain) and the measurement-side gain can be set up to 4 times (400% gain), the output gain can be set up to a maximum of 20 times (2000% gain).

[0119] Since the output gain can be adjusted by the excitation-side gain and the measurement-side gain, the resolution of the load to be measured can be optimized to a desired range while adjusting the measured value. For example, assume that there is a load detection device that can perform a measurement with an accuracy of 0.1 mV by calculating with a full range of 0 to 100 mV. With this assumption, when detecting a physical quantity from 0 to 5000 N, a case where an output of 0 to 10 mV is measured and a case where an output of 0 to 100 mV is measured are compared. In the first case, the load can be detected in increments of 50 N, and in the second case, the load can be detected in increments of 5 N.Thus, it is possible to adjust the resolution to a more optimal resolution and at the same time bring the maximum value of the measured value close to the permissible maximum measured value, which corresponds to the default value of the output gain.

[0120] For example, if the gain is adjusted on the excitation side, the output of the bridge circuit doubles by doubling the excitation-side gain. However, if the excitation-side gain is doubled, the output of the bridge circuit doubles, but the resolution of the load being measured is not reduced. In contrast, if the gain is adjusted on the measurement side, the resolution of the load being measured itself can be adjusted depending on whether the first differential signal is amplified twice or four times.

[0121] For example, if the measurement-side gain is doubled, the output of the second differential signal doubles compared to the first differential signal, while the resolution of the load being measured is halved. Thus, since the output gain can be adjusted by the excitation-side gain and the measurement-side gain, it is possible to optimize the resolution of the load being measured while simultaneously adjusting the measured value to the desired range.

[0122] Furthermore, in the present embodiment, the controller 180 is configured to acquire information about the driving state of the vehicle via the CAN communication driver 183. The controller 180 is also configured to execute a zero-point shift process of the load cell 1 when a predetermined shift process condition is met.

[0123] In the vehicle-mounted load cell 1, such as the six-component force detector described above, a displacement value, which represents a difference between a measured value to be measured with respect to an applied load and an actual measured value, is always subject to change due to a heat history, a mechanical stress history, or the like. To prevent such a displacement value from becoming excessively large, the controller 180 determines, using information about the vehicle's running state, whether the displacement process condition under which the zero-point displacement process can be executed is satisfied. If the displacement process condition is satisfied, the controller 180 executes the zero-point displacement process. Thus, the accuracy of load detection can be further increased. 2.4. Operation of the load detection device

[0124] Next, an example of the operation of the load detection device according to the present embodiment will be described using as an example a load detection device that detects component forces applied to a vehicle tire using the six-component force detector 1. 2.4.1. Specification process

[0125] The control device 180 executes a setting process for setting a condition required for executing the gain adjustment process and the zero shift process. In principle, the setting process can be executed before the load detection device 200 is used for the first time, but can also be executed again when repair, inspection, or replacement work is performed on the load cell 1 or the measuring circuit 160.

[0126] Fig. Figure 5 is a flowchart illustrating the specification process.

[0127] In the specification process, the controller 180 refers to data indicating specifications of the load detection device 200 (step S1). Subsequently, the controller 180 specifies a maximum output gain value Gain_max, a maximum measurable value S_max_sys, and a maximum allowable measurement value S_max_def(gain_x) based on specifications of the respective elements constituting the measurement circuit 160 (step S3). The specification data may be a data sheet, also referred to as a Transducer Electronic Data Sheet (TEDS).

[0128] Predeterminable values ​​of the excitation-side gain and the measurement-side gain (candidate values ​​for the excitation-side gain and candidate values ​​for the measurement-side gain) are predetermined at predetermined intervals. The controller 180 calculates and records the predeterminable maximum value of the output gain Gain_max. The controller 180 also reads and records the data of the maximum value (measurable maximum value) S_max_sys that can be measured by the measuring circuit 160. The controller 180 also reads and records the data of the permissible maximum measured value S_max_def(gain_x), which is the maximum value of the measured value up to which the measuring circuit 160 ensures measurement accuracy according to an output gain Gain. 2.4.2. Gain feedback adjustment process

[0129] Fig. Figure 6 is a flowchart illustrating a gain adjustment process (gain feedback adjustment process) based on measurement history. The gain feedback adjustment process may be executed constantly during the activation of a system of the vehicle or may be configured to be executed during the execution of a specific control using the component forces applied to the tires.

[0130] First, the controller 180 acquires vehicle state information via the CAN communication driver 183 (step S11). The vehicle state information includes information that can be used to determine whether the vehicle is moving, as well as the acceleration / deceleration and yaw rate of the vehicle.

[0131] The vehicle state information may include, but is not limited to, information about the vehicle speed, acceleration / deceleration, accelerator pedal operation amount, and brake pedal operation amount. For example, the vehicle state information may include status information indicating that the vehicle is moving.

[0132] Next, the controller 180 determines, based on the vehicle state information, whether the vehicle is in a running state between a time T seconds before a current time t and the current time t (step S13). For example, the controller 180 determines that the vehicle is in a running state between the time T seconds before the current time t and the current time t if one or more of the following conditions are met during this period. The conditions include that the vehicle speed is a positive value over 0 km / h, that the acceleration / deceleration is not zero, and that the accelerator pedal operation amount is a positive value. The value of T seconds can be set as needed, for example, within a range of 5 to 20 seconds.

[0133] If the vehicle is not in the running state between the time T seconds before the current time t and the current time t (S13 / No), the controller 180 maintains the output gain Gain at a current output gain set value Gain_now (step S25). For example, the controller 180 maintains the excitation-side gain and the measurement-side gain at a current set value for the excitation-side gain and a current set value for the measurement-side gain, respectively. In this case, since the vehicle is in the stopped state and there is no change in the component forces applied to the tires by the vehicle's running, the process of this routine ends without adjusting the output gain Gain and returns to step S11.

[0134] On the other hand, if the vehicle is in the running state (S13 / Yes) between the time T seconds before the current time t and the current time t, the process described below is performed. The controller 180 acquires a maximum measurement value S_max_t between the time T seconds before the current time t and the current time t (tT to t) (step S15). That is, the controller 180 acquires the maximum value (maximum measurement value) S_max_t of a measurement value S measured in a predetermined period already passed.

[0135] Next, the controller 180 determines whether the detected maximum measurement value S_max_t is smaller than the measurable maximum value S_max_sys (step S17). That is, the controller 180 determines whether the maximum measurement value S_max_t measured during the predetermined period in which the vehicle is in the running state is smaller than the measurable maximum value S_max_sys. If the maximum measurement value S_max_t is equal to or greater than the measurable maximum value S_max_sys (step S17 / No), the process described below is performed. The controller 180 sets the output gain Gain as a value Gain_now-1, which is one step lower than the current output gain set value Gain_now (step S27).

[0136] For example, the controller 180 decreases one of the excitation-side gain and the measurement-side gain by one step to reduce the output gain Gain. Consequently, the measured maximum measurement value S_max_t can be brought closer to the measurable maximum value S_max_sys. Furthermore, the possibility that the measured value S, measured when a similar driving condition continues, exceeds the measurable maximum value S_max_sys can be reduced. For example, by maintaining the excitation-side gain and reducing the measurement-side gain, it is possible to increase the resolution of the load to be measured while reducing the range of the measured value S.

[0137] On the other hand, if the maximum measured value S_max_t is smaller than the measurable maximum value S_max_sys (S17 / Yes), the process described below is performed. The controller 180 determines whether a first ratio is smaller than a second ratio (step S19). The first ratio is a ratio of the maximum measured value S_max_t to the allowable maximum measured value S_max_def(gain_now) determined according to the currently set output gain Gain. The second ratio is a ratio of the output gain Gain_now-1 lower by one step to the currently set output gain Gain_now. In step S19, it is determined whether the measured maximum measured value S_max_t does not exceed the allowable maximum measured value S_max_def(gain_now) even if the output gain is increased by one step. That is, it is determined whether there is a margin for increasing the output gain by one step.In order to specify this margin as a design value, the default value for the permissible maximum measured value S_max_def(gain x) of each output gain Gain is specified in advance.

[0138] Note that the gain feedforward adjustment process based on vehicle state information, described later, is performed for each vehicle. However, the comparison between the maximum measured value S_max_t and the allowable maximum measured value S_max_def(gain x) is performed for each component force of the vehicle.

[0139] If the determination is negative in step S19 (S19 / No), the controller 180 maintains the output gain Gain at the current output gain set value Gain_now (step S25). In this case, if the output gain Gain is increased, the measured value S may exceed the allowable maximum measured value S_max_def(gain_x) corresponding to the output gain. Thus, the process of this routine ends without adjusting the output gain Gain and returns to step S11.

[0140] On the other hand, if the determination is affirmative in step S19 (S19 / Yes), the controller 180 determines whether the state satisfying the condition in step S19 is maintained for a first time N1 (seconds) (step S21). The first time N1 can be set as a given time at which a stable continuation of a state in which there is a margin for increasing the output gain by one step can be determined. Note that the information indicating that the condition in step S19 is satisfied is used in the gain feedforward adjustment process described later. Thus, for example, a flag indicating that the condition in step S19 is satisfied is set so that it can be referred to.

[0141] If the condition satisfying the condition in step S19 is not maintained for the first time N1 (S21 / No), the controller 180 maintains the output gain Gain at the current output gain set value Gain_now (step S25). In this case, it cannot be determined that the measured value S cannot exceed the permissible maximum measured value S_max_def(gain_x) corresponding to the output gain even if the output gain Gain is increased. Thus, the process of this routine ends without adjusting the output gain Gain and returns to step S11.

[0142] On the other hand, if the state satisfying the condition in step S19 is maintained for the first time N1 (S21 / Yes), the controller 180 sets the output gain setting Gain as a value Gain_now+1 (step S23). The value Gain_now+1 is one step higher than the current output gain setting value Gain_now.

[0143] For example, the control device 180 increases one of the excitation-side gain and the measurement-side gain by one step to increase the output gain Gain. Thus, the measured value S can be increased such that the permissible maximum measured value S_max_def(gain_x) corresponding to the set output gain (Gain_now+1) is not exceeded. In this case, the excitation-side gain can preferably be increased.

[0144] Fig. 7 is a flowchart illustrating a process for setting the excitation-side gain and the measurement-side gain to increase the output gain.

[0145] The controller 180 reads the currently preset excitation-side gain preset value and determines whether the excitation-side gain can be increased (step S31). For example, the controller 180 determines whether the currently preset excitation-side gain preset value is the maximum value of the excitation-side gain candidate values ​​preset at predetermined intervals. If the excitation-side gain preset value is not the maximum value of the excitation-side gain candidate values, the controller 180 determines that the excitation-side gain can be increased.

[0146] If it is determined that the excitation-side gain can be increased (S31 / Yes), the controller 180 preferentially increases the excitation-side gain to increase the output gain Gain (step S33). Conversely, if it is determined that the excitation-side gain cannot be increased (S31 / No), the controller 180 increases the output gain Gain by increasing the measurement-side gain (step S35). In this way, by preferentially increasing the excitation-side gain, the measured value S can be increased without reducing the resolution of the load to be measured.

[0147] The controller 180 repeatedly executes the process of the above-described steps at a predetermined sampling period. Even if the output range from the bridge circuit of the load cell 1 is large, the controller 180 sets the output gain Gain based on the history of the actual measured values ​​S. The output gain Gain is set so that the measured maximum measured value S_max_t is smaller than the measurable maximum value S_max_sys and the allowable maximum measured value S_max_def(gain_now). Thus, the output of the bridge circuit is amplified so that the measured value S does not exceed the measurable maximum value S_max_sys and the allowable maximum measured value S_max_def(gain_x), and the load measurement accuracy can be increased. 2.4.3. Modification of the gain feedback adjustment process

[0148] In the gain feedback adjustment process according to a modification, a method for setting the output gain Gain when increasing the output gain Gain is different from that in Fig. Example of the gain feedback adjustment process shown in Figure 6.

[0149] Fig. Figure 8 is a flowchart illustrating the modification of the gain feedback adjustment process. In the Fig. The flowchart shown in Fig. 8 is the process from step S19 to step S21 in the Fig. 6 is replaced by the process from step S18 to step S22.

[0150] In the modification, if it is determined in step S17 that the maximum measured value S_max_t is smaller than the measurable maximum value S_max_sys (S17 / Yes), the controller 180 calculates a base measured value ms_max_ori (step S18). The base measured value ms_max_ori corresponds to the maximum measured value S_max_t when the output gain Gain is not adjusted (Gain = 1). For example, the controller 180 calculates the base measured value ms_max_ori by dividing the maximum measured value S_max_t by the currently specified output gain set value Gain_now.

[0151] Subsequently, the control device 180 calculates a maximum output gain Gain_M from the candidate values ​​for the output gain (step S20). Up to the maximum output gain Gain_M, a value S_max obtained by multiplying the base measurement value ms_max_ori by an output gain Gain_x is smaller than the permissible maximum measurement value S_max_def(gain_x) corresponding to the output gain Gain.

[0152] Subsequently, the controller 180 determines whether the obtained output gain Gain_M is less than the currently set output gain set value Gain_now (step S22). If it is determined that the output gain Gain_M is not less than the output gain set value Gain_now (S22 / No), the controller 180 maintains the output gain Gain at the current output gain set 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 returns to step S11.

[0153] On the other hand, if it is determined that the output gain Gain_M is smaller than the output gain set value Gain_now (S22 / Yes), the controller 180 sets the output gain Gain as Gain_now+1 (step S23). The value Gain_now+1 is one step higher than the current output gain set value Gain_now. At this time, the controller 180 may increase the output gain Gain by more than one step. However, if the rate of increase of the output gain Gain is too large, the measured value S may rapidly exceed the allowable maximum measured value S_max_def(gain x) when the driving state of the vehicle changes, and the loads applied to the tires may rapidly increase. Thus, it is preferable to increase the output gain Gain gradually, for example, by one or two steps.

[0154] Also, in the gain feedback adjustment process according to the modification described above, the same effects as in the gain feedback adjustment process described above can be achieved. 2.4.4. Effects of the gain feedback adjustment process

[0155] Fig. 9 and Fig. 10 are explanatory diagrams of an example in which the output gain is increased by the gain feedback adjustment process. Fig. 9 and Fig. 10 both represent measured values ​​of a component force Fy applied to the tire of the vehicle in a curve in the vehicle width direction. Fig. 9 represents a measured value (base measured value) ms in a case where the output gain Gain is set as a value 2 and the gain of the output of the bridge circuit is not adjusted. Fig. Figure 10 shows the measured value S in a case where the bridge circuit output gain is adjusted. In this example, the maximum measurable value S_max_sys is assumed to be 1.50 mV.

[0156] In the Fig. In the example shown in Figure 9, if the gain is not adjusted, in a period (first period) from the start of measurement until 8 seconds later, the base measurement value ms fluctuates between 0.00 and 0.05 mV. Furthermore, in a period (second period) from 8 seconds to 23 seconds after the start of measurement, the base measurement value ms fluctuates between 0.00 and 0.20 mV. Furthermore, in a period (third period) after 23 seconds, the base measurement value ms fluctuates between 0.00 and 0.70 mV. This shows that the driving state of the vehicle changes in each period, and the loads applied to the tires change.

[0157] If the gain is not adjusted, the base measurement value ms is significantly smaller than the maximum measurable value S_max_sys and the maximum permissible measurement value S_max_def(gain_x). Thus, there is room to increase the accuracy of load detection by amplifying the output of the bridge circuit to change the range of the measured value S to the larger side.

[0158] In contrast, in the Fig. In the example shown in Figure 10, the output gain is specified as 5 at the beginning of the measurement, and the measured value S fluctuates between 0.00 and 0.10 mV in the first period. The measured value S in the first period is significantly lower than the measurable maximum value S_max_sys. Furthermore, the measured value S is continuously below a permissible maximum measured value S_max_def(gain_5) corresponding to the output gain. Therefore, the control device 180 doubles the output gain.

[0159] Thus, the measured value S is amplified in the second period and fluctuates between 0.00 and 0.25 mV. The base measured value ms in the second period has a greater fluctuation range than in the first period due to a change in the vehicle's driving condition. However, the measured value S in the second period is significantly lower than the measurable maximum value S_max_sys and is continuously below a permissible maximum measured value S_max_def(gain_10) corresponding to the output gain Gain. As a result, the control device 180 further doubles the output gain Gain.

[0160] Thus, the measured value S is further amplified in the third period and fluctuates between 0.00 and 1.40 mV. The base measured value ms in the third period has a larger fluctuation range than in the second period due to a change in the vehicle's driving condition, and the maximum value of the measured value S in the second period is close to the measurable maximum value S_max_sys. Thus, the load can be detected based on the larger measured value S, and the accuracy of load detection can be increased.

[0161] Fig. 11 and Fig. 12 are explanatory diagrams of an example in which the output gain is reduced by the gain feedback adjustment process. Fig. 11 and Fig. 12 both represent the measured value of a component force Fx in the vehicle longitudinal direction applied to the tire during deceleration of the vehicle. Fig. 11 represents the measured value (base measured value) ms in a case where the output gain Gain is set as a value 10 and the gain of the output of the bridge circuit is not adjusted. Fig. Figure 12 shows the measured value S in a case where the bridge circuit output gain is adjusted. In this example, the maximum measurable value S_max_sys is assumed to be 1.50 mV.

[0162] In the Fig. In the example shown in Figure 11, if the gain is not adjusted, in the period (first period) from the start of measurement until 8 seconds later, the base measurement value ms fluctuates between 0.05 and 0.35 mV. Furthermore, in the period (second period) from 8 seconds to 23 seconds after the start of measurement, the base measurement value ms fluctuates between 0.20 and 1.10 mV. Furthermore, in the period (third period) after 23 seconds, the base measurement value ms fluctuates between 0.20 and 1.80 mV. This shows that the driving condition of the vehicle changes in each period, and the loads applied to the tires change.

[0163] If the gain is not adjusted, the base measurement value ms increases over time, exceeds the allowable maximum measurement value S_max_def(gain_10) in the second period, and exceeds the measurable maximum value S_max_sys 32 seconds after the start of the measurement.

[0164] In contrast, the Fig. In the example shown in Figure 12, the output gain is specified as 20 at the beginning of the measurement, and the measured value S fluctuates between 0.10 and 0.75 mV in the first period. The measured value S in the first period is significantly lower than the measurable maximum value S_max_sys, but exceeds a permissible maximum measured value S_max_def(gain_20) corresponding to the output gain. Thus, the control device 180 specifies the output gain as 0.5 times and outputs the same output gain as in the case according to Fig. 11 before.

[0165] Thus, the measured value S fluctuates between 0.20 and 1.10 mV in the second period. However, as with the base measured value ms in the second period, the range of the measured value S is wider than in the first period due to a change in the vehicle's driving condition. Thus, even though the output gain Gain is reduced, the measured value S exceeds the permissible maximum measured value S_max_def(gain_10) corresponding to the output gain Gain. Therefore, the controller 180 increases the output gain Gain by 0.5 times.

[0166] Thus, the measured value S in the third period is reduced to a small value, fluctuating between 0.10 and 0.75 mV. The base measured value ms in the third period exceeds the maximum measurable value S_max_sys and the permissible maximum measured value S_max_def(gain_5). However, if the output gain Gain is reduced, the base measured value ms in the third period falls below the maximum measurable value S_max_sys and the permissible maximum measured value S_max_def(gain_5). Thus, the accuracy of the measured value S is ensured, and the measurement accuracy can be increased. 2.4.5. Adjustment of the output gain by excitation-side gain and measurement-side gain

[0167] Fig. 13 is an explanatory diagram that the output gain is adjusted by adjusting the excitation side gain and the measurement side gain. Fig. 13 shows the output gain Gain determined by an excitation-side gain Gain_u and a measurement-side gain Gain_d, and the measured value S obtained by amplifying the base measured value ms by means of the output gain Gain. The measured value S is the measured value S of the component force Fy applied in the vehicle width direction to the tires of the vehicle traveling on an uneven road.

[0168] From the start of measurement until 8 seconds later, both the excitation-side gain Gain_u and the measurement-side gain Gain_d are fixed at 1, and the total output gain Gain is fixed at 1. From 8 seconds to 13 seconds, 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. From 13 seconds to 22 seconds, 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 kept at 10.Thus, the base measurement value ms is amplified according to the specification of the output gain Gain, and the range of the measurement value S is changed.

[0169] In the six-component force detector 1, differential signals are output from the bridge circuits of the three force detection systems (Fx, Fy, and Fz) and the three moment detection systems (Mx, My, and Mz). However, if there is a component force for which the output signal of the bridge circuit is insufficient, it is useful to adjust the excitation-side gain and the measurement-side gain to adjust a noise component and the allowable maximum measured value. In this case, if there is room to increase the excitation-side gain Gain_u, even if the total output gain Gain is the same, the excitation-side gain Gain_u is preferentially increased rather than the measurement-side gain Gain_d. Thus, it is possible to set the output gain Gain so as to reduce a decrease in the resolution of the load to be measured while setting the range of the measured value S as the target range.

[0170] In the example described above according to Fig. 13, the control device 180 maintains the total output gain Gain at 10 for 22 seconds after the start of the measurement. At the same time, the control device 180 increases the excitation-side gain Gain_u to 5 and decreases the excitation-side gain Gain_u to 2. Thus, it is possible to increase the resolution of the load to be measured while maintaining the range of the measured value S. 2.4.6. Gain feedforward adjustment process

[0171] Fig. 14 is a flowchart illustrating the gain adjustment process (gain feedforward adjustment process) based on information about the vehicle's driving state. The gain feedforward adjustment process may be executed constantly during activation of the vehicle system or may be configured to be executed during the execution of a specific control using the forces applied to the tires. 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.

[0172] First, the controller 180 acquires the vehicle state information via the CAN communication driver 183 (step S41). The details of the process in step S41 are the same as those in step S11 in the gain feedback adjustment process described above, and steps S11 and S41 may also be a single process.

[0173] Subsequently, the controller 180 determines, based on the vehicle state information, whether the vehicle is in a deceleration state between the time T seconds before the current time t and the current time t (step S43). For example, if the acceleration of the vehicle included in the vehicle state information is a negative value, the controller 180 determines that the vehicle is in a deceleration state. However, the method for determining that the vehicle is in a deceleration state is not limited to the above-described example.

[0174] If the vehicle is not in the deceleration state between the time T seconds before the current time t and the current time t (S43 / No), the process described below is performed. It is determined whether the vehicle is in an acceleration state between the time T seconds before the current time t and the current time t (step S55). For example, when the acceleration of the vehicle included in the vehicle state information is a positive value, the controller 180 determines that the vehicle is in the acceleration state. However, the method for determining that the vehicle is in the acceleration state is not limited to the above-described example.

[0175] If an affirmative determination in step S43 (S43 / Yes), the controller 180 executes a process for determining whether to increase the output gain Gain (steps S45 to S49). Meanwhile, if an affirmative determination in step S55 (S55 / Yes), the controller 180 executes a process for determining whether to decrease the output gain Gain (steps S57 and S59). On the other hand, if a negative determination is made in both steps S43 and S55 (S43 / No and S55 / No), the controller 180 maintains the output gain Gain at the current output gain command value Gain_now (step S53). For example, the controller 180 maintains the excitation-side gain and the measurement-side gain at the current command value for the excitation-side gain and the current command value for the measurement-side gain, 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 returns to step S11.

[0176] If an affirmative determination is made in step S43 (S43 / Yes), the controller 180 determines, based on a gravity acceleration, whether one or both of the following values ​​are smaller than a first threshold value (step S45).

[0177] The values ​​are a value obtained by multiplying the acceleration acting on the vehicle in a predetermined direction by the weight of the vehicle, and a value of the sum of the component forces acting on the respective tires in the predetermined direction. Step S45 is a process for determining whether the vehicle's driving state is a driving state in which the loads applied to the tires are small, and is performed to predict that the base measurement value ms will assume a small value in a state in which the gain is not adjusted.

[0178] In step S45 of the Fig. 14, the controller 180 determines, in the traveling state in which acceleration in the vehicle width direction can be applied to the vehicle, whether one or both of the following absolute values ​​are smaller than a first threshold value kmin*M*g based on a gravitational acceleration g.

[0179] The absolute values ​​are an absolute value abs[M*(G_lat+v*ω)] of a value obtained by multiplying the sum of a lateral acceleration G_lat acting on the vehicle in the vehicle width direction and an acceleration v*ω of a centrifugal force by a weight M of the vehicle, and an absolute value abs(ΣFy) of a sum ΣFy of component forces Fy acting on the respective tires in the vehicle width direction. It is a process for determining whether the loads applied to the tires in the vehicle width direction are small in situations where the loads are applied to the tires in the vehicle width direction.

[0180] Whether the vehicle is in a driving state in which acceleration can be exerted on the vehicle in the vehicle width direction can be determined, for example, based on information about a steering angle detected by a steering angle sensor. Furthermore, the lateral acceleration G_lat and the acceleration v*ω of the centrifugal force are determined based on information about sensor values ​​from an acceleration sensor and a yaw rate sensor, respectively.

[0181] A coefficient kmin of the first threshold value kmin*M*g is a positive preset value, set in advance within a range of 0 to 1, to easily determine that the vehicle is not driving in a manner that causes the tires to be close to their limits in terms of vehicle dynamics. The vehicle's weight M can also be acquired along with the vehicle state information.

[0182] It can be determined whether either of the following absolute values ​​is smaller than the first threshold value kmin*M*g. The absolute values ​​are the absolute value abs[M*(G_lat+v*ω)] of the value obtained by multiplying the sum of the lateral acceleration G_lat and the centrifugal force acceleration v*ω by the vehicle weight M, and the absolute value abs(ΣFy) of the sum ΣFy of the component forces Fy acting on the respective tires in the vehicle width direction. However, by determining whether both values ​​are smaller than the first threshold value kmin*M*g, the reliability of the determination result can be increased.

[0183] When the vehicle is traveling straight, no loads are applied to the tires in the vehicle width direction. In this case, the controller 180 can determine whether the loads applied to the tires in the longitudinal direction are small. For example, when the vehicle is decelerating while traveling straight, the controller 180 determines, based on the acceleration of gravity, whether one or both of the following values ​​are less than the first threshold value kmin*M*g.

[0184] The values ​​are a value abs[M*G_longi] obtained by multiplying an absolute value abs(G_longi) of a longitudinal acceleration G_longi acting on the vehicle in the longitudinal direction by the weight M of the vehicle, and an absolute value abs(ΣFx) of a sum ΣFx of the component forces Fx acting on the corresponding tires in the longitudinal direction.

[0185] Whether the vehicle is traveling straight can be determined, for example, based on the information about the steering angle detected by the steering angle sensor. Furthermore, the longitudinal acceleration G_longi is obtained based on the information about the sensor value of the acceleration sensor. The first threshold value kmin*M*g for determining the loads acting on the tires in the longitudinal direction can be the same as or different from the first threshold value kmin*M*g for determining the loads applied to the tires in the vehicle width direction.

[0186] Furthermore, it can be determined whether either of the following absolute values ​​is smaller than the first threshold value kmin*M*g. The absolute values ​​are the absolute value abs[M*G_longi] of the value obtained by multiplying the longitudinal acceleration G_long by the vehicle weight M, and the absolute value abs(ΣFx) of the sum ΣFx of the component forces Fx acting on the respective tires in the longitudinal direction. However, by determining whether both values ​​are smaller than the first threshold value kmin*M*g, the reliability of the determination result can be increased.

[0187] If the determination is negative in step S45 (S45 / No), the controller 180 maintains the output gain Gain at the current output gain set value Gain_now (step S53). In this case, it cannot be determined that the measured value S cannot exceed the permissible maximum measured value S_max_def(gain_x) corresponding to the output gain even if the output gain Gain is increased. Thus, the process of this routine ends without adjusting the output gain Gain and returns to step S41.

[0188] On the other hand, if the determination is affirmative in step S45 (S45 / Yes), the controller 180 determines whether the state satisfying the condition in step S45 is maintained for a second time N2 (seconds) (step S47). The value of the second time N2 is set to a value smaller than the value of the first time N1 used in the gain feedback adjustment process in step S21. If the state satisfying the condition in step S45 is not maintained for the second time N2 (S47 / No), the controller 180 maintains the output gain Gain at the current output gain set value Gain_now (step S53).

[0189] Even in this case, it cannot be determined that the measured value S cannot exceed the permissible maximum measured value S_max_def(gain_x) corresponding to the output gain, even if the output gain is increased. Thus, the process of this routine is terminated without adjusting the output gain and returns to step S41.

[0190] On the other hand, if the state satisfying the condition in step S45 is maintained for the second time N2 (S47 / Yes), the controller 180 determines whether the condition in step S19 is satisfied in the gain feedback adjustment process (whether an affirmative determination was made in step S19) (step S49). For example, the controller 180 determines whether the flag indicating that the condition in step S19 is satisfied is set.

[0191] If the condition in step S19 is not met (S49 / No), the controller 180 maintains the output gain Gain at the current output gain set value Gain_now (step S53). Even in this case, it cannot be determined that the measured value S cannot exceed the permissible maximum measured value S_max_def(gain_x) corresponding to the output gain, even if the output gain Gain is increased. Thus, the process of this routine is terminated without adjusting the output gain Gain and returns to step S41.

[0192] On the other hand, if the condition in step S19 is met (S49 / Yes), the controller 180 sets the output gain Gain as the value Gain_now+1 (step S51). The value Gain_now+1 is one step higher than the current output gain set value Gain_now. For example, the controller 180 increases one of the excitation-side gain or the measurement-side gain by one step to increase the output gain Gain.

[0193] As in Fig. 7, the excitation-side gain is preferably increased. The second time N2 used in step S47 is specified to be shorter than the first time N1 used in step S21. Thus, the output gain can be quickly increased even before the state in which the first ratio is smaller than the second ratio, which is the condition in step S19, persists for the first time N1 or longer. The output gain is increased when it can be determined from the driving state of the vehicle that the measured value does not exceed the permissible maximum measured value.

[0194] On the other hand, if the determination in step S55 is affirmative (S55 / Yes), the controller 180 determines whether one or both of the following values ​​exceed a second threshold based on the gravitational acceleration (step S57). These values ​​are a value obtained by multiplying the acceleration acting on the vehicle in a predetermined direction by the weight of the vehicle and a value of the sum of the component forces acting on the respective tires in the predetermined direction.

[0195] Step S57 is a process for determining whether the running state of the vehicle is a running state in which the loads applied to the tires are large, and is executed to predict that the base measurement value ms takes a large value in a state in which the gain is not adjusted.

[0196] In step S57 of the Fig. 14, the controller 180 determines, in the traveling state in which acceleration in the vehicle width direction can be applied to the vehicle, whether one or both of the following absolute values ​​exceed a second threshold value kmax*M*g based on the gravitational acceleration g.

[0197] The absolute values ​​are the absolute value abs[M*(G_lat+v*ω)] of the value obtained by multiplying the sum of the lateral acceleration G_lat acting on the vehicle in the vehicle width direction and the acceleration v*ω of the centrifugal force by the weight M of the vehicle, and the absolute value abs(ΣFy) of the sum ΣFy of component forces Fy acting on the respective tires in the vehicle width direction. It is a process for determining whether the loads applied to the tires in the vehicle width direction are large in a situation where the loads are applied to the tires in the vehicle width direction.

[0198] A coefficient kmax of the second threshold value kmax*M*g is a default value of a positive value set in advance within a range of 0 to 1 to easily determine that the vehicle is traveling with the tires close to their limits in terms of vehicle dynamics. It can be determined whether any of the following absolute values ​​exceeds the second threshold value kmax*M*g. The absolute values ​​are the absolute value abs[M*(G_lat+v*ω)] of the value obtained by multiplying the sum of the lateral acceleration G_lat and the acceleration v*ω of the centrifugal force by the weight M of the vehicle, and the absolute value abs(ΣFy) of the sum ΣFy of the component forces Fy acting on the respective tires in the vehicle width direction. However, by determining whether both values ​​exceed the second threshold value kmax*M*g, the reliability of the determination result can be increased.

[0199] When the vehicle is traveling straight, no loads are applied to the tires in the vehicle width direction. In this case, the controller 180 can determine whether the loads applied to the tires in the longitudinal direction are large. For example, when the vehicle is accelerating while traveling straight, the controller 180 determines, based on the acceleration of gravity, whether one or both of the following values ​​exceed the second threshold value kmax*M*g.

[0200] These values ​​are the value abs[M*G_longi], which is obtained by multiplying the absolute value abs(G_longi) of the longitudinal acceleration G_longi acting on the vehicle in the longitudinal direction by the weight M of the vehicle, and the absolute value abs(ΣFx) of the sum ΣFx of the component forces Fx acting in the longitudinal direction on the corresponding tires.

[0201] The second threshold value kmax*M*g for determining the loads applied to the tires in the longitudinal direction may be equal to or different from the second threshold value kmax*M*g for determining the loads applied to the tires in the vehicle width direction. Furthermore, it may be determined whether any of the following absolute values ​​exceed the second threshold value kmax*M*g.

[0202] These absolute values ​​are the absolute value abs[M*G_longi] of the value obtained by multiplying the longitudinal acceleration G_longi by the vehicle's weight M, and the absolute value abs(ΣFx) of the sum ΣFx of the component forces Fx acting on the corresponding tires in the longitudinal direction. However, by determining whether both values ​​exceed the second threshold kmax*M*g, the reliability of the determination result can be increased.

[0203] If the determination is negative in step S57 (S57 / No), the controller 180 maintains the output gain Gain at the current output gain set value Gain_now (step S53). In this case, it cannot be determined that the measured value S cannot exceed the permissible maximum measured value S_max_def(gain_x) corresponding to the output gain even if the output gain Gain is increased. Thus, the process of this routine ends without adjusting the output gain Gain and returns to step S41.

[0204] On the other hand, if the determination is affirmative in step S57 (S57 / Yes), the controller 180 determines whether the state satisfying the condition in step S57 is maintained for the second time N2 (seconds) (step S59). The value of the second time N2 is set to be smaller than the value of the first time N1 used in the gain feedback adjustment process in step S21.

[0205] If the condition satisfying the condition in step S57 is not maintained for the second time N2 (S59 / No), the controller 180 maintains the output gain Gain at the current output gain set value Gain_now (step S53). Even in this case, it cannot be determined that the measured value S cannot exceed the permissible maximum measured value S_max_def(gain_x) corresponding to the output gain even if the output gain Gain is increased. Thus, the process of this routine ends without adjusting the output gain Gain and returns to step S41.

[0206] On the other hand, if the state satisfying the condition in step S57 is maintained for the second time N2 (S59 / Yes), the controller 180 sets the output gain target value Gain as the value Gain_now-1 (step S61). The value Gain_now-1 is one step lower than the current output gain target value Gain_now. Note that the second time N2 used in step S47 may be different from the second time N2 used in step S59.

[0207] For example, the controller 180 decreases one of the excitation-side gain or the measurement-side gain by one step to reduce the output gain. Consequently, the measured maximum measurement value S_max_t can be brought closer to the measurable maximum value S_max_sys. Furthermore, the possibility that the measured value S, measured when a similar driving condition continues, exceeds the measurable maximum value S_max_sys can be reduced. For example, by maintaining the excitation-side gain and reducing the measurement-side gain, it is possible to increase the resolution of the load to be measured while simultaneously reducing the range of the measured value S.

[0208] The controller 180 repeatedly executes the process of each step described above within the predetermined sampling period. Even when the output range of the bridge circuit of the load cell 1 is large, the controller 180 sets the output gain based on the driving state of the vehicle.

[0209] The output gain is set so that the measured maximum value S_max_t is smaller than the measurable maximum value S_max_sys and the permissible maximum value S_max_def(gain_now). Thus, the output of the bridge circuit is amplified so that the measured value S does not exceed the measurable maximum value S_max_sys and the permissible maximum value S_max_def(gain_x), thus increasing the measurement accuracy of the load. 2.4.7 Zero-point shift process

[0210] Fig. Figure 15 is a flowchart illustrating an example of the zero-shift process. The zero-shift process can be executed constantly upon activation of the vehicle system or can be configured to be executed during the execution of a specific control using the component forces applied to the tires.

[0211] First, the controller 180 acquires the vehicle state information via the CAN communication driver 183 (step S71). The details of the process in step S71 are the same as those in step S11 in the above-described gain feedback adjustment process or step S41 in the gain feedforward adjustment process. Step S11, step S41, and step S71 may also be a single process.

[0212] Subsequently, based on the acquired vehicle state information, the controller 180 determines whether a displacement process condition, which is a condition under which the zero-point displacement process can be executed, is satisfied (step S73). The displacement process condition is a condition for determining a state in which no load is applied to the load cell 1. For example, the displacement process condition may be a condition for determining that no acceleration is applied to the vehicle in the longitudinal direction and the vehicle width direction.

[0213] For example, the controller 180 may determine that the shift process condition is met when the vehicle is in a stopped state and the vehicle is not tilted. It may be determined whether the vehicle is stopped based on information about a sensor value from a vehicle speed sensor or status information indicating the stopped state of the vehicle. Furthermore, it may also be determined that the vehicle is not tilted based on information about a sensor value from a tilt sensor.

[0214] If the shift process condition is not met (S73 / No), the controller 180 terminates this routine and returns to step S51. However, if the shift process condition is met (S73 / Yes), the controller 180 executes the zero point shift process (step S75). The zero point shift process can be performed by a known method according to the prior art.

[0215] For example, a value obtained by multiplying a measured value detected in a state where the shift process condition is satisfied by -1 is recorded as a shift correction value. The shift correction value is added to the measured value S input from the lock-in amplifier 165, and the measured value S is corrected by a value corresponding to a shift value. The details of the zero-point shift process are not limited to the example described above. 2.4.8. Effects of the zero-point shift process

[0216] Fig. 16 shows an example in which the zero shift process during the gain adjustment of the measured value (base measured value) ms (dashed line) is carried out according to the same pattern as the example according to Fig. 12 is executed if the gain setting of the output of the bridge circuit is not as in Fig. 11 is carried out.

[0217] In the Fig. In the example shown in Figure 16, the output gain (Gain) is set to 20 at the beginning of the measurement, and the measured value S fluctuates between 0.10 and 0.75 mV in the first period. The measured value S in the first period is significantly lower than the measurable maximum value S_max_sys, but exceeds the permissible maximum measured value S_max_def(gain_20) corresponding to the output gain (Gain).

[0218] Thus, the control device 180 sets the output gain Gain as 0.5 times and outputs the same output gain Gain as in the case of Fig. 11. Thus, the measured value S changes in the same way as in the case according to Fig. 12 from 8 seconds to 12 seconds after the start of the measurement.

[0219] In the Fig. However, in the example shown in Figure 16, the zero shift process is executed 13 seconds after the start of the measurement, and the measured value S is set to zero at this time. Then, the measured value S shifts from the measured value S to the smaller side by the shift correction value when the output gain Gain is set as shown in Fig. 12. In this way, by performing the zero shift process, the accuracy of the measured value S is further ensured, and the measurement accuracy can be further increased.

[0220] A preferred embodiment of the invention has been described in detail above with reference to the accompanying drawings, but the invention is not limited to these examples. It is clear that a person skilled in the art can make various modifications or corrections within the scope of the technical idea described in the claims. It seems obvious that these are naturally within the technical scope of the invention.

[0221] For example, in the above-described embodiment, an example of a load cell using a uniaxial strain gauge is described, but the load cell to which the technology of the present invention can be applied is not limited to such an example. For example, the technology of the present invention can also be applied to a load cell using a Fig. 17 and Fig. 18 shown biaxial shear strain gauge is used.

[0222] Fig. Fig. 17 is a schematic diagram illustrating an arrangement of strain gauges in a six-component force detector according to a modification, and Fig. Figure 18 is an explanatory diagram of a strain measurement pattern of the biaxial shear strain gauge. Fig. The six-component force detector shown in Figure 17 is equipped with the shear strain gauges 271 and 272 of the Fx detection system and the shear strain gauges 275 and 277 of the Fz detection system, which are described below.

[0223] The shear strain gauges 271 and 272 as well as the shear strain gauges 275 and 277 are arranged instead of the strain gauges 21 to 24 of the Fx detection system and the strain gauges 31 to 34 of the Fz detection system. Fig. 18, the shear strain gauge 271 is shown as an example, but the shear strain gauges 272, 275 and 277 also have essentially the same strain measurement pattern.

[0224] The shear strain gauge 271 is designed as a so-called arrow-shaped biaxial (bipolar) strain gauge. In the shear strain gauge 271, a first detector 271a and a second detector 271b formed from a Cr-N thin film or the like are formed on a common insulating layer 271c, which is an insulating thin film. The first detector 271a and the second detector 271b are each formed by arranging linear regions arranged in parallel along the detection directions in series.

[0225] The first detector 271a and the second detector 271b are configured such that the electrical resistance changes easily according to the deformation in the direction (detection direction) in which the linear region expands and contracts. The detection directions of the first detector 271a and the second detector 271b are arranged so as to be substantially orthogonal to each other.

[0226] The shear strain gauge 271 is attached to the outer peripheral surface of a cylinder 250 in the manner described below.

[0227] The detection directions of the first detector 271a and the second detector 271b are inclined by 45° in opposite directions with respect to the central axis direction of the cylinder 250. Note that the shear strain gauges 272, 275, and 277 are mounted on the outer peripheral surface of the cylinder 250 in substantially the same manner.

[0228] As in Fig. As shown in Figure 17, shear strain gauges 271, 272, 275, and 277 are mounted on the outer peripheral surface of the center of cylinder 250 in the central axis direction. Shear strain gauge 271 of the Fx detection system is positioned midway between strain gauges 251 and 252 of the Mx detection system. Shear strain gauge 272 of the Fx detection system is positioned midway between strain gauges 253 and 254 of the Mx detection system (at a position symmetrical to shear strain gauge 271 with respect to the central axis).

[0229] The shear strain gauge 275 of the Fz detection system is arranged midway between the strain gauges 261 and 262 of the Mz detection system. The shear strain gauge 277 of the Fz detection system is arranged midway between the strain gauges 263 and 264 of the Mz detection system (at a position symmetrical to the shear strain gauge 275 with respect to the central axis).

[0230] Furthermore, strain gauges 281 to 284 of the Fy detection system and strain gauges 291 to 294 of the My detection system are arranged at positions offset from the central axis. This serves to avoid interference with strain gauges 271 and 272 of the Fx detection system and strain gauges 275 and 277 of the Fz detection system.

[0231] For example, as 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 and the strain gauge 294 may be arranged sequentially along the circumferential direction of the cylinder 250 at positions offset at intervals of 30° around the central axis.

[0232] Furthermore, 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 also be arranged sequentially along the circumferential direction of the cylinder 250 at positions offset at intervals of 30° around the central axis.

[0233] The first detector and the second detector included in each of the shear strain gauges 271 and 272 of the Fx detection system form a bridge circuit which is essentially the same as in Fig. 3. This bridge circuit produces an output corresponding to a component force applied to cylinder 250 in the Fx direction.

[0234] Similarly, the first detector and the second detector included in each of the shear strain gauges 275 and 277 of the Fz detection system form a bridge circuit substantially similar to that shown in Fig.3. This bridge circuit produces an output corresponding to a component force applied to cylinder 250 in the Fz direction.

[0235] The technology of the present invention can also be applied to a load cell using biaxial shear strain gauges as described above, and the effects obtained by the above-described embodiment can be achieved. List of reference symbols 1 load cell 21, 22, 23, 24 strain gauges 80 bridge circuit 81 first connection 82 second connection 83 third connection 84 fourth connection 160 measuring circuit 161 excitation-side differential amplifier circuit 163 measurement-side differential amplifier circuit 165 Lock-in amplifiers 180 Control device 183 CAN communication drivers 191 CAN bus 200 load detection device 1. A load detection device configured to detect a load applied to a measurement object based on a differential signal output by a load cell having a bridge circuit to which a strain gauge is connected, the load detection device comprising: - an excitation-side differential amplifier circuit designed to amplify an excitation signal to be sent to the load cell; - a measurement-side differential amplifier circuit designed to amplify a first differential signal output by the load cell; and - a control device designed to control the excitation-side differential amplifier circuit and the measurement-side differential amplifier circuit, the control device being designed to: - performing a gain adjustment process for adjusting an output gain by adjusting one or more 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 measured value measured based on a second difference signal output from the measurement-side differential amplifier circuit falls within a predetermined range. 2. Load detection device according to claim 1, wherein the control device is designed for the following measures: - selecting, in the gain setting process, the excitation-side gain and the measurement-side gain from candidate values ​​for the excitation-side gain specified at predetermined intervals as the excitation-side gain or from candidate values ​​for the measurement-side gain specified at predetermined intervals as the measurement-side gain, and - Specify the output gain. 3. Load detection device according to claim 2, wherein the load detection device is a device designed to detect component forces acting on one of the tires of a vehicle, and wherein the control device is designed to take the following measures: in the gain adjustment process, when the vehicle is in a driving state within a predetermined period before a current time and a maximum measured value, which is a maximum value of the measured value within the predetermined period, is smaller than a predetermined measurable maximum value that is measurable by the load detection device, - determining whether a first ratio is smaller than a second ratio, wherein the first ratio is a ratio of the maximum measured value to a permissible maximum measured value up to which the measured value can be guaranteed and which is determined according to the currently specified output gain, wherein the second ratio is a ratio of the output gain lower by one level to the currently specified output gain, and - Increasing the output gain when a condition in which the first ratio is smaller than the second ratio persists for a predetermined first time or longer. 4. Load detection device according to claim 3, wherein the control device is designed for the following measure: even before the condition in which the first ratio is smaller than the second ratio lasts for the predetermined first time or longer, - Increasing the output gain when the vehicle is in the deceleration state and when one or both of a value obtained by multiplying an acceleration acting on the vehicle in a predetermined direction by a weight of the vehicle and a value of a sum of component forces acting on the respective tires in the predetermined direction are continuously smaller than a first threshold value based on a gravitational acceleration for the predetermined period. 5. Load detection device according to claim 4, wherein the control device is designed for the following measure: even before the state in which the first ratio is smaller than the second ratio continues for the predetermined first time or longer, - increasing the output gain when the vehicle is in the deceleration state and when one or both of a value obtained by multiplying a sum of a lateral acceleration acting on the vehicle in the vehicle width direction and a centrifugal acceleration by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the vehicle width direction are continuously smaller than the first threshold value for the predetermined period. 6. Load detection device according to claim 4, wherein the control device is designed for the following measure: even before the condition in which the first ratio is smaller than the second ratio lasts for the predetermined first time or longer, - increasing the output gain when the vehicle is in the deceleration state while the vehicle is traveling straight, and one or both of a value obtained by multiplying an absolute value of a longitudinal acceleration acting on the vehicle in the longitudinal direction by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the longitudinal direction are continuously smaller than the first threshold value for the predetermined period. 7. Load detection device according to claim 3, wherein the control device is designed for the following measure: in the gain adjustment process - Decreasing the output gain when the vehicle is in the driving state within the predetermined period and the maximum measured value within the predetermined period is the predetermined measurable maximum value or more. 8. Load detection device according to claim 3, wherein the control device is designed for the following measure: in the gain adjustment process - reducing the output gain when one or both of a value obtained by multiplying an acceleration acting on the vehicle in a predetermined direction by a weight of the vehicle and a value of a sum of component forces acting on the respective tires in the predetermined direction continuously exceed a second threshold value based on a gravitational acceleration for the predetermined period. 9. Load detection device according to claim 8, wherein the control device is designed for the following measure: - reducing the output gain when the vehicle is in an acceleration state and when one or both of a value obtained by multiplying a sum of a lateral acceleration acting on the vehicle in the vehicle width direction and a centrifugal acceleration by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the vehicle width direction continuously exceed the second threshold value for the predetermined period. 10. Load detection device according to claim 8, wherein the control device is designed for the following measure: - reducing the output gain when the vehicle is continuously traveling straight and when one or both of a value obtained by multiplying an absolute value of a longitudinal acceleration acting on the vehicle in the longitudinal direction by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the longitudinal direction continuously exceed the second threshold value for the predetermined period. 11. Load detection device according to claim 2, wherein the control device is designed for the following measures: in the gain adjustment process - Determine whether it is possible to increase the excitation-side gain, and - preferentially increasing the excitation-side gain over the measurement-side gain when it is possible to increase the excitation-side gain. 12. Load detection device according to claim 1, wherein the control device is designed for the following measures: - Determine whether no load is applied to the strain gauge and whether a suitable posture is maintained, and - Performing a zero shift process of the measured value when no load is applied to the strain gauge and the appropriate posture is maintained. 13. A gain adjustment method of a load detection device for adjusting the gain of a load detection device designed to detect 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, the gain adjustment method comprising the following measures: - amplifying an excitation signal to be sent to the load cell by means of an excitation-side differential amplifier circuit; - amplifying a first differential signal output by the load cell by a measurement-side differential amplifier circuit; and - Adjusting an output gain by adjusting one or more 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 measured value measured based on a second difference signal output from the measurement-side differential amplifier circuit falls within a predetermined range. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2019-39 871 A

[0005]

Claims

[1] A load detection device designed to detect 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, the load detection device comprising: - an excitation-side differential amplifier circuit designed to amplify an excitation signal to be sent to the load cell; - a measurement-side differential amplifier circuit designed to amplify a first differential signal output by the load cell; and - a control device designed to control the excitation-side differential amplifier circuit and the measurement-side differential amplifier circuit, the control device being designed to: - Performing a gain adjustment process for adjusting an output gain by selecting an excitation-side gain by the excitation-side differential amplifier circuit and a measurement-side gain by the measurement-side differential amplifier circuit such that a measured value measured based on a second difference signal output from the measurement-side differential amplifier circuit falls within a predetermined range, wherein the excitation-side gain and the measurement-side gain are selected from candidate values ​​for the excitation-side gain predetermined at predetermined intervals as the excitation-side gain and candidate values ​​for the measurement-side gain predetermined at predetermined intervals as the measurement-side gain, respectively. [2] Load detection device according to claim 1, wherein the load detection device is a device designed to detect component forces acting on one of the tires of a vehicle, and The control device is designed for the following measures: in the gain adjustment process, when the vehicle is in a driving state within a predetermined period before a current time and a maximum measured value, which is a maximum value of the measured value within the predetermined period, is smaller than a predetermined measurable maximum value that is measurable by the load detection device, - determining whether a first ratio is smaller than a second ratio, wherein the first ratio is a ratio of the maximum measured value to a permissible maximum measured value up to which the measured value can be guaranteed and which is determined according to the currently specified output gain, wherein the second ratio is a ratio of the output gain lower by one level to the currently specified output gain, and - Increasing the output gain when a condition in which the first ratio is smaller than the second ratio persists for a predetermined first time or longer. [3] Load detection device according to claim 2, wherein the control device is designed for the following measure: even before the condition in which the first ratio is smaller than the second ratio lasts for the predetermined first time or longer, - Increasing the output gain when the vehicle is in the deceleration state and when one or both of a value obtained by multiplying an acceleration acting on the vehicle in a predetermined direction by a weight of the vehicle and a value of a sum of component forces acting on the respective tires in the predetermined direction are continuously smaller than a first threshold value based on a gravitational acceleration for the predetermined period. [4] Load detection device according to claim 3, wherein the control device is designed for the following measure: even before the condition in which the first ratio is smaller than the second ratio lasts for the predetermined first time or longer, - increasing the output gain when the vehicle is in the deceleration state and when one or both of a value obtained by multiplying a sum of a lateral acceleration acting on the vehicle in the vehicle width direction and a centrifugal acceleration by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the vehicle width direction are continuously smaller than the first threshold value for the predetermined period. [5] Load detection device according to claim 3, wherein the control device is designed for the following measure: even before the condition in which the first ratio is smaller than the second ratio lasts for the predetermined first time or longer, - increasing the output gain when the vehicle is in the deceleration state while the vehicle is traveling straight, and one or both of a value obtained by multiplying an absolute value of a longitudinal acceleration acting on the vehicle in the longitudinal direction by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the longitudinal direction are continuously smaller than the first threshold value for the predetermined period. [6] Load detection device according to claim 2, wherein the control device is designed for the following measure: in the gain adjustment process - Decreasing the output gain when the vehicle is in the driving state within the predetermined period and the maximum measured value within the predetermined period is the predetermined measurable maximum value or more. [7] Load detection device according to claim 2, wherein the control device is designed for the following measure: in the gain adjustment process - reducing the output gain when one or both of a value obtained by multiplying an acceleration acting on the vehicle in a predetermined direction by a weight of the vehicle and a value of a sum of component forces acting on the respective tires in the predetermined direction continuously exceed a second threshold value based on a gravitational acceleration for the predetermined period. [8] Load detection device according to claim 7, wherein the control device is designed for the following measure: - reducing the output gain when the vehicle is in an acceleration state and when one or both of a value obtained by multiplying a sum of a lateral acceleration acting on the vehicle in the vehicle width direction and a centrifugal acceleration by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the vehicle width direction continuously exceed the second threshold value for the predetermined period. [9] Load detection device according to claim 7, wherein the control device is designed for the following measure: - reducing the output gain when the vehicle is continuously traveling straight and when one or both of a value obtained by multiplying an absolute value of a longitudinal acceleration acting on the vehicle in the longitudinal direction by the weight of the vehicle and a value of a sum of component forces acting on the respective tires in the longitudinal direction continuously exceed the second threshold value for the predetermined period. [10] Load detection device according to claim 1, wherein the control device is designed for the following measures: in the gain adjustment process - Determine whether it is possible to increase the excitation-side gain, and - preferentially increasing the excitation-side gain over the measurement-side gain when it is possible to increase the excitation-side gain. [11] Load detection device according to claim 1, wherein the control device is designed for the following measures: - Determine whether no load is applied to the strain gauge and whether a suitable posture is maintained, and - Performing a zero shift process of the measured value when no load is applied to the strain gauge and the appropriate posture is maintained. [12] A gain adjustment method of a load detection device for adjusting the gain of a load detection device designed to detect a load applied to a measurement object on the basis of a differential signal output from a load cell having a bridge circuit to which a strain gauge is connected, the gain adjustment method comprising the following measures: - amplifying an excitation signal to be sent to the load cell by means of an excitation-side differential amplifier circuit; - amplifying a first differential signal output by the load cell by a measurement-side differential amplifier circuit; and - Setting an output gain by selecting an excitation-side gain by the excitation-side differential amplifier circuit and a measurement-side gain by the measurement-side differential amplifier circuit such that a measured value measured on the basis of a second difference signal output from the measurement-side differential amplifier circuit falls within a predetermined range, wherein the excitation-side gain and the measurement-side gain are selected from candidate values ​​for the excitation-side gain predetermined at predetermined intervals as the excitation-side gain and candidate values ​​for the measurement-side gain predetermined at predetermined intervals as the measurement-side gain, respectively.

Images