Tire axle force measuring device

Abstract

This system suppresses the effects of rigid body resonance in the trailer while it is running with the tires under evaluation, as well as vibrations from the towing vehicle, enabling accurate measurement of the dynamic load applied to the axle. [Solution] The tire axle force measuring device comprises a trailer on which the tire to be evaluated is mounted, a towing vehicle that tows the trailer, and a load cell for measuring the axle force of the axle supporting the tire. The device includes a weight structure that fixes the load cell to both sides in the vehicle width direction, an accelerometer attached to the axle side of the load cell to measure the acceleration acting at the axis of the axle, and an axle force calculation unit that calculates a new axle force that compensates for the inertial force by adding the inertial force obtained by multiplying the acceleration detected by the accelerometer by the mass on the axle side of the load cell to the axle force measured by the load cell.

Description

Technical Field

[0001] The present invention relates to a tire axle force measuring device.

Background Art

[0002] There is a known technique for measuring the dynamic load generated on an axle supporting a rotating tire using a chassis dynamometer. However, the measured value of the chassis dynamometer is not the value measured when the vehicle is actually running on the road surface. Therefore, a measured value different from the value obtained when running on the actual road surface is detected.

[0003] A technique for measuring the dynamic load generated on an axle supporting a tire in a state of running on an actual road surface is disclosed in, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-30046). In this document, the tire to be evaluated is mounted on the axle of a trailer, and this trailer is towed by a towing vehicle and runs. At that time, the arithmetic unit measures the impact force applied to the axle when the tire passes over the unevenness of the road surface using a load cell.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The trailer disclosed in the above-mentioned document has a structure in which frame materials are assembled. Therefore, an elastic resonance phenomenon is likely to occur in the trailer. When the load cell support part resonates, an appropriate measured value cannot be obtained, so it is difficult to measure the high-frequency component of the dynamic load.

[0006] Furthermore, in order to apply the appropriate contact pressure to the tire contact surface, the trailer needs to have a mass roughly equivalent to the axle load of the actual vehicle. However, rigid body resonance due to the vertical spring of the tire and the mass of the trailer is unavoidable. When trailer rigid body resonance occurs significantly, the tire contact area fluctuates greatly, making it difficult to obtain accurate measurements.

[0007] Furthermore, during travel, the towing vehicle also vibrates due to road surface irregularities, and dynamic loads are transmitted to the trailer via the vehicle's coupling. The dynamic load transmitted via the vehicle coupling is superimposed on the dynamic load transmitted via the tire being evaluated and is detected by the load cell. Therefore, it is difficult to accurately measure the characteristics of the tire being evaluated.

[0008] The present invention aims to provide a tire axle force measuring device that can accurately measure the dynamic load applied to the axle via the tire being evaluated, while suppressing the effects of rigid body resonance of a trailer traveling with the tire being evaluated mounted on it, and vibrations from the towing vehicle, in a frequency range of approximately 20 Hz to 400 Hz. [Means for solving the problem]

[0009] The present invention relates to a tire axle force measuring device comprising a trailer on which a tire to be evaluated is mounted, a towing vehicle that tows the trailer, and a load cell for measuring the axle force of the axle supporting the tire, wherein the device comprises a weight structure that fixes the load cell on both sides in the vehicle width direction, an accelerometer attached to the axle side of the load cell to measure the acceleration acting at the axis of the axle, and an axle force calculation unit that calculates a new axle force by compensating for the inertial force by adding to the axle force measured by the load cell an inertial force obtained by multiplying the acceleration detected by the accelerometer by the mass of the load cell on the axle side. [Effects of the Invention]

[0010] According to the present invention, load cells are fixed to both sides in the vehicle width direction of a heavy structure in which the effects of elastic and rigid body resonance and vibrations from the towing vehicle are suppressed in the road noise frequency range, and multiple accelerometers are attached to the axle side of the load cells. Time history data of the load value measured by the load cells and the acceleration measured by the accelerometers is acquired by driving on an actual road surface, and the axle force calculation unit calculates the inertial force by multiplying the acceleration by the mass on the axle side of the load cell, thereby compensating for the load value of the load cell. In a frequency range of approximately 20 Hz to 400 Hz, the effects of rigid body resonance and vibrations from the towing vehicle of a trailer equipped with the tires to be evaluated can be suppressed, and the axle dynamic load applied to the axle via the tires to be evaluated can be accurately measured. [Brief explanation of the drawing]

[0011] [Figure 1] Side view showing the overall configuration of the tire axle force measuring device. [Figure 2] Plan view of Figure 1 [Figure 3] Rear view of the trailer [Figure 4] Front view of the trailer [Figure 5] A schematic diagram showing a load cell and accelerometer attached to a heavy structure. [Figure 6] Configuration diagram of the axle force measurement and calculation unit [Figure 7] A chart showing the frequency of axle forces acting in the longitudinal direction on the axle at different frequencies. [Figure 8] Chart showing the frequency of axle forces acting along the axle at different frequencies. [Modes for carrying out the invention]

[0012] An embodiment of the present invention will be described below with reference to the drawings. As shown in Figures 1 and 2, the tire axle force measuring device 1 includes a trailer 3 on which the wheels 2a of the tire 2 to be evaluated are mounted on both sides, and a towing vehicle 4 that tows this trailer 3.

[0013] Trailer 3 has a weight structure 5. This weight structure 5 is a rectangular prism that is elongated horizontally in the width direction of the vehicle. This weight structure 5 is set to have approximately the same mass as the front axle load or rear axle load of the actual vehicle on which the tires 2 are mounted. This applies a load equivalent to that of the actual vehicle to both tires 2.

[0014] Furthermore, this weight structure 5 is set to a high resonant frequency. This resonant frequency is set to a value higher than the high-frequency road noise input from the road surface via the tire 2. For example, if the upper limit of the road noise frequency range is 400 Hz, the resonant frequency of the weight structure 5 is set to approximately 1.5 times that, or 600 Hz or higher. This weight structure 5 is assembled by fastening relatively thick steel plates together with bolts and is set to a predetermined resonant frequency. A mass member is fixed inside this weight structure 5. This mass member adjusts the axle amount (mass of the axle).

[0015] Load cells 6 are fixed to the left and right sides of the weight structure 5 at positions where the axle 7 is supported. As shown in Figure 4, the load cell 6 has a fixing part 6a fixed to the weight structure 5 and an axle fixing part 6b, with a piezoelectric element (piezo element) 6c sandwiched between these two fixing parts 6a and 6b. The axle 7 is rotatably supported and fixed to the outside of the axle fixing part 6b. A well-known hub is integrally formed on this axle 7. The wheel 2a of the tire 2 is fastened to this hub. The load cell 6 measures the load value (axle force) applied to the axle 7 that supports the wheel 2a of the tire 2.

[0016] Furthermore, three-axis accelerometers 11 are attached to the axle fixing portions 6b of the left and right load cells 6. As shown in Figure 4, a pair of these three-axis accelerometers 11 are fixed to each load cell 6, facing each other above and below the axle fixing portion 6b. These three-axis accelerometers 11 measure the acceleration in the three axes acting on the axle center of the axle fixing portion 6b. The acceleration in the three axes consists of axial acceleration and acceleration perpendicular to the axis. The acceleration perpendicular to the axis consists of translational longitudinal acceleration and translational vertical acceleration.

[0017] The weight structure 5 is also connected to the rear part of the towing vehicle 4 via the tow bar 12. A rear connecting part 13 is fixed to the rear end of the tow bar 12. Also, a front connecting part 14 is fixed to the front end of the tow bar 12.

[0018] As shown in FIGS. 2 and 4, the rear connecting part 13 is composed of a connecting plate 13a and a reinforcing member 13b. The connecting plate 13a is formed in a Y shape. The back surface of the connecting plate 13a faces the center of the front surface of the weight structure 5 in a state where the Y shape is inverted. The reinforcing member 13b is fixed to the connecting plate 13a. This reinforcing member 13b is composed of a frustum of a cone.

[0019] Clevis arms 16 project from the back surfaces of three corners of the connecting plate 13a. A clevis 17 is fixed to the front surface of the weight structure 5 facing the clevis arms 16. This clevis 17 has a split formed in the vertical direction. The clevis arms 16 are connected to the clevis 17 via a connecting shaft (not shown) with an anti-vibration bush mounted on the outer periphery. The rear end of the tow bar 12 is fixed to the front side of the rear connecting part 13.

[0020] Also, the front connecting part 14 is fixed to the front end of the tow bar 12 using bolts. A front clevis arm 14a projects from the tip of this front connecting part 14. On the other hand, a vehicle-side connecting part 21 projects rearward from the center in the vehicle width direction of the rear frame (not shown) of the towing vehicle 4. A vehicle-side clevis 22 is provided at the rear end of this vehicle-side connecting part 21.

[0021] This vehicle-side clevis 22 is formed such that the rear end of a support plate fixed to the bottom surface of the rear end part of the vehicle-side connecting part 21 and the base part of a support column 27 provided on a lever mechanism 26, which will be described later, erected on the upper surface, projects rearward. This vehicle-side clevis 22 has a groove formed in the horizontal direction. The tip of the front clevis arm 14a is connected to this vehicle-side clevis 22 via a spherical bearing 24 so as to be swingable with respect to the vehicle-side connecting part 21.

[0022] Furthermore, a lever mechanism 26 is provided spanning the front end of the tow bar 12 and the rear end of the vehicle-side connecting portion 21. This lever mechanism 26 has a support column 27 erected at the rear end of the vehicle-side connecting portion 21. The lever mechanism 26 has a lever 28 at the top of the support column 27 that provides support in the middle. The lever 28 is an integrated rear arm portion 28a and a front arm portion 28b and has a pin 28c that serves as a pivot axis.

[0023] The rear of the front arm portion 28b is supported by a pin 28c on the support column 27 so as to be able to swing freely around the vehicle width axis. The rear arm portion 28a is integrated with the front arm portion 28b. A rod 25 is connected to the rear of this rear arm portion 28a via a ball joint so as to be able to swing freely. One of the pivot points of this rod 25 is positioned on a vertical axis passing through the rotation center of the spherical bearing 24.

[0024] Furthermore, the rear end of the rod 25 is fixed to the upper end of the stand 29. This stand 29 is fixed to the upper surface of the front part of the tow bar 12. Also, the upper end of the damper 30 is connected to the front end of the front arm portion 28b. As shown in Figure 2, a pair of these dampers 30 are arranged on both sides of the vehicle-side connecting portion 21. The main body of each damper 30 is supported so as to be able to swing freely around the vehicle width axis relative to the vehicle-side connecting portion 21. Furthermore, the upper end of the rod protruding from the main body of each damper 30 is fixed so as to be able to swing freely to the fixing plate 31. In addition, this fixing plate 31 is supported so as to be able to swing freely around the vehicle width axis relative to the front end of the front arm portion 28b.

[0025] The moment arms of both arm sections 28a and 28b are set such that the front arm section 28b is longer than the rear arm section 28a. The damper 30 dampens the vertical movement of the weight structure 5 by damping the oscillation angular velocity caused by the relative movement of the tow bar 12 and the vehicle-side connecting section 21 around the vehicle width axis.

[0026] Figure 5 schematically shows the mounting state of the load cell 6 and the pair of 3-axis accelerometers 11. As shown in Figure 6, the left and right load cells 6 and the pair of upper and lower 3-axis accelerometers 11 installed on the left and right are connected to the input side of the axle force measurement calculation unit 41. An output unit 51 such as a monitor and printer is connected to the output side of this axle force measurement calculation unit 41.

[0027] The axle force measurement calculation unit 41 is composed of a microcontroller. The microcontroller includes a CPU, RAM, ROM, rewritable non-volatile memory (flash memory or EEPROM), and peripheral devices. The RAM of the microcontroller is provided as the CPU's work area, where various data from the CPU is temporarily stored. The ROM stores programs and fixed data necessary for the CPU to execute various processes. The CPU is also called an MPU (Microprocessor) or processor. Alternatively, a GPU (Graphics Processing Unit) or GSP (Graph Streaming Processor) may be used instead of the CPU. Alternatively, a selective combination of CPU, GPU, and GSP may be used.

[0028] The axle force measurement calculation unit 41 has an axle force calculation unit 41a that has the function of measuring the axle force input from the tire 2 and applied to the axle 7.

[0029] The axle force calculation unit 41a acquires time-series data of the axle force acting on the left and right axles 7 from the load values ​​measured by each load cell 6. The axle force calculation unit 41a also acquires time-series data of the acceleration (acceleration in three directions) a acting on the axis center on the axle fixing part 6b side of the load cell 6 from the values ​​measured by a pair of three-axis accelerometers 11. Then, the axle force calculation unit 41a calculates the inertial force F based on this acceleration a and the mass m of the axle fixing part 6b on the load cell 6 (F = m·a).

[0030] Incidentally, the load cell 6 is a relatively heavy object. Also, when the trailer 3 is towed by the towing vehicle 4, a relatively large mass is applied to the axle fixing part 6b from the wheel 2a side. As a result, the axle force detected by the load cell 6 is attenuated by the amount of inertial force due to the mass on the axle fixing part 6b side. The axle force calculation unit 41a adds the inertial force F calculated based on the acceleration detected by the 3-axis accelerometer 11 to the axle force detected by the load cell 6 to calculate a new, highly accurate axle force.

[0031] Next, a method for measuring axle force using the tire axle force measuring device 1 with the above configuration will be described. First, as shown in Figures 1 and 2, the tow bars 12 of the trailer 3, on which the tires 2 to be evaluated are mounted on the left and right axles 7, are connected in a predetermined manner to the vehicle-side coupling portion 21 of the towing vehicle 4. Then, the towing vehicle 4 is driven at a predetermined speed.

[0032] The weight structure 5 is set to approximately the same level as the actual front axle load or rear axle load of the vehicle. Therefore, a load approximately the same as the actual axle load is applied to the tire 2. Furthermore, the resonant frequency of this weight structure 5 is set to a value higher than the high-frequency road noise input from the road surface via the tire 2. Consequently, the weight structure 5 does not resonate elastically in the road noise frequency band during driving.

[0033] On the other hand, during travel, the towing vehicle 4 and the trailer 3 move relative to each other in the vertical direction. This relative vertical vibration between the towing vehicle 4 and the trailer 3 causes the lever 28 to oscillate around its vehicle width axis while supported by the support column 27. As a result, the pair of dampers 30 connected to the front arm portion 28b are pressed, and the vibration is dampened. Consequently, rigid body resonance of the trailer 3 itself is suppressed.

[0034] The moment arm of this lever 28 has a front arm portion 28b that is longer than the rear arm portion 28a. The damper 30 generates damping force depending on the vibration velocity. Therefore, by making the front arm portion 28b longer than the rear arm portion 28a of the moment arm, the vibration velocity of the damper 30 becomes faster, and rigid body resonance of the trailer 3 itself can be suppressed more effectively. This prevents the contact pressure of the tire 2 from changing drastically.

[0035] Furthermore, the rear arm portion 28a is connected to the rod 25 via a ball joint. The pivot point of one of the rods 25 is positioned on a vertical axis passing through the rotation center of the spherical bearing 24 that connects the vehicle-side clevis 22 and the front clevis arm 14a. Therefore, even when the towing vehicle 4 is steered and driven in a turning motion, the trailer 3 can be made to follow the towing vehicle 4.

[0036] Furthermore, the clevis 17 fixed to the front of the weight structure 5 and the clevis arm 16 provided on the rear connecting part 13 fixed to the rear end of the tow bar 12 are connected via a connecting shaft (not shown) fitted with vibration-damping bushings around it. As a result, the transmission of vibrations from the tow bar 12 to the weight structure 5 is suppressed, and the effects of resonance in the towing vehicle 4 and the tow bar 12 can be reduced.

[0037] As a result, when the trailer 3 is towed by the towing vehicle 4, rigid body vibrations generated by the trailer 3 itself are suppressed. Therefore, the contact pressure of the tires 2 with the road surface does not fluctuate significantly. Furthermore, vibrations transmitted from the towing vehicle 4 to the trailer 3 can also be suppressed.

[0038] Therefore, the load cell 6 and the three-axis accelerometer 11 installed on the weight structure 5 of the trailer 3 can accurately measure the axle force and acceleration applied to the axle 7 without being affected by vibrations from other structures when the trailer 3 is being towed by the towing vehicle 4.

[0039] As a result, the axle force calculation unit 41a of the axle force measurement calculation unit 41 can determine a highly accurate axle force by compensating the axle force, which has its inertial force damped and is measured by the load cell 6, with an inertial force F (F=m·a) calculated based on the acceleration a measured by the three-axis accelerometer 11.

[0040] Incidentally, Figure 7 shows the frequency response of the axle force acting in the longitudinal direction of the axle 7, and Figure 8 shows the frequency response of the axle force acting along the axle 7. The dashed line represents the measurement value by the load cell 6, and the solid line represents the measurement value with the inertial force added to compensate for the attenuation of the inertial force.

[0041] In this embodiment, in order to eliminate elastic and rigid body resonances of the trailer 3 that fixes the load cell 6 from the frequency range of approximately 20 Hz to 400 Hz of the tire 2 being evaluated, the external shape and structure of the trailer 3 are simplified as much as possible to reduce the number of elastic resonance modes, and the increase in the overall degree of freedom of the system is suppressed by applying a predetermined load to the tire 2 being evaluated by the weight of the trailer 3.

[0042] Furthermore, even when the rigid body resonance of the trailer 3 is below 20 Hz, the vertical resonance phenomenon of the trailer 3 significantly fluctuates the contact pressure of the tire 2 being evaluated. To effectively suppress this, the trailer 3 and the towing vehicle 4 are connected using spherical bearings 24 that can oscillate in all directions, and the oscillating angular velocity is amplified via a link mechanism having a lever mechanism 26 with a rod 25 and a lever 28, and then damped by a damper 30. In addition, to dampen the translational dynamic load transmitted from the towing vehicle 4 to the trailer 3 via the spherical bearings 24, vibration-damping bushings are incorporated into the connecting shaft that connects the clevis 17 on the trailer 3 side.

[0043] Furthermore, to address the problem of inertial force generated by vibrations in the load cell 6 located on the trailer 3, which causes a significant change in the observed value of the load cell 6, multiple 3-axis accelerometers 11 are placed on the axle fixing part 6b of the load cell 6. During the driving test, vibration acceleration is simultaneously acquired, the vibration acceleration at the axle center is calculated, and the inertial force is determined by multiplying this by the mass of the axle fixing part 6b of the load cell 6, thereby compensating for the observed value of the load cell 6. This allows for accurate measurement of the axle force and acceleration acting on the axle 7.

[0044] Furthermore, the present invention is not limited to the embodiments described above. For example, the characteristics of the vibration-damping bush and damper 30 can be appropriately selected according to the rigidity, resonance frequency, etc., of the trailer 3. [Explanation of symbols]

[0045] 1... Tire axle force measuring device, 2... Tires, 2a... Wheel, 3... Trailer, 4...Towing vehicle, 5... Weight structure, 6... Load cell, 6a...Fixed part, 6b...Axle fixing part, 6c... Piezoelectric element, 7... Axle, 11...3-axis accelerometer, 12...Tuber, 13... Rear connecting section, 13a...Connecting plate, 13b…Stiffening member, 14…Front connecting section, 14a... Front clevis arm, 16... Clevis arm, 17...Clevis, 21...Vehicle-side coupling section, 22... Vehicle-side clevis, 24... Spherical bearings, 25... Rod, 26... Lever mechanism, 27...post, 28... Lever, 28a...Rear arm section, 28b...Front arm section, 28c...pin 29... Stand, 30...Dumper, 31… Fixing plate, 41...Axle force measurement and calculation unit, 41a...Axle force calculation section, 51…Output section, F...Inertia force, a...acceleration, m…Mass

Claims

1. The trailer fitted with the tires to be evaluated, A towing vehicle that pulls the aforementioned trailer, A load cell for measuring the axle force of the axle supporting the aforementioned tire, In a tire axle force measuring device having, A weight structure that fixes the load cell on both sides in the vehicle width direction, An accelerometer is attached to the axle side of the load cell to measure the acceleration acting around the axis of the axle, An axle force calculation unit calculates a new axle force by adding the inertial force, which is obtained by multiplying the acceleration detected by the accelerometer by the mass of the load cell on the axle side, to the axle force measured by the load cell, thereby compensating for the inertial force. A tire axle force measuring device characterized by comprising the following features.

2. The trailer has a tow bar at its front that is pivotably connected to the towing vehicle via a spherical bearing, The rear of the tow bar is connected to the weight structure via a vibration-damping bush. The tire axle force measuring device according to claim 1, characterized in that it is a tire axle force measuring device.

3. A damper is provided at the vehicle-side coupling portion located at the rear of the towing vehicle to reduce the oscillation angular velocity of the tow bar relative to the vehicle-side coupling portion. The tire axle force measuring device according to claim 2, characterized in that it is a tire axle force measuring device.

4. The pivot point of the lever is provided at the vehicle-side coupling portion. One end of the lever is connected to the operating part of the damper, The other end of the lever is connected to the tow bar via a rod having ball joints at both ends. The moment arm of the lever is set so that the damper side is longer than the tow bar side. The tire axle force measuring device according to claim 3.

5. The pivot point of either of the ball joints provided at both ends of the rod is positioned on a vertical axis passing through the rotation center of the spherical bearing. The tire axle force measuring device according to feature 4.

Images