Wheel load estimation device, method, and program

Abstract

To provide a wheel load estimation device which can accurately estimate a wheel load with a simple facility.SOLUTION: A wheel load estimation device includes a wheel speed acquisition part, a frequency characteristic ratio calculation part, a load ratio calculation part, and a wheel load calculation part. The wheel speed acquisition part acquires vehicle speed information on each wheel from a wheel speed sensor. The frequency characteristic ratio calculation part calculates each of a front / rear gain ratio changing with changes of a front / rear load ratio that is a ratio of a load acting on a front wheel to a load acting on a rear wheel, and a right / left gain ratio changing with changes of a left / right load ratio that is a ratio of a load acting on a left wheel to a load acting on a right wheel, in two or more specific frequencies. The load ratio calculation part linearly combines the two or more front / rear gain ratios and the two or more right / left gain ratios by different weighting and calculates a front / rear load ratio and a right / left load ratio. The wheel load calculation part calculates a wheel load ratio indicating a relative wheel load for at least one wheel, on the basis of the front / rear load ratio and the right / left load ratio.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a wheel load estimation device, method, and program for estimating the wheel load of wheels included in a vehicle. [Background technology]

[0002] Vehicles are equipped with various control systems to ensure proper operation. In such control systems, the wheel load of each wheel is sometimes used as a control parameter, and therefore, accurate estimation of these parameters is sometimes required. For example, some automatic brake control systems distribute appropriate braking force according to the wheel load of each wheel.

[0003] Patent Document 1 discloses a technique for estimating the wheel load of each wheel based on the wheel speed information of each wheel. According to Patent Document 1, the gain of the frequency spectrum of the acceleration of a rotating wheel changes with the change in wheel load. Under the same load conditions, the gain integral values ​​of the two front wheels and the gain integral values ​​of the two rear wheels are in a generally linear relationship, and the ratio of the two (front-rear frequency characteristic ratio) is generally constant. On the other hand, the wheel load depends on the front-rear frequency characteristic ratio. The same relationship also holds for the left and right wheels of a vehicle. Patent Document 1 utilizes this to calculate the front-rear load ratio and the left-right load ratio based on the ratio of the gain integral values ​​of the frequency spectra of the front and rear wheels and the ratio of the gain integral values ​​of the frequency spectra of the left and right wheels. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-113373 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, according to the present inventors, the gain of the frequency spectrum of wheel acceleration does not change uniformly across all frequency bands in response to changes in wheel load. That is, the gain of the frequency spectrum may change relatively little in response to changes in wheel load in some frequency bands, or it may change in the opposite direction to other frequency bands in response to changes in wheel load. Patent Document 1 does not take this into consideration, leaving room for improvement in the accuracy of wheel load estimation.

[0006] The present invention aims to provide a wheel load estimation device, method, and program that can accurately estimate wheel load with simple equipment. [Means for solving the problem]

[0007] A wheel load estimation device according to a first aspect of the present invention is a wheel load estimation device for estimating the wheel load of a vehicle, comprising: a wheel speed acquisition unit; a frequency response ratio calculation unit; a load ratio calculation unit; and a wheel load calculation unit. The wheel speed acquisition unit acquires wheel speed information for each wheel included in the vehicle from a wheel speed sensor equipped on the vehicle. The frequency response ratio calculation unit calculates, based on the wheel speed information, a front-to-rear frequency response ratio that changes with changes in the front-to-rear load ratio, which is the ratio of the load acting on the front wheels of the vehicle to the load acting on the rear wheels of the vehicle, and a left-to-right frequency response ratio that changes with changes in the left-to-right load ratio, which is the ratio of the load acting on the left wheel of the vehicle to the load acting on the right wheel of the vehicle. The load ratio calculation unit calculates the front-to-rear load ratio and the left-to-right load ratio, respectively, based on the front-to-rear frequency response ratio and the left-to-right frequency response ratio. The wheel load calculation unit calculates a wheel load ratio for at least one wheel of the vehicle, representing the relative wheel load among the wheels included in the vehicle, based on the front-to-rear load ratio and the left-to-right load ratio. The frequency response ratio calculation unit calculates the front-to-rear frequency response ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the front wheel to the gain of the frequency spectrum of the acceleration of the rear wheel, at two or more specific frequencies, and calculates the left-to-right frequency response ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the left wheel to the gain of the frequency spectrum of the acceleration of the right wheel, at two or more specific frequencies. The load ratio calculation unit calculates the front-to-rear load ratio by linearly combining the two or more calculated front-to-rear gain ratios with different weights, and calculates the left-to-right load ratio by linearly combining the two or more calculated left-to-right gain ratios with different weights.

[0008] A wheel load estimation device according to a second aspect of the present invention is a wheel load estimation device according to a first aspect, further comprising a total weight calculation unit that identifies the total weight of the vehicle while it is in motion, and the wheel load calculation unit calculates the wheel load based on the identified total weight of the vehicle and the wheel load ratio.

[0009] A wheel load estimation device according to a third aspect of the present invention is a wheel load estimation device according to a first or second aspect, wherein the wheel load calculation unit calculates the wheel load ratio for each wheel included in the vehicle.

[0010] A wheel load estimation device according to the fourth aspect of the present invention is a wheel load estimation device according to any of the first or third aspects, wherein the frequency characteristic calculation unit calculates the front-to-rear gain ratio in two or more specific frequency bands and calculates the left-to-right gain ratio in two or more specific frequency bands.

[0011] A wheel load estimation method according to the fifth aspect of the present invention is a wheel load estimation method for estimating the wheel load of a vehicle, which is performed by one or more computers, and includes the following steps. Furthermore, a wheel load estimation program according to the sixth aspect of the present invention is a wheel load estimation program for estimating the wheel load of a vehicle, which causes one or more computers to perform the following steps. (1) Step of obtaining wheel speed information for each wheel included in the vehicle from the wheel speed sensor installed in the vehicle. (2) A step of calculating the front-to-rear frequency characteristic ratio which changes in accordance with the change in the front-to-rear load ratio, which is the ratio of the load acting on the front wheels of the vehicle to the load acting on the rear wheels of the vehicle, based on the wheel speed information. (3) A step of calculating the left-right frequency characteristic ratio which changes with the change in the left-right load ratio, which is the ratio of the load acting on the left wheel of the vehicle to the load acting on the right wheel of the vehicle, based on the wheel speed information. (4) A step of calculating the front-to-rear load ratio and the left-to-right load ratio based on the front-to-rear frequency response ratio and the left-to-right frequency response ratio. (5) A step of calculating a wheel load ratio for at least one wheel of the vehicle, based on the front-to-rear load ratio and the left-to-right load ratio, which represents the relative wheel load among the wheels included in the vehicle. Incidentally, (2) the step of calculating the front-rear frequency characteristic ratio is a step of calculating a front-rear gain ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the front wheels to the gain of the frequency spectrum of the acceleration of the rear wheels, at two or more specific frequencies; (3) the step of calculating the left-right frequency characteristic ratio is a step of calculating a left-right gain ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the left wheels to the gain of the frequency spectrum of the acceleration of the right wheels, at two or more specific frequencies; (4) the steps of calculating the front-rear load ratio and the left-right load ratio respectively are steps of calculating the front-rear load ratio by linearly combining the two or more calculated front-rear gain ratios with different weightings, and calculating the left-right load ratio by linearly combining the two or more calculated left-right gain ratios with different weightings.

Advantages of the Invention

[0012] According to the present invention, wheel loads can be accurately estimated with simple equipment.

Brief Description of the Drawings

[0013] [Figure 1] Schematic diagram showing a state where a wheel load estimation device according to an embodiment of the present invention is mounted on a vehicle. [Figure 2] Block diagram showing the electrical configuration of the wheel load estimation device. [Figure 3A] Graph of the frequency spectrum of the acceleration of the front wheels under two load conditions. [Figure 3B] Graph of the frequency spectrum of the acceleration of the rear wheels under two load conditions. [Figure 4] Example of a graph of the frequency spectrum of acceleration under two load conditions. [Figure 5A] Graph showing an approximate relationship between the gain integral value of the front two wheels and the gain integral value of the rear two wheels under two load conditions [Figure 5B] Graph showing an approximate relationship between the gain integral value of the left two wheels and the gain integral value of the right two wheels under two load conditions. [Figure 6]A graph showing the approximate relationship between the front-to-rear (left-to-right) frequency response ratio and the front-to-rear (left-to-right) load ratio. [Figure 7A] A diagram illustrating the concept of principal component analysis. [Figure 7B] A diagram illustrating the gain at each frequency and an example of the corresponding weighting coefficient. [Figure 8] A flowchart illustrating the process for estimating wheel load. [Figure 9A] A graph showing the error in wheel load estimation for FL wheels in the examples and comparative examples. [Figure 9B] A graph showing the error in wheel load estimation for FR wheels in the examples and comparative examples. [Figure 9C] A graph showing the error in wheel load estimation for the RL wheel in the examples and comparative examples. [Figure 9D] A graph showing the error in wheel load estimation for the RR wheel in the examples and comparative examples. [Modes for carrying out the invention]

[0014] The wheel load estimation apparatus, method, and program according to embodiments of the present invention will be described below with reference to the drawings.

[0015] <1. Configuration of the wheel load estimation device> Figure 1 is a schematic diagram showing how the wheel load estimation device 2 according to this embodiment is mounted on a vehicle 1. The vehicle 1 is a four-wheeled vehicle equipped with a left front wheel FL, a right front wheel FR, a left rear wheel RL, and a right rear wheel RR. The wheel load estimation device 2 has the function of estimating the wheel load acting on these wheels FL, FR, RL, and RR. The estimated wheel load data is used for various controls that assist in the driving of the vehicle 1. For example, the estimated wheel load data is transmitted to the brake control system and used for brake control. In addition, the estimated wheel load data is transmitted to the tire pressure monitoring system (TPMS) etc. of the tires mounted on the wheels FL, FR, RL, and RR and used for determining tire pressure reduction. If tire pressure reduction is detected in the TPMS based on the estimated wheel load data, a warning can be issued via the warning display 3 mounted on the vehicle 1. Some TPMS methods determine tire pressure reduction from changes in the dynamic load radius of the tire, but the dynamic load radius of the tire is affected not only by tire pressure reduction but also by wheel load. Therefore, when this method is adopted, tire pressure reduction can be accurately determined by canceling the effect of wheel load from the dynamic load radius of the tire based on the estimated wheel load data. In addition, overloading and uneven loading of vehicle 1 can be detected based on the estimated wheel load data, and if this is detected, a warning can be issued via the warning display 3 installed in vehicle 1. Overloading refers to a state in which vehicle 1 is loaded with a load exceeding the permissible load capacity, and uneven loading refers to a state in which the load inside vehicle 1 is locally uneven.

[0016] In this embodiment, the wheel load acting on wheels FL, FR, RL, and RR is estimated based on the wheel speed (rotational speed) of wheels FL, FR, RL, and RR. Each of wheels FL, FR, RL, and RR is equipped with a wheel speed sensor 6, which detects information representing the wheel speed of the wheel to which it is mounted (hereinafter referred to as wheel speed information) at a predetermined sampling period ΔT. The wheel speed sensors 6 are connected to the wheel load estimation device 2 via a communication line 5, and the wheel speed information detected by each wheel speed sensor 6 is transmitted to the wheel load estimation device 2 in real time.

[0017] Any wheel speed sensor 6 can be used as long as it can detect the wheel speeds of the FL, FR, RL, and RR wheels while the vehicle is in motion. For example, a sensor that measures wheel speed from the output signal of an electromagnetic pickup can be used, or a sensor that generates electricity using rotation, such as a dynamo, and measures wheel speed from the voltage generated at that time can be used. The mounting position of the wheel speed sensor 6 is not particularly limited and can be appropriately selected depending on the type of sensor, as long as it is possible to detect the wheel speed.

[0018] In this embodiment, a wheel torque sensor (hereinafter referred to as WT sensor) 7 is equipped on the left front wheel, which is one of the drive wheels. The WT sensor 7 detects the wheel torque of the vehicle 1. The WT sensor 7 is connected to the wheel load estimation device 2 via a communication line 5, and the wheel torque information detected by the WT sensor 7 is transmitted to the wheel load estimation device 2 in real time.

[0019] The WT sensor 7 is not particularly limited in structure or mounting position, as long as it can detect the wheel torque of the drive wheels of vehicle 1. Various types of WT sensors are commercially available, and their configurations are well known, so a detailed explanation is omitted here. Furthermore, it is possible to detect wheel torque without using the WT sensor 7; for example, wheel torque can be estimated from the engine torque obtained from the engine control unit.

[0020] Figure 2 is a block diagram showing the electrical configuration of the wheel load estimation device 2. As shown in Figure 2, the wheel load estimation device 2 is a control unit (on-board computer) mounted on the vehicle 1, and includes an I / O interface 11, a CPU 12, a ROM 13, a RAM 14, and a non-volatile, rewritable storage device 15. The I / O interface 11 is a communication device for communicating with external devices such as a wheel speed sensor 6, a warning indicator 3, and a WT sensor 7. The ROM 13 stores a program 9 for controlling the operation of various parts of the vehicle 1. The program 9 is written to the ROM 13 from a storage medium 8 such as a CD-ROM. The CPU 12 reads and executes the program 9 from the ROM 13, thereby virtually operating as a wheel speed acquisition unit 21, a torque acquisition unit 22, a total weight calculation unit 23, a frequency characteristic ratio calculation unit 24, a load ratio calculation unit 25, and a wheel load calculation unit 26. Details of the operation of each unit 21 to 26 will be described later. The storage device 15 consists of a hard disk or flash memory, etc. Note that the storage location for program 9 may be the storage device 15 instead of ROM 13. RAM 14 and storage device 15 are used as appropriate for calculations performed by the CPU 12.

[0021] The warning indicator 3 can be implemented in any form, such as a liquid crystal display element or liquid crystal monitor, as long as it can inform the user that tire pressure reduction, overloading, uneven loading, etc., is occurring. The mounting position of the warning indicator 3 can also be selected as appropriate, but it is preferable to install it in a location that is easily visible to the driver, such as on the instrument panel. When the control unit (wheel load estimation device 2) is connected to a car navigation system, the car navigation monitor can also be used as the warning indicator 3. When a monitor is used as the warning indicator 3, the warning can be displayed as an icon or text information on the monitor.

[0022] <2. Principles of Wheel Load Estimation> The principle of the wheel load estimation process for estimating the wheel loads of wheels FL, FR, RL, and RR will be explained below, with reference to the diagram. The algorithm for estimating wheel loads using this process is based on the frequency characteristics of a rotating wheel. More specifically, the frequency characteristics of a rotating wheel change with changes in the load acting on the wheel, i.e., the wheel load. When the wheel load increases, the contact area with the road surface increases, and the force that the tire mounted on the wheel receives from the road surface increases. Also, the elastic energy of the spring in the sidewall of the tire increases. On the other hand, when the wheel load decreases, the contact area with the road surface decreases, and the force that the tire receives from the road surface decreases. Also, the elastic energy of the spring in the sidewall of the tire decreases. The frequency characteristics of the wheel change due to these phenomena associated with changes in wheel load.

[0023] Figure 3A is a graph of the frequency spectrum of the front wheel acceleration (rotational acceleration), showing the gain when one driver is in vehicle 1 (single-occupancy) and when a load is unevenly distributed at the rear of vehicle 1 in addition to the driver being in vehicle 1 (rear-distributed load). Figure 3B is a graph of the frequency spectrum of the rear wheel acceleration (rotational acceleration), showing the gain for the single-occupancy case and the rear-distributed load case. As shown in these figures, the magnitude of the gain changes with changes in wheel load. However, since this example relates to a front-engine vehicle, the rear-distributed load condition does not have much effect on the front wheel gain.

[0024] These figures show a general trend where the frequency spectrum is large for wheels with high wheel loads and small for wheels with low wheel loads. However, after diligent research, the inventors have found that this trend can change depending on the frequency band. In other words, the frequency spectrum and gain may not change uniformly across the entire frequency band between loading condition 1, where the wheel load of a certain wheel is large, and loading condition 2, where the wheel load of the same wheel is small. Figure 4 illustrates this point. In the example shown in Figure 4, the gain under loading condition 2 is larger in the first frequency band, the gain under loading condition 1 is larger in the second frequency band, and the effect of loading conditions on the gain is small in the third frequency band. Therefore, the change in the gain integral value obtained by integrating the gain across the entire frequency band of the frequency spectrum may not actually accurately reflect the change in wheel load.

[0025] Therefore, in a method of estimating the wheel load ratio using an assumed approximate linear relationship between the gain integral values ​​of the two front wheels and the two rear wheels under the same loading conditions (see Figure 5A), and an assumed approximate linear relationship between the ratio of these gain integral values ​​and the front-to-rear load ratio (in this embodiment, the ratio of the sum of the wheel loads of the two front wheels to the sum of the wheel loads of the two rear wheels) (see Figure 6), the accuracy of the wheel load estimation may decrease. The above also applies when estimating the wheel load ratio using an assumed approximate linear relationship between the gain integral values ​​of the two left wheels and the two right wheels under the same loading conditions (see Figure 5B), and an assumed approximate linear relationship between the ratio of these gain integral values ​​and the left-to-right load ratio (in this embodiment, the ratio of the sum of the wheel loads of the two left wheels to the sum of the wheel loads of the two right wheels). Furthermore, according to the inventors' studies, the degree of change in the frequency spectrum associated with wheel load changes can vary depending on the wheel speed and the road surface on which the vehicle 1 travels, even with the same tire.

[0026] To address the above problem, the inventors identified a frequency band in the acceleration frequency spectrum that shows a more pronounced change with changes in wheel load (i.e., is more suitable for wheel load estimation) based on a large amount of wheel speed data obtained by driving on various road surfaces, given that the wheel load of each wheel is known. More specifically, first, based on the wheel speed information from the wheel speed sensors 6 of each wheel equipped on the vehicle 1, a Fast Fourier Transform (FFT) was performed at 10-second intervals on the wheel speed information for a predetermined time (30 seconds) to derive the acceleration frequency spectrum. Subsequently, gains were calculated from the frequency spectrum of each wheel at 0.2 Hz intervals, and based on these gains, the front-to-rear gain ratio, which is the ratio of the gains of the two front wheels to the gains of the two rear wheels, and two types of left-to-right gain ratios (hereinafter, these left-to-right gain ratios will also be called the first left-to-right gain ratio and the second left-to-right gain ratio) were calculated at 0.2 Hz intervals (see Figure 7A).

[0027] Furthermore, principal component analysis was performed on the front-to-rear gain ratio and the first and second left-to-right gain ratios. Two frequency bands were identified in which the front-to-rear gain ratio showed a stronger correlation with the front-to-rear load ratio, and in which the first and second left-to-right gain ratios showed a stronger correlation with the first left-to-right load ratio (the load ratio between the FL wheel and the FR wheel) and the second left-to-right load ratio (the load ratio between the RL wheel and the RR wheel), respectively (see Figure 7B). Specifically, for the front-to-rear gain ratio at each frequency in 0.2 Hz increments, two frequency bands F1 and F2 were identified that contain the frequency at which the absolute value of the weight of the front-to-rear gain ratio constituting the principal component is the largest. Similarly, for the first left-to-right gain ratio at each frequency in 0.2 Hz increments, frequency bands F3 and F4 were identified that contain the frequency at which the absolute value of the weight of the first left-to-right gain ratio constituting the principal component peaks. For the second left-to-right gain ratio at each frequency in 0.2 Hz increments, frequency bands F5 and F6 were identified that contain the frequency at which the absolute value of the weight of the second left-to-right gain ratio constituting the principal component peaks. This allows us to identify at least two frequency bands corresponding to the first and second frequency bands in Figure 4 for each of the front-to-back gain ratio, the first left-to-right gain ratio, and the second left-to-right gain ratio.

[0028] Here, the front-to-rear gain ratio R1 is defined as the ratio of the gain integral values ​​of the front two wheels to the gain integral values ​​of the rear two wheels in frequency band F1, and the front-to-rear gain ratio R2 is defined as the ratio of the gain integral values ​​of the front two wheels to the gain integral values ​​of the rear two wheels in frequency band F2 (hereinafter, the front-to-rear gain ratios R1 and R2 may be collectively referred to as the front-to-rear frequency characteristic ratio). Based on a large dataset of the front-to-rear frequency characteristic ratio and the front-to-rear load ratio L1, if we perform a multiple regression analysis with the front-to-rear load ratio L1 as the dependent variable and the front-to-rear gain ratios R1 and R2 as both independent variables, we can identify the weighting coefficients a and b of the front-to-rear gain ratios R1 and R2 that are optimized for wheel load estimation. That is, the front-to-rear load ratio L1 can be expressed as a linear combination of front-to-rear gain ratios R1 and R2 with different weights, as shown below. L1 = a·R1 + b·R2 (1)

[0029] Furthermore, the gain integral values ​​for the two front wheels and the two rear wheels may be the average or sum of the integral values ​​obtained by integrating the acceleration gains of the two front wheels and the two rear wheels over a predetermined frequency band, respectively; the integral value obtained by integrating the acceleration gain of the average wheel speed of the two front wheels and the two rear wheels over a predetermined frequency band; or the integral value obtained by integrating the gain of the difference in wheel speeds of the two front wheels and the gain of the difference in wheel speeds of the two rear wheels over a predetermined frequency band.

[0030] Similarly, the ratio of the gain integral value of the FL wheel to the gain integral value of the FR wheel in frequency band F3 is defined as the left-right gain ratio R3, and the ratio of the gain integral value of the FL wheel to the gain integral value of the FR wheels in frequency band F4 is defined as the left-right gain ratio R4. Similarly, the ratio of the gain integral value of the RL wheel to the gain integral value of the RR wheel in frequency band F5 is defined as the left-right gain ratio R5, and the ratio of the gain integral value of the RL wheel to the gain integral value of the RR wheel in frequency band F6 is defined as the left-right gain ratio R6 (hereinafter, the left-right gain ratios R3, R4, R5 and R6 may be collectively referred to as the left-right frequency characteristic ratio). Based on a large dataset of left-right frequency characteristic ratios R3, R4 and the first left-right load ratio L2, if multiple regression analysis is performed with the first left-right load ratio L2 as the dependent variable and the left-right gain ratios R3 and R4 as both independent variables, the weighting coefficients c and d of the left-right gain ratios R3 and R4 optimized for wheel load estimation can be identified. Furthermore, based on numerous datasets of left-right frequency response ratios R5 and R6 and second left-right load ratio L3, performing multiple regression analysis with the second left-right load ratio L3 as the dependent variable and the left-right gain ratios R5 and R6 as both independent variables reveals the weighting coefficients e and f for the left-right gain ratios R5 and R6 optimized for wheel load estimation. Specifically, the first left-right load ratio L2 can be expressed as a linear combination of left-right gain ratios R3 and R4 with different weights, and the second left-right load ratio L3 can be expressed as a linear combination of left-right gain ratios R5 and R6 with different weights, as shown below. L2 = c·R3 + d·R4 (2) L3 = e·R5 + f·R6 (3)

[0031] According to the above method, the front-to-rear load ratio and the left-to-right load ratio can be estimated using the front-to-rear frequency response ratio and the left-to-right frequency response ratio, which change more significantly with changes in the front-to-rear load ratio and the left-to-right load ratio, respectively. Furthermore, it is possible to consider cases where there is a negative correlation with the increase in wheel load. The frequency bands F1 to F6 specified above can also be the frequencies at which the absolute values ​​of the weights of the front-to-rear gain ratio and the left-to-right gain ratio that constitute the main components reach their peak. However, from the viewpoint of the stability of wheel load estimation, it is preferable to define F1 to F6 as frequency bands with a predetermined width. In addition, in the above example, the relationship between the left-to-right frequency response ratio and the left-to-right gain ratio was specified separately for the FL wheel and FR wheel pair, and the RL wheel and RR wheel pair, but the relationship between the left-to-right frequency response ratio and the left-to-right gain ratio may be specified without distinguishing between front and rear. Conversely, in the above example, the relationship between the front-to-rear frequency response ratio and the front-to-rear gain ratio was specified without distinguishing between left and right, but the relationship between the front-to-rear frequency response ratio and the front-to-rear gain ratio may be specified separately for the FL wheel and RL wheel pair, and the FR wheel and RR wheel pair. Furthermore, the relationship between the left-right frequency response ratio and left-right gain ratio, as well as the relationship between the front-rear frequency response ratio and front-rear gain ratio, may be identified for each pair of FL and RR wheels, and for each pair of FR and RL wheels. Below, an algorithm for wheel load estimation based on these findings will be described.

[0032] Furthermore, when specifying the relationship between the left-right frequency response ratio and the left-right gain ratio without distinguishing between front and rear, the left-right gain ratio is the ratio of the gain integral values ​​of the left two wheels and the right two wheels. The gain integral values ​​of the left two wheels and the right two wheels may be the average or sum of the integral values ​​obtained by integrating the acceleration gains of the left two wheels and the right two wheels over a predetermined frequency band, respectively; the integral value obtained by integrating the acceleration gain of the average wheel speed of the left two wheels and the right two wheels over a predetermined frequency band; or the integral value obtained by integrating the gain of the difference in wheel speed of the left two wheels and the gain of the difference in wheel speed of the right two wheels over a predetermined frequency band.

[0033] <3. Wheel load estimation process> Figure 8 is a flowchart showing the flow of the wheel load estimation process for estimating the wheel loads of wheels FL, FR, RL, and RR. The wheel load estimation process shown in Figure 8 starts, for example, when vehicle 1 starts moving and ends when it stops moving. For the following processes, the information for identifying frequency bands F1 to F4 and weight coefficients a to d are assumed to have been identified in advance for vehicle 1 based on a large number of datasets and stored in the storage device 15 or ROM 13.

[0034] First, the wheel speed acquisition unit 21 acquires wheel speed information from the wheel speed sensor 6 (step S1). The wheel speed acquisition unit 21 temporarily stores the acquired wheel speed information in the RAM 14 or in the storage device 15. The wheel speed acquisition unit 21 also converts the wheel speed information into V1 to V4, which are the wheel speeds of wheels FL, FR, RL, and RR, respectively.

[0035] Next, the torque acquisition unit 22 acquires the output signal of the WT sensor 7 (step S2). The torque acquisition unit 22 temporarily stores the acquired output signal of the WT sensor 7 in the RAM 14 or in the storage device 15. The torque acquisition unit 22 also converts the output signal of the WT sensor 7 into wheel torque.

[0036] Next, the total weight calculation unit 23 calculates the current total weight (weight) M of the vehicle 1 (step S3). In this embodiment, the total weight M is calculated based on the following equation of motion. In the equation below, WT is the wheel torque derived in step S2. α is the acceleration of the vehicle 1 and is calculated from the wheel speeds V1 to V4. g is the acceleration due to gravity, and θ is the road surface gradient. θ can be calculated, for example, from the data of the GPS (positioning sensor) mounted on the vehicle 1. WT = Mα + Mg·sinθ

[0037] Since various methods are known for estimating the total weight M of vehicle 1, a more detailed explanation will be omitted here. However, for a deeper understanding, one can refer to, for example, the applicant's patents No. 5346659 and No. 4926258.

[0038] Next, the frequency response ratio calculation unit 24 filters the waveform signals of the wheel speeds V1 to V4 (step S4). Specifically, the frequency response ratio calculation unit 24 passes the time-series data of the wheel speeds V1 to V4 through a filter that allows predetermined frequency components to pass through, and extracts frequency components in predetermined frequency bands F1 and F2 from each time-series data. Similarly, the frequency response ratio calculation unit 24 passes the time-series data of the wheel speeds V1 to V4 through a filter that allows predetermined frequency components to pass through, and extracts frequency components in predetermined frequency bands F3 to F6 from each time-series data. This filtering process may also be performed on the time-series data of accelerations A1 to A4, which are obtained by differentiating the time-series data of the wheel speeds V1 to V4 with respect to time. A1 to A4 are the rotational accelerations of wheels FL, FR, RL, and RR, respectively.

[0039] Next, the frequency response ratio calculation unit 24 performs frequency analysis on each time series data in frequency bands F1 to F6 extracted in step S4 and calculates the gain integral values ​​in frequency bands F1 to F6 (step S5). First, the frequency response ratio calculation unit 24 applies Parseval's theorem to each time series data after filtering in step S4 to derive the gain for frequency bands F1 to F6. This derivation can also be performed from fast Fourier transform processing on the time series data of wheel speeds V1 to V4 (step S4 omitted), time series estimation using an autoregressive model, and the variance of the time series data. Next, the frequency response ratio calculation unit 24 calculates the gain integral values ​​of the front two wheels and the rear two wheels in frequency band F1, and the gain integral values ​​of the front two wheels and the rear two wheels in frequency band F2. Furthermore, the gain integral values ​​of the FL wheel and FR wheel in frequency band F3, the gain integral values ​​of the FL wheel and FR wheel in frequency band F4, the gain integral values ​​of the RL wheel and RR wheel in frequency band F5, and the gain integral values ​​of the RL wheel and RR wheel in frequency band F6 are calculated, respectively.

[0040] Subsequently, based on the 12 gain integral values calculated in step S5, the frequency characteristic ratio calculation unit 24 calculates the front-back gain ratios R1 and R2 as the front-back frequency characteristic ratio, and the left-right gain ratios R3 to R6 as the front-back frequency characteristic ratio (step S6).

[0041] Subsequently, the load ratio calculation unit 25 reads the coefficients a to f from the storage device 15 or the ROM 13, and calculates the front-back load ratio L1, the first left-right load ratio L2, and the second left-right load ratio L3 based on (1) to (3) described above (step S7).

[0042] Subsequently, the wheel load calculation unit 26 calculates the front axle load ratio x and the rear axle load ratio y, and based on x and y, calculates the wheel load ratios L RL , RR 、L FR 、L RL 、L RR (step S8). The front axle load ratio x is the ratio of the sum of the wheel loads of the front two wheels to the total weight M of the vehicle 1. The rear axle load ratio y is the ratio of the sum of the wheel loads of the rear two wheels to the total weight M of the vehicle 1. x and y are calculated by the following formulas. x = 1 / (1 + L1) y = 1 - x = L1 / (1 + L1)

[0043] Also, the wheel load ratios L FL 、L FR 、L RL 、L RR are indicators representing the relative wheel loads among the wheels FL, FR, RL, and RR respectively. The wheel load ratios L FL 、L FR 、L RL 、L RR of the present embodiment are defined as the ratios of the wheel loads of the wheels FL, FR, RL, and RR to the total weight M of the vehicle 1 respectively, and are calculated according to the following formula. L FL = x / (1 + L2) L FR == x - L FL L RL = y / (1 + L3) L RR == y - L RL

[0044] Next, the wheel load calculation unit 26 calculates the wheel load ratio L FL , L FR , L RL , L RR Based on the total weight M of vehicle 1, the wheel loads of wheels FL, FR, RL, and RR are calculated according to the following formula (step S9). FL wheel: M×L FL FR Wheel: M x L FR RL wheel: M×L RL RR wheel: M×L RR

[0045] The wheel load estimation process is now complete. However, the wheel load estimation device 2 may further determine whether overloading or uneven loading has occurred based on at least one of the wheel load ratio calculated in step S8 and the wheel load calculated in step S9. If it is determined that at least one of overloading or uneven loading has occurred, the wheel load estimation device 2 may be configured to generate an alarm and output it via the alarm indicator 3.

[0046] <4. Variation> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. For example, the following modifications are possible. Furthermore, the gist of the following modifications can be combined as appropriate.

[0047] (1) In the above embodiment, the wheel load ratio L FL , L FR , L RL , L RR The wheel load of each wheel was calculated using the total weight M of vehicle 1. However, if only the wheel load ratio is required, steps S2, S3, and S9 can be omitted.

[0048] (2) The tire wheel load estimation device according to the above embodiment is not limited to the drive system of a four-wheeled vehicle, and can be applied to any FF, FR, MR, or 4WD vehicle. Furthermore, it is not limited to four-wheeled vehicles, but can also be applied to three-wheeled or six-wheeled vehicles, etc.

[0049] (3) In the above embodiment, the wheel load ratio and wheel load were calculated for each wheel, but these may be calculated only for a portion of the wheels FL, FR, RL, and RR.

[0050] (4) In the above embodiment, two specific frequency bands were determined, but there may be three or more specific frequency bands, and three or more coefficients may be predetermined in at least one of the formulas (1) to (3) used to calculate the front-to-rear load ratio L1, the first left-to-right load ratio L2, and the second left-to-right load ratio L3. [Examples]

[0051] <Experimental conditions> A gasoline hybrid, front-engine, front-wheel-drive (FF) four-wheel vehicle equipped with 205 / 50R17 summer tires was driven on asphalt roads under various load conditions as shown in Table 1. The total vehicle weight and wheel load of each wheel in Table 1 were measured using wheel load scales placed under the tires. [Table 1]

[0052] <Experimental Results> Based on the above sampling data during driving, the total weight of the vehicle and the wheel load of each wheel were estimated using the wheel load estimation process according to the above embodiment, and the results shown in Table 2 were obtained. The lower part of each column in Table 2 shows the percentage of error between the estimated value and the value in Table 1. [Table 2]

[0053] Furthermore, under the same load conditions, the total weight of the vehicle and the wheel load of each wheel were estimated using the method disclosed in Patent Document 1 (the method relating to the comparative example), and the results in Table 3 were obtained. Since the total weight of the vehicle was estimated using the same algorithm in both the example and the comparative example, the data is identical. The lower part of each column in Table 3 shows the percentage of error between the estimated value and the value in Table 1. [Table 3]

[0054] Figures 9A to 9D are graphs showing the error in the wheel load estimation results for the embodiment and the error in the wheel load estimation results for the comparative example for each of the wheels FL, FR, RL, and RR. From these results, the overall high accuracy of the wheel load estimation algorithm in the embodiment was confirmed. [Explanation of Symbols]

[0055] 1 vehicle 2. Wheel load estimation device (computer) 21 Wheel speed acquisition section 22 Torque acquisition unit 23. Total weight calculation unit 24 Frequency Response Ratio Calculation Unit 25 Load ratio calculation section 26 Wheel load calculation unit 6. Wheel speed sensor FL left front wheel FR right front wheel RL Left rear wheel RR Right rear wheel V1 Left front wheel speed V2 Right front wheel speed V3 Left rear wheel speed V4 Right rear wheel speed A1 Acceleration of the left front wheel A2 Acceleration of the right front wheel A3 left rear wheel acceleration A4 Right rear wheel acceleration R1 frequency response ratio R2 Left and right frequency characteristic ratio L1 Front and rear load ratio L2 Left / right load ratio L FL Wheel load ratio of the left front wheel L FR Wheel load ratio of the right front wheel L RL Wheel load ratio of the left rear wheel L RR Wheel load ratio of the right rear wheel M Vehicle gross weight

Claims

1. A wheel load estimation device for estimating the wheel load of a vehicle, A wheel speed acquisition unit that acquires wheel speed information for each wheel included in the vehicle from a wheel speed sensor equipped in the vehicle, A frequency response ratio calculation unit calculates, based on the wheel speed information, a front-to-rear frequency response ratio that changes with changes in the front-to-rear load ratio, which is the ratio of the load acting on the front wheels of the vehicle to the load acting on the rear wheels of the vehicle, and a left-to-right frequency response ratio that changes with changes in the left-to-right load ratio, which is the ratio of the load acting on the left wheel of the vehicle to the load acting on the right wheel of the vehicle. A load ratio calculation unit that calculates the front-to-rear load ratio and the left-to-right load ratio, respectively, based on the front-to-rear frequency characteristic ratio and the left-to-right frequency characteristic ratio, A wheel load calculation unit calculates a wheel load ratio representing the relative wheel load between the wheels included in the vehicle for at least one wheel of the vehicle, based on the front-to-rear load ratio and the left-to-right load ratio. Equipped with, The frequency characteristic ratio calculation unit is, As the front-to-rear frequency characteristic ratio, the front-to-rear gain ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the front wheel to the gain of the frequency spectrum of the acceleration of the rear wheel, is calculated at two or more specific frequencies, and as the left-to-right frequency characteristic ratio, the left-to-right gain ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the left wheel to the gain of the frequency spectrum of the acceleration of the right wheel, is calculated at two or more specific frequencies. The aforementioned load ratio calculation unit is: The front-to-rear load ratio is calculated by linearly combining the two or more front-to-rear gain ratios with different weights, and the left-to-right load ratio is calculated by linearly combining the two or more left-to-right gain ratios with different weights. Wheel load estimation device.

2. Total weight calculation unit that calculates the total weight of the vehicle while it is in motion. Furthermore, The wheel load calculation unit calculates the wheel load based on the specified total weight of the vehicle and the wheel load ratio. The wheel load estimation device according to claim 1.

3. The wheel load calculation unit calculates the wheel load ratio for each wheel included in the vehicle. The wheel load estimation device according to claim 1 or 2.

4. The frequency response ratio calculation unit calculates the front-to-back gain ratio in two or more specific frequency bands, and also calculates the left-to-right gain ratio in two or more specific frequency bands. The wheel load estimation device according to claim 1 or 2.

5. A wheel load estimation method for estimating the wheel load of a vehicle, which is performed by one or more computers, The steps include: obtaining wheel speed information for each wheel included in the vehicle from a wheel speed sensor equipped in the vehicle; A step of calculating the front-to-rear frequency characteristic ratio, which changes in accordance with the change in the front-to-rear load ratio, which is the ratio of the load acting on the front wheels of the vehicle to the load acting on the rear wheels of the vehicle, based on the wheel speed information; The steps include: calculating the left-right frequency characteristic ratio, which changes with the change in the left-right load ratio, which is the ratio of the load acting on the left wheel of the vehicle to the load acting on the right wheel of the vehicle, based on the wheel speed information; A step of calculating the front-to-rear load ratio and the left-to-right load ratio based on the front-to-rear frequency response ratio and the left-to-right frequency response ratio, A step of calculating a wheel load ratio, which represents the relative wheel load between the wheels included in the vehicle, for at least one wheel of the vehicle, based on the front-to-rear load ratio and the left-to-right load ratio. Includes, The step of calculating the front-to-rear frequency characteristic ratio is to calculate the front-to-rear gain ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the front wheel to the gain of the frequency spectrum of the acceleration of the rear wheel, at two or more specific frequencies. The step of calculating the left-right frequency characteristic ratio is to calculate the left-right gain ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the left wheel to the gain of the frequency spectrum of the acceleration of the right wheel, at two or more specific frequencies. The steps for calculating the front-to-rear load ratio and the left-to-right load ratio are as follows: the front-to-rear load ratio is calculated by linearly combining the two or more calculated front-to-rear gain ratios with different weights; and the left-to-right load ratio is calculated by linearly combining the two or more calculated left-to-right gain ratios with different weights. Wheel load estimation method.

6. A wheel load estimation program for estimating the wheel load of a vehicle, The steps include: obtaining wheel speed information for each wheel included in the vehicle from a wheel speed sensor equipped in the vehicle; Based on the wheel speed information, the steps include: calculating the front-to-rear frequency characteristic ratio which changes with a change in the front-to-rear load ratio, which is the ratio of the load acting on the front wheels of the vehicle to the load acting on the rear wheels of the vehicle; and calculating the left-to-right frequency characteristic ratio which changes with a change in the left-to-right load ratio, which is the ratio of the load acting on the left wheel of the vehicle to the load acting on the right wheel of the vehicle. A step of calculating the front-to-rear load ratio and the left-to-right load ratio based on the front-to-rear frequency response ratio and the left-to-right frequency response ratio, A step of calculating a wheel load ratio, which represents the relative wheel load between the wheels included in the vehicle, for at least one wheel of the vehicle, based on the front-to-rear load ratio and the left-to-right load ratio. Run this on one or more computers, The step of calculating the front-to-rear frequency characteristic ratio is to calculate the front-to-rear gain ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the front wheel to the gain of the frequency spectrum of the acceleration of the rear wheel, at two or more specific frequencies. The step of calculating the left-right frequency characteristic ratio is to calculate the left-right gain ratio, which is the ratio of the gain of the frequency spectrum of the acceleration of the left wheel to the gain of the frequency spectrum of the acceleration of the right wheel, at two or more specific frequencies. The steps for calculating the front-to-rear load ratio and the left-to-right load ratio are as follows: the front-to-rear load ratio is calculated by linearly combining the two or more calculated front-to-rear gain ratios with different weights; and the left-to-right load ratio is calculated by linearly combining the two or more calculated left-to-right gain ratios with different weights. Wheel load estimation program.

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