JP7788365B2 - Braking Torque Estimation Device - Google Patents

Description

The present invention relates to a braking torque estimation device used in vehicle motion control to estimate the braking torque of a vehicle.

In vehicle motion control, accurate estimation of tire longitudinal force, slip ratio, vehicle speed, and braking torque enables more precise control of the actuators installed on the vehicle. For example, when braking, vehicle motion is controlled based on estimated braking torque. Braking torque is an important value for vehicle performance and can be calculated from tire longitudinal force, slip ratio, and vehicle speed. Estimating braking torque using a thrust sensor or the like can improve estimation accuracy, but there is the issue of increased costs.

Another method for estimating tire longitudinal forces is to calculate the slip ratio based on the difference between vehicle speed and wheel speed. This method has the drawbacks of making it difficult to eliminate steady-state error when estimating vehicle speed by integrating longitudinal acceleration, and of being costly when adding sensors.

Patent Document 1, for example, discloses a conventional technology for estimating braking force without using vehicle speed or thrust sensors. The brake device disclosed in Patent Document 1 includes a ground load estimation unit that estimates the wheel ground load; a front/rear braking force correction value calculation unit that estimates the front/rear braking force ratio from the wheel angular velocity and ground load during braking and calculates a front/rear braking force correction value for controlling the wheel braking force based on the front/rear braking force ratio; a left/right braking force correction value calculation unit that calculates a left/right braking force correction value from the wheel angular velocity during braking to reduce the difference in braking force between the left and right wheels; and a command value calculation unit that calculates a braking force command value based on the braking force target value, the front/rear braking force correction value, and the left/right braking force correction value.

Non-Patent Document 1 also describes a technique for estimating slip ratio using an observer.

JP 2010-70022 A Thanh Vo-Duy, Minh C. Ta, Slip Ratio Estimation for Traction Control of Electric Vehicles, 2018 IEEE Vehicle Power and Propulsion Conference (VPPC), p.1-6

Conventional technology has the problem of making it difficult to accurately estimate braking torque, and in particular, it is difficult to accurately estimate the tire longitudinal force, slip ratio, and vehicle speed required to estimate braking torque.

The technology described in Patent Document 1 controls the front and rear braking forces using the estimated wheel ground loads, and estimates the tire longitudinal force when the left and right braking forces on at least one of the front and rear wheels are approximately equal. With this technology, it is difficult to estimate the tire longitudinal force when there is a difference in braking force between the left and right wheels.

The technology described in Non-Patent Document 1 uses an observer to estimate the slip ratio from the wheel speed, its derivative, and longitudinal acceleration. While this technology ensures convergence of the estimation by using an observer, it has issues in that it does not guarantee accuracy from moment to moment and requires the derivative of the wheel speed. It is also unclear whether it is possible to estimate values other than the slip ratio that are required for vehicle motion control.

As such, conventional technology has the problem that it is difficult to accurately estimate tire longitudinal forces, slip ratios, and vehicle speed, making it difficult to accurately estimate braking torque. Furthermore, while the accuracy of braking torque estimation can be improved by using a braking torque sensor or thrust sensor, etc., in order to prevent increases in costs, there is a demand for accurate estimation of braking torque using only sensors that are generally equipped on vehicles, without using these sensors.

The object of the present invention is to provide a braking torque estimation device that can estimate braking torque with high accuracy at low cost.

The braking torque estimation device according to the present invention can be installed on a vehicle having multiple wheels with tires, and includes a braking torque calculation unit that calculates the braking torque of the wheels, and inputs the wheel speed of the wheels and longitudinal acceleration, which is the acceleration of the vehicle in the longitudinal direction. The braking torque calculation unit calculates the vehicle speed, the tire longitudinal force of the wheels, and the wheel slip ratio based on the wheel speed, tire load of the wheels, the longitudinal acceleration, and tire characteristics of the wheels, and calculates the braking torque based on the calculated tire longitudinal force.

This invention provides a braking torque estimation device that can estimate braking torque with high accuracy and at low cost.

1 is a diagram showing an example of the configuration of a vehicle equipped with a braking torque estimation device according to a first embodiment of the present invention; 1 is a block diagram showing the configuration of a braking torque estimation device according to a first embodiment; FIG. 2 is a diagram showing an example of the relationship between a slip ratio and a friction coefficient, which are tire characteristics. FIG. 10 is a diagram showing an example of the relationship between the slip ratio and the friction coefficient when the sideslip angle is changed. FIG. 10 is a block diagram showing the configuration of a braking torque estimation device according to a fourth embodiment of the present invention. FIG. 2 is a diagram showing the configuration of a brake device. FIG. 2 is a diagram illustrating a braking torque estimation device connected to a brake control device. FIG. 13 is a block diagram showing the configuration of a brake control device according to an eighth embodiment of the present invention.

The braking torque estimation device according to the present invention can be installed on a vehicle equipped with multiple wheels and tires. It can estimate tire characteristics (e.g., braking coefficient) and tire load using the wheel speed and longitudinal acceleration of the vehicle. The estimated tire characteristics and tire load can then be used to estimate vehicle speed, slip ratio, tire longitudinal force, and braking torque with high accuracy and low cost. Slip ratio, tire longitudinal force, braking torque, etc. vary depending on the brake device and tire, and fluctuate over time due to wear of the brake device and tires. The braking torque estimation device according to the present invention can estimate vehicle speed, slip ratio, tire longitudinal force, and braking torque with high accuracy and low cost, without using a braking torque sensor or thrust sensor, using only sensors typically provided on the vehicle. Using the braking torque estimation device according to the present invention, vehicle motion can be controlled with high accuracy and low cost.

The following describes a braking torque estimation device according to an embodiment of the present invention, using the drawings. Note that in the drawings used in this specification, identical or corresponding components are designated by the same reference numerals, and repeated explanations of these components may be omitted.

This section describes a braking torque estimation device according to a first embodiment of the present invention.

Figure 1 shows an example configuration of a vehicle 10 equipped with a braking torque estimation device according to this embodiment. The vehicle 10 includes a controller 5, wheels 7, a vehicle body 8, a wheel speed sensor 1, an acceleration sensor 2, a gyro sensor 3, a steering angle sensor 4, a brake device 9 that generates braking force, a brake pedal 11, and a power source 14. Furthermore, although not shown, the vehicle 10 also includes an internal combustion engine or electric motor that generates braking/driving force, a steering device, a suspension, and the like.

The controller 5 is equipped with a braking torque estimation device according to this embodiment and controls the internal combustion engine, electric motor, brake device 9, steering device, suspension, etc. The controller 5 may be divided into separate controllers for each of its functions, or into a higher-level controller and a lower-level controller. In this specification, multiple controllers divided in this manner are collectively referred to as the controller 5. The controller 5 may be configured as a computer that provides overall control of the vehicle 10 and includes hardware such as a calculation device such as a CPU, a main memory device such as semiconductor memory, an auxiliary memory device, and a communication device, and various functions are realized by the calculation device executing programs loaded into the main memory device.

In the following explanation, explanations of well-known technologies, such as the above-mentioned configuration of the controller 5, may be omitted.

Wheels 7 are arranged at four locations on the front, rear, left, and right sides of the vehicle body 8, and tires are provided. In this embodiment, the vehicle 10 is a four-wheeled vehicle.

The wheel speed sensor 1, acceleration sensor 2, gyro sensor 3, and steering angle sensor 4 are sensors that are typically provided in a vehicle 10.

The wheel speed sensor 1 detects the rotational speed of the wheels 7 located at four locations on the vehicle body 8. The wheel speed sensor 1 can be configured, for example, as a sensor that detects the relative rotational speed (wheel angular velocity) between a rotating part installed on an axle hub or the like and a fixed part installed on a knuckle, brake carrier, or the like.

The acceleration sensor 2 detects the acceleration acting on the center of gravity of the vehicle body 8, i.e., the acceleration in the longitudinal direction (longitudinal acceleration) and the acceleration in the lateral direction (lateral acceleration) of the vehicle 10.

The gyro sensor 3 detects the yaw rate, which is the angular velocity of rotation around the center of gravity of the vehicle body 8.

The steering angle sensor 4 detects the steering angle, which is the rotation angle of the steering wheel or the steering angle of the wheels 7, generated by the steering of the driver operating the vehicle 10.

The brake devices 9 are, for example, electric brake devices, and are provided on each of the four wheels 7 on the vehicle body 8. That is, the vehicle 10 is equipped with a brake device 9FL for the left front wheel, a brake device 9FR for the right front wheel, a brake device 9RL for the left rear wheel, and a brake device 9RR for the right rear wheel. These brake devices have the same structure and are controlled by the controller 5. Hereinafter, these brake devices 9FL, 9FR, 9RL, and 9RR will be collectively referred to as brake devices 9. Note that the brake devices 9 may be hydraulic brake devices instead of electric brake devices.

The controller 5 transmits a control signal corresponding to the operation of the brake pedal 11 to the brake device 9 via the communication line 12 based on the operation of the brake pedal 11 by the driver of the vehicle 10, the state of the vehicle 10 and wheels 7, and various information about the environment outside the vehicle 10. The brake device 9 is powered by electricity supplied from the power source 14 via the electric wire 13.

The controller 5 has the functionality of the braking torque estimation device according to this embodiment, and brakes the vehicle 10 using the braking torque value estimated by the braking torque estimation device. The braking torque estimation device according to this embodiment will be explained using Figure 2.

Figure 2 is a block diagram showing the configuration of the braking torque estimation device 20 according to this embodiment. The braking torque estimation device 20 includes a tire load estimation unit 21, a tire characteristics reading unit 25, a braking torque estimation unit 26, a tire characteristics estimation unit 22, and a tire characteristics storage unit 24.

The tire load estimation unit 21 calculates and estimates the tire load Fzi. The tire load Fzi is also called the tire vertical force Fzi. The method by which the tire load estimation unit 21 calculates the tire load Fzi will be described later.

The subscript i is an identifier that distinguishes between the four wheels 7 on the vehicle body 8, and represents one of the following: FL (front left wheel), FR (front right wheel), RL (rear left wheel), and RR (rear right wheel). This subscript i will also be used in the following explanation.

The tire characteristics reading unit 25 inputs the tire characteristics stored in the tire characteristics storage unit 24. These tire characteristics are values that indicate the relationship between the tire's slip ratio and friction coefficient. As will be described later, an example of a tire characteristic is the braking coefficient Kbi, which is a proportional coefficient between the slip ratio and friction coefficient. The friction coefficient is the value obtained by dividing the longitudinal force (tire longitudinal force Fxi) that the tire receives at the tire contact surface by the vertical force (tire load Fzi or tire vertical force Fzi) that the tire receives at the tire contact surface.

The braking torque etc. estimation unit 26 calculates and estimates the tire longitudinal force, slip ratio, vehicle speed, and braking torque using the tire load Fzi calculated by the tire load estimation unit 21 and the tire characteristics (e.g., the braking coefficient Kbi, which is a value indicating the relationship between the slip ratio and the friction coefficient) obtained by the tire characteristics reading unit 25. Hereinafter, the tire longitudinal force, slip ratio, vehicle speed, and braking torque will be collectively referred to as "braking torque etc." The braking torque etc. estimation unit 26 will also be referred to as the braking torque calculation unit.

This section explains how the braking torque estimation unit 26, which is a braking torque calculation unit, calculates braking torque, etc.

Figure 3 is a diagram showing an example of the relationship between slip ratio and friction coefficient, which are tire characteristics. In Figure 3, the horizontal axis represents slip ratio and the vertical axis represents friction coefficient, and the relationship between the two is represented by curve 30. It is generally known that the relationship between slip ratio and friction coefficient is as shown in Figure 3.

The slip ratio λi during braking is expressed by equation (1).

Here, Vb indicates the vehicle speed, and Vwi indicates the wheel speed. The vehicle speed Vb is the speed of the vehicle body 8 (the speed of the center of gravity of the vehicle body 8). The wheel speed Vwi is the rotational speed of the wheel 7, which is calculated as (tire radius Ri x wheel angular velocity ωi), and can be detected by the wheel speed sensor 1.

The slip ratio λi during driving (acceleration) is expressed by equation (2).

In Figure 3, a positive slip ratio indicates the friction coefficient during driving, and a negative slip ratio indicates the friction coefficient during braking. That is, in the graph of Figure 3, the upper right area indicates the characteristics during driving, and the lower left area indicates the characteristics during braking.

As shown in Figure 3, the coefficient of friction increases as the slip ratio increases, but reaches a peak at a certain slip ratio and then decreases as the slip ratio increases further. When the absolute value of the slip ratio is small, there is a linear relationship between the slip ratio and the coefficient of friction, and this relationship is represented by the dashed line 31.

As mentioned above, when the absolute value of the slip ratio is small, the slip ratio and the friction coefficient are proportional to each other, so this proportionality coefficient is taken as the braking coefficient Kbi.

The tire longitudinal force Fxi is calculated using equation (3).

The total value of the tire longitudinal force Fxi for all four wheels 7, excluding the effects of gravity due to air resistance and the inclination of the vehicle 10, is expressed by equation (4) from the equation of motion of the vehicle 10.

Here, ax is the longitudinal acceleration of the vehicle 10, axse is the longitudinal acceleration acting on the center of gravity of the vehicle body 8 detected by the acceleration sensor 2, and mb is the mass of the vehicle 10 including occupants. The symbol Σ indicates the sum for the subscript i, i.e., the total for all wheels 7 (4 wheels).

As shown in equation (4), the longitudinal acceleration ax of the vehicle 10 may be the value axse detected by the acceleration sensor 2. However, the longitudinal acceleration ax of the vehicle 10 can be calculated with high accuracy by removing the gravitational acceleration component associated with pitching of the vehicle body 8 contained in the longitudinal acceleration axse. Therefore, the longitudinal acceleration ax of the vehicle 10 can also be calculated using equation (5). Here, θy represents the pitch angle of the vehicle body 8, and g represents gravitational acceleration.

When the pitch angle θy is small, equation (5) can be approximated by equation (6). Therefore, assuming that the pitch angle θy is small, equation (6), which is a linear approximation, may be used instead of equation (5).

When the vehicle 10 is tilted at a tilt angle α, the equation of motion in equation (4) is expressed as equation (7) by adding a term for gravity.

Furthermore, if the pitch angle θy and tilt angle α are small, the longitudinal acceleration ax of the vehicle 10 can be calculated using equation (8) using the longitudinal acceleration axse detected by the acceleration sensor 2.

Then, the total tire longitudinal force Fxi for all four wheels 7 can be calculated from equations (7) and (8) using the longitudinal acceleration axse detected by the acceleration sensor 2, using equation (9).

Here, the pitch angle θy can be calculated using the relationship between longitudinal acceleration and pitch stiffness.

Furthermore, when taking into account the effect of air resistance when calculating the tire longitudinal force Fxi, the equation of motion (Equation (4)) can be used, for example, to find the total value of the tire longitudinal force Fxi for all wheels 7 (four wheels), as shown in Equation (10).

Here, A is the frontal projection area of the vehicle 10, C is the air resistance coefficient, and ρ is the air density. Since the vehicle speed Vb is the value to be calculated (a value included in braking torque, etc.), in equation (10), the most recently calculated value or wheel speed Vwi is used as the vehicle speed Vb.

By using equation (9) or equation (10), the total value of the tire longitudinal forces Fxi can be calculated more accurately.

On the other hand, during braking, the total tire longitudinal force Fxi for all four wheels 7 is expressed by equation (11) by substituting equation (1) into equation (3).

Solving equation (11) for vehicle speed Vb gives equation (12), which represents vehicle speed Vb.

By substituting equation (12) into equation (1), we obtain equation (13), which represents the slip ratio λi of each wheel.

By substituting equation (13) into equation (3), we obtain equation (14) which represents the tire longitudinal force Fxi of each wheel.

From the above, it can be seen that the vehicle speed Vb, the slip ratio λi of each wheel, and the tire longitudinal force Fxi of each wheel can be calculated using the total tire longitudinal force Fxi for all wheels 7, which can be calculated using the longitudinal acceleration axse detected by the acceleration sensor 2, the tire load Fzi (tire vertical force Fzi) of each wheel 7, the braking coefficient Kbi, and the wheel speed Vwi (Equation (12)-Equation (14)).

The braking torque estimation unit 26 uses the value input by the tire characteristics reading unit 25 from the tire characteristics storage unit 24 as the braking coefficient Kbi, and uses the values estimated by the tire load estimation unit 21 as the tire loads Fzi of all wheels 7.

The above explanation describes the case where the braking coefficient Kbi differs between all four wheels 7 of the vehicle 10. If the four wheels 7 are considered to be using the same tires and traveling on similar road conditions, it can be assumed that there are no significant differences in tire characteristics and that the tire characteristics are expressed by the same braking coefficient Kb. If all wheels 7 have the same braking coefficient Kb, then equations (12)-(14) can be expressed as equations (15)-(17), respectively. However, ΣFzi is replaced with mb×g.

In other words, the vehicle speed Vb, slip ratio λi of each wheel, and tire longitudinal force Fxi of each wheel can be calculated using a braking coefficient Kb that is the same for all wheels 7, instead of the braking coefficient Kbi of each wheel.

The relationship between tire longitudinal force Fxi and braking torque during braking, ignoring running resistance, is expressed by equation (18).

Here, Ii represents the moment of inertia of the wheel 7, Tbi represents the braking torque, Ri represents the tire radius, and ωi represents the wheel angular velocity. Note that there is a relationship of ωi x Ri = Vwi.

The braking torque Tbi can be calculated from equation (18) to equation (19).

If we ignore the inertia term in equation (19) because it is small, we obtain equation (20) which represents the braking torque Tbi.

Here, during deceleration, the tire longitudinal force Fxi is a negative value and the braking torque Tbi is a positive value.

The braking torque Tbi includes the braking torque generated by the brake device 9, the torque generated by the electric motor in the electric vehicle, and the torque generated by the internal combustion engine. The torque generated by the electric motor is called regenerative braking torque, and the torque generated by the internal combustion engine is called engine braking torque. The regenerative braking torque and engine braking torque are called driving torque. The braking torque estimation unit 26 can estimate these driving torques according to existing technology.

The braking torque estimation unit 26 can calculate the braking torque applied by the brake device 9 by subtracting the driving torque (regenerative braking torque or engine braking torque) from the braking torque Tbi.

Furthermore, when the regenerative braking torque and engine braking torque are sufficiently small compared to the braking torque by the brake device 9, the braking torque estimation unit 26 can set the value of the braking torque Tbi to the value of the braking torque by the brake device 9.

Furthermore, when the brake device 9 is not operating and no braking torque is being generated by the brake device 9, the braking torque etc. estimation unit 26 can set the value of the braking torque Tbi to the value of the regenerative braking torque or engine braking torque. Furthermore, when the braking torque by the brake device 9 can be measured, the braking torque etc. estimation unit 26 can obtain the regenerative braking torque or engine braking torque by subtracting the measured value of the braking torque by the brake device 9 from the braking torque Tbi.

Next, we will explain how the tire load estimation unit 21 calculates the tire load Fzi (tire vertical force Fzi). The tire load estimation unit 21 can calculate the tire load Fzi using a known method. As an example, we will explain below how to calculate the tire load Fzi when the vehicle 10 is traveling in a straight line.

For example, assuming that the loads on the left and right wheels are equal when there is no acceleration or deceleration, when the vehicle is traveling straight, the tire load Fzi can be calculated using equation (21) for the front wheels and equation (22) for the rear wheels.

Here, mb is the mass of the vehicle 10 including occupants, Lf is the longitudinal distance between the center of gravity of the vehicle 10 and the front wheel axle, Lr is the longitudinal distance between the center of gravity of the vehicle 10 and the rear wheel axle, Lbas is the wheelbase (Lbas = Lf + Lr), and hyc is the height of the center of gravity of the vehicle 10.

From equations (21) and (22), the tire load Fzi (tire vertical force Fzi) can also be calculated using the longitudinal acceleration axse detected by the acceleration sensor 2. The longitudinal acceleration ax can be determined using the longitudinal acceleration axse detected by the acceleration sensor 2 (see, for example, equations (4), (5), (6), and (8)).

In addition, the braking torque estimation unit 26 may use, as the tire load Fzi, a value obtained by actual measurement or calculation from suspension displacement, etc., rather than a value calculated and estimated by the tire load estimation unit 21.

Next, the tire characteristic estimation unit 22 will be described. In this embodiment, the tire characteristic estimation unit 22 estimates and determines the braking coefficient Kbi as a tire characteristic. In this embodiment, it is assumed that all wheels 7 have the same braking coefficient Kb (i.e., Kbi = Kb), and an example of determining this braking coefficient Kb is shown.

The tire characteristics shown in Figure 3 are known to be nearly identical during braking and driving, except for the difference in the sign of the friction coefficient. Therefore, this embodiment shows a method for calculating the braking coefficient Kb during driving, i.e., when the vehicle 10 is accelerating.

We will use an example where the vehicle 10 is accelerating in front-wheel drive. The driving force of the rear wheels is zero, and the braking force is also zero. Therefore, assuming that the rear wheel slip ratio λi (where i is RL and RR) is zero, the vehicle speed Vb can be calculated using equation (23), which is derived from equation (2).

By substituting equation (23) into equation (2), the slip ratio λFL of the left front wheel is calculated using equation (24), and the slip ratio λFR of the right front wheel is calculated using equation (25).

The tire longitudinal force FxFL of the left front wheel and the tire longitudinal force FxFR of the right front wheel are expressed by equations (26) and (27), respectively, based on equation (3). The slip ratios λFL and λFR in equations (26) and (27) use the slip ratios obtained from equations (24) and (25).

Furthermore, if the driving force and braking force of the rear wheels are zero, the total value of the tire longitudinal forces Fxi for all wheels 7 (four wheels) is expressed by equation (28).

The total tire longitudinal force Fxi on the left side of equation (28) can be calculated using the longitudinal acceleration axse detected by the acceleration sensor 2, as shown in equation (4) etc.

Substituting equations (26) and (27) into the right-hand side of equation (28) and solving equation (28) for the damping coefficient Kb, we obtain equation (29).

In other words, the braking coefficient Kb can be calculated using the longitudinal acceleration axse (or the longitudinal acceleration ax of the vehicle 10) detected by the acceleration sensor 2, the four-wheel wheel speed Vwi used in equations (24) and (25), and the front wheel tire loads FzFL and FzFR.

The above explanation has been given for an example in which the vehicle 10 is front-wheel drive. If the vehicle 10 is rear-wheel drive, simply swap the front and rear wheels in the above explanation.

If the driving force of each wheel is known, the tire longitudinal force FxFL of the left front wheel and the tire longitudinal force FxFR of the right front wheel can be determined. On the other hand, the slip ratio λFL of the left front wheel and the slip ratio λFR of the right front wheel can be calculated from equations (24) and (25). Therefore, the braking coefficient Kb can be calculated using equations (26) and (27).

Next, we will explain an example in which the vehicle 10 is four-wheel drive. We assume that in a four-wheel drive vehicle, the front/rear distribution of driving force to the wheels 7 from the engine or electric motor can be detected or estimated using equation (30).

Here, FdxF represents the driving force of the front wheels, FdxR represents the driving force of the rear wheels, and γ represents the ratio between them.

The front wheel tire longitudinal forces FxFL and FxFR can be calculated from the equation of motion of the vehicle 10 using equation (31).

Similarly, the left rear wheel longitudinal tire force FxRL and the right rear wheel longitudinal tire force FxRR can be calculated using equation (32).

On the other hand, from equations (2) and (3), equation (33) is obtained for the front left wheel (i = FL), and equation (34) is obtained for the rear left wheel (i = RL) (assuming Kbi = Kb).

By solving the simultaneous equations of equations (33) and (34) with vehicle speed Vb and braking coefficient Kb as unknowns, we obtain equation (35), which represents braking coefficient Kb.

The braking coefficient Kb expressed by equation (35) was calculated from equation (33) for the left front wheel and equation (34) for the left rear wheel, but braking coefficient Kb may also be calculated from the equation for the right front wheel and the equation for the right rear wheel, or from the equation for the left front wheel and the equation for the right rear wheel, or from the equation for the right front wheel and the equation for the left rear wheel. For example, if braking coefficient Kb is calculated from the equation for the right front wheel and the equation for the right rear wheel, equation (36) is obtained.

As mentioned above, the damping coefficient Kb can be obtained using multiple equations. Therefore, by taking the average value of the damping coefficients Kb obtained from multiple equations (for example, the two equations (35) and (36)), the damping coefficient Kb can be calculated more accurately.

In this way, the tire characteristic estimation unit 22 calculates the damping coefficient Kb (or damping coefficient Kbi), which is a tire characteristic. Note that the tire characteristic estimation unit 22 may estimate the damping coefficient Kb at predetermined time intervals, taking into account that tire characteristics change over time. Furthermore, the tire characteristic estimation unit 22 may improve the accuracy of the damping coefficient Kb by averaging the damping coefficients Kb obtained by multiple estimations and setting the averaged value as the value of the damping coefficient Kb.

The tire characteristic storage unit 24 stores the tire characteristics calculated by the tire characteristic estimation unit 22. In this embodiment, the tire characteristic storage unit 24 stores the damping coefficient Kb (or damping coefficient Kbi) as a tire characteristic.

The braking torque estimation device 20 according to this embodiment can estimate the tire characteristics, braking coefficient Kb (Kbi) and tire load Fzi (tire vertical force Fzi), using the wheel speed Vwi and longitudinal acceleration ax (longitudinal acceleration axse) of the wheels 7 of the vehicle 10, and can calculate the vehicle speed Vb, slip ratio λi, tire longitudinal force Fxi, and braking torque Tbi using the estimated braking coefficient Kb (Kbi) and tire load Fzi. The controller 5 controls the movement of the vehicle 10 using these values calculated by the braking torque estimation device 20. Using the braking torque estimation device 20 according to this embodiment, braking torque can be estimated with high accuracy at low cost, and the movement of the vehicle 10 can also be controlled with high accuracy at low cost.

A braking torque estimation device according to a second embodiment of the present invention will be described. In the first embodiment, an example in which the vehicle 10 mainly travels in a straight line will be described. In this embodiment, a case in which the vehicle 10 travels while turning will be described. When the vehicle 10 travels while turning, the method for estimating the tire load Fzi, for example, differs from when the vehicle 10 travels in a straight line. Below, a method in which the tire load estimation unit 21 calculates the tire load Fzi when the vehicle 10 is turning will be described.

When the vehicle 10 turns, a roll motion occurs in the vehicle 10, and the tire load Fzi is expressed by equations (37)-(40).

Here, DF represents the tread of the front wheels of the vehicle 10, DR represents the tread of the rear wheels of the vehicle 10, and ay represents the lateral acceleration of the vehicle 10.

Furthermore, the wheel speed converted from each wheel speed to the longitudinal speed of the vehicle 10 at the sprung center of gravity position can be calculated by adding or subtracting the speed difference between each wheel based on the actual steering angle δ and yaw rate r that occur during turning to each wheel speed. If the wheel speed measured by wheel speed sensor 1 is Vwsi, the wheel speed Vwi converted to the longitudinal speed of the vehicle 10 at the sprung center of gravity position is expressed by equations (41)-(44).

Figure 4 shows an example of the relationship between the slip ratio and the friction coefficient when the sideslip angle β changes. Figure 4 shows the same curve 30 as Figure 3. As explained in Example 1, the braking coefficient Kb is the proportionality coefficient between the slip ratio and the friction coefficient when the absolute value of the slip ratio is small.

The braking coefficient Kb changes depending on the sideslip angle β when the vehicle 10 is turning. As the sideslip angle β increases from zero, the change in the friction coefficient relative to a change in slip ratio decreases in the range where the absolute value of the slip ratio is small. Therefore, the braking coefficient Kb, which is the proportional coefficient between the slip ratio and the friction coefficient, decreases as the sideslip angle β increases. This braking coefficient Kb, which depends on the value of the sideslip angle β, is denoted as Kb(β).

The tire characteristics reading unit 25 inputs the braking coefficient Kb as a function Kb(β) of the sideslip angle β from the tire characteristics storage unit 24. The sideslip angle β can be calculated using existing methods using the steering angle (actual steering angle δ) and the vehicle speed Vb.

The braking torque estimation unit 26 replaces the braking coefficient Kb with Kb(β) and inputs the value of the wheel speed Vwi (equations (41)-(44)) converted into the longitudinal speed of the vehicle 10 at the sprung center of gravity position as the wheel speed Vwi. Then, using equations (12)-(20), the vehicle speed Vb, slip ratio λi, tire longitudinal force Fxi, and braking torque Tbi can be calculated.

In Example 1, the tire characteristic estimation unit 22 determines the damping coefficient Kb(0) when the sideslip angle β is zero. Based on this damping coefficient Kb(0), the change in the value of the damping coefficient Kb when the sideslip angle β changes from zero (i.e., the change in the value of the damping coefficient Kb from Kb(0)) can be determined through experiments, numerical simulations, etc. By determining the relationship between the sideslip angle β and the damping coefficient Kb in this way in advance, the tire characteristic estimation unit 22 can also store this relationship as the damping coefficient Kb(β).

Alternatively, the side slip angle β1 when the tire load Fzi is estimated when the vehicle 10 is turning can be calculated, and the braking coefficient Kb(β1) corresponding to this side slip angle β1 can be calculated. Based on this braking coefficient Kb(β1), the change in the value of the braking coefficient Kb when the side slip angle β changes from β1 (i.e., the change in the value of the braking coefficient Kb from Kb(β1)) can be calculated through experiments, numerical simulations, etc., and the relationship between the side slip angle β and the braking coefficient Kb can be determined in advance. The tire characteristic estimation unit 22 can also store this relationship as the braking coefficient Kb(β).

According to this embodiment, tire characteristics (braking coefficient Kb) and braking torque (vehicle speed Vb, slip ratio λi, tire longitudinal force Fxi, and braking torque Tbi) can be calculated not only when the vehicle 10 is traveling in a straight line but also when the vehicle is turning, making it possible to estimate braking torque Tbi at low cost and with high accuracy regardless of the traveling state of the vehicle 10.

This section describes a braking torque estimation device according to a third embodiment of the present invention.

In Example 1, an example was described in which there is no problem in assuming that the braking coefficient Kb estimated by the tire characteristic estimation unit 22 and the braking coefficient Kb estimated by the braking torque estimation unit 26 are approximately the same. In reality, tire characteristics change not only depending on the tire, but also on the conditions of the road surface on which the vehicle 10 is traveling (hereinafter simply referred to as "road surface conditions").

In this example, the tire characteristic estimation unit 22 estimates the tire characteristic (braking coefficient Kb) taking into account road surface conditions, and the tire characteristic reading unit 25 inputs the braking coefficient Kb from the tire characteristic storage unit 24. As described in Example 1, the tire characteristic estimation unit 22 calculates and estimates the braking coefficient Kb during driving (acceleration). The braking coefficient Kb estimated by the tire characteristic estimation unit 22 is referred to as the braking coefficient Kbe.

The tire characteristic estimation unit 22 acquires road surface conditions when estimating the braking coefficient Kbe. Road surface conditions include, for example, information about whether the road surface on which the vehicle 10 is traveling is dry, wet, or snowy. The tire characteristic estimation unit 22 acquires road surface conditions from, for example, various sensors (e.g., a front camera) equipped on the vehicle 10 or a server connected to the vehicle 10 via the Internet. The tire characteristic estimation unit 22 can also acquire, as road surface conditions, various types of information that affect the friction coefficient of the road surface, such as information about the weather on the road on which the vehicle 10 is traveling (weather information) and information about the pavement (pavement information). Such weather information and pavement information can be acquired together with location information using a map, etc.

The braking coefficient on a predetermined reference road surface is expressed in Kbs. Any road surface can be defined as the reference road surface, and it is preferable to define a good road surface (such as a dry road) as the reference road surface.

The relationship between the braking coefficient Kbe estimated by the tire characteristic estimation unit 22 and the braking coefficient Kbs on the reference road surface is expressed by equation (45) using a conversion coefficient c.
Kbs=c×Kbe...(45)
The conversion coefficient c is a coefficient for eliminating the influence of road surface conditions, and its value varies depending on the road surface conditions (environment). The conversion coefficient c is determined in advance according to the road surface conditions and is stored in the tire characteristics storage unit 24.

The braking coefficient Kbe estimated by the tire characteristic estimation unit 22 is a value estimated under the specific road surface conditions on which the vehicle 10 is traveling. The braking coefficient Kbs for the reference road surface is calculated by multiplying the estimated braking coefficient Kbe by the conversion coefficient c according to equation (45), eliminating the influence of the road surface conditions (environment). Since the influence of the road surface conditions has been removed from this braking coefficient Kbs, it can be considered a braking coefficient specific to the tire.

The tire characteristics estimation unit 22 preliminarily calculates the braking coefficient Kbs for the reference road surface from the previously estimated braking coefficient Kbe, and stores the calculated braking coefficient Kbs in the tire characteristics storage unit 24. The tire characteristics reading unit 25 inputs the braking coefficient Kbs for the reference road surface stored in the tire characteristics storage unit 24.

As described in the first embodiment, when estimating the braking torque, etc., the braking torque etc. estimator 26 receives the braking coefficient Kb, which is a tire characteristic, from the tire characteristic reader 25. In this embodiment, the braking torque etc. estimator 26 receives the braking coefficient Kbs for the reference road surface from the tire characteristic reader 25 and calculates the braking coefficient Kb according to equation (46). A value according to the road surface conditions is used as the conversion coefficient c.
Kb=Kbs/c...(46)
That is, the braking torque estimating unit 26 calculates the braking coefficient Kb (the braking coefficient when braking the vehicle 10) from the braking coefficient Kbs on the reference road surface, taking into account the influence of the road surface conditions using the conversion coefficient c.

The braking torque estimation unit 26 estimates braking torque, etc. in the same manner as in Example 1, using the braking coefficient Kb calculated using equation (46).

According to this embodiment, braking torque and other parameters can be estimated with greater accuracy by taking into account tire characteristics (braking coefficient Kb), which change depending on road surface conditions.

This section describes a braking torque estimation device according to Example 4 of the present invention.

In Example 1, as shown by line 31 in Figure 3, there is a linear relationship between the slip ratio and the friction coefficient when the absolute value of the slip ratio is small, and the proportionality coefficient of this relationship is used as the braking coefficient Kb (tire characteristic). In other words, in Example 1, tire characteristics in the linear region are obtained.

In this example, we will explain how to determine tire characteristics, including when the relationship between slip ratio and friction coefficient is nonlinear (nonlinear region). That is, we will explain how to determine tire characteristics (the relationship between slip ratio and friction coefficient) in Figure 3, including when the relationship between slip ratio and friction coefficient is expressed by a line other than straight line 31.

Figure 5 is a block diagram showing the configuration of a braking torque estimation device 20 according to a fourth embodiment of the present invention. The braking torque estimation device 20 according to this embodiment differs from the braking torque estimation device 20 according to the first embodiment (Figure 2) in that it includes a tire characteristic map 28 and does not include a tire characteristic estimation unit 22, a tire characteristic storage unit 24, or a tire characteristic reading unit 25.

The tire characteristic map 28 records tire characteristics, including nonlinear regions, i.e., data on the relationship between slip ratio and friction coefficient shown by curve 30 in the graph of Figure 3, taking into account the influence of tire type, road surface conditions, etc. (for each tire type and road surface conditions). The tire characteristic map 28 is created in advance and stored in the braking torque estimation device 20.

The braking torque etc. estimator 26 acquires road surface conditions, inputs data corresponding to the road surface conditions from the data recorded in the tire characteristic map 28, and performs numerical calculations to determine tire characteristics including those in the nonlinear region. The braking torque etc. estimator 26 then uses numerical analysis to determine the slip ratio λi that simultaneously satisfies equations (3) and (4). In this way, the braking torque etc. estimator 26 can estimate braking torque etc., including tire characteristics in the nonlinear region.

According to this embodiment, braking torque and other parameters can be calculated taking into account tire characteristics not only in the linear region but also in the nonlinear region. This allows braking torque and other parameters to be estimated with high accuracy, even when the braking force is large and the relationship between the slip ratio and the friction coefficient is nonlinear, further improving the control accuracy of the vehicle 10.

This section describes a braking torque estimation device according to a fifth embodiment of the present invention.

In this embodiment, conditions are defined for the braking torque etc. estimation unit 26 described in the first to fourth embodiments to estimate the braking torque etc. For example, the braking torque etc. estimation unit 26 estimates the braking torque etc. only when any one condition, any plurality of conditions, or all of the following six conditions are satisfied:
1. The acceleration (longitudinal acceleration) of the vehicle 10 is within a preset range.
2. The wheel speed Vwi is within a preset range and the vehicle 10 is traveling straight ahead.
3. The road surface on which the vehicle 10 is traveling is in a preset condition (or the road surface condition is the same as when the braking coefficient Kb was estimated).
4. The regenerative braking torque (driving torque) generated by the electric motor is smaller than a preset threshold value.
5. The engine brake torque (driving force torque) generated by the internal combustion engine is smaller than a preset threshold value.
6. The brake device 9 is in operation or in operation.

The braking torque estimation unit 26 estimates braking torque etc. only when at least one of these six conditions is met, allowing for highly accurate estimation of braking torque etc. for the following reasons.

Condition 1 will now be described. When the tire characteristics are in a linear range (for example, the range represented by the straight line 31 in FIG. 3 ), that is, when the driving torque (regenerative braking torque or engine braking torque) is not large, braking torque and the like can be estimated with high accuracy. Therefore, braking torque and the like are estimated when the acceleration of the vehicle 10 is within a predetermined range and the driving torque is not large. As the predetermined range, for example, the upper limit of acceleration (including deceleration) can be set so that the deceleration is 4 m/s² or ^less .

On the other hand, when it is desired to calculate only the braking torque by the brake device 9, it is necessary to subtract the driving torque (regenerative braking torque or engine braking torque) from the estimated braking torque Tbi, as described in Example 1. Therefore, by adding the conditions that the brake device 9 is operating (Condition 6) and the deceleration is 1 m/ ^s2 or more (Condition 1), the influence of the driving torque can be reduced and the braking torque by the brake device 9 can be estimated with high accuracy.

Explain condition 2.

Many wheel speed sensors 1 use a method that reads pulses from the rotating shaft. As a result, wheel speed sensors 1 have poor measurement accuracy at low speeds, and their detection accuracy for wheel angular velocity ωi is also poor at low speeds. Taking this into consideration, a condition is added that the wheel speed Vwi must be within a predetermined range (e.g., 20 km/h or higher). Furthermore, because the effects of air resistance increase at high speeds, a condition that the wheel speed Vwi must be within a predetermined range (e.g., 60 km/h or lower) can be added to reduce the effects of air resistance. The effect of air resistance is shown in the second term on the right-hand side of equation (10), but the air resistance calculated using equation (10) contains an error. By adding a condition that sets an upper limit for wheel speed Vwi (e.g., 60 km/h), the effect of any error in the calculated air resistance can be reduced.

The condition that the vehicle 10 is traveling straight is a condition to eliminate the influence of the vehicle 10 turning. When the vehicle 10 is turning, as explained in Example 2, it is necessary to convert the tire load Fzi and wheel speed Vwi due to the influence of steering (Equations (37)-(40), (41)-(44)). Because the values obtained by this conversion contain errors, a condition that the vehicle 10 is not turning, i.e., the vehicle 10 is traveling straight, is added.

Explain condition 3.

Even if the road surface conditions are represented by the same information, the actual condition of the road surface on which the vehicle 10 is traveling may vary depending on the road surface. For example, even if the road surface conditions are wet, the actual wetness of the road surface may vary depending on the road surface, and the friction coefficient may also vary depending on the road surface. For this reason, by limiting the road surface conditions to specific road surface conditions (e.g., dry roads), it is possible to avoid a deterioration in the estimation accuracy of braking torque, etc. Furthermore, by estimating braking torque, etc. under the same road surface conditions as when the braking coefficient Kb was estimated, it is possible to prevent a deterioration in the estimation accuracy of braking torque, etc. due to differences in road surface conditions.

Explain conditions 4 and 5.

The condition that regenerative braking torque or engine braking torque (driving torque) is smaller than a predetermined threshold value is a condition used when estimating braking torque by the brake device 9. Torque by an electric motor (regenerative braking torque) and torque by an internal combustion engine (engine braking torque) cannot always be estimated accurately. Therefore, by estimating braking torque when these driving torques are smaller than a predetermined threshold value, it is possible to accurately estimate braking torque by the brake device 9 even if the estimation accuracy of the driving torque is poor. For example, in a vehicle 10 with an internal combustion engine, if the engine speed is low and the engine braking torque is smaller than a predetermined threshold value, the impact on the estimation of braking torque by the brake device 9 can be reduced even if the estimation accuracy of the engine braking torque is poor.

Explain condition 6.

The condition that the brake device 9 is not operating is a condition when calculating the regenerative brake torque or engine brake torque. When the brake device 9 is not operating, no braking torque is generated by the brake device 9. Therefore, the estimated braking torque Tbi is set as the regenerative brake torque or engine brake torque, and these drive torques can be estimated with high accuracy. The condition that the brake device 9 is operating is a condition when calculating the braking torque by the brake device 9.

The above conditions 1-6 enable the braking torque estimation unit 26 to estimate braking torque, etc. with high accuracy.

Furthermore, like the braking torque etc. estimation unit 26, the tire characteristic estimation unit 22 may estimate tire characteristics only when any one, any plurality of, or all of the six conditions above are satisfied. This enables the tire characteristic estimation unit 22 to estimate tire characteristics with high accuracy.

In this embodiment, an example will be described in which the braking torque Tbi calculated in Examples 1-5 is used for brake control. The controller 5 brakes the brake device 9 of the vehicle 10 using the value of the braking torque Tbi estimated by the braking torque estimation device 20, etc. In the following, as an example, an example will be described in which the brake device 9 is an electric brake device controlled by a motor. The controller 5 is equipped with a brake control device, which will be described later, and controls the brake device 9 using the value of the braking torque Tbi, etc.

Figure 6 shows the configuration of the brake device 9. The brake device 9 mainly comprises a disc rotor 42, a housing 44, brake pads 45a and 45b, a piston 46, a rotary-to-linear motion conversion mechanism 50, and an electric motor 48.

The disc rotor 42 is a rotating member that rotates together with the wheel 7, and when pressed from both sides by the brake pads 45a and 45b, frictional force stops the rotation of the wheel 7.

The housing 44 is a member supported by a carrier (not shown) fixed to a non-rotating portion of the vehicle 10 located inside the disc rotor 42, allowing it to move in the axial direction of the disc rotor 42.

Brake pads 45a and 45b are pressing members arranged on both sides of the disc rotor 42, which press against the disc rotor 42 to apply braking force to the wheel 7.

The piston 46 is installed in the housing 44 so that it can move linearly, and can apply thrust to the brake pads 45a and 45b.

The rotary-to-linear motion conversion mechanism 50 converts the rotational force of the electric motor 48 into linear force, moving the piston 46 in the linear direction.

The electric motor 48 drives the piston 46 via the rotary-to-linear motion conversion mechanism 50, applying thrust to the brake pads 45a, 45b. The output shaft of the electric motor 48 is connected to a reducer 49, and the output shaft of the reducer 49 is connected to the rotary-to-linear motion conversion mechanism 50.

When thrust is applied by the electric motor 48, the brake pads 45a, 45b press against both sides of the disc rotor 42, which rotates together with the wheel 7, and this pressing force applies a braking force to the wheel 7, braking the vehicle 10.

In this embodiment, the brake caliper 43 of the brake device 9 includes a disc rotor 42, a housing 44, brake pads 45a and 45b, a piston 46, an electric motor 48, a reducer 49, and a rotary-to-linear motion conversion mechanism 50. The rotary-to-linear motion conversion mechanism 50 and the piston 46 constitute a linear motion part.

The electric motor 48 is controlled by a brake control device 51 provided in the controller 5.

A control signal line 61 and communication lines 62 and 63 are connected to the brake control device 51. The control signal line 61 is a signal line that inputs control commands from a higher-level control device, such as a vehicle control ECU (Electronic Control Unit), to the brake control device 51. The communication lines 62 and 63 are signal lines that transmit information other than these control commands to the higher-level control device. Furthermore, a control signal line 52 is connected to the brake control device 51. The control signal line 52 is a signal line that inputs control commands from the brake control device 51 to the brake device 9.

The brake control device 51 controls the brake device 9. The brake control device 51 receives a braking torque command Tbir from a higher-level control device (e.g., a vehicle control ECU) or receives a braking torque command Tbir corresponding to the amount of brake pedal operation, etc., and applies a current (command current) to the electric motor 48 based on the detection values of the motor current detection unit (current sensor) and the motor position detection unit (motor position sensor) in accordance with a preset control program, etc.

Note that while Figure 6 shows an example in which the upper control device and the brake control device 51 are configured separately, the upper control device and the brake control device 51 may also be integrated and provided in the controller 5.

The brake control device 51 is connected to the braking torque estimation device 20 according to this embodiment.

Figure 7 shows the braking torque estimation device 20 connected to the brake control device 51. The brake control device 51 inputs the braking torque command Tbir from a higher-level control device or in response to the amount of brake pedal operation, etc., and the braking torque Tbi estimated by the braking torque estimation device 20, and uses these values to generate and output a command to the brake device 9.

The brake control device 51 performs feedback control to control the brake device 9 so that the estimated braking torque Tbi approaches the braking torque command Tbir.

In this embodiment, an example has been described in which the brake device 9 is an electric brake device controlled by a motor, but the brake device 9 may also be a hydraulic brake device equipped with a control valve that controls pressure. Even when the brake device 9 is a hydraulic brake device, it is possible to implement control similar to that of an electric brake device.

According to this embodiment, feedback control is possible so that the estimated braking torque Tbi becomes the commanded braking torque (braking torque command Tbir) without the need for a thrust sensor (for example, a sensor that measures the force pressing the brake pads 45a, 45b against the disc rotor 42), making it possible to control the braking torque with high precision at low cost.

In this embodiment, as in Example 6, an example will be described in which the braking torque Tbi calculated in Examples 1-5 is used for brake control.

In the method shown in Example 1, for example, the braking torque estimation device 20 estimates the braking torque Tbi when the tire characteristics are in a linear range (for example, the range represented by the straight line 31 in Figure 3) and the vehicle 10 is traveling straight. For this reason, depending on the tire characteristics and the traveling state of the vehicle 10, the braking torque estimation device 20 may have difficulty accurately estimating the braking torque Tbi.

In this embodiment, the brake control device 51 (Fig. 7) stores the current I of the electric motor 48 of the brake device 9 (Figs. 6 and 7) when the braking torque estimation device 20 estimates the braking torque Tbi, and controls the brake device 9 by using this current I to set the braking torque to the desired value. This current I is the value when the braking torque estimation device 20 estimates the braking torque Tbi, and can be obtained, for example, by a current sensor installed in the electric motor 48.

In general, braking torque Tb is approximately proportional to the current I minus the current value I0 used for friction in the brake device 9. This proportionality coefficient K is expressed as K = Tb/(I-I0). The current value I0 used for friction is the current value used for friction in mechanisms such as the rotary-to-linear motion conversion mechanism 50, and can be calculated, for example, from the current when the electric motor 48 is driven in a free-running state until the brake pads 45a, 45b come into contact with the disc rotor 42.

If the current value I0 is determined in advance through experiments, numerical simulations, etc., the brake control device 51 can determine the proportionality coefficient K from this current value I0, the stored current I, and the braking torque Tbi estimated by the braking torque estimation device 20. Then, by setting the command current Ir for driving the electric motor 48 to Ir = 1/K × Tbir + I0 for the braking torque command Tbir, which is the commanded braking torque, the brake control device 51 can set the braking torque to the desired value (i.e., the value of the braking torque command Tbir). The brake control device 51 controls the rotational position of the electric motor 48 to the desired position using the command current Ir, thereby setting the braking torque to the desired value.

In this embodiment, the brake device 9 can be controlled with greater precision regardless of tire characteristics or how the vehicle 10 is traveling.

In Example 7, an example was described in which the braking device 9 (Figure 6) was controlled by using the current of the electric motor 48 to set the braking torque to a desired value.

In this embodiment, an example is described in which the brake device 9 is controlled using the relationship between braking torque and the rotational position of the electric motor 48. When the rotational position of the electric motor 48 changes, the positions of the brake pads 45a and 45b change, causing a change in braking torque.

Figure 8 is a block diagram showing the configuration of the brake control device 51 in this embodiment. The brake control device 51 includes a braking torque position relationship creation unit 72, a braking torque position command conversion unit 67, and a position current control unit 74. The brake device 9 to which the brake control device 51 is connected includes a motor position sensor 92 installed in the electric motor 48 and the current sensor 91 described in Example 7.

The braking torque position relationship creation unit 72 stores the rotational position of the electric motor 48 of the brake device 9 when the braking torque estimation device 20 estimates the braking torque Tbi. This rotational position is the value when the braking torque estimation device 20 estimates the braking torque Tbi, and is obtained, for example, by a motor position sensor 92 installed on the electric motor 48. The braking torque position relationship creation unit 72 inputs the braking torque Tbi estimated by the braking torque estimation device 20 and can record the relationship between the braking torque Tbi and the stored rotational position of the electric motor 48 as a map. This allows the brake control device 51 to obtain the relationship between the braking torque and the rotational position of the electric motor 48.

The braking torque position command conversion unit 67 inputs the braking torque command Tbir, which is the commanded braking torque, and references the map recorded by the braking torque position relationship creation unit 72, which shows the relationship between the braking torque and the rotational position of the electric motor 48. When the braking torque position command conversion unit 67 inputs the braking torque command Tbir, it uses this map to convert the braking torque command Tbir into the rotational position of the electric motor 48.

The position current control unit 74 converts the rotational position of the electric motor 48 obtained by the braking torque position command conversion unit 67 into a command current that provides this rotational position. The position current control unit 74 then provides the converted command current to the electric motor 48 of the brake device 9.

In this embodiment, unlike Example 7, which controls the braking torque by controlling the value of the command current Ir, the braking torque is controlled based on the rotational position of the electric motor 48. In this embodiment, the command current is calculated from the rotational position of the electric motor 48, so the braking torque can be controlled without being affected by temperature without using a torque constant whose value changes with temperature, and the brake device 9 can be controlled with higher precision.

In Example 8, when the relationship between the braking torque and the rotational position of the electric motor 48 is always constant, the rotational position of the electric motor 48 can be controlled to the desired position using the command current Ir, thereby generating the desired value of braking torque. However, in reality, the value of the braking torque varies depending on the friction coefficient μp of the brake pads 45a, 45b. The friction coefficient μp is the friction coefficient between the brake pads 45a, 45b and the disc rotor 42, and is expressed primarily as a function of the temperature T of the brake pads 45a, 45b and the rotational speed v of the disc rotor 42. The rotational speed v is the relative speed between the brake pads 45a, 45b and the disc rotor 42.

In this embodiment, the change in braking torque associated with changes in temperature T and the change in braking torque associated with changes in rotational speed v are determined in advance through experiments, numerical simulations, etc. The brake control device 51 stores the previously determined change in braking torque associated with changes in temperature T and the change in braking torque associated with changes in rotational speed v.

The braking torque is calculated by multiplying the thrust generated by the electric motor 48 by the friction coefficient μp between the brake pads 45a, 45b and the disc rotor 42. Generally, the friction coefficient changes depending on the temperature and relative speed of the two contacting objects. Therefore, the brake control device 51 estimates or measures and stores the temperature T of the brake pads 45a, 45b and the rotational speed v of the disc rotor 42.

When the braking torque estimation device 20 estimates the braking torque Tbi, the brake control device 51 stores the temperature T of the brake pads 45a, 45b and the rotational speed v of the disc rotor 42. The brake control device 51 estimates the temperature T and rotational speed v based on records of how much the brake pads 45a, 45b and disc rotor 42 have operated up to now, or measures the temperature T and rotational speed v with a sensor, and then stores the temperature T and rotational speed v.

The brake control device 51 uses the change in braking torque that accompanies changes in the temperature T and rotational speed v that have been determined in advance to estimate the value of braking torque Tbi, taking into account changes in the friction coefficient μp (i.e., changes in the temperature T and rotational speed v).

In this embodiment, the brake device 9 can be controlled with greater precision according to the temperature T of the brake pads 45a, 45b and the rotational speed v of the disc rotor 42.

In Examples 1-9, an example was shown in which the vehicle 10 was a four-wheeled vehicle. In this example, an example will be described in which the vehicle 10 is a two-wheeled vehicle.

A vehicle 10 equipped with a braking torque estimation device 20 according to this embodiment includes, as in the case of a four-wheeled vehicle, a controller 5, a wheel speed sensor 1, an acceleration sensor 2, a gyro sensor 3, a steering angle sensor 4, wheels 7, a vehicle body 8, a brake device 9 that generates braking force, an internal combustion engine or electric motor that generates braking/driving force, a steering device, a suspension, etc. The controller 5 includes the braking torque estimation device 20 according to this embodiment and controls the internal combustion engine, the electric motor, the brake device 9, the steering device, the suspension, etc. The wheels 7 are provided at two locations, front and rear, of the vehicle body 8 and are equipped with tires.

As explained in Example 1, even when the vehicle 10 is a two-wheeled vehicle, equations (1)-(3) hold true. However, the subscript i is an identifier that distinguishes between the front and rear wheels 7 of the vehicle body 8, and represents either F, which indicates the front wheel, or R, which indicates the rear wheel. The total value of the tire longitudinal force Fxi for all wheels 7 (two wheels) can be calculated based on the longitudinal acceleration axse detected by the acceleration sensor 2, as in Example 1.

From these equations, the vehicle speed Vb, slip ratio λi, and tire longitudinal force Fxi can be obtained as equations (47) to (49), respectively.

If the front and rear wheels 7 have the same braking coefficient Kb (i.e., Kbi = Kb), equations (47)-(49) can be expressed as equations (50)-(52), respectively.

When the vehicle 10 is rear-wheel drive, the braking torque estimation unit 26 can calculate the vehicle speed Vb using equation (53) by assuming that the front wheel slip ratio λF is approximately zero.

Using equation (53), the braking torque estimation unit 26 can calculate the rear wheel slip ratio λR as shown in equation (54).

Using this slip ratio λR, the braking torque estimation unit 26 can calculate the rear wheel tire longitudinal force FxR according to equation (55).

The sum of the tire longitudinal forces Fxi for all wheels 7 can be calculated from the longitudinal acceleration axse (or the longitudinal acceleration ax of the vehicle 10) detected by the acceleration sensor 2, as in Example 1. If the vehicle 10 is a two-wheeled vehicle, the sum of the tire longitudinal forces Fxi is equal to the rear wheel tire longitudinal force FxR. The rear wheel tire longitudinal force FxR can be expressed, for example, by equation (56).

From the above, the braking torque estimation unit 26 can calculate the braking coefficient Kb using equation (57) based on equation (29).

The tire load estimation unit 21 can calculate the tire load Fzi (tire vertical force Fzi) using equations (58) and (59) based on equations (21) and (22).

As described above, the braking torque estimation device 20 according to Examples 1-9 can estimate braking torque with high accuracy at low cost, even when the vehicle 10 is a two-wheeled vehicle, and can also control the movement of the vehicle 10 with high accuracy at low cost.

The present invention is not limited to the above-described examples, and various modifications are possible. For example, the above-described examples have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to embodiments that include all of the described configurations. Furthermore, it is possible to replace part of the configuration of one example with the configuration of another example. It is also possible to add the configuration of another example to the configuration of one example. It is also possible to delete part of the configuration of each example, or to add or replace other configurations.

1...wheel speed sensor, 2...acceleration sensor, 3...gyro sensor, 4...steering angle sensor, 5...controller, 7...wheel, 8...vehicle body, 9, 9FL, 9FR, 9RL, 9RR...brake device, 10...vehicle, 11...brake pedal, 12...communication line, 13...electric wire, 14...power source, 20...braking torque estimation device, 21...tire load estimation unit, 22...tire characteristic estimation unit, 24...tire characteristic memory unit, 25...tire characteristic reading unit, 26...braking torque etc. estimation unit, 28...tire characteristic map, 30...curve showing relationship between slip ratio and friction coefficient, 31...straight line showing linear relationship between slip ratio and friction coefficient, 42...disc rotor, 43...brake caliper, 44...housing, 45a, 45b...brake pads, 46...piston , 48...electric motor, 49...reduction gear, 50...rotational-linear motion conversion mechanism, 51...brake control device, 52...control signal line, 61...control signal line, 62, 63...communication lines, 67...braking torque position command conversion unit, 72...braking torque position relationship creation unit, 74...position current control unit, 91...current sensor, 92...motor position sensor, ax...longitudinal acceleration, axse...longitudinal acceleration detected by acceleration sensor, Fxi...tire longitudinal force, Fzi...tire load (tire vertical force), Ii...wheel moment of inertia, Kb, Kbi...braking coefficient, mb...vehicle mass, Tbi...braking torque, Tbir...braking torque command, Vb...vehicle speed, Vwi...wheel speed, Vwsi...wheel speed measured by sensor, Ri...tire radius, ωi...wheel angular velocity, λi...slip ratio.

Claims (13)

It can be installed on a vehicle having multiple wheels with tires,
a braking torque calculation unit that calculates a braking torque of the wheel;
inputting the wheel speed of the wheel and the longitudinal acceleration of the vehicle, which is the acceleration in the longitudinal direction of the vehicle;
the braking torque calculation unit calculates a vehicle speed, a tire longitudinal force of the wheel, and a slip ratio of the wheel based on the wheel speed, the tire load of the wheel, the longitudinal acceleration, and the tire characteristics of the wheel, and calculates the braking torque based on the calculated tire longitudinal force.
A braking torque estimation device characterized by: a tire load estimation unit that calculates the tire load using the longitudinal acceleration,
The braking torque estimation device according to claim 1 . a tire characteristic estimation unit that determines a relationship between a slip ratio and a friction coefficient as the tire characteristic;
The braking torque estimation device according to claim 1 . the tire characteristic estimation unit calculates a braking coefficient, which is a proportional coefficient between the slip ratio and the friction coefficient, as the tire characteristic, and calculates the braking coefficient based on the longitudinal acceleration, the wheel speed, and the tire load when the vehicle is accelerating.
The braking torque estimation device according to claim 3 . The vehicle includes an electric motor or an internal combustion engine that generates a braking/driving force, and a brake device that generates a braking force,
The braking torque calculation unit
1) The longitudinal acceleration of the vehicle is within a preset range;
2) The wheel speed is within a preset range and the vehicle is traveling straight ahead;
3) The road surface on which the vehicle is traveling is in a predetermined condition;
4) the torque generated by the electric motor is less than a preset threshold;
5) the torque generated by the internal combustion engine is less than a predetermined threshold;
6) The brake device is in operation;
The braking torque is calculated when at least one of the six conditions is satisfied.
The braking torque estimation device according to claim 1 . The vehicle includes an electric motor or an internal combustion engine that generates a braking/driving force, and a brake device that generates a braking force,
the braking torque calculation unit calculates the braking torque by the brake device by subtracting the torque by the electric motor or the torque by the internal combustion engine from the calculated braking torque.
The braking torque estimation device according to claim 1 . The vehicle includes an electric motor or an internal combustion engine that generates a braking/driving force, and a brake device that generates a braking force,
The braking torque calculation unit obtains the torque by the electric motor or the torque by the internal combustion engine by setting the calculated braking torque to the torque by the electric motor or the torque by the internal combustion engine, or by subtracting the measured braking torque by the brake device from the calculated braking torque.
The braking torque estimation device according to claim 1 . When the vehicle is turning and traveling, the braking torque calculation unit calculates the braking torque using a lateral acceleration of the vehicle, a steering angle of the wheel, and the tire characteristic that depends on a sideslip angle when the vehicle is turning.
The braking torque estimation device according to claim 1 . It is connected to a brake control device that controls the brake device,
the brake device is an electric brake device installed on the vehicle and including an electric motor,
When calculating the braking torque, the brake control device stores at least one of a current of the electric motor and a rotational position of the electric motor.
The braking torque estimation device according to claim 1 . the tire characteristic estimation unit acquires information on the condition of a road surface on which the vehicle is traveling or weather information on the road on which the vehicle is traveling when calculating the tire characteristics;
The braking torque estimation device according to claim 3 . It is connected to a brake control device that controls the brake device,
the brake device is installed on the vehicle and includes brake pads and a disc rotor;
When calculating the braking torque, the brake control device stores the temperature of the brake pad and the rotational speed of the disc rotor.
The braking torque estimation device according to claim 1 . the vehicle is front-wheel drive or rear-wheel drive;
the tire characteristic estimation unit calculates, as the tire characteristic, a braking coefficient which is a proportional coefficient between the slip ratio and the friction coefficient, and calculates the braking coefficient based on the tire longitudinal force, the wheel speed, and the tire load when the vehicle is accelerating.
The braking torque estimation device according to claim 3 . the vehicle is four-wheel drive;
the tire characteristic estimation unit calculates a braking coefficient, which is a proportional coefficient between the slip ratio and the friction coefficient, as the tire characteristic, based on the longitudinal acceleration during acceleration of the vehicle, the ratio of driving forces of the front wheels and the rear wheels, the wheel speed, and the tire load.
The braking torque estimation device according to claim 3 .