WO2024122504A1 - Brake torque estimation device - Google Patents

Abstract

The present invention provides a brake torque estimation device capable of accurately estimating brake torque at low cost. A brake torque estimation device (20) according to the present invention can be installed in a vehicle (10) having a plurality of wheels (7) with tires, and comprises a brake torque calculation unit (26) that calculates a brake torque (Tbi) of the wheels (7). A wheel speed (Vwi) of the wheels (7) and a longitudinal acceleration (ax), which is acceleration in the longitudinal direction of the vehicle (10), are input to the brake torque estimation device (20). The brake torque calculation unit (26) calculates a vehicle speed (Vb), a tire longitudinal force (Fxi) of the wheels (7), and a slip rate of the wheels (7) on the basis of the wheel speed (Vwi), a tire load (Fzi) of the wheels (7), the longitudinal acceleration (ax), and tire characteristics of the wheels (7), and calculates the brake torque (Tbi) on the basis of the calculated tire longitudinal force (Fxi).

Description

Braking torque estimation device

The present invention relates to a braking torque estimation device that is used for vehicle motion control and estimates the braking torque of a vehicle.

In vehicle motion control, precise estimation of tire longitudinal force, slip ratio, vehicle speed, and braking torque makes it possible to control the actuators mounted on the vehicle more precisely. For example, when braking, the vehicle motion is controlled based on the 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 an issue of increased costs.

Another method for estimating tire longitudinal forces is to determine the slip ratio based on the difference between vehicle speed and wheel speed. This method has issues with the difficulty of eliminating steady-state error when estimating vehicle speed by integrating longitudinal acceleration, and the cost of adding sensors.

As a conventional technology for estimating braking force without using a vehicle speed or thrust sensor, for example, the technology described in Patent Document 1 has been proposed. The brake device described in Patent Document 1 includes a ground load estimation unit that estimates the ground load of the wheels, a front/rear braking force correction value calculation unit that estimates a front/rear braking force ratio from the angular velocity of the wheels during braking and the ground load and calculates a front/rear braking force correction value for controlling the braking force of the wheels 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 for reducing the left/right difference in the braking force of the wheels from the angular velocity of the wheels during braking, and a command value calculation unit that calculates a braking force command value based on a braking force target value, a front/rear braking force correction value, and a left/right braking force correction value.

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

JP 2010-70022 A

　Conventional technology has the problem that it is difficult to accurately estimate braking torque, and in particular, it is difficult to accurately estimate tire longitudinal force, slip ratio, and vehicle speed, which are necessary to estimate braking torque.

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

In the technology described in Non-Patent Document 1, the slip ratio is estimated by an observer from the wheel speed, its derivative, and the longitudinal acceleration. With this technology, the convergence of the estimation is guaranteed by using an observer, but there are issues in that the accuracy from moment to moment is not guaranteed and the derivative value of the wheel speed is required. In addition, it is unclear whether values other than the slip ratio can be estimated among those required for vehicle motion control.

As described above, with conventional technology, it is difficult to accurately estimate tire longitudinal forces, slip ratios, and vehicle speed, and therefore difficult to accurately estimate braking torque. In addition, the accuracy of braking torque estimation can be improved by using a braking torque sensor or thrust sensor, but in order to prevent increases in costs, there is a demand for accurate estimation of braking torque using only sensors that are typically 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 the longitudinal acceleration, which is the acceleration in the longitudinal direction of the vehicle. The braking torque calculation unit calculates the vehicle body speed, the tire longitudinal force of the wheels, and the slip ratio of the wheels based on the wheel speed, the tire load of the wheels, the longitudinal acceleration, and the tire characteristics of the wheels, and calculates the braking torque based on the calculated tire longitudinal force.

The present invention provides a braking torque estimation device that can estimate braking torque with high accuracy 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 a configuration of a braking torque estimation device according to a first embodiment; FIG. 4 is a diagram showing an example of the relationship between a slip ratio and a friction coefficient, which are tire characteristics. FIG. 4 is a diagram showing an example of the relationship between the slip ratio and the friction coefficient when the sideslip angle is changed. FIG. 11 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 a configuration of a brake device. FIG. 2 is a diagram showing 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 having multiple wheels with tires, and can estimate tire characteristics (e.g., braking coefficient) and tire load using the wheel speed of the wheels and the longitudinal acceleration of the vehicle, and can estimate vehicle speed, slip ratio, tire longitudinal force, and braking torque with high accuracy and at low cost using the estimated tire characteristics and tire load. Slip ratio, tire longitudinal force, braking torque, etc. vary depending on the brake device and tire, and fluctuate due to aging caused by 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 at low cost using only sensors that are generally equipped on a vehicle, without using a braking torque sensor or thrust sensor. Using the braking torque estimation device according to the present invention, vehicle motion can be controlled with high accuracy and at low cost.

Below, a braking torque estimation device according to an embodiment of the present invention will be described with reference to the drawings. Note that in the drawings used in this specification, identical or corresponding components are given 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.

FIG. 1 is a diagram showing an example of the 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 a braking force, a brake pedal 11, and a power source 14. Although not shown, the vehicle 10 also includes an internal combustion engine or electric motor that generates a 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, the electric motor, the brake device 9, the steering device, the suspension, etc. The controller 5 may be provided separately for each function it has, or may be provided separately as a higher-level controller and a lower-level controller. In this specification, multiple controllers separated in this way are collectively referred to as the controller 5. The controller 5 may be configured as a computer that has a calculation device such as a CPU, a main storage device such as a semiconductor memory, an auxiliary storage device, and hardware such as a communication device, and that performs overall control of the vehicle 10, and various functions are realized by the calculation device executing a program loaded into the main storage device.

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

The 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 points 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 the axle hub or the like and a fixed part installed on the 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 forward/backward direction (forward/backward 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 who drives the vehicle 10.

The brake devices 9 are, for example, electric brake devices, and are provided on each of the wheels 7 at four locations 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 the wheels 7, and various information about the outside world of the vehicle 10. The brake device 9 is driven by electricity supplied from a power source 14 via an electric wire 13.

The controller 5 has the function 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 described with reference to FIG. 2.

FIG. 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 suffix 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 suffix 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. The tire characteristics are values that indicate the relationship between the slip ratio and friction coefficient of the tire. An example of a tire characteristic is the braking coefficient Kbi, which is a proportional coefficient between the slip ratio and the friction coefficient, as described below. 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., 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 are collectively referred to as "braking torque etc." The braking torque etc. estimation unit 26 is also referred to as a braking torque calculation unit.

The method by which the braking torque estimation unit 26, which is the braking torque calculation unit, calculates the braking torque, etc. will be explained.

Figure 3 is a diagram showing an example of the relationship between the slip ratio and the friction coefficient, which are tire characteristics. In Figure 3, the horizontal axis is the slip ratio and the vertical axis is the friction coefficient, and the relationship between the two is represented by curve 30. It is generally known that the slip ratio and the friction coefficient have the relationship 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 by (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, when the slip ratio is positive, it indicates the friction coefficient during driving, and when the slip ratio is negative, it 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 friction coefficient increases as the slip ratio increases, but has the characteristic of reaching a peak at a certain slip ratio and then decreasing 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 friction coefficient, and this relationship is represented by the dashed straight 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 tire longitudinal force Fxi for all four wheels 7 is expressed by equation (4) based on the equation of motion of the vehicle 10, excluding the effects of gravity due to air resistance and the inclination 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 the occupants. The symbol Σ indicates the sum for the subscript i, that is, 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 the 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 indicates the pitch angle of the vehicle body 8, and g indicates the gravitational acceleration.

When the pitch angle θy is small, equation (5) can be approximated by equation (6). Therefore, when 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 formula (4) is expressed as formula (7) by adding a term for gravity.

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

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, as shown in equation (9).

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

In addition, if the effect of air resistance is taken into consideration when calculating the tire longitudinal force Fxi, the equation of motion (4) can be used to find the total tire longitudinal force Fxi for all wheels 7 (4 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 the braking torque, etc.), in equation (10), the most recently calculated value or the wheel speed Vwi is set to the vehicle speed Vb.

By using equation (9) or equation (10), the total tire longitudinal force 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).

If we solve equation (11) for vehicle speed Vb, we get 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 rate λi of each wheel, and the tire longitudinal force Fxi of each wheel can be calculated using the total tire longitudinal force Fxi of 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 value estimated by the tire load estimation unit 21 as the tire load Fzi of all wheels 7.

In the above explanation, we have described a 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 road surfaces with similar conditions, it can be assumed that there is no significant difference 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, the slip ratio λi of each wheel, and the tire longitudinal force Fxi of each wheel can be calculated by using a braking coefficient Kb that has the same value 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 is expressed by equation (18), ignoring running resistance.

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) as shown in 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 due to the brake device 9, the torque due to the electric motor in the electric vehicle, and the torque due to the internal combustion engine. The torque due to the electric motor is called regenerative braking torque, and the torque due to the internal combustion engine is called engine braking torque. The regenerative braking torque and the engine braking torque are called driving torque. The braking torque etc. estimation unit 26 can estimate these driving torques according to existing technology.

The braking torque estimation unit 26 can obtain 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.

In addition, 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.

In addition, when the brake device 9 is not in operation 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 the engine braking torque. In addition, when the braking torque by the brake device 9 is measurable, the braking torque etc. estimation unit 26 can obtain the regenerative braking torque or the engine braking torque by subtracting the measured value of the braking torque by the brake device 9 from the braking torque Tbi.

Next, a method for the tire load estimation unit 21 to calculate the tire load Fzi (tire vertical force Fzi) will be described. The tire load estimation unit 21 can calculate the tire load Fzi using a known method. As an example, the following describes a method for calculating the tire load Fzi when the vehicle 10 is traveling in a straight line.

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

Here, mb is the mass of the vehicle 10 including occupants, etc., 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 found using the longitudinal acceleration axse detected by the acceleration sensor 2 (see, for example, equations (4), (5), (6), and (8)).

The braking torque estimation unit 26 may use, as the tire load Fzi, a value obtained by actually measuring or calculating from the displacement of the suspension, etc., instead of 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 obtains 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 obtaining this braking coefficient Kb will be shown.

The tire characteristics shown in Figure 3 are known to be almost the same during braking and driving, except that the sign of the friction coefficient is different. Therefore, in this embodiment, a method for calculating the braking coefficient Kb during driving, which is when the vehicle 10 is accelerating, is shown.

We will explain an example in which the vehicle 10 accelerates in front-wheel drive. The driving force of the rear wheels is zero, and the braking force is also zero. Therefore, if we assume that the slip ratio λi (i is RL and RR) of the rear wheels is zero, the vehicle speed Vb can be calculated using equation (23) obtained 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).

If the driving force and braking force of the rear wheels are zero, the total tire longitudinal force Fxi for all four wheels 7 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.

By 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 detected by the acceleration sensor 2 (or the longitudinal acceleration ax of the vehicle 10), the four wheel speeds Vwi used in equations (24) and (25), and the tire loads FzFL and FzFR of the front wheels.

The above explanation is 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 known, and the slip rate λFL of the left front wheel and the slip rate λFR of the right front wheel can be found from equations (24) and (25), so the braking coefficient Kb can be found using equations (26) and (27).

Next, an example will be described in which the vehicle 10 is a four-wheel drive vehicle. It is assumed 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 is the driving force of the front wheels, FdxR is the driving force of the rear wheels, and γ is the ratio between them.

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

Similarly, the left rear wheel tire longitudinal force FxRL and the right rear wheel tire longitudinal 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 that Kbi=Kb).

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

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

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

In this manner, 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. The tire characteristic estimation unit 22 may also increase the accuracy of the damping coefficient Kb by averaging the damping coefficient Kb obtained by multiple estimations and setting the average 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. By using the braking torque estimation device 20 according to this embodiment, the 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, for example, the method of estimating the tire load Fzi differs from the case in which 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 travels while 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.

The wheel speed converted from each wheel speed to the longitudinal speed of the vehicle 10 at the sprung center of gravity is calculated by adding or subtracting the speed difference of each wheel based on the actual steering angle δ and yaw rate r caused by turning motion to each wheel speed. If the wheel speed measured by the 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 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. The same curve 30 as in Figure 3 is shown in Figure 4. As explained in Example 1, the braking coefficient Kb is the proportional coefficient between the slip ratio and the friction coefficient in the range where the absolute value of the slip ratio is small.

The braking coefficient Kb changes depending on the sideslip angle β when the vehicle 10 turns. As the sideslip angle β increases from zero, the change in the friction coefficient relative to the change in slip ratio becomes smaller in the range where the absolute value of the slip ratio is small. For this reason, the braking coefficient Kb, which is the proportional coefficient between the slip ratio and the friction coefficient, becomes smaller as the sideslip angle β increases. This braking coefficient Kb that 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 by 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 as the wheel speed Vwi, and can calculate the vehicle speed Vb, slip ratio λi, tire longitudinal force Fxi, and braking torque Tbi using equations (12)-(20).

In the first embodiment, the tire characteristics 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 by experiment, numerical simulation, or the like. By determining the relationship between the sideslip angle β and the damping coefficient Kb in this way in advance, the tire characteristics estimation unit 22 can also store this relationship as the damping coefficient Kb(β).

In addition, 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 by 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 10 is turning, and braking torque Tbi can be estimated with high accuracy and low cost 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 the first embodiment, an example was described in which it is acceptable to consider 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 to be approximately the same. In reality, tire characteristics change not only depending on the tire, but also on the condition of the road surface on which the vehicle 10 is traveling (hereinafter simply referred to as "road surface condition").

In this embodiment, an example will be described in which the tire characteristic estimation unit 22 estimates the tire characteristics (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 the first embodiment, 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. The road surface conditions are, for example, information on whether the road surface on which the vehicle 10 is traveling is a dry road, a wet road, or a snowy road. The tire characteristic estimation unit 22 acquires the road surface conditions, for example, from various sensors (for example, a front camera, etc.) equipped on the vehicle 10, or from a server connected to the vehicle 10 via the Internet. The tire characteristic estimation unit 22 can also acquire various information that affects 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), as road surface conditions. Such weather information and pavement information can be acquired together with position information using a map, etc.

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

The relationship between the damping coefficient Kbe estimated by the tire characteristic estimation unit 22 and the damping 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 removing the influence of the road surface condition, and its value varies depending on the road surface condition (environment). The conversion coefficient c is determined in advance according to the road surface condition, 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 on the reference road surface is found excluding the influence of the road surface conditions (environment) by multiplying the estimated braking coefficient Kbe by the conversion coefficient c according to equation (45). Since the influence of the road surface conditions has been removed from this braking coefficient Kbs, it can be considered as a braking coefficient specific to the tire.

The tire characteristics estimation unit 22 predetermines the braking coefficient Kbs on the reference road surface from the previously estimated braking coefficient Kbe, and stores the determined braking coefficient Kbs in the tire characteristics storage unit 24. The tire characteristics reading unit 25 inputs the braking coefficient Kbs on 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 inputs the braking coefficient Kb, which is a tire characteristic, from the tire characteristic reader 25. In this embodiment, the braking torque etc. estimator 26 inputs the braking coefficient Kbs on the reference road surface from the tire characteristic reader 25, and calculates the braking coefficient Kb according to equation (46). For the conversion coefficient c, a value according to the road surface conditions is used.
Kb = Kbs / c (46)
That is, the braking torque etc. 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 etc. estimation unit 26 estimates the braking torque etc. in the same manner as in Example 1, using the braking coefficient Kb calculated by equation (46).

According to this embodiment, the braking torque, etc. can be estimated with higher accuracy because it is possible to take into account the tire characteristics (braking coefficient Kb) that change depending on the road surface conditions.

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

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

In this embodiment, a method for determining tire characteristics is described, including cases where the relationship between the slip ratio and the friction coefficient is nonlinear (nonlinear region). That is, a method for determining tire characteristics (relationship between the slip ratio and the friction coefficient) is described, including cases where the relationship between the slip ratio and the friction coefficient is expressed by something other than the straight line 31 in FIG. 3.

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

The braking torque etc. estimation unit 26 acquires the 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 the tire characteristics including the nonlinear region. The braking torque etc. estimation unit 26 then uses numerical analysis to determine the slip ratio λi that simultaneously satisfies both equations (3) and (4). In this way, the braking torque etc. estimation unit 26 can estimate the braking torque etc. including the tire characteristics in the nonlinear region.

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

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. estimator 26 described in the first to fourth embodiments to estimate the braking torque etc. For example, the braking torque etc. estimator 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.
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), which is the 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 the braking torque etc. only when at least one of these six conditions is satisfied, and is therefore able to estimate the braking torque etc. with high accuracy for the following reasons.

Condition 1 will now be described. When the tire characteristics are in a linear range (for example, a range represented by a straight line 31 in FIG. 3), that is, in a range in which the driving torque (regenerative braking torque or engine braking torque) is not large, the braking torque, etc. can be estimated with high accuracy. For this reason, the braking torque, etc. 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 the acceleration (including the deceleration) can be determined 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 the embodiment 1. For this reason, by adding the conditions that the brake device 9 is in operation (condition 6) and the deceleration is ¹ m/s2 or more (condition 1), the influence of the driving torque is reduced, and the braking torque by the brake device 9 can be estimated with high accuracy.

Explain condition 2.

Wheel speed sensors 1 often use a method of reading pulses from a rotating shaft. For this reason, the wheel speed sensor 1 has poor measurement accuracy at low speeds, and the detection accuracy of the wheel angular speed ωi is also poor at low speeds. Taking this into consideration, a condition is added that the wheel speed Vwi is within a specified range (e.g., 20 km/h or higher). In addition, since the effect of air resistance increases at high speeds, a condition can also be added that the wheel speed Vwi is within a specified range (e.g., 60 km/h or lower) in order to reduce the effect of air resistance. Note that the effect of air resistance is shown in the second term on the right side of equation (10), but the air resistance calculated by equation (10) contains an error. By adding a condition that sets an upper limit value (e.g., 60 km/h) for the wheel speed Vwi, the effect can be reduced even if the calculated air resistance contains an error.

The condition that the vehicle 10 is traveling straight is a condition for removing the effects of the vehicle 10 turning. When the vehicle 10 is turning, as explained in the second embodiment, it is necessary to convert the tire load Fzi and the wheel speed Vwi due to the effects of steering (Equations (37)-(40), (41)-(44)). Since the values obtained by this conversion contain errors, a condition that the vehicle 10 is not turning, that is, 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 differ depending on the road surface. For example, even if the road surface conditions are wet, the actual wetness of the road surface may differ depending on the road surface, and the friction coefficient may also differ depending on the road surface. For this reason, by limiting the road surface conditions to a specific road surface condition (e.g., dry road), it is possible to avoid a deterioration in the estimation accuracy of the braking torque, etc. Furthermore, by estimating the braking torque, etc. under the same road surface conditions as when the braking coefficient Kb was estimated, it is possible to prevent the estimation accuracy of the braking torque, etc. from deteriorating due to differences in road surface conditions.

Explain conditions 4 and 5.

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

Explain condition 6.

The condition that the brake device 9 is not in operation is a condition when calculating the regenerative brake torque or engine brake torque. When the brake device 9 is not in operation, 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 in operation is a condition for calculating the braking torque by the brake device 9.

The above conditions 1-6 allow the braking torque estimation unit 26 to estimate the 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 condition, any multiple conditions, or all of the above six conditions 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 the embodiments 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 described later, and controls the brake device 9 using the value of the braking torque Tbi, etc.

FIG. 6 is a diagram showing the configuration of the brake device 9. The brake device 9 includes, as its main components, a disc rotor 42, a housing 44, brake pads 45a and 45b, a piston 46, a rotary-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, 45b, frictional force stops the rotation of the wheel 7.

The housing 44 is a member supported on a carrier (not shown) that is fixed to a non-rotating part of the vehicle 10 located inside the vehicle 10 relative to the disc rotor 42, so that it can move in the axial direction of the disc rotor 42.

The brake pads 45a, 45b are pressing members arranged on both sides of the disc rotor 42, and press the disc rotor 42 to apply a 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-linear motion conversion mechanism 50, providing thrust to the brake pads 45a, 45b. The output shaft of the electric motor 48 is connected to the reducer 49, and the output shaft of the reducer 49 is connected to the rotary-linear motion conversion mechanism 50.

When the electric motor 48 applies thrust to the brake pads 45a, 45b, they press against both sides of the disk rotor 42 that rotates together with the wheel 7, and this pressure exerts a braking force on the wheel 7, braking the vehicle 10.

In this embodiment, the brake caliper 43 of the brake device 9 includes a disk rotor 42, a housing 44, brake pads 45a, 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 form a linear motion section.

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

Note that while FIG. 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 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.

FIG. 7 is a diagram showing the braking torque estimation device 20 connected to the brake control device 51. The brake control device 51 inputs a braking torque command Tbir from a higher-level control device or according to the amount of brake pedal operation, etc., and a braking torque Tbi estimated by the braking torque estimation device 20, and generates and outputs a command to the brake device 9 using these values.

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

In the present 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, even without a thrust sensor (e.g., a sensor that measures the force pressing the brake pads 45a, 45b against the disc rotor 42), feedback control is possible so that the estimated braking torque Tbi becomes the commanded braking torque (braking torque command Tbir), and the braking torque can be controlled with high accuracy at low cost.

In this embodiment, as in embodiment 6, an example is described in which the braking torque Tbi calculated in embodiments 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 FIG. 3) and the vehicle 10 is traveling straight ahead. 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 in 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 a 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 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 obtained in advance by an experiment, a numerical simulation, or the like, the brake control device 51 can obtain a 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, the brake control device 51 can set the braking torque to a desired value (i.e., the value of the braking torque command Tbir) by setting the command current Ir for driving the electric motor 48 to Ir = 1/K x Tbir + I0 for the braking torque command Tbir, which is the commanded braking torque. The brake control device 51 controls the rotational position of the electric motor 48 to a desired position using the command current Ir, and sets the braking torque to the desired value.

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

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

In this embodiment, an example is described in which the brake device 9 is controlled using the relationship between the 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, and the braking torque changes.

FIG. 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 the seventh embodiment.

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 acquired, 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 in a map. This allows the brake control device 51 to acquire 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 refers to the map that is recorded by the braking torque position relationship creation unit 72 and indicates 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 the seventh embodiment in which the braking torque is controlled 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 that the braking torque can be controlled without being affected by temperature without using a torque constant whose value changes with temperature, and therefore the brake device 9 can be controlled with higher precision.

In the eighth embodiment, 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 a desired position by the command current Ir, thereby generating a braking torque of a desired value. 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 mainly 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 a change in temperature T and the change in braking torque associated with a change in rotational speed v are obtained in advance by experiments, numerical simulations, etc. The brake control device 51 stores the previously obtained change in braking torque associated with a change in temperature T and the change in braking torque associated with a change in rotational speed v.

The braking torque has a value obtained by multiplying the thrust force generated by the electric motor 48 by the friction coefficient μp between the brake pads 45a, 45b and the disc rotor 42. In general, the friction coefficient changes depending on the temperature and relative speed of the two objects in contact. 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 the rotational speed v based on a record of how much the brake pads 45a, 45b and the disc rotor 42 have operated up to now, or measures the temperature T and the rotational speed v with a sensor, and stores the temperature T and the rotational speed v.

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

In this embodiment, the brake device 9 can be controlled with higher 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 the braking torque estimation device 20 according to this embodiment includes a controller 5, wheel speed sensor 1, acceleration sensor 2, gyro sensor 3, steering angle sensor 4, wheels 7, a vehicle body 8, a brake device 9 that generates a braking force, an internal combustion engine or electric motor that generates a braking/driving force, a steering device, a suspension, etc., just like a four-wheeled vehicle. 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.

Even if the vehicle 10 is a two-wheeled vehicle, formulas (1)-(3) hold, as explained in Example 1. However, the subscript i is an identifier that distinguishes between the wheels 7 at the front and rear of the vehicle body 8, and represents either F, which means the front wheel, or R, which means 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) assuming that the front wheel slip ratio λF is approximately zero.

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

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

The total tire longitudinal force 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 the first embodiment. If the vehicle 10 is a two-wheeled vehicle, the total tire longitudinal force Fxi coincides with the rear wheel tire longitudinal force FxR. The rear wheel tire longitudinal force FxR is 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) based on equations (21) and (22) as shown in equations (58) and (59).

As described above, the braking torque estimation device 20 according to Examples 1-9 can estimate the braking torque with high accuracy at low cost, even if the vehicle 10 is a two-wheeled vehicle, and can 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 an embodiment that includes all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment. It is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to delete part of the configuration of each embodiment, 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 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)

1. The vehicle may be mounted on a vehicle having a plurality of wheels provided with tires,
   a braking torque calculation unit that calculates a braking torque of the wheel;
   A wheel speed of the wheel and a longitudinal acceleration, which is an acceleration in a longitudinal direction of the vehicle, are inputted;
   the braking torque calculation unit calculates a vehicle body 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 a tire characteristic of the wheel, and calculates the braking torque based on the calculated tire longitudinal force.
   A braking torque estimation device comprising:
2. a tire load estimating unit that calculates the tire load using the longitudinal acceleration,
   The braking torque estimating device according to claim 1 .
3. a tire characteristic estimating unit that obtains a relationship between a slip ratio and a friction coefficient as the tire characteristic;
   The braking torque estimating device according to claim 1 .
4. the tire characteristic estimation unit obtains, as the tire characteristic, a damping coefficient which is a proportional coefficient between the slip ratio and the friction coefficient, and obtains the damping coefficient based on the longitudinal acceleration, the wheel speed, and the tire load when the vehicle is accelerating.
   The braking torque estimating device according to claim 3 .
5. 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 preset condition;
   4) the torque generated by the electric motor is less than a preset threshold;
   5) the torque from the internal combustion engine is less than a preset 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 estimating device according to claim 1 .
6. 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 estimation device according to claim 1 , wherein the braking torque calculation unit determines 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.
7. 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 as 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 estimating device according to claim 1 .
8. the braking torque calculation unit calculates the braking torque by using a lateral acceleration of the vehicle, a steering angle of the wheels, and the tire characteristic that depends on a sideslip angle when the vehicle is turning.
   The braking torque estimating device according to claim 1 .
9. 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 estimating device according to claim 1 .
10. the tire characteristic estimation unit acquires information on a road surface condition on which the vehicle is traveling or weather information on a road on which the vehicle is traveling when calculating the tire characteristics.
    The braking torque estimating device according to claim 3 .
11. It is connected to a brake control device that controls the brake device,
    The brake device is installed on the vehicle and includes a brake pad 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 estimating device according to claim 1 .
12. the vehicle is front-wheel drive or rear-wheel drive;
    the tire characteristic estimation unit calculates, as the tire characteristic, a damping coefficient which is a proportional coefficient between the slip ratio and the friction coefficient, and calculates the damping coefficient based on the tire longitudinal force, the wheel speed, and the tire load during acceleration of the vehicle.
    The braking torque estimating device according to claim 3 .
13. the vehicle is four-wheel drive;
    the tire characteristic estimation unit obtains, as the tire characteristic, a damping coefficient which is a proportional coefficient between the slip ratio and the friction coefficient, and obtains the damping coefficient based on the longitudinal acceleration during acceleration of the vehicle, a ratio of driving forces of the front wheels and the rear wheels, the wheel speed, and the tire load.
    The braking torque estimating device according to claim 3 .

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