Brake torque estimation device

Abstract

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

Description

Technical Field

[0001] The present invention relates to a braking torque estimation device for controlling the movement of a vehicle and estimating the braking torque of the vehicle. Background Art

[0002] In vehicle motion control, by accurately estimating the longitudinal and lateral tire forces, slip ratio, vehicle body speed, and braking torque, it is possible to more finely control the actuators mounted on the vehicle. The motion of the vehicle, for example during braking, is controlled based on the estimated braking torque. The braking torque is an important value for the performance of the vehicle and can be obtained from the longitudinal and lateral tire forces, slip ratio, and vehicle body speed. If a thrust sensor or the like is used to estimate the braking torque, although the estimation accuracy can be improved, there is a problem of increased cost.

[0003] In addition, as a method for estimating the longitudinal and lateral tire forces, there is a method of obtaining the slip ratio based on the difference between the vehicle body speed and the wheel speed. In this method, when integrating the longitudinal and lateral accelerations to estimate the vehicle body speed, there is a problem of difficulty in removing the steady-state deviation, and when additional sensors are added, there is a problem of cost.

[0004] As a prior art for estimating the braking force without using the vehicle body speed or thrust sensor, for example, the technique described in Patent Document 1 has been proposed. The braking device described in Patent Document 1 includes: a ground load estimation unit that estimates the ground load of the wheel; a longitudinal and lateral braking force correction value calculation unit that estimates the longitudinal and lateral braking force ratio based on the angular velocity of the wheel during braking and the ground load, and calculates a longitudinal and lateral braking force correction value for controlling the braking force of the wheel according to the longitudinal and lateral braking force ratio; a left and right braking force correction value calculation unit that calculates a left and right braking force correction value for reducing the left and right difference in the braking force of the wheel based on the angular velocity of the wheel during braking; and a command value calculation unit that calculates a braking force command value based on the braking force target value, the longitudinal and lateral braking force correction value, and the left and right braking force correction value.

[0005] In addition, a technique for estimating the slip ratio using an observer is described in Non-Patent Document 1. Prior Art Documents Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-70022 Non-Patent Document 1: 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 Summary of the Invention Problems to be Solved by the Invention

[0007] In the prior art, there is a problem that it is difficult to accurately estimate the braking torque, especially it is difficult to accurately estimate the longitudinal and lateral forces of the tire, the slip ratio, and the vehicle body speed required for estimating the braking torque.

[0008] In the technology described in Patent Document 1, the estimated ground load of the wheel is used to control the longitudinal and lateral braking forces, and the longitudinal and lateral forces of the tire are estimated when the left and right braking forces of at least one of the front wheels and the rear wheels are substantially equal. In this technology, it is difficult to estimate the longitudinal and lateral forces of the tire when there is a difference in the braking forces between the left and right wheels.

[0009] In the technology described in Non-Patent Document 1, the slip ratio is estimated by an observer based on the wheel speed, its differential value, and the longitudinal and lateral accelerations. In this technology, the convergence of the estimation is ensured by using an observer, but there are problems that the accuracy cannot be guaranteed at all times and the differential value of the wheel speed is required, and in addition, it is not clear whether values other than the slip ratio among the values required for vehicle motion control can be estimated.

[0010] Thus, in the prior art, there are problems that it is difficult to accurately estimate the longitudinal and lateral forces of the tire, the slip ratio, and the vehicle body speed, and it is difficult to accurately estimate the braking torque. In addition, if a braking torque sensor or a thrust sensor is used, the estimation accuracy of the braking torque can be improved, but in order to prevent an increase in cost, it is necessary to accurately estimate the braking torque using only the sensors generally equipped on the vehicle without using these sensors.

[0011] An object of the present invention is to provide a braking torque estimation device that can accurately estimate the braking torque at low cost. Technical Means for Solving the Problems

[0012] The braking torque estimation device of the present invention can be provided on a vehicle having a plurality of wheels provided with tires, and the braking torque estimation device includes: a braking torque calculation unit that calculates the braking torque of the wheel and inputs the wheel speed of the vehicle and the longitudinal acceleration in the longitudinal direction of the vehicle, i.e., the longitudinal acceleration. The braking torque calculation unit calculates the vehicle body speed, the longitudinal and lateral forces of the tire of the wheel, the 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 longitudinal and lateral forces of the tire. Effects of the Invention

[0013] According to the present invention, it is possible to provide a braking torque estimation device that can accurately estimate the braking torque at low cost. Description of the Drawings

[0014] Figure 1 FIG. Figure 1 is a diagram showing a configuration example of a vehicle equipped with the braking torque estimation device according to Embodiment 1 of the present invention. Figure 2 FIG. is a block diagram showing the configuration of the braking torque estimation device according to Embodiment 1. Figure 3 FIG. Figure 2 is a diagram showing an example of the relationship between the slip ratio and the friction coefficient as tire characteristics. Figure 4 FIG. is a diagram showing an example of the relationship between the slip ratio and the friction coefficient when the sideslip angle changes. Figure 5 FIG. Figure 3 is a block diagram showing the configuration of the braking torque estimation device according to Embodiment 4 of the present invention. Figure 6 FIG. is a diagram showing the configuration of the braking device. Figure 7 FIG. Figure 4 is a diagram showing the braking torque estimation device connected to the braking control device. Figure 8 FIG. is a block diagram showing the configuration of the braking control device in Embodiment 8 of the present invention. DETAILED DESCRIPTION

[0015] The braking torque estimation device of the present invention can be provided on a vehicle that includes a plurality of wheels provided with tires, and can estimate tire characteristics (such as a braking coefficient) and a tire load using the wheel speed of the wheels and the longitudinal acceleration of the vehicle. The vehicle speed, slip ratio, longitudinal tire force, and braking torque can be estimated at low cost and with high accuracy using the estimated tire characteristics and tire load. The slip ratio, longitudinal tire force, braking torque, etc. vary individually due to the braking device and the tires, and change due to aging caused by wear of the braking device and the tires. In the braking torque estimation device of the present invention, without using a braking torque sensor or a thrust sensor, and only using sensors generally provided on the vehicle, the vehicle speed, slip ratio, longitudinal tire force, and braking torque can be estimated at low cost and with high accuracy. If the braking torque estimation device of the present invention is used, the movement of the vehicle can be controlled at low cost and with high accuracy.

[0016] Hereinafter, the braking torque estimation device according to an embodiment of the present invention will be described with reference to the drawings. In the drawings used in this specification, the same or corresponding components are denoted by the same reference numerals, and repeated descriptions of these components may be omitted. Embodiment 1

[0017] The braking torque estimation device according to Embodiment 1 of the present invention will be described.

[0018] Figure 1FIG. 0 is a diagram showing a configuration example of a vehicle 10 equipped with the braking torque estimation device of the present 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 braking device 9 that generates a braking force, a brake pedal 11, and a power source 14. In addition, although not shown, it includes an internal combustion engine or an electric motor that generates a braking driving force, a steering device, a suspension, and the like.

[0019] The controller 5 includes the braking torque estimation device of the present embodiment and controls the internal combustion engine, the electric motor, the braking device 9, the steering device, the suspension, and the like. The controller 5 may be separately provided according to each function it has, or may be divided into an upper controller and a lower controller. In this specification, such multiple controllers thus divided are also collectively referred to as the controller 5. In addition, the controller 5 may be constituted by a computer that includes hardware such as an arithmetic device such as a CPU, a main storage device such as a semiconductor memory, an auxiliary storage device, and a communication device, and uniformly controls the vehicle 10. By the arithmetic device executing a program loaded into the main storage device, various functions are realized.

[0020] In the following description, the description of well-known techniques such as the above configuration of the controller 5 may sometimes be omitted.

[0021] The wheels 7 are arranged at four positions, front, rear, left, and right, of the vehicle body 8 and are provided with tires. In the present embodiment, the vehicle 10 is a four-wheeled vehicle.

[0022] The wheel speed sensor 1, the acceleration sensor 2, the gyro sensor 3, and the steering angle sensor 4 are sensors generally equipped in the vehicle 10.

[0023] The wheel speed sensor 1 detects the rotational speed of the wheels 7 located at four positions of the vehicle body 8. The wheel speed sensor 1 may be constituted, for example, by a sensor that detects the relative rotational speed (wheel angular velocity) between a rotating part provided on an axle hub or the like and a fixed part provided on a knuckle or a brake bracket or the like.

[0024] The acceleration sensor 2 detects the acceleration acting on the center of gravity of the vehicle body 8, that is, the longitudinal acceleration (front-rear acceleration) and the lateral acceleration (lateral acceleration) of the vehicle 10.

[0025] The gyro sensor 3 detects the angular velocity of rotation around the center of gravity of the vehicle body 8, that is, the yaw rate.

[0026] The steering angle sensor 4 detects the rotation angle of the steering wheel or the steering angle of the wheels 7 generated by the steering of the driver driving the vehicle 10, that is, the steering angle.

[0027] The braking device 9 is, for example, an electric braking device, and is respectively provided on the wheels 7 at four positions of the vehicle body 8. That is, the vehicle 10 includes a braking device 9FL for the left front wheel, a braking device 9FR for the right front wheel, a braking device 9RL for the left rear wheel, and a braking device 9RR for the right rear wheel. These braking devices have the same structure as each other and are controlled by the controller 5. Hereinafter, these braking devices 9FL, 9FR, 9RL, and 9RR are collectively referred to as the braking device 9. In addition, the braking device 9 may not be an electric braking device but a hydraulic braking device.

[0028] The controller 5 sends a control signal corresponding to the operation of the brake pedal 11 to the braking device 9 via the communication line 12 according to the operation of the brake pedal 11 by the driver of the vehicle 10, the states of the vehicle 10 and the wheels 7, and various information about the outside of the vehicle 10. The braking device 9 is driven by the electric power supplied from the power source 14 via the electric wire 13.

[0029] The controller 5 has the function of the braking torque estimation device of the present embodiment, and brakes the vehicle 10 using the value of the braking torque estimated by the braking torque estimation device. Use Figure 2 The braking torque estimation device of the present embodiment will be described.

[0030] Figure 2 FIG. is a block diagram showing the configuration of the braking torque estimation device 20 of the present embodiment. The braking torque estimation device 20 includes: a tire load estimation unit 21, a tire characteristic reading unit 25, a braking torque and the like estimation unit 26, a tire characteristic estimation unit 22, and a tire characteristic storage unit 24.

[0031] The tire load estimation unit 21 calculates and estimates the tire load F zi . The tire load F zi is also referred to as the tire vertical force F zi . The method for the tire load estimation unit 21 to calculate the tire load F will be described later. zi

[0032] In addition, the subscript i is an identifier for distinguishing the wheels 7 at four positions of the vehicle body 8, and represents one of FL (left front wheel), FR (right front wheel), RL (left rear wheel), and RR (right rear wheel). In the following description, this subscript i is also used.

[0033] The tire characteristic reading unit 25 inputs the tire characteristics stored in the tire characteristic storage unit 24. This tire characteristic is a value representing the relationship between the slip ratio of the tire and the friction coefficient. As an example of the tire characteristic, as will be described later, the braking coefficient K, which is the proportional coefficient between the slip ratio and the friction coefficient, can be cited bi . The friction coefficient is the longitudinal force (tire longitudinal force F xi ​) Divide by the vertical force (tire load F zi or the vertical force of the tire F zi ) on the tire contact patch with the ground.

[0034] The braking torque estimation unit 26 uses the tire load F calculated by the tire load estimation unit 21 zi and the tire characteristics obtained by the tire characteristic reading unit 25 (for example, the braking coefficient K, which is the value representing the relationship between the slip ratio and the friction coefficient bi ), and calculates and estimates the longitudinal tire force, slip ratio, vehicle body speed, and braking torque. Hereinafter, the longitudinal tire force, slip ratio, vehicle body speed, and braking torque are collectively referred to as "braking torque and the like". In addition, the braking torque estimation unit 26 is also referred to as the braking torque calculation unit.

[0035] The method by which the braking torque calculation unit, i.e., the braking torque and the like estimation unit 26, calculates the braking torque and the like will be described.

[0036] Figure 3 is a diagram showing an example of the relationship between the slip ratio and the friction coefficient as tire characteristics. In Figure 3 , the horizontal axis is the slip ratio, the vertical axis is the friction coefficient, and their relationship is represented by the curve 30. It is known that the slip ratio and the friction coefficient are usually in the relationship as Figure 3 shown.

[0037] The slip ratio λ i is expressed by Equation (1) during braking.

[0038] [Formula 1]

[0039] Here, V b represents the vehicle body speed, and V wi represents the wheel speed. The vehicle body speed V b is the speed of the vehicle body 8 (the speed of the center of gravity of the vehicle body 8). The wheel speed V wi is the rotational speed of the wheel 7, which is obtained by (tire radius R i × wheel angular velocity ω i ) and can be detected by the wheel speed sensor 1.

[0040] The slip ratio λ i is expressed by Equation (2) during driving (acceleration).

[0041] [Formula 2]

[0042] In Figure 3 , when the slip ratio is positive, it represents the friction coefficient during driving, and when the slip ratio is negative, it represents the friction coefficient during braking. That is, in Figure 3In the curve graph, the upper right region represents the characteristics during driving, and the lower left region represents the characteristics during braking.

[0043] As Figure 3 shown, the friction coefficient has the following characteristics: it increases as the slip ratio increases, but reaches a peak at a certain slip ratio and then decreases as the slip ratio increases. When the absolute value of the slip ratio is small, there is a linear relationship between the slip ratio and the friction coefficient, and the relationship between the two is represented by the straight line 31 shown by the dashed line.

[0044] As described above, in the range where the absolute value of the slip ratio is small, the slip ratio and the friction coefficient have a proportional relationship. Therefore, this proportional coefficient is used as the braking coefficient K bi .

[0045] The longitudinal force F of the tire xi is obtained by Equation (3).

[0046] [Equation 3] F xi = K bi λ i F zi …(3)

[0047] Regarding the sum of all wheels 7 (4 wheels) of the longitudinal force F of the tire xi , if the influence of gravity caused by air resistance or the inclination of the vehicle 10 is removed, it is expressed by Equation (4) according to the equation of motion of the vehicle 10.

[0048] [Equation 4] ∑F xi = m b a x = m b a xse ···(4)

[0049] Here, a x is the longitudinal acceleration of the vehicle 10, a xse is the longitudinal acceleration acting on the center of gravity of the vehicle body 8 detected by the acceleration sensor 2, and m b is the mass of the vehicle 10 including the occupants, etc. The symbol ∑ represents the sum with respect to the subscript i, that is, the sum of all wheels 7 (4 wheels).

[0050] As shown in Equation (4), the longitudinal acceleration a of the vehicle 10 x can also be the value a detected by the acceleration sensor 2 xse . However, the longitudinal acceleration a of the vehicle 10 x can be accurately obtained by removing the gravitational acceleration component accompanying the pitching of the vehicle body 8 included in the longitudinal acceleration a xse . Therefore, the longitudinal acceleration a of the vehicle 10x can also be obtained using Equation (5). Here, θ y represents the pitch angle of the vehicle body 8, and g represents the acceleration due to gravity.

[0051] [Equation 5]

[0052] In the case where the pitch angle θ y is small, Equation (5) can be approximated by Equation (6). Therefore, when the pitch angle θ y is small, Equation (6), which is a linear approximation formula, can also be used instead of Equation (5).

[0053] [Equation 6] a x = a xse + gθ y …(6)

[0054] In addition, when the vehicle 10 is tilted at an inclination angle α, the terms of gravity are added to the equation of motion of Equation (4) and expressed by Equation (7).

[0055] [Equation 7] ∑F xi = m b a x - m b g sinα…(7)

[0056] In addition, if the pitch angle θ y and the inclination angle α are small, the longitudinal acceleration a x of the vehicle 10 is detected by the longitudinal acceleration sensor 2 and the longitudinal acceleration a xse is obtained by Equation (8).

[0057] [Equation 8] a x = a xse + g(θ y + α)…(8)

[0058] Then, the sum of all the wheels 7 (four wheels) of the longitudinal tire force F xi can be obtained by Equation (9) based on Equations (7) and (8) using the longitudinal acceleration a xse detected by the longitudinal acceleration sensor 2.

[0059] [Equation 9] ∑F xi = m b a xse + m b gθ y …(9)

[0060] Here, the pitch angle θy It can be calculated using the relationship between the longitudinal accelerations and the pitch rigidity.

[0061] In addition, when calculating the longitudinal forces F of the tires xi while taking into account the influence of air resistance, for example, using the equation of motion of Equation (4), the total value of the longitudinal forces F of all the wheels 7 (four wheels) is obtained as in Equation (10). xi

[0062] [Equation 10]

[0063] Here, A is the frontal projected area of the vehicle 10, C is the air resistance coefficient, and ρ is the density of the air. Since the vehicle body speed V b is the value to be obtained (the value included in the braking torque, etc.), in Equation (10), the value obtained in the nearest past or the wheel speed V wi is used as the vehicle body speed V b .

[0064] By using Equation (9) or Equation (10), the total value of the longitudinal forces F of the tires can be obtained with higher accuracy. xi

[0065] On the other hand, during braking, the total value of the longitudinal forces F of all the wheels 7 (four wheels) is expressed by Equation (11) by substituting Equation (1) into Equation (3). xi

[0066] [Equation 11]

[0067] When solving Equation (11) for the vehicle body speed V b , Equation (12) is obtained as the formula representing the vehicle body speed V b .

[0068] [Equation 12]

[0069] When substituting Equation (12) into Equation (1), Equation (13) is obtained as the formula representing the slip ratio λ of each wheel i .

[0070] [Equation 13]

[0071] When substituting Equation (13) into Equation (3), Equation (14) is obtained as the formula representing the longitudinal forces F of each wheel xi .

[0072] [Equation 14]

[0073] As described above, the vehicle body speed V b and the slip ratio λ of each wheel i and the front and rear forces F of the tires of each wheel xi can be obtained using the following (Equations (12) - (14)): the longitudinal acceleration a that can be detected by the acceleration sensor 2 xse the calculated total value of the front and rear forces F of the tires of all the wheels 7 xi and the tire load F of each wheel 7 zi (the vertical tire force F zi ), the braking coefficient K bi and the wheel speed V wi .

[0074] In addition, the braking torque estimation unit 26 uses the value input from the tire characteristic storage unit 24 by the tire characteristic reading unit 25 as the braking coefficient K bi and uses the value estimated by the tire load estimation unit 21 as the tire load F of all the wheels 7 zi .

[0075] In addition, in the above description, the case where the braking coefficient K bi is different among all the wheels 7 (four wheels) of the vehicle 10 has been described. In the case where it is considered that the four wheels 7 are traveling on a road surface in the same condition using the same tires, it can be assumed that the tire characteristics are not very different and the same braking coefficient K b represents the tire characteristics. If all the wheels 7 have the same braking coefficient K b , then Equations (12) - (14) are respectively expressed as Equations (15) - (17). Among them, ∑F zi is replaced by m b ×g.

[0076] [Equation 15]

[0077] [Equation 16]

[0078] [Equation 17]

[0079] That is, the vehicle body speed V b and the slip ratio λ of each wheel i and the front and rear forces F of the tires of each wheel xi can replace the braking coefficient K of each wheel bi and use the braking coefficient K with the same value for all the wheels 7b is obtained.

[0080] If the running resistance is ignored, the front and rear tire forces F during braking xi The relationship with the braking torque is expressed by Equation (18).

[0081] [Equation 18]

[0082] Here, I i represents the moment of inertia of the wheel 7, T bi represents the braking torque, R i represents the tire radius, ω i represents the angular velocity of the wheel. Additionally, there is a relationship of ω i ×R i =V wi relationship.

[0083] The braking torque T bi can be calculated as in Equation (19) according to Equation (18).

[0084] [Equation 19]

[0085] In Equation (19), if the inertia term is ignored due to its small value, Equation (20) is obtained as the formula representing the braking torque T bi formula.

[0086] [Equation 20] T bi =-F xi R i …(20)

[0087] Here, during deceleration, the front and rear tire force F xi is negative, and the braking torque T bi is positive.

[0088] The braking torque T bi includes the braking torque of the braking device 9, the torque of the motor of the electric vehicle, and the torque of the internal combustion engine. The torque of the motor is called the regenerative braking torque, and the torque of the internal combustion engine is called the engine braking torque. The regenerative braking torque and the engine braking torque are called the driving torques. The braking torque and other estimation unit 26 can estimate these driving torques according to the prior art.

[0089] The braking torque and other estimation unit 26 can obtain the braking torque of the braking device 9 by subtracting the driving torque (regenerative braking torque or engine braking torque) from the braking torque T bi .

[0090] In addition, when the regenerative braking torque and the engine braking torque are small enough compared to the braking torque of the braking device 9, the braking torque estimation unit 26 can use the value of the braking torque T bi as the value of the braking torque of the braking device 9.

[0091] In addition, when the braking device 9 is not operating and the braking device 9 does not generate a braking torque, the braking torque estimation unit 26 can use the value of the braking torque T bi as the value of the regenerative braking torque or the engine braking torque. In addition, when the braking torque of the braking device 9 can be measured, the braking torque estimation unit 26 can calculate the regenerative braking torque or the engine braking torque by subtracting the measured value of the braking torque of the braking device 9 from the braking torque T bi .

[0092] Next, a method for the tire load estimation unit 21 to calculate the tire load F zi (the tire vertical force F zi ) will be described. The tire load estimation unit 21 can calculate the tire load F zi using a known method. Hereinafter, as an example, a method for calculating the tire load F zi when the vehicle 10 is traveling straight will be described.

[0093] For example, if it is assumed that the loads on the left and right wheels are equal when there is no acceleration or deceleration, then in the case of straight running, the tire load F zi can be calculated by Equation (21) for the front wheels and by Equation (22) for the rear wheels.

[0094] [Equation 21]

[0095] [Equation 22]

[0096] Here, m b represents the mass of the vehicle 10 including the occupants and the like, L f represents the distance in the front-rear direction between the center of gravity position of the vehicle 10 and the front wheel axle, L r represents the distance in the front-rear direction between the center of gravity position of the vehicle 10 and the rear wheel axle, L bas represents the wheelbase (L bas = L f + L r ), and h yc represents the center of gravity height of the vehicle 10.

[0097] According to Equation (21) and Equation (22), the tire load F zi (the tire vertical force F zi) It is also possible to use the longitudinal acceleration a detected by the acceleration sensor 2 xse to calculate. The longitudinal acceleration a x is the longitudinal acceleration a detected by using the acceleration sensor 2 xse and obtained (for example, refer to Equations (4), (5), (6), and (8)).

[0098] In addition, the braking torque estimation unit 26 and the like may not use the value estimated by the tire load estimation unit 21, but use the value obtained by actual measurement or calculation based on the displacement of the suspension or the like as the tire load F zi .

[0099] 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 K bi as the tire characteristic. In this embodiment, it is assumed that all the wheels 7 have the same braking coefficient K b (i.e., K bi = K b ), and an example of obtaining this braking coefficient K b is shown.

[0100] It is known Figure 3 that the tire characteristics shown are approximately equal except for the different signs of the friction coefficients during braking and driving. Therefore, in this embodiment, a method of calculating the braking coefficient K b during vehicle acceleration, i.e., during driving, is shown.

[0101] Taking the case where the vehicle 10 accelerates by front-wheel drive as an example for explanation. The driving force of the rear wheels is zero, and the braking force is also zero. Therefore, if it is assumed that the slip ratio λ i (i is RL and RR) of the rear wheels is zero, then the vehicle speed V b can be calculated using Equation (23) obtained from Equation (2).

[0102] [Equation 23] V b = V wRL = V wRR …(23)

[0103] If Equation (23) is substituted into Equation (2), then the slip ratio λ FL of the left front wheel is obtained by Equation (24), and the slip ratio λ FR of the right front wheel is obtained by Equation (25).

[0104] [Equation 24]

[0105] [Equation 25]

[0106] The longitudinal force F of the left front tire xFL and the longitudinal force F of the right front tire xFR are represented by Equations (26) and (27) respectively according to Equation (3). The slip ratios λ FL and λ FR in Equations (26) and (27) use the slip ratios obtained from Equations (24) and (25).

[0107] [Equation 26] F xFL = K b λ FL F zFL …(26)

[0108] [Equation 27] F xFR = K b λ FR F zFR …(27)

[0109] In addition, if the driving force and braking force of the rear wheels are zero, the sum of the longitudinal forces F xi of all the wheels 7 (4 wheels) is represented by Equation (28).

[0110] [Equation 28] ∑F xi = F xFL + F xFR ···(28)

[0111] The sum of the longitudinal forces F xi on the left side of Equation (28) can be obtained using the longitudinal acceleration a xse detected by the acceleration sensor 2, as shown in Equation (4) and the like.

[0112] If Equations (26) and (27) are substituted into the right side of Equation (28) and Equation (28) is solved for the braking coefficient K b , Equation (29) is obtained.

[0113] [Equation 29]

[0114] That is, the braking coefficient K b can be calculated using the following: the longitudinal acceleration a xse (or the longitudinal acceleration a x ) of the vehicle 10, the wheel speeds V wi of the four wheels used in Equations (24) and (25), the tire loads F zFL and F zFR of the front wheels.

[0115] In the above description, an example in which the vehicle 10 is front-wheel drive is described. In the case where the vehicle 10 is rear-wheel drive, it is only necessary to replace the front wheels and the rear wheels in the above description.

[0116] In addition, if the driving force of each wheel is known, the longitudinal force F of the left front wheel tire xFL and the longitudinal force F of the right front wheel tire xFR are known. On the other hand, according to Equations (24) and (25), the slip ratio λ of the left front wheel FL and the slip ratio λ of the right front wheel FR are obtained. Therefore, the braking coefficient K can be obtained using Equations (26) and (27). b .

[0117] Next, an example in which the vehicle 10 is four-wheel drive is described. Assume that under four-wheel drive, the front-rear distribution of the driving force of the engine or motor on the wheel 7 can be detected or estimated by Equation (30).

[0118] [Equation 30]

[0119] Here, F dxF represents the driving force of the front wheels, F dxR represents the driving force of the rear wheels, and γ represents their ratio.

[0120] The longitudinal forces F of the front wheel tires xFL , F xFR are obtained by Equation (31) according to the equation of motion of the vehicle 10.

[0121] [Equation 31]

[0122] Similarly, the longitudinal force F of the left rear wheel tire xRL and the longitudinal force F of the right rear wheel tire xRR are obtained by Equation (32).

[0123] [Equation 32]

[0124] On the other hand, according to Equations (2) and (3), Equation (33) for the left front wheel (i = FL) is obtained, and Equation (34) for the left rear wheel (i = RL) is obtained (assuming K bi = K b ).

[0125] [Equation 33]

[0126] [Equation 34]

[0127] When solving for the vehicle body speed V and the braking coefficient K as unknowns from the simultaneous equations of Equations (33) and (34), Equation (35) is obtained as the formula representing the braking coefficient K. b and the braking coefficient K b The braking coefficient K represented by Equation (35) is obtained from Equation (33) for the left front wheel and Equation (34) for the left rear wheel. However, the braking coefficient K b can also be obtained from the formula for the right front wheel and the formula for the right rear wheel, or from the formula for the left front wheel and the formula for the right rear wheel, and the formula for the right front wheel and the formula for the left rear wheel. For example, if the braking coefficient K is obtained from the formula for the right front wheel and the formula for the right rear wheel

[0128] [Formula 35]

[0129] the braking coefficient K represented by Equation (35) b is obtained from Equation (33) for the left front wheel and Equation (34) for the left rear wheel. However, the braking coefficient K b can also be obtained from the formula for the right front wheel and the formula for the right rear wheel, or from the formula for the left front wheel and the formula for the right rear wheel, and the formula for the right front wheel and the formula for the left rear wheel. For example, if the braking coefficient K is obtained from the formula for the right front wheel and the formula for the right rear wheel b then Equation (36) is obtained.

[0130] [Formula 36]

[0131] As described above, the braking coefficient K b can be obtained from multiple formulas. Therefore, by taking the average value of the braking coefficient K obtained from multiple formulas (for example, the two formulas of Equation (35) and Equation (36)) as the value of the braking coefficient K b it is also possible to obtain the braking coefficient K b with higher accuracy. b

[0132] As described above, the tire characteristic estimation unit 22 calculates the braking coefficient K as the tire characteristic b (or the braking coefficient K bi ). In addition, the tire characteristic estimation unit 22 may also consider the change of the tire characteristics over time and estimate the braking coefficient K at every predetermined regular time b . In addition, the tire characteristic estimation unit 22 may also average the braking coefficient K obtained by multiple estimations b and use the averaged value as the value of the braking coefficient K b to improve the accuracy of the braking coefficient K b .

[0133] The tire characteristic storage unit 24 stores the tire characteristics obtained by the tire characteristic estimation unit 22. In this embodiment, the tire characteristic storage unit 24 stores the braking coefficient K b(or braking coefficient K bi ) as a tire characteristic.

[0134] The braking torque estimation device 20 of the present embodiment can use the wheel speed V of the wheel 7 of the vehicle 10 wi and the longitudinal and lateral accelerations a x (longitudinal and lateral accelerations a xse ) to estimate the braking coefficient K b (K bi ) and the tire load F zi (the vertical force on the tire F zi ) of the tire characteristics, and can use the estimated braking coefficient K b (K bi ), the tire load F zi to calculate the vehicle body speed V b , the slip ratio λ i , the longitudinal and lateral forces on the tire F xi and the braking torque T bi . The controller 5 uses these values calculated by the braking torque estimation device 20 to control the movement of the vehicle 10. If the braking torque estimation device 20 of the present embodiment is used, the braking torque can be estimated with low cost and high accuracy, and the movement of the vehicle 10 can also be controlled with low cost and high accuracy. Embodiment 2

[0135] The braking torque estimation device according to Embodiment 2 of the present invention will be described. In Embodiment 1, an example in which the vehicle 10 travels mainly in a straight line was described. In the present embodiment, a case where the vehicle 10 travels in a turn will be described. When the vehicle 10 travels in a turn, for example, the method of estimating the tire load F zi is different from the case where the vehicle 10 travels in a straight line. Hereinafter, a method for the tire load estimation unit 21 to calculate the tire load F zi in the case where the vehicle 10 turns will be described.

[0136] When the vehicle 10 turns, since the vehicle 10 generates a roll motion, the tire load F zi is represented by Expressions (37)-(40).

[0137] [Formula 37]

[0138] [Formula 38]

[0139] [Formula 39]

[0140] [Formula 40]

[0141] Here, D F represents the tread of the front wheel of the vehicle 10, D R represents the tread of the rear wheel of the vehicle 10, a y represents the lateral acceleration of the vehicle 10.

[0142] In addition, the wheel speed in the longitudinal direction of the vehicle 10, which is converted from each wheel speed to the position of the center of gravity above the spring, is obtained by adding and subtracting the speed differences of each wheel based on the actual steering angle δ and the yaw rate r generated by the turning motion to each wheel speed. If the wheel speed measured by the wheel speed sensor 1 is Vwsi, the wheel speed V after being converted to the longitudinal direction speed of the vehicle 10 at the position of the center of gravity above the spring wi is represented by Equations (41)-(44).

[0143] [Equation 41]

[0144] [Equation 42]

[0145] [Equation 43]

[0146] [Equation 44]

[0147] Figure 4 is a diagram showing an example of the relationship between the slip ratio and the friction coefficient when the sideslip angle β changes. In Figure 4 , the same curve 30 as Figure 3 is shown. As described in Embodiment 1, the braking coefficient K b 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.

[0148] The braking coefficient K b varies according to the sideslip angle β of the vehicle 10 during turning. When the sideslip angle β starts to increase from zero, in the range where the absolute value of the slip ratio is small, the change in the friction coefficient with respect to the change in the slip ratio becomes smaller. Therefore, the braking coefficient K b as the proportional coefficient between the slip ratio and the friction coefficient becomes smaller as the sideslip angle β increases. The braking coefficient K b that depends on the value of such a sideslip angle β b is denoted as K

[0149] The tire characteristic reading unit 25 inputs the braking coefficient K b as a function K of the sideslip angle β b(β). The sideslip angle β can be calculated using the steering angle (actual steering angle δ) and the vehicle body speed V b by existing methods.

[0150] When the braking coefficient K b is replaced with K b (β), and the wheel speed V after the input is converted to the longitudinal speed of the vehicle 10 at the center of gravity position above the spring wi (Equations (41)-(44)) is used as the wheel speed V wi at this time, the braking torque estimation unit 26 can calculate the vehicle body speed V using Equations (12)-(20) b , the slip ratio λ i , the front and rear tire forces F xi and the braking torque T bi .

[0151] In addition, in Embodiment 1, the tire characteristic estimation unit 22 obtains the braking coefficient K b (0) when the sideslip angle β is zero. Based on this braking coefficient K b (0), it is possible to obtain the change in the value of the braking coefficient K when the sideslip angle β changes from zero through experiments or numerical simulations, etc. b (i.e., the change in the value of the braking coefficient K b starting from K b (0)). Thus, if the relationship between the sideslip angle β and the braking coefficient K b is obtained in advance, the tire characteristic estimation unit 22 can also store this relationship as the braking coefficient K b (β).

[0152] In addition, the sideslip angle β1 is obtained when estimating the tire load F zi during a turn of the vehicle 10, and the braking coefficient K b (β1) corresponding to this sideslip angle β1 is obtained. Based on this braking coefficient K b (β1), the change in the value of the braking coefficient K when the sideslip angle β changes from β1 is obtained through experiments or numerical simulations, etc. b (i.e., the change in the value of the braking coefficient K b starting from K b (β1)), and the relationship between the sideslip angle β and the braking coefficient K b is obtained in advance. The tire characteristic estimation unit 22 can also store this relationship as the braking coefficient K b (β).

[0153] According to this embodiment, not only during straight running of the vehicle 10, but also during turning, it is possible to calculate tire characteristics (braking coefficient K b ), braking torque, etc. (vehicle body speed V b , slip ratio λi , the front and rear force F of the tire xi , and the braking torque T bi ), can estimate the braking torque T with low cost and high accuracy regardless of the driving state of the vehicle 10 bi . Embodiment 3

[0154] The braking torque estimation device according to Embodiment 3 of the present invention will be described.

[0155] In Embodiment 1, the braking coefficient K when estimated by the tire characteristic estimation unit 22 was described b and the braking coefficient K when estimated by the braking torque etc. estimation unit 26 b were regarded as being of the same degree and there was no problem. In fact, the tire characteristics vary not only according to the tire but also according to the condition of the road surface on which the vehicle 10 travels (hereinafter simply referred to as "road surface condition").

[0156] In the present embodiment, an example in which the tire characteristic estimation unit 22 estimates the tire characteristics (braking coefficient K b ) considering the road surface condition, and the tire characteristic reading unit 25 inputs the braking coefficient K from the tire characteristic storage unit 24 b will be described. As described in Embodiment 1, the tire characteristic estimation unit 22 calculates and estimates the braking coefficient K during driving (acceleration) b . The braking coefficient K estimated by the tire characteristic estimation unit 22 b is denoted as the braking coefficient K be .

[0157] When the tire characteristic estimation unit 22 estimates the braking coefficient K be , it acquires the road surface condition. The road surface condition is, for example, information on whether the road surface on which the vehicle 10 travels is a dry road, a wet road, a snowy road, etc. The tire characteristic estimation unit 22 acquires the road surface condition from various sensors (such as a front camera, etc.) provided in the vehicle 10 or a server connected to the vehicle 10 through a network, for example. In addition, the tire characteristic estimation unit 22 may also acquire various information that affects the friction coefficient of the road surface, such as information on the weather (weather information) on the road on which the vehicle 10 travels and information on the paving (paving information), as the road surface condition. Such weather information and paving information can be acquired together with the position information using a map, etc.

[0158] The braking coefficient on a pre-determined reference road surface is represented by K bs . The reference road surface can be any road surface, and it is preferable to determine a good road surface (such as a dry road, etc.) as the reference road surface, for example.

[0159] The braking coefficient K estimated by the tire characteristic estimation unit 22 beThe relationship with the braking coefficient K on the reference road surface is represented by the conversion coefficient c in Equation (45). bs The relationship with the braking coefficient K on the reference road surface is represented by the conversion coefficient c in Equation (45). K bs = c × K be ···(45) The conversion coefficient c is a coefficient used to eliminate the influence of road surface conditions, and its value varies according to road surface conditions (environment). The conversion coefficient c is determined in advance according to road surface conditions and stored in the tire characteristic storage unit 24.

[0160] The braking coefficient K estimated by the tire characteristic estimation unit 22 be is a value estimated under the conditions of a specific road surface on which the vehicle 10 travels. The braking coefficient K on the reference road surface bs is obtained by multiplying the estimated braking coefficient K be by the conversion coefficient c according to Equation (45) to eliminate the influence of road surface conditions (environment). Since this braking coefficient K bs excludes the influence of road surface conditions, it can be considered as the braking coefficient inherent to the tire.

[0161] The tire characteristic estimation unit 22 pre-estimates the braking coefficient K be to obtain in advance the braking coefficient K on the reference road surface bs , and stores the obtained braking coefficient K bs in the tire characteristic storage unit 24. The tire characteristic reading unit 25 inputs the braking coefficient K on the reference road surface stored in the tire characteristic storage unit 24 bs .

[0162] As described in Embodiment 1, when estimating the braking torque and the like, the braking torque and the like estimation unit 26 inputs the braking coefficient K as a tire characteristic from the tire characteristic reading unit 25 b . In this embodiment, the braking torque and the like estimation unit 26 inputs the braking coefficient K on the reference road surface from the tire characteristic reading unit 25 bs , and obtains the braking coefficient K b according to Equation (46). The conversion coefficient c uses a value corresponding to the road surface conditions. K b = K bs / c···(46) That is, the braking torque and the like estimation unit 26 uses the conversion coefficient c, considers the influence of road surface conditions, and calculates the braking coefficient K bs (the braking coefficient when braking the vehicle 10) according to the braking coefficient K on the reference road surface b .

[0163] The braking torque and the like estimation unit 26 uses the braking coefficient K calculated by Equation (46) b to estimate the braking torque and the like in the same manner as in Embodiment 1.

[0164] According to this embodiment, since it is possible to estimate braking torque, etc. in consideration of tire characteristics (braking coefficient K b ) that vary according to road surface conditions, braking torque, etc. can be estimated with higher accuracy. Embodiment 4

[0165] The braking torque estimation device according to Embodiment 4 of the present invention will be described.

[0166] In Embodiment 1, as shown by Figure 3 straight line 31, when the absolute value of the slip ratio is small, there is a linear relationship between the slip ratio and the friction coefficient. Therefore, the proportional coefficient of this relationship is used as the braking coefficient K b (tire characteristics). That is, in Embodiment 1, the tire characteristics in the linear region are obtained.

[0167] In this embodiment, a method for obtaining tire characteristics including a case where the relationship between the slip ratio and the friction coefficient is non-linear (non-linear region) will be described. That is, in Figure 3 , a method for obtaining tire characteristics (the relationship between the slip ratio and the friction coefficient) including a case where the relationship between the slip ratio and the friction coefficient is represented by a line other than straight line 31 will be described.

[0168] Figure 5 is a block diagram showing the configuration of the braking torque estimation device 20 according to Embodiment 4 of the present invention. The braking torque estimation device 20 of this embodiment is different from the braking torque estimation device 20 of Embodiment 1 ( 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, and a tire characteristic reading unit 25.

[0169] In the tire characteristic map 28, in consideration of the influence of factors such as the type of tire and the road surface condition (by tire type and road surface condition), data on the relationship between the slip ratio and the friction coefficient, which is the tire characteristic including the non-linear region, i.e., Figure 3 the data shown by curve 30 in the curve graph, is recorded. The tire characteristic map 28 is generated in advance and set in the braking torque estimation device 20.

[0170] The braking torque, etc. estimation unit 26 acquires the road surface condition, inputs the data corresponding to the road surface condition from the data recorded in the tire characteristic map 28, performs numerical calculations, and obtains the tire characteristics including the non-linear region. Then, the braking torque, etc. estimation unit 26 numerically analyzes to find the slip ratio λ that simultaneously satisfies formula (3) and formula (4) i . In this way, the braking torque, etc. estimation unit 26 can estimate braking torque, etc. including the tire characteristics in the non-linear region.

[0171] According to this embodiment, when calculating the braking torque and the like, not only the tire characteristics in the linear region but also the tire characteristics in the non-linear region can be considered. Therefore, it is possible to accurately estimate the braking torque and the like, including the case where the braking force is large and the relationship between the slip ratio and the friction coefficient is non-linear, and the control accuracy of the vehicle 10 can be further improved. Embodiment 5

[0172] The braking torque estimation device according to Embodiment 5 of the present invention will be described.

[0173] In this embodiment, conditions for the braking torque estimation unit 26 described in Embodiments 1 to 4 to estimate the braking torque and the like are defined. For example, the braking torque estimation unit 26 estimates the braking torque and the like 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 V wi is within a preset range and the vehicle 10 is traveling straight. 3. The road surface on which the vehicle 10 travels is in a preset condition (or the road surface condition is the same as when estimating the braking coefficient K b ). 4. The torque of the electric motor, i.e., the regenerative braking torque (driving torque), is less than a preset threshold value. 5. The torque of the internal combustion engine, i.e., the engine braking torque (driving force torque), is less than a preset threshold value. 6. The braking device 9 is in an operating state or a non-operating state.

[0174] When the braking torque estimation unit 26 estimates the braking torque and the like only when at least one of these six conditions is satisfied, the braking torque and the like can be accurately estimated for the following reasons.

[0175] Explanation of condition 1. When the tire characteristics are in the linear range (for example, Figure 3 the range shown by the straight line 31), that is, in the range where the driving torque (regenerative braking torque or engine braking torque) is not large, the braking torque and the like can be accurately estimated. Therefore, when the acceleration of the vehicle 10 is within the specified range and the driving torque is not large, the braking torque and the like are estimated. As the specified range, for example, as the deceleration is 4 m / s 2 or less, the upper limit value of the acceleration (including deceleration) can be determined.

[0176] On the other hand, when only the braking torque of the braking device 9 is to be calculated, as described in Embodiment 1, it is necessary to subtract from the estimated braking torque T biSubtract the driving torque (regenerative braking torque or engine braking torque). Therefore, by applying the condition that the braking device 9 is in operation (condition 6) and the deceleration is 1 m / s 2 or more (condition 1), the influence of the driving torque can be reduced, and the braking torque of the braking device 9 can be estimated with high precision.

[0177] An explanation of condition 2 will be given.

[0178] In the wheel speed sensor 1, a method of reading the pulses of the rotating shaft is mostly adopted. Therefore, the measurement accuracy of the wheel speed sensor 1 is poor at low speeds, and the detection accuracy of the wheel angular velocity ω i is also poor at low speeds. Considering this, the condition that the vehicle speed V wi is within a specified range (for example, 20 km / h or more) is added. In addition, if the speed is high, the influence of air resistance increases. Therefore, in order to reduce the influence of air resistance, the condition that the vehicle speed V wi is within a specified range (for example, 60 km / h or less) can also be added. In addition, the influence of air resistance is represented by the second term on the right side of Equation (10), but there is an error in the air resistance calculated by Equation (10). By adding the condition that determines the upper limit value (for example, 60 km / h) to the vehicle speed V wi , even if there is an error in the calculated air resistance, its influence can be reduced.

[0179] The condition that the vehicle 10 is traveling straight ahead is a condition for eliminating the influence caused by the turning of the vehicle 10. When the vehicle 10 turns, as described in Embodiment 2, due to the influence of steering, it is necessary to change the tire load F zi and the vehicle speed V wi (Equations (37)-(40), Equations (41)-(44)). Since the values obtained by this transformation contain errors, the condition that the vehicle 10 is not turning, that is, the condition that the vehicle 10 is traveling straight ahead, is added.

[0180] An explanation of condition 3 will be given.

[0181] Even if the road surface condition is represented by the same information, sometimes the actual condition of the road surface on which the vehicle 10 travels may be different depending on the road surface. For example, even if the road surface condition is a wet road surface, the actual wet condition of the road surface varies depending on the road surface, and the friction coefficient also varies depending on the road surface. Therefore, by limiting the road surface condition to a specific road surface condition (for example, a dry road), the deterioration of the estimation accuracy of the braking torque and the like can be avoided. In addition, by estimating the braking torque and the like under the same road surface condition as when estimating the braking coefficient K b , the deterioration of the estimation accuracy of the braking torque and the like due to the difference in the road surface condition can also be prevented.

[0182] Describe Conditions 4 and 5.

[0183] The condition that the regenerative braking torque or engine braking torque (driving torque) is less than a specified threshold value is a condition used when estimating the braking torque of the braking device 9. The torque of the electric motor (regenerative braking torque) and the torque of the internal combustion engine (engine braking torque) cannot necessarily be estimated with high precision. Therefore, by estimating the braking torque, etc. when these driving torques are less than the specified threshold value, even if the estimation accuracy of the driving torque is poor, the braking torque of the braking device 9 can be estimated with high precision. For example, in the case of the vehicle 10 having an internal combustion engine, when the engine speed is low and the engine braking torque is less than the specified threshold value, even if the estimation accuracy of the engine braking torque is poor, the influence on the estimation of the braking torque of the braking device 9 can be reduced.

[0184] Describe Condition 6.

[0185] The condition that the braking device 9 is in a non-operating state is a condition when calculating the regenerative braking torque or engine braking torque. If the braking device 9 is in a non-operating state, the braking torque of the braking device 9 is not generated. Therefore, by using the estimated braking torque T bi as the regenerative braking torque or engine braking torque, these driving torques can be estimated with high precision. In addition, the condition that the braking device 9 is in an operating state is a condition for calculating the braking torque of the braking device 9.

[0186] Based on the above Conditions 1 - 6, the braking torque estimation unit 26 can estimate the braking torque, etc. with high precision.

[0187] In addition, similar to the braking torque estimation unit 26, the tire characteristic estimation unit 22 can also estimate the tire characteristics only when any one condition, any multiple conditions, or all of the above 6 conditions are satisfied. Thus, the tire characteristic estimation unit 22 can estimate the tire characteristics with high precision. Embodiment 6

[0188] In this embodiment, an example of using the braking torque T calculated in Embodiments 1 - 5 for braking control is described. The controller 5 uses the braking torque T estimated by the braking torque estimation device 20 bi and the like to brake the braking device 9 of the vehicle 10. Hereinafter, as an example, an example in which the braking device 9 is an electric braking device controlled by a motor is described. The controller 5 includes a braking control device described later and controls the braking device 9 using the value of the braking torque T bi and the like. bi

[0189] Figure 6This is a diagram showing the configuration of the braking device 9. The braking device 9 includes 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 as main components.

[0190] The disc rotor 42 is a rotating member that rotates together with the wheel 7, and when pressed by the brake pads 45a and 45b from both sides, the rotation of the wheel 7 is stopped by the frictional force.

[0191] The housing 44 is a member that is supported on a bracket (not shown) so as to be movable in the axial direction of the disc rotor 42, and the bracket is fixed to a non-rotating part of the vehicle 10 located inside the vehicle 10 relative to the disc rotor 42.

[0192] The brake pads 45a and 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.

[0193] The piston 46 is linearly movably provided in the housing 44 and can apply a thrust force to the brake pads 45a and 45b.

[0194] The rotary-linear motion conversion mechanism 50 converts the rotational force of the electric motor 48 into a linear motion force and moves the piston 46 in the linear motion direction.

[0195] The electric motor 48 drives the piston 46 via the rotary-linear motion conversion mechanism 50 and applies a thrust force to the brake pads 45a and 45b. The output shaft of the electric motor 48 is connected to the speed reducer 49, and the output shaft of the speed reducer 49 is connected to the rotary-linear motion conversion mechanism 50.

[0196] When a thrust force is applied by the electric motor 48, the brake pads 45a and 45b press both side surfaces of the disc rotor 42 that rotates together with the wheel 7, and a braking force is applied to the wheel 7 by this pressing force to brake the vehicle 10.

[0197] In this embodiment, the brake caliper 43 of the braking device 9 includes a disc rotor 42, a housing 44, brake pads 45a and 45b, a piston 46, an electric motor 48, a speed reducer 49, and a rotary-linear motion conversion mechanism 50. The rotary-linear motion conversion mechanism 50 and the piston 46 constitute a linear motion part.

[0198] The electric motor 48 is controlled by the braking control device 51 provided in the controller 5.

[0199] A control signal line 61 and communication lines 62 and 63 are connected to the braking control device 51. The control signal line 61 is a signal line for inputting control commands from an upper control device such as a vehicle control ECU (Electronic Control Unit) to the braking control device 51. The communication lines 62 and 63 are signal lines for transmitting information other than the control commands to the upper control device. In addition, the braking control device 51 is connected to a control signal line 52. The control signal line 52 is a signal line for inputting a control command from the braking control device 51 to the braking device 9.

[0200] The braking control device 51 controls the braking device 9. The braking control device 51 inputs a braking torque command T from an upper control device (for example, a vehicle control ECU) bir , or inputs a braking torque command T corresponding to the operation amount of the brake pedal, etc. bir , and based on the detection value of the motor current detection unit (current sensor) or the detection value of the motor position detection unit (motor position sensor), supplies current (command current) to the electric motor 48 according to a preset control program, etc.

[0201] In addition, Figure 6 shows an example in which the upper control device and the braking control device 51 are separately configured, but the upper control device and the braking control device 51 may also be integrally provided on the controller 5.

[0202] The braking control device 51 is connected to the braking torque estimation device 20 of the present embodiment.

[0203] Figure 7 is a diagram showing the braking torque estimation device 20 connected to the braking control device 51. The braking control device 51 inputs a braking torque command T from an upper control device or corresponding to the operation amount of the brake pedal, etc. bir and the braking torque T estimated by the braking torque estimation device 20 bi , and uses these values to generate and output a command for the braking device 9.

[0204] The braking control device 51 performs feedback control in such a way that the estimated braking torque T bi approaches the braking torque command T bir to control the braking device 9.

[0205] In addition, in the present embodiment, an example in which the braking device 9 is an electric braking device controlled by a motor is described, but the braking device 9 may also be a hydraulic braking device having a control valve for controlling pressure. In the case where the braking device 9 is a hydraulic braking device, the same control as in the case of the electric braking device can also be implemented.

[0206] According to this embodiment, even without a thrust sensor (for example, a sensor that measures the force pressing the brake pads 45a, 45b against the disc rotor 42), it is possible to perform feedback control to make the estimated braking torque T bi become the indicated braking torque (braking torque command T bir ), and the braking torque can be controlled with high precision at low cost. Embodiment 7

[0207] In this embodiment, similar to Embodiment 6, an example of using the braking torque T bi calculated in Embodiments 1-5 for braking control will be described.

[0208] The braking torque estimation device 20, for example, in the method shown in Embodiment 1, when the tire characteristics are in a linear range (for example, the range represented by the straight line 31 of Figure 3 ) and the vehicle 10 is traveling straight, estimates the braking torque T bi . Therefore, depending on the tire characteristics and the driving state of the vehicle 10, it may be difficult for the braking torque estimation device 20 to accurately estimate the braking torque T bi .

[0209] Therefore, in this embodiment, the braking control device 51 ( Figure 7 ) stores the current I of the electric motor 48 of the braking device 9 ( bi , Figure 6 , 7 ) when the braking torque estimation device 20 estimates the braking torque T bi , and uses this current I to make the braking torque a desired value, thereby controlling the braking device 9. This current I is the value when the braking torque estimation device 20 estimates the braking torque T bi , and can be obtained, for example, by a current sensor provided on the electric motor 48.

[0210] The braking torque T b is generally approximately proportional to the value obtained by subtracting the current value I0 for the friction of the braking device 9 from the current I. This proportionality coefficient K is expressed as K = T b / (I - I0). The current value I0 used for friction is the current value used for friction in mechanisms such as the rotary-linear motion conversion mechanism 50, and can be calculated, for example, based on the current when driving the electric motor 48 in an idling state before the brake pads 45a, 45b come into contact with the disc rotor 42.

[0211] If the current value I0 is obtained in advance through experiments or numerical simulations, etc., the braking control device 51 can calculate the proportionality coefficient K based on this current value I0, the stored current I, and the braking torque T bi estimated by the braking torque estimation device 20. And when it comes to the indicated braking torque, that is, the braking torque command Tbir When setting the command current Ir for driving the electric motor 48 to Ir = 1 / K × T bir + I0, the braking control device 51 can make the braking torque become a desired value (i.e., the braking torque command T bir value). The braking control device 51 controls the rotational position of the electric motor 48 to a desired position through the command current Ir, making the braking torque become a desired value.

[0212] In this embodiment, the braking device 9 can be controlled with higher precision regardless of the tire characteristics and how the vehicle 10 travels. Embodiment 8

[0213] In Embodiment 7, an example was described in which the braking device 9 is controlled by making the braking torque become a desired value by using the current of the electric motor 48 ( Figure 6 ).

[0214] In this embodiment, an example of controlling the braking device 9 by using the relationship between the braking torque and the rotational position of the electric motor 48 is described. 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.

[0215] Figure 8 is a block diagram showing the configuration of the braking control device 51 in this embodiment. The braking control device 51 includes a braking torque - position relationship generation unit 72, a braking torque - position command conversion unit 67, and a position - current control unit 74. In addition, on the braking device 9 connected to the braking control device 51, there are provided: a motor position sensor 92 provided on the electric motor 48 and the current sensor 91 described in Embodiment 7.

[0216] The braking torque - position relationship generation unit 72 stores the rotational position of the electric motor 48 of the braking device 9 when the braking torque estimator 20 estimates the braking torque T bi This rotational position is the value when the braking torque estimator 20 estimates the braking torque T bi and is obtained, for example, by the motor position sensor 92 provided on the electric motor 48. The braking torque - position relationship generation unit 72 can input the braking torque T estimated by the braking torque estimator 20 bi and set the relationship between the braking torque T bi and the stored rotational position of the electric motor 48 as a mapping diagram and record it. Thus, the braking control device 51 can obtain the relationship between the braking torque and the rotational position of the electric motor 48.

[0217] The braking torque - position command conversion unit 67 inputs the indicated braking torque, that is, the braking torque command T bir, a mapping diagram showing the relationship between the braking torque and the rotational position of the electric motor 48, recorded by the braking torque position relationship generation unit 72. When the braking torque command T bir is input, the braking torque position command conversion unit 67 uses this mapping diagram to convert the braking torque command T bir into the rotational position of the electric motor 48.

[0218] The position current control unit 74 converts the rotational position of the electric motor 48 obtained by the conversion of the braking torque position command conversion unit 67 into the command current given to this rotational position. Then, the position current control unit 74 supplies the command current obtained after the conversion to the electric motor 48 of the braking device 9.

[0219] In this embodiment, different from Embodiment 7 that controls the braking torque by controlling the value of the command current Ir, the braking torque is controlled according to the rotational position of the electric motor 48. In this embodiment, since the command current is obtained based on the rotational position of the electric motor 48, the torque constant whose value changes with temperature is not used, and the braking torque can be controlled without being affected by temperature. Therefore, the braking device 9 can be controlled with higher precision. Embodiment 9

[0220] In Embodiment 8, when the relationship between the braking torque and the rotational position of the electric motor 48 is always fixed, by controlling the rotational position of the electric motor 48 to the desired position through the command current Ir, a braking torque of the desired value can be generated. However, in reality, the value of the braking torque changes according to 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 disk rotor 42, and is mainly represented by a function of the temperature T of the brake pads 45a, 45b and the rotational speed v of the disk rotor 42. The rotational speed v is the relative speed between the brake pads 45a, 45b and the disk rotor 42.

[0221] In this embodiment, the change in the braking torque accompanying the change in temperature T and the change in the braking torque accompanying the change in rotational speed v are obtained in advance through experiments or numerical simulations, etc. The braking control device 51 stores the change in the braking torque accompanying the change in temperature T and the change in the braking torque accompanying the change in rotational speed v obtained in advance.

[0222] The braking torque has a value obtained by multiplying the thrust generated by the electric motor 48 by the friction coefficient μp between the brake pads 45a, 45b and the disk rotor 42. Generally, the friction coefficient changes according to the temperature, relative speed, etc. of the two contacting objects. Therefore, the braking control device 51 estimates or measures the temperature T of the brake pads 45a, 45b and the rotational speed v of the disk rotor 42 and stores them.

[0223] The braking control device 51 stores the temperature T of the brake pads 45a, 45b and the rotational speed v of the disk rotor 42 when the braking torque estimation device 20 estimates the braking torque T. bi For example, the braking control device 51 estimates the temperature T and the rotational speed v based on the record of how much the brake pads 45a, 45b and the disk rotor 42 have operated so far, or measures the temperature T and the rotational speed v with sensors, and thus obtains and stores the temperature T and the rotational speed v.

[0224] The braking control device 51 uses the change in the braking torque accompanying the change in the temperature T and the rotational speed v obtained in advance, and estimates the value of the braking torque considering the change in the friction coefficient μp (i.e., the change in the temperature T and the rotational speed v) based on the temperature T and the rotational speed v obtained when estimating the braking torque T. bi

[0225] In the present embodiment, the braking device 9 can be controlled with higher precision based on the temperature T of the brake pads 45a, 45b and the rotational speed v of the disk rotor 42. Embodiment 10

[0226] In Embodiments 1 - 9, an example in which the vehicle 10 is a four-wheeled vehicle is shown. In the present embodiment, an example in which the vehicle 10 is a two-wheeled vehicle will be described.

[0227] Similar to the case of a four-wheeled vehicle, the vehicle 10 equipped with the braking torque estimation device 20 of the present embodiment includes: 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 braking device 9 that generates a braking force, an internal combustion engine or an electric motor that generates a braking driving force, a steering device, and a suspension, etc. The controller 5 includes the braking torque estimation device 20 of the present embodiment and controls the internal combustion engine, the electric motor, the braking device 9, the steering device, and the suspension, etc. The wheels 7 are provided at two locations, front and rear, of the vehicle body 8 and are equipped with tires.

[0228] Even when the vehicle 10 is a two-wheeled vehicle, as described in Embodiment 1, the formulas (1) - (3) hold. Here, the subscript i is an identifier for distinguishing the wheels 7 located at the front and rear of the vehicle body 8, and represents either F meaning the front wheel or R meaning the rear wheel. Similar to Embodiment 1, the sum of all the wheels 7 (two wheels) regarding the tire longitudinal force F xi can be calculated based on the longitudinal acceleration a detected by the acceleration sensor 2. xse

[0229] Based on these formulas, the vehicle body speed V b , the slip ratio λ i , and the tire longitudinal force F xi are obtained as in formulas (47) to (49) respectively.

[0230] [Formula 45]

[0231] [Formula 46]

[0232] [Formula 47]

[0233] Assume that the front and rear wheels 7 have the same braking coefficient K b (i.e., K bi = K b ), then Equations (47)-(49) are represented by Equations (50)-(52) respectively.

[0234] [Formula 48]

[0235] [Formula 49]

[0236] [Formula 50]

[0237] When the vehicle 10 is rear-wheel drive, the slip ratio λ of the front wheels F is approximately zero, and the vehicle body speed V can be obtained by Equation (53) b .

[0238] [Formula 51] V b = V wF …(53)

[0239] If the braking torque estimation unit 26 uses Equation (53), the slip ratio λ of the rear wheels can be obtained as in Equation (54) R .

[0240] [Formula 52]

[0241] If the braking torque estimation unit 26 uses this slip ratio λ R , the front-rear tire force F of the rear wheels can be obtained according to Equation (55) xR .

[0242] [Formula 53] F xR = K b λ R F zR …(55)

[0243] Regarding the front and rear force F of the tire xi The total value of all the wheels 7, similar to that in the first embodiment, can be obtained based on the longitudinal acceleration a detected by the acceleration sensor 2 xse (or the longitudinal acceleration a of the vehicle 10 x ). In the case where the vehicle 10 is a two-wheeler, the total value of the front and rear tire force F xi is consistent with the front and rear tire force F of the rear wheels xR . The front and rear tire force F of the rear wheels xR is expressed by, for example, Equation (56).

[0244] [Formula 54] F xR = m b a x …(56)

[0245] Based on the above, the braking torque estimation unit 26 can obtain the braking coefficient K through Equation (57) based on Equation (29) b .

[0246] [Formula 55]

[0247] The tire load estimation unit 21 can obtain the tire load F zi (the vertical tire force F zi ) based on Equations (21) and (22), such as Equations (58) and (59).

[0248] [Formula 56]

[0249] [Formula 57]

[0250] As described above, even when the vehicle 10 is a two-wheeler, the braking torque estimation device 20 of the first to ninth embodiments can estimate the braking torque at low cost and high accuracy, and can control the movement of the vehicle 10 at low cost and high accuracy.

[0251] In addition, the present invention is not limited to the above embodiments and can be variously modified. For example, the above embodiments are detailed descriptions for easily understanding the present invention, and the present invention is not necessarily limited to the form having all the described configurations. In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment. In addition, the configuration of another embodiment can be added to the configuration of one embodiment. In addition, for a part of the configuration of each embodiment, other configurations can be deleted, added, or replaced. Symbol description

[0252] 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 supply, 20…Brake torque estimation device, 21…Tire load estimation section, 22…Tire characteristic estimation section, 24…Tire characteristic storage section, 25…Tire characteristic reading section, 26…Brake torque etc. estimation section, 28…Tire characteristic map, 30…Curve showing the relationship between slip ratio and friction coefficient, 31…Straight line showing the relationship between slip ratio and friction coefficient in a linear relationship, 42…Disc rotor, 43…Brake caliper, 44…Housing, 45a, 45b…Brake pad, 46…Piston, 48…Electric motor, 49…Reducer, 50…Rotary-linear motion conversion mechanism, 51…Brake control device, 52…Control signal line, 61…Control signal line, 62, 63…Communication line, 67…Brake torque position command conversion section, 72…Brake torque position relationship generation section, 74…Position-current control section, 91…Current sensor, 92…Motor position sensor, a x …Longitudinal and lateral acceleration, a xse …Longitudinal and lateral acceleration detected by the acceleration sensor, F xi …Longitudinal and lateral forces of the tire, F zi …Tire load (vertical force of the tire), I i …Inertia moment of the wheel, K b 、K bi …Braking coefficient, m b …Mass of the vehicle, T bi …Braking torque, T bir …Braking torque command, V b …Vehicle body speed, V wi …Wheel speed, Vwsi…Wheel speed measured by the sensor, R i …Tire radius, ω i …Wheel angular velocity, λ i …Slip ratio.

Claims

1. A braking torque estimation device, characterized in that it can be installed on a vehicle, and the vehicle is equipped with a plurality of wheels on which tires are installed, the braking torque estimation device is provided with a braking torque calculation unit for calculating the braking torque of the wheel, inputting the wheel speed of the wheel and the acceleration in the longitudinal direction of the vehicle, i.e., the longitudinal acceleration, the braking torque calculation unit calculates the vehicle body speed, the longitudinal and lateral forces of the tire of the wheel, and the slip ratio of the wheel according to the wheel speed, the tire load of the wheel, the longitudinal acceleration, and the tire characteristics of the wheel, and calculates the braking torque according to the calculated longitudinal and lateral forces of the tire.

2. The braking torque estimation device according to claim 1, characterized in that it is provided with a tire load estimation unit for calculating the tire load using the longitudinal acceleration.

3. The braking torque estimation device according to claim 1, characterized in that it is provided with a tire characteristic estimation unit for obtaining the relationship between the slip ratio and the friction coefficient as the tire characteristics.

4. The braking torque estimation device according to claim 3, characterized in that the tire characteristic estimation unit obtains the braking coefficient, which is the proportional coefficient between the slip ratio and the friction coefficient, as the tire characteristics, and calculates the braking coefficient according to the longitudinal acceleration, the wheel speed, and the tire load when the vehicle is accelerating.

5. The braking torque estimation device according to claim 1, characterized in that the vehicle is equipped with an electric motor or an internal combustion engine for generating braking driving force, and a braking device for generating braking force, when at least one of the following 6 conditions is satisfied, the braking torque calculation unit calculates the braking torque: 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, 3) The road surface on which the vehicle is traveling is in a preset condition, 4) The torque of the electric motor is less than a preset threshold value, 5) The torque of the internal combustion engine is less than a preset threshold value, 6) The braking device is in operation.

6. The braking torque estimation device according to claim 1, characterized in that the vehicle is equipped with an electric motor or an internal combustion engine for generating braking driving force, and a braking device for generating braking force, the braking torque calculation unit subtracts the torque of the electric motor or the torque of the internal combustion engine from the calculated braking torque to obtain the braking torque of the braking device.

7. The braking torque estimation device according to claim 1, characterized in that the vehicle is equipped with an electric motor or an internal combustion engine for generating braking driving force, and a braking device for generating braking force, the braking torque calculation unit obtains the torque of the electric motor or the torque of the internal combustion engine by using the calculated braking torque as the torque of the electric motor or the torque of the internal combustion engine, or by subtracting the measured braking torque of the braking device from the calculated braking torque.

8. The braking torque estimation device according to claim 1, characterized in that When the vehicle is turning, the braking torque calculation unit calculates the braking torque by using the lateral acceleration of the vehicle, the steering angle of the wheel, and the tire characteristics depending on the sideslip angle during the vehicle turning.

9. The braking torque estimation device according to claim 1, characterized in that it is connected to a braking control device that controls a braking device, the braking device is an electric braking device provided on the vehicle and having an electric motor, when calculating the braking torque, the braking control device stores at least one of the current of the electric motor and the rotational position of the electric motor.

10. The braking torque estimation device according to claim 3, characterized in that when obtaining the tire characteristics, the tire characteristic estimation unit acquires the condition of the road surface on which the vehicle travels or the weather information on the road on which the vehicle travels.

11. The braking torque estimation device according to claim 1, characterized in that it is connected to a braking control device that controls a braking device, the braking device is provided on the vehicle and has a brake pad and a disc rotor, when calculating the braking torque, the braking control device stores the temperature of the brake pad and the rotational speed of the disc rotor.

12. The braking torque estimation device according to claim 3, characterized in that the vehicle is front-wheel drive or rear-wheel drive, the tire characteristic estimation unit obtains the braking coefficient, which is the proportional coefficient between the slip ratio and the friction coefficient, as the tire characteristic, and obtains the braking coefficient based on the front and rear tire forces, the wheel speed, and the tire load during vehicle acceleration.

13. The braking torque estimation device according to claim 3, characterized in that the vehicle is four-wheel drive, the tire characteristic estimation unit obtains the braking coefficient, which is the proportional coefficient between the slip ratio and the friction coefficient, as the tire characteristic, and obtains the braking coefficient based on the front and rear accelerations, the ratio of the driving forces of the front and rear wheels, the wheel speed, and the tire load during vehicle acceleration.

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