Vehicle control system

Abstract

To provide a vehicle control device that enables acceleration and deceleration control without using vehicle mass information. [Solution] The controller 5, which is a vehicle control device, includes a slip ratio calculation unit 511 that calculates the slip ratio λi of the wheels of the vehicle, a target slip ratio calculation unit 504 that sets a target slip ratio λiref corresponding to the target vehicle acceleration axref, and an operation variable generation unit 52 which is a control variable generation unit that generates a control variable for driving control or braking control of the wheels based on the slip ratio λi and the target slip ratio λiref.

Description

Technical Field

[0001] The present invention relates to a vehicle control device used for vehicle motion control.

Background Art

[0002] In vehicle motion control, by operating the acceleration and deceleration and the vehicle behavior according to the commands of the driver or the controller, the intended operation is possible and the riding comfort and the stabilization of the vehicle behavior are possible. On the other hand, what can be generated by brakes, electric motors, engines, etc. that control braking and driving is braking force and driving force, and it is difficult to control the acceleration and deceleration of the vehicle as intended while making the vehicle behavior follow the command.

[0003] Regarding such problems, in the traction control device described in Patent Document 1, a hybrid control unit that calculates the required driving force of the vehicle based on the driver's request and the vehicle behavior includes a reference wheel speed calculation unit that calculates the target reference wheel speed for each front, rear, left, and right wheel, and a target slip ratio calculation and distribution unit that calculates the target slip ratio of the wheel with respect to the target reference wheel speed. The control unit that controls the motor and the brake device based on the required driving force includes a slip ratio control unit that calculates the actual slip ratio of the wheel and controls each motor and the brake device so that the actual slip ratio is controlled to the target slip ratio. And regarding the target slip ratio, it is described that it is changed according to the required driving force of the vehicle or the difference between the required driving force and the total driving force.

[0004] Also, in the braking torque estimation device described in Patent Document 2, it is described that feedback control is performed so that the estimated braking torque becomes the commanded braking torque.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] However, in all of the above devices, control is performed based on the difference from the target driving force or braking force, and a challenge is that information on vehicle weight is required to convert the target acceleration / deceleration into braking / driving force. [Means for solving the problem]

[0007] A vehicle control device according to an aspect of the present invention includes: a slip ratio calculation unit that calculates the slip ratio of the wheels of a vehicle; a target slip ratio calculation unit that sets a target slip ratio corresponding to a target vehicle acceleration; and a control quantity generation unit that generates a control quantity for driving control or braking control of the wheels based on the slip ratio and the target slip ratio. [Effects of the Invention]

[0008] According to the present invention, acceleration and deceleration can be controlled without using information about the vehicle's mass. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows an example of the configuration of a vehicle equipped with a vehicle control device according to the first embodiment. [Figure 2] Figure 2 is a block diagram illustrating the functions of the controller. [Figure 3] Figure 3 shows the relationship between the slip ratio and the coefficient of friction, which are characteristics of tires. [Figure 4] Figure 4 shows a schematic diagram of the braking system. [Figure 5] Figure 5 is a block diagram illustrating the motor control device. [Figure 6] Figure 6 shows a modified example. [Modes for carrying out the invention]

[0010] The embodiments for carrying out the present invention will be described below with reference to the figures. The following description and drawings are illustrative examples for explaining the present invention, and have been omitted and simplified as appropriate for clarity of explanation. In addition, in the following description, the same or similar elements and processes are denoted by the same reference numerals, and redundant explanations may be omitted. It should be noted that the contents described below are merely examples of embodiments of the present invention, and the present invention is not limited to the embodiments described below, and can be carried out in various other forms.

[0011] (First Embodiment) Figure 1 shows an example configuration of a vehicle 10 equipped with a vehicle control device according to the first embodiment. The vehicle 10 includes a wheel speed sensor 1, an acceleration sensor 2, a gyro sensor 3, a steering angle sensor 4, a controller 5, wheels 7, a vehicle body 8, a brake device 9 (9FR, 9FL, 9RR, 9RL) that generates braking force, a brake pedal 11, and a power supply 14. Although not shown, it also includes an internal combustion engine or electric motor that generates braking and driving force, a steering device, and a suspension, etc.

[0012] Controller 5 functions as a vehicle control device for vehicle 10, controlling the internal combustion engine, electric motor, brake system 9, steering system, and suspension, etc. Controller 5 may be provided separately according to the functions it provides, or it may be provided separately as a higher-level controller and a lower-level controller. In this specification, even if there are multiple controllers separated in this way, they will be collectively referred to as controller 5. Controller 5 can be composed of a computer that comprehensively controls vehicle 10, equipped with hardware such as a CPU or other arithmetic unit, semiconductor memory or other main memory, auxiliary memory, and communication device, and various functions are realized by the arithmetic unit executing a program loaded into the main memory.

[0013] In the following explanation, we may omit explanations of well-known technologies, such as the above configuration of Controller 5.

[0014] The wheels 7 are arranged at four locations around the vehicle body 8, namely, at the front, rear, left, and right positions, and tires are provided thereon. In this embodiment, it is assumed that the vehicle 10 is a four-wheeled vehicle. The wheel speed sensor 1, the acceleration sensor 2, the gyro sensor 3, and the steering angle sensor 4 are sensors that the vehicle 10 generally includes.

[0015] The wheel speed sensor 1 detects the rotational speed (wheel angular velocity) of the wheels 7 located at four locations on the vehicle body 8. The wheel speed sensor 1 can be configured, for example, as a sensor that detects the relative rotational speed (wheel angular velocity) between a rotating part installed on an axle hub or the like and a fixed part installed on a knuckle or a brake carrier or the like.

[0016] 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 (side acceleration) of the vehicle 10. The gyro sensor 3 detects the yaw rate, which is the angular velocity of the 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 operation of the driver who drives the vehicle 10.

[0017] The brake device 9 is, for example, an electric brake device, and is provided for each of the wheels 7 located at four locations on the vehicle body 8. That is, the vehicle 10 includes 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 (9FL, 9FR, 9RL, 9RR) have the same structure and are controlled by the controller 5. Hereinafter, these brake devices (9FL, 9FR, 9RL, 9RR) will be collectively referred to as the brake device 9. Note that the brake device 9 is not limited to an electric brake device, and a hydraulic brake device may also be used.

[0018] The controller 5 transmits a control signal to the brake device 9, the internal combustion engine, the electric motor, etc. via the communication line 12 based on operations of the brake pedal 11, the accelerator pedal, the steering, the states of the vehicle 10 and the wheels 7, and various information about the outside of the vehicle 10 by the driver of the vehicle 10. The brake device 9 is driven by the electric power supplied from the power source 14 via the electric wire 13.

[0019] FIG. 2 is a block diagram for explaining the functions of the controller 5. As described above, the controller 5 functions as a vehicle control device for the vehicle 10 and controls the internal combustion engine, the electric motor, the brake device 9, the steering device, the suspension, etc. In FIG. 2, the control target is described as the actuator 9A, and the actuator 9A includes the internal combustion engine that performs driving and braking, the electric motor, the brake device 9, the distribution mechanism that distributes the torque output by the internal combustion engine or the electric motor to each wheel, etc.

[0020] The controller 5 includes a target slip ratio generation unit 50 that calculates the target slip ratio λiref, a wheel slip ratio estimation unit 51 that calculates the current slip ratio λi, and an operation amount generation unit 52 that calculates an operation amount (a control amount for controlling the actuator 9A) based on the target slip ratio λiref and the slip ratio λi. As described above, the controller 5 realizes these functions by the arithmetic unit executing the program loaded into the main storage device. The subscript i in the symbols λiref and λi represents the distinction of each of the four wheels. For example, in the case of the left front wheel, i is represented by FL, and in the cases of the right front wheel, the left rear wheel, and the right rear wheel, they are represented by FR, RL, and RR in order.

[0021] Controller 5 receives input from the driver input, target vehicle behavior, and vehicle state variables. Driver inputs include accelerator and brake inputs, and steering inputs during turns. Indicators representing the target vehicle behavior include, for example, vertical displacement of the vehicle body, pitch angle, roll angle, yaw angle, or their derivatives (including setting these values ​​to zero), and the contact load on each tire (e.g., front-to-rear distribution). Vehicle state variables include longitudinal acceleration ax, wheel speed Vw, and lateral acceleration and yaw rate during turns.

[0022] The target slip ratio generation unit 50 consists of a tire vertical force ratio calculation unit 501, a distribution ratio calculation unit 502, a target longitudinal acceleration calculation unit 503, a target slip ratio calculation unit 504, and a tire characteristic reading unit 505. The individual wheel slip ratio estimation unit 51 consists of a tire vertical force ratio calculation unit 501, a tire characteristic reading unit 505, and a slip ratio calculation unit 511. The tire vertical force ratio calculation unit 501 and the tire characteristic reading unit 505 function as common elements of the target slip ratio generation unit 50 and the individual wheel slip ratio estimation unit 51.

[0023] <Explanation of the target slip ratio generation unit 50> First, the target slip ratio generation unit 50 will be explained. The tire vertical force ratio calculation unit 501 calculates the tire vertical force distribution ratio αzi based on the longitudinal acceleration ax, which is a state variable of the vehicle. The sum of the tire contact loads (hereinafter referred to as tire vertical forces) Fzi of each wheel of the vehicle 10, Fz, is the vehicle weight and is expressed by equation (1). In equation (1), mb is the mass of the vehicle including the occupants, etc., and g is the acceleration due to gravity.

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[0024] Here, the vehicle weight is distributed to the four wheels, and the vertical force Fzi of each wheel is the vertical force distribution ratio (f-wheel vertical force distribution ratio). If we represent this ratio as αzi, the following relationship is given by equation (2).

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[0025] For example, assuming that the vertical tire forces of the left and right wheels are equal when there is no acceleration or deceleration, the vertical tire forces Fzi of the front and rear wheels when driving in a straight line can be calculated using the following equations (3) and (4). Equation (3) shows the vertical tire forces FzFL and FzFR of the left and right front wheels, and equation (4) shows the vertical tire forces FzRL and FzRR of the left and right rear wheels. In equations (3) and (4), Lf represents the longitudinal distance between the center of gravity of the vehicle 10 and the front axle, Lbas represents the wheelbase (Lbas = Lf + Lr), and hyc represents the height of the center of gravity of the vehicle 10. The longitudinal acceleration ax is obtained using the longitudinal acceleration measurement value axse detected by the acceleration sensor 2.

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[0026] By comparing equations (3) and (4) with equation (2), the vertical force distribution ratio αzi of the tire can be expressed as shown in equation (5) for the front wheel.

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[0027] In the case of the rear wheel, it is expressed as in equation (6).

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[0028] Here, it is assumed that the vertical forces of the left and right wheels are equal and that the center of gravity is known. However, it is also possible to directly measure the vertical forces of each wheel by installing sensors and measuring them when the vehicle is stationary without acceleration or deceleration, and then calculate the vertical force distribution ratio αzi from these measured values. Alternatively, it may be calculated from various vehicle information, such as the displacement of each wheel in the suspension, the pitch angle which can be estimated from longitudinal acceleration, and the roll angle which can be estimated from lateral acceleration. Furthermore, even when acceleration or deceleration is applied, only values ​​proportional to the mass are added or subtracted, and the calculation can be performed in the same way. It should also be noted that even during acceleration or deceleration, the vertical force distribution ratio αzi for each wheel can be determined from various vehicle information. In any case, it is possible to determine the vertical force distribution ratio αzi for each wheel in equation (2).

[0029] The distribution ratio calculation unit 502 calculates the required slip ratio distribution (target distribution ratio αxiref) in the target slip ratio calculation unit 504 based on the driver input, target vehicle behavior, and tire vertical force distribution ratio αzi. For example, when you want to decelerate while driving straight, you can set the target distribution ratio αxiref by determining conditions such as "a predetermined front-to-rear braking force distribution of 7:3, and no difference in braking force between the left and right sides." In that case, the target distribution ratio for the left and right front wheels can be set to 0.35 each, and the target distribution ratio for the left and right rear wheels can be set to 0.15 each. The calculated target distribution ratio αxiref is input to the target slip ratio calculation unit 504.

[0030] The above is just one example of how to determine the distribution; various other methods are possible, such as varying it based on the vertical force of each wheel's tire, or setting the slip ratio to the same value on both sides. Furthermore, when using suspension geometry, it is possible to generate vertical forces on the vehicle body through braking or driving forces, and it is also possible to set distribution ratios that take these actions into account.

[0031] The target longitudinal acceleration calculation unit 503 calculates the target longitudinal acceleration axref based on the driver input (for example, the amount of input to the accelerator or brake). The calculated target longitudinal acceleration axref is input to the target slip ratio calculation unit 504.

[0032] The target slip ratio calculation unit 504 calculates the target slip ratio λiref for each wheel based on the input target distribution ratio αxiref and target longitudinal acceleration axref, and the braking coefficient Kb, described later, input from the tire characteristic reading unit 505. The braking coefficient Kb read by the tire characteristic reading unit 505 may be pre-stored in the memory unit of the controller 5, or it may be estimated by the tire characteristic reading unit 505 based on data such as acceleration data (longitudinal acceleration measurement value axse, wheel speed Vw, tire load (up and down force of the tire)).

[0033] From the definition of slip ratio, the slip ratio during deceleration is expressed by equation (7), and the slip ratio during acceleration is expressed by equation (8). In equations (7) and (8), Vwi represents the wheel speed and Vb represents the vehicle speed. The wheel speed Vwi can be calculated by multiplying the wheel angular velocity detected by the wheel speed sensor 1 by the tire radius.

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[0034] Figure 3 shows the relationship between the slip ratio and the coefficient of friction, which are characteristics of a tire. Generally, tire characteristics are known to be represented by the curve L1. When the slip ratio is positive, it indicates the characteristics during driving (driving region), and when the slip ratio is negative, it indicates the characteristics during braking (braking region). As shown in Figure 3, the magnitude (absolute value) of the coefficient of friction increases as the slip ratio increases, but it reaches a peak at a certain slip ratio and then begins to decrease as the slip ratio increases further. When the absolute value of the slip ratio is small, there is a linear relationship between the slip ratio and the coefficient of friction, which can be approximated by the dashed line L2. The slope of this line L2 will hereafter be called the braking coefficient, and its value is Kb, which is determined by the tire characteristics and road surface conditions.

[0035] The relationship between the longitudinal force Fxi and the vertical force Fzi of each wheel is expressed in equation (9) below, using the slip ratio λi and the braking coefficient Kb. Here, it is assumed that all four wheels are using the same tires and are traveling on the same road surface, and the braking coefficient Kbi of each wheel is expressed in terms of Kb.

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[0036] By replacing the longitudinal tire force Fxi in equation (9) with the target longitudinal tire force Fxiref for each wheel, the target slip ratio λiref for each wheel can be expressed as shown in equation (10).

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[0037] The relationship between the target braking force Fxref to be generated in the vehicle 10 and the target longitudinal force Fxiref of each wheel is expressed by the following equation (11).

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[0038] Here, the target longitudinal force Fxiref for each wheel is obtained by distributing the target braking force Fxref to each of the four wheels, so the target distribution ratio αxiref for each wheel is expressed by the following equation (12).

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[0039] On the other hand, the target braking force Fxref is expressed using the target longitudinal acceleration axref in the following equation (13).

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[0040] Applying equation (13) to equation (12), the target longitudinal force Fxiref for each wheel, which corresponds to the numerator of equation (10), can be expressed as shown in equation (14).

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[0041] Therefore, applying equations (13) and (14) to equation (10), the target slip ratio λiref is expressed by the following equation (15). In this way, the target slip ratio λiref for each wheel is calculated from the target longitudinal acceleration axref and target distribution ratio αxiref of the vehicle 10.

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[0042] In the explanation above, the target longitudinal acceleration axref was calculated based on driver input (e.g., accelerator and brake input), but it can also be determined based on higher-level commands such as those for autonomous driving or driver assistance functions. Furthermore, the target longitudinal acceleration axref should ideally be the value excluding the longitudinal acceleration caused by gravity. For example, if a force is generated in the longitudinal direction of the vehicle 10 due to its inclination relative to the horizontal plane in the longitudinal direction of the vehicle, the portion caused by that inclination will not be reflected in the longitudinal force of the tires, and this is also a portion that cannot be controlled by actuator 9A.

[0043] <Explanation of the slip ratio estimation unit 51 for each wheel> Next, the individual wheel slip ratio estimation unit 51 will be described. As mentioned above, the individual wheel slip ratio estimation unit 51 consists of a tire vertical force ratio calculation unit 501, a tire characteristic reading unit 505, and a slip ratio calculation unit 511. The tire vertical force ratio calculation unit 501 and the tire characteristic reading unit 505 are shared with the target slip ratio generation unit 50. Since the tire vertical force ratio calculation unit 501 and the tire characteristic reading unit 505 have already been described in the description of the target slip ratio generation unit 50, the slip ratio calculation unit 511 will be described below.

[0044] Excluding the effects of gravity due to air resistance, incline, etc., the sum of the longitudinal forces Fxi of the tires Fx can be expressed by the following equation (16) from the equation of motion of the vehicle 10.

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[0045] The longitudinal acceleration ax of the vehicle is obtained from the longitudinal acceleration measurement axse of the acceleration sensor 2 installed in the vehicle 10. Using the longitudinal acceleration measurement axse, the sum of the longitudinal tire forces Fxi, Fx, can be calculated using the following equation (17) (when the pitch angle and incline are small).

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[0046] By the way, the longitudinal acceleration measurement axse in equation (17) is detected by the acceleration sensor 2 installed on the vehicle body 8, and therefore includes a component associated with the vehicle body's pitch angle. Therefore, by removing the component caused by vehicle body pitching from equation (17), the sum of the longitudinal tire forces Fxi, Fx, can be determined with high accuracy. That is, instead of the longitudinal acceleration measurement axse in equation (17), the sum of Fx can be calculated using the value ax given by equation (18), from which the component caused by vehicle body pitching has been removed. In equation (18), θy represents the vehicle body pitch angle.

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[0047] Here, assuming that the vehicle body pitch angle θy is small, we may use equation (19) as a linear approximation instead of equation (18).

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[0048] Furthermore, if the running surface of vehicle 10 is inclined at an angle γ with respect to the horizontal plane, the equation of motion is expressed by the following equation (20), with the addition of a gravity term.

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[0049] Here, assuming that the vehicle body pitch angle θy and inclination γ are small, the longitudinal acceleration ax in equation (20) can be the longitudinal acceleration ax expressed in equation (21).

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[0050] Applying the longitudinal acceleration ax from equation (21) to equation (20) yields equation (22).

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[0051] This allows the sum of the longitudinal tire forces Fxi, Fx, to be determined from the longitudinal acceleration measured by acceleration sensor 2, axse. The vehicle body pitch angle θy can be estimated from the longitudinal acceleration, etc.

[0052] By the way, substituting equation (7), which holds true during braking, into equation (9), which represents the longitudinal force Fxi of the tires mentioned above, and adding up the values ​​for all four wheels, we obtain the following equation (23). Here, we assume Kbi = Kb.

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[0053] From equations (22) and (23), the vehicle speed Vb can be obtained. Substituting the obtained vehicle speed Vb into equation (7), we obtain equation (24).

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[0054] The slip ratio λi can also be similarly determined using equation (8) during driving. Furthermore, if there is driving braking, having both equations (7) and (8) makes the calculation complicated, so since equations (7) and (8) show almost the same value in the linear region where the value is small, one of them may be used to determine the slip ratio.

[0055] Here, by applying equation (2) to Fzi in equation (24), we obtain the following equation (25).

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[0056] As described above, it is possible to determine the slip ratio λi of each wheel using the longitudinal acceleration measurement axse, the wheel speed Vwi of each wheel, and the tire vertical force distribution ratio αzi, without using information on the vehicle mass mb. Note that the above calculation method is just one example, and calculations can be performed using methods other than this one. For example, the vehicle speed Vb can be estimated using the fact that the integral of acceleration is the vehicle speed, or using GPS, and then the vehicle speed Vb and wheel speed Vwi can be substituted into equation (7).

[0057] <Explanation of the manipulated variable generation unit 52> Next, the manipulated amount generation unit 52 will be described. The manipulated amount generation unit 52 calculates a manipulated amount (control amount) for controlling the actuator 9A based on the target slip ratio λiref and the slip ratio λi of the vehicle 10 estimated by the slip ratio estimation unit 51 for each wheel. The manipulated amount here should be one that causes the actuator 9A to output a braking and driving force so that it can follow the target slip ratio.

[0058] For example, during deceleration, the target slip ratio λiref is a negative value, and if the estimated slip ratio λi is a negative value and its absolute value is smaller than the absolute value of the target slip ratio λiref, then the control variable should be one that controls the braking force to increase. In the case of a hydraulic brake, the braking force can be increased by increasing the hydraulic pressure, so it is best to use hydraulic pressure as the control variable.

[0059] Furthermore, considering the driving conditions, the manipulated variables could include brake fluid pressure, motor or engine torque, etc. Additionally, the controllable variables could include position, rotational speed, and current. The manipulated variables can be calculated using PID control based on the target slip ratio λiref and the estimated slip ratio λi. The control method itself is not limited as long as it controls the estimated value to the target value.

[0060] <Brake device 9> The following describes the case where the actuator 9A to be controlled is a brake device (electric brake) 9. In Figure 4, the brake device 9 includes a brake caliper 90 and a motor control device 91. The brake caliper 90 includes a disc rotor 901, a housing 902, brake pads 903a, 903b, a piston 904, an electric motor 905, a reduction gear 906, and a rotary-to-linear motion conversion mechanism 907.

[0061] The disc rotor 901 is a rotating member that rotates together with the wheel 7 (see Figure 1) of the vehicle 10. The housing 902 is supported so as to float in the axial direction of the disc rotor 901 by a brake carrier (not shown) fixed to a non-rotating part of the vehicle 10 located inside the vehicle 10 relative to the disc rotor 901.

[0062] The output shaft of the electric motor 905 is connected to the reduction gear 906, and the output shaft of the reduction gear 906 is connected to the rotary-to-linear motion conversion mechanism 907. The rotary-to-linear motion conversion mechanism 907 converts the rotational force of the electric motor 905 into linear motion, moving the piston 904 in the linear direction (left-right direction in the illustration). When the piston 904 is moved linearly by the rotational force of the electric motor 905, the brake pads 903a and 903b are pressed against the disc rotor 901 so as to clamp it. As a result, braking force is applied to the wheel 7 which rotates together with the disc rotor 901.

[0063] The electric motor 905 is controlled by the motor control device 91. The motor control device 91 is connected to a control signal line 911 and communication lines 912 and 913. The control signal line 911 inputs control commands from a higher-level control device (in this embodiment, the controller 5), such as a vehicle control ECU (Electronic Control Unit), to the motor control device 91. The communication lines 912 and 913 communicate information other than control commands with the higher-level control device. Furthermore, the motor control device 91 is connected to a control signal line 914, which inputs control commands from the motor control device 91 to the brake caliper 90.

[0064] In Figure 4, the higher-level control device and the motor control device 91 are shown as separate units, but they can also be integrated into a single controller 5.

[0065] When motor current is applied to the electric motor 905, the piston 904 moves to the left in the figure, and the disc rotor 901 is gripped by the brake pads 903b and 903a. As the motor current increases, the pad thrust increases. Therefore, the motor current, piston position, pad thrust, etc. are used as manipulated variables, and the brake device (electric brake) 9 is operated based on the manipulated variables calculated by the manipulated variable generation unit 52 in Figure 2.

[0066] For example, as shown in Figure 5, the motor rotation position and current are feedback-controlled using the rotation position sensor 908 and the current sensor 909 based on the control quantity command from the higher-level control device (controller 5 in this embodiment), thereby achieving the target slip ratio (target slip ratio λiref) according to the control quantity command. In this case, even if the friction coefficients of the brake pads 903b and 903a are different, the target slip ratio can be achieved regardless of the friction coefficient because the slip ratio is being fed back.

[0067] As described above, in this embodiment, it is possible to determine the slip ratio λi of each wheel using the longitudinal acceleration measurement value axse, the wheel speed Vwi of each wheel, and the tire vertical force distribution ratio αzi, without using information on the vehicle mass mb. Furthermore, the target slip ratio λiref of each wheel is calculated from the target longitudinal acceleration axref and target distribution ratio αxiref of the vehicle 10. In other words, acceleration and deceleration control becomes possible without using information on the vehicle mass mb, and even when the weight changes due to occupants or luggage, if the acceleration corresponding to the pedal amount (pressure) is set as the target value, it can be achieved, enabling operation without being conscious of the mass.

[0068] Furthermore, by controlling the slip ratio of each wheel, it becomes possible to generate the same longitudinal force on both tires, even if, for example, the friction coefficients of the left and right pads differ during braking. This improves the stability of vehicle behavior (straight-line stability) and enables the achievement of the target deceleration level. It also improves the stability of the longitudinal force on each wheel during cornering. Moreover, when using electric brakes, the control is more responsive and has higher resolution, making it possible to further enhance the effect.

[0069] (modified version) The controller 5 shown in Figure 2 above is just one example, and the following modifications are also possible. Figure 6 is a block diagram showing the configuration of the controller 5 in the modified configuration. In the modified configuration, the tire vertical force ratio calculation unit 501, the distribution ratio calculation unit 502, and the target longitudinal acceleration calculation unit 503, which were included in the controller 5 in Figure 2, are included in the higher-level control device 100. Therefore, the target slip ratio generation unit 50 of the controller 5 is composed of a target slip ratio calculation unit 504 and a tire characteristic reading unit 505, and the individual wheel slip ratio estimation unit 51 is composed of a slip ratio calculation unit 511 and a tire characteristic reading unit 505.

[0070] (Second embodiment) A vehicle control device according to a second embodiment of the present invention will now be described. In the first embodiment described above, the case in which the vehicle 10 mainly decelerates was explained as an example, but in the second embodiment, the case in which the vehicle 10 accelerates will be described. In the case of acceleration, the actuator 9A in Figure 2 becomes an engine or an electric motor.

[0071] When an engine is installed, the torque generated by the engine can be distributed to the left and right wheels in an appropriate ratio using a torque vectoring mechanism, allowing for control based on the distribution ratio. For example, the front and rear wheels can be distributed at a fixed ratio, while the left and right wheels can be distributed at an appropriate ratio.

[0072] Furthermore, in an in-wheel motor vehicle equipped with an electric motor on each wheel, torque can be generated independently for each wheel. Therefore, it is possible to control the torque of each wheel according to the operating amount of each wheel calculated by the operating amount generation unit 52 based on the target slip ratio λiref calculated by the target slip ratio generation unit 50 and the slip ratio λi calculated by the individual wheel slip ratio estimation unit 51.

[0073] Thus, in the second embodiment as well, the acceleration targeted by the driver or higher-level command can be achieved by independent control of the four wheels.

[0074] (Third embodiment) A vehicle control device according to a third embodiment of the present invention will now be described. In the first embodiment described above, the case in which the vehicle 10 mainly travels in a straight line was used as an example, but in the third embodiment, the case in which the vehicle 10 travels while turning will be described. When the vehicle 10 travels while turning, for example, the method for estimating the tire vertical force distribution ratio αzi in the tire vertical force ratio calculation unit 501 differs from that when traveling in a straight line. The method for estimating the tire vertical force distribution ratio αzi when traveling while turning will be described below.

[0075] Taking into account the longitudinal and lateral accelerations that occur during cornering, and assuming that the distribution ratio of the vertical tire force Fzi0 is determined when there is no acceleration or deceleration, the vertical tire force Fzi of each wheel is expressed by the following equations (26) to (29). These equations representing the vertical tire force Fzi (FzFL, FzFR, FzRL, FzRR) of each wheel are in the same form as equation (2) mentioned above. In equations (26) to (29), ay represents the lateral acceleration of the vehicle, and Lbas and Lyc represent the wheelbase and the height of the center of gravity of the vehicle 10, as mentioned above. Also, βi is the side slip angle of each wheel.

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[0076] Furthermore, when determining the wheel speed converted from the above-mentioned individual wheel speeds to the vehicle's longitudinal speed at the sprung mass center position, it is obtained by adding or subtracting the speed difference of each wheel based on the actual steering angle δ generated by the turning motion and the yaw rate r detected by the gyro sensor 3. Here, the wheel speed calculated from the wheel angular velocity measured by the wheel speed sensor 1 is denoted as Vwsi, and the wheel speed converted to the vehicle's longitudinal speed at the sprung mass center position is denoted as Vwi.

[0077] In that case, the wheel speed Vwi is expressed by the following equations (30) to (33) when the front wheels are steered. In equations (30) to (33), df represents the front axle tread and dr represents the rear axle tread.

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[0078] Furthermore, during cornering, the braking coefficient Kb changes with the sideslip angle β. Since this sideslip angle β can also be calculated using the steering angle δ and the vehicle speed Vb, the tire characteristic reading unit 505 reads the braking coefficient Kb as a function of the sideslip angle β, Kb(β). In the slip ratio calculation unit 511 in Figure 2, the braking coefficient Kb is replaced with the function Kb(β) in the aforementioned equation (25), and the value of the wheel speed converted to the longitudinal speed of the vehicle at the sprung mass center position is input as the wheel speed Vwi to calculate the slip ratio λi during cornering.

[0079] Furthermore, the target values ​​for acceleration and deceleration (target longitudinal acceleration axref) can be determined in the same way as in the first embodiment described above. That is, they can be determined based on the driver's accelerator and brake inputs, or based on higher-level commands such as autonomous driving or driver assistance functions.

[0080] The distribution ratio calculation unit 502 further calculates the slip ratio distribution (target distribution ratio αxiref) by considering the steering input, yaw rate, and steering angle. In the case of straight-line driving as in the first embodiment, one method is to apply the same braking force to both sides, but when turning, it is necessary to distribute the force in a way that generates the target acceleration and deceleration while achieving an appropriate yaw rate. Normally, the yaw rate is generated by the steering function, but it is used to distribute the braking and driving forces in a way that prevents oversteer and understeer. This makes it possible to operate in accordance with the driver and higher-level commands even when turning.

[0081] Furthermore, in such cases, a distribution ratio may be applied that reverses the braking and driving functions between the left front wheel and the right rear wheel. For example, braking could be applied only to the inside of a turn, and driving only to the outside. This allows for finer control, improving stability and enabling vehicle motion that aligns with the driver's intentions and the intentions of higher-level commands.

[0082] (Fourth embodiment) While the first to third embodiments described above used four-wheeled vehicles as examples, the fourth embodiment will describe a two-wheeled vehicle. In the case of a two-wheeled vehicle, as with four-wheeled vehicles, it is equipped with a wheel speed sensor 1, an acceleration sensor 2, a gyro sensor 3, a steering angle sensor 4, wheels 7, a vehicle body 8, an internal combustion engine or electric motor (not shown) that generates braking and driving force, a brake device 9 that generates braking force, a steering device, a suspension, etc., and a controller 5 is positioned to control the internal combustion engine, electric motor, brake device, steering device, suspension, etc.

[0083] In two-wheeled vehicles, equations (7) and (8) relating to the slip ratio λi, and equation (9) relating to the longitudinal tire force Fxi, as described in the first embodiment, also hold true. However, the meaning of the subscript i differs from that of four-wheeled vehicles, where i is represented by F for the front wheel and R for the rear wheel. Furthermore, the sum of the longitudinal tire forces Fxi, Fx, can be obtained from the longitudinal acceleration measurement value axse of the acceleration sensor 2, as in the first embodiment.

[0084] The target slip ratio calculation unit 504 calculates the target slip ratio λiref using equation (15), similar to the four-wheeled vehicle. In this case, the calculation of the target distribution ratio αxiref by the distribution ratio calculation unit 502, the calculation of the target longitudinal acceleration axref by the target longitudinal acceleration calculation unit 503, and the reading of the braking coefficient Kb by the tire characteristic reading unit 505 are performed in the same manner as in the first embodiment.

[0085] The slip ratio calculation unit 511 calculates the slip ratio λi shown in the following equation (34) based on equations (22) and (23), similar to the case of the first embodiment. The braking coefficient Kb is read by the tire characteristic reading unit 505.

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[0086] In the tire vertical force ratio calculation unit 501, the vertical force FzF of the front wheels is calculated using equation (35), and the vertical force FzR of the rear wheels is calculated using equation (36), similar to equations (3) and (4) for the vertical force Fzi of the front wheels in the first embodiment.

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[0087] By comparing equations (35) and (36) with equation (2), the vertical force distribution ratio αzi of the tire can be expressed as shown in equation (37) for the front wheel and as shown in equation (38) for the rear wheel.

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[0088] In this way, even in two-wheeled vehicles, it becomes possible to estimate the target slip ratio λiref and the slip ratio λi, and based on these, the control variables can be calculated, and the brakes, engine, electric motor, etc., can be controlled based on these control variables.

[0089] The embodiments and modifications of the present invention described above provide the following effects.

[0090] (C1) As shown in Figures 1 and 6, the controller 5 (vehicle control device) includes a slip ratio calculation unit 511 that calculates the slip ratio λi of the wheels 7 of the vehicle 10, a target slip ratio calculation unit 504 that sets a target slip ratio λiref corresponding to the target vehicle acceleration axref, and an operated variable generation unit 52 which is a control variable generation unit that generates a control variable for drive control or braking control of the wheels 7 based on the slip ratio λi and the target slip ratio λiref.

[0091] As described above, since control quantities for drive control or braking control are generated based on the slip ratio λi and the target slip ratio λiref corresponding to the target vehicle acceleration axref, acceleration and deceleration control becomes possible without using information on the vehicle mass mb. As a result, even when the weight changes due to occupants or cargo, if the acceleration corresponding to the pedal amount (pressure) is set as the target value, it can be achieved, enabling operation without being aware of the mass. Furthermore, independent control of each wheel becomes possible.

[0092] (C2) In (C1) above, as shown in Figures 1 and 2, the vehicle 10 has multiple wheels 7, and is further equipped with a distribution ratio calculation unit 502 that sets a target distribution ratio αxiref of the target slip ratio λiref for each of the multiple wheels 7 based on information on the target vehicle behavior, and the target slip ratio calculation unit 504 sets the target slip ratio λiref for each wheel 7 based on the target vehicle acceleration axref and the target distribution ratio αxiref. In this way, by setting a target slip ratio λiref for each wheel and comparing and controlling it with the actual slip ratio λi for each wheel, independent control of each wheel becomes possible.

[0093] (C3) In (C2) above, as shown in Figure 2, a target longitudinal acceleration calculation unit (target acceleration calculation unit) 503 may be further provided to set the target vehicle acceleration based on target control information (for example, driver inputs or control commands from a higher-level control device).

[0094] (C4) In (C3) above, as shown in Figures 1 and 2, the target longitudinal acceleration calculation unit 503 extracts only the acceleration generated by the longitudinal force Fxi of each wheel 7 and sets the target vehicle acceleration axref. For example, if a force is generated in the longitudinal direction of the vehicle 10 due to inclination, the portion due to that inclination will not be reflected in the longitudinal force Fxi of the tires, so setting it as described above enables more appropriate control.

[0095] (C5) In (C2) above, as shown in Figures 1 and 2, the system further includes a tire vertical force ratio calculation unit 501 that calculates the vertical force distribution ratio αzi of multiple wheels 7 based on the acceleration generated when the vehicle is running, and a target slip ratio calculation unit 504 sets a target slip ratio λiref for each wheel 7 based on the tire vertical force distribution ratio αzi. As a result, the target slip ratio λiref can be set without using information on the vehicle mass mb.

[0096] (C6) In (C2) above, as shown in Figures 1 and 2, the target slip ratio calculation unit 504 calculates the target slip ratio λiref based on the above-mentioned equation (15), where axref is the target vehicle acceleration, Kb is the braking coefficient of wheel 7, and αxiref is the target distribution ratio.

[0097] (C7) In (C2) above, as shown in Figures 1 and 2, the system further includes a tire vertical force ratio calculation unit 501 that calculates the tire vertical force distribution ratio αzi of multiple wheels 7 based on the acceleration generated when the vehicle is running, and a slip ratio calculation unit 511 that calculates the slip ratio λi for each wheel 7 based on the vehicle longitudinal acceleration ax, the tire vertical force distribution ratio αzi, the wheel speed Vwi, and the braking coefficient Kb of the wheel 7. As a result, the slip ratio λi for each wheel 7 can be determined without using information on the vehicle mass mb.

[0098] (C8) In (C2) above, as shown in Figures 1 and 2, the distribution ratio calculation unit 502 sets the target distribution ratio αxiref so that the longitudinal force Fxi of the left and right wheels 7 is the same. By setting it in this way, the straight-line stability can be improved.

[0099] (C9) In (C7) above, as shown in Figure 2, the system may further include a tire characteristic reading unit (tire characteristic estimation unit) 505 that estimates the braking coefficient Kb based on the longitudinal acceleration ax of the vehicle 10, the wheel speed Vw, and the tire load (tire vertical force Fzi).

[0100] (C10) In (C2) above, as shown in Figure 2, the distribution ratio calculation unit 502 may further set the target distribution ratio αxiref by taking into account the input amount related to steering, the yaw rate, and the rudder angle.

[0101] The embodiments and various modifications described above are merely examples, and the present invention is not limited to these, as long as the features of the invention are not impaired. Other embodiments conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of symbols]

[0102] 1...Wheel speed sensor, 2...Accelerometer, 3...Gyro sensor, 4...Steering angle sensor, 5...Controller, 7...Wheel, 8...Vehicle body, 9, 9FR, 9FL, 9RR, 9RL...Brake system, 9A...Actuator, 10...Vehicle, 11...Brake pedal, 14...Power supply, 50...Target slip ratio generation unit, 51...Estimation unit for slip ratio of each wheel, 52...Manipulation unit, 501...Tire vertical force ratio calculation unit, 502...Distribution ratio calculation unit, 503...Target longitudinal acceleration calculation unit, 504...Target slip ratio calculation unit, 505...Tire characteristic reading unit, 511...Slip ratio calculation unit

Claims

1. A slip ratio calculation unit that calculates the slip ratio of the wheels equipped on the vehicle, A target slip ratio calculation unit that sets a target slip ratio corresponding to the target vehicle acceleration, A vehicle control device comprising: a control amount generation unit that generates a control amount for driving control or braking control of the wheel based on the slip ratio and the target slip ratio.

2. In the vehicle control device according to claim 1, The vehicle has multiple wheels, The system further includes a distribution ratio calculation unit that sets the distribution ratio of the target slip ratio for each of the plurality of wheels based on target vehicle behavior information. The vehicle control device includes a target slip ratio calculation unit that sets the target slip ratio for each wheel based on the target vehicle acceleration and the distribution ratio.

3. In the vehicle control device according to claim 2, A vehicle control device further comprising a target acceleration calculation unit that sets the target vehicle acceleration based on target control information.

4. In the vehicle control device according to claim 3, The target acceleration calculation unit is a vehicle control device that sets the target vehicle acceleration by extracting only the acceleration generated by the longitudinal force of each of the wheels.

5. In the vehicle control device according to claim 2, The vehicle further includes a tire vertical force ratio calculation unit that calculates the ratio of vertical force distribution between multiple wheels based on the acceleration generated during vehicle operation. The vehicle control device includes a target slip ratio calculation unit that sets a target slip ratio for each wheel based on the tire vertical force distribution ratio.

6. In the vehicle control device according to claim 2, The target slip ratio calculation unit calculates the target slip ratio λiref using the following formula, where axref is the target vehicle acceleration, Kb is the braking coefficient of the wheels, and αxiref is the target distribution ratio. [Math 1] A vehicle control device that calculates based on the following.

7. In the vehicle control device according to claim 2, The vehicle further includes a tire vertical force ratio calculation unit that calculates the ratio of vertical force distribution between multiple wheels based on the acceleration generated during vehicle operation. The slip ratio calculation unit is a vehicle control device that calculates the slip ratio for each wheel based on the vehicle's longitudinal acceleration, the tire's vertical force distribution ratio, the wheel speed, and the braking coefficient of the wheel.

8. In the vehicle control device according to claim 2, The distribution ratio calculation unit is a vehicle control device that sets the distribution ratio so that the longitudinal force of the left and right wheels is the same.

9. In the vehicle control device according to claim 7, A vehicle control device further comprising a tire characteristic estimation unit that estimates the braking coefficient based on the vehicle's longitudinal acceleration, wheel speed, and tire load.

10. In the vehicle control device according to claim 2, The distribution ratio calculation unit further sets the distribution ratio considering the input amount related to steering, the yaw rate, and the steering angle, in a vehicle control device.

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