vehicle

Abstract

To achieve both suppression of tire wear dust and improvement of fuel efficiency in a vehicle including a regenerative braking device for applying regenerative braking force to a wheel and a friction braking device for applying friction braking force to the wheel.SOLUTION: A regenerative braking device (20) applies regenerative braking force to a regenerative braking wheel (WF). A friction braking device (30) applies friction braking force to each wheel. A control device (50) includes a temperature acquisition unit, a required braking force acquisition unit, and a braking force control unit. The temperature acquisition unit acquires a surface temperature (Twf) of the regenerative braking wheel during traveling of a vehicle. The required braking force acquisition unit acquires required braking force on the basis of a brake pedal operation amount. The braking force control unit distributes the required braking force to the regenerative braking force and the friction braking force for each wheel. On the basis of the surface temperature of the regenerative braking wheel acquired by the temperature acquisition unit, the braking force control unit controls distribution of the regenerative braking force to the required braking force such that the surface temperature of the regenerative braking wheel does not exceed a reference temperature determined in advance during the traveling of the vehicle.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to braking control of a vehicle including a regenerative braking device that applies a regenerative braking force to wheels and a friction braking device that applies a friction braking force.

Background Art

[0002] For example, Japanese Patent Application Laid-Open No. 2022-14403 (Patent Document 1) discloses a driving force control device that controls the driving force distribution ratio between the front and rear wheels so as to suppress the difference in the wear level of the tires of the front and rear wheels in a four-wheel drive vehicle. The driving force control device sets the distribution ratio of the driving force generated between the front and rear wheels such that the distribution ratio of the driving force of the tire with the lower wear level among the front and rear wheels is greater than the distribution ratio of the driving force of the tire with the higher wear level.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a vehicle including a regenerative braking device that applies a regenerative braking force to wheels and a friction braking device that applies a friction braking force, basically, in order to increase the amount of power recovered during braking, it is configured to apply as large a regenerative braking force as possible.

[0005] However, since the distribution of the braking force on the wheels to which the regenerative braking force is applied increases, stress concentrates on the wheels, resulting in an increase in the tire surface temperature and slip ratio of the wheels, and consequently, tire wear is promoted. An increase in the amount of tire wear increases the amount of dust discharged due to tire wear, raising concerns about the impact on the environment.

[0006] This disclosure has been made in view of the above-mentioned problems, and aims to achieve both suppression of tire wear dust and improvement of fuel efficiency in a vehicle equipped with a regenerative braking system that applies regenerative braking force to the wheels and a friction braking system that applies friction braking force. [Means for solving the problem]

[0007] A vehicle having multiple wheels, including regenerative braking wheels, comprises a regenerative braking system, a friction braking system, and a control unit. The regenerative braking system applies regenerative braking force to the regenerative braking wheels. The friction braking system applies friction braking force to each wheel. The control unit controls the braking force of the vehicle. The control unit includes a temperature acquisition unit, a required braking force acquisition unit, and a braking force control unit. The temperature acquisition unit acquires the surface temperature of the regenerative braking wheels while the vehicle is running. The required braking force acquisition unit acquires the required braking force based on the brake pedal operation amount. The braking force control unit distributes the required braking force to the regenerative braking force and the friction braking force of each wheel. Based on the surface temperature of the regenerative braking wheels acquired by the temperature acquisition unit, the braking force control unit controls the distribution of regenerative braking force to the required braking force so that the surface temperature of the regenerative braking wheels does not exceed a predetermined reference temperature while the vehicle is running. [Effects of the Invention]

[0008] According to this disclosure, in a vehicle equipped with a regenerative braking system that applies regenerative braking force to the wheels and a friction braking system that applies friction braking force, it becomes possible to achieve both suppression of tire wear dust and improvement of fuel efficiency. [Brief explanation of the drawing]

[0009] [Figure 1] This figure schematically shows the configuration of a vehicle according to an embodiment of the present disclosure. [Figure 2] This diagram shows the distribution ratio between the braking force on the front wheels and the braking force on the rear wheels. [Figure 3] This flowchart shows an example of a braking control process according to this embodiment. [Figure 4] This flowchart shows an example of a braking control process according to this embodiment. [Figure 5]This figure shows the time changes in required braking force, regenerative braking force, friction braking force, and front tire surface temperature during the execution of the dual braking control system. [Figure 6] This diagram shows the distribution ratio between the braking force on the front wheels and the braking force on the rear wheels. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. The same or corresponding parts in the drawings will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0011] <Vehicle configuration> Figure 1 is a schematic diagram showing the configuration of a vehicle 10 according to an embodiment of the present disclosure. As shown in Figure 1, the vehicle 10 is an electric vehicle. An electric vehicle can be any vehicle that uses the power of a battery 22 as its power source, such as an electric vehicle (hereinafter also referred to as "BEV (Battery Electric Vehicle)") or a plug-in hybrid vehicle (hereinafter also referred to as "PHEV (Plug-in Hybrid Vehicle)"). Hereafter, the Electronic Control Unit will also be referred to as "ECU".

[0012] Vehicle 10 is equipped with multiple wheels (tires), a regenerative braking system 20, a friction braking system 30, an EVECU 40, and a brake ECU 50. The ECU is an electronic control circuit whose main components are a microcomputer including a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), non-volatile memory, and an I / F (Interface). The CPU realizes various functions described later by executing a program stored in the ROM. Note that the EVECU 40 and the brake ECU 50 may be combined into a single ECU.

[0013] The multiple wheels include the left front wheel WFL, the right front wheel WFR, the left rear wheel WRL, and the right rear wheel WRR. In the following description, the left front wheel WFL and the right front wheel WFR may be collectively referred to as "front wheel WF," and the left rear wheel WRL and the right rear wheel WRR may be collectively referred to as "rear wheel WR." In this embodiment, vehicle 10 is assumed to be a front-wheel-drive four-wheeled automobile, but the number of wheels and the drive system can be changed as appropriate. For example, the drive system may be rear-wheel drive or four-wheel drive.

[0014] The regenerative braking system 20 comprises a motor generator 21, a battery 22, an inverter 23, and a transmission 24. The motor generator 21 is composed of an AC synchronous motor. The output shaft of the motor generator 21 is connected to the transmission 24 so as to be able to transmit power to the left front wheel WFL and the right front wheel WFR. The regenerative braking system 20 also functions as a drive system that drives the front wheel WF when the accelerator pedal 51a is pressed.

[0015] The battery 22 is composed of a rechargeable battery, such as a lithium-ion battery, which can be repeatedly charged and discharged. The rechargeable battery is not limited to a lithium-ion battery; other rechargeable batteries (for example, nickel-metal hydride batteries) may also be used. An electrolyte-type rechargeable battery or an all-solid-state rechargeable battery may be used as the rechargeable battery.

[0016] The inverter 23 is electrically connected to the motor generator 21 and the battery 22. When the motor generator 21 operates as a generator, the rotational (driving) energy of the front wheel WF is converted into electrical energy by the motor generator 21. The inverter 23 charges the battery 22 by converting the AC power supplied from the motor generator 21 into DC power and supplying it to the battery 22. At this time, the front wheel WF is given braking torque (regenerative braking force) based on regenerative force. On the other hand, when the motor generator 21 operates as an electric motor, the inverter 23 converts the DC power supplied from the battery 22 into AC power and supplies it to the motor generator 21. As a result, the motor generator 21 is driven and driving torque (driving force) is applied to the front wheel WF.

[0017] Thus, the motor generator 21 is a braking actuator that applies a regenerative braking force to the front wheels WF and a driving actuator that applies a driving force to the front wheels WF. Note that the braking by the regenerative braking device 20 is also referred to as "regenerative brake".

[0018] The friction braking device 30 includes a hydraulic circuit 31 and friction brake mechanisms 32FL, 32FR, 32RL, and 32RR. Hereinafter, for the elements provided for each wheel, a suffix FL indicating the left front wheel WFL, a suffix FR indicating the right front wheel WFR, a suffix RL indicating the left rear wheel WRL, and a suffix RR indicating the right rear wheel WRR are added to the end of their reference numerals. However, when the wheel position is not specified for the elements provided for each wheel, those suffixes are omitted.

[0019] The hydraulic circuit 31 is provided between a master cylinder (not shown) that pressurizes the working fluid by the depressing force of the brake pedal 52a and the friction brake mechanisms 32 provided for the left front wheel WFL, the right front wheel WFR, the left rear wheel WRL, and the right rear wheel WRR, respectively. The hydraulic circuit 31 includes a reservoir, an oil pump, and various valve devices (not shown) and functions as a brake actuator. The hydraulic circuit 31 supplies the pressure of the working fluid (hereinafter also referred to as "hydraulic pressure") to a wheel cylinder 34 built in a brake caliper 33 of the friction brake mechanism 32. When the wheel cylinder 34 is actuated by the hydraulic pressure, a brake pad (not shown) is pressed against a brake disk 35, and a frictional braking force Ffrc is generated. Note that the braking by the friction braking device 30 is also referred to as "friction brake".

[0020] The EVECU 40 is connected to the brake ECU 50 via CAN (Controller Area Network) communication so that they can exchange information with each other. The EVECU 40 is electrically connected to various sensors including an accelerator pedal operation amount sensor 51 and receives output signals from these sensors. The accelerator pedal operation amount sensor 51 outputs a signal indicating the operation amount (hereinafter also referred to as "accelerator opening") AP of the accelerator pedal 51a that can be operated by the driver. The EVECU 40 is electrically connected to the regenerative braking device 20. The EVECU 40 generates a control signal for controlling the regenerative braking device 20 based on the accelerator opening AP and the operation of a shift lever (not shown), and transmits the generated control signal to the regenerative braking device 20.

[0021] The brake ECU 50 is electrically connected to a brake pedal operation amount sensor 52, wheel speed sensors 53 (53FL, 53FR, 53RL, 53RR) and an acceleration sensor 54, and receives output signals from these sensors. The brake pedal operation amount sensor 52 outputs a signal indicating the operation amount (hereinafter also referred to as "brake pedal operation amount") BP of the brake pedal 52a.

[0022] The brake ECU 50 calculates a required braking torque Tr* based on the brake pedal operation amount BP and the vehicle speed SPD, and calculates a required braking force Freq by multiplying the required braking torque Tr* by the dynamic radius r of the front wheels WF. The vehicle speed SPD is calculated, for example, as the average value of the wheel speeds Vwfl, Vwfr, Vwrl, Vwrr of each wheel obtained from the wheel speed sensor 53.

[0023] The brake ECU 50 distributes the required braking force Freq to the target value of the regenerative braking force Frgn (hereinafter also referred to as "target regenerative braking force") Frgnt, the target value of the front wheel friction braking force Ffrcf (hereinafter also referred to as "target front wheel friction braking force") Ffrcft, and the target value of the rear wheel friction braking force Ffrcr (hereinafter also referred to as "target rear wheel friction braking force") Ffrcrt, as described below. The brake ECU 50 applies a regenerative braking force Frgn equal to the target regenerative braking force Frgnt to the front wheel WF using the regenerative braking device 20. The brake ECU 50 applies a front wheel friction braking force Ffrcf equal to the target front wheel friction braking force Ffrcft to the front wheel WF by controlling the braking pressure of the wheel cylinders 34FL and 34FR, respectively. The brake ECU 50 applies a rear wheel friction braking force Ffrcr, equal to the target rear wheel friction braking force Ffrcrt, to the rear wheel WR by controlling the braking pressure of the wheel cylinders 34RL and 34RR, respectively.

[0024] The wheel speed sensor 53 outputs a wheel speed signal Ni corresponding to the rotation speed of the corresponding wheel. The acceleration sensor 54 outputs a signal indicating the vehicle acceleration signal Gx, which is the longitudinal acceleration of the vehicle 10.

[0025] <Braking control> As described above, in the vehicle 10 according to this embodiment, a regenerative braking force Frgn is applied to the front wheel WF by the regenerative braking device 20, and a friction braking force Ffrc is applied to the front wheel WF and rear wheel WR by the friction braking device 30. When the driver operates the brake pedal 52a while the vehicle 10 is in motion, in order to recover as much regenerative power as possible, the brake ECU 50 basically allocates the required braking force Freq corresponding to that operation to the regenerative braking force Frgn rather than the friction braking force Ffrc. In certain situations, if the regenerative braking force Frgn applied (distributed) to the front wheel WF exceeds the maximum regenerative braking force (hereinafter also referred to as "maximum regenerative braking force") Frgnmax that the regenerative braking device 20 can generate, the brake ECU 50 applies the friction braking force Ffrc to the front wheel WF and rear wheel WR in addition to the maximum regenerative braking force Frgnmax. The maximum regenerative braking force Frgnmax primarily depends on the power conversion capability of the inverter 23.

[0026] Next, with reference to Figure 2, we will explain how braking force is distributed when the driver operates the brake pedal 52a to decelerate the vehicle 10 while the vehicle 10 is in motion. Figure 2 is a diagram showing the distribution ratio between the braking force Fbf applied to the front wheel WF (hereinafter also referred to as "front wheel braking force") and the braking force Fbr applied to the rear wheel WR (hereinafter also referred to as "rear wheel braking force").

[0027] In Figure 2, curve L1 is a line representing the distribution ratio based on the contact load ratio of the front wheel WF and the rear wheel WR, and is called the "ideal braking force distribution line L1". Straight line L2 is a line representing the actual braking force distribution ratio, and is called the "normal braking distribution line L2". In order to prevent the behavior of the vehicle 10 from becoming unstable due to the rear wheel WR locking before the front wheel WF, the normal braking distribution line L2 is set such that the ratio of the front wheel braking force Fbf to the rear wheel braking force Fbr is greater than the ratio of the front wheel braking force Fbf to the rear wheel braking force Fbr on the ideal braking force distribution line L1.

[0028] The straight line L3 is a line that connects points where the sum of the front wheel braking force Fbf and the rear wheel braking force Fbr (Fbf + Fbr) is equal, and is called the "equal deceleration line L3". In Figure 2, the points on the equal deceleration line L3 are the points where the sum of the front wheel braking force Fbf and the rear wheel braking force Fbr is 4000N.

[0029] The brake ECU 50 is configured to prioritize regenerative braking by the regenerative braking system 20 over friction braking by the friction braking system 30 in order to improve fuel efficiency (to recover as much power as possible). Therefore, when the brake pedal 52a is pressed, only the front wheel braking force Fbf increases along the regenerative brake distribution line L4 (i.e., along the horizontal axis) from the origin O of the graph shown in Figure 2. In the example in Figure 2, the maximum regenerative braking force Frgnmax is 4000N. In a certain situation, if the driver's requested braking force Freq is 5000N, when the front wheel braking force Fbf reaches 4000N, the brake ECU 50 generates friction braking force Ffrc while maintaining the regenerative braking force Frgn. Therefore, when the front wheel braking force Fbf exceeds 4000N, the regenerative brake distribution line L4 extends with the same slope as the normal brake distribution line L2 until the friction braking force Ffrc becomes 1000N (up to point P0).

[0030] In the following explanation, the distribution of regenerative braking force Frgn and friction braking force Ffrc based on the normal brake distribution line L2 is referred to as the "normal distribution." In the normal distribution, the brake ECU 50 distributes the required braking force Freq to the front wheel braking force Fbf and the rear wheel braking force Fbr according to the ratio represented by the normal brake distribution line L2. The brake ECU 50 then distributes the front wheel braking force Fbf to the target regenerative braking force Frgnt and the target front wheel friction braking force Ffrcft, and sets all of the rear wheel braking force Fbr to the target rear wheel friction braking force Ffrcrt.

[0031] In contrast, the distribution of regenerative braking force Frgn and friction braking force Ffrc based on the regenerative brake distribution line L4 is called "regenerative enhancement distribution." In regenerative enhancement distribution, the brake ECU 50 preferentially allocates the required braking force Freq to the regenerative braking force Frgn rather than the friction braking force Ffrc. With regenerative enhancement distribution, more regenerative power can be recovered when the driver operates the brake pedal 52a, thus improving the fuel efficiency of the vehicle 10. However, on the other hand, compared to the normal distribution, in regenerative enhancement distribution, the distribution of braking force applied to the front wheel WF, which is a regenerative braking wheel, is greater than the distribution of braking force applied to the rear wheel WR. As a result, stress is concentrated on the front wheel WF, which increases the surface temperature and slip ratio of the tire constituting the front wheel WF, and consequently accelerates tire wear. Tire wear is typically expressed as the amount of wear from a new state (decrease in tire radius), and by applying regenerative enhancement distribution, even if the required braking force Freq is the same, tire wear will increase compared to the normal distribution. Furthermore, increased tire wear raises concerns about environmental impacts, as it increases the amount of dust emitted due to tire wear.

[0032] To address these concerns, in this embodiment, as described below, the brake ECU 50 acquires the tire surface temperature Twf of the front wheel WF (regenerative braking wheel) while the vehicle 10 is in motion, and controls the distribution of the regenerative braking force Frgn in the required braking force Freq based on the acquired tire surface temperature Twf, so that the tire surface temperature Twf does not exceed a predetermined reference temperature Tref. The "reference temperature Tref" is the surface temperature at which tire wear is likely to occur, and mainly depends on the components and characteristics of the tire's tread rubber. The reference temperature Tref can be set in advance by the vehicle 10 manufacturer, etc., through experiments and simulations, and stored in the ROM of the brake ECU 50.

[0033] Returning to Figure 1, the vehicle 10 is further equipped with a temperature sensor 60 for detecting the tire surface temperature Twf of the front wheel WF. The temperature sensor 60 is located near the front wheel WF to detect the tire surface temperature Twf of the front wheel WF and outputs a signal indicating the detected value to the brake ECU 50. Alternatively, a temperature sensor 60 may be installed on both the left front wheel WFL and the right front wheel WFR. In this case, the average of the acquired tire surface temperatures Twfr of the right front wheel WFR and Twfl of the left front wheel WFL is calculated as the tire surface temperature Twf of the front wheel WF.

[0034] The brake ECU 50 can be configured to estimate the tire surface temperature Twf from the vehicle 10's driving history, instead of acquiring the detected value of the tire surface temperature Twf from the temperature sensor 60. The vehicle 10's driving history includes information on the vehicle 10's mileage and driving conditions. The vehicle 10's driving conditions include information such as the vehicle 10's driving route, vehicle speed, weather, and outside temperature. The vehicle 10's driving conditions can be acquired, for example, using GPS (Global Positioning System). The brake ECU 50 estimates the current tire surface temperature Twf by applying the current vehicle 10's driving history to a lookup table MapTwf that defines the relationship between the vehicle 10's driving history and the tire surface temperature Twf. The lookup table MapTwf is predetermined through experiments and simulations, etc., and stored in the brake ECU 50's ROM.

[0035] The brake ECU 50 controls the distribution of the regenerative braking force Frgn at the required braking force Freq between the normal distribution and the regenerative-enhanced distribution, depending on the tire surface temperature Twf of the front wheel WF, thereby achieving both suppression of tire wear dust and improvement of fuel efficiency. In the following explanation, this type of braking control will also be referred to as "balance control". The method of distributing the braking force to the front wheel WF and rear wheel WR in this balance control will be explained with reference to Figure 2.

[0036] In Figure 2, multiple lines L5 to L7 are shown between the normal brake distribution line L2 and the regenerative brake distribution line L4. Lines L5 to L7 represent the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr in the dual braking control, and are referred to as the "dual braking distribution lines L5 to L7". Dual braking distribution lines L5 to L7 have the same slope as the normal brake distribution line L2. Dual braking distribution lines L5, L6, and L7 intersect the horizontal axis when the front wheel braking force Fbf is 3000N, 2000N, and 1000N, respectively. The number of dual braking distribution lines is not limited to three; there may be one or more.

[0037] When the driver operates the brake pedal 52a while the vehicle 10 is in motion, the brake ECU 50 selects one of the normal brake distribution line L2, the regenerative brake distribution line L4, and the dual brake distribution lines L5 to L7 according to the tire surface temperature Twf of the front wheel WF, and based on the selected brake distribution line, distributes the required braking force Freq to the target value of friction braking force (hereinafter also referred to as "target friction braking force") Ffrct and the target regenerative braking force Frgnt.

[0038] For example, if the driver's requested braking force Freq is 4000N, in the regenerative braking distribution, all of the requested braking force Freq is distributed to the front wheel braking force Fbf based on the regenerative braking distribution line L4, and the rear wheel braking force Fbr is set to 0. By increasing the distribution of the target regenerative braking force Frgnt to this front wheel braking force Fbf as much as possible, a large amount of regenerative power can be recovered. The distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr is set at point P1 on the regenerative braking distribution line L4.

[0039] In normal distribution, the normal brake distribution line L2 is selected. The distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr to the required braking force Freq is set at point P5, which is the intersection of the normal brake distribution line L2 and the equal deceleration line L3. The front wheel braking force Fbf is distributed to the target regenerative braking force Frgnt and the target friction braking force Ffrcft for the front wheels.

[0040] When the dual-purpose brake distribution line L5 is selected, the brake ECU 50 generates rear-wheel braking force Fbr when the front-wheel braking force Fbf reaches 3000N. The distribution ratio of the front-wheel braking force Fbf and the rear-wheel braking force Fbr with respect to the required braking force Freq is set at point P2, which is the intersection of the dual-purpose brake distribution line L5 and the equal deceleration line L3. The distribution of the target regenerative braking force Frgnt in the required braking force Freq is smaller than the distribution of the target regenerative braking force Frgnt in the regenerative enhancement distribution.

[0041] When the dual-purpose brake distribution line L6 is selected, the brake ECU 50 generates rear-wheel braking force Fbr when the front-wheel braking force Fbf reaches 2000N. The distribution ratio of the front-wheel braking force Fbf and the rear-wheel braking force Fbr with respect to the required braking force Freq is set at point P3, which is the intersection of the dual-purpose brake distribution line L6 and the equal deceleration line L3. The distribution of the target regenerative braking force Frgnt at the required braking force Freq is even smaller than the distribution at the dual-purpose brake distribution line L5.

[0042] When the dual brake distribution line L7 is selected, the brake ECU 50 generates a rear brake force Fbr when the front brake force Fbf reaches 1000N. The distribution ratio of the front brake force Fbf and the rear brake force Fbr with respect to the required brake force Freq is set at point P4, which is the intersection of the dual brake distribution line L7 and the equal deceleration line L3.

[0043] If the required braking force Freq remains unchanged, the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr changes from point P1 on the constant deceleration line L3 through points P2, P3, and P4 to point P5. That is, the distribution of the front wheel braking force Fbf at the required braking force Freq decreases, while the distribution of the rear wheel braking force Fbr increases. As a result, the distribution of the regenerative braking force Frgn at the required braking force Freq decreases, moving from a regenerative-enhanced distribution to a normal distribution.

[0044] In the dual-control system, the brake ECU 50 reduces the distribution of regenerative braking force Frgn in the required braking force Freq when it determines that the tire surface temperature Twf is on an upward trend. As the proportion of the front wheel braking force Fbf in the required braking force Freq decreases, stress concentration on the front wheel WF when the driver operates the brake pedal 52a can be alleviated. Therefore, the rise in tire surface temperature Twf is suppressed, and tire wear can be suppressed. On the other hand, as the proportion of regenerative braking force Frgn in the required braking force Freq decreases, the amount of power recovered decreases.

[0045] By controlling the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr in this way, the rise in tire surface temperature Twf is suppressed. If it is estimated that the tire surface temperature Twf will not exceed the reference temperature Tref while the vehicle 10 is running, the brake ECU 50 returns the distribution of regenerative braking force Frgn and friction braking force Ffrc to the regenerative improvement distribution. Therefore, the decrease in the amount of power recovered can be suppressed. In this balancing control, the brake ECU 50 controls the distribution of the regenerative braking force Frgn at the required braking force Freq according to the tire surface temperature Twf, while satisfying the required braking force Freq. This makes it possible to achieve both suppression of tire wear dust and improvement of fuel efficiency without causing discomfort to the driver.

[0046] Next, an example of braking control in the brake ECU 50 will be described. Figures 3 and 4 are flowcharts showing an example of the braking control process according to this embodiment.

[0047] As shown in Figure 3, in step 10 (hereinafter referred to as "S"), the brake ECU 50 determines whether or not a tire change has been performed. For example, if the tire pressure sensor that monitors the tire pressure of the vehicle 10 has been initialized, S10 is determined to be YES, and if the tire pressure sensor has not been initialized, S10 is determined to be NO.

[0048] If a tire change is performed (YES in S10), the brake ECU 50 proceeds to S20 to determine whether the replacement tire is a genuine part or not. For example, if a dealer confirms that the replacement tire is a genuine part, they can write information to that effect to the ROM of the brake ECU 50. The brake ECU 50 makes the determination in S20 based on the presence or absence of this information. If it is determined that the replacement tire is not a genuine part (NO in S20), the brake ECU 50 prohibits the execution of the compatibility control. This is because the reference temperature Tref mainly depends on the composition and characteristics of the tire's tread rubber. This prevents a decrease in the accuracy of the compatibility control when the reference temperature Tref of a genuine tire and a non-genuine tire differ.

[0049] If the tire change has not been performed (NO in S10) or if the replacement tire is an original part (YES in S20), the brake ECU 50 performs a balance control (see Figure 4). The flowchart shown in Figure 4 is executed repeatedly while the vehicle 10 is in motion.

[0050] The brake ECU 50 calculates the required braking force Freq based on the brake pedal operation amount BP, vehicle speed SPD, and the dynamic radius of the front wheel WF (S01). The brake ECU 50 obtains the tire surface temperature Twf of the front wheel WF (S02). The brake ECU 50 obtains the tire surface temperature Twf based on the output signal of the temperature sensor 60 or the driving record of the vehicle 10.

[0051] The brake ECU 50 determines whether the tire surface temperature Twf is above or below a threshold X (S03). The threshold X is set to a temperature lower than the reference temperature Tref of the front tire WF. If the tire surface temperature Twf is above or below a threshold X (YES in S03), the brake ECU 50 determines whether the vehicle 10's automatic driving control or driver assistance control is active (S04). The determination in S04 can be made, for example, based on communication between the automatic driving system or driver assistance system installed in the vehicle 10 and the brake ECU 50. The automatic driving system is configured to create a driving plan for the vehicle 10. While automatic driving control is active, various vehicle controls are executed so that the vehicle 10 drives according to the created driving plan.

[0052] If vehicle 10 is not equipped with either an autonomous driving system or a driver assistance system, or if vehicle 10 is equipped with either an autonomous driving system or a driver assistance system, but the autonomous driving control or driver assistance control is stopped, then S04 will be judged as NO.

[0053] If the vehicle 10's automatic driving control or driver assistance control is active (YES in S04), the brake ECU 50 transmits a signal to the automatic driving system or driver assistance system indicating that the front wheel WF tire surface temperature Twf is trending upward. Upon receiving this signal from the brake ECU 50, the automatic driving system or driver assistance system changes the vehicle 10's route to a route with less required braking force Freq (S05). As a route with less required braking force Freq, for example, a route with fewer right and left turns and uphill sections is selected. After the route change in S05, the process returns to S06.

[0054] If the tire surface temperature Twf is less than the threshold X (NO in S03), if the vehicle 10's automatic driving control or driver assistance control is not in operation (NO in S04), or if the vehicle 10's driving route is changed (S05), the brake ECU 50 determines whether the rate of increase of the tire surface temperature Twf is greater than or equal to the threshold Y (S06). The rate of increase of the tire surface temperature Twf corresponds to the amount of increase of the tire surface temperature Twf per unit time (ΔTwf / Δt).

[0055] If the rate of increase of the tire surface temperature Twf is greater than or equal to the threshold Y (YES in S06), the brake ECU 50 determines that the tire surface temperature Twf is on an upward trend and reduces the distribution of regenerative braking force Frgn in the required braking force Freq (S07). In S07, the brake ECU 50 selects a brake distribution line that is one step closer to the normal distribution line than the currently selected brake distribution line, and determines the distribution ratio of front wheel braking force Fbf and rear wheel braking force Fbr based on this selected brake distribution line. That is, the brake ECU 50 increases the distribution of rear wheel braking force Fbr in the required braking force Freq and decreases the distribution of front wheel braking force Fbf.

[0056] For example, if the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr is at point P1 on the regenerative brake distribution line L4, the brake ECU 50 changes the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr to point P2 on the balanced brake distribution line L5. If it is determined that the tire surface temperature Twf is still on an upward trend even after changing the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr to point P3 on the balanced brake distribution line L6, the brake ECU 50 further changes the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr to point P3 on the balanced brake distribution line L6.

[0057] Next, the brake ECU 50 predicts the change in the tire surface temperature Twf during vehicle 10's operation based on the current tire surface temperature Twf and the vehicle 10's planned route. The vehicle 10's planned route includes information on the planned distance and driving conditions (driving route, vehicle speed, weather, and outside temperature, etc.). The vehicle 10's driving conditions can be obtained, for example, using GPS. The brake ECU 50 predicts the change in the tire surface temperature Twf by applying the vehicle 10's planned route to a lookup table MapTwf, which defines the relationship between the vehicle 10's driving history and the tire surface temperature Twf. Based on the predicted change in the tire surface temperature Twf, the brake ECU 50 estimates whether the tire surface temperature Twf will exceed the reference temperature Tref during vehicle 10's operation (S08).

[0058] If it is estimated that the tire surface temperature Twf will exceed the reference temperature Tref while the vehicle 10 is in motion (YES in S08), the brake ECU 50 selects the normal brake distribution line L2 in S10 (normal distribution). Based on the normal brake distribution line L2, the brake ECU 50 determines the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr.

[0059] On the other hand, if it is estimated that the tire surface temperature Twf will not exceed the reference temperature Tref while the vehicle 10 is in motion (NO in S07), the brake ECU 50 selects the regenerative brake distribution line L4 in S10 (regenerative enhancement distribution). Based on the regenerative brake distribution line L4, the brake ECU 50 determines the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr.

[0060] Figure 5 shows the time evolution of the target regenerative braking force Frgnt, target friction braking force Ffrct, and front wheel tire surface temperature Twf during the execution of the compatible control. In Figure 5, it is assumed that the required braking force Freq based on the brake pedal operation amount BP is constant. The solid line shows the time evolution of the tire surface temperature Twf, and the dotted line shows the trend (prediction) of the tire surface temperature Twf during driving.

[0061] If the tire surface temperature Twf is on an upward trend while the vehicle 10 is running with the regenerative braking enhancement distribution (YES in S06), the distribution of the target regenerative braking force Frgnt in the required braking force Freq decreases, and the distribution of the target friction braking force Ffrct increases (times t1-t2). Furthermore, if it is estimated that the tire surface temperature Twf will exceed the reference temperature Tref while the vehicle 10 is running (YES in S08), the distribution of the target regenerative braking force Frgnt decreases further, and the distribution of the target friction braking force Ffrct increases further, according to the normal distribution (times t2-t4).

[0062] If it is determined that the tire surface temperature Twf does not exceed the reference temperature Tref while the vehicle 10 is in motion (NO in S08), the allocation of the target regenerative braking force Frgnt in the required braking force Freq increases, and the allocation of the target friction braking force Ffrct decreases, returning the system to a regenerative braking enhancement allocation. In the example in Figure 5, the allocation of the target regenerative braking force Frgnt and the target friction braking force Ffrct changes at a predetermined rate of change.

[0063] As described above, according to the vehicle of this embodiment, the distribution of the regenerative braking force Frgn at the required braking force Freq is controlled based on the tire surface temperature Twf of the front wheel WF, which is a regenerative braking wheel, so that the tire surface temperature Twf does not exceed the reference temperature Tref while the vehicle is running, while satisfying the required braking force Freq. This makes it possible to achieve both the suppression of tire wear dust and improved fuel efficiency.

[0064] <Example of changes> (1) In the above-described embodiment, when an automated driving system or driver assistance system is in operation in a vehicle equipped with an automated driving system or driver assistance system, a configuration was described in which the vehicle's driving route is changed to a route with less required braking force Freq in response to the tire surface temperature Twf of the front wheels WF exceeding a threshold X. Instead of this configuration, a notification device mounted on the vehicle may be used to recommend a driving route with less required braking force Freq to the user.

[0065] (2) In the embodiments described above, braking control in a vehicle in which the front wheel WF is a regenerative braking wheel has been described, but the braking control according to this disclosure can also be applied to vehicles in which the rear wheel WR is a regenerative braking wheel and to four-wheel drive vehicles. For example, the brake ECU of a vehicle in which the rear wheel WR is a regenerative braking wheel can perform simultaneous control using the distribution ratio of the front wheel braking force and the rear wheel braking force shown in Figure 6.

[0066] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of Symbols]

[0067] 10 Vehicle, 20 Regenerative braking system, 30 Friction braking system, 40 EVECU, 50 Brake ECU, 52 Brake pedal actuation sensor, 60 Temperature sensor, BP Brake pedal actuation, WF Front wheel, WR Rear wheel.

Claims

1. A vehicle having multiple wheels, including regenerative braking wheels, A regenerative braking device that applies regenerative braking force to the aforementioned regenerative braking wheel, A friction braking device that applies frictional braking force to each wheel, The vehicle is equipped with a control device that controls the braking force of the vehicle, The control device is A temperature acquisition unit that acquires the surface temperature of the regenerative braking wheel while the vehicle is in motion, A required braking force acquisition unit that acquires the required braking force based on the amount of brake pedal operation, The system includes a braking force control unit that distributes the requested braking force to the regenerative braking force and the frictional braking force of each wheel, A vehicle wherein the braking force control unit controls the distribution of the regenerative braking force to the requested braking force based on the surface temperature of the regenerative braking wheel acquired by the temperature acquisition unit, such that the surface temperature of the regenerative braking wheel does not exceed a predetermined reference temperature while the vehicle is running.

2. The temperature acquisition unit acquires the current surface temperature of the regenerative braking wheel based on the output of the temperature sensor that detects the temperature of the regenerative braking wheel, or based on the vehicle's driving history. The vehicle according to claim 1, wherein the braking force control unit determines that the surface temperature of the regenerative braking wheel is currently on an upward trend, and reduces the distribution of the regenerative braking force in the required braking force.

3. The aforementioned braking force control unit, Based on the current surface temperature of the regenerative braking wheel and the planned route of the vehicle, the change in the surface temperature of the regenerative braking wheel during the vehicle's operation is predicted. Based on the predicted change in the surface temperature of the regenerative braking wheel, it is estimated whether the surface temperature of the regenerative braking wheel will exceed the reference temperature while the vehicle is running. If it is estimated that the temperature of the regenerative braking wheel exceeds the reference temperature while the vehicle is in motion, the distribution of the regenerative braking force in the required braking force is further reduced. The vehicle according to claim 2, wherein when it is estimated that the temperature of the regenerative braking wheel does not exceed the reference temperature while the vehicle is running, the distribution of the regenerative braking force in the required braking force is increased.

4. The system further comprises an automated driving system that creates a driving plan for the aforementioned vehicle. The control device is configured to control the movement of the vehicle in accordance with commands from the automatic driving system. The vehicle according to any one of claims 1 to 3, wherein if the surface temperature of the regenerative braking wheel obtained by the temperature acquisition unit exceeds a predetermined threshold temperature, the automatic driving system changes the vehicle's driving route to a route in which the required braking force is smaller than the current driving route.

5. The vehicle according to claim 1, wherein the control device prohibits the control of the distribution of the regenerative braking force based on the temperature of the regenerative braking wheels when the plurality of wheels are replaced with non-genuine parts.

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