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 equipped with a regenerative braking device that applies a regenerative braking force to wheels and a friction braking device that applies a frictional 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 degree 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 smaller wear degree among the front and rear wheels is larger than the distribution ratio of the driving force of the tire with the larger wear degree.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a vehicle equipped with a regenerative braking device that applies a regenerative braking force to wheels and a friction braking device that applies a frictional 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 accelerating tire wear. The increase in the tire wear amount increases the amount of dust discharged due to tire wear, raising concerns about the impact on the environment.

[0006] The present disclosure has been made in view of the above problems, and in a vehicle equipped with a regenerative braking device that applies a regenerative braking force to a wheel and a friction braking device that applies a frictional braking force, it is to achieve both suppression of tire wear dust and improvement in fuel efficiency.

Means for Solving the Problems

[0007] A vehicle having a plurality of wheels including regenerative braking wheels includes a regenerative braking device, a friction braking device, and a control device. The regenerative braking device applies a regenerative braking force to the regenerative braking wheels. The friction braking device applies a frictional braking force to each wheel. The control device controls the braking force of the vehicle. The control device 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 during the running of the vehicle. 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 frictional braking force of each wheel. The braking force control unit controls the distribution of the regenerative braking force with respect to the required braking force so that the surface temperature of the regenerative braking wheels does not exceed a predetermined reference temperature during the running of the vehicle based on the surface temperature of the regenerative braking wheels acquired by the temperature acquisition unit.

Advantages of the Invention

[0008] According to the present disclosure, in a vehicle equipped with a regenerative braking device that applies a regenerative braking force to a wheel and a friction braking device that applies a frictional braking force, it is possible to achieve both suppression of tire wear dust and improvement in fuel efficiency.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

[0011] <Vehicle Configuration> FIG. 1 is a diagram schematically showing the configuration of a vehicle 10 according to an embodiment of the present disclosure. As shown in FIG. 1, the vehicle 10 is an electric vehicle. The electric vehicle may be a vehicle that uses the power of the battery 22 as a power source. For example, it may be a battery 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)"). Hereinafter, an electronic control unit will also be referred to as an "ECU".

[0012] The vehicle 10 includes a plurality of wheels (tires), a regenerative braking device 20, a frictional braking device 30, an EV ECU 40, and a brake ECU 50. The ECU is an electronic control circuit having a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a non-volatile memory, and an I / F (Interface) as main components. The CPU realizes various functions described later by executing the programs stored in the ROM. Note that the EV ECU 40 and the brake ECU 50 may be combined into one ECU.

[0013] The plurality of wheels includes a left front wheel WFL, a right front wheel WFR, a left rear wheel WRL, and a 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 the "front wheels WF", and the left rear wheel WRL and the right rear wheel WRR may be collectively referred to as the "rear wheels WR". In the present embodiment, the vehicle 10 is assumed to be a front-wheel drive four-wheel vehicle, but the number of wheels and the drive method can be changed as appropriate. For example, the drive method may be rear-wheel drive or four-wheel drive.

[0014] The regenerative braking device 20 includes 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 via the transmission 24 to the left front wheel WFL and the right front wheel WFR so as to be capable of transmitting power. The regenerative braking device 20 also functions as a drive device for driving the front wheels WF when the accelerator pedal 51a is depressed.

[0015] The battery 22 is composed of a secondary battery such as a lithium-ion battery that can repeatedly charge and discharge. The secondary battery is not limited to a lithium-ion battery and may be other secondary batteries (for example, nickel-metal hydride batteries). As the secondary battery, an electrolyte-type secondary battery or an all-solid-state secondary battery may be adopted.

[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 (operating) energy of the front wheels 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, a braking torque (regenerative braking force) based on the regenerative force is applied to the front wheels WF. 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. Thereby, the motor generator 21 is driven, and a driving torque (driving force) is applied to the front wheels WF.

[0017] Thus, the motor generator 21 is a braking actuator that applies a regenerative braking force to the front wheels WF, and is also 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, 32RR. Hereinafter, for 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 elements provided for each wheel, those suffixes are omitted.

[0019] The hydraulic circuit 31 is provided between a master cylinder (not shown) that pressurizes hydraulic oil by the depressing force of the brake pedal 52a and the friction brake mechanisms 32 provided for the left front wheel WFL, right front wheel WFR, left rear wheel WRL, and 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 into 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] As described below, 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 the "target regenerative braking force") Frgnt, the target value of the front-wheel frictional braking force Ffrcf (hereinafter also referred to as the "target front-wheel frictional braking force") Ffrcft, and the target value of the rear-wheel frictional braking force Ffrcr (hereinafter also referred to as the "target rear-wheel frictional braking force") Ffrcrt. The brake ECU 50 applies a regenerative braking force Frgn equal to the target regenerative braking force Frgnt to the front wheels WF using the regenerative braking device 20. The brake ECU 50 applies a front-wheel frictional braking force Ffrcf equal to the target front-wheel frictional braking force Ffrcft to the front wheels WF by controlling the braking pressures of the wheel cylinders 34FL and 34FR, respectively. The brake ECU 50 applies a rear-wheel frictional braking force Ffrcr equal to the target rear-wheel frictional braking force Ffrcrt to the rear wheels WR by controlling the braking pressures of the wheel cylinders 34RL and 34RR, respectively.

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

[0025] <Brake Control> As described above, in the vehicle 10 according to the present embodiment, a regenerative braking force Frgn by the regenerative braking device 20 is applied to the front wheels WF, and a frictional braking force Ffrc by the frictional braking device 30 is applied to the front wheels WF and the rear wheels WR. When the driver operates the brake pedal 52a during the running of the vehicle 10, the brake ECU 50 basically preferentially distributes the required braking force Freq corresponding to the operation to the regenerative braking force Frgn rather than the frictional braking force Ffrc in order to recover as much regenerative power as possible. In a certain situation, when the regenerative braking force Frgn applied to the front wheels WF (distributed) exceeds the maximum regenerative braking force (hereinafter also referred to as the "maximum regenerative braking force") Frgnmax that the regenerative braking device 20 can generate, the brake ECU 50 applies a frictional braking force Ffrc to the front wheels WF and the rear wheels WR in addition to the maximum regenerative braking force Frgnmax. The maximum regenerative braking force Frgnmax mainly depends on the power conversion ability of the inverter 23.

[0026] Next, with reference to FIG. 2, a method for distributing braking force when the driver operates the brake pedal 52a to decelerate the vehicle 10 during the running of the vehicle 10 will be described. FIG. 2 is a diagram showing the distribution ratio between the braking force applied to the front wheels WF (hereinafter also referred to as "front-wheel braking force") Fbf and the braking force applied to the rear wheels WR (hereinafter also referred to as "rear-wheel braking force") Fbr.

[0027] In FIG. 2, the curve L1 is a line representing the distribution ratio based on the grounding load ratio of the front wheels WF and the rear wheels WR, and is referred to as the "braking force ideal distribution line L1". The straight line L2 is a line representing the actual braking force distribution ratio, and is referred to as the "normal brake distribution line L2". In order to prevent the behavior of the vehicle 10 from becoming unstable due to the rear wheels WR locking earlier than the front wheels WF, the normal brake 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 braking force ideal distribution line L1.

[0028] The straight line L3 is a line connecting points where the sum (Fbf + Fbr) of the front-wheel braking force Fbf and the rear-wheel braking force Fbr is equal, and is referred to as the "equal deceleration line L3". In FIG. 2, the points on the equal deceleration line L3 are points where the sum of the front-wheel braking force Fbf and the rear-wheel braking force Fbr is 4000 N.

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

[0030] In the following description, the distribution of the regenerative braking force Frgn and the friction braking force Ffrc based on the normal brake distribution line L2 is referred to as "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. Then, the brake ECU 50 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] On the other hand, the distribution of the regenerative braking force Frgn and the frictional braking force Ffrc based on the regeneration brake distribution line L4 is referred to as "regeneration improvement distribution". In the regeneration improvement distribution, the brake ECU50 preferentially distributes the required braking force Freq to the regenerative braking force Frgn rather than the frictional braking force Ffrc. According to the regeneration improvement distribution, when the driver operates the brake pedal 52a, a large amount of regenerative power can be recovered, so that the fuel consumption of the vehicle 10 can be improved. However, on the other hand, compared with the normal distribution, in the regeneration improvement distribution, the distribution of the braking force applied to the front wheels WF, which are the regenerative braking wheels, is larger than the distribution of the braking force applied to the rear wheels WR. Therefore, due to the concentration of stress on the front wheels WF, the surface temperature and slip ratio of the tires constituting the front wheels WF increase, and as a result, the wear of the tires is promoted. The amount of tire wear is typically represented by the amount of wear from the new state (the amount of decrease in the tire radius). By applying the regeneration improvement distribution, even when the required braking force Freq is the same, the amount of tire wear increases compared to the normal distribution. In addition, since the increase in the amount of tire wear increases the amount of dust discharged due to tire wear, there are concerns about the impact on the environment.

[0032] To address such concerns, in this embodiment, as described below, the brake ECU50 acquires the tire surface temperature Twf of the front wheels WF (regenerative braking wheels) during the running of the vehicle 10, and based on the acquired tire surface temperature Twf, controls the distribution of the regenerative braking force Frgn in the required braking force Freq 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 tread rubber, etc. The reference temperature Tref can be preset by the manufacturer of the vehicle 10, etc. through experiments and simulations, etc., and stored in the ROM of the brake ECU50.

[0033] Returning to FIG. 1, the vehicle 10 further includes a temperature sensor 60 as a configuration for detecting the surface temperature Twf of the tire of the front wheel WF. The temperature sensor 60 is provided 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. Note that the temperature sensor 60 may be installed on each of the left front wheel WFL and the right front wheel WFR. In this case, the average value of the tire surface temperature Twfr of the right front wheel WFR and the tire surface temperature Twfl of the left front wheel WFL obtained is calculated as the tire surface temperature Twf of the front wheel WF.

[0034] Instead of the configuration in which the brake ECU 50 acquires the detected value of the tire surface temperature Twf from the temperature sensor 60, it can be configured to estimate the tire surface temperature Twf from the driving performance of the vehicle 10. The driving performance of the vehicle 10 includes information on the driving distance and driving conditions of the vehicle 10. The driving conditions of the vehicle 10 include information indicating the driving route, vehicle speed, weather, outside air temperature, etc. of the vehicle 10. The driving conditions of the vehicle 10 can be acquired using, for example, GPS (Global Positioning System). The brake ECU 50 estimates the current tire surface temperature Twf by applying the current driving performance of the vehicle 10 to a look-up table MapTwf that defines the relationship between the driving performance of the vehicle 10 and the tire surface temperature Twf. The look-up table MapTwf is determined in advance by experiments, simulations, etc. and is stored in the ROM of the brake ECU 50.

[0035] The brake ECU 50 controls the distribution of the regenerative braking force Frgn in the required braking force Freq between the normal distribution and the regeneration improvement distribution according to the tire surface temperature Twf of the front wheel WF, thereby realizing both the suppression of tire wear dust and the improvement of fuel efficiency. In the following description, such braking control is also referred to as "compatible control". The method of distributing the braking force to the front wheel WF and the rear wheel WR in this compatible control will be described with reference to FIG. 2.

[0036] In FIG. 2, between the normal brake distribution line L2 and the regenerative brake distribution line L4, a plurality of straight lines L5 to L7 are shown. The straight lines L5 to L7 are lines representing the distribution ratios of the front wheel braking force Fbf and the rear wheel braking force Fbr in the compatibility control, and are referred to as "compatibility brake distribution lines L5 to L7". The compatibility brake distribution lines L5 to L7 have the same slope as the normal brake distribution line L2. The compatibility brake distribution lines L5, L6, and L7 intersect the horizontal axis when the front wheel braking force Fbf is 3000 N, 2000 N, and 1000 N, respectively. The number of the compatibility brake distribution lines is not limited to 3, and may be singular or plural.

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

[0038] For example, when the required braking force Freq by the driver is 4000 N, in the regeneration improvement distribution, all of the required braking force Freq is distributed to the front wheel braking force Fbf based on the regenerative brake 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 in 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 the point P1 on the regenerative brake distribution line L4.

[0039] In the 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 with respect to the required braking force Freq is set at the 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 front wheel frictional braking force Ffrcft.

[0040] When the compatible brake distribution line L5 is selected, when the front wheel braking force Fbf reaches 3000 N, the brake ECU50 generates the rear wheel braking force Fbr. 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 a point P2 which is the intersection of the compatible brake distribution line L5 and the equal deceleration line L3. The distribution of the target regenerative braking force Frgnt at the required braking force Freq becomes smaller than the distribution of the target regenerative braking force Frgnt in the regeneration improvement distribution.

[0041] When the compatible brake distribution line L6 is selected, when the front wheel braking force Fbf reaches 2000 N, the brake ECU50 generates the rear wheel braking force Fbr. 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 a point P3 which is the intersection of the compatible 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 becomes even smaller than the distribution in the compatible brake distribution line L5.

[0042] When the compatible brake distribution line L7 is selected, when the front wheel braking force Fbf reaches 1000 N, the brake ECU50 generates the rear wheel braking force Fbr. 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 a point P4 which is the intersection of the compatible brake distribution line L7 and the equal deceleration line L3.

[0043] When the required braking force Freq does not change, the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr is changed from the point P1 on the equal deceleration line L3 through the points P2, P3, and P4 to the point P5. That is, the distribution of the front wheel braking force Fbf at the required braking force Freq decreases, and 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 from the regeneration improvement distribution toward the normal distribution.

[0044] In the compatibility control, when the brake ECU 50 determines that the tire surface temperature Twf is on the rise, it reduces the distribution of the regenerative braking force Frgn in the required braking force Freq. Since the ratio of the front-wheel braking force Fbf in the required braking force Freq decreases, the stress concentration on the front wheels WF when the driver operates the brake pedal 52a can be alleviated. Therefore, the wear of the tire can be suppressed because the rise in the tire surface temperature Twf is suppressed. On the other hand, since the ratio of the regenerative braking force Frgn in the required braking force Freq decreases, the power recovery amount decreases.

[0045] When the rise in the tire surface temperature Twf is suppressed by controlling the distribution ratio of the front-wheel braking force Fbf and the rear-wheel braking force Fbr in this way, and it is estimated that the tire surface temperature Twf does not exceed the reference temperature Tref during the running of the vehicle 10, the brake ECU 50 returns the distribution of the regenerative braking force Frgn and the frictional braking force Ffrc to the regeneration improvement distribution. Therefore, a decrease in the power recovery amount can be suppressed. In this way, in the compatibility control, the brake ECU 50 controls the distribution of the regenerative braking force Frgn in the required braking force Freq according to the tire surface temperature Twf while satisfying the required braking force Freq. According to this, it is possible to achieve both the suppression of tire wear dust and the improvement of fuel efficiency without giving the driver a sense of discomfort.

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

[0047] As shown in FIG. 3, in step (hereinafter, step is abbreviated as "S") 10, the brake ECU 50 determines whether a tire replacement has been executed. For example, when the air pressure sensor that monitors the air pressure of the tires of the vehicle 10 is initialized, S10 is determined to be YES, and when the air pressure sensor is not initialized, S10 is determined to be NO.

[0048] When tire replacement is executed (YES in S10), the brake ECU 50 proceeds to S20 to determine whether the replaced tire is an authentic product. For example, when the dealer confirms that the replaced tire is an authentic product, the dealer can write information indicating so in the ROM of the brake ECU 50. The brake ECU 50 makes the determination in S20 based on the presence or absence of such information. When it is determined that the replaced tire is not an authentic product (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 components and characteristics of the tread rubber of the tire. When the reference temperature Tref of an authentic tire is different from that of a non-authentic tire, it is possible to avoid a situation where the accuracy of the compatibility control deteriorates.

[0049] When tire replacement has not been executed (NO in S10) or when the replaced tire is an authentic product (YES in S20), the brake ECU 50 executes the compatibility control (see FIG. 4). The processing of the flowchart shown in FIG. 4 is repeatedly executed while the vehicle 10 is running.

[0050] The brake ECU 50 calculates the required braking force Freq based on the brake pedal operation amount BP, the vehicle speed SPD, and the dynamic radius of the front wheel WF (S01). The brake ECU 50 acquires the tire surface temperature Twf of the front wheel WF (S02). The brake ECU 50 acquires 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 or not the tire surface temperature Twf of the tire is equal to or higher than the threshold value X (S03). The threshold value X is set to a temperature lower than the reference temperature Tref of the tire of the front wheel WF. When the tire surface temperature Twf is equal to or higher than the threshold value X (YES in S03), the brake ECU 50 determines whether or not the automatic driving control or the driving support control of the vehicle 10 is in operation (S04). The determination in S04 can be made based on, for example, the communication between the automatic driving system or the driving support system mounted on the vehicle 10 and the brake ECU 50. The automatic driving system is configured to create a driving plan for the vehicle 10. During the operation of the automatic driving control, various vehicle controls are executed so that the vehicle 10 travels according to the created driving plan.

[0052] When the vehicle 10 is not equipped with either the automatic driving system or the driving support system, or when the vehicle 10 is equipped with the automatic driving system or the driving support system but the automatic driving control or the driving support control is stopped, S04 is determined as NO.

[0053] When the automatic driving control or the driving support control of the vehicle 10 is in operation (YES in S04), the brake ECU 50 transmits a signal indicating that the tire surface temperature Twf of the front wheel WF is on an upward trend to the automatic driving system or the driving support system. In response to receiving the signal from the brake ECU 50, the automatic driving system or the driving support system changes the driving route of the vehicle 10 to a driving route with a lower required braking force Freq (S05). As a driving route with a lower required braking force Freq, for example, a driving route with fewer right and left turns and slopes is selected. After changing the driving route by S05, the process returns to S06.

[0054] When the tire surface temperature Twf is less than the threshold value X (NO in S03), when the automatic driving control or driving support control of the vehicle 10 is not in operation (NO in S04), or when the driving route of the vehicle 10 is changed (S05), the brake ECU 50 determines whether the rising speed of the tire surface temperature Twf is equal to or higher than the threshold value Y (S06). The rising speed of the tire surface temperature Twf corresponds to the amount of increase in the tire surface temperature Twf per unit time (ΔTwf / Δt).

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

[0056] For example, when 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 compatible brake distribution line L5. When it is determined that the tire surface temperature Twf still has 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 P2, 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 compatible brake distribution line L6.

[0057] Next, the brake ECU 50 predicts the transition of the tire surface temperature Twf during the running of the vehicle 10 based on the current tire surface temperature Twf and the planned running of the vehicle 10. The planned running of the vehicle 10 includes information on the planned running distance of the vehicle 10 and running conditions (such as running route, vehicle speed, weather, and outside air temperature). The running conditions of the vehicle 10 can be obtained using, for example, GPS. The brake ECU 50 predicts the transition of the tire surface temperature Twf by applying the planned running of the vehicle 10 to a look-up table MapTwf that defines the relationship between the running performance of the vehicle 10 and the tire surface temperature Twf. The brake ECU 50 estimates whether the tire surface temperature Twf exceeds the reference temperature Tref during the running of the vehicle 10 based on the predicted transition of the tire surface temperature Twf (S08).

[0058] When it is estimated that the tire surface temperature Twf exceeds the reference temperature Tref during the running of the vehicle 10 (YES in S08), the brake ECU 50 selects the normal brake distribution line L2 by S10 (normal distribution). The brake ECU 50 determines the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr based on the normal brake distribution line L2.

[0059] On the other hand, when it is estimated that the tire surface temperature Twf does not exceed the reference temperature Tref during the running of the vehicle 10 (NO in S07), the brake ECU 50 selects the regenerative brake distribution line L4 by S10 (regenerative improvement distribution). The brake ECU 50 determines the distribution ratio of the front wheel braking force Fbf and the rear wheel braking force Fbr based on the regenerative brake distribution line L4.

[0060] FIG. 5 is a diagram showing the time changes of the target regenerative braking force Frgnt, the target frictional braking force Ffrct, and the tire surface temperature Twf of the front wheel WF during the execution of the compatibility control. In FIG. 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 change of the tire surface temperature Twf, and the dotted line shows the transition (prediction) of the tire surface temperature Twf during running.

[0061] When the tire surface temperature Twf of the vehicle 10 has an upward trend during the running of the vehicle 10 with the regenerative upward 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 frictional braking force Ffrct increases (time t1 to t2). Further, when it is estimated that the tire surface temperature Twf of the vehicle 10 exceeds the reference temperature Tref during the running of the vehicle 10 (YES in S08), according to the normal distribution, the distribution of the target regenerative braking force Frgnt further decreases, and the distribution of the target frictional braking force Ffrct further increases (time t2 to t4).

[0062] When it is determined that the tire surface temperature Twf of the vehicle 10 does not exceed the reference temperature Tref during the running of the vehicle 10 (NO in S08), the distribution of the target regenerative braking force Frgnt in the required braking force Freq increases, and the distribution of the target frictional braking force Ffrct decreases, so that the regenerative upward distribution is restored. In the example of FIG. 5, the distributions of the target regenerative braking force Frgnt and the target frictional braking force Ffrct change at a predetermined change rate.

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

[0064] <Modification example> (1) In the above-described embodiment, in the case where the automatic driving control or the driving support control is in operation in a vehicle equipped with an automatic driving system or a driving support system, the running route of the vehicle is changed to a running route with a small required braking force Freq in response to the tire surface temperature Twf of the front wheel WF exceeding the threshold value X. However, instead of this configuration, it may be configured to recommend to the user a running route with a small required braking force Freq using a notification device mounted on the vehicle.

[0065] (2) In the above-described embodiment, the braking control in a vehicle where the front wheel WF is a regenerative braking wheel has been described. However, the braking control according to the present disclosure can also be applied to a vehicle where the rear wheel WR is a regenerative braking wheel or a four-wheel drive vehicle. For example, the brake ECU of a vehicle where the rear wheel WR is a regenerative braking wheel can perform compatibility control using the distribution ratio of the front wheel braking force and the rear wheel braking force shown in FIG. 6.

[0066] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present disclosure is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Signs

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

Claims

1. A vehicle having a plurality of wheels including a regenerative braking wheel, a regenerative braking device that applies a regenerative braking force to the regenerative braking wheel, a friction braking device that applies a friction braking force to each wheel, and a control device that controls the braking force of the vehicle, wherein the control device includes a temperature acquisition unit that acquires the surface temperature of the regenerative braking wheel during travel of the vehicle, a required braking force acquisition unit that acquires a required braking force based on a brake pedal operation amount, and a braking force control unit that distributes the required braking force to the regenerative braking force and the friction braking force of each wheel, and the braking force control unit controls the distribution of the regenerative braking force with respect to the required braking force so that the surface temperature of the regenerative braking wheel does not exceed a predetermined reference temperature during travel of the vehicle, based on the surface temperature of the regenerative braking wheel acquired by the temperature acquisition unit.

2. The temperature acquisition unit acquires the surface temperature of the regenerative braking wheel at the current time based on the output of a temperature sensor that detects the temperature of the regenerative braking wheel or the driving record of the vehicle, and when it is determined that the surface temperature of the regenerative braking wheel at the current time is on an upward trend, the braking force control unit reduces the distribution of the regenerative braking force in the required braking force. The vehicle according to claim 1.

3. The braking force control unit predicts the transition of the surface temperature of the regenerative braking wheel during travel of the vehicle based on the surface temperature of the regenerative braking wheel at the current time and the driving plan of the vehicle, estimates whether or not the surface temperature of the regenerative braking wheel exceeds the reference temperature during travel of the vehicle based on the predicted transition of the surface temperature of the regenerative braking wheel, and when it is estimated that the temperature of the regenerative braking wheel exceeds the reference temperature during travel of the vehicle, further reduces the distribution of the regenerative braking force in the required braking force, 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 during running of the vehicle, the distribution of the regenerative braking force in the required braking force is increased.

4. The vehicle further includes an automatic driving system that creates a driving plan for the vehicle, The control device is configured to control the running of the vehicle according to a command from the automatic driving system, When the surface temperature of the regenerative braking wheel acquired by the temperature acquisition unit exceeds a predetermined threshold temperature, the automatic driving system changes the driving route of the vehicle to a driving route with a smaller required braking force than the current driving route. The vehicle according to any one of claims 1 to 3.

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

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