Brake control device for a vehicle

Abstract

Brake control device for a vehicle (10) comprising a regenerative braking device (20) configured to apply a regenerative braking force (Frgn) to the front wheels (WF) of the vehicle (10) and a friction braking device (30) configured to apply a front wheel friction braking force (Ffrcf) to the front wheels and a rear wheel friction braking force (Ffrcr) to the rear wheels of the vehicle (WR), comprising: Wheel speed sensors (53FL, 53FR) each configured to receive a signal indicating a wheel speed from each of the front wheels (WF); a brake pedal actuation amount sensor (52) configured to receive a signal indicating the actuation amount of a brake pedal (52a); and an electronic control unit (40, 50) configured to: to determine a front wheel acceleration (DVwf) of the front wheels (WF) based on the signal received from the wheel speed sensors (53FL, 53FR) (step 1020); to determine a required braking force (Freq) based on the signal received from the brake pedal actuation amount sensor (52) (step 1030); to distribute the required braking force (Freq) among a target regenerative braking force (Frgnt), a target front friction braking force (Ffrcft), and a target rear friction braking force (Ffrcrt); and the regenerative braking device (20) to apply the regenerative braking force, which is equal to the target regenerative braking force (Frgnt), to the front wheels (WF), the friction braking device (30) to apply the front wheel friction braking force, which is equal to the target front wheel friction braking force (Ffrcft), to the front wheels (WF), and the friction braking device (30) to apply the rear wheel friction braking force, which is equal to the target rear friction braking force (Ffrcrt), to the rear wheels (WR), where, if the required braking force (Freq) is less than or equal to a maximum regenerative braking force (Frgnmax) that the regenerative braking device (20) can apply to the front wheels (WF), the electronic control unit is configured to: to allocate the total required braking force (Freq) to the target regenerative braking force (Frgnt) (step 1050); and to perform a brake force reduction control to reduce the target regenerative braking force by a first predetermined amount (δ·Freq) without changing the target front friction braking force (Ffrcft) and the target rear friction braking force (Ffrcrt) (step 1070), at a first time (t11) when the front wheel acceleration (DVwf) changes from a value greater than a first acceleration threshold (DVth11), which is a negative value, to a value less than or equal to the first acceleration threshold (DVth11), while all the required braking force (Freq) is allocated to the target regenerative braking force (Frgnt) (steps 810 - 830, step 1040: No, step 1060: Yes).

Description

Technical field

[0001] The present disclosure relates to a brake control device for a vehicle comprising a regenerative braking device (recuperative braking device) configured to apply a regenerative braking force to the wheels and a friction braking device configured to apply a friction braking force to the wheels. State of the art

[0002] A conventional brake control device for a vehicle with a regenerative braking device for applying regenerative braking force to the wheels and a friction braking device for applying friction braking force to the wheels is typically configured to apply as much regenerative braking force to the wheels as possible in order to recover as much electrical energy as possible.

[0003] Such a conventional brake control device can, if necessary, replace part of the regenerative braking force with part of the frictional braking force.

[0004] In particular, one of the conventional brake control devices (hereinafter referred to as the “conventional device”) is configured to replace a portion of the regenerative braking force with a portion of the frictional braking force when, for example, anti-lock braking control (hereinafter referred to as the “ABS control”) is performed. Generally, the response time of the pressure-controlled frictional braking force is slower than that of the regenerative braking force. From this perspective, the conventional device is configured to set a reduction rate of the regenerative braking force such that an increase rate of the frictional braking force can match the reduction rate of the regenerative braking force in order to perform the ABS control (see JP 2017 - 060 343 A). Fig. 4).

[0005] From DE 198 42 472 A1, a vehicle braking system is known in which a friction braking device and a regenerative braking device together generate a total braking torque of the vehicle wheels. A control device regulates the distribution between the friction and regenerative braking torque of the vehicle wheels, depending on the coefficient of friction of a road surface, in order to prevent exceeding an upper limit braking force.

[0006] From US patent 2016 / 0264002A1, a method for controlling vehicle braking force is known in which, when a predetermined brake slip value of a vehicle front wheel is exceeded, the friction braking torque is increased and the regenerative braking torque is decreased. After a certain period of time, the regenerative braking torque is gradually decreased further, while the friction braking torque is gradually increased further.

[0007] From DE 10 2005 000 194 A1, a vehicle braking device is known in which front and rear wheel braking performance is regulated by a fluid pressure braking performance and a regenerative braking performance. Additional braking performance is generated when the brake pedal is additionally actuated to compensate for a lack of braking performance. Summary

[0008] The conventional system begins to replace a portion of the regenerative braking force with a portion of the friction braking force when an ABS start indicator is set. The conventional system only begins performing the ABS control operation (i.e., decreasing and increasing brake fluid pressure) after the replacement of the regenerative braking force with the friction braking force is complete. Therefore, the total braking force during this replacement process remains the same as the total braking force generated before the ABS start indicator was set. This results in a relatively long time for a wheel to return from wheel lockup. Given this, a system of this type can be configured to determine if the wheel is prone to locking up earlier, in order to set the ABS start indicator sooner.However, a device configured in this way may begin to replace some of the regenerative braking force with some of the frictional braking force, even when ABS control is not actually required. This reduces the likelihood of utilizing regenerative braking force, which can impair energy efficiency.

[0009] The present disclosure is intended to solve the problems described above. One of the objectives of the present disclosure is to provide a brake control device that can reduce the unnecessary substitution of regenerative braking force with frictional braking force, thereby increasing the likelihood of utilizing regenerative braking force and improving energy and / or fuel efficiency.

[0010] A brake control device (hereinafter referred to simply as the “present disclosed device”) according to the present disclosure is applied to a vehicle. The vehicle has a regenerative braking device configured to apply a regenerative braking force to the front wheels; and a friction braking device configured to apply a front friction braking force to the front wheels and a rear friction braking force to the rear wheels.

[0011] The present invention comprises wheel speed sensors, each configured to receive a signal indicating the wheel speed of each of the front wheels, a brake pedal actuation amount sensor configured to receive a signal indicating the amount of actuation of a brake pedal, and an electronic control unit configured to determine a front wheel acceleration of the front wheels based on the signal received from the wheel speed sensors, to determine a required braking force based on the signal received from the brake pedal actuation amount sensor, to divide the required braking force into a target regenerative braking force, a target front wheel friction braking force, and a target rear friction braking force, and to cause the regenerative braking device to apply the regenerative braking force equal to the target regenerative braking force to the front wheels, and the friction braking device to apply the front wheel friction braking force.which is equal to the target front wheel friction braking force, and the friction braking device applies the rear wheel friction braking force, which is equal to the target rear friction braking force, to the rear wheels.

[0012] If the required braking force is less than or equal to a maximum regenerative braking force (the greatest regenerative braking force that) the regenerative braking device can apply to the front wheels, the electronic control unit is configured to allocate / distribute all of the required braking force to the target regenerative braking force and to perform a braking force reduction control to decrease the target regenerative braking force by a first predetermined amount without varying (or keeping both at zero) the target front wheel friction braking force and the target rear wheel friction braking force, at a first time when the front wheel acceleration changes from a value greater than a first acceleration threshold, which is a negative value, to a value less than or equal to the first acceleration threshold, while all of the required braking force is allocated to the target regenerative braking force.

[0013] In some embodiments, the electronic control unit is configured to perform a brake force recovery control during the execution of the brake force reduction control, in order to increase the target regenerative braking force such that the target regenerative braking force equals (or returns to or becomes equal to) the required braking force if, in a period from the first time point to a second time point in which a predetermined time has elapsed since the first time point, the front wheel acceleration becomes greater than a second acceleration threshold that is greater than or equal to the first acceleration threshold, and to perform a brake force exchange control in order to increase the target regenerative braking force each time a predetermined time has elapsed if the front wheel acceleration does not become greater than the second acceleration threshold during the period from the first time point to the second time point.to decrease a second predetermined amount, and to increase the target front friction braking force and the target rear friction braking force such that the sum of the target front friction braking force and the target rear friction braking force is increased by the second predetermined amount each time the predetermined time has elapsed, while maintaining a proportional ratio between the target front friction braking force and the target rear friction braking force.

[0014] In other words, in some embodiments, the present disclosed device comprises a front wheel acceleration determination section, a brake force requirement determination section, a brake force distribution calculation section, and a brake force application section. The front wheel acceleration determination section is configured to determine the acceleration of the front wheels based on the front wheel speed. The brake force requirement determination section is configured to determine the required braking force based on the amount of brake pedal actuation. The brake force distribution calculation section is configured to distribute and allocate the required braking force to the target regenerative braking force, the target front wheel friction braking force, and the target rear friction braking force.

[0015] The brake force application section is configured to apply the regenerative braking force to the front wheels using the regenerative braking device, such that the applied regenerative braking force equals (or becomes equal to) the target regenerative braking force; to apply the front wheel friction braking force to the front wheels using the friction braking device, such that the applied front wheel friction braking force equals (or becomes equal to) the target front wheel friction braking force; and to apply the rear wheel friction braking force to the rear wheels using the friction braking device, such that the applied rear wheel friction braking force equals (or becomes equal to) the target rear friction braking force.

[0016] In some embodiments, the brake force distribution calculation section is configured to operate as follows when the required braking force is less than or equal to the maximum regenerative braking force. (1) The brake force distribution calculation section allocates the entire required braking force to the target regenerative braking force. (2) The brake force distribution calculation section performs the brake force reduction control to decrease the target regenerative braking force by the first predetermined amount when the front wheel acceleration changes from a value greater than the first acceleration threshold (which is a negative value) to a value less than or equal to the first acceleration threshold, while the brake force distribution calculation section allocates the entire required braking force to the target regenerative braking force.(3) The brake force distribution calculation section performs the brake force recovery control to increase the target regenerative braking force so that the target regenerative braking force corresponds to the required braking force when the front wheel acceleration becomes greater than the second acceleration threshold, which is equal to or greater than the first acceleration threshold in the period from the first time at which the target regenerative braking force is reduced by the first amount to the second time at which the predetermined time has elapsed from that time.(4) If the front wheel acceleration has not exceeded the second acceleration threshold during the period from time 1 to time 2, the brake force distribution calculation section executes the brake force exchange control to reduce the target useful braking force by the second predetermined amount each time the predetermined time elapses, and to increase the target front friction braking force and the target rear friction braking force by the second predetermined amount each time the predetermined time elapses, while maintaining a proportional relationship between the target front friction braking force and the target rear friction braking force.

[0017] In the manner described above, while the total required braking force is achieved (fulfilled) with the regenerative braking force, the regenerative braking force applied to the front wheels is initially reduced at the first time point when the front wheel acceleration falls below the first acceleration threshold (<0). This reduction in regenerative braking force is expected to cause the front wheel acceleration to begin increasing. Based on this, it is determined whether the front wheel acceleration becomes greater than the second acceleration threshold during the period from time point 1 to time point 2. If it is determined that the front wheel acceleration becomes greater than the second acceleration threshold during this period, it is assumed that the front wheels are unlikely to lock up, since the front wheel acceleration has increased. Therefore, in this case, the regenerative braking force is reduced to the required braking force.In general, the response time of regenerative braking is higher than that of friction braking. Therefore, regenerative braking can quickly return to the previous force level, which is the force before the regenerative braking force was initially reduced.

[0018] If, however, the front wheel acceleration does not exceed the second acceleration threshold during the specified period, it is assumed that the front wheels are likely to still begin to lock up. Therefore, in this case, the target regenerative braking force is reduced by the second predetermined amount each time the predetermined time elapses. Additionally, the target front friction braking force and the target rear friction braking force are increased to compensate for the reduction in the target regenerative braking force. In other words, substitute braking (substitute control) is applied. In this case, the proportional relationship between the target front friction braking force and the target rear friction braking force is maintained.

[0019] In this way, the regenerative braking force is quickly and temporarily reduced when the front wheel acceleration has decreased significantly. This avoids the unnecessary substitution of regenerative braking force with friction braking force. Consequently, energy efficiency can be improved, as the likelihood of using regenerative braking force can be increased.

[0020] In some embodiments, the electronic control unit is configured to use as the first predetermined amount an amount equal to 10 to 15 percent of the (assigned) target regenerative braking force at a time point immediately before the first time point. The target regenerative braking force at the time point immediately before the first time point can simply be referred to as the "target regenerative braking force before reduction".

[0021] If the initial predetermined amount is approximately 1% of the target regenerative braking force before reduction, it is highly unlikely that the driver will experience any strange sensation when the target regenerative braking force is reduced by this initial predetermined amount. However, the probability increases that front wheel acceleration will begin to increase after the reduction in regenerative braking force has also been reduced, and thus the probability of regenerative braking force being replaced by friction braking force. Conversely, if the initial predetermined amount is approximately 20% of the target regenerative braking force before reduction, the probability of regenerative braking force being replaced by friction braking force is lower, but the driver is likely to experience any strange sensation when the target regenerative braking force is reduced by this initial predetermined amount.In light of the foregoing, the previously described embodiment of the electronic control unit is configured to reduce the target regenerative braking force by 10 to 15 percent of the (assigned) target regenerative braking force at a time immediately before the first time point. Therefore, the previously described embodiment can prevent the driver from experiencing an uneasy feeling and reduce the possibility of the front wheels remaining continuously in a state of lock-up.

[0022] In some embodiments, the electronic control unit is configured to perform a first brake force distribution control with the brake force reduction control, the brake force recovery control, and the brake force exchange control, wherein the second acceleration threshold is set to a value equal to the first acceleration threshold.

[0023] For example, if regenerative braking is performed while the vehicle is traveling on a road surface with a low coefficient of friction (referred to hereafter as a "low µ road"), the acceleration of the front wheels will tend to decrease to fall below the first acceleration threshold. At the first time the acceleration of the front wheels falls below the first acceleration threshold, the target regenerative braking force is reduced by the first predetermined amount. If, after this first time, the acceleration of the front wheels begins to increase rather than decrease, it is unlikely that the front wheels will lock up (the front wheels are unlikely to lock).If, however, the acceleration of the front wheels continues to decrease (or decreases continuously) after the first time point, the front wheels are likely still in a state of tendency to lock (the front wheels are likely still on the verge of locking). In light of this, in the embodiment described above, the second acceleration threshold is set to a value equal to (or substantially equal to) the first acceleration threshold. Therefore, the embodiment described above can reliably determine whether the front wheels are likely to lock or not (or are about to lock) while the vehicle is traveling on a road with low µ.

[0024] In some embodiments, the electronic control unit is configured to perform a second brake force distribution control with brake force reduction control, brake force recovery control, and brake force exchange control, wherein the second acceleration threshold is set to a predetermined positive value.

[0025] For example, in a case where regenerative braking is performed while the vehicle is traveling on a road with a surface having a high coefficient of friction (hereinafter referred to as the "high µ road"), the acceleration of the front wheels decreases rapidly when the front wheels pass through (or move along) a section of the low µ road. To detect such a rapid decrease in front wheel acceleration, the initial acceleration threshold is set to a value (negative value) lower than the front wheel acceleration observed when regenerative braking is performed while the vehicle is traveling on the high µ road.According to the previously described embodiment, the target regenerative braking force is reduced by the first amount when the acceleration of the front wheels falls below the first acceleration threshold in the previous case, where the front wheels pass (or move along) the part of the road with low µ. Therefore, the acceleration of the front wheels begins to increase instead of decreasing.

[0026] The increase in front wheel acceleration depends on the condition of the road surface; rather than decreasing, the acceleration of the front wheels begins to increase after passing through it. For example, when the front wheels pass a short section of low µ (low coefficient of friction), such as a bump and a manhole cover, and the vehicle is traveling on a road with high µ and braking force, the acceleration of the front wheels begins to increase rapidly after passing through the low µ section. This is because the front wheels are immediately on a high µ road surface after passing through the low µ section. In this case, the acceleration of the front wheels increases to a positive value (i.e., the front wheels begin to accelerate).

[0027] Conversely, if the low µ section is long, the front wheel acceleration cannot become large once it begins to increase, compared to a case where the low µ section is short. In the previously described embodiment, the second acceleration threshold is set to a positive value, and it is determined that the front wheels are unlikely to be in a tendency to lock up if their acceleration exceeds the second acceleration threshold, whereas it is determined that the front wheels are likely to still be in a tendency to lock up if their acceleration does not exceed the second acceleration threshold.

[0028] In some embodiments, the electronic control unit is configured to perform a first brake force distribution control with brake force reduction control, brake force recovery control, and brake force exchange control, wherein the second acceleration threshold is set to a value equal to the first acceleration threshold when a product of a magnitude of front wheel acceleration and a weight of the vehicle is equal to or greater than a value obtained by adding a third predetermined value to the target regenerative braking force, and a front wheel slip ratio is equal to or greater than a predetermined slip ratio threshold.

[0029] In the previously described embodiment, the electronic control unit is further configured to perform a second brake force distribution control with brake force reduction control, brake force recovery control, and brake force exchange control, wherein the first acceleration threshold of the second brake force distribution control is set to a value less than or equal to the first acceleration threshold used in the first brake force distribution control, and the second acceleration threshold of the second brake force distribution control is set to a predetermined positive value when the product of the magnitude of the front wheel acceleration and the weight is greater than or equal to the value obtained by adding the third predetermined value to the target regenerative braking force, and the slip ratio of the front wheels is less than the predetermined slip ratio threshold.

[0030] Furthermore, in the embodiment described above, the electronic control unit is configured to perform a regenerative braking force maintenance control to maintain a state in which all the required braking force is allocated to the target regenerative braking force when the product of the magnitude of the front wheel acceleration and the weight is less than the value obtained by adding the third predetermined value to the target regenerative braking force.

[0031] According to the previously described embodiment, it is possible to distinguish between a low µ case and a high µ case. The low µ case is one in which regenerative braking is performed on the low µ road surface, and the high µ case is one in which regenerative braking is performed on the high µ road surface and the front wheels temporarily move on the low µ section. Additionally, in the low µ case, the second acceleration threshold is set to a value essentially equal to the first acceleration threshold, and in the high µ case, the second acceleration threshold is set to the positive predetermined value. Therefore, the brake force distribution controls, using the first and second brake force distribution controls, are appropriately adjusted according to the road surface conditions. Brief description of the drawings Fig. Figure 1 is a schematic diagram of a brake control device of a vehicle according to an embodiment of the present disclosure; Fig. Figure 2 is a graph showing the ratios between a front wheel braking force and a rear wheel braking force; Fig. Figure 3 is a time-lapse diagram showing the front wheel acceleration, regenerative braking force, frictional braking force, and vehicle acceleration when braking is performed while the vehicle is traveling on a road with low µ; Fig. 4A shows ratios between the front wheel braking force and the rear wheel braking force to describe a case in which the effective braking force is reduced; Fig. Figure 4B shows ratios between the front wheel braking force and the rear wheel braking force to describe a case in which the effective braking force is increased after it has been reduced; Fig. Figure 5 is another time-lapse diagram showing the front wheel acceleration, regenerative braking force, frictional braking force, and vehicle acceleration when braking is performed while the vehicle is traveling on the road with low µ; Fig. 6A shows ratios between the front wheel braking force and the rear wheel braking force to describe a case in which a substitution of part of the regenerative braking force with part of the frictional braking force is initiated; Fig. 6B shows ratios between the front wheel braking force and the rear wheel braking force to describe a case in which the substitution of part of the regenerative braking force with part of the frictional braking force continues; Fig. Figure 7 is a flowchart representing a "first brake force distribution control routine" executed by a CPU of the brake ECU located in Fig. 1 is shown; Fig. Figure 8 is a flowchart representing a “first determination routine using a first threshold” executed by the CPU of the brake ECU located in Fig. 1 is shown; Fig. Figure 9 is a flowchart representing a "second determination routine using a second threshold" executed by the CPU of the brake ECU located in Fig. 1 is shown; Fig. Figure 10 is a flowchart representing a "brake force distribution routine" executed by the CPU of the brake ECU located in Fig. 1 is shown; Fig. Figure 11 is a flowchart representing a "brake force exchange control final destination routine" executed by the CPU of the brake ECU located in Fig. 1 is shown; Fig. Figure 12 is a time-lapse diagram showing the front wheel acceleration, regenerative braking force, frictional braking force, and vehicle acceleration when braking is performed while the vehicle is traveling on a road with high µ; Fig. Figure 13 is another time-lapse diagram showing the front wheel acceleration, regenerative braking force, frictional braking force, and vehicle acceleration when braking is performed while the vehicle is traveling on a road with high µ; and Fig. Figure 14 is a flowchart representing a “brake force distribution control execution routine” that is executed by the CPU of the brake ECU of a third device according to a further embodiment of the present disclosure. Detailed description | First example implementation | Configuration

[0032] A brake control device (hereinafter referred to as the “first device”) of a vehicle according to a first embodiment of the present disclosure is used for a vehicle 10 as shown in Fig. 1 shown. The vehicle 10 is equipped with a regenerative braking device 20, a friction braking device 30, an EV-ECU 40, a brake ECU 50 or the like.

[0033] ECU stands for Electronic Control Unit. The ECU is an electronic control circuit whose main component is a microcomputer with a CPU, ROM, RAM, backup RAM (or non-volatile memory), and an interface I / F. The CPU performs various functions, described later, by executing instructions (routines) stored in the memory (ROM). The EV-ECU 40 and the brake ECU 50 can be integrated into a single ECU.

[0034] The regenerative braking device 20 comprises a motor-generator 21, a battery 22, an inverter 23, and a gearbox 24. The motor-generator 21 includes an AC synchronous motor. An output shaft of the motor-generator 21 is connected via the gearbox 24 to a front left wheel WFL and a front right wheel WFR. Hereinafter, the front left wheel WFL and the front right wheel WFR may sometimes be referred to collectively as the "front wheels WF." Similarly, the rear left wheel WRL and the rear right wheel WRR may sometimes be referred to collectively as the "rear wheels WF." Power (torque) can be transmitted between the output shaft of the motor-generator 21 and the front wheels WF. The battery 22 is a secondary battery that is rechargeable and dischargeable.The battery 22 is a lithium battery, but it can be a nickel-metal hydride battery, a lead-acid battery, or a rechargeable nickel-cadmium battery, as long as the battery 22 is rechargeable and dischargeable. The regenerative braking device 20 functions not only as a braking device but also as a drive device to power the front wheels WF when an accelerator pedal 51a is depressed.

[0035] The inverter 23 is electrically connected to the battery. When the motor-generator 21 functions as a generator, it converts the rotational energy (kinetic energy) of the front wheels WF into electrical energy (AC power). The inverter 23 converts the AC power supplied by the motor-generator 21 into DC power. The inverter 23 supplies the battery 22 with DC power to charge the battery 21. At this time (when the battery 21 is being charged with the converted DC power), a regenerative braking force Frgn is applied to the front wheels WF.In contrast, the inverter 23 converts the direct current electrical power supplied by the battery 22 into alternating current electrical power and supplies the alternating current electrical power to the motor-generator 21 so that the motor-generator 21 can function as a motor. The motor-generator 21 then applies the drive torque to the front wheels WF.

[0036] In this way, the motor generator 21 is an actuator configured to apply regenerative braking force to the front wheels WF, as well as an actuator configured to apply driving force to the front wheels WF. It should be noted that braking / deceleration by the regenerative braking device 20 is referred to as "regenerative braking / deceleration".

[0037] The friction braking device 30 comprises a hydraulic circuit 31 and friction-based braking mechanisms 32FL, 32FR, 32RL, and 32RR. It should be noted that in this description, for elements intended for specific wheels or for parameters used for specific wheels, one of the following suffixes is appended to the end of the reference numeral of the element or parameter: FL or fl to represent the front left wheel (WFL), FR or fr to represent the front right wheel (WFR), RL or rl to represent the rear left wheel (WRL), and RR or rr to represent the rear right wheel (WRR). The suffix is ​​omitted if the position of the wheel does not need to be specified for each of the elements / parameters intended / used for the respective wheels.

[0038] Hydraulic circuit 31 is provided between a master cylinder (not shown), configured to compress operating fluid (brake oil) with a depressing force of the brake pedal 52a, and the friction-based brake mechanisms 32, located at the front left wheel WFL, front right wheel WFR, rear left wheel WRL, and rear right wheel WRR, respectively. Hydraulic circuit 31 includes a reservoir (not shown), an oil pump (not shown), and various valves (not shown) and is configured to function as a friction brake actuator. Hydraulic circuit 31 applies hydraulic pressure (brake oil pressure) of the operating fluid to a wheel cylinder 34, which is installed in the brake caliper 33 of each of the friction-based brake mechanisms 32. The wheel cylinder 34 operates due to the hydraulic pressure, thereby pressing a brake pad (not shown) against the brake disc 35.This generates a friction braking force Ffrc. It should be noted that braking by the friction braking device 30 is referred to as "friction braking". The friction braking force Ffrc is composed of a front wheel friction braking force Ffrcf and a rear wheel friction braking force Ffrcr. The front wheel friction braking force Ffrcf is a friction braking force applied to the front wheels WF via the friction-based braking mechanisms 32 provided on the front wheels WF. The rear wheel friction braking force Ffrcr is a friction braking force applied to the rear wheels WR via the friction-based braking mechanisms 32 provided on the rear wheels WR.

[0039] The EV-ECU 40 is connected to the brake ECU 50 via a CAN (Controller Area Network) to exchange information. The EV-ECU 40 is electrically connected to various sensors, including an accelerator pedal actuation amount sensor 51. The EV-ECU 40 is configured to receive output signals sent by the sensors. The accelerator pedal actuation amount sensor 51 is configured to generate an output signal indicating an actuation amount AP (hereinafter referred to as "throttle opening degree AP") of the accelerator pedal 51a. The EV-ECU 40 is electrically connected to the regenerative braking device 20. The EV-ECU 40 is configured to transmit various signals to the regenerative braking device 20 to control the regenerative braking device 20 based on the throttle opening degree AP, a signal indicating actuation of a shift lever (not shown), or the like.

[0040] The brake control unit 50 is electrically connected to a brake pedal actuation amount sensor 52, wheel speed sensors 53 (53FL, 53FR, 53RL and 53RR) and an acceleration sensor 54. The brake control unit 50 is configured to receive the output signals sent by the connected sensors. The brake pedal actuation amount sensor 52 is configured to generate an output signal indicating the actuation amount (hereinafter referred to as "brake pedal actuation amount BP") of the brake pedal 52a.

[0041] Brake control 50 calculates a required braking torque Tr* based on the brake pedal actuation amount BP and a vehicle speed SPD (vehicle speed 10). Brake control 50 calculates a required braking force Freq as a product of the required braking torque Tr* and a predefined dynamic roll radius r of the front wheel(s). Brake control 50 calculates the wheel speed SPD as an average of the wheel speeds (Vwfl, Vwfr, Vwrl, and Vwrr). Specifically, brake control 50 derives the required braking torque Tr* by applying the detected brake pedal actuation amount BP and the calculated vehicle speed SPD to a lookup table MapTr* (BP, SPD), which defines a ratio between the required braking torque Tr* and a combination of the brake pedal actuation amount BP and the vehicle speed SPD.According to the lookup table MapTr* (BP, SPD), an absolute value of the required braking torque Tr* is obtained such that the absolute value increases as the brake pedal actuation amount BP increases, and such that the absolute value increases as the vehicle speed SPD increases. The lookup table MapTr* (BP, SPD) was determined in advance based on experiments and / or simulations and stored in the memory (ROM) of the brake controller 50.

[0042] As will be described in detail later, the brake control unit 50 is configured to distribute / assign the required braking force Freq to a target value Frgnt for the regenerative braking force Frgn, a target value Ffrcft for the front wheel friction braking force Ffrcf, and a target value Ffrcrt for the rear wheel friction braking force Ffrcr. The target value Frgnt for the regenerative braking force can be referred to as "target regenerative braking force Frgnt." The target value Ffrcft for the front wheel friction braking force can be referred to as "target front wheel friction braking force Ffrcft." The target value Ffrcrt for the rear wheel friction braking force can be referred to as "target rear friction braking force Ffrcrt."

[0043] The brake control unit 50 is configured to apply the regenerative braking force Frgn, which is equal to the target regenerative braking force Frgnt, to the front wheels WF using the regenerative braking device 20. The brake ECU 50 is configured to apply the front wheel friction braking force Ffrcf, which is equal to the target front wheel friction braking force Ffrcft, to the front wheels WF by controlling the brake oil pressure in the wheel cylinders 34FL and 34FR. The brake ECU 50 is configured to apply the rear wheel friction braking force Ffrcr, which is equal to the target rear friction braking force Ffrcrt, to the rear wheels WR by controlling the brake oil pressure in the wheel cylinders 34RL and 34RR.

[0044] Each of the wheel speed sensors 53 is configured to generate a pulse each time a corresponding wheel rotates through a predetermined angle. The brake ECU 50 counts the number of pulses generated by each of the wheel speed sensors 53 per unit of time to obtain each of the counted values. The brake control 50 calculates / obtains a speed (i.e., wheel speed) from each of the wheels on which the respective wheel speed sensors 53 are located, based on each of the respective counted values. In particular, the brake control unit 50 calculates / obtains each of the wheel speeds (Vw) in accordance with an expression (equation) (1) described below. Vw=r⋅ω=r⋅(2⋅π / N)⋅(Ni / ΔT)

[0045] In expression (1), “r” is a dynamic radius of each of the wheels, “ω” is an angular velocity of each of the wheels, “N” is the number of teeth of a rotor rotating together with a shaft connected to each of the wheels (i.e., “N” is the number of pulses per revolution of the rotor / wheel), and “Ni” are the counted values ​​of the pulses per unit time ΔT. In this way, the brake control 50 is configured to reference the following: the wheel speed Vwfl of the front left wheel WFL, the wheel speed Vwfr of the front right wheel WFR, the wheel speed Vwrl of the rear left wheel WRL, and the wheel speed Vwrr of the rear right wheel WRR.

[0046] The acceleration sensor 54 is attached to a vehicle body (sprung element) of the vehicle 10 and is configured to generate an output signal that indicates a vehicle acceleration Gx, which is a longitudinal (front-to-back) acceleration of the vehicle 10. Overview of operating mode

[0047] As previously described, the first device is adopted for the vehicle 10, which has the regenerative braking device 20, configured to apply the regenerative braking force Frgn only to the front wheels WF, and the friction braking device 30, configured to apply the friction braking force Ffrc to the wheels (i.e., to the front wheels WF as well as the rear wheels WR). In other words, the friction braking device 30 is configured to apply the front wheel friction braking force Ffrcf to the front wheels WF and the rear wheel friction braking force Ffrcr to the rear wheels WR.

[0048] When a driver of vehicle 10 depresses the brake pedal 52a while vehicle 10 is running / driving, the first device is configured to allocate (assign / distribute) the required braking force Freq, which is determined based on the actuation (amount) of the brake pedal 52a, to the regenerative braking force Frgn, which is preferred over the frictional braking force Ffrc in order to recover as much of the regenerated electrical power as possible. In other words, a ratio of regenerative braking force Frgn to the required braking force Freq is made larger than a ratio of frictional braking force Ffrc to the required braking force Freq.If the applied (assigned) regenerative braking force Frgn to the front wheels WF exceeds the maximum regenerative braking force Frgnmax, which is the maximum regenerative braking force Frgn that the regenerative braking device 20 can generate, the first device is configured to apply the frictional braking force Ffrc to the wheels, including the front wheels WF and the rear wheels WR, in addition to the maximum regenerative braking force Frgnmax applied to the front wheels WF. It should be noted that the maximum regenerative braking force Frgnmax varies primarily depending on the power conversion capability of the inverter 23.

[0049] Accordingly, if the required braking force Freq is equal to or less than the maximum regenerative braking force Frgnmax, the first device initially allocates (assigns) the entire required braking force Freq to the target regenerative braking force Frgnt. If, at this stage, the first device determines that the front wheels WF are about to lock or are likely to lock (or detects a tendency of the front wheels WF to lock), the first device reduces the target regenerative braking force Frgnt by an amount determined by a predetermined ratio δ. Subsequently, if the first device determines that the front wheels WF are unlikely to lock (or determines that the tendency of the front wheels WF to lock has disappeared), the first device increases the target regenerative braking force Frgnt to the required braking force Freq.In contrast, if the first device determines that the front wheels WF remain in a tendency to lock (or determines that the front wheels WF are likely to still lock or the tendency of the front wheels WF to lock has not disappeared), after the first device has reduced the target regenerative braking force Frgnt by the amount, the first device gradually reduces the target regenerative braking force Frgnt at a predetermined rate and increases a target value (target wheel friction braking force Ffrct) of the friction braking force at the predetermined rate.

[0050] Next, a procedure for distributing / assigning the braking force to the front wheel WF and the rear wheels WR will be described in relation to Fig. 2 described in a case in which the vehicle 10 is traveling on a road with low µ, which has a low coefficient of friction, and the driver presses down the brake pedal 52a to slow down the vehicle 10. Fig. Figure 2 shows a graph indicating the distribution ratio between the braking force applied to the front wheel WF and the braking force applied to the rear wheels WR. The braking force applied to the front wheel WF is referred to as the "front wheel braking force," and the braking force applied to the rear wheels WR is referred to as the "rear wheel braking force."

[0051] In Fig. 2 is a curved line L1, a line of ideal braking force distribution (or an ideal braking force distribution line L1) based on a ground contact load / force of the front wheels WF and a ground contact load / force of the rear wheels WR. For example, if a distribution ratio between the front wheel braking force Fbf and the rear wheel braking force Fbr lies on the ideal braking force distribution line L1, the front wheels WF and the rear wheels WR will lock up simultaneously.

[0052] In Fig. 2 is a straight line L2, a line representing the actual friction braking force distribution due to the friction braking device 30, and is referred to as the "friction braking force distribution line L2". The friction braking force distribution line L2 is designed / determined to avoid a condition in which the rear wheels WR lock before the front wheels WF lock. If the rear wheels WR lock before the front wheels WF lock, the behavior of the vehicle 10 becomes unstable. With this in mind, the friction braking force distribution line L2 is designed / determined such that a "ratio of front wheel braking force Fbf to rear wheel braking force Fbr" on the friction braking force distribution line L2 (or represented by it) is greater than a "ratio of front wheel braking force Fbf to rear wheel braking force Fbr" on the ideal braking force distribution line L1 (or represented by it).Furthermore, the friction braking force distribution line L2 is designed / determined such that the "ratio of the front wheel braking force Fbf to the rear wheel braking force Fbr" is constant on the friction braking force distribution line L2 (or represented by it) (i.e., the friction braking force distribution line L2, which is in . Fig. 2 is shown (is just).

[0053] In Fig. 2 is a straight line. L3 is a line that connects specific points. Specifically, the sum (Fbf + Fbr) of the front wheel braking force Fbf and the rear wheel braking force Fbr remains constant at each of the specific points on line L3. Line L3 is referred to as the "constant deceleration line L3". The in Fig. The line L3 shown in Figure 2 intersects an abscissa that indicates the front brake force Fbf at a point where the front brake force Fbf is equal to 4000 N. Therefore, the sum (Fbf + Fbr) of the front brake force Fbf and the rear brake force Fbr is always equal to 4000 N if the front brake force Fbf and the rear brake force Fbr vary along / at the constant deceleration line L3. In other words, the constant deceleration line L3 consists of points where the total braking force applied to the vehicle 10 is constant at any one of the points on the line L3. Since the deceleration of the vehicle 10 is proportional to the total braking force applied to the vehicle 10, it can be said that the constant deceleration line L3 consists of points where the deceleration of the vehicle 10 is constant if the front brake force Fbf and the rear brake force Fbr lie on the line L3.

[0054] As previously described, the first device is configured to preferentially use the regenerative braking force Frgn generated by the regenerative braking device 20 rather than the frictional braking force Ffrc generated by the frictional braking device 30, in order to recover as much of the regenerated electrical power as possible to improve energy efficiency. The regenerative braking force Frgn is applied only to the front wheels WF. Therefore, when the brake pedal 52a begins to be depressed, the first device increases only the front wheel braking force Fbf from an origin of the graph located in Fig. Figure 2 shows the curve along a regenerative braking distribution line L4, which lies on the abscissa of the graph. In this example, the maximum regenerative braking force Frgnmax is 4000 N.

[0055] Accordingly, when the front wheel braking force Fbf (which in this case is equal to the regenerative braking force Frgn) reaches 4000 N (increases to 4000 N), which is the maximum regenerative braking force Frgnmax in a case where the required braking force Freq requested by the driver is a value (e.g., 5000 N) greater than the maximum regenerative braking force Frgnmax, the first device begins to generate (increase) the friction braking force Ffrc while maintaining the regenerative braking force Frgn (i.e., at the same force as the maximum regenerative braking force Frgnmax). Consequently, the regenerative braking force distribution line L4 begins to rise (increase) from the point where the front wheel braking force Fbf equals the maximum regenerative braking force Frgnmax (4000 N) with a slope corresponding to the slope of the friction braking force distribution line L2, until the friction braking force Ffrc reaches 1000 N (see point P0).

[0056] In Fig. 2 is a straight line L5, a line that shows the front wheel braking force Fbf when the rotational speed (and thus the wheel speed) of the front wheels WF decreases rapidly, causing the front wheels WF to lock up, and is called the "front wheel locking limit line L5". A value (front wheel braking force) at a point where the front wheel locking limit line L5 intersects the abscissa is correlated with the coefficient of friction µ of a road surface on which the vehicle 10 is traveling. The front wheel locking limit line L5 moves to the left in the graph (i.e., is positioned closer to the origin) as the coefficient of friction µ of the road surface decreases. In the Fig. In example 2, the front wheel locking limit line L5 corresponds to the road with low µ. Fig. 2. The front wheel locking limit line L5 intersects the abscissa at a point where the front wheel braking force Fbf equals 3500 N. This is because the front wheel braking force Fbf at the front wheel locking limit is less than the maximum effective braking force Frgnmax.

[0057] Both the wheel speed Vwf of the front wheels WF and an acceleration of the front wheels DVwf (hereinafter referred to as "front wheel acceleration DVwf") decrease as the front wheel braking force Fbf increases and approaches the front wheel locking limit line L5 during regenerative braking. The first device is configured to determine, based on the front wheel acceleration DVwf, whether the front wheels WF are about to lock or are likely to lock (i.e., detects the tendency of the front wheels WF to lock). Specifically, the first device calculates the front wheel acceleration DVwf as an average of the acceleration of the front left wheel WFL and the acceleration of the front right wheel WFR.The first device determines that the front wheels WF are about to lock up when the front wheel acceleration DVwf is equal to or less than a first acceleration threshold DVth11, which is a negative value (i.e., DVth11 < 0). In this example, the first acceleration threshold DVth11 is set to a value (e.g., -0.24 G, where G is a gravitational acceleration) that is 20% lower than a value (e.g., -0.2 G) corresponding to the locking threshold on a low-µ road.

[0058] The first acceleration threshold DVth11 is set to a value (predetermined) such that the front wheel acceleration DVwf becomes lower than the first acceleration threshold DVth1 immediately before the point at which the wheel speed Vwf of the front wheels WF decreases significantly and the front wheels WF begin to lock (namely, where the ABS control is intended to start). It should be noted that a determination of whether a wheel is about to lock is typically made based on whether a wheel slip ratio, calculated from the wheel speed, exceeds a predetermined slip ratio threshold. In contrast, the first device is configured to determine whether the front wheels WF are about to lock, or likely to lock, by using the front wheel acceleration DVwf before the front wheel slip ratio WF exceeds the slip ratio threshold.It should be noted that a condition in which the front wheels WF are about to / likely to lock up means a condition in which the front wheels WF are in a state of tendency to lock up (or the tendency of the front wheels WF to lock up is being detected). Thus, even if the front wheels WF are in a state of tendency to lock up, they will not necessarily lock up afterwards.

[0059] As in Fig. As shown in Figure 3, the first device reduces the target regenerative braking force Frgnt by the amount (or a first predetermined amount) corresponding to a predetermined ratio δ at a time t11 when the front wheel acceleration DVwf varies from a value greater than the first acceleration threshold DVth11 to a value equal to or less than the first acceleration threshold DVth11. Specifically, the target regenerative braking force Frgnt is reduced at time t11 by the first predetermined amount, which is equal to the product of the ratio δ and the required braking force Freq (which is equal to the target regenerative braking force Frgnt at that time). This control can be called a "brake force reduction control". At this time, as shown in Figure 3, the front wheel acceleration DVwf is moving from a value greater than or less than the first acceleration threshold DVth11 to a value equal to or less than the first acceleration threshold DVth11. Fig. Figure 4A shows the front wheel braking force Fbf from point P1 to point P2. The predetermined ratio δ is set to a value that is unlikely to cause the rider any unusual sensation. According to the inventor's investigation, the predetermined ratio δ is preferably in the range of 10% to 15%. Referring again to Fig. 3. The vehicle acceleration Gx increases (the magnitude (absolute value) of the vehicle acceleration Gx becomes smaller) after time t11, however, the amount of change in the vehicle acceleration Gx is relatively small.

[0060] It is assumed that the front wheels WF are no longer in a tendency to lock up if the acceleration of the front wheels DVwf begins to increase after time t11, whereas it is assumed that the front wheels WF are still in a tendency to lock up if the acceleration of the front wheels DVwf continues to decrease after time t11.In particular, it can be determined that the front wheels WF are not in a state of tendency to lock (or that it becomes unlikely that the front wheels WF will lock or that the tendency of the front wheels WF to lock has disappeared) if the acceleration of the front wheels DVwf becomes greater than a second acceleration threshold DVth12, which is essentially equal to the first acceleration threshold DVth11 at a time t12, which is in a period from time (first time) t11 to a time (second time) t13, at which a predetermined time tw1 has elapsed from time t11.

[0061] In light of the above, the first device restores (increases / sets) the regenerative braking force Frgn to its previous value at time t12. Specifically, the first device increases the target regenerative braking force Frgnt such that the target regenerative braking force Frgnt matches the required braking force Freq (calculated at time t11) when the acceleration of the front wheels DVwf exceeds the second acceleration threshold DVth12 during the period from time t11 to time t13. This control can be referred to as "brake force recuperation control." At this time, as described in Fig. Figure 4B shows the front wheel braking force Fbf from point P2 to point P1. As mentioned previously, the response time of the regenerative braking force is higher than that of the friction braking force. Therefore, the regenerative braking force Frgn can be decreased and increased relatively quickly (see Figure 4B). Fig. 3, time points t11, t13). Consequently, the vehicle acceleration Gx returns to its previous value. In this way, the first device is configured to vary the target regenerative braking force Frgnt to control the regenerative braking force Frgn (that is, the front wheel braking force Fbf) based on the determination of the front wheel locking tendency WF, which is produced before the front wheel slip ratio WF becomes greater than the predetermined slip ratio threshold (or before it is determined that the front wheels WF have locked based on the slip ratio). During the period from time t11 to time t12, or at the latest until time t13 (i.e., when the regenerative braking force Frgn is held at the reduced value), the target wheel friction braking force Ffrct remains at zero, so that the rear wheel braking force Fbr remains unchanged.

[0062] Meanwhile, as in Fig. Figure 5 shows that, assuming the front wheels WF are still in a tendency to lock at time t13, when the predetermined time tw1 has elapsed since time t11, the acceleration of the front wheels DVwf during the period from time t11 to time t13 does not exceed the acceleration threshold DVth12. In this case, starting at time t13, the first device reduces the target regenerative braking force Frgnt at a predetermined rate and increases the target wheel friction braking force Ffrct at the same predetermined rate. Specifically, the first device replaces a portion of the target regenerative braking force Frgnt with a portion of the target wheel friction braking force Ffrct. This control can be referred to as "brake force exchange control".

[0063] It is now assumed that the required braking force Freq remains unchanged. As in Fig. As shown in Figure 6A, after the brake force exchange control is started, a point defined by the front wheel braking force Fbf and the rear wheel braking force Fbr is varied from point P2 to point P3. At this point, a ratio between the front wheel friction braking force Ffrcf and the rear wheel friction braking force Ffrcr is maintained, as represented by the friction braking force distribution line L2. A length F1a between an intersection point C1 and the origin O corresponds to the effective braking force Frgn. The intersection point C1 is a point where a straight line L7 intersects the abscissa, with the straight line L7 passing through point P3 and running parallel to the friction braking force distribution line L2. A length F2a between the intersection point C1 and an intersection point C2 corresponds to the front wheel friction braking force Ffrcf.The intersection point C2 is a point where a line perpendicular to the abscissa intersects the abscissa, with the perpendicular line passing through point P3. A length F3a from point P3 to the abscissa along the perpendicular line corresponds to the rear wheel friction braking force Ffrcr.

[0064] As in Fig. As shown in Figure 6B, if the brake force exchange control continues, a point defined by the front brake force Fbf and the rear brake force Fbr is varied from point P3 to point P4. A length F1b between an intersection point C3 and the origin O corresponds to the regenerative braking force Frgn. Intersection point C3 is a point where a straight line L8 intersects the abscissa, with the straight line L8 passing through point P4 and parallel to the friction brake force distribution line L2. A length F2b between intersection point C3 and an intersection point C4 corresponds to the front friction brake force Ffrcf. Intersection point C4 is a point where a line perpendicular to the abscissa intersects the abscissa, with the perpendicular line passing through point P4. A length F3b from point P4 to the abscissa along the perpendicular line corresponds to the rear friction brake force Ffrcr.In this way, the brake force exchange control reduces the usable braking force Frgn and increases the front wheel friction braking force Ffrcf and the rear wheel friction braking force Ffrcr. However, the brake force exchange control does not change the total braking force, and thus the front wheel braking force Fbf and the rear wheel braking force Fbr vary along a constant deceleration line L6. Consequently, as shown in . Fig. 5 shows the absolute value (the magnitude) of the vehicle acceleration Gx after time t13 gradually.

[0065] The first device is configured to increase the ratio of rear wheel braking force Fbr to the total braking force (i.e., required braking force Freq) without causing the rider any discomfort, in order to avoid / prevent front wheel lock-up WF. It should be noted that the previously mentioned numerical values ​​for maximum usable braking force Frgnmax, first acceleration threshold DVth11, and second acceleration threshold DVth12 are only examples, and the first device should not be limited by these values. Specific operating procedure

[0066] The specific operating mode of the first device is described next. The CPU (hereinafter simply referred to as the "CPU") of the brake control unit 50 is configured to execute a "first brake force distribution control routine" as described by a flowchart in Fig. Figure 7 shows this happening every time a constant time (e.g., 20 ms) elapses. The values ​​of a first identifier X1 and a second identifier X2, which are described later, are set to "0" in an initialization routine that is not shown and is executed separately by the CPU.

[0067] The CPU begins processing step 700 at a suitable time and proceeds sequentially to steps 710 through 740. The processes of steps 710 through 740 are implemented by corresponding subroutines, which are located in the respective... Fig. 8, Fig. 9, Fig. 10 to Fig. 11 are shown. The CPU then proceeds to step 795 to temporarily terminate the current routine.

[0068] Step 710: The CPU performed an initial determination process using the first threshold, as shown in Fig. 8 shown.

[0069] Step 720: The CPU performed a second determination process using the second threshold, as shown in Fig. 9 shown.

[0070] Step 730: The CPU performed a brake force distribution process, as described in Fig. 10 shown.

[0071] Step 740: The CPU executed a brake force exchange control final determination process, as described in Fig. 10 shown.

[0072] (Case 1) A case in which the front wheel acceleration is greater than the first acceleration threshold.

[0073] When the CPU advances to step 710, it advances to step 800, which is in Fig. Figure 8 is shown. The CPU then proceeds to step 810 and determines whether the value of the first identifier X1 is "0" or not. At this point, the value of the first identifier X1 is "0". Thus, in step 810, the CPU makes a "yes" determination to proceed to step 820. In step 820, the CPU determines whether the front wheel acceleration DVwf is equal to or less than the first acceleration threshold value DVth1 or not.

[0074] According to the previously described case 1, the front wheel acceleration DVwf is greater than the first acceleration threshold DVth1. Therefore, at step 820, the CPU makes a "no" decision to proceed directly to step 895. In this case, the value of the first identifier X1 is kept at "0".

[0075] The CPU then proceeds to the task in Fig. The process continues to step 720 as shown in step 1. In step 910, the CPU determines whether the value of the first identifier X1 is "1" or not. At this point, the value of the first identifier X1 is "0". Therefore, in step 910, the CPU makes a "no" determination and proceeds directly to step 995.

[0076] The CPU then proceeds to the task in Fig. Step 730, as shown in step 7, is shown to proceed to the points shown in Fig. The CPU advances to step 1000 as shown in step 10 and executes steps 1010 to 1030 sequentially. Afterward, it advances to step 1040.

[0077] Step 1010: the CPU obtains / receives the brake pedal actuation amount BP and calculates the wheel speed Vwfl of the front left wheel WFL and the wheel speed Vwfr of the front right wheel WFR based on the previously described expression (1).

[0078] Step 1020: the CPU obtains the front wheel acceleration DVwf based on the following expression (2). DVwf=(dVwfl / dt+dVwfr / dt) / 2

[0079] In particular, the CPU obtains the front wheel acceleration DVwf by using the following expression (2A). DVwf=[((Vwfl(n)−Vwfl(n−1)) / Δt+((Vwfr(n)−Vwfr(n−1)) / Δt] / 2 where: Δt is a calculation period; Vwfl(n) is the currently referenced wheel speed Vwfl of the front left wheel WFL (at the present time); Vwfl(n-1) is the previously obtained wheel speed Vwfl of the front left wheel WFL (wheel speed Vwfl obtained at a time point in the calculation period Δt before the present time); Vwfr (n) is the currently referenced wheel speed Vwfr of the front right wheel WFR (at the present time); and Vwfr(n-1) is the previously obtained wheel speed Vwfr of the front right wheel WFR (wheel speed Vwfr obtained at a time point in the calculation period Δt before the present time).

[0080] Step 1030: the CPU obtains / receives the required braking force Freq based on the brake pedal actuation amount BP, the vehicle speed SPD and the dynamic radius r of each of the wheels, as previously described.

[0081] In step 1040, the CPU determines whether the value of the first identifier X1 is "0" or not. As previously described, the value of the first identifier X1 is "0" in this case. Thus, the CPU makes a "yes" determination at 1040 to proceed to step 1050. In step 1050, the CPU distributes (assigns) the required braking force Freq to the target regenerative braking force Frgnt, the target front friction braking force Ffrcft, and the target rear friction braking force Ffrcrt according to the following expressions (3) to (5). That is, in this case, the entire required braking force Freq is assigned to the target regenerative braking force Frgnt. After that, the CPU proceeds to step 1095 and then to step 740, which is in Fig. 7 is shown. Frgnt=Freq Ffrcft=0 Ffrcrt=0

[0082] In the Fig. In step 740, as shown in step 7, the CPU proceeds with the... Fig. Step 1110, as shown in section 11, is advanced by step 1100 and determines whether an exchange control end condition is met or not. The exchange control end condition is met if at least one of the following conditions is met while the value of the second identifier X2 is "1". ▪ The target braking force Frgnt has reached zero. ▪ The front wheel acceleration DVwf has become equal to or greater than a predetermined acceleration threshold (due to an increase in the front wheel acceleration DVwf). ▪ The required braking force Freq has become equal to or less than a predetermined required braking force threshold (due to a reduction in the brake pedal actuation amount BP).

[0083] At this point, the value of the second identifier X2 is "0", and the brake force exchange control is not executed. Therefore, in step 1110, the CPU makes a "no" determination and proceeds directly to step 1195 to advance to step 795, which in Fig. 7 is shown.

[0084] (Case 2) A case in which the front wheel acceleration has become equal to or less than the first acceleration threshold.

[0085] When the CPU progresses from step 700 to step 710, it moves on to step 810, which is in Fig. As shown in Figure 8, the process continues through step 800. In step 810, the CPU makes a "yes" determination to proceed to step 820. In case 2, the front wheel acceleration DVwf has become equal to or less than the first acceleration threshold value DVth1. Therefore, in step 820, the CPU makes a "yes" determination to proceed to step 830. In step 830, the CPU sets the value of the first identifier X1 to "1".

[0086] The CPU then proceeds to step 910 via steps 895, 710, 720, and 900. In step 910, the CPU makes a "yes" determination to proceed to step 920, where it determines whether the front wheel acceleration DVwf is greater than the second acceleration threshold DVth12. As previously described, the second acceleration threshold DVth12 is set to a value equal to the first acceleration threshold DVth11. Therefore, at this point in step 920, the CPU makes a "no" determination and proceeds to step 940 to determine whether the first predetermined time tw1 has elapsed since time t11, when the value of the first identifier X1 changed from "0" to "1".

[0087] In the previously described case 2, the elapsed time from the first time point t11 ​​is almost zero (or shorter than the first specified time tw1). Therefore, in step 940, the CPU makes a "no" decision to proceed directly to step 995. The CPU then proceeds to step 1000, which in Fig. As shown in Figure 10, the CPU proceeds through steps 995, 720, and 730, and then executes steps 1010 through 1030 sequentially. Afterward, the CPU advances to step 1040. At this point, the value of the first identifier X1 is "1," and therefore, in step 1040, the CPU makes a "no" determination to proceed to step 1060. In step 1060, the CPU determines whether the value of the second identifier X2 is "0" or not.

[0088] At this point, the value of the second identifier X2 is "0". Therefore, in step 1060, the CPU makes a "yes" determination and proceeds to step 1070. In step 1070, the CPU distributes (assigns) the required braking force Freq to the target regenerative braking force Frgnt, the target front friction braking force Ffrcft, and the target rear friction braking force Ffrcrt according to the following expressions (6) to (8). Frgnit=(1−δ)⋅Freq Ffrcft=0 Ffrcft=0

[0089] The CPU reduces the target regenerative braking force Frgnt by the amount determined by the predetermined ratio δ (i.e., the amount equal to the product (δ · Freq) of the ratio δ and the required braking force Freq). The ratio δ is set to an appropriate value (e.g., 10%), and thus the reduction in regenerative braking force Frgn caused by the reduction in the target regenerative braking force Frgnt is not too large. Accordingly, the reduction in regenerative braking force Frgn does not cause the driver to experience any unusual sensation. Additionally, the CPU sets both the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt to "0". In other words, the CPU does not change the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt at this time.

[0090] (Case 3) A case in which the front wheel acceleration, which has become less than the first acceleration threshold, has become greater than the second acceleration threshold before the first predetermined time has elapsed.

[0091] When the CPU advances from step 700 to step 710, the CPU advances to step 810, as shown in Fig. As shown in step 8, the CPU proceeds through step 800. In step 810, the CPU makes a "no" decision to proceed directly to step 895. After that, the CPU proceeds to step 910, which is shown in Fig. As shown in Figure 9, the process proceeds through steps 710, 720, and 900. In step 910, the CPU makes a "yes" decision to proceed to step 920. In the previously described case 3, the front wheel acceleration DVwf is greater than the second acceleration threshold DVth12. Therefore, in step 920, the CPU makes a "yes" decision and proceeds to step 930. In step 930, the CPU sets the value of the first identifier X1 to "0" and proceeds to step 995.

[0092] The CPU then proceeds to step 1000, which is in Fig. As shown in Figure 10, the CPU proceeds through steps 995, 720, and 730, and executes steps 1010 to 1030 sequentially. It then proceeds to step 1040. At this point, the value of the first identifier X1 is "0", and therefore, in step 1040, the CPU makes a "yes" determination to proceed to step 1050. In step 1050, the CPU sets the target braking force Frgnt to the required braking force Freq and sets both the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt to zero according to the expressions (3) to (5) mentioned above.

[0093] (Case 4) A case in which the front wheel acceleration, which has become less than the second acceleration threshold, has not become greater than the second acceleration threshold before the first predetermined time has elapsed.

[0094] If the CPU is in Fig. As the process progresses to step 910 as shown in Figure 9, the CPU makes a "yes" decision in step 910 and proceeds to step 920. In the previously described case 4, the front wheel acceleration DVwf is equal to or less than the second acceleration threshold DVth12. Therefore, the CPU makes a "no" decision in step 920 to proceed to step 940, and a "yes" decision in step 940 to proceed to step 950. In step 950, the CPU sets the value of the second identifier X2 to "1" and proceeds to step 995.

[0095] The CPU then proceeds to step 1000, which is in Fig. As shown in Figure 10, the CPU proceeds through steps 995, 720, and 730, and executes steps 1010 through 1030 sequentially. It then advances to step 1040. At this point, the value of the first identifier X1 is "1", and therefore the CPU makes a "no" determination in step 1040 to proceed to step 1060. At this point, the value of the second identifier X2 is "1", and therefore the CPU makes a "no" determination in step 1060 to proceed to step 1080. In step 1080, the CPU performs the brake force exchange control described below. Brake force exchange control

[0096] The CPU reduces the target regenerative braking force Frgnt at a predetermined rate. Furthermore, the CPU increases the target wheel friction braking force Ffrct (i.e., the sum of the target front wheel friction braking force Ffrcft and the target rear wheel friction braking force Ffrcrt) at the predetermined rate. This reduces the ratio of the front wheel braking force Fbf to the total braking force and increases the ratio of the rear wheel braking force Fbr to the total braking force.

[0097] In particular, during brake force exchange control, the CPU reduces the target regenerative braking force Frgnt by a value β at each execution of a computation cycle Δt and increases the target wheel friction braking force Ffrct (i.e., the sum of the target front wheel friction braking force Ffrcft and the target rear friction braking force Ffrcrt) by the value β at each execution of a computation cycle Δt. Therefore, during brake force exchange control, an expression (9) described below is satisfied between a “target regenerative braking force Frgnt (n-1), which is the target regenerative braking force Frgnt at a time point of a computation cycle Δt prior to the present time” and a “target regenerative braking force Frgnt (n), which is the target regenerative braking force Frgnt at the present time”.Furthermore, an expression (10) described below is satisfied between a “target wheel friction braking force Ffrct (n-1) which is the target wheel friction braking force Ffrct at the time of one calculation cycle Δt before the present time” and a “target wheel friction braking force Ffrct (n) which is the target wheel friction braking force Ffrct at the present time”. Frgnt(n)=Frgnt(n−1)−β Ffrct(n)=Ffrct(n−1)+β

[0098] Meanwhile, the CPU increases the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt, while maintaining a constant ratio between them, which corresponds to the slope of the friction braking force distribution line L2. Specifically, if the slope of the friction braking force distribution line L2 is “α”, an expression (11) described below is maintained between the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt. Ffrcrt=α⋅Ffrcft

[0099] Accordingly, the expressions (12) and (13) described below are obtained from the previously mentioned expressions (10) and (11). Ffrcft(n)=Ffrcft(n−1)+β / (1+α) Ffrcft(n)=Ffrcft(n−1)+α⋅β / (1+α)

[0100] The CPU determines the target regenerative braking force Frgnt (n), the target front friction braking force Ffrcft, and the target rear friction braking force Ffrcrt according to expressions (9), (12), and (13). Consequently, the ratio of the front wheel braking force Fbf (= Frgn + Ffrcf) to the total braking force is decreased, and the ratio of the rear wheel braking force Fbr (= Ffrcr) to the total braking force is increased.

[0101] The preceding description is based on the premise that the required braking force Freq remains unchanged. In fact, the required braking force Freq can increase during the braking force exchange control. For example, if the required braking force Freq increases by an amount “ΔFreq”, the target values ​​are determined according to the following expressions (14) to (16). It should be noted that the target regenerative braking force Frgnt (n) is determined such that it does not exceed the value (1 - δ) · Freq. Frgnt(n)=Frgnt(n−1)−β+δ⋅ΔFreq Ffrcft(n)=Ffrcft(n−1)+β / (1+α)+(1−δ)⋅ΔFreq / (1+α) Ffrcrt(n)=Ffrcrt(n−1)+α⋅β / (1+α)+(1−δ)⋅ΔFreq⋅α / (1+α)

[0102] As previously described, the first device includes a distributed braking force calculation section 50 (the brake ECU) configured to distribute / assign the required braking force Freq to the target regenerative braking force Frgnt, the target front friction braking force Ffrcft, and the target rear friction braking force Ffrcrt. The distributed braking force calculation section 50 is configured to perform a "first braking force distribution control" as described below when the required braking force Freq is equal to or less than the maximum regenerative braking force Frgnmax. (1) The calculation section 50 for distributed braking force allocates the total required braking force Freq to the target effective braking force Frgnt. (2) The distributed braking force calculation section 50 performs the brake force reduction control to reduce the target regenerative braking force Frgnt by a first predetermined amount (= δ · Freq) when the front wheel acceleration DVwf deviates from / decreases from the value that is greater than the first acceleration threshold value DVth11, which is a negative value for the value that is equal to or less than the first acceleration threshold value DVth11, while the distributed braking force calculation section 50 allocates the total required braking force Freq to the target regenerative braking force Frgnt. (3) The calculation section 50 for distributed braking force performs the brake force recovery control to increase the target regenerative braking force Frgnt such that the target regenerative braking force Frgnt corresponds to the required braking force Freq when the front wheel acceleration DVwf becomes greater than the second acceleration threshold DVth12, which is equal to or greater than the first acceleration threshold DVth11, in the period from the first time t11, at which the target regenerative braking force Frgnt is reduced by the first amount (= δ · Freq), until the second time t13, at which the predetermined time tw1 from the first time t11 expires. (4) The calculation section 50 for distributed braking force is executed when the front wheel acceleration DVwf is not greater than the second acceleration threshold DVth12 during the period from time t11 to the second time t13, wherein the brake force exchange control reduces the target regenerative braking force Frgnt by a second predetermined amount β each time the predetermined time Δt elapses;and the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt are increased such that the "sum (Ffrcft + Ffrcrt) of the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt" is increased by the second predetermined amount β each time the predetermined time Δt elapses, while maintaining a proportional ratio (Ffrcrt = α · Ffrcft) between the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt (or such that the target front friction braking force Ffrcft and the target rear friction braking force Ffrcrt are proportional to each other).

[0103] According to the first device, in a case where the vehicle 10 slows down on a road with low µ solely by using regenerative braking force Frgn, the probability of unnecessarily replacing a portion of the regenerative braking force Frgn with a portion of the friction braking force Ffrc when the front wheels are prone to locking can be reduced. Consequently, the probability of using regenerative braking force can be increased to improve energy efficiency (to improve the vehicle's fuel consumption). Additionally, the predetermined ratio δ for the first predetermined amount is between 10 and 15%. This allows the first device to prevent the driver from experiencing an unfamiliar sensation and to reduce the possibility of the front wheels WF locking. Second embodiment

[0104] Next, a brake control device (hereinafter referred to as the "second device") of a vehicle according to a second embodiment of the present disclosure is described. The second device differs from the first device in that the second device performs specific brake control (second brake force distribution control) for the "front wheel slip WF" that occurs when the front wheels WF traverse a section / part with low µ, such as a bump and a culvert, in a case where the vehicle 10 is traveling on a road with high µ (e.g., a dry asphalt road) and is being braked (hereinafter referred to as "slow braking"), so that the vehicle is decelerated with a relatively small deceleration magnitude, using only the regenerative braking force. This difference will be the main focus of the following discussion.

[0105] In this description, "slow braking" means braking that causes the vehicle to decelerate from 0.2 G to 0.3 G (according to an acceleration from -0.2 G to -0.3 G). The braking force required, Freq, for slow braking is relatively small and is therefore met solely by the regenerative braking force, Frgn (and does not require the frictional braking force, Ffrc). In other words, during slow braking, the entire required braking force, Freq, can be allocated to the regenerative braking force, Frgn.

[0106] As in Fig. As shown in Figure 12, the front wheel acceleration DVwf decreases from "0" to "DVwf20", that is, for example, between -0.2 and -0.3 G, when slow braking is performed while the vehicle 10 is traveling on the road with high µ. The front wheel acceleration DVwf reaches "DVwf20" at time t21.

[0107] At time t22 after time t21, the front wheels WF pass through the section / part with low µ, which has a relatively short distance / length, and the front wheel acceleration DVwf decreases rapidly. If the front wheel acceleration DVwf becomes equal to or less than a first acceleration threshold DVth21 at time t23, the second device reduces the target regenerative braking force Frgnt by an amount corresponding to the predetermined ratio δ (10% - 15%) of the required braking force Freq. The first acceleration threshold DVth21 is, for example, "-1G".

[0108] The second device rapidly increases the target regenerative braking force Frgnt when the front wheel acceleration DVwf exceeds a second acceleration threshold DVth22, which is a positive value before time t25. At this point, a predetermined second time tw2 begins to elapse from time t23, at which time the second device reduces the target regenerative braking force Frgnt by an amount corresponding to the predetermined ratio δ. Specifically, the second device increases the target regenerative braking force Frgnt such that at time t24, the target regenerative braking force Frgnt equals the required braking force Freq. At this time, only the front wheel braking force Fbf varies, similar to the process described in Fig. Example 4 shows that slow braking is then performed to decelerate vehicle 10 to a level similar to that achieved before vehicle 10 passed through the low µ section. The reason the front wheel acceleration DVwf increases rapidly and becomes greater than the second acceleration threshold DVth22 at time t24 is that the front wheels WF have already passed through the low µ section and are now on the high µ road at time t24, thus accelerating due to the high µ road surface.

[0109] In contrast, the second device begins as shown in Fig. Figure 13 shows how to replace a portion of the target regenerative braking force Frgnt with a portion of the target wheel friction braking force Ffrct (i.e., to begin performing brake force exchange control) when the front wheel acceleration DVwf does not exceed the second acceleration threshold DVth22 before (at) time t25, at which time the predetermined second time tw2 elapses from time t23, at which time the second device reduces the target regenerative braking force Frgnt by the amount corresponding to the predetermined ratio δ. This allows the second device to ensure the braking force required / necessary for a road with low µ.

[0110] Immediately after the second device reduces the target regenerative braking force Frgnt by the amount corresponding to the predetermined ratio δ at time t23, the front wheel acceleration DVwf and the vehicle acceleration Gx temporarily increase. In the Fig. In example 13, the front wheels WF are still on the low µ section, and therefore the front wheel acceleration DVwf begins to decrease again before reaching the second acceleration threshold DVth22. This is because the front wheels WF are still on the low µ section. Specific operating procedure

[0111] The CPU (hereinafter referred to simply as "CPU") of the brake control unit 50A of the second device is configured to execute a "second brake force distribution control routine" that is identical to the "first brake force distribution control routine" as shown by the flowcharts in the Fig. 7, Fig. 8, Fig. 9, Fig. 10 to Fig. 11 shown, with the exception of the following points.

[0112] The first acceleration threshold DVth21, to which the second device refers, differs from the first acceleration threshold DVth11, to which the first device refers. In particular, the first acceleration threshold DVth21 is lower than the first acceleration threshold DVth11.

[0113] The second acceleration threshold DVth22, to which the second device refers, differs from the second acceleration threshold DVth21, to which the first device refers. Specifically, the second acceleration threshold DVth22 is a positive value (i.e., a value on the acceleration side and not on the deceleration side), whereas the second acceleration threshold DVth12 is a negative value (i.e., a value on the deceleration side and not on the acceleration side) and is essentially equivalent to the first acceleration threshold DVth11.

[0114] The second given time tw2 differs from the first given time tw1. However, time tw2 can be the same as time tw1.

[0115] According to the second device configured in this way, the probability of unnecessarily replacing part of the regenerative braking force Frgn with part of the frictional braking force Ffrc can be reduced when the front wheels WF are temporarily moving on the section with low µ. Therefore, the front wheel acceleration DVwf decreases rapidly due to the slippage of the front wheels WF when the vehicle 10 is traveling on the road with high µ and is braking only with regenerative braking force. Consequently, the probability of using regenerative braking force can be increased to improve energy efficiency (to improve the vehicle's fuel consumption). Additionally, the predetermined ratio δ for the first predetermined amount is between 10 and 15%. This also allows the second device to prevent the driver from experiencing an unfamiliar sensation and to reduce the possibility of the front wheels WF locking up. Third example

[0116] Next, a brake control device (hereinafter referred to as the “third device”) of a vehicle according to a third embodiment of the present disclosure is described.

[0117] The third device is configured to be able to execute both the first brake force distribution control described above, which is performed by the first device, and the second brake force distribution control described above, which is performed by the second device. Based on the driving conditions of the vehicle 10, the third device determines whether the first brake force distribution control should be executed and whether the second brake force distribution control should be executed. In other words, based on the driving conditions of the vehicle 10, the third device determines which control should be performed: the first brake force distribution control or the second brake force distribution control. This point is described in detail below. Specific operating procedure

[0118] The CPU (hereinafter referred to simply as "CPU") of the brake control unit 50B of the third device is configured to execute a "brake force distribution control execution determination routine" as described by a flowchart in Fig. As shown in Figure 14, this occurs every time a constant time (e.g., 20 ms) elapses.

[0119] The CPU begins processing step 1400 at an appropriate time and proceeds to step 1410 to determine whether the vehicle is braking or not. Specifically, the CPU determines whether the brake pedal deduction amount BP is equal to or greater than a predefined brake pedal deduction amount threshold BPth.

[0120] If the brake pedal actuation amount BP is less than the threshold BPth, the CPU makes a "no" determination in step 1410 and proceeds directly to step 1495 to temporarily terminate the current routine. In this case, the CPU does not execute either the first or the second brake force distribution control because the vehicle is not being braked.

[0121] If, in contrast, the brake pedal actuation amount BP is equal to or greater than the threshold value BPth, the CPU makes a "yes" determination in step 1410 and proceeds to step 1420. In step 1420, the CPU determines whether a product |Gx| · M is less than the maximum regenerative braking force Frgnmax or not. The "|Gx|" is a quantity (absolute value) |Gx| of the vehicle acceleration Gx, which is obtained / detected by the accelerometer 54. The vehicle acceleration Gx represents an acceleration that the driver perceives more precisely than the front wheel acceleration DVwf. The "M" is a weight (or vehicle weight) of the vehicle 10.

[0122] If the product |Gx| · M of the magnitude of the vehicle acceleration Gx and the vehicle weight M is determined to be equal to or greater than the maximum regenerative braking force Frgnmax, the CPU makes a "no" determination in step 1420 and proceeds to step 1450 to execute a "normal brake control routine". Afterward, the CPU proceeds directly to step 1495 to temporarily terminate the current routine. The "normal brake control routine" is a routine for executing "normal brake control", which is brake control performed when the vehicle is traveling at 10°C and is decelerating on a road with high µ at a relatively high deceleration (i.e., deceleration achieved by using the friction braking force Ffrc in addition to the regenerative braking force Frgn).When normal brake control is performed, the CPU determines a slip ratio (brake slip ratio) SLi for each wheel, based on the wheel speeds (Vwfl, Vwfr, Vwrl, Vwrr), using the following expression, and executes a well-known anti-lock braking (ABS) control for each wheel based on the slip ratio SLi. The CPU executes the ABS control using only the friction braking force Ffrc, while the regenerative braking force Frgn is set to zero accordingly. SLi=100⋅(SPD−Vwi) / SPD (i:fl,fr,rl,or rr)

[0123] If, on the other hand, the product |Gx| · M of the vehicle acceleration Gx and the vehicle weight M is less than the maximum regenerative braking force Frgnmax, the CPU makes a "yes" determination in step 1420 and proceeds to step 1430. In step 1430, the CPU determines whether a product |Dvwf| · M of a quantity (absolute value) |Dvwf| of the front wheel acceleration DVwf and the vehicle weight M is equal to or greater than the target regenerative braking force Frgnt. If the product |Dvwf| · M is less than the target regenerative braking force Frgnt, the CPU makes a "no" determination in step 1430 and proceeds directly to step 1495 to temporarily terminate the current routine. In this case, because the target braking force Frgnt is relatively small and therefore the front wheels WF are unlikely to slip (slide), the CPU does not execute either the first brake force distribution control or the second brake force distribution control.

[0124] In contrast, if the product |Dvwf| · M of the magnitude of the front wheel acceleration DVwf and the vehicle weight M is equal to or greater than the target regenerative braking force Frgnt, the CPU makes a "yes" determination in step 1430 and proceeds to step 1440. In step 1440, the CPU determines whether the product |Dvwf| · M is less than a product γ · Frgnt of a coefficient γ and the target regenerative braking force Frgnt. The coefficient γ is, for example, a value between 1.1 and 1.2. Thus, it can be said that in step 1440, the CPU determines whether the product |Dvwf| · M is less than a value obtained by adding a third predetermined value ((γ - 1) · Frgnt) to the target regenerative braking force Frgnt. In other words, in step 1440, the CPU determines whether the product |Dvwf| · M is located near the target braking force Frgnt or not.If the product |Dvwf| · M is smaller than the product γ · Frgnt, the CPU makes a "yes" determination in step 1440 and proceeds directly to step 1495 to temporarily terminate the current routine. In this case, it can be determined that the vehicle 10 is decelerating with a deceleration required by the driver, and therefore the CPU does not execute either the first or the second brake force distribution control.

[0125] If, on the other hand, the product |Dvwf| · M is equal to or greater than the product γ · Frgnt, the CPU makes a "no" determination in step 1440 and proceeds to step 1460. In step 1460, the CPU determines whether a slip ratio SL (n-1) of the front wheels WF is equal to or greater than a predefined slip ratio threshold SLth. The slip ratio SL (n-1) of the front wheels WF is an average of the braking slip ratio SLfl of the front left wheel WFL, calculated at a time point in the computation period (the constant time) before the present time, and the braking slip ratio SLfr of the front right wheel WFR, calculated at a time point in the computation period (the constant time) before the present time.If the slip ratio SL (n-1) of the front wheels WF is equal to or greater than the specified slip ratio threshold SLth, the CPU makes a "yes" determination in step 1460 and proceeds to step 1470. In step 1470, the CPU executes the first brake force distribution control, which is carried out by the first device (see ). Fig. 3, Fig. 5 and Fig. 7) The CPU then proceeds to step 1495 to complete the current routine.

[0126] In contrast, the CPU makes a "no" determination in step 1460 and proceeds to step 1480 if the slip ratio SL (n-1) of the front wheels WF is less than the specified slip ratio threshold SLth. In step 1480, the CPU executes the second brake force distribution control, which is carried out by the second device (see Fig. 12 and Fig. 14). The CPU then proceeds to step 1495 to complete the current routine.

[0127] In this way, the third device can appropriately determine, based on the driving conditions of the vehicle 10, which control operation should be performed: normal brake control, first brake force distribution control, and second brake force distribution control. Normal control is a brake control operation for braking the vehicle 10, which is traveling on a road with high µ, by using both the regenerative braking force Frgn and the frictional braking force Ffrc, whereby the normal / conventional ABS control is performed using the frictional braking force Ffrc. First brake force distribution control is a brake control operation that is performed when the vehicle 10, which is traveling on a road with low µ, is braked only by using the regenerative braking force Frgn.The second brake force distribution control is a brake control that is executed while the vehicle 10 is driving on the road with high µ, braking slowly only by using the regenerative braking force Frgn. Examples of variations

[0128] The device according to the present disclosure is not limited to the embodiments described above, and various modifications are possible without deviating from the scope of protection of the disclosure.

[0129] Although the first to third devices described above are used for an electric vehicle with the motor generator 21, the battery 22 and the inverter 23, the brake control device according to the present disclosure can be used for a hybrid vehicle with an internal combustion engine, at least one motor generator and a power distribution mechanism, as long as the hybrid vehicle is configured to have the regenerative braking device and the friction braking device.

[0130] In the previously described embodiments, the vehicle speed SPD for calculating the required braking force Freq is an average of the wheel speeds Vwfl, Vwfr, Vwrl, and Vwrr of the wheels. However, the vehicle speed SPD can also be an average of the wheel speed Vrl of the rear left wheel WRL and the wheel speed Vrr of the rear right wheel WRR. The vehicle speed SPD, which is the average of the wheel speeds Vrl and Vrr, is not affected by a decrease in the wheel speeds of the front wheels WF, even if one of the front wheels VF slips (slides). Alternatively, the vehicle speed SPD can be an average of the wheel speeds that are not the lowest among the wheel speeds Vwfl, Vwfr, Vwrl, and Vwrr.

[0131] In the previously described embodiments, the value β (the second predetermined value β), by which the target regenerative braking force Frgnt is reduced per calculation cycle Δt during the brake force exchange control, is a constant value (see the [reference to be added]). Fig. 5 and Fig. Figure 13 shows the rate of change of the target regenerative braking force Frgnt). However, the value β can be variable (it need not necessarily be a constant value) as long as the target regenerative braking force Frgnt is gradually decreased and the target wheel friction braking force Ffrct is gradually increased, while the sum of the target regenerative braking force Frgnt and the target wheel friction braking force Ffrct remains unchanged. For example, the value β can be varied to become larger as the vehicle speed SPD increases, as long as the value β for the friction braking device 30 is not too large.

Claims

[1] Brake control device for a vehicle (10) comprising a regenerative braking device (20) configured to apply a regenerative braking force (Frgn) to the front wheels (WF) of the vehicle (10) and a friction braking device (30) configured to apply a front wheel friction braking force (Ffrcf) to the front wheels and a rear wheel friction braking force (Ffrcr) to the rear wheels of the vehicle (WR), comprising: Wheel speed sensors (53FL, 53FR) each configured to receive a signal indicating a wheel speed from each of the front wheels (WF); a brake pedal actuation amount sensor (52) configured to receive a signal indicating the actuation amount of a brake pedal (52a); and an electronic control unit (40, 50) configured to: to determine a front wheel acceleration (DVwf) of the front wheels (WF) based on the signal received from the wheel speed sensors (53FL, 53FR) (step 1020); to determine a required braking force (Freq) based on the signal received from the brake pedal actuation amount sensor (52) (step 1030); to distribute the required braking force (Freq) among a target regenerative braking force (Frgnt), a target front friction braking force (Ffrcft), and a target rear friction braking force (Ffrcrt); and the regenerative braking device (20) to apply the regenerative braking force, which is equal to the target regenerative braking force (Frgnt), to the front wheels (WF), the friction braking device (30) to apply the front wheel friction braking force, which is equal to the target front wheel friction braking force (Ffrcft), to the front wheels (WF), and the friction braking device (30) to apply the rear wheel friction braking force, which is equal to the target rear friction braking force (Ffrcrt), to the rear wheels (WR), where, if the required braking force (Freq) is less than or equal to a maximum regenerative braking force (Frgnmax) that the regenerative braking device (20) can apply to the front wheels (WF), the electronic control unit is configured to: to allocate the total required braking force (Freq) to the target regenerative braking force (Frgnt) (step 1050); and to perform a brake force reduction control to reduce the target regenerative braking force by a first predetermined amount (δ·Freq) without changing the target front friction braking force (Ffrcft) and the target rear friction braking force (Ffrcrt) (step 1070), at a first time (t11) when the front wheel acceleration (DVwf) changes from a value greater than a first acceleration threshold (DVth11), which is a negative value, to a value less than or equal to the first acceleration threshold (DVth11), while all the required braking force (Freq) is allocated to the target regenerative braking force (Frgnt) (steps 810 - 830, step 1040: No, step 1060: Yes). [2] Brake control device according to claim 1, wherein during the execution of the brake force reduction control the electronic control unit (40, 50) is configured to: to perform a brake force recuperation control (step 1050) to increase the target regenerative braking force (Frgnt) such that the target regenerative braking force (Frgnt) matches the required braking force (Freq) when, in a period from the first time (t11) to a second time (t13), in which a predetermined time (tw1) has elapsed from the first time (t11), the front wheel acceleration (DVwf) becomes greater than a second acceleration threshold (DVth12) that is greater than or equal to the first acceleration threshold (DVth11) (step 920: Yes, step 1040: Yes); and to perform a brake force exchange control (step 1080) in order to, if the front wheel acceleration (DVwf) in the period (tw1) from the first time point (t11) to the second time point (t13) does not become greater than the second acceleration threshold (DVth12) (step 920: No, step 940: Yes, step 1060: No), the target braking force (Frgnt) is reduced by a second predetermined amount (β) each time a predetermined time (Δt) has elapsed; and to increase the target front wheel friction braking force (Ffrcft) and the target rear friction braking force (Ffrcrt) such that a sum (Ffrcft + Ffrcrt) of the target front wheel friction braking force (Ffrcft) and the target rear friction braking force (Ffrcrt) is increased by the second predetermined amount (β) each time the predetermined time (Δt) has elapsed, while maintaining a proportional ratio (Ffrcrt = α · Ffrcft) between the target front wheel friction braking force (Ffrcft) and the target rear friction braking force (Ffrcft). [3] Brake control device according to claim 1, wherein the electronic control unit (40, 50) is configured to use as the first predetermined amount (δ·Freq) an amount of 10 to 15 percent of the target regenerative braking force (Frgnt) at a time immediately before the first time (t11). [4] Brake control device according to claim 2, wherein the electronic control unit (40, 50) is configured to perform a first brake force distribution control with the brake force reduction control, the brake force recovery control and the brake force exchange control, wherein the second acceleration threshold (DVth12) is set to a value equal to the first acceleration threshold (DVth11). [5] Brake control device according to claim 2, wherein the electronic control unit (40, 50) is configured to perform a second brake force distribution control with the brake force reduction control, the brake force recovery control and the brake force exchange control, wherein the second acceleration threshold value (DVth22) is set to a predetermined positive value. [6] Brake control device according to claim 2, wherein the electronic control unit is configured to perform a first brake force distribution control (step 1470) with the brake force reduction control, the brake force recovery control, and the brake force exchange control, wherein the second acceleration threshold (DVth12) is set to a value equal to the first acceleration threshold (DVth11) when a product (|Dvwf| · M) of a quantity (IDvwfl) of the front wheel acceleration and a weight (M) of the vehicle (10) is greater than or equal to a value obtained by adding a third predetermined value ((γ - 1)·Frgnt) to the target regenerative braking force (Frgnt) at a time immediately before the first time (t11), (step 1440: No) and a slip ratio (SL(n-1)) of the front wheels (WF) is greater than or equal to a predetermined slip ratio threshold (SLth) (step 1460: Yes); to perform a second brake force distribution control (step 1480) with the brake force reduction control, the brake force recovery control, and the brake force exchange control, wherein the first acceleration threshold (DVth11) of the second brake force distribution control is set to a value less than or equal to the first acceleration threshold (DVth11) used in the first brake force distribution control, and the second acceleration threshold (DVth12) of the second brake force distribution control is set to a predetermined positive value when the product (|Dvwf| · M) of the magnitude (IDvwfl) of the front wheel acceleration (DVwf) and the weight (M) is greater than or equal to the value obtained by adding the third predetermined value ((γ - 1) · Frgnt) to the target regenerative braking force (Frgnt) at a time immediately before the first time (t11),(Step 1440: No) and the slip ratio (SL(n-1)) of the front wheels (WF) is less than the specified slip ratio threshold (SLth) (Step 1460: No); and, to perform a regenerative braking force maintenance control to maintain a state in which the total required braking force (Freq) is allocated to the target regenerative braking force (Frgnt) when the product (|Dvwf|·M) of the magnitude (|Dvwf|) of the front wheel acceleration (Dvwf) and the weight (M) is less than the value obtained by adding the third predetermined value ((γ - 1)·Frgnt) to the target regenerative braking force (Frgnt) at a time immediately before the first time (t11) (Step 1440: Yes).

Images