Vehicle braking control device

Abstract

To provide a braking control device of a vehicle that can appropriately suppress variation in deceleration when control of switching between regenerative braking power and friction braking power is performed.SOLUTION: A braking control device of a vehicle 1 comprises an auxiliary motor 5 which is consecutively provided in a motor generator 3, and generates auxiliary power with respect to regenerative braking power, and when a divergence occurs between deceleration D and target deceleration Dt during execution of control of switching braking power, makes the auxiliary motor 5 generate auxiliary power for converging the deceleration D to the target deceleration Dt in an BRK_ECU21.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a braking control device for a vehicle that is capable of performing braking using a regenerative braking force generated by a motor generator and a friction braking force generated by a friction brake. [Background technology]

[0002] In general, in electrically powered vehicles such as hybrid vehicles and electric vehicles, braking force cooperative control is performed during braking using a regenerative braking force generated by a motor generator and a friction braking force generated by a friction brake.

[0003] For example, as disclosed in Patent Document 1, when a driver operates the brakes in a vehicle equipped with a motor generator, a target braking force is set according to the amount of brake operation, and further, a braking force to be generated by power regeneration (target regenerative braking force) is set. Then, the target regenerative braking force is subtracted from the target braking force to set a braking force to be generated in the friction brake (target frictional braking force).

[0004] In such a braking force cooperative control in an electric vehicle, the braking force is basically mainly regenerative braking force in order to improve the power consumption rate. However, after the battery is fully charged or after the vehicle speed drops below a set speed just before stopping, braking force switching control from regenerative braking force to friction braking force is generally performed. In this braking force switching control, the regenerative braking force is controlled to gradually decrease, and the friction braking force is controlled to gradually increase in accordance with the amount of decrease in the regenerative braking force. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-42506 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the friction braking force generated by the friction brake may have a certain error with respect to the target friction braking force. Such an error is thought to be caused by the friction coefficient of the brake pads (hereinafter referred to as "pad μ") of the friction brakes changing over time, due to temperature conditions, etc. If an error in the friction braking force caused by such pad μ occurs during braking force switching control, it may cause fluctuations in the deceleration of the vehicle body, causing discomfort to the occupants.

[0007] To address this issue, it is possible to suppress fluctuations in deceleration by using feedback control of brake fluid pressure, etc. However, because braking force switching control is performed in a short period of time, feedback control of brake fluid pressure may not be able to sufficiently suppress fluctuations in deceleration.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a vehicle braking control device that can accurately suppress fluctuations in deceleration when switching control is performed between regenerative braking force and friction braking force. [Means for solving the problem]

[0009] According to one aspect of the present invention, a vehicle braking control device includes a friction brake that generates a frictional braking force, a motor generator that generates a regenerative braking force, and braking control means that sets a target deceleration when braking is requested for the vehicle, generates the target deceleration using a braking force including the regenerative braking force when a preset regenerative condition is met, and performs switching control to generate the target deceleration while replacing the regenerative braking force included in the braking force with the frictional braking force when the regenerative condition is no longer met.The vehicle braking control device further includes an auxiliary motor connected to the motor generator that generates an auxiliary force for the regenerative braking force, and when a deviation in deceleration from the target deceleration occurs during execution of the switching control, the braking control means causes the auxiliary force to be generated by the auxiliary motor to converge the deceleration to the target deceleration. [Effects of the Invention]

[0010] According to the vehicle braking control device of the present invention, it is possible to appropriately suppress fluctuations in deceleration when switching control between regenerative braking force and friction braking force is performed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing a driving control system of an electric vehicle according to a first embodiment of the present invention; [Figure 2] Same as above, brake actuator configuration diagram [Figure 3] 1. A flowchart showing a braking control routine. [Figure 4] 10 is a flowchart showing a braking force replacement control subroutine. [Figure 5] 1 is a time chart showing an example of vehicle speed, target braking force, and deceleration during braking control. [Figure 6] 10 is a time chart showing an example of the target braking force and deceleration when the braking force is insufficient during switching control. [Figure 7] 10 is a time chart showing an example of the target braking force and deceleration when excessive braking force occurs during switching control. [Figure 8] FIG. 10 is a schematic diagram showing a driving control system of an electric vehicle according to a second embodiment of the present invention. [Figure 9] A flowchart showing a subroutine for setting a target assist force in the deceleration direction. [Figure 10] A flowchart showing a subroutine for setting a target assist force in the acceleration direction. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, which relate to a first embodiment of the present invention, and FIG. 1 is a schematic diagram showing the configuration of a driving control system for an electric vehicle.

[0013] 1 is an electric vehicle (EV) as an example of an electrically powered vehicle. The vehicle 1 has a motor generator 3 as a drive source.

[0014] A front differential 7f is connected to the output shaft 3a of the motor generator 3 via a reduction gear 4. Left and right front wheels 8fl, 8fr are connected to left and right drive shafts 7fl, 7fr of the front differential 7f.

[0015] An auxiliary motor 5 is interposed between the motor generator 3 and the reducer 4. The auxiliary motor 5 is configured by a small motor with a smaller output than the motor generator 3.

[0016] The motor generator 3 and the auxiliary motor 5 are connected to a battery 12 via an inverter 11 .

[0017] Depending on the characteristics of the output torque and power consumption efficiency of the motor generator 3, it may be possible to omit the reduction gear 4 from the drive system of the vehicle 1. In this case, the auxiliary motor 5 is interposed between the motor generator 3 and the front differential device 7f. Also, instead of the reduction gear 4, a transmission or the like may be provided between the auxiliary motor 5 and the front differential device 7f.

[0018] Friction brakes 15fl, 15fr, 15rl, and 15rr are provided on the left and right front wheels 8fl, 8fr, which are drive wheels of the vehicle 1, and the left and right rear wheels 8rl, 8rr, which are driven wheels of the vehicle 1. Each of the friction brakes 15fl, 15fr, 15rl, and 15rr has, for example, a caliper 16fl, 16fr, 16rl, and 16rr equipped with a brake pad that engages with a disc rotor as a friction engagement element.

[0019] A brake actuator 17 is connected to each of the calipers 16fl, 16fr, 16rl, and 16rr of the friction brakes 15fl, 15fr, 15rl, and 15rr.

[0020] For example, as shown in FIG. 2, the brake actuator 17 is mainly composed of a brake fluid pressure generating unit 41 and a brake fluid pressure circuit 42 connected to the brake fluid pressure generating unit 41.

[0021] The brake fluid pressure generating unit 41 has a master cylinder 44, a reservoir tank 45 attached to the master cylinder 44, and a brake booster 46 interposed between the brake pedal 26 and the master cylinder 44. A pressure medium (oil) is stored in the reservoir tank 45. The brake pedal 26 is connected to the brake booster 46 via an operating rod 48.

[0022] A master cylinder 44 of the brake fluid pressure generating unit 41 is connected via a brake fluid pressure circuit 42 to calipers 16fl, 16fr, 16rl, and 16rr provided on the wheels 8fl, 8fr, 8rl, and 8rr, respectively.

[0023] The brake hydraulic circuit 42 is made up of two hydraulic lines: a first hydraulic circuit 52 and a second hydraulic circuit 53. The brake hydraulic circuit 42 according to this embodiment is of a cross piping (X piping) type in which the first hydraulic circuit 52 and the second hydraulic circuit 53 are arranged diagonally across the vehicle 1. That is, in the brake hydraulic circuit 42 according to this embodiment, the first hydraulic circuit 52 is connected to the calipers 16fl, 16rr of the left front wheel and the right rear wheel arranged on one diagonal side of the vehicle 1, and the second hydraulic circuit 53 is connected to the calipers 16fr, 16rl of the right front wheel and the left rear wheel arranged on the other diagonal side of the vehicle 1.

[0024] Since the first hydraulic circuit 52 and the second hydraulic circuit 53 have the same configuration, the same reference numerals will be used appropriately to simplify the description below. In addition, when describing the configuration of the brake hydraulic circuits 52 and 53 below, for convenience, the master cylinder 44 side will be described as upstream and the caliper 16fl, 16fr, 16rl, and 16rr side will be described as downstream, based on the flow from the master cylinder 44 to the caliper 16fl, 16fr, 16rl, and 16rr side of the brake calipers.

[0025] The master cylinder 44 is provided with first and second supply / discharge ports 44a, 44b. The upstream of a first fluid passage L1 constituting each of the hydraulic circuits 52, 53 is connected to each of these supply / discharge ports 44a, 44b. The downstream of the first fluid passage L1 is connected midway to a second fluid passage L2. The upstream side of the second fluid passage L2 is connected to a low-pressure accumulator 54 serving as a pressure accumulation means.

[0026] The downstream side of the second fluid path L2 is branched and connected to a third fluid path L3 and a fourth fluid path L4. Furthermore, the downstream side of each fluid path L3, L4 is connected to a caliper 16fl, 16rr (16fr, 16rl) that operates the friction brake 15fl, 15rr (15fr, 15rl) provided on each wheel 8fl, 8rr (8fr, 8rl) to generate a braking force (friction braking force) on each wheel 8fl, 8rr (8fr, 8rl).

[0027] Meanwhile, the upstream of the fifth and sixth fluid paths L5 and L6 are connected to the middle of the third and fourth fluid paths L3 and L4. The downstream of these fifth and sixth fluid paths L5 and L6 is connected to a seventh fluid path, and the downstream of this seventh fluid path L7 is connected to the low-pressure accumulator 54.

[0028] A gate-in valve 55 is provided in the first hydraulic line L1, and a hydraulic pump 56 is provided in the second hydraulic line L2 downstream of the first hydraulic line L1. Furthermore, the hydraulic pumps 56 of the first and second hydraulic circuits 52, 53 are connected to a common electric motor 57.

[0029] The drive shafts of the hydraulic pumps 56, 56 are connected to a motor 57 so that the hydraulic pressure pulsations generated by the hydraulic pumps 56, 56 are in opposite phases to each other.

[0030] The first fluid line L1 upstream of the gate-in valve 55 and the second fluid line L2 downstream of the hydraulic pump 56 are bypass-connected via an eighth fluid line L8. A bypass valve 58 is provided in this eighth fluid line L8. A first brake fluid pressure sensor 59a (a second brake fluid pressure sensor 59b) is provided in the second fluid line L2 downstream of the eighth fluid line L8. The brake fluid pressure sensor 59a (59b) is, for example, a fluid pressure sensor that detects the hydraulic pressure of the brake fluid acting on the second fluid line L2. Pressurizing valves 60 and 61 are provided in the third and fourth fluid lines L3 and L4, and pressure-reducing valves 62 and 63 are provided in the fifth and sixth fluid lines L5 and L6.

[0031] Each of these valves 55, 58, 60 to 63 is, for example, an electromagnetic solenoid valve. In this embodiment, for example, the bypass valve 58 and the pressurizing valves 60 and 61 are configured as normally open electromagnetic solenoid valves. Also, the gate-in valve 55 and the decompression valves 62 and 63 are configured as normally closed electromagnetic solenoid valves.

[0032] Therefore, the brake fluid pressure generated in the master cylinder 44 in accordance with the amount of depression of the brake pedal 26 by the driver is basically supplied to each caliper 16 as is.

[0033] On the other hand, for example, in a vehicle 1 equipped with a driving assistance device not shown, when the electric motor 57 is driven, the gate-in valve 55 is opened, and the bypass valve 58 is closed, the pressure medium pressurized in the master cylinder 44 or the pressure medium supplied directly from the reservoir tank 45 is pressurized to a predetermined brake hydraulic pressure via the hydraulic pump 56, and then supplied from the second hydraulic line L2 to the third and fourth hydraulic lines L3 and L4.

[0034] Furthermore, during braking force cooperative control in which the brakes are coordinated with the regenerative brake and the engine brake, etc., the brake fluid pressure is reduced through drive control of the pressure reducing valves 62, 63 and the electric motor 57, etc. As a result, the friction braking force is controlled to a braking force according to a predetermined braking force distribution value.

[0035] As shown in FIG. 1, a control system that controls the running of a vehicle 1 includes a motor control unit (motor_ECU) 20 and a brake control unit (BRK_ECU) 21.

[0036] The motor_ECU 20 and the BRK_ECU 21 are connected to each other via a CAN (Controller Area Network) or the like so as to be able to communicate with each other.

[0037] The motor_ECU 20 is connected to various sensors such as an accelerator sensor 25a that detects the driver's operation state (accelerator opening) of an accelerator pedal 25. In addition, information such as the remaining capacity (SOC) of the battery 12 is input to the motor_ECU 20 via the inverter 11.

[0038] The BRK_ECU 21 is connected to various sensors such as a brake switch 26a that turns on when the driver depresses the brake pedal 26, wheel speed sensors 27fl, 27fr, 27rl, 27rr that detect the wheel speeds of each wheel 8fl, 8fr, 8rl, 8rr, an acceleration sensor 28 that detects the acceleration of the vehicle 1, and first and second brake fluid pressure sensors 59a, 59b provided in the brake fluid pressure circuit 42.

[0039] Input signals from these various sensors and the like can be exchanged between the motor_ECU 20 and the BRK_ECU 21 via a CAN or the like.

[0040] Furthermore, various control signals calculated in the motor_ECU 20 and the BRK_ECU 21 can be input and output to and from each other via a CAN, etc. For example, various control signals such as a target regenerative braking force Fbr and a target assist force Fa, which will be described later, are input to the motor_ECU 20 from the target BRK_ECU 21.

[0041] The motor_ECU 20 controls the motor generator 3 and the auxiliary motor 5 via the inverter 11 based on various input signals.

[0042] For example, when the driver depresses accelerator pedal 25 and the vehicle 1 is powered, motor_ECU 20 sets a target driving force by referring to a pre-set map or the like based on the accelerator pedal opening and the vehicle speed V of the host vehicle 1. Then, motor_ECU 20 supplies driving power according to the target driving force from battery 12 via inverter 11 to motor generator 3. As a result, motor generator 3 functions as a driving motor and generates driving force (driving torque) for each of wheels 8fl, 8fr, which are drive wheels.

[0043] Furthermore, for example, when the driver releases the accelerator pedal 25 and the vehicle 1 is coasting, the motor_ECU 20 sets a target regenerative braking force by referring to a preset map or the like based on the vehicle speed V of the vehicle 1. Then, the motor_ECU 20 supplies field power according to the target regenerative braking force from the battery 12 to the motor generator 3 via the inverter 11. This causes the motor generator 3 to function as a generator, regenerates running energy into the battery 12, and generates regenerative braking force (regenerative braking torque) for each of the wheels 8fl and 8fr, which are drive wheels.

[0044] Furthermore, the motor_ECU 10 can also perform braking control in cooperation with the BRK_ECU 21, for example, when braking the vehicle 1 by the driver depressing the brake pedal 26. In this case, the target regenerative braking force Fbr and the target assist force Fa are input to the motor_ECU 21 from the BRK_ECU 21 as appropriate.

[0045] When the target regenerative braking force Fbr is input, the motor_ECU 20 supplies field power corresponding to the target regenerative braking force Fbr from the battery 12 to the motor generator 3 via the inverter 11. This causes the motor generator 3 to function as a generator, regenerating the traveling energy into the battery 12, and generating a regenerative braking force (regenerative braking torque) for each of the wheels 8fl and 8fr, which are the drive wheels.

[0046] Furthermore, when the target assist force Fa is input, the motor_ECU 20 supplies drive power according to the target assist force Fa from the battery 12 to the auxiliary motor 5 via the inverter 11. This causes the auxiliary motor 5 to generate an assist force (auxiliary torque) for increasing or decreasing the regenerative braking force generated by the motor generator 3.

[0047] In this embodiment, the control of the auxiliary motor 5 is basically performed when braking the vehicle 1, but the motor_ECU 20 does not perform power regeneration control using the auxiliary motor 5. That is, the auxiliary motor 5 is driven in the forward rotation direction by the driving power supplied from the battery 12 through the control of the motor_ECU 20, for example, thereby reducing the regenerative braking force generated by the motor generator 3. Also, the auxiliary motor 5 is driven in the reverse rotation direction by the driving power supplied from the battery 12 through the control of the motor_ECU 20, for example, thereby increasing the regenerative braking force generated by the motor generator 3. This allows the motor_ECU 21 to generate an auxiliary force with good responsiveness using the auxiliary motor 5.

[0048] The BRK_ECU 21 controls the electric motor 57 for the brake actuator 17, the valves 55, 58, 60 to 63, and the like, to perform braking control using the friction brakes 15fl, 15fr, 15rl, and 15rr.

[0049] In this braking control, when a preset regenerative condition is met, the BRK_ECU 21 coordinates the friction braking force generated by the friction brakes 15fl, 15fr, 15rl, and 15rr with the regenerative braking force generated by the motor generator 3.

[0050] Here, the regeneration conditions by the motor generator 3 are met when, for example, the remaining capacity SOC of the battery 12 is less than a predetermined threshold value and the vehicle speed V of the host vehicle 1 is equal to or greater than a predetermined threshold value Vs.

[0051] In such braking force cooperative control, in order to improve the power consumption rate of the vehicle 1, braking is basically performed with the regenerative braking force generated by the motor generator 3 as the main force, and the friction braking force generated by the friction brakes 15fl, 15fr, 15rl, and 15rr as the secondary force.

[0052] To explain braking force cooperative control in more detail, when a braking request is made, for example, by turning on the brake switch 26a, the BRK_ECU 21 sets a target deceleration Dt (and a target braking force Fbt corresponding to the target deceleration Dt) by referring to a pre-set map, etc., based on the brake fluid pressure detected by the first and second brake fluid pressure sensors 59a, 59b and the vehicle speed V of the vehicle 1, etc.

[0053] Furthermore, the BRK_ECU 21 sets a target regenerative braking force Fbr for the motor generator 3 based on the vehicle speed V of the host vehicle 1, the remaining capacity SOC of the battery 12, and the like, by referring to a preset map or the like.

[0054] The target regenerative braking force Fbr set in this manner is output to the motor_ECU 20 via the CAN etc. As a result, the motor_ECU 20 causes the motor generator 3 to generate a regenerative braking force according to the target regenerative braking force Fbr.

[0055] Furthermore, the BRK_ECU 21 sets a value obtained by subtracting the target regenerative torque Tbr from the target braking torque Tbt as the target frictional braking force Fbf.

[0056] Based on the target friction braking force Fbf thus set, the BRK_ECU 21 controls the brake actuator 42. As a result, the BRK_ECU 21 causes the friction brakes 15fl, 15fr, 15rl, and 15rr to generate friction braking forces according to the target friction braking force Fbf.

[0057] If the above-mentioned regenerative condition is not satisfied, the BRK_ECU 21 does not set the target regenerative braking force Fbr, but sets the target braking force Fbt as the target frictional braking force Fbf.

[0058] Furthermore, if the regeneration condition changes from being satisfied to not being satisfied during the braking force cooperative control, the BRK_ECU 21 performs braking force substitution control. That is, the BRK_ECU 21 performs braking force substitution control by gradually decreasing the target regenerative braking force Fbr and gradually increasing the target frictional braking force Fbf in accordance with the amount of decrease in the target regenerative braking force Fbr.

[0059] More specifically, the BRK_ECU 21 calculates the substitution amount ΔFb as a subtraction amount for gradually reducing the target regenerative braking force Fbr to "0" during the period from when the regeneration condition becomes unsatisfied until the vehicle speed V of the host vehicle 1 becomes equal to or lower than a set vehicle speed (for example, "0 km / h"). Then, the BRK_ECU 21 uses the calculated substitution amount subtraction amount ΔFb to gradually reduce the target regenerative braking force Fbr until the target braking force Fbt becomes "0". At the same time, the BRK_ECU 21 uses the above-mentioned substitution amount ΔFb to gradually increase the target frictional braking force Fbf until the target frictional braking force Fbf matches the target regenerative braking force Fbt. Note that the above-mentioned substitution amount ΔFb may also be a fixed value set in advance.

[0060] However, in the switching control, when the proportion of frictional braking force contributing to braking of the vehicle 1 increases, depending on the state of the friction coefficient μ (pad μ) of the brake pads of each friction brake 15fl, 15fr, 15rl, 15rr, an excess of frictional braking force relative to the target braking force Fbt or a deficiency of frictional braking force relative to the target braking force Fbt occurs.

[0061] Such excess or deficiency in friction braking force can basically be absorbed by feedback control of each of the friction brakes 15fl, 15fr, 15rl, and 15rr. However, because switching control is performed in a short period of time, it may be difficult to fully absorb the excess or deficiency in friction braking force using feedback control of the brake fluid pressure.

[0062] Therefore, the BRK_ECU 21 sets a target assist force Fa for the assist motor 5 when the deceleration D (negative acceleration) detected by the acceleration sensor 28 or the like deviates significantly from the target deceleration Dt.

[0063] Specifically, when the deviation Δd of the deceleration D from the target deceleration Dt (Δd=Dt−D) is smaller than a preset first threshold Dth1, the BRK_ECU 21 sets a target assist force Fa in a direction to decelerate the host vehicle 1. That is, the BRK_ECU 21 sets the target assist force Fa to make the deviation Δd of the deceleration D from the target deceleration Dt "0" by gradually increasing the braking force until the vehicle speed V of the host vehicle 1 becomes equal to or lower than a set vehicle speed, for example.

[0064] On the other hand, when the deviation Δd of the deceleration D from the target deceleration Dt is greater than a preset second threshold Dth2, the BRK_ECU 21 sets a target assist force Fa in a direction that accelerates the host vehicle 1. That is, the BRK_ECU 21 sets the target assist force Fa to make the deviation Δd of the deceleration D from the target deceleration Dt "0" by gradually reducing the braking force until the vehicle speed V of the host vehicle 1 becomes equal to or lower than a set vehicle speed, for example.

[0065] Here, in order to accurately prevent an increase in braking distance due to insufficient braking force, it is desirable that the first threshold Dth1 (absolute value) for the deviation amount on the acceleration side be set smaller than the second threshold Dth2 (absolute value) for the deviation amount on the deceleration side.

[0066] In addition, it is desirable to set the target auxiliary force Fa in the direction to decelerate the vehicle 1 and the target auxiliary force Fa in the direction to accelerate the vehicle 1 to values in a range in which the motor efficiency of the auxiliary motor 5 (driving force generation efficiency relative to the driving current) is high.

[0067] In this manner, in this embodiment, the BRK_ECU 21, together with the motor_ECU 20, realizes the function of a braking control unit.

[0068] Next, the braking control executed by the BRK_ECU 21 will be described with reference to the flowchart of the braking control routine shown in Fig. 3. This routine is repeatedly executed at set time intervals.

[0069] When the routine starts, the BRK_ECU 21 checks in step S101 whether the host vehicle 1 is running.

[0070] Then, in step S101, if it is determined that the host vehicle 1 is not in motion, that is, if it is determined that the host vehicle 1 is stopped, the BRK_ECU 21 exits the routine.

[0071] On the other hand, if it is determined in step S101 that the host vehicle 1 is traveling, the BRK_ECU 21 proceeds to step S102. In step S102, the BRK_ECU 21 checks whether or not there has been a deceleration request for the host vehicle 1. That is, the BRK_ECU 21 checks, for example, whether or not the brake switch 26a is turned on (see FIG. 5), and whether or not there has been a deceleration request from a driving assistance device (not shown) in the vehicle 1 equipped with the driving assistance device.

[0072] If it is determined in step S102 that there is no deceleration request, the BRK_ECU 21 exits the routine.

[0073] On the other hand, if it is determined in step S102 that a deceleration request has been made, the BRK_ECU 21 proceeds to step S103. In step S103, the BRK_ECU 21 sets a target deceleration Dt (and a target braking force Fbt calculated from the target deceleration Dt). That is, for example, when the brake switch 26a is turned on, the BRK_ECU 21 sets the target deceleration Dt and the target braking force Fbt based on the brake fluid pressures detected by the first and second brake fluid pressure sensors 59a and 59b. Alternatively, the BRK_ECU 21 sets the target deceleration Dt and the target braking force Fbt based on the target deceleration input from a driving assistance device (not shown), for example.

[0074] In the following step S104, the BRK_ECU 21 checks whether a predetermined regeneration condition is satisfied, i.e., whether the remaining capacity SOC of the battery 12 is less than a predetermined threshold value and the vehicle speed V of the host vehicle 1 is equal to or greater than a predetermined threshold value Vs.

[0075] If it is determined in step S104 that the regeneration conditions are met, the BRK_ECU 21 proceeds to step S105.

[0076] In step S105, the BRK_ECU 21 sets a target regenerative braking force Fbr based on the vehicle speed V of the host vehicle 1, the remaining capacity SOC of the battery 12, and the like.

[0077] In the following step S106, the BRK_ECU 21 sets a value obtained by subtracting the target regenerative braking force Fbr from the target braking force Fbt as the target frictional braking force Fbf.

[0078] Then, in step S107, the BRK_ECU 21 generates braking forces according to the target regenerative braking force Fbr and the target frictional braking force Fbf, and then exits the routine.

[0079] That is, in step S107, the BRK_ECU 21 outputs the target regenerative braking force Fbr to the motor_ECU 20. As a result, the motor_ECU 20 controls the motor generator 3 through control of the inverter 11, and generates a regenerative braking force according to the target regenerative braking force Fbr.

[0080] In step S107, the BRK_ECU 21 controls the brake fluid pressure supplied to each of the calipers 16fl, 16fr, 16rl, and 16rr through control of the brake actuator 17 based on the target frictional braking force Fbf. As a result, the BRK_ECU 21 causes each of the friction brakes 15fl, 15fr, 15rl, and 15rr to generate a frictional braking force corresponding to the target frictional braking force Fbf.

[0081] Furthermore, if it is determined in step S104 that the regeneration conditions are not met, the BRK_ECU 21 proceeds to step S108.

[0082] In step S108, the BRK_ECU 21 checks whether the target regenerative braking force Fbr is 0. That is, the BRK_ECU 21 checks whether braking force switching control is required based on the target regenerative braking force Fbr.

[0083] If it is determined in step S108 that the target regenerative braking force Fbr is not "0", the BRK_ECU 21 proceeds to step S109, performs braking force replacement control, and then exits the routine.

[0084] On the other hand, if it is determined in step S108 that the target regenerative braking force Fbr is "0", the BRK_ECU 21 proceeds to step S110 and sets the target braking force Fbt as it is as the target frictional braking force Fbf.

[0085] In the following step S111, the BRK_ECU 21 generates a braking force according to the target friction braking force Fbf, and then exits the routine.

[0086] As a result, for example, when a deceleration request is made when the regeneration condition is met, the BRK_ECU 21 performs deceleration by braking force cooperative control using friction braking force and regenerative braking force, as shown in Fig. 5. Thereafter, when the regeneration condition is no longer met, for example, because the vehicle speed V becomes equal to or lower than the threshold value Vs, the BRK_ECU 21 shifts from braking force cooperative control to switching control, and performs deceleration while switching from regenerative braking force to friction braking force.

[0087] Next, the braking force replacement control performed in the above-mentioned step S109 will be described with reference to the flowchart of the braking force replacement control subroutine shown in FIG.

[0088] When this subroutine starts, in step S201, the BRK_ECU 21 performs a subtraction process on the current target regenerative braking force Fbr. That is, the BRK_ECU 21 subtracts a predetermined replacement amount ΔFb from the current target regenerative braking force Fbr.

[0089] In the following step S202, the BRK_ECU 21 performs an addition process on the current target frictional braking force Fbf, that is, the BRK_ECU 21 adds a predetermined replacement amount ΔFb to the current target frictional braking force Fbf.

[0090] In the following step S203, the BRK_ECU 21 checks whether a predicted distance L until the vehicle stops when decelerating at the current target deceleration Dt (target braking force Fbt) (predicted stopping distance) is less than a preset threshold value Lth.

[0091] If it is determined in step S203 that the predicted stopping distance L is less than the threshold value Lth, the BRK_ECU 21 proceeds to step S210. That is, even if the predicted stopping distance L is extremely short, generating a target assist force Fa, which will be described later, may cause discomfort to the occupant. Therefore, the BRK_ECU 21 jumps from step S203 to step S210.

[0092] On the other hand, if it is determined in step S203 that the predicted stopping distance L is equal to or greater than the threshold value Lth, the BRK_ECU 21 proceeds to step S204. In step S204, the BRK_ECU 21 calculates the deviation amount Δd of the deceleration D from the target deceleration Dt (Δd=Dt−D).

[0093] In the next step S205, the BRK_ECU 21 checks whether the deviation Δd is less than a preset first threshold value Dth1. Here, the deviation Δd is less than the first threshold value Dth1 when the deceleration D deviates more significantly on the negative side (acceleration side) than the target deceleration Dt due to insufficient braking force (see, for example, FIG. 6).

[0094] Then, when it is determined in step S205 that the deviation Δd is less than the first threshold value Dth1, the BRK_ECU 21 proceeds to step S206 and sets a target assist force Fa for converging the deceleration D to the target deceleration Dt as the target assist force for the assist motor 5. That is, the BRK_ECU 21 sets the target assist force Fa in the direction of decelerating the host vehicle 1 as the target assist force for the assist motor 5.

[0095] On the other hand, if it is determined in step S205 that the deviation Δd is equal to or greater than the first threshold value Dth1, the BRK_ECU 21 proceeds to step S207.

[0096] In step S207, the BRK_ECU 21 checks whether the deviation Δd is greater than a preset second threshold value Dth2. Here, the deviation Δd is greater than the second threshold value Dth2 when excessive braking force causes the deceleration D to deviate from the target deceleration D1 on the positive side (deceleration side) by more than the second threshold value Dth2 (see, for example, FIG. 7).

[0097] Then, when it is determined in step S207 that the deviation Δd is greater than the second threshold value Dth2, the BRK_ECU 21 proceeds to step S208 and sets a target assist force Fa for converging the deceleration D to the target deceleration Dt as the target assist force for the assist motor 5. That is, the BRK_ECU 21 sets the target assist force Fa in the direction of accelerating the host vehicle 1 as the target assist force for the assist motor 5.

[0098] When the process proceeds from step S206 or step S208 to step S209, the BRK_ECU 21 performs guard processing on the target assist force Fa set in step S206 or step S208. That is, the BRK_ECU 21 performs guard processing to suppress the amount of change in the target assist force Fa to prevent the currently set target assist force Fa from changing suddenly compared to the previous value. That is, the BRK_ECU 21 performs guard processing to prevent the deceleration D, which has deviated, from changing suddenly in a direction converging to the target deceleration Dt. Note that the amount of change (absolute value) limited by this guard processing is set to be larger than the feedback control amount when feedback controlling the frictional braking force with respect to the target frictional braking force Fbf.

[0099] When the process proceeds from step S203 or step S209 to step S210, the BRK_ECU 21 generates a braking force according to the target regenerative braking force Fbr and the target frictional braking force Fbf. In addition, if the target assist force Fa is set, the BRK_ECU 21 generates a braking force according to the target assist force Fa.

[0100] That is, in step S210, the BRK_ECU 21 outputs the target regenerative braking force Fbr after the subtraction process to the motor_ECU 20. As a result, the motor_ECU 20 controls the motor generator 3 through control of the inverter 11, and generates a regenerative braking force according to the target regenerative braking force Fbr.

[0101] In step S210, the BRK_ECU 21 controls the brake fluid pressure supplied to each of the calipers 16fl, 16fr, 16rl, and 16rr through control of the brake actuator 17 based on the target frictional braking force Fbf after the addition process. As a result, the BRK_ECU 21 causes each of the friction brakes 15fl, 15fr, 15rl, and 15rr to generate a frictional braking force corresponding to the target frictional braking force Fbf.

[0102] Furthermore, in step S210, when the target assist force Fa is set, the BRK_ECU 21 outputs the target assist force Fa to the motor_ECU 20. As a result, the motor_ECU 20 controls the auxiliary motor 5 through control of the inverter 11, and generates an assist force according to the target assist force Fa.

[0103] In the following step S211, the BRK_ECU 21 checks whether the target regenerative braking force Fbr has been reduced to "0", that is, whether the braking force replacement has been completed.

[0104] Then, in step S211, if it is determined that the target regenerative braking force Fbr has not been reduced to "0", the BRK_ECU 21 returns to step S201.

[0105] On the other hand, if it is determined in step S211 that the target regenerative braking force Fbr has been reduced to "0", the BRK_ECU 21 exits the subroutine.

[0106] By such braking force switching control, even if the deceleration D deviates from the target deceleration Dt due to the influence of the pad μ, for example, as shown in FIGS. 6 and 7, the deceleration D quickly converges to the target deceleration Dt.

[0107] According to this embodiment, the braking control device of the vehicle 1 includes an auxiliary motor 5 connected to the motor generator 3 and generating an auxiliary force for the regenerative braking force, and when the deceleration D deviates from the target deceleration Dt during braking force replacement control, the BRK_ECU 21 causes the auxiliary motor 5 to generate an auxiliary force for converging the deceleration D to the target deceleration Dt. This makes it possible to accurately suppress fluctuations in the deceleration D when replacement control between the regenerative braking force and the friction braking force is performed.

[0108] Next, Figures 8 to 10 relate to a second embodiment of the present invention, and Figure 8 is a schematic diagram showing a driving control system of an electric vehicle. Note that this embodiment differs from the first embodiment described above mainly in that it is provided with a drive system for driving the front wheels 8fl, 8fr and a drive system for driving the rear wheels 8rl, 8rr. Other configurations that are similar to those of the first embodiment described above will not be described as appropriate.

[0109] As shown in FIG. 8, the drive system on the front wheel side has a first motor generator 3f as a drive source.

[0110] A front differential 7f is connected to an output shaft 3fa of the first motor generator 3f via a first reduction gear 4f. Left and right front wheels 8fl, 8fr are connected to left and right drive shafts 7fl, 7fr of the front differential 7f.

[0111] A first auxiliary motor 5f is interposed between the first motor generator 3f and the first reducer 4f. The first auxiliary motor 5f is a small motor with a smaller output than the first motor generator 3f.

[0112] Similarly, the drive system on the rear wheel side has a second motor generator 3r as a drive source.

[0113] A rear differential 7r is connected to an output shaft 3ra of the second motor generator 3r via a second reducer 4r. Left and right rear wheels 8rl, 8rr are connected to left and right drive shafts 7rl, 7rr of the rear differential 7r.

[0114] A second auxiliary motor 5r is interposed between the second motor generator 3r and the second reducer 4r. The second auxiliary motor 5r is a small motor with a smaller output than the second motor generator 3r.

[0115] The first and second motor generators 3f and 3r and the first and second auxiliary motors 5f and 5r are connected to a battery 12 via an inverter 11.

[0116] For example, when the vehicle 1 is powered, the motor_ECU 20 sets a target driving force based on the accelerator opening and the vehicle speed V, etc., and further sets first and second target driving forces for distributing the target driving force between the front and rear at a predetermined front-rear distribution ratio.

[0117] In addition, when the vehicle 1 is coasting, the motor_ECU 20 sets a target regenerative braking force based on the vehicle speed V, etc., and further sets first and second target regenerative braking forces for distributing the target regenerative braking force between the front and rear at a predetermined front-rear distribution ratio.

[0118] In addition, when a braking request is made, the BRK_ECU21 sets a target deceleration Dt (and a target regenerative braking force Fbt), and further sets first and second target regenerative braking forces Fbft, Fbrt for distributing the target deceleration Fbt to the front and rear at a predetermined front / rear distribution ratio.

[0119] Furthermore, during braking force switching control, the BRK_ECU 21 sets a target assist force Fa, and further sets first and second target assist forces Ffa, Fra for distributing the target assist force Fa between the front and rear at a predetermined front / rear distribution ratio.

[0120] That is, for example, in step S206 shown in FIG. 4, the BRK_ECU 21 sets the first and second target assist forces Ffa and Fra in accordance with the target assist force setting subroutine shown in FIG.

[0121] When the subroutine starts, in step S301, the BRK_ECU 21 sets a target assist force Fa for converging the deceleration D to the target deceleration Dt.

[0122] In the following step S302, it is determined based on the signal from the steering angle sensor 29 whether or not the host vehicle 1 is being steered.

[0123] Then, if it is determined in step S302 that the host vehicle 1 is being steered, the BRK_ECU 21 proceeds to step S304.

[0124] On the other hand, if it is determined in step S302 that the host vehicle 1 is not being steered, the BRK_ECU 21 proceeds to step S303 and checks whether the road on which the host vehicle is traveling is a downward slope.

[0125] If it is determined in step S303 that the road on which the host vehicle is traveling has a downward slope, the BRK_ECU 21 proceeds to step S304.

[0126] When proceeding from step S302 or step S303 to step S304, the BRK_ECU 21 sets a first target assist force Ffa and a second target assist force Fra based on the target assist force Fa at a preset distribution ratio to generate an assist force biased towards the front wheels of the vehicle 1, and then exits the subroutine.

[0127] This improves grip during steering and on downhill gradients.

[0128] Furthermore, if it is determined in step S303 that the road on which the host vehicle is traveling is not a downward slope, the BRK_ECU 21 proceeds to step S305.

[0129] In step S305, the BRK_ECU 21 sets the first target assist force Ffa and the second target assist force Fra for generating an assist force biased to the rear wheels in the vehicle 1 at a preset distribution ratio, and then exits the subroutine.

[0130] This suppresses pitching of the vehicle 1.

[0131] Also, for example, in step S208 shown in FIG. 4, the BRK_ECU 21 sets the first and second target assist forces Ffa and Fra in accordance with a target assist force setting subroutine shown in FIG.

[0132] When the subroutine starts, in step S401, the BRK_ECU 21 sets a target assist force Fa for converging the deceleration D to the target deceleration Dt.

[0133] In the following step S402, it is determined based on the signal from the steering angle sensor 29 whether or not the host vehicle 1 is being steered.

[0134] Then, if it is determined in step S402 that the host vehicle 1 is being steered, the BRK_ECU 21 proceeds to step S404.

[0135] On the other hand, if it is determined in step S402 that the host vehicle 1 is not being steered, the BRK_ECU 21 proceeds to step S403 and checks whether the road on which the host vehicle is traveling is a downward slope.

[0136] If it is determined in step S403 that the road on which the host vehicle is traveling is a downward slope, the BRK_ECU 21 proceeds to step S404.

[0137] When proceeding from step S402 or step S403 to step S404, the BRK_ECU21 sets a first target assist force Ffa and a second target assist force Fra based on the target assist force Fa at a preset distribution ratio to generate an assist force biased towards the front wheels of the vehicle 1, and then exits the subroutine.

[0138] This improves grip during steering and on downhill gradients.

[0139] Furthermore, if it is determined in step S403 that the road on which the host vehicle is traveling is not a downward slope, the BRK_ECU 21 proceeds to step S405.

[0140] In step S405, the BRK_ECU 21 sets the first target assist force Ffa and the second target assist force Fra for generating an assist force biased to the rear wheels in the vehicle 1 at a preset distribution ratio, and then exits the subroutine.

[0141] This suppresses pitching of the vehicle 1.

[0142] According to this embodiment, in addition to the effects obtained in the first embodiment described above, an effect of improving running stability during braking force switching control is achieved.

[0143] In the above-described embodiment, the motor_ECU 20 and the BRK_ECU 21 are configured with a well-known microcomputer including a CPU, RAM, ROM, a nonvolatile storage unit, etc., and its peripheral devices, and the ROM stores programs to be executed by the CPU, fixed data such as data tables, etc. Note that all or part of the functions of the processor may be configured with a logic circuit or an analog circuit, and the processing of various programs may be realized by an electronic circuit such as an FPGA.

[0144] The invention described in the above embodiments is not limited to those embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. For example, in the above embodiments, an example in which the invention is applied to an electric vehicle is described, but the invention is not limited to this and can be applied to, for example, an electrically powered vehicle such as a hybrid vehicle.

[0145] Furthermore, each of the above embodiments includes inventions at various stages, and various inventions can be extracted by appropriate combinations of the disclosed constituent elements.

[0146] For example, if some constituent elements are deleted from all the constituent elements shown in each form, and the stated problem can still be solved and the stated effect can still be obtained, then the configuration from which these constituent elements have been deleted can be extracted as an invention. [Explanation of symbols]

[0147] 1 … Vehicle (own vehicle) 3... Motor generator 3a … Output shaft 3f … First motor generator 3fa ... output shaft 3r ... Second motor generator 3ra ... output shaft 4 … Reducer 4f ... First reducer 4r... Second reducer 5... Auxiliary motor 5f ... 1st auxiliary motor 5r ... Second auxiliary motor 7f ... Front differential device 7fl, 7fr ... drive shaft 7r ... Rear differential device 7rl, 7rr ... drive shaft 8fl,8fr,8rl,8rr … Wheels 10...ECU 11 ... inverter 12... Battery 15fl, 15fr, 15rl, 15rr ... friction brake 16fl, 16fr, 16rl, 16rr ... caliper 17... Brake actuator 20 ... Motor_ECU 21 … BRK_ECU 25...Accelerator pedal 25a ... Accelerator sensor 26...Brake pedal 26a ... Brake switch 27fl, 27fr, 27rl, 27rr ... Wheel speed sensor 28...Accelerometer 29 ... Steering angle sensor

Claims

1. a friction brake that generates a friction braking force; a motor generator that generates regenerative braking force; a braking control device for a vehicle, the braking control device being configured to set a target deceleration when a braking request is made for the vehicle, generate the target deceleration using a braking force including the regenerative braking force when a preset regenerative condition is satisfied, and perform a switching control to generate the target deceleration while switching the regenerative braking force included in the braking force to the frictional braking force when the regenerative condition is not satisfied, an auxiliary motor connected to the motor generator to generate an auxiliary force for the regenerative braking force; The braking control device for a vehicle is characterized in that, when a deviation of the deceleration from the target deceleration occurs during execution of the switching control, the braking control means generates the auxiliary force by the auxiliary motor to converge the deceleration to the target deceleration.

2. 2. The vehicle brake control device according to claim 1, wherein the brake control means generates the assist force by the assist motor when the deceleration deviates from the target deceleration by more than a predetermined threshold value.

3. 3. The vehicle braking control device according to claim 2, wherein the thresholds include a first threshold for determining whether the deceleration deviates from the target deceleration toward acceleration, and a second threshold for determining whether the deceleration deviates from the target deceleration toward deceleration, and the absolute value of the first threshold is set smaller than the absolute value of the second threshold.

4. 4. The vehicle brake control device according to claim 1, wherein the brake control means performs a guard process to suppress a change in the assist force.

5. the auxiliary motor includes a first auxiliary motor that generates a first auxiliary force on a front wheel and a second auxiliary motor that generates a second auxiliary force on a rear wheel; 5. The vehicle brake control device according to claim 1, wherein the brake control means controls the first assist force and the second assist force to be unequal.

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