Vehicle control device

Abstract

To provide a vehicle control device for suppressing the occurrence of vehicle body vibration caused by the inversion of the torsional direction of an axle when a vehicle is stopped.SOLUTION: The brake control device 70 includes the control unit 125 that executes the distribution adjustment control for adjusting the regeneration distribution ratio, which is the ratio of the first regenerative braking torque to the regenerative braking torque, and the stopping time braking control for decreasing the total regenerative braking torque to 0 (zero) and increasing the friction braking torque until the vehicle 10 stops by controlling the first power unit 21, the second power unit 22, and the friction brake unit 40 during braking of the vehicle 10. In the distribution adjustment control, the controller 125 sets the regeneration distribution ratio when the total regenerative braking torque is reduced with the execution of the braking control during vehicle stop to be smaller than the regeneration distribution ratio before the braking control during vehicle stop is started.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vehicle control device. [Background technology]

[0002] Patent Document 1 discloses a control device that performs braking control to suppress a sudden change in the pitch attitude of a vehicle when the vehicle stops. When the vehicle speed drops below a predetermined speed, the control device controls a motor generator so that regenerative braking torque decreases toward zero. When the vehicle speed reaches zero, the control device increases friction braking torque by operating a hydraulic actuator. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-28913 Summary of the Invention [Problem to be solved by the invention]

[0004] When the vehicle is about to come to a stop, a small driving torque such as creep torque is applied to the axle. Regenerative braking torque is applied to the axle. When at least one of driving torque and regenerative braking torque is applied to the axle, twisting occurs in the axle. Torque that causes twisting in the axle is called "axle torque." This axle torque is a torque that depends on the direction of the driving torque acting on the axle, the direction of the regenerative braking torque acting on the axle, the magnitude of the driving torque, and the magnitude of the regenerative braking torque.

[0005] When an axle torque acts on an axle in a forward direction, which is the rotation direction corresponding to the direction of travel of the vehicle, the axle torque is positive. On the other hand, when an axle torque acts on an axle in a reverse direction, which is the opposite direction to the forward rotation direction, the axle torque is negative.

[0006] While a driving torque such as creep torque acts on the axle in the forward direction, a regenerative braking torque acts on the axle in the reverse direction. Therefore, if the magnitude of the regenerative braking torque is greater than the magnitude of the driving torque, the axle torque becomes negative. On the other hand, if the magnitude of the regenerative braking torque is smaller than the driving torque, the axle torque becomes positive.

[0007] When the above-described braking control is being executed, the magnitude of the regenerative braking torque is relatively large at the start of the braking control, so the axle torque is negative. However, as the magnitude of the regenerative braking torque gradually decreases, the axle torque approaches 0 (zero). Then, when the magnitude of the regenerative braking torque becomes smaller than the magnitude of the driving torque, the axle torque reverses in sign. The reversal of the axle torque signifies that the direction of the axle torque acting on the axle has reversed. When the direction of the axle torque acting on the axle reverses, the direction of the axle torsion changes. When the direction of the axle torsion reverses in this way, there is a risk that the vehicle may experience body vibration due to the reversal of the axle torsion direction. [Means for solving the problem]

[0008] A vehicle control device that solves the above problem is a vehicle that includes a first power unit configured to apply a first regenerative braking torque and a first drive torque to a first axle that rotates integrally with a first wheel, which is one of the front wheels and the rear wheels; a second power unit configured to apply a second regenerative braking torque and a second drive torque to a second axle that rotates integrally with a second wheel, which is the other of the front wheels and the rear wheels; and a friction braking unit configured to apply a friction braking torque to at least one of the first wheel and the second wheel, wherein when the first regenerative braking torque and the first drive torque are applied to the first axle, an axle torque is generated on the first axle, and when the second regenerative braking torque and the second drive torque are applied to the second axle, The present invention is applied to a vehicle in which axle torque is generated on the second axle, and is equipped with a control unit that executes: distribution adjustment control that adjusts a distribution ratio, which is the ratio of the first regenerative braking torque to a total regenerative braking torque, which is the sum of the first regenerative braking torque and the second regenerative braking torque; and stationary braking control that controls the first power unit, the second power unit, and the friction braking unit when braking the vehicle, thereby reducing the total regenerative braking torque to 0 (zero) while increasing the friction braking torque until the vehicle stops, and in the distribution adjustment control, the control unit makes the distribution ratio, when the total regenerative braking torque is reduced as the stationary braking control is executed, smaller than the distribution ratio before the stationary braking control was started. [Effects of the Invention]

[0009] The vehicle control device can suppress the occurrence of vehicle body vibrations caused by the axle's torsional direction reversing when the vehicle is stopped. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a vehicle equipped with a braking control device of a first embodiment. [Figure 2] 2(A) to 2(G) are timing charts when stopping the vehicle of the first embodiment. [Figure 3]FIG. 3 is a flowchart illustrating the flow of processing for vehicle-stop braking control executed by the braking control device of the first embodiment. [Figure 4] FIG. 4 is a flowchart illustrating the flow of processing executed by the brake control device of the first embodiment during vehicle-stop braking control. [Figure 5] FIG. 5 is a flowchart illustrating the flow of processing executed by the brake control device of the second embodiment during vehicle-stop braking control. [Figure 6] 6(A) to 6(G) are timing charts for stopping the vehicle in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (First embodiment) A first embodiment of a vehicle control device will be described below. 1 shows a vehicle 10 equipped with a brake control device 70. In the first embodiment, the brake control device 70 corresponds to the "vehicle control device." The vehicle 10 includes a drive operating member 11, a brake operating member 12, a plurality of wheels 13, 14, two axles 15, 16, two power units 21, 22, a drive control device 30, a friction braking unit 40, and a plurality of sensors 61 to 63.

[0012] The multiple wheels 13, 14 include a first wheel 13 corresponding to a front wheel and a second wheel 14 corresponding to a rear wheel. The two axles 15, 16 include a first axle 15 that rotates integrally with the first wheel 13 and a second axle 16 that rotates integrally with the second wheel 14. In other words, the first axle 15 is the axle for the front wheels, and the second axle 16 is the axle for the rear wheels.

[0013] <Operating parts> The drive operating member 11 is a member that the driver operates when adjusting the acceleration of the vehicle 10. An example of the drive operating member 11 is an accelerator pedal. The brake operating member 12 is a member that the driver operates when adjusting the deceleration of the vehicle 10. An example of the brake operating member 12 is a brake pedal.

[0014] <Power unit> The first power unit 21 is configured to be able to apply a first driving torque Td1 and a first regenerative braking torque TbE1 to the first axle 15. The first power unit 21 has at least a motor generator out of an engine and a motor generator as a power source for the vehicle 10. The second power unit 22 is configured to be able to apply a second driving torque Td2 and a second regenerative braking torque TbE2 to the second axle 16. The second power unit 22 has at least a motor generator out of an engine and a motor generator as a power source for the vehicle 10.

[0015] In the following description, the sum of the first drive torque Td1 and the second drive torque Td2 will be referred to as the total drive torque TdT, and the sum of the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 will be referred to as the total regenerative braking torque TbET. Furthermore, the rotation direction of the axles 15, 16 in accordance with the direction of travel of the vehicle 10 will be referred to as the "forward direction," and the direction opposite to the forward direction will be referred to as the "reverse direction." Torque acting on the axles 15, 16 in the forward direction will be referred to as positive torque, and torque acting on the axles 15, 16 in the reverse direction will be referred to as negative torque.

[0016] The motor generator of the first power unit 21 functions as a generator, and a first regenerative braking torque TbE1 is applied to the first axle 15. The application of the first regenerative braking torque TbE1 to the first axle 15 decelerates the rotation of the first axle 15. In other words, when the vehicle 10 is not stopped, the first regenerative braking torque TbE1 is a torque that acts in the reverse direction on the first axle 15. Similarly, the motor generator of the second power unit 22 functions as a generator, and a second regenerative braking torque TbE2 is applied to the second axle 16. The application of the second regenerative braking torque TbE2 to the second axle 16 decelerates the rotation of the second axle 16. In other words, when the vehicle 10 is not stopped, the second regenerative braking torque TbE2 is a torque that acts in the reverse direction on the second axle 16.

[0017] <Axle twist> The first wheel 13 is attached to the tip of the first axle 15. Therefore, the unit including the first wheel 13 and the first axle 15 can be considered a "torsion pendulum." When the portion of the first axle 15 to which torque is transmitted from the first power unit 21 is defined as a transmission section, the amount of relative rotation of the transmission section with the first wheel 13 as the reference is defined as the rotation angle. When no torsion occurs in the first axle 15, the rotation angle is 0 (zero) degrees. When at least one of the first drive torque Td1 and the first regenerative braking torque TbE1 is applied to the first axle 15, torsion may occur in the first axle 15. When torsion occurs in the first axle 15 in this way, the magnitude of the rotation angle increases.

[0018] In the first embodiment, the torque that generates a torsion in the first axle 15 and is applied to the transmission part of the first axle 15 is referred to as the "first axle torque TqS1." The first axle torque TqS1 is the sum of the first regenerative braking torque TbE1 and the first drive torque Td1 that are applied to the first axle 15. Therefore, when the first drive torque Td1 is a positive torque, the difference between the magnitude of the first drive torque Td1 and the magnitude of the first regenerative braking torque TbE1 becomes the first axle torque TqS1. In this case, when the magnitude of the first regenerative braking torque TbE1 is smaller than the magnitude of the first drive torque Td1, the first axle torque TqS1 becomes a positive torque. When the magnitude of the first regenerative braking torque TbE1 is greater than the magnitude of the first drive torque Td1, the first axle torque TqS1 becomes a negative torque. Furthermore, when the first drive torque Td1 is negative, the first axle torque TqS1 becomes negative. Specifically, the greater the sum of the magnitude of the first drive torque Td1 and the magnitude of the first regenerative braking torque TbE1, the greater the magnitude of the first axle torque TqS1. When the first axle torque TqS1 is positive, it can be said that the first axle torque TqS1 acts on the first axle 15 in the forward rotation direction. When the first axle torque TqS1 is negative, it can be said that the first axle torque TqS1 acts on the first axle 15 in the reverse rotation direction.

[0019] While the vehicle 10 is traveling, if the magnitude of the first regenerative braking torque TbE1 and the first drive torque Td1 changes, or if the first drive torque Td1 changes sign, the sign of the first axle torque TqS1 may be reversed. The reversal of the sign of the first axle torque TqS1 means that the direction of torsion of the first axle 15 is reversed. When the direction of torsion of the first axle 15 is reversed, vehicle body vibration occurs due to the reversal of the direction of torsion of the first axle 15. Furthermore, such vehicle body vibration increases as the rate of change of the first axle torque TqS1 when the sign of the first axle torque TqS1 is reversed increases.

[0020] The above has described the torsion of the first axle 15, but the same applies to the torsion of the second axle 16. In other words, the torque that generates torsion in the second axle 16 and is applied to the transmission part of the second axle 16 is referred to as the "second axle torque TqS2." The second axle torque TqS2 is the sum of the second regenerative braking torque TbE2 and the second drive torque Td2 applied to the second axle 16. As with the first axle 15, the second axle 16 also generates vehicle body vibration when the polarity of the second axle 16 reverses. However, in the first embodiment, it is assumed that the magnitude of the first axle torque TqS1 is greater than the magnitude of the second axle torque TqS2. In other words, the rate of change of the first axle torque TqS1 at the time of the polarity reversal is greater than the rate of change of the second axle torque TqS2 at the time of the polarity reversal. In this regard, in order to suppress vibrations of the entire vehicle, it is important to suppress the rate of change of the first axle torque TqS1 at the time of reversing between positive and negative.

[0021] <Drive control device> The drive control device 30 controls the power units 21, 22. The drive control device 30 includes a processing circuit 31. An example of the processing circuit 31 is an electronic control device. In this case, the drive control device 30 includes a CPU 32, a first memory 33, and a second memory 34. The first memory 33 stores a control program executed by the CPU 32. The second memory 34 stores the results of calculations by the CPU 32. The CPU 32 executes the control program in the first memory 33, allowing the processing circuit 31 to control the power units 21, 22.

[0022] The drive control device 30 is configured to be able to send and receive various information and commands to and from the braking control device 70 via the in-vehicle network. Therefore, when braking the vehicle, the drive control device 30 can operate the power units 21, 22 based on the commands received from the braking control device 70.

[0023] The processing circuit 31 functions as a plurality of functional units by the CPU 32 executing the control program in the first memory 33. The plurality of functional units includes a drive control unit 101 and a regeneration control unit 103.

[0024] When the drive operation member 11 is operated, the drive control unit 101 derives the required drive force so that the required drive force increases as the drive operation amount indicating the operation amount of the drive operation member 11 increases. The drive control unit 101 also derives the required drive force when the drive operation member 11 is not operated.

[0025] For example, when the drive operating member 11 is not being operated and the vehicle body speed VS is equal to or greater than a first threshold speed Vth1, the drive control unit 101 derives a negative required drive force. When the drive force output source is an engine, the negative required drive force is a drive force equivalent to engine brake torque. When the drive force output source is a motor generator, the negative required drive force is a drive force equivalent to torque simulating engine brake torque. On the other hand, when the drive operating member 11 is not being operated and the vehicle body speed VS is less than a second threshold speed Vth2 that is lower than the first threshold speed Vth1, the drive control unit 101 derives a positive required drive force. When the drive force output source is an engine, the positive required drive force is a drive force equivalent to creep torque. When the drive force output source is a motor generator, the positive required drive force is a drive force equivalent to torque simulating creep torque. Creep torque is a torque for causing the vehicle 10 to creep. Furthermore, when the drive operating member 11 is not being operated and the vehicle body speed VS is less than the first judgment speed Vth1 and greater than or equal to the second judgment speed Vth2, the drive control unit 101 increases the required drive force as the vehicle body speed VS decreases. Furthermore, the drive control unit 101 converts the required drive force into torque to derive a required drive torque TdRq, which is a required value of the drive torque Td.

[0026] The drive control unit 101 adjusts the drive torques Td1, Td2 applied to the axles 15, 16 by operating the power units 21, 22. Specifically, the drive control unit 101 distributes the required drive torque TdRq based on a drive distribution ratio Rd, which is the ratio of the first drive torque Td1 to the total drive torque TdT. The drive control unit 101 derives the product of the required braking torque TbRq and the drive distribution ratio Rd as a first drive torque command value Tdtr1, which is a command value for the first drive torque Td1. The drive control unit 101 then controls the first power unit 21 based on the first drive torque command value Tdtr1. This allows the drive control unit 101 to adjust the first drive torque Td1 applied to the first axle 15. Meanwhile, the drive control section 101 derives a value obtained by subtracting the first drive torque command value Tdtr1 from the required braking torque TbRq as a second drive torque command value Tdtr2, which is a command value for the second drive torque Td2. The drive control section 101 then controls the second power unit 22 based on the second drive torque command value Tdtr2. This allows the drive control section 101 to adjust the second drive torque Td2 applied to the second axle 16. In the first embodiment, the drive distribution ratio Rd is set to a value greater than 0.5. In other words, the first drive torque Td1 is greater than the second drive torque Td2.

[0027] The regenerative control unit 103 adjusts the regenerative braking torques TbE1 and TbE2 applied to the axles 15 and 16 by operating the power units 21 and 22. Specifically, the regenerative control unit 103 distributes the required total regenerative braking torque TbETRq based on the regenerative distribution ratio Re, which is the ratio of the first regenerative braking torque TbE1 to the total regenerative braking torque TbET. The required total regenerative braking torque TbETRq is a required value of the total regenerative braking torque TbET. As will be described in detail later, the required total regenerative braking torque TbETRq is set to a value equal to or less than the required braking torque TbRq transmitted from the brake control device 70. The regenerative control unit 103 derives the product of the required total regenerative braking torque TbETRq and the regenerative distribution ratio Re as a first regenerative braking torque command value TbEtr1, which is a command value for the first regenerative braking torque TbE1. The regenerative control unit 103 then controls the first power unit 21 based on the first regenerative braking torque command value TbEtr1. This allows the regenerative control unit 103 to adjust the first regenerative braking torque TbE1 applied to the first axle 15. Meanwhile, the regenerative control unit 103 derives a value obtained by subtracting the first regenerative braking torque command value TbEtr1 from the requested total regenerative braking torque TbETRq as a second regenerative braking torque command value TbEtr2, which is a command value for the second regenerative braking torque TbE2. The regenerative control unit 103 then controls the second power unit 22 based on the second regenerative braking torque command value TbEtr2. This allows the regenerative control unit 103 to adjust the second regenerative braking torque TbE2 applied to the second axle 16.

[0028] For example, the required total regenerative braking torque TbETRq is set based on the required braking torque TbRq and a limit regenerative braking torque, which is the upper limit of the total regenerative braking torque TbET that can be generated by the power units 21, 22. If the required braking torque TbRq is equal to or greater than the limit regenerative braking torque, the required total regenerative braking torque TbETRq is set. On the other hand, if the required braking torque TbRq is less than the limit regenerative braking torque, the limit regenerative braking torque is set to the required total regenerative braking torque TbETRq.

[0029] In the first embodiment, the reference regenerative braking torque distribution ratio Re is set to a value greater than 0.5. That is, the first regenerative braking torque TbE1 is greater than the second regenerative braking torque TbE2.

[0030] Note that the drive control unit 101 may derive the first drive torque command value Tdtr1, and the regenerative control unit 103 may derive the first regenerative braking torque command value TbEtr1. In this case, the first power unit 21 is controlled based on both the first drive torque command value Tdtr1 and the first regenerative braking torque command value TbEtr1. That is, the first power unit 21 applies to the first axle 15 a torque that is the sum of the first drive torque command value Tdtr1 and the first regenerative braking torque command value TbEtr1. This sum corresponds to the first axle torque TqS1. Therefore, it can be said that the first power unit 21 can apply to the first axle 15 a first axle torque TqS1 that corresponds to the first drive torque command value Tdtr1 and the first regenerative braking torque command value TbEtr1. The same applies to the case where the drive control unit 101 derives the second drive torque command value Tdtr2 and the regenerative braking torque command value TbEtr2, respectively. In other words, the second power unit 22 can apply to the second axle 16 the second axle torque TqS2 that corresponds to the second drive torque command value Tdtr2 and the second regenerative braking torque command value TbEtr2.

[0031] <Friction brake part> The friction braking unit 40 applies a friction braking torque TbF to the first wheel 13 and the second wheel 14. As a result, a friction braking force is generated in the first wheel 13 and the second wheel 14. The friction braking unit 40 includes a plurality of friction brakes 41 provided respectively for the plurality of wheels 13, 14, and a braking actuator 50.

[0032] Each of the multiple friction brakes 41 applies a friction braking torque TbF to the corresponding wheel 13, 14. The friction brake 41 has a wheel cylinder 42, a rotating body 43, and a friction portion 44. The rotating body 43 rotates integrally with the wheel 13, 14. Therefore, by pressing the friction portion 44 against the rotating body 43, a friction braking torque TbF is applied to the wheel 13, 14. The force pressing the friction portion 44 against the rotating body 43 increases as the wheel pressure, which is the hydraulic pressure in the wheel cylinder 42, increases. Therefore, the friction brake 41 can apply a larger friction braking torque TbF to the wheel 13, 14 as the wheel pressure increases.

[0033] The brake actuator 50 is configured to adjust the friction braking torque TbF applied to the multiple wheels 13, 14 by controlling the wheel pressures of the multiple wheel cylinders 42. For example, the brake actuator 50 has a pressure source that can supply brake fluid to the multiple wheel cylinders 42. The pressure source is, for example, an electric pump and an electric cylinder. The brake fluid discharged from the brake actuator 50 is supplied to the wheel cylinders 42 via a supply flow path 51.

[0034] In the following explanation, the sum of the friction braking torque TbF applied to the first wheel 13 and the friction braking torque TbF applied to the second wheel 14 will be referred to as the "total friction braking torque TbFT", and the sum of the total friction braking torque TbFT and the total regenerative braking torque TbET will be referred to as the total braking torque TbT.

[0035] <Sensor> The plurality of sensors 61 to 63 output signals according to the detection results to the drive control device 30 or the braking control device 70. The plurality of sensors 61 to 63 include an accelerator sensor 61, a brake sensor 62, and a wheel speed sensor 63, for example.

[0036] The accelerator sensor 61 detects information related to the driver's operation of the drive operation member 11. One example of the accelerator sensor 61 is a stroke sensor that detects the amount of drive operation, which is the amount of operation of the drive operation member 11 by the driver. Note that the vehicle 10 may also be equipped with a sensor that detects the operating force of the drive operation member 11 by the driver.

[0037] The brake sensor 62 detects information related to the operation of the brake operating member 12 by the driver. One example of the brake sensor 62 is a stroke sensor that detects the braking operation amount, which is the amount of operation of the brake operating member 12 by the driver. The vehicle 10 may also be equipped with a sensor that detects the operating force of the brake operating member 12 by the driver.

[0038] The vehicle 10 is equipped with wheel speed sensors 63 in the same number as the wheels 13, 14. Each wheel speed sensor 63 detects the rotational speed of the corresponding wheel 13, 14. The rotational speed of the wheels 13, 14 based on the detection signal of the wheel speed sensor 63 is referred to as the "wheel speed VW."

[0039] <Brake control device> The braking control device 70 controls the braking actuator 50 of the friction braking unit 40. The braking control device 70 is configured to be able to send and receive various information and commands to and from the drive control device 30. Therefore, when braking the vehicle, the braking control device 70 can adjust the deceleration of the vehicle 10 by operating the braking actuator 50 and cooperating with the drive control device 30.

[0040] The braking control device 70 includes a processing circuit 71. One example of the processing circuit 71 is an electronic control device. In this case, the processing circuit 71 includes a CPU 72, a first memory 73, and a second memory 74. The first memory 73 stores a control program executed by the CPU 72. The second memory 74 stores the calculation results of the CPU 72. When the CPU 72 executes the control program stored in the first memory 73, the processing circuit 71 activates the friction braking unit 40 to adjust the total friction braking torque TbFT. The processing circuit 71 also transmits instructions regarding the regenerative braking torques TbE1 and TbE2 and instructions regarding the drive torques Td1 and Td2 to the drive control device 30. In this way, the first axle torque TqS1 acting on the first axle 15 and the second axle torque TqS2 acting on the second axle 16 are adjusted.

[0041] The regenerative cooperative control executed by the processing circuit 71 will be described. The processing circuit 71 derives a required braking force, which is a required value of braking force for the vehicle 10. The braking force is the sum of the friction braking force and the regenerative braking force generated by the vehicle 10. When the brake operating member 12 is operated, the processing circuit 71 derives the required braking force so that the required braking force increases as the braking operation amount increases. When deceleration of the vehicle 10 is requested by another control device, the processing circuit 71 derives a value corresponding to the required value of the deceleration of the vehicle 10 as the required braking force. For example, the processing circuit 71 converts the required braking force into braking torque to derive a required braking torque TbRq, which is a required value of the total braking torque TbT. The processing circuit 71 then transmits the required braking torque TbRq to the drive control device 30.

[0042] The processing circuit 71 of the brake control device 70 derives a target value of total friction braking torque TbFT for the vehicle 10 based on the total regenerative braking torque TbET that the power units 21, 22 can generate and the required braking torque TbRq. If the total regenerative braking torque TbET that the power units 21, 22 can generate is equal to the required braking torque TbRq, the processing circuit 71 derives 0 (zero) as the target value of total friction braking torque TbFT. On the other hand, if the total regenerative braking torque TbET that the power units 21, 22 can generate is less than the required braking torque TbRq, the processing circuit 71 derives the difference between the required braking torque TbRq and the total regenerative braking torque TbET as the target value of total friction braking torque TbFT. Then, the processing circuit 71 operates the brake actuator 50 based on the target value of total friction braking torque TbFT.

[0043] <Functional section> The processing circuit 71 functions as a plurality of functional units as a result of the CPU 72 executing the control program in the first memory 73. The plurality of functional units are functional units for stopping the vehicle 10 by generating a braking force on the vehicle 10. The plurality of functional units include a derivation unit 121, a stop-related value acquisition unit 123, and a control unit 125.

[0044] <Derivation part> The derivation unit 121 executes a derivation process at each predetermined control cycle when the vehicle 10 is decelerating due to the generation of a braking force. The derivation process is a process for acquiring various state quantities. For example, in the derivation process, the derivation unit 121 derives a required braking torque TbRq, a wheel speed VW, a vehicle body speed VS, and a vehicle body acceleration DVS. The vehicle body speed VS is the traveling speed of the vehicle 10 that can be derived using at least one of the wheel speeds VW of the multiple wheels 13, 14.

[0045] In the derivation process, the derivation unit 121 derives a stop-maintaining braking force. The stop-maintaining braking force is a braking force required to maintain the vehicle 10 at a stop on the road surface on which the vehicle 10 is traveling. The derivation unit 121 derives the stop-maintaining braking force based on information about the gradient of the road surface and a total driving torque TdT, which is the sum of driving torques Td1 and Td2 applied from the power units 21 and 22 to the axles 15 and 16 while the vehicle is stopped. For example, when the road surface is a slope, the derivation unit 121 derives a braking force that is greater as the stop-maintaining braking force than when the road surface is not a slope. When it is predicted that the total driving torque TdT will be large while the vehicle is stopped, the derivation unit 121 derives a braking force that is greater as the stop-maintaining braking force than when it is predicted that the total driving torque TdT will not be large. The derivation unit 121 then converts the stop-maintaining braking force into torque to derive the stop-maintaining braking torque Tbh.

[0046] <Stopping-related value acquisition section> The stop-related value acquisition unit 123 acquires a stop-related value at every predetermined control period when the vehicle 10 is decelerating due to the generation of a braking force. The stop-related value is a value that decreases as the vehicle 10 approaches a predetermined stop position.

[0047] For example, the stopping-related value acquisition unit 123 estimates a stopping position, which is a position where the vehicle 10 will stop, based on the vehicle body speed VS and the vehicle body acceleration DVS. In this case, the stopping-related value acquisition unit 123 may estimate, as the stopping position, the position of the vehicle 10 when the vehicle body speed VS becomes 0 (zero) based on the current vehicle body acceleration DVS. This stopping position corresponds to the "predetermined stopping position." Then, the stopping-related value acquisition unit 123 acquires, as the stopping-related value, a stopping distance DS, which is the distance from the current position of the vehicle 10 to the stopping position.

[0048] <Control unit> When a braking force is generated on the vehicle 10, the control unit 125 activates the friction braking unit 40 and controls the deceleration of the vehicle 10 by coordinating the power units 21, 22 and the friction braking unit 40.

[0049] As shown in Figures 2(A) to 2(G), the control unit 125 executes braking control when the stopping distance DS is equal to or less than a predetermined threshold. The braking control when the vehicle is stopped is a control that reduces the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 to 0 (zero) while increasing the total friction braking torque TbFT until the vehicle 10 stops. The braking control when the vehicle is stopped is a control that stops the vehicle 10 with the braking torque smaller than the required braking torque TbRq. The conditions for starting the braking control when the vehicle is stopped include the execution of regenerative cooperative control.

[0050] The braking control during a stop includes a switching process, a reduction process, a holding process, and a degeneration process. The switching process corresponds to a "friction braking increase process," and the reduction process corresponds to a "regenerative braking decrease process."

[0051] When the stopping distance DS becomes equal to or less than the first threshold value DSth1, the control unit 125 starts a replacement process for the stationary braking control. In the example shown in FIG. 2, the stopping distance DS becomes equal to or less than the first threshold value DSth1 at timing t13. The first threshold value DSth1 corresponds to a "predetermined threshold value." The replacement process is a process for replacing the total regenerative braking torque TbET with the total friction braking torque TbFT. In the replacement process, the control unit 125 operates the brake actuator 50 to increase the total friction braking torque TbFT to a set braking torque Tbset that is equal to or greater than the stationary holding braking torque Tbh. For example, the stationary holding braking torque Tbh is set to the set braking torque Tbset. Therefore, the control unit 125 increases the target value of the total friction braking torque TbFT to the stationary holding braking torque Tbh and operates the brake actuator 50 based on the target value of the total friction braking torque TbFT. At the same time, the control unit 125 transmits to the regeneration control unit 103 an instruction to decrease the total regenerative braking torque TbET by the amount of increase in the total friction braking torque TbFT resulting from the execution of the switching process.

[0052] When the regenerative control unit 103 receives the above instruction, the regenerative control unit 103 reduces the total regenerative braking torque TbET by the increase in the total friction braking torque TbFT. That is, the regenerative control unit 103 derives a first regenerative braking torque command value TbEtr1 and a second regenerative braking torque command value TbEtr2 according to the increase in the total friction braking torque TbFT. The regenerative control unit 103 then operates the power units 21 and 22 based on the first regenerative braking torque command value TbEtr1 and the second regenerative braking torque command value TbEtr2. This reduces the total regenerative braking torque TbET by the increase in the total friction braking torque TbFT. As a result, changes in the total braking torque TbT due to the execution of the replacement process are suppressed. When the total friction braking torque TbFT is maintained, the control unit 125 ends the replacement process.

[0053] After the execution of the replacement process, when the stopping distance DS becomes equal to or less than the second threshold value DSth2, the control unit 125 starts the reduction process. In the example shown in FIG. 2, the stopping distance DS becomes equal to or less than the second threshold value DSth2 at timing t15. The second threshold value DSth2 is smaller than the first threshold value DSth1. In the reduction process, the control unit 125 transmits an instruction to the regeneration control unit 103 to reduce the total regenerative braking torque TbET to 0 (zero). At this time, the control unit 125 may transmit an instruction to the regeneration control unit 103 to reduce the total regenerative braking torque TbET at a standard reduction speed Vstd. The standard reduction speed Vstd is set so that the total regenerative braking torque TbET becomes 0 (zero) before the vehicle speed VS becomes 0 (zero).

[0054] When the regenerative control unit 103 receives this instruction, the regenerative control unit 103 decreases the first regenerative braking torque command value TbEtr1 and the second regenerative braking torque command value TbEtr2 toward 0 (zero). Specifically, the regenerative control unit 103 decreases the first regenerative braking torque command value TbEtr1 and the second regenerative braking torque command value TbEtr2 while maintaining the regenerative allocation ratio Re at a constant value. Then, the regenerative control unit 103 operates the power units 21, 22 based on the first regenerative braking torque command value TbEtr1 and the second regenerative braking torque command value TbEtr2.

[0055] The control unit 125 maintains the total friction braking torque TbFT during the reduction process. Then, when the control unit 125 determines that the first regenerative braking torque command value TbEtr1 and the second regenerative braking torque command value TbEtr2 have become 0 (zero), the control unit 125 ends the reduction process. In the example shown in FIG. 2, the first regenerative braking torque command value TbEtr1 and the second regenerative braking torque command value TbEtr2 become 0 (zero) at timing t18.

[0056] After the reduction process is completed, the control unit 125 starts a retention process. In the retention process, the control unit 125 retains the target value of the total friction braking torque TbFT. At this time, the control unit 125 also retains the state in which the total regenerative braking torque TbET is 0 (zero).

[0057] If the control unit 125 determines that the vehicle 10 has stopped while the holding process is being executed, the control unit 125 transitions the process from the holding process to the degeneration process. For example, the control unit 125 determines that the vehicle 10 has stopped when the stopping distance DS becomes equal to or less than a third threshold value DSth3. In this case, the third threshold value DSth3 is smaller than the second threshold value DSth2. For example, the third threshold value DSth3 is 0 (zero). In the example shown in FIG. 2, the timing t19 is the timing at which it is determined that the vehicle 10 has stopped.

[0058] In the degeneration process, the control unit 125 increases the total friction braking torque TbFT. For example, the control unit 125 increases the total friction braking torque TbFT to the required braking torque TbRq. At this time, the control unit 125 increases the target value of the total friction braking torque TbFT to the required braking torque TbRq. Then, the control unit 125 operates the brake actuator 50 based on the target value of the total friction braking torque TbFT. When the total friction braking torque TbFT becomes equal to or greater than the required braking torque TbRq, the control unit 125 ends the degeneration process. Then, the control unit 125 ends the stationary braking control.

[0059] As described above, the power units 21, 22 of the vehicle 10 of the first embodiment output positive torque or negative torque as the driving torques Td1, Td2 in accordance with instructions from the drive control unit 101, even when the driver does not operate the drive operating member 11. Specifically, as shown in FIG. 2(E), when the vehicle body speed VS is equal to or greater than the first determination speed Vth1, the power units 21, 22 apply negative torque as the driving torques Td1, Td2 to the axles 15, 16. Subsequently, when a braking force is generated in the vehicle 10 and the vehicle body speed VS becomes less than the first determination speed Vth1, the power units 21, 22 gradually increase the driving torques Td1, Td2 applied to the axles 15, 16 as the vehicle body speed VS decreases. After the vehicle speed VS becomes less than the first judgment speed Vth1 and before the vehicle speed VS becomes equal to or greater than the second judgment speed Vth2, the driving torques Td1, Td2 applied to the axles 15, 16 become greater than 0 (zero). Then, when the vehicle speed VS becomes less than the second judgment speed Vth2, the power units 21, 22 apply constant positive torques to the axles 15, 16 as the driving torques Td1, Td2.

[0060] When the magnitude of the first regenerative braking torque TbE1 is greater than the magnitude of the first drive torque Td1, the first axle torque TqS1 becomes negative, as shown in FIG. 2(F). However, when the first regenerative braking torque TbE1 is reduced by executing the reduction process of the stationary braking control, the first axle torque TqS1 approaches 0 (zero). On the other hand, when a positive torque is applied to the first axle 15 as the first drive torque Td1, and the magnitude of the first drive torque Td1 becomes greater than the magnitude of the first regenerative braking torque TbE1, the first axle torque TqS1 becomes positive. In other words, the sign of the first axle torque TqS1 is reversed. As a result, vehicle vibration occurs due to the reversal of the sign of the first axle torque TqS1 during the reduction process of the stationary braking control. Therefore, when the sign of the first axle torque TqS1 is reversed during the reduction process of the stationary braking control, it is preferable to reduce the rate at which the first axle torque TqS1 is reduced when the first axle torque TqS1 is reversed.

[0061] Therefore, the control unit 125 executes distribution adjustment control to adjust the regenerative distribution ratio Re, thereby slowing the rate at which the first axle torque TqS1 is reduced at the time when the first axle torque TqS1 is reversed. The distribution adjustment control is executed during the period in which the total braking torque TbT is reduced so that the total braking torque TbT becomes smaller than the requested braking torque TbRq, that is, while the switching process is being executed. For this reason, the control unit 125 starts the distribution adjustment control as soon as the start condition for the switching process is satisfied, and ends the distribution adjustment control as soon as the end condition for the switching process is satisfied.

[0062] In the distribution adjustment control, the control unit 125 reduces the regenerative distribution ratio Re compared to before the start of the stationary braking control. Specifically, the control unit 125 gradually reduces the regenerative distribution ratio Re as the switching process progresses so that, of the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2, only the first regenerative braking torque TbE1 is switched to the total friction braking torque TbFT. In other words, the control unit 125 gradually reduces the regenerative distribution ratio Re so that the second regenerative braking torque TbE2 is maintained at a constant torque during the switching process. At this time, the control unit 125 transmits an instruction to the regenerative control unit 103 to reduce the regenerative distribution ratio Re. As a result, the regenerative control unit 103 reduces the first regenerative braking torque command value TbEtr1 without reducing the second regenerative braking torque command value TbEtr2 based on the reduced regenerative distribution ratio Re. In another embodiment, the amount of decrease in the regenerative allocation ratio Re during the execution of the switching process may be an amount of decrease that allows for a decrease in the second regenerative braking torque TbE2. In other words, it is sufficient that the regenerative allocation ratio Re gradually decreases during the execution of the switching process.

[0063] Then, when the switching process ends, the control unit 125 holds the regenerative allocation ratio Re at the end of the switching process. Therefore, in the reduction process executed following the switching process, the regenerative allocation ratio Re becomes smaller than the regenerative allocation ratio Re before the start of the stationary braking control. Therefore, during the reduction process, the rate at which the first regenerative braking torque TbE1 decreases decreases, and the rate at which the first axle torque TqS1 increases decreases.

[0064] <Smooth stop processing> The smooth stop process will be described with reference to Fig. 3. The smooth stop process is a series of processes that the processing circuit 71 executes when braking the vehicle while stationary. The processing circuit 71 repeatedly executes the smooth stop process at each predetermined control cycle.

[0065] 3, the processing circuit 71 functions as the stopping-related value acquisition unit 123 to acquire the stopping distance DS (S11). Subsequently, the processing circuit 71 determines whether or not there is a braking request (S13). If the processing circuit 71 determines that there is a braking request (S13: YES), the processing circuit 71 proceeds to step S17. On the other hand, if the processing circuit 71 determines that there is no braking request (S13: NO), the processing circuit 71 proceeds to step S15.

[0066] In step S15, the processing circuit 71 sets an end flag FLG2 (described later) to OFF, and then the processing circuit 71 temporarily ends the smooth stop processing. In step S17, the processing circuit 71 determines whether the end flag FLG2 is set to OFF. If the end flag FLG2 is set to OFF (S17: YES), the processing circuit 71 proceeds to step S19. On the other hand, if the end flag FLG2 is set to ON (S17: NO), the processing circuit 71 temporarily ends the smooth stop processing.

[0067] In step S19, the processing circuit 71 determines whether the stopping distance DS is equal to or less than the first threshold value DSth1. If the stopping distance DS is greater than the first threshold value DSth1 (S19: NO), the processing circuit 71 temporarily terminates the smooth stop processing. On the other hand, if the stopping distance DS is equal to or less than the first threshold value DSth1 (S19: YES), the processing circuit 71 functions as the control unit 125 to execute stopping braking control. That is, when the stopping distance DS becomes equal to or less than the first threshold value DSth1, the processing circuit 71 starts stopping braking control.

[0068] Specifically, the processing circuit 71 determines whether the replacement from the total regenerative braking torque TbET to the total friction braking torque TbFT due to the execution of the replacement process has been completed (S21). The processing circuit 71 determines that the replacement has been completed if both of the following two conditions (A1) and (A2) are satisfied. On the other hand, the processing circuit 71 determines that the replacement has not been completed if at least one of the two conditions (A1) and (A2) is not satisfied.

[0069] (A1) The total friction braking torque TbFT becomes equal to the set braking torque Tbset by executing the replacement process. (A2) The total regenerative braking torque TbET has decreased by the amount of increase in the total friction braking torque TbFT due to the execution of the switching process.

[0070] If the processing circuit 71 determines that the switching has not been completed (S21: NO), the processing circuit 71 executes the switching process (S23) and then temporarily ends the smooth stop process.

[0071] On the other hand, if the processing circuit 71 determines in step S21 that the switching has been completed (S21: YES), the processing circuit 71 determines whether the stopping distance DS is equal to or less than the second threshold value DSth2 (S31). If the stopping distance DS is greater than the second threshold value DSth2 (S31: NO), the processing circuit 71 temporarily terminates the smooth stop processing. In this case, the processing circuit 71 maintains the total regenerative braking torque TbET and the total friction braking torque TbFT. On the other hand, if the stopping distance DS is equal to or less than the second threshold value DSth2 (S31: YES), the processing circuit 71 determines whether the stopping distance DS is equal to or less than the third threshold value DSth3 (S33). That is, the processing circuit 71 determines whether the vehicle 10 has stopped. If the stopping distance DS is greater than the third threshold value DSth3 (S33: NO), the processing circuit 71 proceeds to step S35. On the other hand, if the stopping distance DS is equal to or less than the third threshold value DSth3 (S33: YES), the processing circuit 71 proceeds to step S41.

[0072] In step S35, the processing circuit 71 determines whether the total regenerative braking torque TbET is 0 (zero). If the processing circuit 71 determines that the total regenerative braking torque TbET is not 0 (zero) (S35: NO), the processing circuit 71 executes a reduction process (S37). Then, the processing circuit 71 temporarily ends the smooth stop process.

[0073] On the other hand, if the processing circuit 71 determines in step S35 that the total regenerative braking torque TbET is 0 (zero) (S35: YES), the processing circuit 71 executes the holding process (S39) and temporarily ends the smooth stop process.

[0074] In step S41, the processing circuit 71 determines whether the execution of the degeneration processing has been completed. For example, if the total friction braking torque TbFT is equal to or greater than the required braking torque TbRq, the execution of the degeneration processing can be considered to have been completed. On the other hand, if the total friction braking torque TbFT is less than the required braking torque TbRq, the execution of the degeneration processing can be considered to have not been completed. If the processing circuit 71 determines that the execution of the degeneration processing has not been completed (S41: NO), the processing circuit 71 executes the degeneration processing (S43). Then, the processing circuit 71 temporarily ends the smooth stop processing.

[0075] On the other hand, if the processing circuit 71 determines in step S41 that the execution of the degeneration processing has been completed (S41: YES), the processing circuit 71 sets the end flag FLG2 to ON (S45). Then, the processing circuit 71 ends the stationary braking control. That is, the end flag FLG2 is a flag that is set to ON when the execution of the degeneration processing of the stationary braking control has been completed. Thereafter, the processing circuit 71 temporarily ends the smooth stop processing.

[0076] <Vehicle body vibration reduction treatment> The vehicle body vibration reduction process will be described with reference to Fig. 4. The processing circuit 71 repeatedly executes the vehicle body vibration reduction process at each predetermined control cycle. The processing circuit 71 functions as the control unit 125 to execute a plurality of processes constituting the vehicle body vibration reduction process.

[0077] As shown in FIG. 4, the processing circuit 71 determines whether or not the start condition for the switching process is satisfied (S51). If the start condition for the switching process is not satisfied (S51: NO), the processing circuit 71 terminates this process. On the other hand, if the start condition for the switching process is satisfied (S51: YES), the processing circuit 71 reduces the regenerative distribution ratio Re according to the switching status of the braking torque (S52). The processing of step S52 corresponds to the distribution adjustment control. Thereafter, the processing circuit 71 determines whether or not the switching process is completed (S53). If the switching process is not completed (S53: NO), the processing circuit 71 proceeds to step S52. In this case, the regenerative distribution ratio Re is gradually reduced as the switching process progresses. On the other hand, if the switching process is completed (S53: YES), the processing circuit 71 terminates the distribution adjustment control and terminates this process. After the switching process is completed, the regenerative distribution ratio Re is maintained at the regenerative distribution ratio Re at the time of completion of the switching process. That is, in the reduction process executed after the switching process, the regenerative allocation ratio Re becomes smaller than the regenerative allocation ratio Re at the start of the switching process. In other words, in the reduction process executed after the switching process, the regenerative allocation ratio Re becomes smaller than the ratio before the start of the stationary braking control.

[0078] <Actions and Effects of the First Embodiment> The operation and effect of the braking control device 70 when stopping the vehicle 10 will be described with reference to FIGS. 2(A) to 2(G).

[0079] Before timing t11, the vehicle 10 is traveling with neither the drive operating member 11 nor the brake operating member 12 being operated. Therefore, the required braking torque TbRq is 0 (zero), and the total driving torque TdT is a negative torque equivalent to engine braking torque, etc. The total driving torque TdT is distributed to a first driving torque Td1 and a second driving torque Td2 based on the reference driving distribution ratio Rd. Therefore, the first driving torque Td1 and the second driving torque Td2 are negative torques. Furthermore, because the required braking torque TbRq is 0 (zero), the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 are also 0 (zero). As a result, before timing t11, the first axle torque TqS1 and the second axle torque TqS2 are negative torques.

[0080] At timing t11, when a braking request is generated, for example, when the driver begins to operate the brake operating member 12, the required braking torque TbRq begins to increase. Then, the total regenerative braking torque TbET increases in accordance with the increase in the required braking torque TbRq. The total regenerative braking torque TbET is distributed to the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 based on the reference regenerative distribution ratio Re. Therefore, the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 increase at a rate according to the regenerative distribution ratio Re. In the example shown in FIG. 2, the increase in the required braking torque TbRq is equal to the increase in the total regenerative braking torque TbET, so the total frictional braking torque TbFT does not increase from 0 (zero). After timing t11, the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 increase, causing the first axle torque TqS1 and the second axle torque TqS2 to decrease. Although not shown, after timing t11, the vehicle speed VS gradually decreases as braking torques act on the axles 15 and 16.

[0081] At timing t12, when the vehicle speed VS becomes less than the first judgment speed Vth1, the first driving torque Td1 and the second driving torque Td2 begin to increase in accordance with the decrease in the vehicle speed VS. Furthermore, as the first driving torque Td1 and the second driving torque Td2 increase, the first axle torque TqS1 and the second axle torque TqS2 begin to increase toward 0 (zero).

[0082] At timing t13, when the stopping distance DS becomes equal to or less than the first threshold value DSth1, a switching process for the stationary braking control is initiated. In the switching process, the total friction braking torque TbFT is increased to the set braking torque Tbset. When the switching process is being executed, the distribution adjustment control is also executed. Therefore, at this time, the execution of the distribution adjustment control reduces the regenerative distribution ratio Re in accordance with the increase in the total friction braking torque TbFT. Therefore, the first regenerative braking torque TbE1 is reduced in accordance with the increase in the total friction braking torque TbFT, but the second regenerative braking torque TbE2 is not reduced. Meanwhile, the rate of increase of the first axle torque TqS1 increases in accordance with the decrease in the first regenerative braking torque TbE1. Here, the first axle torque TqS1 increases at a rate corresponding to the rate at which the first regenerative braking torque TbE1 and the first drive torque Td1 decrease, while the second axle torque TqS2 increases at a rate equal to the rate at which the second drive torque Td2 decreases. As a result, the rate at which the first axle torque TqS1 increases is greater than the rate at which the second axle torque TqS2 increases.

[0083] At timing t14, when the total friction braking torque TbFT reaches the set braking torque Tbset, the switching process ends. When the switching process ends, the distribution adjustment control also ends. Therefore, during the period from timing t14 to timing t15, the first regenerative braking torque TbE1, the second regenerative braking torque TbE2, and the total friction braking torque TbFT are kept constant.

[0084] At timing t15, when the stopping distance DS becomes equal to or less than the second threshold value DSth2, the reduction process of the stationary braking control is initiated. During the reduction process, the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 are gradually reduced to 0 (zero). In the first embodiment, the regenerative allocation ratio Re is reduced during the switching process, so the first regenerative braking torque TbE1 is smaller at the start of the reduction process compared to when the regenerative allocation ratio Re is not reduced during the switching process. In other words, when the allocation ratio control is performed as shown by the two-dot chain line in FIG. 2(C), the first regenerative braking torque TbE1 is smaller at the start of the reduction process compared to when the allocation ratio control is not performed as shown by the dashed line in FIG. 2(C). Furthermore, when distribution ratio control is performed during the reallocation process as shown by the two-dot chain line in Figure 2(C), the rate at which the first regenerative braking torque TbE1 decreases is smaller than when distribution ratio control is not performed during the reallocation process as shown by the dashed line in Figure 2(C).As a result, when distribution ratio control is performed during the reallocation process as shown by the two-dot chain line in Figure 2(F), the rate at which the first axle torque TqS1 increases is smaller than when distribution ratio control is not performed during the reallocation process as shown by the dashed line in Figure 2(F).

[0085] At timing t16, the first axle torque TqS1 becomes 0 (zero). That is, while the rate of increase of the first axle torque TqS1 is slowing down, the sign of the first axle torque TqS1 is reversed. In this way, vehicle vibration caused by the reversal of the sign of the first axle torque TqS1 is suppressed.

[0086] Subsequently, at timing t17, the second axle torque TqS2 becomes 0 (zero). When distribution ratio control is executed, the rate at which the second axle torque TqS2 decreases during the reduction process is greater than when distribution ratio control is not executed. However, as shown in FIGS. 2(F) and 2(G), when distribution ratio control is executed, the rate at which the second axle torque TqS2 increases is smaller than the rate at which the first axle torque TqS1 increases. Therefore, in terms of suppressing vehicle vibration, it is more effective to have a slower rate of increase in the first axle torque TqS1 at the time the first axle torque TqS1 changes direction than to have a fast rate of increase in the second axle torque TqS2 at the time the second axle torque TqS2 changes direction.

[0087] At timing t18, when the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 become 0 (zero), the reduction process ends and the holding process begins. In the holding process, the total friction braking torque TbFT is held at the set braking torque Tbset, and the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 are held at 0 (zero). Therefore, from timing t18 onwards, the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 and the first drive torque Td1 and the second drive torque Td2 no longer change, and therefore the first axle torque TqS1 and the second axle torque TqS2 no longer change.

[0088] At timing t19, when it is determined that the vehicle 10 has stopped, the holding process ends and the degeneration process starts. In the degeneration process, the total friction braking torque TbFT is increased to the required braking torque TbRq. Thereafter, at a timing after timing t19, when the total friction braking torque TbFT increases to the required braking torque TbRq, the degeneration process ends. In other words, the vehicle-stop braking control ends.

[0089] In the first embodiment, the following effects can be further obtained. (1) It can be inferred that the greater the magnitude of the first axle torque TqS, the greater the degree of torsion of the first axle 15. Furthermore, the slower the rate of increase of the first axle torque TqS, the more gradually the degree of torsion of the first axle 15 changes. Therefore, by gradually changing the degree of torsion of the first axle 15 when the axle torque TqS switches from negative to positive, vehicle body vibration caused by the reversal of the direction of torsion of the first axle 15 is less likely to increase. Therefore, the brake control device 70 reduces the rate of increase of the first axle torque TqS1 at the time when the first axle torque TqS1 reverses from positive to negative during execution of the vehicle-stop braking control. Therefore, the brake control device 70 can suppress the occurrence of vehicle body vibration caused by the reversal of the direction of torsion of the first axle 15 while suppressing the occurrence of vehicle body swaying when the vehicle is stopped by executing the vehicle-stop braking control. As a result, the brake control device 70 can improve the comfort of the occupants of the vehicle 10 when the vehicle 10 is stopped by the generation of braking force.

[0090] (2) During vehicle-stop braking control, the brake control device 70 reduces the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 to 0 (zero) when the vehicle-stop maintaining braking torque Tbh is generated in the vehicle 10. This allows the brake control device 70 to stop the vehicle 10 using the friction braking torque TbF even when the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 become 0 (zero). In other words, the brake control device 70 can prevent a period of time during which no braking torque is applied from occurring while the vehicle-stop braking control is being executed.

[0091] (3) By executing distribution adjustment control, the brake control device 70 can shift the time point at which the first axle torque TqS1 and the second axle torque TqS2 reverse positive and negative. As a result, the brake control device 70 can shift the timing at which vehicle vibrations caused by the reversal of positive and negative of the first axle torque TqS1 and the reversal of positive and negative of the second axle torque TqS2 occur.

[0092] (Second embodiment) A second embodiment of the brake control device 70 will be described. The second embodiment differs from the first embodiment in the content of the distribution ratio control that is executed to reduce the increasing speed of the first axle torque TqS1 at the time of positive / negative reversal. Therefore, the following description will mainly focus on the parts that differ from the first embodiment. Furthermore, in the following description, the same reference numerals will be used to designate components that correspond to those in the first embodiment, and redundant description will be omitted.

[0093] In the second embodiment, the control unit 125 executes the distribution ratio control during the execution of the reduction process of the stationary braking control. Specifically, the control unit 125 starts the distribution ratio control when a first determination condition is met during the execution of the stationary braking control, and ends the distribution ratio control when a second determination condition is met during the execution of the stationary braking control.

[0094] The first determination condition is met when the first axle torque TqS1 approaches the point at which it reverses its sign as the reduction process is performed. In this case, the control unit 125 calculates an expected arrival time from the current time until the point at which it reverses its sign based on the change in the first axle torque TqS1 over time. The control unit 125 then determines that the first determination condition is met when the expected arrival time is less than a predetermined first determination time. Alternatively, the control unit 125 may determine that the first determination condition is met when the first axle torque TqS1 is equal to or greater than a predetermined first determination torque. Here, the first determination torque is negative torque.

[0095] In distribution ratio control, when the total regenerative braking torque TbET is reduced by executing stationary braking control, the control unit 125 gradually increases the distribution ratio during the period including the time point when the sign of the first axle torque TqS1 is reversed. At this time, the control unit 125 sends an instruction to the regenerative control unit 103 to increase the regenerative distribution ratio Re. As a result, the regenerative control unit 103 decreases the rate of decrease of the first regenerative braking torque command value TbEtr1 and increases the rate of decrease of the second regenerative braking torque command value TbEtr2.

[0096] The second determination condition is met when the first axle torque TqS1 becomes positive, i.e., after the first axle torque TqS1 reverses between positive and negative. Specifically, the control unit 125 may determine that the second determination condition is met when the time elapsed since the first axle torque TqS1 reverses between positive and negative is equal to or greater than a predetermined second determination time. Alternatively, the control unit 125 may determine that the second determination condition is met when the first axle torque TqS1 becomes equal to or greater than a predetermined second determination torque. Here, the second determination torque is positive torque.

[0097] In the distribution ratio control, when the regenerative distribution ratio Re is increased, it is important that the regenerative distribution ratio Re does not become 1 before the second determination condition is met. This is because if the regenerative distribution ratio Re becomes 1, the rate of decrease of the first regenerative braking torque TbE1 cannot be reduced by increasing the regenerative distribution ratio Re. Therefore, it is preferable that the control unit 125 increases the regenerative distribution ratio Re so that the regenerative distribution ratio Re becomes 1 or less than 1 when the second determination condition is met.

[0098] <Vehicle body vibration reduction treatment> The vehicle body vibration reduction process will be described with reference to Fig. 5. The processing circuit 71 repeatedly executes the vehicle body vibration reduction process at each predetermined control cycle. The processing circuit 71 functions as the control unit 125 to execute a plurality of processes constituting the vehicle body vibration reduction process.

[0099] As shown in Fig. 5, the processing circuit 71 determines whether or not the reduction process is being executed (S61). If the reduction process is not being executed (S61: NO), the processing circuit 71 ends this process. On the other hand, if the reduction process is being executed (S61: YES), the processing circuit 71 determines whether or not a first determination condition is met (S62). If the first determination condition is not met (S62: NO), that is, if the time point at which the positive and negative polarities of the first axle torque TqS1 will reverse is not approaching, the processing circuit 71 ends this process.

[0100] On the other hand, if the first determination condition is met (S62: YES), that is, if the time when the first axle torque TqS1 will reverse positive and negative is approaching, the processing circuit 71 increases the regenerative distribution ratio Re as distribution adjustment control (S63). That is, the distribution of total regenerative braking torque TbET to first regenerative braking torque TbE1 increases and the distribution to second regenerative braking torque TbE2 decreases. Thereafter, the processing circuit 71 determines whether the second determination condition is met (S64).

[0101] If the second determination condition is not met (S64: NO), the processing circuit 71 proceeds to step S63. That is, in this case, the regeneration distribution ratio Re gradually increases as the distribution adjustment control continues. On the other hand, if the second determination condition is met (S64: YES), the reversal of the positive and negative polarities of the first axle torque TqS1 has been completed, so the processing circuit 71 ends the distribution adjustment control and terminates this process. That is, the processing circuit 71 maintains the regeneration distribution ratio Re at the value it had when the second determination condition was met.

[0102] <Actions and Effects of the Second Embodiment> The operation and effect of the braking control device 70 when stopping the vehicle 10 will be described with reference to FIGS. 6(A) to 6(G).

[0103] Timing t21 is a timing at which a braking request occurs, similar to timing t11, and timing t22 is a timing at which the first drive torque Td1 and the second drive torque Td2 begin to increase, similar to timing t12.

[0104] At timing t23, when the stopping distance DS becomes equal to or less than the first threshold value DSth1, the switching process for the stationary braking control is initiated. In the switching process, the total friction braking torque TbFT is increased to the set braking torque Tbset. At the same time, the total regenerative braking torque TbET is reduced by the amount of the increase in the total friction braking torque TbFT. At this time, because the regenerative distribution ratio Re is held constant, the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 decrease as the total friction braking torque TbFT increases. As a result, the rate of increase of the first axle torque TqS1 and the rate of increase of the second axle torque TqS2 increase.

[0105] At time t24, when the total friction braking torque TbFT reaches the set braking torque Tbset, the switching process ends. Therefore, from time t24 to time t25, the first regenerative braking torque TbE1, the second regenerative braking torque TbE2, and the total friction braking torque TbFT are kept constant.

[0106] At timing t25, when the stopping distance DS becomes equal to or less than the second threshold value DSth2, the reduction process of the stationary braking control is initiated. During the reduction process, the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 are gradually reduced to 0 (zero). In the example shown in FIG. 6, the start condition for the reduction process is met, and the start condition for the distribution adjustment control is also met. Therefore, the regenerative distribution ratio Re gradually increases from timing t25 onwards. As a result, when the distribution adjustment control is executed as shown by the two-dot chain line in FIGS. 6(C) and (F), the increase rate of the first axle torque TqS1 is slower because the decrease rate of the first regenerative braking torque TbE1 is slower than when the distribution adjustment control is not executed as shown by the dashed line in FIGS. 6(C) and (F). On the other hand, when distribution adjustment control is performed as shown by the dotted lines in Figures 6(C) and (G), the rate of increase of the second axle torque TqS2 is greater in that the rate of decrease of the second regenerative braking torque TbE2 is greater than when distribution adjustment control is not performed as shown by the dashed lines in Figures 6(C) and (G).

[0107] At timing t26, the first axle torque TqS1 becomes 0 (zero). That is, while the rate of increase of the first axle torque TqS1 is slowing down, the sign of the first axle torque TqS1 is reversed. In this way, vehicle vibration caused by the reversal of the sign of the first axle torque TqS1 is suppressed.

[0108] At timing t27, the second axle torque TqS2 becomes 0 (zero). When distribution ratio control is executed, the rate at which the second axle torque TqS2 decreases during the reduction process is greater than when distribution ratio control is not executed. However, as shown by the dashed line in FIG. 6(G), the rate at which the second axle torque TqS2 increases when distribution ratio control is executed is smaller than the rate at which the first axle torque TqS1 increases when distribution ratio control is not executed, as shown by the dashed line in FIG. 6(F). Therefore, in terms of suppressing vehicle vibration, it is more effective to have a slower rate of increase in the first axle torque TqS1 at the time the first axle torque TqS1 reverses direction than to have a faster rate of increase in the second axle torque TqS2 at the time the second axle torque TqS2 reverses direction.

[0109] If the second determination condition is met at timing t28, distribution ratio control ends. Also, in the example shown in FIG. 6, the second regenerative braking torque TbE2 becomes 0 (zero) at timing t28. Therefore, the regenerative distribution ratio Re is maintained at 1 from timing t28 onwards, and the first regenerative braking torque TbE1 becomes equal to the total regenerative braking torque TbET. In other words, from timing t28 onwards, the first regenerative braking torque TbE1 decreases with the second regenerative braking torque TbE2 maintained at 0 (zero). In the second embodiment, the regenerative distribution ratio Re gradually increases from timing t25 to timing t28, including timing t26 when the sign of the first axle torque TqS1 is reversed.

[0110] When the total regenerative braking torque TbET becomes 0 (zero) at time t29, the reduction process ends and the holding process begins. In the holding process, the total friction braking torque TbFT is held at the set braking torque Tbset, and the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 are held at 0 (zero). Therefore, after time t29, the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 and the first drive torque Td1 and the second drive torque Td2 do not change, and therefore the first axle torque TqS1 and the second axle torque TqS2 do not change.

[0111] When it is determined at timing t30 that the vehicle 10 has stopped, the holding process ends and the degeneration process begins. In the degeneration process, the total friction braking torque TbFT is increased to the required braking torque TbRq. Thereafter, at a timing after timing t30, when the total friction braking torque TbFT increases to the required braking torque TbRq, the degeneration process ends. In other words, the vehicle-stop braking control ends.

[0112] 6, for ease of understanding, the second determination condition is assumed to be met at timing t28, but the second determination condition can be met any time after timing t26, when the positive and negative signs of the first axle torque TqS1 are reversed. For example, if the second determination condition is assumed to be met at timing t27, which is between timing t26 and timing t28, the first regenerative braking torque TbE1 and the second regenerative braking torque TbE2 gradually decrease during the period from timing t27 to timing t29. In other words, the timing at which the second regenerative braking torque TbE2 becomes 0 (zero) is the same as the timing at which the first regenerative braking torque TbE1 becomes 0 (zero).

[0113] The braking control device 70 according to the second embodiment can obtain the same effects as the effects (1) to (3) of the braking control device 70 according to the first embodiment. <Example of change> The above-described embodiments can be modified as follows: The above-described embodiments and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0114] The braking control device 70 may acquire the vehicle speed VS as the stopping-related value instead of the stopping distance DS. In both embodiments, the control unit 125 may set an upper limit or a lower limit for the regenerative distribution ratio Re in the distribution adjustment control.

[0115] 6, the timing at which the distribution adjustment control starts to be executed is not necessarily the same as the timing at which the reduction process of the stationary braking control starts to be executed. The timing at which the distribution adjustment control starts to be executed may be later than the timing at which the reduction process of the stationary braking control starts to be executed.

[0116] 6, the timing at which distribution adjustment control ends does not necessarily coincide with the timing at which second regenerative braking torque TbE2 becomes 0 (zero). The timing at which distribution adjustment control ends may be a timing before second regenerative braking torque TbE2 becomes 0 (zero) as long as first axle torque TqS1 is a positive torque.

[0117] 2 and 6, the timing at which the increase in the drive torques Td1 and Td2 ends does not necessarily coincide with the timing at which the decrease process begins. The increase in the drive torques Td1 and Td2 ends may be later than the start of the decrease process, or may be earlier than the start of the decrease process.

[0118] The creep torque for creeping the vehicle 10 does not have to be output from the second power unit 22 as long as it is output from the first power unit 21. The friction braking unit 40 may be configured to apply a friction braking torque TbF to at least one of the first wheel 13 and the second wheel 14.

[0119] As shown by the dashed lines in Figures 2(F) and 2(G), when distribution adjustment control is not performed, the rate of decrease of the first axle torque TqS1 at the time when the first axle torque TqS1 reverses its sign is greater than the rate of decrease of the second axle torque TqS2 at the time when the second axle torque TqS2 reverses its sign. However, if the torsional rigidity of the second axle 16 is different from that of the first axle 15, the following problem may occur. That is, even if the rate of decrease of the first axle torque TqS1 at the time when the first axle torque TqS1 reverses its sign, the vehicle vibration caused by the reversal of the sign of the second axle torque TqS2 may be greater than the vehicle vibration caused by the reversal of the sign of the first axle torque TqS1. In such a case, the brake control device 70 may perform distribution adjustment control so as to reduce the rate of decrease of the second axle torque TqS2 at the time when the second axle torque TqS2 reverses its sign.

[0120] The brake control device 70 does not need to execute the switching process during braking control when the vehicle is stationary. The vehicle 10 may be equipped with an in-wheel motor as a motor generator. In this case, the "axle" corresponds to the output shaft of the in-wheel motor or the power transmission shaft from the in-wheel motor to the wheels 13, 14.

[0121] In both embodiments, the distribution adjustment control of the stationary braking control and the distribution adjustment control may be a control executed by the drive control device 30. In this case, the drive control device 30 and the braking control device 70 constitute a "vehicle control device."

[0122] The phrase "at least one" as used herein means "one or more" of the desired options. As an example, the phrase "at least one" as used herein means "only one option" or "both of two options" when the number of options is two. As another example, the phrase "at least one" as used herein means "only one option" or "any combination of two or more options" when the number of options is three or more.

[0123] The drive control device 30 and the braking control device 70 are not limited to processing circuits equipped with a CPU and ROM and executing software processing. For example, the drive control device 30 and the braking control device 70 may be equipped with dedicated hardware circuits that execute at least some of the various processes executed in the above-described embodiment. An example of a dedicated hardware circuit is an ASIC. ASIC is an abbreviation for "Application Specific Integrated Circuit." In other words, the drive control device 30 and the braking control device 70 may have any of the following configurations (a) to (c):

[0124] (a) A processing circuit comprising a processing device that executes all of the above processes according to a program, and a program storage device such as a ROM that stores the program. (b) A processing circuit comprising a processing device and a program storage device that execute part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing.

[0125] (c) A processing circuit having dedicated hardware circuitry for performing all of the above processes. Here, there may be a plurality of software execution devices each having a processing device and a program storage device, and a plurality of dedicated hardware circuits.

[0126] <Technical philosophy> The technical ideas that can be understood from the above-described embodiment and modified examples will be described. [Appendix 1] The vehicle control device is applicable to a vehicle including a first power unit configured to apply a first regenerative braking torque and a first drive torque to a first axle that rotates integrally with a first wheel, which is one of the front wheels and the rear wheels; a second power unit configured to apply a second regenerative braking torque and a second drive torque to a second axle that rotates integrally with a second wheel, which is the other of the front wheels and the rear wheels; and a friction braking unit configured to apply a friction braking torque to at least one of the first wheel and the second wheel, wherein an axle torque is generated at the first axle when the first regenerative braking torque and the first drive torque are applied to the first axle, and an axle torque is generated at the second axle when the second regenerative braking torque and the second drive torque are applied to the second axle. The vehicle control system is equipped with a control unit that executes a distribution adjustment control that adjusts a distribution ratio, which is the ratio of the first regenerative braking torque to a total regenerative braking torque, which is the sum of the first regenerative braking torque and the second regenerative braking torque, and a stationary braking control that controls the first power unit, the second power unit, and the friction braking unit when braking the vehicle, thereby reducing the total regenerative braking torque to 0 (zero) while increasing the friction braking torque until the vehicle stops, wherein the sum of the first regenerative braking torque and the first drive torque is an axle torque, and in the distribution adjustment control, when the total regenerative braking torque is reduced by executing the stationary braking control, the control unit gradually increases the distribution ratio during a period including the point in time when the axle torque of the first axle is reversed in sign.

[0127] [Appendix 2] The first wheel is preferably one of the front wheels and the rear wheels to which a larger regenerative braking torque is applied when braking the vehicle before the vehicle-stop braking control is started. [Explanation of symbols]

[0128] 10...Vehicle 13...1st wheel (front wheel) 14…Second wheel (rear wheel) 15…1st axle 16…Second axle 21...First power unit 22...Second power unit 30...Drive control device 40...Friction brake part 70...Brake control device 121…Derivation part 123...Stopping-related value acquisition unit 125...Control unit DS: Stopping distance (stopping related values)

Claims

1. The present invention is applicable to a vehicle including: a first power unit configured to apply a first regenerative braking torque and a first drive torque to a first axle that rotates integrally with a first wheel, which is one of the front wheels and the rear wheels; a second power unit configured to apply a second regenerative braking torque and a second drive torque to a second axle that rotates integrally with a second wheel, which is the other of the front wheels and the rear wheels; and a friction braking unit configured to apply a friction braking torque to at least one of the first wheel and the second wheel, wherein an axle torque is generated on the first axle when the first regenerative braking torque and the first drive torque are applied to the first axle, and an axle torque is generated on the second axle when the second regenerative braking torque and the second drive torque are applied to the second axle, a distribution adjustment control that adjusts a distribution ratio that is a ratio of the first regenerative braking torque to a total regenerative braking torque that is the sum of the first regenerative braking torque and the second regenerative braking torque; a control unit that executes a vehicle-stop braking control that controls the first power unit, the second power unit, and the friction braking unit during braking of the vehicle, thereby reducing the total regenerative braking torque to 0 (zero) while increasing the friction braking torque until the vehicle comes to a stop, In the distribution adjustment control, the control unit reduces the distribution ratio when the total regenerative braking torque is reduced as the stationary braking control is executed, compared to the distribution ratio before the stationary braking control is started. Vehicle control device.

2. a stop-related value acquisition unit that acquires a stop-related value that decreases as the vehicle approaches a predetermined stop position; The control unit In the vehicle stop braking control, when the vehicle stop-related value is equal to or less than a predetermined threshold value, the vehicle is stopped in a state where a total braking torque, which is the sum of the total regenerative braking torque and the friction braking torque, is made smaller than a required braking torque for the vehicle, In the distribution adjustment control, when the total braking torque is reduced so that the total braking torque becomes smaller than the required braking torque as the vehicle-stop braking control is executed, the distribution ratio is reduced. The vehicle control device according to claim 1 .

3. A braking torque that can keep the vehicle stopped on the road surface on which the vehicle is traveling is a stop-keeping braking torque, The vehicle-stop braking control includes: a friction braking increasing process for increasing the friction braking torque to the vehicle stop-holding braking torque; a regenerative braking reduction process that is a process subsequent to the friction braking increase process, and that reduces the total regenerative braking torque to the stop-holding braking torque by reducing the total regenerative braking torque to 0 (zero), The control unit reduces the distribution ratio during the execution of the regenerative braking reduction process in the distribution adjustment control. The vehicle control device according to claim 2.

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