Vehicle control device

Abstract

To provide a vehicle control device for suppressing the generation of vehicle body vibration caused by the inversion of the torsional direction of an axle when a vehicle is stopped.SOLUTION: The braking control device 70 includes a control unit 125 that executes braking control during vehicle stop for reducing the regenerative braking torque to 0 (zero) and increasing the friction braking torque until the vehicle 10 stops, by coordinating the power unit 20 and the friction braking unit 40 during braking of the vehicle 10. In the brake control during vehicle stop, the control unit 125 sets the increase speed of the axle torque at the positive-negative inversion time point of the axle torque to be smaller than that at the reference time point before the inversion time point.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 applied to a vehicle that includes a power unit configured to apply regenerative braking torque and driving torque to an axle that rotates integrally with the wheel, and a friction braking unit configured to apply friction braking torque to the wheel, and includes a control unit that executes stationary braking control that, when the vehicle is braking, coordinates the power unit and the friction braking unit to reduce the regenerative braking torque to 0 (zero) while increasing the friction braking torque until the vehicle stops, the sum of the regenerative braking torque and the driving torque is the axle torque, and in the stationary braking control, the control unit reduces the rate of change of the axle torque at the point at which the axle torque reverses from positive to negative compared to a reference point before the point at which the axle torque reverses. [Effects of the Invention]

[0009] The vehicle control device can suppress the occurrence of vehicle body vibrations caused by the reversal of the torsional direction of the axle 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(F) are timing charts for 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(F) are timing charts for stopping the vehicle in the second embodiment. [Figure 7] FIG. 7 is a flowchart illustrating the flow of processing executed by the brake control device of the third embodiment during vehicle-stop braking control. [Figure 8] 8(A) to 8(F) are timing charts for stopping the vehicle in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (First embodiment) A first embodiment of a vehicle control device will be described below. <Overall vehicle configuration> 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, a power unit 20, a drive control device 30, a friction braking unit 40, and a plurality of sensors 61 to 63.

[0012] <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.

[0013] <Power unit> The power unit 20 is configured to be able to apply a driving torque Td and a regenerative braking torque TbE to the axle 14 that rotates integrally with the wheels 13. The power unit 20 has at least a motor generator out of an engine and a motor generator as a power source for the vehicle 10.

[0014] The rotation direction of the axle 14 in accordance with the direction of travel of the vehicle 10 is referred to as the "forward direction." The opposite direction to the forward direction is referred to as the "reverse direction." Torque acting on the axle 14 in the forward direction is referred to as positive torque, and torque acting on the axle 14 in the reverse direction is referred to as negative torque.

[0015] When the motor generator functions as a generator, a regenerative braking torque TbE is applied to the axle 14. When the regenerative braking torque TbE is applied to the axle 14, the rotation of the axle 14 is decelerated. In other words, when the vehicle 10 is not stopped, the regenerative braking torque TbE can be said to be a torque that acts on the axle 14 in the reverse direction.

[0016] <Axle twist> A wheel 13 is attached to the tip of the axle 14. Therefore, the unit including the wheel 13 and the axle 14 can be considered a "torsion pendulum." When the part of the axle 14 to which torque is transmitted from the power unit 20 is considered to be the transmission part, the amount of rotation of the transmission part relative to the wheel 13 is considered to be the rotation angle. When no torsion occurs in the axle 14, the rotation angle is 0 (zero) degrees. When at least one of the driving torque Td and the regenerative braking torque TbE is applied to the axle 14, torsion may occur in the axle 14. When torsion occurs in the axle 14 in this way, the magnitude of the rotation angle increases.

[0017] In the first embodiment, the torque that generates a twist in the axle 14 and is applied to the transmission part of the axle 14 is referred to as "axle torque TqS." The axle torque TqS is the sum of the driving torque Td and the regenerative braking torque TbE applied to the axle 14. Therefore, when the driving torque Td is a positive torque, the difference between the magnitude of the driving torque Td and the magnitude of the regenerative braking torque TbE becomes the axle torque TqS. In this case, when the magnitude of the regenerative braking torque TbE is smaller than the driving torque Td, the axle torque TqS becomes a positive torque. When the magnitude of the regenerative braking torque TbE is larger than the driving torque Td, the axle torque TqS becomes a negative torque. Furthermore, when the driving torque Td is a negative torque, the axle torque TqS becomes a negative torque. Specifically, the greater the sum of the magnitude of the driving torque Td and the magnitude of the regenerative braking torque TbE, the greater the magnitude of the axle torque TqS. When the axle torque TqS is a positive torque, it can be said that the axle torque TqS acts on the axle 14 in the forward rotation direction. When the axle torque TqS is a negative torque, it can be said that the axle torque TqS acts on the axle 14 in the reverse rotation direction.

[0018] While the vehicle 10 is traveling, if the magnitude of the driving torque Td and the regenerative braking torque TbE changes, or if the driving torque Td changes sign, the axle torque TqS may reverse sign. The reversal of sign of the axle torque TqS means that the direction of torsion of the axle 14 reverses. When the direction of torsion of the axle 14 reverses, vehicle body vibration occurs due to the reversal of the direction of torsion of the axle 14. Furthermore, such vehicle body vibration increases the faster the axle torque TqS increases when the axle torque TqS reverses sign. Here, the increase rate of the axle torque TqS corresponds to the "change rate of the axle torque."

[0019] <Drive control device> The drive control device 30 controls the power unit 20. The drive control device 30 is equipped with a processing circuit 31. An example of the processing circuit 31 is an electronic control device. In this case, the drive control device 30 has 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 unit 20.

[0020] 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 unit 20 based on the command received from the braking control device 70.

[0021] 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.

[0022] When the drive operation member 11 is operated, the drive control unit 101 derives the required drive force such that the required drive force increases as the drive operation amount, which indicates the amount of operation of the drive operation member 11, increases. The drive control unit 101 also derives the required drive force even when the drive operation member 11 is not being operated. For example, when the drive operation member 11 is not being operated and the vehicle speed VS is equal to or greater than the first threshold speed Vth1, the drive control unit 101 derives a negative required drive force. In this case, the required drive force corresponds to engine brake torque if the drive force output source is an engine, and corresponds to torque simulating engine brake torque if the drive force output source is a motor-generator. On the other hand, when the drive operation member 11 is not being operated and the vehicle speed VS is less than the second threshold speed Vth2, the drive control unit 101 derives a positive required drive force. In this case, the required drive force corresponds to creep torque if the drive force output source is an engine, and corresponds to torque simulating creep torque if the drive force output source is a motor-generator. The creep torque is the drive torque Td for realizing creep driving of the vehicle 10. 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 drive torque Td to derive required drive torque TdRq, which is the required value of the drive torque Td.

[0023] The drive control unit 101 adjusts the drive torque Td applied to the axle 14 by operating the power unit 20. The drive control unit 101 derives a drive torque command value Tdtr, which is a command value for the drive torque Td, based on the required drive torque TdRq. Then, the drive control unit 101 controls the power unit 20 based on the drive torque command value Tdtr. In this way, the drive control unit 101 can adjust the drive torque Td applied to the axle 14.

[0024] The regenerative control unit 103 adjusts the regenerative braking torque TbE applied to the axle 14 by operating the power unit 20. The regenerative control unit 103 derives a regenerative braking torque command value TbEtr, which is a command value for the regenerative braking torque TbE, based on the required braking torque TbRq transmitted from the braking control device 70. Then, the drive control unit 101 controls the power unit 20 based on the regenerative braking torque command value TbEtr. This allows the regenerative control unit 103 to adjust the regenerative braking torque TbE applied to the axle 14.

[0025] Note that the drive control unit 101 may derive the drive torque command value Tdtr, and the regenerative braking torque command value TbEtr may derive the regenerative braking torque command value TbEtr. In this case, the power unit 20 is controlled based on both the drive torque command value Tdtr and the regenerative braking torque command value TbEtr. That is, the power unit 20 applies to the axle 14 a torque that is the sum of the drive torque command value Tdtr and the regenerative braking torque command value TbEtr. This sum corresponds to the axle torque TqS. Therefore, it can be said that the power unit 20 can apply to the axle 14 an axle torque TqS that corresponds to the drive torque command value Tdtr and the regenerative braking torque command value TbEtr.

[0026] <Friction brake part> The friction braking unit 40 applies a friction braking torque TbF to the vehicle 10. As a result, a friction braking force is generated at the wheels 13. The friction braking unit 40 includes a plurality of friction brakes 41 provided respectively for the plurality of wheels 13, and a braking actuator 50.

[0027] Each of the multiple friction brakes 41 applies a friction braking torque TbF to the corresponding wheel 13. 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. Therefore, by pressing the friction portion 44 against the rotating body 43, a friction braking torque TbF is applied to the wheel 13. 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 as the wheel pressure increases.

[0028] The brake actuator 50 is configured to adjust the friction braking torque TbF applied to the multiple wheels 13 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. In the following description, the sum of the friction braking torque TbF and the regenerative braking torque TbE is referred to as the total braking torque TbT.

[0029] <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 sensor 63, for example.

[0030] 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.

[0031] 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.

[0032] The vehicle 10 is equipped with wheel sensors 63 in the same number as the wheels 13. Each wheel sensor 63 detects the rotation speed of the corresponding wheel 13. The rotation speed of the wheel 13 based on the detection signal of the wheel sensor 63 is referred to as the "wheel speed VW."

[0033] <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.

[0034] 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 in the first memory 73, the processing circuit 71 can operate the friction braking unit 40 to adjust the friction braking torque TbF. Furthermore, the processing circuit 71 can adjust the axle torque TqS acting on the axle 14 by sending instructions regarding the regenerative braking torque TbE and instructions regarding the drive torque Td to the drive control device 30.

[0035] 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 in 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 braking torque. The processing circuit 71 then transmits the required braking torque TbRq to the drive control device 30.

[0036] The processing circuit 71 of the brake control device 70 derives a target friction braking torque TbFtr, which is a target for the friction braking torque TbF for the vehicle 10, based on the regenerative braking torque TbE that the power unit 20 can generate and the required braking torque TbRq. If the regenerative braking torque TbE that the power unit 20 can generate is equal to the required braking torque TbRq, the processing circuit 71 derives 0 (zero) as the target friction braking torque TbFtr. On the other hand, if the regenerative braking torque TbE that the power unit 20 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 regenerative braking torque TbE as the target friction braking torque TbFtr. Then, the processing circuit 71 operates the brake actuator 50 based on the target friction braking torque TbFtr.

[0037] <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.

[0038] <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.

[0039] In the derivation process, the derivation unit 121 derives the 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 the driving torque Td applied from the power unit 20 to the axles 14 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 than when the road surface is not a slope as the stop-maintaining braking force. When it is possible to predict that the driving torque Td applied from the power unit 20 to the axles 14 while the vehicle is stopped will be large, the derivation unit 121 derives a braking force that is greater than when it is possible to predict that the driving torque Td will not be large as the stop-maintaining braking force. The derivation unit 121 then converts the stop-maintaining braking force into torque to derive the stop-maintaining braking torque Tbh.

[0040] <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.

[0041] 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.

[0042] <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 unit 20 and the friction braking unit 40.

[0043] 2(A) to 2(F), 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 regenerative braking torque TbE to 0 (zero) while increasing the friction braking torque TbF until the vehicle 10 stops, and 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 that the regenerative cooperative control is being executed.

[0044] 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."

[0045] 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 the "predetermined threshold value." The replacement process is a process for replacing the regenerative braking torque TbE with the friction braking torque TbF. In the replacement process, the control unit 125 operates the brake actuator 50 to increase the friction braking torque TbF to a set braking torque Tbset that is equal to or greater than the stationary holding braking torque Tbh. In the example shown in FIG. 2, the set braking torque Tbset is equal to the stationary holding braking torque Tbh. Therefore, the control unit 125 increases the target friction braking torque TbFtr to the stationary holding braking torque Tbh and operates the brake actuator 50 based on the target friction braking torque TbFtr. At the same time, the control unit 125 transmits to the regeneration control unit 103 an instruction to decrease the regenerative braking torque TbE by the amount of increase in the friction braking torque TbF resulting from the execution of the switching process.

[0046] When the regenerative control unit 103 receives the above instruction, the regenerative control unit 103 decreases the regenerative braking torque command value TbEtr by the increase amount of the friction braking torque TbF. Then, the regenerative control unit 103 operates the power unit 20 based on the regenerative braking torque command value TbEtr. This decreases the regenerative braking torque TbE by the increase amount of the friction braking torque TbF. As a result, changes in the total braking torque TbT due to the execution of the replacement process are suppressed. When the friction braking torque TbF is maintained, the control unit 125 ends the replacement process.

[0047] 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 regenerative control unit 103 to reduce the regenerative braking torque TbE to 0 (zero). At this time, the control unit 125 may transmit an instruction to the regenerative control unit 103 to reduce the regenerative braking torque TbE at a standard reduction speed Vstd. The standard reduction speed Vstd is set so that the regenerative braking torque TbE becomes 0 (zero) before the vehicle speed VS becomes 0 (zero).

[0048] When the regenerative control unit 103 receives this instruction, the regenerative control unit 103 decreases the regenerative braking torque instruction value TbEtr toward 0 (zero). Then, the regenerative control unit 103 operates the power unit 20 based on this regenerative braking torque instruction value TbEtr.

[0049] The control unit 125 maintains the friction braking torque TbF during the reduction process. Then, when the control unit 125 determines that the regenerative braking torque command value TbEtr has become 0 (zero), the control unit 125 ends the reduction process. In the example shown in Fig. 2, the regenerative braking torque command value TbEtr becomes 0 (zero) at timing t19.

[0050] After the reduction process is completed, the control unit 125 starts the retention process. In the retention process, the control unit 125 retains the target friction braking torque TbFtr. At this time, the control unit 125 also retains the state in which the regenerative braking torque TbE is 0 (zero).

[0051] If the control unit 125 determines that the vehicle 10 has stopped during the execution of the retention process, the control unit 125 transitions from the retention 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 t20 is the timing at which the control unit 125 determines that the vehicle 10 has stopped.

[0052] In the degeneration process, the control unit 125 increases the friction braking torque TbF. For example, the control unit 125 increases the friction braking torque TbF to the required braking torque TbRq. At this time, the control unit 125 increases the target friction braking torque TbFtr to the required braking torque TbRq. Then, the control unit 125 operates the brake actuator 50 based on the target friction braking torque TbFtr. When the friction braking torque TbF 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.

[0053] As described above, the power unit 20 of the vehicle 10 outputs positive torque or negative torque as the driving torque Td 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 judgment speed Vth1, the power unit 20 applies negative torque as the driving torque Td to the axle 14. Subsequently, when a braking force is applied to the vehicle 10 and the vehicle body speed VS becomes less than the first judgment speed Vth1, the power unit 20 gradually increases the driving torque Td applied to the axle 14 in accordance with the decrease in the vehicle body speed VS. After the vehicle body speed VS becomes less than the first judgment speed Vth1 and before the vehicle body speed VS becomes equal to or greater than the second judgment speed Vth2, the driving torque Td applied to the axle 14 becomes greater than 0 (zero). Then, when the vehicle speed VS becomes less than the second determination speed Vth2, the power unit 20 applies a constant positive torque to the axle 14 as the driving torque Td.

[0054] When the magnitude of the regenerative braking torque TbE is greater than the magnitude of the driving torque Td, the axle torque TqS becomes negative as shown in FIG. 2(F). However, when the regenerative braking torque TbE is reduced by the execution of the reduction process of the stationary braking control, the axle torque TqS approaches 0 (zero). Then, when a positive torque is applied to the axle 14 as the driving torque Td and the magnitude of the driving torque Td becomes greater than the magnitude of the regenerative braking torque TbE, the axle torque TqS becomes positive. In other words, the sign of the axle torque TqS is reversed. As a result, vehicle vibration occurs due to the reversal of the sign of the axle torque TqS during the execution of the reduction process of the stationary braking control. For this reason, when the sign of the axle torque TqS is reversed during the execution of the reduction process of the stationary braking control, it is preferable to reduce the rate of increase of the axle torque TqS at the time when the axle torque TqS is reversed.

[0055] Therefore, in the vehicle-stop braking control, the control unit 125 reduces the rate of increase of the axle torque TqS at the time when the axle torque TqS reverses between positive and negative compared to a reference time point before the time when the axle torque TqS reverses between positive and negative. More specifically, in the vehicle-stop braking control, when the total braking torque TbT is being reduced so that the total braking torque TbT is smaller than the requested braking torque TbRq, that is, when the reduction process is being executed, the control unit 125 reduces the rate of increase of the axle torque TqS at the time when the axle torque TqS reverses between positive and negative.

[0056] In the vehicle-stop braking control, the control unit 125 executes a first adjustment process, a second adjustment process, and a third adjustment process as processes for reducing the rate of increase of the axle torque TqS at the time when the axle torque TqS reverses between positive and negative.

[0057] The control unit 125 starts the first adjustment process when a first determination condition is met. The first determination condition is met when the axle torque TqS approaches the point at which it reverses its positive and negative values ​​as the reduction process is performed. In this case, the control unit 125 calculates an expected arrival time from the current time to the point at which it reverses its positive and negative values, based on the change in the axle torque TqS over time. Subsequently, the control unit 125 may determine that the first determination condition is met when the expected arrival time is shorter than a predetermined first determination time. Alternatively, the control unit 125 may determine that the first determination condition is met when the axle torque TqS becomes equal to or greater than a predetermined first determination torque. In this case, the first determination torque is a negative torque.

[0058] In the first adjustment process, the control unit 125 sets the rate of decrease of the regenerative braking torque command value TbEtr to a first decrease rate V1. That is, the control unit 125 instructs the regenerative control unit 103 to decrease the regenerative braking torque command value TbEtr at the first decrease rate V1. The first decrease rate V1 is greater than the standard decrease rate Vstd described above. Therefore, when the first adjustment process is performed, the rate of decrease of the regenerative braking torque command value TbEtr is greater than when the first adjustment process is not performed.

[0059] If a second determination condition is met during execution of the first adjustment process, the control unit 125 terminates the first adjustment process and starts the second adjustment process. The second determination condition is met after the first determination condition is met and when the time is closer to the time when the axle torque TqS reverses positive and negative signs than when the first determination condition was met. For example, the control unit 125 may determine that the second determination condition is met when the predicted arrival time is shorter than a second determination time that is shorter than the first determination time. Alternatively, the control unit 125 may determine that the second determination condition is met when the axle torque TqS is equal to or greater than a predetermined second determination torque. Here, the second determination torque is a negative torque that is greater than the first determination torque.

[0060] In the second adjustment process, the control unit 125 sets the rate of decrease of the regenerative braking torque command value TbEtr to a second decrease rate V2. That is, the control unit 125 instructs the regenerative control unit 103 to decrease the regenerative braking torque command value TbEtr at the second decrease rate V2. The second decrease rate V2 is smaller than the standard decrease rate Vstd described above. Therefore, while the second adjustment process is being performed, the rate of decrease of the regenerative braking torque command value TbEtr is smaller than when the second adjustment process is not being performed. That is, by reversing the sign of the axle torque TqS during the second adjustment process, the rate of increase of the axle torque TqS at the time when the sign of the axle torque TqS is reversed is reduced.

[0061] If a third determination condition is met during execution of the second adjustment process, the control unit 125 terminates the second adjustment process and starts the third adjustment process. The third determination condition is met when the axle torque TqS becomes positive, i.e., after the axle torque TqS reverses its sign. Specifically, the control unit 125 may determine that the third determination condition is met when the elapsed time from the point in time when the axle torque TqS reverses its sign is equal to or greater than a predetermined third determination time. Alternatively, the control unit 125 may determine that the third determination condition is met when the axle torque TqS becomes equal to or greater than a predetermined third determination torque. Here, the third determination torque is positive torque.

[0062] In the third adjustment process, the control unit 125 sets the rate of decrease of the regenerative braking torque command value TbEtr to a third decrease rate V3. That is, the control unit 125 instructs the drive control unit 101 to decrease the regenerative braking torque command value TbEtr at the third decrease rate V3. The third decrease rate V3 is greater than the standard decrease rate Vstd described above. Therefore, during the third adjustment process, the rate of decrease of the regenerative braking torque command value TbEtr is greater than during the second adjustment process. In the first embodiment, the third decrease rate V3 is equal to the first decrease rate V1, but in other embodiments, the third decrease rate V3 may be different from the first decrease rate V1.

[0063] The control unit 125 ends the third adjustment process when the regenerative braking torque command value TbEtr becomes 0 (zero). That is, the control unit 125 ends the third adjustment process and the reduction process at the same time. When the control unit 125 executes the first, second, and third adjustment processes, if only the rate of decrease of the regenerative braking torque command value TbEtr is changed, the rate of decrease of the total braking torque TbT during the execution of the reduction process may fluctuate. In this case, the total braking torque TbT may increase or decrease just before the vehicle 10 is stopped, which may cause the driver to feel uncomfortable. Therefore, when executing the first, second, and third adjustment processes, the control unit 125 changes the target frictional braking torque TbFtr so that the rate of decrease of the total braking torque TbT is maintained constant. More specifically, when the rate of decrease of the regenerative braking torque command value TbEtr is increased in the first and third adjustment processes, the target frictional braking torque TbFtr is increased to compensate for the insufficient braking torque by increasing the frictional braking torque TbF. Furthermore, in the second adjustment process, when the rate of decrease of the regenerative braking torque command value TbEtr is decreased, the target frictional braking torque TbFtr is decreased to deal with excessive braking torque by decreasing the frictional braking torque TbF. In this way, the control unit 125 changes the target frictional braking torque TbFtr in accordance with the change in the rate of decrease of the regenerative braking torque command value TbEtr.

[0064] As described above, the axle torque TqS changes sign during the second adjustment process. The rate of increase of the axle torque TqS during the second adjustment process is smaller than the rate of increase of the axle torque TqS during the first adjustment process, which occurs before the second adjustment process. In this respect, the control unit 125 reduces the rate of increase of the axle torque TqS at the time when the axle torque TqS changes sign compared to a reference time point before the change. The reference time point here is a time point during the first adjustment process. Similarly, the rate of increase of the axle torque TqS during the second adjustment process is smaller than the rate of increase of the axle torque TqS during the third adjustment process, which occurs after the second adjustment process. In this respect, the control unit 125 reduces the rate of increase of the axle torque TqS at the time when the axle torque TqS changes sign compared to a reference time point after the change. The reference time point here is a time point during the third adjustment process.

[0065] <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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] Specifically, the processing circuit 71 determines whether the switching from the regenerative braking torque TbE to the friction braking torque TbF due to the execution of the switching process has been completed (S21). The processing circuit 71 determines that the switching 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 switching has not been completed if at least one of the two conditions (A1) and (A2) is not satisfied.

[0070] (A1) The friction braking torque TbF becomes equal to the set braking torque Tbset by executing the replacement process. (A2) The regenerative braking torque command value TbEtr is decreased by the amount of increase in the friction braking torque TbF due to the execution of the replacement process.

[0071] 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.

[0072] 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 regenerative braking torque TbE and the friction braking torque TbF. 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.

[0073] In step S35, the processing circuit 71 determines whether the regenerative braking torque TbE is 0 (zero). If the processing circuit 71 determines that the regenerative braking torque TbE 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.

[0074] On the other hand, if the processing circuit 71 determines in step S35 that the regenerative braking torque TbE is 0 (zero) (S35: YES), the processing circuit 71 executes the holding process (S39) and temporarily ends the smooth stop process.

[0075] In step S41, the processing circuit 71 determines whether the execution of the degeneration processing has been completed. For example, if the friction braking torque TbF is equal to or greater than the required braking torque TbRq, the execution of the degeneration processing can be considered to be completed. On the other hand, if the friction braking torque TbF is less than the required braking torque TbRq, the execution of the degeneration processing can be considered to be incomplete. 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.

[0076] 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.

[0077] <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.

[0078] As shown in Fig. 4, the processing circuit 71 determines whether or not the reduction process of the stationary braking control is being executed (S51). If the reduction process is not being executed (S51: NO), the processing circuit 71 ends this process. On the other hand, if the reduction process is being executed (S51: YES), the processing circuit 71 determines whether or not a first determination condition is met (S52). If the first determination condition is not met (S52: NO), that is, if the axle torque TqS is not approaching the time when it will reverse its positive and negative polarities, the processing circuit 71 ends this process.

[0079] On the other hand, if the first determination condition is met (S52: YES), that is, if the axle torque TqS is approaching a time point at which it will reverse its sign, the processing circuit 71 starts the first adjustment process (S53). That is, the rate at which the regenerative braking torque command value TbEtr is reduced in the reduction process becomes the first reduction rate V1. Next, the control unit 125 determines whether the second determination condition is met (S54). If the second determination condition is not met (S54: NO), the processing circuit 71 proceeds to step S54. That is, the processing circuit 71 continues the first adjustment process.

[0080] On the other hand, if the second determination condition is met (S54: YES), the processing circuit 71 ends the first adjustment process and starts the second adjustment process (S55). That is, the reduction rate of the regenerative braking torque command value TbEtr in the reduction process becomes the second reduction rate V2. Next, the control unit 125 determines whether the third determination condition is met (S56). If the third determination condition is not met (S56: NO), the processing circuit 71 proceeds to step S56. That is, the processing circuit 71 continues the second adjustment process.

[0081] On the other hand, if the third judgment condition is met (S56: YES), that is, after the axle torque TqS has reversed its sign, the processing circuit 71 ends the second adjustment process and starts the third adjustment process (S57). That is, the rate at which the regenerative braking torque command value TbEtr is reduced in the reduction process becomes the third reduction rate V3. When the termination condition for the reduction process is met, the control unit 125 terminates the reduction process and the third adjustment process. Thereafter, the control unit 125 terminates this process.

[0082] <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(F).

[0083] 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 drive torque Td is negative. As a result, before timing t11, the axle torque TqS is negative.

[0084] At time t11, when a braking request is made, for example by the driver starting to operate the brake operating member 12, the required braking torque TbRq begins to increase. Then, the regenerative braking torque TbE increases in accordance with the increase in the required braking torque TbRq. In the example shown in FIG. 2, the increase in the required braking torque TbRq is equal to the increase in the regenerative braking torque TbE, so the friction braking torque TbF does not increase from 0 (zero). After time t11, the regenerative braking torque TbE increases, so the axle torque TqS decreases. Although not shown in the figure, after time t11, the vehicle speed VS gradually decreases at the point where the braking torque acts on the axle 14.

[0085] At timing t12, when the vehicle speed VS falls below the first speed determination value, the drive torque Td begins to increase in response to the decrease in the vehicle speed VS. Furthermore, as the drive torque Td increases, the axle torque TqS begins to increase toward 0 (zero).

[0086] At timing t13, when the stopping distance DS becomes equal to or less than the first threshold value DSth1, the switching process of the stationary braking control is initiated. In the switching process, the friction braking torque TbF is increased to the set braking torque Tbset (= stationary holding braking torque Tbh). At this time, the regenerative braking torque TbE is reduced by the increase in the friction braking torque TbF. Therefore, the total braking torque TbT, which is the sum of the regenerative braking torque TbE and the friction braking torque TbF, does not change. Meanwhile, as the regenerative braking torque TbE decreases, the axle torque TqS approaches 0 (zero).

[0087] At timing t14, when the friction braking torque TbF reaches the set braking torque Tbset (=vehicle stop holding braking torque Tbh), the switching process ends. Therefore, during the period from timing t14 to timing t15, the regenerative braking torque TbE and the friction braking torque TbF are kept constant.

[0088] At timing t15, when the stopping distance DS becomes equal to or less than the second threshold value DSth2, a reduction process of the stationary braking control is initiated. In the reduction process, the regenerative braking torque TbE is gradually reduced to 0 (zero). In the example shown in FIG. 2, the start condition of the first adjustment process is also satisfied at the timing when the start condition of the reduction process is satisfied. Therefore, at timing t15, the regenerative braking torque TbE starts to decrease at a relatively large first reduction rate V1. Furthermore, the friction braking torque TbF starts to increase so that the total braking torque TbT does not fluctuate due to the increase in the reduction rate of the regenerative braking torque TbE. Then, after timing t15, the axle torque TqS increases rapidly toward 0 (zero) due to the rapid decrease in the regenerative braking torque TbE.

[0089] At timing t16, when the start condition for the second adjustment process is met, the first adjustment process ends and the second adjustment process starts. Therefore, at timing t16, the regenerative braking torque TbE begins to decrease at a relatively small second decrease rate V2. Also, the friction braking torque TbF begins to decrease so that the total braking torque TbT does not fluctuate due to the slowdown in the decrease rate of the regenerative braking torque TbE. Then, after timing t16, the regenerative braking torque TbE gradually decreases, causing the axle torque TqS to gradually increase toward 0 (zero). More specifically, as shown by the solid line in FIG. 2(C), the decrease rate of the regenerative braking torque TbE during execution of the second adjustment process is smaller than the decrease rate of the regenerative braking torque TbE when the second adjustment process is not executed, as shown by the dashed line in FIG. 2(C). As a result, as shown by the solid line in Figure 2(F), the rate of decrease of the axle torque TqS during execution of the second adjustment process is smaller than the rate of decrease of the axle torque TqS when the same process is not executed, as shown by the dashed line in Figure 2(F).

[0090] At timing t17 while the second adjustment process is being performed, the axle torque TqS becomes 0 (zero). In other words, the sign of the axle torque TqS is reversed while the rate of increase of the axle torque TqS is slowing down. Here, the rate of increase of the axle torque TqS at the time when the axle torque TqS reverses is smaller than that at a reference time point before the time when the axle torque TqS reverses. The reference time point is, for example, any time point between timing t15 and timing t16. In this way, vehicle vibration caused by the reversal of the axle torque TqS is suppressed.

[0091] At timing t18, when the start condition for the third adjustment process is met, the second adjustment process ends and the third adjustment process starts. Therefore, at timing t18, the regenerative braking torque TbE is reduced at a relatively large third reduction rate V3. Furthermore, to prevent the total braking torque TbT from fluctuating due to the increased reduction rate of the regenerative braking torque TbE, the friction braking torque TbF is increased in accordance with the reduction rate of the regenerative braking torque TbE. Then, due to the rapid reduction in the regenerative braking torque TbE, the axle torque TqS increases rapidly.

[0092] At time t19, when the regenerative braking torque TbE becomes 0 (zero), the reduction process ends and the holding process begins. In the holding process, the friction braking torque TbF is held at the set braking torque Tbset (= vehicle-holding braking torque Tbh) and the regenerative braking torque TbE is held at 0 (zero). Furthermore, after time t19, the axle torque TqS also stops changing, as both the drive torque Td and the regenerative braking torque TbE stop changing.

[0093] When it is determined at timing t20 that the vehicle 10 has stopped, the holding process ends and the degeneration process starts. In the degeneration process, the friction braking torque TbF is increased to the required braking torque TbRq. Thereafter, at a timing after timing t20, when the friction braking torque TbF increases to the required braking torque TbRq, the degeneration process ends. In other words, the vehicle-stop braking control ends.

[0094] In the first embodiment, the following effects can be obtained. (1) It can be inferred that the greater the magnitude of the axle torque TqS, the greater the degree of torsion of the axle 14. Furthermore, the slower the rate of increase of the axle torque TqS, the more gradually the degree of torsion of the axle 14 changes. Therefore, by gradually changing the degree of torsion of the axle 14 when the axle torque TqS switches from negative to positive, vehicle body vibration caused by the reversal of the direction of torsion of the axle 14 is less likely to increase. Therefore, the brake control device 70 reduces the rate of increase of the axle torque TqS at the point when the axle torque TqS reverses from positive to negative during vehicle stoppage control. By executing vehicle stoppage control, the brake control device 70 can suppress the occurrence of vehicle body vibration caused by the reversal of the direction of torsion of the axle 14 while suppressing the occurrence of vehicle body sway back when the vehicle is stopped. As a result, the brake control device 70 can improve the comfort of the occupants of the vehicle 10 when braking force is generated to stop the vehicle 10.

[0095] (2) During the vehicle-stop braking control, the brake control device 70 reduces the regenerative braking torque TbE to 0 (zero) while the vehicle-stop maintaining braking torque Tbh is generated in the vehicle 10. As a result, the brake control device 70 can stop the vehicle 10 by the friction braking torque TbF even when the regenerative braking torque TbE becomes 0 (zero). In other words, the brake control device 70 can prevent a period during which no braking torque is applied from occurring while the vehicle-stop braking control is being executed.

[0096] (Second embodiment) A second embodiment of the braking control device 70 will be described. The second embodiment differs from the first embodiment in the method for reducing the increasing speed of the axle torque TqS 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 parts corresponding to those in the first embodiment, and redundant description will be omitted.

[0097] In the second embodiment, the control unit 125 sets the set braking torque Tbset to a value obtained by adding a predetermined offset value Tboff to the vehicle-stop maintaining braking torque Tbh in the switching process of the vehicle-stopping braking control. The offset value Tboff may be, for example, several percent to several tens of percent of the vehicle-stop maintaining braking torque Tbh.

[0098] In the vehicle-stop braking control, the control unit 125 executes an adjustment process to reduce the rate of increase of the axle torque TqS at the point where the axle torque TqS reverses its positive and negative directions. The control unit 125 starts the adjustment process when a determination condition is met. The determination condition is met when the axle torque TqS approaches the point where the axle torque TqS reverses its positive and negative directions while the reduction process is being executed. The control unit 125 may determine that the determination condition is met when the predicted arrival time from the current time to the point where the axle torque TqS reverses its positive and negative directions is shorter than a predetermined determination time. Alternatively, the control unit 125 may determine that the determination condition is met when the axle torque TqS is equal to or greater than a predetermined determination torque. In this case, the determination torque is a negative torque.

[0099] During the adjustment process, the control unit 125 sets the rate of decrease of the regenerative braking torque command value TbEtr to a rate slower than the standard decrease rate Vstd. Therefore, during the adjustment process, the regenerative braking torque TbE decreases more slowly than when the adjustment process is not performed. In other words, the control unit 125 reverses the sign of the axle torque TqS during the adjustment process, thereby slowing down the rate of increase of the axle torque TqS at the time when the sign of the axle torque TqS reverses.

[0100] Furthermore, when the control unit 125 executes the adjustment process, if only the rate of decrease of the regenerative braking torque command value TbEtr is changed, the rate of decrease of the total braking torque TbT during the execution of the reduction process may fluctuate. Therefore, when executing the adjustment process, the control unit 125 changes the target frictional braking torque TbFtr so as not to fluctuate the rate of decrease of the total braking force. More specifically, when the rate of decrease of the regenerative braking torque command value TbEtr is to be reduced during the adjustment process, the target frictional braking torque TbFtr is reduced. Furthermore, the control unit 125 terminates the adjustment process when the target frictional braking torque TbFtr is reduced to the vehicle-holding braking torque Tbh. After the control unit 125 terminates the adjustment process, the rate of decrease of the regenerative braking torque TbE increases at the point where the rate of decrease of the regenerative braking torque command value TbEtr returns to the standard rate of decrease Vstd.

[0101] <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 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 process.

[0102] As shown in FIG. 5, the processing circuit 71 determines whether a determination condition is met (S61). If the determination condition is not met (S61: NO), i.e., if the axle torque TqS is not approaching the time when it will reverse its sign, the processing circuit 71 temporarily terminates this process. On the other hand, if the determination condition is met (S61: YES), i.e., if the axle torque TqS is approaching the time when it will reverse its sign, the processing circuit 71 starts an adjustment process (S62). That is, as the rate of decrease of the regenerative braking torque command value TbEtr decreases, the target frictional braking torque TbFtr begins to decrease. Next, the processing circuit 71 determines whether the target frictional braking torque TbFtr is equal to or less than the stop-holding braking torque Tbh (S63). If the target frictional braking torque TbFtr is greater than the stop-holding braking torque Tbh (S63: NO), the processing circuit 71 proceeds to step S63. That is, the control unit 125 continues the adjustment process. On the other hand, if the target friction braking torque TbFtr is equal to or less than the vehicle-stop maintaining braking torque Tbh (S63: YES), the processing circuit 71 ends the adjustment process. After that, the processing circuit 71 ends this process.

[0103] <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(F).

[0104] Timing t21 is the timing at which a braking request occurs, similar to timing t11, and timing t22 is the timing at which the drive torque Td begins to increase, similar to timing t12.

[0105] At timing t23, 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 frictional braking torque TbF starts to increase toward the set braking torque Tbset. Specifically, the frictional braking torque TbF starts to increase toward a value obtained by adding the offset value Tboff to the stationary holding braking torque Tbh. After timing t23, the regenerative braking torque TbE is reduced by the increase in the frictional braking torque TbF. Therefore, the total braking torque TbT, which is the sum of the regenerative braking torque TbE and the frictional braking torque TbF, does not change. Then, the axle torque TqS increases toward 0 (zero) in response to the decrease in the regenerative braking torque TbE and the increase in the drive torque Td.

[0106] At time t24, when the friction braking torque TbF becomes the vehicle-holding braking torque Tbh, the switching process ends. Therefore, from time t24 to time t25, the regenerative braking torque TbE and the friction braking torque TbF are held constant. Meanwhile, during this period, the drive torque Td is increasing, so the axle torque TqS increases toward 0 (zero).

[0107] 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. In the reduction process, the regenerative braking torque TbE is reduced toward 0 (zero). The reduction rate of the regenerative braking torque TbE is the standard reduction rate Vstd. Then, in response to the reduction of the regenerative braking torque TbE and the increase of the drive torque Td, the axle torque TqS increases toward 0 (zero).

[0108] At timing t26, the adjustment process begins. As a result, the rate of decrease of the regenerative braking torque TbE becomes smaller than the standard decrease rate Vstd. Furthermore, the friction braking torque TbF is decreased in accordance with the amount of decrease of the regenerative braking torque TbE so that the rate of decrease of the total braking torque TbT does not change. As the rate of decrease of the regenerative braking torque TbE decreases, the rate of increase of the axle torque TqS decreases. Specifically, as shown by the solid line in FIG. 6(C), the rate of decrease of the regenerative braking torque TbE during the adjustment process is smaller than the rate of decrease of the regenerative braking torque TbE when the adjustment process is not executed, as shown by the dashed line in FIG. 6(C). As a result, as shown by the solid line in FIG. 6(F), the rate of decrease of the axle torque TqS during the adjustment process is smaller than the rate of decrease of the axle torque TqS when the adjustment process is not executed, as shown by the dashed line in FIG. 6(F).

[0109] At timing t27, the axle torque TqS becomes 0 (zero). In other words, the sign of the axle torque TqS is reversed while the rate of increase of the axle torque TqS is slowing down. Here, the rate of increase of the axle torque TqS at the time when the axle torque TqS reverses is smaller than that at a reference time point before the time when the axle torque TqS reverses. The reference time point is, for example, any time point between timing t25 and timing t26. In this way, vehicle vibration caused by the reversal of the axle torque TqS is suppressed.

[0110] At timing t28, when the friction braking torque TbF reaches the vehicle-stop maintaining braking torque Tbh, the adjustment process ends. As a result, the rate of decrease of the regenerative braking torque TbE returns to the standard decrease rate Vstd, and the friction braking torque TbF is maintained at the vehicle-stop maintaining braking torque Tbh. As the rate of decrease of the regenerative braking torque TbE increases, the rate of increase of the axle torque TqS also increases.

[0111] Timing t29 is the timing when the decrease process ends and the retention process starts, similar to timing t19. Timing t30 is the timing when the retention process ends and the degeneration process starts, similar to timing t20.

[0112] The second embodiment can achieve the same effects as the effects (1) and (2) of the first embodiment. (Third embodiment) A third embodiment of the braking control device 70 will be described. The third embodiment differs from the first embodiment in the method for reducing the increasing speed of the axle torque TqS 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 parts corresponding to those in the first embodiment, and redundant description will be omitted.

[0113] The control unit 125 according to the third embodiment executes a first adjustment process and a second adjustment process as processes for reducing the rate of increase of the axle torque TqS at the time when the axle torque TqS reverses positive and negative during braking control at a standstill.

[0114] The control unit 125 starts the first adjustment process when a first determination condition is met. The first determination condition is met when the axle torque TqS approaches the point at which the positive and negative signs of the axle torque TqS change direction. The control unit 125 may determine that the first determination condition is met when the predicted arrival time from the current time to the point at which the positive and negative signs of the axle torque TqS change direction is less than a predetermined first determination time. Alternatively, the control unit 125 may determine that the first determination condition is met when the axle torque TqS becomes equal to or greater than a predetermined first determination torque. In this case, the first determination torque is negative torque.

[0115] In the first adjustment process, the control unit 125 instructs the drive control unit 101 to reduce the drive torque Td. Therefore, while the first adjustment process is being performed, the rate of increase of the axle torque TqS decreases at the point where the drive torque Td decreases. In other words, by reducing the drive torque Td while the first adjustment process is being performed, the control unit 125 reduces the rate of increase of the axle torque TqS at the point where the axle torque TqS reverses between positive and negative.

[0116] If a second determination condition is met during execution of the first adjustment process, the control unit 125 terminates the first adjustment process and starts the second adjustment process. The second determination condition is met when the axle torque TqS becomes positive, i.e., after the axle torque TqS reverses its sign. Specifically, the control unit 125 may determine that the second determination condition is met when the elapsed time from the point in time when the axle torque TqS reverses its sign is equal to or greater than the second determination time. Alternatively, the control unit 125 may determine that the second determination condition is met when the axle torque TqS becomes equal to or greater than the second determination torque. Here, the second determination torque is positive torque.

[0117] In the second adjustment process, the control unit 125 instructs the drive control unit 101 to increase the drive torque Td. Therefore, while the second adjustment process is being performed, the rate at which the axle torque TqS increases increases in that the drive torque Td increases. In the second adjustment process, it is preferable that the drive torque Td be increased at a constant rate until it reaches the drive torque Td corresponding to the current vehicle speed VS. In other words, the control unit 125 ends the second adjustment process when the drive torque Td becomes the drive torque Td corresponding to the current vehicle speed VS.

[0118] <Vehicle body vibration reduction treatment> The vehicle body vibration reduction process will be described with reference to Fig. 7. The processing circuit 71 repeatedly executes the vehicle body vibration 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 process.

[0119] As shown in FIG. 7, the processing circuit 71 determines whether a first determination condition is met (S71). If the first determination condition is not met (S71: NO), that is, if the axle torque TqS is not approaching a time when it will reverse its sign, the processing circuit 71 ends this process. On the other hand, if the first determination condition is met (S71: YES), that is, if the axle torque TqS is approaching a time when it will reverse its sign, the processing circuit 71 starts a first adjustment process (S72). That is, the processing circuit 71 instructs the drive control device 30 to reduce the drive torque Td. Next, the processing circuit 71 determines whether a second determination condition is met (S73). If the second determination condition is not met (S73: NO), that is, if the axle torque TqS is not reversing its sign, the processing circuit 71 proceeds to step S73. That is, the processing circuit 71 continues the first adjustment process.

[0120] In step S73, if the second judgment condition is met (S73: YES), that is, if the axle torque TqS is inverted in sign, the processing circuit 71 ends the first adjustment process and starts the second adjustment process (S74). That is, the processing circuit 71 instructs the drive control device 30 to increase the drive torque Td. When the drive torque Td output by the power unit 20 becomes the drive torque Td that should be output in accordance with the current vehicle speed VS by increasing the drive torque Td, the processing circuit 71 ends the second adjustment process. Thereafter, the processing circuit 71 ends this process.

[0121] <Actions and Effects of the Third Embodiment> The operation and effect of the braking control device 70 when stopping the vehicle 10 will be described with reference to FIGS. 8(A) to 8(F).

[0122] At timing t31, a braking request is generated, similar to timing t11. At timing t32, the driving torque Td begins to increase, similar to timing t12. At timing t33, the switching process begins, similar to timing t13, and at timing t34, the switching process ends, similar to timing t14. At timing t35, the reduction process begins, similar to timing t15.

[0123] At timing t36, when the first judgment condition is met, the first adjustment process is initiated. That is, from timing t36 onwards, the drive torque Td starts to decrease at a constant rate. As a result, the rate at which the axle torque TqS increases slows down at the point where the regenerative braking torque TbE is decreasing but the drive torque Td is still decreasing. More specifically, as shown by the solid line in Figure 8(E), the rate at which the drive torque Td decreases during the first adjustment process is smaller than the rate at which the drive torque Td decreases (=0 (zero)) when the first adjustment process is not executed, as shown by the dashed line in Figure 8(E). As a result, as shown by the solid line in Figure 8(F), the rate at which the axle torque TqS decreases during the first adjustment process is smaller than the rate at which the axle torque TqS decreases when the first adjustment process is not executed, as shown by the dashed line in Figure 8(F).

[0124] At timing t37, the axle torque TqS becomes 0 (zero). In other words, the sign of the axle torque TqS is reversed while the rate of increase of the axle torque TqS is slowing down. Here, the rate of increase of the axle torque TqS at the time when the axle torque TqS reverses is smaller than that at a reference time point before the time when the axle torque TqS reverses. The reference time point is, for example, any time point between timings t35 and t36. In this way, vehicle vibration caused by the reversal of the axle torque TqS is suppressed.

[0125] At timing t38, when the second judgment condition is met, the first adjustment process ends and the second adjustment process begins. That is, the drive torque Td begins to increase at a constant rate. At timing t39, when the drive torque Td reaches the drive torque Td that the power unit 20 should output in accordance with the vehicle speed VS, the second adjustment process ends. Also at timing t39, the regenerative braking torque TbE becomes 0 (zero). Therefore, the decrease process ends and the retention process begins. Thereafter, at timing t40, similar to timing t20, the retention process ends and the degeneration process begins.

[0126] The third embodiment can achieve the same effects as the effects (1) and (2) of 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.

[0127] As an example of a combination of multiple embodiments, the first embodiment and the second embodiment may be combined. That is, in the replacement process according to the first embodiment, the set braking torque Tbset may be set to a value obtained by adding a predetermined offset value Tboff to the vehicle stop-maintaining braking torque Tbh. In this way, in the second adjustment process according to the first embodiment, the drive torque Td is reduced to the vehicle stop-maintaining braking torque Tbh, thereby further slowing down the rate at which the regenerative braking torque TbE is reduced.

[0128] The braking control device 70 may acquire the vehicle speed VS as the stopping-related value instead of the stopping distance DS. The brake control device 70 does not have to make the total braking torque TbT smaller than the required braking torque TbRq during braking control when the vehicle is stationary. In other words, the brake control device 70 may stop the vehicle 10 in a state where the total braking torque TbT is equal to the required braking torque TbRq during braking control when the vehicle is stationary.

[0129] The brake control device 70 does not need to execute the switching process in the vehicle-stop braking control according to the first and third embodiments. 2, 6, and 8, the timing at which the increase in the drive torque Td ends does not necessarily coincide with the timing at which the decrease process begins. The increase in the drive torque Td may end later than the start of the decrease process, or it may end earlier than the start of the decrease process.

[0130] 8, the start timing of the first adjustment process for reducing the driving force does not necessarily coincide with the end timing of the increase in driving torque Td. The start timing of the first adjustment process may be later than the end timing of the increase in driving torque Td, or may be earlier than the end timing of the increase in driving torque Td.

[0131] 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.

[0132] For example, in the propeller shaft of a rear-wheel drive vehicle or a four-wheel drive vehicle, vibrations may occur due to the reversal of positive and negative torque acting thereon, similar to the axle 14. In this regard, the "axle" in the above embodiment is taken to include a shaft member, such as a propeller shaft, provided in the power transmission path from the power unit 20 to the wheels 13.

[0133] 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.

[0134] 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):

[0135] (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.

[0136] (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. [Explanation of symbols]

[0137] 10...Vehicle 13...Wheel 14...Axle 20...Power unit 30...Drive control device 40...Friction brake part 50...Brake actuator 70...Brake control device (vehicle control device) 101...Drive control unit 103...Regeneration control unit 123...Stopping-related value acquisition unit 125...Control unit DS: Stopping distance (stopping related values)

Claims

1. The present invention is applied to a vehicle including a power unit configured to apply a regenerative braking torque and a driving torque to an axle that rotates integrally with a wheel, and a friction braking unit configured to apply a friction braking torque to the wheel, a control unit that executes vehicle-stop braking control that, when braking the vehicle, coordinates the power unit and the friction braking unit to reduce the regenerative braking torque to 0 (zero) while increasing the friction braking torque until the vehicle stops, the sum of the regenerative braking torque and the driving torque is an axle torque, The control unit, in the vehicle-stop braking control, reduces a rate of change of the axle torque at a time point at which the axle torque reverses between positive and negative directions compared to a reference time point before the time point at which the axle torque reverses between positive and negative directions. 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 vehicle-stopping braking control is a control for stopping the vehicle in a state where a total braking torque, which is a sum of the regenerative braking torque and the friction braking torque, is made smaller than a required braking torque for the vehicle when the vehicle-stopping-related value is equal to or smaller than a predetermined threshold value, The control unit, during the vehicle stop braking control, reduces the rate of change of the axle torque at a time point when the axle torque changes from positive to negative, compared to the rate at the reference time point, during a period when the total braking torque is reduced so that the total braking torque becomes smaller than the required braking torque. 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 a set braking torque equal to or greater than 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 regenerative braking torque to 0 (zero) to thereby reduce the total braking torque to the set braking torque, The control unit, during execution of the regenerative braking reduction process, reduces the rate of change of the axle torque at a time point when the axle torque changes from positive to negative compared to the reference time point. The vehicle control device according to claim 2.

4. The control unit reduces the rate of decrease of the regenerative braking torque during execution of the regenerative braking reduction process, thereby making the rate of change of the axle torque at the time point when the axle torque changes positive and negative less than that at the reference time point. The vehicle control device according to claim 3.

5. the set braking torque is set to a value obtained by adding a predetermined offset value to the vehicle stop-maintaining braking torque, The control unit reduces the frictional braking torque to the vehicle stop-maintaining braking torque during the execution of the regenerative braking reduction process, and reduces the rate of reduction of the regenerative braking torque during the period in which the frictional braking torque is reduced compared to before the start of the period, thereby reducing the rate of change of the axle torque at the time when the axle torque reverses positive and negative compared to the reference time. The vehicle control device according to claim 3.

6. the control unit adjusts the drive torque by controlling the power unit, In the regenerative braking reduction process, the control unit reduces the drive torque while the regenerative braking torque is being reduced, thereby making the rate of change of the axle torque at the time when the axle torque reverses positive and negative directions smaller than that at the reference time. The vehicle control device according to claim 3.

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