Vehicle control device

Abstract

A vehicle 10 comprises: a power unit 20 which is configured to be able to apply a regenerative braking torque and a driving torque to an axle 14; a regeneration control unit 103 which controls the power unit 20 on the basis of a regenerative braking torque instruction value; and a drive control unit 101 which controls the power unit 20 on the basis of a driving torque instruction value. A brake control device 70 of the vehicle 10 functions as: a determination unit 125 which determines whether or not the absolute value of the angular acceleration of the axle 14 is less than or equal to a determination angular acceleration; and a control unit 127 which executes axle torque control in cooperation with the regeneration control unit 103 and the drive control unit 101 such that, when the vehicle 10 is stopped by the generation of braking force, the positive / negative of the axle torque is reversed from a point onwards at which it is determined that the absolute value of the angular acceleration of the axle 14 is less than or equal to the determination angle acceleration.

Description

Vehicle control device

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

[0002] Patent Literature 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. The control device controls a motor generator so that regenerative braking torque decreases toward zero when the vehicle speed drops below a predetermined speed. Then, when the vehicle speed reaches zero, the control device increases friction braking torque by operating a hydraulic actuator.

[0003] JP 2016-28913 A

[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. The torque generated at the axle when at least one of the driving torque and the regenerative braking torque is applied to 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 braking control described above 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 torsion of the axle changes. When the direction of torsion of the axle reverses in this way, there is a risk that vehicle body vibrations will occur in the vehicle due to the reversal of the direction of torsion of the axle.

[0008] A vehicle control device for solving the above problem is applied to a vehicle including a power unit configured to apply regenerative braking torque and driving torque to an axle that rotates integrally with a wheel, a regenerative control unit that controls the power unit based on a regenerative braking torque command value that is a command value for the regenerative braking torque, and a drive control unit that controls the power unit based on a drive torque command value that is a command value for the drive torque. The torque generated at the axle by applying the regenerative braking torque and the drive torque is an axle torque. The vehicle control device includes a determination unit that determines whether the absolute value of the angular acceleration of the axle is equal to or less than a reference angular acceleration, and a control unit that executes axle torque control in cooperation with the regenerative control unit and the drive control unit so that, when the vehicle is stopped due to the generation of a braking force, the sign of the axle torque is reversed after it is determined that the absolute value of the angular acceleration of the axle is equal to or less than the reference angular acceleration.

[0009] The above vehicle control device has the effect of suppressing the occurrence of vehicle body vibrations caused by the reversal of the direction of torsion occurring in the axle when the vehicle is stopped by the generation of braking force.

[0010] Fig. 1 is a schematic diagram showing a vehicle equipped with a braking control device that is one embodiment of a vehicle control device. Fig. 2 is a timing chart for stopping the vehicle of Fig. 1. Fig. 3 is a flowchart showing a series of processes for executing braking control during vehicle stop in the braking control device of Fig. 1. Fig. 4 is a flowchart showing a series of processes for executing axle torque control in the braking control device of Fig. 1. Fig. 5 is a part of a timing chart for stopping a vehicle equipped with a vehicle control device of a modified example.

[0011] An embodiment of a vehicle control device will be described below with reference to Figs. 1 to 4. <Overall configuration of vehicle> Fig. 1 shows a vehicle 10 equipped with a brake control device 70. In this embodiment, the brake control device 70 corresponds to the "vehicle control device." The vehicle 10 is equipped with a brake operating member 11, a plurality of wheels 13, a power unit 20, a drive control device 30, a friction braking unit 40, and a plurality of sensors. The brake operating member 11 is a member operated by the driver when adjusting the deceleration of the vehicle 10. An example of the brake operating member 11 is a brake pedal.

[0012] <Power Unit> The power unit 20 is configured to be able to apply a driving torque Fd and an effective regenerative braking torque FbE 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.

[0013] The rotation direction of the axle 14 corresponding to the direction of travel of the vehicle 10 is referred to as the "forward direction." The direction opposite to the forward direction is referred to as the "reverse direction." The driving torque Fd acting on the axle 14 in the forward direction is a positive driving torque. The driving torque Fd acting on the axle 14 in the reverse direction is a negative driving torque.

[0014] When the motor generator functions as a generator, an effective regenerative braking torque FbE is applied to the axle 14. As a result, a regenerative braking force is generated in the vehicle 10. When the effective regenerative braking torque FbE 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 effective regenerative braking torque FbE can be said to be a torque that acts on the axle 14 in the reverse direction.

[0015] <Axle Torsion> The wheel 13 is attached to the tip of the axle 14. Therefore, the integrated body including the wheel 13 and the axle 14 can be considered a "torsion pendulum." When the portion of the axle 14 to which torque is transmitted from the power unit 20 is defined as a transmission part, the relative rotation angle of the transmission part with the wheel 13 as the reference is defined as a rotation angle θ. When no torsion occurs in the axle 14, the rotation angle θ is 0 (zero) degrees. When at least one of the driving torque Fd and the effective regenerative braking torque FbE 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 θ increases. When torsion occurs in the axle 14, a torque Tq that attempts to eliminate the torsion is generated in the axle 14. This torque Tq can be expressed by the following relational expression (D1). In relational expression (D1), "I" is the inertia of the wheel 13 attached to the tip of the axle 14.

[0016] In the relational formula (D1), "d ２ θ / dt ２ " is the angular acceleration of the axle 14. As shown in the relational expression (D1), as the absolute value of the angular acceleration of the axle 14 increases, the magnitude of the torque Tq increases. On the other hand, as the absolute value of the angular acceleration decreases, the magnitude of the torque Tq decreases.

[0017] In this embodiment, the torque generated on the axle 14 is referred to as "axle torque TqS." The axle torque TqS can be derived based on the effective regenerative braking torque FbE and driving torque Fd applied to the axle 14. When the driving torque Fd is a positive driving torque, the difference between the magnitude of the driving torque Fd and the magnitude of the effective regenerative braking torque FbE becomes the axle torque TqS. In this case, when the magnitude of the effective regenerative braking torque FbE is smaller than the magnitude of the driving torque Fd, the axle torque TqS becomes a positive torque. When the magnitude of the effective regenerative braking torque FbE is greater than the magnitude of the driving torque Fd, the axle torque TqS becomes a negative torque. Furthermore, when the driving torque Fd is a negative driving torque, the axle torque TqS becomes a negative torque. Specifically, the greater the sum of the magnitude of the driving torque Fd and the magnitude of the effective regenerative braking torque FbE, 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 in the forward rotation direction on the axle 14. When the axle torque TqS is a negative torque, it can be said that the axle torque TqS acts in the reverse rotation direction on the axle 14.

[0018] If the magnitude of the effective regenerative braking torque FbE and the driving torque Fd change, or if the driving torque Fd changes sign while the vehicle 10 is traveling, the sign of the axle torque TqS may be reversed. The reversal of the sign of the axle torque TqS means that the direction of torsion of the axle 14 is reversed. When the direction of torsion of the axle 14 is reversed, vehicle body vibration occurs due to the reversal of the direction of torsion of the axle 14.

[0019] While the axle torque TqS is a torque that causes torsion in the axle 14, the torque Tq shown in the above relational expression (D1) is a torque that attempts to eliminate the torsion of the axle 14. Therefore, there is a correlation between the axle torque TqS and the torque Tq. In other words, the sign of the torque Tq reverses at the same time that the sign of the axle torque TqS reverses. Furthermore, according to the above relational expression (D1), the smaller the angular acceleration of the axle 14, the smaller the torque Tq. Therefore, the smaller the angular acceleration of the axle 14 at the time that the sign of the axle torque TqS reverses, the smaller the torque Tq, and therefore the vehicle body vibration caused by the reversal of the direction of torsion of the axle 14 can be reduced.

[0020] <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.

[0021] 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.

[0022] 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 include a drive control unit 101 and a regeneration control unit 103.

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

[0024] The regenerative control unit 103 adjusts the effective regenerative braking torque FbE applied to the axle 14 by operating the power unit 20. That is, the regenerative control unit 103 derives a regenerative braking torque command value FbEtr, which is a command value for the regenerative braking torque. Then, the drive control unit 101 controls the power unit 20 based on the regenerative braking torque command value FbEtr. In this way, the regenerative control unit 103 can adjust the effective regenerative braking torque FbE applied to the axle 14.

[0025] Note that the drive control unit 101 may derive the drive torque command value Fdtr, and the regenerative control unit 103 may derive the regenerative braking torque command value FbEtr. In this case, the power unit 20 is controlled based on both the drive torque command value Fdtr and the regenerative braking torque command value FbEtr. Then, the power unit 20 applies to the axle 14 a torque that is the sum of the drive torque command value Fdtr and the regenerative braking torque command value FbEtr. This sum corresponds to the axle torque TqS. In other words, 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 Fdtr and the regenerative braking torque command value FbEtr.

[0026] <Friction Braking Unit> The friction braking unit 40 applies a friction braking torque FbF 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 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 FbF 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 FbF to the wheel 13 as the wheel pressure increases.

[0028] The brake actuator 50 is configured to adjust the friction braking torque FbF applied to the plurality of wheels 13 by controlling the wheel pressures of the plurality of wheel cylinders 42. For example, the brake actuator 50 has a pressure source that can supply brake fluid to the plurality of 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.

[0029] <Sensors> The multiple sensors output signals according to the detection results to the brake control device 70. The multiple sensors include, for example, a brake sensor 61, a wheel speed sensor 62, and an acceleration sensor 63. The brake sensor 61 detects information related to the operation of the brake operating member 11 by the driver. An example of the brake sensor 61 is a stroke sensor that detects the amount of operation of the brake operating member 11 by the driver. The operation amount based on the detection signal of the brake sensor 61 is referred to as the "braking operation amount X." Note that the vehicle 10 may also be equipped with a sensor that detects the operating force of the brake operating member 11 by the driver.

[0030] The vehicle 10 is equipped with wheel speed sensors 62 in the same number as the wheels 13. Each wheel speed sensor 62 detects the rotational speed of the corresponding wheel 13. The rotational speed of the wheel 13 based on the detection signal of the wheel speed sensor 62 is referred to as the "wheel speed VW."

[0031] The acceleration sensor 63 detects the longitudinal acceleration of the vehicle 10. The longitudinal acceleration based on the detection signal of the acceleration sensor 63 is referred to as the "longitudinal acceleration GX." <Brake Control Device> The brake control device 70 controls the brake actuator 50 of the friction braking unit 40. The brake 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 brake control device 70 can adjust the deceleration of the vehicle 10 by operating the brake actuator 50 and cooperating with the drive control device 30.

[0032] 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 FbF. Furthermore, the processing circuit 71 can adjust the axle torque TqS acting on the axle 14 by transmitting an instruction regarding the effective regenerative braking torque FbE and an instruction regarding the drive torque Fd to the drive control device 30.

[0033] The regenerative cooperative control executed by the processing circuit 71 will be described. The processing circuit 71 derives a required braking force BPRq, which is a required value of the braking force BP for the vehicle 10. The braking force BP is the sum of the friction braking force and the regenerative braking force generated by the vehicle 10. When the brake operating member 11 is operated, the processing circuit 71 derives the required braking force BPRq such that the required braking force BPRq increases as the braking operation amount X 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 BPRq. For example, the processing circuit 71 converts the required braking force BPRq into braking torque to derive a required braking torque FbRq, which is a required value of the braking torque. The processing circuit 71 then transmits the required braking torque FbRq to the drive control device 30.

[0034] The processing circuit 71 of the drive control device 30 derives a regenerative braking torque command value FbEtr based on the required braking torque FbRq, and then operates the motor generator of the power unit 20 based on the regenerative braking torque command value FbEtr.

[0035] The processing circuit 71 of the brake control device 70 derives a target frictional braking torque FbFtr, which is a target for the frictional braking torque for the vehicle 10, based on the effective regenerative braking torque FbE and the required braking torque FbRq. If the effective regenerative braking torque FbE is equal to the required braking torque FbRq, the processing circuit 71 derives 0 (zero) as the target frictional braking torque FbFtr. On the other hand, if the effective regenerative braking torque FbE is less than the required braking torque FbRq, the processing circuit 71 derives the difference between the required braking torque FbRq and the effective regenerative braking torque FbE as the target frictional braking torque FbFtr. Then, the processing circuit 71 operates the brake actuator 50 based on the target frictional braking torque FbFtr.

[0036] <Functional Units> The processing circuit 71 functions as multiple functional units as a result of the CPU 72 executing the control program in the first memory 73. The multiple functional units are functional units for suppressing the body of the vehicle 10 from swaying back when stopping the vehicle 10 by generating a braking force BP in the vehicle 10. The multiple functional units include a derivation unit 121, a stop-related value acquisition unit 123, a determination unit 125, and a control unit 127.

[0037] <Derivation Unit> The derivation unit 121 executes a derivation process at each predetermined control cycle when the vehicle 10 is decelerating due to the generation of the braking force BP. The derivation process is a process of acquiring various state quantities. For example, in the derivation process, the derivation unit 121 derives the required braking torque FbRq, the longitudinal acceleration GX, the wheel speed VW, the vehicle body speed VS, the vehicle body acceleration DVS, and the wheel acceleration DVW. 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. The vehicle body acceleration DVS can be derived by differentiating the vehicle body speed VS with respect to time. The wheel acceleration DVW can be derived by differentiating the wheel speed VW with respect to time.

[0038] In the derivation process, the derivation unit 121 derives the stop-maintaining braking force BPh. The stop-maintaining braking force BPh 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 BPh based on information regarding the gradient of the road surface and the drive torque Fd 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 as the stop-maintaining braking force BPh a braking force that is greater than when the road surface is not a slope. When it is possible to predict that the drive torque Fd applied from the power unit 20 to the axles 14 while the vehicle is stopped will be large, the derivation unit 121 derives as the stop-maintaining braking force BPh a braking force that is greater than when it is possible to predict that the drive torque Fd will not be large. The derivation unit 121 then converts the stop-maintenance braking force BPh into braking torque to derive the stop-maintenance braking torque Fbh.

[0039] <Stop-related value acquisition unit> 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 braking force BP. The stop-related value is a value that decreases as the vehicle 10 approaches a predetermined stop position.

[0040] 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 speed VS and the vehicle 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 speed VS becomes 0 (zero) at the current vehicle 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.

[0041] <Determination Unit> The determination unit 125 executes a process for determining whether the absolute value of the angular acceleration of the axle 14 is equal to or less than the reference angular acceleration at each predetermined control cycle. The axle 14 rotates integrally with the wheel 13. Therefore, the angular acceleration of the axle 14 is substantially equal to the wheel acceleration DVW. Therefore, for example, if the absolute value |DVW| of the wheel acceleration DVW is equal to or less than the reference wheel acceleration DVWth, the determination unit 125 determines that the absolute value of the angular acceleration of the axle 14 is equal to or less than the reference angular acceleration. On the other hand, if the absolute value |DVW| of the wheel acceleration is greater than the reference wheel acceleration DVWth, the determination unit 125 determines that the absolute value of the angular acceleration of the axle 14 is greater than the reference angular acceleration. In this case, the reference wheel acceleration DVWth is used as the criterion for determining whether the absolute value of the angular acceleration of the axle 14 is equal to or less than the reference angular acceleration.

[0042] <Control Unit> When a braking force is generated on the vehicle 10 , the control unit 127 controls the deceleration of the vehicle 10 by operating the friction braking unit 40 and cooperating with the regeneration control unit 103 and the drive control unit 101 .

[0043] 2, when the stopping distance DS is equal to or less than a predetermined threshold, the control unit 127 executes stationary braking control to stop the vehicle 10 with the braking force BP set smaller than the required braking force BPRq. In this embodiment, the start condition for the stationary braking control includes the execution of regenerative cooperative control.

[0044] The stationary braking control includes a replacement process, a reduction process, a maintenance process, and a degeneration process. The control unit 127 starts the replacement process of the stationary braking control when the stopping distance DS becomes equal to or less than the first threshold value DSth1. 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 of replacing the effective regenerative braking torque FbE with the frictional braking torque FbF. In the replacement process, the control unit 127 operates the brake actuator 50 to increase the frictional braking torque FbF to a braking torque equal to or greater than the stationary holding braking torque Fbh. For example, the control unit 127 increases the target frictional braking torque FbFtr to the stationary holding braking torque Fbh and operates the brake actuator 50 based on the target frictional braking torque FbFtr. At the same time, the control unit 127 transmits to the regeneration control unit 103 an instruction to decrease the effective regenerative braking torque FbE by the amount of increase in the friction braking torque FbF resulting from the execution of the switching process.

[0045] When the regenerative control unit 103 receives the above instruction, the regenerative control unit 103 decreases the regenerative braking torque command value FbEtr by the amount of increase in the friction braking torque FbF. Then, the regenerative control unit 103 operates the power unit 20 based on the regenerative braking torque command value FbEtr. This decreases the effective regenerative braking torque FbE by the amount of increase in the friction braking torque FbF. As a result, changes in the braking force BP due to the execution of the switching process are suppressed.

[0046] When the friction braking torque FbF is maintained, the control unit 127 ends the replacement process. After the replacement process is performed, the control unit 127 starts the reduction process when the stopping distance DS becomes equal to or less than the second threshold value DSth2. 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 127 transmits an instruction to the regenerative control unit 103 to reduce the effective regenerative braking torque FbE to 0 (zero). At this time, the control unit 127 may transmit an instruction to the regenerative control unit 103 to reduce the effective regenerative braking torque FbE at a predetermined reduction rate. The predetermined reduction rate is set so that the effective regenerative braking torque FbE becomes 0 (zero) before the vehicle speed VS becomes 0 (zero).

[0047] When the regenerative control unit 103 receives this instruction, the regenerative control unit 103 decreases the regenerative braking torque instruction value FbEtr toward 0 (zero). Then, the regenerative control unit 103 operates the power unit 20 based on the regenerative braking torque instruction value FbEtr.

[0048] The control unit 127 maintains the friction braking torque FbF during the reduction process. When the control unit 127 determines that the regenerative braking torque command value FbEtr has become 0 (zero), the control unit 127 terminates the reduction process. In the example shown in FIG. 2 , the regenerative braking torque command value FbEtr becomes 0 (zero) at timing t16.

[0049] After the reduction process is completed, the control unit 127 starts the retention process. In the retention process, the control unit 127 retains the target friction braking torque FbFtr. At this time, the control unit 127 also retains the effective regenerative braking torque FbE at 0 (zero).

[0050] If the control unit 127 determines that the vehicle 10 has stopped during the execution of the retention process, the control unit 127 transitions from the retention process to the degeneration process. For example, the control unit 127 determines that the vehicle 10 has stopped when the stopping distance DS is equal to or less than the 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 control unit 127 determines that the vehicle 10 has stopped at timing t17.

[0051] In the degeneration process, the control unit 127 increases the friction braking torque FbF. For example, the control unit 127 increases the friction braking torque FbF to the required braking torque FbRq. At this time, the control unit 127 increases the target friction braking torque FbFtr to the required braking torque FbRq. Then, the control unit 127 operates the brake actuator 50 based on the target friction braking torque FbFtr. When the friction braking torque FbF becomes equal to or greater than the required braking torque FbRq, the control unit 127 ends the degeneration process. Then, the control unit 127 ends the stationary braking control.

[0052] The control unit 127 executes axle torque control just before the vehicle 10 is stopped by the generation of braking force BP. When the driver of the vehicle 10 releases the accelerator pedal, the power unit 20 applies a negative drive torque as drive torque Fd to the axle 14 in accordance with an instruction from the drive control unit 101 in order to suppress an increase in the rotation speed of the output shaft of the power unit 20, as shown in (F) of FIG. 2. Then, when the rotation speed of the output shaft of the power unit 20 decreases as the vehicle speed VS decreases, the power unit 20 applies a positive drive torque as drive torque Fd to the axle 14 in accordance with an instruction from the drive control unit 101. The drive torque Fd at this time is a drive torque for suppressing the rotation speed of the output shaft of the power unit 20 from falling below a predetermined speed.

[0053] When the magnitude of the effective regenerative braking torque FbE is greater than the magnitude of the drive torque Fd, the axle torque TqS becomes negative, as shown in (G) of Figure 2. However, if the effective regenerative braking torque FbE 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 drive torque is applied to the axle 14 as the drive torque Fd, if the magnitude of the drive torque Fd becomes greater than the magnitude of the effective regenerative braking torque FbE, the axle torque TqS becomes positive. In other words, the sign of the axle torque TqS is reversed. As described above, if the sign of the axle torque TqS is reversed when the angular acceleration of the axle 14 is small, vehicle body vibration caused by the reversal of the direction of torsion of the axle 14 is unlikely to increase.

[0054] Therefore, in the axle torque control, the control unit 127 cooperates with the regenerative control unit 103 and the drive control unit 101 to reverse the sign of the axle torque TqS after it is determined that the angular acceleration of the axle 14 is equal to or less than the reference angular acceleration. In this embodiment, as shown in (F) and (G) of FIG. 2, the control unit 127 adjusts the drive torque Fd applied to the axle 14 from the power unit 20 in accordance with instructions from the drive control unit 101, thereby delaying the timing at which the sign of the axle torque TqS is reversed, compared to when the axle torque control is not executed. For example, the control unit 127 reverses the sign of the axle torque TqS when the braking force BP is smaller than half the required braking force BPRq at the start of the stationary braking control.

[0055] The axle torque control includes a first adjustment process, a second adjustment process, and a third adjustment process. The control unit 127 starts the first adjustment process of the axle torque control when a predetermined start condition is met. Examples of the predetermined start condition include a negative drive torque being applied to the axle 14 as the drive torque Fd and a time before the start of the switching process of the stationary braking control. In the example shown in FIG. 2 , the predetermined start condition is met at timing t12. In the first adjustment process, the control unit 127 instructs the drive control unit 101 to increase the drive torque Fd to 0 (zero).

[0056] When the drive control unit 101 receives this instruction, the drive control unit 101 changes the drive torque instruction value Fdtr to 0 (zero). Then, the drive control unit 101 operates the power unit 20 in accordance with this drive torque instruction value Fdtr.

[0057] When the drive torque command value Fdtr becomes 0 (zero) as a result of executing the first adjustment process, the control unit 127 shifts the process from the first adjustment process to the second adjustment process. In the example shown in Fig. 2, the drive torque command value Fdtr becomes 0 (zero) at timing t14. In the second adjustment process, the control unit 127 instructs the drive control unit 101 to maintain the drive torque command value Fdtr at 0 (zero).

[0058] When the drive control unit 101 receives this instruction, the drive control unit 101 holds the drive torque instruction value Fdtr at 0 (zero). Then, the drive control unit 101 operates the power unit 20 in accordance with this drive torque instruction value Fdtr.

[0059] When the effective regenerative braking torque FbE becomes 0 (zero), the axle torque TqS also becomes 0 (zero). When the axle torque TqS becomes 0 (zero) due to the decrease in the effective regenerative braking torque FbE in this way, the control unit 127 shifts the processing from the second adjustment processing to the third adjustment processing. In the example shown in FIG. 2 , the regenerative braking torque command value FbEtr becomes 0 (zero) at timing t16. In the third adjustment processing, the control unit 127 instructs the drive control unit 101 to increase the drive torque command value Fdtr from 0 (zero).

[0060] When the drive control unit 101 receives this instruction, the drive control unit 101 increases the drive torque instruction value Fdtr from 0 (zero). Then, the drive control unit 101 operates the power unit 20 in accordance with this drive torque instruction value Fdtr.

[0061] When the magnitude of the drive torque command value Fdtr reaches the target, the control unit 127 ends the third adjustment process. That is, the control unit 127 ends the axle torque control. <Smooth Stop Process> The smooth stop process will be described with reference to FIG. 3. The smooth stop process is a series of processes that cause the processing circuit 71 to execute stationary braking control when braking the vehicle. The processing circuit 71 repeatedly executes the smooth stop process at each predetermined control cycle.

[0062] In step S11, the processing circuit 71 functions as the stopping-related value acquisition unit 123 to acquire the stopping distance DS. In the following step S13, the processing circuit 71 determines whether or not a braking request is present. If the processing circuit 71 determines that a braking request is present (S13: YES), the processing circuit 71 proceeds to step S17. On the other hand, if the processing circuit 71 determines that a braking request is not present (S13: NO), the processing circuit 71 proceeds to step S15.

[0063] In step S15, the processing circuit 71 sets an end flag FLG2 (described later) to OFF. 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.

[0064] 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 127 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.

[0065] Specifically, in step S21, the processing circuit 71 determines whether the switching from regenerative braking torque to friction braking torque due to the execution of the switching process has been completed. 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.

[0066] (A1) The friction braking torque FbF becomes equal to the vehicle-stop maintaining braking torque Fbh as a result of the execution of the replacement process. (A2) The regenerative braking torque command value FbEtr decreases by the amount of the increase in the friction braking torque FbF resulting from the execution of the replacement process.

[0067] If the processing circuit 71 determines that the switching has not been completed (S21: NO), the processing circuit 71 proceeds to step S23. In step S23, the processing circuit 71 executes the switching process. Then, the processing circuit 71 temporarily ends the smooth stop process.

[0068] 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 proceeds to step S31. In step S31, the processing circuit 71 determines whether the stopping distance DS is equal to or less than the second threshold value DSth2. 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 effective regenerative braking torque FbE and the friction braking torque FbF. 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 proceeds to step S33.

[0069] In step S33, the processing circuit 71 determines whether the stopping distance DS is equal to or less than the third threshold value DSth3. 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.

[0070] In step S35, the processing circuit 71 determines whether the effective regenerative braking torque FbE is 0 (zero). If the processing circuit 71 determines that the effective regenerative braking torque FbE is not 0 (zero) (S35: NO), the processing circuit 71 proceeds to step S37. In step S37, the processing circuit 71 executes a reduction process. Then, the processing circuit 71 temporarily ends the smooth stop process.

[0071] On the other hand, if the processing circuit 71 determines in step S35 that the effective regenerative braking torque FbE is 0 (zero) (S35: YES), the processing circuit 71 proceeds to step S39. In step S39, the processing circuit 71 executes a holding process. Then, the processing circuit 71 temporarily ends the smooth stop process.

[0072] 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 FbF is equal to or greater than the required braking torque FbRq, the execution of the degeneration processing can be considered to be completed. On the other hand, if the friction braking torque FbF is less than the required braking torque FbRq, 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 proceeds to step S43. In step S43, the processing circuit 71 executes the degeneration processing. Then, the processing circuit 71 temporarily ends the smooth stop processing.

[0073] 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 proceeds to step S45. In step S45, the processing circuit 71 sets the end flag FLG2 to ON. 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.

[0074] <Vehicle body vibration reduction process> The vehicle body vibration reduction process will be described with reference to Fig. 4. The vehicle body vibration reduction process is a series of processes that the processing circuit 71 executes to control the axle torque during vehicle braking. The processing circuit 71 repeatedly executes the vehicle body vibration reduction process at each predetermined control cycle.

[0075] In step S61, the processing circuit 71 functions as the stopping-related value acquisition unit 123 to acquire the stopping distance DS. In the following step S63, the processing circuit 71 determines whether or not a braking request is present. If the processing circuit 71 determines that a braking request is present (S63: YES), the processing circuit 71 proceeds to step S67. On the other hand, if the processing circuit 71 determines that a braking request is not present (S63: NO), the processing circuit 71 proceeds to step S65.

[0076] In step S65, the processing circuit 71 sets an end flag FLG1 (described later) to OFF. Then, the processing circuit 71 temporarily ends the vehicle body vibration reduction process. In step S67, the processing circuit 71 determines whether the stopping distance DS is equal to or less than a start threshold value DSth0. The start threshold value DSth0 is a criterion for determining whether to start axle torque control. For example, the start threshold value DSth0 is set to a value greater than the first threshold value DSth1. If the stopping distance DS is greater than the start threshold value DSth0 (S67: NO), the processing circuit 71 proceeds to step S65. On the other hand, if the stopping distance DS is equal to or less than the start threshold value DSth0 (S67: YES), the processing circuit 71 proceeds to step S69.

[0077] In step S69, the processing circuit 71 determines whether the end flag FLG1 is set to OFF. If the end flag FLG1 is set to ON, it is considered that the execution of the axle torque control during the current vehicle braking has been completed. On the other hand, if the end flag FLG1 is set to OFF, it is considered that the execution of the axle torque control has not yet been completed. If the end flag FLG1 is set to ON (S69: NO), the processing circuit 71 temporarily terminates the vehicle body vibration reduction process. On the other hand, if the end flag FLG1 is set to OFF (S69: YES), the processing circuit 71 proceeds to step S71.

[0078] In step S71, the processing circuit 71 determines whether the drive torque Fd is negative. If the drive torque Fd is negative (S71: YES), the processing circuit 71 proceeds to step S73. In step S73, the processing circuit 71 functions as the control unit 127 to perform a first adjustment process for axle torque control. The processing circuit 71 then temporarily terminates the vehicle body vibration reduction process.

[0079] On the other hand, if the driving torque Fd is not negative (S71: NO), the processing circuit 71 proceeds to step S75. That is, if the driving torque Fd is equal to or greater than 0 (zero), the processing circuit 71 proceeds to step S75.

[0080] In step S75, the processing circuit 71 determines whether the absolute value |DVW| of the wheel acceleration DVW is equal to or less than the reference wheel acceleration DVWth by functioning as the determination unit 125. If the absolute value |DVW| is greater than the reference wheel acceleration DVWth (S75: NO), the processing circuit 71 proceeds to step S77.

[0081] In step S77, the processing circuit 71 executes the second adjustment process for the axle torque control by functioning as the control unit 127. Then, the processing circuit 71 temporarily ends the vehicle body vibration reduction process.

[0082] In step S75, if the absolute value |DVW| is equal to or less than the determination wheel acceleration DVWth (S75: YES), the processing circuit 71 proceeds to step S79. In step S79, the processing circuit 71 determines whether the effective regenerative braking torque FbE is 0 (zero). If the processing circuit 71 determines that the effective regenerative braking torque FbE is greater than 0 (zero) (S79: NO), the processing circuit 71 proceeds to step S77. In this case, the processing circuit 71 continues the second adjustment process, thereby maintaining the state in which the driving torque command value Fdtr is 0 (zero). On the other hand, if the processing circuit 71 determines that the effective regenerative braking torque FbE is 0 (zero) (S79: YES), the processing circuit 71 proceeds to step S81.

[0083] In step S81, the processing circuit 71 functions as the control unit 127 to perform a third adjustment process for axle torque control. In the following step S83, the processing circuit 71 determines whether the drive torque Fd is equal to or greater than the target drive torque Fdth. The target drive torque Fdth is the target value of the drive torque Fd when the vehicle is stopped. If the processing circuit 71 determines that the drive torque Fd is less than the target drive torque Fdth (S83: NO), the processing circuit 71 temporarily terminates the vehicle body vibration reduction process. On the other hand, if the processing circuit 71 determines that the drive torque Fd is equal to or greater than the target drive torque Fdth (S83: YES), the processing circuit 71 proceeds to step S85. In step S85, the processing circuit 71 sets the end flag FLG1 to ON. Then, the processing circuit 71 terminates the axle torque control. That is, the end flag FLG1 is a flag that is set to ON when the execution of the axle torque control for the current braking operation has been completed. Thereafter, the processing circuit 71 temporarily terminates the vehicle body vibration reduction processing.

[0084] <Functions and Effects of the Present Embodiment> The functions and effects of stopping the vehicle 10 by generating a braking force BP will be described with reference to Figure 2. The dashed line in Figure 2(B) shows the transition of vehicle body acceleration when it is assumed that the driving torque Fd is maintained at 0 (zero) during vehicle braking. The dashed line in Figure 2(F) shows the transition of the driving torque Fd when axle torque control is not performed.

[0085] In the example shown in Figure 2, the vehicle 10 is traveling with the accelerator pedal not being operated. Therefore, as shown in Figure 2 (F), a negative drive torque is applied to the axle 14 as the drive torque Fd. At timing t11 in this state, a braking request is generated, for example, when the driver begins a braking operation. Then, the processing circuit 71 of the brake control device 70 increases the required braking force BPRq as shown in Figure 2 (A). In other words, the processing circuit 71 increases the required braking torque FbRq.

[0086] The processing circuit 71 instructs the drive control device 30 to increase the effective regenerative braking torque FbE in accordance with the increase in the required braking torque FbRq. The processing circuit 31 of the drive control device 30 functions as the regenerative control unit 103, thereby increasing the regenerative braking torque command value FbEtr as shown in FIG. 2(D). Furthermore, the processing circuit 31 functions as the drive control unit 101, thereby deriving a negative drive torque as the drive torque command value Fdtr as shown in FIG. 2(F). The processing circuit 31 then operates the power unit 20 based on the regenerative braking torque command value FbEtr and the drive torque command value Fdtr. This applies an axle torque TqS corresponding to the regenerative braking torque command value FbEtr and the drive torque command value Fdtr to the axle 14. As a result, the vehicle acceleration DVS changes as shown by the solid line in FIG. 2(B).

[0087] During the period from timing t11 to timing t13, the regenerative braking torque command value FbEtr is equal to the required braking torque FbRq. Therefore, as shown in FIG. 2E, the processing circuit 71 of the braking control device 70 derives 0 (zero) as the target friction braking torque FbFtr. As a result, the friction braking torque FbF is not applied to the wheels 13.

[0088] 2C, when the vehicle 10 is decelerating due to the application of braking force BP to the vehicle 10, the stopping distance DS becomes equal to or less than the start threshold DSth0 at timing t12, and the axle torque control start condition is met. Then, the processing circuit 71 functions as the control unit 127 to execute a first adjustment process for the axle torque control. In the first adjustment process, the processing circuit 71 instructs the drive control device 30 to increase the drive torque Fd to 0 (zero).

[0089] As shown by the solid line in (F) of Figure 2, the processing circuit 31 of the drive control device 30 functions as the drive control section 101 to change the drive torque command value Fdtr to 0 (zero). As a result, although the axle torque TqS is a negative torque, the absolute value of the axle torque TqS becomes smaller. In other words, the axle torque TqS approaches 0 (zero).

[0090] At timing t13, while the drive torque command value Fdtr is changing due to the execution of the first adjustment process, the stopping distance DS becomes equal to or less than the first threshold value DSth1. Then, the processing circuit 71 of the brake control device 70 functions as the control unit 127 to start stationary braking control. Specifically, the processing circuit 71 executes a switching process for the stationary braking control. In the switching process, the processing circuit 71 increases the target frictional braking torque FbFtr to the stationary holding braking torque Fbh. At this time, the processing circuit 71 instructs the processing circuit 31 of the drive control device 30 to reduce the effective regenerative braking torque FbE by the increase in the target frictional braking torque FbFtr.

[0091] Then, the processing circuit 31 functions as the regenerative control unit 103 to decrease the regenerative braking torque command value FbEtr by the amount of increase in the target friction braking torque FbFtr. As a result, the axle torque TqS approaches 0 (zero) in response to the decrease in the regenerative braking torque command value FbEtr.

[0092] At timing t14, immediately after the switching process is performed, the drive torque command value Fdtr becomes 0 (zero). Then, the processing circuit 71 of the braking control device 70 functions as the control unit 127, and shifts the axle torque control process from the first adjustment process to the second adjustment process. In the second adjustment process, the processing circuit 71 instructs the drive control device 30 to maintain the drive torque command value Fdtr at 0 (zero).

[0093] The processing circuit 31 of the drive control device 30 functions as the drive control section 101, thereby holding the drive torque command value Fdtr at 0 (zero). From timing t14 to timing t15, both the drive torque command value Fdtr and the regenerative braking torque command value FbEtr are held. Therefore, the axle torque TqS is also held.

[0094] At timing t15 while the second adjustment process is being performed, the stopping distance DS becomes equal to or less than the second threshold value DSth2. Therefore, the processing circuit 71 of the braking control device 70 functions as the control unit 127 to start a reduction process of the stationary braking control. In the reduction process, the processing circuit 71 instructs the drive control device 30 to reduce the effective regenerative braking torque FbE to 0 (zero).

[0095] 2D, the processing circuit 31 of the drive control device 30 functions as the regenerative control unit 103 to reduce the regenerative braking torque command value FbEtr to 0 (zero). As the regenerative braking torque command value FbEtr is reduced, the axle torque TqS approaches 0 (zero). Then, at timing t16 when the regenerative braking torque command value FbEtr reaches 0 (zero), the axle torque TqS also reaches 0 (zero).

[0096] When the regenerative braking torque command value FbEtr becomes 0 (zero), it can be determined that the effective regenerative braking torque FbE has also become 0 (zero). Although not shown in FIG. 2 , at timing t16, the absolute value of the wheel acceleration |DVW| becomes equal to or less than the reference wheel acceleration DVWth. In other words, the processing circuit 71 of the braking control device 70 can determine that the angular acceleration of the axle 14 is equal to or less than the reference angular acceleration. Therefore, the processing circuit 71 functions as the control unit 127, thereby shifting the axle torque control process from the second adjustment process to the third adjustment process. In the third adjustment process, the processing circuit 71 instructs the drive control device 30 to increase the drive torque Fd from 0 (zero).

[0097] The processing circuit 31 of the drive control device 30 functions as the drive control section 101 to increase the drive torque command value Fdtr from 0 (zero). As a result, the axle torque TqS increases from 0 (zero). In other words, the axle torque TqS becomes positive. Therefore, it can be said that timing t16 is the timing when the axle torque TqS reverses its positive and negative sign.

[0098] Now, consider a comparative example in which axle torque control is not performed. In this comparative example, the drive torque command value Fdtr changes as shown by the dashed line in (F) of FIG. 2. That is, there is no period during which the drive torque command value Fdtr is held at 0 (zero). Therefore, the axle torque TqS becomes 0 (zero) earlier than in the present embodiment. As a result, the sign of the axle torque TqS is reversed when the absolute value of the angular acceleration of the axle 14 is relatively large.

[0099] In contrast, in this embodiment, the axle torque TqS reverses sign after the absolute value of the angular acceleration of the axle 14 becomes relatively small compared to the comparative example. As a result, the magnitude of vehicle body vibration caused by the reversal of the torsional direction of the axle 14 is reduced compared to the comparative example. Therefore, the brake control device 70 can suppress the occurrence of vehicle body vibration caused by the reversal of the torsional direction of the axle 14 when the vehicle 10 is stopped by the generation of the braking force BP.

[0100] At a subsequent timing t18, the drive torque command value Fdtr reaches the target drive torque Fdth. Therefore, the processing circuit 71 of the brake control device 70 ends the axle torque control. Regarding the stationary braking control, since it can be determined at timing t16 that the effective regenerative braking torque FbE has become 0 (zero), the processing circuit 71 functions as the control unit 127 and shifts the stationary braking control processing from the reduction processing to the holding processing. In the holding processing, the processing circuit 71 maintains both that the friction braking torque FbF is equal to the stationary holding braking torque Fbh and that the effective regenerative braking torque FbE is 0 (zero).

[0101] Then, when it is determined at timing t17 that the vehicle 10 has stopped, the processing circuit 71 transitions the processing of the stationary braking control from the holding processing to the degeneration processing. In the degeneration processing, the processing circuit 71 increases the target frictional braking torque FbFtr to the required braking torque FbRq. The processing circuit 71 operates the brake actuator 50 based on the target frictional braking torque FbFtr. As a result, the frictional braking torque FbF increases to the required braking torque FbRq. Thereafter, the processing circuit 71 terminates the stationary braking control.

[0102] The present embodiment can further provide the following advantages. (1) The processing circuit 71 of the brake control device 70 executes axle torque control while executing stationary braking control. As a result, the brake control device 70 can suppress the occurrence of vehicle body vibration caused by reversing the direction of torsion of the axle 14 while suppressing the occurrence of vehicle body sway back when the vehicle is stopped by executing stationary 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 generating the braking force BP.

[0103] (2) The processing circuit 71 of the brake control device 70 reverses the sign of the axle torque TqS when the braking force BP is smaller than half the required braking force BPRq at the start of the vehicle-stop braking control. A small braking force BP means that the absolute value of the angular acceleration of the axle 14 is small. Therefore, the brake control device 70 can reverse the sign of the axle torque TqS after making the absolute value of the angular acceleration of the axle 14 sufficiently small.

[0104] (3) During vehicle-stop braking control, the processing circuit 71 of the brake control device 70 reduces the effective regenerative braking torque FbE to 0 (zero) when a frictional braking force equal to or greater than the vehicle-stop maintaining braking force BPh is generated in the vehicle 10. As a result, the brake control device 70 can stop the vehicle 10 by the frictional braking force even when the effective regenerative braking torque FbE becomes 0 (zero).

[0105] (4) When the friction braking torque FbF applied to the wheel 13 is large, the axle 14 is likely to twist more strongly relative to the wheel 13. Such large torsion is likely to cause vehicle body vibration when the axle torque TqS reverses sign. In this regard, the processing circuit 71 of the brake control device 70 reduces the effective regenerative braking torque FbE to 0 (zero) while maintaining the friction braking torque FbF at the vehicle stop-maintaining braking torque Fbh during vehicle stop control. The vehicle stop-maintaining braking torque Fbh is the minimum braking torque capable of maintaining the vehicle stop, or a torque equivalent to this braking torque. Therefore, the brake control device 70 can stop the vehicle 10 by applying the friction braking torque FbF to the wheel 13 while suppressing vehicle body vibration when the axle torque TqS reverses sign.

[0106] <Modifications> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0107] In the axle torque control, the brake control device 70 may delay the timing at which the axle torque TqS is reversed in sign by changing the manner in which the effective regenerative braking torque FbE is changed.

[0108] The slower the rate of increase of the axle torque TqS when the axle torque TqS reverses sign, the smaller the vehicle body vibration caused by the reversal of the torsional direction of the axle 14. The rate of increase of the axle torque TqS is an example of the "rate of change of the axle torque TqS." Therefore, as shown in FIG. 5, for example, in the axle torque control, the processing circuit 71 of the braking control device 70 may reduce the rate of decrease of the regenerative braking torque command value FbEtr when the axle torque TqS approaches zero (0), thereby reducing the rate of increase of the axle torque TqS. This allows the braking control device 70 to further reduce vehicle body vibration caused by the reversal of the torsional direction of the axle 14.

[0109] The processing circuit 71 of the brake control device 70 may increase the frictional braking torque FbF to a braking torque greater than the vehicle-stop maintaining braking torque Fbh during the replacement process of the stationary braking control. Even in this case, the processing circuit 71 can suppress changes in the braking force BP due to the replacement process by reducing the effective regenerative braking torque FbE by the amount of increase in the frictional braking torque FbF.

[0110] The braking control during a stop does not have to include the switching process. In this case, the processing circuit 71 of the brake control device 70 may increase the friction braking torque FbF at the timing when it is determined that the vehicle 10 has stopped.

[0111] The vehicle-stop braking control does not need to include degeneration processing as long as the vehicle 10 can be kept stopped. The processing circuit 71 of the brake control device 70 does not need to increase the friction braking torque FbF to the required braking torque FbRq in the degeneration processing of the vehicle-stop braking control as long as the vehicle 10 can be kept stopped.

[0112] In the axle torque control, the processing circuit 71 of the brake control device 70 may start increasing the axle torque TqS from 0 (zero) while the holding process of the vehicle-stop braking control is being executed.

[0113] The processing circuit 71 of the brake control device 70 may reverse the sign of the axle torque TqS when the effective regenerative braking torque FbE is reduced by the reduction process of the vehicle-stop braking control during the axle torque control. In this case, the processing circuit 71 may reverse the sign of the axle torque TqS when the braking force BP is greater than half the required braking force BPRq.

[0114] The vehicle body acceleration DVS is correlated with the wheel acceleration DVW. Therefore, the processing circuit 71 of the brake control device 70 may use the vehicle body acceleration DVS to determine whether the absolute value of the angular acceleration of the axle 14 is equal to or less than the reference angular acceleration.

[0115] When the process of the stationary braking control shifts to the holding process, the processing circuit 71 of the brake control device 70 may determine that the absolute value of the angular acceleration of the axle 14 has become equal to or less than the reference angular acceleration.

[0116] The processing circuit 71 of the braking control device 70 may use the stopping distance DS to determine that the absolute value of the angular acceleration of the axle 14 has become equal to or less than the reference angular acceleration. The processing circuit 71 of the braking control device 70 may acquire the vehicle speed VS as the stopping-related value instead of the stopping distance DS.

[0117] In the above embodiment, the axle torque control is executed on the condition that the vehicle-stop braking control is executed. However, the processing circuit 71 of the brake control device 70 may execute the axle torque control even when the vehicle-stop braking control is not executed. For example, the processing circuit 71 may reverse the sign of the axle torque TqS after the absolute value of the angular acceleration of the axle 14 becomes equal to or less than the reference angular acceleration due to the driver's braking operation.

[0118] The processing circuit 71 of the braking control device 70 may be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware that executes at least some of the various processes, or a combination thereof. Dedicated hardware can include, for example, an application-specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0119] <Other Technical Ideas> The following describes technical ideas that can be understood from the above-described embodiment and modified examples. [Supplementary Note 1] In the vehicle-stop braking control, it is preferable that the control unit controls the friction control unit so that the vehicle stops in a state where the friction braking force generated in the vehicle by operation of the friction braking unit is maintained at the vehicle-stop maintaining braking force.

[0120] It should be noted that the expression "at least one" used in this specification means "one or more" of the desired options. As an example, the expression "at least one" used in this specification means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

Claims

1. A vehicle control device applied to a vehicle equipped with a power unit configured to be able to apply regenerative braking torque and driving torque to an axle that rotates integrally with a wheel, a regenerative control unit that controls the power unit based on a regenerative braking torque command value that is a command value for the regenerative braking torque, and a driving control unit that controls the power unit based on a driving torque command value that is a command value for the driving torque, wherein the torque generated at the axle by applying the regenerative braking torque and the driving torque is axle torque, a determination unit that determines whether the absolute value of the angular acceleration of the axle is equal to or less than a determined angular acceleration, and a control unit that executes axle torque control in cooperation with the regenerative control unit and the driving control unit so that, when the vehicle is stopped due to the generation of a braking force, the positive and negative signs of the axle torque are reversed after the absolute value of the angular acceleration of the axle is determined to be equal to or less than the determined angular acceleration.

2. A vehicle control device as described in claim 1, wherein the vehicle is equipped with a friction braking unit that applies friction braking torque to the vehicle, the braking force being a braking force generated in the vehicle based on the friction braking torque and the regenerative braking torque, and a stopping-related value acquisition unit that acquires a stopping-related value that decreases as the vehicle approaches a predetermined stopping position, and the control unit, when the stopping-related value is equal to or less than a predetermined threshold, executes stopping-time braking control to stop the vehicle with the braking force smaller than a required braking force, which is a required value for the braking force, and in the axle torque control, reverses the sign of the axle torque after the absolute value of the angular acceleration of the axle is determined to be equal to or less than the determined angular acceleration and when the braking force is smaller than the required braking force due to the execution of the stopping-time braking control.

3. A vehicle control device as described in claim 2, wherein the control unit controls the friction braking unit during the stop-time braking control so that the vehicle stops when a friction braking force equal to or greater than a stop-maintaining braking force, which is the braking force capable of maintaining the vehicle at a stop on the road surface on which the vehicle is traveling, is generated in the vehicle by the operation of the friction braking unit.

4. A vehicle control device according to claim 1 or claim 2, wherein the control unit, in the axle torque control, reduces the rate of change of the axle torque at the point when the axle torque becomes 0 (zero) compared to before that point.

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