Vehicle control device

Abstract

To quickly start up a regenerative torque of a travel motor.SOLUTION: A vehicle control device has a first travel motor which is connected to a first wheel positioned on the front side in a travel direction, a second travel motor which is connected to a second wheel positioned on the rear side in the travel direction, and a control system for controlling the first travel motor and the second travel motor. When a distance to a collision prediction location or a collision object during traveling is less than a brake prediction threshold, the control system decreases a power running torque of the first travel motor and increases the power running torque of the second travel motor. When the distance to the collision object during traveling is less than a brake determined threshold smaller than the brake prediction threshold, the control system increases a regenerative torque of the first travel motor, and increases a regenerative torque of the second travel motor.SELECTED DRAWING: Figure 10

Description

[Technical Field]

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

[0002] Vehicles such as electric vehicles are provided with a traction motor connected to the wheels (see Patent Documents 1 and 2). Furthermore, electric vehicles and other vehicles that automatically activate the brakes based on collision predictions have also been developed (see Patent Document 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-89044 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-210798 [Patent Document 3] Japanese Patent Publication No. 2020-77266 Summary of the Invention [Problem to be solved by the invention]

[0004] In vehicles such as electric vehicles, the traction motor is often controlled from a powering state to a regenerative state when the automatic brake is activated. When controlling the traction motor from a powering state to a regenerative state, there is a risk of shock occurring when switching the direction of motor torque generation. Therefore, it is necessary to change the motor torque gradually, but this gradual torque change causes a delay in the rise of regenerative torque. Furthermore, because a delayed rise in the regenerative torque of the traction motor causes a decrease in the braking performance of the automatic brake, it is necessary to quickly raise the regenerative torque of the traction motor.

[0005] An object of the present invention is to quickly raise the regenerative torque of the traction motor. [Means for solving the problem]

[0006] One embodiment of a vehicle control device is a vehicle control device installed in a vehicle, and includes a first traction motor connected to a first wheel located at the front in the direction of travel, a second traction motor connected to a second wheel located at the rear in the direction of travel, and a control system having a processor and memory communicatively connected to each other, and controlling the first traction motor and the second traction motor, wherein the control system reduces the traction torque of the first traction motor and increases the traction torque of the second traction motor when the distance to the predicted collision point or collision object falls below a braking prediction threshold while driving, and the control system increases the regenerative torque of the first traction motor and increases the regenerative torque of the second traction motor when the distance to the collision object falls below a braking confirmation threshold which is smaller than the braking prediction threshold while driving. [Effects of the Invention]

[0007] In one embodiment, when the distance to the predicted collision point or the distance to the collision object falls below a braking prediction threshold while the vehicle is traveling, the vehicle control device reduces the traction torque of the first traction motor and increases the traction torque of the second traction motor, thereby enabling the regenerative torque of the first traction motor to be quickly increased. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing an example of the configuration of a vehicle provided with a vehicle control device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram showing an example of a front drive unit, a rear drive unit, and a control system. [Figure 3] FIG. 2 is a diagram simply illustrating the basic structure of each control unit. [Figure 4] FIG. 4 is a diagram showing an example of a driving force map showing a required driving force. [Figure 5] FIG. 10 is a diagram showing changes in the required driving force and motor torque when the accelerator operation is released. [Figure 6] FIG. 10 is a diagram illustrating an example of an execution status of zero-cross control. [Figure 7] FIG. 10 is a diagram illustrating an example of a driving situation in which a braking prediction flag and a braking determination flag are set. [Figure 8] FIG. 10 is a diagram illustrating an example of a driving situation in which a braking prediction flag and a braking determination flag are set. [Figure 9] 10 is a flowchart showing an example of a procedure for executing pre-torque increase / decrease control executed during forward traveling. [Figure 10] 6 is a timing chart showing an example of an execution state of pre-torque increase / decrease control. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. In the following description, identical or substantially identical configurations and elements are designated by the same reference numerals and will not be described repeatedly.

[0010] [Vehicle configuration] FIG. 1 is a diagram showing an example of the configuration of a vehicle 11 equipped with a vehicle control device 10 according to one embodiment of the present invention. As shown in FIG. 1, the vehicle 11 is provided with a front drive unit 13 that drives front wheels 12, and a rear drive unit 15 that drives rear wheels 14. A front motor 16 and a front differential 17 are incorporated into the front drive unit 13. A rear motor 18 and a rear differential 19 are incorporated into the rear drive unit 15. In this way, the front motor (first traction motor) 16 is connected to the front wheels (first wheels) 12, and the rear motor (second traction motor) 18 is connected to the rear wheels (second wheels) 14.

[0011] FIG. 2 is a diagram illustrating an example of the front drive unit 13, the rear drive unit 15, and the control system 20. As shown in FIG. 2, the front drive unit 13 has a front motor 16 and a front differential 17. A drive gear 21 is connected to a rotor 16r of the front motor 16, and a driven gear 22 fixed to the front differential 17 is meshed with the drive gear 21. The front wheels 12 are connected to an axle 23 extending from the front differential 17. Similarly, the rear drive unit 15 has a rear motor 18 and a rear differential 19. A drive gear 24 is connected to a rotor 18r of the rear motor 18, and a driven gear 25 fixed to the rear differential 19 is meshed with the drive gear 24. The rear wheels 14 are connected to an axle 26 extending from the rear differential 19.

[0012] An inverter 30 is connected to the stator 16s of the front motor 16, and a battery pack 31 is connected to the inverter 30. Similarly, an inverter 32 is connected to the stator 18s of the rear motor 18, and the inverter 32 is connected to the battery pack 31. The battery pack 31 is provided with a battery module 33 made up of a plurality of battery cells, and a battery control unit 34 that monitors the charging and discharging of the battery module 33. Furthermore, the battery pack 31 is provided with a battery sensor 35 that detects charging and discharging current, terminal voltage, etc. The battery control unit 34 has a function of calculating a state of charge (SOC) of the battery module 33 based on the charging and discharging current, terminal voltage, etc. detected by the battery sensor 35.

[0013] A front motor control unit 40 is connected to the inverter 30 of the front motor 16. The front motor control unit 40 controls the inverter 30, which is made up of a plurality of switching elements and the like, to control the energization state of the stator 16s and thereby control the motor torque (powering torque, regenerative torque) of the front motor 16. When the front motor 16 is controlled to be in a powering state, power is supplied from the battery module 33 to the stator 16s via the inverter 30. On the other hand, when the front motor 16 is controlled to be in a regenerative state, i.e., a power generating state, power is supplied from the stator 16s to the battery module 33 via the inverter 30.

[0014] Similarly, a rear motor control unit 41 is connected to the inverter 32 of the rear motor 18. The rear motor control unit 41 controls the inverter 32, which is made up of a plurality of switching elements and the like, to control the energization state of the stator 18s and thereby control the motor torque (powering torque, regenerative torque) of the rear motor 18. When the rear motor 18 is controlled to be in a powering state, power is supplied from the battery module 33 to the stator 18s via the inverter 32. On the other hand, when the rear motor 18 is controlled to be in a regenerative state, i.e., a power generating state, power is supplied from the stator 18s to the battery module 33 via the inverter 32.

[0015] The vehicle 11 is provided with a brake device 42 that brakes the front and rear wheels 12, 14. The brake device 42 includes a master cylinder 44 that outputs brake fluid pressure in conjunction with a brake pedal 43, and calipers 46 that brake disc rotors 45 of the front and rear wheels 12, 14. A brake actuator 47 that controls the brake fluid pressure supplied to each caliper 46 is provided between the master cylinder 44 and the caliper 46. The brake actuator 47 is composed of an electric pump, an accumulator, an electromagnetic valve, and the like, all of which are not shown. A brake control unit 48 that controls the brake actuator 47 is connected to the brake actuator 47.

[0016] The vehicle 11 is provided with a front camera 50 that captures images in front of the vehicle and a front radar 51 that detects the distance to an obstacle located in front of the vehicle. The vehicle 11 is also provided with a rear camera 52 that captures images behind the vehicle and a rear radar 53 that detects the distance to an obstacle located behind the vehicle. A driving assistance control unit 54 that executes automatic brake control is connected to these cameras 50, 52 and radars 51, 53. The driving assistance control unit 54 determines whether the vehicle 11 traveling forward is at risk of colliding with a collision object such as another vehicle, based on image data from the front camera 50 and distance data from the front radar 51. Similarly, the driving assistance control unit 54 determines whether the vehicle 11 traveling backward is at risk of colliding with a collision object such as another vehicle, based on image data from the rear camera 52 and distance data from the rear radar 53. When the driving assistance control unit 54 determines that there is a risk of a vehicle collision, it executes automatic brake control, thereby activating the brake device 42 via the brake control unit 48 and causing the front motor 16 and the rear motor 18 to regenerate energy via the motor control units 40, 41. In this way, in the automatic brake control, the front and rear wheels 12, 14 are braked not only by the braking force of the brake device 42, but also by the regenerative torque of the front motor 16 and the rear motor 18.

[0017] The vehicle 11 is equipped with a navigation system 60 that provides route guidance to a destination. The navigation system 60 includes a navigation control unit 61 that provides route guidance, a memory unit 62 that stores map data, and a communication unit 63 that receives map update data from an external server or the like. The memory unit 62 of the navigation system 60 also stores, as one piece of data that makes up the map data, predicted collision points such as intersections where accidents are likely to occur, i.e., predicted collision points where automatic braking control is likely to be executed. In the illustrated example, a fixed navigation system 60 installed in the vehicle 11 is used, but the present invention is not limited to this, and a portable information terminal such as a smartphone may also be used as the navigation system.

[0018] [Control System] The vehicle control device 10 is provided with a control system 20 consisting of multiple electronic control units to control the front drive unit 13, rear drive unit 15, etc. The electronic control units that make up the control system 20 include the battery control unit 34, front motor control unit 40, rear motor control unit 41, brake control unit 48, driving assistance control unit 54, and navigation control unit 61. Another electronic control unit that makes up the control system 20 is a vehicle control unit 65 that outputs control signals to the control units 34, 40, 41, 48, 54, and 61. These control units 34, 40, 41, 48, 54, 61, and 65 are connected to each other so as to be able to communicate with each other via an in-vehicle network 66 such as CAN or LIN. The vehicle control unit 65 sets operation targets for the front motor 16, rear motor 18, etc. based on input data from the various control units 34, 40, 41, 48, 54, and 61 and various sensors (described later). Then, the control circuit generates control signals according to the operation targets of the front motor 16, the rear motor 18, etc., and outputs these control signals to the various control units 34, 40, 41, 48, 54, and 61.

[0019] Sensors connected to the vehicle control unit 65 include an accelerator sensor 70 that detects the amount of accelerator pedal operation (hereinafter referred to as accelerator opening) and a brake sensor 71 that detects the amount of brake pedal operation 43. Sensors connected to the vehicle control unit 65 also include a vehicle speed sensor 72 that detects the vehicle speed, which is the traveling speed of the vehicle 11, and a GPS sensor 73 that receives signals from GPS (Global Positioning System) satellites to detect the traveling position. Sensors connected to the front motor control unit 40 also include a motor rotation sensor 74, such as a resolver, that detects the rotation speed of the front motor 16, and sensors connected to the rear motor control unit 41 include a motor rotation sensor 75, such as a resolver, that detects the rotation speed of the rear motor 18. A start switch 76 that is operated by the driver when starting up the control system 20 is connected to the vehicle control unit 65.

[0020] FIG. 3 is a simplified diagram illustrating the basic structure of each of the control units 34, 40, 41, 48, 54, 61, and 65. As shown in FIG. 3, each of the control units 34, 40, 41, 48, 54, 61, and 65 has a microcontroller 82 incorporating a processor 80, a memory 81, and the like. A predetermined program is stored in the memory 81, and the processor 80 executes an instruction set of the program. The processor 80 and the memory 81 are connected to each other so that they can communicate with each other. In the illustrated example, the microcontroller 82 incorporates one processor 80 and one memory 81, but this is not a limitation. The microcontroller 82 may incorporate multiple processors 80, and the microcontroller 82 may incorporate multiple memories 81.

[0021] Each control unit 34, 40, 41, 48, 54, 61, 65 is also provided with an input conversion circuit 83, a drive circuit 84, a communication circuit 85, an external memory 86, a power supply circuit 87, and the like. The input conversion circuit 83 converts signals input from various sensors into signals that can be input to the microcontroller 82. The drive circuit 84 generates drive signals for actuators such as the front motor 16 and the rear motor 18 based on signals output from the microcontroller 82. The communication circuit 85 converts signals output from the microcontroller 82 into communication signals for other control units. The communication circuit 85 also converts communication signals received from other control units into signals that can be input to the microcontroller 82. The power supply circuit 87 supplies a stable power supply voltage to the microcontroller 82, the input conversion circuit 83, the drive circuit 84, the communication circuit 85, the external memory 86, and the like. The external memory 86, such as a nonvolatile memory, stores data that should be retained even when power is off.

[0022] [Required driving force] Fig. 4 is a diagram showing an example of a driving force map showing the required driving force. As shown in Fig. 4, the driving force map has characteristic lines L1 to L4 set to indicate the required driving force for each accelerator opening Acp. That is, when the accelerator opening Acp is 0%, the vehicle control unit 65 sets the required driving force for the vehicle 11 along characteristic line L1, and when the accelerator opening Acp is 25%, the vehicle control unit 65 sets the required driving force for the vehicle 11 along characteristic line L2. When the accelerator opening Acp is 50%, the vehicle control unit 65 sets the required driving force for the vehicle 11 along characteristic line L3, and when the accelerator opening Acp is 100%, the vehicle control unit 65 sets the required driving force for the vehicle 11 along characteristic line L4.

[0023] For example, when the vehicle speed is "V1" and the accelerator pedal is depressed so that the accelerator opening Acp is "50%," the vehicle control unit 65 sets "Fa" as the required driving force. Also, when the vehicle speed is "V1" and the accelerator pedal is released so that the accelerator opening Acp is "0%," the vehicle control unit 65 sets "Fb" as the required driving force. The vehicle control unit 65 then sets the target motor torque of the front motor 16 and the rear motor 18 so that the required driving force, i.e., the total driving force of the wheels 12, 14, is "Fa" or "Fb."

[0024] That is, when the accelerator pedal is depressed and the required driving force is set to the acceleration side, the target motor torque of the front motor 16 and the rear motor 18 is set to the powering side. On the other hand, when the accelerator pedal is released and the required driving force is set to the deceleration side, i.e., the braking side, the target motor torque of the front motor 16 and the rear motor 18 is set to the regeneration side. Note that, for ease of explanation, four characteristic lines L1 to L4 are set in the driving force map shown in Figure 4, but this is not limited to this, and it goes without saying that five or more characteristic lines may be set in the driving force map.

[0025] [Zero cross control] Figure 5 is a diagram showing the transition of the required driving force and motor torque when the accelerator operation is released. Note that the example shown in Figure 5 illustrates an example in which both the front motor 16 and the rear motor 18 are controlled based on a common target motor torque Tmt. Furthermore, in the example shown in Figure 5, the motor torque actually output from the front motor 16 and the motor torque actually output from the rear motor 18 are indicated by the common symbol "MT."

[0026] As shown in Fig. 4, when the driver depresses the accelerator pedal, the required driving force for the vehicle 11 is set to the acceleration side. On the other hand, when the driver releases the accelerator pedal, the required driving force for the vehicle 11 is set to the deceleration side. Therefore, as shown at time t1a in Fig. 5, when the accelerator pedal is released while the vehicle is traveling and the accelerator opening Acp decreases toward "0%" (symbol a1), the required driving force Rdf for the vehicle 11 is switched from the acceleration side to the deceleration side (symbol b1), and the target motor torque Tmt of the front motor 16 and the rear motor 18 is switched from the power running side to the regeneration side (symbol c1).

[0027] When the motor torque MT of the front motor 16 and the rear motor 18 switches from the power running side to the regenerative side, the meshing tooth surfaces of the various gear trains connected to the front motor 16 and the rear motor 18 switch, which could cause a shock when the motor torque MT passes through zero. Therefore, in order to suppress the shock when the motor torque MT passes through zero, the front motor control unit 40 and the rear motor control unit 41 execute zero-crossing control to slow down the rate of change of the motor torque MT when the motor torque MT passes through a predetermined deceleration range that includes zero. This allows the motor torque TM to change gradually, as shown by the symbol α in FIG. 5, and suppresses the shock when the motor torque MT passes through zero.

[0028] FIG. 6 is a diagram showing an example of the execution status of zero-cross control. As shown by the solid line in FIG. 6, a case will be described in which the accelerator pedal is released while the vehicle is running, and the motor torque MT is changed from "T1" to "-T2." When the accelerator pedal is released as shown at time t1b, the rate of change Smt of the motor torque MT is set to "-S1" (symbol a1), and the motor torque MT on the powering side begins to be controlled toward zero (symbol b1). Then, as shown at time t2b, when the motor torque MT reaches a deceleration range β that includes zero (symbol b2), the rate of change Smt of the motor torque MT is reduced to a predetermined value of "-S2" (symbol a2). Thereafter, when the motor torque MT passes through zero and leaves the deceleration range β (symbol b3) as shown at time t3b, the rate of change Smt of the motor torque MT is increased again to "-S1" (symbol a3), and as shown at time t4b, the motor torque is controlled to "-T2" on the regenerative side (symbol b4).

[0029] Furthermore, as shown by the dashed line in FIG. 6, even when the accelerator pedal is depressed while the vehicle is traveling, zero-cross control is similarly executed to reduce the rate of change Smt of motor torque MT. That is, as shown at time t1b, when the accelerator pedal is depressed while the vehicle is decelerating, the rate of change Smt of motor torque MT is set to "S3" (symbol c1), and the regeneration-side motor torque MT begins to be controlled toward zero (symbol d1). Then, as shown at time t2b, when the motor torque MT reaches a deceleration range β that includes zero (symbol d2), the rate of change Smt of motor torque MT is reduced to a predetermined "S4" (symbol c2). Thereafter, as shown at time t3b, when the motor torque MT passes through zero and leaves the deceleration range β (symbol d3), the rate of change Smt of motor torque MT is increased again to "S1" (symbol c3), and as shown at time t4b, the motor torque MT is controlled to "T1" on the powering side (symbol d4).

[0030] In this way, when the control system 20 changes the motor torque (torque) MT from the powering side through the deceleration range β to the regenerative side, it reduces the rate of change (torque change rate) Smt of the motor torque MT within the deceleration range β compared to the rate of change Smt of the motor torque MT outside the deceleration range β. Also, when the control system 20 changes the motor torque MT from the regenerative side through the deceleration range β to the powering side, it reduces the rate of change Smt of the motor torque MT within the deceleration range β compared to the rate of change Smt of the motor torque MT outside the deceleration range β. This makes it possible to suppress shock when the motor torque MT changes beyond zero. Note that the rate of change Smt of the motor torque MT, "-S1, -S2, S3, S4," may be a preset target speed, or may be a target speed set based on, for example, the torque difference between the target motor torque Tmt and the motor torque MT.

[0031] [Pre-torque increase / decrease control] As described above, when the motor torque passes through zero, zero-cross control is executed to slow the rate of change of the motor torque below the most recent rate of change. Furthermore, as described above, if it is determined that the vehicle 11 is at risk of a collision, automatic braking control is executed to activate the brake device 42, the front motor 16, and the rear motor 18 to brake the front and rear wheels 12, 14. However, executing zero-cross control in automatic braking control delays the rise of the motor torque MT, i.e., the regenerative torque, and reduces the braking performance of automatic braking control. Therefore, in order to quickly raise the regenerative torque in automatic braking control, the control system 20 executes pre-torque increase / decrease control to increase / decrease the motor torque of the front motor 16 and the rear motor 18 in advance in preparation for automatic braking control.

[0032] <Braking prediction flag FLa, braking determination flag FLb> The following describes the settings of the braking prediction flag FLa and the braking determination flag FLb used in the pre-torque increase / decrease control. The braking prediction flag FLa is a control flag that is set when the execution of automatic brake control is predicted, and the braking determination flag FLb is a control flag that is set when the execution of automatic brake control is started.

[0033] 7 and 8 are diagrams showing an example of a driving situation in which the braking prediction flag FLa and the braking confirmation flag FLb are set. As shown by the symbol x1 in Fig. 7, when the vehicle 11 approaches a pre-registered intersection 100 with poor visibility (anticipated collision point) and the distance to the intersection 100 falls below a braking prediction threshold D1a, the braking prediction flag FLa, which predicts the execution of automatic brake control, is set (FLa = 1). Subsequently, as shown by the symbol x2, when the vehicle 11 further approaches the intersection 100 and the distance to another vehicle (collision object) 200 traveling through the intersection 100 falls below a braking confirmation threshold D2a that is smaller than the braking prediction threshold D1a, the braking confirmation flag FLb, which indicates the start of the execution of automatic brake control, is set (FLb = 1).

[0034] In the above explanation, the braking confirmation flag FLb is set after the braking prediction flag FLa is set, but if there are no other vehicles 200 or the like at the intersection 100, there is no risk of collision with the vehicle 11 and the braking confirmation flag FLb is not set. Furthermore, if the braking prediction flag FLa is set as the vehicle 11 approaches the intersection 100 and then the vehicle 11 passes through the intersection 100, the setting of the braking prediction flag FLa is canceled (FLa=0).

[0035] The braking prediction threshold D1a used to set the braking prediction flag FLa is a threshold that increases or decreases based on the vehicle speed of the vehicle 11. That is, as the vehicle speed of the vehicle 11 decreases, the braking prediction threshold D1a is set to a smaller value, and as the vehicle speed of the vehicle 11 increases, the braking prediction threshold D1a is set to a larger value. Similarly, the braking confirmation threshold D2a used to set the braking confirmation flag FLb is a threshold that increases or decreases based on the vehicle speed of the vehicle 11. That is, as the vehicle speed of the vehicle 11 decreases, the braking confirmation threshold D2a is set to a smaller value, and as the vehicle speed of the vehicle 11 increases, the braking confirmation threshold D2a is set to a larger value. Furthermore, the braking confirmation threshold D2a may be increased or decreased based on the relative speed between the vehicle 11 and the other vehicle 200. In this case, as the relative speed between the vehicle 11 and the other vehicle 200 decreases, the braking confirmation threshold D2a is set to a smaller value, and as the relative speed between the vehicle 11 and the other vehicle 200 increases, the braking confirmation threshold D2a is set to a larger value.

[0036] 8, when the vehicle 11 approaches the preceding vehicle (object of collision) 300 and the distance to the preceding vehicle 300 falls below a braking prediction threshold D1b, a braking prediction flag FLa that predicts the execution of automatic brake control is set (FLa=1). Then, when the vehicle 11 approaches the preceding vehicle 300 further and the distance to the preceding vehicle 300 falls below a braking confirmation threshold D2b that is smaller than the braking prediction threshold D1b, as shown by the symbol x4, a braking confirmation flag FLb that indicates the start of execution of automatic brake control is set (FLb=1). Note that when the vehicle 11 moves away from the preceding vehicle 300 beyond the braking prediction threshold D1b due to deceleration of the vehicle 11 or acceleration of the preceding vehicle 300, the setting of the braking prediction flag FLa is canceled (FLa=0).

[0037] The braking prediction threshold D1b used to set the braking prediction flag FLa is a threshold that increases or decreases based on the vehicle speed of the vehicle 11. That is, as the vehicle speed of the vehicle 11 decreases, the braking prediction threshold D1b is set to a smaller value, and as the vehicle speed of the vehicle 11 increases, the braking prediction threshold D1b is set to a larger value. The braking prediction threshold D1b may also be increased or decreased based on the relative speed between the vehicle 11 and the preceding vehicle 300. In this case, the braking prediction threshold D1b is set to a smaller value as the relative speed between the vehicle 11 and the preceding vehicle 300 decreases, and the braking prediction threshold D1b is set to a larger value as the relative speed between the vehicle 11 and the preceding vehicle 300 increases. Similarly, the braking confirmation threshold D2b used to set the braking confirmation flag FLb is a threshold that increases or decreases based on the vehicle speed of the vehicle 11. That is, as the vehicle speed of the vehicle 11 decreases, the braking confirmation threshold D2b is set to a smaller value, and as the vehicle speed of the vehicle 11 increases, the braking confirmation threshold D2b is set to a larger value. The braking confirmation threshold D2b may be increased or decreased based on the relative speed between the vehicle 11 and the preceding vehicle 300. In this case, the braking confirmation threshold D2b is set to be smaller as the relative speed between the vehicle 11 and the preceding vehicle 300 decreases, and the braking confirmation threshold D2b is set to be larger as the relative speed between the vehicle 11 and the preceding vehicle 300 increases.

[0038] <Flowchart> Fig. 9 is a flowchart showing an example of the procedure for executing pre-torque increase / decrease control during forward travel. Each step shown in the flowchart in Fig. 9 represents processing executed by one or more processors 80 constituting the control system 20. The pre-torque increase / decrease control shown in Fig. 9 is control that is executed by the control system 20 at predetermined intervals after the driver operates the start switch 76 and the control system 20, which is composed of the vehicle control unit 65 and the like, is started up.

[0039] As shown in FIG. 9 , in step S10, it is determined whether the braking prediction flag FLa is set, i.e., whether "FLa = 1". If it is determined in step S10 that the braking prediction flag FLa is set, it means that the execution of automatic brake control is predicted, and so the process proceeds to step S11, where the control system 20 reduces the traction torque of the front motor 16 from its most recent value and increases the traction torque of the rear motor 18 from its most recent value. In step S11, in order to reduce the traction torque of the front motor 16, the front motor 16 is controlled toward a predetermined target motor torque (for example, 0 [Nm] or -1 [Nm]). Then, the control system 20 sets an increase in the traction torque of the rear motor 18 to compensate for the decrease in the traction torque of the front motor 16, and increases the traction torque of the rear motor 18 to meet this increase.

[0040] Next, in step S12, it is determined whether the braking prediction flag FLa remains set, i.e., whether "FLa = 1" is true. If it is determined in step S12 that the braking prediction flag FLa remains set, the process proceeds to step S13, where it is determined whether the braking determination flag FLb is set, i.e., whether "FLb = 1" is true. If it is determined in step S13 that the braking determination flag FLb is set, the process proceeds to step S14, where automatic brake control is executed to increase the regenerative torque of each motor 16, 18. In step S14, the control system 20 increases the regenerative torque of the front motor 16 from its most recent value, and also increases the regenerative torque of the rear motor 18 from its most recent value. This allows the front and rear wheels 12, 14 to be braked by the regenerative torque of the front motor 16 and the rear motor 18.

[0041] As described above, if it is determined in step S10 that the braking prediction flag FLa is set, that is, if it is determined that the execution of automatic brake control is predicted, the process proceeds to step S11, where the control system 20 reduces the traction torque of the front motor 16. This allows the traction torque of the front motor 16 to be reduced at a timing before the automatic brake control is executed, so there is no need to reduce the traction torque of the front motor 16 after the start of automatic brake control, and the regenerative torque of the front motor 16 can be quickly built up. In this way, when the automatic brake control is executed, the regenerative torque of the front motor 16 can be quickly built up, and the vehicle 11 can be stopped in a short braking distance.

[0042] On the other hand, if it is determined in step S12 that the braking prediction flag FLa has been cleared, it is not a situation in which automatic brake control should be executed, so the process proceeds to step S15, where the control system 20 increases the traction torque of the front motor 16 from its most recent value and decreases the traction torque of the rear motor 18 from its most recent value. In step S15, for example, the traction torque of the front motor 16 is increased and the traction torque of the rear motor 18 is decreased so that the driving forces of the front and rear wheels 12, 14 are matched. Thereafter, the process returns to step S10, and it is again determined whether the braking prediction flag FLa has been set. It goes without saying that in step S15, the traction torques of the front motor 16 and the rear motor 18 may be controlled so that the driving forces of the front and rear wheels 12, 14 are different from each other.

[0043] <Timing chart> FIG. 10 is a timing chart showing an example of the execution status of pre-torque increase / decrease control. As indicated by solid lines and dashed-dotted lines in FIG. 10, "MTf" is the motor torque output from the front motor 16, "MTr" is the motor torque output from the rear motor 18, "Fv" is the vehicle driving force obtained by combining the driving forces of the front and rear wheels 12, 14 due to the motor torque, and "Vv" is the vehicle speed. As indicated by dashed lines in FIG. 10, FIG. 10 also shows, as a comparative example, a situation in which the motor torque is maintained after the braking prediction flag FLa is set. Note that "mt2" is the motor torque of the comparative example output from the front motor 16 and the rear motor 18, "fv2" is the vehicle driving force of the comparative example, and "vv2" is the vehicle speed of the comparative example. In the following description, the motor torques MTf, MTr, and mt2 that increase or decrease on the powering side will be referred to as powering torques MTf, MTr, and mt2. Furthermore, the motor torques MTf, MTr, and mt2 that increase or decrease on the regenerative side are described as regenerative torques MTf, MTr, and mt2.

[0044] As shown at time t1c in Figure 10, when the braking prediction flag FLa is not set (symbol a1), the traction torque MTf and the traction torque MTr are controlled (symbols b1 and c1) toward a predetermined target motor torque that is set based on the required driving force. In the example shown, the traction torque MTf and the traction torque MTr are made to match each other, but this is not limitative. For example, the traction torque MTf and the traction torque MTr may be made different from each other to cause the driving forces of the front and rear wheels 12, 14 to be different from each other.

[0045] Subsequently, as shown at time t2c, when the braking prediction flag FLa is set as the vehicle 11 approaches an intersection, a preceding vehicle, or the like (symbol a2), the control system 20 reduces the powering torque MTf of the front motor 16 (symbol b2) and increases the powering torque MTr of the rear motor 18 (symbol c2). Here, as shown by the enlarged portion γ in FIG. 10 , the motor torque MTf of the front motor 16 is controlled toward a target motor torque (e.g., −1 [Nm]) set on the regeneration side (negative side) (symbol b3). In this way, when the braking prediction flag FLa is set (symbol a2), the control system 20 reduces the powering torque MTf of the front motor 16 (symbol b2) and controls the motor torque MTf of the front motor 16 toward the regeneration side (symbol b3).

[0046] Furthermore, the control system 20 sets an increase ΔTr in the traction torque MTr of the rear motor 18 so as to compensate for the decrease ΔTf in the traction torque MTf of the front motor 16, and increases the traction torque MTr of the rear motor 18 to satisfy this increase ΔTr (symbol c3). As a result, even when the traction torques MTf and MTr are increased or decreased (symbols b3 and c3), the decrease in the traction torque MTf can be compensated for by the increase in the traction torque MTr, and the vehicle driving force Fv can be maintained substantially constant so as not to cause discomfort to the driver (symbol d1). Note that in this embodiment, because the gear ratios of the front and rear drive units 15 and the tire diameters of the front and rear wheels 12 and 14 are the same, the decrease ΔTf and increase ΔTr in the traction torque MTf and MTr are the same.

[0047] Next, as shown at time t3c, when the vehicle 11 approaches the preceding vehicle or the like further and the braking confirmation flag FLb is set (symbol e1), the control system 20 executes automatic brake control to increase the regenerative torques MTf and MTr of the motors 16 and 18. At this time, because the traction torque MTf of the front motor 16 has already decreased, there is no need to decrease the traction torque MTf after the automatic brake control starts, and the regenerative torque MTf of the front motor 16 can be quickly increased (symbol b4). Moreover, because the front motor 16 is already in a regenerative state, there is no need to execute zero-cross control for the front motor 16, which also allows the regenerative torque MTf to be quickly increased (symbol b4). Meanwhile, because the rear motor 18 is in a powering state, the control system 20 decreases the traction torque MTr (symbol c4), and then increases the regenerative torque MTr through zero-cross control (symbols c5 and c6).

[0048] In this way, when the braking prediction flag FLa is set, that is, when the execution of automatic brake control is predicted, the control system 20 reduces the powering torque MTf of the front motor 16 (symbol b3). That is, because the powering torque MTf of the front motor 16 is reduced at a timing before the automatic brake control is executed, when the automatic brake control is subsequently executed, the regenerative torque MTf of the front motor 16 can be quickly increased (symbol b4). This allows the vehicle driving force Fv to be quickly changed to the deceleration side (symbol d2), and the vehicle speed Vv can be quickly reduced to stop the vehicle 11 in a short braking distance Dv.

[0049] Furthermore, by quickly raising the regenerative torque MTf of the front motor 16, the braking force of the front wheels 12 located at the front in the direction of travel can be quickly raised, thereby increasing the vehicle braking force and improving the braking performance of the automatic brake control. In other words, the front wheels 12 located at the front in the direction of travel when the vehicle is traveling forward are subjected to a greater load during vehicle braking than the rear wheels 14 located at the rear in the direction of travel. By quickly raising the regenerative torque MTf transmitted to the front wheels 12, a large braking force can be quickly generated on the front wheels 12, thereby increasing the vehicle braking force and improving the braking performance of the automatic brake control. It goes without saying that in the automatic brake control, the front and rear wheels 12, 14 are braked not only by the front motor 16 and the rear motor 18, but also by the brake device 42.

[0050] Here, as shown as a comparative example, a case will be considered where the braking prediction flag FLa is set (symbol a2) and the powering torque mt2 of the front motor 16 and the rear motor 18 is maintained (symbol f1). In this case, the motor torque mt2 of the front motor 16 and the rear motor 18 needs to be changed from the powering side to the regenerative side, so zero-cross control needs to be executed for both motors 16, 18 (symbol f2). For this reason, it is difficult to quickly increase the regenerative torque mt2 of the front motor 16 and the rear motor 18 in accordance with the execution of automatic brake control. In other words, because it is difficult to quickly change the vehicle driving force fv2 to the deceleration side (symbol g1), the vehicle speed vv2 decreases more gradually than the vehicle speed Vv in the embodiment, and the braking distance dv2 is longer than the braking distance Dv in the embodiment.

[0051] <Another example of target motor torque in pre-torque increase / decrease control> In the example shown in Fig. 10, when the braking prediction flag FLa is set (symbol a2), the control system 20 reduces the powering torque MTf of the front motor 16 (symbol b2) and controls the motor torque MTf of the front motor 16 to the regenerative side (symbol b3), but this is not limited to this. For example, by setting the target motor torque of the front motor 16 to "0 [Nm]," when the braking prediction flag FLa is set, the powering torque MTf of the front motor 16 may be reduced and the motor torque MTf of the front motor 16 may be controlled to zero. In this way, even when the motor torque MTf of the front motor 16 is controlled to zero, the regenerative torque MTf of the front motor 16 can be quickly increased when automatic brake control is executed.

[0052] In other words, by reducing the powering torque MTf of the front motor 16 in preparation for the execution of automatic brake control, there is no need to reduce the powering torque MTf of the front motor 16 after the start of automatic brake control, and the regenerative torque MTf of the front motor 16 can be quickly increased. Moreover, by controlling the motor torque MTf of the front motor 16 to zero, it is possible to avoid changing the motor torque MTf from the powering side to the regenerative side when executing automatic brake control. As a result, there is no need to execute zero-cross control on the front motor 16 when executing automatic brake control, which also makes it possible to quickly increase the regenerative torque MTf.

[0053] Furthermore, for example, by setting the target motor torque of the front motor 16 to "+1 [Nm]," when the braking prediction flag FLa is set, the traction torque MTf of the front motor 16 may be reduced and controlled to be close to zero on the traction side. In this way, even when the motor torque MTf of the front motor 16 is controlled to be close to zero, the regenerative torque MTf of the front motor 16 can be quickly increased when automatic brake control is executed. In other words, by reducing the traction torque MTf of the front motor 16 in preparation for the execution of automatic brake control, there is no need to reduce the traction torque MTf of the front motor 16 after the start of automatic brake control, and therefore the regenerative torque MTf of the front motor 16 can be quickly increased.

[0054] If the target motor torque of the front motor 16 is set to "+1 [Nm]," the motor torque MTf of the front motor 16 is controlled from the powering side to the regenerative side by the automatic brake control. Therefore, depending on the setting of the deceleration range β shown in FIG. 6, it is possible that zero-cross control will also be executed when the automatic brake control is executed. In such a case, the zero-cross control executed in conjunction with the automatic brake control may be prohibited to quickly increase the regenerative torque MTf of the front motor 16.

[0055] [Pre-torque increase / decrease control during reverse driving] In the above explanation, the pre-torque increase / decrease control during forward traveling has been described using Figures 9 and 10, but this is not limiting, and a similar pre-torque increase / decrease control may be executed during reverse traveling. In this case, the rear wheels 14 located at the front in the traveling direction function as the first wheels, and the front wheels 12 located at the rear in the traveling direction function as the second wheels. In addition, the rear motor 18 functions as the first traveling motor, and the front motor 16 functions as the second traveling motor.

[0056] That is, when the braking prediction flag FLa is set during reverse driving, the traction torque MTr of the rear motor 18 is decreased, and the traction torque MTf of the front motor 16 is increased. Thereafter, when the braking determination flag FLb is set, the regenerative torque MTr of the rear motor 18 is increased, and the regenerative torque MTf of the front motor 16 is increased. This allows the regenerative torque MTr of the rear motor 18 to be quickly increased, thereby increasing the vehicle braking force and improving the braking performance of the automatic brake control. In other words, when the vehicle is reverse driving, the rear wheels 14, which are located at the front of the vehicle in the direction of travel, are subjected to a greater load during vehicle braking than the front wheels 12, which are located at the rear of the vehicle in the direction of travel. By quickly increasing the regenerative torque MTr transmitted to the rear wheels 14, a large braking force can be quickly generated on the rear wheels 14, and therefore the vehicle braking force can be increased, and the braking performance of the automatic brake control can be improved.

[0057] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit and scope of the present invention. In the above description, the control system 20 is configured with multiple control units 34, 40, 41, 48, 54, 61, and 65. However, this is not limiting. For example, the control system 20 may be configured with a single control unit. In the above description, one front motor 16 is connected to the pair of left and right front wheels 12, and one rear motor 18 is connected to the pair of left and right rear wheels 14. However, this is not limiting. For example, two front motors 16 may be provided for the front wheels, thereby connecting one front motor 16 to one front wheel 12. Furthermore, two rear motors 18 may be provided for the rear wheels, thereby connecting one rear motor 18 to one rear wheel 14. The vehicle 11 is not limited to the electric vehicle shown in the drawings, and may be a fuel cell vehicle or a hybrid vehicle.

[0058] In the above description, predicted collision points such as intersections are registered in the navigation system 60, but this is not limiting, and intersections without traffic lights may be identified based on image data captured by the front camera 50 or the like and used as predicted collision points. Also, in the example shown in Fig. 10, zero-cross control of the rear motor 18 is executed in conjunction with the automatic brake control (reference symbol c5), but this is not limiting, and the rise of the regenerative torque MTr may be further accelerated by stopping the zero-cross control.

[0059] As described above, the braking prediction threshold D1a is a variable value that increases or decreases based on the vehicle speed, but is not limited to this, and a fixed value may be used as the braking prediction threshold D1a. Furthermore, the braking confirmation threshold D2a is a variable value that increases or decreases based on the vehicle speed or the relative speed, but is not limited to this, and a fixed value may be used as the braking confirmation threshold D2a. Similarly, the braking prediction threshold D1b is a variable value that increases or decreases based on the vehicle speed or the relative speed, but is not limited to this, and a fixed value may be used as the braking prediction threshold D1b. Furthermore, the braking confirmation threshold D2b is a variable value that increases or decreases based on the vehicle speed or the relative speed, but is not limited to this, and a fixed value may be used as the braking confirmation threshold D2b. [Explanation of symbols]

[0060] 10 Vehicle control device 11 vehicles 12 Front wheels (1st wheel, 2nd wheel) 14 Rear wheel (2nd wheel, 1st wheel) 16 Front motor (first driving motor, second driving motor) 18 Rear motor (second driving motor, first driving motor) 20 Control System 80 processors 81 memory 100 Intersection (collision predicted point) 200 Vehicle (collision object) 300 Leading vehicle (object of collision) D1a Braking prediction threshold D2a Braking decision threshold D1b Braking prediction threshold D2b Braking decision threshold MTf Motor torque (power torque, regenerative torque) MTr Motor torque (power torque, regenerative torque) MT Motor torque (torque) Smt change rate (torque change rate) β Deceleration range

Claims

1. A vehicle control device provided in a vehicle, a first traction motor connected to a first wheel located at the front in the traveling direction; a second traction motor connected to a second wheel located at the rear in the traveling direction; a control system including a processor and a memory communicatively connected to each other, the control system controlling the first traction motor and the second traction motor; and the control system reduces a traction torque of the first traction motor and increases a traction torque of the second traction motor when a distance to a predicted collision point or a collision object falls below a braking prediction threshold during driving; the control system increases the regenerative torque of the first traction motor and increases the regenerative torque of the second traction motor when a distance to an object to be hit during driving falls below a braking determination threshold that is smaller than the braking prediction threshold. Vehicle control device.

2. 2. The vehicle control device according to claim 1, the first wheel is a front wheel, the second wheel is a rear wheel, the control system reduces a traction torque of the first traction motor and increases a traction torque of the second traction motor when a distance to a predicted collision point or a collision object falls below the braking prediction threshold during forward travel; the control system increases the regenerative torque of the first traction motor and increases the regenerative torque of the second traction motor when a distance to an object to be hit falls below the braking determination threshold during forward travel. Vehicle control device.

3. 3. The vehicle control device according to claim 1, when the torque of the first traction motor is changed from a powering side to a regenerating side through a deceleration range including zero, the control system reduces a torque change rate of the first traction motor within the deceleration range to a torque change rate of the first traction motor outside the deceleration range. Vehicle control device.

4. The vehicle control device according to any one of claims 1 to 3, the control system reduces the power torque of the first traction motor and controls the torque of the first traction motor to a regeneration side when a distance to a predicted collision point or a collision object falls below the braking prediction threshold during travel. Vehicle control device.

5. The vehicle control device according to any one of claims 1 to 3, the control system reduces the power torque of the first traction motor and controls the torque of the first traction motor to zero when a distance to a predicted collision point or a collision object falls below the braking prediction threshold during travel. Vehicle control device.

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