Vehicle control system

Abstract

The present invention provides a vehicle control device that can reduce sudden fluctuations in driving force in a vehicle while appropriately protecting the electric motor from thermal load. [Solution] The vehicle 10 includes a front motor MGf that drives a pair of front wheels 14 and a rear motor MGr that drives a pair of rear wheels 54. The electronic control unit 90 switches to a normal four-wheel drive mode when (a) the rear motor temperature THmgr rises to a first determination temperature TH1 or higher in the MGr two-wheel drive mode, (b) the high-temperature four-wheel drive mode when the rear motor temperature THmgr rises to a second determination temperature TH2 or higher in the normal four-wheel drive mode, and (c) the protective control mode when the rear motor temperature THmgr rises to a third determination temperature TH3 or higher in the high-temperature four-wheel drive mode.

Description

Technical Field

[0001] The present invention relates to a control device for a vehicle including a first electric motor and a second electric motor that drive one and the other of a pair of front wheels and a pair of rear wheels, respectively.

Background Art

[0002] A control device for a vehicle including an electric motor and an engine that drive one and the other of a pair of front wheels and a pair of rear wheels, respectively, is known. For example, the control device for the vehicle described in Patent Document 1 is such a device. In the vehicle described in Patent Document 1, a two-wheel drive mode is adopted when the required driving force of the vehicle is low, and a four-wheel drive mode is adopted when the required driving force is high.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, it is conceivable to configure the vehicle to include a first electric motor and a second electric motor that drive one and the other of a pair of front wheels and a pair of rear wheels, respectively. Generally, for an electric motor that drives a pair of front wheels or a pair of rear wheels, when the inverter that drives and controls the electric motor overheats, the load on the electric motor is limited, resulting in a limited output torque or the electric motor stops. As a result, there is a risk of sudden driving force fluctuations in the vehicle.

[0005] The present invention has been made against the background of the above circumstances, and an object thereof is to provide a control device for a vehicle that can appropriately protect against the thermal load of an electric motor while reducing sudden driving force fluctuations in the vehicle.

Means for Solving the Problems

[0006] The gist of the present invention is a control device for a vehicle comprising a first electric motor that drives one of a pair of front wheels and a pair of rear wheels, and a second electric motor that drives the other of the pair of front wheels and a pair of rear wheels, wherein (a) in a two-wheel drive mode in which the first electric motor is in a driven state and the second electric motor is in a non-driven state, when the temperature of the first electric motor rises to a predetermined first determination temperature or higher, the control device switches the second electric motor from a non-driven state to a driven state to switch to a four-wheel drive mode; (b) in the four-wheel drive mode, when the temperature of the first electric motor rises to a predetermined second determination temperature or higher which is higher than the first determination temperature, the control device switches to a drive force limiting mode in which the drive force output by the first electric motor is limited; and (c) in the drive force limiting mode, when the temperature of the first electric motor rises to a predetermined third determination temperature or higher which is higher than the second determination temperature, the control device switches to a protection control mode in which the first electric motor is in a non-driven state and the second electric motor is in a driven state. [Effects of the Invention]

[0007] According to the vehicle control device of the present invention, (a) in a two-wheel drive mode in which the first motor is in a driving state and the second motor is in a non-driving state, when the temperature of the first motor rises to a predetermined first determination temperature or higher, the second motor is switched from a non-driving state to a driving state, thereby switching to a four-wheel drive mode; (b) in the four-wheel drive mode, when the temperature of the first motor rises to a predetermined second determination temperature or higher, which is higher than the first determination temperature, the vehicle is switched to a driving force limiting mode in which the driving force output by the first motor is limited; and (c) in the driving force limiting mode, when the temperature of the first motor rises to a predetermined third determination temperature or higher, which is higher than the second determination temperature, the vehicle is switched to a protection control mode in which the first motor is in a non-driving state and the second motor is in a driving state. In this way, as the temperature of the first motor rises, the following are performed sequentially: switching from a two-wheel drive mode to a four-wheel drive mode by the first motor, switching to a driving force limiting mode in which the driving force of the first motor is limited, and switching to a protection control mode in which the first motor is in a non-driving state. This ensures that the first motor is adequately protected from thermal loads while reducing sudden fluctuations in the vehicle's driving force. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram illustrates the schematic configuration of a vehicle to which the present invention is applied. [Figure 2] This is an example of a flowchart illustrating the key aspects of the control operation of an electronic control unit. [Figure 3] This figure shows an example of a time chart when the control operation shown in the flowchart in Figure 2 is executed. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that in the embodiments, the drawings have been simplified or modified as appropriate, and the dimensional ratios and shapes of each part are not necessarily depicted accurately. [Examples]

[0010] Figure 1 is a diagram illustrating the schematic configuration of a vehicle 10 to which the present invention is applied.

[0011] Vehicle 10 is equipped with a front motor MGf and a rear motor MGr as power sources for driving. The front motor MGf and rear motor MGr are well-known motor generators. The "rear motor MGr" corresponds to the "first electric motor" in this invention, and the "front motor MGf" corresponds to the "second electric motor" in this invention.

[0012] Vehicle 10 is equipped with a power transmission path between the front motor MGf and a pair of front wheels 14 (hereinafter simply referred to as "front wheels 14"), in order from the front motor MGf side, a disconnection device 30, a front differential gear 16, and a pair of front drive shafts 18, which are well-known configurations. Vehicle 10 is equipped with a power transmission path between the rear motor MGr and a pair of rear wheels 54 (hereinafter simply referred to as "rear wheels 54"), in order from the rear motor MGr side, a rear differential gear 56 and a pair of rear drive shafts 58, which are well-known configurations. "Front wheels 14" corresponds to "the other of the pair of front wheels and the pair of rear wheels" in the present invention, and "rear wheels 54" corresponds to "one of the pair of front wheels and the pair of rear wheels" in the present invention. Vehicle 10 can select between a two-wheel drive mode that realizes two-wheel drive (2WD) driving and a four-wheel drive mode that realizes four-wheel drive (4WD) driving as driving modes. When the disconnection device 30 is engaged (connected), the vehicle 10 is set to four-wheel drive mode. When the disconnection device 30 is released, the vehicle 10 is set to two-wheel drive mode. For example, the rear wheels 54 are the main drive wheels, which are driven wheels in both two-wheel drive and four-wheel drive modes. For example, the front wheels 14 are the secondary drive wheels, which are driven wheels in two-wheel drive mode and drive wheels in four-wheel drive mode. The disconnection device 30 is, for example, a well-known dog clutch. When the disconnection device 30 is engaged, the dog clutch is in a meshed state, and when the disconnection device 30 is released, the dog clutch is in a dismeshed state.

[0013] Vehicle 10 includes an inverter 60 for front motor drive control, an inverter 62 for rear motor drive control, and an electronic control unit 90. Inverters 60 and 62 are well-known power supply circuits that convert DC to AC and AC to DC, respectively. The front motor MGf and rear motor MGr are connected to a battery (not shown) via inverters 60 and 62, respectively. The output torque of the front motor MGf and rear motor MGr is controlled by the control of inverters 60 and 62 by the electronic control unit 90, respectively. In this specification, unless otherwise specified, torque, driving force, power, and force (=power) are synonymous.

[0014] The electronic control unit 90 is a controller that includes a control device for controlling the front motor MGf, the disconnection device 30, the rear motor MGr, etc. The electronic control unit 90 is composed of a so-called microcomputer equipped with, for example, a CPU, RAM, ROM, input / output interface, etc. In this embodiment, the electronic control unit 90 is composed of a front motor ECU 94 for controlling the front motor MGf, a disconnection device ECU 96 for controlling the disconnection state of the disconnection device 30, a rear motor ECU 98 for controlling the rear motor MGr, and an integrated ECU 92 for integrated control of them. ECU stands for Electronic Control Unit, and is an acronym formed by taking the first letter of each word. In the electronic control unit 90, the front motor ECU 94, the disconnection device ECU 96, the rear motor ECU 98, and the integrated ECU 92 are each connected to a communication network using, for example, a CAN communication circuit. The electronic control unit 90 corresponds to the "control device" in this invention.

[0015] The integrated ECU 92 receives various signals based on values ​​detected by various sensors (e.g., vehicle speed sensor 70, accelerator pedal position sensor 72, MGf rotation speed sensor 74, MGr rotation speed sensor 76, temperature sensor 80, temperature sensor 82, etc.). These signals include, for example, vehicle speed V [km / h], accelerator pedal position θacc [%], MGf rotation speed Nmgf [rpm] (the rotation speed of the front motor MGf), MGr rotation speed Nmgr [rpm] (the rotation speed of the rear motor MGr), front motor temperature THmgf [°C] (the temperature of the front motor MGf), and rear motor temperature THmgr [°C] (the temperature of the rear motor MGr). The integrated ECU 92 calculates the requested drive torque Trdem [N·m], which is the drive torque requested by the driver for the vehicle 10, based on, for example, vehicle speed V and accelerator pedal position θacc. The front motor ECU 94 outputs a control signal Smgf to the inverter 60 to control the rotation of the front motor MGf. The ECU 96 for the disconnect / disconnect device outputs a control signal Sdclt to the actuator that controls the disconnect / disconnect device 30. The ECU 98 for the rear motor outputs a control signal Smgr to the inverter 62 that controls the rotation of the rear motor MGr. The integration ECU 92 controls the front motor MGf, the disconnect / disconnect device 30, and the rear motor MGr, respectively, via the ECU 94 for the front motor, the ECU 96 for the disconnect / disconnect device, and the ECU 98 for the rear motor, based on the selected driving mode and the requested drive torque Trdem.

[0016] From here, we will explain the switching of the driving mode and the switching of the drive control of the front motor MGf and the rear motor MGr in response to the temperature change of the rear motor temperature THmgr while driving in the two-wheel drive mode using the rear motor MGr (hereinafter referred to as "MGr two-wheel drive mode"). "MGr two-wheel drive mode" corresponds to the "two-wheel drive mode in which the first motor is in a driven state and the second motor is in a non-driven state" in this invention. "Rear motor temperature THmgr" corresponds to the "temperature of the first motor" in this invention.

[0017] The electronic control unit 90 determines whether the rear motor temperature THmgr has risen to or above the first determination temperature TH1 [°C] while driving in MGr two-wheel drive mode. The "first determination temperature TH1" corresponds to the "predetermined first determination temperature" in this invention. The "first determination temperature TH1" is a predetermined temperature that has been experimentally or design-defined in advance, at which continuing to drive the vehicle in MGr two-wheel drive mode may cause a sudden change in driving force even when switching the driving mode to four-wheel drive mode due to the rise in the rear motor temperature THmgr. If it is determined that the rear motor temperature THmgr has risen to or above the first determination temperature TH1, the electronic control unit 90 executes control to switch the driving mode from MGr two-wheel drive mode to the normal four-wheel drive mode described later. In the normal four-wheel drive mode, four-wheel drive driving is achieved, and the front wheel drive torque Tlf [N·m] and rear wheel drive torque Trr [N·m] are controlled regardless of the rear motor temperature THmgr, as long as the rear motor temperature THmgr is below the second determination temperature TH2 [°C] described later. The "normal four-wheel drive mode" corresponds to the "four-wheel drive mode" in the present invention. For example, the total drive torque Tr[N·m], which is the sum of the front-wheel drive torque Tlf and the rear-wheel drive torque Trr, is controlled to become the required drive torque Trdem, and the front-wheel drive torque Tlf and the rear-wheel drive torque Trr are controlled to have a predetermined distribution ratio based on energy efficiency and driving stability. The front-wheel drive torque Tlf is the torque transmitted to the front wheels 14 by the output torque of the front motor MGf, MGf torque Tmgf[N·m], and the rear-wheel drive torque Trr is the torque transmitted to the rear wheels 54 by the output torque of the rear motor MGr, MGr torque Tmgr[N·m].

[0018] The electronic control unit 90 determines whether the rear motor temperature THmgr has risen to or above the second determination temperature TH2 (>TH1) while driving in the normal four-wheel drive mode. The "second determination temperature TH2" corresponds to the "predetermined second determination temperature" in this invention. The "second determination temperature TH2" is a predetermined temperature that has been experimentally or design-defined in advance, at which, if the vehicle continues to drive in the normal four-wheel drive mode, a sudden change in driving force may occur even if the driving mode is switched to the high-temperature four-wheel drive mode described later due to the rise in the rear motor temperature THmgr. If the electronic control unit 90 determines that the rear motor temperature THmgr has risen to or above the second determination temperature TH2 while driving in the normal four-wheel drive mode, it executes control to switch the driving mode from the normal four-wheel drive mode to the high-temperature four-wheel drive mode. The high-temperature four-wheel drive mode is a driving mode that achieves four-wheel drive driving, in which the rear-wheel drive torque Trr is reduced in accordance with the rise in rear motor temperature THmgr, and the front-wheel drive torque Tlf is increased to compensate for the decrease in rear-wheel drive torque Trr. In other words, in accordance with the rise in rear motor temperature THmgr, the MGr torque Tmgr is reduced and the MGf torque Tmgf is increased. The "high-temperature four-wheel drive mode" corresponds to the "driving force limiting mode" in this invention. In the "high-temperature four-wheel drive mode," the rear motor temperature THmgr is reduced, i.e., the MGr torque Tmgr is limited, in an attempt to lower the rear motor temperature THmgr.

[0019] During running in the four-wheel drive mode at high temperature, the electronic control unit 90 determines whether the rear motor temperature THmgr has risen to or above the third determination temperature TH3 [°C] (> TH2). The "third determination temperature TH3" corresponds to the "predetermined third determination temperature" in the present invention. The "third determination temperature TH3" is a predetermined temperature determined experimentally or by design such that if the vehicle running in the four-wheel drive mode at high temperature continues, rapid drive force fluctuations may occur even when the protection control mode described below is executed due to the rise in the rear motor temperature THmgr. When it is determined that the rear motor temperature THmgr has risen to or above the third determination temperature TH3 during running in the four-wheel drive mode at high temperature, the electronic control unit 90 executes switching control to a protection control mode, which is a control mode in which the MGr torque Tmgr is set to zero and the vehicle 10 is run only with the MGf torque Tmgf. In the protection control mode, since the MGr torque Tmgr is set to zero, that is, the rear motor MGr is set to the non-driving state, an attempt is made to lower the rear motor temperature THmgr.

[0020] When it is determined that the rear motor temperature THmgr is equal to or lower than the first subtraction temperature TH1_hys [°C] during running in the four-wheel drive mode under normal conditions, the electronic control unit 90 executes switching control of the running mode from the four-wheel drive mode under normal conditions to the MGr two-wheel drive mode. The first subtraction temperature TH1_hys is a determination temperature (= TH1 - ΔTHhys1) obtained by subtracting the hysteresis temperature ΔTHhys1 [°C] from the first determination temperature TH1. The hysteresis temperature ΔTHhys1 is a predetermined temperature determined experimentally or by design that can suppress the relatively frequent occurrence of the four-wheel drive mode under normal conditions and the MGr two-wheel drive mode in a short period of time.

[0021] When it is determined that the rear motor temperature THmgr is less than or equal to the second subtraction temperature TH2_hys [°C] during running in the four-wheel drive mode at high temperature, the electronic control unit 90 executes switching control of the running mode from the four-wheel drive mode at high temperature to the four-wheel drive mode in normal operation. The second subtraction temperature TH2_hys is a determination temperature (= TH2 - ΔTHhys2) obtained by subtracting the hysteresis temperature ΔTHhys2 from the second determination temperature TH2. The hysteresis temperature ΔTHhys2 is a predetermined temperature determined experimentally or by design that can suppress the relatively frequent occurrence of the four-wheel drive mode at high temperature and the four-wheel drive mode in normal operation within a short period of time.

[0022] FIG. 2 is an example of a flowchart for explaining the main part of the control operation of the electronic control unit 90. The flowchart of FIG. 2 is repeatedly executed during running in the MGr two-wheel drive mode.

[0023] First, in step S10 (hereinafter, "step" will be omitted), it is determined whether the rear motor temperature THmgr has risen to or above the first determination temperature TH1. If the determination in S10 is YES, in S20 the normal four-wheel drive mode is selected, in S30 the total drive torque Tr is controlled to become the required drive torque Trdem, and in S40 it is determined whether the rear motor temperature THmgr has risen to or above the second determination temperature TH2. If the determination in S40 is YES, in S50 the high-temperature four-wheel drive mode is selected, and in S60 it is determined whether the rear motor temperature THmgr has risen to or above the third determination temperature TH3. If the determination in S60 is YES, in S70 the protection control mode is selected. If the determination in S40 is NO, in S80 it is determined whether the rear motor temperature THmgr is less than or equal to the first subtraction temperature TH1_hys. If the determination in S80 is NO, S40 is executed. If the determination in S80 is YES, in S90 the MGr two-wheel drive mode is selected. If the result of S60 is NO, S100 determines whether the rear motor temperature THmgr is less than or equal to the second subtraction temperature TH2_hys. If the result of S100 is NO, S60 is executed. If the result of S100 is YES, S80 is executed. After the execution of S70, S100 is executed. After the execution of S90 and if the result of S10 is NO, the program returns.

[0024] Figure 3 shows an example of a time chart when the control operation shown in the flowchart of Figure 2 is executed. The horizontal axis of Figure 3 represents time t [s].

[0025] Time point t1 is the point in time when the rear motor temperature THmgr rises to or above the first determination temperature TH1 while driving in MGr two-wheel drive mode. At time point t1, control to switch the driving mode from MGr two-wheel drive mode to normal four-wheel drive mode is initiated. Time point t2 (>t1) is the point in time when the rotational speed of the front motor MGf side (=Nmgf) in the disconnection device 30 by the front motor MGf and the rotational speed Nsyn [rpm] of the front differential gear 16 side in the disconnection device 30, corresponding to the vehicle speed V due to the driven force from the front wheels 14, are synchronized. Based on the MGr rotational speed Nmgr, the wheel speed of the rear wheels 54 can be calculated. Since the wheel speed of the front wheels 14 and the wheel speed of the rear wheels 54 are the same while driving, for example, the rotational speed Nsyn of the front differential gear 16 side in the disconnection device 30 can be calculated based on the wheel speed of the rear wheels 54, which is the same as the wheel speed of the front wheels 14. During the period from time t1 to time t2, the front motor MGf is controlled to rotate so that its rotational speed Nmgf becomes Nyn. At time t2, control is initiated to switch the disconnection device 30 from the open state to the engaged state. Once the disconnection device 30 is switched to the engaged state, the front wheel drive torque TRF and rear wheel drive torque Trr are controlled to have a predetermined distribution ratio based on energy efficiency and driving stability. Time t3 (>t2) is the time when the control to switch the driving mode to the normal four-wheel drive mode is completed. Time t4 (>t3) is the time when the rear motor temperature THmgr rises to the second judgment temperature TH2 or higher while driving in the normal four-wheel drive mode. At time t4, control is initiated to switch the driving mode from the normal four-wheel drive mode to the high-temperature four-wheel drive mode. Time t5 (>t4) is the time when the rear motor temperature THmgr rises to the third judgment temperature TH3 or higher while driving in the high-temperature four-wheel drive mode. From time t5 onward, the protection control mode is executed.

[0026] According to this embodiment, (a) in the MGr two-wheel drive mode, when the rear motor temperature THmgr rises to the first determination temperature TH1 or higher, the system switches to the normal four-wheel drive mode; (b) in the normal four-wheel drive mode, when the rear motor temperature THmgr rises to the second determination temperature TH2 or higher, the system switches to the high-temperature four-wheel drive mode; and (c) in the high-temperature four-wheel drive mode, when the rear motor temperature THmgr rises to the third determination temperature TH3 or higher, the system switches to the protection control mode. In this way, as the rear motor temperature THmgr rises, the system sequentially switches from the MGr two-wheel drive mode to the normal four-wheel drive mode, then to the high-temperature four-wheel drive mode, and finally to the protection control mode. This ensures that the rear motor MGr is appropriately protected from thermal load while reducing sudden fluctuations in the driving force of the vehicle 10.

[0027] The above-described examples are embodiments of the present invention, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, without departing from its spirit.

[0028] In the above-described embodiment, the "rear motor MGr" and "front motor MGf" corresponded to the "first motor" and "second motor" in the present invention, respectively. However, the "front motor MGf" and "rear motor MGr" may also correspond to the "first motor" and "second motor" in the present invention, respectively. [Explanation of symbols]

[0029] 10: Vehicles 14: Pair of front wheels (the other of the pair of front wheels and the pair of rear wheels), 54: Pair of rear wheels (one of the pair of front wheels and the other of the pair of rear wheels), 90: Electronic control unit (control unit), MGf: Front motor (second motor), MGr: Rear motor (first motor), TH1: First determination temperature (predetermined first determination temperature), TH2: Second determination temperature (predetermined second determination temperature), TH3: Third determination temperature (predetermined third determination temperature), THmgr: Rear motor temperature (temperature of the first motor)

Claims

[Claim 1] A control device for a vehicle comprising a first electric motor that drives one of a pair of front wheels and a pair of rear wheels, and a second electric motor that drives the other of the pair of front wheels and the pair of rear wheels, In a two-wheel drive mode in which the first motor is in a driven state and the second motor is in a non-driven state, when the temperature of the first motor rises to a predetermined first determination temperature or higher, the second motor is switched from a non-driven state to a driven state, thereby switching to a four-wheel drive mode. In the four-wheel drive mode, if the temperature of the first motor rises to a predetermined second determination temperature or higher than the first determination temperature, the system switches to a driving force limiting mode that limits the driving force output by the first motor. In the driving force limiting mode, if the temperature of the first motor rises to a predetermined third determination temperature or higher than the second determination temperature, the system switches to a protective control mode in which the first motor is in a non-driving state and the second motor is in a driving state. A vehicle control device characterized by the following features.

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