Vehicle control device

Abstract

To keep a high level of traveling performance or drivability of a vehicle which rotationally drives one of a front-wheel axle and a rear-wheel axle by an internal combustion engine and the other thereof by an electric motor, while executing 4WD traveling with the electric motor used in combination to a minimum necessary extent and avoiding lack of a power storage amount in a power storage device.SOLUTION: A vehicle control device controls a vehicle which rotationally drives one of a front-wheel axle and a rear-wheel axle by an internal combustion engine generating torque through the combustion of fuel, and rotationally drives the other thereof by an electric motor generating torque through power supply from a power storage device. The vehicle control device variably adjusts a ratio between driving torque input by the internal combustion engine to its corresponding axle and driving torque input by the electric motor to its corresponding axle, according to a current vehicle speed VSP and a rotation number difference (NFr-NRr) between a front wheel and a rear wheel.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a control device for controlling a vehicle in which one of a front axle and a rear axle is rotationally driven by an internal combustion engine and the other is rotationally driven by an electric motor. [Background technology]

[0002] Recently, hybrid vehicles equipped with two power sources, an internal combustion engine and an electric motor, have become popular. In series hybrid vehicles (see, for example, the following patent documents), the internal combustion engine drives a generator to generate electricity, which is stored in a power storage device, i.e., a battery such as a lithium-ion secondary battery or a nickel-metal hydride secondary battery, and / or a capacitor, and is then supplied to a traction motor generator. The traction motor generator then rotates the axles and, ultimately, the drive wheels to propel the vehicle.

[0003] The traction motor generator performs regenerative braking by utilizing the inertial rotation torque of the axle to generate electricity when braking the vehicle, and can recover and store the generated electricity in the power storage device.

[0004] In a series hybrid vehicle, the internal combustion engine is used solely for generating electricity. The internal combustion engine is mechanically decoupled from the axle and does not input drive torque to the axle for running. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-156134 Summary of the Invention [Problem to be solved by the invention]

[0006] As a type different from the series type, there is a parallel type hybrid vehicle in which an internal combustion engine mainly inputs drive torque to the axles for running, and an electric motor appropriately assists this.

[0007] One way to realize the parallel system is to use an internal combustion engine to drive the front axle and a motor generator to drive the rear axle. This is similar to a front-wheel drive vehicle (especially a front-engine front-drive (FF) vehicle) with a motor generator attached to the rear wheels.

[0008] By firing the internal combustion engine and operating the motor generator as an electric motor, a (pseudo) four-wheel drive is possible. If the motor generator is not operated as an electric motor, the vehicle will operate as a two-wheel drive. The motor generator can also be operated as a generator to perform regenerative braking.

[0009] The motor generator, which operates as an electric motor, is powered by a power storage device, but if the amount of charge currently stored in the power storage device has decreased significantly, the power storage device will no longer be able to supply the motor generator with enough power to rotate the axle.

[0010] In a series hybrid vehicle, the internal combustion engine is started to generate electricity and the generated electricity is supplied to the motor generator. However, in a parallel hybrid vehicle such as the one described above, the engine torque output by the internal combustion engine is already used to drive the vehicle, making it difficult to instantly generate a large amount of electricity using the internal combustion engine and supply it to the motor generator. In fact, in a parallel hybrid vehicle, the internal combustion engine is not necessarily equipped with a generator capable of generating a large amount of electricity.

[0011] Therefore, when driving on bad roads such as during snowfall, frozen roads, or muddy roads, a lack of stored electricity in the electricity storage device may prevent 4WD driving at a crucial time, which may result in wheel slippage.

[0012] The present invention was developed in response to the above problems, and has as its intended purpose the maintenance of high off-road capability or drivability of the vehicle by performing 4WD driving to the minimum extent necessary, while avoiding a shortage of the stored charge in the power storage device. [Means for solving the problem]

[0013] In the present invention, the front wheel axle of It is driven by an internal combustion engine that burns fuel to generate torque, rear wheel axle The vehicle is controlled by an electric motor that receives power from a power storage device and generates torque, and the ratio of the drive torque input to the corresponding axle by the internal combustion engine and the drive torque input to the corresponding axle by the electric motor is variably adjusted according to the current vehicle speed and the difference in rotation speed between the front and rear wheels. When the rotation speed difference obtained by subtracting the rotation speed of the rear wheels from the rotation speed of the front wheels is larger, the ratio of the drive torque input by the electric motor to the drive torque input by the internal combustion engine to the corresponding axle is made larger compared to when the rotation speed difference is smaller, provided that when the rotation speed difference is negative and its absolute value exceeds a predetermined value, the drive torque input by the electric motor to the corresponding axle is set to 0. A vehicle control device was configured.

[0014] More specifically, when the vehicle speed is higher, the ratio of the drive torque input by the electric motor to the corresponding axle to the drive torque input by the internal combustion engine to the corresponding axle is made smaller compared to when the vehicle speed is lower. [Effects of the Invention]

[0016] According to the present invention, in a vehicle in which one of the front axles and the rear axles is driven by an internal combustion engine and the other by an electric motor, 4WD driving can be performed using the electric motor in combination to the minimum extent necessary, thereby avoiding a shortage of the storage capacity of the storage device and maintaining high vehicle off-road capability or drivability. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing an overview of a parallel hybrid vehicle according to an embodiment of the present invention; [Figure 2] 2 is a diagram showing an outline of an internal combustion engine mounted on the vehicle of the embodiment; FIG. [Figure 3] 3 is a flowchart showing an example of a procedure of a process executed by the control device for the vehicle according to the embodiment in accordance with a program. [Figure 4] 4 is a table illustrating the ratio of the drive torque input to the axle by the internal combustion engine to the drive torque input to the axle by the electric motor, which is determined by the vehicle control device of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows an overview of a vehicle according to this embodiment. The vehicle according to this embodiment is a parallel hybrid vehicle in which an axle 51 of front wheels 52 is rotationally driven by an internal combustion engine 1, and an axle 61 of rear wheels 62 is rotationally driven by a motor generator 2 serving as an electric motor. This configuration is just like a so-called front-wheel drive vehicle with a transversely mounted engine, in which the motor generator 2 is attached to the rear wheel 62 side.

[0019] Similar to existing FF vehicles, a drivetrain transmission 3, such as a torque converter, a clutch, a manual transmission or an automatic transmission (which may be a continuously variable transmission (Continuously Variable Transmission)), a differential gear, etc., is interposed between the output shaft (crankshaft) of the internal combustion engine 1 and the axle 51 of the front wheels 52. When the internal combustion engine 1 is fired, that is, when fuel is supplied to the cylinders 11 and burned, the engine torque is generated and transmitted to the axle 51 via the transmission 3, causing the front wheels 52 to rotate. Even when the internal combustion engine 1 is not fired (typically, when a fuel cut is performed to temporarily halt the supply of fuel to the cylinders 11), if the front wheels 52 and the axle 51 continue to rotate by inertia, the rotational torque is transmitted to the output shaft of the internal combustion engine 1, and the rotation of the internal combustion engine 1 is maintained, unless the clutch of the transmission 3 is disengaged.

[0020] A differential gear 4 is interposed between the output shaft of the motor generator 2 and the axle 61 of the rear wheels 62. When power is supplied from the power storage device 71 to the motor generator 2 and the motor generator 2 is operated as an electric motor, the generated motor torque is transmitted to the axle 61 via the differential gear 4, causing the rear wheels 62 to rotate. Even if the motor generator 2 is not operated as an electric motor, if the rear wheels 62 and the axle 61 continue to rotate by inertia, the rotational torque is transmitted to the output shaft of the motor generator 2, and the rotation of the motor generator 2 is maintained.

[0021] The axles 51 of the front wheels 52 and the axles 61 of the rear wheels 62 are mechanically separated. That is, the axles 51 of the front wheels 52 can rotate independently of the axles 61 of the rear wheels 62, and the axles 61 of the rear wheels 62 can also rotate independently of the axles 51 of the front wheels 52. The engine torque output by the internal combustion engine 1 is not transmitted to the axles 61 of the rear wheels 62, and the motor torque output by the motor generator 2 is not transmitted to the axles 51 of the front wheels 52.

[0022] By firing the internal combustion engine 1 and operating the motor generator 2 as an electric motor, 4WD driving is possible with both the front wheels 52 and the rear wheels 62 as drive wheels. If the motor generator 2 is not operated as an electric motor, 2WD driving is possible with only the front wheels 52 as drive wheels. In addition, the motor generator 2 can be operated as a generator to perform regenerative braking.

[0023] The power storage device 71, which serves as a power supply source for the motor generator 2, is made up of a battery and / or a capacitor. In this embodiment, the power storage device 71 is assumed to be a lithium-ion secondary battery, a nickel-metal hydride secondary battery, or the like. The power storage device 71 has a relatively large capacity and can store a large amount of electric power. It is possible to apply the voltage and current required for the motor generator 2 that drives the rear wheels 62.

[0024] In addition to the power storage device 71, the vehicle of this embodiment is provided with a sub-power storage device 72 for supplying power to the spark plugs 112, injectors 111, throttle motor, etc. of the internal combustion engine 1, and to electric loads 9 of the electrical system, such as lighting, mounted on the vehicle body. The sub-power storage device 72 is also formed by a battery and / or a capacitor. In this embodiment, a lead secondary battery or the like is assumed as the sub-power storage device 72. Compared to the power storage device 71, the sub-power storage device 72 has a smaller capacity and also has smaller output voltage and output current.

[0025] The internal combustion engine 1 is accompanied by an alternator 17, which is a generator. The alternator 17 is one of the auxiliary machines that is mechanically connected to the output shaft of the internal combustion engine 1 and is operated by receiving engine torque. The alternator 17 can generate electricity while the internal combustion engine 1 is in firing operation, and can charge the sub-power storage device 72 with the generated electricity.

[0026] However, the alternator 17 is smaller than the motor generator 2, and its power generation output is also smaller than the output of the motor generator 2. The power generated by the alternator 17 cannot be used to charge the power storage device 71.

[0027] The power storage device 71 is basically charged by regenerative braking. When the driver of the vehicle releases the accelerator pedal to request deceleration of the vehicle, a fuel cut is performed to temporarily halt fuel injection into the cylinders 11 of the internal combustion engine 1, or the amount of intake air and fuel injection into the cylinders 11 is reduced without performing a fuel cut, allowing firing to continue. In this state, the motor generator 2 is operated as a generator, and the inertial rotation torque transmitted from the axle 61 of the rear wheels 62 to the output shaft of the motor generator 2 is used to rotate the motor generator 2. The motor generator 2, which rotates along with the rear wheels 62, generates electricity and stores the generated electricity in the power storage device 71. Through such regenerative braking, the kinetic energy of the vehicle can be recovered as electrical energy and reused later.

[0028] The motor generator 2 and the power storage device 71 are electrically connected via a VCU (Voltage Control Unit) 81 and an inverter 82, which are responsible for voltage adjustment, AC / DC conversion, and AC frequency control of the power exchanged between the motor generator 2 and the power storage device 71.

[0029] The motor generator 2 and the axle 61 of the rear wheels 62 remain mechanically connected and are not separated from each other (there is no clutch or the like that can be switched between connecting and disconnecting between the motor generator 2 and the axle 61). Therefore, without operating the motor generator 2 as an electric motor, as long as the vehicle is running and the rear wheels 62 are rotating, an electromotive force can be generated in the motor generator 2, which is dragged by the rear wheels 62. If the amount of charge stored in the electricity storage device 71 is significantly reduced and it is desired to restore this as quickly as possible, the amount of intake air and the amount of fuel injected into the cylinders 11 can be increased, in other words, the engine torque can be corrected to increase and the internal combustion engine 1 can be operated in firing mode, and while the vehicle is running in 2WD mode, the motor generator 2 can be operated as a generator to generate electricity and charge the electricity storage device 71.

[0030] From another perspective, when the vehicle is running in 2WD mode, motor generator 2 can operate as a generator and become a load. Therefore, when the vehicle is running in 2WD mode, unless there is a need to charge power storage device 71, it is preferable to cut off the electrical connection between motor generator 2 and power storage device 71 in VCU 81 or inverter 82, and put motor generator 2, which is rotated by rear wheels 62, into a no-load operating state.

[0031] Incidentally, power storage device 71 and sub power storage device 72 are electrically connected via DC / DC converter 83, and it is not possible for sub power storage device 72 to supply electric charge to power storage device 71, but it is possible for power storage device 71 to supply electric charge to sub power storage device 72. If the amount of electric charge stored in power storage device 71 has reached its upper limit and further charging is difficult, the electric power generated by motor generator 2 or the electric power discharged by power storage device 71 can be stepped down by DC / DC converter 83 and charged into sub power storage device 72.

[0032] FIG. 2 shows an overview of an internal combustion engine 1 mounted on a vehicle according to this embodiment. The internal combustion engine 1 is, for example, a spark-ignition four-stroke reciprocating engine and includes a plurality of cylinders 11 (for example, three cylinders, one of which is shown in FIG. 2). An injector 111 that injects fuel toward the intake port is provided near the intake port of each cylinder 11. An ignition plug 112 is attached to the ceiling of the combustion chamber of each cylinder 11. The ignition plug 112 receives an induced voltage generated by an ignition coil and generates a spark discharge between a center electrode and a ground electrode.

[0033] The intake passage 13 for supplying intake air takes in air from the outside and directs it to the intake ports of each cylinder 11. An air cleaner 131, an electronic throttle valve 132, a surge tank 133, and an intake manifold 134 are arranged in this order from upstream to downstream in the intake passage 13. The air cleaner 131 is located at the intake port that takes in air, which is the most upstream part of the intake passage 13. The intake port opens toward the front of the vehicle to take in cool air and increase the charging efficiency of the internal combustion engine.

[0034] The exhaust passage 14 for discharging exhaust gases guides the exhaust gases generated as a result of fuel combustion in the cylinders 11 to the outside from the exhaust ports of each cylinder 11. An exhaust manifold 142 and a three-way catalyst 141 for purifying exhaust gases are arranged on the exhaust passage 14.

[0035] The EGR device 12 includes, as its elements, an external EGR passage 121 that connects the exhaust passage 14 and the intake passage 13, an EGR cooler 122 provided on the EGR passage 121, and an EGR valve 123 that opens and closes the EGR passage 121 to control the flow rate of EGR gas flowing through the EGR passage 121. The inlet of the EGR passage 121 is connected to a location downstream of the catalyst 141 in the exhaust passage 14. The outlet of the EGR passage 121 is connected to a location downstream of the throttle valve 132 in the intake passage 13 (in particular, a surge tank 133 or an intake manifold 134).

[0036] The internal combustion engine 1 is equipped with a brake booster 15 for reducing the operating force required when braking the vehicle, i.e., the force required to press down on the brake pedal. The brake booster 15 introduces intake negative pressure from a location downstream of the throttle valve 132 in the intake passage 13 (particularly, the surge tank 133 or the intake manifold 134) and uses that negative pressure to boost the force required to press down on the brake pedal, and is a well-known device in this field.

[0037] An ECU (Electronic Control Unit) 0, which is a vehicle control device that controls the operation of the internal combustion engine 1 and the motor generator 2, is a microcomputer system having a processor, memory, an input interface, an output interface, etc. The ECU 0 may be configured by connecting multiple ECUs or controllers to each other so that they can communicate with each other via an electric communication line such as a CAN (Controller Area Network).

[0038] The input interface of the ECU 0 includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed VSP of the vehicle, a crank angle signal b output from a crank angle sensor that detects the rotation angle of the crankshaft, which is the output shaft of the internal combustion engine 1, and the engine speed, an accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal by the driver, an intake air temperature / intake pressure signal d output from a temperature / pressure sensor that detects the intake air temperature and intake pressure in the intake passage 13 (particularly, the surge tank 133 or the intake manifold 134) connected to the cylinder 11 of the internal combustion engine 1, a battery SOC (State Of Charge) signal e output from a sensor (particularly, a battery current and / or battery voltage sensor) that detects the amount of charge stored in the power storage device 71, a coolant temperature signal f output from a water temperature sensor that detects the temperature of the coolant of the internal combustion engine 1, and a rotation speed N of the front wheels 52 of the vehicle. Fr The wheel speed signal g output from the wheel speed sensor that detects the rotation speed N of the rear wheel 62 of the vehicle RrThe signals input to the system include a wheel speed signal h output from a wheel speed sensor that detects the speed of the wheels, a signal s provided by a switch that allows the driver to select whether or not to actively drive in 4WD, and an outside air temperature signal t output from an air temperature sensor that detects the outside air temperature.

[0039] However, the wheel speed sensor may also function as a vehicle speed sensor. In such a case, a separate vehicle speed sensor is not provided. The ECU 0 calculates the actual vehicle speed VSP by referring to either the wheel speed signals f or g or by combining these signals.

[0040] The output interface of ECU0 outputs an ignition signal i to the igniter associated with the spark plug 112 of each cylinder 11 of the internal combustion engine 1, a fuel injection signal j to the injector 111, an opening operation signal k to the throttle valve 132, an opening operation signal l to the EGR valve 123, and a signal o to the motor generator 2 (or VCU 81) to control the magnitude of the motor torque it outputs.

[0041] The processor of ECU0 interprets and executes programs stored in memory, calculates operating parameters, and controls the operation of the internal combustion engine 1. ECU0 acquires various pieces of information a, b, c, d, e, f, g, h, s, and t required for control via an input interface, determines the engine speed, and estimates the amount of air (fresh air) to be drawn into cylinder 1. It then determines various operating parameters, such as a required fuel injection amount (enough to achieve a stoichiometric air-fuel ratio or a target air-fuel ratio close to the stoichiometric air-fuel ratio) commensurate with the intake air amount, fuel injection timing (including the number of fuel injections per combustion), fuel injection pressure, ignition timing (including the number of ignitions per combustion), required EGR rate (or EGR gas amount or EGR gas partial pressure), and output torque of the motor-generator 2. ECU0 applies various control signals i, j, k, l, and o corresponding to the operating parameters via an output interface.

[0042] The ECU 0 of this embodiment determines the magnitude of the drive torque to be applied to the drive wheels of the vehicle based on the accelerator opening operated by the driver. The greater the accelerator opening, the greater the required drive torque.

[0043] Then, ECU0 determines the ratio of the required driving torque based on the accelerator opening amount, i.e., how much of the required driving torque will be input from the internal combustion engine 1 to the axle 51 of the front wheels 52, and how much will be input from the motor generator 2 to the axle 61 of the rear wheels 62.

[0044] As shown in Fig. 3, ECU0 first checks whether the 4WD switch is ON or OFF (step S1). If the driver has turned the 4WD switch ON, it means that the driver actively desires 4WD driving. If the driver has turned the switch OFF, it means that the driver does not actively desire 4WD driving, but rather desires 2WD driving.

[0045] When the 4WD switch is ON, the vehicle runs in 4WD mode as long as the conditions in steps S2 and S3 below are met. The ECU 0 determines whether the amount of charge currently stored in the power storage device 71 is greater than a threshold value, in other words, whether the current SOC is greater than or equal to a threshold SOC. min It is checked whether it exceeds (step S2).

[0046] The current amount of stored electricity in the electricity storage device 71 has decreased to or below the threshold value, or the SOC has reached the threshold SOC min If it is equal to or less than this, the motor generator 2 is not operated as an electric motor. In other words, motor torque is not input from the motor generator 2 to the axle 61 of the rear wheels 62. Then, 100% of the required drive torque based on the accelerator opening is provided by the engine torque output by the internal combustion engine 1, and this engine torque is input to the axle 51 of the front wheels 52 (step S9). In short, the vehicle is made to run in 2WD. This is intended to prevent the charge stored in the power storage device 71 from being consumed and causing a shortage.

[0047] The current amount of stored electricity in the electricity storage device 71 is greater than the threshold value, or the SOC is greater than the threshold SOC min If the current vehicle speed VSP is greater than the threshold VSP max It is checked whether it is equal to or less than this (step S3).

[0048] Current vehicle speed VSP is the threshold VSP max If the acceleration / decrease ratio is higher than 0.05, there is little concern that the front wheels 52, which are the drive wheels, will slip and cause problems in driving the vehicle. Therefore, the motor generator 2 is not operated as an electric motor, and motor torque is not input from the motor generator 2 to the axle 61 of the rear wheels 62. Then, 100% of the required drive torque based on the accelerator opening is covered by the engine torque output by the internal combustion engine 1, and this engine torque is input to the axle 51 of the front wheels 52 (step S9).

[0049] Current vehicle speed VSP is the threshold VSP max If it is lower than this, the motor generator 2 is operated as an electric motor, and the motor torque output by the motor generator 2 is permitted to be input to the axle 61 of the rear wheels 62 (step S4). In other words, the vehicle is made to run in 4WD. At this time, the ECU 0 calculates the current vehicle speed VSP and the current rotation speed N of the front wheels 52. Fr and the rotation speed of the rear wheel 62 N Rr The difference between (N Fr -N Rr ) the ratio of the engine torque input to the axle 51 of the front wheels 52 and the motor torque input to the axle 61 of the rear wheels 62 is variably adjusted.

[0050] FIG. 4 shows the ratio of the motor torque input by the motor generator 2 to the axle 61 of the rear wheels 62 to the required drive torque based on the accelerator opening. Note that the values ​​in the figure are merely examples. In accordance with the illustrated example, the current vehicle speed VSP is 20 km / h, and the current rotation speed difference (N Fr -N Rr) is 10 rpm, 28% of the required drive torque is output by the motor generator 2 and applied to the axle 61 of the rear wheels 62, and the remaining 72% is output by the internal combustion engine 1 and applied to the axle 51 of the front wheels 52. In other words, the engine torque output by the internal combustion engine 1 is reduced by the 28% that is covered by the motor torque.

[0051] The ECU 0 stores in advance in its memory the vehicle speed VSP and the rotation speed difference (N Fr -N Rr ) and the ratio of motor torque to the required drive torque. Fr -N Rr ) is used as a key to search the map and determine the proportion of the required drive torque that should be accounted for by the motor torque.

[0052] As a trend of the map data, the difference in rotation speed between the front wheel 52 and the rear wheel 62 (N Fr -N Rr ) are the same, the lower the vehicle speed VSP, the more the motor torque input to the axle 61 of the rear wheels 62 increases and the more the engine torque input to the axle 51 of the front wheels 52 decreases. Conversely, the higher the vehicle speed VSP, the more the engine torque input to the axle 51 of the front wheels 52 increases and the more the motor torque input to the axle 61 of the rear wheels 62 decreases.

[0053] When attempting to start or accelerate the vehicle from a situation where the vehicle speed VSP is 0 or low, there is a high possibility that the front wheels 52, which are the drive wheels, will slip. Therefore, not only the front wheels 52 but also the rear wheels 62 are used as drive wheels to ensure that the vehicle can be started or accelerated reliably.

[0054] Conversely, the higher the vehicle speed VSP, the less likely front wheels 52 are to slip, and even if they do slip, the smaller the impact on the vehicle's running. Therefore, the motor torque output by motor generator 2 is reduced to suppress the power consumption by motor generator 2. This suppresses a decrease in the amount of electricity stored in power storage device 71 and a drop in SOC.

[0055] In addition, if the vehicle speed VSP is the same, the rotation speed difference between the front wheels 52 and the rear wheels 62 (N Fr -N Rr ) is larger, the motor torque input to the axle 61 of the rear wheel 62 is increased, and the engine torque input to the axle 51 of the front wheel 52 is reduced. Fr -N Rr ) is larger, the engine torque input to the axle 51 of the front wheels 52 is increased, and the motor torque input to the axle 61 of the rear wheels 62 is reduced.

[0056] RPM difference (N Fr -N Rr ) becomes large because the front wheels 52, which are the drive wheels, are actually slipping, causing the rotation speed of the front wheels 52 to be higher than the rotation speed of the rear wheels 62. Therefore, the engine torque input to the axle 51 of the front wheels 52 is reduced, and at the same time, the motor torque input to the axle 61 of the rear wheels 62, which are also drive wheels, is increased, so that the vehicle can be reliably started or accelerated.

[0057] On the other hand, the difference in rotation speed (N Fr -N Rr ) is a small positive value or close to 0, it can be said that front wheels 52 are not slipping. Therefore, the motor torque output by motor generator 2 is reduced to suppress the power consumption by motor generator 2. This suppresses the decrease in the amount of electricity stored in power storage device 71 and the drop in SOC.

[0058] In addition, the rotation speed difference (N Fr -N Rr When the rotation speed difference (N Fr -N Rr ) is negative and its absolute value exceeds a predetermined value, the motor generator 2 is stopped from operating as an electric motor, and the motor torque input to the axle 61 of the rear wheels 62 is set to 0. Then, 100% of the required drive torque based on the accelerator opening is provided by the engine torque output by the internal combustion engine 1, and this engine torque is input to the axle 51 of the front wheels 52. In the illustrated example, the rotation speed difference (N Fr -N Rr) is -20 rpm or less, the motor torque is set to 0% and the engine torque is set to 100%.

[0059] Thus, the ECU 0 calculates the engine torque and the motor torque so that the required drive torque based on the accelerator opening is achieved. The ECU 0 controls the opening of the throttle valve 132 to introduce a required amount of intake air into the cylinder 11 and inject a required amount of fuel into the cylinder 11 for combustion so that the engine torque can be output from the internal combustion engine 1. The ECU 0 also controls the magnitude of the voltage and / or current applied to the motor generator 2, which is an electric motor, so that the motor torque can be output from the motor generator 2.

[0060] Returning to step S1 in FIG. 3, when the 4WD switch is OFF, the vehicle will generally run in 2WD mode. However, if all of the conditions in steps S5 to S8 below are met, the vehicle will automatically switch to temporary 4WD mode in order to prevent slippage of the front wheels 52, which are the driving wheels. The ECU 0 determines whether the current outside air temperature T is equal to or lower than the threshold T min It is checked whether the threshold T min is set to, for example, 0°C or a value close to it.

[0061] The current outside temperature T is the threshold T min If the difference is higher than , the motor generator 2 is not operated as an electric motor. In other words, motor torque is not input from the motor generator 2 to the axle 61 of the rear wheels 62. Then, 100% of the required drive torque based on the accelerator opening is provided by the engine torque output by the internal combustion engine 1, and this engine torque is input to the axle 51 of the front wheels 52 (step S9). In short, the vehicle is made to run in 2WD. This is because there is little risk of the front wheels 52, which are the drive wheels, slipping due to snowfall or frozen road surfaces, rather than because the outside air temperature is not low, such as below zero.

[0062] The current outside temperature T is the threshold T min If the temperature is lower than the current value, then the current rotation speed N of the front wheels 52 is Fr and the rotation speed of the rear wheel 62 NRr The difference between (N Fr -N Rr ) is the threshold N min It is checked whether it exceeds (step S6).

[0063] The current difference in rotation speed between the front wheel 52 and the rear wheel 62 (N Fr -N Rr ) is the threshold N min If it is below this, it is assumed that no particular slippage is occurring. Therefore, the motor generator 2 is not operated as an electric motor, and motor torque is not input from the motor generator 2 to the axle 61 of the rear wheels 62. Then, 100% of the required drive torque based on the accelerator opening is covered by the engine torque output by the internal combustion engine 1, and this engine torque is input to the axle 51 of the front wheels 52 (step S9).

[0064] The current difference in rotation speed between the front wheel 52 and the rear wheel 62 (N Fr -N Rr ) is the threshold N min If the current SOC is greater than the threshold SOC, it is assumed that a slip is occurring and that it is necessary to suppress the slip. min It is checked whether it exceeds (step S7).

[0065] The current amount of stored electricity in the electricity storage device 71 has decreased to or below the threshold value, or the SOC has reached the threshold SOC min If it is equal to or less than this, the motor generator 2 is not operated as an electric motor, and motor torque is not input from the motor generator 2 to the axle 61 of the rear wheels 62, even though slippage is occurring. Then, 100% of the required drive torque based on the accelerator opening is provided by the engine torque output by the internal combustion engine 1, and this engine torque is input to the axle 51 of the front wheels 52 (step S9). This is intended to prevent the charge stored in the power storage device 71 from being consumed and causing a shortage.

[0066] The current amount of stored electricity in the electricity storage device 71 is greater than the threshold value, or the SOC is greater than the threshold SOC minIf the current vehicle speed VSP is greater than the threshold VSP max It is checked whether it is equal to or less than this (step S8).

[0067] Current vehicle speed VSP is the threshold VSP max If the slippage is greater than or equal to 100%, there is little concern that the vehicle will be hindered from running even if slippage occurs. Therefore, the motor generator 2 is not operated as an electric motor, and motor torque is not input from the motor generator 2 to the axle 61 of the rear wheels 62. Then, 100% of the required drive torque based on the accelerator opening is covered by the engine torque output by the internal combustion engine 1, and this engine torque is input to the axle 51 of the front wheels 52 (step S9).

[0068] Current vehicle speed VSP is the threshold VSP max If the vehicle speed VSP is lower than the predetermined value, the motor generator 2 is operated as an electric motor, and the motor torque output by the motor generator 2 is permitted to be input to the axle 61 of the rear wheels 62 (step S4). In other words, the vehicle is made to run in 4WD mode. At this time, the ECU 0, as already described in detail, calculates the current vehicle speed VSP and the current rotation speed N of the front wheels 52. Fr and the rotation speed of the rear wheel 62 N Rr The difference between (N Fr -N Rr ) the ratio of the engine torque input to the axle 51 of the front wheels 52 and the motor torque input to the axle 61 of the rear wheels 62 is variably adjusted.

[0069] In this embodiment, a vehicle is controlled in which the axles 51 of the front wheels 52 are rotationally driven by an internal combustion engine 1 that burns fuel to generate torque, and the axles 61 of the rear wheels 62 are rotationally driven by a motor generator 2 that is an electric motor that receives power supply from an electricity storage device 71 and generates torque, and the current vehicle speed VSP and the rotation speed difference (N Fr -N Rr The vehicle control device 0 is configured to variably adjust the ratio between the drive torque input from the internal combustion engine 1 to the axle 51 of the front wheels 52 and the drive torque input from the motor generator 2 to the axle 61 of the rear wheels 62, depending on the vehicle speed.

[0070] In detail, when the vehicle speed VSP is higher, the ratio of the driving torque input by the motor generator 2 to the axle 61 of the rear wheels 62 to the driving torque input by the internal combustion engine 1 to the axle 51 of the front wheels 52 is made smaller than when the vehicle speed VSP is lower.

[0071] Also, the rotation speed N of the front wheel 52 Fr from rear wheel 62 rotation speed N Rr The difference in rotation speed (N Fr -N Rr ) is larger, the rotation speed difference (N Fr -N Rr ) is smaller, the ratio of the driving torque input by the motor generator 2 to the axle 61 of the rear wheels 62 to the driving torque input by the internal combustion engine 1 to the axle 51 of the front wheels 52 is made larger.

[0072] According to this embodiment, 4WD driving is performed to effectively prevent slippage and ensure the vehicle's off-road capability and drivability when driving on rough roads such as during snowfall, frozen roads, rainy weather, or muddy conditions when slippage of the wheels 52, 62 is likely to occur, and the vehicle is driven in 2WD driving mode most of the time. In other words, the period during which the rear wheels 62 are driven by the motor generator 2 is minimized, so the charge stored in the power storage device 71 is not consumed excessively, and it is possible to constantly maintain the SOC at a certain level or above.

[0073] There is no need to install a generator that is larger and has a higher output than the existing alternator 17 as an accessory driven by the internal combustion engine 1. This eliminates the need to take up space in the limited engine room (engine compartment) and avoids cost increases. The increase in weight and the resulting deterioration in fuel economy that would result from installing a large generator can also be avoided.

[0074] It should be noted that the present invention is not limited to the embodiments described above. For example, in the vehicle of the above embodiment, the axle 51 of the front wheels 52 is driven to rotate by the internal combustion engine 1, and the axle 61 of the rear wheels 62 is driven to rotate by the motor generator 2, which is an electric motor. However, it goes without saying that the control of the present invention can also be applied to a vehicle configured to drive the axle of the rear wheels to rotate by the internal combustion engine, and the axle of the front wheels to rotate by the motor generator, which is an electric motor.

[0075] In addition, the specific configuration of each part and the contents of processing can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0076] 0...Control unit (ECU) 1...Internal combustion engine 2...Electric motor (motor generator) 51...Front wheel axle 52...Front wheel 61...Rear wheel axle 62...Rear wheel

Claims

1. This system controls a vehicle in which the front axle is driven to rotate by an internal combustion engine that burns fuel to generate torque, and the rear axle is driven to rotate by an electric motor that receives power from an electricity storage device and generates torque, The ratio of the drive torque input to the corresponding axle from the internal combustion engine and the drive torque input to the corresponding axle from the electric motor is variably adjusted according to the current vehicle speed and the difference in rotation speed between the front wheels and the rear wheels, When the rotation speed difference obtained by subtracting the rotation speed of the rear wheels from the rotation speed of the front wheels is larger, the ratio of the drive torque input by the electric motor to the drive torque input by the internal combustion engine to the corresponding axle is made larger compared to when the rotation speed difference is smaller; However, if the rotation speed difference is negative and its absolute value exceeds a predetermined value, the vehicle control device sets the drive torque input from the electric motor to the corresponding axle to zero.

2. 2. The vehicle control device according to claim 1, wherein the ratio of the drive torque input by the electric motor to the corresponding axle to the drive torque input by the internal combustion engine to the corresponding axle is made smaller when the vehicle speed is higher than when the vehicle speed is lower.

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