JP2014034340A - Vehicle control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vehicle control unit making it possible to shorten a delay in a response to shift to a four-wheel drive state when a four-wheel drive shift condition is satisfied during turning of a vehicle whose front and rear wheels can be steered.SOLUTION: A front-wheel cornering drag and a rear-wheel cornering drag in a 4WS (Four-Wheel Steering) vehicle are estimated. As the rear-wheel drag, a larger value is estimated when steering directions of the front and rear wheels are in phase with each other than when the steering directions are out of phase from each other. A vehicle body deceleration is estimated from the estimated cornering drag forces, and electronically controlled couplings are controlled so that a pre-torque which is set to be larger as the vehicle body deceleration is higher is applied to the rear wheels during turning acceleration of the vehicle. The pre-torque is applied to the rear wheels, and when a condition for shift to a four-wheel drive state is satisfied later, the shift to the four-wheel drive state is immediately completed.

Description

  The present invention relates to a vehicle control device capable of changing a distribution ratio of drive torque applied to main drive wheels and slave drive wheels. In particular, the present invention relates to control during turning of this type of vehicle.

  A vehicle equipped with a driving force source such as an engine is equipped with a driving torque distribution device that can change the distribution ratio of the driving torque applied to the front and rear wheels. There is known a vehicle capable of switching between a two-wheel drive state in which a vehicle is driven on one side of a wheel and a four-wheel drive state in which the vehicle is driven on both front wheels and rear wheels (see, for example, Patent Document 1 below) ).

  In this type of vehicle, when a four-wheel drive transition condition is established such as when the main drive wheel slips during traveling in the two-wheel drive state, the drive torque distribution device operates to drive torque to the slave drive wheel. A part of the vehicle is allocated and switched to a four-wheel drive state, thereby achieving driving stability.

JP 2005-145334 A JP 2008-290665 A JP 2011-225019 A

  Incidentally, as disclosed in Patent Document 2, it is generally known that when a vehicle turns, the vehicle is decelerated by a cornering drag (cornering resistance) that acts on the steered wheels. The deceleration of the vehicle due to the cornering drag similarly occurs in a vehicle that can switch between the two-wheel drive state and the four-wheel drive state described above. That is, for example, in the case of a four-wheel drive vehicle based on the FF (front engine / front drive) system, the vehicle decelerates by cornering drag when turning while traveling in a two-wheel drive state. Accordingly, the rotational speed of the rear wheel, which is a driven wheel, is also reduced.

  In addition, if the driver requests acceleration while turning in such a two-wheel drive state, the driving speed of the front wheels, which are the main drive wheels, increases and the vehicle speed increases accordingly. The rotational speed of the rear wheels also increases.

  When the four-wheel drive transition condition is satisfied in such a situation, the fastening force of the drive torque distribution device is increased to shift to the four-wheel drive state.

  However, in this case, when the condition for shifting to the four-wheel drive state is satisfied, no driving force is generated in the rear wheels, and the rear wheels are in a rotated state due to frictional force with the road surface. That is, the rotational inertia of the rear wheel is low. For this reason, even if the fastening force of the drive torque distribution device is increased with the establishment of the condition for shifting to the four-wheel drive state, the drive force is applied to the rear wheels during the period until the rotational inertia of the rear wheels is increased to a predetermined value. Can no longer be generated. That is, it takes time until the transition to the four-wheel drive state is actually completed after the four-wheel drive transition condition is satisfied. As a result, a response delay occurs in the transition to the four-wheel drive state during turning of the vehicle, which may give the driver a sense of discomfort.

  The inventor of the present invention considered the control for suppressing the response delay of the transition to the four-wheel drive state due to the influence of the cornering drag. In particular, in a vehicle capable of steering not only the front wheels of the vehicle but also the rear wheels (for example, a four-wheel steering vehicle disclosed in Patent Document 3), the steering directions of the front wheels and the rear wheels are the same direction. Response delay when shifting to the four-wheel drive state due to the difference in the size of the cornering drag between the case of the same phase and the case of the opposite phase where the steering directions of the front and rear wheels are different We paid attention to the difference between the two. Then, it was considered that the response delay due to the influence of the cornering drag in this type of vehicle is suppressed and the response to the transition to the four-wheel drive state is improved.

  The present invention has been made in view of such a point, and an object of the present invention is to enter a four-wheel drive state when a four-wheel drive transition condition is satisfied during turning of a vehicle capable of steering front and rear wheels. It is an object of the present invention to provide a vehicle control device capable of shortening the response delay of transition.

  Specifically, the present invention includes a driving force source that outputs a driving torque for traveling, and one of the front wheels and the rear wheels is a main driving wheel, and the other is a sub driving wheel, with respect to the main driving wheel and the sub driving wheel. By changing the distribution ratio of the drive torque, it is possible to switch between a two-wheel drive state in which the drive torque is transmitted only to the main drive wheel and a four-wheel drive state in which the drive torque is transmitted to both the main drive wheel and the slave drive wheel. A vehicle control device is assumed. When the vehicle accelerates when turning, the vehicle control device applies a pre-torque corresponding to the rotational inertia of the driven wheels to the driven wheels, and the front and rear wheels are steered as the pre-torque applied at this time. The case where the direction is the same as compared with the case where the direction is the opposite phase is set larger, and then, when the condition for shifting to the four-wheel drive state is satisfied, the driving torque for setting the four-wheel drive state is set to the subordinate. It is set as the structure provided to a driving wheel.

  The application of the pre-torque to the driven wheels in the present solution is executed on the condition that the vehicle accelerates when turning, and is executed even if the condition for shifting to the four-wheel drive state is not satisfied. . Then, when the transition condition to the four-wheel drive state is satisfied, the transition to the four-wheel drive state is made by applying a drive torque larger than the pre-torque to the slave drive wheels.

  The effect | action by the specific matter of this solution is demonstrated below. First, when the vehicle turns, the rotational inertia of the driven wheels decreases as the vehicle speed decreases due to the influence of the cornering drag. For this reason, on the condition that the vehicle is accelerating at the time of turning, a pre-torque corresponding to the rotational inertia is applied to the driven wheels so as to increase the rotational inertia of the lowered driven wheels. . The pre-torque applied at this time is set to be larger when the front wheels and the rear wheels are in the same phase than when the steering directions are in opposite phases. In this way, a pre-torque is applied to the driven wheel according to the rotational inertia of the driven wheel, which is correlated to the size of the total cornering drag, which is the sum of the cornering drag generated at the front wheel and the cornering drag generated at the rear wheel. Is done. After that, when the condition for shifting to the four-wheel drive state is satisfied, the distribution ratio of the drive torque to the driven wheels is increased and the four-wheel drive state is shifted to. At the time of transition, the pre-torque is preliminarily applied to the driven wheels as described above, and the rotational inertia of the driven wheels is high. For this reason, the driving force can be generated in the driven wheels almost simultaneously with the increase in the distribution ratio of the driving torque to the driven wheels when the condition for shifting to the four-wheel drive state is established, and immediately the four-wheel drive state is entered. Will complete the transition. In particular, in the present solution, as described above, it is possible to optimize the pre-torque according to the steering direction of the front wheels and the rear wheels (whether the phase is the same or opposite), and the steering direction of the front wheels and the rear wheels. Regardless of whether they are in the opposite phase or in the same phase, it is possible to stably suppress a response delay in shifting to the four-wheel drive state. In other words, when the steering directions of the front wheels and the rear wheels are in phase (when the amount of decrease in rotational inertia of the driven wheels is relatively large), the response delay in shifting to the four-wheel drive state becomes large. In the case where the steering directions of the front wheels and the rear wheels are in opposite phases (when the amount of decrease in rotational inertia of the driven wheels is relatively small), it is possible to avoid a situation where pre-torque is applied more than necessary, It is possible to optimize the responsiveness of the transition to the four-wheel drive state while the vehicle is turning.

  Specifically, as the pre-torque applied to the driven wheels, the value of the pre-torque is set to be larger as the rotational inertia of the driven wheels when the vehicle accelerates when turning.

  As a result, a pre-torque suitable for the rotational inertia of the driven wheels can be applied to the driven wheels, and the transition to the four-wheel drive state is completed after the transition condition to the four-wheel drive state is satisfied. Can be made uniform regardless of the rotational inertia of the driven wheel.

  Parameters correlated with the rotational inertia of the driven wheel include vehicle body deceleration due to the effects of front wheel cornering drag and rear wheel cornering drag, total cornering drag which is the sum of front wheel cornering drag and rear wheel cornering drag, front wheel And the steering angle of the rear wheels. Specifically, the rotational inertia of the driven wheel is influenced by the front wheel cornering drag that acts on the front wheel when the vehicle turns and the rear wheel cornering drag that acts on the rear wheel when the rear wheel is steered. There is a correlation with the vehicle body deceleration due to, and the greater the vehicle body deceleration, the lower the rotational inertia of the driven wheel. Further, the rotational inertia of the driven wheel is correlated with the front wheel cornering drag that acts on the front wheel when the vehicle turns, and the rear wheel cornering drag that acts on the rear wheel when the rear wheel is steered, The larger the total cornering drag that is the sum of the front wheel cornering drag and the rear wheel cornering drag, the lower the rotational inertia of the driven wheel. The rotational inertia of the driven wheel is correlated with the steering angle of the front wheel and the steering angle of the rear wheel when the vehicle turns. The larger the steering angle, the lower the rotational inertia of the driven wheel.

  For this reason, it is possible to estimate the rotational inertia of the driven wheel based on any one of the vehicle body deceleration, the total cornering drag, and the steering angle. The pre-torque is obtained according to the rotational inertia of the driven wheel, and the pre-torque Can be applied to the driven wheel. As a result, the rotational inertia of the driven wheel can be estimated by a relatively simple means, the arithmetic processing for estimating the rotational inertia can be simplified, and the load on the arithmetic means such as the ECU can be reduced. Can be reduced.

  Further, the pre-torque applied to the slave drive wheel is limited to a pre-torque upper limit value set based on the difference between the rotational speed of the front wheel and the rotational speed of the rear wheel. That is, when the pre-torque calculated according to the rotational inertia exceeds the pre-torque upper limit value, the pre-torque applied to the driven wheels is limited to the pre-torque upper limit value.

  In this case, the pre-torque upper limit value is set lower as the difference between the rotational speed of the front wheels and the rotational speed of the rear wheels is smaller.

  In order to improve the turning ability of the vehicle at the time of turning, it is desirable that the rear wheels pass through a movement locus on the outside (outside the corner) with respect to the movement locus of the front wheels. That is, it is desirable for the vehicle to turn in a state where the rotational speed of the rear wheels is higher than the rotational speed of the front wheels. If the rotational speed of the rear wheel decreases to the rotational speed of the front wheel, there is a possibility that the turning ability of the vehicle cannot be improved. Therefore, a pre-torque upper limit value is set based on the difference between the rotational speed of the front wheels and the rotational speed of the rear wheels, and the pre-torque is limited so that the rotational speed of the rear wheels is sufficiently higher than the rotational speed of the front wheels. To ensure the vehicle's turning ability. That is, the minimum necessary pre-torque is applied to the rear wheel while ensuring the turning ability of the vehicle. As a result, it is possible to achieve both ensuring the turning ability of the vehicle and improving the responsiveness to the four-wheel drive state.

  Further, when at least one of turning and acceleration of the vehicle is released without satisfying the condition for shifting to the four-wheel drive state with pre-torque applied to the slave drive wheels, the four-wheel drive state is set. The application of the pre-torque is canceled without applying the driving torque to the slave driving wheel.

  Thereby, as described above, even when the condition for shifting to the four-wheel drive state is not satisfied, during the turning acceleration of the vehicle, the driving force accompanying the application of the pre-torque is generated in the driven wheel, The turn is performed in a state where the turning performance of the vehicle is enhanced. When at least one of turning and acceleration of the vehicle is released, the pre-torque is released, so that it is possible to shift to traveling in a two-wheel drive state that can improve the fuel consumption rate. Become.

  In the present invention, during the turning acceleration of the vehicle, pre-torque corresponding to the case where the steering directions of the front wheels and the rear wheels are in opposite phases and in the same phase is applied to the driven wheels to increase the rotational inertia. For this reason, when the four-wheel drive transition condition is subsequently satisfied, the transition to the four-wheel drive state can be completed without causing a response delay.

1 is a schematic configuration diagram illustrating a power transmission system of a vehicle according to an embodiment. It is a schematic block diagram which shows the steering system of the vehicle which concerns on embodiment. It is a block diagram which shows schematic structure of the control system of the vehicle which concerns on embodiment. It is a figure which shows the relationship between the exciting current to an electronically controlled coupling, and the transmission torque of an electronically controlled coupling. It is a flowchart figure which shows the procedure of pretorque control. It is a figure which shows a front wheel cornering drag map. It is a figure which shows a rear-wheel cornering drag map. It is a figure which shows a pre-torque upper limit map. Shows the temporal change of the rear wheel torque when switching from the two-wheel drive state to the four-wheel drive state during turning, and the solid line shows the temporal change of the rear wheel torque when the front wheel and the rear wheel are in phase in the embodiment. In the embodiment, the temporal change of the rear wheel torque when the front wheels and the rear wheels are in opposite phases is indicated by a broken line, and the temporal change of the rear wheel torque in the prior art is indicated by a two-dot chain line. It is a figure which shows the pre-torque upper limit map in the modification 1. FIG. 10 is a schematic configuration diagram showing a vehicle according to a second modification. FIG. 10 is a block diagram showing a schematic configuration of a vehicle control system according to Modification 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a conventional vehicle equipped with a four-wheel steering mechanism capable of steering the front and rear wheels and adopting a standby four-wheel drive system based on the FF (front engine / front drive) system (only the engine as a driving force source). A case where the present invention is applied to a mounted vehicle) will be described.

  First, a schematic configuration of the vehicle according to the present embodiment will be described. Hereinafter, each of the power transmission system and the steering system of the vehicle will be described.

(Vehicle power transmission system)
FIG. 1 is a schematic configuration diagram showing a power transmission system of a vehicle according to the present embodiment.

  As shown in FIG. 1, the power transmission system of the vehicle includes an engine (internal combustion engine) 1 that generates driving torque for vehicle travel, a torque converter 2, an automatic transmission 3, a front wheel differential device 41, a front wheel axle (front wheel). Drive shaft) 42, front wheels (main drive wheels) 43L and 43R, transfer 51, propeller shaft 52, electronic control coupling 6, rear wheel differential device 71, rear wheel axle (rear drive shaft) 72, rear wheel (slave drive) Wheel) 73L, 73R. The engine 1 and the electronic control coupling 6 are controlled by an ECU 10. The vehicle control device according to the present invention is realized by a program executed by the ECU 10.

  Next, components such as the engine 1, the torque converter 2, the automatic transmission 3, the transfer 51, and the electronic control coupling 6 will be described.

-Engine-
The engine 1 is a known power device that is configured by a gasoline engine, a diesel engine, or the like, and outputs power by burning fuel. The engine 1 also includes, for example, a throttle opening (opening for adjusting the intake air amount) of a throttle valve (not shown) provided in the intake passage, fuel injection amount, ignition timing (in the case of a gasoline engine). It is comprised so that the driving | running state, such as, can be controlled.

-Torque converter, automatic transmission, etc.-
The torque converter 2 includes an input-side pump impeller, an output-side turbine runner, and the like, and transmits power between the pump impeller and the turbine runner via a fluid (hydraulic oil). The pump impeller is connected to a crankshaft (not shown) that is an output shaft of the engine 1. The turbine runner is connected to the input shaft of the automatic transmission 3 via a turbine shaft.

  The automatic transmission 3 is a stepped (planetary gear type) automatic transmission that sets a gear stage using a friction engagement device such as a clutch and a brake and a planetary gear unit. The automatic transmission 3 may be a continuously variable transmission (CVT) such as a belt type that continuously adjusts the gear ratio. Further, the transmission may be a manual transmission (manual transmission).

  An output gear (not shown) is connected to the output shaft of the automatic transmission 3 so as to rotate together. The output gear meshes with the differential driven gear 41a of the front wheel differential device 41, and the drive torque transmitted to the output shaft of the automatic transmission 3 is transmitted through the front wheel differential device 41 and the front wheel axle 42 to the left and right front wheels 43L, 43R. The rotational speeds of the left and right front wheels 43L and 43R are detected by the left front wheel speed sensor 94L and the right front wheel speed sensor 94R, respectively.

-Transfer etc.-
The transfer 51 includes a drive gear 51a that is rotatably coupled to the front wheel differential device 41 and a driven gear 51b that meshes with the drive gear 51a, and changes the torque transmission direction from the vehicle width direction to the rear of the vehicle body. . A propeller shaft 52 is rotatably connected to the driven gear 51b. The propeller shaft 52 is connected to the left and right rear wheels 73L and 73R via the electronic control coupling 6, the rear wheel differential device 71, and the rear wheel axle 72. The driving torque transmitted from the front wheel differential device 41 to the transfer 51 is transmitted to the propeller shaft 52 and the electronic control coupling 6, and the electronic control coupling 6 is in an engaged state (coupling torque transmission state; hereinafter). In this case, the drive torque is transmitted (distributed) to the left and right rear wheels 73L and 73R via the rear wheel differential device 71 and the rear wheel axle 72. The rotational speeds of the left and right rear wheels 73L and 73R are detected by the left rear wheel speed sensor 95L and the right rear wheel speed sensor 95R, respectively.

-Electronically controlled coupling-
The electronically controlled coupling (drive torque distribution device) 6 is, for example, a pilot clutch type, and includes a main clutch composed of a multi-plate friction clutch, a pilot clutch (electromagnetic multi-plate clutch), a cam mechanism, an electromagnet, and the like. The pilot clutch is engaged by the electromagnetic force of the electromagnet, and the engagement force is transmitted to the main clutch by the cam mechanism so that the main clutch is engaged (specific configuration) For example, refer to JP 2010-254135 A).

  In the electronically controlled coupling 6, the torque capacity, that is, the coupling torque Tc is controlled by controlling the exciting current Ie supplied to the electromagnet, and the rear wheels 73L and 73R with respect to the total driving torque. The drive torque distribution ratio to the side can be adjusted steplessly within a range of 0 to 50%, for example. The exciting current Ie to the electromagnet of the electronic control coupling 6 is controlled by the ECU 10.

  FIG. 4 shows the relationship between the excitation current Ie to the electromagnet of the electronic control coupling 6 and the transmission torque (coupling torque) Tc of the electronic control coupling 6. In this way, it is possible to variably control the transmission torque Tc of the electronic control coupling 6 according to the excitation current Ie that is the actuator operation amount.

  For example, when the exciting current Ie to the electronic control coupling 6 is “0”, the main clutch is disengaged (released) and the transmission rate of the transmission torque Tc is “0%”. A traveling state equivalent to the front wheel drive state (two-wheel drive state by front wheel drive) is realized. On the other hand, when the excitation current Ie to the electronic control coupling 6 is increased, the transmission torque Tc increases. When the excitation current Ie is I1 in the figure, the transmission rate of the transmission torque Tc is “100% (drive torque distribution rate). Is equal to 50%), that is, the driving torque distribution to the rear wheels 73L and 73R is maximized, and a traveling state equivalent to the directly connected four-wheel driving state is realized. In this manner, the drive torque distribution between the front and rear wheels can be variably controlled in accordance with the excitation current Ie to the electronic control coupling 6.

  As one of the basic controls of the electronic control coupling 6 by the ECU 10, for example, during traveling in a two-wheel drive state in which the exciting current Ie to the electromagnet of the electronic control coupling 6 is “0”, the front wheels When a slip occurs at 43L and 43R, the excitation current Ie is supplied to generate the transmission torque Tc. As a result, the vehicle shifts from the two-wheel drive state to the four-wheel drive state, and traveling stability is ensured. In this case, the value of the excitation current Ie is set to a higher value as the slip amount of the front wheels 43L and 43R is larger, and the transmission torque Tc is set higher. In addition, the presence or absence of the occurrence of slip on the front wheels 43L and 43R is performed by comparing the wheel speeds detected by the wheel speed sensors 94L, 94R, 95L, and 95R. Further, even when the driver selects the 4WD travel mode by the 2WD-4WD selection switch arranged in the passenger compartment, the exciting current Ie is supplied to generate the transmission torque Tc, whereby the vehicle is driven by two wheels. The state shifts from the state to the four-wheel drive state.

(Vehicle steering system)
FIG. 2 is a schematic configuration diagram showing a vehicle steering system according to the present embodiment.

  The vehicle steering system according to the present embodiment includes a four-wheel steering mechanism 8 that controls the steering angle of the front wheels 43L and 43R and the steering angle of the rear wheels 73L and 73R, respectively. With this four-wheel steering mechanism 8, the steering direction of the front wheels 43L, 43R and the steering direction of the rear wheels 73L, 73R are in the same phase state, or the steering direction of the front wheels 43L, 43R and the rear wheels 73L, 73R It is possible to set the anti-phase state to a direction different from the steering direction.

  The front wheels 43L and 43R indicated by broken lines in FIG. 2 are steered to the right, and the rear wheels 73L and 73R indicated by broken lines in FIG. 2 are in phase with the steering direction of the front wheels 43L and 43R (right Steered). On the other hand, the rear wheels 73L and 73R indicated by the alternate long and short dash line in FIG. 2 are in a state of being opposite in phase (steered to the left) with respect to the steering direction (right direction) of the front wheels 43L and 43R.

  Hereinafter, the four-wheel steering mechanism 8 will be specifically described.

  The four-wheel steering mechanism 8 includes a steering wheel 81, a steering shaft 82, a front wheel steering angle sensor 92F, a front wheel steering actuator 83, a front wheel steering shaft (rack bar) 84, a rear wheel steering actuator 85, a rear wheel steering angle sensor 92R, A rear-wheel steering shaft 86 is provided, and the front wheels 43L and 43R and the rear wheels 73L and 73R can be steered independently of each other.

  The steering wheel 81 is a physical operation means configured to allow a steering input by a driver.

  The steering shaft 82 is a shaft body having one end connected to the steering wheel 81 and configured to be rotatable in conjunction with the rotation of the steering wheel 81.

  The front wheel steering angle sensor 92F is a sensor configured to be able to detect a steering angle that is a steering amount of the steering wheel 81 (a steering amount by a driver). The front wheel steering angle sensor 92F is electrically connected to the ECU 10.

  The front wheel steering actuator 83 is configured to be able to steer the front wheels 43L and 43R by moving a front wheel steering shaft 84 that interconnects the left front wheel 43L and the right front wheel 43R along the vehicle width direction. . The front wheel steering actuator 83 is electrically connected to the ECU 10, and the steering angle of the front wheels 43L and 43R is controlled by the ECU 10. That is, the front wheel steering actuator 83 receives a control signal from the ECU 10 and applies a driving force to one of the front wheel steering shaft 84 in the vehicle width direction. When the front wheel steering shaft 84 is displaced in one direction in the vehicle width direction, the left front wheel 43L and the right front wheel 43R connected to the front wheel steering shaft 84 via a tie rod, a knuckle arm or the like are steered in the same direction.

  The rear wheel steering actuator 85 can steer the rear wheels 73L and 73R by moving a rear wheel steering shaft 86 that interconnects the left rear wheel 73L and the right rear wheel 73R along the vehicle width direction. It is configured. The rear wheel steering actuator 85 is electrically connected to the ECU 10, and the steering angle of the rear wheels 73L and 73R is controlled by the ECU 10. That is, the rear wheel steering actuator 85 receives a control signal from the ECU 10 and applies a driving force to one of the rear wheel steering shaft 86 in the vehicle width direction. When the rear wheel steering shaft 86 is displaced in one direction in the vehicle width direction, the left rear wheel 73L and the right rear wheel 73R connected to the rear wheel steering shaft 86 via a tie rod, a knuckle arm, etc. are steered in the same direction. To do.

  The ECU 10 controls the same direction so that the steering direction of the front wheels 43L and 43R and the steering direction of the rear wheels 73L and 73R are the same in accordance with the traveling state of the vehicle, and the steering direction of the front wheels 43L and 43R. In some cases, the control is performed in the opposite phase so that the steering directions of the rear wheels 73L and 73R are different from each other. For example, when the four-wheel steering mechanism 8 is a vehicle speed sensitive type, the steering direction of the front wheels 43L, 43R and the steering direction of the rear wheels 73L, 73R are in phase when the vehicle is traveling at high speed, and the front wheels 43L, The steering direction of 43R and the steering directions of the rear wheels 73L and 73R are in opposite phases. Specifically, when the vehicle speed is equal to or higher than a predetermined threshold, the ECU 10 controls to the same phase. The threshold value of the vehicle speed is set to 60 km / h, for example. This value is not limited to this. Thereby, the running stability of the vehicle during high speed running can be ensured. On the other hand, when the vehicle speed is less than the predetermined threshold, the ECU 10 controls to the opposite phase. As a result, the turning performance of the vehicle during low-speed running can be improved.

  The four-wheel steering mechanism 8 is incorporated not only in the vehicle speed-sensitive type but also in a comprehensive driving control system of the vehicle, and cooperative control can be performed together with a well-known electronically controlled suspension system, traction control system, anti-lock brake system, and the like. It is good also as a structure performed.

(ECU)
The ECU 10 is an electronic control unit that performs operation control of the engine 1 and includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a backup RAM, and the like.

  The ROM stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU executes arithmetic processing based on various control programs and maps stored in the ROM. The RAM is a memory for temporarily storing calculation results from the CPU, data inputted from each sensor, and the backup RAM is a non-volatile memory for storing data to be saved when the engine 1 is stopped. It is.

  As shown in FIG. 3, the ECU 10 includes an accelerator opening sensor 91 that detects an accelerator opening degree acc that is a depression amount of an accelerator pedal, a front wheel steering angle sensor 92F that detects a steering angle of the steering wheel 81, a rear wheel 73L, A rear wheel steering angle sensor 92R that detects the steering angle of 73R, a crank position sensor 93 that transmits a pulse signal each time the crankshaft that is the output shaft of the engine 1 rotates by a predetermined angle, and the rotational speed (number of rotations) of the left front wheel 43L ) To detect the rotation speed of the right front wheel 43R, the right front wheel speed sensor 94R to detect the rotation speed of the right front wheel 43R, the left rear wheel speed sensor 95L to detect the rotation speed of the left rear wheel 73L, and the rotation speed of the right rear wheel 73R. Detects right rear wheel speed sensor 95R to be detected and brake pedal ON / OFF (including detection of brake pedal force) A brake pedal sensor 96 is connected. Further, the ECU 10 is connected with a water temperature sensor for detecting the engine cooling water temperature, a throttle opening sensor for detecting the opening of a throttle valve disposed in the intake passage, an air flow meter for detecting the intake air amount, and the like. The signals from these sensors are input to the ECU 10.

  The ECU 10 executes various controls of the engine 1 including the throttle opening control (intake air amount control), the fuel injection amount control, the ignition timing control, and the like based on the output signals of the various sensors described above. To do. Further, the ECU 10 transmits a steering control signal to the front wheel steering actuator 83 and the rear wheel steering actuator 85, and independently controls the steering angles of the front wheels 43L and 43R and the steering angles of the rear wheels 73L and 73R. Further, the ECU 10 controls the electronically controlled coupling 6 to execute “pre-turn pre-torque control” described later, in addition to the switching control between the two-wheel drive state and the four-wheel drive state described above.

-Pre-torque control during turning-
Next, turning pre-torque control, which is a characteristic feature of this embodiment, will be described.

  In general, when the vehicle turns, the vehicle speed decreases due to cornering drag (cornering resistance) that acts along with the steering of the front wheels 43L and 43R and the rear wheels 73L and 73R. When the vehicle turns while traveling in the two-wheel drive state, the vehicle speed is reduced by the cornering drag, and accordingly, the rotational speeds of the rear wheels 73L and 73R that are the driven wheels are also reduced.

  In addition, when the driver requests acceleration (such as when the accelerator pedal is depressed) during a turn in such a two-wheel drive state, the front wheels are increased as the output torque of the engine 1 increases. As the driving force of 43L, 43R increases, the vehicle speed increases, and the rotational speed of the rear wheels 73L, 73R also increases accordingly.

  In such a situation, when the four-wheel drive transition condition (when slip occurs in the front wheels 43L, 43R, etc.) is satisfied, the fastening force (engagement force) of the electronically controlled coupling 6 is increased to shift to the four-wheel drive state. Will do.

  However, in this case, the driving force cannot be generated in the rear wheels 73L and 73R during the period in which the rotational inertia of the rear wheels 73L and 73R, which has been lowered during turning in the two-wheel drive state, is increased to a predetermined value. As a result, it takes time until the transition to the four-wheel drive state is completed after the driving force is actually generated in the rear wheels 73L and 73R after the four-wheel drive transition condition is established. That is, a response delay occurs in the transition to the four-wheel drive state during the turning of the vehicle.

  In particular, in a vehicle including the four-wheel steering mechanism 8 as in the present embodiment, the front wheels 43L and 43R have the same direction in which the steering direction of the front wheels 43L and 43R and the steering direction of the rear wheels 73L and 73R are the same direction, and the front wheels Response when shifting to the four-wheel drive state due to the difference in the size of the cornering drag between the steering direction of 43L and 43R and the opposite phase in which the steering direction of the rear wheels 73L and 73R is different. There will be a difference in the delay.

  In view of this point, in the present embodiment, at the time of turning acceleration of the vehicle, the rear wheels 73L and 73R correspond to the rotational inertia of the rear wheels 73L and 73R (rotational inertia that has been lowered due to the influence of the cornering drag). The fastening force of the electronic control coupling 6 is controlled so that a pre-torque is applied to the electronic control coupling 6. In other words, even if the condition for shifting to the four-wheel drive state is not satisfied, the fastening force of the electronically controlled coupling 6 is controlled on the condition that the vehicle is turning accelerated, thereby rear wheels 73L and 73R. A pre-torque is applied to.

  In this case, the magnitude of the pre-torque applied to the rear wheels 73L and 73R is the same as that in the case where the steering direction of the front wheels 43L and 43R and the steering direction of the rear wheels 73L and 73R are in opposite phases. The case is set larger.

  After that, when the condition for shifting to the four-wheel drive state is satisfied, for example, when slip occurs in the front wheels 43L and 43R, the fastening force of the electronically controlled coupling 6 is increased so that the four-wheel drive state is achieved. Is applied to the rear wheels 73L and 73R to shift to the four-wheel drive state.

  Thus, before the transition condition to the four-wheel drive state is established, the size according to the steering direction of the front wheels 43L and 43R and the rear wheels 73L and 73R (the size corresponding to the reverse phase and the same phase). ) By applying pre-torque to the rear wheels 73L and 73R, the response delay when the condition for shifting to the four-wheel drive state is satisfied while the vehicle is turning can be shortened.

  Next, a specific procedure for pre-torque control during the turning will be described. FIG. 5 is a flowchart showing an operation procedure of pre-torque control. The flowchart shown in FIG. 5 is executed every several milliseconds while the vehicle is traveling in the two-wheel drive state.

  Note that the rotational inertia of the rear wheels 73L and 73R is the vehicle body deceleration caused by the cornering drag that acts on the wheel that is steered when the vehicle turns, the cornering drag that acts on the steered wheel when the vehicle turns, There is a correlation in the steering angle when the vehicle turns, and any of these can be treated as an index representing the magnitude of the rotational inertia of the rear wheels 73L and 73R. That is, as the vehicle body deceleration increases, the rotational inertia decreases. As the cornering drag increases, the rotational inertia decreases. As the steering angle increases, the rotational inertia decreases. In the pre-torque control described below, a case will be described in which the vehicle body deceleration due to the influence of the cornering drag is handled as an index representing the magnitude of the rotational inertia of the rear wheels 73L and 73R.

  First, in step ST1, the current running state quantity of the vehicle is acquired. The travel state quantity includes wheel speed, input torque to the drive system, and the like. The wheel speed is detected for each of the wheels 43L, 43R, 73L, and 73R by the wheel speed sensors 94L, 94R, 95L, and 95R. The input torque to the drive system corresponds to the output torque of the engine 1 and is calculated based on the accelerator opening degree acc detected by the accelerator opening degree sensor 91 and the output signal from the crank position sensor 93. Calculated from speed. For example, the output torque of the engine 1 is calculated by dividing the required driving force (required power) set according to the accelerator opening degree acc by the engine rotation speed, thereby obtaining the input torque to the drive system.

  After acquiring the current running state amount of the vehicle in this way, the process proceeds to step ST2, and the operation amount by the driver (driver) is acquired. Examples of the operation amount include an accelerator opening degree acc, a steering angle delta of the steering wheel, and the like. The accelerator opening degree acc is detected by the accelerator opening degree sensor 91. Further, the steering angle delta of the steering is detected by the front wheel steering angle sensor 92F.

  Next, the process proceeds to step ST3, where cornering drag (cornering resistance; hereinafter referred to as front wheel cornering drag) acting on the front wheels 43L and 43R is estimated. The estimation of the front wheel cornering drag is performed based on a front wheel cornering drag map stored in advance in the ROM. The front wheel cornering drag map defines the relationship between the steering angle delta of the steering wheel and the front wheel cornering drag, and is created in advance by experiments and simulations. FIG. 6 shows an example of a front wheel cornering drag map. Thus, the cornering drag map is created so that the front wheel cornering drag is obtained as a larger value as the front wheel steering angle delta is larger. As is well known, the size of the front wheel cornering drag is opposite to the vehicle traveling direction of the lateral force acting in the direction orthogonal to the steering direction, which is the front wheel rotation direction, due to friction between the front wheels 43L and 43R and the road surface. The front wheel cornering drag increases as the front wheel steering angle increases.

  Further, since the front wheel cornering drag acts as running resistance, the larger the front wheel cornering drag, that is, the greater the front wheel steering angle, the greater the deceleration of the vehicle body. And the rotational inertia of the said rear wheels 73L and 73R becomes low, so that the deceleration of this vehicle body is large.

  The estimation of the front wheel cornering drag is not limited to that performed based on the front wheel cornering drag map, but the front wheel cornering drag is determined from the front wheel slip angle (the difference between the steering angle of the front wheels 43L and 43R and the center of gravity slip angle of the vehicle). It is also possible to obtain an arithmetic expression for obtaining the front wheel cornering drag in advance by obtaining the front wheel cornering drag by substituting the current front wheel slip angle into the arithmetic expression.

  After estimating the front wheel cornering drag, the process proceeds to step ST4, and the steering direction and the steering angle of the rear wheels 73L and 73R are acquired. The steering direction and steering angle of the rear wheels 73L and 73R are detected by the rear wheel steering angle sensor 92R. In other words, in the case of the vehicle speed sensitive four-wheel steering mechanism 8 described above, the steering direction of the rear wheels 73L and 73R is the same as the steering direction of the front wheels 43L and 43R when the vehicle speed is equal to or greater than a predetermined threshold. The same steering angle is detected by the rear wheel steering angle sensor 92R. Further, when the vehicle speed is less than a predetermined threshold, the steering direction of the rear wheels 73L and 73R is different from the steering direction of the front wheels 43L and 43R (reverse phase), and the steering angle of this reverse phase is the rear wheel. It is detected by the steering angle sensor 92R.

  Next, the process proceeds to step ST5, where cornering drag acting on the rear wheels 73L and 73R (hereinafter referred to as rear wheel cornering drag) is estimated. The estimation of the rear wheel cornering drag is performed based on a rear wheel cornering drag map stored in advance in the ROM. The rear wheel cornering drag map defines the relationship between the steering angle of the rear wheels 73L and 73R and the rear wheel cornering drag, and is created in advance through experiments and simulations. Further, when the steering direction of the rear wheels 73L and 73R is in phase with respect to the steering direction of the front wheels 43L and 43R, the rear wheel cornering drag is maintained even when the rear wheel steering angle is the same, as compared with the case of the opposite phase. Will grow. Therefore, the rear wheel cornering drag map shows the relationship between the rear wheel steering angle and the rear wheel cornering drag when the steering direction of the rear wheels 73L and 73R is in phase with the steering direction of the front wheels 43L and 43R, and The relationship between the rear wheel steering angle and the rear wheel cornering drag when the steering direction of the rear wheels 73L and 73R is in an opposite phase to the steering direction of the front wheels 43L and 43R is defined. FIG. 7 shows an example of a rear wheel cornering drag map. The solid line in FIG. 7 shows the relationship between the rear wheel steering angle and the rear wheel cornering drag when the steering direction of the rear wheels 73L and 73R is in phase with the steering direction of the front wheels 43L and 43R. 7 indicates the relationship between the rear wheel steering angle and the rear wheel cornering drag when the steering direction of the rear wheels 73L and 73R is in an opposite phase to the steering direction of the front wheels 43L and 43R. Thus, the larger the rear wheel steering angle, the larger the rear wheel cornering drag is obtained, and the larger the rear wheel cornering drag is obtained in the case of the same phase than in the case of the opposite phase. A rear wheel cornering drag map has been created. In this rear wheel cornering drag map, the ratio of the size of the rear wheel cornering drag when it is in phase with the same rear wheel steering angle and the size of the rear wheel cornering drag when it is in reverse phase is different depending on the vehicle. Become.

  In addition, since the rear wheel cornering drag also acts as a running resistance, the larger the rear wheel cornering drag, that is, the larger the rear wheel steering angle, and the case where the steering direction is in the same phase than in the opposite phase. However, the deceleration of the car body becomes larger. And the rotational inertia of the said rear wheels 73L and 73R becomes low, so that the deceleration of this vehicle body is large.

  The estimation of the rear wheel cornering drag is not limited to that performed based on the rear wheel cornering drag map, but the rear wheel slip angle (in the case of the same phase, the vehicle center of gravity slip angle and the rear wheel 73L, In the case of the sum and the reverse phase of the steering angle of 73R, an arithmetic expression for obtaining the rear wheel cornering drag from the difference between the slip angle of the center of gravity of the vehicle and the steering angle of the rear wheels 73L and 73R is based on experiments and simulations in advance. The rear wheel cornering drag may be obtained by substituting the current rear wheel slip angle into this arithmetic expression.

  After estimating the front wheel cornering drag and the rear wheel cornering drag as described above, the deceleration of the vehicle body due to the influence of these cornering drags is acquired in step ST6. The deceleration of the vehicle body is proportional to the sum of the front wheel cornering drag and the rear wheel cornering drag (hereinafter referred to as total cornering drag). For example, a map that defines the relationship between the total cornering drag and the deceleration of the vehicle body is created in advance by experiments and simulations, and the deceleration of the vehicle body is obtained from this map.

  Further, the deceleration of the vehicle body may be obtained by the following equation (1).

Vd = (CDf + CDr) / M (1)
Vd: deceleration of the vehicle body, CDf: front wheel cornering drag, CDr: rear wheel cornering drag, M: vehicle weight The vehicle body deceleration may be measured by a sensor or the like. For example, the rotational speeds of the wheels 43L, 43R, 73L, and 73R detected by the wheel speed sensors 94L, 94R, 95L, and 95R, the output from an acceleration sensor (not shown), and the output from a vehicle speed sensor (not shown) The deceleration of the vehicle body may be obtained based on the above.

  Next, the process proceeds to step ST7, and the pre-torque necessary for increasing the rotational inertia of the rear wheels 73L and 73R is obtained. This pre-torque is obtained as a value corresponding to the deceleration of the vehicle body. That is, the greater the deceleration of the vehicle body, the lower the rotational inertia of the rear wheels 73L and 73R. In this case, the pre-torque is obtained as a large value.

  For example, a map for obtaining the pre-torque from the deceleration of the vehicle body based on experiments and simulations is created in advance, and this map (pre-torque map) is stored in the ROM, and the pre-torque is obtained from the pre-torque map. Good. As described above, since the deceleration of the vehicle body is greater when the steering direction is the opposite phase than when the steering direction is the opposite phase, the steering direction is the opposite phase even if the steering angles of the rear wheels 73L and 73R are the same. The pre-torque is obtained as a larger value in the case of the same phase than in the case of. The pre-torque required here is, for example, about several tens of Nm, and is a low value of about 1/10 with respect to the driving torque (about several hundred Nm) applied to the rear wheels 73L and 73R during four-wheel drive. Yes.

  Further, the pre-torque may be obtained by a predetermined arithmetic expression using the deceleration of the vehicle body as a variable. As an arithmetic expression in this case, for example, the following expression (2) is given.

T = 2 · Iw · ω ² (2)
T: Pre-torque, Iw: Rear wheel inertia moment, ω: Rear wheel deceleration (= Vd / Rw), Rw: Rear wheel radius Note that this pre-torque is not limited to the deceleration of the vehicle body, but the total cornering drag You may make it obtain | require as a value according to a magnitude | size. That is, the greater the total cornering drag, the greater the deceleration of the vehicle body. In such a case, the pre-torque is obtained as a large value. Further, the pre-torque may be obtained as a value corresponding to the steering angle of the front wheels 43L and 43R, the steering direction and the steering angle of the rear wheels 73L and 73R. That is, the larger the steering angle of the front wheels 43L and 43R, the larger the pre-torque, the larger the steering angle of the rear wheels 73L and 73R, the larger the pre-torque, and the same phase as compared with the case where the steering direction is in the opposite phase. In some cases, the pre-torque is obtained so that the pre-torque has a larger value. As described above, the deceleration of the vehicle body, the size of the total cornering drag, and the size of the steering angle are all correlated with the rotational inertia of the rear wheels 73L and 73R. In other words, the greater the deceleration of the vehicle body, the lower the rotational inertia of the rear wheels 73L, 73R, and the greater the total cornering drag, the lower the rotational inertia of the rear wheels 73L, 73R, and the larger the steering angle, the larger the rear wheel 73L, The rotational inertia of 73R is low. Therefore, the pre-torque is determined according to the deceleration of the vehicle body, the pre-torque is determined according to the size of the total cornering drag, and the pre-torque is determined according to the size of the steering angle and the steering direction of the rear wheels 73L and 73R. Is synonymous with obtaining the pre-torque according to the rotational inertia of the rear wheels 73L and 73R.

  After obtaining the pre-torque in this way, the process proceeds to step ST8, where an upper limit value of the pre-torque is set. Hereinafter, the upper limit value of the pre-torque will be described.

  When the fastening force of the electronic control coupling 6 is increased while the vehicle is turning, the rotational speed of the front wheels 43L and 43R approaches the rotational speed of the rear wheels 73L and 73R.

  In general, in order to improve the turning ability of the vehicle at the time of turning, the rear wheels 73L and 73R pass through a movement locus on the outside (outside the corner) with respect to the movement locus (cornering locus) of the front wheels 43L and 43R. It is desirable (it is desirable to turn with a so-called oversteer tendency). That is, it is desirable for the vehicle to turn in a state in which the rotational speeds (revolutions) of the rear wheels 73L and 73R are higher than the rotational speeds of the front wheels 43L and 43R.

  For this reason, when the fastening force of the electronically controlled coupling 6 is increased to increase the pre-torque, if the fastening force is increased more than necessary, the rotational speed of the front wheels 43L and 43R and the rotational speed of the rear wheels 73L and 73R. (The rotational speed of the rear wheels 73L and 73R is reduced to the rotational speed of the front wheels 43L and 43R) and the turning ability of the vehicle cannot be improved. In order to avoid such a situation, an upper limit value of the pre-torque is set.

  Specifically, the differential rotational speed of the front and rear wheels (deviation of the rotational speed of the front and rear wheels) is calculated, and the upper limit value of the pre-torque is set lower as the differential rotational speed is smaller. That is, the pre-torque is limited so that the rotational speed of the rear wheels 73L and 73R does not decrease to the rotational speed of the front wheels 43L and 43R.

  Here, the differential rotational speed of the front and rear wheels is calculated as follows. First, an average value of the rotational speed of the left front wheel 43L detected by the left front wheel speed sensor 94L and the rotational speed of the right front wheel 43R detected by the right front wheel speed sensor 94R is obtained as a front wheel speed. Further, an average value of the rotation speed of the left rear wheel 73L detected by the left rear wheel speed sensor 95L and the rotation speed of the right rear wheel 73R detected by the right rear wheel speed sensor 95R is obtained as a rear wheel speed. . Then, a value obtained by subtracting the front wheel speed from the rear wheel speed is calculated as the differential rotational speed of the front and rear wheels.

  FIG. 8 is a diagram showing a pre-torque upper limit value map for obtaining a pre-torque upper limit value corresponding to the differential rotational speeds of the front and rear wheels. As shown in FIG. 8, the lower the differential rotational speed of the front and rear wheels, that is, the rotational speed of the rear wheels 73L and 73R approaches the rotational speed of the front wheels 43L and 43R. The more the situation is, the lower the pre-torque upper limit value is set (the fastening force of the electronic control coupling 6 is lowered) and the pre-torque size is limited so that the turning ability of the vehicle can be maintained. In other words, by restricting the pre-torque by this pre-torque upper limit value, while maintaining high turning performance of the vehicle, a minimum necessary pre-torque is applied to the rear wheels 73L and 73R, so that four-wheel drive is performed thereafter. When the condition transition condition is satisfied, the response delay to the four-wheel drive state can be shortened.

  After setting the upper limit value of the pre-torque in this way, the process proceeds to step ST9, where the steering angle (the absolute value of the steering angle) detected by the front wheel steering angle sensor 92F exceeds a predetermined threshold value α, and It is determined whether or not the accelerator opening detected by the accelerator opening sensor 91 exceeds a predetermined threshold value β.

  This determination determines whether or not the vehicle is turning acceleration, and determines whether or not the vehicle is in a vehicle running state that requires pre-torque to be applied to the rear wheels 73L and 73R. . For example, the steering angle threshold α is set to 10 °, and the accelerator opening threshold β is set to 10%. These values are not limited to this, and are set as appropriate based on experiments and simulations.

  When the steering angle is equal to or smaller than the predetermined threshold value α or when the accelerator opening is equal to or smaller than the predetermined threshold value β, a NO determination is made in step ST9, the process proceeds to step ST10, and the pre-torque is set to “0”. . That is, the electronic control coupling 6 is set in the released state so that the pre-torque is not transmitted to the rear wheels 73L and 73R. When the steering angle is small or when the steering angle is “0”, the cornering drag is small or “0”, and the deceleration of the vehicle body is also small or “0”. This is because it is not necessary to apply pre-torque. In this case, each cornering drag estimated in step ST3 and step ST5 has a small value, and the pre-torque obtained in step ST7 has a small value.

  Further, when the accelerator opening is small or the accelerator opening is “0”, the output torque of the engine 1 is small or “0”, and the rear wheel is engaged even when the electronic control coupling 6 is engaged. Since the pre-torque is not transmitted to 73L and 73R, the pre-torque is set to “0” in this case as well.

  On the other hand, when the steering angle of the steering exceeds the predetermined threshold α and the accelerator opening exceeds the predetermined threshold β, YES is determined in step ST9 and the process proceeds to step ST11. In step ST11, pre-torque is applied to the rear wheels 73L and 73R. As the pre-torque in this case, when the pre-torque obtained in step ST7 is equal to or less than the upper limit value of the pre-torque set in step ST8, the pre-torque obtained in step ST7 is applied to the rear wheels 73L and 73R. Thus, the electronic control coupling 6 is controlled. On the other hand, when the pre-torque obtained in step ST7 exceeds the upper limit value of the pre-torque set in step ST8, the pre-torque regulated by this upper limit value is applied to the rear wheels 73L and 73R. The electronic control coupling 6 is controlled.

  In this case, the electronic control coupling 6 is controlled by controlling the excitation current Ie supplied to the electromagnet of the electronic control coupling 6 so that the transmission torque Tc shown in FIG. 4 matches the pre-torque.

  With the pre-torque applied to the rear wheels 73L and 73R in this way, the process proceeds to step ST12, and it is determined whether or not the four-wheel drive transition condition is satisfied. Specifically, it is determined whether or not a condition for shifting to the four-wheel drive state is satisfied, for example, by slipping on the front wheels 43L and 43R. Whether or not the four-wheel drive transition condition is satisfied is determined in a four-wheel drive control routine (not shown) different from the pre-torque control routine shown in FIG. If it is determined that the four-wheel drive transition condition is satisfied (eg, when the four-wheel drive flag becomes “1” due to the occurrence of slip on the front wheels 43L and 43R), the step in the pre-torque control routine is performed. A YES determination is made at ST12.

  If the four-wheel drive transition condition is not satisfied and a NO determination is made in step ST12, the process returns with the pre-torque applied to the rear wheels 73L and 73R. In the routine after the next time, on the condition that the operation state is determined to be YES in step ST9 (provided that the vehicle is accelerating turning), the above-described steps ST1 to ST9, step ST11, The operation of step ST12 is repeated. That is, the state where the pre-torque according to the traveling state of the vehicle is applied to the rear wheels 73L and 73R is continued. In this case, when the steering angle or the vehicle speed of the steering is changed, the total cornering drag is also changed, and the deceleration of the vehicle body is changed accordingly. Therefore, the value of the pre-torque obtained in step ST7 is also changed. That is, each time the operations of step ST1 to step ST9, step ST11, and step ST12 are repeated, the pre-torque applied to the rear wheels 73L and 73R changes according to the steering angle and vehicle speed of the steering (in step ST7). When the obtained pre-torque is not subject to the pre-torque upper limit).

  In addition, in the state in which the pre-torque is applied to the rear wheels 73L and 73R, when the NO determination is made in step ST9, the pre-torque is set to “0”. That is, the pre-torque is set to “0”, assuming that it is no longer in the traveling state that requires the pre-torque.

  On the other hand, if the four-wheel drive transition condition is satisfied with the pre-torque applied, and YES is determined in step ST12, the process proceeds to step ST13 and the pre-torque is released to shift the vehicle to the four-wheel drive state. Then, the electronic control coupling 6 is controlled so as to transmit the driving torque necessary for setting the four-wheel drive state to the rear wheels 73L and 73R. That is, drive torque distribution control (for example, torque distribution control according to the slip amount of the front wheels 43L and 43R) is performed in the above-described four-wheel drive control routine.

  By repeating the above operation, the electronic control coupling 6 is controlled and pre-torque is applied to the rear wheels 73L and 73R during acceleration of turning of the vehicle.

  FIG. 9 shows a change in torque applied to the rear wheels 73L and 73R during the turn from the two-wheel drive state to the four-wheel drive state, and a two-dot chain line shows a temporal change in the rear wheel torque in the prior art. Show. The solid line indicates the temporal change of the rear wheel torque when the steering direction of the front wheels 43L and 43R and the steering direction of the rear wheels 73L and 73R are in phase, and the broken line indicates the steering of the front wheels 43L and 43R. This shows a temporal change in the rear wheel torque when the direction and the steering direction of the rear wheels 73L and 73R are in opposite phases. In FIG. 9, the turning acceleration of the vehicle is started at the timing t1, and slip occurs in the front wheels 43L and 43R at the timing t2, so that the four-wheel drive transition condition is satisfied.

  In the prior art, torque is not applied to the rear wheels 73L and 73R until the four-wheel drive transition condition is satisfied, and electronic control is performed from the time when the four-wheel drive transition condition is satisfied (timing t2). The coupling 6 is controlled to distribute drive torque to the rear wheels 73L and 73R, and the transition to the four-wheel drive state is completed at timing t4.

  On the other hand, in the present embodiment, the electronic control coupling 6 is controlled from the time when the turning acceleration of the vehicle is started (timing t1), and the pre-torque is applied to the rear wheels 73L and 73R. The pre-torque applied in this case is set larger when the front wheels 43L and 43R and the rear wheels 73L and 73R are in the same phase than when they are in the opposite phase. That is, pre-torque is applied according to the size of the total cornering drag. Then, the electronic control coupling 6 is further controlled from the time when the four-wheel drive transition condition is satisfied (timing t2), and the driving torque is distributed to the rear wheels 73L and 73R, and the transition to the four-wheel driving state is performed at timing t3. Has been completed.

  In this way, in the present embodiment, the shift to the four-wheel drive state is completed earlier than that of the prior art in the present embodiment by the deviation between the timing t3 and the timing t4. Response delay has been greatly improved.

  As described above, in this embodiment, since the pre-torque is applied to the rear wheels 73L and 73R at the time of turning acceleration of the vehicle, the rotation inertia of the rear wheels 73L and 73R is reduced due to the influence of the cornering drag. When the four-wheel drive transition condition is satisfied after that, the rotational inertia can be increased, and the driving force is generated at the rear wheels 73L and 73R substantially simultaneously with the increase of the fastening force of the electronic control coupling 6. As a result, the transition to the four-wheel drive state is completed immediately. That is, there is no response delay in the transition to the four-wheel drive state during turning of the vehicle, and the driver does not feel uncomfortable due to this response delay. In the present embodiment, the pre-torque to be applied is set larger when the front wheels 43L and 43R and the rear wheels 73L and 73R are in the same phase than when they are in the opposite phase. That is, a pre-torque according to the size of the total cornering drag is applied. For this reason, it is possible to optimize the pre-torque, and it is possible to stably suppress the response delay in the transition to the four-wheel drive state regardless of the case of the reverse phase and the case of the same phase. .

  In addition, when the four-wheel drive transition condition is not satisfied in a state in which the pre-torque is applied to the rear wheels 73L and 73R, the pre-torque is released thereafter, but the rear wheel 73L is being turned while the vehicle is turning. , 73R can be imparted with an appropriate pre-torque to keep the turning performance of the vehicle high. Further, the pre-torque in this case is limited by the upper limit value of the pre-torque, so that high turnability can be maintained.

(Modification 1)
Next, Modification 1 will be described. The first modification is a modification of the pre-torque upper limit value map. In the embodiment, the relationship between the front and rear wheel differential rotational speed and the pre-torque upper limit value is linear (see the pre-torque upper limit value map in FIG. 8). On the other hand, the pre-torque upper limit value map of this modification is as shown in FIG.

  In the pre-torque upper limit value map shown in FIG. 10, the positive side of the front and rear wheel differential rotational speed axis that is the horizontal axis is a range in which the rotational speed of the rear wheels 73L and 73R is higher than the rotational speed of the front wheels 43L and 43R. The negative side is a range in which the rotational speeds of the front wheels 43L and 43R are higher than the rotational speeds of the rear wheels 73L and 73R.

  In this pre-torque upper limit value map, when the front-rear wheel differential rotational speed is in a relatively small range (a range from -ΔN1 to + ΔN1 in FIG. 10), that is, the rotational speeds of the rear wheels 73L, 73R are the front wheels 43L, 43R. In a situation where the turning ability of the vehicle cannot be increased as the vehicle approaches the rotational speed, the pre-torque upper limit value is set to a low value (PT1 in the figure). On the other hand, when the front-rear wheel differential rotation speed is in a relatively large range (a range of −ΔN2 or less and a range of + ΔN2 or more in FIG. 10), that is, the rotation speed of the front wheels 43L and 43R and the rotation speed of the rear wheels 73L and 73R. Is sufficiently large and the pre-torque upper limit value is set to a high value (PT2 in the figure). The pre-torque upper limit value PT2 is a value that does not limit the pre-torque obtained in step ST7 of the flowchart of FIG. 5, that is, the pre-torque obtained in step ST7 is applied to the rear wheels 73L and 73R as it is. Is set as the value of

  Further, when the front-rear wheel differential rotational speed is in the range of -ΔN1 to -ΔN2 in FIG. 10 or in the range of + ΔN1 to + ΔN2, the smaller the absolute value of the front-rear wheel differential rotational speed, the smaller the pre-torque upper limit value. Is set to a low value.

  When the pre-torque is limited by such a pre-torque upper limit map, it is possible to reliably improve the turning ability of the vehicle by securing a region where the pre-torque upper limit is set to a low value (PT1 in the figure).

(Modification 2)
Next, Modification 2 will be described. In the above-described embodiment, the conventional vehicle adopting the standby four-wheel drive system based on the FF system has been described as an example. In this modification, a hybrid vehicle (a vehicle equipped with an engine and an electric motor as a driving force source) employing a standby four-wheel drive system based on the FF system will be described.

  FIG. 11 is a schematic configuration diagram showing a vehicle in the present modification. The hybrid vehicle according to the present embodiment includes an engine 1 that generates driving torque for vehicle travel, a first motor generator MG1 that mainly functions as a generator, a second motor generator MG2 that mainly functions as an electric motor, and a power split mechanism 100. , Reduction mechanism 110, counter drive gear 121, counter driven gear 122, final gear 123, front wheel differential device 41, front wheel axle (front drive shaft) 42, front wheels (main drive wheels) 43L, 43R, transfer 51, propeller shaft 52, The electronic control coupling 6, the rear wheel differential device 71, the rear wheel axle (rear drive shaft) 72, the rear wheels (secondary drive wheels) 73L and 73R, the ECU 10, and the like are provided.

  The ECU 10 includes, for example, an HV (hybrid) ECU, an engine ECU, a battery ECU, and the like, and these ECUs are connected to be communicable with each other.

  Since the configuration of the engine 1, the transfer 51, and the electronic control coupling 6 is the same as that of the above-described embodiment, the description thereof is omitted here. The output of the engine 1 is transmitted to the input shaft 13 via the crankshaft 11 and the damper 12. The damper 12 is a coil spring type transaxle damper, for example, and absorbs torque fluctuations of the engine 1.

  Hereinafter, motor generators MG1 and MG2, power split device 100, and reduction mechanism 110 will be described.

-Motor generator-
The first motor generator MG1 is an AC synchronous generator including a rotor MG1R made of a permanent magnet that is rotatably supported with respect to the input shaft 13, and a stator MG1S around which a three-phase winding is wound. It functions as a generator and also as an electric motor (electric motor). Similarly, the second motor generator MG2 includes an AC synchronous generator including a rotor MG2R made of a permanent magnet rotatably supported by the input shaft 13, and a stator MG2S wound with a three-phase winding. And it functions as a generator while functioning as an electric motor (electric motor).

  As shown in FIG. 12, first motor generator MG <b> 1 and second motor generator MG <b> 2 are each connected to battery (power storage device) 300 via inverter 200. Inverter 200 is controlled by ECU 10, and regeneration or power running (assist) of each motor generator MG 1, MG 2 is set by the control of inverter 200. The regenerative power at that time is charged into the battery 300 via the inverter 200. In addition, driving power for each of the motor generators MG1 and MG2 is supplied from the battery 300 via the inverter 200.

-Power split mechanism-
As shown in FIG. 11, the power split mechanism 100 includes an external gear sun gear S3 that rotates at the center of a plurality of gear elements, and an external gear pinion gear P3 that revolves around the sun gear S3 while rotating around its periphery. And a planetary gear mechanism that has a ring gear R3 of an internal gear formed in a hollow ring so as to mesh with the pinion gear P3, and a planetary carrier CA3 that supports the pinion gear P3 and rotates through the revolution of the pinion gear P3. Yes. The planetary carrier CA3 is connected to the input shaft 13 on the engine 1 side so as to rotate together. The sun gear S3 is connected to the rotor MG1R of the first motor generator MG1 so as to rotate together.

  The power split mechanism 100 transmits the driving force of at least one of the engine 1 and the second motor generator MG2 via the counter drive gear 121, the counter driven gear 122, the final gear 123, the front wheel differential device 41, and the front wheel axle 42. It is transmitted to the left and right front wheels 43L, 43R.

-Reduction mechanism-
The reduction mechanism 110 is rotatably supported by an external gear sun gear S4 that rotates at the center of a plurality of gear elements and a carrier (transaxle case) CA4, and is an external gear pinion gear P4 that rotates while circumscribing the sun gear S4. And a planetary gear mechanism having a ring gear R4 of an internal gear formed in a hollow annular shape so as to mesh with the pinion gear P4. The ring gear R4 of the reduction mechanism 110, the ring gear R3 of the power split mechanism 100, and the counter drive gear 121 are integrated with each other. Sun gear S4 is connected to rotor MG2R of second motor generator MG2 so as to rotate together.

  This reduction mechanism 110 decelerates the driving force of at least one of engine 1 and second motor generator MG2 at an appropriate reduction ratio. The reduced driving force is transmitted to the left and right front wheels 43L and 43R via the counter drive gear 121, the counter driven gear 122, the final gear 123, the front wheel differential device 41, and the front wheel axle 42.

  Also in the hybrid vehicle configured as described above, the same turning pre-torque control as in the above-described embodiment is executed. That is, at the time of turning acceleration of the vehicle, the pre-torque is applied to the rear wheels 73L and 73R according to the rotational inertia of the rear wheels 73L and 73R (rotational inertia that has been lowered due to the influence of the total cornering drag). The fastening force of the electronic control coupling 6 is controlled. After that, when the condition for shifting to the four-wheel drive state is satisfied, for example, when slip occurs in the front wheels 43L and 43R, the fastening force of the electronically controlled coupling 6 is increased so that the four-wheel drive state is achieved. Drive torque is applied to the rear wheels 73L and 73R to shift to the four-wheel drive state.

  Also in this modification, the same effect as the above-described embodiment can be obtained. That is, the rotational inertia of the rear wheels 73L, 73R, whose rotational inertia is low due to the influence of the total cornering drag, can be increased by applying pre-torque, and after that, when the four-wheel drive transition condition is satisfied, The driving force can be generated in the rear wheels 73L and 73R substantially simultaneously with increasing the fastening force of the electronic control coupling 6, and the transition to the four-wheel drive state is completed immediately. That is, there is no response delay in the transition to the four-wheel drive state while the vehicle is turning. The pre-torque applied in this case is set larger when the front wheels 43L and 43R and the rear wheels 73L and 73R are in the same phase than when they are in the opposite phase. That is, a pre-torque according to the size of the total cornering drag is applied. For this reason, it is possible to optimize the pre-torque, and it is possible to stably suppress the response delay in the transition to the four-wheel drive state regardless of the case of the reverse phase and the case of the same phase. .

  In addition, when the four-wheel drive transition condition is not satisfied in a state in which the pre-torque is applied to the rear wheels 73L and 73R, the pre-torque is released thereafter, but the rear wheel 73L is being turned while the vehicle is turning. , 73R can be imparted with an appropriate pre-torque to keep the turning performance of the vehicle high. Further, the pre-torque in this case is limited by the upper limit value of the pre-torque, and high turnability can be obtained.

-Other embodiments-
The embodiment and each modification described above have described the case where the present invention is applied to a vehicle that employs a standby four-wheel drive system based on the FF system. The present invention is not limited to this, and can also be applied to a vehicle (conventional vehicle or hybrid vehicle) adopting a standby four-wheel drive system based on the FR (front engine / rear drive) system. In this case, the rear wheel is the main drive wheel, and the front wheel is the slave drive wheel.

  In the embodiment and each modification, a pilot clutch type is used as the electronic control coupling 6. The present invention is not limited to this, and a clutch direct pressing electronic control coupling may be used. Further, the present invention is not limited to such an electronically controlled coupling 6, and any other type of drive torque distribution device can be used as long as the device can change the distribution ratio of the drive torque to the front and rear wheels. Also good.

  Further, in the above-described embodiment and each modification, the example in which the present invention is applied to the standby four-wheel drive vehicle on which the transfer 51 including the counter gear is mounted is shown, but the form of the transfer is not particularly limited. For example, it may be a transfer provided with a mechanism for connecting a sprocket on the main drive wheel side and a sprocket on the slave drive wheel side with a chain.

  INDUSTRIAL APPLICABILITY The present invention can be used for control during turning acceleration of a vehicle that includes a four-wheel steering mechanism that can steer front and rear wheels and that can selectively switch between a two-wheel drive state and a four-wheel drive state.

1 Engine (drive power source)
43L, 43R Front wheel (main drive wheel)
73L, 73R Rear wheel (slave drive wheel)
6 Electronically controlled coupling 8 Four-wheel steering mechanism 83 Front wheel steering actuator 85 Rear wheel steering actuator 91 Accelerator opening sensor 92F Front wheel steering angle sensor 92R Rear wheel steering angle sensor 94L Left front wheel speed sensor 94R Right front wheel speed sensor 95L Left rear wheel speed Sensor 95R Right rear wheel speed sensor 10 ECU
MG1, MG2 Motor generator (drive power source)

Claims (8)

A driving force source that outputs driving torque for traveling is provided, and one of the front wheels and the rear wheels is a main driving wheel, and the other is a sub driving wheel, and the distribution ratio of the driving torque to the main driving wheel and the sub driving wheel is changed. Thus, the two-wheel drive state in which the drive torque is transmitted only to the main drive wheel and the four-wheel drive state in which the drive torque is transmitted to both the main drive wheel and the slave drive wheel can be switched, and the front wheel and the rear wheel In a vehicle control device equipped with a steering mechanism capable of steering,
When the vehicle accelerates when turning, a pre-torque corresponding to the rotational inertia of the driven wheel is applied to the driven wheel, and the pre-torque applied at this time is when the steering directions of the front and rear wheels are in reverse phase. Compared to the same phase, it is set larger.
After that, when the condition for shifting to the four-wheel drive state is satisfied, the vehicle control device is configured to apply a drive torque for setting the four-wheel drive state to the slave drive wheels. The vehicle control device according to claim 1,
The vehicle control device according to claim 1, wherein the pre-torque is set to be larger as the rotational inertia of the driven wheel is lower when the vehicle accelerates when turning. The vehicle control device according to claim 1 or 2,
The rotational inertia of the driven wheel is the vehicle body deceleration due to the effects of the front wheel cornering drag that acts on the front wheels when the vehicle turns and the rear wheel cornering drag that acts on the rear wheels when the rear wheels are steered. There is a correlation, and the greater the vehicle body deceleration, the lower the rotational inertia of the driven wheels. The vehicle control device according to claim 1 or 2,
The rotational inertia of the driven wheel correlates with the front wheel cornering drag that acts on the front wheel when the vehicle turns and the rear wheel cornering drag that acts on the rear wheel when the rear wheel is steered. The vehicle control apparatus according to claim 1, wherein the rotational inertia of the driven wheel decreases as the total cornering drag, which is the sum of the cornering drag and the rear wheel cornering drag, increases. The vehicle control device according to claim 1 or 2,
The rotational inertia of the driven wheel correlates with the steering angle of the front wheel and the steering angle of the rear wheel when the vehicle turns. The larger the steering angle, the lower the rotational inertia of the driven wheel. A vehicle control device. In the vehicle control device according to any one of claims 1 to 5,
The vehicle pre-torque is limited to a pre-torque upper limit value set based on a difference between a rotational speed of a front wheel and a rotational speed of a rear wheel. The vehicle control device according to claim 6,
The pre-torque upper limit value is set lower as the difference between the rotational speed of the front wheels and the rotational speed of the rear wheels is smaller. In the vehicle control device according to any one of claims 1 to 7,
When at least one of turning and acceleration of the vehicle is canceled without pre-torque being applied to the driven wheels without satisfying the transition condition to the four-wheel drive state, the four-wheel drive state is set. The vehicle control device is characterized in that the application of the pre-torque is canceled without applying the drive torque to the slave drive wheel.

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