JP2015110405A - Four-wheel-drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a yaw response during both of additional turn and return of a steering wheel steered by a driver.SOLUTION: During additional turn of a steering wheel 49, an amount of drive force distribution to front wheels 14 is larger than that during return of the steering wheel 49. For this reason as well as characteristics that self aligning torque (SAT) becomes lower as driving power of the front wheels 14 is higher, during the additional turn, the SAT decreases, a steering force decreases, and yaw response of a vehicle 10 can improve. On the other hand, during return of the steering wheel 49, the SAT increases but the steering force decreases since a steering direction is reversed, so that the yaw response of the vehicle 10 can improve. That is, during both the additional turn and the return of the steering wheel 49, a steering angle can be set to a steering angle θsw for achieving an intended steering behavior (or yaw rate) with a low steering force.

Description

  The present invention relates to a four-wheel drive vehicle for controlling a driving force distribution amount between front wheels and rear wheels.

  A four-wheel drive vehicle that controls the amount of driving force distribution between the front wheels and the rear wheels according to the operation of the steering wheel by the driver is well known. For example, this is the vehicle described in Patent Document 1. This Patent Document 1 proposes a technique for quickly stabilizing the turning behavior during steering turning by increasing the amount of distribution of driving force to the rear wheels as the steering angle differential value of the driver increases.

JP 2007-55476 A

  By the way, when the tire rolls with a certain slip angle, torque (hereinafter referred to as self-aligning torque (SAT)) is generated on the tire contact surface in the direction of decreasing the slip angle. . This SAT is a characteristic that affects the steering force of the driver. For this reason, the steering force required when the driver makes the target turning behavior is changed by the SAT. When the necessary steering force changes, it is considered that the yaw response of the vehicle changes. Therefore, it is desired to obtain an appropriate steering force according to the steering state. The technique of Patent Document 1 is aimed at stabilizing the turning behavior (for example, suppressing the understeer state). In the technique of Patent Document 1, the driving force distribution amount of the front and rear wheels is controlled to perform appropriate steering. It is impossible to realize such a demand as to become a force. The above-described problem is not known, and focusing on the relationship between the SAT and the driving force, controlling the driving force distribution amount of the front and rear wheels provides an appropriate steering force according to the steering state. It has not yet been proposed to do so.

  The present invention has been made against the background of the above circumstances. The purpose of the present invention is to improve the yaw response of the vehicle both when the steering wheel is operated by the driver and when the switch is operated. It is an object of the present invention to provide a four-wheel drive vehicle that can be used.

  The subject matter of the first invention for achieving the above object is as follows: (a) a steering device that mechanically transmits the rotation of the steering wheel to the front wheels, and the amount of driving force distributed between the front wheels and the rear wheels is controlled. A four-wheel drive vehicle equipped with a front / rear wheel driving force distribution control device, wherein (b) a steering direction in which the driver operates the steering wheel is an additional steering operation or a steering direction in which a switching operation is performed And (c) the front and rear wheel driving force distribution control device is further determined by the steering direction determination control device to determine that the steering direction is an additional operation. Therefore, the driving force distribution amount or the driving force distribution ratio to the front wheels is increased as compared with the case where the steering direction determination control device determines that the steering direction is the reversing operation.

  In this way, when the steering wheel operation is an additional operation (the cutting operation is also agreed), the amount of driving force distribution to the front wheels is greater than that at the time of the switching back operation. Combined with the characteristic that the self-aligning torque (SAT) is reduced, the SAT is reduced and the steering force is reduced (that is, the steering is lightened) and the yaw response of the vehicle is improved when the turning operation is increased. be able to. That is, at the time of turning-up operation, the SAT is reduced by increasing the driving force of the front wheels, and the steering amount (steering angle) for achieving the target turning behavior (or yaw rate) with a small steering force can be obtained. . Further, during the switch back operation, the SAT increases, but the steering direction is reversed, so that the steering force is reduced (that is, the steering is lightened), and the yaw response of the vehicle can be improved. That is, at the time of the switch back operation, the SAT is increased by reducing the driving force of the front wheels, the steering becomes lighter, and the response to the steering can be improved.

  Here, according to a second aspect of the present invention, in the four-wheel drive vehicle according to the first aspect, the front and rear wheel driving force distribution control device has a steering direction that is increased by the steering direction determination control device. When the determination is made, the driving force distribution ratio to the rear wheels is made smaller than in the case where the steering direction determination control device determines that the steering direction is the steering back operation. In this way, the driving force distribution amount to the front wheels is relatively large during the turning increase operation, while the driving force distribution amount to the rear wheels is relatively large during the switch back operation.

  According to a third aspect of the present invention, in the four-wheel drive vehicle according to the first aspect or the second aspect of the invention, the front and rear wheel driving force distribution control device performs a steering operation by the steering direction determination control device. When it is determined that the steering direction is a direction, the driving force distribution ratio to the rear wheels is set to zero, while the steering direction determination control device determines that the steering direction is a reverting operation. The driving force distribution ratio to the rear wheels is set to a predetermined distribution ratio exceeding zero. In this way, the driving force is not distributed to the rear wheel during the turning-up operation, and the driving force distribution amount to the front wheel is maximized, while the predetermined driving force is applied to the rear wheel during the switching-back operation. The power is distributed, and the amount of driving force distributed to the front wheels is reduced.

  According to a fourth aspect of the present invention, there is provided the four-wheel drive vehicle according to any one of the first to third aspects of the present invention, wherein (a) the steering direction determination control device is (i) an actual steering angle. A holding value setting unit that sets a holding value that is the steering angle of the comparison destination when calculating a steering angle difference value that is a difference between the steering angle and the steering angle of the comparison destination, and (ii) a current value of the steering angle difference value A first determination unit that determines whether or not the sign has changed from the previous time; and (iii) if the first determination unit determines that the sign of the steering angle difference value has changed, A second determination unit that determines whether or not the current absolute value exceeds a predetermined value; and (iv) the second determination unit determines that the current absolute value of the steering angle difference value exceeds a predetermined value. If it is determined that the steering direction has changed, the second determination unit determines that the steering angle difference value is the current absolute value. A third determination unit that determines that the steering direction has not changed, and (b) the hold value setting unit is determined by the second determination unit. When it is determined that the current absolute value of the steering angle difference value does not exceed a predetermined value, the holding value used when calculating the current steering angle difference value is used as the next steering angle difference value. It is to set as a holding value used when calculating. In this case, the condition for determining that the steering direction has changed is that the sign of the steering angle difference value changes and the absolute value of the steering angle difference value exceeds a predetermined value. In addition, when it is determined that the steering direction has not changed because the absolute value of the steering angle difference value does not exceed a predetermined value despite the change in the sign of the steering angle difference value, Since the hold value used when calculating the steering angle difference value is not updated, it becomes difficult to be influenced by small changes in the steering amount at the time of steering. Judgment can be made promptly. As described above, when determining the steering direction of the steering wheel by the driver, it is possible to suppress hunting (incorrect determination) of determination, and it is possible to suppress delay in determination.

  According to a fifth aspect of the present invention, in the four-wheel drive vehicle according to the fourth aspect of the present invention, the third determination unit determines that the sign of the steering angle difference value has not changed by the first determination unit. In the case where the steering direction has not changed, the hold value setting unit determines that the sign of the steering angle difference value has not been changed by the first determination unit. Alternatively, when the second determination unit determines that the current absolute value of the steering angle difference value exceeds a predetermined value, the second steering unit is used to calculate the current steering angle difference value. The actual steering angle value is set as a hold value used when the next steering angle difference value is calculated. In this way, it is possible to more accurately and promptly determine the steering wheel turning-up operation and the switching-back operation by the driver.

  According to a sixth aspect, in the four-wheel drive vehicle according to the fourth aspect or the fifth aspect, it is determined whether or not the absolute value of the actual steering angle is within a predetermined range including zero. A fourth determination unit; and when the fourth determination unit determines that the absolute value of the actual steering angle is within the predetermined range, the first determination unit The third determination unit does not determine whether or not the sign has changed, the steering direction is increased to a steering direction to be operated, and the hold value setting unit holds the actual steering angle value. It is to set as a value. In this way, when the absolute value of the actual steering angle is within a predetermined range including zero, if the steering wheel is steered by the driver, the operation is increased. Since the steering direction is set to the steering direction to be increased without performing the determination by the determination unit, it is possible to prepare for the increased operation in advance. Further, it is possible to more correctly and promptly determine the steering wheel turning-up operation and the switching-back operation by the driver.

  Further, a seventh invention is the four-wheel drive vehicle according to any one of the fourth to sixth inventions, wherein whether or not the actual steering angle has crossed zero with respect to the previous value. A fifth determination unit for determining; and when the fifth determination unit determines that the actual steering angle has crossed zero with respect to the previous value, the first determination unit determines whether the steering angle difference Without determining whether the sign of the value has changed, the third determination unit increases the steering direction to a steering direction that is an operation, and the hold value setting unit determines the value of the actual steering angle. The holding value is set. In this way, when the actual steering angle crosses zero, the determination by the first determination unit is made that the operation direction of the steering wheel by the driver is increased in the opposite direction. Without performing this, the steering direction is set to the steering direction that is the rounding-up operation, so that it is possible to respond to the rounding-up operation quickly. Further, it is possible to more correctly and promptly determine the steering wheel turning-up operation and the switching-back operation by the driver.

  According to an eighth aspect of the present invention, in the four-wheel drive vehicle according to any one of the fourth to seventh aspects, the front and rear wheel drive force distribution control device is a steering direction by the steering direction determination control device. The amount of driving force distribution between the front wheels and the rear wheels is controlled based on the determination result. In this way, the driving force distribution amount is appropriately controlled in accordance with the increase operation or return operation during steering, and the yaw response of the vehicle is improved during both the increase operation and the return operation.

It is a figure explaining the schematic structure of the four-wheel drive vehicle to which this invention is applied, and is a figure explaining the principal part of the control function for various controls in a four-wheel drive vehicle, and a control system. It is a figure explaining the schematic structure of the steering device with which the vehicle was equipped. It is a figure which shows the relationship between a driving force and a self aligning torque. It is a figure which shows the relationship between a steering torque and a yaw rate, Comprising: (a) is the case at the time of a rounding-up operation, (b) is the case at the time of driving | running | working which increased front wheel torque (FF driving | running | working), and small front wheel torque This is the case of running (4WD running). 4 is a chart summarizing the relationship between the driving force and steering force of front and rear wheels. 7 is a flowchart illustrating a control operation for improving the yaw responsiveness of the vehicle at the time of the main operation of the electronic control device, that is, when the steering wheel operation by the driver is increased and when the operation is switched back. It is a flowchart explaining the control action for suppressing the hunting of judgment or the judgment delay when judging the main part of the control action of the electronic control unit, that is, the steering direction of the steering wheel by the driver. It is a figure explaining the schematic structure of the vehicle to which this invention is applied, Comprising: It is an Example different from the vehicle of FIG.

  In the present invention, preferably, the four-wheel drive vehicle is a four-wheel drive vehicle in which power of a driving force source is distributed to a sub drive wheel from a power transmission path on the main drive wheel side via an electronic control coupling, for example. A vehicle equipped with a drive system, or a driving force source and power transmission path on the side of the main driving wheel and a driving force distribution amount of the front and rear wheels in the driving force source and power transmission path on the side of the auxiliary driving wheel independent of the main driving wheel side It is a vehicle provided with the four-wheel drive system which is controlled. The four-wheel drive vehicle includes a transmission that forms part of a power transmission path between the drive force source and the main drive wheels. This transmission includes a manual transmission such as a known synchronous mesh type parallel two-shaft transmission having a plurality of pairs of transmission gears that are always meshed between two shafts, various automatic transmissions (planetary gear automatic transmission, synchronous mesh). Type parallel two-shaft automatic transmission, DCT, CVT, etc.). This automatic transmission is constituted by an automatic transmission alone, an automatic transmission having a fluid transmission, or an automatic transmission having a sub-transmission. As the driving force source, for example, a gasoline engine such as an internal combustion engine that generates power by combustion of fuel, a diesel engine, or the like is preferably used. However, another prime mover such as an electric motor is used alone or in combination with the engine. You can also

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of a four-wheel drive vehicle 10 (hereinafter, referred to as a vehicle 10) to which the present invention is applied, and shows control functions and various parts of a control system for various controls in the vehicle 10. It is a figure explaining. In FIG. 1, a vehicle 10 includes an engine 12, left and right front wheels 14L and 14R (hereinafter referred to as front wheels 14 unless otherwise specified), and left and right rear wheels 16L and 16R (hereinafter referred to as rear wheels 16 unless otherwise specified). A first power transmission path for transmitting the power of the engine 12 to the front wheels 14 as a power transmission path between the engine 12 and the front wheels 14, and an engine as a power transmission path between the engine 12 and the rear wheels 16. A second power transmission path for transmitting 12 power to the rear wheel 16 is provided. The engine 12 is an internal combustion engine such as a gasoline engine or a diesel engine, and is a driving force source that generates a driving force. The front wheels 14 are drive wheels to which power is transmitted from the engine 12 via the first power transmission path in both the two-wheel drive travel state (2WD travel state) and the four-wheel drive travel state (4WD travel state). The main drive wheel. The rear wheel 16 is a sub-drive wheel that becomes a driven wheel when in the 2WD running state and a drive wheel that receives power from the engine 12 via the second power transmission path when in the 4WD running state. Accordingly, the vehicle 10 is an FF-based front and rear wheel drive vehicle (four wheel drive vehicle).

  The first power transmission path includes a transmission 18, a front differential 20, left and right front wheel axles 22L and 22R (hereinafter referred to as front wheel axle 22 unless otherwise distinguished), and the like. The second power transmission path includes a transmission 18, a transfer 24 that is a front and rear wheel power distribution device that distributes power of the engine 12 to the rear wheels 16, and power of the engine 12 distributed by the transfer 24 to the rear wheels 16. Propeller shaft 26 which is a driving force transmission shaft for transmission, electromagnetic driving force distribution coupling (hereinafter referred to as coupling) 28 as a friction engagement device arranged in series with propeller shaft 26, rear differential 30, left and right rear Wheel axles 32L, 32R (hereinafter referred to as rear wheel axle 32 unless otherwise distinguished) are provided. The vehicle 10 is an example of an electronically controlled torque split type four-wheel drive vehicle that distributes the torque generated by the engine 12 to the front and rear wheels in accordance with the traveling state of the vehicle 10, and the coupling 28 improves traction performance with low fuel consumption. An excellent drive system (power transmission device) can be provided.

  The transmission 18 is a part of a common power transmission path among the first power transmission path between the engine 12 and the front wheel 14 and the second power transmission path between the engine 12 and the rear wheel 16. The power of the engine 12 is transmitted to the front wheel 14 side and the rear wheel 16 side. The transmission 18 is, for example, a known planetary gear type multi-stage transmission in which a plurality of shift stages having different transmission ratios γ (= transmission input rotational speed Nin / transmission output rotational speed Nout) are selectively established. Is a known continuously variable transmission that can be continuously changed steplessly, or a known synchronous mesh type parallel twin-shaft transmission.

  The coupling 28 is provided between the propeller shaft 26 and the rear differential 30 and is connected to the one rotation element 28a connected to the propeller shaft 26 and the other rotation element 28b connected to the drive pinion 34 that meshes with the ring gear of the rear differential 30. Torque is transmitted to and from. The coupling 28 is an electronically controlled coupling constituted by, for example, a wet multi-plate clutch. By controlling the transmission torque of the coupling 28, the torque distribution of the front and rear wheels is continuously performed between 100: 0 and 50:50. Can be changed. Specifically, when a current is supplied to an electromagnetic solenoid (not shown) that controls the transmission torque of the coupling 28, the coupling 28 is engaged with an engagement force proportional to the current value. For example, when the current of the electromagnetic solenoid is not supplied, the engagement force of the coupling 28 is zero, that is, the transmission torque is zero, and the torque distribution of the front and rear wheels is 100: 0. When the current of the electromagnetic solenoid is increased and the coupling 28 is completely engaged, the torque distribution between the front and rear wheels is 50:50. Thus, as the current value supplied to the electromagnetic solenoid increases, the torque distribution transmitted to the rear wheel increases, and by controlling this current value, the torque distribution of the front and rear wheels can be continuously changed. Can do. Since the coupling 28 is a known technique, a specific structure and operation are omitted.

  FIG. 2 is a diagram illustrating a schematic configuration of the steering device 40 provided in the vehicle 10. In FIG. 2, the steering device 40 includes a steering shaft 42, a steering gear box 44, left and right tire rods 46L and 46R (hereinafter referred to as tire rods 46 unless otherwise specified), and left and right knuckle arms 48L and 48R (hereinafter referred to as tire rods 46L and 48R). The knuckle arm 48 is provided unless otherwise distinguished, and the rotation of the steering wheel 49 is mechanically transmitted to the front wheel 14 through them. Since the steering device 40 is a known technology, for example, a rack and pinion type steering gear mechanism is used in the steering gear box 44, a specific structure and operation are omitted.

  Returning to FIG. 1, for example, in the vehicle 10, the front and rear wheel driving force distribution control device 72 that controls the driving force distribution amount between the front wheels 14 and the rear wheels 16, and the steering wheel 49 operated by the driver are added to the steering operation. An electronic control unit 70 including a control unit for the vehicle 10 such as a steering direction determination control unit 74 for determining whether the direction is a steering direction or a steering direction for a switchback operation is provided. The electronic control unit 70 includes, for example, a so-called microcomputer having a CPU, a RAM, a ROM, an input / output interface, and the like. The CPU uses a temporary storage function of the RAM and follows a program stored in the ROM in advance. Various controls of the vehicle 10 are executed by performing signal processing. For example, the electronic control unit 70 performs output control of the engine 12, switching control of the driving state of the vehicle 10, etc., and is used for engine control, coupling control of the coupling 28, etc. as necessary. It is configured separately. The electronic control unit 70 includes various sensors (for example, various rotational speed sensors 50, 52, 54, and 56, an accelerator opening sensor 58, a throttle valve opening sensor 60, a G sensor 62, a yaw rate sensor 64, a steering sensor 66, and the like). Various actual values based on the detection signal (for example, engine rotation speed Ne, transmission input rotation speed Nin, transmission output rotation speed Nout, rotation speed of each wheel (that is, front wheels 14L and 14R and rear wheels 16L and 16R) (each wheel Speed) wheel speeds Nwfl, Nwfr, Nwrl, Nwrr corresponding to Nw, accelerator opening θacc, throttle valve opening θth, longitudinal acceleration Gx of the vehicle 10, lateral acceleration Gy of the vehicle 10, rotation about the vertical axis of the vehicle 10 The yaw rate Ryaw, which is the angular velocity, the steering angle θsw of the steering wheel 49 (also referred to as the steering angle θsw), etc.) are supplied. From the electronic control unit 70, for example, an engine output control command signal Se for controlling the output of the engine 12 and a torque command signal Sc for controlling the engagement torque of the coupling 28, that is, the rear wheel 16 side are transmitted (distributed). ) A 4WD torque control command signal Sc for controlling torque is output to an engine control device such as a fuel injection device, an ignition device, a throttle actuator, an electromagnetic solenoid for driving the coupling 28, and the like. The electronic control unit 70 calculates a speed V (hereinafter referred to as a vehicle speed V) of the vehicle 10 as one of various actual values based on each wheel speed Nw. The electronic control unit 70 sets the average wheel speed of each wheel speed Nw as the vehicle speed V, for example.

  The front and rear wheel driving force distribution control device 72 includes vehicle running state determining means, that is, a vehicle running state determining unit 76, 4WD driving force calculating unit, that is, 4WD driving force calculating unit 78, and actuator output instruction unit, that is, actuator output instruction unit 80. Yes.

  The vehicle travel state determination unit 76 determines an optimal drive state (travel state) of the vehicle 10 based on information such as the various signals. Specifically, the vehicle running state determination unit 76 obtains and stores a change in driving force of the vehicle 10 experimentally or in advance based on the accelerator opening θacc, the vehicle speed V, and the like (that is, predetermined). When it is determined that the vehicle 10 is in a steady running state smaller than the driving force change threshold, the running state of the vehicle 10 is determined to be 2WD running in which the coupling 28 is released. On the other hand, when the vehicle running state determination unit 76 determines that the driving force change exceeds the driving force change threshold, the vehicle running state is determined by engaging or slipping the coupling 28. It is determined to be a 4WD traveling. In addition, when the vehicle travel state determination unit 76 determines that any of the rotational speed differences between the wheels has exceeded a predetermined rotational difference based on each wheel speed Nw, the vehicle travel state of the vehicle 10 is determined as 4WD travel. It is determined that The vehicle running state determination unit 76 also turns the vehicle 10 based on whether or not the absolute values of the steering angle θsw, the lateral acceleration Gy, and the yaw rate Ryaw are equal to or greater than the respective turning determination threshold values θswth, Gyth, Ryawth. If it is determined whether the vehicle 10 is turning, and if it is determined that the vehicle 10 is turning, the traveling state of the vehicle 10 is determined to be 4WD traveling. The turning determination threshold values θswth, Gyth, and Ryawth are predetermined determination values for determining, for example, that the vehicle 10 is turning. In addition, although it is fundamental to set it as 4WD driving | running | working during the turning of the vehicle 10, it is not necessarily required to set it as 4WD driving | running | working.

  The 4WD driving force calculating unit 78 calculates the optimal driving force distribution amount for the front and rear wheels based on information such as the various signals. Specifically, the 4WD driving force calculation unit 78 calculates an estimated value (estimated engine torque) Tep of the engine torque Te based on the engine speed Ne, the throttle valve opening θth, etc., and ensures the maximum acceleration performance. As described above, the driving force distribution ratio of the front and rear wheels is calculated, and the total torque (total driving torque) based on the estimated engine torque Tep is multiplied by the driving force distribution ratio of the front and rear wheels, respectively. For example, the front torque Tf and the rear torque Tr) are calculated. When the 4WD driving force calculation unit 78 determines that the operation state of the driver or the driving force change of the vehicle 10 is stable based on the throttle valve opening θth, the vehicle speed V, each wheel speed Nw, and the like. Reduces the driving force distribution amount (or driving force distribution ratio) to the rear wheels 16 to improve the fuel efficiency in a situation close to that of front wheel driving. Further, the 4WD driving force calculation unit 78 is configured to distribute the driving force distribution amounts of the front and rear wheels (or the front wheels) so that appropriate turning performance can be obtained based on the steering direction of the steering wheel 49 by the driver and the target yaw rate Ryawtgt during turning. Driving force distribution ratio) is calculated. Note that the 4WD driving force calculation unit 78 sets the driving force distribution (rear distribution ratio) to the rear wheels 16 to zero when the vehicle traveling state determination unit 76 determines to enter the 2WD traveling state.

  The actuator output instructing unit 80 controls the transmission torque of the coupling 28 so that the traveling state determined by the vehicle traveling state determining unit 76 and the front / rear wheel driving force distribution calculated by the 4WD driving force calculating unit 78 are obtained. A torque command signal Sc is output to an electromagnetic solenoid (not shown). Specifically, the actuator output instructing unit 80 outputs a command for setting the transmission torque of the coupling 28 to zero to the electromagnetic solenoid when the vehicle traveling state determining unit 76 determines to enter the 2WD traveling state. . When the vehicle travel state determination unit 76 determines that the 4WD travel state is set, the actuator output instruction unit 80 performs the 4WD travel with the driving force distribution of the front and rear wheels calculated by the 4WD driving force calculation unit 78. In addition, a command for controlling the transmission torque of the coupling 28 is output to the electromagnetic solenoid.

  As described above, when the vehicle traveling state determination unit 76 determines that the vehicle 10 is turning, the traveling state of the vehicle 10 is determined to be 4WD traveling, and 4WD driving force calculation is performed during the turning. The unit 78 calculates the driving force distribution amount (or driving force distribution ratio) of the front and rear wheels based on the steering direction of the steering wheel 49 by the driver. With respect to the driving force distribution of the front and rear wheels during such turning, this embodiment proposes a method for controlling the steering torque so as to have an appropriate steering torque.

  FIG. 3 is a diagram showing the relationship between the driving force and the self-aligning torque (SAT; see FIG. 2) generated in the tire at a certain slip angle. In FIG. 3, it can be seen that as the driving force increases, the SAT tends to decrease. This SAT is a characteristic that affects the operating force Fsw (see FIG. 2) on the steering wheel 49 by the driver. For example, in the case of a turning-up operation, a larger steering force is required as the SAT is larger (that is, the rudder is heavier), whereas a smaller steering force is not required (that is, the rudder is lighter). From these facts, it can be seen that when the driving force is increased, the SAT is reduced when the driving force is increased, and a large steering force is not required. As shown in FIG. 4 (a), this means that a small steering force is sufficient to achieve the target yaw rate (that is, until the same yaw rate (steering angle θsw) is reached), and the yaw response of the vehicle Sexuality is improved. On the other hand, in the case of the turning-up operation, it can be seen that if the driving force decreases, the SAT increases and a steering force is required. As shown in FIG. 4A, this requires a large steering force to achieve the target steering angle θsw, and the yaw response of the vehicle is deteriorated. Further, in the return operation in which the steering direction is opposite to the increase operation, a large steering force is required if the SAT is small, and the steering force is decreased if the SAT is large. For this reason, as shown in FIG. 4B, in the case of traveling with increased front wheel torque (FF traveling), the yaw response of the vehicle is deteriorated during the switchback operation, and during traveling with reduced front wheel torque (4WD). In the case of driving), the yaw response of the vehicle is deteriorated during the rounding operation.

  FIG. 5 summarizes the above-mentioned attention points in correspondence with the driving forces of the front and rear wheels. In FIG. 5, if the front torque Tf is relatively large (that is, if the rear torque Tr is relatively small), the SAT decreases, and the steering force is small during the increase operation (that is, the rudder becomes light). The yaw response of the vehicle to torque is improved. However, a large steering force is required during the switchback operation (that is, the rudder becomes heavy), and the yaw response of the vehicle is deteriorated. On the other hand, if the front torque Tf is relatively small (that is, if the rear torque Tr is relatively large), the SAT increases, and a large steering force is required for the turning operation (that is, the rudder becomes heavy). Yaw response is poor. However, the steering force is small at the time of the switchback operation (that is, the rudder becomes light), and the yaw response of the vehicle to the steering torque is improved.

  Incidentally, it is desirable that the yaw responsiveness of the vehicle with respect to the steering torque is good both when the steering wheel 49 is turned on (when the turning operation is performed) and when the steering wheel 49 is turned back. On the other hand, when the torque distribution of the front and rear wheels is uniform between the increase operation and the return operation when the influence of the SAT acts in reverse, as shown in FIG. May not be improved. Therefore, the front / rear wheel driving force distribution control device 72 moves to the front wheel 14 when the driver operates the steering wheel 49 in the steering direction in which the steering wheel 49 is turned on more than in the steering direction in which the operation is turned back on. Increase the driving force distribution amount. For example, the 4WD driving force calculation unit 78 reduces the driving force distribution ratio to the rear wheels 16 when the steering direction is a turning-over operation compared to the steering direction when a turning-back operation is performed. The drive power distribution amount to the front wheels 14 is increased. In addition, although it is fundamental to set it as 4WD driving | running | working during the turning of the vehicle 10, it is not necessarily required to set it as 4WD driving | running | working. Therefore, the 4WD driving force calculation unit 78 sets the driving force distribution ratio to the rear wheel 16 to zero when the steering direction is a turning-up operation, while the steering direction is a turning-back operation. By setting the driving force distribution ratio to the rear wheel 16 to a predetermined distribution ratio exceeding zero, the front wheel 14 is more steered when the steering direction is a turning-over operation than when the steering direction is a turning-back operation. The driving force distribution amount to the may be increased.

  As described above, the control mode of the driving force distribution amount of the front and rear wheels differs between the steering wheel 49 turning operation and the switching back operation. For this reason, it is desirable to appropriately determine the steering direction during traveling. The actual steering angle θsw (hereinafter referred to as the actual steering angle θsw) is determined by the fluctuation of the steering angle θsw in the driver's steering operation, the fluctuation of the steering angle θsw due to the change in the road surface resistance transmitted to the steering wheel 49 via the front wheels 14, and the like. There is a possibility that minor fluctuations that are not the user's intention to operate will be on board. Then, depending on the method of determining the steering direction, there is a possibility that hunting occurs in the determination, and control that switches the control mode in accordance with the determination of the steering direction may be busy. In addition, in the steering direction determination method whose main purpose is to suppress or prevent determination hunting, there is a possibility that a determination delay occurs in the determination of switching the steering direction.

  The present embodiment also proposes a steering direction determination method that can suppress determination hunting and suppress determination delay. The aim of the determination method of the steering direction in the present embodiment is, for example, that it is not determined that the steering direction has changed only by changing the changing direction of the steering angle θsw, and further, the change amount of the steering angle θsw exceeds a predetermined value. In this case, it is determined that the steering direction has changed. Thereby, the hunting of the judgment as described above is suppressed. In addition, even if the change direction of the steering angle θsw is switched, if it is determined that the steering direction has not changed because the change amount of the steering angle θsw does not exceed the predetermined value, the change amount of the steering angle θsw is The holding value θswhld, which is a comparison steering angle compared with the actual steering angle θsw when calculating, is not updated. As a result, compared to the case where the change in the steering angle θsw is always calculated by the difference between the previous value and the actual value (current value) of the steering angle θsw, the steering angle θsw is changed after the change direction of the steering angle θsw is switched. Change easily exceeds a predetermined value, and the determination delay as described above is suppressed.

  Specifically, the steering direction determination control device 74 includes a holding value setting unit, that is, a holding value setting unit 82, a steering angle difference value calculation unit, that is, a steering angle difference value calculation unit 84, and a steering direction determination unit, that is, a steering direction determination unit 86. It has.

  The hold value setting unit 82 sets a hold value θswhld that is a comparison target steering angle with respect to the actual steering angle θsw when calculating the change in the steering angle θsw used when determining the steering direction. As will be described later, the change in the steering angle θsw is a steering angle difference value Δθsw that is a difference between the actual steering angle θsw and the hold value θswhld. Further, the steering angle difference value Δθsw is roughly classified according to whether the steering wheel 49 is a steering direction that is a turning-up operation or a steering direction that is a turning-back operation based on whether the steering angle difference value Δθsw is a positive value or a negative value. It is a value to do. Therefore, in calculating the steering angle difference value Δθsw, the absolute value is used for both the holding value θswhld and the actual steering angle θsw. The hold value setting unit 82 sets the hold value θswhld based on the determination result by the steering direction determination unit 86, and the specific setting of the hold value θswhld will be described later by the steering direction determination unit 86. This will be described in detail in association with the determination result.

  The steering angle difference value calculation unit 84 calculates a steering angle difference value Δθsw (= θswhld− | θsw |) that is a difference between the hold value θswhld and the absolute value of the actual steering angle θsw as a change in the steering angle θsw. The steering angle difference value Δθsw is calculated as a value obtained by subtracting the absolute value of the actual steering angle θsw from the hold value θswhld. Therefore, the steering angle difference value Δθsw becomes a negative value when the absolute value of the actual steering angle θsw increases, and becomes an actual steering angle θsw. It becomes a positive value at the time of switching operation in which the absolute value of is decreased. In other words, the hold value θswhld is set as an absolute value by the hold value setting unit 82 so as to be so.

  The steering direction determination unit 86 functionally includes first determination means that determines whether or not the current sign of the steering angle difference value Δθsw has changed from the previous time, that is, a first determination unit 88. Specifically, if it is determined by the steering direction determination unit 86 that the steering direction determination unit 86 is determining that the steering angle is being increased, the first determination unit 88 increases the steering angle difference value Δθsw and is a negative value corresponding to the operation. By determining whether or not, it is determined whether or not the current sign of the steering angle difference value Δθsw has changed from the previous time. On the other hand, if it is determined by the steering direction determination unit 86 that the switchback determination is being performed, the first determination unit 88 determines whether or not the steering angle difference value Δθsw is a positive value corresponding to the switchback operation. It is determined whether or not the current sign of the steering angle difference value Δθsw has changed from the previous time.

  The steering direction determination unit 86 determines that the current absolute value of the steering angle difference value Δθsw exceeds a predetermined value when the first determination unit 88 determines that the current sign of the steering angle difference value Δθsw has changed from the previous time. The second determination means for determining whether or not the second determination unit 90 is functionally provided. Specifically, the second determination unit 90 determines that the steering angle difference value Δθsw is a positive value corresponding to the switch back operation by the first determination unit 88 when the steering direction determination unit 86 determines that the increase in turning is being determined. If so, it is determined whether or not the steering angle difference value Δθsw is greater than a predetermined value A (> 0). On the other hand, the second determination unit 90 determines that the steering angle difference value Δθsw is increased by the first determination unit 88 and is a negative value corresponding to the operation when the steering direction determination unit 86 determines that the switchback determination is being performed. In this case, it is determined whether or not the steering angle difference value Δθsw is smaller than a predetermined value B (<0). The predetermined value A (> 0) or the predetermined value B (<0) as the predetermined value exceeds, for example, a fine fluctuation that is not the driver's intention to operate (in other words, the steering direction according to the driver's intention to operate). This is a predetermined steering direction change determination threshold value for determining that the steering angle difference value Δθsw is such that it can be determined that has been changed. Predetermined value A (> 0) is a determination threshold value for determining that the operation has been changed from the round-up operation to the return operation, and predetermined value B (<0) is a determination for determining that the operation has been changed from the switch-back operation to the back-up operation. It is a threshold value, and the absolute value of the predetermined value B (<0) may be the same value as the predetermined value A (> 0) or a different value.

  When the second determination unit 90 determines that the current absolute value of the steering angle difference value Δθsw exceeds the predetermined value, the steering direction determination unit 86 determines that the steering direction has changed, 2 When the determination unit 90 determines that the current absolute value of the steering angle difference value Δθsw does not exceed the predetermined value, a third determination unit that determines that the steering direction has not changed, that is, the third determination unit 92 Is functionally equipped. Specifically, the third determination unit 92 determines that the steering angle difference value Δθsw is greater than the predetermined value A (> 0) by the second determination unit 90 when the steering direction determination unit 86 determines that the increase is being made. If it is determined that the steering direction has been changed to the switch back operation, the increase flag is turned off. On the other hand, the third determination unit 92 determines that the steering angle difference value Δθsw is equal to or smaller than the predetermined value A (> 0) by the second determination unit 90 when the steering direction determination unit 86 determines that the increase is being made. In such a case, it is determined that the steering direction remains the increase operation, and the increase flag is not changed from ON. On the other hand, the third determination unit 92 determines that the steering angle difference value Δθsw is smaller than the predetermined value B (<0) by the second determination unit 90 when the steering direction determination unit 86 determines that the switchback determination is being performed. In this case, it is determined that the steering direction has been increased and the operation has been changed, and the increase flag is turned on. On the other hand, the third determination unit 92 determines that the steering angle difference value Δθsw is equal to or greater than the predetermined value B (<0) by the second determination unit 90 when the steering direction determination unit 86 determines that the switchback determination is being performed. In this case, it is determined that the steering direction remains the switchback operation, and the switch-over flag is not changed from OFF.

  When the second determination unit 90 determines that the current absolute value of the steering angle difference value Δθsw does not exceed the predetermined value, the hold value setting unit 82 determines that the steering angle difference value calculation unit 84 The holding value θswhld used when calculating the difference value Δθsw is set as the holding value θswhld used when the steering angle difference value calculation unit 84 calculates the next steering angle difference value Δθsw. That is, when the second determination unit 90 determines that the current absolute value of the steering angle difference value Δθsw does not exceed the predetermined value, the hold value setting unit 82 does not update the hold value θswhld. Accordingly, after the current sign of the steering angle difference value Δθsw has changed from the previous time, while the current absolute value of the steering angle difference value Δθsw does not exceed the predetermined value, the hold value θswhld is a peak value (maximum value or minimum value). ) Is used.

  As described above, a steering direction determination method that can suppress determination hunting or suppress determination delay has been proposed. Further, a preferred mode in which the driver can more accurately and quickly determine the steering wheel 49 turning operation and the turning back operation will be described below.

  When the second determination unit 90 determines that the current absolute value of the steering angle difference value Δθsw exceeds the predetermined value, the hold value setting unit 82 determines that the steering angle difference value calculation unit 84 The actual steering angle θsw value (absolute value here) used when calculating the difference value Δθsw is set as the hold value θswhld used when the steering angle difference value calculation unit 84 calculates the next steering angle difference value Δθsw. To do. The actual steering angle θsw set as the hold value θswhld is the previous value of the actual steering angle θsw when the next steering angle difference value Δθsw is calculated.

  If the first determination unit 88 determines that the sign of the steering angle difference value Δθsw has not changed, the third determination unit 92 determines that the steering direction has not changed. In this case, the hold value setting unit 82 calculates the actual steering angle θsw (the absolute value here) used when the steering angle difference value calculation unit 84 calculates the current steering angle difference value Δθsw. The steering angle difference value calculation unit 84 sets the hold value θswhld used when the next steering angle difference value Δθsw is calculated. Specifically, the third determination unit 92 determines that the steering angle difference value Δθsw is increased by the first determination unit 88 and is a negative value corresponding to the operation when the steering direction determination unit 86 determines that the increase is being performed. If it is determined that the steering direction is still increased, the increased flag is not changed from ON. In this case, the hold value setting unit 82 sets the absolute value of the actual steering angle θsw as the hold value θswhld. On the other hand, the third determination unit 92 determines that the steering angle difference value Δθsw is a positive value corresponding to the switchback operation by the first determination unit 88 when the steering direction determination unit 86 determines that the switchback determination is being performed. In this case, it is determined that the steering direction remains the switchback operation, and the switch-over flag is not changed from OFF. In this case, the hold value setting unit 82 sets the absolute value of the actual steering angle θsw as the hold value θswhld.

  The steering direction determination unit 86 further functionally includes fourth determination means, that is, a fourth determination unit 94 that determines whether or not the absolute value of the actual steering angle θsw is within a predetermined range including zero. When the fourth determination unit 94 determines that the absolute value of the actual steering angle θsw is within the predetermined range, the first determination unit 88 changes the current sign of the steering angle difference value Δθsw from the previous time. Without determining whether or not, the third determining unit 92 determines that the steering direction is to be increased and the steering direction is an operation, and turns on the increased flag. In this case, the hold value setting unit 82 sets the absolute value of the actual steering angle θsw as the hold value θswhld. Here, when the steering wheel 49 is operated by the driver so that the vehicle 10 goes straight, if the steering wheel 49 is operated with the intention of turning thereafter, the steering direction is always increased. Become. On the other hand, without making the determination by the first determination unit 88 (determination after the first determination unit 88), the steering direction is set to the steering direction that is the additional operation, so that it is prepared in advance for the additional operation. I will leave it. In order to check the straight traveling state of the vehicle 10, it is only necessary to determine whether the actual steering angle θsw is zero. However, as described above, the actual steering angle θsw is fluctuated, and the value detected by the steering sensor 66 is detected. In consideration of the fact that there is an error (individual difference), the zero is given a certain range, and it is determined whether or not the absolute value of the actual steering angle θsw is within a predetermined range including zero. Specifically, the fourth determination unit 94 determines whether or not the absolute value of the actual steering angle θsw is less than a predetermined steering angle that is a maximum value in a predetermined range. The predetermined steering angle is also a lower limit value of an absolute value of a predetermined actual steering angle θsw for determining that the driver has operated the steering wheel 49 with the intention of turning, for example.

  The steering direction determination unit 86 further functionally includes a fifth determination unit that determines whether or not the actual steering angle θsw has crossed zero with respect to the previous value, that is, a fifth determination unit 96. When the fifth determination unit 96 determines that the actual steering angle θsw has crossed zero with respect to the previous value, the first determination unit 88 changes the current sign of the steering angle difference value Δθsw from the previous value. Without determining whether or not, the third determination unit 92 determines that the steering direction is increased and the steering direction is an operation, and turns on the increased flag. In this case, the hold value setting unit 82 sets the absolute value of the actual steering angle θsw as the hold value θswhld. Here, when the actual steering angle θsw crosses zero with respect to the previous value, the operation direction of the steering wheel 49 by the driver is increased to the opposite direction. On the other hand, without making the determination by the first determination unit 88 (determination after the first determination unit 88), the steering direction is changed to the steering direction that is the operation to be increased, so that the increase operation can be quickly handled. It is. Specifically, the fifth determination unit 96 determines whether the actual steering angle θsw is the previous value based on whether or not the multiplication value of the actual steering angle θsw (current value) and the previous value of the actual steering angle θsw is a negative value. It is determined whether or not the value crosses zero.

  In this embodiment, the steering direction is determined by the steering direction determination method as described above. Then, the 4WD driving force calculation unit 78 controls (calculates) the driving force distribution amount of the front and rear wheels based on the determination result of the steering direction by the steering direction determination unit 86 (third determination unit 92). Thereby, the driving force distribution amount is appropriately controlled in accordance with the increase operation or return operation during steering, and the yaw response of the vehicle 10 is improved during both the increase operation and the return operation.

  FIG. 6 illustrates the main part of the control operation of the electronic control unit 70, that is, the control operation for improving the yaw response of the vehicle 10 both when the operation of the steering wheel 49 by the driver is increased and when the operation is switched back. This flowchart is repeatedly executed with an extremely short cycle time of about several milliseconds to several tens of milliseconds, for example. FIG. 6 is an example of a case where the vehicle is traveling based on 2WD traveling.

  In FIG. 6, first, in step S1 corresponding to the steering direction determination unit 86 (hereinafter, step is omitted), for example, whether or not a round-up operation is being performed based on whether or not a round-up flag is on or switch back. It is determined whether the operation is in progress. When the determination of S1 is affirmative (that is, when it is determined that the operation is increased), in S2 corresponding to the 4WD driving force calculation unit 78, for example, the driving force distribution ratio (rear distribution ratio) to the rear wheels 16 is The rear torque Tr is reduced to zero. On the other hand, when the determination of S1 is negative (that is, when it is determined that the switchback operation is performed), in S3 corresponding to the 4WD driving force calculation unit 78, for example, the total torque (total driving torque based on the estimated engine torque Tep) ) Is multiplied by a predetermined rear distribution ratio (> 0) to calculate the rear torque Tr.

  FIG. 7 is a flowchart for explaining the main part of the control operation of the electronic control unit 70, that is, the control operation for suppressing the hunting of the determination or the determination delay when determining the steering direction of the steering wheel 49 by the driver. For example, it is repeatedly executed with an extremely short cycle time of about several milliseconds to several tens of milliseconds. 7 may be executed in parallel with the flowchart of FIG. 6, for example, or may be executed in S2 of FIG.

  In FIG. 7, first, in S10 corresponding to the fifth determination unit 96, for example, whether or not the multiplication value of the actual steering angle θsw (current value) and the previous value of the actual steering angle θsw is less than zero (negative value). Is determined. If the determination in S10 is affirmative, in S20 corresponding to the third determination unit 92 and the hold value setting unit 82, it is determined that the increase operation is performed, the increase flag is turned on, and the absolute steering angle θsw is absolute. The value is set as the next hold value θswhld. If the determination in S10 is negative, it is determined in S30 corresponding to the fourth determination unit 94 whether or not the absolute value of the actual steering angle θsw is less than a predetermined steering angle near zero. If the determination in S30 is affirmative, in S40 corresponding to the third determination unit 92 and the hold value setting unit 82, it is determined that the increase operation is performed, the increase flag is turned on, and the absolute steering angle θsw is absolute. The value is set as the next hold value θswhld. If the determination in S30 is negative, it is determined in S50 corresponding to the steering direction determination unit 86 whether or not the increase flag is on (that is, the increase determination is being performed). If the determination in S50 is affirmative, it is determined in S60 corresponding to the first determination unit 88 whether or not the steering angle difference value Δθsw is less than zero (that is, a negative value corresponding to the increase operation). The If the determination in S60 is affirmative, in S70 corresponding to the third determination unit 92 and the hold value setting unit 82, it is determined that the increase operation is still being performed, and the increase flag is not changed from ON, and the actual steering is performed. The absolute value of the angle θsw is set as the next holding value θswhld. If the determination in S60 is negative, it is determined in S80 corresponding to the second determination unit 90 whether or not the steering angle difference value Δθsw is greater than a predetermined value A (> 0). If the determination in S80 is affirmative, in S90 corresponding to the third determination unit 92 and the hold value setting unit 82, it is determined that the operation has changed to the switch back operation, the increase flag is turned off, and the actual steering angle is turned off. The absolute value of θsw is set as the next hold value θswhld. On the other hand, if the determination in S80 is negative, in S100 corresponding to the third determination unit 92 and the hold value setting unit 82, it is determined that the rounding operation remains, and the rounding flag is not changed from ON. The hold value θswhld used when calculating the current steering angle difference value Δθsw is set as the next hold value θswhld (that is, the hold value θswhld is not updated). If the determination in S50 is negative, in S110 corresponding to the first determination unit 88, whether or not the steering angle difference value Δθsw exceeds zero (that is, a positive value corresponding to the switchback operation). Is determined. If the determination in S110 is affirmative, it is determined in S120 corresponding to the third determination unit 92 and the hold value setting unit 82 that the switchback operation is still being performed, and the increase flag is not changed from OFF, and the actual steering is performed. The absolute value of the angle θsw is set as the next holding value θswhld. If the determination in S110 is negative, it is determined in S130 corresponding to the second determination unit 90 whether or not the steering angle difference value Δθsw is smaller than a predetermined value B (<0). If the determination in S130 is affirmative, in S140 corresponding to the third determination unit 92 and the hold value setting unit 82, it is determined that the operation has been changed to the increase operation, the increase flag is turned on, and the actual steering angle The absolute value of θsw is set as the next hold value θswhld. On the other hand, if the determination in S130 is negative, in S150 corresponding to the third determination unit 92 and the hold value setting unit 82, it is determined that the switchback operation remains, and the round-up flag is not changed from OFF. The hold value θswhld used when calculating the current steering angle difference value Δθsw is set as the next hold value θswhld (that is, the hold value θswhld is not updated).

  As described above, according to the present embodiment, when the operation of the steering wheel 49 is a turning-up operation, the amount of driving force distribution to the front wheels 14 is larger than that during the switching-back operation. In combination with the characteristic that the self-aligning torque (SAT) decreases as the engine speed increases, the SAT decreases and the steering force decreases (that is, the steering becomes lighter), and the yaw response of the vehicle 10 increases. Can be improved. Further, during the switch back operation, the SAT increases, but the steering direction is reversed, so the steering force is reduced (that is, the steering is lightened), and the yaw response of the vehicle 10 can be improved. In other words, the steering angle θsw for achieving the desired turning behavior (or yaw rate) with a small steering force can be obtained at both the turning increase operation and the return operation.

  Further, according to the present embodiment, the rear distribution ratio is made smaller during the increase operation compared to during the return operation, so that the drive force distribution amount to the front wheels 14 is made relatively large during the increase operation. On the other hand, the amount of driving force distribution to the rear wheels 16 is made relatively large during the switchback operation.

  Further, according to the present embodiment, the rear distribution ratio is set to zero during the rounding operation, while the rear ratio is set to a predetermined distribution ratio exceeding zero during the switching back operation. While the driving force is not distributed to the wheels 16 and the amount of driving force distributed to the front wheels 14 is maximized, a predetermined driving force is distributed to the rear wheels 16 and the driving force applied to the front wheels 14 during the switchback operation. The distribution amount is reduced.

  Further, according to the present embodiment, the condition for determining that the steering direction has changed that the sign of the steering angle difference value Δθsw has changed and that the absolute value of the steering angle difference value Δθsw exceeds a predetermined value, In addition, when the sign of the steering angle difference value Δθsw has changed, but the absolute value of the steering angle difference value Δθsw does not exceed the predetermined value, so it is determined that the steering direction has not changed. Since the holding value θswhld used when calculating the steering angle difference value Δθsw is not updated, it is difficult to be influenced by a small change in the actual steering angle θsw during steering, and the driver increases the steering wheel 49. The switch-back operation can be determined more correctly and promptly. As described above, when the steering direction of the steering wheel 49 by the driver is determined, it is possible to suppress hunting (misjudgment) of determination and to suppress determination delay.

  As mentioned above, although the Example of this invention was described in detail based on drawing, this invention is applied also in another aspect.

  For example, in the above-described embodiment, the vehicle 10 is an electronically controlled torque split type four-wheel drive vehicle in which the torque generated by the engine 12 is distributed to the front and rear wheels by the coupling 28 according to the traveling state. Not limited to. For example, as in a vehicle 100 shown in FIG. 8, a four-wheel drive vehicle in which the front wheels 14 are driven by the engine 12 and the rear wheels 16 are driven by the electric motor M may be used. Further, a four-wheel drive vehicle of a type in which the same type of coupling as the coupling 28 is arranged not in series with the propeller shaft 26 but in series with each of the rear wheel axles 32L and 32R may be used. Further, the vehicle 10 has a structure in which power is constantly transmitted to the front wheels 14 and the rear wheels 16 serve as auxiliary driving wheels, but this is not a limitation. For example, the vehicle 10 may have a structure in which power is constantly transmitted to the rear wheels 16 and the front wheels 14 are auxiliary driving wheels. For example, the vehicle 10 may be an FR-based four-wheel drive vehicle.

  Moreover, although the flowchart of FIG. 6 in the above-described embodiment is an embodiment in which the rear torque Tr is set to zero at the time of the increase operation, the present invention is not limited to this. For example, the predetermined rear torque Tr may be set at the time of the turning increase operation, and the predetermined rear torque Tr may be set to the rear torque Tr increased by a predetermined amount at the time of the return operation. In short, the rear distribution ratio (or the amount of driving force distribution to the rear wheels 16) may be made smaller during the turning-up operation than during the switching-back operation. As described above, in the flowchart of FIG. 6, each step can be changed as appropriate without departing from the scope.

  The above description is only an embodiment, and the present invention can be implemented in variously modified and improved forms based on the knowledge of those skilled in the art.

10, 100: Four-wheel drive vehicle 14 (14L, 14R): Front wheels (left and right front wheels)
16 (16L, 16R): Rear wheels (left and right rear wheels)
40: Steering device 49: Steering wheel 72: Front and rear wheel driving force distribution control device 74: Steering direction determination control device

Claims (3)

A four-wheel drive vehicle comprising a steering device that mechanically transmits the rotation of the steering wheel to the front wheels, and a front and rear wheel drive force distribution control device that controls a drive force distribution amount between the front wheels and the rear wheels,
A steering direction determination control device for determining whether an operation of the steering wheel by the driver is a steering direction that is a turning operation or a steering direction that is a turning back operation;
When the steering direction determination control device determines that the front / rear wheel driving force distribution control device is in the steering direction to be turned up, the steering direction determination control device has the steering direction to be turned back in. A four-wheel drive vehicle characterized by increasing a driving force distribution amount or a driving force distribution ratio to the front wheels as compared with a case where the determination is made.   When the steering direction determination control device determines that the front / rear wheel driving force distribution control device is in the steering direction to be turned up, the steering direction determination control device has the steering direction to be turned back in. 2. The four-wheel drive vehicle according to claim 1, wherein a driving force distribution ratio to the rear wheels is made smaller than a case where the determination is made.   The front and rear wheel driving force distribution control device sets the driving force distribution ratio to the rear wheels to zero when it is determined by the steering direction determination control device that the steering direction is a steering operation. 3. The driving force distribution ratio to the rear wheels is set to a predetermined distribution ratio exceeding zero when the steering direction determination control device determines that the steering direction is a switchback operation. The four-wheel drive vehicle as described in.

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