JP4368271B2 - Vehicle travel control device - Google Patents

Description

  The present invention relates to a four-wheel drive vehicle that travels by transmitting rotational output from an engine to front wheels and rear wheels.

  Automobiles travel by transmitting the rotational driving force from the engine to the front wheels and rear wheels after shifting with the transmission, but not only the two-wheel drive type that drives only the front wheels or rear wheels, but also the front and rear There are also four-wheel drive types that drive all the wheels. In a four-wheel drive type automobile, a control device that controls the distribution of driving force to each wheel and applies an appropriate driving force to all four wheels is also provided. In addition, various devices for improving driving safety in automobiles are also used. For example, an anti-lock brake device that performs brake control for preventing the wheel from being locked during sudden braking, or an engine driving force that is optimal for the wheel is transmitted. In addition, there are traction control devices that can perform safe driving by controlling engine output and controlling left and right driving force distribution during curve driving.

  For example, Patent Document 1 discloses a four-wheel drive including an anti-lock brake device (referred to as an anti-skid control mechanism in Patent Document 1) and a driving force distribution control mechanism that controls the distribution of driving force to the front and rear wheels. A type of car is disclosed. In this automobile, the antilock brake device and the driving force distribution control mechanism are configured to share the wheel rotation speed sensor, and are configured to be controlled by one control means. In addition, when detecting an abnormality of the wheel rotation sensor sharing the detection signal in this way, a fail-safe technique is adopted in which both controls are stopped in order to prevent malfunction due to mutual interference.

Japanese Patent No. 2754721

  By the way, in a four-wheel drive vehicle, a throttle control device that controls the throttle opening of the engine, a rotational drive force distribution device that distributes and transmits the rotational drive force from the engine to the front wheels and the rear wheels, and the rotational drive force distribution device A four-wheel drive control device that performs four-wheel drive travel control by performing the above-described operation control, and a travel stability control device that performs vehicle travel control including operation control of the throttle control device and performs control to maintain vehicle travel stability. The present applicant has developed a four-wheel drive vehicle. In this four-wheel drive vehicle, the four-wheel drive control device performs a control to stop the four-wheel drive control and reduce the throttle opening by the throttle control device when a failure occurs due to a malfunction of the four-wheel drive travel control. Is considered. However, the travel stability control device also performs throttle control at the same time, and the throttle control device may receive two different throttle control signals simultaneously from the four-wheel drive control device and the travel stability control device.

  In such a case, it is conceivable to adopt a method of stopping both controls as in Patent Document 1 described above. However, such a method lowers the running stability and impairs the four-wheel drive running control. There is a problem that it tends to be stable.

  Further, the control signal for reducing the throttle opening from the four-wheel drive control device is sent to the throttle control device via the communication line, and the throttle opening control is performed. When an abnormality occurs in this communication line, Since the four-wheel drive control control becomes inaccurate, the four-wheel travel control is stopped. However, since the communication line is abnormal, a control signal for reducing the throttle opening that should be performed when the four-wheel traveling control is stopped is not sent to the throttle control device, and the traveling stability when the four-wheel traveling control is stopped. There is also a problem that there is a risk of lowering.

  In view of such a problem, the present invention is configured such that appropriate travel control can be performed even when the throttle control device receives two different throttle control signals simultaneously from the four-wheel drive control device and the travel stability control device. An object of the present invention is to provide a traveling control of the vehicle. The present invention further relates to stopping the four-wheel drive control regardless of the abnormality of the communication line when an abnormality occurs in the communication line connecting the four-wheel drive control device and the throttle control device and the four-wheel drive control is stopped. It is an object of the present invention to provide a travel control device configured to be able to appropriately perform the throttle control.

In order to achieve such an object, a travel control device according to the present invention is a throttle control device that controls the throttle opening of an engine in a four-wheel drive vehicle that travels by transmitting rotational output from an engine to front wheels and rear wheels ( For example, the engine control unit 20 and the throttle actuator 2a) in the embodiment, the rotational driving force distribution device that distributes and transmits the rotational driving force from the engine to the front wheels and the rear wheels, and the operation control of the rotational driving force distribution device are performed. A four-wheel drive control device that performs four-wheel drive travel control (for example, the four-wheel drive control unit 30 in the embodiment) and a control for maintaining vehicle travel stability by performing vehicle travel control including operation control of the throttle control device. The running stability control device to perform (for example, the running stability control unit 4 in the embodiment) ) And configured to include a. The four-wheel drive control device has a failure detection means for detecting a failure related to the four-wheel drive travel control. When the failure detection means detects a failure, the four-wheel drive control is stopped and the two-wheel drive is stopped. There line control of reducing the throttle opening by sending a first throttle control signal for reducing the throttle opening to the throttle control device as well as transition to the throttle control device, a first throttle control signal from the four-wheel drive control device and when the second throttle control signal from the running stability control device is sent to the throttle opening control is input simultaneously, of the first and second throttle control signal, the control signal towards the throttle opening is small 4-wheel drive system by 4-wheel drive control device of the throttle opening control have rows, the failure detecting means detects a failure based on the When the control is shifted to two-wheel drive and the target transmission torque distributed by the rotational driving force distribution device is greater than the specified value, the first throttle control signal is sent to the throttle control device and the four-wheel drive control is performed. However, when the target transmission torque is less than the specified value, the four-wheel drive control is stopped and the two-wheel drive is shifted to without sending the first throttle control signal.

  In the travel control device having this configuration, the four-wheel drive control device preferably stops the four-wheel drive control and shifts to the two-wheel drive state when the failure detection means detects a failure.

  The travel control device further includes a communication abnormality detector for detecting an abnormality in a communication line between the four-wheel drive control device and the throttle control device, and when the failure detection means detects the failure, the throttle control device Condition information for determining whether or not to perform control to reduce the opening degree is constantly sent from the four-wheel drive control device to the throttle control device via the communication line and is updated and stored in the throttle control device to detect communication abnormality. When the abnormality of the communication line by the detector is detected, the four-wheel drive control device stops the four-wheel drive control, and the throttle control device decreases the throttle opening based on the condition information at the time of abnormality detection that is updated and stored. It is configured to perform control.

  In this case, the four-wheel drive control device preferably stops the four-wheel drive control and shifts to the two-wheel drive state when a communication line abnormality is detected by the communication abnormality detector.

  According to the present invention having the above-described configuration, first, the four-wheel drive control is stopped and the throttle opening is decreased by the throttle control device when the failure related to the malfunction of the four-wheel drive travel control occurs. A first throttle control signal for reducing the throttle opening is input from the drive control device to the throttle control device. At this time, when the second throttle control signal from the running stability control device is also input to the throttle control device at the same time, the throttle control device controls the control signal having the smaller throttle opening degree among the first and second throttle control signals. Accordingly, the throttle opening degree control is performed based on the above, and the four-wheel drive stop control and the traveling stability control can be appropriately ensured while ensuring safety.

In addition, when the four-wheel drive control is stopped, if the target transmission torque distributed by the rotational driving force distribution device is equal to or greater than the specified value, the drive torque fluctuation of the two wheels on the drive side becomes large when the shift to the two-wheel drive is continued. Therefore, when the target transmission torque is equal to or higher than the specified value, the first throttle control signal is sent to the throttle control device and the four-wheel drive control is stopped to shift to the two-wheel drive. The four-wheel drive control is stopped without sending the first throttle control signal, and the shift to the two-wheel drive is made, so that the drive torque transmitted to the wheels at the time of the shift to the two-wheel drive is reduced and smooth. Transition to two-wheel drive is possible.

  In this travel control device, the four-wheel drive control device stops the four-wheel drive control when the communication abnormality detector detects an abnormality in the communication line between the four-wheel drive control device and the throttle control device. . At this time, the communication line is abnormal, and a control signal for reducing the throttle opening cannot be sent from the four-wheel drive control device to the throttle control device. However, the throttle control device is controlled to reduce the throttle opening by the throttle control device. Since the condition information for determining whether or not is constantly updated and stored, the throttle opening can be controlled to be reduced based on the condition information at the time of abnormality detection that is updated and stored in this way, and the four-wheel drive Stop control can be performed appropriately. In this case, it is preferable to stop the four-wheel drive control and shift to the two-wheel drive state, and avoid the unstable four-wheel drive control and perform the traveling while ensuring safety by the two-wheel drive. be able to.

  A power transmission device for a four-wheel drive vehicle equipped with a travel control device according to the present invention will be described below with reference to FIG.

  In an automobile 1 shown in FIG. 1, an engine 2 is disposed horizontally at the front of the vehicle body, and a transmission 3 is attached to the output end of the engine 2 so as to be integrated therewith. A front differential mechanism 4 and a transfer mechanism 5 are provided in the transmission 3. The rotational driving force of the engine 2 shifted by the transmission 3 is divided and transmitted to the left and right front axle shafts 6a and 6b in the front differential mechanism 4 to drive the left and right front wheels 7a and 7b. The engine power is also divided in the transfer mechanism 5 and transmitted to the rear axle device 9 via the propeller shaft 8. The rear axle device 9 has a rotational driving force distribution device 10 where the rotational driving force is divided into left and right parts and transmitted to the left and right rear wheels 12a and 12b via the left and right rear axle shafts 11a and 11b. To drive them.

  The engine 2 is provided with a throttle actuator 2a that controls the throttle opening, and the throttle actuator 2a that receives the throttle control signal from the engine control unit (ENG.CU) 20 controls the engine throttle opening. Perform the operation. The engine control unit 20 receives a detection signal from an accelerator sensor 15 that detects the operation amount of the accelerator pedal of the automobile, and the engine control unit 20 controls the operation of the throttle actuator 2a according to the operation amount of the accelerator pedal. It is like that. However, the engine throttle opening is controlled by the throttle actuator 2a. Therefore, the operation of the throttle actuator 2a can be arbitrarily controlled regardless of the operation of the accelerator pedal.

  The automobile 1 further includes a four-wheel drive control unit (AWD C.U.) 30 that performs four-wheel drive traveling control. The four-wheel drive control unit 30 sends a control signal to the rotational driving force distribution device 10 to control its operation, and distributes torque transmitted to the front wheels 7a and 7b and the rear wheels 12a and 12b. , Torque distribution control to be transmitted to the left and right rear wheels 12a and 12b is performed. Further, a four-wheel drive running state in which driving force is transmitted from the rotational driving force distribution device 10 to the left and right rear wheels 12a and 12b (note that driving force is always transmitted to the left and right front wheels 7a and 7b), It is also possible to perform control for switching between a two-wheel drive running state in which driving force transmission to the rear wheels 12a and 12b is interrupted. The throttle control signal (first throttle control signal, which will be described later) is sent from the four-wheel drive control unit 30 to the engine control unit 20 to correct the throttle opening set by the accelerator pedal operation. Yes.

  The automobile 1 also has a traveling stability control unit (VSA C.U.) 40 that performs control for maintaining traveling stability. This travel stability control unit 40 improves oversteer suppression control due to excessive steering operation, understeer suppression control during cornering acceleration, start control corresponding to the difference in road surface conditions between left and right wheels, and stability during cornering braking The turning braking control is performed. Therefore, detection signals from a steering operation sensor, a yaw rate sensor, a lateral G (lateral acceleration) sensor, a longitudinal G (front / rear acceleration) sensor, and the like are input to the traveling stability control unit 40, and these detection signals are rotationally driven. In addition to being sent to the force distribution device 10, an operation control signal is sent to the engine control unit 20 to operate the throttle actuator 2a to perform engine throttle control, and further to perform front / rear / right / left brake operation control to maintain vehicle running stability. Take control.

  The engine control unit 20, the four-wheel drive control unit 30, and the traveling stability control unit 40 are connected to each other via a network, and the detection signal input to each unit is a detection signal from a common sensor. For example, an engine rotation detection signal detected by an engine rotation sensor 2b attached to the engine 2 is sent to the engine control unit 20 through a signal line 2c, as shown in FIG. The four-wheel drive control unit 30 and the travel stability control unit 40 are also used for the respective controls. Therefore, when the engine rotation sensor 2b breaks down or the signal line 2c is disconnected, not only the fail safe control is performed in the engine control unit 20, but also the four-wheel drive control unit 30 and the travel stability control unit. At 40, fail-safe control is performed.

  Next, the control contents of the four-wheel drive control unit 30 will be described with reference to the flowchart of FIG. The unit 30 first calculates a rear target transmission torque TTr to be distributed to the rear wheels (step S1), and proceeds to step S3 unless a functional defect failure for performing four-wheel drive control is detected in step S2. Operation control of the rotational driving force distribution device 10 is performed so as to transmit the transmission torque TTr to the rear wheels 12a and 12b. The four-wheel drive control unit 30 includes a failure detector that detects a failure related to the four-wheel drive travel control, that is, a functional defect failure (the details of the failure will be described later).

  A method of calculating the rear target transmission torque TTr in step S3 will be described with reference to the block diagrams shown in FIGS. In this calculation, first, the engine output torque Te is obtained from the engine output characteristic map based on the relationship between the engine speed Ne and the intake negative pressure Pb (block B1), and the retard signal, engine coolant temperature, atmospheric pressure, The actual engine output torque Tea is calculated by multiplying the correction coefficient (block B2) based on the engine load such as the intake air temperature, the presence or absence of the air conditioner operation, and the alternator load. A transmission output torque Ttm is calculated by multiplying the actual engine output torque Tea by the torque ratio of the torque converter and the transmission gear ratio (block B3). Further, if the correction amount of the inertia torque accompanying the rotation fluctuation is calculated (block B4) and the internal loss torque of the rear wheel drive system is calculated (block B5), and these are subtracted from the transmission output torque Ttm, the estimated rear wheel drive torque Test is calculated (block B6).

  Next, the process proceeds to the block diagram of FIG. 4, and the basic torque distribution ratio DRr (the torque distribution ratio of the front and rear wheels) for the rear wheels is read (block B7). The basic torque distribution ratio DRr is set in advance to an appropriate value according to each vehicle, for example, 30%. At the same time, when the vehicle is turning as in curve driving, an increase ΔDR in the rear wheel torque distribution ratio is obtained according to the magnitude of the lateral acceleration (lateral G) acting on the vehicle body (block B8). Then, the rear wheel torque distribution ratio DR obtained by adding the increment ΔDR to the basic torque distribution ratio DRr is multiplied by the rear wheel estimated drive torque Test calculated in the block B6 as described above, and the rear target transmission distributed to the rear side. Torque TTr is calculated (block B9).

  However, the rear target transmission torque TTr is a total torque transmitted to the left and right rear wheels 12a and 12b. For example, different torque transmission is performed to the left and right with a predetermined distribution ratio during turning. Therefore, in block B10, the distribution ratio DRw to be distributed to the outer wheel side according to the lateral acceleration of the vehicle body is calculated, and this is multiplied by the rear target transmission torque TTr to calculate the target transmission torque Tro to the rear wheel on the outer wheel side. Further, the inner ring target transmission torque Tri is calculated by subtracting the outer ring target transmission torque Tro from the rear target transmission torque TTr (block B12). However, during braking, the power transmission to the left and right rear wheels 12a and 12b is interrupted to perform antilock brake control, and the processing for this is performed in block B11. That is, both the outer ring and inner ring target transmission torques Tro and Tri are set to zero during braking.

  Referring back to FIG. 2, when the outer ring and inner ring target transmission torques Tro and Tri are calculated as described above, the four wheels are set so that the target transmission torque is transmitted to the left and right rear wheels 12a and 12b. The drive control unit 30 sends a control signal to the rotational driving force distribution device 10 to control its operation (step S3). As a result, the distribution control of the torque transmitted to the front wheels 7a and 7b and the torque transmitted to the rear wheels 12a and 12b and the torque distribution control transmitted to the left and right rear wheels 12a and 12b during turning are performed. As can be seen from this control content, the rotational driving force distribution device 10 is composed of, for example, left and right clutches provided at portions connected to the left and right rear axle shafts 11a and 11b, and controls the engagement of these left and right clutches. The front and rear wheel torque distribution and the left and right rear wheel torque distribution control are performed.

  On the other hand, when a functional defect failure for performing the four-wheel drive control is detected in step S2, the process proceeds to step S10, and the 4WD fail action control shown in FIG. 5 is performed. The functional defect failure referred to here is a failure in which the functions required for performing the above-described front and rear wheel torque distribution and left and right rear wheel torque distribution control are lost. For example, a function of a lateral acceleration (lateral G) sensor Failure. Further, a failure of a sensor for detecting a parameter value necessary for calculating an estimated driving torque such as the engine rotation sensor 2b, a failure of a sensor shared by network communication in the four-wheel drive control unit 30, the traveling stability control unit 40, etc. A failure of the rotational driving force distribution device 10 can also be mentioned.

  In this 4WD fail action control, it is determined whether or not the rear target transmission torque Tr (the sum of the outer ring and inner ring target transmission torques Tro and Tri) calculated as described above is equal to or greater than a specified value (step S11). . When a functional defect failure is detected, the four-wheel drive state is switched to the two-wheel drive state, as will be described later, so that the drive torque transmitted to the rear wheels becomes zero, and the front wheel drive torque increases accordingly, and the front wheels and The rear wheel drive torque changes abruptly and the driving stability change or the driving behavior change of the vehicle increases. Since this change increases as the rear target transmission torque TTr increases, as shown below, when the rear target transmission torque TTr is equal to or greater than a specified value, control is performed to reduce these changes by reducing the engine throttle opening. When the rear target transmission torque TTr is less than the specified value, the running stability change and the running behavior change are at a level that can be tolerated as it is, so that the process proceeds to step S14 and the engine throttle opening correction control is not performed.

  When it is determined in step S11 that the rear target transmission torque TTr is equal to or greater than the specified value, the process proceeds to step S12, and it is determined whether or not the transmission torque to the front wheels 7a and 7b, that is, the front transmission torque TTf is equal to or greater than the specified value. This is to judge the same purpose as described above. When the front transmission torque TTf is less than the specified value, the change in running stability and the change in running behavior are acceptable levels, so the process proceeds to step S14 and the engine throttle opening Correction control is not performed. On the other hand, when the front transmission torque TTf is equal to or greater than the specified value, the process proceeds to step S13, and a required value for reducing the engine throttle opening θTH is calculated.

  When the 4WD fail action control (step S10) is performed as described above, the process proceeds to step S4 in FIG. 2 and the requested throttle opening degree control signal calculated in step S13 is transmitted to the engine control device 20. Furthermore, it progresses to step S5, the operation | movement of the rotational driving force distribution apparatus 10 is controlled, and it is made to transfer from a four-wheel drive state to a two-wheel drive state, without performing driving force transmission to the rear wheels 12a and 12b. In this way, the requested throttle opening control signal sent in step S4 reduces the throttle opening to the requested throttle opening at the time point to when the four-wheel drive state shifts to the two-wheel drive state as shown in FIG. This is a signal for performing a control for gradually returning to the original throttle opening (throttle opening corresponding to the operation of the accelerator pedal) after holding this for a predetermined time (until time t1).

  When the required throttle opening control signal is sent to the engine control device 20 in this way, the engine control device 20 controls the operation of the throttle actuator 2a so as to set the throttle opening as shown in FIG. As described above, since the throttle control signal is also sent from the running stability control unit 40 to the engine control device 20, the engine control device 20 receives two different control signals. The control in this case will be described with reference to FIG.

  As shown in FIG. 7, the requested throttle opening control signal (referred to as a first throttle control signal) is sent from the four-wheel drive control unit 30 to the engine control unit 20, and the traveling stability control unit 40 When a requested throttle opening control signal (referred to as a second throttle control signal) is sent, the smaller one of the first and second throttle control signals is selected in the engine control unit 20. Then, the operation control of the throttle actuator 2a is performed based on the throttle control signal thus selected. As a result, the engine throttle opening degree reduction control for the traveling stability control by the traveling stability control unit 40 and the engine throttle opening degree control for the traveling stability control by the traveling stability control unit 40 are both performed. These can be performed together, and these are safe side controls, and do not impair running stability.

  Next, another control mode according to the present invention will be described with reference to FIG. As described above, the engine control unit 20, the four-wheel drive control unit 30, and the traveling stability control unit 40 are connected via a communication line to form a network, and various detection signals used for control are shared. It has become. For this reason, when the communication line forming the network is abnormal, it is required to have its own fail-safe control. In the four-wheel drive control unit 30, the four-wheel drive control is stopped when such an abnormality occurs, particularly when the communication between the engine control unit 20 and the four-wheel drive control unit 30 is abnormal. The control will be described below with reference to FIG.

  First, a communication abnormality detector 50 that detects such a communication abnormality is provided on the network. For example, when the communication abnormality detector 50 detects a communication abnormality between the engine control unit 20 and the four-wheel drive control unit 30, for example. An abnormality detection signal is sent to the engine control unit 20 and the four-wheel drive control unit 30. Further, it is usually sent to the traveling stability control unit 40 in many cases.

  When this abnormality detection signal is received, the four-wheel drive control unit 30 controls the operation of the rotational driving force distribution device 10 so that the driving force is not transmitted to the rear wheels 12a and 12b, and the two-wheel drive control unit 30 starts from the four-wheel drive state. Transition to the driving state. At this time, the control for lowering the engine throttle opening degree is required as in the case of stopping the four-wheel drive control described above, but communication abnormality between the engine control unit 20 and the four-wheel drive control unit 30 occurs. A throttle opening control signal (first throttle opening signal) cannot be sent from the four-wheel drive control unit 30 to the engine control unit 20.

  Therefore, condition information necessary for 4WD fail action control (control in step S10 shown in FIGS. 2 and 5) in the four-wheel drive control unit 30 is sent to the engine control unit 20 via the communication line. The memory of the control unit 20 is always updated and stored. When a communication abnormality occurs as described above and an abnormality detection signal is received from the communication abnormality detector 50, the four-wheel drive control unit 30 shifts from the four-wheel drive state to the two-wheel drive state, while the engine control The unit 20 reads the latest condition information updated and stored in the memory (that is, the condition information at the time (immediately before) when the communication abnormality occurs), and 4WD fail action control (FIGS. 2 and 5) based on this condition information Step S10 shown in FIG.

  Thereby, the first throttle opening signal as shown in FIG. 6 is obtained, and the operation of the throttle actuator 2a is controlled based on the first throttle opening signal. As a result, even when communication abnormality occurs between the engine control unit 20 and the four-wheel drive control unit 30, the engine throttle opening is reduced and control is performed to switch from the four-wheel drive state to the two-wheel drive state.

  When the engine throttle opening is reduced in this way, if the requested throttle opening control signal (this is referred to as the second throttle control signal) is also sent from the traveling stability control unit 40, For the same reason, the smaller one of the first and second throttle control signals is selected in the engine control unit 20, and the operation control of the throttle actuator 2a is performed based on the throttle control signal thus selected. .

1 is a schematic diagram showing a travel control device according to the present invention and a power transmission system of a four-wheel drive vehicle equipped with the same. It is a flowchart which shows the 4WD control content by the four-wheel drive control unit which comprises the said traveling control apparatus. It is a block diagram which shows the calculation method of the rear target transmission torque in the said 4WD control. It is a block diagram which shows the calculation method of the rear target transmission torque in the said 4WD control. It is a flowchart which shows the 4WD fail action control content in the said 4WD control. It is a graph which shows the engine throttle opening control content calculated | required by the said 4WD fail action control. It is a block diagram which shows the control content when an engine control unit receives a different throttle opening degree control signal from a four-wheel drive control unit and a traveling stability control unit. It is a block diagram which shows the control content of an engine control unit and a four-wheel drive control unit when a communication abnormality with an engine control unit and a four-wheel drive control unit is detected.

Explanation of symbols

2 Engine 2a Throttle actuator 3 Transmission 7a, 7b Front wheel 8 Propeller shaft 9 Rear axle device 10 Rotational driving force distribution device 12a, 12b Rear wheel 15 Accelerator sensor 20 Engine control unit 30 Four-wheel drive control unit 40 Driving stability control unit 50 Communication abnormality Detector

Claims (2)

In a four-wheel drive vehicle that travels by transmitting rotational output from the engine to the front and rear wheels,
A throttle control device for controlling the throttle opening of the engine;
A rotational driving force distribution device that distributes and transmits the rotational driving force from the engine to the front wheels and the rear wheels;
A four-wheel drive control device that performs four-wheel drive traveling control by performing operation control of the rotational driving force distribution device;
A travel stability control device that performs vehicle travel control including operation control of the throttle control device and performs control to maintain vehicle travel stability;
The four-wheel drive control device has a failure detection means for detecting a failure related to the four-wheel drive travel control. When the failure detection means detects a failure, the four-wheel drive control is stopped and the two-wheel drive control is performed. There line control of reducing the throttle opening by sending a first throttle control signal for reducing the throttle opening to the throttle control device as well as moves to,
The throttle control device, when the second throttle control signal sent to the throttle opening control from the first throttle control signal and the running stability control device from said four-wheel drive control device is inputted simultaneously is of the pre-Symbol first and second throttle control signal, it has rows throttle opening control based on the control signal towards the throttle opening is small,
When the failure detection means detects a failure and stops the four-wheel drive control by the four-wheel drive control device and shifts to the two-wheel drive control, a target transmission torque distributed by the rotational drive force distribution device is defined. When the value is equal to or greater than the value, the first throttle control signal is sent to the throttle control device and the four-wheel drive control is stopped to shift to the two-wheel drive control. When the target transmission torque is less than the specified value, the first A travel control device that stops four-wheel drive control without sending a throttle control signal and shifts to two-wheel drive control . A communication abnormality detector for detecting an abnormality in a communication line between the four-wheel drive control device and the throttle control device;
Condition information to determine whether to perform control for reducing the throttle opening by the previous SL throttle control device when said failure detecting means detects failure, the from the four-wheel drive control device via the communication line It is constantly sent to the throttle control device and updated and stored in the throttle control device,
When the communication line abnormality is detected by the communication abnormality detector, the four-wheel drive control device stops four- wheel drive control and shifts to two-wheel drive control, and the throttle control device is updated and stored. The travel control device according to claim 1, wherein the travel control device is configured to perform control to reduce the throttle opening based on the condition information at the time of abnormality detection.

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