Vehicle control device

Abstract

To provide a controller of a vehicle in which a driving force distribution between a front wheel and a rear wheel is controlled by output torque of a motor to be capable of appropriately stabilizing a behavior of the vehicle.SOLUTION: A controller of a vehicle includes a transfer which controls motor torque outputted from a motor to be capable of changing a distribution ratio between torque of a front wheel and torque of a rear wheel. When detecting or predicting, while performing the drive force distribution control controlling motor torque so that the distribution ratio of drive torque becomes a target distribution ratio, an understeer or an oversteer larger than reference value on the basis of a behavior of the vehicle and a travel state at the time of turning travel of the vehicle, the controller of the vehicle temporarily increases the motor torque to go out of the normal drive force distribution control (step S5).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control device for a four-wheel drive vehicle capable of generating driving force from both the front wheels and the rear wheels. [Background technology]

[0002] Patent Document 1 describes an invention related to a four-wheel drive vehicle. The four-wheel drive vehicle described in Patent Document 1 is a hybrid vehicle equipped with an engine and a motor as driving power sources, and is equipped with a hybrid drive system for four-wheel drive. In addition to the engine and motor, the hybrid drive system includes a transmission, a rear drivetrain, a front drivetrain, and an electric transfer. The electric transfer includes a housing attached to the transmission, a first input shaft, a second input shaft, a planetary gear set, a rear output shaft, and a front output shaft. The first input shaft transmits engine output torque via the transmission. The second input shaft transmits torque to the front output shaft via a chain transmission mechanism. The planetary gear set includes a sun gear, a ring gear, multiple planetary gears, and a carrier. The sun gear is selectively connected to the rotor of the motor by a motor clutch. The ring gear is connected to the first input shaft. The carrier is connected to the front output shaft via the second input shaft and the chain transmission mechanism. The rear output shaft is connected to a rear propeller shaft. The rear output shaft is selectively connected to the first input shaft and the ring gear by a first mode clutch, and the front output shaft is connected to the front propeller shaft, and the rotation of the front output shaft is selectively limited by a second mode clutch.

[0003] Patent Document 2 describes a driving force distribution device for a four-wheel drive vehicle that can change the distribution ratio of driving force to the front and rear wheels by adjusting the transmission torque (clutch engagement force) of a limited slip differential clutch. In the driving force distribution device for a four-wheel drive vehicle described in Patent Document 2, the clutch engagement force is calculated based on the difference in rotation speed between the front and rear wheels. The clutch engagement force is corrected by multiplying it by a correction coefficient calculated based on the difference between the target yaw rate and the actual yaw rate. When oversteer or understeer occurs during cornering, the driving force distribution device for a four-wheel drive vehicle described in Patent Document 2 can correct the vehicle's behavior so that the target yaw rate is achieved regardless of whether oversteer or understeer occurs. As a result, stable cornering performance can be achieved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Application Publication No. 2012 / 0077633 [Patent Document 2] Japanese Patent Application Publication No. 05-278490 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, the four-wheel drive vehicle described in Patent Document 1 is equipped with an electric transfer and can control the drive force distribution between the front and rear wheels (the drive torque distribution ratio between the front output shaft and the rear output shaft) using the motor's output torque. For example, by changing the drive force distribution using the motor's output torque while the vehicle is turning, understeer or oversteer can be suppressed and the vehicle's behavior can be stabilized. Generally, when a vehicle has a large drive force distribution to the front wheels, understeer is more likely to occur during a turn. Conversely, when a vehicle has a large drive force distribution to the rear wheels, oversteer is more likely to occur during a turn. Furthermore, at the beginning of a turn, the rotation speeds of the front and rear wheels are determined naturally or passively. Therefore, there is no significant difference in rotation speed between the front and rear wheels, and the vehicle's behavior is stable. A vehicle usually has a tendency to understeer even when it is in a stable state with no difference in rotation speed between the front and rear wheels. In contrast, in a vehicle equipped with a transfer case capable of controlling the distribution of driving force as described above, if the difference in rotation speed between the front and rear wheels becomes large and excessive understeer or oversteer occurs, the drive force distribution of the transfer case can be controlled with the output torque of the motor to converge the difference in rotation speed between the front and rear wheels, thereby suppressing excessive understeer or oversteer and stabilizing the behavior of the vehicle.

[0006] However, for example, if the engine output torque is small and the motor is already outputting a large torque, the motor output torque may be insufficient for the drive force distribution control of the transfer case. In such a case, convergence of the rotation speed difference between the front and rear wheels is delayed. As a result, excessive understeer or oversteer may not be suppressed. Alternatively, a large rotation speed difference between the front and rear wheels may persist for a long period of time, causing erratic vehicle behavior.

[0007] This invention was devised with an eye on the above-mentioned technical problems, and aims to provide a vehicle control device that can control the torque distribution ratio distributed to the front and rear wheels by the transfer case, thereby appropriately stabilizing the vehicle's behavior. [Means for solving the problem]

[0013] To achieve the above objectives, The present invention provides a control device for a vehicle that is capable of generating driving force at both the front and rear wheels and that includes a main driving force source that outputs driving torque, a motor that outputs motor torque different from the driving torque, and a transfer that distributes the driving torque to front wheels and rear wheels and is capable of changing the distribution ratio of the torque distributed to the front wheels and the torque distributed to the rear wheels, wherein the transfer has a differential mechanism in which three rotating elements, namely a first rotating element, a second rotating element, and a third rotating element, rotate differentially relative to one another, a front output shaft that transmits torque to the front wheels, and a rear output shaft that transmits torque to the rear wheels, and the first rotating element is The driving force distribution control system may further include a controller that controls the motor, the second rotating element being connected to the front output shaft so as to be able to transmit torque, and the third rotating element being connected to the main driving force source and the rear output shaft so as to be able to transmit torque, the controller executing driving force distribution control that controls the motor torque so that the distribution ratio becomes a predetermined target distribution ratio, and, when a rotation speed difference between the front output shaft and the rear output shaft is larger than a predetermined reference value, departing from the driving force distribution control and executing rotation speed difference suppression control that temporarily increases the motor torque.

[0014] Furthermore, the rotation speed difference suppression control in the present invention may be control that, when the rotation speed of the front output shaft is higher than the rotation speed of the rear output shaft, increases the motor torque in a direction in which the rotation speed of the rear output shaft becomes equal to or greater than the rotation speed of the front output shaft (i.e., in a direction in which understeer is suppressed or in a direction in which understeer occurs), and, when the rotation speed of the rear output shaft is higher than the rotation speed of the front output shaft, increases the motor torque in a direction in which the rotation speed of the front output shaft becomes equal to or greater than the rotation speed of the rear output shaft (i.e., in a direction in which oversteer is suppressed or in a direction in which understeer occurs).

[0015] The controller in the present invention may be configured to change the reference value based on the behavior and driving conditions of the vehicle, and to reduce the reference value (i.e., to make it easier to execute the rotation speed difference suppression control) when it is determined that the behavior or driving conditions are such that the rotation speed difference will increase. For example, the controller may reduce the reference value as the coefficient of friction of the road surface on which the vehicle is driving decreases. Alternatively, the controller may reduce the reference value when the vehicle is driving on a rough road with large bumps.

[0016] The differential mechanism in the present invention may be a planetary gear mechanism having a sun gear as the first rotating element, a carrier as the second rotating element, and a ring gear as the third rotating element. Reporter driver The power source and the planetary gear mechanism may be arranged on the same rotational axis. The front output shaft in the present invention may be arranged on a rotational axis different from that of the rear output shaft. [Effects of the Invention]

[0017] The vehicle that is the subject of control in this invention is a four-wheel drive vehicle in which drive torque is distributed to the front and rear wheels by a transfer differential mechanism. A motor is connected to the transfer differential mechanism, and by controlling the motor's output torque (motor torque), it is possible to change the distribution ratio of the torque distributed to the front wheels and the torque distributed to the rear wheels. The vehicle control device of this invention controls the motor torque as described above to perform drive force distribution control, which controls the distribution ratio of the drive torque distributed to the front and rear wheels according to a predetermined target distribution ratio.

[0018] Furthermore, the vehicle control device of the present invention executes cornering stability control to suppress excessive understeer or oversteer during cornering. In the cornering stability control, when understeer or oversteer greater than a reference value occurs or when the occurrence of such large understeer or oversteer is predicted, the motor torque is temporarily or instantaneously increased. The motor torque in this case deviates from the basic driving force distribution control and can exceed the torque output according to the driving force distribution control under normal circumstances. Therefore, when large understeer or oversteer occurs during cornering of the vehicle, a large motor torque can be instantaneously output to quickly suppress the excessive understeer or oversteer. Alternatively, when large understeer or oversteer is predicted during cornering of the vehicle, a large motor torque can be instantaneously output to prevent the occurrence of excessive understeer or oversteer.

[0019] On the other hand, the vehicle control device of the present invention executes rotation speed difference suppression control when the rotation speed difference between the front output shaft and the rear output shaft exceeds a reference value, i.e., when the rotation speed difference between the front and rear wheels is large. In the rotation speed difference suppression control, motor torque is temporarily or instantaneously increased when a large rotation speed difference between the front and rear wheels that exceeds the reference value occurs or when such a large rotation speed difference is predicted to occur. The motor torque in this case deviates from the basic driving force distribution control and can exceed the torque output under normal driving force distribution control. Therefore, when the rotation speed difference between the front and rear wheels becomes excessive and there is a possibility that the vehicle behavior will become unstable, a large motor torque can be output instantaneously to quickly suppress such an excessive rotation speed difference. Alternatively, when it is predicted that the rotation speed difference between the front and rear wheels will become excessive, a large motor torque can be output instantaneously to prevent such an excessive rotation speed difference from occurring.

[0020] Therefore, the vehicle control device of the present invention can appropriately stabilize the behavior of the vehicle by controlling the torque distribution ratio between the front and rear wheels using the motor torque of the motor connected to the transfer case. [Brief explanation of the drawings]

[0021] [Figure 1] Fig. 1 is a diagram for explaining a vehicle that is the subject of control in this invention. Fig. 1(a) is a schematic diagram showing the overall configuration of the vehicle. Fig. 1(b) is a skeleton diagram showing the detailed configuration of a transfer case mounted on the vehicle. [Figure 2] FIG. 2 is a flowchart for explaining an example of the "turning stability control" executed by the vehicle control device of the present invention. [Figure 3] FIG. 3 is a nomographic diagram illustrating changes in the rotation speed of each rotating element in the planetary gear mechanism and the direction of motor torque when the control shown in the flowchart of FIG. 2 is executed to suppress excessive understeer during cornering. [Figure 4] FIG. 4 is a nomographic diagram illustrating changes in the rotation speed of each rotating element in the planetary gear mechanism and the direction of motor torque when the control shown in the flowchart of FIG. 2 is executed to suppress excessive oversteer during cornering. [Figure 5] FIG. 5 is a flowchart for explaining an example of the "rotation speed difference suppression control" executed by the vehicle control device of the present invention. [Figure 6] FIG. 6 is a nomographic diagram illustrating the change in rotation speed of each rotating element in the planetary gear mechanism and the direction of motor torque when the control shown in the flowchart of FIG. 5 is executed to suppress an excessive difference in rotation speed between the front and rear wheels (rear wheel rotation speed > front wheel rotation speed). [Figure 7] FIG. 7 is a nomographic diagram illustrating the change in rotation speed of each rotating element in the planetary gear mechanism and the direction of motor torque when the control shown in the flowchart of FIG. 5 is executed to suppress an excessive difference in rotation speed between the front wheels and the rear wheels (front wheel rotation speed > rear wheel rotation speed). DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are merely examples of specific embodiments of the present invention and are not intended to limit the scope of the present invention.

[0023] The vehicle to be controlled in this embodiment of the present invention is a four-wheel drive vehicle in which drive torque output from a main drive power source is distributed to the front and rear wheels, generating drive force at both the front and rear wheels. The vehicle is equipped with a transfer for distributing drive torque to the front and rear wheels. The transfer includes a differential mechanism in which three rotating elements rotate differentially relative to one another, and a motor connected to one of the rotating elements of the differential mechanism. The transfer can change the torque distribution ratio between the front and rear wheels by controlling the motor's output torque (motor torque). The vehicle also includes at least an engine (internal combustion engine) or a motor as its main drive power source. Since the motor constituting the transfer can also serve as a drive power source, if the vehicle is equipped with an engine as its main drive power source, it becomes a hybrid vehicle using both the engine and the motor as drive power sources. Alternatively, if another motor is equipped as its main drive power source, it becomes an electric vehicle using multiple motors as drive power sources. Figure 1 shows an example of a vehicle Ve to be controlled in this embodiment of the present invention.

[0024] 1(a), a vehicle Ve is equipped with an engine (ENG) 1 as a main driving force source. The vehicle Ve is a four-wheel drive vehicle that generates driving force by transmitting driving torque output by the engine 1 to front wheels 2 and rear wheels 3, and is equipped with an automatic transmission (AT) 4 and a transfer case (TF) 5 that transmit the driving torque. The vehicle Ve is also equipped with a detection unit 6 and a controller 7.

[0025] The engine 1 is an internal combustion engine, such as a gasoline engine or a diesel engine, that obtains power by burning fuel. The engine 1 is electrically controlled in terms of output adjustment and operating states, such as starting and stopping. Note that the main driving power source of the vehicle Ve that is the subject of control in the embodiment of the present invention is not limited to the engine 1. The main driving power source of the vehicle Ve may be, for example, a "motor" that outputs driving torque. Alternatively, the main driving power source of the vehicle Ve may be a "hybrid drive unit" equipped with an "engine" and a "motor."

[0026] The automatic transmission 4 is connected to an output shaft (not shown) of the engine 1 via, for example, a torque converter (not shown). The automatic transmission 4 changes the rotation speed of the engine 1 and transmits the driving torque output by the engine 1 to a transfer case 5.

[0027] The transfer 5 distributes drive torque to the front wheels 2 and the rear wheels 3. Furthermore, the transfer 5 is configured to be able to change the distribution ratio between the torque distributed to the front wheels 2 and the torque distributed to the rear wheels 3. Specifically, as shown in FIG. 1(b), the transfer 5 has a "differential mechanism," a front output shaft 8, a rear output shaft 9, and a motor (MG) 10.

[0028] A "differential mechanism" is a power transmission device in which three rotating elements, a "first rotating element," a "second rotating element," and a "third rotating element," rotate differentially relative to one another. In the example shown in FIG. 1(b), a single-pinion planetary gear mechanism 11 is used as the "differential mechanism."

[0029] The planetary gear mechanism 11 has a sun gear 11a as a "first rotating element," a carrier 11b as a "second rotating element," and a ring gear 11c as a "third rotating element." The sun gear 11a is connected to a rotating shaft 10a of a motor 10 (described later) so as to be able to transmit torque. The carrier 11b is connected to a front output shaft 8 (described later) so as to be able to transmit torque. The ring gear 11c is connected to an output shaft of the engine 1 and a rear output shaft 9 (described later) so as to be able to transmit torque.

[0030] The front output shaft 8 is a rotating shaft that transmits torque to the front wheels 2. One end (left side in FIG. 1) of the front output shaft 8 is connected to a front drive shaft 12. The front drive shaft 12 is connected to the front wheels 2 via a differential gear 13, a drive shaft 14, and the like. The other end (right side in FIG. 1) of the front output shaft 8 is connected to a carrier 11b of a planetary gear mechanism 11 via, for example, a chain transmission mechanism 15. The front output shaft 8 is disposed on a rotation axis ALf that is different from that of a rear output shaft 9, which will be described later.

[0031] The rear output shaft 9 is a rotating shaft that transmits torque to the rear wheels 3. One end (the right side in FIG. 1) of the rear output shaft 9 is connected to a rear drive shaft 16. The rear drive shaft 16 is connected to the rear wheels 3 via a differential gear 17, a drive shaft 18, and the like. The other end (the left side in FIG. 1) of the rear output shaft 9 is connected to a ring gear 11c of the planetary gear mechanism 11 and the output shaft of the engine 1. The rear output shaft 9 is disposed on the same rotation axis ALr as the engine 1 and the planetary gear mechanism 11.

[0032] The motor 10 is disposed on the same rotational axis ALr as the engine 1 and the planetary gear mechanism 11. The motor 10 outputs a motor torque different from the drive torque output by the engine 1. The rotating shaft 10a of the motor 10 is connected to the sun gear 11a of the planetary gear mechanism 11. The motor 10 functions as an electric motor that is driven by a supply of electric power to output torque. The motor 10 also functions as a generator that generates electric power by receiving torque from an external source. In other words, the motor 10 is a motor-generator with a power generating function, and may be, for example, a permanent magnet synchronous motor or an induction motor. As shown in FIG. 1(b), the motor 10 is disposed inside the housing (not shown) of the transfer 5 together with the planetary gear mechanism 11, the front output shaft 8, and the rear output shaft 9. Alternatively, the motor 10 may be disposed outside the housing of the transfer 5, separate from the planetary gear mechanism 11, the front output shaft 8, and the rear output shaft 9.

[0033] The transfer 5 configured as described above divides or distributes the drive torque of the engine 1 transmitted to the ring gear 11c of the planetary gear mechanism 11 and transmits it to the front output shaft 8 and the rear output shaft 9. Therefore, the transfer 5 serves as a kind of "power split device." Furthermore, the transfer 5 can change the differential state of each rotating element in the planetary gear mechanism 11 by controlling the motor torque of the motor 10 transmitted to the sun gear 11a of the planetary gear mechanism 11. Therefore, the transfer 5 can control the distribution ratio between the torque distributed to the front output shaft 8 and the torque distributed to the rear output shaft 9 by controlling the motor torque. In a positive manner In the vehicle control device, the state in which the torque distribution ratio between the front output shaft 8 and the rear output shaft 9 is controlled by the motor torque as described above will be referred to as the "power split mode."

[0034] The detection unit 6 detects various data used to control the vehicle Ve. The detection unit 6 includes various sensors and devices, such as a wheel speed sensor 6a that detects the rotation speed of each of the front wheels 2 and the rear wheels 3, a rotation speed sensor 6b that detects the rotation speed of the motor 10 and the rotation speed of the front output shaft 8 and the rear output shaft 9, a steering angle sensor 6c that detects the steering angle of the vehicle Ve, an acceleration sensor 6d that detects the acceleration of the vehicle Ve, a yaw rate sensor 6e that detects the yaw rate of the vehicle Ve, and a driving mode select switch 6f that detects the driving mode of the vehicle Ve. The detection unit 6 is electrically connected to a controller 7 (described later) and outputs electrical signals corresponding to the detected or calculated values ​​of the above-mentioned various sensors, devices, and apparatuses to the controller 7 as detection data.

[0035] The controller 7 is an electronic control device mainly composed of, for example, a microcomputer. In the vehicle control device according to the embodiment of the present invention, the controller 7 controls, in particular, the driving force distribution ratio of the transfer case 5. Specifically, the controller 7 controls the motor torque of the motor 10 connected to the transfer case 5. The controller 7 receives various data detected or calculated by the detection unit 6. The controller 7 performs calculations using the input data, pre-stored data, calculation formulas, and the like. The controller 7 then outputs the calculation results as a control command signal to control the motor torque as described above. Note that while FIG. 1 shows an example in which one controller 7 is provided, multiple controllers 7 may be provided, one for each device or equipment to be controlled, or for each control content.

[0036] It should be noted that the configuration (gear train) of the vehicle Ve in the embodiment of the present invention is not limited to the example shown in FIG. 1 above. For example, the configuration of a "hybrid vehicle" as disclosed in the aforementioned Patent Document 1, or a configuration in which the above-described transfer 5 is applied to the "vehicle" disclosed in the aforementioned Patent Document 2, can also be the subject of control in the embodiment of the present invention. Furthermore, the "differential mechanism" constituting the transfer 5 may be, in addition to the above-described single-pinion planetary gear mechanism 11, a "double-pinion planetary gear mechanism" or "other types of planetary gear mechanisms," for example.

[0037] The vehicle control device according to the embodiment of the present invention executes driving force distribution control in the power split mode. The driving force distribution control controls the motor torque so that the torque distribution ratio distributed to the front output shaft 8 and the rear output shaft 9 by the planetary gear mechanism 11 of the transfer case 5 is set to a predetermined target distribution ratio. The target distribution ratio is set as appropriate depending on the driving state of the vehicle Ve, the driver's operation, and the like.

[0038] Furthermore, in the power split mode, the vehicle control device according to the embodiment of the present invention not only executes the driving force distribution control as described above, but also executes cornering stability control if the vehicle Ve experiences understeer or oversteer greater than a reference value when cornering. The cornering stability control temporarily deviates from the driving force distribution control and instantaneously causes the motor 10 to output a large motor torque in order to suppress the excessive understeer or oversteer described above.

[0039] In another example, the vehicle control device according to the embodiment of the present invention executes the driving force distribution control as described above in the power split mode, and also executes rotation speed difference suppression control when the rotation speed difference between the front wheels 2 and the rear wheels 3, i.e., the rotation speed difference between the front output shaft 8 and the rear output shaft 9, is greater than a reference value. The rotation speed difference suppression control is a control that temporarily deviates from the driving force distribution control and instantaneously outputs a large motor torque to the motor 10 in order to suppress the excessive rotation speed difference as described above, thereby reducing the excessive rotation speed difference.

[0040] Specifically, the vehicle control device in this embodiment of the present invention executes the control shown in the following flowchart. The flowchart in Figure 2 shows an example in which driving force distribution control is executed and cornering stability control is executed in the power split mode.

[0041] In the flowchart of Fig. 2, first, in step S1, it is determined whether the driving mode of the vehicle Ve is the power split mode. The power split mode is set, for example, by the driver operating a driving mode selector switch (not shown). Alternatively, the power split mode is set as the default, and the setting is canceled by the driver operating the selector switch. Alternatively, the power split mode is set automatically depending on the driving state of the vehicle Ve.

[0042] If the driving mode of the vehicle Ve is not the power split mode and therefore the answer to step S1 is "No," the routine shown in the flowchart of FIG. 2 is temporarily terminated without executing any further control.

[0043] On the other hand, if the driving mode of the vehicle Ve is the power split mode and therefore the answer in step S1 is "Yes," the process proceeds to step S2.

[0044] In step S2, it is determined whether the vehicle Ve has started turning. Whether the vehicle Ve is turning can be determined, as in the conventional case, based on, for example, the detection value of the steering angle sensor 6c, the operating state of the steering device (not shown), etc.

[0045] If the vehicle Ve has not yet started turning and therefore the answer to step S2 is "No," the process proceeds to step S3.

[0046] In step S3, driving force distribution control is executed. As described above, in driving force distribution control, the motor torque of the motor 10 is controlled based on a predetermined target distribution ratio. Once driving force distribution control is executed in step S3, the routine shown in the flowchart of FIG. 2 is temporarily terminated.

[0047] On the other hand, if the vehicle Ve has started turning and the answer to step S3 is "Yes," the process proceeds to step S4.

[0048] In step S4, it is determined whether or not the turning stability control should be started. That is, it is determined whether or not the conditions for starting the turning stability control are met. The turning stability control is executed when the vehicle Ve experiences understeer or oversteer greater than a predetermined standard when turning. Alternatively, the turning stability control is executed when the vehicle Ve predicts that understeer or oversteer greater than a predetermined standard will occur when turning.

[0049] Understeer or oversteer of the vehicle Ve can be determined based on the steering angle and the detected values ​​of the acceleration sensor 6d and the yaw rate sensor 6e. For example, if the center-of-gravity slip angle of the vehicle Ve calculated from the detected values ​​of the acceleration sensor 6d and the yaw rate sensor 6e is small relative to the steering angle, it can be determined that understeer is occurring. Conversely, if the center-of-gravity slip angle is large relative to the steering angle, it can be determined that oversteer is occurring. Also, if the rotation speed of the front output shaft 8 is greater than the rotation speed of the rear output shaft 9, it can be determined that understeer is occurring. Conversely, if the rotation speed of the rear output shaft 9 is greater than the rotation speed of the front output shaft 8, it can be determined that oversteer is occurring. Alternatively, the occurrence of understeer or oversteer can be predicted based on the behavior and driving conditions of the vehicle Ve. For example, the occurrence of understeer can be predicted when the vehicle speed is higher than a predetermined reference vehicle speed. Also, the occurrence of understeer can be predicted when the steering angle is greater than a predetermined reference steering angle. In addition, the occurrence of understeer can be predicted when the friction coefficient of the road surface on which the vehicle Ve is traveling is lower than a predetermined reference friction coefficient. Also, the occurrence of understeer can be predicted when the vehicle Ve is traveling on a rough road with large bumps, sand, mud, snow, etc. Furthermore, the occurrence of understeer can be predicted when the cant (or bank angle) of the road surface on which the vehicle Ve is traveling is a reverse cant (reverse bank angle) with respect to the turning direction.

[0050] If the condition for starting the cornering stability control is not met and the answer is "No" in step S4, the process proceeds to step S3. In this case, although the vehicle Ve is cornering, it is determined that excessive understeer or oversteer that would disrupt the behavior of the vehicle Ve will not occur, so cornering stability control is not executed and normal driving force distribution control is executed.

[0051] On the other hand, if the condition for starting the turning stability control is met and the answer is "Yes" in step S4, the process proceeds to step S5.

[0052] In step S5, cornering stability control is executed. The cornering stability control may be called understeer suppression control or oversteer suppression control, and is control for suppressing excessive understeer or oversteer that has occurred or is predicted to occur during cornering.

[0053] As described above, the cornering stability control is initiated when the vehicle Ve experiences actual understeer or oversteer greater than the reference value when cornering. Alternatively, the cornering stability control is initiated when the vehicle Ve predicts that understeer or oversteer greater than the reference value will occur based on the vehicle Ve's behavior and driving conditions. In addition, if the vehicle Ve is provided with a selector switch or the like for manually selecting a driving mode suited to the road conditions on which the vehicle Ve is traveling, the cornering stability control can be initiated when a driving mode suited to rough roads, snowy roads, or the like is selected. Therefore, the cornering stability control is executed when the control start condition is satisfied immediately after the vehicle Ve begins cornering. Note that, for example, if a driving mode suited to sporty driving intended for driving on a circuit (such as a sports mode or a circuit mode) is selected, the cornering stability control may be executed whenever the vehicle Ve is cornering.

[0054] During cornering stability control, the normal driving force distribution control is temporarily deviated from, and a large motor torque is momentarily output from the motor 10. The motor torque is usually output within a range equal to or less than the upper limit torque based on the rated output of the motor 10, etc. However, it is possible to output a torque exceeding the upper limit torque temporarily or momentarily. For example, for an extremely short period of time determined in advance based on the results of experiments or simulations, it is possible for the motor 10 to output a large motor torque exceeding the upper limit torque. Note that, for example, when the sport mode as described above is selected, a larger motor torque than normal (e.g., larger than normal mode) may be output. Alternatively, a large motor torque exceeding the normal driving force distribution ratio range (0:100 to 100:0) may be output. Once cornering stability control is executed in step S5, the routine shown in the flowchart of FIG. 2 is temporarily terminated.

[0055] To explain the operation of the cornering stability control as described above, FIG. 3 shows a collinear diagram (or speed diagram) of the planetary gear mechanism 11. In the collinear diagram of FIG. 3, the vertical axis marked with "S" represents the rotation speed of the sun gear 11a and the motor 10, the vertical axis marked with "C" represents the rotation speed of the carrier 11b and the front output shaft 8, and the vertical axis marked with "R" represents the rotation speed of the ring gear 11c, the engine 1, and the rear output shaft 9. In the collinear diagram of FIG. 3, the dashed line indicates a state in which excessive understeer occurs. In a state in which the vehicle Ve is understeered, the rotation speed of the front wheels 2 is higher than the rotation speed of the rear wheels 3. Therefore, in the collinear diagram of FIG. 3, the rotation speed of the carrier 11b and the front output shaft 8 is higher than the rotation speed of the ring gear 11c and the rear output shaft 9. In order to suppress such excessive understeer, cornering stability control outputs a large motor torque from motor 10 so that vehicle Ve temporarily or momentarily oversteers, as shown by the solid line in the nomographic diagram of Fig. 3. As shown by the thick black arrow in the nomographic diagram of Fig. 3, motor torque is output in a direction that reduces the rotation speed of sun gear 11a and motor 10 (approaches 0). Such cornering stability control can suppress excessive understeer during cornering and stabilize the behavior of vehicle Ve.

[0056] In addition, in the nomogram of FIG. 4, the dashed line indicates a state in which excessive oversteer occurs. When the vehicle Ve is in an oversteer state, the rotation speed of the rear wheels 3 is higher than the rotation speed of the front wheels 2. Therefore, in the nomogram of FIG. 4, the rotation speed of the ring gear 11c and the rear output shaft 9 is higher than the rotation speed of the carrier 11b and the front output shaft 8. To suppress such excessive oversteer, in the cornering stability control, as shown by the solid line in the nomogram of FIG. 4, a large motor torque is output from the motor 10 so that the vehicle Ve temporarily or momentarily understeers. As shown by the thick black arrow in the nomogram of FIG. 4, the motor torque is output in a direction that increases the rotation speed of the sun gear 11a and the motor 10 (moves away from 0). This cornering stability control can suppress excessive oversteer during cornering and stabilize the behavior of the vehicle Ve.

[0057] The flowchart in FIG. 5 shows an example in which, in the power split mode, driving force distribution control is executed and rotation speed difference suppression control is executed.

[0058] In the flowchart of Fig. 5, first, in step S11, it is determined whether the driving mode of the vehicle Ve is the power split mode. The power split mode is set, for example, by the driver operating a driving mode selector switch (not shown). Alternatively, the power split mode is set as a default, and the setting is canceled by the driver operating the selector switch. Alternatively, the power split mode is set automatically depending on the driving state of the vehicle Ve.

[0059] If the drive mode of the vehicle Ve is not the power split mode and therefore the answer to step S11 is "No," the routine shown in the flowchart of FIG. 5 is temporarily terminated without executing any further control.

[0060] On the other hand, if the driving mode of the vehicle Ve is the power split mode and therefore the determination in step S11 is "Yes," the process proceeds to step S12.

[0061] In step S12, it is determined whether or not a difference in rotation speed has occurred between the front wheels 2 and the rear wheels 3. Specifically, it is determined whether or not a difference in rotation speed has occurred between the front output shaft 8 and the rear output shaft 9. For example, the difference in rotation speed can be determined based on the detected values ​​of the wheel speed sensor 6a, the rotation speed sensor 6b, etc.

[0062] If the determination in step S12 is "No" because there is no difference in the rotational speed between the front output shaft 8 and the rear output shaft 9, the process proceeds to step S13.

[0063] In step S13, driving force distribution control is executed. As described above, in driving force distribution control, the motor torque of the motor 10 is controlled based on a predetermined target distribution ratio. Once driving force distribution control is executed in step S3, the routine shown in the flowchart of FIG. 5 is temporarily terminated.

[0064] On the other hand, if a difference in rotation speed between the front output shaft 8 and the rear output shaft 9 occurs and the answer in step S12 is "Yes," the process proceeds to step S14.

[0065] In step S14, if the difference in rotation speed between the front output shaft 8 and the rear output shaft 9 is greater than a predetermined reference value, squid The reference value in this case is a threshold value for determining whether or not there is a difference in rotation speed that may cause the behavior of the vehicle Ve to become unstable. If the difference in rotation speed between the front output shaft 8 and the rear output shaft 9 is greater than the reference value, it is determined that there is a risk of the behavior of the vehicle Ve becoming unstable. This reference value is determined in advance based on, for example, the results of experiments or simulations.

[0066] If the rotation speed difference between the front output shaft 8 and the rear output shaft 9 is equal to or less than the reference value and therefore the determination in step S14 is "No," the process proceeds to the above-mentioned step S13. In this case, although a rotation speed difference between the front output shaft 8 and the rear output shaft 9 has occurred, it can be determined that the rotation speed difference is not so large as to disturb the behavior of the vehicle Ve, so cornering stability control is not executed and normal driving force distribution control is executed.

[0067] On the other hand, if the difference in rotation speed between the front output shaft 8 and the rear output shaft 9 is greater than the reference value and therefore "Yes" is determined in step S13, the process proceeds to step S15.

[0068] In step S15, it is determined whether or not rotation speed difference suppression control should be initiated. That is, it is determined whether or not a condition for initiating rotation speed difference suppression control is established. The rotation speed difference suppression control is basically executed when the rotation speed difference between the front output shaft 8 and the rear output shaft 9 exceeds a predetermined reference value, as described above, which is used as a threshold value. In addition, the reference value used to determine whether or not to initiate rotation speed difference suppression control can be changed based on the behavior and driving conditions of the vehicle Ve. If it is determined that the behavior or driving conditions of the vehicle Ve are such that the rotation speed difference between the front output shaft 8 and the rear output shaft 9 will increase, the reference value may be reduced. Reducing the reference value, which is a threshold value, makes it easier to execute rotation speed difference suppression control. For example, the reference value is reduced as the friction coefficient of the road surface on which the vehicle Ve is traveling is lower. Alternatively, the reference value is reduced when the vehicle Ve is traveling on a rough road with large bumps, sand, mud, snow, or the like. In addition, for example, if the vehicle Ve is provided with a selector switch or the like for manually selecting a driving mode suitable for the road conditions on which the vehicle is traveling, the above-mentioned reference value may be reduced when a driving mode suitable for rough roads or snowy roads as described above is selected.

[0069] If the condition for starting rotation speed difference suppression control is not met and therefore the determination in step S15 is "No," the process proceeds to the above-mentioned step S13. In this case as well, although a rotation speed difference occurs between the front output shaft 8 and the rear output shaft 9, it can be determined that the rotation speed difference is not so large as to require rotation speed difference suppression control and to disturb the behavior of the vehicle Ve, so cornering stability control is not executed and normal driving force distribution control is executed.

[0070] On the other hand, if the condition for starting the rotation speed difference suppression control is met and therefore the determination in step S15 is "Yes," the process proceeds to step S16.

[0071] In step S16, rotation speed difference suppression control is executed. The rotation speed difference suppression control is a control for suppressing an excessive rotation speed difference between the front output shaft 8 and the rear output shaft 9 as described above. As described above, the rotation speed difference suppression control temporarily deviates from the normal driving force distribution control, and a large motor torque is output from the motor 10 instantaneously. The motor torque is usually output within a range below the upper limit torque based on the rated output of the motor 10, etc. However, it is also possible to output a torque exceeding the upper limit torque temporarily or instantaneously. For example, ,fruit It is possible for the motor 10 to output a large motor torque exceeding the upper limit torque for an extremely short period of time that is determined in advance based on the results of experiments and simulations. When the rotation speed difference suppression control is executed in step S16, the routine shown in the flowchart of FIG. 5 is temporarily ended.

[0072] To explain the operation of the rotation speed difference suppression control as described above, FIG. 6 shows a collinear diagram (or speed diagram) of the planetary gear mechanism 11. In the collinear diagram of FIG. 6, the vertical axis marked with "S" represents the rotation speeds of the sun gear 11a and the motor 10, the vertical axis marked with "C" represents the rotation speeds of the carrier 11b and the front output shaft 8, and the vertical axis marked with "R" represents the rotation speeds of the ring gear 11c, the engine 1, and the rear output shaft 9. In the collinear diagram of FIG. 6, the dashed line indicates a state in which an excessive rotation speed difference occurs, in which the rotation speed of the rear output shaft 9 is greater than the rotation speed of the front output shaft 8. In order to suppress such an excessive rotation speed difference, the rotation speed difference suppression control outputs a large motor torque from the motor 10 so that the rotation speed difference becomes zero temporarily or instantaneously, as shown by the solid line in the collinear diagram of FIG. 5. 5, motor torque is output in the direction in which the rotation speeds of the sun gear 11a and the motor 10 increase (moving away from 0). By performing this rotation speed difference suppression control, excessive rotation speed differences during driving can be suppressed, stabilizing the behavior of the vehicle Ve.

[0073] Furthermore, in the alignment chart of FIG. 7, the dashed line indicates a state in which an excessive rotation speed difference occurs, where the rotation speed of the front output shaft 8 is greater than the rotation speed of the rear output shaft 9. In order to suppress such an excessive rotation speed difference, the rotation speed difference suppression control outputs a large motor torque from the motor 10 so that the rotation speed difference becomes zero temporarily or instantaneously, as shown by the solid line in the alignment chart of FIG. 7. As shown by the thick black arrow in the alignment chart of FIG. 7, the motor torque is output in a direction in which the rotation speeds of the sun gear 11a and the motor 10 decrease (approach zero). Such rotation speed difference suppression control can suppress an excessive rotation speed difference while the vehicle Ve is traveling, stabilizing the behavior of the vehicle Ve.

[0074] Therefore, according to the vehicle control device of this embodiment of the present invention, the behavior of the vehicle Ve can be appropriately stabilized by controlling the torque distribution ratio distributed to the front wheels 2 and rear wheels 3 using the motor torque of the motor 10 connected to the transfer 5. [Explanation of symbols]

[0075] 1 Engine (main driving force source: ENG) 2 front wheels 3 rear wheels 4 Automatic transmission (AT) 5 Transfer (TF) 6. Detection unit 6a (detection part) wheel speed sensor 6b (detection part) rotation speed sensor 6c (detection part) steering angle sensor 6d Acceleration sensor (detection section) 6e Yaw rate sensor (detection section) 6f (Detector) Operation mode select switch 7 Controller (ECU) 8 Front output shaft 9 Rear output shaft 10 Motor (MG) 10a (Motor) rotating shaft 11 Planetary gear mechanism (differential mechanism) 11a Sun gear (of planetary gear mechanism) 11b (planetary gear mechanism) carrier 11c (planetary gear mechanism) ring gear 12 Front drive shaft 13 Differential gear 14 Drive shaft 15 Chain transmission mechanism 16 Rear drive shaft 17 Differential gear 18 Drive shaft Vehicle

Claims

1. A control device for a vehicle that is capable of generating driving force at both the front wheels and the rear wheels, the control device comprising: a main driving force source that outputs driving torque; a motor that outputs motor torque different from the driving torque; and a transfer that distributes the driving torque to front wheels and rear wheels and is capable of changing the distribution ratio of the torque distributed to the front wheels and the torque distributed to the rear wheels, The transfer a differential mechanism in which a first rotating element, a second rotating element, and a third rotating element rotate differentially relative to one another; a front output shaft that transmits torque to the front wheels; and a rear output shaft that transmits torque to the rear wheels, the first rotating element is coupled to the motor so as to be able to transmit torque; the second rotating element is connected to the front output shaft so as to be able to transmit torque; the third rotating element is connected to the main driving power source and the rear output shaft so as to be able to transmit torque; a controller for controlling the motor; The controller a driving force distribution control for controlling the motor torque so that the distribution ratio becomes a predetermined target distribution ratio; When the rotation speed difference between the front output shaft and the rear output shaft is larger than a reference value, the driving force distribution control is deactivated and rotation speed difference suppression control is temporarily executed to increase the motor torque. A vehicle control device characterized by:

2. The vehicle control device according to claim 1, The rotation speed difference suppression control is When the rotation speed of the front output shaft is higher than the rotation speed of the rear output shaft, the motor torque is increased in a direction such that the rotation speed of the rear output shaft becomes equal to or higher than the rotation speed of the front output shaft, and when the rotation speed of the rear output shaft is higher than the rotation speed of the front output shaft, the motor torque is increased in a direction such that the rotation speed of the front output shaft becomes equal to or higher than the rotation speed of the rear output shaft. A vehicle control device characterized by:

3. 3. The vehicle control device according to claim 1, The differential mechanism includes: a planetary gear mechanism having a sun gear as the first rotating element, a carrier as the second rotating element, and a ring gear as the third rotating element, the rear output shaft is disposed on the same rotational axis as the main driving force source and the planetary gear mechanism, The front output shaft is disposed on a rotation axis different from that of the rear output shaft. A vehicle control device characterized by:

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