Vehicle drive force transmission control device

Abstract

To stabilize behavior even in any of traveling causing a slip in a wheel and traveling not causing the slip.SOLUTION: A controller 13 includes: a traveling state determination unit 13a that determines whether or not a vehicle is in a traveling state in which differential rotation speed becomes smaller than a threshold or in a traveling state in which the differential rotation speed becomes larger than the threshold; a differential rotation speed deviation determination unit 13b that determines whether or not there is deviation between the differential rotation speed and target differential rotation speed when it is determined that the vehicle is the traveling state in which the differential rotation speed becomes smaller than the threshold; a first torque control unit 13c that controls torque of a motor based on the deviation so as to reduce the deviation; a driving force distribution ratio correction unit 13d that corrects a target driving force distribution ratio between a first output-side and a second output-side based on a correction torque value that reduces the deviation between the target differential rotation speed and the differential rotation speed when it is determined that the vehicle is the traveling state in which the differential rotation speed becomes equal to or greater than the threshold; and a second torque control unit 13e that controls the torque of the motor based on the target driving force distribution ratio corrected by the driving force distribution ratio correction unit.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a driving force transmission control device that distributes and transmits torque output from a driving force source to a plurality of wheels. [Background technology]

[0002] In a vehicle with four wheels, the ground load and the coefficient of friction between the wheels and the road surface may differ for each wheel, and the turning radius during cornering is different not only for the inner and outer wheels but also for the front and rear wheels. Furthermore, in a vehicle in which the front and rear wheels are mechanically connected, such as a four-wheel drive vehicle, it is necessary to transmit driving force to the front and rear wheels and allow their differential rotation, and further, when the front or rear wheels spin, it is necessary to limit the differential rotation of the front and rear wheels in order to avoid a situation known as torque loss.

[0003] In a vehicle capable of driving the front and rear wheels, it is preferable to allow differential rotation between the front and rear wheels as described above, limit the differential rotation depending on the situation, and control the torque share rate of each wheel depending on the road surface condition or the running condition of the vehicle. Patent Document 1 discloses an example of a mechanism configured to actively control the distribution of driving force to the front and rear wheels. To briefly explain the configuration, a distribution mechanism that distributes the torque output from the engine to the front and rear wheels is mainly configured with a planetary gear mechanism having a sun gear, a ring gear, and a carrier as rotating elements, and when distributing the driving force, the torque from the engine is input to the ring gear, and torque is output from the ring gear to the rear wheels, and torque is output from the carrier to the front wheels, and in this state, the torque of the sun gear is changed by a motor or a motor-generator (hereinafter, these will be collectively referred to as a motor) connected to the sun gear, thereby controlling the torque and rotation speed of the front and rear wheels. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-131153 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to the distribution mechanism of Patent Document 1, it is possible to control the distribution of power transmitted to the front and rear wheels by the torque output from the motor connected to the sun gear. However, Patent Document 1 does not disclose how to control the differential rotation speed between the front and rear wheels or how to control the driving force distribution for that purpose.

[0006] If the differential rotation speed between the front and rear wheels and the torque distribution rate can be appropriately controlled, it is possible to perform grip driving with the grip force secured by all four wheels, or drift driving with all four wheels or either the front or rear wheels slipping. However, if the distribution of torque (driving force) to the front and rear wheels becomes inappropriate during grip driving and the differential rotation speed between the front and rear deviates from the target differential rotation speed, the steering characteristics may become under or over, and driving stability may be impaired.

[0007] In addition, in the case of drift driving, at least one of the front and rear wheels is made to slip, and therefore the rotation speed of the slipping wheel is not uniquely determined, and therefore the differential rotation speed between the front and rear wheels cannot be uniquely determined. Therefore, for example, as in the case of grip driving, it is possible to estimate the turning radius, obtain the vehicle's running track (running path) from the estimated turning radius, and set the target differential rotation speed between the front and rear wheels based on the running path. However, if the estimated turning radius differs from the actual running path, the behavior of the vehicle will differ from the behavior intended by the driver. In addition, if the differential rotation speed between the front and rear wheels is calculated based on the rotation speed detected by the wheel speed sensors provided on the front and rear wheels, the difference between the target differential rotation speed and the actual differential rotation speed cannot be calculated accurately due to differences in detection accuracy or detection responsiveness of the rotation speed and the differential rotation speed, and therefore the front and rear driving force distribution cannot be controlled appropriately, and the behavior of the vehicle may become unstable.

[0008] This invention has been made with a focus on the above-mentioned technical problems, and aims to provide a driving force transmission control device that can improve the behavior stability of a vehicle regardless of whether it is grip driving, drift driving, or any other driving mode. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides a vehicle driving force transmission control device including a distribution mechanism that distributes torque output from a driving force source to a first output side and a second output side and causes differential rotation between the first output side and the second output side, and a motor that controls a differential rotation speed between the first output side and the second output side by the distribution mechanism, wherein the distribution mechanism is composed of a differential mechanism that performs a differential action by a first rotating element that receives torque from the driving force source and outputs torque to the first output side, a second rotating element that outputs torque to the second output side, and a third rotating element to which the motor is connected, and the control device further includes a controller that controls the motor, and the controller further includes a driving condition determination unit that determines whether the driving condition is such that the differential rotation speed is smaller or larger than a predetermined threshold value, and a control unit that determines whether the differential rotation speed is larger than a predetermined threshold value. The vehicle speed control system is characterized in that it comprises a differential rotation speed deviation determination unit that determines whether or not there is a deviation between the differential rotation speed and a predetermined target differential rotation speed when it is determined that the vehicle is in a driving state in which the differential rotation speed is smaller than the threshold value; a first torque control unit that controls the torque of the motor based on the deviation so as to reduce the deviation when it is determined by the differential rotation speed deviation determination unit that there is the deviation; a driving force distribution ratio correction unit that corrects a target driving force distribution ratio to the first output side and the second output side based on a correction torque value that reduces the deviation between the predetermined target differential rotation speed and the differential rotation speed when it is determined by the driving state determination unit that the vehicle is in a driving state in which the differential rotation speed is equal to or greater than the predetermined threshold value; and a second torque control unit that controls the torque of the motor based on the target driving force distribution ratio corrected by the driving force distribution ratio correction unit.

[0010] In the present invention, the controller may be configured to determine the differential rotation speed based on the rotation speed of the motor.

[0011] In the present invention, the controller may set the predetermined target differential rotation speed to "0" when the running state determination unit determines that the differential rotation speed is equal to or greater than the predetermined threshold value.

[0012] In the present invention, the running state determination unit may determine, based on the differential rotation speed, a running state in which the differential rotation speed becomes smaller or larger than a predetermined threshold value.

[0013] In this invention, the vehicle further includes a mode selection switch for selecting between a grip driving mode in which driving is performed with suppressed wheel slippage and a drift driving mode in which wheel slippage occurs, and the driving state determination unit may be configured to determine a driving state in which the grip driving mode is selected by the mode selection switch as a driving state in which the differential rotation speed is smaller than a predetermined threshold value, or to determine a driving state in which the drift driving mode is shifted by the mode selection switch as a driving state in which the differential rotation speed is greater than a predetermined threshold value.

[0014] In this invention, the vehicle may further include a mode selection switch that selects a rough road driving mode for driving on rough roads where there is a high possibility that one of the wheels will lose grip, and the driving condition determination unit may be configured to determine a driving condition in which the rough road driving mode is selected by the mode selection switch as a driving condition in which the differential rotation speed is greater than a predetermined threshold value. Effect of the Invention

[0015] In this invention, the torque distributed to the first output side and the second output side can be changed by the motor connected to the distribution mechanism that performs the differential action. That is, the differential action of the distribution mechanism can be limited or the torque distribution ratio can be controlled by driving the motor. The control of the torque of the motor is made different depending on the running state of the vehicle. For example, in a running state in which the rotation speed difference between the first output side and the second output side is not particularly generated or is not large, the torque of the motor is controlled based on the deviation between the target differential rotation speed and the detected differential rotation speed (so-called actual differential rotation speed). For example, the control is a feedback control that controls the torque of the motor so that the deviation is reduced, and therefore, excessive slippage is not generated in all the wheels on the first output side and the second output side, and stable running can be performed while maintaining the grip force.

[0016] In addition, during drift driving in which the wheels are actively or intentionally slipped while turning, or during driving on a rough road such as a rough road with many bumps, a muddy road, or a low μ road, the target driving force distribution ratio, which is the distribution ratio of the torque (driving force) to the first output side and the second output side, is corrected with a correction torque value, which is the motor torque for eliminating the difference rotation speed deviation at that time, and the torque of the motor is controlled based on the corrected target driving force distribution ratio. The correction of the target driving force distribution ratio is essentially a correction that changes the target driving force distribution ratio, which is the basis of the torque control, so that the motor outputs torque in a direction that reduces the deviation between the difference rotation speed and the target difference rotation speed. Therefore, in this case, the torque (or difference rotation speed) of the motor is controlled based on the corrected target driving force distribution ratio, and the target driving force distribution ratio is corrected based on the control of the torque of the motor, so that the change in the difference rotation speed caused by controlling the torque of the motor during the process in which the difference rotation speed converges to the target difference rotation speed becomes gentle, and the behavior of the vehicle is stabilized.

[0017] In addition, in this invention, the differential rotation speed between the first output side and the second output side changes according to the rotation speed of the motor connected to the third rotating element of the distribution mechanism, and the rotation speed of the motor can be detected accurately and without any particular delay. Therefore, by detecting the differential rotation speed based on the rotation speed of the motor, the detection of the differential rotation speed and control of the motor based on it can be performed accurately and without any delay. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram showing an example of a vehicle equipped with a driving force transmission control device according to the present invention; [Diagram 2] The diagrams are nomographic diagrams of the planetary gear mechanism that constitutes the distribution mechanism. (a) shows the state in which driving force is transmitted from the engine to the front and rear wheels and the motor is subjected to a so-called differential limiting operation while the vehicle is traveling in a straight line. (b) shows the state in which the sun gear is rotated by the motor, thereby generating differential rotation between the front and rear wheels. [Diagram 3] FIG. 2 is a block diagram for explaining a functional configuration of an ECU which corresponds to a controller of the present invention. [Figure 4] 10 is a nomographic diagram of a planetary gear mechanism constituting a distribution mechanism, illustrating a state in which a motor outputs torque so as to make a differential rotation speed coincident with a target differential rotation speed. FIG. [Diagram 5] 6 is a time chart for explaining a situation in which the differential rotation speed deviates from a target value and the deviation is corrected by the motor. [Figure 6] 4 is a flowchart illustrating an example of a control executed in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention will be described with reference to the embodiments shown in the drawings. Note that the embodiments described below are merely examples of the case where the present invention is implemented, and are not intended to limit the present invention.

[0020] Fig. 1 is a schematic diagram of a vehicle 1 equipped with a driving force transmission control device according to the present invention, which includes a distribution mechanism 3 that distributes torque output from a driving force source 2 to a first output side and a second output side. The first output side and the second output side may be the front wheels 4 and the rear wheels 5, or may be the right wheel and the left wheel. The example shown in Fig. 1 is an example configured to distribute and transmit torque to the front wheels 4 and the rear wheels 5, and therefore the vehicle 1 shown here is a four-wheel drive vehicle, and the distribution mechanism 3 is a center differential.

[0021] The driving force source 2 is not particularly limited, but may be any power source capable of burning an appropriate fuel to output driving force for traveling, such as an internal combustion engine (ENG) that uses gasoline, diesel, hydrogen, etc. The driving force source (hereinafter, engine) 2 is configured so that the amount of intake air and the amount of fuel supplied (injection amount) can be electrically controlled, and therefore the output can be controlled not only based on the operation by the driver (not shown) of the vehicle 1, but also, as necessary, independently of the driver's operation.

[0022] The distribution mechanism 3 is configured by a differential mechanism that performs differential action by three rotating elements. The differential mechanism may be a planetary gear mechanism or a differential gear mechanism configured by meshing a pinion gear held inside a differential case with a pair of left and right side gears, and the example shown in Fig. 1 is an example in which the distribution mechanism 3 is configured by a single-pinion planetary gear mechanism. Therefore, the distribution mechanism 3 shown in Fig. 1 includes, as rotating elements, a sun gear S, a ring gear R that is an internal gear arranged concentrically with the sun gear S, and a carrier C that is arranged between the sun gear S and the ring gear R and rotates while rotatably holding the pinion gear that is meshed with the sun gear S and the ring gear R.

[0023] In the example shown in Fig. 1, torque is transmitted from the engine 2 to the ring gear R. In addition, a rear wheel output shaft 6 that outputs torque to rear wheels 5 is connected to the ring gear R. The ring gear R corresponds to a first rotating element in this embodiment of the present invention, and the output of torque toward the rear wheels 5 corresponds to an output to a first output side in this embodiment of the present invention.

[0024] The carrier C corresponds to the second rotating element in the embodiment of the present invention, and distributes and outputs torque from the carrier C to the front wheel 4 side, which corresponds to the second output side. A transfer 8 is provided to transmit torque from the carrier C to the front wheel output shaft 7. The transfer 8 is configured by a winding transmission mechanism that transmits torque by a chain, a belt, or the like, and for example, a sprocket is attached to the carrier C, and a transmission member wound around the sprocket is wound around another sprocket attached to the front wheel output shaft 7. The transfer 8 can also be configured by a gear mechanism that transmits torque by gears. The front wheel output shaft 7 is also arranged parallel to the central axis of rotation of the distribution mechanism 3. In other words, the front wheel output shaft 7 is arranged on a countershaft.

[0025] Torque input to the ring gear R is distributed to the carrier C. A motor 9 that controls the distribution ratio between the torque distributed to the front wheel output shaft 7 side via the carrier C and the torque distributed from the ring gear R to the rear wheel output shaft 6 side is connected to the sun gear S, which corresponds to the third rotating element in this embodiment of the present invention. The motor 9 may be a motor (motor generator) with a power generating function such as a permanent magnet synchronous motor, or a motor equipped with a device that detects the rotation angle (or rotation speed) such as a resolver. This motor 9 is connected to a power storage device (battery) (not shown) via an inverter, and the rotation speed and torque are controlled by the inverter or the like.

[0026] Like a normal vehicle, the vehicle 1 is provided with an accelerator pedal 10 for accelerating and decelerating, a brake pedal 11 for braking, a steering mechanism (not shown), and a mode selection switch 12 for manually selecting a driving mode by the driver. The driving modes selected by the mode selection switch 12 include a grip driving mode, a drift driving mode, and a rough road driving mode for driving on so-called rough roads such as muddy roads and rocky roads. Although not shown, the vehicle 1 is provided with various sensors for detecting the depression amount of the accelerator pedal 10, which indicates the required driving force, the depression amount or depression force of the brake pedal 11, the rotation speed of the front wheels 4 and the rear wheels 5, and the like.

[0027] Here, the torque distribution action by the distribution mechanism 3 and the control of the torque distribution ratio by the motor 9 will be described. Fig. 2 shows a collinear diagram of the planetary gear mechanism constituting the distribution mechanism 3. The collinear diagram is a diagram in which three straight lines, a straight line indicating the sun gear S, a straight line indicating the carrier C, and a straight line indicating the ring gear R, are drawn parallel to one another, with the distance between the straight line indicating the sun gear S and the straight line indicating the carrier C being set to "1", and the distance between the straight line indicating the carrier C and the straight line indicating the ring gear R being set to the gear ratio of the planetary gear mechanism (the ratio of the number of teeth of the sun gear S to the number of teeth of the ring gear R). The position on these three straight lines from a base line perpendicular to these three straight lines indicates the rotation speed of each rotating element.

[0028] 2(a) shows a state in which the vehicle 1 is traveling straight ahead with driving force transmitted from the engine 2 to the front and rear wheels 4, 5 and with the motor 9 performing so-called differential limiting (i.e., splitting the power of the engine 2 between the front and rear wheels 4, 5), and the torque of the engine 2 is transmitted to the ring gear R, and the torque output by the engine 2 is transmitted to the rear wheels 5. In response to this, the motor 9 rotates the sun gear S so that the differential rotation speed between the front wheels 4 and the rear wheels 5 is nearly zero, and therefore the carrier C and the front wheels 4 connected thereto rotate in the same manner as the rear wheels 5.

[0029] When the front and rear wheels 4, 5 are to be rotated differentially from this state, the rotation speed of the sun gear S is changed by the motor 9. An example is shown in FIG. 2(b), in which the rotation speed of the rear wheels 5 is increased relative to the rotation speed of the front wheels 4, and the rotation speed of the sun gear S is reduced by the motor 9 from the rotation speed shown in FIG. 2(a). In this case, the rotation speed of the carrier C is represented by the point where a straight line L connecting a point indicating the rotation speed of the ring gear R and a point indicating the rotation speed of the sun gear S intersects with a line indicating the carrier C. Therefore, the inclination of the straight line L can be obtained from the rotation speed of the motor 9 (sun gear S) and the rotation speed of the engine 2 (the rotation speed of the ring gear R or the vehicle speed) and the interval between the vertical lines indicating each rotating element, and the differential rotation speed ΔN between the carrier C and the ring gear R (i.e., the differential rotation speed between the front and rear wheels 4, 5) can be calculated from the inclination. In other words, if the rotation speed of the motor 9 is detected while the vehicle 1 is traveling at a predetermined vehicle speed, the differential rotation speed between the front and rear wheels 4, 5 can be calculated based on the rotation speed of the motor 9. Since the rotation speed of the motor 9 can be detected by a highly accurate sensor such as a resolver, in this embodiment of the present invention, it is preferable to find the differential rotation speed between the front and rear wheels 4, 5 based on the rotation speed of the motor 9.

[0030] As described above, the distribution mechanism 3 can control the differential rotation speed and driving force distribution ratio of the front and rear wheels 4, 5 by controlling the motor 9, and an electronic control unit (ECU) 13 is provided to perform this control in accordance with the running state of the vehicle 1. The ECU 13 corresponds to a controller in the embodiment of the present invention, and is mainly composed of a microcomputer including a processing element (CPU), memory elements (RAM, ROM), an interface, etc., and is configured to perform calculations according to a preset program using data obtained by various sensors and data stored in advance, and to output the results of the calculations as a control command signal.

[0031] Examples of the input data include data from wheel speed sensors that detect the rotation speeds of the front and rear wheels 4 and 5, the longitudinal and lateral accelerations of the vehicle 1, the rotation speed of the motor 9, and data related to the driving mode selected by the mode selection switch 12. Examples of pre-stored data include threshold values ​​that serve as reference values ​​for determining the driving mode or driving state of the vehicle 1 from the differential rotation speeds of the front and rear wheels 4 and 5, and correction values ​​for correcting the target driving force distribution ratio by feed-forward control (F / F control) based on the control amount (correction torque value) of the torque of the motor 9. The ECU 13 is configured to perform calculations based on these data, determine a target value for the differential rotation speeds of the front and rear wheels 4 and 5, and output the rotation speed of the motor 9 for achieving the target value, or the torque of the motor 9 for achieving the target driving force distribution ratio, as a control command signal.

[0032] The ECU 13 is configured to use the input data and pre-stored data to determine the driving state or driving mode in which differential limiting by the motor 9 is performed, and when the determination is established, to perform differential rotation speed control or driving force distribution control suitable for the driving state or driving mode. That is, as shown in Fig. 3, the ECU 13 is functionally configured to include a driving state determination unit 13a, a differential rotation speed deviation determination unit 13b, a first torque control unit 13c, a driving force distribution ratio correction unit 13d, and a second torque control unit 13e.

[0033] The running state determination unit 13a is a functional configuration that determines a running state in which the differential rotation speed between the front and rear wheels 4, 5 (hereinafter, sometimes simply referred to as differential rotation speed) is smaller than a predetermined threshold value or is larger than the threshold value, and the running state may be the current running state or a running state that is scheduled to be run in the near future. Therefore, the running state determination unit 13a can be configured to determine the current running state by comparing the detected difference between the rotation speed of the front wheel 4 and the rotation speed of the rear wheel 5 with a predetermined threshold value. Alternatively, the running state determination unit 13a can be configured to determine the current running state or a running state that is scheduled to be run in the near future based on the running mode selected by the mode selection switch 12.

[0034] The differential rotation speed may be calculated based on a wheel speed sensor (not shown) provided for each wheel, or may be calculated based on the rotation speed of the motor 9. The threshold value may be determined in advance in design by assuming possible driving conditions in which the vehicle 1 may travel and conducting experiments or simulations for each assumed driving condition.

[0035] The driving conditions to be judged include a state in which the vehicle is driven on a road with a high road friction coefficient (road surface μ) while minimizing wheel slippage as much as possible (so-called grip driving), cornering in a so-called grip driving state, a state in which the vehicle is driven on a road with a low road surface μ such as a packed snow road, a muddy road where the vehicle is likely to get stuck, or a rocky road with severe bumps, and a state in which the vehicle is driven by actively or intentionally causing the wheels to slip by applying a large torque to the front and rear wheels 4, 5 (so-called drift driving).

[0036] The differential rotation speed deviation judgment unit 13b is a functional configuration that judges whether or not there is a deviation between the differential rotation speed and a predetermined target differential rotation speed when it is determined that the vehicle is in a driving state in which the differential rotation speed is smaller than the threshold value. When the vehicle 1 runs without actively or intentionally causing the wheels to slip, the slippage of the wheels is zero, except for the small slippage that is unavoidable for generating a driving force between the road surface. Therefore, when the vehicle 1 runs straight, the differential rotation speed is substantially zero. In contrast, when the vehicle 1 runs in a turn, a differential rotation occurs between the front wheels 4 and the rear wheels 5 based on the difference in turning radius. In addition, in the case of temporary fallen objects, puddles, or crossing points of a narrow river, only one of the four wheels may slip temporarily, or may slip repeatedly, or even the four wheels may continue to slip repeatedly. As described above, the occurrence of the differential rotation speed varies depending on the road surface condition or the driving state, although it can be expected to some extent, so the target differential rotation speed is set according to the detected driving state or the driving state in which the vehicle 1 is scheduled to run in the near future.

[0037] To further explain the target differential speed, it is preferable to change the target differential speed according to the running state of the vehicle 1 and the road surface conditions such as the friction coefficient and the unevenness of the road surface. For example, when turning in grip driving, the target differential speed is calculated based on the trajectory of the front and rear wheels 4, 5 that is geometrically determined from the turning radius. In drift driving, the wheels are actively made to slip, so the rotation speeds of the front and rear wheels 4, 5 cannot be determined geometrically, and therefore the target differential speed is set to "0". This is also true when driving on a bad road such as a muddy road, a low μ road, or a rocky road with severe unevenness, and the target speed is set to "0". The determination of drift driving may be made based on whether it is selected by the mode selection switch 12 described above. The determination of grip driving may be made based on whether drift driving is not selected by the mode selection switch 12 described above.

[0038] If the differential rotation speed is equal to the target differential rotation speed, there is no excessive or unexpected slippage in either the front or rear wheels 4, 5, and the vehicle 1 can run with a stable behavior. On the other hand, if a deviation occurs, either the front or rear wheels 4, 5 rotates off the target or is locked, and the running stability of the vehicle 1 is impaired or there is a possibility of this. The first torque control unit 13c is provided as a functional configuration for eliminating or correcting such a state. This first torque control unit 13c is configured to control the torque of the motor 9 so as to reduce the deviation between the differential rotation speed and the target differential rotation speed.

[0039] An example of the torque control will be described with reference to FIG. 4. FIG. 4 is a collinear diagram of the differential mechanism constituting the distribution mechanism 3, showing an example in which the differential rotation speed deviates from the target differential rotation speed when the vehicle 1 is gripping a straight road, causing a deviation between the two, and the torque of the motor 9 is controlled to correct the deviation. If the vehicle is gripping a straight road, the differential rotation speed should be substantially zero, so the rotation speeds of the rotating elements constituting the differential mechanism become the same, for example, as shown by the straight line L1 in FIG. 4. That is, the target differential rotation speed is zero. In contrast, if the rotation speed of the rear wheels 5 increases for some reason, such as slippage of the rear wheels 5, causing a differential rotation speed between the rear wheels 5 and the front wheels 4, the rotation speed of the ring gear R increases relative to the rotation speed of the carrier C, and the rotation speeds of the sun gear S and the motor 9 connected thereto decrease, as shown by the dashed line L2 in FIG. 4.

[0040] In order to reduce the deviation of the differential rotation speed thus generated from the target differential rotation speed, the rotation speed of the sun gear S can be increased by the motor 9. That is, the first torque control unit 13c increases the torque of the motor 9 in the forward rotation direction (upward in FIG. 4). This torque control is for reducing the deviation of the differential rotation speed, and therefore the torque of the motor 9 is controlled by feedback control (F / B control) using the deviation between the differential rotation speed and the target differential rotation speed as the control deviation. The first torque control unit 13c is configured to control the torque of the motor 9 by F / B control so as to reduce the deviation between the detected or calculated differential rotation speed and the target differential rotation speed at that time, not only when the target differential rotation speed is zero, but also when a predetermined differential rotation speed needs to be generated, such as during cornering.

[0041] FIG. 5 shows a schematic time chart of the change in the torque of the motor 9 to reduce the difference in rotation speed deviation when the rotation speed deviates from the target value. In FIG. 5, the target value of the difference in rotation speed is shown by a straight line Ln, and the torque of the motor 9 in a state where the difference in rotation speed coincides with the target value is shown by a straight line Lt. In a state where the difference in rotation speed coincides with the target value, the torque of the motor 9 is controlled to maintain the rotation state, and the distribution ratio of the driving force to the front wheels 4 and the rear wheels 5 changes according to the controlled torque of the motor 9. That is, the driving force distribution ratio control according to the running state such as the turning radius is executed. When the difference in rotation speed changes from this state and a deviation occurs from the target value as shown by the thin line in FIG. 5, the torque of the motor 9 is F / B controlled (rotation speed F / B control) to eliminate or reduce the deviation, and the torque of the motor 9 changes as shown by the thin line in FIG. 5.

[0042] The driving force distribution ratio correction unit 13d is a functional configuration that performs the distribution ratio of the driving force to the front wheels 4 and the rear wheels 5, which is the basis for controlling the torque of the motor 9, prior to controlling the motor torque, and is configured to perform the correction in a driving state in which the differential rotation speed becomes larger than a predetermined threshold value, such as when driving on a rough road such as a low μ road, a muddy road, or a rocky road, and during drift driving in which the front and rear wheels 4, 5 are actively or intentionally made to slip. When the wheels slip unintentionally or intentionally, a differential rotation speed of the front and rear wheels 4, 5 occurs, but since the rotation speed of the slipped wheel cannot be defined, in this embodiment of the present invention, the target differential rotation speed is set to "0", and the torque of the motor 9 for converging the differential rotation speed of the front and rear wheels 4, 5 to zero is controlled based on a value obtained by correcting the target driving force distribution ratio with the F / B control amount of the motor torque. The driving force distribution ratio correction unit 13d performs the correction of the target driving force distribution ratio.

[0043] The differential rotation speed calculated based on the rotation speed of the motor 9 reflects the actual state of the vehicle 1, and if the differential rotation speed deviates from the target differential rotation speed, the torque of the motor 9 is controlled to eliminate the deviation (deviation). If the torque of the motor 9 is controlled to eliminate the deviation of the differential rotation speed, the torque between the front wheels 4 and the rear wheels 5, i.e., the driving force distribution ratio, changes. Therefore, the driving force distribution ratio correction unit 13d replaces the control amount of the torque of the motor 9 for correcting or eliminating the deviation of the differential rotation speed with the change amount of the driving force distribution ratio, and corrects the target driving force distribution ratio using this as the correction amount of the target driving force distribution ratio. In this case, since the torque of the motor 9 changes successively by the F / B control as described above, the driving force distribution ratio changes gradually in response to the change. The target driving force distribution ratio can be determined based on the front / rear load distribution, which is calculated by calculating the dynamic load of the front / rear four wheels from the longitudinal acceleration and lateral acceleration of the vehicle 1.

[0044] The second torque control unit 13e is configured to control the torque of the motor 9 so as to achieve the target driving force distribution ratio corrected as described above. The torque of the motor 9 for making the differential rotation speed coincide with the target value is geometrically determined based on the configuration of the differential mechanism constituting the distribution mechanism 3, as described with reference to the alignment chart shown in Fig. 4. That is, the second torque control unit 13e controls the motor 9 so as to achieve the torque determined by the corrected target driving force distribution ratio, in the same manner as described with reference to Fig. 5 above.

[0045] An example of the control executed by the ECU 13 will be described with reference to FIG. 6. FIG. 6 is a flowchart for explaining the control executed in the embodiment of the present invention, and the routine shown here is repeatedly executed when the vehicle 1 is traveling. First, it is determined whether or not the control (differential limiting control) for limiting the differential rotation of the front and rear wheels 4, 5 is prohibited (OFF or not) (step S1). If a situation occurs in which any of the rotating elements in the differential mechanism constituting the distribution mechanism 3 spins freely, torque is not transmitted to the other rotating elements, and conversely, if the differential rotation is prohibited, the rotation of the front wheels 4 or the rear wheels 5 is limited during turning, causing a braking phenomenon or the like. The system is configured to be able to selectively execute the differential limiting so as to be able to respond to any of these situations, and in step S1, it is determined whether or not such a differential limiting has been selected. The selection of the differential limiting is usually performed by the driver by operating a switch, and therefore the determination in step S1 can be made by determining whether or not the switch operation is being performed. Furthermore, if the vehicle is scheduled to travel on a rough road such as a muddy road, a low μ road, or a rocky road, or if the driver is aware of this, a mode for traveling on such road surfaces is selected by the above-mentioned mode selection switch 12. In this case, the differential limiting control is turned ON together with the selection of the travel mode.

[0046] If the determination result in step S1 is "Yes", the torque of the motor 9 is calculated based on the target driving force distribution ratio (step S2). Then, the process returns. The distribution ratio of the driving force to the front and rear wheels 4, 5 can be determined according to the driving conditions, such as when accelerating the vehicle 1 or traveling uphill, it is preferable to increase the torque borne by the rear wheels 5, and when decelerating or traveling downhill, it is preferable to have the torque borne by the front wheels 4. In step S2, the torque of the motor 9 is calculated based on a target driving force distribution ratio that is predetermined according to the condition of the road.

[0047] On the other hand, if the result of the determination in step S1 is "no", that is, if differential limiting control is to be performed, the differential rotation speed is calculated (step S3). The differential rotation speed may be calculated from the rotation speeds obtained by the wheel speed sensors of the front and rear wheels 4, 5, but it is preferable to calculate it based on the rotation speed of the motor 9, as described above. The differential rotation speed calculated in step S3 may be a rotation speed determined by design in accordance with the selected driving mode. In other words, when drifting or driving on a bad road such as a packed snow road or a rocky road, there is a high possibility that one of the front and rear wheels 4, 5 will spin, and assuming such a condition, the differential rotation speed is set to a large value in advance. In that case, in step S3, the differential rotation speed is calculated by reading the differential rotation speed corresponding to the selected driving mode, etc.

[0048] Next, it is determined whether the differential rotation speed obtained in step S3 is smaller than a predetermined threshold value (step S4). This threshold value is, for example, a value that is predetermined as a value approximately equal to the maximum differential rotation speed that is assumed in a normal driving state in which all four wheels maintain grip and no abnormality such as a tire burst occurs. Therefore, in step S4, it is determined whether the driving state is such that either the front or rear wheels 4, 5 is slipping significantly. In other words, the functional configuration that executes the control of the above step S1, as well as steps S3 and S4, corresponds to the driving state determination unit in the embodiment of the present invention.

[0049] If the result of the determination in step S4 is "Yes" because the differential rotation speed is less than the threshold value, it is determined whether or not the differential rotation speed matches the target differential rotation speed (step S5). If the result of the determination in step S5 is "Yes" because the differential rotation speed matches the target differential rotation speed, the process proceeds to the above-mentioned step S2, where the torque of the motor 9 is calculated based on the target driving force distribution ratio.

[0050] On the other hand, if the result of the determination in step S5 is "no", that is, if slippage occurs in either the front or rear wheels 4, 5 while driving without causing the wheels to slip, the torque of the motor 9 is F / B controlled so that the differential rotation speed coincides with the target differential rotation speed, that is, so that the deviation between the differential rotation speed and the target value is reduced (step S6). Then, the control returns. Therefore, in this case, since sufficient grip force is maintained in all four wheels without causing excessive or unexpected slippage of the wheels, the behavior of the vehicle 1 can be stabilized. It is preferable to set upper and lower limit values ​​for the rotation speed F / B control of the torque of the motor 9. In that case, in the vehicle 1 in which a driving mode such as a normal mode or a sports mode can be selected, it is preferable to change the upper and lower limit values ​​according to the selected driving mode. For example, the upper and lower limit values ​​are set wider in the sports mode than in the normal mode.

[0051] On the other hand, if drift driving is selected or driving on a bad road causes the differential rotation speed to exceed the threshold value, and as a result the determination result in step S4 is "no", the target driving force distribution ratio is corrected (step S7). This correction is as described above for the driving force distribution ratio correcting unit 13d, and the target driving force distribution ratio is corrected by adding a correction value according to the rotation speed F / B control amount of the torque of the motor 9 that reduces the deviation between the differential rotation speed and the target differential rotation speed to the target driving force distribution ratio calculated from the longitudinal acceleration and the lateral acceleration.

[0052] Next, the torque of the motor 9 is calculated based on the corrected target driving force distribution ratio (step S8), and then the process returns. The control in step S8 is similar to the control in step S2, and is the control by the second torque control unit 13e described above.

[0053] Therefore, in this case, the target driving force distribution ratio is corrected based on the differential rotation speed actually occurring in the vehicle 1, and the torque of the motor 9 is controlled based on the corrected target driving force distribution ratio, so that changes in the torque of the front and rear wheels 4, 5 or their distribution ratio are mitigated, and as a result, the behavior of the vehicle 1 can be stabilized.

[0054] The present invention is not limited to the above-described embodiment, and can be modified as appropriate. For example, the differential mechanism constituting the distribution mechanism may be a differential mechanism other than a single-pinion type planetary gear mechanism, and therefore the rotating element connecting the motor may be a rotating element other than a ring gear. Also, the motor may not be directly connected to the distribution mechanism, but may be connected via a transmission mechanism such as a gear mechanism. [Explanation of symbols]

[0055] 1 vehicle 2. Driving power source (engine) 3 Distribution mechanism 4 Front Wheel 5 Rear wheel 6 Rear wheel output shaft 7 Front wheel output shaft 8 Transfer 9 Motor 10. Accelerator pedal 11. Brake pedal 12 Mode selection switch 13 Electronic control unit (ECU, controller) 13a Driving state determination unit 13b Differential rotation speed deviation judgment unit 13c Torque control section 13d Driving force distribution ratio correction section 13e Torque control section C Carrier R ring gear S Sun gear

Claims

1. A driving force transmission control device for a vehicle, comprising: a distribution mechanism that distributes torque output from a driving force source to a first output side and a second output side and causes differential rotation between the first output side and the second output side; and a motor that controls a differential rotation speed between the first output side and the second output side by the distribution mechanism, the distribution mechanism is composed of a differential mechanism that performs a differential action using a first rotating element that receives torque from the driving force source and outputs the torque to the first output side, a second rotating element that outputs torque to the second output side, and a third rotating element to which the motor is connected; A controller for controlling the motor is further provided. The controller: a running state determination unit that determines whether the vehicle is in a running state in which the differential rotation speed is smaller than or larger than a predetermined threshold value; a differential rotation speed deviation determination unit that, when it is determined that the vehicle is in a running state in which the differential rotation speed is smaller than the threshold value, determines whether or not there is a deviation between the differential rotation speed and a predetermined target differential rotation speed; a first torque control unit that controls a torque of the motor based on the deviation so as to reduce the deviation when the differential rotation speed deviation determination unit determines that the deviation exists; a driving force distribution ratio correction unit that corrects a target driving force distribution ratio to the first output side and the second output side based on a correction torque value that reduces a deviation between a predetermined target differential rotation speed and the differential rotation speed when the driving state determination unit determines that the vehicle is in a driving state in which the differential rotation speed is equal to or greater than the predetermined threshold value; a second torque control unit that controls the torque of the motor based on the target driving force distribution ratio corrected by the driving force distribution ratio correction unit. A vehicle driving force transmission control device comprising:

2. 2. A vehicle driving force transmission control device according to claim 1, The controller determines the differential rotation speed based on the rotation speed of the motor. A vehicle driving force transmission control device comprising:

3. 3. A vehicle driving force transmission control device according to claim 1, The controller sets the predetermined target differential rotation speed to "0" when the running state determination unit determines that the differential rotation speed is equal to or greater than the predetermined threshold value. A vehicle driving force transmission control device comprising:

4. 3. A vehicle driving force transmission control device according to claim 1, The running state determination unit determines, based on the differential rotation speed, a running state in which the differential rotation speed becomes smaller or larger than a predetermined threshold value. A vehicle driving force transmission control device comprising:

5. 3. A vehicle driving force transmission control device according to claim 1, The vehicle further includes a mode selection switch for selecting between a grip driving mode in which the vehicle is driven while suppressing wheel slippage and a drift driving mode in which the vehicle is driven while causing wheel slippage, The running state determination unit determines a running state in which the grip running mode is selected by the mode selection switch as a running state in which the differential rotation speed is smaller than a predetermined threshold value, or determines a running state in which the drift running mode is shifted by the mode selection switch as a running state in which the differential rotation speed is larger than a predetermined threshold value. A vehicle driving force transmission control device comprising:

6. 3. A vehicle driving force transmission control device according to claim 1, The vehicle further includes a mode selection switch for selecting a rough road driving mode for driving on a rough road where there is a high possibility that any one of the wheels will lose gripping force, The driving state determination unit determines a driving state in which the rough road driving mode is selected by the mode selection switch as a driving state in which the differential rotation speed is greater than a predetermined threshold value. A vehicle driving force transmission control device comprising:

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