Vehicle power 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 the torque output from a driving force source to a plurality of wheels.

Background Art

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

[0003] In a vehicle that can drive the front and rear wheels, it is preferable to allow differential rotation between the front and rear wheels as described above, limit differential rotation according to the situation, and further control the torque sharing ratio of each wheel according to the road surface condition or the driving state of the vehicle. Patent Document 1 discloses an example of a mechanism configured to be able to actively control the distribution of the driving force to the front and rear wheels. Briefly explaining the configuration, the distribution mechanism that distributes the torque output from the engine to the front wheel side and the rear wheel side is mainly composed of a planetary gear mechanism having a sun gear, a ring gear, and a carrier as rotating elements. When distributing the driving force, the torque from the engine is input to the ring gear, and the torque is output from the ring gear to the rear wheel side. Also, the torque is output from the carrier to the front wheel side. In that state, the torque of the sun gear is changed by a motor or a motor-generator (hereinafter, these are collectively referred to as a motor) connected to the sun gear, so as to control the torque and rotational speed of the front and rear wheels.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-131153 [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0006] If the difference in rotational speed between the front and rear wheels and the torque distribution ratio can be appropriately controlled, it becomes possible to perform grip driving, where grip is maintained on all four wheels, or drift driving, where all four wheels or either the front or rear wheels slip, at will. However, if the distribution of torque (driving force) to the front and rear wheels is inappropriate during grip driving, and the difference in rotational speed between the front and rear wheels deviates from the target difference in rotational speed, the steering characteristics may become understeer or oversteer, potentially compromising driving stability.

[0007] Furthermore, in drift driving, at least one of the front or rear wheels slips, and since the rotational speed of the slipping wheel is not uniquely determined, the difference in rotational speed between the front and rear wheels cannot be uniquely determined. Therefore, for example, as in grip driving, one could estimate the turning radius, determine the vehicle's trajectory (driving path) from the estimated turning radius, and set the target difference in rotational speed between the front and rear wheels based on that trajectory. However, if the estimated turning radius differs from the actual driving path, the vehicle's behavior will differ from the driver's intended behavior. Also, if the difference in rotational speed between the front and rear wheels is determined based on the rotational speed detected by wheel speed sensors installed on each wheel, differences in the detection accuracy or responsiveness of rotational speed and difference in rotational speed may make it impossible to accurately determine the difference between the target difference in rotational speed and the actual difference in rotational speed. As a result, the control of the front and rear driving force distribution may not be appropriate, and the vehicle's behavior may become unstable.

[0008] This invention was made in view of the above-mentioned technical problems, and aims to provide a drive force transmission control device that can improve the stability of vehicle behavior in any type of driving, such as grip driving or drift driving. [Means for solving the problem]

[0009] This invention provides a vehicle drive force transmission control device that, in order to achieve the above objective, comprises a distribution mechanism that distributes torque output by a drive 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 the 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 to which torque is input from the drive force source and which outputs torque to the first output side, a second rotating element to which torque is output to the second output side, and a third rotating element to which the motor is connected, and further comprises a controller that controls the motor, wherein the controller includes a driving state determination unit that determines whether the driving state is such that the differential rotation speed is smaller than or larger than a predetermined threshold, and the differential rotation speed The system is characterized by comprising: a differential rotation speed deviation determination unit that determines whether there is a deviation between the differential rotation speed and a predetermined target differential rotation speed when it is determined that the driving state is smaller than a predetermined threshold; 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 a deviation; a drive force distribution ratio correction unit that corrects the target drive force distribution ratio to the first output side and the second output side based on a correction torque value that reduces the deviation between a predetermined target differential rotation speed and the differential rotation speed when it is determined by the driving state determination unit that the differential rotation speed is greater than or equal to a predetermined threshold; and a second torque control unit that controls the torque of the motor based on the target drive force distribution ratio corrected by the drive force distribution ratio correction unit.

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

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

[0012] In this invention, the driving state determination unit may determine, based on the difference in rotational speed, a driving state in which the difference in rotational speed is less than or greater than a predetermined threshold.

[0013] In this invention, the vehicle further includes a mode selection switch for selecting between a grip driving mode that suppresses wheel slip and a drift driving mode that causes wheel slip, and the driving state determination unit may be configured to determine that a driving state in which the grip driving mode is selected by the mode selection switch is a driving state in which the differential rotation speed is less than a predetermined threshold, or to determine that a driving state in which the drift driving mode is selected by the mode selection switch is a driving state in which the differential rotation speed is greater than a predetermined threshold.

[0014] In this invention, the vehicle further comprises a mode selection switch for selecting an off-road driving mode for driving on rough roads where there is a high possibility that any of the wheels will lose grip, and the driving state determination unit may be configured to determine that a driving state in which the off-road driving mode is selected by the mode selection switch is a driving state in which the differential rotations exceed a predetermined threshold. [Effects of the Invention]

[0015] In this invention, the torque distributed to the first output side and the second output side can be changed by a motor connected to a distribution mechanism that performs differential action. That is, by driving the motor, the differential action of the distribution mechanism can be limited or the torque distribution ratio can be controlled. The control of the motor's torque is varied according to the vehicle's driving conditions. For example, in driving conditions where there is no particular difference in rotational speed between the first output side and the second output side, or where it does not become large, the motor's torque is controlled based on the deviation between the target difference in rotational speed and the detected difference in rotational speed (so-called actual difference in rotational speed). This control is a feedback control that controls the motor's torque so that the deviation becomes small, and therefore, stable driving can be performed while maintaining grip without causing excessive slippage on all wheels on the first and second output sides.

[0016] Furthermore, during drift driving, where the wheels are actively or intentionally made to slip to turn, or when driving on rough roads with many bumps, muddy roads, or low-friction surfaces, the target driving force distribution ratio, which is the ratio of torque (driving force) distributed between the first output side and the second output side, is corrected by a correction torque value, which is the motor torque to eliminate the differential rotation speed deviation at that time. The motor torque is then controlled based on this corrected target driving force distribution ratio. In essence, this correction of the target driving force distribution ratio is a correction that changes the target driving force distribution ratio, which is the basis for controlling the torque, so that the motor outputs torque in a direction that reduces the deviation between the differential rotation speed and the target differential rotation speed. Therefore, in this case, the motor torque (or differential rotation speed) is controlled based on the corrected target driving force distribution ratio, and the target driving force distribution ratio is further corrected based on the control of the motor torque. As a result, the change in differential rotation speed associated with controlling the motor torque during the process of the differential rotation speed converging to the target differential rotation speed becomes gradual, and the vehicle's behavior becomes more stable.

[0017] Also, in this invention, the differential rotational speed between the first output side and the second output side changes according to the rotational speed of the motor connected to the third rotating element of the distribution mechanism, and the rotational speed of the motor can be detected accurately and without causing any delay. Therefore, by detecting the differential rotational speed based on the rotational speed of the motor, the detection of the differential rotational speed and the control of the motor based thereon can be performed accurately and without causing any delay.

Brief Description of the Drawings

[0018] [Figure 1] It is a schematic diagram showing an example of a vehicle equipped with a driving force transmission control device according to this invention. [Figure 2] It is a collinear diagram of the planetary gear mechanism constituting the distribution mechanism. (a) shows a state where the driving force is transmitted from the engine to the front and rear wheels and the motor performs so-called differential restriction and the vehicle is traveling straight, and (b) shows a state where the differential rotation of the front and rear wheels is caused by rotating the sun gear by the motor. [Figure 3] It is a block diagram for explaining the functional configuration of an ECU corresponding to the controller of this invention. [Figure 4] It is a collinear diagram of the planetary gear mechanism constituting the distribution mechanism, showing a state where the motor outputs torque so that the differential rotational speed matches the target differential rotational speed. [Figure 5] It is a time chart for explaining the situation where the differential rotational speed deviates from the target value and the motor controls to correct the deviation. [Figure 6] It is a flowchart for explaining an example of the control executed in this invention.

Embodiments for Carrying Out the Invention

[0019] This invention will be described with reference to the embodiments shown in the drawings. Note that the embodiments described below are only examples of implementing this invention and do not limit this 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. The driving force transmission control device according to the present invention includes a distribution mechanism 3 that distributes the torque output by 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 wheel 4 side and the rear wheel 5 side, 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. 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 as long as it is a power unit that can output a driving force for traveling by burning an appropriate fuel, and is an internal combustion engine (ENG) that uses gasoline, light oil, hydrogen, or the like as fuel. Note that the driving force source (hereinafter, the engine) 2 is configured to be able to electrically control the intake air amount and the fuel supply amount (injection amount), and therefore its output can be controlled not only based on the operation by the driver (not shown) of the vehicle 1, but also can be controlled as necessary regardless of the driver's operation.

[0022] The distribution mechanism 3 is constituted by a differential mechanism that performs a differential action by three rotating elements. The differential mechanism may be a planetary gear mechanism or a differential gear mechanism in which a pinion gear held inside a differential case is engaged with a pair of left and right side gears. The example shown in FIG. 1 is an example in which the distribution mechanism 3 is constituted by a single pinion type planetary gear mechanism. Therefore, the distribution mechanism 3 shown in FIG. 1 includes 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 rotatably holds a pinion gear engaged with the sun gear S and the ring gear R as rotating elements.

[0023] In the example shown in Figure 1, torque is transmitted from the engine 2 to the ring gear R. Furthermore, a rear wheel output shaft 6, which outputs torque to the rear wheel 5, is connected to the ring gear R. The ring gear R corresponds to the first rotating element in this embodiment of the invention, and the torque output directed towards the rear wheel 5 corresponds to the output to the first output side in this embodiment of the invention.

[0024] Carrier C corresponds to the second rotating element in this embodiment of the invention, and distributes torque from carrier C to the front wheel 4, which corresponds to the second output side. A transfer 8 is provided to transmit torque from carrier C to the front wheel output shaft 7. The transfer 8 is composed of a winding transmission mechanism that transmits torque by chain or belt, for example, a sprocket is attached to carrier C, and a transmission member wrapped around it is wrapped around another sprocket attached to the front wheel output shaft 7. The transfer 8 can also be composed of a gear mechanism that transmits torque by gears. Furthermore, the front wheel output shaft 7 is arranged parallel to the rotational center axis of the distribution mechanism 3. That is, the front wheel output shaft 7 is arranged on a sub-shaft.

[0025] The torque input to the ring gear R is distributed to the carrier C. A motor 9, which controls the distribution ratio between the torque distributed to the front wheel output shaft 7 via the carrier C and the torque distributed from the ring gear R to the rear wheel output shaft 6, is connected to the sun gear S, which corresponds to the third rotating element in this embodiment of the invention. The motor 9 may be a motor with a power generation function (motor generator), 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 an energy storage device (battery) (not shown) via an inverter, and its rotation speed and torque are controlled by the inverter or the like.

[0026] Vehicle 1 is equipped with an accelerator pedal 10 for acceleration and deceleration, a brake pedal 11 for braking, a steering mechanism (not shown), and other components similar to those found in a normal vehicle. It is also equipped with a mode selection switch 12 for the driver to manually select a driving mode. The driving modes selected by this mode selection switch 12 include a grip driving mode, a drift driving mode, and an off-road driving mode for driving on so-called rough roads such as muddy or rocky roads. In addition, although not specifically shown, Vehicle 1 is equipped with various sensors that detect the amount of depression of the accelerator pedal 10, which represents the required driving force, the amount of depression or force applied to the brake pedal 11, and the rotational speed of the front wheels 4 and rear wheels 5.

[0027] Here, we will explain the torque distribution function of the distribution mechanism 3 described above, and the control of the torque distribution ratio by the motor 9. Figure 2 shows a collinear diagram of the planetary gear mechanism that constitutes the distribution mechanism 3. The collinear diagram is a diagram in which three lines are drawn parallel to each other: a line representing the sun gear S, a line representing the carrier C, and a line representing the ring gear R. The distance between the line representing the sun gear S and the line representing the carrier C is set to "1", and the distance between the line representing the carrier C and the line representing the ring gear R is 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 lines, from a baseline perpendicular to these three lines, indicates the rotational speed of each rotating element.

[0028] Figure 2(a) shows the state in which vehicle 1 is traveling in a straight line, with driving force transmitted from engine 2 to the front and rear wheels 4 and 5, and differential limiting performed by motor 9 (i.e., the power of engine 2 is divided between the front and rear wheels 4 and 5). Torque from engine 2 is transmitted to the ring gear R, and torque output by engine 2 is also transmitted to the rear wheel 5. In response, motor 9 rotates the sun gear S so that the difference in rotational speed between the front wheel 4 and the rear wheel 5 is almost zero, and therefore the carrier C and the front wheel 4 connected to it rotate in the same way as the rear wheel 5.

[0029] When the front and rear wheels 4 and 5 are to rotate differentially from this state, the motor 9 changes the rotational speed of the sun gear S. An example of this is shown in Figure 2(b), where the rotational speed of the rear wheel 5 is increased relative to the rotational speed of the front wheel 4, and the motor 9 decreases the rotational speed of the sun gear S from the rotational speed shown in Figure 2(a). In this case, the rotational speed of the carrier C is represented by the point where the straight line L, which connects the point representing the rotational speed of the ring gear R and the point representing the rotational speed of the sun gear S, intersects with the line representing the carrier C. Therefore, the slope of the straight line L can be determined from the rotational speed of the motor 9 (sun gear S) and the rotational speed of the engine 2 (rotational speed of the ring gear R or vehicle speed), and the spacing of the vertical lines representing each rotational element, and the difference in rotational speed between the carrier C and the ring gear R (i.e., the difference in rotational speed between the front and rear wheels 4 and 5) ΔN can be calculated from that slope. In other words, if the rotational speed of the motor 9 is detected while the vehicle 1 is traveling at a predetermined speed, the difference in rotational speed of the front and rear wheels 4 and 5 can be calculated based on the rotational speed of the motor 9. Since the rotational speed of the motor 9 can be detected by a high-precision sensor such as a resolver, in this embodiment of the invention, it is preferable to determine the difference in rotational speed of the front and rear wheels 4 and 5 based on the rotational speed of the motor 9.

[0030] As described above, the distribution mechanism 3 allows control of the difference in rotational speed and the driving force distribution ratio of the front and rear wheels 4 and 5 by controlling the motor 9, and an electronic control unit (ECU) 13 is provided to perform this control according to the driving state of the vehicle 1. The ECU 13 corresponds to the controller in this embodiment of the invention and is mainly composed of a microcomputer consisting of a processing element (CPU), memory elements (RAM, ROM), and interfaces. It is configured to perform calculations according to a preset program using data obtained from various sensors and data that has been stored in advance, and to output the result of the calculation as a control command signal.

[0031] Examples of input data include data from wheel speed sensors that detect the rotational speeds of the front wheels 4 and rear wheels 5, longitudinal and lateral acceleration of the vehicle 1, rotational speed of the motor 9, and data related to the driving mode selected by the mode selection switch 12 mentioned above. Examples of pre-stored data include threshold values ​​that serve as a reference value for determining the driving mode or driving state of the vehicle 1 from the difference in rotational speeds of the front and rear wheels 4 and 5, and correction values ​​that correct the target driving force distribution ratio using feed-forward control (F / F control) based on the control amount (correction torque value) of the motor 9's torque. The ECU 13 is configured to perform calculations based on this data to determine the target value for the difference in rotational speeds of the front and rear wheels 4 and 5, and to output control command signals such as the rotational speed of the motor 9 required to achieve that target value, or the torque of the motor 9 required to achieve the target driving force distribution ratio.

[0032] The ECU 13 uses the input data and pre-stored data described above to determine the driving state or driving mode for which differential limiting by the motor 9 is performed. If the determination is successful, it is configured to perform differential rotation speed control or drive force distribution control appropriate to that driving state or driving mode. Specifically, as shown in Figure 3, the ECU 13 has a functional configuration comprising a driving state determination unit 13a, a differential rotation speed deviation determination unit 13b, a first torque control unit 13c, a drive force distribution ratio correction unit 13d, and a second torque control unit 13e.

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

[0034] The differential rotation speed may be calculated based on wheel speed sensors (not shown) provided for each wheel, or it may be calculated based on the rotation speed of motor 9. Furthermore, the threshold value may be predetermined in the design by conducting experiments or simulations for each assumed driving condition in which vehicle 1 may operate.

[0035] Furthermore, the driving conditions to be judged include driving on roads with a high coefficient of road friction (road surface μ) while minimizing wheel slippage as much as possible (so-called grip driving), cornering in so-called grip driving conditions, driving on roads with a low road surface μ such as compacted snow roads, muddy roads where getting stuck is likely to occur, and rocky roads with severe unevenness (rocky roads), and driving while applying large torque to the front and rear wheels 4 and 5 to actively or intentionally cause wheel slippage (so-called drift driving).

[0036] The differential rotation speed deviation determination unit 13b is a functional unit that determines whether 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 where the differential rotation speed is smaller than a threshold. When driving without actively or intentionally causing slippage of the wheels, the slippage of the wheels is zero, except for the minute slippage that is unavoidable in order to generate driving force between the wheels and the road surface. Therefore, when vehicle 1 is driving in a straight line, the differential rotation speed is virtually zero. In contrast, when turning, a differential rotation occurs between the front wheels 4 and the rear wheels 5 due to the difference in turning radii. Also, in places such as over temporary fallen objects, puddles, or at river crossing points in narrow rivers, only one of the four wheels may slip temporarily, or it may slip repeatedly, or all four wheels may slip repeatedly. Thus, although the way in which differential rotation speed occurs can be predicted to some extent for each road surface condition or driving state, it varies, so the target differential rotation speed is set according to the detected driving state or the driving state that is scheduled to be driven in the near future.

[0037] To further explain the target difference rotation speed, it is preferable to change the target difference rotation speed according to the driving state of vehicle 1 and the road surface conditions, such as the coefficient of friction and the state of unevenness of the road surface. For example, when turning in grip driving, the target difference rotation speed is calculated based on the trajectories of the front and rear wheels 4 and 5, which are 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 and 5 cannot be geometrically determined, and therefore the target difference rotation speed is set to "0". This is also the case when driving on rough roads such as muddy roads, low-μ roads, or rocky roads with many uneven surfaces, and the target rotation speed is set to "0". The determination of drift driving can be made based on whether the mode selection switch 12 mentioned above is selected. The determination of grip driving can be made based on whether drift driving is not selected in the mode selection switch 12 mentioned above.

[0038] If the differential rotation speed matches the target differential rotation speed, neither the front nor rear wheels 4 or 5 will experience excessive or unexpected slippage, and vehicle 1 will be able to drive in a stable manner. Conversely, if a deviation occurs, either the front or rear wheels 4 or 5 will rotate outside the target range or become locked, impairing or potentially impairing the driving stability of vehicle 1. A first torque control unit 13c is provided as a functional configuration to resolve or correct such conditions. This first torque control unit 13c is configured to control the torque of the motor 9 to reduce the deviation between the differential rotation speed and the target differential rotation speed.

[0039] An example of torque control will be explained with reference to Figure 4. Figure 4 is a collinear diagram of the differential mechanism constituting the distribution mechanism 3, showing an example where, when vehicle 1 is driving on a straight road with grip, the differential rotation speed deviates from the target differential rotation speed, creating a deviation between the two, and the torque of motor 9 is controlled to correct this deviation. If the vehicle is driving on a straight road with grip, the differential rotation speed should be virtually zero, so the rotation speeds of each rotating element constituting the differential mechanism will be the same, for example, as shown by the straight line L1 in Figure 4. That is, the target differential rotation speed is zero. On the other hand, if the rotation speed of the rear wheel 5 increases for some reason, such as slippage in the rear wheel 5, and a differential rotation speed is created between it and the front wheel 4, the rotation speed of the ring gear R increases relative to the rotation speed of the carrier C, as shown by the dashed line L2 in Figure 4, and the rotation speeds of the sun gear S and the motor 9 connected to it decrease.

[0040] To reduce the deviation of the resulting differential rotation speed from the target differential rotation speed, the rotation speed of the sun gear S should 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 direction in Figure 4). Since this torque control is for reducing the deviation of the differential rotation speed, the torque of the motor 9 is controlled by feedback control (F / B control) with 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 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 it is necessary to generate a predetermined differential rotation speed, such as during turning.

[0041] Figure 5 shows a schematic time chart illustrating the change in motor 9's torque to minimize the differential rotation speed deviation when the rotation speed deviates from its target value. In Figure 5, the target value of the differential rotation speed is shown by a straight line Ln, and the torque of motor 9 when the differential rotation speed matches the target value is shown by a straight line Lt. When the differential rotation speed matches the target value, the torque of motor 9 is controlled to maintain that rotation state, and the ratio of the driving force distribution to the front wheels 4 and rear wheels 5 changes according to the controlled torque of motor 9. In other words, driving force distribution ratio control is performed according to the driving conditions such as the turning radius. If the differential rotation speed changes from this state and a deviation from the target value occurs, as shown by the thin line in Figure 5, the torque of motor 9 is F / B controlled (rotation speed F / B control) to eliminate or reduce the deviation, and the torque of motor 9 changes as shown by the thin line in Figure 5.

[0042] The drive force distribution ratio correction unit 13d is a functional configuration that performs the drive force distribution ratio to the front wheels 4 and rear wheels 5, which is the basis for controlling the torque of the motor 9, prior to controlling the motor torque. This correction is performed in driving conditions where the difference in rotational speed exceeds a predetermined threshold, such as when driving on rough roads such as low-μ roads, muddy roads or rocky roads, or when drifting, in which the front and rear wheels 4 and 5 are actively or intentionally slipped. When the wheels slip unintentionally or intentionally, a difference in rotational speed occurs between the front and rear wheels 4 and 5, but since the rotational speed of the slipped wheel cannot be defined, in this embodiment of the invention, the target difference in rotational speed is set to "0", and the torque of the motor 9 to converge the difference in rotational speed between the front and rear wheels 4 and 5 to zero is controlled based on a value obtained by correcting the target drive force distribution ratio with the F / B control amount of the motor torque. The drive force distribution ratio correction unit 13d performs the correction on the target drive force distribution ratio.

[0043] The differential rotational speed, determined based on the rotational speed of motor 9, reflects the actual state of vehicle 1. If this differential rotational speed deviates from the target differential rotational speed, the torque of motor 9 is controlled to eliminate the deviation. Controlling the torque of motor 9 to eliminate the deviation in differential rotational speed changes the torque between the front wheels 4 and the rear wheels 5, i.e., the driving force distribution ratio. Therefore, the driving force distribution ratio correction unit 13d replaces the amount of torque control of motor 9 to correct or eliminate the deviation in differential rotational speed with an amount of change in the driving force distribution ratio, and corrects the target driving force distribution ratio using this as the correction amount for the target driving force distribution ratio. In this case, as mentioned above, the torque of motor 9 changes sequentially by F / B control, so the driving force distribution ratio changes gradually in accordance with that change. The target driving force distribution ratio can be determined by calculating the dynamic load of the four front and rear wheels from the longitudinal and lateral acceleration of vehicle 1 to determine the front-to-rear load distribution.

[0044] The second torque control unit 13e is configured to control the torque of the motor 9 to achieve the corrected target driving force distribution ratio as described above. The torque of the motor 9 required to match the differential rotation speed to the target value is determined geometrically based on the configuration of the differential mechanism constituting the distribution mechanism 3, as explained with reference to the collinear diagram shown in Figure 4. That is, the second torque control unit 13e controls the motor 9 to achieve the torque determined by the corrected target driving force distribution ratio, as explained with reference to Figure 5 above.

[0045] An example of the control performed by the ECU13 described above will be explained with reference to Figure 6. Figure 6 is a flowchart for explaining the control performed in this embodiment of the invention, and the routine shown here is repeatedly executed when the vehicle 1 is running. First, it is determined whether or not the control that limits the differential rotation of the front and rear wheels 4 and 5 (differential limiting control) is prohibited (OFF or not) (step S1). If any of the rotating elements in the differential mechanism that constitutes the distribution mechanism 3 slip, torque will not be transmitted to the other rotating elements, and conversely, if differential rotation is prohibited, the rotation of the front wheel 4 or rear wheel 5 will be restricted when turning, causing braking phenomena, etc. The differential limiting is configured to be selectively executed so as to respond to either of these situations, and in step S1, it is determined whether or not such differential limiting has been selected. The selection of differential limiting is usually done by the driver by operating a switch, and therefore the determination in step S1 can be made by whether or not that switch operation has been performed. Furthermore, if driving on so-called rough roads such as muddy roads, low-friction roads, or rocky roads is planned or recognized by the driver, a mode for driving on such road surfaces is selected using the mode selection switch 12 mentioned above. In this case, the differential limiting control is turned ON along with the selection of the driving mode.

[0046] If the result of the judgment in step S1 is "yes", the torque of motor 9 is calculated based on the target driving force distribution ratio (step S2). Then, the process returns. When accelerating vehicle 1 or driving uphill, it is preferable to increase the torque handled by the rear wheels 5, and when decelerating or driving downhill, it is preferable for the torque to be handled by the front wheels 4. The distribution ratio of the driving force to the front and rear wheels 4 and 5 can be determined according to the driving conditions. In step S2, the torque of motor 9 is calculated based on the target driving force distribution ratio predetermined according to the conditions of the road.

[0047] On the other hand, if the result of the judgment 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 from the wheel speed sensors of the front and rear wheels 4 and 5, but as mentioned above, it is preferable to calculate it based on the rotation speed of the motor 9. In addition, the differential rotation speed calculated in step S3 may be a rotation speed determined in the design corresponding to the selected driving mode. That is, when drifting or driving on rough roads such as compacted snow or rocky roads, there is a high possibility that either the front or rear wheels 4 or 5 will slip, and the differential rotation speed is set to a large value in advance to anticipate such conditions. In that case, in step S3, the differential rotation speed is determined by reading the differential rotation speed corresponding to the selected driving mode.

[0048] Next, it is determined whether the differential rotation speed obtained in step S3 is smaller than a predetermined threshold (step S4). This threshold is predetermined to be approximately the maximum value of the differential rotation speed expected in a normal driving state where all four wheels maintain grip and no abnormalities such as tire bursts occur. Therefore, in step S4, it is determined whether the vehicle is in a driving state where either the front or rear wheels 4 or 5 are slipping significantly. In other words, the functional configuration that performs the control of steps S1, S3, and S4 above corresponds to the driving state determination unit in this embodiment of the invention.

[0049] If the result of the judgment in step S4 is "yes" because the differential rotation speed is below the threshold, it is determined whether the differential rotation speed matches the target differential rotation speed (step S5). If the result of the judgment in step S5 is "yes" because the differential rotation speed matches the target differential rotation speed, the process proceeds to step S2 as described above, and the torque of the motor 9 is calculated based on the target driving force distribution ratio.

[0050] Conversely, if the result of the judgment in step S5 is "no," that is, if slip occurs in either the front or rear wheel 4 or 5 while driving in a manner that prevents the wheels from slipping, the torque of motor 9 is fed-basis controlled to match the differential rotation speed to the target differential rotation speed, that is, to reduce the deviation between the differential rotation speed and the target value (step S6). Then, the vehicle returns. In this case, sufficient grip is maintained on all four wheels without causing excessive or unexpected slip, thus stabilizing the behavior of vehicle 1. It is preferable to set upper and lower limits for the rotation speed fed-basis control of the torque of motor 9. In that case, in vehicle 1, which allows selection of driving modes such as normal mode and sport mode, it is preferable to change the upper and lower limits according to the selected driving mode. For example, in sport mode, the range of the upper and lower limits is wider than in normal mode.

[0051] In contrast, if the differential rotation speed exceeds a threshold due to drift driving or driving on rough roads, and as a result the judgment 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 correction unit 13d, and the target driving force distribution ratio is corrected by adding a correction value corresponding to the rotational speed F / B control amount of the motor 9's torque, which reduces the deviation between the differential rotation speed and the target differential rotation speed, to the target driving force distribution ratio obtained from the longitudinal acceleration and 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 the same as the control in step S2, and is the control performed by the second torque control unit 13e described above.

[0053] Therefore, in this case, the target drive force distribution ratio is corrected based on the actual difference in rotational speed occurring in vehicle 1, and the torque of motor 9 is controlled based on the corrected target drive force distribution ratio. As a result, changes in the torque of the front and rear wheels 4 and 5 or their distribution ratio are mitigated, and the behavior of vehicle 1 can be stabilized.

[0054] It should be noted that this invention is not limited to the embodiments described above and can be implemented with appropriate modifications. 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. Power source (engine) 3 Distribution mechanism 4 Front wheels 5 Rear wheels 6. Rear wheel output axle 7 Front wheel output axle 8 Transfer 9 Motors 10. Accelerator pedal 11 Brake pedal 12 Mode Selection Switch 13. Electronic control units (ECUs, controllers) 13a Driving state determination unit 13b Differential rotation speed deviation determination unit 13c Torque Control Unit 13d Drive force distribution ratio correction unit 13e Torque Control Unit C Carrier R Ring Gear S Sangiya

Claims

1. A vehicle drive force transmission control device comprising a distribution mechanism that distributes the torque output by a drive 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 the 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 drive 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. The system further includes a controller for controlling the motor, The aforementioned controller, A driving state determination unit that determines whether the driving state is such that the difference in rotational speed is smaller than or larger than a predetermined threshold, When it is determined that the driving condition is such that the differential rotation speed is smaller than the threshold, a differential rotation speed deviation determination unit determines whether or not there is a deviation between the differential rotation speed and a predetermined target differential rotation speed. When the differential rotation speed deviation determination unit determines that the aforementioned deviation exists, a first torque control unit controls the torque of the motor based on the deviation so that the deviation becomes smaller, When the driving state determination unit determines that the differential rotation speed is equal to or greater than the predetermined threshold, the driving force distribution ratio correction unit corrects the 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. The system includes a second torque control unit that controls the torque of the motor based on the target drive force distribution ratio corrected by the drive force distribution ratio correction unit. A vehicle power transmission control device characterized by the following features.

2. A vehicle drive 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 power transmission control device characterized by the following features.

3. A vehicle drive force transmission control device according to claim 1 or 2, The controller sets the predetermined target differential rotation speed to "0" when the driving state determination unit determines that the differential rotation speed is equal to or greater than the predetermined threshold. A vehicle power transmission control device characterized by the following features.

4. A vehicle drive force transmission control device according to claim 1 or 2, The driving state determination unit determines, based on the differential rotation speed, whether the driving state is one in which the differential rotation speed is less than or greater than a predetermined threshold. A vehicle power transmission control device characterized by the following features.

5. A vehicle drive force transmission control device according to claim 1 or 2, The vehicle further includes a mode selection switch for selecting between a grip driving mode that suppresses wheel slip and a drift driving mode that causes wheel slip. The driving state determination unit determines that a driving state in which the grip driving mode is selected by the mode selection switch is a driving state in which the differential rotation speed is less than a predetermined threshold, or that a driving state in which the drift driving mode is shifted by the mode selection switch is a driving state in which the differential rotation speed is greater than a predetermined threshold. A vehicle power transmission control device characterized by the following features.

6. A vehicle drive force transmission control device according to claim 1 or 2, The vehicle further includes a mode selection switch for selecting an off-road driving mode for driving on rough terrain where there is a high possibility that any of the wheels will lose grip. The driving state determination unit determines that the driving state in which the rough road driving mode is selected by the mode selection switch is a driving state in which the differential rotation speed is greater than a predetermined threshold. A vehicle power transmission control device characterized by the following features.

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