JP4662060B2 - Vehicle driving force distribution control device - Google Patents

Description

  The present invention relates to a driving force distribution control device that controls driving force distribution between front and rear wheels of a vehicle.

  A full-time four-wheel drive vehicle that always distributes the engine driving force to the four wheels, or the engine driving force is always transmitted to one of the front wheels or the rear wheels, and a part of the driving force is front wheels or rear wheels as required. In an on-demand four-wheel drive vehicle that distributes to the other side, an electronically controlled drive force distribution device provided between the front and rear wheels causes the drive force distribution to act between the front and rear wheels according to the running state of the vehicle. The driving characteristics of the vehicle are realized (for example, see Patent Document 1).

The technique disclosed in Patent Document 1 is intended to suppress understeer and oversteer during turning of the vehicle, and is applied to an FR vehicle-based four-wheel drive vehicle. A transfer limiting device is provided between the front and rear wheels of the vehicle as a driving force distribution device that distributes a part of the driving force of the rear wheel to the front wheel side, and generates a differential limiting force between the left and right wheels of the rear wheel. When the wheel speed of the outer turning wheel is higher than the wheel speed of the inner turning wheel and the inner wheel is estimated to be gripping, the driving force distributed to the front wheels is reduced by reducing the driving force distribution between the front and rear wheels by the transfer. And the differential limiting force between the left and right wheels by the differential limiting device is reduced, thereby suppressing understeer.
Japanese Patent No. 2527204

  The technique of Patent Document 1 focuses on the differential rotation between the left and right wheels, and controls the driving force distribution by the transfer and the differential limiting force by the differential limiting device. The differential rotation is only one of the indices indicating the turning state of the vehicle, and is insufficient for appropriately controlling the driving force distribution and the differential limiting force. For example, even if the differential rotation between the left and right wheels or the front and rear wheels is the same, the optimal driving force distribution and differential limiting force differ depending on whether the vehicle's steering characteristics are understeer or oversteer. Depending on the turning state of the vehicle, the driving force distribution of the transfer and the differential limiting force of the differential limiting device are improperly controlled, resulting in a problem that good steering characteristics cannot be realized.

  The present invention has been made to solve such problems, and the object of the present invention is to appropriately control the driving force distribution between the front and rear wheels based on an index that represents the turning state of the vehicle. Accordingly, it is an object of the present invention to provide a driving force distribution control device for a vehicle that can realize a good steering characteristic regardless of the turning state of the vehicle.

  In order to achieve the above object, the invention according to claim 1 is provided between the front and rear wheels of the vehicle, and constantly distributes the driving force from the driving source to the front and rear wheels and can vary the driving force distribution, Control amount calculation means for calculating a control amount corresponding to turning as a correction amount for driving force distribution between the front and rear wheels based on the turning state of the vehicle, steer characteristic determination means for determining the current steering characteristic of the vehicle, and wheels of the front and rear wheels The turning correspondence control amount is determined according to the combination of the wheel speed detecting means for detecting each speed, the steer characteristic determined by the steer characteristic determining means and the magnitude relationship between the wheel speeds of the front and rear wheels detected by the wheel speed detecting means. And a driving force distribution control unit that operates on the increase correction side or the decrease correction side and controls the driving force distribution unit based on the corrected driving force distribution.

  Accordingly, the control amount calculation means calculates a turning correspondence control amount as a correction amount for the driving force distribution between the front and rear wheels based on the turning state of the vehicle, and the steering characteristic determination means calculates the current vehicle steering characteristic, for example, understeer. Whether there is oversteer or not is determined. On the other hand, the wheel speeds of the front and rear wheels are detected by the wheel speed detection means, and the turning correspondence control amount is increased or decreased by the driving force distribution control means according to the combination of the steering characteristic and the wheel speed relationship of the front and rear wheels. Acting on the correction side, the corrected driving force distribution is applied to the control of the driving force distribution means.

  While the vehicle is turning, the torque moves between the front and rear wheels via the driving force distribution means according to the relationship between the front and rear wheel speeds, and the driving force generated by the front and rear wheels increases and decreases according to the amount of torque movement. The yaw moment of the vehicle changes. Assuming the direction of torque movement between the front and rear wheels based on the magnitude relationship between the front and rear wheels, the driving between the front and rear wheels so that the yaw moment of the vehicle changes to an appropriate direction, for example, the direction of suppressing understeer or oversteer. Force distribution is increased or decreased. As a result, not only the wheel speeds of the front and rear wheels but also the steering characteristics of the vehicle are reflected and the driving force distribution between the front and rear wheels is controlled in an integrated manner, and a good steering characteristic is realized regardless of the turning state of the vehicle.

  As a preferred embodiment, the control amount calculation means includes a control amount for differential rotation based on a difference in wheel speed between the front and rear wheels, an acceleration corresponding control amount based on an acceleration state of the vehicle accompanying an accelerator operation, and a brake It is configured to calculate at least one of the deceleration control amount based on the deceleration state of the vehicle accompanying the operation as the base control amount of the driving force distribution, and the driving force distribution control means controls the base control amount to turn. It is desirable to configure to increase or decrease based on the amount.

  Accordingly, at least one of the control amount corresponding to the differential rotation, the control amount corresponding to the acceleration, and the control amount corresponding to the deceleration is calculated as the base control amount of the driving force distribution, and this base control amount is corrected to increase or decrease based on the turning control amount. It is corrected. In other words, since the base control amount is corrected based on the turning control amount, not only the increase correction but also the reduction correction is always possible, and the turning control amount is reliably reflected in the driving force distribution between the front and rear wheels. Can do.

  According to a second aspect of the present invention, in the first aspect, the steering characteristic determining unit detects a target turning state index determining unit that determines a target turning state index based on a running state of the vehicle, and detects an actual turning state index of the vehicle. An actual turning state index detecting means for determining the current vehicle steer characteristic based on the target turning state index and the actual turning state index, and the control amount calculating means is determined as the steer characteristic by the steer characteristic determining means. Grip limit index estimating means for identifying the slip wheel of the front and rear wheels based on the understeer and oversteer and estimating the grip limit index correlating with the grip limit from the driving force and lateral force of the slip wheel, and understeer based on the turning state of the vehicle Or, calculate the required yaw moment to suppress oversteer and the slip wheel that can achieve the required yaw moment. The slip wheel required to achieve the required lateral force calculated by the required lateral force calculating means on the premise of the required lateral force calculating means for calculating the lateral force and the grip limit index calculated by the grip limit index calculating means. Driving force reduction amount calculating means for calculating the driving force reduction amount of the slip wheel, and the slip wheel driving force reduction amount calculated by the driving force reduction amount calculating means as a correction amount for the driving force distribution to be applied between the front and rear wheels. The turn control amount is calculated according to the above.

  Therefore, the steering characteristic of the vehicle is determined based on the target turning state index determined by the target turning state index determination unit and the actual turning state index detected by the actual turning state index detection unit. The occurrence of understeer during turning of the vehicle is caused by slip due to insufficient lateral force of the front wheel, and occurrence of oversteer is caused by slip due to insufficient lateral force of the rear wheel, so when the understeer is determined as the steer characteristic, the front wheel becomes a slip wheel. When the vehicle is oversteered, the rear wheel is specified as a slip wheel.

  Then, a grip limit index correlating with the grip limit from the driving force and lateral force of the slip wheel, for example, a friction circle defining a grip limit for the driving force and the lateral force is estimated by the grip limit index estimating means. Further, after calculating the required yaw moment for suppressing understeer or oversteer by the required lateral force calculation means based on the turning state of the vehicle, the required lateral force of the slip wheel that can achieve the required yaw moment is calculated, and the grip The driving force decrease amount of the slip wheel for achieving the required lateral force on the assumption of the limit index is calculated by the driving force decrease amount calculating means, and the turning control amount is calculated by the control amount calculating means according to the driving force decrease amount. Is done.

  That is, the vehicle steer characteristic is determined based on the specific target turning state index and the actual turning state index, and on the premise of the grip limit index that correlates with the grip limit of the slip wheel, Turning based on specific calculated values such as the required yaw moment to suppress oversteer, the required lateral force of the slip wheel that can achieve the required yaw moment, and the amount of decrease in the driving force of the slip wheel to achieve the required lateral force Since the corresponding control amount is calculated, it is possible to calculate the turn corresponding control amount that is more realistic compared to, for example, the case where the turn corresponding control amount is set based on past empirical rules and experimental results.

As a preferred aspect, the required lateral force calculating means calculates a required yaw moment for suppressing understeer or oversteer based on a deviation between the target yaw rate determined from the turning state of the vehicle and the actual yaw rate, and the required yaw moment It is desirable that the required lateral force of the slip wheel is calculated from the above.
With such a configuration, it is possible to calculate an appropriate required yaw moment and thus a more appropriate turning correspondence control amount based on a yaw rate that directly represents the turning state of the vehicle.

  According to a third aspect of the present invention, in the second aspect, when the driving force distribution control means determines that the front wheel speed is higher than the rear wheel speed, the steer characteristic determined by the steer characteristic determination means is understeer. While the driving force distribution between the front and rear wheels is increased and corrected based on the turning control amount, when the steering characteristic is oversteer, the driving force distribution between the front and rear wheels is reduced and corrected based on the turning control amount, and the front wheel speed is adjusted to the rear wheel. If the steering speed is determined to be lower than the vehicle wheel speed, the steering force distribution between the front and rear wheels is reduced and corrected based on the turning control amount when the steering characteristic determined by the steering characteristic determination means is understeer, while when the steering characteristic is oversteer The driving force distribution between the wheels is corrected to increase based on the turning control amount.

  Therefore, the torque movement by the driving force distribution between the front and rear wheels is performed from the high wheel speed side to the low wheel speed side. Therefore, when the front wheel speed is higher than the rear wheel speed, the front wheel is connected via the driving force distributing means. If the torque is moving from the rear wheel to the rear wheel, and the driving force distribution is corrected to be increased based on the turning control amount, assuming that the steering is understeer, the lateral force increases and the yaw moment increases as the driving force of the front wheel decreases. If understeer is suppressed by this and the driving force distribution is corrected to be reduced because it is oversteering, the lateral force increases as the rear wheel driving force decreases, and the oversteer is suppressed due to the decrease in yaw moment.

  Further, when the front wheel speed is lower than the rear wheel speed, the torque is moved from the rear wheel to the front wheel via the driving force distributing means, and the driving force is distributed based on the turn corresponding control amount as being understeer. Is corrected to decrease, the lateral force increases with a decrease in the driving force of the front wheels, and understeer is suppressed due to an increase in the yaw moment, and if the driving force distribution is corrected to increase due to oversteering, the driving force of the rear wheels With the decrease, the lateral force increases and the oversteer is suppressed by the decrease of the yaw moment.

As described above, according to the vehicle driving force distribution control device of the first aspect of the present invention, the front and rear according to the combination of the current steering characteristic that directly represents the turning state of the vehicle and the magnitude relationship between the wheel speeds of the front and rear wheels. Since the driving force distribution between the wheels is corrected to increase or decrease, the driving force distribution between the front and rear wheels can be appropriately controlled, and a good steering characteristic can be realized regardless of the turning state of the vehicle.
According to the vehicle driving force distribution control device of the second and third aspects of the invention, in addition to the first aspect, the vehicle steering force index is determined based on the specific target turning state index and the actual turning state index. Based on the grip limit index that correlates with the grip limit of the slip wheel, the specific yaw moment to suppress the understeer and oversteer determined as the steer characteristics, the required lateral force of the slip wheel, the amount of decrease in driving force, etc. Since the turning control amount applied to the driving force distribution means is calculated based on the calculated value, the driving force distribution between the front and rear wheels can be appropriately controlled based on the turning correspondence control amount that is more realistic, and the vehicle understeer and Oversteer can be reliably suppressed.

Hereinafter, an embodiment of a vehicle driving force distribution control apparatus embodying the present invention will be described.
FIG. 1 is an overall configuration diagram showing a vehicle driving force distribution control device of this embodiment, and FIG. 2 is a partially enlarged view showing details of a center differential and a front differential. As shown in these drawings, a center differential 1 (driving force distribution means) and a front differential 2 (hereinafter referred to as a center differential 1 and a front differential 2) are provided at the front portion of the vehicle, and ring gears on the outer periphery of the center differential 1 are provided. The driving force of an engine (drive source) (not shown) is input to 1a through the transmission. The center differential 1 has a general configuration in which a pair of side gears 4a and 4b are engaged with a pinion gear 3. When the pinion gear 3 is rotated together with the ring gear 1a by the engine, the driving force is a rotational difference between the left and right side gears 4a and 4b. Is distributed at a ratio of 50:50.

  One side gear 4 a of the center differential 1 is connected to the inner casing 5 of the front differential 2, and a pair of planetary gears 6 provided in the inner casing 5 is connected to a sun gear 8 formed at the inner ends of the left and right drive shafts 7. Each is engaged. When the inner casing 5 rotates together with the one side gear 4a, the rotation is transmitted to the drive shaft 7 via the planetary gear 6 and the sun gear 8, and the left and right front wheels 9 are rotationally driven while allowing a rotation difference by the rotation of the planetary gear 6. The

  The other side gear 4 b of the center differential 1 is connected to the outer casing 10 of the front differential 2, and a ring gear 10 a on the outer periphery of the outer casing 10 meshes with a pinion gear 12 fixed to the front end of the propeller shaft 11. The pinion gear 13 fixed to the rear end of the propeller shaft 11 meshes with a ring gear 14a of a rear differential (hereinafter referred to as rear differential) 14, and when the outer casing 10 rotates together with one side gear 4b, the rotation causes the propeller shaft 11 to rotate. Then, it is transmitted to the rear differential 14, and the left and right rear wheels 16 are rotationally driven through the drive shaft 15 while allowing a rotational difference by the rear differential 14.

  An electromagnetic clutch 17 (driving force distribution means) is provided between the inner casing 5 and the outer casing 10 of the front differential 2, and depending on the engagement state of the electromagnetic clutch 17, between the inner casing 5 and the outer casing 10, That is, the driving force distribution between the front wheel 9 and the rear wheel 16 changes from the above 50:50. The principle of adjusting the driving force distribution is not limited to this, and can be arbitrarily changed as long as the driving force distribution can be adjusted using a control device such as a pump or a motor. The engagement state of the clutch may be adjusted by operating the hydraulic piston with the supplied hydraulic oil.

  On the other hand, a 4WD ECU 21 is installed in the interior of the vehicle. The 4WD ECU 21 includes an input / output device (not shown), a storage device (ROM, RAM, etc.) for storing control programs and control maps, and a central processing unit ( CPU), a timer counter, and the like. On the input side of the 4WD ECU 21 are a steering angle sensor 22 that detects the steering angle θstr of the steering, a vehicle speed sensor 23 that detects the vehicle speed V, a yaw rate sensor 24 that detects the yaw rate YR of the vehicle, and the wheels 4 and 14 of the vehicle. Various sensors such as a wheel speed sensor 25 for detecting wheel speeds NFR, NFL, NRR, NRL and a lateral acceleration sensor 26 for detecting a lateral acceleration GY generated when the vehicle turns are connected, and on the output side of the ECU for 4WD, Various devices such as the electromagnetic clutch 17 are connected.

  The 4WD ECU 21 controls the engagement state of the electromagnetic clutch 17 based on the detection information from the various sensors. In the present embodiment, the driving force between the front and rear wheels 9 and 16 by the electromagnetic clutch 17 is based on a friction circle (grip limit index) that correlates with the grip limit of the front and rear wheels 9 and 16 for the purpose of suppressing understeer and oversteer during vehicle turning. The distribution control is executed, and the procedure for setting the control amount of the electromagnetic clutch 17 will be described below.

  The setting of the control amount of the electromagnetic clutch 17 is executed according to a different procedure depending on whether the vehicle steer characteristic is understeer or oversteer, and will be described separately for each steer characteristic. In the present embodiment, the ECU 21 is currently based on a comparison result between an actual yaw rate YR (actual turning state index) detected by the yaw rate sensor 24 (actual turning state index detecting means) and a target yaw rate YT (target turning state index) described later. After determining the steering characteristic occurring in the vehicle (steer characteristic determination means), the control amount is set according to the steering characteristic. However, the steer characteristic determination method is not limited to this, and can be arbitrarily changed.

  FIG. 3 is a block diagram showing the procedure for setting the control amount of the electromagnetic clutch 17 executed by the ECU 21 when understeer occurs, and FIGS. 4 and 5 are schematic views showing the control status of the driving force distribution based on the set control amount. First, the case where understeer occurs according to these figures will be described. 4 and 5 schematically show a two-wheel model by averaging the wheel speeds NFR and NFL of the left and right front wheels 9 and the wheel speeds NRR and NRL of the left and right rear wheels 16, and FIG. 4 shows the front wheel average wheel speed NFave. FIG. 5 shows a case where the rear wheel average wheel speed N Rave is lower than the rear wheel average wheel speed N Rave.

  4 and 5, the length and direction of the solid black and white arrows Adrv in the vertical direction attached to the front and rear wheels 9 and 16 represent the magnitude and direction of the driving force, and the left direction attached to the front and rear wheels 9 and 16. The length of the black painted straight arrow Acornering represents the magnitude of the lateral force, while the white straight arrows Adrv and Acornering represent the driving force and the lateral force based on the control amount (yaw rate corresponding control amount Ty) corresponding to the steering characteristic. It shows the correction status for force. The lengths of the white rotating arrows Arev attached to the front and rear wheels 9 and 16 represent the front wheel average wheel speed NFave and the rear wheel average wheel speed NRave. The direction represents the torque movement amount and the movement direction by the driving force distribution according to the final control amount T of the electromagnetic clutch 17.

  Understeer of the vehicle is a phenomenon caused by slip due to insufficient lateral force of the front wheel 9, and it is assumed that the front wheel 9 at this time uses the driving force and the grip against the lateral force defined by its own friction circle to the limit. In other words, it can be interpreted that there is room for increasing the lateral force due to a decrease in the driving force of the front wheels 9 to suppress understeer. On the other hand, the driving force of the front wheel 9 changes according to the torque distributed from the front wheel 9 to the rear wheel 16 via the electromagnetic clutch 17 or the torque transmitted from the rear wheel 16 to the front wheel 9. It can be adjusted according to the driving force distribution among the sixteen.

  Under the above viewpoint, the control amount of the electromagnetic clutch 17 during understeering is set according to FIG. First, the front wheel driving force calculation unit 31 calculates the driving force FX generated by the front wheels 9 based on the engine torque and the driving force distribution between the front and rear wheels 9 and 16, and the front wheel lateral force calculation unit 32 calculates the driving force FX. A lateral force FCF generated by the front wheels 9 is calculated according to the following equation (1) from the detected lateral acceleration GY and the previously determined front wheel shared mass MF.

FCF = MF × | GY | ... (1)
The front wheel driving force FX from the front wheel driving force calculation unit 31 and the front wheel lateral force FCF from the front wheel lateral force calculation unit 32 are input to the front wheel friction circle calculation unit 33. Based on these information, the front wheel friction circle calculation unit 33 calculates the following equation: According to (2), the front wheel friction circle FFR is calculated as the radius of the friction circle FFR (grip limit index estimation means).

FFR = √ (FX ² + FCF ² ) (2)
The grip force exerted by the front wheels 9 is affected by various factors such as differences in tire wear, differences in road surface friction coefficient depending on weather (sunny weather and snowfall) and road surface form (paved road and dirt), Since the friction circle FFR is estimated from the driving force FX and lateral force FCF when the front wheel 9 reaches the grip limit and causes understeer, the estimated friction circle FFR has a magnitude that accurately correlates with the grip force of the front wheel 9. Become.

  The yaw moment calculation unit 34 calculates a target yaw rate YT based on the steering angle θstr from the steering angle sensor 22 and the vehicle speed V from the vehicle speed sensor 23 (target turning state index determination means), and the target yaw rate YT and the yaw rate sensor 24 Based on the detected deviation ΔY from the actual yaw rate YR, a required yaw moment YAWM required to suppress understeer is calculated. The required yaw moment YAWM is input to the front wheel required lateral force calculation unit 35, and the front wheel required lateral force calculation unit 35 calculates the required lateral force FCFT of the front wheels 9 required to achieve the required yaw moment YAWM according to the following equation (3). (Required lateral force calculation means).

FCFT = YAWM / LF (3)
Here, LF is the distance from the center of gravity to the front axis.
The front wheel friction circle FFR from the front wheel friction circle calculation unit 33, the front wheel lateral force FCF from the front wheel lateral force calculation unit 32, and the front wheel requested lateral force FCFT from the front wheel requested lateral force calculation unit 35 are supplied to the front wheel driving force decrease amount calculation unit 36. The front wheel driving force decrease amount calculation unit 36 receives the front wheel 9 driving force decrease amount FXT necessary to increase the lateral force FCF of the front wheel 9 by the amount corresponding to the required lateral force FCFT on the assumption of the front wheel friction circle FFR. It is calculated according to the following equation (4) (driving force reduction amount calculating means).

FXT = | FX | −√ (FFR ² − (FCF + FCFT) ² ) (4)
The calculated driving force decrease amount FXT of the front wheel 9 is input to the control amount calculation unit 37, and the control amount calculation unit 37 calculates the yaw rate corresponding control amount Ty as the driving force distribution corresponding to the driving force decrease amount FXT by the following equation (5). (Control amount calculation means).
Ty = FXT × R / FHG ……… (5)
Here, R is the tire radius of the front wheel 9, and FHG is the gear ratio between the ring gear 10a and the pinion gear 12.

  On the other hand, the base control amount calculation unit 38 calculates a base control amount Tbase other than the yaw rate corresponding control amount Ty. For example, a differential rotation control amount is calculated based on the difference between the front wheel average wheel speed NFave and the rear wheel average wheel speed NRave when the vehicle is turning, and the initial slip is suppressed based on the accelerator operation amount during acceleration of the vehicle accompanying the accelerator operation. The acceleration-related control amount is calculated, and when the vehicle decelerates due to the braking operation, the deceleration-related control amount for stabilizing the vehicle posture is calculated based on the vehicle deceleration, etc., and the sum total of these control amounts is the base Set as control amount Tbase. The wheel speed determination unit 39 calculates the front wheel average wheel speed NFave and the rear wheel average wheel speed NRave from the wheel speeds NFR, NFL, NRR, and NR, and the front wheel average wheel speed NFave and the rear wheel average wheel speed NRave are calculated. A magnitude relationship is determined.

  The magnitude of the yaw rate corresponding control amount Ty from the control amount calculation unit 37, the base control amount Tbase from the base control amount calculation unit 38, and the front wheel average wheel speed NFave and the rear wheel average wheel speed NRave from the wheel speed determination unit 39. The relationship is input to the final control amount calculation unit 40, and the final control amount calculation unit 40 calculates the final control amount T according to the conditions shown in FIG. The actual driving force distribution between the front and rear wheels 9 and 16 is controlled based on the final control amount T set in this way. That is, the duty ratio corresponding to the final control amount T is set from a map (not shown), and the engagement state is adjusted by the excitation of the electromagnetic clutch 17 based on the duty ratio. As a result, the driving force is distributed between the front and rear wheels 9 and 16. Is adjusted to a value corresponding to the final control amount T (driving force distribution control means).

  The principle that the distribution ratio of the driving force to the front and rear wheels 9 and 16 changes according to the distribution of the driving force by the electromagnetic clutch 17 is that the wheel speed of the front and rear wheels 9 and 16 changes from the higher side to the lower side according to the driving force distribution. This is based on the occurrence of torque movement via the electromagnetic clutch 17. In the traveling state (NFave> NRave) where the average front wheel speed NFave is higher than the average rear wheel speed NRave shown in FIG. 4, the torque is moved from the front wheel 9 to the rear wheel 16 via the electromagnetic clutch 17, as described above. The front wheel 9 is at the grip limit. As shown in FIG. 3, in the final control amount calculation unit 40, the final control amount T is corrected to increase by the yaw rate corresponding control amount Ty, so that the actual driving force between the front and rear wheels 9 and 16 in accordance with the increase in the final control amount T. Distribution also increases. As a result, the amount of torque movement from the front wheel 9 to the rear wheel 16 increases, and the driving force of the rear wheel 16 increases while the driving force of the front wheel 9 decreases as shown by the white arrows Adrv and Acornering in FIG. At this time, the driving force of the front wheels 9 is reduced by an amount corresponding to the driving force reduction amount FXT calculated by the front wheel driving force reduction amount calculating unit 36, and the required lateral force calculated by the front wheel required lateral force calculating unit 35 is accordingly reduced. The lateral force of the front wheel 9 increases by the amount corresponding to FCFT, and the yaw moment of the vehicle increases by the amount corresponding to the requested yaw moment YAWM calculated by the yaw moment calculation unit 34 with the increase of the lateral force of the front wheel 9 and is generated in the vehicle. Understeer is suppressed.

  Further, in the traveling situation (NFave <NRave) where the average front wheel speed NFave shown in FIG. 5 is lower than the average rear wheel speed NRave, the torque is moved from the rear wheel 16 to the front wheel 9 via the electromagnetic clutch 17. 9 is at the grip limit. As shown in FIG. 3, since the final control amount T is corrected to decrease by the yaw rate corresponding control amount Ty in the final control amount calculation unit 40, the actual driving force between the front and rear wheels 9 and 16 in accordance with the decrease in the final control amount T. Distribution also declines. As a result, the amount of torque movement from the rear wheel 16 to the front wheel 9 decreases, and the driving force of the rear wheel 16 increases while the driving force of the front wheel 9 decreases as shown by the white arrows Adrv and Acornering in FIG. Accordingly, as described above, the lateral force increases as the driving force of the front wheels 9 decreases, and understeer is suppressed as the yaw moment increases.

Although not shown in FIG. 3, the yaw rate control amount Ty is not reflected in the calculation of the final control amount T when the steering characteristic is neutral steer even when the vehicle is not turning or is turning, and the base control amount is not reflected. Since Tbase is set as the final control amount T as it is, the driving force distribution control for suppressing the understeer as described above is not executed.
On the other hand, a case where oversteer occurs in a turning vehicle will be described. FIG. 6 is a block diagram showing a procedure for setting the control amount of the electromagnetic clutch 17 executed by the ECU 21 when oversteer occurs, and FIGS. 7 and 8 are schematic diagrams showing the control status of driving force distribution based on the set control amount. FIG. 7 shows a case where the front wheel average wheel speed NFave is higher than the rear wheel average wheel speed NRave, and FIG. 8 shows a case where the front wheel average wheel speed NFave is lower than the rear wheel average wheel speed NRave.

  Oversteer of the vehicle is a phenomenon caused by slip due to insufficient lateral force of the rear wheel 16, and the rear wheel 16 at this time uses the driving force and the grip against the lateral force defined by its own friction circle to the limit. In other words, it can be interpreted that there is room for oversteer to be suppressed by increasing the lateral force due to a decrease in the driving force of the rear wheels 16. On the other hand, the driving force of the rear wheel 16 changes according to the torque distributed from the front wheel 9 to the rear wheel 16 via the electromagnetic clutch 17 or the torque transmitted from the rear wheel 16 to the front wheel. It can be adjusted according to the driving force distribution among the sixteen.

  Under the above viewpoint, the control amount of the electromagnetic clutch 17 during oversteering is set according to FIG. First, the rear wheel driving force calculating unit 31 ′ calculates the driving force RX generated by the rear wheel 16 based on the engine torque and the driving force distribution between the front and rear wheels 9 and 16, and the rear wheel lateral force calculating unit 32 ′. From the lateral acceleration GY detected by the lateral acceleration sensor 26 and the rear wheel shared mass MR that is known in advance, the lateral force RCF generated by the rear wheel 16 is calculated according to the following equation (6).

RCF = MR × | GY |… (6)
The rear wheel driving force RX from the rear wheel driving force calculating unit 31 ′ and the rear wheel lateral force RCF from the rear wheel lateral force calculating unit 32 ′ are input to the rear wheel friction circle calculating unit 33 ′, and based on these information, the rear wheel driving force RX In the wheel friction circle calculation unit 33 ′, the rear wheel friction circle RFR is calculated as the radius of the friction circle RFR according to the following equation (7) (grip limit index estimation means).

RFR = √ (RX ² + RCF ² ) (7)
As with the front wheel 9, the friction circle RFR is also estimated for the rear wheel 16 from the driving force RX and lateral force RCF when the grip limit is reached and oversteer is generated. The magnitude correlates accurately with force.
The yaw moment calculation unit 34 ′ calculates a required yaw moment YAWM necessary for suppressing oversteer according to the same procedure as that for the understeer, and the rear wheel required lateral force calculation unit 35 ′ calculates the next required yaw moment YAWM. The required lateral force RCFT of the rear wheel 16 necessary for achieving the required yaw moment YAWM is calculated according to the equation (8) (required lateral force calculating means).

RCFT = YAWM / LR (8)
Here, LR is the distance from the center of gravity to the rear axis.
The rear wheel friction circle RFR from the rear wheel friction circle calculation unit 33 ′, the rear wheel lateral force RCF from the rear wheel lateral force calculation unit 32 ′, and the rear wheel requested lateral force RCFT from the rear wheel requested lateral force calculation unit 35 ′ are The rear wheel driving force decrease amount calculation unit 36 ′ inputs the rear wheel driving force decrease amount calculation unit 36 ′, which assumes the rear wheel friction force RFCF corresponding to the required lateral force RCFT on the premise of the rear wheel friction circle RFR. A driving force reduction amount RXT of the rear wheel 16 necessary for increasing the driving force is calculated according to the following equation (9) (driving force reduction amount calculating means).

RXT = | RX | −√ (RFR ² − (RCF + RCFT) ² ) (9)
The calculated driving force decrease amount RXT of the rear wheel 16 is input to the control amount calculation unit 37 ′, and the control amount calculation unit 37 ′ calculates the yaw rate corresponding control amount Ty as the driving force distribution corresponding to the driving force decrease amount RXT by the following equation. Calculated according to (10) (control amount calculation means).
Ty = RXT × R / RHG (10)
Here, RHG is a gear ratio between the ring gear 14 a and the pinion gear 13.

On the other hand, the processing of the base control amount calculation unit 38 ′ and the wheel speed determination unit 39 ′ is the same as that during the understeer, the base control amount calculation unit 38 ′ calculates the base control amount Tbase, and the wheel speed determination unit 39 ′ The magnitude relationship between the front wheel average wheel speed NFave and the rear wheel average wheel speed NRave is determined.
Based on the above information, the final control amount calculation unit 40 ′ calculates the final control amount T according to the conditions shown in FIG. 6, and the electromagnetic clutch 17 distributes the driving force between the front and rear wheels 9, 16 based on the final control amount T. Is adjusted (driving force distribution control means).

  In the driving situation (NFave> NRave) where the average front wheel speed NFave is higher than the average rear wheel speed NRave shown in FIG. 7, the torque is moved from the front wheel 9 to the rear wheel 16 via the electromagnetic clutch 17 as in FIG. In this case, the rear wheel 16 is at the grip limit. As shown in FIG. 6, in the final control amount calculation unit 40 ′, the final control amount T is corrected to decrease by the yaw rate corresponding control amount Ty, so that the actual driving between the front and rear wheels 9 and 16 in accordance with the decrease in the final control amount T. Power distribution also decreases. As a result, the amount of torque movement from the front wheel 9 to the rear wheel 16 decreases, and the driving force of the front wheel 9 increases while the driving force of the rear wheel 16 decreases as indicated by the white arrows Adrv and Acornering in FIG. At this time, the driving force of the rear wheel 16 is reduced by an amount corresponding to the driving force reduction amount RXT calculated by the rear wheel driving force reduction amount calculation unit 36 ′, and is calculated by the rear wheel required lateral force calculation unit 35 ′ accordingly. The lateral force of the rear wheel 16 increases by the amount corresponding to the requested lateral force RCFT, and the yaw moment of the vehicle is increased by the amount corresponding to the requested yaw moment YAWM calculated by the yaw moment calculating unit 34 ′ with the increase in the lateral force of the rear wheel 16. And the oversteer occurring in the vehicle is suppressed.

  Further, when the average front wheel speed NFave shown in FIG. 8 is lower than the average rear wheel speed NRave (NFave <NRave), the torque moves from the rear wheel 16 to the front wheel 9 via the electromagnetic clutch 17 as in FIG. In this case, the rear wheel 16 is at the grip limit. As shown in FIG. 6, since the final control amount T is corrected to increase by the yaw rate corresponding control amount Ty in the final control amount calculation unit 40 ′, the actual driving between the front and rear wheels 9 and 16 according to the increase in the final control amount T. Power distribution also increases. As a result, the amount of torque movement from the rear wheel 16 to the front wheel 9 increases, and the driving force of the front wheel 9 increases while the driving force of the rear wheel 16 decreases as indicated by the white arrows Adrv and Acornering in FIG. Accordingly, as described above, the lateral force increases as the driving force of the rear wheel 16 decreases, and oversteer is suppressed as the yaw moment decreases.

  As described above, in the vehicle driving force distribution control apparatus according to the present embodiment, the vehicle steer characteristics are integrated in addition to the magnitude relationship between the front wheel average wheel speed NFave and the rear wheel average wheel speed NRave during the turning of the vehicle. Therefore, the driving force distribution between the front and rear wheels 9 and 16 is controlled. The steer characteristic of the vehicle indicates in which direction the yaw moment of the vehicle should be corrected, and the magnitude relationship between the front wheel average wheel speed NFave and the rear wheel average wheel speed NRave is the direction of torque movement between the front and rear wheels 9 and 16, and hence the drive. Since the change direction of the yaw moment due to the increase / decrease of the force distribution is expressed, the optimum driving force distribution between the front and rear wheels 9, 16 can be set for the turning state of the vehicle based on the combination of both conditions. Therefore, understeering and oversteering can be reliably suppressed by appropriately controlling the driving force distribution between the front and rear wheels 9 and 16, so that a good steering characteristic can always be realized regardless of the turning state of the vehicle.

  Further, in the present embodiment, after determining the vehicle steer characteristic based on the specific target yaw rate YT and the actual yaw rate YR, slip wheels that exceed the grip limit based on the steer characteristic are the front and rear wheels 9, 16. Based on the friction circles FFR and RFR estimated from the driving forces FX and RX and the lateral forces FCF and RCF of the slip wheel, the required yaw moment YAWM and the required yaw moment for suppressing understeer and oversteer Yaw rate control amount based on specific calculated values such as slip wheel driving force reduction amounts FXT, RXT for achieving the required lateral force FCFT, RCFT of the slip wheel that can achieve YAWM, and the required lateral force FCFT, RCFT Ty is calculated. Therefore, compared with the case where the yaw rate corresponding control amount Ty is set based on, for example, past empirical rules and experimental results, the yaw rate corresponding control amount Ty more realistic can be calculated, and thus the front and rear wheels 9 can be more appropriately calculated. , 16 can be controlled.

  In addition, since the friction circles FFR and RFR that accurately correlate with the grip force of the slip wheel are estimated based on the driving forces FX and RX and the lateral forces FCF and RCF, for example, a difference in tire wear state, weather (clear weather or snowfall) ) And the road surface form (paved road or dirt), the appropriate yaw rate control amount Ty can be calculated without being affected by the difference in the road surface friction coefficient. In other words, there is an advantage that it is not necessary to detect the tire wear state and the road surface friction coefficient by the sensor and to perform the compensation process in order to eliminate the influence of these disturbance factors.

  On the other hand, the actual yaw rate YR and the target yaw rate YT are applied to the determination process of the vehicle steering characteristic and the calculation process of the required yaw moment YAWM in the yaw moment calculation units 34 and 34 '. These yaw rates YR and YT are applied to the vehicle. It can be regarded as an index that directly represents the turning state of. Therefore, the determination of the steering characteristic and the calculation of the required yaw moment YAWM can be accurately executed based on these yaw rates YR and YT, and the driving force distribution between the front and rear wheels 9 and 16 can be further appropriately controlled.

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the yaw rate YR is applied as the target turning state index. However, the present invention is not limited to this as long as the index correlates with the turning state of the vehicle. For example, the lateral acceleration detected by the lateral acceleration sensor 26 instead of the yaw rate is used. The acceleration GY may be applied.

1 is an overall configuration diagram illustrating a vehicle driving force distribution control device according to an embodiment. It is the elements on larger scale which show the detail of a center differential and a front differential. It is a block diagram which shows the setting procedure of the control amount of the electronic control coupling performed by ECU at the time of understeer. It is a schematic diagram which shows the control condition of driving force distribution when front wheel average wheel speed is higher than rear wheel average wheel speed in understeer. It is a schematic diagram which shows the control condition of driving force distribution when a front-wheel average wheel speed is lower than a rear-wheel average wheel speed by understeer. It is a block diagram which shows the setting procedure of the control amount of the electronic control coupling performed by ECU at the time of oversteer. It is a schematic diagram showing a control situation of driving force distribution when the front wheel average wheel speed is higher than the rear wheel average wheel speed in oversteer. It is a schematic diagram showing a control situation of driving force distribution when the front wheel average wheel speed is lower than the rear wheel average wheel speed in oversteer.

Explanation of symbols

1 Center differential (driving force distribution means)
9 Front wheel 16 Rear wheel 17 Electromagnetic clutch (driving force distribution means)
21 4WD ECU (control amount calculation means, steer characteristic determination means, driving force distribution control means,
(Grip limit index estimating means, required lateral force calculating means, driving force decrease calculating means)
24 Yaw rate sensor (actual turning state index detection means)
25 Wheel speed sensor (wheel speed detection means)

Claims (3)

A driving force distribution means provided between the front and rear wheels of the vehicle, which constantly distributes the driving force from the driving source to the front and rear wheels and can vary the driving force distribution;
A control amount calculating means for calculating a turn corresponding control amount as a correction amount for the driving force distribution between the front and rear wheels based on the turning state of the vehicle;
Steer characteristic determining means for determining the current steering characteristic of the vehicle;
Wheel speed detecting means for detecting the wheel speeds of the front and rear wheels,
Depending on the combination of the steering characteristic determined by the steering characteristic determination means and the magnitude relationship between the wheel speeds of the front and rear wheels detected by the wheel speed detection means, the turning control amount is increased or decreased. A driving force distribution control device for a vehicle, comprising: a driving force distribution control unit configured to act and control the driving force distribution unit based on the corrected driving force distribution. The steer characteristic determining means includes
Target turning state index determining means for determining a target turning state index based on the running state of the vehicle;
An actual turning state index detecting means for detecting an actual turning state index of the vehicle,
A steering characteristic of the current vehicle is determined based on the target turning state index and the actual turning state index,
The control amount calculation means is
The grip limit for identifying the slip wheel of the front and rear wheels based on the understeer and oversteer determined as the steer characteristic by the steer characteristic determination means, and estimating a grip limit index correlated with the grip limit from the driving force and lateral force of the slip wheel Index estimation means;
A requested lateral force calculating means for calculating a requested yaw moment for suppressing the understeer or oversteer based on the turning state of the vehicle, and calculating a requested lateral force of the slip wheel capable of achieving the requested yaw moment;
Based on the grip limit index calculated by the grip limit index calculating means, the driving force decrease that calculates the slip wheel driving force reduction amount required to achieve the required lateral force calculated by the required lateral force calculating means. A quantity calculating means,
As the correction amount for the driving force distribution to be applied between the front and rear wheels, the turning correspondence control amount is calculated according to the driving force decrease amount of the slip wheel calculated by the driving force decrease amount calculating means. The vehicle driving force distribution control device according to claim 1.   When the driving force distribution control means determines that the wheel speed of the front wheel is higher than the wheel speed of the rear wheel, the driving force distribution control means distributes the driving force between the front and rear wheels when the steering characteristic determined by the steering characteristic determination means is understeer. On the other hand, when the steering characteristic is oversteer, the driving force distribution between the front and rear wheels is decreased and corrected based on the turning control amount, and the front wheel speed is adjusted to the rear wheel speed. When the steering characteristic is determined to be lower, when the steering characteristic determined by the steering characteristic determination means is understeer, the driving force distribution between the front and rear wheels is corrected to decrease based on the turning control amount, while when the steering characteristic is oversteer 3. The vehicle driving force distribution control according to claim 2, wherein the driving force distribution between the front and rear wheels is increased and corrected based on the turning control amount. Apparatus.

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