JP4901701B2 - Power transmission device for four-wheel drive vehicles - Google Patents

Description

  The present invention relates to a power transmission device for a four-wheel drive vehicle, and more particularly to a power transmission device for a four-wheel drive vehicle that can reduce understeer without delay in control even when a tire grip force is saturated during turning. is there.

  As a conventional power transmission device for a general four-wheel drive vehicle, a FF vehicle (front engine / front drive system) is used as a base, and power from the engine is output to the front wheels via an automatic transmission. A part of the motive power is distributed to the rear wheel side via the power transmission clutch.

  In this case, the power transmission amount to the rear wheels is controlled by controlling the engagement force of the power transmission clutch calculated by the sum (TΔN + Ty) of the clutch torque TΔN corresponding to the rotational speed difference and the clutch torque Ty corresponding to the yaw rate feedback. Adjusted. The clutch torque TΔN corresponding to the rotational speed difference is obtained by calculating the front wheel rotational speed Nf and the rear wheel rotational speed Nr detected by the wheel speed sensor as the average rotational speed (Nf = (Nfl + Nfr) / 2, Nr = (Nrl + Nrr) / 2), and is calculated by multiplying the deviation between the front wheel speed Nf and the rear wheel speed Nr by a constant K1 set according to the lateral acceleration. The yaw rate feedback-compatible clutch torque Ty is set such that the yaw rate deviation, which is the difference between the target yaw rate calculated from the vehicle speed and the steering angle, and the actual yaw rate detected by the yaw rate sensor approaches zero. As described above, a technique for changing the power distribution of the front and rear wheels to realize the vehicle behavior according to the traveling state of the vehicle has been proposed. (For example, see Patent Document 1)

  By the way, in the four-wheel drive vehicle equipped with such a power transmission device, when the road surface condition changes during turning, the road surface friction coefficient μ decreases rapidly, and the grip of the front wheel tire is saturated. Immediately maximize the engagement torque of the power transmission clutch (directly connected to the power transmission clutch), and distribute the driving force of the slipping front wheels to the rear wheels to alleviate the saturation of the grip on the front tires, Understeer generated in the vehicle by using the four-wheel grip as effectively as possible (equalizing the tire load on the four wheels) (when the car is turning at a certain steering wheel angle, the car moves outward as the speed increases) It is desirable to suppress the swelling characteristics).

Japanese Patent Publication No. 7-64218

  However, the conventional power transmission apparatus described above has the following problems in the clutch torque TΔN corresponding to the rotational speed difference and the clutch torque Ty corresponding to the yaw rate feedback.

[Problem of clutch torque TΔN corresponding to rotational speed difference]
The clutch torque TΔN corresponding to the rotational speed difference is calculated by multiplying the deviation between the front wheel rotational speed Nf and the rear wheel rotational speed Nr by a constant K1 set according to the lateral acceleration. Even if the friction coefficient μ decreases and the grip of the front tire is saturated, if the driving force generated on the front wheels is relatively small (the throttle opening is relatively small), the front tire As shown in FIG. 2, the rotational speed difference corresponding clutch torque TΔN, which is substantially proportional to this, is also reduced, so that the idling of the wheel is reduced and the deviation between the front wheel speed Nf and the rear wheel speed Nr is reduced. The clutch engagement torque cannot be maximized (direct transmission of the power transmission clutch).

[Problem of clutch torque Ty with yaw rate feedback]
Also, under the same conditions as above, the clutch torque Ty corresponding to the yaw rate feedback determines the distribution torque to the rear wheels so that the deviation between the target yaw rate and the actual yaw rate becomes zero. When the tire grip force is saturated, understeer occurs, the actual yaw rate decreases with respect to the target yaw rate, and the yaw rate deviation increases, so the clutch torque Ty corresponding to the yaw rate feedback increases to increase the actual yaw rate. It will be.

However, the actual yaw rate can be obtained as information when the front wheel tire grip is saturated and the yaw rate sensor detects the resulting vehicle behavior, so it responds to changes in the actual yaw rate. There will be a delay.
That is, as shown in FIG. 6, immediately after the grip of the front wheel tire is saturated, a response delay occurs in the change of the actual yaw rate as shown by a one-dot chain line, as shown in FIG. Since the deviation between the target yaw rate and the actual yaw rate does not increase immediately, a response delay occurs when the yaw rate feedback-compatible clutch torque Ty increases.

  Therefore, in the conventional power transmission device shown in Patent Document 1, the driving state where the deviation between the front wheel rotational speed Nf and the rear wheel rotational speed Nr is small, for example, the driving force generated in the front wheels is relatively small (throttle opening degree). When the road surface friction coefficient μ decreases during turning and the front wheel tire grip is saturated, a response delay occurs in the increase of the yaw rate feedback clutch torque Ty, and the power transmission clutch Since the combined torque (TΔN + Ty) cannot be maximized immediately (directly connected to the power transmission clutch), there is a problem that understeer cannot be sufficiently reduced due to a control delay.

  The present invention has been made to solve the above-described problems. When the saturation of the road surface reaction torque generated between the front tire and the road surface is detected, the grip force of the front wheel tire is saturated. By maximizing the power transmitted to the other of the front and rear wheels immediately, the saturation of the grip force of the front wheel tire is alleviated (equal load on the tires of the four wheels), and the grip of the four wheels is effective It is an object of the present invention to provide a power transmission device for a four-wheel drive vehicle that can reduce understeer.

A power transmission device for a four-wheel drive vehicle according to the present invention is a power transmission device for a four-wheel drive vehicle in which power is constantly transmitted to one of the front and rear wheels and the power is transmitted to the other of the front and rear wheels via a power transmission mechanism. A power transmission control means for adjusting the power transmitted to the other of the front and rear wheels by controlling the transmission mechanism, and a road surface for determining whether or not a road surface reaction force state caused by steering the steering wheel is saturated Reaction force state determination means, the road surface reaction force state determination means, road surface reaction force torque calculation means for calculating road surface reaction force torque Ta by motor acceleration, motor current and steering torque, steering angle θ and vehicle speed V A road surface reaction force torque calculating means for calculating a road surface reaction force torque To from the road surface reaction force torque Ta and the road surface reaction force torque To. And above When the road surface reaction torque deviation ΔT is greater than the predetermined deviation amount α by comparing the road surface reaction torque deviation ΔT with the predetermined deviation amount α set according to the vehicle and the vehicle speed V, the road surface reaction force state And a road surface reaction force state determination unit that determines that is saturated,
When the road surface reaction force state is determined to be saturated by the road surface reaction force state determination unit, the upper limit at which the power transmitted to the other of the front and rear wheels by the power transmission control unit can be transmitted by the transmission mechanism. The power is increased in accordance with the deviation between the power and the power transmitted to the other of the front and rear wheels at the previous calculation.

  According to the power transmission device for a four-wheel drive vehicle of the present invention, when it is determined that the contact state between the steered wheels and the road surface is in the saturation region, the power transmitted to the other of the front and rear wheels is transmitted by the transmission mechanism. Since the maximum power that can be transmitted is set, for example, when the road surface condition changes from a slippery road surface to a slippery road surface during turning, and the tire grip force is saturated, the vehicle state such as wheel rotation speed and yaw rate is changed. Regardless, by increasing the engagement torque of the electronically controlled coupling, the driving force on the front wheel side is distributed to the rear wheels as much as possible, and the saturation of the tire grip force is alleviated (the tire load on the four wheels is made uniform). By effectively using the four-wheel grip, understeer can be reduced without control delay as in the conventional example.

Embodiment 1 FIG.
Next, embodiments of the present invention will be described below with reference to the drawings. 1 to 9 explain a first embodiment of the present invention.
FIG. 1 shows an overall configuration diagram of vehicle control to which the present invention is applied. In the figure, a front differential 1 (hereinafter referred to as a front differential) is provided between the left and right wheels 4 on the front wheel side, and engine power (not shown) is input to the ring gear 2 fixed to the front differential 1 via a transmission. Is done. The front differential 1 is connected to the left and right front wheels 4 via a drive shaft 3 and transmits the engine power input to the ring gear 2 to the left and right front wheels 4 via a transmission while allowing a differential. is there.

  A pinion gear 6 fixed to the front end of the front propeller shaft 5 meshes with the ring gear 2 of the front differential 1, and the front propeller shaft 5 is extended toward the rear of the vehicle, and the rear end thereof is an electronically controlled coupling 7. To the front end of the rear propeller shaft 8. A pinion gear 9 fixed to the rear end of the rear propeller shaft 8 meshes with a ring gear 11 of a rear differential 10 (hereinafter referred to as a rear differential), and left and right rear wheels 13 are connected to the rear differential 10 via a drive shaft 12. It is connected.

  As is well known, the electric power steering device 30 determines the motor current I flowing through the motor 31 according to the steering torque when the driver operates the handle 32, and generates assist torque. The power transmission mechanism 7 is composed of, for example, an electronic control coupling, and the front propeller shaft 5 through the rear propeller shaft 8 according to the engagement state (engagement torque of the electronic control coupling) of a built-in electromagnetic clutch (not shown). The power distributed to the rear wheel 13 side is adjusted. The power distributed to the rear wheel 13 via the electronic control coupling 7 is input to the rear differential 10 and is transmitted to the left and right rear wheels 13 while allowing the differential by the rear differential 10.

  A power transmission control means 14 is provided as a device for controlling the engagement state (engagement torque of the electronic control coupling) of the electromagnetic clutch of the electronic control coupling 7. This power transmission control means 14 comprises a rotational speed difference corresponding clutch torque calculating means (front / rear differential rotation restraint torque calculating section) 19 and a yaw rate feedback corresponding clutch torque calculating means 20, which are not shown in the figure. ), Memory (ROM, RAM) and I / O interface. The power transmission control means 14 receives signals from various sensors such as a lateral acceleration sensor 15, a steering angle sensor 16, a yaw rate sensor 17, and wheel speed sensors 18a to 18d provided on the wheels.

Based on these input parameters, the front-rear differential rotation restraint torque calculator 19 obtains the rotational speed difference corresponding clutch torque TΔN according to the deviation between the front wheel speed and the rear wheel speed, and the yaw rate feedback corresponding clutch torque calculator In 20, the yaw rate feedback-compatible clutch torque Ty is calculated according to the yaw rate deviation. From these, the electronically controlled coupling engagement torque Tecc (= TΔN + Ty) is calculated.
On the other hand, the power transmission control means 14 is connected to a road surface reaction force state determination means 21 that determines whether or not the tire grip of the front wheels is saturated. Is determined to be saturated, the electronic control coupling engagement is performed by adding the temporary incremental torque Tup to the previous calculated value Tecc (previous value) of the electronic control coupling engagement torque Tecc. Increase torque Tecc.

  Next, details of the road surface reaction force state determination means 21 will be described with reference to FIG. In the figure, a road surface reaction force torque calculation means 26 is connected to a motor acceleration sensor 23, a motor current sensor 24, and a steering torque sensor 25, and the motor acceleration that is the output of the motor acceleration sensor 23 and the output of the motor current sensor 24. And the steering torque which is the output of the steering torque sensor 25 are input, and the road surface reaction force torque Ta is calculated by a method described in detail later.

The reference road surface reaction force torque calculation unit 27 calculates a reference road surface reaction force torque To (= ka · θ) from the steering angle θ that is the output of the steering angle sensor 16 and the vehicle speed V that is the output of the vehicle speed sensor 22. The road surface reaction force torque deviation calculating unit 28 calculates a road surface reaction force torque deviation ΔT from the road surface reaction force torque Ta and the reference road surface reaction force torque To.
Further, the road surface reaction force state determination unit 29 compares the road surface reaction force torque deviation ΔT with a predetermined deviation amount α set according to the vehicle and the vehicle speed V, so that the road surface reaction force torque deviation ΔT is a predetermined deviation amount. In the case of α or more, if the road surface reaction force state is saturated and the vehicle behavior is determined to be unstable (the tire grip is saturated), the saturation determination flag is set to 1 and output.

Subsequently, the operation of the road surface reaction force torque calculation means 26 will be described together with the calculation method.
The equation of motion of the electric power steering mechanism is expressed by the following equation.
J ・ dωs / dt = Thdl + Tmtr-Tfric-Ta
In the above equation, dωs / dt is a steering shaft rotational acceleration detected by the motor acceleration sensor 23 attached to the motor 31 that drives the electric power steering mechanism, and J is preset according to the power steering mechanism. Steering inertia moment.

  Further, Tmtr is a motor output torque (assist torque) calculated by multiplying the motor current I detected by the motor current sensor 24 attached to the motor 31 driving the electric power steering by the torque constant K2. Thdl is the steering torque detected by the steering torque sensor 25 attached to the electric power steering, and Tfric is a friction torque in the steering mechanism preset by the electric power steering mechanism. Accordingly, the road surface reaction force torque Ta in the above equation can be obtained from the values of the steering torque, the motor output torque, the steering shaft rotational acceleration, and the friction torque in the steering mechanism. The road surface reaction torque Ta is not limited to the above, and may be directly detected by, for example, a known road surface reaction torque sensor.

Next, a determination method of the road surface reaction force state determination unit 29 will be described.
The road surface reaction force torque Ta received by the vehicle is approximately proportional to the steering angle θ when the vehicle is in a stable state (the tire is in a grip state), but when the vehicle approaches the stability limit (the tire grip When the vehicle approaches a saturated state), the road surface reaction torque Ta decreases, and the proportional relationship with respect to the steering angle θ cannot be maintained. Therefore, the road surface reaction force state can be detected using this characteristic.

  The reference road surface reaction torque calculation unit 27 follows the control map for setting the steering reaction force torque gain ka shown in FIG. 4, that is, the steering reaction force torque for the steering angle θ set in advance according to the vehicle speed V. By multiplying the gain ka by the steering angle θ, the reference road surface reaction torque Tor (= ka · θ) is calculated. The gain Ka can be obtained experimentally by measuring the relationship between the steering angle and the road surface reaction force torque in accordance with the vehicle speed V in the actual running test of the vehicle.

  FIG. 5 is an explanatory diagram showing characteristics of the actual road surface reaction torques Ta1 and Ta2 with respect to the steering angle θ according to the road surface condition. The horizontal axis corresponds to the steering angle θ, the vertical axis corresponds to the road surface reaction torque Ta, the alternate long and short dash line to the reference road surface reaction torque To, the solid line to the actual road surface reaction torque Ta1 against the dry asphalt road surface, and the broken line to the slippery road surface The actual road reaction torque Ta2 is shown. The characteristic curve of the actual road reaction torque Ta2 on the slippery road surface (see broken line) begins to decrease at a steering angle θ smaller than the actual road reaction torque Ta1 characteristic curve on the dry asphalt road surface (see solid line) that is difficult to slip. Further, in a region where the steering angle θ is small, linearity according to the reference road surface reaction torque Tor is maintained as in the characteristic curve Ta1.

  Therefore, in a region where the steering angle θ is small, the gain (inclination ka in FIG. 5) with respect to the steering angle θ of the reference road surface reaction torque Tor set according to the vehicle can be used regardless of the road surface condition. . The road surface reaction torque deviation calculating unit 28 calculates the absolute value of the deviation between the reference road surface reaction force torque To and the actual road surface reaction force torque Ta calculated by the road surface reaction force torque calculating means 26, and the road surface reaction force torque deviation ΔT. Calculate as

The road surface reaction force state determination unit 29 compares the road surface reaction force torque deviation ΔT with a predetermined deviation amount α set according to the vehicle and the vehicle speed V, so that the road surface reaction force torque deviation ΔT is equal to or larger than the predetermined deviation amount α. When the road reaction force state is saturated and the vehicle behavior is unstable (the tire grip is saturated), the saturation determination flag is set to 1 and output.
The predetermined deviation amount α can be experimentally determined from the correlation between the vehicle behavior and the predetermined deviation amount α when the vehicle speed V is changed in the actual running test of the vehicle.

  Thus, the road surface reaction force torque Ta actually generated in the vehicle and the reference road surface reaction force torque To with respect to the steering angle θ are calculated, and the actual road surface reaction force torque Ta and the reference road surface reaction force torque To are compared. Thus, saturation of the road surface reaction force state (saturation of the grip force of the tire) or its sign can be detected.

The operation of the drive transmission device for the four-wheel drive vehicle will be described with reference to the time chart of FIG.
Reference numeral 33 represents a steering angle θ that varies with time, and 34 represents a road surface reaction force torque Ta determined by the steering angle and the road surface state. 35 represents a saturation determination flag indicating that the road surface reaction force torque is in a saturated state, and 36 represents an engagement torque of the electronically controlled coupling.
The road surface reaction force torque 34 during steering should be a road surface reaction force as indicated by a broken line if the road surface does not slip as in the region A. However, the grip of the front tire is saturated at the point C on a slippery road surface. Since a certain region B is entered, the linearity is not maintained and saturation occurs as shown by the solid line. When the road surface reaction force determination means 21 determines that the road surface reaction force is saturated (the front wheel tire grip is saturated), the saturation determination flag 35 is set to 1.

  When the vehicle is in a region A that is a road surface on which the vehicle does not slip, the saturation determination flag 35 is 0, and as in the conventional example, the rotational speed difference corresponding clutch torque TΔN calculated by the front-rear difference rotation restraint torque calculation unit 19, and The electronically controlled coupling engagement torque Tecc (= TΔN + Ty) is set from the yaw rate feedback compatible clutch torque Ty calculated by the yaw rate feedback compatible clutch torque calculation unit 20, but enters the region B where the vehicle is slippery. When the saturation determination flag 35 is set to 1, the maximum transmission torque Teccmax preset as the upper limit torque that can be transmitted by the electronic control coupling with respect to the engagement torque Tecc of the electronic control coupling and the previous calculation time The temporary control set by the map as shown in FIG. 11 according to the difference from the electronically controlled coupling engagement torque (Tecc (previous value)) Since the incremental torque Tup is added and Tecc = Tecc (previous value) + Tup is set, depending on the magnitude of the temporary increase torque Tup, as shown by the solid line in FIG. The engagement torque Tecc increases and finally reaches the maximum transmission torque Teccmax.

  On the other hand, as in the conventional example, electronically from the clutch torque TΔN corresponding to the rotational speed difference calculated by the front-rear differential rotation restraint torque calculating unit 19 and the clutch torque Ty corresponding to the yaw rate feedback calculated by the clutch torque calculating unit 20 corresponding to the yaw rate feedback. When the control coupling engagement torque Tecc = TΔN + Ty is set, the clutch torque TΔN corresponding to the rotational speed difference is set according to the lateral acceleration with respect to the deviation between the front wheel speed Nf and the rear wheel speed Nr. Since the calculation is performed by multiplying by the constant K1, even when the grip of the front tire is saturated at the point C, when the driving force generated on the front wheel is relatively small (the throttle opening is relatively small), The idling of the front tire is reduced, and the deviation between the front wheel rotational speed Nf and the rear wheel rotational speed Nr is reduced. , It does not increase to a maximum transmitted torque.

The yaw rate feedback clutch torque Ty determines the distribution torque to the rear wheels so that the deviation between the target yaw rate and the actual yaw rate is zero. At point C, the grip of the front tire is saturated and understeer occurs. Therefore, since the actual yaw rate becomes smaller than the target yaw rate and the yaw rate deviation becomes larger, the clutch torque Ty corresponding to the yaw rate feedback increases.
However, the actual yaw rate can be obtained as information when the front wheel tire grip is saturated and the yaw rate sensor detects the resulting vehicle behavior, so it responds to changes in the actual yaw rate. As described above, since a delay occurs, a response delay also occurs when the yaw rate feedback-compatible clutch torque Ty increases.

Therefore, the behavior of the electronically controlled coupling engagement torque (Tecc = TΔN + Ty) calculated from the sum of the clutch torque TΔN corresponding to the rotational speed difference and the clutch torque Ty corresponding to the yaw rate feedback is as shown by the broken line in FIG. Thus, a response delay occurs with respect to the solid line shown in FIG. 7A representing the behavior of (c) Tecc = Tecc (previous value) + Tup described above.
If the saturation determination flag 35 is set to 1, the engagement torque Tecc of the electronic control coupling may be set to the maximum transmission torque Teccmax (Tecc = Teccmax).

  Therefore, if the road surface condition changes from a slippery road surface to a slippery road surface during turning, and the tire grip is saturated, the engagement torque of the electronically controlled coupling is set to Tecc = Tecc (previous value) + Tup. By increasing the engagement torque of the control coupling, the engagement torque Tecc of the electronic control coupling is set earlier than when the engagement torque of the electronic control coupling is always set to Tecc = TΔN + Ty as in the conventional example. The maximum transmission torque can be increased and the driving force of the front wheels is distributed to the rear wheels as much as possible to alleviate the grip saturation of the front wheel tires (equalize the tire load on the four wheels), and the four wheel grips are effective. Therefore, as shown in FIG. 8, the timing at which the engagement torque Tecc of the electronically controlled coupling is maximized is faster than in the conventional example, and understeer can be reduced.

The operation of the power transmission device for a four-wheel drive vehicle according to the first embodiment of the present invention will be described below with reference to the flowchart of FIG. First, in S101, the steering angle, yaw rate, wheel speed of each wheel, vehicle speed, and lateral acceleration are read. Next, in S102, the rotational speed difference corresponding clutch torque setting means 19 calculates the rotational speed difference corresponding clutch torque TΔN. In the calculation of the clutch torque TΔN corresponding to the rotational speed difference, the front wheel rotational speed Nf and the rear wheel rotational speed Nr detected by the wheel speed sensors 18a to 18d are calculated as the average rotational speed (Nf = (Nfl + Nfr ) / 2, Nr = (Nrl + Nrr) / 2), and is set according to the lateral acceleration Yg detected by the lateral acceleration sensor with respect to the deviation between the front wheel speed Nf and the rear wheel speed Nr By multiplying the constant K1, the clutch torque TΔN corresponding to the rotational speed difference is calculated. (See the following formula)
TΔN = K1 ・ (Nf-Nr)
However, K1 = A / Yg (A: constant)

Next, in S103, the yaw rate feedback corresponding clutch torque calculating means 20 calculates the yaw rate feedback torque. In the calculation of the yaw rate feedback torque Ty, the yaw rate deviation is calculated from the target yaw rate γ ′ of the vehicle body determined by the following equation based on the steering angle θ and the vehicle speed V and the actual yaw rate γ detected by the yaw rate sensor. Yaw rate feedback torque Ty is calculated so that becomes close to zero. Specifically, as shown in the map of FIG. 10, when the yaw rate deviation γ′−γ is near 0, the yaw rate feedback torque Ty is set to 0 as a dead zone, and in the region where the absolute value of the yaw rate deviation is a predetermined value or more, the yaw rate The yaw rate feedback torque Ty is set to increase in proportion to the increase in the absolute value of the deviation.
γ '= θ · V / (1 + A · V ² ) / L
Where V: vehicle speed, θ: steering angle, A: vehicle stability factor,
L: The wheel base of the vehicle.

  In S104, it is determined whether the road surface reaction force torque of the front wheel tire is saturated by the road surface reaction force state determination means 21, and if it is determined that the road surface reaction force torque of the front wheel tire is not saturated, a saturation determination is made. If the flag is set to 0 and it is determined that the road surface reaction torque of the front tire is saturated, the saturation determination flag is set to 1 and the process proceeds to S105. In S105, it is determined whether or not the saturation determination flag is 1. If the flag is 1, the process proceeds to S107, and if the flag is 0, the process proceeds to S106.

  In S106, since it was determined that the front wheel grip was not saturated, the engagement torque Tecc of the electronically controlled coupling that controls the power transmission amount as in the conventional example was changed to the clutch torque TΔN corresponding to the rotational speed difference and the clutch torque corresponding to the yaw rate feedback. Set as the sum of Ty. (Tecc = TΔN + Ty)

  Next, in S107, since it is determined that the front wheel grip is saturated, a temporary incremental torque Tup for increasing the engagement torque Tecc of the electronically controlled coupling is calculated. As shown in the map of FIG. 11, the temporary incremental torque Tup is a maximum transmission torque Teccmax that is preset as an upper limit torque that can be transmitted by the electronic control coupling, and an engagement torque (Tecc of the electronic control coupling at the previous calculation). (Previous value)) is set according to the deviation. Here, the temporary incremental torque Tup increases when the deviation between Teccmax and Tecc (previous value) is large, and the temporary incremental torque Tup decreases as the deviation between Teccmax and Tecc (previous value) decreases. Yes.

Next, in S108, the electronic control coupling engagement torque Teccup at the time of saturation determination is calculated by adding the temporary incremental torque Tup to the electronic control coupling engagement torque (Tecc (previous value)) at the previous calculation. . (Teccup = Tecc (previous value) + Tup)
Accordingly, the temporary increase electronic control coupling engagement torque Teccup increases in accordance with the magnitude of the temporary incremental torque Tup.
Next, in S109, the electronic control cup is set by setting the smaller value of the electronic control coupling engagement torque Teccup and the maximum transmission torque Teccmax during the temporary increase calculated in S108 as the electronic control coupling engagement torque Tecc. The ring engagement torque Tecc increases until the maximum transmission torque Teccmax is reached.

  Thus, when Tecc is increased, the temporary incremental torque Tup increases when the deviation is large, as shown in FIG. 11, according to the deviation between Teccmax and Tecc (previous value). Since the temporary incremental torque Tup is reduced as the torque becomes smaller, when the saturation of the front wheel grip is detected, the engagement torque Tecc of the electronically controlled coupling is increased without losing responsiveness at the initial stage where the deviation is large. However, since the engagement torque Tecc of the electronic control coupling approaches the maximum transmission torque Teccmax (the electronic control coupling is in the direct connection state) and the deviation becomes smaller, the engagement torque Tecc of the electronic control coupling can be gradually increased. If the engagement torque Tecc of the electronically controlled coupling reaches the maximum transmission torque Teccmax (the electronically controlled coupling is in the direct connection state), the shock generated at that time is It can Rageru.

  Therefore, according to the embodiment of the present invention, when it is determined that the road surface reaction torque of the front wheels is saturated regardless of the vehicle state such as the wheel rotation speed and the yaw rate, the electronic control coupling is engaged. By increasing the torque to the maximum transmission torque Teccmax and allocating the driving force to the rear wheel to the maximum, the saturation state of the front wheel grip is alleviated (equal load on the four wheels), and the four wheel tires By utilizing the grip effectively, understeer can be reduced without control delay as in the conventional example.

  When it is determined that the road surface reaction torque of the front wheel is saturated, the engagement torque of the electronic control coupling is maximized while increasing the engagement torque of the electronic control coupling without impairing the responsiveness. Since the shock at the time of reaching the transmission torque (the electronic control coupling is directly connected) can be reduced, understeer can be reduced without control delay as in the conventional example while preventing the drivability from deteriorating.

The vehicle system block diagram in embodiment of this invention, FIG. 5 is a characteristic diagram for explaining the problem of the rotational speed difference corresponding clutch torque in the conventional example; The block diagram explaining the detail of the road surface reaction force state determination means in Embodiment 1 of this invention, A control map for setting a gain Ka necessary for calculation of the reference road surface reaction force torque in the first embodiment of the present invention; The characteristic view explaining the road surface reaction force which arises in the tire in Embodiment 1 of the present invention, FIG. 5 is a characteristic diagram for explaining a response delay of an electronically controlled coupling engagement force in a conventional example; Time chart of power transmission control calculation processing in Embodiment 1 of the present invention, The characteristic view explaining the difference of the vehicle behavior in Embodiment 1 of this invention and the vehicle behavior in a prior art example, The flowchart which shows the power transmission control calculation process in this invention, A control map for setting the torque corresponding to the yaw rate feedback in the present invention, It is a control map which sets the temporary incremental torque in this invention.

Explanation of symbols

1 front differential, 2 front ring gear, 3 drive shaft,
4 front wheel, 5 front propeller shaft, 6 front pinion gear,
7 Electronically controlled coupling, 8 Rear drive shaft,
9 Rear pinion gear, 10 Rear differential, 11 Rear ring gear,
12 rear drive shaft, 13 rear tire, 14 power transmission control means,
19 front-rear differential rotation restraint torque calculation unit, 20 yaw rate feedback-compatible clutch torque calculation unit, 21 road surface reaction force state determination means, 30 electric power steering device,
31 Electric power steering motor, 32 Handle.

Claims (5)

In a power transmission device for a four-wheel drive vehicle in which power is constantly transmitted to one of the front and rear wheels, and the power is transmitted to the other of the front and rear wheels via a power transmission mechanism, the transmission mechanism is controlled to the other of the front and rear wheels. Power transmission control means for adjusting the power to be transmitted, and road surface reaction force state determination means for determining whether or not a road surface reaction force state caused by steering the steering wheel is saturated, the road surface reaction force state The judging means includes road surface reaction force torque calculating means for calculating road surface reaction force torque Ta based on motor acceleration, motor current and steering torque, and reference road surface reaction force for calculating reference road surface reaction force torque To from steering angle θ and vehicle speed V. Torque calculation means, a road surface reaction force torque deviation calculating section for calculating a road surface reaction force torque deviation ΔT from the road surface reaction force torque Ta and the reference road surface reaction force torque To, the road surface reaction force torque deviation ΔT, the vehicle and the vehicle speed According to V If the road surface reaction force torque deviation ΔT is greater than or equal to the predetermined deviation amount α, the road surface reaction force state determination is made to determine that the road surface reaction force state is saturated. And consists of
When the road surface reaction force state is determined to be saturated by the road surface reaction force state determination unit, the upper limit at which the power transmitted to the other of the front and rear wheels by the power transmission control unit can be transmitted by the transmission mechanism. A power transmission device for a four-wheel drive vehicle, characterized in that the power is increased in accordance with a deviation between the power and the power transmitted to the other of the front and rear wheels at the previous calculation.   The transmission mechanism is constituted by an electronically controlled coupling, and the power transmission control means is constituted by a rotational speed difference corresponding clutch torque calculating means and a yaw rate feedback corresponding clutch torque calculating means, and the rotational speed difference corresponding clutch torque calculation. In the means, a clutch torque TΔN corresponding to the rotational speed difference is calculated according to the deviation between the front wheel speed Nf and the rear wheel speed Nr, and the above-mentioned clutch torque calculating means corresponding to the yaw rate feedback corresponds to the yaw rate deviation between the target yaw rate and the actual yaw rate. The clutch torque Ty corresponding to the yaw rate feedback is calculated, and the engagement torque Tecc of the electronically controlled coupling is calculated from the clutch torque TΔN corresponding to the rotational speed difference and the clutch torque Ty corresponding to the yaw rate feedback. 4 wheel drive as described in Power transmission device.   When the road surface reaction force state is determined to be saturated by the road surface reaction force state determination means, the temporary incremental torque Tup is added to the previous calculated value Tecc (previous value) of the coupling engagement torque Tecc. The power transmission device for a four-wheel drive vehicle according to claim 2, wherein the coupling engagement torque Tecc is increased. The clutch torque TΔN corresponding to the rotational speed difference is a constant set according to the lateral acceleration Yg detected by the lateral acceleration sensor with respect to the deviation between the front wheel rotational speed Nf and the rear wheel rotational speed Nr detected by the wheel speed sensor. 3. The power transmission device for a four-wheel drive vehicle according to claim 2, wherein the calculation is performed according to the following equation by multiplying by K1.
TΔN = K1 ・ (Nf−Nr)
However, K1 = A / Yg (A: constant)   The yaw rate feedback compatible clutch torque calculating means calculates a yaw rate deviation from the target yaw rate γ ′ of the vehicle body determined by the steering angle θ and the vehicle speed V and the actual yaw rate γ detected by the yaw rate sensor, and this yaw rate deviation is near zero. In this case, the yaw rate feedback torque Ty is set to 0 as a dead zone, and in the region where the absolute value of the yaw rate deviation is greater than or equal to the predetermined value, the clutch torque Ty corresponding to the yaw rate feedback is set to increase in proportion to the increase in the absolute value of the yaw rate deviation. The power transmission device for a four-wheel drive vehicle according to claim 2.

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