JP2003194106A - Four-wheel drive control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimally set conformity of transmission torque of a torque distribution clutch and driving torque of a rotational driving source on a four-wheel drive control device transmitting the rotational driving source directly to a main driving wheel and to a driven wheel through the torque distribution clutch. <P>SOLUTION: Driving force output from an engine 2 is transmitted directly to the main driving wheel at one of a front wheel side or a rear wheel side and to the driven wheel at the other side through a torque distribution clutch 6. The transmission torque of the torque distribution clutch 6 is controlled with a clutch control unit 10. Slipping between input and output of the clutch 6 is detected in accordance with a detected value of rotating speed sensors 9F and 9R provided at the input and output side, and the driving torque of the engine 2 is lowered based on a detected rotating speed difference. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to driving a driven wheel through a torque distribution clutch when a main driving wheel to which a driving force output from a rotary drive source is directly transmitted slips due to acceleration. The present invention relates to a four-wheel drive control device that transmits power.

[0002]

2. Description of the Related Art As a conventional four-wheel drive control device, for example, one described in Japanese Patent Laid-Open No. 2000-85393 is known. In this conventional example, one of the front and rear wheels is a main drive wheel that is directly connected to a power source, and the other of the front and rear wheels is a controllable coupling that changes the torque distribution ratio of the front and rear wheels according to the running state. In a four-wheel drive vehicle that has auxiliary drive wheels connected to a power source via a (torque distribution clutch), the wheel speed of each four wheels is detected by a speed detector, and the detected change in the wheel speed of the four wheels is detected. A four-wheel drive system in which the speed change determining means determines whether the speed is small, and when the speed change is small as a result of the determination, the coupling control means controls the coupling so that the transmission torque to the auxiliary drive wheels becomes zero. The car is listed.

[0003]

In such a four-wheel drive vehicle, the maximum transmission torque of the torque distribution clutch, that is, the maximum engagement force is set in advance from the durability strength of the components of the drive system. However, in a torque distribution clutch that is combined with an engine that produces large torque,
It is possible to use a clutch with a large capacity,
In addition to the increase in weight and cost, there are restrictions on the mounting space for clutch parts. Therefore, a small-capacity clutch will be combined, but in this case, the frequency of exceeding the preset transmission torque from the durability strength of the drive system components will increase and the components can be protected, but the running performance will be sacrificed. There is an unsolved problem of becoming.

Therefore, the present invention has been made by paying attention to the unsolved problem of the above-mentioned conventional example, and it is easy to control the drive torque output from the rotary drive source and the maximum transmission torque of the small-sized torque distribution clutch. It is an object of the present invention to provide a four-wheel drive control device capable of ensuring the required traveling performance by matching with the above.

[0005]

In order to achieve the above object, a four-wheel drive control device according to a first aspect of the present invention provides a drive force output from a rotary drive source to one of the front wheel side and the rear wheel side. The torque is transmitted directly to the driving wheel and is transmitted to the other driving wheel via a torque distribution clutch, and the torque distribution clutch is controlled by the clutch control means according to the running state of the vehicle. In a wheel drive control device, a slip state of a torque distribution clutch is detected based on a driving force reduction means for reducing a driving force output from the rotary drive source and a rotational speed difference between an input side and an output side of the torque distribution clutch. And a driving force reduction control unit that controls the driving force reduction amount of the driving force reduction unit based on the rotational speed difference detected by the clutch slip detection unit. There.

Further, in the four-wheel drive control device according to a second aspect of the present invention, in the invention according to the first aspect, the driving force reduction control means is equal to or greater than a torque reduction permission threshold value for which the transmission torque of the torque distribution clutch is set. Moreover, when the speed difference detected by the clutch slip detection means is equal to or greater than a predetermined rotational speed difference, the driving force reduction means starts the reduction of the driving force. Further, in the four-wheel drive control device according to a third aspect of the present invention, in the invention according to the second aspect, the torque reduction permission threshold value is lower than the clutch transmission torque required on a low friction coefficient road surface that frequently has a four-wheel drive state. It is characterized by being set to a high value.

Furthermore, a four-wheel drive control device according to a fourth aspect of the present invention is the four-wheel drive control device according to any one of the first to third aspects of the invention, wherein the maximum drive torque and the maximum transmission of the torque distribution clutch that the rotary drive source considers to be constant are used. When traveling on a high friction coefficient road surface where the frequency of four-wheel drive is low, the torque is
It is characterized in that the total driving force obtained by summing the maximum driving forces that can be transmitted to the road surface by the front wheels and the rear wheels is set to a value that satisfies the condition that the total driving force generated by the rotary drive source is equal to or greater than the normal maximum torque equivalent driving force. There is.

Furthermore, a four-wheel drive control device according to a fifth aspect of the present invention is the four-wheel drive control device according to any one of the first to fourth aspects of the invention, wherein the clutch control means is the drive force reduction control means. It is characterized in that the transmission torque of the torque distribution clutch is maintained at a constant value while the reduction control is being performed. Still further, a four-wheel drive control device according to a sixth aspect of the present invention is the four-wheel drive control device according to any one of the first to fifth aspects of the present invention, further comprising a clutch temperature detection means for detecting a temperature of the torque distribution clutch, wherein the driving force reduction control means is The reduction amount of the driving force output from the rotary drive source is set according to the clutch temperature detected by the clutch temperature detecting means.

A four-wheel drive control device according to a seventh aspect of the present invention is the four-wheel drive control device according to any one of the first to sixth aspects, wherein the drive force reduction control means reduces the drive force output from the rotary drive source. In this case, a driving force value at which acceleration slip does not occur on the main drive wheels is set as the driving force lower limit value.

[0010]

According to the first aspect of the present invention, the clutch slip is detected based on the rotational speed difference between the input side and the output side of the torque distribution clutch, and the drive output from the rotary drive source is detected accordingly. Since the force is reduced, slippage of the torque distribution clutch can be suppressed, heat generation and wear that occur when a small capacity torque distribution clutch is applied are suppressed, and
Since the fastening force of the torque distribution clutch is not reduced, the required traveling performance can be secured.

According to the second aspect of the present invention, when the transmission torque of the torque distribution clutch is equal to or greater than the set torque threshold and the speed difference detected by the clutch slip detecting means is equal to or greater than the predetermined rotational speed difference. Since the drive force output from the rotary drive source is reduced, it is possible to prevent the drive force output from the rotary drive from being unnecessarily reduced due to transient clutch slippage due to road surface disturbances, etc. The effect that it can prevent being produced is acquired.

Further, according to the third aspect of the present invention, the torque reduction permission threshold value is set to a value higher than the clutch transmission torque required on the low friction coefficient road surface where the frequency of four-wheel drive is high. Therefore, when traveling on a low friction coefficient road surface such as a snowy road or an icy road where the frequency of four-wheel drive is high, it is possible to suppress the reduction of the driving force output from the rotary drive source and ensure the traveling performance. The effect is obtained. Furthermore, according to the invention of claim 4, the maximum driving torque for normal use and the maximum transmission torque of the torque distribution clutch, which are considered to be normally used by the rotary drive source, travel on a high friction coefficient road surface in which the four-wheel drive condition is low. In this case, the total driving force obtained by summing the maximum driving forces that can be transmitted to the road surface by the front wheels and the rear wheels is set to a value that satisfies the condition that the total driving force generated by the rotary drive source is equal to or greater than the common maximum torque equivalent driving force Therefore, when traveling on a high friction coefficient road surface such as a paved road including a wet road, it is possible to secure a four-wheel grip state and exhibit sufficient traveling performance based on the drive torque generated by the rotary drive source. The effect is obtained.

Still further, according to the invention of claim 5, the transmission torque of the torque distribution clutch is held at a constant value while the driving force output from the rotary drive source is being reduced.
It is possible to obtain the effect that it is possible to reduce the occurrence of vibration due to interference with the clutch control. Still further, claim 6
According to the invention, the reduction amount of the driving force output from the rotary drive source is set according to the temperature of the torque distribution clutch, so that it is possible to prevent the driver from feeling uncomfortable due to the driving force reduction. The effect is obtained.

Further, according to the invention of claim 7, the reduction of the driving force output from the rotary drive source is set as the lower limit value of the driving force value at which the acceleration slip of the main driving wheels does not occur. It is possible to obtain an effect that it is possible to prevent the overload of the rotary drive source due to the excessive reduction of.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, in which 1FL and 1FR are front wheels as main driving wheels, 1RL and 1RR are rear wheels as sub-driving wheels, and front wheels 1FL, The driving force output from the engine 2 as a rotational drive source is directly transmitted to the 1FR via an automatic transmission 3 and a transfer 4 incorporating a front differential, and is rotationally driven. The driving force output from the transfer 4 is transmitted to the rear wheels 1RL and 1RR via the propeller shaft 5, the torque distribution clutch 6, and the final reduction gear unit 7 to be rotationally driven.

Front wheels 1FL, 1FR and rear wheels 1RL, 1R
R is a wheel speed sensor 8F for detecting the speed of each wheel.
L, 8FR and 8RL, 8RR are arranged. Further, an input side rotation speed sensor 9F and an output side rotation speed sensor 9R that detect the rotation speeds of the torque distribution clutch 6 are provided on the input side and the output side, respectively. Then, the transmission torque of the torque distribution clutch 6 is controlled by the clutch control unit 10. The clutch control unit 10 includes wheel speeds Vw _{FL to} Vw detected by the wheel rotation speed sensors 8FL to 8RR.
_RR , input side rotation speed Vc _F and output side rotation speed V detected by the input side and output side rotation speed sensors 9F and 9R
c _R is input, the transmission torque of the torque distribution clutch 6 is controlled based on these, the engine torque target value is calculated, and the calculated engine torque target value is output to the drive torque control unit 12 described later.

In the vehicle, the operating state of the engine 2
Select gear ratio of automatic transmission 3 and throttle valve 1
By controlling the throttle opening of 1
A drive torque control unit 12 is provided as a drive force reducing unit that controls the drive torque output from the drive torque control unit 12. The operation state control of the engine 2 can be controlled, for example, by controlling the fuel injection amount and the ignition timing, and at the same time, by controlling the throttle opening. The drive torque control unit 12 can independently control the drive torque output from the engine 2. However, when the engine torque target value is input from the clutch control unit 10 described above, the engine torque target value can be controlled. The drive wheel torque is controlled with reference to the target torque value.

The clutch control unit 1
At 0, the clutch control process shown in FIG. 2 is executed. This clutch control processing is started, for example, when the clutch control unit 10 is powered on. First, in step S1, the average speed V of the wheel speeds Vw _FL , Vw _FR on the front wheel side.
w _F is calculated and the wheel speeds Vw _RL and Vw on the rear wheel side are calculated.
The average speed Vw _{R of RR} is calculated, then the process proceeds to step S2, the average speed Vw _{R R} of the rear wheels is subtracted from the calculated average speed Vw _F of the front wheels to calculate the front and rear wheel speed difference ΔVw, Next, in step S3, the transmission torque T _ETS of the torque distribution clutch 6 is calculated based on the calculated front and rear wheel speed difference ΔVw.

Then, the process proceeds to step S4 to calculate.
Transmission torque T_ETSIs the maximum transmission torque T preset
_MAXIt is determined whether or not_ETS> T_MAXIs
In step S5, the maximum transmission torque T_MAX
Transmission torque T_ETSAnd then set to step S6
Transition, T_ETS≤T_MAXIf it is
Go to 6. In step S6, the calculated transmission
Luk T_ETSHas decided to allow the preset drive torque reduction.
The above-mentioned maximum transmission torque T for disconnecting_MAXIn the vicinity of
Torque reduction permission threshold T set to a value smaller than this_OK
It is determined whether or not the above, T _ETS≧ T_OKWhen
Judges that it is possible to permit the reduction of the engine driving force.
Go to step S7, input side of torque distribution clutch 6
And output side rotation speed Vc_FAnd Vc_RRead and input
Side rotation speed Vc_FTo output side rotation speed Vc_RSubtract
The input / output rotational speed difference ΔVc is calculated. Where the torque is low
Decrease permission threshold T_OKAs a low friction coefficient road surface such as a snow road,
Vehicle has more than four wheels spinable transmission torque
It is preferable to set a high value.

Then, the process proceeds to step S8, where the torque is
Reduction permission flag F_OKSet to “1”, then
Then, the calculated input / output rotation speed ΔVc is predicted.
Drive torque reduction start threshold value ΔV_ONIs it over
It is determined whether or not ΔVc ≧ ΔV _ONDrive
If it is determined that it is possible to start the reduction of luck, the process proceeds to step S10
Drive torque reduction flag F_DOWNSet to "1"
Then, the process proceeds to step S11, and the current transmission torque is
Ku T_ETSHold transmission torque T_ETS0Set as
Go to step S12.

In step S12, the actual drive torque T read from the drive torque control unit 12 is read.
Based on _ER , the following equation (1) is calculated to calculate the engine torque target value T _E ^*, and then the process proceeds to step S13. T _E ^* = T _ER −αΔT (1) Here, α is a function of the input / output rotation speed difference ΔVc of the torque distribution clutch 6 described above, and the input / output rotation speed difference ΔVc.
It is calculated based on c by referring to the function α calculation map shown in FIG. Here, in the function α calculation map, as shown in FIG. 3, when the horizontal axis represents the input / output speed difference ΔVc and the vertical axis represents the function α, the function α increases as the input / output speed difference ΔVc increases. The value of is set to increase. Further, ΔT is a constant value.

In step S13, the calculated engine torque target value T _E ^* is such that the front wheel slip does not occur near the road friction coefficient at which the rear wheel driving force begins to be limited by the maximum transmission torque T _MAX of the torque distribution clutch 6. It is determined whether or not the driving torque lower limit value T _EL set to the torque is less than, and if T _E ^* <T _EL , step S
14, the engine torque target value T _E ^* is set to the drive torque lower limit value T _EL , and then the process proceeds to step S15. When T _E ^* ≧ T _EL , the process directly proceeds to step S15.

In step S15, the clutch exciting current Ic corresponding to the calculated transfer torque T _ETS is output to the torque distribution clutch 6 and the engine torque target value T _E ^*.
Is output to the drive torque control unit 12 and then returns. On the other hand, when the determination result of step S9 is ΔVc <ΔV _ON , the process proceeds to step S16, and the torque reduction end when the input / output rotational speed difference ΔVc is set to a value smaller than the torque reduction start threshold ΔV _ON described above. It is determined whether or not it is less than or equal to the threshold value T _OFF , and ΔVc> Δ
When V _OFF , the process proceeds to step S22 described later, and when ΔVc ≦ ΔV _OFF , the process proceeds to step S17.

In step S17, the actual drive torque T _ER corresponding to the accelerator pedal depression amount calculated by the drive torque control unit 12 is set as the engine torque target value T _E ^* . Then, the process proceeds to step S18, and the transmission torque T calculated in step S3 is calculated.
_The clutch exciting current Ic corresponding to the _ETS is output to the torque distribution clutch 6 and the set engine torque target value T _E ^* is output to the drive torque control unit 12, and then the process proceeds to step S19.

In step S19, the drive torque reduction flag F _DOWN is reset to "0" and then the process returns. Furthermore, the determination result of step S6 is T _ETS <
When it is T _OK , the process proceeds to step S20, the clutch exciting current Ic corresponding to the transmission torque T _ETS is output to the torque distribution clutch 6, then the process proceeds to step S21, and the torque reduction permission flag F _{OK is set} to “0”. It resets to "and returns.

Further, the determination result of step S16 is ΔV
When c> ΔV _OFF , the process proceeds to step S22,
It is determined whether or not the torque reduction flag F _DOWN is set to "1". When F _DOWN = "1", the process proceeds to step S11. When F _DOWN = "0", the process proceeds to step S17. To do. In the process of FIG. 2, the process of step S7 and the input / output side rotation speed sensor 8F are performed.
And 8R correspond to the clutch slip detection means, the processes of steps S6, S8 to S10 and S12 to S19 correspond to the driving force reduction control means, and steps S3 to S5 and S.
The processing of 11 and S20 corresponds to the clutch control means.

Next, the operation of the above embodiment will be described with reference to FIG. Now, assume that the vehicle is in a stopped state with the accelerator pedal released and the engine 2 in an idle rotation state, as shown in FIG. 4 (a). In this stopped state, the engine torque T _ER has a small value as shown in FIG. 4 (b), and the vehicle is in a stopped state. Therefore, the wheel speed difference ΔVw between the front and rear wheels is shown in FIG. 4 (d). As shown, since it is "0", the transmission torque T _ETS to the torque distribution clutch 6 calculated in step S3 is also "0" as shown in FIG. 4 (c). Also, the torque reduction permission flag F _OK
The torque reduction flag F _{DOWN is} also reset to "0" as shown in FIGS. 4 (e) and 4 (f).

In this stop state, the transmission torque T _ETS is set to "0", which is smaller than the torque reduction permission threshold T _OK, so that the process of FIG.
From step S19, the clutch exciting current Ic of "0" corresponding to the transfer torque T _ETS calculated in step S3 is output to the torque distribution clutch 6, so that the transfer torque of the torque distribution clutch 6, that is, the engagement. The force is controlled to "0", the transmission of the driving torque output from the engine 2 to the rear wheels 1RL, 1RR is cut off, and only the front wheels 1FL, 1FR, which are the main driving wheels, are driven. There is.

From this stopped state, depress the accelerator pedal.
When the vehicle is started, the
Calculated by the drive torque control unit 12
Engine drive torque T_ERIncreases as shown in Fig. 4 (b)
Then, this engine drive torque T _ERIs automatic gear shift 3 and tiger
It is transmitted to the front wheels 1FL and 1FR via the interface 4.
Then, the vehicle is in a starting state. In this starting state, the main drive wheels
The front wheels 1FL and 1FR will have an acceleration slip and
If the rear wheel speed difference ΔVw increases in the positive direction, step S
4 wheel drive transmission torque T calculated in 3_ETSIs increased
The engine drive torque output from the engine 2 by this
Ku T_ERVia transfer 4 and propeller shaft 5
Is transmitted to the torque distribution clutch 6 and the torque distribution clutch 6
Transmission from the latch 6 to the rear wheels 1RL and 1RR via the final reduction gear 7.
It is reached and becomes a four-wheel drive state, and it is possible to perform a smooth start.
it can.

In this starting state, the engine drive torque T
_{Since ETS} is smaller than the torque reduction permission threshold T _OK, even if the input / output rotational speed difference ΔVc of the torque distribution clutch 6 becomes a relatively large value during this period, the process proceeds from step S6 to step S20. Only the excitation current control is performed, the engine torque reduction process is maintained in the prohibited state, and the engine torque reduction process is prevented from being executed against the transient slip of the torque distribution clutch 6.

Thereafter, at time t1 in FIG. 4, step S3
The transmission torque T _ETS calculated by is the torque reduction permission threshold T
_When it becomes _OK or more, the process proceeds from step S6 to step S7 to calculate the input / output rotational speed difference ΔVc, and the torque reduction permission flag F _OK is set to “1” in step S8. At this time, the input / output rotational speed difference ΔVc is the torque reduction start threshold Δ.
In a state where it is smaller than V _ON , steps S9 to S
16, the value is smaller than the torque reduction end threshold value ΔV _OFF , so the process proceeds to step S17 to calculate the engine torque target value T _E ^* according to the accelerator pedal depression amount, which is the drive torque control unit 12. Is output to the throttle valve 11, the throttle opening of the throttle valve 11 is controlled to a value corresponding to the accelerator pedal depression amount, the required engine torque T _ER is output from the engine 2 and the transmission torque T _ETS . The clutch exciting current is output to the torque distribution clutch 6 to control the transmission torque.

Thereafter, at time t2, the torque distribution clutch 6
Transmission torque T_ETSIs the maximum torque T _MAXWhen you reach
Reaching torque T_ETSIs the maximum torque T_MAXMaintained at. That
After that, due to the occurrence of slippage in the torque distribution clutch 6,
At time t3, the input / output rotation speed of the torque distribution clutch 6
The difference ΔVc is the torque reduction start threshold ΔV_ONAnd over
Then, the process proceeds from step S9 to step S10,
Torque reduction flag F_DOWNSet to “1”, then
Transfer to step S11, the previous transmission torque T_EST(n-
1) is the transmission torque T of this time_ESTSet to (n) and
Ku T_ESTKeep constant. Then to step S12
Transition to current engine drive torque T_ERTo torque min
Constant with the function α of the input / output rotational speed difference ΔVc of the distribution clutch 6
The value obtained by subtracting the multiplication value αΔT with the reduction amount ΔT is used as the engine
Luk target value T_E ^*And then step S13
And the calculated engine torque target value T_E ^*Drive
Output to the dynamic torque control unit 12. others
Therefore, the drive torque control unit 12 throttles
Drive torque output from the engine 2 by decreasing the opening
As shown in Fig. 4 (b),
Required torque T based on stepping amount_AP0More reduced,
Therefore, the slip on the torque distribution clutch 6 is eliminated.

After that, if the engine torque target value T _E ^* becomes less than the drive torque lower limit value T _EL set to the drive torque at which the acceleration slip of the main drive wheels does not occur, for example, by repeating the processing of step S12, step S13 To step S14, the engine torque target value T
_E ^* is maintained at the drive torque lower limit value T _EL . Then, when the input / output rotational speed difference ΔVc falls below the torque reduction start threshold ΔV _ON at time t4, steps S9 to S9 are performed.
16 and the torque reduction end threshold value ΔV _OFF is larger than the torque reduction end threshold value ΔV _{OFF.
Since DOWN} is set to "1", step S11
And the state where the transmission torque T _EST is maintained at a constant value is continued, and the state where the drive torque output from the engine 2 is reduced is continued.

Thereafter, at time t5, the input / output rotational speed difference ΔVc of the torque distribution clutch 6 becomes equal to the torque reduction end threshold value ΔV.
_When it becomes _OFF or less, step S16 to step S17
Then, the engine torque target value T _E ^* is set to the required torque T _AP0 according to the amount of depression of the accelerator pedal, which causes the drive torque control unit 12 to reach the required torque T _AP0 of the throttle opening of the throttle valve 11. Will be gradually increased until. At the same time, the torque reduction flag F _DOWN is reset to “0”, and then the time t6
Then, when the transmission torque T _ETS becomes less than the torque reduction permission threshold T _OK , the process shifts from step S6 to step S20 to return to the state where only the transmission torque T _ETS is controlled.

As described above, according to the first embodiment, when the transmission torque T _ETS of the torque distribution clutch 6 becomes equal to or larger than the torque reduction permission threshold T _OK , the input / output rotational speed difference ΔVc of the torque distribution clutch 6 is increased. When the torque reduction start threshold ΔV _ON is exceeded, the throttle opening is reduced to reduce the drive torque output from the engine 2. Therefore, the slip of the clutch distribution torque 6 is reliably suppressed and deterioration is prevented. In addition, since the transmission torque T _ETS to the torque distribution clutch 6 is maintained at a constant value during the reduction period of the driving torque output from the engine 2, the torque distribution clutch 6 may vary in torque. It is possible to reliably prevent the occurrence of interference.

Further, since the reduction of the drive torque output from the engine 2 is limited to the drive torque lower limit value T _EL set to the drive torque at which the acceleration slip does not occur on the main drive wheels, the engine torque is reduced too much. It is possible to reliably prevent engine overload. Here, if an engine with an excessively large torque for the drive train capacity is installed, the engine torque may be reduced frequently in order to protect the drive train and the torque distribution clutch. Not only will it not be used, but the driver will feel uncomfortable due to the engine torque reduction operation. Therefore, the maximum transmission torque T _MAX of the torque distribution clutch 6 is set to an optimum state based on the normal maximum torque of the engine 2, the friction coefficient of the road surface, and the driving force on the tires so that the torque reduction processing is not executed in daily driving scenes. There is a need.

The normal maximum torque of the engine 2 is
Not limited to the maximum output torque of the engine 2, a road surface having a low road friction coefficient μ among road surfaces that are frequently encountered in general vehicle traveling (in this embodiment, μ0.5 to 0 assuming a wet road surface). .8), the output torque of the engine 2 can be transmitted to the road surface without acceleration slip (idling) of the four wheels. For example, in the present embodiment, when the wet road surface is considered to be in service, the maximum output torque of the engine 2 × 0.8 is set as the service maximum torque.

That is, as shown in FIG. 5, when the road surface friction coefficient μ is plotted on the horizontal axis and the driving force on the tire is plotted on the vertical axis,
In a low friction coefficient region where the road surface friction coefficient μ is 0 to 0.5 such as a snowy road or an icy road, the front wheel driving force representing the maximum driving force that can be transmitted to the road surface by the front wheels is expressed by the road surface friction as shown by the characteristic line L1. The rear wheel driving force, which represents the maximum driving force that can be transmitted to the road surface by the rear wheels, increases according to the increase of the road surface friction coefficient μ, as shown by the characteristic line L2, while increasing with a relatively gentle constant gradient in accordance with the increase of the coefficient μ. In the low friction coefficient region of snowy roads and icy roads, the road friction coefficient increases with a gradient smaller than the front wheel driving force, but the road surface friction coefficient is 0.5.
In a friction coefficient region exceeding, the torque distribution clutch 6 is set to a constant value determined by the maximum transmission torque T _MAX .

At this time, it is preferable to determine the maximum transmission torque T _MAX of the torque distribution clutch 6 so that the point where the maximum rear wheel driving force becomes constant does not fall in the low friction coefficient region of 0.5 or less. In the embodiment, the road surface friction coefficient is 0.5 when the road surface friction coefficient is switched from the low friction coefficient area to the medium friction coefficient area of more than 0.5 and less than 0.8, and the maximum rear wheel driving force is set to be constant. There is. As a result, in the medium friction coefficient road surface region, the total driving force including the front-rear driving force is kept smaller than the engine normal maximum torque equivalent driving force as indicated by the characteristic line L3 (solid line), so that the road surface grip on the rear wheel side is maintained. Since there is a possibility that the vehicle will be in a state and the front wheels will idle, a process of reducing the torque output from the engine 2 is executed in this medium friction coefficient road surface region.

Further, in the high friction coefficient region where the road surface friction coefficient corresponding to a general road such as a paved road including a wet road is 0.8 or more, the total driving force including the front-rear driving force represented by the characteristic line L3 is the engine normal use. It is preferable to select the maximum transmission torque T _MAX of the torque distribution clutch 6 so as to be equal to or greater than the maximum torque equivalent driving force. If this is not the case, there is also a method of reducing the engine torque at a rate when the automatic transmission 3 is in the first speed. In this way, by setting the maximum transmission torque T _MAX of the torque distribution clutch 6 from the normal maximum torque of the engine 2, the road surface friction coefficient, and the driving force on the tire, 4
On a road surface having a low friction coefficient of less than 0.5, such as a snowy road or an icy road, which frequently has a wheel drive condition, only the front wheels are prevented from idling and the ability as a four-wheel drive is 100%.
% Can be demonstrated. The road friction coefficient is 0.5
In the medium friction coefficient region of less than 0.8, the slip generated in the torque distribution clutch 6 is suppressed by performing the process of reducing the drive torque output from the engine 2 without reducing the drive force of the rear wheels. , While suppressing heat generation and wear,
By reducing the engine drive torque, idling of the front wheels is suppressed to ensure the required running performance. Further, on a high friction coefficient road surface having a road surface friction coefficient of 0.8 to 1.0 such as a paved road including a wet road, 100% of engine torque can be exhibited in a four-wheel grip state, and a small and lightweight four-wheel drive. By combining the drive train and the high-torque engine to match them, it is possible to realize a lightweight, low-cost vehicle with excellent running performance, fuel efficiency, and comfort.

In the first embodiment described above, the torque reduction permission threshold T _OK is set to a value smaller than the maximum transmission torque T _MAX of the torque distribution clutch 6, but the present invention is not limited to this. Alternatively, the torque reduction permission threshold T _OK may be set to a value that matches the maximum transmission torque T _MAX . Further, in the first embodiment, the input / output rotational speed difference Δ of the torque distribution clutch 6 is set.
Although Vc is calculated from the values detected by the input-side and output-side rotation speed sensors 9F and 9R, the wheel speed sensor 8F is used instead of the input-side and output-side rotation speed sensors 9F and 9R.
Input / output rotation speed difference ΔV based on the difference between the average value of the left and right front wheel speeds and the average value of the left and right rear wheel speeds using the detected values of L to 8RR.
It does not matter if c is calculated.

Further, in the first embodiment,
The input / output rotational speed difference ΔVc of the torque distribution clutch 6 is ΔV.
_When it is smaller than _ON, larger than ΔV _OFF , and F _DOWN = “1”, the engine torque target value T _E ^* is determined in step S12 ^.
Is calculated from the actual drive torque T _ER and a value determined based on the input / output rotational speed difference ΔVc. When the required torque T _AP0 > T _E ^* , the engine torque target value T _E ^*
May be held at the previous value calculated in the previous calculation cycle.

Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, torque reduction when slippage occurs in the torque distribution clutch 6 is performed while suppressing a temperature rise in the torque distribution clutch 6. That is, in the second embodiment, as shown in FIG. 6, a temperature sensor 21 as clutch temperature detecting means is arranged in the case of the torque distribution clutch 6, and the clutch temperature Tc detected by this temperature sensor 21 is used for clutch control. It has the same configuration as that of FIG. 1 in the above-described first embodiment except that it is input to the unit 10 and the clutch control unit 10 executes the clutch control processing shown in FIG. 7, and corresponds to FIG. The same reference numerals are given to the parts, and the detailed description thereof will be omitted.

The clutch control process is as shown in FIG.
First, in steps S1 to S5, the transmission torque T _ETS of the torque distribution clutch 6 is calculated as in the first embodiment, and then the process proceeds to step S31 to read the clutch temperature Tc detected by the temperature sensor 21, and then , Step S3
Then, it is determined whether the read clutch temperature Tc is equal to or higher than the preset torque reduction start threshold value Tc _ON . If Tc <Tc _ON , the process proceeds to step S33 to transfer torque T _ETS Excitation current Ic according to
Is output to the torque distribution clutch 6 and then step S
Returning to step 1, when Tc ≧ Tc _ON , step S34
Move to.

In step S34, the engine torque target value T _E ^* is calculated by performing the calculation of the following equation (2) based on the actual drive torque T _ER of the engine 2 input from the drive torque control unit 12. T _E ^* = T _ER −ΔT _E (2) Here, ΔT _E is calculated with reference to the ΔT _E calculation map shown in FIG. 9 based on the temperature detected by the temperature sensor 21. The [Delta] T _E calculation map, as shown in FIG. 9, the temperature on the horizontal axis, when taking a [Delta] T _E on the vertical axis, the temperature during the rise to Tc ₁ increases [Delta] T _E is slowly, then the temperature Is Tc
While rises to ₂ relatively large increase in [Delta] T _E, then is set so that [Delta] T _E increases even greater. Also, instead of calculating from the ΔT _E calculation map, ΔT _E
E may be a torque reduction amount set by an experiment so that the clutch temperature rise of the torque distribution clutch 6 can be suppressed without giving the driver a feeling of strangeness in traveling.

Then, the process proceeds to step S35, where the calculated engine torque target value T _E ^* is the drive torque lower limit value T
It is determined whether or not it is less than _EL . If T _E ^* <T _EL , the process proceeds to step S36, and the drive torque lower limit value T _EL is set as the engine torque target value T _E ^* , and then the process proceeds to step S37. If T _E ^* ≧ T _EL , the process directly goes to step S37. In step S37, the calculated engine torque target value T _E ^* is output to the drive torque control unit 12, and then the process returns to step S1.

In the process of FIG. 7, steps S1 to S1
The processes of S5 and S33 correspond to the clutch control means,
The processing of steps S31 to S37 corresponds to the driving force reducing means.
ing. According to this second embodiment, as described above,
Depress the accelerator pedal while the vehicle is stopped
When the vehicle is started, the clutch temperature Tc starts to reduce the torque.
Threshold Tc_ONIf it is lower, the procedure starts from step S32.
Transfer to the transfer torque T_ETSAccording to
Output the excitation current Ic to the torque distribution clutch 6 and
Clutch control is always performed, but clutch temperature Tc is torque
Reduction start threshold Tc _ONIf so, move to step S34.
Engine torque target value T for performing torque reduction_E ^*
And the drive torque control unit 12
To reduce the throttle opening and output
The output torque of engine 2 is reduced as shown in Fig. 8 (d).
Let Therefore, the input / output rotation speed of the torque distribution clutch 6
As shown by the solid line in FIG. 8B, the difference ΔVc is low in torque.
Compared to the characteristic shown by the dotted line without reduction,
By eliminating the slip, the torque distribution clutch 6
As shown in FIG. 8C, the clutch temperature Tc of
Run to warn the clutch overheat condition
To release the engagement force of the torque distribution clutch 6
Torque distribution before the latch protection control start temperature Tcs is reached
It is possible to reduce the clutch temperature Tc of the clutch 6.
It

At this time, the engine torque reduction amount ΔT
As described above, since it is set so as not to cause the driver to feel uncomfortable with running, it is possible to reliably prevent the driver from feeling uncomfortable even if the engine torque reduction operation is started, while the torque distribution clutch 6 operates. Since it is possible to prevent overheating and prevent the clutch protection control from being started to release the engagement force of the torque distribution clutch, it is possible to maintain the four-wheel drive state and secure the traveling performance.

In the first and second embodiments, the front wheels 1FL and 1FR are the main driving wheels, and the rear wheels 1R.
The case where the present invention is applied to a four-wheel drive vehicle having L and 1RR as driven wheels has been described. However, the present invention is not limited to this, and rear wheels 1RL and 1RR are used as main driving wheels and front wheels 1FL and 1FR are used. The present invention can also be applied to a four-wheel drive vehicle that uses driven wheels.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing an example of a clutch control processing procedure executed by a clutch control unit.

FIG. 3 is an explanatory diagram showing a control map for calculating a function α.

FIG. 4 is a time chart used for explaining the operation of the first embodiment.

FIG. 5 is an explanatory diagram showing a relationship between a road surface friction coefficient and a driving force on a tire.

FIG. 6 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 7 is a flowchart showing an example of a clutch control processing procedure executed by a clutch control unit according to the second embodiment.

FIG. 8 is a time chart used for explaining the operation of the second embodiment.

FIG. 9 is an explanatory diagram showing a ΔT _E calculation map.

[Explanation of symbols]

1FL, 1FR front wheel 1RL, 1RR rear wheel 2 engine 3 automatic transmission 4 Transfer 5 Propeller shaft 6 Torque distribution clutch 7 Final reduction gear 8FL to 8RR Wheel speed sensor 9F Input side rotation speed sensor 9R Output side rotation speed sensor 10 Clutch control unit 11 Throttle valve 12 Driving force control unit 21 Clutch temperature sensor

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3D043 AA01 AB01 AB17 EA02 EA16                       EE01 EE02 EE03 EE06 EF14                       EF19 EF21 EF24                 3J057 AA04 BB03 GA02 GA26 GB13                       GB14 GB23 GB27 GB36 GC09                       HH01 JJ01

Claims (7)

[Claims] 1. A drive force output from a rotary drive source is directly transmitted to one of the main drive wheels on the front wheel side and the rear wheel side, and is transmitted to the other drive wheel via a torque distribution clutch. And the torque distribution clutch is controlled by the clutch control means in accordance with the running state of the vehicle.
In a wheel drive control device, a slip state of a torque distribution clutch is detected based on a driving force reduction unit that reduces a driving force output from the rotary drive source and a rotational speed difference between an input side and an output side of the torque distribution clutch. And a drive force reduction control unit that controls the drive force reduction amount of the drive force reduction unit based on the rotational speed difference detected by the clutch slip detection unit. Drive controller. 2. The driving force reduction control means, when the transmission torque of the torque distribution clutch is equal to or more than a set torque reduction permission threshold value, and the speed difference detected by the clutch slip detection means is equal to or more than a predetermined rotation speed difference. The four-wheel drive control device according to claim 1, wherein the driving force reduction means starts the driving force reduction. 3. The torque reduction permission threshold value is set to a value higher than the clutch transmission torque required on a road surface with a low friction coefficient that frequently results in a four-wheel drive state. 4-wheel drive control device. 4. The normal maximum driving torque and the maximum transmission torque of the torque distribution clutch, which are considered to be commonly used by the rotary drive source, are a front wheel and a rear wheel when traveling on a high friction coefficient road surface in which a four-wheel drive condition is low. The total driving force obtained by summing the maximum driving forces that can be transmitted to the road surface by the wheels is set to a value that satisfies the condition that the total driving force generated by the rotary drive source is equal to or greater than the normal maximum torque equivalent driving force. The four-wheel drive control device according to any one of 1 to 3. 5. The clutch control means is configured to hold the transmission torque of the torque distribution clutch at a constant value when the driving force reduction control means is performing reduction control of the driving force of the driving force reduction means. The four-wheel drive control device according to any one of claims 1 to 4, which is provided. 6. A clutch temperature detecting means for detecting the temperature of the torque distribution clutch, wherein the driving force reduction control means is a drive output from a rotary drive source according to the clutch temperature detected by the clutch temperature detecting means. The four-wheel drive control device according to any one of claims 1 to 5, wherein the four-wheel drive control device is configured to set a reduction amount of force. 7. The drive force reduction control means sets a drive force value at which acceleration slip does not occur in the main drive wheels as a drive force lower limit value when reducing the drive force output from the rotary drive source. 7. The method according to claim 1, wherein
4. The four-wheel drive control device according to any one of 1.