JP2000085393A - Four-wheel drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fuel consumption in a straight advance state of the constant velocity of a car, and realize high traveling stability even when a steering wheel is turned with the straight advance state of the constant velocity of the car. SOLUTION: A coupling 20 is controlled so as to adjust a transmitting torque to rear wheels RT3, RT4 to zero when a speed change is small. When it advance almost straightly at a nearly constant speed, fuel consumption is suppressed by eliminating a transmitting loss of power to the rear wheels. On the other hand, when it is judged that a speed difference between right and left wheels is large, the distribution of the transmitting torque to the rear wheels is restarted. Therefore, when a driver changes a lane, it is possible to restart the transmission of power to sub-driving wheels at once to stably make a vehicle travel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque distribution device for a four-wheel drive vehicle having a main drive wheel directly connected to a power source and an auxiliary drive wheel connected to the power source via a coupling. It is.

[0002]

2. Description of the Related Art Four-wheel drive vehicles include a part-time system in which four-wheel drive and two-wheel drive are appropriately switched, and a full-time system in which four wheels are always driven. Generally, in the part-time system, the front and rear wheels are directly connected by manually switching to four-wheel drive by a driver. On the other hand, in the full-time system, a center differential is provided between the front wheel and the rear wheel to allow the differential between the front and rear wheels and always realize four-wheel drive. Further, a four-wheel drive vehicle of a standby system is widely used at present. This standby system changes from a two-wheel drive state to a four-wheel drive state as needed, and includes a main drive wheel directly connected to a power source, and an auxiliary drive wheel connected to the power source via a coupling. The driving force distribution to the auxiliary drive wheels is adjusted to be optimal by changing the coupling force (engagement force) of the coupling according to the road surface condition, the running condition, and the like.

[0003]

However, the above-mentioned four-wheel drive vehicle of the standby type only needs to apply a driving force to four wheels (main drive wheels and sub-drive wheels) on a low μ road or the like. For example, when different diameter tires are attached, even if the vehicle is traveling straight at a constant speed, a difference in rotational speed occurs between the wheels, and the driving force is applied even when it is not necessary to apply the driving force to the auxiliary driving wheel side. Was. Here, if the driving force is transmitted to the sub-drive wheel side while traveling straight at such a constant speed, a transmission loss occurs in the coupling and the differential gear on the sub-drive wheel side, and the fuel loss is higher than in the two-wheel drive vehicle. Consumption is increasing.

To cope with such a problem, for example, Japanese Patent Application Laid-Open No. 7-145522 has been proposed. In this technique, acceleration is detected by an acceleration sensor, and the driving force distribution to the sub-drive wheels is reduced to zero during constant speed traveling. here,
In order to maintain the driving force distribution to the auxiliary driving wheels at zero, when the acceleration is small, a dead zone is provided when adjusting the driving force distribution. Therefore, in this technique, as long as the acceleration is small, the responsiveness deteriorates by the offset amount of the dead zone. For this reason, even when a lane change is performed or the steering wheel is taken while the vehicle is traveling straight at a constant speed in which the driving force is not distributed to the auxiliary driving wheel side, the driving force distribution to the auxiliary driving wheel side is restored. And the running stability in such a state was low.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to suppress fuel consumption in a straight running state at a constant vehicle speed and to reduce fuel consumption in the straight running state at a constant vehicle speed. An object of the present invention is to provide a four-wheel drive vehicle that can realize high running stability even when the steering wheel is turned.

[0006]

In order to achieve the above object, one of the front and rear wheels is a main drive wheel directly connected to a power source, and the other of the front and rear wheels is in a running state. Speed detection for detecting the wheel speed of each of the four wheels in a four-wheel drive vehicle that is a sub-drive wheel connected to the power source via a controllable coupling that varies the torque distribution ratio between the front and rear wheels in response to the change Speed change determining means for determining whether the change in wheel speed of each of the four wheels detected by the speed detector is small, and when the speed change determining means determines that the speed change is small, A coupling control means for controlling the coupling so as to reduce the transmission torque to the drive wheels to zero.

According to a second aspect of the present invention, one of the front and rear wheels is a main drive wheel directly connected to a power source, and the other of the front and rear wheels is configured to vary the torque distribution ratio of the front and rear wheels according to a running state. In a four-wheel drive vehicle that is an auxiliary drive wheel connected to the power source via a possible coupling, a speed detector that detects the wheel speed of each of the four wheels, and a four-wheel drive that is detected by the speed detector. Speed change determining means for determining whether the change in wheel speed of the wheels is small, and speed difference determining means for determining whether the speed difference between the left and right wheels is large from the wheel speeds of the four wheels detected by the speed detector. When the speed change judging means judges that the speed change is small, and when the speed difference judging means judges that the speed difference between the left and right wheels is small, the transmission torque to the auxiliary driving wheel is set to zero. Control the coupling to Coupling control means for controlling the coupling so as to restart distribution of transmission torque to the auxiliary drive wheels when the speed difference determination means determines that the speed difference between the left and right wheels is large. Is a technical feature.

According to a third aspect of the present invention, one of the front and rear wheels is a main drive wheel directly connected to a power source, and the other of the front and rear wheels has a variable torque distribution ratio between the front and rear wheels according to a running state. In a four-wheel drive vehicle that is an auxiliary drive wheel connected to the power source via a controllable coupling, a speed detector that detects the wheel speed of each of the four wheels, and the speed detector detects the wheel speed of each of the four wheels. Speed change determining means for determining whether the change in wheel speed of each of the four wheels is small, and speed difference determination for determining whether the speed difference between the left and right wheels is large based on the wheel speed of each of the four wheels detected by the speed detector. Means, an acceleration operation amount determining means for determining whether the change in the acceleration operation amount is large, and the speed change determining means determining that the speed change is small, and determining that the speed difference between the left and right wheels is small by the speed change determining means. And said acceleration When it is determined that the change in the acceleration operation amount is small by work quantity determining means, to control the coupling to the transmission torque of the the auxiliary drive wheels to zero,
When the speed difference judging means judges that the speed difference between the left and right wheels is large, or when the acceleration operation amount judging means judges that the change of the acceleration operation amount is large, the transmission torque to the auxiliary driving wheel And a coupling control means for controlling the coupling so as to restart the distribution of the coupling.

According to a fourth aspect of the present invention, in the first to third aspects, the coupling control means distributes the transmission torque to the auxiliary drive wheels when the speed change determining means determines that the speed change is large. It is a technical feature that the coupling is controlled so as to gradually restart.

According to the first aspect of the present invention, when the speed change is small, the coupling is controlled so that the torque transmitted to the auxiliary drive wheels becomes zero. For this reason, when the vehicle is traveling substantially straight at a substantially constant speed, fuel consumption can be suppressed by eliminating power transmission loss to the auxiliary drive wheels.

According to the second aspect of the present invention, when the speed change is small, the coupling is controlled so that the torque transmitted to the auxiliary drive wheels is reduced to zero. For this reason, when the vehicle is traveling substantially straight at a substantially constant speed, fuel consumption can be suppressed by eliminating power transmission loss to the auxiliary drive wheels. On the other hand, when it is determined that the speed difference between the left and right wheels is large, the distribution of the transmission torque to the auxiliary drive wheels is restarted. Therefore, when the driver performs a lane change, a turn, or the like, or a handle is taken by a rut or the like and operates the handle, when the speed difference between the left and right wheels becomes large, the transmission of power to the auxiliary drive wheels is performed. It can be restarted immediately and stable running is possible.

According to the third aspect of the present invention, when the speed change is small, the coupling is controlled so that the torque transmitted to the auxiliary drive wheels is made zero. For this reason, when the vehicle is traveling substantially straight at a substantially constant speed, fuel consumption can be suppressed by eliminating power transmission loss to the auxiliary drive wheels. On the other hand, when it is determined that the speed difference between the left and right wheels is large, or when it is determined that the change in the acceleration operation amount is large, the distribution of the transmission torque to the auxiliary drive wheels is restarted. Therefore, when the driver performs a lane change or the like, and the speed difference between the left and right wheels becomes large, or when the depression amount of the accelerator pedal or the like is adjusted for acceleration or deceleration, the power to the auxiliary driving wheel is supplied. Since the transmission can be resumed, stable running is possible.

According to the fourth aspect of the present invention, the coupling is controlled so that the distribution of the transmission torque to the auxiliary drive wheels is gradually restarted when the speed change becomes large. Therefore, when the distribution of the transmission torque is restarted, the influence on the power source (engine) side can be reduced, and the engine rotation does not change rapidly.
Therefore, the driver does not feel uncomfortable when the transmission torque distribution is restarted.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a torque distribution device for a four-wheel drive vehicle according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a case where a torque distribution device according to one embodiment is mounted on a vehicle.
It is a conceptual block diagram of a wheel drive vehicle. In the four-wheel drive vehicle 10, the drive torque from the engine 12 is given to the front wheels RT1 and RT2, and the drive torque is adjusted according to the running situation and transmitted to the rear wheels RT3 and RT4. A transmission 14 mounted on one side of the engine 12 is provided with a front differential 15 for outputting power from the engine 12 to an axle shaft 16 and driving the front wheels R as main driving wheels.
T1 and RT2 are driven and output to the first propeller shaft 18. The first propeller shaft 18 is connected to a second propeller shaft 22 via a coupling 20.

The coupling 20 has an electromagnetic clutch 19 and is configured to adjust the transmission of torque from the first propeller shaft 18 to the second propeller shaft 22. The current of the electromagnetic clutch 19 is controlled by a signal from the electronic control circuit 50. When the supplied current is high, a plurality of clutch plates (not shown) are directly connected, and
The torque of the propeller shaft 18 is directly transmitted to the second propeller shaft 22, and when the supplied current is low, the clutch plate separates and no torque is transmitted to the second propeller shaft 22. Further, the configuration is such that the frictional engagement force of the clutch plate is changed in accordance with the level of the supplied current, so that the transmission torque supplied from the first propeller shaft 18 to the second propeller shaft 22 can be adjusted.

The driving force from the second propeller shaft 22 drives rear wheels RT3 and RT4 as auxiliary driving wheels via a rear differential 25 and an axle shaft 26. Front wheel RT
Brakes B1, B2, B3, B4 and wheel speed sensors S1, S2, S3, S4 for detecting wheel speeds are disposed on the rear wheels 1, RT2 and the rear wheels RT3, RT4, respectively.

The electronic control circuit 50 controls the coupling 20 as described above. The electronic control circuit 50 includes a CPU 52 that performs various calculations and controls, a ROM 54 that holds a control program, a RAM 56 used as a work area of the CPU, and an input / output circuit 58, and includes wheel speed sensors S1, S2, The traveling state of the vehicle is detected based on the outputs from S3 and S4, and the electromagnetic clutch 1 of the coupling 20 is detected.
9 is controlled. The wheel speed sensor S1,
S2, S3, S4 are the brakes B1, B2, B3, B
4 independently controls the wheel speed sensor for an antilock brake system (ABS).

Next, the operation of detecting the running condition and controlling the coupling 20 by the electronic control circuit 50 will be described with reference to FIGS.
This will be described with reference to FIG. In the four-wheel drive vehicle of the present invention, in addition to the control of the coupling force (engagement force) of the coupling 20 according to the traveling state that is normally performed, the coupling of the coupling 20 is detected when the tight corner braking phenomenon is detected. Control is performed to reduce the resultant force, and control is performed to release the engaging force of the coupling 20 when steady traveling (traveling substantially straight and traveling at a constant speed) is detected.

FIG. 2 shows a main routine of the control performed by the electronic control circuit 50 for this specific control. First, the electronic control circuit 50 controls the wheel speed sensors S1, S2, S3, S4.
, The rotational speeds ω1, ω2, ω3, ω4 of the front wheels RT1, RT2 and the rear wheels RT3, RT4 are input (S1).
0). Next, it is determined whether or not a tight corner braking phenomenon has occurred in the vehicle at present (S12). here,
The tight corner braking phenomenon means that when turning at a large steering angle, the turning radius of the front wheel and the rear wheel are different, so if the rotation difference between the rear wheel and the front wheel is eliminated in a four-wheel drive vehicle, the brake will be applied to the front wheel side. We say that we are in the same state as when we multiplied. In the present embodiment, when a situation in which the tight corner braking phenomenon can occur is detected as described above, the engagement force of the coupling 20 is weakened to allow the differential between the front wheel and the rear wheel.
Avoid the occurrence of tight corner braking.

The processing for detecting the tight corner braking phenomenon in step 12 will be described with reference to FIGS. 3 and 4 showing a subroutine of the processing. The electronic control circuit 50 first determines whether the rotation speeds ω1 to ω4 of the respective wheels are not 0, that is, whether the vehicle is running (S32). Here, when the vehicle is not traveling (No in S32), the process proceeds to step 42, and when the vehicle is traveling (Yes in S32), the inner wheel RT3 and the outer wheel R of the rear wheels are used.
The turning radius R3 is determined from the wheel speeds ω3, ω4 at T4 (S34).

The calculation of the turning radius R3 will be described with reference to FIG. In the drawing, the radius of each wheel (tire) is r, the turning radii of each of the wheels RT1, RT2, RT3, and RT4 are R1, R2, R3, and R4, the turning angular velocity of the vehicle 10 is ω, and the inner wheels RT1 and the outer wheels RT2 of the front wheels. Is the front tread Lf, the rear tread between the rear inner wheel RT3 and the outer wheel RT4 is Lr, the front inner wheel RT1 and the outer wheel RT2.
The wheel base between the inner wheel RT3 and the outer wheel RT4 of the rear wheel is L. Here, wheels RT1, RT2, RT
3. If RT4 does not slip, the rotation speed can be expressed by the following equation (1).

R1ω = rω1 R2ω = rω2 R3ω = rω3 R4ω = rω4

As a result, the following equation 2 is established.

R1 / ω1 = R2 / ω2 = R3 / ω3 = R4 / ω4 Further, the turning radius R4 of the rear wheel outer wheel RT4 is the inner wheel RT3.
To which the rear tread Lr is added.

## EQU3 ## R4 = R3 + Lr

Here, the turning radius R3 of the inner wheel RT3 of the rear wheel can be obtained from the following Expression 4 from Expressions 2 and 3.

R3 = Lr / {(ω4 / ω3) −1}

The control by the electronic control circuit 50 will be described with reference to FIG. Here, the wheel speeds .omega.3 and .omega.4 of the inner wheel RT3 and the outer wheel RT4 of the rear wheels are obtained from the above equation (4).
After the turning radius R3 is calculated from (S34), it is determined whether the calculated turning radius R3 is equal to or smaller than the turning radius α (threshold) at which the tight corner braking phenomenon can occur (S34).
36). Here, when the turning radius R3 exceeds the turning radius α, that is, when the vehicle is traveling straight, and when the vehicle is turning on a curve whose turning radius is large enough to prevent the tight corner braking phenomenon from occurring (S36: No), step 42
Then, control is performed in the straight traveling mode.

On the other hand, when the turning radius R3 is equal to or smaller than the turning radius α at which the tight corner braking phenomenon can occur, (S3
6 is Yes), in addition to the case where the vehicle is actually turning with the turning radius or less, or the case where only one of the inner wheel and the outer wheel is running on the low μ road, for example, when the vehicle is turning on a rut such as a truck formed on the road. Even when only the outer wheel enters the rut while traveling straight ahead, the outer wheel slips because the outer wheel slips and the turning radius R3 is α.
May be: For this reason, it is further determined whether or not the tight corner braking phenomenon actually occurs. Here, in step 34, the turning radius R3 is calculated from the wheel speeds of the rear inner wheel RT3 and the outer wheel RT4.
In step 38, the front wheels RT1, RT
From the wheel speeds of the rear wheels RT3 and RT4, the turning radius R3
Ask again.

The calculation of the turning deformation R3 'will be described again with reference to FIG. Here, since the difference between the front tread Lf between the front inner wheel RT1 and the outer wheel RT2 and the rear tread Lr between the rear inner wheel RT3 and the outer wheel RT4 is small, the following equation 5 is established.

(Lf-Lr) ≫R3 If Lf ≒ Lr, the following equation (6) holds.

[6] In summary by ^{R1 2 = R3 2 + L 2} R2 2 = R4 2 + L 2 Equation 6 using equation 2 R3, number 7 is established.

Equation 7] ^{R3 '2 = {1- (ω2} / ω1) 2} L 2 /
｛(Ω2 / ω1) ² − (ω4 / ω3) ² ｝

The control operation of the electronic control circuit 50 will be described again with reference to FIG. Front wheel RT as described above
1, a turning radius R3 'is determined in step 38 from the wheel speeds of RT2 and the rear wheels RT3 and RT4. Then, in step 40, the turning radius R3' and the wheels of the inner wheel RT3 and the outer wheel RT4 of the rear wheels in step 34 are determined. The turning radius R3 obtained from the speed is compared with the turning radius R3. Here, the value obtained by squaring the turning radius R3 is equal to the value obtained by squaring the turning radius R3 'unless there is slippage of the wheel. However, a difference actually occurs due to a difference in distribution of the driving force between the front and rear wheels. For this reason, it is determined from the following equation 8 whether or not the difference is large by comparing with a preset threshold value β.

[Equation 8] ^{| R3 2 -R3 '2 | ≦} β

If the difference is equal to or smaller than β, the determination at step 36 is correct, that is, it is determined that the tight corner braking phenomenon has occurred (S40: Ye).
s) Go to step 44 to set the tight corner braking mode. Thereby, step 14 shown in FIG.
The command value of the electromagnetic clutch 19 of the coupling 20 is calculated so as to avoid tight corner braking.

On the other hand, when the difference exceeds β, when only one of the inner wheel and the outer wheel is running on the low μ road as described above, for example, only the outer wheel enters a rut formed on the road while traveling straight, Although the calculated turning radius R3 is smaller than α, the tight corner braking phenomenon has not occurred (S3).
(No at 40), the process proceeds to step 42 to set the straight traveling mode. Thus, in step 16 shown in FIG. 2, a command value is calculated so that the electromagnetic clutch 19 is controlled normally (in a straight-ahead mode).

In this embodiment, ABS wheel speed sensors S1, S2, S3, and S provided in advance in many vehicles in recent years.
By using only 4, it is possible to reliably detect the tight corner braking phenomenon without newly providing a steering angle sensor for detecting whether the steering wheel is largely turned.

Subsequently, at step 18 shown in FIG.
A command value to be output to the command value calculated in steps 14 and 16 is determined. Thereafter, it is determined whether the vehicle is in a steady state (running at a constant speed in a substantially straight traveling state) (S
20) In a steady state (S20: Yes), the command value is gradually reduced to zero. That is, by setting the engagement force of the coupling 20 to zero, transmission of the driving force to the rear wheels RT3 and RT4 is released, transmission loss at the rear differential 25 and the like is eliminated, and fuel consumption is suppressed.

The steady state determination in step 20 will be described with reference to FIG. 7 showing a subroutine of the processing. The electronic control circuit 50 first determines the rotational speeds ω1 to ω4 of the wheels.
Is determined to be large (S110). Here, for example, when the vehicle is accelerating as shown at time 0 to t1 shown in FIG. Is large (S110 is Yes), it is necessary to apply a driving force also to the rear wheel (sub-drive wheel) side, so the normal mode is set (S122). On the other hand, at time t1 in FIG.
When the vehicle is traveling at a constant speed as in t2 and the change in each wheel speed is small (No in S110), it is determined whether the change in the acceleration operation amount is large (S114). In the present embodiment, the amount of change in the acceleration operation amount is determined from the amount of change in the throttle valve opening per predetermined time based on an input signal from a throttle valve opening sensor (not shown). here,
For example, when the driver depresses an accelerator pedal (not shown) for acceleration and the change in the throttle valve opening is large (114 is Yes), the driving force is also applied to the rear wheels (auxiliary driving wheels) to increase running stability. Therefore, the normal mode 122 is set.

Subsequently, a different diameter difference correction process is performed (S11).
6). This different diameter difference correction processing is performed when the difference between the left and right wheel speeds becomes large, as described later, that is, when the rotational speeds ω1 and ω2 between the left front wheel and the right front wheel, or between the left rear wheel and the right rear wheel. When the rotation speeds ω3 and ω4 are significantly different, it is determined that the steering wheel operation has been performed. For this reason, when emergency tires of different diameters are mounted due to puncture or the like, a difference in wheel speed occurs between straight wheels even during straight traveling, and it is determined that a steering wheel operation has been performed. Is performed to prevent the determination that the steering operation has been performed. Here, by determining a change in the wheel speed detected a predetermined number of times in the past, it is determined whether the left-right difference in the wheel speed is constantly occurring, and when the left-right difference is constantly occurring, Assuming that a tire having a different diameter is mounted, a process of converting the rotational speed of the wheel into a value when a tire having a normal diameter is mounted is performed. Even if a tire having a different diameter is attached and a difference in wheel speed occurs due to the different diameter difference correction processing, the transmission of the driving force to the sub-drive wheels is cut off as described later to reduce the fuel consumption. You will get.

Subsequently, at step 118, the difference between the left and right wheel speeds is increased, that is, the rotational speeds ω1, ω2 between the left front wheel and the right front wheel, or the rotational speeds ω3, ω3 between the left rear wheel and the right rear wheel, It is determined whether ω4 is significantly different from ω4. Here, when a lane change is performed at a substantially constant vehicle speed as in times t5 to t6 in FIG. 8C, the vehicle turns left and right at a constant speed, or the handle is taken by a cross wind, a rut, or the like. When the difference between the left and right wheel speeds becomes large (eg, when the steering wheel is operated to reestablish the posture) (S118: Yes), it is necessary to apply a driving force to the rear wheels (auxiliary driving wheels) to increase running stability. Therefore, the normal mode is set (S122). As a result, the steady state determination shown in FIG. 2 becomes No, and the main routine ends. As described above, in the present embodiment, when the steering wheel is operated at a constant speed, the sub-drive wheel (the rear wheel RT
3, RT4), so that the drive torque distribution can be resumed.
Driving stability can be improved.

On the other hand, the change in each wheel speed is small (S110).
Is No), the change in the throttle valve opening is small (S1
14 is No), and time t4 to t5 in FIG.
As shown at t6, when the difference between the left and right wheel speeds is small (S1
18 is No), it is determined that the vehicle is almost straight traveling at a constant speed on a maintained road where no slip occurs, and a steady mode is set (S120). With the setting of the steady mode, the steady state determination shown in FIG. 2 becomes Yes, the engagement force of the coupling 20 is gradually reduced to 0, and the transmission of the driving force to the auxiliary driving wheel (rear wheel) is cut off, so that the fuel consumption is reduced. To reduce. Here, the reason why the engagement force is gradually reduced to zero is to cut off the transmission of the driving force without making the driver conscious and to prevent the driver from feeling uncomfortable.

Next, the calculation of the command value in the straight traveling mode in step 16 shown in FIG. 2 will be described with reference to the maps shown in FIGS. 6 and 8A showing a subroutine of the process. First, the wheel speed sensors S1, S shown in FIG.
2, the signals from S3 and S4 are input, and the differential rotation speed of the front and rear wheels is calculated (S75). Then, the engagement force of the electromagnetic clutch 19 is determined from the map indicated by the solid line in FIG. Here, when the differential rotation speed of the front and rear wheels is large, it is determined that the road is a low μ road such as a muddy or snowy road, and control is performed so as to increase the engaging force.

Next, the vehicle speed is input from a vehicle speed sensor (not shown) (S76). Then, a correction coefficient for the engagement force of the electromagnetic clutch 19 is obtained from a map (not shown) according to the vehicle speed (S78). Here, when the vehicle speed is low, the engagement force is increased to enhance the running stability, and when the vehicle speed is high, the correction coefficient is determined so as to decrease the engagement force so as to enhance the maneuverability.

Further, the throttle valve opening is input from a throttle valve opening sensor (not shown) (S80).
Then, the electromagnetic clutch 1 is set in accordance with the throttle valve opening.
A correction coefficient of the engaging force of No. 9 is obtained from a map (not shown) (S82). Here, in order to enhance the starting performance and the acceleration performance, a correction coefficient is determined so that the engagement force increases as the throttle valve opening increases.

Next, the determination as to whether the change in each wheel speed is large and the change in each wheel speed is large in step 110 described above with reference to FIG. 7 is Yes, and it is determined whether the mode has shifted to the normal mode (S84). ). For example, once the torque distribution to the sub-drive wheels is stopped, the main drive wheels slip on a frozen road or the like, the change in each wheel speed increases, and again,
It is determined whether the mode has just been shifted to the normal mode. in this way,
When the mode is shifted from the normal mode to the normal mode based on the change in each wheel speed (Yes in S84), the engagement force is gradually increased (S86). This reduces the influence on the power source (engine 12) side when the engagement force is applied to the coupling 19 and the distribution of the transmission torque to the auxiliary drive wheels is resumed, so that the engine rotation is not suddenly changed. To do that. Thereby, even when the distribution of the transmission torque is resumed when the normal mode is switched to the normal mode, the driver does not feel uncomfortable. When the mode is shifted to the normal mode due to the change in the throttle valve opening or the difference between the wheel speeds (S84: No), it is not necessary to gradually increase the engaging force. Immediately increase to the optimal value.

At step 88, steps 78, 81,
The engagement force of the electromagnetic clutch 19 is determined based on the correction coefficient obtained at 84, and the applied current is controlled. The map shown in FIG. 8A and the map (not shown) are stored in the ROM 54 in advance.

Next, the calculation of the command value in the tight mode in step 14 shown in FIG. 2 will be described with reference to a map shown by a broken line in FIG. 5 and FIG. First, the wheel speed sensor S shown in FIG.
The signals from 1, S2, S3 and S4 are input, and the differential rotation speed of the front and rear wheels is calculated (S50). Then, the engagement force of the electromagnetic clutch 19 is determined from the map indicated by the broken line in FIG. Here, when the differential rotation speed of the front and rear wheels is small, the tight corner braking phenomenon is strongly generated, so that the engagement force is controlled to be weakened.

Next, the turning radius R3 calculated in step 34 is input (S52). Then, a correction coefficient for the engaging force of the electromagnetic clutch 19 is obtained from a map (not shown) according to the turning radius (S54). Here, when the turning radius is small, a tight corner braking phenomenon occurs strongly, so a correction coefficient is determined so as to weaken the engaging force. Next, the vehicle speed is input from a vehicle speed sensor (not shown) (S5).
6). Then, a correction coefficient for the engagement force of the electromagnetic clutch 19 is obtained from a map (not shown) according to the vehicle speed (S58).
Here, when the vehicle speed is low, a tight corner braking phenomenon occurs strongly, so that a correction coefficient is obtained so as to weaken the engaging force.

Further, the throttle valve opening is input from a throttle valve opening sensor (not shown) (S60).
Then, the electromagnetic clutch 1 is set in accordance with the throttle valve opening.
A correction coefficient of the engagement force of No. 9 is obtained from a map (not shown) (S62). Here, when the engaging force with respect to the throttle valve opening is high, the tight corner braking phenomenon occurs strongly. Therefore, a correction coefficient is calculated so as to weaken the engaging force. Thereafter, the engagement force of the electromagnetic clutch 19 is determined based on the correction coefficients obtained in steps 54, 58 and 62 (S62).

Thereafter, it is determined whether the mode has just been switched from the straight traveling mode to the tight mode (S64). Immediately after the switching (S64: Yes), a correction value is determined so as to gradually weaken the engaging force (S66). this is,
In this embodiment, since the steering angle sensor is not used, when starting from the stop state with the steering wheel largely turned, the straight traveling mode is initially selected and the wheel speed sensor S
The mode is switched to the tight mode based on the outputs of S1, S2, S3, and S4. Here, at the time of switching to the tight mode, the auxiliary drive wheels (rear wheels) RT3,
When the torque distribution to the RT4 is reduced, the circulating torque accumulated at the time of starting is released at a stretch, and a shock is applied to the vehicle.

Here, as described above, by reducing the supply current based on the command value of the engagement force, the engagement force of the electromagnetic clutch 19 is weakened, and the front wheels RT1, RT2 and the rear wheels R
By allowing the differential between T3 and RT4, the tight corner braking phenomenon is prevented from occurring. In this embodiment, the control amount of the transmission torque by the electromagnetic clutch 19 when the tight corner braking phenomenon occurs depends on the differential rotation speed of the front and rear wheels, turning radius, vehicle speed, and acceleration operation amount (throttle valve opening). Therefore, the transmission torque can be optimally controlled in accordance with the running condition of the vehicle.

In the above-described embodiment, an example in which an electromagnetic clutch is used as the coupling differential control device has been described. Instead, a device capable of changing various transmission torques such as a hydraulic clutch can be used. Further, in the electronic control circuit 50, the turning radius is obtained from the rotation speed of the inner and outer wheels of the rear wheel, but may be obtained from the rotation speed of the inner and outer wheels of the front wheel. Also, instead of the throttle valve opening, the transmission torque can be controlled in accordance with another acceleration operation amount such as an accelerator pedal opening.

Further, in the above-described embodiment, since the four-wheel drive vehicle is configured based on the front wheel drive vehicle, the rear wheel R
The T3 and RT4 sides are auxiliary drive wheels, but in a four-wheel drive vehicle based on a rear wheel drive vehicle, the front wheel side is an auxiliary drive wheel. In this case, the torque distribution to the front wheels is adjusted.

[0048]

As described above, according to the first aspect of the present invention, when the speed change is small, the coupling is controlled so that the torque transmitted to the auxiliary drive wheels is made zero. For this reason, when the vehicle is traveling substantially straight at a substantially constant speed, fuel consumption can be suppressed by eliminating power transmission loss to the auxiliary drive wheels.

According to the second aspect of the present invention, when the speed change is small, the coupling is controlled so that the torque transmitted to the auxiliary drive wheels is reduced to zero. For this reason, when the vehicle is traveling substantially straight at a substantially constant speed, fuel consumption can be suppressed by eliminating power transmission loss to the auxiliary drive wheels. On the other hand, when it is determined that the speed difference between the left and right wheels is large, the distribution of the transmission torque to the auxiliary drive wheels is restarted. Therefore, when the driver performs a lane change, a turn, or the like, or a handle is taken by a rut or the like and operates the handle, when the speed difference between the left and right wheels becomes large, the transmission of power to the auxiliary drive wheels is performed. It can be restarted immediately and stable running is possible.

According to the third aspect of the present invention, when the speed change is small, the coupling is controlled so that the torque transmitted to the auxiliary drive wheels becomes zero. For this reason, when the vehicle is traveling substantially straight at a substantially constant speed, fuel consumption can be suppressed by eliminating power transmission loss to the auxiliary drive wheels. On the other hand, when it is determined that the speed difference between the left and right wheels is large, or when it is determined that the change in the acceleration operation amount is large, the distribution of the transmission torque to the auxiliary drive wheels is restarted. Therefore, when the driver performs a lane change or the like, and the speed difference between the left and right wheels becomes large, or when the depression amount of the accelerator pedal or the like is adjusted for acceleration or deceleration, the power to the auxiliary driving wheel is supplied. Since the transmission can be resumed, stable running is possible.

According to the fourth aspect of the present invention, the coupling is controlled so that the distribution of the transmission torque to the auxiliary drive wheels is gradually restarted when the speed change becomes large. Therefore, when the distribution of the transmission torque is restarted, the influence on the power source (engine) side can be reduced, and the engine rotation is not changed. Therefore, the driver does not feel uncomfortable when the transmission torque distribution is restarted.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a four-wheel drive vehicle including a torque distribution device according to one embodiment of the present invention.

FIG. 2 is a flowchart showing main processing by an electronic control circuit.

FIG. 3 is a flowchart illustrating a subroutine for tight corner determination in FIG. 2;

FIG. 4 is an explanatory diagram showing a method of calculating a turning radius.

FIG. 5 is a flowchart illustrating a subroutine for calculating a command value in a tight mode in FIG. 2;

FIG. 6 is a flowchart showing a subroutine for calculating a command value in a straight traveling mode in FIG. 2;

FIG. 7 is a flowchart showing a subroutine of a steady state determination in FIG. 2;

FIG. 8A is a graph showing the contents of a map of a correspondence relationship between rotational speeds of front and rear wheels and engagement forces, and FIG.
FIG. 8B is a graph showing switching between a normal mode and a steady mode based on a change in wheel speed, and FIG. 8C is a graph showing switching between a normal mode and a steady mode based on a difference between left and right wheels. .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 4 wheel drive vehicle 12 Engine 15 Front differential 18 1st propeller shaft 19 Electromagnetic clutch 20 Coupling 22 2nd propeller shaft 50 Electronic control circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3D043 AA01 AA05 AB01 AB17 EA02 EA16 EA39 EA42 EA44 EB03 EB07 EB12 EB13 EE07 EF02 EF09 EF12 EF19 EF27

Claims (4)

[Claims] 1. A controllable cup in which one of the front and rear wheels is a main drive wheel directly connected to a power source, and the other of the front and rear wheels varies a torque distribution ratio between the front and rear wheels according to a running state. In a four-wheel drive vehicle that is an auxiliary drive wheel connected to the power source via a ring, a speed detector that detects a wheel speed of each of the four wheels, and a wheel of each of the four wheels that is detected by the speed detector Speed change determining means for determining whether the change in speed is small, and when the speed change determining means determines that the speed change is small, the coupling is set such that the transmission torque to the auxiliary drive wheels is reduced to zero. And a coupling control means for controlling the vehicle. 2. A controllable cup wherein one of the front and rear wheels is a main drive wheel directly connected to a power source, and the other of the front and rear wheels is a controllable cup which varies a torque distribution ratio between the front and rear wheels according to a running state. In a four-wheel drive vehicle that is an auxiliary drive wheel connected to the power source via a ring, a speed detector that detects a wheel speed of each of the four wheels, and a wheel of each of the four wheels that is detected by the speed detector Speed change determining means for determining whether the change in speed is small; speed difference determining means for determining whether the speed difference between the left and right wheels is large based on the wheel speeds of the four wheels detected by the speed detector; When the speed change is judged to be small by the change judgment means, and when the speed difference between the left and right wheels is judged to be small by the speed difference judgment means, the cup is set so that the transmission torque to the auxiliary drive wheels is reduced to zero. Control the ring, said speed Coupling control means for controlling the coupling so as to restart distribution of the transmission torque to the auxiliary drive wheels when the speed difference between the left and right wheels is determined to be large by the degree difference determination means. Features a four-wheel drive vehicle. 3. A controllable cup, wherein one of the front and rear wheels is a main drive wheel directly connected to a power source, and the other of the front and rear wheels is a controllable cup that varies a torque distribution ratio between the front and rear wheels according to a running state. In a four-wheel drive vehicle that is an auxiliary drive wheel connected to the power source via a ring, a speed detector that detects a wheel speed of each of the four wheels, and a wheel of each of the four wheels that is detected by the speed detector Speed change determining means for determining whether a change in speed is small; speed difference determining means for determining whether the speed difference between the left and right wheels is large based on the wheel speeds of the four wheels detected by the speed detector; Acceleration operation amount determining means for determining whether the change in the amount is large; and the speed change determining means determining that the speed change is small; the speed change determining means determining that the speed difference between the left and right wheels is small; and Acceleration operation amount judgment means When it is determined that the change in the acceleration operation amount is small, the coupling is controlled so that the transmission torque to the auxiliary drive wheel is set to zero, and when the speed difference between the left and right wheels is large by the speed difference determination means. When the determination is made, or when the change in the acceleration operation amount is determined to be large by the acceleration operation amount determination means, the cup that controls the coupling so as to restart the distribution of the transmission torque to the auxiliary drive wheels. A four-wheel drive vehicle comprising: a ring control unit. 4. The coupling control means, when the speed change determining means determines that the speed change is large, controls the coupling such that the distribution of the transmission torque to the auxiliary drive wheels is gradually restarted. The four-wheel drive vehicle according to any one of claims 1 to 3, wherein the vehicle is controlled.