JPH082278A - Driving force control device for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To provide a driving force control device for a four-wheel drive vehicle with which a turning condition can be detected securely. CONSTITUTION:Wheel speed sensors are provided to detect wheel speed of four wheels respectively, and differential speed DELTANR, DELTANL between a front and outer wheel and a rear and inner wheel is calculated (steps 100,150). When DELTANL is a determination value N1 in accordance with differential speed at a turning radius at which a tight corner brake is generated or more, and less than a determination value N2 in accordance with differential speed at the minimum rotation radius, it is judged as a turning condition at a large steering angle (steps 110, 120, 160, 170). When it is judged as the turning condition at the large steering angle, a differential limiting clutch is controlled to decrease transmission torque (step 130), thereby generation of tight corner brake phenomenon can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention avoids the phenomenon of tight corner braking that occurs during turning during four-wheel drive.
The present invention relates to a driving force control device for a wheel drive vehicle.

[0002]

2. Description of the Related Art Conventionally, in a four-wheel drive vehicle equipped with a center differential, if one wheel slips on a muddy or snowy road, only that wheel may rotate and the vehicle may not run. It is known that a differential limiting means for limiting the differential of the speeds of the front and rear wheels due to the center differential is provided, but if the differential is limited during turning, a tight corner braking phenomenon occurs.

As a means for avoiding the tight corner braking phenomenon, as disclosed in Japanese Patent Publication No. 3-51605, the steering angle of a steered wheel is detected by a steering angle detection sensor, and the steering angle becomes a predetermined value or more. In this case, it is known to control the differential limiting means to release the differential limitation. However, the steering angle detected by the steering angle detection sensor may be different from the actual turning state of the vehicle, and the differential limiting means may not properly release the steering angle. As a solution to this,
As disclosed in Japanese Unexamined Patent Publication No. 37849, the difference between the rotational speeds of the left and right wheels of the front wheels or the rear wheels is detected, and when the difference between the rotational speeds is equal to or more than a predetermined value, the two-wheel drive is switched by the differential limiting means. What you have done is known.

[0004]

However, in such a conventional vehicle, the speed difference between the left and right wheels in the turning state is small, and it is difficult to distinguish between the straight traveling state and the turning state. When the speed difference is large, it is inevitable to control the differential limiting means so as to release the differential limiting. Therefore, the differential limiting is released even if the slip occurs in the straight traveling state. However, there is a problem that one wheel may slip and one wheel may slip, making it difficult to run on a muddy road or a snowy road.

Therefore, the present invention has an object to solve the above problems, and can reliably detect a turning state.
An object of the present invention is to provide a driving force control device for a wheel drive vehicle.

[0006]

In order to achieve such an object, the present invention has the following constitution as means for solving the problem. That is, in the driving force control device for a four-wheel drive vehicle, which outputs the output from the internal combustion engine M1 directly to one of the front and rear wheels and to the other of the front and rear wheels via the differential limiting means M2 capable of changing the transmission torque. , A speed detection means M3 for detecting the wheel speed of each of the four wheels, a speed difference calculation means M4 for calculating the speed difference between the front outer wheel and the rear inner wheel, and a turn in which the speed difference causes a tight corner brake. When it is larger than the speed difference in the radius and smaller than the speed difference in the minimum turning radius, the judgment means M5 for judging the turning state at the large steering angle, and the judgment means M5 for judging the turning state at the large steering angle. In this case, the driving force control device for a four-wheel drive vehicle is characterized in that it is provided with differential limiting control means M6 for controlling the differential limiting means M2 to reduce the transmission torque.

The differential limiting control means M6 may be configured to change the transmission torque of the differential limiting means M2 according to the speed difference calculated by the speed difference calculating means M4, or the judgment When the means M5 determines that the turning state is not at a large steering angle, the differential limiting control means M6 may control the differential limiting means M2 to transmit the transmission torque to the front wheels.

[0008]

In the driving force control device for a four-wheel drive vehicle having the above structure, each speed detecting means M4 detects the wheel speed of each four wheels,
The speed difference calculating means M4 calculates the speed difference between the front outer wheel and the rear inner wheel. When the speed difference is larger than the speed difference at the turning radius where the tight corner brake is generated and smaller than the speed difference at the minimum turning radius, the determining means M5 determines that
It is determined that the vehicle is turning at a large steering angle. Further, when the differential limiting control means M6 is judged by the judging means M5 to be in a turning state at a large steering angle, the differential limiting means M2 is controlled to reduce the transmission torque and prevent the occurrence of the tight corner braking phenomenon. .

When the differential limiting control means M6 changes the transmission torque of the differential limiting means M2 according to the speed difference calculated by the speed difference calculating means M4, the differential limiting according to the turning radius can be implemented. . Further, when the determining means M5 determines that the turning state is not at a large steering angle, the differential limiting control means M
When 6 controls the differential limiting means M2 to transmit the transmission torque to the front wheels, the differential limiting can be performed except when turning.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a schematic configuration diagram of a driving force control device for a four-wheel drive vehicle that is an embodiment of the present invention. 1 is an internal combustion engine,
The output of the internal combustion engine 1 is transmitted to the transfer 4 via the transmission 2 and the output shaft 3, and the output from the transfer 4 is transmitted to the left and right front wheels 14FL and 14FR via the front drive shaft 6, the front differential 8, and the front axles 10 and 12. Is configured to be transmitted. See also Transfer 4
The output from is configured to be transmitted to the left and right rear wheels 14RL, 14RR via the rear drive shaft 16, the rear differential 18, and the rear axles 20, 22.

A front drive shaft 6 is provided in the transfer 4.
Center differential 26 that absorbs the difference in rotation between the rear drive shaft 16 and
Is provided. Further, in the transfer 4, a differential limiting clutch 30 is provided which limits the differential by the center differential 26 by the action of the hydraulic pressure supplied via the control valve 28 connected to the hydraulic pressure supply source.

The control valve 28 can change the level of the hydraulic pressure supplied to the differential limiting clutch 30 according to the magnitude of the input current. In addition, the differential limiting clutch 30
In this embodiment, when the supplied hydraulic pressure is high, a plurality of clutch plates (not shown) are frictionally engaged with each other to directly transmit the rotation of the output shaft 3 to the front drive shaft 6 and the rear drive shaft 16 to be supplied. When the hydraulic pressure is low, the clutch plate separates. Moreover, the degree of coupling of the clutch plates can be changed by changing the level of the supplied hydraulic pressure, and the torque transmitted from the output shaft 3 to the front drive shaft 6 and the rear drive shaft 16 can be changed.

On the other hand, each wheel 14FL, 14FR, 14R
Wheels 14FL, 1 corresponding to L, 14RR
Wheel speed sensors 32FL, 32FR, 32RL, 32RR for detecting wheel speeds of 4FR, 14RL, 14RR are provided. Each wheel speed sensor 32FL, 32FR, 3
The 2RL and 32RR are connected to an electronic control circuit 50, and the electronic control circuit 50 includes a well-known CPU 52 and ROM 5
4, the RAM 56 and the like are mainly configured as a logical operation circuit, and the input / output circuit 58 for performing input / output with the outside is the common bus 6
They are connected to each other via 0.

The CPU 52 uses the wheel speed sensors 32FL, 3FL.
Input signals from 2FR, 32RL, and 32RR are input via the input / output circuit 58, and these signals and the ROM 54,
The CPU 52 outputs a signal to the control valve 28 via the input / output circuit 58 based on the data in the RAM 56 and the control program stored in advance.

Next, the differential limiting control process performed in the electronic control circuit 50 described above will be described with reference to the flowchart of FIG. First, the speed difference ΔNR (= NFL-N is obtained from the difference between the wheel speed NFL output from the wheel speed sensor 32FL of the left front wheel 14FL and the wheel speed NRR output from the wheel speed sensor 32RR of the right rear wheel 14RR during traveling.
RR) is calculated (step 100). Next, it is judged whether or not this speed difference ΔNR is less than the first judgment value N1 (step 110). The first determination value N1 is a speed difference between the front wheel outer wheel and the rear wheel inner wheel at a turning radius at which a tight corner brake generated in advance is generated.

When the speed difference ΔNR is equal to or larger than the first judgment value N1, it is judged whether or not the speed difference ΔNR is smaller than the second judgment value N2 (step 120). The second determination value N2 is a speed difference between the front wheel outer wheel and the rear wheel inner wheel at a predetermined minimum turning radius of the vehicle. For example, as shown in FIG. 5, when the vehicle is turning at a constant speed, the front drive shaft 6
Is constant, the speed of the rear drive shaft 16 is smaller than that, the wheel speed of the outer wheel of the front wheel is the highest, the outer wheel of the rear wheel is second, and the wheel speed of the inner wheel of the rear wheel is lowest. .

Therefore, as shown in FIG. 4, when the vehicle is turning to the right, the wheel speed N of the left front wheel 14FL, which is the outer wheel of the front wheels, is increased.
The FL is the largest, and the wheel speed NRR of the right rear wheel 14RR, which is the rear inner wheel, is the smallest. Therefore, when the vehicle is turning to the right, each wheel 14FL, 14FR, 14RL, 14RR
As for the difference in the wheel speed of, the speed difference ΔNR between the wheel speed NFL of the left front wheel 14FL and the wheel speed NRR of the right rear wheel 14RR becomes the largest.

If the speed difference ΔNR is the first judgment value N1 or more, the second difference is obtained.
When it is less than the determination value N2, it is determined that the vehicle is in the right turning state at the large steering angle where the tight corner braking phenomenon occurs (steps 110 and 120), and the differential limitation is suppressed (step 130). To suppress the differential limitation, the control valve 28 is controlled to reduce the hydraulic pressure supplied to the differential limiting clutch 30, and the differential limiting by the differential limiting clutch 30 is released. Further, as the speed difference ΔNR is larger, the hydraulic pressure is greatly reduced to change the degree of engagement of the limited slip differential clutch 30, as shown in FIG.

When the speed difference ΔNR is equal to or larger than the second judgment value N2 (step 120), it is judged that the vehicle is in a slip state such as running on a muddy road or a snowy road, and the differential limitation is carried out. (Step 140). In the differential limiting, the control valve 28 is controlled to increase the hydraulic pressure supplied to the differential limiting clutch 30, and the differential limiting clutch 30 is connected to output the output of the output shaft 3 to the front drive shaft 6 and the rear drive. Direct transmission to the shaft 16 to implement differential limiting.

On the other hand, when the speed difference ΔNR is less than the first judgment value N1 (step 110), it is judged that a large right turn, straight ahead, or left turn is made, and the right front wheel 14 is detected.
Wheel speed N output from the FR wheel speed sensor 32FR
From the difference between FR and the wheel speed NRL output from the wheel speed sensor 32RL of the left rear wheel 14RL, the speed difference ΔNL (= NF
R-NRL) is calculated (step 150).

During a left turn, the front outer wheel is the right front wheel 14FR, and the rear inner wheel is the left rear wheel 14RL. While turning left, these wheels 1
The difference between the wheel speeds of 4FR and 14RL is the largest. Next, it is determined whether or not the speed difference ΔNL is less than the first determination value N1 (step 160). When the difference is less than the first determination value N1, the vehicle is traveling straight or a large radius where a tight corner braking phenomenon does not occur. It is judged that it is turning left at
Differential limitation is performed (step 140). This allows
The output of the output shaft 3 is the front drive shaft 6 and the rear drive shaft 16.
It is possible to prevent a state in which only one wheel is idly transmitted to the vehicle.

When the speed difference ΔNL is greater than or equal to the first determination value N1 and less than the second determination value N2, it is determined that the vehicle is in the left turning state at the large steering angle at which the tight corner braking phenomenon occurs (step 160). , 170) and suppress the differential limitation (step 130). Therefore, the center differential 26 absorbs the difference in rotation between the front drive shaft 6 and the rear drive shaft 16 to allow turning without causing a tight corner braking phenomenon.

On the other hand, when the speed difference ΔNL is equal to or greater than the second judgment value N2 (step 170), it is judged that the vehicle is in a slip state such as running on a muddy road or a snowy road, and the differential limitation is carried out. (Step 140). As a result, the output of the output shaft 3 is directly transmitted to the front drive shaft 6 and the rear drive shaft 16.

As described above, the driving force control apparatus for the four-wheel drive vehicle of this embodiment calculates the speed difference ΔNR calculated in step 100 and the speed difference ΔNL calculated in step 150, Since the turning state at a large steering angle can be determined without detecting the steering angle and the like, it is possible to make a determination according to the actual turning state of the vehicle. Further, when turning, the speed difference ΔNR, ΔN between the outer wheels of the front wheels and the inner wheels of the rear wheels.
Since L is the largest, it can be reliably determined that the vehicle is turning.

When the speed differences ΔNR and ΔNL are equal to or larger than the first judgment value N1 and smaller than the second judgment value N2, it is judged that the vehicle is in a turning state at a large steering angle where a tight corner braking phenomenon occurs. Suppress differential limitation. Therefore, the center differential 26 absorbs the difference in rotation between the front drive shaft 6 and the rear drive shaft 16 to allow turning without causing a tight corner braking phenomenon.

Further, by changing the degree of engagement of the differential limiting clutch 30 according to the magnitude of the speed differences ΔNR and ΔNL, differential limiting can be carried out according to the radius of gyration.
While preventing the occurrence of the tight corner braking phenomenon, the driving force is transmitted to the front wheels 14FL and 14FR as well, so that it is possible to avoid an operating state in which only one wheel slips and cannot run.

Further, when the vehicle is not in a turning state with a large steering angle, the differential limitation is carried out to obtain a good driving force in a straight traveling state, and only one wheel slips so that the vehicle cannot run. The operating state can be avoided. Incidentally, step 10
The execution of the processing of 0,150 works as the speed difference calculating means M4, the execution of the processing of steps 110,120,160,170 works as the judging means M5, and the steps 130,14.
The execution of the processing of 0 works as the differential limiting control means M6.

The present invention is not limited to the embodiments as described above, and may be carried out in various modes without departing from the gist of the present invention.

[0029]

As described above in detail, in the driving force control apparatus for a four-wheel drive vehicle of the present invention, the speed difference between the outer wheels of the front wheels and the inner wheel of the rear wheels becomes the largest at the time of turning, and based on this speed difference. Since the turning state is judged by the turning, the turning at a large steering angle where the tight corner braking phenomenon occurs can be surely detected, and the differential limitation is suppressed, so that the occurrence of the tight corner braking phenomenon can be prevented. Play.

Further, by changing the transmission torque according to the magnitude of the speed difference, it is possible to limit the differential according to the turning radius, and while preventing the occurrence of the tight corner braking phenomenon, the front wheel is also Also, the driving force can be transmitted to avoid an operating state in which only one wheel slips and cannot run.

Further, when the vehicle is not in a turning state with a large steering angle, the differential limitation is performed to obtain a good driving force in a straight traveling state, and only one wheel slips so that the vehicle cannot run. The operating state can be avoided.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a basic configuration of a driving force control device for a four-wheel drive vehicle according to the present invention.

FIG. 2 is a schematic configuration diagram of a driving force control device for a four-wheel drive vehicle according to the present embodiment.

FIG. 3 is a flowchart showing an example of a differential limitation control process performed in the electronic control circuit of this embodiment.

FIG. 4 is an explanatory diagram showing a state when the vehicle turns right.

FIG. 5 is a graph showing the speed of each wheel during turning.

FIG. 6 is a graph showing the relationship between speed difference and coupling degree in the present embodiment.

[Explanation of symbols]

M1, 1 ... Internal combustion engine M2 ... Differential limiting means M
3 ... Speed detecting means M4 ... Speed difference calculating means M5 ... Judging means M
6 ... Differential limiting control means 4 ... Transfer 6 ... Front drive shaft 8
... Front differential 14FL ... Left front wheel 14FR ... Right front wheel 1
4RL ... left rear wheel 14RR ... right rear wheel 16 ... rear drive shaft 1
8 ... Rear differential 26 ... Center differential 30 ... Limited differential clutch 5
0 ... Electronic control circuit

Claims (3)

[Claims] 1. A driving force control device for a four-wheel drive vehicle, wherein an output from an internal combustion engine is directly transmitted to one of the front and rear wheels and is transmitted to the other of the front and rear wheels through a differential limiting means capable of changing a transmission torque. A speed detecting means for detecting the wheel speed of each of the four wheels, a speed difference calculating means for calculating a speed difference between the front outer wheel and the rear inner wheel, and a turning radius at which the speed difference causes a tight corner brake. Is larger than the speed difference at the minimum turning radius and smaller than the speed difference at the minimum turning radius, the determining means determines that the turning state is at the large steering angle, and the determining means determines that the turning state is at the large steering angle, A driving force control device for a four-wheel drive vehicle, comprising: a differential limiting control means for controlling the differential limiting means to reduce a transmission torque. 2. The four-wheel system according to claim 1, wherein the differential limiting control means changes the transmission torque of the differential limiting means according to the speed difference calculated by the speed difference calculating means. Driving force control device for driving vehicle. 3. The differential limiting control means controls the differential limiting means to transmit the transmission torque to the front wheels when the determining means determines that the vehicle is not in a turning state at a large steering angle. The driving force control device for a four-wheel drive vehicle according to claim 1 or 2.