JPH111129A - Slip control device for four-wheel drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a slip positively by making the width of a dead band in slip control as narrow as possible while preventing a tight corner brake phenomenon during extremely low speed turning. SOLUTION: On the basis of signals from a steering wheel angle sensor 22 and a yaw rate sensor 23, a correction quantity computing part 41 computes the correction quantity of wheel speed of each wheel so as to dissolve the locus difference of each wheel during turning. On the basis of this correction quantity, a front outer wheel speed computing part 42, a front inner wheel speed computing part 43, a rear outer wheel speed computing part 44 and a rear inner wheel speed computing part 45 respectively correct the wheel speed read from an ABS unit 30. A clutch control part 46 makes the fastening force of a transfer clutch variable on the basis of the wheel speed difference of the front and rear wheels after correction. The width of a dead band to the wheel speed difference of the front and rear wheels at the time of slip control can therefore be made narrower than before while suppressing the generation of a tight corner brake phenomenon during extremely low speed turning, and a slip at the time of steering start can be positively prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slip control device for a four-wheel drive vehicle that prevents a wheel from slipping by varying the torque transmission distribution between a front wheel side and a rear wheel side via a transfer clutch.

[0002]

2. Description of the Related Art As is well known, in a four-wheel drive vehicle, when turning while steering in a four-wheel drive state, a rotational speed difference occurs between the front and rear wheels due to a difference in turning radius, and a tight corner brake is applied. The phenomenon occurs.

[0003] For this reason, the present applicant has previously disclosed
In Japanese Patent No. 29725, a hydraulic clutch having a variable capacity is used as a transfer clutch for switching between two-wheel drive and four-wheel drive, and the capacity of the transfer clutch is changed according to the slip ratio of the front and rear wheels during turning by turning. Reduce
A technique for reducing the driving force on the front wheel side or the rear wheel side has been proposed.

[0004]

One of the functions for controlling a four-wheel drive vehicle is to vary the torque transmission distribution between the front and rear wheels in accordance with the rotation difference between the front and rear wheels, so that the excess of the front wheels or the rear wheels is achieved. In the system using the above-mentioned transfer clutch, the hydraulic pressure supplied to the transfer clutch is controlled to vary the transfer clutch engagement force, and the torque transmission distribution between the front and rear wheels is determined. ing.

However, in order to prevent the wheels from slipping, it is necessary to control the transfer clutch in the direct connection direction according to the rotation difference between the front and rear wheels. On the other hand, in order to prevent the tight corner braking phenomenon, When a rotation difference occurs between the front and rear wheels, it is necessary to set the transfer clutch in the release direction.

For this reason, in the conventional slip control, by providing a relatively large dead zone (region in which control is not performed) with respect to the difference in wheel speed between the front and rear wheels, the difference in rotation between the front and rear wheels during extremely low speed turning is absorbed. The tight corner braking phenomenon is prevented, and there is a problem that it is difficult to start the slip control due to a large dead zone at the time of steering start.

In this case, if the dead zone is simply narrowed, a difference in wheel speed due to a difference in the trajectory of the wheel during extremely low speed turning is erroneously determined as a slip and is controlled in a direction to increase the engagement force of the transfer clutch. This will cause the tight corner braking phenomenon to occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to prevent a tight corner braking phenomenon at an extremely low speed turning and to make a width of a dead zone in a slip control as narrow as possible to surely prevent a slip. It is an object of the present invention to provide a slip control device for a four-wheel drive vehicle that can be operated.

[0009]

According to the first aspect of the present invention,
In a slip control device of a four-wheel drive vehicle that varies a torque transmission distribution between a front wheel side and a rear wheel side via a transfer clutch to prevent wheel slippage, a trajectory difference of each wheel at the time of vehicle turning is eliminated. Means for correcting the wheel speed;
Means for varying the engagement force of the transfer clutch according to the difference between the corrected wheel speeds on the front wheel side and the rear wheel side.

According to a second aspect of the present invention, in the first aspect of the invention, any one of the four wheels is used as a reference wheel, and a difference between a turning locus of the reference wheel and a turning locus of another wheel is determined. The wheel speeds of the other wheels are corrected based on

According to a third aspect of the present invention, in the first aspect of the invention, one of the front wheel side and the rear wheel side is used as a reference wheel, and the turning locus of the reference wheel and the turning of the front wheel side or the rear wheel side. It is characterized in that the wheel speed on the front wheel side or the rear wheel side is corrected based on the difference from the trajectory.

That is, in the slip control device for a four-wheel drive vehicle according to the present invention, the wheel speed is corrected so as to eliminate the difference in trajectory of each wheel when the vehicle turns, and the corrected wheel speed for the front wheels and the rear wheels is corrected. By varying the engagement force of the transfer clutch according to the difference between the two, the torque transmission distribution between the front wheel side and the rear wheel side is changed to prevent the wheels from slipping.

At this time, any one of the four wheels is set as a reference wheel, and the wheel speed of the other wheel is corrected based on the difference between the turning locus of this reference wheel and the turning locus of the other wheel. One of the front wheel side and the rear wheel side may be used as a reference wheel, and a wheel on the front wheel side or the rear wheel side may be determined based on a difference between a turning locus of the reference wheel and a turning locus on the front wheel side or the rear wheel side. The speed may be corrected.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 show a first embodiment of the present invention.
FIG. 1 is a block diagram of a clutch control function,
2 is an overall configuration diagram of a drive control system, FIG. 3 is a flowchart of a clutch control routine, FIG. 4 is an explanatory diagram of calculating a wheel speed correction amount by a four-wheel model, and FIG. 5 is an explanatory diagram of a slip determination map.

In FIG. 2, reference numeral 1 denotes an engine disposed at the front of the vehicle. The output shaft of the engine 1 is provided with a transmission such as an automatic transmission using a fluid torque converter or a manual transmission including a clutch mechanism. A mechanism 2 is provided in series, and a center differential device 3 is provided in a rear portion of the transmission mechanism 2.

The above-mentioned center differential device 3
Is connected to a front differential device 7 via a transfer drive gear 4, a transfer driven gear 5, and a front drive shaft 6 serving as a drive pinion shaft, and is connected to a rear drive shaft 9 via a hydraulic multi-plate transfer clutch 8. The rear differential device 12 is connected to the rear drive shaft 9 via a propeller shaft 10 and a drive pinion shaft 11.
It is connected to.

In the transfer clutch 8, the fastening force is varied by hydraulic pressure supplied from a hydraulic system (not shown) via a clutch control valve 13. In the disengaged state, the torque distribution of the center differential device 3 is distributed. When the output is performed as it is and the vehicle is completely fastened, a direct connection state is achieved in which the torque is equally distributed to the front and rear wheels.

The transmission mechanism 2, the center differential device 3, the front differential device 7, and the like are integrally provided in a case 14.

The front differential 7 has a front left wheel 16L via a front left drive shaft 15L.
And a right front wheel 16R is continuously provided via a front right drive shaft 15R. A left rear wheel 18L is continuously provided to the rear differential device 12 via a rear left drive shaft 17L. In addition, a right rear wheel 18R is continuously provided via a rear wheel right drive shaft 17R.

On the other hand, reference numeral 30 denotes front and rear wheels 16L, 16L.
An ABS unit that controls the hydraulic pressure of a brake system (not shown) based on signals from wheel speed sensors 19L, 19R, 20L, and 20R attached to R, 18L, and 18R, respectively, to avoid locking the wheels during braking. Reference numeral 40 denotes a control unit that controls the engagement force of the transfer clutch 8, and is connected to the ABS unit 30 via, for example, a serial line.

The control unit 40 is connected to sensors such as a steering wheel angle sensor 22 provided on a steering column of the steering wheel 21 for detecting a steering wheel angle θ and a yaw rate sensor 23 for detecting an actual yaw rate γ of the vehicle. In addition, actuators such as the above-described clutch control valve 13 for controlling the hydraulic pressure to the transfer clutch 8 are connected, and control the engagement force of the transfer clutch 8 so as to control the hydraulic pressure applied to the front and rear wheels according to the speed difference between the front and rear wheels. Slip control is performed to vary the torque distribution to the wheels and to prevent the wheels from slipping on a road surface having a low friction coefficient μ.

That is, when a difference in wheel speed (difference in rotational speed) between the front and rear wheels occurs, for example, when starting on a road surface having different front and rear friction coefficients μ, or when accelerating with 4WD with rear wheel bias, The fastening force of the transfer clutch 8 is strengthened via the valve 13 to reduce the slip by approaching the direct coupling direction.

In this case, the control unit 40 has a built-in slip determination map relating to the wheel speed difference as shown in FIG. 5, for example, and refers to the slip determination map to determine a dead zone (region where no control is performed). The transfer clutch 8 is controlled in the direct connection direction via the clutch control valve 13 so that the engagement force proportional to the exceeded value is generated. However, in order to improve the control efficiency of the slip control, the transfer control in the slip determination map is performed. It is desirable to make the width of the dead zone as narrow as possible.

However, in extremely low-speed turning on a road surface having a relatively high friction coefficient μ, a difference in trajectory between the wheels causes a difference in wheel speed between the front and rear wheels. Therefore, if the dead zone of the slip determination map is simply narrowed, The wheel speed difference due to this trajectory difference is erroneously determined to be a slip, and is controlled in a direction to increase the engagement force of the transfer clutch 8, and as a result, the occurrence of a tight corner braking phenomenon is promoted.

For this reason, the control unit 40 uses one of the wheels as a reference wheel, and corrects the wheel speed of each of the remaining wheels so as to match the reference wheel. The error is removed, and the slip control is performed based on the corrected wheel speed difference.

The function of the control unit 40 relating to the clutch engagement control is, as shown in FIG. 1, a correction amount for calculating a correction amount of the wheel speed of each wheel based on signals from the steering wheel angle sensor 22 and the yaw rate sensor 23. The calculating unit 41 corrects each wheel speed read from the ABS unit 30 based on the correction amount and calculates each wheel speed after the correction, that is, a front wheel outer wheel speed calculating unit 42 that calculates a front wheel outer wheel speed. A front wheel inner wheel speed calculator 43 for calculating front wheel inner wheel speeds; a rear wheel outer wheel speed calculator 4 for calculating rear wheel outer wheel speeds.
4. a rear wheel inner wheel speed calculator 45 for calculating a rear wheel inner wheel speed;
The clutch control unit 46 controls the clutch control valve 13 based on the corrected wheel speed difference between the front and rear wheels, and varies the engagement force of the transfer clutch 8.

Hereinafter, the clutch engagement control process according to the above configuration will be described with reference to the flowchart of FIG.
In the following description, an example of correcting the wheel speed of each of the remaining wheels with respect to the turning center using the outer wheel of the front wheel as a reference wheel will be described, and the correction amount of the front wheel outer wheel speed is set to 0.

In the clutch engagement control routine shown in FIG. 3, first, in step S10, the steering wheel angle θ detected by the steering wheel angle sensor 22 and the yaw rate γ detected by the yaw rate sensor 23 are read, and the wheels of the respective wheels from the ABS unit 3 are read. Read speed data. The wheel speed data for the turning center is the front wheel outer wheel speed Vα01, the front wheel inner wheel speed Vα02, the rear wheel outer wheel speed Vα03, and the rear wheel inner wheel speed Vα04.

Next, the process proceeds to step S20, in which the front wheel outer wheel is used as a reference wheel, and the speed correction amount of each wheel based on the difference in turning radius with respect to this reference wheel is calculated. For example, as illustrated in FIG. 4, assuming that the vehicle makes a left turn, the speed differences ΔV12, ΔV13, and ΔV14 of the respective wheels with respect to the reference wheel are represented by the following (1) to
As shown in equation (3), the difference between the turning radius of the reference wheel and the turning radius of each wheel can be obtained as a value obtained by multiplying the difference by the yaw rate γ, and these are used as the correction amounts of each wheel. ΔV12 = (R1−R2) · γ (1) ΔV13 = (R1−R3) · γ (2) ΔV14 = (R1−R4) · γ (3) where R1: the front wheel outer wheel (reference wheel) Turning radius R2: Turning radius of front wheel inner wheel R3: Turning radius of rear wheel outer wheel R4: Turning radius of rear wheel inner wheel

Here, as shown in FIG. 4, when the steady turning of the vehicle is described geometrically, the turning radius R2 of the front inner wheel is calculated.
Can be regarded as substantially equal to the value obtained by subtracting the tread Df of the front wheel from the turning radius R1 of the front wheel outer wheel, as shown in the following equation (4). Assuming that the side slip angle of the center of gravity of the vehicle during traveling is β0, the side slip angle β0 and the wheel base L of the vehicle can be approximated by the following equation (5). R2 = R1−Df (4) R3 = R1−L · sin β0 (5)

The turning radius R4 of the rear wheel inner wheel can be regarded as being equal to a value obtained by subtracting the rear wheel tread Dr from the turning radius R3 of the rear wheel outer wheel. It can be expressed by the following equation (6). R4 = R3−Dr = R1−L · sin β0−Dr (6)

Further, the geometric relationship between the side slip angle β0 of the vehicle center of gravity, the turning radius RM of the vehicle center of gravity, and the distance Lr between the rear axle and the center of gravity can be obtained by the following equation (7). The turning radius RM can be obtained from the wheel base L and the actual steering angle δ (δ = θ / N; N is the steering gear ratio) as shown in the following equation (8). Using these equations, the sideslip angle β0 can be obtained by the following equation (9). tanβ0 = Lr / RM (7) RM = L / tanδ (8) β0 = tan ^-1 (Lrtanδ / L) (9)

Therefore, finally, the correction amounts ΔV12, ΔV13, ΔV14 of the respective wheels shown in the above equations (1) to (3) are transformed using the above equations (4) to (6). By using the sideslip angle β0 according to the equation (9), it can be obtained by the following equations (10) to (12). ΔV12 = Df · γ (10) ΔV13 = L · sin (tan ⁻¹ (Lr · tan δ / L)) · γ (11) ΔV14 = L · sin (tan ⁻¹ (Lr · tan δ / L)) · γ + Dr · γ (12)

As described above, the correction amounts ΔV12, ΔV13,
After calculating ΔV14, the process proceeds to step S30, where ABS
Wheel speed Vα01, Vα0 of each wheel read from unit 30
2, Vα03 and Vα04 are corrected according to the following (13) to (16),
The wheel speeds Vα1, Vα2, Vα3, Vα4 of each wheel are calculated.
Note that the wheel speed of the front outer wheel, which is the reference wheel, is not corrected (correction amount is 0), and data read from the ABS unit 30 is adopted. Vα1 = Vα01 (13) Vα2 = Vα02 + ΔV12 (14) Vα3 = Vα03 + ΔV13 (15) Vα4 = Vα04 + ΔV14 (16)

Thereafter, the process proceeds to step S40, in which the front wheel speed is represented by the sum of the wheel speeds (Vα1 + Vα2) of the front wheel outer wheel and the front wheel inner wheel, and the wheel speed (Vα) of the rear wheel outer wheel and the rear wheel inner wheel.
3 + Vα4) is representative of the rear wheel speed, and it is determined whether or not the speed difference between the front wheel and the rear wheel exceeds the dead zone of the slip determination map shown in FIG. As a result, when the speed difference between the front wheel and the rear wheel is within the dead zone width, the routine exits from the step S40, and when the speed difference exceeds the dead zone, the step S4
From 0, the process proceeds to step S50 to perform clutch control relating to the engagement force of the transfer clutch 8.

In the clutch control in step S50, the control amount for the clutch control valve 13, for example, the clutch control amount, depends on the value of the speed difference (Vαf−Vαr) between the front wheel and the rear wheel exceeding the dead zone of the slip determination map shown in FIG. When a duty solenoid valve is used as the control valve 13, a duty ratio for controlling the operating oil pressure of the transfer clutch 8 is calculated, and the engagement force of the transfer clutch 8 is increased or decreased.

In this case, since the speed difference between the front and rear wheels is corrected so as to remove the wheel trajectory error at extremely low speed turning, even if the dead zone width of the slip determination map is made narrower than before, the tight corner braking phenomenon occurs. Is not generated, and the improvement of the slip control efficiency by the appropriate dead zone width and the prevention of the tight corner braking phenomenon can be achieved at the same time. That is, it is possible to reliably prevent the slippage at the time of turning start and the like, and to prevent the deterioration of the riding comfort due to the occurrence of the tight corner braking phenomenon at the extremely low speed turning.

6 to 8 relate to a second embodiment of the present invention. FIG. 6 is an overall configuration diagram of a drive control system, FIG. 7 is a block diagram of a clutch control function, and FIG. FIG. 9 is an explanatory diagram of correction amount calculation.

This embodiment differs from the first embodiment in that a front wheel speed signal corresponding to an average value of left and right wheel speeds on the front wheel side and a rear wheel side speed signal are not measured for each of the four wheels. And a rear wheel speed signal corresponding to the average value of the left and right wheel speeds, and the correction is performed based on one of the rear wheel side and the front wheel side.

For this reason, as shown in FIG. 6, the control unit 40 does not use a wheel speed sensor for each wheel, but uses the front differential device 7 of the transmission mechanism 2.
The front wheel-side wheel speed data is obtained from a first vehicle speed sensor 24 in an instrument panel connected to the vehicle via a cable, and the rotation of the output shaft of the transfer clutch 8 is detected. The rear wheel side wheel speed data is acquired from the second vehicle speed sensor 25.

As shown in FIG. 7, the function relating to the clutch control of the control unit 40 in the present embodiment changes the processing of the correction amount calculating section 41 of the first embodiment, and
2 and a correction amount calculation unit 41A that calculates a correction amount of the wheel speed based on the trajectory difference between the rear wheel side and the front wheel side based on the signal from the yaw rate sensor 23, the signal from the first vehicle speed sensor 24 and the correction amount. A front wheel speed calculating unit 47 that calculates a wheel speed on the front wheel side based on a signal from the second vehicle speed sensor and a rear wheel speed calculating unit 48 that calculates a wheel speed on the rear wheel side based on the correction amount; Similarly to the above, the clutch control unit 13 controls the clutch control valve 13 on the basis of the corrected wheel speed difference between the front and rear wheels, and varies the engagement force of the transfer clutch 8.

In the processing of the correction amount calculator 41A of the present embodiment,
In order to correct the wheel speed based on either the front wheel side or the rear wheel side, when the rear wheel side is used as a reference, the front wheel side wheel speed Vαf0 based on a signal from the first vehicle speed sensor 24 is used.
The correction amount for the rear wheel speed Vαr0 based on the signal from the second vehicle speed sensor 25 is set to 0. When the front wheel side is used as a reference, the front wheel side wheel speed Vα based on the signal from the first vehicle speed sensor 24 is used.
The correction amount for f0 is set to 0, and the correction amount for the rear-wheel-side wheel speed Vαr0 based on the signal from the second vehicle speed sensor 25 is calculated.

As shown in FIG. 8, a description will be given of an example in which the vehicle turns left on the basis of the rear wheel side. The speed difference Δ between the rear wheel side and the rear wheel side is expressed by the following equation (18). Can be obtained as a value obtained by multiplying the difference between the turning radius Rr on the rear wheel side and the turning radius Rf on the front wheel side by the yaw rate γ. Δ = (Rr−Rf) · γ (17)

As described in the first embodiment, when the steady turning of the vehicle is geometrically described, the turning radius Rr on the rear wheel side is determined from FIG. From this, it can be approximated by the following equation (18). Rr = Rf−L · sin β0 (18)

Similarly to the first embodiment, the side slip angle β0 is calculated by the following equation (19) obtained from the geometric relationship between the turning radius Rr on the rear wheel side and the distance Lr between the rear axle and the center of gravity. L and the actual steering angle δf (δf = θ / N; N is the steering gear ratio) determine the turning radius Rr on the rear wheel side.
It can be obtained by the following equation (21) using the equation (20). tan β 0 = Lr / Rr (19) Rr = L / tan δf (20) β 0 = tan ^-1 (Lr · tan δf / L) (21)

Therefore, the speed difference (correction amount) Δ by the above equation (17) can be obtained by the following equation (22) using the above equations (18) and (21), and the following equation (23) As shown in the equation (24), the wheel speed Vα on the front wheel side by the first vehicle speed sensor 24 is obtained.
The wheel speed Vα on the front wheel side after correction by adding the correction amount Δ to f0
On the other hand, the rear wheel speed Vαr0 obtained by the second vehicle speed sensor 25 is used as it is as the rear wheel speed Vαr. Δ = −L · sin (tan ⁻¹ (Lr · tan δf / L)) · γ (22) Vαf = Vαf0 + Δ (23) Vαr = Vαr0 (24)

Then, similarly to the first embodiment, the clutch control unit 46 controls the front wheel side wheel speed Vαf and the rear wheel side wheel speed Vαr.
The control amount for the clutch control valve 13 is calculated in accordance with the value of which the difference exceeds the dead zone of the slip determination map, and the engagement force of the transfer clutch 8 is increased or decreased.

In this embodiment, as in the case of the first embodiment described above, it is possible to reliably prevent the occurrence of the tight corner braking phenomenon at the time of extremely low speed turning, and to surely prevent the slippage at the time of starting the steering.

[0049]

As described above, according to the present invention, the wheel speed is corrected so as to eliminate the difference between the trajectories of the wheels when the vehicle turns, and the difference between the corrected wheel speeds of the front wheel and the rear wheel is obtained. The width of the dead zone for the difference in wheel speed between the front and rear wheels is increased by changing the transfer clutch engagement force according to the change in the torque transmission distribution between the front and rear wheels to prevent the wheels from slipping. The tight corner braking phenomenon does not occur when turning at extremely low speeds even if it is narrow, so that it is possible to improve the slip control efficiency and prevent the tight corner braking phenomenon from occurring with an appropriate dead zone width. In addition to the above, excellent effects can be obtained, such as being able to reliably prevent slippage and the like, and to prevent deterioration of ride comfort due to the occurrence of a tight corner braking phenomenon during extremely low speed turning.

[Brief description of the drawings]

FIG. 1 is a block diagram of a clutch control function according to a first embodiment of the present invention.

FIG. 2 is an overall configuration diagram of a drive control system according to the first embodiment;

FIG. 3 is a flowchart of a clutch control routine according to the first embodiment;

FIG. 4 is an explanatory diagram of calculating a wheel speed correction amount by using a four-wheel model.

FIG. 5 is an explanatory diagram of a slip determination map according to the embodiment;

FIG. 6 is an overall configuration diagram of a drive control system according to a second embodiment of the present invention.

FIG. 7 is a block diagram of a clutch control function according to the first embodiment;

FIG. 8 is an explanatory diagram of calculating a wheel speed correction amount using a two-wheel model;

[Explanation of symbols]

 8 Transfer clutch 41 Correction amount calculation unit 42 Front wheel outer wheel speed calculation unit 43 Front wheel inner wheel speed calculation unit 44 Rear wheel outer wheel speed calculation unit 45 Rear wheel inner wheel speed calculation unit 46 Clutch control unit

Claims (3)

[Claims] 1. A slip control device for a four-wheel drive vehicle that varies a torque transmission distribution between a front wheel side and a rear wheel side via a transfer clutch to prevent wheel slippage. Means for correcting the wheel speed, and means for varying the fastening force of the transfer clutch according to the difference between the corrected wheel speeds on the front wheel side and the rear wheel side. A slip control device for a four-wheel drive vehicle. 2. A method according to claim 1, wherein any one of the four wheels is used as a reference wheel, and the wheel speeds of the other wheels are corrected based on the difference between the turning locus of the reference wheel and the turning locus of another wheel. The slip control device for a four-wheel drive vehicle according to claim 1, wherein: 3. One of the front wheel side and the rear wheel side is set as a reference wheel, and a front wheel side or a rear wheel side is determined based on a difference between a turning track of the reference wheel and a turning track of the front wheel side or the rear wheel side. The slip control device for a four-wheel drive vehicle according to claim 1, wherein the wheel speed is corrected.