JPH0699762A - Control method for rear wheel differential limiting device - Google Patents

Abstract

PURPOSE:To ensure safety of a vehicle through prevention of the occurrence of the simultaneous slip of two rear wheels and a vehicle spin. CONSTITUTION:When one of left and right rear wheels 13L and 13R is slipped during running of a low mu, road, rear differential limit torque responding to a slip state is generated at a rear clutch 28 to prevent the occurrence of a slip. In this case, the ones, being lower in a wheel speed, of front and rear wheels are compared with each other by means of a control unit 50. During running on the split mu road, the wheels on the one side of left and rear front wheels 9L and 9R are similarly slipped and when a wheel speed on the high muroad side increased owing to rear differential limit torque is increased over a dead zone to a value higher than the wheel speed on the high side road of a front wheel. The rear differential limit torque thereof is reduced for correction by means of a correction factor, the increase of the wheel speed on the high muroad side of a rear wheel is suppressed, and the simultaneously slip of two rear wheels are prevented from occurring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for controlling the rear differential limiting torque of a rear wheel differential limiting device mounted on a rear differential of a vehicle in accordance with each driving and running condition. The present invention relates to control for preventing simultaneous slipping of two rear wheels in slip control.

[0002]

2. Description of the Related Art Generally, in a vehicle, when one of the left and right rear wheels slips or a braking force difference occurs between the two wheels due to an accelerator off or the like, a yaw moment in an understeer direction or an oversteer direction is generated, and It is known to greatly affect stability. Therefore, it has been proposed to control the torque distribution of the left and right rear wheels by the rear differential limiting torque of the rear wheel differential limiting device to prevent slip-in and tack-in behavior when the accelerator is off.

Conventionally, regarding the control of the rear wheel differential limiting device, for example, there is an application of Japanese Patent Laid-Open No. 3-123036. Here, the wheel speeds of the left and right rear wheels are detected, and when the wheel speed difference is equal to or greater than a set value, slip determination is performed and the rear differential limiting torque is controlled in the maximum differential lock direction. It is shown that the rear differential lock prevents slippage.

[0004]

By the way, in the above-mentioned prior art, it is possible to suppress the slip of the left and right rear wheels to improve the traction performance. However, since it is a method of controlling the rear differential limiting torque in the diff lock direction by making a slip determination based only on the wheel speeds of the left and right rear wheels, there are the following problems.

That is, as shown in FIG. 5, when traveling on a split μ road in which the right side of the road surface is a low μ road and the left side is a high μ road, for example, the rear wheels 13R or the front wheels 9R of the right drive wheels are run.
Then, the rear wheel 13R may slip. At this time, if the rear differential limiting torque Tr of the rear wheel differential limiting device 11 is controlled in the differential lock direction by the slip of the right rear wheel 13R as in the prior art, the left rear wheel 13L also slips due to the differential lock and the rear 2 Simultaneous wheel slip may occur. Further, in this case, the wheel speed Nrl of the left rear wheel 13L increases to be equal to or higher than the wheel speed Nfl of the left front wheel 9L, which may cause a vehicle spin and impair the directional stability of the vehicle. The rear inner wheels are most likely to slip when turning on a low μ road, but if the same control is performed in this case as well, the two rear wheels may slip simultaneously and the stability of the vehicle may be impaired.

The present invention has been made in view of this point, and in the slip control of the rear wheel differential limiting device, it is possible to prevent the two rear wheels from simultaneously slipping, the vehicle spin, and the like to ensure the stability of the vehicle. With the goal.

[0007]

In order to achieve the above object, the present invention provides a rear differential limiting torque of a rear wheel differential limiting device attached to rear differentials of left and right rear wheels, at least according to a slip state. In the control system for controlling, if the rear wheel speed is smaller than the front wheel speed is smaller than the dead zone, the rear two wheels are simultaneously slipped. A correction coefficient is set accordingly, and the rear differential limiting torque is reduced and corrected.

[0008]

According to the above method, when one of the left and right rear wheels slips while traveling on a low μ road, a rear differential limiting torque is generated in the rear wheel differential limiting device according to the slip state to prevent the slip. Whether or not there is simultaneous slip on the two rear wheels is determined by comparing the two who have the smaller wheel speed.
Therefore, one of the left and right front wheels also slips when traveling on a split μ road, etc., and the wheel speed on the high μ road side increased due to the rear differential limiting torque of the rear wheels against the wheel speed on the high μ road side of the front wheels, and the dead zone. When it becomes larger, the rear differential limiting torque is reduced and corrected by the correction coefficient, and the increase in the wheel speed of the rear wheels on the high μ road side is suppressed. Thus, the rear two wheels can be simultaneously slipped while suppressing the rear wheel slip. It will be surely prevented.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 2, an outline of a drive system of a full-time four-wheel drive vehicle having a center differential will be described. Reference numeral 1 is an engine, 2 is a clutch, 3 is a transmission, and the transmission output shaft 4 is a center differential 20. Are typing in. Center differential 2
0 to the front drive shaft 5 in the front and rear drive shaft 6 in the rear
The front drive shaft 5 is output to the left and right front wheels 9L and 9R through the front differential 7 and the axle 8, and the rear drive shaft 6 is the propeller shaft 10 and the rear differential 1.
1 and the left and right rear wheels 13L and 13R via the axle 12, respectively.

The rear differential 11 is of a bevel gear type, and a hydraulic multi-plate type rear clutch 28 is attached as a differential limiting device between the differential case 11a and one side gear 11b of the rear differential 11 in a bypass manner. When the rear differential limiting torque Tr of the rear clutch 28 is zero, the left and right rear wheels 13L, 1
When the torque is distributed equally to 3R and a predetermined rear differential limiting torque Tr is generated, the torque is moved from the high speed wheel to the low speed wheel by this torque Tr, and the largest rear differential limiting torque Tr is generated.
Diff locks, and in this case the left and right rear wheels 13L, 13
Torque is distributed according to the product W · μ of the vehicle weight W applied to R and the road surface friction coefficient μ.

The center differential 20 is a compound planetary gear type, and has a first sun gear 21 integrated with the transmission output shaft 4 and a second sun gear 2 integrated with the rear drive shaft 6.
2 and a plurality of pinions 23 arranged around the sun gears 21 and 22. The first pinion gear 23 a of the pinion 23 meshes with the first sun gear 21, and the second pinion gear 23 b of the pinion 23 meshes with the second sun gear 22. A drive gear 25 is rotatably provided on the transmission output shaft 4, and a pinion 23 is pivotally supported by a carrier 24 integrated with the drive gear 25. The drive gear 25 is a driven gear 26 integrated with the front drive shaft 5.
It is configured to mesh with. On the other hand, the center differential 20 is provided with a hydraulic multi-plate center clutch 27 as a differential limiting device. The center clutch 27 is coaxially arranged, for example, immediately after the center differential 20 by coupling the drum 27a to the carrier 24 and the hub 27b to the rear drive shaft 6.

With the configuration of this center differential 20, the speed change power input to the first sun gear 21 is
It is transmitted separately to the carrier 24 and the second sun gear 22 with a predetermined reference torque distribution. Further, the rotation difference between the front and rear wheels during turning is absorbed by the planetary rotation of the pinion 23. Here, the reference torque distribution is two sun gears 21 and 22.
It is possible to set the reference torque distribution of the front and rear wheels sufficiently to the rear wheel bias because the four gear meshing pitch circle radii of the two pinion gears 23a and 23b are freely set. Further, when the front engine is mounted, the static weight distribution of the front wheel weight and the rear wheel weight of the vehicle is biased to the front wheels, and when the hydraulic clutch 27 is directly connected by the differential limitation,
According to this weight distribution, torque is distributed more heavily on the front wheels. Therefore, the center differential limiting torque Tc of the hydraulic clutch 27 is
The torque distribution of the front and rear wheels can be controlled in a wide range from the reference torque distribution of the rear wheel bias to the weight distribution of the front wheel bias.

Next, the hydraulic control system for the center clutch 27 and the rear clutch 28 will be described. First, when the transmission is an automatic transmission, the oil pump 3 of its hydraulic control system is used.
It is configured by using the line pressure obtained by adjusting the hydraulic pressure of 0 with the regulator valve 31. Therefore, the center clutch hydraulic pressure control means 32 has a clutch control valve 34 that communicates with the line pressure oil passage 33, and this clutch control valve 34 communicates with the center clutch 27 through an oil passage 35. Further, the line pressure oil passage 33 communicates with the solenoid valve 40 through an oil passage 38 having a pilot valve 36 and an orifice 37, and the duty pressure by the solenoid valve 40 acts on the control side of the clutch control valve 34 through the oil passage 39. . The solenoid valve 40 is
When a duty signal corresponding to each traveling condition is input from the control unit 50, the hydraulic pressure is drained thereby to generate a duty pressure. The clutch control valve 34 is operated according to the duty pressure to operate the center clutch 27.
The center differential limiting torque Tc is variably controlled. Also,
The rear clutch hydraulic pressure control means 32 ′ is similar to the oil passage 33,
Clutch control valve 34 'and solenoid valve 4 in communication with 38
0 ', and the rear differential limiting torque Tr of the rear clutch 28 is variably controlled by the duty pressure of the solenoid valve 40'.

Referring to FIG. 1, the slip-time control system of the rear wheel differential limiting device will be described. As input information, the rotation speed sensors 42 and 43 for detecting the wheel speeds Nfl and Nfr of the left and right front wheels 9L and 9R, and the wheel speed N of the left and right rear wheels 13L and 13R.
The rotation speed sensors 44 and 45 for detecting rl and Nrr are provided, and these sensor signals are input to the control unit 50.

The basic control system of the control unit 50 will be described. The control unit 50 has a wheel speed difference calculation unit 51 to which the wheel speeds Nrl and Nrr of the left and right rear wheels are input, and the wheel speed difference ΔNr is obtained by subtracting the wheel speeds of both wheels. This wheel speed difference ΔNr is P
It is input to the motion correction value setting unit 52, and a correction value Tp for P motion is set by multiplying a predetermined gain by the amount exceeding the dead zone in consideration of the locus difference between the left and right rear wheels. That is, even in the four-wheel grip state, the wheel speed difference ΔNr between the left and right rear wheels is, for example, 8 km / h at maximum.
Therefore, the dead zone is set to 8 km / h. When the wheel speed difference ΔNr exceeds this dead zone, for example, 2 kgf
The correction value Tp is set by multiplying the gain of m / km / h, and the correction value Tp is input to the rear differential limiting torque calculation unit 53.

In order to prevent hunting, the wheel speed difference Δ
Nr is input to the change rate calculation unit 54 and the change rate d of the wheel speed difference is input.
ΔNr / dt is obtained, and this change rate dΔNr / dt is input to the D motion correction value setting unit 55. And the change rate dΔNr
/ Dt is multiplied by a gain of, for example, 0.01 kgfm / km / h / s to determine a correction value Td for the D operation, and this correction value Td
Is also input to the rear differential limit torque calculation unit 53. The rear differential limiting torque calculation unit 53 has a basic differential limiting torque Tb set by a map according to a general traveling state, and the basic differential limiting torque Tb is corrected by the above-described correction values for P operation and D operation. By adding Tp and Td, a rear differential limiting torque Tr that corresponds to prevention of rear wheel slip and hunting is calculated.

Next, the control system for preventing the two rear wheels from slipping simultaneously will be described. First, explaining the control law,
The presence or absence of simultaneous rear two-wheel slip cannot be judged only by the rear wheel speeds, and therefore it is necessary to monitor the four wheel speeds. When the rear wheel speed is smaller than the front wheel speed is smaller than the dead zone considering the trajectory difference, it can be determined that the rear two wheels are simultaneously slipping. Therefore, at this time, the rear differential limiting torque may be corrected so as to be loosened.

Therefore, the wheel speeds Nfl and Nfr of the left and right front wheels are set.
And the wheel speeds Nrl, Nrr of the left and right rear wheels are input to the selection units 56, 57 for selecting the smaller wheel speeds, and the wheel speed Nfl or Nfr, Nfr, is selected for the wheel speed of the front and rear wheels.
Nrl or Nrr is a rear two-wheel simultaneous slip determination unit 58.
To enter. Here, the locus difference between the front and rear wheels is, for example, a maximum of 4 km / h when the front inner wheel is gripped by the rear differential lock and fully steered. Therefore, the rear wheel side has a small wheel speed Nfl or Nfr. When the wheel speed Nrl or Nrr exceeds this dead zone, the rear two wheels simultaneous slip is determined, and the correction coefficient setting unit 59 determines the correction coefficient K according to the slip state.

Here, the correction coefficient setting unit 59 divides into, for example, 25 km / h or less set vehicle speed and above, in consideration of sensor accuracy and the like. Wheel speed difference ΔN below the set vehicle speed
(For example, Nrl−Nfl) is calculated, and the correction coefficient K is applied to the wheel speed difference ΔN that exceeds the dead zone as shown in FIG.
Is set as a decreasing function. When the vehicle speed is equal to or higher than the set vehicle speed, the slip ratio S (ΔN / V) is calculated, and the correction coefficient K is similarly set for the slip ratio S exceeding the dead zone corresponding to 4 km / h as shown in FIG. To do.

This correction coefficient K is input to the correction section 60 and is corrected by multiplying the rear differential limiting torque Tr by the correction coefficient K. Then, this torque is further applied to the duty ratio converter 61.
Is converted into a predetermined duty ratio D, and this duty signal is output to the solenoid valve 40 '.

Next, the operation of this embodiment will be described. First, when the vehicle is running, the power of the engine 1 is input to the transmission 3 via the clutch 2, and the power of the shift is input to the first sun gear 21 of the center differential 20. Here, since the reference torque distribution is set to the rear wheel bias by the gear specifications of the center differential 20, the power is output by distributing the torque to the carrier 24 and the second sun gear 22 by this torque distribution. At this time, if the center clutch 27 is released, the power is further transmitted to the front and rear wheels by the above-mentioned reference torque distribution, and the drive system becomes FR even though it is a four-wheel drive, so that the turning performance and maneuverability are improved. Further, the center differential 20 becomes free, and it becomes possible to freely turn while absorbing the rotation difference between the front and rear wheels.

On the other hand, when the center differential limiting torque Tc is generated in the center clutch 27 by the hydraulic control means 32,
According to the torque Tc, the torque is further bypassed between the second sun gear 22 and the carrier 24, and the torque is variably controlled from the rear wheel heavy load to the front wheel heavy load torque distribution according to the vehicle weight distribution at the time of direct connection, and the front wheel is distributed. Alternatively, slip of the rear wheels and the like are prevented. At this time, due to the limited differential of the center differential 20, power is effectively transmitted to improve escape, running performance, stability and the like.

Power transmitted to the rear wheels by distributing the torque by the center differential 20 and the center clutch 27 is input to the rear differential 11, and the rear differential 11 and the rear clutch 28 further distribute the torque to the left and right rear wheels 13L, 13R. Controlled and transmitted. That is, when the rear clutch 28 is disengaged, the rear differential 11 becomes free, and equal torque is distributed according to its gear specifications.

In this four-wheel drive running, the wheel speeds Nfl, Nfr, Nrl of the four-wheel speed sensors 42 to 45 are determined.
Nrr is input to the control unit 50 and processed. That is, the wheel speed difference ΔNr between the left and right rear wheels is calculated, the rear wheel slip is determined based on this wheel speed difference ΔNr, and in the case of non-slip, the torque Tr is calculated only with the basic differential limiting torque Tb corresponding to the running state. It Then, the duty signal of this torque Tr is output to the hydraulic control means 32 ', and the rear clutch 28 produces a predetermined rear differential limiting torque Tr. Therefore, the left and right rear wheels 1 according to the rear differential limiting torque Tr
3L and 13R are distributed to predetermined unequal torque.

On the other hand, when the vehicle travels on a low μ road, if the wheel speed difference ΔNr between the left and right rear wheels increases beyond the dead zone to cause a slip, the rear differential limit is set by the correction values Tp and Td for the P operation and the D operation. The torque Tr is largely controlled. Therefore, torque is transferred from the high-speed slip wheel to the low-speed grip wheel,
The torque of the slip wheels is reduced and the slip is prevented. When slip is prevented in this way, the wheel speed difference Δ
Although Nr decreases, the rear differential limiting torque Tr is maintained in a relatively large state by the correction value Td of the D operation, which prevents hunting by repeating slip and non-slip.

At this time, the wheel speed Nf on the front wheel side is further reduced.
1 or Nfr and a small wheel speed Nrl or Nrr on the rear wheel side are selected, and these smaller ones are compared in consideration of the dead zone. Therefore, when both the left and right front wheels 9L and 9R grip, both wheel speeds Nfl and Nfr are substantially equal, and even on the rear wheel side, both wheel speeds Nrl and Nrr are controlled to be substantially equal by slip control by the rear differential limiting torque Tr. Become. Therefore, the wheel speed difference ΔN between the two becomes smaller,
The two rear wheels do not slip at the same time, and the above-described slip-time control state is maintained.

On the other hand, when the vehicle runs on the split μ road in FIG. 5, the wheel speeds of the left and right front wheels 9L and 9R also change according to the difference in road surface μ, and the low μ road side wheel 9R of the front wheels slips as shown in FIG. The wheel speed Nfr is high, and the wheel speed Nfl of the same-height μ road-side wheel 9L may be low. On the other hand, on the rear wheel side, as described above, the rear differential limiting torque Tr is generated and the slip control is performed, so that the wheel speed No becomes substantially equal to the one-dot chain line.
Therefore, in this case, the small wheel speed Nfl on the front wheel side and the wheel speed No on the rear wheel side are compared, and as shown in the figure, the wheel speed Nfl.
On the other hand, when the wheel speed No becomes greater than the dead zone, it is determined that the two rear wheels are slipping at the same time. Then, the correction coefficient setting unit 59 sets the correction coefficient K according to the wheel speed difference ΔN or the slip ratio S depending on the vehicle speed. In addition, the correction coefficient K is corrected by the correction unit 60 to reduce the rear differential limiting torque Tr.

Therefore, at the rear wheels, the rear differential limiting torque T
As r is loosened, as shown in FIG.
The wheel speed Nrl of L is suppressed so as to fall below the dead zone with respect to the wheel speed Nfl of the front wheels on the high μ road side. In this way, the rear two-wheel simultaneous slip and the vehicle spin are prevented in a state where the rear wheel slip is suppressed and the traction performance is improved. Even when the vehicle is turning on a low μ road, the same control is performed by determining whether or not the two rear wheels simultaneously slip.

The embodiment of the present invention has been described above, but the present invention is not limited to this.

[0030]

As described above, according to the present invention,
In the slip-time control of the rear wheel differential limiting device, the wheel speeds of the four wheels are monitored and controlled so that the smaller rear wheel speed does not rise beyond the dead zone with respect to the smaller front wheel speed. Therefore, it is possible to effectively prevent the rear two wheels from slipping simultaneously and the vehicle spin on a low μ road, and improve the directional stability of the vehicle. This is a method of setting the correction coefficient to reduce the rear differential limiting torque, so that the control is easy and the rear wheel slip is suppressed to improve the traction performance.
The stability of the vehicle can also be secured. Since the correction coefficient is set according to the wheel speed difference between the front and rear wheels and the slip ratio, the rear wheel slip and the two rear wheel simultaneous slips can be effectively prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment suitable for a control method of a rear wheel differential limiting device of the invention.

FIG. 2 is a configuration diagram showing a configuration of a drive system and a hydraulic control system of a four-wheel drive vehicle to which the present invention is applied.

FIG. 3 is a characteristic diagram of a correction coefficient for a wheel speed difference and a slip ratio.

FIG. 4 is a diagram showing a control state for preventing rear two wheels from slipping simultaneously.

FIG. 5 is a diagram showing a traveling state on a split μ road.

[Explanation of symbols]

 9L, 9R Front wheel 11 Rear differential 13L, 13R Rear wheel 28 Rear clutch 42-45 Rotation speed sensor 50 Control unit 53 Rear differential limiting torque calculation unit 58 Rear two-wheel simultaneous slip determination unit 59 Correction coefficient setting unit 60 Correction unit

Claims (2)

[Claims] 1. A control system for controlling a rear differential limiting torque of a rear wheel differential limiting device attached to rear differentials of left and right rear wheels at least in accordance with a slip state, with respect to one having a lower front wheel speed. When the rear wheel speed is smaller than the dead zone and increases, the rear two wheels are simultaneously slipped. In this case, a correction coefficient is set according to the amount of the dead zone, and the rear differential limiting torque is set. A method for controlling a rear wheel differential limiting device, characterized by performing reduction correction. 2. The method for controlling a rear wheel differential limiting device according to claim 1, wherein the correction coefficient is set in a decreasing function with respect to the wheel speed difference or the slip ratio.