JP3355767B2 - Differential limit torque control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential limiting torque control device for electronically controlling a differential limiting torque between left and right driving wheels based on left and right driving wheel speed difference information.

[0002]

2. Description of the Related Art Conventionally, as a differential limiting torque control device, for example, one disclosed in Japanese Patent Application Laid-Open No. 1-215628 is known.

[0003] In the conventional source described above, the differential limiting torque component given as a larger value as the turning radius is larger and the lateral acceleration is larger, and the differential based on the left and right driving wheel slip amount (difference between left and right driving wheel speed values) detected by a sensor. An apparatus for calculating a target differential limiting torque based on the sum of the limiting torque components and performing control for obtaining the target differential limiting torque is shown.

[0004]

However, in the above-described conventional differential limiting torque control device, the left and right driving wheel slip amount is obtained from the difference between the sensor detection values. Includes the difference between the left and right drive wheel speeds due to the turning trajectory difference at the time of turning (the turning outer wheel side has a larger turning radius and the turning inner wheel side has a smaller turning radius). Even though no slip has occurred in the left and right drive wheels, the amount of left and right drive wheel slip is detected based on the turning trajectory difference, and a tight corner brake is generated by applying the differential limiting torque between the left and right drive wheels. Problem.

Therefore, there is a method of estimating the turning radius based on the difference between the vehicle speed and the right and left driven wheel speeds or the vehicle speed and the lateral acceleration, and correcting the slip amount of the right and left driving wheels detected by the sensor with the turning locus difference. When turning the grip at low speed, the influence of the variation of the tire diameter and the lateral acceleration sensor is large,
The correction value of the turning locus deviates from the true value. If the correction is insufficient, the tight corner brake remains. If the correction is excessive, the difference between the left and right driving wheel speeds is proportionally controlled by the differential limiting torque. No improvement in traction performance when turning left / right split μ road.

To solve this problem, the applicant has
In Japanese Patent Application No. 292617/1992, the wheel speed difference between the front and rear wheels becomes small due to the small wheel speed difference due to the difference in the turning radius of each wheel when turning the grip. Focusing on the fact that the value of the front and rear wheel speed difference increases as the road side drive wheel slip increases, it is determined whether the vehicle is gripping or right / left split μ road running based on the front and rear wheel speed difference. The invention was proposed.

However, when the difference between the front and rear wheel speeds at which the traveling is determined is calculated from the difference between the average value of the left and right driving wheel speeds and the average value of the left and right driven wheel speeds, when entering from a high μ road to a split μ road, Even if only one of the driving wheels on the low μ road starts to idle, the average value of the left and right driving wheel speeds is used, so that the difference between the front and rear wheel speeds gradually increases, and the differential between the right and left driving wheel speed difference that ensures traction performance The start timing of the limit control is delayed.

Further, when a difference in front and rear wheel rotation speed occurs, as in an electronically controlled four-wheel drive vehicle or a four-wheel drive vehicle with a viscous coupling, the engine torque transmitted to the drive wheels is distributed to the driven wheels. In the case of a vehicle that performs a split μ running on a low μ road, the difference between the front and rear wheel rotation speeds is kept small if the control that the engine torque is distributed to the front and rear wheels works.
When the vehicle is traveling on a road, the differential limiting control in proportion to the difference between the left and right driving wheel speeds is released, and good acceleration cannot be obtained. For example, when traveling on a split μ road, both the driving wheels and the driven wheels on the low μ road side run idle due to the distribution of the engine torque between the front and rear wheels, and the difference between the front and rear wheel speeds based on the average value becomes almost zero. In addition, low μ
When the control that distributes the engine torque to the front and rear wheels during road driving is performed, the vehicle may enter a diagonal idling state or a three-wheel idling state, but even in such a case, the difference between the front and rear wheel speeds by the average value is almost zero. Will be.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a first object is to provide a differential control for electronically controlling a differential limiting torque between left and right driving wheels based on left and right driving wheel speed difference information. An object of the limit torque control device is to achieve both the prevention of tight corner braking during turning of a grip and the securing of traction performance by high response during running when one wheel of a driving wheel idles.

A second object of the present invention is to provide a four-wheel-drive vehicle that performs control corresponding to the difference between the front and rear wheel rotational speeds in various modes including prevention of tight corner braking during turning of the grip and idle rotation of the drive wheel. The purpose is to ensure both traction performance and the traction performance in the idling state.

A third object is to obtain high-precision left-right driving wheel speed difference information excluding the influence of turning, in addition to the above objects.

A fourth object, in addition to the above objects, is to prevent control hunting between right and left drive wheel speed difference proportional control and tight corner corresponding control.

[0013]

In order to achieve the first object, a differential limiting torque control device according to a first aspect of the present invention has a structure as shown in FIG.
As shown in the claim correspondence diagram, differential limiting torque applying means a provided between the left and right driving wheels and applying a differential limiting torque according to an external control command, left and right driving wheels and left and right driven wheels Left driving wheel speed detecting means b, right driving wheel speed detecting means c, left driven wheel speed detecting means d,
Right driven wheel speed detecting means e, left and right driving wheel speed difference calculating means f for calculating left and right driving wheel speed differences, and selecting the larger of the left driving wheel detected value and the right driving wheel detected value to select the driving wheel speed Driven wheel speed determining means g; and driven wheel speed calculating means h which calculates an average value of the left driven wheel detected value and the right driven wheel detected value to obtain the driven wheel speed.
A front and rear wheel speed difference calculating means i for calculating a front and rear wheel speed difference based on a difference between the determined drive wheel speed and the calculated driven wheel speed;
When the calculated front and rear wheel speed difference is equal to or less than the set value, the differential limiting torque is determined to be zero or a small value close to zero regardless of the occurrence of the left and right drive wheel speed difference, and the calculated front and rear wheel speed difference is determined. Is larger than the set value, the differential limiting torque determining means j that determines the differential limiting torque according to the left and right driving wheel speed difference, and the differential limiting torque determined by the differential limiting torque determining means j A differential limiting torque control unit k that outputs the obtained control command to the differential limiting torque applying unit a,
It is characterized by having.

In order to achieve the second object, in the differential limiting torque control device according to the second aspect of the present invention, as shown in the claim correspondence diagram of FIG. Is transmitted directly to one of the front and rear wheels, and is transmitted to the other driven wheel via a transfer clutch m. This transfer clutch m is used to generate a front-rear wheel rotational speed difference. From the two-wheel drive state where there is no difference between the front and rear wheel rotation speeds.
It is mounted on a four-wheel drive vehicle whose driving force distribution is changed to a wheel drive state.

According to a third aspect of the present invention, there is provided a differential limiting torque control apparatus according to the third aspect of the present invention, as shown in FIG. In the device, a turning trajectory left / right driving wheel speed difference calculating means n for calculating a turning trajectory left / right driving wheel speed difference generated by a difference in turning radius between the inner wheel and the outer wheel at the time of turning is provided. It is a means for calculating a left-right driving wheel speed difference by subtracting a turning locus left-right driving wheel speed difference calculation value from an absolute value of a difference between a left driving wheel detection value and a right driving wheel detection value.

According to a fourth aspect of the present invention, there is provided a differential limiting torque control apparatus according to the fourth aspect of the present invention, as shown in FIG. In the device, as the set value of the front and rear wheel speed difference,
A first set value that is a start threshold value of the left / right drive wheel speed difference-based differential limit control and a second set value that is an end threshold value of the left / right drive wheel speed difference-based differential limit control are set. Set value setting means o having hysteresis between the first set value and the second set value
Is provided.

[0017]

The operation of the first invention will be described.

When the vehicle is running, the drive wheel speed determining means g selects the larger of the left drive wheel detected value and the right drive wheel detected value to determine the drive wheel speed. The average value of the detected value of the moving wheel and the detected value of the right driven wheel is calculated to be the driven wheel speed. The front and rear wheel speed difference calculating means i calculates the front and rear wheel speed based on the difference between the determined driving wheel speed and the calculated driven wheel speed. The difference is calculated. When the calculated difference between the front and rear wheel speeds is equal to or less than the set value in the front and rear wheel speed difference calculating means i, the differential limiting torque determining means j determines whether or not the difference between the left and right driving wheel speeds has occurred. The torque is determined to be zero or a small value close to zero, and the differential limiting torque control unit k sets the differential limiting torque applied between the left and right driving wheels to the differential limiting torque applying unit a to a small value close to zero or zero. Is output.

Here, for example, when turning the grip left in a rear-wheel drive vehicle, the turning radius of each wheel is different, so that right front wheel speed> right rear wheel speed> left front wheel speed> left rear wheel speed. The relationship is shown, and the front and rear wheel speed difference is equal to or less than the set value. That is, the grip turning is determined based on the condition that the front and rear wheel speed difference is equal to or less than the set value. At this time, by giving the differential limiting torque to zero or a small value close to zero, tight corner braking is reliably prevented.

On the other hand, when the calculated difference between the front and rear wheel speeds exceeds the set value in the front and rear wheel speed difference calculating means i, the difference between the left and right driving wheel speed differences is calculated by the differential limiting torque determining means j. Is determined to be the differential limiting torque according to the difference between the left and right driving wheel speeds.
A control command for obtaining the determined differential limiting torque is output to the differential limiting torque applying means a.

Here, for example, when considering the wheel speed of a rear-wheel drive vehicle on a left / right split μ road with a low μ on the left wheel side and a high μ on the right wheel side, only the left rear wheel speed shows a large value. And the front and rear wheel speed difference exceeds the set value. That is,
Slippery road running, including when the vehicle is stuck, is determined based on the condition that the front and rear wheel speed difference exceeds the set value. At this time, differential limiting torque corresponding to the left and right drive wheel speed difference is applied to improve traction performance. I do. In addition, by selecting the larger of the left driving wheel detection value and the right driving wheel detection value as the driving wheel speed, the difference between the front and rear wheel speeds is smaller than the average wheel driving speed. The timing of exceeding the speed is advanced, and the differential limiting torque control corresponding to the difference between the left and right drive wheel speeds can be started with a good response to one wheel idling of the drive wheels.

The operation of the second invention will be described.

According to the first aspect of the present invention, the differential limiting torque control device increases the fastening force in accordance with the difference between the front and rear wheel rotational speeds, and changes from the two-wheel drive state where no front and rear wheel rotational speed difference occurs to the four-wheel drive state. The vehicle is mounted on a four-wheel drive vehicle whose driving force distribution is changed, and the front and rear wheels on the low μ road side are both idle due to the driving force distribution effect when running on a split μ road, When the driving force distribution function is applied during traveling on the μ road, a diagonal idling or a three-wheel idling may occur. In such a case, when calculating the front and rear wheel speed difference from the difference between the driving wheel speed and the driven wheel speed based on the average value, the front and rear wheel speed difference becomes equal to or less than the set value and the differential limitation corresponding to the left and right driving wheel speed difference is obtained. Although the torque control is not performed, the drive wheel speed is determined by the select high, and the difference between the front and rear wheel speeds in the one-side idling, diagonal idling, and three-wheel idling conditions specific to four-wheel drive vehicles is set. In this case, the traction performance for obtaining good acceleration performance by the differential limiting torque control corresponding to the difference between the left and right driving wheel speeds is secured.

The operation of the third invention will be described.

In calculating the left-right driving wheel speed difference, the turning locus left-right driving wheel speed difference calculating means n calculates the turning locus left-right driving wheel speed difference caused by the difference in turning radius between the inner wheel and the outer wheel during turning. In the driving wheel speed difference calculating means f, the left and right driving wheel speed difference is calculated by subtracting the turning locus left and right driving wheel speed difference calculating value from the absolute value of the difference between the left driving wheel detected value and the right driving wheel detected value.

Therefore, the influence of the difference between the left and right driving wheel speeds based on the radius of the inner and outer wheels and the vehicle speed at the time of turning is eliminated, and accurate left and right driving wheel speed difference information can be obtained.

The operation of the fourth invention will be described.

In determining the differential limiting torque, the set value setting means o includes a first set value which is a start threshold value of the differential limiting control corresponding to the left and right driving wheel speed difference, and a difference between the left and right driving wheel speed difference. Since the second set value, which is the end threshold value of the dynamic limit control, is set, and the first set value and the second set value have hysteresis, the difference between the front and rear wheel speeds is set. In the case of fluctuation in the vicinity, control hunting between the right and left drive wheel speed difference proportional control having a drop in the differential limiting torque and the tight corner corresponding control is prevented.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

First, the configuration will be described.

FIG. 2 is an overall system diagram of an electronically controlled torque split four-wheel drive vehicle based on a rear wheel drive vehicle to which the differential limiting torque control device according to the embodiment of the present invention is applied.

In FIG. 2, 1 is an engine, 2 is a transmission, 3 is a propeller shaft, 4 is an electronically controlled limited slip differential (hereinafter abbreviated as an electronically controlled LSD), 5, 6 are rear wheels, and 7 and 8 are front wheels. , 23 are electronically controlled transfer devices (equivalent to transfer clutch m),
Reference numeral 24 denotes a front differential.

The electric control LSD 4 has a built-in differential limiting clutch 10 for generating a differential limiting torque between the left and right rear wheels 5, 6 in accordance with the clutch control pressure applied from the hydraulic unit 9.

The hydraulic unit 9 includes a hydraulic source 11 and an LS
And a D control valve 12. The hydraulic unit 9 and the differential limiting clutch 10 correspond to differential limiting torque applying means a.

The LSD control valve 12 operates in accordance with a control current ILSD from the active LSD controller 13 to generate a clutch control pressure for the differential limiting clutch 10.

The active LSD controller 13 includes a left front wheel rotation speed NFL from the left front wheel rotation sensor 14 and
Right front wheel rotation speed NFR from right front wheel rotation sensor 15, left rear wheel rotation speed NRL from left rear wheel rotation sensor 16, right rear wheel rotation speed NRR from right rear wheel rotation sensor 17, and lateral acceleration sensor 18 , A longitudinal acceleration XG from the longitudinal acceleration sensor 19, an accelerator opening ACC from the accelerator opening sensor 20, a switch signal BS from the brake switch 21, and an ABS operation signal AS from the ABS controller 22. Is entered.

The electric transfer device 23 has a built-in wet multi-plate clutch (not shown), and the clutch engagement hydraulic pressure is generated by electronic control, so that the clutch is moved toward the front wheels 7 and 8 according to the clutch engagement force. Transmits engine torque. The clutch engagement hydraulic pressure is controlled to a hydraulic pressure that increases with a higher gain as the lateral acceleration YG is smaller, in accordance with the generation of the front and rear wheel rotational speeds. Therefore, the front and rear wheel drive force distribution control is a control in which the drive force distribution to the front wheels is increased from the rear wheel drive state where there is no front and rear wheel rotation speed difference to the front wheel side according to the occurrence of the front and rear wheel rotation speed difference.

Next, the operation will be described.

[Differential Limiting Torque Control Operation Process] FIG. 3 is a flowchart showing the flow of the differential limiting torque control operation process performed by the active LSD controller 13. Each step will be described below.

In step 30, the left front wheel speed NFL, the right front wheel speed NFR, the left rear wheel speed NRL, and the right rear wheel speed NRR
And the lateral acceleration YG are read.

In step 31, the left front wheel speed NFL, the right front wheel speed NFR, the left rear wheel speed NRL, and the right rear wheel speed NRR
From the front left wheel speed VFL, front right wheel speed VFR and rear left wheel speed V
RL and right rear wheel speed VRR are calculated (each wheel speed detecting means b to
e).

In step 32, the vehicle speed VF is obtained by selecting the smaller one of the front left wheel speed VFL and the front right wheel speed VFR, and the rear wheel speed VRM is obtained from the rear left wheel speed VRL and the rear right wheel speed VRR. The left and right front wheel speed difference ΔVF is calculated by selecting the larger one (corresponding to the drive wheel speed determination means g), and the left and right front wheel speed difference ΔVR is calculated from the absolute value of the difference between the left front wheel speed VFL and the right front wheel speed VFR. Is calculated by the absolute value of the difference between the left rear wheel speed VRL and the right rear wheel speed VRR, and the front and rear wheel speed difference ΔVFR is calculated by the difference between the rear wheel speed VRM and the front wheel speed average value VFA (the driven wheel speed calculating means). h and front and rear wheel speed difference calculating means i).

In step 33, the first turning radius R1, the second turning radius R2, and the limit turning radius RL, which is the limit value of the second turning radius R2, are calculated by the following equations.

[0044] ^{R1 = VF 2 / YG R2 =} VF / (K1 · ΔVF) K1; constant ^{RL = max (f (VF 2} ), x) x; In example 5m step 34, the vehicle speed VF and the lateral acceleration YG size Thus, the turning radius R is selected as described below.

I) VF ≦ VFO VFO; for example, 5 km / h R = x ii) VF> VFO, and YG ≦ YGO YGO; for example, 0.05 [G] R = max (R2, RL) iii) VF> VFO And YG> YGO R = R1 In step 35, a turning trajectory left / right rear wheel speed difference ΔVR ′ generated by a turning trajectory difference between the inner and outer wheels at the time of turning is calculated by the following equation (turning trajectory left / right / right driving wheel speed difference calculation). Means n).

ΔVR ′ = K2 · VF / RK2; constant In step 36, the left and right rear wheel speed difference ΔVR ′, which is a correction element, is subtracted from the detected right and left rear wheel speed difference ΔVR to obtain the following formula for control. The wheel speed difference ΔVRR is calculated (corresponding to the left / right drive wheel speed difference calculating means f).

ΔVRR = ΔVR−ΔVR ′ In step 37, the differential limiting torque TΔV proportional to the difference between the left and right rear wheel speeds is calculated by the following equation.

TΔV = C · ΔVRC C is a proportional gain, and as shown in FIG. 5, is set to a large value C1 in order to enhance the starting performance at the vehicle speed VF in the starting region, and is used for correcting steering and the like at the vehicle speed VF in the running region. In order to improve the effectiveness of the rudder, a small value C2 is set.

In step 38, the front and rear wheel speed difference ΔVFR
The differential limiting torque T is determined as follows (corresponding to the differential limiting torque determining means j) as shown below.

I) When TFLAG = 0 and ΔVFR ≧ V1, set TFLAG = 1. Ii) When TFLAG = 1 and ΔVFR ≦ V2, set TFLAG = 0. Iii) When TFLAG = 1, T = TΔV iv. ) TFLAG = 0 T = 0 Here, TFLAG = 0 indicates the control during grip turning with zero differential limiting torque T, and TFLAG = 1 indicates the right / left rear wheel speed difference proportional control.

The front and rear wheel speed difference values V1, V2
As shown in FIG. 4, the differential limiting torque T is changed from 0 to TΔ
When shifting to V, the first set value V1 is used.
When shifting from V to 0, the second set value V2 (<V1)
The setting values V1 and V2 have hysteresis (corresponding to the setting value setting means o).

In step 39, the control current ILSD for obtaining the differential limiting torque T determined in step 38 is LS
It is output to the D control valve 12 (corresponding to the differential limiting torque control means k). Incidentally, during the right and left rear wheel speed difference proportional control given by T = TΔV, the differential limiting torque is applied between the left and right rear wheels 5 and 6 by the characteristic shown in FIG.

[Estimation of Turning Radius] When turning at an extremely low speed, such as at the start of turning or at the stop of turning, the turning radius R is given as a constant value x at step 34.

That is, when the vehicle speed is 5 km / h or less, the tires also rotate at a very low speed, so that the wheel speed detection accuracy from each of the wheel speed sensors 14, 15, 16, and 17 that obtains the wheel speed by counting the pulse signals is not sufficient. It is not guaranteed, and the turning radius R cannot be accurately calculated even if the right and left front wheel speed difference ΔVF is used.
Of course, when the lateral acceleration sensor 18 is used, the influence of the output offset is large in the extremely low lateral acceleration range, and the detection accuracy is not guaranteed.

Therefore, when the vehicle speed is 5 km / h or less, the turning radius R is set to a constant value x (5) so as not to affect the turning correction.
m).

The vehicle speed VF exceeds the set vehicle speed VFO (5 km / h), and the lateral acceleration YG is equal to the set lateral acceleration YGO (0.05 G).
At the time of the following low lateral acceleration turning, in step 34, the turning radius R is given by R = max (R2, RL).

That is, the output from the lateral acceleration sensor 18 in the low lateral acceleration range is largely affected by the G sensor output offset, and the detection accuracy is not guaranteed. On the other hand, in the low lateral acceleration region, the road surface grip state of the tire is good, so that the wheel speed detection accuracy from each of the wheel speed sensors 14, 15, 16, 17 is sufficiently guaranteed.

Therefore, when turning at low lateral acceleration, basically,
By selecting, as the turning radius R, the second turning radius R2 obtained from the vehicle speed VF and the difference between the front left and right wheel speeds ΔVF, the turning radius R with high accuracy is estimated.

The vehicle speed VF exceeds the set vehicle speed VFO (5 km / h), and the lateral acceleration YG is the set lateral acceleration YGO (0.05 G).
When the vehicle is turning at a high lateral acceleration exceeding R, the turning radius R is given by R = R1 in step 34.

That is, in the output from the lateral acceleration sensor 18 in the high lateral acceleration range, the influence of the G sensor output offset is suppressed to a small degree, and the detection accuracy is sufficiently ensured. On the other hand, each wheel speed sensor 14, 15, 1 in the high lateral acceleration region
The wheel speed detection accuracy from Nos. 6 and 17 is largely affected by tire slip and variations in tire diameter, and the wheel speed detection accuracy is not guaranteed.

Therefore, when turning at a high lateral acceleration, the turning radius R with high accuracy is estimated by selecting the first turning radius R1 obtained from the vehicle speed VF and the lateral acceleration YG as the turning radius R.

[Grip turning] When the grip is turned at a low speed or the like on a high μ road, by estimating the turning radius R, the right and left rear wheel speed difference ΔVR detected and the turning trajectory right and left rear wheel speed difference ΔVR 'are originally the same. And the calculation result of the differential limiting torque TΔV proportional to the difference between the left and right rear wheel speeds in step 37 should be zero. However, as long as the turning radius R is estimated, the differential limiting torque TΔV = 0 is not always satisfied, and the differential limiting torque may be applied to generate a tight corner brake.

Thus, for example, consider a left turn at a low speed where the tire diameter is constant, there is no drive slip between the left and right rear wheels 5 and 6, and a tight corner brake is generated by applying a differential limiting torque. As shown in FIG. 6, the relationship between the turning radii of the respective wheels indicates a relationship of right front wheel turning radius> right rear wheel turning radius> left front wheel turning radius> left rear wheel turning radius.
Since the turning radii are different in this manner, the right front wheel speed VFR> the right rear wheel speed VRR ≧ the left front wheel speed VFL> the left rear wheel speed VRL, and the difference between the rear wheel speed VRM due to the select high and the front wheel speed average value VFA is obtained. A certain front and rear wheel speed difference ΔVFR becomes smaller than the first set value V1.

Therefore, when the wheel speed is determined by the turning radius, the front-rear wheel speed difference ΔVFR, which is the difference between the rear wheel speed VRM and the driven wheel speed average value VFA, becomes smaller than the first set value V1, so that when the grip is turned. Can be determined.

Focusing on this point, in step 38, the TFL
When AG = 0, T = 0, and when TFLAG = 0, the grip turning corresponding control is performed to maintain T = 0 until the front and rear wheel speed difference ΔVFR reaches the set value V1, thereby ensuring the grip turning. Tight corner braking is prevented.

[Driving on Slippery Road Surface Including Stacking Time] For example, as shown in FIG. 7A, a right and left split μ road with a constant tire diameter, a low μ on the left wheel side, and a high μ on the right wheel side. As shown in FIG. 7 (b), only the left rear wheel speed VRL, which is a low-μ roadside drive wheel, is idle at first while the vehicle is stationary, and then the front wheels , The front left wheel speed VFL, which is a low μ roadside driven wheel, starts to idle, and the right rear wheel speed VRR and the right front wheel speed VFR on the high μ roadside rise smoothly as the vehicle slowly accelerates. Show characteristics.

Therefore, when starting on the right or left split μ road,
As shown in FIG. 8, the vehicle enters a one-sided idling state, and the difference between the front and rear wheel speeds is the difference ΔVF between the rear wheel speed average value VRA and the front wheel speed average value VFA.
When given by R ′, ΔVFR ′ ≒ 0, the differential limiting torque is not applied, one-sided idling is allowed, and the traction performance is inferior.

On the other hand, when the front and rear wheel speed difference ΔVFR is given by the difference between the rear wheel speed VRM due to the select high and the front wheel speed average value VFA, ΔVFR becomes equal to or larger than the first set value V1.

Similarly to the single-wheel idle state, in each of the diagonal idle state, three-wheel idle state, and single-wheel idle state shown in FIG. 8, one of the rear wheels, which is the drive wheel, is idle. The idling rear wheel speed is selected as the rear wheel speed VRM by the select high, and when the rear wheel speed difference ΔVFR becomes equal to or more than the first set value V1, the vehicle travels on a slippery road surface including when the vehicle is stuck. Time can be determined.

Focusing on this point, in step 83, the TFL
When AG = 1, T = TΔV, and when TFLAG = 1, the left and right rear wheel speed difference proportional control for maintaining T = ΔV until the front and rear wheel speed difference ΔVFR reaches the set value V2 is performed, thereby reducing the stacking time. The traction performance is improved when traveling on slippery road surfaces.

Furthermore, since the rear wheel speed VRM is selected by the select high and set as the drive wheel speed, the front and rear wheel speed difference ΔVFR exceeds the first set value V1 as compared with the case where the average value is set to the drive wheel speed. The timing is advanced, and the differential limiting torque control in proportion to the difference between the left and right rear wheel speeds can be started with a good response to one wheel idling of the rear wheel.

Next, the effects will be described.

(1) In a differential limiting torque control device for electronically controlling the differential limiting torque between the left and right rear wheels 5 and 6 based on the left and right rear wheel speed difference information, the rear wheel speed VRM and the average front wheel speed by select high The running discrimination is made based on whether or not the front-rear wheel speed difference ΔVFR, which is a difference from VFA, is larger than a first set value V1, and when it is judged that the vehicle is in a grip turning operation, the tight limiting brake T that sets the differential limiting torque T to zero is prevented. When the control is performed, and when it is determined that the vehicle is traveling on a slippery road surface including when the vehicle is stuck, the device performs the right-left drive wheel speed difference proportional control of the differential limiting torque T so that tight corner braking is prevented when the grip is turned and the drive wheels are prevented. Thus, it is possible to achieve both high responsiveness and high traction performance at the time of traveling in which one-wheel idling occurs.

(2) A vehicle to which the differential limiting control device of the embodiment is applied is provided with an electronic control torque split for increasing the distribution of the driving force to the front wheels in accordance with the generation of the front and rear wheel rotation speed on the rear wheel drive base. Since the vehicle is a four-wheel drive vehicle, it is possible to achieve both the prevention of tight corner braking during turning of the grip and the securing of traction performance in various modes of wheel idling, including single-wheel idling of the rear wheel shown in FIG. .

(3) The control left / right rear wheel speed difference ΔV is obtained by subtracting the turning trajectory left / right rear wheel speed difference ΔVR ′ based on the turning radius R estimated from the detected left / right rear wheel speed difference ΔVR.
Since the apparatus for obtaining RR is used, it is possible to obtain accurate left and right drive wheel speed difference information excluding the influence of turning.

(4) Set value V1 of front and rear wheel speed difference ΔVFR for discriminating whether the vehicle is turning on a grip or traveling on a slippery road surface.
Since V2 has hysteresis, when switching between tight corner brake prevention control and right / left drive wheel speed difference proportional control with one set value, the front and rear wheel speed difference ΔV before and after the set value is used.
It is possible to prevent the control hunting in which the differential limiting torque repeatedly changes in level under the situation where FR occurs.

Although the embodiments have been described with reference to the drawings, the specific configuration is not limited to the embodiments, and any changes or additions without departing from the gist of the present invention are included in the present invention. It is.

For example, even if the applicable vehicle is a rear-wheel drive vehicle or a front-wheel drive vehicle, it is possible to prevent a tight corner brake during turning of the grip and to secure traction performance by high response during running when one of the drive wheels idles. And can be applied to a front-wheel drive-based four-wheel drive vehicle (viscus type or electronic control type).

In the embodiment, the example in which the differential limiting torque is applied by the hydraulic multi-plate clutch has been described. However, if the differential limiting torque can be variably controlled by an external control command, the electromagnetic clutch may be used. And so on.

[0080]

According to the first aspect of the present invention,
In a differential limiting torque control device that electronically controls a differential limiting torque between left and right driving wheels based on left and right driving wheel speed difference information,
A driving wheel speed determining means for selecting a larger one of the left driving wheel detection value and the right driving wheel detection value and setting the driving wheel speed as a driving wheel speed is provided, and the front and rear wheel wheels are a difference between the determined driving wheel speed and the calculated driven wheel speed. A device that performs tight corner brake prevention control when the speed difference is equal to or less than a set value, and performs right and left drive wheel speed difference proportional control of the differential limiting torque when the calculated front and rear wheel speed difference exceeds the set value. As a result, it is possible to achieve an effect that it is possible to achieve both tight corner braking prevention at the time of grip turning and securing of traction performance by high response at the time of traveling in which one-wheel idling of the drive wheel occurs.

According to the second aspect of the present invention, the differential limiting torque control device according to the first aspect is driven from a two-wheel drive state where there is no difference between the front and rear wheel rotational speeds to a four-wheel drive state. Installed on a four-wheel drive vehicle whose power distribution is changed, aiming to achieve both tight corner braking prevention during grip turning and ensuring traction performance in various modes of wheel idling, including single wheel idling of the drive wheel The effect that it can be obtained is obtained.

According to a third aspect of the present invention, in the differential limited torque control device according to the first or second aspect, the absolute value of the difference between the detected value of the left driving wheel and the detected value of the right driving wheel is determined. Since the left and right driving wheel speed difference is calculated by subtracting the turning trajectory left and right driving wheel speed difference calculation value from the value, in addition to the above-described effects, accurate left and right driving wheel speed difference information excluding the turning effect can be obtained. The effect that it can be obtained is obtained.

According to a fourth aspect of the present invention, in the differential limited torque control device according to any one of the first to third aspects, the starting threshold value of the differential limiting control corresponding to the difference between left and right driving wheel speeds is set. Since the device has a hysteresis between a certain first set value and a second set value which is an end threshold value of the left / right drive wheel speed difference-dependent differential limiting control, in addition to the above effects, the right / left drive wheel speed difference proportional An effect is obtained that control hunting between control and tight corner corresponding control can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims showing a differential limiting torque control device of the present invention.

FIG. 2 is an overall system diagram of a rear wheel drive vehicle to which the differential limiting torque control device of the embodiment is applied.

FIG. 3 is a flowchart showing a flow of a differential limiting torque control operation process performed by an active LSD controller of the embodiment device.

FIG. 4 shows front and rear wheel speed difference set values V1 and V in the embodiment device.
2 is a hysteresis characteristic diagram of FIG.

FIG. 5 is a characteristic diagram of a differential limiting torque in proportion to the difference between the left and right rear wheel speeds in the embodiment device.

FIG. 6 is an explanatory view of a turning state when the grip is turned.

FIG. 7 is a wheel speed characteristic diagram of each wheel at the time of gentle acceleration start on a right and left split μ road.

FIG. 8 is a diagram showing a state of occurrence of a front-rear wheel speed difference used for control in each running state.

[Explanation of symbols]

 a differential limiting torque applying means b left driving wheel speed detecting means c right driving wheel speed detecting means d left driven wheel speed detecting means e right driven wheel speed detecting means f left / right driving wheel speed difference calculating means g driving wheel speed determining means h Driven wheel speed calculating means i front and rear wheel speed difference calculating means j differential limiting torque determining means k differential limiting torque controlling means m transfer clutch n turning locus left / right driving wheel speed difference calculating means o setting value setting means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B60K 23/00-23/04 B60K 17/28-17/36

Claims (4)

(57) [Claims] 1. A differential limiting torque providing means provided between left and right driving wheels for applying a differential limiting torque according to a control command from the outside, and a wheel speed of the left and right driving wheels and a left and right driven wheel respectively. A left driving wheel speed detecting device, a right driving wheel speed detecting device, a left driven wheel speed detecting device, a right driven wheel speed detecting device, a left / right driving wheel speed difference calculating device for calculating a left / right driving wheel speed difference, A driving wheel speed determining means for selecting a larger one of the detected driving wheel value and the detected right driving wheel value to determine a driving wheel speed, and calculating an average value of the detected value of the left driven wheel and the detected value of the right driven wheel to calculate the driven wheel speed. Driven wheel speed calculation means for calculating the front and rear wheel wheel speed difference based on the difference between the determined drive wheel speed and the calculated driven wheel speed; and When the difference is less than the set value, the differential limiting torque is set to zero regardless of the difference between the left and right driving wheel speeds. Or, determined to a small value close to zero, and when the calculated front and rear wheel speed difference exceeds a set value, a differential limiting torque determining means for determining a differential limiting torque according to the left and right driving wheel speed difference, Differential limiting torque control means for outputting a control command for obtaining the differential limiting torque determined by the differential limiting torque determining means to the differential limiting torque applying means. Limiting torque control device. 2. The differential limiting torque control device according to claim 1, wherein the driving force from the engine is directly transmitted to one of the front and rear wheels and a transfer clutch is applied to the other driven wheel. The transfer clutch increases the fastening force in accordance with the difference between the front and rear wheel rotation speeds, and the driving force distribution is changed from a two-wheel drive state where no front and rear wheel rotation speed difference occurs to a four-wheel drive state. Differential limiting torque control device mounted on a four-wheel drive vehicle. 3. The turning trajectory left / right driving wheel according to claim 1 or 2, wherein a turning trajectory left / right driving wheel speed difference caused by a difference in turning radius between an inner wheel and an outer wheel at the time of turning is calculated. The left-right driving wheel speed difference calculating unit is provided with a left-right driving wheel speed difference calculating unit, the left-right driving wheel speed difference calculating unit subtracting the turning locus left-right driving wheel speed difference calculating value from the absolute value of the difference between the left driving wheel detection value and the right driving wheel detection value. A differential limiting torque control device, which is means for calculating a wheel speed difference. 4. The differential limiting torque control device according to claim 1, wherein the set value of the front and rear wheel speed difference is a start threshold value of the differential limiting control corresponding to the left and right drive wheel speed difference. 1 set value and a second set value which is an end threshold value of the differential limiting control corresponding to the difference between left and right driving wheel speeds, and a set value setting in which the first set value and the second set value have hysteresis. Means for providing differential limiting torque control.