JP3397844B2 - Vehicle differential limiting 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 control device, and more particularly to a differential limiting control device for holding a differential limiting holding with a holding torque set according to the differential limiting torque.

[0002]

2. Description of the Related Art Conventionally, various devices have been proposed as a differential limiting device for limiting the differential in accordance with the differential rotation between wheels or axles. For example, Japanese Patent Laid-Open No. 5-4528.
The publication discloses a differential limiting control device that holds the differential limiting torque at a constant torque for a holding time set according to the vehicle speed under a predetermined condition. Also, the actual development 63-
In Japanese Patent No. 2624, in differential limiting control for a differential limiting device that limits the differential between the left and right rear wheels or the front and rear wheels,
A drive system clutch for a vehicle in which the differential limiting torque in the accelerator depressed state is held for a while when the accelerator depressed state is released, and the differential limited holding torque is lowered when traveling on a low friction road surface. A controller is described.

[0003]

In the conventional differential limiting control, when holding the differential limiting torque, one of the maximum differential limiting torque and the constant limiting torque near the maximum torque is limited. It was common to hold at the holding torque. However, the control for holding the differential limiting torque is a control for stabilizing the differential limiting control, preventing hunting, and suppressing frequent switching between differential limiting and differential limiting cancellation. Although the motion restriction should be removed,
Since it is a control that limits the differential, if the differential limit holding torque is uniformly set to a large value, the degree of limitation that limits the behavior of the vehicle becomes too large, and the acceleration is slightly reduced,
There is a problem such as a decrease in turning performance.

Therefore, when the differential limit holding torque is set to an excessively small value, the action of holding the differential limit is reduced, and frequent switching between differential limit and differential limit release (hunting phenomenon) occurs. Become. After all, the differential limiting holding torque is set to an appropriate torque value that correlates with the differential limiting torque at the start of differential limiting, and the vehicle behavior (acceleration, turning degree, etc.)
It is desirable to set the torque value appropriately corrected according to the above. An object of the present invention is to enable the setting of the differential limiting holding torque that can reliably prevent hunting without excessively limiting the behavior of the vehicle in the differential limiting control.

[0005]

According to another aspect of the present invention, there is provided a differential limiting control device for a vehicle according to a differential rotation between wheels or between axles.
The differential of the vehicle controlling the differential limiting means for limiting the differential
In the limit control device , a torque calculation unit that calculates a differential limit torque by applying a detection value of a predetermined physical parameter related to the running state of the vehicle to preset fastening torque characteristics, and the torque calculation unit. Control means for controlling the differential limiting means so as to perform differential limiting with the calculated differential limiting torque, and frequent hunting conditions for differential limiting and differential limiting cancellation.
Differential through the differential limiting means to prevent switching
A holding control unit for holding the limit, wherein the differential limiting torque according to the differential limiting torque calculated by the torque calculating unit and smaller than the differential limiting torque when a predetermined differential limiting holding condition is satisfied. Holding control means for controlling the differential limiting means so as to hold the differential limiting means for a predetermined time with the holding torque.

[0006] Here, when the vehicle is in a predetermined traveling state, a correction means for correcting the differential limiting holding torque is provided (claim 2 subordinate to claim 1), and the degree of turning of the vehicle is detected. And a correcting means for correcting the differential limiting holding torque according to the degree of turning detected by the turning detecting means (claim 3 dependent on claim 1), the correcting means Is configured to correct the differential limiting holding torque to be small according to the increase in the turning degree (claim 4 dependent on claim 3), and the correction means is configured to respond to the increase in yaw acceleration. A configuration in which the differential limiting holding torque is corrected to a small value (claim 5 dependent on claim 4), acceleration / deceleration detecting means for detecting an acceleration / deceleration in the longitudinal direction of the vehicle, and the acceleration / deceleration detecting means detect the acceleration / deceleration. Depending on the acceleration / deceleration, the differential control A configuration including a correction means for correcting the holding torque (claim 6 dependent on claim 1), wherein the correction means largely corrects the differential limiting holding torque in accordance with an increase in acceleration acting on the vehicle. And the like (Claim 7 dependent on Claim 6).

[0007]

In the vehicle differential limiting control device according to the present invention, the torque is calculated when the differential limiting means limits the differential according to the differential rotation between the wheels or between the axles. The means applies the detected value of a predetermined physical parameter related to the running state of the vehicle to a preset differential limiting torque characteristic to calculate the differential limiting torque. The control means controls the differential limiting means so as to differentially limit the differential limiting torque. Frequent hunting of differential limitation and differential limitation release
Via the differential limiting means to prevent switching
Holding control means for holding the differential limit
By controlling the differential limiting means by the controlling means, when the predetermined differential limiting holding condition is satisfied , the differential limiting holding torque corresponding to the differential limiting torque and smaller than the differential limiting torque is used for a predetermined time. during differential limiting holding rows Utame, a differential limiting
Preventing frequent hunting-like switching of differential limitation release
The differential limiting control can be stabilized.

As described above, since the holding control means is provided to hold the differential limiting holding torque that corresponds to the differential limiting torque and is smaller than the differential limiting torque, the difference in the behavior of the vehicle is not excessively limited. It is possible to stabilize the dynamic limitation control to prevent hunting, and to reliably prevent frequent switching between differential limitation and differential limitation cancellation.

According to the second aspect of the present invention, the correction means for correcting the differential limiting holding torque is provided when the traveling state of the vehicle is in a predetermined state. Therefore, for example, each state is provided in a predetermined state such as turning or accelerating. The differential limit holding torque can be appropriately set according to According to the present invention, the turning detection means for detecting the turning degree of the vehicle and the correction means for correcting the differential limiting holding torque according to the detected turning degree are provided. Therefore, the differential limiting is performed according to the turning state of the vehicle. The holding torque can be appropriately corrected. According to the fourth aspect, the correction means corrects the differential limiting holding torque to be small according to the detected degree of turning, so that the turning performance can be prevented from lowering.

According to a fifth aspect, in the apparatus of the fourth aspect,
The correction means corrects the differential limiting holding torque to be small according to the increase in the yaw acceleration, so that the turning performance can be prevented from being deteriorated. According to the sixth aspect, the correction unit can appropriately correct the differential limit holding torque according to the acceleration / deceleration detected by the acceleration / deceleration detection unit. In claim 7,
7. The apparatus according to claim 6, wherein the correction means largely corrects the differential limiting holding torque in response to an increase in acceleration acting on the vehicle, so slip during acceleration is appropriately suppressed, and deterioration in acceleration is suppressed. Can be prevented.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. The present embodiment is an example in which the present invention is applied to a four-wheel drive vehicle of a type in which the front wheels are driven during normal traveling and the rear wheels are also driven in a traveling state where differential limitation is required. First, the schematic overall configuration of the four-wheel drive vehicle MC will be described. As shown in FIG. 1, in a four-wheel drive vehicle MC, a left front wheel axle 5 and a right front wheel axle 6 are provided between the left and right front wheels 1 and 2.
Is provided, a left rear wheel axle 8 and a right rear wheel axle 9 are provided between the left and right rear wheels 3, 4, and the left front wheel axle 5 and the right front wheel axle 6 are the left and right front wheels 1, 2. The left rear wheel axle 8 and the right rear wheel axle 9 are interlocked and connected by the front wheel differential device 7 that allows differential operation.
The rear wheel differential device 10 that allows the left and right rear wheels 3 and 4 to be differentially coupled is interlocked.

A power unit 11 including an engine and an automatic transmission directly connected to the engine is arranged in the front-rear direction at the center of the front portion of a vehicle body (not shown). A front wheel drive force transmission system 13 for transmitting drive force to the front wheel differential device 7 and a rear wheel drive force transmission system 14 for transmitting drive force from the output shaft 12 of the power unit 11 to the rear wheel differential device 10 are provided. Has been.
The front wheel driving force transmission system 13 transmits the driving force from the gear 15 fixed to the output shaft 12 to the gear 16, and transmits the driving force of the gear 16 to the front wheel differential device 7 via the front wheel driving shaft 17. It is configured to do. The rear wheel drive force transmission system 14 includes a rear wheel drive shaft 1 that is interlocked with a rear wheel differential device 10.
8 and an electromagnetic clutch 19 provided between the output shaft 12 and the rear wheel drive shaft 18 and capable of controlling the differential limiting torque (this corresponds to the differential limiting means). There is.

The electromagnetic clutch 19 includes a case 20 which rotates integrally with the output shaft 12, and a plurality of clutch plates 21 which are disposed in the case 20 and rotate integrally with the case 20.
A plurality of clutch discs 22 that are arranged in the case 20 and rotate integrally with the rear wheel drive shaft 18, and electromagnets that exert a magnetic force on the plurality of clutch plates 21 and clutch discs 22. (Including a member), and is composed of an electromagnet or the like fixed to the vehicle body. In a state where the coil 23 of the electromagnetic clutch 19 is not energized, the electromagnetic clutch 19 is in a disengaged state and only the left and right front wheels 1 and 2 are driven, and the driving force is not transmitted to the rear wheel drive shaft 18, but to the coil 23. When energized, a drive torque equal to the fastening torque proportional to the magnitude of the coil current is transmitted to the rear wheel drive shaft 18 and the four-wheel drive state is set.

Next, the control system will be described. A power unit controller 30 for controlling the power unit 11,
ABS control device 31 for controlling a brake device (not shown)
A (control device for anti-skid control) and a clutch control device 32 for controlling the electromagnetic clutch 19 are provided. Further, as sensors, the rotational speed N1 of the left front wheel 1
Is detected via a disk 33 that rotates integrally with the left front wheel axle 5, and a rotation speed N2 of the right front wheel 2 is detected through a disk 35 that rotates integrally with the right front wheel axle 6.

The wheel speed sensor 36, the left rear wheel speed sensor 38 for detecting the rotational speed N3 of the left rear wheel 3 via a disk 37 fixed to the left rear wheel axle 8, and the right rear wheel 4 are detected. Disk 3 that rotates integrally with the right rear wheel axle 9 at a rotation speed N4
The right rear wheel speed sensor 40, the brake switch 41, the steering angle sensor 43 for detecting the steering angle θh of the steering wheel 42, the neutral / inhibitor switch 44, and the longitudinal acceleration A acting on the vehicle body. A yaw rate sensor 45 for detecting, an acceleration sensor 49 for detecting longitudinal acceleration acting on the vehicle body, an idle switch 46, a throttle opening sensor 47, and a crank angle sensor 48 provided on the engine are provided.

The wheel speed sensors 34, 36, 38, 40
The wheel speed signals N1, N2, N3, N4 are input to the ABS control device 31, and from the ABS control device 31, the ABS signal and the wheel speed signals N1, N2, N3, N4 which are turned on during the execution of the anti-skid control. Are supplied to the clutch control device 32. The switch signal BR from the brake switch 41, the steering angle signal θh from the steering angle sensor 43, the yaw rate signal ψv from the yaw rate sensor 45, and the longitudinal acceleration signal A from the acceleration sensor 49 are sent to the clutch control device 32. It is entered directly.

The neutral / inhibitor switch 4
4, a switch signal NI from the idle switch 46, a switch signal ID from the idle switch 46, a throttle opening signal TVO from the throttle opening sensor 47, and a crank angle sensor 4
The crank angle signal CA from 8 is supplied to the clutch control device 32 via the power unit control device 30. The clutch controller 32 is configured to output a coil current I to the coil 23 of the electromagnetic clutch 19,
The clutch control device 32 has the ignition switch turned on.
When the ignition switch is off, the power is supplied from the backup battery when the ignition switch is OFF, and the clutch control device 32 is basically
It is configured to operate when an ignition signal IG input when the ignition switch is ON is input.

The clutch control device 32 includes an A / D converter for A / D converting the detection signal as needed, a waveform shaping circuit for shaping the detection signal as necessary, an input / output interface, a CPU and a ROM. It is composed of a microcomputer including a RAM, a coil drive circuit that outputs a coil current I to the coil 23, and the like. The four-wheel drive vehicle M is stored in the ROM of the microcomputer as described later.
A control program for a differential limiting control, which will be described later, including a drive force distribution control for controlling the drive force distribution to the four wheels 1 to 4 by controlling the engagement torque according to the traveling state of C, and is attached to the control program. Maps etc. are input and stored in advance
The RAM is provided with various memories necessary for the arithmetic processing of the control.

Here, the outline of the differential limiting control for the electromagnetic clutch 19 will be briefly described. The differential rotation speed ΔN between the front and rear wheels, the estimated lateral acceleration α obtained from the yaw rate ψv and the vehicle speed V, and the vehicle speed V, which is the vehicle body speed, are used as parameters for the preset predetermined torque characteristic. The differential limiting torque T is obtained by applying the detected values of the yaw rate ψv and the vehicle speed V, and the electromagnetic clutch 19 is controlled so that the differential limiting torque T becomes the differential limiting torque T.

The torque characteristics are, for example, as shown in FIGS.
The torque characteristic shown in FIG. 4 is applicable, and as the differential limiting torque T, only the differential limiting torque obtained from the torque characteristic shown in FIG. 2 may be used, or from the torque characteristic shown in FIG. The differential limiting torque obtained by adding the differential limiting torque obtained from the torque characteristic of FIG. 3 and / or the differential limiting torque obtained from the torque characteristic of FIG. 4 to the obtained differential limiting torque may be used.

On the other hand, when the predetermined holding condition for holding the differential limiting torque T is satisfied, the current differential limiting torque T obtained as described above and the detected values of the vehicle body acceleration A and the yaw acceleration ψa are set, The differential limiting holding torque Th is obtained from the predetermined map shown in FIG. 6, and the electromagnetic clutch 1 is set to have the differential limiting holding torque Th for a predetermined time t0.
Control 9

Here, the map of FIG. 6 shows the calculated present differential limiting torque T, the vehicle body acceleration A and the yaw acceleration ψ.
It is a map for calculating a differential limiting holding torque Th that is smaller than the differential limiting torque T and that corresponds to the differential limiting torque T from the detected value of a. The basic characteristic line L0 of this map is applied when the vehicle body acceleration A is less than or equal to the predetermined dead zone and the yaw acceleration ψa is less than or equal to the predetermined dead zone. In order to correct the differential limiting holding torque Th according to the vehicle body acceleration A, the characteristic lines L1, L corresponding to the increase of the vehicle body acceleration A
2, L3 are set, and the differential limiting holding torque Th is corrected to increase in accordance with the increase in the vehicle body acceleration A. Further, in order to correct the differential limiting holding torque Th according to the yaw acceleration ψa, the characteristic lines L4, L5, L6 corresponding to the increase of the yaw acceleration ψa are set, and the differential limiting according to the increase of the yaw acceleration ψa. The holding torque Th is corrected to be small.

The applicable range of the characteristic lines L0 to L6 is as follows. Line L0 ... A ≦ Δa and ψa ≦ Δψ
a line L1 ... Δa <A ≦ a1 line L2 ... a1 <A ≦ a2 line L3 ... a2 <A line L4 ... Δψa <ψa ≦ ψ1 line L5 ... ψ1 <ψa ≦ ψ2 line L6 ... ψ2 <ψa where Δa is a predetermined value for setting the dead zone, a1 to a2 are predetermined values, and Δψa is a predetermined value for setting the dead zone,
ψ1 and ψ2 are predetermined values.

Next, the above-mentioned differential limiting control will be described. FIG. 5 shows a differential limiting control routine. In the figure, reference symbols Si (i = 10, 11, ...) Show each step. After the control is started, various signals (N1 to N4, A, ψv, ID) necessary for the control are read (S1
0), then the differential speed ΔN, the yaw rate ψv and the vehicle speed V
Is calculated (S11). The differential rotation speed ΔN is
Calculated as the difference between the maximum wheel speed and the minimum wheel speed, and
The vehicle speed V is calculated by multiplying the minimum wheel speed by a predetermined constant.

Next, the differential rotation speed ΔN and the estimated lateral acceleration α
(This is calculated from the product of the yaw rate ψv and the vehicle speed V and a predetermined constant), and the vehicle speed V is applied to the torque characteristics of FIGS. Is calculated (S12). Next, in S13, the vehicle speed acceleration A is calculated from the detection signal of the acceleration sensor 49, and the yaw acceleration ψa is calculated as a time differential value of the yaw rate ψv. Next, in S14, a predetermined differential holding torque is held. It is determined whether the holding condition is satisfied.

The predetermined holding conditions are, for example, that the differential limiting torque T is, for example, 70% or more of the maximum engaging torque of the electromagnetic clutch 19, the differential rotational speed ΔN is a predetermined value or more, and during acceleration. Some or all of that. If the determination result in S14 is No, the process proceeds to S15, and the differential limiting torque T is applied to a predetermined map, a calculation formula, or a table, and the coil 23 of the electromagnetic clutch 19 is applied.
The coil current I to be energized to is calculated, then the coil current I is output to the coil 23 in S16, the process then returns, and S10 and subsequent steps are repeatedly executed. When the determination result of S14 is Yes, the differential limiting torque T, the vehicle body acceleration A, and the yaw acceleration ψa are applied to the map of FIG. 6 to calculate the differential limiting holding torque Th. However, regarding the calculation of the differential limiting holding torque Th, the differential limiting holding torque Th corrected according to the vehicle body acceleration A and the differential limiting holding torque Th corrected according to the yaw acceleration ψa may be calculated. However, when the steering angle θh is generated, the turning limit is emphasized and the differential limiting holding torque Th corrected according to the yaw acceleration ψa is adopted. When the yaw acceleration ψa is generated due to the influence of cross wind in a state where the steering angle θh is not generated, the differential limiting holding torque Th corrected according to the vehicle body acceleration A is adopted. Next, in S18, the timer TM is reset and then started.

Next, in S19, it is determined whether or not the count time TM of the timer TM is equal to or longer than the predetermined time t0, and if the determination result is No, it is determined in S20 whether the ardle switch signal ID is ON, ID is OFF
Then, when the vehicle is accelerating, the process proceeds to S21, and in S21, the holding torque Th is applied to the predetermined map, the arithmetic expression, and the table as in S15, and the coil current I
Is calculated.

Next, in S22, the coil current I is output to the coil of the electromagnetic clutch 19, then the process proceeds to S19, and S19 to S22 are repeatedly executed as long as the vehicle is being accelerated. In this way, the engagement torque of the electromagnetic clutch 19 is maintained at the differential limit holding torque Th set according to the differential limit torque T for the predetermined time t0 from the time point when it is determined Yes in S14. When the acceleration state is released, the determination result of S20 is Yes, the process proceeds from S20 to S15, and S15 and S16 are executed as described above. However, the step S20 may be omitted if necessary.

A supplementary explanation will be given with reference to FIG. 7. When the holding is started at time t1, the differential limiting holding torque Th is delayed from the differential limiting torque T at that time with a time delay.
The holding torque Th is held for a predetermined time t0, the holding is released thereafter, and the normal differential limiting control is performed. The predetermined time t0 may be set so as to decrease as the vehicle speed V increases.

As described above, when the predetermined holding condition is satisfied, by holding the differential limiting holding torque, it is possible to reliably prevent frequent switching (hunting phenomenon) between differential limiting and differential limiting cancellation. In addition to being able to
The effect is obtained. Since the characteristic of the map of FIG. 6 is set as described above and the differential limit holding torque Th is largely corrected according to the increase of the vehicle body acceleration A, the differential during acceleration of the four-wheel drive vehicle MC is obtained. Since an appropriate differential limiting holding torque Th that does not excessively limit the torque can be applied for a predetermined time, slipping of the drive wheels during acceleration can be appropriately suppressed and acceleration performance can be improved. Also, the yaw acceleration ψa
Since the differential limit holding torque Th is corrected to be small in accordance with the increase of the torque difference, an appropriate differential limit holding torque Th that does not excessively limit the differential when turning the four-wheel drive vehicle MC is provided. Since it can be operated for a predetermined time, it is possible to prevent the turning performance from deteriorating.

In the above embodiment, the yaw acceleration ψa is adopted as the parameter of the turning degree, but the yaw acceleration ψa or the yaw rate ψv or the steering angle θh × the vehicle speed V is estimated in combination with the yaw acceleration ψa. The lateral acceleration α may be adopted. In the map of FIG. 6, instead of setting correction characteristic lines L1 to L6 for correction according to the acceleration A and the yaw acceleration ψa, the acceleration A
And a yaw acceleration ψa for correcting the yaw acceleration ψa may be provided, and the yaw acceleration ψa may be configured to be corrected based on the table and the arithmetic expression.

Next, the differential limiting control is applicable not only to the four-wheel drive vehicle MC but also to a four-wheel drive vehicle of the type that always drives the rear wheels 3 and 4 as described below. . Less than,
The four-wheel drive vehicle MCA will be briefly described. However,
The same parts as those in the above embodiment are designated by the same reference numerals and will be briefly described. As shown in FIG. 8, the four-wheel drive vehicle MCA includes left and right front wheels 1, 2, left and right rear wheels 3, 4, a left front wheel axle 5, a right front wheel axle 6, and both axles 5, 6. A front differential 50 for interlocking and connecting the left rear wheel axle 8, a right rear wheel axle 9, and a rear differential 51 for interlocking both axles 8 and 9.
And a power unit including an engine 52 and an automatic transmission 53, and a transfer device 54 that is interlocked with the power unit and distributes the driving force to the front wheels 1 and 2 and the rear wheels 3 and 4.
A front wheel drive shaft 17 for interlockingly connecting the transfer device 54 to the front differential device 50;
Is provided with a rear wheel drive shaft 18 and the like for interlocking with the rear differential device 51.

The transfer device 54 includes a drive force transmission mechanism for constantly transmitting the drive force from the power unit to the rear wheel drive shaft 18, and an electromagnetic multi-disc clutch for limiting the differential drive force from the power unit (this is the center. It is constituted by a differential limiting mechanism which transmits to the front wheel drive shaft 17 via a differential device). Here, the electromagnetic multi-plate clutch 55 will be described. As shown in FIG. 9, an input member 57 that integrally rotates with a shaft member 56 that is interlocked with an output shaft of a power unit via a gear train, and a drive shaft 17 for the front wheels.
A multi-plate clutch 59 is provided between the outer shaft 58 and the outer shaft 58 that rotates together with the outer shaft 58. An electromagnetic actuator 60 including a coil 61 and a magnetic path forming member 62 is fixed to the vehicle body side. A bearing 63 is attached to the armature 64, and an armature 64 is fixed to the outer shaft 58.

When the coil 61 of the electromagnetic actuator 60 is not energized, the electromagnetic multi-plate clutch 55 is OFF (disengaged state), and when the coil 61 is energized, the electromagnetic multi-plate clutch 55 is ON (connected state). Then, the differential limiting torque (that is, the front wheel drive torque) proportional to the coil current is transmitted to the front wheel drive shaft 17. As the differential limiting characteristic itself for the center differential device 55, a characteristic which is appropriately changed from the characteristic of the above-described embodiment (the characteristic of FIGS. 2 to 4) is adopted. The front differential device 50 includes a differential gear mechanism and a differential limiting electromagnetic multi-plate clutch similar to the above, and a rear differential device 51.
Is composed of a differential gear mechanism and a differential limiting electromagnetic multi-plate clutch similar to the above.

Further, the control system of this four-wheel drive vehicle MCA is
The control system is the same as that of the above embodiment, and includes a power unit device 30, an ABS control device 31, a clutch control device 65,
Four wheel speed sensors 34, 36, 38, 40, brake switch 41, steering angle sensor 43, neutral inhibitor switch 44, yaw rate sensor 45, idle switch 46, throttle opening sensor 47, crank angle sensor 48, acceleration sensor 49, etc. Are provided, and various detection signals are sent to the respective control devices 30, 31, 65 in the same manner as in the above embodiment.
Is supplied to. Further, the clutch control device 65 is connected to a mode setter 66 or the like for selectively setting the auto mode, the C mode, the R mode, and the F mode.

In the automatic mode, the electromagnetic multi-plate clutch of the front differential device 50 is controlled to the free state, and the center differential device 55 and the electromagnetic multi-plate clutch of the rear differential device 51 are connected to the four-wheel drive vehicle MCA. It is automatically controlled according to the running condition. In the C mode, the electromagnetic multi-plate clutch of the front differential device 50 is controlled in the free state, the center differential device 55 is controlled in the completely locked state, and the rear differential device 5 is controlled.
The one electromagnetic multi-disc clutch is automatically controlled according to the traveling state of the four-wheel drive vehicle MCA. In the R mode, the electromagnetic multi-plate clutch of the front differential device 50 is controlled to the free state, and the center differential device 55 and the electromagnetic multi-plate clutch of the rear differential device 51 are controlled to the completely locked state. In the F mode, the electromagnetic multi-plate clutch of the front differential device 50, the center differential device 55, and the electromagnetic multi-plate clutch of the rear differential device 51 are controlled to be completely locked, respectively.

It is needless to say that the present invention can be similarly applied to a device provided with a hydraulic or pneumatic differential limiting mechanism instead of the electromagnetic multi-plate clutch of the above embodiment. The present invention is not limited to the example, and various modifications may be added to the above-described embodiment by appropriately combining existing well-known techniques.

[Brief description of drawings]

FIG. 1 is a schematic overall configuration diagram of a four-wheel drive vehicle according to an embodiment.

FIG. 2 is a torque characteristic diagram for obtaining a differential limiting torque from a differential rotation speed.

FIG. 3 is a torque characteristic diagram for obtaining a differential limiting torque from estimated lateral acceleration.

FIG. 4 is a torque characteristic diagram for obtaining a differential limiting torque from a vehicle speed.

FIG. 5 is a flowchart of differential limitation control.

FIG. 6 is a diagram of a map for setting a differential limiting holding torque.

FIG. 7 is a diagram showing a change state of the differential limiting torque when holding the differential limiting torque.

FIG. 8 is a schematic overall configuration diagram of a four-wheel drive vehicle according to another embodiment.

9 is a sectional view of the center differential of the four-wheel drive vehicle of FIG.

[Explanation of symbols]

MC 4-wheel drive vehicle 19 Electromagnetic clutch 32 clutch control device 34, 36, 38, 40 Wheel speed sensor 45 Yaw rate sensor 49 Accelerometer MCA 4-wheel drive vehicle 50 front differential 51 Rear differential 55 Center differential (electromagnetic multiple disc clutch) 65 Clutch control device

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Claims (7)

(57) [Claims] 1. A vehicle differential control for controlling differential limiting means for limiting the differential in accordance with the differential rotation between wheels or between axles.
In the limit control device , a torque calculation unit that applies a detected value of a predetermined physical parameter related to the traveling state of the vehicle to a preset engagement torque characteristic to calculate a differential limit torque, and the torque calculation unit. Control means for controlling the differential limiting means so as to perform differential limiting with the calculated differential limiting torque, and frequent hunting-like switching between differential limiting and differential limiting releasing
Holds the differential limit through the differential limiting means to prevent
And a differential limit holding torque that corresponds to the differential limit torque calculated by the torque calculating means and is smaller than the differential limit torque when a predetermined differential limit holding condition is satisfied. And a holding control unit that controls the differential limiting unit so as to hold the differential limiting unit for a predetermined time . 2. The differential limitation control device for a vehicle according to claim 1, further comprising a correction unit that corrects the differential limiting holding torque when the running state of the vehicle is a predetermined state. 3. A turning detection means for detecting a turning degree of a vehicle, and a correction means for correcting the differential limit holding torque according to the turning degree detected by the turning detection means. The differential limiting control device for a vehicle according to claim 1. 4. The differential limiting device for a vehicle according to claim 3, wherein the correcting unit is configured to correct the differential limiting holding torque to be small according to an increase in the degree of turning. Control device. 5. The differential limiting control device for a vehicle according to claim 4, wherein the correcting unit is configured to correct the differential limiting holding torque to be small according to an increase in yaw acceleration. . 6. An acceleration / deceleration detecting means for detecting an acceleration / deceleration in the front-rear direction of the vehicle, and a correcting means for correcting the differential limit holding torque according to the acceleration / deceleration detected by the acceleration / deceleration detecting means. The differential limiting control device for a vehicle according to claim 1, further comprising: 7. The vehicle differential according to claim 6, wherein the correction means is configured to largely correct the differential limiting holding torque in accordance with an increase in acceleration acting on the vehicle. Limit control device.