JP2918330B2 - Torque distribution control device for four-wheel drive vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention actively controls the torque distribution of front and rear wheels according to running conditions in a four-wheel drive vehicle provided with a center differential device and controlled in torque distribution. More particularly, the present invention relates to a torque distribution control device for a four-wheel drive vehicle, and more particularly, to a measure for alleviating an impact torque in a case where the vehicle is shifted to a travel range and suddenly starts while depressing an accelerator pedal.

[Conventional technology]

In a full-time four-wheel drive vehicle equipped with a center differential device, the reference torque distribution of the center differential device is set to rear wheel biased. Also, a differential limiting device is attached to the center differential device to electronically control the differential limiting torque during the vehicle weight distribution when the rear wheel is directly connected to the rear wheel. With this unequal torque distribution control system, the rear wheels are always slipped first to prevent four-wheel slippage, driving (trench front / rear drive) tends to improve maneuverability, turning performance, etc., and a wider control range Has already been proposed by the present applicant. Then, it has been developed to appropriately determine the differential limiting torque in accordance with each traveling condition in this wide control region and to perform optimal electronic control.

Here, in this type of four-wheel drive vehicle equipped with a torque converter and an automatic transmission, if the vehicle is shifted to the travel range while depressing the accelerator pedal and suddenly starts, the drive system stopped via the torque converter is activated. Large engine power is transmitted rapidly. At this time, the drive system is distributed to the front and rear wheels by the center differential device, and the tire has a high grip performance, so that an excessive impact torque is generated as compared with the 2WD vehicle. This impact torque is immediately input to the automatic transmission, and an excessive load may be applied to each of the friction engagement elements and components.

Further, in a state where the unequal torque is distributed to the rear wheels by the center differential device as in the case of the four-wheel drive vehicle, a large amount of the impact torque is also transmitted to the rear wheels. For this reason, especially on a low μ road, the behavior of the vehicle changes, and it is easy to cause a tail swing and wheel spin. Therefore, in a four-wheel drive vehicle that is subjected to such unequal torque distribution control, it is desired to perform control so as not to generate excessive impact torque even when a sudden start operation is performed.

In order to mitigate the impact at the time of the sudden start, there is a prior art disclosed in, for example, JP-A-61-282135. Here, in a vehicle equipped with an automatic transmission, when the engine load is equal to or more than a predetermined value when operating from the stop range to the travel range, the engine torque is reduced simultaneously with engagement of the friction engagement device, and a discoloration shock is generated. It has been shown to prevent.

[Problems to be solved by the invention]

By the way, in the above-mentioned prior art, the load applied to the frictional engagement device of the automatic transmission is reduced to reduce the shift shock, and the shock torque at the time of sudden start cannot be reliably reduced. In other words, when the vehicle shifts suddenly while depressing the accelerator and starts suddenly, even if the torque is reduced at the same time as the engagement of the friction engagement device, the excessive output of the engine is already input to the drive system at this time, and The torque cannot be appropriately reduced from the beginning.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an unequal torque distribution control that controls the torque of the front and rear wheels in a wide range of vehicle weight distribution from rear wheel bias due to differential limiting torque. A torque distribution control device for a four-wheel drive vehicle that can reliably reduce the impact torque when suddenly starting after shifting to the travel range while depressing the accelerator pedal. Is to do.

[Means for solving the problem]

In order to achieve the above object, a torque distribution control device for a four-wheel drive vehicle according to the present invention restricts the differential between the center differential device and the center differential device that determines the reference torque distribution as unequal torque distribution of rear wheel imbalance. A four-wheel drive vehicle equipped with a sensor differential device, comprising a differential limiting device, and variably controlling a differential limiting torque by the differential limiting device according to an operation state to vary torque distribution to front and rear wheels to rear wheel bias or front wheel bias. A control unit that controls the differential limiting device includes: a unit that detects a shift operation from a stop range to a travel range; a unit that detects an engine operating state; and an engine output when the shift operation is performed from the stop range to the travel range. When the vehicle is in a sudden start condition, the center differential is locked and the front and rear wheels are Means for controlling the differential limiting torque by the differential limiting device so as to be in a coupling state, and controlling the differential limiting torque by the differential limiting device in an increasing function relationship with respect to the engine load at the time of starting except sudden start. It is characterized by having.

(Operation)

In the present invention, when limiting the differential of the center differential device, which determines the reference torque distribution to the unequal torque distribution of the rear wheel bias, by the differential limiting device, the differential limiting torque by the differential limiting device is variably controlled according to the operating state. Then, the torque distribution to the front and rear wheels is changed to the rear wheel bias or the front wheel bias. Then, when the shift operation from the stop range to the travel range is detected, and when the shift operation from the stop range to the travel range is performed and the engine output is in a sudden start state,
The differential limiting torque by the differential limiting device is controlled so that the center differential device is locked and the front and rear wheels are substantially directly connected. Also, when starting except for sudden start,
The differential limiting torque by the differential limiting device is limited in an increasing function relationship with respect to the engine load.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In FIG. 2, the outline of the drive system of a full-time four-wheel drive vehicle equipped with a center differential device will be described. Reference numeral 1 denotes an engine, 2 denotes a clutch, 3 denotes a transmission, and the transmission output shaft 4 is a center. The input is to the differential device 20. A front drive shaft 5 is output from the center differential device 20 forward, and a rear drive shaft 6 is output rearward. The front drive shaft 5 is connected to the left and right front wheels 9 via the front differential device 7 and the axle 8, and the rear drive shaft 6 is Shaft 10, rear differential device 11,
It is connected to the left and right rear wheels 13 via the axle 12 to form a transmission.

The center differential device 20 is a compound planetary gear type, and includes a first sun gear 2 integrated with the transmission output shaft 4.
1, a second sun gear 22 integrated with the rear drive shaft 6 and a plurality of pinions 23 arranged around the sun gears 21 and 22; a first pinion 23 gear 23a of the pinion 23 is connected to the first sun gear 21; , The second pinion 23 gear 23b is
Are engaged with each other. A reduction drive gear 25 is rotatably provided on the transmission output shaft 4, and a pinion 23 is supported by a carrier 24 integrated with the drive gear 25. The drive gear 25 is a driven gear integrated with the front drive shaft 5. It is composed by meshing with 26.

On the other hand, the center differential device 20 includes:
A hydraulic clutch 27 is provided as a differential limiting device.
The hydraulic clutch 27 is provided, for example, with the drum 27a attached to the carrier 24 immediately after the center differential device 20, and the hub 2
7b are respectively connected to the rear drive shaft 6 and arranged coaxially.

With the configuration of the center differential device 20, the shifting power input to the first sun gear 21 is transmitted to the carrier 24.
And the second sun gear 22 with a predetermined reference torque distribution. In addition, the difference in rotation between the front and rear wheels during turning
Absorbed by 23 planet rotations. Here, the reference torque distribution is freely set by four gear meshing pitch radii of the two sun gears 21 and 22 and the two pinion gears 23a and 23b. Therefore, the reference torque distribution e _TS of the front wheel torque TF and the rear wheel torque TR, it is possible to set the rear wheel unbalance example sufficiently as follows.

e _TS = TF: TR ≒ 34: 66 When a front engine is mounted, the static weight distribution e _W of the front wheel weight WF and the rear wheel weight WR of the vehicle is, for example, as follows.

e _W = WF: WR ≒ 62: 38 Therefore, in the case of the direct connection due to the differential limitation of the hydraulic clutch 27, the torque is distributed to the front wheels according to the weight distribution. By the above, the torque distribution between the front and rear wheels by controlling differential limiting torque of the hydraulic clutch 27, and the reference torque distribution e _TS of the rear wheel unbalance, be controlled in a wide range of weight distribution e _W of the front wheel unbalance It becomes possible.

 Next, a hydraulic control system of the hydraulic clutch 27 will be described.

First, when the transmission is an automatic transmission, the transmission is configured using a line pressure obtained by adjusting the oil pressure of an oil pump 30 of the oil pressure control system by a regulator valve 31. Therefore, the line pressure oil passage
32 communicates with the hydraulic clutch 27 via an orifice 36, a clutch control part 33, and an oil passage 34. The line pressure oil passage 32 communicates with a solenoid valve 38 through an oil passage 37 having a pilot valve 35 and an orifice 36, and the duty pressure of the solenoid valve 38 acts on the control side of the clutch control valve 33 via an oil passage 39. . When a duty signal corresponding to each traveling condition is input from the control unit 50, the solenoid valve 38 drains the hydraulic pressure to generate a duty pressure, and operates the clutch control valve 33 according to the duty pressure, The differential limiting torque of the hydraulic clutch 27 is variably controlled.

In FIG. 1, an electronic control system of an embodiment of the unequal torque distribution control device of the present invention, which is applied to the four-wheel drive vehicle, will be described.

First, as input information, a front wheel rotation sensor 40 for detecting the rotation speed NF of the front wheel, a rear wheel rotation sensor 41 for detecting the rotation speed NR of the rear wheel, a throttle opening sensor 42, and a shift position for detecting a shift position of the transmission. It has a sensor 43, a brake switch 44, an engine speed sensor 45, and the like.

The control unit 50 has a vehicle speed detection unit 51 and a front / rear rotation ratio calculation unit 52 to which the front wheel rotation speed NF and the rear wheel rotation speed NR are input. When the engine speed Ne is equal to or higher than the set value,
For example, the vehicle speed V is calculated from the average value of the front wheel rotation speed NF and the rear wheel rotation speed NR.

The front / rear rotation ratio calculation unit 52 determines the slip, turning, and other running conditions that are important in this control, as well as the state of slip and the like.
It is provided in consideration of the fact that it can be determined and detected based on the rotation ratio. Therefore, the rotation ratio e _N by the front wheel rotation speed NF and the rear wheel rotational speed NR, set as follows.

e _N = NR / NF Also, the control unit 50 receives the vehicle speed V, the front-rear rotation ratio e _N , the throttle opening θ and the shift position signal, and inputs the normal mode determination unit 53, the start mode determination unit 54, and the steering mode determination. Part 5
5. It has a slip mode determination unit 56. Also, a braking mode determining unit 57 that receives a signal of a throttle switch θ and a brake switch, a one-range mode determining unit 58 that receives a signal of one range of a shift position, an ABS mode determination that receives a signal of an ABS operation and a brake switch. A portion 59 is provided.

The normal mode judging section 53 judges the state of the normal running based on the shift position of the first to fourth forward speeds or the reverse speed, and θ and V.
Determining the differential limiting basic torque Tc ₁ in 60. In the torque setting section 60, the torque Tc is stored in the relationship between θ and V for each shift position.
₁ are given by a map, as in the first speed or reverse speed of the map M ₁ is 3 (a), in increasing function with respect to the torque Tc ₁ theta, at decreasing function with respect to V Is set. That is, in the region where θ is small, the torque Tc ₁ is reduced to prevent the tight corner braking phenomenon at the time of large turning, and in this case, as V is lower, the torque Tc ₁ is increased to improve the running performance.

On the other hand, if the same tendency as in the above map is set in the second gear or higher high-speed gear, if the accelerator is returned after turning acceleration at the high gear, the torque decreases in accordance with the decrease in θ, the rear wheel brake torque increases, and the spin speed increases. Become a trend. Therefore, the map M ₂ fast stage than the second speed, as in FIG. (B), is set larger torque Tc ₁ in a small area of theta, also adapted to increase hold operation restricting torque after returning the accelerator ing.

The launch mode determination unit 54 V is zero, when the rotational ratio e _N is determined to go straight at the set value or more, determines start running. Then, the torque Tc ₂ at the time of starting is determined in the torque setting section 61 by the mode determination signal.
c _2, like the map M ₃ in FIG (c), is set at a higher level increasing function with respect to theta.

Slip mode determination unit 56 to the front wheel slip if rotation ratio e _N is equal to or less than the set value, determines the rear wheel slip when the set value or more. Then, the torque setting unit 63 in the slip determination signal determines the torque Tc ₃ in the map M ₄ where the θ and V as a parameter. In this case, the rear wheels slip to increase torque Tc ₃ as solid line in (d) of FIG. In the front wheel slip reduces the torque Tc ₃ as dashed lines.

Further, the turning mode determination unit 59 determines that the vehicle is turning by turning when the rotation ratio e _N is within the range between the lower limit set value for full turning and the upper limit set value for small turning. In this steering mode, the torque during traveling in each of the above modes may be reduced and corrected so as not to cause the tight corner braking phenomenon. Therefore, as in the map M ₅ of the same in the correction coefficient setting unit 62 FIG. (E), the correction coefficient k is increased function for rotation ratio e _N, is set at an increased function against V, the low speed Correction coefficient k for larger turning
Is set small.

The braking mode determining unit 57 determines the normal braking when the ON signal of the brake switch 44 is input when the throttle is fully closed. Then, with this braking signal, the torque setting unit 64
The differential braking torque is set to zero to maximize the braking performance.

1 range mode determination unit 58 determines the input of the 1 range shift signal, this case allows the escape from a bad road is set to the torque Tc ₃ force the slip mode.

Further, the ABS mode determination unit 59 determines whether the brake switch is
Determined by both the input of the actuation signal, set to a predetermined small torque Tc ₄ by the torque setting unit 65, adapted to urge the return of wheel rotation.

The torques Tc _{1 to} Tc ₄ and the correction coefficient k set in each of these modes are input to the differential limiting torque calculator 70. In the calculation unit 70, starting the normal torque Tc ₁ mode, and select wire torque Tc ₂ or Tc ₃ slip mode,
The selected torque is multiplied by a correction coefficient k to calculate a differential limiting torque Ts as follows.

Ts = k · Tc (Tc = Tc ₁ , Tc ₂ , Tc ₃ , Tc ₄ ) The differential limiting torque Ts is input to the duty ratio converter 71,
Converting the duty ratio D by using a conversion map M ₆ in FIG (f) with respect to the torque Ts, is configured to output to the solenoid valve 38 a signal of the duty ratio (D) via the drive unit 72 ing.

Next, a description will be given of a countermeasure for reducing the impact torque under the starting condition in which the vehicle shifts to the travel range while stepping on the accelerator and suddenly starts.

First, it has a sudden start determination unit 66 to which a signal of the shift position and the throttle opening θ is input, and detects a shift operation from the stop range of P and N to the driving range of D and R. At this time, the throttle opening θ Is determined to be a sudden start when is greater than or equal to the set value θs. Here, in this control system, since the start mode is set to increase the driving force of the front and rear wheels at the time of normal start, the sudden start determination signal is input to the torque setting unit 61 of the start mode, The differential control torque Ts is changed to the direct connection torque TD so that the center differential device 20 that determines the reference torque distribution to be the unequal torque distribution of the rear wheel bias and locks the front and rear wheels in a substantially directly connected state so that the torque distribution to the front and rear wheels becomes uniform.
Is corrected. Further, when the engine output is forcibly reduced during such a sudden start, the impact torque can be more effectively prevented. Therefore, the sudden start signal is input to the retard correction section 67 and the predetermined ignition timing retard amount is set. Set -R. Then, the retard correction signal is input to the ignition timing control unit 68.

 Next, the operation of this embodiment will be described.

First, during traveling of the vehicle, the power of the engine 1 is input to the transmission 3 via the clutch 2, and the power for shifting is input to the first sun gear 21 of the center differential device 20. Here, since the reference torque distribution is set to the rear wheel biased by each gear specification of the center differential device 20,
With this torque distribution, the power is distributed to the carrier 24 and the second sun gear 22 and output.

On the other hand, at this time the front wheel rotation speed to the control unit 50 of the electronic control system NF, rear-wheel rotation speed NR, shift position, entered the signals of the throttle opening theta, vehicle speed V, the front and rear speed ratio e _N is calculated . These signals are input to each of the mode determination sections 53 to 59, and the signals are normally set for starting, turning, slipping, braking, 1 range, and ABS.
Each running condition of the control is determined.

Therefore, at the time of starting at a high μ road is determined by the mode determination unit 54, the map M ₃ in this case is set to a high torque Tc _2, the duty signal is inputted to the solenoid valve 38. The high duty pressure P _D from the solenoid valve 38 of the hydraulic control system is applied to the clutch control valve 38, the clutch pressure Pc rises increases the oil amount of the hydraulic clutch 27 Accordingly,
This produces a predetermined high differential limiting torque Ts. For this reason, the differential is limited in the center differential device 20, and the power is bypassed and transmitted from the second sun gear 22 to the carrier 24 side in accordance with the differential limiting torque Ts, so that the torque is distributed from rear wheel bias to front wheel bias. Become. And carrier 24
From the front side, of respectively power transmission to the rear wheel side from the second sun gear 22, unequal torque distribution such as rolling P ₂ of FIG. 5 4
The vehicle is driven by wheels, and the vehicle starts and accelerates well with the front and rear wheels.

After starting, the rotational speeds NF and NR of the front and rear wheels become approximately equal and the rotational ratio
When e _N is below the set value, the normal mode is determined in the determination section 53. At this time, in the low-speed stage of first gear and reverse gear, is set to a relatively low torque Tc ₁ by the map M _1, is a hydraulic control on the basis of this, the differential limiting torque of the hydraulic clutch 27
Ts is controlled to be low. Therefore, the torque of the front and rear wheels in accordance with substantially standard torque distribution becomes the torque distribution of wheel unbalance after closer to the point P ₁ of FIG. 5, becomes FR manner yet four-wheel drive, turning performance, maneuverability Becomes better. In this case, in particular, θ
When the vehicle turns in a region where is small, the center differential device 20 is substantially free, and the vehicle can freely turn while absorbing the rotation difference ΔN between the front and rear wheels.

In addition, when the vehicle is running in the above-described starting and normal modes, under a high load condition where θ is large, the differential limiting torque Ts is controlled to increase, so that the front and rear wheels tend to be directly connected, and the running performance and the like are sufficiently exhibited. On the other hand, especially when steered in such traveling conditions, it is detected by the steered mode determination unit 55, the correction coefficient k in accordance with the rotation ratio e _N, and the like are set. Then, the larger the steering is, the more the differential limiting torque Ts is temporarily reduced and corrected, so that it is possible to turn without causing the tight corner braking phenomenon.

At the time of braking by a normal brake operation, the braking operation is determined by the braking mode determination unit 57, and the differential restriction is released, whereby the four wheels can sufficiently exhibit braking performance.

Next, when traveling on a low μ road, the presence or absence of a slip is determined by the slip mode determination unit 56. When a normal slip occurs, the rear wheel always slips first due to unequal torque distribution of rear wheel bias, and the four wheel Slip is avoided. During this rear wheel slip, the differential limiting torque Ts is higher controlled by the map M _4, thereby center differential 20
Differential is limited, and will migrate to the torque distribution of the front wheel unbalance as a point P ₃ in Figure 5. On the other hand, when the front wheel slip is determined, the differential limiting torque Ts is reduced to control the rear wheel biased torque distribution, and thus the non-slip side wheel driving force is controlled to always increase. Slip is prevented.

Incidentally, of course if the rotation ratio e _N is out of the set value in the slip mode, or the vehicle speed V increases and the throttle opening θ is determined is to slip avoidance decreases, control of the slip mode It is released and returns to the control of the normal mode.

When braking on this low μ road, lock the wheels and use the brake system
When the ABS control is activated, it is determined by the ABS mode determination unit 59. In this case, since the differential limiting torque is set to a small value, the wheel rotation is restored without impairing the braking action, and the ABS control function is promoted.

Further, when shifting to one range on a rough road or the like, a large differential limiting torque similar to that in the slip mode is set, and the running performance is improved.

FIG. 6 shows the control of the modes under the respective driving conditions described above.

Further, when the vehicle actually shifts from the stop range to the travel range, the flowchart of FIG. 4 is executed. That is, when this shift operation is detected in step S1, the process proceeds to step S2, where the throttle opening θ is checked. Therefore, in the case of the normal start with the throttle opening θ being equal to or less than the set value S, the process ends as it is, and in the straight start, the vehicle is in the start mode.
When turning, the torque distribution control is performed in the steering mode as described above.

On the other hand, in the case of sudden acceleration in the throttle opening θ is set value θs above, direct torque T _D is set the routine proceeds to step S3, the differential limiting torque Ts in accordance with the direct torque T _D of the hydraulic clutch 27, the front and rear The torque distribution of the wheels is directly connected with 50:50 equal torque. Therefore, the excessive torque generated at the time of the sudden start is uniformly distributed and transmitted to the drive systems on the front and rear wheel sides by the center differential device 20 and the hydraulic clutch 27, so that concentration to one of the drive systems is avoided. In this way, by applying the excessive torque to the entire drive system of the four-wheel drive vehicle in a finely divided manner, the impact torque is absorbed and alleviated, and the behavior of the vehicle is also maintained in a stable state. Further, at this time, the process proceeds from step S3 to step S4, and the ignition timing is retarded, so that the engine output is forcibly reduced. As a result, the excessive torque itself input to the drive system immediately after the start is reduced, and thereafter, the generation of the impact torque is effectively prevented.

Although the embodiment of the present invention has been described above, the present invention is not limited to this. For example, the operating state at the time of sudden start may use the engine speed other than the throttle opening, and the torque down control is not necessarily required.

〔The invention's effect〕

As described above, according to the present invention, the shift operation from the stop range to the travel range is detected, and when the shift operation from the stop range to the travel range is performed, when the engine output is in a sudden start state, the reference torque distribution is performed. The differential torque is controlled by the differential limiting device so that the front and rear wheels are substantially directly connected by locking the center differential device, which is determined as the unequal torque distribution of the rear wheel bias. Even in a four-wheel drive vehicle that employs a center differential device defined in unequal torque distribution, it is possible to uniformly distribute and transmit excessive torque generated at the time of sudden start to the drive system on the front and rear wheel side, As a result, the excessive impact torque at the time of sudden start can be subdivided and absorbed by the entire drive system, and can be absorbed and mitigated. It is possible to maintain the stable.

In addition, at the time of starting except for a sudden start, the differential limiting torque by the differential limiting device is controlled in an increasing function relationship with respect to the engine load. An appropriate torque distribution can be obtained for the front and rear wheels from the start to the start of acceleration. That is, when the engine load is low and the vehicle is slowly accelerated, the rear wheel biased torque distribution is performed. The rear wheel biased torque distribution increases the rear wheel drive torque relative to the front wheel drive torque, thereby improving the startability. In addition, as the engine load increases at the time of starting, torque distribution from rear wheel bias to front wheel bias occurs, and at the time of acceleration start, front wheel drive force increases with respect to rear wheel drive torque due to front wheel bias torque distribution. It is possible to effectively transmit the torque to the road surface, so that the startability of the vehicle can be improved and the behavior of the vehicle can be kept stable.

[Brief description of the drawings]

FIG. 1 is a skeleton diagram showing an electronic control system of an embodiment of a torque distribution control device for a four-wheel drive vehicle according to the present invention, and FIG. 2 is a configuration diagram showing the overall configuration of a four-wheel drive vehicle to which the present invention is applied. 3 (a) to 3 (f) are diagrams showing respective maps, FIG. 4 is a diagram showing a flowchart of an operation at the time of sudden start operation, FIG. 5 is a diagram showing a control state of unequal torque distribution, FIG. 6 is a diagram showing a control state of each mode under each traveling condition. 1 ... engine, 9 ... front wheel, 13 ... rear wheel, 20 ... center differential device, 27 ... differential limiting hydraulic clutch, 33 ... clutch control valve, 38 ... solenoid valve,
50: control unit, 53: normal mode determination unit, 54:
Start mode determination unit, 55: turning mode determination unit, 56: slip mode determination unit, 57: braking mode determination unit, 58:
1 range mode judgment unit, 59 ... ABS mode judgment unit, 60,6
1, 63, 64, 65 ... torque setting section, 62 ... correction coefficient setting section,
70: Differential limit torque calculation unit, 66: Sudden start determination unit, 42
…… Throttle opening sensor, 43 …… Shift position sensor.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B60K 17/35 B60K 23/08

Claims (1)

(57) [Claims] 1. A center differential device which determines a reference torque distribution to be an unequal torque distribution of rear wheel imbalance, and a differential limiting device which limits a differential of the center differential device, wherein the differential limiting device is provided according to an operation state. In a four-wheel drive vehicle with a center differential device that variably controls the differential limiting torque of the front and rear wheels to vary the torque distribution between the front and rear wheels to the rear wheel or the front wheel, Means for detecting a shift operation to the drive range; means for detecting an engine operating state; and a shift operation from the stop range to the drive range. Differential limiting torque by the differential limiting device so that the front and rear wheels are almost directly connected Controlling, at the time of starting, except the sudden acceleration, increased functional relationship with a limited slip differential torque distribution control device for a four-wheel drive vehicle, characterized in that it comprises a means for controlling the differential limiting torque due to the engine load.