JPH02227339A - Power transmission for automobile - Google Patents

Abstract

PURPOSE:To eliminate any effect to a steering characteristic by resetting a 4WD state to a 2WD state at a time when a resultant value of longitudinal acceleration and lateral acceleration detected each at the 4WD state becomes smaller than that at time of a changeover from 2WD to 4WD. CONSTITUTION:When a controller 44 is in a 4WD state as both front and rear clutches 10, 18 are engaged with each other, it is reset to a 2 WD state by front wheels 14, 16 when a resultant value of longitudinal acceleration and lateral acceleration being detected by sensors 48, 50 becomes smaller than that at a time when a power transmission system is selected from a 2WD state to a 4WD state, for example, engagement of the rear clutch 18 is released. With this constitution, when it is selected to the 4WD state from the 2WD state during turning travel, by way of example, even if throttle opening of an engine 2 is varied to some extent, it is not reset to the 2WD state unless acceleration acting on a car body becomes smaller. Thus, even in turning, any effect is no longer given to a steering characteristic at all.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power transmission device for a motor vehicle, particularly a four-wheel drive vehicle.

[Conventional technology]

2. Description of the Related Art In recent years, many four-wheel drive vehicles have been put into practical use that can provide excellent driving force and steering stability even on slippery roads such as snowy roads. However, although four-wheel drive vehicles are effective on slippery roads, on roads with a high coefficient of friction, there is a problem in that fuel efficiency worsens due to an imbalance in the rotational speed between the front and rear wheels.

Therefore, as shown in Japanese Patent Application Laid-open No. 61-27729, for example, the difference in slip ratio between the driving wheels and non-driving wheels in the two-wheel drive state is detected, and when the set condition is satisfied, the four-wheel drive state is switched to the four-wheel drive state. Devices configured for switching are known.

However, in the device disclosed in the above publication, the rotation speeds of the front and rear wheels are almost the same when in four-wheel drive mode, so the conditions for returning to two-wheel drive mode are determined based on the respective rotation speeds of the same front and rear wheels. It is difficult to judge.

Therefore, as disclosed in, for example, Japanese Patent Application Laid-open No. 61-44031, a device configured to return from a four-wheel drive state to a two-wheel drive state when the vehicle speed and the engine throttle opening meet predetermined conditions is proposed. It has been known.

[Problem to be solved by the invention]

However, with the device disclosed in this publication, for example, if the engine throttle opening degree changes during the same cornering after switching from a two-wheel drive state to a four-wheel drive state, the four-wheel drive state changes. The vehicle may switch from the drive state to the two-wheel drive state again, and in that case, the steering characteristics will also change, giving the driver a very strange feeling, which is undesirable in terms of feeling. There is a problem.

[Means to solve the problem]

The present invention has been devised in view of the above, and provides a power transmission system that can switch between a two-wheel drive state in which the output of a prime mover is transmitted only to two wheels and a four-wheel drive state in which the output is transmitted to four wheels, and a A power transmission device that acts on a vehicle body and includes a switching control means that detects a difference in slip ratio between driving wheels and non-driving wheels and switches the power transmission system to a four-wheel drive state when a set condition is satisfied. a longitudinal acceleration detection means for detecting acceleration in the longitudinal direction; a lateral acceleration detection means for detecting lateral acceleration acting on the vehicle body; The combined value of the longitudinal acceleration and lateral acceleration detected by the acceleration detection means is determined by the longitudinal acceleration detection means and the lateral acceleration when the power transmission system is switched from the two-wheel drive state to the four-wheel drive state by the switching control means. A return control means for returning the power transmission system from a four-wheel drive state to a two-wheel drive state when the longitudinal acceleration and lateral acceleration detected by the acceleration detection means become smaller than a combined value. This is a power transmission device for automobiles.

[Effect]

According to the present invention, when in a four-wheel drive state, the return control means determines that a value obtained by combining the longitudinal acceleration and lateral acceleration detected by the longitudinal acceleration detection means and the lateral acceleration detection means is determined by the switching control means. Therefore, the above power transmission system becomes 2
When the longitudinal acceleration and lateral acceleration detected by the longitudinal acceleration detection means and the lateral acceleration detection means when the wheel drive state is switched to the four-wheel drive state are smaller than the combined value, the power transmission system is Wheel drive condition 2
Return to wheel drive mode.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 1 to 12.

FIG. 1 is an explanatory diagram showing the configuration of this embodiment. In the figure, reference numeral 2 denotes an engine, and the output of the engine 2 is transmitted to an output shaft 8 via a clutch 4 and a transmission 6. The power of the output shaft 8 is transmitted to the left and right front wheels 1 via a front clutch 10 and a front differential gear 12.
4.1.6, and is transmitted to the left and right rear wheels 22.4 through the rear clutch 18 and rear differential gear 20.
24. The front clutch 10 and the rear clutch 18 are wet multi-disc clutches that can take any engagement state with slippage from 0% (directly connected state) to 100% (disconnected state) depending on the hydraulic pressure acting on chambers 10a and 18a, respectively. It is made up of.

Reference numeral 30 is a hydraulic pump that is turned on by the engine 2 or electric motor and sucks oil in the reservoir 32 and discharges it.
The pressure is regulated by a regulator valve 34 interposed between the two. In addition, the discharge port of the hydraulic pump 30 is connected to the electromagnetic switching valve 3.
6 to the chamber 10a of the front clutch 10, and is also connected to the chamber 18a of the rear clutch 18 via the electric six competition switching valve 38. These electromagnetic switching valves 3638
is connected to the hydraulic pump 30 via the electromagnetic control valve 40 on the one hand.
connected to the outlet of the The electromagnetic switching valve 36 switches between a position where the chamber 10a of the front clutch 10 and the hydraulic pump 30 are directly communicated (as shown) and a position where the chamber 10a of the front clutch 10 and the downstream side of the electromagnetic control valve 40 are communicated with each other in accordance with a control signal. It can take a position that communicates with the other side. Similarly, the electromagnetic switching valve 38 is set in a position where the chamber 18a of the rear clutch 18 and the hydraulic pump 30 are in direct communication, and a position where the chamber 18a of the rear clutch 18 and the electric I! 1 control valve 40 on the downstream side (as shown).

The solenoid control valve 40 operates according to the control signal.
The hydraulic pressure on the downstream side of the hydraulic pump 30 can be reduced and adjusted to any pressure from the maximum hydraulic pressure Pmax, which is equal to the discharge hydraulic pressure of the hydraulic pump 30, to zero. Note that reference numeral 32a indicates a reservoir for returning oil discharged when lowering the hydraulic pressure on the downstream side of the electromagnetic control valve 40, and for convenience of drawing, the reservoir 32a is
Although shown separately, it is actually the same as the reservoir 32.

A controller 44 includes a CPU, ROM, and RAM necessary for calculation, and an input circuit and an output circuit necessary for input/output, although not shown. The input circuit of the controller 44 includes a wheel speed sensor 46 that independently detects the rotational speed of each wheel, and a longitudinal acceleration sensor 5 that acts on the center of gravity of the vehicle.
0, a steering sensor 52 that detects the steering condition, a throttle sensor 54 that detects the throttle condition of the engine 2, and an engine rotation speed sensor 56 that detects the rotation speed of the engine 2.
, a brake sensor 58 that detects the state of the brakes, a shift sensor 60 that detects the shift position of the transmission 6, and a yaw rate sensor 6 that detects the yaw rate of the vehicle body.
Each detection signal of 2 is manually generated.

Reference numeral 64 is a mode selector provided on the instrument panel in front of the driver's seat of the vehicle, and a switch 64 is used to manually select FF moto, PR mode, and 4WD mode.
6, 68, and 70, and switches 72 and 74 for selecting the normal mode and sport mode, respectively, which will be detailed later. The signal is also input manually to the input circuit of controller 44.

Next, the operation of the controller 44 will be explained according to FIGS. 2 to 12.

First, in step M2 of the main routine shown in FIG. 2, the controller 44 initializes each flag and memory area in the RAM necessary for control, that is, sets them to zero. Next, in step M4, the signal from the mode selector 64 is read, and in step M6, it is determined whether or not the signal is on the manual side. If it is determined in step M6 as "YESJ", the process proceeds to step M8 and it is determined which mode the output signal of the mode selector 64 is in. If it is determined in step M8 that it is rFF mode, the process proceeds to step MIO and the output signal is output from the output circuit. Outputs a control signal that sets the drive state to FF mode. In other words, in this case, the controller 44 controls the front clutch 10
The hydraulic pressure in the chamber 10a of the rear clutch 18 is maximized.
In order to set the hydraulic pressure in the chamber 18a to zero, a control signal is sent to the electromagnetic switching valve 36 so that the switching valve 36 takes a position where the chamber 10a and the hydraulic pump 30 are directly communicated, and the switching valve 38 sends a control signal to the electromagnetic switching valve 38 so that the switching valve 38 takes a position where the switching valve 36 directly communicates with the chamber 10a and the hydraulic pump 30. A control signal is output to the electromagnetic control valve 40 so that the pressure on the downstream side of the control valve 40 becomes zero. As a result, the front clutch 10 is in a directly connected state and the rear clutch 18 is in a disconnected state, thereby achieving an FF state in which the driving force of the engine 2 is transmitted only to the front wheels 14, 16.

If it is determined in step M8 that the drive state is "rFR mode," the process proceeds to step M12, where the output circuit outputs a control signal that sets the drive state to FR mode. That is, in this case, the controller 44 controls the chamber 10 of the front clutch 10.
In order to make the hydraulic pressure in the rear clutch 180 zero and the hydraulic pressure in the rear clutch chamber 18a maximum, the electromagnetic switching valve 36 is controlled to take a position where the switching valve 36 communicates between the chamber 10a and the downstream side of the electromagnetic control valve 40. The signal is sent to the electromagnetic switching valve 38, which is connected to the chamber 1.
8a and the hydraulic pump 30 are output to the electromagnetic control valve 40 such that the pressure on the downstream side of the control valve 40 becomes zero. As a result, the front clutch 10 is in a disengaged state and the rear clutch 18 is in a directly connected state, making it possible to obtain an FR state in which the driving force of the engine 2 is transmitted only to the rear wheels 22 and 24.

Furthermore, if it is determined in step M8 that the drive state is "r4WD mode", the process proceeds to step M14, where the output circuit outputs a control signal that sets the drive state to direct 4WD mode. In other words, in this case, the controller 44 controls the front clutch 10
In order to maximize the oil pressure in each chamber 10a and 18a of the rear clutch 18, the electromagnetic switching valves 36 and 38 are connected to the same switching valve 3.
6 and 38 respectively output control signals that position the chambers 10a and 18a to be in direct communication with the hydraulic pump 30. As a result, the front clutch 10 and the rear clutch 18 are brought into a direct connection state, respectively, and the front wheels 14.16 and the rear wheels 22.24 are connected to each other.
It is possible to obtain a direct connection 4'vVD state in which the driving force of the engine 2 is transmitted to both.

On the other hand, if the determination in step M6 is "NO", step M
Proceeding to step 16, it is determined whether the output signal of the mode selector 64 is in the normal mode. If rYESJ is determined in step M16, the process proceeds to step M18 to execute normal mobile processing described later, and if "NO"
If so, the program proceeds to step M20 and executes a sports motor routine process which will be described later.

Next, the normal motor routine of step M18 in the main routine will be explained with reference to FIG.

First, in step 5100, it is determined whether the detection signal from the mode selector 64 was the normal mode last time as well. Immediately after switching to normal mode, this step 510
0, the determination is "NO" and the process advances to step 5102. In step 5102, necessary flags and memory areas necessary for control by this normal motor routine are initialized, that is, set to zero. Next, the process proceeds to step 5104, where control signals are output to the electromagnetic switching valves 36, 38 and the electromagnetic control valve 40 so that the drive state becomes the FF mode. Note that the content of control by this control signal is the same as the content of step MIO described above. Next, in step 5106, flag A is set to "
0'', the flag C is set to rQJ in step 5IO8, and the process returns to step M4 of the main routine. This flag A will be explained in detail later, but the front clutch 10
It becomes "1" when both the rear clutches 18 and 18 are in the disengaged state and control is performed such that the driving force is not transmitted to either the front wheels 14, 16 or the rear wheels 22, 24. Flag C also indicates that both the front clutch 10 and the rear clutch 18 have zero slippage, which will be explained in detail later.
In other words, when performing control to transmit driving force to both the front wheels 14.16 and the rear wheels 22.24 in a direct connection state, "1
”.

If rYESJ is determined in step 5100, the detection signals of each sensor are read in step 511O.

Next, in step 5112, it is determined whether flag A is "1", and if the determination is "NO" in step 5112, the process advances to step 5114. In step 5114, flag B
is "1".

This flag B becomes "1" when traction control is being performed, as will be described in detail later. Step 511
If rNOJ is determined in step 4, the process proceeds to step 8116, where it is determined whether flag C is "1". Step 5116
If it is determined that it is rNOJ, the process advances to step 8118.

In step 3118, it is determined whether the vehicle is in a starting state. The details of this judgment are specifically described below (i) ~
This is to determine whether all conditions (iii) are satisfied.

(i) The vehicle speed V is equal to or lower than the set vehicle speed (for example, 10 km/h).

(ii) The throttle opening θth detected by the throttle sensor 54 is greater than or equal to the set opening (for example, 50%).

(iii) The steering angle θ of the steering wheel detected by the steering sensor 52 is within a set range (for example, −180°≦
(θ≦180°).

Note that the smallest value among the wheel speeds detected by the wheel speed sensor 46 is adopted as the vehicle speed V under condition (i). If the determination in step Sll8 is "NO", the process advances to step 5120.

In step 5120, it is determined whether the difference ΔS between the slip ratio of the front wheels 12.14 (slip ratio of the wheels relative to the road surface) and the slip ratio of the rear wheels 22.24 is larger than a set value (for example, 0.03). Since this determination is made in the FF mode, one possible method is to obtain ΔS based on the difference obtained by subtracting the wheel speed of the rear wheels 22i24 from the wheel speed of the front wheels 12 and 14 detected by the wheel speed sensor 46. In order to find the actual slip ratio difference ΔS between the front and rear wheels, since there is a difference in the turning radius (so-called inner wheel difference) between the front and rear wheels when turning, it is necessary to correct the amount corresponding to the difference in the turning radius. In this case, the turning center of the vehicle moves forward due to an increase in the lateral acceleration acting on the vehicle body, and the difference between the inner wheels decreases, so it is necessary to correct the decrease.

Therefore, the following calculation is performed in the determination at step 5120.

That is, in the model shown in Fig. 4, f is the front wheel, r is the rear wheel, G is the center of gravity of the vehicle, l is the wheel base, j7r is the distance from the center of the rear wheel f to the center of gravity G, C is the turning center,
Rf is the distance from the turning center C to the center of the front wheel f, RG is the distance from the turning center C to the center of gravity G, Rr is the distance from the turning center C to the center of the rear wheel r, δ is the steering angle of the front wheel f, γ is the angular velocity of the vehicle center of gravity G around the turning center 0.

Here, according to Atsushiman geometry, Vf=r-Rf
= (VG/RG) ・RfR(-C1/δ)(TT
71" RG -1/δ) 1+ lr/R)', so equation (1) is: Vf=VG + 1+ r 1
)...(2) Also, Vr=r ・Rr= (VG /RG ) ・Rr・
... (3) Rr=j! /δ, so equation (3) is Vr=VG/
+ r = 14).

Here, in equation (2), af = + 1 + δ” (j! r / 1
)')...(5) Then, Vf=αf-VG...(6)
In formula (4), ar=1/ + 1 r/i 2 − (7)
Then, Vr=ar-VG-(8). (αf, αr Niatskaman correction coefficient) Therefore,
The correction coefficients αf and αr in equations (6) and (8) can define characteristics with respect to the steering angle δ, as shown in FIG.

On the other hand, as mentioned above, the lateral acceleration G acting on the center of gravity G of the vehicle
As Y increases, the turning center C moves forward and the difference between the inner wheels decreases.Generally, when the lateral acceleration GY is zero, there is a difference between the inner wheels due to the above-mentioned force man correction coefficient, but the lateral acceleration GY When is the set value GYP, the inner ring difference becomes zero, and for lateral acceleration GY between the values, the inner ring difference changes almost in proportion to the size of the lateral acceleration GY, and exhibits a roughly linear shape. has been confirmed. According to experiments, GYP is approximately 0 in a normal passenger car.
．． It has been decreed that it will be 5G. Therefore, as shown in FIG. 6, when GY≦GYP, the characteristics of the correction coefficient αY of the inner ring difference with respect to the lateral acceleration GY are as follows: αY = (GY-.GYP) +1. 0 ・
...(9) When GY>GYP, αY=0 ...(10)
It can be defined as

As a result, the slip ratio difference between the front and rear wheels can finally be determined by (11). In addition, in equation (11), ωf is the wheel speed of the front wheel f,
ωr is the wheel speed of the rear wheel r.

As a result, in step 5120, the wheel speed sensor 46
The wheel speed of the front wheel 12.14 and the rear wheel 22.2 detected from
4 wheel speed, the lateral acceleration obtained from the lateral acceleration sensor 50,
Based on the steering angle obtained from the steering sensor 52, the above formula (9
), and it is determined whether or not the slip ratio difference ΔS is larger than a set value (for example, 0°03). In addition, in the calculation, α'', αr in equation (11)
, αY is expressed by equations (5), (7), (9),
(10), but instead of Figs. 5 and 6.
It is also possible to make a map of the characteristics shown in the figure and store it in the ROM in the controller 44, and to refer to this map each time to obtain the characteristic.

If rNOJ is determined in step 5120, step 5
The process proceeds to step 122 to determine whether or not the turning limit is reached. The content of the determination in step 5122 will be explained here. In the model shown in Figure 7, f is the front wheel, r is the rear wheel, m is the vehicle mass, G is the center of gravity of the vehicle, ■ is the yaw moment of inertia around the center of gravity G, L is the wheelbase between the front and rear wheels, and Lf is the front wheel. f
and the distance between the center of gravity G, Lr is the distance between the rear wheel r and the center of gravity G, T is the yaw rate around the center of gravity G, δ is the steering angle of the front wheel f, UX is the forward speed of the center of gravity G, UY is the lateral speed of the center of gravity G, ■ is the vehicle speed,
GX is the longitudinal acceleration of the center of gravity G, GY is the lateral acceleration of the center of gravity G,
β is the sideslip angle at the center of gravity G, βf is the sideslip angle of the front wheel f, β
r is the sideslip angle of the rear wheel r, Cf is the cornering force of the front wheel, and Cr is the cornering force of the rear wheel r.

In this model, the lateral motion of the vehicle is m-V(
dβ/d t+r)=2Cf+2Cr...(12) Yawing motion is 1-dr/dt=2Lf-Cf-2Lr-Cr...
(13) It can be expressed as

Furthermore, if Kf is the equivalent cornering power of the front wheel f and Kr is the equivalent cornering power of the rear wheel r, then Cf = Kf
・βf=Kf・ (δ−β−γ・Lf/V)・・・(
14) Cr= to +”βr- to r・ (−β+γ・Lr/■)・
...(15) becomes.

Here, the condition for steady circular turning dβ/d t =0. Applying d r/d t =0 and considering the relationship r=V/R=GY/V,
From equations (12) to (15), r2/δ=GY/L・1/ (1+A-R-GY)・
...(16) However, A= -m/2L' ・(Lf -Kf-Lr・Kr)
/ (Kf-Kr): Stability factor
...(17) can be obtained.

This equation (17) is expressed as the steering angle δ generated with respect to the lateral acceleration GY.
The value of A in the equation can be used to determine whether the turning characteristics are on the US (understeer) side or the O3 (oversteer) side, as shown in FIG.

As shown in FIG. 9, in a FF vehicle used for boat fishing, the steering characteristic changes from a weak US characteristic to a strong US characteristic as the lateral acceleration GY increases. This characteristic has a tendency that as the driving force increases, the magnitude of the lateral acceleration GY decreases when changing to the strong US characteristic. However, it can be seen that the value increases as the lateral acceleration GY increases, reaches a maximum value, and then rapidly decreases, resulting in an uncontrollable state, and that the maximum value occurs just before the turning limit.

Therefore, the condition for the maximum value that occurs just before the turning limit is d(r''/δ)/dGY=0...(18)
You can get it at

By the way, in actual turning, if the steering angle of the front wheel f is on the increasing side, the actual turning limit will be smaller than the value calculated from equation (18), and if the engine throttle is on the depressed side, The actual turning limit is expressed by the formula (1
8) is smaller than the value obtained from 8).

Therefore, in step 5122, it is determined that the turning limit is exceeded when the following (19) is satisfied, based on detection signals from required sensors. When determining according to equation (19), the determination is made based on the detected value of the yaw rate sensor 62, the detected value of the steering sensor 52, the detected value of the lateral acceleration sensor 50, and the detected value of the throttle sensor 54.

Also, instead of formula (19), r=GY/V in opening formula (19)
It is also possible to adopt (20) by substituting . When determining according to this equation (20), the determination is made based on the detected value of the steering sensor 52, the detected value of the lateral acceleration sensor 52, and the detected value of the wheel speed sensor 46. In this judgment, the detection value of the wheel speed sensor 46 (
The smallest value among the four wheels is adopted as the vehicle speed V.
Even if even the wheel with the lowest rotational speed is in a slipping state and its value is larger than the actual V, the error will work on the safe side and there will be no problem. Rather, it has a great effect of not requiring the use of the currently expensive yaw rate sensor.

Note that ε and ε in these equations (19) and (20) are coefficients that are appropriately windowed depending on the characteristics of the vehicle. Further, in both equations (19) and (20>, the right-hand side is "0", but it is also possible to set a numerical value as appropriate depending on the characteristics of the vehicle.

If the determination in step 5122 is "NO", the process advances to step 5104 described above. As a result, in this normal mode routine, after entering the FF mode in step 5104, the rNO mode is activated in step 8118.
J (the conditions for starting are not satisfied), as long as the determination in step 3120 is "NO" (the slip ratio difference is small), and the determination in step 5122 is "NO" (not at the turning limit), step 5100 is performed. ,5ilo,5112,
5l14.5116. 5118, 5120. Sl, 2
The processes of 2°5104, 5106, and 5108 are respectfully returned and the drive state is maintained in the FF mode.

On the other hand, if "YES" is determined in step 5122, that is, if it is determined that the vehicle is at the turning limit, the process proceeds to step 5124, where a control signal is output to set the drive state to cut-off mode. That is, in this case, the controller 44 controls the front clutch 10
and a position where the electromagnetic switching valves 36 and 38 communicate the chambers 10a and 18a with the downstream side of the electromagnetic control valve 40 in order to zero the oil pressure in each chamber 10a and 18a of the rear clutch 18. A control signal is output to the electromagnetic control valve 40 so that the pressure on the downstream side of the control valve 40 becomes zero. As a result, the front clutch 10 and the rear clutch 18 are in a disconnected state, and the driving force of the engine 2 is not transmitted to both the front wheels 12.14 and the rear wheels 22.24 at all.

Next, in step 5126, the rotation speed of the engine 2 is controlled. The content of the control is to control the control device 2a of the engine 2 so that the rotation speed of the front wheels 12, 14 (or rear wheels 22, 24) on the engine 2 side of the front clutch 10 (or rear clutch 18) is the same as that of the front wheels 12, 14 (or rear wheels 22, 24). be. For this reason, the target rotation speed of the engine 2 is determined based on the wheel speed obtained from the wheel speed sensor 4 and the shift position obtained from the shift sensor 60, taking into account the gear ratio of each power transmission path, and The engine rotation speed obtained from the engine rotation speed is fed back and controlled so that the engine rotation speed becomes the target rotation speed. Note that in this embodiment, the control device 2a
As shown in FIG. 10, in addition to the main throttle valve 2b that controls the engine 2 during normal operation, a second throttle valve 2c and a servo device 2d that drives the valve 2C are used. , in the engine 2 rotation speed control, the main throw/)le valve 2b
The detection signal of the throttle sensor 54 that detects the opening degree of the engine is also taken into consideration.

Next, in step 5128, a control signal is output to activate the warning device 76, such as a buzzer or lamp, which gives a warning to the driver, and flag 8 in the memory is set to "1". Therefore, the next determination in step 5l12 is "rYEs", so as long as flag A is "1", step 52
00. Sll0.5112.3122.5124,31
The processing at 26° 5128 and 5130 is repeated, and the cutoff mode in which the driving force is not transmitted to either the front wheels 12.14 or the rear wheels 22.24 continues. As a result, the front wheel 12
．． 14 and rear wheels 22, 24 have increased cornering force.

On the other hand, if "YES" in step 5118, that is, the above-mentioned starting conditions are satisfied, the process proceeds to step 5132, and a control signal is output to the electromagnetic switching valves 35 and 38 so that the drive state becomes the direct 4WD mode. Note that the content of control by this control signal is the same as the content of step M14 described above. Similarly, if the determination in step 5120 is "YES", the process goes through the process in step 5121 and then goes to step 513.
Proceed to step 2. In addition, in step 5121, the magnitude Gc of the acceleration acting on the center of gravity G at that time (that is, T at F
弌] Ding P) is stored in memory.

When the control signal is output in step 5132, step 5
At step 134, flag C is set to "1", and then at step 8
The process advances to step 136 to determine whether the vehicle is at its turning limit.

The determination in step 5136 is substantially the same as the determination in step 5122 described above, based on the detection signal from the required sensor according to (21) or (22). Since the determination made in step 8136 is in the direct 4WD mode, the influence on the turning limit when the steering angle of the front wheels is on the increasing side during turning or when the engine throttle is on the depressed side. is smaller than the determination made in step 5122 in the FF mode, and therefore the equation (21)
Coefficient ε1 in (22). For ε2, use formula (19)
.

Coefficient ε1 in (20). It is set appropriately smaller than ε. Of course, it is also possible to set the right-hand side of both equations (21) and (22) to a numerical value that is appropriately set depending on the characteristics of the vehicle.

If the determination in step 5136 is "NO", the process proceeds to step 3138, where it is determined whether or not there is a vertical slip.

This determination is based on the wheel speed r detected by the wheel speed sensor 46.
The slip ratio in the longitudinal direction is calculated based on ω and the longitudinal acceleration GX detected by the longitudinal acceleration sensor 48, and it is determined whether the slip ratio is equal to or higher than a set value (for example, 1.1). Specifically, Mi(d r ω/d t )/GX≧1.1
- When (23) is satisfied, it is determined that there is a vertical slip.

If “NO” is determined in step 5138, step 3
At step 140, flag B is set to "zero".

Next, in step 5142, it is determined whether the return conditions for switching from the direct 4WD mode to the FF mode are satisfied. The content of this determination is that the magnitude of the acceleration acting on the center of gravity G (that is, E-UT-P) determined from the longitudinal acceleration GX and lateral acceleration GY detected by the acceleration sensor 50 this time is determined to be "rYEs" in step 5120. When the slip ratio difference ΔS between the front and rear wheels exceeds the set value, the FF
When it is determined that it is necessary to switch from the 4WD mode to the 4WD mode, the magnitude of the acceleration GC acting on the center of gravity G memorized in step 5121 (that is, the r
It is determined that the return condition is satisfied when the temperature is smaller than 17°C (17°C).

If rNOJ is determined in step 5142, step 5
The process advances to step 144 to determine the state of the brake detected by the brake sensor 58, that is, whether the brake switch (not shown) is on. In this step 5144, rNOJ
If so, the process returns to step M4 of the main routine.

If rYEsJ is determined in step 5136, flag C is set to "O" in step 5146, and step 5
Clear the memory GC at 148, then step 512
Proceeding to step 4, a control signal is output to set the drive state to cut-off mode.

If rYEsJ is determined in step 5138, the process proceeds to step 5150 and outputs a control signal for performing traction control to control the drive output of the engine 2 according to the slip ratio of the wheels. Although various well-known methods can be adopted for this traction control method, in this embodiment, the second throttle valve 2C shown in FIG. Therefore, it is preferable to control this servo device 2d to control the output of the engine 2.

When the control signal is output in step 5150, step 5
At step 152, flag B is set to "l" and the process returns to step S4 of the main routine. In addition, in relation to this flag B,
rYES" in step 5114, the process is configured to proceed to step 8138.

If it is determined as "YES" in step 5142 or 5144, "0" is set in 7 lag C in step 5154,
In step 5156, the GC is cleared and the process returns to step M4 of the main routine.

In this way, in the normal motor routine, after determining rYEsJ in step 5118 or 5120 and entering 4WD mode in step 5132, as long as rNOJ is determined in step 3136, 8138, 5142, 5144, step 5116 Since it is determined as rYESJ and the process proceeds to step 8132, the drive state is 4'v.
Retained in VD mode. Then, in step 5132, when the turning limit is reached while the 4WD mode is set, it is determined that rYEsJ is present in step 5136, and step 51
In step 24, the driving state becomes the cut-off mode, and if the maneuverability is recovered thereafter, a determination of "NO" is made in step 5122, and the drive state becomes the FF mode in step 5104. Also step 3113
If the determination in step 8 is ``YES'', traction control is performed in step 5150 while the drive state remains in the 4WD mode.

Furthermore, when the conditions for returning from 4WD mode to FF mode are satisfied, or when the brake switch is turned on,
At step 5142 or 5144, rYESJ is determined and the drive state becomes FF mode.

Next, the sports motor routine of step M20 in the main routine will be explained. In this sports motor routine, processes (steps) having the same contents as those in the normal mode flowchart shown in FIG. 3 are given the same reference numerals as those used in FIG. 3, and detailed explanations thereof will be omitted.

This sports mot routine differs from the normal mot routine shown in FIG. 3 in step 520.
0.5202.5204 and 5208, and these steps will now be described in turn.

In step 5200, it is determined whether or not the detection signal from the mode selector 64 was in the sports mode last time.
If YES, step Sil.

If it is rNOJ, the process advances to step 5102. In step 5202, control signals are output to the electromagnetic switching valves 36, 38 and the electromagnetic control valve 40 so that the driving state becomes the FR mode. Note that the content of control by this control signal is the same as the content of step M12 described above.

In step 5204, the slip ratio of the rear wheels 22.24 (
It is determined whether the difference ΔS between the slip ratio of the wheels relative to the road surface) and the slip ratio of the front wheels 12.14 is larger than a set value (for example, 0.05). In this step 3204, as in the case of step 5120, the turning radius difference between the front and rear wheels during a turn is determined based on the difference obtained by subtracting the wheel speed of the front wheel 12.14 from the wheel speed of the rear wheel 22.24. The correction is made for the difference in turning radius which is reduced due to the increase in lateral acceleration acting on the vehicle body. For this reason,
In detail, the calculation is performed according to (24). In addition, ωr in this formula (24) is the wheel speed of the rear wheel r, ωf is the wheel speed of the front wheel, αf1α
r is a correction coefficient determined by the above-mentioned formulas (5) and (7), respectively, and αY is a correction coefficient determined by formulas (9) and (10). Then, if "rYEs" is determined in step 5204, the process proceeds to step 5121, where Gc=
x+d' is stored in memory, and if rNOJ, step 520
Proceed to step 6.

In step 8206, it is determined whether the turning limit is reached. The content of this determination will be explained. In conjunction with step 5122 of the normal motor routine, r''/δ=GY
/L・1/ (1+A-R-GY)... (16) As explained above with reference to FIG. 9, similarly, the relationship between lateral acceleration GY and r2/δ for a general FR vehicle is As shown in FIG. 12, the steering characteristic changes from a weak US characteristic to a strong O8 characteristic as the lateral acceleration GY increases. If we pay attention to the value of r''/δ, no matter the magnitude of the driving force, its value increases as the lateral acceleration GY increases, and after crossing the 1/L line, it rapidly increases and becomes impossible to tangent. It can be seen that the state is

Therefore, the condition that occurs just before this turning limit is d(γ
2/δ)/dGY≧ε, · (1/L) (25). ε is a coefficient appropriately determined depending on the characteristics of the vehicle. Furthermore, in actual turning, if the steering angle of the front wheel f is on the increasing side, the actual turning limit will be smaller than the value calculated from equation (25), and if the engine throttle is on the depressed side, It is also smaller than the value calculated from equation (25).

Therefore, in step 8206, it is determined that the turning limit is exceeded when the following (26) is satisfied. When determining according to equation (26), the determination is made based on the detected value of the yaw rate sensor 62, the detected value of the steering sensor 52, the detected value of the lateral acceleration sensor 50, and the detected value of the throttle sensor 54.

Also, instead of formula (26), r=GY/V in opening formula (26)
By substituting... (27) can also be adopted. When determining according to this equation (27), the determination is made based on the detected value of the steering sensor 52, the detected value of the lateral acceleration sensor 52, and the detected value of the wheel speed sensor 46. In this judgment, the detection value of the wheel speed sensor 46 (
The smallest value among the four wheels is adopted as the vehicle speed V.
Even if the wheel with the lowest rotational speed is in a slip state, the value is .

Note that ε3. in equations (25) to (27). ε.

ε is a coefficient appropriately determined depending on the characteristics of the vehicle.

If rYESJ is determined in this step 5206, the process proceeds to step 5124, and if "NO", step 52
Proceed to 02.

Note that the return condition in step 5142 is satisfied when + −IJ< smaller than the GC determined in step 5121 after rYESJ is determined in step 5204. In this way, in the sports motor routine, after the FR mode is entered in step 5202, the result is rNO in step 5118 (the start condition is not satisfied), and rNOJ in step 5204 (the slip ratio difference is small). and in step 5206 rNO
As long as it is determined to be J (not at the turning limit), the drive state is maintained in the FR mode. Also step 5118
Or determine rYEsJ in step 5204 and step 513
After entering 4WD mode in step 2, step 5136.5
As long as "NO" is determined in 138, 5142, and 5144, the driving state is maintained in 4WD mode. Then, if the turning limit is reached while the 4WD mode is set in step 5132, it is determined as rYESJ in step 5136, and the drive state becomes cut-off mode in step 5124, and if the maneuverability is restored thereafter, "NO" is determined in step 8206. It is determined that, in step 5202, the FR mode is set. Also, if rYESJ is determined in step 5138, the drive state is 4.
Traction control is performed in step S150 while in the WD mode. Furthermore, if the conditions for returning from 4WD mode to FF mode are satisfied or the brake switch is turned on, rYE is selected in step 5142 or 5144.
S'' and the drive state becomes FF mode.

According to this embodiment configured as described above, by operating the mode selector 64, not only can the driving state be set to any of FF mode, FF mode, and 4WD mode as manual mode, but also the driving state can be set as normal mode as auto mode. When driving, the drive state is in FF mode and the 4'
You can set the normal mode, which switches to vVD mode, and the sport mode, which switches to FF mode during normal driving and switches to 4WD mode when necessary, so you can set the control mode to either normal mode or sport mode. By setting this, the system will switch to 2-wheel drive when 4-wheel drive is not required, improving fuel efficiency, and maintain the 2-wheel drive mode selected according to the driver's preference. It has a drooping effect.

In normal mode, as explained according to the flowchart shown in Figure 3, when the turning limit is detected while driving in FF mode, the mode is automatically switched to cutoff mode to increase the cornering force of the tires (front wheels), and at the same time The driver can be alerted to this condition. When it recovers to a stable side than the turning limit, it returns to the FF mode, but at the same time the front clutch 1
Since the rotation speed of the engine 2 is controlled to match the rotation speed of the input end and the rotation speed of the output side, even if the front clutch 10 is suddenly connected when returning from the cutoff mode to the FF mode, the Shock can be prevented.

In particular, since the turning limit is determined according to the conditions according to equation (19) or equation (20), it is possible to detect the turning limit with high accuracy, which prevents the situation from becoming uncontrollable during a turn. It can be prevented. In addition, while driving in FF mode, the vehicle is in a starting state, or the front wheels 12.1
The slip ratio difference ΔS obtained by subtracting the slip ratio of the rear wheel 22.24 side from the slip ratio of the 4 side is greater than or equal to the set value (
In other words, when it detects that the front wheels 12.14, which are the driving wheels, are in a slipping state, it automatically switches to 4WD mode and the driving force is transmitted to the road surface through both the front wheels 12.14 and the rear wheels 22.24. Therefore, slips at the time of starting or on slippery road surfaces are prevented. Note that even when starting, if the steering angle is large, the 4WD mode will not be entered, so the braking phenomenon of so-called direct 4WD can be prevented. In particular, the slip ratio difference △S can be determined using equation (11).
Since the slip ratio difference ΔS is detected with high accuracy, it is possible to appropriately switch to the 4WD mode. While driving in this 4WD mode, if it detects that the turning limit is reached, it will automatically switch to cut-off mode to ensure steering stability, and if vertical slip (slip in the longitudinal direction of the vehicle body) is detected, it will automatically switch to cut-off mode. Traction control is performed to ensure more reliable driving force on slippery roads. Then, when it determines that it is no longer necessary to drive in 4'vVD mode based on the acceleration acting on the vehicle body while driving in 4'vVD mode, it can automatically return to FF mode. If it is determined that the brake is on while the vehicle is running, the vehicle automatically returns to the FF mode, so that the operation of the so-called 3-channel or 4-channel anti-skid brake device can be prevented from being inhibited.

On the other hand, in sports mode, as explained according to the flowchart shown in Fig. 11, when the turning limit is detected while driving in FF mode, the mode is automatically switched to cut-off mode and the cornering force of the tires (rear wheels) is increased to control the steering. It is possible to restore stability and at the same time alert the driver of the situation. When the turning limit is restored to a stable side, the FF mode is returned to, but when it is determined that the turning limit has been exceeded and the switch is switched to the cutoff mode, the rotation speed of the input side of the rear clutch 18 and the output side of the rear clutch 18 are simultaneously changed. Since the rotational speed of the engine 2 is controlled to match the rotational speed of the engine 2, even if the rear clutch 18 is suddenly connected when returning from the cutoff mode to the FF mode, the occurrence of a shock can be prevented. In particular, since the turning limit is determined according to the conditions according to equation (26) or equation (27), it is possible to detect the turning limit with high accuracy, which prevents the situation from becoming uncontrollable during a turn. It can be prevented. In addition, by setting the value of the coefficient ε slightly larger than 1 in equation (26) or equation (27), it is possible to obtain a weak oversteer characteristic that provides excellent turning response of the vehicle to steering wheel operation. Can be done. In addition, while driving in FR mode, the vehicle is in a starting state, or the rear wheels 22.24
It is detected that the slip ratio difference ΔS obtained by subtracting the slip ratio of the front wheel 12.14 from the slip ratio of the side is greater than the set value (that is, the rear wheel 22.24, which is the driving wheel, is in a slipping state). Then, the vehicle automatically switches to the 4WD mode and the driving force is transmitted to the road surface through both the front wheels 12.14 and the rear wheels 22.24, thereby preventing slips at the time of starting or on slippery road surfaces. Note that even when starting, if the steering angle is large, the 4WD mode will not be entered, so the braking phenomenon of so-called direct 4WD can be prevented. In particular, the slip ratio difference ΔS can be determined using the formula (24
), it is possible to detect the slip ratio difference ΔS with high accuracy and appropriately switch to the 4WD mode. Note that the setting value regarding the slip ratio difference ΔS in this FR mode (as a specific example, 0.05
) is the setting value in normal mode (for example,
0.03), but this is because when driving in FR mode, a slightly larger slip ratio difference ΔS allows driving in FR mode, which makes it easier to operate the steering wheel. This is to enable the vehicle to be driven to a weak overteer characteristic region where the vehicle has excellent turning response. Also, in this sport mode, when the turning limit is detected while driving in 4WD mode, it can automatically switch to cut-off mode to ensure steering stability, as in the case of normal mode mentioned above. When longitudinal slip is detected, traction control is automatically performed to more reliably obtain driving force on slippery roads. Then, if it is determined from the acceleration acting on the vehicle body while traveling in 4WD mode that it is no longer necessary to travel in 4WD mode, or if it is determined that the brake is on, the vehicle automatically returns to FR mode.

Note that in the above embodiment, step 5 is performed in both the normal thousand-do routine and the sports moto routine.
144 uses the detection signal of the brake sensor 58 to detect whether the brake switch is on or not, but instead it uses the detection signal of the brake sensor 58 to detect whether the brake switch is on or not. When it is detected by the brake sensor 58 and it is determined that the anti-skid brake device has operated for anti-skid based on the detection signal, the mode changes from 4WD mode to FF mode or FF mode.
It is also possible to configure the device to switch to R mode.

Next, a modification of the above embodiment will be explained.

13 and 14 are modifications of the sports motor routine shown in FIG. 11 in the above embodiment. This modification differs from the flowchart of the sports motor routine shown in FIG. 11 in that step N2, which is a 4WD control routine, is adopted instead of step 5132 in FIG.

The 4WD control routine of step N2 will be explained according to the flowchart shown in FIG. First, step 530
At 0, a control signal is output so that the rear clutch 18 is in a directly connected state. That is, in this case, the chamber 1 of the rear clutch 18
In order to maximize the oil pressure in the chamber 8a, a control signal is output to the electromagnetic switching valve 38 so that the switching valve 38 assumes a position where the chamber 18a and the hydraulic pump 30 are in direct communication. Then step 5302
It is determined whether the first control has been completed or not. This initial control is step 5, which is proceeded to when the answer in step 5302 is "NO".
304 and therefore step 5116
．． 5118, 5204, and when the first determination is made in step 5302, the result is "NO". The content of the initial control performed in step 5304 is to set the oil pressure in the chamber 10a of the front clutch 10 to the setting oil pressure PS.
Specifically, a control signal is sent to the electromagnetic control valve 36 to set the position where the switching valve 36 communicates between the chamber 10a and the downstream side of the electromagnetic control valve 40, and a control signal is sent to the electromagnetic control valve 40 to control the control valve 40. A control signal is output in which the downstream oil pressure becomes the set oil pressure PS. Next, in step 8306, it is determined whether the slip ratio difference ΔS obtained by equation (24) is smaller than a set value S (for example, 0.04). If "YES" is determined in step 8306, that is, it is determined that the slip ratio difference ΔS is smaller than the set value S1, the process proceeds to step 5308, where the front clutch 1
A control signal is output to the electromagnetic control valve 40 in order to reduce the oil pressure in the zero chamber 10a by ΔP0. rN in step 8306
If it is determined that OJ, that is, the slip ratio difference ΔS is greater than or equal to the set value S2, the process proceeds to step 5310, where it is determined whether the slip ratio difference ΔS is larger than the set value Si (for example, 0.06). If "YES" in step 5310, that is, it is determined that the slip ratio difference ΔS is larger than the set value S, the process proceeds to step 5312, where the electromagnetic control valve 40 is activated to increase the oil pressure in the chamber 10a of the front clutch 10 by ΔP0. Outputs a control signal to. In step 5310, "
If it is determined that the slip ratio difference ΔS is equal to or less than the set value S, the process proceeds to step 5314, where it is determined whether the value dΔS/dt obtained by differentiating the slip ratio difference ΔS with respect to time is greater than or equal to zero.

“YES” in step 5314, that is, slip ratio difference Δ
If it is determined that S does not change or tends to increase, the process advances to step 8316 and the electromagnetic control valve 4 is activated to increase the oil pressure in the chamber 10a of the front clutch IO by ΔP.
Outputs a control signal to 0. “NO” in step 5314
, that is, if it is determined that the slip ratio difference ΔS tends to decrease, the process proceeds to step 5318 and the front clutch 1
A control signal is output to the electromagnetic control valve 40 in order to reduce the oil pressure in the chamber 10a by ΔP. and step 530
8. Upon completion of either step 3312, 5316 or 5318, the process proceeds to step 5134 in the flowchart of FIG. It should be noted that the set value S
, is set to 0.04, and the set value S, is set to 0.06, which ultimately means that the slip ratio difference ΔS is set to the target value (0.05
) in 4WD mode, that is, the front wheel is 12.14
This is to obtain a 4WD mode in which the torque on the rear wheel 22.24 side is always kept larger by a setting ratio corresponding to the target value than the torque on the rear wheel 22.24 side. Also, in step 5314, the slip ratio difference Δ
The differential value dΔS/dt of S is determined and the oil pressure in the chamber 10a of the front clutch 10 is controlled based on the result. 1
This is because the pressure inside 0a is large enough to cause hunting. Therefore, in this variation, step 5316.
ΔP1 of 5318 is ΔP of step 3308.5312
It is set to a value smaller than 0.

In addition, in step 5314, it is determined whether dΔS/d t≧0, and if rYEsJ, the process proceeds to step 5316 with “NO”.
”, the process is configured to proceed to step 8318, but between steps 5314 and 8316, dΔS/
It is also possible to provide a step of determining whether dt=0, and to proceed to return when rYESJ is determined in that step.

Therefore, according to the modification shown in FIGS. 13 and 14, in step 5118 or 5204, rYESJ
If it is determined that 4WD mode is selected, the rear wheel 2 is always
Since the driving force is transmitted with the torque on the 2.24 side being larger than the torque on the front wheel 12.14 side by the set ratio, acceleration performance is improved, and the steering characteristics approach neutral characteristics, improving maneuverability on slippery roads. can be improved.

In addition, in the above embodiments and modified examples, in FF mode or 4WD mode.
At step 5122. Judgment of the turning limit by 5136 is performed using equations (19) or (20) and equation (21), respectively.
Or, according to (22), only the turning limit on the US side is targeted, and the determination of the turning limit by Stella 7S206 at the time of 'FR is targeted only on the turning limit on the O8 side according to equation (26) or (27), but preferably Step S
In the determination of 122°8136, formula (26) or (27) is also incorporated as a determination condition, and in the determination of step 5206, formula (19) or (20), or formula (21) or (22) is also incorporated as a determination condition. By incorporating these steps 5122, 51 as
36 or 5206, US side turning limit and O8
Both side turning limits can be determined at all times.

FIG. 15 is a modification of the main routine shown in FIG. 2 in the above embodiment. The difference in this modification from the flowchart shown in FIG. 2 is that step M22 is added after step M18 in FIG.
This is because step M24 is added after 0.

This step M22 sets "1" to any of the flags A, B, and C in the normal motor routine of step M18.
Determine if is set. rYEsJ in step M22
If so, the process advances to step M18, which is step 8100 of the normal motor routine, and if "NO", the process returns, that is, returns to step M4.

Similarly, step M24 sets flags A and B in the sports motor routine of step M20.

It is determined whether any of C is set to "1".

If “YES” in step M24, step M20;
That is, the process advances to step 5100 of the sports motor routine, and if "NO", returns, that is, returns to step M4.

Therefore, as long as any of the flags A, B, and C is set to "1" in the normal moat routine of step M18, the normal mote routine processing is continued. In other words, if flag A is "1", the cutoff mode continues until rNOJ is determined in step 5122 of the normal motor routine, and if flag B is "1", until it is determined "NO" in step 8138. Traction control is continued, and if flag C is "1", 4WD mode is continued until rNC)+ is determined in step 5142 or 5144.

Also in the sports mot routine of step M20, as long as any of the flags A, B, and C is set to "1", the sports mot routine continues.

In other words, if flag A is "1", the cutoff mode will continue until it is determined as "NO" in step 5206 of the sports motor routine, and if flag B is "1", the traction mode will continue until rNOJ is determined in step 5138. If control continues and flag C is "1", step 514
The processing of the 4WD control routine continues until the determination is "NO" at 2 or 5144.

As a result, when the normal mode or sport mode is selected and the cut-off mode is executed to restore maneuverability, the 4WD mode or 4WD control routine is activated to improve the transmission of driving force to the road surface. In addition, when traction control is being executed, that control mode will be executed until maneuverability is restored or until the driving force is reliably transmitted to the road surface, so even if the control mode is Even if another mode is selected by the mode selector 64, that signal will be ignored.

Therefore, according to this modification, for example, when the cut-off mode is being executed to restore maneuverability, the crew member may accidentally select one of the manual modes and become unable to control the vehicle again. In order to improve the transmission of driving force to the road surface on slippery roads, the driver may accidentally select either the 4'vVD mode, the mode based on the 4WD control routine, or the manual mode when traction control is being executed. Therefore, it is possible to avoid a situation in which the transmission of the driving force to the road surface decreases again.

〔Effect of the invention〕

As described above, according to the present invention, when in the four-wheel drive state, the value obtained by combining the longitudinal acceleration and lateral acceleration detected by the longitudinal acceleration detection means and the lateral acceleration detection means is determined by the switching control means. when the value becomes smaller than the combined value of the longitudinal acceleration and lateral acceleration detected by the longitudinal acceleration detection means and the lateral acceleration detection means when the power transmission system switches from the two-wheel drive state to the four-wheel drive state. The power transmission system is then returned from the four-wheel drive state to the two-wheel drive state. As a result, for example, when switching from 2-wheel drive to 4-wheel drive while cornering, even if the engine throttle opening changes, the acceleration acting on the vehicle body changes from 2-wheel drive to 4-wheel drive. If the acceleration is less than when switching to drive mode, the vehicle will not return to two-wheel drive mode.
This makes it possible to eliminate the problems of the conventional device described above. In other words, in the present invention, the acceleration acting on the vehicle body when returning from the four-wheel drive state to the two-wheel drive state is the same as the acceleration acting on the vehicle body when switching from the two-wheel drive state to the four-wheel drive state. Since the acceleration is smaller than the actual acceleration, the driver hardly feels the influence of the steering characteristics even when turning, and the above-mentioned problems of the conventional device can be solved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the entire system showing one embodiment of the present invention;
FIG. 2 is a flowchart showing the control of the embodiment of FIG. 1;
Fig. 3 is a flowchart showing the normal motor routine of Fig. 2, Fig. 4 is an explanatory diagram for explaining the determination of the slip ratio difference in the flowchart of Fig. 3, and Fig. 5 shows the front wheel steering angle δ and the heat force. A characteristic diagram showing the relationship between the Mann correction coefficients αf and αr, FIG. 6 is a characteristic diagram showing the relationship between the lateral acceleration GY and the correction coefficient αY, and FIG. 7 is for explanation regarding the determination of the turning limit in the flow chart of FIG. FIG. 8 is an explanatory diagram showing the relationship between r''/δ and GY related to the determination of the turning limit. FIG. 9 is a characteristic diagram for a typical FF vehicle.
Figure 0 is an explanatory diagram showing details of the control device 2a in Figure 1;
1 is a flowchart showing the sports moto routine in FIG. 2, FIG. 12 is a characteristic diagram for a general FR vehicle, and FIG. 13 is a flowchart showing a modification of the flowchart (sports moto routine) in FIG. FIG. 14 is a flowchart showing the 4WD control routine of FIG. 13, and FIG. 15 is a flowchart showing a modification of the flowchart (main routine) of FIG. 2. 2... Engine, 10... Front clutch, 18
...Rear clutch, 44...Controller, 48.
...Longitudinal acceleration sensor, 50...Lateral acceleration sensor No. 4
Figure 7 Applicant Mitsubishi Motors Corporation Figure (iY Figure 7 Figure Y Figure A 4

Claims (1)

[Claims] A power transmission system that can switch between a two-wheel drive state that transmits the output of the prime mover to only two wheels and a four-wheel drive state that transmits it to all four wheels, and the difference in slip ratio between the drive wheels and non-drive wheels in the two-wheel drive state. and a switching control means for detecting a set condition and switching the power transmission system to a four-wheel drive state when a set condition is satisfied. , lateral acceleration detection means for detecting lateral acceleration acting on the vehicle body;
When the power transmission system is in a four-wheel drive state, a value obtained by combining the longitudinal acceleration and lateral acceleration detected by the longitudinal acceleration detection means and the lateral acceleration detection means is determined by the switching control means so that the power transmission system is in a four-wheel drive state. When the longitudinal acceleration and lateral acceleration detected by the longitudinal acceleration detecting means and the lateral acceleration detecting means are smaller than the combined value when switching from the drive state to the four-wheel drive state, the power transmission system is switched to the four-wheel drive state. A power transmission device for an automobile, comprising a return control means for returning from a drive state to a two-wheel drive state.