JP2552321B2 - Drive force distribution ratio detector for four-wheel drive vehicle - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a drive force distribution ratio detection device for a four-wheel drive vehicle capable of changing front-rear drive force distribution by increasing / decreasing clutch engagement force.

(Prior Art) As a conventional driving force distribution display device for a four-wheel drive vehicle, for example, a device described in Japanese Utility Model Laid-Open No. 62-47430 is known.

This conventional device detects the driving force distribution ratio based only on the command value detection of the clutch engagement force that generates the transmission torque to one of the front and rear wheels, and continuously determines the driving force distribution state based on the detected driving force distribution ratio. It is intended to be displayed in multiple stages.

(Problems to be Solved by the Invention) However, in this conventional device, even though the driving force distribution state is displayed, the clutch engagement force itself is merely displayed assuming the front-rear driving force distribution ratio. Even if it is possible to know the rough front-rear driving force distribution situation, it is not possible to convey to the driver the accurate front-rear driving force distribution ratio information that is actually transmitted from the tires to the road surface. Had a problem that the change in vehicle behavior due to the change in driving force distribution ratio could not be predicted.

That is, actually, due to the influence of the road friction coefficient and the tire, for example, even if the same clutch engagement force is applied, the driving force transmitted from the tire to the road surface is not constant, and the front-rear driving force distribution ratio also changes sequentially. To do.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above problems. To achieve this object, the present invention has the following means.

According to the first aspect of the present invention, as shown in the conceptual diagram of the claim of FIG. 1, a drive system clutch means 1 is provided in the middle of an engine drive system for distributing and transmitting the engine drive force to the front and rear wheels, and the drive system clutch means 1 In a four-wheel drive vehicle in which the driving force distribution ratio to the front and rear wheels is changed by increasing / decreasing the engaging force, the clutch engaging force detecting means 2 for detecting at least the clutch engaging force directly or indirectly as the detecting means.
A vehicle speed detecting means 3 for detecting a vehicle speed, and a front / rear wheel rotational speed difference detecting means 4 for detecting a front / rear wheel rotational speed difference, and the front / rear driving force distribution ratio Tf is based on detection values from these detecting means. % Is the following formula However, V is a vehicle speed, T is a clutch engagement force, ΔN is a front / rear wheel rotational speed difference, and K ₁ and K ₂ are front-rear driving force distribution ratio calculating means 5 for detecting the four-wheel drive vehicle. Driving force distribution ratio detection device.

According to a second aspect of the present invention, the front-rear driving force distribution ratio calculation means 5 is the following equation, wherein K ₁ and K ₂ are functions of the front-rear weight distribution of the vehicle in the equation of the first claim. K ₂ = K ₃ * Wr where Wf is the front weight Wr is the rear weight, and the driving force distribution ratio detection device for a four-wheel drive vehicle according to claim 1.

According to a third aspect of the present invention, the front-rear driving force distribution ratio calculating means 5 is means for obtaining the coefficient K ₃ by a function of the road surface friction coefficient μ in the formula of the second aspect. Vehicle driving force distribution ratio detector.

According to a fourth aspect of the present invention, the front-rear driving force distribution ratio calculation means 5 is means for obtaining the coefficient K ₃ by a function of the centripetal acceleration Yg and the front-rear wheel rotational speed difference ΔN in the equation of the second aspect. 2. The drive force distribution ratio detection device for a four-wheel drive vehicle according to 2.

(Operation) When the front-rear driving force distribution ratio is detected during traveling, the front-rear driving force distribution ratio calculating means 5 detects the clutch engaging force detecting means 2 for directly or indirectly detecting the clutch engaging force and the vehicle speed. Based on the detected values from the vehicle speed detecting means 3 and the front / rear wheel rotational speed difference detecting means 4 for detecting the front / rear wheel rotational speed difference, the front-rear driving force distribution ratio is calculated by a predetermined arithmetic expression including at least these detected values. Detected by.

Therefore, the vehicle speed and the front-rear wheel rotation speed difference indirectly provide information such as the road surface friction coefficient and the tire condition, and the theoretical driving force distribution ratio by the clutch engagement force considers the road surface friction coefficient effect and the tire effect. It is possible to detect the front-rear driving force distribution ratio with high accuracy by correcting the actual driving force distribution ratio.

(Examples) Hereinafter, examples of the present invention will be described in detail with reference to the drawings. In the description of this embodiment, a drive force distribution ratio detection device for a four-wheel drive vehicle based on a rear wheel drive in which the drive force distribution is changed by external electronic control will be taken as an example.

 First, the configuration will be described.

The four-wheel drive vehicle to which the driving force distribution control device D of the embodiment is applied has a transfer device 10, an engine 11, a transmission 12, a transfer input shaft 1 as shown in FIG.
3, rear wheel side drive shaft 14, multi-disc friction clutch (drive system clutch means) 15, rear differential 16, rear wheel 17, front differential 18, front wheel 19, jeer train 20,
A front wheel side drive shaft 21 is provided.

The multi-plate friction clutch 15 is the transfer input shaft.
It is interposed between the front wheel drive shaft 21 and the rear wheel drive shaft 14 (directly connected to the rear wheel drive shaft 14).
It is possible to change the transmission torque to the side.

Incidentally, FIG. 3 shows a specific example of the transfer device 10, and the multi-plate friction clutch 15, gears and shafts are housed in a transfer case 22.

In FIG. 3, 15g is a dish plate, 15h is a return spring, 24 is a clutch pressure oil input port, 25 is a clutch pressure oil passage, 26 is a rear wheel side output shaft, 27 is a lubricating oil passage, and 28 is a speedometer. Pinion, 29 is an oil seal, 30 is a bearing, 31 is a needle bearing, 32 is a thrust bearing, and 33 is a joint flange.

Next, as shown in FIG. 4, the electronic control unit 40 for controlling the clutch hydraulic pressure P for engaging the multi-plate friction clutch 15 and detecting the driving force distribution ratio, as shown in FIG.
A rear wheel rotation speed sensor 41, a left front wheel speed sensor 42, and a right front wheel speed sensor 43 are provided, a control unit 45 is provided as control processing means, and an electromagnetic proportional relief valve 46 and a driving force distribution ratio display device 60 are provided as output means. Is equipped with.

The wheel speed sensors 41, 42, 43 are provided in the positions of the left and right front wheels 19 and in the middle of the rear wheel side drive shaft 14, respectively, and detect a sensor rotor fixed to the shaft and a magnetic force change due to rotation of the sensor rotor. A rotation sensor or the like based on the pickup is used, and wheel speed signals (nr), (wf ₁ ) and (wf ₂ ) corresponding to the shaft rotation are output from these sensors 41, 42 and 43, respectively.

The control unit 45, a circuit centered on a vehicle-mounted microcomputer is used, as an internal circuit, an input interface 451, RAM452, ROM453, CPU454,
It has an output interface 455.

The electromagnetic proportional relief valve 46 outputs the command current signal (i) from the control unit 45 as a command current value I.
^{When *} = 0, the clutch oil pressure P = 0, but when the output of the command current signal (i) is the command current value I ^* > 0, the valve moves in the closing direction and the line pressure from the hydraulic power source 50 is reduced. By controlling the drain oil amount, the clutch hydraulic pressure P is set according to the magnitude of the command current value I ^* (Fig. 5). The relationship between the clutch hydraulic pressure P and the clutch engaging force T is expressed by the following equation (6th
Figure).

P = T / (μ ・ A ・ 2n ・ Rm) where μ is the friction coefficient of the clutch plate, A is the pressure acting area on the piston, n is the number of friction discs, and Rm is the effective torque transmission radius of the friction disc. When the hydraulic pressure P is increased, the clutch engagement force T is also increased proportionally.

The driving force distribution ratio display device 60 is provided at a position visible to the driver in the vehicle compartment, and the calculation result of the driving force distribution ratio performed by the control unit 45 is displayed in digital or analog form.

 Next, the operation will be described.

In describing the operation, the front-rear driving force distribution control operation and the front-rear driving force distribution ratio detecting operation will be described separately.

[Front-rear driving force distribution control action] First, the overall flow of the driving force distribution control operation in the embodiment will be described with reference to the flowchart shown in FIG. 7.

In step a, the left front wheel speed wf ₁ ,
The right front wheel speed wf ₂ and the rear wheel rotation speed Nr are read.

In step b, the vehicle speed Vf, the front and rear wheel rotation speed difference ΔN, and the left and right front wheel rotation speed difference Δn are calculated from the left front wheel speed wf ₁ , the right front wheel speed wf _2, and the tire diameter r read in step a. . The vehicle speed Vf is obtained by the following equation from the smaller _{one of} the left and right front wheel speeds wf ₁ and wf ₂ and the tire diameter r.

Vf = r * {min (wf ₁ , wf ₂ )} The vehicle speed Vf may be obtained by an average value of the left and right front wheel speeds wf ₁ , wf ₂ , or the absolute vehicle speed may be directly detected. .

The front-rear wheel rotation speed difference ΔN is obtained from the following equation from the rear-wheel rotation speed Nr and the average front-wheel rotation speed.

ΔN = Nr − {(wf ₁ + wf ₂ ) / 2} This may be directly detected by detecting the operating rotation of the front and rear wheels.

The difference between the left and right front wheel rotation speeds Δn is the left front wheel speed wf ₁ and the right front wheel speed w.
It is calculated from f ₂ and the following formula.

Δn (= | wf ₁ −wf ₂ |) Since this left / right front wheel rotational speed difference Δn is for obtaining the turning radius R and the lateral acceleration Yg,
The turning radius R may be obtained from the steering angle θ, or the lateral acceleration Yg may be directly detected by a lateral acceleration sensor or the like.

In step c, it is determined whether the front-rear wheel rotational speed difference ΔN obtained in step b is ΔN ≧ 0 or ΔN <0.

From step b, the control based on the front-rear wheel rotation speed difference ΔN, which proceeds to step d (control during constant speed / acceleration) or step e (control during deceleration) based on the determination in step c, and step f Vehicle speed to proceed to (control at high speed)
Control based on Vf is executed in parallel.

In the constant speed / acceleration control of step d, the lateral acceleration Yg is obtained from the left / right front wheel rotational speed difference Δn and the vehicle speed Vf, and the clutch engagement force Tx is calculated from the lateral acceleration Yg and the front / rear wheel rotational speed difference ΔN. . The details will be described later with reference to FIG.

In the control during deceleration of step e, the clutch engagement force Tneg is calculated from the vehicle speed Vf and the front and rear wheel rotation speed difference absolute value | ΔN |. The details will be described later with reference to FIGS.

In the high speed control of step f, the clutch engagement force Tv is calculated only by the vehicle speed Vf. The details will be described later with reference to FIG. 12 and FIG.

In steps g and h, the clutch engaging forces Tx and Tneg on the opposite side are set to 0 (zero).

In step i, the target clutch engagement force T ^* is obtained by selecting the maximum value among the clutch engagement forces Tx, Tneg, Tv.

T ^* = max (Tx, Tneg, Tv) In step j, the clutch pressure control signal (i) that obtains the target clutch engagement force T ^* is output to the electromagnetic proportional relief valve 46.

Next, the contents of control processing at the time of constant speed / acceleration in step d will be described with reference to the flowchart of FIG.
62-36036).

In step 100, the turning radius R is calculated based on each data in step b.

 The formula for calculating the turning radius R is as follows.

In the next step 101 to step 109, a low-pass filter that restricts the increasing rate of the turning radius R and the changing speed in the increasing direction is realized.

In step 101, the amount of change ΔR per unit time is calculated by the difference between the turning radius R obtained in step 100 and the turning radius R ₀ one cycle before.

In step 102, it is determined whether ΔR is positive or negative, and the turning radius R
Is determined to be an increasing direction or a decreasing direction, and the subsequent processing route is changed.

When ΔR is positive in step 102, that is, when the turning radius R is in the increasing direction, the change width is set value A in step 103.
_It is determined whether or not it is greater than ₄ , and this set value A ₄ becomes the value of the low-pass filter when the turning radius R increases.

Then, if ΔR is larger than A ₄ in step 103,
Proceed to step 104, filtered, turning radius Rx
Is calculated by the arithmetic expression of R ₀ + A ₄ .

If ΔR is smaller than A ₄ at step 103, the routine proceeds to step 105, where the calculated turning radius R is set as it is as the turning radius Rx.

On the other hand, if ΔR is negative in step 102, that is, if the turning radius R is in the decreasing direction, it is determined in step 106 whether or not the change width is larger than the set value A ₅ , and this set value A ₅ is turned. It is the value of the low-pass filter when the radius R decreases. The set value A ₅ is larger than the set value A ₄ .

Then, if | ΔR | is larger than A ₅ in step 106, the process proceeds to step 107 to be filtered, and the turning radius Rx is obtained by the arithmetic expression of R ₀ −A ₅ .

If | ΔR | is smaller than A ₅ in step 106,
The routine proceeds to step 108, where the calculated turning radius R is set as it is as the turning radius Rx.

In step 109, the value of the turning radius Rx obtained in this control cycle is stored as R ₀ for calculating ΔR.

In step 110, the lateral acceleration Yg is calculated by the following calculation based on the turning radius Rx that has been low-pass filtered and the vehicle speed Vf.

In step 111, the proportional coefficient (gain) K is obtained by the following arithmetic expression using the lateral acceleration Yg.

In step 112, the correction value ΔNx of the front-rear wheel rotational speed difference ΔN obtained in step b is obtained. When ΔN <0, the correction value ΔNx is regarded as a tight corner and ΔNx
When Nx = 0 and ΔN ≧ 0, the turning locus is corrected and ΔNx = ΔN−f (Rx, Vf).

In step 113, the clutch engagement force Th (= K · ΔNx) is calculated from the proportional coefficient K and the correction value ΔNx.

In step 114, the clutch engagement force Tl (= K · ΔN) is calculated from the predetermined proportional coefficient Kl and the front-rear wheel rotation speed difference ΔN.

In step 115, the larger one of the clutch engagement forces Th and Tl is selected as the clutch engagement force Tx.

 That is, when Th ≧ Tl, Tx = Th Th <Tl is set as Tx = Tl.

As described above, the clutch engagement force Tx is normally the turning radius R
The lateral acceleration Yg is indirectly obtained by filtering the value of
The clutch engagement force Th obtained by filtering the value of the proportionality coefficient K determined by the above is obtained. However, the predetermined clutch engagement force Tl obtained based on the actual measurement value is obtained so as not to become an extremely small value. I am allowed to do so.

Next, the control processing contents at the time of deceleration in step e will be described with reference to the flowchart of FIG.

At step 120, the gain Kneg is obtained as a function of the vehicle speed Vf. As shown in FIG. 10 and FIG. 11, this gain Kneg is Kneg = 0 until the vehicle speed V ₀ at which the front and rear wheel rotation speed difference ΔN turns from negative to positive, and Kneg from the vehicle speed V ₀ to the vehicle speed V _1.
Eg gradually increases from ₀ to K _0, and if the vehicle speed exceeds V ₁ , Kneg ＝
It becomes the value of K ₀ .

In step 121, the gain obtained in step 200
From Kneg and the absolute value of front-rear wheel rotation speed difference | ΔN |, the clutch engagement force Tneg is calculated by the following equation.

Tneg = Kneg * | ΔN | Next, the control processing contents at the time of the high speed at step f will be described with reference to the flowchart of FIG.

In step 130, the clutch engagement force Tv is calculated by the following equation using a function based only on the vehicle speed Vf.

Tv = f (Vf) This vehicle speed function f (Vf) has the content shown in FIG. 13. The increase in the clutch engagement force due to the vehicle speed response is mainly due to the stability at high speeds. The vehicle speed V _{2 at the} starting point where Tv becomes zero or more is about 80 km / h, and the vehicle speed V ₃ that reaches the maximum clutch engagement force Tvmax is about 120 km / h, which is a range that does not affect the turning performance at low and medium speeds. And

Further, the maximum clutch engagement force Tvmax is a value that satisfies high-speed straight traveling stability, and is a value that is sufficient to make the steer characteristic a weak understeer characteristic during an acceleration turn.

By the control operation described above, the clutch engagement force Tx corresponding to the vehicle speed is almost zero at the time of constant speed / acceleration at a low / medium speed of 80 km / h or less, so the clutch engagement force Tx is the target clutch engagement force Tx. Selected as ^*

During deceleration, the clutch engagement force Tneg is selected as the target clutch engagement force T ^* unless the vehicle speed is high.

Further, for example, when traveling at a high speed of 80 km / h or more, the larger value of the clutch engagement force Tx and the clutch engagement force Tv is selected as the target clutch engagement force T ^* . That is,
When the vehicle speed Vf is high even when the front-rear wheel rotation speed difference ΔN is small, the value of the clutch engagement force Tv is selected as the target clutch engagement force T ^* .

Therefore, it is possible to obtain the effect of satisfying all of the stability of acceleration / deceleration at low / medium speed running, the stability at high speed straight running, and the optimum steer characteristic at high speed turning acceleration.

It should be noted that, in actual traveling, the traveling conditions rarely differ from each other as described in (a) to (c) above, and each element is complex, but the degree of influence of the clutch engagement force due to each element depends on the degree of influence. By selecting the largest maximum value, the stable side will be controlled in any case (Japanese Patent Application No. 62-30).
See 2473).

[Front-rear driving force distribution ratio detecting action] First, theoretical calculation for obtaining the driving force distribution ratio from the wheel speed will be described with reference to FIGS. 14 and 15. However, Wf, Wr; wheel load, Sf, Sr; slip ratio, wf, wr; wheel speed, Qf, Qr; driving force,
Tf, Tr; axial torque, μ; tire-road friction coefficient, r: tire radius, V: vehicle speed.

Ti = Qi ・ r Qi = μi ・ Wi μi = k ・ Si on the other hand, By (1) and (2), Front wheel side driving force distribution ratio Tf% = Tf / (Tf + Tr) Thus, the front wheel side driving force distribution ratio Tf% can be calculated.

Next, regarding the calculation method of each variable of the equation (4),
It will be described with reference to FIG.

・ Front shaft torque Tf Tf = T × if if; Final gear ratio ・ Vehicle speed V ・ Wheel load Wf, Wr ・ Front and rear wheel rotation speed difference ΔN ΔN = wr-wf ・ Braking / driving stiffness coefficient k A calculation example based on the above theoretical calculation formula will be shown.

In the case of rigid 4WD If ΔN = 0 in equation (4), And is equal to the weight distribution ratio.

Is it possible to perform control with a constant driving force distribution ratio? Solving as Tf% input and Tf output in the equation (4), Therefore, constant control of the driving force distribution ratio is possible.

However, the braking / driving stiffness coefficient k changes depending on the road surface friction coefficient and the tire condition, and the front-rear wheel rotation speed difference ΔN and the vehicle speed V require turning correction.

Next, the flow of the driving force distribution ratio detection processing operation performed by the control unit 45 based on the above theoretical calculation will be described.
This will be described with reference to the flowchart shown in FIG.

In step 200, the front-rear wheel rotational speed difference ΔN, the vehicle speed Vf, and the turning radius obtained in the driving force distribution control processing operation described above.
R, target clutch engagement force T ^* is read.

In step 201, the centripetal acceleration Yg and the longitudinal acceleration Xg are calculated by the following formulas based on the input values in step 200.

Yg = Vf ² / R Xg = (Vf−Vfo) / Δt Vfo is the vehicle speed read before the predetermined control cycle Δt Xg
Is calculated from the differential value of the vehicle speed.

The centripetal acceleration Yg and the longitudinal acceleration Xg may be directly detected using a G sensor.

In step 202, the front wheel load Wf and the rear wheel load Wr are calculated by the following formulas as a function of the longitudinal acceleration Xg.

_{Wf = (A 1 -A 0 ·} Xg) / 2 Wr = (A 2 + A 0 · Xg) / 2 Note that the front and rear wheel load Wf, Wr can be directly detected by the stroke sensor or the like.

In step 203, the braking / driving stiffness coefficient k _{x of} the tire is calculated as a function of the centripetal acceleration Yg and the front / rear wheel rotational speed difference ΔN by the following equation.

Here, the braking / driving stiffness coefficient k _x is a value that changes depending on the road surface friction coefficient μ, and as shown in FIG. 18, there is a relationship of k _x (high μ road)> k _x (low μ road). .

However, since the road surface friction coefficient μ cannot be directly detected, it is indirectly detected by the centripetal acceleration Yg and the front and rear wheel rotation speed difference ΔN. In other words, the centripetal acceleration is large → high μ road The centripetal acceleration is small → low μ road Furthermore, as shown in Fig. 19, large front / rear wheel rotational speed difference → large slip → low μ road small front / rear wheel rotational speed difference → small slip → Express the relationship of high μ road.

k _x = f (Yg, ΔN) A ₃ + A ₆ · Yg−A ₄ · ΔN where A ₃ , A ₆ and A ₄ are constants.

In step 204, the front wheel side driving force distribution ratio Tf% and the rear wheel side driving force distribution ratio Tr% are calculated by the following formulas.

Tr% = 1-Tf% However, A ₅ is a constant. In step 205, the driving force is transmitted in order to inform the driver of the front wheel side driving force distribution ratio Tf% and the rear wheel side driving force distribution ratio Tr% obtained in step 204. Output to the distribution ratio display device 60.

Through the driving force distribution ratio detection process described above, the target clutch engagement force T ^* is used as basic information, and the vehicle speed Vf and the front / rear wheel rotation speed difference ΔN are used as indirect information sources such as the road surface friction coefficient μ and the tire condition. The theoretical driving force distribution ratio due to the force T ^* is corrected to the actual driving force distribution ratio in consideration of the road surface friction coefficient influence, tire influence, etc., and the highly accurate front-rear driving force distribution ratio Tf%, Tr% is detected. To be done.

Therefore, the driving force distribution ratio detecting device of the embodiment has the following effects.

The accurate information of the front-rear driving force distribution ratio Tf%, Tr% is transmitted to the driver by the driving force distribution ratio display device 60, and the driver can change the behavior of the vehicle by the front-rear driving force distribution ratio Tf%, Tr%. Can accurately predict.

By feeding back the detected front-rear driving force distribution ratios Tf% and Tr% as input information of the driving force distribution control, control for keeping the driving force distribution ratio constant, and not the clutch engagement force but the front-rear driving force distribution ratio Tf %, Tr% as the control target, it is possible to perform the optimum driving force distribution control corresponding to actual driving.

The sensors installed in the vehicle are only three sensors, a rear wheel rotation speed sensor 41, a left front wheel speed sensor 42, and a right front wheel speed sensor 43, which are cost-effective and reliable devices, and only drive force distribution control is possible. Therefore, the driving force distribution ratio can be detected.

Although the embodiment has been described in detail with reference to the drawings, the specific configuration and control contents are not limited to this embodiment.

For example, in the embodiment, the example in which the driving force distribution ratio of the front and rear wheels is determined only by the clutch whose engagement force is controlled from the outside has been shown, but the transfer device is a combination of this electronically controlled clutch and a planetary gear set or the like. In this case, when obtaining the driving force distribution ratio, the final driving force distribution ratio is determined by considering the distribution ratio based on the target clutch engagement force and the distribution ratio based on the planetary gear set or the like.

Further, when a viscous clutch that itself generates an engaging force is used as the drive system clutch means, the clutch engaging force T is
The value is estimated and calculated by the function {T = f (ΔN)} of the rotational speed difference ΔN of the input / output shaft, which is the cause of the fastening force generation.

(Effects of the Invention) As described above, in the drive force distribution ratio detection device for a four-wheel drive vehicle of the present invention, as the detection means, at least the clutch engagement force for directly or indirectly detecting the clutch engagement force is detected. A force detection means, a vehicle speed detection means for detecting a vehicle speed, and a front / rear wheel rotation speed difference detection means for detecting a front / rear wheel rotation speed difference, and a front / rear driving force distribution ratio based on detection values from these detection means. Tf% is calculated by the following formula However, V is the vehicle speed, T is the clutch engagement force, ΔN is the difference between the front and rear wheel rotational speeds, and K ₁ and K ₂ are the front and rear driving force distribution ratio calculation means that are detected by the coefficient. Information such as the road surface friction coefficient and tire condition is brought about, and the theoretical driving force distribution ratio due to the clutch engagement force is corrected to the actual driving force distribution ratio in consideration of the road surface friction coefficient effect and the tire effect. The effect that the front-rear driving force distribution ratio can be detected with high accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a driving force distribution ratio detecting device for a four-wheel drive vehicle according to the present invention, FIG. 2 is a diagram showing a four-wheel drive vehicle to which the embodiment device is applied, and FIG. 3 is an embodiment device. 4 is a sectional view showing the transfer device of FIG. 4, FIG. 4 is a block diagram showing the control unit of the embodiment device, FIG. 5 is a characteristic diagram of the relationship between the clutch hydraulic pressure and the clutch engaging force, and FIG. 6 is the command current value and the clutch pressure. FIG. 7 is a flow chart showing the flow of the driving force distribution control operation in the control unit of the embodiment apparatus, FIG. 8 is a flow chart showing the flow of the control processing operation at constant speed / acceleration, and FIG. FIG. 10 is a flow chart showing the flow of control processing operation during deceleration, FIG. 10 is a gain characteristic diagram with respect to vehicle speed, FIG. 11 is a front-rear wheel rotational speed difference characteristic diagram with respect to vehicle speed, and FIG. 12 is control processing operation at high speed. Flower showing flow Figure, FIG. 13 the clutch engagement force characteristic chart with respect to the vehicle speed, FIG. 14 is dynamic model view of the driving system at the time of running, FIG. 15 road surface friction coefficient characteristic diagram with respect to the slip rate,
FIG. 16 is a dimensional model diagram of the vehicle, FIG. 17 is a flowchart diagram showing the flow of the driving force distribution ratio detection processing operation in the control unit of the embodiment apparatus, and FIG. 18 is a low μ road and a high μ road. FIG. 19 is a comparison diagram of road surface friction coefficient characteristics, and FIG. 19 is a correspondence diagram of a relationship between front and rear wheel rotational speed differences and road surface friction coefficient characteristics. 1 ... Drive system clutch means 2 ... Clutch engagement force detecting means 3 ... Vehicle speed detecting means 4 ... Front / rear wheel rotational speed difference detecting means 5 ... Front / rear driving force distribution ratio calculating means

Claims (4)

(57) [Claims] 1. A drive system clutch means is provided in the middle of an engine drive system for distributing and transmitting the engine drive force to the front and rear wheels, and the drive force distribution ratio to the front and rear wheels is changed by increasing or decreasing the engagement force of the drive system clutch means. In a four-wheel drive vehicle, as a detecting means, at least a clutch engaging force detecting means for directly or indirectly detecting the clutch engaging force, a vehicle speed detecting means for detecting a vehicle speed, and a front and rear wheel rotation detecting a front and rear wheel rotation speed difference. And a speed difference detection means, and based on the detection values from these detection means, the front-rear driving force distribution ratio Tf% However, V is a vehicle speed, T is a clutch engagement force, ΔN is a front / rear wheel rotational speed difference, and K ₁ and K ₂ are provided with front-rear driving force distribution ratio calculating means for detecting by a coefficient. Driving force distribution ratio detector. 2. The front-rear driving force distribution ratio calculating means in the formula according to claim 1, wherein K ₁ and K ₂ are functions of front-rear weight distribution of the vehicle. K ₂ = K ₃ * Wr where Wf is the front weight Wr is the rear weight, and the driving force distribution ratio detection device for a four-wheel drive vehicle according to claim 1. 3. The driving force of a four-wheel drive vehicle according to claim 2, wherein the front-rear driving force distribution ratio calculating means is a means for obtaining the coefficient K ₃ by a function of the road surface friction coefficient μ in the expression described in claim 2. Distribution ratio detector. 4. The front-rear driving force distribution ratio calculating means is means for calculating the coefficient K ₃ in the formula of claim 2 by a function of the centripetal acceleration Yg and the front-rear wheel rotational speed difference ΔN.
A driving force distribution ratio detecting device for a four-wheel drive vehicle as described above.