JPH02106442A - Control of differential movement control clutch for front/rear-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To prevent the traveling performance of a vehicle from being deteriorated by suppressing the differential movement restricting force of a differential movement control clutch for controlling the differential movement between the front and rear wheels, when it is judged that each effective diameter of the front and rear wheels is less than a previously set standard judgement value during the traveling of the vehicle. CONSTITUTION:The driving torque outputted from an automatic transmission 14 is divided by a center differential gear device 20 and transmitted to a differential gear device 22 for front wheels and a differential gear device 26 for rear wheels. A differential movement control clutch 82 is installed between the differential gear case 32 of the center differential gear device 20 and a front wheel driving shaft 44, and controlled according to the instruction supplied from an electronic controller 86 by a clutch hydraulic control circuit 84. In this case, each tire pneumatic pressure corresponding to each effective diameter of the right and left front and rear wheels 24 and 26 is read from each output of a front wheel pneumatic pressure sensor 102 and a rear wheel pneumatic pressure sensor 104, and when the effective diameter is less than a standard judgement value, a differential movement control clutch 82 is controlled so that the differential movement restricting force is suppressed afterwards.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for controlling a differential control clutch in a front-wheel drive vehicle equipped with a differential control clutch.

BACKGROUND ART In a front-wheel drive vehicle such as a four-wheel drive vehicle, a switch is used to selectively connect one of a front-wheel drive member and a rear-wheel drive member to the other to switch between a two-wheel drive state and a four-wheel drive state. The so-called part-time type equipped with a clutch,
There are so-called full-time types that are equipped with a differential limiting clutch for limiting the differential operation of a center differential device that distributes drive torque between front wheel drive members and rear wheel drive members. The switching clutch and the differential limiting clutch as described above are called differential control clutches because they control the differential rotational speed between the front wheels and the rear wheels of the vehicle.

In vehicles equipped with the differential control clutch described above, it is normally determined that either the front or rear wheels are slipping relative to the road surface when the rotational speed difference between the front and rear wheels becomes large. In this way, the differential limiting force of the differential control clutch is increased to limit the differential between the front and rear wheels.

However, if there is a difference in the effective diameter of the wheels due to the load applied to each wheel, tire wear, tire air pressure, etc., and the above differential limiting control is executed, the differential limiting will cause the power to circulate. occurs, resulting in overload, tire wear,
There was a problem in that fuel consumption decreased.

On the other hand, when the vehicle is in a stable running state, the differential rotation speed of the front and rear wheels is detected, and if the differential rotation speed is determined to be less than a predetermined value, the differential rotation speed is determined at the low speed of the vehicle. This is done so that differential rotation speeds between the front and rear wheels are equal to or higher than a predetermined value in the second judgment. A control method has been proposed in which a plurality of determinations are made in succession and differential rotational speed is suppressed when it is determined that the differential rotation speed is equal to or higher than a predetermined value a predetermined number of times in succession. For example, JP-A-63-13703
This is what is described in Publication No. 0.

Problems to be Solved by the Invention However, in the control method for a front-wheel drive vehicle as described above, once it is determined that the differential rotational speed of the front and rear wheels is below a predetermined value, the vehicle does not run at low speed or until it stops. That judgment is not made. However, while the vehicle is running, there are cases where the air pressure in the tires drops due to a flat tire, etc., and the vehicle continues to drive. The above differential torque is generated, which impairs the driving performance of the vehicle and causes energy loss.

The present invention has been made against the background of the above circumstances,
The purpose is to provide a control method that does not cause unnecessary differential torque to be generated in the differential control clutch even when the tire air in the wheels decreases while the vehicle is running.

Means for Solving the Problems The gist of the present invention to achieve the above object is to provide a front-wheel drive vehicle equipped with a differential control clutch that controls the differential between the front wheels and the rear wheels. A control method for a control clutch, comprising: (a) an air pressure detection step of detecting the effective diameters of front wheels and rear wheels respectively while the vehicle is running; and (g) the effective diameter is less than or equal to a predetermined judgment reference value. (C) If it is determined that the effective diameter is less than or equal to a predetermined reference value, the differential limiting force is thereafter suppressed. There is a particular thing.

Operation and Effect of the Invention With this method, if it is determined that the effective diameters of the front and rear tires are less than a predetermined criterion value while the vehicle is running, the differential control will be performed thereafter. The differential limiting force of the clutch is suppressed. Therefore, when the tire air in the wheels decreases while the vehicle is running, unnecessary differential torque is not generated in the differential control clutch, which impairs the vehicle's driving performance or causes energy loss. It eliminates the need to do things.

EXAMPLE Hereinafter, an application example of the present invention will be explained in detail based on the drawings.

FIG. 1 is a diagram showing a power transmission system, a control device for a differential control clutch 82, etc. of a transverse engine four-wheel drive vehicle. In the figure, the output of an engine 10 is supplied to an automatic transmission 14 via a clutch 12. This clutch 12
It consists of a torque converter, fluid coupling, magnetic particle electromagnetic clutch, hydraulic multi-disc clutch, etc. The automatic transmission 14 is configured by, for example, a planetary gear type stepped transmission or a belt type continuously variable transmission. The hydraulic control circuit 16 operates a hydraulic actuator that changes the gear ratio of the automatic transmission 14 to automatically change the gear stage or the effective diameter of the variable pulley.

The drive torque output from the automatic transmission 14 is divided into two by the center differential device 20, one drive torque is transmitted to the front wheels 24 via the front wheel differential device 22, and the other drive torque is transmitted to the rear wheels. Differential equipment! 26 to the rear wheels 28.

The center differential device 20 is the automatic transmission 14
A differential case 32 is integrally provided with an input gear 30 that meshes with an output gear 1, and is rotatably provided around one axis, and a pinion shaft 34 is mounted in the differential case 32 in a direction perpendicular to the above-mentioned axis. A pair of differential small gears 36 and 38 that are rotatably supported, respectively, and a large differential gear 4 for front wheels that is meshed with the differential small gears 36 and 38, respectively.
0 and a large differential gear 42 for rear wheels, the automatic transmission 1
The drive torque input through the output gear 18 of No. 4 is distributed to the large differential gear 40 for front wheels and the large differential gear 42 for rear wheels.

The front wheel differential device 22 includes a differential case 46 that is connected to the front wheel differential large gear 40 via a hollow front wheel drive shaft 44 and is rotatably provided around the - axis, and a differential case 46 that is connected to the front wheel differential gear 40 via a hollow front wheel drive shaft 44 and is rotatably provided around the - axis. A pair of differential small gears 50 and 52, each rotatably supported by a pinion shaft 48 mounted in a direction perpendicular to the shaft, and a pair of differential large gears meshed with the differential small gears 50 and 52, respectively. 5
4 and 56, and distributes the drive torque transmitted via the front wheel drive shaft 44 to the left and right front wheels 24 via a pair of differential large gears 54 and 56.

The driving torque transmitted through the rear wheel differential large gear 42 of the center differential device 20 is transmitted to a bevel gear 5 fixed to the rear wheel differential large gear 42, a bevel gear 60 meshing therewith, and a universal bevel gear 60 at both ends. The signal is transmitted to a bevel gear 64 via a rear wheel drive propeller shaft 62 equipped with a joint. The bevel gear 5, the bevel gear 60, the propeller shaft 62, and the bevel gear 64 are transfer gears for transmitting driving torque for driving the rear wheels 28 from the center differential device 20 to the rear wheel differential device 26. The bevel gear 64 functions as an output gear of the transfer device 66.

The rear wheel differential device 26 includes the bevel gear 64
a differential case 70 equipped with a ring gear 68 that meshes with the differential case 70; a pair of differential pinions 74 and 76 rotatably supported by a pinion shaft 72 attached to the differential case 70; and a pair of differential large gears 78 and 80 that are meshed with each other, and distributes the driving torque transmitted through the transfer device 66 to the left and right rear wheels 28 via the pair of differential large gears 78 and 80. do.

A differential control clutch 82 is provided between the differential case 32 that functions as an input member of the center differential device 20 and the front wheel drive shaft 44 that functions as an output member of the center differential device 20. This differential control clutch 82 is configured, for example, by a wet multi-plate hydraulic clutch, and when the differential limiting force of the differential control clutch 82 is zero, it is used for differential operation between the front and rear wheels by the center differential device 20, i.e. Torque distribution action is permitted, but as the differential limiting force increases, the torque distribution action of the center differential device 20 is restricted, and when the differential control clutch 82 is fully engaged, the differential of the center differential device 20 Case 32 and differential gears 40 and 42 are integrally connected to prevent torque distribution.

The clutch hydraulic control circuit 84 supplies hydraulic oil to a hydraulic actuator 90 for driving the differential control clutch 82 or discharges hydraulic oil from the hydraulic actuator 90 in response to a command signal from an electronic control device 86. to adjust the differential limiting force of the differential control clutch 82. As shown in detail in FIG. 2, the hydraulic actuator 90
A piston 95 that forms a hydraulic chamber 93 by being slidably fitted into a cylinder bore 91;
and a return spring 97 that biases the hydraulic chamber 9.
The piston 95 is configured to press the friction plate of the differential control clutch 82 as the working oil pressure in the differential control clutch 82 increases. The clutch hydraulic pressure control circuit 84 also includes a pressure regulating valve 94 that regulates the pressure of the hydraulic fluid pumped from the vehicle's hydraulic pump 92 to clutch hydraulic pressure, and supplies the clutch hydraulic pressure regulated by the pressure regulating valve 94 to the hydraulic actuator 90. Alternatively, the clutch control valve 98 continuously changes the differential limiting force of the differential control clutch 82 by discharging hydraulic oil from the hydraulic actuator 90 to a drain 96. The clutch control valve 98 includes, for example, a linear control valve (flow rate control servo valve) that is equipped with a linear solenoid and can continuously change the flow rate, or an on/off opening/closing valve that adjusts the flow rate through on/off control. In the case of a linear control valve, it is driven by an analog signal, and in the case of an on-off on-off valve, it is duty-controlled by an on-off signal.

The electronic control device 86 includes, for example, a steering wheel steering angle detection sensor 100 that detects a steering angle θ□ of a steering wheel (not shown), a front wheel air pressure sensor 102 that detects tire air pressures PFL and PFR of the left and right front wheels 24, and left and right sensors. Rear wheel 2nd tire pressure PRL
Rear wheel air pressure sensor 1 that detects and PRII, respectively.
04. Throttle sensor 106 that detects the throttle valve opening θ corresponding to the amount of operation of the accelerator pedal; Gear ratio sensor 108 that detects the actual gear ratio of the automatic transmission 14.
, a vehicle speed sensor 110 that detects the vehicle speed, a differential control changeover switch 111 for automatically selecting a mode for controlling differential limiting force, and a front wheel rotational speed sensor 112 that detects the rotational speed of the pair of front wheels 24, respectively. 114, rear wheel 28
Signals are supplied from a rear wheel rotation speed sensor 116 that detects the rotation speed of the engine 10, and an engine rotation speed sensor 117 that detects the rotation speed of the engine 10, respectively.

The electronic control unit 86 is composed of a so-called microcomputer consisting of a CPU, RAM, and ROM, and has an RA
The hydraulic control circuit 16 processes input signals according to a program stored in advance in the ROM while utilizing the memory function of M.
and outputs a control signal to the clutch oil pressure control circuit 84 and the like. That is, the electronic control unit 86 constantly executes automatic shift control according to a program (not shown), and controls the automatic transmission based on, for example, the actual accelerator pedal operation amount, vehicle speed, shift lever operation position, etc. from a pre-stored shift diagram. 14 is determined, and a control signal for switching to this speed ratio is output to the hydraulic control circuit 16. Further, the electronic control device 86 executes differential limiting control according to a pre-stored program, and calculates the driving force of the vehicle from the throttle valve opening θ and the gear ratio i of the automatic transmission 14, and calculates the driving force as determined in advance. A control signal for adjusting the differential limiting force Fc is output to the clutch hydraulic control circuit 84 based on the relationship determined based on the driving force of the vehicle.

Hereinafter, the main part of the operation of the differential limiting control will be explained using the flowcharts of FIGS. 3, 4, 5, and 6.

First, in step S1, initialization is executed, and timer counters Ta, Ti, Tc and flags F1°F, , F
, etc. are cleared. In step S2, various input signals are read, and various variables representing the state of the vehicle are calculated based on the input signals. For example, in this step S2, the tire air pressures PFL, P□ corresponding to the effective diameters of the left and right front wheels 24, and the tire air pressures PRL% PRR corresponding to the effective diameters of the left and right rear wheels 28 are read, and these four Minimum value PMIN (=MrN(PFt,, PFR
SP, +L, PRII)) are determined. and,
In step S3, it is determined whether the minimum value P□8 of the tire air pressure is less than or equal to a predetermined reference value P1. This judgment reference value P is a value for judging whether or not the tire pressure is excessively insufficient.
It is set to about 1/2 or less of the tire's standard air pressure. That is, in step S3, it is determined whether or not the minimum effective diameter among the effective diameters of the four wheels has become equal to or less than the determination reference value (diameter dimension) corresponding to P+.

When the air pressure of each tire is in a normal state, the minimum value P of the tire air pressure is set in step S3, 4. , is determined to be not less than the criterion value P, so the following step S
After the timer counter TA is reset in Step 4 and the content of the flag F is cleared to "0" in Step S5, the differential limiting clutch 82 is reset in Step S6.
The differential limiting force is 3 levels FLOW (low) +FMIDD
LE (middle), F) F of IIGM (high)
It is set to LOW. Further, in step S7, it is determined whether the minimum value PKIN of the tire air pressure is less than or equal to a predetermined determination reference value P2. This determination reference value P2 is a value for determining whether or not the tire air pressure is slightly insufficient, and is set to about 2/3 of the standard tire air pressure.

When the air pressure of each tire is in a normal state, it is determined in step S7 that the minimum value of the tire air pressure PHIM is not less than the judgment reference value P, so the following step S
After the timer counter T is reset in Step 8 and the content of the flag F2 is cleared to "0" in Step S9, the maximum value P of each tire air pressure is determined to be equal to or higher than the judgment reference value 21 in Step SIO. It is determined whether or not there is. This determination reference value P is a value for determining whether the tire air pressure is excessively high, and is set to about 4/3 of the standard tire air pressure.

When the air pressure of each tire is in a normal state, it is determined in step 310 that the maximum values P and AX of the tire air pressure are not equal to or greater than the judgment reference value 21, so the following step S
After the timer counter Tc is reset in step 11 and the contents of the flag F3 are cleared to "0" in step S12, the differential is limited based on the throttle valve opening degree θ corresponding to the driving force of the vehicle in steps 313 and subsequent steps. Power is determined.

That is, if it is determined in step S13 that the automatic transmission 14 is in the first gear position, step S31
4 and 315, it is determined whether the throttle valve opening degree θ is equal to or greater than a predetermined criterion value 01, and whether or not it is equal to or greater than a predetermined criterion value 62, respectively. The above-mentioned judgment reference value θ1° θ2 and the judgment reference value θ3 described below are for judging the magnitude of the driving force of the vehicle,
Their mutual relationship is determined to be θ1>θ2>θ3. If it is determined in step 314 that the throttle valve opening degree θ is equal to or greater than the judgment reference value 69, the driving force of the vehicle is relatively large, so that the differential limiting force is predetermined in step S16. FIIIGII is the highest state among the three stages. Further, if it is determined in step S14 that the throttle valve opening θ is not greater than or equal to the criterion value 01, and in step 315 that the throttle valve opening θ is greater than or equal to the criterion value 62, the driving force of the vehicle is Therefore, in step 317, the differential limiting force is in the intermediate state among the three predetermined stages.
It is considered to be E. If it is determined in step S15 that the throttle valve opening degree θ is not equal to or greater than the determination reference value 62, the driving force of the vehicle is relatively small.
In step 318, the differential limiting force is predetermined 3
The lowest state of the stages is FLOW.

Furthermore, if it is determined in step 313 that the gear is not the first gear, it is determined in step 319 whether or not the gear is the second gear.

If it is determined that the gear is not in the second gear, it means that the gear is in the third gear or higher and the driving force of the vehicle is small.
In step 51B, the differential limiting force is FLOlil
It is said that However, if it is determined that the gear position is 2nd speed, it is determined in step S20 whether or not the throttle valve opening θ is equal to or greater than a predetermined criterion value 03. For example, the differential limiting force is set to F Ml nott in step 317, but if it is less than the judgment reference value θ3, the differential limiting force is set to F LOW in step 31B.

Here, the minimum value P of tire air pressure while the vehicle is running
If there is a slight shortage of ■, the judgment in step S7 is affirmed, so step 32
1, it is determined whether the content of the flag F2 is "1". Initially, it is not "l", so step 322
In step S23, the timer counter Ti starts counting, and the content of the flag F2 is set to "1". Therefore, in the next cycle, since the determination in step s21 is affirmative, it is determined in the following step S24 whether or not the count content of the timer counter T has reached a predetermined constant determination reference value T2. . This judgment reference value T2 is for excluding cases where the abnormality judgment in step S7 is temporarily affirmed due to unevenness of the road surface during driving, and corresponds to the number of times or duration of the abnormality judgment in step S7. It is something. Initially, the determination at step 324 is negative, so the timer counter T
8 is performed, and when it is determined that the count content of the timer counter T8 has reached the judgment reference value Tz, the differential limiting force Fc is set to one of the three levels F L (greater than IW) in step S25. After this is prevented, the contents of the timer counter TII are reset in step S26, and the contents of the flag F2 are cleared to "0" in step S27.As a result, when the vehicle is running, the air pressure of any tire is If F, is slightly insufficient, the differential limiting force F, is prevented from becoming larger than F,.8.

Also, while the vehicle is running, the minimum tire pressure P
If there is an excessive shortage of HIM, the determination in step S3 is affirmed, so step S3 is performed.
At 28, it is determined whether the content of the flag F is rl. Initially, it is not "1", so step S2
At step 9, the timer counter TA starts counting, and at step s30, the content of the flag F1 is set to "1".

Therefore, in the next cycle, since the determination in step 328 is affirmative, it is determined in the subsequent step S31 whether or not the count content of the timer counter TA has reached a predetermined constant determination reference value T1. This judgment reference value T is used to exclude cases where the abnormality judgment in step S3 is temporarily affirmed due to unevenness of the road surface during driving, and corresponds to the number of times or duration of the abnormality judgment in step S3. It is something to do. Initially, since the determination in step S31 is negative, the timer counter TA performs counting, but when it is determined that the count content of the timer counter TA has reached the determination reference value T, step S332 After the differential control clutch 82 is released and the differential limiting force FC is made zero, the contents of the timer counter TA are reset in step S33, and the contents of the flag F are cleared to "O" in step S34. As a result, when the air pressure of any tire becomes excessively insufficient while the vehicle is running, the differential limiting force F is set to zero.

Further, if the maximum tire pressure PMAX is excessively high, the determination in step 310 is affirmed, so the content of the flag F1 is changed to "1" in step S35.
” is determined.

Initially, it is not "1", so the timer counter T starts counting in step S36, and the timer counter T starts counting in step S36.
At step 7, the content of flag F3 is set to "1". Therefore, in the next cycle, since the determination in step S35 is affirmative, in the following step 338, the count content of the timer counter Tc is set to a predetermined constant determination reference value T3.
It is determined whether or not it has been reached. This judgment reference value T3 is σ in order to exclude cases where the abnormality judgment in step S10 is temporarily affirmed due to unevenness of the road surface during driving, and corresponds to the number of times or duration of the abnormality judgment in step S10. It is something. Initially, step 3 above
Since the determination in step S38 is negative, counting is performed at the timer counter T, but when it is determined that the count content of the timer counter Tc has reached the determination reference value T3, the differential limiting force Fc is increased in step S39. After being prevented from becoming larger than F_LOW, the contents of the timer counter T are reset in step S40, and the contents of the flag F3 are cleared to "0" in step 341. This prevents the differential limiting force Fc from becoming larger than FLOW if the air pressure of any tire of the vehicle is excessively high.

As described above, according to this application example, when the air pressure of either the front wheel 24 or the rear wheel 28 tire becomes excessively low while the vehicle is running, in other words, the effective diameter of either wheel decreases. Since the differential limiting force F is suppressed when it becomes excessively small, the differential control clutch 82 is suppressed even if the tire air in the wheels decreases while the vehicle is running.
Therefore, unnecessary differential torque is not generated, and problems such as impaired running performance of the vehicle or energy loss caused by relatively large differential rotational speeds are suitably eliminated.

Furthermore, according to this application example, the differential limiting force FC is suppressed not only when the tire pressure is extremely insufficient, but also when the tire pressure is excessively high, so that a relatively large differential Impairment of running performance of the vehicle or occurrence of energy loss due to rotational speed is suitably eliminated.

In addition, according to this application example, if either the front or rear tire is under-inflated, the determination reference values P and P2 are determined.
There is an advantage that the degree of suppression of the differential limiting force can be appropriately changed depending on the degree of the deficiency.

Next, another application example of the present invention will be explained. In addition, in the following description, the same reference numerals are given to the parts common to the above-mentioned application example, and the description will be omitted.

In FIG. 7, initialization processing is first executed in step S31, and various input signals are read in step S32. (In step S33, it is determined whether the differential control changeover switch 111 has been operated to the automatic side. If it has not been operated to the automatic side, the differential control clutch 82 is released in step S34. However, if the operation is to the automatic side, differential limiting control of the differential control clutch 82 is permitted (clutch ON) in step SS5.In subsequent steps S86 and SS7, the contents of the flags FA and F@ are changed. rl”
It is determined whether or not.

Flag FA indicates a state in which there is no difference in tire diameter when its content is "1", and flag Fll indicates a high-speed running state when its content is "1".

Initially, the determinations in steps 336 and SS7 are negative, so it is determined in step SS8 whether or not the vehicle speed ■ is equal to or greater than a predetermined determination reference value 72. This determination reference value v2 is a value for determining whether the vehicle is running at a high speed, and is predetermined to be, for example, about 1100 km/h. If the vehicle speed V is smaller than the judgment reference value V2,
In step S89, differential limiting control of the differential control clutch 82 is permitted, and differential limiting force is applied to the front and rear wheels.

However, when the vehicle is in a high-speed running state, step SS8
Since the determination is affirmative, the differential limiting force of the differential control clutch 82 is set to zero in step 5310, and the content of the flag F is set to "1" in step 5SII.
It is said that

Therefore, in the next cycle, the determination in step SS7 is affirmed, so in step 3312, the differential rotational speed ΔNF,I of the front and rear wheels is set to the predetermined determination reference value ΔN1.
It is determined whether or not the above is satisfied.

This determination reference value ΔNI is a value for determining whether or not a differential limiting force should be applied during high-speed running. In step 5S12, the differential rotational speed ΔN□ of the front and rear wheels is the determination reference value ΔN.

If it is determined that the above is the case, the timer counter TD is reset in step 5S13, and the flag F is reset in step 5S14.

After the content of is cleared to "0", it is determined in step 5S15 whether the vehicle speed V is less than or equal to a predetermined determination reference value (2). This judgment reference value (3) is used to judge the lower limit value of the high-speed running state of the vehicle, and is set to a value of about 90 km/h, for example.

When it is determined in step 5S15 that the vehicle speed ■ has decreased to the judgment reference value ■3 or less, differential limiting control is permitted in step 5316, and the content of flag F is cleared to "0" in step 3317. Therefore, steps SS7 and S88 in subsequent cycles
Since the determination is negative, normal differential limiting control is executed in step SS9 and the like. However, step 5
If it is determined in s15 that the vehicle speed V does not fall below the determination reference value v3, steps ss1 and subsequent steps are simply repeatedly executed and application of the differential limiting force is not permitted.

After the vehicle speed V once exceeds the judgment reference value v2, when the differential rotation speed ΔNFII of the front and rear wheels is smaller than the judgment reference value ΔN in a running state at the judgment reference value 73 or more, the judgment in step 5S12 is made. Since the answer is negative, it is determined in step 5sis whether the content of the flag Fc is "1". This flag F, when its content is "1", indicates that the timer counter Tl1l is in the process of counting. Initially, since the timer counter To is not counting, the determination in step 5S18 is negative, and after the timer counter To starts counting in step 5519, the content of the flag Fc is set to "1" in step 5S20. In the next cycle, since the determination in step 5S18 is affirmative, it is determined in step SS21 whether or not the count of the timer counter T has reached a predetermined determination reference value T4. Initially, it does not reach the target, so steps 5S15 and subsequent steps are repeatedly executed. During such repetition, timer counter T0
When the count content reaches the judgment reference value T4, step 3
At 322, the differential limiting force of the differential control clutch 82 is F
At the same time, in step 5S23, the contents of the flag FA are set to "1", the contents of the flag Fc are cleared to "0", and the contents of the timer counter TD are cleared.

In this way, the content of the flag FA indicating that the differential rotational speed ΔNFT1 is small when the vehicle is running at high speed is set to "1".
'', the determination at step 336 is affirmed from the next cycle. Therefore, in step 5S24, the vehicle speed ■ is set to the predetermined judgment reference value ■
It is determined whether or not it is 1 or less. This judgment standard value■1
is the differential rotational speed Δ of the front and rear wheels when the vehicle is running at high speed.
This is a value for determining whether or not to perform the operation of determining the effective diameter difference between the front and rear wheels based on the NFR, that is, step 3312 and subsequent steps, and is set to a value of about 10 km/h, for example.

If the judgment in step 5S24 is affirmative, flags FA and F are
The contents of are cleared. However, if the vehicle speed ■ is not so low and the judgment in step 5324 is negative, in step 5S27, the minimum value PMIN of the air pressure of each tire corresponding to the effective diameter of each wheel is set to a predetermined judgment reference value. It is determined whether or not it is below P2. If it is below, steps 5S25 and 5S26 are executed, and from the next cycle onwards, it is determined whether the differential rotational speeds ΔN and R during high-speed running are greater than or equal to the determination reference value ΔN. Therefore, the minimum air pressure of each tire PMIN
If it is determined that is less than the determination reference value P2, application of differential limiting force during high-speed running is not permitted. On the contrary, in step 5327, the minimum value PM of the air pressure of each tire is determined.
If it is determined that IN is not less than the determination reference value P2, differential limiting control of the differential control clutch 82 is permitted in step 5S2B.

As described above, when it is determined that the minimum value PMIN of the air pressure of each tire corresponding to the effective diameter of each wheel is less than or equal to the judgment reference value P2, the steps from step 5SI-2 onwards are executed again, and the high-speed driving When the differential rotation speed ΔNFR is equal to or higher than the judgment reference value ΔNI, application of the differential limiting force during high-speed driving is not permitted, so even if the tire air in the wheels decreases while driving, the differential control clutch 82 No unnecessary differential torque is generated,
Impairment of the driving performance of the vehicle or energy loss caused by a relatively large differential rotation speed is advantageously eliminated.

One application example of the present invention has been described above based on the drawings, but
The invention also applies in other aspects.

For example, in the above application, the differential limiting force is F. W
, F MIDOLE, , F WIG)l, but it may also be changed continuously.

In addition, in the above application example, the reduction in the effective diameter of the wheel is determined based on whether the minimum value PMIN of each tire air pressure of the left and right front wheels 24 and rear wheels 28 is below the judgment reference value P or P2. However, the maximum value PMAX and minimum value PMI of each tire air pressure of the left and right front wheels 24 and rear wheels 28
The differential limiting force may be suppressed depending on whether or not the difference ΔP from N exceeds a predetermined criterion value.

In addition, in the above application example, the left and right front wheels 24 and the rear wheels 24
The minimum value PMIN of each tire air pressure in 8 is the judgment reference value P,
Alternatively, the reduction in the effective diameter of the wheel was determined based on whether or not it was below P2. Changes in the effective diameter of the wheel may be detected based on the ratio or the like.

Furthermore, in the above application example, a so-called full-time four-wheel drive vehicle was explained, but a so-called part-time four-wheel drive vehicle equipped with a switching clutch that switches between four-wheel drive mode and two-wheel drive mode is also applicable. The present invention can also be applied to control the switching clutch in a vehicle.

It should be noted that the above description is merely an example of application of the present invention, and various modifications may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a device to which the present invention is applied. FIG. 2 is a diagram illustrating the clutch hydraulic control device of FIG. 1. 3, 4, 5, and 6 are flowcharts illustrating the operation of the apparatus of FIG. 1. FIG. 7 is a flowchart illustrating the operation in another embodiment of the present invention. 24: Front wheel 28: Rear wheel 82: Differential control clutch

Claims (1)

[Scope of Claims] A method for controlling the differential control clutch in a front and rear wheel drive vehicle equipped with a differential control clutch that controls the differential between the front wheels and the rear wheels, the method comprising: an air pressure detection step of detecting the effective diameter of each ring; a step of determining whether the effective diameter is less than or equal to a predetermined criterion value; and a step of determining whether the effective diameter is less than or equal to a predetermined criterion value. A method for controlling a differential control clutch for a front-rear wheel drive vehicle, comprising the steps of: suppressing the differential limiting force thereafter if it is determined that the differential control clutch is