JPH06286436A - Vehicle controller - Google Patents

Abstract

PURPOSE:To secure travel stability or reduce tire load at the time of tire pneumatic pressure trouble (pneumatic pressure lowering and a puncture). CONSTITUTION:In the case of a four wheel drive vehicle which can be switched into 2WD-4WD, the three differential gears 9-11 of the center, the front and the rear are provided, and a controller 40 conducts the differential limit control of the three differential gears 9-11 in various modes on the basis of signals from wheel speed sensors 25-28, a throttle opening sensor 16, speed shift step switches 17, 18, a clutch switch 19 and a mode setting switch 20. The controller 40 executes tire pneumatic pressure judgement control on the basis of signals from the wheel speed sensors 25-28, a brake switch 41, a steering angle sensor 42 and an initial setting switch 43, and when tire pneumatic pressure lowering is judged, at least the front differential gear 10 and the rear differential gear 11 are switched into a lock state (or a lock release state).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle control device, and more particularly to a technique for controlling a differential limiting device capable of switching between locking and unlocking when a tire pressure determination device determines that a tire pressure is abnormal. Regarding the improved ones.

[0002]

2. Description of the Related Art Since it is not preferable to drive a vehicle in which the air pressure of the tire is lowered to some extent, various tire air pressure determination devices have been proposed. For example, the tire pressure is detected by a sensor to determine a decrease in the tire pressure, or when the tire pressure decreases, the number of rotations of the wheel whose pressure has decreased decreases. It has been proposed that a wheel speed sensor for detecting is provided and a decrease in tire air pressure is determined based on the wheel speed detected by these wheel speed sensors.

For example, in Japanese Patent Laid-Open No. 63-305011, the outputs from the wheel speed sensors of the four wheels are used to calculate the total wheel speed of a pair of wheels on the diagonal line and the other wheel on the other diagonal line. When the difference between the total wheel speed of a pair of wheels is greater than or equal to a predetermined value, it is determined that the tire pressure of any one of the pair of wheels with the larger total wheel speed has decreased, and When the larger one of the wheel speeds of the wheels is higher than the average value of the wheel speeds of the four wheels by a predetermined value or more, it is determined that the air pressure of the wheel has decreased, and the determination result is warned. A configured tire pressure determination device is described.

On the other hand, in a four-wheel drive type vehicle capable of switching between two-wheel drive and four-wheel drive through a center differential that limits the differential between the front and rear wheels, a front differential that limits the differential between the left and right front wheels is used. And a rear differential that limits the differential between the left and right rear wheels are often provided. Recently, the front differential, the center differential, and the rear differential are configured to be switchable between a locked state, an unlocked state, and an intermediate state between the two states via an electromagnetic clutch means.

[0005]

When the tire pressure of a vehicle is lowered, the running resistance of the wheel whose tire pressure is lowered is increased, so that the running stability is lowered. In particular, when the tire is punctured during highway driving, the running It is known that stability is extremely reduced, but in the prior art, there is a technique for controlling a differential limiting device that can switch between lock and unlock in association with a decrease in tire pressure and a flat tire. Has not been proposed at all, for example, when the tire air pressure is reduced or when the tire is flat, the running stability is reduced due to the increased resistance of the tire.

On the other hand, when the tire pressure decreases, the load on the tire increases and the tire wear progresses to damage the tire, resulting in deterioration of the reliability of the tire. An object of the present invention is to provide a vehicle control device capable of ensuring running stability and a vehicle control device capable of suppressing tire damage when tire air pressure is abnormal (air pressure drop or puncture).

[0007]

According to a first aspect of the present invention, there is provided a vehicle control device, which is capable of switching between a locked state and an unlocked state, a differential limiting device, and detects an abnormality in tire air pressure of a wheel and outputs an alarm. A vehicle provided with a tire air pressure determination device is provided with switching control means for receiving a determination of tire air pressure abnormality from the tire air pressure determination device and switching the differential limiting device to a locked state.

According to a second aspect of the present invention, there is provided a vehicle control system according to the first aspect, wherein the tire air pressure determination device includes a puncture determination means for determining a puncture state of the tire, and the switching control means includes a puncture determination means. The differential limiting device is configured to be switched to the locked state in response to the determination indicating the punctured state of the tire. The vehicle control device according to claim 3 is provided with a differential limiting device that can switch between a locked state and an unlocked state, and a tire pressure determination device that detects an abnormality in tire pressure of a wheel and outputs an alarm. In the above, there is provided switching control means for switching the differential limiting device to the unlocked state upon receiving a tire pressure abnormality determination from the tire pressure determination device.

According to another aspect of the vehicle control device of the present invention, the tire air pressure determination device includes puncture determination means for determining a punctured state of the tire, and the switching control means determines the punctured state of the tire from the puncture determination means. In response to this, the differential limiting device is configured to switch to the unlocked state. According to a fifth aspect of the present invention, there is provided the vehicle control device according to the third aspect, further comprising changeover switch means for changing over the differential limiting device to an unlocked state for a predetermined time.

[0010]

In the vehicle control device according to the present invention, when the tire air pressure determination device determines that the tire air pressure of the wheel is abnormal, the switching control means determines the tire air pressure abnormality from the tire air pressure determination device. In response, the differential limiting device is switched to the locked state. Therefore, it is possible to suppress a decrease in running stability due to an abnormal tire pressure,
Driving stability can be ensured.

In the vehicle control device of the present invention, when the puncture judging means of the tire air pressure judging device judges the punctured state of the tire, the switching control means judges from the puncture judging means to indicate the punctured state of the tire. In response, the differential limiting device is switched to the locked state. Therefore,
It is possible to secure the traveling stability by suppressing the deterioration of the traveling stability due to the flat tire.

According to another aspect of the vehicle control device of the present invention, when the tire air pressure determination device determines that the tire air pressure of the wheel is abnormal, the switching control means receives the abnormality of the tire air pressure determination device from the tire air pressure determination device, and determines the difference. Switch the motion limiter to the unlocked state. Therefore, if the differential limiting device is held in the locked state even when the tire pressure is abnormal, the tire with reduced air pressure will be significantly damaged, but by switching to the unlocked state, damage to the tire can be suppressed and tire reliability is reduced. Can be prevented.

In the vehicle control device according to the present invention, when the puncture judging means of the tire air pressure judging device judges the punctured state of the tire, the switching control means judges from the puncture judging means to indicate the punctured state of the tire. In response, the differential limiting device is switched to the unlocked state. Therefore, if the differential limiting device is held in the locked state with the tire flat, the load on the axle and the electromagnetic clutch of the differential limiting device may increase, impairing their durability. By switching the device to the unlocked state, it is possible to prevent deterioration of durability of the electromagnetic clutch of the axle and the limited slip differential.

According to a fifth aspect of the present invention, in the vehicle control system of the third aspect, the changeover switch means for changing over the differential limiting device to the unlocked state for a predetermined time is provided. By switching the differential limiting device to the unlocked state for a predetermined period of time via the switch, the locked state can be realized as appropriate, such as exiting from the stuck state, so that the function of the differential limiting device can be secured to some extent. .

[0015]

Embodiments of the present invention will be described below with reference to the drawings. The present embodiment is an example of the case in which the present invention is applied to a differential limiting device and a tire pressure determination device provided in a four-wheel drive vehicle. FIG. 1 shows the drive system and differential limiting of this four-wheel drive vehicle. It is a whole lineblock diagram of a device and a tire pressure judging device. As shown in FIG. 1, a transmission 2 is connected to an engine 1, and the transmission 2 is a five-speed forward and one-reverse speed transmission composed of a main transmission and an auxiliary transmission linked to the main transmission. is there. A transfer 3 is connected to the transmission 2,
The output of the engine 1 is transferred to the front wheel 2 by this transfer 3.
Front propeller shaft 5 and engine 1 that are transmitted to
A rear propeller shaft 6 for transmitting the output of the to the rear wheels 23 and 24 is connected.

Left and right front wheels 21, 22 are connected to the front propeller shaft 5 via a front axle 7.
Left and right rear wheels 23, 24 are connected to the rear propeller shaft 6 via a rear axle 8. Transfer 3
Is provided with a center differential 9 (center differential), the front axle 7 is provided with a front differential 10 (front differential), and the rear axle 8 is provided.
Is provided with a rear differential 11 (rear differential).

Next, the electromagnetic multi-plate clutch 30 incorporated in the center differential 9 will be described with reference to FIG. The electromagnetic multi-plate clutch 30 selectively switches the center differential 9 among three states of an unlocked state, an intermediate locked state, and a completely locked state. The electromagnetic multi-plate clutch 30 may be of any type as long as it can limit the differential between the front propeller shaft 5 and the rear propeller shaft 6, but the electromagnetic multi-plate clutch 3 of the present embodiment.
Reference numeral 0 is composed of a clutch plate 31 composed of a plurality of inner discs and an outer disc, and an electromagnetic actuator 32 for generating a pressing force on the clutch plate 31.

In the figure, 33 is a bearing, 34 is a transmission member connected to one propeller shaft, and 35 is a transmission member connected to the other propeller shaft. The electromagnetic actuator 32
Is configured so that the armature 37 presses the clutch plate 31 with the magnetic force generated when a current flows through the solenoid 36 (SOLC). This electromagnetic multi-plate clutch 30
In the above, since there is a proportional relationship between the current flowing through the solenoid SOL C and the pressing force for frictionally engaging the clutch plate 31, that is, the torque transmitted by the electromagnetic multi-plate clutch 30, the operating speed of the center differential 9 is continuously increased or decreased by increasing or decreasing the current. Can be changed. Further, the front differential 10 is also provided with the same electromagnetic multi-plate clutch (which is equipped with the solenoid SOL F), and the rear differential 11 is also equipped with the same electromagnetic multi-plate clutch (which is equipped with the solenoid SOL R). Are provided, but they are the same, and the description thereof will be omitted.

Next, a control system for controlling the three electromagnetic multi-plate clutches (that is, the three solenoids SOLF, C, R) will be described with reference to FIG. First, the left and right front wheels 21, 22 are used as switches and sensors necessary for controlling the center differential 9, the front differential 10, and the rear differential 11.
And wheel speed sensors 25, 26, 27, 28 for detecting the rotational speeds of the left and right rear wheels 23, 24, a throttle opening sensor 16 for detecting the throttle opening of the engine 1, and a gear stage of the transmission 2. Gear shift switch 17, an auxiliary variable gear shift switch 18 that detects the gear shift stage of the auxiliary transmission, and the clutch between the engine 1 and the transmission 2 is turned on (connected) or turned off.
A clutch switch 19 for detecting (non-connection) and a mode setting switch 20 for setting operation modes of the center differential 9, the front differential 10, and the rear differential 11 are provided.

Further, the wheel speed sensors 25 to 28 are used as switches and sensors necessary for the tire air pressure determination device.
In addition, a brake switch 41 for detecting the depression of the brake pedal, and a steering angle sensor 4 for detecting the steering angle of the steering wheel.
2, an initial setting switch 43 for instructing the start of the initial setting process in the tire air pressure determination control, and a warning lamp 44 for displaying an alarm when it is determined that the tire air pressure has dropped. Then, the signals from the above sensors and switches are supplied to the control unit 40 which also serves as the control unit for the differential limitation control and the control unit for the tire pressure determination control, and the warning lamp 44 causes the control unit 4 to operate.
Drive is controlled at 0. Reference numeral 45 is a battery.

The wheel speed sensors 25 to 28 are composed of detection disks 25a to 28a which rotate integrally with the axle and electromagnetic pickups 25b to 28b which face the detection disks, and each of the detection disks 25a to 28a has a corresponding one. ,
For example, 44 detected portions are formed at equal intervals in the circumferential direction.

The control unit 40 includes a waveform shaping circuit for shaping the detection signals from the sensors and switches as required, an A / D converter for A / D converting the detection signals as required, and an input. The microcomputer includes an output interface, a microcomputer including a CPU, a ROM and a RAM, a drive circuit for the three solenoids SOL F, C and R, and the like. The ROM of the microcomputer includes the three electromagnetic multi-disc clutches (that is, 3 solenoids SOLF,
A control program for differential limiting control performed by controlling C, R) and a control program for tire air pressure determination control, which will be described later, are input and stored in advance, and the RAM is provided with memories necessary for these controls. Has been.

Next, the center differential 9 and the front differential 1
The outline of the differential limiting control for 0 and the rear differential 11 will be described. The mode setting switch 20 is a switch for setting the operation modes of the three differentials 9 to 11, and includes AUTO (A mode), C (C mode), R (R mode) and F (F mode). It is configured so that it can be set alternatively.
As shown in.

[0024]

[Table 1]

Referring to Table 1, in the A mode, the front differential 10 is unlocked and the center differential 9 and the rear differential 11 are set to the automatic mode control. In the A mode, the drive current is set based on the differential rotation speed and the throttle opening of the engine. In the automatic mode control in the A mode, the unlocked state, the completely locked state, and the both There are intermediate states.

In the C mode, the front differential 10 is in an unlocked state, and the center differential 9 is in an intermediate locked state for limiting the differential (however, in a predetermined state where the torque acting on the differential is increased, it is in a completely locked state). The rear differential 11 is set to the automatic mode control. In the R mode, the front differential 10 is in the unlocked state, and the center differential 9 and the rear differential 11 are in the intermediate locked state (however, in a predetermined state in which the torque acting on the differential is increased, they are completely locked). In the F mode, the front differential 10, the center differential 9, and the rear differential 1
All of 1 are in the intermediate lock state (however, in a predetermined state where the torque acting on the differential is increased, they are in the complete lock state).

The operation mode is the mode setting switch 2
Although it is arbitrarily set by the driver via 0, in the A mode, the front diff 10 is in an unlocked state, so that the drivability is less affected and the operability is excellent, and the normal road such as an urban area. Suitable for on-road driving. On the other hand, in the F mode, all diffs are in the intermediate lock state, so the operability is slightly reduced, but the drivability is excellent, and it is suitable for off-road traveling on rough roads. The C mode and the R mode have characteristics in between these characteristics and are selected according to the driver's preference.

The tire pressure determination device is basically
The wheel speed sensors 25 to 28, a brake switch 41, a steering angle sensor 42, an initial setting switch 43, a warning lamp 44, a control unit 40 and the like are included.
Hereinafter, the tire pressure determination control executed by the control unit 40 will be described with reference to the drawings starting from FIG. However, in the drawings of the flowchart, reference sign Si (i =
1, 2, ...) Each step is shown.

First, the outline of the tire air pressure determination control will be described. Basically, four wheel speed sensors 25 are provided.
The tire air pressure is determined based on the wheel speeds Vw1 to Vw4 detected at .about.28, but the coefficient Cx (compensation coefficient) is initially set when the vehicle is started to be used or when one or more tires are replaced. By executing the processing, the coefficient Cx for compensating the manufacturing error and the characteristics of the tire is initialized. After that, the tire pressure determination process is executed periodically (for each predetermined mileage or for each predetermined period) to determine whether the tire pressure is abnormal. If the tire pressure is low, a warning lamp is issued. An alarm is output via 34.

The initial setting process is executed in the vehicle speed range set according to the road surface condition, and when the center differential 9, the front differential 10, and the rear differential 11 are in the locked state or the intermediate locked state, the tire pressure is set. Since the change in the wheel speed due to the decrease cannot be detected, it is executed in the state where the lock is forcibly released. The tire air pressure determination process is executed in the vehicle speed range that is separately set according to the road surface condition. The tire pressure determination control includes the initial setting process, the tire pressure determination process, and the road surface friction coefficient calculation process (the flowchart is omitted).

Next, the initial setting process of the coefficient Cx will be described with reference to FIG. This initial setting process of the coefficient Cx is performed by turning on the a-contact type initial setting switch 33 attached to the instrument panel when the tire is replaced.
It starts when operated and then the sensors 25-28, 4
Various data obtained by digitizing the signals from the switch 2 and the switches 41 and 43 are read (S1), and then the warning lamp 44 is turned on to indicate that the initial setting process is being executed, and the tire air pressure determination process is prohibited. Flag F to do
Is reset to 0 (S2).

Next, in S3, it is determined whether or not the initial setting condition of the coefficient Cx is satisfied. However, the vehicle is not in the acceleration / deceleration state, is in the steady straight traveling state, and the vehicle speed V is V.
Is satisfied, it is determined that the coefficient Cx set in accordance with the road surface condition shown in the map of FIG. 7 is within the initial permission vehicle speed range, and at least the center differential 9 is in the locked state. Move to S4,
If the condition is not satisfied, the process proceeds to S10. The lock / unlock of the center differential 9 is determined based on the data from the differential limiting control, the vehicle speed is applied as the vehicle speed V, and the average value of the left and right driven wheels (front wheels 21 and 22) is determined. The acceleration / deceleration is detected from the change in the vehicle speed V.

Here, the lower limit value of the initially permitted vehicle speed range of the coefficient Cx shown in FIG. 7 is set to a predetermined value (for example, 20 Km / H) which is not excessively low, and the upper limit value of the initially permitted vehicle speed range is The value is set to a value in the range of 40 to 50 Km / H according to the road surface friction. The upper limit value is set to linearly increase from 40 Km / H in the low μ state to 50 Km / H in the high μ state. Note that μ is the friction coefficient of the road surface. And, in the high speed state of more than 50 Km / H, the slip amount of the driving wheels increases or the front wheels 1, 2 and the rear wheels
Since the wheel load of 3 and 4 changes and the detection accuracy of the wheel speeds Vw1 to Vw4 decreases, when the vehicle speed is 50 Km / H or less,
It is desirable to execute the initial setting process. Also, when the value of μ is low, the slip amount of the drive wheels increases, so 40 km / H
It is desirable to execute the initial setting process at the following vehicle speeds. The method of calculating the road surface μ will be described later.

Next, when it is determined in S3 that the condition is satisfied, in S5, the coefficient Cx for compensating the initial state of the four tires at the time of tire replacement, etc. is added to the four wheels in consideration of the tire manufacturing error and characteristics. Using the wheel speeds Vw1 to Vw4 of
The sum of the wheel speeds of the left front wheel 1 and the right rear wheel 4 (Vw1 + Vw4) in one diagonal relationship, and the right front wheel 2 in the other diagonal relationship
And the sum of the wheel speeds of the left rear wheel 3 (Vw2 + Vw3) are calculated by the following equation. Coefficient Cx = (Vw1 + Vw4) / (Vw2 + Vw3) Next, in S5, it is determined whether or not the coefficient Cx is an appropriate value, but the tire diameter error due to the tire manufacturing error is 0.
Since it is 3%, it is determined that the coefficient Cx is an appropriate value when the coefficient Cx is within a predetermined range of approximately 1 (for example, 0.95 to 1.05).

When the coefficient Cx is an appropriate value, the coefficient Cx is rewritten in S6, the current coefficient Cx (i-1) is given to the current coefficient Cx (i-1), and then the warning lamp 44 is turned on. The flag F is turned off and the flag F is set to 1 to permit the tire pressure determination process, and then the process proceeds to S7. On the other hand, when the determination result in S5 is No, it is determined in S8 whether or not the coefficient Cx is indefinite, and when it is indefinite, the process proceeds to S10. Flashes for 2 seconds, and then proceeds to S10. In S10,
It is determined whether or not the flag F is 1, and when the flag F = 1, this initialization processing ends, and when the flag F is not 1, the process returns and the processes from S1 onward are repeatedly executed.

However, in the condition determination of S3, it may be added to the condition that both the front differential 10 and the rear differential 11 are in the unlocked state. Also, switch 3 once
It is also possible to perform a plurality of initialization processes based on the ON operation of No. 3 to obtain a plurality of coefficients Cx, and to determine the final coefficient Cx from the average value of the plurality of coefficients Cx. . In this way, the coefficient Cx for compensating the initial state of the four tires at the time of tire replacement is determined,
It is stored in the RAM memory.

Here, the calculation processing for obtaining the road surface μ of the traveling road surface will be described. First, the vehicle speed V is set equal to the average value of the wheel speeds Vw1 and Vw2 of the driven wheels, and the vehicle speed V is
It is applied to the initial setting process and the tire air pressure determination process. The road surface μ is calculated based on the vehicle speed V and its acceleration Vg. For this calculation, a 500 ms timer and 100
Using the ms timer, the vehicle body acceleration Vg is calculated by the following equation from the change of the vehicle speed V for 100 ms every 100 ms until the vehicle body acceleration Vg does not become sufficiently large after the start of acceleration.

Vg = K1 × [V (i) −V (i-100)] After the lapse of 500 ms when the vehicle body acceleration Vg becomes sufficiently large, a change in the vehicle speed V between 500 ms every 100 ms is calculated as follows.
The vehicle body acceleration Vg is calculated by the following equation. Vg = K2 × [V (i) -V (i-500)] In the above equation, V (i) is the current vehicle speed, V (i-1).
00) is the vehicle speed 100 ms before, V (i-500) is 50
The vehicle speed before 0 ms, K1 and K2 are predetermined constants.
The road surface μ is calculated by three-dimensional complementation from the μ table shown in Table 1 using the vehicle speed V and the vehicle body acceleration Vg obtained as described above, and the road surface μ is subjected to the initialization processing and the tire air pressure determination processing. Applied to.

[0039]

[Table 2]

Next, the tire pressure determination process will be described with reference to the flow charts of FIGS. This tire air pressure determination process is, for example, a process executed for each mileage of 100 km, and after starting this process, various data obtained by digitizing the signals from the sensors 25 to 28, 42 and the switch 41 are read. (S20) Next, it is determined whether the flag F is 1 (S21), Yes.
In case of, it is determined in S22 whether or not the tire air pressure determination condition is satisfied. Regarding this tire pressure determination condition, the vehicle is not in an acceleration / deceleration state, is in a steady straight traveling state, and the vehicle speed is within the tire pressure determination permission vehicle speed range set according to the road surface condition shown in the map of FIG. If at least the center differential 9 is in the unlocked state, it is determined that the condition is satisfied and S2 is satisfied.
If the condition is not satisfied, the process proceeds to S24.
Incidentally, the lock / unlock of the center differential 9 is determined based on the data from the differential limiting control.

Here, the lower limit value of the tire pressure determination permission vehicle speed range shown in FIG. 8 is set to a predetermined value (for example, 20 Km / H) which is not excessively low, and the upper limit value of the tire pressure determination permission vehicle speed range. Is 4 depending on the road friction on the road surface.
It is set to a value in the range of 0 Km / H to maximum vehicle speed. The upper limit value is set to linearly increase from 40 Km / H in the low μ state to the maximum vehicle speed in the high μ state. Then, in the high speed state of more than 50 km / h, the slip amount of the driving wheels increases and the detection accuracy of the wheel speeds Vw1 to Vw4 decreases, but even if the accuracy decreases to some extent, the high speed running state of more than 50 km / h. Since it is desirable to detect the decrease of the tire air pressure in the above, the setting is made as described above. When the μ is low, the slip amount of the drive wheels increases, so it is desirable to execute the tire pressure determination process when the vehicle speed is 40 km / H or less.

In S23, the tire air pressure determination subroutine of FIGS. 5 and 6 is executed, and then the process returns.
If the determination result in S21 or S22 is No, the timer T in the tire pressure determination subroutine is determined in S24.
Is reset, the flags Fa and Ft are reset to 0, the counters I and J are reset to 0, and then the process returns. Next, the tire air pressure determination subroutine of S23 will be described with reference to FIGS. 5 and 6.
First, it is determined whether or not the flag Ft is 1 (S30). Since it is initially No, the timer T is started and the flag Ft is set to 1 in S31, and the process proceeds to S32. When the flag Ft is set to 1, S3
The process proceeds from 0 to S32. Next, in S32, the air pressure determination variable D is calculated by the equation shown, that is, the following equation.

D = 2 × [Cx (Vw2 + Vw3)-(Vw1 + Vw4)]
/ [Vw1 + Vw2 + Vw3 + Vw4] In the above equation, the coefficient Cx is set in advance so as to compensate for the initial state of the tire. Therefore, when the tire air pressure is normal, the air pressure determination variable D becomes a value substantially equal to 0. However, when the tire air pressure of the right front wheel 22 or the left rear wheel 23 is decreasing, the wheel speed Vw2 or the wheel speed Vw3 increases, so the air pressure determination variable D increases in the positive direction, and the left front wheel 21 or When the tire air pressure of the right rear wheel 24 is decreasing, the wheel speed Vw1 or the wheel speed Vw4 increases, so the air pressure determination variable D increases in the negative direction.

Next, in S33, it is judged whether or not the judgment variable D is a predetermined value D0 (for example, a predetermined value in the range of 0.020 to 0.050), and when the judgment result is Yes, the flag F
It is determined whether or not a is 1 (S34), and when the flag Fa is not 1, the counter I that counts the number of times the determination variable D is the predetermined value D0 or more is set to 1 and the flag Fa is set to 1 (S35). , And then the process proceeds to S41.
When the flag Fa is set to 1, S
The process proceeds from S34 to S36, the counter I is incremented, and then the process proceeds to S41.

On the other hand, if the determination result of S33 is No, S
37, it is determined whether the determination variable D is less than or equal to the predetermined value −D0. If Yes, it is determined whether the flag Fa is 2 (S38). If the flag Fa is not 2, the determination variable D is the predetermined value. -Counter J for counting the number of times D0 or less
Is set to 1 and the flag Fa is set to 2 (S
39) and then the process moves to S41. Further, when the flag Fa is set to 2, the process proceeds from S38 to S40, the counter J is incremented, and then S41.
Go to F.

Next, in S41, it is determined whether or not the count value T of the timer T has passed a predetermined time T0 (for example, 2 seconds). However, since the determination result is No at the beginning, S41 Repeatedly returning from
The steps S20 to S22 and S30 to S41 of FIG. 4 are repeatedly executed, and the count value T of the timer T and the count value I of the counter I or the count value J of the counter J are increased. 9 shows the behavior of the air pressure determination variable D when the tire pressure is normal, and FIG. 10 shows the behavior of the air pressure determination variable D when the tire pressure of the right front wheel 22 or the left rear wheel 23 is abnormal. .

When the predetermined time T0 has elapsed, S41
Since the determination result of No is Yes, the process proceeds to S42, and the count value I of the counter I is equal to or greater than the predetermined value K0 or the counter J
It is determined whether or not the count value J of is equal to or greater than the predetermined value K0. If the determination result is No, it is determined in S43 that the tire pressure is normal, and the process proceeds to S47.
When the determination result of 42 is Yes, it is determined in S44 that the tire pressure is abnormal (decreased), and in S45, the warning lamp 34 is lit for a predetermined time (for example, 2 seconds) in order to warn the driver of the decrease in tire pressure.
The process moves to S46. Next, in S46, a control signal for switching the front differential 10 and the rear differential 11 to the locked state is output to the differential limiting control, and the differential limiting control brings the front differential 10 and the rear differential 11 into the locked state. Can be switched. Next, in S47, the timer T, the flag Fa, the flag Ft, the counter I, and the counter J are set to 0 respectively in preparation for the next tire air pressure determination process.
Is reset, and the tire air pressure determination processing this time is completed.

Next, the operation of the tire air pressure determination device described above will be described. An initial setting switch 33 is provided on the instrument panel, and by operating the switch 33, the initial setting process for initializing the coefficient Cx is executed when necessary, such as when the tire is replaced. It is possible to set the coefficient Cx that compensates for the manufacturing error and characteristics of the. Since the initial setting process is executed in the vehicle speed range set according to the road friction state of the traveling road surface in the steady straight running, it is caused by the slip of the driving wheel on the low μ road, the fluctuation of the wheel load, etc. It is possible to eliminate the error factors that occur as much as possible and initialize the coefficient Cx with high accuracy.
Further, in this initial setting process, this process is executed on condition that at least the center differential 9 is in the unlocked state, so that the initial state of the tire can be surely reflected in the coefficient Cx.

After the initial setting process, the tire air pressure determination process is executed using the coefficient Cx every time a predetermined distance travels or a predetermined period elapses. This tire air pressure determination processing is executed at the time of steady straight traveling and in the vehicle speed range set according to the road friction state of the traveling road surface, and is executed at least when the center differential 9 is in the unlocked state. Similar to the case of the processing, the error factor due to the slip of the driving wheel on the low μ road, the fluctuation of the wheel load, etc. can be eliminated as much as possible, and the accuracy and reliability of the tire air pressure determination can be improved.

Moreover, when it is determined that the tire pressure is abnormal (decreased), at least the front differential 10 and the rear differential 11 are switched to the locked state, so that the reduction in running stability due to the decrease in the tire pressure of the front wheels or the rear wheels is suppressed. As a result, traveling stability can be ensured. In particular, when traveling on a highway, if the tire pressure drops sharply, the running stability will drop significantly, but the tire pressure determination process is configured to be executed constantly, and when the tire pressure drops sharply. In addition, by switching to the locked state as described above, it is possible to secure the traveling stability immediately after the air pressure is reduced.
However, in this case, it is desirable that the locked state be continued for at least a predetermined short time, but after the predetermined short time has elapsed, the states of the differentials 9 to 11 are set through the operation of the mode setting switch 20 by the driver. It may be configured to.

Next, a plurality of modified examples in which a part of the above embodiment is modified will be described. (1) Instead of the step S46 in FIG. 6, a control signal for switching the front differential 10 and the rear differential 11 to the unlocked state is output to the differential limiting control. As described above, when it is determined that the tire pressures of the front wheels or the rear wheels are decreased, by switching the front differential 10 and the rear differential 11 to the unlocked state, it is possible to reduce the load of the tires having the decreased air pressure and suppress the damage. . That is,
When the air pressure of the tire decreases, the load on the tire increases and the tire is significantly damaged, but the damage to the tire can be suppressed.

(2) In the above-described embodiment, the control for detecting the tire whose air pressure has dropped is not provided, but the tire with the lowered air pressure is detected by the abnormal air pressure wheel detection process described below, and either of the left and right tires is detected. When the tire pressure of any of the front wheels is reduced, only the front differential 10 is switched to the locked state in the step of S46, and when the tire pressure of any of the left and right rear wheels is reduced, only the rear differential 11 is operated in the step of S46. May be switched to the locked state. Next, the abnormal air pressure wheel detection processing will be described with reference to FIG. This abnormal wheel detection process is a calculation process for every minute time, which is the same as the routine of FIG. 4, and is executed by an interrupt process for the routine of FIG. After start, wheel speed Vw1 ≧
The determination as to whether Vw4 or not (S110) and the determination as to whether or not the wheel speed Vw2 ≧ Vw3 (S113) are executed, and the counters K1 to K4 that are determined to be larger are incremented (S).
111-S115).

The time T measured by the timer T in FIGS.
Until S reaches a predetermined time T0, S110 to S116 are repeatedly executed and the counters K1 to K4 are incremented. Then, when the predetermined time T0 has elapsed after the start of the tire air pressure determination process, in S117, S4 of FIG.
The same determination as in 2 is made, and if the determination result is No, the flag FA is reset to 0 in S125,
Further, when the determination result in S117 is Yes and the tire air pressure is abnormal, it is determined in S118 whether the flag Fa is 1 (S118), and when the flag Fa is 1,
In S119, it is determined whether the count value K2 is greater than or equal to the count value K3. If K2 ≧ K3, it is determined in S120 that the tire pressure of the right front wheel 22 is abnormal, and the flag FA is set to 2. The determination result of S119, K2
When ≧ K3 is not satisfied, the left rear wheel 23 in S121
The tire pressure is judged to be abnormal and the flag FA is set to 3.

When the determination result of S118 is No,
That is, when the flag Fa is 2, it is determined in S122 whether the count value K1 is greater than or equal to the count value K4, and K
If 1 ≧ K4, the tire pressure of the left front wheel 21 is determined to be abnormal in S123, and the flag FA is set to 1. If the determination result in S122 is not K1 ≧ K4, the tire pressure of the right rear wheel 24 is determined to be abnormal in S124, and the flag FA is set to 4. Incidentally, S1
At 25, after the counters K1 to K4 are cleared, this process ends.

As described above, the air pressure decrease flag FA is set to 1 when the air pressure of the left front wheel 21 is decreased, is set to 2 when the air pressure of the right front wheel 22 is decreased, and is set to 2 when the air pressure of the left rear wheel 23 is decreased. When the air pressure of the right rear wheel 24 is low, it is set to 4, and when the air pressure of all four wheels is normal, it is set to 0. Based on the data of the air pressure drop flag FA, the wheel whose air pressure has dropped is specified. To configure.

(3) Instead of the coefficient Cx in the above-described embodiment, an initial deviation Δ for compensating a tire manufacturing error, characteristics, etc., which is expressed by the following equation, can be applied. . Δ = 2 [(Vw1 + Vw4)-(Vw2 + Vw3)] / (Vw1 + Vw2 +
Vw3 + Vw4) When the initial deviation Δ is applied, the air pressure determination variable D in the tire air pressure determination processing is calculated by the following equation. D = 2 [(Vw1 + Vw4)-(Vw2 + Vw3)] / (Vw1 + Vw2 +
Vw3 + Vw4) When the initial deviation Δ and the air pressure determination variable D are used, the determination in S33 in FIG. 5 is a determination as to whether or not (D−Δ) ≧ D0, and the determination in S37 is (D−Δ). )
It is determined whether ≦ −D0.

Next, another embodiment in which a part of the tire air pressure determination sub routine of FIGS. 5 and 6 of the above embodiment is modified will be described with reference to FIG. In this tire air pressure determination sub routine, it is determined whether the tire air pressure has dropped or a flat tire with a particularly low air pressure has fallen, and when any of the four tires has a flat tire, the front differential 10 and the rear differential 11 are switched to the locked state.

After S32 in FIG. 5, the process proceeds to S50 in FIG. 12, where it is determined whether the air pressure determination variable D is a predetermined value D0 or more. If D ≧ D0, the flag Fa is set to 1 in S51.
When the determination is No, the counter I1 is set to 1 and the flag Fa is set to 1 in S52, and when the determination in S51 is Yes, the counter I1 is incremented in S53. Next, in S54, it is determined whether or not the air pressure determination variable D is greater than or equal to a predetermined value D1 that is greater than the predetermined value D0. If the determination is No, the process proceeds to S66. If the determination is Yes, the flag is set in S55. It is judged whether Fa is 2 or not, and the judgment is No.
In case of, the counter I2 is set to 1 in S56 and the flag Fa is set to 2, and when the determination in S55 is Yes, the counter I2 is incremented in S57,
The process proceeds from S57 to S66.

On the other hand, when the determination result of S50 is No,
In S58, it is determined whether or not the air pressure determination variable D is less than or equal to a predetermined value -D0. If D≤-D0, it is determined in S59 whether the flag Fa is 3 or not. If the determination is No, the counter I3 is determined in S60. 1 and flag Fa is 3
, Respectively, and when the determination in S59 is Yes, S61
At, the counter I3 is incremented. next,
In S62, it is determined whether or not the air pressure determination variable D is less than or equal to the predetermined value -D1. If the determination is No, the process proceeds to S66, but if the determination is Yes, it is determined in S63 whether the flag Fa is 4 or not. If the determination is No, the counter I4 is set to 1 and the flag Fa is set to 4 in S64.
, Respectively, and when the determination in S63 is Yes, S65
In, the counter I4 is incremented, and the process proceeds from S65 to S66.

The predetermined values D0, -D0 are thresholds for determining a decrease in tire air pressure including the punctured state, and the predetermined values D1, -D1 set to D1> D0.
Is a threshold value for determining the puncture state. When the tire is punctured, the air pressure is significantly reduced, the effective diameter of the tire is significantly reduced, and the wheel speed of the puncture wheel is significantly increased. Therefore, the determination can be made via the predetermined values D1 and -D1.

Next, in S66, it is judged whether or not the measured time T of the timer T is a predetermined time T0 or more, and the judgment is N
When it is o, the routine returns and is repeatedly executed. Then, when the measured time T becomes the predetermined time T0 or more, in S67, the count value I1 of the counter I1 is the predetermined value K0 or more, or the count value I3 of the counter I3 is the predetermined value. Value K0
The above determination is executed. And the judgment result is N
When it is o, it is determined in S68 that the air pressure is normal, and the tire air pressure determination control ends.

On the other hand, when the tire pressure of any of the four wheels is abnormal, the determination result in S67 is Yes.
In the next step S69, it is determined whether the count value I2 of the counter I2 is greater than or equal to the predetermined value K1 or the count value I4 of the counter I4 is greater than or equal to the predetermined value K1. Then, when the determination result is No, the air pressure of any of the tires is low, but it is determined that the puncture has not occurred and it is determined in S70 that the air pressure is low, and then the process proceeds to S73.

On the other hand, when the result of the determination in S69 is Yes,
In S71, it is determined that one of the tires of the four wheels has punctured, and then in S72, a control signal for switching the front differential 10 and the rear differential 11 to the locked state is output for the differential limiting control, and the differential limiting control is performed. As a result, the front differential 10 and the rear differential 11 are switched to the locked state, and the locked state is maintained for at least several seconds. S
70 or S72 to S73, and in S73,
The warning lamp 44 is lit for a predetermined time, and then S74.
, The timer T is reset to 0 and the flags Fa, F
t, when the counters I1 to I4 are reset to 0,
This tire air pressure determination control ends.

As described above, when one of the tires is punctured, the front differential 10 and the rear differential 11 are forcibly switched to the locked state, so that the deterioration of traveling stability due to the puncture is suppressed to the minimum. Stability can be secured. However, after the front differential 10 and the rear differential 11 are held in the locked state for at least several seconds when a puncture occurs, the states of the differentials 9 to 11 are set through the operation of the mode setting switch 20 by the driver. You may comprise.

Here, as a modified example in which a part of the other embodiment is modified, instead of forcibly switching the front differential 10 and the rear differential 11 to the locked state in S72, the front differential 10 and the rear differential 11 are replaced in S72. Is configured to forcibly switch to the unlocked state. That is, with the tire flat, the front differential 1
If 0 and the rear differential 11 are held in a locked state, damage to a flat tire will progress significantly, and the durability of the axle and the electromagnetic multi-plate clutch 30 will be deteriorated. Then, release the lock.

In S72, the instrument panel is provided with a selection switch for selectively setting whether to switch to the locked state or the unlocked state, and the front diff 10 and the front differential 10 are selected in accordance with the selection by the selection switch. The rear differential 11 and the rear differential 11 may be configured to be locked or unlocked. Drivers who place importance on driving stability can select the locked state,
In addition, a driver who attaches great importance to preventing tire damage can select the unlocked state. Further, the abnormal pneumatic wheel detection process described with reference to FIG. 11 is executed to identify the puncture wheel, and only the differential corresponding to the puncture wheel (front differential 10 or rear differential 11) is locked or unlocked in S72. It may be configured to switch to the state.

Here, instead of using the wheel speed as in the above-described embodiment, the tire number is set using the cumulative number Nw1 to Nw4 of output pulses of the wheel speed sensors 27 to 30 in a predetermined period of continuous or intermittent as a parameter. It is also possible to perform the air pressure determination, and it is also possible to perform the tire air pressure determination using the time Tw1 to Tw4 per wheel rotation calculated from the predetermined period and the pulse numbers Nw1 to Nw4 as parameters. . Then, in this case, similarly to the above, the initial setting process is executed, and the cumulative output of the wheel speed sensors 27 to 30 in the continuous or intermittent predetermined period (the predetermined period is the same or different predetermined period). Calculate the number of pulses INw1 to INw4,
It is also possible to execute the tire pressure determination using the pulse number ratio (Nw1 / INw1) to (Nw4 / INw4) as a parameter.

The tire air pressure determination process of the tire air pressure determination control may be constantly executed while the vehicle is running. Further, instead of the tire air pressure determination device, a tire air pressure determination device configured to detect the air pressures of the tires of the four wheels with an air pressure sensor and determine a tire air pressure abnormality based on the detected air pressure can be applied. Of course,

[Brief description of drawings]

FIG. 1 is a configuration diagram of a drive system, a differential limiting device, and a tire air pressure determination device of a four-wheel drive type automobile according to an embodiment.

FIG. 2 is a sectional view of a main part of a center differential.

FIG. 3 is a flowchart of an initial setting process of tire air pressure determination control.

FIG. 4 is a flowchart of tire air pressure determination processing of tire air pressure determination control.

5 is a part of a flowchart of a tire air pressure determination subroutine of FIG.

6 is the rest of the flowchart of the tire air pressure determination sub-routine in FIG.

FIG. 7 is a diagram showing a map of an initially permitted vehicle speed range of a coefficient Cx.

FIG. 8 is a diagram showing a map of a vehicle speed range in which tire pressure determination is permitted.

FIG. 9 is a diagram showing the behavior of the air pressure determination variable D when the tire air pressure is normal.

FIG. 10 is a diagram showing the behavior of the air pressure determination variable D when the tire air pressure is abnormal.

FIG. 11 is a flowchart of an abnormal pressure wheel detection process in the tire air pressure determination process.

FIG. 12 is a partial view of a flowchart of a tire air pressure determination subroutine in tire air pressure determination control according to another embodiment.

[Explanation of symbols]

 9 center differential 10 front differential 11 rear differential 21,22 front wheels 23,24 rear wheels 25-28 wheel speed sensor 40 control unit 41 brake switch 42 rudder angle sensor 43 initial setting switch 44 warning lamp

Claims (5)

[Claims] 1. A vehicle including a differential limiting device capable of switching between a locked state and an unlocked state, and a tire air pressure determination device that detects an abnormality in tire air pressure of a wheel and outputs an alarm, wherein the tire air pressure is A vehicle control device comprising switching control means for switching the differential limiting device to a locked state in response to a tire pressure abnormality determination from a determination device. 2. The tire pressure determination device includes puncture determination means for determining a punctured state of the tire, and the switching control means receives the determination indicating the punctured state of the tire from the puncture determination means, and the differential limitation. The vehicle control device according to claim 1, wherein the device is configured to switch to a locked state. 3. A vehicle including a differential limiting device capable of switching between a locked state and an unlocked state, and a tire air pressure determination device that detects an abnormality in tire air pressure of a wheel and outputs an alarm. A control device for a vehicle, comprising switching control means for switching the differential limiting device to an unlocked state in response to a determination of a tire pressure abnormality from a determination device. 4. The tire air pressure determination device includes puncture determination means for determining a puncture state of a tire, and the switching control means receives the determination indicating the puncture state of the tire from the puncture determination means, and the differential limitation. The control device for a vehicle according to claim 3, wherein the control device is configured to switch the device to an unlocked state. 5. The vehicle control device according to claim 3, further comprising changeover switch means for changing over the differential limiting device to an unlocked state for a predetermined time.