JPH05346394A - Apparatus for detecting coefficient of friction of road surface - Google Patents

Abstract

PURPOSE:To estimate a road surface mu before becoming a limit state by estimating the coefficient of friction of the road surface mu on the basis of the relation between the change quantity of differential restriction quantity and that of rotational speed difference. CONSTITUTION:A rear wheel differential device 22 equipped with a differential restricting device 41 partially restricting differential is utilized in the detection of a road surface muand a rotational speed difference change quantity detection means is constituted of wheel speed sensors 54, 56 and the reading function of a rear wheel rotary angular velocity of a differential restriction quantity control device 60, the calculation function of angular velocity difference thereof and the reading function of rear wheel angular velocity after the elapse of a set time. A differential restriction quantity change means is constituted of a liquid pressure source 46, a solenoid liquid pressure control valve 44 and the liquid pressure setting function of the device 60 and the function finally estimating the road surface mu is provided to the device 60. The change quantity of the absolute value of the rotary angular velocity difference between rear wheels generated by enhancing the liquid pressure of the device 41 by set liquid pressure is calculated and, when the change quantity is a set value or more, a road is judged to be a low mu road and, when the change quantity is the set value or less, the road is judged to be a high mu road. By this constitution, the road surface p can be estimated even in a non-limit state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting a friction coefficient of a road surface, and more particularly to an apparatus for detecting a friction coefficient of a road surface capable of detecting the friction coefficient of the road surface even when the slip between the wheels and the road surface is relatively small. It is about.

[0002]

2. Description of the Related Art Conventionally, a device for detecting a friction coefficient μ of a road surface (hereinafter, abbreviated as road surface μ) has been known, and the device described in Japanese Patent Laid-Open No. 262033/1990 is one example. FIG. 5 and FIG. 12 of this publication describe an apparatus for estimating the road surface μ from the speed and acceleration during acceleration of the vehicle. If the drive torque applied to the drive wheels at the time of acceleration is excessive in relation to the road surface μ, the slip of the drive wheels becomes excessive and the acceleration performance deteriorates.
Traction control has been conventionally performed to control the drive torque to an appropriate level, but the acceleration immediately before the start of this traction control increases as the road surface μ increases, so estimate the road surface μ from this acceleration. You can
However, to be precise, the road surface μ varies not only with the magnitude of the acceleration at the start of traction control but also with the magnitude of the speed. Therefore, the device described in the above publication estimates the road surface μ from both the acceleration and the speed. It is configured.

Further, the road surface μ is determined from the hydraulic pressure of the wheel cylinder or the deceleration of the vehicle body at the start of the anti-skid control for preventing the slip of the wheels from becoming excessive during braking.
It has been traditionally also estimated. The large wheel cylinder hydraulic pressure or vehicle body deceleration at the start of anti-skid control means that the slip did not become large until a large braking force was applied.
The road surface μ is estimated to be a large value.

[0004]

However, the above-mentioned conventional device has a problem that the road surface μ cannot be estimated in a vehicle that is not provided with a traction control device or an anti-skid control device. Also, the road surface μ is estimated only after a considerably large slip occurs,
It was difficult to estimate the road surface μ before the vehicle was close to the limit state. The present invention is based on the above circumstances.
The purpose is to obtain a device capable of estimating the road surface μ before the vehicle approaches the limit state.

[0005]

In order to solve the above problems, a road surface μ detecting device according to the present invention is provided with a differential limiting device for partially limiting the differential, as shown in FIG. And a rotational speed difference change amount detecting means for detecting an amount of change in rotational speed difference between two output shafts connected by the differential device, and a differential limiting amount for changing the differential limiting amount of the differential device. Change means and estimating means for estimating the road surface μ based on the relationship between the change amount of the differential limit amount by the differential limit amount changing means and the change amount of the rotation speed difference detected by the rotation speed difference change amount detecting means. Is configured to include and.

[0006]

The differential limiting device for partially limiting the differential has been conventionally provided for the purpose of, for example, improving the running stability of the vehicle. When the dynamic limit amount is changed, the difference in rotational speed between the two output shafts connected by the differential device is changed. For example, when the differential limiting device does not apply the differential limiting force during turning of the vehicle, the radius of the running locus of the turning inner wheel is larger than the radius of the running locus of the turning outer wheel of the vehicle (the distance between the left and right wheels). ), The difference in the rotational speeds of the left and right wheels will occur. On the other hand, if a differential limiting force is applied, the rotational speed difference between the left and right wheels decreases.The differential limiting force suppresses the relative rotation of the left and right wheels, so a braking force that reduces the speed is applied to the turning outer wheel with a large turning radius. On the other hand, a driving force for increasing the speed acts on the inner turning wheel having a small turning radius, and a braking slip or a driving slip is generated on the wheel to reduce the rotational speed difference between the left and right wheels. Since the magnitude of the braking slip and the driving slip with respect to the differential limiting force changes depending on the road surface μ, the road surface μ can be estimated by comparing the change in the differential limiting amount and the change in the rotational speed difference between the left and right wheels. You can This circumstance is the same when the differential limiting amount is increased from the state in which the constant differential amount is already applied and the constant rotational speed difference occurs, and in general, the differential limiting amount is increased. If the relationship between the amount of change in the rotational speed difference and the amount of change in the rotational speed difference is known, the road surface μ can be estimated from the relationship.

In a four-wheel drive vehicle, the differential device is provided not only between the left and right wheel shafts but also between the front wheel side drive shaft and the rear wheel side drive shafts. The transmission system is such that the front wheel and the rear wheel have slightly different diameters, or the front wheel drive shaft and the rear wheel drive shaft have different rotational speeds when the front wheel and the rear wheel having the same diameter rotate at the same speed. With this configuration, it is possible to use this differential device for carrying out the invention of the present application while the vehicle is traveling straight, and it is possible to use it even when the diameters of the front wheels and the rear wheels are the same during turning. .. In either case, if the differential limitation is not applied, a rotational speed difference occurs between the output shafts of the differential device. In that case, if the differential limitation is applied, the rotational speed difference changes and the change occurs. Since the amount changes depending on the magnitude of the road surface μ, the road surface μ can be estimated from the relationship between the change amount of the differential limiting amount and the change amount of the rotational speed difference.

Therefore, in the road surface μ detecting device of the present invention, the differential limiting amount changing means changes the differential limiting amount of the differential limiting device in order to detect the road surface μ, resulting in 2
The rotation speed difference change amount detecting means detects the change amount of the rotation speed difference between the two output shafts, and the estimating means estimates the road surface μ from the relationship between the change amount of the differential limiting amount and the change amount of the rotation speed difference.

The differential limiting amount changing means is configured to generate a predetermined constant differential limiting amount, or 2
If the differential limiting amount is increased until the change amount of the rotational speed difference between the two output shafts reaches a predetermined constant value, the estimation of the road surface μ can be simplified. In the former case, the differential limiting amount is always constant, so the estimating means estimates the road surface μ only from the apparent change amount of the rotational speed difference. When the amount of change in the rotational speed difference is large, the road surface μ is estimated to be a small value, and when the amount of change in the rotational speed difference is small, the road surface μ is estimated to be a large value. on the other hand,
In the latter case, the amount of change in the rotational speed difference is always constant, so the estimation means estimates the road surface μ only from the apparent amount of change in the differential limiting amount. When the differential limiting amount is large, the road surface μ is estimated to be a large value, and when the differential limiting amount is small, the road surface μ is estimated to be a small value.

As described above, if the differential limiting amount changing means changes the differential limiting amount, the difference in rotational speed between the two output shafts changes, so that the running state of the vehicle also changes. The road surface μ can be estimated even if this change does not cause the driver to feel uncomfortable.

[0011]

Therefore, the road surface μ can be detected by operating the road surface μ detecting device according to the present invention at any time during the traveling of the vehicle. In this respect, in contrast to the conventional device, which can only detect the road surface μ at the time of operation of the traction control device or the anti-skid control device,
According to the present invention, the road surface μ can be detected before the vehicle approaches the limit state, and at that time, it is possible to make the driver hardly feel uncomfortable.

If the driver is informed of the detected road surface μ, the driver can perform an appropriate driving operation with the road surface μ in mind. Further, in recent years, for the purpose of increasing the running stability of the vehicle, running stabilization control has been performed to control the steering amount of the rear wheel steering device and the roll rigidity distribution between the front wheel suspension and the rear wheel suspension depending on the situation. It is said that
If the detected road surface μ is added to the traveling stabilization control, the effect of the traveling stabilization control can be further enhanced.

In addition, if the vehicle is equipped with a differential limiting device capable of partially limiting the differential, the road surface μ detecting device according to the present invention can be constructed using the differential limiting device. Therefore, the purpose can be achieved at low cost.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is a detailed description of the case where a road surface friction coefficient detecting device according to an embodiment of the present invention is mounted on a four-wheel drive and four-wheel steering vehicle. The drive system of the automobile of this embodiment is shown in FIG. Reference numerals 10, 12, 14, and 16 respectively denote a left front wheel, a right front wheel, a left rear wheel, and a right rear wheel, and reference numerals 18 and 2 respectively.
Reference numerals 0 and 22 respectively denote a front wheel differential, a center differential and a rear wheel differential. The central differential 20, the front differential 18, and the rear differential 22 are connected by propeller shafts 24 and 26, respectively, and the front differential 18 and the left and right front wheels 10 and 12 are respectively connected to a front drive shaft 28. , 30 are connected. Similarly, the rear wheel differential device 22 and the left and right rear wheels 14 and 16 are connected by rear drive shafts 32 and 34, respectively.

A transmission 38 is connected to the central differential 20, and the drive torque of the engine is transmitted to the central differential 20 via the transmission 38, and the drive torque is transmitted by the central differential 20 to the propeller. The shafts 24, 26 are distributed. The drive torque transmitted to the propeller shaft 24 is applied to the front drive shaft 2 by the front wheel differential device 18.
8 and 30 are distributed and transmitted to the front wheels 10 and 12. Similarly, the drive torque transmitted to the propeller shaft 26 is transmitted to the rear wheels 14 and 16 via the rear wheel differential device 22 and the rear drive shafts 32 and 34.

Of the differentials 18 to 22, the central differential 20 and the rear wheel differential 22 have a differential limiting device 40,
41 is provided. These differential limiting devices 40, 41
Is a hydraulic multi-plate clutch type, which is connected to a hydraulic pressure source 46 via electromagnetic hydraulic pressure control valves 42 and 44, respectively, to control the exciting currents of the solenoids of the electromagnetic hydraulic pressure control valves 42 and 44. As a result, the hydraulic pressure of the hydraulic pressure source 46 is controlled to an appropriate height and transmitted to the differential limiting devices 40 and 41. The differential limiting device 40 is provided between the propeller shafts 24 and 26, and the differential limiting device 41 is the rear drive shaft 3
It is provided between 2 and 34.

The differential limiting device 40 includes the propeller shaft 2
6 includes a plurality of clutch plates C that rotate integrally with 6, a plurality of clutch plates D that rotate integrally with the propeller shaft 24, pistons, cylinders, etc. These clutch plates C, D alternate one by one. Are arranged so as to be movable in the axial direction, and a piston is arranged so as to be able to press the clutch plate. When hydraulic pressure is transmitted to the cylinder and the piston is moved, the clutch plates C and D are moved along with the movement.
Are pressed against each other, which causes a friction torque between the clutch plates C and D. The differential limiting device 41 has the same configuration. This friction torque itself is also a kind of differential limiting amount, but since the magnitude of this differential limiting amount is controlled by controlling the height of the hydraulic pressure transmitted to the cylinder, the differential limiting device is used here. The command signal value of the hydraulic pressure supplied to 40 and 41 will be considered as the differential limiting amount.

In the differential limiting devices 40 and 41, when the hydraulic pressure in the cylinder is 0, differential limiting is not performed, the relative rotation of the clutch plates C and D is allowed, and the rotational speed difference between both output shafts is allowed. Is acceptable. Therefore, the rotational speed difference between the left and right rear wheels or the front and rear wheels is allowed, and the vehicle turns smoothly.

When the hydraulic pressure in the cylinder is high, the differential limiting amount is large, the relative rotation of the clutch plates C and D is limited, and the rotational speed difference between the output shafts is limited.
Therefore, even if the friction coefficient between one wheel and the road surface is significantly reduced, the difference in rotational speed between that wheel and the other wheels is limited, and the drive torque of the other wheels is not reduced. And good acceleration is obtained. in this way,
When the hydraulic pressure in the cylinder is low, the swirling property is good, and when it is high, the accelerating property is good. Therefore, it is difficult to completely satisfy both the requirements of the swirling property and the accelerating property. Therefore, in the present embodiment, the hydraulic pressure is controlled so as to increase with an increase in the accelerator opening, and both turning and acceleration requirements are adjusted.

The hydraulic pressure of these differential limiting devices 40 and 41 is
It is controlled by the differential limiting amount control device 60. Although not shown, the differential limiting amount control device 60 includes a CPU, ROM,
It has a RAM, an input unit, an output unit, and the like. Wheel speed sensors 50 to 56 and an accelerator opening sensor 58 are connected to the input unit, an alarm device 62 and electromagnetic hydraulic pressure control valves 42 and 44 described later are connected to the output unit, and the ROM is connected to the ROM. Figure 1
The programs shown in the flowcharts 1 to 3 and the programs for calculating the vehicle body speed and the vehicle body acceleration based on the wheel speed sensors 50 to 56 are stored, and the table shown in FIG. 7 is stored. The wheel speed sensors 50 to 56 detect the rotational angular velocities of the wheels 10 to 16.
The alarm device 62 is provided with a lamp mounted in the passenger compartment, and the switch for the lamp is controlled to be turned on or off by the differential limiting amount control device 60.

Next, the steering system will be described with reference to FIG. Left and right front wheels 10, 12 are knuckle arms 80, 8
It is connected to the front steering mechanism 86 via the tie rods 83 and 84. The front steering mechanism 86 is a rack and pinion type power steering equipped with a steering wheel 90, a steering shaft 91, a hydraulic pressure control valve 92, a steering gear (not shown), a power cylinder and the like. Tie rod 8
Reference numerals 3 and 84 are connected to a rack bar (not shown) and can be moved as the rack bar moves.

The rack bar constitutes a steering gear by meshing with a pinion (not shown) provided at the tip of the steering shaft 91, and is moved left and right as the steering wheel 90 rotates. In addition, the cylinder bore is divided into the left and right hydraulic chambers by the piston part fixed to the rack bar, and the hydraulic fluid is supplied to the left hydraulic chamber to assist the rack bar to move to the right and the right hydraulic chamber. By supplying the hydraulic fluid to the pressure chamber, the movement to the left is assisted.
The hydraulic pressure control valve 92 is provided between the steering wheel 90 and the pinion, and is switched by rotation of the steering wheel 90 to control the supply / discharge of hydraulic fluid from the hydraulic pressure source 46 to the left and right hydraulic chambers. Therefore, the rotational torque of the steering wheel 90 is boosted by the power cylinder and transmitted to the wheels 10 and 12 via the tie rods 83 and 84 and the knuckle arms 80 and 81, and these are steered.

The front steering mechanism 86 is provided with a reaction force device (not shown), and the hydraulic pressure transmitted to this reaction force device is controlled by the solenoid valve 93. The solenoid valve 93 is controlled by the steering control device 94. The steering control device 94 is connected to the input unit of the above-described differential limiting amount control device 60 and the steering angle sensor 96, and to the output unit of the solenoid valve 93. The steering control device 94 is a vehicle speed V and steering angle sensor 96 supplied from the control device 60 such as the limited differential amount.
The reaction force of the reaction device is controlled by controlling the solenoid valve 93 on the basis of the steering angle θ supplied from the control unit, and the force required to operate the steering wheel 90 is prevented from changing significantly between low speed and high speed. ..

The left and right rear wheels 14 and 16 are knuckle arms 10.
It is connected to the rear steering mechanism 106 via 0, 101 and tie rods 103, 104. The rear steering mechanism 106 includes a solenoid valve 108 and a rear wheel steering angle sensor 11
0, a relay rod (not shown), a power cylinder, etc. are provided. The tie rods 103 and 104 are connected by a relay rod and can be moved as the relay rod moves. Further, the relay rod is moved by the power cylinder. A hydraulic pressure source 46 is connected to the power cylinder via an electromagnetic valve 108, and the rear wheel steering angle control device 112 supplies the hydraulic fluid from the hydraulic pressure source 46 to the power cylinder via the electromagnetic valve 108. Control. As a result, the left and right rear wheels 14 and 16 are steered.

A rear wheel steering angle sensor 110, a yaw rate sensor 120, a differential limiting amount control device 60, etc. are connected to an input portion of the rear wheel steering angle control device 112, and the solenoid valve 108 is connected to an output portion. Has been done. The ROM stores the programs shown in the flowchart of FIG. 4 and the table shown in FIG.

In the vehicle constructed as described above, the hydraulic pressure applied to the differential limiting device 41 of the rear wheel differential device 22 by the differential limiting amount control device 60 and the left and right rear wheels 14, 16 are set. The road surface μ is estimated on the basis of the relationship with the absolute value of the rotational angular velocity difference. The estimation of the road surface μ is performed according to the program represented by the flowchart of FIG. 1. First, the principle will be described.

When the vehicle is turning on a uniform road surface with a uniform road surface μ, a difference in rotational speed occurs between the left and right rear wheels 14, 16. Of the left and right rear wheels 14 and 16, the rotation angular velocity of the outer wheel having the larger rotation speed is ωa, and the rotation angular velocity of the inner wheel having the smaller rotation speed is ωb, and the load applied to the outer wheels and the inner wheels is the same. I assume.

In order to match the wheel peripheral speeds of the outer wheels and the inner wheels to the vehicle body speed V (speed at the center of the vehicle body in the width direction) to eliminate the rotational speed difference between the two wheels, the braking force is applied to the outer wheels. Must be added to reduce the rotational angular velocity, and a driving force must be applied to the inner wheels to increase the rotational angular velocity. As a result, braking slips Sa occur on the outer wheels and drive slips Sb occur on the inner wheels, and the slip ratios are represented by the following equations. Sa = (rωa−V) / V Sb = (rωb−V) / rωb where r is the wheel radius of each wheel

FIG. 12 shows a general relationship between the braking force, the driving force and the slip ratio. The solid line represents the high μ road, and the broken line represents the low μ road. From this graph, when a difference in rotational speed occurs between the left and right wheels, the differential limiting amount required to eliminate the difference in rotational speed can be obtained. From the figure, in the case of the high μ road, the braking force required for the outer wheels is represented by D, and the driving force required for the inner wheels is represented by D '. The braking force D and the driving force D ′ are equal under the assumption that the outer wheels and the inner wheels have the same load. Therefore, in order to match the wheel peripheral speeds of the outer wheels and the inner wheels with the vehicle body speed V, the braking force D (=
The differential limiting amount (friction torque when the differential limiting device is a hydraulic multi-plate clutch) corresponding to the driving force D ′) is required, and is required to eliminate the rotational speed difference between the outer wheel and the inner wheel. The differential limiting amount can be calculated from this braking force D. On the other hand, on a low μ road, the braking force required for the outer wheels is the magnitude represented by E, and the driving force required for the inner wheels is the magnitude represented by E ′. , The differential limiting amount required between the inner wheels is equal to the braking force E (= driving force E ′), and the differential limiting amount required on the high μ road is the differential amount required on the low μ road. Greater than the limit. Therefore, when the wheel peripheral speeds of the outer wheels and the inner wheels are made to coincide with the vehicle body speed V, and the differential limiting amount necessary to eliminate the rotational speed difference therebetween is small, the road is low μ, and if it is large, the road μ is high. It is a road.

The differential limiting amount is calculated based on the assumption that the loads applied to the outer wheels and the inner wheels during turning are the same. The load on the inner wheels is reduced and the load on the outer wheels is increased. As a result, when a limited amount of differential is applied between the outer wheels and the inner wheels, the wheel peripheral speeds of the outer wheels and the inner wheels do not change so as to match the vehicle body speed, but rather the outer peripheral wheels rather than the vehicle body speed. It will be a value close to the peripheral speed of. However, even if this is the case, the above estimation that the smaller the differential limiting amount added to cause the same change in rotational speed difference is on the low μ road is valid, and the flowchart of FIG. 1 is based on this principle. It shows an example of road surface μ estimation based on.

First, the accelerator opening a is read in step 1 (hereinafter abbreviated as S1), and it is determined in step S2 whether or not the value a is smaller than the set value s. If the accelerator opening a is equal to or larger than the set value s, it is determined as NO, and the program is not executed, and it is waited for the value to become equal to or smaller than the set value s. When the road surface μ is estimated in this embodiment, it is desirable that the wheels 10 to 16 are rotated by the frictional force of the road surface. That is, it is desirable that the propeller shafts 24 and 26 have almost no torsional moment, and it is desirable that the vehicle is slightly decelerated due to running resistance.
That is, it is desirable that the engine is in a state where neither the drive torque nor the brake torque is applied to the wheels 10 to 16, and that the vehicle is in a state where the vehicle is gently decelerated by the running resistance. However, the maximum value is the time during which the vehicle is traveling at a substantially constant speed, and the road surface μ can be estimated even when the engine brake is applied. Therefore, in this embodiment, the set value s is set.
Is set to a value that is slightly larger than the accelerator opening that allows the vehicle to run at a constant speed.

When the accelerator opening a is smaller than the set value s, YES is determined, the vehicle stabilization control flag F1 is set to 1 in S3, and the left and right rear wheels 1 are set in S4.
The rotational angular velocities ω1 and ω2 of 4, 16 and the steering angle θ of the steering wheel 90 are read respectively. Here, as the rotational speeds of the rear drive shafts 32 and 34, the rotational angular velocities of the rear wheels 14 and 16 are the wheel speed sensors 54 and
It is detected by 56.

In S5, it is determined whether the absolute value of the steering angle θ is between the set value θ1 and the set value θ2, that is, whether the vehicle is turning with a relatively large turning radius. .. If the vehicle is turning, a difference in rotational angular velocity occurs between the wheels 14 and 16. The larger the steering angle θ is and the smaller the turning radius is, the larger the rotational angular velocity difference is, which is desirable in estimating the road surface μ. Therefore, the upper limit value is set because it may be felt. Further, the detection accuracy of the road surface μ is improved as the rotational angular velocity difference between the rear wheels 14 and 16 is large and the change amount of the absolute value of the rotational angular velocity difference is large, so the lower limit value is set so that a certain rotational angular velocity difference occurs. -ing Steering angle θ
The lower limit value θ1 and the upper limit value θ2 of are different depending on the traveling speed of the vehicle, but for example, a lower limit value of 20 ° and an upper limit value of 90 ° can be adopted. If YES is determined in S5, S6 and subsequent steps are executed, and if NO is determined, the process returns to S1.

In S6, the absolute value Δωa of the rotational angular velocity difference ω2-ω1 between the rear wheels 14 and 16 is calculated, and in S7, the hydraulic pressure of the differential limiting device 41 is increased by the set hydraulic pressure P1 and the set time elapses. Can be waited for. The set hydraulic pressure P1 is, for example, 10 kgf / cm ^2, which is a magnitude that causes a clear change in the absolute value of the rotational angular velocity difference and does not make the driver feel uncomfortable. The timer is started in S8, and it is determined in S9 whether the time t is the set time T or more. When S9 is first executed, it is naturally determined to be NO, and S10 to S12 are executed.

At S10, the accelerator opening a'and the steering angle θ'at that time are read, and at S11, the absolute value of the difference between the accelerator opening a'and the accelerator opening a read at S1 is set value as. It is determined whether or not it is smaller. If the value a and the value a ′ are substantially the same and YES is determined, it is determined in step S12 whether the absolute value of the difference between the steering angle θ ′ and the steering angle θ read in step S4 is smaller than the set value θs. To be judged. If YES, S9
If NO is determined, the process returns to S1. S9 ~
S12 is repeatedly executed, the time t reaches the set time T, and if YES is determined in S9, S13 and thereafter are executed.

Steps S9 to S12 are steps for determining whether or not the driving operation state such as steering operation or accelerator pedal operation has substantially changed during the lapse of the set time T. The set time T is, for example, 0.5 seconds, and as shown in FIG. 9, after the hydraulic pressure of the differential limiting device 41 is increased by the set hydraulic pressure P1, the pressing force of the clutch plates C and D increases. This is the time required for the difference in the rotational angular velocity between the rear wheels 14 and 16 to change.

The rotational angular velocity difference between the rear wheels 14 and 16 changes as the hydraulic pressure of the differential limiting device 41 is increased by the set hydraulic pressure P1, but naturally also changes depending on changes in the accelerator opening and the steering angle. Therefore, if the accelerator opening and the steering angle change while the set time T elapses after the hydraulic pressure increases, the change amount Δω (S15) of the absolute value of the rotational angular velocity difference is caused by the change of the accelerator opening and the steering angle. Difference and differential limiting device 4
Both the difference caused by the increase in the hydraulic pressure of 1 is included, and the road surface μ cannot be accurately detected.

Further, as shown in FIG. 7, the hydraulic pressure value of the differential limiting device 41 is controlled so as to change in accordance with the change in the accelerator opening, so that the accelerator opening during the set time T elapses. When it changes, the hydraulic pressure of the differential limiting device 41 changes due to the execution of the differential limiting device control routine described later. Therefore, the change amount of the differential limiting amount includes both the set hydraulic pressure P1 increased in S7 and the change amount of the hydraulic pressure controlled by the differential limiting device control routine. Therefore, if the values of the accelerator opening and the steering angle change more than the values read in S1 and S4 during the set time T, it is determined as NO in either S11 or S12, and the road surface μ is estimated. S13 and the subsequent steps are not executed because the situation is not met.

In S13, the rear wheel 1 after the set time T has elapsed
The rotational angular velocities ω3, ω4 of 4, 16 are read, and the absolute value Δωb of the rotational angular velocity difference ω4-ω3 is calculated. S14
In, the hydraulic pressure of the differential limiting device 41 is returned by the set hydraulic pressure P1, and the influence on the driver is minimized. Furthermore, S
15, the change amount of the absolute value of the rotational angular velocity difference Δω (= Δ
It is determined whether ωa−Δωb) is larger than the set value ε. As shown in FIG. 9, on a low μ road, the absolute value of the rotational angular velocity difference after the elapse of the set time T is Δωb, and the change amount Δω of the absolute value of the rotational angular velocity difference is larger than the set value ε, so it is determined to be YES. Then, in S16, the low μ flag F2 is set to 1 because the road surface μ is small. On the other hand, on a high μ road, the absolute value of the rotational angular velocity difference ω4-ω3 is Δωc, and the change amount Δω ′ of the absolute value of the rotational angular velocity difference is Δω ′.
Since (= Δωa−Δωc) is smaller than the set value ε, N
O is determined, and in S17, the vehicle stabilization control flag F
1 and low μ flag F2 are both reset to 0. S1
After executing 6 or S17, the process returns to S1 and this routine is executed again. This routine is repeatedly executed to detect the road surface μ at each time, set flags F1 and F2,
Reset is performed. Then, these flags F1 and F2
Based on the state of, the alarm logic, the differential limiting device control routine, the steering characteristic control routine, and the like described below are executed. The detection result of the road surface μ is notified to the driver and used for controlling the acceleration and running stability of the vehicle.

The alarm logic is shown in the flow chart of FIG. 2. In S21, it is determined whether or not the low μ flag F2 is 1, and if YES is determined, S2 is executed.
The lamp of the alarm device 62 lights up in 2 and the driver has a low μ
Notify that it is a road. If NO is determined,
The lamp of the alarm device 62 is not turned on. In this way, by informing the driver that the road is on a low μ road, it becomes possible to perform appropriate steering operation, braking device, and the like.

The differential limiting device control routine is shown in the flow chart of FIG. This routine controls the hydraulic pressure applied to the differential limiting devices 40 and 41 based on the state of the low μ flag F2. Low μ in S31
The flag F2 is referred to, and the accelerator opening a in S32
Is read. In S33, the hydraulic pressure P transmitted to the differential limiting devices 40 and 41 based on the table shown in FIG.
2, the hydraulic pressure P2 is transmitted to the differential limiting devices 40 and 41 in S34.

In FIG. 7, the solid line indicates that the low μ flag F2 is 0.
And the broken line indicates the case where the flag F2 is 1. When the flag F2 is 1 and the road is a low μ road, the amount of increase in the hydraulic pressure due to the increase in the accelerator opening a is small, and the differential limitation is relaxed. Further, when the flag F2 is 0, the amount of increase in hydraulic pressure due to the increase in the accelerator opening a is large, and the differential limitation is strengthened. In this embodiment, the central differential 20 and the rear wheel differential 22 have the same differential limiting hydraulic pressure, but they may have different hydraulic pressures.

The steering characteristic control routine is shown in the flow chart of FIG. 4, and controls the steering of the rear wheels 14 and 16 based on the vehicle stabilization control flag F1.
The vehicle body speed V and the yaw rate γ are read in S51, and the value of the vehicle stabilization control flag F1 is referred to in S52. In S53, the flag F1 and the vehicle speed V
From this, the magnitude of the yaw rate feedback gain K is determined based on the table shown in FIG. 8, and the target rear wheel steering angle δ * = K · γ is calculated in S54. In S55, the power cylinder of the rear steering mechanism 106 is controlled so that the rear wheels 14 and 16 match the target rear wheel steering angle δ *.

In FIG. 8, the solid line shows the case where the vehicle stabilization control flag F1 is 0, and the broken line shows the case where the flag F1 is 1. The value of the yaw rate feedback gain K is larger when the road surface μ is smaller and the flag F1 is set to 1, and the target rear wheel steering angle δ * is also set to a larger value. Since the value of the gain K is 0 or more, the rear wheels 14, 16
Is steered to the same phase as the front wheels 10 and 12 so as to match the target rear wheel steering angle δ *. When the road surface μ is small, the control characteristics of the rear wheel steering angle control device 112 are closer to the understeer side than when the road surface μ is large, and the running stability is improved.

As is apparent from the above description, in the present embodiment, the differential limiting device 41 that partially limits the differential.
The rear wheel differential device 22 having the above is used for detecting the road surface μ, and the rotation speed is determined by the wheel speed sensors 54, 56 and the portion of the differential limit amount control device 60 that executes S4, S6, S13, etc. Difference change amount detection means is configured. Further, the hydraulic pressure source 46, the electromagnetic hydraulic pressure control valve 44, and the differential limiting amount control device 6
The part for executing S7 of 0 constitutes a differential limiting amount changing means, and S15 and S1 of the differential limiting amount control device 60.
The estimating unit for estimating the road surface friction coefficient is configured by the portion that executes S6 and S17.

In this embodiment, the hydraulic pressure of the differential limiting device 41 of the rear wheel differential 22 is increased by the set hydraulic pressure P1 to change the rotational angular velocity difference between the rear wheels 14 and 16, and If the variation Δω of the absolute value of the rotational angular velocity difference is larger than the set value ε, it is estimated that the road is a low μ road, and if it is equal to or less than the set value ε, the road is a high μ road. If there is a rotational angular velocity difference between the left and right rear wheels 14 and 16, even if the road surface μ is not close to the limit state where anti-skid control or traction control is started.
Can be detected, and the driving state is hardly changed and the driver does not feel a sense of discomfort.

When the road surface μ detection routine is executed, when the accelerator opening is relatively small, the differential limiting device 4 is used.
Since the hydraulic pressure of No. 1 is increased by the set hydraulic pressure P1, the vehicle speed V tends to decrease due to the tight corner braking phenomenon. To reduce this tendency, the idle control valve may be opened wide. .. further,
Since the differential limiting amount of the differential limiting device 41 changes during turning, the steer characteristic tends to change. However, the rear wheel steering angle may be controlled to reduce this tendency.

Further, the road surface μ detecting device of the present invention is constructed by utilizing a differential device if the vehicle is equipped with a differential device having a differential limiting device capable of partially limiting the differential. Therefore, the cost increase can be avoided.

In the road surface μ detection routine of the above embodiment, the change amount Δω of the absolute value of the rotational angular velocity difference caused by increasing the hydraulic pressure of the differential limiting device by the set hydraulic pressure P1.
And the road surface μ was estimated by determining whether the variation Δω is larger than the set value ε.
2 is provided with a pressure sensor for detecting the hydraulic pressure of the differential limiting device 41, and the hydraulic pressure is increased until the change amount Δωn of the absolute value of the rotational angular velocity difference reaches a set value, at which time the increased hydraulic pressure P3 is set to the set hydraulic pressure. The road surface μ may be estimated by determining whether or not it is larger than P4. When the increased hydraulic pressure P3 is smaller than the set hydraulic pressure P4, the low μ road is determined.

Further, as shown in FIG. 10, after the hydraulic pressure of the differential limiting device 41 is increased, the rotation at a time point during which the rotational angular velocity difference is changing (for example, between the set times T and T '). The amount of change Δωm in the absolute value of the angular velocity may be obtained, and the road surface μ may be estimated based on this amount of change. Alternatively, the change amount Δωm at a plurality of time points may be detected, the average value of the change amounts may be obtained, and the road surface μ may be estimated based on the average value.

Further, in the road surface μ detection routine of the above-described embodiment, after the set time T elapses while the rotational speed difference is changing after the hydraulic pressure of the differential limiting device 41 is increased by the set hydraulic pressure P1. Although the rotational angular velocities of the wheels 14 and 16 were read, as shown in FIG. 11, after the set hydraulic pressure P5 was increased and a steady state was reached (after the passage of T1).
The rotational angular velocities of the wheels 10 and 12 may be read.

In the above embodiment, whether the road is a high μ road or a low μ road is determined by whether or not the amount of change itself in the absolute value of the rotational angular velocity difference is larger than the set value. Change in absolute value of rotation angular velocity difference (Δωv /
It may be determined whether or not V) is larger than the set value εv.

Further, in the above embodiment, the road surface μ is detected in two steps of high and low, but it is also possible to detect the actual value of the road surface μ. For example, a table showing the relationship among the value of the road surface μ, the change amount of the differential limiting amount, and the change amount of the rotational speed difference is stored in advance in the estimating means, and the actually obtained change amount of the differential limiting amount and the rotation The value of the road surface μ is estimated from the change amount of the speed difference.

Further, in the road surface μ detection routine of the above embodiment, the road surface μ is estimated based on the amount of change in the rotational angular velocity difference between the rear wheels 14 and 16, but either one of the left and right rear wheels 14 and 16 is estimated. The road surface μ may be estimated based on the amount of change in the difference between the wheel peripheral speed and the vehicle body speed V or the amount of change in the slip ratio of one of the rear wheels 14 and 16. In a region where the wheel slip is not large, the vehicle body speed (which can be detected by the ground speed sensor etc.) is almost equal to the average value of the peripheral speeds of the left and right wheels. Then, if the absolute value of the difference between the average value and the rotational peripheral speed of one wheel is doubled, the rotational speed difference between the left and right wheel shafts can be obtained. Further, since the slip ratio is the difference between the vehicle body speed and the wheel peripheral speed divided by the vehicle body speed, it can be used for the same purpose. Although these seem to be different methods on the surface, they are substantially the same as the method of estimating the road surface μ based on the rotational speed difference between the rear drive shafts 32 and 34.

Further, in the road surface μ detection routine of the above embodiment, the rear wheels 14, 16 are determined by determining in S5 whether or not the absolute value of the steering angle θ is between the set values θ1 and θ2. It was determined whether or not there is a rotational speed difference between the two. However, whether or not the absolute value of the yaw rate γ is within the set value, the absolute value of the output value of the lateral G sensor is within the set value. It may be determined whether or not the absolute value of the front wheel steering angle is within the set value. When making the determination based on the front wheel steering angle, even if the front wheel steering angle is obtained from the steering angle θ based on the steering gear ratio, various conditions of the front steering mechanism 86, etc., a front wheel steering angle sensor is provided to directly determine the front wheel steering angle. May be asked. In addition, the distribution ratio of the front-rear driving force is 0: 100.
In the case of a four-wheel drive vehicle that can be controlled to, it may be determined whether the rotational speed difference between the left and right wheels (non-driving wheels) whose distribution ratio is 0 is within a set value. Since the driving force is not transmitted to the non-driving wheels, the difference in rotational speed of the non-driving wheels accurately indicates the turning state of the automobile.

Further, in the road surface μ detection routine of the above-described embodiment, it is determined in S2 whether the accelerator opening a is smaller than the set value s, and if YES is determined, the road surface μ is detected. However, this determination of S2 is a means for more easily detecting the road surface μ,
Not essential.

Further, in the above embodiment, the rear wheel differential device 22 is used.
Although the road surface μ is detected by using, it is possible to detect the road surface μ by using the central differential device 20.
It is also possible to use a differential limiting device provided in the.
In the former, the propeller shafts 24 and 26 are two output shafts whose rotational speed difference is to be detected, and in the latter, the rear drive shafts 32 and 34 are two output shafts. When the central differential device 20 is used, even if a rotational speed sensor is provided on each of the propeller shafts 24 and 26 to detect a rotational speed difference, the average value of the rotational angular velocities of the front wheels 10 and 12 and the rear wheel 14 are detected. , 16 may be used as the difference in rotation speed between the shafts 24, 26.
In a four-wheel drive vehicle, since the differential limiting device is often provided only in the central differential device 20, in that case, it is desirable to use the central differential device 20 in order to suppress an increase in cost. Since the rotational angular velocity difference between the two output shafts during turning of the automobile is greater between the drive shafts of the front wheels 10 and 12 or the rear wheels 14 and 16 than between the propeller shafts 24 and 26, a differential device between the drive shafts. Therefore, it is better to detect the road surface μ.

Further, in the above-described embodiment, when it is estimated that the road is a low μ road, the rear wheel steering angle control, the differential limiting amount control, etc. are performed, but in addition, the reaction force device is controlled. The steering operation may be heavy.

Further, in the above embodiment, the four programs are executed independently of each other, but at least two programs may be executed in a dependent manner. Further, the four programs may be executed by the same control device.

Further, in the above embodiment, the road surface μ detecting device of the present invention is mounted on a four-wheel drive vehicle.
It may be mounted on a rear-wheel drive vehicle. In that case, steps S4 and S6 and subsequent steps will be performed on the drive wheels.

Although not specifically exemplified, the present invention can be carried out in various modified and improved modes based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief description of drawings]

FIG. 1 is a flowchart of a road surface μ estimation routine in a road surface μ detection device that is an embodiment of the present invention.

FIG. 2 is a flowchart of an alarm logic in an automobile equipped with the road surface μ detection device.

FIG. 3 is a flowchart of a differential limiting device hydraulic pressure control routine in the vehicle.

FIG. 4 is a flowchart of a steering characteristic control routine in the automobile.

FIG. 5 is a system diagram of a drive system of the automobile.

FIG. 6 is a system diagram of a steering system of the automobile.

FIG. 7 is a table showing a relationship between an accelerator opening degree and a differential limit amount in the automobile.

FIG. 8 is a table showing a relationship between a vehicle body speed and a rear wheel steering control gain in the automobile.

FIG. 9 is a graph showing changes in rotational angular velocity difference in the automobile.

FIG. 10 is a graph showing changes in rotational angular velocity difference in another example of the present invention.

FIG. 11 is a graph showing changes in rotational angular velocity difference in still another example of the present invention.

FIG. 12 is a graph showing a relationship among a slip ratio, a braking force, and a driving force.

FIG. 13 is a block diagram conceptually showing the structure of the present invention.

[Explanation of symbols]

 22 Rear Wheel Differential Device 32, 34 Rear Drive Shaft 41 Differential Limiting Device 46 Hydraulic Pressure Source 50, 52, 54, 56 Wheel Speed Sensor 58 Accelerator Opening Sensor 60 Differential Limiting Device Control Device 62 Alarm Device 96 Steering Angle Sensor

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Claims (1)

[Claims] 1. A differential gear including a differential limiting device for partially limiting differential, and a rotational speed difference for detecting an amount of change in rotational speed difference between two output shafts connected by the differential gear. Change amount detecting means, differential limit amount changing means for changing the differential limit amount of the differential device, change amount of the differential limit amount by the differential limit amount changing means, and rotation speed difference change amount detecting means A road surface friction coefficient detecting device for estimating a road surface friction coefficient on the basis of a relationship with a variation amount of the rotational speed difference detected by the road surface friction coefficient detecting device.