JP2914048B2 - Vehicle front and rear wheel rotational speed difference detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting a difference in rotational speed between front and rear wheels of a vehicle, and more particularly to a rotation of front and rear wheels when controlling distribution of driving force to front and rear wheels in a four-wheel drive vehicle. The present invention relates to a device effective for detecting a speed difference.

[0002]

2. Description of the Related Art When a driving force is applied to a wheel beyond a frictional force that can be generated between the wheel and a road surface, the wheel slips and acceleration and running stability are impaired. Therefore, for example, in a four-wheel drive vehicle capable of changing the distribution of the driving force to the front and rear wheels, the difference in rotation speed between the front and rear wheels is detected, and the difference in rotation speed between the front and rear wheels is eliminated based on the difference in rotation speed. Thus, the distribution of the driving force to the front and rear wheels is controlled.

[0003] Generally, the rotational speed of a wheel is detected by generating a pulse signal corresponding to the rotation of the wheel by a magnetic sensor or an optical sensor and counting the pulse signal. However, the detection device is based on the premise that the effective radius of the front wheel and the rear wheel is the same, so if there is a difference in the effective radius of the front and rear wheels due to use of a tempered tire or mounting of a chain, etc. Then, a difference occurs between the rotational speeds of the front wheel and the rear wheel, and this is detected. Since this rotational speed difference is not caused by slip, the detected value cannot be used as it is for controlling the distribution of the driving force to the front and rear wheels.
According to the invention described in Japanese Patent No. 275028, a correction value is calculated from the rotation speeds of the front and rear wheels in a straight coasting state, and the rotation speed of the front wheels or the rear wheels is corrected by the correction value. . Also, JP-A-63-137030
In the invention described in the above publication, the differential limitation of the front and rear wheels is temporarily released during stable running, and when the differential ratio at that time (that is, the rotational speed difference between the front and rear wheels) is equal to or more than a predetermined value, the differential limitation is reduced. Is banned.

[0004]

When a correction value based on the effective radius of the front and rear wheels is obtained from the difference in rotation speed, it is necessary to exclude the rotation of the wheel in the slip state. In the invention described in the official gazette, a correction value is obtained during coasting straight ahead. However, a straight coasting state in which neither driving nor braking is performed is extremely rare in actual running.
It is difficult to put the invention described in Japanese Patent No. 028 to practical use.

On the other hand, in the invention described in Japanese Patent Application Laid-Open No. 63-137030, a state in which the vehicle speed satisfies a predetermined value or more, the steering angle satisfies a predetermined value or less, and the engine load satisfies the conditions of a predetermined value or less. Therefore, even when a small amount of driving force is applied to the wheels, the difference between the effective radii of the front and rear wheels can be obtained based on the rotational speed difference between the front and rear wheels. It is also possible to determine a correction coefficient due to the difference. However, this is based on the premise that the wheels will not slip even if they get tired, so that an error occurs when the vehicle is traveling on an extremely low μ road with a small road surface friction coefficient μ. That is, even when the vehicle is traveling straight and stable, the wheels on which the driving force is applied may slip on an extremely low μ road, and therefore, the rotational speed difference between the front and rear wheels in such a state is the same as the peripheral speed of each wheel. If the rotational speed of the front wheel or the rear wheel is corrected with a correction value based on this, the correction accuracy will deteriorate, for example, the distribution of the driving force to the front and rear wheels will be , The durability of the clutch deteriorates. Even if there is no difference in diameter between the front and rear wheels, if a slip occurs on an extremely low μ road, it is determined that there is a difference in diameter due to a difference in rotational speed between the front and rear wheels, and a correction value is set. As a result, when the driving force is distributed by the friction clutch, the clutch may be unnecessarily engaged to deteriorate the durability.

The present invention has been made in view of the above circumstances, and has as its object to provide an apparatus capable of preventing an error in correcting a difference in rotational speed between front and rear wheels on an extremely low μ road. is there.

[0007]

According to the present invention, in order to achieve the above-mentioned object, the configuration shown in FIG. 1 is adopted. That is, the present invention provides a front wheel rotational speed detecting means 3 for detecting the rotational speed of the front wheel 1, a rear wheel rotational speed detecting means 4 for detecting the rotational speed of the rear wheel 2, and a condition that the running state including at least yawing is determined in advance. A deviation detecting means 5 for calculating a relative deviation from the rotational speeds of the front wheels 1 and the rear wheels 2 when the rotational speed is satisfied, and a rotational speed difference obtained from the rotational speeds of the front wheels 1 and the rear wheels 2 based on the deviation. In a vehicle front and rear wheel rotational speed difference detecting device provided with a rotational speed difference detecting means 7 for performing correction and detecting a rotational speed difference between the front and rear wheels 1 and 2, the deviation detecting means 5 includes:
Upper limit of the range where the relative deviation of the rotation speed of the rear wheels is a predetermined range
If the value or the lower limit is exceeded,
Or the lower limit is adopted as the deviation and already detected.
The calculation of noise removal is performed taking the deviation
Means for determining the difference, and the difference is detected by the deviation detecting means.
Has a determination unit 6 other range or囲内whether the previous SL deviation predetermined that, the rotational speed difference detection means 7,
When the deviation is other within the limits of the predetermined is characterized in that for detecting the rotational speed difference between the front and rear wheels 1 and 2 without correcting the rotational speed difference based on the deviation.

[0008]

In the apparatus according to the present invention, the rotational speed of the front wheel 1 and the rotational speed of the rear wheel 2 are detected by detecting means 3 and 4 provided respectively. When the running condition such as the yaw rate being equal to or less than a predetermined value satisfies a predetermined condition, a relative deviation of the rotational speed between the front wheel 1 and the rear wheel 2 is obtained by the deviation detecting means 5 . Time between front wheel 1 and rear wheel 2
When the deviation of the rotation speed is within the predetermined range, it is detected.
Is adopted, and the upper or lower limit of the range
If the limit is exceeded, the upper or lower limit
Is used, and the noise
Is calculated, and the calculation result is calculated based on the deviation.
It is said. Deviation of its, the determination means other predetermined by 6
Whether the within range is determined, if it is within that range,
No correction of the rotational speed difference between the front wheels and the rear wheels based on the deviation is performed. That is, the rotational speed difference detecting means 7 directly detects the difference between the front wheel rotational speed detected by the front wheel rotational speed detecting means 3 and the rear wheel rotational speed detected by the rear wheel rotational speed detecting means 4 as the front and rear wheel rotational speed difference. Therefore, when traveling on an extremely low μ road with wheels with no diameter difference attached to the front and rear wheels,
Even if a slip occurs in the front wheel or the rear wheel, the rotation speed difference between the front wheel 1 and the rear wheel 2 is not corrected by this, so that erroneous correction is prevented.

[0009]

Next, an embodiment in which the present invention is applied to a four-wheel drive vehicle will be described with reference to the drawings. FIG. 2 is a view schematically showing an embodiment of the present invention. An output shaft of a transmission 11 connected to an engine 10 includes a front wheel propeller shaft 13 and a rear wheel propeller shaft 14 via a center differential 12.
And are linked to Center differential 12
Is a general differential device used in a so-called full-time four-wheel drive vehicle, which performs a differential operation between a front wheel 15 and a rear wheel 16, and includes a driving force applied from the engine 10 to the rear wheel 16. The parts are unequally distributed to the front wheels 15. A differential limiting clutch 17 for limiting the differential action is provided. The differential limiting clutch 17 is a wet-type multi-plate clutch in which a friction plate is brought into contact with a hydraulic pressure, and the hydraulic pressure is controlled by, for example, a linear solenoid valve 18 so that the differential limiting torque, that is, the driving force distribution ratio to the front and rear wheels is reduced. Is changed steplessly or stepwise.

An electronic control unit (4WD-ECU) 19 for controlling the output pressure of the linear solenoid valve 18 is provided to change the distribution ratio of the driving force to the front wheels 15 and the rear wheels 16. The electronic control unit 19 mainly includes a central processing unit (CPU), memories (ROM, RAM) and an input / output interface. The electronic control unit 19 includes a steering angle sensor 20, a yaw rate sensor 21, Signals from various sensors such as a wheel speed sensor 22, a lateral acceleration (lateral G) sensor 23, a longitudinal acceleration (longitudinal G) sensor 24, and a throttle sensor 25 provided for each wheel are input. Then, the electronic control unit 19 obtains the rotational speeds of the front and rear wheels and their correction values, or the target yaw rate at the time of turning, based on these input parameters, and calculates the difference between the rotational speeds of the front and rear wheels, the target yaw rate, and the actual yaw rate. Of the differential limiting clutch 17 is controlled so as to reduce the deviation.

The detection control of the rotational speed difference between the front and rear wheels executed in the electronic control unit 19 will be described with reference to the flowchart of FIG. First, in step 1 reads the vehicle speed V, the yaw rate gamma, pressure P _CD differential limiting clutch 17, the throttle opening theta, the rotational speed N _R of the rotational speed N _F and the rear wheel 16 of the front wheel 15, and a shift position. Next, in step 2, the running state is determined. I.e. the vehicle speed V is equal to or less than the lower limit vehicle speed V1 or more and the upper limit vehicle speed V2, the absolute value of the yaw rate gamma is a predetermined reference value gamma ₁ or less, predetermined engagement pressure P _CD differential limiting clutch 17 It is determined whether or not all the conditions are satisfied that the hydraulic pressure is equal to or less than the reference hydraulic pressure P0 and that the throttle opening θ is equal to or less than the reference opening θi set for each shift speed. Here, the reason why the vehicle speed V is within the above-mentioned vehicle speed range is to avoid the influence of relatively large noise of the wheel speed in the low speed region and the high speed region. The reason for determining the yaw rate γ is to avoid the influence of the inner wheel difference between the front and rear wheels.
Further, the reference hydraulic pressure P0 is a pressure close to "0",
By the engaging pressure P _CD between the reference hydraulic pressure P0 or less, thus avoiding the effects of differential limiting. The reason why the throttle opening θ is determined is that the wheel slips if the driving force is large, and the limit of the driving force differs depending on the shift speed. It has been set for each.

If all the above conditions are satisfied, that is, if the determination result in step 2 is "yes", in step 3, the ratio of the radius of the front wheel 15 to the rear wheel 16, that is, the different diameter ratio K is calculated. . This different diameter ratio K is the front wheel rotation speed N
_It is obtained as a ratio (N _R / N _F ) between _F and the rear wheel rotation speed N _R, and is calculated every time the condition of step 2 is satisfied.

Next, a guard for removing noise is applied to the determined different diameter ratio K. That is, the different diameter ratio K
Is not more than the lower limit value A (step 4) and whether it is not less than the upper limit value B (step 5). If the different diameter ratio K is smaller than the lower limit value A, the lower limit value A is adopted as the value of the different diameter ratio K (step 6).
Is exceeded, the upper limit B is adopted as the value of the different diameter ratio K (step 7).

Subsequent to the processing in steps 4 to 7, noise is removed by a filter (step 8). That is, the different diameter ratio obtained in step 3 is calculated as K0
Further, assuming that the different diameter ratio obtained one cycle before the cycle in which judgment is made is Kn-1, noise is removed by the calculation of Kn = (15.times.Kn-1 + K0) / 16.

Next, in order to determine the magnitude of the deviation of the radius between the front wheel 15 and the rear wheel 16, in other words, the magnitude of the deviation of the rotational speed, the diameter difference between the value Kn obtained in step 8 and the front and rear wheels is determined. The absolute value .DELTA.Kn of the difference from "1", which is the value when there is no value, is obtained (step 9). The absolute value (hereinafter, referred to as a different diameter width) ΔKn is different in tire diameters when tires of different sizes are mounted on the front wheel 15 and the rear wheel 16 or when a chain is mounted on one of them. In this case, if the different diameter width .DELTA.Kn is equal to or less than the predetermined value C in a running state satisfying the condition of step 2, there is no diameter difference between the front and rear wheels, and there is a rotation speed difference due to slip. Is determined. Therefore, in step 10, the different diameter width Δ
It is determined whether Kn is equal to or less than a predetermined value C (that is, whether it is within a range having a width of C). If the determination result is “yes”, the value of the different diameter ratio K is determined. "1" is adopted (step 11). Then proceed to step 14,
The rotational speed difference ΔN _FR between the front and rear wheels is calculated as the measured front wheel rotational speed N _F
And the absolute value of the difference between the measured value of the rear wheel speed N _R and the measured value of the rear wheel speed N _R

On the other hand, if the result of the determination in step 10 is "NO",
In this case, it is determined whether or not the different diameter width ΔKn is equal to or greater than a predetermined upper limit value D (step 12). If the determination result is "yes", it means that the control limit has been exceeded, and a control cut process for canceling the differential limit control described later is performed (step 13). Also if the result of determination at step 12 is "no", in step 14, the different diameter ratio Kn obtained measured values N _F of the front wheel rotational speed in Step 8
(Accumulated), and the measured value N of the rear wheel rotational speed is calculated from the value.
R is subtracted and the absolute value of the difference is calculated as the rotational speed difference ΔN between the front and rear wheels.
_Ask as _FR .

If the result of the determination in step 2 is "NO", the value Kn-1 obtained in the previous cycle is adopted as the different diameter ratio K (step 15), and thereafter the routine proceeds to step 12.

The rotational speed difference ΔN _FR between the front and rear wheels thus obtained is used for driving force distribution control for the front and rear wheels, and an example thereof will be described below. Figure 4 illustrates a control routine for controlling the hydraulic pressure of the differential limiting clutch 17 by correcting the engaging pressure P (ΔNFR) based on the rotation speed difference .DELTA.N _FR of the front and rear wheels by a factor based on the yaw rate deviation. That is, in FIG. 4, in step 20, the actual steering angle δ obtained from the steering angle, the speed v of each wheel, the yaw rate γ, the front and rear Gx,
Then, the lateral Gy is read, and then in step 21, the vehicle speed (vehicle speed) V is estimated from the wheel speed v, and the rotational speed N of each wheel is obtained.

In step 22, the front wheel rotation speed N _F and the rear wheel rotation speed N _R are calculated by averaging the respective left and right wheel rotation speeds (N _F = (N _FL + N _FR ) / 2, N _R = (N _RL + N _RR )
/ 2). The obtained rotational speeds N _F , N of the front and rear wheels
It is corrected by a different diameter ratio K described above the front wheel rotational speed N _F of _R, the rear wheel rotational speed from the corrected values N _R
Is subtracted, and the absolute value ΔN _{FR of the} difference is obtained (step 23). Next, at step 24, a target yaw rate γ ₀ is obtained. This is obtained from the coefficient K _{1 (v)} corresponding to the vehicle speed V and the steering angle δ. Conventionally, the coefficient K _{1 (v)} is generally determined by the vehicle speed V, the wheel base L, and the stability factor K.
_{From h} , an operation is performed using the following equation: K _{1 (v)} = V / {L (1 + K _h · V ² )}. Note that the coefficient K _{1 (v)} may be a coefficient corrected according to the acceleration, the friction coefficient μ of the road surface, and the like.

Since the actual yaw rate γ is a second-order lag element with respect to the steering angle δ, the target yaw rate γ ₀ shows the same response as the steering angle δ. Correction of the first-order lag to the target yaw rate γ ₀ by the time constant T determined according to the vehicle speed V (γ ₀ /
(1 + Ts), s: Laplace operator).

Based on the target yaw rate γ ₀ and the actual yaw rate γ obtained in this manner, a deviation Δγ
(= Γ (γ ₀ −γ)) is calculated in step 26. Here, as the deviation Δγ, the product of the difference between the target yaw rate γ ₀ and the actual yaw rate γ and the actual yaw rate γ is
For the following reasons. That is, the yaw rate is a directional parameter, and the deviation Δγ also indicates the understeer tendency and the oversteer tendency with positive (+) and negative (−) signs. Regardless of whether the vehicle is turning left or right, a positive value is obtained when the vehicle is understeering, and a negative value is displayed when the vehicle is oversteering.

Then, based on the deviation Δγ of the yaw rate,
By correcting the differential limiting clutch pressure P _CD by the rotational speed difference .DELTA.N _FR of the front and rear wheels, and controls the differential limiting clutch pressure P _CD in consideration of the steering characteristic. That is, the four-wheel drive vehicle shown in FIG. 2 is a four-wheel drive vehicle based on rear-wheel drive, and the distribution of the driving force to the front wheels increases by increasing the differential restriction. In the case of, it is necessary to increase the distribution ratio of the driving force to the rear wheel side to compensate for the oversteer tendency, and conversely, in the case of the spin tendency, the distribution ratio of the driving force to the front wheel side Need to be raised to understeer. Therefore, as shown in FIG. 5, the correction coefficient K _{2 (Δγ)} according to the deviation Δγ is set to a value smaller than “1” when Δγ is large in the plus direction, and is set to a value smaller than “1” when Δγ is large in the minus direction. Is set to a value greater than "1".

On the other hand, the engagement pressure P of the differential limiting clutch 17 based on the rotation speed difference .DELTA.N _FR of the front and rear wheels (ΔNFR), as shown in FIG. 6 in a normal state of straight running, etc., the rotational speed difference .DELTA.N _FR
However, if there is a deviation between the actual yaw rate during turning and the target yaw rate, the engagement hydraulic pressure P (ΔNFR) is corrected by multiplying by the correction coefficient K _{2 (} Δγ) ( step 27) to the differential limiting clutch 17 that value as an actual engaging pressure P _CD. The relationship between the rotational speed difference .DELTA.N _FR of the actual engaging pressure P _CD and front and rear wheels, the deviation Δγ
Is represented as a parameter as shown in FIG.

In the above embodiment, the differential limiting is performed by the clutch to change the distribution ratio of the driving force. However, the present invention is not limited to the above embodiment. it is sufficient to configure so as to alter the driving force distribution ratio to front rear wheels by the driving force distribution means such as switches.

[0025]

As apparent from the above description, according to the present invention, the relative deviation between the front wheel rotation speed and the rear wheel rotation speed is determined.
When detecting the difference, the detected value is a predetermined
Exceeds the upper or lower limit of the range
The upper or lower limit is adopted and the value already detected
The calculation of noise removal is performed taking into account
Since the result is regarded as the deviation, an accurate deviation without disturbance is obtained.
When the deviation is within a predetermined range, for example, when the above-described different diameter ratio of the front and rear wheels is smaller than the different diameter ratio when there is a difference in the effective radius between the front wheel and the rear wheel. Since it is determined that a slip has occurred on the wheel, and the rotational speed difference between the front and rear wheels in that case is obtained using the actual measurement value as it is, it is sure to correct the rotational speed difference including disturbance due to slip. it is possible to prevent, when further using the rotation speed difference of that the control of the engagement pressure of the clutch to perform the driving force distribution control for the front and rear wheels are prevented from engaging the clutch unnecessarily , Its durability can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention in principle.

FIG. 2 is a block diagram schematically showing one embodiment of the present invention.

FIG. 3 is a flowchart showing a control routine for obtaining a rotational speed difference between front and rear wheels by correcting the difference with a different diameter ratio.

FIG. 4 is a flowchart showing a control routine of an engagement hydraulic pressure of a differential limiting clutch.

FIG. 5 is a diagram illustrating a correction coefficient based on a yaw rate deviation.

FIG. 6 is a diagram showing engagement hydraulic pressure of a differential limiting clutch based on a rotation speed difference between front and rear wheels.

FIG. 7 is a graph showing the relationship between the rotational speed difference between the front and rear wheels and the actual engagement oil pressure of the differential limiting clutch using the yaw rate deviation as a parameter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 front wheel 2 rear wheel 3 front wheel rotational speed detecting means 4 rear wheel rotational speed detecting means 5 deviation detecting means 6 determining means 7 rotational speed difference detecting means

Claims (1)

(57) [Claims] 1. A front wheel rotational speed detecting means for detecting a rotational speed of a front wheel, a rear wheel rotational speed detecting means for detecting a rotational speed of a rear wheel, and a running state including at least yawing satisfies a predetermined condition. front and rear wheels do and deviation detection means for determining the relative deviation of the rotation <br/> speed of the front wheels and the rear wheels, the correction of the rotational speed difference obtained from the rotational speed of the front wheels and the rear wheels based on the deviation of the time of the front and rear wheel rotation speed difference detecting apparatus for a vehicle and a rotational speed difference detecting means for detecting a rotational speed difference, said deviation detecting means, the rotational speed of the front wheels and rear wheels
Upper or lower limit of relative deviation within a predetermined range
If it exceeds, deviate the upper or lower limit
As well as taking into account already detected deviations
Means for performing a noise removal operation to determine the deviation.
Has, and has a determining means for determining another within range whether the previous SL deviation detected by the deviation detecting means is predetermined, the rotational speed difference detection means, defined the deviation is the pre was another when in the within range front and rear wheel rotational speed difference detection device for a vehicle, characterized in that for detecting the rotational speed difference between the front and rear wheels without correction of the rotational speed difference based on the deviation.