JP2853478B2 - Driving force distribution device for four-wheel drive vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention is related to a driving force distribution device for controlling the distribution of driving force to the front and rear wheels in the four-wheel drive vehicle
It is to shall.

[0002]

2. Description of the Related Art If tires slip due to excessive torque applied to driving wheels, the driving force for moving the vehicle forward is lost. Therefore, in a four-wheel drive vehicle that can change the distribution of driving force to the front and rear wheels, the distribution ratio of driving force is controlled based on the difference between the rotation speeds of the front and rear wheels to prevent tires from slipping due to excessive torque To obtain excellent power performance.

Since the sum of the frictional force generated by the tires, that is, the sum of the vector of the driving force and the lateral force, is almost constant, if the distribution of the driving force to the front and rear wheels is changed when the vehicle is yawed, Since the lateral force generated at the rear wheels changes, the steering characteristics of the vehicle can be changed. In other words, in a four-wheel drive vehicle that can change the distribution of driving force to the front and rear wheels, turning performance (turning performance) and stability are improved by controlling the distribution of driving force so that the actual yaw rate matches the target yaw rate. Can be done. The applicant of the present invention has disclosed a device for performing the so-called yaw rate tracking control in Japanese Patent Application No.
-99614.

In the device proposed by the present applicant, a target yaw rate γ ₀ is obtained based on a steering angle and a vehicle speed, and a difference (γ ₀ −γ) between the target yaw rate γ ₀ and the actual yaw rate γ is obtained.
The product of the actual yaw rate γ (Δγ = γ (γ ₀ −γ)) is calculated, and the hydraulic pressure of the differential limiting clutch is controlled based on the product, that is, the steering characteristic value (yaw rate deviation) Δγ, so that it is suitable for the traveling state. To obtain the best steering characteristics. The above product is adopted as the steering characteristic value Δγ for the following reason. That is, the yaw rate is a directional parameter, and the steering characteristic value Δγ also indicates the tendency of drift-out (understeer) and the tendency of spin (oversteer) with positive (+) and negative (-) signs. Therefore, if the product is taken as described above, the value becomes positive when the vehicle tends to drift out and negative when the vehicle tends to spin, regardless of whether the vehicle is turning left or right.

[0005]

In the apparatus proposed by the present applicant, the yaw rate follow-up control is performed based on the steering characteristic value. The steering characteristic value includes a target yaw rate γ ₀ and an actual yaw rate γ. And the actual yaw rate γ, the difference (γ ₀ −
If the actual yaw rate γ decreases even if γ) increases, there is no change in the steering characteristic value Δγ or the difference (γ ₀
−γ), the actual yaw rate γ may increase and the steering characteristic value Δγ may become excessive. Therefore, if the control of the clutch engagement force for optimizing the steering characteristic is performed based only on the steering characteristic value Δγ, there is a possibility that the turning performance or the stability may not always be sufficient.

[0006] This invention provides the above circumstances was made against the background of, the driving force distribution device capable of controlling the distribution of driving force distribution to become by the Hare driving force to the best front and rear wheels to the running state The purpose is to do so.

[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 relates to a driving force distribution device for a four-wheel drive vehicle including a driving force distribution unit 3 capable of changing the distribution of driving force to the front wheel 1 and the rear wheel 2.
An actual yaw rate detecting means 4 for detecting an actual yaw rate, a target yaw rate setting means 5 for setting a target yaw rate,
A coefficient determined based on the product of the difference between the target yaw rate and the actual yaw rate and the actual yaw rate should be at least the actual yaw rate.
And control means 6 for controlling the distribution of the driving force by the driving force distribution means based on the coefficient corrected in accordance with the following.

[0008]

In the present invention, the actual yaw rate is detected by the actual yaw rate detecting means 4, the target yaw rate is set by the target yaw rate setting means 5, and the driving force of the drive distribution means 3 is determined based on the actual yaw rate and the target yaw rate. The distribution is controlled by the control means 6. Here, the control means 6 calculates a coefficient determined based on the product of the difference between the target yaw rate and the actual yaw rate and the actual yaw rate,
The drive distribution means 3 is controlled based on the coefficient further corrected according to the rate . Therefore, in the present invention, the distribution of the driving force can be changed according to the magnitude of the actual yaw rate in addition to the steering characteristic value, so that the distribution of the driving force, that is, the steering characteristic is set to an optimum characteristic according to the traveling state.

[0009]

Next, the present invention will be described based on embodiments. FIG. 2 is a schematic diagram showing one embodiment of the present invention,
The four-wheel drive transfer 10 to be controlled is provided on the output side of an automatic transmission 12 connected to an engine 11. The transfer 10 distributes driving force to a rear wheel side and a front wheel side by a center differential 13 of a planetary gear type. A drive shaft 14 which is an output shaft of the automatic transmission 12 is connected to a carrier 15. A ring gear 16 is connected to a rear propeller shaft 18 via an output shaft 17. In contrast, sun gear 19
Are connected to a drive sprocket 20 and transmit a driving force to a front propeller shaft 23 via a chain 21 and a driven sprocket 22 wound around the drive sprocket 20. Carrier 15 and sun gear 19
And a differential limiting clutch 24 is provided between them, and by increasing the engagement hydraulic pressure, that is, by increasing the torque capacity, the distribution ratio of the driving force to the front wheels is increased. . Therefore the differential limiting clutch
24 is a driving force distribution means.

As a device for controlling the hydraulic pressure applied to the differential limiting clutch 24, a hydraulic control device 25 mainly composed of a linear solenoid valve and a four-wheel drive electronic control device (4WD-ECU) 26 are provided. I have. The electronic control unit 26 is mainly composed of a central processing unit (CPU), memories (ROM, RAM) and an input / output interface.
Includes a steering angle sensor 27, a yaw rate sensor 28, a wheel speed sensor 29 provided for each wheel, a lateral acceleration (lateral G) sensor 30, and a longitudinal acceleration (longitudinal G) sensor 31.
And other signals from each sensor. Then, the electronic control unit 26 calculates the target yaw rate during turning based on these input parameters and controls the hydraulic pressure for the differential limiting clutch 24 so that the deviation between the target yaw rate and the actual yaw rate is reduced. Has become.

FIG. 3 shows a control routine for controlling the hydraulic pressure of the differential limiting clutch 24 so that the actual yaw rate matches the target yaw rate. That is, in FIG. 3, in step 1, 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, and the lateral Gy are read, and then in step 2, the vehicle speed (vehicle speed) V is calculated from the wheel speed v. And the rotational speed N of each wheel is obtained. In addition Step 3, the front wheel speed N _F and the rear wheel rotational speed N and _R, the average rotational speed of the respective left and right wheels (N _F = (N _FL
+ N _FR ) / 2, N _R = (N _RL + N _RR ) / 2). From the obtained rotational speeds N _F and N _R of the front and rear wheels, an absolute value ΔN _FR of the rotational speed difference between the front and rear wheels is obtained (step 4). Next, at step 5, a target yaw rate γ ₀ is determined. This is obtained from the coefficient K _{1 (v)} corresponding to the vehicle speed V and the steering angle δ. In general, the coefficient K _{1 (v)} is calculated based on the vehicle speed V and the wheel base L
As well as from the stability factor _{K h, K 1 (v)} = V /
Computed by Equation _{{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.

In step 6, a target yaw rate (γ ₀ / (1 + Ts)) with a first-order lag corrected is obtained, where T is a time constant, which increases in accordance with a predetermined constant value or an increase in vehicle speed. Variables can be adopted.
S is a Laplace operator. The reason for correcting such a first-order lag is as follows. That is, as described above, the target yaw rate γ ₀ can be obtained based on the vehicle speed V and the steering angle δ, and shows a response about the same as the steering angle δ in performing the yaw rate follow-up control. On the other hand, the actual yaw rate γ is detected by the occurrence of a side slip angle in the tire due to steering, and subsequently, when the direction of the vehicle body changes, and becomes a second-order lag element in control. Therefore, if the deviation is obtained by using the actual yaw rate and the target yaw rate as they are, the deviation during the turning transition becomes large, and the control error becomes large. Therefore, by correcting the target yaw rate with a first-order lag, the control error during turning transition is reduced.

On the basis of the target yaw rate γ ₀ and the actual yaw rate γ thus determined, a deviation Δγ
(= Γ (γ ₀ −γ)) is calculated in step 7. Here, as the deviation Δγ, the target yaw rate γ ₀ and the actual yaw rate γ
The reason for taking the product of the difference with the actual yaw rate γ is
This is as described in the related art.

The deviation Δ of the yaw rate thus obtained is
Based on gamma, by correcting the differential limitation by the rotational speed difference .DELTA.N _FR of the front and rear wheels clutch pressure P (ΔNFR), and controls the differential limiting clutch pressure P _CD in consideration of the steering characteristic.

That is, the vehicle provided with the transfer 10 shown in FIG. 2 is a four-wheel drive vehicle based on rear-wheel drive, and the distribution ratio of the driving force to the front wheels increases by increasing the differential restriction. Therefore, if there is a tendency to drift out, it is necessary to increase the distribution ratio of the driving force to the rear wheel side and correct it to the spin side, and conversely, if there is a tendency to spin, drive to the front wheel side It is necessary to increase the force distribution ratio and correct for the drift-out side. Therefore, as shown in FIG. 4, 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".

The correction coefficient K _{2 (Δγ)} is based on only the yaw rate deviation Δγ which is the product of the difference between the target yaw rate γ ₀ and the actual yaw rate γ and the actual yaw rate γ.
Because do not reflect the running states of the vehicle to always accurate, the pressure value P based on the rotation speed difference .DELTA.N _FR of the front and rear wheels (ΔNFR)
Is used as a coefficient for correcting the correction coefficient K _{2 (Δγ, γ, V)} obtained by further correcting the correction coefficient K _{2 (Δγ)} based on the actual yaw rate γ and the vehicle speed V. This coefficient K
_{2 (Δγ, γ, V)} is stored as a map using the actual yaw rate γ and the vehicle speed V as parameters, and a value corresponding to the detected actual yaw rate γ and the vehicle speed V can be selected. FIG. 5 shows an example of the above. The coefficient K _{2 (Δγ) ij} (= K _{2 (Δγ, γ, V)} ) shown in FIG.
When the yaw rate deviation Δγ is a negative value, the coefficient K _{2 (Δγ) ij} having a larger value is selected as the absolute value of the actual yaw rate γ decreases, as the vehicle speed increases.

Meanwhile, the engagement pressure P of the differential limiting clutch 24 based on the rotation speed difference .DELTA.N _FR of the front and rear wheels (ΔNFR) is in a normal state of straight running such as shown in FIG. 6, the rotational speed difference .DELTA.N _FR If the deviation occurs between the actual yaw rate during turning and the target yaw rate, the engagement hydraulic pressure P (ΔNFR ₎ is multiplied by the coefficient K _{2 (Δγ, γ, V)} for correction. (step 8) to the differential limiting clutch 24 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, if indicated conceptually deviation Δγ as the parameter, is shown in Figure 7.

[0018] That engaging pressure P _CD in the state of the yaw rate deviation Δγ is "0", but is based on the rotational speed difference .DELTA.N _FR of the front and rear wheels, as the steering characteristic in addition to the rotational speed difference between the front and rear wheels If the spin tendency has occurred, the coefficient K _{2 (Δγ, γ, V)} having a value larger than “1” is determined by the rotation speed difference ΔN _FR between the front and rear wheels.
Since is multiplied to the engaging pressure P (ΔNFR) by actually set engagement hydraulic pressure P _CD should becomes higher pressures.
Therefore, in the four-wheel drive vehicle shown in FIG. 2, the distribution ratio of the driving force to the front wheels is increased, and in addition to suppressing the rotational speed difference ΔN _FR between the front and rear wheels, the spin tendency is suppressed, and as a result,
Stable steering characteristics can be obtained. If a drift-out tendency occurs in addition to the difference between the rotational speeds of the front and rear wheels, the correction coefficient K _{2 (Δγ, γ, V)} becomes a value smaller than “1”. since is multiplied with the engagement hydraulic pressure P (ΔNFR), actually set engagement hydraulic pressure P _CD should will lower pressure. Therefore, at the time of turning, the engagement hydraulic pressure P _{CD of the} differential limiting clutch is determined by the rotational speed difference ΔN _FR between the front and rear wheels.
Is determined to be higher, the pressure is corrected based on the deviation of the yaw rate to reduce the pressure, so that in the four-wheel drive vehicle shown in FIG. As a result, the drift-out tendency is suppressed, and a stable steering characteristic is obtained.

The steering characteristic is set by controlling the engagement pressure P _CD differential limiting clutch 24 as described above, the above-mentioned factor _{K 2 (Δγ, γ, V} ) is the actual yaw rate gamma
And the vehicle speed V is also taken into consideration.
Steering characteristics suitable for the running state of the vehicle are obtained. Specifically, when the yaw rate deviation Δγ is a negative value and tends to spin, the smaller the absolute value of the actual yaw rate γ, the larger the value of the coefficient K _{2 (Δ, γ, V)} and the clutch since the engagement pressure P _CD increases, the it is possible to prevent the cut into large despite a small steering angle, also by increasing the turning in opposite to pivot according to the request. Further, when a high vehicle speed, the coefficient _{K 2 (Δγ, γ, V} ) and increases, since the engagement pressure P _CD of the clutch is increased, stability is increased.

In the above embodiment, a coefficient using both the actual yaw rate γ and the vehicle speed V as parameters is adopted as the coefficient K _{2 (Δγ) ij} for reflecting the steering characteristic. A coefficient obtained by further correcting the correction coefficient based on the deviation Δγ according to only the actual yaw rate γ may be adopted.

As is known from the above-described embodiment, the engagement pressure of the clutch for controlling the distribution of the driving force to the front and rear wheels is a value P (ΔNFR) based on the difference in the driving performance between the front and rear wheels.
And a coefficient K _{2 (Δγ, γ, V)} relating to the steering characteristic. Of these, the former value P (ΔNFR) is
Since the value increases with an increase in the rotational speed difference ΔN _FR between the front and rear wheels, the pressure value is not limited to the case where there is a certain difference in the tire diameter between the front and rear wheels other than when the front and rear wheels slip. P (ΔNFR) is set to a large value. Therefore, if there is a tire diameter difference between the front and rear wheels, the clutch pressure is always maintained at a relatively high pressure, and the durability of the clutch may be reduced.

Since the slip of the clutch when a different diameter tire is mounted becomes more remarkable at a higher vehicle speed, the map for determining the pressure value P (ΔNFR) based on the difference in the rotational speeds of the front and rear wheels when the different diameter tire is mounted is as follows. , It is preferable to employ the map shown in FIG. In the map shown in FIG. 8, it is determined in that the pressure value P (ΔNFR) decreases as vehicle speed increases, further when the vehicle speed is equal to or higher than a predetermined vehicle speed, the rotational speed difference .DELTA.N _FR of the front and rear wheels is constant Pressure value P (ΔNF
A dead zone where R) is "0" is set.

Therefore, if the pressure value P (ΔNFR) is set based on the map shown in FIG. 8, the excessive slip of the clutch is suppressed even if the vehicle speed increases, so that its durability is prevented from lowering. In addition, when a dead zone is provided, the rotational speed difference between the front and rear wheels at a certain level or less at a high vehicle speed is considered to be based on the tire diameter difference, and the clutch is maintained in the released state. Can be prevented.

The control of the clutch pressure using the map shown in FIG. 8 can also be applied to a control device for controlling the distribution of the driving force based only on the difference between the rotational speeds of the front and rear wheels.

In each of the above embodiments, the driving force is distributed to the front and rear wheels by a planetary gear type transfer.
And has been configured to change the distribution ratio of driving force that differential limiting performed by the clutch, the invention is not limited to the above embodiment, principal is the driving force distribution means
It is sufficient to configure so as to alter the driving force distribution ratio to the front-rear wheel I.

[0026]

According to apparent this invention from the above description, when the actual yaw rate to control the allocation of the driving force to the front and rear wheels so as to match the target yaw rate, the target yaw rate and the actual yaw rate Since the configuration is such that the driving force distribution is controlled not only according to the product of the difference and the actual yaw rate, but also according to the magnitude of the actual yaw rate, a steering characteristic more suitable for the running state of the vehicle can be obtained. In addition, the turning performance at low vehicle speed and the stability at high vehicle speed can be improved.

[Brief description of the drawings]

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

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

FIG. 3 is a flowchart illustrating a control routine of an engagement hydraulic pressure of a differential limiting clutch.

FIG. 4 is a diagram showing a correction coefficient based on a yaw rate deviation Δγ.

FIG. 5 is a map of a correction coefficient set corresponding to an actual yaw rate and a vehicle speed.

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.

FIG. 8 is a map for correcting the engagement hydraulic pressure of the differential limiting clutch based on the rotation speed difference between the front and rear wheels according to the vehicle speed when different-diameter tires are mounted.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 front wheel 2 rear wheel 3 driving force distribution means 4 actual yaw rate detection means 5 target yaw rate setting means 6 control means

Claims (1)

(57) [Claims] 1. A driving force distribution device for a four-wheel drive vehicle having driving force distribution means capable of changing distribution of driving force to front wheels and rear wheels, wherein an actual yaw rate detecting means for detecting an actual yaw rate; A target yaw rate setting means for setting a yaw rate; and a product of a difference between the target yaw rate and the actual yaw rate and the actual yaw rate.
At least according to the actual yaw rate.
Control means for controlling the distribution of the driving force by the driving force distribution means based on the corrected coefficient .