JP2734285B2 - Driving force distribution control device for four-wheel drive vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle capable of changing a distribution ratio of driving force to front and rear wheels so that a yaw rate at the time of turning becomes a target yaw rate obtained based on a running state of the vehicle. The present invention relates to a control device for changing a distribution ratio of a control signal.

[0002]

2. Description of the Related Art As is well known, the steering characteristics of a vehicle when turning are different between a front wheel drive vehicle and a rear wheel drive vehicle, and also differ in a four wheel drive vehicle depending on a distribution ratio of driving force to front and rear wheels. On the other hand, the yaw rate (yaw angular velocity) during turning is
This is one factor that expresses the performance or characteristics of the vehicle. Generally, an ideal target yaw rate is determined for each vehicle type,
Further, the value differs depending on the running state such as the vehicle speed and the steering angle. For example, Japanese Patent Application Laid-Open No. 61-229616 discloses that in a four-wheel drive vehicle, a target yaw rate is obtained based on a vehicle speed and a steering angle, and the torque capacity of a clutch means in a drive system is controlled so as to reach the target yaw rate. An apparatus is described. Further, Japanese Patent Application Laid-Open Nos. 62-99213 and 3-70633 describe that a target yaw rate is obtained based on a vehicle speed and a steering angle, and a distribution ratio of a driving force to front and rear wheels is set so as to reach the target yaw rate. An apparatus for controlling is described.

[0003]

A general steering characteristic of an automobile is that if the driving force of the rear wheels is large, the tendency of oversteering increases, and if the driving force of the front wheels is large, the tendency of understeering increases. Is well known. Therefore, as described in the above-mentioned publications, the yaw rate at the time of turning can be made close to or substantially equal to the target yaw rate by appropriately changing the driving force of the front and rear wheels. However, as described in the above-mentioned publications, conventionally, the target yaw rate is uniquely determined based on the vehicle speed and the steering angle, so that the steering stability may be reduced. That is, the acceleration acting on the vehicle at the time of turning greatly affects the behavior of the vehicle. For example, when the target yaw rate is set in accordance with the state where the acceleration is large, the vehicle easily turns at a low acceleration state, so that the sensitive yaw rate control is performed. As a result, stability may decrease. Conversely, if the target yaw rate is determined in accordance with the state where the acceleration is small, the turning performance may be deteriorated in the high acceleration state because the followability of the yaw rate control is poor.

The present invention has been made in view of the above circumstances, and has as its object to bring the turning performance of a four-wheel drive vehicle closer to the turning performance expected by a driver.

[0005]

According to the present invention, in order to achieve the above-mentioned object, the configuration shown in FIG. 1 is adopted. That is, according to the present invention, target yaw rate setting means 1 for setting a target yaw rate based on the running state of a vehicle, actual yaw rate detecting means 2 for detecting an actual yaw rate of a running vehicle, and comparing the target yaw rate with the actual yaw rate Comparing means 3, a driving force distribution device 4 for distributing driving force to the front and rear wheels of the vehicle, and a driving force distribution device 4 controlled based on a comparison result by the comparing means 3 so that the actual yaw rate matches or approximates the target yaw rate. A driving force distribution control device for a four-wheel drive vehicle comprising: a driving force distribution ratio control unit for changing a distribution ratio of driving force to wheels; and an acceleration sensor for detecting an acceleration of the vehicle. The target yaw rate setting means 1 is configured to set the target yaw rate to a smaller value as the detected acceleration is smaller. .

[0006]

According to the present invention, the actual yaw rate during the running of the vehicle is detected by the actual yaw rate detecting means, and the acceleration is detected by the acceleration sensor. The target yaw rate setting means 1 sets the target yaw rate to a smaller value as the acceleration detected by the acceleration sensor 6 is smaller, and the comparing means 3 compares the actual yaw rate with the target yaw rate. Then, the driving force distribution ratio control means 5 controls the driving force distribution ratio so that the actual yaw rate approximates or coincides with the target yaw rate. Therefore, in both the state where it is difficult to turn due to a large acceleration and the state where it is easy to turn due to a small acceleration, a turn close to the image held by the driver is performed, and the operability is improved.

[0007]

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. .

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 as to reach the target yaw rate.
FIG. 4 shows a control routine for obtaining the target yaw rate. That is, first in FIG. 3, in step 1, the steering angle δ, the speed v of each wheel, the yaw rate γ, the front and rear G, and the lateral G are read, and then in step 2, the vehicle speed (vehicle speed) V is estimated from the wheel speed v, and Number of rotations N of each wheel
Ask for. 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). Obtained front and rear wheel rotation speeds N _F and N _R
Then, the 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. Conventionally, the coefficient K _{1 (v)} is generally determined by the vehicle speed V, the wheel base L, and the stability factor K.
and a _{h, K 1 (v) =} V / {L (1 + K h · V 2)} ... will be computed by the formula, coefficient K varied depending on the electronic control unit 26 in the acceleration G according to the present invention _The target yaw rate γ ₀ is calculated using _{1 (v)} .

That is, in FIG.
Reads the acceleration G of the vehicle. The acceleration G may be a lateral acceleration or a value obtained by combining the lateral acceleration and the longitudinal acceleration ((Gx ² + Gy ² ) ^1/2 ). Next, in step 21, the acceleration G is set to a predetermined first value.
Is determined to be less than or equal to a reference value (for example, 0.2). If the determination result is “yes”, in step 22,
K _{L (v)} is adopted as K _{1 (v)} . The coefficient K _{L (v)} is previously mapped value according to the vehicle speed V, the which was substituted into the equation described above for calculating a target yaw rate gamma ₀ (step 23).

On the other hand, if the result of the determination in step 21 is "NO"
If so, it is determined in step 24 whether the acceleration G is equal to or less than a second reference value (for example, 0.4). If the determination result is “yes”, the value of K _{1 (v)} is determined in step 25. as employs the interpolated value for a K _L a _(v) and K _M was determined in advance mapped to a slightly larger value than this _(v) in the acceleration G. If the determination result in step 24 is “NO”, it is determined in step 26 whether the acceleration G is equal to or less than a third reference value (for example, 0.6). If the result is “YES”, in step 27, the value of K 1 _(v), to adopt a value obtained by interpolating the K _{M (v)} and a slightly larger value than this previously mapped to set the K _{H (v)} in the acceleration G. Further, the determination result of step 26 is “No”
If so, the aforementioned K _{H (v)} is adopted as the value of K _{1 (v)} . Regardless of which of the steps 25, 27, and 28, the target yaw rate γ _o is calculated using K _{1 (v)} corresponding to the acceleration G adopted in each of the steps 25, 27, and 28. (Step 23).

Step 23 in FIG. 4 corresponds to step 5 in FIG. 3, and based on the target yaw rate γ ₀ and the actual yaw rate γ obtained in this way, a deviation Δγ (= γ (γ ₀ -Γ)) is calculated in step 6. If the deviation Δγ is large in the positive direction, it tends to drift out (understeer), and if it is large in the negative direction, it tends to spin (oversteer).
The engagement hydraulic pressure of No. 4 is corrected. 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 is increased by strengthening the differential restriction. If there is a tendency to out, it is necessary to increase the distribution ratio of the driving force to the rear wheel side to correct for oversteering, and conversely, if there is a tendency to spin, the driving force to the front wheel side must be corrected. It is necessary to increase the distribution ratio so that the vehicle tends to understeer. Therefore, the correction coefficient K _{2 (Δγ)} corresponding to the deviation Δγ is _calculated as shown in FIG.
As shown in the above, when Δγ is large in the plus direction,
The value is set to a value smaller than “1”, and if the value is larger in the negative direction, the value is set to a value larger than “1”.

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), as shown in FIG. 6 in a normal state of straight running, etc., the rotational speed difference .DELTA.N _RF
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 7), and supplies 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, the deviation Δγ
Is represented as a parameter as shown in FIG.

Therefore, in the above-described apparatus, if the vehicle is traveling in a state where the vehicle is hard to turn due to a large acceleration G, the target yaw rate itself is corrected to be larger than the normal state, and the distribution of the driving force to the front and rear wheels is controlled so as to match the target yaw rate. On the other hand, if the vehicle is in a running state where the acceleration G is small and the vehicle is easy to turn, the target yaw rate itself is corrected to be smaller than the normal state, and the distribution of the driving force to the front and rear wheels is controlled to match the target yaw rate. The (steering characteristic) becomes substantially constant without being affected by the acceleration, and as a result, it is possible to obtain a vehicle motion characteristic suitable for the driver's sensitivity.

In the above embodiment, the distribution of the driving force to the front and rear wheels is performed by the planetary gear type transfer, and the differential is limited by the clutch to change the distribution ratio of the driving force. The present invention is not limited to the above-described embodiment, but may be configured to change the distribution ratio of the driving force to the front and rear wheels based on the comparison result between the target yaw rate and the actual yaw rate. The comparison between the target yaw rate and the actual yaw rate may be performed by taking the ratio between the two and not by multiplying the difference between the two by the actual yaw rate value. Anything may be used as long as it can be compared so that it can be grasped. Further, in the above embodiment, three types of values of K _{1 (v)} are prepared in a map form, selected according to the acceleration G, and intermediate values between them are obtained by interpolation. However, depending on conditions such as the calculation speed of the calculation device, K
The value of _{1 (v)} may be directly calculated and obtained based on the acceleration G.

[0016]

As is apparent from the above description, according to the present invention, the acceleration affecting the turning characteristics is included as one of the parameters for obtaining the target yaw rate. Is set to a small value, and conversely, if the acceleration is large, the target yaw rate is set to a large value, so that the turning characteristics are almost always constant irrespective of the acceleration, and the vehicle turns in accordance with the driver's sensitivity, In addition, the vehicle motion characteristics can be obtained, and the maneuverability 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 illustrating a control routine of an engagement hydraulic pressure of a differential limiting clutch.

FIG. 4 is a flowchart illustrating a control routine for obtaining a target yaw rate.

FIG. 5 is a diagram illustrating a relationship between a deviation between a target yaw rate and an actual yaw rate and a hydraulic pressure correction coefficient.

FIG. 6 is a diagram showing a relationship between a rotational speed difference between front and rear wheels and an engagement hydraulic pressure of a differential limiting clutch.

FIG. 7 is a diagram showing a relationship between a difference in rotation speed between front and rear wheels and an actual engagement hydraulic pressure of a differential limiting clutch when a deviation between a target yaw rate and an actual yaw rate occurs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Target yaw rate setting means 2 Actual yaw rate detecting means 3 Comparison means 4 Driving force distribution device 5 Driving force distribution ratio control means 6 Acceleration sensor

Claims (1)

(57) [Claims] 1. A target yaw rate setting means for setting a target yaw rate based on a running state of a vehicle, an actual yaw rate detecting means for detecting an actual yaw rate of a running vehicle, and a comparison for comparing the target yaw rate with the actual yaw rate. Means, a driving force distribution device for distributing the driving force to the front and rear wheels of the vehicle, and a driving force for the front and rear wheels controlled based on a comparison result by the comparing means so that an actual yaw rate matches or approximates a target yaw rate. A driving force distribution control device for a four-wheel drive vehicle, comprising: a driving force distribution ratio control unit that changes a distribution ratio of the vehicle. An acceleration sensor that detects acceleration of the vehicle, wherein the target yaw rate setting unit detects the target yaw rate. A driving force distribution control device for a four-wheel drive vehicle, wherein the target yaw rate is set to a smaller value as the acceleration is smaller.