JP2996023B2 - Driving force distribution device for four-wheel drive vehicle with four-wheel steering device - Google Patents

Abstract

PURPOSE:To improve turning performance and stability by providing a locking force computing means for obtaining the locking force of a clutch by setting at least one of the pressure value and a coefficient in the case of four-wheel steering in the yaw increasing direction to the larger value than the value in the case of four-wheel steering in the yaw suppressing direction. CONSTITUTION:A driving force distributing device for a four-wheel drive vehicle with four-wheel steering system is provided with a four-wheel steering control detecting means 5 for detecting the four-wheel steering state performed by a four-wheel steering system. In the case of detecting four-wheel steering in the yaw increasing direction by a four-wheel steering control detecting means 5, a locking force computing means 6 obtains, by multiplication, the locking force of a clutch 4 with at least one of the pressure value and a coefficient set to the larger value than the value in the case of detecting four-wheel steering in the yaw suppressing direction by the four-wheel steering control detecting means 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a four-wheel steering system (4W
The present invention relates to a device for controlling distribution of driving force to front and rear wheels in a four-wheel drive vehicle provided with S).

[0002]

2. Description of the Related Art As is well known, turning of a four-wheeled vehicle is performed by generating a side slip angle on a running tire and generating a cornering force corresponding thereto, but a cornering force generated on a front wheel and a rear wheel. The situation of the turning motion of the vehicle differs depending on the size of the vehicle. On the other hand, since the frictional force of the tire, that is, the vector sum of the driving force and the lateral force is substantially constant, the lateral force changes due to the driving force applied to the tire. Therefore, by appropriately controlling the driving force applied to the front wheels and the rear wheels, the steering characteristics can be controlled by changing the cornering force generated at each wheel, and recently, the distribution of the driving force to the front and rear wheels of a four-wheel drive vehicle has been recently performed. Is controlled so that the actual yaw rate follows the target yaw rate, and the present applicant controls such a so-called yaw rate follow-up control by controlling a clutch pressure for driving force distribution control in a four-wheel drive transfer. An apparatus has already been filed.

That is, the engagement force of the clutch for controlling the distribution of the driving force to the front and rear wheels of the four-wheel drive vehicle is basically
The drive performance is ensured by increasing as the difference between the rotational speeds of the front and rear wheels increases, but as described above, the steering characteristics also change according to the driving force applied to the front and rear wheels. Therefore, in the device according to the present applicant's application, the clutch engaging force based on the rotational speed difference between the front and rear wheels is corrected by a coefficient based on the deviation between the target yaw rate and the actual yaw rate, and the stability is secured together with the driving performance. ing.

[0004]

Since the steering characteristics of the vehicle differ depending on the cornering forces generated at the front and rear wheels as described above, the four wheels which steer the rear wheels according to the running conditions such as the steering of the front wheels and the vehicle speed. In a vehicle equipped with a steering device, the steering characteristics differ depending on the conditions of the four-wheel steering. For example, at low vehicle speeds, reverse-phase steering, in which the rear wheels are steered in the opposite direction to the front wheels, ensures turning performance.At high vehicle speeds, in-phase steering, in which the rear wheels are steered in the same direction as the front wheels, is stabilized. Therefore, the steering characteristics differ according to the vehicle speed.

Conventionally, however, control of distribution of driving force to the front and rear wheels by the above-described four-wheel drive device and control of rear wheels by the four-wheel steering device have not been particularly controlled.
In some cases, the turning characteristics were not always satisfactory. Specifically, in a four-wheel drive vehicle that controls the distribution of driving force to the front and rear wheels so that the yaw rate is relatively large, when the above-described general four-wheel steering control is performed,
There is a possibility that the yaw rate during turning acceleration at low vehicle speed may become too large, and conversely, in a four-wheel drive vehicle that controls the distribution of driving force to the front and rear wheels so that the yaw rate becomes relatively small, turning at high vehicle speed There was a possibility that the turning property at the time of acceleration was deteriorated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a driving force distribution device capable of improving turning performance and stability in a four-wheel drive vehicle with a four-wheel steering device. It is assumed that.

[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 four-wheel steering device 3 for turning the rear wheel 2 in accordance with the turning of the front wheel 1,
A four-wheel steering device equipped with a clutch 4 that is engaged with the engagement force determined based on the rotational speed difference of 2 and the deviation between the target yaw rate and the actual yaw rate to change the distribution of the driving force to the front and rear wheels. In the driving force distribution device for a wheel drive vehicle, the four-wheel steering control detecting means 5 for detecting the condition of the four-wheel steering by the four-wheel steering device 3 and the four-wheel steering in the direction to increase the yaw. When detected by the steering control detecting means 5, the engagement force of the clutch is transmitted to the front wheels.
Depending on the deviation of the yaw rate so that the driving force distribution increases
When the four-wheel steering control detecting means detects that the four-wheel steering is performed in the direction of correcting and suppressing the yaw,
Increases the clutch engagement force by increasing the distribution of driving force to the rear wheels.
And it is characterized in that it comprises a tightening force calculating means 6 you corrected according to the yaw rate deviation to large.

[0008]

In the four-wheel drive vehicle to which the present invention is applied, the front wheels 1
, The rear wheel 2 is steered by the four-wheel steering device 3. The direction in which the rear wheels 2 are steered differs depending on the state of the vehicle such as the steering angle of the front wheels 1 and the vehicle speed, and may be either the direction of increasing yaw or the direction of suppressing yaw. Further, the engagement force of the clutch 4 that controls the distribution of the driving force to the front and rear wheels 1 and 2 is obtained based on the difference between the rotational speeds of the front and rear wheels 1 and 2 and the difference between the target yaw rate and the actual yaw rate. Further, the engagement force of the clutch 4 is corrected according to the yaw rate deviation so as to correct the turning performance based on the four-wheel steering.
Is, specifically, in a case that is a four-wheel steered in a direction to increase the yaw increased, as a result, the driving force distribution is
The driving force distribution enhances the understeer characteristics.
When the four-wheel steering is performed in the direction to suppress the yaw, the engagement force of the clutch 4 is reduced, and as a result, the driving force distribution is performed so that the understeer characteristic is weakened or the oversteer characteristic is obtained.

[0009]

Next, the present invention will be described based on embodiments. FIG. 2 is a block diagram schematically showing one embodiment of the present invention. In the four-wheel drive vehicle shown here, the output shaft of a transmission 21 connected to an engine 20 changes the distribution ratio of the driving force. The vehicle is connected to a rear wheel 23 and a front wheel 24 via a four-wheel drive device 22 which can be used. This four-wheel drive device 22
For example, the one generally used in the past can be used.For example, the differential rotation of the front and rear wheels is allowed and the torque is distributed through a differential gear or a planetary gear, and the differential action is performed by a multi-plate clutch. It is possible to use a device having a configuration in which the torque distribution ratio is changed steplessly or stepwise by limiting.

The control for changing the distribution ratio of the torque to the front and rear wheels can be executed directly by controlling the hydraulic pressure for engaging the above-described differential limiting clutch. (4WD-ECU)
(Hereinafter abbreviated as a four-wheel drive control device) 25 is provided. This is mainly composed of a central processing unit (CPU), a storage device (RAM, ROM) and an input / output interface (not shown), and performs calculations based on input data. The hydraulic pressure of the differential limiting clutch is changed according to the following. As a means for changing the hydraulic pressure of the differential limiting clutch, widely known hydraulic control devices and hydraulic circuits such as a linear solenoid valve and a duty solenoid valve can be adopted. In addition, signals such as vehicle speed, longitudinal acceleration, lateral acceleration, rotation speeds of front and rear wheels, stop signals, failure signals of various sensors, and the like are input to the four-wheel drive control device 25 as data for control.

The four-wheel drive vehicle shown in FIG. 2 is provided with a four-wheel steering device for steering the front wheels 24 or the rear wheels 23 according to the running state of the vehicle, which is picked up from the front wheel steering mechanism 26. A four-wheel steering electronic control unit (4WS) that performs calculations based on the steering angle δ, the actual yaw rate γ detected by the yaw rate sensor 27, and other data such as the vehicle speed.
-ECU) (hereinafter abbreviated as four-wheel steering control device) 28
And a rear wheel steering mechanism 29 controlled by the four-wheel steering control device 28. The four-wheel steering control device 28 includes a central processing unit (CPU) and a storage device (RAM, RO, etc.), similarly to the four-wheel drive control device 25 described above.
M) and an input / output interface (not shown) as main components. Based on the calculation result, the rear wheel 23 is steered in a direction to increase the yaw, that is, in a phase opposite to that of the front wheel 24, or the yaw is controlled. It is configured to steer in the suppressing direction, that is, in the same phase as the front wheels 24. In addition,
As the rear wheel steering mechanism 29, a structure that drives a rear wheel steering linkage to give a steering angle to the rear wheel 23, or that moves a suspension bar to give a steering angle to the rear wheel 23 is adopted. be able to.

A four-wheel drive control device 25 and a four-wheel steering control device 28 are connected so as to be able to perform data communication. The distinction between the in-phase steering and the reverse-phase steering of the wheel 23 and the actual yaw rate γ and the steering angle δ are transmitted.

The four-wheel steering control device 28 controls the steering of the rear wheel 23 based on input data such as the steering angle δ and the actual yaw rate γ. Based on input data such as γ, vehicle speed V, steering angle δ, etc., the rotational speed difference between the front and rear wheels and the deviation between the target yaw rate and the actual yaw rate are obtained, and the clutch hydraulic pressure of the differential limiting clutch is controlled according to these differences. Then, a target yaw rate serving as basic data for the control is obtained. Hereinafter, an example of a control routine performed by the four-wheel drive control device 25 will be described.

[0014] Figure 3 is a flow chart for controlling the clutch oil pressure P _CD differential limiting clutch for determining the distribution ratio of the driving force to the front and rear wheels, the actual steering angle [delta], each wheel calculated from the steering angle in step 1 Speed v, yaw rate γ, front and back Gx
, And the lateral Gy, and then in step 2, the vehicle speed (vehicle speed) V is estimated 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 RR) / 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, the target yaw rate γ ₀ is calculated. This target yaw rate γ ₀ is determined by the vehicle speed V
And determined based on the steering angle delta] f of the front wheels 24, One example of the operation expression, a _{γ 0 = K1 (v) ·} δf, and this factor K1 (v) is K1 (v) = V / [L (1 + Kh) V ² ]. Here, L is the wheelbase and Kh is the stability factor.

Next, in step 6, a deviation Δγ (= γ (γ ₀ −γ)) between the target yaw rate γ ₀ and the actual yaw rate γ is calculated. Here, 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 used as the deviation Δγ for the following reason. 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.

[0016] Then the engagement pressure P _CD differential limiting clutch to vary the distribution of drive force to front and rear wheels, the rotational speed difference between the front and rear wheels Δ
The value is obtained by multiplying a value based on N _FR by a value based on the deviation Δγ between the target yaw rate γ ₀ and the actual yaw rate γ. These values or the control gain for obtaining the values differ depending on the situation of the four-wheel steering. Hereinafter, a value based on the rotational speed difference ΔN _FR between the front and rear wheels and a target yaw rate γ ₀
And a value based on the deviation Δγ between the actual yaw rate γ and the actual yaw rate γ will be described.

The four-wheel steering controller 28 sets the steering angle δr of the rear wheel 23 based on the following equation when the front wheel 24 is steered.

Δr = R1 (V) · δf + R2 (V) · γ Here, R1 (V) is a steering angle proportional coefficient, and a value shown in the map of FIG. 4 is adopted as an example. Δf is the actual steering angle of the front wheels. Further, R2 (V) is a yaw rate feedback coefficient, and the value shown in the map of FIG. 5 is adopted as an example. And γ is the actual yaw rate. These coefficients R1
Since (V) and R2 (V) are the values shown in FIGS. 4 and 5, the value of the rear wheel steering angle δr at the time of low vehicle speed becomes negative, so-called reverse phase steering. When the vehicle speed is high, the value of the rear wheel steering angle δr becomes positive and the steering is performed in phase.

[0019] Figure 6 according to the condition of four-wheel steering, which shows a subroutine for setting the pressure value P (ΔNFR) based on the rotation speed difference .DELTA.N _FR of the front and rear wheels, the four-wheel steering in step 10 Status From the four-wheel steering control device 28 to the four-wheel control device 2
5 is received, the status of the four-wheel steering is determined in step 11
If the rear wheel steering angle δr is in the direction to suppress yaw, the routine proceeds to step 12, where the predetermined pressure value P
Select 1 (ΔNFR). Conversely, if the rear wheel steering angle δr is in the direction to increase the yaw and the determination result in step 11 is “no”, the process proceeds to step 13 and the pressure value P1 (ΔNFR) adopted in step 12 A pressure value P2 (ΔNFR) having a larger gain is selected. These pressure values basically have a functional relationship that increases with an increase in the difference between the rotational speeds of the front and rear wheels.
It is as follows. Therefore, in the control in step 12 or step 13, the map in FIG. 7 may be stored in advance, and a predetermined pressure value may be selected from the map based on the determination result in step 11.

The pressure value according to the control condition of the four-wheel steering can also be obtained by directly calculating. For example, P (ΔNFR) = K3 [sign (γ) · δr] · P0 ( ΔNFR). Where K3 [sign (γ) · δr] is
In the correction coefficient, sign (γ) is the sign of the yaw rate, and P0 (ΔNFR) is a predetermined reference pressure value.

FIG. 8 shows a subroutine for setting the pressure correction coefficient K2 (Δγ) based on the yaw rate deviation Δγ according to the state of the four-wheel steering. After the four-wheel drive control device 25 receives from the steering control device 28, the state of the four-wheel steering is determined in step 21. If the rear wheel steering angle δr is in the direction to suppress yaw, the process proceeds to step 22. Then, a predetermined pressure correction coefficient Ka (Δγ) is selected. Conversely, when the rear wheel steering angle δr is in the direction to increase the yaw, step 2
If the result of the determination in step 1 is "no", the process proceeds to step 23, where the pressure correction coefficient Ka (Δγ) adopted in step 22 is used.
A pressure correction coefficient Kb (Δγ) having a larger gain is selected. Basically, these pressure correction coefficients are set to values smaller than “1” when the yaw rate deviation Δγ has a negative (−) understeer tendency (drift out tendency),
Also a coefficient is set to "1" value greater than when oversteer as the yaw rate deviation Δγ is positive (+) of (spin tendency), the far Riyo 9 One example thereof
Is a coefficient that changes according to the rate deviation Δγ . Therefore, the control in step 22 or step 23 is performed as shown in FIG.
May be stored in advance, and a predetermined pressure correction coefficient may be selected from the map based on the determination result of step 21.

The pressure correction coefficient according to the control condition of the four-wheel steering can also be obtained by directly calculating. For example, K (Δγ) = K3 [sign (γ) · δr] · K0 (Δγ). Where K3 [sign (γ) · δr] is
In the correction coefficient, sign (γ) is the sign of the yaw rate, and K0 (Δγ) is a pressure correction coefficient serving as a predetermined reference.

The pressure value P (Δ
NFR) and the pressure correction coefficient K2 (Δγ)
Is multiplied by engaging pressure P _CD differential limiting clutch required in. The pressure value P multiplied here (ΔNFR)
And pressure compensation coefficient K2 ([Delta] [gamma]), since is set to a larger value when it is steered wheel so as to increase the yaw, engagement pressure P _CD differential limiting clutch to increase the yaw High pressure in the state of four-wheel steering,
As a result, the driving force is distributed to the front and rear wheels so that the vehicle tends to understeer. Also if it is steered wheel to suppress yaw, to the contrary, becomes lower engaging pressure P _CD, weaken the understeer, or driven against the front and rear wheels so that the oversteer Power is distributed.

That is, the distribution of the driving force to the front and rear wheels by the four-wheel drive device 22 takes into account not only the rotational speed difference between the front and rear wheels and the deviation between the target yaw rate and the actual yaw rate, but also the steering situation of the four-wheel steering device. Since the driving force is distributed to the front and rear wheels so as to suppress the increase and decrease of the yaw caused by the four-wheel steering device, the understeer characteristics may become excessively strong or vice versa. Is prevented. In other words, both the stability and the turning property are improved.

In the above-described embodiment, a map of the pressure value based on the rotational speed difference between the front and rear wheels and a map of the pressure correction coefficient based on the yaw rate deviation are used, and two kinds of values are selected according to the situation of the four-wheel steering. Although the maps that can be used are shown, these maps may be maps that can select more various values according to the situation of the four-wheel steering. Further, in the above embodiment, both the pressure value based on the rotational speed difference between the front and rear wheels and the pressure correction coefficient based on the yaw rate deviation are changed according to the condition of the four-wheel steering.
In the present invention, only one of the pressure value and the pressure correction coefficient may be changed according to the condition of the four-wheel steering to control the engagement hydraulic pressure of the clutch of the four-wheel drive device. Also, in the above-described embodiment, the distribution of the driving force to the front and rear wheels is described as an example in which the configuration is changed by limiting the differential action by the differential gear mechanism by the clutch.
The present invention is not limited to the above embodiments,
In short, what is necessary is just to change the distribution ratio of the driving force to the front and rear wheels according to the clutch engagement force.

[0026]

As described above, according to the present invention,
When the vehicle is steered by the four-wheel steering system to increase the yaw, the driving force is distributed to the front and rear wheels so that the vehicle tends to understeer, and conversely, the steering is performed by the four-wheel steering system to suppress the yaw. In this case, since the driving force is distributed to the front and rear wheels so that the vehicle tends to oversteer, for example, even when the reverse phase steering is performed at a low vehicle speed, the vehicle does not excessively oversteer. In addition, even if in-phase steering is performed at a high vehicle speed, an excessive understeering tendency is prevented. Therefore, according to the present invention, the distribution control of the driving force in consideration of the situation of the four-wheel steering can be performed, and the stability and the turning performance 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 map of a steering angle proportional coefficient for obtaining a rear wheel steering angle.

FIG. 5 is a map of a yaw rate feedback coefficient for obtaining a rear wheel steering angle.

FIG. 6 is a flowchart showing a subroutine for selecting a pressure value based on a rotational speed difference between front and rear wheels according to a situation of four-wheel steering.

FIG. 7 is a map that defines pressure values based on the difference between the rotational speeds of the front and rear wheels.

FIG. 8 is a flowchart showing a subroutine for selecting a pressure correction coefficient based on a yaw rate deviation in accordance with a four-wheel steering situation.

FIG. 9 is a map that defines a pressure correction coefficient based on a yaw rate deviation.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 front wheel 2 rear wheel 3 four-wheel steering device 4 clutch 5 four-wheel steering control detecting means 6 fastening force calculating means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B60K 17/348 B62D 6/00 B62D 101: 00 B62D 113: 00 B62D 137: 00

Claims (1)

(57) [Claims] 1. A four-wheel steering device that steers a rear wheel in accordance with steering of a front wheel, and engages with a fastening force determined based on a difference in rotation speed between front and rear wheels and a deviation between a target yaw rate and an actual yaw rate. A driving force distribution device for a four-wheel drive vehicle with a four-wheel steering device having a clutch that changes the distribution of the driving force to the front and rear wheels, wherein the four-wheel steering device detects a situation of four-wheel steering by the four-wheel steering device When the four-wheel steering control detecting means detects that the four-wheel steering is being performed in the direction to increase the yaw, the steering force of the clutch is transmitted to the front wheel.
Corrected according to yaw rate deviation to increase power distribution
And , when it is detected by the four-wheel steering control detection means that the four-wheel steering in the direction to suppress the yaw ,
The distribution of the driving force to the rear wheels increases due to the engagement force of the clutch.
Driving force distribution device for a four-wheel steering system with four-wheel drive vehicle, characterized in that it comprises a tightening force calculating means you corrected according to the yaw rate deviation to so that.