JPH05278488A - Driving force distribution control device for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To provide vehicle operation characteristics which fit the sensitivity of drivers by using a target yaw rate setting means with an acceleration sensor detecting the acceleration of a vehicle to set a smaller value for a target yaw rate as a detected acceleration is smaller. CONSTITUTION:During traveling, an actual yaw rate is detected by an actual yaw rate detection means 2 and acceleration is detected by an acceleration sensor 6. A target yaw rate setting 1 means sets a smaller value for a target yaw rate as acceleration becomes smaller and a comparison means 3 compares an actual rate and a target yaw rate. A driving force distribution rate control means 5 controls driving force distribution rate in such a way that the actural yaw rate will approximate or match the target yaw rate.

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 in which the distribution ratio of the drive force to the front and rear wheels can be changed so that the yaw rate during turning becomes a target yaw rate obtained based on the running state of the vehicle. The present invention relates to a control device that changes the distribution ratio of the.

[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 in a four-wheel drive vehicle also depending on the distribution ratio of the driving force to the front and rear wheels. On the other hand, the yaw rate (yaw angular velocity) when turning is
It is one factor that represents the performance or characteristics of the vehicle, and generally the ideal target yaw rate is determined for each vehicle type,
Further, the value varies depending on the traveling state such as vehicle speed and steering angle. Therefore, for example, in Japanese Unexamined Patent Publication No. 61-229616, a target yaw rate is obtained based on the vehicle speed and the steering angle in a four-wheel drive vehicle, and the torque capacity of the clutch means in the drive system is controlled so as to be the target yaw rate. The device is described. Further, in Japanese Unexamined Patent Publication No. 62-99213 and Japanese Unexamined Patent Publication No. 3-70633, a target yaw rate is obtained based on a vehicle speed and a steering angle, and a distribution ratio of driving force to front and rear wheels is set so as to reach the target yaw rate. The controlling device is described.

[0003]

Generally, the steer characteristic of an automobile is that if the driving force of the rear wheels is large, the tendency of oversteering increases, and conversely, if the driving force of the front wheels is large, the tendency of understeering increases. Is well known. Therefore, as described in each of the above-mentioned publications, the yaw rate at the time of turning can be brought close to or almost equal to the target yaw rate by appropriately changing the driving force at the front and rear wheels. However, as described in each of the above-mentioned publications, the target yaw rate has conventionally been 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 has a great influence on the behavior of the vehicle. For example, when the target yaw rate is set in accordance with the state where the acceleration is large, it is easy to turn in the low acceleration state. The stability may decrease. On the other hand, when the target yaw rate is set according to the low acceleration state, the yaw rate control has poor followability in the high acceleration state, so that the turning performance may decrease.

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

[0005]

The present invention is characterized in that it has the structure shown in FIG. 1 in order to achieve the above object. That is, the present invention compares the target yaw rate setting means 1 for setting the target yaw rate based on the running state of the vehicle, the actual yaw rate detecting means 2 for detecting the actual yaw rate of the running vehicle, and the target yaw rate and the actual yaw rate. And a driving force distribution device 4 that distributes the driving force to the front and rear wheels of the vehicle, and is controlled based on the comparison result of the comparison unit 3 so that the actual yaw rate matches or approximates the target yaw rate. A drive force distribution control device for a four-wheel drive vehicle, comprising: a drive force distribution rate control means 5 for changing a drive force distribution rate to wheels; an acceleration sensor 6 for detecting 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]

In the present invention, the actual yaw rate of the running vehicle is detected by the actual yaw rate detecting means 2 and the acceleration is detected by the acceleration sensor 6. 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 comparison 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 matches the target yaw rate. Therefore, in both the state where it is difficult to turn due to the high acceleration and the state where it is easy to turn due to the small acceleration, on the other hand, the turn is similar to the image held by the driver, and the steering stability is improved.

[0007]

EXAMPLES The present invention will now be described based on examples. FIG. 2 is a schematic view showing an embodiment of the present invention,
The four-wheel drive transfer 10, which is a control target, is provided on the output side of an automatic transmission 12 connected to an engine 11. This transfer 10 distributes the driving force to the rear wheel side and the front wheel side by a planetary gear type center differential 13, and a drive shaft 14 which is an output shaft of an automatic transmission 12 is connected to a carrier 15. The ring gear 16 is connected to the rear propeller shaft 18 via the output shaft 17. On the other hand, sun gear 19
Is connected to a drive sprocket 20, and transmits a driving force to a front propeller shaft 23 via a chain 21 and a driven sprocket 22 wound around the drive sprocket 20. Also, the carrier 15 and the sun gear 19
And a differential limiting clutch 24 is provided between the differential limiting clutch 24 and the differential limiting clutch 24 to increase the distribution ratio of the driving force to the front wheels by increasing the engaging hydraulic pressure, that is, increasing the torque capacity. ..

As a device for controlling the hydraulic pressure 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. There is. The electronic control unit 26 mainly includes 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.
The signal from each sensor is input. Then, the electronic control unit 26 determines the target yaw rate at the time of turning based on these input parameters and controls the hydraulic pressure to the differential limiting clutch 24 so that the deviation between the target yaw rate and the actual yaw rate becomes small. Is becoming

FIG. 3 shows a control routine for controlling the hydraulic pressure of the differential limiting clutch 24 so that the target yaw rate is obtained.
Further, 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 longitudinal G, and the lateral G are read, then in step 2, the vehicle speed (vehicle speed) V is estimated from the wheel speed v, and Rotational speed N of each wheel
Ask for. In step 3, the front wheel rotation speed N _F and the rear wheel rotation speed N _R are calculated as the average rotation speeds of the left and right wheels (N _F = (N _FL + N _FR ) / 2, N _R = (N _RL + N _RR). ) /
See 2). The obtained rotational speeds N _F , N _{R of} the front and rear wheels
From this, the absolute value ΔN _FR of the rotational speed difference between the front and rear wheels is obtained (step 4). Next, in step 5, the target yaw rate γ ₀ is obtained. This is determined by the coefficient K _{1 (v)} corresponding to the vehicle speed V and the steering angle δ. The coefficient K _{1 (v)} is generally the vehicle speed V, the wheel base L, and the stability factor K in the past.
_{From h} and, K _{1 (v)} = V / {L (1 + K _h · V ² )} is calculated by the following equation. However, in the electronic control unit 26 according to the present invention, the coefficient K is changed according to the acceleration G. _The target yaw rate γ ₀ is calculated by using _{1 (v)} .

That is, in FIG. 4, first, in step 20,
To read the vehicle acceleration G. The acceleration G may be a lateral acceleration or a value ((Gx ² + Gy ² ) ^1/2 ) obtained by combining the lateral acceleration and the longitudinal acceleration. Next, at step 21, the acceleration G is set to a predetermined first value.
Is less than or equal to the reference value (for example, 0.2), and if the determination result is “yes”, in step 22,
To adopt the K _{L (v)} as K 1 _(v). This coefficient K _{L (v)} is a value that is mapped in advance according to the vehicle speed V, and is substituted into the above-mentioned equation to calculate the target yaw rate γ ₀ (step 23).

On the other hand, the determination result of step 21 is "no".
If so, it is determined in step 24 whether or not the acceleration G is the second reference value (eg, 0.4) or less. If the determination result is “yes”, then in step 25, the value of K _{1 (v)} is determined. 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 or not the acceleration G is equal to or less than the third reference value (eg, 0.6). If the result is "yes", In step 27, as the value of K _{1 (v),} a value obtained by interpolating K _{H (v)} , which is a value slightly larger than the above K _{M (v)} and which is previously mapped, by the acceleration G is adopted. Furthermore, the judgment result of step 26 is “No”.
If so, the above K _{H (v)} is adopted as the value of K _{1 (v)} . Then, no matter which of the steps 25, 27 and 28 is used, the target yaw rate γ _o is calculated using K _{1 (v)} according to the acceleration G adopted in the respective 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 thus obtained, their deviation Δγ (= γ (γ ₀ -Γ)) is calculated in step 6. If this deviation Δγ is large in the positive direction, there is a tendency to drift out (understeer), and if it is large in the negative direction, there is a tendency to spin (oversteer). To correct this, the differential limiting clutch 2
Correct the engagement hydraulic pressure of No. 4. That is, the vehicle equipped with the transfer 10 shown in FIG. 2 is a four-wheel drive vehicle based on the rear wheel drive, and the distribution ratio of the drive force to the front wheel side is increased by increasing the differential limitation. In the case of the out tendency, it is necessary to increase the distribution ratio of the driving force to the rear wheel side to correct it to the oversteer tendency. On the contrary, in the case of the spin tendency, the driving force of the front wheel side It is necessary to increase the distribution ratio and make it understeer. Therefore, the correction coefficient K _{2 (Δγ)} according to the deviation Δγ is shown in FIG.
As shown in, when Δγ is large in the positive direction,
A value smaller than "1" is set, and a value larger than "1" is set when the value is larger in the negative direction.

On the other hand, the engagement oil pressure P (ΔNFR) of the differential limiting clutch 24 based on the rotation speed difference ΔN _FR between the front and rear wheels is, as shown in FIG. 6, the rotation speed difference ΔN _{RF in} a normal state such as straight running.
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 the correction coefficient K _{2 (} Δγ) ( In step 7), the value is supplied to the limited slip differential clutch 24 as the actual engagement hydraulic pressure P _CD . The relationship between the actual engagement hydraulic pressure P _CD and the front-rear wheel rotational speed difference ΔN _FR is expressed by the deviation Δγ.
If is expressed as a parameter, it is as shown in FIG.

Therefore, in the above-mentioned device, in a traveling state in which the acceleration G is large and it is difficult to turn, the target yaw rate itself is corrected so as to be larger than the normal state, and the distribution of the driving force to the front and rear wheels is controlled to match it. On the contrary, if the vehicle is in a traveling state in which the acceleration G is small and it is easy to turn, the target yaw rate itself is corrected to be smaller than that in the normal state, and the distribution of the driving force to the front and rear wheels is controlled so as to match it, so The (steer characteristic) becomes almost constant without being influenced by the acceleration, and as a result, the vehicle motion characteristic suitable for the driver's sensitivity can be obtained.

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

[0016]

As is apparent from the above description, according to the present invention, the acceleration affecting the turning characteristic is included as one of the parameters for obtaining the target yaw rate, and when the acceleration is small, the target yaw rate is set. Is set to a small value, and conversely, when the acceleration is large, the target yaw rate is set to a large value, so that the turning characteristic is almost constant regardless of the acceleration, and the turning is performed according to the driver's sensitivity. In addition, it is possible to obtain the vehicle motion characteristics, which in turn can improve the maneuverability.

[Brief description of drawings]

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

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

FIG. 3 is a flowchart showing a control routine of an engagement hydraulic pressure of a limited slip differential clutch.

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

FIG. 5 is a diagram showing 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 rotational speed difference 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]

 1 Target Yaw Rate Setting Means 2 Actual Yaw Rate Detecting Means 3 Comparing Means 4 Driving Force Distribution Device 5 Driving Force Distribution Ratio Controlling Means 6 Acceleration Sensors

Claims (1)

[Claims] 1. A target yaw rate based on a running state of a vehicle.
Target yaw rate setting means for setting the
Yaw rate detection to detect the actual yaw rate
Means and ratio comparing target yaw rate and actual yaw rate
Comparing means and driving force for distributing the driving force to the front and rear wheels of the vehicle
Control based on the distribution device and the comparison result of the comparison means
The actual yaw rate matches or approaches the target yaw rate.
Driving force component that changes the distribution ratio of driving force to the front and rear wheels in a similar manner
A drive force distribution control device for a four-wheel drive vehicle equipped with a ratio control means.
In an arrangement, an acceleration sensor for detecting the acceleration of the vehicle,
The target yaw rate setting means has detected a small acceleration.
It is configured to set the target yaw rate to a small value.
Drive force distribution control for four-wheel drive vehicles
apparatus.