JPH05278489A - Driving force distribution control device for four-wheel drive vehicle - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain vehicle motion characteristics that match the driver's sensitivity. A target yaw rate setting means 1, an actual yaw rate detecting means 2, a comparing means 3 for comparing a target yaw rate and an actual yaw rate, a driving force distribution device 4 for distributing a driving force to front and rear wheels of a vehicle, and a comparing means. Of the four-wheel drive vehicle, which is controlled based on the comparison result in 3 to change the distribution ratio of the driving force to the front and rear wheels so that the actual yaw rate matches or approximates the target yaw rate. A force distribution control device having a road surface friction coefficient detecting means 6 for detecting a road surface friction coefficient, and the target yaw rate setting means 1
However, the target yaw rate is set to a smaller value as the detected road friction coefficient is smaller.

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, since the turning of the vehicle is performed by the side force generated between the tire and the road surface, the road surface friction coefficient greatly affects the behavior of the vehicle at the time of turning, and for example, the target yaw rate is set according to the high μ road having a large friction coefficient. In this case, on a low μ road having a small friction coefficient, the driver may try to turn more gently than on a high μ road, but the control may act sensitively to reduce stability. On the other hand, when the target yaw rate is set according to the low μ road, the followability of the yaw rate control may be deteriorated on the high μ road, and the turning performance may be deteriorated.

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 regardless of the friction coefficient (μ) of the road surface. To do.

[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 ratio control means (5) for changing a drive power distribution ratio to wheels, comprising a road surface friction coefficient detection means (6) for detecting a road surface friction coefficient. The target yaw rate setting means 1 is configured to set the target yaw rate to a smaller value as the detected road surface friction coefficient is smaller. Than it is.

[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 road surface friction coefficient is detected by the road surface friction coefficient detecting means 6. The target yaw rate setting means 1 sets the target yaw rate to a smaller value as the road surface friction coefficient detected by the road surface friction coefficient detecting means 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 matches the target yaw rate. Therefore, even if the road surface friction coefficient is small and it is difficult to turn, and on the other hand, the road surface coefficient is large and it is easy to turn, the vehicle makes a turn that is close to the driver's image and improves maneuverability. To do.

[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.
The steering angle sensor 27, the yaw rate sensor 28, the wheel speed sensor 29 provided for each wheel, the road surface friction coefficient (road surface μ) sensor 30, and other sensors are input to the. 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, and the road surface μ are read, then in step 2, the vehicle speed (vehicle speed) V is estimated from the wheel speed v, and The rotation speed N is obtained. Further, in step 3, the front wheel rotational speed N _F and the rear wheel rotational speed N _R are calculated as the average rotational speeds of the left and right wheels (N _F =
It is _{calculated as} (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, 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, it is calculated by the following equation: K _{1 (v)} = V / {L (1 + K _h · V ² )}. However, in the above electronic control unit 26 according to the present invention, according to the road surface μ (coefficient of friction). Changed coefficient K _{1 (v)}
To calculate the target yaw rate γ ₀ .

That is, in FIG. 4, first, in step 20,
To determine the road surface μ. Next, at step 21, it is judged whether or not the road surface μ is equal to or less than a first reference value (for example, 0.2) set in advance, and if the judgment result is “yes”, at step 22, K _{1 (v)} KL _(v) is adopted as This coefficient K _{L (v)} is a value that is mapped in advance according to the vehicle speed V,
The target yaw rate γ ₀ is calculated by substituting this into the above equation (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 road surface μ is equal to or less than a second reference value (for example, 0.4). If the determination result is “yes”, in step 25, the value of K _{1 (v)} is determined. As the above, a value obtained by interpolating the above-mentioned K _{L (v)} and a slightly larger value K _{M (v)} which is previously mapped and determined by the road surface μ is adopted. If the determination result in step 24 is "no", it is determined in step 26 whether or not the road surface μ is the third reference value (eg, 0.6) or less, and if the result is "yes", In step 27, as the value of K _{1 (v),} a value obtained by interpolating the above-mentioned K _{M (v)} and a value slightly larger than this K _{H (v)} determined by mapping in advance on the road surface μ is adopted. Furthermore, if the result of the determination in step 26 is "no", then 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 used by using K _{1 (v)} corresponding to the road surface μ adopted in the respective steps 25, 27 and 28.
Is calculated (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, when the road surface μ is small and the vehicle is in a traveling state where it is difficult 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 accordingly. On the other hand, on the other hand, if the road surface μ is large and the vehicle is in a traveling state in which it is easy to turn, 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 to match it,
If you judge that the road surface is slippery and try to make a gentle turn, the turning characteristics (steer characteristics) will be appropriate, and if you decide that the road surface is difficult to slip and try to make a swift turn, you will make a corresponding turn. As a result, it is possible to obtain a vehicle motion characteristic suitable for the driver's sensitivity.

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-mentioned embodiment, three kinds of values of K _{1 (v)} are prepared by mapping, and these are selected according to the road surface μ, and the intermediate value between them is 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 road surface μ.

[0016]

As is apparent from the above description, according to the present invention, the road surface μ that affects the turning characteristics is configured to be included as one of the parameters for obtaining the target yaw rate, and when the road surface μ is small, The target yaw rate is set to a small value, and on the contrary, when the road surface μ is large, the target yaw rate is set to a large value, so that the turning characteristics match the running image that the driver holds by judging the road surface state.
In other words, it is possible to obtain the vehicle motion characteristics that match the driver's sensibilities, which in turn improves 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]

 DESCRIPTION OF SYMBOLS 1 target yaw rate setting means 2 actual yaw rate detection means 3 comparison means 4 driving force distribution device 5 driving force distribution ratio control means 6 road surface friction coefficient detection means

Claims (1)

[Claims] 1. A comparison for comparing a target yaw rate and a real yaw rate with 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. Means, a driving force distribution device for distributing the driving force to the front and rear wheels of the vehicle, and the driving force to the front and rear wheels so that the actual yaw rate matches or approximates to the target yaw rate controlled based on the comparison result by the comparison means. In a drive force distribution control device for a four-wheel drive vehicle, which comprises a drive force distribution rate control means for changing the distribution rate of the vehicle, a road surface friction coefficient detecting means for detecting a road surface friction coefficient is provided,
The drive force distribution control device for a four-wheel drive vehicle, wherein the target yaw rate setting means is configured to set the target yaw rate to a smaller value as the detected road surface friction coefficient is smaller.