JP2887827B2 - Differential limit control device for left and right wheels of 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 differential limiting control device for left and right wheels of a vehicle having a differential limiting mechanism for limiting differential between left and right wheels at least depending on a steering angle.

[0002]

2. Description of the Related Art When a differential limiting force is applied between the left and right wheels of a turning vehicle, the force acts in a direction that impedes turning, that is, in a direction that attempts to return the vehicle to a straight traveling state. This effect will be referred to herein as an anti-yaw moment due to differential limiting. This anti-yaw moment works regardless of whether the vehicle is accelerating or decelerating, as long as the right and left wheels are within the limits of the tire friction circle. Therefore,
By effectively utilizing this effect, it becomes possible to control the behavior of the vehicle due to turning and turning back of the steering in a direction more in line with the driver's intention.

[0003] Conventionally, as a technique for limiting and controlling the differential between left and right wheels at the time of turning of a vehicle and using the action of an anti-yaw moment to improve the responsiveness and convergence of the vehicle to steering, there are the following techniques. Have been proposed.

For example, Japanese Patent Application Laid-Open No. 1-1101236 proposes a technique for reducing the differential limiting force when the steering angle (δ) is smaller than a predetermined value or when the steering angle (δ) is larger than a predetermined value. Have been.

Japanese Patent Laid-Open Publication No. Sho 62-241732 discloses that the turning start or the turning end is judged based on the lateral acceleration (Yg) of the vehicle body, and the differential limiting force is reduced at the start of turning to improve the turning performance. A technology has been proposed that improves the return of the vehicle to a straight line by increasing the differential limiting force in the latter half of the turn.

Further, Japanese Patent Application Laid-Open No. 4-244429 discloses that when the steering wheel is turned more and when the steering wheel is turned back, the case is further divided. As the additional turning speed (dδ / dt) is higher, the differential limiting force is reduced to enable a small turning, and when turning back, the larger the turning back amount (dδ) is, the higher the turning back speed (dδ / dt) is. A technique has been proposed in which the higher the dt), the greater the differential limiting force to enable a stable large turning.

[0007]

However, the differential limiting control at the time of turning includes a) cutting from a state close to straight running, b) returning from a state close to straight running, and c) steering already considerably turned. If it is attempted to perform appropriate control under various conditions, such as turning back from the set state, or d) further turning, e) steering during acceleration, f) steering during deceleration, the control becomes complicated. In addition, there is still a problem that it is very difficult to find an index of the differential limiting force that is optimal for the running state at that time.

For example, Japanese Patent Application Laid-Open No. 4-244429 described above
Also in the technology proposed in
In practice, the differential limiting force is determined in consideration of the vehicle speed V, the accelerator opening A, the centripetal acceleration Yg, and the like in addition to the additional turning speed dδ / dt. Although required, nevertheless, complete control may not always be possible.

[0009] To explain this situation more specifically, the technology disclosed in Japanese Patent Application Laid-Open No. 4-244429 is
No consideration is given to the steering angle δ itself, that is, how much the steering is currently turned. However, each state, such as zero steering angle (straight running state), small steering angle (large turning), or large steering angle (small turning), is actually greatly involved in determining the differential limiting force. Should.

However, even if the steering angle δ has the same value, the meaning to be taken is completely different depending on whether it is a value taken when the steering wheel is turned back or a value taken when the steering wheel is turned further. Come. for that reason,
In the technology disclosed in JP-A-4-244429,
It is considered that the absolute value of the steering angle is not used as a control index, but the centripetal acceleration Yg, the vehicle speed V, the accelerator opening A, and the like are considered instead.

However, in reality, it is not easy to consider these comprehensively, and the required capacity of the computer becomes enormous, and the design may become inappropriate due to the large number of parameters to be considered. It gets higher.

Further, as a more realistic problem, the expected movement of the vehicle is completely reversed between the turning (turning) and the turning back, so that it is an essential requirement to be judged.
How to determine this is also an important issue.
Generally, one direction is positive and the other direction is negative with reference to zero steering (straight running). In the positive region, the steering angle increases when the steering angle δ increases and returns when the steering angle δ decreases. There is a method of dividing the cases.

However, in the method of judging the turning back and returning from the positive / negative value of the area and the increase / decrease state of the steering angle δ in this manner, the command value of the differential limit is discontinuous when switching between the turning back and the returning. There is a problem of drastic change. This problem is particularly remarkable when the vehicle shifts from a positive steering range to a negative steering range while the steering itself is continuously turned to one side on an S-shaped road or the like.

As for the problem of the discontinuity of the command value, no effective solution has been proposed in the past.

The present invention has been made in view of such a conventional problem, and has a small number of parameters to be taken into consideration. The difference between the left and right wheels of the vehicle can be obtained without any discontinuous sudden change in the command value, and an appropriate differential limiting force can be obtained in any turning state (with regard to the responsiveness and convergence control of the vehicle to steering). It is an object to provide a control device.

[0016]

SUMMARY OF THE INVENTION As shown in FIG. 1, the present invention provides a vehicle with a differential limiting mechanism for limiting the differential between left and right wheels at least depending on the steering angle. In the differential limiting control device, means for detecting the steering angle δ with one direction being positive and the other direction being negative based on zero steering angle, and calculating the steering angular velocity dδ / dt from the detected steering angle δ. Calculation means, steering angle δ and steering angular velocity d
means for multiplying each value of δ / dt, and at least the multiplication result δ
Depending on * dδ / dt, when the multiplication result δ * dδ / dt is small, the differential limiting force of the differential limiting mechanism is increased, and when the multiplication result δ * dδ / dt is large, the differential limiting force is increased. And means for reducing the above problem.

The present invention further considers the vehicle speed, and increases the gain when the multiplication result δ * dδ / dt is reflected in the increase / decrease of the differential limiting force when the vehicle speed is high, and increases the gain when the vehicle speed is low. If the gain is reduced, a better effect can be obtained.

[0018]

In the present invention, in order to obtain the optimum value of the differential limiting force during turning of the vehicle, the invention was developed by drastically revising what parameter should be used and how it should be reflected.

As a result, the steering angle δ is detected in consideration of whether the steering angle is positive or negative with reference to zero steering angle, the steering angular velocity dδ / dt is obtained from the detected steering angle δ, and these values are multiplied. When the multiplication result δ * dδ / dt is small, the differential limiting force is increased, and when it is large, the differential limiting force is decreased.

In the present invention, since the product of the steering angle δ and the steering angular velocity dδ / dt is obtained as described above, the steering angle δ is either positive or negative, that is, whether the steering angle δ is left or right. Δ * dδ even when steering to the side
When / dt is positive, it can be determined that the wheel is turned (increased), and when / dt is negative, it is determined that the wheel is returned.

When the steering wheel is turned, the differential limiting force is reduced as the steering angle δ at the time of turning is increased and as the turning speed dδ / dt is increased. As a result, the anti-yaw moment due to the differential limitation is reduced, and the vehicle is more easily turned. That is, the larger the steering angle δ when turning, and the faster the steering speed dδ / dt when turning, the more easily the vehicle turns.

On the other hand, at the time of turning back, the differential limiting force increases as the steering angle δ at the time of turning back increases and the steering speed dδ / dt at which the turning back increases increases. As a result, the anti-yaw moment due to the differential limitation increases, and the vehicle is easily returned to the straight traveling state. That is,
As the steering angle δ at the time of turning back is larger, and as the steering speed dδ / dt at the time of turning back is faster, a state in which the vehicle returns to the straight traveling state more strongly is formed.

If the gain when reflecting the multiplication result δ * dδ / dt in the increase / decrease of the differential limiting force is made dependent on the vehicle speed, finer control can be realized.
For example, when accelerating while turning back the steering wheel after turning right or left at an intersection or the like, if the gain for the multiplication result δ * dδ / dt is large, tight corner braking may occur in some cases. , While increasing the gain at high vehicle speeds, it is possible to easily realize such control as to secure the straight running stability at high speed running or the change stability of the running lane.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 2 schematically shows a system according to this embodiment.

In the figure, reference numerals 2 and 4 denote left and right wheels of the vehicle, 6
Is a differential device (differential device). By the function of the differential device 6, even when the vehicle turns in a corner or in a state where a difference in rotation between the left and right wheels is to be generated, the vehicle can be driven with an appropriate rotation speed difference without slipping both wheels.

The differential limiting means 8 is attached to the differential device 6, and specifically, the drive shafts 2a, 4a of the left and right wheels.
These members can be connected by, for example, a wet multi-plate clutch or the like driven by a duty solenoid 8a so that the members cannot rotate relative to each other. The differential limiting force of the differential limiting means 8 is controlled by the differential limiting control means 10. The vehicle speed V from the vehicle speed detecting means 12 and the steering angle δ of the steering from the steering angle detecting means 14 are input to the differential limit control means 10, and based on these input signals, the differential to be generated in accordance with a control flow described later. The command value of the limiting force is obtained, and the corresponding duty signal is sent to the duty solenoid 8a of the differential limiting means 8.

In response to the duty signal, the duty limiting means 8 drives the duty solenoid 8a, and by adjusting the hydraulic pressure of the multi-plate clutch by this driving,
The coupling force between the drive shafts 2a, 4a, that is, the differential limiting force is increased or decreased.

As for the hardware configuration of the system relating to the differential limitation, various configurations are already known.
Here, we will only give an overview of the system.

Next, a control flow executed by the differential limit control means 10 will be described with reference to FIG.

First, at step 102, the steering angle δ is detected. In step 104, the vehicle speed V is detected.

In step 106, a steering angular velocity dδ / dt is calculated from the steering angle δ. In step 108, δ *
The value of dδ / dt is calculated.

In step 110, the calculation of the command value T1 for limiting the differential (in order to improve the responsiveness and convergence of the vehicle to the steering) includes the value of δ * dδ / dt and the gain K1.
Obtained from the map as a function f1 of _* .

FIG. 4 shows the value of δ * dδ / dt and the gain K1 _*.
And the relationship between the differential limiting command value T1 and the differential limiting command value T1. In the figure, the horizontal axis indicates the value of δ * dδ / dt, and the vertical axis indicates the differential limit command value T1. δ * dδ / dt becomes negative at the time of cutback and positive at the time of cut. As apparent from the figure, the gain K1 _* When cut, K1 _P is set, [delta] * d? / As when dt is large, i.e., as when a large steering angle, the more time or cut speed is high differential limiting The command value T1 is set to be small. The origin of the vertical axis is determined in relation to T2 described later. In any case, the value of T1 increases in the upper part of the figure.

On the other hand, because when the cuts back the gains K1 _*, K1 _M is set, [delta] * d? / As the value of dt is small ([delta] * d? / Dt is the time switches back is a negative value, |
The greater the value of δ * dδ / dt |), the greater the differential limit command value T1. The larger the value, that is, the closer the δ * dδ / dt approaches zero, the greater the differential limit command value T1. It is set to be smaller. As a result, when turning back, the differential limiting force is strengthened as the steering angle δ at the time of turning back is increased, and as the speed dδ / dt at the time of turning back is increased, the vehicle is kept straight ahead. You can get a strong return.

In this embodiment, since the value of δ * dδ / dt (specifically, the sign thereof) is used to judge whether the steering wheel is to be turned or turned back, it is generated when the steering wheel is turned and when the steering wheel is turned back. While making the differential limiting force greatly different as a whole, the generated differential limiting force is always continuous in any of the notch → cutback, cutback → cut, and the differential limiting force becomes discontinuous. There is no sudden change. That is, for example, when the steering continuously changes from right turning to left turning in an S-shape or the like,
On the way, there occurs a point in time when the state changes from cutback to cut. However, even in such a case, since the steering angle δ = 0 is passed, δ * dδ / dt increases from a large negative value toward zero, and then the sign is changed to increase the positive value. It becomes a mode. Therefore, the differential limit command value T1 will continue to decrease as long as the steering wheel is rotating in a fixed direction, regardless of switching from turning back to turning. For this reason, while in the cutback area, it is easy to return in a straight running state due to a very strong differential restriction, and after entering the cut area, the effect that the differential limiting force is further reduced and it becomes easy to cut becomes very natural. And it can be obtained smoothly.

When returning to the state again from this state, since δ * dδ / dt becomes a large negative value again, the differential limiting command value T1 again becomes a large value, and as a result, a large differential limiting force is obtained. As a result, a force that makes it easy to return to the straight traveling state acts. Even in this case, since δ * dδ / dt is continuously changed while dδ / dt always passes through zero, δ * dδ / dt is never discontinuous even if it greatly changes rapidly according to the steering movement. The change is completely consistent with the change in steering movement intended by the driver.

Further, according to the method of this embodiment, the differential limiting force is further reduced at the time of further turning from the turning state than at the time of turning from the straight traveling state, and the turning state at a larger steering angle is reduced. When the vehicle returns to the straight traveling state, a larger differential limiting force is applied.

Further, at the time of faster steering, the speed of increase and decrease of the differential limiting force is faster than at the time of slow steering. Such a tendency completely corresponds to a traveling state in which the driver desires a behavior in which the driver easily turns, and a traveling state in which the behavior in which the driver easily returns to the straight traveling state is desired.

Therefore, by obtaining the command value of the differential limiting command value T1 using the value of δ * dδ / dt as an index, it becomes possible to obtain appropriate vehicle behavior at any steering operation.

Incidentally, the inclination angle K1 _* (K
1 _M, K1 _P) is, [delta] * gain when the value of d? / Dt is reflected to the differential limiting force, i.e. [delta] * d? / Dt is the how differential limiting force depending on it when changed a predetermined amount This corresponds to a gain that determines whether to change. This gain K1 _*
The by gain K2 shown in FIG. 5, and change according to the vehicle speed, i.e. the gain K1 _* * K2, the vehicle speed is a value very close to zero when low, even when such a higher gain as the vehicle speed becomes higher Good.

That is, when the vehicle speed is low, δ * dδ /
Since the gain with respect to dt is small, even if the vehicle accelerates while turning back after turning right or left at an intersection, etc. (because the differential limiting force is not set so large)
Tight corner braking can be prevented from occurring. Also, at high vehicle speed, δ or dδ / dt does not originally become so large, but by increasing the gain and increasing or decreasing the differential limiting force even when the value of δ * dδ / dt is small, It is possible to change the traveling lane and obtain more stable high-speed straightness.

Returning to the control flow of FIG.
In step 2, the differential limit command value T2 is calculated from the map as a function f2 of the vehicle speed V. This differential limit command value T2 is a command value related to a so-called differential limit which has been generally performed in the related art, and in this embodiment, is a command value which increases according to the vehicle speed V as shown in FIG. 6, for example. You. However, the command value T2 here may have such a characteristic that it decreases in accordance with the absolute value of the steering angle δ as shown in FIG. 7, for example. Of course, the characteristics may be a combination of these.

In step 114, the final differential limit command value T is obtained as T1 + T2. As a result, the steering is turned into the so-called conventional differential limit command value T2,
The control value T1 relating to the vehicle behavior accompanying the return is added, and the differential limit command value T as a whole is determined.

In step 116, a duty signal corresponding to the command value T is output as a hydraulic command value.

[0046]

As described above, according to the present invention,
The turning and turning back of the steering is captured using the value of δ * dδ / dt as an index, and the differential limiting force is increased or decreased accordingly, so that the steering completely matches the vehicle behavior desired by the driver. Vehicle behavior can be assisted by increasing or decreasing the differential limiting force (with continuity of the control command value), and the response and convergence of the vehicle to steering can be improved very smoothly. An excellent effect of being able to do so is obtained.

[Brief description of the drawings]

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

FIG. 2 is a block diagram schematically showing a system of a differential limiting control device to which the present invention is applied;

FIG. 3 is a flowchart showing a control flow executed in the apparatus of the embodiment.

[4] [delta] * d? / Dt and the gain K1 _* (K1 _M, K1
_P ) and a diagram showing the relationship between the differential limit command value T1

FIG. 5 is a diagram showing how the gain K2 depends on the vehicle speed V;

FIG. 6 is a diagram showing how the differential limit command value T2 is made dependent on the vehicle speed V, which has been conventionally performed.

FIG. 7 is a diagram showing how the differential limit command value T2 is made dependent on the steering angle δ, which has been conventionally performed.

[Explanation of symbols]

 δ: Steering angle dδ / dt: Steering angular velocity 2: Left wheel 4: Right wheel 6: Differential device (differential device) 8: Differential limiting means 10: Differential limiting control means

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B60K 23/04 B60K 17/34-17/358

Claims (2)

(57) [Claims] 1. A left and right wheel differential limiting control device provided with a differential limiting mechanism for limiting a differential between left and right wheels at least depending on a steering angle, wherein the steering angle δ is set based on zero steering angle. Means for taking one direction as positive and taking the other direction as negative, means for calculating the steering angular velocity dδ / dt from the detected steering angle δ, and calculating the values of the steering angle δ and the steering angular velocity dδ / dt. Means for multiplying, at least depending on the multiplication result δ * dδ / dt, when the multiplication result δ * dδ / dt is small, the differential limiting force of the differential limiting mechanism is increased, and the multiplication result δ * dδ / dt is increased. means for reducing the differential limiting force when dt is large, and a differential limiting control device for left and right wheels of a vehicle. 2. The vehicle according to claim 1, further comprising means for detecting a vehicle speed, wherein a gain when the multiplication result δ * dδ / dt is reflected in an increase / decrease of the differential limiting force depends on the vehicle speed, and when the vehicle speed is high. A differential limiting control device for left and right wheels of a vehicle, wherein the gain is set large when the vehicle speed is low when the gain is large.