JP3191465B2 - Vehicle turning limit judgment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for determining whether a vehicle is at a turning limit.

[0002]

2. Description of the Related Art Several techniques for judging whether or not a vehicle is at a turning limit have been already proposed, one of which is disclosed in Japanese Patent Application Laid-Open No. 62-218281. this is,
A technology that detects an actual lateral acceleration of a vehicle, determines a reference lateral acceleration based on a vehicle speed and a steering angle, and determines that the vehicle has reached a turning limit when the actual lateral acceleration becomes smaller than the reference lateral acceleration. It is.

[0003] This conventional technique does not usually determine that the vehicle has reached the turning limit if the actual lateral acceleration is slightly smaller than the reference lateral acceleration, but only when the difference between the two exceeds a certain value. Is determined to have reached the turning limit. If the actual lateral acceleration is slightly smaller than the reference lateral acceleration, the vehicle is determined to have reached the turning limit if the actual lateral acceleration is slightly smaller than the reference lateral acceleration. This is because there is a possibility that an erroneous determination that the condition has been reached may be made, and sufficient reliability for the determination is not ensured.

[0004]

However, if the conventional technique is implemented in a desirable mode, it is determined that the vehicle has reached the turning limit unless the actual lateral acceleration deviates significantly at a time from the reference lateral acceleration. Therefore, there is a new problem that the fact that the vehicle has reached the turning limit cannot be detected early.

[0005] Based on the above circumstances, the present invention achieves simultaneous suppression of erroneous determination and early detection of a turning limit by using the accumulated value of deviation of the actual value of the turning state amount of the vehicle from the reference value. This was done as an issue.

[0006]

According to the present invention, as shown in FIG. 1, (a) actual turning state quantity obtaining means 1 for obtaining an actual turning state quantity of a vehicle is provided. , (B)
A turning limit determining means for determining that the vehicle is at a turning limit when a cumulative value of a deviation of the obtained actual turning state amount from the reference turning state amount is larger than a reference value; The point is to provide.

The "turning amount" in the present invention includes not only the lateral acceleration but also the yaw rate of the vehicle body.

In the present invention, the "reference turning state amount" is used.
In general, when a cornering characteristic of a wheel, which actually has a linear region and a nonlinear region, is regarded as being an extension of the linear region (hereinafter, “the cornering characteristic is linear, If you consider it ")
The turning state quantity expected to occur in the vehicle is selected.

Further, the "turn limit" in the present invention can be selected from various causes. For example,
A turning limit caused by a shift of the cornering characteristic from a linear region to a non-linear region due to an increase in a tire slip angle, a turning limit caused by a large load transfer between inner and outer wheels of a vehicle, and a road surface It is possible to select a turning limit or the like due to a decrease in the coefficient of friction.

The term "accumulated value" in the present invention generally means the sum of the deviations that have occurred up to this time. There are a narrow sense sum in which the weights of the deviations are made equal to each other and the entirety of the deviations are added, and a weighted sum in which the older the occurrence time, the smaller the weight and the totality of the deviations are added. When selecting the sum in a narrow sense for the “accumulated value”, the value is forcibly restored to 0 every time a certain condition is satisfied, such as when it is determined that the vehicle is at the turning limit. In the case of selecting a weighted sum, if the normal state of the vehicle continues for a long time, the value is automatically attenuated and restored to 0, so that it is forcibly restored to 0. It is not essential.

[0011]

The difference between the actual turning state quantity and the reference turning state quantity, not the deviation itself, is compared with the reference value. Occurs relatively frequently, it is determined that the vehicle is at the turning limit.

Based on such facts, in the vehicle turning limit determining device according to the present invention, the actual turning state amount obtaining means 1 obtains the actual turning state amount of the vehicle and the turning limit determining means 2 obtains the actual turning state amount. If the cumulative value of the deviation of the actual turning state amount from the reference turning state amount is larger than the reference value,
It is determined that the vehicle is at the turning limit.

[0013]

As described above, according to the present invention, since the turning limit of the vehicle is determined from the cumulative value of the deviation of the actual turning state amount of the vehicle from the reference turning state amount, the error of the turning state amount itself is reduced. The effect is obtained that it is possible to detect the turning limit early, while suppressing the erroneous determination due to.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a vehicle turning limit judging apparatus according to an embodiment of the present invention.

This vehicle turning limit determination device is provided in a four-wheel vehicle having wheels disposed on the front, rear, left and right sides of a vehicle body, and determines whether or not the vehicle has reached a turning limit.

The vehicle turning limit determination system will first be described briefly. The yaw rate γ and the lateral acceleration at the center of gravity of the vehicle which are expected to occur in the vehicle when the cornering characteristics of each wheel are considered to be linear. _Gy are respectively calculated to obtain a reference yaw rate γ ^* and a reference lateral acceleration _Gy ^*.
And a cumulative yaw rate deviation ΣΔγ which is a cumulative value of a yaw rate deviation Δγ which is a deviation of the reference yaw rate γ ^{* from} the actual yaw rate γ, and an actual lateral acceleration G _{y of the} reference lateral acceleration G _y ^*.
A cumulative lateral acceleration deviation ShigumaderutaG _y is an accumulated value of the lateral acceleration deviation .DELTA.G _y which is a deviation respectively calculated from either the cumulative yaw rate deviation ΣΔγ is greater than the reference value A, or cumulative lateral acceleration deviation ShigumaderutaG _y reference When the value becomes larger than the value B, it is determined that the vehicle has reached the turning limit.

Reference yaw rate γ ^* and reference lateral acceleration G
_y ^* is based on the equation of motion for the plane motion of the vehicle,
It is determined based on the vehicle speed V and the front wheel steering angle [delta] _f. The details will be described below.

Except for the transient vehicle motion when the vehicle is suddenly accelerated or decelerated or when the steering wheel is quickly operated, both the change in the vehicle speed V and the rolling motion of the vehicle can be ignored. As described above, when it is possible to focus only on the motion of the vehicle traveling at a constant speed in the horizontal plane without the rolling motion, that is, only the planar motion of the vehicle, only the translational motion and the rotational motion of the vehicle need to be considered. In this case, the following two equations of motion generally hold.

[0019] and equation of motion regarding mG _y = F _f + F _r becomes translational movement (also called lateral motion) is the equation of motion related to _{Iγ '= a f F f -a} r F r becomes rotational motion (also referred to as yawing motion) .

Where m: inertial mass of the vehicle (fixed value) F _f : front wheel cornering force (for two left and right wheels) F _r : rear wheel cornering force (for two right and left wheels) I: yaw moment of inertia of vehicle (fixed value) ) Γ ': Yaw rate derivative which is a time derivative of yaw rate γ a _f : Distance between front wheel axle and center of gravity (fixed value) a _r : Distance between rear wheel axle-center of gravity (fixed value)

Since the cornering characteristics are considered to be linear over the entire range of changes in the sideslip angles α _f , α _r of each wheel, the front wheel cornering force F _f is represented by −2C _f α _f , , The rear wheel cornering force F _r is represented by -2C _r α _r .

Here, C _f : front wheel cornering power (average value of left and right wheels) C _r : rear wheel cornering power (average value of left and right wheels) α _f : front wheel side slip angle (average value of left and right wheels) α _r : Rear wheel side slip angle (average value of left and right two wheels)

The front wheel side slip angle α _f is represented by β + a _f γ / V−δ _f , while the rear wheel side slip angle α _r is represented by β−a _r γ / V. Here, “β” represents the vehicle body slip angle at the vehicle center of gravity.

The lateral acceleration G _y and the vehicle body slip angle β
In general, a relationship represented by the following formula is established between the vehicle side slip angle derivative β ′, which is a time differential value of the above, the yaw rate γ, and the vehicle speed V. _Gy = V (β ′ + γ)

As a result, a system that inputs the front wheel steering angle δ _f and outputs the lateral acceleration G _y and the yaw rate γ, respectively,

[0026]

(Equation 1)

This will be described by the following equation.

[0028] In addition, the input of the front wheel steering angle δ _f, the yaw rate γ
The system that outputs

[0029]

(Equation 2)

[0030] made as described by the formula, also enter the front wheel steering angle [delta] _f, systems and outputs a lateral acceleration G _y is

[0031]

(Equation 3)

This will be described by the following expression.

[0033] With such a premise fact, in this vehicle turning limit determination device, based on the vehicle speed V and the front wheel steering angle [delta] _f, and by using them expressions, the reference yaw rate gamma ^* and the reference lateral acceleration G _y ^* Is calculated sequentially.

On the other hand, it is calculated as a weighted sum obtained by adding their entirety deviation by reducing the weighting the older generation timing of the cumulative yaw rate deviation ΣΔγ and cumulative lateral acceleration deviation ShigumaderutaG _y respectively, each deviation Δγ and .DELTA.G _y . Specifically, the cumulative yaw rate deviation ΣΔγ is

[0035]

(Equation 4)

The cumulative lateral acceleration deviation ΣΔG _y is calculated using the following equation:

[0037]

(Equation 5)

Calculated using the following equation. Where s: Laplace operator ΣΔγ (s): Laplace transform of cumulative yaw rate deviation ΣΔγ | Δγ | (s): Laplace transform of absolute value of yaw rate deviation Δγ ΣΔG _y (s): Cumulative lateral acceleration deviation ΣΔG _y what was Laplace transform | ΔG _y | (s): the absolute value of the lateral acceleration deviation .DELTA.G _y as Laplace transformation T: time constant (fixed value)

That is, these two equations are both first-order lag integral equations. When the time constant T is increased to infinity, the accumulated yaw rate deviation ΣΔγ is a narrow sense of the absolute value of the yaw rate deviation Δγ. The cumulative lateral acceleration deviation ΣΔG _y is a sum in a narrow sense of the absolute value of the lateral acceleration deviation ΔG _y .

The reason why the cumulative yaw rate deviation ΣΔγ is not defined as the sum of absolute values of the yaw rate deviation Δγ in the narrow sense is as follows. That is, the sum in a narrow sense is equivalent to assigning the same weight to the plurality of yaw rate deviations Δγ obtained up to this time regardless of the new or old timing of occurrence thereof. Information will be treated equally as information in the past,
This is because the value of the cumulative yaw rate deviation ΣΔγ does not correctly reflect the current turning state of the vehicle. That is, if the weighted sum is adopted, even if there is a time when the yaw rate deviation Δγ is not 0 in the past, if the state where the yaw rate deviation Δγ is 0 continues for a long time, the accumulated yaw rate deviation ΣΔγ is automatically restored to 0 in due course. And
As a result, the value of the cumulative yaw rate deviation ΣΔγ correctly reflects the current turning state of the vehicle. Note that this is also true for the cumulative lateral acceleration deviation ΣΔG _y.

When the above two equations are discretized with respect to time, the following two equations are derived. That is, for the cumulative yaw rate deviation ΣΔγ,

[0042]

(Equation 6)

The following equation is derived, while for the accumulated lateral acceleration deviation ΣΔG _y :

[0044]

(Equation 7)

The following equation is derived.

[0046] In the present embodiment, the cumulative yaw rate deviation ΣΔγ and cumulative lateral acceleration deviation ShigumaderutaG _y is calculated by using them each discretized equations.
However, in these equations, both “k ₁ ” and “k ₂ ” are weight coefficients larger than 0 and smaller than 1, and in the present embodiment, the weight coefficient k ₁ is 1 more than the weight coefficient k _2.
The value is about 00 times smaller . The current information is prioritized over the past information , and the accumulated value is calculated.

[0047] Incidentally, the cumulative yaw rate deviation ΣΔγ and cumulative lateral acceleration deviation ShigumaderutaG _y can be calculated using their respective discretized further simplified equation equation. That is, for example, the cumulative yaw rate deviation ΣΔγ is given by ΣΔγ _(i) = k ₁ ΣΔγ _(i-1) + k ₂ ′ | Δγ | _(i)
Δt can be calculated using the following equation, and the cumulative lateral acceleration deviation ΣΔG _y is given by ΣΔG _{y (i)} = k ₁ ΣΔG _{y (i−1)} + k ₂ ′ | ΔG _y
| _(I) It can be calculated using the equation Δt. However, in these two equations, “Δt” represents a sampling cycle.

As shown in FIG. 2, the vehicle turning limit determining apparatus for executing the above-described contents includes a yaw rate sensor 10, a lateral acceleration sensor 12, a front wheel steering angle sensor 14, a vehicle speed sensor 16, It is configured to include the computer 20. The yaw rate sensor 10 detects the actual yaw rate γ of the vehicle as positive when counterclockwise and negative when clockwise. The lateral acceleration sensor 12 is for detecting the right the actual lateral acceleration G _y of the vehicle center of gravity forward, the negative left. The front wheel steering angle sensor 14 detects the front wheel steering angle δ _f
Is detected as positive for counterclockwise and negative for clockwise.
The vehicle speed sensor 16 detects a vehicle speed V which is a running speed of the vehicle.

The computer 20 stores in its ROM various routines including a turning limit routine shown in the flowchart of FIG.
The above-mentioned contents are executed by executing these routines.

The turning limit routine of FIG. 3 is executed at regular intervals. In each execution, first, in step S1 (hereinafter simply referred to as S1; the same applies to other steps), the actual yaw rate γ, the actual lateral acceleration G _y , the front wheel steering angle δ _f and the vehicle speed V are respectively detected by various sensors. Is done.

[0051] Subsequently, in S2, as described above, the reference yaw rate gamma ^* is calculated based on the front wheel steering angle [delta] _f and the vehicle speed V. Thereafter, in S3, the current value of the deviation Δγ between the reference yaw rate γ ^* and the actual yaw rate γ is calculated, and using this, the current value of the cumulative yaw rate deviation ΣΔγ is calculated as described above.

[0052] Subsequently, in S4, as described above, the reference lateral acceleration G _y ^* is calculated based on the front wheel steering angle [delta] _f and the vehicle speed V. Thereafter, in S5, the current value of the deviation Δγ between the reference lateral acceleration G _y ^* and the actual lateral acceleration G _y is calculated, using the same, in the manner described above, the current value of the cumulative lateral acceleration deviation ShigumaderutaG _y is calculated You.

[0053] Then, in S6, the current value or not greater than the reference value A determination of the cumulative yaw rate deviation Shigumaderutaganma, the determination current value or not greater than the reference value B of the cumulative lateral acceleration deviation ShigumaderutaG _y Are respectively executed. If any of these determinations is YES, the determination in S6 becomes YES, and in S7, the limit determination flag provided in the RAM is turned ON, whereby the limit determination flag indicates that the vehicle is at the turning limit. Is shown. This completes one execution of this routine.

On the other hand, the cumulative yaw rate deviation ΣΔγ
Determines whether the present value is larger than the reference value A also, when the current value of the cumulative lateral acceleration deviation ShigumaderutaG _y is the reference value B is larger than whether the determination is also NO,, S6 judgment also becomes NO , S8, the limit determination flag is turned off, whereby the limit determination flag is set to a state indicating that the vehicle is not at the turning limit. This completes one execution of this routine.

In short, the computer 20 is configured as shown in FIG.
As shown in, (a) on the basis of the front wheel steering angle [delta] _f and vehicle speed V, the reference yaw rate gamma ^* and the reference lateral acceleration G _y ^* and the calculating respective turning state quantity respectively reference turning state quantity The calculation unit 30 calculates (b) a cumulative yaw rate deviation ΣΔγ as a cumulative value based on the deviation Δγ between the actual yaw rate γ and the reference yaw rate γ ^* ,
Based on the _y and the reference lateral acceleration G _y ^* deviation between [Delta] [gamma], and the accumulated value calculating section 32 for calculating a cumulative lateral acceleration deviation ShigumaderutaG _y as the cumulative value, the cumulative lateral acceleration cumulative yaw rate deviation ΣΔγ that is their operation (c) based on the deviation ΣΔG _y, is the vehicle is configured to include a determining turning limit determination section 34 whether or not the turning limit.

As is apparent from the above description, in the present embodiment, the yaw rate sensor 10 and the lateral acceleration sensor 12 each constitute one aspect of the "actual turning state amount acquiring means 1" of the present invention. The computer 20 cooperates with the front wheel steering angle sensor 14 and the vehicle speed sensor 16 to
This constitutes one aspect of the "turn limit determination means 2" in the present invention.

In the above embodiment, the fact that the vehicle is at the turning limit is output visually or audibly to the driver.
Thereby, it can be used by connecting to a warning device that prompts a driving operation that matches the actual turning state. Further, the present embodiment is connected to a vehicle control device that controls the motion state of the vehicle, such as a rear wheel steering control device or a driving force distribution control device,
The vehicle control device may change the control characteristics according to the actual turning state.

Although the embodiment of the present invention has been described in detail with reference to the drawings, various modifications and improvements may be made based on the knowledge of those skilled in the art without departing from the scope of the claims. It is needless to say that the present invention can be implemented in the above-described embodiment.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a configuration of a vehicle turning limit determination device according to one embodiment of the present invention.

FIG. 3 is a flowchart showing a turning limit determination routine executed by a computer in FIG. 2;

[Explanation of symbols]

 Reference Signs List 10 Yaw rate sensor 12 Lateral acceleration sensor 14 Front wheel steering angle sensor 16 Vehicle speed sensor 20 Computer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI B62D 13:00

Claims (3)

(57) [Claims] An actual turning state quantity acquiring means for acquiring an actual turning state quantity of the vehicle, wherein when a cumulative value of a deviation of the acquired actual turning state quantity from the reference turning state quantity is larger than a reference value, A turning limit determining unit that determines that the vehicle is at a turning limit. 2. The method according to claim 1, wherein the turning limit determining unit determines the accumulated value.
And the time of occurrence of each of the plurality of deviations that constitute it
The older, the smaller the weight, and the total
The weighted sum is calculated as
The vehicle turning limit determination device according to any one of the preceding claims. 3. The vehicle according to claim 2, wherein the weighted sum is a normal state of the vehicle.
If the state continues for a long time, the value will automatically decay and restore to 0
3. The vehicle turning limit determination device according to claim 2, wherein