JP3039071B2 - Vehicle turning limit judgment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a vehicle which reaches a turning limit.
The present invention relates to a technique for determining whether or not a warning has occurred .

[0002]

2. Description of the Related Art As one type of a device for controlling the motion of a vehicle, the motion of the vehicle is controlled, and a change in the control characteristics thereof causes
There are already known ones that change the relationship between the steering response of the vehicle and the running stability in the vehicle motion characteristics. For example, (a) a four-wheel steering control device (so-called 4WS) that appropriately controls the rear wheel steering angle of the vehicle in relation to the front wheel steering angle and changes the rear wheel steering angle gain as a control characteristic; A driving force distribution control device for appropriately controlling a ratio of distributing the driving force of the engine to the front wheels and the rear wheels in relation to a road surface condition and changing a driving force distribution ratio gain as a control characteristic; A suspension control device that maintains the body posture horizontally regardless of the inclination of the vehicle, acceleration and deceleration of the vehicle, turning, etc., and changes the vehicle body posture angle gain as control characteristics; (d) steering applied to the steering wheel of the vehicle by the driver A power steering device that assists torque and changes the steering assist characteristic as a control characteristic. (E) Wheel brakes to prevent the wheels from locking when braking the vehicle. Anti-lock control device that controls the brake pressure gain as a control characteristic, and (f) reduces the driving force of the drive wheel so that excessive slip does not occur on the drive wheel when the vehicle starts and accelerates. A traction control device that changes the driving force attenuation gain.

The applicant of the present invention has previously proposed the following for such a vehicle motion control device. This includes whether the vehicle from the vehicle body slip angle reaches the turning limit, i.e., the body attitude during turning is determined whether the transition to the unstable state from the stable state, if so, steering response Running stability
It is a proposal to change the control characteristic so as to realize a vehicle motion characteristic emphasizing performance .

[0004] By the way, the sideslip angle of a vehicle body is generally not directly obtained, but a parameter related thereto is detected and then obtained indirectly. An example of a technique for indirectly obtaining the sideslip angle is described in Japanese Utility Model Laid-Open Publication No. 2-43765. This means that the vehicle speed is detected by a vehicle speed sensor, the steering angle of a steering wheel steered by a driver is detected by a steering angle sensor, and based on the detected vehicle speed and the detected steering angle, the tire slip angle and the This is a technique for estimating a side slip angle of a vehicle body on the assumption that a relationship with a generated cornering force (hereinafter, simply referred to as tire characteristics) is in a linear (proportional) region.

[0005]

The time when the vehicle reaches the turning limit is usually when its tire characteristics are about to transition from a linear region to a non-linear region, or at some point within the non-linear region. Therefore, in order to accurately determine whether the vehicle has reached the turning limit, the sideslip angle of the vehicle body must be accurately obtained regardless of whether the tire characteristics are in the linear region or the non-linear region. Is essential.

However, the above-described conventional skid angle acquiring technique estimates the skid angle of the vehicle body based on the detected vehicle speed and the detected steering angle on the assumption that the tire characteristics are in a linear region. When the tire characteristics are in the non-linear region, the sideslip angle of the vehicle body cannot be estimated accurately. Therefore, when this conventional side slip angle acquisition technology is employed to determine whether or not the vehicle has reached a turning limit, there is a problem that the accuracy of the determination cannot be sufficiently increased.

The present invention eliminates this problem,
It is an object to accurately determine that the vehicle has reached a turning limit.

[0008]

SUMMARY OF THE INVENTION In order to solve this problem, the gist of the present invention is to provide an apparatus for determining whether or not a vehicle has reached a turning limit, comprising: (a) a vehicle speed detecting a traveling speed of the vehicle; A sensor, (b) a lateral acceleration sensor that detects the acceleration of the vehicle center of gravity in the vehicle lateral direction, (c) a yaw rate sensor that detects the yaw rate of the vehicle body, and (d) a value obtained by dividing the detected lateral acceleration by the detected vehicle speed. The speed of change of the sideslip angle at the center of gravity of the vehicle, which is the value obtained by subtracting the detected yaw rate from
Is the limit for determining that the vehicle has reached the turning limit if
And determination means . The present invention can be applied to a vehicle motion control device that controls the motion of a vehicle and changes the relationship between the steering responsiveness and the running stability of the vehicle in the vehicle motion characteristics by changing the control characteristics,
One aspect thereof further includes a controller that changes the control characteristic so that a vehicle motion characteristic in which traveling stability is more important than steering responsiveness is realized if the side slip angle change speed is equal to or higher than a reference speed. .

Since the vehicle speed generally means a composite value of the longitudinal speed and the lateral speed of the vehicle, the "body speed sensor" in the present invention generally uses the rotational speeds of a plurality of wheels of the vehicle. It is to be detected. Note that this detection method includes, for example, a method of individually detecting the rotational speed of each wheel and using them collectively to detect the vehicle speed, and a method of detecting the rotational speed of the output shaft of the transmission by the average speed of the left and right drive wheels. As a vehicle speed. However, the “vehicle body speed” in the present invention is not limited thereto, and may mean the longitudinal speed of the vehicle body. In this case, the “vehicle speed sensor” in the present invention is, for example, a Doppler speed that detects the longitudinal speed. It can be a sensor.

[0010]

In the normal turning motion of the vehicle, the absolute value of the sideslip angle β (positive in the counterclockwise direction) of the center of gravity of the vehicle is almost 0, which can be regarded as considerably smaller than 1. Accordingly, the side slip angle β can be expressed as follows using the longitudinal speed v _x of the vehicle body (positive in the forward direction) and the lateral speed v _y (positive in the left direction). β ≒ v _y / v _x Here, it is assumed that the vehicle speed V means a composite value of the front-rear direction speed v _x and the lateral direction speed v _y of the vehicle body. However, because they are considered to be the side slip angle β is approximately 0, the vehicle speed V would can be regarded as substantially equal to the longitudinal direction velocity v _x. Therefore, the side slip angle β can be expressed as follows using the vehicle speed V and the lateral speed v _y . β ≒ v _y / V

In a normal turning motion having such a premise, the lateral acceleration G _y, which is the acceleration in the vehicle lateral direction at the vehicle center of gravity, depends on whether the tire characteristics are in the linear region or the non-linear region. However, it is already known that it is represented by the following equation. However _{G y = Dv y + V ·} γ, Dv y in this formula means a time differential value of the lateral velocity v _y, gamma refers to the vehicle body yaw rate (counterclockwise direction is positive). By transforming this equation, the following equation is obtained. Dβ = G _y / V−γ where Dβ is a time differential value of the side slip angle β, that is, “the side slip angle changing speed of the vehicle center of gravity” in the present invention.

The guiding process of this equation is described in detail in the document "Vehicle Motion and Control (Kyoritsu Shuppan Co., Ltd., 1st edition, published on October 20, 1979)", pp. 31-33. Therefore, detailed description is omitted here.

On the other hand, in a turning motion of a vehicle, generally,
As the sideslip angle β increases, the posture of the vehicle body becomes unstable, and the possibility of falling into spin or drift-out increases. In addition, the slip velocity change rate Dβ may be large.
Means that the sideslip angle β suddenly increases. But
Therefore, the vehicle is at the turning limit due to the slip angle change speed Dβ.
Can be determined.

[0014] In view of these circumstances, the vehicle turning limit determination device according to the present invention, the lateral acceleration G _y of the vehicle speed V
Is a value obtained by subtracting the yaw rate γ from a value obtained by dividing the case side slip angle change rate Dβ is the reference speed or higher, the vehicle
Is determined to have reached the turning limit.

[0015]

As described above, according to the present invention, regardless of whether the tire characteristics are in the linear region or the non-linear region, the side slip angle change speed is accurately obtained, and is obtained from the reference speed.
When it is above, it is determined that the turning limit has been reached, so that the effect of improving the determination accuracy is obtained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydraulic power steering apparatus according to an embodiment of the present invention will be described below in detail with reference to the drawings.
As shown in FIG. 2, the power steering apparatus includes a vehicle lateral acceleration sensor (hereinafter, simply referred to as a lateral acceleration) that detects an acceleration in a vehicle lateral direction at a vehicle center of gravity (hereinafter, simply referred to as a lateral acceleration) when the left direction is positive. 10)
A vehicle speed sensor 20 that detects the forward direction as positive with the average speed of the left and right driven wheels of the vehicle as the vehicle speed, and a vehicle yaw rate sensor that detects the yaw rate around the vertical axis passing through the vehicle center of gravity as the counterclockwise direction as positive , Simply referred to as a yaw rate sensor) 30. These are computer-based state estimation ECUs (Electronic Con
Control Unit) 40 is connected to the input port. The state estimating ECU 40 estimates a turning state of the vehicle by executing a turning state determination program represented by a flowchart in FIG. 1 based on the lateral acceleration G _y , the vehicle speed V, and the yaw rate γ.

Specifically, first, in step S1 (hereinafter, referred to as step S1)
It is simply represented by S1. The same applies to other steps), the lateral acceleration G _y , the vehicle speed V
And the yaw rate γ are read, and the reference speed Dβ ₀ corresponding to the vehicle speed V is stored in the ROM of the computer.
Read from The ROM stores in advance the relationship between the vehicle speed V and the reference speed Dβ ₀ , in which the higher the vehicle speed V, the lower the reference speed Dβ _0. reference speed D.beta ₀ to it that is obtained.

Subsequently, in S2, the yaw rate γ is subtracted from the value obtained by dividing the lateral acceleration G _y by the vehicle speed V to calculate the side slip angle change speed Dβ. In S3, the side slip angle change speed Dβ is calculated based on the current reference value. Speed Dβ
It is determined whether it is ₀ or more. Otherwise, the determination is NO, and in S4, the limit determination flag of the RAM is turned off. The limit determination flag indicates that the vehicle has not reached the turning limit in the OFF state, while the ON state is ON.
This indicates that the vehicle has reached the turning limit in the state where the vehicle has been turned. Therefore, this time, the limit determination flag indicates that the vehicle has not reached the limit limit. This completes one execution of the program.

[0019] On the contrary, when the side slip angle change rate D.beta is the current reference speed D.beta ₀ or more, YES becomes the determination of S3, the limit determination flag at S5 is turned ON, one of the program or Execution is terminated.

The state estimation ECU 4 configured as described above
As shown in FIG. 2, a power steering reaction force control ECU (hereinafter referred to as a ECU) mainly comprising a computer
(Hereinafter simply referred to as a reaction force control ECU) 50.

By the way, this power steering device is
A control valve (not shown) that hydraulically applies a steering assist torque based on a difference between a steering torque applied to a steering wheel by a driver and a road surface reaction force torque applied to the steered wheels from the road surface to the steering wheel. A power steering reaction force control actuator (hereinafter, simply referred to as a reaction force control actuator) that applies a hydraulic reaction force torque in a direction to cancel the steering assist torque based on the control valve and electrically controls the magnitude thereof.
60 is provided. The reaction force control actuator 60 is controlled by the reaction force control ECU 50. Since the control valve and the reaction force control actuator 60 are well known and are not indispensable for understanding the present invention, their description is omitted here.

The present power steering apparatus is provided with a reaction control E
The CU 50 subtracts a substantial steering assist torque (ie, a steering assist torque based on the control valve from a hydraulic reaction torque based on the reaction control actuator 60) via the reaction force control actuator 60, and This is a so-called vehicle speed sensitive type in which the torque applied from the wheels to the driver is changed according to the vehicle speed V. The reaction force control ECU 50 determines its RO
In M, two types of relations (hereinafter simply referred to as steering assist characteristics) between the vehicle body speed V and the hydraulic reaction torque are stored in advance, and the reaction force control actuator 60 is controlled by selecting one of the steering assist characteristics. is there. One of the steering assist characteristics is used for normal operation, and the other is used for turning limit. The steering assist characteristic for turning limit is set so as to realize a steering feeling heavier than the normal steering assist characteristic. .

If the limit determination flag is turned off by the state estimation ECU 40, the reaction force control ECU 50 controls the reaction force control actuator 60 in accordance with the normal steering assist characteristic, but if the limit determination flag is turned on. For example, the reaction force control actuator 60 is controlled in accordance with the steering assist characteristic for turning limit. Therefore, when the vehicle has reached the turning limit, the steering feeling is heavier than when the vehicle has not reached the turning limit. Therefore, the driver can reliably recognize that the vehicle has reached the turning limit via the steering wheel, and can perform steering by the driver. Excessive steering of the wheel (for example, large steering angle steering or fast steering) is prevented, and ultimately, driving stability is more important than steering responsiveness.
Thus, the vehicle motion characteristics with emphasis on are realized.

As is apparent from the above description, in this embodiment, the computer of the state estimation ECU 40
"Limit is in the present invention portions for performing the S1~S5 in Figure 1
It constitutes " field determination means ".

[0025] It is added, the vehicle speed sensor 20 in this embodiment is the method for detecting the vehicle speed V by using a rotational speed of the wheel, its vehicle body speed V and the front-rear direction velocity v _x of the vehicle body Not exactly. And when it is necessary to detect the true longitudinal velocity v _x ,
If the vehicle speed sensor 20 for example, a Doppler velocity sensor, it is possible to detect the true longitudinal direction velocity v _x.

Further, in this embodiment, in this embodiment,
Although reference speed D.beta ₀ has been variable values vary depending on the vehicle speed V, the be a variable value that varies depending on other parameters, can be a fixed value.

Further, this embodiment is an example in which the present invention is applied to a power steering device, but the present invention can be applied to other vehicle motion control devices. For example, the present invention can be applied to the aforementioned four-wheel steering control device, driving force distribution control device, suspension control device, power steering device, antilock control device, traction control device, and the like.

Other than these, the present invention can be carried out in various modified and improved forms based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a turning state determination program used by a power steering device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an electric system of the power steering device.

[Explanation of symbols]

 Reference Signs List 10 vehicle lateral acceleration sensor 20 vehicle body speed sensor 30 vehicle yaw rate sensor 40 state estimation ECU 50 power steering reaction force control ECU 60 power steering reaction force control actuator

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

Claims (1)

(57) [Claims] An apparatus for determining whether a vehicle has reached a turning limit, comprising: a vehicle speed sensor for detecting a running speed of a vehicle; and a lateral acceleration sensor for detecting an acceleration of a vehicle center of gravity in a lateral direction of the vehicle. A yaw rate sensor that detects a yaw rate of the vehicle body ; Reaches the turning limit
And a limit determining means for determining that the vehicle has turned.