JP2009113509A - Vehicle steering system - Google Patents

Abstract

A vehicle steering apparatus that effectively compensates for a steering delay of a driver and prevents an overshoot of a steering angle is provided.
A vehicle steering apparatus 1 is based on a steering input unit 30 in which a driver inputs a steering operation, an operation amount detection unit 91 that detects an operation amount of the steering input unit, and an operation amount history of the steering input unit. Based on a comparison result between the predicted operation amount calculation means 90 that calculates the predicted operation amount, the actual operation amount of the steering input unit detected by the operation amount detection means, and the predicted operation amount calculated by the prediction operation amount calculation means. An additional steering angle calculating means 90 for calculating an additional steering angle added to the basic steering angle according to the operation amount of the steering input unit, and a steering mechanism for steering the front wheels according to the basic steering angle and the additional steering angle The units 50 and 80 are provided.
[Selection] Figure 3

Description

  The present invention relates to a steering device that steers front wheels of a vehicle such as an automobile, and more particularly to a steering device that superimposes an additional steering angle according to a driver's sudden steering operation on a basic steering angle proportional to a steering operation amount. .

In general, a steering apparatus for an automobile transmits a rotational movement of a steering wheel to a steering gear box via a steering shaft, and converts the movement into a straight movement in the vehicle width direction to steer a front wheel.
In recent years, for example, a steering device has been proposed in which a steering angle correction mechanism having an actuator is disposed in the middle of the steering shaft, and the actual steering angle of the front wheels is controlled by superimposing the operation angle of the steering angle correction mechanism on the steering wheel operation amount. Has been. A steering device equipped with such an actuator automatically controls, for example, a steering gear ratio variable control that changes the apparent steering gear ratio according to the traveling speed of the vehicle or an unstable behavior in the vehicle. Control such as restoring the vehicle by correcting the steering angle is possible, which is commonly referred to as active steering.

In the above-described steering apparatus, it is known to perform so-called differential steering control in which an additional steering angle proportional to the differential value of the steering wheel operation amount is added to the steering angle corresponding to the steering wheel operation amount (for example, non-patent) Reference 1). When such differential steering control is performed, the response of the vehicle yaw motion can be improved by compensating for the delay in the steering operation of the driver.
In addition, in a vehicle steering apparatus that performs active steering control, it is known to guard the angular velocity and angular acceleration of the steering angle based on the motor drive so as not to exceed predetermined values in order to suppress fluctuations in the reaction torque. (For example, refer to Patent Document 1).
Masato Suzumura et al. “Development of Front Steer Control System” 34-03 JP 2006-335250 A

However, when differential steering control is performed, for example, when the driver's steering speed is fast, such as when an obstacle is urgently avoided, the additional steering angle corresponding to the differential value becomes excessively large, and the actual front wheel steering angle becomes There may be an overshoot that is cut larger than the target rudder angle intended by the driver. In this case, the front wheels are cut back after being cut beyond the target rudder angle, and an excessive yaw movement unintended by the driver is generated, giving a strong sense of incongruity to the driver.
On the other hand, it is possible to reduce the effect of overshoot by reducing the gain of the additional steering angle according to the differential value, but in this case, the effect of compensating the driver's steering delay by differential steering control is also reduced. End up.
In view of the above problems, an object of the present invention is to provide a vehicle steering apparatus that effectively compensates for a driver's steering delay and prevents steering angle overshoot.

The present invention solves the above-described problems by the following means.
According to the first aspect of the present invention, a steering input unit for a driver to input a steering operation, an operation amount detection means for detecting an operation amount of the steering input unit, and a prediction operation based on the operation amount history of the steering input unit Based on a comparison result between a predicted operation amount calculation unit that calculates an amount, an actual operation amount of the steering input unit detected by the operation amount detection unit, and the predicted operation amount calculated by the prediction operation amount calculation unit. , Additional steering angle calculation means for calculating an additional steering angle added to the basic steering angle according to the operation amount of the steering input unit, and a steering mechanism for steering the front wheels according to the basic steering angle and the additional steering angle And a vehicle steering apparatus.
Here, the predicted operation amount is typically the latest operation amount on the premise of smooth steering operation, and can be obtained by sampling the operation amount at a plurality of past points in time and performing Taylor expansion, for example. it can.

According to a second aspect of the present invention, in the vehicle steering apparatus according to the first aspect, the vehicle steering apparatus further includes a differential value detection unit that detects a differential value of the operation amount of the steering input unit, The vehicle steering apparatus is characterized in that the additional steering angle is obtained by multiplying the differential steering control gain, which increases with an increase in the deviation between the operation amount and the predicted operation amount, by the differential value.
According to a third aspect of the present invention, in the vehicle steering apparatus according to the first aspect, the additional steering angle calculation means multiplies a deviation between the actual operation amount and the predicted operation amount by a predetermined gain to perform the addition. A control apparatus for a vehicle characterized by obtaining a rudder angle.

According to the present invention, the following effects can be obtained.
(1) By calculating the additional rudder angle based on the comparison result between the predicted operation amount calculated based on the operation amount history of the steering input unit and the actual operation amount, for example, steering steeper as in danger avoidance When the operation is performed (when the deviation between the predicted operation amount and the actual operation amount is large), the driver's steering delay can be effectively compensated by giving a large additional steering angle. Further, since the deviation becomes small from the middle to the latter half of the steering operation, it is possible to prevent an actual steering angle overshoot caused by an excessive additional steering angle.
(2) By increasing the differential steering control gain in accordance with an increase in the deviation between the actual operation amount and the predicted operation amount, when a sudden steering operation is started and the deviation and the steering speed are large, these products are Accordingly, the steering angle of the driver can be reliably compensated by increasing the additional steering angle. In addition, when the steering operation is converging and the deviation and the steering speed are reduced, the additional steering angle can be reduced to reliably prevent overshoot.
(3) By multiplying the deviation between the actual operation amount and the predicted operation amount by a predetermined gain to obtain the additional steering angle, there is no need to differentiate the operation amount of the steering input unit, and the calculation load is reduced. Thus, it is possible to eliminate the influence of waveform disturbance, signal output delay, and the like that occur during differentiation processing.

An object of the present invention is to provide a vehicular steering apparatus that effectively compensates for a driver's steering delay and prevents steering angle overshoot. This is solved by calculating a predicted steering operation amount based on the above and setting a gain of differential steering control according to a deviation between the predicted steering operation amount and the actual steering operation amount.
According to another aspect of the present invention, the above-described problem is solved by calculating the additional steering angle by multiplying the deviation between the predicted operation amount and the actual steering operation amount by a predetermined constant.

A vehicle steering apparatus according to a first embodiment to which the present invention is applied will be described below.
The steering device according to the first embodiment steers the front wheels of, for example, a four-wheeled passenger car.
FIG. 1 is a diagram illustrating the configuration of the steering device according to the first embodiment. Note that the left and right components are illustrated with L and R subscripts attached to the left and right, respectively.
The steering device 1 steers the left and right front wheels 10 and the housing 20.
The housing 20 is a member that houses a hub bearing unit (not shown) that rotatably supports the front wheel 10. The housing 20 includes a knuckle arm 21 that protrudes from the steering axis (kingpin shaft) toward the vehicle rear side.

The steering device 1 includes a steering wheel 30, an upper steering shaft 40, a steering angle correction mechanism 50, a lower steering shaft 60, a joint unit 70, a steering gear box 80, a steering control unit 90, a motor driving unit 100, and the like. Yes.
The steering wheel 30 is a steering input unit through which a driver inputs a steering operation.
The upper steering shaft 40 is a rotating shaft that connects the steering wheel 30 and the steering angle correction mechanism 50 and transmits the rotation of the steering wheel 30 to a sun gear 51 described later of the steering angle correction mechanism 50.

The steering angle correction mechanism 50 superimposes a desired additional steering angle on the input steering angle from the upper steering shaft 40 and transmits it to the lower steering shaft 60. The additional steering angle is generated when the steering angle correction mechanism 50 rotates the lower steering shaft 60 with respect to the upper steering shaft 40.
The steering angle correction mechanism 50 includes sun gears 51 and 52, planetary gears 53 and 54, a pinion shaft 55, a carrier 56, a motor 57, a drive gear 58, a driven gear 59, and the like.

The sun gear 51 is fixed to the end of the upper steering shaft 40 on the rudder angle correction mechanism 50 side.
The sun gear 52 is fixed to the end of the lower steering shaft 60 on the rudder angle correction mechanism 50 side.
These sun gears 51 and 52 are arranged so that their rotation center axes coincide.

Planetary gears 53 and 54 mesh with sun gears 51 and 52, respectively.
These planetary gears 53 and 54 are arranged such that their rotation center axes coincide with each other.
The pinion shaft 55 is a rotation shaft in which the planetary gears 53 and 54 are fixed to both ends.
The carrier 56 supports the pinion shaft 55 and the planetary gears 53 and 54 so that they can revolve around the same rotation center axis as the sun gears 51 and 52, respectively, and can rotate around the center axis of the pinion shaft 55. It is a member to do.

The motor 57 is driven by the motor drive unit 100 and generates a desired additional steering angle by rotating the carrier 56.
The drive gear 58 is fixed to the output shaft of the motor 57.
The driven gear 59 is provided on the outer diameter side of the end of the carrier 56 on the steering wheel 30 side, meshed with the drive gear 58, and driven by the drive gear 58.

The lower steering shaft 60 is a rotating shaft that connects the rudder angle correction mechanism 50 and the joint part 70 and transmits the rotation of the sun gear 52 of the rudder angle correction mechanism 50 to the joint part 70.
The joint unit 70 connects the lower steering shaft 60 and the pinion shaft 81 of the steering gear box 80, and transmits the rotation of the lower steering shaft 60 to the pinion shaft 81 while changing the direction.
The joint part 70 includes universal joints 71 and 72 arranged in series, and a joint shaft 73 that connects them.

The steering gear box 80 includes a rack and pinion mechanism that converts a rotational motion input from the pinion shaft 81 into a linear reciprocating motion in the vehicle width direction of a steering rack (not shown).
Further, the steering gear box 80 includes tie rods 82 that transmit the movement of the steering rack to the knuckle arm 21 of the housing 20 at both ends in the vehicle width direction.

The steering control unit 90 includes a steering angle sensor (operation amount detection means) 91 that detects a position (angle) of the steering wheel 30 around the rotation center axis, and a steering angle correction mechanism according to the output of the steering angle sensor 91. The additional steering angle calculating means calculates the additional steering angle added at 50.
The rudder angle sensor 91 is provided, for example, in a steering column, and includes a magnetic body and a magnetic detection element arranged to move relative to each other in conjunction with the rotation of the upper steering shaft 40. The angle of the steering shaft 40 (equal to the angle of the steering wheel 30) is detected.
The calculation of the additional steering angle in the steering control unit 90 will be described in detail later.
The motor driving unit 100 drives the motor 57 of the rudder angle correction mechanism 50 according to the additional rudder angle calculated by the steering control unit 90, and controls the rudder angle correction mechanism 50 to generate a target additional rudder angle. To do.

Next, calculation of the additional steering angle in the steering device 1 described above will be described.
Steering control unit 90, a steering wheel angle of the angle theta _H of the steering wheel 30 to the steering angle sensor 91 detects sampling at a predetermined sampling rate, for example, the last three points (k-1, k-2 , k-3) _{Is used} to determine the steering wheel angle predicted value θ _{H — P} (k) at time k calculated by secondary Taylor expansion centered on time k−1. And the prediction error value e in k time is calculated _| required by taking the difference of steering angle prediction value (theta) _{H_P} (k) and steering wheel angle (theta) _H (k) in actual k time. That is, here, the steering control unit 90 functions as a predicted operation amount calculation unit.

The steering wheel angle predicted value θ _{H — P} (k) is obtained by the following expression 1.

θ _{H_P} (k) = θ _H (k−1) + (θ _H (k−1) −θ _H (k−2))
+0.5 ((θ _H (k−1) −θ _H (k−2)) − (θ _H (k−2) −θ _H (k−3))) Equation 1

Further, the prediction error value (deviation) e is obtained by the following equation 2.
e = θ _H (k) −θ _{H —P} (k) Equation 2

θ _H (k): Actual steering wheel angle at time k

ここで、ステアリングホイール角度θ_Hと予測誤差値ｅとが同符号である場合とは、ドライバが急激にステアリングホイールを切り増した場合を意味する。
図２は、実施例１における予測誤差値ｅと微分ステアリング制御ゲインＫ_ｄとの相関を示すグラフである。図２において、横軸は予測誤差値ｅ、縦軸はゲインＫ_ｄをそれぞれ示している（後述する図４において同じ）。 Further, the steering control unit 90 _calculates the differential steering control gain K _d and the additional steering angle θ _{H — d} (rotation angle of the lower steering shaft 60 with respect to the upper steering shaft 40) in the steering angle correction mechanism 50 by the following equations 3 and 4. Set as follows.

Here, the case where the steering wheel angle θ _H and the prediction error value e have the same sign means that the driver has suddenly increased the steering wheel.
FIG. 2 is a graph showing the correlation between the prediction error value e and the differential steering control gain _{Kd in the} first embodiment. In FIG. 2, the horizontal axis represents the prediction error value e, and the vertical axis represents the gain _Kd (the same applies to FIG. 4 described later).

このとき、前輪１０の実舵角は、δ_ｆ＋δ_{f_a}となる。ここで、舵角δ_ｆは、舵角補正機構５０によって舵角補正を行わない場合（モータ５７を駆動しない場合）における前輪の舵角である。 The front wheel additional rudder angle δ _{f_a} which is the amount of change in the front wheel 10 turning angle due to the additional rudder angle θ _{H_d} of the rudder angle correction mechanism 50 described above is expressed by the following Expression 5.

At this time, the actual steering angle of the front wheel 10 is δ _f + δ _{f_a} . Here, the steering angle [delta] _f is the steering angle of the front wheels in the case of no steering angle correction by steering angle correction mechanism 50 (without driving the motor 57).

Next, the effect of the first embodiment will be described in comparison with comparative examples 1 and 2 of the present invention described below. In Comparative Examples 1 and 2 and Example 2 to be described later, description of portions substantially similar to Example 1 is omitted, and differences are mainly described.
The comparative example 1 is an existing steering device that does not give an additional steering angle corresponding to the steering wheel angular velocity (does not perform differential steering control).
Comparative Example 2 is a steering device that sets an additional steering angle by multiplying a steering wheel angular velocity by a certain gain.

FIG. 3 is a graph showing an example of the steering angle when the same steering operation is performed in Example 1 and Comparative Examples 1 and 2, the deviation in the Example, and the history of the steering speed in Comparative Example 2.
In FIG. 3, the horizontal axis indicates time, and the vertical axis indicates the magnitude of the value of each item.
In FIG. 3, the steering angle and the prediction error value in Example 1 are indicated by a solid line and a broken line, the steering angle in Comparative Example 1 is indicated by a one-dot chain line, and the steering angle and the steering speed in Comparative Example 2 are indicated by a two-dot chain line and a three-dot chain line, respectively. Show.

As shown in FIG. 3, in the first comparative example in which the differential steering control is not performed, the steering angle rises early in the initial stage due to the steering delay of the driver, and as a result, the generation of the yaw motion generated in the vehicle is also delayed.
On the other hand, in the case of the comparative example 2 in which the differential steering control for calculating the additional steering angle by multiplying the steering wheel angular velocity by a certain gain is performed, the initial steering angle rises earlier than the comparative example 1, and the early stage The yaw movement of the vehicle can be generated. However, in Comparative Example 2, the rudder angle is cut larger than the target rudder angle intended by the driver, and then an overshoot of the rudder angle that is returned to the target rudder angle occurs, giving the driver an uncomfortable feeling.

On the other hand, according to the first embodiment, the following effects can be obtained.
(1) By calculating the additional steering angle θ _{H_d} based on the prediction error value e which is a deviation between the predicted operation amount obtained by Taylor expansion of the steering wheel angle θ _H at the past three time points and the actual operation amount. For example, when a sudden steering operation is performed as in danger avoidance, the steering delay of the driver is effectively compensated by the additional steering angle, and the yaw motion of the vehicle can be generated early. In addition, since the above-described deviation becomes small from the middle to the latter half of the steering operation, it is possible to prevent an actual steering angle overshoot caused by an excessive additional steering angle.
(2) By increasing the differential steering control gain _Kd in accordance with the increase in the prediction error value e, when a sudden steering operation is started and the prediction error value e and the steering speed are large, the difference is made proportional to these products. Thus, the additional steering angle can be increased to reliably compensate for the driver's steering delay. In addition, when the steering operation is converging and the deviation is small, the additional steering angle can be reduced to reliably prevent overshoot.

図４は、実施例２における予測誤差値ｅと微分ステアリング制御ゲインＫ_ｄとの相関を示すグラフである。
以上説明した実施例２によれば、上述した実施例１と同様の効果に加えて、所定の予測誤差値ｅに対するゲインＫ_ｄの絶対値が大きくなることによって、微分ステアリング制御の効果を増大し、ドライバの操舵遅れの補償効果を高めることができる。 Next, a second embodiment of the vehicle steering apparatus to which the present invention is applied will be described.
In the vehicle steering apparatus according to the second embodiment, the gain _Kd of the differential steering control is represented by the following expression 6 instead of the expression 3 according to the first embodiment.

FIG. 4 is a graph showing the correlation between the prediction error value e and the differential steering control gain _{Kd in the} second embodiment.
According to the second embodiment described above, the effect of differential steering control is increased by increasing the absolute value of the gain _Kd with respect to the predetermined prediction error value e in addition to the same effects as in the first embodiment. Thus, the effect of compensating the driver's steering delay can be enhanced.

以上説明した実施例３によれば、上述した実施例１と同様の効果に加えて、微分処理を行う必要がないことから、ハードウェアの演算負荷を軽減することができ、また、微分に伴う波形の乱れや微分値出力の遅れといった問題を防止することができる。 Next, a third embodiment of the vehicle steering apparatus to which the present invention is applied will be described.
The vehicular steering apparatus of the third embodiment, in place of the differential steering control in the first embodiment described above, are multiplied directly by a predetermined gain K _c to the prediction error value e obtained in equation 2, the steering angle correction mechanism The additional steering angle θ _{H_d at} 50 is set.
That is, in the third embodiment, the additional steering angle θ _{H_d} in the steering angle correction mechanism 50 is _expressed by the following Expression 7.

According to the third embodiment described above, in addition to the same effects as those of the first embodiment described above, it is not necessary to perform a differentiation process, so that it is possible to reduce the calculation load of hardware and to accompany the differentiation. Problems such as waveform disturbance and differential value output delay can be prevented.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
(1) Although the steering device of each embodiment is configured to provide a planetary gear-type steering angle correction mechanism in the middle of the steering column, the configuration of the steering angle correction mechanism is not limited to this and can be changed as appropriate. For example, a steering angle correction mechanism using a wave gear device may be used. Further, the present invention is not limited to the use of such a steering angle correction mechanism, and may be applied to a so-called steer-by-wire steering apparatus in which a steering wheel and a steering gear box are not mechanically connected. Can do.
(2) Although the steering apparatus of each embodiment uses only the steering wheel operating speed according to the steering wheel operation speed as the additional steering angle by the steering angle correction mechanism, this is used in combination with the additional steering angle based on other controls. May be. For example, to stabilize the behavior when an additional steering angle based on variable gear ratio control that changes the apparent steering gear ratio according to the traveling speed of the vehicle, or when a behavior such as oversteer or understeer occurs in the vehicle It is good also as a structure which superimposes the additional steering angle set to 1 and the additional steering angle by this invention.
(3) The mechanical and hardware configuration of the steering device is not limited to those of the above-described embodiments. For example, the structure and arrangement of the rudder angle correction mechanism, the rear placement and the front placement with respect to the kingpin shaft of the steering gear box can be changed as appropriate. Each control means can be integrated into a common ECU or can be distributed to a plurality of ECUs.
(4) In Example 1, the output of the steering angle sensor is differentiated to obtain the differential value of the operation amount of the steering input unit. However, the present invention is not limited to this, and a speed sensor for detecting the operation speed of the steering input unit is provided. This output may be used as a differential value.

It is a figure which shows the structure of Example 1 of the steering apparatus for vehicles to which this invention is applied. 2 is a graph showing a correlation between a prediction error value e and a differential steering control gain _Kd in the vehicle steering apparatus of FIG. 2 is a graph illustrating an example of a time history of a steering wheel angle, a steering speed, and a front wheel actual steering angle in the vehicle steering device of FIG. 1. It is a graph which shows the correlation with the prediction error value e in Example 2 of the steering apparatus for vehicles to which this invention is applied, and differential steering control gain _Kd .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering device 10 Front wheel 20 Housing 21 Knuckle arm 30 Steering wheel 40 Upper steering shaft 50 Steering angle correction mechanism 51,52 Sun gear 53,54 Planetary gear 55 Pinion shaft 56 Carrier 57 Motor 58 Drive gear 59 Driven gear 60 Lower steering shaft 70 Joint part 71 , 72 Universal joint 73 Joint shaft 80 Steering gear box 81 Pinion shaft 90 Steering control section 91 Steering angle sensor 100 Motor drive section

Claims (3)

A steering input unit for a driver to input a steering operation;
An operation amount detection means for detecting an operation amount of the steering input unit;
Predicted operation amount calculation means for calculating a predicted operation amount based on a history of the operation amount of the steering input unit;
Based on the result of comparison between the actual operation amount of the steering input unit detected by the operation amount detection unit and the predicted operation amount calculated by the predicted operation amount calculation unit, the operation amount of the steering input unit is determined. Additional steering angle calculating means for calculating an additional steering angle added to the basic steering angle;
A vehicle steering apparatus comprising: a steering mechanism that steers front wheels according to the basic steering angle and the additional steering angle. The vehicle steering apparatus according to claim 1,
A differential value detecting means for detecting a differential value of an operation amount of the steering input unit;
The additional steering angle calculating means obtains the additional steering angle by multiplying the differential steering control gain that increases in accordance with an increase in the deviation between the actual operation amount and the predicted operation amount by the differential value. A vehicle steering device. The vehicle steering apparatus according to claim 1,
The vehicle control apparatus according to claim 1, wherein the additional steering angle calculating means obtains the additional steering angle by multiplying a deviation between the actual operation amount and the predicted operation amount by a predetermined gain.

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