JP3582334B2 - Power steering device - Google Patents

Description

したがって、操舵角θに対する操舵トルクＴの伝達関数Ｔ（ｓ） ／θ（ｓ） は下記（５）式で表すことができる。
【００４３】
【数１】

【００４４】
ここで、ｓはラプラス演算子である。
今、横加速度α／操舵トルクＴの伝達関数をＧ_ｄ にすること即ちα（ｓ） ／Ｔ（ｓ） ＝Ｇ_ｄ が目標であるので、
【００４５】
【数２】

【００４６】
となればよい。
ここで、横加速度αは、車輪スリップ角速度をβ′とすると、
α＝Ｖ（β′＋γ） …………（７）
で表されるので、上記（６）式は、
【００４７】
【数３】

【００４８】
となる。
そして、上記（５）式と（８）式とは一致するので、
【００４９】
【数４】

【００５０】
となる。
この（９）式から操舵補助力Ｆ_Ａ ／トーションバー捩れ角φの制御伝達関数Ｙ_Ｃ （ｓ） を求めることができる。
【００５１】
ここで、先ず、（９）式中のβ（ｓ） ／θ（ｓ） 及びγ（ｓ） ／θ（ｓ） を求めることにする。車両の運動方程式は、
【００５２】
【数５】

【００５３】
となる。
ここで、ｍは車両質量（ｋｇ）、Ｃ_ｒ は後輪コーナリングパワー（Ｎ／ｒａｄ）、Ｉは車両ヨー慣性モーメント（ｋｇｍ^２ ）、γ′はヨー加速度（ｒａｄ／ｓ^２ ）である。
【００５４】
そして、上記（１０）式及び（１１）式を整理すると、
【００５５】
【数６】

【００５６】
但し、ａ_１１＝−（Ｌ_ｆ ^２ Ｃ_ｆ ＋Ｌ_ｒ ^２ Ｃ_ｒ ）／ＩＶ
ａ_１２＝（Ｌ_ｒ Ｃ_ｒ −Ｌ_ｆ Ｃ_ｆ ）／Ｉ
ａ_２１＝（Ｌ_ｒ Ｃ_ｒ −Ｌ_ｆ Ｃ_ｆ ）／ｍＶ^２ −１
ａ_２２＝（−Ｃ_ｆ −Ｃ_ｒ ）／ｍＶ
ｂ_１１＝Ｌ_ｆ Ｃ_ｆ ／ＩＮ
ｂ_２１＝Ｃ_ｆ ／ｍＶＮ
となるので、γ_（ｓ） ／θ_（ｓ） 及びβ_（ｓ） ／θ_（ｓ） は、
【００５７】
【数７】

【００５８】
となる。
これら（１３）〜（１５）式を前記（９）式に代入して整理をする。
このとき、車両を制御する時の遅れは、ない方がよいものとして、目標伝達関数Ｇ_ｄ の位相遅れはあらゆる周波数で零とする。すなわち、目標伝達関数Ｇ_ｄ は定数として扱うことにする。
【００５９】
すると、求める制御伝達関数Ｙ_Ｃ は、
【００６０】
【数８】

【００６１】
但し、
Ａ＝−Ｐ_１（ａ_１１＋ａ_２２）＋Ｐ_２ ｂ_２１＋Ｐ_３（−ｂ_２１ａ_１１＋ｂ_１１ａ_２１）＋Ｐ_４ ｂ_１１
Ｂ＝Ｐ_１ （ａ_１１ａ_２２−ａ_１２ａ_２１）
Ｃ＝Ｐ_２ （−ｂ_２１ａ_１１＋ｂ_１１ａ_２１）
Ｄ＝Ｐ_４ （−ｂ_１１ａ_２２＋ｂ_２１ａ_１２）
Ｅ＝Ｐ_５ （−ｂ_２１ａ_１１＋ｂ_１１ａ_２１＋ｂ_１１）
Ｆ＝Ｐ_５ （−ｂ_１１ａ_２２＋ｂ_２１ａ_１２）
Ｐ_１ ＝（Ｋ／Ｎ）Ｃ_ｆ ｔ_ｒ Ｇ_ｄ ｒ
Ｐ_２ ＝−Ｃ_ｆ ｔ_ｒ Ｇ_ｄ ｒＫ
Ｐ_３ ＝−ＫｄＶ
Ｐ_４ ＝−Ｋ（Ｌ_ｆ Ｃ_ｆ ｔ_ｒ Ｇ_ｄ ｒ／Ｖ＋ｄＶ）
Ｐ_５ ＝ｄｒＶ
となり、２次／２次の伝達関数として表すことができる。
【００６２】
次に、目標伝達関数Ｇ_ｄ の値の計算方法について説明する。
操舵補助をしない時即ちマニュアル操舵時の操舵トルクＴに対する横加速度αの伝達関数の定常ゲインをＧ_ｄ０とすると、この定常ゲインＧ_ｄ０は、
【００６３】
【数９】

【００６４】
但し、Ｘ＝（ａ_１１ａ_２２−ａ_１２ａ_２１）／Ｎ
Ｙ＝−ｂ_１１ａ_２１＋ａ_１１ｂ_２１
Ｚ＝Ｌ_ｆ （ｂ_２１ａ_１２−ｂ_１１ａ_２２）／Ｖ
で表される。
【００６５】
そして、操舵補助モータ１３で操舵補助力を発生すると、操舵力は軽くなるので、目標伝達関数Ｇ_ｄ は、
Ｇ_ｄ ＝η×Ｇ_ｄ０ （η＞１） …………（１９）
に設定すればよい。因みに、η＝１ のときには、低周波数での操舵力は、マニュアル操舵車両と同じになる。
【００６６】
したがって、例えば車速が１００ｋｍ／ｈで走行するときにη＝８／５として、目標伝達関数Ｇ_ｄ を算出し、これに応じて操舵補助力Ｆ_ａ ／トーションバーの捩れ角φの制御伝達関数Ｙ_Ｃ を算出し、この制御伝達関数Ｙ_Ｃ となるように、コントロールユニット１５のチューニングを行うと、このときの制御伝達関数Ｙ_Ｃ の周波数特性は、図３に示すように、ゲインは周波数が１Ｈｚ近傍までは比較的低い一定値となるが、１Ｈｚを越えて２Ｈｚ迄の間で上昇し、それ以降は周波数の増加に応じて緩やかに減少し、位相は、０．１Ｈｚから緩やかに上昇して０．６Ｈｚから比較的急峻に増加して１．３Ｈｚ当たりでピークとなり、その後急激に減少し、３Ｈｚ以降で緩やかに減少する特性となる。
【００６７】
このため、横加速度α／操舵トルクＴの周波数特性は、ゲインが図４（ａ）で実線図示のような周波数にかかわらず"０"近傍の一定値となり、位相も図４（ｂ）で実線図示のような周波数にかかわらず"０"を維持することになり、初期特性を実現していることが理解される。また、制御伝達関数Ｙ_C はハイパスフィルタを構成している。
【００６８】
因みに、本発明の制御を行わない場合には、図４（ａ）及び（ｂ）で破線図示のように、ゲインが１Ｈｚを越えると比較的急激に減少し、２Ｈｚ以上で緩やかに増加すると共に、位相が０．１Ｈｚから緩やかに減少して０．８Ｈｚ近傍から急激に減少し、１．４Ｈｚ程度でピークとなりその後急激に増加し３Ｈｚ以上で緩やかに増加することになり、１Ｈｚ〜２Ｈｚの間で大きな位相遅れを生じるが、上記実施形態では、非制御時即ちマニュアル操舵時のゲイン及び位相が変動している周波数領域で制御伝達関数Ｙ_Ｃ のゲイン及び位相が図３（ａ）及び（ｂ）に示すように逆特性に設定されることにより、ゲイン及び位相の変動が確実に抑制され、ドライバーの操舵感覚に応じた最適な操舵補助制御を行うことができる。
【００６９】
特に、制御伝達関数Ｙ_C の位相特性は、図３（ｂ）で明らかなように、マニュアル操舵の場合に横加速度α／操舵トルクＴの位相が遅れる周波数域で位相進み量を大きくして動特性を補償している。
【００７０】
つまり、コントロールユニット１５のチューニングに際しては、先ず、マニュアル操舵の状態で横加速度α／操舵トルクＴの周波数特性を測定し、位相遅れの大きな周波数域で且つ位相角が大きな周波数域で位相進みが大きくなるようにコントロールユニット１５を調整すればよい。
【００７１】
また、位相を進ませる量に関しては、上記実施形態では理想状態を数式で導いた場合について説明したが、少なくとも制御伝達関数Ｙ_Ｃ の位相を少しでも進ませれば、横加速度α／操舵トルクＴの位相が改善されるので、運転者のフィーリングに合わせながら、その量をチューニングすれば良い。
【００７２】
なお、上記実施形態で扱っているパワーステアリングは、操舵補助量の目標値に対する操舵補助力は１対１で発生することを前提としており、パワーステアリング自体の実操舵補助力／目標操舵補助力を実現するためにいわばハードウェア性能を実現させるために位相進みを付加する通常のＰＤ制御又はＰＩＤ制御とは本質的に異なるものである。
【００７３】
次に、本発明の第２の実施形態を図５及び図６について説明する。
この第２の実施形態は、トーションバー捩れ角φに対する操舵補助力Ｆ_Ａ の制御伝達関数Ｙ_Ｃ の特性を車速変化に応じて変化させるようにしたものである。
【００７４】
この第２の実施形態においては、車速が増加すると、横加速度α／操舵トルクＴの位相遅れは大きくなるため、コントロールユニット１５での制御伝達関数Ｙ_C の進み量も車速の増加に応じて大きくする必要がある。ここで、本来は横変位／操舵トルクと言うべきであるが、横加速度αは横変位の２階微分値であるので、横加速度αで代用している。
【００７５】
したがって、理想特性の場合の横加速度α／操舵トルクＴの周波数応答及び操舵補助力Ｆ_A ／トーションバー捩れ角φの制御伝達関数Ｙ_C の周波数応答を夫々図５及び図６に示す。
【００７６】
これら図５及び図６は、車速を４０ｋｍ／ｈから１２０ｋｍ／ｈまで２０ｋｍ／ｈ毎に変化させたときの周波数応答を示すもので、本発明の制御を行わない場合には、横加速度α／操舵トルクＴのゲイン特性は、図５（ａ）に示すように、０．３〜約１．４の範囲でゲインが車速の増加に伴って増加し、逆に約１．４〜４の範囲では車速の増加に伴って減少し、位相特性は図５（ｂ）に示すように、周波数が０．１Ｈｚ〜１Ｈｚの間では車速の増加に伴って位相遅れが少なくなるが、１Ｈｚ〜約２．３Ｈｚの間では逆に車速が増加するに伴って位相遅れが大きくなる。
【００７７】
このため、操舵補助力Ｆ_A ／トーションバー捩れ角φの制御伝達関数Ｙ_C を、図６に示すように、ゲイン特性を図６（ａ）に示すように周波数が０．３〜約１．４Ｈｚの間で車速の増加に伴って減少させ、約１．４〜３Ｈｚの間で車速の増加に伴って増加させ、且つ位相特性を図６（ｂ）に示すように周波数が０．１〜０．８Ｈｚの間で車速の増加に伴って位相遅れ量を大きくし、０．８〜約２．２Ｈｚの間で車速の増加に伴って位相進み量を大きくするように設定する。
【００７８】
これによって、操舵補助を行わない場合には遅れてしまう横加速度Ｇ／操舵トルクＴの特性を制御伝達関数Ｙ_Ｃ で補償することができ、図５（ａ）及び（ｂ）において特性線Ｌ_１ 及びＬ_２ で示すように、車速の変化にかかわらず一定のゲインを維持しながら位相遅れのない最適な操舵補助制御を行うことができる。
【００７９】
なお、上記第１及び第２の実施形態においては、全ての車速域で横変位（＝横加速度）／操舵トルクの位相遅れを低減するようにした場合について説明したが、これに限定されるものではなく、前述した従来技術の項で説明したように、運転者は低速では操舵角情報をもとに車両を操舵しているので、運転者が操舵トルクをもとに操舵する高車速領域に限って制御伝達関数Ｙ_C に進み要素を付加するようにしてもよい。
【００８０】
すなわち、横変位／操舵角及び横変位／操舵トルクの伝達関数の周波数応答における位相特性を４０ｋｍ／ｈ，５０ｋｍ／ｈ，６０ｋｍ／ｈ及び７０ｋｍ／ｈの各車速について測定したところ、これらの測定結果は図７（ａ），（ｂ），（ｃ）及び（ｄ）に示すようであった。
【００８１】
この図７から明らかなように、車速が４０ｋｍ／ｈであるときには図７（ａ）のように横変位／操舵トルクの伝達関数の方が横変位／操舵角の伝達関数に対して位相遅れを生じているが、車速が５０〜６０ｋｍ／ｈとなる図７（ｂ）及び（ｃ）の間で横変位／操舵角の伝達関数と横変位／操舵トルクの伝達関数との位相遅れ量が逆転している。
【００８２】
したがって、所定車速例えば５０ｋｍ／ｈ未満では操舵補助力Ｆ_Ａ ／トーションバー捩れ角φの制御伝達関数Ｙ_Ｃ に位相進み量を付加せず、５０ｋｍ／ｈ以上で位相進み量を徐々に増加させるようにすることが好ましい。
【００８３】
また、上記各実施形態においては、ラック８に操舵補助モータ１３に連結されたアシストピニオン１１を噛合させた場合について説明したが、これに限定されるものではなく、ピニオンシャフト７に歯車等の動力伝達手段を介して操舵補助モータ１３を連結するようにしてもよく、要は操舵補助モータ１３で発生する操舵補助トルクを操舵系に伝達可能に構成されていればよい。
【００８４】
さらに、上記各実施形態においては、操舵補助力を操舵補助モータ１３で発生するようにした場合について説明したが、これに限定されるものではなく、油圧式パワーステアリングであっても、油圧制御系における操舵補助力Ｆ_Ａ ／トーションバー捩れ角φの制御伝達関数Ｙ_Ｃ に進み要素を付加することにより、上記第１及び第２の実施形態と同様の作用効果を得ることができる。
【００８５】
さらに、上記各実施形態においては、コントロールユニット１５からの指令トルクに対して操舵補助モータ１３で実際に発生する実操舵補助トルクには遅れがない場合について説明したが、これに限定されるものではなく、指令トルクと操舵補助モータ１３で発生させる実操舵補助トルクとの間に遅れが存在する場合には、その遅れ分を補償することは言うまでもない。例えば実操舵補助トルク／指令トルクの伝達関数がＨ（ｓ） であり、実現すべき制御伝達関数がＹ_ｃ （ｓ） であるときには、
【００８６】
【数１０】

【００８７】
に設定すればよい。
【図面の簡単な説明】
【図１】本発明の第１の実施形態を示す概略構成図である。
【図２】関数を導出するための２輪モデルを示す説明図である。
【図３】操舵補助力／トーションバーの捩れ角の制御伝達関数Ｙ_Ｃ の周波数応答を示す特性線図であり、（ａ）はゲイン特性を、（ｂ）は位相特性を夫々示す。
【図４】横加速度／操舵トルクの周波数応答を示す特性線図であり、（ａ）はゲイン特性を、（ｂ）は位相特性を夫々示す。
【図５】本発明の第２の実施形態における横加速度／操舵トルクの周波数応答を示す特性線図であり、（ａ）はゲイン特性を、（ｂ）は位相特性を夫々示す。
【図６】第２の実施形態における制御伝達関数Ｙ_Ｃ の周波数応答示す特性線図であり、（ａ）はゲイン特性を、（ｂ）は位相特性を夫々示す。
【図７】本発明の他の実施形態における横変位／操舵角及び横変位／操舵トルクの位相特性を示す特性線図である。
【図８】従来のパワーステアリングを装着していない車両における低速走行時の横変位／操舵角と横変位／操舵トルクとの周波数応答を示す特性線図であり、（ａ）はゲイン特性を、（ｂ）は位相特性を夫々示す。
【図９】従来のパワーステアリングを装着していない車両における高速走行時の横変位／操舵角と横変位／操舵トルクとの周波数応答を示す特性線図であり、（ａ）はゲイン特性を、（ｂ）は位相特性を夫々示す。
【図１０】油圧式パワーステアリング装着車と未装着車の横加速度／操舵トルクの周波数応答を示す特性線図であり、（ａ）はゲイン特性を、（ｂ）は位相特性を夫々示す。
【符号の説明】
１ ステアリングホイール
２ ステアリングシャフト
６ ピニオン
８ ラック
１０ 転舵輪
１１ 操舵補助ピニオン
１３ 操舵補助モータ
１５ コントロールユニット
１６ トルク検出機構
１７ 操舵トルクセンサ
１８ 車速センサ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power steering device that detects a steering torque generated in a steering state and a steering holding state of a steering wheel, and generates a steering assist torque corresponding to the detected steering torque.
[0002]
[Prior art]
2. Description of the Related Art As a conventional power steering device, there is one described in, for example, Japanese Patent Application Laid-Open No. 5-77750.
[0003]
In this conventional example, the vehicle speed and the steering angular velocity are repeatedly stored at predetermined time intervals, the upper and lower limits are deleted from these stored data, and the remaining stored data is deleted.ToAn electric power steering apparatus that sets the power assist force by averaging to calculate an average speed and an average steering angular speed, and comparing the calculation results with a standard steering pattern to determine whether or not the vehicle is sporty. Is described.
[0004]
[Problems to be solved by the invention]
However, the conventional power steering device has an unsolved problem as described below.
[0005]
That is, it is generally said that a driver steers a vehicle by "steering at a steering wheel angle at a low speed and a steering force at a high speed". The purpose of the driver operating the vehicle is to match the vehicle trajectory intended by the driver with the vehicle trajectory through which the vehicle passes. Therefore, what is important for the driver is “lateral displacement of the vehicle”.
[0006]
Therefore, an experiment was conducted on a vehicle not equipped with a power steering device, and the frequency response of the lateral displacement / steering angle (steering angle) of the vehicle and the lateral displacement / steering torque of the vehicle was determined at low speed running (for example, 40 km / h). ) And during high-speed running (for example, 120 km / h), the results shown in FIGS. 8 and 9 were obtained.
[0007]
As is clear from FIGS. 8 and 9, the phase lag of the lateral displacement / steering angle of the vehicle is smaller than the phase lag of the lateral displacement / steering torque of the vehicle at the time of low-speed running, and these may be reversed at the time of high-speed running. I understand.
[0008]
Needless to say, when the driver controls the lateral displacement of the vehicle, the smaller the phase delay, the better. Therefore, it is considered that the driver selectively uses the steering angle as the main information at a low speed and the steering torque at a high speed.
[0009]
As an aside, in a four-wheel steering vehicle, the phase lag of lateral displacement / steering angle is reduced, so that the driver can control the vehicle based on the steering angle information at high speed as well as at low speed, thereby reducing the burden on the driver. We are trying to reduce it. However, a four-wheel steering vehicle requires a rear-wheel steering actuator and various sensors, and mounting these on a vehicle increases costs and weight.
[0010]
Further, in a power steering apparatus using a hydraulic pressure which is currently mounted on a vehicle, the steering torque is detected by the torsion of the torsion bar, so that a steering assist hydraulic pressure is generated with a delay, so that as shown in FIG. There is an unsolved problem that the phase of lateral displacement / steering torque is delayed with respect to a vehicle without steering.
[0011]
Further, in recent years, an electric power steering device of a type in which steering assist torque is added by an electric motor instead of hydraulic pressure has been proposed, and the aim of this electric power steering device is to reduce the weight and improve fuel efficiency. Since the characteristics are intended to be close to a hydraulic power steering device, there is an unsolved problem that the unique degree of control freedom cannot be fully utilized.
[0012]
Therefore, the present invention has been made by focusing on the unsolved problem of the conventional example, and adds a steering assist torque such that the phase advances with respect to the steering torque detected by the torsion angle of the torsion bar or the like. Accordingly, an object of the present invention is to provide a power steering device that can solve the above-mentioned unsolved problem.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a power steering apparatus according to claim 1 includes a steering torque detection unit that detects a steering torque generated in a steering state and a steering state of a steering wheel, and a steering detected by the steering torque detection unit. An auxiliary steering torque generating means for generating a steering assist torque based on the torque, wherein the auxiliary steering torque generating means is configured to generate a steering assist torque based on a steering torque detected by the steering torque detecting means.steeringTransfer function of auxiliary torqueThe phase delay of the frequency response of lateral acceleration to steering torqueAnd a configuration in which elements are added.
[0014]
In the invention according to the first aspect, the auxiliary steering torque generating means generates the input steering torque and generates the steering torque based on the input steering torque.steeringTransfer function with auxiliary torqueThe phase delay of the frequency response of lateral acceleration to steering torqueTo the torsion bar used in the steering torque sensor.steeringThe phase delay of the lateral displacement / steering torque due to the delay of the generation of the auxiliary torque can be eliminated.
[0015]
A power steering apparatus according to a second aspect is characterized in that, in the invention according to the first aspect, the advance element is set to a large value according to an increase in vehicle speed.
[0016]
According to the second aspect of the present invention, the advance element has a large value as the vehicle speed increases, so that an increase in the phase delay of the lateral displacement / steering torque due to the increase in the vehicle speed can be offset.
[0017]
Further, in the power steering apparatus according to claim 3, in the invention according to claim 1, the frequency at which the phase advance maximum value of the frequency response of the steering assist torque with respect to the steering torque occurs is determined by the steering torque when the steering assist torque is not generated. Is set near the frequency at which the maximum value of the phase delay of the frequency response of the lateral acceleration with respect to is generated.
[0018]
In the invention according to the third aspect, the phase delay in the frequency region where the phase response of the frequency response of the lateral acceleration / steering torque when the steering assist torque is not generated is large,steeringIt can be surely canceled by the maximum value of the phase advance of the frequency response of the assist torque / steering torque.
[0019]
Still further, in the power steering apparatus according to claim 4, in the invention according to any one of claims 1 to 3, the auxiliary steering torque generating means adds an element to the transfer function when the vehicle speed is equal to or higher than a predetermined vehicle speed. It is characterized by having such a configuration.
[0020]
According to the fourth aspect of the present invention, the driver can perform steering of the vehicle based on the steering angle information in a low vehicle speed traveling state below a predetermined vehicle speed, and transmit the vehicle in a high vehicle speed traveling state above the predetermined vehicle speed. By adding an element to the function, optimal steering based on the steering torque can be performed.
[0021]
【The invention's effect】
According to the invention according to claim 1, the steering torque corresponds to the detected steering torque value.steeringTransfer function to calculate auxiliary torqueThe phase delay of the frequency response of lateral acceleration to steering torqueTo add the element,Eliminate the delay in the frequency response of lateral acceleration to steering torque,When the driver steers the vehicle, it is possible to obtain an effect that it is possible to realize easy-to-handle vehicle characteristics based on the steering force.
[0022]
According to the second aspect of the present invention, the advance element added to the transfer function is set to a large value in accordance with an increase in the vehicle speed, so that it is possible to realize vehicle characteristics that are easy to handle in all vehicle speed ranges. The effect is obtained.
[0023]
Furthermore, according to the third aspect of the present invention, the frequency at which the phase advance maximum value of the frequency response of the steering assist torque with respect to the steering torque occurs is set to the phase delay of the frequency response of the lateral acceleration with respect to the steering torque when the steering assist torque is not generated. Since the frequency is set near the frequency at which the maximum value occurs, the phase lead is increased in the frequency band where the phase delay is large, and the effect that dynamic characteristics can be compensated can be obtained.
[0024]
Still further, according to the invention according to claim 4, the auxiliary steering torque generating means is configured to add an element to the transfer function when the vehicle speed is equal to or higher than the predetermined vehicle speed. Optimal steering torque control by controlling the steering assist torque based on the steering torque and adding the advance element to the transfer function only in the high-speed region where the driver controls based on the steering torque, to maintain the driver's steering feeling properly Can be obtained.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. In the drawing, a steering wheel 1 is connected to an upper end of a steering shaft 2, and the steering shaft 2 is rotatably supported by a fixed portion. .
[0026]
The lower end of the steering shaft 2 is connected via a universal joint 3, a column shaft 4 and a universal joint 5 to a pinion shaft 7 having a pinion 6 attached to the lower end.
[0027]
The pinion 6 meshes with a rack 8 that extends horizontally in the vehicle width direction to form a steering gear. You.
[0028]
Both ends of the horizontally extending rack 8 are connected to a knuckle and steered wheels 10 via tie rods 9 respectively, and the left and right steered wheels 10 are steered by the rack 8 moving horizontally (translational movement). Is done.
[0029]
An assist pinion 11 is also meshed with the rack 8. The assist pinion 11 is connected to a rotation shaft of a steering assist motor 13 serving as a drive source via a speed reducer 12. Control is performed to generate a steering assist force according to the steering torque by the duty-controlled pulse current output from the unit 15.
[0030]
Further, a torque detection mechanism 16 is provided on the pinion shaft 7. The torque detecting mechanism 16 includes a torsion bar (not shown) that connects the lower end of the pinion shaft 7 and the upper end of the pinion 6, and a steering torque sensor 17 disposed on the outer periphery thereof.
[0031]
The steering torque sensor 17 detects a steering torque from the amount of twist of the torsion bar, and turns the steering wheel 1 to the right according to the magnitude of the steering torque (to the left from the input from the pinion 6). A torque detection value T, which is a positive value or a negative value voltage signal when the steering wheel 1 is turned left (clockwise with respect to the input from the pinion 6), is supplied to a control unit 15 described later.
[0032]
The vehicle is provided with a vehicle speed sensor 18 for detecting a vehicle speed. The vehicle speed sensor 18 detects a vehicle speed in the vehicle front-rear direction, and a vehicle speed detection value V, which is a voltage signal corresponding to the magnitude of the vehicle speed, is described later. Supplied to the control unit 15.
[0033]
The control unit 15 performs a predetermined calculation based on the input vehicle speed detection value V and steering torque detection value T to calculate a steering torque command value for the steering assist motor 13, Output to
[0034]
Here, the steering assist torque command value output from the control unit 15 and the actual steering assist force generated by the steering assist motor 13 based on the steering assist torque command value have a one-to-one correspondence.ofThere is no phase delay between them.
[0035]
The transfer function of the steering assist torque to the steering torque T in the assist steering system torque generating means including the steering assist motor 13 and the control unit 15 is set as follows.
[0036]
That is, the target transfer function of the lateral acceleration detection value α (α / T) with respect to the steering torque T is represented by G_dAnd when the rigidity of the torsion bar is K (Nm / rad), the steering assist force F for the torsion bar torsion angle φ_AControl transfer function of Y_C(= F_A.K / T) and the control transfer function Y_CAsk for.
[0037]
Here, the transfer function G_dThe reason is that the lateral displacement is the second-order integral value of the lateral acceleration, and the purpose of the present invention is to improve the phase of the lateral displacement / steering torque as described above in the section of the prior art.
[0038]
These functions G_dAnd Y_CIs derived using the two-wheel model shown in FIG.
In FIG. 2, L is a vehicle wheelbase (m), L_fIs the distance (m) between the front wheel and the center of gravity in the front-rear direction, L_rIs the longitudinal distance (m) between the rear wheel and the center of gravity, and α is the vehicle lateral acceleration (m / s).²), Β is the vehicle body slip angle (rad), γ is the yaw rate (rad / s), δ is the front wheel steering angle (rad), F_fIs the front wheel lateral force (N), F_rRepresents rear wheel lateral force (N), and V represents vehicle speed (m / s).
[0039]
First, Y_CControl transfer function, the steering assist force F_AThe steering torque T at the time of occurrence of is generated.
A certain self-aligning torque T_S, Steering assist force F_AWhen the knuckle arm radius is d (m), the rack axial force when_S/ D-F_AIt becomes.
[0040]
By multiplying this rack axial force by the pinion rotation radius r (m), a steering torque T is obtained as in the following equation (1).
T = (T_S/ D-F_A) R ............ (1)
However, the self-aligning torque T_SAnd steering assist force F_ACan be represented by the following equations (2) and (3).
[0041]
T_S= C_f(Θ / N-β-L_F・ Γ / V) t_r  ............ (2)
F_A= Y_C・ Φ = Y_C・ T / K ………… (3)
Where C_fIs the front wheel cornering power (N / rad), θ is the steering angle (rad), N is the steering gear ratio, t_rIs a front wheel trail (m).
[0042]
By substituting the equations (2) and (3) into the equation (1), the following equation (4) is obtained.

Therefore, the transfer function T (s) / θ (s) of the steering torque T with respect to the steering angle θ can be expressed by the following equation (5).
[0043]
(Equation 1)

[0044]
Here, s is a Laplace operator.
Now, the transfer function of lateral acceleration α / steering torque T is represented by G_dThat is, α (s) / T (s) = G_dIs the goal,
[0045]
(Equation 2)

[0046]
It should just be.
Here, assuming that the wheel slip angular velocity is β ′, the lateral acceleration α is
α = V (β ′ + γ) (7)
Thus, the above equation (6) is
[0047]
(Equation 3)

[0048]
It becomes.
Then, since the above equations (5) and (8) match,
[0049]
(Equation 4)

[0050]
It becomes.
From this equation (9), the steering assist force F_A/ Control transfer function Y of torsion bar torsion angle φ_C(S) can be obtained.
[0051]
Here, first, β (s) / θ (s) and γ (s) / θ (s) in Expression (9) are determined. The equation of motion of the vehicle is
[0052]
(Equation 5)

[0053]
It becomes.
Here, m is the vehicle mass (kg), C_rIs the rear wheel cornering power (N / rad) and I is the vehicle yaw moment of inertia (kgm²), Γ 'is the yaw acceleration (rad / s²).
[0054]
Then, when the above equations (10) and (11) are arranged,
[0055]
(Equation 6)

[0056]
Where a₁₁=-(L_f ²C_f+ L_r ²C_r) / IV
a₁₂= (L_rC_r-L_fC_f) / I
a₂₁= (L_rC_r-L_fC_f) / MV²-1
a₂₂= (-C_f-C_r) / MV
b₁₁= L_fC_f/ IN
b₂₁= C_f/ MVN
Γ_(S)/ Θ_(S)And β_(S)/ Θ_(S)Is
[0057]
(Equation 7)

[0058]
It becomes.
The formulas (13) to (15) are substituted into the formula (9) to organize.
At this time, it is assumed that there is no delay in controlling the vehicle._dIs zero at all frequencies. That is, the target transfer function G_dIs treated as a constant.
[0059]
Then, the desired control transfer function Y_CIs
[0060]
(Equation 8)

[0061]
However,
A = -P₁(A₁₁+ A₂₂) + P₂b₂₁+ P₃(-B₂₁a₁₁+ B₁₁a₂₁) + P₄b₁₁
B = P₁(A₁₁a₂₂-A₁₂a₂₁)
C = P₂(-B₂₁a₁₁+ B₁₁a₂₁)
D = P₄(-B₁₁a₂₂+ B₂₁a₁₂)
E = P₅(-B₂₁a₁₁+ B₁₁a₂₁+ B₁₁)
F = P₅(-B₁₁a₂₂+ B₂₁a₁₂)
P₁= (K / N) C_ft_rG_dr
P₂= -C_ft_rG_drK
P₃= -KdV
P₄= -K (L_fC_ft_rG_dr / V + dV)
P₅= DrV
And can be expressed as a second-order / second-order transfer function.
[0062]
Next, the target transfer function G_dThe method of calculating the value of will be described.
When the steering assist is not performed, that is, when a manual steering is performed, the steady gain of the transfer function of the lateral acceleration α with respect to the steering torque T is represented by_d0Then, this steady gain G_d0Is
[0063]
(Equation 9)

[0064]
However, X = (a₁₁a₂₂-A₁₂a₂₁) / N
Y = -b₁₁a₂₁+ A₁₁b₂₁
Z = L_f(B₂₁a₁₂-B₁₁a₂₂) / V
Is represented by
[0065]
When the steering assisting force is generated by the steering assisting motor 13, the steering force is reduced._dIs
G_d= Η × G_d0  (Η> 1) (19)
Should be set to. Incidentally, when η = 1, the steering force at the low frequency is the same as that of a manually steered vehicle.
[0066]
Therefore, for example, when traveling at a vehicle speed of 100 km / h, η = 8/5 and the target transfer function G_dIs calculated, and the steering assist force F is accordingly calculated._a/ Control transfer function Y of torsion bar torsion angle φ_CAnd the control transfer function Y_CWhen the control unit 15 is tuned such that the control transfer function Y_CAs shown in FIG. 3, the frequency characteristic of the gain becomes a relatively low constant value until the frequency is around 1 Hz, but rises from 1 Hz to 2 Hz, and thereafter, as the frequency increases, A characteristic that gradually decreases, the phase gradually increases from 0.1 Hz, increases relatively steeply from 0.6 Hz, peaks at about 1.3 Hz, then rapidly decreases, and gradually decreases after 3 Hz. It becomes.
[0067]
Therefore, the frequency characteristic of the lateral acceleration α / steering torque T is such that the gain is as shown by the solid line in FIG.WhatRegardless of the frequency, it becomes a constant value near "0", and the phase is as shown by the solid line in FIG.WhatIt is understood that "0" is maintained irrespective of the frequency, and the initial characteristics are realized. Further, the control transfer function Y_CConstitutes a high-pass filter.
[0068]
Incidentally, when the control of the present invention is not performed, as shown by the broken lines in FIGS. 4A and 4B, the gain decreases relatively sharply when the gain exceeds 1 Hz, and increases gradually when the gain exceeds 2 Hz. , The phase gradually decreases from 0.1 Hz, sharply decreases from around 0.8 Hz, peaks at about 1.4 Hz, then rapidly increases, and gradually increases at 3 Hz or more. Causes a large phase delay, but in the above embodiment, the control transfer function Y in the frequency range where the gain and the phase fluctuate during non-control, that is, during manual steering._C3 (a) and 3 (b), the gain and phase are set to the opposite characteristics, whereby the gain and phase fluctuations are reliably suppressed, and the optimal steering assist control according to the driver's steering feeling. It can be performed.
[0069]
In particular, the control transfer function Y_CFig. 3 (bAs is clear from the above, in the case of manual steering, the dynamic characteristics are compensated by increasing the amount of phase lead in a frequency range where the phase of the lateral acceleration α / the steering torque T is delayed.
[0070]
That is, when tuning the control unit 15, first, the frequency characteristic of the lateral acceleration α / the steering torque T is measured in the state of manual steering, and the frequency characteristic is measured in a frequency range where the phase delay is large.andRankPhase angleThe control unit 15 may be adjusted so that the phase advance becomes large in a frequency range where the frequency is large.
[0071]
Further, with respect to the amount by which the phase is advanced, a case has been described in the above embodiment where the ideal state is derived by a mathematical expression._CIs slightly advanced, the phase of the lateral acceleration α / steering torque T is improved. Therefore, the amount may be tuned in accordance with the driver's feeling.
[0072]
In the power steering system described in the above embodiment, it is assumed that the steering assist force for the target value of the steering assist amount is generated on a one-to-one basis, and the actual steering assist force / the target steering assist force of the power steering itself is calculated. This is essentially different from ordinary PD control or PID control in which a phase lead is added to realize hardware performance.
[0073]
Next, a second embodiment of the present invention will be described with reference to FIGS.
In the second embodiment, the steering assist force F with respect to the torsion bar twist angle φ_AControl transfer function Y_CIs changed according to the change in vehicle speed.
[0074]
In the second embodiment, when the vehicle speed increases, the phase delay of the lateral acceleration α / the steering torque T increases.UnitControl transfer function Y at 15_CAlso needs to be increased in accordance with an increase in vehicle speed. Here, although it should be originally called lateral displacement / steering torque, since the lateral acceleration α is a second-order differential value of the lateral displacement, the lateral acceleration α is substituted.
[0075]
Therefore, the frequency response of the lateral acceleration α / the steering torque T and the steering assist force F in the case of the ideal characteristic_A/ Control transfer function Y of torsion bar torsion angle φ_COf the frequency response of5And figure6Shown in
[0076]
5 and 6 show the frequency response when the vehicle speed is changed from 40 km / h to 120 km / h every 20 km / h. When the control of the present invention is not performed, the lateral acceleration α / As shown in FIG. 5A, the gain characteristic of the steering torque T increases with increasing vehicle speed in the range of 0.3 to about 1.4, and conversely, in the range of about 1.4 to 4. As shown in FIG. 5 (b), the phase delay decreases with increasing vehicle speed when the frequency is between 0.1 Hz and 1 Hz, but the phase characteristic decreases with increasing vehicle speed. On the other hand, when the vehicle speed increases between 0.3 Hz, the phase delay increases.
[0077]
Therefore, the steering assist force F_A/ Control transfer function Y of torsion bar torsion angle φ_CAs shown in FIG. 6, the gain characteristic is reduced as the vehicle speed increases between a frequency of 0.3 and about 1.4 Hz as shown in FIG. 6B, the phase characteristic is increased as the vehicle speed increases, and the phase delay is increased as the vehicle speed increases, as shown in FIG. In the range of 0.8 to about 2.2 Hz, the amount of phase lead increases as the vehicle speed increases.AsSet.
[0078]
As a result, the characteristic of lateral acceleration G / steering torque T, which is delayed when steering assist is not performed, can be controlled by the transfer function Y._C5 (a) and 5 (b).₁And L₂As shown by, optimal steering assist control without phase delay can be performed while maintaining a constant gain regardless of changes in vehicle speed.
[0079]
Note that, in the first and second embodiments, the lateral displacement (= SidewaysAlthough the case where the phase delay of (acceleration) / steering torque is reduced has been described, the present invention is not limited to this, and as described in the above-described related art section, the driver can obtain the steering angle information at low speed. Since the vehicle is originally steered, the control transfer function Y is limited to a high vehicle speed region where the driver steers based on the steering torque._CMay be added to add an element.
[0080]
SandChiWhen the phase characteristics in the frequency response of the transfer function of lateral displacement / steering angle and lateral displacement / steering torque were measured for each vehicle speed of 40 km / h, 50 km / h, 60 km / h and 70 km / h, these measurement results were as follows. This was as shown in FIGS. 7 (a), (b), (c) and (d).
[0081]
This figure7As is clear from the above, when the vehicle speed is 40 km / hAs shown in FIG.Although the transfer function of the lateral displacement / steering torque has a phase lag with respect to the transfer function of the lateral displacement / steering angle, FIG. 7 (b) and FIG.(During c), the phase lag between the lateral displacement / steering angle transfer function and the lateral displacement / steering torque transfer function is reversed.
[0082]
Therefore, at a predetermined vehicle speed, for example, less than 50 km / h, the steering assist force F_A/ Control transfer function Y of torsion bar torsion angle φ_CIt is preferable that the amount of phase advance is not increased and the amount of phase advance is gradually increased at 50 km / h or more.
[0083]
In each of the above embodiments, the rack 8steeringThe case where the assist pinion 11 connected to the auxiliary motor 13 is meshed has been described. However, the present invention is not limited to this.steeringThe auxiliary motor 13 may be connected.steeringGenerated by auxiliary motor 13steeringWhat is necessary is just to be able to transmit the assist torque to the steering system.
[0084]
Furthermore, in each of the above embodiments, the case where the steering assist force is generated by the steering assist motor 13 has been described. However, the present invention is not limited to this. Steering assist force F at_A/ Control transfer function Y of torsion bar torsion angle φ_CBy adding the elements, the same operation and effect as those of the first and second embodiments can be obtained.
[0085]
Further, in each of the above-described embodiments, a case has been described in which the actual steering assist torque actually generated by the steering assist motor 13 has no delay with respect to the command torque from the control unit 15; If there is a delay between the command torque and the actual steering assist torque generated by the steering assist motor 13, it goes without saying that the delay is compensated for. For example, the transfer function of actual steering assist torque / command torque is H (s), and the control transfer function to be realized is Y_c(S)
[0086]
(Equation 10)

[0087]
Should be set to.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a two-wheel model for deriving a function.
FIG. 3 is a control transfer function Y of steering assist force / torsion bar torsion angle._C7A and 7B are characteristic diagrams showing the frequency response of FIG. 7A, wherein FIG. 9A shows a gain characteristic and FIG.
FIG. 4 is a characteristic diagram showing a frequency response of lateral acceleration / steering torque, wherein (a) shows a gain characteristic and (b) shows a phase characteristic.
FIGS. 5A and 5B are characteristic diagrams illustrating a frequency response of lateral acceleration / steering torque according to the second embodiment of the present invention, wherein FIG. 5A illustrates a gain characteristic and FIG. 5B illustrates a phase characteristic.
FIG. 6 shows a control transfer function Y in the second embodiment._C5A is a characteristic diagram showing a frequency response of FIG. 5A, and FIG. 5A shows a gain characteristic, and FIG.
FIG. 7 is a characteristic diagram showing phase characteristics of lateral displacement / steering angle and lateral displacement / steering torque in another embodiment of the present invention.
FIG. 8 is a characteristic diagram showing the frequency response of lateral displacement / steering angle and lateral displacement / steering torque in a vehicle not equipped with the conventional power steering when the vehicle is traveling at a low speed. (B) shows the phase characteristics.
FIG. 9 is a characteristic diagram showing the frequency response of lateral displacement / steering angle and lateral displacement / steering torque during high-speed running in a vehicle not equipped with a conventional power steering, where (a) shows a gain characteristic; (B) shows the phase characteristics.
FIGS. 10A and 10B are characteristic diagrams showing frequency response of lateral acceleration / steering torque of a vehicle equipped with a hydraulic power steering and a vehicle not equipped with the hydraulic power steering. FIG.
[Explanation of symbols]
1 Steering wheel
2 Steering shaft
6 Pinion
8 racks
10 Steering wheel
11 Steering assist pinion
13 Steering assist motor
15 Control unit
16 Torque detection mechanism
17 Steering torque sensor
18 Vehicle speed sensor

Claims (4)

A steering torque detecting unit that detects a steering torque generated in a steering state and a steering maintaining state of the steering wheel; and an auxiliary steering torque generating unit that generates a steering assist torque based on the steering torque detected by the steering torque detecting unit. In the power steering device, the auxiliary steering torque generating means may advance the transfer function of the steering assist torque with respect to the steering torque detected by the steering torque detecting means so that the phase delay of the frequency response of the lateral acceleration with respect to the steering torque becomes small. A power steering device having a configuration in which elements are added. 2. The power steering apparatus according to claim 1, wherein the advance element is set to a large value as the vehicle speed increases. The frequency at which the phase advance maximum value of the frequency response of the steering assist torque with respect to the steering torque occurs is set near the frequency at which the phase delay maximum value of the frequency response of the lateral acceleration with respect to the steering torque when the steering assist torque is not generated occurs. The power steering device according to claim 1, wherein: The power steering apparatus according to any one of claims 1 to 3, wherein the auxiliary steering torque generating means is configured to add an element to the transfer function when the vehicle speed is equal to or higher than a predetermined vehicle speed.

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