JP4145534B2

JP4145534B2 - Road surface state estimation method and apparatus

Info

Publication number: JP4145534B2
Application number: JP2002059397A
Authority: JP
Inventors: 啓詩森永; 英俊横田
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 2002-03-05
Filing date: 2002-03-05
Publication date: 2008-09-03
Anticipated expiration: 2022-03-05
Also published as: JP2003252191A

Description

【０００１】
【発明の属する技術分野】
本発明は、車両の走行時の路面状態を推定する方法とその装置とに関するものである。
【０００２】
【従来の技術】
自動車の走行安定性を高めるため、タイヤと路面との間の摩擦係数（路面摩擦係数）あるいは路面状態を精度良く推定し、車両制御へフィードバックすることが求められている。特に、制駆動や操舵といった危険回避の操作を起こす前に、予め路面摩擦係数を推定することができれば、例えば、ＡＢＳブレーキのより高度な制御等が可能になり、安全性を一段と高められると考えられる。また、運転者にその危険度を伝えるだけでも、運転者が早めの減速動作を行えるようになり、事故の減少が期待できる。
本出願人は、例えば、特願２００１−３６０４８において、走行中の路面状態を精度良く推定するとともに、上記推定された路面状態に基づいて車両の走行状態をフィードバック制御することのできる路面状態の推定方法とその装置を提案している。この手法は、タイヤが定常走行時においても踏面内で滑りを生じているという事実に基づいており、伝播されたタイヤ内の気体の微小変動を検出して、これを周波数分析し、得られた圧力変動スペクトルの所定の周波数帯域における圧力変動レベルを検出して路面摩擦係数を推定するものである。
上記技術を更に具体的に説明すると、タイヤは、定常走行時においても、その踏面においてワイピング変形に伴う滑りを生じており、路面摩擦係数が低下するとこの滑り量が増大する。この現象により、タイヤの１ｋＨｚ以上の高周波振動が増大し、この振動がタイヤ内の気体にも伝播する。したがって、タイヤ内の微小圧力変動をモニタリングして周波数分析し、更に必要とされる幾つかの周波数帯域の圧力変動レベル（帯域値）を求め、係数を掛けるなどの演算処理を行うことにより、路面摩擦係数を推定することができる。ここで、上記周波数帯域としては、上記路面の滑りの寄与が大きい複数の帯域に対して、速度や路面の凹凸などの路面入力が大きい帯域を複数選び、補正演算を行うことにより、速度などの情報がなくとも、路面摩擦係数を推定することができる。
【０００３】
【発明が解決しようとする課題】
しかしながら、上記システムでは、一定速の直進走行中、あるいは、緩やかな加減速、操舵時には、路面摩擦係数を精度良く推定できるが、路面の凹凸が激しい場合には、タイヤ内において、非常に大きなピークを発生する空洞共鳴音が増大し、推定精度の低下を招くことがある。すなわち、上記空洞共鳴音は、タイヤ内圧を検出して路面滑り振動の推定を行う上での外乱要素となる。
【０００４】
本発明は、従来の問題点に鑑みてなされたもので、タイヤ内で発生する空洞共鳴音を抑制して路面状態を精度良く検出する方法とその装置を提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明の請求項１に記載の路面状態推定装置は、ヘルムホルツ共鳴吸音器を備えたホイールと、上記ホイールのタイヤ気室側に取付けられる、タイヤ内圧を検出する圧力検出手段と、この圧力検出手段で検出されたタイヤ内圧の微小圧力変動の信号を車体側に送信する無線通信装置と、上記微小圧力変動の信号を周波数分析して所定の周波数帯域内での圧力変動値を算出する圧力変動値算出手段と、上記算出された圧力変動値から走行時の路面状態を推定する路面状態推定手段とを備え、上記圧力変動値算出手段は、１０００Ｈｚ未満の周波数帯域での圧力変動値と１０００Ｈｚ以上の周波数帯域での圧力変動値とを算出し、上記路面状態推定手段は上記２つの周波数帯域での圧力変動値を比較して路面状態を推定することを特徴とするものである。これにより、上記１０００Ｈｚ未満の周波数帯域に出現する、タイヤ内圧の微小圧力変動の信号に対するノイズ成分となるタイヤ内の空洞共鳴音を低減して、路面状態を精度良く検出することができる。
上記ヘルムホルツ共鳴吸音器は、ホイール内に蓋部材などを用いて副気室を形成するとともに、この副気室とタイヤ主気室とを連通孔により連通させ、上記副気室による音の共鳴吸収現象を利用してタイヤ空洞共鳴音の大きさを低減するもので、本発明者らが検討したところ、副気室の体積をＶ(ｃｍ³)、連通孔の総断面積をＳ(ｃｍ²)、連通孔長さをＬ(ｃｍ)、連通孔の個数をＮとすると、ヘルムホルツ共鳴吸音器の共鳴周波数Ｆ₀(Ｈｚ)は、下記の式で表わせる。

但し、ｃはタイヤ気室内での音速(ｃｍ／ｓｅｃ)である。
したがって、上記ヘルムホルツ共鳴吸音器の各設計値を適宜設定することにより、上記空洞共鳴音周辺の周波数帯域の音を大幅に低減することができる。
【０００６】
請求項２に記載の路面状態推定装置は、タイヤの滑り振動を精度良く検出して路面状態の推定精度を向上させるため、上記圧力検出手段として、上記微小圧力変動に対して、少なくとも１ｋＨｚ以上の応答性を有するものを用いるようにしたものである。
【０００７】
請求項３に記載の路面状態推定装置は、タイヤのサイズ（タイヤ気室内の平均周長）で決まる、上記ホイールに装着されるタイヤの空洞共鳴周波数をＦ_cとしたときに、上記ヘルムホルツ共鳴吸音器の共鳴周波数Ｆ₀の設定範囲を、Ｆ_c−１００Ｈｚ≦Ｆ₀≦Ｆ_c＋１００Ｈｚとなるようにしたもので、これにより、タイヤの空洞共鳴音を確実にかつ大幅に低減することができ、路面状態の推定精度を著しく向上させることが可能となる。
【０００８】
請求項４に記載の路面状態推定装置は、上記ヘルムホルツ共鳴吸音器を、ホイールのリムとリムの径方向外側に配置される複数の蓋部材との間に形成され、周方向に間隔をあけて設けられた少なくとも３個以上の密閉隔壁により分割された複数の副気室と、タイヤ主気室と上記副気室とを連通する連通孔とから構成したものである。なお、上記連通孔は蓋部材に設けてもよいし、隣接する蓋部材間に隙間を設けて連通孔を形成してもよい。
【０００９】
請求項５に記載の路面状態推定装置は、操縦安定性を確保しつつタイヤ空洞共鳴音の低減を効率的に行うため、上記副気室の総体積を、タイヤ主気室の２％以上、２５％以下としたものである。
【００１０】
また、請求項６に記載の路面状態推定方法は、ホイールのタイヤ気室側に取り付けられた圧力検出手段で検出されたタイヤ内圧の時間変動を周波数分析して、１０００Ｈｚ未満の周波数帯域での圧力変動値と１０００Ｈｚ以上の周波数帯域での圧力変動値とを算出し、上記算出された２つの周波数帯域での圧力変動値の比を求め、この圧力変動値の比のデータから走行時の路面状態を推定するとともに、上記ホイールにヘルムホルツ共鳴吸音器を設けて、上記１０００Ｈｚ未満の周波数帯域に出現するタイヤの空洞共鳴に起因する圧力変動成分を除去するようにしたことを特徴とする。
【００１１】
【発明の実施の形態】
以下、本発明の実施の形態について、図面に基づき説明する。
図１は、本発明の一実施の形態を示す模式図で、１はタイヤ２を装着するためのホイール、３はホイールのタイヤ装着部であるホイールリム（以下、リムという）、４はリム３の径方向外側に配置された、タイヤ２とリム３との間に形成される、タイヤ気室５をタイヤ主気室６と副気室７とに分離するための蓋部材、８は上記タイヤ主気室６と副気室７とを連通する連通孔、１０は圧力センサ，バッテリ，センサ駆動回路，無線送信回路などが１つのケース内に収納され、上記リム３に設けられたスナップイン型タイヤバルブと一体化されたバルブ固定型圧力センサユニットで、上記圧力センサの検出面が上記主気室６側に位置するように上記リム３のウエル部３ｗに取付けらる。
本例では、図２（ａ）に示すように、上記蓋部材４を周方向に複数個配置するとともに、上記蓋部材４との間、周方向に間隔をあけて少なくとも３個以上の密閉隔壁９を設けて、周方向に不連続な複数の副気室７（７ａ，７ｂ，‥‥）を形成し、上記副気室７ａ，７ｂ，‥‥のそれぞれに、タイヤ主気室６と副気室７ａ，７ｂ，‥‥とを連通する連通孔８（８ａ，８ｂ，‥‥）を形成することにより、ヘルムホルツ共鳴吸音器を構成する。これにより、製造が容易で、かつ、十分な空洞共鳴効果を有するホイール１を得ることができる。
なお、図２（ｂ）に示すように、各蓋部材４１を周方向に一定間隔をあけながら配置して、スリット状の連通孔８１を形成することもできる。この場合には、位置決めのため、リム３と蓋部材４１に嵌め合わせ構造を形成するためのスペ−サ４１ｚを蓋部材４１の端部に設けておく等の工夫が必要となるが、工数的には最小限で、目的とする形態を得ることができる。
【００１２】
上記ヘルムホルツ共鳴吸音器の共鳴周波数Ｆ₀(Ｈｚ)は、それぞれの副気室の体積をＶ(ｃｍ³)、連通孔の総断面積をＳ(ｃｍ²)、連通孔長さをＬ(ｃｍ)、連通孔の個数をＮ、タイヤ気室内での音速をｃ(ｃｍ／ｓｅｃ)とすると、下記の式で表わせる。

一方、周知のように、装着されるタイヤの空洞共鳴周波数をＦ_cは、タイヤのサイズ（タイヤ気室内の平均周長）で決まる。そこで、本例では、上記副気室７（７ａ，７ｂ，‥‥）の体積Ｖや連通孔８（８ａ，８ｂ，‥‥）の総断面積Ｓなどのヘルムホルツ共鳴吸音器の各設計値を適宜設定して、上記ヘルムホルツ共鳴吸音器の共鳴周波数Ｆ₀の設定範囲を、上記タイヤの空洞共鳴周波数Ｆ_cの±１００Ｈｚの範囲（Ｆ_c−１００Ｈｚ≦Ｆ₀≦Ｆ_c＋１００Ｈｚ）となるように設定することにより、タイヤの空洞共鳴音を大幅に低減するようにしている。
なお、副気室７の総体積が、タイヤ主気室６の体積の２％未満になると、空洞共鳴音低減効果が小さくなり、２５％より大きいと、タイヤバネ定数が下がりすぎるので、振動減衰性や操縦安定性が低下して好ましくないので、副気室総体積としては、タイヤ主気室６の体積の２％〜２５％とすることが好ましく、更に好ましくは３〜１５％がよい。
【００１３】
本発明のホイール１は、詳細には、リム３のウエル部３ｗが、従来品より軸方向に幅広であるか、あるいは、径方向に深い構造になっている。径方向に深い構造とはビ−ド部２ａとホイールベース部３ａの径差が大きいという意味で、ブレーキスペースに余裕がある場合は、ホイールベース部３ａの径を小さくすることで径差を大きくできるが、余裕がない場合はビート部２ａの径を大きくし、タイヤ高さを小さくする（タイヤ外径を同じにする）、いわゆるインチアップ手法により径差を大きくする。また、ウエル部３ｗを軸方向に幅広にすることに対しては、実質的に大きな制約はない。但し、ウエル部３ｗの幅を広くしても必要とする副気室体積は得られるが、より大きな体積を確保できるという観点からは、径方向に深くした方が好ましい。上記構成のホイール１は、従来の鋳造法、あるいは鍛造法などにより製造することができ、安価に製造することができる。
【００１４】
なお、リム３の径方向外側に結合され、複数の副気室７を形成する複数の蓋部材４の外周面、及び、リム３の上記蓋部材４で覆われていない外周面のプロファイルは、ウエル部３ｗを有する通常のＪＡＴＭＡ規格に従うラインになるように設定される。また、蓋部材４（あるいは蓋部材４１）の材質はホイール１本体と同じ金属材料であってもよいし、異なる金属材料や樹脂などの材料でもよい。蓋部材の結合方式は、同一の金属材料であれば溶接が好ましく選択されるが、異なる部材の場合はボルトや接着、嵌め合わせによる固定方式となる。
蓋部材４（あるいは蓋部材４１）の厚みは、材質に依存するが、タイヤリム組み時に塑性変形せず、かつ走行中の遠心力により大きく変形しない程度の剛性を確保する範囲で、薄くすることが重量増加を抑制するので好ましい。但し、連通孔の厚みは、共鳴周波数に影響する要素であるので、厚み設定は厳密に行う必要がある。
このような構成とすることによって、ホイール１本体とは別に製造した蓋部材４を結合するだけで副気室を形成できるので、製造工数やコスト、重量の増加が少なく、また、回転バランスも従来レベルを確保した上で、簡便に副気室を形成することができる。また、ホイール１本体とタイヤ２の中に蓋部材４を配置し、副気室７を形成する方式になっているので、エア漏れの懸念がない。また、ホイール１本体と蓋部材４（あるいは蓋部材４１）との結合後は、ホイール１のリム形状は、従来のホイールのリムと同様のプロファイルとなるため、タイヤのリム組み、リム解きを従来の手法で行うことができる。
【００１５】
また、上記副気室７の数は３つ以上必要であることが、検討の結果判明した。すなわち、副気室７の数が少ないと、共鳴吸音遅れが生じ、結果として、タイヤ内の空洞共鳴音を効果的に低減できない。この場合、隔壁９の数を多くすることが効果的であり、例えば、連通孔８だけを周方向に分散しても効果が上がらない。好ましくは、副気室７の数は４個以上が良く、５個以上であれば更に好ましい。また、回転バランスを悪化させないように、各隔壁９は同寸法で、周上等配分位置に設置することが好ましい。隔壁９の厚みには特に制約はなく、重量抑制の意味では、薄くすることが好ましい。また、材質も特に制約はなく、ホイール１本体と一体で作成するのであれば、アルミ、鉄などのホイール１本体と同じ材質としてもよい。あるいは、密閉性を向上させるという観点からは、ゴムなどの圧縮性を持ち、かつ低比重の材料も好ましく使用しうる。
【００１６】
次に、本発明による路面状態推定方法について説明する。
図３は、本発明の路面状態推定装置２０の構成を示す図で、本装置２０は、圧力センサ１１を有しタイヤバルブと一体化されたバルブ固定型圧力センサユニット１０が取付けられた転動側（ホイール側）Ａと、非転動側である車体側Ｂの後述する演算部とを無線により接続するように構成したものである。
ホイール側Ａのバルブ固定型圧力センサユニット１０は、タイヤ内の気体の圧力を検出する圧力センサ１１と、この圧力センサ１１の出力の時間軸上における微小振動成分（ＡＣ成分）からその微小の圧力変動を検出する圧力センサ回路１２と、Ａ／Ｄ変換器１３ａ，情報圧縮回路１３ｂ，送信器１３ｃを備え、上記検出されたタイヤ内の気体の圧力変動の情報信号をデジタル信号に変換して圧縮し、この圧縮された信号をアンテナ１４から車体側Ｂに無線により送信する送信回路１３と、圧力センサ１１，圧力センサ回路１２，送信回路１３を駆動するためのバッテリ１５とを備える。ここで、上記圧力センサユニット１０としては、少なくとも１ｋＨｚ以上、好ましくは５ｋＨｚ以上、更に好ましくは１０ｋＨｚ以上の応答性を有する圧力センサ１１及び圧力センサ回路１２を備えたものを使用する。これにより、上記圧力変動の測定精度を向上させることができる。
なお、上記バルブ固定型圧力センサユニット１０は、図１に示すように、ホイール１のリム３に設けられたスナップイン型タイヤバルブと一体化され、リム３のウエル部３ｗに取付けらる。また、本例では、上記タイヤバルブにアンテナ機構を持たせるようにしているが、アンテナ１４を別途設けてもよい。
また、車体側Ｂには、上記圧縮された振動情報信号を受信するアンテナ２１を備えた受信器２２と、上記受信された圧力変動情報信号を復元して周波数分析する周波数分析手段であるＦＦＴアナライザー２３と、ＦＦＴアナライザー２３で得られた圧力変動スペクトルから路面摩擦係数を推定する演算回路２４とを備えた路面摩擦係数演算手段２５を備える。
また、車体側Ｂには、上記推定された路面摩擦係数の値を表示するμ表示器３１と、上記路面摩擦係数に基づいてＡＢＳブレーキの油圧を制御するＡＢＳブレーキ制御器（車両制御手段）３２が設置される。
【００１７】
次に、上記構成の路面状態推定装置２０の動作について説明する。
バルブ固定型圧力センサユニット１０では、圧力センサ１１及び圧力センサ回路１２により走行中のタイヤに充填されている気体の圧力変動を検出し、送信回路１３にて上記データをＡ／Ｄ変換して圧縮し、アンテナ１４から車体側Ｂに送信する。車体側Ｂでは、上記送信された圧縮信号を、アンテナ２１を介して受信器２２で受信し、これをＦＦＴアナライザー２３に送って周波数分析し、圧力変動スペクトルを求める。演算回路２４では、上記圧力変動スペクトルの少なくとも２つの周波数帯域内での圧力変動の平均値を算出して、上記算出された圧力変動の平均値から路面摩擦係数μの推定値を演算する。
図４は、タイヤのサイズが１９５／６０Ｒ１５のタイヤを搭載した１８００ＣＣの乗用車を使用し、乾燥アスファルト路と氷盤路とをそれぞれ速度６０ｋｍ／ｈｒで走行して得られたタイヤ内圧力変動スペクトルの一例を示す図である。同図から明らかなように、路面摩擦係数の低い氷盤路における圧力変動スペクトルは、乾燥アスファルト路の場合に比較して１．５ｋＨｚ以上の周波数帯域で圧力変動レベルが高くなっていることが判る。したがって、得られた圧力変動スペクトルのうち、路面の滑り易さの影響を受けにくい帯域である３００Ｈｚ〜１０００Ｈｚ帯域の圧力変動平均値と、路面状態による圧力変動レベルの差が大きい１０００Ｈｚ〜５０００Ｈｚ帯域の圧力変動平均値とのそれぞれの平均値を算出して、上記算出された圧力変動の平均値の比を求め、予め上記と同様の走行試験により求めた、路面摩擦係数μと圧力変動値の比のデータとを比較することにより、路面摩擦係数の推定値を求めることができる。
【００１８】
ところで、路面の凹凸が激しい場合には、タイヤ内において、非常に大きなピークを発生する空洞共鳴音が増大するので、路面摩擦係数の推定精度が低下する場合がある。図５は、通常ホイ−ルを搭載した車両と、本発明によるヘルムホルツ共鳴吸音器付きホイ−ル１を搭載した車両とを路面凹凸が大きい乾燥アスファルト路を速度６０ｋｍ／ｈｒで走行したときのタイヤ内圧力の周波数解析結果を示す図で、本発明のホイール１を備えた路面状態推定装置２０で測定したタイヤ内の圧力変動スペクトルは、空洞共鳴音の発生による圧力変動レベルのピ−クが大きく低減し、外乱要因が減少していることが判る。
【００１９】
上記路面状態推定装置２０で推定された路面摩擦係数の値は、μ表示器３１に送られ表示される。また、ＡＢＳブレーキ制御器３２に送り、上記推定された路面摩擦係数に応じてＡＢＳブレーキの油圧を制御する。
本例では、上記のように、ヘルムホルツ共鳴吸音器により、上記タイヤ内圧の微小圧力変動の信号に対するノイズ成分となるタイヤ内の空洞共鳴音を大幅に低減するようにしているので、路面摩擦係数を精度良く推定することがき、車両の走行状態を安定して制御することができる。
【００２０】
なお、上記実施の形態では、圧力センサ１１で検出したタイヤ内圧の変動情報から路面摩擦係数の値を推定してこれをμ表示器３１に表示するようにしたが、タイヤが接地している路面状態を通常状態、要注意状態、危険状態などに分類して走行時における路面の滑り易さ＝危険度を表示するようにしてもよい。
また、上記例では、路面摩擦係数演算手段２５を車体側Ｂに設けたが、これをホイール側Ａに設け、上記送信回路１３により、上記路面摩擦係数演算手段２５で推定された路面摩擦係数の値を車体側Ｂに送信するようにしてもよい。
また、上記例では、圧力変動値の比から路面摩擦係数の推定値を求めるようにしたが、必要とされる幾つかの周波数帯域の圧力変動レベル（帯域値）を求め、係数を掛けるなどの演算処理を行うことにより、路面摩擦係数を推定するようにしてもよい。ここで、上記周波数帯域としては、上記路面の滑りの寄与が大きい複数の帯域に対して、速度や路面の凹凸などの路面入力が大きい帯域を複数選び、補正演算を行えば、速度などの情報がなくとも、路面摩擦係数を精度良く推定することができる。
【００２１】
＜実施例＞
本発明の路面状態推定装置２０を搭載した車両を、路面凹凸が大きい乾燥アスファルト補修路を走行し、連続的に路面摩擦係数を測定した結果を図６示す。また、比較例として、ヘルムホルツ共鳴吸音器が付いていない通常のホイールに本発明と同様の圧力センサユニットを配し、路面摩擦係数を推定した結果も併せて示す。なお、同路面の路面摩擦係数は、通常の制動試験によって計測したところ、０．９１であった。
同図から明らかなように、本発明品は、摩擦係数推定値が安定している。これは、空洞共鳴音を大幅に低減することにより、外乱要因を減少していることによるもので、本発明により、路面摩擦係数を精度良く求めることができることが確認された。
【００２２】
【発明の効果】
以上説明したように本発明の路面状態推定装置は、ヘルムホルツ共鳴吸音器を備えたホイールと、上記ホイールのタイヤ気室側に取付けられる、タイヤ内圧を検出する圧力検出手段と、上記微小圧力変動の信号を周波数分析して所定の周波数帯域内での圧力変動値を算出する圧力変動値算出手段と、上記算出された圧力変動値から走行時の路面状態を推定する路面状態推定手段とを備え、上記ヘルムホルツ共鳴吸音器により、上記タイヤ内圧の微小圧力変動の信号に対するノイズ成分となるタイヤ内の空洞共鳴音を大幅に低減するようにしたので、路面摩擦係数を精度良く推定することがき、車両の走行状態を安定して制御することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態を示す図である。
【図２】本実施の形態に係わるホイールの構成を示す図である。
【図３】本実施の形態に係わる路面状態推定装置の構成を示す図である。
【図４】乾燥アスファルト路と氷盤路におけるタイヤ内圧の変動スペクトルを示す図である。
【図５】空洞共鳴音の減衰効果を示す図である。
【図６】本発明による路面摩擦係数の推定結果を示す図である。
【符号の説明】
１ホイール、２タイヤ、２ａビ−ド部、３ホイールリム、
３ａホイールベース部、３ｗウエル部、４蓋部材、５タイヤ気室、
６タイヤ主気室、７副気室、８連通孔、９隔壁、
１０バルブ固定型圧力センサユニット、１１圧力センサ、１２圧力センサ回路、１３送信回路、１３ａＡ／Ｄ変換器、１３ｂ情報圧縮回路、
１３ｃ送信器、１４送信用のアンテナ、１５バッテリ、
２０路面摩擦係数推定装置、２１受信用のアンテナ、２２受信器、
２３ＦＦＴアナライザー、２４演算回路、２５路面摩擦係数演算手段、
３１ μ表示器、３２ＡＢＳブレーキ制御器。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for estimating a road surface state during travel of a vehicle.
[0002]
[Prior art]
In order to improve the running stability of an automobile, it is required to accurately estimate a friction coefficient (road surface friction coefficient) or a road surface state between a tire and a road surface and feed it back to vehicle control. In particular, if the road surface friction coefficient can be estimated in advance before a risk avoidance operation such as braking / driving or steering, for example, more advanced control of the ABS brake or the like can be achieved, and safety can be further improved. It is done. In addition, simply telling the driver of the degree of danger enables the driver to perform an early deceleration operation, and can reduce the number of accidents.
The present applicant, for example, in Japanese Patent Application No. 2001-36048, estimates the road surface state during traveling with high accuracy, and estimates the road surface state capable of feedback-controlling the traveling state of the vehicle based on the estimated road surface state. A method and apparatus are proposed. This method is based on the fact that the tire slips in the tread even during steady running, and is obtained by detecting the minute fluctuations of the gas in the propagated tire and performing frequency analysis on this. The pressure fluctuation level in a predetermined frequency band of the pressure fluctuation spectrum is detected to estimate the road surface friction coefficient.
More specifically, the above-described technique causes the tire to slip on the tread surface due to wiping deformation even during steady running, and the slip amount increases as the road surface friction coefficient decreases. Due to this phenomenon, high-frequency vibration of 1 kHz or more of the tire increases, and this vibration propagates to the gas in the tire. Therefore, by monitoring the minute pressure fluctuations in the tire and analyzing the frequency, further calculating the pressure fluctuation levels (band values) of several required frequency bands and performing arithmetic processing such as multiplying by a coefficient, the road surface The coefficient of friction can be estimated. Here, as the frequency band, a plurality of bands having a large road surface input such as speed and road surface unevenness are selected with respect to a plurality of bands having a large contribution of the slip of the road surface, and a speed calculation is performed by performing a correction calculation. Even if there is no information, the road surface friction coefficient can be estimated.
[0003]
[Problems to be solved by the invention]
However, in the above system, the road surface friction coefficient can be accurately estimated during straight traveling at a constant speed, or during gentle acceleration / deceleration and steering. However, if the road surface is extremely uneven, a very large peak is generated in the tire. The cavity resonance sound that generates noise increases, which may lead to a decrease in estimation accuracy. That is, the cavity resonance sound is a disturbance element in estimating tire slip vibration by detecting tire internal pressure.
[0004]
The present invention has been made in view of the conventional problems, and an object of the present invention is to provide a method and an apparatus for accurately detecting a road surface state by suppressing cavity resonance generated in a tire.
[0005]
[Means for Solving the Problems]
The road surface state estimating apparatus according to claim 1 of the present invention includes a wheel having a Helmholtz resonance sound absorber, pressure detecting means for detecting a tire internal pressure attached to the tire chamber side of the wheel, and the pressure detecting means. A wireless communication device that transmits a signal of a minute pressure fluctuation of the tire internal pressure detected in the vehicle to the vehicle body side, and a pressure fluctuation value that calculates a pressure fluctuation value within a predetermined frequency band by frequency analysis of the signal of the minute pressure fluctuation Calculating means, and road surface condition estimating means for estimating a road surface condition during traveling from the calculated pressure fluctuation value, wherein the pressure fluctuation value calculating means has a pressure fluctuation value in a frequency band of less than 1000 Hz and a frequency fluctuation value of 1000 Hz or more. A pressure fluctuation value in the frequency band is calculated, and the road surface state estimating means compares the pressure fluctuation value in the two frequency bands to estimate the road surface state. A. Thus, appears in the frequency band less than the 1000 Hz, to reduce the cavity resonance in the tire according to a noise component to the signal of the minute pressure fluctuations of the tire pressure, Ru can it to accurately detect the road surface condition.
The Helmholtz resonance sound absorber forms a secondary air chamber using a lid member or the like in the wheel, and communicates the secondary air chamber and the tire main air chamber with a communication hole so that resonance absorption of sound by the secondary air chamber is achieved. This phenomenon is used to reduce the size of the tire cavity resonance sound. The present inventors have investigated that the volume of the auxiliary air chamber is V (cm ³ ) and the total cross-sectional area of the communication hole is S (cm ^2). ), Where the communication hole length is L (cm) and the number of communication holes is N, the resonance frequency F ₀ (Hz) of the Helmholtz resonance absorber can be expressed by the following equation.

Where c is the speed of sound (cm / sec) in the tire chamber.
Therefore, by appropriately setting each design value of the Helmholtz resonance sound absorber, it is possible to greatly reduce the sound in the frequency band around the cavity resonance sound.
[0006]
The road surface state estimation device according to claim 2 detects the slip vibration of the tire with high accuracy and improves the road surface state estimation accuracy, so that the pressure detection means has at least 1 kHz or more with respect to the minute pressure fluctuation. What has responsiveness is used.
[0007]
The road surface state estimating device according to claim 3 is characterized in that the Helmholtz resonance sound absorption when the cavity resonance frequency of the tire mounted on the wheel, which is determined by the size of the tire (average circumference in the tire chamber), is F _c. The setting range of the resonance frequency F ₀ of the vessel is such that F _c −100 Hz ≦ F ₀ ≦ F _c +100 Hz, and thereby, the cavity resonance sound of the tire can be reliably and significantly reduced, The estimation accuracy of the road surface condition can be significantly improved.
[0008]
Road surface condition estimating apparatus according to claim 4, the upper Symbol Helmholtz resonance sound absorber, is formed between the plurality of cover members disposed radially outside the rim and the rim of the wheel, at intervals in the circumferential direction And a plurality of sub air chambers divided by at least three or more sealed partition walls, and a communication hole that connects the tire main air chamber and the sub air chamber. The communication hole may be provided in the lid member, or the communication hole may be formed by providing a gap between adjacent lid members.
[0009]
In order to efficiently reduce the tire cavity resonance sound while ensuring steering stability, the road surface state estimation device according to claim 5 has a total volume of the auxiliary air chamber of 2% or more of the tire main air chamber, 25% or less.
[0010]
Moreover, road surface condition estimation method according to claim 6, the time variation of the tire pressure detected by the pressure detecting means attached to the tire air chamber side of the wheel circumference and wavenumber analysis, in a frequency band lower than 1000Hz A pressure fluctuation value and a pressure fluctuation value in a frequency band of 1000 Hz or more are calculated, a ratio of the pressure fluctuation values in the two calculated frequency bands is obtained, and a road surface during traveling is calculated from the data of the ratio of the pressure fluctuation values. The condition is estimated , and a Helmholtz resonance sound absorber is provided on the wheel so as to remove a pressure fluctuation component caused by tire cavity resonance appearing in the frequency band of less than 1000 Hz .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing an embodiment of the present invention, in which 1 is a wheel for mounting a

tire

2, 3 is a wheel rim (hereinafter referred to as a rim) which is a tire mounting portion of the wheel, and 4 is a rim 3. A lid member for separating the tire air chamber 5 into a tire main air chamber 6 and a sub air chamber 7 formed between the tire 2 and the

rim

3, and 8 is the tire described above. A communication hole 10 for communicating the main air chamber 6 and the sub air chamber 7 includes a pressure sensor, a battery, a sensor driving circuit, a wireless transmission circuit, and the like housed in one case, and a snap-in type provided in the rim 3. A valve-fixed pressure sensor unit integrated with a tire valve is attached to the well portion 3w of the rim 3 so that the detection surface of the pressure sensor is located on the main air chamber 6 side.
In this example, as shown in FIG. 2 (a), a plurality of the lid members 4 are arranged in the circumferential direction, and at least three or more sealed partition walls are spaced apart from the lid member 4 in the circumferential direction. 9 are formed to form a plurality of auxiliary air chambers 7 (7a, 7b,...) That are discontinuous in the circumferential direction, and each of the auxiliary air chambers 7a, 7b,. A Helmholtz resonance sound absorber is formed by forming communication holes 8 (8a, 8b,...) That communicate with the air chambers 7a, 7b,. Thereby, the wheel 1 which is easy to manufacture and has a sufficient cavity resonance effect can be obtained.
In addition, as shown in FIG.2 (b), each cover member 41 can also be arrange | positioned at predetermined intervals in the circumferential direction, and the slit-shaped communicating hole 81 can also be formed. In this case, for positioning, it is necessary to devise such as providing a spacer 41z for forming a fitting structure between the rim 3 and the lid member 41 at the end of the lid member 41. The desired form can be obtained at a minimum.
[0012]
The resonance frequency F ₀ (Hz) of the Helmholtz resonance sound absorber is such that the volume of each auxiliary air chamber is V (cm ³ ), the total cross-sectional area of the communication holes is S (cm ² ), and the communication hole length is L (cm ), The number of communication holes is N, and the sound velocity in the tire chamber is c (cm / sec).

On the other hand, as is well known, the cavity resonance frequency F _c of the tire to be mounted is determined by the size of the tire (the average circumference of the tire chamber). Therefore, in this example, design values of the Helmholtz resonance sound absorber such as the volume V of the auxiliary air chamber 7 (7a, 7b,...) And the total cross-sectional area S of the communication hole 8 (8a, 8b,. By appropriately setting, the setting range of the resonance frequency F ₀ of the Helmholtz resonance sound absorber is within a range of ± 100 Hz (F _c −100 Hz ≦ F ₀ ≦ F _c +100 Hz) of the cavity resonance frequency F _c of the tire. By setting, the cavity resonance noise of the tire is greatly reduced.
If the total volume of the auxiliary air chamber 7 is less than 2% of the volume of the tire main air chamber 6, the effect of reducing the cavity resonance noise is reduced. If the total volume is greater than 25%, the tire spring constant is excessively lowered, so that the vibration damping property is reduced. Further, the total stability of the auxiliary air chamber is preferably 2% to 25% of the volume of the tire main air chamber 6, and more preferably 3 to 15%.
[0013]
In detail, the wheel 1 of the present invention has a structure in which the well portion 3w of the rim 3 is wider in the axial direction than the conventional product or deeper in the radial direction. The deep structure in the radial direction means that the diameter difference between the bead portion 2a and the wheel base portion 3a is large. If there is a margin in the brake space, the diameter difference is increased by reducing the diameter of the wheel base portion 3a. If there is not enough room, the diameter of the beat portion 2a is increased, the tire height is decreased (the tire outer diameter is the same), and the diameter difference is increased by a so-called inch-up method. Further, there is no substantial restriction on the well portion 3w being wide in the axial direction. However, although the required sub-air chamber volume can be obtained even if the width of the well portion 3w is widened, it is preferable to make it deep in the radial direction from the viewpoint of securing a larger volume. The wheel 1 having the above-described configuration can be manufactured by a conventional casting method or a forging method, and can be manufactured at low cost.
[0014]
The profile of the outer peripheral surface of the plurality of lid members 4 coupled to the outer side in the radial direction of the rim 3 and forming the plurality of auxiliary air chambers 7 and the outer peripheral surface of the rim 3 not covered by the lid member 4 are as follows: The line is set so as to be in line with a normal JATMA standard having a well portion 3w. The material of the lid member 4 (or the lid member 41) may be the same metal material as that of the main body of the wheel 1, or may be a different metal material or resin. As a method of joining the lid members, welding is preferably selected as long as they are the same metal material, but in the case of different members, a fixing method by bolts, adhesion, or fitting is used.
Although the thickness of the lid member 4 (or the lid member 41) depends on the material, it can be made thin as long as it does not undergo plastic deformation when assembling the tire rim and ensures rigidity that does not greatly deform due to centrifugal force during traveling. This is preferable because an increase in weight is suppressed. However, since the thickness of the communication hole is an element affecting the resonance frequency, it is necessary to set the thickness strictly.
By adopting such a configuration, the auxiliary air chamber can be formed simply by connecting the lid member 4 manufactured separately from the wheel 1 main body, so that the number of manufacturing steps, cost, and weight are small, and the rotation balance is also conventional. The auxiliary air chamber can be easily formed while ensuring the level. Further, since the lid member 4 is arranged in the wheel 1 body and the tire 2 and the auxiliary air chamber 7 is formed, there is no fear of air leakage. In addition, after the wheel 1 body and the lid member 4 (or the lid member 41) are joined, the rim shape of the wheel 1 has the same profile as that of a conventional wheel rim. It can be done by the method.
[0015]
Further, as a result of examination, it has been found that the number of the auxiliary air chambers 7 is required to be three or more. That is, if the number of auxiliary air chambers 7 is small, a resonance sound absorption delay occurs, and as a result, the cavity resonance sound in the tire cannot be effectively reduced. In this case, it is effective to increase the number of partition walls 9. For example, even if only the communication holes 8 are dispersed in the circumferential direction, the effect is not improved. Preferably, the number of auxiliary air chambers 7 is four or more, and more preferably five or more. Moreover, it is preferable to install each partition wall 9 in the same distribution position on the circumference so as not to deteriorate the rotation balance. There is no restriction | limiting in particular in the thickness of the partition 9, It is preferable to make thin in the meaning of weight suppression. Also, the material is not particularly limited, and may be made of the same material as that of the wheel 1 body such as aluminum and iron as long as the material is integrally formed with the wheel 1 body. Alternatively, from the viewpoint of improving the sealing performance, a material having a compressibility such as rubber and having a low specific gravity can be preferably used.
[0016]
Next, the road surface state estimation method according to the present invention will be described.
FIG. 3 is a diagram showing the configuration of the road surface state estimating device 20 according to the present invention. This device 20 includes a pressure sensor 11 and a rolling device to which a valve fixed pressure sensor unit 10 integrated with a tire valve is attached. The side (wheel side) A and a calculation unit (described later) on the non-rolling side vehicle body side B are configured to be connected by radio.
The valve-fixed pressure sensor unit 10 on the wheel side A includes a pressure sensor 11 that detects the pressure of gas in the tire, and a minute pressure from a minute vibration component (AC component) on the time axis of the output of the pressure sensor 11. A pressure sensor circuit 12 for detecting fluctuation, an A / D converter 13a, an information compression circuit 13b, and a transmitter 13c are provided, and the information signal of the pressure fluctuation of the detected gas in the tire is converted into a digital signal and compressed. In addition, a transmission circuit 13 that wirelessly transmits the compressed signal from the antenna 14 to the vehicle body side B, and a pressure sensor 11, a pressure sensor circuit 12, and a battery 15 for driving the transmission circuit 13 are provided. Here, the pressure sensor unit 10 includes a pressure sensor 11 and a pressure sensor circuit 12 having responsiveness of at least 1 kHz or more, preferably 5 kHz or more, and more preferably 10 kHz or more. Thereby, the measurement accuracy of the pressure fluctuation can be improved.
The valve-fixed pressure sensor unit 10 is integrated with a snap-in type tire valve provided on the rim 3 of the wheel 1 and is attached to the well portion 3w of the rim 3 as shown in FIG. In this example, the tire valve is provided with an antenna mechanism, but the antenna 14 may be provided separately.
The vehicle body side B includes a receiver 22 including an antenna 21 that receives the compressed vibration information signal, and an FFT analyzer that is a frequency analysis unit that performs frequency analysis by restoring the received pressure fluctuation information signal. 23 and a road surface friction coefficient calculating means 25 including a calculation circuit 24 for estimating a road surface friction coefficient from the pressure fluctuation spectrum obtained by the FFT analyzer 23.
Further, on the vehicle body side B, a μ indicator 31 for displaying the estimated road surface friction coefficient value, and an ABS brake controller (vehicle control means) 32 for controlling the hydraulic pressure of the ABS brake based on the road surface friction coefficient. Is installed.
[0017]
Next, the operation of the road surface state estimation device 20 having the above configuration will be described.
In the fixed valve type pressure sensor unit 10, the pressure sensor 11 and the pressure sensor circuit 12 detect the pressure fluctuation of the gas filled in the running tire, and the transmission circuit 13 A / D converts the data to compress it. And transmitted from the antenna 14 to the vehicle body side B. On the vehicle body side B, the transmitted compressed signal is received by the receiver 22 via the antenna 21 and sent to the FFT analyzer 23 for frequency analysis to obtain a pressure fluctuation spectrum. The arithmetic circuit 24 calculates an average value of pressure fluctuations in at least two frequency bands of the pressure fluctuation spectrum, and calculates an estimated value of the road surface friction coefficient μ from the calculated average value of pressure fluctuations.
FIG. 4 shows a tire pressure fluctuation spectrum obtained by using a 1800CC passenger car equipped with a tire having a tire size of 195 / 60R15 and traveling on a dry asphalt road and an ice board road at a speed of 60 km / hr, respectively. It is a figure which shows an example. As is clear from the figure, the pressure fluctuation spectrum in the ice road with a low road surface friction coefficient has a higher pressure fluctuation level in the frequency band of 1.5 kHz or more than in the case of the dry asphalt road. . Therefore, in the obtained pressure fluctuation spectrum, the difference between the pressure fluctuation average value in the 300 Hz to 1000 Hz band, which is a band that is not easily affected by the slipperiness of the road surface, and the pressure fluctuation level depending on the road surface state is large in the 1000 Hz to 5000 Hz band. Calculate the average value of each of the pressure fluctuation average values, determine the ratio of the calculated average values of pressure fluctuations, and calculate the ratio of the road surface friction coefficient μ and the pressure fluctuation value obtained in advance by the same running test as described above. The estimated value of the road surface friction coefficient can be obtained by comparing with the above data.
[0018]
By the way, when the road surface is very uneven, the cavity resonance noise that generates a very large peak increases in the tire, and the estimation accuracy of the road surface friction coefficient may decrease. FIG. 5 shows a tire when a vehicle equipped with a normal wheel and a vehicle equipped with a wheel 1 with a Helmholtz resonance sound absorber according to the present invention travels on a dry asphalt road with large road surface irregularities at a speed of 60 km / hr. FIG. 5 is a diagram showing the frequency analysis result of the internal pressure, and the pressure fluctuation spectrum in the tire measured by the road surface state estimation device 20 equipped with the wheel 1 of the present invention has a large peak of the pressure fluctuation level due to the generation of the cavity resonance sound. It can be seen that the disturbance factor is reduced.
[0019]
The value of the road surface friction coefficient estimated by the road surface state estimating device 20 is sent to the μ display 31 and displayed. Moreover, it sends to the ABS brake controller 32 and controls the hydraulic pressure of the ABS brake according to the estimated road surface friction coefficient.
In this example, as described above, the Helmholtz resonance sound absorber significantly reduces the cavity resonance sound in the tire, which is a noise component with respect to the signal of the minute pressure fluctuation of the tire internal pressure. It is possible to estimate with high accuracy and to stably control the running state of the vehicle.
[0020]
In the above embodiment, the value of the road surface friction coefficient is estimated from the variation information of the tire internal pressure detected by the pressure sensor 11 and displayed on the μ display 31. However, the road surface on which the tire is grounded is used. The state may be classified into a normal state, a cautionary state, a dangerous state, etc., and the slipperiness of the road surface during traveling = the degree of danger may be displayed.
Further, in the above example, the road surface friction coefficient calculating means 25 is provided on the vehicle body side B. However, this is provided on the wheel side A, and the road surface friction coefficient estimated by the road surface friction coefficient calculating means 25 is estimated by the transmission circuit 13. The value may be transmitted to the vehicle body side B.
In the above example, the estimated value of the road surface friction coefficient is obtained from the ratio of the pressure fluctuation values. However, the pressure fluctuation levels (band values) of several required frequency bands are obtained, and the coefficient is multiplied. The road surface friction coefficient may be estimated by performing arithmetic processing. Here, as the frequency band, if a plurality of bands having a large road surface input such as speed and road surface unevenness are selected with respect to a plurality of bands having a large contribution of the slip on the road surface, information such as a speed can be obtained by performing a correction calculation. Even without this, the road surface friction coefficient can be estimated with high accuracy.
[0021]
<Example>
FIG. 6 shows the result of continuously measuring the road surface friction coefficient by running a vehicle equipped with the road surface state estimating device 20 of the present invention on a dry asphalt repair road with large road surface unevenness. As a comparative example, the result of estimating the road surface friction coefficient by arranging a pressure sensor unit similar to the present invention on a normal wheel without a Helmholtz resonance sound absorber is also shown. The road surface friction coefficient of the road surface was 0.91 as measured by a normal braking test.
As is clear from the figure, the estimated coefficient of friction of the product of the present invention is stable. This is because the cause of the disturbance is reduced by greatly reducing the cavity resonance noise, and it was confirmed that the road surface friction coefficient can be obtained with high accuracy according to the present invention.
[0022]
【The invention's effect】
As described above, the road surface state estimating device of the present invention includes a wheel provided with a Helmholtz resonance sound absorber, a pressure detecting means for detecting a tire internal pressure attached to the tire chamber side of the wheel, and the minute pressure fluctuation. A pressure fluctuation value calculating means for calculating a pressure fluctuation value within a predetermined frequency band by performing frequency analysis of the signal, and a road surface state estimating means for estimating a road surface condition during traveling from the calculated pressure fluctuation value, Since the Helmholtz resonance sound absorber significantly reduces the cavity resonance sound in the tire, which is a noise component for the signal of the minute pressure fluctuation of the tire internal pressure, the road surface friction coefficient can be accurately estimated, and the vehicle The running state can be controlled stably.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of a wheel according to the present embodiment.
FIG. 3 is a diagram showing a configuration of a road surface state estimation apparatus according to the present embodiment.
FIG. 4 is a diagram showing a fluctuation spectrum of tire internal pressure on a dry asphalt road and an ice board road.
FIG. 5 is a diagram illustrating an attenuation effect of cavity resonance sound.
FIG. 6 is a diagram showing an estimation result of a road surface friction coefficient according to the present invention.
[Explanation of symbols]
1 wheel, 2 tires, 2a bead part, 3 wheel rim,
3a Wheel base part, 3w well part, 4 lid member, 5 tire air chamber,
6 tire main air chamber, 7 sub air chamber, 8 communication hole, 9 partition,
DESCRIPTION OF SYMBOLS 10 Valve fixed type pressure sensor unit, 11 Pressure sensor, 12 Pressure sensor circuit, 13 Transmission circuit, 13a A / D converter, 13b Information compression circuit,
13c Transmitter, 14 Transmitting antenna, 15 Battery,
20 road surface friction coefficient estimating device, 21 receiving antenna, 22 receiver,
23 FFT analyzer, 24 calculation circuit, 25 road friction coefficient calculation means,
31 μ display, 32 ABS brake controller.

Claims

A wheel equipped with a Helmholtz resonance sound absorber, a pressure detection means for detecting a tire internal pressure, which is attached to the tire chamber side of the wheel, and a signal of a minute pressure fluctuation of the tire internal pressure detected by the pressure detection means A wireless communication device for transmitting to the pressure, a pressure fluctuation value calculation means for calculating a pressure fluctuation value within a predetermined frequency band by frequency analysis of the signal of the minute pressure fluctuation, and Road surface state estimating means for estimating a road surface state, the pressure fluctuation value calculating means calculates a pressure fluctuation value in a frequency band below 1000 Hz and a pressure fluctuation value in a frequency band of 1000 Hz or more, and the road surface state The estimation means compares the pressure fluctuation values in the two frequency bands to estimate the road surface state, and the road surface state estimation device.

The road surface state estimation device according to claim 1, wherein the pressure detection means has a response of at least 1 kHz to the minute pressure fluctuation.

3. The resonance frequency F ₀ of the Helmholtz resonance absorber is set in the following range, where F _c is a cavity resonance frequency of a tire mounted on the wheel. The road surface state estimation apparatus described.
F _c −100 Hz ≦ F ₀ ≦ F _c +100 Hz

On SL Helmholtz resonance sound absorber, is formed between the plurality of lid members disposed in the rim and the radially outer rim of the wheel, at least three or more sealed bulkhead provided at intervals in the circumferential direction The road surface state estimation according to any one of claims 1 to 3, comprising a plurality of divided sub air chambers, and a communication hole that communicates the tire main air chamber and the sub air chamber. apparatus.

The road surface state estimating device according to claim 4, wherein the total volume of the auxiliary air chamber is 2% or more and 25% or less of the tire main air chamber.

Analyzing the time variation of the tire internal pressure detected by the pressure detection means attached to the tire chamber side of the wheel, and analyzing the pressure fluctuation value in the frequency band below 1000 Hz and the pressure fluctuation value in the frequency band above 1000 Hz Is calculated, the ratio of the pressure fluctuation values in the two calculated frequency bands is obtained, the road surface condition at the time of traveling is estimated from the data of the ratio of the pressure fluctuation values, and a Helmholtz resonance sound absorber is provided on the wheel. A road surface state estimation method characterized in that pressure fluctuation components due to tire cavity resonance appearing in a frequency band of less than 1000 Hz are removed.