JP2004338456A

JP2004338456A - Slip ratio computing method, tire pneumatic pressure decrease detection method and device, program of slip ratio computation and program of tire decompression determination

Info

Publication number: JP2004338456A
Application number: JP2003134816A
Authority: JP
Inventors: Toshifumi Sugisawa; 利文杉澤
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2003-05-13
Filing date: 2003-05-13
Publication date: 2004-12-02
Anticipated expiration: 2023-05-13
Also published as: JP4004990B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slip ratio computing method to find a slip ratio of a tire on a four-wheel drive vehicle. <P>SOLUTION: This slip ratio computing method to find the slip ratio of the tire installed on the four-wheel vehicle capable of controlling the distribution of driving torque to a front axle and a rear axle includes a process to find a difference of the slip ratio of the front wheel tires and the slip ratio of the rear wheel tires from wheel rotation information provided from the tires, a process to find a relational expression from a relation of the difference of the slip ratios and a distribution ratio of the driving torque to the front axle and the rear axle provided from the four-wheel vehicle, a process to find the distribution of grounding loads of the right and left front wheels and grounding loads of the right and left rear wheels and a process to find the slip ratios of the front wheel tires and the rear wheel tires from the relational expression in accordance with a relation in which changing ratios of the respective slip ratios of the front wheel tires and the rear wheel tires in accordance with a torque increasing amount of the driving torque are in reverse proportion to the distribution of the grounding loads of the right and left front wheels and the grounding loads of the right and left rear wheels. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明はスリップ率演算方法、タイヤ空気圧低下検出方法および装置、ならびにスリップ率演算のプログラムおよびタイヤ減圧判定のプログラムに関する。さらに詳しくは、４輪駆動車におけるタイヤのスリップ率を求めるスリップ率演算方法および装置、なたびにスリップ率演算のプログラムを用いて、タイヤの空気圧低下の判定を向上させることができるタイヤ空気圧低下検出方法および装置、ならびにタイヤ減圧判定のプログラムに関する。
【０００２】
【従来の技術】
従来より、車輪回転情報を用いてタイヤの空気圧低下（減圧）を検出するタイヤ空気圧低下検出装置（ＤＷＳ）がある。この装置では、減圧の検出性能を向上させるための種々の方法がある。たとえば駆動輪に生じているスリップ率（駆動輪と従動輪の車輪速度比から１を引いたもの）を算出したのち、得られたスリップ率と駆動輪の左右輪比の関係を用いて、現在走行中の駆動力による左右輪比を補正し、タイヤの空気圧低下を判定する方法がある（特許文献１参照）。
【０００３】
かかる方法では、摩耗度合の異なるタイヤや仕様違いのタイヤを混用した場合でも、減圧の判定精度を向上させて、誤報（誤判定）を防止することができる。
【０００４】
【特許文献１】
特開平１１−１７０８２８号公報
【０００５】
【発明が解決しようとする課題】
しかしながら、従来の方法では、駆動輪と従動輪の車輪速度比から１を引いたスリップ率を用いているが、従動輪を有しない４輪駆動車では正確なスリップ率を求めることができないため、判定精度を向上させることが難しい。
【０００６】
本発明は、叙上の事情に鑑み、４輪駆動車におけるタイヤのスリップ率を求めるスリップ率演算方法および装置、ならびにスリップ率演算のプログラム、および該スリップ率演算方法および装置を用いてタイヤの空気圧低下の判定を向上させて、誤報を防止することができるタイヤ空気圧低下検出方法および装置、ならびにタイヤ減圧判定のプログラムを提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明のスリップ率演算方法は、前軸と後軸への駆動トルクの配分を制御することができる４輪車両に装着したタイヤのスリップ率を求めるスリップ率演算方法であって、前記タイヤから得られる車輪回転情報から前輪タイヤのスリップ率と後輪タイヤのスリップ率との差を求める工程と、該スリップ率の差と前記４輪車両から得られる前軸と後軸への駆動トルクの配分率との関係から、関係式を求める工程と、左右前輪の接地荷重と左右後輪の接地荷重の配分を求める工程と、前記駆動トルクのトルク増分に伴う前輪タイヤと後輪タイヤそれぞれのスリップ率の変化率が前記左右前輪の接地荷重と左右後輪の接地荷重の配分に反比例する関係に基づいて、前記関係式から前記前輪タイヤおよび後輪タイヤのスリップ率を求める工程を含むことを特徴とする。
【０００８】
本発明のスリップ率演算装置は、前軸と後軸への駆動トルクの配分を制御することができる４輪車両に装着したタイヤのスリップ率を求めるスリップ率演算装置であって、前記タイヤから得られる車輪回転情報から前輪タイヤのスリップ率と後輪タイヤのスリップ率との差を求める差演算手段と、該スリップ率の差と前記４輪車両から得られる前軸と後軸への駆動トルクの配分率との関係から、関係式を求める関数演算手段と、左右前輪の接地荷重と左右後輪の接地荷重の配分を求める荷重配分演算手段と、前記駆動トルクのトルク増分に伴う前輪タイヤと後輪タイヤそれぞれのスリップ率の変化率が前記左右前輪の接地荷重と左右後輪の接地荷重の配分に反比例する関係に基づいて、前記関係式から前記前輪タイヤおよび後輪タイヤのスリップ率を求めるスリップ率演算手段を備えてなることを特徴とする。
【０００９】
本発明のスリップ率演算のプログラムは、前軸と後軸への駆動トルクの配分を制御することができる４輪車両に装着したタイヤのスリップ率を求めるためにコンピュータを、前記タイヤから得られる車輪回転情報から前輪タイヤのスリップ率と後輪タイヤのスリップ率との差を求める差演算手段、該スリップ率の差と前記４輪車両から得られる前軸と後軸への駆動トルクの配分率との関係から、関係式を求める関数演算手段、左右前輪の接地荷重と左右後輪の接地荷重の配分を求める荷重配分演算手段、前記駆動トルクのトルク増分に伴う前輪タイヤと後輪タイヤそれぞれのスリップ率の変化率が前記左右前輪の接地荷重と左右後輪の接地荷重の配分に反比例する関係に基づいて、前記関係式から前記前輪タイヤおよび後輪タイヤのスリップ率を求めるスリップ率演算手段として機能させることを特徴とする。
【００１０】
また、本発明のタイヤ空気圧低下検出方法は、前軸と後軸への駆動トルクの配分を制御することができる４輪車両に装着したタイヤから得られる車輪回転情報に基づいてタイヤ空気圧の低下を検出するタイヤ空気圧低下検出方法であって、前記各タイヤから得られる車輪回転情報を求める工程と、該車輪回転情報を記憶する工程と、請求項１記載のスリップ率を演算する各工程と、走行中の駆動輪の相対速度比を補正し、タイヤの空気圧の低下を判定する工程を含むことを特徴とする。
【００１１】
さらに本発明のタイヤ空気圧低下検出装置は、前軸と後軸への駆動トルクの配分を制御することができる４輪車両に装着したタイヤから得られる車輪回転情報に基づいてタイヤ空気圧の低下を検出するタイヤ空気圧低下検出装置であって、前記各タイヤから得られる車輪回転情報を求める回転情報検出手段と、該車輪回転情報を記憶する記憶手段と、請求項２記載のスリップ率演算装置と、走行中の駆動輪の相対速度比を補正し、タイヤの空気圧の低下を判定する減圧判定手段を備えてなることを特徴とする。
【００１２】
本発明のタイヤ減圧判定のプログラムは、前軸と後軸への駆動トルクの配分を制御することができる４輪車両に装着したタイヤから得られる車輪回転情報に基づいてタイヤ空気圧の低下を判定するためにコンピュータを、請求項３記載のスリップ率演算のプログラムとして機能させるともに、前記車輪回転情報を記憶する記憶手段、走行中の駆動輪の相対速度比を補正し、タイヤの空気圧の低下を判定する減圧判定手段として機能させることを特徴とする。
【００１３】
【発明の実施の形態】
以下、添付図面に基づいて、本発明のスリップ率演算方法、タイヤ空気圧低下検出方法および装置、ならびにスリップ率演算のプログラムおよびタイヤ減圧判定のプログラムを説明する。
【００１４】
図１に示されるように、本発明の一実施の形態にかかわるタイヤ空気圧低下検出装置は、たとえば車両のエンジンの駆動トルクが前軸と後軸とにそれぞれ配分される比率を制御する駆動制御装置を搭載する４輪車両（４輪駆動車）に備えられた４つのタイヤＦＬ、ＦＲ、ＲＬおよびＲＲの空気圧が低下しているか否かを検出するものであり、タイヤにそれぞれ関連して設けられた通常の回転情報検出手段１を備えている。前記駆動制御装置は、通常車両の走行性（運動特性）を向上させるものである。前後のトルク配分率は、電子制御方式のものであればＣＡＮ（ＣｏｎｔｒｏｌＡｒｅａＮｅｔｗｏｒｋ）などの通信によって知ることが可能である。また、機械式のものであっても、その特性を理解すれば、車輪の走行状態からある程度予想することができる。たとえばエンジンのトルクによって前後のトルク配分がほぼ決定されるものであれば、エンジンのトルクを入手することでトルク配分率を推測することができる。
【００１５】
前記回転情報検出手段１としては、電磁ピックアップなどを用いて回転パルスを発生させてパルスの数から回転角速度および車輪速度を測定するための車輪速センサまたはダイナモのように回転を利用して発電を行ない、この電圧から回転角速度および車輪速度を測定するためのものを含む角速度センサなどを用いることができる。前記回転情報検出手段１の出力はＡＢＳなどのコンピュータである制御ユニット２に与えられる。制御ユニット２には、空気圧が低下したタイヤを知らせるための液晶表示素子、プラズマ表示素子またはＣＲＴなどで構成された表示器３、ドライバーによって操作することができる初期化スイッチ４および警報器５が接続されている。
【００１６】
制御ユニット２は、図２に示されるように、外部装置との信号の受け渡しに必要なＩ／Ｏインターフェイス２ａと、演算処理の中枢として機能するＣＰＵ２ｂと、該ＣＰＵ２ｂの制御動作プログラムが格納されたＲＯＭ２ｃと、前記ＣＰＵ２ｂが制御動作を行なう際にデータなどが一時的に書き込まれたり、その書き込まれたデータなどが読み出されるＲＡＭ２ｄとから構成されている。
【００１７】
前記回転情報検出手段１では、タイヤの回転数に対応したパルス信号（以下、車輪速パルスという）が出力される。またＣＰＵ２ｂでは、回転情報検出手段１から出力された車輪速パルスに基づき、所定のサンプリング周期ΔＴ（ｓｅｃ）、たとえばΔＴ＝１秒ごとに各タイヤの回転角速度Ｆｉが算出される。
【００１８】
ところで、タイヤは規格内でのばらつき（初期差異）が含まれて製造されるため、各タイヤの有効転がり半径（一回転により進んだ距離を２πで割った値）は、すべてのタイヤがたとえ正常内圧であっても、同一とは限らない。そのため、各タイヤの回転角速度Ｆｉはばらつくことになる。そこで、たとえば回転角速度Ｆｉから初期差異の影響を排除する方法がある。この方法では、まず、つぎに示される初期補正係数Ｋ１、Ｋ２、Ｋ３を算出する。
Ｋ１＝Ｆ１／Ｆ２・・・（１）
Ｋ２＝Ｆ３／Ｆ４・・・（２）
Ｋ３＝（Ｆ１＋Ｋ１×Ｆ２）／（Ｆ２＋Ｋ２×Ｆ４）・・・（３）
【００１９】
ついで、この算出された初期補正係数Ｋ１、Ｋ２、Ｋ３を用いて式（４）〜（７）に示されるように新たな回転角速度Ｆ１_ｉを求めるようにしている。
Ｆ１_１＝Ｆ１・・・（４）
Ｆ１_２＝Ｋ１×Ｆ２・・・（５）
Ｆ１_３＝Ｋ３×Ｆ３・・・（６）
Ｆ１_４＝Ｋ２×Ｋ３×Ｆ４・・・（７）
【００２０】
ここで、初期補正係数Ｋ１は、前左右タイヤ間の初期差異による有効ころがり半径の差を補正するための係数である。初期補正係数Ｋ２は、後左右タイヤ間の初期差異による有効ころがり半径の差を補正するための係数である。初期補正係数Ｋ３は、前左タイヤと後左右タイヤとのあいだの初期差異による有効ころがり半径の差を補正するための係数である。そして、前記Ｆ１_ｉに基づき、各車輪のタイヤの車輪速度Ｖｉを算出する。
【００２１】
一般に４輪駆動車の場合、常に駆動トルクがかかっている車輪と、その車輪が充分に駆動できない場合に補助的に駆動する車輪が存在する。以下、前者を主駆動輪、後者を従駆動輪と呼ぶ。また、後輪が主駆動輪（常に駆動がかかっている）、前輪が従駆動輪（補助的に駆動がかかる）の車両を例として説明する。
【００２２】
まず、駆動輪の相対速度比である左右輪比が、駆動力（これは（前後輪比−１）から計算されるスリップ率で表わされる）によって、どのように変化するかを求め、走行中の駆動輪の相対速度比を補正したのち、タイヤの空気圧の低下を判定することができる。
【００２３】
そこで、本実施の形態にかかわるタイヤ空気圧低下検出装置は、４輪駆動車においてもスリップ率による車輪速度の補正を行なうスリップ率演算装置、回転情報検出手段１、車輪速度を記憶する記憶手段および減圧判定手段から構成されている。この減圧判定手段において、空気圧の低下を検出するための判定値ＤＥＬとして、つぎの式（８）に示されるように、対角線上にある一対の車輪からの信号の合計から対角線上にある他の一対の車輪からの信号の合計を引算し、その結果と２つの合計の平均値との比率を用いる。

【００２４】
ここで、Ｖ１〜Ｖ４は、それぞれ前左タイヤ、前右タイヤ、後左タイヤおよび後右タイヤの車輪速度である。
【００２５】
前記スリップ率演算装置では、前後輪のタイヤそれぞれに生じているスリップ率を推定するにあたり、つぎの式（９）に示されるように、車輪速度から得られる、前２輪の車輪速度の和と後２輪の車輪速度の和の比から１を引いたもの（以下、ＤＦＲという）と、駆動トルクの前後配分率と、左右前輪と左右後輪それぞれの軸荷重（接地荷重）との関係を用いている。

【００２６】
このＤＦＲは、２輪駆動車の場合、駆動輪（後２輪）のスリップ率を表すものであるが、４輪駆動車の場合、前後輪タイヤのスリップ率の差を表す。
【００２７】
したがって、前記スリップ率演算装置は、車輪速度から前輪タイヤのスリップ率と後輪タイヤのスリップ率との差ＤＦＲを求める差演算手段と、該スリップ率の差ＤＦＲと前記４輪車両の駆動制御装置から得られる前軸と後軸への駆動トルクの配分率との関係から、関係式を求める関数演算手段と、左右前輪の接地荷重と左右後輪の接地荷重の配分を求める荷重配分演算手段と、前記駆動トルクのトルク増分に伴う前輪タイヤと後輪タイヤそれぞれのスリップ率の変化率、すなわち減少率または増加率が前記左右前輪の接地荷重と左右後輪の接地荷重の配分に反比例する関係に基づいて、前記関係式から前記前輪タイヤおよび後輪タイヤのスリップ率を求めるスリップ率演算手段から構成されている。
【００２８】
さらにタイヤ減圧判定のプログラムは、制御ユニット２を、差演算手段、関数演算手段、荷重配分演算手段、スリップ率演算手段（スリップ率演算のプログラム）として機能させるとともに、記憶手段、減圧判定手段として機能させている。
【００２９】
つぎにスリップ率演算処理について説明する。まず４輪駆動車の駆動トルクの配分率が、（従駆動輪／主駆動輪）で、０／１００〜５０／５０である場合、前記スリップ率の差ＤＦＲと従駆動輪（前輪）への駆動配分率Ｔｆ（０≦Ｔｆ≦５０）との関係は、つぎの式（１０）のような一次関数で表される。
ＤＦＲ＝Ａ×Ｔｆ＋Ｃ・・・（１０）
【００３０】
この式は、駆動配分率Ｔｆ＝０のときには従駆動輪（前輪）のスリップ率がゼロとなり、すべてのトルクが主駆動輪（後輪）に作用するため、ＤＦＲは最大になる。しかし、駆動配分率Ｔｆが大きくなるにしたがい、従駆動輪（前輪）へトルクが配分されるため、従駆動輪（前輪）のスリップが生じ、さらに主駆動輪（後輪）へのトルクが減少するために、主駆動輪（後輪）のスリップが減少することを示している。また、係数Ｃ（＞０）は、駆動配分率Ｔｆ＝０のときの初期値である。
【００３１】
前記係数Ａ（Ａ＜０）は、差ＤＦＲの減少率（勾配）であり、図３に示されるように、主駆動輪（後輪）のスリップ率Ｓｒの減少率（勾配ｍ_ｒ＜０）と従駆動輪（前輪）のスリップ率Ｓｆの増加率（勾配ｍ_ｆ＞０）により、Ｓｒ−Ｓｆ＝（ｍ_ｒ−ｍ_ｆ）Ｔｆ＋Ｃであることから、つぎの式（１１）のように表される。

【００３２】
ここで、駆動配分率Ｔｆの増加による主駆動輪（後輪）のスリップ率Ｓｒの減少率と従駆動輪（前輪）のスリップ率Ｓｆの増加率は、ほぼ左右前輪の接地荷重と左右後輪の接地荷重に反比例している。つまり、（左右後輪の接地荷重）：（左右前輪の接地荷重）＝４：６であるならば、（主駆動輪（後輪）のスリップ率の減少率）：（従駆動輪（前輪）のスリップ率の増加率）＝６：４になる。したがって、駆動配分率Ｔｆと荷重配分がわかれば、従駆動輪（前輪）と主駆動輪（後輪）のスリップ率Ｓｆ、Ｓｒを推定することができる。たとえば前記車両の左右前輪の接地荷重の割合（％）と左右後輪の接地荷重の割合（％）をそれぞれＭｆ、（１００−Ｍｆ）とすると、つぎの式（１２）の関係が得られる。
（主駆動輪（後輪）のスリップ率の減少率）：（従駆動輪（前輪）のスリップ率の増加率）＝Ｍｆ：（１００−Ｍｆ）・・・（１２）
【００３３】
前記式（１０）〜（１２）から、駆動配分率Ｔｆであるときの主駆動輪（後輪）のスリップ率Ｓｒ（Ｔｆ）と従駆動輪（前輪）のスリップ率Ｓｆ（Ｔｆ）は、つぎの式（１３）、（１４）のようにして求めることができる。
Ｓｒ（Ｔｆ）＝Ｃ−（Ａ×Ｍｆ／１００）×Ｔｆ・・・（１３）
Ｓｆ（Ｔｆ）＝｛Ａ×（１００−Ｍｆ）／１００｝×Ｔｆ・・・（１４）
【００３４】
なお、前記係数Ａは、差ＤＦＲと駆動配分率Ｔｆのデータから回帰演算を行なうことにより、つぎの式（１５）から求めることもできる。

【００３５】
また、前記初期値Ｃは、駆動配分率Ｔｆ＝０のときの実測値を用いてもよいが、つぎの式（１６）から求めることもできる。
Ｃ＝ΣＤＦＲ／ｎ−（Ａ／ｎ）×ΣＴｆ・・・（１６）
【００３６】
また、前記左右前輪の接地荷重Ｆｚｆと左右後輪の接地荷重Ｆｚｒは、たとえばつぎの式（１７）、（１８）から求めることができる。
Ｆｚｆ＝Ｍｖ×ｇ×Ｌｒ／Ｌ−Ｍｖ×Ｇｘ×Ｈ／Ｌ・・・（１７）
Ｆｚｒ＝Ｍｖ×ｇ×Ｌｆ／Ｌ＋Ｍｖ×Ｇｘ×Ｈ／Ｌ・・・（１８）
ここで、Ｍｖ：車両の質量
ｇ：重力加速度
Ｌｒ：車両の重心と後輪車軸とのあいだの車両前後方向の距離
Ｌｆ：車両の重心と前輪車軸とのあいだの車両前後方向の距離
Ｌ：前輪車軸と後輪車軸とのあいだの距離
Ｇｘ：前後方向加速度
Ｈ：車両の重心高さ
である。
【００３７】
つぎに本発明を実施例に基づいて説明するが、本発明はかかる実施例のみに限定されるものではない。
【００３８】
【実施例】
車両として、正常空気圧（２．２×１０^５Ｐａ）の３つの新品タイヤと１つの摩耗タイヤ（摩耗度合：８０％）が装着された電子制御式４輪駆動車（後輪主導タイプ：排気量３０００ｃｃ）を用意した。前記タイヤのタイヤサイズは２３５／６５Ｒ１７である。前軸と後軸への駆動トルクの配分率は、（前輪／後輪）＝０／１００〜５０／５０の範囲で駆動制御装置のコンピュータにより制御されている。また、この駆動トルクの配分率は、駆動制御装置からＣＡＮ経由でタイヤ空気圧低下検出装置に取り込まれる。
【００３９】
まず前記駆動制御装置と前記実施の形態におけるスリップ率演算のプログラムおよびタイヤ減圧判定のプログラムを格納するタイヤ空気圧低下検出装置を搭載した車両の走行試験を行なった（実施例）。ついで従来のタイヤ空気圧低下検出装置を搭載した車両の走行試験も行なった（比較例）。その結果、本実施例では、駆動輪に異種タイヤを装着していても空気圧判定の精度が向上しているため、誤報を発することがなかった。これに対し、比較例では、タイヤが正規圧であるのにかかわらず、誤報を発した。
【００４０】
【発明の効果】
以上説明したとおり、本発明によれば、摩耗度合の異なるタイヤや仕様違いのタイヤを混用した場合でも、誤警報なく空気圧判定を行なうことができるため、車両性能を向上させることができる。
【図面の簡単な説明】
【図１】本発明のタイヤ空気圧低下検出装置の一実施の形態を示すブロック図である。
【図２】図１のタイヤ空気圧低下検出装置の電気的構成を示すブロック図である。
【図３】４輪駆動車の前後輪のスリップ率と駆動配分率との関係を示す図である。
【符号の説明】
１回転情報検出手段
２制御ユニット
３表示器
４初期化スイッチ
５警報器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a slip ratio calculation method, a method and an apparatus for detecting a decrease in tire air pressure, a program for calculating a slip ratio, and a program for determining tire pressure reduction. More specifically, a method and apparatus for calculating a slip rate of a tire in a four-wheel drive vehicle, and a tire pressure drop detection that can improve determination of a decrease in tire pressure by using a program for calculating a slip rate each time. The present invention relates to a method and apparatus, and a program for determining tire pressure reduction.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is a tire pressure drop detection device (DWS) that detects a tire pressure drop (decompression) using wheel rotation information. In this apparatus, there are various methods for improving the performance of detecting reduced pressure. For example, after calculating a slip ratio (a value obtained by subtracting 1 from a wheel speed ratio between a drive wheel and a driven wheel) generated in a drive wheel, the current slip ratio and a right / left wheel ratio of the drive wheel are used to calculate a slip ratio. There is a method of correcting a left / right wheel ratio due to a driving force during traveling and determining a decrease in tire air pressure (see Patent Document 1).
[0003]
According to such a method, even when tires having different degrees of wear or tires having different specifications are mixed, it is possible to improve the accuracy of the determination of the decompression and prevent false reports (erroneous determinations).
[0004]
[Patent Document 1]
JP-A-11-170828 [0005]
[Problems to be solved by the invention]
However, in the conventional method, although the slip ratio obtained by subtracting 1 from the wheel speed ratio between the drive wheel and the driven wheel is used, an accurate slip ratio cannot be obtained in a four-wheel drive vehicle having no driven wheel. It is difficult to improve the judgment accuracy.
[0006]
SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method and a device for calculating a slip ratio of a tire in a four-wheel drive vehicle, a program for calculating a slip ratio, and a tire pressure calculation method and device. It is an object of the present invention to provide a method and an apparatus for detecting a decrease in tire air pressure that can improve the judgment of a decrease and prevent a false report, and a program for judging a decrease in tire air pressure.
[0007]
[Means for Solving the Problems]
A slip ratio calculating method according to the present invention is a slip ratio calculating method for calculating a slip ratio of a tire mounted on a four-wheel vehicle capable of controlling distribution of a driving torque to a front shaft and a rear shaft. Obtaining the difference between the slip ratio of the front wheel tire and the slip ratio of the rear wheel tire from the wheel rotation information obtained, and the difference between the slip ratio and the distribution ratio of the driving torque to the front shaft and the rear shaft obtained from the four-wheeled vehicle From the relationship, the step of obtaining a relational expression, the step of determining the distribution of the grounding load of the left and right front wheels and the distribution of the grounding load of the left and right rear wheels, A step of obtaining a slip ratio of the front wheel tire and the rear wheel tire from the relational expression based on a relationship in which a change rate is inversely proportional to a distribution of the ground load of the left and right front wheels and a distribution of the ground load of the right and left rear wheels. The features.
[0008]
The slip ratio calculating device according to the present invention is a slip ratio calculating device for obtaining a slip ratio of a tire mounted on a four-wheel vehicle capable of controlling distribution of driving torque to a front shaft and a rear shaft. Calculating a difference between the slip ratio of the front wheel tires and the slip ratio of the rear wheel tires from the wheel rotation information obtained, and calculating the difference between the slip ratios and the driving torque to the front shaft and the rear shaft obtained from the four-wheel vehicle. A function calculating means for obtaining a relational expression from a relationship with the distribution ratio; a load distribution calculating means for determining a distribution of a ground load of the left and right front wheels and a ground load of the right and left rear wheels; Based on the relationship in which the rate of change of the slip ratio of each wheel tire is inversely proportional to the distribution of the ground load of the left and right front wheels and the distribution of the ground load of the left and right rear wheels, the slip of the front wheel tire and the rear wheel tire is calculated from the above relational expression. And characterized in that it comprises a slip rate calculating means for obtaining a flop index.
[0009]
The program for calculating the slip ratio according to the present invention is a computer for calculating the slip ratio of a tire mounted on a four-wheel vehicle capable of controlling the distribution of the driving torque to the front axle and the rear axle. A difference calculating means for calculating a difference between a slip ratio of a front wheel tire and a slip ratio of a rear wheel tire from rotation information; a difference between the slip ratio and a distribution ratio of drive torque to a front shaft and a rear shaft obtained from the four-wheel vehicle; Function calculating means for obtaining a relational expression from the relationship, load distribution calculating means for determining the distribution of the ground load of the left and right front wheels and the ground load of the left and right rear wheels, slip of the front wheel tire and the rear wheel tire accompanying the torque increase of the driving torque. Based on the relationship that the rate of change of the rate is inversely proportional to the distribution of the ground load of the left and right front wheels and the distribution of the ground load of the left and right rear wheels, the slip of the front wheel tire and the rear wheel tire is calculated from the relational expression. It characterized in that to function as a slip rate calculating means for calculating a.
[0010]
In addition, the method for detecting a decrease in tire air pressure according to the present invention detects a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a four-wheel vehicle capable of controlling distribution of driving torque to a front shaft and a rear shaft. 2. A method for detecting a decrease in tire air pressure, comprising: obtaining wheel rotation information obtained from each of the tires; storing the wheel rotation information; and calculating the slip ratio according to claim 1; The method includes a step of correcting the relative speed ratio of the middle drive wheel and determining a decrease in tire air pressure.
[0011]
Further, the tire pressure drop detection device of the present invention detects a drop in tire pressure based on wheel rotation information obtained from a tire mounted on a four-wheel vehicle capable of controlling the distribution of driving torque to the front shaft and the rear shaft. 3. A slip pressure calculating device according to claim 2, wherein the tire pressure drop detecting device performs a rotation information detecting device for obtaining wheel rotation information obtained from each of the tires; a storage device for storing the wheel rotation information; It is characterized by comprising a decompression determining means for correcting the relative speed ratio of the middle drive wheel and determining a decrease in tire air pressure.
[0012]
The program for determining tire pressure reduction according to the present invention determines a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a four-wheel vehicle capable of controlling distribution of driving torque to a front shaft and a rear shaft. For this purpose, the computer is caused to function as a program for calculating a slip ratio according to claim 3, and a storage means for storing the wheel rotation information is corrected to determine a decrease in tire air pressure by correcting a relative speed ratio of driving wheels during traveling. It is characterized by functioning as a decompression determining means for performing the pressure reduction.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a slip rate calculation method, a tire air pressure drop detection method and apparatus, a slip rate calculation program, and a tire pressure reduction determination program according to the present invention will be described with reference to the accompanying drawings.
[0014]
As shown in FIG. 1, a tire pressure drop detecting device according to one embodiment of the present invention includes, for example, a drive control device that controls a ratio at which a driving torque of an engine of a vehicle is distributed to a front shaft and a rear shaft. It detects whether the air pressure of the four tires FL, FR, RL, and RR provided in the four-wheel vehicle (four-wheel drive vehicle) on which the tires are mounted is reduced, and is provided in association with each of the tires. Normal rotation information detecting means 1. The drive control device generally improves the traveling performance (movement characteristics) of the vehicle. The torque distribution ratio before and after can be known by communication such as CAN (Control Area Network) if it is of an electronic control type. Moreover, even if it is a mechanical type, if its characteristics are understood, it can be predicted to some extent from the running state of the wheels. For example, if the front and rear torque distribution is substantially determined by the engine torque, the torque distribution rate can be estimated by obtaining the engine torque.
[0015]
The rotation information detecting means 1 generates a rotation pulse by using an electromagnetic pickup or the like and measures the rotation angular speed and the wheel speed from the number of pulses. And an angular velocity sensor or the like including those for measuring the rotational angular velocity and the wheel velocity from this voltage can be used. The output of the rotation information detecting means 1 is given to a control unit 2 which is a computer such as an ABS. Connected to the control unit 2 are a liquid crystal display element for notifying a tire whose air pressure has decreased, a display unit 3 composed of a plasma display element or a CRT, an initialization switch 4 operable by a driver, and an alarm unit 5. Have been.
[0016]
As shown in FIG. 2, the control unit 2 stores an I / O interface 2a necessary for exchanging signals with an external device, a CPU 2b functioning as a center of arithmetic processing, and a control operation program of the CPU 2b. It comprises a ROM 2c and a RAM 2d from which data and the like are temporarily written when the CPU 2b performs a control operation, and from which the written data and the like are read.
[0017]
The rotation information detecting means 1 outputs a pulse signal (hereinafter, referred to as a wheel speed pulse) corresponding to the number of rotations of the tire. Further, the CPU 2b calculates the rotational angular velocity Fi of each tire at a predetermined sampling period ΔT (sec), for example, every ΔT = 1 second, based on the wheel speed pulse output from the rotation information detecting means 1.
[0018]
By the way, since the tires are manufactured by including the variation (initial difference) within the standard, the effective rolling radius of each tire (the value obtained by dividing the distance traveled by one revolution by 2π) is normal for all tires. The internal pressure is not always the same. Therefore, the rotational angular velocities Fi of the tires vary. Therefore, for example, there is a method of eliminating the influence of the initial difference from the rotational angular velocity Fi. In this method, first, the following initial correction coefficients K1, K2, and K3 are calculated.
K1 = F1 / F2 (1)
K2 = F3 / F4 (2)
K3 = (F1 + K1 × F2) / (F2 + K2 × F4) (3)
[0019]
Then, and to determine a new rotational angular velocities F1 _i as shown in equation (4) to (7) using the initial correction coefficients K1, K2, K3 This calculated.
F1 ₁ = F1 (4)
F1 ₂ = K1 × F2 (5)
F1 ₃ = K3 × F3 (6)
F1 ₄ = K2 × K3 × F4 (7)
[0020]
Here, the initial correction coefficient K1 is a coefficient for correcting a difference in effective rolling radius due to an initial difference between the front left and right tires. The initial correction coefficient K2 is a coefficient for correcting the difference in the effective rolling radius due to the initial difference between the rear left and right tires. The initial correction coefficient K3 is a coefficient for correcting a difference in effective rolling radius due to an initial difference between the front left tire and the rear left and right tires. Based on the F1 _i, calculates the wheel speeds Vi of the respective tires.
[0021]
In general, in the case of a four-wheel drive vehicle, there are wheels to which drive torque is constantly applied, and wheels to be driven supplementarily when the wheels cannot be driven sufficiently. Hereinafter, the former is referred to as a main drive wheel, and the latter is referred to as a slave drive wheel. Further, a vehicle in which a rear wheel is a main drive wheel (always driven) and a front wheel is a slave drive wheel (auxiliary drive) will be described as an example.
[0022]
First, it is determined how the left / right wheel ratio, which is the relative speed ratio of the drive wheels, changes depending on the driving force (this is represented by a slip ratio calculated from (front / rear wheel ratio-1)). After the correction of the relative speed ratio of the driving wheels, it is possible to determine a decrease in tire air pressure.
[0023]
Therefore, the tire pressure drop detecting device according to the present embodiment includes a slip ratio calculating device that corrects the wheel speed based on the slip ratio even in a four-wheel drive vehicle, a rotation information detecting unit 1, a storing unit that stores wheel speed, and a pressure reducing device. It is composed of a judgment means. In this decompression determining means, as shown in the following equation (8), a determination value DEL for detecting a decrease in air pressure is obtained from the sum of signals from a pair of wheels on a diagonal line and another value on a diagonal line. The sum of the signals from the pair of wheels is subtracted and the ratio of the result to the average of the two sums is used.

[0024]
Here, V1 to V4 are wheel speeds of a front left tire, a front right tire, a rear left tire, and a rear right tire, respectively.
[0025]
In the slip ratio calculation device, when estimating the slip ratio occurring in each of the front and rear wheels, as shown in the following equation (9), the sum of the wheel speeds of the front two wheels, which is obtained from the wheel speeds, The relationship between the ratio of the sum of the wheel speeds of the rear two wheels minus one (hereinafter referred to as DFR), the front-rear distribution ratio of drive torque, and the axial load (ground load) of each of the left and right front wheels and the left and right rear wheels is shown. Used.

[0026]
This DFR indicates the slip ratio of the drive wheels (two rear wheels) in the case of a two-wheel drive vehicle, but indicates the difference in the slip ratio of front and rear wheel tires in the case of a four-wheel drive vehicle.
[0027]
Therefore, the slip ratio calculating device calculates a difference DFR between the front wheel tire slip ratio and the rear wheel tire slip ratio from the wheel speed, a difference DFR between the slip ratio and the drive control device of the four-wheel vehicle. A function calculating means for obtaining a relational expression from a relationship between the distribution ratio of the driving torque to the front shaft and the rear shaft obtained from the above; The change rate of the slip rate of each of the front wheel tire and the rear wheel tire according to the torque increase of the driving torque, that is, the reduction rate or the increase rate is inversely proportional to the distribution of the ground load of the left and right front wheels and the ground load of the right and left rear wheels. And a slip ratio calculating means for calculating a slip ratio of the front wheel tire and the rear wheel tire from the relational expression based on the relational expression.
[0028]
Further, the program for determining tire pressure reduction causes the control unit 2 to function as difference calculation means, function calculation means, load distribution calculation means, slip rate calculation means (slip rate calculation program), and also functions as storage means and pressure reduction determination means. Let me.
[0029]
Next, the slip ratio calculation processing will be described. First, when the distribution ratio of the driving torque of the four-wheel drive vehicle is (slave drive wheel / main drive wheel) and is 0/100 to 50/50, the difference DFR between the slip ratio and the slave drive wheel (front wheel). The relationship with the drive distribution ratio Tf (0 ≦ Tf ≦ 50) is expressed by a linear function such as the following equation (10).
DFR = A × Tf + C (10)
[0030]
In this equation, when the drive distribution ratio Tf = 0, the slip ratio of the slave drive wheel (front wheel) becomes zero, and all the torque acts on the main drive wheel (rear wheel), so that the DFR becomes maximum. However, as the drive distribution ratio Tf increases, torque is distributed to the sub-drive wheels (front wheels), so that the sub-drive wheels (front wheels) slip and the torque to the main drive wheels (rear wheels) decreases. Therefore, the slip of the main drive wheel (rear wheel) is reduced. The coefficient C (> 0) is an initial value when the drive distribution ratio Tf = 0.
[0031]
The coefficient A (A <0) is a decreasing rate (gradient) of the difference DFR, and as shown in FIG. 3, a decreasing rate (gradient _mr <0) of the slip ratio Sr of the main drive wheel (rear wheel). Table as the increase rate of the slip ratio Sf of the auxiliary driving wheels (front wheels) (gradient _m f> 0), since it is _{_{Sr-Sf = (m r -m}} f) Tf + C, of the following formula (11) Is done.

[0032]
Here, the decrease rate of the slip ratio Sr of the main drive wheel (rear wheel) and the increase rate of the slip ratio Sf of the slave drive wheel (front wheel) due to the increase in the drive distribution ratio Tf are substantially the same as the ground load of the left and right front wheels and the left and right rear wheels. Is inversely proportional to the grounding load. In other words, if (ground contact load of left and right rear wheels) :( ground contact load of left and right front wheels) = 4: 6, (reduction rate of slip ratio of main drive wheel (rear wheel)): (slave drive wheel (front wheel)) = 6: 4). Therefore, if the drive distribution ratio Tf and the load distribution are known, the slip ratios Sf and Sr of the sub-drive wheels (front wheels) and the main drive wheels (rear wheels) can be estimated. For example, if the ratio (%) of the ground contact load of the left and right front wheels and the ratio (%) of the ground contact load of the left and right rear wheels are Mf and (100−Mf), respectively, the following equation (12) is obtained.
(Reduction rate of slip rate of main drive wheel (rear wheel)): (increase rate of slip rate of slave drive wheel (front wheel)) = Mf: (100−Mf) (12)
[0033]
From the equations (10) to (12), the slip ratio Sr (Tf) of the main drive wheel (rear wheel) and the slip ratio Sf (Tf) of the slave drive wheel (front wheel) when the drive distribution ratio is Tf are as follows. Equations (13) and (14) can be used.
Sr (Tf) = C− (A × Mf / 100) × Tf (13)
Sf (Tf) = {A × (100−Mf) / 100} × Tf (14)
[0034]
The coefficient A can also be obtained from the following equation (15) by performing a regression operation on the data of the difference DFR and the drive distribution ratio Tf.

[0035]
The initial value C may be an actual measurement value when the drive distribution ratio Tf = 0, but can also be obtained from the following equation (16).
C = ΣDFR / n- (A / n) × ΣTf (16)
[0036]
The ground contact load Fzf of the left and right front wheels and the ground contact load Fzr of the left and right rear wheels can be obtained from, for example, the following equations (17) and (18).
Fzf = Mv × g × Lr / L−Mv × Gx × H / L (17)
Fzr = Mv × g × Lf / L + Mv × Gx × H / L (18)
Here, Mv: mass of the vehicle g: gravitational acceleration Lr: distance in the vehicle longitudinal direction between the center of gravity of the vehicle and the rear wheel axle Lf: distance in the vehicle longitudinal direction between the center of gravity of the vehicle and the front wheel axle L: front wheel The distance Gx between the axle and the rear wheel axle: longitudinal acceleration H: height of the center of gravity of the vehicle.
[0037]
Next, the present invention will be described based on examples, but the present invention is not limited to only these examples.
[0038]
【Example】
As a vehicle, an electronically controlled four-wheel drive vehicle equipped with three new tires with normal air pressure (2.2 × 10 ⁵ Pa) and one worn tire (degree of wear: 80%) (rear wheel driven type: displacement) 3000 cc) was prepared. The tire size of the tire is 235 / 65R17. The distribution ratio of the drive torque to the front shaft and the rear shaft is controlled by the computer of the drive control device in the range of (front wheel / rear wheel) = 0/100 to 50/50. Further, the distribution ratio of the drive torque is taken into the tire pressure drop detection device from the drive control device via the CAN.
[0039]
First, a running test of a vehicle equipped with the drive control device and the tire pressure drop detecting device storing the slip ratio calculation program and the tire pressure reduction determination program in the embodiment was performed (Example). Next, a running test of a vehicle equipped with a conventional tire pressure drop detecting device was also performed (Comparative Example). As a result, in the present embodiment, even when different kinds of tires are mounted on the driving wheels, the accuracy of the air pressure determination is improved, and thus no erroneous report is issued. On the other hand, in the comparative example, an erroneous report was issued irrespective of the normal pressure of the tire.
[0040]
【The invention's effect】
As described above, according to the present invention, even when tires having different degrees of wear or tires having different specifications are mixed, the air pressure can be determined without a false alarm, so that the vehicle performance can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a tire pressure drop detecting device according to the present invention.
FIG. 2 is a block diagram showing an electrical configuration of the tire pressure drop detecting device of FIG.
FIG. 3 is a diagram illustrating a relationship between a slip ratio of front and rear wheels of a four-wheel drive vehicle and a drive distribution ratio.
[Explanation of symbols]
1 rotation information detecting means 2 control unit 3 display 4 initialization switch 5 alarm

Claims

A method of calculating a slip ratio of a tire mounted on a four-wheeled vehicle capable of controlling distribution of driving torque to a front axle and a rear axle, wherein a slip of a front wheel tire is obtained from wheel rotation information obtained from the tire. Calculating a difference between the slip ratio of the rear wheel tire and a slip ratio of the rear wheel tire, and obtaining a relational expression from a relationship between the difference of the slip ratio and a distribution ratio of the driving torque to the front shaft and the rear shaft obtained from the four-wheel vehicle. Determining the distribution of the ground contact load of the left and right front wheels and the ground load of the left and right rear wheels; and the rate of change of the slip ratio of each of the front wheel tires and the rear wheel tires with the torque increase of the driving torque, And calculating a slip ratio of the front wheel tires and the rear wheel tires from the relational expression based on a relationship inversely proportional to the distribution of the ground load of the right and left rear wheels.

A slip ratio calculation device for calculating a slip ratio of a tire mounted on a four-wheel vehicle capable of controlling distribution of driving torque to a front shaft and a rear shaft, wherein a slip of a front wheel tire is obtained from wheel rotation information obtained from the tire. Calculating means for calculating a difference between the ratio and the slip ratio of the rear wheel tires, and a relational expression based on a relationship between the difference between the slip ratios and a distribution ratio of the driving torque to the front shaft and the rear shaft obtained from the four-wheel vehicle. Calculating means for determining the distribution of the grounding load of the left and right front wheels and the grounding load of the left and right rear wheels; and the rate of change of the slip rate of each of the front wheel tire and the rear wheel tire with the torque increase of the driving torque. Is a slip ratio calculating method for calculating the slip ratio of the front wheel tire and the rear wheel tire from the relational expression based on a relationship inversely proportional to the distribution of the ground load of the left and right front wheels and the ground load of the right and left rear wheels. Slip rate calculating device including a.

In order to determine the slip ratio of a tire mounted on a four-wheel vehicle capable of controlling the distribution of the driving torque to the front axle and the rear axle, a computer is used to determine the slip ratio of the front wheel tire and the rear tire from the wheel rotation information obtained from the tire. Difference calculating means for calculating a difference between the slip rate of the wheel tires and a function calculating a relational expression from a relationship between the difference in the slip rate and a distribution ratio of the driving torque to the front shaft and the rear shaft obtained from the four-wheel vehicle. Means, load distribution calculating means for determining the distribution of the ground load of the left and right front wheels and the ground load of the right and left rear wheels, and the change rate of the slip rate of each of the front wheel tires and the rear wheel tires accompanying the torque increase of the driving torque is obtained by the grounding of the left and right front wheels. Functions as a slip ratio calculating means for obtaining a slip ratio of the front wheel tire and the rear wheel tire from the relational expression based on a relationship inversely proportional to the distribution of the load and the contact load of the left and right rear wheels. Slip rate calculating program for causing.

A method for detecting a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a four-wheel vehicle capable of controlling distribution of drive torque to a front shaft and a rear shaft, the method comprising: A step of obtaining wheel rotation information obtained from each tire, a step of storing the wheel rotation information, each step of calculating a slip ratio according to claim 1, and correcting a relative speed ratio of driving wheels during traveling, A method for detecting a decrease in tire air pressure, including a step of determining a decrease in air pressure of a tire.

A tire pressure drop detection device that detects a decrease in tire pressure based on wheel rotation information obtained from a tire mounted on a four-wheel vehicle capable of controlling distribution of drive torque to a front shaft and a rear shaft, 3. A rotation information detecting means for obtaining wheel rotation information obtained from each tire, a storage means for storing the wheel rotation information, a slip ratio calculation device according to claim 2, and correcting a relative speed ratio of driving wheels during traveling. An apparatus for detecting a decrease in the air pressure of a tire, comprising: a pressure-reducing judging means for judging a decrease in the air pressure of the tire.

4. The computer according to claim 3, wherein the computer is configured to determine a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a four-wheel vehicle capable of controlling distribution of driving torque to the front axle and the rear axle. A tire for functioning as a program for calculating a slip ratio, a storage means for storing the wheel rotation information, a tire for functioning as a decompression determining means for correcting a relative speed ratio of driving wheels during running and determining a decrease in tire air pressure. Decompression judgment program.