JP3669320B2

JP3669320B2 - Inter-vehicle distance measuring device

Info

Publication number: JP3669320B2
Application number: JP2001308409A
Authority: JP
Inventors: 美佳大友; 和貴溝口
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 2001-10-04
Filing date: 2001-10-04
Publication date: 2005-07-06
Anticipated expiration: 2021-10-04
Also published as: JP2003114277A

Description

【０００１】
【発明の属する技術分野】
本発明は先行車との車間距離を計測する装置に関する。
【０００２】
【従来の技術】
自車前方にレーザー光を送光して前方物体からの反射光を受光し、レーザー光の送光から受光までの時間を計測して前方物体までの距離を算出する車間距離計測装置が知られており、例えば特開平０７−１０４０６６号公報では、路面からの反射光や太陽光などの外乱光の混入を阻止するために、送受光部の前面にカバーを取り付けたものが提案されている。この種の車間距離計測装置にフロントカバーの汚れ検知機能を付加する場合、送受光部とフロントカバーとの距離が充分にあるため、汚れ検知専用の受光部を設けなくても、距離計測用の受光素子を用いてフロントカバーに付着した汚れに起因する散乱光を検出することができる。
【０００３】
図７はフロントカバー付き車間距離計測装置の受光素子出力信号の受光強度を示す。図において、横軸はレーザー光を自車前方に送光してからの経過時間の測定値を表し、この測定時間は自車前方の障害物までの距離に比例する。至近距離にあるフロントカバーの汚れによる散乱光は測定時間が短い所に現れ、また、自車前方の障害物からの反射光は測定時間が長い所に現れる。つまり、受光素子の出力信号には、フロントカバーからの散乱光と障害物からの反射光とが混在する。そして、障害物からの反射光の受光強度が予め設定した物体検知しきい値を超えた場合に、その反射光の測定時間に基づいて障害物までの距離を算出する。
【０００４】
また、受光素子の出力信号を処理しやすくするために、出力信号を増幅する増幅器の増幅ゲインを出力信号レベルに応じて制御するようにしたＡＧＣ（Auto Gain Control）機能付き車間距離計測装置が知られている（例えば特開平０５−０２４４９２号公報参照）。図８および図９はＡＧＣ機能付き車間距離計測装置の受光素子出力信号の受光強度を示す。これらの図において、横軸はレーザー光を自車前方に送光してからの経過時間の測定値を表し、この測定時間は自車前方の障害物までの距離に比例する。この装置では、図８および図９に示すように、物体検知しきい値の他にゲインダウンしきい値とゲインアップしきい値が設定されている。今、図８(ａ)に示すように、受光素子の出力信号を増幅ゲイン４で増幅しているときに、受光素子出力信号の光強度最大値がゲインダウンしきい値を超えた場合には、図８(ｂ)に示すように増幅ゲインを４から３に下げる。逆に、図９(ａ)に示すように、受光素子の出力信号を増幅ゲイン３で増幅しているときに、受光素子出力信号の光強度最大値がゲインアップしきい値を下回った場合には、図９(ｂ)に示すように増幅ゲインを３から４に上げている。
【０００５】
【発明が解決しようとする課題】
しかしながら、上述したＡＧＣ機能を備えた車間距離計測装置では、図１０(ａ)に示すように、フロントカバーの汚れがひどくなると、フロントカバーの汚れによる散乱光強度が障害物からの反射光強度よりも大きくなるので、このフロントカバーからの散乱光強度を受光素子出力信号の光強度最大値と判断してＡＧＣ制御が実行され、図１０(ｂ)に示すように増幅ゲインが４から３へ下げられる。その結果、障害物からの反射光強度も低下して物体検知しきい値を下回ってしまい、自車前方にまだ充分に認識できる程度の受光強度の障害物があるのに、物体として認識できなくなってしまうという問題がある。
【０００６】
本発明の目的は、前方物体までの距離計測とフロントカバーの汚れ検知とを正確に行う車間距離計測装置を提供することにある。
【０００７】
【課題を解決するための手段】
（１）請求項１の発明は、レーザー光パルスを送光する送光手段と、レーザー光を受光する受光手段と、前記送光手段と前記受光手段の前面に設置されるカバーと、前記受光手段から出力される受光信号を増幅する増幅手段と、前記増幅手段の増幅ゲインを制御するゲイン制御手段と、前記送光手段による送光から前記受光手段による受光までの時間を測定するとともに、測定時間を、前記送光手段から送光されたレーザー光パルスが前記カバーの汚れに散乱した散乱光を前記受光手段で受光する散乱光領域と、前記送光手段から送光されたレーザー光パルスが前記カバーより遠方にある物体に反射した反射光を前記受光手段で受光する反射光領域とに区分する計時手段と、前記反射光領域における前記受光手段の受光信号強度の最大値が所定の強度範囲に入るように前記ゲイン制御手段により前記増幅手段の増幅ゲインを制御し、前記反射光領域における反射光受光までの前記計時手段による測定時間に基づいて障害物までの距離を演算する距離演算手段と、前記ゲイン制御手段により前記増幅手段の増幅ゲインを所定値に設定して前記散乱光領域における前記受光手段の受光信号強度の最大値を検出し、この最大値に基づいて前記カバーの汚れを検知する汚れ検知手段と、前記距離演算手段による距離計測処理と前記汚れ検知手段による汚れ検知処理とを切り替える動作切替制御手段とを備える。
（２）請求項２の車間距離計測装置は、前記汚れ検知手段によって、前記汚れ検知処理において、前記散乱光領域における前記受光手段の受光信号強度の最大値を汚れ検知しきい値と比較して前記カバーの汚れ診断を行う。
（３）請求項３の車間距離計測装置は、前記動作切替制御手段によって、前記距離演算手段が前記物体までの距離を計測する動作を複数回以上実行するたびに、前記汚れ検知手段が前記カバーの汚れを診断する動作を１回実行するように前記距離計測処理と前記汚れ検知処理とを切り替える。
（４）請求項４の車間距離計測装置は、前記動作切替制御手段によって、前記増幅手段の増幅ゲインを前記所定値としたときに、前記散乱光領域における前記受光手段の受光信号強度の最大値が前記汚れ検知しきい値よりも小さい汚れ検知実行しきい値を超えた場合に、前記カバーの汚れ診断の実行を許可する。
（５）請求項５の車間距離計測装置は、前記汚れ検知手段により、前記散乱光領域における前記受光手段の受光信号強度の最大値が前記汚れ検知しきい値を超えて前記カバーの汚れが検知された場合に、前記カバーの汚れを報知する報知手段を備える。
【０００８】
【発明の効果】
（１）請求項１の発明によれば、反射光領域の受光信号強度の最大値が所定の強度範囲に入るように増幅手段の増幅ゲインを制御し、反射光受光までの測定時間に基づいて障害物までの距離を演算する距離計測処理と、増幅手段の増幅ゲインを所定値に設定して散乱光領域の受光信号強度の最大値を検出し、この最大値に基づいてカバーの汚れを検知する汚れ検知処理とを切り替えるようにした。これにより、散乱光強度の最大値に応じて増幅ゲインの調整が行われないので、カバーの汚れによる散乱光の強度が大きくてもそのような散乱光の影響を受けることなく、反射光を適切な強度に調整することができ、自車前方の障害物を正確に認識してその障害物までの距離を正確に演算することができる。
（２）請求項２の発明によれば、汚れ検知処理において、散乱光領域における受光信号強度の最大値を汚れ検知しきい値と比較してカバーの汚れ診断を行うようにしたので、汚れ検知専用のレーザー受光部を設けずに、カバーの汚れを正確に診断することができる。
（３）請求項３の発明によれば、物体までの距離を計測する動作を複数回以上実行するたびに、カバーの汚れを診断する動作を１回実行するように距離計測処理と汚れ検知処理とを切り替えるようにした。カバーの汚れは短時間のうちに急激にひどくなるようなことはなく、また、汚れ診断動作を実行するときは距離測定動作を実行できないから距離測定値が得られないが、その間の距離測定値を補間演算により求めることによって実際には何ら支障はなく、したがって、障害物までの距離を正確に測定しながら、カバーの汚れを正確に検知することができる。
（４）請求項４の発明によれば、増幅ゲインを所定値としたときに、散乱光領域における受光信号強度の最大値が汚れ検知しきい値よりも小さい汚れ検知実行しきい値を超えた場合に、カバーの汚れ診断の実行を許可するようにしたので、カバーがある程度汚れて汚れ診断が必要になったときに汚れ診断動作を行うことができ、汚れ診断動作の無駄な実行を避けることができる。
（５）請求項５の発明によれば、散乱光領域における受光信号強度の最大値が前記汚れ検知しきい値を超えてカバーの汚れが検知された場合に、カバーの汚れを報知する報知手段を備えるようにしたので、乗員にカバーの清掃を促すことができ、常にカバーを汚れのない状態に保って車間距離計測装置の信頼性を確保することができる。
【０００９】
【発明の実施の形態】
図１は一実施の形態の構成を示す。レーザー送光部１１はパルス状のレーザー光を前方に照射する。レーザー受光部１２は、レーザー送光部１１から送光されたレーザー光が前方の障害物で反射した反射光を受光する。これらのレーザー送光部１１とレーザー受光部１２の前面には、汚れが直接、レーザー送光部１１とレーザー受光部１２に付着するのを防止するためのフロントカバー１０が設置される。レーザー受光部１２は、上述したように前方障害物からの反射光を受光すると同時に、レーザー送光部１１から送光されたレーザー光がフロントカバー１０の汚れで散乱された散乱光も受光する。
【００１０】
ＡＧＣ制御部１３は、レーザー受光部１２で受光した前方障害物からの反射光とフロントカバー１０からの散乱光の受光強度が最適なレベルになるように、レーザー受光部１２の受光信号を増幅する増幅回路１４の増幅ゲインを調整する。パルス信号処理部１５は、レーザー送光部１１から送光されるパルス状のレーザー光と、レーザー受光部１２で受光され増幅回路１４で増幅されるパルス状の受光信号を処理する。距離演算部１６はタイマー１６ａを備え、タイマー１６ａによりレーザー送光部１１によるレーザー光パルスの送光からレーザー受光部１２による反射光受光までの時間を計時し、タイマー１６ａによる測定時間に基づいて障害物までの距離を演算する。
【００１１】
汚れ診断部１７は、フロントカバー１０に付着した汚れによる散乱光の受光信号に基づいて汚れの付着を診断する。記憶部１８は、予め設定されたゲインダウンしきい値、ゲインアップしきい値、物体検知しきい値などを記憶する。ゲインダウンしきい値は、受光信号がこのしきい値を超えたら増幅回路１４の増幅ゲインを下げるために設けたしきい値である。また、ゲインアップしきい値は、受光信号がこのしきい値を下回ったら増幅回路１４の増幅ゲインを上げるために設けたしきい値である。物体検知しきい値は、障害物からの反射光の受光強度がこのしきい値を超えたら、その障害物を自車前方の障害物として認識するためのしきい値である。動作切替制御部１９は、汚れ検知モードが設定されているときに、距離演算部１６による距離測定動作と汚れ診断部１７による汚れ検知動作とを切り換える。この切替方法については後述する。報知部２０は、汚れ診断部１７によりフロントカバー１０に汚れが付着したと診断された場合に汚れ付着を報知する。
【００１２】
図２は一実施の形態の車間距離計測動作を示すフローチャートである。車間距離計測装置は、不図示のメインスイッチが投入されるとこの車間距離計測動作を繰り返し実行する。ステップ１でレーザー送光部１１からレーザー光パルスを送光し、ステップ２でレーザー受光部１２で前方障害物からの反射光とフロントカバー１０の汚れによる散乱光を受光する。ステップ３において、レーザー受光部１２で受光したフロントカバー１０からの散乱光の受光強度に基づいて汚れ検知動作を行う汚れ検知モードが設定されているかどうかを確認する。
【００１３】
図３は、一実施の形態の通常の距離計測モードと汚れ検知モードの切り換え動作を示す。フロントカバー１０の汚れによる散乱光の強度は、泥や雪などの付着によるフロントカバー１０の汚れ具合により変化するが、通常では散乱光の強度が一瞬の内に急激に変化するようなことはない。そこで、図３に示すように、フロントカバー１０に汚れが付着したと判断するための汚れ検知判断しきい値の他に、汚れ検知動作を開始するための上記汚れ検知判断しきい値よりも低い汚れ検知実行しきい値を設定し、これらのしきい値を記憶部１８に記憶しておく。そして、図２に示す車間距離計測動作を実行するたびに、増幅回路１４の増幅ゲインに固定値（例えば１）を設定してフロントカバー１０の汚れによる散乱光の受光強度を監視し、汚れによる散乱光の受光強度が汚れ検知実行しきい値を超えたら汚れ検知モードを設定し、汚れ検知判断しきい値を用いて汚れ検知動作を開始する。また、汚れによる散乱光の受光強度が汚れ検知実行しきい値を下回ったら汚れ検知モードを解除する。このようにすると、カバーがある程度汚れて汚れ検知動作が必要になったときに汚れ検知動作を行うことができ、汚れ検知動作の無駄な実行を避けることができる。
【００１４】
また、通常、汚れは少しずつ堆積していくので、汚れによる散乱光の受光強度は比較的緩やかに変化する。したがって、図２に示す車間距離計測動作を実行するたびに汚れ検知動作を実行せず、車間距離計測動作を複数回以上、例えば４、５回以上実行するたびに汚れ検知動作を１回実行するようにしても、汚れ検知動作を実行しなかった車間距離計測動作の間に汚れが急激にひどくなるようなことはない。具体的には、図３に示すように、汚れ検知モードが設定されても、車間距離計測動作を複数回以上実行するたびに１回だけ、距離計測用ＡＧＣから汚れ検知用ゲインに切り換えて汚れ検知動作を実行する。なお、図２に示す車間距離計測動作は繰り返し実行されるサイクル動作であり、車間距離計測動作を行うサイクルを距離計測サイクルと呼び、汚れ検知動作を行うサイクルを汚れ検知サイクルと呼ぶ。
【００１５】
フロントカバー１０はレーザー送光部１１およびレーザー受光部１２から至近距離にあり、自車前方の障害物はフロントカバー１０よりはるか遠方にあるから、フロントカバー１０の汚れによる散乱光は測定時間が短い範囲に現れ、障害物からの反射光は測定時間が長い範囲に現れる。したがって、レーザー送受光部１１，１２の位置を基準とするフロントカバー１０と障害物との位置関係に基づいて、タイマー１６ａによるレーザー受光部１２の受光信号の測定時間を、図４に示すように汚れ散乱光領域と障害物反射光領域とに区分する。図４はレーザー受光部１２の受光信号の強度を示す。図において、横軸はレーザー光を自車前方に送光してからの経過時間の測定値を表し、この測定時間は自車前方の障害物までの距離に比例する。フロントカバー１０からの散乱光の受光信号に基づいてフロントカバー１０の汚れを検知する汚れ検知サイクルにおいて、ＡＧＣ制御部１３は汚れ検知用ゲインを設定する。ここでは、汚れ検知用増幅ゲインとして固定値１を設定する例を示す。一方、障害物からの反射光の受光信号に基づいて障害物までの距離を測定する距離計測サイクルでは、ＡＧＣ制御部１３は距離計測用ＡＧＣを実行する。すなわち、障害物反射光領域における反射光強度の最大値が所定の強度範囲、すなわちゲインアップしきい値からゲインダウンしきい値までの範囲に入るように、増幅回路１４の増幅ゲインを調整する。
【００１６】
汚れ検知サイクルでは汚れ検知用増幅ゲインに固定値（例えば１）を設定し、ＡＧＣを行わない。そのため、図１０(ａ)に示すように、フロントカバー１０がひどく汚れていて散乱光強度が障害物からの反射光強度よりもはるかに大きいような場合でも、フロントカバー１０からの散乱光強度に合わせて増幅ゲインを下げることはしないから、図１０(ｂ)に示すように障害物からの反射光強度が小さくなって障害物を正しく認識できなくなってしまうという不具合は起きない。
【００１７】
ふたたび図２のフローチャートに戻り、車間距離計測動作を説明する。汚れ検知モードが設定されていないときは、通常の距離計測動作を行うためにステップ７へ進む。通常の距離計測動作については後述する。汚れ検知モードが設定されているときはステップ４へ進み、今回の動作サイクルが汚れ検知サイクルかどうかを確認する。汚れ検知サイクルでないときは、通常の距離計測動作を行うためにステップ７へ進む。
【００１８】
ここで、図２のステップ５〜６がフロントカバー１０の汚れを検知する動作ステップであり、図２のステップ７〜８が自車前方の障害物までの距離を計測する動作ステップである。動作切替制御部１９は、汚れ検知モードが設定されているときに、距離計測動作を複数回以上、例えば４，５回以上実行するたびに汚れ検知動作を１回実行するように、距離計測サイクルと汚れ検知サイクルを切り換える。
【００１９】
汚れ検知モードが設定されており、かつ今回の動作サイクルが汚れ検知サイクルのときは、ステップ５でＡＧＣ制御部１３により汚れ検知用固定増幅ゲイン（例えば１）を設定し、続くステップ６で汚れ検知処理を行う。具体的には、図４に示すように、汚れ散乱光領域における受光強度最大値（図中に○で囲む箇所）を記憶部１８に記憶されている汚れ検知しきい値と比較判定し、散乱光強度最大値が汚れ検知しきい値を超えていれば報知部２０によりフロントカバー１０の汚れを報知する。これにより、乗員にカバーの清掃を促すことができ、常にカバーを汚れのない状態に保って車間距離計測装置の信頼性を確保することができる。
【００２０】
汚れ検知処理後のステップ９で、ＡＧＣ制御部１３により増幅回路１４の増幅ゲインに固定値（例えば１）を設定する。続くステップ１０において、汚れ散乱光領域における受光信号強度の最大値を記憶部１８に記憶されている汚れ検知実行しきい値と比較判定する。汚れ散乱光強度の最大値が汚れ検知実行しきい値以下のときはステップ１１へ進み、汚れ検知モードを解除する。一方、汚れ散乱光強度の最大値が汚れ検知実行しきい値を超えるときはステップ１２へ進み、汚れ検知モードを設定する。
【００２１】
ステップ３において汚れ検知モードが設定されていないと判定された場合、あるいはステップ４において汚れ検知サイクルでないと判定された場合にはステップ７へ進み、ＡＧＣ制御部１３により図６に示す距離計測用ＡＧＣ動作を実行し、障害物反射光領域における反射光強度の最大値に応じて増幅ゲインを調整する。
【００２２】
図６のステップ２１において、障害物反射光領域の受光信号の最大値を算出する。続くステップ２２で障害物反射光強度の最大値を記憶部１８に記憶されているゲインダウンしきい値と比較判定し、障害物反射光強度の最大値がゲインダウンしきい値より大きい場合はステップ２３へ進む。ステップ２３では、現在、最小の増幅ゲインが設定されているかどうかを確認し、最小ゲインが設定されている場合はこれ以上ゲインを下げることはできないのでステップ２５へ進む。一方、最小ゲインが設定されていない場合はステップ２４へ進み、増幅ゲインを１段下げる。なお、増幅回路１４の増幅ゲインは所定幅ずつステップ状に調整する。増幅ゲインを１段下げた後、ふたたびステップ２２へ戻って障害物反射光強度がゲインダウンしきい値以下になったかどうかを確認し、上述したゲイン調整を繰り返す。
【００２３】
障害物反射光強度の最大値がゲインダウンしきい値以下の場合は、ステップ２５で障害物反射光強度を記憶部１８に記憶されているゲインアップしきい値と比較判定する。障害物反射光強度がゲインアップしきい値より小さい場合はステップ２６へ進み、現在、最大の増幅ゲインが設定されているかどうかを確認する。最大ゲインが設定されている場合はこれ以上ゲインを上げることはできないのでＡＧＣ動作を終了する。一方、最大ゲインが設定されていない場合はステップ２７へ進み、増幅ゲインを１段上げる。増幅ゲインを１段上げた後、ふたたびステップ２２へ戻って障害物反射光強度がゲインダウンしきい値とゲインアップしきい値の範囲内にあるかどうかを確認し、上述したゲイン調整を繰り返す。以上の距離計測用ＡＧＣ動作を実行することによって、障害物反射光領域における反射光強度の最大値に応じて最適な増幅ゲインを設定することができる。
【００２４】
図５は、図４に示す受光信号に対して距離計測用ＡＧＣ動作を実行し、増幅ゲインを１から４に上げた場合の受光信号強度を示す。図５において、横軸はレーザー光を自車前方に送光してからの経過時間の測定値を表し、この測定時間は自車前方の障害物までの距離に比例する。距離計測用ＡＧＣを実行したことにより、障害物反射光領域における受光信号強度の最大値（図中に○で囲った箇所）はゲインダウンしきい値とゲインアップしきい値の範囲内の適切なレベルに調整され、後述する障害物までの距離計測処理がし易くなる。
【００２５】
距離計測用ＡＧＣ動作を実行した後、図２のステップ８で距離計測処理を実行する。具体的には、障害物反射光領域において受光信号強度が物体検知しきい値を超える障害物反射光が計測された場合に、タイマー１６ａによりレーザー送光部１１からレーザー光パルスを送光してからレーザー受光部１２で当該障害物反射光を受光するまでの時間を計測し、障害物までの距離を演算する。距離計測処理を終了したらステップ９へ進み、増幅ゲインを１に戻してステップ１０〜１２で上述した汚れ検知モードの設定または解除を行う。
【００２６】
このように、レーザー光パルスの送光から受光までの測定時間を、送光されたレーザー光パルスがフロントカバー１０の汚れに散乱した散乱光を受光する散乱光領域と、送光されたレーザー光パルスがフロントカバー１０より遠方にある物体に反射した反射光を受光する反射光領域とに区分し、物体までの距離を計測するときは、反射光領域における受光信号強度の最大値が所定の強度範囲に入るように増幅ゲインを制御し、物体からの反射光の受光信号強度が物体検知しきい値を超えた場合に、当該反射光受光までの測定時間に基づいて障害物までの距離を演算するようにした。これにより、散乱光強度の最大値に応じて増幅ゲインの調整が行われないので、フロントカバー１０の汚れによる散乱光の強度が大きくてもそのような散乱光の影響を受けることなく、反射光を適切な強度に調整することができ、自車前方の障害物を正確に認識してその障害物までの距離を正確に演算することができる。また、フロントカバー１０の汚れを診断するときは、増幅ゲインに所定値を設定し、散乱光領域における受光信号強度の最大値を汚れ検知しきい値と比較して診断を行うようにしたので、汚れ検知専用のレーザー受光部を設けずに、カバーの汚れを正確に診断することができる。
【００２７】
特許請求の範囲の構成要素と一実施の形態の構成要素との対応関係は次の通りである。すなわち、レーザー送光部１１が送光手段を、レーザー受光部１２が受光手段を、フロントカバー１０がカバーを、増幅回路１４が増幅手段を、ＡＧＣ制御部１３がゲイン制御手段を、タイマー１６ａが計時手段を、距離演算部１６が距離演算手段をそれぞれ構成する。
【図面の簡単な説明】
【図１】一実施の形態の構成を示す図である。
【図２】一実施の形態の車間距離計測動作を示すフローチャートである。
【図３】通常の距離計測モードと汚れ検知モードの切り換え動作を示す図である。
【図４】汚れ散乱光領域における受光信号強度の最大値に基づく汚れ検知動作を説明する図である。
【図５】障害物反射光領域における受光信号強度の最大値に基づく距離計測動作を説明する図である。
【図６】距離計測用ＡＧＣ動作を示すフローチャートである。
【図７】レーザー光受光素子の出力信号を示す図である。
【図８】障害物からの反射光強度に基づいてＡＧＣを行った場合の動作を説明する図である。
【図９】障害物からの反射光強度に基づいてＡＧＣを行った場合の動作を説明する図である。
【図１０】フロントカバーからの汚れによる散乱光強度に基づいてＡＧＣを行った場合を説明する図である。
【符号の説明】
１０フロントカバー
１１レーザー送光部
１２レーザー受光部
１３ＡＧＣ制御部
１４増幅回路
１５パルス信号処理部
１６距離演算部
１６ａタイマー
１７汚れ診断部
１８記憶部
１９切替制御部
２０報知部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for measuring an inter-vehicle distance from a preceding vehicle.
[0002]
[Prior art]
An inter-vehicle distance measuring device is known that calculates the distance to a front object by measuring the time from laser light transmission to light reception by transmitting laser light in front of the vehicle and receiving reflected light from the front object. For example, Japanese Patent Application Laid-Open No. 07-104066 proposes a cover attached to the front surface of the light transmitting / receiving unit in order to prevent disturbance light such as reflected light from the road surface and sunlight. When adding a front cover dirt detection function to this type of inter-vehicle distance measuring device, the distance between the light transmitter / receiver and the front cover is sufficient, so even if there is no light receiving part dedicated to dirt detection, it can be used for distance measurement. It is possible to detect scattered light caused by dirt attached to the front cover using the light receiving element.
[0003]
FIG. 7 shows the light receiving intensity of the light receiving element output signal of the inter-vehicle distance measuring apparatus with a front cover. In the figure, the horizontal axis represents the measured value of the elapsed time since the laser beam was transmitted forward of the vehicle, and this measurement time is proportional to the distance to the obstacle ahead of the vehicle. Scattered light due to dirt on the front cover at a close distance appears in a place where the measurement time is short, and reflected light from an obstacle ahead of the vehicle appears in a place where the measurement time is long. That is, scattered light from the front cover and reflected light from the obstacle are mixed in the output signal of the light receiving element. Then, when the received light intensity of the reflected light from the obstacle exceeds a preset object detection threshold, the distance to the obstacle is calculated based on the measurement time of the reflected light.
[0004]
Also, an inter-vehicle distance measuring device with an AGC (Auto Gain Control) function that controls the amplification gain of an amplifier that amplifies the output signal according to the output signal level in order to facilitate processing of the output signal of the light receiving element is known. (See, for example, Japanese Patent Laid-Open No. 05-024492). 8 and 9 show the light receiving intensity of the light receiving element output signal of the inter-vehicle distance measuring apparatus with an AGC function. In these figures, the horizontal axis represents the measured value of the elapsed time since the laser beam was transmitted forward of the host vehicle, and this measured time is proportional to the distance to the obstacle ahead of the host vehicle. In this apparatus, as shown in FIGS. 8 and 9, in addition to the object detection threshold, a gain down threshold and a gain up threshold are set. As shown in FIG. 8A, when the light intensity maximum value of the light receiving element output signal exceeds the gain down threshold when the output signal of the light receiving element is amplified by the amplification gain 4, The amplification gain is lowered from 4 to 3 as shown in FIG. On the contrary, as shown in FIG. 9A, when the light intensity maximum value of the light receiving element output signal falls below the gain-up threshold when the output signal of the light receiving element is amplified by the amplification gain 3. Increases the amplification gain from 3 to 4 as shown in FIG.
[0005]
[Problems to be solved by the invention]
However, in the inter-vehicle distance measuring device having the above-described AGC function, as shown in FIG. 10A, when the front cover becomes dirty, the scattered light intensity due to the dirt on the front cover is greater than the reflected light intensity from the obstacle. Therefore, the scattered light intensity from the front cover is determined to be the maximum value of the light intensity of the light receiving element output signal, and AGC control is executed, and the amplification gain is lowered from 4 to 3 as shown in FIG. It is done. As a result, the reflected light intensity from the obstacle also decreases and falls below the object detection threshold, and even though there is an obstacle with a light reception intensity that can still be recognized sufficiently in front of the host vehicle, it cannot be recognized as an object. There is a problem of end.
[0006]
An object of the present invention is to provide an inter-vehicle distance measuring device that accurately measures a distance to a front object and detects a dirt on a front cover.
[0007]
[Means for Solving the Problems]
(1) The invention of claim 1 is a light transmitting means for transmitting a laser light pulse, a light receiving means for receiving a laser light, a cover installed on a front surface of the light transmitting means and the light receiving means, and the light receiving. Amplifying means for amplifying the received light signal output from the means, gain control means for controlling the amplification gain of the amplifying means, and measuring the time from light transmission by the light transmitting means to light reception by the light receiving means , and measurement The scattered light region in which the laser light pulse transmitted from the light transmission means receives scattered light scattered by the dirt on the cover by the light receiving means, and the laser light pulse transmitted from the light transmission means The time measuring means for dividing the reflected light reflected by the object far from the cover into the reflected light area received by the light receiving means, and the maximum value of the received light signal intensity of the light receiving means in the reflected light area. The gain control means controls the amplification gain of the amplification means so as to fall within a predetermined intensity range, and calculates the distance to the obstacle based on the measurement time by the time measuring means until the reflected light is received in the reflected light region. The gain calculation means sets the amplification gain of the amplification means to a predetermined value by the distance calculation means and the gain control means to detect the maximum value of the light reception signal intensity of the light reception means in the scattered light region, and based on this maximum value, the cover A dirt detecting means for detecting the dirt on the surface, and an operation switching control means for switching between a distance measuring process by the distance calculating means and a dirt detecting process by the dirt detecting means .
(2) In the inter-vehicle distance measuring device according to claim 2, the dirt detection means compares the maximum value of the light reception signal intensity of the light receiving means in the scattered light region with the dirt detection threshold in the dirt detection processing. Dirty diagnosis of the cover is performed.
(3) The inter-vehicle distance measuring device according to claim 3 is configured such that the dirt detection unit is configured to perform the operation when the distance calculation unit performs the operation of measuring the distance to the object a plurality of times. The distance measurement process and the dirt detection process are switched so that the operation of diagnosing the dirt is executed once.
(4) In the inter-vehicle distance measuring device according to claim 4, when the amplification gain of the amplifying means is set to the predetermined value by the operation switching control means, the maximum value of the received light signal intensity of the light receiving means in the scattered light region. There if it exceeds a small stain detection execution threshold than the stain detection threshold, are allowed to run stain diagnosis of the cover.
(5) In the inter-vehicle distance measuring device according to claim 5, the dirt detection means detects the dirt on the cover when the maximum value of the received light signal intensity of the light receiving means in the scattered light region exceeds the dirt detection threshold. In such a case, it is provided with an informing means for informing the cover of the dirt .
[0008]
【The invention's effect】
(1) According to the invention of claim 1, the amplification gain of the amplification means is controlled so that the maximum value of the received light signal intensity in the reflected light region falls within a predetermined intensity range, and based on the measurement time until the reflected light is received. Distance measurement processing that calculates the distance to the obstacle, and the amplification gain of the amplification means is set to a predetermined value to detect the maximum value of the received signal intensity in the scattered light region, and the dirt on the cover is detected based on this maximum value Changed to perform dirt detection processing. As a result, the amplification gain is not adjusted according to the maximum value of the scattered light intensity, so that even if the intensity of the scattered light due to the dirt on the cover is large, the reflected light is not affected by such scattered light. It is possible to adjust the distance to an appropriate level, and it is possible to accurately recognize an obstacle ahead of the host vehicle and accurately calculate the distance to the obstacle.
(2) According to the second aspect of the present invention, in the dirt detection process, the maximum value of the received light signal intensity in the scattered light region is compared with the dirt detection threshold value, so that the dirt diagnosis of the cover is performed. The dirt on the cover can be accurately diagnosed without providing a dedicated laser receiving unit.
(3) According to the invention of claim 3 , the distance measurement process and the dirt detection process are performed so that the operation of diagnosing the dirt of the cover is executed once every time the action of measuring the distance to the object is executed a plurality of times. And switched . The dirt on the cover does not become abruptly abrupt in a short time, and when the dirt diagnosis operation is executed, the distance measurement operation cannot be performed, so the distance measurement value cannot be obtained. In practice, there is no hindrance by obtaining the interpolation calculation. Therefore, it is possible to accurately detect the dirt on the cover while accurately measuring the distance to the obstacle.
(4) According to the invention of claim 4, when the amplification gain is set to a predetermined value, the maximum value of the received light signal intensity in the scattered light region exceeds the stain detection execution threshold value smaller than the stain detection threshold value. In this case , the dirt diagnosis operation of the cover is permitted to be performed, so that the dirt diagnosis operation can be performed when the cover is dirty to some extent and the dirt diagnosis is necessary, and the waste diagnosis operation is avoided. Can do.
(5) When, according to the invention of claim 5, dirt maximum cover beyond the stain detection threshold of the light-receiving signal intensity at scattering light region is detected, the notification to inform the dirt cover Since the means is provided, it is possible to prompt the occupant to clean the cover, and the reliability of the inter-vehicle distance measuring device can be ensured by always keeping the cover clean.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the configuration of an embodiment. The laser transmitter 11 irradiates the pulsed laser beam forward. The laser light receiving unit 12 receives the reflected light that the laser light transmitted from the laser light transmitting unit 11 is reflected by an obstacle in front. A front cover 10 is installed on the front surfaces of the laser transmitter 11 and the laser receiver 12 to prevent dirt from directly adhering to the laser transmitter 11 and the laser receiver 12. As described above, the laser light receiving unit 12 receives the reflected light from the front obstacle, and also receives the scattered light in which the laser light transmitted from the laser light transmitting unit 11 is scattered by the dirt of the front cover 10.
[0010]
The AGC control unit 13 amplifies the light reception signal of the laser light receiving unit 12 so that the received light intensity of the reflected light from the front obstacle received by the laser light receiving unit 12 and the scattered light from the front cover 10 becomes an optimum level. The amplification gain of the amplifier circuit 14 is adjusted. The pulse signal processing unit 15 processes the pulsed laser light transmitted from the laser light transmitting unit 11 and the pulsed light reception signal received by the laser light receiving unit 12 and amplified by the amplifier circuit 14. The distance calculation unit 16 includes a timer 16a. The timer 16a measures the time from the transmission of the laser light pulse by the laser light transmission unit 11 to the reception of the reflected light by the laser light reception unit 12, and based on the measurement time by the timer 16a. Calculate the distance to the object.
[0011]
The dirt diagnostic unit 17 diagnoses the adhesion of dirt on the basis of the light reception signal of scattered light due to dirt attached to the front cover 10. The storage unit 18 stores a preset gain-down threshold value, gain-up threshold value, object detection threshold value, and the like. The gain-down threshold value is a threshold value provided for lowering the amplification gain of the amplifier circuit 14 when the received light signal exceeds this threshold value. The gain-up threshold is a threshold provided to increase the amplification gain of the amplifier circuit 14 when the received light signal falls below this threshold. The object detection threshold value is a threshold value for recognizing the obstacle as an obstacle ahead of the host vehicle when the received light intensity of the reflected light from the obstacle exceeds the threshold value. The operation switching control unit 19 switches between the distance measurement operation by the distance calculation unit 16 and the contamination detection operation by the contamination diagnosis unit 17 when the contamination detection mode is set. This switching method will be described later. The notification unit 20 notifies the adhesion of dirt when the dirt diagnosis unit 17 diagnoses that the front cover 10 has dirt.
[0012]
FIG. 2 is a flowchart showing an inter-vehicle distance measurement operation according to one embodiment. The inter-vehicle distance measuring device repeatedly executes this inter-vehicle distance measuring operation when a main switch (not shown) is turned on. In step 1, a laser beam pulse is transmitted from the laser transmitter 11, and in step 2, reflected light from a front obstacle and scattered light due to dirt on the front cover 10 are received by the laser receiver 12. In step 3, it is confirmed whether or not a stain detection mode for performing a stain detection operation is set based on the received light intensity of scattered light from the front cover 10 received by the laser light receiver 12.
[0013]
FIG. 3 shows a switching operation between the normal distance measurement mode and the dirt detection mode according to the embodiment. The intensity of scattered light due to dirt on the front cover 10 changes depending on the degree of dirt on the front cover 10 due to adhesion of mud or snow, but normally the intensity of scattered light does not change suddenly in an instant. . Therefore, as shown in FIG. 3, in addition to the dirt detection judgment threshold value for judging that the front cover 10 is dirty, the threshold value is lower than the dirt detection judgment threshold value for starting the dirt detection operation. The contamination detection execution threshold values are set, and these threshold values are stored in the storage unit 18. Each time the inter-vehicle distance measurement operation shown in FIG. 2 is executed, a fixed value (for example, 1) is set to the amplification gain of the amplifier circuit 14 to monitor the received light intensity of the scattered light due to the dirt on the front cover 10, and When the received light intensity of the scattered light exceeds the stain detection execution threshold, the stain detection mode is set, and the stain detection operation is started using the stain detection determination threshold. Also, when the received light intensity of scattered light due to dirt falls below the dirt detection execution threshold, the dirt detection mode is canceled. In this way, the dirt detection operation can be performed when the cover is dirty to some extent and the dirt detection operation is required, and wasteful execution of the dirt detection operation can be avoided.
[0014]
Further, since dirt is usually accumulated little by little, the received light intensity of scattered light due to the dirt changes relatively slowly. Therefore, the dirt detection operation is not executed every time the inter-vehicle distance measurement operation shown in FIG. 2 is executed, and the dirt detection operation is executed once every time the inter-vehicle distance measurement operation is executed a plurality of times, for example, four or five times. Even if it does in this way, dirt does not become abruptly worse during the inter-vehicle distance measurement operation in which the dirt detection operation is not executed. Specifically, as shown in FIG. 3, even when the dirt detection mode is set, the distance measurement AGC is switched to the dirt detection gain only once every time the inter-vehicle distance measurement operation is performed more than once. Execute the detection operation. The inter-vehicle distance measurement operation shown in FIG. 2 is a cycle operation that is repeatedly executed. The cycle that performs the inter-vehicle distance measurement operation is called a distance measurement cycle, and the cycle that performs the dirt detection operation is called a dirt detection cycle.
[0015]
Since the front cover 10 is at a short distance from the laser transmitter 11 and the laser receiver 12, and the obstacle ahead of the host vehicle is far from the front cover 10, the scattered light due to dirt on the front cover 10 has a short measurement time. The reflected light from the obstacle appears in the range where the measurement time is long. Therefore, based on the positional relationship between the front cover 10 and the obstacle based on the positions of the laser transmitting / receiving units 11 and 12, the measurement time of the received light signal of the laser receiving unit 12 by the timer 16a is as shown in FIG. It is divided into a dirt scattered light region and an obstacle reflected light region. FIG. 4 shows the intensity of the light reception signal of the laser light receiving unit 12. In the figure, the horizontal axis represents the measured value of the elapsed time since the laser beam was transmitted forward of the vehicle, and this measurement time is proportional to the distance to the obstacle ahead of the vehicle. In a dirt detection cycle for detecting dirt on the front cover 10 based on a light reception signal of scattered light from the front cover 10, the AGC control unit 13 sets a dirt detection gain. Here, an example is shown in which a fixed value 1 is set as the stain detection amplification gain. On the other hand, in the distance measurement cycle in which the distance to the obstacle is measured based on the light reception signal of the reflected light from the obstacle, the AGC control unit 13 executes AGC for distance measurement. That is, the amplification gain of the amplifier circuit 14 is adjusted so that the maximum value of the reflected light intensity in the obstacle reflected light region falls within a predetermined intensity range, that is, a range from the gain up threshold value to the gain down threshold value.
[0016]
In the dirt detection cycle, a fixed value (for example, 1) is set for the dirt detection amplification gain, and AGC is not performed. Therefore, as shown in FIG. 10A, even when the front cover 10 is extremely dirty and the scattered light intensity is much larger than the reflected light intensity from the obstacle, the scattered light intensity from the front cover 10 is increased. At the same time, since the amplification gain is not lowered, there is no problem that the reflected light intensity from the obstacle becomes small and the obstacle cannot be recognized correctly as shown in FIG.
[0017]
Returning to the flowchart of FIG. 2, the inter-vehicle distance measurement operation will be described. When the dirt detection mode is not set, the routine proceeds to step 7 in order to perform a normal distance measurement operation. The normal distance measurement operation will be described later. When the dirt detection mode is set, the process proceeds to step 4 to check whether or not the current operation cycle is a dirt detection cycle. When it is not the dirt detection cycle, the routine proceeds to step 7 in order to perform a normal distance measuring operation.
[0018]
Here, Steps 5 to 6 in FIG. 2 are operation steps for detecting dirt on the front cover 10, and Steps 7 to 8 in FIG. 2 are operation steps for measuring the distance to the obstacle ahead of the host vehicle. When the dirt detection mode is set, the operation switching control unit 19 performs the distance measurement cycle so that the dirt detection operation is performed once every time the distance measurement operation is performed a plurality of times, for example, four or five times or more. And the dirt detection cycle.
[0019]
When the dirt detection mode is set and the current operation cycle is a dirt detection cycle, a fixed amplification gain for dirt detection (for example, 1) is set by the AGC control unit 13 at step 5, and the dirt detection is performed at the subsequent step 6. Process. Specifically, as shown in FIG. 4, the maximum received light intensity value in the dirt scattered light region (the part surrounded by a circle in the figure) is compared with the dirt detection threshold value stored in the storage unit 18 to determine the scattering. If the maximum light intensity exceeds the contamination detection threshold, the notification unit 20 notifies the front cover 10 of contamination. Accordingly, the occupant can be prompted to clean the cover, and the reliability of the inter-vehicle distance measuring device can be ensured by always keeping the cover clean.
[0020]
In step 9 after the stain detection process, the AGC control unit 13 sets a fixed value (for example, 1) for the amplification gain of the amplifier circuit 14. In subsequent step 10, the maximum value of the received light signal intensity in the dirt scattered light region is compared with the dirt detection execution threshold value stored in the storage unit 18. When the maximum value of the dirt scattered light intensity is less than or equal to the dirt detection execution threshold value, the process proceeds to step 11 to cancel the dirt detection mode. On the other hand, when the maximum value of the dirt scattered light intensity exceeds the dirt detection execution threshold value, the routine proceeds to step 12, and the dirt detection mode is set.
[0021]
If it is determined in step 3 that the dirt detection mode is not set, or if it is determined in step 4 that it is not a dirt detection cycle, the process proceeds to step 7, and the AGC controller 13 performs AGC for distance measurement shown in FIG. The operation is executed, and the amplification gain is adjusted according to the maximum value of the reflected light intensity in the obstacle reflected light region.
[0022]
In step 21 of FIG. 6, the maximum value of the light reception signal in the obstacle reflected light region is calculated. In the next step 22, the maximum value of the obstacle reflected light intensity is compared with the gain down threshold value stored in the storage unit 18. If the maximum value of the obstacle reflected light intensity is greater than the gain down threshold value, the step is performed. Proceed to 23. In step 23, it is confirmed whether or not the minimum amplification gain is currently set. If the minimum gain is set, the gain cannot be lowered any further, and the process proceeds to step 25. On the other hand, if the minimum gain is not set, the process proceeds to step 24, and the amplification gain is lowered by one step. The amplification gain of the amplifier circuit 14 is adjusted stepwise by a predetermined width. After the amplification gain is lowered by one step, the process returns to step 22 again to check whether the obstacle reflected light intensity is equal to or lower than the gain-down threshold, and the above-described gain adjustment is repeated.
[0023]
If the maximum value of the obstacle reflected light intensity is equal to or smaller than the gain-down threshold value, the obstacle reflected light intensity is compared with the gain-up threshold value stored in the storage unit 18 in step 25. If the obstacle reflected light intensity is smaller than the gain-up threshold value, the process proceeds to step 26 to check whether or not the maximum amplification gain is currently set. If the maximum gain is set, the AGC operation is terminated because the gain cannot be increased any further. On the other hand, if the maximum gain is not set, the process proceeds to step 27 to increase the amplification gain by one level. After increasing the amplification gain by one step, the process returns to step 22 again to check whether the obstacle reflected light intensity is within the range between the gain-down threshold and the gain-up threshold, and the above-described gain adjustment is repeated. By executing the distance measuring AGC operation described above, an optimum amplification gain can be set according to the maximum value of the reflected light intensity in the obstacle reflected light region.
[0024]
FIG. 5 shows the received light signal intensity when the AGC operation for distance measurement is executed on the received light signal shown in FIG. 4 and the amplification gain is increased from 1 to 4. In FIG. 5, the horizontal axis represents the measured value of the elapsed time since the laser beam was transmitted forward of the host vehicle, and this measurement time is proportional to the distance to the obstacle ahead of the host vehicle. By executing the AGC for distance measurement, the maximum value of the received light signal intensity in the obstacle reflected light region (the part circled in the figure) is an appropriate value within the range of the gain down threshold and the gain up threshold. The level is adjusted, and distance measurement processing to an obstacle described later is facilitated.
[0025]
After the distance measurement AGC operation is executed, a distance measurement process is executed in step 8 of FIG. Specifically, when obstacle reflected light whose received light signal intensity exceeds the object detection threshold in the obstacle reflected light region is measured, a laser light pulse is transmitted from the laser transmitter 11 by the timer 16a. Until the laser light receiving unit 12 receives the obstacle reflected light, the distance to the obstacle is calculated. When the distance measurement process is completed, the process proceeds to step 9 where the amplification gain is returned to 1, and the above-described dirt detection mode is set or canceled in steps 10-12.
[0026]
As described above, the measurement time from the transmission of the laser light pulse to the reception of light is determined based on the scattered light region in which the transmitted laser light pulse receives scattered light scattered on the dirt of the front cover 10 and the transmitted laser light. When a pulse is divided into a reflected light region that receives reflected light reflected by an object far from the front cover 10 and the distance to the object is measured, the maximum value of the received light signal intensity in the reflected light region is a predetermined intensity. Amplification gain is controlled so that it falls within the range, and when the received light intensity of the reflected light from the object exceeds the object detection threshold, the distance to the obstacle is calculated based on the measurement time until the reflected light is received. I tried to do it. Thereby, since the amplification gain is not adjusted according to the maximum value of the scattered light intensity, the reflected light is not affected by the scattered light even if the intensity of the scattered light due to the dirt on the front cover 10 is large. Can be adjusted to an appropriate strength, an obstacle ahead of the host vehicle can be accurately recognized, and a distance to the obstacle can be accurately calculated. Further, when diagnosing dirt on the front cover 10, a predetermined value is set for the amplification gain, and the maximum value of the received light signal intensity in the scattered light region is compared with the dirt detection threshold value. It is possible to accurately diagnose the dirt on the cover without providing a laser light receiving unit dedicated to dirt detection.
[0027]
The correspondence between the constituent elements of the claims and the constituent elements of the embodiment is as follows. That is, the laser transmitter 11 is the transmitter, the laser receiver 12 is the receiver, the front cover 10 is the cover, the amplifier 14 is the amplifier, the AGC controller 13 is the gain controller, and the timer 16a is the timer 16a. The distance calculating unit 16 constitutes the time calculating means and the distance calculating means.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an embodiment.
FIG. 2 is a flowchart showing an inter-vehicle distance measurement operation according to one embodiment.
FIG. 3 is a diagram illustrating a switching operation between a normal distance measurement mode and a dirt detection mode.
FIG. 4 is a diagram illustrating a dirt detection operation based on a maximum value of received light signal intensity in a dirt scattered light region.
FIG. 5 is a diagram for explaining a distance measurement operation based on the maximum value of the received light signal intensity in the obstacle reflected light region.
FIG. 6 is a flowchart showing an AGC operation for distance measurement.
FIG. 7 is a diagram showing an output signal of a laser light receiving element.
FIG. 8 is a diagram illustrating an operation when AGC is performed based on the intensity of reflected light from an obstacle.
FIG. 9 is a diagram illustrating an operation when AGC is performed based on the intensity of reflected light from an obstacle.
FIG. 10 is a diagram illustrating a case where AGC is performed based on scattered light intensity due to dirt from a front cover.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Front cover 11 Laser transmission part 12 Laser light receiving part 13 AGC control part 14 Amplifying circuit 15 Pulse signal processing part 16 Distance calculation part 16a Timer 17 Dirt diagnosis part 18 Storage part 19 Switching control part 20 Notification part

Claims

A light transmitting means for transmitting a laser light pulse;
A light receiving means for receiving laser light;
A cover installed in front of the light transmitting means and the light receiving means;
Amplifying means for amplifying the received light signal output from the light receiving means;
Gain control means for controlling the amplification gain of the amplification means;
The time from the light transmission by the light transmission means to the light reception by the light reception means is measured , and the measurement time is measured based on the scattered light scattered by the cover by the laser light pulse transmitted from the light transmission means. A time measuring means for classifying the scattered light area received by the means into the reflected light area received by the light receiving means and the reflected light reflected by the object far from the cover from the laser light pulse transmitted from the light sending means; When,
The gain control means controls the amplification gain of the amplifying means so that the maximum value of the received light signal intensity of the light receiving means in the reflected light area falls within a predetermined intensity range, and the reflected light is received in the reflected light area until the reflected light is received. Distance calculating means for calculating the distance to the obstacle based on the measurement time by the time measuring means ;
The gain control means sets the amplification gain of the amplification means to a predetermined value, detects the maximum value of the light reception signal intensity of the light reception means in the scattered light region, and detects dirt on the cover based on this maximum value. Dirt detection means;
An inter-vehicle distance measuring device comprising: an operation switching control unit that switches between a distance measuring process by the distance calculating unit and a dirt detecting process by the dirt detecting unit.

In the inter-vehicle distance measuring device according to claim 1,
In the dirt detection process, the dirt detection means compares the maximum value of the light reception signal intensity of the light receiving means in the scattered light region with a dirt detection threshold value, and performs dirt diagnosis on the cover. Distance measuring device.

In the inter-vehicle distance measuring device according to claim 2,
Said operation control means, each time said distance computing means is executed more than several times the operation of measuring the distance to the object, the operation of the stain detection means to diagnose the contamination of the cover to run once An inter-vehicle distance measurement device that switches between the distance measurement process and the dirt detection process .

In the inter-vehicle distance measuring device according to claim 2 or claim 3,
The operation switching control means executes the dirt detection when the amplification gain of the amplification means is the predetermined value, and the maximum value of the light receiving signal intensity of the light receiving means in the scattered light region is smaller than the dirt detection threshold value. An inter-vehicle distance measuring device that permits execution of a dirt diagnosis of the cover when a threshold value is exceeded.

In the inter-vehicle distance measuring device according to any one of claims 2 to 4,
By the stain detection unit, wherein when the dirt of the cover the maximum value of the light-receiving signal intensity exceeds the stain detection threshold of the light-receiving means in the scattered light region is detected, the notification to inform the contamination of the cover vehicle distance measuring apparatus characterized in that it comprises means.