JP5918475B2 - EGR device - Google Patents

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JP5918475B2
JP5918475B2 JP2011071831A JP2011071831A JP5918475B2 JP 5918475 B2 JP5918475 B2 JP 5918475B2 JP 2011071831 A JP2011071831 A JP 2011071831A JP 2011071831 A JP2011071831 A JP 2011071831A JP 5918475 B2 JP5918475 B2 JP 5918475B2
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water
cooled
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egr cooler
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JP2012207549A (en
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悦弘 舩山
悦弘 舩山
登 内田
登 内田
清広 下川
清広 下川
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Hino Motors Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

本発明は、排気側から吸気側へ排気ガスの一部をＥＧＲガスとして再循環してＮＯxの低減化を図るためのＥＧＲ装置に関するものである。   The present invention relates to an EGR device for reducing NOx by recirculating a part of exhaust gas as EGR gas from the exhaust side to the intake side.

従来より、自動車のエンジンなどでは、排気側から排気ガスの一部を抜き出して吸気側へと戻し、その吸気側に戻された排気ガスでエンジン内での燃料の燃焼を抑制させて燃焼温度を下げることによりＮＯx（窒素酸化物）の発生を低減するようにした、いわゆる排気ガス再循環（ＥＧＲ：Exhaust Gas Recirculation）が行われている。   Conventionally, in an automobile engine or the like, a part of the exhaust gas is extracted from the exhaust side and returned to the intake side, and the exhaust gas returned to the intake side suppresses the combustion of fuel in the engine to increase the combustion temperature. So-called exhaust gas recirculation (EGR) is performed in which the generation of NOx (nitrogen oxide) is reduced by lowering.

一般的に、この種の排気ガス再循環を行う場合には、排気マニホールドから排気管に亘る排気通路の適宜位置と、吸気管から吸気マニホールドに亘る吸気通路の適宜位置との間をＥＧＲパイプにより接続し、該ＥＧＲパイプを通して排気ガスをＥＧＲガスとして再循環するようにしている。   In general, when this type of exhaust gas recirculation is performed, an EGR pipe is used between an appropriate position of the exhaust passage extending from the exhaust manifold to the exhaust pipe and an appropriate position of the intake passage extending from the intake pipe to the intake manifold. The exhaust gas is recirculated as EGR gas through the EGR pipe.

尚、エンジンに再循環するＥＧＲガスをＥＧＲパイプの途中で冷却すると、ＥＧＲガスの温度が下がり且つその容積が小さくなることにより、エンジンの出力を余り低下させずに燃焼温度を低下して効果的にＮＯxの発生を低減させることができるため、エンジンにＥＧＲガスを再循環するＥＧＲパイプの途中に水冷式のＥＧＲクーラが装備されている。   In addition, when the EGR gas recirculated to the engine is cooled in the middle of the EGR pipe, the temperature of the EGR gas is lowered and the volume is reduced, so that the combustion temperature is effectively reduced without reducing the engine output much. Since the generation of NOx can be reduced, a water-cooled EGR cooler is provided in the middle of an EGR pipe for recirculating EGR gas to the engine.

図６は前述した排気ガス再循環を行うためのＥＧＲ装置の一例を示すもので、図中１はディーゼル機関であるエンジンを示し、該エンジン１は、ターボチャージャ２を備えており、エアクリーナ３から導いた吸気４を吸気管５を通し前記ターボチャージャ２のコンプレッサ２ａへ送り、該コンプレッサ２ａで加圧された吸気４をインタークーラ６へと送って冷却し、該インタークーラ６から更に吸気マニホールド７へと吸気４を導いてエンジン１の各気筒（図６では直列６気筒の場合を例示している）に分配するようにしてある。   FIG. 6 shows an example of the EGR device for performing the above-described exhaust gas recirculation. In FIG. 6, reference numeral 1 denotes an engine that is a diesel engine. The engine 1 includes a turbocharger 2, and includes an air cleaner 3. The guided intake air 4 is sent to the compressor 2 a of the turbocharger 2 through the intake pipe 5, the intake air 4 pressurized by the compressor 2 a is sent to the intercooler 6, and the intake manifold 7 is further cooled from the intercooler 6. The intake 4 is guided to the engine and distributed to each cylinder of the engine 1 (in FIG. 6, the case of in-line 6 cylinders is illustrated).

また、このエンジン１の各気筒から排出された排気ガス８を排気マニホールド９を介し前記ターボチャージャ２のタービン２ｂへ送り、該タービン２ｂを駆動した排気ガス８を排気管１０を介し車外へ排出するようにしてある。   The exhaust gas 8 discharged from each cylinder of the engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 9, and the exhaust gas 8 driving the turbine 2b is discharged out of the vehicle through the exhaust pipe 10. It is like that.

そして、排気マニホールド９の一端部と吸気マニホールド７の入口付近の吸気管５との間がＥＧＲパイプ１１により接続されており、排気マニホールド９から排気ガス８の一部をＥＧＲガス８’として抜き出して吸気管５に導き得るようにしてある。   An end portion of the exhaust manifold 9 and the intake pipe 5 near the inlet of the intake manifold 7 are connected by an EGR pipe 11, and a part of the exhaust gas 8 is extracted from the exhaust manifold 9 as EGR gas 8 ′. It can be led to the intake pipe 5.

前記ＥＧＲパイプ１１には、ＥＧＲガス８’の再循環量を適宜に調節し得るよう開度調整可能なＥＧＲバルブ１２と、ＥＧＲガス８’を冷却するための水冷式ＥＧＲクーラ１３とが装備されており、該水冷式ＥＧＲクーラ１３では、冷却水１４とＥＧＲガス８’とを熱交換させることによりＥＧＲガス８’の温度を低下し得るようになっている。   The EGR pipe 11 is equipped with an EGR valve 12 whose opening degree can be adjusted so that the recirculation amount of the EGR gas 8 ′ can be appropriately adjusted, and a water-cooled EGR cooler 13 for cooling the EGR gas 8 ′. In the water-cooled EGR cooler 13, the temperature of the EGR gas 8 ′ can be lowered by exchanging heat between the cooling water 14 and the EGR gas 8 ′.

ここで、前記水冷式ＥＧＲクーラ１３では、エンジン１の冷却に使用している冷却水１４の一部が抜き出されて冷媒として用いられるようになっており、ＥＧＲガス８’との熱交換により昇温した冷却水１４は、サーモスタットケース１５を介しエンジン１の冷却水１４を冷却する系統に戻され、該エンジン１を経た冷却水１４と共にラジエータ１６に送られて外気との熱交換により冷却され、然る後に、サーモスタット１７を経由してサーモスタットケース１５に戻され、ここからクーラントポンプ１８によりエンジン１へ再び送り込まれるようになっている。   Here, in the water-cooled EGR cooler 13, a part of the cooling water 14 used for cooling the engine 1 is extracted and used as a refrigerant, and is exchanged by heat exchange with the EGR gas 8 '. The heated cooling water 14 is returned to the system for cooling the cooling water 14 of the engine 1 via the thermostat case 15, and is sent to the radiator 16 together with the cooling water 14 passed through the engine 1 to be cooled by heat exchange with the outside air. After that, it is returned to the thermostat case 15 via the thermostat 17 and is sent again to the engine 1 by the coolant pump 18 from here.

尚、冷間始動時等における冷却水１４の温度が低い時には、サーモスタット１７の作動によりエンジン１とラジエータ１６との間で冷却水１４を循環する水路が閉じ且つエンジン１からの冷却水１４をラジエータ１６を経由させずにエンジン１に戻す水路が開くことにより、冷却水１４をラジエータ１６を経由させずに循環させてエンジン１の暖機を優先するようになっている。   When the temperature of the cooling water 14 is low during cold starting or the like, the operation of the thermostat 17 closes the water path for circulating the cooling water 14 between the engine 1 and the radiator 16 and allows the cooling water 14 from the engine 1 to pass through the radiator. By opening a water channel that returns to the engine 1 without passing through the engine 16, the cooling water 14 is circulated without passing through the radiator 16 to give priority to warming up the engine 1.

この種のＥＧＲ装置に関連する先行技術文献情報としては下記の特許文献１等がある。   As prior art document information related to this type of EGR apparatus, there is the following Patent Document 1.

特表２００７−５３０８６９号公報JP-T-2007-530869

しかしながら、斯かる従来のＥＧＲ装置においては、エンジン１の冷却に使用している冷却水１４の一部を抜き出して水冷式ＥＧＲクーラ１３でのＥＧＲガス８’の冷却に使用しているため、該ＥＧＲガス８’の温度をエンジン１の冷却水１４より低い温度まで下げることができないという問題があり、将来的に排気ガス規制が益々厳しくなることを考えると、更なるＮＯx低減を図るためには、ＥＧＲガス８’の温度を吸気温度レベルまで低減する必要があると考えられているが、ＥＧＲガス８’の過度な冷却は、エンジン１の冷機状態において白煙の排出を招き、暖機後においても、軽負荷運転時に大量のＨＣ，ＣＯを排出してしまう問題があった。   However, in such a conventional EGR device, since a part of the cooling water 14 used for cooling the engine 1 is extracted and used for cooling the EGR gas 8 ′ in the water-cooled EGR cooler 13, the Considering that there is a problem that the temperature of the EGR gas 8 'cannot be lowered to a temperature lower than the cooling water 14 of the engine 1, and considering that exhaust gas regulations will become increasingly severe in the future, in order to further reduce NOx It is considered that the temperature of the EGR gas 8 ′ needs to be reduced to the intake air temperature level. However, excessive cooling of the EGR gas 8 ′ causes white smoke to be discharged in the cold state of the engine 1, and However, there is a problem that a large amount of HC and CO is discharged during light load operation.

本発明は上述の実情に鑑みてなしたもので、白煙やＨＣ，ＣＯの排出を招くことなく適切な運転状態でＥＧＲガスの温度をエンジンの冷却水より低い温度まで下げてＮＯx低減効果の向上を図り得るＥＧＲ装置を提供することを目的とする。   The present invention has been made in view of the above circumstances, and reduces the temperature of the EGR gas to a temperature lower than the engine cooling water in an appropriate operating state without incurring the emission of white smoke, HC, and CO, and has an NOx reduction effect. An object of the present invention is to provide an EGR device that can be improved.

本発明は、排気側から排気ガスの一部を抜き出してＥＧＲガスとして吸気側へ再循環するＥＧＲパイプと、該ＥＧＲパイプの途中に装備された前段水冷式ＥＧＲクーラと、該前段水冷式ＥＧＲクーラより下流側のＥＧＲパイプに装備された後段水冷式ＥＧＲクーラと、該後段水冷式ＥＧＲクーラを迂回してＥＧＲガスを流す第一バイパスパイプと、前段水冷式ＥＧＲクーラを迂回してＥＧＲガスを流す第二バイパスパイプと、ＥＧＲパイプを流れるＥＧＲガスの流れを第一バイパスパイプ及び第二バイパスパイプの夫々に切り替える流路切替手段とを備え、前段水冷式ＥＧＲクーラに対しエンジンの冷却水を冷媒として経由せしめ且つ後段水冷式ＥＧＲクーラに対し専用の水冷系統から前記エンジンの冷却水より低い温度の冷却水を冷媒として経由せしめるように構成すると共に、前記流路切替手段によりＥＧＲガスを前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方に流したり、何れか一方に流したり、両方を迂回させて流したりすることで、エンジンの運転状態に応じてＥＧＲガスの温度を適宜に変更し得るように構成したことを特徴とするＥＧＲ装置、に係るものである。 The present invention relates to an EGR pipe that extracts a part of exhaust gas from the exhaust side and recirculates it as EGR gas to the intake side, a front-stage water-cooled EGR cooler installed in the middle of the EGR pipe, and the front-stage water-cooled EGR cooler A downstream water-cooled EGR cooler installed in the downstream EGR pipe, a first bypass pipe that bypasses the downstream water-cooled EGR cooler and flows EGR gas, and bypasses the upstream water-cooled EGR cooler and flows EGR gas A second bypass pipe and flow path switching means for switching the flow of EGR gas flowing through the EGR pipe to the first bypass pipe and the second bypass pipe, respectively, and using the engine cooling water as a refrigerant for the preceding water-cooled EGR cooler Cooling water having a temperature lower than that of the engine cooling water from a dedicated water cooling system is used as a refrigerant for the intermediate water-cooled EGR cooler. Together configured to allowed to through, to or flowed the EGR gas or flowed both front water-cooled EGR cooler and subsequent water-cooled EGR cooler, or flow to either, to bypass both by the flow path switching unit Thus, the present invention relates to an EGR device configured to be able to appropriately change the temperature of the EGR gas in accordance with the operating state of the engine .

而して、流路切替手段によりＥＧＲパイプを流れるＥＧＲガスの流れを前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方に流すように切り替えると、ＥＧＲガスが前段水冷式ＥＧＲクーラにてエンジンの冷却水を冷媒として先行して冷却された後、下流側の後段水冷式ＥＧＲクーラにて専用の水冷系統からの冷却水を冷媒として更に冷却されることになり、排気側から吸気側へ再循環されるＥＧＲガスの温度をエンジンの冷却水より低い温度まで下げることが可能となる。   Thus, when the flow switching means switches the flow of the EGR gas flowing through the EGR pipe to both the front-stage water-cooled EGR cooler and the rear-stage water-cooled EGR cooler, the EGR gas is discharged from the engine in the front-stage water-cooled EGR cooler. After the cooling water is cooled in advance as a refrigerant, the downstream water-cooled EGR cooler on the downstream side further cools the cooling water from the dedicated water cooling system as a refrigerant and recirculates from the exhaust side to the intake side. It is possible to lower the temperature of the EGR gas to be lower than the engine cooling water.

しかも、流路切替手段によりＥＧＲパイプを流れるＥＧＲガスの流れを第一バイパスパイプに切り替えれば、後段水冷式ＥＧＲクーラを迂回させてＥＧＲガスを流すことが可能となり、流路切替手段によりＥＧＲパイプを流れるＥＧＲガスの流れを第二バイパスパイプに切り替えれば、前段水冷式ＥＧＲクーラを迂回させてＥＧＲガスを流すことが可能となるので、エンジンの運転状態に応じ流路切替手段を切り替えてＥＧＲガスを前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの何れか一方に対して流したり、或いは、前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方を迂回させて流したりすることが可能となる。   In addition, if the flow of the EGR gas flowing through the EGR pipe is switched to the first bypass pipe by the flow path switching means, it becomes possible to flow the EGR gas by bypassing the rear-stage water-cooled EGR cooler. If the flow of the EGR gas is switched to the second bypass pipe, it becomes possible to flow the EGR gas by bypassing the pre-stage water-cooled EGR cooler. Therefore, the EGR gas is switched by switching the flow path switching means according to the operating state of the engine. It is possible to flow to either the front-stage water-cooled EGR cooler or the rear-stage water-cooled EGR cooler, or to bypass and flow both the front-stage water-cooled EGR cooler and the rear-stage water-cooled EGR cooler.

例えば、エンジンの冷間始動時及び極軽負荷時に、流路切替手段によりＥＧＲガスを前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方を迂回させて流すようにすれば、高温のＥＧＲガスを冷却せずに再循環することでエンジンの暖機が優先されることになり、過度に冷却されたＥＧＲガスにより燃焼性が低下して白煙の排出を招く虞れが回避される。   For example, when the engine is cold-started and at an extremely light load, if the EGR gas is caused to flow by bypassing both the front-stage water-cooled EGR cooler and the rear-stage water-cooled EGR cooler by the flow path switching means, the hot EGR gas is allowed to flow. By recirculating without cooling, priority is given to warming up the engine, and the possibility of causing exhaust of white smoke due to excessively cooled EGR gas is avoided.

また、エンジンの軽負荷時に、流路切替手段によりＥＧＲガスを後段水冷式ＥＧＲクーラを迂回させて前段水冷式ＥＧＲクーラだけに流すようにすれば、ＥＧＲガスの冷却を前段水冷式ＥＧＲクーラの冷却だけに留めて前記ＥＧＲガスの温度を過度に冷却しなくて済み、大量のＨＣ，ＣＯを排出してしまう虞れが回避される。   In addition, when the engine is lightly loaded, the EGR gas can be cooled only by the first-stage water-cooled EGR cooler by bypassing the second-stage water-cooled EGR cooler by the flow path switching means and cooling the first-stage water-cooled EGR cooler. Therefore, there is no need to excessively cool the temperature of the EGR gas, and the possibility of discharging a large amount of HC and CO is avoided.

尚、エンジンの中・高負荷時にあっては、流路切替手段によりＥＧＲパイプを流れるＥＧＲガスの流れを前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方に流し、ＥＧＲガスの温度をエンジンの冷却水より低い温度まで下げても、白煙やＨＣ，ＣＯの増大を招く虞れがなく、これまで以上のＥＧＲガスの温度低下によりＮＯxを効果的に低減することが可能となる。   When the engine is at medium or high load, the flow of EGR gas flowing through the EGR pipe is flowed to both the front-stage water-cooled EGR cooler and the rear-stage water-cooled EGR cooler by the flow path switching means, and the temperature of the EGR gas is adjusted. Even if the temperature is lowered to a temperature lower than that of the cooling water, there is no possibility of increasing white smoke, HC, and CO, and NOx can be effectively reduced by the temperature decrease of the EGR gas more than ever.

また、本発明においては、第一バイパスパイプ及び第二バイパスパイプにおける中途箇所、最上流端の分岐箇所、最下流端の合流箇所の何れかに設けられた開閉式の切替バルブ、或いは、開度調整可能な切替バルブにより流路切替手段を構成することが可能であり、開閉式の切替バルブを採用すれば、前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方を迂回したり、何れか一方を選択したり、両方に流したりする切り替えを選択的に行うことが可能となり、開度調整可能な切替バルブを採用すれば、同様の切り替えを段階的に行うことが可能となる。   Further, in the present invention, an opening / closing type switching valve provided at any of the midway location, the most upstream end branch location, and the most downstream end merge location in the first bypass pipe and the second bypass pipe, or the opening degree It is possible to configure the flow path switching means with an adjustable switching valve. If an open / close switching valve is employed, either the front-stage water-cooled EGR cooler or the rear-stage water-cooled EGR cooler may be bypassed, or either It is possible to selectively switch between the two and flow to both, and if a switching valve capable of adjusting the opening is employed, the same switching can be performed in stages.

上記した本発明のＥＧＲ装置によれば、ＥＧＲパイプを流れるＥＧＲガスの流れを流路切替手段により切り替え、前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方を迂回させたり、何れか一方を選択させたり、両方を流させたりすることができ、エンジンの運転状態に応じてＥＧＲガスの温度を適宜に変更することができるので、ＥＧＲガスの過度な冷却によりエンジンの冷機状態において白煙の排出を招いてしまったり、暖機後において負荷の低い運転状態で大量のＨＣ，ＣＯを排出してしまったりすることを確実に防止することができ、しかも、ＥＧＲガスの温度をエンジンの冷却水より低い温度まで下げても支障のない暖機後の負荷の高い運転状態では、前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方を使用してＥＧＲガスを二段階で冷却し、ＥＧＲガスの温度をエンジンの冷却水より低い温度まで下げることができるので、同じＥＧＲ率でＥＧＲガスを再循環しても従来よりＮＯx低減効果を大幅に向上することができる等種々の優れた効果を奏し得る。   According to the above-described EGR device of the present invention, the flow of the EGR gas flowing through the EGR pipe is switched by the flow path switching means, and both the front-stage water-cooled EGR cooler and the rear-stage water-cooled EGR cooler are bypassed, or either one is selected. Or both of them can be flowed, and the temperature of the EGR gas can be appropriately changed according to the operating state of the engine. Or exhausting a large amount of HC and CO in a low-load operating state after warm-up, and the temperature of EGR gas is lower than that of engine cooling water. In the high-load operating state after warming up, which can be lowered to a low temperature, both the front-stage water-cooled EGR cooler and the rear-stage water-cooled EGR cooler are used. Since the EGR gas can be cooled in two stages and the temperature of the EGR gas can be lowered to a temperature lower than the engine cooling water, even if the EGR gas is recirculated at the same EGR rate, the NOx reduction effect is greatly improved compared to the conventional case. Various excellent effects can be obtained.

本発明の第一形態例を示す概略図である。It is the schematic which shows the example of 1st form of this invention. 本発明の第二形態例を示す概略図である。It is the schematic which shows the 2nd form example of this invention. 本発明の第三形態例を示す概略図である。It is the schematic which shows the 3rd form example of this invention. 本発明の第四形態例を示す概略図である。It is the schematic which shows the example of a 4th form of this invention. 本発明の第五形態例を示す概略図である。It is the schematic which shows the 5th example of a form of this invention. 従来例を示す概略図である。It is the schematic which shows a prior art example.

以下本発明の実施の形態を図面を参照しつつ説明する。   Embodiments of the present invention will be described below with reference to the drawings.

図１は本発明の第一形態例を示すもので、図６と同一の符号を付した部分は同一物を表わしている。   FIG. 1 shows a first embodiment of the present invention, and the parts denoted by the same reference numerals as those in FIG. 6 represent the same items.

図１に示す如く、本形態例のＥＧＲ装置においては、排気マニホールド９の一端部と吸気マニホールド７の入口付近の吸気管５との間を接続しているＥＧＲパイプ１１の途中に、水冷式ＥＧＲクーラ１３（前段水冷式ＥＧＲクーラ）が従来と同様に装備されていると共に、該水冷式ＥＧＲクーラ１３より下流側のＥＧＲパイプ１１には、別の水冷式ＥＧＲクーラ１９（後段水冷式ＥＧＲクーラ）が新たに装備されている。   As shown in FIG. 1, in the EGR device of this embodiment, a water-cooled EGR is provided in the middle of an EGR pipe 11 connecting one end of the exhaust manifold 9 and the intake pipe 5 near the inlet of the intake manifold 7. A cooler 13 (front-stage water-cooled EGR cooler) is installed in the same manner as in the past, and another water-cooled EGR cooler 19 (rear-stage water-cooled EGR cooler) is connected to the EGR pipe 11 downstream of the water-cooled EGR cooler 13. Is newly equipped.

更に、前記ＥＧＲパイプ１１には、水冷式ＥＧＲクーラ１３の出側から水冷式ＥＧＲクーラ１９を迂回してＥＧＲバルブ１２の入側に繋がる第一バイパスパイプ２０と、排気マニホールド９の出側から水冷式ＥＧＲクーラ１３を迂回して水冷式ＥＧＲクーラ１３と切替バルブ２２との間のＥＧＲパイプ１１に繋がる第二バイパスパイプ２１とが付設されている。   Furthermore, the EGR pipe 11 includes a first bypass pipe 20 that bypasses the water-cooled EGR cooler 19 from the outlet side of the water-cooled EGR cooler 13 and is connected to the inlet side of the EGR valve 12, and water-cooled from the outlet side of the exhaust manifold 9. A second bypass pipe 21 that bypasses the EGR cooler 13 and is connected to the EGR pipe 11 between the water-cooled EGR cooler 13 and the switching valve 22 is attached.

また、前記ＥＧＲパイプ１１に対する第一バイパスパイプ２０の最上流端の分岐箇所には、ＥＧＲパイプ１１を流れるＥＧＲガス８’の流れを第一バイパスパイプ２０に切り替える流路切替手段としてスリーウェイ方式の切替バルブ２２が配設されており、前記第二バイパスパイプ２１の中途箇所には、ＥＧＲパイプ１１を流れるＥＧＲガス８’の流れを第二バイパスパイプ２１に切り替える流路切替手段としてツーウェイ方式の切替バルブ２３が配設されている。   A three-way type switching means for switching the flow of the EGR gas 8 ′ flowing through the EGR pipe 11 to the first bypass pipe 20 is provided at the most upstream end of the first bypass pipe 20 with respect to the EGR pipe 11. A switching valve 22 is provided, and in the middle of the second bypass pipe 21, a two-way switching is performed as a flow path switching means for switching the flow of the EGR gas 8 ′ flowing through the EGR pipe 11 to the second bypass pipe 21. A valve 23 is provided.

ここで、上流側の水冷式ＥＧＲクーラ１３には、先に図６で説明したものと同様に、エンジン１の冷却に使用している冷却水１４の一部が抜き出されて冷媒として用いられるようになっているが、下流側の水冷式ＥＧＲクーラ１９には、専用の水冷系統から前記エンジン１の冷却水１４より低い温度の冷却水２４が冷媒として用いられるようになっており、ＥＧＲガス８’との熱交換により昇温した冷却水２４は、該冷却水２４のための低温用ラジエータ２５に送られて外気との熱交換により冷却され、然る後に、低温用サーモスタット２６を介し低温用サーモスタットケース２７に戻され、ここから低温用クーラントポンプ２８により下流側の水冷式ＥＧＲクーラ１９へ再び送り込まれるようになっている。   Here, in the water-cooled EGR cooler 13 on the upstream side, a part of the cooling water 14 used for cooling the engine 1 is extracted and used as a refrigerant in the same manner as described above with reference to FIG. However, in the water-cooled EGR cooler 19 on the downstream side, cooling water 24 having a temperature lower than that of the cooling water 14 of the engine 1 is used as a refrigerant from a dedicated water cooling system. The cooling water 24 raised in temperature by heat exchange with 8 'is sent to a low-temperature radiator 25 for the cooling water 24 and cooled by heat exchange with the outside air. The thermostat case 27 is returned to the water-cooled EGR cooler 19 on the downstream side by a low-temperature coolant pump 28.

また、図１に示している例では、ターボチャージャ２のコンプレッサ２ａで加圧されて昇温した吸気４を冷却するためのインタークーラ６を水冷式としており、前記水冷式ＥＧＲクーラ１９に送り込まれる冷却水２４の一部を前記インタークーラ６に振り分けて冷媒として用いるようにしており、該インタークーラ６で吸気４との熱交換により昇温した冷却水２４は、前記水冷式ＥＧＲクーラ１９からの冷却水２４と共に前記低温用ラジエータ２５に送り込まれるようになっている。   In the example shown in FIG. 1, the intercooler 6 for cooling the intake air 4 that has been pressurized by the compressor 2 a of the turbocharger 2 and raised in temperature is a water-cooled type, and is sent to the water-cooled EGR cooler 19. A part of the cooling water 24 is distributed to the intercooler 6 and used as a refrigerant. The cooling water 24 heated by the heat exchange with the intake air 4 in the intercooler 6 is supplied from the water-cooled EGR cooler 19. Along with the cooling water 24, it is fed into the low-temperature radiator 25.

尚、冷間始動時等における冷却水２４の温度が低い時には、低温用サーモスタット２６の作動により低温用ラジエータ２５を経由する水路が閉じ且つインタークーラ６からの冷却水２４を低温用ラジエータ２５を経由させずに低温用サーモスタットケース２７に戻す水路が開くことにより、冷却水２４を低温用ラジエータ２５を経由させずに循環させて吸気４の過冷却を回避（エンジン１の暖機を優先）するようになっている。   When the temperature of the cooling water 24 is low at the time of cold start or the like, the operation of the low-temperature thermostat 26 closes the water passage through the low-temperature radiator 25 and passes the cooling water 24 from the intercooler 6 through the low-temperature radiator 25. In order to avoid overcooling of the intake air 4 (prioritizing warm-up of the engine 1) by circulating the cooling water 24 without passing through the low-temperature radiator 25 by opening a water channel that returns to the low-temperature thermostat case 27 without doing so. It has become.

而して、このようにＥＧＲ装置を構成した場合に、切替バルブ２２，２３によりＥＧＲパイプ１１を流れるＥＧＲガス８’の流れを水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の両方に流すように切り替えると、ＥＧＲガス８’が上流側の水冷式ＥＧＲクーラ１３にてエンジン１の冷却水１４を冷媒として先行して冷却された後、下流側の水冷式ＥＧＲクーラ１９にて専用の水冷系統からの冷却水２４を冷媒として更に冷却されることになり、排気側から吸気側へ再循環されるＥＧＲガス８’の温度をエンジン１の冷却水１４より低い温度まで下げることが可能となる。   Thus, when the EGR device is configured as described above, the flow of the EGR gas 8 ′ flowing through the EGR pipe 11 is caused to flow to both the water-cooled EGR cooler 13 and the water-cooled EGR cooler 19 by the switching valves 22 and 23. When switched, the EGR gas 8 ′ is cooled in advance by using the cooling water 14 of the engine 1 as a refrigerant in the upstream water-cooled EGR cooler 13, and then in the downstream water-cooled EGR cooler 19 from a dedicated water cooling system. The cooling water 24 is further cooled as a refrigerant, and the temperature of the EGR gas 8 ′ recirculated from the exhaust side to the intake side can be lowered to a temperature lower than the cooling water 14 of the engine 1.

しかも、切替バルブ２２によりＥＧＲパイプ１１を流れるＥＧＲガス８’の流れを第一バイパスパイプ２０に切り替えれば、下流側の水冷式ＥＧＲクーラ１９を迂回させてＥＧＲガス８’を流すことが可能となり、切替バルブ２３によりＥＧＲパイプ１１を流れるＥＧＲガス８’の流れを第二バイパスパイプ２１に切り替えれば、上流側の水冷式ＥＧＲクーラ１３を迂回させてＥＧＲガス８’を流すことが可能となるので、エンジン１の運転状態に応じ切替バルブ２２，２３を切り替えてＥＧＲガス８’を水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の何れか一方に対して流したり、或いは、水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の両方を迂回させて流したりすることが可能となる。   Moreover, if the flow of the EGR gas 8 ′ flowing through the EGR pipe 11 is switched to the first bypass pipe 20 by the switching valve 22, it becomes possible to flow the EGR gas 8 ′ by bypassing the downstream water-cooled EGR cooler 19, If the flow of the EGR gas 8 ′ flowing through the EGR pipe 11 is switched to the second bypass pipe 21 by the switching valve 23, it becomes possible to flow the EGR gas 8 ′ by bypassing the upstream water-cooled EGR cooler 13. The switching valves 22 and 23 are switched in accordance with the operating state of the engine 1 so that the EGR gas 8 'flows through one of the water-cooled EGR cooler 13 and the water-cooled EGR cooler 19, or the water-cooled EGR cooler 13 and the water-cooled It is possible to flow by bypassing both of the EGR coolers 19.

例えば、エンジン１の冷間始動時及び極軽負荷時（一般車両のアイドリング時、若しくは、ミキサー車等の特装車におけるエンジン動力による補機駆動時等）に、切替バルブ２２の下流側の水冷式ＥＧＲクーラ１９に向かう流路を閉じた上で切替バルブ２３を開け、ＥＧＲガス８’を第二バイパスパイプ２１及び第一バイパスパイプ２０を介し水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の両方を迂回させて流すようにすれば、高温のＥＧＲガス８’を冷却せずに再循環することでエンジン１の暖機が優先されることになり、過度に冷却されたＥＧＲガス８’により燃焼性が低下して白煙の排出を招く虞れが回避される。   For example, the water-cooled EGR on the downstream side of the switching valve 22 during cold start of the engine 1 and extremely light load (when idling a general vehicle or when driving an auxiliary machine with engine power in a specially equipped vehicle such as a mixer vehicle). After closing the flow path toward the cooler 19, the switching valve 23 is opened, and the EGR gas 8 ′ bypasses both the water-cooled EGR cooler 13 and the water-cooled EGR cooler 19 via the second bypass pipe 21 and the first bypass pipe 20. If it is made to flow, the warm-up of the engine 1 is given priority by recirculating the high-temperature EGR gas 8 ′ without cooling, and the EGR gas 8 ′ that has been cooled excessively has combustibility. The risk of lowering and causing white smoke emission is avoided.

また、エンジン１の軽負荷時に、切替バルブ２２の水冷式ＥＧＲクーラ１９に向かう流路のみを閉じた上で切替バルブ２３を閉じることにより、ＥＧＲガス８’を下流側の水冷式ＥＧＲクーラ１９を迂回させて上流側の水冷式ＥＧＲクーラ１３だけに流すようにすれば、ＥＧＲガス８’の冷却を上流側の水冷式ＥＧＲクーラ１３の冷却だけに留めて前記ＥＧＲガス８’の温度を過度に冷却しなくて済み、大量のＨＣ，ＣＯを排出してしまう虞れが回避される。   In addition, when the engine 1 is lightly loaded, the switching valve 23 is closed after closing only the flow path of the switching valve 22 toward the water-cooled EGR cooler 19, so that the EGR gas 8 ′ is supplied to the downstream water-cooled EGR cooler 19. By bypassing and flowing only to the upstream water-cooled EGR cooler 13, the cooling of the EGR gas 8 ′ is limited only to the cooling of the upstream water-cooled EGR cooler 13, and the temperature of the EGR gas 8 ′ is excessively increased. There is no need for cooling, and the possibility of discharging a large amount of HC and CO is avoided.

尚、エンジン１の中・高負荷時にあっては、切替バルブ２２の第一バイパスパイプ２０に向かう流路のみを閉じた上で切替バルブ２３を閉じ、ＥＧＲパイプ１１を流れるＥＧＲガス８’の流れを水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の両方に流し、これによりＥＧＲガス８’の温度をエンジン１の冷却水１４より低い温度まで下げても、白煙やＨＣ，ＣＯの増大を招く虞れがなく、これまで以上のＥＧＲガス８’の温度低下によりＮＯxを効果的に低減することが可能となる。   Note that, when the engine 1 is at a medium or high load, only the flow path of the switching valve 22 toward the first bypass pipe 20 is closed, the switching valve 23 is closed, and the flow of the EGR gas 8 ′ flowing through the EGR pipe 11. Is caused to flow through both the water-cooled EGR cooler 13 and the water-cooled EGR cooler 19, so that even if the temperature of the EGR gas 8 ′ is lowered to a temperature lower than the cooling water 14 of the engine 1, white smoke, HC, and CO increase. There is no fear, and NOx can be effectively reduced by the temperature drop of the EGR gas 8 'more than ever.

また、本形態例のＥＧＲ装置においては、切替バルブ２２，２３がオン・オフ的な開閉式のものであっても良いし、開度調整可能なものであっても良く、開閉式の切替バルブ２２，２３を採用すれば、水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の両方を迂回したり、何れか一方を選択したり、両方に流したりする切り替えを選択的に行うことが可能となり、開度調整可能な切替バルブ２２，２３を採用すれば、同様の切り替えを段階的に行うことが可能となる。   Further, in the EGR device of the present embodiment, the switching valves 22 and 23 may be of an open / close type that can be turned on / off, or may be adjustable in opening degree. By adopting 22 and 23, it becomes possible to selectively switch between bypassing both the water-cooled EGR cooler 13 and the water-cooled EGR cooler 19, selecting either one, and flowing to both. If the switching valves 22 and 23 capable of adjusting the opening are employed, the same switching can be performed step by step.

従って、上記形態例によれば、ＥＧＲパイプ１１を流れるＥＧＲガス８’の流れを切替バルブ２２，２３により切り替え、水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の両方を迂回させたり、何れか一方を選択させたり、両方を流させたりすることができ、エンジン１の運転状態に応じてＥＧＲガス８’の温度を適宜に変更することができるので、ＥＧＲガス８’の過度な冷却によりエンジン１の冷機状態において白煙の排出を招いてしまったり、暖機後において負荷の低い運転状態で大量のＨＣ，ＣＯを排出してしまったりすることを確実に防止することができ、しかも、ＥＧＲガス８’の温度をエンジン１の冷却水１４より低い温度まで下げても支障のない暖機後の負荷の高い運転状態では、水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の両方を使用してＥＧＲガス８’を二段階で冷却し、ＥＧＲガス８’の温度をエンジン１の冷却水１４より低い温度まで下げることができるので、同じＥＧＲ率でＥＧＲガス８’を再循環しても従来よりＮＯx低減効果を大幅に向上することができる。   Therefore, according to the above embodiment, the flow of the EGR gas 8 ′ flowing through the EGR pipe 11 is switched by the switching valves 22 and 23 to bypass both the water-cooled EGR cooler 13 and the water-cooled EGR cooler 19, or either Can be selected, or both of them can be allowed to flow, and the temperature of the EGR gas 8 'can be appropriately changed according to the operating state of the engine 1. Therefore, the engine 1 can be cooled by excessive cooling of the EGR gas 8'. It is possible to reliably prevent white smoke from being discharged in the cold state of the engine, and to discharge a large amount of HC and CO in a low-load operating state after the warm-up. In the operation state with a high load after warming up without causing any trouble even if the temperature of 8 'is lowered to a temperature lower than the cooling water 14 of the engine 1, the water-cooled EGR cooler 13 and the water-cooled type Since both of the GR coolers 19 are used to cool the EGR gas 8 'in two stages and the temperature of the EGR gas 8' can be lowered to a temperature lower than the cooling water 14 of the engine 1, the EGR gas 8 'is maintained at the same EGR rate. Even if 'is recirculated, the NOx reduction effect can be greatly improved.

図２は本発明の第二形態例を示すもので、図１の第一形態例で第二バイパスパイプ２１の中途箇所に配設されていたツーウェイ方式の切替バルブ２３を、ＥＧＲパイプ１１に対する第二バイパスパイプ２１の最上流端の分岐箇所にスリーウェイ方式の切替バルブ２３として変更すると共に、水冷式ＥＧＲクーラ１３と切替バルブ２２との間のＥＧＲパイプ１１に繋がるようになっていた第二バイパスパイプ２１の最下流端を、第一バイパスパイプ２０の途中に繋がるように変更し、更に、ＥＧＲパイプ１１に対する第一バイパスパイプ２０の最上流端の分岐箇所に配設されていたスリーウェイ方式の切替バルブ２２を、ＥＧＲパイプ１１に対する第一バイパスパイプ２０の最下流端の合流箇所にスリーウェイ方式の切替バルブ２２として変更したものである。   FIG. 2 shows a second embodiment of the present invention. A two-way switching valve 23 arranged in the middle of the second bypass pipe 21 in the first embodiment of FIG. The second bypass pipe 21 is changed to a branch point at the most upstream end of the two bypass pipe 21 as a three-way switching valve 23 and connected to the EGR pipe 11 between the water-cooled EGR cooler 13 and the switching valve 22. The most downstream end of the pipe 21 is changed so as to be connected to the middle of the first bypass pipe 20, and further, the three-way system of the three-way system disposed at the most upstream end of the first bypass pipe 20 with respect to the EGR pipe 11. The switching valve 22 is changed as a three-way switching valve 22 at the junction of the most downstream end of the first bypass pipe 20 with respect to the EGR pipe 11. Those were.

また、図３は本発明の第三形態例を示すもので、図２の第二形態例で第一バイパスパイプ２０に対する第二バイパスパイプ２１の最下流端の合流箇所に配設されていたスリーウェイ方式の切替バルブ２３を、ＥＧＲパイプ１１に対する第二バイパスパイプ２１の最上流端の分岐箇所に変更したものである。   FIG. 3 shows a third embodiment of the present invention. In the second embodiment shown in FIG. 2, the three-portion arranged at the most downstream end of the second bypass pipe 21 with respect to the first bypass pipe 20 is arranged. The way type switching valve 23 is changed to a branch point at the most upstream end of the second bypass pipe 21 with respect to the EGR pipe 11.

更に、図４は本発明の第四形態例を示すもので、図３の第三形態例でＥＧＲパイプ１１に対する第二バイパスパイプ２１の最上流端の分岐箇所に配設されていたスリーウェイ方式の切替バルブ２３を、ＥＧＲパイプ１１に対する第二バイパスパイプ２１の最下流端の合流箇所に変更したものである。   Further, FIG. 4 shows a fourth embodiment of the present invention. In the third embodiment of FIG. 3, the three-way system arranged at the most upstream end of the second bypass pipe 21 with respect to the EGR pipe 11 is arranged. The switching valve 23 is changed to a joining point at the most downstream end of the second bypass pipe 21 with respect to the EGR pipe 11.

また、図５は本発明の第五形態例を示すもので、図４の第四形態例でＥＧＲパイプ１１に対する第二バイパスパイプ２１の最下流端の合流箇所に配設されていたスリーウェイ方式の切替バルブ２３を、第二バイパスパイプ２１の中途箇所にツーウェイ方式の切替バルブ２３として変更したものである。   FIG. 5 shows a fifth embodiment of the present invention. In the fourth embodiment of FIG. 4, the three-way method is arranged at the junction of the most downstream end of the second bypass pipe 21 with respect to the EGR pipe 11. The switching valve 23 is changed to a two-way switching valve 23 in the middle of the second bypass pipe 21.

以上に述べた第二〜第五形態例の何れにおいても、前述した第一形態例の場合と同様に、ＥＧＲパイプ１１を流れるＥＧＲガス８’の流れを切替バルブ２２，２３により切り替え、水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の両方を迂回させたり、何れか一方を選択させたり、両方を流させたりすることができ、同様の作用効果を奏することができる。
ここで、水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の何れか一方を選択する場合につき補足しておくと、第一及び第二形態例では、水冷式ＥＧＲクーラ１３及び水冷式ＥＧＲクーラ１９の何れかを択一的に選択できる一方、第三〜第五形態例では、水冷式ＥＧＲクーラ１３のみを選択することができる。 In any of the second to fifth embodiments described above, the flow of the EGR gas 8 ′ flowing through the EGR pipe 11 is switched by the switching valves 22 and 23 as in the case of the first embodiment described above, and the water-cooled type Both the EGR cooler 13 and the water-cooled EGR cooler 19 can be bypassed, either one can be selected, or both can be flowed, and the same effect can be obtained.
Here, supplementing the case where one of the water-cooled EGR cooler 13 and the water-cooled EGR cooler 19 is selected, in the first and second embodiments, the water-cooled EGR cooler 13 and the water-cooled EGR cooler 19 On the other hand, in the third to fifth embodiments, only the water-cooled EGR cooler 13 can be selected.

尚、本発明のＥＧＲ装置は、上述の形態例にのみ限定されるものではなく、形態例中に一例として挙げた制御例は、定常運転時の制御手法に関するものであり、過渡運転時では、流路切替手段を吸気温度、排気温度、冷却水温度、吸気酸素濃度等を勘案して別の制御手法を用いても良いこと、その他、本発明の要旨を逸脱しない範囲内において種々変更を加え得ることは勿論である。   The EGR device of the present invention is not limited only to the above-described embodiment. The control example given as an example in the embodiment relates to a control method during steady operation, and during transient operation, Other control methods may be used for the flow path switching means in consideration of the intake air temperature, exhaust gas temperature, cooling water temperature, intake air oxygen concentration, etc., and various other changes are made within the scope not departing from the gist of the present invention. Of course you get.

１ エンジン
４ 吸気
５ 吸気管
７ 吸気マニホールド
８ 排気ガス
８’ ＥＧＲガス
９ 排気マニホールド
１０ 排気管
１１ ＥＧＲパイプ
１３ 水冷式ＥＧＲクーラ（前段水冷式ＥＧＲクーラ）
１４ 冷却水
１９ 水冷式ＥＧＲクーラ（後段水冷式ＥＧＲクーラ）
２０ 第一バイパスパイプ
２１ 第二バイパスパイプ
２２ 切替バルブ（流路切替手段）
２３ 切替バルブ（流路切替手段）
２４ 冷却水 DESCRIPTION OF SYMBOLS 1 Engine 4 Intake 5 Intake pipe 7 Intake manifold 8 Exhaust gas 8 'EGR gas 9 Exhaust manifold 10 Exhaust pipe 11 EGR pipe 13 Water-cooled EGR cooler (front-stage water-cooled EGR cooler)
14 Cooling water 19 Water-cooled EGR cooler (second-stage water-cooled EGR cooler)
20 First bypass pipe 21 Second bypass pipe 22 Switching valve (flow path switching means)
23 Switching valve (flow path switching means)
24 Cooling water

Claims (3)

排気側から排気ガスの一部を抜き出してＥＧＲガスとして吸気側へ再循環するＥＧＲパイプと、該ＥＧＲパイプの途中に装備された前段水冷式ＥＧＲクーラと、該前段水冷式ＥＧＲクーラより下流側のＥＧＲパイプに装備された後段水冷式ＥＧＲクーラと、該後段水冷式ＥＧＲクーラを迂回してＥＧＲガスを流す第一バイパスパイプと、前段水冷式ＥＧＲクーラを迂回してＥＧＲガスを流す第二バイパスパイプと、ＥＧＲパイプを流れるＥＧＲガスの流れを第一バイパスパイプ及び第二バイパスパイプの夫々に切り替える流路切替手段とを備え、前段水冷式ＥＧＲクーラに対しエンジンの冷却水を冷媒として経由せしめ且つ後段水冷式ＥＧＲクーラに対し専用の水冷系統から前記エンジンの冷却水より低い温度の冷却水を冷媒として経由せしめるように構成すると共に、前記流路切替手段によりＥＧＲガスを前段水冷式ＥＧＲクーラ及び後段水冷式ＥＧＲクーラの両方に流したり、何れか一方に流したり、両方を迂回させて流したりすることで、エンジンの運転状態に応じてＥＧＲガスの温度を適宜に変更し得るように構成したことを特徴とするＥＧＲ装置。 An EGR pipe that extracts a part of the exhaust gas from the exhaust side and recirculates it as an EGR gas to the intake side, a front-stage water-cooled EGR cooler installed in the middle of the EGR pipe, and a downstream side of the front-stage water-cooled EGR cooler A rear-stage water-cooled EGR cooler installed in the EGR pipe, a first bypass pipe that flows EGR gas bypassing the rear-stage water-cooled EGR cooler, and a second bypass pipe that flows EGR gas bypassing the front-stage water-cooled EGR cooler And a flow path switching means for switching the flow of EGR gas flowing through the EGR pipe to each of the first bypass pipe and the second bypass pipe, and passing the engine cooling water as a refrigerant to the front-stage water-cooled EGR cooler and the rear-stage Cooling water having a temperature lower than that of the engine cooling water is passed as a refrigerant from a dedicated water cooling system to the water-cooled EGR cooler. Together constitute a so that the EGR gas or flowed both front water-cooled EGR cooler and subsequent water-cooled EGR cooler, or flow to either, that both diverts or flowed by the flow path switching unit An EGR device configured to be able to change the temperature of the EGR gas as appropriate according to the operating state of the engine . 流路切替手段が、第一バイパスパイプ及び第二バイパスパイプにおける中途箇所、最上流端の分岐箇所、最下流端の合流箇所の何れかに設けられた開閉式の切替バルブにより構成されていることを特徴とする請求項１に記載のＥＧＲ装置。   The flow path switching means is constituted by an open / close switching valve provided at any of the midway location, the most upstream end branch location, and the most downstream end merge location in the first bypass pipe and the second bypass pipe. The EGR device according to claim 1. 流路切替手段が、第一バイパスパイプ及び第二バイパスパイプにおける中途箇所、最上流端の分岐箇所、最下流端の合流箇所の何れかに設けられた開度調整可能な切替バルブにより構成されていることを特徴とする請求項１に記載のＥＧＲ装置。   The flow path switching means is constituted by a switching valve with adjustable opening provided in any of the midway location, the most upstream branch location, and the most downstream junction location in the first bypass pipe and the second bypass pipe. The EGR device according to claim 1, wherein
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