Engine device

An engine device including a cylinder head provided with a plurality of intake fluid passages for taking fresh air into a plurality of intake ports and a plurality of exhaust fluid passages for emitting an exhaust gas from a plurality of exhaust ports. An intake manifold which aggregates the plurality of intake fluid passages is formed integrally with one of left and right side portions of the cylinder head.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a national stage application pursuant to 35 U.S.C. § 371 of International Application No. PCT/JP2017/010039, filed on Mar. 13, 2017 which claims priority of under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-066826 filed on Mar. 29, 2016, the disclosures of which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to an engine device.

BACKGROUND ART

Traditionally, a cylinder head having an intake port and an exhaust port has an intake manifold and an exhaust manifold coupled to left and right and left side surfaces thereof (see Patent Literature 1; hereinafter, PTL 1). Further, as a countermeasure against exhaust gas of diesel engines and the like, there has been a technology that adopts an EGR device (exhaust-gas recirculation device), which circulates a portion of exhaust gas to an intake side, to keep the combustion temperature low, thereby reducing an amount of NOx (nitrogen oxide) in the exhaust gas (see Patent Literature 2 to Patent Literature 4; hereinafter, respectively referred to as PTL 2 to PTL 4).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

An installation space for a diesel engine varies depending on a work vehicle (such as a construction machine or an agricultural machine) to which the diesel engine is installed. Recently, due to demand for weight reduction and compactification, the installation space is often restricted (confined). It therefore is necessary that component parts of the diesel engine are arranged in a compact layout. In addition to such a problem of the restricted installation space, a structure with a high rigidity is required of a cylinder head because component parts such as an EGR device and a turbocharger are coupled to and supported by the cylinder head.

In a cylinder head of an engine as disclosed in each of PTL 2 and PTL 3, an EGR gas fluid passage is structured in the cylinder head. Structuring an EGR gas fluid passage in a cylinder head however leads to a complicated structure as in PTL 2, resulting in a low degree of freedom in the layout of passages, and increased time and costs of processing.

If the EGR cooler is connected through a pipe, the volume of the EGR gas increases due to an increase in the temperature of the EGR gas caused by generated heat of the diesel engine. Due to this, a sufficient amount of the EGR gas is cannot be maintained, and reduction of the NOx in the exhaust gas becomes difficult. On the other hand, if the EGR gas is excessively cooled by having the EGR pipe exposed to cooling air from a cooling fan and the like, the combustion in the cylinder is affected. For the reasons above, appropriate arrangement and structure of parts in the diesel engine and an appropriate cooling structure need to be considered for the purpose of supplying the EGR gas at an appropriate temperature. To add this, if there is unevenness in the mixture distribution of the EGR gas and fresh air, the amounts of EGR gas in the fresh air supplied to a plurality of cylinders will be uneven. This affects actions of reducing the NOx and combustion in each of the cylinders, thus deteriorating the operation efficiency of the diesel engine.

A technical problem of the present invention is to provide an engine device that is improved based on studies on the existing circumstances as mentioned above.

Solution to Problem

An aspect of the present invention is an engine device including a cylinder head provided with a plurality of intake fluid passages for taking fresh air into a plurality of intake ports and a plurality of exhaust fluid passages for emitting an exhaust gas from a plurality of exhaust ports, in which an intake manifold which aggregates the plurality of intake fluid passages is formed integrally with one of left and right side portions of the cylinder head.

The above engine device may further include an exhaust manifold in communication with the exhaust fluid passages; an EGR device configured to circulate, as EGR gas, a portion of exhaust gas exhausted from the exhaust manifold to the intake manifold; and an EGR cooler configured to cool the EGR gas, wherein the cylinder head is configured such that the exhaust manifold is coupled to a second surface of the cylinder head which is opposite to a first surface where the intake manifold is provided, the EGR cooler is coupled to a third surface of the cylinder head which is adjacent to the first and second surfaces, and coupling bases to which the EGR cooler is coupled are provided so as to protrude from the third surface of the cylinder head, and the coupling bases on the third surface are provided therein with EGR gas fluid passages and coolant passages.

The above engine device may be such that the EGR device is coupled to the intake manifold on the first surface of the cylinder head, and the coupling bases forming a pair are disposed on the intake manifold side and on the exhaust manifold side, respectively, one of the coupling bases has a downstream EGR gas relay fluid passage through which the EGR gas fluid passage of the EGR device communicates with the EGR gas fluid passage of the EGR cooler, and the other of the coupling bases has an upstream EGR gas relay fluid passage through which the EGR gas fluid passage of the exhaust manifold communicates with the EGR gas fluid passage of the EGR cooler.

The above engine device may be such that the EGR cooler includes a heat exchanger in which coolant passages and EGR gas fluid passages are alternately stacked and a pair of left and right flange portions provided respectively at right and left end portions of one side surface of the heat exchanger; an inlet of a coolant is disposed in one of the left and right flange portions and an outlet of the coolant is disposed in the other of the left and right flange portions; an inlet of EGR gas is disposed in one of the left and right flange portions and an outlet of the EGR gas is disposed in the other of the left and right flange portions; and the left and right flange portions are connected to the coupling bases of the cylinder head.

Advantageous Effects of Invention

With the above aspect of the present invention, since the cylinder head is integrated with the intake manifold, a gas sealability between the intake manifold and the intake fluid passages can be enhanced, and in addition, the rigidity of the cylinder head can be increased. In addition, when a part such as an EGR device is coupled to the cylinder head, the support rigidity of the cylinder head can be increased, and the number of parts of a seal member on the intake side seal in the cylinder head can be reduced.

In the above aspect of the present invention, the EGR cooler is directly coupled to the cylinder head. Therefore, it is not necessary that coolant piping and EGR gas piping are disposed between the EGR cooler and the cylinder head. This can give a sealability to a coupling portion coupled to the EGR cooler without any influence of, for example, extension and contraction of piping caused by the EGR gas or the coolant. This can also enhance a resistance (structural stability) against external fluctuation factors such as heat and vibration, and moreover can make the configuration compact. Since the EGR gas fluid passages and the coolant passages are provided in the coupling bases, the shapes of the fluid passages formed in the cylinder head are simplified, so that the cylinder head can be easily formed by casting without using a complicated core.

With the above-aspect of the present invention, since the EGR gas fluid passages and the coolant passages are provided in the coupling bases protruding at a distance from each other, a mutual influence between thermal deformations of the EGR cooler coupling bases is relieved. In the coupling bases, the EGR gas flowing in the EGR gas fluid passages is cooled by the coolant flowing in the coolant passages, so that thermal deformations of the coupling bases are suppressed. In addition, the up-down positional relationship of the EGR gas fluid passages and the coolant passages in one of the coupling bases is reverse to that in the other of the coupling bases. As a result, heat distributions in the respective coupling bases are in opposite directions with respect to the up-down direction, which can reduce an influence of thermal deformation in the height direction in the cylinder head.

With the above aspect of the present invention, since each of the pair of left and right flange portions has a coolant opening and an EGR gas opening, it is possible that the flange portions are made from a common member, and moreover material costs of the flange portions can be suppressed. In addition, a coupling portion where the flange portions are coupled to the heat exchanger can be minimized, so that the amount of heat transfer from the cylinder head to the heat exchanger can be reduced, which increases the effect of cooling the EGR gas by the heat exchanger.

DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present invention will be described with reference to the drawings. First, referring toFIG. 1toFIG. 8, an overall structure of a diesel engine (engine device)1will be described. In the descriptions below, opposite side portions parallel to a crankshaft5(side portions on opposite sides relative to the crankshaft5) will be defined as left and right, a side where a flywheel housing7is disposed will be defined as front, and a side where a cooling fan9is disposed will be defined as rear. For convenience, these are used as a benchmark for a positional relationship of left, right, front, rear, up, and down in the diesel engine1.

As shown inFIG. 1toFIG. 8, an intake manifold3and an exhaust manifold4are disposed in one side portion and the other side portion of the diesel engine1parallel to the crankshaft5. In the embodiment, the intake manifold3provided on a right surface of a cylinder head2is formed integrally with the cylinder head2. The exhaust manifold4is provided on a left surface of the cylinder head2. The cylinder head2is mounted on a cylinder block6in which the crankshaft5and a piston (not shown) are disposed.

The crankshaft5has its front and rear distal ends protruding from front and rear surfaces of the cylinder block6. The flywheel housing7is fixed to one side portion of the diesel engine1(in the embodiment, a front surface side of the cylinder block6) intersecting the crankshaft5. A flywheel8is disposed in the flywheel housing7. The flywheel8, which is pivotally supported on the front end side of the crankshaft5, is configured to rotate integrally with the crankshaft5. The flywheel8is configured such that power of the diesel engine1is extracted to an actuating part of a work machine (for example, a hydraulic shovel, a forklift, or the like) through the flywheel8. The cooling fan9is disposed in the other side portion of the diesel engine1(in the embodiment, a rear surface side of the cylinder block6) intersecting the crankshaft5. A rotational force is transmitted from the rear end side of the crankshaft5to the cooling fan9through a V-belt10.

An oil pan11is disposed on a lower surface of the cylinder block6. A lubricant is stored in the oil pan11. The lubricant in the oil pan11is suctioned by an oil pump (not shown) disposed on the right surface side of the cylinder block6, the oil pump being arranged in a coupling portion where the cylinder block6is coupled to the flywheel housing7. The lubricant is then supplied to lubrication parts of the diesel engine1through an oil cooler13and an oil filter14that are disposed on the right surface of the cylinder block6. The lubricant supplied to the lubrication parts is then returned to the oil pan11. The oil pump (not shown) is configured to be driven by rotation of the crankshaft5.

In the coupling portion where the cylinder block6is coupled to the flywheel housing7, a fuel feed pump15for feeding a fuel is attached. The fuel feed pump15is disposed below an EGR device24. A common rail16is fixed to a side surface of the cylinder block6at a location below the intake manifold3of the cylinder head2. The common rail16is disposed above the fuel feed pump15. Injectors (not shown) for four cylinders are provided on an upper surface of the cylinder head2which is covered with a head cover18. Each of the injectors has a fuel injection valve of electromagnetic-controlled type.

Each of the injectors is connected to a fuel tank (not shown) through the fuel feed pump15and the common rail16having a cylindrical shape. The fuel tank is mounted in a work vehicle. A fuel in the fuel tank is pressure-fed from the fuel feed pump15to the common rail16, so that a high-pressure fuel is stored in the common rail16. By controlling the opening/closing of the fuel injection valves of the injectors, the high-pressure fuel in the common rail16is injected from the injectors to the respective cylinders of the diesel engine1.

A blow-by gas recirculation device19is provided on an upper surface of the head cover18covering intake and exhaust valves (not shown), etc. disposed on the upper surface of the cylinder head2. The blow-by gas recirculation device19takes in a blow-by gas that has leaked out of a combustion chamber of the diesel engine1or the like toward the upper surface of the cylinder head2. A blow-by gas outlet of the blow-by gas recirculation device19is in communication with an intake part of a two-stage turbocharger30through a recirculation hose68. A blow-by gas, from which a lubricant component is removed in the blow-by gas recirculation device19, is then recirculated to the intake manifold3via the two-stage turbocharger30.

An engine starting starter20is attached to the flywheel housing7. The engine starting starter20is disposed below the exhaust manifold4. A position where the engine starting starter20is attached to the flywheel housing7is below a coupling portion where the cylinder block6is coupled to the flywheel housing7.

A coolant pump21for smoothing a coolant is provided in a portion of the rear surface of the cylinder block6, the portion being a little left-hand. The coolant pump21is disposed below the cooling fan9. Rotation of the crankshaft5causes the coolant pump21as well as the cooling fan9to be driven through the cooling fan driving V-belt10. Driving the coolant pump21causes a coolant in a radiator (not shown) mounted in the work vehicle to be supplied to the coolant pump21. The coolant is then supplied to the cylinder head2and the cylinder block6, to cool the diesel engine1.

The coolant pump21is disposed below the exhaust manifold4, and a coolant inlet pipe22is provided on the left surface of the cylinder block6and is fixed at a height equal to the height of the coolant pump21. The coolant inlet pipe22is in communication with a coolant outlet of the radiator. A coolant outlet pipe23that is in communication with a coolant inlet of the radiator is fixed to an upper rear portion of the cylinder head2. The cylinder head2has a coolant drainage35that protrudes rearward from the intake manifold3. The coolant outlet pipe23is provided on an upper surface of the coolant drainage35.

The inlet side of the intake manifold3is coupled to an air cleaner (not shown) via a collector (EGR main body case)25of an EGR device24(exhaust-gas recirculation device) which will be described later. Fresh air (outside air) suctioned by the air cleaner is subjected to dust removal and purification in the air cleaner, then fed to the intake manifold3through the collector25, and then supplied to the respective cylinders of the diesel engine1. In the embodiment, the collector25of the EGR device24is coupled to the right side of the intake manifold3which is formed integrally with the cylinder head2to form the right surface of the cylinder head2. That is, an outlet opening of the collector25of the EGR device24is coupled to an inlet opening of the intake manifold3provided on the right surface of the cylinder head2. In this embodiment, the collector25of the EGR device24is coupled to the air cleaner via an intercooler (not shown) and the two-stage turbocharger30, as will be described later.

The EGR device24includes: the collector25serving as a relay pipe passage that mixes a recirculation exhaust gas of the diesel engine1(an EGR gas from the exhaust manifold4) with fresh air (outside air from the air cleaner), and supplies a mixed gas to the intake manifold3; an intake throttle member26that communicates the collector25with the air cleaner; a recirculation exhaust gas tube28that constitutes a part of a recirculation flow pipe passage connected to the exhaust manifold4via an EGR cooler27; and an EGR valve member29that communicates the collector25with the recirculation exhaust gas tube28.

The EGR device24is disposed on the right lateral side of the intake manifold3in the cylinder head2. The EGR device24is fixed to the right surface of the cylinder head2, and is in communication with the intake manifold3in the cylinder head2. In the EGR device24, the collector25is coupled to the intake manifold3on the right surface of the cylinder head2, and an EGR gas inlet of the recirculation exhaust gas tube28is coupled and fixed to a front portion of the intake manifold3on the right surface of the cylinder head2. The EGR valve member29and the intake throttle member26are coupled to the front and rear of the collector25, respectively. An EGR gas outlet of the recirculation exhaust gas tube28is coupled to the rear end of the EGR valve member29.

The EGR cooler27is fixed to the front surface of the cylinder head2. The coolant and the EGR gas flowing in the cylinder head2flows into and out of the EGR cooler27. In the EGR cooler27, the EGR gas is cooled. EGR cooler coupling bases33,34for coupling the EGR cooler27to the front surface of the cylinder head2protrude from left and right portions of the front surface of the cylinder head2. The EGR cooler27is coupled to the coupling bases33,34. That is, the EGR cooler27is disposed on the front side of the cylinder head2and at a position above the flywheel housing7such that a rear end surface of the EGR cooler27and the front surface of the cylinder head2are spaced from each other.

The two-stage turbocharger30is disposed on a lateral side (in the embodiment, the left lateral side) of the exhaust manifold4. The two-stage turbocharger30includes a high-pressure turbocharger51and a low-pressure turbocharger52. The high-pressure turbocharger51includes a high-pressure turbine53in which a turbine wheel (not shown) is provided and a high-pressure compressor54in which a blower wheel (not shown) is provided. The low-pressure turbocharger52includes a low-pressure turbine55in which a turbine wheel (not shown) is provided and a low-pressure compressor56in which a blower wheel (not shown) is provided.

An exhaust gas inlet57of the high-pressure turbine53is coupled to the exhaust manifold4. An exhaust gas inlet60of the low-pressure turbine55is coupled to an exhaust gas outlet58of the high-pressure turbine53via a high-pressure exhaust gas tube59. An exhaust gas introduction side end portion of an exhaust gas discharge pipe (not shown) is coupled to an exhaust gas outlet61of the low-pressure turbine55. A fresh air supply side (fresh air outlet side) of the air cleaner (not shown) is connected to a fresh air inlet port (fresh air inlet)63of the low-pressure compressor56via an air supply pipe62. A fresh air inlet port66of the high-pressure compressor54is coupled to a fresh air supply port (fresh air outlet)64of the low-pressure compressor56via a low-pressure fresh air passage pipe65. A fresh air introduction side of the intercooler (not shown) is connected to a fresh air supply port67of the high-pressure compressor54via a high-pressure fresh air passage pipe (not shown).

The high-pressure turbocharger51is coupled to the exhaust gas outlet58of the exhaust manifold4, and is fixed to the left lateral side of the exhaust manifold4. On the other hand, the low-pressure turbocharger52is coupled to the high-pressure turbocharger51via the high-pressure exhaust gas tube59and the low-pressure fresh air passage pipe65, and is fixed above the exhaust manifold4. Thus, the exhaust manifold4and the high-pressure turbocharger51with a small diameter are disposed side-by-side with respect to the left-right direction below the low-pressure turbocharger52with a large diameter. As a result, the two-stage turbocharger30is arranged so as to surround the left surface and the upper surface of the exhaust manifold4. That is, the exhaust manifold4and the two-stage turbocharger30are arranged so as to form a rectangular shape in a rear view (or front view), and are compactly fixed to the left surface of the cylinder head2.

Next, referring toFIG. 9toFIG. 16, a configuration of the cylinder head2will be described. As shown inFIG. 9toFIG. 16, the cylinder head2is provided with a plurality of intake fluid passages36for taking fresh air into a plurality of intake ports (not shown) and a plurality of exhaust fluid passages37for emitting an exhaust gas from a plurality of exhaust ports. The intake manifold3which aggregates the plurality of intake fluid passages36is formed integrally with a right side portion of the cylinder head2. Since the cylinder head2is integrated with the intake manifold3, a gas sealability between the intake manifold3and the intake fluid passages36can be enhanced, and in addition, the rigidity of the cylinder head2can be increased.

The cylinder head2is configured such that the exhaust manifold4is coupled to the left surface of the cylinder head2which is opposite to the right surface where the intake manifold3is provided, and the EGR cooler27is coupled to the front surface (a surface on the flywheel housing7side) of the cylinder head2which is adjacent to the left and right surfaces. Coupling bases (EGR cooler coupling bases)33,34to which the EGR cooler27is coupled are provided so as to protrude from the front surface of the cylinder head2. The coupling bases33,34are provided therein with EGR gas fluid passages (EGR gas relay fluid passages)31,32and coolant passages (coolant relay fluid passages)38,39.

Since the EGR gas relay fluid passages31,32and the coolant passages38,39are provided in the coupling bases33,34to which the EGR cooler27is coupled, it is not necessary that coolant piping and EGR gas piping are disposed between the EGR cooler27and the cylinder head2. This can give a sealability to a coupling portion coupled to the EGR cooler27without any influence of, for example, extension and contraction of piping caused by the EGR gas or the coolant. This can also enhance a resistance (structural stability) against external fluctuation factors such as heat and vibration, and moreover can make the configuration compact.

The cylinder head2includes an upstream EGR gas relay fluid passage31through which a front portion of the left surface is in communication with the front surface. An EGR gas outlet41disposed at the front end of the exhaust manifold4is in communication with the upstream EGR gas relay fluid passage31. The cylinder head2also includes a downstream EGR gas relay fluid passage32through which a front portion of the right surface (on the front side of the intake manifold3) is in communication with the front surface. The EGR gas inlet of the recirculation exhaust gas tube28is in communication with the downstream EGR gas relay fluid passage32. The cylinder head2has the EGR cooler coupling bases33,34which are formed by left and right edges of the front surface of the cylinder head2(a front-left corner portion and a front-right corner portion of the cylinder head2) being protruded frontward. The upstream EGR gas relay fluid passage31is provided inside the coupling base33, and the downstream EGR gas relay fluid passage32is provided inside the coupling base34.

The EGR device24is coupled to the intake manifold3which is provided on the right surface of the cylinder head2so as to protrude therefrom. The intake manifold3is disposed in a portion of the right surface of the cylinder head2, the portion being relatively close to the rear side (the cooling fan9side). The intake manifold3is formed by a lower portion of the right surface of the cylinder head2being protruded rightward. The intake manifold3has an intake inlet40at its middle portion with respect to the front-rear direction. An intake outlet83of the collector25of the EGR device24is coupled to the intake inlet40of the intake manifold3which protrudes from the right surface of the cylinder head2, and the EGR device24is fixed to the right lateral side of the cylinder head2.

On the front side (the flywheel housing7side) of the right surface of the cylinder head2, the coupling base34coupled to the EGR cooler27protrudes frontward, and an EGR gas outlet of the downstream EGR gas relay fluid passage32is opened in a right surface of the coupling base34. One end of the recirculation exhaust gas tube28of the EGR device24is coupled to the right surface of the coupling base34, and thereby the collector25of the EGR device24is in communication with the downstream EGR gas relay fluid passage32provided inside the cylinder head2via the recirculation exhaust gas tube28and the EGR valve member29.

On the rear side (the cooling fan9side) of the right surface of the cylinder head2, the coolant drainage (thermostat case)35whose upper surface is opened to communicate with a coolant outlet pipe (thermostat cover)23protrudes rearward, and a thermostat (not shown) is installed therein. The coolant drainage35is offset at the rear of the right surface of the cylinder head2, and therefore it is possible that the V-belt10wound on a fan pulley9ato which the cooling fan9is fixed extends through a space below the coolant drainage35. Thus, the length of the diesel engine1in the front-rear direction can be shortened. The coolant drainage35also protrudes from the right surface of the cylinder head2. On the right surface of the cylinder head2, the intake manifold3and the coolant drainage35are arranged one behind the other with respect to the front-rear direction.

On the front side (the flywheel housing7side) of the left surface of the cylinder head2, the coupling base33coupled to the EGR cooler27protrudes frontward, and an EGR gas inlet of the upstream EGR gas relay fluid passage31is opened in a left surface of the coupling base33. That is, in the left surface of the cylinder head2, the EGR gas inlet of the upstream EGR gas relay fluid passage31and exhaust gas outlets of the plurality of exhaust fluid passages37are disposed in the front-rear direction, and are opened. The exhaust manifold4has, in its right surface which is coupled to the left surface of the cylinder head2, the EGR gas outlet41which is in communication with the upstream EGR gas relay fluid passage31and exhaust gas inlets42which are in communication with the plurality of exhaust fluid passages37are arranged in the front-rear direction, and are opened. Since the EGR inlet and the exhaust gas outlets are disposed side-by-side in the same surface of the cylinder head2, it is easy for a coupling portion where the cylinder head2is coupled to the exhaust manifold4to obtain an airtightness (gas sealability) by sandwiching a single gasket45therebetween.

The exhaust manifold4is provided therein with an exhaust aggregate part43which is in communication with the EGR gas outlet41and the exhaust gas inlets42. The exhaust aggregate part43is disposed such that its longitudinal direction is parallel to the front-rear direction. An exhaust gas outlet44which is in communication with the exhaust aggregate part43is opened in a rear portion of the left surface of the exhaust manifold4. The exhaust manifold4is configured such that, after an exhaust gas coming from the exhaust fluid passages37of the cylinder head2flows into the exhaust aggregate part43via the exhaust gas inlets42, part of the exhaust gas serves as an EGR gas and flows into the upstream EGR gas relay fluid passage31of the cylinder head2via the EGR gas outlet41while the rest of the exhaust gas flows into the two-stage turbocharger30via the exhaust gas outlet44.

On the front surface of the cylinder head2, the left and right pair of EGR cooler coupling bases33,34are disposed on the exhaust manifold4side and on the intake manifold3side, respectively. The EGR cooler coupling base33has the upstream EGR gas relay fluid passage31through which the EGR gas fluid passage of the exhaust manifold4communicates with the EGR gas fluid passage of the EGR cooler27. The EGR cooler coupling base34has the downstream EGR gas relay fluid passage32through which the EGR gas fluid passage of the EGR device24communicates with the EGR gas fluid passage of the EGR cooler27. The EGR cooler coupling base33also has the downstream coolant passage38to which a coolant is discharged from the EGR cooler27. The EGR cooler coupling base34has the upstream coolant passage39that supplies a coolant to the EGR device24and to the EGR cooler27.

Since the EGR cooler coupling bases33,34are configured in a protruding manner, there is no need for EGR gas piping that communicates the exhaust manifold4, the EGR cooler27, and the EGR device24. Thus, the number of coupling portions of the EGR gas fluid passage is small. Accordingly, in the diesel engine1that aims to reduce NOx by the EGR gas, EGR gas leakage can be reduced, and moreover deformation can be suppressed which may otherwise be caused by a change in a stress due to extension and contraction of piping. Since the EGR gas relay fluid passages31,32and the coolant passages38,39are provided in the EGR cooler coupling bases33,34, the shapes of the fluid passages31,32,38,39formed in the cylinder head2are simplified, so that the cylinder head2can be easily formed by casting without using a complicated core.

The EGR cooler coupling base33on the intake manifold3side and the EGR cooler coupling base34on the exhaust manifold4side are distant from each other. This can suppress a mutual influence between thermal deformations of the coupling bases33,34. Accordingly, gas leakage and damage of coupling portions where the EGR cooler coupling bases33,34are coupled to the EGR cooler27can be prevented, and in addition, a balance of the rigidity of the cylinder head2can be maintained. Moreover, the volume of the front surface of the cylinder head2can be reduced, which leads to weight reduction of the cylinder head2. Furthermore, it is possible that the EGR cooler27is disposed at a distance from the front surface of the cylinder head2, to provide a space on the front and rear sides of the EGR cooler27. This enables cool air to flow around the EGR cooler27, thus increasing the cooling efficiency of the EGR cooler27.

In the EGR cooler coupling base33, the downstream coolant passage38is disposed above the upstream EGR gas relay fluid passage31. In the EGR cooler coupling base34, the downstream EGR gas relay fluid passage32is disposed above the upstream coolant passage39. A coolant inlet of the downstream coolant passage38and an EGR gas inlet of the downstream EGR gas relay fluid passage32are disposed at the same height. A coolant outlet of the upstream coolant passage39and an EGR gas outlet of the downstream EGR gas relay fluid passage32are disposed at the same height.

Since the EGR gas relay fluid passages31,32and the coolant passages38,39are provided in the EGR cooler coupling bases33,34protruding at a distance from each other, a mutual influence between thermal deformations of the EGR cooler coupling bases33,34is relieved. In the EGR cooler coupling bases33,34, the EGR gas flowing in the EGR gas relay fluid passages31,32is cooled by the coolant flowing in the coolant passages38,39, so that thermal deformations of the EGR cooler coupling bases33,34are suppressed. In addition, the up-down positional relationship of the EGR gas relay fluid passages31,32and the coolant passages38,39in one of the EGR cooler coupling bases33,34is reverse to that in the other of the EGR cooler coupling bases33,34. As a result, heat distributions in the respective EGR cooler coupling bases33,34are in opposite directions with respect to the up-down direction, which can reduce an influence of thermal deformation in the height direction in the cylinder head2.

An outer peripheral wall of the cylinder head2stands upward at a peripheral edge of the upper surface of the cylinder head2, to provide a spacer46which is coupled to a peripheral edge of a lower surface of the head cover18. The spacer46has, in a right surface thereof, a plurality of openings47. Fuel pipes48which couple injectors (not shown) provided in the cylinder head2to the common rail16pass through the openings47. Since the spacer46integrated with the cylinder head2is disposed above the cylinder head2, the rigidity of the cylinder head2is increased, which can reduce distortion of the cylinder head2itself and also can allow component parts coupled to the cylinder head2to be supported with a high rigidity.

A configuration of the EGR device24will now be described with reference toFIG. 9toFIG. 15, andFIG. 17toFIG. 21. As shown inFIG. 9toFIG. 15, andFIG. 17toFIG. 21, the EGR device24includes the collector (main body case)25that mixes fresh air with an EGR gas, and supplies a mixture to the intake manifold3. The intake manifold3and the intake throttle member26for taking fresh air in are connected in communication with each other via the collector25. The EGR valve member29which leads to an outlet side of the recirculation exhaust gas tube28is connected in communication with the collector25.

In the collector25, a fresh air flow direction and an EGR gas flow direction cross each other perpendicularly or with an obtuse angle, and a direction in which a mixed gas of the EGR gas and the fresh air is taken into the intake manifold3intersects each of the fresh air flow direction and the EGR gas flow direction. A fresh air inlet81to which the fresh air is supplied is opened in one of front and rear surfaces of the collector25, whereas an EGR gas inlet82to which the EGR gas is supplied is opened in the other of the front and rear surfaces of the collector25. The intake outlet83which is coupled to the intake manifold3is opened in a left surface of the collector25. The EGR gas inlet82and the intake outlet83are disposed at the same height, and the fresh air inlet81and the EGR gas inlet82are disposed at different heights.

In the collector25, fresh air taken from the intake throttle member26into the fresh air inlet81flows in the front-rear direction and then in the up-down direction while curving in an L-shape, whereas an EGR gas taken from the EGR valve member29into the EGR gas inlet82flows obliquely upward. As a result, the EGR gas flows in toward a flow of the fresh air, which facilitates mixing of the EGR gas with the fresh air. The mixed gas of the fresh air and the EGR gas flows in the up-down direction and then in the left-right direction while curving in an L-shape, to flow into the intake manifold3through the intake outlet83. A direction in which the mixed gas is emitted intersects not only the directions in which the fresh air and the EGR gas are taken in but also the directions in which the fresh air and the EGR gas flow within the collector25. Consequently, a distribution of mixture of the EGR gas with the fresh air can be made uniformed.

In the collector25, as described above, the EGR gas flow direction is at an angle of 90° or more relative to the fresh air flow direction, and the fresh air flow and the EGR gas flow intersect each other, so that a distribution of mixture of the EGR gas with the fresh air can be made uniform, and an uneven flow of the EGR gas in the intake manifold3can be suppressed. As a result, a concentration of the intake EGR gas supplied to each of the plurality of intake fluid passages36of the cylinder head2can be made uniform. Thus, a variation in combustion action among cylinders of the diesel engine1can be suppressed. Consequently, generation of black smoke is suppressed, and the amount of NOx can be reduced while a good combustion state of the diesel engine1is maintained. That is, purifying (cleaning) the exhaust gas by a recirculation flow of the EGR gas can be achieved without causing a misfire in a specific cylinder.

The collector25includes an upper case (first case)84with the fresh air inlet81and a lower case (second case)85with the EGR gas inlet82and the intake outlet83being coupled to each other. Since the collector25is divisible in the up-down direction into the upper case84and the lower case85, a mixed fluid passage where the EGR gas flow and the fresh air flow intersect each other at an angle of 90° or more can be easily formed in the collector25. It therefore is possible that the collector25is formed as a casting with a high rigidity, and moreover, weight reduction of the collector25can be obtained by forming the collector25as an aluminum-based casting product.

The upper case84is provided therein with a downstream EGR gas fluid passage (first EGR gas fluid passage)86awhich is a part of the EGR gas fluid passage86where the EGR gas flows and a mixing chamber87in which the fresh air and the EGR gas are mixed. The lower case85is provided therein with an upstream EGR gas fluid passage (second EGR gas fluid passage)86bthrough which the downstream EGR gas fluid passage86ais in communication with the EGR gas inlet82and a mixed gas fluid passage88through which a mixed gas obtained by mixing the fresh air with the EGR gas is supplied from the mixing chamber87to the intake manifold3.

The EGR gas inlet82is disposed in the lower case85while the fresh air inlet81and the mixing chamber87are disposed in the upper case84. In the mixing chamber87, therefore, the fresh air flowing from the fresh air inlet81and the EGR gas flowing from the lower case85intersect each other, so that the fresh air and the EGR gas can be efficiently mixed. In addition, the intake outlet83is disposed in the lower case85, and the fresh air having entered the upper case84tends to flow toward the lower case85. As a result, mixing of the EGR gas flowing toward the upper case84with the fresh air is made uniform. Furthermore, each of the EGR gas fluid passage86, the mixing chamber87, and the mixed gas fluid passage88can be compactly configured within the collector25, and thus the collector25can be downsized.

In a plan view, the downstream EGR gas fluid passage86ais coupled with an offset to a side surface (right side surface) of the mixing chamber87opposite to a side surface (left side surface) thereof having the intake outlet83relative to a central axis of the mixing chamber87, and the downstream EGR gas fluid passage86aand the upstream EGR gas fluid passage86bare in communication with each other so that the EGR gas fluid passage86is formed in a spiral manner. The EGR gas fluid passage86composed of the downstream EGR gas fluid passage86aand the upstream EGR gas fluid passage86bhas a bent shape curved toward the side (right side) opposite to the intake outlet83in a plan view. A bottom of the upstream EGR gas fluid passage86bis constituted by a slope (a slope inclined upward toward the rear) extending from the EGR gas inlet82toward the upper case84.

A portion of the mixing chamber87that is in communication with the EGR gas fluid passage86is on the side opposite to the intake outlet83. The EGR gas flowing into the mixing chamber87, therefore, reaches the intake outlet83while being guided by a fresh air flow, which allows the EGR gas to be uniformly mixed with the fresh air. The EGR gas flowing from the EGR gas fluid passage86into the mixing chamber87flows in a direction against the direction from the mixing chamber87toward the mixed gas fluid passage88. This causes the fresh air and the EGR gas to collide with each other while flowing within the mixing chamber87. Accordingly, the EGR gas is smoothly mixed with the fresh air.

Since the EGR gas flows along the EGR gas fluid passage86having a spiral shape, the EGR gas creates a swirling flow having a clockwise vortex when flowing into the mixing chamber87. Such a turbulent EGR gas flows in a direction against the fresh air gas flow. Thus, simultaneously with flowing into the mixing chamber87, the EGR gas is smoothly mixed with the fresh air flowing within the mixing chamber87. In the collector25, therefore, the fresh air and the EGR gas can be efficiently mixed (the EGR gas can be smoothly dispersed in the mixed gas) by agitation before they are fed to the intake manifold3, so that a variation (unevenness) in the gas mixing state within the collector25can be suppressed more reliably. As a result, a mixed gas having less unevenness can be distributed to the respective cylinders of the diesel engine1, and a variation in the EGR gas amount among the cylinders can be suppressed. Accordingly, it is possible to suppress generation of black smoke, and to reduce the amount of NOx while maintaining a good combustion state of the diesel engine1. In addition, the EGR gas fluid passage86having a spiral shape gives sufficient swirling properties to the EGR gas flowing into the mixing chamber87. Thus, the collector25can be shaped with a shortened length in the front-rear direction.

A lower surface flange84aof the upper case84and an upper surface flange85aof the lower case85are fastened with bolts, to form the collector25having openings (the fresh air inlet81, the EGR gas inlet82, and the intake outlet83) in three directions (toward the front, rear, and left). The upper case84has a rear surface flange84bin which the fresh air inlet81is opened, and a fresh air outlet of the intake throttle member26is fastened to the rear surface flange84bwith bolts. The intake throttle member26adjusts the degree of opening of an intake valve (butterfly valve)26aprovided therein, to thereby adjust the amount of fresh air supply to the collector25.

The lower case85has a front surface flange85bin which the EGR gas inlet82is opened, and an EGR gas outlet of the EGR valve member29is fastened with bolts to the front surface flange85bwith interposition of a relay flange89having a rectangular pipe shape. The EGR valve member29adjusts the degree of opening of an EGR valve (not shown) provided therein, to thereby adjust the amount of EGR gas supply to the collector25. A reed valve90inserted in the EGR gas inlet82is fixed inside the front surface flange85bof the lower case85. The relay flange (spacer)89which is fastened to the front surface flange85bwith bolts covers the front side of the reed valve90. As a result, the collector25is provided therein with the reed valve90disposed in a portion of the EGR gas fluid passage86, the portion being on the EGR gas inlet82side.

The relay flange89has, in its rear surface coupled to the collector25, an EGR gas outlet89awhich is in communication with the EGR gas inlet82. The relay flange89has a front surface from which valve coupling bases89b,89cto be coupled to the EGR valve member29protrude. Openings of the valve coupling bases89b,89care in communication with the EGR gas outlet of the EGR valve member29. In the relay flange89, the EGR gas is merged at EGR gas inlets of the upper and lower valve coupling bases89b,89c, and then is caused to flow from the EGR gas inlet82into the EGR gas fluid passage86provided inside the collector25via the reed valve90.

The EGR valve member29is configured such that: a valve body29ehas an EGR gas fluid passage29fin which an EGR valve (not shown) is disposed; an actuator29dfor adjusting the degree of opening of the EGR valve is disposed above the valve body29e; the EGR valve member29has its longitudinal direction in parallel to the up-down direction; and the EGR valve member29is coupled to the front side of the collector25with interposition of the relay flange89. The EGR valve member29has, in a rear surface of the valve body29ewhich is arranged lower, outlet side flanges29a,29bto be coupled respectively to the valve coupling bases89b,89cof the relay flange89. The outlet side flanges29a,29bare arranged one above the other. The EGR valve member29also has, in its front surface, an inlet side flange29chaving an EGR gas inlet that is in communication with the EGR gas outlet of the recirculation exhaust gas tube28.

The EGR valve member29is configured such that: after an EGR gas cooled by the EGR cooler27flows into the EGR gas inlet of the inlet side flange29cthrough the downstream EGR gas relay fluid passage32of the EGR cooler coupling base34and the recirculation exhaust gas tube28, the EGR gas is distributed to upper and lower parts via the EGR gas fluid passage29fof the valve body29e. The EGR gas flow distributed to upper and lower parts through the EGR gas fluid passage29fis then subjected to a flow rate adjustment by the EGR valve, and then enters the relay flange89through the EGR gas outlets of the upper and lower outlet side flanges29a,29b.

The recirculation exhaust gas tube28includes a gas pipe portion28aand a rib28b, the gas pipe portion28abeing bent to have an L-shape in a plan view, the rib28bhaving a flat-plate shape protruding from an inner peripheral side of an outer wall of the gas pipe portion28a. The recirculation exhaust gas tube28has, at one end (rear end) of the gas pipe portion28a, an outlet side flange28cto be coupled to the inlet side flange29cof the EGR valve member29, and also has, at the other end (left end) of the gas pipe portion28a, an inlet side flange28dto be coupled to the right surface of the EGR cooler coupling base34. The recirculation exhaust gas tube28further has, in an upper surface of a bent portion of the gas pipe portion28a, a sensor attachment base28eto which an EGR gas temperature sensor is attached.

In the EGR device24, the collector25can be configured with a shortened length, and therefore the distance between the EGR valve member29and the intake throttle member26can be shortened, which enables the length of the EGR device24in the front-rear direction to be shortened. In the EGR valve member29, the actuator29dis disposed on the upper side. It therefore is possible that topmost portions of the EGR valve member29, the collector25, and the intake throttle member26are at the same height. This can lower the height of the EGR device24in the up-down direction, and also can narrow the width of the EGR device24in the left-right direction. Since the EGR device24can be configured compactly, coupling the EGR device24to the right side of the cylinder head2integrated with the intake manifold3can be easily implemented merely by adjusting the recirculation exhaust gas tube28. In addition, such a configuration contributes to downsizing of the diesel engine1.

The recirculation exhaust gas tube28has the flat-plate rib28bthat is coupled so as to connect the opposite ends of the gas pipe portion28a. This gives a high rigidity to the recirculation exhaust gas tube28, and also increases a strength with which the front end side of the EGR device24is supported on the cylinder head2. In addition, the recirculation exhaust gas tube28has the flat-plate rib28bthat is disposed along an EGR gas fluid passage28fprovided inside the gas pipe portion28a. Due to the rib28b, the gas pipe portion28ahas a wide heat dissipation area, which increases the effect of cooling the EGR gas flowing in the EGR gas fluid passage28f. This contributes to cooling a mixed gas prepared in the EGR device24, and exerts an effect that reduction in the amount of NOx generated from the mixed gas can be easily kept in a proper state.

A configuration of the EGR cooler27will now be described with reference toFIG. 9toFIG. 16, andFIG. 22toFIG. 24. As shown inFIG. 9toFIG. 16, andFIG. 22toFIG. 24, the EGR cooler27includes a heat exchanger91and a pair of left and right flange portions92,93. The heat exchanger91has a coolant passage and an EGR gas fluid passage alternately stacked. The pair of left and right flange portions92,93are disposed in left and right end portions of one side surface of the heat exchanger91. The coolant outlet94is disposed in one of the left and right flange portions92,93, while the coolant inlet95is disposed in the other of the left and right flange portions92,93. The EGR gas inlet96is disposed in one of the left and right flange portions92,93, while the EGR gas outlet97is disposed in the other of the left and right flange portions92,93. The left and right flange portions92,93are coupled to the front surface of the cylinder head2, so that the EGR cooler27is fixed to the cylinder head2.

Since each of the pair of left and right flange portions92,93has a coolant opening and an EGR gas opening, it is possible that the flange portions92,93are made from a common member, and moreover material costs of the flange portions92,93can be suppressed. The flange portions92,93are formed by a flat plate being bored to have through holes94to97corresponding to the coolant and the EGR gas, the flat plate being coupled to the cylinder head2. Thus, forming the flange portions92,93in the EGR cooler27is easy. In addition, a coupling portion where the flange portions92,93are coupled to the heat exchanger91can be minimized, so that the amount of heat transfer from the cylinder head2to the heat exchanger91can be reduced, which increases the effect of cooling the EGR gas by the heat exchanger91.

Since the EGR cooler27has the flange portions92,93protruding from the rear surface of the heat exchanger91, a space is formed between the heat exchanger91and the cylinder head2. As a result, the EGR cooler27is in a state where a wide area of the front and rear surfaces of the heat exchanger91is exposed to outside air. Heat dissipation occurs in the heat exchanger91, too. Thus, the effect of cooling the EGR gas by the EGR cooler27is increased. This configuration can reduce the degree of stacking in the heat exchanger91as compared to a configuration in which the rear surface and the front surface of the heat exchanger91are attached. The length of the EGR cooler27in the front-direction can be shorted, and thus the diesel engine1can be downsized.

The left flange portion92has the coolant outlet94and the EGR gas inlet96, while the right flange portion93has the coolant inlet95and the EGR gas outlet97. In the left flange portion92, the coolant outlet94is disposed above the EGR gas inlet96, while in the right flange portion93, the EGR gas outlet97is disposed above the coolant inlet95. The coolant outlet94and the EGR gas outlet97are disposed at the same height, while the coolant inlet95and the EGR gas inlet96are disposed at the same height.

The left and right flange portions92,93of the EGR cooler27are coupled respectively to the EGR cooler coupling bases33,34protruding from the front surface of the cylinder head2. The upstream EGR gas relay fluid passage31and the downstream coolant relay fluid passage38of the left EGR cooler coupling base33are in communication with the EGR gas inlet96and the coolant outlet94of the left flange portion92, respectively. The downstream EGR gas relay fluid passage32and the upstream coolant relay fluid passage39of the right EGR cooler coupling base34are in communication with the EGR gas outlet97and the coolant inlet95of the right flange portion93, respectively.

The EGR gas relay fluid passages31,32and the coolant passages38,39are provided in the coupling bases33,34to which the flange portions92,93of the EGR cooler27are coupled, and are in communication with the EGR gas inlet and outlet96,97and the coolant outlet and inlet94,95of the flange portions92,93. It is not necessary that coolant piping and EGR gas piping are disposed between the EGR cooler27and the cylinder head2. Accordingly, a sealability can be given to a coupling portion where the EGR cooler27and the cylinder head2are coupled to each other without any influence of, for example, extension and contraction of piping caused by the EGR gas or the coolant. In addition, the EGR cooler27is given an enhanced resistance against external fluctuation factors such as heat and vibration, and can be compactly installed in the cylinder head2.

The coolant outlet94is disposed above the EGR gas inlet96in the flange portion92, while the EGR gas outlet97is disposed above the coolant inlet95in the flange portion93. Thus, the flange portions92,93having identical shapes with their postures mutually upside-down are attached to the heat exchanger91. This can reduce the number of types of component parts included in the EGR cooler27, thus improving an assemblability of the EGR cooler27and reducing costs of the component parts.

The flange portion92is provided with the coolant outlet94and the EGR gas inlet96through which a coolant or an EGR gas having a large quantity of heat passes, while the flange portion93is provided with the coolant inlet95and the EGR gas outlet97through which a coolant or an EGR gas having a small quantity of heat passes. Accordingly, distortion caused by thermal deformation of each of the flange portions92,93can be suppressed. In addition, the flange portions92,93are configured as separate members whose thermal deformation is less influential to each other, and therefore damage and breakdown of the EGR cooler27can be prevented.

In the EGR cooler27, the coolant outlet94and the coolant inlet95are disposed at diagonal positions, and the EGR gas inlet96and the EGR gas outlet97are disposed at diagonal positions in a rear view. Since EGR gases having different quantities of heat and coolants having different quantities of heat are respectively supplied or discharged at diagonal positions, thermal deformations of coupling portions where the EGR cooler27is coupled to the cylinder head2can be mutually relieved, so that deflection or slackness of the coupling portions can be suppressed. Accordingly, leakage of an EGR gas or a coolant in the EGR cooler27and in the cylinder head2can be prevented, and moreover a decrease in the coupling strength can be prevented.

A plate-shaped gasket98is sandwiched between the cylinder head2and the flange portions92,93so as to extend across the left and right flange portions92,93. A coolant inlet and a coolant outlet of the cylinder head2, which are respectively in communication with the coolant outlet94and the coolant inlet95of the flange portions92,93, have O-rings99embedded therein, the O-rings99being ring-shape seal members. The O-rings99are covered with the flange portions92,93.

Since the flange portions92,93configured as separate members are coupled to the coupling bases33,34of the cylinder head2with the gasket98interposed therebetween, a tension is exerted on the gasket98due to thermal deformation of the coupling portion coupled to the cylinder head2. This enhances a sealability (hermetic sealing performance) of the gasket98in a coupling portion of each of the EGR gas inlet96and the EGR gas outlet97. Thus, leakage of an EGR gas flowing from one to the other between the cylinder head2and the EGR cooler27can be prevented. The O-rings99are embedded in spaces defined by rear end surfaces of the flange portions92,93and the coolant inlet and the coolant outlet of the coupling bases33,34of the cylinder head2. When a coolant flows, therefore, the coolant is in contact with the O-rings99in communication portions where the coupling bases33,34are in communication with the flange portions92,93. Thus, a sealability (hermetic sealing performance) of the coupling portions of the coolant outlet and inlet can be obtained. Accordingly, even though the EGR cooler27where a liquid and a gas enter and exit is coupled to the cylinder head2, a sealability for each of the liquid and the gas can be obtained, so that leakage of each of the EGR gas and the coolant can be prevented.

An outer peripheral portion of each of the flange portions92,93is bored to have through holes100for bolt fastening, at outer positions. Specifically, the left flange portion92has five through holes100disposed in its upper, lower, and left sides, and the right flange portion93has five through holes100disposed in its upper, lower, and right sides. Since the left flange portion92has the through holes100disposed above the coolant outlet94, below the EGR gas inlet96, and to the left of a portion between the coolant outlet94and the EGR gas inlet96, a sealability of the coolant outlet94and the EGR gas inlet96can be exerted when the left flange portion92is fastened to the coupling base33of the cylinder head2with bolts. Likewise, since the right flange portion93has the through holes100disposed below the coolant inlet95, above the EGR gas outlet97, and to the right of a portion between the coolant inlet95and the EGR gas outlet97, a sealability of the coolant inlet95and the EGR gas outlet97can be exerted when the right flange portion93is fastened to the coupling base34of the cylinder head2with bolts.

The gasket98is constituted by a lamination of two plates98a,98beach having through holes101to103. The EGR gas passes through the through holes (EGR gas through holes)101. The coolant passes through the through holes (coolant through holes)102. Fastening bolts are inserted into the through holes (bolt through holes)103. The gasket98has such a shape that an inner peripheral edge at the EGR gas through hole101is branched so as to be warped in the front-rear direction and is configured such that the open areas of the coolant through holes102are larger than the open areas of the coolant outlet and inlet94,95.

In the gasket98, the front plate98ahas its inner peripheral edge at the EGR gas through hole101being warped frontward, while the rear plate98bhas its inner peripheral edge at the EGR gas through hole101being warped rearward. The front plate98aand the rear plate98bare bonded by welding, so that the inner peripheral edge at the EGR gas through hole101has a Y-shaped cross-section. Since the inner peripheral edge at the EGR gas through hole101is warped in the front-rear direction, front and rear surfaces of the inner peripheral edge at the EGR gas through hole101can be in tight contact with end surfaces of the coupling bases33,34and the flange portions92,93. Accordingly, a sufficient airtightness can be obtained.

The gasket98is configured such that the openings of the coolant through holes102is larger than those of the coolant outlet and inlet94,95. Thus, the O-rings99are inserted in the coolant through holes102. Communication portions where the coolant outlet and inlet of the flange portions92,93are in communication with the coolant relay fluid passages38,39of the coupling bases33,34are hermetically sealed by the O-rings99fitted in the coolant through holes102of the gasket98.

The coupling bases33,34of the cylinder head2have the coolant outlet and inlet opened with steps, and thereby the openings of the coolant outlet and inlet are given larger diameters than the fluid passage diameters of the coolant relay fluid passages38,39formed inside the coupling bases33,34. The O-rings99disposed to the coolant outlet and inlet of the coupling bases33,34are fitted on the outer circumferential sides of the coolant relay fluid passages38,39. The O-rings99are inserted in the gasket98, and also fitted in the step portions of the coolant outlet and inlet in the coupling bases33,34. Thereby, the O-rings99are sandwiched between the coupling bases33,34and the flange portions92,93.

When a coolant passes inside the O-rings99made of an elastic material, the O-rings99are deformed to expand outward and come into tight contact with the coupling bases33,34and the flange portions92,93, thus providing a sealability for the coolant.

The ring-shape O-ring has its inner circumferential portion bulging frontward and rearward. A coolant passing through the inner circumferential portion of the O-ring99pushes the inner circumferential portion, so that its front and rear edges are deformed to protrude frontward and rearward. This brings the inner circumferential portion of the O-ring99into tight contact with the coupling bases33,34and the flange portions92,93. Thus, a sealability for the coolant can be enhanced in the coupling portion where the cylinder head2is coupled to the EGR cooler27.

The ring-shape O-ring99whose inner circumferential portion is bulged frontward and rearward is shaped such that its inner circumferential surface has a recessed portion. The inner circumferential surface of the O-ring is warped frontward and rearward so as to have a Y-shaped cross-section. A coolant passing through the inner circumferential portion of the O-ring99pushes the inner circumferential portion, so that its front and rear edges are further protruded frontward and rearward, to increase the degree of tight contact of the inner circumferential portion of the O-ring99with the coupling bases33,34and the flange portions92,93. Accordingly, a sealability for the coolant can be enhanced in the coupling portion where the cylinder head2is coupled to the EGR cooler27.

The configurations of respective parts of the present invention are not limited to those of the illustrated embodiment, but can be variously changed without departing from the gist of the invention.

REFERENCE SIGNS LIST