Engine device

Abstract

The two-stage turbocharger is arranged compactly. The engine device includes a turbocharger. The turbocharger is configured as a two-stage turbocharger 30 consisting of a high-pressure stage turbocharger 51 and a low-pressure stage turbocharger 52. A high-pressure stage exhaust outlet 58 of the high-pressure stage turbocharger 51 and a low-pressure stage exhaust inlet 60 of the low-pressure stage turbocharger 52 are connected via a flexible high-pressure exhaust gas pipe 59.

Description

Technical Field

[0001] The present invention relates to an engine device provided with a supercharger.

Background Art

[0002] Conventionally, for the purpose of improving engine output and fuel efficiency, a supercharger that compresses fresh air with exhaust energy has been mounted on an engine device to increase the air density in the cylinder of the engine (see Patent Document 1). In a diesel engine, by supplying a large amount of high-density air into the cylinder, not only can a large amount of fuel be burned to increase engine output and engine torque, but also pre-mixed combustion can be suppressed by promoting the mixing of fuel and air, thereby reducing NOx emissions.

[0003] In addition, since a single-stage supercharger using one supercharger has limitations in meeting the requirements of a high-output engine, an engine equipped with a two-stage supercharger in which two superchargers are connected in series in a high-pressure stage and a low-pressure stage has been proposed (see Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, the engine mounting space varies depending on the work vehicle (construction machinery, agricultural work machinery, etc.) on which it is mounted. In recent years, due to the requirements for weight reduction and compactness, there are often restrictions (narrowness) in the mounting space. For this reason, it is necessary to layout the components of the engine compactly.

[0006] The technical problem of the present invention is to provide an engine device that has been improved in consideration of the above-mentioned current situation.

Means for Solving the Problem

[0007] An engine device according to one aspect is an engine device provided with a supercharger, and the supercharger is composed of a two-stage supercharger including a high-pressure stage supercharger and a low-pressure stage supercharger. The exhaust outlet of the high-pressure stage supercharger and the exhaust inlet of the low-pressure stage supercharger are connected via a flexible pipe.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. First, with reference to FIGS. 1 to 5, the overall structure of the engine 1 as an example of the engine device will be described. In this embodiment, the engine 1 is composed of a diesel engine. Note that in the following description, both side portions parallel to the crankshaft 5 (the side portions on both sides with the crankshaft 5 in between) are referred to as left and right, the side where the flywheel housing 7 is installed is referred to as the front side, and the side where the cooling fan 9 is installed is referred to as the rear side. These are conveniently used as the reference for the positional relationships of the four directions and up and down in the engine 1.

[0010] As shown in FIGS. 1 to 5, an intake manifold 3 is arranged on one side parallel to the crankshaft 5 in the engine 1, and an exhaust manifold 4 is arranged on the other side. In the embodiment, the intake manifold 3 is integrally formed with the cylinder head 2 on the right side surface of the cylinder head 2. The exhaust manifold 4 is installed on the left side surface of the cylinder head 2. The cylinder head 2 is mounted on a cylinder block 6 containing the crankshaft 5 and a piston (not shown).

[0011] The front and rear end sides of the crankshaft 5 protrude from the front and rear side surfaces of the cylinder block 6. A flywheel housing 7 is fixed to one side intersecting the crankshaft 5 in the engine 1 (the front side surface side of the cylinder block 6 in the embodiment). A flywheel 8 is arranged in the flywheel housing 7. The flywheel 8 is fixed to the front end side of the crankshaft 5 and is configured to rotate integrally with the crankshaft 5. The power of the engine 1 is configured to be taken out to the operating part of a working machine (such as a hydraulic excavator or a forklift) via the flywheel 8. A cooling fan 9 is provided on the other side intersecting the crankshaft 5 in the engine 1 (the rear side surface side of the cylinder block 6 in the embodiment). A rotational force is configured to be transmitted from the rear end side of the crankshaft 5 to the cooling fan 9 via a belt 10.

[0012] An oil pan 11 is arranged on the lower surface of the cylinder block 6. Lubricating oil is stored in the oil pan 11. The lubricating oil in the oil pan 11 is sucked by a lubricating oil pump (not shown) arranged on the right side surface of the cylinder block 6 at the connection part of the cylinder block 6 and the flywheel housing 7, and is supplied to each lubricating part of the engine 1 via an oil cooler 13 and an oil filter 14 arranged on the right side surface of the cylinder block 6. The lubricating oil supplied to each lubricating part is then returned to the oil pan 11. The lubricating oil pump is configured to be driven by the rotation of the crankshaft 5.

[0013] As shown in FIG. 4, a fuel supply pump 15 for supplying fuel is attached to a connecting portion of the right side of the engine 1 with the flywheel housing 7 of the cylinder block 6. The fuel supply pump 15 is disposed below the EGR device 24. A common rail 16 is disposed between the intake manifold 3 of the cylinder head 2 and the fuel supply pump 15. The common rail 16 is fixed to an upper front portion of the right side surface of the cylinder block 6. On the upper surface portion of the cylinder head 2 covered by the cylinder head cover 18, injectors (not shown) for four cylinders each having an electromagnetic on-off control type fuel injection valve are provided.

[0014] Each injector is connected to a fuel tank (not shown) mounted on the work vehicle via the fuel supply pump 15 and the cylindrical common rail 16. Fuel in the fuel tank is pumped from the fuel supply pump 15 to the common rail 16, and high-pressure fuel is stored in the common rail 16. By controlling the opening and closing of the fuel injection valves of each injector respectively, the high-pressure fuel in the common rail 16 is injected from each injector into each cylinder of the engine 1.

[0015] As shown in FIGS. 2 and 5, a blow-by gas reduction device 19 for taking in blow-by gas that has leaked from the combustion chamber of the engine 1 to the upper surface side of the cylinder head 2 is provided on the upper surface of the cylinder head cover 18 that covers the intake valve and the exhaust valve (not shown) provided on the upper surface portion of the cylinder head 2. The blow-by gas outlet of the blow-by gas reduction device 19 communicates with the intake portion of the two-stage supercharger 30 via a reduction hose 68. The blow-by gas from which the lubricating oil component has been removed in the blow-by gas reduction device 19 is returned to the intake manifold 3 via the two-stage supercharger 30 and the like.

[0016] As shown in Fig. 3, on the left side of the engine 1, a starter 20 for engine starting is attached to the flywheel housing 7. The starter 20 for engine starting is disposed below the exhaust manifold 4. The starter 20 for engine starting is attached to the left part of the rear side surface of the flywheel housing 7 at a position below the connecting part between the cylinder block 6 and the flywheel housing 7.

[0017] As shown in Fig. 2, a cooling water pump 21 for cooling water lubrication is disposed at the leftward part of the rear side surface of the cylinder block 6. Further, an alternator 12 as a generator that generates electricity by the power of the engine 1 is provided to the left side of the cooling water pump 21. Rotational power is transmitted from the front end side of the crankshaft 5 via a belt 10 to the cooling fan 9, the alternator 12, and the cooling water pump 21. The cooling water in a radiator (not shown) mounted on the work vehicle is supplied to the cooling water pump 21 by driving the cooling water pump 21. Then, the cooling water is supplied into the cylinder head 2 and the cylinder block 6, and the engine 1 is cooled.

[0018] As shown in Fig. 3, the cooling water pump 21 is disposed at a height position lower than that of the exhaust manifold 4, and a cooling water inlet pipe 22 that communicates with the cooling water outlet of the radiator is fixedly provided on the left side surface of the cylinder block 6 at a position substantially the same height as the cooling water pump 21. On the other hand, a cooling water outlet pipe 23 that communicates with the cooling water inlet of the radiator is fixedly provided at the rear rightward part of the upper surface of the cylinder head 2 as shown in Figs. 2 and 5. The cylinder head 2 has a cooling water drain part 35 at its right rear corner, and the cooling water outlet pipe 23 is installed on the upper surface of the cooling water drain part 35.

[0019] As shown in FIGS. 4 and 5, the EGR device 24 is disposed on the right side of the cylinder head 2. The EGR device 24 includes a collector 25 as a relay pipe that mixes recirculated exhaust gas (EGR gas from the exhaust manifold 4) and fresh air (external air from the air cleaner) of the engine 1 and supplies the mixture to the intake manifold 3, an intake throttle member 26 that connects the collector 25 to the air cleaner, a recirculated exhaust gas pipe 28 that forms a part of a reflux pipe connecting to the exhaust manifold 4 via an EGR cooler 27, and an EGR valve member 29 that connects the collector 25 to the recirculated exhaust gas pipe 28.

[0020] In this embodiment, the collector 25 of the EGR device 24 is integrally formed with the cylinder head 2 and is connected to the right side surface of the intake manifold 3 that constitutes the right side surface of the cylinder head 2. That is, the outlet opening of the collector 25 is connected to the inlet opening of the intake manifold 3 provided on the right side surface of the cylinder head 2. Further, the EGR gas inlet of the recirculated exhaust gas pipe 28 is connected to the EGR gas outlet of the EGR gas passage provided in the cylinder head 2 at a forward portion of the right side surface of the cylinder head 2. By attaching the collector 25 to the intake manifold 3 and attaching the recirculated exhaust gas pipe 28 to the cylinder head 2, the EGR device 24 is fixed to the cylinder head 2.

[0021] In the EGR device 24, the intake manifold 3 and the intake throttle member 26 for introducing fresh air are connected in communication via the collector 25. An EGR valve member 29 connected to the outlet side of the recirculated exhaust gas pipe 28 is connected in communication to the collector 25. The collector 25 is formed in a substantially cylindrical shape with a longitudinal length in the front-rear direction. The intake throttle member 26 is bolted to the air intake side (front side in the longitudinal direction) of the collector 25. The air supply and discharge side of the collector 25 is bolted to the inlet side of the intake manifold 3. The EGR valve member 29 adjusts the supply amount of EGR gas to the collector 25 by adjusting the opening degree of the EGR valve inside thereof.

[0022] Fresh air is supplied into the collector 25, and EGR gas (a part of the exhaust gas discharged from the exhaust manifold 4) is supplied into the collector 25 from the exhaust manifold 4 via the EGR valve member 29. After the fresh air and the EGR gas from the exhaust manifold 4 are mixed in the collector 25, the mixed gas in the collector 25 is supplied to the intake manifold 3. That is, a part of the exhaust gas discharged from the engine 1 to the exhaust manifold 4 is returned from the intake manifold 3 to the engine 1, so that the maximum combustion temperature during high-load operation is lowered, and the NOx (nitrogen oxides) emission amount from the engine 1 is reduced.

[0023] As shown in FIGS. 1 and 3 to 5, the EGR cooler 27 is fixed to the front side surface of the cylinder head 2. The cooling water flowing in the cylinder head 2 and the EGR gas flow into and out of the EGR cooler 27, and the EGR gas is cooled in the EGR cooler 27. On the front side surface of the cylinder head 2, a pair of left and right EGR cooler connecting parts 33, 34 for connecting the EGR cooler 27 project. And the EGR cooler 27 is connected to the front side surfaces of the EGR cooler connecting parts 33, 34. That is, the EGR cooler 27 is arranged at a position above the flywheel housing 7 and in front of the cylinder head 2 so that the rear side surface of the EGR cooler 27 and the front side surface of the cylinder head 2 are separated from each other.

[0024] As shown in FIGS. 1 to 3 and 5, a two-stage supercharger 30 is arranged on the left side of the cylinder head 2. The two-stage supercharger 30 includes a high-pressure stage supercharger 51 and a low-pressure stage supercharger 52. The high-pressure stage supercharger 51 has a high-pressure stage turbine case 53 incorporating a turbine wheel (not shown) and a high-pressure stage compressor case 54 incorporating a blower wheel (not shown). The low-pressure stage supercharger 52 has a low-pressure stage turbine case 55 incorporating a turbine wheel (not shown) and a low-pressure stage compressor case 56 incorporating a blower wheel (not shown).

[0025] In the exhaust path of the two-stage supercharger 30, the high-pressure stage turbine case 53 is connected to the exhaust manifold 4, the low-pressure stage turbine case 55 is connected to the high-pressure stage turbine case 53 via the high-pressure exhaust gas pipe 59, and the exhaust connection pipe 119 is connected to the low-pressure stage turbine case 55. The high-pressure exhaust gas pipe 59 is formed of a flexible pipe. In this embodiment, a part of the high-pressure exhaust gas pipe 59 is formed in a bellows shape.

[0026] A tail pipe (not shown) is connected to the exhaust connection pipe 119 via the exhaust gas purification device 100. The exhaust gas discharged from each cylinder of the engine 1 to the exhaust manifold 4 is discharged to the outside from the tail pipe via the two-stage supercharger 30, the exhaust gas purification device 100, etc.

[0027] In the intake path of the two-stage supercharger 30, the low-pressure stage compressor case 56 is connected to the air cleaner via the air supply pipe 62, the high-pressure stage compressor case 54 is connected to the low-pressure stage compressor case 56 via the low-pressure fresh air passage pipe 65, and the intake throttle member 26 of the EGR device 24 is connected to the high-pressure stage compressor case 54 via an intercooler (not shown). The fresh air (outside air) sucked into the air cleaner is dust-removed and purified by the air cleaner, and then sent to the intake manifold 3 via the two-stage supercharger 30, the intercooler, the intake throttle member 26, the collector 25, etc., and supplied to each cylinder of the engine 1.

[0028] The exhaust gas purification device 100 is for collecting particulate matter (PM) etc. in the exhaust gas. As shown in FIGS. 1 to 5, the exhaust gas purification device 100 has a substantially cylindrical shape that extends long in the left-right direction intersecting the crankshaft 5 in plan view. In this embodiment, the exhaust gas purification device 100 is disposed above the front surface of the cylinder head 2. The exhaust gas purification device 100 is supported at the front part of the cylinder head 2 via the left support bracket 117, the right support bracket 118, and the support base 121.

[0029] On both the left and right sides (one end side in the longitudinal direction and the other end side in the longitudinal direction) of the exhaust gas purification device 100, an exhaust gas intake side and an exhaust gas discharge side are provided separately on the left and right. The exhaust gas inlet pipe 116 on the exhaust gas intake side of the exhaust gas purification device 100 is connected to the exhaust gas outlet of the low-pressure stage turbine case 55 of the two-stage supercharger 30 via an exhaust connection member 120 having a substantially L-shaped exhaust gas passage in a side view and a straight exhaust connection pipe 119. The exhaust connection member 120 is fixed to the left side surface of the support base 121. The exhaust gas discharge side of the exhaust gas purification device 100 is connected to the exhaust gas intake side of a tail pipe (not shown).

[0030] The exhaust gas purification device 100 has a structure in which a diesel oxidation catalyst 102 such as platinum and a honeycomb-structured soot filter 103 are arranged in series and housed inside. In the above configuration, nitrogen dioxide (NO2) generated by the oxidation action of the diesel oxidation catalyst 102 is taken into the soot filter 103. The particulate matter contained in the exhaust gas of the engine 1 is collected by the soot filter 103 and continuously oxidized and removed by nitrogen dioxide. Therefore, in addition to removing particulate matter (PM) in the exhaust gas of the engine 1, the contents of carbon monoxide (CO) and hydrocarbons (HC) in the exhaust gas of the engine 1 are reduced.

[0031] The exhaust gas purification device 100 includes an upstream case 105 having an exhaust gas inlet pipe 116 on its outer peripheral surface, an intermediate case 106 connected to the upstream case 105, and a downstream case 107 connected to the intermediate case 106. The upstream case 105 and the intermediate case 106 are connected in series to form a gas purification housing 104 made of a heat-resistant metal material. Inside the gas purification housing 104, the diesel oxidation catalyst 102 and the soot filter 103 are housed via a cylindrical inner case (not shown). Further, the downstream case 107 is equipped with an inner case (not shown) in which a large number of sound-absorbing holes are opened, and a sound-absorbing material made of ceramic fiber is filled between the inner case to form a muffler.

[0032] When the exhaust gas passes through the diesel oxidation catalyst 102 and the soot filter 103, if the exhaust gas temperature exceeds the renewable temperature (for example, about 300°C), nitric oxide in the exhaust gas is oxidized to unstable nitrogen dioxide by the action of the diesel oxidation catalyst 102. Then, the particulate matter deposited on the soot filter 103 is oxidized and removed by the oxygen released when nitrogen dioxide returns to nitric oxide, whereby the particulate matter collection ability of the soot filter 103 is restored and the soot filter 103 is regenerated.

[0033] Next, with reference to FIGS. 6 to 10 and the like, the configuration and mounting structure of the two-stage supercharger 30 will be described. The two-stage supercharger 30 compresses the fresh air that flows into the intake manifold 3 of the cylinder head 2 by the fluid energy of the exhaust gas discharged from the exhaust manifold 4. The two-stage supercharger 30 is composed of a high-pressure stage supercharger 51 connected to the exhaust manifold 4 and a low-pressure stage supercharger 52 connected to the high-pressure stage supercharger 51.

[0034] As shown in FIGS. 7 and 8, the high-pressure stage supercharger 51 is disposed on the left side of the exhaust manifold 4. The low-pressure stage supercharger 52 is disposed above the exhaust manifold 4. That is, while the small-capacity high-pressure stage supercharger 51 is disposed facing the left side surface of the exhaust manifold 4, the large-capacity low-pressure stage supercharger 52 is disposed facing the left side surfaces of the cylinder head 2 and the cylinder head cover 18. Therefore, not only can the exhaust manifold 4 and the two-stage supercharger 30 be compactly arranged within a substantially square frame in a front view and a rear view in the space on the left side of the cylinder head 2, but also the uppermost position of the two-stage supercharger 30 can be made lower than the uppermost position of the engine 1. Therefore, it can contribute to the miniaturization of the engine 1.

[0035] Also, as shown in FIGS. 3 and 6, when viewing the engine 1 from the left side, the low-pressure stage supercharger 52 is disposed on the left side of the cylinder head 2 and in front of the high-pressure stage supercharger 51. Therefore, a wider space for arranging other application parts can be provided around the front part of the left side surface of the cylinder block 6 below the low-pressure stage supercharger 52. For example, an external auxiliary machine such as a hydraulic pump that operates by the rotational force of the crankshaft 5 can be arranged between the low-pressure stage supercharger 52 and the engine starter 20 for starting.

[0036] As shown in FIGS. 6 to 8 and the like, the high-pressure stage supercharger 51 includes a high-pressure stage turbine case 53, a high-pressure stage compressor case 54 disposed on the rear side of the high-pressure stage turbine case 53, and a high-pressure stage center housing 72 that connects the two cases 53 and 54. The high-pressure stage turbine case 53 includes a high-pressure stage exhaust inlet 57 that communicates with the exhaust manifold exhaust outlet 49 of the exhaust manifold 4, and a high-pressure stage exhaust outlet 58 that communicates with the upstream end of the high-pressure exhaust gas pipe 59. The high-pressure stage compressor case 54 includes a high-pressure stage fresh air inlet 66 that communicates with the downstream end of the low-pressure fresh air passage pipe 65, and a high-pressure stage fresh air supply port 67 that is connected to an intercooler (not shown). Here, the upstream end of the pipe means the upstream end of the gas flow, and the downstream end means the downstream end of the gas flow.

[0037] On the other hand, the low-pressure stage supercharger 52 includes a low-pressure stage turbine case 55, a low-pressure stage compressor case 56 disposed on the rear side of the low-pressure stage turbine case 55, and a low-pressure stage center housing 75 that connects the two cases 55 and 56. The low-pressure stage turbine case 55 includes a low-pressure stage exhaust inlet 60 that communicates with the downstream end of the high-pressure exhaust gas pipe 59, and a low-pressure stage exhaust outlet 61 that communicates with the upstream end of the exhaust connection pipe 119. The low-pressure stage compressor case 56 includes a low-pressure stage fresh air inlet 63 that communicates with the downstream end of the air supply pipe 62, and a low-pressure stage fresh air supply port 64 that communicates with the upstream end of the low-pressure fresh air passage pipe 65.

[0038] The exhaust manifold 4 has an exhaust manifold exhaust outlet 49 for discharging exhaust gas opened toward the left. And while the high-pressure stage turbine case 53 has a high-pressure stage exhaust inlet 57 opened toward the exhaust manifold 4, it has a high-pressure stage exhaust outlet 58 opened forward. Also, while the low-pressure stage turbine case 55 has a low-pressure stage exhaust inlet 60 opened downward, it has a low-pressure stage exhaust outlet 61 opened forward.

[0039] As shown in FIGS. 6 to 8, in the two-stage supercharger 30, while the high-pressure stage compressor case 54 has a high-pressure stage fresh air inlet 66 opened rearward, it has a high-pressure stage fresh air supply port 67 opened downward. Also, while the low-pressure stage compressor case 56 has a low-pressure stage fresh air inlet 63 opened rearward, after protruding the low-pressure stage fresh air supply port 64 from the left side and then configuring it rearward. And while the downstream end of the U-shaped low-pressure fresh air passage pipe 65 is connected to the high-pressure stage fresh air inlet 66, the low-pressure stage fresh air supply port 64 is connected to the upstream end of the low-pressure fresh air passage pipe 65.

[0040] As shown in FIGS. 6 to 8, the exhaust manifold exhaust outlet 49 of the exhaust manifold 4 and the high-pressure stage exhaust inlet 57 of the high-pressure stage turbine case 53 are bolt-connected with a flange portion. Thereby, the high-pressure stage supercharger 51 is fixed to the robust exhaust manifold 4. Also, while the high-pressure stage exhaust outlet 58 of the high-pressure stage turbine case 53 is bolt-connected with a flange portion to the downstream end (rear end) of the substantially L-shaped high-pressure exhaust gas pipe 59, the low-pressure stage exhaust inlet 60 of the low-pressure stage turbine case 55 is bolt-connected with a flange portion to the upstream end (upper end) of the high-pressure exhaust gas pipe 59. The substantially L-shaped high-pressure exhaust gas pipe 59 is composed of a flexible pipe, and in this embodiment, it is provided with a bellows pipe portion 59a in the portion extending in the front-rear direction.

[0041] As shown in FIGS. 9 and 10, the low-pressure stage supercharger 52 is fixed to the left side surface (exhaust side surface) of the cylinder head 2. In this embodiment, a low-pressure stage supercharger mounting portion 131 is provided at a position closer to the front of the central portion of the left side surface of the cylinder head 2 (see also FIGS. 12, 16, and 19). The low-pressure stage supercharger mounting portion 131 is provided above the exhaust manifold 4 and at a position facing the low-pressure stage turbine case 55. The low-pressure stage supercharger 52 is attached to the low-pressure stage supercharger mounting portion 131 via a substantially L-shaped mounting bracket 132. The mounting bracket 132 includes a supercharger side flat portion 132a disposed in the left-right direction and a head side flat portion 132b protruding forward from the right end of the supercharger side flat portion 132a.

[0042] The supercharger side flat portion 132b of the mounting bracket 132 is fixed to the right edge portion of the front side surface of the low-pressure stage compressor case 56 by bolts 133. The head side flat portion 132a of the mounting bracket 132 is fixed to the low-pressure stage supercharger mounting portion 131 by a pair of front and rear bolts 133. Thereby, the low-pressure stage supercharger 52 is fixed to the robust cylinder head 2.

[0043] In this embodiment, since the low-pressure stage supercharger 52 is fixed to the left side surface (exhaust side surface) of the cylinder head 2 and the high-pressure stage supercharger 51 is fixed to the exhaust manifold 4, the high-pressure stage supercharger 51 and the low-pressure stage supercharger 52 constituting the two-stage supercharger 30 can be firmly fixed by being distributed to the robust cylinder head 2 and the exhaust manifold 4. Further, since the low-pressure stage supercharger 52 is connected to the support base 121 fixed to the front portion of the cylinder head 2 via the exhaust connection pipe 119 and the exhaust connection member 120, the low-pressure stage supercharger 52 can be reliably fixed to the engine 1, and thus the two-stage supercharger 30 can be reliably fixed to the engine 1.

[0044] In addition, since the high-pressure stage exhaust outlet 58 of the high-pressure stage supercharger 51 and the low-pressure stage exhaust inlet 60 of the low-pressure stage supercharger 52 are connected via the flexible high-pressure exhaust gas pipe 59, the risk of low-cycle fatigue failure of the high-pressure exhaust gas pipe 59 due to thermal expansion can be reduced. Furthermore, the stress applied to the two-stage supercharger 30 due to the thermal expansion of the high-pressure exhaust gas pipe 59 can be reduced. As a result, the stress applied to the connection part between the high-pressure stage supercharger 51 and the exhaust manifold 4 and the stress applied to the connection part between the low-pressure stage supercharger 52 and the cylinder head 2 can be reduced, and connection failure and damage to the connection members at these connection parts can be prevented.

[0045] As shown in FIGS. 9 and 10, the cylinder head 2 is provided therein with a rib 135 extending from the low-pressure stage supercharger mounting portion 131 toward the right side surface (intake side surface) of the cylinder head 2. The rib 135 projects upward from the bottom surface 136 of the cylinder head. Thereby, the rigidity around the low-pressure stage supercharger mounting portion 131 in the cylinder head 2 can be improved, and deformation of the cylinder head 2 caused by the attachment of the low-pressure stage supercharger 52 to the cylinder head 2 can be prevented. Further, on the bottom surface 136 of the cylinder head, a valve arm mechanism mounting seat 137 extending in the left-right direction is continuously projected upward at the right end portion of the rib 135. Thereby, the rigidity of the rib 135 can be improved, and thus the rigidity around the low-pressure stage supercharger mounting portion 131 can be improved.

[0046] In this embodiment, the engine 1 is of the OHV type, and the space surrounded by the cylinder head 2 and the cylinder head cover 18 is configured as a valve arm chamber. As shown in FIG. 9, an injector 138 and a valve operating mechanism are accommodated in the valve arm chamber. A plurality of valve arm mechanism mounting seats 137 are arranged at equal intervals in the front-rear direction, a valve arm shaft support portion 139 for supporting a valve arm shaft (not shown) is arranged on the valve arm mechanism mounting seat 137, and a plurality of valve arms 140 are swingably supported on the valve arm shaft. By swinging each valve arm 189 around the valve arm shaft, the intake valve and the exhaust valve (not shown) of each cylinder are configured to open and close.

[0047] As shown in FIGS. 3, 5, and 6, the low-pressure stage supercharger 52 is disposed near the front side surface (one side surface) of the cylinder head 2 when viewed from the left side, while the low-pressure stage exhaust outlet 61 of the low-pressure stage turbine case 55 is provided facing the front side surface side of the cylinder head 2. Further, the exhaust gas inlet pipe 116 constituting the exhaust inlet of the exhaust gas purification device 100 is disposed near the corner where the front side surface and the right side surface (exhaust side surface) of the cylinder head 2 intersect. Therefore, the exhaust connection pipe 119 and the exhaust connection member 120 as the pipes connecting the low-pressure stage exhaust outlet 61 of the low-pressure stage supercharger 52 and the exhaust gas inlet pipe 116 of the exhaust gas purification device 100 can be made short and simple. Thereby, the exhaust gas supplied to the exhaust gas purification device 100 can be maintained at a high temperature, and a decrease in the regeneration ability of the exhaust gas purification device 1 can be prevented.

[0048] In the present invention, as long as the exhaust inlet of the exhaust gas purification device 100 is configured to be disposed near the corner where the front side surface (one side surface) and the right side surface (exhaust side surface) of the cylinder head 2 intersect, the same effects as those of this embodiment can be obtained regardless of the mounting position and arrangement direction of the exhaust gas purification device 100. For example, the exhaust gas purification device 100 may be disposed horizontally and longitudinally above the flywheel housing 7 in front of the cylinder head 2 (see, for example, Japanese Patent Application Laid-Open No. 2011-012598), or may be disposed horizontally and longitudinally in the front-rear direction (in the direction along the crankshaft 5) above the cylinder head 2 (see, for example, Japanese Patent Application Laid-Open No. 2016-079870).

[0049] As shown in FIGS. 3, 5, and 6, a blow-by gas reduction device 19 for taking in blow-by gas is installed on the cylinder head 2. The blow-by gas reduction device 19 is placed and fixed on the upper surface of a cylinder head cover 18 that covers the upper surface of the cylinder head 2. Above the cylinder head 2, a blow-by gas outlet 70 of the blow-by gas reduction device 19 is arranged on the left side surface side at a position near the rear side surface (the other side surface) of the cylinder head 2. Further, a low-pressure stage fresh air inlet 63 of a low-pressure stage supercharger case 56 of the low-pressure stage supercharger 52 is opened rearward. An air supply pipe 62 extending in the front-rear direction is connected to the low-pressure stage fresh air inlet 63. Thereby, the air supply pipe 62 can be arranged near the blow-by gas outlet 70, and the reduction hose 68 connecting the blow-by gas outlet 70 and the air supply pipe 62 can be shortened, preventing freezing inside the reduction hose 68 in a low-temperature environment.

[0050] As shown in FIG. 6, the low-pressure stage compressor case 56 and the high-pressure stage compressor case 54 have the low-pressure stage fresh air inlet 63, the low-pressure stage fresh air supply port 64, and the high-pressure stage fresh air inlet 66 opened in the same direction (rearward). Therefore, it is easy to connect the air supply pipe 62 communicating with the air cleaner to the low-pressure stage fresh air inlet 63, and it is also easy to connect the low-pressure fresh air passage pipe 65 to the low-pressure stage fresh air supply port 64 and the high-pressure stage fresh air inlet 66, so the assembly workability can be improved.

[0051] Further, the low-pressure fresh air passage pipe 65 is composed of a substantially U-shaped metal pipe 65a whose one end is bolted to the high-pressure stage fresh air inlet 66 by flange connection, and a resin pipe 65b that communicates the other end of the metal pipe 65a with the low-pressure stage fresh air supply port 64 of the low-pressure stage compressor case 56. Thereby, the low-pressure fresh air passage pipe 65 can have the metal pipe 65a fixed to the high-pressure stage compressor case 54 with high rigidity, while the resin pipe 65b can relieve the assembly error between the low-pressure stage compressor case 56 and the metal pipe 65a and allow communication.

[0052] In addition, since the low-pressure stage fresh air supply port 64 of the low-pressure stage compressor case 56 extends obliquely upward to the left from the lower left part of the outer peripheral surface of the low-pressure stage compressor case 56 and is further curved rearward, the curvature of the bent portion of the low-pressure fresh air passage pipe 65 (metal pipe 65a) can be increased. Therefore, the generation of turbulent flow in the low-pressure fresh air passage pipe 65 is suppressed, and the compressed air discharged from the low-pressure stage compressor case 56 is smoothly supplied to the high-pressure stage compressor case 54.

[0053] As shown in FIG. 8, the high-pressure stage supercharger 51 includes a fresh air supply port 64 that extends downward at a position slightly to the right of the lower part of the outer peripheral surface of the high-pressure stage compressor case 54. The high-pressure stage compressor case 54 is connected to a high-pressure fresh air passage pipe 71 that communicates with the intercooler, and supplies compressed air to the intercooler through the high-pressure fresh air passage pipe 71. Further, a cooling water inlet pipe 22 that opens toward the left side is provided below the high-pressure stage compressor case 54. A cooling water pipe 150 connected to the radiator is connected to the cooling water inlet pipe 22. Therefore, since the routing of the high-pressure fresh air passage pipe 71 and the cooling water pipe 150 can be aggregated, not only can the piping structure on the machine side mounting the engine 1 be simplified, but also the assembly work and maintenance work can be made easier to perform.

[0054] In addition, as shown in FIGS. 2, 4, and 5, the engine 1 arranges a cooling water outlet pipe 23, an air supply pipe 62, and an intake throttle member 26 at its rear part (the cooling fan 9 side). Therefore, when a radiator, an air cleaner, and an intercooler that utilize the cooling air of the cooling fan 9 are arranged behind the cooling fan 9 on the machine side mounting the engine 1, not only can the cooling water pipes connected to the radiator and the fresh air pipes communicating with the air cleaner and the intercooler be shortened, but also the pipe connection work can be performed collectively. Therefore, not only does the assembly workability and maintenance workability on the machine side become easier, but also the components to be connected to the engine 1 can be efficiently arranged on the machine side.

[0055] As shown in FIGS. 6 to 8, in the high-pressure stage supercharger 51, a high-pressure lubricating oil supply pipe 73 and a high-pressure lubricating oil return pipe 74 are connected to the upper and lower portions of the outer peripheral surface of a high-pressure stage center housing 72, which is a connecting portion between a high-pressure stage turbine case 53 and a high-pressure stage compressor case 54. In the low-pressure stage supercharger 52, a low-pressure lubricating oil supply pipe 76 and a low-pressure lubricating oil return pipe 77 are connected to the upper and lower portions of the outer peripheral surface of a low-pressure stage center housing 75, which is a connecting portion between a low-pressure stage turbine case 55 and a low-pressure stage compressor case 56.

[0056] The lower end of the high-pressure lubricating oil supply pipe 73 is connected to a connecting member 78a provided at the center of the left side surface of the cylinder block 6, while the upper end is connected to the upper portion of the high-pressure stage center housing 72 of the high-pressure stage supercharger 51. A connecting joint 78b for communicating the upper end of the high-pressure lubricating oil supply pipe 73 and the lower end of the low-pressure lubricating oil supply pipe 76 is installed at the upper portion of the high-pressure stage center housing 72. The upper end of the low-pressure lubricating oil supply pipe 76 is connected to a connecting member 78c provided at the upper portion of the low-pressure stage center housing 75 of the low-pressure stage supercharger 52. Thereby, the lubricating oil flowing through the oil passage in the cylinder block 6 is supplied to the high-pressure stage center housing 72 of the high-pressure stage supercharger 51 through the high-pressure lubricating oil supply pipe 73, and is also supplied to the low-pressure stage center housing 75 of the low-pressure stage supercharger 52 through the high-pressure lubricating oil supply pipe 73 and the low-pressure lubricating oil supply pipe 76.

[0057] The high-pressure lubricating oil supply pipe 73 is led obliquely upward rearward from the connecting member 78a on the left side surface of the cylinder block 6, and is led to a position facing the left side surface of the cylinder head 2 through between the high-pressure stage compressor case 54 and the cylinder block 6. Further, the high-pressure lubricating oil supply pipe 73 is led to the connecting joint 78b while bypassing the rear end portion of the exhaust manifold 4 and passing through the right side of the high-pressure stage center housing 72. Also, the low-pressure lubricating oil supply pipe 76 has a substantially L shape in side view, and is led from the connecting joint 78b along the high-pressure stage supercharger 51 and the high-pressure exhaust gas pipe 59 to the connecting member 78c. In this way, by shortening the lubricating oil supply pipes 73 and 76 and arranging them so as to be surrounded by the two-stage supercharger 30 which is a high-rigidity component, lubricating oil can be efficiently supplied to the two-stage supercharger 30, and at the same time, breakage of the lubricating oil supply pipes 73 and 76 due to external force can be prevented.

[0058] Also, one end (lower end) of the high-pressure lubricating oil return pipe 74 is connected to the tip surface of the connecting joint 80 installed at the center of the left side surface of the cylinder block 6 above the connecting member 78a. The other end (upper end) of the high-pressure lubricating oil return pipe 74 is connected to the lower part of the outer peripheral surface of the high-pressure stage center housing 72 of the high-pressure stage supercharger 51. Also, one end (lower end) of the low-pressure lubricating oil return pipe 77 is connected to a connecting portion protruding obliquely upward forward from the middle part of the connecting joint 80. On the other hand, the other end (upper end) of the low-pressure lubricating oil return pipe 77 is connected to the lower part of the outer peripheral surface of the low-pressure stage center housing 75 of the low-pressure stage supercharger 52. Therefore, the lubricating oil flowing through the high-pressure stage supercharger 51 and the low-pressure stage supercharger 52 merges at the connecting joint 80 through the lubricating oil return pipes 74 and 77 from the lower parts of the center housings 72 and 75, and is returned to the oil passage in the cylinder block 6.

[0059] The high-pressure lubricating oil return pipe 74 is led to the connecting joint 80 through below the exhaust manifold exhaust outlet 49 of the exhaust manifold 4 from below the high-pressure stage turbine case 53. Further, the low-pressure operation return pipe 77 is led to the connecting joint 80 through between the high-pressure exhaust gas pipe 59 and the exhaust manifold 4. In this way, by shortening the lubricating oil return pipes 74 and 77 and arranging them so as to be covered by the two-stage supercharger 30 which is a high-rigidity component, the lubricating oil can be efficiently supplied to the two-stage supercharger 30, and at the same time, breakage of the lubricating oil return pipes 74 and 77 due to external force can be prevented.

[0060] Next, with reference to FIGS. 11 to 16 and the like, the mounting structure of the exhaust gas purification device 100 will be described. The exhaust gas purification device 100 is configured by connecting an upstream case 105, an intermediate case 106, and a downstream case 107 in series in that order, and is arranged horizontally and longitudinally above the front part of the cylinder head 2.

[0061] The connecting portion between the upstream case 105 and the intermediate case 106 is connected by sandwiching from both sides in the exhaust gas moving direction with a pair of thick plate-shaped clamping flanges 108 and 109. That is, the joining flange provided at the downstream opening edge of the upstream case 105 and the joining flange provided at the upstream opening edge of the intermediate case 106 are clamped by the clamping flanges 108 and 109, and the downstream side of the upstream case 105 and the upstream side of the intermediate case 106 are connected to constitute the gas purification housing 104. At this time, by bolt-fastening the clamping flanges 108 and 109, the upstream case 105 and the intermediate case 106 are detachably connected.

[0062] Also, the connecting portion between the intermediate case 106 and the downstream case 107 is connected by sandwiching from both sides in the exhaust gas moving direction with a pair of thick plate-shaped clamping flanges 110 and 111. That is, the joining flange provided at the downstream opening edge of the intermediate case 106 and the joining flange provided at the upstream opening edge of the downstream case 107 are clamped by the clamping flanges 108 and 109, and the downstream side of the intermediate case 106 and the upstream side of the downstream case 107 are detachably connected.

[0063] An exhaust gas inlet pipe 116 is provided at the outer peripheral portion on the exhaust inlet side of the upstream case 105. The exhaust intake side of the exhaust gas inlet pipe 116 communicates with the low-pressure stage exhaust outlet 61 (see Fig. 6 etc.) of the two-stage supercharger 30 via an exhaust connection member 120 and an exhaust connection pipe 119 serving as an exhaust relay path. The exhaust connection member 120 is configured in a substantially L shape in side view. While having the exhaust intake side at the rear and being connected to the exhaust connection pipe 119, it has the exhaust discharge side at the upper side and is connected to the exhaust gas inlet pipe 116 of the exhaust gas purification device 100. As shown in Figs. 11, 12, and 16, the exhaust connection member 120 is detachably attached to the front portion of the left side surface of the support base 121 by a pair of upper and lower bolts 122, 122.

[0064] As shown in Figs. 11 and 15, the exhaust gas purification device 100 is attached to the front portion of the cylinder head 2 via left and right support brackets 117, 118 and a support base 121. The exhaust gas purification device 100 includes a left bracket fastening leg 112 welded and fixed to the lower portion of the outer peripheral surface of the upstream casing 105, and a right bracket fastening leg 113 formed at the lower portion of the clamping flange 110.

[0065] The left and right support brackets 117, 118 have a substantially L shape including a horizontal portion and upright portions protruding upward from the left and right outer ends of the horizontal portion. The horizontal portion of the left support bracket 117 is fixed to the upper left-side portion of the upper surface of the flat portion 121a of the support base 121 by a pair of front and rear bolts. The horizontal portion of the right support bracket 118 is fixed to the upper right-edge portion of the upper surface of the flat portion 121a of the support base 121 by a pair of front and rear bolts. The left and right bracket fastening legs 112, 113 of the exhaust gas purification device 100 are attached to the left and right support brackets 117, 118 respectively by a pair of front and rear bolts and nuts.

[0066] On the upper surface of the standing portion of the right support bracket 118, a notch portion 118a is formed that can temporarily hold the heads of the bolts for fastening the lower portions of the clamping flanges 110 and 111. When assembling the exhaust gas purification device 100 to the engine 1, with the left and right support brackets 117 and 118 and the exhaust connection member 120 attached to the support base 121, the heads of the bolts for fastening the lower portions of the clamping flanges 110 and 111 are aligned with the notch portion 118a of the right support bracket 118. As a result, the exhaust gas purification device 100 can be aligned with the engine device 1, and the bolt fastening operation when assembling the exhaust gas purification device 100 to the engine 1 becomes easier, improving the assembly workability.

[0067] As shown in FIGS. 11 to 16, the flat portion 121a of the support base 121 has a substantially L shape in plan view where the right portion is longer than the left portion. The flat portion 121a is arranged in plan view so as to cover the front portion of the cylinder head 2 along the front side surface and the right side surface of the cylinder head 2. The exhaust gas purification device 100 is mounted on the flat portion 121a.

[0068] Further, the support base 121 includes a plurality of leg portions 121b, 121c, 121d, and 121e that project downward from the flat portion 121a and are fixed to the cylinder head 2. Between the leg portions 121b, 121c, 121d, and 121e, it is formed in a convex arch shape on the upper side. On the cylinder head 2, an exhaust side attachment portion 123b is provided at the front portion of the left side surface, a first central attachment portion 123c is provided at a position above the center of the front side surface, a second central attachment portion 123d is provided at the right edge portion of the front side surface, and an intake side attachment portion 123e is provided at the front end portion of the upper surface of the intake manifold 3 integrally formed on the right side surface.

[0069] The lower end of the exhaust-side leg portion 121b is fixed to the exhaust-side mounting portion 123b by a pair of front and rear bolts. The lower end of the first central leg portion 121c is fixed to the first central mounting portion 123c by one bolt. The lower portion of the second central leg portion 121d is fixed to the second central mounting portion 123d by a pair of upper and lower bolts. The intake-side leg portion 121e is provided with a pair of front and rear bolt insertion holes drilled in the vertical direction, and is attached to the intake-side mounting portion 123e by a pair of front and rear bolts inserted through these bolt insertion holes.

[0070] As shown in FIGS. 11, 13 to 15, and 21, an intake manifold 3 is integrally formed on the right side surface of the cylinder head 2. And since the intake-side leg portion 121e is fixed to the intake-side mounting portion 123e provided on the intake manifold 3, the intake-side leg portion 121e can be placed and firmly fixed on the robust intake manifold 3. Also, the tightening and loosening operations of a pair of front and rear bolts for fixing the intake-side leg portion 121e to the intake manifold 3 can be performed from the upper side of the cylinder head 2. Therefore, for example, with the EGR device 24 (see FIG. 5 etc.) arranged on the right side of the cylinder head 2 attached to the intake manifold 3, the attachment and removal operations of the support base 121 can be carried out, improving the assembly workability and maintainability of the engine 1.

[0071] As shown in FIGS. 11, 13, and 15, a pair of front and rear reinforcing ribs 124, 124 project from the right side surface and the lower surface of the intake manifold 3 below the intake-side mounting portion 123e. The reinforcing ribs 124, 124 extend in the vertical direction and can improve the strength of the intake manifold 3 around the intake-side mounting portion 123e. Thereby, deformation of the intake manifold 3 and the cylinder head 2 caused by the attachment of the support base 121 to the intake manifold 3 can be prevented.

[0072] As shown in FIGS. 11 to 16, while the support base 121 has a flat portion 121a and leg portions 121b, 121c, 121d, 121e integrally formed, and an arch shape is formed between the leg portions 121b, 121c, 121d, 121e, weight reduction can be achieved while ensuring the rigidity of the support base 121. Further, by making the support base 121 an integrally formed part, the number of parts can be reduced. Further, since an arch-shaped gap is formed between the leg portions 121b, 121c, 121d, 121e, it is possible to prevent the formation of heat accumulation around the leg portions 121b, 121c, 121d, 121e. Thereby, for example, heat damage to electronic components mounted around the leg portions such as the exhaust pressure sensor 151 described later and insufficient cooling of cooling components such as the EGR cooler 27 can be prevented.

[0073] Further, the support base 121 includes an exhaust-side leg portion 121b fixed to the left side surface of the cylinder head 2, an intake-side leg portion 121e fixed to the right side surface of the cylinder head 2, and central leg portions 121c, 121d fixed to the front side surface of the cylinder head 2. Therefore, the support base 121 can be fixed to a total of three surfaces, i.e., the right side surface, the left side surface, and the front side surface of the cylinder head 2, and the support rigidity of the exhaust gas purification device 100 can be improved.

[0074] As shown in FIGS. 11, 13, and 15, the arch shape between the intake-side leg portion 121e and the second central leg portion 121d, the arch shape between the central leg portions 121c, 121d, and the arch shape between the exhaust-side leg portion 121b and the first central leg portion 121c have different arch heights and sizes (widths). Further, the exhaust-side leg portion 121b and the intake-side leg portion 121e have different lengths in the vertical direction. By appropriately designing these arch shapes and the lengths of the leg portions, it becomes possible to cancel out the vibrations on the intake side and the exhaust side with the support base 121, and the vibration of the exhaust gas purification device 100 can be reduced.

[0075] As shown in FIGS. 11 and 16, the flat portion 121a and the leg portions 121b, 121c, 121d, 121e of the support base 121 are arranged at intervals from the cylinder head cover 18. Thereby, a cooling air passage 148 is formed between the support base 121 and the cylinder head cover 18, through which the cooling air 149 from the cooling fan 9 (see FIG. 3 etc.) arranged at the rear portion of the engine 1 flows. Therefore, the cooling air 149 from the cooling fan 9 can be guided to the front side surface side of the cylinder head 2 through the cooling air passage 148, and the periphery of the front side surface of the cylinder head 2 can be appropriately cooled. In this embodiment, since the EGR cooler 27 and the exhaust pressure sensor 151 described later are attached to the front side surface of the cylinder head 2, the cooling of the EGR cooler 27 is promoted and the heat damage to the exhaust pressure sensor 151 can be prevented by the cooling air 149 guided to the front side surface of the cylinder head 2 from the cooling fan 9 through the cooling air passage 148.

[0076] Next, referring to FIGS. 17 to 21 etc., the configuration around the front side surface of the cylinder head 2 will be described. As shown in FIG. 21, the cylinder head 2 is formed with a plurality of intake passages 36 for introducing fresh air into a plurality of intake ports (not shown) and a plurality of exhaust passages 37 for leading out exhaust gas from a plurality of exhaust ports. And an intake manifold 3 that aggregates the plurality of intake passages 36 is integrally formed on the right side portion of the cylinder head 2. By integrally configuring the cylinder head 2 and the intake manifold 3, the gas sealability of the intake manifold 3 with respect to the intake passage 36 can be improved, and the rigidity of the cylinder head 2 can be enhanced.

[0077] On the right side surface of the exhaust manifold 4 connected to the left side surface of the cylinder head 2, an EGR gas outlet 41 communicating with the upstream EGR gas passage 31 in the cylinder head 2 and an exhaust inlet 42 communicating with a plurality of exhaust passages 37 are opened side by side in the front-rear direction. An exhaust collecting portion 43 communicating with the EGR gas outlet 41 and the exhaust inlet 42 is formed in the exhaust manifold 4. An exhaust manifold exhaust outlet 49 communicating with the exhaust collecting portion 43 is opened at the rear part of the left side surface of the exhaust manifold 4. When the exhaust gas from the exhaust passage 37 of the cylinder head 2 flows into the exhaust collecting portion 43 through the exhaust inlet 42, a part of the exhaust gas flows into the upstream EGR gas passage 31 in the cylinder head 2 as EGR gas from the EGR gas outlet 41, and the rest of the exhaust gas flows into the two-stage supercharger 30 (see FIG. 7 etc.) from the exhaust manifold exhaust outlet 49.

[0078] The cylinder head 2 has an exhaust manifold 4 connected to the left side surface (exhaust side surface) opposite to the right side surface (intake side surface) where the intake manifold 3 is integrally formed, and an EGR cooler 27 is connected to the front side surface (one of the two side surfaces intersecting the exhaust side surface). On the left and right edge portions of the front side surface of the cylinder head 2 (the left front corner portion and the right front corner portion of the cylinder head 2), left and right EGR cooler connecting portions 33, 34 project forward. The EGR cooler 27 is connected to the front side surfaces of the left and right EGR cooler connecting portions 33, 34. EGR gas passages 31, 32 and cooling water passages 38, 39 are formed in the EGR cooler connecting portions 33, 34.

[0079] By configuring the EGR gas passages 31, 32 and the cooling water passages 38, 39 in the EGR cooler connecting portions 33, 34, it is not necessary to provide pipes for cooling water and pipes for EGR gas between the EGR cooler 27 and the cylinder head 2. Therefore, not only can the sealing performance at the connecting portion with the EGR cooler 27 be ensured without being affected by the expansion and contraction of the pipes due to EGR gas or cooling water, etc., but also the resistance (structural stability) to external variable factors such as heat and vibration is improved, and it can be configured compactly.

[0080] As shown in FIGS. 17, 20, and 21, an upstream EGR gas passage 31 is provided in the left EGR cooler connection portion 33, and a downstream EGR gas passage 32 is provided in the right EGR cooler connection portion 34. The upstream EGR gas passage 31 is substantially L-shaped in plan view, with one end and the other end opening to the front surface and the left side surface of the left EGR cooler connection portion 33, connecting the lower left part of the back surface of the EGR cooler 27 and the EGR gas outlet 41 provided at a position near the front of the right side surface of the exhaust manifold 4. The downstream EGR gas passage 32 is substantially L-shaped in plan view, with one end and the other end opening to the front surface and the right side surface of the right EGR cooler connection portion 34, connecting the upper right part of the back surface of the EGR cooler 27 and the EGR gas inlet of the recirculation exhaust gas pipe 28.

[0081] In the left EGR cooler connection portion 33, a downstream cooling water passage 38 led from the front surface of the left EGR cooler connection portion 33 to the rear side is formed. The downstream cooling water passage 38 is provided above the upstream EGR gas passage 31, and sends the cooling water discharged from the upper left part of the back surface of the EGR cooler 27 to the cooling water passage in the cylinder head 2. Further, in the right EGR cooler connection portion 34, an upstream cooling water passage 39 led from the front surface of the right EGR cooler connection portion 34 to the rear side is formed. The upstream cooling water passage 39 is provided below the downstream EGR gas passage 32, and sends the cooling water flowing through the cooling water passage in the cylinder head 2 to the lower right part of the back surface of the EGR cooler 27.

[0082] As shown in FIGS. 17 to 20, an exhaust pressure sensor 151 for detecting the exhaust gas pressure in the exhaust manifold 4 is provided on the front surface of the cylinder head 2. The exhaust pressure sensor 151 is attached to an exhaust pressure sensor attachment portion 152 that protrudes forward at a position above the center of the front surface of the cylinder head 2. The exhaust pressure sensor attachment portion 152 is provided between the left and right EGR cooler connection portions 33, 34. In the engine 1 of this embodiment, the left edge portion of the exhaust pressure sensor attachment portion 152 is continuously formed at a position above the right edge portion of the left EGR cooler connection portion 33.

[0083] The exhaust pressure sensor 151 is connected to the exhaust manifold 4 via an exhaust pressure bypass passage 153 provided in the cylinder head 2 and an exhaust pressure detection pipe 154 that connects the exhaust pressure bypass passage 153 and the exhaust manifold 4. The exhaust pressure bypass passage 153 is drilled from the front end portion of the left side surface of the cylinder head 2 toward the right side, and is guided into the inside of the exhaust pressure sensor mounting portion 152 through the inside of the left EGR cooler connection portion 33. Further, the exhaust pressure bypass passage 153 is bent forward in the exhaust pressure sensor mounting portion 152 and opens to the front side surface of the exhaust pressure sensor mounting portion 152. A hole filling member 155 that closes the end portion of the exhaust pressure bypass passage 153 is attached to the front side surface of the exhaust pressure sensor mounting portion 152.

[0084] As shown in FIG. 18, the exhaust pressure sensor mounting portion 152 includes a sensor mounting hole 152a that is drilled downward from its upper surface and leads to the exhaust pressure bypass passage 153. With the exhaust pressure sensor 151 attached to the sensor mounting hole 152a, the lower end portion of the exhaust pressure sensor 151 is exposed to the exhaust pressure bypass passage 153.

[0085] On the other hand, the exhaust pressure detection pipe 154 is disposed above the exhaust manifold 4 on the left side of the front part of the left side surface of the cylinder head 2. A detection pipe mounting pedestal 156 projects upward at a frontward position on the upper surface of the exhaust manifold 4. A rear joint member 157 is attached to the upper surface of the detection pipe mounting pedestal 156. Further, a front joint member 158 is attached to the end portion of the exhaust pressure bypass passage 153 that opens at the front end portion of the left side surface of the cylinder head 2. The front end of the exhaust pressure detection pipe 154 is connected to the exhaust pressure bypass passage 153 via the front joint member 158. The rear end of the exhaust pressure detection pipe 154 is connected to an exhaust gas collecting portion 43 (see FIG. 21) in the exhaust manifold 4 via the rear joint member 157. Note that an exhaust gas temperature sensor 159 is attached to the upper surface of the detection pipe mounting pedestal 156 at a position in front of the rear joint member 157. The exhaust gas temperature sensor 159 detects the temperature of the exhaust gas flowing through the exhaust gas collecting portion 43 in the exhaust manifold 4.

[0086] The heat transmitted from the exhaust manifold 4, which becomes hot, to the exhaust pressure detection pipe 154 is diffused by the cylinder head 2 via the front joint member 158. As a result, the heat of the exhaust manifold 4 and the heat of the exhaust pressure detection pipe 154 do not directly reach the exhaust pressure sensor 151, which is vulnerable to heat. Therefore, while preventing malfunctions and misoperations of the exhaust pressure sensor 151 caused by the heat of the exhaust manifold 4 and the exhaust pressure detection pipe 154, the length of the exhaust pressure detection pipe 154 can be shortened. Further, by shortening the length of the exhaust pressure detection pipe 154, the reliability of the exhaust pressure detection pipe 154 is improved, the arrangement of the exhaust pressure detection pipe 154 becomes easy, and the design man-hours can be reduced, and the manufacturability and assemblability of the engine 1 can be improved.

[0087] As shown in FIGS. 17 and 20, since the downstream cooling water passage 38 is provided in the left EGR cooler connection portion 33 in the vicinity of the exhaust pressure bypass passage 153, the gas temperature in the exhaust pressure bypass passage 153 can be efficiently reduced. Therefore, the exhaust pressure bypass passage 153 can be shortened while keeping the heat transmitted from the gas in the exhaust pressure bypass passage 153 to the exhaust pressure sensor 151 within an allowable range, and the formation of the exhaust pressure bypass passage 153 to the cylinder head 2 becomes easy. Further, since the exhaust pressure bypass passage 153 passes through the inside of the left EGR cooler connection portion 33 and the exhaust pressure sensor mounting portion 152 protruding from the front surface of the cylinder head 2, the gas in the exhaust pressure bypass passage 153 can be efficiently cooled, and malfunctions and misoperations of the exhaust pressure sensor 151 caused by heat can be prevented. Furthermore, since the exhaust pressure sensor 151 is attached to the exhaust pressure sensor mounting portion 152 protruding from the front surface of the cylinder head 2 between the pair of EGR cooler connection portions 33, 34, the exhaust pressure sensor 151 can be efficiently cooled, and malfunctions and misoperations of the exhaust pressure sensor 151 caused by heat can be prevented.

[0088] Also, as shown in Fig. 19, the mounting position of the front joint member 158 is provided at a position higher than the upper surface of the detection pipe mounting pedestal 156. The exhaust pressure detection pipe 154 extends obliquely forward to the left from the rear joint member 157, then bypasses the exhaust gas temperature sensor 159 and is guided obliquely upward while curving to the right, and then is disposed substantially horizontally forward along the left side surface of the cylinder head 2 and connected to the front joint member 158. The end of the exhaust pressure detection pipe 154 on the front joint member 158 side is disposed at a position higher than the end on the rear joint member 157 side. Therefore, it is possible to prevent oil and moisture contained in the exhaust gas from becoming liquid in the exhaust pressure detection pipe 154 and entering the exhaust pressure bypass path 153, and accurately detect the exhaust gas pressure.

[0089] As shown in Figs. 17 to 21, by adopting a configuration in which the EGR cooler connecting portions 33 and 34 project, the pipes for EGR gas that communicate the exhaust manifold 4, the EGR cooler 27, and the EGR device 24 become unnecessary, and the number of connection points in the EGR gas passage is reduced. Therefore, in the engine 1 for reducing NOx by EGR gas, not only can EGR gas leakage be reduced, but also deformation due to stress changes caused by the expansion and contraction of the pipes can be suppressed. Further, since the EGR gas passages 31 and 32 and the cooling water passages 38 and 39 are formed in the EGR cooler connecting portions 33 and 34, the shapes of the respective passages 31, 32, 38, and 39 formed in the cylinder head 2 are simplified, so that the cylinder head 2 can be easily cast without using complicated cores.

[0090] In addition, since the left EGR cooler connection part 33 on the exhaust manifold 4 side and the right EGR cooler connection part 34 on the intake manifold 3 side are separated from each other, the mutual influence due to thermal deformation in each of the EGR cooler connection parts 33 and 34 can be suppressed. Therefore, not only can gas leakage, cooling water leakage, breakage, etc. at the connection part between the EGR cooler connection parts 33 and 34 and the EGR cooler 27 be prevented, but also the rigidity balance of the cylinder head 2 can be maintained. Further, since the volume on the front side surface of the cylinder head 2 can be reduced, the cylinder head 2 can be made lighter. Furthermore, since the EGR cooler 27 can be arranged separated from the front side surface of the cylinder head 2 and a configuration with a space in front of and behind the EGR cooler 27 can be achieved, cooling air can flow around the EGR cooler 27, and the cooling efficiency of the EGR cooler 27 can be enhanced.

[0091] As shown in FIG. 17, in the left EGR cooler connection part 33, the downstream cooling water passage 38 and the upstream EGR gas passage 31 are arranged vertically, and in the right EGR cooler connection part 34, the downstream EGR gas passage 32 and the upstream cooling water passage 39 are arranged vertically. And while the cooling water inlet of the downstream cooling water passage 38 and the EGR gas inlet of the downstream EGR gas passage 32 are arranged at the same height, the cooling water outlet of the upstream cooling water passage 39 and the EGR gas outlet of the downstream EGR gas passage 32 are arranged at the same height.

[0092] By adopting a configuration in which the EGR gas passages 31 and 32 and the cooling water passages 38 and 39 are provided inside the EGR cooler connection parts 33 and 34 that are separated and protruded, the influence of thermal deformation in both of the EGR cooler connection parts 33 and 34 is alleviated. Also, inside the EGR cooler connection parts 33 and 34, the EGR gas flowing through the EGR gas passages 31 and 32 is cooled by the cooling water flowing through the cooling water passages 38 and 39, and the thermal deformation itself in the EGR cooler connection parts 33 and 34 is also suppressed. Further, in each of the EGR cooler connection parts 33 and 34, the EGR gas passages 31 and 32 and the cooling water passages 38 and 39 are arranged by replacing their respective vertical height positions. Therefore, the thermal distribution in the EGR cooler connection parts 33 and 34 becomes in the vertically reverse direction, and the influence of thermal deformation in the height direction of the cylinder head 2 can be reduced.

[0093] Next, with reference to FIGS. 22 and 23 and the like, a part of the harness structure disposed around the front side surface of the cylinder head 2 will be described. In the engine 1 of this embodiment, a harness assembly 171 in which a plurality of harnesses are bundled is disposed in the front-rear direction along the right side surface of the cylinder head cover 18. The harness assembly 171 is branched from a main harness assembly (not shown) extending from an external connection harness connector (not shown) attached to the engine 1.

[0094] The front end portion of the harness assembly 171 is disposed between the cylinder head cover 18 and the intake side leg portion 121e of the support base 121. The harness assembly 171 branches into an EGR valve harness 172, an EGR gas temperature sensor harness 173, and a sensor harness assembly 174 in the vicinity of the right front corner portion of the cylinder head cover 18. The EGR valve harness 172 is electrically connected to the EGR valve member 29 through between the second central leg portion 121d and the intake side leg portion 121e of the support base 121. The EGR gas temperature sensor harness 173 is electrically connected to an EGR gas temperature sensor 181 that detects the exhaust gas temperature in the recirculation exhaust gas pipe 28 through between the second central leg portion 121d and the intake side leg portion 121e.

[0095] The sensor harness assembly 174 is led from the harness assembly 171 toward the left side, and is bent downward in front of a position on the right side of the front side surface of the cylinder head cover 18. The front end portion of the sensor harness assembly 174 branches into a rotation angle sensor harness assembly 175 and an exhaust pressure sensor harness 176. The exhaust pressure sensor harness 176 is led from the harness assembly 174 to the left side through between the cylinder head cover 18 and the first central leg portion 121c of the support base 121, and is electrically connected to the exhaust pressure sensor 151.

[0096] The rotational angle sensor harness assembly 175 extends downward along the front side surface of the cylinder head 2 from the sensor harness assembly 174. Further, the rotational angle sensor harness assembly 175 is bent leftward at a position directly above the flywheel housing 7 and guided to a position in front of the lower left corner portion of the front side surface of the cylinder head 2. The rotational angle sensor harness assembly 175 branches into a crankshaft rotational angle sensor harness 177 and a camshaft rotational angle sensor harness 178. The crankshaft rotational angle sensor harness 177 is electrically connected to a crankshaft rotational angle sensor 182 (see FIG. 1) attached to an upper left-side portion of the front part of the flywheel housing 7. The camshaft rotational angle sensor harness 178 is electrically connected to a camshaft rotational angle sensor 183 (see FIG. 1) attached to the upper left edge of the flywheel housing 7.

[0097] As shown in FIG. 17, locking member attachment portions 185 and 186 arranged vertically are formed at the left and right center portions of the front side surface of the cylinder head 2. The upper locking member attachment portion 185 is disposed at an upper portion of the front side surface of the cylinder head 2 and at a position between the right EGR cooler connection portion 34 and the first central attachment portion 123c. The lower locking member attachment portion 186 is disposed at a lower portion of the front side surface of the cylinder head 2 and directly below the upper locking member attachment portion 185 between the left and right EGR cooler connection portions 33 and 34.

[0098] As shown in FIGS. 22 and 23, the rotational angle sensor harness assembly 175 at a portion facing the front side surface of the cylinder head 2 is attached to the front side surface of the cylinder head 2 by locking members 187 and 188 attached to the upper and lower locking member attachment portions 185 and 186. Then, the rotational angle sensor harness assembly 175 is guided from the harness assembly 174 through a space between the right EGR cooler connection portion 34 and the first central leg portion 121c of the support base 121 and through a space between the cylinder head 2 and the EGR cooler 27 to a position facing the lower edge portion of the front side surface of the cylinder head 2.

[0099] The EGR cooler 27 is attached to a pair of left and right EGR cooler connecting parts 33 and 34 that project forward on the front side surface of the cylinder head 2. And a space is formed between the back surface of the EGR cooler 27 and the cylinder head 2. By arranging the rotation angle sensor harness assembly 175 in the vertical direction in this space, the rotation angle sensor harness assembly 175 can be protected and the layout design of the rotation angle sensor harness assembly 175 becomes easy.

[0100] Also, a space is formed between the side surface of the cylinder head cover 18 and the support base 121. By arranging the harness assemblies 171 and 174 and the harnesses 172, 173, and 176 using this space, these harnesses and harness assemblies can be protected and the layout design of the harness becomes easy.

[0101] As shown in FIGS. 1 to 10, the engine 1 includes an exhaust manifold 4 provided on the exhaust side surface (for example, the left side surface) which is one side surface of the cylinder head 2, and a two-stage supercharger 30 driven by the exhaust gas discharged from the exhaust manifold 4. The two-stage supercharger 30 is composed of a high-pressure stage supercharger 51 connected to the exhaust manifold 4 and a low-pressure stage supercharger 52 connected to the high-pressure stage supercharger 51. Since the high-pressure stage supercharger 51 is arranged on the side of the exhaust manifold 4 and the low-pressure stage supercharger 52 is arranged above the exhaust manifold 4, the exhaust manifold 4 and the two-stage supercharger 30 can be compactly arranged within a substantially square frame, and miniaturization of the engine 1 can be achieved. Further, since the high-pressure stage exhaust outlet 58 of the high-pressure stage supercharger 51 and the low-pressure stage exhaust inlet 60 of the low-pressure stage supercharger 52 are connected via a high-pressure exhaust gas pipe 59 which is an example of a flexible pipe, the risk of low-cycle fatigue failure of the high-pressure exhaust gas pipe 59 due to thermal expansion can be reduced.

[0102] In the engine 1, since the low-pressure stage supercharger 52 is fixed to the exhaust side surface of the cylinder head 2 and the high-pressure stage supercharger 51 is fixed to the exhaust manifold 4, the high-pressure stage supercharger 51 and the low-pressure stage supercharger 52 that constitute the two-stage supercharger 30 can be distributed and firmly fixed to the robust cylinder head 2 and the exhaust manifold 4. Further, since the high-pressure stage exhaust outlet 58 of the high-pressure stage supercharger 51 and the low-pressure stage exhaust inlet 60 of the low-pressure stage supercharger 52 are connected via the flexible high-pressure exhaust gas pipe 59, the stress applied to the two-stage supercharger 30 due to the thermal expansion of the high-pressure exhaust gas pipe 59 can be reduced. Thereby, the stress applied to the connection part between the high-pressure stage supercharger 51 and the exhaust manifold 4 and the stress applied to the connection part between the low-pressure stage supercharger 52 and the cylinder head 2 can be reduced, and connection failure and breakage of the connection member at these connection parts can be prevented.

[0103] Furthermore, the cylinder head 2 is provided with a rib 135 extending from the low-pressure stage supercharger mounting portion 131 on the exhaust side surface to the intake side surface (for example, the right side surface) facing the exhaust side surface inside the cylinder head 2. Therefore, the rigidity around the low-pressure stage supercharger mounting portion 131 in the cylinder head 2 can be improved, and deformation of the cylinder head 2 caused by the attachment of the low-pressure stage supercharger 52 to the cylinder head 2 can be prevented.

[0104] The engine 1 further includes an exhaust gas purification device 100 for purifying the exhaust gas from the engine 1. The exhaust gas inlet pipe 116 as the exhaust inlet of the exhaust gas purification device 100 is arranged near the corner where one of the two side surfaces of the cylinder head 2 intersecting the exhaust side surface and the exhaust side surface intersect. The low-pressure stage supercharger 52 is arranged closer to the one side surface as viewed from the exhaust side surface side, and the low-pressure stage exhaust outlet 61 of the low-pressure stage supercharger 52 is provided toward the one side surface side. Therefore, the engine 1 can shorten and simplify the exhaust connection pipe 119 and the exhaust connection member 120 as an example of the pipe connecting the low-pressure stage exhaust outlet 61 of the low-pressure stage supercharger 52 and the exhaust gas inlet pipe 116 of the exhaust gas purification device 100. Thereby, the exhaust gas supplied to the exhaust gas purification device 100 can be maintained at a high temperature, and a decrease in the regeneration ability of the exhaust gas purification device 100 can be prevented.

[0105] Furthermore, above the cylinder head 2, the blow-by gas outlet 70 of the blow-by gas reduction device 19 is arranged toward the exhaust side surface at a position closer to the other side surface of the cylinder head 2, which is opposite to the one side surface, and the low-pressure stage fresh air inlet 63 of the low-pressure stage supercharger 52 is provided toward the other side surface side. Also, the blow-by gas outlet 70 is connected to the air supply pipe 62 connected to the low-pressure stage fresh air inlet 63 of the low-pressure stage supercharger 52 via a reduction hose 68. Therefore, the engine 1 can shorten the reduction hose 68 by arranging both the blow-by gas outlet 70 of the blow-by gas reduction device 19 and the air supply pipe 62 connected to the low-pressure stage fresh air inlet 63 of the low-pressure stage supercharger 52 at positions closer to the other side surface of the cylinder head 2, and the freezing countermeasure inside the reduction hose 68 becomes unnecessary.

[0106] As shown in FIGS. 1 to 5 and FIGS. 11 to 16, the engine 1 includes an exhaust gas purification device 100 via a support base 121 above the cylinder head 2. The support base 121 includes a flat portion 121a on which the exhaust gas purification device 100 is mounted, and a plurality of legs 121b, 121c, 121d, 121e that project downward from the flat portion 121a and are fixed to the cylinder head 2. The flat portion 121a and the legs 121b, 121c, 121d, 121e are integrally formed. Also, an arch shape is formed between the legs 121b, 121c, 121d, 121e. Therefore, due to the above-described integral molding structure and arch shape, weight reduction can be achieved while ensuring the rigidity of the support base 121. Also, by using the support base 121 as an integrally molded part, the number of parts can be reduced. Further, since an arch-shaped gap is formed between the plurality of legs 121b, 121c, 121d, 121e, it is possible to prevent heat accumulation from occurring around the legs of the support base 121, and for example, heat damage to electronic components such as an exhaust pressure sensor 151, which is an example of a sensor mounted around the legs, and insufficient cooling of cooling components such as the EGR cooler 27 can be prevented.

[0107] The engine 1 is configured such that the exhaust manifold 4 and the intake manifold 3 are distributively arranged on the exhaust side surface and the intake side surface of the cylinder head 2 facing each other. The support base 121 is arranged above one of the two side surfaces of the cylinder head 2 that intersects the axial direction of the crankshaft 5, and includes an exhaust side leg portion 121b fixed to the exhaust side surface, an intake side leg portion 121e fixed to the intake side surface, and central leg portions 121c and 121d fixed to the one side surface as leg portions. Therefore, the engine 1 can fix the support base 121 to a total of three surfaces, namely, the exhaust side surface, the intake side surface, and the one side surface of the cylinder head 2, and can improve the support rigidity of the exhaust gas purification device 100. Further, by making the heights and sizes of the two arch shapes different between the exhaust side leg portion 121b and the first central leg portion 121c and between the intake side leg portion 121e and the second central leg portion 121d, or by making the lengths of the exhaust side leg portion 121b and the intake side leg portion 121e different, it becomes possible to cancel out the vibrations on the intake side and the exhaust side with the support base 121, and the vibration of the exhaust gas purification device 100 can be reduced.

[0108] Also, the engine 1 is configured to include a cooling fan 9 on the other side surface side of the two side surfaces of the cylinder head 2. And a cooling air passage 148 through which the cooling air 149 from the cooling fan 9 flows is formed between the cylinder head cover 18 and the support base 121 on the cylinder head 2. Therefore, the engine 1 can guide the cooling air from the cooling fan 9 to the one side surface side of the cylinder head 2 via the cooling air passage 148, and can appropriately cool the periphery of the one side surface of the cylinder head 2.

[0109] Furthermore, the engine 1 is configured to include an EGR device 24 that returns a part of the exhaust gas discharged from the exhaust manifold 4 to the intake manifold 3 as EGR gas, an EGR cooler 27 that cools the EGR gas, and an exhaust pressure sensor 151 that detects the exhaust gas pressure in the exhaust manifold 4. The EGR cooler 27 and the exhaust pressure sensor 151 are attached to the one side surface of the cylinder head 2. Therefore, the cooling of the EGR cooler 27 and the prevention of heat damage to the exhaust pressure sensor 151 can be realized by the cooling air 149 guided to the one side surface via the cooling air passage 148 from the cooling fan 9.

[0110] In the engine 1, an intake manifold 3 is integrally formed on the intake side surface of the cylinder head 2, and the intake side leg portion 121e is fixed to the upper surface of the intake manifold 3. Thus, the intake side leg portion 121e can be placed on the robust intake manifold 3 and firmly fixed. Further, since the tightening and loosening operation of the bolts for fixing the intake side leg portion 121e to the intake manifold 3 can be performed from the upper side of the cylinder head 2, the attachment and removal operations of the support base 121 can be carried out with the EGR device 24 disposed on the side of the intake side surface of the cylinder head 2 attached to the intake manifold 3, improving the assembly workability and maintainability of the engine 1.

[0111] As shown in FIGS. 1 to 5 and FIGS. 17 to 21, the engine 1 includes an exhaust manifold 4 provided on the exhaust side surface of the cylinder head 2, and an exhaust pressure sensor 151 for detecting the exhaust gas pressure in the exhaust manifold 4. The exhaust pressure sensor 151 is attached to the cylinder head 2, and the exhaust manifold 4 and the exhaust pressure sensor 151 are connected via an exhaust pressure bypass passage 153 provided in the cylinder head 2 and an exhaust pressure detection pipe 154 connecting the exhaust pressure bypass passage 153 and the exhaust manifold 4. Therefore, the heat of the exhaust pressure detection pipe 154 can be diffused by the cylinder head 2. Accordingly, the engine 1 can prevent the failure and malfunction of the exhaust pressure sensor 151 caused by the heat of the exhaust manifold 4 and the exhaust pressure detection pipe 154, and can shorten the length of the exhaust pressure detection pipe 154. Further, by shortening the length of the exhaust pressure detection pipe 154, the reliability of the exhaust pressure detection pipe 154 is improved, the arrangement of the exhaust pressure detection pipe 154 becomes easy, and the design man-hours can be reduced, and the manufacturability and assemblability of the engine 1 can be improved. Further, in the engine 1, since the cooling water passage 38 is provided in the cylinder head 2 in the vicinity of the exhaust pressure bypass passage 153, the gas temperature in the exhaust pressure bypass passage 153 can be efficiently reduced. Therefore, the engine 1 can shorten the exhaust pressure bypass passage 153 while keeping the heat transmitted from the gas in the exhaust pressure bypass passage 153 to the exhaust pressure sensor 151 within an allowable range, and it becomes easy to form the exhaust pressure bypass passage 153 in the cylinder head 2.

[0112] The engine 1 is configured to include an EGR device 24 that returns a part of the exhaust gas discharged from the exhaust manifold 4 to the intake manifold 3 as EGR gas, and an EGR cooler 27 that cools the EGR gas. The cylinder head 2 includes a pair of EGR cooler connection parts 33 and 34 protruding from one of the two side surfaces of the cylinder head 2 that intersect the exhaust side surface. The cooling water passage 38 is connected to the EGR cooler 37 through the inside of one EGR cooler connection part 33, and the exhaust pressure bypass passage 153 passes through the inside of the EGR cooler connection part 33. Therefore, the engine 1 can efficiently cool the gas in the exhaust pressure bypass passage 153 and can prevent the failure and malfunction of the exhaust pressure sensor 151 caused by heat.

[0113] Furthermore, the exhaust pressure sensor 151 is attached to an exhaust pressure sensor mounting portion 152 protruding from the one side surface of the cylinder head 2 between the pair of EGR cooler connecting portions 33 and 34. Therefore, the engine 1 can efficiently cool the exhaust pressure sensor 151 and prevent failure or malfunction of the exhaust pressure sensor 151 due to heat.

[0114] Note that the configuration of each part in the present invention is not limited to the illustrated embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0115] (Addendum) (Addendum 1) In an engine device including an exhaust manifold provided on an exhaust side surface which is one side surface of a cylinder head, and a supercharger driven by exhaust gas discharged from the exhaust manifold, the supercharger is composed of a two-stage supercharger including a high-pressure stage supercharger connected to the exhaust manifold and a low-pressure stage supercharger connected to the high-pressure stage supercharger, the high-pressure stage supercharger is fixed to the exhaust manifold and disposed laterally of the exhaust manifold, the low-pressure stage supercharger is fixed to the exhaust side surface of the cylinder head and disposed above the exhaust manifold, and an exhaust outlet of the high-pressure stage supercharger and an exhaust inlet of the low-pressure stage supercharger are connected, the engine device.

[0116] (Addendum 2) The cylinder head according to Addendum 1, which includes, inside thereof, a rib extending from a mounting portion of the low-pressure stage supercharger on the exhaust side surface toward an intake side surface facing the exhaust side surface.

[0117] (Addendum 3) A configuration including an exhaust gas purification device for purifying exhaust gas from the exhaust manifold, an exhaust inlet of the exhaust gas purification device is disposed in the vicinity of a corner where one of two side surfaces of the cylinder head intersecting the exhaust side surface and the exhaust side surface intersect. The low-pressure stage supercharger according to appended claim 1, wherein the low-pressure stage supercharger is arranged closer to the one side surface when viewed from the exhaust side surface side, and an exhaust outlet of the low-pressure stage supercharger is provided toward the one side surface side.

[0118] (Appended claim 4) Above the cylinder head, an outlet of blow-by gas of the blow-by gas reduction device is arranged toward the exhaust side surface side at a position closer to the other side surface opposite to the one side surface of the cylinder head, a fresh air inlet of the low-pressure stage supercharger is provided toward the other side surface side, and the outlet of the blow-by gas is connected to an air supply pipe connecting to the fresh air inlet of the low-pressure stage supercharger via a reduction hose. The engine device according to appended claim 3.

[0119] (Appended claim 5) The low-pressure stage supercharger according to any one of appended claims 1 to 4, wherein a fresh air inlet is provided at a position closer to the cylinder head than a fresh air supply port.

[0120] (Appended claim 6) The engine device according to appended claim 5, wherein a fresh air supply port of the low-pressure stage supercharger and a fresh air inlet of the high-pressure stage supercharger are opened in the same direction.

[0121] (Appended claim 7) The engine device according to any one of appended claims 1 to 6, wherein an exhaust outlet of the high-pressure stage supercharger and an exhaust inlet of the low-pressure stage supercharger are connected via a flexible pipe.

[0122] In the engine device described in Supplementary Note 1, since the small-capacity high-pressure stage supercharger is arranged on the side of the exhaust manifold and the large-capacity low-pressure stage supercharger is arranged above the exhaust manifold, the exhaust manifold and the two-stage supercharger can be compactly arranged within a substantially square frame, and miniaturization of the engine device can be achieved. Further, if the exhaust outlet of the high-pressure stage supercharger and the exhaust inlet of the low-pressure stage supercharger are connected via a flexible pipe, the risk of low-cycle fatigue failure of the pipe due to thermal expansion can be reduced. Also, since the low-pressure stage supercharger is fixed to the exhaust side surface of the cylinder head and the high-pressure stage supercharger is fixed to the exhaust manifold, the high-pressure stage supercharger and the low-pressure stage supercharger constituting the two-stage supercharger can be firmly fixed by distributing them to the robust cylinder head and exhaust manifold. Further, if the exhaust outlet of the high-pressure stage supercharger and the exhaust inlet of the low-pressure stage supercharger are connected via a flexible pipe, the stress applied to the two-stage supercharger due to the thermal expansion of the pipe can be reduced. Thereby, the stress applied to the connection part between the high-pressure stage supercharger and the exhaust manifold and the stress applied to the connection part between the low-pressure stage supercharger and the cylinder head can be reduced, and connection failure and breakage of the connection member at these connection parts can be prevented.

[0123] Furthermore, the engine device of the present invention is an engine device including an exhaust manifold and a supercharger, wherein the supercharger is composed of a two-stage supercharger including a high-pressure stage supercharger and a low-pressure stage supercharger, the high-pressure stage supercharger is attached to the exhaust manifold, the low-pressure stage supercharger is arranged above the exhaust manifold, and the high-pressure stage supercharger and the low-pressure stage supercharger are connected.

[0124] In the engine device of the present invention, the high-pressure stage supercharger may be arranged in the vicinity of the exhaust manifold.

[0125] Also, in the engine device of the present invention, the low-pressure stage supercharger may be arranged on the exhaust outlet side of the high-pressure stage supercharger with respect to the high-pressure stage supercharger.

[0126] Further, in the engine device of the present invention, an exhaust gas purification device for purifying exhaust gas from the exhaust manifold may be provided, and the exhaust gas inlet of the exhaust gas purification device may be arranged on the exhaust gas outlet side of the low-pressure stage supercharger.

[0127] With the engine device of the present invention, the exhaust manifold and the two-stage supercharger can be arranged compactly.

Explanation of Reference Numerals

[0128] 1 Engine (engine device) 2 Cylinder head 3 Intake manifold 4 Exhaust manifold 30 Two-stage supercharger 51 High-pressure stage supercharger 52 Low-pressure stage supercharger 59 High-pressure exhaust gas pipe (flexible pipe) 131 Low-pressure stage supercharger mounting portion 135 Rib 100 Exhaust gas purification device 116 Exhaust gas inlet pipe (exhaust gas inlet of exhaust gas purification device) 19 Blow-by gas reduction device 70 Blow-by gas outlet 63 Low-pressure stage fresh air inlet (fresh air inlet of low-pressure stage supercharger) 62 Air supply pipe 68 Reduction hose

Claims

1. An engine device provided with a supercharger, wherein the supercharger is a two-stage supercharger composed of a high-pressure stage supercharger and a low-pressure stage supercharger, an exhaust outlet of the high-pressure stage supercharger and an exhaust inlet of the low-pressure stage supercharger are connected via a pipe having flexibility at least in part, and the pipe has a substantially L-shaped bent portion, the pipe, has a straight portion having flexibility separately from the bent portion at a portion on the high-pressure stage supercharger side than the bent portion, is connected in the order of the straight portion, the bent portion, and the low-pressure stage supercharger from the high-pressure stage supercharger side, engine device.

2. The straight portion is formed in a bellows shape, The engine device according to claim 1.

3. The low-pressure stage supercharger is arranged on the exhaust outlet side of the high-pressure stage supercharger with respect to the high-pressure stage supercharger, The engine device according to claim 1 or 2.

4. The low-pressure stage supercharger is arranged above the high-pressure stage supercharger, The engine device according to any one of claims 1 to 3.

5. The low-pressure stage supercharger is arranged above the exhaust manifold, The engine device according to any one of claims 1 to 4.

Images