阅读说明：本技术 发动机的egr系统 (EGR system of engine ) 是由 藤平伸次 木之下浩 刈谷乔 富永敬幸 吉田健 于 2021-02-23 设计创作，主要内容包括：本发明公开了一种发动机的EGR系统。EGR通路(40)具有在EGR冷却器(41)的上游侧通过气缸盖(11)的内部的EGR内部通路(44)和在气缸盖(11)的外部进行连接的中继通路(45)。EGR冷却器(41)以气体流入口(41a)位于第一端面(11c)一侧且气体流出口(41b)位于第二端面(11d)一侧的方式布置在进气歧管(23)的上方,中继通路(45)在气缸盖EGR气体出口(16)的一旁与EGR内部通路(44)相连接,且中继通路(45)与EGR内部通路(44)连通。EGR冷却器(41)倾斜,中继通路(45)以弯曲状态与气体流入口(41a)相连接。因此能够抑制高度且提高EGR冷却器的排水性。(The invention discloses an EGR system of an engine. The EGR passage (40) has an EGR internal passage (44) that passes through the interior of the cylinder head (11) on the upstream side of the EGR cooler (41), and a relay passage (45) that connects to the exterior of the cylinder head (11). The EGR cooler (41) is disposed above the intake manifold (23) such that the gas inlet (41a) is located on the first end surface (11c) side and the gas outlet (41b) is located on the second end surface (11d) side, the relay passage (45) is connected to the EGR internal passage (44) near the cylinder head EGR gas outlet (16), and the relay passage (45) communicates with the EGR internal passage (44). The EGR cooler (41) is inclined, and the relay passage (45) is connected to the gas inlet (41a) in a bent state. Therefore, the height can be suppressed and the water drainage of the EGR cooler can be improved.)

1. An EGR system of an engine, characterized in that:

the EGR system of the engine comprises an engine body, an air inlet passage, an exhaust passage and an EGR passage,

the engine body includes, in an upper portion thereof, a cylinder head constituting a plurality of combustion chambers that perform combustion, the plurality of combustion chambers being arranged side by side between a first end face and a second end face of the cylinder head,

the intake passage is used for introducing intake air into each of the combustion chambers through an intake manifold mounted on the cylinder head,

the exhaust passage is connected with the cylinder head and discharges exhaust gas from each of the combustion chambers,

the EGR passage is connected between the exhaust passage and the intake passage and recirculates exhaust gas as EGR gas to the intake passage,

the EGR passage has an EGR cooler, an EGR internal passage, and a relay passage,

the EGR cooler cools the EGR gas while the EGR gas flows in from the gas inlet port to the gas outlet port,

the EGR internal passage passes through the inside of the cylinder head on the upstream side of the EGR cooler,

the relay passage is outside the cylinder head, and connects the EGR internal passage and the EGR cooler between the EGR internal passage and the EGR cooler,

the cylinder head having a cylinder head EGR gas outlet on the first end face, the cylinder head EGR gas outlet for outflow of EGR gas passing through an interior of the cylinder head,

the EGR cooler is formed as a cylinder, the EGR cooler having the gas inflow port at one end side in a longitudinal direction and the gas outflow port at the other end side in the longitudinal direction, the EGR cooler being disposed above the intake manifold in such a manner that the gas inflow port is located on the first end face side and the gas outflow port is located on the second end face side, and the relay passage being connected to the EGR internal passage at a side of the cylinder head EGR gas outlet and communicating with the EGR internal passage,

the EGR cooler is inclined so as to be lower from the gas outlet toward the gas inlet, and the relay passage is connected to the gas inlet in a curved state so as to be lower toward the upstream side.

2. The EGR system of an engine according to claim 1, characterized in that:

the EGR system of the engine further includes a first attachment member mounted on the first end surface of the cylinder head,

the first attachment member has an extension passage located beside the first end surface and constituting the EGR internal passage,

the relay passage is connected to the first accessory member and communicates with the extension passage.

3. The EGR system of the engine according to claim 1 or 2, characterized in that:

the EGR passage further has an EGR valve that adjusts a flow rate of EGR gas,

the EGR valve is disposed on a downstream side of the EGR cooler through a linking passage connected to the gas flow outlet,

the EGR valve is directly fixed to an upper portion of the intake manifold, and the connection passage is connected to the upper portion of the EGR valve in a state of extending toward the second end surface side above the EGR valve.

4. An EGR system of an engine according to any one of claims 1 to 3, characterized in that:

the EGR cooler is arranged in a laterally inclined state in such a manner that the gas flow outlet is farther from the cylinder head than the gas flow inlet, and the relay passage is arranged in a longitudinally inclined state.

5. The EGR system of the engine according to any one of claims 1 through 4, characterized in that:

the EGR system of the engine further includes a second attachment member provided in the vicinity of the first end surface of the cylinder head,

the second attachment member is disposed in a space below the EGR cooler and the relay passage.

6. The EGR system of the engine according to any one of claims 1 to 5, characterized in that:

when the engine is operated in a high load section including a full load, combustion is performed in the combustion chamber with a stoichiometric air-fuel ratio as a target value.

Technical Field

The technology disclosed herein relates to an EGR system of an engine.

Background

There is known a technique of returning a part of Exhaust Gas (also called EGR Gas) to an intake side in an engine that drives a vehicle or the like, so-called EGR (Exhaust Gas Recirculation). In general, an EGR system that performs EGR is often provided with an EGR cooler in order to cool high-temperature EGR gas.

With regard to the technology disclosed herein, there has been disclosed an engine in which an EGR cooler is disposed on an upper side of an intake manifold (patent document 1).

Patent document 1: japanese laid-open patent publication No. 2016-102429

Disclosure of Invention

Technical problems to be solved by the invention

In the interior of the EGR cooler, condensed water containing oxidized substances is generated. Therefore, when the EGR cooler is disposed horizontally as in the engine of patent document 1, it is preferable to avoid accumulation of condensed water in the EGR cooler. A common method conceivable for this is to tilt the EGR cooler to cause the condensed water to flow down.

However, the engine is provided in a limited space of the engine room. Further, when the EGR cooler is disposed on the upper side of the intake manifold as in the engine of patent document 1, the gap between it and the engine cover covering the upper side of the EGR cooler becomes narrow. The size of the gap needs to be secured to a predetermined amount or more so that the bonnet deforms at the time of collision to mitigate the impact.

In contrast, in order to incline the horizontal EGR cooler and cause the condensed water to flow down, it is necessary to raise one end of the EGR cooler greatly. As a result, it is difficult to secure a gap having a size of a predetermined amount or more. Therefore, it is not easy to improve the drainage of the condensed water only by tilting the EGR cooler. Therefore, in order to improve the drainage of the EGR cooler disposed transversely to the engine while securing the clearance between the engine and the engine cover, the layout of the entire EGR system has been newly studied.

That is, the main purpose of the technology disclosed herein is: provided is an EGR system of an engine, which can improve the water drainage of an EGR cooler without affecting the cooling performance in a state of suppressing the height of the whole EGR system including the EGR cooler.

Technical solutions for solving technical problems

The technology disclosed herein relates to an EGR system of an engine. The EGR system of the engine includes an engine body including a cylinder head at an upper portion, the cylinder head constituting a plurality of combustion chambers that perform combustion, the plurality of combustion chambers being arranged side by side between a first end surface and a second end surface of the cylinder head, an intake passage for introducing intake air into each of the combustion chambers through an intake manifold mounted on the cylinder head, an exhaust passage connected with the cylinder head and discharging exhaust gas from each of the combustion chambers, and an EGR passage connected between the exhaust passage and the intake passage and recirculating exhaust gas as EGR gas to the intake passage.

The EGR passage includes an EGR cooler that cools EGR gas while the EGR gas flows from a gas inlet port to a gas outlet port, an EGR internal passage that passes through an inside of the cylinder head on an upstream side of the EGR cooler, and a relay passage that is outside the cylinder head and connects the EGR internal passage and the EGR cooler between the EGR internal passage and the EGR cooler. The cylinder head has a cylinder head EGR gas outlet on the first end face, the cylinder head EGR gas outlet for outflow of EGR gas passing through an interior of the cylinder head.

The EGR cooler is formed as a cylinder, the EGR cooler has the gas inflow port at one end side in a longitudinal direction and the gas outflow port at the other end side in the longitudinal direction, the EGR cooler is disposed above the intake manifold such that the gas inflow port is located on the first end face side and the gas outflow port is located on the second end face side, and the relay passage is connected to the EGR internal passage at a side of the cylinder head EGR gas outlet and communicates with the EGR internal passage.

The EGR cooler is inclined so as to be lower from the gas outlet toward the gas inlet, and the relay passage is connected to the gas inlet in a curved state so as to be lower toward the upstream side.

According to the EGR system of the engine, the EGR passage has an EGR cooler. Therefore, the EGR gas can be cooled by the EGR cooler. The EGR passage has an EGR internal passage that passes through the inside of the cylinder head on the upstream side of the EGR cooler. Generally, a water cooling passage for cooling the combustion chamber is formed inside the cylinder head. Therefore, the EGR gas flowing through the EGR internal passage can be cooled by heat exchange with the cooling water flowing through the water-cooling passage. That is, the EGR gas can be cooled efficiently.

The EGR cooler is formed in a cylindrical shape that is long in the direction in which EGR gas flows (gas flow direction). By making the overall length longer, the cooling performance of the EGR cooler can be ensured even if the longitudinal width is made smaller. The longitudinal width of the EGR cooler can be made small to suppress the height.

The EGR cooler is arranged to extend in the longitudinal direction of the cylinder head in a state where the direction thereof coincides with the gas flow direction. Thus, smooth inflow and outflow of the EGR gas can be ensured. Further, the EGR cooler can be controlled over the entire length of the cylinder head while suppressing the height.

The relay passage is connected to the EGR internal passage at a position near the end surface of the cylinder head, and the relay passage communicates with the EGR internal passage. That is, the cylinder head has an outlet (a cylinder head EGR gas outlet) on the first end surface, which causes EGR gas passing through the interior of the cylinder head to flow out of the cylinder head. The relay passage is configured to be connected to the EGR internal passage at a position that is away sideways from the cylinder head EGR gas outlet. By connecting the relay passage at a position away sideways from the first end surface, the distance to the EGR cooler becomes longer, enabling the relay passage to be made longer.

The EGR cooler is inclined so as to be lower from the gas outlet toward the gas inlet. Since the EGR cooler has a long shape in the gas flow direction, even if the inclination is gentle, the condensed water generated in the EGR cooler can be smoothly made to flow down toward the upstream side. Further, the condensed water can be suppressed from entering the downstream side of the EGR valve.

The relay passage is connected to the gas inlet in a curved state that is lower toward the upstream side. When a large amount of EGR gas flows through the EGR passage, the cross-sectional flow area of the relay passage is preferably large, and the flow resistance of the relay passage is preferably small. Therefore, it is preferable that the relay passage is formed by a pipe having a large diameter bent in the gas flow direction, and both end portions of the relay passage are smoothly connected to each other.

However, if the diameter becomes large, the bending cannot be made large, and the radius of curvature becomes large. In this regard, in this engine, the relay passage is connected at a position that is further away from the end face of the cylinder head. Therefore, the distance to the gas inlet becomes longer.

In this way, the entire length of the relay passage can be made longer, and the relay passage can be configured by a pipe having a large pipe diameter and a large curvature radius. Both ends of the relay passage can be smoothly connected to each other even in a curved state that is lower toward the upstream side. As a result, even a large amount of EGR gas can flow smoothly. The condensed water flowing down from the EGR cooler to the relay pipe also smoothly flows down. Therefore, it is possible to improve the water drainage of the EGR cooler without affecting the cooling performance in a state where the height of the entire EGR system including the EGR cooler is suppressed.

The EGR system of the engine may also be: the EGR cylinder head further includes a first attachment member attached to the first end surface of the cylinder head, the first attachment member having an extension passage located beside the first end surface and constituting the EGR internal passage, and the relay passage being connected to the first attachment member and communicating with the extension passage.

That is, in the EGR system of the engine, the first additional member is attached to the first end surface of the cylinder head, and the first additional member has an extension passage constituting the EGR internal passage. The first attachment member extends the EGR passage from the first end surface of the cylinder head to a position next to the first end surface and away from the first end surface. Therefore, if the water cooling passage is also formed in the first additional member, the EGR gas can be cooled more efficiently by heat exchange with the cooling water.

Further, since the relay passage is connected to the first additional member and communicates with the extension passage, the distance to the gas inlet can be made longer as described above. Therefore, even a large amount of EGR gas can flow smoothly, and the water discharge performance of the EGR cooler can be improved.

The EGR system of the engine may also be: the EGR passage further includes an EGR valve that adjusts a flow rate of EGR gas, the EGR valve is disposed downstream of the EGR cooler through a connection passage connected to the gas flow outlet, the EGR valve is directly fixed to an upper portion of the intake manifold, and the connection passage is connected to the upper portion of the EGR valve in a state of extending to the second end surface side through an upper portion of the EGR valve.

That is, the layout of the downstream portion of the EGR passage located on the downstream side of the EGR cooler is also devised. Since the EGR valve is directly fixed to the upper portion of the intake manifold, the supporting strength of the EGR valve is improved, and the rattling of the EGR valve can be suppressed. Further, the height of the EGR valve can be suppressed.

A connection passage connecting the EGR valve and the EGR cooler between the EGR valve and the EGR cooler is connected to an upper portion of the EGR valve in a state of extending toward the second end surface side through an upper portion of the EGR valve. Therefore, even if the connecting passage has a shape with a long lateral length, the connecting passage can be arranged without protruding sideways from the second end surface of the cylinder head. As a result, the entire engine including the EGR system can be efficiently provided in the engine room.

The EGR system of the engine may also be: the EGR cooler is arranged in a laterally inclined state in such a manner that the gas flow outlet is farther from the cylinder head than the gas flow inlet, and the relay passage is arranged in a longitudinally inclined state.

That is, according to the EGR system of this engine, the EGR cooler is arranged in a state of being also inclined in the lateral direction. Specifically, the EGR cooler is inclined such that the gas outlet port is farther from the cylinder head than the gas inlet port when viewed in the up-down direction.

At the same time, the relay passage is also arranged in a longitudinally inclined state. Specifically, the relay passage is inclined in the vertical direction such that the upstream side is farther from the gas inlet than the downstream side, as viewed in the horizontal direction. In this way, the EGR cooler and the relay passage can be made longer. Therefore, it is possible to improve the smoothness of the EGR gas flow and the smoothness of the condensed water discharge in a state where they are efficiently arranged in a small space.

The EGR system of the engine may also be: the EGR system of the engine further includes a second attachment member provided in the vicinity of the first end surface of the cylinder head, the second attachment member being disposed in a space below the EGR cooler and the relay passage.

That is, according to the EGR system of the engine, the portion constituted by the EGR cooler and the relay passage extends through the upper side of the intake manifold toward the side of the first end portion of the cylinder head. In this case, a certain space is created below the EGR cooler and the relay pipe.

If the second attached member is disposed in the space, the second attached member can be disposed compactly and efficiently, and the dead space can be prevented from being generated.

The EGR system of the engine may also be: when the engine is operated in a high load section including a full load, combustion is performed in the combustion chamber with a stoichiometric air-fuel ratio as a target value.

In general, when the engine is operated in such a high load section, the combustion temperature rises and abnormal combustion occurs. Therefore, the amount of fuel is increased, and the mixture is cooled by its latent heat of vaporization, thereby suppressing abnormal combustion. This method is poor in fuel economy because the amount of fuel increases.

On the other hand, if combustion is performed at the stoichiometric air-fuel ratio, fuel economy is improved, but the latent heat of vaporization cannot be sufficiently utilized, and therefore abnormal combustion cannot be suppressed. If the amount of recirculation of the EGR gas is increased, the oxygen concentration of the intake air decreases, and abnormal combustion can be suppressed. However, when combustion is performed at the stoichiometric air-fuel ratio, the temperature of the exhaust gas becomes high.

Therefore, if combustion is performed at the stoichiometric air-fuel ratio while increasing the amount of EGR gas recirculated to suppress abnormal combustion when the engine is operated in the high load range, more EGR gas may be recirculated at a higher temperature than in the prior art. Because the amount of heat of the EGR gas is excessive with respect to the performance of the EGR cooler, the durability of the EGR cooler may be reduced.

In contrast, in the EGR system of the engine, as described above, the heat of the EGR gas flowing into the EGR cooler can be effectively removed. Therefore, even if a higher temperature and a larger amount of EGR gas are recirculated, the amount of heat of the EGR gas can be suppressed from being excessive with respect to the performance of the EGR cooler. That is, according to the EGR system of the engine, the fuel economy can be improved.

Effects of the invention

According to the EGR system of the engine to which the technology disclosed herein is applied, it is possible to improve the drainage of condensed water of the EGR cooler without affecting the cooling performance in a state in which the height of the entire EGR system including the EGR cooler is suppressed.

Drawings

Fig. 1 is a diagram illustrating the configuration of a main device of an engine;

fig. 2 is a schematic perspective view showing a specific overall structure of the engine;

FIG. 3 is a diagrammatic view of an upper portion of the engine as viewed from the front;

fig. 4 is a schematic view of the upper portion of the engine viewed from the left side;

fig. 5 is a schematic perspective view of an upper portion of the engine viewed from obliquely above;

fig. 6 is a schematic perspective view showing a main portion on the left side of the engine in an enlarged manner;

fig. 7 is a schematic view of the upper front side of the engine viewed from the upper side;

fig. 8 is a schematic perspective view showing an enlarged view of a main portion of the upper front side of the engine.

-description of symbols-

1-an engine; 2-the engine cover; 10-an engine block; 10 a-a cylinder block; 11-a cylinder head; 11 a-front side; 11 b-rear side; 11 c-a first end face; 11 d-a second end face; 12-a combustion chamber; 16-cylinder head EGR gas outlet; 20-an intake passage; 21-a throttle valve; 22-a pressure relief tank; 23-an intake manifold; 30-an exhaust passage; 31-an exhaust manifold; 32-a tail gas purification device; 40-EGR passage; 41-an EGR cooler; 41 a-gas inlet port; 41 b-gas outflow; 42-an EGR valve; 45-trunk pipe (trunk path); 47-connecting pipes (connecting passages); 70-curved tube portion.

Detailed Description

The technology disclosed herein will be explained below. However, the following description is merely exemplary. And do not limit the invention, its objects of use, or its uses.

Fig. 1 is a diagram illustrating a configuration of a main device of an EGR system integrated with an engine (hereinafter, the whole of these is simply referred to as "engine 1"). Fig. 2 is a schematic perspective view showing a specific overall structure of the engine 1. Fig. 3 is a schematic view of the upper portion of the engine 1 as viewed from the front. Fig. 4 is a schematic view of an upper portion of the engine 1 as viewed from the first end surface 11c side of the cylinder head 11. Fig. 5 is a schematic perspective view of the upper portion of the engine 1 viewed from obliquely above. Fig. 6 is a schematic perspective view showing a main portion of the engine 1 in an enlarged manner.

Arrows shown in the drawings indicate directions of "front-back", "right-left", and "up-down" used in the description. In addition, references to "upstream" and "downstream" used in the description are directions of fluid flows as objects. For convenience of explanation, the engine is not shown in each drawing.

The engine 1 is mounted on a four-wheel vehicle. Specifically, the vehicle is housed in an engine room of an automobile. As shown in fig. 3 and 4, the upper side of the engine 1 is covered with an engine cover 2. The gap G between the engine 1 and the hood 2 needs to be secured to a predetermined amount or more so that the hood 2 deforms at the time of collision to alleviate the impact. In the engine 1, the clearance G can be ensured by suppressing the overall height including the EGR system.

The engine 1 is operated in accordance with an operation by a driver, thereby running the vehicle. The engine 1 burns an air-fuel mixture containing gasoline in a combustion chamber 12 described later. The engine 1 is a four-stroke engine that repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.

The engine 1 includes an intake passage 20 and an exhaust passage 30, the intake passage 20 feeds intake air to each combustion chamber 12 in accordance with a combustion cycle, and the exhaust passage 30 discharges exhaust gas from the combustion chamber 12 in accordance with the combustion cycle. Moreover, the engine 1 further includes the EGR system described above. That is, the engine 1 performs EGR to recirculate a part of the exhaust gas discharged to the exhaust passage 30 to the intake passage 20 as EGR gas.

In the engine 1, the amount of EGR gas recirculated is made larger than in the conventional art, and abnormal combustion is suppressed. In this way, combustion with the stoichiometric air-fuel ratio as the target value can be performed even when the engine 1 is operated in the high load section.

In general, when the engine 1 is operated in a high load range in which a large torque output is required, the combustion temperature rises and abnormal combustion occurs. Therefore, when the engine 1 is operated in the high load range, the mixture enrichment control is performed so that the ratio of the air amount to the fuel amount (so-called a/F, air-fuel ratio) is reduced. The mixture is cooled by the latent heat of vaporization of the fuel thus increased, and abnormal combustion is suppressed. However, in the mixture enrichment control, the fuel economy is deteriorated because the amount of fuel is increased.

On the other hand, if fuel and oxygen are properly combusted, that is, if the combustion is performed at the stoichiometric air-fuel ratio, the fuel economy is improved. However, when combustion is performed at the stoichiometric air-fuel ratio, the latent heat of vaporization cannot be sufficiently utilized, and therefore, abnormal combustion cannot be suppressed. On the other hand, if the amount of EGR gas recirculated is increased, the oxygen concentration of the intake air decreases. Thus, the self-ignition timing is retarded, and abnormal combustion can be suppressed.

This engine 1 performs combustion with the stoichiometric air-fuel ratio as a target value during operation in a high load range. Then, the amount of recirculation of the EGR gas is increased to suppress abnormal combustion. The high load section referred to herein is, for example, a section including a predetermined load or more of the full load. The high load section is, for example, a section located on the high load side when the operating section of the engine 1 is halved in the load direction. The high load section may be a section located on the highest load side, in which the operation section of the engine 1 is divided into three equal parts in the load direction.

When combustion is performed at the stoichiometric air-fuel ratio, the temperature of the exhaust gas becomes high. Therefore, when the engine 1 is operated in the high load section, the EGR gas is refluxed in a higher temperature and more amount than in the related art. In contrast, in the engine 1, in detail, in the EGR system, contrivances are made so as to solve the problems that occur (details will be described later).

< engine body 10 >

As shown in fig. 2, the engine 1 includes an engine body 10 including a cylinder block 10a, a cylinder head 11, and the like. The cylinder head 11 is mounted on the cylinder block 10 a. The cylinder head 11 constitutes an upper portion of the engine body 10, and the cylinder block 10a constitutes a lower portion of the engine body 10. In the engine body 10, a plurality of combustion chambers 12 are provided. As shown in fig. 1, the engine 1 of the example is a so-called four-cylinder engine having four combustion chambers 12.

The four combustion chambers 12 are arranged in a row in a direction in which a crankshaft (not shown) extends (output shaft direction). The engine body 10 has a shape that is long in the output shaft direction. The engine body 10 is disposed in the engine compartment, and the direction of the output shaft of the engine body 10 substantially coincides with the vehicle width direction (left-right direction).

Therefore, as shown in fig. 1, each of a pair of side surfaces of the cylinder head 11 that are relatively long faces forward (front side surface 11a) and backward (rear side surface 11b), respectively, with the cylinder head 11 as a reference. The four combustion chambers 12 are arranged in a row between the left and right end faces (the first end face 11c and the second end face 11d) of the cylinder head 11. The small black dots of the cylinder head 11 indicate the joint surfaces to which the attached components are attached.

In the cylinder block 10a, four cylinders are formed, and illustration thereof is omitted. In each cylinder, a piston is provided for reciprocating motion. The lower surface of each cylinder is sealed by a piston. The upper surface of each cylinder is closed by a cylinder head 11. Each combustion chamber 12 is defined by the cylinder block 10a, the piston, and the cylinder head 11, and is formed inside the engine body 10.

When the engine 1 is operated, the temperature of the engine body 10 becomes high. A water cooling system for cooling the engine body 10 by cooling water is attached to the engine 1. The water cooling system is constituted by a water pump, a radiator, and the like, and is not shown. The water cooling system cools the engine body 10, the EGR cooler 41, a heater core for air conditioning, and an ATF cooler (a cooler that cools transmission oil) by exchanging heat with cooling water.

Specifically, as shown in fig. 1, a water cooling passage 50 through which cooling water flows is formed around each combustion chamber 12 of the cylinder block 10a and the cylinder head 11. The water pump 51 operates to circulate the cooling water through the water cooling passage 50.

A water outlet portion 52 (first additional member) is attached to the first end surface 11c of the cylinder head 11, and the water outlet portion 52 distributes a part of the cooling water flowing through the water cooling passage 50 to the EGR cooler 41, the ATF cooler, and the like. A thermostat 54 (shown by a two-dot chain line in fig. 6) is attached to the water outlet portion 52. The thermostat 54 switches the flow path of the cooling water. The engine 1 is further provided with a combustion supply system for supplying fuel to each combustion chamber 12, a spark plug for igniting an air-fuel mixture, a valve operating mechanism, and the like, but for convenience of description, illustration and description thereof are omitted.

< intake passage 20 >

Eight intake ports 13 are formed in the front side surface 11a of the cylinder head 11. Each combustion chamber 12 has two inlet channels 13 communicating with it. Each intake passage 13 communicates with each combustion chamber 12 through an intake valve, and the opening and closing of the intake valve is controlled. In this engine 1, the inlet of each intake duct 13 is open (eight in total) on the front side surface 11a of the cylinder head 11. An intake passage 20 is connected to the front side surface 11a of the cylinder head 11, and the intake passage 20 communicates with the intake port 13.

As shown in fig. 1, the intake passage 20 is provided with a throttle valve 21, a surge tank 22, an intake manifold 23, and the like. The throttle valve 21 adjusts the amount of air (fresh air) drawn into the intake passage 20. As shown in fig. 3 and 4, the throttle valve 21 is disposed on the left front side of the upper portion of the engine body 10.

The surge tank 22 is a large-capacity container, and is disposed on the downstream side of the throttle valve 21. As shown in fig. 3 and 4, the surge tank 22 is integrated with the intake manifold 23. The surge tank 22 is disposed near the front side of the engine body 10. The intake manifold 23 has four flow paths communicating with the surge tank 22, and distributes intake air to the combustion chambers 12 through the flow paths.

Specifically, the intake manifold 23 has four intake branch pipes 23a and a connecting bracket 23 b. Each intake branch pipe 23a is bent upward from a lower end portion of the front surface of the surge tank 22 and branched. Thus, each intake branch pipe 23a extends across the front surface of the surge tank 22 toward the front side surface 11a of the cylinder head 11.

As shown in fig. 2, the connecting bracket 23b is a bracket having a long lateral length to which the intake branch pipes 23a are connected. The coupling bracket 23b is mounted on the front side surface 11a of the cylinder head 11 and extends laterally of the cylinder head 11. As shown in fig. 1, a plurality of branch passages 24a, 24b that communicate inlets of the intake ducts 13 with the intake branch pipes 23a are formed inside the connecting bracket 23 b.

As shown in fig. 1, the downstream end of each intake branch pipe 23a branches into two passages inside thereof. The passages are connected to a pair of branch passages (a first branch passage 24a and a second branch passage 24b) formed in the coupling holder 23 b.

In each first branch passage 24a, a swirl control valve 25 is provided. The swirl control valve 25 adjusts the opening degree of the flow path of the first branch passage 24 a. The swirl control valve 25 is driven by one drive motor 26 (second attached member) attached to the engine body 10. The strength of the swirl generated in the combustion chamber 12 changes according to the opening and closing of the swirl control valve 25.

In this engine 1, supercharging is not performed. The engine 1 is charged at atmospheric pressure. The engine 1 is a so-called natural intake engine.

< exhaust passage 30 >

As shown in fig. 1, eight exhaust ports 14 are formed in the rear side surface 11b of the cylinder head 11. Each combustion chamber 12 has two exhaust ports 14 communicating with it. Each exhaust passage 14 communicates with each combustion chamber 12 through an exhaust valve, the opening and closing of which is controlled. In this engine 1, the outlet port where the two exhaust passages 14 each merge opens (four in total) on the rear side surface 11b of the cylinder head 11. An exhaust passage 30 is connected to the rear side surface 11b of the cylinder head 11, and the exhaust passage 30 communicates with the exhaust port 14.

The exhaust passage 30 is provided with an exhaust manifold 31, an exhaust gas purification device 32, and the like. As shown in fig. 2 and 5, the exhaust manifold 31 includes a pipe group 31a including a plurality of pipes and a connecting bracket 31 b. The group of pipes 31a branches to form four flow paths communicating with the exhaust ports 14. The connecting bracket 31b is constituted by a plate-like bracket having a long lateral length.

The upstream end of the tube group 31a is attached to the connection bracket 31 b. The connecting bracket 31b is attached to the rear side surface 11b of the cylinder head 11 so that the respective ducts constituting the duct group 31a communicate with the respective exhaust ports 14. The downstream end of the tube group 31a merges into one flow path (merging portion 31 c). The exhaust manifold 31 is connected to the gas introduction portion 32a of the exhaust gas purification device 32 through the junction portion 31 c.

As shown in fig. 2 and 4, the exhaust gas purifying device 32 has a capsule-shaped housing. The exhaust gas purifying device 32 is disposed near the rear side of the engine body 10. A three-way catalyst and a filter are housed in the case. The gas extraction portion 32b of the exhaust gas purification device 32 is connected to a flexible duct 33 extending rearward, and an unillustrated exhaust duct extends to the outside of the engine compartment through the flexible duct 33.

< EGR passage 40 >

As shown in fig. 1, the EGR passage 40 is connected between the exhaust passage 30 and the intake passage 20. EGR gas flows in the EGR passage 40 in the direction indicated by the arrow. Specifically, the upstream end of the EGR passage 40 is connected to the downstream side portion of the exhaust passage 30 located on the downstream side of the exhaust gas purification device 32. The downstream-side end portion of the EGR passage 40 is connected to a portion of the intake passage 20 between the throttle valve 21 and the surge tank 22.

The EGR passage 40 is provided with an EGR cooler 41, an EGR valve 42, and the like. The EGR cooler 41 has a gas inlet 41a at one end portion thereof and a gas outlet 41b at the other end portion thereof. The EGR cooler 41 cools the EGR gas (a part of the exhaust gas) while the EGR gas flows in from the gas inlet 41a to the gas outlet 41 b. The EGR valve 42 adjusts the flow rate of the EGR gas flowing through the EGR passage 40. The EGR valve 42 is disposed on the downstream side of the EGR cooler 41. The EGR passage 40, the EGR cooler 41, and the EGR valve 42 constitute an EGR system.

As shown in fig. 2, 3, and 5, the EGR cooler 41 and the EGR valve 42 are disposed in an adjacent state above the intake manifold 23. As shown in fig. 1, the EGR passage 40 is constituted by an EGR introduction pipe 43, an EGR internal passage 44, a relay pipe 45 (relay passage), and the like.

The EGR introduction pipe 43 is a pipe constituting an upstream side portion of the EGR passage 40. As shown in fig. 2, the upstream end portion of the EGR introduction pipe 43 is connected to the gas extraction portion 32b of the exhaust gas purification device 32. As shown in fig. 2 and 5, the downstream end of the EGR introduction pipe 43 is attached to the end of the connecting bracket 31 b. The EGR introduction pipe 43 is mounted on the rear side 11b of the cylinder head 11 through the connecting bracket 31 b. The EGR introduction pipe 43 extends upward from the upstream side toward the downstream side.

The EGR internal passage 44 is a tubular passage formed in the cylinder head 11. The EGR internal passage 44 passes through the inside of the cylinder head 11. The EGR introduction pipe 43 communicates with the EGR internal passage 44.

As shown in fig. 1, a passage (water-cooling passage 50) through which cooling water flows is formed inside the cylinder head 11. The EGR internal passage 44 is configured to: the heat of the EGR gas flowing through the EGR internal passage 44 is removed by heat exchange with the cooling water flowing through the water cooling passage 50. In the engine 1, the shape and layout of the EGR system are devised so that the EGR gas can be efficiently cooled before flowing into the EGR cooler 41 (the EGR internal passage 44 will be described later).

As shown in fig. 5 and 6, the relay duct 45 is a duct connected to the gas inlet 41a of the EGR cooler 41. The relay duct 45 extends toward the first end surface 11c side of the cylinder head 11. A water outlet unit 52, which will be described later, is attached to the first end surface 11c of the cylinder head 11. The upstream end of the relay pipe 45 is connected to the water outlet portion 52. In this way, the relay pipe 45 forms a relay passage connecting the EGR internal passage 44 and the EGR cooler 41 between the EGR internal passage 44 and the EGR cooler 41 outside the cylinder head 11.

In the engine 1, in order to improve the cooling performance of the EGR gas and to improve the water drainage of the EGR cooler 41 disposed in the transverse direction of the engine 1 while ensuring the gap G between the engine 1 and the engine cover 2, the layout of the entire EGR system is newly studied (details thereof will be described later).

< EGR internal passage 44 >

As described above, the engine 1 performs combustion with the stoichiometric air-fuel ratio as a target value during operation in the high load range. Then, the amount of recirculation of the EGR gas is increased to suppress abnormal combustion. Therefore, EGR gas having a higher temperature and a larger amount than in the related art flows in the EGR passage 40.

As a result, heat exceeding the cooling performance of the EGR cooler 41 is applied to the EGR cooler 41, possibly resulting in a reduction in the durability of the EGR cooler 41. In contrast, in the engine 1, the shape and layout of the EGR internal passage 44 are devised so that the EGR gas flowing into the EGR cooler 41 can be efficiently cooled, and the heat of the EGR gas flowing into the EGR cooler 41 can be removed.

Specifically, the EGR passage 44 is provided not only inside the cylinder head 11 but also inside the water outlet portion 52.

As shown in fig. 1 and 5, the upstream end of the EGR internal passage 44 is open to the left (near the first end surface 11c) of the rear surface 11b of the cylinder head 11. An upstream-side end portion of the EGR internal passage 44 is connected to the EGR introduction pipe 43. The upstream side portion of the EGR internal passage 44 extends toward the front side surface 11a in the interior of the cylinder head 11 in a state of following the first end surface 11 c. The upstream side portion of the EGR internal passage 44 is substantially horizontal.

As shown in fig. 1, a part of the upstream portion of the EGR internal passage 44 is arranged to cross the inside of the water cooling passage 50 (first cooling portion CP 1). At the first cooling portion CP1, the EGR gas flowing through the EGR internal passage 44 is in a state of being indirectly in contact with the cooling water flowing through the water cooling passage 50 through the tube wall having a small thickness. Therefore, heat exchange can be efficiently performed, and the EGR gas can be efficiently cooled.

Further, a curved pipe portion 70 having a curved shape is provided at a downstream side portion of the EGR internal passage 44 that is connected to the first cooling portion CP 1. As shown in fig. 5, the curved pipe portion 70 straddles both the cylinder head 11 and the water outlet portion 52. And, a water cooling passage 50 is arranged around the curved pipe portion 70. The EGR gas flowing in the curved pipe portion 70 collides with the wall surface thereof. At the curved pipe portion 70, the flow of EGR gas stagnates.

As a result, the heat radiation performance of the EGR gas at the curved pipe portion 70 is improved. Around the curved pipe portion 70, a water cooling passage 50 is arranged. Therefore, heat exchange between the EGR gas and the cooling water is promoted. That is, the EGR gas can be efficiently cooled (the second cooling portion CP2 shown in fig. 1). The combination of the bent pipe portion 70 and the water cooling passage 50 can effectively remove the heat of the EGR gas. Therefore, the durability of the EGR cooler 41 and the cooling performance for the EGR gas are improved.

< layout of EGR System >

As described above, in the engine 1, more EGR gas flows back than in the related art. In order to smoothly recirculate a large amount of EGR gas, it is necessary to enlarge the flow path cross section of the EGR passage 40 or to suppress flow path resistance. Therefore, in the engine room in which the space is limited, it is necessary to further secure the space around the engine body 10.

As described above, the gap G of a predetermined size must be ensured between the engine 1 and the engine cover 2. Therefore, when the EGR cooler 41 is disposed horizontally above the intake manifold 23, the height of the EGR cooler 41 needs to be reduced.

If the amount of EGR gas recirculated increases, the condensed water produced in the EGR cooler 41 also increases. Therefore, when the EGR cooler 41 is placed horizontally, it is also necessary to improve the water drainage of the EGR cooler 41.

In view of this, in the engine 1, the layout of the entire EGR system is newly studied, and a lot of effort is made to intensively solve the above-described problems.

(EGR cooler 41, intermediate pipe 45)

The EGR cooler 41 is of a flat type with a long lateral length. As shown in fig. 5 and 7, the EGR cooler 41 has a shape with a long lateral length in which the distance from the gas inlet 41a to the gas outlet 41b is long. The EGR cooler 41 also has a flat cylindrical shape in which the transverse width of the flow path cross section is larger than the longitudinal width. Therefore, the EGR cooler 41 can suppress the height by making the longitudinal width small. By making the entire length longer, the cooling performance can be ensured.

Here, the columnar shape may be a rectangular parallelepiped or a cylindrical shape. Further, the surface of the EGR cooler 41 is provided with a pipe through which cooling water flows in and out, and irregularities for ensuring rigidity, and the cylindrical shape mentioned here also includes a cylindrical shape having the above-described irregular shape.

The EGR cooler 41 is disposed above the intake manifold 23 such that the gas inlet 41a is located on the first end surface 11c side and the gas outlet 41b is located on the second end surface 11d side. That is, the EGR cooler 41 is arranged to extend in the longitudinal direction of the cylinder head 11 in a state where the direction thereof coincides with the direction in which EGR gas flows (gas flow direction). In this way, it is possible to control the EGR cooler 41 over the entire length of the cylinder head 11 while ensuring smooth inflow and outflow of EGR gas and suppressing the height.

As shown in fig. 5 and 7, the relay pipe 45 is connected to the EGR internal passage 44 on the left side (one side) of the first end surface 11c of the cylinder head 11, and the relay pipe 45 communicates with the EGR internal passage 44. Specifically, the relay pipe 45 is connected to the outlet portion 52 attached to the first end surface 11 c.

As described above, the downstream side portion of the EGR passage 44 including the curved pipe portion 70 is formed inside the water outlet portion 52. The downstream side portion of the EGR internal passage 44 is located next to the first end surface 11c, and constitutes an extension passage.

That is, an outlet (cylinder head EGR gas outlet 16) through which EGR gas flows out from the cylinder head 11 is formed on the first end surface 11 c. The EGR gas passing through the interior of the cylinder head 11 flows into the interior of the water outlet portion 52 through the cylinder head EGR gas outlet 16. The downstream side portion of the EGR passage 44 including the curved pipe portion 70 is formed in both the interior of the cylinder head 11 and the interior of the water outlet portion 52 through the cylinder head EGR gas outlet 16.

The relay duct 45 is configured to be connected at a position away sideways from the first end surface 11c of the cylinder head 11. That is, the relay pipe 45 communicates with the EGR internal passage 44 at the side of the cylinder head EGR gas outlet 16. By connecting the relay duct 45 at a position away sideways from the first end surface 11c, the distance to the EGR cooler 41 becomes longer, enabling the relay duct 45 to be longer.

As shown in fig. 3, the EGR cooler 41 is gently inclined so as to be lowered from the gas outlet 41b toward the gas inlet 41 a. The gas outlet 41b is located at the substantial center of the engine room and the gas inlet 41a is located on the left side of the engine room in the vehicle width direction. In this way, the EGR cooler 41 is arranged to be gently inclined downward from the right side toward the left side.

As described above, since the EGR cooler 41 has a flat shape, it can be inclined with the height suppressed. Since the EGR cooler 41 has a long shape in the gas flow direction, even if the inclination is gentle, the condensed water generated in the EGR cooler 41 can be smoothly made to flow down toward the upstream side. Further, the condensed water can be suppressed from entering the downstream side of the EGR valve 42.

Normally, as shown in fig. 3, the engine cover 2 has a shape bulging upward. Therefore, the middle portion of the hood 2 is higher than both side portions in the vehicle width direction. By inclining the EGR cooler 41 as such, the EGR cooler 41 can be arranged in a state along the shape of the engine cover 2. Therefore, the gap G between the EGR cooler 41 and the engine cover 2 is easily ensured.

As shown in fig. 3 and 6, the relay duct 45 is connected to the gas inlet 41a in a curved state that is lower toward the upstream side.

In the EGR passage 40, a large amount of EGR gas flows. Therefore, the cross section of the flow path of the relay duct 45 is preferably large, and the flow path resistance of the relay duct 45 is preferably small. As a result, it is preferable that the relay duct 45 be formed of a large-diameter duct bent in the gas flow direction, and the relay duct 45 be smoothly connected to the gas inlet 41a and the water outlet 52, respectively.

By inclining the EGR cooler 41, the condensed water flows down the relay duct 45. Therefore, the condensed water also needs to smoothly flow down to the upstream side in the relay duct 45. As a result, the relay duct 45 also needs to be lower toward the upstream side. In order to be smoothly connected to the gas inlet 41a, the downstream side portion of the relay duct 45 needs to be inclined at the same angle as the EGR cooler 41. Similarly, the upstream side portion of the relay pipe 45 needs to be smoothly connected to the water outlet portion 52.

However, if the diameter becomes large, the bending cannot be made large, and the radius of curvature becomes large. In this regard, in this engine 1, the relay passage 45 is connected at a position away sideways from the first end surface 11c of the cylinder head 11. Therefore, the distance to the gas inlet 41a becomes longer.

Thus, the entire length of the relay duct 45 can be made long, and the relay duct 45 can be configured by a duct having a large duct diameter and a large curvature radius. The relay duct 45 can be smoothly connected to the gas inlet 41a and the water outlet 52, respectively. As a result, a large amount of EGR gas can be smoothly flowed, and condensed water can be smoothly discharged. By bending the relay duct 45, the amount of protrusion sideways from the first end surface 11c of the cylinder head 11 can also be suppressed. Therefore, it is not necessary to secure a large installation space in the engine room.

Also, the EGR cooler 41 is arranged in a laterally inclined state as well. Specifically, as shown in fig. 7, the EGR cooler 41 is arranged in the following state: the gas outlet port 41b is inclined in the front-rear direction so as to be farther from the cylinder head 11 than the gas inlet port 41a when viewed in the up-down direction.

Meanwhile, as shown in fig. 4, the relay passage is also arranged in a longitudinally inclined state. Specifically, the following states are arranged: as viewed in the left-right direction, the upstream side is inclined in the up-down direction so as to be farther from the gas inlet 41a than the downstream side. In this way, the EGR cooler 41 and the relay duct 45 can be made longer. Therefore, it is possible to improve the smoothness of the EGR gas flow and the smoothness of the condensed water discharge in a state where they are efficiently arranged in a small space.

Further, the layout of the downstream portion of the EGR passage 40 located on the downstream side of the EGR cooler 41 has also been devised.

Specifically, as shown in fig. 2, 7, and 8, the EGR valve 42 is directly fixed to the upper portion of the intake manifold 23. Specifically, the EGR valve 42 is constituted by a valve body 42a, a valve driving motor 42b, and the like. The valve drive motor 42b is fitted to the valve body 42a to be integrated with the valve body 42 a.

A gas passage through which EGR gas flows and a valve core for adjusting the opening degree of the gas passage are provided in the valve body 42a, and are not shown. The gas flow path extends in the vertical direction. The valve drive motor 42b drives the valve core in accordance with the control, and adjusts the opening degree of the gas flow path. A flange portion 42c is provided outside the valve body 42a, and the flange portion 42c extends around the valve body 42 a.

As shown in fig. 8, a mounting bracket 23c is provided at an upper portion of the intake manifold 23. Specifically, a mounting bracket 23c is provided at a portion between the two intake branch pipes 23a and 23a on the right side above the intake manifold 23. The flange portion 42c is fastened to the mounting bracket 23c by a plurality of bolts, whereby the EGR valve 42 is directly fixed to the upper portion of the intake manifold 23.

By directly fixing the EGR valve 42 to the intake manifold 23, the supporting strength of the EGR valve 42 is improved, and the rattling of the EGR valve 42 can be suppressed. Further, the height of the EGR valve 42 can be suppressed.

As shown in fig. 5, 7, and 8, the gas outlet 41b of the EGR cooler 41 is connected to a connection pipe 47 (connection passage). The connection pipe 47 is connected to the upper portion of the EGR valve 42 in a state of passing above the EGR valve 42 and extending toward the second end surface 11d side.

The linking duct 47 has a shape long in the lateral length that is long in the gas flow direction. The linking duct 47 also has a flat shape in which the transverse width of the flow path cross section is larger than the longitudinal width. As shown in fig. 3 and 8, the linking duct 47 is arranged in the following state: the downstream side is inclined gradually lower than the upstream side. Therefore, even if the condensed water passes through the EGR cooler 41, the condensed water is not accumulated in the EGR cooler 41, and the condensed water can be made to flow down to the gas flow passage of the EGR valve 42 through the connecting pipe 47.

Further, the connecting duct 47 can also be arranged along the shape of the engine cover 2, as with the EGR cooler 41. Therefore, the gap G between the coupling duct 47 and the engine cover 2 is easily ensured.

The connection pipe 47 extends toward the second end surface 11d through the upper side of the EGR valve 42 (more specifically, the valve driving motor 42 b). Therefore, even if the linking duct 47 has a shape with a long lateral length, the linking duct 47 can be arranged without protruding the linking duct 47 rightward from the second end face 11d of the cylinder head 11. As a result, the entire engine 1 including the EGR system can be efficiently provided in the engine room.

As described above, the plurality of swirl control valves 25 are provided on the connecting bracket 23b of the intake manifold 23. The engine body 10 is provided with a drive motor 26 for driving the swirl control valve 25. The driving motor 26 needs to be provided near the coupling bracket 23b due to its structure.

In contrast, in the engine 1, the upstream side portion of the EGR passage 40 constituted by the EGR cooler 41 and the relay pipe 45 is arranged to pass above the intake manifold 23 and extend toward the first end surface 11c of the cylinder head 11. In this case, a certain space is created below the EGR cooler 41 and the relay pipe 45.

As shown in fig. 4 and 6, the drive motor 26 is disposed in the space. Therefore, the drive motor 26 can be compactly and efficiently arranged. Dead space can be prevented from being generated.

In this way, in the engine 1, the EGR passage 40 is provided with the EGR internal passage 44 having a contrived structure and layout, whereby the heat of the EGR gas can be effectively removed. The durability of the EGR cooler 41 and the cooling performance for the EGR gas are improved.

Further, since the layout of the entire EGR system is devised, a large amount of EGR gas can be smoothly recirculated, and condensed water generated in the EGR cooler 41 can be smoothly discharged. Further, since the overall height of the engine 1 is suppressed, a gap G of a predetermined size can be secured between the engine 1 and the engine cover 2.

Thus, in the engine 1, a larger amount of EGR gas having a higher temperature than in the related art can be recirculated. As a result, even if combustion is performed with the stoichiometric air-fuel ratio as a target value during operation in the high load range, the amount of EGR gas recirculated is increased, and abnormal combustion can be suppressed. Therefore, the fuel economy of the EGR system of the engine 1 can be improved.

The EGR system of the engine according to the technology disclosed herein is not limited to the above embodiment, and includes various configurations other than the above embodiments. For example, in the embodiment, a gasoline engine is shown as an example, but the present invention can also be applied to a diesel engine. A naturally aspirated engine is also shown as an example, but can also be applied to an engine with a superchargable supercharger.