JP5513469B2 - Engine intake system - Google Patents

Description

  The present invention relates to an intake device for an engine, and more particularly to a device that suppresses gas-liquid separation of an air-fuel mixture on an intake port wall surface with a simple configuration.

In a general-purpose engine for industrial use or the like, an air-fuel mixture is supplied to the engine from a carburetor provided on the inlet side of the intake port.
In addition, between the cylinder head in which the intake port is formed and the carburetor, a heat insulator made of a material having a lower thermal conductivity than that of the cylinder head such as phenol resin is disposed for the purpose of blocking heat. The

  As a conventional technique related to such a general-purpose engine heat insulator, for example, Patent Document 1 discloses a heat insulation heat insulator provided between a cylinder head and a carburetor for the purpose of reducing the intake resistance of the engine. An engine is described in which a portion of the intake port is extended into the cylinder head to form a portion of the intake port so that the intake port is gently curved.

In addition, when liquid fuel separates from the air-fuel mixture supplied from the carburetor and adheres to the inner wall surface of the intake port, these are sucked into the engine as droplets, resulting in hydrocarbon (HC) due to incomplete combustion, etc. Cause generation of harmful substances, reduced startability and drivability.
For example, in Patent Document 2, as a conventional technique related to measures against fuel adhesion in the intake pipe of a general-purpose engine, fuel accumulated in a recess in the intake passage is sucked into the engine as oil droplets, resulting in engine rotation fluctuations and the like. In order to prevent this, it is described that a pulsation pressure hole that communicates with the crank chamber is opened in a portion of the intake passage where fuel tends to accumulate.

JP 2007-192176 A JP-A 61-135975

In such a cylinder head, when the axial angle of the intake port and the axial angle of the barrel portion of the carburetor are different, a hollow shape is inevitably formed at the joint portion.
When the air-fuel mixture flows into this hollow shape, the air-fuel mixture collides with the port wall surface at an obtuse angle and gas-liquid separation occurs, and the fuel adhering to the port wall surface flows into the combustion chamber as droplets. Combustion increases emissions of toxic substances such as HC.
Here, it is conceivable to provide a pulsation pressure injection hole as described in Patent Document 2 in such a hollow shape, but in this case, it is necessary to provide a communication pipe between the crankcase and the like. The structure becomes complicated.
In view of the above-described problems, an object of the present invention is to provide an engine intake device that suppresses gas-liquid separation of an air-fuel mixture on an intake port wall surface with a simple configuration.

The present invention solves the above-described problems by the following means.
The invention according to claim 1 is a heat insulator having a cylinder head having an intake port for introducing an air-fuel mixture into a combustion chamber, and an opening connected to an inlet portion of the intake port for introducing the air-fuel mixture into the intake port An air intake apparatus for an engine comprising: a recessed portion in which a wall surface angle of an air-fuel mixture passage changes suddenly at a connection portion between the heat insulator and the intake port; and the heat insulator is inserted into the intake port The air-fuel mixture passes through the inside, and the front end portion is disposed downstream of the recess, and has a cylindrical air guide portion that guides the air- fuel mixture so as to collide with the wall surface of the intake port at an acute angle. This is an air intake device for an engine.
According to this, when the air-fuel mixture collides with the port wall surface, the angle formed between the traveling direction of the air-fuel mixture and the port wall surface becomes small (acute angle collision), so that gas-liquid separation is suppressed and incomplete combustion occurs. It is possible to suppress the discharge of harmful substances such as HC.
In addition, by suppressing gas-liquid separation, startability at low temperatures is improved, and delay in fuel supply when load is increased is reduced, thereby reducing engine hunting frequency and improving acceleration performance. Drivability can also be improved.
Furthermore, the intake air flow velocity is increased by the rectifying effect of the air guide portion, the charging efficiency is improved, and the engine output is improved.
In addition, since the present invention can be applied only by replacing the heat insulator with one having an air guide portion, the above-described effects can be obtained at a low cost, and can be easily applied to an existing engine.

The invention according to claim 2 is characterized in that the air guide portion is formed in a cylindrical shape having an axial angle substantially coincident with an axial angle of a barrel portion of a carburetor attached to the upstream side of the heat insulator. The engine intake device according to claim 1.
The invention according to claim 3 is the engine intake device according to claim 2, wherein an axial angle of the air guide portion is inclined with respect to an axial angle of an inlet portion of the intake port.
According to a fourth aspect of the present invention, the heat insulator is formed with a tapered opening such that the intake port side has a larger diameter with respect to the carburetor side, and the air guide portion is formed on the carburetor side of the opening. The engine intake device according to claim 3, wherein the engine intake device projects from the intake port to the intake port side.

  As described above, according to the present invention, it is possible to provide an engine intake device that suppresses gas-liquid separation of the air-fuel mixture at the intake port wall surface with a simple configuration.

It is sectional drawing which looked at the engine provided with the Example of the engine intake device of the engine to which this invention was cut | disconnected by the plane orthogonal to a crankshaft direction and containing a cylinder axis. FIG. 2 is a partial cross-sectional perspective view around a heat insulator of the engine of FIG. 1. It is an external appearance perspective view of the heat insulator and carburetor in the engine of FIG. It is a fragmentary sectional perspective view in the heat insulator periphery in the intake device of the engine of the comparative example of the present invention. It is a figure which shows the simulation result of the flow-velocity distribution in the air-fuel mixture flow path in the intake device of the engine of the comparative example. It is a figure which shows the simulation result of the flow-velocity distribution in an air-fuel | mixture flow path in the intake device of the engine of an Example.

  An object of the present invention is to provide an intake device for an engine in which gas-liquid separation of an air-fuel mixture at an intake port wall surface is suppressed with a simple configuration, and a heat insulator is provided with a cylindrical air guide portion inserted into the intake port. Solved by.

Embodiments of an engine intake device to which the present invention is applied will be described below.
FIG. 1 is a cross-sectional view of an engine provided with an intake device for an engine according to an embodiment, cut along a plane orthogonal to the crank axis direction and including the cylinder axis.
FIG. 2 is a partial cross-sectional perspective view around the heat insulator of the engine of FIG.
FIG. 3 is an external perspective view of a heat insulator and a carburetor in the engine of FIG.

The engine 1 is, for example, a single-cylinder four-stroke OHC industrial general-purpose engine that uses gasoline as fuel.
As shown in FIG. 1, the engine 1 includes a crankshaft 10, a piston 20, a connecting rod 30, a crankcase 40, a cylinder head 50, a carburetor 60, an air cleaner 70, a heat insulator 80, a muffler 90, and the like. .

The crankshaft 10 is an output shaft of the engine 1, and both ends thereof are rotatably supported by bearings.
In addition, a crank pin to which the large end portion of the connecting rod 30 is connected, a crank arm that supports the crank pin, and a crank weight are formed at an intermediate portion of the crank shaft 10.
The piston 20 reciprocates in the cylinder and transmits the pressure of the combustion gas to the crankshaft 10.
The connecting rod 30 has a small end portion connected to the piston 20 via the piston pin and a large end portion connected to the crank pin of the crankshaft 10, and connects them.

The crankcase 40 is a container-like member that houses the crankshaft 10 and the like, and is a part that constitutes the main body of the engine 1.
In the upper part of the crankcase 40, a cylinder part 41 is formed in which the piston 20 is inserted and reciprocates inside. The cylinder part 41 has a central axis arranged substantially along the vertical direction.
A cylindrical cylinder sleeve 42 is inserted on the inner diameter side of the cylinder portion 41, and the piston 20 is inserted therein.

The cylinder head 50 is provided at an upper end portion of the cylinder portion 41 and is fastened to the cylinder portion 41 with a head gasket sandwiched therebetween.
The cylinder head 50 includes a combustion chamber 51, an intake port 52, an exhaust port 53, an intake valve 54, an exhaust valve 55, and the like.
The combustion chamber 51 is a recess formed by recessing a region facing the crown surface of the piston 20 of the cylinder head 50, and is a portion where the air-fuel mixture is combusted inside.
The combustion chamber 51 is provided with a spark plug (not shown).

The intake port 52 is a passage through which the air-fuel mixture generated in the carburetor 60 (in which fuel atomized and vaporized exists in the combustion air) is introduced into the combustion chamber 51.
The inlet of the intake port 52 is opened on the side surface of the cylinder head 50 on the carburetor 60 side, and the outlet is opened on the upper portion of the combustion chamber 51. The intake port 52 is formed in a curved portion in the middle portion thereof.

The exhaust port 53 is a passage for producing burned gas (exhaust gas) from the combustion chamber 51.
The inlet of the exhaust port 53 opens to the upper portion of the combustion chamber 51 opposite to the intake port 52, and the outlet opens to the side surface of the cylinder head 50 on the muffler 90 side. It is curved.

  The intake valve 54 and the exhaust valve 55 are driven by a valve drive system such as a camshaft and rocker arms 54a and 55a (not shown), and open and close the ends of the intake port 52 and the exhaust port 53 on the combustion chamber 51 side, respectively. It is.

The carburetor 60 supplies an air-fuel mixture to the engine 1.
As shown in FIG. 2 and the like, the carburetor 60 is formed with a venturi portion 62 having an inner diameter smaller than that of the other portion in a middle portion of a passage (barrel) 61 through which fresh air passes, and chokes on the upstream side and the downstream side thereof. A valve 63 and a throttle valve 64 are respectively arranged.
The choke valve 63 and the throttle valve 64 are butterfly valves that can swing around a rotation shaft that is disposed substantially horizontally.
In addition, a heat shield plate 65 is provided outside the carburetor 60 so as to cover the main body.

  The air cleaner 70 is provided on the inlet side of the carburetor 60 and removes dust and the like from the introduced outside air and introduces it into the passage 61 of the carburetor 60.

The heat insulator 80 is a member that is fixed in a state of being sandwiched between the cylinder head 50 and the carburetor 60 in order to suppress the carburetor 60 from being heated by heat conduction from the cylinder head 50.
The heat insulator 80 is formed of a material having low thermal conductivity with respect to the material of the cylinder head 50 (for example, an aluminum alloy) such as phenol resin.

As shown in FIG. 3, the heat insulator 80 is configured by integrally molding a flange portion 81 and a heat shield plate portion 82 and further mounting an air guide portion 83.
The flange portion 81 is a portion sandwiched between the cylinder head 50 and the carburetor 60, and an opening 81a through which air-fuel mixture passes is formed in the center portion.
The opening 81 a is a circular through hole, and the central axis substantially coincides with the passage 61 of the carburetor 60. The opening 81a is formed in a tapered shape so that the intake port 52 side has a larger diameter than the carburetor 60 side.
A bolt hole 81b is formed around the opening 81a.
Bolt holes 81b are for receiving bolts (not shown) that fasten the air cleaner 70, the carburetor 60, and the heat insulator 80 to the cylinder head 50 together.
The heat shield plate portion 82 is a flat plate-like portion formed around the flange portion 81, and suppresses heat transfer due to radiation from the cylinder head 50 to the carburetor 60.

The air guide portion 83 is a cylindrical portion that is formed to protrude from the end portion on the small diameter side (carburetor 60 side) of the opening 81a of the flange portion 81 toward the intake port 52 side.
The air guide portion 83 is formed substantially concentrically with the opening 81a, and an end edge portion on the intake port 52 side is disposed along a plane orthogonal to the central axis.
The upper end portion at the distal end portion of the air guide portion 83 is disposed so as to face the upper surface portion (the inner surface portion on the outer diameter side with respect to the curvature of the intake port 52) on the inner surface of the intake port 52 with a minute gap therebetween. Yes.
Further, the lower end portion at the distal end portion of the air guide portion 83 is disposed away from the lower surface portion on the inner surface of the intake port 52.
The end portion of the air guide portion 83 on the carburetor 60 side is fixed to the flange portion 81 so that no gap is formed between the outer peripheral surface thereof and the inner peripheral edge portion of the opening 81a.
The air guide portion 83 is arranged so that the central axis thereof substantially coincides with the passage 61 of the carburetor 60, and the axis angle is different (inclined) from the inlet portion of the intake port 52 into which the air guide portion 83 is inserted. )
Note that such an air guide portion 83 may be formed integrally with the other portion of the heat insulator 80 (such as the flange portion 81).

The muffler 90 reduces the acoustic energy of the exhaust gas discharged from the exhaust port 53 and discharges it to the outside.
The muffler 90 is fixed to a side surface portion of the cylinder head 50 on the exhaust port 53 side.

Hereinafter, the effect of the above-described embodiment will be described in comparison with a comparative example of the present invention described below.
In addition, in a comparative example, the same code | symbol is attached | subjected about the location substantially common with the Example mentioned above, description is abbreviate | omitted, and a difference is mainly demonstrated.
FIG. 4 is a partial cross-sectional perspective view around the heat insulator in the intake device of the engine of the comparative example.
The intake device of the comparative example includes a heat insulator 80 in which the air guide portion 83 in the embodiment is omitted.

FIG. 5 is a diagram showing a simulation result of the flow velocity distribution in the mixture flow path in the intake device of the engine of the comparative example. The throttle opening shows a state of, for example, about 50%. At this time, the valve body of the throttle valve 64 is in relation to the axial angle of the carburetor 60 so that the lower end is on the upstream side and the upper end is on the downstream side. (Also in FIG. 6 described later).
In the comparative example, the mixed air flow that is lifted above the throttle valve 64 flows along the upper surface portion of the tapered opening 81 a, and then mainstream with respect to the upper surface portion of the intake port 52 at the inlet portion of the intake port 52. Colliding with a relatively large angle (obtuse angle collision).
In this vicinity, a concave portion (recessed shape) R in which the upper surface angle of the air-fuel mixture passage changes rapidly due to the difference in angle between the upper surface portion of the opening 81a and the upper surface portion of the intake port 52 is formed.
At this time, gas-liquid separation of the air-fuel mixture occurs in the vicinity of the recess R, and the fuel that has become droplets flows along the wall surface of the intake port 52 into the combustion chamber.
Thus, the fuel that has entered the combustion chamber in a liquid state is discharged together with the exhaust gas as HC due to incomplete combustion.

FIG. 6 is a diagram illustrating a simulation result of the flow velocity distribution in the mixture flow path in the engine intake device of the example.
In the embodiment, the air-fuel mixture exiting from the air guide portion 83 is introduced into the intake port 52 from the downstream side of the recess R. Further, since the angle formed by the upper surface of the air guide portion 83 and the upper surface of the intake port 52 is smaller than the angle formed by the upper surface of the opening 81 a and the upper surface of the intake port 52, the air-fuel mixture reaches the upper surface portion of the intake port 52. On the other hand, a collision (acute collision) occurs in a state where the angle formed by the mainstream is relatively small, and the gas-liquid separation amount of the air-fuel mixture is reduced and the HC emission amount is reduced.

According to the embodiment described above, when the air-fuel mixture collides with the wall surface of the intake port 52, the angle formed between the traveling direction of the air-fuel mixture and the inner wall surface (upper surface) of the intake port 52 becomes small (acute angle collision occurs). Therefore, since the gas-liquid separation is suppressed, the gas is guided to the combustion chamber 51 and burned, so that discharge of harmful substances such as HC due to incomplete combustion can be suppressed. For example, the amount of HC in the exhaust gas can be reduced by about 15% compared to the comparative example.
In addition, by suppressing gas-liquid separation, startability at low temperatures is improved, and delay in fuel supply when load is increased is reduced, thereby reducing engine operation such as reducing hunting times and improving acceleration performance. Can also improve.
Further, the flow rate of intake air is increased by the rectifying effect of the air guide portion 83, the charging efficiency is improved, and the output of the engine is improved.
In addition, since the present invention can be applied only by replacing the heat insulator 80 with one having the air guide portion 83, the above-described effects can be obtained at a low cost, and can be easily applied to an existing engine. .

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
The shape, structure, material, and the like of the heat insulator and the air guide portion are not limited to the above-described embodiments, and can be changed as appropriate.
Further, the engine of the embodiment is, for example, a single cylinder OHC and the cylinder is upright. However, the present invention is an engine having two or more cylinders, an engine having a different valve drive system such as an OHV, or a cylinder inclined or horizontally. It is also possible to apply to an engine or the like arranged in

DESCRIPTION OF SYMBOLS 1 Engine 10 Crankshaft 20 Piston 30 Connecting rod 40 Crankcase 41 Cylinder part 42 Cylinder sleeve 50 Cylinder head 51 Combustion chamber 52 Intake port 53 Exhaust port 54 Intake valve 54a Rocker arm 55 Exhaust valve 55a Rocker arm 60 Carburetor 61 Passage 62 Venturi part 63 Choke valve 64 Throttle valve 65 Heat shield plate 70 Air cleaner 80 Heat insulator 81 Flange portion 81a Opening 81b Bolt hole 82 Heat shield plate portion 83 Air guide portion 90 Muffler R Concavity

Claims (4)

A cylinder head having an intake port for introducing an air-fuel mixture into the combustion chamber;
A heat insulator connected to an inlet portion of the intake port and formed with an opening for introducing an air-fuel mixture into the intake port;
A concave portion is formed in which the wall surface angle of the air-fuel mixture passage suddenly changes at the connection portion between the heat insulator and the intake port,
The heat insulator is inserted into the intake port, the air-fuel mixture passes through the inside , and the tip is disposed downstream of the recess, and guides the air-fuel mixture to collide with the wall surface of the intake port at an acute angle. An air intake device for an engine having a cylindrical air guide portion. 2. The engine according to claim 1, wherein the air guide portion is formed in a cylindrical shape having an axial angle substantially coincident with an axial angle of a barrel portion of a carburetor attached to an upstream side of the heat insulator. Inhalation device. The engine intake device according to claim 2, wherein an axial angle of the air guide portion is inclined with respect to an axial angle of an inlet portion of the intake port. The heat insulator is formed with a tapered opening having a larger diameter on the intake port side than the carburetor side, and the air guide portion protrudes from the carburetor side of the opening to the intake port side. The engine intake device according to claim 3, wherein the intake device is formed.