Intake passage structure for an engine

An intake passage structure for an engine includes an intake port in a cylinder head of the engine, and connected to a combustion chamber to define an intake passage. The intake passage structure further includes a heat insulating member disposed along an inner surface of the intake port, and including a bulge having an upstream end surface which is a portion of an upstream end surface of the heat insulating member, the bulge has a radially outwardly protruding radially outer surface and has an increased wall thickness. The wall thickness of the bulge increases from downstream to upstream of the intake port. The upstream end surface of the bulge includes an injection machine connecting portion facing an injection gate configured to inject resin for forming the heat insulating member into the intake port.

TECHNICAL FIELD

The present invention relates to an intake passage structure for an engine which achieves favorable combustion in a combustion chamber.

BACKGROUND ART

Air is fed into a combustion chamber of an engine through an intake passage in the intake manifold (hereinafter referred to as the “intake manifold passage”) and an intake passage in the cylinder head (hereinafter referred to as the “intake port”).

Since the intake manifold and the cylinder head are heated by heat transferred from the combustion chamber, suction air tends to be heated by heat from the inner surfaces of the intake manifold passage and the intake port.

Especially in a high-compression-ratio engine, an increased suction air temperature tends to cause knocking more frequently than in a low-compression-ratio engine. To prevent knocking, it is necessary to e.g., retard the ignition timing. Since retarding the ignition timing worsens fuel economy, it is desired to minimize the temperature rise of the suction air.

To minimize the temperature rise of the suction air, the below-identified Patent Document 1 proposes a heat insulating member for suction air which comprises a material low in thermal conductivity, such as resin, and closely adhered to the inner surface of the intake port, which is made of metal.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Object of the Invention

When forming a member by injecting resin into a mold form, the formation of weld lines is inevitable in many cases. This is also the case when forming a heat insulating member on the inner surface of the intake port by resin injection molding.

Weld lines form especially when molten resin in a mold frame is divided into multiple flows to avoid an obstacle, at positions where the portions of the resin divided into multiple flows to avoid the obstacle meet again. This is because the leading ends of the portions of the resin flowing in different directions in the mold frame cool down most quickly and thus hardens first, and the divided portions are integrated by the cooled and hardened leading ends merging each other.

Weld lines appear on the surface of a molded product, and are visually recognizable as thin lines. Ribs and/or grooves may form along such weld lines. Besides weld lines, the position of the molded product that has been opposed to an injection gate through which molten resin is injected also appears on the surface of the molded product, and is thus visually recognizable, as e.g., a circular protrusion or contour in plan view.

Especially in the case of a heat insulating member in the intake port, undulations on the inner surface of the heat insulating member could interfere with the flow of suction air. It is therefore desired to avoid the formation of such undulations.

A conventional injection gate is disposed at an intermediate portion of the intake port in the flow direction of air in the intake port, and comprises a through hole extending upwardly from the bottom of the cylinder head and communicating with the interior space in the intake port.

With the injection gate disposed at the described position, resin injected into the intake port divides into an upstream flow and a downstream flow, and the respective flows are turned and merge somewhere at an intermediate portion of the intake portion in the air flow direction. As a result, a weld line (in the form of a rib or a groove) that extends in a direction crossing the air flow direction tends to form. A weld line in a direction crossing the air flow direction resists and interferes with the flow of suction air, and thus is not preferable.

An object of the present invention is to prevent the formation of weld lines that could interfere with the flow of suction air on a heat insulating member formed in the intake port by injection molding.

Means for Achieving the Object

In order to achieve the above object, the present invention provides an intake passage structure for an engine, comprising: an intake port disposed in a cylinder head of the engine, and connected to a combustion chamber, the intake port defining an intake passage; and a heat insulating member disposed along an inner surface of the intake port, the heat insulating member including a bulge having an upstream end surface which is a portion of an upstream end surface of the heat insulating member, and a radially outer surface protruding radially outwardly beyond a radially outer surface of a portion of the heat insulating member other than the bulge so that the bulge has a wall thickness larger than a wall thickness of the portion of the heat insulating member other than the bulge.

The bulge of the heat insulating member may have a maximum wall thickness portion where the wall thickness is the largest, the maximum wall thickness portion being located within a range between the upstream end surface of the heat insulating member and a downstream end surface of the heat insulating member.

The maximum wall thickness portion may be located at the upstream end surface of the heat insulating member.

The wall thickness of the bulge may increase toward the maximum wall thickness portion of the bulge at the upstream end surface of the heat insulating member, from a downstream side of the intake port.

The upstream end surface of the bulge may include an injection machine connecting portion facing an injection gate configured to inject resin for forming the heat insulating member into the intake port.

The intake passage structure may further comprise an intake manifold connected to the cylinder head, and defining, in cooperation with the intake port, the intake passage. The intake manifold includes at a downstream end thereof a flange connected to the intake port, the flange including a bulged flange portion opposed to the bulge so as to correspond to the upstream end surface of the bulge.

The downstream end of the intake manifold and an upstream end of the intake port may define seal surfaces between the flange and the cylinder head.

The bulge may be disposed on a lower side of the intake port.

The bulge may be one of two bulges of the intake passage structure that are opposed to each other across a center of a flow passage cross-section of the intake port.

Advantages of the Invention

According to the present invention, the heat insulating member disposed along the inner surface of the intake port includes a bulge having an upstream end surface which is a portion of an upstream end surface of the heat insulating member, and having a radially outer surface protruding radially outwardly beyond the radially outer surface of the portion of the heat insulating member other than the bulge. Thus, by using the thick bulge as the injection port for injecting the material for the heat insulating member, it is possible to prevent the formation of weld lines that could interfere with the flow of suction air, on the heat insulating member in the intake port.

EMBODIMENTS

An embodiment of the present invention is described with reference to the drawings.FIG. 1Ais a sectional view of an engine of the embodiment, showing a portion of a combustion chamber3, a portion of a cylinder head1, and a portion of an intake manifold30connected to the cylinder head1.FIG. 1Bis a similar sectional view showing how a heat insulating member20made of resin is formed in an intake port of the engine.

The engine has a cylinder in which a piston is received. The combustion chamber3is defined by a top surface and an inner peripheral surface of the cylinder, and the top surface of the piston. The cylinder head1, located over the combustion chamber3, includes the intake port5for feeding intake air into the combustion chamber3, an exhaust port extending from the combustion chamber3, and a fuel injector10for injecting fuel into the combustion chamber3or the intake port5.

An intake valve hole4through which the intake port5communicates with the combustion chamber3is opened and closed by an intake valve2. Similarly, an exhaust valve hole through which an exhaust port communicates with the combustion chamber3is opened and closed by an exhaust valve.

InFIGS. 1 and 2, members and means of the engine intake side, which directly concerns the present invention, are mainly shown, and other members of the engine are not shown. While only one cylinder is shown inFIGS. 1 and 2, the engine may be a single cylinder engine or a multi-cylinder engine, i.e., an engine having a plurality of cylinders.

As mentioned above, the intake manifold30is connected to the cylinder head1, which includes the intake port5. In the intake manifold30, an intake manifold passage31is formed such that the intake manifold passage31and the intake port5constitute a portion of an intake line for supplying intake air introduced from the atmosphere through e.g., an air cleaner into the combustion chamber3.

In this embodiment, the cylinder head1is made of a metal (aluminum), while the intake manifold30is made of a resin. However, the intake manifold30may be made of a metal such as a cast metal.

The intake port5has, at its upstream end portion connected to the intake manifold passage31, a cross-section of a horizontally long oval shape, i.e., an oval shape of which the maximum distance between the upper and lower surfaces of the intake port5(i.e., the vertical diameter) is smaller than the maximum horizontal width of the intake port5(i.e., the diameter perpendicular to the vertical diameter). Similarly, the intake manifold passage31has, at its end connected to the intake port5, a cross-section of a horizontally long oval shape, i.e., an oval shape of which the maximum distance between the upper and lower surfaces of the intake manifold passage31(i.e., the vertical diameter) is smaller than the maximum horizontal width of the intake manifold passage31(i.e., the diameter perpendicular to the vertical diameter).

The intake manifold30is fixed to the cylinder head1by inserting bolts extending from the cylinder head1through holes in a flange32at the downstream end of the intake manifold passage31of the intake manifold30, and tightening the bolts with e.g., nuts. By tightening the nuts, the upstream end surface6of the intake port5comes into surface contact with an intake manifold end surface32a, i.e., the downstream end surface of the intake manifold passage31such that the intake port5and the intake manifold passage31are airtightly connected together.

The intake manifold end surface32ais formed with an annular seal groove in which an annular packing member33is received. When the nuts are tightened, the packing member33is pressed against the upstream end surface6of the intake port5, thereby increasing airtightness between the two end surfaces.

A heat insulating member20is positioned on the inner surface of the intake port5. The heat insulating member20has a predetermined thickness along the entire circumference of the inner surface of the intake port5, and has, at its upstream portion close to the intake manifold30, a tubular shape corresponding to the tubular inner surface portion13of the intake port5. The portion of the heat insulating member20having the tubular shape is hereinafter referred to as the “tubular portion23”.

A mounting hole11for mounting the fuel injector10opens to the top surface of the intake port5in its downstream region close to the combustion chamber3. The portion of the inner surface of the intake port5surrounding the mounting hole11forms a downwardly concave, mounting hole peripheral portion12including an upstream inclined surface12aand a downstream inclined surface12b. The mounting hole11opens to the upstream inclined surface12a, which faces the intake valve hole4. In the region around the mounting hole peripheral portion12too, the heat insulating member20has a predetermined thickness along the entire circumference of the inner surface of the intake port5. The portion of the heat insulating member20around the mounting hole peripheral portion12is hereinafter referred to as the “mounting hole periphery covering portion22”.

The heat insulating member20has, at the upstream end portion thereof, a bulge24which protrudes in a direction away from the center of the flow passage cross-section of the intake port5. Thus, the bulge24is a portion of the heat insulating member20having a radially outwardly expanded radially outer surface and thus having an increased wall thickness.

The bulge24is formed at the upstream end portion of the heat insulating member20so as to include at least its upstream end surface, and has a maximum wall thickness portion where the wall thickness of the bulge24is the largest, the maximum wall thickness portion being located at a point of the heat insulating member20between the upstream end surface and the downstream end surface of the heat insulating member20.

In the embodiment, the maximum wall thickness portion of the bulge24is located at the upstream end surface of the heat insulating member20, and the wall thickness of the bulge24increases from the downstream side of the intake port5toward the maximum wall thickness portion at the upstream end surface of the heat insulating member20.

Alternatively, the maximum wall thickness portion of the bulge24may be located at any point of the bulge24other than the upstream end surface of the heat insulating member20, between the upstream and downstream ends of the bulge24. In this case, the bulge24may be shaped such that its wall thickness increases gradually from the downstream end of the bulge24to the maximum wall thickness portion, and decreases gradually from the maximum wall thickness portion to the upstream end of the bulge24.

The above-mentioned “center of the flow passage cross-section of the intake port5” corresponds to, as shown inFIGS. 3A and 3B, which show such flow passage cross-section, the centerline c of the space through which the intake air in the intake port5flows. That is, the center line c is the center of the space through which intake air flows, both in the vertical direction and in the width direction, which is perpendicular to the vertical direction.

Corresponding to the bulge24, the inner surface of the intake port5has, at its upstream end portion, a bulge-forming recess14into which the bulge24is received.

The bulge-forming recess14is located upstream of the tubular inner surface portion13of the intake port5, and is recessed downwardly from the tubular inner surface portion13in the direction outwardly away from the center of the flow passage cross-section of the intake port5. The bulge-forming recess14opens to the upstream end surface6of the intake port5.

The inner surface of the bulge-forming recess14gradually approaches the center of the flow passage cross-section of the intake port5, from the upstream end surface6of the intake port5toward the tubular inner surface portion13, which is located downstream of the bulge-forming recess14. As a result, the contact surface24bbetween the bulge24and the bulge-forming recess14also gradually approaches the center of the flow passage cross-section of the intake port5, from upstream to downstream of the intake port5.

In this embodiment, the contact surface24bbetween the bulge24and the bulge-forming recess14is inclined in an arc shape, as viewed in section along the flow direction between upstream and downstream of the intake port5(direction of the centerline e). However, the contact surface24bmay be inclined in a straight line instead.

While in the embodiment, a single bulge24and a corresponding single bulge-forming recess14are disposed on the underside of the air intake port5, a plurality of bulges24and corresponding bulge forming recesses14may be disposed along the circumference of the flow passage cross-section.

The bulge24is arranged such that with the intake manifold30connected to the cylinder head1such that the intake port5communicates with the intake manifold passage31, the upstream end surface24aof the bulge24is in surface contact with the intake manifold end surface32a, which is the downstream end surface of the flange32at the downstream end of the intake manifold passage31.

The flange32of the intake manifold30includes, at its position opposed to the bulge24of the heat insulating member20, a bulged flange portion32bcorresponding to the upstream end surface24aof the bulge24. The bulged flange portion32bhas an end surface which is in surface contact with the upstream end surface24aof the bulge24and the end surface of the intake port5. Thus, the downstream end of the intake manifold30and the upstream end of the intake port5define seal surfaces between the flange32and the cylinder head1.

The heat insulating member20is formed by resin injection molding. The injection molding is carried out using a mold form40inserted in the intake port5.

As shown inFIG. 1B, the mold form40includes a tubular portion41configured to be opposed to the tubular inner surface portion13and the bulge-forming recess14, i.e., the upstream portion of the intake port5. The mold form40further includes divided portions42,43, and44configured to be opposed to the vicinity of the mounting hole peripheral portion12, i.e., the downstream portion of the intake port5.

The tubular portion41of the mold form40is tubular in shape so as to be opposed to the tubular inner surface portion13of the intake port5with a predetermined gap left therebetween, and opposed to the bulge-forming recess14with a gap left therebetween which is larger than the gap between the tubular portion41and the tubular inner surface portion13. The tubular portion41can be inserted into and taken out of the intake port5through the upstream opening of intake port5.

The divided portions42,43, and44of the mold form40are complimentary in shape to the vicinity of the mounting hole peripheral portions12and configured to be opposed to the inner surface of the intake port5with a predetermined gap left therebetween. The divided portions42,43, and44are separate from each other so that they can be inserted into and removed from the intake port5through the downstream end of the intake port5, which opens to the combustion chamber3. The divided portions42,43, and44can be joined together in the intake port5, and can be disconnected from each other, and taken out through the intake valve hole4, after the resin has hardened.

The upstream end of the mold form40defines an upstream flange45to be in surface contact with the upstream end surface6of the intake port5. The upstream flange45has an injection gate46extending through the upstream flange45in the thickness direction thereof, and open to the bulge-forming recess14, which is a portion of the mold form space defined between the inner surface of the intake port5and the outer surface of the mold form40. The bulge24is shaped such that the area of the upstream end surface24aof the bulge24is larger than the sectional area of the injection gate46, through which injected resin passes, and the height (vertical dimension) and the lateral width of the bulge24are both larger than the diameter of the injection gate46(which has a circular cross-section).

As shown inFIGS. 1B and 2A, with the mold form40inserted into the intake port5and fixed in position, the injection port of an injection machine A is inserted into the injection gate46, and the mold form space between the inner surface of the intake port5and the outer surface of the mold form40is filled with resin injected from the injection machine A. Then, after the resin has hardened, the mold form40is removed to form the heat insulating member20fixedly attached to the inner surface of the intake port5.

The thus formed heat insulating member20is shown inFIG. 2B. In this arrangement, since the upstream end surface24aof the bulge24is an injection machine connecting portion that faces the injection gate46, through which the resin to be formed into the heat insulating member20is injected into the intake port5, the heat insulating member20has a weld line w extending between upstream and downstream of the intake port5.

That is, the resin injected from the injection machine A flows through the injection gate46, and enters the mold form space through the injection machine connecting portion facing the injection gate46(i.e., through the upstream end surface of the bulge24of the heat insulating member20to be formed by the injected resin). The resin then moves from upstream to downstream, while moving in the opposite circumferential directions until its leading ends merge at a position opposite from the injection machine connecting portion, i.e., the upstream end surface of the bulge24, across the center of the flow passage cross-section of the intake port5, thus forming the weld line w at this position.

The weld line w forms because when the two separate masses of the molten resin collide against each other, they cool down and harden before they completely melt into each other. In the embodiment, as shown inFIG. 3, the weld line w forms at a position opposite from the injection machine connecting portion, i.e., the bulge24across the center of the flow passage cross-section of the intake port5(see letter B at the upper portion ofFIG. 3A) so as to extend substantially in the direction of, i.e., substantially parallel to, the centerline c of the intake port5.

Since, according to the present invention, the upstream end surface24aof the bulge24of the heat insulating member20serves as the injection machine connecting portion, the injection gate46can be provided in the mold frame40. This eliminates the necessity of providing an injection gate in the cylinder head1as in conventional arrangements, and thus simplifies the structure and increase the strength, of the cylinder head1.

Another advantage of using the upstream end surface24aof the bulge24of the heat insulating member20as the injection machine connecting portion is that it is not necessary to use a seal plug to fill the injection gate46after the resin has hardened. Furthermore, the injection gate46will never affects the flow of intake air in the intake port5.

Moreover, since the weld line w forms in the direction of the centerline c of the intake port5, the undulation resulting from such weld line w will never affect the flow of intake air.

Furthermore, the thick-walled bulge24, as the injection machine connecting portion, provides an anchoring effect to the heat insulating member20, that is, the bulge24increases the adhesion between the heat insulating member20, which is made of resin, and the intake port5, made of metal, thereby preventing displacement therebetween under external forces or due to shrinkage with time.

By configuring the bulge24such that it includes the upstream end surface of the heat insulating member20and such that the maximum wall thickness portion of the bulge24, i.e., its portion where the wall thickness is the largest, is located at the upstream end surface of the heat insulating member20, the heat insulating member20can be formed without disturbing the flow of resin in the mold frame40. However, the position of the maximum wall thickness portion of the bulge24is not limited at the upstream end surface of the heat insulating member20. That is, if the maximum wall thickness portion of the bulge24is disposed at any point between the upstream end surface and the downstream end surface of the heat insulating member20, the bulge24will effectively prevent separation of the heat insulating member20from the intake port5, and allow the heat insulating member20to more effectively insulate intake air from heat.

By the provision of the bulge24and the corresponding bulge forming recess14, the intake manifold30can be more rigidly fixed to the cylinder head1. This is because the bulge24and the bulge forming recess14increase the contour of the contact portion between the upstream end surface6of the intake port5and the flange32of the intake manifold passage31, and thus the contact area therebetween. The upstream end surface24aof the bulge24is prevented from moving upstream by abutting the end surface32aof the bulged flange portion32b, which is formed on part of the flange32of the intake manifold passage31. The bulged flange portion32bis disposed at a position corresponding to the upstream end surface24aof the bulge24to cover the upstream end surface24a.

FIGS. 4A-4Cshow other embodiments, in which a plurality of bulges24, and bulge forming recesses14corresponding to the respective bulges24are disposed around the flow passage cross-section of the intake port5.

In the embodiment ofFIG. 4A, two bulges24(and corresponding two bulge forming recesses14) are disposed so as to be vertically opposed to each other across the center of the flow pass cross-section of the intake port5, and two injection gates46are opposed to the respective upper and lower bulge forming recesses14.

By providing two injection gates46so as to be opposed to each other across the center of the flow passage cross-section of the intake port5, the resin can be filled more uniformly, the heat insulating member has a more uniform wall thickness, and the heat insulating member can be formed in a shorter period of time. This improves the adhesion between the resin forming the heat insulating member20and the metal forming the inner surface of the intake port5. Further, by providing the injection gates46so as to be vertically opposed to each other, two weld lines w form on the right and left of the center of the flow passage cross-section of the intake port5. This minimizes undulations near the top and bottom of the inner surface of the intake port5, which could disturb the tumble flow of the intake air in the combustion chamber3.

If the engine includes more than one cylinder, and the distance between the intake ports5of adjacent cylinders is short, the two bulges24(and thus the two bulge forming recesses14) are preferably disposed above and below the intake port5, respectively, as in the embodiment ofFIG. 4A, to ensure installation space and for maintenance.

InFIG. 4B, two bulges24(and corresponding two bulge forming recesses14) are disposed on the right and left of the center of the flow pass cross-section of the intake port5, respectively, and two injection gates46are opposed to the respective right and left bulge forming recesses14.

By providing two injection gates46on the right and left of the center of the flow passage cross-section of the intake port5, two weld lines w form above and below the center of the flow passage cross-section of the intake port5. By arranging two bulges24(and thus two bulge forming recesses14) on the right and left of the intake port5as in the embodiment ofFIG. 4B, a large installation space is created for the fuel injector10.

In the embodiment ofFIG. 4C, two bulges24(and corresponding two bulge forming recesses14) are disposed so as to be vertically opposed to each other across the center of the flow pass cross-section of the intake port5, and additional two bulges24(and corresponding additional two bulge forming recesses14) are disposed on the right and left of the center of the flow pass cross-section of the intake port5, respectively. Four injection gates46are opposed to the respective upper and lower, and right and left bulge forming recesses14.

By providing two vertically opposed injection gates46and two additional horizontally opposed injection gates46, weld lines form at the upper left, upper right, lower left, and lower right corners so as to be opposed to each other across the center of the flow passage cross-section of the intake port5. Also, by providing four injection gates46in this manner, as in the previously described embodiments, the resin can be filled more uniformly, the heat insulating member has a more uniform wall thickness, and the heat insulating member can be formed in a shorter period of time. Moreover, since it is possible to reduce the amount of resin injected through one injection gate46, it is possible to reduce the sectional area of each injection gate46.

DESCRIPTION OF THE REFERENCE NUMERALS