Air-intake device for internal combustion engine

An air-intake device includes a throttle valve pivotally movable around a shaft connected to one end of the throttle valve and an airflow passage formed in the intake air passage above an upper end of the throttle valve. In a region where an amount of intake air is small (i.e., in a region where an opening-degree of the throttle valve is small), an amount of intake air passing through the airflow passage is precisely controlled. In the same region, a high-speed airflow is generated in the airflow passage thereby to formulate a uniform air-fuel mixture in a combustion chamber of an internal combustion engine. These functions are easily realized by simply adding a member for forming the airflow passage to a throttle valve unit disposed in the intake air passage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority of Japanese Patent Application No. 2006-119956 filed on Apr. 25, 2006, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air-intake device for an internal combustion engine, in which a function for adjusting an amount of an intake-air volume and a function for generating a desired air stream are included.

2. Description of Related Art

An example of an air-intake device is disclosed in JP-A-7-269375. In this device, a rotary-type throttle valve rotatable around a shaft supporting a diametric center of the throttle valve is disposed in an intake air passage. An amount of air supplied to an internal combustion engine is controlled according to an opening-degree of the rotary-type throttle valve. An additional air passage for a low air volume, corresponding to a region of a low opening-degree of the throttle valve, is provided at an upstream portion of the throttle valve in order to control an amount of air more precisely in a low air volume region. The rotary-type throttle valve in this device, however, does not generate a desired airflow directed toward an intake port of an engine cylinder. If it is necessary to generate the airflow, an airflow control valve has to be additionally provided at a downstream portion of the throttle valve, thereby increasing a manufacturing cost of the device.

Another example of this kind of device is proposed in JP-A-9-222063. In this device, an airflow control valve rotatable around its center axis is provided downstream of a throttle valve that controls an amount of air supplied to an engine. Further, a guide-groove for generating a high speed airflow when the airflow control valve is closed is provided along a wall of an intake air passage. The airflow control valve and the guide-groove in this device, however, do not has a function for precisely controlling an amount of air at a low air volume region though the airflow is generated. Further, since the airflow control valve is rotatable around its center axis, air also flows through an opening formed at an opposite side of the guide-groove when the airflow control valve is opened. Accordingly, the guide-groove cannot generate a desired airflow effectively.

A conventional throttle valve is usually made rotatable around its center axis, and intake air flows though openings at both sides of the throttle valve when it is opened. Therefore, it is difficult to precisely control an amount of intake air at a region where a volume of the intake air is low.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved air-intake device for an internal combustion engine, in which an amount of intake air is precisely controlled at its low volume region while providing a function for generating a desired airflow toward an intake port. Another object of the present invention is to provide such a device at a low cost.

The air-intake device includes a throttle valve unit disposed in an intake air passage of an internal combustion engine. The throttle valve unit is composed of a housing, a throttle valve disposed in the housing and a member for forming an airflow passage. A lower end of the throttle valve is connected to the intake air passage so that it pivotally rotates around a shaft thereby to change an open area between an upper end of the throttle valve and inner wall of the intake air passage.

The throttle valve takes a fully closed position when it becomes perpendicular to a center line of the intake air passage and takes a fully closed position when it becomes parallel to the center line. An opening-degree of the throttle valve is zero at its fully closed position and 90 degrees at its fully open position. In a predetermined region of the opening-degree of the throttle valve (where a small amount of intake air is supplied), an amount of intake air flowing through the airflow passage is precisely controlled, and at the same time an airflow having a high speed is generated in the airflow passage thereby to promote formation of uniform air-fuel mixture in a combustion chamber of the engine.

The predetermined region of the opening-degree of the throttle valve may be set so that an amount of intake air taken in that region is equal to or higher than an amount required at an warming-up idling operation of the engine and equal to or lower than an amount required for driving at a constant high speed on a flat road.

The airflow passage may be made in a tunnel-shape covered by a cover wall to reduce airflow attenuation in the passage. The tunnel-shaped passage may be branched out to form plural branch passages, each corresponding to each intake valve provided in a cylinder of the engine. An outlet port of the tunnel-shaped passage or the tunnel-shaped branch passage may be inclined so that the airflow is directed to the inlet valve. An entrance fringe of the cover wall may be slanted, curved or bent thereby to eliminate an insensitive region where an amount of intake air does not change according to the opening-degree of the throttle valve. A swollen or projected member may be formed on a rear surface of the throttle valve to prevent turnaround airflow from the front surface to the rear surface of the throttle valve. The member for forming the airflow passage may be made separately from other components of the air-intake device, so that existing device is easily modified by installing the separately made member.

According to the present invention, an amount of intake air is precisely controlled in a region where an intake air volume is low. A high-speed airflow is generated in the same region to formulate a uniform air-fuel mixture in a combustion chamber. These functions are easily provided by simply adding the member for forming the airflow passage to the throttle valve unit. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described with reference toFIGS. 1-6. Referring toFIG. 1, an entire structure of an air-intake device will be described. Intake air is supplied to each cylinder of an internal combustion engine11through an intake pipe12, a surge tank13and intake manifold14, connected in this order from an upstream end of the intake air. A throttle valve unit15is disposed in each manifold pipe connected to each cylinder of the engine11. A fuel injector (not shown) for injecting fuel toward an intake port16of each cylinder is disposed downstream of the throttle valve unit15. A spark plug for igniting mixture gas is installed in each cylinder head of the engine11. A throttle valve19of each throttle valve unit15are connected to a common shaft20that is driven by a motor21.

Now, referring toFIGS. 2-6, the throttle valve unit15will be described in detail. As shown inFIGS. 2 and 3, the throttle valve unit15is composed of a housing17made of resin, a throttle valve12pivotally supported by a shaft20, and a member23for forming an airflow passage24. The throttle valve unit15is disposed in a depressed portion25of the intake manifold14. The housing17has an intake air passage18having a square cross-section, and the intake air passage is closed or opened by the throttle valve19. The cross section of the housing is not limited to a square shape, but it could be other shapes such a half circular or a half-oval shape. The throttle valve19is connected to the common shaft20supported in the intake manifold14(FIG. 1). As shown inFIG. 2, the throttle valve19is connected to the shaft20at its lower end so that it pivotally moves around the shaft20.

The shaft20common to all throttle valves19is driven by the motor21, and thereby an opening-degree of the throttle, i.e., an amount of air supplied to the engine, is controlled according to operating conditions of the engine. It is also possible to connect the shaft20to an accelerator pedal to be driven thereby. When the throttle valve19is closed, an upper end of the throttle valve19is very close to the upper wall of the housing17(almost contacting) so that no air passes therethrough. The throttle valve19is so made that no air passes through a space between the bottom end of the throttle valve19and a lower wall of the housing17. A depressed portion22is formed in the intake manifold14, so that the throttle valve19is accommodated in the depressed portion22not to disturb airflow when the throttle valve19is fully closed, as shown with dotted line inFIG. 2.

As shown inFIGS. 2 and 3, a member23having a U-shaped cross-section is disposed in a depressed portion25positioned downstream of the throttle valve19. The member23forms an elongated airflow passage24therein, so that a speed of airflow passing through the passage24is increased for forming a uniform mixture in the cylinder. As shown inFIG. 4, the member23is formed separately from the housing17and connected to the depressed portion25of the housing17. The member23is disposed in the depressed portion25so that an upper surface23a, side surfaces23b, lower ends23cand a front end23dclosely contact the housing17, respectively. The member23is connected to the housing17by press-fitting or with adhesive.

With reference toFIGS. 5A and 5B, an opening degree of the throttle valve19will be described. As shown inFIG. 5A, the throttle valve19takes a fully closed position when an angle made between a vertical line VL (that is perpendicular to a center line of an intake airflow) and the throttle valve is 0°, while the throttle valve19takes a fully closed position when that angle is 90° (when the throttle valve19becomes parallel to the center line of the intake airflow). The opening-degree of the throttle valve19is defined as zero at the fully closed position. In a region, where the opening-degree is about 3° to 10° (this region is referred to as a low air volume region), the upper wall of the airflow passage24is made in an arc-shape so that a gap between the upper wall of the airflow passage24and the upper end of the throttle valve19gradually increases as the opening-degree increases. By disposing the member23for forming the airflow passage24in the housing17, a volume of the intake air is decreased in the low air volume region, and the volume of the intake air is more precisely controlled in this region. The gap between the inner wall of the housing17and the upper end of the throttle valve19is made very small at the fully closed position, e.g. 50 μm.

As shown inFIG. 5A, in a region “A” where the opening-degree is 0°-3°, the gap (that corresponds to an amount of the intake air passing through the throttle valve19) increases linearly. The upper end of the throttle valve19meets an inlet of the airflow passage24at the opening-degree 3°.FIG. 6shows the amount of the intake air relative to the opening-degree of the throttle valve19. In the region “A”, the amount of the intake air increases linearly. In the region “A”, the engine is operated at a speed lower than a warming-up idling speed that is 200 rpm higher than a normal idling speed. The normal idling speed is a speed at which the engine is operated after it is warmed up. In the region “A”, the airflow is not positively generated, suppressing a pumping loss that causes an increase in fuel consumption.

In a region “B” where the opening-degree is 3°-6° and a region “C” where the opening-degree is 6°-10°, a cross-sectional area of the airflow passage24(i.e., its width W×depth d) becomes gradually large according to an increase in the opening-degree. The amount of the intake air gradually increases as shown inFIG. 6, and the airflow is rectified in the passage24while increasing its flow speed at the same time. In this manner, a desirable airflow that forms a uniform mixture in a combustion chamber is generated.

In the region “B”, an amount of intake air required at a warming-up speed (a so-called fast idling speed for a cold engine) is supplied to the engine. A changing rate of an amount of the intake air relative to increase in the opening-degree of the throttle valve19is smaller in the region “B” than that in the region “C”. In the region “C”, an amount of intake air required in a high speed drive on a flat road (e.g., 120 km/h) is supplied to the engine. In a region beyond the region “C”, an amount of intake air becomes the same as that of an comparative example, in which no airflow passage is formed, as shown inFIG. 6. In other words, in a region beyond the region “C”, the amount of intake air increases according to the opening-degree of the throttle valve19.

As explained above, in the region “B” corresponding to the warming-up idling and the region “C” corresponding to the high speed drive on a flat road, a high speed airflow is generated in the airflow passage24. Therefore, an amount of fuel adhering to an inside wall of the intake port at the warming-up idling speed is reduced, and combustion in the engine is stabilized by forming a uniform mixture. Further, an amount of EGR (Exhaust Gas Recirculation) can be increased without worsening fuel economy and a pumping loss can be reduced because the uniform mixture is formed in the combustion chamber by means of the airflow generated in the airflow passage24. In the present invention, a predetermined region of the opening-degree of the throttle valve is set to cover the regions B and C. In other words, the predetermined region of the opening-degree of the throttle valve corresponds to an engine speed from the warming-up idling speed (e.g., 200 rpm higher than the normal idling speed) to a high driving speed on a flat road (e.g., 120 km/h).

Though the throttle valve19takes the fully closed position at its opening-degree 0° in the embodiment described above, it is possible to set the fully closed position at the opening-degree 3°-6°, which is usually adopted. This setting is appropriate to a small engine having a small area of the throttle valve because an amount of intake air relative to the opening-degree of the throttle valve becomes large in this setting. The upper limit of the region “B” and region “C” could be increased up to 18° and 30°, respectively, according to an area of the throttle valve19and a cross-sectional area of the airflow passage24.

Advantages attained in the first embodiment described above will be summarized below. In the predetermined region where an amount of intake air is low (i.e., in the regions B and C), the amount of intake air is precisely controlled, and an airflow for formulating a uniform mixture in the combustion chamber is generated. These advantages are attained by providing the airflow passage24in the intake air passage.

Since the throttle valve19that pivots around the shaft20connected to its bottom end is used, the amount of intake air is controlled only by changing an air passage above the throttle valve19. Accordingly, the amount of intake air is precisely controlled in the region where a small amount of intake air is required. Since the member23for forming the airflow passage24is manufactured separately from other parts such as the throttle valve19and the housing17and is installed in the depressed portion25of the housing17, it is easy to change characteristics of the airflow passage24without changing other parts. In other words, the amount of intake air and the airflow speed in the airflow passage24in the predetermined region (the regions B and C) can be easily changed only by changing the member23for forming the airflow passage.

A second embodiment of the present invention will be described with reference toFIGS. 7-11. In this embodiment, the airflow passage24is covered by a cover wall26, thereby forming a tunnel-shaped passage24, as shown inFIG. 7. Other structures are the same as those of the first embodiment. By making the tunnel-shaped airflow passage24, the airflow can reach a combustion chamber even if a distance from the airflow passage24to the combustion chamber is long. In other words, attenuation of the airflow in the airflow passage24is suppressed by forming the passage24in a tunnel-shape.

The tunnel-shaped airflow passage24may be formed as a single passage, as shown inFIG. 8. Alternatively, it may be branched out to form two branch passages, as shown inFIG. 9. The branch passages extend toward respective outlet ports24athat are directed to respective intake valves27(refer toFIG. 10) of a cylinder of the engine. The number of branch passages is not limited to two, but the number may be equal to the number of intake valves27provided in each cylinder. As shown inFIG. 10, the outlet port24aof the branch passage may be slanted or curved so that the airflow passing through the branch passage24is directed to the intake valve27. In this manner, attenuation in the airflow is suppressed. As shown inFIG. 11, a target position may be set on the intake valve27, and the airflow passing through the branch passage may be directed to the target position. For example, the target position on each intake valve27may be set at a position close to a center of the combustion chamber.

The following advantages are attained in the second embodiment in addition to the advantages attained in the first embodiment. Since the airflow passage24is made in the tunnel-shape, attenuation of the airflow is suppressed. Accordingly, the airflow can reach the combustion chamber even if a distance to the combustion chamber is long. Since the airflow is directed to each intake valve27by branching out the airflow passage24, the airflow is equally distributed to each intake valve27, thereby forming a uniform mixture in the combustion chamber. Since the outlet port24aof each branch passage24is slanted or curved, the airflow is surely directed toward each intake port and smoothly introduced into the combustion chamber.

A third embodiment of the present invention will be described with reference toFIGS. 12-14. As shown inFIGS. 14A and 14B, in the case where an entrance fringe of the cover wall26is formed in parallel to the shaft20(i.e., in parallel to the upper end of the throttle valve19), an insensitive region, where an amount of intake air does not change in response to changes in the opening-degree of the throttle valve19, is formed. This insensitive region is the region where the upper end of the throttle valve19faces the entrance fringe of the cover wall26, as shown inFIG. 14A.

In the third embodiment, in order to eliminate the insensitive region, the entrance fringe of a cover wall28is slanted relative to the direction of the shaft20by θ, as shown inFIG. 12B. Other structures are the same as those of the second embodiment. The angle θ may be set to 15°-75°. By slanting the entrance fringe of the cover wall28, the amount of intake air gradually changes according to rotation of the throttle valve even in the range where the upper end of the throttle valve19faces the entrance fringe of the cover wall28. Alternatively, the entrance fringe of the cover wall29may be formed in an arc-shape, as shown inFIG. 13B. In this manner, the insensitive region can be eliminated. The arc-shape may be convex downward or concave upward, or it may be other shapes such a V-shape or a triangular shape. By making the entrance fringe of the cover wall slanted, curved or bent relative to the direction of the shaft20, the insensitive region can be eliminated.

A fourth embodiment of the present invention will be described with reference toFIGS. 15 and 16. In this embodiment, a portion30for preventing turnaround air is formed on a downstream surface (rear surface) of the throttle valve19, as shown inFIG. 15. Other structures are the same as those of the foregoing embodiments. Air may flow (turnaround) from an upstream surface (front surface) of the throttle valve19to the rear surface. Swirls may be developed by the turnaround air on the rear surface, causing a certain flow loss in the airflow passing through the passage24. By forming the swollen portion30on the rear surface, turning around of the air is prevented or suppressed.

In place of the swollen portion30, a projected portion31may be formed on the rear surface, as shown inFIG. 16. The throttle valve19allows the intake air to flow only through the upper portion of the throttle valve19, and the throttle valve is accommodated in the depressed portion22(as shown inFIG. 2) at its fully open position. Therefore, the swollen portion30or the projected portion31formed on the rear surface does not hinder the airflow passing through the air passage18. Rather, the air supply efficiency at the fully open position is improved by preventing the swirls from being developed by the turnaround air on the rear surface.

A fifth embodiment of the present invention will be described with reference toFIG. 17. In the foregoing embodiments, the throttle valve unit15is installed in each pipe of the manifold14to supply intake air to each cylinder. In the fifth embodiment, a single throttle valve unit15common to all the cylinders is installed in the intake pipe12, as shown inFIG. 17. A tunnel-shaped passage32is extended to a surge tank13and branched out to tunnel-shaped branch passages33, each extending through the intake manifold to an intake port16of each cylinder. In this manner, the airflow generated in the tunnel-shaped passage32can be led into respective cylinders of the engine11, while suppressing attenuation in the airflow.

The present invention is not limited to the embodiments described above, but it may be variously modified. For example, a throttle valve that is pivotally movable around an axis disposed at an upper end of the throttle valve may be used. The axis around which the throttle valve is pivotally movable may be disposed at an either side (left or right) of the throttle valve. Though the fuel is injected into the intake ports in the foregoing embodiments, it may be directly injected into cylinders of the engine.