SECONDARY AIR SUPPLY DEVICE FOR INTERNAL COMBUSTION ENGINE

The disclosure of Japanese Patent Application No. 2007-217287 filed on Aug. 23, 2007 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a secondary air supply device for an internal combustion engine. In particular, the invention relates to a secondary air supply device for an internal combustion engine that supplies secondary air from an air cleaner to the portion of an exhaust pipe that is upstream of a catalyst provided in an exhaust pipe.

2. Description of the Related Art

In order to a catalyst appropriately purify exhaust gas discharged from an internal combustion engine mounted in a vehicle such as an automobile, the temperature of platinum, palladium or other catalytic component formed on a surface of a ceramic honeycomb substrate or the like needs to be raised to a predetermined activation temperature. Therefore, there is minimal purification of the exhaust gas until the temperature of the catalyst reaches the predetermined activation temperature after the internal combustion engine is started.

In order to solve such a problem, there is a vehicle with a secondary air supply device that supplies air to the exhaust pipe to purify hydrocarbon (HC) or carbon monoxide (CO) in exhaust gas after an an internal combustion engine is started while the catalyst is cold. Such a secondary air supply device is shown in FIG. 10 (see Japanese Patent Application Publication No. 2005-163708 (JP-A-2005-163708), for example).

As shown in FIG. 10, an internal combustion engine 1 is connected to the exhaust manifold 2, which is connected to an exhaust pipe 3 via a catalytic device 4. A secondary air supply pipe 6 is connected to the exhaust manifold 2 via an electromagnetic air switching valve (ASV) 5 that controls the opening and closing of the secondary air supply pipe 6 to communicate the secondary air supply pipe 6 and the exhaust manifold 2 with each other or to block this communication. Furthermore, a secondary air lead-out port 7a of an air pump 7 is connected to the secondary air supply pipe 6 so that air is drawn in through a secondary air introduction port 7b of the air pump 7 as shown by the arrow in the drawing and then supplied to the secondary air supply pipe 6.

In the secondary air supply device as shown, once the air introduced from the secondary air introduction port 7b is supplied by the air pump 7 to the exhaust manifold 2 via the secondary air supply pipe 6 and electromagnetic ASV 5, the oxidation of unburned components such as hydrocarbon (HC) or carbon monoxide (CO) contained in exhaust gas is accelerated and, as a result, a catalyst of the catalytic device 4 may be activated promptly by the combustion heat generated by the oxidation of the unburned components of the exhaust gas.

However, in the secondary air supply device described above, when the vehicle travels in the rain or over puddles of water, air containing water is introduced from the secondary air introduction port 7b to the air pump 7 and then supplied from the air pump 7 to the exhaust manifold 2 via the secondary air supply pipe 6 and electromagnetic ASV 5, the water is drawn directly into the catalyst.

Especially in an overcab in which the engine 1 is installed below the driver seat, the air pump 7 easily introduces the air containing water because the engine 1 is installed in a position near a road surface, and the air is easily supplied from the air pump 7 to the catalytic device 4 via the secondary air supply pipe 6, electromagnetic ASV 5 and exhaust manifold 2.

Moreover, if the water comes into contact with the high-temperature catalyst carried on the honeycomb substrate of the catalytic device 4, the catalyst may be damaged, resulting in deterioration of catalyst performance.

SUMMARY OF THE INVENTION

This invention provides a secondary air supply device for an internal combustion engine that prevents the entry of water into a catalyst.

A first aspect of the invention relates to a secondary air supply device for an internal combustion engine. The secondary air supply device includes: a secondary air supply pipe, one end of which is connected to an exhaust pipe at a position upstream of a catalyst that is provided in the exhaust pipe; a supply pump, connected to the other end of the secondary air supply pipe, that supplies secondary air via the secondary air supply pipe to the exhaust pipe; an air cleaner that includes a main body provided with an air introduction port for introducing air, an air lead-out port for leading the air out, and a filter element, provided within the main body, that is positioned between the air introduction port and the air lead-out port; a secondary air lead-out pipe, one end of which is connected to the supply pump and the other end connected to the main body; and a secondary air discharge pipe, which is provided in the main body and discharges the secondary air from the main body to the supply pump via the secondary air lead-out pipe, wherein the secondary air discharge pipe is positioned apart from the air introduction port in the main body in relation to a direction of flow of the air within the main body.

According to the above constitution, the secondary air discharge pipe, which leads the secondary air out of the main body of the air cleaner to the supply pump, is positioned apart from the air introduction port in relation to a direction of flow of the air within the main body. Therefore, any water that is introduced into the air introduction port along with air when the vehicle travels in the rain or over puddles of water is separated from the air as the water moves from the air introduction port to the secondary air discharge pipe. As a result, only the air is led out of the secondary air discharge pipe to the supply pump through the secondary air lead-out pipe.

Consequently, only the secondary air is supplied from the supply pump to the discharge pipe through the secondary air supply pipe and water is prevented from entering a high-temperature catalyst. As a result, damage of the catalyst and deterioration of catalyst performance may be prevented.

A second aspect of the invention relates to an air cleaner. The air cleaner includes: a main body that is provided with an air introduction port for introducing air and a first air lead-out port for leading the air out; a filter element that is provided within the main body and positioned between the air introduction port and the first air lead-out port; and a second air lead-out port provided in the main body that is positioned apart from the air introduction port in relation to a direction of air flow within the main body.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements, and wherein:

FIG. 1 is a schematic configuration diagram of a secondary air supply device for an internal combustion engine according to a first embodiment of the invention;

FIG. 2 is a top view of an air cleaner shown in FIG. 1;

FIG. 3 is a perspective cross-sectional view taken along a direction III-III of FIG. 2;

FIG. 4 is a schematic perspective view of the air cleaner shown in FIG. 1;

FIG. 5 is a diagram showing the flow of air introduced from an air introduction port of the air cleaner shown in FIG. 1 into the casing of the air cleaner;

FIG. 6 is a perspective view showing the shape of a secondary air discharge pipe of a secondary air supply device for an internal combustion engine according to a second embodiment of the invention;

FIG. 7A is a perspective view showing the shape of a secondary air discharge pipe of a secondary air supply device for an internal combustion engine according to a third embodiment of the invention;

FIG. 7B is a cross-sectional view of the secondary air discharge pipe of the secondary air supply device for an internal combustion engine according to the third embodiment of the invention;

FIG. 8A is a top view of an air cleaner of a secondary air supply device for an internal combustion engine according to a fourth embodiment of the invention;

FIG. 8B is a cross-sectional view taken along a direction X-X of FIG. 8A;

FIG. 9 is a top view of the air cleaner that has a secondary air discharge pipe of a shape different from that of the secondary air supply device for an internal combustion engine according to the fourth embodiment of the invention; and

FIG. 10 is a schematic configuration diagram of a secondary air supply device of a related art.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, secondary air supply devices for an internal combustion engine according to the first to fourth embodiments of the invention are described with reference to the drawings.

FIGS. 1 to 5 are diagrams showing a secondary air supply device for an internal combustion engine according to the first embodiment of the invention.

The configuration of the secondary air supply device according to the first embodiment of the invention will now be described. As shown in FIG. 1, in an internal combustion engine 11 with four cylinders, the combustion chamber of each cylinder is communicated with an exhaust manifold 12 via an exhaust port. The exhaust manifold 12 is connected to an exhaust pipe 13 via a catalytic device 14.

The catalytic device 14 is configured by a product in which a main body case thereof accommodates a substance obtained by applying a catalyst such as platinum or palladium to a honeycomb substrate or a granular active alumina support. The catalytic device 14 reduces NOx or oxidizes CO and HC.

One end of a secondary air supply pipe 16 is connected to the exhaust manifold 12 via an electromagnetic air switching valve (ASV) 15 that controls opening and closing of the secondary air supply pipe 16 to communicate the secondary air supply pipe 16 and the exhaust manifold 12 with each other or to block this communication.

A secondary air lead-out port 17a of an air pump 17, which serves as a supply pump, is connected to the other end of the secondary air supply pipe 16, and a cyclone air cleaner 20 is connected to a secondary air introduction port 17b of the air pump 17 via a secondary air lead-out pipe 18. Specifically, one end of the secondary air lead-out pipe 18 is connected to the air pump 17, while the other end of the same is connected to the air cleaner 20. The electromagnetic ASV 15 is connected to the exhaust pipe upstream of the catalytic device 14 provided in the exhaust pipe 13 to introduce secondary air from the air pump 17 into the portion of the exhaust pipe upstream of the catalytic device 14. Note that “secondary air” means air that is supplied to the portion of the exhaust pipe upstream of the catalytic device 14 and is then mixed with gas discharged from the combustion chambers. Also, the electromagnetic ASV 15 and the air pump 17 are controlled by an engine control unit (ECU), which is not shown.

The air cleaner 20 filters outside air to remove debris (dust, dirt, oil and the like) to the combustion chambers of the engine 11. As shown in FIGS. 2 and 3, the air cleaner 20 is configured by a casing 24, which is a main body having an air introduction port 21 and air lead-out port 22, a cylindrical filter element 27 accommodated in the casing 24, and a fastener 25, which is a supporting member for suspending the filter element 27 in the casing 24.

As shown in FIG. 2, the casing 24 is roughly cylindrical in shape and is provided with the air introduction port 21 that is tilted at approximately 45° to an axial direction of the casing 24. Furthermore, an upper wall of the casing 24 is provide with the air lead-out port 22, and the air introduction port 21 and air lead-out port 22 are opened inward of the casing 24.

The air lead-out port 22 is provided with a resonator 23. The resonator 23, which has a chassis having a space therein and a communication hole that communicates the chassis and the air lead-out port 22 with each other, functions to reduce the sound of the air led out of the air lead-out port 22. The air lead-out port 22 is connected to an intake pipe, which is not shown, and the intake pipe is communicated with the combustion chamber of each cylinder of the engine 11 via an intake manifold and the exhaust port, which are not shown.

Moreover, the bottom of the casing 24 is provided with a dust pan 26. Debris that is separated from the air is accumulated in the dust pan 26. Note that the casing 24 of the present embodiment is shaped and formed of a metallic material such as a steel plate, or a resin material such as a polypropylene.

The filter element 27 is in the shape of a hollow cylinder. Although not described in detail, the filter element 27 is a conventional element in which an annular end plate is joined to each axial end of a filter element main body, and this element is formed of a filtering medium that is obtained by forming filter paper or the like into a chrysanthemum-shaped cylinder.

A hollow portion 27a configured by an inner peripheral part of the filter element 27 and the opening 22a of the air lead-out port 22 are disposed substantially coaxially, and the air lead-out port 22 is bent at the opening 22a toward a downstream in an air lead-out direction.

Also, the fastener 25 for securing the filter element 27 in the casing 24 and on the bottom part in a lower part of the casing 24 is provided within the hollow portion 27a of the filter element 27.

An upper end of the fastener 25 is attached to the opening 22a of the air lead-out port 22, while a lower end of the fastener 25 is screwed to a partition board 29 by a tightening tool 28. The fastener 25 has a stay 30 that is obtained by bending a belt-like steel plate into a rough U-shape, a screw 31 that can be screwed into the tightening tool 28, and straightening vanes 32. The stay 30 and screw 31 are each configured by a U-shape supporting member of a conventional structure that suspends the filter element 27 in the casing 24.

Note that the screw 31 and a screw part of the tightening tool 28 that are screwed together may not be limited to a male screw and a female screw such as a nut, as shown in FIG. 3, and thus the screw may be a female screw and the tightening tool may be a male screw.

The stay 30 is configured by a pair of arms 30a that extend in substantially an axial direction of the hollow portion 27a of the filter element 27, and the lower end 30b that couples the pair of arms 30a together. The upper end side of the arms 30a is welded to the inner periphery of the air lead-out port 22. Also, one of axial ends of the screw 31 is latched to the lower end 30b of the stay 30.

The straightening vanes 32, made of metallic plates, are disposed coaxially with the filter element 27. Specifically, the straightening vanes 32 are disposed such as to divide the inner periphery of the hollow portion 27a into two, as shown in FIG; 2. The straightening vanes 32 are disposed so as to form a cross-link between the arms 30a, and forms a dividing wall that cross-links a predetermined axial range between the arm parts 30a.

The casing 24 of the air cleaner 20 is provided with a secondary air discharge pipe 33. The secondary air discharge pipe 33 has a cylindrical main body 33a that is connected to the secondary air lead-out pipe 18, and a flange portion 33b that is provided in the main body 33a and secured to the casing 24 of the air cleaner 20 by screws 34. A communication hole 33c provided within the main body 33a communicates the secondary air lead-out pipe 18 with the inside of the casing 24.

The secondary air discharge pipe 33 is also disposed in the upper portion of the casing 24, and the secondary air discharge pipe 33 and air introduction port 21 are provided in the casing 24 to be apart from each other with respect to a swirling direction of the air introduced into the casing 24. In the cyclone air cleaner 20 the secondary air discharge pipe 33 is provided near the air introduction port 21 in the casing 24 at a downstream position in the air flow direction from the air introduction port 21.

In the present embodiment, the air pump 17, the secondary air lead-out pipe 18 and the air cleaner 20 configure the secondary air supply device.

A secondary air supply method of the engine 11 of the present embodiment is described next. In an overcab in which the engine 11 may be installed below the driver seat, there is a high possibility that air is drawn into the air cleaner 20 along with water when the vehicle travels in the rain or through puddles of water, because the engine 11 is positioned near a road surface. A secondary air supply method that is used when the vehicle travels in the rain or through puddles of water will now be described.

Once the engine 11 is started, air is drawn into the casing 24 by the negative pressure generated by a piston during its intake stroke. When traveling in the rain or over puddles of water, the air and water are introduced from the air introduction port 21 into the casing 24.

The air with water that is introduced into the casing 24 swirls between an inner peripheral surface of the casing 24 and an outer peripheral surface of the filter element 27, and relatively coarse debris and the water that are contained in the air are pressed toward the inner periphery of the casing 24 by the centrifugal force generated by the swirling air flow, while the air containing water swirls between the inner peripheral surface of the casing 24 and the outer peripheral surface of the filter element 27. The debris and water are dropped along the inner periphery of the casing 24 by the centrifugal action of the swirling flow and the weight of the debris and water, and the dropped debris and water accumulate in the dust pan 26 provided in the bottom part of the casing 24.

On the other hand, because the air swirling in a spiral manner circulates around the entire outer periphery of the filter element 27, the air is introduced from the entire outer periphery toward inner periphery of the filter element 27 and merges at the hollow portion 27a. The air that is filtered by the element main body of the filter element 27 flows out toward the central of the hollow portion 27a.

The filtered air that merges at the hollow portion 27a flows toward the opening 22a of the air lead-out port 22 and is then supplied from the intake pipe connected to the air lead-out port 22 to the combustion chamber of each of the cylinders of the engine 11 via the intake manifold and an intake port.

Because the secondary air discharge pipe 33 is provided in proximity to the air introduction port 21 on the downstream side in the swirling direction of the air with respect to the air introduction port 21, and the water contained in the air is pressed toward the inner periphery of the casing 24 by the centrifugal force generated by the swirling air flow, the water is then dropped along the inner periphery of the casing 24 by the centrifugal action of the swirling flow and the weight of the water, as described above.

Therefore, the air that is introduced from the air introduction port 21 into the casing 24 and separated from the water is discharged from the secondary air discharge pipe 33 to the secondary air lead-out pipe 18, as shown by B in FIG. 5. The secondary air that is led out to the secondary air lead-out pipe 18 is drawn in by the air pump 17, supplied from the air pump 17 to the secondary air supply pipe 16, and thereafter supplied to the exhaust manifold 12 via the opened electromagnetic ASV 15.

The secondary air supplied to the exhaust manifold 12 is mixed with exhaust gas discharged from the combustion chambers of the engine. As a result, oxidation of unburned components, such as hydrocarbon (HC) or carbon monoxide (CO) contained in the exhaust gas, is accelerated and, consequently, the catalyst of the catalytic device 14 is promptly activated by the combustion heat generated by the oxidation of the unburned components of the exhaust gas.

In the present embodiment, the secondary air discharge pipe 33 for leading the secondary air out of the casing 24 of the air cleaner 20 to the air pump 17 is provided, and this secondary air discharge pipe 33 is provided in proximity to the air introduction port 21 on the downstream side in the swirling direction of the air with respect to the air introduction port 21 as described above. Therefore, when traveling in the rain or over puddles, air containing water that is introduced from the air introduction port 21 is separated from the water while the air moves from the air introduction port 21 to the secondary air discharge pipe 33. As a result, only the air can be led out of the secondary air discharge pipe 33 to the air pump 17 via the secondary air lead-out pipe 18.

Therefore, only the secondary air can be supplied from the air pump 17 to the exhaust manifold 12 via the secondary air supply pipe 16, and the water is prevented from being supplied to the high-temperature catalyst of the catalytic device 14. As a result, damage of the catalyst and deterioration of catalyst performance can be prevented.

In addition, in the present embodiment, the air cleaner 20, which has the cylindrical filter element 27, is configured such that the air introduced from the air introduction port 21 into the casing 24 via the secondary air discharge pipe 33 swirls along the inner peripheral surface of the casing 24, and is then filtered by the filter element 27, caused to merge at the hollow portion 27a formed on the inside of the filter element 27, and then led out by the air lead-out port 22. Accordingly, the air introduced from the air introduction port 21 into the casing 24 is caused to swirl significantly along the inner peripheral surface of the casing 24 and then discharged from the secondary air discharge pipe 33.

Therefore, the air introduced from the air introduction port 21 into the casing 24 is moved a long distance between the air introduction port 21 and the secondary air discharge pipe 33. As a result, the size of the air cleaner 20 may be reduced and the water is efficiently separated from the air introduced into the casing 24. Moreover, only air is supplied from the secondary air discharge pipe 33 to the air pump 17 via the secondary air lead-out pipe 18.

In the present embodiment, the secondary air discharge pipe 33 is provided in the upper part of the casing 24. Therefore, if the water separated from the air is dropped on the bottom surface of the casing 24 as the air moves from the air introduction port 21 to the secondary air discharge pipe 33, the water may be securely prevented from being discharged from the secondary air discharge pipe 33.

Specifically, when the engine 11 is operated, although there is a possibility that the water that is dropped on the bottom surface of the casing 24 is drawn by the negative pressure of the piston during its intake stroke, in the present embodiment the water drawn from the bottom surface of the casing 24 is prevented from reaching the secondary air discharge pipe 33 by providing the secondary air discharge pipe 33 in the upper part of the casing 24, so that the water is securely prevented from being discharged from the secondary air discharge pipe 33.

FIG. 6 is a diagram showing a secondary air supply device for an internal combustion engine according to the second embodiment of the invention. Because only the configuration of a secondary air discharge pipe of this secondary air supply device differs from that of the first embodiment, the components that are identical to those of the first embodiment are assigned with the same reference numerals, and thus explanations of these components are omitted.

In FIG. 6, the secondary air discharge pipe 41 has a cylindrical main body 41a that is connected to the secondary air lead-out pipe 18, and a flange (not shown) that is provided in the main body 4 la and secured to the casing 24 of the air cleaner 20 by a screw. A communication hole 41b provided within the main body 41a communicates the secondary air lead-out pipe 18 with the inside of the casing 24.

The main body 41a has a projection 41c that projects inward of the casing 24 from the inner peripheral surface of the casing 24. The communication hole 41b is formed within the projection 41c. Specifically, the main body 41a is an integrated component having the communication hole 41b therein, wherein the projection 41c projects inward of the casing 24 from the inner peripheral surface of the casing 24.

In the present embodiment, the air swirling on the inner peripheral surface of the casing 24 may be directed to collide with the projection 41c to create an air flow that is divided into upper and lower flows, as shown by B1 and B2 in FIG. 6. Therefore, even if water reaches the secondary air discharge pipe 41 along with the air that is drawn in from the air introduction port 21 into the casing 24, the amount of water entrained into the projection 41c is reduced by a wall surface of the projection 41c. Consequently, it is possible to more securely prevent the water from being discharged from the secondary air discharge pipe 41 and in to the secondary air lead-out pipe 18.

FIG. 7A or B is a diagram showing a secondary air supply device for an internal combustion engine according to the third embodiment of the invention. Because only the configuration of a secondary air discharge pipe of this secondary air supply device differs from that of the first embodiment, the components that are identical to those of the first embodiment are assigned with the same reference numerals, and thus explanations of these components are omitted.

In FIG. 7B, a secondary air discharge pipe 45 has a cylindrical main body 45a that is connected to the secondary air lead-out pipe 18, and a flange 45b that is provided in the main body 45a and secured to the casing 24 of the air cleaner 20 by a screw 46. A communication hole 45c provided within the main body 45a communicates the secondary air lead-out pipe 18 with the inside of the casing 24.

The main body 45a has a projection 45e that projects inward of the casing 24 from the inner peripheral surface of the casing 24, and the projection 45e has formed therein a communication hole 45c. Specifically, the main body 45a is an integrated component having the communication hole 45c therein, wherein the projection 45e projects inward of the casing 24 from the inner peripheral surface of the casing 24.

Moreover, the communication hole 45c of the projection 45e is configured such that its diameter increases from the inner peripheral surface of the casing 24 toward the inside of the casing 24, and the projection 45a is formed into a trumpet shape.

As with the second embodiment, in this embodiment the air swirling on the inner peripheral surface of the casing 24 may be directed to collide with the projection 45e to create an air flow that is divided into upper and lower flows. Therefore, even if water reaches the secondary air discharge pipe 45 along with the air that is drawn from the air introduction port 21 into the casing 24, the amount of water entrained into the projection 45e may be reduced by the wall surface of the projection 45e.

In addition, because the communication hole 45c of the projection 45e is configured so that its diameter increases from the inner peripheral surface of the casing 24 toward the inside of the casing 24, a flow passage of the communication hole 45c on an upstream side in a secondary air lead-out direction may be made wider than a flow passage of the communication hole 45c on a downstream side in the secondary air lead-out direction.

Therefore, the speed of the air introduced into the communication hole 45c of the projection 45e on the upstream side in the secondary air lead-out direction may be reduced, and the water is prevented from being introduced into the secondary air discharge pipe 45 along with the air. Consequently, the water is more securely prevented from being drawn from the secondary air discharge pipe 45 to the secondary air lead-out pipe 18.

FIGS. 8 and 9 are diagrams each showing a secondary air supply device for an internal combustion engine according to the fourth embodiment of the invention. Note that the fourth embodiment is provided in the position of the cyclone air cleaner 20, and thus only the configuration of the air cleaner of the present embodiment is different from that of the first embodiment. Therefore, the components that are identical to those of the first embodiment are assigned with the same reference numerals, and explanations of these components are provided using FIG. 1 if required.

In FIG. 8, an air cleaner 51 is configured by a casing 52, which is a main body having an air introduction port 53 and air lead-out port 54, and a rectangular filter element 55 accommodated in the casing 52.

The casing 52 is formed into a rectangular shape, and the air introduction port 53 and the air lead-out port 54 are attached to front and rear ends of the casing 52 so as to be disposed in a linear fashion.

The air lead-out port 54 is connected to an intake pipe, which is not shown. The intake pipe is communicated with the combustion chamber of each cylinder of the engine 11 via the intake manifold and exhaust port, which are not shown. Also, the casing 52 of the present embodiment is shaped and formed of a metallic material such as a steel plate, or a resin material such as a polypropylene. The rectangular filter element 55 is formed of a filtering medium that is obtained by forming filter paper or the like into a wave-shape.

The casing 52 of the air cleaner 51 is provided with a secondary air discharge pipe 56. The secondary air discharge pipe 56 has a cylindrical main body 56a that connected to the secondary air lead-out pipe 18, and a flange 56b that is provided in the main body 56a and secured to the casing 52 of the air cleaner 51 by a screw 57. A communication hole 56c provided within the main body 56a communicates the secondary air lead-out pipe 18 with the inside of the casing 52.

The secondary air discharge pipe 56 is also disposed in an upper part of the casing 52. The secondary air discharge pipe 56 is farther provided in the casing 52 so as to be apart from the air introduction port 53 with respect to a direction of flow of the air introduced into the casing 52. Furthermore, the main body 56a of the secondary air discharge pipe 56 extends in a direction perpendicular to the straight line that connects the air introduction port 53 with the air lead-out port 54.

In the present embodiment, the air pump 17, the secondary air lead-out pipe 18 and the air cleaner 51 configure the secondary air supply device.

A secondary air supply method of the engine 11 of the present embodiment is described next. In an overcab in which the engine 11 is installed below the driver seat, there is a high possibility that water is drawn into the air cleaner 51 along with air when the vehicle travels in the rain or puddles, because the engine 11 is installed in a position near a road surface. A secondary air supply method that is used when the vehicle travels in the rain or over puddles.

Once the engine 11 is running, air is drawn into the casing 52 by the negative pressure generated by a piston during its intake stroke. When the vehicle travels in the rain or on puddles of water, the air and water are introduced from the air introduction port 53 into the casing 52.

The air and water that are introduced into the casing 52 are filtered by the filter element 55 to remove relatively coarse debris and the water. Subsequently, the filtered air is supplied from the intake pipe connected to the air lead-out port 54 to the combustion chamber of each of the cylinders of the engine 11 via the intake manifold and intake port.

On the other hand, if the water that is not filtered by the filter element 55 moves to a downstream side in the direction of flow of the air with respect to the filter element 55, the movement force of the unfiltered water is weakened by a shock of collision with the filter element 55. Therefore, the unfiltered water is dropped on the bottom surface of the casing 52 by the weight of the unfiltered water while moving from the filter element 55 to the secondary air discharge pipe 56.

Therefore, the air that is introduced from the air introduction port 53 into the casing 52 and separated from the water is discharged from the secondary air discharge pipe 56 to the secondary air lead-out pipe 18. The secondary air that is led out to the secondary air lead-out pipe 18 is drawn by the air pump 17, supplied from the air pump 17 to the secondary air supply pipe 16, and thereafter supplied to the exhaust manifold 12 via the opened electromagnetic ASV 15.

The secondary air supplied to the exhaust manifold 12 is mixed with exhaust gas discharged from the combustion chambers of the engine. As a result, oxidation of the unburned components such as hydrocarbon (HC) or carbon monoxide (CO) contained in the exhaust gas is accelerated and, consequently, the catalyst of the catalytic device 14 is activated promptly by the combustion heat generated by the oxidation of the unburned components of the exhaust gas.

In the present embodiment, the air cleaner 51 is connected to the air pump 17 via the secondary air lead-out pipe 18, and the secondary air lead-out pipe 18 is connected to the casing 52 of the air cleaner 51 as described above. Moreover, the secondary air discharge pipe 56 is provided in the upper part of the casing 52 downstream of the filter element 55 to separate the secondary air discharge pipe 56 and the air introduction port 53 from each other with respect to the direction of flow of the air. Therefore, when the vehicle travels in the rain or over puddles of water, air containing water that is introduced from the air introduction port 53 is separated from the water while the air moves from the air introduction port 53 to the secondary air discharge pipe 56. As a result, only air is led out of the secondary air discharge pipe 56 to the air pump 17 via the secondary air lead-out pipe 18.

Therefore, only secondary air is supplied from the air pump 17 to the exhaust manifold 12 via the secondary air supply pipe 16, and the water is prevented reaching the high-temperature catalyst of the catalytic device 14. As a result, damage of the catalyst and deterioration of catalyst performance may be prevented.

In the present embodiment, the secondary air discharge pipe 56 is provided in the upper part of the casing 52. Therefore, if the water separated from the air is dropped on the bottom surface of the casing 52 as the air moves from the air introduction port 53 to the secondary air discharge pipe 56, the water is securely prevented from being discharged through the secondary air discharge pipe 56.

Note that the secondary air discharge pipe 56 of the present embodiment may be configured such that a part of the secondary air discharge pipe projects inward from the casing 52 as shown in FIG. 9. In FIG. 9, a secondary air discharge pipe 60 has a cylindrical main body 60a that is connected to the secondary air lead-out pipe 18, and a flange 60b that is provided in the main body 60a and secured to the casing 52 of the air cleaner 51 by a screw 61. A communication hole 60c provided within the main body 60a communicates the secondary air lead-out pipe 18 with the inside of the casing 52.

The main body 60a has a projection 60e that projects inward of the casing 52 from the inner peripheral surface of the casing 52. The communication hole 60c is formed within the projection 60e. Specifically, the main body 60a is an integrated component having the communication hole 60c therein, wherein the projection 60e projects inward from the casing 52 from the inner peripheral surface of the casing 52.

Therefore, even if the water that passes through the filter element 55 reaches the secondary air discharge pipe 60, the amount of water that enters the projection 60e is reduced by a wall surface of the projection 60e. Consequently, the water can be prevented more securely from being discharged from the secondary air discharge pipe 60 to the secondary air lead-out pipe 18.

Moreover, the communication hole 60c of the projection 60e may be configured so that its diameter increases from the inner peripheral surface of the casing 52 toward the inside of the casing 52. In this case, the width of a flow passage of the communication hole 60c on an upstream side in a secondary air lead-out direction may be wider than a flow passage of the communication hole 60c on a downstream side in the secondary air lead-out direction. Therefore, the speed of the air introduced into the communication hole 60c of the projection 60e on the upstream side in the lead-out direction is reduced, and water is prevented from being introduced into the secondary air discharge pipe 60 along with the air. Consequently, water can be prevented more securely from being led out of the secondary air discharge pipe 60 to the secondary air lead-out pipe 18.

The described embodiments are merely illustrative in all respects and are not intended to limit the invention. The scope of the invention is defined not by the above description of the embodiments but by the scope of claims. Therefore, the invention is intended to include all modifications with the means and scope equivalent to the scope of claims.

As described above, the secondary air supply device for an internal combustion engine according to the invention prevents the entry of water into a catalyst and thus prevents possible damage of the catalyst that may result, as well as preventing deterioration of catalyst performance. The secondary air supply device for an internal combustion engine according to the invention is useful as a secondary air supply device for an internal combustion engine that supplies secondary air from an air cleaner provided upstream of a catalyst provided in an exhaust pipe.

SECONDARY AIR SUPPLY DEVICE FOR INTERNAL COMBUSTION ENGINE

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