JPH0835423A - Secondary air supplying device - Google Patents

Abstract

PURPOSE:To prevent exhaust gas from being allowed to back flow on an intake system side by supplying the sufficient amount of secondary air, when required, with high responsiveness according to the operating state of the engine. CONSTITUTION:A first body member 31 and a second body member 32 are connected to each other, so as to constitute a valve body. An air passage 33 and an upper chamber 34 communicated with each other are formed in the first body member 31. The air passage 33 is connected to a piping on the intake system side. An upper part outer wall 31a of the first body member 31 is recessed, and the volume of the upper chamber 34 is lower than that of the air passage 33. The passage area of the upper chamber 34 is smaller than that of the air passage 33, and it is so determined that the flow velocity of secondary air to flow into the upper chamber 34 from the piping may be prevented from being suddenly decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for supplying secondary air to an exhaust system in order to promote the exhaust gas purifying action of an oxidation catalyst provided in the exhaust system.

[0002]

2. Description of the Related Art Conventionally, there is known an exhaust gas purification system in which an exhaust gas is purified by providing an oxidation catalyst in an exhaust system of an internal combustion engine and oxidizing carbon monoxide and hydrocarbons contained in the exhaust gas. In such an exhaust purification system, a device for supplying secondary air to the oxidation catalyst is provided in order to promote the purification action of the oxidation catalyst. For example, in an internal combustion engine with a relatively small displacement, a reed valve that opens and closes due to exhaust pulsation is usually provided in the middle of a pipe that connects the downstream side of an air cleaner of the intake system and the upstream side of an oxidation catalyst as a secondary air supply device. Also, an air suction type device is provided.

[0003]

However, the exhaust pulsation changes depending on the operating conditions of the engine, and a sufficient amount of secondary air may not be supplied to the exhaust system during acceleration operation, for example. In this case, there arises a problem that the exhaust gas purification function becomes insufficient. Further, during high load operation, the followability of the opening / closing operation of the valve may be reduced depending on the spring constant and natural frequency of the reed valve, and exhaust gas may flow back to the intake system side.

The present invention, according to the operating state of the engine,
An object of the present invention is to provide a secondary air supply device capable of supplying a sufficient amount of air with high responsiveness when necessary and cutting air (preventing backflow) when not needed.

[0005]

A secondary air supply device according to the present invention is provided with a pipe for supplying secondary air from an intake system to an oxidation catalyst provided in an exhaust system, and a pipe provided in the middle of this pipe. And a reed valve that is disposed in the valve body and that opens and closes according to exhaust pulsation,
The flow passage area of the upper chamber formed in the valve body on the intake system side of the reed valve should have a size such that the flow velocity of the secondary air flowing from the pipe into the upper chamber does not suddenly decrease. It has a feature.

[0006]

[Effect] Even under an operating condition where secondary air is difficult to be supplied to the exhaust system such as during acceleration operation, the flow velocity of the secondary air introduced from the intake system to the valve body does not drastically decrease in the upper chamber. A good and sufficient amount of secondary air is supplied to the exhaust system. Further, due to the throttling effect of the upper chamber, the passage resistance that acts on the exhaust gas that tries to flow back from the exhaust system side to the upper chamber is large, and therefore the backflow is less likely to occur.

[0007]

The present invention will be described below with reference to illustrated embodiments. FIG. 1 shows a schematic structure of an engine having a secondary air supply system according to a first embodiment of the present invention.

A pipe member 12 forming an intake passage is connected to one side surface of the engine body 11, and a pipe member 13 forming an exhaust passage is connected to the other side surface. An air cleaner 14 is provided on the inlet side of the pipe member 12 of the intake system, and a carburetor 15 is provided in the middle of the pipe member 12. An oxidation catalyst 16 is provided in the middle of the exhaust pipe member 13.
Is provided. One end of the pipe 21 is connected to the air cleaner 14, and the other end of the pipe 21 is connected to the oxidation catalyst 1 of the pipe member 13.
6 is connected to the upstream side. With this pipe 21,
Secondary air is supplied to the oxidation catalyst 16 from the intake system. A chamber 22 having a predetermined volume is formed in the middle of the pipe 21, and a valve device 30 is provided on the downstream side of the chamber 22.

FIG. 2 shows a valve device 30. The valve body is configured by joining a first body member 31 and a second body member 32. An air passage 33 and an upper chamber 34 that communicate with each other are formed in the first body member 31. The air passage 33 has a circular cross section and is connected to a portion of the pipe 21 on the intake system side. The upper outer wall 31a of the first body member 31 is recessed to minimize the volume of the upper chamber 34. The volume of the upper chamber 34 is smaller than the volume of the air passage 33, and is, for example, 5 cc or less. The flow passage area of the upper chamber 34 is smaller than that of the air passage 33, and is set to a size such that the flow velocity of the secondary air flowing from the pipe 21 into the upper chamber 34 does not suddenly decrease.

An air passage 35 and a lower chamber 36, which communicate with each other, are formed in the second body member 32. The air passage 35 has a circular cross section and is connected to a portion of the pipe 21 on the exhaust system side. Therefore, the exhaust pulsation is guided to the lower chamber 36 via the pipe 21 and the air passage 35. The lower chamber 36
Has a larger volume than the upper chamber 34.

A plate-shaped support member 43 having an opening 42 is fitted to the annular support surface 41 formed on the second body member 32, and the outer peripheral portion of the support member 43 and the annular support surface 41.
A packing 44 is provided between them. Stopper 46
The stopper 46 is made of a metal plate or the like that is not substantially deformed.
One end of is fixed to the lower chamber 36 side surface of the support member 43 by a screw 45. The reed valve 47 is made of an elastically deformable thin metal plate or the like, and is provided between the support member 43 and the stopper 46. One end of the reed valve 47 is sandwiched between the support member 43 and the stopper 46, is deformed by the pressure of the lower chamber 36, and opens and closes the opening 42.

Next, the operation of this embodiment will be described. The exhaust pulsation, that is, the pressure fluctuation in the lower chamber 36, is linked to the opening / closing operation of the exhaust valve and the intake valve of the engine as shown in FIG.
The pressure in the lower chamber 36 becomes a positive pressure when the exhaust valve opens (t ₂ ) and a negative pressure when both the exhaust valve and the intake valve open (t ₁ ). The opening time (t ₂ ) of the exhaust valve is longer than the opening time (t ₁ ) of the intake / exhaust valve. Therefore, in most of one cycle of the engine, the lower chamber 36 has a positive pressure, and in a part thereof, the lower chamber 36 has a negative pressure.

The reed valve 47 opens and closes in response to exhaust pulsation, and when the reed valve 47 opens, the secondary air is sucked from the upper chamber 34 to the lower chamber 36 side and supplied to the oxidation catalyst 16. The flow rate of the secondary air is indicated by the symbol F1 in FIG. Since the opening / closing operation of the reed valve 47 is short, the reed valve 47 does not completely close the opening 42, and the reed valve 47 is closed even in the closed state.
There is a slight gap between the and the opening 42. Therefore, even in the valve closed state, a substantially constant amount of air flows backward from the lower chamber 36 to the upper chamber 34 side, as indicated by the symbol F2 in FIG.

As described above, in this embodiment, the flow passage area of the upper chamber 34 is smaller than that of the air passage 33, so that the flow velocity of the secondary air is higher in the upper chamber 34 than in the air passage 33. Therefore, as compared with the conventional device, the responsiveness of the reed valve 47 is improved (faster) and the intake amount of the secondary air is increased, so that the amount of the secondary air supplied to the oxidation catalyst 16 is increased and the exhaust gas purification action is performed. Is improved. In FIG. 3, reference numeral G1 indicates the amount of secondary air suctioned in the conventional device.

Further, in this embodiment, the volume of the upper chamber 34 is greatly reduced as compared with the conventional device and is set to 5 cc or less. As a result, a throttling effect is produced by the upper chamber 34, and the passage resistance to the exhaust gas that attempts to flow backward from the exhaust system side to the upper chamber 34 is large. Therefore, even in an operating state in which the opening / closing operation of the reed valve 47 cannot sufficiently follow the intake pulsation, such as when the engine is under high-load and high-speed rotation, backflow is unlikely to occur in the valve device 30. When the volume of the upper chamber 34 exceeds 5cc, this effect becomes small. Incidentally, in FIG.
Reference numeral 2 indicates the reverse flow rate of exhaust gas in the conventional device.

Further, according to this embodiment, since the upper outer wall 31a of the first body member 31 is recessed, the valve device 30 can be made smaller than the conventional device.

FIG. 4 shows a valve device 30 provided in the secondary air supply system of the second embodiment. In this figure, the same or corresponding parts as those of the valve device of the first embodiment are designated by the same reference numerals. Only the configuration different from that of the first embodiment will be described below.

The valve body is constructed by joining a first body member 31 and a second body member 32, and an air passage 33 bent in an L shape is formed in the first body member 31. The tip of the first body member 31 projects into the second body member 32 and is formed in a convex shape, that is, a truncated cone shape. The support member 43 is formed in a concave shape, that is, has a conical inner wall surface matching the outer peripheral surface of the tip of the first body member 31, and has the first and second body members 31, 32.
It is provided between the first body member 31 and the first body member 31. An upper chamber 34 is formed inside the support member 43, and the upper chamber 34 is adjacent to the outlet of the air passage 33. Two openings 42 are formed in the support member 43, and each of these openings 42 is opened and closed by a reed valve 47.

The other structure is the same as that of the first embodiment.

In the second embodiment, the flow passage area of the upper chamber 34 is smaller than that of the air passage 33, and the air passage 33 is close to the opening 42. Therefore, the flow velocity of the secondary air introduced from the air passage 33 is introduced into the lower chamber 36 without lowering in the upper chamber 34 and is supplied to the oxidation catalyst 16. Further, in the present embodiment, since the volume of the upper chamber 34 is significantly reduced as compared with the conventional device, the throttling effect is generated by the upper chamber 34, and the passage resistance to the exhaust gas that tries to flow backward from the exhaust system side to the upper chamber 34 is obtained. Is big.

As described above, the operation of the second embodiment is similar to that of the first embodiment, and the same effect as that of the first embodiment can be obtained.

[0022]

As described above, according to the present invention, a sufficient amount of secondary air can be supplied to the exhaust system with good responsiveness when necessary according to the operating conditions of the engine, and the exhaust gas Backflow to the intake system side is prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an engine having a secondary air supply device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the valve device of the first embodiment.

FIG. 3 is a diagram showing pressure fluctuations in a lower chamber and flow rates of secondary air with respect to opening / closing operations of an exhaust valve and an intake valve of an engine.

FIG. 4 is a sectional view showing a valve device according to a second embodiment.

[Explanation of symbols]

 12 pipe member of intake system 13 pipe member of exhaust system 14 air cleaner 21 piping 30 valve device 31 first body member 32 second body member 33 air passage 34 upper chamber 42 opening 43 support member 46 stopper 47 reed valve

Claims (4)

[Claims] 1. A pipe for supplying secondary air from an intake system to an oxidation catalyst provided in an exhaust system, a valve body provided in the middle of the pipe, and a valve body provided in the valve body, A reed valve that opens and closes according to exhaust pulsation, and the flow passage area of the upper chamber formed in the valve body on the intake system side of the reed valve is a secondary air flowing into the upper chamber from the pipe. A secondary air supply device having a size such that the flow velocity of the air does not decrease sharply. 2. A valve body, a first body member having an air passage communicating with the pipe and the upper chamber formed therein, and a first body member joined to the first body member to accommodate the reed valve. The secondary air supply device according to claim 1, further comprising two body members, wherein a volume of the upper chamber is smaller than a volume of the air passage. 3. The secondary air supply device according to claim 2, wherein the volume of the upper chamber is 5 cc or less. 4. The valve body is connected to the pipe, a first body member having an air passage is formed, and a second body joined to the first body member and connected to the exhaust system. A first support member and a concave support member provided between the first and second body members, to which the reed valve is attached, and in which an upper chamber communicating with the air passage is formed. The secondary air supply device according to claim 1, wherein the tip of the member is formed in a convex shape and is fitted into the support member.