JPH0455219Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust purification device for an internal combustion engine using a catalyst.

[Conventional technology]

In an exhaust gas purification system for an internal combustion engine that uses a catalyst, in order to improve the catalyst purification performance when the engine is cold, the exhaust manifold and the exhaust pipe upstream of the catalyst are kept warm to prevent the temperature of the exhaust gas introduced into the catalyst from decreasing.
Techniques for accelerating catalyst activation are well known.

On the other hand, in order to ensure the durability of the catalyst, the exhaust manifold and the exhaust pipe upstream of the catalyst are cooled with water or air to lower the temperature of the exhaust gas introduced into the catalyst.
A technique for preventing the catalyst from becoming excessively high temperature is also well known (see Japanese Utility Model Application Publication No. 87114/1983).

[Problem that the invention attempts to solve]

As mentioned above, conventional exhaust purification devices are designed to maintain only the exhaust temperature or to lower the exhaust temperature, so in order to improve the catalyst purification performance when the engine is cold, However, with a structure that retains heat, there is a problem in that during high-load operation after warming up, the catalyst temperature becomes higher than in a normal exhaust gas purification device, reducing the durability of the catalyst.

On the other hand, in a structure in which the upstream side of the catalyst is cooled in order to ensure the durability of the catalyst, there is a problem that the catalyst purification performance decreases because the temperature of the exhaust gas to be introduced into the catalyst decreases when the catalyst is cold.

Therefore, the present invention aims to provide an exhaust gas purification device that can meet the requirements both when the engine is cold and when the engine is warmed up.

[Means for solving problems]

In order to solve the above problems, the present invention provides an exhaust purification device in which a catalyst is provided in the exhaust passage of an engine to purify the exhaust, and the exhaust passage on the upstream side of the catalyst is made up of an inner pipe and an outer pipe. It has a sealed double pipe structure, and the outer pipe is connected to the pump via a switching valve, and the switching valve is switched depending on whether the engine is cold or warmed up. Air between the space and the inner pipe is discharged by a pump, and air is supplied into the space by the pump during warm-up. The outer tube is provided with a relief valve, the outer tube and the pump are connected through a circulation passage, and each passage connecting the outlet and inlet of the outer tube with the pump is provided with a three-way switching valve. The three-way switching valves are arranged so that the three-way switching valves are switched depending on whether the engine is cold or warmed up.

[Effect]

In the present invention having the above configuration, when the engine is cold, the three-way switching valve interposed between the outer pipe outlet and the pump is controlled to communicate between the outer pipe outlet and the pump, and the pump suction side and the atmosphere. On the other hand, a three-way switching valve interposed between the outer pipe inlet and the pump is controlled to cut off the outer pipe inlet and the pump, and to communicate between the pump discharge side and the atmosphere. let Therefore, the air existing in the space between the outer tube and the inner tube is discharged into the atmosphere by the pump, and the air in the space decreases, reducing the thermal conductivity and reducing the temperature of the exhaust gas introduced into the catalyst. To prevent.

When the engine is warmed up, the two three-way switching valves are switched to cut off the connection between the outer pipe outlet and the pump, while also communicating the pump suction side with the atmosphere, and communicating the outer pipe inlet with the pump on the pump discharge side. and the atmosphere. Therefore, cold air is supplied to the space between the outer tube and the inner tube to cool this space. Therefore, the temperature of the exhaust gas passing through the inner tube is lowered before it is introduced into the catalyst. At this time, if the pressure in the space increases due to the introduction of atmospheric air and exceeds a predetermined pressure, a relief valve provided on the outer pipe is activated to relieve the atmospheric air in the space and circulate the cold air into the space. More effectively prevents excessive pressure build-up within.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes an exhaust manifold, which is connected to a catalyst 3 via a front pipe 2 on the downstream side thereof, and is connected to a center pipe 4 on the downstream side of the catalyst 3. Front pipe 2 is flange 2
1 and a flange 22, the catalyst 3 is connected to the front pipe 2 by a flange 23 and a flange 24, and the center pipe 4 is connected to the catalyst 3 by a flange 25 and a flange 26.

The front pipe 2 is a double pipe with a sealed structure consisting of an outer pipe 11 and an inner pipe 12, and the inner pipe 12 is connected to the exhaust manifold 1 on the upstream side, and the catalyst 3 on the downstream side.
They are connected to each other. A space 13 between the outer tube 11 and the inner tube 12 is connected to an air exhaust pipe 31 and an air introduction pipe 32 via an outlet port 14 and an inlet port 15 provided in the outer tube 11. Furthermore, the air exhaust pipe 31 is the first
The air introduction pipe 32 is connected to one port of a second three-way switching valve 62, and the air introduction pipe 32 is connected to one port of a second three-way switching valve 62. 1st 3
The other two ports of the directional switching valve 61 are connected to the atmosphere opening passage 63 and the pump connection pipe 65, and similarly, the other two ports of the second three-way switching valve 62 are connected to the atmosphere opening passage 64 and the pump connection pipe 65. It is connected to a pipe 66. and the first three-way switching valve 61
The pump connection pipe 65 on the side is connected to the suction port of the pump 5, and the pump connection pipe 66 on the second three-way switching valve 62 side is connected to the discharge port of the pump 5.

These first and second three-way switching valves 61, 6
2 has a structure in which switching is controlled by an input signal S. For example, a detection signal of the engine cooling water temperature may be used as the above signal, and the three-way switching valves 61 and 62 may be switched by switching a bimetal with this signal, or a detection signal of the exhaust temperature may be used and The three-way switching valves 61 and 62 may be switched by a solenoid valve.

Further, the outer tube 11 is provided with a check valve 6 as a relief valve. Normally, the check valve 6 is closed because the valve body 67 is urged by the spring 68 and pressed against the valve seat, but when the pressure in the space 13 between the outer tube 11 and the inner tube 12 increases, When the biasing force of the spring 68 is exceeded, the valve body 67 is separated from the valve seat, the check valve 6 is opened, and the air in the space 13 is released to the atmosphere.

The operation of this embodiment configured as described above will be explained.

When the engine is cold, such as when the engine is started, the atmosphere opening passage 63 of the first three-way switching valve 61 is closed, and the air exhaust pipe 31 and the pump connection pipe 65 are communicated with each other. On the other hand, in the second three-way switching valve 62, the pump connection pipe 66 and the atmosphere release passage 64 are communicated with each other, and the air introduction pipe 32 side is closed. Therefore, the air existing in the space 13 between the outer pipe 11 and the inner pipe 12 in the front pipe 2 is sucked out by the pump 5 and released into the atmosphere opening passage 64.
released into the atmosphere. Therefore, the air in the space 13 becomes thinner and its thermal conductivity decreases, and the exhaust gas flowing inside the inner tube 12 is introduced into the catalyst 3 in a heat-retained state, with the temperature of the exhaust gas flowing inside the inner tube 12 being prevented from decreasing due to heat conduction from the tube wall. Therefore, activation of the catalyst 3 is accelerated and its purification performance is improved.

FIGS. 2 and 3 are graphs showing the relationship between exhaust temperature, catalyst purification rate, and HC emissions, and
As is clear from the figure, the higher the exhaust temperature, the higher the exhaust gas purification rate by the catalyst, and the lower the amount of HC emissions. Therefore, it can be seen that according to this example, the exhaust gas temperature is prevented from decreasing when the engine is cold, so that the exhaust purification performance of the catalyst is improved.

When the engine is under high load after warming up, the first and second three-way switching valves 61 and 62 are switched based on a detection signal of the engine cooling water temperature or exhaust temperature. That is, the first three-way switching valve 61 opens its atmosphere opening passage 63 to communicate with the pump connection pipe 65, and closes the air discharge pipe 31 side. On the other hand, the second three-way switching valve 62 connects the pump connection pipe 66 and the air introduction pipe 32,
The atmosphere opening passage 64 is closed. Therefore, cold air is introduced into the space 13 between the outer tube 11 and the inner tube 12 from the atmosphere opening passage 63 via the pump 5 and the air introduction pipe 32. The introduced cold air cools the exhaust gas flowing through the inner pipe 12 and introduces it into the catalyst 3. Therefore, excessive temperature rise of the catalyst 3 is avoided, and its durability is ensured. In addition, when the internal pressure increases by introducing the atmosphere into the space 13 and exceeds a predetermined pressure, the valve body 67 of the check valve 6 is opened by this pressure, and the air accumulated in the space 13 is released into the atmosphere. The cool air is circulated. This makes the cooling effect described above more efficient.

The structure of this embodiment configured as described above can also be applied to the exhaust manifold and the outer wall of the catalyst, if necessary.

[Effect of idea]

As described above, according to the present invention, compared to conventional exhaust purification devices, the exhaust gas is kept warm when the engine is cold, so the purification performance of the catalyst is improved and the emission is improved.

Furthermore, when the engine is warmed up and under high load, the exhaust gas is cooled, thereby avoiding excessive temperature rise of the catalyst, preventing melting and damage thereof, and improving the durability of the catalyst.

Furthermore, during high load during warm-up, the exhaust capacity is reduced by the amount of temperature drop in the exhaust gas, making it possible to reduce exhaust noise and exhaust back pressure, and as the exhaust noise is reduced, the exhaust muffler can be made smaller. be able to.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an embodiment of the present invention, Fig. 2 is a graph showing the relationship between exhaust gas temperature and catalyst purification performance, and Fig. 3 is a graph showing the relationship between exhaust temperature and HC emission amount. . 1... Exhaust manifold, 2... Front pipe, 3... Catalyst, 5... Pump, 6... Relief valve, 11... Outer pipe, 12... Inner pipe, 13... Space, 14... Outlet port, 15...Inlet port,
31...Air discharge pipe, 32...Air introduction pipe, 61, 62...3-way switching valve.

Claims (1)

[Claims for Utility Model Registration] 1. In an exhaust purification device that purifies exhaust gas by installing a catalyst in the exhaust passage of an engine,
The exhaust passage on the upstream side of the catalyst has a sealed double-pipe structure consisting of an inner pipe and an outer pipe, and the outer pipe is connected to a pump via a switching valve, and the switching valve is connected to a pump when the engine is cold and when the engine is warm. The pump is configured to switch according to the timing, and when the system is cold, the air in the space between the outer tube and the inner tube is discharged by the pump, and when the engine is warmed up, air is supplied to the space by the pump. Exhaust purification device. 2 A relief valve is provided in the outer tube, and the air in the space between the outer tube and the inner tube is relieved when the pressure in the space exceeds a predetermined pressure. The exhaust purification device according to item 1. 3. Utility model registration claim 1, wherein the outer pipe and the pump are connected by a circulation passage, and each passage connecting the outlet and inlet of the outer pipe and the pump is provided with a three-way switching valve, respectively. Or the exhaust gas purification device according to item 2.