JPH04353215A - Exhaust device for engine - Google Patents

Abstract

PURPOSE:To accelerate the activation of an O2 sensor by keeping the temperature of the exhaust gas in the exhaust manifold for an engine. CONSTITUTION:An O2 sensor 7 is installed at the collection part of an exhaust manifold 6, which is covered by a heat protector 10 through a gap C. A cooling water passage 13 is formed in the heat protector 10, and allowed to communicate to the cooling water passage of an engine body 15. The cooling water which is heated by the engine body 15 is circulated into the cooling water passage 13 of the heat protector 10 by a water pump 17, and the heat protector 10 is heated. The radiation heat quantity supplied to the heat protector 10 from the exhaust manifold 6 heated by the exhaust gas is reduced by raising the temperature of the heat protector 10, and the lowering of the temperature of the exhaust gas in an exhaust pipe 6 is reduced, and the activation of the O2 sensor is accelerated.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is an O
This invention relates to an engine exhaust system equipped with two sensors.

0002

2. Description of the Related Art Some automobile engines are designed to purify their exhaust gas by passing it through a three-way catalytic converter. In order for the three-way catalyst to work efficiently, it is necessary to maintain the air-fuel mixture near the stoichiometric air-fuel ratio.

[0003] For this reason, feedback control is performed to control the air-fuel ratio by changing the fuel injection amount by detecting the oxygen concentration in the exhaust gas using an O2 sensor and feeding it back to the ECU (engine control computer). .

[0004] Conventionally, this type of engine exhaust system has an O2 sensor 3 installed at a gathering part of an exhaust manifold 2 connected to an engine body 1, as shown in FIG.
is installed. Also, exhaust manifold 2
Heat protector 4 is manufactured by molding a metal plate.
is attached by bolt 5.

With this configuration, the O2 sensor 3 detects the oxygen concentration in the exhaust gas within the exhaust manifold 2. Further, the heat protector 4 prevents the heat of the exhaust manifold 2 from being directly transmitted to surrounding components. Furthermore, the heat protector 4 is
The exhaust gas inside the exhaust manifold 2 is kept warm and O
Promotes activation of 2 sensors.

On the other hand, as a prior art related to an engine exhaust system, Japanese Utility Model Application Publication No. 63-87213 discloses a method for adjusting the temperature of the exhaust gas introduced into the catalytic converter by supplying cooling air around the exhaust passage during warm-up. An exhaust gas purification device is disclosed. Also, Utsukai Showa 60-13481
No. 1 discloses an exhaust system heat retention device that adjusts the exhaust temperature by supplying outside air around an exhaust manifold when the exhaust gas has a predetermined temperature or higher.

[0007]

By the way, in order to activate the O2 sensor 3 and detect the oxygen concentration in the exhaust gas, it is necessary to make the exhaust gas temperature higher than the activation temperature. O
When the 2 sensor 3 is inactive, the ECU stops feedback control of the air-fuel ratio and determines the air-fuel ratio based on the basic fuel injection characteristics. Therefore, in order to maintain feedback control of the air-fuel ratio, it is desirable to maintain the temperature of the exhaust gas as much as possible above the activation temperature of the O2 sensor.

However, in the conventional example shown in FIG. 4, when the engine is operated in an idling state for a long time, the exhaust gas temperature decreases and the O2 sensor 3 becomes inactive, so the exhaust gas temperature becomes activated again. Feedback control of the air-fuel ratio will be temporarily stopped until the temperature is reached. When the air-fuel ratio feedback control stops, the purification efficiency of the three-way catalyst decreases, so there is a problem that the capacity of the catalytic converter needs to be increased in order to obtain sufficient exhaust gas purification ability during long periods of idling. There is.

[0009] Furthermore, by increasing the idling speed of the engine or delaying the ignition timing,
Although it is possible to increase the temperature of the exhaust gas, there is a problem in that the amount of fuel consumed increases in this case.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an engine exhaust system that promotes the activation of an O2 sensor by sufficiently insulating the exhaust gas in the exhaust manifold. purpose.

[0011]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an exhaust manifold equipped with an O2 sensor for detecting the oxygen concentration of engine exhaust gas;
An engine exhaust system comprising a heat protector that covers the exhaust manifold through a gap, characterized in that the heat protector is provided with a cooling water passage, and the cooling water passage is communicated with the cooling water passage of the engine. shall be.

0012

[Operation] With this configuration, the amount of heat dissipated from the exhaust manifold to the heat protector can be reduced by circulating the coolant heated by the engine through the coolant passage of the heat protector and increasing the temperature of the heat protector. This reduces the temperature drop of exhaust gas in the exhaust pipe.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, an O2 sensor 7 and an exhaust temperature sensor 8 are attached to a gathering part of an exhaust manifold 6 connected to the exhaust side of an engine (not shown). The exhaust manifold 6 has Figure 3
As shown in the figure, a heat protector 1 that covers the periphery of the exhaust manifold 6 with a sufficiently small heat insulating material 9 in a part thereof.
0 is attached with bolts 11 and nuts 12, and a gap C is formed between the exhaust manifold 6 and the heat protector 10.

Inside the heat protector 10, there is an inlet 1.
A cooling water passage 13 having an inlet 3a and an outlet 13b is provided, and the cooling water introduced from the inlet 13a is
The cooling water circulates within the heat protector 10 through the cooling water passage 13 and is discharged from the outlet 13b.

The inlet 13a of the cooling water passage 13 of the heat protector 10 is connected to the port 1 of the solenoid valve (3-port valve) 14.
Connected to 4a. Of the other two ports of the solenoid valve 14, one port 14b is connected to a cooling water passage (not shown) of the engine body 15 and the outlet side of the radiator 16, and the other port 14c is connected to a water pump. 17 is connected to the suction side. The discharge side of the water pump 17 is connected to the inlet side of the coolant passage of the engine body 15, and the outlet side of the coolant passage of the engine body 15 is connected to the inlet side of the radiator 16. In addition, the outlet 13b of the cooling water passage 13 of the heat protector 10
is connected to the suction side of the water pump 17.

The solenoid valve 14 is connected to the ECU 18 and
In response to the output signal of the CU 18, a port 14b on the cooling water passage of the engine body 15 and the radiator 16 side, a port 14a on the inlet 13a side of the heat protector 10,
Alternatively, communication with the port 14c on the water pump 17 side is selectively established.

The ECU 18 is connected to the O2 sensor 7 and the exhaust temperature sensor 8, and performs feedback control of the air-fuel ratio according to the detected value of the O2 sensor 7. In addition, the solenoid valve 14 is operated according to the detected value of the exhaust temperature sensor 7, and when the exhaust gas temperature is equal to or higher than a predetermined temperature T that is sufficiently higher than the activation temperature of the O2 sensor 7, the engine main body 15, the radiator 16
side port 14b and water pump 17 side port 1
4c, and when the exhaust gas temperature is less than the predetermined temperature T, the port 14b on the radiator 16 side and the port 14a on the inlet 13a side of the heat protector 10 are communicated. Note that the predetermined temperature T can be set based on experiments as an appropriate exhaust gas temperature at which the activated state of the O2 sensor 7 can be stably obtained.

The operation of this embodiment constructed as above will be explained next. By detecting the oxygen concentration in the exhaust gas with the O2 sensor 7 and feeding it back to the ECU 18, the air-fuel ratio is controlled by changing the fuel injection charge. Furthermore, the heat protector 10 prevents the heat of the exhaust manifold 6 from being directly transmitted to surrounding components.

When the exhaust gas temperature detected by the exhaust gas temperature sensor 8 is lower than the predetermined temperature T due to long-term idling, etc., the ECU 18 closes the port 14a of the solenoid valve 14.
and port 14b are communicated with each other. Therefore, as shown by the arrow in FIG. 1, the cooling water discharged from the water pump 17 circulates within the cooling water passage of the engine body 15.
If necessary, the water circulates through the radiator 16, passes through the solenoid valve 14, and flows into the cooling water passage 13 of the heat protector 10 from the inlet 13a. The water then circulates through the cooling water passage 13 and flows from the outlet 13b to the suction side of the water pump 17. In this way, the coolant heated in the coolant passage of the engine body 15 is transferred to the coolant passage 1 of the heat protector 10.
By circulating the heat protector 13, the heat protector 13 is heated to a high temperature. Here, since a gap C is formed between the exhaust manifold 6 and the heat protector 10, the heat of the exhaust manifold 6 heated by the exhaust gas is transmitted to the heat protector 10 mainly by radiation. , heat protector 10
When the temperature becomes high, the amount of heat radiated from the exhaust manifold 6 to the heat protector 10 decreases, so the temperature of the exhaust gas in the exhaust manifold 9 decreases less, and the temperature of the exhaust gas becomes equal to or higher than the activation temperature of the O2 sensor 7. is maintained. Therefore, feedback control of the air-fuel ratio can be maintained even during long-term idling, and the purification efficiency of the three-way catalytic converter can be improved.

When the exhaust gas temperature detected by the exhaust gas temperature sensor 8 is higher than the predetermined temperature T, the ECU 18 activates the solenoid valve 14.
The ports 14c and 14b are communicated with each other. Therefore, as shown by the arrow in FIG.
The cooling water discharged from 7 circulates within the cooling water passage of the engine body 15, and if necessary circulates through the radiator 16.
It flows through the solenoid valve 14 to the suction side of the water pump 17. Further, the cooling water in the cooling water passage 13 of the heat protector 10 is sucked out to the suction side of the water pump 17. In this way, when the temperature of the exhaust gas in the exhaust manifold 9 is sufficiently higher than the activation temperature of the O2 sensor 7, cooling water is not circulated through the cooling water passage 13 of the heat protector 10, thereby reducing the load on the water pump 17. Reduce.

[0021]

Effects of the Invention With the configuration described in detail above, the present invention circulates cooling water heated by the engine through the cooling water passage of the heat protector to raise the temperature of the heat protector. This reduces the amount of heat radiated from the exhaust gas to the heat protector, thereby minimizing the drop in temperature of exhaust gas in the exhaust pipe. As a result, the temperature of the exhaust gas is maintained above the activation temperature of the O2 sensor even during long periods of idling, making it possible to maintain feedback control of the air-fuel ratio.
This has an excellent effect of improving the purification efficiency of the three-way catalytic converter.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a state in which engine cooling water is circulated through a cooling water passage of a heat protector in an embodiment of the present invention.

FIG. 2 is a diagram showing a state in which engine cooling water is circulated by bypassing the cooling water passage of the heat protector in the apparatus of FIG. 1;

FIG. 3 is a cross-sectional view showing a part of the attachment portion between the exhaust manifold and the heat protector of the device shown in FIG. 1;

FIG. 4 is a partially exploded perspective view of a conventional engine exhaust system.

[Explanation of symbols]

6 Exhaust manifold 7 O2 sensor 10 Heat protector 13 Cooling water passage 15　Engine body C Gap

Claims (1)

[Claims] Claim 1: An exhaust manifold equipped with an O2 sensor that detects the oxygen concentration of engine exhaust gas;
An engine exhaust system comprising a heat protector that covers the exhaust manifold through a gap, characterized in that the heat protector is provided with a cooling water passage, and the cooling water passage is communicated with the cooling water passage of the engine. Exhaust system for the engine.