JPH0526249Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an exhaust system for an engine, and more particularly to an exhaust system for an engine having an exhaust passage provided independently for each cylinder.

(Prior art and its problems) In a multi-cylinder engine, the exhaust port of each cylinder is closed in order to prevent so-called exhaust interference, which causes exhaust pressure from each cylinder to interfere with each other and cause exhaust resistance, resulting in a decrease in output. They are connected by independent exhaust passages, and are configured to merge downstream where there is no influence of exhaust interference.

The larger the diameter of the upstream side of the independent exhaust passage connected to each cylinder, the better from the point of view of exhaust efficiency, but there are conflicting demands such as improving economic efficiency by making the engine smaller and lighter and making it easier to install it in a car. The reality is that we have no choice but to compromise on a predetermined size in order to achieve both.

As a result, at high speeds and high loads, the exhaust gas becomes hot and pressurized in the exhaust passage, leading to early deterioration of the exhaust manifold and the O ₂ sensor and exhaust purification device installed in the downstream exhaust passage. There is. In addition, due to the high pressure, exhaust gas is not sufficiently discharged and remains in the cylinder, and during the overlap period between the exhaust valve and intake valve, the exhaust gas blows back into the cylinder, diluting the air-fuel mixture and reducing combustibility. There are problems that are worsening the situation.

In order to solve such problems, the present applicant communicated the independent exhaust passages of each cylinder with a communication passage, as in Japanese Patent Application No. 123742/1982, and installed an on-off valve in the communication passage. - We have proposed an engine exhaust system that is configured to open an on-off valve to communicate a communication passage during high loads, allowing exhaust gas to escape to the exhaust passages of other cylinders, thereby lowering pressure and cooling the engine.

However, with the above configuration, if the engine is operated at high speed and under high load when the engine temperature is low immediately after starting,
Since the on-off valve opens and the communication passage is communicated, the exhaust gas is dispersed by the communication passage and becomes low pressure.
Further, as the pressure decreases, the temperature also decreases, and the cooling effect increases due to the contact area with the exhaust passage and the surface area of the exhaust passage increasing, which weakens the promotion of warming up the engine.

On the other hand, downstream of the exhaust passage, there is an O ₂ sensor that detects the oxygen concentration in the exhaust, which is necessary to control the air-fuel ratio to the stoichiometric air-fuel ratio and suppress the generation of harmful components in the exhaust, and a sensor that detects the oxygen concentration in the exhaust. This O ₂ sensor is equipped with a catalyst to react and remove (CO, HC, _NO ,
Similarly, the catalyst has a predetermined reaction temperature, and if the temperature is higher than that, the reaction speed is slow and the desired exhaust purification effect cannot be obtained. Therefore, when the engine temperature is low, the O ₂ sensor and catalyst will react more quickly. It is desirable to raise the temperature to

(Purpose of the invention) In view of the above-mentioned circumstances, the present invention quickly eliminates the overcooling condition of the exhaust system including the O ₂ sensor and catalyst when the engine is at low temperature, thereby achieving normal air-fuel ratio control and exhaust purification. The purpose of the present invention is to provide an engine exhaust system that enables the following.

(Structure of the invention) In order to achieve the above object, the engine exhaust system according to the invention is installed in a communication passage that communicates the upstream side of the exhaust passage independently connected to each cylinder, and is operated at high rotation and high load. A means for detecting parameters related to the engine temperature and an output from the detecting means are used to close the on-off valve, which is opened when the engine is operating at high speed and under high load, when the engine temperature is below a predetermined temperature, thereby opening the exhaust system. It is configured to promote temperature rise.

(Embodiment of the invention) FIG. 1 is a system configuration diagram of a four-cylinder engine using an engine exhaust system according to the invention.
is the engine body, and 1A, 1B, 1C, and 1D are the respective cylinders.

A piston 2 is provided in each cylinder 1A, 1B, 1C, 1D, and two sets of exhaust valves 10, 10 and intake valves 11, 11 are provided at the top, respectively, and the piston 2 moves up and down to move the intake valve 1.
It is configured to repeat the steps 1 and 11 of air-fuel mixture intake, compression, explosion, and exhaust by opening exhaust valves 10 and 10.

In the engine body 1, each cylinder 1A, 1B, 1
C, 1D through the exhaust valves 10...
Exhaust port 20 communicating with A, 1B, 1C, 1D
... are provided independently and communicate with the exhaust manifold 3 connected to the side surface.

The connection portion of the exhaust manifold 3 with the engine body 1 is formed into independent cylinder passages 31, 32, 33, 34 for each cylinder 1A, 1B, 1C, 1D, and the cylinder passages 31, 32, 33,3
4 is formed by merging into a single line downstream, and an O ₂ sensor 8 and a catalyst 9 are installed at predetermined positions further downstream.

In addition, in the cylinder passages 31, 32, 33, 34,
A communication passage 35 that communicates with each other is connected, and an on-off valve 4 is installed in the central area of the communication passage 35, that is, at a position that divides the communication passage 35 into two cylinders 1A and 1B and 1C and 1D on both sides. has been done.

The on-off valve 4 is configured to be opened and closed by an actuator 6 based on an actuation signal from an electronic control unit 5. Further, an opening/closing sensor 7 is installed to detect the open/closed state of the opening/closing valve 4, and is configured to send its detection signal to the electronic control unit 5.

Detection signals from an engine speed detection sensor 51, a throttle sensor 52, an exhaust temperature sensor 53, and an ignition sensor 54 are input to the electronic control unit 5. Therefore, a switching temperature that is a predetermined temperature higher than the reaction temperature of the O ₂ sensor 8 and the catalyst 9 is set and input in advance to the electronic control unit 5, and the switching temperature is set and input in advance to the electronic control unit 5. When the exhaust temperature detected by the temperature sensor is below the switching temperature, the on-off valve is closed, and when the exhaust temperature is above the switching temperature and at high load/high rotation (determined on a two-dimensional table based on engine speed and load). The program is programmed to control the opening and closing of the on-off valve.

In addition, when driving in normal urban areas, the exhaust temperature does not rise, or even if the exhaust temperature rises, the operating condition is not under high load and high rotation, so the on-off valve 4
Continuing to operate the on-off valve 4 in the closed state for a long time causes sticking and seizure due to oxidation of the on-off valve 4. In order to avoid such a situation, the on-off valve 4 is configured to open when the ignition switch is OFF, and furthermore, the on-off valve 4 is opened intermittently by a timer when the on-off valve 4 is in the closed state. All you have to do is configure it so that it does.

Further, it is preferable that the on-off valve 4 is a normally open type which is normally open, and is configured to be in the open state when the on-off signal from the electronic control unit 5 is not transmitted due to some reason such as a signal failure. This is to prevent failures due to high temperature and high pressure even in the event of a system failure.

An example of the opening/closing control flow of the opening/closing valve 4 by the electronic control unit 5 is as shown in the second figure. That is, first, when the ignition switch is turned off, the on-off valve 4 is kept open, and when the ignition switch is turned on, it is closed simultaneously.

Next, when the exhaust temperature detected by the exhaust temperature sensor 53 is below the specified value A, that is, when the engine temperature is low, such as immediately after starting, the closed state is continued. At this time, for example, the exhaust gas discharged from the cylinder 1A is exhausted through the original cylinder-specific passage 31 and the adjacent cylinder-specific passage 32 that is not blocked by the on-off valve 4, and when the on-off valve 4 is open, all the cylinder Passage 31, 32, 3
Compared to the case where the exhaust gas passes through the exhaust gases 3 and 34, the high temperature and pressure are maintained, and as a result, the temperature of the exhaust system including the O ₂ sensor 8 and the catalyst 9 is quickly raised.

Then, when the temperature of the exhaust system rises and the exhaust temperature exceeds the specified value A, and the operating state becomes high load and high rotation, the on-off valve 4 opens for the first time, and all the exhaust gas from the cylinder 1A passes through the communication passage 35. The exhaust manifold 3, O ₂ sensor 8
and prevent early deterioration of the catalyst 9.

In addition, the exhaust efficiency improves due to the reduction in exhaust pressure,
Therefore, the exhaust gas remains in the cylinders 1A, 1B, 1C, 1D, and the exhaust valves 10... and the intake valves 1
During the overlap period with 1..., exhaust gas is blown back into the cylinders 1A, 1B, 1C, 1D, which prevents dilution of the air-fuel mixture, maintains combustibility, and prevents the emission of harmful components and a decrease in output. .

If the on-off valve 4 is to be temporarily opened every predetermined time B while it remains closed, a step indicated by a chain line may be added to the control flow in FIG. 2.

In the above embodiment, one on-off valve 4 is provided in the center of the communication passage 35, but it would be more effective if it was installed between each cylinder passage 31, 32, 33, and 34. It is. Further, although two sets of exhaust valves are provided per cylinder, it goes without saying that the present invention can also be applied to one set of exhaust valves.

(Effects of the invention) According to the engine exhaust system according to the invention, during high loads and high rotations, by opening the on-off valve, the exhaust gas remains in the cylinder due to high temperature and high pressure exhaust, and the exhaust gas is removed. This prevents dilution of the air-fuel mixture caused by exhaust blowing back into the cylinder during the overlap period with the intake valve, preventing the emission of harmful components and reducing output due to decreased combustibility, and also prevents high-temperature, high-pressure exhaust. In addition to preventing premature deterioration of the exhaust manifold, _O2 sensor, and catalyst due to exposure to By being able to raise the exhaust system temperature to the reaction temperature of the O ₂ sensor and catalyst in a short period of time, normal air-fuel ratio control can be performed and the emission of harmful exhaust components can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram of an engine exhaust structure according to the present invention, and FIG. 2 is a chart diagram showing the opening/closing control flow of an on-off valve. 20...Exhaust port, 3...Exhaust manifold (exhaust passage), {31, 32, 33, 34}...Cylinder-specific passage (independent exhaust passage), 35...Communication passage,
4...Opening/closing valve.

Claims (1)

[Scope of utility model registration request] An exhaust passage whose upstream side is independently connected to the exhaust port of each cylinder and which merges on the downstream side, a communication passage that communicates the upstream side of the independent part of the exhaust passage, and a communication passage that communicates with the exhaust port of each cylinder at high speed and high load. In an engine exhaust system equipped with an on-off valve that is sometimes opened, the on-off valve is closed when the engine temperature is lower than a predetermined temperature by receiving the output of the detecting means and the detecting means for detecting a parameter related to the engine temperature. An engine exhaust system characterized by being configured to.