JP2827671B2 - Evaporative gas purifier for lean-burn internal combustion engines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for purifying vaporized gas generated from fuel stored in a fuel tank of a lean burn internal combustion engine.

[0002]

2. Description of the Related Art In an engine, a mixture of air and fuel is introduced into a combustion chamber. When the mixture is compressed and ignited, it explodes to obtain a driving force. In this case, it is necessary to obtain the minimum air-fuel ratio (A / F) of the theoretically necessary fuel so that the air and fuel are completely burned, and the engine must control this air-fuel ratio. This air-fuel ratio is about 14.4 to 15.0 in the case of gasoline, and it is considered that the control of this air-fuel ratio is fundamental for controlling the combustion so as to conform to the exhaust gas regulations.

As a countermeasure against air pollution caused by harmful substances in exhaust gas, there is a lean burn engine. The lean burn engine is an engine having a lean burn operation range in which the actual air-fuel ratio burns in a lean state that is larger than the stoichiometric air-fuel ratio. Therefore, the amount of carbon monoxide, hydrocarbons, or nitrogen oxides contained in the combustion exhaust gas of the engine can be suppressed, and the fuel efficiency can be improved.

[0004] By the way, a required amount of fuel such as gasoline is stored in a fuel tank of an automobile, but this fuel evaporates due to a difference in temperature between the engine warm air and the outside air. The vaporized gas includes hydrocarbons (Hydrocarbo).
Hereafter, it is called HC. ), The vaporized gas cannot be released to the outside as it is, but is temporarily stored in a canister, and when the engine starts, it is processed by inhaling into the engine.

FIG. 3 schematically shows the intake and exhaust systems of a conventional lean burn engine.

As shown in FIG. 3, the lean burn engine 10 is provided with an intake port 11 and an exhaust port 12, and can be opened and closed by an intake valve 13 and an exhaust valve 14. A piston 17 is connected to the crankshaft 15 via a connecting rod 16 and is supported so as to be able to move up and down in the cylinder. A combustion chamber 18 is formed above the piston 17, and a spark plug 19 is attached here.

[0007] The air cleaner 20 is for removing floating dust in the air to be taken in, and is connected to a surge tank 22 and an intake port 11 of the engine 10 by an intake pipe 21. An air flow sensor 23 is provided on the air cleaner 20 side of the intake pipe 21, and a throttle valve 25 and a throttle position sensor 24 are provided on the surge tank 22 side of the intake pipe 21. The air flow sensor 23 and the throttle position sensor 24 are connected to an engine control unit (hereinafter, referred to as an ECU) 26, and can output a detection result. Further, an injector 27 is attached to the intake port 11 of the engine 10, and the gasoline stored in the fuel tank 28
A predetermined amount can be injected based on a command from the CU 26.

An exhaust pipe 29 is connected to the exhaust port 12 of the engine 10, and a catalytic converter (three-way catalyst) is provided in the middle.
30 and a silencer 31 are mounted. An O ₂ sensor 32 is attached to the exhaust pipe 29. In addition,
The engine 10 is provided with a water temperature sensor 33 for engine cooling water, and a crank angle position sensor 34 is provided in a distributor (not shown) of the engine 10.

A canister 35 is connected to the fuel tank 28 described above. The canister 35 temporarily stores harmful substances such as HC which has evaporated, and the engine 1
The fuel tank 28 is connected to a canister 35 via a discharge pipe 37 having a check valve 36. The canister 35 is connected to the intake pipe 21 via a supply pipe 39 having a purge amount control valve 38 controlled by the ECU 26.

The air sucked from the air cleaner 20 is sent to a surge tank 22 through an intake pipe 21.
Then, the air is supplied to the intake port 11 of the engine 10.
At this time, the intake air amount is controlled by the throttle valve 25. On the other hand, the ECU 26
The fuel injection amount is determined based on the intake air amount detected by the throttle valve and the throttle opening detected by the throttle position sensor 24, and the injector 27 injects a predetermined amount of gasoline in the fuel tank 28 based on a command from the ECU 26. Therefore, a mixture of air and gasoline is generated in the combustion chamber 18.
Will be supplied within.

An air-fuel mixture is supplied from the intake port 11 into the combustion chamber 18, and the air-fuel mixture in the combustion chamber 18 is compressed by driving the crankshaft 15 to move up and down the piston 17, and the spark plug 19 generates a spark. As a result, the compressed air-fuel mixture explodes and expands, and the engine operates.

When the engine 10 is stopped, gasoline in the fuel tank 28 evaporates due to a temperature difference between the engine warm air and the outside air. When the vaporized gas reaches a predetermined gas pressure or higher, the check valve 36 opens and is sent to the canister 35 via the discharge pipe 37, where it is adsorbed and stored. The vaporized gas stored in the canister 35 is discharged to the intake pipe 21 through the supply pipe 39 by opening the purge amount control valve 38. Accordingly, the vaporized gas discharged to the intake pipe 21 is sent to the combustion chamber 18 of the engine 10 together with the intake air and burned.

[0013]

In the above-described conventional lean burn engine, the vaporized gas generated from gasoline in the fuel tank 28 is stored in the canister 35.
In this case, for example, if the vehicle is used less frequently in a region where the temperature difference between day and night is large, or if the traveling time is short even if used, the amount of evaporative gas generated increases and exceeds the adsorption capacity of the canister 35. There is a problem that HC overflows and is discharged outside the vehicle.

Conventionally, as a countermeasure, the capacity of the canister 35 is increased in order to increase the adsorption capacity of the canister 35, and a large amount of HC is discharged from the canister 35 to the intake pipe 21 during operation of the engine 10 so that the engine 10 Combustion chamber 18
It is considered to be burned by. By the way, in order to stabilize the combustion in the combustion chamber 18 of the engine 10,
Generally, the ECU 26 controls the weight ratio between the intake air and the injected fuel, that is, the air-fuel ratio (A / F). As described above, the intake air is calculated from the detection results of the air flow sensor 23 and the throttle position sensor 24, and the ECU 26 determines the fuel injection amount corresponding to this. However, when a large amount of HC is discharged from the canister 35 to the intake pipe 21, this air-fuel ratio shifts. In particular, the lean burn operation state in which the actual air-fuel ratio burns in a lean state larger than the stoichiometric air-fuel ratio. When a large amount of HC enters, the state changes from a lean state to a rich state, and there is a problem that drivability is deteriorated.

Therefore, the timing of HC discharge from the canister 35 to the intake pipe 21 is controlled so that when the engine 10 is operating stably, for example, during low load operation or low rotation,
Although it is conceivable to discharge HC only outside the lean burn operation area, a large number of valves and the like for detecting the operating state of the engine 10 in detail and discharging HC are required. , It becomes large.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a vaporized gas purifying apparatus for a lean burn internal combustion engine, which purifies the vaporized gas efficiently.

[0017]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, a vaporized gas purifying apparatus for a lean burn internal combustion engine according to the present invention is provided.
Lean combustion In a device for purifying vaporized gas generated from fuel stored in the fuel tank of an internal combustion engine, an oxidation catalyst is installed in the exhaust passage and the generated vaporized gas is subjected to lean combustion.
A vaporized gas supply means for supplying the gas to the exhaust passage upstream of the oxidation catalyst during operation is provided.

[0018]

[Action] transpiration gas generated from the fuel tank is lean combustion luck
At the time of rotation, it is supplied to the exhaust passage by the evaporation gas supply means,
The mixture is mixed with a large amount of air contained in the combustion exhaust gas to form an air-fuel mixture, which is oxidized by an oxidation catalyst provided in the exhaust passage to remove harmful substances such as hydrocarbons.

[0019]

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

FIG. 1 is a schematic diagram of a device for purifying a vaporized gas of a lean burn internal combustion engine according to an embodiment of the present invention, and FIG. 2 is a flowchart thereof. Note that members having the same functions as those in the related art are denoted by the same reference numerals, and redundant description will be omitted.

In the vaporized gas purifying apparatus of this embodiment,
A vaporized gas supply means for supplying the vaporized gas upstream of the oxidation catalyst mounted on the exhaust passage is provided.

That is, as shown in FIG.
0 is connected to the intake port 11 of the engine 10 via a surge tank 22 by an intake pipe 21.
An airflow sensor 23, a throttle valve 25, and a throttle position sensor 24 are provided in the middle part. An injector 27 is attached to the intake port 11 of the engine 10, and is connected to a fuel tank 28. On the other hand, an exhaust pipe 29 is connected to the exhaust port 12 of the engine 10, and catalytic converters 30 (three-way catalysts) and 51 (oxidation catalyst) and a muffler 31 are mounted in the middle.

The canister 35 is connected to the fuel tank 28 via a discharge pipe 37 having a check valve 36. The canister 35 temporarily stores harmful substances such as HC which has evaporated, and causes the harmful substances to be sucked when the engine 10 starts. The canister 35 is supplied to the intake pipe 21 and the exhaust pipe 29 via two supply pipes 39 and 52. Are linked. That is, the canister 35 is connected to the intake pipe 21 via a supply pipe 39 having a purge amount control valve 38, and is connected to the exhaust pipe 29 via a supply pipe 52 having a switching valve 53, a frame arrestor 54, and a reed valve 55. Are linked.

The switching valve 53 is ON / OFF controlled by the ECU 26, and is opened under a predetermined condition so that the vaporized gas can be supplied to the exhaust pipe 29. The flame arrester 54 is a mesh metal mesh for preventing backflow of the combustion flame, and the reed valve 55 is opened by the negative pressure on the exhaust pipe 29 side.

The air sucked from the air cleaner 20 is supplied to the intake port 11 of the engine 10 through the intake pipe 21 and the surge tank 22, while the injector 27 injects a predetermined amount of gasoline in the fuel tank 28. And
A mixture of air and gasoline is supplied into the combustion chamber 18. Then, the air-fuel mixture is compressed by the vertical movement of the piston 17 in the combustion chamber 18, and the spark plug 19 generates a spark, causing an explosion and expansion to operate the engine.

While the engine 10 is stopped, the gasoline in the fuel tank 28 evaporates due to the temperature difference between the engine warm air and the outside air. When the vaporized gas (HC) reaches a gas pressure higher than a predetermined value, the check valve 36 is opened and sent to the canister 35 through the discharge pipe 37, where it is adsorbed and stored. The vaporized gas is discharged from the canister 35 to the intake pipe 21 via the supply pipe 39, and is sent to the combustion chamber 18 of the engine 10 together with the intake air to be burned.

At this time, if the frequency of use of the vehicle is low or the running time is short even if it is used in an area where the temperature difference between day and night is large, the amount of evaporative gas generated increases and exceeds the adsorption capacity of the canister 35. Sometimes. In this case, the evaporated gas of the canister 35 is supplied to the exhaust pipe 29 by the supply pipe 52. On the other hand, when the engine 10 is operated in the lean burn operation region in which the actual air-fuel ratio burns in a lean state larger than the stoichiometric air-fuel ratio, a large amount of air (oxygen) is contained in the exhaust gas. Is mixed with the vaporized gas in the exhaust pipe 29 to form a mixture, which is reacted by the oxidation catalyst 51.

That is, the ECU 26 constantly detects the cooling water temperature from the water temperature sensor 33, constantly detects the engine speed by the crank angle position sensor 34, and further detects the oxygen concentration of the exhaust gas by the O ₂ sensor 32. doing. Therefore, as shown in FIG. 2, in step S1, it is determined whether or not the oxidation catalyst 51 is warmed up when the water temperature is equal to or higher than a certain temperature, and if so, the process proceeds to step S2. If the water temperature is not equal to or lower than the predetermined temperature, step S4
Then, the switching valve 53 is turned off. In step S2, it is determined whether the engine 10 has a low load and a low speed and whether the exhaust gas has a high oxygen concentration and is in a lean burn operation state.
Then, the switching valve 53 is turned on.

Then, the switching valve 53 is opened and the vaporized gas from the canister 35 is supplied to the exhaust pipe 29 by the supply pipe 52. On the other hand, a large amount of air (oxygen) is contained in the exhaust gas.
The mixture is mixed inside to form a gas mixture, which is reacted by the oxidation catalyst 51, and HC is removed. In step S2, if the engine 10 is not in the low-load, low-speed or lean-burn operation state, the process proceeds to step S4, and the switching valve 53 is turned off.

When the engine 10 is in the lean burn operation state, when the vaporized gas (HC) adsorbed by the canister 35 is supplied to the exhaust pipe 29 by the supply pipe 52, oxygen contained in the exhaust gas is reduced to the vaporized gas. And the reaction by the oxidation catalyst 51, the evaporated gas is supplied from the canister 35 through the supply pipe 39 to the intake pipe 21.
Can be simplified at a low cost or can be eliminated, and it is not necessary to increase the size of the canister 35. Then, a large amount of HC is no longer discharged from the canister 35 to the intake pipe 21, so that the air-fuel ratio of the engine 10 is not adversely affected, a stable combustion state is obtained, exhaust gas is reduced, and deterioration of drivability is prevented. Is done.

In each of the above embodiments, the supply of the vaporized gas to the exhaust pipe 29 is performed by negative pressure, but may be performed by providing an air pump or the like.

As described above in detail with reference to the embodiments, according to the apparatus for purifying the vaporized gas of the lean burn internal combustion engine of the present invention, the oxidation catalyst is mounted in the exhaust passage and the vaporized gas generated is lean burned. Since the evaporative gas supply means for supplying the evaporative gas upstream of the oxidation catalyst during operation is provided, the evaporative gas generated from the fuel tank is supplied to the exhaust passage, where it mixes with the air contained in the exhaust gas to oxidize. It reacts and removes harmful substances such as hydrocarbons, so there is no need to increase the size of the canister.
Is not discharged, and no adverse effect is exerted on the air-fuel ratio, so that a stable combustion state can be obtained. Thus, the exhaust gas can be reduced, the evaporated gas can be efficiently purified, and the drivability can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a device for purifying a vaporized gas of a lean burn internal combustion engine according to one embodiment of the present invention.

FIG. 2 is a flowchart showing an operation.

FIG. 3 is a schematic diagram showing an intake and exhaust system of a conventional lean burn internal combustion engine.

[Explanation of symbols]

 Reference Signs List 10 engine 18 combustion chamber 20 air cleaner 21 intake pipe 26 engine control unit (ECU) 28 injection 29 exhaust pipe 30 catalytic converter (three-way catalyst) 35 canister 37 exhaust pipe 51 catalytic converter (oxidation catalyst) 52 supply pipe 53 switching valve

Claims (1)

(57) [Claims] 1. A device for purifying vaporized gas generated from fuel stored in a fuel tank of a lean-burn internal combustion engine, wherein an oxidation catalyst is mounted in an exhaust passage and the generated vaporized gas is exhausted during lean-burn operation. A vaporized gas purifying apparatus for a lean burn internal combustion engine, further comprising a vaporized gas supply means for supplying the vaporized gas upstream of the oxidation catalyst.