JP2778337B2 - Exhaust system for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system for an internal combustion engine, and more particularly, to an improvement in the efficiency of purifying vaporized gas generated from fuel in a fuel tank.

[0002]

2. Description of the Related Art A required amount of fuel such as gasoline is stored in a fuel tank of an automobile. However, the fuel evaporates due to a difference in temperature between the engine warm air and the outside air. This vaporized gas contains harmful substances such as hydrocarbons (hereinafter, referred to as HC). Therefore, the vaporized gas cannot be discharged to the outside as it is, but is temporarily stored in a canister, and the engine is operated. When the engine starts, it is processed by inhaling it into this engine.

FIG. 4 schematically shows a conventional intake and exhaust system of an engine.

[0004] As shown in FIG. 4, an 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.

[0005] The air cleaner 20 is for removing floating dust in the air to be taken in. The air cleaner 20 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.

[0006] An exhaust pipe 29 is connected to the exhaust port 12 of the engine 10, and a catalytic converter (three-way catalyst) is provided at an intermediate position.
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 that 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 piston 17 moves up and down by driving the crankshaft 15 to compress the air-fuel mixture in the combustion chamber 18, 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, the 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.

[0011]

In the above-described intake and exhaust systems of the conventional engine, the vaporized gas generated from the 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 the 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, there is a problem that the air-fuel ratio is shifted and the drivability is deteriorated.

Therefore, the timing of discharging HC from the canister 35 to the intake pipe 21 is controlled, and the HC is discharged only when the engine 10 is operating stably, for example, during low load operation or low rotation. Although it is conceivable to do so, a large number of valves and the like for performing detailed detection of the operating state of the engine 10 and discharging HC are required, and the device becomes complicated and large.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide an exhaust device for an internal combustion engine that efficiently purifies vaporized gas.

[0015]

SUMMARY OF THE INVENTION The aforementioned exhaust system of the present invention for achieving the objects of the front O ₂ before and after the catalyst together with the catalyst is mounted in an exhaust passage of the combustion gas of the internal combustion engine Sensor and rear O ₂ sensor are installed,
In an exhaust system of an internal combustion engine in which an engine control unit controls an air-fuel ratio by an output of each O ₂ sensor,
A vaporized gas supply unit that supplies vaporized gas generated from fuel in a fuel tank upstream of the catalyst in the exhaust passage and an air supply unit that supplies air to the exhaust passage together with the vaporized gas are provided, and the vaporized gas and The output of the rear O ₂ sensor is stopped when air is supplied to the exhaust passage.

[0016]

The vaporized gas generated from the fuel tank is supplied to the exhaust passage by the vaporized gas supply means, while the air is supplied to the exhaust passage together with the vaporized gas by the air supply means, thereby causing an oxidizing reaction to cause harmful effects such as hydrocarbons. Material is removed. When the vaporized gas and air are being supplied to the exhaust passage, the output of the rear O ₂ sensor is stopped, and the engine control unit controls the air-fuel ratio by the output of only the front O ₂ sensor.

[0017]

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

FIG. 1 is a schematic diagram of an intake and exhaust system of an engine showing an exhaust system of an internal combustion engine according to an embodiment of the present invention, FIG. 2 is a flowchart of a process for purifying evaporated gas, and FIG.
2 shows a flowchart of the air-fuel ratio control. 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 exhaust system of this embodiment, a vaporized gas supply means for supplying vaporized gas to the exhaust passage and an air supply means for supplying air to the exhaust passage are provided in the exhaust system.

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 exhaust pipe 29 has a front O ₂ sensor 32.
And a rear O ₂ sensor 50. The front O ₂ sensor 32 detects the oxygen concentration before passing through the catalytic converters 30 and 51 and outputs it to the ECU 26 to perform air-fuel ratio control. The rear O ₂ sensor 50 detects the oxygen concentration after passing through the catalytic converters 30 and 51. Output to the ECU 26 to correct the air-fuel ratio.

The fuel tank 28 is connected to a canister 35 via a discharge pipe 37 having a check valve 36. The canister 35 temporarily stores harmful substances such as HC which has evaporated, and inhales when the engine 10 is started. The canister 35 is supplied to the intake pipe 21 and the exhaust pipe 29 through 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.

On the other hand, an air cleaner 56 for sucking secondary air is provided separately from the above-described air cleaner 20 for sucking primary air and introducing it into the combustion chamber 18 of the engine 10 through the intake pipe 21. The air cleaner 56 is connected to the exhaust pipe 29 via an intake pipe 59 having a switching valve 57 and a reed valve 58. The switching valve 57 is ON / OFF controlled by the ECU 26 and is opened under predetermined conditions so that secondary air can be supplied to the exhaust pipe 29. The reed valve 59 is opened by a 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.
At this time, the front O ₂ sensor 3 the oxygen concentration of exhaust gas
2 and rear O ₂ sensor 50 detect and detect the detection result by ECU
26, the air-fuel ratio control is performed.

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, while the vaporized gas from the canister 35 is supplied to the exhaust pipe 29 by the supply pipe 52, the secondary air sucked from the air cleaner 56 is supplied to the exhaust pipe 29 together with the vaporized gas,
The reaction is carried out by the oxidation catalyst 51.

That is, the ECU 26 constantly detects the cooling water temperature from the water temperature sensor 33 and constantly detects the engine speed by the crank angle position sensor 34. 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 lower than the predetermined temperature, the process proceeds to step S4, and the switching valves 53 and 57 are turned off.
In step S2, it is determined whether the engine 10 has a low load and a low speed. If so, the process proceeds to step S3, and the switching valves 53 and 57 are 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, while the switching valve 57 is opened and the secondary air from the air cleaner 56 is supplied to the exhaust pipe 29. Then, the air and the vaporized gas are mixed to form a gas mixture, which is reacted by the oxidation catalyst 51 to remove HC. Also,
In step S2, if the engine 10 is not at low load and low speed, the process proceeds to step S4, and the switching valves 53 and 57 are turned off.

Further, the vaporized gas and the secondary air are supplied to the exhaust pipe 29.
, The air-fuel ratio control is performed based on the detection result of only the front O ₂ sensor 32. If this is the exhaust pipe 29 upstream of the rear O ₂ sensor 50 secondary air is supplied, the rear O ₂ sensor 50 is detected values of the front O ₂ sensor 32 detects that the air-fuel ratio is small (the air-fuel ratio) Is corrected, and the air-fuel ratio is increased. When the vaporized gas is supplied to the exhaust pipe 29, the rear O ₂ sensor 50 detects that the air-fuel ratio is high and detects the detected value (air-fuel ratio) of the front O ₂ sensor 32.
And the air-fuel ratio is reduced. Then, the air-fuel ratio for performing stable combustion in the combustion chamber 18 is shifted, which is a factor of deteriorating drivability.

That is, the ECU 26 constantly detects the ON / OFF state of the switching valves 53 and 57.
Therefore, as shown in FIG. 3, in step P1, the ON state of the switching valves 53 and 57 is determined, and the ON state is determined.
If so, the process proceeds to Step P2. Then, in Step P2, performs feedback control of the air-fuel ratio by the detection value of the front O ₂ sensor 32 only. On the other hand, if the switching valves 53 and 57 are not ON in Step P1, the process shifts to Step P3. In step P3, the output value of the rear O ₂ sensor 50 is detected,
In step P4, it corrects the detected value of the front O ₂ sensor 32 (lean / rich decision level). Then, in Step P2, performs feedback control of the air-fuel ratio by the corrected detected value of the front O ₂ sensor 32.

While the vaporized gas (HC) adsorbed by the canister 35 is supplied to the exhaust pipe 29 by the supply pipe 52, the secondary air sucked from the air cleaner 56 is supplied to the exhaust pipe 29 together with the vaporized gas to oxidize. Since the reaction is carried out by the catalyst 51, the vaporized gas is supplied to the canister 3.
5 to the intake pipe 21 via the supply pipe 39 can be simplified at a low cost or can be eliminated, and the canister 35
There is no need to increase the size. 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.

Then, the vaporized gas and the secondary air are exhausted by the exhaust pipe 2.
Since the air-fuel ratio control when it is being supplied to the 9 to perform the detection result of only the front O ₂ sensor 32, the front O ₂ by the detection value of the rear O ₂ sensor 50 at this time
Since the detection value of the sensor 32 is not corrected, the air-fuel ratio for performing stable combustion in the combustion chamber 18 is positive, and the drivability does not deteriorate.

In each of the above embodiments, the air cleaner 56 is provided separately from the air cleaner 20 for inhaling the primary air in order to inhale the secondary air for forming the vaporized gas and the air-fuel mixture. Although provided, the air cleaner 20 may be shared. For example, even if the intake pipe 21 from the air cleaner 20 is branched in the middle and one is connected to the surge tank 22 and the other is connected to the exhaust pipe 29 to supply the primary air and the secondary air, the same as described above. It is possible to achieve the function and effect. Further, the supply of the vaporized gas and the secondary air to the exhaust pipe 29 is performed by the negative pressure, but may be performed by providing an air pump or the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an intake and exhaust system of an engine representing an exhaust device of an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a flowchart of a vaporized gas purification process.

FIG. 3 is a flowchart of air-fuel ratio control.

FIG. 4 is a schematic view of a conventional intake and exhaust system of an internal combustion engine.

[Explanation of symbols]

Reference Signs List 10 engine 18 combustion chamber 20, 56 air cleaner 21, 59 intake pipe 26 engine control unit (ECU) 28 injection 29 exhaust pipe 30 catalytic converter (three-way catalyst) 32 front O ₂ sensor 35 canister 37 discharge pipe 50 rear O ₂ sensor 51 Catalytic converter (oxidation catalyst) 52 Supply pipe 53, 57 Switching valve

Claims (1)

(57) [Claims] 1. A catalyst is mounted in an exhaust passage of combustion gas of an internal combustion engine, a front O ₂ sensor and a rear O ₂ sensor are mounted before and after the catalyst, and an engine control unit is emptied by the output of each O ₂ sensor. In an exhaust device for an internal combustion engine for controlling a fuel ratio, a vaporized gas supply means for supplying vaporized gas generated from fuel in a fuel tank to the exhaust passage upstream of the catalyst and air to the exhaust passage together with the vaporized gas. An exhaust device for an internal combustion engine, further comprising an air supply means, wherein the output of the rear O ₂ sensor is stopped when the evaporated gas and air are supplied to the exhaust passage.