JP2530953Y2 - Diesel engine exhaust recirculation system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an exhaust gas recirculation device for a diesel engine.

(Prior Art) An exhaust gas recirculation device that recirculates part of exhaust gas into intake air has been widely put into practical use for the purpose of reducing NO emitted from a diesel engine.

Exhaust gas recirculation uses the pressure difference between the exhaust system and the intake system to circulate exhaust gas.However, a diesel engine does not have an intake throttle valve like a gasoline engine, and the intake negative pressure is small.
In order to ensure the required amount of exhaust gas recirculation, for example,
As described in Japanese Patent Publication No. 52, a throttle valve is provided in the intake passage, and an exhaust gas recirculation passage is connected downstream of the throttle valve.

The throttle valve is throttled in an operation region requiring exhaust gas recirculation, for example, in a partial load region, and the exhaust gas recirculation amount is relatively increased by increasing the downstream intake negative pressure. In order to control accurately in response to the above, a flow control valve is provided in the middle of the exhaust gas recirculation passage, and the opening of the control valve is changed according to the lever opening of the fuel injection pump and the engine speed.

(Problems to be solved by the present invention) By the way, exhaust gas recirculation is effective in reducing NO, but when a large amount of exhaust gas is recirculated, it causes deterioration of combustion.
It also increases smoke and CO, and reduces fuel economy.

In particular, when the intake air is throttled by an intake throttle valve, the amount of fresh air introduced tends to decrease and the smoke tends to increase significantly during exhaust gas recirculation.

As one measure for improving combustion in a partial load region or the like, there is an intake swirl (for example, Japanese Patent Application Laid-Open No. 61-175233 and many others), but these are all subjected to swirl control in relation to exhaust gas recirculation. Therefore, it does not always contribute to the improvement of combustion at the time of exhaust gas recirculation, and it is necessary to harmonize both the exhaust gas recirculation control and the swirl control, and the control system becomes complicated.

The purpose of the present invention is to solve such a problem.

(Means for Solving the Problems) Accordingly, the present invention provides a diesel engine having a plurality of cylinders, a first exhaust throttle valve interposed in an exhaust passage from some of the cylinders, and the partial cylinder. A second exhaust throttle valve interposed in the exhaust passage downstream of the junction between the exhaust passage from the cylinder and the exhaust passage from another cylinder, and exhaust air upstream of the first exhaust throttle valve. An exhaust gallery communicating with the passage,
An ejection nozzle for ejecting the recirculated exhaust gas of the exhaust gallery to the intake port in the swirl generation direction; and selectively closing the first exhaust throttle valve or the second exhaust throttle valve to control the exhaust gas recirculation amount in a stepwise manner. I got it.

(Operation) When one of the first exhaust throttle valve and the second exhaust throttle valve is throttled in a partial load region or the like, the exhaust gas of the cylinder connected to the upstream of the first exhaust throttle valve or the second exhaust throttle valve is discharged from the exhaust gallery through the ejection nozzle of each cylinder. It is returned to the intake port. The exhaust gas recirculation amount at this time is the first
When the exhaust throttle valve is throttled, only a part of the cylinders is exhausted, so that the amount is relatively small. When the second exhaust throttle valve is throttled, the exhaust gas that is merged with other cylinders is introduced. It becomes a large amount. Therefore, the exhaust gas recirculation amount can be accurately controlled stepwise according to the engine load state.

The ejection nozzle guides the exhaust flow to generate swirl in the cylinder, and the ejected exhaust gas and fresh air mix while forming swirl in the cylinder in an engine intake process. The swirl intensity is substantially proportional to the exhaust gas recirculation amount.

Therefore, NO or NOx can be reduced without deteriorating combustion due to homogeneous mixing of the recirculated exhaust gas and gas flow in the cylinder, and CO,
Also suppresses the generation of HC. Exhaust gas recirculation does not involve an intake throttle, so that a sufficient amount of fresh air is ensured, thus reducing inevitable smoke during exhaust gas recirculation.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. 1 and 2, each cylinder 10 has two intake valves.
11a, 11b and exhaust valves 12a, 12b are provided to face each other, and a siamese-type intake port 13 and exhaust passages 14 (14A to 14D) are respectively connected to these.

As shown in FIG. 1, in the exhaust passage 14, the exhaust passage 14A of the # 1 cylinder and the exhaust passage 14D of the # 4 cylinder, the exhaust passage 14B of the # 2 cylinder, and the exhaust passage 14C of the # 3 cylinder merge on the way. It is formed so that.

A first exhaust throttle valve 15A is provided in the exhaust passage 14A of the # 1 cylinder.
And an exhaust passage 14 downstream of the junction of the # 1 cylinder exhaust passage 14A and the # 4 cylinder exhaust passage 14D.
Is provided with a second exhaust throttle valve 15B. These two exhaust throttle valves 15A and 15B are respectively connected via a diaphragm actuator or the like (not shown), for example, only the first exhaust throttle valve 15A in a relatively low load operation range, and the second exhaust throttle valve 15A in a relatively high load operation range. Only the exhaust throttle valve 15B is controlled to close.

An exhaust gas recirculation passage 16 is formed in the exhaust gas passage 14A so as to branch off from an upstream side of the first exhaust throttle valve 15A. The exhaust gas recirculation passage 16 is further connected to an exhaust gallery 17.
The exhaust gallery 17 supplies recirculated exhaust gas introduced from the exhaust passage 14A to the intake port 13. As shown in FIG.
An ejection nozzle 18 for ejecting exhaust gas to 13 is branched in parallel.

The ejection nozzle 18 is extended to a position close to the back of the umbrella of the intake valve 11b, and when the intake valve 11b is opened, ejects recirculation exhaust gas in a tangential direction on the inner circumference of the cylinder to generate a swirl (swirl flow) in the cylinder. .

 The configuration is as described above, and the operation will be described next.

When exhaust gas recirculation is not necessary, such as during engine idling or high-load operation, both the first and second exhaust throttle valves 15A and 15B are kept fully open. As a result, the exhaust gas of the # 1 and # 4 cylinders flows downstream without change, so that no exhaust gas recirculation is performed.

When the load increases to some extent from this state, first, the first exhaust throttle valve 15A is closed. This makes it upstream #
Since the exhaust pressure from one cylinder rises, the exhaust
The air flows into the exhaust gallery 17 via the nozzle 16 and then jets out to the intake port 13 of each cylinder through the jet nozzle 18 of each cylinder. At this time, only the exhaust gas from the # 1 cylinder is recirculated, so that a small amount of exhaust gas recirculation rate commensurate with the generation of NOx at a relatively low load. Although the swirl momentum decreases as much as the amount of exhaust gas recirculation is small, there is no inconvenience under the condition where the amount of exhaust gas recirculation is small because combustion hardly occurs.

When the load further increases, the first exhaust throttle valve 15A is opened and the second exhaust throttle valve 15B is closed. This allows
Since the exhaust gas of the # 1 cylinder and the # 4 cylinder is recirculated, the exhaust gas recirculation amount is doubled as described above, and a relatively large amount of exhaust gas is introduced from each ejection nozzle 18 to the intake port 13 of each cylinder. At this time, since the exhaust gas recirculation amount is increasing, a strong swirl is obtained by the recirculated exhaust gas from the ejection nozzle 18. Exhaust gas recirculation is performed while generating a strong swirl in this way, so that NOx, which tends to be generated under relatively high load operation conditions, without deteriorating combustion, that is, without increasing CO or H, is effective. Can be suppressed. In particular, since the newly introduced amount is not reduced by the intake throttle valve, smoke, which is likely to be generated at the time of exhaust gas recirculation, is also minimized.

Since the swirl is generated by the exhaust gas recirculation, the swirl having an appropriate strength can be naturally generated according to the opening / closing operation of the two exhaust throttle valves 15A and 15B without performing special swirl control. The exhaust gas recirculation rate is determined by two exhaust throttle valves 15A.
Or by the selective opening and closing operation of 15B, it can be kept constant even if the engine speed and load fluctuate,
Together with the swirl control, the configuration of the control system can be simplified.

Also, since the recirculated exhaust gas can be ejected at a high temperature, even if the passage 16 leading to the exhaust gallery 17 or the ejection nozzle 18 has a small diameter, there is little fear of clogging due to carbon or the like,
Furthermore, since the exhaust gas recirculation system becomes compact, the weight on the vehicle and the freedom of layout increase.

(Effects of the Invention) As described above, according to the present invention, an appropriate amount of gas can be obtained by selectively operating two exhaust throttle valves interposed in the exhaust passage toward the ejection nozzle desired at the intake port. Since exhaust gas is recirculated and swirl is generated in the cylinder, it is possible to suppress the generation of NO etc. without deteriorating combustion in a wide operating range, and from the point where it is not necessary to perform intake throttle,
The effect is obtained that a sufficient fresh air is secured and the occurrence of unavoidable swirl and exhaust gas during exhaust gas recirculation can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of one embodiment of the present invention, and FIG. 2 is a schematic sectional view of the # 1 cylinder. 10 ... cylinder, 11a, 11b ... intake valve, 12a, 12b ... exhaust valve, 13 ... intake port, 14a, 14b ... exhaust port, 15 ...
... exhaust throttle valve, 17 ... exhaust gallery, 18 ... jet nozzle.

Claims (1)

(57) [Scope of request for utility model registration] In a diesel engine having a plurality of cylinders, a first exhaust throttle valve interposed in an exhaust passage from some of the cylinders, and an exhaust passage from one of the cylinders and another of the other cylinders A second exhaust throttle valve interposed in the exhaust passage downstream of the junction with the exhaust passage, an exhaust gallery communicating with the exhaust passage upstream of the first exhaust throttle valve, An ejection nozzle for ejecting recirculated exhaust gas from the gallery to the intake port in a swirl generation direction, and the exhaust gas recirculation amount can be controlled stepwise by selectively closing the first exhaust throttle valve or the second exhaust throttle valve. An exhaust gas recirculation device for a diesel engine, characterized in that: