JPS63239353A - Exhaust reflux device for diesel engine - Google Patents

Abstract

PURPOSE:To effecitvely restrain a half-misfire at time of highland driving from occurring, by compensating an exhaust reflux value at both high speed and low load areas within the exhaust reflux range of an engine to the more decrement side than that at time of being high in atmospheric pressure, when a drop in the atmospheric pressure is detected. CONSTITUTION:In the exhaust reflux passage 4 installed astride between a suction passage 2 and an exhaust passage 3 of an engine, there is provided with an exhaust reflux control valve 5. And this exhaust reflux control valve 5 is controlled for its opening or closing by a controller 7 via an actuator 6. And, each detection signal out of an atmospheric pressure sensor 8, a speed sensor 9 and a load sensor 10 is inputted into the controller 7. At this time, when a drop in atmospheric pressure at time of highland driving is detected, an exhaust reflux value at both high speed and low load areas within the exhaust reflux range of the engine 1 is compensated to the more decrement side than that at time of being high in the atmospheric pressure. With this constitution, a half-misfire at time of highland driving is effectively restrained from occurring in particular.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an exhaust gas recirculation device for a diesel engine.6 (Prior Art) Conventionally, in a diesel engine, exhaust gas recirculation control has been applied to an exhaust passage and an intake passage. A part of the exhaust gas is recirculated to the intake system in the exhaust recirculation area, which is connected to the exhaust recirculation passage equipped with a valve and set in the low speed and low load range of the engine (for example, Japanese Patent Laid-Open No. 57 (Refer to Publication No.-157047).

By the way, in this way, the exhaust recirculation area is
The reason for setting it in the low load range is as follows.

First, regarding the influence of load, when the load is low, the amount of fuel supplied is smaller than when the load is high, and the combustion chamber wall temperature is correspondingly low, making it difficult to ignite the fuel. This reflux actively heats the intake air and improves the ignitability of the fuel.

On the other hand, at high loads, when exhaust gas is recirculated, the amount of air introduced into the combustion chamber is relatively reduced, which reduces engine output and increases smoke due to lack of air. This is to stop exhaust gas recirculation.

On the other hand, regarding the effect of engine speed, in the high-speed range near the engine's rated speed, the 1-cycle time is short and the combustion speed needs to be increased accordingly, and when exhaust gas is recirculated, the amount of air is relatively reduced. Therefore, exhaust gas recirculation is not performed in this rotation range because the effect of lowering the combustion speed becomes greater and the combustion characteristics deteriorate.

In other words, one of the purposes of exhaust gas recirculation is to use the heat of the exhaust gas to heat the intake air6, thereby improving the ignitability of the fuel, as mentioned above, but there is also another major purpose. The purpose is to reduce NOx in exhaust gas. In other words, since NOx has the characteristic that the amount of NOx generated increases as the combustion temperature rises,
The exhaust gas is recirculated into the intake system to forcibly reduce the combustion temperature, thereby suppressing the generation of NOx.

Therefore, in the sense of NOx reduction, it is desirable that exhaust gas recirculation be performed over as wide an operating range as possible, and in reality, taking into consideration this NOx reduction perspective and the above-mentioned intake air heating perspective, is set.

However, in a diesel engine equipped with such an exhaust recirculation device, if the engine is adjusted at a low altitude such as an urban area where it is normally used and then used at a high altitude, a half-misfire condition tends to occur and the output performance of the engine decreases. The problem was that it got worse.

(Purpose of the Invention) The present invention aims to solve the problems pointed out in the above section of the prior art. The objective is to achieve both the effect of reducing NOx during driving and the effect of suppressing half-misfire during high-altitude driving.

(Technical Background of the Invention) As mentioned above, when a diesel engine equipped with an exhaust gas recirculation device is operated at high altitude, semi-misfires are likely to occur.
The cause of this is not clear, and therefore, in order to investigate this cause, the inventors of the present application investigated the correlation between the state of occurrence of half-misfire and the operating state of the engine. As a result, it was found that half-misfires occur particularly at high speeds and low loads within the exhaust gas recirculation region where exhaust gas recirculation occurs. From this,
The inventor of the present application has discovered the following.

When an engine is operated at high altitudes, one of the causes of semi-misfires, particularly in the exhaust recirculation region and at high speeds and low load regions, is changes in oxygen density and intake temperature due to altitude differences. That is, in highlands, the atmospheric pressure is naturally lower than in lowlands, and the oxygen density in the atmosphere (in the intake air) decreases, as well as the intake air temperature (outside air temperature).

Therefore, if exhaust gas recirculation is performed during low-load operation at high altitudes, the combustion reaction will be faster due to the fact that in this state the fuel supply itself is small and the heat of combustion is low, as well as the oxygen density in the intake air and the intake air temperature are low. It becomes even slower, and especially at high speeds, the combustion reaction becomes difficult to follow the engine rotation, resulting in poor fuel ignitability! Shi l M:
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It is thought that. In the low speed range, even if the combustion reaction is slow due to the above-mentioned adverse conditions, it is thought that half-misfire hardly occurs because the reaction can sufficiently follow the engine rotation.

Furthermore, other causes of half-misfire include the influence of swirl generated within the combustion chamber and the cooling performance of the combustion chamber wall surface.

In other words, the swirl generated in the combustion chamber causes a decrease in the combustion chamber wall temperature, but its effect is influenced by the flow velocity of the swirl, and the faster the flow velocity, in other words, the higher the engine speed, the lower the combustion chamber wall temperature. The lowering effect becomes greater. On the other hand, the cooling effect of the combustion chamber by the cooling water flowing in the water jacket formed around the combustion chamber is influenced by the flow rate of the cooling water, that is, the engine rotation speed (the water pump rotation speed). At high engine speeds, the effect of lowering the combustion chamber wall temperature by the throat cooling water increases. Therefore, in the high-speed range of the engine, the combustion chamber wall temperature is lower than in the low-speed range due to the effects of both swirl and cooling water. If this is reduced, the ignitability of the fuel will further deteriorate, making it more likely that a half-misfire condition will occur.

Based on these facts, the inventor of the present application has determined that in order to ensure the NOx reduction effect during low-altitude driving due to exhaust gas recirculation over as wide a driving range as possible, and to effectively suppress the occurrence of half-misfires during high-altitude driving, it is necessary to In addition, when the operating condition is in the exhaust gas recirculation region and in the high speed/low load region, it is more effective to reduce the amount of exhaust gas recirculation than in other regions. .

(Means for Achieving the Object) As a means for achieving the above object, the present invention provides an exhaust gas recirculation passage that communicates an exhaust passage with an intake passage, and controls the circulation of exhaust gas flowing through the exhaust gas recirculation passage. An exhaust recirculation system for a diesel engine is equipped with an exhaust recirculation control valve for a diesel engine that includes a speed sensor that detects engine rotational speed, a load sensor that detects engine load, an atmospheric pressure sensor that detects atmospheric pressure, and atmospheric pressure. Exhaust recirculation correction means is provided for correcting the exhaust recirculation amount in the high-speed, low-load range in the exhaust gas recirculation region of the engine to be smaller than that at high atmospheric pressure when detecting a decrease in the atmospheric pressure.

(Function) In the present invention, by the above-mentioned means, when operating in a lowland area with high atmospheric pressure, exhaust gas recirculation is performed with a predetermined amount of exhaust gas recirculation in the entire exhaust gas recirculation area, and NOx generation is effectively suppressed. When operating at high altitudes with low atmospheric pressure, the exhaust recirculation amount is set to a lower value in the high-speed, low-load range of the exhaust recirculation region than in low-lying areas, and the occurrence of half-misfires is suppressed as much as possible. .

(Embodiment) Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. 19 to 3.

FIG. 1 shows a system diagram of an intake/exhaust system of an automobile diesel engine equipped with an exhaust gas recirculation device according to an embodiment of the present invention, in which reference numeral 1 is the engine, 2 is an intake passage, and 3 1 is an exhaust passage, and 1 is an exhaust gas recirculation passage provided spanning between the intake passage 2 and the exhaust passage 3. This exhaust gas recirculation passage 4 is for recirculating part of the exhaust gas from the exhaust passage 3 side to the intake passage 2 side, and an exhaust gas recirculation control valve 5 for controlling the amount of exhaust gas recirculation is provided in the middle of the passage. It is provided. The exhaust gas recirculation control valve 5 is opened and closed by an actuator 6 that operates in response to a control signal from a controller 7, and in particular, in this embodiment, it is turned on and off depending on atmospheric pressure and outside temperature, as will be described later. configured to operate. In addition, the above controller 7
An atmospheric pressure signal S1 from the atmospheric pressure sensor 8, a speed signal S2 from the speed sensor 9, and a load signal S3 from the load sensor 1O are inputted to the .

In this embodiment, as shown in Fig. 2, the exhaust recirculation control valve 5 is basically opened to perform exhaust recirculation in the exhaust recirculation region set in the low speed and low load range of the engine. In other non-exhaust recirculation restricted areas, the exhaust recirculation control valve 5 is closed to stop exhaust recirculation.

Furthermore, in this embodiment, the present invention is applied to stop exhaust recirculation within the exhaust recirculation region during high-altitude driving, particularly in high speed and low load regions.

That is, in this embodiment, as shown in FIG. 3, the outside air environment of the place where the engine is operated is made to correspond to the atmospheric pressure and outside temperature, and is set to the lowest pressure and lowest temperature (that is, the highest altitude).
A first zone located on the side (straight line σ, the zone below the twist) and a second zone located on the slightly higher pressure/higher temperature side than the first zone (between the straight line σ and the straight line) zone) and a higher pressure and temperature than the second zone (i.e.,
The area is divided into three zones: a third zone (straight detour, higher zone); corresponds to high altitude). Since the first zone is the zone where semi-misfires are most likely to occur, in this case, the first exhaust recirculation restricted area (point a - (area surrounded by b - c)
Inside, the exhaust gas recirculation control valve 5 is forcibly closed to stop exhaust gas recirculation and to suppress the occurrence of half-misfires as much as possible. In addition, the second zone is a region where misfires are less likely to occur, although it is slightly more than the first zone, so in this case, the second zone is located on the higher speed/lower load side than the ring line L2 in Fig. 2. The exhaust gas recirculation control valve 5 is forcibly closed within the second exhaust gas recirculation restricted area (the area surrounded by points d-e-c) to stop the exhaust gas recirculation. That is, in this embodiment, in order to prevent half-misfire of the engine when driving at high altitudes, exhaust recirculation is stopped in the exhaust recirculation region, especially in high speed and low load areas, when driving at high altitudes. In this case, the engine operating range in which exhaust gas recirculation is stopped is selected and set in two stages depending on the altitude.

Therefore, for example, when an automobile is driven from a lowland to a highland, exhaust gas recirculation is performed throughout the exhaust gas recirculation region while the vehicle is traveling at a lowland where the outside air environment is in the third zone. When the outside air environment reaches the second zone after climbing further, exhaust recirculation is stopped in the second exhaust recirculation restriction area, which is the highest speed/lowest load side of the exhaust recirculation area, and exhaust recirculation is performed in other areas. It will be done. When the altitude further increases and the outside air environment reaches the first zone, the exhaust gas recirculation is stopped in a wider range (i.e., the first exhaust gas recirculation restricted area) than in the second zone.

As described above, according to the exhaust gas recirculation device of this embodiment, when driving at low altitudes where semi-misfires are less likely to occur, exhaust gas recirculation is performed throughout the exhaust recirculation region, thereby effectively reducing NOx in the exhaust gas, and - When driving at high altitudes, where rear-end misfires are likely to occur, the occurrence of half-misfires is suppressed as much as possible by stopping exhaust recirculation in the high-speed/low-load range, where half-misfires are particularly likely to occur. It is something.

In the embodiments described above, the operating range in which exhaust gas recirculation is performed is reduced, but the amount of exhaust gas recirculation itself may be varied linearly.

(Effects of the Invention) The present invention provides an exhaust recirculation device for a diesel engine that includes an exhaust recirculation passage that communicates an exhaust passage with an intake passage, and an exhaust recirculation control valve that controls the flow rate of exhaust gas flowing through the exhaust recirculation passage. , a speed sensor that detects the rotational speed of the engine, a load sensor that detects the engine load, an atmospheric pressure sensor that detects atmospheric pressure, and a The present invention is characterized by the provision of an exhaust gas recirculation correction means for correcting the amount of exhaust gas recirculation in a high speed/low load range to a value smaller than that in a high atmospheric pressure.

Therefore, according to the exhaust gas recirculation device for a diesel engine of the present invention, when operating in a lowland where atmospheric pressure is high, exhaust gas recirculation is performed with a predetermined exhaust gas recirculation 1 in the entire exhaust gas recirculation area, and the generation of NOx is effectively suppressed. Furthermore, when operating at high altitudes with low atmospheric pressure, the amount of exhaust recirculation is set to a lower level in the high-speed, low-load range of the exhaust recirculation region than in low-lying areas, suppressing the occurrence of half-misfires as much as possible. Such,
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[Brief explanation of drawings]

Fig. 1 is a diagram of the intake/exhaust system of a diesel engine equipped with an exhaust gas recirculation device according to an embodiment of the present invention, and Fig. 2 shows a diagram of the engine load and engine speed in the exhaust gas recirculation device shown in Fig. 1. Exhaust recirculation area diagram, FIG. 3 is an exhaust gas recirculation area diagram corresponding to outside temperature and atmospheric pressure. ! - Engine 2... Intake passage 3... Exhaust passage 4... Exhaust recirculation passage 5... Exhaust recirculation control valve 6... Actuator 7. ... Controller 8 ... Atmospheric pressure sensor 9 ... Speed sensor 10 ... Load sensor Figure 3

Claims (1)

[Claims] 1. an exhaust recirculation passage that communicates the exhaust passage and the intake passage;
An exhaust recirculation device for a diesel engine, comprising an exhaust recirculation control valve that controls the flow rate of exhaust gas flowing through the exhaust recirculation passage, a speed sensor that detects the rotational speed of the engine, and a load sensor that detects the load of the engine. and an atmospheric pressure sensor that detects atmospheric pressure, and when a drop in atmospheric pressure is detected, the amount of exhaust recirculation in the engine's exhaust recirculation area at high speeds and low loads is reduced compared to when the atmospheric pressure is high. An exhaust gas recirculation device for a diesel engine, characterized in that it is provided with an exhaust gas recirculation correction means for correcting the exhaust gas recirculation.