JPS5947149B2 - Engine exhaust gas recirculation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas recirculation system for an engine, and particularly to an exhaust gas recirculation system for recirculating engine exhaust gas upstream and downstream of a throttle valve of a carburetor.

In general, the technical concept of suppressing the maximum combustion temperature and preventing the generation of large amounts of NOx is well known by circulating part of the exhaust gas emitted from the engine into the intake system and introducing it into the combustion chamber together with the air-fuel mixture. Various reflux methods have been proposed in the past.

By the way, in this type of conventional technical thinking, when the air-fuel ratio of the air-fuel mixture is around the stoichiometric air-fuel ratio (A/F = 15), N
Since the amount of Ox generated is the maximum, the operating conditions are set to the one side (or rich side) to avoid the stoichiometric air-fuel ratio and reduce the amount of NOx generated, and under that operating condition, the Returning a small amount of exhaust gas to the intake system reduces NOx
It was considered to be the most efficient way to suppress

However, it has become clear that conventional engine exhaust gas recirculation devices that adopt this type of concept naturally have a limit to their ability to suppress NOx, and are unable to meet recent strict exhaust gas control standards.

That is, if the amount of exhaust gas recirculation is increased in order to suppress the amount of NOx generated below the regulatory standard value, the operating conditions of the engine will deteriorate extremely, resulting in a decrease in the output dog rl-1f, f. .

In order to solve this problem, we use a mixture with the air-fuel ratio set to the stoichiometric air-fuel ratio to ensure the necessary combustion speed, while
Technological ideas have been proposed to drastically increase the amount of exhaust gas recirculated, to avoid deterioration of engine performance due to a large amount of recirculated exhaust gas, and to thoroughly reduce NOx that can be generated in large amounts.

From this point of view, in order to guarantee a large amount of exhaust gas recirculation, exhaust gas is recirculated upstream and downstream of the throttle valve of the carburetor, and the recirculation amount of exhaust gas upstream of the throttle valve is equal to the exhaust gas in the exhaust pipe. The exhaust gas recirculation rate remains constant from low to high loads by utilizing a special feature that increases as the pressure increases, and by utilizing the characteristic that the amount of exhaust gas recirculation downstream of the throttle valve is proportional to the negative pressure in the intake pipe. An exhaust gas recirculation device has been proposed that is designed to obtain a ratio of various permanent fixtures,
In particular, (a) A large amount of exhaust gas is recirculated when the engine is running at high speeds and under high load, resulting in a decrease in output and worsening of fuel consumption. (b) Exhaust gas is recirculated upstream of the throttle valve of the carburetor. Due to the high temperature of the fuel, the temperature of the wall near the float chamber of the carburetor rises, causing percolation that causes fuel to leak out of the carburetor.

The present invention has been made in view of the following problems, and includes:
By recirculating exhaust gas upstream and downstream of the carburetor throttle valve, the above-mentioned permanent situation can be prevented, and the strict exhaust gas regulation standards of today can be met without reducing engine output or deteriorating fuel consumption. The object of the present invention is to provide a practical engine exhaust gas recirculation device that can achieve the following.

Therefore, in the present invention, during operation when a large amount of NOx is generated, the exhaust gas is recirculated upstream and downstream of the throttle valve of the carburetor to ensure a constant and high recirculation ratio, while a relatively small amount of NOx is recirculated. When the engine is running at high speed or under high load, when the engine generates NOx, a means is provided to cut only the recirculation of exhaust gas upstream of the throttle valve, which is proportional to the exhaust pressure in the exhaust pipe. By recirculating exhaust gas from the engine, the exhaust gas recirculation ratio is reduced to an appropriate range that does not reduce engine output or fuel consumption rate, and the generation of NOx is suppressed.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

In FIG. 1, 1 is an intake passage, 2 is an air cleaner with a built-in filter 2a, 3 is a carburetor, and 4 is a throttle valve provided downstream of a venturi portion 5 provided in the carburetor 3. is linked to an accelerator pedal (not shown) to control the amount of air-fuel mixture supplied to the engine, and the carburetor 3 adjusts the intake air amount to the air taken in from the air cleaner 2 according to the opening degree of the throttle valve 4. Fuel corresponding to the amount is injected from the main nozzle 3a to the center of the venturi part 5 to generate an air-fuel mixture having an appropriate air-fuel ratio, and the air-fuel mixture is supplied to the engine E from the intake passage 1.

On the other hand, 6 is a first exhaust gas recirculation passage which has a recirculation port 6a further upstream than the venturi portion 5 on the upstream side of the throttle valve 4 in the intake passage 1, and 7 is a recirculation passage downstream of the throttle valve 4 in the intake passage 1. In the second exhaust gas recirculation passage where the port 1a is set, these first
, the second exhaust gas recirculation passages 6 and 7 are formed as passages branching from a common exhaust gas recirculation passage 9 connected to an arbitrary position of the exhaust pipe 8 of the engine E.

Further, 10 is a first flow control valve that opens and closes a valve seat 6-b set in the middle of the first exhaust gas recirculation passage 6 so as to control the flow rate;
11 is a first diaphragm device in which the first flow control valve 10 is supported on a diaphragm 13 via an operating rod 12;
15 is a first control fluid introduction pipe for introducing control fluid such as intake negative pressure into the negative pressure chamber 11a of the first diaphragm device 11; It is an on-off valve.

At the same time, a second flow control valve 16 is set for the valve seat 7b provided in the middle of the second exhaust gas recirculation passage 7, and the second flow control valve 16 is connected to the diaphragm 19 via the actuating rod 18. The second diaphragm device 20 supported by the
In the middle of the second control fluid introduction pipe 21 for controlling the opening degree of the second flow control valve 16 and for introducing the control fluid into the negative pressure chamber 20a of the second diaphragm device 20, there is provided a valve for opening and closing. A second on-off valve 22 is provided.

The first and second on-off valves 15.22 provided in the first and second control fluid introduction pipes 14.21, respectively, operate at a rotational speed r of the engine.
It is controlled by a control device 23 which uses input information such as load and load.

These eleventh second on-off valves 15.22 include, for example,
Although a normally open electromagnetic solenoid valve can be used, a diaphragm type on-off valve may also be used.

When the first and second on-off valves 15.22 are electromagnetic solenoid valves, the control device 23 performs electrical control to apply ON and OFF electric signals to the first and second on-off valves 15.22. The engine rotation speed r as input information is detected by, for example, an engine rotation speed detection switch (not shown).

), and the engine load can be determined by, for example, an intake negative pressure detection switch (not shown).

) can be used.

Roughly speaking, the control device 23 applies, for example, an on signal p to both the normally open first and second on-off valves 15 and 22 in response to a detection signal from a switch that detects warm-up operation of the engine.
, the second on-off valves 15 and 22 are both closed, and the first and second on-off valves 15 and 22 are closed.
The introduction of the control fluid to the diaphragm device IL20 is cut off, and the first and second flow control valves 10.17 are fully closed by the spring force of the coil springs 11b and 20b, respectively, to cut back the exhaust gas and stop the engine from rotating. stabilize and quickly warm up the engine.

On the other hand, when the rotation speed r or the load of the engine E exceeds a preset value and reaches a high rotation or high load, the control device 23 sends an on signal q only to the first on-off valve 15. is applied to cut the recirculation of exhaust gas from the first exhaust gas recirculation passage 6 to the upstream side of the throttle valve 4.

Now, considering the exhaust gas recirculation control method according to the present invention, as shown in Fig. 2, the vehicle speed corresponding to the engine rotation speed or engine load, for example, 30 mph.
In the range of ~70k11, the exhaust gas recirculation ratio a is set to 15 to 2.
Within the range of 0%, the exhaust gas recirculation ratio a can be maintained at a constant high rate, while at speeds of 70 kjn or more, the exhaust gas recirculation ratio a can be reduced to a low level of the 5th coefficient or lower.

That is, the exhaust gas recirculation ratio a is the percentage of the ratio of the exhaust gas recirculation amount to the intake air mixture amount (the sum of the intake air amount and the intake fuel amount) ((exhaust gas recirculation amount)/(intake mixture amount)) xtoo), and the exhaust gas recirculation ratio C on the upstream side of the throttle valve 4 is the sum of the exhaust gas recirculation ratio C on the downstream side of the throttle valve 4.

The exhaust gas recirculation ratio on the upstream side of the throttle valve 4 is determined by the vehicle speed (engine speed (or load) tends to increase in proportion to the exhaust pressure in the exhaust pipe 8.

On the other hand, since the recirculation lower a of the second exhaust gas recirculation passage 7 is set downstream of the throttle valve 4 of the intake passage 1, the exhaust gas recirculation ratio C on the downstream side of the throttle valve 4 is It tends to decrease in proportion to the pressure, and as the intake negative pressure decreases as the vehicle speed (engine speed or load) increases.

Therefore, the overall exhaust gas recirculation ratio a is maintained constant by mutually compensating for the contradictory recirculation trends upstream and downstream of the throttle valve 4.

By the way, in this embodiment, when the vehicle speed exceeds 70 km/h, which corresponds to high engine rotation or high load, as described above, the recirculation of exhaust gas on the upstream side of the throttle valve 4 is cut, and the overall exhaust gas is reduced. The reflux ratio a is lowered to the exhaust gas reflux ratio C on the downstream side of the throttle valve 4, and
The reflux ratio is set to 4.

As shown in Figure 3, looking at the relationship between the exhaust gas recirculation ratio and the fuel consumption rate, under conditions of constant engine speed (1500 rpm) and constant output (average effective output pressure P e = 3 kg shoulder), the intake Air-fuel ratio of mixture (man/F)14.
15.16 In either case, the exhaust gas recirculation ratio is 507
The fuel consumption rate tends to be minimum near 0, and reducing the level of the exhaust gas recirculation ratio a at high speeds and high loads as described above is extremely favorable for the fuel consumption rate. As a result, the output of the engine can be ensured, and the emission of NOx can be suppressed, and good high-speed operation can be performed with a minimum fuel consumption rate.

The reason why the fuel consumption rate becomes minimum near the exhaust gas recirculation ratio of 5 is considered to be as follows.

In other words, the thermal efficiency of the Otto cycle that the engine repeats is:
It is influenced by the cylinder pressure at the beginning of compression and the specific heat ratio of the mixed gas (in this case, the mixture of the air-fuel mixture and the recirculated exhaust gas).

However, the specific heat ratio of the mixed gas does not change much between when the exhaust gas is recirculated and when it is not recirculated (for example, 1.38:1.40), and the difference can be virtually ignored. , Therefore, the above thermal efficiency is directly controlled by the cylinder internal pressure, in other words, the amount of exhaust gas recirculation that governs the cylinder internal pressure, and theoretically,
The thermal efficiency should improve as the amount of exhaust gas recirculation increases.

However, on the other hand, when the amount of exhaust gas recirculation increases, the inert exhaust gas tends to slow down the combustion rate and deteriorate the thermal efficiency. This is determined by the synergistic effect of the positive factor and the negative factor due to the slowing of the combustion speed, and the range of the exhaust gas recirculation ratio that minimizes the thermal efficiency is a factor of 5 to 10.

As is clear from the detailed explanation above, the present invention provides an engine exhaust gas recirculation device that recirculates engine exhaust gas upstream and downstream of a throttle valve of a carburetor, at high rotation speeds or high loads. The present invention is characterized by a control method for recirculating exhaust gas that stops the recirculation of exhaust gas upstream of the throttle valve, and according to the present invention, it is possible to prevent a large amount of exhaust gas from being brought in when the engine is running at high speed or under high load. By cutting the recirculation of the recirculated exhaust gas upstream of the throttle valve, it is possible to prevent as much as possible the dangers of clogging and freezing of the carburetor system, or conversely percolation of the carburetor. Exhaust gas downstream of the throttle valve has no negative impact on the system, so it is possible to minimize the fuel consumption rate and ensure an optimal recirculation amount, ensuring high engine output and suppressing NOx emissions. It is possible to achieve the effect that it is possible.

Note that the present invention is not limited to the configuration of the embodiment shown in FIG. It goes without saying that various changes and modifications can be made as long as the system can be realized.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram of a main part of an engine intake system showing an embodiment of the present invention, and FIG. 2 shows a vehicle speed (unit: Ian/
h) A graph showing the exhaust gas recirculation control method according to the present invention, in which the vertical axis is the exhaust gas recirculation ratio, and FIG. 3 is a graph where the horizontal axis is the exhaust gas recirculation ratio, and the vertical axis is the fuel consumption rate, It is a graph showing the relationship between the fuel consumption rate and the exhaust gas recirculation ratio when the air-fuel ratio of the air-fuel mixture is used as a parameter. ; 1... Intake passage, 3... Carburetor, 4... Throttle valve, 5... Vent +)
Part, s, 7...First and second exhaust gas recirculation passages, 10...First flow control valve, 11...
...First diaphragm device, 14...First control fluid introduction pipe, 15...First on-off valve, 16...
...Second flow rate control valve, 20...Second diaphragm device, 21...Second control fluid introduction pipe, 22
...Second on-off valve, 23...First, second
Control device for on-off valves.

Claims (1)

[Claims] 1 In an engine exhaust gas recirculation system that recirculates exhaust gas from the engine to the upstream and downstream of the throttle valve of the carburetor, only the recirculation upstream of the throttle valve is stopped at high speeds or high loads. The featured engine exhaust gas recirculation device.