JPH05209558A - Exhaust gas recirculation system for alcohol engine - Google Patents

Abstract

PURPOSE:To efficiently suppress the discharge of unburnt alcohol and aldehyde out of a system at the engine starting time by controlling the recirculation quantity of exhaust gas in such a way as to be increased in proportion to the rise of alcohol concentration in alcohol containing fuel. CONSTITUTION:In an alcohol engine 3 using alcohol containing fuel, plural catalytic layers 51, 52 for removing alcohol content and aldehyde content in exhaust gas are installed in an exhaust passage 5. In this case, the alcohol concentration in alcohol containing fuel is detected by an alcohol concentration detecting means 22. On the other hand, an exhaust gas recirculation pipe 8 provided with a recirculation gas regulating valve 81 is disposed as an exhaust gas recirculation means for making exhaust gas flow back to an intake passage 31. The recirculation gas regulating valve 81 is then controlled by the reflux gas flow control means 61 of a control device 6 in such a way as to increase the recirculation quantity of exhaust gas in proportion to the rise of alcohol concentration in the alcohol containing fuel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation system for an alcohol engine when an alcohol-containing fuel is used to drive the engine.

[0002]

2. Description of the Related Art In recent years, as a measure against the problem of petroleum resource depletion, research on alternative fuels has been actively conducted, and alcohols such as methanol or ethanol as a kind of alternative fuels are fuels for automobiles, which will be the next generation. As a result, an alcohol-containing fuel obtained by mixing alcohol with gasoline has been developed.

By the way, when alcohol burns completely,
As exemplified by the following methanol, water and carbon dioxide gas are generated based on the reaction formula of 2CH ₃ OH + 3O ₂ → 4H ₂ O + 2CO ₂ , so that it is completely harmless.

However, it is not always completely burned, and when the amount of oxygen is small or the burning time is short, for example, 2CH ₃ OH + O ₂ → 2HCHO + 2H ₂ O reacts to form formaldehyde (HCHO). .. In addition, unburned alcohol may be directly discharged as exhaust gas.

Among alcohols, methanol is particularly harmful to the human body, and aldehydes are harmful to the human body regardless of the type.

For this reason, a catalyst layer for removing alcohol and aldehyde present in the exhaust gas is provided in the exhaust gas exhaust path of the conventional engine, and the exhaust gas is made harmless by contact with the catalyst layer. Is configured. However, for example, the harmful components may not be sufficiently removed when the engine is cold when the catalyst temperature is low and the catalyst activity cannot be exhibited.

As a gas treatment method for such exhaust gas of an alcohol engine, for example, Japanese Patent Laid-Open No.
It is disclosed by Japanese Patent No. 267309. The method for treating exhaust gas from a methanol-fueled automobile disclosed in this publication is characterized in that the air-fuel ratio is set to 15 to 19 to burn methanol fuel, and the exhaust gas is treated with a catalyst. Is. It is introduced that the purification rate of exhaust gas becomes good by setting the air-fuel ratio to 15 to 19 as described above.

Although the purpose is different from that of the present invention, in Unexamined Utility Model Publication No. 1-142570, unburned exhaust gas is positively generated, and this unburned exhaust gas is near the fuel discharge port of the fuel injection valve. Is disclosed and a starting promotion device for an internal combustion engine is disclosed, which heats the injected fuel with exhaust heat. That is, the object of this publication is to accelerate the start of the engine,
Although different from the purpose of purifying the exhaust gas of the present invention, it suggests that detoxification of the unburned exhaust gas will be achieved by burning it again in the engine.

[0009]

However, the method disclosed in Japanese Patent Application Laid-Open No. 1-267309 described above targets methanol fuel with an air-fuel ratio of 15-.
Although the theoretical air-fuel ratio of methanol is usually 6.5, the above 15 to 19 are very large values, and combustion failure and insufficient output are likely to occur.

Further, the method disclosed in Japanese Utility Model Laid-Open No. 142570/1989, although its purpose is to accelerate the starting of the engine as described above and to feed the exhaust gas back to the engine, the method is not suitable for cold starting. Since the exhaust is throttled only and the recirculation passage is opened only during the fuel injection period, removal of unburned alcohol and aldehyde is not sufficiently achieved.

The present invention has been made in order to eliminate the above-mentioned conventional inconveniences, and it is effective to discharge unburned alcohol and aldehyde to the outside of the system at the time of engine start when an alcohol-containing fuel is used. It is an object of the present invention to provide an exhaust gas recirculation device for an alcohol engine that can be effectively suppressed.

[0012]

According to a first aspect of the present invention, there is provided an exhaust gas recirculation system for an alcohol engine, wherein an alcohol-containing fuel having a catalyst layer for removing alcohol and aldehyde in exhaust gas is provided in an exhaust passage. In an alcohol engine using, the alcohol concentration detecting means for detecting the alcohol concentration in the alcohol-containing fuel, the exhaust gas recirculation means for recirculating exhaust gas to the intake passage, and the alcohol concentration in proportion to the increase in the alcohol concentration of the alcohol-containing fuel. A control device for controlling to increase the recirculation amount of the exhaust gas is provided.

An exhaust gas recirculation system for an alcohol engine according to a second aspect of the present invention is the exhaust gas recirculation system for an alcohol engine according to the first aspect, wherein the exhaust gas recirculation means regulates a recirculation exhaust gas flow rate. A gas control valve is provided, a thermometer for detecting the temperature of the catalyst is provided in the catalyst layer, and the control device opens the reflux gas control valve while the temperature of the catalyst layer is below the catalyst activation temperature. A reflux gas flow rate control means for adjusting the flow rate of the reflux gas according to the alcohol concentration is provided.

An exhaust gas recirculation apparatus for an alcohol engine according to a third aspect of the present invention is the exhaust gas recirculation apparatus for an alcohol engine according to the first or second aspect, wherein a plurality of catalyst layers are provided in series in the exhaust passage. , The exhaust passage between the catalyst layers is arranged at a lower position than the catalyst layer,
One end of the exhaust gas recirculation pipe is connected to the path located at the lower position.

[0015]

According to the exhaust gas recirculation system for an alcohol engine of the above-mentioned claim 1, alcohol concentration detecting means for detecting the alcohol concentration in the alcohol-containing fuel is provided in the intake passage to recirculate the exhaust gas into the intake passage. Exhaust gas recirculation means is provided, and a control device for controlling the exhaust gas recirculation amount to be increased in proportion to an increase in the alcohol concentration of the alcohol-containing fuel is provided. The harmful components consisting of unburned alcohol and aldehyde in the exhaust gas, which increase in proportion to the increase in the concentration, are fed back to the engine in accordance with the increase and are burned again to be rendered harmless.

According to the exhaust gas recirculation system for an alcohol engine of the second aspect, the exhaust gas recirculation pipe is provided with a recirculation gas control valve for controlling the flow rate of the recirculation exhaust gas,
The catalyst layer is provided with a thermometer that detects the temperature of the catalyst. The control device is provided with a reflux gas flow rate control means for opening the reflux gas control valve in a state where the temperature of the catalyst layer is equal to or lower than the catalyst activation temperature and controlling the flow rate of the reflux gas according to the alcohol concentration. Therefore, exhaust gas is actively recirculated to the engine in a low temperature range until the catalyst layer exhibits catalytic activity, and the harmful components in the exhaust gas are harmless in the engine only while the catalytic activity of the catalyst layer is insufficient. Be converted. Further, the reflux gas control valve is always opened at an appropriate opening while being controlled by the reflux gas flow rate control means in accordance with the alcohol concentration of the fuel, and wasteful reflux of the reflux gas is suppressed.

In the exhaust gas recirculation system for an alcohol engine according to claim 3, a plurality of catalyst layers are provided in series in the exhaust passage, and the exhaust passage between the catalyst layers is positioned lower than the catalyst layer. Since the one end of the exhaust gas recirculation pipe is connected to the path located at the lower position, the water generated by the combustion of the alcohol-containing fuel may be collected at the lower part of the path. You can do this by absorbing the aldehyde in the exhaust gas with this water,
The aldehyde can be removed even more effectively.

[0018]

FIG. 1 is an overall explanatory view showing an example in which an exhaust gas recirculation system for an alcohol engine of the present invention is applied. As shown in this figure, the fuel tank 1 stores an alcohol-containing fuel in which gasoline fuel and alcohol fuel are mixed. The alcohol concentration of the alcohol-containing fuel is various depending on the purpose of mixing the alcohol and varies from 5% to 95%, but in general, the alcohol-containing fuel often indicates about 85%.

The top end of the fuel tank 1 is connected to the oil supply pipe 11. Fuel tank 1 from outside the system via refueling pipe 11
The alcohol-containing fuel supplied to the fuel pump 12 is pumped up by the drive of the fuel pump 12, reaches the injector 24 via the fuel supply pipe 2, the filter 21, the alcohol concentration detecting means 22 and the pressure regulator 23. Is injected into the intake passage (intake manifold 31), is atomized, and is mixed with air and supplied to the engine 3. Injector 24
As for the filter 21, which employs a so-called air-mixture side feed injector,
The filter 2 is a filter for filtering and removing foreign matter in the alcohol-containing fuel supplied from the fuel tank 1.
The alcohol concentration is detected by the alcohol concentration detecting means 22 for the fuel that has passed through 1 and has been cleaned.
As the alcohol concentration detecting means 22, it is practical to detect the alcohol concentration based on the electric resistance value peculiar to gasoline and alcohol (alcohol has a smaller resistance value than gasoline). That is, a pair of electrodes are arranged to face each other, fuel is introduced between the electrodes, a predetermined voltage is applied, and the resistance value between the electrodes is measured to measure the alcohol value of the fuel passing through the fuel supply pipe 2. The concentration is detected. The pressure regulator 23 guides the pressure in the intake manifold 31 as a control pressure so that the difference between the fuel pressure and the intake manifold 31 pressure is always constant.

The tip of the injector 24 has a PCT heater 7 (positive temperature c) as a fuel heating means.
oefficient heater) is provided. The PTC heater 7 is a heater that uses a semiconductor temperature sensitive element whose electric resistance greatly changes with temperature changes, and the electric resistance increases in proportion to the increase in temperature. When fuel is injected from the injector 24 while the PCT heater 7 is energized, the PCT heater 7 generates heat and is heated before the fuel reaches the combustion chamber 3a.

The fuel sprayed in the intake manifold 31 together with the air for combustion is supplied into the combustion chamber 3a of the engine 3 through the intake valve 32, and a spark is emitted from the spark plug 34 to explode and the piston 3b. Down,
The generated exhaust gas is guided to the exhaust manifold 35 via the exhaust valve 33 as the return gas moves upward. The exhaust manifold 35 is provided with an O ₂ sensor 35a, and the detected oxygen amount in the exhaust gas is input to the control device 6 to detect the air-fuel ratio.

The temperature of the cooling water in the jacket 36 provided on the outer periphery of the engine 3 is detected by the thermometer 4, and the detected value is input to the controller 6.

In the exhaust passage (exhaust pipe 5) following the exhaust manifold 35, the first catalyst layer 5 for cleaning exhaust gas is provided.
The first and second catalyst layers 52 are provided in series. The exhaust pipe 5 that connects the first catalyst layer 51 and the second catalyst layer 52 is curved in an arcuate shape downward, and its bottom is positioned below the catalyst layers 51 and 52. The set elbow 5a is formed.

The bottom of the elbow 5a and the intake manifold 3
1 and 1 are connected to each other by an exhaust gas recirculation pipe 8. The exhaust gas recirculation pipe 8 is provided with a recirculation gas control valve 81. The recirculation gas control valve 81 is based on a command signal transmitted from the recirculation gas flow rate control means 61 provided in the control device 6. The opening / closing of the valve and the opening of the valve when the valve is opened are set. In the case of this embodiment, the exhaust gas recirculation means is composed of the exhaust gas recirculation pipe 8 and the recirculation gas control valve 81.

In the engine 3 using the alcohol-containing fuel as described above, the value of the alcohol concentration in the fuel detected by the alcohol concentration detecting means 22 is input to the control device 6, and the control device 6 receiving this value is input in advance. The spark plug 34
The optimum ignition timing for the injector 24
To indicate the optimum fuel injection amount, and in some cases, the amount of electricity, the duration of electricity, etc. to the PTC heater 7 are set based on the alcohol concentration value, and these are continuously executed.

FIG. 2 is a flowchart of the control according to the present invention and a graph associated with this flowchart,
(A) is a flow chart, (B) is a graph showing the relationship between the measured methanol concentration at the start of opening of the control valve and the measured jacket water temperature, and (C) is a graph showing the relationship between the methanol concentration and the methanol correction coefficient. Show.

The operation of the present invention performed under the control of the control device 6 will be described below with reference to FIG. In this example, methanol is used as the alcohol mixed in the alcohol-containing fuel.

First, as shown in step S1 of FIG.
The engine speed (N) as an initial value, engine load value (Tp), jacket water temperature actual measurement value (Ts), reflux gas control valve opening (V), and methanol concentration (MD) in fuel are input to the controller 6. To be done.

In the next step S2, the jacket water temperature (Tw) at the start of opening the control valve is calculated according to the methanol concentration (MD). This jacket water temperature (Tw)
Is calculated from the inverse proportional relation Tw = f (MD) between the methanol concentration (MD) and the jacket water temperature (Tw) when the control valve needs to be opened, as illustrated in (A) of the figure. You can This relational expression has been input to the control device 6 in advance. Therefore, in step S2, the jacket water temperature (Tw ₁ ) corresponding to the methanol concentration (MD ₁ ) currently input to the control device 6 is calculated.

Then, in step S3, the jacket water temperature (Tw ₁ ) is compared with the jacket water temperature measured value (Ts). If Tw ₁ ≤Ts, the following steps S4 to S9 are skipped to return. Is programmed to. The case of Tw ₁ ≦ Ts means that when the measured value of methanol concentration (MD ₁ ) and the measured value of jacket water temperature (Ts) are plotted on the graph, for example, it is inversely proportional to the point B in the graph of FIG. 2 (B). It is a state of being located above the curve. In such a case, the water temperature of the jacket 36 is sufficiently high, and it is considered that each of the catalyst layers 51 and 52 has a catalytic activity sufficient to remove unburned components corresponding to the methanol concentration at that time. The operation of circulating the gas is unnecessary and therefore step S4
~ Step S9 is not executed.

On the contrary, when Tw ₁ > Ts in step S3, the measured methanol concentration (MD ₁ ) and the jacket water temperature (Ts) are plotted in the graph of (B), for example. In this case, since the jacket water temperature measured value (Ts) has not reached Tw ₁ required at that time, that is, f (MD ₁ ), the catalyst layers 51, 52 still have sufficient activity. It is determined that the state is not in the state, and the steps after step S4 of circulating the exhaust gas are executed.

In this case, first, in step S4, the reference opening of the recirculation gas control valve 81 is calculated. The reference control valve opening (Vo) is obtained from a map according to the engine load value (Tp) (a value obtained by dividing the intake air amount by the rotation speed) input in step S1 and the engine rotation speed (N). It is a value, and is the valve opening degree when the alcohol concentration in the fuel corresponds to 0. In other words, the opening is appropriate for the original accumulation of exhaust gas recirculation when only gasoline fuel is used.

Then, in the next step S5,
A methanol correction factor (k) is calculated. This methanol correction coefficient (k) is a coefficient set so as to increase with the increase of the methanol concentration (MD) of the fuel with respect to the reference control valve opening (Vo), and is shown in (C) of FIG. As shown, when the methanol concentration (MD) is 0, k = 1,
The value of the methanol correction coefficient (k) gradually increases as the methanol concentration (MD) increases. The relationship is k = g (MD). This formula is previously input to the control device 6,
In this step S5, the value of k is calculated.

In the next step S6, the methanol correction coefficient (k) is multiplied by the value of the reference control valve opening (Vo) calculated in step S4 to calculate the control valve opening (V ₁ ) actually opened. To be done.

Then, in the next step S7, step S
The recirculation gas control valve opening (V) previously input in ₁ is compared with the control valve opening (V ₁ ) actually opened, and V <V ₁
At this time, step S8 is executed, and the operation control means 61 in the control device 6 sends a command signal in the control valve opening direction to the recirculation gas control valve 81. It operates in the direction of increasing power and returns.

On the contrary, when V> V ₁ , step S9 is executed, and the operation control means 61 in the control device 6 sends a command signal in the closing direction of the control valve to the recirculation gas control valve 81. The recirculation gas control valve 81 that has received the actuation operates in a direction in which the opening degree decreases, and returns.

When V = V ₁ , the desired set value matches the control valve opening (V ₁ ) calculated in step S6, and therefore the return is particularly non-action.

When the return of the final step is reached, each step is repeated from step S1 again, and the recirculation amount of the exhaust gas is adjusted according to the situation of whether the catalyst of each catalyst layer 51, 52 is activated. Therefore, unnecessary exhaust gas recirculation can be prevented, and the engine 3 can be driven in a state where the unburned alcohol and aldehyde are not always discharged outside the system.

By the way, as described above, when alcohol (particularly methanol) is burned, a larger amount of H ₂ than gasoline is burned.
Generate O. The generated H ₂ O condenses in the catalyst layers 51 and 52 which have not been heated yet in the initial stage of starting the engine 3 and become water droplets. In this case, between the first catalyst layer 51 and the second catalyst layer 52, the elbow 5a portion of the exhaust pipe 5 which is curved in a bow shape at a position lower than those is formed.
The condensed water accumulates in the elbow 5a.

Since the end of the exhaust gas recirculation pipe 8 is connected to the bottom of the elbow 5a, the exhaust gas recirculating from the exhaust gas recirculation pipe 8 comes into contact with the condensed water, so The highly soluble alcohol and aldehyde are absorbed and trapped in this water, and the alcohol and aldehyde in the exhaust gas are effectively removed. The condensed water that has absorbed the alcohol and the aldehyde is entrained in the reflux exhaust gas to be refluxed.

FIG. 3 is a flowchart showing another example of the control method. In this example, an operation of inputting the temperature (Tc) of the catalyst layer is added to step S1 of the flowchart of FIG. 2, and step S2 ′ as shown between step S1 and step S4 is referred to as step S2. The difference from FIG. 2 is that the step S3 is replaced instead of the step S3, and the other points are the same as those in FIG.

That is, in the case of the control system shown in FIG. 3, the temperature sensor 52a is provided in the second catalyst layer 52 (the temperature of each catalyst layer 51, 52 is represented by the temperature of the second catalyst layer 52). The temperature of the catalyst layers 51 and 52 detected by the temperature sensor 52a is input to the control device 6.

The controller 6 judges whether or not the input temperature is a temperature sufficient for the first catalyst layer 51 and the second catalyst layer 52 to exhibit catalytic activity (input as a preset value in advance). Is determined by comparing the temperature at which the present catalytic activity is exhibited with the temperature (Tc) of the catalyst layer that is currently input),
In a state where the temperature is so low that the catalytic activity cannot be exhibited, step S4 and subsequent steps in FIG. 2 are executed.

When it is determined that the temperature of each of the catalyst layers 51 and 52 can exert the catalytic activity, the steps S4 to S9 are skipped and the program is returned.

[0045]

As described above, according to the exhaust gas recirculation system for an alcohol engine of the present invention, the exhaust gas recirculation pipe for recirculating the exhaust gas to the intake passage is provided in the exhaust passage, and the alcohol of the alcohol-containing fuel is consumed. Since a control device is provided to control so as to increase the recirculation charge of the exhaust gas in proportion to the increase in the concentration, the unreacted gas in the exhaust gas which is controlled in proportion to the increase in the alcohol concentration while being controlled by the control device is provided. The harmful components composed of the burned alcohol and the aldehyde are fed back to the engine in accordance with the increase and supplied for combustion again, and the exhaust gas is rendered harmless always with the optimum exhaust gas recirculation amount.

If a portion of the exhaust pipe is arranged lower than the catalyst layer and one end of the exhaust gas recirculation pipe is connected to this lower portion, the alcohol-containing fuel burns. The water that is generated and condensed in the catalyst layer is accumulated in the lower portion, so that by absorbing the aldehyde in the exhaust gas with this water, the aldehyde can be removed even more effectively.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an exhaust gas recirculation device for an alcohol engine of the present invention.

FIG. 2 is a flow chart of control according to the present invention and a graph related to this flow chart, (A) shows a flow chart, and (B) shows a relationship between a measured methanol concentration at the start of opening of a control valve and a measured value of jacket water temperature. The graph showing (C) shows the graph showing the relationship between the methanol concentration and the methanol correction coefficient.

FIG. 3 is a flowchart showing another example of FIG.

[Explanation of symbols]

 1 Fuel Storage Device 11 Oil Supply Pipe 12 Fuel Pump 2 Fuel Supply Pipe 21 Filter 22 Alcohol Concentration Detection Means 23 Pressure Regulator 24 Injector 3 Engine 3a Combustion Chamber 3b Piston 31 Intake Manifold 32 Intake Valve 33 Exhaust Valve 34 Spark Plug 35 Exhaust Manifold 4 Thermometer 5 Exhaust pipe 5a Elbow 51 First catalyst layer 52 Second catalyst layer 52a Temperature sensor 6 Control device 61 Reflux gas flow rate control means 7 PTC heater 8 Exhaust gas reflux pipe 81 Reflux gas control valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Taeko Shimizu, 3-1, Shinchi Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Naoko Sakata, 3-1-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Corporation Within

Claims (3)

[Claims] 1. An alcohol engine using an alcohol-containing fuel, wherein an exhaust passage is provided with a catalyst layer for removing alcohol and aldehyde in exhaust gas,
Alcohol concentration detection means for detecting the alcohol concentration in the alcohol-containing fuel, exhaust gas recirculation means for recirculating exhaust gas to the intake passage, and recirculation amount of the exhaust gas in proportion to an increase in alcohol concentration of the alcohol-containing fuel. An exhaust gas recirculation device for an alcohol engine, which is provided with a control device for controlling to increase. 2. The exhaust gas recirculation means is provided with a recirculation gas control valve for controlling the flow rate of recirculation exhaust gas, the catalyst layer is provided with a thermometer for detecting the temperature of the catalyst, and the control device is provided with the control device. The reflux gas flow rate control means for opening the reflux gas control valve and controlling the flow rate of the reflux gas according to the alcohol concentration when the temperature of the catalyst layer is equal to or lower than the catalyst activation temperature is provided. The exhaust gas recirculation device for an alcohol engine according to 1. 3. A plurality of catalyst layers are provided in series in the exhaust passage, the exhaust passage between the catalyst layers is arranged at a position lower than the catalyst layer, and one end of the exhaust gas recirculation pipe is The exhaust gas recirculation device for an alcohol engine according to claim 1 or 2, wherein the exhaust gas recirculation device is connected to a path located at a lower position.