JPH11294222A - Control device for gas fuel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce exhaust emission and improve a converging characteristic of air-fuel ratio at acceleration in a gas fuel engine using natural gas. SOLUTION: An ECU 33 controls the closing time of a fuel injection valve 19 (injection termination time) to be that within intake TDC±100 CA, and preferably in the vicinity of intake TDC. Thereby, gas fuel is injected at the time when intake flow in a combustion chamber is at a certain large degree to prevent at upper layer part in the combustion chamber from becoming overrich, and injected fuel is taken in the combustion chamber before the injected fuel is diffused over a wide area in an intake pipe 20. In this case, injection pressure is controlled to be not more than 5 kgf/cm<2> , and preferably within 3.5-4.5 kgf/cm<2> . When the injection pressure becomes too high, the ratio of injected fuel that collides on an intake valve 15 and flies up increases and the ratio thereof that is taken in the chamber decreases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a gaseous fuel engine using a gaseous fuel such as natural gas as a fuel.

[0002]

2. Description of the Related Art In recent years, for example, in an engine using natural gas as a fuel, as shown in JP-A-7-71296, a fuel injection valve for injecting gaseous fuel into an intake port of each cylinder is provided. It has been proposed to inject gaseous fuel at the end of the intake stroke each time to stratify the air-fuel mixture in the combustion chamber to form a rich air-fuel mixture near the ignition plug, thereby stabilizing ignition. Here, the reason that the mixture of natural gas can be stratified is that natural gas lighter than air naturally rises and stays in the upper part of the combustion chamber because the intake air flow in the combustion chamber is small in the latter part of the intake stroke. That's why.

[0003]

However, in the low rotation speed and low load range, the amount of intake air is small, and the flow of intake air in the combustion chamber becomes extremely small. There is a possibility that the upper layer becomes over-rich, causing misfire and an increase in unburned hydrocarbon (HC) emission.

Such a problem can be improved to some extent by increasing the injection pressure to promote the flow of the intake air in the combustion chamber. However, as the injection pressure is increased, the rate at which the injected fuel collides with the intake valve and flies is increased. And the proportion of injected fuel drawn into the combustion chamber decreases. As a result, at the time of acceleration / deceleration, a response delay of the fuel supply occurs, and a lean spike (a phenomenon in which the air-fuel ratio temporarily becomes lean) and a rich spike (a phenomenon, in which the air-fuel ratio becomes rich temporarily) occur, and this is the exhaust gas. It causes emission increase and drivability decrease.

The present invention has been made in view of such circumstances, and accordingly, has as its object to provide a control device for a gaseous fuel engine that can prevent misfires and reduce exhaust emissions and improve drivability. It is in.

[0006]

In order to achieve the above object, a control apparatus for a gaseous fuel engine according to a first aspect of the present invention is characterized in that an injection control means determines the injection end timing of a fuel injection valve of each cylinder. The control is performed within ± 100 ° C. of the top dead center of the piston during the intake stroke (hereinafter referred to as “intake TDC”). The injection end timing is after the intake TDC (ATD
C) If the temperature is lower than 100 ° C., the latter stage of the intake stroke occurs, and the flow of intake air in the combustion chamber is reduced. Therefore, light gaseous fuel is excessively collected in the upper layer of the combustion chamber, and the upper layer becomes over-rich, resulting in an increase in HC emission. Increases or a misfire occurs. If the injection end time is before the intake TDC,
As the period from the injection end timing to the intake TDC becomes longer, the range of the injected fuel that diffuses into the intake pipe before the intake valve is opened increases, so that the proportion of the injected fuel not taken into the combustion chamber increases, and the air-fuel ratio varies. And the convergence of the air-fuel ratio during acceleration / deceleration tends to decrease. In consideration of such characteristics, the injection end timing is set at the intake TDC ± 100 ° C.
If it is set within this range, gaseous fuel can be injected at a time when the intake air flow in the combustion chamber is large to some extent, so that the upper part of the combustion chamber can be prevented from becoming over-rich and the injected fuel can be spread over a wide range in the intake pipe. Before the fuel is diffused into the combustion chamber, the injected fuel can be sucked into the combustion chamber, thereby preventing misfire, reducing exhaust emissions and improving drivability.

[0007] In this case, the injection end timing of the fuel injection valve of each cylinder is set near the intake TDC of each cylinder.
That is, it is preferable that the control be performed near the opening timing of the intake valve. With this configuration, the injected fuel can be quickly taken into the combustion chamber before the injected fuel is diffused in the intake pipe, so that the diffusion of the injected fuel in the intake pipe can be minimized, and Fuel can be efficiently sucked into the combustion chamber, and fluctuations in the air-fuel ratio can be minimized.
The convergence time after air-fuel ratio fluctuation during acceleration / deceleration can be minimized.

It is preferable that the injection pressure of the fuel injection valve is adjusted to 5 kgf / cm ² or less by the injection pressure adjusting means, more preferably, 3.5 to 4 kg. It may be adjusted within the range of 0.5 kgf / cm ² . As is clear from the experimental results of the inventor described later (see FIG. 7), the fluctuation of the air-fuel ratio tends to increase as the injection pressure increases. It is considered that the reason for this is that as the injection pressure increases, the rate at which the injected fuel collides with the intake valve and flies increases, and the rate of the injected fuel drawn into the combustion chamber decreases. Generally, when the injection pressure is higher than 5 kgf / cm ² , the fluctuation of the air-fuel ratio becomes too large, and the lean spike and the rich spike due to the delay of the fuel supply response during acceleration / deceleration become too large.
Therefore, if the injection pressure is adjusted to 5 kgf / cm ² or less, the fluctuation of the air-fuel ratio can be suppressed moderately, and the effect of lean spikes and rich spikes due to a delay in fuel supply response during acceleration / deceleration can be reduced. In particular, when the injection pressure is 3.5 to
By adjusting the flow rate within the range of 4.5 kgf / cm ² , the difference between the flow rate of the injected fuel and the flow rate of the intake air is reduced, so that the injected fuel is more likely to flow into the combustion chamber and the fluctuation of the air-fuel ratio can be minimized. .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a gas engine using natural gas as a fuel (gas fuel engine) will be described below with reference to the drawings. Gas engine 11
Has basically the same structure as a gasoline engine, a piston 13 is housed in a cylinder 12, and an intake valve 15, an exhaust valve 16, a spark plug 1
7 is attached. A fuel injection valve 19 is attached near the intake port 18 of each cylinder.
The intake pipe 20 connected to is provided with a throttle valve (not shown). On the other hand, an exhaust pipe 22 connected to the exhaust port 21 is provided with an air-fuel ratio sensor 23 for detecting an air-fuel ratio of exhaust gas and a three-way catalyst 24 for purifying exhaust gas. Note that, instead of the air-fuel ratio sensor 23, an oxygen sensor that detects the oxygen concentration of the exhaust gas may be used.

Further, the crankshaft 34 of the gas engine 11
A crank angle sensor 26 is provided so as to face the signal rotor 25 fitted to the engine. The engine frequency is detected based on the frequency of the pulse signal output from the crank angle sensor 26, and the count value of the pulse signal is counted. The determination of the crank angle and the cylinder determination are performed based on the output pulse of the cam sensor (not shown).

Next, the configuration of the fuel supply system will be described. One or more fuel cylinders 27 are mounted on the vehicle, and each fuel cylinder 27 is filled with a gaseous fuel such as natural gas (CNG) at a high pressure. A fuel pressure regulator 31 (injection pressure adjusting means) is connected via a fuel cutoff valve 30 to one high pressure side fuel pipe 29 connected to a fuel outlet of each fuel cylinder 27 via a cylinder cutoff valve 28. The gaseous fuel regulated by the fuel pressure regulator 31 is supplied to the fuel injection valve 19 of each cylinder via the low pressure side fuel pipe 32.

In this case, the fuel pressure regulator 31 sets the pressure (injection pressure) of the gaseous fuel supplied to the fuel injection valve 19 to 5
kgf / cm ² or less, more preferably 3.5 to 4.5 k
It is set so as to be adjusted within the range of gf / cm ² (the reason will be described later). Also, the fuel injection valve 1
Numeral 9 is designed so that the required injection amount can be injected within a period corresponding to the maximum engine speed of 180 ° C. A (in the case of a four-cylinder engine) when the injection is performed at the above-described injection pressure, and It is designed such that the relationship between the valve opening time (injection time) of the fuel injection valve 19 and the injection amount is linear in the entire operation range from to the idle speed.

The outputs of various sensors such as the above-described crank angle sensor 26 and air-fuel ratio sensor 23 are taken into an engine control circuit (hereinafter referred to as "ECU") 33. The ECU 33 mainly includes a microcomputer, and a built-in ROM (not shown) stores various engine control programs such as an injection control program shown in FIG. Hereinafter, the injection control, which is a feature of the present embodiment, will be described with reference to the flowchart of FIG.

The injection control program shown in FIG.
, And is repeatedly executed at every predetermined crank angle, and functions as an injection control means referred to in the claims. When this program is started, first, in step 101, information on engine operating conditions output from various sensors such as the crank angle sensor 26 is read, and in the next step 102
Then, the basic injection time (basic injection amount) is calculated from a map or the like according to the engine operating conditions. After this, step 103
It is determined whether the air-fuel ratio feedback condition is satisfied. Here, the air-fuel ratio feedback conditions include, for example, that various fuel increase corrections are not performed, that fuel is not being cut, that high-load operation is not being performed, that the air-fuel ratio sensor 23 is activated, and the like. When all of these conditions are satisfied, the air-fuel ratio feedback condition is satisfied. If at least one of the conditions is not satisfied, the air-fuel ratio feedback condition is not satisfied.

If the air-fuel ratio feedback condition is not satisfied, the routine proceeds to step 104, where the air-fuel ratio correction coefficient FA
F is set to "1.0", and the routine proceeds to step 107. In this case, no feedback correction of the air-fuel ratio is performed.

On the other hand, if it is determined in step 103 that the air-fuel ratio feedback condition is satisfied, step 1
In step 108, the output of the air-fuel ratio sensor 23 is read, and in the next step 108, the air-fuel ratio correction coefficient FA based on the deviation between the target air-fuel ratio and the output (actual air-fuel ratio) of the air-fuel ratio sensor 23.
After calculating F, the process proceeds to step 107.

In step 107, various correction coefficients other than the air-fuel ratio correction coefficient FAF, for example, a correction coefficient depending on the engine temperature, a correction coefficient during acceleration / deceleration, and the like are calculated. Then, in the next step 108, the final injection time (final injection amount) is calculated by multiplying the basic injection time by the air-fuel ratio correction coefficient FAF and various correction coefficients. Final injection time = basic injection time x FAF x various correction coefficients

Thereafter, at step 109, the valve opening timing (injection start timing) of the fuel injection valve 19 of each cylinder is calculated. At this time, each cylinder according to the final injection time is set so that the valve closing timing (injection end timing) of the fuel injection valve 19 becomes a timing within a preset intake TDC ± 100 ° C., more preferably near the intake TDC. Of the fuel injection valve 19 is calculated. Thereafter, in step 110, it is determined whether or not the current crank angle has reached the valve opening timing calculated in step 109, and when the current crank angle has reached this valve opening timing, the process proceeds to step 111, The fuel injection valve 19 of the corresponding cylinder is opened to start gaseous fuel injection.

During injection, at step 112, it is determined whether or not the current crank angle has reached a preset valve closing timing (preferably near the intake TDC) within the range of intake TDC ± 100 ° C. When the crank angle reaches the valve closing timing, the routine proceeds to step 113, where the fuel injection valve 19 of the corresponding cylinder is closed to terminate the injection of gaseous fuel, and this program is terminated.

The present embodiment described above provides a fuel injection valve for a gas engine 11 using gaseous fuel, such as natural gas, which is lighter than air, from the viewpoint of reducing exhaust emissions and improving the convergence of the air-fuel ratio during acceleration and deceleration. The valve closing timing (injection end timing) is controlled so as to be within the intake TDC ± 100 ° C., more preferably in the vicinity of the intake TDC, and the injection pressure is set to 5 kgf / cm ² or less, more preferably 3 It is characterized in that it is adjusted within the range of 0.5 to 4.5 kgf / cm ² . Hereinafter, the reason for such setting will be described.

The present inventor measured the relationship between the injection end timing and the HC emission amount by experiment, and the measured result is shown in FIG.
Shown in From this measurement result, the injection end timing is determined by the intake TDC
Later (ATDC), it was found that when the temperature exceeded 100 ° C., the amount of HC emission increased rapidly and a misfire occurred. AT
The time exceeding DC 100 ° A is the latter half of the intake stroke,
Since the lowering speed of the piston 13 is slowed down, the flow of intake air in the combustion chamber is reduced. For this reason, light gaseous fuel gathers too much in the upper part of the combustion chamber due to the difference in specific gravity between air and gaseous fuel, and the upper part becomes over-rich, so that HC emission increases and misfire occurs. Conceivable.

Based on the measurement results shown in FIG.
It was confirmed that if the temperature was set before DC 100 ° C., the amount of HC emission was extremely reduced. If the temperature is before ATDC 100 ° C., the injection ends at a time when the intake air flow in the combustion chamber is large to some extent, so that the air-fuel mixture sucked into the combustion chamber is appropriately stirred by the intake air flow, and the upper layer of the combustion chamber is over-rich. Is prevented.

As shown in FIG. 4, a lean spike or a rich spike occurs due to a sudden change in the intake pipe pressure during acceleration / deceleration, and the air-fuel ratio temporarily deviates from the target air-fuel ratio. As the convergence time until the air-fuel ratio converges to the vicinity of the target air-fuel ratio after the occurrence of the lean / rich spike becomes longer, the state in which the air-fuel ratio deviates from the target air-fuel ratio continues for a longer time. descend. Therefore, it is preferable that the convergence time of the air-fuel ratio during acceleration / deceleration is short.

The inventor measured the relationship between the injection end timing and the convergence time of the air-fuel ratio at the time of acceleration / deceleration by experiments. The measurement results are shown in FIGS. 5 and 6. In both cases of acceleration and deceleration, when the injection end timing is near the intake TDC,
The convergence time of the air-fuel ratio becomes the shortest, and the convergence time tends to be longer as the injection end timing is farther from the intake TDC. When the injection end time is before the intake TDC, as the period from the injection end time to the intake TDC becomes longer, the range of the injected fuel that diffuses into the intake pipe 20 before the intake valve 15 is opened increases. The proportion of injected fuel that is not sucked increases, causing a delay in fuel supply response during acceleration and deceleration. As a result, fluctuations of the air-fuel ratio during acceleration / deceleration (lean spikes, rich spikes) increase, and the convergence time increases.

If the injection end timing is set to 100 ° C. or more before the intake TDC (BTDC) as in the present embodiment, the injected fuel burns before the injected fuel diffuses in a wide range in the intake pipe 20. The proportion of injected fuel that is drawn into the chamber and drawn into the combustion chamber increases, so that the response delay of fuel supply during acceleration / deceleration decreases, and the convergence time of the air-fuel ratio during acceleration / deceleration decreases accordingly. In particular, if the injection end timing is set near the intake TDC, that is, near the opening timing of the intake valve 15, the injected fuel is quickly drawn into the combustion chamber before the injected fuel is diffused in the intake pipe 20. , Intake pipe 20
The diffusion of the injected fuel in the air is minimized, the response delay of fuel supply during acceleration / deceleration is minimized, and the convergence time of the air-fuel ratio during acceleration / deceleration is minimized. Therefore, when the injection end timing is set near the intake TDC, the effect of reducing exhaust emission and the effect of improving drivability are maximized.

In this embodiment, the injection pressure is set at 5 kg.
f / cm ² or less, more preferably 3.5 to 4.5 kg
f / cm ² . As is clear from the inventor's experimental results shown in FIG. 7, as the injection pressure increases, the air-fuel ratio tends to fluctuate more. This is because, as the injection pressure is increased, the injected fuel collides with the intake valve 15 and soars, so that the ratio of the injected fuel remaining in the intake pipe 20 increases, and the ratio of the injected fuel sucked into the combustion chamber decreases. Conceivable. Generally, injection pressure is 5kg
If it is higher than f / cm ² , the fluctuation of the air-fuel ratio becomes too large, and the lean spike and the rich spike due to the delay of the fuel supply response during acceleration / deceleration become too large. Therefore, if the injection pressure is adjusted to 5 kgf / cm ² or less, the fluctuation of the air-fuel ratio can be suppressed moderately, and the effect of lean spikes and rich spikes due to a delay in fuel supply response during acceleration / deceleration can be reduced.

In particular, the injection pressure is set to 3.5 to 4.5 kgf /
When the flow rate is adjusted within the range of cm ² , the difference between the flow rate of the injected fuel and the flow rate of the intake air is reduced, so that the injected fuel is more likely to flow into the combustion chamber, and the fluctuation of the air-fuel ratio can be minimized. Further, as the injection pressure decreases, the valve sliding portion of the fuel injection valve 19 increases, and accordingly, the wear of the valve sliding portion increases and the durability of the fuel injection valve 19 decreases. Therefore, it is not preferable that the injection pressure is too low from the viewpoint of durability.
As in the present embodiment, the injection pressure is set to 3.5 kgf / cm ^2.
By doing so, the valve sliding portion of the fuel injection valve 19 becomes smaller, and accordingly, the wear of the valve sliding portion is reduced, and the durability of the fuel injection valve 19 is improved.

In the present embodiment, the injection end timing is controlled within ± 100 ° A of the intake TDC in the entire operation range. However, for example, the injection end timing is controlled in a specific operation range such as a low rotation speed and a low load range. Only, the injection end timing is ± 100 ° C of intake TDC
The control may be performed within the range.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a control system and a fuel supply system of a gas engine according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of processing of an injection control program;

FIG. 3 is a diagram showing data obtained by measuring a relationship between an injection end timing and an HC emission amount.

FIG. 4 is a time chart showing the behavior of the intake pipe pressure and the air-fuel ratio during acceleration / deceleration.

FIG. 5 is a diagram showing data obtained by measuring a relationship between an injection end timing and an air-fuel ratio convergence time during acceleration.

FIG. 6 is a diagram showing data obtained by measuring the relationship between the injection end timing and the convergence time of the air-fuel ratio during deceleration.

FIG. 7 is a diagram showing data obtained by measuring the relationship between the injection end timing, the injection pressure, and the air-fuel ratio fluctuation.

[Explanation of symbols]

11 gas engine (gas fuel engine), 13 piston, 15 intake valve, 16 exhaust valve, 18 intake port, 19 fuel injection valve, 20 intake pipe, 21 exhaust port, 22 exhaust pipe, 23 ... air-fuel ratio sensor, 24 ...
Three-way catalyst, 26 ... crank angle sensor, 27 ... fuel cylinder, 31 ... fuel pressure regulator (injection pressure adjusting means), 3
3. ECU (injection control means).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Kanehara 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Prefecture Inside the Japan Automotive Parts Research Institute (72) Inventor Motomasa Iizuka 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Prefecture Shares (72) Inventor Yoshihiko Kuroda 1-1-1, Showa-cho, Kariya-shi, Aichi Pref.

Claims (4)

[Claims] 1. A control apparatus for a gaseous fuel engine, comprising: a fuel injection valve for injecting gaseous fuel into an intake port of each cylinder; and an injection control means for controlling an injection amount and an injection timing of the fuel injection valve of each cylinder. In the above, the injection control means sets the injection end timing of the fuel injection valve of each cylinder to ± 100 ° C. of the top dead center of the piston in the intake stroke of each cylinder.
A control device for a gaseous fuel engine, wherein the control is performed within A. 2. The gas according to claim 1, wherein the injection control means controls the injection end timing of the fuel injection valve of each cylinder to be near a top dead center of a piston in an intake stroke of each cylinder. Control unit for fuel engine. 3. An injection pressure of the fuel injection valve is set to 5 kgf /
^3. The control device for a gaseous fuel engine according to claim 1, further comprising an injection pressure adjusting means for adjusting the pressure to not more than cm ² . 4. The gaseous fuel engine according to claim 3, wherein said injection pressure adjusting means adjusts an injection pressure of said fuel injection valve within a range of 3.5 to 4.5 kgf / cm ² . Control device.