JPH0584383B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an air-fuel ratio control for an internal combustion engine that can control the amount of fuel supplied to the internal combustion engine and constantly operate the internal combustion engine under optimal conditions. Regarding the method.

[Prior Art] Conventionally, the amount of fuel supplied to an internal combustion engine mounted on a vehicle or the like has been controlled in order to operate the engine under optimal conditions. The same is true when starting the internal combustion engine, and the injection time of the fuel injection device is appropriately set in order to supply an amount of fuel according to the starting characteristics of the internal combustion engine.

However, with the method of determining the amount of fuel to be supplied to the internal combustion engine in proportion to the injection time of the fuel injection device, the fuel in the fuel pipe of the fuel injection device is at a high temperature due to reasons such as high-load long-term operation of the internal combustion engine. In such a case, when vapor is generated, fuel is not supplied for the amount of vapor even during the same injection time, resulting in an air-fuel mixture that is considerably thinner than the desired air-fuel ratio. This phenomenon is particularly problematic when starting the internal combustion engine, and there is a possibility that sufficient fuel will not be supplied to start the internal combustion engine, making starting the engine impossible.

Therefore, as disclosed in JP-A-56-81230 or JP-A-57-10741, when starting an internal combustion engine when the fuel is at a high temperature, the amount of fuel injection is increased for a predetermined period of time. A device has been proposed that increases the amount of fuel injection depending on the device and fuel temperature.

[Problems to be Solved by the Invention] However, even the above-mentioned apparatus has the following problems, and is still not satisfactory.

In other words, the vapor generated in the fuel piping varies depending on the various internal combustion engine systems and their usage conditions, from those generated very close to the fuel injection valve to those generated near the fuel tank side, so the vapor is injected. The amount of time that will be spent is not uniquely determined. Therefore, by simply increasing the fuel injection amount based only on the passage of time from startup, it is not possible to determine whether the vapor has completely disappeared from the fuel pipe, and it is not possible to determine whether the vapor is still in the fuel pipe. If you stop increasing the amount of fuel injected even though the amount remains, vapor lock may occur, and conversely, if you continue increasing the amount for too long, the fuel injection will become abnormally rich, resulting in deterioration of fuel efficiency and emissions. There was a problem of inviting such things.

Furthermore, even though the fuel injection amount is increased according to the fuel temperature, the relationship between the fuel temperature and the amount of vapor generated is not unambiguous, and as above, it depends on the internal combustion engine system and its usage conditions. This method has the same problem as described above because it is not possible to determine at what point the generated vapor is injected into the combustion chamber of the internal combustion engine.

As mentioned above, a state in which the amount of fuel supplied to the internal combustion engine is small and the air-fuel ratio is greater than a predetermined value is hereinafter simply referred to as lean, and conversely, a state in which the air-fuel ratio is smaller than the predetermined value is referred to as rich.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems, and the present invention corrects the fuel injection amount according to the vapor generated in the fuel piping. It is an object of the present invention to provide an air-fuel ratio control method for an internal combustion engine that improves starting characteristics by appropriately correcting the injection amount and improves fuel efficiency and emissions.

[Means for Solving the Problems] The configuration of the present invention to achieve the above object is as shown in the basic configuration diagram of FIG. In an air-fuel ratio control method for an internal combustion engine using a control injection device, at the time of starting the internal combustion engine (P1), it is determined whether the fuel temperature is above a predetermined temperature (P2), and it is determined that the fuel temperature is above the predetermined temperature. When this occurs, the fuel injection amount of the internal combustion engine is increased (P3), and after a predetermined time has elapsed from the start of the internal combustion engine (P4), when the air-fuel ratio of the internal combustion engine is below a predetermined value (P5), the amount is increased. The gist of this invention is an air-fuel ratio control method for an internal combustion engine, which is characterized by gradually decreasing the control increase value (P6).

[Operation] The fuel temperature determination at the time of startup of the present invention is to determine whether or not vapor is generated in the fuel pipe. Therefore, the present invention is not limited to the method of directly detecting the fuel temperature at startup and comparing it with a predetermined value, but may also be a method of detecting the temperature of the cooling water of the internal combustion engine, the temperature of the intake air, etc., and estimating the fuel temperature. .

Note that the fact that the internal combustion engine is starting is determined by detecting a state in which the ignition key is turned on, a state in which the rotational speed of the internal combustion engine is low, or the like.

The increase control of the fuel injection amount, which is executed when the fuel temperature at the time of starting the internal combustion engine is determined to be above a predetermined value using the above method, is to increase the fuel injection amount so that the amount of vapor increases To prevent an internal combustion engine from being unable to start due to a lean fuel ratio. The amount of increase is calculated using a map stored in the storage means or from a relational expression that includes variables representing the operating state of the internal combustion engine, such as the rotational speed. The method of increasing the amount may be either by lengthening the time during which fuel injection is performed or by increasing the injection pressure of fuel injection.

The predetermined period of time from the start of the engine is the period of time until the vapor generated in the fuel pipe is pumped and injected into the internal combustion engine. Therefore, the time may be set as a time specific to the internal combustion engine system, or the time may be set based on the rotational speed of the internal combustion engine or the number of injection executions.

Based on the air-fuel ratio of the internal combustion engine after the above-mentioned predetermined time has elapsed, that is, depending on whether the air-fuel ratio is larger or smaller than the predetermined value, the increase value of the above-mentioned increase control is decreased, or the decrease is By discontinuing the operation, the air-fuel ratio of the internal combustion engine can be appropriately controlled.

EXAMPLES Hereinafter, in order to explain the present invention more specifically, the present invention will be described in detail with reference to Examples.

[Example] First, FIG. 2 is an explanatory diagram showing a gasoline engine and its peripheral equipment to which the method of the present invention is applied.

1 is the gasoline engine body, 2 is the piston, 3
4 is a spark plug, 4 is an exhaust manifold, 5 is an oxygen sensor provided in the exhaust manifold 4 and detects the residual oxygen concentration in the exhaust gas, 6 is a fuel injection valve that injects fuel into the intake air of the gasoline engine body 1, 7 8 is an intake manifold, 8 is an intake air temperature sensor that detects the temperature of the intake air sent to the gasoline engine body 1, 9 is a water temperature sensor that detects the temperature of gasoline engine cooling water, and 10 is for adjusting the intake air amount of the gasoline engine 1. Throttle valve, 1
Reference numeral 1 represents a throttle sensor that detects the opening degree of the throttle valve 10, 14 an air flow meter that measures the amount of intake air, and 15 a surge tank that absorbs pulsation of the intake air.

16 is an igniter that outputs the high voltage necessary for ignition; 17 is a distributor that is linked to a crankshaft (not shown) and distributes the high voltage generated by the igniter 16 to the spark plugs 3 of each cylinder; 18 is a distributor A rotation angle sensor 19 is installed in the distributor 17 and outputs 24 pulse signals per one revolution of the distributor 17, that is, two revolutions of the crankshaft. 20 is an electronic control circuit, 21 is a key switch, and 22 is a starter motor. 26 represents a vehicle speed sensor that is linked to the axle and transmits a pulse signal according to the vehicle speed.

Next, FIG. 3 shows a block diagram of the electronic control circuit 20 and its related parts.

30 is a central processing unit (hereinafter simply referred to as CPU) that inputs and calculates the data output from each sensor according to a control program and also performs processing for controlling the operation of various devices; 31 is a central processing unit for controlling the control program and initialization; 32 is a read-only memory (hereinafter simply referred to as ROM) in which data is stored, and a random access memory (hereinafter simply referred to as ROM) in which data input to the electronic control circuit 20 and data required for arithmetic control are temporarily read and written.
33 is a backup random access memory (hereinafter referred to simply as backup RAM) which is a non-volatile memory backed up by a battery so as to retain the data necessary for subsequent operation of the internal combustion engine even when the key switch 21 is turned off. 34 to 37 are buffers for the output signals of each sensor, 38 is a multiplexer that selectively outputs the output signals of each sensor to the CPU 30, 39 is an A/D converter that converts analog signals to digital signals, 4
0 is an input/output port that sends each sensor signal to the CPU 30 via a buffer or via the buffer, multiplexer 38 and A/D converter 39, and outputs control signals for the multiplexer 38 and A/D converter 39 from the CPU 30. It represents.

Reference numeral 41 represents a buffer that sends the output signal of the oxygen sensor 5 to the comparator 42, and 43 represents a shaping circuit that shapes the waveforms of the output signals of the rotation angle sensor 18 and the cylinder discrimination sensor 19. The output of the throttle opening sensor 11 and the operation signal of the key switch 21 are sent to the CPU 30 through an input/output port 46 either directly or via a buffer 41 or the like.

Furthermore, 47 and 48 are the fuel injection valves 6 and 48 in response to signals from the CPU 30 via output ports 49 and 50, respectively.
Each of the drive circuits that drive the igniter 16 is shown. Also, 51 is a bus line that serves as a path for signals and data, and 52 is a bus line for the CPU 30 and ROM 3.
1, represents a clock circuit that sends a clock signal serving as a control timing to the RAM 32, etc. at predetermined intervals.

Next, the control program of this embodiment will be explained.

4 and 5 are flowcharts of this embodiment.

First, the processing of the starting air-fuel ratio control routine shown in FIG. 4 will be explained step by step.

This routine is interrupted by the CPU 30 when the key switch 21 is turned on when the gasoline engine 1 is started.

When the processing of this routine starts, the step
100 is executed and it is determined whether the throttle valve 10 is fully closed based on the output of the throttle opening sensor 11, and if it is fully closed, the next step is executed.
110 is executed, otherwise this routine ends.

In step 110, the temperature of the cooling water of the gasoline engine 1 is detected and determined as one method for estimating the temperature of the fuel supplied to the gasoline engine 1. If the output of the water temperature sensor 9 is higher than 85° C. in this step, the process proceeds to the next step 120, and if it is lower than that, the routine ends.

In step 120, the temperature of the intake air of the gasoline engine 1, which is another piece of information for estimating the fuel temperature, is detected and determined. At this time, if the output of the intake air temperature sensor 8 is higher than 65°C, the process advances to the next step 130, and if it is lower than that, the routine ends.

Therefore, the operating status of gasoline engine 1 when step 130 is executed is that the ignition key has just been turned on, the accelerator has not been operated yet, water temperature TW > 85 degrees Celsius, and intake temperature TA > 65 degrees Celsius.
℃ state, that is, at the time of high temperature restart. This step is only executed under these special conditions, and the elapsed time from start to start is 4.
A determination is made as to whether it is greater than or equal to [s]. This elapsed time is the period from when the key switch 21 is turned on to when the oscillation clock of the clock circuit 52 is turned on by the CPU 3.
By counting at 0, it is possible to easily know the elapsed time after starting. 4 in this step
If it is determined that it is less than [s], the process advances to step 140.
If it is 4 [s] or more, the process moves to step 150.

In step 140, Fhot, which is one of the correction coefficients for correcting the basic fuel injection amount (fuel injection time) Tp, which will be described later, is set to "0.5" for determining the amount of fuel to be injected and supplied to the gasoline engine 1. This process allows the fuel injection time to be extended, as will be described later, and allows control to increase the desired fuel injection amount.

As described above, the fuel increase control continues to be executed immediately after starting, but after 4 [s] have elapsed from the start of starting, steps 150 and subsequent steps are executed.

In step 150, the output of the oxygen sensor 5 is detected, and it is determined whether the residual oxygen concentration in the exhaust gas is higher (lean) or lower (rich) than a predetermined value.
That is, the air-fuel ratio is determined. That is, the air-fuel ratio at which fuel is actually combusted in the gasoline engine 1 is estimated from the exhaust gas by the increase control of the fuel injection amount executed in step 140. In this step, if it is determined that the amount of fuel supplied to the gasoline engine 1 is small, that is, it is lean because a large amount of vapor still exists in the fuel pipe, this routine is terminated without executing the subsequent processing. Fhot continues to maintain the value of "0.5". On the other hand, when it is determined that the amount of vapor in the fuel pipe has decreased and the amount of fuel injected and supplied to the gasoline engine 1 has increased due to the large value of Fhot = 0.5 and has become a value smaller than the predetermined air-fuel ratio, the following Step 160 is processed.

In step 160, it is determined whether or not Fhot is still greater than "0" and control to increase the fuel injection amount continues to be executed. Then, if Fhot>0, the process proceeds to step 170; otherwise, this routine ends.

In step 170, it is determined whether or not the time measured by timer D is 1 [s] or more.

Here, timer D is a timer that starts timing when the key switch 21 is turned on, and also starts timing from the time when the key switch 21 is turned on.
It is configured to be reset at step 190 and start counting again. Therefore, when this step 170 is executed for the first time after starting the gasoline engine 1, the content of timer D becomes 4 [s] or more as a result of the processing in step 130, so the judgment becomes true and the process proceeds to the next step 180. be.

As described above, at least 4 [s] have elapsed after the movement of the gasoline engine 1, and the oxygen sensor 5
is outputting a rich signal, and if Fhot is greater than "0", step 180 is executed to decrease Fhot by "0.01".

In the next step 190, the aforementioned timer D is reset, and this routine ends.

As mentioned above, after the timer D is reset, this routine is executed again and steps 150 and 150 are executed.
Even if the condition is to reduce the fuel amount by setting Fhot to a small value in step 160, the next step will not be executed.
At step 170, if the timer D has not counted 1 [s] since the previous process of decreasing Fhot by "0.01", this routine is ended, and if it has counted 1 [s], then in step 180 again, Fhot is decreased by "0.01". Then, in step 190, the timer D is reset, and the same process is continued until Fhot=0.

Fuel injection, which is performed in synchronization with the rotation speed of the gasoline engine 1 and determines the actually executed fuel injection amount (fuel injection time) T shown in FIG. 5, using the correction coefficient Fhot determined as described above. time T
A decision routine is processed.

When the CPU 30 enters the processing of this routine, first step 200 is executed, and the rotation speed NE and intake air amount Q of the gasoline engine 1 are calculated based on the outputs of the rotation angle sensor 18 and the air flow meter 14, and the next step 210 is executed. Subjected to processing.

In step 210, the load Q/NE is calculated from these two basic operation information of the gasoline engine 1, and then the basic fuel injection amount (basic fuel injection time) Tp, which is the optimal fuel supply amount for the load, is calculated.
is searched from the map in ROM31.

In the following step 220, a correction coefficient K for the basic fuel injection amount Tp is calculated based on information from various sensors provided in the gasoline engine system. For example, the correction coefficient K is calculated by integrating various correction values such as the correction coefficient learned from the previous operating state of the gasoline engine 1, the warm-up state of the gasoline engine, and the air-fuel ratio feedback correction coefficient based on the output of the oxygen sensor 5. will be done.

Then, in the next step 230, the amount of fuel injection (fuel injection time) T to be actually executed is determined using the correction coefficient K obtained as described above and Fhot obtained using the flowchart of FIG. 4A using the following formula. It is calculated using

T=Tp×(K+Fhot) At the next step 240, the fuel injection amount T calculated at the previous step 230 is stored in the RAM 32, and the processing of this routine is ended.

In this way, another fuel injection execution routine reads out the fuel injection amount T stored in the RAM 32 as appropriate, and injects fuel into the gasoline engine 1 from the fuel injection valve 6 according to the fuel injection amount T. Therefore, the gasoline engine 1 can be operated at a desired air-fuel ratio.

As described above, according to this embodiment, which controls the air-fuel ratio of the gasoline engine 1, how the air-fuel ratio of the gasoline engine 1, the output of the oxygen sensor 5, and the correction coefficient Fhot of the fuel injection amount (fuel injection time) change over time. The time chart in FIG. 6 shows the change.

In the figure, the leftmost side shows a state in which the key switch 21 of the gasoline engine 1 is turned on, and the horizontal axis shows changes in three state variables over time.

First, in this embodiment, the fuel injection time is increased by 50% unconditionally for 4 seconds after starting the engine. During this time, the air-fuel ratio drops rapidly,
The output of the oxygen sensor 5 is rich. This is because the location in the fuel pipe in which the vapor is generated determines how many seconds after startup this change occurs. That is, in a normal gasoline engine system, vapor does not occur very close to the fuel injection valve, but often occurs closer to the gasoline tank. Also,
At the time of starting, the injection amount is originally large because there is an increase in starting amount, etc. For this reason, for a few seconds immediately after startup,
Alternatively, the fuel supplied to the gasoline engine 1 during several tens of revolutions has no vapor content, and an extremely large amount of fuel is injected, resulting in a momentary rich state.

In this embodiment, this period of 4 [s] is the oxygen sensor 5
Execute increase control without detecting the output. Thereafter, when vapor is generated, the fuel injected to the gasoline engine 1 decreases, the air-fuel ratio increases, and the output of the oxygen sensor 5 indicates lean. This state is period A in the figure. As described above, in this embodiment, the correction coefficient Fhot is not decreased while the output of the oxygen sensor 5 is lean. Therefore,
The fuel injection time T is increased by 50% to compensate for the decrease in the amount of fuel supplied due to vapor in the fuel pipe, and the air-fuel ratio of the gasoline engine 1 approaches a predetermined value as the vapor decreases during that time.

Then, when the air-fuel ratio falls below a predetermined value, the output of the oxygen sensor 5 is reversed to the rich side, and this change in output starts the reduction control of the correction coefficient Fhot. The amount of fuel supplied to the gasoline engine 1 is gradually reduced so as not to cause a sudden change in the output torque of the gasoline engine 1, and the air-fuel ratio of the gasoline engine 1 begins to gradually increase again and approaches a predetermined value. The startup is now complete.

As is clear from the detailed description above, the air-fuel ratio control method of the present embodiment is such that when it is determined that the fuel in the gasoline engine 1 is at a predetermined temperature or higher, the The fuel injection time is extended to unconditionally increase the amount of fuel injection by 50% (step 140). Then, the increased amount is reduced as appropriate according to the output of the oxygen sensor 5 after 4 [s] have elapsed from the start of the gasoline engine 1, that is, the air-fuel ratio of the gasoline engine (step 180).
It is.

Therefore, when the combustion temperature is high and vapor is generated, the fuel injection amount is reliably increased regardless of the location where the vapor is generated, so fuel suitable for the starting characteristics of the gasoline engine 1 is supplied and the gasoline engine 1 is started. At the same time, when the vapor decreases and the fuel supply to the gasoline engine 1 increases, and the air-fuel ratio falls below a predetermined value, the fuel injection time is reduced.

Because of this excellent method of supplying fuel, the starting characteristics of the gasoline engine 1 are good regardless of where vapor is generated in the fuel piping, and fuel efficiency is improved by preventing excessive fuel supply. This has the effect of preventing deterioration of the emission.

[Effects of the Invention] As described above with reference to embodiments, the air-fuel ratio control method for an internal combustion engine according to the present invention controls the fuel injection amount of the internal combustion engine when the fuel temperature at the time of starting the internal combustion engine is equal to or higher than a predetermined value. This method is characterized in that the amount is increased unconditionally immediately after starting the engine, and after a predetermined period of time, the amount increased by the amount increased control is decreased in accordance with the air-fuel ratio of the internal combustion engine.

Therefore, it improves the starting characteristics of the internal combustion engine regardless of where vapor is generated in the fuel piping, and prevents excessive fuel supply when the internal combustion engine starts to start and the air-fuel ratio falls below a predetermined value. In order to do so, the amount of fuel supplied is reduced.

This provides an excellent air-fuel ratio control method that allows various internal combustion engine systems to start smoothly regardless of where vapor is generated, and prevents deterioration of fuel efficiency and emissions due to excessive fuel supply. It is.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is a schematic configuration diagram of a gasoline engine system to which this embodiment is applied, and FIG. 3 is a block diagram of its control circuit.
FIG. 4 is a flowchart of air-fuel ratio control at startup, FIG. 5 is a flowchart of fuel injection time determination, and FIG. 6 is a time chart of air-fuel ratio, oxygen sensor output, and correction coefficient Fhot. 1...Gasoline engine, 6...Fuel injection valve,
8...Intake temperature sensor, 9...Water temperature sensor, 14...
... Air flow meter, 18 ... Rotation angle sensor, 20
...Electronic control circuit.

Claims (1)

[Claims] 1. In an air-fuel ratio control method for an internal combustion engine using an electronically controlled injection device that operates the internal combustion engine by injecting fuel from a fuel injection valve, the fuel temperature is equal to or higher than a predetermined temperature at the time of starting the internal combustion engine. and when it is determined that the temperature is higher than a predetermined temperature, the fuel injection amount of the internal combustion engine is increased and the air-fuel ratio of the internal combustion engine is increased after a predetermined period of time has elapsed since the start of the internal combustion engine. An air-fuel ratio control method for an internal combustion engine, characterized in that the increase value of the increase control is gradually decreased when the increase value is equal to or less than a predetermined value.