JPH0665858B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control method for an internal combustion engine, and more particularly to an air-fuel ratio control method for increasing the amount of fuel when restarting at a high temperature.

2. Description of the Related Art In a normal internal combustion engine, when the engine is started, the valve opening time of the fuel injection valve is lengthened to increase the fuel supply amount, thereby ensuring good engine startability. Further, as the engine temperature becomes lower, a larger amount of fuel is required to start the engine. Therefore, the fuel supply amount is made to increase as the engine temperature becomes lower. However, when the temperature of the fuel near the fuel injection valve is high, as in the case where the engine is restarted immediately after it is stopped, vapor (fuel vapor) is generated in the fuel and the time is determined by the engine temperature. Even if the fuel injection valve is opened to increase the fuel amount, the fuel supply amount becomes smaller than the required amount, and as a result, the air-fuel ratio of the fuel supplied to the engine cylinder becomes thinner than the required air-fuel ratio. This causes a problem that it becomes difficult to restart the engine.

Therefore, at the time of high temperature restart, the fuel pressure applied to the fuel injection valve is increased for a certain period of time, and the fuel injection time is increased to make the air-fuel ratio closer to the required air-fuel ratio. Controls are being made to improve.
However, in the conventional control to increase the fuel injection time at high temperature restart, a certain amount of fuel was increased when the intake air temperature was above a certain set value, so a detailed control according to the occurrence of vapor in the fuel pipe etc. Was difficult to achieve.

Therefore, in order to improve the accuracy of detecting the fuel temperature of the fuel injection valve, a method is provided in which a temperature sensor is provided on the wall surface of the fuel injection valve to detect the temperature of the fuel injection valve and correct the fuel injection amount at the time of high temperature restart. It is proposed by JP-A-58-135332.

Problems to be Solved by the Invention However, providing the temperature sensor on the wall surface of the fuel injection valve in this manner is not always mass-producible because there are many difficult aspects in actual processing, and the number of fuel injection valves is not necessarily required. Only the temperature sensor is required, and it is difficult to measure the temperature of this portion with high accuracy.

The present invention has been made in view of the above circumstances, and an object of the present invention is to control the amount of fuel increase when the engine is restarted according to the change in intake air temperature based on the atmospheric temperature and the elapsed time after the engine is stopped. An air-fuel ratio control method for an internal combustion engine is provided.

Means and Actions for Solving Problems The present invention is based on the finding that the required fuel increase amount depends on the engine stop time (dead soak time) and the outside temperature when restarting at high temperature. FIG. 5 shows the relationship between the fuel temperature (injector temperature) at the engine start and the required increase value. When the fuel temperature exceeds a certain value (for example, 60 ° C. or more), it is necessary to increase the amount of fuel when starting the engine due to the generation of vapor.

Further, as shown in FIG. 2, the injector temperature (fuel temperature) changes under the influence of the atmospheric temperature and the elapsed time after the engine is stopped. At this time, it was found that the intake air temperature of the engine was affected by the atmospheric temperature as shown in FIG. 3 and peaked almost at the same time as the fuel temperature shown in FIG. Further, it was found that the higher the intake air temperature during engine operation, the smaller the increase in intake air temperature after the engine was stopped, as shown in FIG. However, as shown in FIG. 4, the water temperature is not affected by the atmospheric temperature during engine operation, and the elapsed time at which the engine reaches a peak after the engine is stopped is significantly different from the peaks of the fuel temperature and the intake air temperature.

Therefore, in the present invention, the startup high temperature increase coefficient FHOT is obtained based on the temperature difference DLTHA between the intake temperature THAE during engine operation and the intake temperature THAE during engine operation and the intake temperature THA during engine restart,
The feature is that the amount of fuel is increased when the engine is restarted to obtain an appropriate air-fuel ratio.

That is, the present invention calculates the basic fuel injection time based on the engine load, corrects the basic fuel injection time according to the engine operating state, and controls the fuel injection time of the fuel injection valve. In the air-fuel ratio control method for an internal combustion engine, which detects in the vicinity of the engine, the intake air temperature during engine operation is detected, and the detected intake air temperature is stored by a storage means that can be stored even after the engine is stopped. The temperature difference between the stored intake air temperature during engine operation and the intake air temperature during engine restart is calculated, and the restart high temperature increase coefficient is calculated based on this temperature difference and the intake air temperature during engine operation stored by the storage means. Seeking
There is provided an air-fuel ratio control method for an internal combustion engine, which is characterized in that the basic fuel injection time is increased according to the increase coefficient to increase the fuel amount.

According to the present invention, the higher the intake air temperature during engine operation or the higher the intake air temperature during engine start, the less the difference DLTHA between the intake air temperature during engine start and the intake air temperature during engine operation, the more The high temperature increase coefficient FHOT is set to a large value to make it easy to increase fuel.

EXAMPLES The present invention will be described below in detail based on examples shown in the drawings.

FIG. 6 shows an example of a schematic configuration of an internal combustion engine to which the air-fuel ratio control method of the present invention is applied.

In the figure, 1 is an internal combustion engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is a spark plug, 7 is an intake valve, 8 is an exhaust valve, and 9 is an exhaust manifold 10. An oxygen sensor for detecting the oxygen concentration in the exhaust gas, 15 a water temperature sensor for measuring the cooling water temperature, 16 an ignition switch, and 21 a battery power source.

In the intake system, the intake amount of intake air taken in from the air cleaner 24 is measured by the air flow meter 25, the intake temperature is measured by the intake temperature sensor 26, and the intake is performed by the throttle valve 28 that opens and closes according to the stroke of the accelerator pedal 27. A predetermined amount of air is sent to the intake manifold 30. The throttle body 31 is provided with a throttle sensor 32 for detecting the opening degree and the fully closed position of the throttle valve 28 interposed therein. Further, in the vicinity of the intake valve 7 of the intake manifold 30, a fuel injection valve 38 for injecting and supplying a predetermined amount of fuel pumped by a fuel pump 37 from a fuel tank 35 via a passage 36 is attached.

In the ignition system, the high voltage generated by the igniter 40 is supplied to the distributor 41,
While performing the known ignition timing control, the high voltage is distributed and supplied to the ignition plug 6 of each cylinder at a predetermined timing. The distributor 41 is provided with a rotation speed sensor 43 that detects a rotation angle and a rotation speed from a rotation position of a distributor shaft 42 that rotates in synchronization with a crankshaft (not shown). Thus, the pulse signal is output 24 times every two revolutions of the crankshaft, and the pulse signal is output once at a predetermined angle every one revolution of the crankshaft.

The control device 50 is a microcomputer operated by a battery power source 21, and in the microcomputer, as shown in FIG. 7, a central processing unit (CPU) 51 is provided.
A read only memory (ROM) 52, a random access memory (RAM) 53, and a backup random access memory (RAM) 54 that retains memory even when the ignition switch 16 is off. Of these, the ROM 52 stores programs such as a main routine, a fuel injection amount control routine, an ignition timing control routine, and various fixed data and constants necessary for these processes. Further, in the microcomputer, A having a multiplexer is provided.
/ D converter 55 and I / O device 56 having a buffer memory
, And 55 and 56 are connected to each other by 51-54 and a common bus 57.

In the A / D converter 55, the output signals of the respective sensors such as the air flow meter 25 and the intake air temperature sensor 26 are input to a multiplexer via a buffer, these data are A / D converted, and predetermined by a command from the CPU 51. It outputs to CPU51 and RAM53 or 54 at the time. As a result, the RAM 53 or 54 fetches the latest detection data such as the intake air amount, the intake air temperature, and the water temperature, and stores these data in a predetermined area. In the I / O device 56, the throttle sensor 3
2, input the detection signal of each sensor such as the rotation speed sensor 43,
These data are sent to the CPU51 at a specified time according to the instruction from the CPU51.
Also, the data is output to the RAM 53 or 54.

The CPU 51 calculates the fuel injection amount based on the data detected by each sensor according to the program stored in the ROM 52, and outputs a pulse signal based on the calculated fuel injection amount to the fuel injection valve 38 via the I / O device 56. That is, basically, the intake air amount detected by the air flow meter 25 and the rotation speed sensor 43
The basic fuel amount (basic fuel injection time) is calculated from the engine speed detected by the engine, and this is corrected according to the detected intake air temperature, cooling water temperature, etc., and the pulse signal corresponding to this corrected fuel amount
A drive circuit (not shown) in the O device 56 sends the fuel to the fuel injection valve 38.

An embodiment of the air-fuel ratio control method for an internal combustion engine of the present invention will be described below with reference to the flowcharts of FIGS. 8 to 10.

The processing routines of FIGS. 8 to 10 are performed as part of the main routine.

First, in the processing routine of FIG. 8, it is determined whether the current engine state is the starting state. That is, in step 101, it is determined whether or not the flag XSTA, which is set when the ignition switch is turned on, is set. Step
If the flag XSTA is set in 101,
In step 102, it is determined whether the engine speed is, for example, 500 rpm or more. If it is 500 rpm or more, it is determined that the engine is out of the starting state, and the flag XSTA is reset in step 103. Next, the routine proceeds to step 104, where the intake air temperature THA when the engine is not in the starting state is stored in the backup RAM 54 as THAE.
Memorize as.

On the other hand, if the engine speed N is less than 500 rpm in step 102, it is determined that the engine is in the starting state and the routine proceeds to step 106 where the flag XSTA is set. If the flag XSTA is reset in step 101, the routine proceeds to step 105, where it is determined whether the engine speed N is less than 200 rpm, for example.
When the engine speed N is less than 200 rpm, it is determined that the engine has entered the starting state, the routine proceeds to step 106, where the flag XSTA is set, and when the engine speed N is 200 rpm or more, the step is performed.
Proceed to 103 to reset the flag XSTA.

As described above, in the processing routine of FIG. 8, it is determined whether or not the current engine state is the starting state. If it is determined that the engine is not in the starting state and the engine is operating, the current intake air temperature THA is determined in step 104. It is updated and stored as THAE in the backed up RAM 54 each time.

Next, with reference to the flowchart of FIG. 9, a processing routine will be described in which the starting high temperature increase coefficient FHOT is obtained from the THAE thus obtained, and the FHOT is attenuated after the engine is started every constant rotation. First, in step 201, it is determined whether or not the current engine state is a starting state, that is, whether or not the flag XSTA is set, and if the flag is set, a routine for obtaining the high temperature increase coefficient at startup FHOT is executed. . First, in step 202, the previous intake air temperature when the engine stored in the backup RAM 54 is not in the starting state
Find the difference DLTHA between THAE and the current intake air temperature THA at engine start. Next, proceeding to step 203, based on the above-mentioned THAE and DLTHA, based on the two-dimensional map of the startup high temperature increase coefficient FHOT made up of THAE and DLTHA as shown in FIG. High temperature increase coefficient at startup required this time
Calculate FHOT, and proceed to step 204, and increase the high temperature increase coefficient at startup F
After the HOT is stored in the RAM 53, the routine proceeds to step 205, where the counter CREV which is counted up each time the engine makes one revolution is cleared.

On the other hand, if it is determined in step 201 that the current engine state is not the starting state, for example, a process of attenuating the startup high-temperature increase coefficient FHOT until it becomes zero is executed every predetermined number of revolutions. First, in step 206, the counter CREV
Has exceeded a preset number of revolutions A (for example, 50 revolutions). In the case of negative determination, it is determined that it is not the decay timing, and the processing of this routine ends. If the counter CREV is equal to or greater than A in step 206, it is determined that the damping timing is reached, and the routine proceeds to step 207, where the high temperature increase coefficient at startup FHOT is decremented. Then step 20
At 8, it is determined whether or not the startup high temperature fuel increase coefficient FHOT is negative, and if negative, the routine proceeds to step 209, where the startup high temperature fuel increase coefficient FHOT is cleared. If the startup high temperature increase coefficient FHOT is positive in step 208 and after the startup high temperature increase coefficient FHOT is cleared in step 209, step 210
Go to to clear the cow CREV and prepare for the next decay timing. That is, the damping processing of the startup high temperature increase coefficient FHOT in steps 206 to 210 is performed at every constant engine speed A after the engine is started, and the startup high temperature increase coefficient FHOT is gradually attenuated until it becomes zero. Although not shown, the counter CREV is incremented in the processing routine that is started every one revolution of the engine.

Next, referring to the flowchart of FIG. 10, the fuel injection time TA is calculated according to the high temperature increase coefficient FHOT at the start obtained in this way.
A processing routine for obtaining U will be described. First, in step 301, the intake air amount Q is determined from the signal output from the air flow meter 25, and in step 302 the engine speed N is determined from the signal output from the speed sensor 43,
In step 303, the basic fuel injection time TP is calculated based on the Q and N thus obtained. Then step
At 304, the fuel injection time TAU is obtained by obtaining a correction coefficient based on the engine cooling water temperature, the intake air temperature, etc. and correcting the basic fuel injection time TP. Next, at step 305, the high temperature increase coefficient at start FH obtained by the processing routine of FIG. 9 is calculated.
Final fuel injection time TAU by correcting TAU by OT
Ask for.

In the embodiment described above, the two-dimensional map of the startup high temperature increase coefficient FHOT stored in advance in the ROM 52 is the startup high temperature increase coefficient FHOT in the above described embodiment,
It is obtained from the two-dimensional map of the intake air temperature THAE pre-stored in the ROM 52 and the temperature difference DLTHA between the intake air temperature THA during engine operation and the intake air temperature THAE during engine operation, but is not limited to this. Not a thing.

As described in detail above, the present invention is configured to control the fuel amount increase at the time of high temperature restart according to the intake air temperature and the outside air temperature that change according to the engine stop time (dead soak time). The required amount of fuel can be increased according to the engine condition, the wall temperature of the fuel injection valve is detected, and the air-fuel ratio is controlled based on this detected temperature. Accurate control of the air-fuel ratio at the time of high temperature restart can be achieved without the above-mentioned difficulties and cost increase due to mounting of the temperature sensor.

[Brief description of drawings]

Fig. 1 is a two-dimensional map of the high temperature increase coefficient FHOT at startup based on the intake air temperature THAE during engine operation and the intake air temperature at engine startup and the intake air temperature difference DLTHA during engine operation. Fig. 2 shows the fuel temperature (injector Temperature) is affected by the atmospheric temperature and the elapsed time after the engine is stopped. Figure 3 shows how the intake air temperature after the engine is stopped is affected by the atmospheric temperature and the elapsed time after the engine is stopped. 4 is a graph showing the state of the cooling water temperature after the engine is stopped, FIG. 5 is a graph showing the change in the required fuel increase value when the fuel temperature (injector temperature) changes, and FIG. 6 Is a schematic configuration diagram of an internal combustion engine suitable for applying the air-fuel ratio control method of the present invention, FIG. 7 is a block diagram showing an example in which a control circuit is configured by a microcomputer, and FIGS. 8 to 10 are present inventions. Air-fuel ratio control method It is a flow chart which shows an example of Chin. 1 ... Internal combustion engine body, 2 ... Cylinder block, 3 ... Cylinder head, 6 ... Spark plug, 9 ... Oxygen sensor, 15 ... Water temperature sensor, 16 ... Ignition switch, 21 ... Battery power supply, 25 ...... Air flow meter, 26 ...... Intake temperature sensor, 28 ...... Throttle valve, 32 ...... Throttle switch, 38 ...... Fuel injection valve, 50 ...... Control device, 51 ...... Central processing unit (CPU), 52 ...... Read-only memory (ROM), 53 ... Random access memory (RAM), 54 ... Backup RAM, 55 ... A / D converter, 56 ... I / O device.

Claims (1)

[Claims] Claim: What is claimed is: 1. A basic fuel injection time is calculated based on the engine load, and the basic fuel injection time is corrected according to the engine operating condition to control the fuel injection time of the fuel injection valve. In an air-fuel ratio control method for an internal combustion engine that is detected in the vicinity, the intake air temperature during engine operation is detected, and the detected intake air temperature is stored in a storage means that can be stored even after the engine is stopped. A temperature difference between the stored intake air temperature during engine operation and the intake air temperature during engine restart is calculated, and the high temperature increase during restart is calculated based on this temperature difference and the intake air temperature during engine operation stored by the storage means. An air-fuel ratio control method for an internal combustion engine, characterized in that a coefficient is obtained, and the basic fuel injection time is increased according to the increase coefficient to increase the fuel quantity.