JPH089972B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device that cuts off fuel supply when an internal combustion engine has a high load.

2. Description of the Related Art In an internal combustion engine, in particular, an internal combustion engine equipped with a turbine type supercharger, control is performed to cut off the fuel supply when the operating state becomes abnormally high (Japanese Patent Laid-Open No. 57-200338). ). This is done to protect the engine by preventing the exhaust system from overheating and damaging the turbine section and the piston section due to excessive supercharging caused by a failure of the wastegate valve.

Problems to be Solved by the Invention However, in the conventional fuel cutoff control, the fuel cutoff is performed when the load of the engine becomes higher than a predetermined constant value. There was the inconvenience of cutting off the necessary fuel.

Generally, at low temperatures, the air density is high and the performance of the intercooler is improved in engines with an intercooler.Therefore, even if the wastegate valve is operating normally, it is determined that the load is high and fuel cutoff occurs. As a result, the driving characteristics are deteriorated. Since there is little occurrence of pre-ignition or knocking at low temperature, it is not necessary to cut off the fuel under the same high load condition as at high temperature.

Even when the engine temperature is high and the load is high, when the outside air temperature is low, the parts may be cooled by the outside air, and engine protection due to fuel cut may not be necessary. It is necessary to avoid cutting.

Means for Solving Problems The configuration of the present invention for solving the above problems will be described with reference to FIG. 1. According to the present invention, the means b for detecting the load state of the engine a and the intake air temperature of the engine a are described. Means c for detecting
A means d for increasing the threshold value of the engine load for fuel cutoff when the detected intake air temperature is low and a case where the detected engine load is higher than the threshold value. Is equipped with means e for cutting off the fuel supply to the engine a.

Action The threshold value of the engine load for shutting off the fuel supply is determined according to the intake air temperature, which is a function of the outside air temperature and the engine temperature. When the intake air temperature is high, the load can be set to a lower load side.As a result, the engine protection when both the outside air temperature and the engine temperature are high is performed as before, while the outside air temperature is low and the outside air temperature is high even when the engine temperature is high. It is possible to prevent unnecessary fuel cutoff when both the temperature and the engine temperature are low, and prevent the deterioration of operating characteristics.

Examples Examples of the present invention will be described in detail below.

FIG. 2 schematically shows an internal combustion engine with a turbine type supercharger as an embodiment of the present invention. In the figure, 10 is an air flow sensor which is provided in the intake passage 12a and generates a voltage according to the intake air flow rate Q, and 14 is an intake temperature sensor which is also provided in the intake passage 12a and generates a voltage according to the intake air temperature THA. Is. A compressor 16 is provided in the intake passage 12a downstream of the air flow sensor 10 and the intake air temperature sensor 14. The compressor 16 works in conjunction with the turbine 20 provided in the exhaust passage 18 to supercharge the combustion chamber 22 with the airflow flowing into the intake passage 12b.

An intercooler 17 is provided in the intake passage 12b downstream of the compressor 16 in this embodiment.
17 is connected to a water pump 19 and a radiator 21. A throttle valve 24 that interlocks with an accelerator pedal (not shown) is further provided in the intake passage 12b, and a fuel injection valve 26 is provided in the intake manifold portion downstream thereof.

A branch passage 28 that bypasses the turbine 20 is provided in the exhaust passage 18, and a waste gate valve 30 is provided in this branch passage.
Is provided. The opening of the waste gate valve 30 is controlled according to the supercharging pressure generated in the intake passage 12b, a part of the exhaust gas flow is bypassed through the branch passage 28, and the pressure of the exhaust gas flow flowing into the turbine 20 is substantially constant. To maintain.

A cylinder block 32 of the engine is provided with a water temperature sensor 34 that generates a voltage according to the cooling water temperature THW.

Air flow sensor 10, intake air temperature sensor 14 and water temperature sensor
The detected voltage from 34 is sent to the control circuit 38.

The distributor 40 is provided with a cylinder discrimination sensor 42 and a rotation angle sensor 44. The cylinder discrimination sensor 42 outputs a pulse signal every predetermined angular position before the top dead center of the reference cylinder, for example, every 360 ° crank angle, and the rotation angle sensor 46 outputs a pulse signal every 30 ° crank angle. It These pulse signals are sent to the control circuit 38.

On the other hand, a drive pulse is applied from the control circuit 38 to the fuel injection valve 26, whereby the fuel injection valve 26 transfers the pressurized fuel sent from the fuel supply system (not shown) into the intake passage near the combustion chamber 22. Fires intermittently.

FIG. 3 shows a circuit configuration of the control circuit 38 shown in FIG. As is clear from the figure, the control circuit 38 has a microcomputer, which has a central processing unit (CPU) 52 and a random access memory (R).
AM) 54, read only memory (ROM) 56, first and second
Input / output ports 58 and 60, output port 62, clock generation circuit 66, and a bus for interconnecting these to transfer data
It is mainly composed of 68 and.

Air flow sensor 10, intake air temperature sensor 14 and water temperature sensor
The detection voltage from 34 is sequentially selected by the multiplexer 70, and the analog / digital (A / D) converter 72 outputs the detected voltage.
After being converted into a binary signal, it is applied to the microcomputer through the first input / output port 58.

The pulse signals from the cylinder discrimination sensor 42 and the rotation angle sensor 44 are waveform-shaped by the shaping circuit 74 and then applied to the microcomputer via the second input / output port 60.

When an injection pulse signal is output from the microcomputer to the drive circuit 76 via the output port 62, this is converted into a drive pulse, the fuel injection valve 26 is energized, and fuel injection is performed.

Next, the operation of the microcomputer will be described with reference to the flowchart of FIG.

FIG. 4 is a routine for calculating the fuel injection pulse width τ, which is executed during the main routine or the interrupt processing routine at predetermined time intervals.

First, in step 100, Q / N, THW, and THA are fetched from the RAM 54. Intake air flow rate Q, cooling water temperature THW and intake air temperature THA
The input data representing is stored in a predetermined position of the RAM 54 every time the conversion of the A / D converter 72 is completed. Also at this time,
The intake air amount Q / N per unit rotation corresponding to the load of the engine is calculated from the rotation speed N and the intake air flow rate Q and stored in the RAM 54. The rotation speed N is obtained by a known method of measuring the time interval in which the pulse signal from the rotation angle sensor 44, that is, the pulse signal at every 30 ° of crank angle is applied.

In the next step 101, the fuel injection pulse width τ is obtained by a known method from operating state parameters such as Q / N, THW, THA.

Next, at step 102, it is judged if Q / N is larger than 1.0 / rev. If Q / N> 1.0 / rev, it is determined that the engine is in a high load state, and the process proceeds to the next step 103 to perform fuel amount increase control. That is, the injection pulse width τ obtained in step 101
Is increased by 1.15 to increase the fuel amount. The exhaust gas temperature can be lowered by increasing the fuel amount when the load is high.

If Q / N ≦ 1.0 / rev, skip all the following steps and end this processing routine.

After increasing the fuel injection pulse width τ in step 103, the program proceeds to step 104 and sets the threshold value (Q / N) FC that determines whether or not fuel cutoff is performed to the intake air temperature THA.
Ask from. In the ROM 56, a function table of the threshold (Q / N) FC with respect to the intake air temperature THA as shown in FIG. 5 is stored in advance. In step 104, (Q / N) FC corresponding to THA is obtained from this function table by using an interpolation method or the like. The relationship of THA- (Q / N) FC is (Q / N) when THA is low.
N) FC increases and THA increases (Q / N) FC decreases.

In the next step 105, the threshold value (Q / N) FC obtained in step 104 is compared with the current Q / N to determine whether Q / N> (Q / N) FC. Only when Q / N> (Q / N) FC, the routine proceeds to step 106, the injection pulse width τ is set to “0”, and this processing routine is ended. Therefore, in this case, the fuel supply is cut off. When Q / N ≦ (Q / N) FC, fuel injection is performed with the injection pulse width τ obtained in step 103.

In the embodiment described above, Q / N is used as the operating condition parameter representing the load condition, but other operating condition parameters representing the load condition such as the intake pipe pressure may be used.

EFFECTS OF THE INVENTION According to the present invention, the threshold value of the engine load for interrupting the fuel supply is determined according to the intake air temperature which is a function of the outside air temperature and the engine temperature. By setting the intake air temperature to a value on the higher load side than when the temperature is high, it is possible to prevent unnecessary fuel cutoff when the temperature of the outside air is low even when the engine is at a high temperature, and when both the outside air temperature and the engine temperature are low. It is possible to prevent the deterioration of the driving characteristics.

[Brief description of drawings]

1 is a block diagram of the present invention, FIG. 2 is a schematic diagram of an embodiment of the present invention, FIG. 3 is a block diagram of the control circuit of FIG. 2, and FIG.
FIG. 5 is a flow chart showing a part of the program of the microcomputer of the control circuit of FIG. 3, and FIG. 5 is THA- (Q /
N) FC characteristic diagram. 10 …… Air flow sensor, 14 …… Intake air temperature sensor, 26 …… Fuel injection valve, 34 …… Water temperature sensor, 38 …… Control circuit, 42 …… Rotation angle sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Harada 1 Toyota-cho, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-58-28553 (JP, A) JP-A-56-126644 (JP, A) JP 58-126435 (JP, A) JP 57-49035 (JP, A)

Claims (1)

[Claims] 1. A means for detecting a load state of an engine, a means for detecting an intake air temperature of the engine, and a threshold value of an engine load for fuel cutoff being higher than when the detected intake air temperature is low and high. A fuel injection control device for an internal combustion engine, comprising: means for determining as described above; and means for cutting off fuel supply to the engine when the detected engine load becomes higher than the threshold value.