JPH0223813Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention] This invention relates to a fuel injection device for an internal combustion engine that uses liquefied petroleum gas (hereinafter abbreviated as LPG) as fuel, and in particular:
The present invention relates to an electronically controlled fuel injection device that can supply a predetermined amount of fuel and control the air-fuel ratio to a constant level even when the fuel pressure changes.

[Background of the idea]

Compared to gasoline fuel injection devices, LPG fuel injection devices equipped with fuel injection valves have fuel vapor pressure itself, which varies greatly depending on the fuel composition and liquid temperature (0 to 20 kg/ ^cm2 )
Therefore, it is necessary to either regulate the pressure in the fuel injection valve and keep it constant, or to sense the pressure in the fuel injection valve and correct and control the opening time of the fuel injection valve in response to pressure fluctuations. However, keeping the former pressure constant is
Either increase the pressure to a high pressure of 20Kg/cm ² or more, or use a refrigerator etc. to maintain a constant low pressure, and control the liquid temperature while sensing the pressure so that the pressure remains constant.
Bubbles are generated, liquid metering is difficult, and liquid jetting cannot be accurately controlled. When installing the above method in an actual automobile engine, when the pressure is constant, there are problems in terms of safety and cost, and even when the pressure is constant, it is impractical due to the cost, size, etc. of the entire system. Poor. A method of sensing pressure and controlling correction is described in Japanese Utility Model Application Laid-Open No. 59-43659. However, the above correction to the fuel pressure is merely a product of the square root of the theoretical standard pressure and the actual pressure. Furthermore, even when the above is corrected by multiplying it by a certain correction coefficient, experiments have confirmed that due to the characteristics of electromagnetic injection valves, accurate correction cannot be made due to the difference in injection time (valve opening time). However, there was a problem that correction based on fuel pressure was not performed accurately over the entire injection period.

[Purpose of invention]

The purpose of this proposal is to perform accurate pressure correction even if the fuel pressure of LPG fuel applied to the electromagnetic injection valve changes and there is a difference in the injection time of the injection valve due to changes in the amount of intake air. An object of the present invention is to provide an electronically controlled fuel injection device that makes the amount of fuel constant at various injection times under each pressure so that the air-fuel ratio is the same as that in the air-fuel ratio.

[Summary of the idea]

In order to measure the fuel pressure applied to the electromagnetic injection valve with a fuel pressure sensor and perform correction control based on its output, the reference pressure should theoretically be set to AKg/cm ² (in this example, 5Kg/cm as shown in Figure 2). ² ), and the fuel pressure is PKg/cm ²
In this case, for the same amount of air, the injection time _{t P at} pressure PKg/cm ² is
t _P = t _A ×√, but in reality, the valve closing force due to fuel pressure increases sequentially as the fuel pressure rises, and what happens is
The short valve opening time of mS has a large effect on the time until the valve fully opens, and when the valve opening time is the same, the increase in fuel injection amount due to pressure increase is √
smaller than A, and as shown in Figure 2,
This varies depending on the length of the valve opening time, and the shorter the valve opening time, the greater the influence.

This project grasps the above characteristics and controls the pressure correction coefficient, which is the reciprocal of the increase in fuel injection amount due to pressure, according to the injection time as shown in Figure 3, so that it can be used as a standard even in different air amount ranges under a certain pressure. This is to correct the air-fuel ratio under the same amount of air under pressure.

[Example of idea]

An embodiment of the present invention will be described with reference to figures. FIG. 4 is a system diagram of an embodiment using this method.
LPG fuel passes through the fuel cut solenoid 8 from the fuel cylinder 7, is pressurized by the cylinder pressure by the fuel pump 9, and is sent to the fuel reservoir 10 as completely liquid fuel without air bubbles, and is applied to the electromagnetic injection valve 6. The fuel pressure and liquid temperature are detected by a fuel pressure sensor 2 and a temperature sensor 13 such as a thermistor, and are sent to an electromagnetic injection valve 6, injected into an intake pipe 1, and supplied to an engine 17. Not injected into suction pipe 1
The LPG fuel passes through a return passage 14, passes through a regulator 11 that controls the pressure difference with the cylinder pressure to be constant, passes through a fuel cut solenoid 12, and returns to the gas phase side of the LPG cylinder 7.

LPG fuel is a mixture of propane and butane,
It is generally well known that fuel itself has its own fuel vapor pressure, and that the fuel vapor pressure changes greatly depending on temperature and mixture ratio. At a pressure lower than the vapor pressure, it will vaporize, so it is very difficult to control the pressure at a constant level with liquid LPG.
In this method, the fuel pump 9 pressurizes to suppress the generation of bubbles, and the fuel pressure is transferred to the fuel pressure sensor 2.
The controller 18 performs correction control.

Figure 5 shows the general flow of injection time calculation.
FIG. 1 shows a chart of the correction calculation, and FIG. 1 shows a chart of the fuel pressure correction control method of the present invention.

When the key is turned on and power is turned on to the controller 18, initialization processing is performed, the solenoids 8 and 12 are turned on, and LPG fuel is supplied to the fuel passage. Next, it is determined whether or not a cranking signal is input, and if a cranking signal is input, the fuel pump 9 is driven and cranking injection is performed.
Then, when the injection timing signal (TOP) is input while determining the engine stall, the intake pipe pressure sensor 16
A/D converter 3 converts the analog signal from
After conversion, CPU 4 calculates the suction pipe pressure, and
The rotation speed is calculated from the ignition signal from the ignition coil, the steady injection time under standard pressure is calculated from the suction pipe pressure and the rotation speed, and the injection time is calculated by multiplying by various correction coefficients.

The injection time T is T = T _B × (1 + C _TW + C _ST ) × C _CA ×
C _LPG ×C _FPo +C _BAT (T _B : Standard injection time, calculated using suction pipe pressure and rotation speed, C _TW : Water temperature correction coefficient,
C _CA : Intake temperature correction coefficient, C _LPG : LPG correction coefficient, determines fuel composition based on liquid temperature and fuel pressure, corrects liquid specific gravity and theoretical air-fuel ratio, C _FPo : Pressure correction coefficient, C _BAT :
Calculated from the battery correction coefficient ( _CST : startup correction coefficient), which has the least time impact among the various correction coefficients.
The five items C _CA , C _TW , C _LPG , C _FPo , and C _BAT are processed in a time-sharing manner, and the correction values are sequentially updated as shown in FIG. 6, and the latest values at the time of injection time calculation are adopted.

FIG. 1 shows a detailed chart of the pressure correction coefficient therein, and a method of calculating the pressure correction coefficient will be explained.
As shown in the table in Figure 7, the pressure correction coefficient C _FPo has eight types of maps divided by the size of the standard injection time (T _B ), for example up to C _FPI C _FP8 where n = 8. When the magnitude of the fuel pressure taken in from the fuel pressure sensor 2 is determined, different values are updated according to the magnitude of the pressure according to eight reference injection times, and when calculating the injection time, the magnitude of the reference injection time is updated. , one is selected and adopted as a correction coefficient and multiplied.

The pressure correction coefficient is determined by interpolating the fuel pressure taken in every certain time, and when the pressure value is determined, the values of the pressure correction coefficients C _FP1 to _{C FP8} corresponding to the pressure value are updated.

When the injection timing signal is input, the suction pipe pressure and rotation speed are calculated, and the standard injection time is calculated,
The magnitude of the reference injection time is determined, pressure correction coefficients are selected (C _FP1 to C _FP8 ), and the selected correction coefficients are used. The correction coefficient is rewritten at regular intervals, and the extra time required to calculate the injection time is only the time to determine how many mS the reference injection time (T _B ) is, which increases the calculation time. There is no need to worry about delays.

[Effect of idea]

According to this proposal, even if the absolute pressure of LPG fuel applied to the electromagnetic injection valve changes, the same amount of air will be maintained under the same air amount under the reference pressure at the opening time of various injection valves with different intake air amounts. It gives the injection time to maintain the same fuel ratio, responds to changes in fuel vapor pressure due to changes in LPG liquid temperature and composition, and can maintain the same air-fuel ratio for the same amount of air and load under any conditions.

[Brief explanation of the drawing]

Figure 1 is a detailed chart of the pressure correction coefficient, Figure 2
The figure is a pressure-flow rate ratio characteristic diagram of an electromagnetic injection valve.
The figure is a graph of the pressure correction coefficient, Fig. 4 is a system diagram of this system, Fig. 5 is a general flow diagram of injection time calculation, Fig. 6 is a flow chart of correction calculation, and Fig. 7 is an example of the pressure correction coefficient. FIG. 1...Suction pipe, 2...Fuel pressure sensor, 3...
... A/D converter, 4 ... CPU, 5 ... Injector drive circuit, 6 ... Electromagnetic injection valve, 7 ... Fuel cylinder, 8, 12 ... Solenoid, 9 ... Fuel pump, 10 ... Fuel Tame, 11...regulator,
13...Fuel temperature sensor, 14...Return passage, 15...Rotational speed sensor, 16...Suction pipe pressure sensor, 17...Engine, 18...Controller.

Claims (1)

[Scope of utility model registration request] An electronically controlled fuel injection device that controls the amount of fuel supplied to a liquefied petroleum gas internal combustion engine based on the injection time of an electromagnetic injection valve includes a sensor that detects the operating state of the internal combustion engine and a reference injection time that determines the reference injection time based on the operating state. a reference injection time determining means; a fuel pressure sensor for detecting fuel pressure applied to the electromagnetic injection valve; and a pressure correction coefficient determining means for retrieving a pressure correction coefficient from a storage means in accordance with the fuel pressure and the reference injection time. . An electronically controlled fuel injection device, comprising injection time determining means for determining an injection time from the reference injection time and the pressure correction coefficient.