KR100936303B1 - Method for controling amount of fuel on reduction of speed in LPI engine - Google Patents

Abstract

The present invention relates to a method of controlling the fuel amount during deceleration in an LPI engine to improve the rich air-fuel ratio problem during deceleration caused by a decrease in the temperature of the cutsol due to the latent heat of vaporization after starting. Setting a weight factor that is a function of; And increasing the fuel amount at the time of deceleration by multiplying a predetermined deceleration fuel amount by the weight factor.

LPI, Cut Solenoid, Coolant Temperature, Weight

Description

Method for controlling amount of fuel on reduction of speed in LPI engine

The present invention relates to a method of controlling fuel amount during deceleration in an LPI engine to improve the problem of rich air-fuel ratio during deceleration caused by a decrease in cutsol temperature due to latent heat of vaporization after starting.

The LPG engine vaporizes fuel supplied from the Bombe through a mixer and a carburetor to supply the engine. In the system using a mixer and a carburetor, it is difficult to start the winter season because it is difficult to control precisely by the ECU (Electronic Control Unit), low power performance and low fuel efficiency, and children due to the failure of the maintenance cycle due to the tar problem of LPG fuel. There are several problems, including instability and start-up.

The proposed engine to solve the problems of the existing LPG engine is LPI (Liquefied Petroleum Injection). Unlike conventional LPG engines that push fuel only by steam pressure of fuel, LPI engine installs fuel pump in LPG cylinder to pump liquid LPG fuel through fuel supply line and then injects through injector from engine. do. In other words, the LPI engine adopts a method of injecting LPG directly into the combustion chamber through an injector like a gasoline vehicle, thereby supplying LPG to the combustion chamber by precise control of the ECU through the injector without using a mixer and a carburetor, thereby improving fuel efficiency, power performance, It has been able to solve many of the problems of LPG vehicles in the past, such as improved startability in winter and maintenance cycle complaints. However, there are a number of problems that need to be improved in these LPI systems.

In the existing LPI system, an injector (Cut-off solenoid valve) is added to the bottom of the injector to improve the start-up delay caused by fuel leakage during soaking and the increase of HC emission. "Cutsol injectors" have been developed. However, the fuel injected in the low temperature region is not smoothly injected due to the resistance of the cutoff solenoid valve, which causes a problem that the air-fuel ratio is excessively lean / rich during acceleration and deceleration.

Conventional mass injectors use a bottom-feed gasoline injector as shown in FIG. 1, but the fuel pressure is 7 to 11 bar during driving and 2 to 6 bar during soaking (depending on ambient temperature and fuel composition). It keeps higher than (3.8bar during driving, 1bar or higher during soaking), so the wear of the injector needle and valve seat is fast, and the fuel keeps high pressure during soaking, making it vulnerable to fuel leakage. Do. In Fig. 1, reference numeral 11 denotes a "gasoline injector", reference numeral 12 denotes an "injector housing", reference numeral "13" denotes that fuel injected from the injector rapidly expands at the injector injection port, and is thus applied to the injector injection hole by latent heat. It is a "teflon tube" that does not cause icing.

2 shows a cutsol injector developed for an LPL system.

Referring to FIG. 2, the cutsol injector includes a solenoid 21, a spring 22, a plunger 23, a plunger hole 24, a plunger tip 25, a valve seat 26, and an icing tip hole. (27) and the like. The solenoid 21 serves to lift the plunger 23, and the spring 22 returns the plunger to its original position by its elastic restoring force when the solenoid 21 is not magnetized. The plunger tip 25 blocks the icing tip hole 27 to block fuel leakage during soaking. The valve seat 26 is made of a rubber material and is mounted at a position where the plunger tip 25 is seated to closely contact the plunger tip 25 to block leakage of fuel. The icing tip hole 27 provides a path through which the fuel passing through the plunger hole 24 is discharged to the intake pipe. In Fig. 2, reference numeral 28 denotes a "teflon tube". The cutsol injector as shown in FIG. 2 was developed in such a way that the cutsol valve for blocking leakage at the end of the injector was integrally connected to the end of the injector in consideration of development cost and unit cost compared to the number of production vehicles.

Meanwhile, the acceleration / deceleration fuel correction of the port injection system is a phenomenon caused by the injection of the injected fuel around the intake valve seat, that is, the correction of the transport delay in the wall wetting phenomenon. As shown in FIG. 3, the intake valve seat temperature (intake port ambient temperature) that affects fuel evaporation and atomization is important.

On the other hand, in the case of a cutsol injector, as shown in FIG. 4, a transport delay also occurs due to the flow resistance of the cutsol valve. In this case, the transport delay varies greatly depending on the gas phase or the liquid phase of the injected fuel, so the composition of the fuel (propane content) and the temperature inside the cutsol valve are the main factors. At low temperatures where the injected fuel maintains liquid phase, the fuel is wetted inside the cutsol valve and the transport delay increases dramatically. The higher the propane ratio, the higher the break point (butane: 0.5℃@1atm, propane: -41 ℃ @ 1atm), the smaller the transport delay, and the higher the temperature inside the cutsol valve, the less fuel wetting inside the cutsol valve. The transport delay of the fuel is also reduced.

The transport delay caused by wetting on the intake valve is generated over a relatively long time as shown in FIG. 5, whereas the delay caused by the cutsol valve is instantaneously generated as shown in FIG. 6, so that the application time of the acceleration / deceleration fuel is shorter than that of gasoline. The fuel must be calibrated.

The cutsol valve temperature characteristics are described in detail as follows. As the cutsol valve receives heat from the engine through a low intake manifold, the temperature rise is very slow compared to the valve seat temperature, and the cutsol valve temperature drops and rises at the initial stage by the latent heat of vaporization of the LPG fuel. Figure 7 shows the results of measuring the coolant temperature, the intake valve model temperature, and the cutsol valve temperature when driving the FTP-75 mode after starting the ambient temperature -25 ° C. It can be seen that it takes about 340 seconds for the cutsol valve temperature to rise above 0 ° C. .

Due to the cutsol valve structure, a throttling phenomenon occurs in the icing tip hole 27 because an empty space exists inside the cutsol valve. Therefore, during engine acceleration and deceleration, the intake pressure and the pressure inside the cutsol valve continuously reverse. Figure 8 is a result of measuring the pressure fluctuations during acceleration and deceleration, the acceleration intake pressure is 5 ~ 10kPa higher than the internal pressure of the cutsol valve to form a pressure difference in the direction of preventing fuel injection, the deceleration of the cutsol valve The internal pressure is up to 200 kPa above the intake pressure, so that the residual fuel inside the cutsol valve is sucked out by the high pressure differential. In particular, butane, which occupies 70% or more of LPG fuel, maintains a liquid state at 0 ° C. or lower, so when the fuel is decelerated after starting at 0 ° C., the liquid fuel is rapidly sucked out and the RPM drop and engine stall as shown in FIG. 9 due to the excessive rich air-fuel ratio. Stall Problems may occur.

On the other hand, the injected fuel is not all introduced into the cylinder, but a certain ratio (Impact factor (FLWLIMPF) = f (intake pressure, intake valve temperature)) is wetted to the intake port and the valve seat. The amount of fuel wetted to the port and the valve is called a puddle mass (GMFLONW), and the puddle mass has a constant ratio (Remainder fraction = FDECAY = f () due to evaporation and suction due to the flow rate as shown in FIG. Intake valve temperature)). In Fig. 10, FLWLIMPF = f (intake pressure, intake valve temperature) and FDECAY = g (intake valve temperature).

In Figure 10, solving the equilibrium equation (Puddle mass preservation) in the control volume CV1. Equation 1 below, and solving the equation (amount of fuel sucked into the cylinder) in the control volume CV2 is shown in Equation 2.

이 된다.In Equation 2,

Becomes

When the equations 1 and 2 are solved together, the final fuel injection amount FPCFIN to meet the target air-fuel ratio is the sum of the basic fuel injection amount and the acceleration / deceleration fuel amount. At this time, the basic fuel injection amount (FPCCOMP) is the amount of the intake air divided by the target air-fuel ratio, and does not consider the acceleration / deceleration fuel due to the wall wetting phenomenon, and the acceleration / deceleration fuel amount (TFGPCDLT) is determined by the wall wetting phenomenon. The amount of fuel to be added or subtracted.

If the driver accelerates, the acceleration / deceleration fuel (TFGPCDLT) is greater than zero, and this is called the acceleration fuel amount. If the driver decelerates, the acceleration / deceleration fuel (TFGPCDLT) is less than 0, which is called the deceleration fuel amount. As a result, the acceleration / deceleration fuel amount of the prior art has the same value at the same intake pressure and intake valve model temperature as a function of only the intake pressure and the intake valve temperature.

As can be seen in FIG. 11, the temperature of the cutsol valve is maintained at or below -30 ° C at the point where the intake valve seat model temperature (red solid line) reaches 20 ° C after starting the cooling water temperature at -20 ° C. Intake valve seat model temperature and cutsol valve temperature immediately after start-up are both 20 ° C. However, since the amount of acceleration / deceleration fuel of the prior art is calculated based on the model temperature of the intake valve seat, the same amount of acceleration / deceleration fuel is applied to the two cases where the temperature of the cut sole valve differs by 50 ° C or more. Therefore, the air-fuel ratio in both cases cannot be controlled by the amount of acceleration / deceleration fuel in the prior art. Acceleration can be improved through the "Lost Fuel Multiplier", but the problem that occurs during deceleration is a problem that only appears in the cutsol injector. Here, the Lost Fuel Multiplier is a weighting factor that is multiplied by the base acceleration / deceleration fuel amount to further increase the acceleration / deceleration fuel amount in order to improve the air-fuel ratio scarcity problem during acceleration in the absence of wet fuel after starting. It is a widely used logic.

As can be seen in Figures 12 and 13, since the intake valve model temperature is the same inside and outside 5 ° C, the same amount of acceleration and deceleration fuel is applied in the prior art. However, the air-fuel ratio during deceleration is slim when the temperature reaches 5 ° C after starting the cooling water temperature of 0 ° C. When the same intake valve temperature (5 ° C) is reached after the cooling water temperature is -25 ° C, Relief occurs.

The problem of the prior art is that in the case of gasoline, the acceleration / deceleration fuel characteristics are influenced by the valve seat temperature, and the valve seat temperature continuously increases after starting, but the acceleration / deceleration characteristic of the cutsol injector is higher than the intake valve temperature. This is because the cutsol valve temperature is greatly influenced by the latent heat of vaporization and then decreases and rises for a certain period of time after starting.

Accordingly, an object of the present invention is to solve the problems of the prior art as a method of controlling the amount of fuel during deceleration in the LPI engine to improve the rich air-fuel ratio problem during deceleration caused by the reduction of the cut-sol temperature by the latent heat of vaporization after starting. To provide.

In order to achieve the above object, the fuel amount control method during deceleration in the LPI engine according to an embodiment of the present invention comprises the steps of setting a weight factor which is a function of the cooling water temperature and the elapsed time after starting the LPI engine; And increasing the fuel amount at the time of deceleration by multiplying a predetermined deceleration fuel amount by the weight factor.

In the LPI engine according to the embodiment of the present invention, the method for controlling fuel amount during deceleration is started by setting a weighting factor that additionally occurs to the deceleration reduction according to the elapsed time for a predetermined period after the engine is started, thereby increasing the amount of fuel during deceleration. Due to the latent latent heat of vaporization, the problem of rich air-fuel ratio at the time of deceleration caused by the decrease of the cutsol temperature can be improved.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 14 to 16 and Equations 3 and 4. FIG.

In the LPI engine according to an embodiment of the present invention, the method of controlling fuel amount during deceleration is an LPI engine equipped with a cutsol injector. The amount of fuel at deceleration is increased by multiplying the weighting factor as a function of.

Final deceleration fuel amount = (Weighting Factor A) * (Base deceleration fuel amount)

Where Weighting Factor A = f (coolant temperature at start-up, engine cycle counter)

The weight factor is increased as the starting cooling water temperature is lower as shown in FIG. 14, and the deceleration fuel amount may be increased in a section in which latent heat of vaporization is reduced by holding the weight value for a predetermined period after starting.

If the engine is turned off before the LPI engine is fully warmed up (within 200 seconds of startup), the cutsol valve temperature is kept low due to latent heat of vaporization, but the coolant temperature or valve seat temperature of the cutsol injector is steep after startup. To maintain a high temperature. Therefore, when the weight is initialized according to the cooling water temperature at startup as shown in Equation 3, the deceleration fuel amount may be insufficient at restart. To compensate for this, when the engine is turned off and restarted before the engine is completely warmed up, the weighted value at start-off is stored in memory and the existing value is changed according to the soaking time (start-up hold time). In short, the weight factor is initialized as shown in Equation 4. However, when the soaking time is long enough (eg, 20 minutes or more), the cooling water temperature and the cut solenoid valve temperature are in equilibrium.

(Weighting Factor A) _new = (Weighting Factor A) _old * (SoakingTime Factor)

Where (Soaking time factor) = f (soaking time)

The weight factor is stored in a memory in the ECU, and the ECU controls the fuel amount during deceleration in the LPL engine using an algorithm such as Equations 3 and 4 by using the weight factor initialization and the weight factor. 15 shows a control procedure of such a control method step by step. As shown in FIG. 15, when the soaking time in the LPL engine is smaller than the predetermined soaking time for initializing the weight, the weighting value is initialized by reducing the last stored weight value, while when the soaking time is long enough, Therefore, the fuel amount is controlled during deceleration.

16 is a diagram showing experimental results showing the effects of the present invention in comparison with the prior art. As can be seen in Figure 16, according to the prior art, the RPM drop phenomenon appears excessively due to the excessive rich air-fuel ratio due to the lack of deceleration fuel amount, the weight factor is applied to the existing deceleration fuel amount when the present invention is applied to the fuel amount control method during deceleration in the LPI engine. By multiplying, the amount of fuel can be increased during deceleration to prevent RPM drop.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

1 is a cross-sectional view showing a gasoline injector of a bottom feed method.

2 is a cross-sectional view showing a cutsol injector developed for application in an LPL system.

3 is a cross-sectional view for explaining a temperature around an intake valve seat.

4 is a cross-sectional view for explaining a temperature around a cutsol valve seat.

5 is a graph showing the transport delay characteristics in the intake valve seat.

6 is a graph showing the transport delay characteristics in the cut sole valve seat.

8 is a graph showing a measurement result of internal pressure of a cut sole.

9 is a graph showing a problem occurring during deceleration due to the pressure inside the cutsol valve.

10 shows some fuel wetting on the intake port and valve seat.

Fig. 11 is a diagram showing the intake valve seat model temperature and the cutsol valve temperature immediately after starting at the cooling water temperature of -20 ° C and 20 ° C.

Fig. 12 is a diagram showing an experimental result in which the air-fuel ratio during deceleration is diminished when the cooling water temperature reaches 5 ° C after starting the cooling water temperature at 0 ° C under the intake valve temperature of 5 ° C.

FIG. 13 is a view showing an experimental result in which engine relief occurs due to an excessive rich air-fuel ratio during deceleration when the same intake valve temperature (5 ° C.) as in the experiment of FIG. 12 is reached after starting the cooling water temperature of −25 ° C. FIG.

14 is a view showing a weight factor according to the cooling water temperature in the fuel amount control method during deceleration in the LPI engine according to an embodiment of the present invention.

15 is a flowchart showing step by step a control procedure of a method for controlling fuel amount during deceleration in an LPI engine according to an embodiment of the present invention.

Figure 16 is a test result showing the presence or absence of the RPM drop phenomenon during deceleration compared to the prior art and the present invention.

Claims (2)

A method of controlling fuel amount at deceleration in an LPI engine equipped with a cutsol injector, Setting a weight factor that is a function of cooling water temperature and elapsed time after startup of the LPI engine; And And decrementing the amount of fuel at the time of deceleration by multiplying a predetermined deceleration fuel amount by the weight factor. The method according to claim 1, Storing the last value of the weight factor at startup off when the LPI engine is powered off and restarted before it is fully warmed up; And initializing the weight factor by decreasing a last value of the stored weight factor according to a soaking maintained for a predetermined period after starting-off.

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