KR100819962B1 - Method for controlling the fuel injection of g.d.i engine using piezo injector - Google Patents

Abstract

A method for controlling fuel injection of a GDI(Gasoline Direct Injection) engine using a piezo injector is provided to raise volumetric efficiency by increasing density of intake air and to prevent knocking phenomenon from occurring at an engine due to cooling effect. A method for controlling fuel injection of a GDI engine using a piezo injector comprises steps of performing primary fuel injection by calculating primary target injection time in consideration of driving conditions and then calculating target amount of air and target injection time, and performing secondary fuel injection by determining if an engine operation mode is ultra lean burn mode or constant driving mode. It is determined if the target injection time is smaller than minimum reference injection time and the engine operation mode is the ultra lean burn mode. If the target injection time is smaller than minimum reference injection time and the engine operation mode is the ultra lean burn mode, the target injection time is corrected.

Description

TECHNICAL FOR CONTROLLING THE FUEL INJECTION OF G.D.I ENGINE USING PIEZO INJECTOR}

1 is a view showing the structure of a wall / air guided GDI engine according to the prior art,

2 shows a direct injection engine fuel system,

3 shows an operation map of the lean direct injection engine,

FIG. 4 is a diagram showing test results of a European fuel efficiency mode (NEDC) vehicle of a conventional first generation ultra thin direct injection engine; FIG.

5 is a view showing the structure and operation principle of the piezo injector system,

6 is a view showing a combustion chamber configuration of the spray guide GDI engine of the present invention;

7 is a view showing an arrangement of the injector and the spark plug,

8 illustrates fuel injection logic of an existing first generation ultra thin GDI engine;

9 is a conventional first generation ultra-thin GDI engine fuel injection control logic flow chart,

10 is a configuration diagram of a piezo injector system of the present invention.

11A to 11D are schematic views showing an injector fuel injection method in the spray guide GDI engine according to the present invention;

12 is a flow chart showing a method for controlling the thermal spraying of the spray guide GDI engine according to the present invention;

Figure 13 is a graph showing the results of single injection and piezo high pressure injection test.

<Description of Signs of Major Parts of Drawings>

10: piezo injector 30: piezo injector driver

50: terminal trigger interface

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling fuel injection of a G.D.I. (GDI) engine using a piezo injector, and particularly, when the target injection time becomes less than the minimum reference injection time during ultra-lean operation. Fuel injection control method of a GDI engine with a piezo injector that can be operated without a torque change due to a reduction in injection time or a mode change by operating the injection time by reducing and correcting the weight by an arbitrary value for the current air volume. It is about.

In general, the power generation stage of a gasoline internal combustion engine that burns by using a spark plug can be classified into the following engines. A port injection engine using a fuel injection injector at an intake port from an initial engine carburetor, a first-generation wall / air-guided gasoline direct injection engine with the concept of directly injecting fuel into a cylinder, and recently a piezo. The development of (Piezo) injectors can be divided into spray-guided direct injection engines using high pressure injectors. A brief introduction to this can be summarized as follows:

1) Port Injection Engine (MPI) Engine

The conventional MPI engine has a fuel injector installed at the port inlet toward the intake valve, injecting fuel before the intake valve is opened to vaporize the injected fuel, and mixing the inflow flow with the fuel during the intake process. Flows into the cylinder. That is, the fuel injected in the port is supplied to the combustion chamber in the form of a fuel-air mixer, and thus a fuel-air mixer is formed uniformly throughout the combustion chamber. This mixer is compressed during compression and burned by supplying ignition energy with a spark plug.

2) Wall / Air-Guided GDI (Gasoline Direct Injection) Engine

1 is a diagram illustrating the structure of a Wall / Air-Guided Gasoline Direct Injection (GDI) engine according to the related art.

Referring to the drawings, the injector development companies Bosch, Denso, Siemens, etc. developed a GDI system (1st generation DI-Motronic) using a high pressure fuel pressure (100bar) compared to the existing port injection injector Has been developed to improve fuel efficiency, high power, particulate matter and combustion noise by directly injecting fuel into the combustion chamber. It is a first generation ultra-thin direct injection engine and is called a wall-guided GDI engine or an air-guided GDI engine depending on the type of inducing flow in the engine. Intake port is specially designed to induce flow, such as the use of a port or reverse tumble, and the air sucked through the intake port is mixed with fuel injected directly into the combustion chamber and spark plug It is designed to lead to. This engine uses an ultra-lean region and uses lean combustion of λ = 3.0 or more. This ultra-thin direct injection engine has no throttle operation and can reduce fuel consumption by 20% compared to port injection due to reduced cylinder wall heat loss, high compression ratio and low idle speed.

The characteristics of the first generation ultra-thin GDI engine are as follows.

First, it has the characteristics of the first generation high pressure injection injector system,

  i) High pressure injection up to 120 bar for optimum mixer formation,

  ii) It can be applied to a single fuel injection logic due to the characteristics of the injector.

Second, as shown in FIG. 2, it has been developed based on port injection common lanes to accommodate various injection ranges.

2 is a diagram illustrating a direct injection engine fuel system.

Third, the first generation of GDI: adopts the wall & air guided combustion method,

 i) Air and fuel flow must be well matched for ignition near the spark plugs, forming a stratified mixer at partial load, and injecting fuel well.

 ii) At full load, injected fuel should not cause spray penetration in the combustion chamber. A swirl control valve is used for this.

Fourth, to use a high-pressure pump of 1 to 3 pistons driven by the camshaft. In this case, cost reduction can be achieved by extending the camshaft and installing a pump.

By using the above method, a fuel / air mixture that can be ignited is formed around the spark plug in the low speed / low load region of the engine speed of 3500 rpm or less and the BMEP 4 bar or less, and the stratified combustion is realized throughout the combustion chamber. do. Substantially, the operating area to which ultra-thin area can be applied is limited, and in this area, the air-fuel ratio is operated in the low speed / low load area of about 30 ~ 50, and the pumping loss due to throttling is reduced, so that the actual fuel efficiency improvement effect is It is known to have about 5% fuel efficiency compared to a port injection engine.

Hereinafter, the problems of the prior art will be described.

The problem of the first generation ultra thin direct injection engine is theoretically able to improve the engine fuel efficiency by more than 20%, but it must be able to control the various operating areas to accommodate the whole operating area. (See Figure 3)

3 is a diagram illustrating an operation map of an ultra lean direct injection engine.

   1) Formation of stratified mixer at low load below 3000 rpm: EGR required for fuel injection and NOx reduction during compression process. In other words, an external EGR is essential for ultra thin direct injection GDI engines.

   i2) At high loads, the soot is partially produced in the rich mixer zone: it operates in a uniform lean mixer mode as the rpm is difficult to maintain the stratified mixer.

   3i) Switch to λ = 1 homogeneous mixer mode as load and rpm increase

  -The operating area is determined by the engine torque and efficiency in order to adjust the exhaust gas and match the OBD conditions.

  -Exhaust gas treatment: CCC for HC conversion, precise control of exhaust gas with oxygen sensor and temperature sensor

In the first generation ultra thin direct injection engines described above, despite the advantages such as high thermodynamic efficiency in ultra lean combustion, there are many limitations in placing the fuel / air mixture around the spark plug during the ignition time that can be ignited. . In areas of heavy load and above, a large amount of fuel must be injected and therefore the timing of injection must be advanced, but the position of the piston must be in a constant section for the injected fuel to move around the spark plug with the aid of the piston top shape. In the above, it is impossible to meet this condition. In addition, in the medium and high speed range, the piston moves faster and the injection timing that can ensure combustion stability cannot be achieved. Therefore, the ultra lean combustion section that can actually perform ultra lean combustion is limited to the engine speed of 3500rpm or less, BMEP 4bar, and inevitably, the theoretical performance ratio operation is inevitable. Therefore, the first generation ultra thin direct injection engine does not take full advantage of ultra lean stratified combustion, and the analysis of vehicle NEDC mode, which is the European exhaust regulation mode, shows that stratified combustion operation takes about 30% of the time. The% drive theoretical fuel economy, and the fuel efficiency improvement of the vehicle is only about 5%. (See Figure 4)

4 is a diagram illustrating a test result of a European fuel efficiency mode (NEDC) vehicle of a conventional engine (first generation ultra thin direct injection engine).

In addition, since the first generation ultra-thin direct injection engine injects fuel to the piston upper surface, part of the injected fuel does not participate in combustion and stays on the piston upper surface in the form of a wall film. Causes material formation.

Accordingly, the present invention is to solve the above-described conventional problems, when the target injection time is less than the minimum reference injection time during ultra-thin operation, the target injection time is calculated and the weight loss correction by any value for the current amount of air injection It is an object of the present invention to provide a method of controlling fuel injection of a GDI engine using a piezo injector, which enables operation without time or by reducing the injection time or by changing the torque according to the mode change.

The fuel injection control method of the GDI engine applying the piezo injector of the present invention for achieving the above object,

Calculating a first target injection time in consideration of operation conditions, calculating a target air amount and a target injection time, and performing a first stage fuel injection;

Determining whether the engine driving region is an ultra-thin driving region or an even driving region and performing secondary fuel injection;

Determining whether the target injection time is less than or equal to the minimum reference injection time and ultra-thin driving;

 Correcting the target injection time if the target injection time is less than or equal to the minimum reference injection time and the ultra-thin operation;

Reducing the target injection time corrected in the target injection time correction step by a current amount of air;

Operating the injection system with a reduced injection time.

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Hereinafter, a fuel injection control method of a GDI engine to which the piezo injector of the present invention is applied will be described in detail with reference to the accompanying drawings.

The spray-guided GDI engine of the present invention is a piezo injector capable of carrying a high pressure fuel of 200 bar, which operates a needle using a piezo element, and the piezo injector is a fuel type injected. Is not affected by the internal flow of the engine. In addition, the injector and spark plugs are located in the center and the spacing is small, which requires a large amount of fuel injection and a mixture to make the fuel evaporate well. In other words, it is important to ensure that the mixer is well transferred from the injector to the spark plug. Compared to other injectors (injectors of the first generation ultra thin direct injection engines), the piezo injector using the Outward Opening Conical Spray Nozzle shows the smallest spray penetration. Features of this injector are advantageous for fuel atomization (up to 15 μm in diameter when atomizing fuel) and have the form of outward opening conical spray nozzle to prevent wetting of spark plug electrodes by fuel, and to ensure the stability of the mixer by being located close to the fuel sprayed with spark plugs. It is a ignitable injector.

5 is a diagram showing the structure and operation principle of the piezo injector system.

The characteristics of the piezo injector are summarized as follows (see FIG. 5).

-Outward opening injection nozzle using piezo actuator

-Using the piezoelectric effect by generating an electric field, injector needle opening and closing by tensioning and contracting the actuator ceramic element

-Injector needle stroke is 30 μm at 20Mpa and maximum ceramic element length is 40mm

-Injector nozzles, piezo actuators and compensating elements are arranged in a row as major components and functionally independent

-Compensation mechanism: Compensation of needle stroke by using hydraulic pressure because thermal expansion of piezo ceramic element is smaller than that of injector housing.

-Maximum stroke arrival time when opening and closing the injector is 200 μs each and partial stroke is also possible.

-Injector and spark plug should be installed in a narrow space of the cylinder head: Change the injector shape by reducing the outer diameter compared to B sample (see Fig. 5)

The Spray-Guided GDI engine above is currently being designed, tested and tested by our team, and the associated combustion chamber geometry is currently pending. A brief summary of the patent pending combustion chamber form follows. In other words, in the Spray-Guided GDI engine, both the injector (piezo injector) and the spark plug are located above the combustion chamber. The injector is located on the relatively low temperature intake valve side, and the spark plug uses the M12 long-reach type to favor the combustion chamber layout. In order to install both the injector and the spark plug in the space above the limited combustion chamber, the exhaust valve size was reduced by 1mm compared to the port injection engine, and the pitch between the valves was increased by 5mm compared to the port injection engine. (See Figure 6)

6 is a perspective view showing the construction of the technology (Spray-Guided GDI engine) combustion chamber (pending patent application) of the present invention.

As shown, the high-pressure piezo injector and spark plug are centrally located, ensuring compliance with the design guidelines for clearance between the intake and exhaust valves and ensuring an assembling clearance with the intake / exhaust cam caps In order to maintain the wall thickness between the plug insertion holes of 2 mm or more, the injector was arranged at an inclination of 9 degrees in the intake direction and the spark plug was inclined at 3.5 degrees in the exhaust direction. At this time, the position of the injector and the spark plug is designed to ignite the injected fuel spray. (See Figure 7)

Fig. 7 is a view showing the arrangement of the injector and the spark plug (prior patent pending).

The above-mentioned application relates to the combustion chamber shape of a Spray-Guided GDI engine using a piezo injector. The logic should apply different logic from the existing first generation ultra thin direct injection engine or port injection engine. The present patent proposal relates to injection logic in this regard.

For convenience of description, a conventional injection control method will be described first.

8 is a diagram illustrating fuel injection logic of a conventional first generation ultra thin GDI engine,

9 is a conventional first generation ultra-thin GDI engine fuel injection control logic flow chart.

To compare the fuel control method of this proposal, the fuel injection control method of the existing first generation ultra-thin GDI engine is as follows (in the first generation, a single fuel injection logic is applied).

In general, in the case of the first generation ultra thin direct injection engine, as shown in FIG. 9, the fuel injection amount control of the engine determines the amount of fuel required at each time by determining the signal input from each sensor of the vehicle in the injector. Will be sprayed through. At this time, the fuel injection amount is proportional to the injection timing, and the control means determines the air-fuel ratio with respect to the signals input from the sensors, and the fuel according to the determined air-fuel ratio is set by setting the driving time of the injector, that is, the injection time. Therefore, when the fuel injection amount is increased, the injection time is increased, and when the injection amount is small, the injection time is controlled by shortening the injection time.

In performing fuel injection control as described above, conventionally, the injection time is determined for the injection amount determined for the intake air amount of the engine during operation, i.e., the basic injection amount necessary for the air-fuel ratio to be a constant reference value, and then the injection time for the basic injection amount is calculated. The operation is performed by calculating the target injection time T1 considering the purge according to the operating conditions.

Hereinafter, the operation logic in the fuel injection control method of the GDI engine to which the piezo injector is applied will be described.

The proposal is directed to a Spray-Guided GDI engine consisting of a four-cylinder piezo system. A schematic of the system is shown in FIG.

10 is a block diagram of a piezo injector system of the present invention.

As shown, in the system of the present invention, an injector driver 30 capable of driving the piezo injector 10 separately from the existing system is configured in the system. The driving conditions of each related injector system are as follows.

1) External trigger signal requirement

 -Sising edge of control signal: 5 μs or less

 -Signal level: CMOS (5V)

 -External trigger: active high (no external trigger signal output when setting piezo driver)

2) Piezo Driver Checklist

 Energy level: always 20% or more

 Dual fuel injection limit: 4500 rpm

 Triple fuel injection limit: 3000 rpm

Unlike the existing first generation ultra thin direct injection engine, this system can not only adjust the fuel level but also control the piezo injector power level, perform the special functions of the piezo, and fuel injection control logic that enables triple fuel injection as follows. .

 -Piezo needle opening and closing: The voltage level is adjusted according to the load situation of the piezo stack for each cylinder to control the opening and closing degree

 -The same injection characteristics by compensating for the difference in injection volume of each injector

 -Up to three injection pulses during injection: Depending on the combustion process and exhaust gas aftertreatment

   Adjustable fuel injection degree, increase the combustible mixer area.

11A to 11D are schematic diagrams showing an injector fuel injection method in the spray guide GDI engine according to the present invention.

The fuel injection system control logic using the system of the present invention is summarized as follows according to the operating conditions of the Spray-Guided GDI engine.

Spray-Guided GDI Engine Piezo Injector Fuel Injection Strategies

 1) Homogeneous single injection (see FIG. 11A)

   Injection timing is based on valve timing, BTDC 300˚CA (depending on nearby intake and in-cylinder flow)

2) Homogeneous single injection with post pulse (see Figure 11b)

 -The initial injection is determined by the valve timing, intake and in-cylinder flow near BTDC 300˚CA,

 -Post injection time is near ATDC 25˚CA, Post injection is about 2 ~ 4 mg / stk

3) Stratified single injection (see FIG. 11C)

  Injection termination depends on cylinder flow, fuel pressure and RPM near 1 to 5˚CA before ignition

4) Stratified double injection (see FIG. 11D)

 -The second injection finish takes into account cylinder flow, fuel pressure, and RPM in the range of 4˚CA before ignition and 4˚CA after ignition.

 2nd injection volume is about 2-4 mg / stk

 Initial injection and second injection intervals approx. 0.3-0.5 ms

The biggest advantage of the piezo injector system is that the secondary injection duration can be adjusted to less than 0.1ms and the injection interval between 1st Injection and 2nd Injection can be controlled to 0.3 ~ 0.5ms. The proposed injection control logic for this is as follows (see Fig. 12).

12 is a flowchart illustrating a method of controlling the thermal spraying in the spray guide GDI engine according to the present invention.

A fuel injection control method of a GDI engine using a piezo injector according to the present invention includes calculating a first target injection time in consideration of operating conditions, calculating a target air amount and a target injection time, and performing a first stage fuel injection; Determining whether the area is an ultra-thin driving area or an equal driving area, and performing secondary fuel injection, that is, determining whether the target injection time is less than or equal to the minimum reference injection time and whether the target is ultra-thin driving, and the target injection time is minimum If it is less than the standard injection time and the ultra-thin operation, characterized in that it comprises the steps of correcting the target injection time, reducing the target injection time corrected in the step by the current amount of air, operating the injection system with a reduced injection time do.

Therefore, the present proposal is to reduce the injection time by driving the target injection time when the target injection time during the ultra-thin operation is less than the minimum reference injection time, and to operate with the injection time reduced by any value for the current amount of air. It is possible to operate without changing the torque according to the mode change.

The flow chart of the target injection timing correction control method of the engine of this proposal is as follows.

 It is determined whether the driving condition is an ultra-thin driving condition or an equal driving area, and the value is returned. If the driving condition is an equal driving area, the engine calculates the basic target time considering the basic first injection, and calculates the engine in the state where the basic target time is calculated. Calculating the target air volume considering the operating conditions, the target injection time, and operating the piezo injector for the first injection time using the calculated target injection time; and if the operating condition is ultra-thin operation, the target injection time is the minimum reference injection. Determining whether the time is less than the time, if the target injection time is less than the minimum reference injection time and the ultra-thin operation, correcting the target injection time to an arbitrary value from the previous target injection time, and calculating the target injection time by the current amount of air. In this case, the piezo fuel injection driver is operated by adjusting the secondary injection with reduced air volume.

  The test results using the above dual injection logic are as follows.

In order to compare the characteristics of the results of applying the single injection and the multiple injection, which are the conventional injection methods, the results of the present injection method and the single injection method are compared in FIG. 13.

13 is a graph showing the results of the single injection and piezo high pressure injection test.

As in the above results, soot generation increases with a single spray. Test results of engine operation, misfire and exhaust characteristics show similar HC and CO emissions, but the soot generation is considerably reduced in the area where piezo high-pressure injection is larger than single injection. EGR is needed because the amount of NOx generated during double injection increases. This is consistent with the findings that external EGR is indispensable for ultra-lean combustion (see Figure 14).

14 is a graph showing the results of the combustion stability test in the single injection and piezo high pressure injection application.

As described above, the fuel injection control method of the GDI engine to which the piezo injector according to the present invention has the following effects.

First, in terms of improving the performance of the present technology, incidental occurrence of a cooling effect by directly injecting gasoline fuel into the combustion chamber, and by the inflow flow into the combustion chamber in which the combustion chamber temperature is lowered by latent heat of evaporation of the fuel in the combustion chamber. do. As a result, the density of intake air increases, thereby improving the filling efficiency (Volumetric Efficiency), it is possible to suppress the knocking (knocking) phenomenon generated in the engine by the cooling effect. This effect is about 3% higher torque, especially at low to medium speeds of 1500 to 2500 rpm. In addition, by utilizing the low and medium speed torque increase, it is possible to improve the maximum torque or the maximum power at high speed while maintaining the low and medium speed torque as the port injection engine by adjusting the intake system or changing the cam profile.

Next, in terms of fuel efficiency improvement, ultra-thin combustion is possible by applying the present control technology, and in particular, ultra-thin stratified combustion is possible in a low and medium speed region of less than 4000rpm, BMEP 6bar or less, which is the main driving area of vehicle users. This results in at least 15% engine fuel economy achieved in Dyno by reducing pumping losses in consideration of ultra-thin operation and reducing throttling losses in practically popular operating areas, and by expanding the ultra-lean operating area. As described above, the fuel efficiency in the actual vehicle driving and the mode driving is improved by 10% or more through the expansion of the ultra-thin driving range.

In addition, in terms of improving the merchandise, assuming that fuel consumption is reduced by 10% in real road driving and 20,000 km per year, the vehicle using this technology saves about 296,000 won in fuel costs per year compared to a port injection vehicle. . Considering the rise of vehicle consumers due to the cost increase in applying this technology, the savings will be realized 5-6 years after the operation. This is based on oil prices (KRW 1,553 per liter) as of July 2006. If oil prices rise further in the future, marketability will increase.

Claims (2)

As a fuel injection control method of a GDI engine using a piezo injector, Calculating a first target injection time in consideration of operation conditions, calculating a target air amount and a target injection time, and performing a first stage fuel injection; Determining whether the engine driving region is an ultra-thin driving region or an even driving region and performing secondary fuel injection; Determining whether the target injection time is less than or equal to the minimum reference injection time and ultra-thin driving;  Correcting the target injection time if the target injection time is less than or equal to the minimum reference injection time and the ultra-thin operation; Reducing the target injection time corrected in the target injection time correction step by a current amount of air; A method of controlling fuel injection of a GDI engine using a piezo injector, comprising: operating an injection system with a reduced injection time. delete

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