JP4089635B2 - Fuel injection control method for bi-fuel direct injection engine - Google Patents

Description

  The present invention relates to a fuel injection control method for a bi-fuel in-cylinder direct injection engine. More specifically, the present invention relates to a bi-fuel in-cylinder direct injection capable of suppressing deposit adhesion to a nozzle portion of a liquid fuel injection valve when liquid fuel injection is stopped. The present invention relates to an engine fuel injection control method.

  There has been proposed a bi-fuel in-cylinder direct injection engine in which a liquid fuel only operation mode and a gas fuel only operation mode are set, and a liquid fuel injection valve for directly injecting liquid fuel into a combustion chamber is provided (for example, , See Patent Document 1).

JP-A-11-324750

  In the conventional bi-fuel in-cylinder direct injection engine, the temperature of the tip portion (inlet portion) of the liquid fuel injection valve is higher than the 90% distillation temperature (T90) of the liquid fuel during the operation mode of only the gaseous fuel. In the case where the value is higher, most of the fuel remaining in the nozzle part evaporates, so that it is considered that the precursor material that becomes the nucleus for deposit formation aggregates on the inner wall surface of the nozzle part.

  The precursor in such a state is difficult to be washed away at the time of the next liquid fuel injection, and remains in the nozzle part, so that deposition of deposit proceeds. If deposit accumulation progresses at the injection port of the fuel injection valve, the fuel injection amount may decrease, causing a deviation in the air-fuel ratio, resulting in a decrease in output, or in the worst case, fuel injection may not be possible. .

  The present invention has been made in view of the above, and provides a fuel injection control method for a bi-fuel in-cylinder direct injection engine that can suppress deposit adhesion to a nozzle portion of a liquid fuel injection valve when liquid fuel injection is stopped. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, a fuel injection control method for a bi-fuel direct injection engine according to claim 1 of the present invention includes: a liquid fuel injection valve that directly injects liquid fuel into the cylinder; A gas fuel injection valve for injecting the gas fuel into the cylinder or into the intake port, injecting either the liquid fuel or the gas fuel according to the operation mode of the engine, and stratified combustion according to the operation conditions In a fuel injection control method of a bi-fuel direct injection engine configured to be able to switch between homogeneous combustion, the injection pressure of the liquid fuel injection valve is increased at the time of switching between injection of the liquid fuel and the gaseous fuel. And jetting for a predetermined time.

  According to claim 2 of the present invention, there is provided a fuel injection control method for a bi-fuel direct injection engine according to claim 1, wherein the liquid fuel is gasoline, alcohol, or a mixed fuel of gasoline and alcohol. It is any one of these.

  According to a third aspect of the present invention, there is provided a fuel injection control method for a bi-fuel in-cylinder direct injection engine according to the first or second aspect, wherein the gaseous fuel is compressed natural gas, hydrogen, or dimethyl ether. It is any one of them.

  According to the fuel injection control method for a bi-fuel direct injection engine according to the present invention (Claim 1), at the time of switching between injection of liquid fuel and gaseous fuel, that is, immediately before switching to gaseous fuel and immediately after switching to liquid fuel. In addition, deposits adhering to the nozzle portion of the liquid fuel injection valve can be cleaned by high-pressure liquid fuel injection. Thereby, it can suppress that a deposit adheres and accumulates in the said nozzle part at the time of liquid fuel injection stop (at the time of gaseous fuel injection), and can suppress that fuel injection quantity falls. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel.

  According to the fuel injection control method for a bi-fuel direct injection engine according to the present invention (Claim 2), any one of gasoline, alcohol, and a mixed fuel of gasoline and alcohol is used as a liquid fuel. In a fuel in-cylinder direct injection engine, deposits adhering to the injection port of the liquid fuel injection valve can be washed by high-pressure liquid fuel injection when switching between injection of liquid fuel and gaseous fuel.

  According to the fuel injection control method for a bi-fuel in-cylinder direct injection engine according to the present invention (Claim 3), the bi-fuel in-cylinder uses any one of compressed natural gas, hydrogen, and dimethyl ether as gaseous fuel. In the direct injection engine, the deposit attached to the nozzle portion of the liquid fuel injection valve can be cleaned by high-pressure liquid fuel injection when switching between injection of liquid fuel and gaseous fuel.

  Embodiments of a fuel injection control method for a bi-fuel direct injection engine according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 2 is a cross-sectional view showing a schematic configuration of the bi-fuel in-cylinder direct injection engine, and shows one cylinder of the multi-cylinder bi-fuel in-cylinder direct injection engine. As shown in FIG. 2, a bi-fuel in-cylinder direct injection engine (hereinafter simply referred to as an engine) 10 directly injects gasoline (liquid fuel) into a combustion chamber 10a by an injector (liquid fuel injection valve) 23, and (Gaseous fuel injection valve) 24 is configured to inject gaseous fuel such as compressed natural gas (CNG) into the intake port 15, and either gasoline or gaseous fuel is injected depending on the operation mode of the engine. It is configured to be able to switch between stratified combustion and homogeneous combustion depending on the operating conditions.

  That is, the combustion chamber 10 a of the engine 10 is constituted by a cylinder bore 11, a cylinder head 13, and a piston 12 that is disposed in the cylinder bore 11 so as to be reciprocally movable. A concave cavity 12a is formed in the intake side portion of the top surface of the piston 12 in order to establish stratified combustion.

  A spark plug 14 is disposed substantially at the center of the combustion chamber 10a. An intake valve 16 is disposed at the intake port 15 facing the combustion chamber 10a, and an exhaust valve 20 is disposed at the exhaust port 18 facing the combustion chamber 10a. Further, an injector 23 for gasoline injection is disposed in the vicinity of the intake valve 16 of the combustion chamber 10a so that the injection port portion 23a faces the combustion chamber 10a.

  The fuel injection pressure of the injector 23 is adjusted by a pump (not shown). This pump is configured to increase the fuel injection pressure to a predetermined pressure at which in-cylinder injection can be performed at the normal time and to increase the fuel injection pressure at the time of deposit cleaning control to be described later than during normal injection.

  As described above, the engine 10 basically has the same configuration as that of a normal direct injection type gasoline engine. However, in order to allow the gaseous fuel to be injected from the injector 24, the configuration of the fuel supply system is the gasoline. It is different from the engine. That is, the system of the engine 10 includes a gaseous fuel cylinder for storing gaseous fuel in a high pressure state, and a sensor for detecting the pressure and temperature in the cylinder, although the illustrated example is omitted.

  Also, a delivery pipe that distributes the gaseous fuel fed from the gaseous fuel cylinder to each injector 24, a sensor that detects the pressure and temperature in the delivery pipe, and a gas that is fed from the gaseous fuel cylinder to the delivery pipe. A regulator or the like for adjusting the fuel to a predetermined pressure is provided.

  The engine 10 described above is basically controlled by an electronic control unit (not shown) (hereinafter referred to as “ECU”) based on various sensor information (not shown), and to suppress deposits on the nozzle portion 23a of the injector 23. The fuel injection is controlled as follows (see FIG. 1).

  In the present embodiment, the engine 10 shown in FIG. 2 described above is described as a basic configuration. However, as shown in FIG. 3, the configuration includes two in-cylinder direct injectors 23 and 25. It is also possible to adopt a configuration in which the injector 23 is for gasoline injection and the injector (gaseous fuel injection valve) 25 is for gaseous fuel injection.

  Next, a fuel injection control method according to the present embodiment will be described with reference to FIG. Here, FIG. 1 is a flowchart showing a fuel injection control method for a bi-fuel direct injection engine according to an embodiment of the present invention.

  In this example, when switching between injection of liquid fuel and gaseous fuel, i.e. immediately before switching from gasoline to gaseous fuel, and immediately after switching from gaseous fuel to gasoline, gasoline is injected at a high pressure for a certain period of time to control combustion. The deposit generation substance (fuel residue) in the nozzle part 23a of the injector 23 is washed, and is controlled as follows.

  First, it is determined whether or not the engine 10 is burning with gasoline (step S10). If it is burning with gasoline (Yes at Step S10), it is determined whether or not there is an instruction to switch to gaseous fuel (Step S11). If there is no instruction to switch to gaseous fuel (No at Step S11), combustion control with normal gasoline is performed, and the process waits until there is an instruction to switch (Step S20).

  If there is an instruction to switch to gaseous fuel (Yes in step S11), the control for deposit cleaning cannot be performed by stratified combustion without robustness, so it is determined whether or not the current combustion is stratified combustion. (Step S12). If it is stratified combustion (Yes in step S12), it switches to homogeneous combustion (step S13), and proceeds to deposit cleaning control in step S14. If it is not stratified combustion (No in step S12), it proceeds to deposit cleaning control in step S14. Migrate as it is.

  In step S14, the deposit adhering to the injection hole 23a (see FIG. 2 or 3) of the injector 23 is washed by high-pressure gasoline fuel injection, so that the fuel injection pressure is increased to the maximum pressure of a pump (not shown). The injection time is corrected according to the pressure. Thereafter, homogeneous combustion control by high-pressure injection is performed until time T1 sufficient to clean the deposit. The cleaning time T1 is an empirical value, and an optimal value is set in advance through experiments or the like.

  Thereby, it can suppress that a deposit adheres and deposits on the nozzle part 23a of the injector 23, and can suppress that a fuel injection amount falls. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel.

  Then, after the deposit cleaning control in step S14 is completed, switching to gaseous fuel is performed (step S15), and the process returns to step S10 again.

  On the other hand, if it is determined in the first step S10 that it is not burned with gasoline, that is, it is burned with gaseous fuel (No at step S10), combustion control with normal gaseous fuel is performed (step S16), It is determined whether or not there is an instruction to switch to gasoline (step S17). If there is no instruction to switch to gasoline (No at Step S17), combustion control with normal gaseous fuel is performed until there is an instruction to switch (Step S16).

  If there is an instruction to switch to gasoline (Yes at step S17), the deposit adhering to the injection port 23a of the injector 23 is washed by high-pressure gasoline fuel injection, so the fuel injection pressure is shown under homogeneous combustion by switching to gasoline injection. Do not increase the maximum pressure of the pump. The injection time is corrected according to the pressure. Thereafter, homogeneous combustion control by high-pressure injection is performed until time T2 sufficient for cleaning the deposit is reached (step S18). The cleaning time T2 is an empirical value, and an optimum value is set in advance through experiments or the like.

  Thereby, it is possible to suppress deposits from adhering to and depositing on the injection hole portion 23a of the injector 23 when gasoline injection is stopped, and it is possible to suppress a decrease in the fuel injection amount. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel.

  When the deposit cleaning control in step S18 is completed, the normal fuel injection pressure is restored and the combustion control with gasoline is performed at the injection pressure (step S19). At that time, if the stratified combustion control is performed immediately before the deposit cleaning control in step S18, the control is switched to the stratified combustion control. And it returns to step S10 again.

  As described above, according to the fuel injection control method of the bi-fuel direct injection engine according to this embodiment, it is possible to suppress deposits from adhering to and depositing on the injection hole portion 23a of the injector 23 when gasoline injection is stopped. It is possible to suppress the fuel injection amount from decreasing. Therefore, it is possible to suppress the occurrence of problems such as a deviation in the air-fuel ratio or the inability to inject fuel.

  In the above embodiment, the gasoline is used as the liquid fuel and CNG is used as the gaseous fuel. However, the present invention is not limited to this. For example, the liquid fuel is alcohol or gasoline mixed with alcohol. , Liquefied petroleum gas (LPG), hydrogen, dimethyl ether (DME), etc. may be used as the gaseous fuel, and gasoline, these liquid fuels, and gaseous fuels may be used in any combination. .

  As described above, the fuel injection control method for a bi-fuel direct injection engine according to the present invention includes a liquid fuel injection valve that directly injects liquid fuel into the cylinder, and a gas that injects gaseous fuel into the cylinder or the intake port. The present invention is useful for a bi-fuel in-cylinder direct injection engine that includes a fuel injection valve and injects one of the liquid fuel and the gaseous fuel according to the operation mode of the engine. It is suitable for a fuel injection control method capable of suppressing deposit adhesion to the nozzle orifice of the valve.

It is a flowchart which shows the fuel-injection control method of a bi-fuel direct injection engine. It is sectional drawing which shows schematic structure of a bi-fuel direct injection engine. It is sectional drawing which shows schematic structure of the other bi-fuel in-cylinder direct injection engine.

Explanation of symbols

10 engine (bi-fuel direct injection engine)
10a Combustion chamber 11 Cylinder bore 15 Intake port 23 Injector (liquid fuel injection valve)
24, 25 injector (gaseous fuel injection valve)
23a nozzle

Claims (3)

A liquid fuel injection valve for directly injecting liquid fuel into the cylinder;
A gaseous fuel injection valve that injects gaseous fuel into the cylinder or into the intake port;
With
Fuel injection of a bi-fuel in-cylinder direct injection engine configured to inject either one of the liquid fuel and the gaseous fuel in accordance with the operation mode of the engine and switch between stratified combustion and homogeneous combustion in accordance with the operation conditions In the control method,
A fuel injection control method for a bi-fuel in-cylinder direct injection engine, wherein an injection pressure of the liquid fuel injection valve is increased and injection is performed for a predetermined time under homogeneous combustion when switching between injection of the liquid fuel and the gaseous fuel.   The fuel injection control method for a bi-fuel direct injection engine according to claim 1, wherein the liquid fuel is any one of gasoline, alcohol, and a mixed fuel of gasoline and alcohol.   3. The fuel injection control method for a bi-fuel direct injection engine according to claim 1, wherein the gaseous fuel is one of compressed natural gas, hydrogen, and dimethyl ether.

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