Fuel injection system for internal combustion engines

Abstract

To prevent clogging of an injector.SOLUTION: A fuel injection device for an internal combustion engine of the present invention includes a control unit 16 for performing control to stop injection of fuel from respective ones of injectors having injected fuel up to that time among gas fuel injectors 31a-31d and liquid fuel injectors 32a-32d when acceleration off is detected by an accelerator operation detecting unit 15, and to inject a minute amount of fuel from the respective others of the injectors having not injected fuel up to that time after injection of fuel from the respective ones of the injectors is stopped.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel injection device for an internal combustion engine that can use two types of fuel, gaseous fuel and liquid fuel. [Background technology]

[0002] Bi-fuel vehicles that can use two types of fuel, gas fuel and liquid fuel, have been known for some time. Patent Document 1 discloses a bi-fuel vehicle equipped with a fuel selector switch for switching the type of fuel supplied to the internal combustion engine. In such a bi-fuel vehicle, the driver selects a fuel via the fuel selector switch and supplies the selected fuel to the internal combustion engine. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-98720 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, fuels not selected by the driver are not supplied to the internal combustion engine and therefore have no opportunity to be used. For example, if the driver selects gaseous fuel as the fuel to be used, the fuel used during normal driving is gaseous fuel, and there is no opportunity for liquid fuel to be used. Conversely, if the driver selects liquid fuel as the fuel to be used, the fuel used during normal driving is liquid fuel, and there is no opportunity for gaseous fuel to be used.

[0005] Even if the driver does not select the fuel to be used, gaseous fuel may be mainly used to improve fuel efficiency, in which case liquid fuel is used less frequently. Therefore, unused fuel may remain inside an injector that injects fuel that is used infrequently or never used, causing clogging.

[0006] The present invention has been made in view of the above-mentioned problems, and has as its object to prevent clogging of the injector. [Means for solving the problem]

[0007] The present invention provides a fuel injection device for an internal combustion engine that can use two types of fuel, gaseous fuel and liquid fuel, comprising: a gas fuel injector that injects the gaseous fuel; a liquid fuel injector that injects the liquid fuel; an accelerator operation detection unit that detects accelerator operation by a driver; a catalyst for purifying exhaust gas from the internal combustion engine; When the accelerator operation detection unit detects that the accelerator is released, the fuel injection by one of the gas fuel injector and the liquid fuel injector, which is the injector that has been injecting fuel up until now, is stopped, and after the fuel injection by the one injector is stopped, When the air-fuel ratio is leaner than the theoretical A small amount of fuel is injected from the other injector, which has not previously injected fuel. and then supplied to the catalyst A control unit that controls the of It is characterized by being equipped with: [Effects of the Invention]

[0008] According to the present invention, clogging of the injector can be prevented. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a bi-fuel vehicle. [Figure 2] FIG. 2 is a flowchart showing an example of processing by the ECU of this embodiment. [Figure 3] FIG. 3 is a diagram showing a time chart based on the process of the modified example. DETAILED DESCRIPTION OF THE INVENTION

[0010] In an embodiment of the present invention, a fuel injection device for engine 11 capable of using two types of fuel, gas fuel and liquid fuel, includes gas fuel injectors 31a-31d that inject gas fuel, liquid fuel injectors 32a-32d that inject liquid fuel, an accelerator operation detection unit 15 that detects accelerator operation by a driver, and a control unit 16 that, when accelerator operation detection unit 15 detects accelerator release, stops fuel injection from one of gas fuel injectors 31a-31d and liquid fuel injectors 32a-32d that has been injecting fuel, and, after fuel injection from one injector has stopped, controls the other injector that has not been injecting fuel to inject a small amount of fuel. This embodiment can prevent clogging of injectors that inject fuel that is infrequently used or never used. In addition, when the accelerator is detected to be off, a small amount of fuel is injected from an injector that injects fuel that is used less frequently or that has no opportunity to be used, thereby preventing clogging of the injector without affecting the running of the vehicle. [Example]

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a fuel injection device for an internal combustion engine according to the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing an example of the configuration of a bi-fuel vehicle 10 equipped with a fuel injection device for an internal combustion engine according to the present invention. Note that Fig. 1 is simplified for the sake of convenience in explaining the technology of the present disclosure, and components that are normally included in a vehicle are considered to be included even if they are not shown in the figure.

[0012] The bi-fuel vehicle 10 of this embodiment includes an engine 11 as an internal combustion engine and an ECU (Electrical Control Unit) 12 that controls the engine 11 and related equipment. The engine 11 is powered by switching between two types of fuel: gaseous fuel and liquid fuel. For example, compressed natural gas (CNG) can be used as the gaseous fuel, and for example, gasoline can be used as the liquid fuel. Liquid fuel has better engine starting performance than gaseous fuel. On the other hand, gaseous fuel has better fuel economy than liquid fuel. Although the engine 11 of this embodiment will be described as having four cylinders, it may also be a single-cylinder engine or a multi-cylinder engine other than four-cylinder engine.

[0013] The bi-fuel vehicle 10 has an intake system including an air cleaner 21, an intake pipe 22, an electronically controlled throttle valve 23, and an intake manifold 24. The intake pipe 22 is provided with a MAF sensor 25 that detects the intake air flow rate and a MAP sensor 26 that detects the intake air pressure. The intake air purified by the air cleaner 21 flows through the intake pipe 22 to the intake manifold 24, branches from the intake manifold 24, and flows into each cylinder of the engine 11. The ECU 12 controls the electronically controlled throttle valve 23 based on information detected by the MAF sensor 25 and the MAP sensor 26, thereby adjusting the amount of intake air flowing into each cylinder of the engine 11 to suit the operating conditions of the bi-fuel vehicle 10, etc.

[0014] The bi-fuel vehicle 10 includes a fuel supply system that includes gas fuel injectors 31a-31d that inject gas fuel and liquid fuel injectors 32a-32d that inject liquid fuel. The gas fuel injector 31a and the liquid fuel injector 32a inject fuel toward the first cylinder, the gas fuel injector 31b and the liquid fuel injector 32b inject fuel toward the second cylinder, the gas fuel injector 31c and the liquid fuel injector 32c inject fuel toward the third cylinder, and the gas fuel injector 31d and the liquid fuel injector 32d inject fuel toward the fourth cylinder.

[0015] The gaseous fuel injected from the gaseous fuel injectors 31a to 31d mixes with intake air taken in from the intake system to generate an air-fuel mixture, and the generated air-fuel mixture flows into each cylinder of the engine 11. Similarly, the liquid fuel injected from the liquid fuel injectors 32a to 32d mixes with intake air taken in from the intake system to generate an air-fuel mixture, and the generated air-fuel mixture flows into each cylinder of the engine 11.

[0016] The engine 11 also includes ignition coils 33a-33d corresponding to each cylinder. The ignition coils 33a-33d apply high voltage to spark plugs provided in combustion chambers connected to the cylinders. When the spark plugs ignite, the air-fuel mixture in the combustion chambers ignites and burns. The ECU 12 controls the ignition timing of the spark plugs by controlling the timing at which the ignition coils 33a-33d apply high voltage to the spark plugs. When the air-fuel mixture in the combustion chambers burns, pistons reciprocate within the cylinders of the engine 11, and the reciprocating motion of the pistons is converted into rotational motion of the crankshaft. The rotation of the crankshaft is transmitted to the driveshaft via the transmission, which rotates the drive wheels connected to the driveshaft, causing the bi-fuel vehicle 10 to travel. The engine 11 also includes a crank angle sensor 34 that detects the rotation speed of the crankshaft. The ECU 12 calculates the engine speed based on information detected by the crank angle sensor 34.

[0017] The bi-fuel vehicle 10 has an exhaust system including an exhaust manifold 41, a catalytic converter 42 including a catalyst, and a muffler 43. An AF sensor 44 that linearly detects the oxygen concentration in the exhaust gas is disposed between the exhaust manifold 41 and the catalytic converter 42, and an O2 sensor 45 that detects whether the exhaust gas contains oxygen is disposed between the catalytic converter 42 and the muffler 43. Exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber of each cylinder flows into the exhaust manifold 41 and is purified by the catalytic converter 42. The exhaust gas purified by the catalytic converter 42 is muffled by the muffler 43 and then discharged. Based on the information detected by the AF sensor 44 and the O2 sensor 45, the ECU 12 controls the electronically controlled throttle valve 23 so that the air-fuel mixture has a stoichiometric air-fuel ratio.

[0018] The bi-fuel vehicle 10 also includes an accelerator pedal 13 operated by the driver, and a fuel selector switch 14. When the driver operates the accelerator pedal 13, accelerator operation information is transmitted to the ECU 12. The fuel selector switch 14 is a switch that the driver uses to select whether gas fuel or liquid fuel is to be supplied to the engine 11. Information on the fuel selector switch 14 selected by the driver is transmitted to the ECU 12.

[0019] The ECU 12 also has an accelerator operation detector 15 and a controller 16. The accelerator operation detector 15, the controller 16, the gas fuel injectors 31a to 31d, and the liquid fuel injectors 32a to 32d constitute a fuel injection device for the internal combustion engine. Accelerator operation detection unit 15 detects accelerator operation when the driver operates accelerator pedal 13. Accelerator operation detection unit 15 may detect whether or not the driver operates accelerator pedal 13, or may linearly detect the amount of operation (stroke amount) when the driver operates accelerator pedal 13.

[0020] The control unit 16 switches the fuel supplied to the engine 11 between gas fuel and liquid fuel based on information from the fuel selector switch 14 selected by the driver. Specifically, when gas fuel is selected by the fuel selector switch 14, the control unit 16 controls the injection timing and injection amount of gas fuel injected from the gas fuel injectors 31a to 31d. On the other hand, when liquid fuel is selected by the fuel selector switch 14, the control unit 16 controls the injection timing and injection amount of liquid fuel injected from the liquid fuel injectors 32a to 32d. However, the control unit 16 can automatically select the fuel supplied to the engine 11, regardless of the fuel selector switch 14. For example, the control unit 16 may start the engine 11 with liquid fuel at startup and then switch from liquid fuel to gas fuel after the engine speed has stabilized.

[0021] In the bi-fuel vehicle 10 configured as described above, clogging may occur in the injectors that inject the gaseous fuel or liquid fuel that is used less frequently or that is never used. The ECU 12 of the bi-fuel vehicle 10 according to this embodiment controls the injectors to prevent clogging without affecting the running of the vehicle.

[0022] An example of processing by the ECU 12 according to this embodiment will be described below with reference to the flowchart of Fig. 2. The flowchart of Fig. 2 is implemented by the CPU included in the ECU 12 periodically executing a program stored in memory after the engine 11 has started. Note that Fig. 2 will be described assuming that gaseous fuel is selected by the fuel selector switch 14.

[0023] In S10, the ECU 12 performs normal engine control processing. Here, the normal engine control processing refers to processing in which the ECU 12 controls the electronically controlled throttle valve 23 to adjust the intake amount based on information detected by various sensors, controls the timing at which the ignition coils 33a to 33d apply high voltage to the spark plugs, and the control unit 16 of the ECU 12 controls the injection timing and injection amount of gaseous fuel, thereby driving the crankshaft of the engine 11 at a rotation speed corresponding to the accelerator operation detected by the accelerator operation detection unit 15.

[0024] In S11, the accelerator operation detection unit 15 of the ECU 12 determines whether or not it has detected an accelerator-off state, where the driver has switched from operating the accelerator pedal 13 to not operating the accelerator pedal 13. If it has detected an accelerator-off state, the process proceeds to S12, and if it has not detected an accelerator-off state, the process returns to S10 and performs normal engine control processing.

[0025] In S12, the control unit 16 of the ECU 12 stops the injection of gaseous fuel from the gaseous fuel injectors 31a to 31d that had been injecting fuel up until then. Also, the ECU 12 controls the ignition coils 33a to 33d so as not to ignite the spark plugs of the cylinders.

[0026] In S13, the control unit 16 of the ECU 12 stops the injection of gas fuel from the gas fuel injectors 31a to 31d, and then injects a small amount of liquid fuel from the liquid fuel injectors 32a to 32d that have not been injecting fuel. Here, the small amount refers to an injection amount per unit time that does not generate torque in the engine 11. Specifically, the small amount is preferably equal to or less than the injection amount per unit time when liquid fuel is injected while the engine 11 is idling. Injecting a small amount of liquid fuel from the liquid fuel injectors 32a to 32d that have not been injecting fuel thus far can prevent clogging of the liquid fuel injectors 32a to 32d. Note that the small amount of liquid fuel is preferably injected from the liquid fuel injectors 32a to 32d immediately (within 1 second, preferably within 0.1 seconds) after the injection of gas fuel from the gas fuel injectors 31a to 31d has stopped; however, the time until the liquid fuel is injected may be longer as in a modified example described below.

[0027] A small amount of liquid fuel injected from the liquid fuel injectors 32a to 32d adheres to the inside of each cylinder or to the intake port of each cylinder. The liquid fuel thus adhered is burned the next time the spark plug ignites (in the normal engine control process at S16, which will be described later).

[0028] In S14, the control unit 16 of the ECU 12 determines whether the cumulative injection amount exceeds a threshold value after the liquid fuel is injected in S13. If the cumulative injection amount exceeds the threshold value, the process proceeds to S15. On the other hand, if the cumulative injection amount does not exceed the threshold value, the process returns to S13, where the control unit 16 of the ECU 12 continues injection until the cumulative injection amount exceeds the threshold value. The reason why liquid fuel is injected until the threshold value is exceeded is that there are cases where clogging of the liquid fuel injectors 32a to 32d cannot be completely cleared by simply injecting a small amount of liquid fuel. The threshold value can be determined by adding a value that takes error into account to the cumulative value when the clogging is cleared by injecting a small amount of liquid fuel from a clogged liquid fuel injector of the same type as the liquid fuel injectors 32a to 32d through a verification test in advance. This threshold value is pre-stored in the memory of the ECU 12.

[0029] In S15, the control unit 16 of the ECU 12 stops the injection of liquid fuel from the liquid fuel injectors 32a to 32d. By stopping the injection of liquid fuel from the liquid fuel injectors 32a to 32d when the threshold value is exceeded in this manner, it is possible to prevent unnecessary injection of liquid fuel.

[0030] In S16, the ECU 12 performs normal engine control processing, which is the same as S10. If the accelerator operation detection unit 15 of the ECU 12 detects that the accelerator is on between the injection of the liquid fuel and the cumulative value of the injection amount exceeding the threshold value, the injection of the liquid fuel from the liquid fuel injectors 32a to 32d is immediately stopped, the process returns to S10, and the gas fuel injectors 31a to 31d inject the gas fuel while controlling the injection timing and injection amount.

[0031] In this embodiment, when accelerator release is detected, the gas fuel injectors 31a-31d that had been injecting fuel stop injecting gas fuel, and after the gas fuel injectors 31a-31d stop injecting gas fuel, a small amount of liquid fuel is injected from the liquid fuel injectors 32a-32d that had not been injecting fuel until then. Therefore, clogging of injectors that inject fuel that is used infrequently or that is never used can be prevented. Furthermore, by injecting a small amount of liquid fuel from the liquid fuel injectors 32a-32d at a timing when the driver does not require torque, such as when the accelerator is released, as in this embodiment, clogging of the injectors can be prevented without affecting the running of the bi-fuel vehicle 10.

[0032] In this embodiment, a small amount of liquid fuel is injected at an injection amount per unit time that does not generate torque, and the injection is controlled to continue until the integrated value of the injection amount exceeds a threshold value. Therefore, it is possible to reliably prevent the engine 11 from generating torque. Furthermore, by continuing the injection of fuel until the load value exceeds a threshold value, it is possible to reliably prevent clogging of the injector.

[0033] (Variation) In the above-described embodiment, the liquid fuel injected from the liquid fuel injectors 32a-32d adheres to the inside of each cylinder, but this is not limited to this. After the injection of gaseous fuel is stopped, the control unit 16 of the ECU 12 may inject a small amount of liquid fuel from the liquid fuel injectors 32a-32d in a state leaner than the stoichiometric air-fuel ratio, and supply the liquid fuel to the catalyst of the catalytic converter 42. In order to supply the lean liquid fuel to the catalyst of the catalytic converter 42, the bi-fuel vehicle 10 is equipped with a variable valve timing system (VVT) that changes the valve timing of the intake valve or exhaust valve, and an exhaust gas recirculation (EGR) device.

[0034] 2, while the control unit 16 of the ECU 12 is injecting minute amounts of liquid fuel from the liquid fuel injectors 32a-32d, the ECU 12 opens the electronically controlled throttle valve 23 and drives the exhaust gas recirculation device to take in intake air and make the liquid fuel leaner than the stoichiometric air-fuel ratio. Furthermore, the ECU 12 drives the variable valve timing system (VVT) to supply the liquid fuel from each cylinder through the exhaust manifold 41 to the catalyst of the catalytic converter 42 without depositing the liquid fuel inside the cylinder. By supplying the lean liquid fuel to the catalyst of the catalytic converter 42 in this way, the liquid fuel is combusted by the catalyst. Therefore, by lengthening the time until liquid fuel is injected after gas fuel injection has stopped, it is possible to suppress a drop in catalyst temperature even when a fuel cut state in which neither gas fuel nor liquid fuel is injected continues.

[0035] Fig. 3 is a diagram showing a time chart based on the processing of the modified example, in which Fig. 3(a) shows the on / off of accelerator operation, Fig. 3(b) shows the fuel cut state, Fig. 3(c) shows the injection amount of gas fuel, Fig. 3(d) shows the injection amount of liquid fuel, Fig. 3(e) shows the integrated value of liquid fuel, and Fig. 3(f) shows the air-fuel ratio. As shown in FIG. 3(a), when the accelerator pedal is released from the normal engine control process, the gas fuel injection amount becomes zero as shown in FIG. 3(c). Thereafter, a fuel cut state in which neither gas fuel nor liquid fuel is injected continues as shown in FIG. 3(b). After a predetermined time has elapsed, a minute amount of liquid fuel is injected until the cumulative value exceeds a threshold as shown in FIGS. 3(d) and 3(e). At this time, liquid fuel is supplied to the catalyst of the catalytic converter 42 in a state leaner than the stoichiometric air-fuel ratio as shown in FIG. 3(f). Thereafter, the cumulative value exceeds a threshold as shown in FIGS. 3(d) and 3(e), and the liquid fuel injection amount becomes zero. As shown in FIG. 3(a), when the accelerator pedal is released, gas fuel is injected as shown in FIG. 3(c), and the process returns to the normal engine control process. In this manner, according to the modified example, fuel is injected in a lean state and supplied to the catalyst, thereby making it possible to suppress a drop in catalyst temperature when fuel is cut.

[0036] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and modifications, and modifications can be made within the scope of the present invention. In the above-described embodiment and modified example, when accelerator release is detected, the gas fuel injectors 31a-31d stop injecting gas fuel and the liquid fuel injectors 32a-32d inject a small amount of liquid fuel. However, this is not limiting, and the order of gas fuel injection from the gas fuel injectors 31a-31d and liquid fuel injection from the liquid fuel injectors 32a-32d may be reversed. That is, when accelerator release is detected, the control unit 16 may control the liquid fuel injectors 32a-32d to stop injecting liquid fuel, and then the gas fuel injectors 31a-31d to inject a small amount of gas fuel after stopping the liquid fuel injection from the liquid fuel injectors 32a-32d. In this case, clogging of the gas fuel injectors 31a-31d can be prevented.

[0037] In the above-described embodiment and modified example, gasoline, which is a petroleum-based fuel, is described as the liquid fuel, but this is not limited to this and petroleum-based fuels such as heavy oil, light oil, kerosene, etc. may also be used, alcohols may also be used, and oils and fats may also be used. In the above-described embodiment and modified example, CNG is described as the gas fuel, but this is not limited to this and LPG, etc. may also be used. [Explanation of symbols]

[0038] 10: Bi-fuel vehicle 11: Engine (internal combustion engine) 12: ECU 15: Accelerator operation detector 16: Control unit 31a to 31d: Gas fuel injectors 32a to 32d: Liquid fuel injectors 42: Catalytic converter

Claims

1. A fuel injection device for an internal combustion engine that can use two types of fuel, gas fuel and liquid fuel, a gas fuel injector that injects the gas fuel; a liquid fuel injector that injects the liquid fuel; an accelerator operation detection unit that detects an accelerator operation by a driver; a catalyst for purifying exhaust gas from the internal combustion engine; When the accelerator operation detection unit detects that the accelerator is released, the injection of fuel by one of the gas fuel injector and the liquid fuel injector, which is the injector that has been injecting fuel up until now, is stopped, a control unit that controls the other injector, which has not been injecting fuel until now, to inject a small amount of fuel to the catalyst in a state leaner than the stoichiometric air-fuel ratio after stopping fuel injection from the one injector.

2. The control unit 2. The fuel injection device for an internal combustion engine according to claim 1, wherein the minute amount of fuel is injected at an injection amount per unit time that does not generate torque, and the injection is controlled to continue until an integrated value of the injection amount exceeds a threshold value.

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