JP5798055B2 - Fuel injection system - Google Patents

Description

 The present invention relates to a fuel injection system.

  Conventionally, as a technology for improving the fuel efficiency and environmental protection performance of a vehicle, there is a bi-fuel system that selectively switches between liquid fuel such as gasoline and gaseous fuel such as compressed natural gas (CNG) and supplies it to a single engine. Are known. This bi-fuel system is often constructed by adding a new gas injection system to an existing gasoline injection system in order to reduce development costs.

  In this bi-fuel system, during a gas operation, an existing electronic control device that controls the gasoline injection amount (hereinafter referred to as a first control device) calculates the gasoline injection amount based on various sensor signals indicating the engine operating state. In addition, a gasoline pulse having a pulse width corresponding to the calculation result is output to a new electronic control unit, while the new electronic control unit (hereinafter referred to as a second control unit) adapts the gasoline pulse to gas fuel. The converted gas pulse is output to a gas injector (see Patent Document 1 below).

JP-T 6-502472

  By the way, it is generally known that the minimum flow rate injection capability of a gas injector is lower than that of a gasoline injector. In other words, when the energization time of both injectors is shortened in the same way, the gasoline injector can accurately inject a small amount of fuel in response to a shorter energization time as compared with the gas injector. .

  Therefore, when adopting a system configuration in which the gasoline pulse output from the first control device is converted into a gas pulse suitable for gas fuel by the second control device, the pulse width of the gasoline pulse (gasoline injector energization time) becomes shorter, Although the pulse width (gas injector energization time) of the gas pulse is shortened, if the gas injector energization time becomes shorter than the minimum flow rate guarantee time of the gas injector (minimum energization time that can guarantee the fuel injection at the minimum flow rate), the gas injector There is a possibility that the engine will misfire without being injected with gas fuel.

  To avoid this, during gas operation, if the pulse width of the gas pulse, that is, the gas injector energization time falls below a predetermined threshold, the fuel injection by the gasoline injector, that is, switch to gasoline operation, and the gas injector energization time is changed. There has been proposed a technique of switching back to gas operation when the threshold value is exceeded. The above-described threshold is set to a longer time with a margin than the minimum flow rate guarantee time of the gas injector.

  However, in this prior art, since the switching control of the injected fuel is performed based on the comparison determination result between the gas injector energization time and one threshold value, the operation in which the gas injector energization time greatly varies across the threshold value is performed. Under certain conditions, gas operation and gasoline operation are frequently switched, and combustion in the cylinder may not be stable, resulting in unstable engine operation.

 The present invention has been made in view of the above-described circumstances, and even under operating conditions in which the gas fuel injection valve energization time largely fluctuates in a region near the minimum flow rate guarantee time of the gas fuel injection valve, It is an object of the present invention to provide a fuel injection system capable of avoiding unstable engine operation by suppressing the frequency of switching between gas fuel operation and liquid fuel operation.

 In order to achieve the above object, in the present invention, as a first solving means related to a fuel injection system, a first control device that outputs a first pulse signal whose pulse width is set to a liquid fuel injection valve energization time; A gaseous fuel injection valve energization time is calculated based on the first pulse signal input from the first control device, and a pulse width is set to the gaseous fuel injection valve energization time in the gaseous fuel injection mode. And a second control device that outputs the first pulse signal to the liquid fuel injection valve in the liquid fuel injection mode, wherein the second control device is configured to output the gas to the gaseous fuel injection valve. In the fuel injection mode, the time measurement of the first time is started after the gas fuel injection valve energization time becomes equal to or lower than the low threshold value having a hysteresis, and the gas is discharged within the first time. When the fuel injection valve energization time does not exceed the high threshold of the threshold having the hysteresis, the output of the second pulse signal is stopped and switched to the output of the first pulse signal to the liquid fuel injection valve Adopt means.

 Further, in the present invention, as the second solving means relating to the fuel injection system, in the first solving means, the second control device is configured such that the gas fuel injection valve energization time is less than or equal to the low threshold value. The time measurement of the first time and the second time longer than that is started, and the first pulse to the liquid fuel injection valve without exceeding the high-side threshold value within the first time without the gas fuel injection valve energizing time being exceeded. After switching to signal output, if the gaseous fuel injection valve energization time does not exceed the high-side threshold within the second time, a shutoff valve inserted in the gaseous fuel delivery path to the gaseous fuel injection valve Is used to close the valve and shift to the liquid fuel injection mode.

 Further, in the present invention, as a third solving means relating to the fuel injection system, in the second solving means, the second control device is configured such that the gas fuel injection valve energization time after the transition to the liquid fuel injection mode. Exceeds the mode return threshold set higher than the high-side threshold, the shut-off valve is opened and the output of the first pulse signal is stopped, and the second pulse signal to the gaseous fuel injection valve is stopped. A means of switching to output is adopted.

  Further, in the present invention, as a fourth solving means relating to the fuel injection system, in the third solving means, the second control device is configured to perform the first operation after the gaseous fuel injection valve energization time exceeds the mode return threshold. The time measurement for 3 hours is started, and when the gas fuel injection valve energization time does not fall below the high-side threshold within the third time, the gas fuel injection mode is restored.

In the present invention, the second control device starts counting the first time after the gas fuel injection valve energization time becomes equal to or lower than a low threshold value having a hysteresis in the gaseous fuel injection mode, If the gas fuel injection valve energization time does not exceed the high threshold value having the hysteresis within one hour, the output of the second pulse signal is stopped and the first pulse signal to the liquid fuel injection valve is stopped. Switch to the output.
In other words, the second control device, when the gaseous fuel injection valve energization time exceeds the threshold having the hysteresis with the hysteresis within the first time, the second pulse signal to the gaseous fuel injection valve. Is continued (that is, the gaseous fuel injection mode is continued).
As described above, in the gaseous fuel injection mode, by performing the injection fuel switching control based on the comparison determination result between the threshold having hysteresis and the gaseous fuel injection valve energization time, the gaseous fuel injection valve energization time is It is possible to avoid unstable engine operation by suppressing the frequency of switching between gas fuel operation and liquid fuel operation even under operating conditions that fluctuate greatly in the region near the minimum flow rate guarantee time of the valve Become.

It is a schematic structure figure of fuel injection system A concerning this embodiment. It is a flowchart showing the injection fuel switching control which 2nd-ECU4 implements at the time of gas injection mode. It is a flowchart showing the injection fuel switching control which 2nd-ECU4 implements at the time of gas injection mode. It is a timing chart for demonstrating the process which 2nd-ECU4 implements with respect to the time change of gas injector energization time TG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a fuel injection system A according to the present embodiment. The fuel injection system A is a bi-fuel system that selectively switches between liquid fuel (for example, gasoline) and gaseous fuel (for example, compressed natural gas) and supplies it to a single engine (not shown). And a gaseous fuel supply system 2, a 1st-ECU (Electronic Control Unit) 3, a 2nd-ECU 4, and a fuel changeover switch 5.

 The liquid fuel supply system 1 includes a gasoline tank 11, a gasoline supply pipe 12, and a gasoline injector 13 (liquid fuel injection valve). The gasoline tank 11 is a corrosion-resistant container that stores gasoline as liquid fuel, and has a built-in pump and regulator (not shown) that sucks the gasoline and sends it to the gasoline supply pipe 12.

 The gasoline supply pipe 12 is a pipe for delivering gasoline from the gasoline tank 11 to the gasoline injector 13. The gasoline injector 13 is an electromagnetic valve (for example, a solenoid valve) mounted on the intake pipe so that the injection port is exposed toward the intake port of the engine, for example, and corresponds to a gasoline pulse signal input from the 2nd-ECU 4. A predetermined amount of gasoline is injected.

 The gaseous fuel supply system 2 includes a gas tank 21, a high pressure gas supply pipe 22, a shutoff valve 23, a regulator 24, a low pressure gas supply pipe 25, a gas injector 26 (gaseous fuel injection valve), and a gas fuel pressure sensor 27. And a gas fuel temperature sensor 28.

 The gas tank 21 is a high pressure vessel filled with compressed natural gas (CNG) as gaseous fuel. The high-pressure gas supply pipe 22 is a high-pressure pipe for delivering high-pressure gas fuel from the gas tank 21 to the regulator 24. The shut-off valve 23 is an electromagnetic valve inserted in the high-pressure gas supply pipe 22 and opens or closes according to a shut-off valve drive signal input from the 2nd-ECU 4.

 The regulator 24 is a pressure reducing valve disposed on the downstream side of the shutoff valve 23, and decompresses the high pressure gas fuel supplied from the gas tank 21 to a desired pressure when the shutoff valve 23 is opened to the low pressure gas supply pipe 25. Send it out. The low-pressure gas supply pipe 25 is a low-pressure piping for delivering low-pressure gas fuel from the regulator 24 to the gas injector 26. The gas injector 26 is an electromagnetic valve attached to the intake pipe so that, for example, the injection port is exposed toward the intake port of the engine, and injects a predetermined amount of gas fuel according to a gas pulse signal input from the 2nd-ECU 4. To do.

 The gas fuel pressure sensor 27 detects the internal pressure of the low-pressure gas supply pipe 25 (gas fuel pressure on the low-pressure side) from the regulator 24, and outputs a gas fuel pressure signal indicating the detection result to the 2nd-ECU 4. . The gas fuel temperature sensor 28 detects the internal temperature (low pressure gas fuel temperature) of the low pressure gas supply pipe 25 and outputs a gas fuel temperature signal indicating the detection result to the 2nd-ECU 4.

 The 1st-ECU 3 (first control device) calculates the gasoline injection amount based on various sensor signals indicating engine operation states input from various sensors (not shown), and is necessary for obtaining the gasoline injection amount. An energization time (liquid fuel injection valve energization time; hereinafter referred to as gasoline injector energization time) of the gasoline injector 13 is calculated, and a gasoline pulse signal (first pulse signal) in which the pulse width is set to the gasoline injector energization time is generated. To 2nd-ECU4.

 The 2nd-ECU 4 (second control device) includes a gas fuel pressure signal input from the gas fuel pressure sensor 27, a gas fuel temperature signal input from the gas fuel temperature sensor 28, and a gasoline pulse input from the 1st-ECU 3. Based on the signal and the fuel switching signal input from the fuel switch 5, energization control of the gasoline injector 13, the gas injector 26 and the shutoff valve 23 is performed.

 When the 2nd-ECU 4 recognizes that gasoline is selected as the fuel to be used based on the fuel switching signal input from the fuel selector switch 5, the 2nd-ECU 4 shifts to the gasoline injection mode (liquid fuel injection mode) while using the fuel to be used. When it is recognized that the gas is selected, the gas injection mode (gaseous fuel injection mode) is entered.

 The 2nd-ECU 4 calculates an energization time of the gas injector 26 (a gas fuel injection valve energization time; hereinafter referred to as a gas injector energization time) based on the gasoline pulse signal input from the 1st-ECU 3. The shutoff valve 23 is opened to start supplying gas fuel from the gas tank 21 to the gas injector 26, and a gas pulse signal (second pulse signal) whose pulse width is set to the gas injector energizing time is output to the gas injector 26. On the other hand, a gasoline pulse signal is output to the gasoline injector 13 in the gasoline injection mode.

 The fuel change-over switch 5 is a switch that enables the fuel to be changed by a manual operation of the user, and indicates the state of the switch, that is, a fuel that indicates whether gasoline is selected as the fuel to be used or whether gas is selected. A switching signal is output to the 2nd-ECU 4.

 Next, the operation of the fuel injection system A configured as described above, particularly the operation during gas operation will be described in detail with reference to FIGS.

 When the engine is in operation, the 1st-ECU 3 does not depend on the state of the fuel changeover switch 5 (that is, regardless of gasoline operation or gas operation), and every time the fuel injection timing is based on the engine operation state recognized from various sensor signals. The gasoline injection amount to be injected from the gasoline injector 13 is calculated at the same time, the gasoline injector energization time necessary to obtain the gasoline injection amount is calculated, and a gasoline pulse signal whose pulse width is set to the gasoline injector energization time is generated. And output to the 2nd-ECU 4.

 In the case of a 4-cycle engine, it is necessary to perform fuel injection once while the crankshaft rotates twice. Therefore, every time the crankshaft rotates twice, a gasoline pulse having a predetermined pulse width is transferred from the 1st-ECU 3 to the 2nd-ECU 4. A signal will be output.

 The 2nd-ECU 4 measures the pulse width of the gasoline pulse signal input from the 1st-ECU 3 as described above as the gasoline injector energization time, and uses this gasoline injector energization time as a flow characteristic of the gas injector 26, gas fuel pressure, and gas fuel. By correcting based on the temperature, the gas injector energization time is calculated.

  In the gas injection mode, the 2nd-ECU 4 generates a gas pulse signal whose pulse width is set to the gas injector energization time and outputs the gas pulse signal to the gas injector 26 with the shut-off valve 23 opened. Thus, a required amount of gas fuel is injected from the gas injector 26 according to the engine operating state.

  Here, as already described, since the minimum flow rate injection capability of the gas injector 26 is lower than that of the gasoline injector 13, the gas injector energization time is calculated from the gasoline injector energization time as described above. If the energization time is shorter than the minimum flow rate guarantee time of the gas injector 26, the gas fuel may not be injected from the gas injector 26 and the engine may be misfired.

  As a conventional technique for avoiding this, there is known a technique for performing injection fuel switching control based on a comparison determination result between the gas injector energization time and one threshold value. However, the gas injector energization time exceeds the threshold value. Under such operating conditions that fluctuate greatly, gas operation and gasoline operation are frequently switched, and combustion in the cylinder may not be stable, which may result in unstable engine operation.

  In contrast to such a conventional technique, the 2nd-ECU 4 in the present embodiment performs the injection fuel switching control based on the comparison determination result between the threshold having hysteresis and the gas injector energization time in the gas injection mode. It avoids stable engine operation. Hereinafter, the injected fuel switching control that the 2nd-ECU 4 performs in the gas injection mode will be specifically described.

  2 and 3 are flowcharts showing the injected fuel switching control performed by the 2nd-ECU 4 in the gas injection mode. The 2nd-ECU 4 repeatedly performs a series of processes (processes from START to EXIT) shown in FIGS. 2 and 3 at a constant period in the gas injection mode. The 2nd-ECU 4 can always read the latest gas injector energization time by overwriting and saving the gas injector energization time calculated every time a gasoline pulse signal is input from the 1st-ECU 3 in the internal memory. .

  As shown in FIG. 2, the 2nd-ECU 4 first determines whether or not the minimum flow rate determination start flag FLG is set to “1” as a process of step S <b> 1. If “No”, the process proceeds to step S <b> 2. On the other hand, if "Yes", the process proceeds to step S6. Note that the minimum flow rate determination start flag FLG is set to “0” as a default value.

  If “No” in step S1, the 2nd-ECU 4 determines whether or not the latest gas injector energization time TG stored in the internal memory as the process of step S2 has exceeded the low threshold value TG_Lo, which is a threshold value having a hysteresis Thys. If “No”, the process proceeds to step S3, whereas if “Yes”, the process proceeds to EXIT. Here, the low threshold value TG_Lo is set to a longer time with a margin than the minimum flow rate guarantee time TG_min of the gas injector 26 (see FIG. 4).

  The 2nd-ECU 4 starts measuring the first time T1 (timer count) as the process of step S3 when “No” is determined in step S2 (that is, when the gas injector energization time TG is equal to or lower than the low-side threshold TG_Lo). At the same time, the timing of the second time T2 is started as the process of step S4. Here, the second time T2 is set longer than the first time T1 (see FIG. 4). Then, the 2nd-ECU 4 sets the minimum flow rate determination start flag FLG to “1” as the process of step S5, and then proceeds to EXIT.

  On the other hand, the 2nd-ECU 4 sends a gas pulse signal to the current gas injector 26 as a process of step S6 when “Yes” is determined in step S1 (that is, when the minimum flow rate determination start flag FLG is set to “1”). It is determined whether the fuel is being output, that is, whether or not fuel injection is currently being performed by the gas injector 26. If “Yes”, the process proceeds to step S7 in FIG. 3, whereas if “No”, the process proceeds to step S18. Migrate to

  As shown in FIG. 3, in the case of “Yes” in step S6 (that is, when fuel injection is currently being performed by the gas injector 26), the 2nd-ECU 4 determines that the current mode is the gasoline injection mode as the process of step S7. In the case of “No”, the process proceeds to step S8, whereas in the case of “Yes”, the process proceeds to step S39.

  If “No” is determined in step S7 (that is, if the current mode is the gas injection mode), the 2nd-ECU 4 determines whether or not the current fuel cut is in progress as a process in step S8. In step S9, the process proceeds to step S15. On the other hand, in the case of “Yes”, the process proceeds to step S15. Here, if the fuel cut is in progress, the output of the gasoline pulse signal from the 1st-ECU 3 is stopped. Therefore, the 2nd-ECU 4 determines whether or not the fuel cut is currently in progress from the input state of the gasoline pulse signal.

  If “No” is determined in step S8 (that is, if the fuel cut is not currently being performed), the 2nd-ECU 4 determines whether or not the time measurement of the first time T1 has ended (timer count has ended) as the processing of step S9. If "No", the process proceeds to step S10, whereas if "Yes", the process proceeds to step S12.

  When “No” is determined in step S9 (that is, when the time measurement of the first time T1 has not ended), the 2nd-ECU 4 determines the latest gas injector energization time TG stored in the internal memory as the process of step S10. Determines whether or not the threshold value has exceeded the high threshold value TG_Hi having a hysteresis Thys. If “Yes”, the process proceeds to step S11. If “No”, the process proceeds to EXIT. Here, the high side threshold value TG_Hi is set to a value obtained by adding hysteresis Thys to the low side threshold value TG_Lo (see FIG. 4).

  When “Yes” is determined in Step S10 (that is, when the gas injector energization time TG exceeds the high-side threshold value TG_Hi), the 2nd-ECU 4 resets the minimum flow rate determination start flag FLG to “0” as a process in Step S11. After that, move to EXIT.

  On the other hand, the 2nd-ECU 4 determines that the latest gas injector energization time TG stored in the internal memory as the process of step S12 when “Yes” is determined in step S9 (that is, when the time measurement of the first time T1 is completed). Is determined to exceed the high threshold TG_Hi. If “Yes”, the process proceeds to step S13, whereas if “No”, the process proceeds to step S14.

  When “Yes” is determined in step S12 (that is, when the gas injector energization time TG exceeds the high-side threshold value TG_Hi), the 2nd-ECU 4 resets the minimum flow rate determination start flag FLG to “0” as a process in step S13. After that, move to EXIT.

  In addition, when “No” is determined in Step S12 (that is, when the gas injector energization time TG is equal to or lower than the high-side threshold value TG_Hi), the 2nd-ECU 4 stops the output of the gas pulse signal as the process of Step S14, and the gasoline injector 13 After switching to the output of the gasoline pulse signal to (switching to fuel injection by the gasoline injector 13), the routine proceeds to EXIT.

  In addition, when “Yes” is determined in Step S8 (that is, when the fuel cut is currently being performed), the 2nd-ECU 4 forcibly ends the time measurement of the first time T1 as a process of Step S15 (resets the timer count). At the same time, the time measurement of the second time T2 is also forcibly terminated as a process of step S16. Then, after the process of step S16, the 2nd-ECU 4 resets the minimum flow rate determination start flag FLG to “0” as the process of step S17, and then proceeds to EXIT.

  Returning to FIG. 2, in the case of “No” in step S <b> 6 (that is, when fuel injection by the gasoline injector 13 is currently being performed), the 2nd-ECU 4 determines whether or not the current mode is the gasoline injection mode as a process of step S <b> 18. If “No”, the process proceeds to step S19. If “Yes”, the process proceeds to step S32.

  In the case of “No” in step S18 (that is, in the case where the current mode is the gas injection mode), the 2nd-ECU 4 determines whether or not the current fuel cut is in progress as a process of step S19. However, if “Yes”, the process proceeds to step S28.

  If “No” is determined in step S19 (that is, if the fuel cut is not currently being performed), the 2nd-ECU 4 determines whether or not the time measurement of the second time T2 has ended (timer count has ended) as the processing of step S20. If “No”, the process proceeds to step S 21, while if “Yes”, the process proceeds to step S 24.

  If “No” is determined in step S20 (that is, if the time measurement of the second time T2 has not ended), the 2nd-ECU 4 is the latest gas injector energization time TG stored in the internal memory as the process of step S21. Is determined to exceed the high threshold TG_Hi. If “Yes”, the process proceeds to step S22, whereas if “No”, the process proceeds to EXIT.

  When “Yes” is determined in step S21 (that is, when the gas injector energization time TG exceeds the high-side threshold value TG_Hi), the 2nd-ECU 4 stops the output of the gasoline pulse signal as the process of step S22, and the gas injector 26 Is switched to the output of the gas pulse signal to (the fuel injection by the gas injector 26 is switched). Then, the 2nd-ECU 4 resets the minimum flow rate determination start flag FLG to “0” as the process of step S23, and then proceeds to EXIT.

  On the other hand, the 2nd-ECU 4 determines that the latest gas injector energization time TG stored in the internal memory as the process of step S24 when “Yes” is determined in step S20 (that is, when the time measurement of the second time T2 is completed). Is determined to exceed the high-side threshold TG_Hi. If “Yes”, the process proceeds to step S25, whereas if “No”, the process proceeds to step S26.

  In the case of “Yes” in step S24 (that is, when the gas injector energization time TG exceeds the high-side threshold value TG_Hi), the 2nd-ECU 4 stops the output of the gasoline pulse signal as the process of step S25, and the gas injector 26 After switching to the output of the gas pulse signal to (switching to fuel injection by the gas injector 26), the routine proceeds to EXIT.

  In addition, when “No” is determined in Step S24 (that is, when the gas injector energization time TG is equal to or less than the high-side threshold value TG_Hi), the 2nd-ECU 4 closes the shutoff valve 23 as a process of Step S26, After the transition from the gas injection mode to the gasoline injection mode as the processing of S27, the routine proceeds to EXIT.

  Further, in the case of “Yes” in the above step S19 (that is, when the fuel cut is currently being performed), the 2nd-ECU 4 forcibly terminates the time measurement of the first time T1 as a process of step S28 and as a process of step S29. The time measurement at the second time T2 is also forcibly terminated. Then, the 2nd-ECU 4 closes the shut-off valve 23 as a process of step S30, and after shifting from the gas injection mode to the gasoline injection mode as a process of step S31, shifts to EXIT.

  On the other hand, if “Yes” is determined in Step S18 (that is, if the current mode is the gasoline injection mode), the 2nd-ECU 4 determines whether or not the current fuel cut is in progress as a process of Step S32, and “No”. In the case of, the process proceeds to step S33, whereas in the case of “Yes”, the process proceeds to step S38.

  If “No” is determined in step S32 (that is, if fuel cut is not currently being performed), the 2nd-ECU 4 sets the mode return threshold value TG_MR as the latest gas injector energization time TG stored in the internal memory as the process of step S33. If “Yes”, the process proceeds to step S34. If “No”, the process proceeds to EXIT. Note that the mode return threshold TG_MR is set longer (higher) than the high threshold TG_Hi (see FIG. 4).

  If “Yes” in step S33 (that is, if the gas injector energization time TG exceeds the mode return threshold TG_MR), the 2nd-ECU 4 starts fuel return from gasoline to gas as the process of step S34, and continues. As a process of step S35, time measurement of the third time T3 is started.

  Then, the 2nd-ECU 4 opens the shut-off valve 23 as the process of step S36, stops the output of the gasoline pulse signal as the process of the subsequent step S37, and switches to the output of the gas pulse signal to the gas injector 26 (the gas injector 26). Switch to FUJI fuel injection) and then proceed to EXIT.

  Further, when “Yes” is determined in Step S32 (that is, when the fuel cut is currently being performed), the 2nd-ECU 4 continues the gasoline injection mode and proceeds to EXIT as the process of Step S38.

  On the other hand, in the case of “Yes” in Step S7 of FIG. 3 (that is, when the current mode is the gasoline injection mode), the 2nd-ECU 4 determines whether or not the current fuel cut is in progress as a process of Step S39. If “No”, the process proceeds to step S40, whereas if “Yes”, the process proceeds to step S49.

  In the case of “No” in step S39 (that is, when the fuel cut is not currently being performed), the 2nd-ECU 4 determines whether or not the time measurement of the third time T3 has ended as a process of step S40. In the case, the process proceeds to step S41, whereas in the case of “Yes”, the process proceeds to step S44.

  If “No” is determined in step S40 (that is, if the time measurement of the third time T3 is not completed), the 2nd-ECU 4 is the latest gas injector energization time TG stored in the internal memory as the process of step S41. Is determined to exceed the high-side threshold TG_Hi. If “Yes”, the process proceeds to EXIT, while if “No”, the process proceeds to step S42.

  If “No” in step S41 (that is, if the gas injector energization time TG is equal to or lower than the high threshold value TG_Hi), the 2nd-ECU 4 stops the output of the gas pulse signal to the gasoline injector 13 as a process of step S42. Switch to gasoline pulse signal output (switch to fuel injection by gasoline injector 13). Then, the 2nd-ECU 4 closes the shut-off valve 23 as a process of step S43, and then proceeds to EXIT.

  In addition, when “Yes” is determined in Step S40 (that is, when the time measurement of the third time T3 is completed), the 2nd-ECU 4 determines the latest gas injector energization time TG stored in the internal memory as the process of Step S44. Is determined to exceed the high-side threshold TG_Hi. If “Yes”, the process proceeds to step S45. If “No”, the process proceeds to step S47.

  In the case of “Yes” in step S44 (that is, when the gas injector energization time TG exceeds the high-side threshold value TG_Hi), the 2nd-ECU 4 returns from the gasoline injection mode to the gas injection mode as the process of step S45. In the subsequent step S46, the minimum flow rate determination start flag FLG is reset to “0” and the process proceeds to EXIT.

  In addition, when “No” is determined in step S44 (that is, when the gas injector energization time TG is equal to or lower than the high-side threshold value TG_Hi), the 2nd-ECU 4 stops the output of the gas pulse signal as the process of step S47 and the gasoline injector 13 Is switched to the output of the gasoline pulse signal to (the fuel injection by the gasoline injector 13 is switched). Then, the 2nd-ECU 4 closes the shutoff valve 23 as a process of step S48, and then proceeds to EXIT.

  In addition, when “Yes” is determined in Step S39 (that is, when the fuel cut is currently being performed), the 2nd-ECU 4 forcibly terminates the time measurement of the third time T3 as a process of Step S49, and then performs a process of Step S50. After returning from the gasoline injection mode to the gas injection mode, the routine proceeds to EXIT.

In the following, based on the above-described injected fuel switching control, a process performed by the 2nd-ECU 4 with respect to a temporal change in the gas injector energization time TG will be specifically described.
As shown in FIG. 4, in the gas injection mode, the 2nd-ECU 4 measures the first time T1 and the second time T2 after the gas injector energization time TG becomes equal to or less than the low-side threshold value TG_Lo having a hysteresis Thys. (See time t1 in FIG. 4).

  Then, the 2nd-ECU 4 stops the output of the gas pulse signal and the gasoline pulse to the gasoline injector 13 when the gas injector energization time TG does not exceed the threshold high-side threshold TG_Hi having the hysteresis Thys within the first time T1. The output is switched to the signal output (fuel injection by the gasoline injector 13) (see time t2 in FIG. 4).

  The 2nd-ECU 4 continues fuel injection by the gas injector 26 when the gas injector energization time TG exceeds the high-side threshold value TG_Hi within the first time T1, or when a fuel cut occurs within the first time T1. (That is, the gas injection mode is continued).

  Then, after switching to fuel injection by the gasoline injector 13, the 2nd-ECU 4 closes the shut-off valve 23 when the gas injector energization time TG does not exceed the high side threshold value TG_Hi within the second time T <b> 2, and gasoline injection. The mode is changed (see time t3 in FIG. 4).

  Note that the 2nd-ECU 4 switches to the fuel injection by the gas injector 26 again when the gas injector energization time TG exceeds the high-side threshold value TG_Hi within the second time T2 after switching to the fuel injection by the gasoline injector 13. Continue injection mode. Further, after switching to fuel injection by the gasoline injector 13, the 2nd-ECU 4 closes the shut-off valve 23 and shifts to the gasoline injection mode when a fuel cut occurs within the second time T2.

  When the gas injector energizing time TG exceeds the mode return threshold TG_MR after the transition to the gasoline injection mode, the 2nd-ECU 4 opens the shutoff valve 23 and stops the output of the gasoline pulse signal to stop the gas injector. It switches to the output of the gas pulse signal to 26 (fuel injection by the gas injector 26) (see time t4 in FIG. 4).

  Note that the 2nd-ECU 4 continues the gasoline injection mode when the gas injector energization time TG does not exceed the mode return threshold TG_MR after the transition to the gasoline injection mode or when a fuel cut occurs.

  Then, the 2nd-ECU 4 starts measuring the third time T3 after the gas injector energization time TG exceeds the mode return threshold value TG_MR, and if the gas injector energization time TG falls below the high side threshold value TG_Hi within the third time T3. If not, the gas injection mode is restored (see time t5 in FIG. 4).

  The 2nd-ECU 4 switches to fuel injection by the gasoline injector 13 when the gas injector energization time TG becomes equal to or lower than the high-side threshold TG_Hi within the third time T3, and closes the shut-off valve 23 to change the gasoline injection mode. continue. The 2nd-ECU 4 also shifts to the gas injection mode when a fuel cut occurs within the third time T3.

  According to the present embodiment as described above, in the gas injection mode, the injection fuel switching control is performed based on the comparison determination result between the threshold value having the hysteresis Thys (low side threshold value TG_Lo, high side threshold value TG_Hi) and the gas injector energization time TG. As a result, the switching frequency between the gas operation and the gasoline operation is suppressed even under an operating condition in which the gas injector energization time TG varies greatly in a region close to the minimum flow rate guarantee time TG_min of the gas injector 26. Unstable engine operation can be avoided.

  In addition, this invention is not limited to the said embodiment, Of course, you may change embodiment in the range which does not deviate from the meaning of this invention. For example, the present invention can be applied to a bi-fuel system that selectively switches a gaseous fuel other than CNG and a liquid fuel other than gasoline and supplies the fuel to a single engine.

  A ... fuel injection system, 1 ... liquid fuel supply system, 2 ... gaseous fuel supply system, 3 ... 1st-ECU (first control device), 4 ... 2nd-ECU (second control device), 5 ... fuel changeover switch, 13 ... Gasoline injector (liquid fuel injection valve), 26 ... Gas injector (gaseous fuel injection valve), 23 ... Shut-off valve

Claims (3)

A first control device that outputs a first pulse signal having a pulse width set to a liquid fuel injection valve energization time;
A gaseous fuel injection valve energization time is calculated based on the first pulse signal input from the first control device, and a pulse width is set to the gaseous fuel injection valve energization time in the gaseous fuel injection mode. A second control device that outputs the first pulse signal to the liquid fuel injection valve during the liquid fuel injection mode,
In the gaseous fuel injection mode, the second control device starts measuring the first time after the gas fuel injection valve energization time becomes equal to or lower than a low threshold value having a hysteresis, and within the first time, When the gas fuel injection valve energization time does not exceed the high threshold value having the hysteresis, the output of the second pulse signal is stopped and switched to the output of the first pulse signal to the liquid fuel injection valve. A fuel injection system. The second control device starts measuring the first time and a second time longer than the low-side threshold after the gaseous fuel injection valve energizing time is less than or equal to the low-side threshold, and the gaseous fuel is within the first time. After switching to the output of the first pulse signal to the liquid fuel injection valve without exceeding the high-side threshold without exceeding the high-side threshold, the gaseous fuel injection valve energizing time within the second time is the high-side threshold. 2. The fuel injection system according to claim 1, wherein when the pressure does not exceed, the shutoff valve inserted in the gas fuel delivery path leading to the gas fuel injection valve is closed . After closing the shut-off valve , the second control device opens the shut-off valve when the gas fuel injection valve energization time exceeds a mode return threshold set higher than the high-side threshold. The fuel injection system according to claim 2, wherein the output of the first pulse signal is stopped and the output is switched to the output of the second pulse signal to the gaseous fuel injection valve.

Images