Fuel system, engine, and engine control method

Abstract

To realize a fuel system capable of suppressing excessive rise in fuel pressure after an engine stops, at low cost.SOLUTION: When an instruction to stop an engine 1 is given by an ignition switch 80, an ECU 70 closes a shutoff valve 54 provided on an outlet side of a cylinder 52. Then, when a predetermined condition is satisfied, the ECU 70 continues operation of the engine 1 for a predetermined period after the instruction to stop the engine 1 is given, and then stops the engine 1. The predetermined condition includes a first condition that an intake air temperature is lower than a threshold value T1 when the engine 1 is started, and a second condition that an engine water temperature is lower than a threshold value T2 when the instruction to stop the engine 1 is given.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a fuel system, an engine, and a method for controlling an engine, and particularly to a fuel system for an engine using liquefied gas as fuel, an engine including the same, and a method for controlling the engine.

Background Art

[0002] Japanese Utility Model Publication No. 62-180644 (Patent Document 1) describes a fuel injection control device for an engine using LPG (Liquefied Petroleum Gas) as fuel. In this fuel injection control device, when the ignition switch is turned off, a shut-off valve that blocks the fuel circulation path to the fuel injection valve operates. Then, the fuel pressure in the blocked circulation path is detected, and fuel injection and ignition continue until the detected fuel pressure drops below a predetermined value. Thereby, unburned LPG fuel is eliminated from the fuel circulation path, and an undesirable phenomenon in which LPG fuel remains in the circulation path after the engine stops can be avoided (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The fuel injection control device described in Patent Document 1 requires a fuel pressure sensor for detecting the fuel pressure in the fuel pipe, and cannot be applied to a fuel system without a fuel pressure sensor. Further, even if fuel remains in the fuel pipe after the engine stops, in a highly airtight fuel system (for example, a system that eliminates a mixer and uses only an injector), the retention of fuel itself is not a problem. Rather, an excessive pressure increase due to vaporization of liquefied fuel mixed in the fuel pipe (hose, etc.) through which the originally vaporized fuel flows after the engine stops can be a problem.

[0005] To address these issues, the aforementioned fuel injection control device continues fuel injection and ignition until the fuel pressure drops below a predetermined value, regardless of whether there is an excessive rise in fuel pressure. This means that fuel injection and ignition may continue unnecessarily after the engine has stopped. Another option is to increase the pressure resistance of the fuel system against excessive fuel pressure increases, but improving the pressure resistance of the equipment would increase costs.

[0006] This disclosure was made to solve the aforementioned problem, and its purpose is to realize a low-cost fuel system capable of suppressing excessive fuel pressure increases after engine shutdown. [Means for solving the problem]

[0007] The fuel system of this disclosure is a fuel system for an engine that uses liquefied gas as fuel, comprising: a cylinder for storing liquefied gas; a shut-off valve provided on the outlet side of the cylinder; a regulator for reducing the pressure of the fuel supplied from the cylinder; an injection valve for supplying the fuel that has passed through the regulator to the engine; an input device for instructing the starting and stopping of the engine; and a control device for controlling the engine and the fuel system. The control device closes the shut-off valve when the input device instructs the engine to stop, and stops the engine after continuing to operate for a predetermined period of time after being instructed to stop the engine, provided that predetermined conditions are met. The predetermined conditions include a first condition in which the temperature of the air drawn into the engine at engine startup is lower than a first threshold, and a second condition in which the engine water temperature is lower than a second threshold when the engine is instructed to stop.

[0008] Furthermore, the control method of the present disclosure is a control method for an engine that uses liquefied gas as fuel, and includes the steps of: closing a shut-off valve provided on the outlet side of a cylinder that stores liquefied gas when the engine is instructed to stop; continuing to operate the engine for a predetermined period of time after the engine is instructed to stop, when predetermined conditions are met; and stopping the engine after the predetermined period has elapsed. The predetermined conditions include a first condition in which the temperature of the air drawn into the engine at the time of engine startup is lower than a first threshold, and a second condition in which the engine water temperature is lower than a second threshold when the engine is instructed to stop.

[0009] In the fuel system of an engine that uses liquefied gas as fuel, the fuel is vaporized by the regulator and supplied to the injectors. However, at low temperatures, even if the fuel pressure is reduced by the regulator, the fuel may not vaporize sufficiently, and some of the fuel may flow downstream of the regulator in liquid form. Nevertheless, once the engine has warmed up and the engine water temperature has risen, the heat promotes the vaporization of the fuel, so liquid fuel does not flow downstream of the regulator.

[0010] However, when the engine is started at low temperatures and has not yet warmed up, some of the fuel flows downstream of the regulator in liquid form. If the engine stops under these conditions, liquid fuel accumulates in the fuel line downstream of the regulator. Then, as the temperature rises, this accumulated liquid fuel vaporizes, causing an excessive increase in fuel pressure in the fuel line downstream of the regulator.

[0011] Therefore, in the fuel system and control method of this disclosure, when a first condition (low temperature condition) is met, where the temperature of the air drawn into the engine at engine startup is lower than a first threshold, and a second condition (incomplete warm-up condition) is met, where the engine water temperature is lower than a second threshold when the engine is instructed to stop, the engine is stopped after continuing to operate for a predetermined period of time after the engine is instructed to stop. This allows residual fuel in the piping to be consumed, and prevents an excessive rise in fuel pressure. When at least one of the first condition (low temperature condition) and the second condition (incomplete warm-up condition) is not met, no fuel remains in liquid form in the fuel piping after the engine is stopped, and the engine is stopped without continuing to operate for a predetermined period of time after the engine is instructed to stop.

[0012] Thus, according to the fuel system and control method of this disclosure, it is possible to suppress an excessive rise in fuel pressure after the engine has stopped without using a fuel pressure sensor. Furthermore, there is no need to increase the pressure resistance of the fuel system to prepare for an excessive rise in fuel pressure.

[0013] The predetermined period may be set to be longer the lower the engine water temperature.

[0014] The lower the engine water temperature, the greater the amount of fuel that remains in the piping as liquid after the engine stops. By setting a predetermined period as described above, the fuel remaining in the piping can be consumed appropriately.

[0015] The predetermined period may be the period until the engine water temperature rises above the third threshold. Furthermore, the third threshold may be the same value as the second threshold.

[0016] By setting a predetermined period as described above, the amount of fuel remaining in the piping as liquid after the engine is stopped can be reduced. Therefore, an excessive rise in fuel pressure after the engine is stopped can be suppressed. [Effects of the Invention]

[0017] According to the fuel system, engine, and control method of the present disclosure, a fuel system capable of suppressing excessive fuel pressure rise after engine stop can be realized at low cost.

Brief Description of the Drawings

[0018] [Figure 1] It is an overall configuration diagram of an engine to which a fuel system according to an embodiment is applied. [Figure 2] It is a configuration diagram of the ECU shown in FIG. 1. [Figure 3] It is a flowchart for explaining the flow of processing executed by the ECU. [Figure 4] It is a diagram for explaining a predetermined period in step S50 of FIG. 3. [Figure 5] It is a flowchart for explaining the flow of processing executed by the ECU in a modified example.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their descriptions will not be repeated.

[0020] FIG. 1 is an overall configuration diagram of an engine to which a fuel system according to an embodiment of the present disclosure is applied. In FIG. 1, the engine 1 is an engine that uses liquefied gas as fuel. Hereinafter, the engine 1 will be a LPG engine that uses LPG as fuel. Note that the engine 1 is not limited to a LPG engine, and may be an engine that uses other liquefied gases as fuel.

[0021] Referring to FIG. 1, the engine 1 includes an engine body 10, an intake pipe 12, an air cleaner 14, a throttle device 16, an injector 18, a spark plug 20, an exhaust pipe 22, and a catalyst device 24.

[0022] The engine body 10 includes multiple cylinders. In this example, the engine body 10 is assumed to include four cylinders, but the number of cylinders is not limited to this. The intake pipe 12 is connected to an intake manifold (not shown) provided on the intake side of the engine body 10.

[0023] The air cleaner 14 is installed in the intake manifold 12 and cleans the intake air by adsorbing impurities contained in the air drawn in from the intake port. The throttle device 16 is installed downstream of the air cleaner 14 in the intake manifold 12 and adjusts the intake airflow rate by driving the throttle valve based on a control signal from the ECU 70.

[0024] Each injector 18 is provided for each cylinder; in this example, there are four injectors for four cylinders. The injectors 18 are supplied with fuel by the fuel system described later. The injectors 18 are driven by control signals from the ECU 70 and inject fuel into the intake port of each cylinder.

[0025] A spark plug 20 is also provided for each cylinder; in this example, there are four spark plugs for the four cylinders. The spark plug 20 is driven by a control signal from the ECU 70 and ignites the mixture of intake air and fuel inside the cylinder. As a result, the mixture burns inside the cylinder, generating combustion energy.

[0026] The exhaust pipe 22 is connected to an exhaust manifold (not shown) located on the exhaust side of the engine body 10. The catalytic converter 24 is installed in the exhaust pipe 22 and purifies the exhaust gas discharged from the engine body 10 using a catalyst.

[0027] Engine 1 further includes an intake air temperature sensor 26, an intake pressure sensor 28, and O2 sensors 30 and 32. The intake air temperature sensor 26 is installed in the intake manifold 12 and detects the temperature of the air drawn into the intake manifold 12 (hereinafter also referred to as "intake air temperature"). The intake air temperature sensor 26 outputs the detected intake air temperature value to the ECU 70.

[0028] The intake pressure sensor 28 is located downstream of the throttle device 16 in the intake manifold 12. The intake pressure sensor 28 detects the pressure of the intake air in the intake manifold (hereinafter also referred to as "intake pressure") downstream of the throttle device 16 and outputs the detected value to the ECU 70.

[0029] O2 sensor 30 is installed in the exhaust pipe 22 upstream of the catalytic converter 24. O2 sensor 30 detects the oxygen concentration in the exhaust gas before it passes through the catalytic converter 24 and outputs the detected value to the ECU 70. O2 sensor 32 is installed in the exhaust pipe 22 downstream of the catalytic converter 24. O2 sensor 32 detects the oxygen concentration in the exhaust gas after it has passed through the catalytic converter 24 and outputs the detected value to the ECU 70. Note that an A / F sensor (air-fuel ratio sensor) may be used instead of O2 sensors 30 and 32.

[0030] Engine 1 further includes a cylinder 52, a shut-off valve 54, a regulator 56, a gas phase filter 58, fuel lines 60, 62, fuel pressure sensors 64, 66, and a fuel temperature sensor 68. The cylinder 52 and the regulator 56 are connected by fuel line 60, and the regulator 56 and the injector 18 are connected by fuel line 62. Fuel lines 60 and 62 are lines for supplying fuel from the cylinder 52 to the injector 18.

[0031] Cylinder 52 is a high-pressure resistant cylinder for storing liquefied LPG. The pressure inside cylinder 52 is, for example, about 1.5 MPa. The shut-off valve 54 is installed in the fuel piping 60 and is driven by a control signal from the ECU 70. When the shut-off valve 54 is closed, it shuts off the fuel supply from cylinder 52 to regulator 56.

[0032] The regulator 56 is a pressure regulating device for reducing the pressure of liquefied, high-pressure LPG supplied from the cylinder 52 to atmospheric pressure. The liquefied, high-pressure LPG supplied from the cylinder 52 through the fuel piping 60 is reduced in pressure by the regulator 56, essentially vaporizing, and then supplied to the injector 18 through the fuel piping 62.

[0033] Therefore, the fuel piping 60 and the connections between the fuel piping 60 and the cylinder 52 and the regulator 56 are designed to withstand high pressure because high-pressure LPG flows through the fuel piping 60. The fuel piping 60 is made of, for example, a metal pipe. On the other hand, the fuel piping 62 and the connections between the fuel piping 62 and the regulator 56 and the injector 18 are not designed to withstand high pressure like the upstream side of the regulator 56. The fuel piping 62 is made of, for example, a hose.

[0034] The gas phase filter 58 is installed in the fuel piping 62 and removes impurities contained in the fuel (LPG) that is vaporized by the regulator 56 and supplied to the injector 18.

[0035] The fuel pressure sensor 64 is installed downstream of the shut-off valve 54 in the fuel line 60 and detects the fuel pressure in the fuel line 60 (hereinafter, fuel pressure is also referred to as "fuel pressure"). The fuel pressure sensor 64 outputs the detected value of the fuel pressure in the fuel line 60 to the ECU 70.

[0036] The fuel pressure sensor 66 and the fuel temperature sensor 68 are installed in the fuel piping 62. The fuel pressure sensor 66 detects the fuel pressure in the fuel piping 62 and outputs the detected value to the ECU 70. The fuel temperature sensor 68 detects the fuel temperature in the fuel piping 62 and outputs the detected value to the ECU 70.

[0037] In the fuel pressure system of this disclosure, the fuel pressure sensors 64, 66 and the fuel temperature sensor 68 are not essential components, and the fuel pressure system of this disclosure is also applicable to fuel pressure systems that do not have these sensors.

[0038] Engine 1 further includes an ECU (Electronic Control Unit) 70, an ignition switch 80, and a water temperature sensor 82. The ignition switch 80 is operated by the user of engine 1; when the ignition switch 80 is turned on, engine 1 starts, and when the ignition switch 80 is turned off, engine 1 stops. This ignition switch 80 corresponds to an input device that instructs the starting and stopping of engine 1.

[0039] The water temperature sensor 82 detects the temperature of the coolant in the engine 1 (hereinafter also referred to as "engine water temperature"). For example, the water temperature sensor 82 detects the engine water temperature in the coolant passage provided within the engine body 10. The water temperature sensor 82 outputs the detected engine water temperature to the ECU 70.

[0040] The ECU70 acquires the detection values ​​from the various sensors mentioned above and uses these acquired detection values ​​to perform various controls on the engine 1. The configuration of the ECU70 and the controls performed by the ECU70 will be explained in detail later.

[0041] In an LPG engine, liquefied LPG is stored in a cylinder, and the high-pressure liquefied LPG supplied from the cylinder is reduced in pressure and vaporized by a regulator before being supplied to the engine. However, at low temperatures (e.g., below 0°C) and when the engine is not warmed up, even if the fuel pressure is reduced by the regulator, the fuel may not vaporize sufficiently, and some of the fuel remains liquefied downstream of the regulator. When this liquefied fuel vaporizes, an excessive increase in fuel pressure exceeding the pressure resistance of the fuel piping can occur downstream of the regulator.

[0042] When the engine is running, fuel is injected from the injectors, so the excessive fuel pressure increase described above does not occur. The excessive fuel pressure increase described above can occur after the engine is stopped. However, once the engine has warmed up and the engine water temperature has risen, fuel vaporization is promoted, and the fuel is almost completely vaporized in the regulator, so the excessive fuel pressure increase described above does not occur after the engine is stopped.

[0043] In other words, if the engine is started at a low temperature and then stopped before it has fully warmed up, some of the fuel remains in liquid form downstream of the regulator. As the temperature rises, this remaining liquid fuel vaporizes, causing an excessive increase in fuel pressure in the fuel line downstream of the regulator.

[0044] Therefore, in this embodiment, when the conditions for an excessive fuel pressure increase as described above are met, the engine 1 is stopped after it has been instructed to stop for a predetermined period of time. This consumes the residual fuel in the fuel pipe 62 downstream of the regulator, thereby suppressing an excessive fuel pressure increase. The above conditions include a first condition (low temperature condition) in which the intake air temperature is lower than a first threshold (e.g., 0°C) when the engine 1 is started, and a second condition (incomplete warm-up condition) in which the engine water temperature is lower than a second threshold (e.g., 30°C) when the engine 1 is instructed to stop.

[0045] If at least one of the first condition (low temperature condition) and the second condition (incomplete warm-up condition) is not met, no portion of the fuel will remain in liquid form in the fuel pipe 62 after the engine is stopped, and the engine 1 will stop without continuing to operate for a predetermined period of time after being instructed to stop the engine 1.

[0046] According to this embodiment, it is possible to address the excessive fuel pressure rise that may occur in the fuel line 62 after the engine has stopped, without increasing the pressure resistance of the fuel system. Furthermore, in inexpensive engines, a fuel pressure sensor may not be provided, but according to this embodiment, it is possible to suppress the excessive fuel pressure rise after the engine has stopped without using a fuel pressure sensor.

[0047] Figure 2 is a diagram of the configuration of the ECU 70 shown in Figure 1. Referring to Figure 2, the ECU 70 consists of a CPU (Central Processing Unit) 72, RAM (Random Access Memory) 74, and ROM (Read Only Memory) 76. The ROM 76 stores processing programs executed by the CPU 72, and the CPU 72 loads the processing programs stored in the ROM 76 into the RAM 74 and executes them.

[0048] The ECU 70 receives the detection values ​​from the intake air temperature sensor 26 and the water temperature sensor 82. In addition, the engine 1 is equipped with various other sensors as described above, and receives detection values ​​from these sensors as well (not shown). The ECU 70 also receives a signal from the ignition switch 80 indicating its state (on / off).

[0049] Then, when the ignition switch 80 is turned on, the ECU 70 opens the shut-off valve 54 on the outlet side of the cylinder 52 and drives the injectors 18 and spark plugs 20 based on the values ​​detected by various sensors (engine 1 running state).

[0050] Furthermore, when the ignition switch 80 is turned off, the ECU 70 closes the shut-off valve 54. The ECU 70 then determines whether the first condition (low temperature condition) and the second condition (incomplete warm-up condition) described above are met. If both conditions are met, the engine 1 continues to operate until a predetermined period has elapsed (the injectors 18 and spark plugs 20 continue to drive). On the other hand, if at least one of the first and second conditions is not met, the engine 1 is stopped immediately (the injectors 18 and spark plugs 20 are stopped).

[0051] The predetermined period for continuing to operate engine 1 when both the first and second conditions are met is set according to the engine water temperature when the engine is stopped. In this embodiment, the lower the engine water temperature, the longer the predetermined period is set. The lower the engine water temperature, the greater the amount of liquefied fuel remaining in the fuel pipe 62, and the longer it takes for that remaining fuel to be consumed. Therefore, the lower the engine water temperature, the longer the period for continuing to operate engine 1 is set.

[0052] Figure 3 is a flowchart illustrating the flow of processes performed by the ECU 70. The series of processes shown in this flowchart begin when the ignition switch 80 is turned on. Referring to Figure 3, when the ignition switch 80 is turned on, the ECU 70 starts the engine 1 (step S10). Specifically, the ECU 70 opens the shut-off valve 54 on the outlet side of the cylinder 52 and drives the injectors 18 and spark plugs 20 to achieve the desired operating state. Furthermore, the ECU 70 obtains the intake air temperature at the time of engine startup from the intake air temperature sensor 26 and stores the obtained intake air temperature (step S15).

[0053] Next, the ECU 70 determines whether the ignition switch 80 is turned off or not (step S20). If it is determined that the ignition switch 80 is turned off (YES in step S20), the ECU 70 closes the shut-off valve 54 (step S25). This stops the fuel supply from the cylinder 52. Furthermore, the ECU 70 obtains the engine water temperature from the water temperature sensor 82 (step S30).

[0054] Next, the ECU 70 determines whether the intake air temperature at engine startup, which was acquired and stored in step S15, is lower than the threshold T1 (step S35). This determination process corresponds to the low-temperature condition described above, and the threshold T1 is, for example, 0°C.

[0055] If, in step S35, it is determined that the intake air temperature at engine startup is lower than the threshold T1 (YES in step S35), the ECU 70 further determines whether the engine water temperature obtained in step S30 is lower than the threshold T2 (step S40). This determination process corresponds to the above-mentioned condition of incomplete warm-up, and the threshold T2 is, for example, 30°C.

[0056] If, in step S40, it is determined that the engine water temperature is lower than the threshold T2 (YES in step S40), the ECU 70 continues the operation of the engine 1 without stopping it (step S45). That is, the ECU 70 continues fuel injection from the injector 18 and ignition from the spark plug 20. Then, the ECU 70 determines whether a predetermined period of time has elapsed (step S50).

[0057] Figure 4 is a diagram illustrating the predetermined period in step S50. Referring to Figure 4, the horizontal axis represents the engine water temperature obtained in step S30 of Figure 3, and the vertical axis represents the predetermined period. As shown in the figure, in this embodiment, the predetermined period in step S50 of Figure 3 is set such that the lower the engine water temperature obtained in step S30, the longer the period during which the engine 1 continues to operate after the ignition switch 80 is turned off. This makes it possible to appropriately control the operating period of the engine 1 according to the amount of liquid fuel remaining in the fuel pipe 62.

[0058] The relationship between engine water temperature and a predetermined period is determined in advance through prior evaluation tests, mapped, and stored in ROM76.

[0059] Referring again to Figure 3, if the predetermined period elapses in step S50 (NO in step S50), the process returns to step S45, and the engine 1 continues to operate. Then, if it is determined in step S50 that the predetermined period has elapsed (YES in step S50), the ECU 70 stops the engine 1 (step S55). That is, the ECU 70 stops the fuel injection from the injector 18 and the ignition of the spark plug 20.

[0060] Furthermore, if it is determined in step S35 that the intake air temperature at engine startup is greater than or equal to threshold T1 (NO in step S35), or if it is determined in step S40 that the engine water temperature is greater than or equal to threshold T2 (NO in step S40), the ECU 70 proceeds to step S55 without executing the processes in steps S45 and S50, and stops engine 1. In other words, only if the low temperature condition at engine startup is met (YES in step S35) and the warm-up condition at engine shutdown is met (YES in step S40) will the engine 1 continue to operate for a predetermined period after the ignition switch 80 is turned off.

[0061] In the above, the order of processing in steps S10 and S15 does not matter. Similarly, the order of processing in steps S25 and S30, and the order of processing in steps 35 and S40, also does not matter.

[0062] As described above, in this embodiment, when the low temperature condition at engine start-up and the incomplete warm-up condition at engine stop operation are met, the engine 1 is stopped after the ignition switch 80 is turned off, after continuing to operate for a predetermined period of time. This consumes the liquefied fuel remaining in the fuel line 62 and suppresses the occurrence of an excessive rise in fuel pressure in the fuel line 62. When at least one of the low temperature condition and the incomplete warm-up condition is not met, no part of the fuel remains in liquid form in the fuel line 62 after the engine is stopped, so the engine 1 stops without continuing to operate for a predetermined period of time after being instructed to stop the engine 1.

[0063] Thus, according to this embodiment, it is possible to deal with an excessive increase in fuel pressure that may occur after the engine has stopped without increasing the pressure resistance of the fuel system. Furthermore, even in fuel systems that are not equipped with a fuel pressure sensor, it is possible to suppress an excessive increase in fuel pressure after the engine has stopped.

[0064] Furthermore, according to this embodiment, the lower the engine water temperature, the longer the period during which the engine 1 continues to operate after being instructed to stop, thereby allowing the fuel remaining in the fuel pipe 62 to be consumed appropriately.

[0065] [Differentiation] In the above embodiment, when low temperature conditions and incomplete warm-up conditions are met, the period (predetermined period) during which the engine 1 continues to operate after the ignition switch 80 is turned off is set according to the relationship shown in Figure 4. In this modified example, when low temperature conditions and incomplete warm-up conditions are met, the engine 1 continues to operate after the ignition switch 80 is turned off until the engine water temperature reaches a predetermined threshold.

[0066] Figure 5 is a flowchart illustrating the processing flow performed by the ECU 70 in this modified example. This flowchart corresponds to the flowchart in Figure 3 described in the above embodiment.

[0067] Referring to Figure 5, steps S110 to S145 and S155 are the same as steps S10 to S45 and S55 in the flowchart of Figure 3, respectively. In this flowchart, in step S140, it is determined that the engine water temperature obtained in step S130 is lower than the threshold T2 (YES in step S140), and after continuing to operate engine 1 (step S145), the ECU 70 obtains the detected engine water temperature value again from the water temperature sensor 82 (step S150).

[0068] Then, the ECU70 determines whether the engine coolant temperature obtained in step S150 is higher than the threshold T3 (step S152). If the engine coolant temperature is less than or equal to the threshold T3 (NO in step S152), the process returns to step S145 and the operation of engine 1 continues.

[0069] On the other hand, if it is determined in step S152 that the engine water temperature is higher than the threshold T3 (YES in step S152), the ECU 70 stops the engine 1 (step S155). That is, the ECU 70 stops fuel injection from the injector 18 and ignition from the spark plug 20.

[0070] The threshold T3 may be the same as or different from the threshold T2 in step S140. For example, the threshold T3 may be set to a temperature slightly higher than the threshold T2.

[0071] As described above, this modification allows for an appropriate operating period for engine 1 when low temperature conditions are met during engine startup and when warm-up conditions are not completed during engine shutdown. This is achieved by continuing to operate engine 1 until the engine water temperature reaches the threshold T3 after the ignition switch 80 is turned off.

[0072] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The technical scope provided herein is defined by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0073] 1 Engine, 10 Engine block, 12 Intake pipe, 14 Air cleaner, 16 Throttle device, 18 Injector, 20 Spark plug, 22 Exhaust pipe, 24 Catalytic converter, 26 Intake air temperature sensor, 28 Intake pressure sensor, 30, 32 O2 sensor, 52 Cylinder, 54 Shut-off valve, 56 Regulator, 58 Gas phase filter, 60, 62 Fuel lines, 64, 66 Fuel pressure sensor, 68 Fuel temperature sensor, 70 ECU, 72 CPU, 74 RAM, 76 ROM, 80 Ignition switch, 82 Water temperature sensor.

Claims

1. A fuel system for an engine that uses liquefied gas as fuel, A cylinder for storing liquefied gas, A shut-off valve is provided on the outlet side of the aforementioned cylinder, A regulator for reducing the pressure of the fuel supplied from the cylinder, An injection valve that supplies fuel that has passed through the regulator to the engine, An input device for instructing the starting and stopping of the engine, The engine and the fuel system are controlled by a control device, When the control device is instructed by the input device to stop the engine, Close the aforementioned shut-off valve, When the predetermined conditions are met, the engine will continue to operate for a predetermined period after being instructed to stop, and then stop the engine. The aforementioned predetermined conditions are: A first condition is that the temperature of the air drawn into the engine at the time of engine startup is lower than a first threshold, This includes a second condition in which the engine water temperature is lower than a second threshold when the engine is instructed to stop, The predetermined period is a period determined from the engine water temperature, using a predetermined relationship between the period for consuming the liquefied fuel remaining in the fuel piping downstream of the regulator and the engine water temperature.

2. The fuel system according to claim 1, wherein the predetermined period is longer the lower the water temperature.

3. A fuel system for an engine that uses liquefied gas as fuel, A cylinder for storing liquefied gas, A shut-off valve is provided on the outlet side of the aforementioned cylinder, A regulator for reducing the pressure of the fuel supplied from the cylinder, An injection valve that supplies fuel that has passed through the regulator to the engine, An input device for instructing the starting and stopping of the engine, The engine and the fuel system are controlled by a control device, When the control device is instructed by the input device to stop the engine, Close the aforementioned shut-off valve, When the predetermined conditions are met, the engine will continue to operate for a predetermined period after being instructed to stop, and then the engine will be stopped. The aforementioned predetermined conditions are: A first condition is that the temperature of the air drawn into the engine at the time of engine startup is lower than a first threshold, This includes a second condition in which the engine water temperature is lower than a second threshold when the engine is instructed to stop, The predetermined period is the period until the water temperature rises above a third threshold, in a fuel system.

4. The fuel system according to claim 3, wherein the third threshold is equal to the second threshold.

5. An engine comprising the fuel system according to any one of claims 1 to 4.

6. A control method for an engine that uses liquefied gas as fuel, If the engine is ordered to be stopped, The steps include closing a shut-off valve located on the outlet side of a cylinder that stores liquefied gas, When certain conditions are met, the engine continues to operate for a predetermined period after being instructed to stop, The step includes stopping the engine after the predetermined period has elapsed, The aforementioned predetermined conditions are: A first condition is that the temperature of the air drawn into the engine at the time of engine startup is lower than a first threshold, This includes a second condition in which the engine water temperature is lower than a second threshold when the engine is instructed to stop, A control method in which the predetermined period is a period determined from the engine's water temperature, using a predetermined relationship between the period for consuming the liquefied fuel remaining in the fuel piping downstream of the regulator that reduces the pressure of the fuel supplied from the cylinder and the engine's water temperature.

7. The control method according to claim 6, wherein the predetermined period is longer the lower the water temperature.

8. A control method for an engine that uses liquefied gas as fuel, If the engine is ordered to be stopped, The steps include closing a shut-off valve located on the outlet side of a cylinder that stores liquefied gas, When certain conditions are met, the engine continues to operate for a predetermined period after being instructed to stop, The step includes stopping the engine after the predetermined period has elapsed, The aforementioned predetermined conditions are: A first condition is that the temperature of the air drawn into the engine at the time of engine startup is lower than a first threshold, This includes a second condition in which the engine water temperature is lower than a second threshold when the engine is instructed to stop, A control method in which the predetermined period is the period until the water temperature rises above a third threshold.

9. The control method according to claim 8, wherein the third threshold value is the same as the second threshold value.

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