Internal combustion engine system

Abstract

To provide an internal combustion engine system capable of improving determination accuracy of a state related to gas shortage.SOLUTION: An internal combustion engine system 1 includes a regulator 9 for decompressing and gasifying fuel in an LPG cylinder 6, an upstream fuel pressure sensor 14 for detecting a fuel pressure on an upstream side of the regulator 9, a vapor pressure estimating unit 21 for estimating a saturation vapor pressure in the LPG cylinder 6 and acquiring an in-cylinder vapor pressure estimation value on the basis of a detection value of the upstream fuel pressure sensor 14 just after starting of an engine 2, a determination threshold calculating unit 22 for calculating a gas shortage caution determination threshold in correspondence with the in-cylinder vapor pressure estimation value, and a gas shortage caution determination unit 23 comparing a value in correspondence with the fuel pressure on the upstream side of the regulator 9 with the gas shortage caution determination threshold and determining a gas shortage caution state in which a filling amount of the fuel in the LPG cylinder 6 is less than a predetermined specific amount when the value in correspondence with the fuel pressure on the upstream side of the regulator 9 is equal to or less than the gas shortage caution determination threshold.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an internal combustion engine system.

Background Art

[0002] As a conventional internal combustion engine system, for example, the technology described in Patent Document 1 is known. When the operating state of the internal combustion engine is in a deceleration state and a fuel cut state, the internal combustion engine system described in Patent Document 1 executes a minute injection control for injecting a minute amount of gaseous fuel from an injector so as to temporarily achieve a specified air-fuel ratio, and based on the air-fuel ratio detected in a subsequent predetermined period and the specified air-fuel ratio, it determines whether the remaining amount of gaseous fuel in the fuel tank is less than or equal to a predetermined amount, thereby estimating whether the fuel tank is out of fuel, and issues a warning according to the estimation result.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For example, when the pressure in the LPG cylinder becomes less than or equal to a threshold value, there is a system that warns of the remaining amount of LPG in the LPG cylinder. However, the saturated vapor pressure in the LPG cylinder varies depending on the component ratio and temperature of the LPG. Therefore, when the threshold value for determination is a constant value, the determination accuracy of the state related to fuel exhaustion (gas shortage) decreases.

[0005] An object of the present invention is to provide an internal combustion engine system capable of improving the determination accuracy of the state related to gas shortage.

Means for Solving the Problems

[0006] (1) An internal combustion engine system according to one aspect of the present invention includes an internal combustion engine, an intake passage through which air supplied to the internal combustion engine flows, a throttle valve disposed in the intake passage and controlling the flow rate of air supplied to the internal combustion engine, a fuel cylinder filled with fuel in a liquid state, a regulator that reduces the pressure of the fuel in the fuel cylinder and vaporizes it, an injector that supplies the fuel vaporized by the regulator into the internal combustion engine, an upstream pressure detection unit that detects the fuel pressure upstream of the regulator, a vapor pressure estimation unit that estimates the saturated vapor pressure in the fuel cylinder and obtains an estimated vapor pressure value in the cylinder based on the value detected by the upstream pressure detection unit immediately after starting the internal combustion engine, and the estimated vapor pressure value in the cylinder obtained by the vapor pressure estimation unit When the difference obtained by subtracting atmospheric pressure from the estimated vapor pressure inside the cylinder is greater than or equal to a predetermined lower limit for determining a gas shortage warning state, the difference obtained by subtracting atmospheric pressure from the estimated vapor pressure inside the cylinder and the lower limit for determining the change between the difference obtained by subtracting atmospheric pressure from the estimated vapor pressure inside the cylinder and the lower limit for determining the change A determination threshold calculation unit that calculates a determination threshold for fuel shortage warning, and an upstream pressure detection unit. of detection The difference obtained by subtracting atmospheric pressure from the value. This is compared with the fuel shortage warning threshold calculated by the judgment threshold calculation unit. The difference between the value detected by the upstream pressure detection unit and atmospheric pressure. The system includes a fuel shortage warning determination unit that determines that a fuel shortage warning state exists when the amount of fuel in the fuel cylinder is less than a predetermined specified amount, when the amount of fuel is below a fuel shortage warning threshold. The judgment threshold calculation unit calculates the fuel shortage warning judgment threshold by adding the judgment lower limit value and a value obtained by multiplying the value obtained by subtracting atmospheric pressure and the judgment lower limit value from the estimated vapor pressure inside the cylinder by a coefficient. .

[0007] In such an internal combustion engine, the upstream pressure detection unit detects the fuel pressure upstream of the regulator (the pressure inside the fuel cylinder). Based on the value detected by the upstream pressure detection unit immediately after the engine starts, the saturated vapor pressure inside the fuel cylinder is estimated, and the estimated vapor pressure value is obtained. The difference between the estimated vapor pressure inside the cylinder and atmospheric pressure, and the lower limit for determining a low-gas-out warning state, are used to determine the change between the difference between the estimated vapor pressure inside the cylinder and atmospheric pressure and the lower limit for determining the low-gas-out state. The threshold for triggering a low fuel warning is calculated. Then, The difference obtained by subtracting atmospheric pressure from the value detected by the upstream pressure detection unit. When the value is below the threshold for a fuel shortage warning, it is determined that the amount of fuel in the fuel cylinder is less than the specified amount, indicating a fuel shortage warning state. Using Since a fuel shortage warning threshold is calculated, this threshold changes in accordance with changes in the estimated vapor pressure inside the cylinder. Therefore, even if the saturated vapor pressure inside the fuel cylinder changes due to the fuel's component ratio or temperature, a fuel shortage warning threshold appropriate to the fuel's component ratio or temperature can be obtained. This improves the accuracy of detecting a fuel shortage. Furthermore, if the difference between the estimated vapor pressure inside the cylinder and atmospheric pressure is smaller than the lower limit for determining a low-fuel-consumption warning state, it is not necessary to calculate the low-fuel-consumption warning threshold, thus simplifying the calculation process. Furthermore, the threshold for determining whether a fuel tank is running low can be easily calculated using a simple formula that utilizes the difference between the estimated vapor pressure inside the cylinder and atmospheric pressure, and the lower limit for determining whether a fuel tank is running low. Furthermore, as the throttle valve opening increases, the intake pressure of the internal combustion engine approaches atmospheric pressure. Therefore, when calculating the fuel shortage warning threshold, using the difference between the estimated vapor pressure inside the cylinder and atmospheric pressure allows for a fuel shortage warning threshold that takes atmospheric pressure into account. Furthermore, as the throttle valve opening increases, the intake pressure of the internal combustion engine approaches atmospheric pressure. Therefore, by using the difference obtained by subtracting atmospheric pressure from the value detected by the upstream pressure detection unit, it is possible to determine the fuel shortage warning state while taking atmospheric pressure into account.

[0011] ( 2 ) The above (1 ) In this configuration, the vapor pressure estimation unit may calculate the average value of the detection value from the upstream pressure detection unit within a predetermined period immediately after starting the internal combustion engine, and obtain the average value of the detection value from the upstream pressure detection unit as the estimated vapor pressure in the cylinder.

[0013] ( 3 ) (1) or (2) In this configuration, the internal combustion engine system may further include an alarm unit that issues an alarm notifying the user of a fuel shortage when the fuel shortage warning unit determines that a fuel shortage warning state has been reached. In such a configuration, the user immediately understands that a fuel shortage warning state has been reached by the alarm. Therefore, the user can be prompted to be aware of the fuel shortage warning state.

[0014] ( 4 ) (1) ~ ( 3 In any of the above, the internal combustion engine system may further include a throttle control unit that controls the opening of the throttle valve to limit it when the fuel shortage warning unit determines that a fuel shortage warning state has been detected. With such a configuration, for example, it is possible to ensure the vehicle can travel a certain distance before running out of fuel and to drive the vehicle to a refueling station. In addition, deterioration of the fuel combustion state can be suppressed.

[0015] ( 5 ) (1) ~ ( 4 In either of the above, the internal combustion engine system includes a downstream pressure detection unit that detects the fuel pressure downstream of the regulator, and a downstream pressure detection unit of detection The difference obtained by subtracting atmospheric pressure from the value. The value is compared with a predetermined fuel depletion threshold. The difference obtained by subtracting atmospheric pressure from the value detected by the downstream pressure detection unit.When the value is less than or equal to the gas shortage determination threshold, a gas shortage determination unit may be further provided that determines that the fuel filling amount in the fuel cylinder is in a gas shortage state where it is less than that in the gas shortage caution state. In such a configuration, the downstream pressure detection unit of detects The difference obtained by subtracting atmospheric pressure from the value. When the value is less than or equal to the gas shortage determination threshold, it is determined that the fuel filling amount in the fuel cylinder is in a gas shortage state where it is less than that in the gas shortage caution state. Therefore, the accuracy of determining the gas shortage state is improved. Furthermore, as the throttle valve opening increases, the intake pressure of the internal combustion engine approaches atmospheric pressure. Therefore, by using the difference obtained by subtracting atmospheric pressure from the value detected by the downstream pressure detection unit, it is possible to determine the fuel shortage condition while taking atmospheric pressure into account.

[0017] ( 6 )In the above (5) , the internal combustion engine system may further include an alarm unit that issues an alarm notifying that it is in a gas shortage state when it is determined to be in a gas shortage state by the gas shortage determination unit. In such a configuration, the user can immediately know that it is in a gas shortage state from the alarm. Therefore, it is possible to prompt the user to pay attention to the fact that it is in a gas shortage state.

[0018] ( 7 )In the above (5) or (6) , the internal combustion engine system may further include a throttle control unit that controls to limit the opening degree of the throttle valve when it is determined to be in a gas shortage state by the gas shortage determination unit. In such a configuration, the situation of completely running out of gas can be delayed. Also, the deterioration of the fuel combustion state can be suppressed.

[0019] ( 8 )In the above ( 7 ), the throttle control unit The difference obtained by subtracting atmospheric pressure from the value detected by the downstream pressure detection unit. compares the value with a throttle opening limit threshold smaller than the gas shortage determination threshold, The difference obtained by subtracting atmospheric pressure from the value detected by the downstream pressure detection unit. and when the value is less than or equal to the throttle opening limit threshold, The difference obtained by subtracting atmospheric pressure from the value detected by the downstream pressure detection unit. it may be controlled to reduce the opening degree of the throttle valve compared to when the value is greater than the throttle opening limit threshold. In such a configuration, the situation of completely running out of gas can be further delayed. Also, the deterioration of the fuel combustion state can be further suppressed.

Advantages of the Invention

[0020] According to the present invention, the accuracy of determining conditions related to running out of gas can be improved. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic diagram showing an internal combustion engine system according to one embodiment of the present invention. [Figure 2] Figure 1 is a functional block diagram of the ECU. [Figure 3] Figure 2 is a flowchart showing the procedure for the vapor pressure estimation process performed by the ECU. [Figure 4] Figure 2 is a flowchart showing the procedure for calculating and controlling the judgment threshold, which is performed by the ECU. [Figure 5] This timing diagram shows an example of the fuel pressure upstream of the regulator and the result of determining a fuel shortage warning state. [Figure 6] Figure 2 is a flowchart showing the procedure for fuel shortage warning detection and control processing performed by the ECU. [Figure 7] This table shows an example of the throttle valve opening that is restricted when a fuel shortage warning is detected. [Figure 8] Figure 2 is a flowchart showing the procedure for fuel shortage detection and control processing performed by the ECU. [Figure 9] This timing diagram shows an example of the fuel pressure and fuel shortage detection results downstream of the regulator. [Figure 10] This table shows an example of the throttle valve opening degree that is restricted when a fuel shortage is detected. [Modes for carrying out the invention]

[0022] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0023] Figure 1 is a schematic diagram showing an internal combustion engine system according to one embodiment of the present invention. In Figure 1, the internal combustion engine system 1 of this embodiment is mounted on a vehicle. The vehicle may be an automobile or an industrial vehicle such as a forklift.

[0024] In the internal combustion engine system 1 of this embodiment, LPG (Liquefied Petroleum Gas) is used as fuel. LPG is liquefied petroleum gas mainly composed of propane and butane. The vapor pressure of LPG changes depending on the ratio of propane to butane and the temperature of the LPG.

[0025] The internal combustion engine system 1 comprises an engine 2 (internal combustion engine), an intake passage 3, an air cleaner 4, a throttle valve 5, an LPG cylinder 6, a fuel passage 7, a solenoid valve 8, a regulator 9, a fuel passage 10, and multiple injectors 11.

[0026] Engine 2 is, for example, a four-cylinder engine. Engine 2 has a spark plug 12 that ignites the fuel-air mixture to ignite the fuel.

[0027] The intake passage 3 is connected to the engine 2. The intake passage 3 is the passage through which air supplied to the engine 2 (intake air) flows. The air cleaner 4 is located in the intake passage 3. The air cleaner 4 removes foreign matter such as dust and dirt contained in the intake air. The throttle valve 5 is located between the air cleaner 4 and the engine 2 in the intake passage 3. The throttle valve 5 is an electromagnetic flow control valve that controls the flow rate of the intake air.

[0028] The LPG cylinder 6 is a fuel cylinder filled with LPG in liquid form. The fuel passage 7 connects the LPG cylinder 6 and the regulator 9. The fuel passage 7 is the passage through which liquid fuel flows from the LPG cylinder 6 to the regulator 9. A filter (not shown) is placed at the connection point between the LPG cylinder 6 and the fuel passage 7. The solenoid valve 8 is an on / off valve that opens and closes the fuel passage 7.

[0029] The regulator 9 is a pressure reducing valve that reduces the pressure of the fuel in the LPG cylinder 6 and vaporizes it. The fuel passage 10 connects the regulator 9 to multiple (for example, four) injectors 11. The fuel passage 10 is the passage through which the fuel (fuel gas) vaporized by the regulator 9 flows toward each injector 11.

[0030] The injector 11 is an electromagnetic fuel injection valve that supplies fuel gas into the engine 2. The injector 11 injects fuel gas between the throttle valve 5 and the engine 2 in the intake passage 3. Alternatively, the injector 11 may directly inject fuel gas into the engine 2.

[0031] Furthermore, the internal combustion engine system 1 includes an upstream fuel pressure sensor 14, a fuel temperature sensor 15, a downstream fuel pressure sensor 16, an intake pressure sensor 17, a rotational speed sensor 18, an alarm 19, and an ECU (Electronic Control Unit) 20.

[0032] The upstream fuel pressure sensor 14 is a pressure sensor that detects the pressure of the liquid fuel flowing through the fuel passage 7 or the outlet pressure of the LPG cylinder 6. The upstream fuel pressure sensor 14 constitutes an upstream pressure detection unit that detects the fuel pressure upstream of the regulator 9. The fuel pressure upstream of the regulator 9 corresponds to the pressure inside the LPG cylinder 6.

[0033] The fuel temperature sensor 15 is a temperature sensor that detects the temperature of the fuel gas flowing through the fuel passage 10. The downstream fuel pressure sensor 16 is a pressure sensor that detects the pressure of the fuel gas flowing through the fuel passage 10. The downstream fuel pressure sensor 16 constitutes a downstream pressure detection unit that detects the fuel pressure downstream of the regulator 9.

[0034] The intake pressure sensor 17 is a pressure sensor that detects the pressure of the intake air flowing through the intake air passage 3. The rotational speed sensor 18 is a sensor that detects the rotational speed of the engine 2.

[0035] The alarm device 19 is located in the driver's seat of the vehicle. The alarm device 19 provides a warning about running out of gas (fuel) by displaying an alarm. Alternatively, the alarm device 19 may provide a warning about running out of gas by sounding an alarm instead of displaying an alarm, or in conjunction with displaying an alarm.

[0036] The ECU20 consists of a CPU, RAM, ROM, and input / output interfaces, etc. Based on the detection values ​​of the upstream fuel pressure sensor 14, fuel temperature sensor 15, downstream fuel pressure sensor 16, intake pressure sensor 17, and rotational speed sensor 18, the ECU20 performs predetermined processing and controls the throttle valve 5, solenoid valve 8, injector 11, and alarm 19.

[0037] As shown in Figure 2, the ECU 20 includes a vapor pressure estimation unit 21, a judgment threshold calculation unit 22, a fuel shortage warning determination unit 23, a fuel shortage determination unit 24, an alarm control unit 25, and a throttle control unit 26.

[0038] The vapor pressure estimation unit 21 estimates the saturated vapor pressure in the LPG cylinder 6 based on the value detected by the upstream fuel pressure sensor 14 immediately after the engine 2 is started, and obtains an estimated vapor pressure value in the cylinder. The vapor pressure estimation unit 21 calculates the average value of the value detected by the upstream fuel pressure sensor 14 within a predetermined period immediately after the engine 2 is started, and obtains the average value of the value detected by the upstream fuel pressure sensor 14 as the estimated vapor pressure value in the cylinder.

[0039] The determination threshold calculation unit 22 calculates a gas shortage warning determination threshold according to the estimated vapor pressure inside the cylinder obtained by the vapor pressure estimation unit 21. The gas shortage warning determination threshold is a determination threshold used to determine whether or not the LPG cylinder 6 is in a gas shortage warning state (described later). When the value according to the estimated vapor pressure inside the cylinder is equal to or greater than a predetermined lower limit for determining a gas shortage warning state, the determination threshold calculation unit 22 calculates a gas shortage warning determination threshold using the value according to the estimated vapor pressure inside the cylinder and the lower limit for determining a gas shortage warning.

[0040] The fuel shortage warning determination unit 23 compares the value corresponding to the fuel pressure upstream of the regulator 9 detected by the upstream fuel pressure sensor 14 with the fuel shortage warning determination threshold calculated by the determination threshold calculation unit 22. When the value corresponding to the fuel pressure upstream of the regulator 9 is less than or equal to the fuel shortage warning determination threshold, it determines that the amount of fuel in the LPG cylinder 6 is less than a predetermined specified amount and is in a fuel shortage warning state.

[0041] The fuel depletion detection unit 24 compares a value corresponding to the fuel pressure downstream of the regulator 9 detected by the downstream fuel pressure sensor 16 with a predetermined fuel depletion detection threshold. When the value corresponding to the fuel pressure downstream of the regulator 9 is less than or equal to the fuel depletion detection threshold, it determines that the amount of fuel in the LPG cylinder 6 is less than that of a fuel depletion warning state. The fuel depletion detection threshold is a determination threshold used to determine whether or not the LPG cylinder 6 is in a fuel depletion state.

[0042] The alarm control unit 25 controls the alarm device 19 to issue an alarm notifying the user of a fuel shortage warning when the fuel shortage warning determination unit 23 determines that a fuel shortage warning is in effect. The alarm control unit 25 also controls the alarm device 19 to issue an alarm notifying the user of a fuel shortage when the fuel shortage determination unit 24 determines that the user has run out of fuel. The alarm control unit 25 works in cooperation with the alarm device 19 to form an alarm unit that issues alarms notifying the user of a fuel shortage warning and the user of a fuel shortage.

[0043] When the fuel shortage warning determination unit 23 determines that a fuel shortage warning state is in effect, the throttle control unit 26 controls the opening degree of the throttle valve 5 according to the rotational speed of the engine 2 detected by the rotational speed sensor 18.

[0044] Furthermore, when the fuel depletion detection unit 24 determines that the vehicle is out of fuel, the throttle control unit 26 controls the throttle valve 5 to limit its opening degree according to the rotational speed of the engine 2. The throttle control unit 26 compares a value corresponding to the fuel pressure downstream of the regulator 9 with an opening degree limit threshold that is smaller than the fuel depletion detection threshold. When the value corresponding to the fuel pressure downstream of the regulator 9 is less than or equal to the opening degree limit threshold, the throttle control unit 26 controls the throttle valve 5 to open less than when the value corresponding to the fuel pressure downstream of the regulator 9 is greater than the opening degree limit threshold.

[0045] Figure 3 is a flowchart showing the procedure for the vapor pressure estimation process performed by the ECU 20. This process is performed by the vapor pressure estimation unit 21. This process is executed when the ignition switch 29 (see Figure 1) is turned ON.

[0046] In Figure 3, the ECU 20 first obtains the detected value Pin from the upstream fuel pressure sensor 14 (procedure S101). Next, the ECU 20 determines whether a specified time (e.g., 5 seconds) has elapsed since the ignition switch 29 was turned ON (procedure S102). If the ECU 20 determines that the specified time has not elapsed, it repeats procedure S101.

[0047] When the ECU 20 determines that a specified time has elapsed, it calculates the average value of all the detected values ​​Pin from the upstream fuel pressure sensors 14 acquired within that specified time (procedure S103). The ECU 20 then determines the average value of the detected values ​​Pin from each upstream fuel pressure sensor 14 as the estimated vapor pressure Pbom inside the cylinder (procedure S104).

[0048] Figure 4 is a flowchart showing the procedure for the judgment threshold calculation and control process performed by the ECU 20. This process is performed by the judgment threshold calculation unit 22, the alarm control unit 25, and the throttle control unit 26. This process is also performed when the ignition switch 29 is turned ON.

[0049] In Figure 4, the ECU20 first calculates the difference D between the estimated vapor pressure Pbom inside the cylinder and the atmospheric pressure Pa (see Figure 5(a)) (procedure S111). The difference D is the value obtained by subtracting the atmospheric pressure Pa from the estimated vapor pressure Pbom inside the cylinder. The difference D corresponds to the value corresponding to the estimated vapor pressure Pbom inside the cylinder.

[0050] The ECU 20 then determines whether the difference D between the estimated vapor pressure Pbom inside the cylinder and the atmospheric pressure Pa is greater than or equal to the lower limit Pw for determining a fuel shortage warning state (see Figure 5(a)) (procedure S112). At this time, the ECU 20 may also determine that the difference D is greater than or equal to the lower limit Pw for a predetermined period of time. The lower limit Pw is predetermined.

[0051] When the ECU20 determines that the difference D between the estimated vapor pressure Pbom inside the cylinder and the atmospheric pressure Pa is greater than or equal to the lower limit Pw, it calculates the fuel shortage warning threshold R (procedure S113). The fuel shortage warning threshold R is a value that changes between the difference D and the lower limit Pw (see arrow Z in Figure 5(a)).

[0052] The fuel depletion warning threshold R is calculated using the following formula. Specifically, the fuel depletion warning threshold R is the sum of the lower limit Pw and the value obtained by multiplying the difference between the estimated vapor pressure inside the cylinder Pbom and the atmospheric pressure Pa and the lower limit Pw by a coefficient A. The coefficient A is a constant between 0.0 and 1.0 (for example, 0.5). R = Pw + {(Pbom - Pa) - Pw} × A

[0053] If the ECU20 determines in step S112 that the difference D between the estimated vapor pressure Pbom inside the cylinder and atmospheric pressure Pa is smaller than the lower limit Pw, it determines that an unexpected condition exists (unexpected condition determination is ON) (step S114). The unexpected condition here includes the fuel shortage warning condition described later. In other words, an unexpected condition is when engine 2 is started when it is already on the verge of running out of fuel, or when engine 2 is started when the fuel has low vapor pressure and is at a low temperature.

[0054] Next, the ECU 20 controls the alarm device 19 to issue an alarm notifying that an unexpected condition has occurred (procedure S115). Subsequently, the ECU 20 controls the throttle valve 5 to limit its opening degree (procedure S116). At this time, the opening degree of the throttle valve 5 is limited, for example, to a predetermined specified opening degree.

[0055] Here, the judgment threshold calculation unit 22 executes steps S111 to S114. The alarm control unit 25 executes step S115. The throttle control unit 26 executes step S116.

[0056] Figure 6 is a flowchart showing the procedure for the fuel shortage warning detection and control process performed by the ECU 20. This process is performed by the fuel shortage warning detection unit 23, the alarm control unit 25, and the throttle control unit 26. This process is also performed when the ignition switch 29 is turned ON.

[0057] In Figure 6, the ECU 20 first obtains the detected value Pin from the upstream fuel pressure sensor 14 (procedure S121). Then, the ECU 20 calculates the difference value Qin (see Figure 5(a)) between the detected value Pin from the upstream fuel pressure sensor 14 and the atmospheric pressure Pa (procedure S122). The difference value Qin is the value obtained by subtracting the atmospheric pressure Pa from the detected value Pin from the upstream fuel pressure sensor 14. The difference value Qin is a value corresponding to the fuel pressure on the upstream side of the regulator 9.

[0058] The ECU 20 then determines whether the difference value Qin between the detected value Pin from the upstream fuel pressure sensor 14 and the atmospheric pressure Pa is less than or equal to the fuel shortage warning threshold R (procedure S123). At this time, the ECU 20 may determine that the difference value Qin is less than or equal to the fuel shortage warning threshold R if the state in which the difference value Qin is less than or equal to the fuel shortage warning threshold R continues for a predetermined time.

[0059] When the ECU 20 determines that the difference value Qin between the upstream fuel pressure sensor 14's detected value Pin and atmospheric pressure Pa is less than or equal to the fuel shortage warning threshold R, it determines that the vehicle is in a fuel shortage warning state (fuel shortage warning is ON), as shown in Figure 5(b) (procedure S124). The fuel shortage warning state is a state in which attention is required because the vehicle is approaching a fuel shortage. Subsequently, the ECU 20 controls the alarm device 19 to issue an alarm notifying that the vehicle is in a fuel shortage warning state (procedure S125).

[0060] Next, the ECU 20 acquires the value detected by the rotation speed sensor 18 (procedure S126). Then, the ECU 20 controls the throttle valve 5 to limit its opening degree according to the value detected by the rotation speed sensor 18 (procedure S127). Specifically, as shown in Figure 7, the ECU 20 controls the throttle valve 5 so that the opening degree of the throttle valve 5 decreases as the rotation speed of the engine 2 increases. Note that when the throttle valve 5 is fully open, the opening degree of the throttle valve 5 is 100%.

[0061] If the ECU20 determines in step S123 that the difference value Qin between the detected value Pin of the upstream fuel pressure sensor 14 and the atmospheric pressure Pa is greater than the fuel shortage warning threshold R, it determines that there is no fuel shortage warning (fuel shortage warning is OFF) as shown in Figure 5(b) (step S128).

[0062] After performing step S127 or step S128, ECU20 performs step S121 again.

[0063] At this point, the fuel shortage warning unit 23 executes procedures S121 to S124 and S128. The alarm control unit 25 executes procedure S125. The throttle control unit 26 executes procedures S126 and S127.

[0064] Figure 8 is a flowchart showing the procedure for fuel shortage detection and control processing performed by the ECU 20. This process is performed by the fuel shortage detection unit 24, the alarm control unit 25, and the throttle control unit 26. This process is also executed when the ignition switch 29 is turned ON.

[0065] In Figure 8, the ECU 20 first obtains the detected value Pout from the downstream fuel pressure sensor 16 (procedure S131). Then, it calculates the difference value Qout (see Figure 9(a)) between the detected value Pout from the downstream fuel pressure sensor 16 and the atmospheric pressure Pa (procedure S132). The difference value Qout is the value obtained by subtracting the atmospheric pressure Pa from the detected value Pout from the downstream fuel pressure sensor 16. The difference value Qout is a value corresponding to the fuel pressure downstream of the regulator 9.

[0066] Next, the ECU 20 determines whether the difference value Qout between the value Pout detected by the downstream fuel pressure sensor 16 and the atmospheric pressure Pa is less than or equal to the fuel depletion threshold S1 (procedure S133). The fuel depletion threshold S1 is a threshold used to determine when the vehicle is close to running out of fuel, and is predetermined. At this time, the ECU 20 may also determine that the difference value Qout is less than or equal to the fuel depletion threshold S1 if the state in which the difference value Qout is less than or equal to the fuel depletion threshold S1 continues for a predetermined period of time.

[0067] When the ECU20 determines that the difference value Qout between the value Pout detected by the downstream fuel pressure sensor 16 and the atmospheric pressure Pa is less than or equal to the fuel depletion detection threshold S1, it determines that the vehicle is in a fuel depletion state (fuel depletion detection is ON) as shown in Figure 9(b) (procedure S134). The fuel depletion state is a condition close to complete fuel depletion, which renders the vehicle inoperable.

[0068] Next, the ECU 20 determines whether the difference value Qout between the value Pout detected by the downstream fuel pressure sensor 16 and the atmospheric pressure Pa is greater than the throttle opening limit threshold S2 (procedure S135). The throttle opening limit threshold S2 is a value smaller than the fuel depletion detection threshold S1 and is predetermined. At this time, the ECU 20 may determine that the difference value Qout is greater than the throttle opening limit threshold S2 if the condition in which the difference value Qout is greater than the throttle opening limit threshold S2 continues for a predetermined period of time.

[0069] When the ECU 20 determines that the difference value Qout between the value Pout detected by the downstream fuel pressure sensor 16 and the atmospheric pressure Pa is greater than the throttle limit threshold S2, it controls the alarm device 19 to issue an alarm indicating that the vehicle is running out of fuel (procedure S136).

[0070] Next, the ECU 20 acquires the value detected by the rotation speed sensor 18 (procedure S137). Then, the ECU 20 controls the throttle valve 5 to limit its opening degree according to the value detected by the rotation speed sensor 18 (procedure S138). Specifically, as shown in Figure 10(a), the ECU 20 controls the throttle valve 5 so that the opening degree of the throttle valve 5 decreases as the rotation speed of the engine 2 increases. At this time, the opening degree of the throttle valve 5 is limited to be smaller than when the fuel shortage warning state is in effect.

[0071] If the ECU 20 determines in step S135 that the difference value Qout between the detected value Pout from the downstream fuel pressure sensor 16 and the atmospheric pressure Pa is less than or equal to the throttle limit threshold S2, it controls the alarm device 19 to issue an alarm indicating that a further fuel shortage has occurred (step S139).

[0072] Next, the ECU 20 acquires the value detected by the rotation speed sensor 18 (procedure S140). Then, the ECU 20 controls the throttle valve 5 to further restrict its opening degree according to the value detected by the rotation speed sensor 18 (procedure S141). Specifically, as shown in Figure 10(b), the ECU 20 controls the throttle valve 5 so that the opening degree of the throttle valve 5 decreases as the rotation speed of the engine 2 increases. At this time, the opening degree of the throttle valve 5 is restricted to be smaller than when procedure S138 is executed.

[0073] If the ECU20 determines in step S133 that the difference value Qout between the value Pout detected by the downstream fuel pressure sensor 16 and the atmospheric pressure Pa is greater than the fuel shortage determination threshold S1, it determines that there is no fuel shortage (fuel shortage determination is OFF) as shown in Figure 9(b) (step S142).

[0074] ECU20 performs one of the following steps: S138, S141, or S142, and then performs step S131 again.

[0075] Here, the fuel shortage detection unit 24 executes procedures S131 to S135 and S142. The alarm control unit 25 executes procedures S136 and S139. The throttle control unit 26 executes procedures S137, S138, S140 and S141.

[0076] In the internal combustion engine system 1 described above, when the engine 2 is started, the average value of the detection value Pin of the upstream fuel pressure sensor 14 during a predetermined period immediately after the engine 2 is started is calculated, and the estimated vapor pressure value Pbom in the cylinder is obtained.

[0077] Next, the difference D between the estimated vapor pressure Pbom inside the cylinder and the atmospheric pressure Pa is compared with the lower limit Pw for determining a low-fuel condition. If the difference D between the estimated vapor pressure Pbom and the atmospheric pressure Pa is greater than or equal to the lower limit Pw, the low-fuel condition threshold R is calculated using a formula that includes the estimated vapor pressure Pbom, the atmospheric pressure Pa, and the lower limit Pw.

[0078] Next, the difference value Qin between the detected value Pin from the upstream fuel pressure sensor 14 and the atmospheric pressure Pa is compared with the fuel shortage warning threshold R. If the difference value Qin between the detected value Pin from the upstream fuel pressure sensor 14 and the atmospheric pressure Pa is greater than the fuel shortage warning threshold R, it is determined that the system is in a normal state and not in a fuel shortage warning state.

[0079] On the other hand, if the difference value Qin between the detected value Pin of the upstream fuel pressure sensor 14 and the atmospheric pressure Pa falls below the fuel shortage warning threshold R, it is determined that a fuel shortage warning is in effect. The alarm 19 then issues a warning indicating that a fuel shortage warning is in effect. In addition, the opening degree of the throttle valve 5 is limited according to the rotational speed of the engine 2.

[0080] Subsequently, the difference value Qout between the detected value Pout from the downstream fuel pressure sensor 16 and the atmospheric pressure Pa is compared with the fuel depletion detection threshold S1. When the difference value Qout between the detected value Pout from the downstream fuel pressure sensor 16 and the atmospheric pressure Pa falls below the fuel depletion detection threshold S1, it is determined that the vehicle is running out of fuel. The alarm 19 then sounds an alarm indicating that the vehicle is running out of fuel. In addition, the opening degree of the throttle valve 5 is further restricted according to the rotational speed of the engine 2.

[0081] Furthermore, the difference value Qout between the detection value Pout from the downstream fuel pressure sensor 16 and the atmospheric pressure Pa is compared with the throttle opening limit threshold S2. When the difference value Qout between the detection value Pout from the downstream fuel pressure sensor 16 and the atmospheric pressure Pa falls below the throttle opening limit threshold S2, it is determined that a further fuel shortage has occurred. The alarm 19 then issues a warning indicating a further fuel shortage, and the opening of the throttle valve 5 is further restricted.

[0082] As described above, in this embodiment, the upstream fuel pressure sensor 14 detects the fuel pressure upstream of the regulator 9 (pressure inside the LPG cylinder 6). Based on the value detected by the upstream fuel pressure sensor 14 immediately after starting the engine 2, the saturated vapor pressure inside the LPG cylinder 6 is estimated and the estimated vapor pressure inside the cylinder Pbom is obtained. Then, a fuel shortage warning threshold R is calculated according to the estimated vapor pressure inside the cylinder Pbom. When the value corresponding to the fuel pressure upstream of the regulator 9 is less than or equal to the fuel shortage warning threshold R, it is determined that the amount of fuel in the LPG cylinder 6 is less than the specified amount and a fuel shortage warning state is in effect. In this way, the fuel shortage warning threshold R is calculated according to the estimated vapor pressure inside the cylinder Pbom, so the fuel shortage warning threshold R changes in accordance with the change in the estimated vapor pressure inside the cylinder Pbom. Therefore, even if the saturated vapor pressure inside the LPG cylinder 6 changes due to the fuel component ratio or temperature, a fuel shortage warning threshold R suitable for the fuel component ratio or temperature can be obtained. This improves the accuracy of determining the fuel shortage warning state. As a result, it prevents the engine 2 from suddenly stopping and rendering the vehicle immobile. Furthermore, if the vehicle is an industrial vehicle, it prevents sudden interruptions to work, thus mitigating a decrease in work efficiency.

[0083] Furthermore, in this embodiment, the gas shortage warning threshold R is calculated when the value corresponding to the estimated vapor pressure Pbom inside the cylinder is equal to or greater than the lower limit Pw for determining a gas shortage warning state. Therefore, when the value corresponding to the estimated vapor pressure Pbom inside the cylinder is less than the lower limit Pw, it is not necessary to calculate the gas shortage warning threshold R, thus simplifying the calculation process.

[0084] Furthermore, in this embodiment, the fuel shortage warning threshold R can be easily calculated using a simple formula that uses a value corresponding to the estimated vapor pressure Pbom inside the cylinder and the lower limit value Pw for determining a fuel shortage warning state.

[0085] Furthermore, in this embodiment, the value corresponding to the estimated vapor pressure Pbom inside the cylinder is the difference D obtained by subtracting the atmospheric pressure Pa from the estimated vapor pressure Pbom inside the cylinder. As the opening of the throttle valve 5 increases, the intake pressure of the engine 2 approaches atmospheric pressure. Therefore, when calculating the fuel shortage warning threshold R, by using the difference D obtained by subtracting the atmospheric pressure Pa from the estimated vapor pressure Pbom inside the cylinder, a fuel shortage warning threshold R that takes atmospheric pressure Pa into account can be obtained.

[0086] Furthermore, in this embodiment, the average value of the detection value Pin of the upstream fuel pressure sensor 14 during a predetermined period immediately after starting the engine 2 is calculated, and the average value of the detection value Pin of the upstream fuel pressure sensor 14 is obtained as the estimated vapor pressure value Pbom inside the cylinder. Therefore, even if the fuel pressure upstream of the regulator 9 fluctuates and becomes unstable immediately after starting the engine 2, an appropriate estimated vapor pressure value Pbom inside the cylinder can be obtained.

[0087] Furthermore, in this embodiment, the value corresponding to the fuel pressure upstream of the regulator 9 is the difference value Qin obtained by subtracting the atmospheric pressure Pa from the detected value Pin of the upstream fuel pressure sensor 14. As described above, as the opening degree of the throttle valve 5 increases, the intake pressure of the engine 2 approaches the atmospheric pressure Pa. Therefore, by using the difference value Qin obtained by subtracting the atmospheric pressure Pa from the detected value Pin of the upstream fuel pressure sensor 14, it is possible to determine the fuel shortage warning state while taking the atmospheric pressure Pa into consideration.

[0088] Furthermore, in this embodiment, when it is determined that the vehicle is in a low-fuel-consumption state, an alarm is issued to notify the user of this state. Therefore, the user, the driver of the vehicle, will immediately know that the vehicle is in a low-fuel-consumption state through the alarm. Consequently, the driver can be prompted to take note of the low-fuel-consumption state.

[0089] Furthermore, in this embodiment, when a fuel shortage warning state is detected, the opening degree of the throttle valve 5 is controlled to be limited. This ensures that the vehicle can travel a sufficient distance before running out of fuel, allowing it to be driven to a refueling station. It also helps to suppress deterioration of the fuel combustion state.

[0090] Furthermore, in this embodiment, when the value corresponding to the fuel pressure downstream of the regulator 9 detected by the downstream fuel pressure sensor 16 is less than or equal to the fuel shortage determination threshold S1, it is determined that the amount of fuel in the LPG cylinder 6 is less than that of a fuel shortage warning state, resulting in a fuel shortage condition. Therefore, the accuracy of fuel shortage determination is improved. As a result, the vehicle becoming inoperable is further prevented. In addition, if the vehicle is an industrial vehicle, the decrease in work efficiency can be further suppressed.

[0091] Furthermore, in this embodiment, the value corresponding to the fuel pressure downstream of the regulator 9 is the difference value Qout obtained by subtracting the atmospheric pressure Pa from the detected value Pout of the downstream fuel pressure sensor 16. As described above, as the opening degree of the throttle valve 5 increases, the intake pressure of the engine 2 approaches atmospheric pressure. Therefore, by using the difference value Qout obtained by subtracting the atmospheric pressure Pa from the detected value Pout of the downstream fuel pressure sensor 16, it is possible to determine the fuel shortage state while taking atmospheric pressure Pa into consideration.

[0092] Furthermore, in this embodiment, when it is determined that the vehicle is out of fuel, an alarm is issued to notify the driver of this fact. Therefore, the driver immediately understands that the vehicle is out of fuel through the alarm. Consequently, it is possible to prompt the driver to be aware of the situation.

[0093] Furthermore, in this embodiment, when it is determined that the vehicle is out of fuel, the opening of the throttle valve 5 is controlled to be limited. This delays the situation in which the vehicle completely runs out of fuel. It also further suppresses the deterioration of the fuel combustion state.

[0094] Furthermore, in this embodiment, when the value corresponding to the fuel pressure downstream of the regulator 9 is less than or equal to the throttle valve opening limit threshold S2, the throttle valve 5 is controlled to open less than when the value corresponding to the fuel pressure downstream of the regulator 9 is greater than the throttle valve opening limit threshold S2. This further delays the situation in which the vehicle runs out of fuel completely. It also further suppresses the deterioration of the fuel combustion state.

[0095] It should be noted that the present invention is not limited to the above embodiments. For example, in the above embodiments, the average value of the detection value Pin of the upstream fuel pressure sensor 14 during a predetermined period immediately after starting the engine 2 is calculated, and this calculated value is used as the estimated vapor pressure value Pbom in the cylinder, but the invention is not limited to such an embodiment. For example, the midpoint value of the detection value Pin of the upstream fuel pressure sensor 14 during a predetermined period immediately after starting the engine 2 may be used as the estimated vapor pressure value Pbom in the cylinder. Also, if there is little fluctuation in the fuel pressure upstream of the regulator 9 immediately after starting the engine 2, the first detection value Pin of the upstream fuel pressure sensor 14 obtained immediately after starting the engine 2 may be used as the estimated vapor pressure value Pbom in the cylinder.

[0096] Furthermore, in the above embodiment, the difference value D obtained by subtracting the atmospheric pressure Pa from the estimated vapor pressure Pbom inside the cylinder is compared with the lower limit value Pw for determining a gas shortage warning state. However, the form is not particularly limited, and for example, the estimated vapor pressure Pbom inside the cylinder itself may be compared with a predetermined lower limit value.

[0097] Furthermore, in the above embodiment, the difference value Qin obtained by subtracting atmospheric pressure Pa from the detected value Pin of the upstream fuel pressure sensor 14 is compared with the fuel shortage warning threshold R. However, the embodiment is not limited to this form, and for example, the detected value Pin of the upstream fuel pressure sensor 14 itself may be compared with a predetermined fuel shortage warning threshold.

[0098] Furthermore, in the above embodiment, the difference value Qout obtained by subtracting atmospheric pressure Pa from the detected value Pout of the downstream fuel pressure sensor 16 is compared with the fuel depletion detection threshold S1 and the opening degree limit threshold S2. However, the embodiment is not limited to this form, and for example, the detected value Pout of the downstream fuel pressure sensor 16 itself may be compared with a predetermined fuel depletion detection threshold and an opening degree limit threshold.

[0099] Furthermore, in the above embodiment, the fuel depletion detection and control process shown in Figure 8 involves a two-stage determination using a fuel depletion detection threshold S1 and an opening degree limit threshold S2, but the system is not limited to this configuration. For example, only a determination using the fuel depletion detection threshold S1 may be performed, or a three-stage or more determination may be performed using a fuel depletion detection threshold and multiple opening degree limit thresholds.

[0100] Furthermore, in the above embodiment, when it is determined that the vehicle is in a low-fuel-out state, an alarm is issued indicating that the vehicle is in a low-fuel-out state, and the opening of the throttle valve 5 is restricted. However, the embodiment is not limited to this configuration, and either an alarm indicating a low-fuel-out state or restriction of the opening of the throttle valve 5 may be performed alone.

[0101] Furthermore, in the above embodiment, when it is determined that the vehicle is out of fuel, an alarm is issued indicating that it is out of fuel and the opening of the throttle valve 5 is restricted. However, the embodiment is not limited to this configuration, and either an alarm indicating that the vehicle is out of fuel or restriction of the opening of the throttle valve 5 may be performed alone.

[0102] Furthermore, in the above embodiment, the fuel shortage state is determined using the fuel pressure downstream of the regulator 9 detected by the downstream fuel pressure sensor 16. However, the system is not limited to this configuration, and the fuel shortage state may also be determined using the fuel pressure upstream of the regulator 9 detected by the upstream fuel pressure sensor 14. In this case, a fuel shortage determination threshold is calculated according to the estimated vapor pressure Pbom inside the cylinder.

[0103] Furthermore, although LPG is used as fuel in the above embodiment, the present invention is not limited to this form, and can also be applied to internal combustion engines that use, for example, DME (dimethyl ether) as fuel. [Explanation of Symbols]

[0104] 1...Internal combustion engine system, 2...Engine (internal combustion engine), 3...Intake passage, 5...Throttle valve, 6...LPG cylinder (fuel cylinder), 9...Regulator, 11...Injector, 14...Upstream fuel pressure sensor (upstream pressure detection unit), 16...Downstream fuel pressure sensor (downstream pressure detection unit), 19...Warmer (warning unit), 21...Vapor pressure estimation unit, 22...Judgment threshold calculation unit, 23...Fuel shortage warning determination unit, 24...Fuel shortage determination unit, 25...Warmer control unit (warning unit), 26...Throttle control unit, Pin...Detected value, Pout...Detected value, Pbom...Estimated vapor pressure value inside cylinder, Pa...Atmospheric pressure, D...Difference value, Pw...Judgment lower limit value, R...Fuel shortage warning judgment threshold, Qin...Difference value, Qout...Difference value, S1...Fuel shortage judgment threshold, S2...Opening degree limit threshold.

Claims

1. Internal combustion engines and An intake passage through which air supplied to the internal combustion engine flows, A throttle valve is disposed in the intake passage and controls the flow rate of air supplied to the internal combustion engine, A fuel cylinder that is filled with fuel in liquid form, A regulator that reduces the pressure of the fuel in the fuel cylinder and vaporizes it, An injector that supplies fuel vaporized by the regulator into the internal combustion engine, An upstream pressure detection unit for detecting the fuel pressure upstream of the regulator, A vapor pressure estimation unit estimates the saturated vapor pressure in the fuel cylinder and obtains an estimated vapor pressure value based on the value detected by the upstream pressure detection unit immediately after the start of the internal combustion engine, When the difference obtained by subtracting atmospheric pressure from the estimated vapor pressure inside the cylinder obtained by the vapor pressure estimation unit is equal to or greater than a predetermined lower limit for determining a low-fuel-out warning state, a determination threshold calculation unit calculates a low-fuel-out warning threshold that changes between the difference obtained by subtracting atmospheric pressure from the estimated vapor pressure inside the cylinder and the lower limit for determining a low-fuel-out warning state, using the difference obtained by subtracting atmospheric pressure from the estimated vapor pressure inside the cylinder and the lower limit for determining a low-fuel-out warning state. The system includes a fuel shortage warning determination unit that compares the difference obtained by subtracting atmospheric pressure from the value detected by the upstream pressure detection unit with the fuel shortage warning determination threshold calculated by the determination threshold calculation unit, and determines that a fuel shortage warning state exists when the amount of fuel filled in the fuel cylinder is less than a predetermined specified amount, if the difference obtained by subtracting atmospheric pressure from the value detected by the upstream pressure detection unit is less than or equal to the fuel shortage warning determination threshold. The judgment threshold calculation unit calculates the fuel shortage warning judgment threshold by adding the judgment lower limit value and a value obtained by multiplying the estimated value of the vapor pressure inside the cylinder minus atmospheric pressure and the judgment lower limit value by a coefficient.

2. The internal combustion engine system according to claim 1, wherein the vapor pressure estimation unit calculates the average value of the detection value of the upstream pressure detection unit within a predetermined period immediately after starting the internal combustion engine, and obtains the average value of the detection value of the upstream pressure detection unit as the estimated vapor pressure in the cylinder.

3. The internal combustion engine system according to claim 1, further comprising an alarm unit that provides an alarm to notify that the fuel shortage warning state is in effect when the fuel shortage warning determination unit determines that the fuel shortage warning state is in effect.

4. The internal combustion engine system according to claim 1, further comprising a throttle control unit that controls the opening degree of the throttle valve to be limited when the fuel shortage warning determination unit determines that the fuel shortage warning state is in effect.

5. A downstream pressure detection unit for detecting the fuel pressure downstream of the regulator, The internal combustion engine system according to claim 1, further comprising: a fuel shortage determination unit that compares the difference obtained by subtracting atmospheric pressure from the value detected by the downstream pressure detection unit with a predetermined fuel shortage determination threshold, and determines that the amount of fuel in the fuel cylinder is less than that of the fuel shortage warning state when the difference obtained by subtracting atmospheric pressure from the value detected by the downstream pressure detection unit is less than or equal to the fuel shortage determination threshold.

6. The internal combustion engine system according to claim 5, further comprising an alarm unit that issues an alarm notifying that the system is in a state of running out of gas when the gas shortage determination unit determines that the system is running out of gas.

7. The internal combustion engine system according to claim 5, further comprising a throttle control unit that controls the opening degree of the throttle valve to be limited when the fuel shortage determination unit determines that the fuel shortage condition is present.

8. The internal combustion engine system according to claim 7, wherein the throttle control unit compares the difference obtained by subtracting atmospheric pressure from the detected value of the downstream pressure detection unit with an opening degree limiting threshold that is smaller than the fuel depletion determination threshold, and controls the throttle valve to open less when the difference obtained by subtracting atmospheric pressure from the detected value of the downstream pressure detection unit is less than or equal to the opening degree limiting threshold, compared to when the difference obtained by subtracting atmospheric pressure from the detected value of the downstream pressure detection unit is larger than the opening degree limiting threshold.

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