JP7215444B2 - Fuel property detector - Google Patents

Description

The present disclosure relates to a fuel property detection device, and more particularly to a fuel property detection device for detecting properties of internal combustion engine fuel, which is natural gas supplied from an LNG (Liquefied Natural Gas) tank.

Internal combustion engines that use natural gas as fuel are known, and vehicles equipped with such internal combustion engines as power sources, ie, natural gas vehicles, are known.

JP-A-2003-12097

Fuel, which is natural gas, may be stored in a fuel tank in liquid form, ie, as LNG. In this case, the methane concentration in the LNG decreases over a long period of time, and the composition of the LNG changes, causing a weathering phenomenon in which the fuel becomes heavy. If this change in fuel properties is ignored and no countermeasures are taken, there is a risk that the operation of the internal combustion engine will be hindered.

Therefore, it is desirable to detect the fuel property and reflect the result in the control, but the actual situation is that there is no suitable fuel property detection device.

Accordingly, the present disclosure was created in view of such circumstances, and an object of the present disclosure is to provide a fuel property detection device capable of suitably detecting fuel properties.

According to one aspect of the present disclosure,
A fuel property detection device for detecting the property of fuel in an internal combustion engine, which is natural gas supplied from an LNG tank,
a CNG tank that stores natural gas as CNG;
a fuel passage switchably connected to the LNG tank and the CNG tank;
a sensor provided in the fuel passage and configured to detect a flow rate of natural gas;
a first output value of the sensor when a predetermined flow of natural gas from the CNG tank is flowing through the fuel passage; and said predetermined flow of natural gas from the LNG tank when flowing through the fuel passage. an estimating unit configured to estimate fuel heaviness based on the second output value of the sensor;
A fuel property detection device is provided.

Preferably, the estimation unit estimates the fuel heaviness based on the difference between the first output value and the second output value of the sensor.

Preferably, a downstream end of the fuel passage is connected to an intake passage of the internal combustion engine.

Preferably, natural gas flows through the fuel passage at times other than when the internal combustion engine is in a fuel cut state.

Preferably, natural gas from said CNG tank is used as fuel for said internal combustion engine.

Preferably, the fuel property detection device includes a control unit that controls at least one of ignition timing and fuel injection amount based on the fuel heaviness estimated by the estimation unit.

According to the present disclosure, it is possible to suitably detect fuel properties.

1 is a schematic diagram showing an internal combustion engine according to an embodiment; FIG. 4 shows a map for calculating ignition timing and fuel injection amount; It is a schematic diagram showing a fuel supply device. 4 is a graph showing output characteristics of a fuel sensor; A map showing the relationship between the output difference and the weighting index is shown. 4 is a flow chart showing a procedure for estimating the degree of severity; 4 shows a map showing the relationship between the weighting index, the ignition timing correction amount, and the fuel correction amount. 5 is a time chart showing how the weighting index fluctuates. 11 is a flow chart showing a procedure for estimating a severity according to a modification;

Embodiments of the present disclosure will be described below with reference to the accompanying drawings. Note that the present disclosure is not limited to the following embodiments.

FIG. 1 is a schematic diagram showing an internal combustion engine according to this embodiment. An internal combustion engine (also referred to as an engine) 1 uses natural gas as a fuel and is mounted on a vehicle, particularly a large vehicle such as a truck, as a power source. However, the use of the engine is arbitrary, and it may be applied to moving bodies other than vehicles, such as ships, construction machines, or industrial machines. Also, the engine may not be mounted on a moving object, and may be of a stationary type. The fuel is stored as LNG in a fuel tank (not shown) at very low temperatures.

The engine 1 includes an engine body 2 , an intake passage 3 and an exhaust passage 4 connected to the engine body 2 , and a fuel injection device 5 . The engine body 2 includes structural parts such as a cylinder head, a cylinder block, and a crankcase, and movable parts such as pistons, crankshafts, and valves housed therein. Intake and exhaust flows are indicated by white and black arrows, respectively.

The fuel injection device 5 includes a fuel injection valve, that is, an injector 7 provided in each cylinder, and a fuel rail 8 commonly connected to the injector 7 of each cylinder. Injector 7 injects fuel into intake port or cylinder 9 . Fuel sent through the fuel supply passage 13 is stored in the fuel rail 8 in a gaseous state.

Each cylinder is provided with a spark plug 6 for igniting the air-fuel mixture in the cylinder 9 .

The intake passage 3 is mainly defined by an intake manifold 10 connected to the engine body 2 (particularly the cylinder head) and an intake pipe 11 connected to the upstream end of the intake manifold 10 . The intake pipe 11 is provided with an air cleaner 12, a compressor 14C of the turbocharger 14, an intercooler 15, and an electronically controlled intake throttle valve 16 in this order from the upstream side.

The exhaust passage 4 is mainly defined by an exhaust manifold 20 connected to the engine body 2 (especially a cylinder head) and an exhaust pipe 21 arranged downstream of the exhaust manifold 20 . A turbine 14T of the turbocharger 14 is provided between the exhaust pipe 21 or the exhaust manifold 20 and the exhaust pipe 21 . A three-way catalyst 22 is provided in the exhaust pipe 21 on the downstream side of the turbine 14T. A bypass passage 23 is provided to bypass the turbine 14T, and a wastegate valve 24 is provided in this.

The engine 1 also has an EGR device 30 . The EGR device 30 includes an EGR passage 31 for recirculating part of the exhaust gas (referred to as EGR gas) in the exhaust passage 4 (in particular, the exhaust manifold 20) into the intake passage 3 (in particular, the intake manifold 10), and an EGR passage. An EGR cooler 32 for cooling the EGR gas flowing through 31 and an EGR valve 33 for adjusting the flow rate of the EGR gas are provided.

A control device for controlling the engine 1 is mounted on the vehicle. The control device includes an electronic control unit (called an ECU (Electronic Control Unit)) 100 that serves as a control unit, circuitry, or a controller. In the case of this embodiment, the ECU 100 constitutes the estimation unit referred to in the claims. ECU 100 includes a CPU (Central Processing Unit) having a computing function, ROM (Read Only Memory) and RAM (Random Access Memory) as storage media, input/output ports, storage devices other than ROM and RAM, and the like.

The controller also includes the following sensors. That is, a rotational speed sensor 40 for detecting the rotational speed of the engine (specifically, the number of revolutions per minute (rpm)), an accelerator opening sensor 41 for detecting the accelerator opening, and a three-way catalyst. A lambda sensor 42 for detecting the excess air ratio of the exhaust at the inlet of 22, and an intake air temperature sensor 43 and an intake air pressure sensor 44 for detecting the temperature and pressure of the intake air downstream of the intake throttle valve 16. . The ECU 100 controls the aforementioned various devices, namely the injector 7, the spark plug 6, the intake throttle valve 16, the wastegate valve 24, and the EGR valve 33, based on the outputs of these sensors.

Regarding basic control of the engine, the ECU 100 controls a predetermined map (or function good, the same applies hereinafter) to calculate or estimate the inspiratory flow rate Ga. Alternatively, the intake flow rate Ga may be directly detected by an intake flow rate sensor provided in the intake passage 3 .

Further, the ECU 100 calculates a basic injection amount Qib, which is a basic value of the fuel injection amount injected from the injector 7, according to the map shown in FIG. Calculate

Further, the ECU 100 calculates the basic ignition timing θigb, which is the basic value of the ignition timing of the spark plug 6, according to the map shown in FIG. .

Further, the ECU 100 determines that the accelerator opening Ac detected by the accelerator opening sensor 41 is a value corresponding to the fully closed accelerator, and the engine speed Ne detected by the rotation speed sensor 40 is higher than the predetermined return speed Nes. (referred to as a fuel cut execution condition) is established, fuel cut control for stopping the fuel injection by the injector 7 is executed. On the other hand, the ECU 100 ends the fuel cut control and returns to the normal control when the fuel cut execution condition is switched from satisfied to not satisfied. The return rotation speed Nes is set to a value slightly higher than the predetermined idle rotation speed Ni.

Further, the ECU 100 feedback-controls the fuel injection amount so that the actual excess air ratio λ detected by the lambda sensor 42 approaches a predetermined target excess air ratio λt. This is called lambda feedback control. The target excess air ratio λt is, for example, 1, which corresponds to the theoretical air-fuel ratio. The excess air ratio is an index value representing the mixing ratio of fuel and air. As such an index value, an air-fuel ratio may be used instead of the excess air ratio.

The ECU 100 controls the opening of the intake throttle valve 16 based on the detected accelerator opening Ac. Specifically, the opening of the intake throttle valve 16 is controlled so that the opening of the intake throttle valve 16 increases as the accelerator opening Ac increases.

Now, as mentioned above, in a fuel tank that stores fuel as LNG, the methane concentration in the LNG decreases over a long period of time, etc., the composition of the LNG changes, and a weathering phenomenon occurs in which the fuel becomes heavier. . For example, new fuel immediately after replenishing the fuel tank, ie, reference fuel, has the same composition as 13A city gas, and contains 90% methane as the main component and the rest ethane, propane, and butane. However, when LNG evaporates due to heat input into the fuel tank, methane is preferentially vaporized and discharged as boil-off gas, and the methane concentration of LNG decreases and becomes heavy. As the fuel becomes heavier, the methane number of the fuel decreases and the density increases.

If this change in fuel properties is ignored and no countermeasures are taken, there is a risk that the control of the internal combustion engine will be hindered. In particular, when the fuel becomes heavy, the octane number decreases and knocking is likely to occur. Therefore, in order to protect the engine, it is preferable to correct at least one of the ignition timing and the fuel injection amount in accordance with changes in fuel properties.

Therefore, in the present embodiment, a fuel property detection device is provided to detect (specifically, estimate) the fuel properties, particularly the degree of heaviness of the fuel. Then, the ignition timing and the fuel injection amount are corrected according to the detected degree of heaviness of the fuel to avoid knocking. It should be noted that the degree of heaviness of the fuel means the degree of heavyness of the fuel. Hereinafter, the fuel property detection device of this embodiment will be described in detail.

FIG. 3 shows a fuel supply system FS for supplying fuel to the engine 1. As shown in FIG. The fuel supply system FS includes a fuel tank that stores fuel as LNG, that is, an LNG tank 50 , and a fuel supply passage 13 that connects the LNG tank 50 to the fuel rail 8 . In this embodiment, a plurality of (specifically, two) LNG tanks 50 are provided, and specifically, a first LNG tank 50A and a second LNG tank 50B are provided in parallel. A fuel supply passage 13 connects these two LNG tanks 50 to the fuel rail 8 .

The fuel supply passage 13 includes a first LNG passage 51A for extracting and sending liquid fuel (liquid natural gas) from the bottom of the first LNG tank 50A, a second LNG passage 51B for extracting and sending liquid fuel from the bottom of the second tank 50B, and a third passage 53 whose upstream end is connected to the junction 52 of the first LNG passage 51A and the second LNG passage 51B. A downstream end of the third passage 53 is connected to the fuel rail 8 .

The first LNG passage 51A is provided with a first vaporizer 54A that vaporizes the liquid fuel and a cutoff valve 55A that opens and closes the outlet of the first vaporizer 54A. The cutoff valve 55A is configured by an electromagnetic valve. Outside the first LNG tank 50A, a first gas passage 56A is provided that connects the upstream side of the first vaporizer 54A and the upper surface of the first LNG tank 50A. A first economizer 57A is provided in the first gas passage 56A.

In the first LNG tank 50A, when the methane in the LNG is vaporized and boil-off gas is generated, the pressure inside the tank increases. When the tank internal pressure exceeds a predetermined value, the first economizer 57A opens like a relief valve to discharge the boil-off gas downstream. As a result, the pressure in the tank is lowered, and at the same time the LNG becomes heavier. The first economizer 57A is closed when the tank internal pressure is less than a predetermined value.

Separately, a first vent passage 58A is connected to the upper surface of the first LNG tank 50A, and a first tank vent valve 59A is provided in the first vent passage 58A. The first tank vent valve 59A is a kind of safety valve that opens when the tank internal pressure reaches a predetermined pressure higher than the valve opening pressure of the first economizer 57A, and releases the boil-off gas in the tank to the atmosphere. This will reduce the pressure in the tank.

The first LNG tank 50A is provided with a first remaining amount gauge 60A for detecting the remaining amount of liquid fuel in the tank.

Since the above configuration is the same on the side of the second LNG tank 50B, the description is omitted. Each element on the side of the second LNG tank 50B is renamed as "second...B". For example, the first vaporizer 54A is renamed the second vaporizer 54B.

Both tanks 50A and 50B are connected to a common filling port 61 through which LNG is filled or refilled into both tanks 50A and 50B.

The third passage 53 is provided with a pressure sensor 62, a cutoff valve 63, an LNG regulator 64, and a cutoff valve 65 in this order from the upstream side. The shutoff valves 63, 65 are composed of solenoid valves. The LNG regulator 64 decompresses and regulates the pressure of the gaseous fuel sent from the upstream side and sends it to the downstream side.

On the other hand, the fuel supply system FS of the present embodiment also includes a fuel tank, that is, a CNG tank 70 that stores natural gas in a high-pressure gaseous state, that is, as CNG (Compressed Natural Gas). The CNG-derived natural gas supplied from the CNG tank 70 is used as fuel for the engine 1 in the case of this embodiment.

CNG-derived natural gas is compositionally stable and non-heavy, and has substantially the same composition as non-heavy LNG-derived fuel.

The fuel supply system FS has a fourth passage 71 for connecting the CNG tank 70 to the fuel supply passage 13 and thus to the fuel rail 8 . The upstream end of the fourth passage 71 is connected to the CNG tank 70 and the downstream end of the fourth passage 71 is connected to the third passage 53 at the junction 72 .

The fourth passage 71 is provided with a shutoff valve 73, a pressure sensor 74, a shutoff valve 75, a CNG regulator 76, and a shutoff valve 77 in this order from the upstream side. The shutoff valves 73, 75, 77 are composed of solenoid valves. The CNG regulator 76 also decompresses and regulates the gaseous fuel sent from the upstream side and sends it to the downstream side.

By appropriately switching the shutoff valves, the fuel from the first LNG tank 50A, the second LNG tank 50B, and the CNG tank 70 (referred to as the first LNG fuel, the second LNG fuel, and the CNG fuel) can be appropriately switched and supplied to the engine 1. .

Next, the fuel property detector CD will be described. The fuel property detector CD includes a fuel extraction passage 81 connected to the third passage 53 and the fourth passage 71 . The fuel extraction passage 81 is bifurcated at its upstream portion at a branch point 84, one upstream end is connected to the third passage 53 at a branch point 82, and the other upstream end is connected at a branch point 83 to the fourth passage. 71. The branch point 82 is located downstream of the LNG regulator 64 and upstream of the cutoff valve 65 in the third passage 53 . The branch point 83 is located downstream of the CNG regulator 76 and upstream of the cutoff valve 77 in the fourth passage 71 .

The downstream end of the fuel extraction passage 81 is connected to the intake passage 3 or intake pipe 11 downstream of the air cleaner 12 and upstream of the compressor 14C (see FIG. 1). As a result, the gaseous fuel that has flowed through the fuel extraction passage 81 can be circulated to the intake passage 3 and prevented from being released into the atmosphere. The fuel extraction passage 81 constitutes the fuel passage referred to in the claims.

In the fuel extraction passage 81, a cutoff valve 85 is provided between the branch point 82 and the branch point 84, a cutoff valve 86 is provided between the branch point 83 and the branch point 84, and the branch point 84 and the downstream end are provided. A shutoff valve 87 is provided at a position between .

A sensor or fuel sensor 88 configured to detect the flow of natural gas is provided in the fuel extraction passage 81 downstream of the isolation valve 87 . Details of the fuel sensor 88 will be described later.

Each of the shutoff valves 55A, 55B, 63, 65, 73, 75, 77, 85, 86, and 87 described above is connected to the ECU 100 and controlled to be opened/closed by the ECU 100 . The first and second fuel gauges 60A and 60B, the pressure sensors 62 and 74 and the fuel sensor 88 are also connected to the ECU 100 and send their respective outputs to the ECU 100.

When the engine is operated with the first LNG fuel, the shutoff valves 55A, 63, 65 are opened and the shutoff valves 55B, 73, 75, 77 are closed to send the first LNG fuel to the fuel rail 8. At this time, when the output value of the fuel sensor 88 is detected at the same time, the cutoff valves 85 and 87 are opened and the cutoff valve 86 is closed, so that the first LNG fuel flows through the fuel extraction passage 81 and passes through the fuel sensor 88. Let me. When the output value of the fuel sensor 88 is not detected, the cutoff valves 85, 86, 87 are closed.

Similarly, when the engine is operated with the second LNG fuel, the shutoff valves 55B, 63, 65 are opened, the shutoff valves 55A, 73, 75, 77 are closed, and the second LNG fuel is sent to the fuel rail 8. At the same time, when detecting the output value of the fuel sensor 88, the shutoff valves 85 and 87 are opened and the shutoff valve 86 is closed, so that the second LNG fuel flows through the fuel extraction passage 81 and passes through the fuel sensor 88. Let me. When the output value of the fuel sensor 88 is not detected, the cutoff valves 85, 86, 87 are closed.

When the engine is operated with CNG fuel, the shutoff valves 73, 75, 77 are opened and the shutoff valves 55A, 55B, 63, 65 are closed to send CNG fuel to the fuel rail 8. At the same time, when the output value of the fuel sensor 88 is detected, the cutoff valves 86 and 87 are opened and the cutoff valve 85 is closed, causing the CNG fuel to flow through the fuel extraction passage 81 and pass through the fuel sensor 88. be done. When the output value of the fuel sensor 88 is not detected, the cutoff valves 85, 86, 87 are closed.

Thus, the fuel extraction passage 81 is switchably connected to the first LNG tank 50A, the second LNG tank 50B and the CNG tank 70 .

The fuel sensor 88 is a sensor configured for volume flow detection of natural gas (specifically, 13A city gas). The output characteristic of the fuel sensor 88 is as indicated by the solid line a in FIG. As the natural gas volumetric flow rate Q (l/min) increases, the output value of the sensor, that is, the output voltage VA (V) increases. As the fuel sensor 88, for example, a volumetric flowmeter with a fixed gas density using a MEMS sensor can be used. The output voltage when Q=0 is VA0.

When the fuel is sent to the shutoff valve 87 positioned immediately before the fuel sensor 88, the shutoff valve 87 shuts off the flow of fuel when the valve is closed. l/min)) of fuel is sent downstream. Therefore, when the shut-off valve 87 is open, a predetermined flow rate Qs of fuel is allowed to pass through the fuel sensor 88 .

Next, a method for estimating the fuel heaviness in the ECU 100 will be described.

A solid line a in FIG. 4 indicates the relationship between the volumetric flow rate Q when CNG fuel is flowed through the fuel sensor 88 and the output voltage VA of the fuel sensor 88 .

On the other hand, virgin first or second LNG fuel (collectively referred to as LNG fuel), or reference LNG fuel, has substantially the same composition as CNG fuel, and its methane number and density are also those of CNG. substantially equal to fuel. Therefore, when the reference LNG fuel is supplied to the fuel sensor 88, the output characteristic of the fuel sensor 88 becomes as shown by the solid line a.

However, it has been found that as the LNG fuel becomes heavier from the reference LNG fuel, the output characteristics of the fuel sensor 88 gradually change as shown by dashed-dotted lines b1, b2, b3, and b4. That is, the output voltage VA gradually increases, and the rate of increase (slope) of the output voltage VA with respect to the increase in the volumetric flow rate Q also gradually increases.

Therefore, the difference ΔV in output voltage between an arbitrary dashed line (eg, b3) and the solid line a when the volume flow Q is a constant predetermined flow Qs is nothing but a parameter reflecting the heaviness of the LNG fuel. Therefore, in this embodiment, the heaviness of the LNG fuel is estimated based on the output difference ΔV.

That is, the ECU 100 determines the first output value, that is, the first output voltage Va of the fuel sensor 88 when the CNG fuel of the predetermined flow rate Qs is flowing through the fuel extraction passage 81, and the LNG fuel of the predetermined flow rate Qs in the fuel extraction passage 81. The heaviness of the LNG fuel is estimated based on the second output value of the fuel sensor 88 when flowing, that is, the output difference ΔV (=Vb−Va) from the second output voltage Vb.

As shown in FIG. 5, in this embodiment, the heaviness of the fuel is represented by a value called a heaviness index X for the sake of simplicity. When the LNG fuel is the reference LNG fuel, the output difference ΔV is ΔVb=0, and the weighting index X at this time is assumed to be X0. It is assumed that the heavier the LNG fuel, the larger the weight of the LNG fuel than the reference LNG fuel, the larger the weighting index X becomes from X0. In this embodiment, X0=0.

A map showing the relationship between the output difference ΔV and the weighting index X is stored in the ECU 100 in advance. The ECU 100 calculates a heavy weight index X corresponding to the output difference ΔV from the map, and estimates the heavy weight of the fuel. According to the map, a larger weighting index X is obtained as the output difference ΔV increases.

When the engine is running on CNG fuel, the ECU 100 causes the CNG fuel of the predetermined flow rate Qs to flow through the fuel sensor 88 as described above, and detects and obtains the first output voltage Va. Then, this value is stored or learned and used for subsequent severity estimation.

The first output voltage Va is detected at an appropriate timing, which will be described later, and the heaviness of the LNG fuel is estimated from the output difference ΔV therebetween. Quality estimation accuracy can be improved. That is, if the first output voltage Va is a fixed value, the influence of the deviation cannot be eliminated when the output of the fuel sensor 88 deviates due to deterioration of the sensor or the like. However, according to this embodiment, it is possible.

Heaviness estimates are made separately for the first LNG fuel and the second LNG fuel. However, since the method is the same, for convenience, only the first LNG fuel may be considered.

Detection of each fuel by the fuel sensor 88 occurs simultaneously when the engine is running on each fuel. While LNG fuel is the main fuel, CNG fuel is a reserve fuel, for example, when the LNG fuel is completely consumed, when the LNG fuel becomes too heavy and becomes unusable, the CNG fuel is used. It is used when it is in a more favorable operating state (for example, idling).

The first LNG fuel and the second LNG fuel are alternately used so that their residual amounts detected by the first fuel gauge 60A and the second fuel gauge 60B are as uniform as possible. That is, the first LNG tank 50A and the second LNG tank 50B, which supply LNG fuel to the engine, are periodically alternately switched each time the remaining amount in the tank decreases by a predetermined value. Gravity estimation is performed immediately after this switching. Specifically, it is performed after a predetermined time (for example, several minutes) elapses from the time of switching until the fuel components passing through the fuel sensor 88 become stable. In addition, the timing for estimating the degree of heaviness includes immediately after the engine is started, immediately after the tank is replenished with new LNG fuel, and at every timing when the integrated value of the fuel injection amount reaches a predetermined value.

Further, detection of LNG fuel by the fuel sensor 88 is performed when the pressure detected by the pressure sensor 62 is equal to or less than a predetermined value. As described above, for example, when the tank internal pressure of the first LNG tank 50A reaches a predetermined value or higher, the first economizer 57A opens to discharge the boil-off gas in the tank. As a result, the high-pressure boil-off gas is flowed downstream at once, and this may cause the flow rate passing through the fuel sensor 88 to deviate from the predetermined flow rate Qs, degrading the heaviness degree estimation accuracy. Therefore, in the present embodiment, the LNG fuel is detected only when the pressure detected by the pressure sensor 62 is equal to or lower than a predetermined value when there is no discharge of the boil-off gas, thereby avoiding deterioration of the heaviness degree estimation accuracy. .

The pressure detected by the other pressure sensor 74 is mainly used for detecting the remaining amount in the CNG tank 70 .

A downstream end of the fuel extraction passage 81 is connected to the intake passage 3 on the upstream side of the compressor 14C. Therefore, the fuel after flowing through the fuel extraction passage 81 is discharged to the intake passage 3 on the upstream side of the compressor 14C. In general, the intake pressure fluctuates easily downstream of the compressor 14C and downstream of the intake throttle valve 16, but is stable near atmospheric pressure upstream of the compressor 14C. Therefore, by discharging the fuel to the intake passage 3 on the upstream side of the compressor 14C, the fuel can be stably discharged without being affected by the outlet pressure of the fuel extraction passage 81.

LNG fuel or CNG fuel (that is, natural gas) is flowed through the fuel extraction passage 81 for detection by the fuel sensor 88 at times other than when the engine fuel is cut. When the natural gas flows through the fuel extraction passage 81 , the natural gas after flowing through the fuel extraction passage 81 is discharged to the intake passage 3 . If such a discharge is performed during a fuel cut, the discharged natural gas is not ignited in the cylinder 9 and is discharged to the exhaust passage 4 in an unburned state. In order to prevent this, the natural gas is prevented from flowing into the fuel extraction passage 81 when the fuel is cut.

Note that even if the downstream end of the fuel extraction passage 81 is not connected to the intake passage 3, it is preferable to flow the natural gas when the fuel is not cut. This is because allowing natural gas to flow through the fuel extraction passage 81 and cutting fuel are considered to be contradictory actions.

Next, referring to FIG. 6, a procedure for estimating the severity will be described.

First, in step S101, the first output voltage Va of the fuel sensor 88 when CNG fuel of a predetermined flow rate Qs is passed through the fuel extraction passage 81, and the fuel sensor when LNG fuel of a predetermined flow rate Qs is passed through the fuel extraction passage 81 A second output voltage Vb of 88 is detected. As described above, the first output voltage Va is detected by opening the shutoff valves 86 and 87 and closing the shutoff valve 85 when the engine is running on CNG fuel. Further, the second output voltage Vb is detected by opening the shutoff valves 85 and 87 and closing the shutoff valve 86 when the engine is operated with LNG fuel (one of the first LNG fuel and the second LNG fuel). be done.

When detecting the first output voltage Va, CNG fuel may be supplied to the fuel extraction passage 81 for a predetermined period of time, and the average value of the first output voltage Va during that period may be used as the final detected value of the first output voltage Va. The same applies to the second output voltage Vb.

After detecting the first output voltage Va, the value is stored in the ECU 100 as a learned value.

Next, in step S102, the ECU 100 calculates the output difference ΔV=Vb−Va, which is the difference between these output voltages.

Then, in step S103, the weighting index X corresponding to the output difference ΔV is calculated by the ECU 100 from the map shown in FIG. Substantially, the properties of the current LNG fuel, that is, the degree of heaviness, can be preferably detected. This calculated weighting index X is also stored in the ECU 100 as a learned value.

Finally, in step S104, the ECU 100 calculates the ignition timing θig and the fuel injection amount Qi based on the weighting index X thus calculated. The contents are described below.

First, regarding the ignition timing θig, the ECU 100 calculates an ignition timing correction amount Δθig corresponding to the weighting index X from a predetermined map as shown in FIG. 7(A). The ignition timing correction amount Δθig is zero when the weighting index X is zero (=X0), that is, the fuel is not heavy, and increases as the weighting index X increases.

Next, the ECU 100 calculates the ignition timing θig from the formula f1: θig=θigb−Δθig. The ignition timing θig is advanced as its value increases. Therefore, as the severity increases, the ignition timing θig can be retarded, and knocking can be suppressed appropriately.

Next, regarding the fuel injection amount Qi, the ECU 100 calculates a fuel correction amount ΔQi corresponding to the weighting index X from a predetermined map as shown in FIG. 7(B). The fuel correction amount ΔQi is zero when the weighting index X is zero, that is, when the fuel is not heavy, and increases as the weighting index X increases.

Next, the ECU 100 calculates the fuel injection amount Qi from the formula f2: Qi=Qib+Qifb+ΔQi.

Qifb is a lambda feedback correction amount calculated based on the difference between the actual excess air ratio λ detected by the lambda sensor 42 and the target excess air ratio λt.

The reason for adding the positive fuel correction amount ΔQi when the fuel becomes heavy is as follows. It has been found that when the fuel becomes heavy, the detected value of the excess air ratio λ detected by the lambda sensor 42 deviates from the true value toward the rich side. Then, the control works in the direction of decreasing the fuel injection amount. As a result, if no countermeasures are taken, the amount of fuel will be insufficient, and the excess air ratio will be controlled to deviate to the lean side. Therefore, a positive fuel correction amount ΔQi is added for the purpose of eliminating such sensor rich displacement. Thereby, the deviation of the excess air ratio to the lean side can be suitably suppressed.

The actual ignition timing and fuel injection amount are controlled by the ECU 100 according to the ignition timing θig and fuel injection amount Qi thus calculated. As a result, the heaviness of the fuel can be reflected in the control, and even when the fuel becomes heavy, problems such as knocking can be suppressed, and deterioration of exhaust emissions can be suppressed.

Note that while the LNG fuel or CNG fuel is flowing through the fuel extraction passage 81, it is preferable to calculate the fuel injection amount Qi from the equation f2': Qi=Qib+Qifb-Qid+ΔQi. Qid (>0) is a subtraction amount for subtracting the amount of fuel supplied to the cylinder 9 via the fuel extraction passage 81 . Qid is calculated based on the fuel flow rate Qs in the fuel extraction passage 81 . By considering the fuel passing through the fuel extraction passage 81 in this way, the fuel injection amount Qi from the injector 7 can be calculated favorably.

Regarding the fuel injection amount control based on the severity, an upper guard value may be set for the fuel injection amount according to the severity. For example, an upper guard value may be set for the fuel injection amount Qi only when the weighting index X is equal to or greater than a predetermined value. Alternatively, an upper guard value that increases as the weighting index X increases may be set. By doing so, the fuel injection amount Qi can be limited to the upper guard value when the fuel becomes heavy, which is advantageous in suppressing knocking.

Detection of a first output voltage Va when CNG fuel flows through the fuel extraction passage 81, a second output voltage Vb when the first LNG fuel flows, and a second output voltage Vb when the second LNG fuel flows. The timing is different and random. Therefore, the calculation of the output difference ΔV and the weighting index X is performed based on the latest values every time those output voltages are detected. This makes it possible to always detect the latest fuel properties.

Of course, when the first LNG fuel is used, the weighting index X calculated based on the second output voltage Vb when the first LNG fuel is flowed is used for control. The same applies when using the second LNG fuel.

Next, the 1st modification is demonstrated.

As described above, the detection of the second output voltage Vb with the LNG fuel flowing through the fuel extraction passage 81 is performed when the pressure detected by the pressure sensor 62 is equal to or less than a predetermined value. However, since the LNG fuel is gas fuel, its pressure is still unstable, and the pressure of the fuel supplied to the fuel extraction passage 81 may fluctuate. Due to this pressure fluctuation, the output voltage VA of the fuel sensor 88 fluctuates, and the finally estimated heaviness, that is, the value of the heaviness index X may fluctuate.

FIG. 8 shows the situation at this time. The horizontal axis is time t. As shown in the figure, even if the value of the weighting index X fluctuates, the value of the weighting index X generally tends to increase as weight increases. Therefore, as indicated by points c1 to c3, if the value of the weighting index X is learned each time the maximum value is updated, the heaviness of the fuel can be very easily and accurately estimated. . Also, if the engine is controlled based on such a maximum value, it becomes the safest control, and problems such as knocking can be avoided as much as possible.

Therefore, in this modified example, severity estimation is performed based on this point of view. The procedure for estimating the severity of this modification will be described below with reference to FIG. 9 .

In the procedure of this modified example, steps S201 to S204 are the same as steps S101 to S104 of the basic embodiment (FIG. 6). The difference is that steps S203A and S203B are added between steps S203 and S204.

After calculating weighting index X in step S203, ECU 100 determines in step S203A whether weighting index X that has been calculated is greater than the already stored learning value Xmax.

If it is larger, in step S203B, the calculated weighting index X is replaced with the learned value Xmax, and the learned value Xmax is updated. As a result, every time the weighting index X exceeds the learning value Xmax, the learning value Xmax is updated, and the weighting index X is substantially fixed at the maximum value up to this point.

In step S204, the ignition timing θig and the fuel injection amount Qi are calculated based on the learned value Xmax. As a result, even if the weighting index X fluctuates, the ignition timing .theta.ig and the fuel injection amount Qi can be preferably controlled by eliminating the influence thereof.

On the other hand, when the weighting index X is equal to or less than the learned value Xmax in step S203A, step S203B is skipped and the process proceeds to step S204 without updating the learned value Xmax.

Note that the learned value Xmax is initialized to an initial value X0 (see FIG. 5) at an appropriate timing, such as when the LNG tank 50 is replenished with new fuel.

Although the embodiments of the present disclosure have been described in detail above, various other embodiments and modifications of the present disclosure are conceivable.

(1) For example, in the above embodiment, the output voltages Va and Vb are used as the output values of the fuel sensor 88. However, the present invention is not limited to this, and a volumetric flow rate obtained by converting the output voltages Va and Vb may be used. .

(2) The parameter or index value representing the degree of weight is not limited to the weighting index X, and any index value can be used. For example, the output difference ΔV may be used. Also, the weighting index X0 may be set to 1 when the fuel is the reference fuel.

(3) In the above embodiment, the severity is estimated based on the difference ΔV between the output voltages Va and Vb. can be estimated.

(4) Natural gas from the CNG tank 70 may not be used as engine fuel. That is, it may be used exclusively for detecting the output voltage Va.

(5) In the above embodiment, both the ignition timing θig and the fuel injection amount Qi are controlled based on the weighting index X, but either one may be controlled.

(6) In the above embodiment, the fuel extraction passage 81 is bifurcated and its upstream end is connected to the third passage 53 and the fourth passage 71 on the upstream side of the fuel rail 8, but this is not restrictive. For example, the fuel extraction passage 81 may be straight and its upstream end may be connected to the third passage 53 on the downstream side of the junction 72 or to the fuel rail 8 . In this case, the cutoff valves 85 and 86 can be omitted.

The configurations of the above-described embodiments and modifications can be partially or wholly combined as long as there is no particular contradiction. Embodiments of the present disclosure are not limited to the above-described embodiments, and include all modifications, applications, and equivalents encompassed by the concept of the present disclosure defined by the claims. Accordingly, the present disclosure should not be construed in a restrictive manner, and can be applied to any other technology that falls within the spirit of the present disclosure.

1 Internal combustion engine (engine)
3 intake passage 50 LNG tank 70 CNG tank 81 fuel extraction passage 88 fuel sensor 100 electronic control unit (ECU)
CD fuel property detector

Claims (6)

A fuel property detection device for detecting the property of fuel in an internal combustion engine, which is natural gas supplied from an LNG tank,
a CNG tank that stores natural gas as CNG;
a fuel passage switchably connected to the LNG tank and the CNG tank;
a sensor provided in the fuel passage and configured to detect a flow rate of natural gas;
a first output value of the sensor when a predetermined flow of natural gas from the CNG tank is flowing through the fuel passage; and said predetermined flow of natural gas from the LNG tank when flowing through the fuel passage. an estimating unit configured to estimate fuel heaviness based on the second output value of the sensor;
A fuel property detection device comprising: The fuel property detection device according to claim 1, wherein the estimation unit estimates the heaviness of the fuel based on the difference between the first output value and the second output value of the sensor. 3. The fuel property detection device according to claim 1, wherein natural gas flows through the fuel passage at a time other than when the internal combustion engine is in a fuel cut state. The fuel property detection device according to any one of claims 1 to 3, further comprising a control unit that controls at least one of ignition timing and fuel injection amount based on the fuel weight estimated by the estimation unit. The fuel property detection device according to any one of claims 1 to 4, wherein a downstream end of the fuel passage is connected to an intake passage of the internal combustion engine. The fuel property detection device according to any one of claims 1 to 5, wherein the natural gas from the CNG tank is used as fuel for the internal combustion engine.

Images