JP2021131054A - Fuel property detection device - Google Patents

Abstract

To suitably detect fuel properties.SOLUTION: A fuel property detection device CD for detecting properties of fuel of an internal combustion engine, which is natural gas supplied from an LNG tank 50, includes: a CNG tank 70 storing natural gas as CNG; a fuel passage 81 connected to the LNG tank and the CNG tank in a switchable manner; a sensor 88 provided in the fuel passage and configured to detect a flow rate of natural gas; and an estimation unit 100 configured to estimate heaviness of the fuel on the basis of a first output value obtained by the sensor when the natural gas at a predetermined flow rate from the CNG tank is flowing in the fuel passage and a second output value obtained by the sensor when the natural gas at the predetermined flow rate from the LNG tank is flowing in the fuel passage.SELECTED DRAWING: Figure 3

Description

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

An internal combustion engine that uses natural gas as a fuel is known, and a vehicle equipped with such an internal combustion engine as a power source, that is, a natural gas vehicle is known.

Japanese Unexamined Patent Publication No. 2003-12097

Fuel, which is a natural gas, may be stored in a fuel tank in a liquid state, that is, as LNG. In this case, the methane concentration in LNG decreases due to a long period of time or the like, the composition of LNG changes, and a weathering phenomenon occurs in which the fuel becomes heavy. If this change in fuel properties is ignored and no measures are taken, the operation of the internal combustion engine may be hindered.

Therefore, it is desirable to detect the fuel property and reflect the result in the control, but the actual situation is that a suitable fuel property detection device cannot be found.

Therefore, the present disclosure was devised 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
It is a fuel property detection device for detecting the properties of the fuel of an internal combustion engine, which is a 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 the flow rate of natural gas,
The first output value of the sensor when the natural gas from the CNG tank of the predetermined flow rate is flowing in the fuel passage, and the said when the natural gas from the LNG tank of the predetermined flow rate is flowing in the fuel passage. An estimation unit configured to estimate the fuel severity based on the second output value of the sensor, and
The fuel property detection device is provided.

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

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

Preferably, natural gas is flowed through the fuel passage at a time other than when the internal combustion engine is fuel-cut.

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

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

According to the present disclosure, fuel properties can be suitably detected.

It is the schematic which shows the internal combustion engine which concerns on this embodiment. A map for calculating ignition timing and fuel injection amount is shown. It is the schematic which shows the fuel supply apparatus. It is a graph which shows the output characteristic of a fuel sensor. A map showing the relationship between the output difference and the weighting index is shown. It is a flowchart which shows the procedure of severity estimation. A map showing the relationship between the heaviness index and the ignition timing correction amount and the fuel correction amount is shown. It is a time chart showing the state of fluctuation of the weighting index. It is a flowchart which shows the procedure of the severity estimation of the modification.

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to the following embodiments.

FIG. 1 is a schematic view showing an internal combustion engine according to the present embodiment. The internal combustion engine (also referred to as an engine) 1 uses natural gas as 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 a moving body other than a vehicle, for example, a ship, a construction machine, or an industrial machine. Further, the engine does not have to be mounted on a moving body, and may be a stationary engine. The fuel is stored as LNG in a fuel tank (not shown) in an ultra-low temperature state.

The engine 1 includes an engine main body 2, an intake passage 3 and an exhaust passage 4 connected to the engine main 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 a piston, a crankshaft, and a valve housed therein. The intake and exhaust flows are indicated by white arrows 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. The injector 7 injects fuel into the intake port or the cylinder 9. The 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 a 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 a 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 (particularly a cylinder head) and an exhaust pipe 21 arranged on the downstream side of the exhaust manifold 20. A turbine 14T of a 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 bypassing the turbine 14T is provided, which is provided with a waistgate valve 24.

The engine 1 also includes an EGR device 30. The EGR device 30 includes an EGR passage 31 for recirculating a part of the exhaust gas (referred to as EGR gas) in the exhaust passage 4 (particularly in the exhaust manifold 20) into the intake passage 3 (particularly in the intake manifold 10), and an EGR passage. An EGR cooler 32 for cooling the EGR gas flowing through the 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 a control unit, a circuit element (circuitry), or an electronic control unit (referred to as an ECU (Electronic Control Unit)) 100 that forms a controller. In the case of this embodiment, the ECU 100 constitutes an estimation unit as defined in the claims. The ECU 100 includes a CPU (Central Processing Unit) having a calculation function, a ROM (Read Only Memory) and a RAM (Random Access Memory) as storage media, an input / output port, and a storage device other than the ROM and the RAM.

The control device also includes the following sensors. That is, a rotation speed sensor 40 for detecting the rotation speed of the engine (specifically, the rotation speed (rpm) per minute), an accelerator opening sensor 41 for detecting the accelerator opening, and a ternary catalyst. It includes a lambda sensor 42 for detecting the excess air rate of the exhaust at the inlet of the 22 and an intake temperature sensor 43 and an intake pressure sensor 44 for detecting the temperature and pressure of the intake air on the downstream side of the intake throttle valve 16. .. The ECU 100 controls the above-mentioned various devices, that is, the injector 7, the spark plug 6, the intake throttle valve 16, the waist gate valve 24, and the EGR valve 33 based on the outputs of these sensors.

Regarding the basic control of the engine, the ECU 100 has a predetermined map (also as a function) based on the engine speed Ne, the intake air temperature T, and the intake pressure P detected by the rotation speed sensor 40, the intake air temperature sensor 43, and the intake pressure sensor 44, respectively. It is good. The same applies hereinafter), and the intake flow rate Ga is calculated or estimated. Alternatively, the intake flow rate Ga may be directly detected by the intake flow rate sensor provided in the intake passage 3.

Further, the ECU 100 is based on the detected and estimated engine speed Ne and the intake air flow Ga, and according to the map as shown in FIG. 2A, the basic injection amount Qib which is the basic value of the fuel injection amount injected from the injector 7. Is calculated.

Further, the ECU 100 calculates the basic ignition timing θigb, which is the basic value of the ignition timing in the spark plug 6, based on the detected and estimated engine speed Ne and the intake air flow Ga according to the map as shown in FIG. 2 (B). ..

Further, in the ECU 100, the accelerator opening degree Ac detected by the accelerator opening degree sensor 41 is a value equivalent to the accelerator fully closed, and the engine speed Ne detected by the rotation speed sensor 40 is higher than the predetermined return speed Nes. When the condition (referred to as the fuel cut execution condition) is satisfied, the fuel cut control for stopping the fuel injection by the injector 7 is executed. On the other hand, when the fuel cut execution condition is switched from being satisfied to not being satisfied, the ECU 100 ends the fuel cut control and returns to the normal control. 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 air excess ratio λt is, for example, 1 corresponding to the stoichiometric air-fuel ratio. The excess air ratio is an index value indicating the mixing ratio of fuel and air. As such an index value, the air-fuel ratio may be used instead of the excess air ratio.

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

As described above, in the fuel tank that stores fuel as LNG, the methane concentration in LNG decreases due to a long period of time, the composition of LNG changes, and a weathering phenomenon occurs in which the fuel becomes heavy. .. For example, a new fuel immediately after being refilled in a fuel tank, that is, a reference fuel, has the same composition as 13A city gas and contains 90% methane as a main component and other 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 value of the fuel decreases and the density increases.

If this change in fuel properties is ignored and no measures are taken, there is a risk that the control of the internal combustion engine will be hindered. In particular, when the fuel becomes heavier, the octane number decreases and knocking is more 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 according to the change in fuel properties.

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

FIG. 3 shows a fuel supply device FS for supplying fuel to the engine 1. The fuel supply device FS includes a fuel tank for storing fuel as LNG, that is, an LNG tank 50, and a fuel supply passage 13 for connecting the LNG tank 50 to the fuel rail 8. In the present embodiment, a plurality of (specifically, two) LNG tanks 50 are provided, and specifically, the first LNG tank 50A and the second LNG tank 50B are provided in parallel. The 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 that extracts and sends out liquid fuel (liquid natural gas) from the bottom of the first LNG tank 50A, and a second LNG passage 51B that extracts and sends out liquid fuel from the bottom of the second tank 50B. A third passage 53 having an upstream end connected to a confluence 52 of the first LNG passage 51A and the second LNG passage 51B is provided. The 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 for vaporizing liquid fuel and a shutoff valve 55A for opening and closing the outlet of the first vaporizer 54A. The shutoff valve 55A is composed of a solenoid valve. Outside the first LNG tank 50A, a first gas passage 56A connecting the upstream side of the first vaporizer 54A and the upper surface portion of the first LNG tank 50A is provided. A first economizer 57A is provided in the first gas passage 56A.

When methane in LNG vaporizes in the first LNG tank 50A and boil-off gas is generated, the pressure in the tank rises. When the pressure in the tank becomes equal to or higher than a predetermined value, the first economizer 57A opens like a relief valve and discharges the boil-off gas to the downstream side. As a result, the pressure inside the tank is reduced, and at the same time, the LNG becomes heavier. The first economizer 57A is closed when the pressure inside the tank is less than a predetermined value.

Separately from this, 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, and opens when the pressure inside the tank becomes 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 decompresses the inside of the tank.

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

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

Both tanks 50A and 50B are connected to a common filling port 61, and LNG is filled or replenished in both tanks 50A and 50B from the filling port 61.

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

On the other hand, the fuel supply device FS of the present embodiment also includes a fuel tank, that is, a CNG tank 70, which stores natural gas in a high-pressure gas 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 the present embodiment.

The CNG-derived natural gas has a stable composition, does not become heavy, and has substantially the same composition as the non-heavy LNG-derived fuel.

The fuel supply device FS includes 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 confluence 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 valve, fuels (referred to as first LNG fuel, second LNG fuel, and CNG fuel) from the first LNG tank 50A, the second LNG tank 50B, and the CNG tank 70 can be appropriately switched and supplied to the engine 1. ..

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

The downstream end of the fuel extraction passage 81 is connected to the intake passage 3 or the intake pipe 11 on the downstream side of the air cleaner 12 and on the upstream side 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 to prevent its release to the atmosphere. The fuel extraction passage 81 forms a fuel passage as defined in the claims.

In the fuel extraction passage 81, a shutoff valve 85 is provided at a position between the branch point 82 and the branch point 84, a shutoff valve 86 is provided at a position 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 the two.

In the fuel extraction passage 81, on the downstream side of the shutoff valve 87, a sensor configured to detect the flow rate of natural gas, that is, a fuel sensor 88 is provided. Details of the fuel sensor 88 will be described later.

Each of the above-mentioned shutoff valves 55A, 55B, 63, 65, 73, 75, 77, 85, 86, 87 is connected to the ECU 100 and is controlled to open and close by the ECU 100. Further, 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 each output is sent to the ECU 100.

When the engine is operated by the first LNG fuel, the shutoff valves 55A, 63, 65 are opened, the shutoff valves 55B, 73, 75, 77 are closed, and the first 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, the shutoff valves 86 are closed, and the first LNG fuel flows through the fuel extraction passage 81 and passes through the fuel sensor 88. Be made to. When the output value of the fuel sensor 88 is not detected, the shutoff valves 85, 86 and 87 are closed.

Similarly, when the engine is operated by 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, the shutoff valves 86 are closed, and the second LNG fuel flows through the fuel extraction passage 81 and passes through the fuel sensor 88. Be made to. When the output value of the fuel sensor 88 is not detected, the shutoff valves 85, 86 and 87 are closed.

When the engine is operated by CNG fuel, the shutoff valves 73, 75, 77 are opened, the shutoff valves 55A, 55B, 63, 65 are closed, and the CNG 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 86 and 87 are opened, the shutoff valves 85 are closed, and the CNG fuel is allowed 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 shutoff valves 85, 86 and 87 are closed.

In this way, 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 detecting the volumetric flow rate of natural gas (specifically, 13A city gas). The output characteristics of the fuel sensor 88 are as shown by the solid line a in FIG. As the volumetric flow rate Q (l / min) of natural gas increases, the output value of the sensor, that is, the output voltage VA (V) increases. As the fuel sensor 88, for example, a volume flow meter having a fixed gas density using a MEMS sensor can be used. The output voltage when Q = 0 is VA0.

When fuel is sent to the shutoff valve 87 located immediately before the fuel sensor 88, the shutoff valve 87 shuts off the flow of fuel when the valve is closed, but when the valve is opened, a constant predetermined flow rate Qs (for example, 2 (for example, 2 (for example) l / min)) fuel is sent to the downstream side. Therefore, when the shutoff valve 87 is opened, fuel having a predetermined flow rate of Qs is passed through the fuel sensor 88.

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

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

On the other hand, a new non-heavy-weighted first LNG fuel or second LNG fuel (collectively referred to as LNG fuel), that is, a reference LNG fuel has substantially the same composition as CNG fuel, and its methane value and density are also CNG. Substantially equal to fuel. Therefore, when the reference LNG fuel is passed through the fuel sensor 88, the output characteristic of the fuel sensor 88 becomes as shown by the solid line a.

However, it was found that as the LNG fuel becomes heavier than the standard LNG fuel, the output characteristics of the fuel sensor 88 gradually change as shown by the alternate long and short dash 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 between the output voltage of an arbitrary broken line (for example, b3) and the solid line a when the volumetric flow rate Q is a constant predetermined flow rate Qs is nothing but a parameter that reflects the severity of the LNG fuel. Therefore, in the present embodiment, the severity of the LNG fuel is estimated based on the output difference ΔV.

That is, in the ECU 100, the first output value of the fuel sensor 88 when the CNG fuel having a predetermined flow rate Qs is flowing in the fuel extraction passage 81, that is, the first output voltage Va, and the LNG fuel having a predetermined flow rate Qs in the fuel extraction passage 81. It is configured to estimate the severity of the LNG fuel based on the second output value of the fuel sensor 88 when it is flowing, that is, the output difference ΔV (= Vb−Va) from the second output voltage Vb.

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

A map as shown in the figure 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 the weighting index X corresponding to the output difference ΔV from the map, and estimates the fuel weight based on this. According to the map, as the output difference ΔV increases, a larger weighting index X is obtained.

When the engine is operated with CNG fuel, the ECU 100 flows CNG fuel having a predetermined flow rate Qs through the fuel sensor 88 as described above, and detects and acquires the first output voltage Va. Then, this value is memorized or learned, and is used for the subsequent severity estimation.

Since the first output voltage Va is detected at an appropriate timing described later and the severity of the LNG fuel is estimated from the output difference ΔV from this, it is heavier than the case where the first output voltage Va is set to an invariant fixed value. The quality estimation accuracy can be improved. That is, if the first output voltage Va is set to a fixed value, the influence of the deviation cannot be eliminated when the output of the fuel sensor 88 deviates due to sensor deterioration or the like. However, according to this embodiment, it is possible.

Severity estimation is performed 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.

The detection of each fuel by the fuel sensor 88 is performed 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 total amount of LNG fuel is consumed, when the LNG fuel becomes excessively heavy and becomes unusable, CNG fuel is used. It is used when a more preferable operating condition (for example, idling) is used.

The first LNG fuel and the second LNG fuel are used alternately so that the remaining amounts detected by the first remaining amount meter 60A and the second remaining amount meter 60B are as even as possible. That is, the first LNG tank 50A and the second LNG tank 50B that supply the LNG fuel to the engine are periodically and alternately switched each time the remaining amount in the tank decreases by a predetermined value. Severity estimation is performed immediately after this switching. Specifically, this is performed after a predetermined time (for example, several minutes) has elapsed from the time of switching to the stabilization of the fuel component passing through the fuel sensor 88. In addition, as the timing for estimating the severity, immediately after starting the engine, immediately after replenishing the tank with new LNG fuel, every timing when the integrated value of the fuel injection amount becomes a predetermined value, and the like can be mentioned.

Further, the LNG fuel is detected by the fuel sensor 88 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 pressure in the tank of the first LNG tank 50A reaches a predetermined value or more, the first economizer 57A opens the valve and discharges the boil-off gas in the tank. Then, the high-pressure boil-off gas is flowed to the downstream side at once, and as a result, the flow rate passing through the fuel sensor 88 may deviate from the predetermined flow rate Qs, and the severity estimation accuracy may deteriorate. Therefore, in the present embodiment, LNG fuel is detected only when the detection pressure of the pressure sensor 62 is equal to or less than a predetermined value without such boil-off gas emission, and the severity estimation accuracy is avoided from deteriorating. ..

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

The 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. Generally, the intake pressure tends to fluctuate on the downstream side of the compressor 14C and the downstream side of the intake throttle valve 16, but the intake pressure is stable near the atmospheric pressure on the upstream side 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 in order to be detected by the fuel sensor 88 at a time other than when the fuel of the engine 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 discharge is performed at the time of fuel cutting, the discharged natural gas is not ignited in the cylinder 9 and is discharged to the exhaust passage 4 without being burned. In order to prevent this, natural gas is prevented from flowing into the fuel extraction passage 81 at the time of fuel cutting.

Even if the downstream end of the fuel extraction passage 81 is not connected to the intake passage 3, it is preferable that the natural gas flows at a time other than the fuel cut. This is because it is considered that flowing natural gas through the fuel extraction passage 81 and fuel cutting are contradictory acts.

Next, the procedure for estimating the severity will be described with reference to FIG.

First, in step S101, the first output voltage Va of the fuel sensor 88 when the CNG fuel of the predetermined flow rate Qs is passed through the fuel extraction passage 81, and the fuel sensor when the LNG fuel of the predetermined flow rate Qs is flown through the fuel extraction passage 81. The 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 valves 85 when the engine is being operated with CNG fuel. The second output voltage Vb is detected by opening the shutoff valves 85 and 87 and closing the shutoff valves 86 when the engine is being operated with LNG fuel (either the first LNG fuel or the second LNG fuel). Will be done.

When detecting the first output voltage Va, CNG fuel may be allowed to flow through the fuel extraction passage 81 for a predetermined 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 the detection of the first output voltage Va, the value is stored in the ECU 100 as a learning value.

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

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. This makes it possible to suitably detect the properties, that is, the severity of the current LNG fuel. The calculated weighting index X is also stored in the ECU 100 as a learning value.

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

First, regarding the ignition timing θig, the ECU 100 calculates the 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, when the fuel is not weighted, and increases as the weighting index X increases.

Next, the ECU 100 calculates the ignition timing θig from the equation f1: θig = θigb−Δθig. The ignition timing θig is set to the advance angle side as the value increases. Therefore, as the severity increases, the ignition timing θig can be retarded, and knocking can be suitably suppressed.

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

Next, the ECU 100 calculates the fuel injection amount Qi from the equation 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 was found that when the fuel became heavier, the detected value of the excess air ratio λ detected by the lambda sensor 42 shifted to the rich side from the true value. Then, the control works in the direction of trying to reduce and correct the fuel injection amount. As a result, if no measures are taken, the amount of fuel will be insufficient, and the excess air rate will be controlled by shifting to the lean side. Therefore, a positive fuel correction amount ΔQi is added for the purpose of eliminating such rich deviation of the sensor. As a result, the deviation of the excess air rate toward 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 the fuel injection amount Qi calculated in this way. As a result, the severity 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.

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 formula 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 via the fuel extraction passage 81 in this way, the fuel injection amount Qi from the injector 7 can be suitably calculated.

Regarding the fuel injection amount control based on the severity, an upper limit guard value may be set for the fuel injection amount according to the severity. For example, the upper limit guard value may be set for the fuel injection amount Qi only when the weighting index X is equal to or higher than a predetermined value. Alternatively, an upper limit 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 limit guard value when the fuel becomes heavy, which is advantageous in suppressing knocking.

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

As a matter 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 flown is used for control. The same applies when the second LNG fuel is used.

Next, a first modification will be described.

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

FIG. 8 shows the state at this time. The horizontal axis is time t. As shown in the figure, even if the value of the aggravation index X fluctuates, the value of the aggravation index X generally tends to increase with the aggravation. Therefore, as shown by the points c1 to c3, if the weighting index X learns the value every time the maximum value is updated, the fuel weight can be estimated extremely easily and accurately. .. Further, if the engine is controlled based on such a maximum value, the control is on the safest side, and problems such as knocking can be avoided as much as possible.

Therefore, in this modification, the severity is estimated based on this viewpoint. Hereinafter, the procedure for estimating the severity of this modification will be described with reference to FIG.

In the procedure of this modification, steps S201 to S204 are the same as steps S101 to S104 of the above-mentioned basic embodiment (FIG. 6). The difference is that steps S203A and 203B are added between step S203 and step S204.

After calculating the weighting index X in step S203, the ECU 100 determines whether or not the calculated weighting index X is larger than the already stored learning value Xmax in step S203A.

If it is large, in step S203B, the calculated weighting index X is replaced with the learning value Xmax, and the learning 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 to the maximum value up to the present time.

In step S204, the ignition timing θig and the fuel injection amount Qi are calculated based on the learning value Xmax. As a result, even when the weighting index X fluctuates, the influence can be eliminated and the ignition timing θig and the fuel injection amount Qi can be preferably controlled.

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

The learning value Xmax is initialized to the initial value X0 (see FIG. 5) at an appropriate timing, for example, 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 can be considered.

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

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

(3) In the above embodiment, the severity is estimated based on the difference ΔV between the output voltages Va and Vb, but the severity is not limited to this, and is not limited to this, for example, the severity is estimated based on the ratio (Vb / Va) of the output voltages Va and Vb. The degree may be estimated.

(4) Natural gas from the CNG tank 70 does not have to be used as fuel for the engine. 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 the present invention is not limited to this. For example, the fuel extraction passage 81 may be formed into a straight tube, and the upstream end thereof may be connected to the third passage 53 on the downstream side of the confluence 72 or the fuel rail 8. In this case, the shutoff valves 85 and 86 can be omitted.

The configurations of the above-described embodiments and modifications can be combined partially or wholly, unless otherwise inconsistent. The embodiments of the present disclosure are not limited to the above-described embodiments, and all modifications, applications, and equivalents included in the ideas of the present disclosure defined by the claims are included in the present disclosure. Therefore, this disclosure should not be construed in a limited way and may be applied to any other technique that falls within the scope of the ideas of this 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)

It is a fuel property detection device for detecting the properties of the fuel of an internal combustion engine, which is a 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 the flow rate of natural gas,
The first output value of the sensor when the natural gas from the CNG tank of the predetermined flow rate is flowing in the fuel passage, and the said when the natural gas from the LNG tank of the predetermined flow rate is flowing in the fuel passage. An estimation unit configured to estimate the fuel severity based on the second output value of the sensor, and
A fuel property detection device characterized by being equipped with. The fuel property detection device according to claim 1, wherein the estimation unit estimates the severity of fuel based on the difference between the first output value and the second output value of the sensor. The fuel property detection device according to claim 1 or 2, wherein natural gas is flowed through the fuel passage at a time other than when the internal combustion engine is fuel-cut. 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 the ignition timing and the fuel injection amount based on the fuel severity estimated by the estimation unit. The fuel property detection device according to any one of claims 1 to 4, wherein the downstream end of the fuel passage is connected to the 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 a fuel for the internal combustion engine.

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