JP7234862B2 - natural gas engine fuel supply - Google Patents

Description

The present disclosure relates to a fuel supply system for natural gas engines using natural gas as fuel.

Some fuel supply systems for such natural gas engines are provided with a plurality of tanks for liquefying and storing fuel.

JP 2014-152869 A

In such, it is preferred that the liquid fuel in each tank be consumed as evenly as possible. Therefore, each tank is provided with a valve, and by appropriately opening and closing the valve of each tank, the liquid fuel consumption of each tank is made uniform as much as possible.

However, when a certain valve is closed, it becomes very difficult to reduce the pressure in the tank corresponding to that valve. Therefore, there is a risk that the pressure inside the tank will rise abnormally, and it is necessary to take some sort of countermeasure.

Accordingly, the present disclosure was created in view of such circumstances, and an object of the present disclosure is to provide a fuel supply system for a natural gas engine that can avoid an abnormal increase in pressure within the tank.

According to one aspect of the present disclosure,
a first tank and a second tank that liquefy and store a fuel that is natural gas;
a first valve and a second valve respectively provided for the first tank and the second tank;
a detection unit for detecting amounts of liquid components of fuel respectively stored in the first tank and the second tank;
a control unit that controls opening and closing of the first valve and the second valve based on the amount of the liquid component of the fuel detected by the detection unit;
with
The control unit controls a predetermined closing prohibition condition for prohibiting closing of one of the first valve and the second valve even when a predetermined closing condition for closing one of the first valve and the second valve is satisfied. There is provided a fuel supply system for a natural gas engine, characterized in that closing of the one valve is prohibited when is established.

Preferably, the closing prohibition condition is set when the pressure in the tank corresponding to the one is equal to or higher than a predetermined abnormality judgment value, or when a pressure sensor provided for the tank corresponding to the one is abnormal. To establish.

According to the present disclosure, an abnormal increase in pressure inside the tank can be avoided.

It is a schematic diagram showing a fuel supply system of a natural gas engine concerning this embodiment. It is a figure which shows the method of opening-and-closing control of a 1st valve and a 2nd valve. 4 is a flow chart of a control routine of the embodiment; 4 is a time chart showing an example of control of the present embodiment; It is a time chart which shows an example of control of a modification. 10 is a flow chart of a control routine of a modified example;

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 a fuel supply system for a natural gas engine according to this embodiment. An engine (not shown) as an internal combustion engine is a natural gas engine that uses natural gas as fuel, and is used as a power source for vehicles, particularly large vehicles such as trucks. 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 engine is provided with an injector 1 for each cylinder. A fuel supply device is for supplying fuel to the injector 1 . The supplied fuel is injected from the injector 1 when the injector 1 is opened.

The fuel supply device includes a first tank T1 and a second tank T2 that liquefy and store fuel, a first valve V1 and a second valve V2 provided for the first tank T1 and the second tank T2, respectively; a detection unit for detecting (including estimating) the amount of the liquid component of the fuel respectively stored in the first tank T2 and the second tank T2; and a control unit that controls the opening and closing of the valve V1 and the second valve V2.

Since the first tank T1 and the second tank T2 are the same, only the first tank T1 will be described as a representative. The first tank T1 stores therein compressed and liquefied natural gas (LNG (Liquefied Natural Gas)). A liquid component of the fuel is accumulated in the lower layer in the first tank T1. The liquid component of this fuel is referred to as liquid fuel and is denoted by L. A gaseous component of the fuel is accumulated in the upper layer in the first tank T1. The gaseous component of this fuel is called a gaseous fuel and denoted by the symbol G. When no distinction is made between liquid and gaseous fuels, they are collectively referred to as fuels and denoted by the symbol F.

As is well known, the fuel F contains carbon compounds such as methane, ethane, propane and butane as compositions. Each composition has a different boiling point and a different octane number. Methane has the highest octane rating, followed by ethane, propane, and butane.

The upstream ends of the first tank outlet pipe B1 and the second tank outlet pipe B2 are individually connected to the upper ends of the first tank T1 and the second tank T2, respectively. The downstream ends of the first tank outlet pipe B1 and the second tank outlet pipe B2 are joined and connected to the upstream end of a common fuel supply pipe 2 . The downstream end of the fuel supply pipe 2 is branched and connected to the injector 1 of each cylinder (only one cylinder is shown). A pressure reducing valve 3 is provided in the middle of the fuel supply pipe 2 to reduce the pressure of the fuel to an appropriate pressure.

Since the first valve V1 and the second valve V2 are the same, only the first valve V1 will be described as a representative. The first valve V1 is formed by a solenoid valve and installed in the first tank outlet pipe B1. When the first valve V1 is opened, gaseous fuel in the first tank T1 is allowed to be supplied to the injector 1 through the first tank outlet pipe B1 and the fuel supply pipe 2. On the other hand, when the first valve V1 is closed, such supply of gaseous fuel is prohibited.

A first pressure sensor Sp1 for detecting the pressure in the first tank T1 and a first pressure sensor Sp1 for detecting the temperature in the first tank T1 are provided on the upstream side of the first valve V1 in the first tank outlet pipe B1. A temperature sensor St1 is provided. The first pressure sensor Sp1 and the first temperature sensor St1 substantially detect the pressure and temperature of the gaseous fuel G in the first tank T1. A second pressure sensor Sp2 and a second temperature sensor St2 are also provided in the second tank outlet pipe B2. These pressure sensor and temperature sensor may be provided in the tank.

The control unit is formed by an electronic control unit (referred to as an ECU (Electronic Control Unit)) 100 . The ECU 100 also controls the entire engine including the injector 1 . 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 ECU 100 receives output signals from the above-described sensors and the like, and outputs instruction signals to the above-described valves, the injector 1, and the like, via wiring and wireless communication devices (not shown).

The ECU 100 detects the amount M1 of the liquid fuel L in the first tank T1 based on the pressure P1 detected by the first pressure sensor Sp1 and the temperature T1 detected by the first temperature sensor St1 (specifically, presume.

Specifically, the ECU 100 calculates the volume Vg of the gaseous fuel G by applying the pressure P1 and the temperature T1 to the gaseous state equation (PV=nRT). Next, the ECU 100 calculates the amount (remaining amount) M1 of the liquid fuel L by subtracting the volume Vg of the gaseous fuel G from the prestored total volume of the first tank T1 and the first tank outlet pipe B1.

Similarly, the ECU 100 detects the amount M2 of the liquid fuel L in the second tank T2 based on the pressure P2 detected by the second pressure sensor Sp2 and the temperature T2 detected by the second temperature sensor St2.

Thus, the aforementioned detection unit is configured by the first pressure sensor Sp1, the first temperature sensor St1, the second pressure sensor Sp2, the second temperature sensor St2, and the ECU 100. FIG.

Generally, a method of installing a fuel level sensor in the tank is adopted to detect the amount of liquid fuel in the tank. However, fuel level sensors are generally expensive. On the other hand, pressure sensors and temperature sensors are generally inexpensive because they are general purpose items that are also used in other applications. In this embodiment, since the detection unit is composed of the pressure sensor and the temperature sensor, there is an advantage that the detection unit can be manufactured at low cost. However, the fuel level sensor may be used if there is no cost problem.

The pressure in each tank is highly dependent on the ambient temperature of the tank. However, in a vehicle, the ambient temperature of each tank is not always equal due to the layout of engine cooling water and fuel pipes. Therefore, in the tank with the higher atmospheric temperature, the vaporization rate of the liquid fuel L to the gaseous fuel G becomes higher than in the tank with the lower atmospheric temperature, and the pressure of the gaseous fuel G becomes higher. Therefore, if both the first valve V1 and the second valve V2 are opened, the gaseous fuel G in the tank with the higher pressure continues to be consumed preferentially or unilaterally, and the liquid fuel L in that tank continue to decline. In other words, the amount of fuel consumed may be uneven, and one tank may continue to consume fuel, while the other tank may not consume fuel.

In this case, in the tank that does not consume fuel, the composition ratio of the composition of the gaseous fuel G with a high carbon number (e.g., propane) increases, and the composition ratio of a composition with a low carbon number (e.g., methane) The phenomenon of heavy weight progresses. Then, since the octane number of the gaseous fuel G is lowered, the engine knocks when the gaseous fuel G in the tank is started to be used.

Therefore, it is preferable that the fuel consumption amount of each tank is not biased and equalized. For this reason, in this embodiment, the opening and closing of the first valve V1 and the second valve V2 are controlled to equalize the amount of liquid fuel in each tank as much as possible.

Specifically, as will be described later, the ECU 100 calculates the difference in the amount of liquid fuel in each tank, and controls the opening and closing of the first valve V1 and the second valve V2 so that this difference is equal to or less than a certain value. As a result, it is possible to equalize the amount of liquid fuel in each tank, thereby suppressing the heavy fuel and the resulting knocking and output reduction.

By the way, when one of the first valve V1 and the second valve V2 is closed, it becomes very difficult to reduce the pressure in the tank corresponding to that one valve. Therefore, there is a risk that the pressure inside the tank will rise abnormally, and it is necessary to take some sort of countermeasure.

Therefore, in this embodiment, the following control is performed to avoid an abnormal increase in the pressure inside the tank.

FIG. 2 shows a method of opening/closing control of the first valve V1 and the second valve V2 executed by the ECU 100. As shown in FIG. The vertical axis represents the remaining amount difference ΔM (=M1−M2), which is the difference between the amounts of liquid fuel L in the first tank T1 and the second tank T2, which is calculated by the ECU 100. FIG.

The ECU 100 compares the remaining amount difference ΔM with predetermined threshold values β, α, −α, −β (α, β>0, β>α), and each time the remaining amount difference ΔM exceeds or falls below the threshold, One of the first valve V1 and the second valve V2 is switched between open and closed states. Such switching has a hysteresis characteristic to prevent hunting. Specifically, it is as follows.

(1) The ECU 100 switches the second valve V2 from open to closed when a predetermined second valve closing condition (referred to as a V2 closing condition) is satisfied. The V2 closing condition is that (i) the first valve V1 is open, (ii) the second valve V2 is open, and (iii) the remaining amount difference ΔM exceeds the second valve closing threshold value (referred to as the V2 closing threshold value) β. established when This corresponds to the transition from state I to state II in FIG.

When the V2 closing condition is established, the remaining amount difference ΔM is large, and the liquid fuel amount M2 in the second tank T2 is much smaller than the liquid fuel amount M1 in the first tank T1. Therefore, in this case, the second valve V2 is closed in order to eliminate the fuel consumption of the second tank T2. This makes it possible to equalize the amount of liquid fuel.

(2) The ECU 100 switches the second valve V2 from closed to open when a predetermined second valve open condition (referred to as V2 open condition) is satisfied. The V2 open condition is that (i) the first valve V1 is open, (ii) the second valve V2 is closed, and (iii) the remaining amount difference ΔM is below the second valve opening threshold value (referred to as the V2 opening threshold value) α. established when This corresponds to the transition from state II to state III in FIG.

When the V2 open condition is established, the remaining amount difference ΔM is smaller than before, and the liquid fuel amount M1 in the first tank T1 is reduced due to consumption and approaches the liquid fuel amount M2 in the second tank T2. Therefore, in this case, the second valve V2 is opened to allow fuel consumption of the second tank T2.

(3) The ECU 100 switches the first valve V1 from open to closed when a predetermined first valve closing condition (referred to as V1 closing condition) is satisfied. The V1 closing conditions are as follows: (i) the first valve V1 is open, (ii) the second valve V2 is open, and (iii) the remaining amount difference ΔM exceeds the first valve closing threshold (referred to as the V1 closing threshold) −β. Established when below This corresponds to the transition from state III to state IV in FIG.

When the V1 closing condition is satisfied, the absolute value of the remaining amount difference ΔM is large, and the liquid fuel amount M1 in the first tank T1 is much smaller than the liquid fuel amount M2 in the second tank T2. Therefore, in this case, the first valve V1 is closed in order to eliminate the fuel consumption of the first tank T1. This makes it possible to equalize the amount of liquid fuel.

In this embodiment, the absolute value of the V1 close threshold-β is equal to the absolute value of the V2 close threshold β, but they may be different.

(4) The ECU 100 switches the first valve V1 from closed to open when a predetermined first valve open condition (referred to as V1 open condition) is satisfied. The V1 open conditions are as follows: (i) the first valve V1 is closed, (ii) the second valve V2 is open, and (iii) the remaining amount difference ΔM exceeds the first valve opening threshold (referred to as the V1 opening threshold) −α. Formed when exceeded. This corresponds to the transition from state IV to state V in FIG.

When the V1 open condition is satisfied, the absolute value of the remaining amount difference ΔM is smaller than before, and the amount of liquid fuel M2 in the second tank T2 decreases due to consumption and approaches the amount of liquid fuel M1 in the first tank T1. there is Therefore, in this case, the first valve V2 is opened to allow fuel consumption of the first tank T1.

In this embodiment, the absolute value of the V1 open threshold value -α is equal to the absolute value of the V2 open threshold value α, but they may be different.

In the state (I, III, V) where the first valve V1 is open and the second valve V2 is open (I, III, V), only the gaseous fuel G having the higher pressure flows toward the injector 1. supplied.

By the way, for example, even if the V2 closing condition is satisfied as described in (1), if the second valve V2 is closed as it is according to this, the pressure in the second tank T2 may rise abnormally and cause a problem. .

This case is, for example, the case where boil-off gas is generated in the second tank T2. When the boil-off gas is generated, the pressure in the second tank T2 may rise abnormally. In that case, the second tank T2 may be damaged.

Therefore, in the present embodiment, a second valve closing prohibition condition (referred to as a V2 closing prohibition condition) for prohibiting the closing of the second valve V2 is set in advance, and even when the V2 closing condition is satisfied, the V2 closing When the prohibition condition is satisfied, the closing of the second valve V2 is prohibited. As a result, the second valve V2 is opened, and an abnormal increase in pressure in the second tank T2 can be avoided.

Specifically, the V2 closing prohibition condition is established when the pressure P2 detected by the second pressure sensor Sp2 is equal to or greater than a predetermined abnormality determination value P2s, or when the second pressure sensor Sp2 is abnormal. When the pressure P2 becomes equal to or higher than the abnormality determination value P2s, it can be considered that the pressure in the second tank T2 has abnormally increased due to the generation of boil-off gas. To avoid. By opening the second valve V2, the generated boil-off gas can be consumed and the pressure in the tank can eventually be reduced to less than the abnormality determination value P2s. On the other hand, when the second pressure sensor Sp2 is abnormal, the detection value itself of the second pressure sensor Sp2 to be compared with the abnormality determination value P2s is unreliable. Therefore, the second valve V2 is closed for safety. to avoid an abnormal rise in tank internal pressure. Whether or not the second pressure sensor Sp2 is abnormal can be determined by the diagnosis function of the ECU 100 or the self-diagnosis function of the second pressure sensor Sp2 itself.

Prohibition of closing the valve based on such a closing prohibition condition is similarly applied under the V1 closing condition as described in (3) above. Briefly described below, a first valve closing prohibition condition (referred to as a V1 closing prohibition condition) is set in advance, and even when the V1 closing condition is satisfied, when the V1 closing prohibition condition is satisfied, the first valve Closing of V1 is prohibited. Specifically, the V1 closing prohibition condition is established when the pressure P1 detected by the first pressure sensor Sp1 is equal to or greater than a predetermined abnormality determination value P1s, or when the first pressure sensor Sp1 is abnormal.

Next, a control routine in this embodiment will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 100 at predetermined calculation intervals τ (for example, 10 msec).

First, in step S101, it is determined whether or not the V1 open condition is established. If not established, the process proceeds to step S103, and if established, the first valve V1 is opened in step S102, and then the process proceeds to step S103.

In step S103, it is determined whether or not the V2 open condition is established. If not established, the process proceeds to step S105, and if established, the second valve V2 is opened in step S104, and then the process proceeds to step S105.

In step S105, it is determined whether or not the V1 closing condition is established. If not established, the process proceeds to step S108.

If satisfied, it is determined in step S106 whether or not the V1 closing prohibition condition is satisfied. If not established, the process advances to step S107 to close the first valve V1, and then the process advances to step S108.

On the other hand, if it is established, skip step S107 and proceed to step S108. As a result, closing of the first valve V1 is substantially prohibited, and the first valve V1 is opened.

Similarly, in step S108, it is determined whether or not the V2 closing condition is established. If not satisfied, terminate the routine.

If so, it is determined in step S109 whether or not the V2 close prohibition condition is established. If not, the process proceeds to step S110, the second valve V2 is closed, and then the routine ends.

On the other hand, if the condition is established, step S110 is skipped and the routine ends. As a result, closing of the second valve V2 is substantially prohibited, and the second valve V2 is opened.

FIG. 4 shows an example of control in this embodiment. The horizontal axis is time t. Before time t1, the first valve V1 is open and the second valve V2 is open, and only the gaseous fuel G in the second tank T2, which has the higher pressure, is unilaterally consumed, and the liquid in the second tank T2 is consumed. Only the fuel quantity M2 is reduced.

At time t1, the remaining amount difference ΔM exceeds the V2 closing threshold value β, the V2 closing condition is established, and the V2 closing prohibition condition is not established, so the second valve V2 is closed. As a result, consumption of the gaseous fuel G in the second tank T2 is stopped, and only the gaseous fuel G in the first tank T1 is consumed, so that the amount of liquid fuel can be equalized.

After that, at time t2, the second valve V2 is opened because the remaining amount difference ΔM is below the V2 opening threshold value α.

After that, at time t3, the remaining amount difference ΔM falls below the V1 closing threshold value −β, and the V1 closing condition is established. However, at this time, since the V1 close prohibition condition is satisfied, the first valve V1 is prohibited from being closed, and the first valve V1 is still kept open.

Although not shown, after this, the first valve V1 is closed when the V1 close prohibition condition is no longer satisfied.

Next, a modified example will be described. As shown in FIG. 5, in this modification, basically, the open/closed states of the first valve V1 and the second valve V2 are alternately switched each time the engine operating time tk elapses a predetermined time γ. As a result, the fuel in the first tank T1 and the fuel in the second tank T2 are alternately consumed at equal intervals, so that the amount of liquid fuel in each tank can be equalized.

On the other hand, when the condition for prohibiting the closing of the V1 is satisfied even after the predetermined time γ has passed, the switching to close the first valve V1 is not performed. Similarly, when the V2 closing prohibition condition is satisfied even after the predetermined time γ has passed, switching to close the second valve V2 is not performed.

The ECU 100 counts the operating time tk using its own timer, and resets the operating time tk to zero when switching between the open and closed states of both valves is performed.

The basic control of this modified example is as follows.

(1) When a predetermined V2 closing condition is satisfied, the ECU 100 switches the second valve V2 from open to closed and switches the first valve V1 from closed to open. The V2 closed condition is satisfied when (i) the first valve V1 is closed, (ii) the second valve V2 is open, and (iii) the operation time tk exceeds the predetermined time γ. This corresponds to switching at time t1 in FIG.

(2) When a predetermined V1 closing condition is satisfied, the ECU 100 switches the first valve V1 from open to closed and switches the second valve V2 from closed to open. The V1 closed condition is satisfied when (i) the first valve V1 is open, (ii) the second valve V2 is closed, and (iii) the operating time tk exceeds the predetermined time γ. This corresponds to switching at time t2 in FIG.

On the other hand, the V1 close prohibition condition and the V2 close prohibition condition in this modified example are the same as those in the above-described basic embodiment.

Even when the V2 close condition is satisfied, when the V2 close prohibition condition is satisfied, the switching of the second valve V2 to closed and the switching of the first valve V1 to open are not performed. . This corresponds to the state at time t3 in FIG.

Similarly, although not shown, even when the V1 closing condition is satisfied, when the V1 closing prohibition condition is satisfied, the first valve V1 is switched to closed and the second valve V2 is opened. switching is not performed.

FIG. 6 shows the control routine of this modification. In this modification, steps S101 to S104 of the basic embodiment (FIG. 3) are omitted, and only steps S205 to S210 similar to steps S105 to S110 of the basic embodiment are executed. Thereby, the control of this modified example can be executed smoothly.

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, the number of tanks storing fuel and valves corresponding thereto may be three or more. In this case, the present disclosure can be applied to any two.

(2) Similarly, the number of tank outlet pipes, pressure sensors, and temperature sensors corresponding to the tank may be three or more.

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.

T1 First tank T2 Second tank V1 First valve V2 Second valve Sp1 First pressure sensor Sp2 Second pressure sensor 100 Electronic control unit (ECU)

Claims (2)

a first tank and a second tank that liquefy and store a fuel that is natural gas;
a first valve and a second valve respectively provided for the first tank and the second tank;
a detection unit for detecting amounts of liquid components of fuel respectively stored in the first tank and the second tank;
a control unit that controls opening and closing of the first valve and the second valve based on the amount of the liquid component of the fuel detected by the detection unit;
with
The control unit is
opening and closing the first valve and the second valve so as to equalize the amount of the liquid component in the first tank detected by the detection unit and the amount of the liquid component in the second tank; ,
Even when a predetermined closing condition for closing one of the first valve and the second valve is satisfied, a predetermined closing prohibition condition for prohibiting closing of the one valve is satisfied. sometimes prohibiting closing of said one valve ,
The closing prohibition condition is when the pressure in the tank corresponding to the one abnormally rises to a predetermined abnormality judgment value or more, or when the pressure sensor provided for the tank corresponding to the one is abnormal. be established in
A fuel supply device for a natural gas engine, characterized by: The control unit controls the opening and closing of the first valve and the second valve so that the difference between the amount of the liquid component in the first tank and the amount of the liquid component in the second tank is equal to or less than a predetermined value. The fuel supply system for a natural gas engine according to claim 1, characterized by:

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