WO2020111630A1

WO2020111630A1 - Device and method for calculating pressure of fuel tank for compressed natural gas vehicle

Info

Publication number: WO2020111630A1
Application number: PCT/KR2019/015848
Authority: WO
Inventors: 이민광; 오승영
Original assignee: 주식회사 컨트롤웍스
Priority date: 2018-11-30
Filing date: 2019-11-19
Publication date: 2020-06-04
Also published as: KR102114830B1

Abstract

The present invention presents a device for calculating the pressure of a fuel tank, for calculating the pressure of a fuel tank to measure the amount of remaining fuel in the fuel tank of a compressed natural gas vehicle comprising the fuel tank, a regulator valve, a fuel rail, and an injector, the device comprising: an ECU for providing an injection flow amount of a fuel being injected from the injector, and an operation rate of the regulator valve; a rail pressure sensor for measuring and providing a rail pressure of the fuel rail for distributing the fuel to the injector; and a fuel amount calculation unit which derives a valve flow amount of the regulator valve on the basis of the rail pressure measured by the rail pressure sensor and the injection flow amount provided by the ECU, and which calculates, on the basis of the valve flow amount and the operation rate of the regulator valve provided by the ECU, a primary-side pressure of the fuel being introduced to the regulator valve, and which calculates the pressure of the fuel tank on the basis of the primary-side pressure.

Description

Compressed natural gas vehicle fuel tank pressure calculation device and calculation method

Embodiments disclosed herein relates to a fuel tank pressure calculation device and a calculation method for a compressed natural gas vehicle, and more specifically, by calculating the pressure of the fuel tank without the configuration of a pressure sensor that directly measures the pressure of the fuel tank. It relates to a fuel tank pressure calculation device for a compressed natural gas vehicle that can measure the residual amount of fuel.

2019 assignment number and resignation

1. Assignment No.: 1415162606

2. Remarks: This study was conducted as a result of the research of the core technology development project of the automobile industry by the Ministry of Trade, Industry and Energy and the Korea Institute of Industrial Technology Evaluation and Management (detailed task number: 10080284, core control algorithm and ECU development of the passenger Turbo CNG engine).

In general, compressed natural gas (CNS) is a fuel that can replace fuels such as gasoline or diesel, which are conventional fuels. It is used a lot.

Unlike a conventional gasoline vehicle, the amount of fuel is determined by the filling pressure in the fuel tank, and is usually charged at a pressure of about 200 to 300 bar.

Here, it is very important to check the residual amount of fuel in the fuel tank, regardless of whether it is a natural gas vehicle or a gasoline or diesel engine. This is because when the fuel in the fuel tank runs out, the vehicle stops while driving.

Accordingly, a general vehicle is equipped with a device capable of measuring the fuel condition in the fuel tank.

Specifically, in relation to the technology for measuring the fuel amount of a compressed natural gas vehicle, Korean Patent Nos. 10-0435720 and 10-1998-022008 disclose the pressure signal of a pressure sensor installed in a fuel tank. A technique for estimating and measuring the remaining amount of a fuel tank is disclosed.

However, it is difficult to accurately measure the pressure of the fuel tank because it varies depending on the operating conditions and temperature, such as the injection flow rate of the injector.

However, in the related art, since the residual amount of fuel was measured only through the measured value of the pressure sensor directly installed in the fuel tank, there was a problem in that it is impossible to accurately measure the residual amount of fuel.

Therefore, a technique for solving the above-described problem is needed.

On the other hand, the above-mentioned background technology is the technical information acquired by the inventor for the derivation of the present invention or acquired in the derivation process of the present invention, and is not necessarily a known technology disclosed to the general public before filing the present invention. .

Embodiments disclosed herein can measure the residual amount of fuel by calculating the pressure of the fuel tank through data based on the operating conditions of the engine without the configuration of a pressure sensor that directly measures the pressure of the fuel tank. The purpose of the present invention is to present an apparatus and method for calculating the pressure of a fuel tank for a compressed natural gas vehicle.

Specifically, the embodiments disclosed in this specification are based on the operating condition data of the engine, such as the injection flow rate of the injector or the driving rate of the regulator valve, while interpolating and deriving the pressure value through the pre-stored measurement value, thereby obtaining accurate measurement. It is an object of the present invention to provide a fuel tank pressure calculation device and a calculation method for compressed natural gas vehicles that can omit the configuration of the tank pressure sensor.

In addition, in the embodiments disclosed herein, in deriving the pressure of the fuel tank, the pressure of the fuel rail based on the temperature of the fuel can be compensated for more accurate measurement by compressing the pressure of the fuel tank fuel tank vehicle fuel tank pressure The purpose is to present a calculation device and a calculation method.

As a technical means for achieving the above-described technical problem, one aspect of the fuel tank pressure calculating device for a compressed natural gas vehicle includes a fuel tank, a regulator valve, a fuel rail, and an injector. In the fuel tank pressure calculating device for calculating the pressure of the fuel tank to measure the, comprising: an ECU providing an injection flow rate of the fuel injected from the injector and a driving rate of the regulator valve; A rail pressure sensor for measuring and providing rail pressure of a fuel rail that distributes fuel to the injector; And deriving a valve flow rate of the regulator valve based on the rail pressure measured by the rail pressure sensor and the injection flow rate provided by the ECU, and based on the valve flow rate and the driving rate of the regulator valve provided by the ECU. In addition, it may include a fuel amount calculating unit for calculating a primary pressure of fuel flowing into the regulator valve and calculating the pressure of the fuel tank based on the primary pressure.

In addition, as a technical means for achieving the above-described technical problem, one aspect of the method for calculating the pressure of a fuel tank for a compressed natural gas vehicle includes fuel provided in a compressed natural gas vehicle including a fuel tank, a regulator valve, a fuel rail, and an injector. In the fuel tank pressure calculation method that is performed by a tank pressure calculating device and calculates the pressure of the fuel tank to measure the fuel remaining amount of the fuel tank, the injection flow rate of the fuel injected from the injector and the driving of the regulator valve Collecting rates; Collecting rail pressure of a fuel rail that distributes fuel to the injector; Deriving a valve flow rate of the regulator valve based on the rail pressure of the fuel rail and the injector injection flow rate; Deriving a primary pressure of fuel flowing into the regulator valve based on a valve flow rate of the regulator valve and a driving rate of the regulator valve; And calculating the pressure of the fuel tank based on the primary pressure.

According to any one of the above-described problem solving means, without the configuration of a pressure sensor that directly measures the pressure of the fuel tank, the residual amount of fuel can be measured by calculating the pressure of the fuel tank through data based on the operating conditions of the engine. Compressed natural gas vehicle fuel tank pressure calculation device and calculation method can be presented.

In particular, it is possible to calculate the accurate measurement value by interpolating and deriving the pressure value through the pre-stored measurement value based on the operating condition data of the engine, such as the injection flow rate of the injector or the driving rate of the regulator valve, and constructing the tank pressure sensor. Since it can be omitted, it is possible to present a fuel tank pressure calculation device and a calculation method for a compressed natural gas vehicle that can simplify the configuration and volume of the device.

In addition, when the configuration of the rail temperature sensor is added, a fuel tank pressure calculation device and a calculation method for a compressed natural gas vehicle that can achieve a more accurate measurement by correcting the measured value of the rail pressure sensor according to the temperature of the fuel are presented. Can be.

The effects obtained in the disclosed embodiments are not limited to the above-mentioned effects, and other effects not mentioned are obvious to those skilled in the art to which the embodiments disclosed from the following description belong. Can be understood.

1 is a system diagram showing a fuel tank pressure calculating device for a compressed natural gas vehicle according to an embodiment.

2 is a configuration diagram showing a fuel tank pressure calculating device for a compressed natural gas vehicle according to an embodiment.

3 is an exemplary diagram illustrating graphically data for each condition stored in a valve pressure deriving unit of a fuel tank pressure calculating device for a compressed natural gas vehicle according to an embodiment.

FIG. 4 is a configuration diagram showing a valve pressure lead portion shown in FIG. 2.

5 is a flow chart showing a method for calculating the pressure of a fuel tank for a compressed natural gas vehicle according to an embodiment.

Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. The embodiments described below may be embodied in various different forms. In order to more clearly describe the features of the embodiments, detailed descriptions of the items well known to those of ordinary skill in the art to which the following embodiments pertain are omitted. In the drawings, parts irrelevant to the description of the embodiments are omitted, and like reference numerals are assigned to similar parts throughout the specification.

Throughout the specification, when a component is "connected" to another component, this includes not only a case of'directly connecting', but also a case of'connecting another component in between.' In addition, when a configuration is said to "include" a configuration, this means that, unless specifically stated otherwise, it may mean that other configurations may be included as well.

1 is a system diagram showing a fuel tank pressure calculating device for a compressed natural gas vehicle according to an embodiment, and FIG. 2 is a configuration diagram showing a fuel tank pressure calculating device for a compressed natural gas vehicle according to an embodiment, and FIG. 3 is one embodiment It is an exemplary diagram illustrating graphically data for each condition stored in a valve pressure deriving unit of a fuel tank pressure calculating device for a compressed natural gas vehicle according to an example. In addition, it is a configuration diagram showing the valve pressure delivery unit shown in Figure 2, Figure 5 is a flow chart showing a fuel tank pressure calculation method for a compressed natural gas vehicle according to an embodiment.

Compressed natural gas vehicle fuel tank pressure calculation device according to an embodiment is applied to a vehicle using compressed natural gas (CNS) as fuel, and fuel for measuring the remaining amount of a fuel tank in which compressed natural gas is stored It is a device that can calculate the pressure of the tank without the tank pressure sensor.

Here, the fuel tank pressure calculation device for a compressed natural gas vehicle according to an embodiment is compressed, including a fuel tank 1, a regulator valve 2, a fuel rail 3, and an injector 4 as shown in FIG. It can be applied to natural gas vehicles.

Specifically, the fuel tank 1 is a component in which the compressed natural gas is filled at a set pressure, and the compressed natural gas may be filled at a pressure of 200 to 300 bar.

The regulator valve 2 is a component that supplies fuel discharged from the fuel tank 1 to the engine at a uniform flow rate and pressure. The regulator valve 2 can supply fuel while being opened and closed by the control of the ECU 100 of the vehicle.

The fuel rail 3 is a component that distributes the fuel supplied from the regulator valve 2 to the injector 4, and the injector 4 operates under the control of the ECU 100 of the vehicle while the fuel rail 3 is operated. It is a component that injects fuel into the engine.

Here, the fuel tank pressure calculating device for a compressed natural gas vehicle according to an embodiment may form a compressed natural gas vehicle together with the above components, and form a separate independent module to the fuel supply line of the compressed natural gas vehicle. It may be installed.

Specifically, the fuel tank pressure calculating device for a compressed natural gas vehicle may include an ECU 100, a rail pressure sensor 200, and a fuel amount calculating unit 10 as shown in FIG. 1.

The ECU 100 is an electronic control unit and is a conventional computer that controls a vehicle. As is known, the ECU 100 can control the flow rate of fuel, ignition timing, engine rotation speed, and valve timing.

In particular, the ECU 100 is applied to the fuel tank pressure calculating device for a compressed natural gas vehicle according to an embodiment, and the injection flow rate injected from the injector 4 and the driving rate of the regulator valve 2, that is, the operating conditions of the engine Accordingly, the degree to which the regulator valve 2 is opened can be provided.

Here, the ECU 100 may calculate and provide the injection flow rate of the injector 4 and the driving rate of the regulator valve 2 through a set program, or may be provided by sensing through a detection signal of a separate detection sensor. .

In addition, the ECU 100 can measure the injection flow rate of the injector 4 and the driving rate of the regulator valve 2 on the same time, and unlike this, the injection flow rate of the injector 4 and the driving rate of the regulator valve 2 Each can be measured as the average value of the values collected over a period of time.

The rail pressure sensor 200 is a component that measures and applies the rail pressure of the fuel rail 3 described above.

The rail pressure sensor 200 can measure the rail pressure of the fuel rail 3 at the same time as the injection flow rate of the injector 4 by the ECU 100 and the driving rate of the regulator valve 2, unlike this It can also be measured as the average value of the values collected over a set period of time.

The fuel amount calculating unit 10 derives the valve flow rate of the regulator valve 2 based on the rail pressure measured by the rail pressure sensor 200 and the injection flow rate provided by the ECU 100, and the derived valve flow rate and ECU The pressure of the fuel tank 1 is calculated based on the calculated primary pressure by calculating the primary pressure of the fuel flowing into the regulator valve 2 based on the driving rate of the regulator valve 2 provided in (100). Component.

The fuel amount calculating unit 10 may be mounted on the ECU 100 described above in a program form, or alternatively, may be mounted on a separate substrate and installed on a vehicle fuel supply line.

Here, the fuel amount calculating unit 10 may calculate the pressure of the fuel tank 1 when the engine state of the compressed natural gas vehicle is in a normal state, and the calculated ECU 100 of the pressure of the fuel tank 1 is described above. However, the pressure calculated by applying the fuel gauge of a vehicle instrument panel, not shown, may be displayed as a residual amount that can be recognized by the user.

Specifically, as shown in FIG. 2, the fuel amount calculating unit 10 may be configured to include a valve flow rate guiding part 300, a valve pressure guiding part 400 and a tank pressure calculating part 500.

The valve flow rate deriving part 300 is a component that derives a flow rate of fuel supplied from the regulator valve 2 described above.

The valve flow rate introduction part 300 includes the rail pressure P1 of the fuel rail 3 measured by the rail pressure sensor 200 and the injection flow rate Q1 of the injector 4 provided by the ECU 100. Based on the can calculate the valve flow rate (Q2) of the regulator valve (2).

Specifically, the valve flow rate deriving unit 300 may calculate the valve flow rate Q2 of the regulator valve 2 through Equation 1 below.

[Equation 1]

Here, P1: rail pressure of the fuel rail 3, Q1: injection flow rate of the injector 4, Q2: valve flow rate of the regulator valve 2, β: elastic modulus, V: volume of the fuel rail 3.

Meanwhile, a rail temperature sensor 600 may be installed on the fuel rail 3 as shown in FIG. 1.

The rail temperature sensor 600 may measure the fuel temperature of the fuel rail 3 and provide it to the valve flow rate deriving unit 300 described above.

Here, the higher the temperature of the fuel, the higher the pressure, and the measured value of the rail pressure sensor 200 may be measured higher than the actual fuel pressure.

That is, the rail temperature sensor 600 is a component for correcting an error as the pressure of the fuel increases with the temperature of the fuel.

Accordingly, the above-described valve flow rate deriving unit 300 in deriving the valve flow rate Q2 of the regulator valve 2, the rail pressure sensor 200 based on the temperature of the fuel measured by the rail temperature sensor 600 After correcting the rail pressure (P1) of the fuel measured in can be derived the valve flow rate (Q2).

The valve pressure introduction unit 400 is a component that derives the primary pressure of fuel flowing from the fuel tank 1 into the regulator valve 2.

As shown in FIG. 3, the valve pressure deriving unit 400 includes the valve flow rate Q2 of the regulator valve 2 derived from the aforementioned valve flow deriving unit 300 and the regulator valve 2 provided by the ECU. The primary pressure P2 of the regulator valve 2 can be derived based on the driving rate C.

Here, the valve pressure leading part 400 may include a valve characteristic data part 410 and an interpolation leading part 420 as shown in FIG. 4.

The valve characteristic data unit 410 is a component that stores valve characteristic data indicating a relationship between a valve flow rate Q2 and a driving rate C for the regulator valve 2 for a plurality of different primary pressure condition values.

For example, as shown in FIG. 3, the valve characteristic data unit 410 correlates the valve flow rate Q2 and the driving rate C under the conditions that the primary pressure of the regulator valve 2 is 300 bar, 250 bar, 200 bar, and 100 bar. Relationships can be stored as data.

The valve characteristic data unit 410 may be applied with an artificial intelligence module such as machine learning to store the valve flow rate Q2 and the driving rate C according to the primary pressure condition value.

The interpolation lead-out unit 420 is a component that derives the primary pressure P2 of the regulator valve 2 based on the condition values stored in the aforementioned valve characteristic data unit 410.

Specifically, the interpolation lead section 420 includes a valve flow rate Q2 of the regulator valve 2 derived from the valve flow guide section 300, a driving rate C of the regulator valve 2 provided by the ECU, and valve characteristics Based on the condition values stored in the data portion 410, a primary pressure value corresponding to the measured values of the valve flow rate Q2 and the drive rate C can be derived, and the conditions pre-stored in the valve characteristic data portion 410 The primary pressure P2 can be derived while interpolating through the values.

The tank pressure calculating part 500 is a component for calculating the pressure of the fuel tank 1 based on the primary pressure P2 of the regulator valve 2 derived from the valve pressure extracting part 400.

The tank pressure calculating unit 500 may be calculated by applying a correction value of the fuel pipe 1a to the primary pressure P2 of the regulator valve 2 derived from the valve pressure extracting unit 400.

Specifically, the tank pressure calculating unit 500 is a primary side of the regulator valve 2 with a correction value having different characteristics according to the length or diameter of the fuel pipe 1a connecting the fuel tank 1 and the regulator valve 2 By applying to the pressure P2, the pressure of the fuel tank 1 can be calculated.

A method of calculating the pressure of the fuel tank using the fuel tank pressure calculating device for a compressed natural gas vehicle according to an embodiment including the above components will be described with reference to FIG. 5.

First, the ECU 100 constituting the fuel tank pressure calculating device for the compressed natural gas vehicle determines whether the state of the engine of the compressed natural gas vehicle is maintained in a normal state, and in the normal state, determines the pressure of the fuel tank 1. Calculate (S10).

At this time, the ECU 100 detects and provides the injection flow rate Q1 of the injector 4 and the driving rate C of the regulator valve 2 (S100).

The rail pressure sensor 200 measures and provides the rail pressure P1 of the fuel rail 3 (S200).

The valve flow rate deriving unit 300 calculates the flow rate Q2 of the regulator valve 2 by applying the injection flow rate Q1 and the rail pressure P1 to [Equation 1] (S300).

[Equation 1]

(β: Elastic modulus, V: Fuel rail volume)

The valve pressure introduction unit 400 calculates the primary pressure P2 of the regulator valve 2 through the flow rate Q2 of the regulator valve 2 and the driving rate C of the regulator valve 2 (S400). .

At this time, the valve pressure deriving unit 400 stores the valve flow rate Q2 and the driving rate C according to the primary pressure condition value in the valve characteristic data unit 410 (S410), and the interpolation introducing unit 420 Based on the data stored in the valve characteristic data unit 410, the primary pressure P2 of the regulator valve 2 is derived (S420).

At this time, the interpolation lead-out section 420 provides valve flow rate Q2 of the regulator valve 2 derived from the valve flow rate guide section 300 and the driving rate C of the regulator valve 2 provided from the ECU. While deriving the pressure values corresponding to the measured valve flow rate (Q2) and drive rate (C) by applying to the unit 410, interpolating through the pre-stored condition values in the valve characteristic data unit 410, the primary pressure (P2) Can be derived.

In addition, the tank pressure calculating unit 500 applies the correction value of the fuel pipe 1a to the primary pressure P2 of the regulator valve 2 derived from the valve pressure extracting unit 400 to apply the pressure of the fuel tank 1. Calculate

The pressure of the fuel tank 1 calculated as described above may be displayed as a residual amount corresponding to the calculated pressure while being applied to the fuel gauge of a vehicle instrument panel not shown.

As described above, the fuel tank pressure calculation device and calculation method for a compressed natural gas vehicle according to an embodiment include an engine such as an injection flow rate Q1 of the injector 4 or a driving rate C of the regulator valve 2. It is possible to calculate the accurate measurement value by interpolating and deriving the pressure value (P2) of the regulator valve (2) through the pre-stored measurement value based on the operating condition data of the device, since the configuration of the tank pressure sensor can be omitted. Its configuration and volume can be simplified.

The above-described embodiments are for illustration only, and those having ordinary knowledge in the technical field to which the above-described embodiments belong can easily be modified into other specific forms without changing the technical idea or essential features of the above-described embodiments. You will understand. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope to be protected through the present specification is indicated by the claims, which will be described later, rather than the detailed description, and should be interpreted to include all modified or modified forms derived from the meaning and scope of the claims and equivalent concepts thereof. .

Claims

In the fuel tank pressure calculation device for calculating the pressure of the fuel tank in order to measure the fuel level of the fuel tank of the compressed natural gas vehicle including a fuel tank, a regulator valve, a fuel rail, an injector,

An ECU providing an injection flow rate of fuel injected from the injector and a driving rate of the regulator valve;

A rail pressure sensor for measuring and providing rail pressure of a fuel rail that distributes fuel to the injector; And

The valve flow rate of the regulator valve is derived based on the rail pressure measured by the rail pressure sensor and the injection flow rate provided by the ECU, and based on the valve flow rate and the driving rate of the regulator valve provided by the ECU. A fuel tank pressure calculating device for a compressed natural gas vehicle, comprising a fuel amount calculating unit for calculating a primary pressure of fuel flowing into the regulator valve and calculating the pressure of the fuel tank based on the primary pressure.
According to claim 1,

The fuel amount calculation unit,

A valve flow rate deriving unit for deriving a valve flow rate of the regulator valve based on the rail pressure measured by the rail pressure sensor and the injection flow rate provided by the ECU;

A valve pressure deriving unit for deriving a primary pressure of fuel flowing into the regulator valve based on the valve flow rate derived from the valve flow rate deriving unit and a driving rate of the regulator valve provided by the ECU; And

Compressed natural gas vehicle fuel tank pressure calculating device including a tank pressure calculating unit for calculating the pressure of the fuel tank based on the primary pressure derived from the valve pressure deriving unit.
According to claim 1,

The fuel amount calculation unit,

A fuel tank pressure calculating device for a compressed natural gas vehicle, which calculates the pressure of the fuel tank when the engine of the compressed natural gas vehicle is in a normal state.
According to claim 2,

The valve pressure introduction unit,

A valve characteristic data unit for storing valve characteristic data representing a relationship between a valve flow rate and a driving rate for the regulator valves for each condition value of a plurality of different primary pressures; And

The primary pressure value is derived based on the valve flow rate derived from the valve flow rate deriving part, the driving rate of the regulator valve provided by the ECU, and the valve characteristic data part, and the condition value stored in the valve characteristic data part Vehicle interpolation pressure calculation device including an interpolation lead to derive the primary pressure value based on interpolation.
According to claim 2,

The tank pressure calculation unit,

Compressed natural gas vehicle fuel for calculating the pressure of the fuel tank by applying a correction value according to characteristics to the primary pressure of the regulator valve derived from the valve pressure deriving unit, and to a fuel pipe connecting the fuel tank and the regulator valve Tank pressure calculator.
According to claim 1,

The injection flow rate of the fuel, the driving rate of the regulator and the rail pressure of the fuel rail,

Compressed natural gas vehicle fuel tank pressure calculation device, characterized in that each is an average value collected over a period of time.
A fuel tank that is performed by a fuel tank pressure calculating device provided in a compressed natural gas vehicle including a fuel tank, a regulator valve, a fuel rail, and an injector, and calculates the pressure of the fuel tank to measure the fuel level of the fuel tank. In the pressure calculation method,

Collecting the injection flow rate of the fuel injected from the injector and the driving rate of the regulator valve;

Collecting rail pressure of a fuel rail that distributes fuel to the injector;

Deriving a valve flow rate of the regulator valve based on the rail pressure of the fuel rail and the injector injection flow rate;

Deriving a primary pressure of fuel flowing into the regulator valve based on a valve flow rate of the regulator valve and a driving rate of the regulator valve; And

And calculating the pressure of the fuel tank based on the primary pressure.
The method of claim 7,

The step of deriving the primary pressure,

Storing the valve flow rate and the driving rate for the regulator valve for each condition value of different primary pressures; And

Interpolating based on the derived value of the step of deriving the valve flow rate of the regulator valve and the condition value stored in the step of storing the primary pressure value corresponding to the measured value of the step of measuring the driving rate of the regulator valve. Compressed natural gas vehicle fuel tank pressure calculation method comprising the step of deriving.
The method of claim 7,

The step of calculating the pressure of the fuel tank,

Compression to calculate the pressure of the fuel tank by applying a correction value set differently according to the fuel pipe connecting the fuel tank and the regulator valve to the primary pressure of the regulator valve derived in the step of deriving the primary pressure. How to calculate the fuel tank pressure for natural gas vehicles.
The method of claim 7,

The fuel tank pressure calculation method,

Further comprising the step of determining whether the state of the engine of the compressed natural gas vehicle is maintained in a normal state,

If the state of the engine is a normal state, performing the remaining steps, the method for calculating the fuel tank pressure for a compressed natural gas vehicle.