This application is based on and claims the benefit of priority from Japanese Patent Application No. 2018-069351, filed on 30 Mar. 2018, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a gas filling method. To be more particular, the invention relates to a gas filling method of filling a tank of a moving object, in which a supply source of a compressed gas and the tank mounted on the moving object are connected via a tube system.

Related Art

In a fuel cell vehicle, oxygenated air and hydrogen gas which is a fuel gas are supplied to a fuel cell, thereby, generating power, and an electric motor is driven by using the power. In this manner, the fuel cell vehicle runs. In recent years, the fuel cell vehicle using the fuel cell as an energy source for generating power is promoted to a practical use. It is necessary to use hydrogen gas in order to generate power with the fuel cell; in recent years, the fuel cell vehicle, in which a sufficient amount of hydrogen gas is stored in a hydrogen tank having a high-pressure tank or a storage alloy in advance, and the hydrogen gas in the tank is used for running is in a process of going mainstream. In addition, in accordance with this, studies on a filling technology of rapidly filling the tank with hydrogen gas as much as possible in a hydrogen station are actively progressed.

In addition, in order to rapidly fill the tank with hydrogen gas, it is necessary to acquire information on the tank as rapid as possible by the hydrogen station side. Therefore, a step of filling the tank with the hydrogen gas in the hydrogen station is divided into an initial filling step of tentatively filling the tank with gas in order to acquire information of the hydrogen tank and a main filling step of filling the tank with gas so as to set a target pressure increase ratio by using the information acquired in the initial filling step and realize the target pressure increase ratio.

In addition, a tank volume is one item of the information of the tank, which needs to be acquired by the hydrogen station side. In addition, a specific device that acquires the volume of the tank includes 1. estimating by using an infrared communication signal (IR communication signal) that is transmitted from a vehicle side and 2. estimating by filling the tank with a small amount of gas in the initial filling step. Incidentally, in a case where it is not possible to acquire the volume, the filling is performed at a slowest filling rate. In addition, a specific example of 2. is described in PCT International Publication No. WO2017/159314 by the applicant of the present application. In a method disclosed in Patent Document 2, a tank volume is estimated by a simultaneous gas equation which is established at two different time points. Hence, in a case where the tank volume is estimated by the method, estimation accuracy of the volume improves as an amount of hydrogen gas, with which filling is performed in the initial filling step, increases.

SUMMARY OF THE INVENTION

Besides, in recent years, the fuel cell vehicles are further widely used, and thereby development of a large-sized fuel cell vehicle such as a bus or a small-sized fuel cell vehicle such as a two-wheel vehicle is also progressed. A tank used in the large-sized or small-sized fuel cell vehicle is assumed to have a volume that is larger or smaller than a range of 2.0 to 10.0 kg that is set for a fuel cell vehicle assumed to be a general automobile in the related art. Incidentally, hereinafter, a tank having a volume within the range of 2.0 to 10.0 kg is referred to as a regular-sized tank, a tank having a volume larger than 10.0 kg is referred to as a large-sized tank, and a tank having a volume smaller than 2.0 kg is referred to as a small-sized tank.

However, in a case where the volume of the large-sized tank is estimated by using an estimation method of the related art, an amount of hydrogen gas filling is insufficient, and thus pressure changes little. As a result, there is a concern that estimation accuracy is degraded. In addition, in a case where the volume of the small-sized tank is estimated by using an estimation method of the related art, an amount of hydrogen gas filling is too much, and thus there is a concern that a temperature increases too high and filling is performed with too much amount before the tank volume is estimated.

An object of the invention is to provide a gas filling method in which it is possible to estimate a volume of a tank having various sizes with high accuracy.

(1) A gas filling system includes a gas supply device having a supply source of a compressed gas, a moving object having a tank that contains the gas, a tube system that connects the supply source and the tank, and a flow rate sensor and a pressure sensor provided on the tube system. A gas filling method according to the invention is a method of filling the tank with the gas from the supply source by the gas filling system and includes a volume estimating step of estimating a tank volume, which is a volume of the tank, based on detection values of the flow rate sensor and the pressure sensor and a volume value of the tube system, after a start of filling of the tank with the gas from the supply source.

(2) In this case, it is preferable that the gas filling method further includes a coefficient calculating step of calculating a value of a coefficient related to a pressure loss, which occurs when the gas flows in the tube system, based on the detection values of the flow rate sensor and the pressure sensor when the filling of the tank with the gas from the supply source is stopped, in which, in the volume estimating step, the tank volume is estimated based on the detection values of the flow rate sensor and the pressure sensor, the volume value of the tube system, and a pressure loss value calculated based on the value of the coefficient.

(3) In this case, it is preferable that a step of filling the tank with the gas is divided into an initial filling step of filling the tank with the gas in order to know a state of the tank and a main filling step of filling the tank with the gas so as to realize a predetermined target pressure increase ratio, in which, in the volume estimating step, the tank volume is estimated based on the detection values of the flow rate sensor and the pressure sensor, during the main filling step.

(4) In this case, it is preferable that the gas filling method further includes an initial pressure estimating step of estimating an initial pressure of the tank before a start of the initial filling step, based on the detection value of the pressure sensor, after the initial filling step is started, in which, in the main filling step, the filling of the gas is started immediately after the initial pressure estimating step is ended, and the filling of the gas is performed so as to realize a target pressure increase ratio set based on an estimation value of the initial pressure calculated in the initial pressure estimating step.

(5) In this case, it is preferable that, when an estimation value of the tank volume calculated in the volume estimating step is out of a predetermined range, the filling of the tank with the gas from the supply source is stopped.

(6) In this case, it is preferable that the gas filling system includes an input device that receives an operation performed by a user to designate a type of tank, in which the gas filling method further includes a determining step of determining whether or not a type of tank designated via the input device is a small-sized tank having a volume smaller than a predetermined standard volume or a large-sized tank having a volume larger than the standard volume and, in the main filling step, a period of filling time corresponding to a period of time from a predetermined filling start time point to a scheduled filling end time point, is calculated based on the detection values of the pressure sensor and the flow rate sensor during the filling with the gas, the target pressure increase ratio is determined such that the tank is fully filled at the scheduled filling end time point based on the period of filling time, and the filling start time point is set to a start time point of the initial filling step when a type of tank is determined as a small-sized tank in the determining step.

(7) In this case, it is preferable that, in the volume estimating step, an estimation value V′ of the tank volume is calculated based on Equation (1) to be described below.

V′=[(Δ⁢⁢M+ρ0⁢Vtube)⁢z1⁢R⁢⁢T1P⁢⁢1-Vtube]/[1-ρ0⁢z1⁢R⁢⁢T1P⁢⁢1](1)

In Equation (1), “ΔM” represents a mass of a gas passing through the tube system between any two time points t0and t1after the start of the filling of the gas, “Vtube” represents a volume value of the tube system, “R” represents a gas constant, “T1” represents a temperature of the gas in the tank at the time point t1, “P1” represents a pressure in the tank at the time point t1, “z1” represents a coefficient of compressibility of the gas in the tank at the time point t1, and “ρ0” represents density of the gas in the tank at the time point t0.

(1) In the invention, the tank volume is estimated, based on the detection values of the flow rate sensor and the pressure sensor provided on the tube system, which connects the supply source and the tank, and the volume value of the tube system, after the start of the filling of the tank with the gas from the supply source. A part of the gas flowing from the supply source does not fill the tank but remains in the tube system. Hence, in the invention, the tank volume is estimated by using the volume value of the tube system. In this manner, of the gas flowing out of the supply source, it is possible to consider an amount of gas that does not fill the tank but remains in the tube system, and thus it is possible to estimate the tank volume with high accuracy. Incidentally, in a case where the tank has a small volume, a proportion of the volume of the tube system to the volume of the tank increases. Hence, the invention is particularly suitable for estimating the volume of the tank having the small volume with high accuracy.

(2) On the moving object, a communication device that transmits information of a tank volume, a temperature or a pressure in the tank, or the like to the gas supply device side is mounted in many cases. However, filling control that is performed in the gas supply device is basically performed, based on a sensor that performs detection with relatively high accuracy and is mounted on the gas supply device. However, in a case obtaining the detection value of the pressure sensor that is mounted on the gas supply device side is obtained, the pressure loss occurs in the tube system when the gas flows in the tube system during the filling. Therefore, the detection value of the pressure sensor on the gas supply device side indicates a value higher than an actual pressure in the tank of the moving object by an amount corresponding to the pressure loss. As a result, an error is caused to occur in the estimation of the volume. By comparison, in the invention, the value of the coefficient related to the pressure loss, which occurs when the gas flows in the tube system during the filling, is calculated based on the detection values of the flow rate sensor and the pressure sensor when the filling of the tank with the gas from the supply source is stopped, in which, when the volume is estimated, the tank volume is estimated based on the detection values of the flow rate sensor and the pressure sensor, the volume value of the tube system, and the pressure loss value calculated based on the value of the coefficient. Hence, according to the invention, it is possible to estimate the pressure in the tank based on the detection value of the pressure sensor provided on the tube system and the pressure loss value in the tube system, and thus it is possible to estimate the tank volume with high accuracy without interruption to the filling in order to estimate the volume.

(3) In the invention, when the step of filling the tank with the gas is divided into the initial filling step of filling the tank with the gas in order to know the state of the tank and the main filling step of filling the tank with the gas so as to realize a target filling ratio, the tank volume is estimated in the volume estimating step, based on the detection values of the flow rate sensor and the pressure sensor, during the main filling step. Consequently, in the invention, it is possible to estimate the tank volume based on the detection values of the flow rate sensor and the pressure sensor while the filling is performed such that the known target pressure increase ratio is realized, and thereby it is possible to further improve estimation accuracy. In other words, a so-called “a fixed-time period filling method” is derived from a so-called “fixed-quantity filling method” of filling a tank with a certain amount of gas set in advance estimating a volume of the tank in the related art. The fixed-time period filling method is a method of filling the tank for a certain period of time in a main filling step of filling the tank with a gas at a flow rate suitable for the tank and estimating the volume of the tank. In this manner, in a state in which the connected tanks are filled with amounts of gases, which are suitable for the respective volumes of the tanks, it is possible to estimate the tank volume, and thus it is possible to obtain the same estimation information on all sizes of tanks, regardless of a large size, a regular size, or a small size.

(4) In the invention, in the initial pressure estimating step, immediately after the initial pressure of the tank before the start of the initial filling step is estimated, the main filling step is started. In addition, in the main filling step, the gas is filled to realize the target pressure increase ratio set based on the estimation value of the initial pressure calculated in the initial pressure estimating step.

(5) In the invention, when the calculated estimation value of the tank volume is out of the predetermined range, the filling of the tank with the gas from the supply source is stopped. Consequently, a state of not selecting a filling mode suitable for a tank to be filled or a filling map is detected, and the filling is likely to be continuously performed even at an erroneous target pressure increase ratio. In this manner, it is possible to avoid having a temperature reaching a too high temperature.

(6) In the invention, in the main filling step, the period of filling time corresponding to the period of time from the predetermined filling start time point to the scheduled filling end time point is calculated, based on the detection values of the pressure sensor and the flow rate sensor during the filling with the gas, and the target pressure increase ratio is determined such that the tank is fully filled at the scheduled filling end time point based on the period of filling time. In addition, in a case where the user designates the type of tank to the small-sized tank, in the main filling step, the filling start time point which is a reference point of the main filling step is set to the start time point of the initial filling step. Consequently, it is possible to perform the main filling step with consideration for the amount of gas that tentatively fills the tank in the initial filling step, and thereby it is possible to fully fill the tank with accuracy without reaching overfilling of the tank having the small volume.

(7) In the invention, the tank volume is estimated based on Equation (1) described above, and thereby it is possible to estimate the tank volume with high accuracy.

