Fuel efficiency measurement system and method for fuel cell vehicle

A fuel efficiency measurement system includes a fuel supply tank for supplying hydrogen to be used as a fuel to a fuel cell of the vehicle during measurement of fuel efficiency and a precision electronic balance for detecting a weight of the fuel supply tank so as to perform the measurement of fuel efficiency based on a vehicle driving distance and a change in weight of the fuel supply tank measured by the electronic balance during measurement of fuel efficiency. According to the fuel efficiency measurement system, it is possible to more accurately calculate fuel efficiency without using hydrogen of a hydrogen tank installed in the vehicle.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2007-0071962 filed Jul. 18, 2007, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present invention relates to a fuel efficiency measurement system and method for a fuel cell vehicle, which can accurately measure fuel efficiency of a fuel cell vehicle.

(b) Background Art

Generally a fuel cell is considered as a future electricity generation system due to its high efficiency of electricity generation and its zero emission characteristic. The fuel cell has been extensively studied as a promising power source for a vehicle, which can solve various problems such as environmental pollution and global warming that has been recently issued.

The fuel cell is a device that converts chemical energy, generated by oxidizing a material having activity such as hydrogen (e.g. LNG, LPG, methanol, etc.) through an electrochemical reaction, directly into electrical energy. In general, the fuel cell uses hydrogen, which is easily generated from natural gas, and oxygen in air.

In case of a hydrogen fuel cell vehicle equipped with the above-described fuel cell that uses hydrogen as a fuel, it is impossible to measure fuel efficiency by a method applied to internal combustion engine vehicles, i.e., with the carbon content contained in the exhaust gas, and thus a new fuel efficiency measurement method for the hydrogen fuel cell vehicle is required.

The fuel efficiency measurement method applied to the hydrogen fuel cell vehicle shown inFIG. 1includes measurement based on a change in temperature and pressure of a hydrogen tank11, measurement based on an amount of hydrogen supplied to a fuel cell14, and measurement based on the current of the fuel cell14. In this case, sensors provided for the fuel efficiency measurement include a temperature sensor1and a pressure sensor2of the hydrogen tank11, a flow sensor3for measuring the amount of hydrogen supplied to the fuel cell14, and a current sensor4for measuring the current amount of the fuel cell14.

The fuel efficiency of the hydrogen fuel cell vehicle is measured based on an amount of hydrogen used in the fuel cell14and a driving distance and expressed as gasoline equivalent fuel efficiency through an equivalent energy amount of hydrogen for the purpose of comparison with that of the internal combustion engine vehicle.

Like this, in calculating the fuel efficiency of the hydrogen fuel cell vehicle, it is important to accurately measure the amount of hydrogen supplied from the hydrogen tank11, and the conventional fuel efficiency measurement methods have the following drawbacks.

Although the measurement method based on the change in temperature and pressure of the hydrogen tank has an advantage of calculating a hydrogen purge amount, the errors of the pressure and temperature sensors are large, and soaking is required.

Moreover, although the measurement method based on the amount of hydrogen supplied has an advantage of calculating the hydrogen purge amount, the error of the hydrogen flow sensor is quite large.

Furthermore, although the measurement method based on the current amount of the fuel cell has an advantage in that the calculation of the current amount and the reactivity are excellent, it is impossible to estimate the hydrogen purge amount and the error of the current sensor is quite large.

SUMMARY OF THE DISCLOSURE

The present invention has been made in an effort to solve the above-described problems associated with prior art.

In one aspect, the present invention provides a fuel efficiency measurement system for a fuel cell vehicle equipped with a fuel cell that uses hydrogen as a fuel, the system comprising: a fuel supply tank for supplying hydrogen to be used as a fuel to the fuel cell; a main pipe having an inlet end connected to a hydrogen supply pipe coupled to an outlet valve of the fuel supply tank and an outlet end connected to a hydrogen injection pipe of the vehicle such that hydrogen from the fuel supply tank is supplied to the hydrogen injection pipe so as to be used as a fuel in the fuel cell; a high pressure regulator provided on the main pipe and reducing the pressure of hydrogen supplied from the fuel supply tank to a pressure that can be used in the fuel cell; a plurality of valves provided on the main pipe; a hydrogen discharge pipe connected to an excess flow valve of the fuel supply tank to discharge hydrogen at an excess pressure of the fuel supply tank to the outside when the excess flow valve is opened; an electronic balance for detecting a weight of the fuel supply tank; and a system control unit for receiving a detection value based on the weight of the fuel supply tank from the electronic balance, communicating with a power control unit in a state where the system is connected to the vehicle, and controlling the overall operation of various valves in the system and the vehicle and the overall operation of the system, wherein the system control unit calculates fuel efficiency based on a vehicle driving distance transmitted from the power control unit and a difference between weights of the fuel supply tank before and after driving the vehicle, detected by and transmitted from the electronic balance.

In another aspect, the present invention provides a fuel efficiency measurement method for a fuel cell vehicle equipped with a fuel cell that uses hydrogen as a fuel, the method comprising: connecting a main pipe of a fuel efficiency measurement system to a hydrogen injection pipe of the vehicle; receiving the information of a weight of a fuel supply tank in the fuel efficiency measurement system before turning on a starter key; supplying through the main pipe and the hydrogen injection pipe of the vehicle hydrogen of the fuel supply tank in the fuel efficiency measurement system to the fuel cell of the vehicle to be used as a fuel in a state where the hydrogen supply to a hydrogen supply system in the vehicle is cut off during measurement of fuel efficiency; calculating fuel efficiency based on a vehicle driving distance and a difference between weights a change in weight of the fuel supply tank before and after driving the vehicle.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like.

DETAILED DESCRIPTION

FIG. 2is a conceptual diagram illustrating a fuel efficiency measurement method for a fuel cell vehicle in accordance with the present invention. As shown in the figure, a fuel efficiency measurement system100includes a fuel supply tank110having the same specification as a hydrogen tank11installed in the vehicle, and an electronic balance102for measuring a change in the amount of hydrogen supplied from the fuel supply tank110.

In the above-described configuration, during the measurement of fuel efficiency, the hydrogen supply of the hydrogen tank11already installed in the vehicle is cut off by a valve V8, and instead the fuel supply tank110provided in the fuel efficiency measurement system100supplies hydrogen as a fuel to a fuel cell14of the vehicle. During vehicle operation, the amount of hydrogen supplied from the fuel supply tank110, i.e., a change in weight of the fuel supply tank110is measured using the electronic balance102to calculate fuel efficiency.

FIG. 3is a configuration diagram showing a fuel efficiency measurement system in accordance with a preferred embodiment of the present invention, andFIG. 4is a block diagram showing a signal connection between a system control unit, a power control unit, and affiliated components in the fuel efficiency measurement system in accordance with the present invention. As shown in the figures, as basic components of a hydrogen fuel cell vehicle, the vehicle is equipped with the fuel cell14that uses hydrogen as a fuel, the hydrogen tank11in which hydrogen as the fuel is filled at a high pressure of about 350 bar, a high pressure regulator HPR2for regulating the pressure of the hydrogen tank11to a pressure of about 10 bar that can be applied to the fuel cell14, and a power control unit (PCU)10for controlling the overall operation of a fuel cell system.

Moreover, a hydrogen injection pipe15branched from a hydrogen supply pipe12disposed between the high pressure regulator HPR2and the fuel cell14and used to inject hydrogen into the vehicle, a 3-way valve V8disposed at the branch position between the hydrogen supply pipe12and the hydrogen injection pipe15, and an inlet valve V7installed on the hydrogen injection pipe15are provided.

Meanwhile, the fuel efficiency measurement system100in accordance with the present invention includes a purge hydrogen tank120as well as the fuel supply tank110and the precision electronic balance102.

The fuel supply tank110is a tank for supplying hydrogen to the vehicle during measurement of fuel efficiency. Preferably, it has the same specification as the hydrogen tank11mounted in the vehicle.

Moreover, a hydrogen discharge pipe140connected to the fuel supply tank110is provided to discharge the high-pressure hydrogen of the fuel supply tank110to the outside in emergency situations. The hydrogen discharge pipe140is connected to an excess flow valve E1of the fuel supply tank110.

The excess flow valve E1is a kind of emergency discharge valve that is configured to be opened to discharge hydrogen in the fuel supply tank110to the outside through the hydrogen discharge pipe140in emergency situations where the tank pressure exceeds a predetermined pressure due to an excessive amount of hydrogen stored in the fuel supply tank110, due to an increase in the internal temperature of the fuel supply tank110above a predetermined level, or due to a malfunction.

A hydrogen supply pipe111for supplying hydrogen stored in the fuel supply tank110to be used as a fuel is connected to the fuel supply tank110, and an electronic outlet valve (e.g., solenoid valve)110ais provided at the outlet of the fuel supply tank110to control the hydrogen supply through the hydrogen supply pipe111.

Moreover, the fuel efficiency measurement system100includes a main pipe130connected to the hydrogen supply pipe111by a coupler C1. A high pressure regulator HPR1for reducing the pressure (about 350 bar) of hydrogen supplied from the fuel supply tank110through the hydrogen supply pipe111to a pressure of about 10 bar that can be used in the fuel cell14of the vehicle is provided in the main valve130. Preferably, the high pressure regulator HPR1has the same specification as the high pressure regulator HPR2installed in the vehicle.

A break-away coupler C3is provided at the outlet of the main pipe130for the connection with the vehicle. Through the break-away coupler C3, the main pipe130is connected to an injection hole of the hydrogen injection pipe15installed in the vehicle so that hydrogen to be used as a fuel is supplied from the fuel supply tank110to the vehicle through the main pipe130.

Break-away couplers conventionally used to connect the vehicle to a hydrogen filling system can be used as the break-away coupler C3. The break-away coupler C3is provided to safely and efficiently separate the fuel efficiency measurement system100from the vehicle when the vehicle goes out of a chassis dynamometer during the fuel efficiency test.

Meanwhile, the purge hydrogen tank120is connected to a hydrogen supply pipe121through which hydrogen for purge stored in the purge hydrogen tank120is supplied. An electronic outlet valve120a(e.g., solenoid valve) is provided at the outlet of the purge hydrogen tank120to control the hydrogen supply through the hydrogen supply pipe121.

Moreover, a pressure gauge R1for detecting a pressure of purge hydrogen is installed on the hydrogen supply pipe121of the purge hydrogen tank120. The hydrogen supply pipe121is connected to a supply branch pipe122coupled to the main pipe130by a coupler C2. A valve V1for controlling the hydrogen supply is installed on the supply branch pipe122.

A first discharge branch pipe131branched between the coupler C1and the high pressure regulator HPR1, provided to connect the fuel supply tank110to the main pipe130, is connected to the hydrogen discharge pipe140from which hydrogen is discharged to the outside. A separate discharge pipe132is connected from the high pressure regulator HPR1to the hydrogen discharge pipe140so that hydrogen discharged through a pressure relief valve PRV is sent to the hydrogen discharge pipe140. Moreover, a second discharge branch pipe133branched between the high pressure regulator HPR1and the break-away coupler C3is also connected to the hydrogen discharge pipe140.

The pressure relief valve PRV is a valve provided to prevent any problems that may occur in the fuel cell system when the high-pressure hydrogen is supplied to the vehicle in the event of a failure of the high pressure regulator HPR1. The pressure relief valve PRV is opened when an excess pressure occurs at the outlet side of the high pressure regulator HPR1, and thus hydrogen is forcibly discharged to the discharge pipe132and the hydrogen discharge pipe140.

Valves V1and V2for opening and closing the flow path are provided on the supply branch pipe122and the first discharge branch pipe131, and a valve V3for opening and closing the flow path is provided on the main pipe130between the high pressure regulator HPR1and the branch position of the supply branch pipe122and the first discharge branch pipe131.

Moreover, a gauge G1for measuring the hydrogen pressure is installed on the main pipe130at a downstream side of the high pressure regulator HPR1, a valve V4is provided on the main pipe130between the high pressure regulator HPR1and the branch position of the second discharge branch pipe133, a valve V5is provided on the main pipe130between the break-away coupler C3and the branch position of the second discharge branch pipe133, and a valve V6is provided on the second discharge branch pipe133, respectively.

Here, the valves V1to V6may, preferably, be embodied as explosion proof solenoid valves capable of opening and closing corresponding flow paths by electric signals output from a controller.

Meanwhile, the fuel efficiency measurement system100includes a system control unit101for controlling the overall operation of the system. The system control unit101receives a detection signal, i.e., a signal detected by measuring the change in weight of the fuel supply tank110, from the electronic balance102and a vehicle driving distance during the measurement of fuel efficiency from the power control unit10. Accordingly, the fuel efficiency measurement system100calculates fuel efficiency based on the amount of hydrogen used, a detection value of the electronic balance102, and the vehicle driving distance transmitted from the power control unit10.

The system control unit101outputs control signals to control the opening and closing operations of the respective valves110a,120a, and V1to V8provided in the fuel efficiency measurement system100and makes the power control unit10control the opening and closing operations of the valves11a, V7and V8provided in the vehicle through communications with the power control unit10.

Moreover, the system control unit101controls the valves and the respective safety devices through communications with the power control unit10to ensure the safety of the system that uses hydrogen.

Reference numeral103denotes a hydrogen sensor connected to the system control unit101so as to input a detection signal and, when a hydrogen amount above a predetermined value is detected based on the detection signal of the hydrogen sensor103, the system control unit101closes the respective valves in the fuel efficiency measurement system100, thus shutting down the fuel efficiency measurement system100.

Next, the process of measuring fuel efficiency of the fuel cell vehicle using the above-described fuel efficiency measurement system will be described.

In principle, during the measurement of fuel efficiency, a test vehicle is driven on the chassis dynamometer and, at this time, the fuel supply tank110of the fuel efficiency measurement system100supplies hydrogen to the vehicle, in which the hydrogen supply system within the vehicle is shut down, so that the fuel cell14uses as a fuel hydrogen supplied from the fuel supply tank110. Then, the fuel efficiency is calculated based on the change in weight of the fuel supply tank110before and after driving the vehicle and based on the vehicle driving distance on the chassis dynamometer.

As a first step, the residual air in the pipes is removed prior to the measurement of fuel efficiency. More specifically, the break-away coupler C3is connected to the injection hole of the hydrogen injection pipe15in the vehicle. The break-away coupler C3enables the system to be separated from the vehicle when the vehicle goes out of the chassis dynamometer during the fuel efficiency test, thus ensuring a stable hydrogen supply. Then, the valve V4in the fuel efficiency measurement system100is closed, the 3-way valve V8in the vehicle is shifted to connect the hydrogen injection pipe15and the hydrogen tank11of the vehicle, and the inlet valve V7in the vehicle, the valve V5in the fuel efficiency measurement system100, the outlet valve11aof the hydrogen tank11, and the valve V6are sequentially opened to remove the air in the pipes connected to the vehicle that uses hydrogen supplied from the hydrogen tank11of the vehicle, and then the valves are closed.

As a result, the purge and hydrogen filling process is performed using hydrogen supplied from the vehicle side, i.e., hydrogen of the hydrogen tank11in the vehicle. In particular, as the hydrogen of the hydrogen tank11in the vehicle is discharged to the outside through the main pipe130, the second discharge branch pipe133, and the hydrogen discharge pipe140connected through the hydrogen injection pipe15and the break-away coupler C3, the residual air in the system pipe after the valve V4and the pipe in the vehicle is removed. Then, as the respective pipes are closed, hydrogen is filled in the pipes.

Here, if the respective valves in the fuel efficiency measurement system100are electronic valves, the operations of the respective valves in the fuel efficiency measurement system100and the vehicle are electrically controlled by the system control unit101and the power control unit10. Such a control is applied to the operations of the respective valves to be described later in the same manner.

Meanwhile, the weight g1of the fuel supply tank110prior to the measurement is transmitted to the system control unit101by the electronic balance102.

To remove residual air in the pipes in the fuel efficiency measurement system100in a state where residual air between the valve V4and the vehicle is removed, the valve V3is closed, and then the valve V1, the outlet valve120aof the purge hydrogen tank120, and the valve V2are sequentially opened to remove residual air in the pipe between the purge hydrogen tank120and the valve V3using hydrogen of the purge hydrogen tank120, and then the corresponding valves are closed. During removal of residual air, the hydrogen of the purge hydrogen tank120purges the corresponding pipes and is then discharged to the outside through the first discharge branch pipe131and the hydrogen discharge pipe140.

In a state where the valve V5is closed, the valves V1, V3and V4, the outlet valve120aof the purge hydrogen tank120, and the valve V6are opened to remove residual air in the pipe between the valves V3and V4using hydrogen of the purge hydrogen tank120and, at the same time, hydrogen is filled in the pipe, and then the respective valves are closed. During removal of residual air, the hydrogen of the purge hydrogen tank120purges the corresponding pipes and is then discharged to the outside through the second discharge branch pipe133and the hydrogen discharge pipe140. Then, as the respective valves are closed, hydrogen is filled in the pipe.

On the other hand, the hydrogen discharge pipe140connected to the excess flow valve E1of the fuel supply tank110discharges hydrogen at an excess pressure to the outside upon occurrence of a malfunction in the fuel supply tank110, and the discharge pipe132connected to the pressure relief valve PRV of the high pressure regulator HPR1discharges the high-pressure hydrogen to the hydrogen discharge pipe140in the event of a failure in the high pressure regulator HPR1. Accordingly, hydrogen is safely discharged to the outside through the hydrogen discharge pipe140in an emergency situation, thus preventing any risk.

When the residual air in the system pipes is all removed as described above, the conditions for carrying out the measurement of fuel efficiency are established. First, when a starter key is turn on for the measurement of fuel efficiency, the power control unit10sends an order to the system control unit101of the fuel efficiency measurement system100to open the outlet valve110aof the fuel supply tank110and the valves V3to V5. Moreover, the inlet valve V7in the vehicle is opened and, at the same time, the 3-way valve V8in the vehicle is shifted to connect the hydrogen injection pipe15and the pipe of the fuel cell14. As a result, the hydrogen of the hydrogen tank11in the vehicle is not supplied to the vehicle during the measurement of fuel efficiency, instead, the fuel supply tank110of the fuel efficiency measurement system100supplies the whole quantity of hydrogen to be used as a fuel to the fuel cell14of the vehicle. Accordingly, the amount of hydrogen consumed in the fuel cell14to drive the vehicle during the measurement of fuel efficiency is equal to the amount of hydrogen supplied from the fuel supply tank110of the fuel efficiency measurement system100, which corresponds to the change in weight of the fuel supply tank110.

When the starter key is turned off to terminate the measurement of fuel efficiency, the power control unit10issues an order to the system control unit101of the fuel efficiency measurement system100to close the outlet valve110aof the fuel supply tank110and the valves V3to V5at the very point of time when the vehicle is shut down. Moreover, the inlet valve V7in the vehicle is closed and, at the same time, the 3-way valve V8in the vehicle is shifted to connect the pipe of the hydrogen tank11and the pipe of the fuel cell14.

After the external supply of hydrogen is cut off, the valve V2is opened, and the weight g2of the fuel supply tank110is transmitted to the system control unit101by the electronic balance102. Since the high-pressure hydrogen is filled before and after the coupler C1, the hydrogen removal by opening the valve V2facilitates the separation of the coupler C1due to the pressure.

A difference between the weight g1of the fuel supply tank110before the test and the weight g2of the fuel supply tank110after the test is calculated, and the difference in weight and the driving distance received from the power control unit10are analyzed to calculate a gasoline equivalent fuel efficiency.

In the event that the amount of hydrogen of the fuel supply tank110is below an amount required to drive the vehicle, the hydrogen of the purge hydrogen tank120may be supplied as a fuel to perform the fuel efficiency test.

As described above, according to the fuel efficiency measurement system and method for a fuel cell vehicle, it is possible to accurately calculate fuel efficiency based on the change in weight of the external fuel supply tank before and after driving the vehicle using the fuel supply tank and the precision electronic balance, instead of using hydrogen of the hydrogen tank installed in the vehicle, thus allowing a more accurate measurement of fuel efficiency.