Fuel cell vehicle

When a calibration starting condition of a pressure sensor is satisfied while a fuel cell vehicle is traveling, the fuel cell vehicle starts to travel by using electric power supplied from a secondary battery. In the fuel cell vehicle, a pressure sensor is calibrated based on hydrogen pressure in a hydrogen gas flow channel downstream of a pressure reducing valve after a shut-off valve of a hydrogen tank is closed, and the hydrogen in a hydrogen gas flow channel is exhausted until hydrogen pressure upstream of the pressure reducing valve and hydrogen pressure downstream of the pressure reducing valve become substantially equal to each other. The fuel cell vehicle travels by using electric power supplied from the secondary battery while the pressure sensor is being calibrated, so that calibration processing of the pressure sensor can be performed without causing a noise.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2016-226185 filed on Nov. 21, 2016 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a fuel cell vehicle.

2. Description of Related Art

A fuel cell is a power generator that directly converts chemical energy into electrical energy through an electrochemical reaction between hydrogen gas and oxidation gas. In a fuel cell vehicle mounting a fuel cell as an on-vehicle power source, hydrogen gas under high pressure supplied from a hydrogen tank storing hydrogen gas is reduced in pressure by a pressure reducing valve, and then the hydrogen gas reduced in pressure is supplied to the fuel cell. Some fuel cell vehicles of this type include a high-pressure sensor provided in a hydrogen gas flow channel from a hydrogen tank to a pressure reducing valve, and a low-pressure sensor provided in a hydrogen gas flow channel from the pressure reducing valve to a fuel cell. High-pressure sensors each have a wide measurement range, but have relatively low detection accuracy of pressure with respect to low-pressure sensors. Meanwhile, the low-pressure sensors each have a narrow measurement range, but have high detection accuracy of pressure. In a high-pressure sensor placed under high-pressure environment, measurement errors may successively increase. In light of the above-mentioned circumstances, Japanese Patent Application Publication No. 2013-177910 provides a method of calibrating a high-pressure sensor on the basis of hydrogen pressure detected by a low-pressure sensor by exhausting hydrogen gas in a hydrogen gas flow channel while a stopcock valve of a hydrogen tank is closed.

SUMMARY

Unfortunately, when calibration processing of a pressure sensor is performed while a fuel cell vehicle is stopped (e.g., when power generation of a fuel cell is stopped, or started up), a sound generated during the calibration processing may become noticeable to be felt as a noise.

Then, the present disclosure provides a fuel cell vehicle in which calibration processing of a pressure sensor can be performed without causing a noticeable sound.

A fuel cell vehicle according to the present disclosure includes: (i) a fuel cell that generates power by using an electrochemical reaction between hydrogen gas and oxidation gas; (ii) a hydrogen tank that supplies the hydrogen gas to the fuel cell through a hydrogen gas flow channel; (iii) a shut-off valve that performs supply and interruption of the hydrogen gas from the hydrogen tank to the fuel cell through the hydrogen gas flow channel; (iv) a pressure reducing valve that reduces hydrogen pressure in the hydrogen gas flow channel; (v) a pressure sensor that detects the hydrogen pressure in the hydrogen gas flow channel between the shut-off valve and the pressure reducing valve; (vi) a secondary battery that stores electric power generated by the fuel cell; and (vii) a control device that calibrates the pressure sensor based on the hydrogen pressure in the hydrogen gas flow channel downstream of the pressure reducing valve after the shut-off valve is closed and the hydrogen gas in the hydrogen gas flow channel is exhausted until the hydrogen pressure upstream of the pressure reducing valve and the hydrogen pressure downstream of the pressure reducing valve become substantially equal to each other when a calibration starting condition of the pressure sensor is satisfied during traveling of the fuel cell vehicle. While the pressure sensor is being calibrated, the fuel cell vehicle travels by using electric power supplied from the secondary battery.

According to the present disclosure, the fuel cell vehicle travels by using electric power supplied from the secondary battery while the pressure sensor is being calibrated, so that a sound generated during calibration processing can be prevented from being felt as a noise.

DETAILED DESCRIPTION OF EMBODIMENT

An embodiment according to the present disclosure will be described below with reference to each drawing.FIG. 1is a block diagram illustrating a configuration of a fuel cell vehicle10according to the present embodiment. The fuel cell vehicle10includes: a fuel cell20that generates power by using an electrochemical reaction between hydrogen gas and oxidation gas; an oxidation gas supply system30that supplies air as oxidation gas to a cathode of the fuel cell20; a hydrogen gas supply system40that supplies hydrogen gas to an anode of the fuel cell20; an electric power system50that controls charge and discharge of electric power; and a control device60that controls operation of the fuel cell20. The fuel cell20is a cell stack of a solid polymer electrolyte type formed by stacking a plurality of cells in series, for example, and serves as an on-vehicle power supply device. In the fuel cell20, an oxidation reaction of Expression (1) occurs in the anode, and a reductive reaction of Expression (2) occurs in the cathode.
H2→2H++2e−(1)
(½)O2+2H++2e−→H2O  (2)

The oxidation gas supply system30includes an oxidation gas flow channel34through which oxidation gas to be supplied to the cathode of the fuel cell20flows, and an oxidation off-gas flow channel36through which oxidation off-gas discharged from the fuel cell20flows. The oxidation gas flow channel34is provided with an air compressor32configured to take in oxidation gas from the atmosphere through a filter31, a humidifier33configured to humidify oxidation gas to be supplied to the cathode of the fuel cell20, and a throttle valve35configured to adjust the amount of supply of oxidation gas. The oxidation off-gas flow channel36is provided with a back pressure valve37configured to adjust supply pressure of oxidation gas. The humidifier33humidifies oxidation gas by performing moisture exchange between the oxidation gas (dry gas) and oxidation off-gas (wet gas).

The hydrogen gas supply system40includes a hydrogen tank41, a hydrogen gas flow channel45through which hydrogen gas to be supplied to the anode of the fuel cell20from the hydrogen tank41flows, a circulation flow channel46configured to return hydrogen off-gas discharged from the fuel cell20to the hydrogen gas flow channel45through a circulation pump47, and an exhaust-drain flow channel48that is connected to the circulation flow channel46by branch connection. The hydrogen tank41includes a high pressure hydrogen tank and a hydrogen-storing alloy, for example, and stores hydrogen gas under high pressure (e.g., 35 MPa to 70 MPa). The shut-off valve42performs supply and interruption of hydrogen gas from the hydrogen tank41to the fuel cell20through the hydrogen gas flow channel45. The shut-off valve42serves as a stopcock valve of the hydrogen tank41.

The pressure of hydrogen gas is reduced to a pressure equal to or lower than 1000 kPa through a pressure reducing valve43and an injector44, for example, to be supplied to the fuel cell20. The pressure reducing valve43is a regulator that adjusts primary pressure upstream thereof to a preset secondary pressure, for example, and includes a mechanical pressure reducing valve that reduces primary pressure, and the like. The mechanical pressure reducing valve includes a case in which a back pressure chamber and a pressure adjusting chamber are formed across a diaphragm, and reduces primary pressure in the pressure adjusting chamber to predetermined pressure by using back pressure in the back pressure chamber to form secondary pressure. A pressure sensor P1detects hydrogen pressure (primary pressure upstream of the pressure reducing valve43) in the hydrogen gas flow channel45between the shut-off valve42and the pressure reducing valve43. A pressure sensor P2detects hydrogen pressure (secondary pressure downstream of the pressure reducing valve43) in the hydrogen gas flow channel45downstream of the pressure reducing valve43. The pressure sensor P1is a high-pressure sensor that has a wide measurement range, and has detection accuracy lower than that of the pressure sensor P2. Meanwhile, the pressure sensor P2is a low-pressure sensor that has a narrow measurement range, and has detection accuracy higher than that of the pressure sensor P1.

The injector44is an on-off valve of an electromagnetic driving type that can adjust a gas flow rate and gas pressure by separating a valve element from a valve seat by driving the valve element in a predetermined drive cycle using electromagnetic driving force. The injector44includes a valve seat with an injection hole for injecting gas fuel such as hydrogen gas, a nozzle body that supplies and guides the gas fuel to the injection hole, and a valve element that is accommodated and held in the nozzle body to be movable in an axial direction (gas flow direction) to open and close the injection hole. The exhaust-drain flow channel48is provided with an exhaust-drain valve49. The exhaust-drain valve49is opened to discharge hydrogen off-gas containing impurities and moisture in the circulation flow channel46to the outside.

The electric power system50includes a DC-DC converter51, a secondary battery52, a traction inverter53, a traction motor54, and auxiliary machines55. The DC-DC converter51has a function of increasing DC voltage applied from the secondary battery52and outputting it to the traction inverter53, and a function of reducing voltage of DC power generated by the fuel cell20, or of regenerative electric power recovered by the traction motor54through regenerative braking, and charging the secondary battery52with the voltage. Charge and discharge of the secondary battery52are controlled through these functions of the DC-DC converter51. In addition, voltage conversion control by the DC-DC converter51controls operation points (output voltage and output current) of the fuel cell20.

The secondary battery52serves as: a storage source of surplus electric power; a regenerative energy storage source during regenerative braking; and an energy buffer during load fluctuation caused by acceleration or deceleration of a fuel cell vehicle10. For example, a secondary battery, such as a nickel-cadmium battery, a nickel-hydrogen battery, and a lithium secondary battery, is suitable for the secondary battery52.

The traction inverter53is a PWM inverter driven by a pulse width modulation method, for example, and converts DC voltage output from the fuel cell20or the secondary battery52into three-phase AC voltage in response to a control command from the control device60to control rotational torque of the traction motor54. The traction motor54is a three-phase AC motor, for example, and serves as a power source of the fuel cell vehicle10.

The auxiliary machines55is a general name for each of motors (e.g., a power source such as a pump group) disposed in the corresponding portions of the fuel cell vehicle10, an inverter group configured to drive the motors above, and various on-vehicle auxiliary machine groups (e.g., an air compressor, an injector, a cooling water circulation pump, a radiator, and the like).

The control device60is an electronically controlled unit including a processor61, a storage resource62, and an input-output interface63. The processor61interprets and executes a control program64stored in the storage resource62, and inputs and outputs a signal to control each system (the oxidation gas supply system30, the hydrogen gas supply system40, and the electric power system50) of the fuel cell vehicle10through the input-output interface63. When receiving a seizure signal output from an ignition switch, the control device60starts operation of the fuel cell20, for example, and acquires required electric power on the basis of an accelerator operation amount signal output from an accelerator sensor, a vehicle speed signal output from a vehicle speed sensor, and the like. The required electric power is a total value of vehicle traveling electric power and auxiliary machine electric power. The auxiliary machine electric power includes: electric power consumed by the on-vehicle auxiliary machine group (e.g., the humidifier, the air compressor, the hydrogen pump, the cooling water circulation pump, and the like); electric power consumed by equipment necessary for vehicle traveling (a transmission, a wheel control device, a steering gear, a suspension, and the like); and electric power consumed by equipment (an air conditioner, a lighting fixture, audio equipment, and the like) disposed in an occupant space, for example. The control device60determines an allocation of output electric power to each of the fuel cell20and the secondary battery52, and calculates a power generation command value, and also controls the oxidation gas supply system30and the hydrogen gas supply system40so as to cause the amount of power generation of the fuel cell20to coincide with target electric power. In addition, the control device60controls the DC-DC converter51so as to adjust output voltage of the fuel cell20, thereby controlling operation points (output voltage and output current) of the fuel cell20. The control device60outputs an AC voltage command value of each phase, U-phase, V-phase, and W-phase to the traction inverter53as a switching command to acquire target torque in accordance with an accelerator operation amount, for example, thereby controlling output torque and rotation speed of the traction motor54.

Subsequently, calibration processing of the pressure sensor P1will be described with reference toFIGS. 2 to 4. Steps201to209shown inFIG. 2, steps301to311shown inFIG. 3, and steps401to411shown inFIG. 4, are invoked as sub routines in the control program64and then are executed. The control program64includes a software module to execute each step shown inFIGS. 2 to 4. While a function of this kind of software module is achieved by collaboration between the processor61and the control program64, an equivalent function may be achieved by using a dedicated hardware resource (e.g., an integrated circuit for a specific application), firmware, or the like.

First, first calibration processing of the pressure sensor P1will be described with reference toFIG. 2. The control device60determines whether the fuel cell vehicle10is traveling by a method for reading out a vehicle speed signal output from the vehicle speed sensor, for example (step201). When the fuel cell vehicle10is traveling (YES at step201), the control device60determines whether a calibration starting condition of the pressure sensor P1is satisfied (step202). The control device60predicts a measurement error of the pressure sensor P1in accordance with map data or prediction expression that is preliminarily stored in the storage resource62, on the basis of history information on hydrogen pressure detected by the pressure sensor P1, temperature in the hydrogen tank41, outside-air temperature, and the like, and determines that the calibration starting condition of the pressure sensor P1is satisfied when the predicted measurement error exceeds a threshold value.

When the calibration starting condition of the pressure sensor P1is satisfied (YES at step202), the control device60switches an electric power supply source of the traction motor54from the fuel cell20to the secondary battery52to start battery traveling (step203). Subsequently, the control device60causes the shut-off valve42of the hydrogen tank41to close (fully closed) (step204) to interrupt hydrogen supply to the hydrogen gas flow channel45.

Subsequently, the control device60causes hydrogen gas in the hydrogen gas flow channel45to be exhausted from the injector44through the exhaust-drain flow channel48by opening the injector44(step205), and determines whether hydrogen pressure (secondary pressure downstream of the pressure reducing valve43) detected by the pressure sensor P2is less than a threshold value Th1(step206). The threshold value Th1is hydrogen pressure downstream of the pressure reducing valve43when hydrogen pressure upstream of the pressure reducing valve43becomes substantially equal to the hydrogen pressure downstream of the pressure reducing valve43. When most of the hydrogen gas in the hydrogen gas flow channel45is exhausted, atmospheric pressure can be used as the threshold value Th1, for example.

When hydrogen pressure detected by the pressure sensor P2decreases to less than the threshold value Th1(YES at step206), the control device60calibrates the pressure sensor P1on the basis of hydrogen pressure in the hydrogen gas flow channel45downstream of the pressure reducing valve43(step207). The hydrogen pressure in the hydrogen gas flow channel45downstream of the pressure reducing valve43is detected by the pressure sensor P2to calibrate the pressure sensor P1in this embodiment. However, hydrogen pressure detected by the pressure sensor P2is not necessarily used when the hydrogen gas in the hydrogen gas flow channel45is exhausted until the hydrogen pressure in the hydrogen gas flow channel45becomes atmospheric pressure, and then the pressure sensor P1may be calibrated on the basis of atmospheric pressure, for example. It can be determined whether the pressure downstream of the shut-off valve42is atmospheric pressure based on the opening period of the injector44. In this case, the pressure sensor P2may not be provided in the fuel cell vehicle10. As described above, in step207, the calibration processing of the pressure sensor P1is performed such that hydrogen pressure detected by pressure sensor P1coincides with hydrogen pressure detected by the pressure sensor P2or atmospheric pressure.

When the calibration processing of the pressure sensor P1is finished, the control device60causes the shut-off valve42of the hydrogen tank41to open (fully open) (step208) to restart hydrogen supply to the hydrogen gas flow channel45, as well as stops battery traveling by switching the electric power supply source of the traction motor54from the secondary battery52to the fuel cell20(step209).

As described above, the fuel cell vehicle10travels by using electric power supplied from the secondary battery52while the pressure sensor P1is being calibrated, so that a sound generated during calibration processing of the pressure sensor P1can be prevented from being felt as a noise.

Subsequently, second calibration processing of the pressure sensor P1will be described with reference toFIG. 3. Steps301,302,305to311are identical to steps201to209, respectively, so that detailed description of step301,302,305to311is eliminated.

When the calibration starting condition of the pressure sensor P1is satisfied (YES at step302), the control device60determines whether a state of charge of the secondary battery52is a threshold value Th or more (step303). The threshold value Th is the amount of charge of the secondary battery52required to allow the fuel cell vehicle10to travel by using electric power supplied from the secondary battery52. When a state of charge of the secondary battery52is less than the threshold value Th (NO at step303), the control device60controls the secondary battery52so as to be charged with electric power generated by the fuel cell20until the state of charge of the secondary battery52reaches the threshold value Th (step304).

As described above, when the state of charge of the secondary battery52is less than the threshold value Th at the time when the calibration starting condition of the pressure sensor P1is satisfied, battery traveling is started after the secondary battery52is charged with electric power generated by the fuel cell20until the state of charge of the secondary battery52reaches the threshold value Th, thereby enabling adequate traveling performance to be secured.

Subsequently, third calibration processing of the pressure sensor P1will be described with reference toFIG. 4. The control device60determines whether the fuel cell vehicle10is traveling by a method for reading out a vehicle speed signal output from the vehicle speed sensor, for example (step401). When the fuel cell vehicle10is traveling (YES at step401), the control device60determines whether a calibration starting condition of the pressure sensor P1is satisfied (step402).

When the calibration starting condition of the pressure sensor P1is satisfied (YES at step402), the control device60causes the shut-off valve42of the hydrogen tank41to close (fully closed) (step403) to reduce hydrogen pressure in the hydrogen gas flow channel45through consumption of hydrogen gas remaining in the hydrogen gas flow channel45by the fuel cell20(step404).

The control device60determines whether hydrogen pressure (secondary pressure downstream of the pressure reducing valve43) detected by the pressure sensor P2is less than a threshold value Th2(step405). The threshold value Th2is threshold pressure required to allow the fuel cell vehicle10to travel by using electric power generated by the fuel cell20through consumption of hydrogen gas remaining in the hydrogen gas flow channel45. Until hydrogen pressure detected by the pressure sensor P2decreases to less than the threshold value Th2after the shut-off valve42of the hydrogen tank41is closed, the control device60controls the fuel cell vehicle10such that the fuel cell vehicle10travels by using electric power generated by the fuel cell20.

When hydrogen pressure detected by the pressure sensor P2decreases to less than the threshold value Th2(YES at step405), the control device60switches an electric power supply source of the traction motor54from the fuel cell20to the secondary battery52to start battery traveling (step406). Subsequently, the control device60causes hydrogen gas in the hydrogen gas flow channel45to be exhausted from the injector44through the exhaust-drain flow channel48(step407), and determines whether hydrogen pressure (secondary pressure downstream of the pressure reducing valve43) detected by the pressure sensor P2is less than the threshold value Th1(step407).

When hydrogen pressure detected by the pressure sensor P2decreases to less than the threshold value Th1(YES at step408), the control device60calibrates the pressure sensor P1on the basis of hydrogen pressure in the hydrogen gas flow channel45downstream of the pressure reducing valve43(step409).

When the calibration processing of the pressure sensor P1is finished, the control device60causes the shut-off valve42of the hydrogen tank41to open (fully open) (step410) to restart hydrogen supply to the hydrogen gas flow channel45, as well as stops battery traveling by switching the electric power supply source of the traction motor54from the secondary battery52to the fuel cell20(step411).

As described above, hydrogen gas remaining in the hydrogen gas flow channel45can be used for traveling energy by closing the shut-off valve42of the hydrogen tank41, so that deterioration in fuel consumption of hydrogen gas can be reduced.

The embodiment described above is for easy understanding of the present disclosure, and is not to be interpreted by limiting the present disclosure. The embodiment can be changed or modified, and the present disclosure includes its equivalent. That is, a modification in which a person skilled in the art appropriately makes a design change to the embodiment is included in the scope of the present disclosure. For example, each element provided in the embodiment, and its placement, material, conditions, shape, size, and the like, are not limited to those described above, and may be appropriately changed. In the embodiment described above, when only the first calibration processing or the second calibration processing is performed, the pressure sensor P2may be eliminated from the fuel cell vehicle10. In addition, a positional relationship, such as up and down, left and right, is not limited to a ratio illustrated unless otherwise noted. Further, each of elements provided in the embodiment may be combined with each other as far as technically possible, so that a combination of the elements is also included in the scope of the present disclosure.