Vehicle fuel cell and fuel cell control system

A vehicle includes a fuel cell stack, an ejector, a first injector, a second injector, and a controller. The fuel cell stack is configured to generate power to propel the vehicle. The fuel cell stack has an anode side. The ejector is configured to deliver hydrogen to the anode side. The ejector has a nozzle configured to accelerate and direct the hydrogen toward the anode side. The first and second injectors are configured to deliver hydrogen to the nozzle. The controller is programmed to, in response to a command to deliver hydrogen to the anode side, open each of the first and second injectors and subsequently close the second injector while the first injector remains open.

TECHNICAL FIELD

The present disclosure relates to vehicles having fuel cells.

BACKGROUND

Vehicles may include fuel cell systems that generate electrical power.

SUMMARY

A vehicle includes a fuel cell stack, an ejector, a first injector, a second injector, a recirculation loop, and a controller. The fuel cell stack is configured to generate power to propel the vehicle. The fuel cell stack has an anode side. The ejector is configured to deliver hydrogen to the anode side. The ejector defines a mixing chamber having an outlet that is in fluid communication with the anode side. The ejector has a nozzle configured to accelerate and direct the hydrogen into the mixing chamber. The first injector is configured to deliver hydrogen to the nozzle. The second injector is configured to deliver hydrogen to the nozzle separately from the first injector. The first and second injectors are configured to open to deliver hydrogen to the nozzle and close to forgo delivering hydrogen to the nozzle. The recirculation loop is configured to direct unconsumed hydrogen from the fuel cell stack to the mixing chamber. The controller is programmed to operate the first and second injectors via injection pulses to deliver hydrogen to the nozzle. The controller is further programmed to, during each injection pulse, open each of the first and second injectors to initiate the injection pulse and subsequently close the second injector while the first injector remains open.

A vehicle includes a fuel cell stack, an ejector, a first injector, and a second injector. The fuel cell stack is configured to generate power to propel the vehicle. The fuel cell stack has an anode side. The ejector is configured to deliver hydrogen to the anode side. The ejector defines a mixing chamber having an outlet that is in fluid communication with the anode side, a nozzle chamber having an outlet end that is in fluid communication with the mixing chamber, a first inlet port in direct fluid commination with the nozzle chamber, and a second inlet port in direct fluid commination with the nozzle chamber. The first injector is configured to inject hydrogen into the nozzle chamber via the first inlet port. The second injector is configured to inject hydrogen into the nozzle chamber via the second inlet port.

A vehicle includes a fuel cell stack, an ejector, a first injector, a second injector, and a controller. The fuel cell stack is configured to generate power to propel the vehicle. The fuel cell stack has an anode side. The ejector is configured to deliver hydrogen to the anode side. The ejector has a nozzle configured to accelerate and direct the hydrogen toward the anode side of the fuel cell stack. The first and second injectors are configured to deliver hydrogen to the nozzle. The controller is programmed to, in response to a command to deliver hydrogen to the anode side, open each of the first and second injectors and subsequently close the second injector while the first injector remains open.

DETAILED DESCRIPTION

It is recognized that any circuit or other electrical device disclosed herein may include any number of microprocessors, integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or other suitable variants thereof) and software which co-act with one another to perform operation(s) disclosed herein. In addition, any one or more of the electrical devices as disclosed herein may be configured to execute a computer-program that is embodied in a non-transitory computer readable medium that is programmed to perform any number of the functions as disclosed herein.

FIG.1schematically illustrates a fuel cell system (“the system”)10as a process flow diagram according to at least one embodiment. For example, system10may be used in a vehicle to provide electrical power to operate an electric motor to propel the vehicle or perform other vehicle functions. The system10may be implemented in a fuel cell based electric vehicle or a fuel cell based hybrid vehicle or any other such apparatus that uses electrical current to drive various devices.

The system10has a fuel cell stack (“the stack”)12. The stack12includes multiple cells, with each cell13having an anode side14(including an anode catalyst), a cathode side16(including a cathode catalyst), and a membrane18between the anode and cathode catalyst. Only one fuel cell13of the fuel cell stack12is illustrated inFIG.1, although the stack12contains any number of cells. The stack12electrically communicates with and provides energy, for example, to a high voltage bus or a traction battery20. The stack12generates stack current in response to electrochemically converting hydrogen and oxygen. The stack12may also have a cooling loop (not shown).

Various electrical devices may be coupled to the battery20to consume such power in order to operate. If the system10is used in connection with a vehicle, the devices may include a motor or a plurality of vehicle electrical components that each consume power to function for a particular purpose. For example, such devices may be associated with and not limited to a vehicle powertrain, cabin heating and cooling, interior/exterior lighting, entertainment devices, and power locking windows. The particular types of devices implemented in the vehicle may vary based on vehicle content, the type of motor used, and the particular type of fuel cell stack implemented.

During operation of the system10, product water, residual fuel such as hydrogen, and byproducts such as nitrogen, may accumulate at the anode side14of the stack12. Attempts have been made to remove the liquid product water and byproducts and to reuse the residual hydrogen and at least a portion of the water vapor. One approach is to collect those constituents in a purge assembly36downstream of the stack12, separate at least a portion of the liquid water, and return the remaining constituents to the stack12via a return passageway in a recirculation loop.

A primary fuel source22is connected to the anode side14of the stack12, such as a primary hydrogen source, to provide a supply fuel stream (or an anode stream). Non-limiting examples of the primary hydrogen source22are a high-pressure hydrogen storage tank or a hydride storage device. For example, liquid hydrogen, hydrogen stored in various chemicals such as sodium borohydride or alanates, or hydrogen stored in metal hydrides may be used instead of compressed gas. A tank valve23controls the flow of the supply hydrogen. A pressure regulator25may be included to regulate the flow of the supply hydrogen. The tank valve23may also be referred to as an inlet valve or an injection valve. The tank valve23is configured open to deliver the hydrogen to the anode side14and close to restrict hydrogen from flowing into the anode side14.

The hydrogen source22is connected to one or more ejectors24. The ejector may be a variable or multistage ejector or other suitable ejector. The ejector24is configured to combine the supply hydrogen (e.g., hydrogen received from the source22) with unused hydrogen (e.g., recirculated from the fuel cell stack12) to generate an input fuel stream. The ejector24controls the flow of the input fuel stream to the stack12. The ejector24has a nozzle26supplying hydrogen into a mixing chamber28. The mixing chamber28is connected to the input30of the anode side14. A plurality of injectors27are configured are configured to deliver hydrogen from the source22directly to the nozzle26. Each injector27is configured to deliver hydrogen to the nozzle26separately from the other injectors27. The injectors27may be solenoid operated valves that open to deliver hydrogen to the nozzle26and close to forgo delivering hydrogen to the nozzle26. The injectors27may open and close intermittently (e.g., via a pulse modulation method), when the stack12requires additional hydrogen based on a power demand, or when a pressure on the anode side14decreases to less than a threshold value. Although only two injectors27are illustrated, it should be understood that the system10may include two or more injectors.

The output32of the anode side14is connected to a recirculation loop34. The recirculation loop34may be a passive recirculation loop, as shown, or may be an active recirculation loop according to another embodiment. Typically, an excess of hydrogen gas is provided to the anode side14to ensure that there is sufficient hydrogen available to all of the cells in the stack12. In other words, under normal operating conditions, hydrogen is provided to the fuel cell stack12above a stoichiometric ratio of one, i.e. at a fuel-rich ratio relative to exact electrochemical needs. The unused fuel stream, or recirculated fuel stream, at the anode output32may include various impurities such as nitrogen and water both in liquid and vapor form in addition to hydrogen. The recirculation loop34is provided such that excess hydrogen unused by the anode side14is returned to the input30so it may be used and not wasted.

Accumulated liquid and vapor phase water is an output of the anode side14. The anode side14requires humidification for efficient chemical conversion and to extend membrane life. The recirculation loop34may be used to provide water to humidify the supply hydrogen gas before the input30of the anode side14. Alternatively, a humidifier may be provided to add water vapor to the input fuel stream.

The recirculation loop34contains a purging assembly36to remove impurities or byproducts such as excess nitrogen, liquid water, and/or water vapor from the recirculation stream. The purging assembly36includes a water separator or knock-out device38, a drain line40and a control valve42, such as a purge valve. The separator38receives a stream or fluid mixture of hydrogen gas, nitrogen gas, and water from the output32of the anode side14. The water may be mixed phase and contain both liquid and vapor phase water. The separator38removes at least a portion of the liquid phase water, which exits the separator through drain line40. At least a portion of the nitrogen gas, hydrogen gas, and vapor phase water may also exit the drain line40, and pass through a control valve42, for example, during a purge process of the fuel cell stack12. The control valve42may be a solenoid valve or other suitable valve. The remainder of the fluid in the separator38exits through passageway44in the recirculation loop34, which is connected to the ejector24(or more specifically is connected to the mixing chamber28of the ejector24), as shown, or an active anode recirculation rotary device. The stream in passageway44may contain a substantial amount of hydrogen compared to the stream in drain line40. The hydrogen in passageway44is fed into the mixing chamber28where it mixes with incoming hydrogen from the nozzle26and hydrogen source22.

The cathode side16of the stack12receives oxygen in a cathode stream, for example, as a constituent in an air source46such as atmospheric air. In one embodiment, a compressor48is driven by a motor50to pressurize the incoming air. The pressurized air, or cathode stream, may be humidified by a humidifier52before entering the cathode side16at inlet54. The water may be needed to ensure that membranes18for each cell13remain humidified to provide for optimal operation of the stack12. The output56of the cathode side16is configured to discharge excess air and is connected to a valve58. Drain line60from the purging assembly36, may be connected to an outlet62downstream of the valve58. In other embodiments, the drain lines may be plumbed to other locations in the system10.

The stack12may be cooled using a coolant loop64as is known in the art. The coolant loop64has an inlet66and an outlet68to the stack12to cool the stack. The coolant loop64may have a temperature sensor70to determine the coolant temperature. The coolant temperature may correspond to a temperature of the stack12or a separate sensor may be used to determine the temperature of the stack12, which may be communicated to the controller (74)

The stack12may also have a humidity sensor72positioned at the inlet54to the cathode side16of the stack12. The sensor72may also include a temperature sensing module. Pressure sensors73may be utilized to determine the respective pressures within the anode side14of the stack12and the cathode side16of the stack12. Temperature sensors (not shown) may also be utilized to determine the respective temperature within the anode side14of the stack12and the cathode side16of the stack12.

A controller74receives signals from the sensors70,72,73, and any other sensor that may be associated with the fuel cell system10. The controller74may be a single controller or multiple controllers in communication with one another. The controller74may also be in communication with the valve23, regulator25, valve42, valve58, compressor48, and motor50.

During operation, the stoichiometric ratio of total reactant per reactant electrochemically needed for both reactants of the fuel cell system may be controlled based on the fuel cell operating state, environmental conditions, and the like. The stoichiometry may be controlled by using the valve23and regulator25on the anode side14to control the flow rate of fuel or hydrogen to the stack12, and by using the compressor48and motor50on the cathode side16to control the flow rate of air to the stack12. The system10may be operated through a range of fuel and air stoichiometric ratios. As the system10is operated at a lower power level, the amount of water byproduct will decrease, as the amount of current drawn from the stack12decreases.

FIG.2illustrates a vehicle100having a fuel cell system (“the system”)102according to an embodiment. The system102may be a fuel cell system as described with respect toFIG.1. The system102receives hydrogen from a storage tank104and air from the ambient environment to operate, and provides electrical power and energy to a battery106for storage. The battery106is connected to an inverter108, which in turn powers an electric machine110. The electric machine110may act as a motor to propel the vehicle100, and in some embodiments, act as a generator to charge the battery106. The electric machine110is connected to a transmission112. The transmission112is connected to wheels114of the vehicle100.

The vehicle has a control system116. The control system116may include any number of controllers, and may be integrated into a single controller, or have various modules. Some or all of the controllers may be connected by a controller area network (CAN) or other system. The control system116may be connected to random access memory118or another data storage system. In some embodiments, the vehicle has a user interface120in communication with the control system116. The user interface120may include an on-board vehicle system, and may also include a receiver configured to receive information and inputs from a remote user using a cellular phone, a computer, or the like. The user interface may also include a navigation system.

The control system116is in communication and is configured to control the system102, battery106, inverter108, electric machine110, and transmission112. The control system116is also configured to receive signals from these vehicle components related to their status and the vehicle state.

The control system116has a receiver121, which may include one or more antennae. Each antenna may be configured to wirelessly receive signals from various sources, including, but not limited to, cellular towers122, satellites124, wireless network servers, and the like.

The controllers74,116described herein, may be part of a larger control system and may be controlled by various other controllers throughout the vehicle100or fuel cell system10, such as a vehicle system controller (VSC). It should therefore be understood that the controllers74,116, and one or more other controllers, can collectively be referred to as a “controller” that controls various actuators in response to signals from various sensors to control various functions of the vehicle100or fuel cell system10. The controllers74,116may include a microprocessor or central processing unit (CPU) in communication with various types of computer readable storage devices or media. Computer readable storage devices or media may include volatile and nonvolatile storage in read-only memory (ROM), random-access memory (RAM), and keep-alive memory (KAM), for example. KAM is a persistent or non-volatile memory that may be used to store various operating variables while the CPU is powered down. Computer-readable storage devices or media may be implemented using any of a number of known memory devices such as PROMs (programmable read-only memory), EPROMs (electrically PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electric, magnetic, optical, or combination memory devices capable of storing data, some of which represent executable instructions, used by the controller in controlling the vehicle100or fuel cell system10.

Low current operation of a fuel cell system may be challenging for an ejector-based anode subsystem. Recirculation flow (e.g., the flowing of excess hydrogen unused by the anode side14to the mixing chamber28via recirculation loop34) is typically accomplished via a pump or blower during such a low current operation. This is because the low primary flow from a proportional injector cannot provide a sufficient difference in pressure between the mixing chamber28and the recirculation loop34to generate recirculation through the recirculation loop34. It may also be challenging to maintain an accurate measurement of primary flow from such a proportional injector. If an on/off injector is utilized, the duration of recirculation flow is fixed by the pressure limits of the stack. If the flow period is too long the cross-pressure limits between the anode and the cathode may be exceeded, which may place excessive stress on the membrane18, which may decrease the lifetime of the membrane18. Long injection pulses at low current operation may result in long off times because of the low hydrogen usage rate, which can reduce cell stability.

These potential issues can be solved by adding parallel injectors27to the supply side of the ejector24. At the start of an injection pulse, all the injectors27are turned on in unison. This provides for a quick filling of the nozzle26and allows the ejector24to quickly achieve design flow velocity, which may be supersonic. Once the design pressure and flow conditions are present in the ejector24, flow in the anode side14of the stack12achieves design delta pressure within a short period of time (typically less than 20 milliseconds). Once the flow is moving through the anode side14as desired, one or more of the injectors27may be turned off in order to slow or reverse the buildup of pressure in the system while still maintaining acceptable anode flow. In some operating regions this may also result in one injector27staying on and the other injector27or injectors27switching on and off. The net result will increase average recirculation flow and reduce the number of pressure fluctuations during the lifetime of the fuel cell stack12. Such a control scheme will reduce the number of pressure pulses during the lifetime of the fuel cell stack12, as well as the number of on and off pulses of the injectors27, increasing lifetime of both the fuel cell stack12and the injectors27.

By implementing a staged or asynchronous injection termination where multiple injectors27work collaboratively, the velocity of the hydrogen flow can be controlled in the primary jet (i.e., the flow from the nozzle26) entering the anode side14of the stack12and more accurately account for the quantity of gas dispensed by the injectors27. Such an approach eliminates the necessity of a pump or blower to recirculate gas in the anode loop at low current operation, by maintaining stream momentum. In addition, since the pump or blower is eliminated, there will be a net power gain to the fuel cell system10due to the elimination of parasitic power consumption by the pump or blower. Such an approach will increase the lifetime of the fuel cell stack12by delivering a more consistent and higher quantity of humidity to the inlet (e.g., input30) of the anode side14of the stack12. Such an approach will also increase the lifetime of the fuel cell stack12by reducing the number of pressure fluctuations that the membrane18is subjected to over the lifetime of the membrane18. The lifetime of the injectors27will also be increased due to the reduction in the number of injection cycles.

Referring toFIG.3, the ejector24and the injectors27are described in further detail. The mixing chamber28has an outlet126that is in fluid communication with the anode side14. The nozzle26is configured to accelerate and direct the hydrogen into the mixing chamber28. The nozzle26defines a nozzle chamber128that has an outlet end130that is in fluid communication with the mixing chamber28. A recirculation port132connects and establishes fluid communication between the recirculation loop34(or more specifically passageway44) and the mixing chamber28. The recirculation port132may be disposed behind the nozzle26from a side perspective. The flow of hydrogen from the recirculation port132within the mixing chamber28may be substantially perpendicular to the flow of hydrogen from the nozzle26within the mixing chamber28. Substantially perpendicular may refer to any incremental angle between exactly perpendicular and 15° from exactly perpendicular.

The ejector24further defines a plurality of inlet ports134that are in direct fluid communication with the nozzle chamber128. The ejector24also defines a plurality of injector cavities136that are each configured to receive one of the injectors27. Each injector cavity136is in fluid communication with one of the inlet ports134. Each injector27is disposed within one the injectors cavities136and is positioned to inject hydrogen into the nozzle chamber128via the corresponding inlet port134(i.e., the inlet port134that is in fluid communication with the specific injector cavity136that the specific injector27is disposed in). Each inlet port134is arranged in parallel so that each injector27may deliver hydrogen to the nozzle chamber128independently and separately from the other injectors27. Although only two injector cavities136and corresponding inlet ports134and are illustrated, it should be understood that the ejector24may define two or more injector cavities136and corresponding inlet ports134(e.g., one injector cavity136and corresponding inlet port134for each injector27).

Referring toFIG.4, a flowchart illustrating a method200of controlling the delivery of hydrogen to the fuel cell stack12is illustrated. The method200may be implemented by any of the controllers described herein (e.g., controller74). The method200may be stored as control logic and/or algorithms within the controller. The controller may be configured to control the operation of various components of the fuel cell system10and/or vehicle100in response to various conditions of the fuel cell system10and/or vehicle100. The method200begins at start block202. The method200may be initiated at start block202once an ignition of the vehicle100has been turn to an “on” position.

The method200depicted inFIG.4may be representative of a single injection pulse where hydrogen is delivered from the injectors27via a series of spaced apart pulses according to a pulse method. It is noted that when such a pulse method is utilized, the injectors27are closed between pulses such that no hydrogen flows therefrom. Alternatively, the method200depicted inFIG.4may be representative of method where there is a continuous flow of hydrogen from at least one of the injectors27.

Next, the method200moves on to block204where a command is generated and received to deliver hydrogen to the anode side14of the fuel cell stack12. The command may be generated and received (i) intermittently (a pulse modulation method), (ii) in response to the stack12requiring additional hydrogen based on a power demand, (iii) in response to difference between a pressure on the anode side14and a pressure of the cathode side16decreasing to less than a threshold value, (iv) or in response to the ignition of the vehicle100being turned to the “on” position. In response to the command at block204, each of the injectors27(e.g., the first and second injectors27if two are utilized) are then be opened at block206to deliver hydrogen to the nozzle26and ultimately to the anode side14of the fuel cell stack12. If a pulse method is being employed, opening each of the injectors27initiates, starts, or is the beginning of a single injection pulse. Also, at block206each of the injectors27may be opened simultaneously or in unison.

Next, the method200moves on to block208where it is determined if the anode side pressure (i.e., the pressure of the anode side14) has increased to greater than a first threshold or if a first predetermined time period has expired. If the anode side pressure has not increased to greater than the first threshold or if the first predetermined time period has not expired, the method200recycles back to the beginning of block208. If the anode side pressure has increased to greater than the first threshold or if the first predetermined time period has expired, the method200moves on to block210where one or more of the injectors27are closed while one or more of the injectors27remains open. It is noted that if two injectors27are utilized, a second of the injectors27is closed while a first of the injectors27remains open at block210.

Next, the method200moves on to block212where it is determined if the anode side pressure has decreased to less than a second threshold or if a second predetermined time period has expired. If the anode side pressure has not decreased to less than the second threshold or if the second predetermined time period has not expired, the method200recycles back to the beginning of block212. If the anode side pressure has decreased to less than the second threshold or if the second predetermined time period has expired, the method200returns to block206where each of the injectors27that was closed at block210are reopened such that each of the injectors27(first and second injectors27if only two are utilized) are again in an open state. The first and second threshold may have the same value. Alternatively, the second threshold may be less than the first threshold to provide a hysteresis in order to eliminate the injectors being opened and closed at an excessive frequency.

At any time while the method200is in process, if the command to deliver hydrogen to the anode side14of the fuel cell stack12that was generated at block204is retracted, the method200may end. The command to deliver hydrogen to the anode side14of the fuel cell stack12may be retracted in response to a difference between the anode pressure (i.e., the pressure of the anode side14) and the cathode pressure (i.e., the pressure of the cathode side16) exceeding a third threshold, which is indicative of too high cross pressure, which could accelerate the mechanical wear of the membrane18. In the event the method200ends, each of the injectors27(i.e., the first and second injectors27if only two injectors are utilized) are closed to prevent further hydrogen from being delivered to the anode side14of the fuel cell stack12. If the difference between the anode pressure and the cathode pressure later decreases to less than the third threshold, the method200may generate another command to deliver hydrogen to the anode side14of the fuel cell stack12, which may be received at block204.

It should be understood that the flowchart inFIG.4is for illustrative purposes only and that the method200should not be construed as limited to the flowchart inFIG.4. Some of the steps of the method200may be rearranged while others may be omitted entirely.

It should be understood that the designations of first, second, third, fourth, etc. for any component, state, or condition described herein may be rearranged in the claims so that they are in chronological order with respect to the claims. Furthermore, it should be understood that any component, state, or condition described herein that does not have a numerical designation may be given a designation of first, second, third, fourth, etc. in the claims if one or more of the specific component, state, or condition are claimed.