CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0073074 filed on Jun. 16, 2020, which is hereby incorporated by reference for all purposes as if set forth herein

BACKGROUND

Field

Exemplary embodiments relate to a fuel cell system for a vehicle, and more particularly, to a fuel cell system including a fuel cell stack for a vehicle, which is capable of ensuring a high output from the fuel cell stack and improving safety and reliability.

Discussion of the Background

A fuel cell system refers to a system that produces electrical energy by means of a chemical reaction of fuel. Research and development are consistently performed on the fuel cell system as an alternative capable of solving global environmental issues.

Based on types of electrolytes used for the fuel cell system, the fuel cell system may be classified into a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), a polymer electrolyte membrane fuel cell (PEMFC), an alkaline fuel cell (AFC), a direct methanol fuel cell (DMFC), and the like. Based on operating temperatures, output ranges, and the like as well as types of used fuel, the fuel cell systems may be applied to various application fields related to mobile power, transportation, distributed power generation, and the like.

The fuel cell system includes a fuel cell stack configured to generate electrical energy, a fuel supply device configured to supply fuel (e.g., hydrogen) to the fuel cell stack, an air supply device configured to supply an oxidant (e.g., oxygen in air) required for an electrochemical reaction in the fuel cell stack, and a thermal management system (TMS) configured to remove reaction heat in the fuel cell stack out of the system, control the operating temperature of the fuel cell stack, and perform a function of managing water.

The thermal management system (TMS) refers to a kind of cooling device that maintains an appropriate temperature (e.g., 60 to 70° C.) by circulating an anti-freezing liquid, which serves as a coolant, to the fuel cell stack. The thermal management system may include a TMS line in which a coolant for cooling the fuel cell stack is circulated, a reservoir in which the coolant is stored, a pump configured to circulate the coolant, an ion filter configured to remove ions contained in the coolant, and a radiator configured to radiate heat of the coolant to the outside. In addition, the thermal management system may include a heater configured to heat the coolant, and an air conditioner (e.g., a HVAC unit) configured to cool and heat an interior of a vehicle by using the coolant.

Meanwhile, various attempts have recently been made to apply the fuel cell system to construction machines as well as passenger vehicles (or commercial vehicles).

Passenger vehicles require a high output from the fuel cell stack while traveling and may cool the fuel cell stack by the radiator using vehicle-induced wind generated in accordance with a vehicle speed.

In contrast, because construction machines performs work (e.g., leveling or loading) while stationary, a high output is required from the fuel cell stack while the construction machine is stationary. However, there is a problem in that it is difficult to sufficiently cool the fuel cell stack only with the amount of air flow generated by a cooling fan, which causes a deterioration in safety and durability of the fuel cell stack.

Therefore, recently, various types of research are being conducted into ways to effectively cool a fuel cell stack in a situation in which a high output is required from the fuel cell stack while a vehicle is stationary, but the research result is still insufficient. Accordingly, there is a need for development of a fuel cell system capable of effectively cooling the fuel cell stack in the above-mentioned situation.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and, therefore, it may contain information that does not constitute prior art.

SUMMARY

Exemplary embodiments of the present invention provide a fuel cell system for a vehicle, which is capable of ensuring a high output from a fuel cell stack and improving safety and reliability.

Another object of the present invention is to effectively cool a fuel cell stack and improve operating performance and operational efficiency of the fuel cell stack in a situation in which a high output is required from the fuel cell stack while a vehicle is stationary.

Still another object of the present invention is to minimize a deterioration in cooling performance which is caused by a decrease in flow rate of a coolant introduced into a fuel cell stack.

The object to be achieved by the exemplary embodiment is not limited to the above-mentioned objects, but also includes objects or effects that may be recognized from the solutions or the exemplary embodiments described below.

In order to achieve the above-mentioned objects of the present invention, a fuel cell system for a vehicle according to an exemplary embodiment includes a first cooling line configured to pass through a fuel cell stack in a vehicle and to circulate a first coolant therein, a first cooler provided in the first cooling line and configured to cool the first coolant, and a second cooler provided in the first cooling line and configured to cool the first coolant independently from the first cooler.

This is to ensure a high output from the fuel cell stack and improve safety and reliability.

For example, a passenger vehicle requires a high output from a fuel cell stack while traveling and may cool the fuel cell stack by a radiator using vehicle-induced wind generated in accordance with a vehicle speed. In contrast, because the construction machine performs work (e.g., leveling or loading) while the construction machine is stationary, a high output is required from the fuel cell stack while the construction machine is stationary. However, there is a problem in that it is difficult to sufficiently cool the fuel cell stack only with the amount of air flow generated by a cooling fan, which causes a deterioration in safety and durability of the fuel cell stack.

However, in the exemplary embodiment, the first coolant introduced into the fuel cell stack is cooled individually by the first cooler and the second cooler, such that it is possible to obtain an advantageous effect of ensuring a high output from the fuel cell stack and improving safety and reliability.

In particular, the exemplary embodiment may lower the temperature of the first coolant while a vehicle (e.g., a construction machine), which cannot use the vehicle-induced wind, is stationary, such that it is possible to obtain an advantageous effect of ensuring a high-output operation of the fuel cell stack and improving safety and durability.

Various cooling means capable of cooling the first coolant may be used as the first cooler.

As an example, the first cooler may include a first radiator provided in the first cooling line and configured to cool the first coolant.

Various cooling means capable of cooling the first coolant independently from the first cooler may be used as the second cooler.

As an example, the second cooler may include a first branch line branching off from the first cooling line, and a second radiator provided in the first branch line. The second radiator may be connected in parallel to the first radiator through the first branch line and configured to cool the first coolant.

In particular, one end of the first branch line may be connected to the first cooling line between an outlet of the fuel cell stack and an inlet of the first radiator, and the other end of the first branch line may be connected to the first cooling line between an outlet of the first radiator and an inlet of the fuel cell stack.

More particularly, a first on-off valve configured to selectively open or close the first branch line may be provided in the first branch line.

In a state in which the first on-off valve opens the first branch line, the first coolant may be cooled while passing through both the first radiator and the second radiator. In contrast, in a state in which the first on-off valve closes the first branch line, the first coolant passes only through the first radiator without passing through the second radiator, and as a result, the first coolant may be cooled only by the first radiator.

The fuel cell system for a vehicle according to the exemplary embodiment may include the first pump provided in the first cooling line and configured to pump the first coolant, and a flow rate adjuster provided in the first cooling line and configured to adjust a flow rate of the first coolant to be introduced into the fuel cell stack independently from the first pump.

This is to prevent the efficiency in cooling the fuel cell stack from being degraded due to a low flow rate of the first coolant. For example, in a case in which a flow rate of the first coolant is lower than a target flow rate (e.g., a predetermined flow rate) during the high-output operation of the fuel cell stack, there is a problem in that the efficiency in cooling the fuel cell stack deteriorates even though the temperature of the first coolant is within an appropriate temperature range.

However, according to the exemplary embodiments, since the flow rate adjuster configured to adjust a flow rate of the first coolant is provided in the first cooling line, it is possible to obtain an advantageous effect of minimizing a decrease in flow rate of the first coolant to be introduced into the fuel cell stack.

The flow rate adjuster may have various structures capable of adjusting a flow rate of the first coolant.

As an example, the flow rate adjuster may include a second branch line branching off from the first cooling line, and a second pump provided in the second branch line. The second pump may be connected in parallel to the first pump through the second branch line and configured to pump the first coolant.

In particular, one end of the second branch line may be connected to the first cooling line between the outlet of the first radiator and the first pump, and the other end of the second branch line may be connected to the first cooling line between the first pump and the inlet of the fuel cell stack.

More particularly, a second on-off valve configured to selectively open or close the second branch line may be provided in the second branch line.

In a state in which the second on-off valve opens the second branch line, the first coolant may be pumped by both the first pump and the second pump. In contrast, when the second on-off valve closes the second branch line, the first coolant may be pumped only by the first pump, and the first coolant pumped by the first pump may be prevented from being introduced into the second pump.

According to the exemplary embodiment, the fuel cell system may include a second cooling line configured to pass through a power electronic part of the vehicle and configured to circulate a second coolant therein, and a third radiator provided in the second cooling line and configured to cool the second coolant.

As an example, the power electronic part may include at least one of a bi-directional high-voltage DC-DC converter (BHDC) provided between the fuel cell stack and a high-voltage battery of the vehicle, a blower pump control unit (BPCU) configured to control a blower configured to supply outside air for operating the fuel cell stack, a low-voltage DC-DC converter (LDC) configured to convert a high direct-current voltage, which is supplied from the high-voltage battery, into a low direct-current voltage, an air compressor (ACP) configured to compress air to be supplied to the fuel cell stack, and an air cooler.

In particular, the first radiator and the third radiator may be disposed in parallel, and the fuel cell system may include a first cooling fan configured to blow outside air to the first radiator and the third radiator.

As described above, since the first radiator and the third radiator are simultaneously cooled by the same first cooling fan, it is possible to obtain an advantageous effect of simplifying the structure, improving a degree of design freedom and spatial utilization, and minimizing consumption of electric power required to cool the first radiator and the third radiator.

According to the exemplary embodiment, the fuel cell system may include a second cooling fan configured to blow outside air to the second radiator.

The fuel cell system for a vehicle according to the exemplary embodiment may include: a first connection line having one end connected to the first cooling line between an outlet of the first radiator and an inlet of the fuel cell stack, and the other end connected to the first cooling line between an outlet of the fuel cell stack and an inlet of the first radiator; a heater provided in the first connection line and configured to heat the first coolant flowing through the first connection line; and a second connection line configured to pass through an air conditioner in the vehicle, connected to the first cooling line between the outlet of the first radiator and the inlet of the fuel cell stack, and configured to circulate the first coolant therein.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

