SYSTEM FOR PROTECTING A FUEL CELL FROM COLD TEMPERATURES

Abstract

A protection system for a fuel cell is provided that has two different modes of operation. The protection system includes a fuel cell, a cooling system for the fuel cell that controls the temperature of the fuel cell responsive to a controller. The controller is operable in a first mode of operation when a time T for the next start-up is not known and a second mode of operation when the time T for the next start-up is known. In the first mode, a time T.sub.F is the time an estimated future ambient temperature is estimated to fall to near freezing wherein at T.sub.F the cooling system purges the fuel cell. In the second mode, at T.sub.F the cooling system turns on without starting the fuel cell. The controller turns of the cooling system when the fuel cell stack is warmed to a nominal temperature.

Claims

1. A protection system for a fuel cell for a fuel cell comprising: a fuel cell stack; a cooling system for the fuel cell stack that controls a temperature of the fuel cell; and a controller operable when a time T for a next start-up is known and a time T.sub.F that an estimated future ambient temperature is estimated to fall to near freezing before T, at T.sub.F the cooling system is turned on without starting the fuel cell stack.

2. The protection system for a fuel cell of claim 1, wherein the controller is programmed to estimate the time Y.sub.1 required for a fuel cell stack temperature to fall to near freezing, and estimate the time Y.sub.2 required for the fuel cell stack to drop from fully warmed to near freezing, and wherein T must be less than sum of Y.sub.1 .sub.+ Y.sub.2, before the cooling system is turned on without starting the fuel cell.

3. The protection system for a fuel cell of claim 1, wherein the controller is operable in a second mode when a time T of the next start-up is not known, wherein when T.sub.F is estimated to fall to near freezing, at T.sub.F the cooling system purges the fuel cell stack.

4. The protection system for a fuel cell of claim 3 wherein the cooling system purges the fuel cell stack by blowing heated air through the through the fuel cell stack to remove water from the fuel cell stack.

5. The protection system for a fuel cell of claim 1, wherein T.sub.F is selected from one of the following sources: a temperature sensor; a temperature data source; and a manual input from a user.

6. The protection system for a fuel cell of claim 1, wherein the controller turns off the cooling system after the cooling system is turned on without starting the fuel cell stack and coolant is warmed to a predetermined level.

7. A protection system for a fuel cell comprising: a fuel cell stack; a cooling system for the fuel cell that controls a temperature of the fuel cell; and a controller operable in a first mode of operation when a time T for a next start-up is not known and a second mode of operation when the time T for the next start-up is known, wherein in the first mode and a time T.sub.F is the time an estimated future ambient temperature is estimated to fall to near freezing, at T.sub.F the cooling system purges the fuel cell, and in the second mode at T.sub.F the cooling system turns on without starting the fuel cell.

8. The protection system for a fuel cell of claim 7, wherein the controller is programmed to estimate the time Y.sub.1 required for a fuel cell stack temperature to fall to T.sub.F, and estimate the time Y.sub.2 required for the fuel cell stack temperature to drop from fully warmed to T.sub.F, and wherein T must be less than a sum of Y.sub.1 + Y.sub.2, before the cooling system is turned on without starting the fuel cell.

9. The protection system for a fuel cell of claim 7 wherein the cooling system purges the fuel cell by blowing heated air through the through the fuel cell stack to remove water from the fuel cell stack.

10. The protection system for a fuel cell of claim 7 wherein T.sub.F is based upon one of the following sources: a temperature sensor; a temperature data source; and a manual input from a user.

11. A protection system for a fuel cell comprising: a fuel cell stack; a cooling system for the fuel cell that controls a temperature of the fuel cell stack when operating and warms the fuel cell stack for start-up, and a controller programmed to - shutdown the fuel cell stack when requested, store a predicted start-up time T, store an ambient temperature value; estimate the time Y.sub.1 required for the fuel cell stack temperature to fall to a selected near freezing fuel cell temperature, estimate the time Y.sub.2 required for the fuel cell stack to drop from fully warmed to the selected near freezing fuel cell temperature, and start the cooling system when T known and Y.sub.1 < T and T < Y.sub.1 + Y.sub.2.

12. The protection system for a fuel cell of claim 11, wherein the controller is operable in a second mode when a time T of the next start-up is not known, the controller estimates a time T.sub.F that is an estimated time that an ambient temperature is estimated to fall to near freezing, the cooling system purges the fuel cell.

13. The protection system for a fuel cell of claim 11 wherein the cooling system purges the fuel cell by blowing heated air through the through the fuel cell stack to remove water from the fuel cell stack.

14. The protection system for a fuel cell of claim 11 wherein T.sub.F is estimated based upon one of the following sources: a temperature sensor; a temperature data source; and a manual input from a user.

15. The protection system for a fuel cell of claim 11 wherein the controller turns the cooling system off when a nominal temperature is reached.

16. The protection system for a fuel cell of claim 11 wherein the controller turns the cooling system off when T < Y.sub.1 + Y.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a flow chart illustrating the steps of one embodiment of the cold temperature protection system for a fuel cell in a vehicle.

[0021] FIG. 2 is a flow chart illustrating protection strategy A wherein the fuel cell is protected by purging the fuel cell stack with heated air when the temperature falls to near freezing.

[0022] FIG. 3 is a flow chart illustrating protection strategy B wherein the fuel cell is protected by turning the cooling system on without starting the fuel cell when the temperature falls to near freezing.

DETAILED DESCRIPTION

[0023] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0024] Referring to FIG. 1, the controller begins at 10. The initial decision at 12 made comprises is vehicle shutdown requested. If not, the routine ends at 14. If yes, the vehicle shuts down the fuel cell and the vehicle at 16. Next, a decision follows at 18 - Is the ambient temperature likely to drop below freezing? If not, the routine ends at 14. If yes, the decision follows at 20 -Can the next vehicle start time be predicted? If not, at 22 control strategy A described below with reference to FIG. 2 is initiated. If yes, at 24 the controller estimates the time until the next vehicle key start (X). The controller at 26 estimates the time Y.sub.1 required for the stack coolant temperature to drop to near freezing (5°). The controller at 28 estimates the time Y.sub.2 required for the stack coolant temperature to drop from fully warmed up to near freezing (5°). At 30 a decision is made as to whether the time until the next vehicle key start (X) is less than the sum of the time Y.sub.1 required for the stack coolant temperature to drop to near freezing (5°) plus the time Y.sub.2 required for the stack coolant temperature to drop from fully warmed up to near freezing (5°). If not, at 22 control strategy A is initiated. If yes, at 32 control strategy B described below with reference to FIG. 3 is initiated.

[0025] Referring to FIG. 2, a purge protection control strategy is illustrated beginning with the start of strategy A at 34. The decision is made at 36 - Is vehicle power up requested? If not, at the further decision is made at 38 - Did stack coolant drop below near freezing (5°). If not, the system returns to the beginning of strategy A.

[0026] If at 36 the decision is yes, the controller at 40 starts the vehicle.

[0027] If at 38 the decision is yes, the controller at 42 initiates a purge event by blowing heated air through the fuel cell stack to eliminate water from the fuel stack.

[0028] Referring to FIG. 3, control strategy B is illustrated beginning at 44. The decision is made at 46 - Is vehicle power up requested? If not, at the further decision is made at 48 - Did stack coolant drop below near freezing (5°). If not, the system returns to the beginning of strategy B.

[0029] If at 46 the decision is yes, the controller at 50 starts the vehicle.

[0030] If at 48 the decision is yes, the controller at 52 starts the fuel cell warming the fuel cell to a nominal temperature and then shuts down the cooling system. After warming the system returns to the beginning of strategy B.

[0031] In the broadest sense, the controller executes a time-based system for protecting a fuel cell in freezing and near freezing conditions (5°). The cooling system is controlled by the controller to heat the fuel stack when a time T for the next start-up is known and the time T.sub.F that an estimated future ambient temperature is estimated to fall to near freezing before T. At T.sub.F the cooling system is turned on without starting the fuel cell.

[0032] A dual mode protection system is provided wherein, the protection system includes a fuel cell, a cooling system for the fuel cell that controls the temperature of the fuel cell in response to the controller. The controller is operable in a first mode of operation when a time T for the next start-up is not known and a second mode of operation when the time T for the next start-up is known. In the first mode, a time TF is the time an estimated future ambient temperature is estimated to fall to near freezing and at TF the cooling system purges the fuel cell. In the second mode, at TF the cooling system turns on without starting the fuel cell.

[0033] The strategy implemented by the controller of the protection system for a fuel cell is implemented by at a request to shut down shut down the fuel cell stack storing a predicted start-up time T and storing a predicted ambient temperature value. The controller estimates the time Y.sub.1 required for the fuel cell stack temperature to fall to a selected near freezing fuel cell temperature, and estimate the time Y.sub.2 required for the fuel cell stack to drop from fully warmed to the selected near freezing fuel cell temperature. The controller is programmed to operate the cooling system when T known and Y.sub.1 < T and T < Y.sub.1 .sub.+ Y.sub.2.

[0034] The controller may be operable in a conventional mode when the time T of the next start-up is not known, wherein when T.sub.F is estimated to fall to near freezing, at T.sub.F the cooling system purges the fuel cell. The cooling system may purge the fuel cell by blowing heated air through the through the fuel cell stack to remove water from the fuel cell stack.

[0035] In the protection system for a fuel cell T.sub.F may be based upon a temperature sensor in or near the fuel cell stack, a temperature data source such as a network weather forecast, or a manual input from a user entering the time expected for a predicted low temperature.

[0036] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.