JPH0343652Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a fuel cell, and particularly to a tightening structure thereof.

[Prior art and its problems]

FIG. 1 shows this type of fuel cell. A unit cell 1 consists of a fuel electrode 2, a matrix 3 holding an electrolyte, an air electrode 4, and a separate plate 5. A fuel cell is constructed by stacking a large number of these unit cells 1. A laminate 6 is constructed. At both ends of the fuel cell stack 6, current collecting plates 7 for extracting electric power to the outside are provided, and clamping plates 9 are provided above and below with an insulating plate 8 in between. The fuel cell stack 6 is tightened in the stacking direction by tightening a disc spring 10 provided on the top of a tightening plate 9 with a tightening rod 11 and a nut 12. In such a configuration, it is important to maintain the clamping load applied to the cell stack 6 at an appropriate value in order to fully demonstrate the performance of the battery.

However, since the carbon that makes up the fuel cell stack and the carbon steel that is the material of the tightening rods have different coefficients of thermal expansion, temperature changes that occur during battery operation can cause a difference in the amount of elongation in the stacking direction, resulting in a tightening load. decreases. For this reason, in the past, the reduction in the tightening load was prevented by making the stroke of the disc spring 5 to 10 times the difference in the amount of extension, but in order to lengthen the stroke of the disc spring, a large number of disc springs were used. The need arose.

In order to solve this problem, a structure shown in FIG. 2 has been proposed.

The structure of FIG. 2 differs from the structure of FIG. 1 in that a spacer 13 having a larger coefficient of thermal expansion than the tightening rod 11 is provided between the disc spring 10 and the nut 12. Here, the length l of the spacer 13 is determined by the tightening rods 11, α _L , α _C and α _S , respectively.
Thermal expansion coefficients of the fuel cell stack 6 and the spacer 13,
When h is the cell stack height, the value is expressed by the following formula.

l=(α _L −α _C )・h/(α _S −α _L ) …(1) As an example, consider a fuel cell stack with stack height h=3 m (α _C =4×10 ^-6 /℃). No. 1 when tightened at room temperature (25℃) and operated at an operating temperature of 190℃.
The differences between the figure and FIG. 2 will be explained. If the material of the tightening rod 11 is mild steel (α=11×10 ^-6 /℃), the thermal expansion of the fuel cell stack 6 is 2.1 mm, while the thermal expansion of the tightening rod 11 is 5.8 mm. The difference in thermal expansion between the laminate and the tightening rod is approximately 3.7 mm. 1st
In the conventional structure shown in the figure, in order to absorb this difference in thermal expansion, the stroke of the disc spring is lengthened, for example 35
mm, the reduction in tightening load was limited to about -10%. For this reason, the number of disc springs required varies depending on the spring constant of the disc spring, but if a disc spring with a thickness of 3.5 mm is used, 10 disc springs are required for one tightening rod. On the other hand, according to the configuration shown in Fig. 2, the material of the spacer is a glass laminated polyimide plate (α _S = 55
×10 ^-6 /℃), l≒480mm according to equation (1)
Therefore, by using a spacer of about 480 mm, it is possible to absorb the difference in thermal expansion without using a disc spring.

As described above, according to the configuration shown in FIG. 2 above, the difference in thermal expansion between the fuel cell stack and the tightening rod can be absorbed by using a spacer with a larger coefficient of thermal expansion than the tightening rod. This has the advantage that the number of disc springs can be reduced or eliminated.

However, the configuration shown in FIG. 2 also has the following problems. The fuel cell stack, tightening rods, and spacers usually do not reach the same temperature during fuel cell operation, and the temperature of the tightening rods and spacers is lower than that of the fuel cell stack. It varies depending on the battery load and cooling conditions. Therefore, depending on the situation, there is a problem that the difference in thermal expansion between the fuel cell stack and the tightening rod cannot be absorbed within an allowable range.

[Purpose of invention]

In view of the above-mentioned problems, an object of the present invention is to provide a fuel cell equipped with a new tightening structure for absorbing the difference in thermal expansion between the fuel cell stack and the tightening rod within an appropriate limit. There is a particular thing.

[Key points of the idea]

According to the present invention, the above object is to provide a fuel cell stack formed by stacking a plurality of single cells, a clamping plate disposed at both ends of the fuel cell stack, and a fuel cell stack that connects the clamping plates to fuel the fuel cell stack. By comprising a tightening rod for tightening the battery stack, a spacer having a larger coefficient of thermal expansion than the tightening rod and inserted into the tightening rod, and a spacer heating means for heating the spacer at a predetermined time. achieved.

[Example of idea]

FIG. 3 shows an embodiment of the present invention, in which a spacer 13 inserted into a tightening rod 11 is provided with a heater 15 as spacer heating means.
Further, a strain gauge 17 is attached to the tightening rod 11, and the stress in the axial direction applied to the tightening rod 11 is measured by the strain gauge 17. Power supply circuit 16
is connected to a computing unit 18 which inputs the signal from the strain gauge 17 that measures the tightening surface pressure, and the computing unit 1
It operates with control signals from 8. In such a configuration, if the tightening load is lower than the set value, the control signal of the calculator will issue a signal to heat the heater,
If it is high, power to the heater is stopped. As a result, if the tightening load is lower than the set value, the spacer is heated by the heater and thermally expands, so a tensile load is added to the tightening rod by the amount of thermal expansion of the spacer, increasing the tightening load. . Then, when the tightening load reaches the set value, the energization to the heater is stopped, and the increase in the tightening load is also stopped. Therefore, it is possible to absorb the difference in thermal expansion that occurs when the temperature of the spacer portion is lower than the temperature of the fuel cell stack.

The heating control of the heater can also be controlled in a predetermined manner according to the load of the fuel cell, instead of depending on the signal from the strain gauge as described above. It is also conceivable to provide a heating means as described above in the tightening rod part without using a spacer, but in this case, the frequency of heating by the heater increases, which is not preferable in terms of energy saving.

According to the method of the present invention in which a spacer is provided and the spacer is heated, the difference in thermal expansion can be absorbed by the spacer in most cases, and the heater only needs to be heated when the allowable limit is exceeded, which is suitable for energy saving. .

[Effect of idea]

As is clear from the above description, according to the present invention, a spacer having a coefficient of thermal expansion larger than that of the tightening rod is inserted into the tightening rod, and the spacer is heated at a predetermined time to separate the cell stack and the tightening rod. The difference in thermal expansion between the spacer and can be provided.

[Brief explanation of drawings]

Figure 1 is a front view showing a conventional fuel cell tightening structure, Figure 2 is a front view showing a proposed tightening structure to improve the conventional structure, and Figure 3 is an embodiment of the present invention. FIG. 1: Single cell, 6: Fuel cell stack, 11: Tightening rod, 13: Spacer, 15: Heater as spacer heating means.

Claims (1)

[Scope of utility model registration request] A fuel cell stack formed by stacking a plurality of single cells;
A clamping plate disposed at both ends of the fuel cell stack, a clamping rod that connects the clamping plate and tightens the fuel cell stack, and a clamping rod having a coefficient of thermal expansion larger than that of the clamping rod. 1. A fuel cell comprising: a spacer inserted into a rod; and spacer heating means for heating the spacer at a predetermined time.