Rolling bearing, rolling bearing for fuel cell, compressor for fuel cell system and fuel cell system

Abstract

The rolling bearing of the invention to be incorporated in the compressor for fuel cell system comprises a fluorine-based grease containing a fluororesin and a fluorine-based oil, a urea grease containing a urea compound and a synthetic oil or a lithium complex grease containing a lithium complex and a synthetic oil encapsulated therein. In this arrangement, the grease deterioration of the rolling bearing incorporated in the compressor for force-feeding various fluids between machines can be prevented, making it possible to provide a fuel cell system which can maintain stable operation over an extended period of time.

Description

BACKGROUND OF THE INVENTION [0001] 1. Technical Field [0002] The present invention relates to a rolling bearing, a rolling bearing for fuel cell, a compressor for fuel cell system and a fuel cell system. The present invention relates to a fuel cell system which operates to gasify a fuel such as methanol and water, modify the gas in a modifier, remove CO from the gas in a CO remover, and then supply the fuel into a stack of fuel cells (fuel cell main body) where electricity is generated, a fuel cell system which operates to supply hydrogen as a fuel from a hydrogen storage unit such as hydrogen tank and hydrogen storage alloy into a stack of fuel cells where electricity is generated, a fuel cell system which operates to withdraw hydrogen from a hydrogen-containing compound such as methanol and water in a modifier, remove impurities from the fuel in an impurity remover such as CO remover, and then supply hydrogen into a stack of fuel cells where electricity is generated, a compressor ...

AI Technical Summary

Benefits of technology

[0011] The invention has been worked out under these circumstances. It is an aim of the invention to provide a rolling bearing for fuel cell which causes the grease to be scattered little and, if any scattered, gives no adverse effect on the stack of fuel cells and thus allows the fuel cell system to operate in a stable manner over an extended period of time.

[0047] As a result of extensive studies, the inventors further found that a grease composition which comprises an alkaline material incorporated therein and thus is capable of neutralizing an acidic material is suitable for use in an atmosphere having an acidic material present therein while maintaining its excellent lubricating properties and heat resistance.

Problems solved by technology

However, the lithium soap-mineral oil-based grease is subject to deterioration at high temperatures and thus can deteriorate the life of the compressor and even the entire system.

Further, when the grease has much volatile content, the volatile content can be a catalyst poison to the stack of fuel cells to disadvantage.

In a hydrogen tank process fuel cell system, too, the ejector compressor has similar problems.

Since some of these metal ions can act as a catalyst poison to the stack of fuel cells, it is likely that the reaction efficiency of the fuel cell can be deteriorated when the grease is scattered and attached to the stack of fuel cells.

However, the related art synthetic oil-urea-based grease and fluorine-based grease leave much to be desired in comprehensive durability against hydrogen, water content, acid, alkali, etc.

However, this proposal is to cope with the leakage of the grease but is not intended to inhibit dusting from the grease.

In a hydrogen tank process fuel cell system, too, the rolling bearing to be incorporated in an ejector compressor can cause similar problems.

When water or water vapor penetrates into the interior of the rolling bearing, white structure flaking can occur in the bearing constituents due to hydrogen as often seen in automobile electrical parts, reducing the life of the compressor and even the entire system.

However, sulfonates which are widely used because of its excellent rust preventing effect can easily cause white structure flaking attributed to hydrogen analogous to the aforementioned inner starting point flaking as described in Japanese Patent No. 2878749.

Further, the grease to be encapsulated in the rolling bearing is also essentially required that it have a low volatility because when the evaporation content of the base oil is transported with a gas, it is then attached to the stack of fuel cells in particulate form to reduce the electricity generation efficiency.

For example, in a cold district, unusual noise can easily occur due to drop of fluidity at low temperatures.

Thus, in a fuel cell system, the rolling bearing incorporated in the compressor is subject to rusting or corrosion due to contact with water content.

When water content in gas penetrates in the grease, the grease then softens and thus can leak out.

However, it has never been practiced to render the encapsulation grease rust-proof or corrosion-resistant.

However, the added amount of such an extreme pressure agent is limited because it gives an adverse effect on lubricating properties and, when released and attached to the stack of fuel cells in the form of particles containing metal ions, it can act as a catalyst poison.

Thus, the improvement of abrasion resistance by the single use of an extreme pressure agent is limited.

However, such a grease composition is disadvantageous in that it normally exhibits a high vapor pressure and some of these additives contain a component that can act as a catalyst poison to the stack of fuel cells and thus can be a source of catalyst poison.

Thus, in a fuel cell system, the rolling bearing incorporated in the compressor is subject to rusting or corrosion due to contact with water content or acidic matter.

However, the grease composition comprising a urea compound incorporated therein as a thickening agent has a lower basicity than the grease composition comprising a metal soap incorporated therein as a thickening agent.

Thus, when used in an atmosphere having the aforementioned acidic matter present therein, the grease composition can easily deteriorate.

However, since sulfonates or succinic acid derivatives having an excellent rustproofness can be difficultly dissolved in the fluorine-based lubricant or silicone-based lubricant which is a base oil, the content of these components cannot be great, making it impossible to render the grease composition fully rustproof.

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