In automobiles, reduction of the engine room space is progressing in response to conversion to Front Wheel Drive (FF) for the purpose of achieving size and weight reduction and to a demand for a larger interior space.  Size and weight reduction of every component in an engine room is required for reduction of the engine room space, and thus achieving further size and weight reduction is being advanced in the aforementioned electrical parts and engine accessories.  Meanwhile, higher performance and greater output are also being required of electrical parts and engine accessories.  However, decrease in output with smaller size is unavoidable, and for example, in alternators and electromagnetic clutches for automotive air conditioners, decrease in output is compensated for by increasing their speed.  Accordingly, idler pulleys speed up as well, and heat generation is promoted at lubricated points.  Additionally, hermeticity of engine rooms is accelerated in order to improve silence during engine operation, and in this case, increase in temperature in such engine rooms is promoted as well. 
Moreover, double row angular contact ball bearings have been used as bearings for compressor pulleys and magnetic clutches for automotive air conditioners, but nowadays, the tendency is that single row bearings are used for lighter weight and lower cost of the pulleys and the clutches.  As for a single row ball bearing used under the same conditions as double row angular contact ball bearing, due to its larger PV value (a product of the bearing surface pressure P and the slip velocity V), which represents the load capacity limit of the bearing, smaller bearing space volume, and the like, the tendency is that the bearing is used under a condition that the grease filling amount is small and the grease heat generation amount is large. 
Thus, since the use conditions of the electrical parts and engine accessories become increasingly severer, improvement in its durability particularly at high temperatures has been necessary for grease to be applied to these roller bearings. 
In Patent Literatures 1 to 5, grease compositions in which a urea thickening agent is used are disclosed as conventional grease. 
In Patent Literatures 6 to 7, grease compositions in which an imide thickening agent is used are disclosed as well.