1.  Technical Field
The present invention relates to a battery frame structure for an electric motorcar. 
2.  Description of the Related Art
In the general electric motorcar, batteries loaded thereon account for considerable weight and load space.  In order to mount the batteries, hitherto, an exclusive frame of rigid structure, which will be referred as battery frame" hereinafter, has been arranged under a vehicle floor.  Further, being mounted on the battery frame, a plurality of batteries have been arranged between the vehicle floor and the battery frame in a sealed manner. 
With such an arrangement as mentioned above, the battery function is influenced and lowered by the batteries' heatup.  In order to avoid such a problem, there have been disclosed Japanese Unexamined Patent Publications (Kokai) Nos.  52-35023 and 5-193366 etc.  in which cooling fluid, e.g. air, is introduced into the battery frame through a front section thereof is discharged from a rear section thereof so that the batteries contained therein are cooled down by the flow of fluid. 
In the so-constructed arrangement, however, the batteries are mounted on a bottom plate attached on the battery frame, it is hard to direct the cooling fluid toward the bottom side of the batteries sufficiently.  Furthermore, since the temperature of the cooling fluid is increased before it reaches some batteries at the rear, it is impossible to cool the every battery loaded on the battery frame uniformly.  In particular, in case of highly efficient batteries utilizing lithium ion or the like as a main constituent, effective cooling would not be expected because of the heat such batteries generate. 
Now, the battery frame generally includes an outer frame consisting of a front frame element, a rear frame element, a left frame element and a right frame element, and a bottom plate for closing an inside bottom of the outer frame.  In the so-constructed battery frame, the bottom surface of the outer frame is at the plane with of bottom plate.  Therefore, if the battery frame interferes with a road surface accidentally, both the bottom surface of the outer frame and the bottom plate would be in contact with the road surface, so that the batteries on the bottom plate may be damaged.