The invention relates to a coolable trunk piston for internal combustion engines.
Such pistons are known from U.S. Pat. No. 4,377,967. The wall part (shaped sheet metal) which is used in those pistons to cover the cavity which forms the cooling oil space is flanged onto the outer periphery of the annular wall which carries the piston rings. This type of fixing is not secure, because flanging of the relatively thin-gauge wall part can become detached in the long term under the conditions in which engines operate.
The use of a one-piece thick gauge and thus, by reason of its greater rigidity, a wall part which guarantees a more reliable attachment is in turn undesirable for different reasons. The outer annular part of the piston head which accommodates the piston rings ought during operation of the engine to be able to change its shape at its bottom end without being hindered by the incorporated wall part. Such deformations take place due to the combustion processes which take place in the manner of explosions and, if they are inhibited, they can cause cracks in the piston head material. In this respect, one-piece sheet metal covering such as are known from FR-A 23 23 022 or coverings which consist of individual parts rigidly connected to each other, such as are described in the case of pistons in U.S. Pat. No. 2,698,210 are equally unsuitable for the necessary covering of the annular cooling oil cavity.
It is on this premise that the invention is based on the problem in the case of the piston known from U.S. Pat. No. 4,377,967, of providing a covering which ensures on the one hand movements of the bottom end of the outer annular wall of the piston head while on the other is sufficiently securely attached to the piston head.