1. Field of the Invention
The invention relates to a piston mechanism. More particularly, the invention relates to a piston for such a mechanism with a flow passage therethrough.
2. Description of the Related Art
Such a piston mechanism allows the sucking in or intake of gaseous medium into the cylinder through the piston without an extra valve in the piston.
BE-A-378.946 describes a compressor with such a piston mechanism. However, the passage in the piston only extends partly thereover, namely from the front side up to an opening in the side which, in the utmost extended position, is not yet situated at the back side of the piston. Consequently, this passage does not open at the back side of the piston.
Gaseous medium is sucked in via chambers situated on the outside of the cylinder and consequently not via the crank chamber which is filled with oil. This oil serves to lubricate the bearings with which the piston rod is connected to the crank shaft and the piston. Hereby, the heating of the bearings is avoided, but traces of oil will be present in the obtained compressed air, which is not desirable for certain applications.
The presence of chambers at the outside of the cylinder and the use of oil to lubricate do not make the construction simple.
The gaseous medium which is sucked in through the passage flows along the wall of the cylinder which may be rather hot during operation, resulting in the heating of the medium, disadvantageously affecting the efficiency of the compressor.
A piston mechanism whereby the piston is provided with a passage which opens at the rear side of the piston and whereby the piston ring forms a valve in the passage is known from CH-A-308,083. However, this piston mechanism is not of the type concerned by the invention because the piston is stiffly connected with the piston rod and a crank chamber is not present. Therefore, such a piston mechanism does not show the problem of heating of the bearings.