1. Technical Field
This invention relates generally to pistons for diesel engine applications, and more particularly to those having a closed oil gallery.
2. Related Art
It is known in diesel engine applications to provide a piston whose piston body is formed with a closed gallery for cooling oil. The oil circulates through the gallery and cools parts of the piston which are susceptible to damage from the heat of combustion. Such cooling galleries are generally annular or ring-shaped and are provided just inside of the ring belt adjacent the top wall of the piston body. The gallery is bounded by the inner wall and closed at the bottom by a bottom wall. One or more inlets are provided for receiving cooling oil into the gallery. Various outlets are also provided for directing portions of the oil from the gallery into other regions of the piston for cooling or lubrication purposes. It is know to provide an oil passage leading from the cooling gallery to the pin bores of the pin bosses for lubricating the wrist pin. The entry point for the lubrication is rather localized and provides a limited supply of oil for lubrication which may not be present during the entire stroke of the piston.
It is an object of the present invention to improve the lubrication of the pin bore and closed gallery diesel piston applications.
A piston for diesel engines constructed according to a presently preferred embodiment of the invention includes a piston body having an oil gallery and a pair of pin bosses having pin bores disposed about a common pin bore axis and pin bore surfaces which are spaced from one another about their circumference by an intervening space between the pin bosses. According to the invention, at least one recess is formed in at least one of the pin bore surfaces and extends axially across the at least one pin bore surface. At least one associated oil passage extends from the gallery to the recess for feeding oil from the gallery to the recess.
The invention has the advantage of providing improved lubrication to the pin bosses of diesel engine pistons having closed oil cooling galleries which serves as a reservoir for lubricating oil for the pin bosses.
The invention has the further advantage of providing an axial relief or recess in the pin bore surface which itself acts as a localized oil reservoir for lubricating oil adjacent the pin bore surface. The recess, fed by the oil passage, captures or wicks the oil and then feeds the oil to the pin bore surface during the full stroke of the piston, including at the top of the stroke when less oil is available in the gallery to be fed to the pin bores. At such times, the pocket of oil retained in the pin bore recess is available to feed the pin bore surfaces with lubricating oil.
Another advantage of the invention is that it provides a simple solution for greatly improving the lubrication of the pin bore of closed gallery diesel pistons. The recess may be formed in the pin bore surface by a simple machining operation and could be readily adapted to existing manufacturing processes during the machining of the pin bore surfaces.
The invention has the further advantage of prolonging the life of pistons, connecting rods and wrist pin by improving the lubrication to their interactive surfaces during operation.