Piston with a skirt having oil flow slots and method of construction thereof

#1. Technical Field

#This invention relates generally to internal combustion engines, and more particularly to pistons for heavy duty diesel engines.

#2. Related Art

#These and other aspects, features and advantages of the invention will become readily apparent to those skilled in the art in view of the following detailed description of the presently preferred embodiments and best mode, appended claims, and accompanying drawings, in which:

#FIG. 1 is a partial perspective view of a piston construction according to a presently preferred embodiment of the invention;

#FIG. 2 is a cross-sectional view taken generally along the line 2-2 of FIG. 1;

#Referring in more detail to the drawings, FIGS. 1 and 2 illustrate a piston 10 constructed according to one presently preferred embodiment of the invention for reciprocating movement in a cylinder bore (not shown) of an internal combustion engine, such as a diesel engine. The piston 10 has a body 12, either cast or forged, or by any other process of manufacture, extending along a central axis 14 along which the piston 10 reciprocates in the cylinder bore. The body 12 is represented, by way of example and without limitation, as having an upper crown 16 joined to a lower crown 18 having a pair of pin bosses 20 depending from the upper crown to provide laterally spaced pin bores 22 aligned along a pin bore axis 24 that extends generally transverse to the central axis 14. By way of example and without limitation, the pin bosses 20 are joined to laterally spaced skirt portions 26 via strut portions 28, thereby forming a so called “monobloc” piston wherein the skirt portions 26 are formed as one piece of material with the pin bosses 20. The skirt portions 26 are diametrically spaced from one another across the pin bore axis 24 and have convex outer surfaces 30 contoured for cooperation with the cylinder bore to maintain the piston 10 in a desired orientation as it reciprocates through the cylinder bore. During reciprocation, a hydrodynamic oil film is developed and maintained between the outer surfaces 30 of the skirt portions 26 and the wall of the cylinder bore to minimize dynamic friction therebetween. To facilitate maintaining the desired hydrodynamic oil film thickness and distribution of oil across the outer surfaces 30 of the skirt portions 26, through slots, referred to hereafter as openings 32 unless otherwise stated, are formed in the skirt portions 26.

#The upper crown 16 of the piston 10 is represented here as having an upper surface 36 with a combustion bowl 38 recessed therein to provide a desired gas flow with the cylinder bore. An outer wall or ring belt 40 extends downwardly from the upper surface 36, with at least one annular ring groove 42 being formed in the ring belt 40 for floating receipt of a piston ring 44. The piston ring 44, when properly functioning in its free floating state, facilitates guiding the piston 10 during reciprocation within the cylinder bore, while also sealing combustion gases and inhibiting the passage of oil upwardly thereby from below the piston body 12.

#The lower crown 18 is represented here as being formed separately from the upper crown 16, such as in a forging process, and then joined thereto, wherein the upper and lower crowns 16, 18 can be joined together by a weld joint 46, for example.