The present invention relates to piston mold assemblies for molding pistons with weight reduction pockets above pin holes formed in the pistons. More specifically, the present invention relates to a piston mold assembly that includes a cam assembly which operates to open and close the piston mold assembly.
The demand for reduction of fuel consumption in internal combustion engines has resulted in the development of lightweight, high performance pistons. Such pistons have to withstand high loads, pressures and temperatures and be structurally and mechanical stable while at the same time, provide desired weight reduction.
In the past, piston weight reduction was achieved by providing a cavity in the area beneath the piston crown, i.e. on the side of the piston crown remote from the combustion chamber. In particular it is known to provide weight reduction cavities above the pin holes in the sides of the piston heads. However, these areas are not readily accessible, so that it becomes a challenge to form such weight reduction cavities during the fabrication of pistons.
The present invention provides a modified single cavity mold assembly having a unique cam system that can be used to form weight reduction cavities above the pin holes of a piston during a molding process.
According to various features, characteristics and embodiments of the present invention which will become apparent as the description thereof proceeds, the present invention provides a piston mold assembly that includes:
a base;
a core extending upward from the base for shaping an interior of a piston;
a set of mold segments that are horizontally movable with respect to the core so as to converge upon the core to define a mold cavity that forms sides of a piston;
a set of pin members that are horizontally movable with respect to the core so as to converge upon the core to form pin holes of a piston;
a set of windows which are movable upward and downward at inclined angles with respect to the core so as to form weight reduction pockets in opposite outer sides of a piston above pin hole formed in the piston; and
a cam assembly that coordinates the movement of the pin members and the windows so that after a piston is molded, downward movement of the windows is delayed until horizontal movement of the pin members has occurred.
The set of pin members are configured to move horizontally through the windows. The cam assembly includes elongate cam elements that are movable horizontally together with the pin members. This simultaneous movement can be achieved by a pair of horizontally movable holders to which the pin members and elongate cam elements are coupled for horizontal movement therewith.
Lower portions of the windows are provided with cam followers. The elongate cam elements have curved portions which are configured to push against the cam followers and thereby move the windows downward as the elongate cam elements move horizontally outward with respect to the windows.
The lower portions of the windows further include horizontal surfaces above the cam followers. The curved portions of the elongate cam elements are configured to push against the horizontal surfaces of the windows and thereby move the windows upward as the elongate cam elements move horizontally inward with respect to the windows.
A set of cam plates are held in a fixed position with respect to base. The cam plates are configured so that inward portions of the elongate cam elements brace the windows upward against surfaces of the cam plates.
The windows can include guide structures on opposite sides that guide the upward and downward movement of the windows. The upper portions of the windows are configured to define the shape of the weight reduction pockets and to define the shape of a lower lip formed on a piston head of a piston formed in the mold assembly.
The present invention further provides a method of molding a piston which comprises the steps of:
a) providing a piston mold assembly that involves:
b) positioning the mold segments, pin members and windows into position in the mold assembly to produce a mold cavity;
c) delivering molten metal into the mold cavity to mold a piston therein and thereafter;
d) moving the pin members outward from the mold;
e) moving the windows downward;
f) moving the mold segments outward; and
g) removing the cast piston from the mold assembly.
When a piston is removed during this method, step d) is performed before step e). Moreover, the pin members continue to move outward as the windows move downward. When the mold assembly elements are moved into a closed position to form a mold cavity, steps d) and e) are reversed.
The present invention further provides an improvement for a piston mold assemblies configured to mold a pistons therein that have a set of retractable pin members for forming pin holes in the cast piston and a set of windows for forming weight reduction pockets over the pin holes, the improvement involving the inclusion of a cam assembly that coordinates horizontal movement of the pin members and upward and downward movement of the windows at inclined angles so as to form weight reduction pockets in opposite sides of the cast piston above pin holes formed in the piston.
The improvement further includes providing a cam assembly that coordinates the movement of the pin members and the windows so that after the piston is molded downward movement of the windows is delayed until horizontal movement of the pin members has occurred.
The present invention will be described with reference to the attached drawings which are given as non-limiting examples only, in which:
The present invention is directed to mold assemblies that are used for molding pistons with weight reduction pockets and pistons produced from such mold assemblies. The piston mold assemblies of the present invention are single cavity molds that are designed and configured to produce lightweight pistons that require minimum post-molding processing. The mold assemblies can be based on conventional mold machines which would require according to the present invention, minimum modification to produce the lightweight pistons. No retro kit is needed to modify an existing or conventional mold machine for use according to the present invention. Any necessary modification is accomplished by simple mold tooling and saddle modifications. The piston mold assemblies of the present invention include cam systems that are designed to produce sufficient force to remove inclined windows from a cast piston and require only minimal force in the horizontal direction so that springs can be used to hold mold blocks in a closed position until the inclined windows clear the cast piston.
The lightweight pistons of the present invention are configured to include weight reduction pockets above the pin holes on opposite outer sides of the pistons. According to the present invention, these weight reduction pockets are formed by the use of movable mold pieces (referred herein to as “windows”). Since the direction of travel for conventional mold designs is horizontal in the area where the weight reduction pockets of the present invention are provided, such weight reduction pockets cannot be produced using conventional mold assembly designs.
The mold assembly of the present invention was designed by first determining, from the geometry of a piston structure having desired weight reduction pockets, how to configure and manipulate the various structural elements of the mold assembly to enable removal of the cast lightweight piston.
It was ultimately determined that the windows used to mold the weight reduction pockets had to be moved downward to clear the weight reduction pockets using horizontal force applied to pins used to form pin holes in the cast piston. Moreover, depending on the configuration of the weight reduction pockets, the windows had to be moved downward at an angle. Once the windows were moved downward to provide sufficient clearance, the cast lightweight pistons are removed from the mold assembly by removing the side blocks of the mold assembly a conventional manner.
According to the present invention, the movement of the windows used to form the weight reduction pockets is coordinated with the movement of the pins that are used to form the pin holes in the pistons. In this regard, it was determined during the course of the present invention that since the pins used to form the pin holes have to travel horizontally though the windows, the pins had to be withdrawn from the windows before the windows could move downward to clear the weight reduction pockets that are formed in the cast piston.
The movement of the pins and the windows is coordinated by means of a cam assembly. The cam assembly includes an elongate cam element that moves horizontally and is configured to cooperate with cam surfaces provided on the windows to cause the windows to move upward when the elongate cam element is moved inward and to move downward when the elongate cam element is moved outward. In addition the cam assembly includes a cam plate near the base of the mold assembly which cooperates with the elongate cam element to brace the windows in their upper or closed positions.
The elongate cam element can be coupled to the pin members to move horizontally therewith. In one embodiment a pin and cam holder is provided which couples the elongate cam elements to the pin members.
In the following description which is made with reference to the attached non-limiting drawings, the same reference numerals have been used to identify similar elements when possible to simplify the description.
The lower portion of window 13 includes a cam follower 23 that is positioned beneath the pin 14 and cooperates with a movable elongate cam element 25 (See
The window 13 depicted in
Once the pin 14 has been pulled out of the window 13 and the window 13 has moved downward so as to be release from a cast piston 1, further horizontal outward movement of the pin and cam holder assembly 33 can engage a suitable pull back plate (See
The process sequence depicted in
Further inward movement of the pin and cam holder assembly 33 causes the pin 14 to pass through the window 13 so that the inner end of the pin 14 engages or seats against a receiving surface provided on the core 11 as shown in
The forward movement of the pin and cam holder assembly can also be used to push the mold blocks of the mold assembly together either by direct contact or any suitable pushing block arrangement. (See
The horizontal guide bar 43 is fixed relative to the side block 12. Push back plate 42 is movable alone horizontal guide bar 43 and is prevented from passing off the outer end 45 of horizontal guide bar 43 by any suitable abutment means such as nut 46 which can be used to adjust the force applied by spring 44.
In operation, when the pin and cam holder assembly 33 is moved inward toward the center of the mold assembly, the push back plate 42 which is coupled to the pin and cam holder assembly 33 moves inward and pushes against spring 44. The force applied to spring 44 pushes side blocks 12 toward their closed position. When the pin and cam holder assembly 33, is moved to its innermost position, the resulting increased force of the spring 44 is sufficient to hold the side blocks 12 in their closed position for casting a piston.
As the pin and cam holder assembly 33 is moved outward the force of spring 44 is reduced as the push back plate 42 moves outward. Eventually as the pin and cam holder assembly 33 is moved outward, the push back plate 42 which is coupled thereto contacts and pushes against nut 46 which applies the outward force to the horizontal guide bar 43 and causes the side blocks 12 to be pulled outward.
Form the above description it can be understood how the method and means of forming weight reduction pockets above the pin holes in the outer sides of a piston can be accomplished by making rather simple machine modifications to a single cavity mold assembly.
Structural elements of the piston mold assembly can be made from conventional materials that are heat resistant. Although the above description focuses on the elements that are used to coordinate the movement of the windows and pin members, it is to be understood that when other, more conventional elements of the piston mold assembly such as the core and dome are used, these elements can be manipulated in conventional ways by conventional means that are understood to those skilled in the art.
Although the present invention has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention and various changes and modifications can be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as described above and set forth in the attached claims.