Complex-shaped forged piston oil galleries

Abstract

A steel piston with an oil gallery, and process for forming a steel piston oil gallery channel, which corresponds to the complex shape of the combustion bowl in the piston crown. The oil gallery channel is first forged to the basic shape that corresponds to the shape of the walls of the combustion bowl. Machine-turning surfaces in the oil gallery channel can be machine-finished as desired. Surfaces in the oil gallery which cannot be machined with conventional turning operations, such as recesses and protrusions into the channel, are left in the original forged condition.

Claims

1. A piston for an internal combustion engine comprising a piston body that is at least partially fabricated of forged steel including at least one pin boss, at least one piston skirt portion; a combustion bowl recessed in an upper surface of said piston body, and an oil gallery below said combustion bowl, and wherein said oil gallery has a radially inner wall surface with machined portions thereof that have a machine-turned finish and recessed unmachined portions that do not have a machine-turned finish.

2. The piston of claim 1 wherein the machined portions are adjacent to the unmachined portions.

3. The piston of claim 1 wherein the oil gallery includes a bottom wall.

4. The piston of claim 1 wherein the piston is made of two pieces joined together.

5. The piston of claim 1 wherein the combustion bowl has a complex shape and the inner wall surface of the oil gallery at least in part corresponds in shape to that of the combustion bowl.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appending drawings, wherein:

(2) FIG. 1 illustrates a piston with a closed oil gallery.

(3) FIGS. 2A, 2B and 2C schematically illustrate three general types of complex combustion bowls.

(4) FIG. 3 is a schematic plan view of a piston crown depicting a representative complex shape of a combustion bowl.

(5) FIG. 4 is a cross-section of the piston crown as shown in FIG. 1 taken along line 4-4 and in direction of the arrows.

(6) FIG. 5 is another cross-section of the piston crown similar to FIG. 4, following machining-turning of at least one surface of the oil gallery.

(7) FIG. 6 is a flow chart of an embodiment of a system and method in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) A representative piston 100 in which the present invention can be utilized if the combustion bowl has a complex shape is shown in FIG. 1. The piston 100 includes a piston crown member 10 and a lower member 102 which includes sidewalls 104 and pin bosses 106. The piston crown 10 and lower member 102 are fixedly secured together, preferably by friction welding, to form the complete piston 100.

(9) The piston 100 has an oil gallery in which oil is circulated in order to maintain the temperature of the piston, particularly the upper surface, combustion bowl and outer rim within acceptable temperature limits. The oil gallery includes an oil gallery channel 105 positioned in the crown member 10. The oil gallery can be either opened or closed as well known in the art. If closed, the bottom wall of the oil gallery is typically included as part of the lower member 102.

(10) A piston crown member 10 with a representative complex combustion bowl 12 is depicted in FIG. 3. The shape of the bowl 12 is essentially a square shape with four sides 15, 16, 17 and 18. In the shape depicted, the sides are straight with rounded corners 21, 22, 23 and 24.

(11) It is to be understood that the shape of the combustion bowl and the linearity of the sides 15-18 is merely one example of a complex combustion bowl. In accordance with the invention, the combustion bowl can have any perimeter or internal shape, with any number of sides or side portions. The sides and internal surfaces can also have any shape, such as being straight as shown or curved or arced, and can have sections or portions which are straight, curved or arced, or have bumps, protrusions, recesses, ribs and the like. In addition, the corners 21-24, or the intersections or joints between the side portions, can have any shape, and can protrude into the bowl or be recessed from it.

(12) The shape of the piston bowl can be complex either in its outer periphery, as shown in FIG. 2A, be complex in the radially inner areas of the bowl, as shown in FIG. 2B, or be complex with respect to both the outer periphery and the inner areas as shown in FIG. 2C. FIGS. 2A, 2B and 2C are representative of these three general types of complex shaped combustion bowls. The present invention provides an oil gallery and oil gallery channel that can accommodate combustion bowls with such complex shapes.

(13) The piston crown and the entire piston are made of a steel material. The shape of the piston crown 10 is formed by a forging process.

(14) In accordance with a preferred embodiment of the invention, the oil gallery channel in the piston crown is made by the same process as the combustion bowl, or portions thereof. In the embodiment shown, the oil gallery channel is made by a forging process, followed by a machining process.

(15) In accordance with a preferred embodiment, the forging die for forming the combustion bowl and the forging die for forming the oil gallery channel have corresponding shapes. The two dies have similar straight sections and similar curved sections that correspond to one another.

(16) A cross-section of the piston crown 10 after the forging process is shown in FIG. 4. The forging process forms an annular groove 30 that does not necessarily have a circumferential uniform width W or a uniform depth D. The width of the groove 30 is greater in the portions where the sides of the combustion bowl are furthest from the outside surface of the piston crown. These areas are designated by the numeral 40 in FIG. 3. Similarly, the areas where the groove 30 is the narrowest is at the corners or intersections between the side portions.

(17) The depth D of the groove 30 made by the forging is dependent on the dies used in the forging process. There is a practical limit to the depth that forging dies can penetrate in a steel crown member and still be used repeatedly before they need replacing or refurbishing.

(18) As a subsequent step in forming the oil galleries in accordance with a preferred embodiment of the invention, the shape of the oil gallery is machined to the shape shown in FIG. 5. In one step in the machine processing, a machining tool represented by the member 50 is inserted into the oil gallery 30 formed by the forging process (in the direction of arrow 52) and used to finish the outer surface of the oil gallery channel and to form an annular groove 60, entirely around the bowl. This machine-turning extends the oil gallery channel into the upper reaches of the piston crown (near the top ring groove and adjacent the top face or rim 80 of the piston). The groove 60, which is fully machined, extends above the initial channel 30 made in the forging process.

(19) Machine-turning or simply turning is a machining process in which a cutting tool, typically a non-rotary tool bit, moves linearly while the workpiece rotates, such as on a lathe. Maching turning can refer to such a cutting or finishing operation on either the internal surfaces or the external surfaces of a workpiece. In machining some of the surfaces of an oil gallery channel thereon, the machine-turning finishes or forms internal surfaces.

(20) The machine-turning processing can also be used to machine and finish some of the inner surfaces of the oil gallery channel 30, such as surface 31. Due to the complex shape in the oil gallery in order to follow the complex shape of the combustion bowl, a plurality of bumps or recesses can be formed on the inside gallery surface by the forging die in the forging process. Due to the turning procedure used in the machining process, the recesses (or pocket portions) and areas between bumps are left unfinished (i.e. not machined) in this step. Inner gallery channel surfaces 32 and 33 in FIG. 5 are not finished and remain in their original condition after forging.

(21) In FIG. 3, the outer circumference of the finished annular groove 60 is indicated by hidden line 60. In addition, an inner finished surface of the complex shaped oil gallery (such as surface 31) is indicated by the hidden line 31. The areas (e.g. recesses) left unfinished are indicated by the reference numeral 32 in FIG. 3 and numerals 32 and 33 in FIG. 5. An oil gallery channel having the shape 30 shown in FIG. 4 can be formed by a forging die.

(22) In a typical forging operation, the oil gallery channel in the lower surface of the piston crown member 10 will be formed at the same time that another forging die is forming the complex shaped combustion bowl on the upper surface or upper side of the piston crown member.

(23) The inventive process provides an annular oil gallery for a piston which has a similar or substantially the same perimeter inner shape as the outer perimeter shape of a complex-shaped combustion bowl. This minimizes the thicknesses of the wall areas 70 between the oil gallery and combustion bowl 12 and makes the wall thicknesses around the outside of the combustion bowl uniform. Due to practical limits of the forging and machining processes, the thicknesses of all of the walls will not be exactly the same around the circumference of the combustion bowl. The present invention, however, makes the wall thickness 70 as thin and uniform as practical around the entire oil gallery. This allows oil introduced in the oil gallery when the piston is finished to maintain the temperature of the bowl wall surfaces and rim 80 within appropriate limits and avoids harmful hot spots.

(24) With the present invention, thick wall sections which can create hot spots are minimized or eliminated. Areas of a piston which overheat (also called hot spots) can create weak spots that could crack or fail. Failure of pistons in this manner could lead to expensive repairs, and possibly to the replacement of the engine.

(25) Preferred cooling for a piston can be provided when the walls have a uniform thickness and are relatively thin. Pistons with thinner walls also have less weight which provides less strain on the engine. This results in better gas mileage and less harmful emissions.

(26) FIG. 6 presents a flow chart 108 of the preferred method of forming an oil gallery channel in a piston crown that corresponds in shape to the shape of a complex combustion bowl in the piston crown. First, a piston crown member is made of a steel material 110. This can be done by any conventional manufacturing procedure.

(27) Then, a complex shaped combustion bowl is formed in the top or upper surface of the piston crown member 112. This step is formed by a steel forging process.

(28) At the same time or thereafter, an oil gallery channel 30 is formed in the lower surface or lower side of the piston crown member with a shape that is similar to, or corresponds to, the shape of the combustion bowl. This is shown in box 114. This step is also performed by a forging process, and preferably simultaneously with forging the bowl.

(29) Finally, the oil gallery channel in the piston crown member is machine finished 116 to enlarge its size and bring it closer to the upper rim of the piston crown member and the combustion bowl. In this step, an annular groove 60 is formed by a cutting tool, and the other surfaces of the gallery channel which can be finished by a machine-turning operation (i.e. other than recesses and areas between bumps) can be finished as desired.

(30) Although the invention has been described with respect to preferred embodiments, it is to be also understood that it is not to be so limited since changes and modifications can be made therein which are within the full scope of this invention as detailed by the following claims.