PISTON CROWN HAVING CONICAL VALVE SEAT AND METHOD FOR MANUFACTURING A PISTON CROWN HAVING A CONICALLY SHAPED VALVE SEAT

Abstract

A piston has a piston crown and a top land extending circumferentially around the piston crown, as well as a combustion bowl and at least one valve pocket machined therein. The valve pocket has a side wall and a bottom, and wherein the side wall extends at an angle of between 110 and 120 from the bottom. A method for forming such valve pockets in the piston crown includes machining the valve pockets with a rotating cutter having an inverted frustoconical shape such that an angle between a bottom of the cutter and a side wall of the cutter amounts to between 110 and 120.

Claims

1. A piston comprising: a piston crown and a top land extending circumferentially around the piston crown, the piston crown having a combustion bowl and at least one valve pocket machined therein, wherein the at least one valve pocket has a side wall and a bottom wall, and wherein the side wall extends at an angle of between 110 and 120 from the bottom wall.

2. The piston according to claim 1, wherein there are four valve pockets, each pocket being the same size and having the same side wall angle.

3. The piston according to claim 1, wherein the bottom wall is disposed at an angle of between 70-80 from a piston center axis.

4. The piston according to claim 3, wherein the bottom wall is disposed at an angle of between 73-77 from a piston center axis.

5. The piston according to claim 1, wherein the side wall extends at an angle of between 111 and 118 from the bottom wall.

6. The piston according to claim 1, wherein the at least one valve pocket extends into the top land.

7. The piston according to claim 1, wherein a ratio of a height of the top land to a diameter of the piston amounts to between 0.05:1 to 0.07:1.

8. The piston according to claim 1, wherein a ratio of a depth of the at least one valve pocket to a diameter of the piston amounts to between 0.03:1 to 0.05:1.

9. The piston according to claim 1, wherein a ratio of a depth of the at least one valve pocket to a height of the top land amounts to approximately 1:1.5.

10. A method for forming valve pockets in a piston crown, comprising machining said valve pockets with a rotating cutter, the cutter having an inverted frustoconical shape such that an angle between a bottom of the cutter and a side wall of the cutter amounts to between 110 and 120.

11. The method according to claim 10, wherein the cutter is applied to the piston crown at an angle such that the bottom of the cutter is disposed tilted relative to a top surface of the piston crown.

12. The method according to claim 10, wherein the valve pockets are machined such that each valve pocket extends through a top land of the piston.

13. The method according to claim 10, wherein four valve pockets are machined into the piston crown.

14. The method according to claim 10, wherein the angle between the bottom of the cutter and the side wall of the cutter amounts to between 111 and 118.

15. The method according to claim 10, wherein a ratio of a radius of the cutter to a diameter of the piston amounts to between 0.18:1 to 0.24:1.

16. The method according to claim 10, wherein the pocket is cut to a depth such that a ratio of the depth of the pocket to a diameter of the piston amounts to between 0.03:1 to 0.05:1.

17. The method according to claim 11, wherein the bottom of the cutter during cutting is disposed at an angle of between 73-77 to a piston center axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

[0013] In the drawings, wherein similar reference characters denote similar elements throughout the several views:

[0014] FIG. 1 shows a view of a piston having a valve pocket cut with a cutting method according to the prior art;

[0015] FIG. 2 shows a piston having a valve pocket cut with a cutting method according to the invention;

[0016] FIG. 3 shows an enlarged view of a valve pocket in the piston according to the invention, with the prior art valve pocket being drawn in broken lines for comparison;

[0017] FIG. 4 shows several different cutting tools cutting into a piston to form the valve pocket according to the invention, in comparison with a cutter according to the prior art;

[0018] FIG. 5 shows another view of the valve pocket of the invention in comparison with a prior valve pocket;

[0019] FIG. 6 shows a complete piston and cutter according to the invention in a cutting process;

[0020] FIG. 7 shows a top view of the piston according to FIG. 6, with four valve pockets cut therein; and

[0021] FIG. 8 shows a front view of the piston according to FIG. 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] FIG. 1 shows a prior art piston 1 and method for cutting valve pockets into the piston. In the method, a cutting tool 2 having a cylindrical shape, i.e., with an angle of about 90 between the bottom and side wall, is used to cut the individual valve pockets 3, which each have a bottom 4 and side wall 5. As will be discussed below, the pockets created with such a cutter are unnecessarily deep and remove more piston material than necessary to accommodate the valve.

[0023] FIG. 2 shows a similar view of a piston 10 in which valve pockets are cut using the method according to the invention. Here, a cutter 20 having a bottom 21 and a side wall 22 is placed on the crown 9 of piston 10, and a pocket 15 is cut into the crown 9 of piston 10. Pocket 15 has a side wall 17 and a bottom surface 16. Because of the inverted frustoconical shape of cutter 20, both the cutter 20 and the pocket 15 form an angle of between 110 and 120 between the side wall 17, 22 and the bottom surface 16, 21, and preferably an angle of between 111 and 118.

[0024] The difference in shape between the pocket 15 of the invention and a pocket 3 according to the prior art are shown in FIG. 3. As can be seen there, pocket 15 has a much wider clearance than pocket 3, due to the angled sidewall 17.

[0025] The valve pocket 15 is formed by disposing the cutter at an angle, so that the angle between the bottom 16 of pocket 15 and a piston center axis M is between 70 and 80, and preferably between 73 and 77. Other angles could also be used.

[0026] FIG. 4 shows the practical advantages of the pocket 15 and cutter 20 of the invention over the prior art. Using a traditional cutter 3, a person would have to cut farther into the piston 10 by a distance w in order to achieve the clearance in the piston crown that is achieved by a cutter 20 having an angle a between the side wall and bottom of 111 . If an angle of 118 is used instead as indicated by cutter 20 in FIG. 4, then the difference between the cuts required by the prior art cutter 5 and the cutter 20 according to the invention are even greater.

[0027] The specific angles of the cutter 20, 20 allow the piston 10 to achieve specific ratios that are not possible using the prior art cylindrical cutter 5. For example, as shown in FIG. 2, in the piston according to the invention, the ratio between the height h of the top land 11 and the piston diameter d.sub.1 can be optimized between 0.05:1 to 0.07:1. With the prior art, much larger ratios are required in order to avoid compromising the integrity of the piston by reducing the distance between the valve pocket and the first ring groove. In addition, the ratio of the depth of the piston pocket h.sub.2 to the piston diameter can be in the range of 0.03:1 to 0.05:1. Valve pockets according to the prior art require much larger ratios in order to achieve the necessary valve clearance. Finally, the ratio between the radius of the cutter and the piston diameter can be between 0.18:1 to 0.24:1.

[0028] FIG. 5 shows another view of the valve pocket 15 according to the invention in comparison with a prior art valve pocket 3, which share the same tilt angle and boundary p at the top of the piston. As can be seen by the comparison between distance j and k, the prior art valve pocket formed from a cylindrical cutter extends much farther into the piston and thus much closer to the first ring groove 19, thus weakening the piston. Distance j is approximately 1.5 times greater than distance k, leading to a much stronger and more durable piston. In addition, the height h of the top land 11 can be made smaller if needed using the valve pocket according to the invention. The depth of the valve pocket to the height of the top land of the piston is generally in a ratio of about 1:1.5. The difference between the depth m of the valve pocket 15 of the invention and the depth n of the prior art pocket having the same boundary p and tilt angle is significant, as the depth m can be smaller by at least 8%. Thus, by using a conical cutter to form the valve pocket where the angle between the side wall and bottom is over 110, significant advantages in piston strength and performance can be achieved. In addition, the depth of the valve pocket m using the invention allows for a higher ratio of the minimal distance j, between the bottom surface of the valve pocket to the first ring groove 19. In one form this ratio of distances m:j is approximately within a range of 0.3 to 1.0, which is significant especially in pistons that have a shorter top land height h, and in another form the m:j ratio is targeted to be about 0.7.

[0029] FIGS. 6-8 show the entire piston 10 according to the invention both during the cutting process (FIG. 6) and after completion (FIGS. 7-8). Cutter 20 can be used to cut all four valve pockets 15 shown in FIG. 7, rather than having to change out the cutter between intake and exhaust pockets. As shown in FIG. 7, the pockets 15 are hemispherical in shape and can extend through the top land 11 of the piston in certain areas.

[0030] Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.