Machining process for trapezoid rings with small axial dimensions, used in pistons of internal combustion engines

Abstract

A method for producing a piston for internal combustion engines, where the piston includes a circumferential trapezoid annular groove for receiving trapezoid rings with small axial dimensions the groove having a groove base with adjoining surfaces and groove flanks. The groove base with adjoining surfaces is created in a first method step by machining using a cutting steel tool and the groove flanks are created in a further method step. Also disclosed are a piston produced according to the method and a cutting steel tool.

Claims

1. A method for producing a piston for internal combustion engines comprising: machining in a first step a trapezoidal circumferential annular ring groove in a piston blank operable to receive trapezoidal-shaped rings, the first machining step further comprising: plunge cutting a groove base with a tool steel, the groove base having ends defining a height h4 greater than zero (0) millimeters and less than one (1) millimeter (mm); plunge cutting two flanks in the piston blank with the tool steel, each flank connected to a respective one of the base ends and extending radially and horizontally outward from a piston stroke axis, the two flanks oriented parallel to one another; plunge cutting two groove flanks in the piston blank with the tool steel, each groove flank connected to a respective one of the flanks and extending radially and angularly outward from the piston stroke axis; and machining in a second step the trapezoidal ring groove in the piston blank, the second machining step comprising finish machining the two groove flanks.

2. The method of claim 1 wherein the second machining step comprises finish machining of only the two groove flanks without further machining of the two flanks or the groove base.

3. A method for producing a piston for internal combustion engines comprising: machining in a first step a trapezoidal circumferential annular ring groove in a piston blank operable to receive trapezoidal-shaped rings, the first machining step further comprising: plunge cutting a groove base having ends defining a height h4 greater than zero (0) millimeters and less than one (1) millimeter (mm); plunge cutting a radius R2 of 0.2 millimeters (mm) at each groove base end; plunge cutting two flanks in the piston blank, each flank connected to a respective one of the base ends and extending radially and horizontally outward from a piston stroke axis, the two flanks oriented parallel to one another; plunge cutting two groove flanks at an angle alpha () of 15 degrees and 12 minutes relative to one another in the piston blank, each groove flank connected to a respective one of the flanks and extending radially and angularly outward from the piston stroke axis; and machining in a second step the trapezoidal ring groove in the piston blank, the second machining step comprising finish machining the two groove flanks.

Description

DETAILED DESCRIPTION OF THE DRAWING

(1) The present method is explained further by means of the figures described below.

(2) FIG. 1 shows a schematic illustration of a piston;

(3) FIG. 2 shows a detail of a ring zone having a trapezoid groove corresponding to a current state;

(4) FIG. 3 shows a schematic sectional view of a tool steel corresponding to a current state;

(5) FIG. 4 shows an enlarged schematic sectional view of the trapezoid groove of FIG. 1 after the first machining step according to the method;

(6) FIG. 5 shows a schematic sectional view of a tool steel for performing the machining process; and

(7) FIG. 6 shows a schematic sectional view of the trapezoid groove of FIG. 4 after the performance of the second machining step.

DETAILED DESCRIPTION

(8) FIGS. 2 and 3 show the current state and FIGS. 1, 4, 5 and 6 show the solution according to the present method.

(9) The same reference signs are used for the same elements in both illustrative embodiments.

(10) In the following description of FIGS. 1-6, terms such as top, bottom, left, right, front, rear etc. relate exclusively to the illustrative depiction and position of the device and of other elements chosen in the respective Figures. These terms are not to be taken as restrictive, that is to say, these terms can change owing to differences in position and/or mirror-symmetrical design or the like.

(11) FIG. 1 shows a schematic view of a piston 1 having a trapezoid, radially encircling annular groove 2, which has groove flanks 3, 4 and a groove base 5. Arranged adjacent to the groove base 5 are flanks 6, 7, which are oriented almost parallel to one another. Annular groove 2 is part of a ring zone 8, which has further annular grooves 9, 10 and 11 of different design.

(12) In FIG. 2, it can be seen that the minimum overall height h.sub.1 of annular groove 2 is 1.96 mm in this example. The ideal case shown there, that the trapezoid groove narrows further toward the inside, e.g. to an overall height h.sub.2 of 0.17 mm, cannot be achieved in practice since wear occurs with tool steels 12 having an overall height h.sub.3 less than or equal to 1 mm. This wear is caused by the complete trapezoid profile of the surfaces 13, 14 from the outside inward in the direction of the piston stroke axis (when FIG. 3 showing the tool steel 12 is viewed from left to right). This means that, with this design, the tool steel 12 shown there and the production method, it is not possible for trapezoid rings with a small height and annular grooves 2 which are of trapezoid design to be used with the desired small overall height. A radius R.sub.1 of 0.3 is provided for the transition from the groove base 5 to the flanks 6, 7, for example. The opening angle provided is 15 degrees and 12 minutes, for example.

(13) Referring to FIGS. 4 and 5, in contrast, a groove 2 is first of all plunge cut in advance according to the solution according to the present method (shown in FIG. 4). For this purpose, a special tool steel 15 (shown in FIG. 5) as regards its cross section is used. The cross section initially narrows from the outside inward with trapezoid surfaces 16, 17 and then ends in two parallel surfaces 18, 19. Using this shown cross section of the tool steel 15, the groove 2 is plunge cut in advance forming groove flanks 3,4, flanks 6,7 and groove base 5 as shown in FIG. 4, making it possible to achieve a groove base 5 with the overall height h.sub.4 of at least one millimeter or even smaller. A radius R.sub.2 of 0.2 millimeters is provided for the transition from the groove base 5 to the flanks 6, 7, for example. The opening angle provided is 15 degrees and 12 minutes, for example.

(14) In a second step, which is shown in FIG. 6, the groove flanks 3, 4 are finish-machined, and it is therefore no longer necessary to machine all the material out of the piston blank by means of a second tool steel (not shown) with a correspondingly shaped cross section; instead, only superficial machining of the groove flanks 3, 4 now takes place.