The invention relates to an upper part of a composite piston in accordance with the preamble of claim 1.
A composite piston consisting of an upper part and a lower part is known from the patent DE 36 33 134 C2, in which a highly wear-resistant layer is disposed between the surfaces of the upper part and the lower part that are in contact with one another, in order to reduce the friction wear of these surfaces. The layer is applied to one of the two contact surfaces according to the detonation spray method, in order to guarantee good adhesion of the layer to the contact surface. The layer can consist of a tungsten carbide/cobalt alloy, or of a copper/nickel/indium alloy. This brings with it the disadvantage that both the materials of which the layer can consist and the detonation spray method are very cost-intensive.
It is the task of the invention to avoid this disadvantage of the state of the art. This task is accomplished with the characteristics that stand in the characterizing part of the main claim, whereby it is a way that is simple to implement and therefore price-advantageous, for avoiding wear of the contact surfaces of the upper part and lower part of a composite piston, to provide the contact surface of the upper part with a groove-shaped profile.
Practical embodiments of the invention are the object of the dependent claims.
Some exemplary embodiments of the invention will be described below, using the drawings. These show:
The upper part 1 has a combustion bowl 5 formed into its piston crown 4. The region of the radial outside of the upper part 1, on the piston crown side, is configured as a top land 6 that is followed, in the direction facing away from the piston crown, by a ring belt 7 having three ring grooves 8, 9, and 10.
The underside of the upper part 1, facing away from the piston crown, has a threaded bolt 12, coaxial to the piston axis 11, by way of which the upper part 1 is screwed to the lower part of the piston. A radially inner, ring-shaped recesses 13 and a radially outer, ring-shaped recess 14 are disposed on the underside of the upper part 1, concentric to the piston axis 11 and concentric to one another, which form ring channels for passing through cooling oil, together with recesses in the lower part, on the piston crown side. The inner recess 13 is delimited, radially on the inside, by the threaded bolt 12, and radially on the outside by a ring rib 15 disposed between the recesses 13 and 14. The outer recess 14 is delimited, radially on the inside, by the ring rib 15, and radially on the outside by a ring wall 25 formed onto the piston crown 4, on the radial outside of which wall the top land 6 and the ring belt 7 are disposed.
The underside of the ring rib 15, facing away from the piston crown, carries the inner contact surface 2. Radially on the inside, a circumferential recess 16 is formed into the end region of the ring wall 25, facing away from the piston crown, which recess has the outer contact surface 3.
Because of the ignition pressures that have risen in newer engines, the composite pistons used in them, which consist of an upper part and a lower part, whereby the upper part is screwed to the lower part, the contact pressure and the relative movements between the surfaces of the upper part and the lower part that are in contact with one another, are also increasing. The results are increased friction wear (fretting) of the contact surfaces as the result of material welding (microwelding), with partial material dissolution that is attributable to it.
In experiments, it has been shown that this can be remedied by roughing up the contact surfaces 2 and 3 of the upper part 1 of the piston, whereby a groove-shaped profile has proven to be particularly effective in avoiding wear of the contact surfaces 2, 3, which has a roughness between Rz 10 and Rz 25, i.e. a profile structure in which the average deviation of the profile from an O axis, in the positive and the negative direction, amounts to 10 μm to 25 μm. In this connection, the profile of the contact surfaces 2 and 3 can have the shape of concentric grooves (see standard DIN EN ISO 1302, designated with the graphic symbol C), with a groove spacing of 300 to 1200 μm, as it is shown in
A profile having a groove shape that is likewise based on the standard DIN EN ISO 1302, and designated, in greater detail, with the graphic symbols X (crossed grooves) or the graphic symbol R (grooves in the form of radially disposed lamellae), is also possible.
To avoid wear of the contact surfaces of upper part and lower part of a composite piston, it is also possible to provide one or more radially oriented contact surfaces of the lower piston part, on the piston crown side, with the groove-shaped profiling, which has the aforementioned dimensions, i.e. roughness and groove spacing, and the DIN shapes indicated above.
1 upper part of a composite piston
2 inner contact surface
3 outer contact surface
4 piston crown
5 combustion bowl
6 top land
7 ring belt
8, 9, 10 ring groove
11 piston axis
12 threaded bolt
13 inner recess
14 outer recess
15 ring rib
16 recess
17 upper part of a composite piston
18 dead-end bore
19 inside thread
20 inner contact surface
21 ring rib
22 outer recess
23 inner recess
24 piston axis
25 ring wall
Number | Date | Country | Kind |
---|---|---|---|
10 2006 015 587.4 | Apr 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE2007/000536 | 3/23/2007 | WO | 00 | 10/21/2008 |