Patent Application
20090260593
The invention relates to a two-part piston for an internal combustion engine, in accordance with the preambles of the main claim and of secondary claims 5, 8, and 9.
A two-part piston for an internal combustion engine, which consists of an upper part and a lower part, is known from the patent application having the file number 10 2005 021 427.4. The upper part forms the piston crown and has a cylindrical pin having an outside thread, which pin lies coaxial to the piston axis, on the underside facing away from the piston crown. The lower part has an upper, thin-walled, and elastically resilient crown part, at the central region of which a sleeve pointing in the direction of the piston crown is formed on, having walls that are so thin that this sleeve has the function of an expansion sleeve. An opening that lies coaxial to the piston axis is formed into this expansion sleeve, into which opening the pin is introduced, so that the upper part can be connected with the lower part by means of a nut screwed onto the pin, whereby the elastic resilience of the upper crown part and the expandability of the expansion sleeve puts the screw connection under bias, and thereby imparts great reliability to the latter.
It is disadvantageous that the production of the upper crown part of the lower part, with the expansion sleeve formed on, is very complicated. In this connection, time-consuming machining of the central region of the upper crown part and, in particular, of the expansion sleeve, is required, independent of whether the lower part is cast or forged, whereby attention must be paid to the adherence of close tolerances, so that the central region of the upper crown part and the expansion sleeve adhere to the desired elasticity properties.
Proceeding from this, the invention is based on the task of making the production of a two-part piston whose upper part and lower part are connected with one another by way of an expansion sleeve, simpler and less expensive.
This task is accomplished with the characteristics that stand in the characterizing part of the main claim and the secondary claims. Practical embodiments of the invention are the object of the dependent claims. In this connection, the advantage is obtained that a separate expansion sleeve can be produced in simpler and more cost-advantageous manner than a central region of the upper crown part re-functioned to become an expansion sleeve, and that the material used for this purpose can be of higher quality than the material of which the upper crown part of the lower part consists.
Some exemplary embodiments of the invention will be described below, using the drawing. This shows:
Two pin bosses 9, 9′ each having a pin bore 10, 10′ are disposed on the underside of the lower part 3, facing away from the piston crown 4. The pin bosses 9, 9′ are connected with one another by way of skirt element 13.
The upper part 2 and the lower part 3 of the piston 1 are connected with one another by way of an inner contact surface 14 and by way of an outer contact surface 15 disposed concentric to the former. The upper part 2 and the lower part 3 each have a dead-end hole 16 and 17, which lie opposite one another when the upper and lower parts 2, 3 are positioned appropriately. A fixation pin 11 introduced into the two dead-end holes 16, 17 ensures that the upper part 2 and the lower part 3 always assume the same rotational position relative to one another.
An outer cooling channel 22 disposed in the edge region of the piston 1, on the piston crown side is formed by the upper part 2 and the lower part 3 of the piston 1, the radially outer limit of which channel is formed by the ring wall 6, the radially inner limit of which channel is formed partly by a lower part foot 18 disposed on the upper side of the lower part 3 and partly by the piston crown 4, and the axially lower limit of which is formed by the lower part 3 of the piston 1. Cooling oil is introduced into the cooling channel 22 by way of at least one oil feed channel 52 (
The piston 1 has another, ring-shaped, inner cooling channel 24 disposed coaxial to the piston axis 12, which channel has a lesser radial diameter than the outer cooling channel 22, and which is disposed within the outer cooling channel 22, seen in the radial direction. Axially on the top, the inner cooling channel 24 is delimited by the piston crown 4, radially on the outside it is delimited by the lower part foot 18, axially on the bottom it is delimited by an upper crown part 25 of the lower part 3, and radially on the inside it is delimited by a pin 31, whereby the crown part 25 of the lower part 3 has an opening 27 radially on the inside.
The pin 31 is configured in cylindrical shape and formed onto the underside of the piston crown 4, coaxial to the piston axis 12, whereby the mantle surface of the pin 31 has an end region facing away from the piston crown, having an outside thread 32 (
The upper part 2 is screwed to the lower part 3 by means of the hexagonal nut 29, by way of an expansion sleeve 26 disposed between the upper face surface 23 of the hexagonal nut 29 and the upper crown part 25 of the lower part 3. For this purpose, the expansion sleeve 26 has a collar 28 directed inward on its end facing the piston crown, and a contact surface 19 that widens conically, radially toward the outside, in the direction facing away from the piston crown, at its end facing away from the piston crown.
When the upper part 2 and the lower part 3 are screwed together, the fixation pin 11 is first introduced into the dead-end hole 17 disposed in the upper crown part 25 of the lower part 3.
Subsequently, the upper part 2 and the lower part 3 are oriented coaxial to one another. For this purpose, the edge of the lower part 3, on the piston crown side, has a support crosspiece 46 that has the shape, in section, of a step directed radially inward and axially in the direction of the piston crown 4. Furthermore, a cylindrical recess 47 is formed into the inside of the lower face side of the ring wall 6, the inside shape of which recess is configured to be complementary to the outside shape of the support crosspiece 46. A coaxial orientation of upper part 2 and lower part 3 can thereby be achieved, in that the support crosspiece 46 is first introduced, at least partway, into the recess 47. In this connection, however, it is necessary to rotate the upper part 2 about the piston axis 12 until the dead-end hole 16 comes to lie above the fixation pin, after which the support crosspiece 46 can be introduced into the recess 47 in its entirety, and furthermore, the fixation pin 11 can be introduced into the dead-end hole 16.
Subsequently, the expansion sleeve 26 is pushed through the opening 27, and the hexagonal nut 29 is screwed onto the outside thread 32 of the pin 31. In this connection, the hexagonal nut 29 comes to rest against an inside surface 20 of the collar 28, facing away from the piston crown, by way of its upper face surface 23, and the contact surface 19 of the expansion sleeve 26 comes to rest against a surface 21 disposed on the radial inside of the opening 27, which surface opens conically downward. In this connection, the conicity of the surface 21 is at least approximately equal to the conicity of the contact surface 19. Then the hexagonal nut 29 is screwed tight with such a torque that because of the pressure of the hexagonal nut 29 onto the inside surface 20 of the collar 28 and because of the tensile stress exerted on the expansion sleeve 26 as a result, the expansion sleeve 26 undergoes an expansion that exerts a permanent bias on the screw connection, thereby imparting great reliability to this screw connection. Furthermore, the pin 31 undergoes expansion, in this connection, and the radially inner part of the piston crown 4 undergoes deformation in the manner of a disk spring, in the direction of the pin bosses 9, 9′. Furthermore, the expansion sleeve 26 is made from a high-quality steel material, thereby contributing to the reliability of the screw connection between upper part 2 and lower part 3 of the piston 1.
In this connection, the contact surface 19 on the side of the expansion sleeve 26 that faces away from the piston crown can also be configured to be spherical or ball-shaped, in an embodiment not shown in the figures, whereby the contact surface 21 of the upper crown part 25 of the lower piston part 3 that stands in contact with it can have a shape complementary to it.
As can be clearly seen in
As indicated by the line 38, this results in a continuous oil channel, whereby first of all, cooling oil is introduced into the outer cooling channel 22 by way of the oil feed channel 52, which oil flows into the inner cooling channel 24 by way of the overflow channels 37, 37′, and flows back into the piston interior 36 by way of the gap 33, by way of the grooves 34, 34′, and by way of the interstice 35.
A perspective representation of the hexagonal nut 29 is shown in
The embodiment of the present invention according to
In
When the upper piston part 2″ is screwed together with the lower piston part 3″, the contact surface 19′ comes to lie against the surface 21′, whereby not only longitudinal expansion of the expansion sleeve 26″ and of the pin 31, and deformation of the center region of the piston crown 4′, in the manner of a disk spring, in the direction of the piston skirt, but also deformation of the cantilever 45, in the manner of a disk spring, in the direction of the piston crown 4′, occur. The deformations of the piston elements last mentioned lead to a bias that acts on the screw connection, which imparts great reliability to this connection.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 041 409.5 | Sep 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE2006/001527 | 8/31/2006 | WO | 00 | 6/17/2008 |
