Piston Having Outer Thread

Abstract

The invention relates to a piston for an internal combustion engine formed from a lower part and an upper part which are threadingly connected to one another to form a piston. In one example, an anti-rotation safeguard device is used to prevent unwanted rotation of the upper part relative to the lower part. In another example, a forged extension and a nut are used to obtain a prestress during operation of the piston. In another example, a cooling gallery including extension bores are used to increase the cooling capacity.

Claims

1. A piston of an internal combustion engine, formed from a lower part and an upper part, having a piston crown, the lower part and the upper part being joined to form the piston by way of one of a non-positive or positively locking connection, characterized in that an external thread is arranged between the lower part and the upper part.

2. The piston of claim 1, characterized in that at least two supports are provided between the lower part and the upper part.

3. The piston of claim 2, characterized in that there is a gap between the lower part and the upper part in a static state, at least in the region of one of the at least two supports.

4. The piston of claim 2, characterized in that at least one nut is provided for maintaining the prestress between the lower part and the upper part of the piston during the operation of the internal combustion engine.

5. The piston of claim 4, characterized in that a cup spring (6) is provided for abutting engagement with the at least one nut for maintaining the prestress between the lower part and the upper part during the operation of the internal combustion engine.

6. The piston of claim 1, characterized in that the external thread is formed by a circumferential land of the upper part and a corresponding circumferential land of the lower part.

7. A piston for use in an internal combustion engine comprising: a lower part having an external threaded portion positioned circumferentially about a piston stroke axis, the lower part having a first contact surface and a second contact surface positioned radially distant from the first contact surface; an upper part having an external threaded portion positioned circumferentially about a piston stroke axis and a first contact surface and a second contact surface positioned radially distant from the first contact surface, the upper part threaded portion selectively threadingly engaging the lower part portion to connect the upper part to the lower part; a main support defined by the abutting engagement of the lower part first contact surface and the upper part contact surface on the threaded engagement of the upper and the lower part; and an auxiliary support defined by the lower part second contact surface and the upper part second contact surface on threaded engagement of the upper part and the lower part.

8. The piston of claim 7 wherein the lower part further comprises a circumferential land defining the lower part external threaded portion; the upper part further comprises a circumferential land defining the upper part external threaded portion.

9. The piston of claim 8 wherein the lower part external threaded portion extends in a direction radially outward from the piston stroke axis; and the upper part external threaded portion extends in a direction radially inward toward the piston stroke axis.

10. The piston of claim 7 wherein the upper part further comprises an extension extending downwardly toward the lower portion along the piston stroke axis; and a nut threadingly engaging the extension operable to selectively axially compress the lower part against the upper part.

11. The piston of claim 10 further comprising a cup spring positioned between the nut and the extension, the cup spring operable to apply an axially biasing force against the nut and the extension on tightening engagement of the nut to the extension.

12. The piston of claim 7 further wherein the upper part and the lower part define an axial anti-rotation bore extending through the main support; and an anti-rotation device positioned within the anti-rotation bore, the anti-rotation device operable to prevent rotation of the upper part relative to the lower part about the piston stroke axis.

13. The piston of claim 7 wherein the upper part and the lower part define an inner region cavity positioned vertically above a pin bore along the piston stroke axis.

14. The piston of claim 7 further comprising: a cooling gallery defined by the upper part and the lower part extending circumferentially about the piston stroke axis, the cooling gallery further defining a plurality of extension bores in fluid communication with the cooling gallery.

15. The piston of claim 7 wherein the lower part further comprises a third contact surface and the upper part further comprises a third contact surface, the lower part third contact surface and the upper part third contact surface defining a third support.

16. The piston of claim 7 wherein the auxiliary support defines a spatial gap between the lower part second contact surface and the upper part second contact surface when the upper part is fully threadingly engaged with the lower part wherein the upper part first contact surface is abuttingly engaged with the lower part first contact surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Different embodiments of a piston according to the invention will be described in the following text and will be explained using the figures, in which:

[0014] FIG. 1 shows a sectional view of a piston along its pin axis;

[0015] FIG. 2 shows a sectional view of the piston in accordance with FIG. 1 transversely with respect to its pin axis;

[0016] FIG. 3 shows a further exemplary embodiment of a piston transversely with respect to its pin axis; and

[0017] FIG. 4 shows a further exemplary embodiment of a piston.

DETAILED DESCRIPTION

[0018] FIGS. 1 and 2 show a piston 11 in two different views, the piston 11 being formed by way of a lower part 12 and an upper part 13. Said two parts 12, 13 are produced in a suitable way (for example, by way of forging, casting or the like). The materials can be identical or different. The lower part 12 has elements which are known per se such as load-bearing skirt wall sections, pin bosses, pin bores and the like. The upper part 13 which comprises a piston stroke axis 14 in the same way as the lower part 12 has elements which are known per se such as a ring zone, optionally a combustion chamber recess and optionally a cooling gallery 15. The cooling gallery 15 is present in the case of the exemplary embodiment, but can also be dispensed with.

[0019] On account of the geometries of the lower part 12 and the upper part 13, they are connected to one another concentrically around the piston stroke axis 14 by means of an external thread 1. Moreover, a main support 2, an auxiliary support 4 and optionally a third support 3 are provided. The upper part 13 and the lower part 12 are screwed to one another via the external thread 1. The main loading during the connection of said two parts is therefore supported by way of said external thread 1. Said thread therefore serves to actually hold (connect) the upper part 13 with respect to the lower part 12. After the assembly, at least the main support 2 which is required in every case is produced. In addition, an auxiliary support 4 is produced which, in the static state, either allows the associated faces of the two parts 12, 13 to bear against one another after ending of the screwing operation, or forms a gap. The configuration of a gap in the region of said auxiliary support is particularly advantageous if the two parts 12, 13 are screwed to one another in a completed manner Via said gaps, deformations of the piston during the operation of the internal combustion engine can firstly be compensated for, said gap secondly being present only in the static state. The gap decreases as a consequence of temperature increases and/or deformations of the piston during the operation of the piston in the internal combustion engine, with the result that the associated regions of the lower part 12 and the upper part 13, just like the regions of the main support 2, come into contact in the region of the auxiliary support 4, with the result that stability of the piston during the operation of the internal combustion engine is achieved effectively in this way, but at the same time stresses and therefore damage, such as cracks, are also avoided.

[0020] In the case of the piston 11 of the exemplary embodiment in FIGS. 1 and 2, a nut 5 is also arranged in the region of the piston stroke axis 14, which nut 5 can interact with a cup spring 6, but does not have to. The third support 3 is formed as a result if the nut 5 is tightened against the cup spring 6. The nut 5 and the cup spring 6 do not have the object, however, of connecting the upper part 13 to the lower part 12, but rather of obtaining the prestress even during the operation of the piston 11 in the internal combustion engine. To this end, it is proposed to increase the effect of the nut 5 by way of the effect of the cup spring 6, it also possibly being possible for the cup spring 6 to be dispensed with. Furthermore, the lower part 12 is configured in a region 7 (marked in FIG. 2) in such a way that, during tightening of the nut 5, the region 7 is pulled (pressed) against the upper part 13. This results in a further prestress between the upper part 13 and the lower part 12. The cup spring 6 can be dispensed with if it proves that the prestress can be applied solely by the region 7. As shown, the thread of the nut 5 is attached on a forged extension 8 of the upper part 13. This serves only for explanation, since the extension 8 of the upper part 13 can also be replaced by a screw.

[0021] In the case of the exemplary embodiment in accordance with FIGS. 1 and 2, the upper part 13 forms a circumferential land 20 and, in a manner which corresponds to this, the lower part 12 forms a circumferential land 21 for configuring the external thread 1. As shown, the circumferential land 20 is of approximately rectangular and relatively thin cross section, whereas the circumferential land 21 of the lower part 12 is configured in a solid manner by way of the lower part 12. It goes without saying that other forms of the upper part 13 and the lower part 12 for forming the external thread 1 are conceivable.

[0022] FIG. 3 shows a further exemplary embodiment of the piston 11A. It can be seen that the annular circumferential cooling gallery 15 can have upwardly directed extension bores 16. In order to increase the cooling effect, a plurality of extension bores which are distributed over the circumference are made in the upper part 13, starting from the cooling gallery 15. In the case of said exemplary embodiment, 17 likewise denotes an external thread (in an analogous manner with respect to the external thread 1 in the case of the preceding exemplary embodiment), there also being the at least one main support 2 and the auxiliary support 4 (optionally the third support 3) here in the case of said piston 11A in accordance with FIG. 3. There are also once again the lands 20, 21 which correspond to one another.

[0023] In a difference from the exemplary embodiment in accordance with FIGS. 1 and 2, the piston 11A in accordance with FIG. 3 has an inner region 18 without a nut 5, without a cup spring 6 and without an extension 8. Moreover, said piston 11A does not have a combustion chamber recess, it optionally being possible for said combustion chamber recess to be present, however. The inner region 18 is shaped out above the pin bore and can likewise be used for cooling purposes

[0024] FIG. 4 shows details of the piston 11B, approximately in accordance with the piston 11A in accordance with FIG. 3, an anti-rotation safeguard 19 also being provided between the lower part 12 and the upper part 13. Said anti-rotation safeguard 19 can be a pin, a screw, a spring-loaded pin for engaging into a recess of the opposite part or the like. This is a non-positive or positively locking anti-rotation safeguard 19. As an alternative or in addition to this, the two parts 12, 13 can also be prevented from rotating with respect to one another during the operation in the internal combustion engine in an integrally joined manner, such as soldering, welding, adhesive bonding or the like.

[0025] The following is also to be noted with regard to the manufacture. The upper part 13 and the lower part 12 can be manufactured on a counter spindle machine. After the machining of the external thread 1, 17 (that is to say, of the corresponding thread regions on the lower part 12 and the upper part 13) and optionally of the inner contour (for example, of the inner region 18), the two parts 12, 13 are screwed together. The precision machining (that is to say, the running clearance) therefore takes place in the assembled state, with the result that no concentricity is produced between the upper part 13 and the lower part 12. In addition, a fitting slot 9 (shown in FIG. 2) can also be made on the forged extension 8 and the lower part 12, with the result that the relative movement between the upper part and the lower part is as low as possible or even does not exist at all anymore during the operation of the piston 11, 11A or 11B in the internal combustion engine. To this end, the anti-rotation safeguard 19 can be used, but does not have to be used.

[0026] In general, it is to be noted once again that there can be a gap between the lower part and the upper part in the static state, at least in the region of a support. A simple and effective piston connection is provided, without welding. A simple and secure connection of the lower part and the upper part takes place without welding or clamping. The lower part and the upper part are therefore joined releasably by way of a non-positive and/or positively locking connection to form a piston. If the screw connection between the lower part and the upper part is of prestressed configuration, this is a non-positive connection. If the screw connection between the lower part and the upper part is not of prestressed configuration, this is a positively locking connection. Mixed forms between a non-positive connection and a positively locking connection can likewise exist in the case of the connection of the lower part and the upper part to form a piston.

LIST OF DESIGNATIONS

[0027] 1 External thread [0028] 2 Main support [0029] 3 Third support [0030] 4 Auxiliary support [0031] 5 Nut [0032] 6 Cup spring [0033] 7 Region [0034] 8 Extension [0035] 9 Fitting slot [0036] 11 Piston [0037] 12 Lower part [0038] 13 Upper part [0039] 14 Piston stroke axis [0040] 15 Cooling gallery [0041] 16 Extension bore [0042] 17 External thread [0043] 18 Inner region [0044] 19 Anti-rotation safeguard [0045] 20 Circumferential land [0046] 21 Circumferential land