DE102018109639A1 - Closing of cooling holes in pistons (in particular steel pistons) by dowel pins or wire sections - Google Patents

Abstract

Piston (1) of an internal combustion engine, comprising a piston main body (6) and two oppositely disposed piston hubs, each with a pin bore (4) for receiving a piston pin, wherein in the piston main body (6) at least one cavity (5) and introduced by a closure element (7 ) is sealed after a coolant has been introduced into the cavity (5), characterized in that the closure element (7) is a wire section, wherein the wire section is pressed into the cavity (5).

Description

The invention relates to a piston of an internal combustion engine, comprising a piston base body and two oppositely disposed piston hubs, each with a pin bore for receiving a piston pin, wherein in the piston body at least one cavity is introduced and sealed by a closure element, after a coolant has been introduced into the cavity, according to the features of the preamble of claim 1.

Which technical task should be solved by the invention?

Securely closing cooling holes in a piston of an internal combustion engine that are filled with a coolant, such as sodium or the like.

How was the task solved so far?

Insert grub screws or steel balls into the cooling holes followed by spot welding.

How is the problem solved according to the invention?

This object is inventively achieved in that the closure element is a wire section, wherein the wire section is pressed into the cavity. It can be used in an advantageous manner, a conventional wire, from the corresponding length of a section is cut to length, which thus forms the closure element. With this wire section, the cavity is closed after the refrigerant has been filled in the cavity. The coolant can be filled directly into the cavity. Alternatively, it is conceivable to fill the coolant itself into a container, for example a metal tube, wherein the closed container is again inserted into the cavity after the coolant has been introduced. Also in this variant, the cavity can be closed by pressing the wire section.

In development of the invention it is provided that the wire section is designed as a dowel pin. After or even before the section of the wire is cut to length, this part, which forms the closure element, is brought into a shape deviating from its original shape so that the shape of the section of the shape of the region into which the closure element is pressed in is adapted for pressing in is to achieve an optimal closure. To achieve higher overlaps (firmer press fit), the dowel pin is cooled for injection immediately prior to pressing (for example, with liquid nitrogen, analogously to Buchseeneindehnen) and / or the piston or the piston body previously heated.

In a further development of the invention, it is provided that the region of the cavity into which the closure element is pressed in is designed to widen conically outwardly before it is pressed in. This results in the introduction of a closure element, in particular of the dowel pin, into the cavity (the cooling bore) with overlap. As a result, a secure press fit is given. For this purpose, the pin is pressed into the hole, the outer part of the hole can be made slightly conical.

In a further development of the invention, it is provided that the dowel pin of the conical design of the cavity is also correspondingly conical. As a result, a particularly high blackmail is achieved, so that also a secure press fit is given. Alternatively, it is also conceivable that the inwardly facing surface of the cavity into which the closure element is pressed, and the outwardly facing surface of the closure element, in particular the dowel pin are formed with corresponding elevations or depressions. As a result, a toothing can be realized, whereby the firm seat of the closure element is significantly improved. The surface of the dowel pin can be brought, for example, viewed in cross-section in a waveform, a sawtooth or the like, or even provided with a survey or only one depression. The inwardly facing surface of the cavity corresponds inversely to the shape of the dowel pin. At those locations of the dowel pin in a waveform where valleys are present, bumps are present in the cavity and vice versa. The same applies to the case that the dowel pin and the cavity in the sense of a tongue and groove connection correspond to each other. If at least one groove is arranged in the locating pin, the cavity has the corresponding spring (elevation which engages in the groove) or vice versa.

In a further development of the invention, it is provided that the closure element terminates flush with the surface of the piston main body. The flush termination is achieved either by the fact that it automatically results after pressing the closure element into the cavity. Alternatively, the closure element, in particular the dowel pin, after pressing into the cavity over the surface of the cavity surrounding the piston body protrude and this supernatant then be removed. The removal takes place, for example, by twisting, wegfräsen, grinding or the like. The removal of the supernatant has the advantage that the Closing element for closing the cavity can also be arranged in those areas of the piston, which represent functional areas of the piston. For example, functional areas are those areas (such as the tread of the piston) that may come into contact with other elements (such as the cylinder inner surface of the engine) during operation of the piston with the piston.

In a further development of the invention, it is provided that the closure element, in particular the dowel pin, consists of the same material as the piston main body. The dowel pins are ideally made of a steel which is as similar as possible or even identical to the piston material in terms of thermal expansion coefficient and electrochemical potential. This ensures that the secure press fit (the overlap) is given in the entire temperature range of the piston operation and no corrosion problems due to galvanic element formation occur. Other materials are also considered.

As dowels you can use directional wire sections or a continuous wire that is cut off (cut to length) after pressing on the piston surface (pinched, sheared or the like).

This process is well suited for automation (especially saving of cycle time and costs), since the feeding, if necessary straightening, possibly cooling, positioning and pressing of the dowel pin or the wire can be performed by a robot.

An embodiment of closure elements, which are formed as a wire section, is shown in the figure and described below.

In the figure, the reference numeral 1 a fragment of a piston shown, for example, a cooling channel 2 and / or a combustion bowl 3 can, but does not have to. In known manner, the piston 1 pin bores 4 on that in pin bosses of the piston 1 are arranged and receive a piston pin, with which the piston 1 is connected to a connecting rod, not shown. In addition, the piston 1in a known manner a ring field not shown in detail and at least one piston shaft, for example, two opposing shaft wall sections.

The piston 1 has at least one cavity 5 on, wherein a piston body 6 of the piston 1 is made in a suitable manner, for example by casting, welding or the like. In the piston body 6 is the at least one cavity 5 for example, when casting the piston body 6 made with. Alternatively or additionally, the cavity 5 also by other methods, such as drilling, erosion or the like in the piston body 6 be introduced.

After the cavity 5 has been made available, there is a non-illustrated coolant, such as sodium, filled directly or in a separate container. After this filling process, the cavity 5 from a closure element 7 locked. According to the invention, this closure element 7 formed as a wire section, in the opening portion of the cavity 5 is pressed.

The invention achieves the following in general or in connection with the exemplary embodiment:

Effect:

Safe closing of cooling holes (generally cavities) in steel pistons, preferably without subsequent welding.

Technical progress:

Avoiding welding defects (cracks, connection errors), since no welding is required. Automation of the manufacturing step "hole closing" by introducing the dowel pin or the wire section by means of robots.

Closing of cooling holes in the piston (especially steel piston) by dowels or wire sections by introducing a dowel pin in the cooling hole with overlap to achieve a secure interference fit, to which the pin is pressed into the hole and the outer part of the hole can be made slightly conical.

It should be noted that the term "cavity" is used here in the sense that it is filled once with a coolant and this coolant remains permanently in the cavity after it has been closed with the closure element according to the invention. Thus, the cavity or the cooling hole is not a cavity in a piston into which a coolant (usually engine oil) is introduced, then remains in the cavity for a certain time and is then removed again from the cavity.

LIST OF REFERENCE NUMBERS

1

piston

2

cooling channel

3

Combustion bowl

4

pin bores

5

cavity

6

Piston base body

7

closure element

Claims (6)

Piston (1) of an internal combustion engine, comprising a piston main body (6) and two oppositely disposed piston hubs, each with a pin bore (4) for receiving a piston pin, wherein in the piston main body (6) at least one cavity (5) and introduced by a closure element (7 ) is sealed after a coolant has been introduced into the cavity (5), characterized in that the closure element (7) is a wire section, wherein the wire section is pressed into the cavity (5). Piston (1) after Claim 1 , characterized in that the wire section is designed as a dowel pin. Piston (1) after Claim 1 or 2 , characterized in that the region of the cavity (5), in which the closure element (7) is pressed, is designed to widen conically outwardly before being pressed in. Piston (1) after Claim 3 , characterized in that the dowel pin of the conical configuration of the cavity (5) is also correspondingly conical. Piston (1) according to one of the preceding claims, characterized in that the closure element is flush with the surface of the piston main body (6). Piston (1) according to one of the preceding claims, characterized in that the closure element consists of the same material as the piston base body (6).

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