DE102017202462A1 - Method for producing a piston - Google Patents

Abstract

The present invention relates to a method for producing a piston (1) for an internal combustion engine, wherein the piston (1) comprises a piston head (2) and a piston skirt (18), in which a connecting line (8) is provided, which via an opening (9) is fluidically connected to the environment, wherein the opening (9) is closed by a closure element (11). Essential to the invention here is that the closure element (11) by capacitor discharge welding to the piston (1) is welded. In this way, a stable connection between the closure element (11) and the piston (1) and a fluid-tight closure of the opening (9) with minimal damage to the piston (1) and the closure element (11) is achieved.
The invention further relates to such a piston (1).

Description

The present invention relates to a method of manufacturing a piston for an internal combustion engine. The invention further relates to such a piston.

Pistons are used in internal combustion engines, where they are arranged adjustable in cylinders and each defining a combustion chamber. During operation of the internal combustion engine, the pistons transmit the energy released to a tapping unit, in particular a crankshaft, at which a corresponding torque can be tapped. Desirable increases in performance and efficiency of such internal combustion engines cause such a piston is always exposed to more extreme thermodynamic conditions, especially elevated temperatures.

From the DE 10 2011 114 105 A1 Such a piston is known. The piston has a piston head with a combustion chamber trough facing the combustion chamber and a piston shaft, wherein a circumferential cooling channel for cooling the piston is provided in the piston head. As a result, the piston can be exposed to elevated temperatures. In addition, the piston has at least one bore which extends through the piston shaft and connects the cooling channel via an opening with the environment. A coolant can be introduced into the cooling channel via the opening and the bore. The opening is subsequently closed by means of a closure element. The DE 10 2011 114 105 A1 suggests in this case the pressing of the closure element into the opening or the welding of the closure element with the piston.

The pressing of the closure element in the opening can cause during operation of the piston to cause leakage in the region of the opening, which can lead to an undesirable leakage of coolant from the piston. If this mixes with the oil in the crankcase, such leaks can lead to damage to the piston and / or the associated internal combustion engine.

The usual welding of the closure element with the piston leads through the necessary heat input to a structural change of the closure element and / or the piston, in particular by the high load and / or high temperatures during operation of the internal combustion engine to damage the piston and / or the formation of Leaks can lead in the region of the opening, which in turn can cause a leakage of coolant through the leaks.

The present invention is therefore concerned with the task of providing a method for producing a piston of the aforementioned type and for such a piston improved or at least alternative embodiments, which are characterized in particular by a simple production and / or increased stability of the piston.

This object is achieved by the subjects of the independent claims. Advantageous embodiments are the subject of the dependent claims.

The present invention is based on the general idea of welding a closure element to a piston by a resistance welding process, the closure element serving to close an opening connecting a connecting line of the piston with the environment. In accordance with the invention, capacitor discharge welding, which was previously specialized in the production of pistons, is used to connect the closure element to the piston and thus to close the opening. In this case, at least one electrical current pulse originating from at least one capacitor is sent through a connection region between the piston and the closure element, which results in a heat input which is essentially limited to the connection region, so that on the one hand a stable and fluid-tight connection between the closure element and the piston is achieved and on the other hand reduced by the welding structural changes of the piston and / or the closure element and / or are substantially limited to the connection area. Thus, a fluid-tight closing of the opening with a prolonged service life and / or increased stability, in particular mechanical and / or thermal stability, of the piston and / or the closure element is achieved. In accordance with the concept of the invention, a piston is initially provided which has a piston head and a piston skirt. Furthermore, the piston has at least one such connecting line, which extends through the piston and is connected via the opening with the environment. Subsequently, the opening is closed with such a closure element by the closure element is welded to the piston by capacitor discharge welding.

The connecting line can be a bore introduced into the piston, in particular into the piston skirt.

The connecting line can serve in the piston for any purpose. The connecting line can in particular serve the cooling of the piston. It is conceivable, the connecting line via the opening with a coolant to fill. It is also conceivable, other rooms within the piston, for example, a circulating in the piston head cooling channel to fill via the opening and the connecting line with a coolant. Accordingly, at least one such connecting line can be fluidically connected to the cooling channel, in particular open into the cooling channel. The closing of the opening takes place here after filling with the respective coolant.

In the piston skirt a hub is preferably provided, which serves to connect the piston to a crankshaft, for example via a connecting rod. It is conceivable to manufacture or form the piston skirt in such a way that, during operation, it bears against an associated cylinder outside the hubs.

It is to be contemplated variants in which the piston skirt has at least one in operation or in the assembled state on the cylinder piston skirt and at least one piston box, which is arranged offset inwardly and has the hub or the hub forming apertures. It is preferred if the opening is arranged in such a piston box.

In preferred embodiments, the closure element for capacitor discharge welding is pressed against the piston with a predetermined force and at least one electrical current pulse is sent through the connection region between the piston and the closure element. As a result, the compound, in particular in terms of stability, can be improved.

In principle, any number of current pulses which each have an arbitrary duration and are temporally spaced from one another as desired can be used for connecting the closure element to the piston.

It is preferred if at least one such current pulse with a duration of less than 20 ms is used. It is particularly preferred if at least one such current pulse is used with a duration of 10 ms. As a result, the region of the heat input and thus the region in which structural changes take place in the piston and / or the closure element are at least reduced.

According to advantageous variants, at least two current pulses are used. It is particularly advantageous if exactly two current pulses are used. It is also advantageous if the current pulses are used at a distance of between 0.1 s and 1 s in each case. It is particularly preferred if the successive current pulses are spaced apart for 0.5 s. These measures each lead to an optimization with regard to the most efficient possible heat input and the smallest possible range of heat input in the piston and / or in the closure element.

Embodiments in which at least one such current pulse, preferably all current pulses, having an amperage between 8 kA and 12 kA prove to be advantageous. Variants in which a current of 10 kA is used prove to be particularly advantageous. As a result, the heat input can optimally lead to the welding of the closure element to the piston.

In preferred embodiments, the closure element is pressed against the piston with a force between 1.5 kN and 3.5 kN. It is particularly preferred if the closure element is pressed against the piston with a force of 2.5 kN. This leads in particular to a more stable connection of the closure element to the piston.

Advantageously, the cooling channel is filled before closing the opening with the closure element with a coolant. Here, any coolant, for example. A water-containing mixture and the like. Be used. It is also conceivable to use as coolant sodium or potassium or a mixture of sodium and potassium.

The method is preferably carried out in such a way that a heat-influencing region or a heat-affected zone in which structural changes of the piston and the closure element are caused by the capacitor discharge welding is less than 400 μm, in particular less than 200 μm. This extension preferably relates to a depth of the heat-affected zone running transversely to the contact region between the piston and the closure element. Such a compound has sufficient mechanical strength due to the low heat-affected area. By choosing this welding method, the energy required for the realization of the connection is also optimized, in particular reduced, which is also reflected by the low heat-affected area.

It goes without saying that in addition to the method according to the invention, a piston produced in this way also belongs to the scope of this invention.

The piston head of the piston may have a combustion bowl, which limits a combustion chamber of the internal combustion engine when mounted in an associated internal combustion engine. It is preferred if the opening on the of the combustion chamber trough facing away from the piston is arranged.

It is conceivable that the piston head has an outer peripheral ring portion for receiving at least one piston ring. It is preferred if the cooling channel is arranged in the region of the ring part in the piston head.

The piston and the closure element can in principle be made of any materials, provided that they can be welded to the capacitor discharge welding. They are each made in particular of a metal or a metal alloy.

The closure element can in principle have any desired shape, provided that the opening can be sealed fluid-tight with the closure element. It is conceivable that the closure element has a shaft and a head, wherein the shaft is disposed within the opening and the head rests on the outside of the piston.

It is also conceivable that the closure element is arranged in the opening or the connecting line in such a way, in particular recessed, that the closure element is flush with the outside of the piston.

It should be understood that use of capacitor discharge welding to weld such a closure member to such a piston is also within the scope of this invention.

Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated figure description with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

• 1 einen Schnitt durch einen Kolben mit einem Verschlusselement,
• 2 den Schnitt aus 1 im Bereich des Verschlusselements und bei einem anderen Ausführungsbeispiel,
• 3 eine vergrößerte Darstellung des in 2 mit III bezeichneten Bereichs,
• 4 eine Darstellung des Kolbens bei einem weiteren Ausführungsbeispiel,
• 5 einen Schnitt des Kolbens aus 4 im Bereich des Verschlusselements.

Show, in each case schematically,

• 1 a section through a piston with a closure element,
• 2 the cut out 1 in the region of the closure element and in another embodiment,
• 3 an enlarged view of the in 2 area designated III,
• 4 a representation of the piston in a further embodiment,
• 5 a section of the piston 4 in the region of the closure element.

A piston 1 an otherwise not shown internal combustion engine has, as in 1 you can see a piston head 2 as well as one with the piston head 2 connected piston shirt 18 on. The piston shirt 18 has a piston stem in the example shown 24 and a piston box 25 on. The piston box 25 has at least one box wall 19 and the piston shaft 24 at least one shaft wall 3 on, in the example shown two Schäftwände3 and two box walls 19 are provided. The piston head 2 has a combustion bowl on the front side 4 on, which limits an otherwise not shown combustion chamber of the internal combustion engine. The piston shirt 18 is on the from the combustion chamber 4 opposite side of the piston head 2 arranged. piston head 2 and piston shirt 18 are preferably of the same material, in particular monolithic, for example of aluminum, an alloy, steel and the like., Produced. The piston head 2 has on the outside a circumferential ring section 5 on, in the at least one outwardly open groove 6 is provided for receiving a piston ring, not shown, wherein when in 1 shown example, several such grooves 6 are provided. In the area of the ring section 5 is inside the piston head 2 a circumferential cooling channel 7 intended. In the piston shirt 18 or in the box walls 19 is a hub 17 provided that the connection of the piston 1 with a crankshaft, not shown, for example. Via a connecting rod, not shown, is used. The hub 17 is through opposite breakthroughs 20 in the box walls 19 is formed, of which in the sectional plane according to the 1 only a piston wall 19 and a breakthrough 20 you can see. The piston 1 also has at least one connection line 8th on, based on that of the combustion chamber 4 opposite side of the cooling channel 7 from the cooling channel 7 with respect to a piston axis 23 of the piston 1 extends axially away. In the example shown are two such connecting lines 8th to see. Both visible connection lines 8th In the example shown, they are fluidic with the cooling channel 7 connected and open into these, being one of the connecting lines 8th one on the one from the combustion bowl 4 opposite side of the piston 1 , especially in the area of the visible box wall 19 , arranged opening 9 with the Environment is connected. Thus, also the cooling channel 7 over the connecting line 8th and the opening 9 connected to the environment. The cooling channel 7 and / or the connecting lines 8th can over the opening 9 with a coolant 10 be filled. The coolant 10 can in principle be any. In particular, the coolant 10 Contain sodium and / or potassium. The respective connection line 8th , In particular, via the opening 9 connected to the environment connecting line 8th , can be considered a bore 22 in the piston 1 be introduced.

The opening 9 will after filling the piston 1 with the coolant 10 with the help of a closure element 11 sealed fluid-tight. To close the opening 9 becomes the closure element 11 according to the invention by capacitor discharge welding with the piston 1 , especially with the box wall 19 , welded. For this purpose, the closure element 11 with a force, preferably between 1.5 kN and 3.5 kN, in particular 2.5 kN, against the piston 2 pressed. Subsequently, at least one electrical current pulse is passed through a connection region 12 between the piston 2 and the closure element 11 cleverly. The respective current pulse preferably has a current intensity between 8 kA and 12 kA, in particular of 10 kA. The respective current pulse lasts less than 20 ms. Preferably, the respective current pulse lasts 10 ms. Particularly preferably, at least two such current pulses, advantageously exactly two such current pulses, are used which have a distance of 0.1 s to 1 s, in particular of 0.5 s from one another. As a result, these measures each lead to a stable connection between the closure element 11 and the piston 1 as well as a stable, fluid-tight closure of the opening 9 through the closure element 11 , In addition, there is a heat affected zone 16 (please refer 2 and 3 ), in which due to the capacitor discharge welding to structural changes of the closure element 11 and / or the piston 1 , in particular a fusion of the closure element 11 with the piston 1 , comes, optimizes, this heat affected zone 16 in a transverse to the contact area between pistons 1 and closure element 11 running depth 21 preferably less than 400 microns, in particular less than 200 microns, is.

When in 1 embodiment shown is the closure element 11 as one in the opening 9 sunk or received closure element 11 trained in that with the piston 1 welded state flush with the outside of the piston 1 concludes. The closure element 11 So is in particular bolt-like or as a bolt 13 educated.

The 2 and 3 show another embodiment of the piston 1 , where in 3 an enlarged view of the in 2 III area is shown. This embodiment differs from that in FIG 1 shown embodiment in particular by the formation of the closure element 11 that a shaft 14 as well as a head 15 having. Here is the shaft 14 the closure element 11 in the connection line 8th or the opening 9 arranged while the head 15 on the outside of the piston 1 is applied. In the 2 and 3 it can be seen that the heat affected zone 16 in the connection area 12 is arranged. The heat affected zone 16 is caused by the heat input in the capacitor discharge welding, thereby causing structural changes of the closure element 11 and / or the piston 1 comes. This occurs in the heat affected zone 16 in particular to a melting of the connecting element 11 and / or the piston 1 leading to a stable connection between the closure element 11 and the piston 1 leads. In particular in 3 can be seen that the heat affected zone 16 is very small. The heat affected zone 16 extends, as already mentioned above, over a depth of less than 400 .mu.m, in particular as 200 microns.

Such a heat affected zone 16 exists also in the 1 shown example, although this is not visible due to the presentation.

In the 4 and 5 is another embodiment of the piston 1 shown. This embodiment differs from that in FIG 1 shown embodiment in particular by the fact that the visible connecting lines 8th in no fluid communication with the cooling channel 7 stand. The connection lines 8th run inclined to the piston axis 23 , The respective connection line 8th is at one end over in the box wall 19 arranged opening 9 connected to the environment, while the other end is closed and below the combustion bowl 4 is arranged. The respective connection line 8th is with a coolant 10 filled, the same or different than the coolant 10 in the cooling channel 7 can be. After filling the respective connecting line 8th becomes the associated opening 9 , as in 5 can be seen with such a closure element 11 sealed fluid-tight, wherein the closure element 11 in 5 for better understanding outside the piston 1 is shown. Also in this embodiment is the closure element 11 by means of capacitor discharge welding with the piston 1 or the box wall 19 connected. Although not shown, such a heat-affected zone also forms 16 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102011114105 A1 [0003]

Claims (10)

Method for producing a piston (1) for an internal combustion engine, wherein a piston (1) is provided which comprises: a piston head (2) and a piston skirt (18), one extending through the piston (1) and one over the piston Opening (9) connected to the environment connecting line (8), wherein the opening (9) is closed by a closure element (11), characterized in that the closure element (11) by capacitor discharge welding to the piston (1) is welded. Method according to Claim 1 characterized in that, for capacitor discharge welding, the closure element (11) is pressed against the piston (1) with a force and at least one electrical current pulse is sent through a connection region (12) between the piston (1) and the closure element (11). Method according to Claim 2 , characterized in that at least one current pulse having a duration of less than 20 ms, in particular of 10 ms, is used. Method according to Claim 2 or 3 , characterized in that at least two current pulses at a distance of between 0.1 s and 1 s, in particular of 0.5 s, are used. Method according to one of Claims 2 to 4 , characterized in that at least one current pulse having a current intensity between 8 kA and 12 kA, in particular 10 kA, is used. Method according to one of Claims 2 to 5 , characterized in that the closure element (11) with a force between 1.5 kN and 3.5 kN, in particular 2.5 kN, against the piston (1) is pressed. Method according to one of Claims 1 to 6 , characterized in that the connecting line (8) or the piston (1) via the connecting line (8) before closing the opening (9) by the closure element (11) with a coolant (10), in particular with sodium and / or potassium , is filled. Piston (1) for an internal combustion engine, wherein the piston according to the method of one of Claims 1 to 7 is made. Piston after Claim 8 , characterized in that the piston head (2) has a combustion chamber trough (4), wherein the opening (9) on the side facing away from the combustion chamber trough (4) side of the piston (1) is arranged. Piston after Claim 8 or 9 , characterized in that the piston (1) in the piston head (2) encircling cooling channel (7) which is fluidly connected to at least one such connecting line (8).

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