EP2561205B1 - Piston upper part of an assembled or welded piston with extended cooling spaces - Google Patents

Description

The invention relates to a one-piece and two-piece piston of an internal combustion engine and a method for producing such pistons according to the respective preambles of the independent claims.

In order to comply with emission limit values or to achieve emission targets and consumption targets, the combustion temperatures and the combustion pressures are increased in order to optimize the combustion, so that the upper part of the piston in particular is subjected to high thermal loads. The operating temperature of the piston of such internal combustion engines can exceed the permissible limits of the piston material, associated with the risk of heat aging in which the alloy of the piston material loses strength and dimensional stability. In order to minimize the thermal loads on the piston, pistons are used in which an annular cooling channel is integrated, in which a partial amount of the lubricating oil of the internal combustion engine is injected as a coolant via an injection nozzle, flows through the cooling channel and then exits. The DE 197 50 021 A1 discloses a cooling duct piston which, in the area of the annular field, encloses an annular cooling duct, radially offset from a lateral surface. The coolant flowing through the cooling channel effects heat dissipation, the effectiveness of this liquid cooling being essentially determined by the volume throughput of the cooling medium through the cooling channel.

As the specific power of the internal combustion engine increases, it is necessary to optimize known concepts of liquid-cooled pistons. In addition to an annular cooling channel, it is therefore necessary to specifically apply coolant to other areas of the piston. To implement this measure, the DE 41 18 400 A1 a built-up piston which, starting from the cooling channel, includes cooling slots running in the direction of the piston crown with walls running parallel to one another.

The invention is based on the object of optimizing the cooling effect of the upper piston part of a one-piece and of a two-part piston in thermally highly stressed zones by means of an inexpensive measure and accordingly specifying a piston and a method for producing such pistons.

Based on the prior art, the present invention provides an upper piston part of a one-piece and a two-piece piston with integrated recesses according to the features of claims 1 and 2, as well as a method for producing the recesses according to the features of claims 12, 13 and 14.

The two-part piston is designed as a liquid-cooled piston, consisting of a lower piston part and an upper piston part having a combustion chamber bowl. These piston components are supported by joining webs that are radially spaced from one another and form a parting plane and are preferably joined together in a materially bonded manner, preferably by means of a welded connection, or preferably frictionally, preferably by means of a screw connection. The assembled piston is thus preferably assembled from an upper piston part and a lower piston part, for example by means of a screw connection, or preferably welded together, for example by means of a welded connection. In the upper piston part is an annular one that extends into the lower piston part Introduced cooling channel, which is in communication with an inner cooling space via connecting channels. To enlarge the cooling space, the upper piston part includes recesses that are oriented in the direction of a piston crown and designed as a blind hole and connected to the cooling channel.

According to claim 2, it is also possible that the liquid-cooled piston of an internal combustion engine consists of a piston lower part and a piston upper part having a combustion chamber bowl, the piston being designed as a one-piece piston that has no parting plane.

To solve the problem, according to the invention according to claim 1 and claim 2, the at least one circumferential recess starting from the cooling duct is designed in the upper piston part so that its walls widen in a conically increasing manner. As a result of the spreading of the walls, a maximum cross-section is established in the area of greatest depth of the recess. The invention advantageously increases the depth of the cooling space through which the coolant flows, while maintaining defined wall thicknesses, and thus optimizes the cooling of the upper piston part. A preferred structural shape of the recess according to the invention follows, at a distance, a central contour of the trough-shaped combustion bowl introduced in the piston head. In conjunction with a large-volume cavity of the recess which increases the coolant absorption, the shaker effect can be improved and consequently the cooling effect can be increased. The size and extent of the recess according to the invention, which forms an extension of the cooling duct, is advantageously not limited by design-related requirements, for example the position and arrangement of the separation plane between the lower piston part and the upper piston part or the cooling duct, but can, for example, expand in a targeted manner in the direction of the combustion bowl . The recesses designed according to the invention are preferably intended for piston tops with a relatively small combustion bowl diameter in order to optimally cool the resulting large wall thicknesses and material accumulations in the piston crown. In this way, coking up to the point of burning and a reduction in strength of the material can be avoided. The exhaust gas requirements (Tier 3 and IMO) for assembled pistons with a small combustion bowl diameter can advantageously be achieved in conjunction with the measures to optimize the cooling of the upper piston part. It is advantageous to combine the upper piston part designed according to the invention with existing, tried and tested lower piston parts. In the case of a one-piece, liquid-cooled piston of an internal combustion engine, the type of piston lower part and the piston upper part are also designed to be suitable, as described above.

According to the invention, the size and extent of the recess is not limited by the outer diameter of the joining webs or the support surfaces in the area of the plane of separation between the upper piston part and the lower piston part. Rather, the measure according to the invention enables the recess according to the invention intended for cooling to be expanded into the thermally highly stressed zone. The cross-sectional profile in the recess base consequently exceeds the cross-sectional profile in the area of a transition from the recess to the cooling channel due to the conical widening. The piston head preferably includes a plurality of recesses distributed around the circumference and connected to the cooling channel. These recesses, designed as blind holes and specifically enlarging the cooling space, bring about improved, efficient cooling of the upper piston part. In this case, the recesses lead, at least locally, to reduced wall thicknesses of the upper piston part, as compared with the combustion chamber bowl, the ring zone, the top land and the piston crown. Due to coordinated wall thicknesses between the recesses designed according to the invention and the adjacent thermally A structurally stable upper piston part that can withstand the highest demands is realized in areas subject to high loads.

The measure according to the invention reduces the component temperature to a level below the flash point of conventional cooling oils, which at the same time reduces the risk of coking for the lubricating oil of the internal combustion engine, which is preferably used as the coolant. In addition, there is no risk of an insulating oil carbon layer which reduces the cooling effect forming, and of disadvantageous thermal piston deformation due to a reduced strength of the piston material. Due to the decisively improved heat dissipation and thus the cooling effect of the recess according to the invention, the piston upper part and consequently the entire piston are suitable for higher combustion temperatures and pressures, i.e. can be used in internal combustion engines with high power density. In addition, the large-volume, inexpensive to manufacture recesses, particularly in the case of small combustion bowl diameters, advantageously reduce the weight of the upper piston part.

A preferred embodiment of the recesses, according to the invention, which widen conically over the longitudinal extent provides that these are designed, distributed circumferentially in the upper piston part, in particular as slots, bores or channels. In this case, webs formed by the material of the upper piston part are provided between the recesses and the cooling channel. As an alternative to the webs, walls or support ribs can also be used, the walls or support ribs differing from the webs in their respective shape. In order to achieve a high structural strength of the piston upper part, it is advisable to design the conically widened recesses as pie-shaped cooling chamber chambers with a honeycomb structure, which at the same time positively influences the cooling properties and which leads to an increase in the cooling surface. In addition, the cold room is expanded spatially.

According to a further structural design, the adjacent recesses designed according to the invention are made in the upper piston part in opposite directions, alternately in matching or differing geometric sizes and / or inclinations to one another. This measure enables a targeted extension of the recesses up to thermally highly stressed zones without the risk of component weakening.

According to a preferred design, the walls of the recess are inclined at an angle of inclination "α, β" between 0 ° to 40 °, preferably ≤ 15 °, to a longitudinal piston axis to achieve largely matching wall thicknesses compared to the thermally highly stressed zones. Adapted to the design of the piston head, it is also advisable to design the angles of inclination of opposing walls, in particular an inner wall and an outer wall, to match or differ from one another.

For cost-optimized production and avoidance of component weakening, the conically expanding recesses are each provided with a rounded recess base that has a positive effect on the structural strength. For the rounded contour, a radius "R" between 1.5 mm and D / 2 (D = maximum diameter of the tool used for the cutting process, for example a milling tool, for the rounded contour) is preferably provided. As an alternative to this, it is advisable to provide the bottom of the recess with a double-rounded contour that forms a dome-like hollow vault. Furthermore, to adapt to the structural design of the piston head, the double-rounded recess base can be designed in a stepped manner. The recess base can be a strongly undulating surface, which creates an enlarged surface, or as a finely undulating surface Surface. Additional machining manufacturing steps, for example milling cuts, reduce the stepped transition between the bulges, whereby the surface of the bulges is qualitatively improved by a lower waviness on the surface and whereby the size of the surface is reduced. It is thus possible to create a finely wavy surface with a larger number of cuts. As an alternative to a rounded end contour, the invention includes a beveled recess base. The recesses in the cooling duct also lead to increased turbulence of the coolant in the cooling duct. By adapting the surface of the recess base and reducing the diameter of the recess base, it is possible to reduce or optimize the emissions during operation of the piston. By adapting the stepped transition, emissions during operation can also be reduced. By varying the depth of the recess, viewed from the lower piston part in the direction of the upper piston part, the cooling chamber can be adapted to the shape of the depression in the combustion chamber depression. In the case of a one-piece piston, the adaptation and configuration of the recess base is possible by means of the shape of the casting mold body, the shape of which in certain areas is the negative shape of the shape of the recess base.

Another embodiment of the invention provides for the recesses, which are preferably designed as channels, bores or slots, to be arranged symmetrically or asymmetrically on the circumference in the upper piston part. The position, orientation and size of the recess can be adapted to the different thermal loads. For example, it is advisable to design the cooling space or cross-sectional volume of the recess on the pressure side (DS) to be different from the corresponding cross-sectional volume on the counterpressure side (GDS) of the piston upper part. The location and interpretation of the The recess is made in such a way that a weakening of the strength of the upper piston part is avoided.
According to a method according to the invention according to claim 12, the following steps are provided for producing the recesses. First, a casting mold body corresponding to the shape of the recesses, preferably a salt core, is fixed in position in the casting mold intended for the upper piston part. After the upper part of the piston has been cast and cooled, the casting mold body is removed by rinsing.

According to a further alternative method according to the invention according to claim 13, the following steps are provided for producing the recesses in a one-piece piston. First, a casting mold body corresponding to the shape of the recesses, preferably a salt core, is fixed in position in the casting mold intended for the one-piece piston, which has a piston upper part and a piston lower part. After the one-piece piston has been cast and cooled, the casting mold body is removed by rinsing.

Another alternative method for producing the recesses provides for mechanical, three-dimensional machining. A turning and milling process is preferably suitable for this, with which cavities are introduced to represent recesses in the piston upper part. It is also a good idea to represent the recesses by means of milling or drilling tools.

An exemplary designed upper piston part according to the invention, to which this is not limited, is described below and explained with reference to the figures.

Figur 1:

ein Kolbenoberteil in einem Längsschnitt mit einer erfindungsgemäß gestalteten Ausnehmung,

Figur 2:

ein Detail des Kolbenoberteils gemäß Figur 1 in einem vergrößerten Maßstab,

Figur 3:

die Draufsicht auf ein Kolbenoberteil mit mehreren schlitzförmigen Ausnehmungen,

Figur 4:

eine räumliche Darstellung von Kühlschlitzen in einem Kolbenoberteil und

Figur 5:

eine räumliche Darstellung eines Kolbenoberteils mit erweiterten Kühlschlitzen.

Show it:

Figure 1:

an upper piston part in a longitudinal section with a recess designed according to the invention,

Figure 2:

a detail of the piston top according to Figure 1 on an enlarged scale,

Figure 3:

the top view of an upper piston part with several slot-shaped recesses,

Figure 4:

a three-dimensional representation of cooling slots in a piston upper part and

Figure 5:

a three-dimensional representation of an upper piston part with expanded cooling slots.

Figure 1 shows a longitudinal section through an upper piston part 1, which is, for example, a component made from a steel alloy by means of a forging process. Alternatively, the upper piston part 1 can also be made from aluminum, an aluminum alloy or an iron alloy. Alternatively, the upper piston part 1 can also be produced by means of any other desired forming process or primary forming process. The piston upper part 1 forms together with an in Figure 1 Piston lower part not shown, for example, a two-part piston that is built with a friction fit or welded with a material fit and is liquid-cooled. The upper piston part 1 is supported on corresponding joining webs of the lower piston part via two circumferential joining webs 2, 3 that are radially offset from one another. All joining webs together form a separation plane 4 via which the lower piston part and the upper piston part 1 are permanently connected to one another by means of a frictional connection, preferably by means of a screw connection, or by means of a material connection, preferably by means of a welded connection. On the other hand it is The lower piston part and the upper piston part 1 rest positively on one another by means of the parting plane 4. A combustion chamber bowl 7, which is delimited on the outside by a stepped bowl rim 8, is introduced concentrically to a piston longitudinal axis 5 in a piston head 6 of the upper piston part 1. The upper piston part 1 is enclosed by a top land 9 which adjoins the piston crown 6 and which is adjoined by an annular zone 10 intended to accommodate piston rings. To cool the upper piston part 1, an annular cooling channel 11 is provided in the area of the parting plane 4, which extends into the lower piston part and through which coolant, in particular lubricating oil of the internal combustion engine, circulates when the internal combustion engine is in operation. For this purpose, the cooling medium enters the cooling channel 11 via an inlet and leaves the cooling channel 11 via a plurality of connection channels 15, also known as transfer bores, via an outlet. The coolant supply can alternatively also take place via the center of the piston, that is to say the inner cooling space 16. The coolant is conducted into the cooling channel 11 via the connecting channels 15 and then flows out of the cooling channel 11 via drainage bores. The cooling channel 11 is connected to a plurality of recesses 12 distributed around the circumference and aligned in the direction of the piston head 6. These recesses 12, which are distributed around the circumference and are introduced in the manner of blind holes, are designed as channels, bores and / or slots and enlarge the cooling space in the piston upper part 1, which is acted upon by the coolant. To ensure sufficient rigidity of the piston crown 1, there are a transition area between the cooling channel 11 and the recesses 12 Web 13 is provided. Starting from the cooling channel 11, the recesses 12 widen conically up to a maximum at a recess bottom 14. The recesses 12 are connected to a central inner cooling chamber 16 positioned below the combustion bowl 7 via connecting channels 15 positioned on the circumference.

Figure 2 illustrates the geometric design of the recess 12 in an enlarged illustration. The recesses 12 distributed circumferentially in the upper piston part 1 can alternatively also be designed as cavities running around the periphery. Preferably, the recess 12 according to the exemplary embodiment is made in the piston upper part 1 subsequently during production by means of the forging process by means of mechanical three-dimensional machining. As an alternative to this, in the case of an upper piston part 1 produced by means of a casting process, it is advisable to mold the recess 12 into the upper piston part 1 by means of a casting mold body. To show largely matching wall thicknesses to the outer contours of the upper piston part 1, for example opposite the piston crown 6, the top land 9 and the bowl edge 8 of the combustion bowl 7, the recess 12 forms a stepped recess base 14. The dome-like recess base forming a bowl vault. 14 includes a double-rounded contour enclosing the radius "R". The depth of the recess base 14 located between the radii "R" in the recess 12 can be adjusted by the number of cuts. The inner wall 17, which is closer to the piston longitudinal axis 5 in the radial direction, and the outer wall 18, which is farther away from the piston longitudinal axis 5 in the radial direction, are to be closed to the recess 12, in particular to adapt to the structural design of the upper piston part 1 as well as almost identical wall thicknesses compared to the thermally heavily loaded zones the piston longitudinal axis 5 is inclined. The angle of inclination α of the inner wall 17 and the angle of inclination β of the outer wall 18, the inner wall 17 and the outer wall 18 being inclined opposite to one another, can be designed to be the same or different from one another.

In Figure 3 a further embodiment of an upper piston part 1 according to the invention is shown. The same components are given the same reference numbers and new components are given new reference numbers.

Figure 3 shows the top view of the upper piston part 1 of a two-part piston in the direction of the two joining webs 2, 3. The upper piston part 1 has several slot-shaped recesses 19, in the example five slot-shaped recesses 19, arranged tangentially around the piston longitudinal axis 5 according to Figure 3 on. The tangential rotation around the piston longitudinal axis 5 is also known under the term radial rotation around the piston longitudinal axis 5. Alternatively, it is possible that the piston upper part 1 has more than five or fewer than five slot-shaped recesses 19.

In Figure 3 For clarity, the inner cooling space 16 is also shown, around which the five slot-shaped recesses 19 are arranged distributed around the circumference. The slot-shaped recesses 19 are not connected to one another, so that a spacing in the form of webs 20 exists between the respective slot-shaped recesses 19.

In Figure 4 two cooling slots 21, 22 with shaft cooling are shown in an upper piston part 1 of a two-part piston, the two cooling slots 21, 22 being assigned to the recess 12 shown. It is possible to further reduce the trough diameter of the respective cooling slot 21, 22 or to introduce a step trough. On the one hand, the shaft cooling results in an enlargement of the cooling surface and a turbulence. In Figure 4 the inner cooling space 16 is also shown for the sake of clarity.

In Figure 5 two expanded cooling slots 21, 22 with a smoothed surface are shown, the two cooling slots 21, 22 being assigned to the illustrated recess 12. It is possible to make the trough diameter smaller or to edit the step trough, which is used to reduce emissions.

By varying the slot depth of the respective cooling slots 21, 22 of the recess 12, it is possible for the cooling space to be adapted to the bowl shape of the combustion bowl 7. The degree of smoothing is achieved by the number of slots between cooling slot 21 and cooling slot 22. In Figure 5 the inner cooling space 16 is also shown for the sake of clarity.

List of reference symbols

1

Piston top

2

Joining web

3

Joining web

4th

Level of separation

5

Piston longitudinal axis

6th

Piston crown

7th

Combustion bowl

8th

Trough edge

9

Top land

10

Ring field

11

Cooling duct

12

Recess

13

web

14th

Recess reason

15th

Connection channel

16

Inner fridge

17th

Inner wall

18th

Outer wall

19th

slot-shaped recess

20th

web

21st

Cooling slot

22nd

Cooling slot

Claims (16)

1. Piston of an internal combustion engine, designed as a liquid-cooled piston, composed of a piston lower part and of a piston upper part (1) which has a combustion chamber depression (7), which piston lower part and piston upper part are supported and joined together by means of joining webs (2, 3) which are radially spaced apart from one another and which form a parting plane (4), wherein, in the piston upper part (1), there is formed a ring-shaped cooling channel (11) which extends into the piston lower part and which is connected via connecting channels (15) to an internal cooling chamber (16) and which has recesses (12) which are oriented in the direction of a piston crown (6) and which are formed as blind holes and which form cooling chambers, characterized in that the recesses (12) are designed to conically widen proceeding from the cooling channel (11) to a recess base (14) of the respective recess (12).
2. Piston of an internal combustion engine, designed as a single-part liquid-cooled piston, having a piston lower part and a piston upper part (1) which has a combustion chamber depression (7), wherein, in the piston upper part (1), there is formed a ring-shaped cooling channel (11) which is connected via connecting channels (15) to an internal cooling chamber (16) and which has recesses (12) which are oriented in the direction of a piston crown (6) and which are designed as blind holes and which form cooling chambers, characterized in that the recesses (12) are designed to conically widen proceeding from the cooling channel (11) to a recess base (14) of the respective recess (12).
3. Piston according to Claim 1, characterized in that the piston upper part (1) and the piston lower part are joined together cohesively, preferably by means of a welded connection, or in frictionally locking fashion, preferably by means of a screw connection.
4. Piston according to any of Claims 1 to 3, characterized in that the recesses (12) which are formed in a circumferentially distributed manner in the piston upper part (1) and which are designed to rise in a conical shape are formed as bores, channels and/or slots.
5. Piston according to any of Claims 1 to 4, characterized in that webs (13, 20) formed from a material of the piston upper part (1) are provided between the recesses (12) and the cooling channel (11).
6. Piston according to any of Claims 1 to 5, characterized in that the recesses (12) formed in a circumferentially distributed manner in the piston upper part (1) form a honeycomb structure.
7. Piston according to any of Claims 1 to 6, characterized in that recesses (12) formed adjacently in the piston upper part (1) are arranged so as to be inclined alternately radially inwards or radially outwards.
8. Piston according to any of Claims 1 to 7, characterized in that the recesses (12) have oppositely inclined walls, in particular an inner wall (17) and an outer wall (18), the corresponding or mutually different angles of inclination "α, β" of which amount to between 0° to 40°.
9. Piston according to any of Claims 1 to 8, characterized in that the recesses (12) have a recess base (14) which is of rounded or bevelled form with a radius "R" between 1.5 mm and D/2.
10. Piston according to any of Claims 1 to 9, characterized in that the recesses (12) include a recess base (14) which is doubly rounded and/or rounded in a stepped manner.
11. Piston according to any of Claims 1 to 10, characterized in that the conically widened recesses (12) formed as a bore, channel or slot are integrated in a circumferentially symmetrical or asymmetrical manner in the piston upper part (1).
12. Method for producing a piston upper part (1) of a liquid-cooled piston of an internal combustion engine, which piston upper part is joined together with a piston lower part, wherein the piston upper part (1) has a combustion chamber depression (7) and a cooling channel (11) which is connected to recesses (12) which are oriented in the direction of a piston crown (6) and which are formed as blind holes, characterized in that, for the production of the recesses (12), the following steps are provided:

    - inserting a casting mould body which corresponds to the shape of the recess (12) and which is designed to conically widen proceeding from the cooling channel (11) to a recess base (14) of the respective recess (12) and which, prior to a casting process, is positioned in a casting mould designed for the piston upper part (1);

    - removing the casting mould body after casting has been performed, and cooling the piston upper part (12) by rinsing.
13. Method for producing a single-piece liquid-cooled piston of an internal combustion engine, having a piston upper part (1) and a piston lower part, wherein the piston upper part (1) has a combustion chamber depression (7) and a cooling channel (11) which is connected to recesses (12) which are oriented in the direction of a piston crown (6) and which are formed as blind holes, characterized in that, for the production of the recesses (12), the following steps are provided:

    - inserting a casting mould body which corresponds to the shape of the recess (12) and which is designed to conically widen proceeding from the cooling channel (11) to a recess base (14) of the respective recess (12) and which, prior to a casting process, is positioned in a casting mould designed for the piston upper part (1) of the single-piece piston;

    - removing the casting mould body after casting has been performed, and cooling the piston upper part (12) of the single-piece piston by rinsing.
14. Method for producing a piston upper part (1) of a liquid-cooled piston of an internal combustion engine, which piston upper part is joined together with a piston lower part, wherein the piston upper part (1) has a combustion chamber depression (7) and a cooling channel (11) which is connected to recesses (12) which are oriented in the direction of a piston crown (6) and which are formed as blind holes, characterized in that the production of the recesses (12) in the piston upper part (1) is performed by means of a mechanical, three-dimensional cutting machining process, such that the recesses (12) are designed to conically widen proceeding from the cooling channel (11) to a recess base (14) of the respective recess (12).
15. Method according to Claim 14, characterized in that the piston upper part (1) is, prior to the formation of the recesses (12), produced by means of a deformation process, preferably by means of a forging process.
16. Method according to Claim 12, 14 or 15, characterized in that the piston upper part (1) and the piston lower part are joined together cohesively, preferably by means of a welded connection, or in frictionally locking fashion, preferably by means of a screw connection.

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