EP2188513A1

EP2188513A1 - Two-piece piston for an internal combustion engine

Info

Publication number: EP2188513A1
Application number: EP08801217A
Authority: EP
Inventors: Jochen Kortas; Timo Estrum; Dieter Messmer
Original assignee: Mahle International GmbH
Current assignee: Mahle International GmbH
Priority date: 2007-09-15
Filing date: 2008-08-23
Publication date: 2010-05-26
Anticipated expiration: 2028-08-23
Also published as: JP5295245B2; CN101802381B; KR101484352B1; US8225765B2; WO2009033446A1; KR20100069646A; EP2188513B1; JP2010539369A; CN101802381A; DE102007044106A1; US20100307445A1

Abstract

The invention relates to a two-piece piston (1) for an internal combustion engine, comprising a piston base body (2) and a ring element (3), which is soldered to the piston base body (2) by an upper solder connection (23) having the length b, which is disposed on the radial inside of a piston crown (4) formed at least partially by the ring element (3), and by a lower solder connection (24) having the length c, which is disposed radially outside on the top of a center part (9). In order to improve the strength of the solder connections (23) and (24) due to pressure and temperature-related deformations of the upper piston part, the ring element (3) has a peripheral, upper, thinner wall region (49) in the region of the piston crown (4) radially outside the upper solder connection (23) and further a peripheral, lower, thinner wall region (50) between the ring section (5) and the lower solder connection (24), wherein the thickness a and b of the thinner wall regions (49) and (50) has a lower value than the length b and c of the solder connections (23) and (24).

Description

Two-piece piston for an internal combustion engine

The invention relates to a two-part piston for an internal combustion engine according to the preamble of claim 1.

From the published patent application DE-OS 24 34 902 a multi-part piston for an internal combustion engine is known which has a base body, on the underside of two pin bosses are formed. On the underside of the body is connected to a piston skirt and on the top radially outward with a ring member. It is also known from the above DE-OS, for joining the main body to the piston skirt and to the ring element, to use a brazing process, i.e., a brazing process. In this case, the ring element has a first solder joint on the radial inner side of the part of the piston crown formed by the ring element. Since both the part of the piston crown formed by the main body and by the ring element are very thin-walled, there is the disadvantage that the solder joint also has a very small axial length and thus a very low strength.

On the side facing away from the piston crown, the ring element is also connected to the base body via a relatively long, lower solder joint seen in the radial direction. If in this case the piston crown due to a pressure load due to the taking place in the combustion chamber cavity, explosive combustion of the fuel-air mixture and because of prevailing in the region of the piston crown, very high temperatures in the radial direction partly pressure and partly due to temperature expands, the ring element widened funnel-shaped, and the lower solder joint is subjected to a large tensile load. The known from the prior art piston has the disadvantage that in the area of the lower solder joint no constructive measures are provided to reduce this tensile load on the lower solder joint. To avoid these disadvantages of the prior art is an object of the invention. This problem is solved with the features in the characterizing part of the main claim. Advantageous embodiments of the invention are the subject of the dependent claims.

Here, in a funnel-shaped widening of the ring element near the solder joints arranged, dilute, circumferential wall portions are hingedly deformed, which brings a significant reduction in the force acting on the braze joints in engine operation tension with it.

Some embodiments of the invention will be described below with reference to FIG

Drawings described. Show it

1 is an exploded view of the piston according to the invention, consisting of a piston body and a ring member,

2 is a perspective view of the piston according to the invention after its assembly,

3 shows a section through the piston along the piston axis and the line III-III in Fig. 2,

4 shows a partial section through the piston in the region of the cooling channel to illustrate an embodiment of the solder joints,

5 shows a partial section through the piston in the region of the cooling channel to illustrate a further embodiment of the solder joints and

6 shows a partial section through the piston blank in the region of the cooling channel.

FIG. 1 shows an exploded view of a piston 1, which consists of a piston base body 2 and a ring element 3. The piston base body 2 and the ring element 3 are made of AFP steel, ie, of a microalloyed, precipitation-hardening, ferritic-pearlitic manganese-vanadium-based steel according to DIN EN 10267. The piston main body 2 and the ring element 3 are used in the context of Assembly of the piston 1 soldered together.

The ring member 3 forms the essential part of the annular piston crown 4 and has on its radial outer side a ring portion 5 to Recording in the figure not shown piston rings. In the ring member 3 is centrally and rotationally symmetrical to the piston axis 6, a round opening 7 is introduced, which is bounded near the piston head 4 by a first, cylindrical surface 8, which serves as a soldering surface during assembly of the piston 1.

The piston main body 2 consists of a substantially plate-shaped and round center part 9, on its underside facing away from the piston bottom 4, two opposing shaft elements 10 and two opposing and this shaft elements 10 interconnecting pin bosses 11 are formed. The radially outer end faces 12 of the pin bosses 11 are set back relative to the radially outer boundary 13 of the middle part 9 in the direction of the piston axis 6.

In the upper side of the middle part 9, a peripheral, channel-shaped recess 14 is formed radially outwardly, surrounded by a circumferential inner annular rib 15 arranged radially on the upper side of the middle part 9, the interior of which forms the combustion recess 16 of the piston 1.

In the present embodiment of the piston 1, the annular rib 15 and the combustion bowl 16 are not rotationally symmetrical to the piston axis 6, but have radially outward a dent 17 whose purpose is to improve the combustion of the fuel-air mixture in the combustion bowl 16.

The piston crown side, the boundary of the annular rib 15 is circular, so that a part of the piston head 4 ^{1 is} formed thereof. Of this, a radially outer, second cylindrical surface 18 is also formed, which also serves as a counterpart to the first surface 8 of the ring member 3 as a soldering surface and the surface 8 an upper solder joint (23, see Fig. 3) between the ring member 3 and the Piston body 2 forms.

Radially outward, the center part 9 on its upper side an annular, third surface 19, which serves as a soldering surface and with a not shown in Fig. 1, on - A -

the lower end face of the ring member 3, fourth and also serving as a soldering surface 20 forms a lower solder joint between the ring member 3 and the piston body 2. (See also Fig. 3.)

If the ring element 3 is placed on the piston base body 2 and soldered therewith, the piston 1 shown in FIG. 2 results, which reveals the piston crown 4, 4 ', the combustion bowl 16, the ring section 5, a shaft element 10 and a pin boss 11.

The section shown in Fig. 3 by the piston along the piston axis 6 and the line IH-III in Fig. 2 shows a radially outside of the ring member 3, radially inwardly of the annular rib 15 and below of the recess 14 of the central part 9 of the piston main body second limited, annular, cooling channel 21, not shown in the figure and opening into the piston interior 22 Ölzuführ- and Ölabführkanä- Ie. Shown are also formed by the first and second surfaces 8 and 18, axially aligned, upper solder joint 23 and formed by the third and fourth surfaces 19 and 20, radially oriented, lower solder joint 24 between the piston body 2 and the ring member third

The first surface 8 in this case represents the radially inner boundary of the piston crown 4 forming deck portion 25 of the ring member 3, wherein in the piston bottom side facing away from the deck area 25 an upwardly directed, circumferential recess 26 is formed, here a peripheral, upper, diluted wall portion 49 forms. Here, the ratio between the length b of the upper solder joint 23 and the minimum thickness a of the upper thinned wall portion 49 is between 1 and 3, that is, 1 <b / a <3.

On the piston crown side adjoins the fourth surface 20, which forms the lower end face of the ring element 3, another, formed in the radial inner side of the ring member 3 and directed radially outward, circumferential recess 27, here a lower, circumferential, thinned wall portion 50th wherein the ratio between the length c of the lower solder joint 24 and the minimum thickness d of the lower, thinned wall portion 50 is also between 1 and 3, ie, 1 <c / d <3. The recess 27 is disposed between the ring portion 5 and the lower solder joint 24.

At a temperature and / or pressure load of the piston 1, 1 ', 1 "results, as shown in Fig. 5 is enlarged to illustrate the facts, a widening 28 of the upper part of the piston 1, 1', 1". The tensile load acting on the solder joints 23, 24, 24 'in this case is deformed by the thinned and thus elastically yielding regions of the ring element 3, 3', which are formed by the recesses 26 and 27, and which hinge at the widening 28 of the upper piston part in that reduced, that the solder joints 23, 24, 24 'hold even after prolonged engine operation.

4, an embodiment of the piston V in the region of the cooling channel 21 'is shown, in which the upper deck area 25' of the ring element 3 "in the region of the upper, thinned wall portion 49 extends radially inwards only up to the area of the smallest wall thickness a and Here, a radially inner, cylindrical surface 31 forms, which forms an upper solder joint 32 with a radially outer, cylindrical surface 29 of a piston crown side integrally formed on the annular rib 15, circumferential and radially outwardly directed collar 30.

On the side facing away from the piston crown, the surface 29 is delimited by a step-shaped circumferential molding 34 on which the radially inner end of the cover region 25 'rests.

The piston bottom facing away from end face 20 'of the ring member 3 "has in the embodiment of FIG. 4 radially inside a circumferential, stepped recess 35 which is dimensioned so that they on a piston bottom side on the radially outer boundary 13' of the central part 9 'integrally formed, circumferential Collar 36 fits, so that upon assembly of the piston 1 ', the ring member 3 "is pushed onto the collar 36 until the collar 36 is seated in the recess 35, and the cover portion 25' of the ring member 3" comes to rest on the Anformung 34. An lower solder joint 33 is in the region of the end face facing away from the piston crown. side 20 'of the ring element 3 "formed by the piston bottom side end face 51 of the collar 36 and the shaft-side inner surface 52 of the recess 35.

This ensures that the ring member 3 "when sliding on the piston body 2 'is not only guided and centered over the surfaces 29 and 31 of the upper solder joint 32, but that in the assembly of the piston 1' an additional guide and centering of the ring element. 3 is achieved via the recess 35 and the collar 36 of the lower solder joint 33.

Instead of a single, radially inwardly disposed recess 27 according to the embodiment shown in FIGS. 3 and 5 of the piston 1, 1 ", the embodiment of the piston 1 ^{1 shown in} FIG. 4 above the lower solder joint 33 on both the inside and on the Outside of the ring member 3 "per a circumferential recess 47 and 48, which here create a lower, thinned wall portion 50 'with the thickness d, which deforms at a widening 28 of the piston upper part (as shown in FIG. 5) hinge-like and thus hereby resulting tensile load on the lower solder joint 33 is reduced. The recesses 47 and 48 are arranged between the lower solder joint 33 and the ring portion 5. .

Fig. 5 shows an embodiment of the piston 1 ", in which the solder joint 24 'of the conically tapering down, lower end face 37 of the ring member 3 ¹ and the conically tapered down surface 38 is formed, wherein the surface 38th the radially outer region of the central part 9 "limited piston bottom side. As a result, an enlargement of the surfaces 37 and 38 and thus an enlargement of the lower, tapered downwardly tapered solder joint 24 'is achieved with the length c, which leads to a further improvement in the strength of the lower solder joint 24'.

The piston 1 according to the invention is produced by first forging a blank 39 for the piston main body 2 and a blank 40 for the ring element 3, as shown in FIG. 6, in which the two blanks 39 and 40 are hatched, and in FIG the piston 1 ultimately produced from this is shown in dashed lines within the hatched area. The ring member 3 can also be made by the method of rolling or drawing. Here, the piston bottom side, radially inner edge of the blank 40 with a chamfer 41 and the piston bottom side, radially outer edge of the blank 39 are provided with a chamfer 42, which, as shown in FIG. 6, a wedge-shaped, circumferential recess 43 result, if the two blanks 39 and 40 are composed.

Furthermore, as part of the forging of the blank 39 to the radially outer, piston bottom side edge of the third surface 19, a circumferential, in section at least approximately rectangular projection 44 is integrally formed. Both the recess 43 and the projection 44 have in the context of the joining of the two blanks by means of the Lot explained below in more detail purpose.

Subsequently, in the radially outer surface of the annular rib 15 of the blank 39 and in the surface of the central part 9, the rotationally symmetrical contours shown in particular in Fig. 1 are screwed, wherein the recess 14 is made. The indentation 17 shown in FIG. 1 is milled into the radial outer side of the annular rib 15. By turning then the rotationally symmetrical contours of the radial inner surface 45 of the ring member 3 and in particular the recesses 26, 27, 47, 48 are made.

Following this, the two blanks 39 and 40 are soldered together. In this case, it is first necessary to assemble the blanks 39 and 40 in such a way that, between the surfaces 8 and 18 and between the surfaces 19 and 20, a gap results which is between 10 μm and 200 μm wide. When assembling the blanks 39 and 40, a gap having this width is already achieved in that both the surfaces 8 and 18 and the surface 19 and 20 are brought into contact with each other without positive engagement.

The recess 43 and the piston bottom side surface of the projection 44 are then coated with a nickel-based solder paste, after which the two blanks 39, 40 including solder paste to 1150 ⁰ C are heated. The solder paste liquefies here and penetrates due to the capillary effect between the surfaces 8 and 18 and the surfaces 19 and 20, wherein the liquefied solder enforces a gap with the above dimensions between the surfaces 8 and 18 and between the surfaces 19 and 20 due to the capillary action. As a result, the surfaces 8, 18, 19 and 20 are completely wetted. As part of the targeted cooling of the piston 1, the solder paste solidifies and results in a defect-free solder joint between the two partially processed blanks 39 and 40.

4, the gap between the surfaces 29 and 31 of the upper solder joint 32 of 10 μm to 200 μm, which gap is sufficient for an error-free solder joint, is achieved by the surfaces 29 and 31 being produced in the design of the piston body 2 'and the ring element 3 " be processed by means of a fine turning process to the extent that the gap between the two surfaces 29 and 31 has the dimensions given above of 10 .mu.m to 200 .mu.m, after the collar 36 is fixed in the recess 35 with close play.

The molding 34, on which the cover area 25 'of the ring element 3 "comes to rest during assembly of the piston 1 ¹ , ensures that the piston bottom-side end face 51 of the collar 36 and the shaft-side inner surface 52 of the recess 35 after the piston assembly have a distance of 10 .mu.m to 200 .mu.m from each other, so that here too results in a sufficiently wide gap for a defect-free solder joint.

In the embodiment of the piston base body 2 "and of the ring element 3 'according to FIG. 5, a gap with a constant width of 10 μm to 200 μm between the surfaces 8 and 18 results for a secure upper solder joint 23 in that after a corresponding fine working the surfaces 8 and 18, the ring member 3 ¹ via the conically oriented, lower end face 37 is placed on the conically shaped, radially outer, piston bottom end face 38 of the piston body 2 ", wherein the ring member 3 'alone by the taper of the two surfaces 37 and 38 is aligned symmetrically to the piston axis. The effect of the capillary effect is that the liquefied liquefied solder in the Gap between the surfaces 37 and 28 penetrates to securely solder these surfaces together.

The application of the soldering method for connecting the two piston parts has the advantage that the soldering temperature of 1150 ⁰ C, to which the piston is heated in this case, equal to the forging temperature, with which the two blanks 39 and 40 are forged so that when cooling targeted can be adjusted for the AFP steel typical material properties.

Thereafter, the piston 1 is completed by the dashed lines in Fig. 6, rotationally symmetrical outer contours of the piston 1 by turning and also drawn dashed, non-rotationally symmetric boundary surfaces 46 of the combustion bowl 16 are made by milling. In this case it is also possible to weld the piston base body 2, 2 ', 2 "and the ring element 3, 3', 3" together.

LIST OF REFERENCE NUMBERS

a thickness of the upper, thinned wall portion 49 b length of the upper solder joint

C length of the lower solder joint d thickness of the lower, thinned wall portion 50, 50

1, 1 ", 1" piston

2, 2 \ 2 "piston body

3, 3 \ 3 "ring element

4, 4 'piston crown

5 ring game

6 piston axis

7 opening

8 first area

9, 9 \ 9 "midsection

10 shaft element

11 pin hub

12 end face of the pin boss 11

13, 13 ¹ Limitation of the middle part 9

14 recess

15 ring rib

16 combustion bowl

17 Dentation

18 second area

19 third area

20, 20 'fourth surface

21, 21 'cooling channel

22 piston interior

23 upper solder joint

24, 24 'lower solder joint

25, 25 "deck area

26, 27 recess

28 expansion Surface collar surface upper solder joint lower solder joint Anformung recess collar surface, lower end face of the ring element 3 'surface, face blank for the piston body 2 blank for the ring member 3, 42 chamfer recess projection inner surface of the ring member 3 boundary surface of the combustion recess 16, 48 recess upper, thinner Wall area, 50 'lower, thinned wall area piston-bottom-side end face of the collar 36 shank-side inner surface of the recess 35th

Claims

claims

1. Two-piece piston (1, 1 ', 1 ") for an internal combustion engine,

consisting of a piston main body (2, 2 ', 2 ") and a ring element (3, 3 \ 3"),

- wherein the piston base body (2, 2 \ 2 ") has a round substantially plate-shaped center part (9, 9 \ 9") whose radial diameter is at least approximately identical to the radial diameter of the piston (1, V, 1 ")

- Wherein on the underside of the central part (9, 9 ', 9 ") are formed two opposing shaft elements (10) and two opposing and the shaft elements (10) interconnecting pin bosses (11), and

- Wherein on the upper side of the central part (9, 9 \ 9 ") a circumferential, with respect to the radially outer edge of the central part (9, 9 \ 9") in the direction of the piston axis (6) recessed annular rib (15) is formed, which is the radial outer boundary of a combustion bowl (16) forms,

- Wherein the ring element (3, 3 \ 3 ") on its radial outer surface has a ring portion (5), and

- wherein the ring element (3, 3 ', 3 ") via an upper solder joint (23, 32) with the length b, on the radially inner side of a ring element (3, 3', 3") at least partially formed piston crown (4th ) is arranged, and via a lower solder joint (24, 24 ', 33) with the length c, which is arranged radially outwardly on the upper side of the central part (9, 9', 9 "), with the piston main body (2, 2 ¹ , 2 ") is soldered, characterized in that the ring element (3, 3 ', 3") on the one hand in the region of the piston head (4) radially outside the upper solder joint (23, 32) has a circumferential, upper, thinned wall portion (49 ) and on the other between the ring portion (5) and the lower solder joint (24, 24 ', 33) has a circumferential, lower, thinned wall portion (50, 50'), wherein the thickness (a, d) of the thinned wall portions (49 , 50, 50 ') has a lower value than the length (b, c) of the solder joints (23, 24, 24 ", 32, 33).

Second piston (1, 1 ¹ , 1 ") according to claim 1, characterized in that the ratio between the length b of the upper solder joint (23, 32) and the thickness a of the upper, thinned wall portion (49) is greater than 1 and smaller 3, so that 1 <b / a <3.

3. piston (1, 1 ', 1 ") according to claim 1 or 2, characterized in that the ratio between the length c of the lower solder joint (24, 24', 33) and the thickness d of the lower, thinned wall portion (50 , 50 ') is greater than 1 and small is 3, so that 1 <c / d <3.

4. Piston (1, 1 ') according to one of the preceding claims, characterized in that the ring element (3, 3 ¹ ) has a piston bottom (4) partially forming ceiling region (25), wherein in the piston bottom side facing away from the ceiling region (25 ) is formed an upwardly directed, circumferential recess (26) which forms the upper, thinned wall portion (49).

5. Piston (1, 1 ') according to any one of the preceding claims, characterized in that between the lower solder joint (24, 24') and the ring portion (5) in the radial inner side of the ring element (3, 3 ') a radially outwardly directed, circumferential recess (27) is formed, which forms the lower thinned wall portion (50).

6. piston (1 ') according to one of claims 1 to 4, characterized in that between the lower solder joint (33) and the ring portion (5) in the radial inner side of the ring element (3 ") a circumferential, radially outwardly directed recess (47) and in the radial outer side of the ring element (3 ") a circumferential, radially inwardly directed recess (48) are formed, and that the two recesses (47, 48) face each other and the lower thinned wall portion (50 ') form ,

7. piston (1 '') according to any one of the preceding claims, characterized in that the lower solder joint (24 ¹ ) of a conically Tapered, lower end face (37) of the ring element (3 ') and of a conically also downwardly tapering and the radially outer region of the central part (9 ") piston bottom side defining surface (38) is formed.