EP3004610A1

EP3004610A1 - Piston for an internal combustion engine

Info

Publication number: EP3004610A1
Application number: EP14753001.8A
Authority: EP
Inventors: Rainer Scharp; Peter Kemnitz
Original assignee: Mahle International GmbH
Current assignee: Mahle International GmbH
Priority date: 2013-05-31
Filing date: 2014-05-28
Publication date: 2016-04-13
Also published as: WO2014190963A1; CN105283655A; JP2016520175A; CN105283655B; US20160115901A1; BR112015029824A2; DE102013009161A1; US9869269B2

Abstract

The invention relates to a piston (10, 110, 210, 310, 410) for an internal combustion engine, comprising a piston crown (11) and a piston skirt (21), said piston crown (11) comprising a piston head (12), a peripheral top land (14), a peripheral annular zone (15) with annular grooves (16, 17, 18) and in the region of the annular zone (15), a peripheral cooling channel (19) which is open towards the base and which is closed by means of a closure element. Said cooling channel (19) has a cooling channel base (26) and a cooling channel cover (27). According to the invention, said closure element (35, 135, 235, 335, 435) is arranged in such a manner in the piston crown (11) that the cooling channel base (26) is arranged above the lowest annular groove (18).

Description

Piston for an internal combustion engine

The present invention relates to a piston for an internal combustion engine, with a piston head and a piston skirt, wherein the piston head has a piston crown, a circumferential land land, a circumferential ring section with annular grooves and in the region of the ring part a circumferential, downwardly open, closed with a closure element cooling channel wherein the cooling channel has a cooling channel bottom and a cooling channel cover.

In modern internal combustion engines, the pistons in the region of the piston crown and the combustion bowl are exposed to ever higher temperature loads. Inadequate heat dissipation from the piston head results in malfunction of the piston during engine operation, in particular coking or carbon formation on the piston. This is especially true for pistons made of steel materials, since steel has a low coefficient of thermal conductivity and thus is a poor conductor of heat.

The object of the present invention is to further develop a generic piston so that an optimized heat dissipation takes place from the piston head during engine operation.

The solution is that the closure element is arranged in the piston head such that the cooling channel bottom is arranged above the lowermost annular groove.

In the prior art, the cooling channel in the axial direction usually extends to the level of the lowest annular groove and below, in order to achieve with the aid of the largest possible cooling channel sufficient cooling, especially of steel pistons in engine operation. Due to the shaker effect, the cooling oil moves between the cooling duct ceiling, i. a very hot area, and the cooling channel bottom, i. a comparatively cool area, back and forth. Due to the significantly lower temperatures in the area of the cooling channel bottom, there is virtually no heat

| Confirmation copy | Meaufnahme from the piston head into the cooling oil more instead. Furthermore, due to the low thermal gradient in the direction of the ring section and piston shaft, only a comparatively small heat dissipation from the cooling oil takes place.

The piston according to the invention is distinguished by the fact that the cooling channel is shortened in the axial direction compared to the prior art. This has the consequence that the cooling oil in particular in the region of the cooling channel bottom in greater proximity to the highly heat-loaded cooling channel bottom and thus moves in total in hotter areas than is the case in the prior art. Therefore, in each phase of the piston movement takes place heat absorption from the hot areas of the piston head into the cooling oil. In particular, if the amount of cooling oil known from the prior art is maintained and the cooling oil supply is set up so that the cooling oil is rapidly exchanged during engine operation, a significantly improved cooling of the piston head results in comparison with the prior art.

Advantageous developments emerge from the subclaims.

The cooling channel bottom is preferably arranged at the level of the second annular groove, particularly preferably between the first annular groove and the second annular groove, in order to further increase the cooling capacity by moving the cooling oil even closer to the hot piston bottom during engine operation.

An advantageous development provides that the closure element is arranged in the piston head such that a circumferential annular gap is formed in the piston crown. This eliminates the need to provide oil drain holes.

A further preferred embodiment provides that the height of the top land is at most 9% of the nominal diameter of the piston head. This causes a particularly advantageous for heat dissipation positioning of the cooling channel with respect to the piston crown and the ring section. In this case, the distance between the piston crown and the bottom of the cooling channel can be between 11% and 17% of the nominal diameter of the piston head. In addition or instead, the height of the cooling channel can be 0.8 times to 1, 7 times its width. Furthermore, alternatively or cumulatively, the distance between the piston head and the cooling channel ceiling can be between 3% and 7% of the nominal diameter of the piston head. These design rules allow an optimized design and positioning of the cooling channel for all piston sizes.

The compression height may, for example, be between 38% and 45% of the nominal diameter of the piston head.

Another particularly preferred embodiment is that a combustion bowl is formed in the piston head and that the smallest wall thickness in the radial direction between the combustion bowl and the cooling channel is between 2.5% and 4.5% of the nominal diameter of the piston head. Thus, an improved heat transfer between the combustion bowl and the cooling channel is achieved.

The combustion bowl may, for example, be provided with an undercut in order to determine the wall thickness between the combustion bowl and the cooling channel.

The closure element may be formed with decoupled piston shaft as a separate component which is fixed to the piston.

The piston according to the invention may be formed as a one-piece piston. Then, the cooling channel is introduced in a conventional manner by machining in a cast or forged blank. However, it is preferred that the piston is composed of at least two non-detachably interconnected components. In particular, the piston according to the invention may have a piston main body and a piston ring element. In this case, the closure element may be formed both as a separate component fastened to the piston and as a component integrally connected to the piston. In the latter case the closure element can be integrally connected either to the piston main body or to the piston ring element.

The present invention is particularly suitable for pistons of at least one steel material.

Embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. In a schematic, not to scale representation:

Figure 1 shows a first embodiment of a piston according to the invention in

Cut;

FIG. 2 shows the piston according to FIG. 1 in a representation rotated by 90 °;

Figure 3 shows another embodiment of a piston according to the invention in

Cut;

FIG. 4 shows the piston according to FIG. 3 in a representation rotated by 90 °;

Figure 5 is an overall view of two further embodiments in section;

Figure 6 is an enlarged partial view of the piston of Figure 5, left side, in section;

Figure 7 is an enlarged partial view of another embodiment in the

Cut;

Figure 8 is an enlarged partial view of the embodiment of Figure 7;

Figures a schematic representation of the cooling oil movement in a piston 9 a, 9 b according to the present invention; Figures a schematic representation of the cooling oil movement in a piston 10 a, 10 b according to the prior art.

FIGS. 1 and 2 show a first exemplary embodiment of a piston 10 according to the invention. As is known in principle, the piston 10 can be forged or cast as a one-piece blank, wherein the cooling channel is introduced into the blank by machining. In the exemplary embodiment, the piston 10 is composed of a piston main body 31 and a piston ring member 32, which may be cast or forged in a conventional manner and which are connected to each other via a weld 33, for example by electron beam welding or laser welding. The weld 33 is arranged in the embodiment at the lowest point of the combustion bowl at an acute angle to the piston center axis A. The piston 10 is made in the embodiment of a steel material.

The piston 10 has a piston head 11 with a combustion bowl 13 having a piston head 12, a peripheral land 14 and a revolving ring portion 15 with annular grooves 16, 17, 18 for receiving piston rings (not shown). In height of the ring section 15, a circumferential cooling channel 19 is provided.

The piston 10 further includes a piston stem 21 thermally decoupled from the piston head 11 with piston bosses 22 and hub bores 23 for receiving a piston pin (not shown). The piston bosses 22 are connected via hub connections 24 to the underside of the piston head 11. The piston hubs 22 are connected to each other via running surfaces 25.

The cooling channel 19 is open at the bottom and closed with a separate closure element 35, in the exemplary embodiment a closure plate. The closure element 35 is fixed in a conventional manner below the ring portion 15 on the piston head 11 and extends in the direction of the combustion bowl 13 such that the annular free end of the closure element 35 together forms a circumferential annular gap 36 with the outer wall of the combustion bowl 13.

Of course, can be dispensed with the annular gap 36. Instead, in a conventional manner, the cooling channel 19 may be completely closed by the closure element 35, wherein in the closure element 35 inlet and outlet openings are provided for cooling oil.

The closure element 35 is bent in the direction of the piston head 12 such that a cooling channel bottom 26 is formed, which in the exemplary embodiment lies approximately at the level of the second annular groove 17. The cooling channel bottom 26 may also be arranged between the first annular groove 16 and the second annular groove 17.

The cooling channel 19 also has a cooling channel cover 27.

The compression height KH is in the embodiment between 38% and 45% of the nominal diameter DN of the piston head eleventh

Figures 3 and 4 show a further embodiment of a piston 110 according to the invention. The piston 110 is constructed in a similar manner as the piston 10 according to Figures 1 and 2. Therefore, matching structural elements are provided with the same reference numerals, and it is in this respect to the description refer to Figures 1 and 2.

The essential difference between the piston according to FIGS. 3 and 4 and the piston according to FIGS. 1 and 2 is that the inner surfaces 128 of the running surfaces 25 of the piston 110 are connected to the underside of the piston head 11 via a connecting wall 129.

FIG. 5 shows in an illustration according to FIG. 2 an overall view of second further exemplary embodiments of pistons 210, 310 according to the invention. The representations of the respective exemplary embodiments are separated by the center line M. The pistons 210, 310 are constructed in a similar manner as the piston 10 according to Figures 1 and 2. Therefore, matching structural elements are provided with the same reference numerals, and reference is made in this regard to the description of Figures 1 and 2.

The essential differences exist on the one hand in the design of the piston main body 231, 331 and the piston ring element 132, 332 and on the other hand in that the pistons 210, 310 have a differently designed closure element 235, 335 in relation to the piston 10 according to FIGS ,

Both embodiments each have a closure element 235, 335 in the form of an integral with the piston body 231, 331 connected peripheral flange. Each closure element 235, 335 extends in the direction of the ring portion 15 such that the free end of each closure element 235, 335 together with the inner wall of the ring portion 15 forms a circumferential annular gap 236, 336.

The piston 210 (illustration on the right of the center line M) consists of a piston main body 231 and a piston ring element 232. The piston ring element 232 comprises in the exemplary embodiment a part of the well wall and the well edge of the combustion bowl 13 and the piston head 12, the top land 14 and the ring section 15. The piston ring element 232 may in particular be connected to the piston main body 131 by a welding process, for example electron beam welding, laser welding or friction welding, wherein the weld seam 233 is arranged in the recess wall of the combustion bowl 13.

The piston 310 (illustration left of the center line M) (see also the enlarged partial view in Figure 6) consists of a piston body 331 and a piston ring member 332. The piston ring member 332 includes in the embodiment of a portion of the piston crown 12, the top land 14 and the ring section 15th In particular, the piston ring element 332 can be connected to the piston main body 331 by a welding process, for example electron beam welding or laser welding, wherein the weld seam 333 is arranged in the piston crown. Figure 7 shows an enlarged partial view of another embodiment of a piston 410. The piston 410 is constructed in a similar manner as the piston 210 of Figure 5, right side. Therefore, matching structural elements are provided with the same reference numerals, and reference is made in this regard to the description of Figure 5.

The essential difference is that the closure element 435 is designed in the form of a circumferential flange connected in one piece with the piston ring element 432. The closure element 435 extends in the direction of the combustion bowl 13 such that the free end of the closure element 435 forms a circumferential annular gap 436 together with the outer wall of the combustion bowl 13.

The piston 410 likewise consists of a piston main body 431 and a piston ring element 432. The piston ring element 432 comprises in the exemplary embodiment a part of the well wall and the well edge of the combustion bowl 13 and the piston crown 12, the top land 14 and the ring section 15. The piston ring element 432 is in the exemplary embodiment be connected by friction welding to the piston body 431, wherein the weld 433 is disposed in the in the trough wall of the combustion bowl 13.

Figure 8 shows an example in an enlarged partial view of the cooling channel 19 with cooling channel bottom 26 and cooling duct ceiling 27 and the piston crown 12, a portion of the combustion bowl 13 the top land 14, the ring section 15 with the annular grooves 16, 17, 18 and the closure element 435 of the piston 410 according to the invention according to FIG. 7.

The combustion bowl 13 is provided with an undercut 29 to determine the wall thickness between the combustion bowl 13 and the cooling channel 19 (see below).

It is preferred that the height h of the top land 14 is at most 9% of the nominal diameter DN of the piston head 11 (see FIGS. 1 and 2). This will be a for the heat dissipation particularly advantageous positioning of the cooling channel 19 with respect to the piston head 12 and the ring portion 15 causes.

On the basis of this dimensioning rule for the land 14, it is preferred that the distance a between the piston head 12 and the cooling channel bottom 26 is between 11% and 17% of the nominal diameter DN of the piston head 11 (see FIGS. 1 and 2). Thus, the cooling channel 19 is positioned in optimum proximity to the hot piston bottom 12 and in an optimal position relative to the cooler annular grooves 16, 17, 18.

Moreover, it is preferable that the height c of the cooling passage 19 is 0.8 times to 1.7 times its width d. This design rule causes an optimal volume of the cooling channel 19 and an optimal orientation relative to the hot combustion bowl 13, in particular to the bowl rim, and the hot piston bottom 12 and the cooler annular grooves 16, 17, 18th

Finally, it is preferred that the distance b between the piston head 12 and the cooling channel cover 27 is between 3% and 7% of the nominal diameter DN of the piston head 11 (compare FIGS. 1 and 2). This design rule also causes optimal positioning of the cooling channel 19 with respect to the hot piston bottom 12.

Finally, it is preferred that the smallest wall thickness w in the radial direction between the combustion bowl 13 and the cooling channel 19 is between 2.5% and 4.5% of the nominal diameter DN of the piston head 11. For an improved heat transfer between the combustion bowl 13 and the cooling channel 19 is achieved.

FIGS. 9a and 9b and 10a and 10b schematically show the cooling oil movement during engine operation and the temperature zones in the region of the combustion bowl, the piston head, the cooling channel and the annular grooves both for a piston according to the invention (FIGS. 9a and 9b) and for a piston according to the prior art the technique (Figures 10a and 10b). In Figures 9a, 9b, 10a, 10b schematically three heat zones, namely "hot", "warm" and "cool" are designated to illustrate the relative temperature differences in the individual piston areas.

According to the present invention (Figures 9a and 9b), the cooling channel is compared to the prior art in the axial direction is shortened. As a result, the cooling oil moves almost exclusively along the "hot" regions of the piston crown and the combustion bowl, so that heat absorption from the "hot" regions of the piston head into the cooling oil takes place in each phase of the piston movement. The known from the prior art amount of cooling oil should be maintained and the engine management be set up so that the cooling oil is quickly replaced during engine operation.

In the prior art (Figures 10a and 10b), the cooling channel in the axial direction usually extends to the level of the lowest annular groove and below, in order to achieve by means of the largest possible cooling channel sufficient cooling during engine operation. Due to the shaker effect, the cooling oil moves between a "hot" area, namely the piston crown and the bowl rim of the combustion bowl and a "cool" area, namely the cooling channel bottom. Due to the significantly lower temperatures in the region of the cooling channel bottom, practically no heat absorption from the piston head into the cooling oil takes place there.

As a result, the piston according to the invention has a significantly improved cooling of the piston head compared to the prior art.

Claims

claims

A piston (10, 110, 210, 310, 410) for an internal combustion engine, comprising a piston head (11) and a piston shaft (21), the piston head (11) having a piston crown (12), a peripheral land (14), a circumferential ring part (15) with annular grooves (16, 17, 18) and in the region of the ring part (15) has a circumferential, downwardly open, closed with a closure element cooling channel (19), wherein the cooling channel (19) has a cooling channel bottom (26 ) and a cooling channel cover (27), characterized in that the closure element (35, 135, 2235, 335, 435) is arranged in the piston head (11), that the cooling channel bottom (26) above the lowermost annular groove (18) is arranged ,

2. Piston according to claim 1, characterized in that the cooling channel bottom (26) in the amount of the second annular groove (17) is arranged.

3. Piston according to claim 1, characterized in that the cooling channel bottom (26) between the first annular groove (16) and the second annular groove (17) is arranged.

4. Piston according to claim 1, characterized in that the closure element (35, 135, 235, 335, 435) is arranged in such a manner in the piston head (11), that a circumferential annular gap (36, 136, 236, 336, 436) in the cooling channel bottom (26) is formed.

5. Piston according to claim 1, characterized in that the height (h) of the top land (14) is at most 9% of the nominal diameter (DN) of the piston head (11).

6. Piston according to claim 5, characterized in that the distance (a) between the piston head (12) and the cooling channel bottom (26) between 11% and 17% of the nominal diameter (DN) of the piston head (11).

7. Piston according to claim 5, characterized in that the height (c) of the cooling channel (19) is 0.8 times to 1, 7 times its width (d).

8. Piston according to claim 5, characterized in that the distance (b) between the piston head (12) and the cooling channel cover (27) between 3% and 7% of the nominal diameter (DN) of the piston head (11).

9. Piston according to claim 5, characterized in that the compression height (KH) between 38% and 45% of the nominal diameter (DN) of the piston head (11).

10. Piston according to claim 5, characterized in that in the piston head (11) a combustion bowl (13) is formed and that the smallest wall thickness (w) in the radial direction between the combustion bowl (13) and the cooling channel (19) between 2.5 % and 4.5% of the nominal diameter (DN) of the piston head (11).

11. Piston according to claim 10, characterized in that the combustion bowl (13) is provided with an undercut (29).

12. Piston according to claim 1, characterized in that the closure element (35) is designed as a separate component.

13. Piston according to claim 1, characterized in that the piston (10, 110, 20, 310, 410) consists of at least two non-detachably interconnected components (31, 32, 131, 132, 231, 232, 331, 332, 432, 432). 433) is composed.

14. Piston according to claim 13, characterized in that it comprises a piston main body (31, 131, 231, 331, 431) and a piston ring element (32, 132, 232, 332, 432).

15. Piston according to claim 14, characterized in that the closure element (135, 235) is formed integrally with the piston main body (131, 231).

16. Piston according to claim 14, characterized in that the closure element (335, 435) is formed integrally with the piston ring element (332, 432).

17. Piston according to claim 1, characterized in that it consists of at least one steel material.