EP3004609A1

EP3004609A1 - Piston for an internal combustion engine

Info

Publication number: EP3004609A1
Application number: EP14753000.0A
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: DE102013009164A1; JP2016520174A; US9771891B2; BR112015029647A2; CN105308299A; US20160115900A1; WO2014190962A1

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, 119, 419) which is open towards the base and which is closed by means of a closure element (35, 135, 235, 335, 435). Said cooling channel (19, 119, 419) has a cooling channel base (26, 126, 226, 326, 426) and a cooling channel cover (27), and the piston skirt (21) has two piston hubs (22) which are interconnected by means of two running surfaces (25a, 25b). According to the invention, the inner surface (37), exclusively a running surface (25a) of the piston (10, 110, 210, 310, 410) is connected to the lower side (11a) of the piston crown (11) by means of a connecting bar (38).

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, and wherein the piston skirt has two piston hubs, which are connected to one another via two running surfaces.

In modern internal combustion engines, the pistons in the region of the piston crown and the combustion bowl are exposed to increasingly higher mechanical and thermal loads. In addition to optimizing the piston cooling, it is therefore necessary on the one hand to provide the piston with the necessary stability in order to withstand the mechanical loads that occur, and on the other hand to make the piston so flexible that damage, in particular cracks, which are caused by these mechanical loads, is avoided could be caused.

The object of the present invention is to develop a generic piston so that an optimized balance between stability and flexibility and at the same time the cooling is improved.

The solution is that the inner surface is connected exclusively to a running surface of the piston via a connecting web with the underside of the piston head.

The piston according to the invention is thus constructed asymmetrically. One of its running surfaces is tied to the two piston hubs. The other tread is additionally bonded to the underside of the piston head. This structure provides both a good stability (additional connection of a running surface to the underside of the piston head), but on the other hand also a certain flexibility (connection of a

Bestätigungskopiel Running surface only to the piston hubs). It does not matter whether the additional connection of a tread to the underside of the piston head is provided on the pressure side or the counter-pressure side of the piston. Furthermore, the connecting web, which connects one of the running surfaces to the underside of the piston head, can be used to selectively direct an oil jet onto the surface of the connecting web in engine operation such that the underside of the piston head is specifically cooled. Thus, the cooling of the piston according to the invention is improved.

Advantageous developments emerge from the subclaims.

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

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.

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 cooling channel may extend in the axial direction usually up 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. However, due to the shaker effect, the cooling oil reciprocates between the cooling channel ceiling, ie a very hot area, and the cooling channel floor, ie a comparatively cool area. 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.

A particularly effective cooling is therefore preferably achieved in that the cooling channel is shortened in the axial direction. This has the consequence that the cooling oil moves in particular in the region of the cooling channel bottom in greater proximity to the highly heat-loaded cooling channel bottom and thus in hotter areas than in a cooling channel extending to the lowest annular groove or below. 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 cooling oil quantity 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 particularly effective cooling of the piston head results.

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.

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 be fold of 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.

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 present invention is suitable both for pistons of at least one steel material and for pistons of at least one light metal alloy.

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;

Figure 4 shows another embodiment of a piston according to the invention in

Cut; Figure 5 shows another embodiment of a piston according to the invention in section;

Figure 6 is an enlarged partial view of another embodiment in the

Cut;

Figures a schematic representation of the cooling oil movement in a piston 7 a, 7 b according to the present invention;

Figures a schematic representation of the cooling oil movement in a piston 8a, 8b 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. But it can also be made of a light metal material or a combination of both materials.

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 comprises a piston stem 21 thermally decoupled from the piston head 11 with piston hubs 22 and hub bores 23 for receiving a piston rod. benbolzens (not shown) on. The piston bosses 22 are connected via hub connections 24 to the underside 11 a of the piston head 11. The piston hubs 22 are connected to each other via running surfaces 25a, 25b.

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 member 35 forms a circumferential annular gap 36 together with the outer wall of the combustion bowl 13.

According to the invention, the inner surface 37 is connected exclusively to a running surface, namely the running surface 25a of the piston 10 via a connecting web 38 with the underside 11a of the piston head 11.

In engine operation, a cooling oil jet may be directed along the inner surface 37 of the tread 25a toward the surface of the tie bar 38 to enhance cooling of the underside 11a of the piston head 11, as indicated by the arrow P.

To further improve the cooling of the piston 10, 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 is approximately at the height 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 Figure 3 shows 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, the same structural elements are provided with the same reference numerals, and it is in this respect to the description of the figures 1 and 2 referenced.

The essential difference between the piston 110 according to FIG. 3 and the piston 10 according to FIGS. 1 and 2 is that the closure element 135 is designed as an annular disc which completely closes the cooling channel 119. In this case, inlet and outlet openings for cooling oil are provided in the closure element 135. The cooling channel bottom 126 of the resulting cooling channel 119 is thus approximately at the level of the lowest annular groove 18th

Figure 4 shows a further embodiment of a piston 210 according to the invention. The piston 210 is constructed in a similar manner as the piston 10 according to Figures 1 and 2. Therefore, the same structural elements are provided with the same reference numerals, and it is in this respect to the description of the figures 1 and 2 referenced.

The essential differences exist on the one hand in the design of the piston main body 231 and the piston ring element 232 and, on the other hand, in that the piston 210 has a closure element 235 designed differently from the piston 10 according to FIGS. 1 and 2.

The piston 210 has a closure element 235 in the form of a circumferential flange connected in one piece with the piston main body 231. The closure element 235 extends in the direction of the ring portion 15 such that its free end together with the inner wall of the ring portion 15 forms a circumferential annular gap 236. The closure element 235 forms the cooling channel bottom 226. The cooling channel bottom 226 is in the embodiment approximately between the first annular groove 16 and the second annular groove 17 is located. The cooling channel 219 also has a cooling channel ceiling 227. In the exemplary embodiment, the piston ring element 232 of the piston 210 comprises part of the piston crown 12, the top land 14 and the ring section 15. The piston ring element 232 can be connected to the piston main body 231, in particular by a welding process, for example electron beam welding or laser welding, wherein the weld seam 233 is arranged in the piston head.

FIG. 5 shows a further exemplary embodiment of a piston 310 according to the invention. The piston 310 is constructed in a similar manner to the piston 210 according to FIG. 4. Therefore, identical structural elements are provided with the same reference numerals, and reference is made to the description of FIG.

The essential difference between the piston 310 according to FIG. 5 and the piston 210 according to FIG. 4 is that the closure element 335 is integrally connected to the piston main body 331 such that the cooling channel bottom 326 of the resulting cooling channel 319 is approximately at the level of the lowest annular groove 18 lies. The closure element 335 extends in the direction of the ring part 15 formed by the piston ring element 332 such that its free end together with the inner wall of the ring part 15 forms a circumferential annular gap 336.

FIG. 6 shows, in an enlarged partial view, a further exemplary embodiment of a piston 410, in which 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 formed by the piston base body 431 such that the free end of the closure element 435 together with the outer wall of the combustion bowl 13 forms a circumferential annular gap 436.

The combustion bowl 13 is provided with an undercut 429 to determine the wall thickness between the combustion bowl 13 and the cooling channel 419 (see below). The following information applies to pistons 10, 210, 410 according to FIGS. 1, 2, 4 and 6.

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). Thus, a particularly advantageous for the heat dissipation positioning of the cooling channel 419 with respect to the piston head 12 and the ring section 15 is effected.

On the basis of this design rule for the land 14, it is preferred that the distance a between the piston head 12 and the cooling channel bottom 426 is between 11% and 17% of the nominal diameter DN of the piston head 11 (see FIGS. 1 and 2). Thus, the cooling channel 419 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 419 is 0.8 times to 1.7 times its width d. This design rule causes an optimal volume of the cooling channel 419 and an optimal alignment relative to the hot combustion bowl 13, in particular to the bowl rim, and to the hot piston bottom 12 and to 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 427 is between 3% and 7% of the nominal diameter DN of the piston head 11 (compare FIGS. 1 and 2). Also, this design rule causes optimal positioning of the cooling channel 419 with respect to the hot piston bottom 12th

Finally, it is preferred that the smallest wall thickness w in the radial direction between the combustion bowl 13 and the cooling channel 419 is between 2.5% and 4.5% of the nominal diameter DN of the piston head 11. Thus, an improved heat transfer between the combustion bowl 13 and the cooling channel 419 is achieved. Figures 7a and 7b and 8a and 8b show schematically the cooling oil movement during engine operation and the temperature zones in the region of the combustion bowl, the piston crown, the cooling channel and the annular grooves both for a piston according to the invention with axially shortened cooling channel (Figures 7a and 7b) and for a Piston with over all three annular grooves extending cooling channel (Figures 8a and 8b).

In Figures 7a, 7b, 8a, 8b schematically three heat zones, namely "hot", "warm" and "cool" are designated to illustrate the relative temperature differences in the individual piston areas.

According to FIGS. 7a and 7b, the cooling channel is shortened in the axial direction. 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 usual amount of cooling oil should be retained and the engine management set up so that the cooling oil is exchanged quickly during engine operation.

According to FIGS. 8a and 8b), the cooling channel extends in the axial direction approximately to the level of the lowermost annular groove or even below, in order to achieve sufficient cooling during engine operation with the aid of the largest possible cooling channel. 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, in the case of pistons with an axially shortened cooling channel, a further improved cooling of the piston head results.

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) a circumferential, downwardly open, with a closure element (35, 135, 235, 335, 435) closed cooling channel (19, 119 , 419), wherein the cooling channel (19, 119, 419) has a cooling channel bottom (26, 126, 226, 326, 426) and a cooling channel cover (27), and wherein the piston shaft (21) has two piston hubs (22), the two surfaces (25a, 25b) are interconnected, characterized in that the inner surface (37) excluding a running surface (25a) of the piston (10, 110, 210, 310, 410) via a connecting web (38) with the underside (11a) of the piston head (11) is connected.

2. Piston according to claim 1, characterized in that the compression height (KH) between 38% and 45% of the nominal diameter (DN) of the piston head (11).

3. Piston according to claim 1, characterized in that the closure element (35, 235, 335, 435) is arranged in the piston head (11) such that a circumferential annular gap (36, 236, 336, 436) in the cooling channel bottom (26, 226 , 326, 426) is formed.

4. Piston according to claim 1, characterized in that the closure element (35, 135) is designed as a separate component.

5. Piston according to claim 1, characterized in that the piston (10, 110, 210, 310, 410) consists of at least two non-detachably interconnected components (31, 32, 131, 132, 231, 232, 331, 332, 431, 431). 432) is composed.

6. Piston according to claim 5, characterized in that it comprises a piston main body (31, 131, 231, 331, 431) and a piston ring element (32; 132; 232; 332; 432).

7. Piston according to claim 6, characterized in that the closure element (235.335) is formed integrally with the piston main body (231, 331).

8. Piston according to claim 6, characterized in that the closure element (435) is formed integrally with the piston ring element (432).

9. Piston according to claim 1, characterized in that the closure element (35, 235, 435) is arranged in such a manner in the piston head (11), that the cooling channel bottom (26, 226, 426) above the lowermost annular groove (18) is arranged.

10. Piston according to claim 9, characterized in that the cooling channel bottom (26) in the amount of the second annular groove (17) is arranged.

11. Piston according to claim 9, characterized in that the cooling channel bottom (226, 426) between the first annular groove (16) and the second annular groove (17) is arranged.

12. 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).

13. Piston according to claim 12, characterized in that the distance (a) between the piston head (12) and the cooling channel bottom (26, 226, 426) between 11% and 17% of the nominal diameter (DN) of the piston head (11).

14. Piston according to claim 12, characterized in that the height (c) of the cooling channel (19, 219, 419) is 0.8 times to 1, 7 times its width (d).

15. Piston according to claim 12, characterized in that the distance (b) between the piston head (12) and the cooling channel cover (27, 227, 427) between 3% and 7% of the nominal diameter (DN) of the piston head (11).

16. Piston according to claim 12, 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, 219, 419) between 2.5% and 4.5% of the nominal diameter (DN) of the piston head (11).

17. Piston according to claim 16, characterized in that the combustion bowl (13) is provided with an undercut (429).