Lightweight construciton of a diesel piston

Abstract

The invention relates to a piston (10) for an internal combustion engine, comprising a piston crown (22), a cylindrical piston head (11), which adjoins the piston crown (22), and an at least partially hollow piston skirt (40), which is formed on the piston head (11) on the side facing away from the piston crown (22) and which has two opposite skirt wall segments (50) and two opposite connecting walls (60) that connect the skirt wall segments (50), wherein the connecting walls (60) each have a pin bore (61), wherein the piston head (11) has an annular cooling channel (18), which has at least one inlet opening (28) and at least one outlet opening (30), and the two skirt wall segments (50) widen toward the piston head (11) in such a way that the sector length (L1) of the side of the skirt wall segment (50) formed on the piston head (11) is greater than the sector length (L2) of the side of the skirt wall segment (50) facing away from the piston head (11).

Claims

1. A piston for an internal combustion engine, the piston being cast of aluminum or an aluminum alloy and comprising a piston crown, a cylindrical piston head, which adjoins the piston crown, and an at least partially hollow piston skirt, which is formed on the piston head on the side facing away from the piston crown and which has two opposing skirt wall segments and two opposing connecting walls that connect the skirt wall segments, wherein the connecting walls each has a pin bore extending along a pin axis, wherein the piston head has an annular cooling channel, which has at least one inlet opening and at least one outlet opening, and the two skirt wall segments widen towards the piston head in such a way that a sector length (L1) of the side of the skirt wall segment formed on the piston head is greater than a widest sector length (L2) of the side of the skirt wall segment facing away from the piston head, and a shortest sector length (L3) of at least one of the skirt wall segments is located between the side formed on the piston head and the side facing away from the piston head, and the width of the at least one of the skirt wall segments increases continuously from the shortest sector length (L3) to the widest sector length (L2) of the side facing away from the piston head, two reinforcing ribs, which run largely parallel to the pin axis or run in an arch shape and extend essentially from one pin bore to the other pin bore, are formed on the piston head and extend into a cavity of the piston skirt, and the inlet opening and the outlet opening are each provided between an associated one of the reinforcing ribs and the associated nearest skirt wall segment.

2. The piston according to claim 1, wherein the inlet opening and/or outlet opening is located in the region of the associated nearest skirt wall segment and/or in the region of an associated one of the connecting walls.

3. The piston according to claim 1, wherein the shortest sector length (L3) is located closer to the side formed on the piston head than the side facing away from the piston head.

4. The piston according to claim 1, wherein the opposing skirt wall segments have two edges which join the side of the skirt wall segment formed on the piston head to the side of the same skirt wall segment facing away from the piston head, wherein the edges have a portion which is convexly curved starting from the piston head.

5. The piston according to claim 4, wherein the convexly curved portions of the edges each transition into a concave curvature and then extend substantially in a straight line.

6. The piston according to claim 5, wherein the straight line portions of the edges do not run parallel and/or their distance from the side of the skirt wall segment, which faces away from the piston head, increases.

7. The piston according to claim 1, wherein the connecting walls each has a pin boss in which the relevant pin bore is located and which has an increased wall thickness relative to thinner wall segments of the connecting walls.

8. The piston according to claim 7, wherein the pin bosses extend substantially outwards starting from the segments with thinner wall thickness of the relevant connecting walls.

9. A piston for an internal combustion engine, the piston being cast of aluminum or an aluminum alloy and comprising a piston crown, a cylindrical piston head, which adjoins the piston crown, and an at least partially hollow piston skirt, which is formed on the piston head on the side facing away from the piston crown and which has two opposing skirt wall segments and two opposing connecting walls that connect the skirt wall segments, wherein the connecting walls each has a pin bore extending along a pin axis, wherein the piston head has an annular cooling channel, which has at least one inlet opening and at least one outlet opening, and the two skirt wall segments widen towards the piston head in such a way that a first sector length (L1) of the side of the skirt wall segment formed on the piston head is greater than a second sector length (L2) of the side of the skirt wall segment facing away from the piston head, and a shortest sector length (L3) of at least one of the skirt wall segments is located between the first sector length (L1) of the side of the skirt wall segment formed on the piston head and the second sector length (L2) of the side of the skirt wall segment facing away from the piston head, the skirt wall segments include a concavely curved portion in a section extending from the piston head, a tapered portion extending from the concavely curved section, and straight sections extending from the tapered portion which gradually diverge.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a three-dimensional representation of a piston at an angle from above;

(2) FIG. 2 shows the piston of FIG. 1 in a partially transparent form of representation;

(3) FIG. 3 shows the piston of FIG. 1 at an angle from below;

(4) FIG. 4 is a lateral view of the piston of FIG. 1;

(5) FIG. 5 is a different lateral view of the piston of FIG. 1;

(6) FIG. 6 shows the piston of FIG. 1 from below;

(7) FIG. 7 is a sectional view of the piston of FIG. 1;

(8) FIG. 8 is a three-dimensional view of the sliced open piston of FIG. 1;

(9) FIG. 9 is a lateral view of the piston according to a second embodiment;

(10) FIG. 10 shows the piston of FIG. 9 from below;

(11) FIG. 11 is another lateral view of the piston of FIG. 9;

(12) FIG. 12 shows the piston according to a third embodiment from below;

(13) FIG. 13 shows the piston of FIG. 12 from the side;

(14) FIG. 14 is another lateral view of the piston of FIG. 12;

(15) FIG. 15 shows the piston of FIG. 12 at an angle from below.

DETAILED DESCRIPTION

(16) FIGS. 1 to 8 show a piston 10 according to a first embodiment in various views and perspectives. The reference numbers are used uniformly and are not described again for each figure. Moreover, some reference numbers have been omitted in one or other view if required for the sake of clarity.

(17) FIG. 1 shows a piston 10 in a three-dimensional view at an angle from above. The piston 10, which is preferably cast from aluminium or an aluminium alloy, comprises a combustion bowl 12 which in the present example is w-shaped, as is particularly clear from FIG. 7. The piston 10 is shown there in a sectional view. Starting from the piston crown 22, the combustion bowl 12 extends into the piston head 11. The curvature of the wall forming the combustion bowl 12 is initially convex, then transitions into a concave curvature which, in the manner of an undercut, cuts not only into the depth but also the width of the piston head 11, then adjoining this displays an approximately straight line section which transitions into a centrally located protrusion (the central protrusion of the ?), This curve progression is rotationally symmetrical, i.e. mirror-symmetrical in the section of FIG. 7, relative to the central axis of the piston 10.

(18) Several annular grooves 14 are provided for piston rings which are not illustrated. Holes, blind holes, through-holes or other openings 15 may be introduced in one or more of the annular grooves 14 to improve the oil supply to the piston and inside the skirt. The oil that is stripped from the piston rings, which are not illustrated, may be transported, for example, into the interior of the piston through the openings 15.

(19) Located in the piston head 11 is an annular cooling channel 18 which is shown in FIG. 2 and is also apparent in FIGS. 7 and 8. The cooling channel 18 runs approximately circular and concentrically to the cylindrical periphery of the piston 10. The diameter of the cooling channel ring is adjusted in such a way that it is provided in the vicinity of the largest depressions of the combustion bowl 12 and at the same time has a sufficient distance from it so as not to compromise the mechanical strength of the piston head 11 due to any thin wall thickness between combustion bowl 12 and cooling channel 18. It can be seen from FIG. 2 that the cooling channel 18 does not necessarily have to extend exactly in a plane which is present parallel to the piston crown 22. In fact, in the present example the cooling channel 18 has a curved shape in which high-lying areas and low-lying areas (in the direction of the piston axis) are connected to each other in a gently curved manner.

(20) The cooling channel 18 has a coolant inlet opening 28 and a coolant outlet opening 30. The coolant inlet opening 28 and the coolant outlet opening 30 extend into the cavity of the piston 10 which is defined by the piston skirt 40 and is described in greater detail below. The coolant inlet opening 28 and the coolant outlet opening 30 are preferably provided in the low-lying areas of the cooling channel 18, as is apparent from FIG. 2. Coolant may be actively injected into the coolant inlet opening 28 or the coolant outlet opening 30 via a nozzle which is not illustrated. Additionally or alternatively, splash oil may be supplied. In addition, coolant exits from the coolant inlet opening 28 and/or coolant outlet opening 30 and, due to the favourable position of the openings, reaches areas of the piston pin, the bearing of the pin in the pin bores and the connection between the piston pin and connecting rod eye to be cooled and lubricated. A representation of the piston pin and the connecting rod has been omitted for the sake of clarity.

(21) The piston skirt 40 comprises two opposing skirt wall segments 50 and two opposing connecting walls 60 connecting the skirt wall segments 50. The connecting walls 60 are moved inwards in relation to the cylindrical piston head 11 such that the overall contour in the section in FIG. 6 of the piston skirt 40 assumes not a circular cylindrical but rather a rectangular shape. In this case, however, the skirt wall segments 50, in conformity with the circular cylindrical contour of the piston head 11, display a circular cylindrical curve which transitions essentially into straight connecting walls 60. It should be noted here that the connecting walls 60 need not be exactly straight but, as is particularly clearly shown in FIG. 6, may be slightly arched or curved. Particularly in the connecting areas to the skirt wall segments 50, the connecting walls 60 display a curvature directed outwards, as a result of which the connecting areas between skirt wall segments 50 and connecting wall 60 may be widened for stabilisation.

(22) The cavity 41 of the piston skirt 40 is comparatively narrow due to moving the connecting walls 60 inwards. A pin bore 61 which is reinforced with pin boss 62 is provided in each of the connecting walls 60. The pin bores 61 may have one or more side reliefs 64. On the underside of the piston 10, the pin bosses 62 are flattened, as is particularly apparent from FIG. 6. The pin bores 61 may be fitted with a circlip which is incorporated in a groove 63 formed in the pin bore 61.

(23) Two reinforcing ribs 45 extend parallel to the pin axis which is defined by the two pin bores 61. The two reinforcing ribs 45 are provided symmetrically on both sides of the pin, which is not shown, and connect the opposing connecting walls 60 in the region of the rear of the pin boss 62. The reinforcing ribs 45 extend into the cavity of the piston skirt 40. In the present example, they end at the height along the piston axis approximately where the vertex of the pin bore 61, which is closest to the piston head 11, is located. In the section which is shown in FIG. 6, the reinforcing ribs 45 extend in an approximately straight line along the pin axis. The upper edges of the reinforcing ribs 45, i.e. the edges which face away from the piston head 11, are rounded off. Moreover, the reinforcing ribs 45 widen in the region of their connection to the connecting walls 60. Overall, all the connections of various components of the piston skirt 40 are executed smoothly, i.e. sharp edges and corners are avoided, to minimise the occurrence of cracks and fractures in these sensitive areas. In addition, openings 67 may be provided in the reinforcing ribs 45 or other skirt segments to improve oil circulation or coolant circulation in the piston skirt 40.

(24) The reinforcing ribs need not run in a straight line along the pin axis, as is apparent from FIG. 10 which, together with FIGS. 9 and 11, represents a second embodiment. In it, the reference numbers which correspond to the components of the first embodiment are provided with an a. The reinforcing ribs 45a are curved in the direction of the pin axis, the curvature following the cylindrical profile of the piston head 11, i.e. seen from the piston axis the reinforcing ribs 45a are convexly curved. With the curvature of the reinforcing ribs 45a illustrated in FIG. 10, the stability of the piston 10 is further improved without increasing the overall weight.

(25) In the embodiment which is shown in FIGS. 9 and 10, the skirt wall segments 50a are additionally bulbous. In this case, the inner contour of the skirt wall segments in the section in FIG. 10 have a curved shape such that widening of the skirt wall segments occurs, with the greatest thickness on the central axis of the piston, said central axis being perpendicular to the pin axis and the piston axis.

(26) The special shape of the skirt wall segments 50 is apparent from FIG. 5. A widening 51 is provided in the region of the connection of the skirt wall segment 50 to the piston head 11. In other words, the sector length L1 in the region of the connection to the piston head 11 is greater than the sector length L2 of the opposing edge 54, i.e. the edge of the skirt wall segment 50 which opposes the piston head 11. Starting from the connecting region on the piston head 11, a rapid tapering initially takes place via segments 52 to a minimum sector length L1 Segments 52 are convexly curved and transition in the region of the minimum sector length L3 into concavely curved segments. Adjoining this are straight line segments 53 which do not run parallel but gradually diverge up to sector length L2. The following applies here: L1>L2>L3

(27) As is apparent from FIG. 5, the edge 54 may be irregular, i.e. it may have depressions, bevels, curvatures of different types and the like. Reference is made here, by way of example, to the recess 55a in FIGS. 9 and 11 which ensures the piston runs correctly with a coolant nozzle placed in the region of the recess for injecting cooling oil into the coolant inlet opening 28a.

(28) With the design of the skirt wall segments 50 described above and illustrated in the figures, there is an excellent connection to the connecting walls 60 as a result of which high stability and strength is achieved with simultaneous reduction of the piston weight.

(29) As is apparent from FIG. 6, the coolant inlet opening 28 and the coolant outlet opening 30 are provided between the reinforcing ribs 45 and the nearest skirt wall segment 50. Moreover, they are located in the connecting region between skirt wall segment 50 and connecting wall 60, i.e. in the corner between the two, as a result of which excellent guidance of the coolant inflow occurs along the corresponding inner walls of the piston skirt 40. The openings 28, 30 are thus offset from the central axis of the piston 10 which runs perpendicular to the pin axis and perpendicular to the piston axis. Targeted injection using a nozzle which is not illustrated is thus simplified, thereby improving the cooling effect. It should be pointed out at this point that the terms coolant inlet opening and coolant outlet opening are to be understood synonymously since the entrance and the exit may be reversed or both openings may serve as entrances and exits at the same time.

(30) FIGS. 12 to 15 show various views of a third embodiment. In them, the reference numbers which correspond to the components of the first embodiment are provided with a b.

(31) According to the third embodiment, the coolant inlet opening 28b and the coolant outlet opening 30b are not provided in the connecting region of the skirt edge segment 50b and the connecting wall 60b, and also not between the piston skirt 40 and the nearest reinforcing rib, the coolant inlet opening 28b is rather provided outside the piston skirt 40 in the region of the joint between pin boss 62b and connecting wall 60b. In addition, the coolant outlet opening 30b is provided approximately on the plane bisecting the piston which is perpendicular to the pin axis and between the skirt wall segment 50b, which is distant from the coolant inlet opening 28b, and the nearest reinforcing rib 45b to this. According to an embodiment which is not illustrated, both the coolant inlet opening 28b and also the coolant outlet opening 30b are provided outside the piston skirt, especially preferably in the region of the connection between pin boss 62b and connecting wall 60b.

(32) In FIG. 15, the piston of the third embodiment is shown at an angle from below. Here, the pin boss 62b nearest the coolant inlet opening 28b has a recess 29b which makes it easier to introduce the cooling oil into the coolant inlet opening 28b. The other pin boss 62b has a reinforcement 63b for stabilisation.

(33) In addition to the position of the coolant inlet opening, the coolant outlet opening and the shape and nature of the reinforcing ribs, the embodiments also differ in the shape of the skirt wall segments. From FIG. 9, which comprises a lateral view of the second embodiment, it is apparent that, starting from the connecting region on the piston head, there is no need for any convex curvature of the segments 52, they may, however, be concavely curved, taper rapidly and straight sections 53 which are not parallel but gradually diverge may subsequently adjoin. A gently undulating shape of the segments 52 is apparent from FIG. 14 of the third embodiment.

(34) To avoid redundancy, the description of the second and third embodiments is kept less detailed than that of the first embodiment. It is therefore explicitly pointed out that the features and technical effects of the first embodiment also apply to the second and third embodiments as long as they do not contradict the representations of the first embodiment.