PISTON FOR AN ENGINE

Description

[0001] The invention relates to a piston for an internal combustion engine according to the features of the preamble of patent claim 1.

[0002] A piston for internal combustion engines is known from the generic document DE 197 40 065 A1. In this piston, the bosses are set back in the direction of the piston pin axis such that the outer boss distance is 60% to 65% of the piston diameter or less. The boss outer surfaces, which connect the two sliding surfaces, have a straight (linear) profile across the height of the sliding surfaces. In this piston, the boss outer surfaces (also called box walls) are not fundamentally flat, but also curved, both in sections parallel and perpendicular to the piston axis. However, the direction of curvature of the surface in sections perpendicular to the piston axis is always the same for the entire area of ​​the box wall. This results in a width of the supporting sliding surface that decreases towards the top (towards the piston crown) as the distance between the box walls decreases.

[0003] DE 197 40 065 A1 thus discloses a light metal piston for internal combustion engines with a roof-shaped piston crown with a combustion chamber bowl, wherein the bosses are set back in the direction of the pin axis in such a way that the outer boss distance is 60% to 65% of the piston diameter or less, and wherein above the outer surfaces of the set-back bosses there is provided an open cavity which encloses an angle of between 45° and 60° in the circumferential direction and extends in the direction of the piston crown into the area behind the annular field, and wherein the inner boss surfaces are trapezoidal or stepped, and the skirt length is 40% to 45% of the piston diameter.

[0004] Furthermore, a piston is known from DE 101 45 589 A1. This piston has a piston crown consisting of an annular zone with several annular grooves and, optionally, a combustion chamber bowl. A piston skirt is arranged below the piston crown in the direction of piston movement. This piston skirt consists of two skirt wall sections that support the piston during operation in the internal combustion engine and serve to guide the piston in the cylinder of the internal combustion engine. The skirt wall sections are connected to one another via recessed connecting walls, whereby the connecting walls have no connection to the cylinder's running surface.

[0005] In the piston of this DE 101 45 589 A1, the connecting walls have a curved profile, which can be convex, concave, or a combination of these curvatures. Furthermore, in this known piston, the lower edge of the annular zone is designed to protrude beyond the connecting walls (overhang) and is at least partially hollowed out there, creating a clearance for the purpose of weight reduction.

[0006] US 2002 / 0178909 A1 describes a piston for an internal combustion engine, comprising a crown, a pair of piston pin projections each integrated into the crown and facing each other, and a pair of skirt walls each integrated into the crown and facing each other, a lower end of the pair of skirt walls being located on top of a lower end of the pair of piston pin projections.

[0007] The invention is based on the object of producing a piston for an internal combustion engine with a reduction in the piston mass and improved stress distribution in the box area of ​​the piston.

[0008] This problem is solved by the features of patent claim 1.

[0009] According to the invention, it is provided that the piston on its pressure side has a box wall distance of the box walls between 35% and 51% of the piston diameter and / or that the piston on its counterpressure side has a box wall distance of the box walls between 26% and 39% of the piston diameter.

[0010] The thrust side is the side of the piston or cylinder on which the piston rests during combustion. The thrust side is opposite the direction of rotation of the crankshaft. The counter-thrust side is the side of the piston or cylinder opposite the thrust side. The skirt support designed according to the invention achieves a more homogeneous stress distribution within the piston. This allows for even larger annular field undercuts. The mass of the piston is significantly reduced, yet at the same time it withstands the demands of today's internal combustion engines with their extreme thermal and mechanical loads.

[0011] Furthermore, the invention provides that the piston, on its pressure side, has a distance between the box walls of between 40% and 51%, preferably between 46% and 49% of the piston diameter. The invention also provides that the piston, on its counterpressure side, has a distance between the box walls of between 30% and 39%, preferably between 34% and 37% of the piston diameter. This brings the box walls closer together, resulting in further material savings. Smaller skirt surfaces on the pressure side and counterpressure side of the piston lead to reduced friction.

[0012] Furthermore, the invention provides that the distance between the upper edge of a top land and the apex of a clearance perpendicular to the piston pin bore axis is smaller than the extent of the top land. Furthermore, the invention provides that the distance between the upper edge of the top land and the apex of the clearance parallel to the piston pin bore axis is smaller than the extent of the top land. The stronger undercuts in the weight pockets of the ring zone enable the use of optimized casting tool technology.

[0013] Furthermore, the invention provides that the distance between the upper edge of the top land and the apex of the clearance transverse to the piston pin bore axis and / or the distance between the upper edge of the top land and the apex of the clearance parallel to the piston pin bore axis is between 50% and 95%, preferably between 65% and 90%, smaller than the extension of the top land. This results in material savings and a reduction in piston mass.

[0014] Furthermore, the invention provides that the radial depth of a lifting groove has a dimension of greater than or equal to 2 millimeters (mm), preferably greater than or equal to 3 mm, in particular greater than or equal to 4 mm. By making the radial depth of the lifting groove as large as possible, the piston mass in this area is reduced.

[0015] Furthermore, the invention provides that a distance between a centerline of the box wall on the pressure side and a centerline of the piston transverse to the pin bore axis is greater than a distance between a centerline of the box wall on the pressure side and the centerline of the piston transverse to the pin bore axis on the circumference of the piston. The box walls designed according to the invention have reduced the draft angle for the casting tool inserts. This, in turn, enables an increase in the clearance behind the ring zone, which leads to a reduction in the piston mass.

[0016] Furthermore, the invention provides that the distance between a centerline of the box wall on the counterpressure side and the centerline of the piston perpendicular to the pin bore axis is smaller than the distance between the centerline of the box wall on the pressure side and the centerline of the piston perpendicular to the pin bore axis. The box walls designed according to the invention have reduced the draft angle for the casting tool inserts. This, in turn, allows for an increase in the clearance behind the ring area, which leads to a reduction in the piston mass.

[0017] Furthermore, the invention provides that the distance between the centerline of the box wall on the counterpressure side and the centerline of the piston perpendicular to the pin bore axis on the circumference of the piston is smaller than the distance between the centerline of the box wall on the counterpressure side and the centerline of the piston perpendicular to the pin bore axis. The box walls designed according to the invention have reduced the draft angle for the casting tool inserts. This, in turn, allows for an increase in the clearance behind the annular zone, which leads to a reduction in the piston mass.

[0018] Furthermore, the invention provides that the position of an intersection point between the distance between the centerline of the box wall on the pressure side and the centerline of the piston transverse to the pin bore axis and the centerline of the box wall is 10% to 35%, preferably 15% to 30%, in particular 20% to 25% of the piston diameter. The curved hub, in conjunction with the newly designed skirt connection, makes it possible to minimize stresses in the combustion chamber bowl in highly turbocharged direct-injection internal combustion engines through the resulting bottom support.

[0019] Hub faces fully integrated into the box contour. Compared to the state of the art, a mass reduction of approximately 15% is achieved, and improved stress distribution is achieved thanks to the homogeneous box wall design.

[0020] By using suitable piston alloys, in particular the applicant's KS 309 piston alloy, and consistently adapting the piston design to the resulting material-specific advantages, the wall thickness of the piston crown could be reduced by up to 30%. This results in a reduction in the piston's mass.

[0021] The basic concept is explained below with reference to the figures. Further details of the invention are described below with reference to exemplary embodiments.

[0022] It shows Fig. 1 a view of a piston according to the prior art DE 10 2005 041 002 A1, Fig. 2 a sectional view of a piston according to the prior art DE 10 2005 041 002 A1, Fig. 3 a sectional view from below of a piston according to the invention, Fig. 4 a further sectional view from below of the piston according to Figure 3, Fig. 5 a further sectional view from below of the piston according to Figure 3 , Fig. 6 a side sectional view (counterpressure side) of the piston according to Figure 3 and for comparison the outline of a piston according to Fig. 2 , Fig. 7 a side sectional view (pressure side) of the piston according to Figure 3 and for comparison the outline of a piston according to Fig. 2 , Fig. 8 a side sectional view (counterpressure side) of the piston according to Figure 3 , Fig. 9 a side sectional view (counterpressure side) of the piston according to Figure 2 , Fig. 10 a bottom view of the piston according to Figure 3 , Fig. 11 a sectional view of the piston according to Figure 3 transverse to the pin bore axis, Fig. 12 a sectional view of the piston according to Figure 3 outside the pin bore axis, and Fig. 13 a sectional view of a piston according to Figure 3 along the bolt bore axis.

[0023] The Figure 1shows a view of a piston 101 according to the prior art DE 10 2005 041 002 A1, the Figure 2shows a sectional view of the piston 101. Such a piston 101 consists of a piston skirt 102 with an attached piston crown 103, wherein the piston skirt 102 and piston crown 103 are formed as one piece or consist of two parts that are joined together after production. During operation of the internal combustion engine, the piston 101 moves in a cylinder (not shown) along a piston stroke axis 111. Furthermore, the piston 101 has an annular zone 104 with, as a rule, three annular grooves 109. The piston skirt 102 consists of skirt wall sections 105 supporting the piston 111, wherein the skirt wall sections 105 are connected to one another by recessed connecting walls 106. The connecting walls 106 have a curved profile, wherein the curved profile of the connecting walls 106 can be designed in various ways.The recessed connecting walls 106 further include a pin bore 107 for receiving a pin for connecting the piston 111 to a connecting rod (not shown). The piston crown 103 includes an optional combustion chamber bowl 110. Furthermore, it is shown that a free space 121 is present in the area of ​​the piston crown 3, behind the annular zone 104 and above the pin bore 107.

[0024] In the presentation of the Figure 1a drainage opening 126 is shown. The drainage opening 126 is arranged in the region of the annular groove 109, so that a connection from the annular groove 109 to the free space 121 is created when the annular groove 109 is introduced into the piston blank. The region of the drainage opening 126 behind the annular groove 109, i.e. in the region of the free space 121, can be cup-shaped. When using in particular a three-part oil ring in the annular groove 109, oil can be drained from the surface of the piston 101 or the cylinder bore towards the inner region of the piston 101 via the drainage opening 126. For this purpose, the drainage opening 126, in which in particular a drainage opening is arranged to the right and left of the pin bore 107, in particular symmetrically, is located in the region of the rear connecting walls 106, since sufficient space is available here for the drained oil.

[0025] The Figures 3 to 13show various views of an embodiment of a piston 1 of an internal combustion engine, which can be designed as a lightweight piston, but does not have to be. In the case of a lightweight piston, a piston blank is first cast from a lightweight material, in particular aluminum or an aluminum alloy, and then finished, for example by machining. The basic construction of such a piston 1 consists of a piston skirt 2 with an attached piston crown 3, wherein the piston skirt 2 and piston crown 3 are formed in one piece or consist of two parts that are joined together after their production. During operation of the internal combustion engine, the piston 1 moves in a cylinder (not shown) along a piston stroke axis 11. The piston 1 also has an annular zone 4 with, as a rule, three annular grooves.

[0026] The piston skirt 2 consists of skirt wall sections 5 supporting the piston 1, wherein the skirt wall sections 5 are connected to one another by recessed connecting walls 6. The connecting walls 6 have a curved profile, wherein the connecting walls 6 can be designed differently with regard to the curved profile. Reference is made to this curved profile (concave and / or convex from one skirt wall section to the other skirt wall section and / or in its profile along the piston stroke axis 11), as this profile is particularly important with regard to saving mass while simultaneously maintaining the required strength. The recessed connecting walls 6 also have a pin bore 7 for receiving a pin for connecting the piston 1 to a connecting rod (not shown). A pin bore axis 8 is shown within the pin bore 7. The piston crown 3 has an optional combustion chamber bowl 10.Furthermore, it is shown that in the area of ​​the piston crown 3, behind the ring field 4 and above the pin bore 7, there is a free space 21.

[0027] The Figure 3 shows a sectional view from below of a piston 1 according to the invention. A curvature 24 of the box wall 14 in a lower apex 18 is opposite to a curvature 26 of inner hub end faces 17 and the box wall 14 in an upper apex 19. In the Figure 3 The pressure side 12 of the piston 1 is shown at the top and the counterpressure side 13 at the bottom. The course and / or extension of the curvature 24 also has the advantage that a free space 21 is created in the interior of the piston 1, which is necessary for the clearance requirement of a trapezoidal connecting rod (not shown), via which the piston 1 can be connected to the crankshaft (also not shown).

[0028] R1 denotes the radius of the box wall 14 above the pin bore 7. R2 denotes the radius of the box wall 14 on the pressure side 12 of the piston 1. R3, in turn, represents the radius of the box wall 14 on the counterpressure side 13 of the piston 1.

[0029] The Figure 4 shows a further sectional view from below of the piston 1 according to Figure 3. The position of the box wall 14 in the lower apex 18 is shown. The center line 15 of the box wall 14 on the pressure side 12 of the piston 1 and the center line 16 of the box wall 14 on the counterpressure side 13 are shown.

[0030] The Figure 5 shows yet another sectional view from below of the piston 1 according to Figure 3 , here the position of the box wall 14 in the lower vertex 18 is shown.

[0031] "A" denotes the distance between centerline 15 of the box wall 14 on the pressure side 12 and the centerline 25 of the piston 1 perpendicular to the pin bore axis 8. "B" denotes the distance between centerline 15 of the box wall 14 on the pressure side 12 and the centerline 25 of the piston 1 perpendicular to the pin bore axis 8 on the circumference of the piston 1. "C" stands for the distance between centerline 16 of the box wall 14 on the counterpressure side 13 and the centerline 25 of the piston perpendicular to the pin bore axis 8. "D" denotes the distance between centerline 16 of the box wall 14 on the counterpressure side 13 and the centerline 25 of the piston 1 perpendicular to the pin bore axis 8 on the circumference of the piston 1.

[0032] Positions of the intersection points with the applicable conditions Position of intersection point A: 20% to 25% of the piston diameter 20 Position of intersection point B: B < A Position of intersection point C: C < A Position of intersection point D: D < C

[0033] The Figure 6 shows a lateral sectional view (counterpressure side 13) of the piston 1 according to Figure 3and for comparison the outline of a piston 101 according to Fig. 2 , to show the position of the box wall 14. The Figure 7 shows a lateral sectional view (pressure side 12) of the piston 1 according to Figure 3 and for comparison the outline of a piston 101 according to Fig. 2 , to show the position of the box wall 14. The piston 1 has free spaces 21 behind the annular field 4. The box walls 14 are closer together than in previously conventional lightweight pistons as known from DE 10 2005 041 002 A1.

[0034] "X1" denotes a distance between the box walls on the counterpressure side according to DE 10 2005 041 002 A1. "X2" denotes the distance between the box walls on the counterpressure side according to the embodiment from Figure 3. "Y1" represents the distance between the box walls on the pressure side according to DE 10 2005 041 002 A1. "Y2" in turn represents the distance between the box walls on the pressure side according to the embodiment Figure 3 represents.

[0035] The following conditions apply: X2 > X2 und Y1 > Y2

[0036] The Figure 8 shows a lateral sectional view (pressure side 12) of the piston 1 according to Figure 3 and the Figure 9 shows a lateral sectional view (pressure side 12) of the piston 1 according to Figure 3 The position of the box wall 14 is clearly visible. The newly designed box walls 14 reduce the draft angle 22 for the casting tool inserts. This, in turn, allows for an increase in the clearances 21 compared to lightweight pistons, as known from DE 10 2005 041 002 A1, which leads to a further reduction in mass.

[0037] "W1" denotes the angle of the extension bevel 22 on the pressure side 12 of the piston 1. "W2" denotes the angle of the extension bevel 22 on the counterpressure side 13 of the piston 1.

[0038] The following condition applies: W1 > W2

[0039] In the Figure 10 is a bottom view of the piston 1 according to Figure 3 Shown here. Piston 1 has smaller skirt surfaces in the area of ​​skirt wall sections 5 on the thrust side 12 and on the counter-thrust side 13 to reduce friction. For pistons for internal combustion engines with crankshaft offset, the skirt surfaces must be compensated for the resulting lateral forces. A box wall clearance of 27 is shown on the thrust side 12 and a box wall clearance of 28 on the counter-thrust side 13. The piston diameter 20 is also shown.

[0040] The pressure side 12 has a distance between the skirt surfaces or box wall distance 27 between 46% and 51% of the piston diameter 20. On the counterpressure side 13, the distance between the skirt surfaces or box wall distance 28 is between 34% and 39% of the piston diameter 20.

[0041] From the prior art DE 10 2005 041 002 A1, distances between the skirt surfaces on the pressure side between 52% and 57% and on the counterpressure side between 40% and 45% of the piston diameter 20 are known. Thus, a significant reduction in the skirt surfaces was achieved.

[0042] The Figure 11 shows a sectional view of the piston 1 according to Figure 3 transverse to the bolt bore axis 8 and the Figure 12 shows a sectional view of the piston 1 according to Figure 3outside the pin bore axis 8, the features for reducing the mass of the piston 1 are shown here. A top land 29 is shown, which forms an apex 30 at its greatest extent in the direction of the piston crown 3.

[0043] "X" describes the distance between the upper edge of the top land 29 and the apex 30 of the clearance 21 perpendicular to the bolt bore axis 8. "Y" in turn represents the distance between the upper edge of the top land 29 and the apex 30 of the clearance 21 parallel to the bolt bore axis 8. "FS" represents the dimension of the top land 29. The dimension X and / or the dimension Y are smaller than the dimension FS, preferably between 65% and 90%.

[0044] The conditions apply FS > X und FS > Y

[0045] The Figure 13 shows a sectional view of a piston 1 according to Figure 3Along the pin bore axis 8, another feature for mass reduction can be seen. The radial depth of a removal groove 23 has the dimension Z with a value greater than or equal to 4 mm. LIST OF REFERENCE SYMBOLS

[0046] 1Piston 2Piston skirt 3Piston crown 4Ring zone 5Skirt wall section 6Connecting wall 7Pin bore 8Pin bore axis 9Ring groove 10Combustion chamber bowl 11Piston stroke axis 12Thrust side 13Backpressure side 14Box wall 15Centerline of the box wall on the pressure side 16Centerline of the box wall on the backpressure side 17Hub face 18Lower apex 19Upper apex 20Piston diameter 21Clearance 22Extraction chamfer 23Extraction groove 24Curvature of the box wall in the lower apex 25Centerline of the piston transverse to the pin bore axis 26Curvature of the box wall in the upper apex 27Box wall distance on the pressure side 28Box wall distance on the backpressure side 29Top land 30Apex 101 State-of-the-art piston 102 Piston skirt 103 Piston crown 104 Annular zone 105 Skirt wall section 106 Connecting wall 107 Pin bore 109 Annular groove 110 Combustion chamber bowl 111 Piston stroke axis 121 Clearance 126 Drainage opening R1Radius of the box wall above the piston pin bore R2Radius of the box wall on the pressure side of the piston R3Radius of the box wall on the counter-pressure side of the piston ADistance between the center line of the box wall on the pressure side and the center line of the piston perpendicular to the pin bore axis BDistance between the center line of the box wall on the pressure side and the center line of the piston perpendicular to the pin bore axis on the circumference of the piston CDistance between the center line of the box wall on the counter-pressure side and the center line of the piston perpendicular to the pin bore axis DDistance between the center line of the box wall on the counter-pressure side and the center line of the piston perpendicular to the pin bore axis on the circumference of the piston X1Distance between the box walls on the counter-pressure side according to DE 10 2005 041 002 A1 X2Distance between the box walls on the counter-pressure side according to the exemplary embodiment Y1Distance between the box walls on the pressure side according to DE 10 2005 041 002 A1 Y2Distance between theBox walls on the pressure side according to the design example W1Angle of the extraction slope on the pressure side of the piston W2Angle of the extraction slope on the counter-pressure side of the piston XDistance between the upper edge of the top land and the apex of the clearance transverse to the bolt bore axis YDistance between the upper edge of the top land and the apex of the clearance parallel to the bolt bore axis ZRadial depth of the extraction groove FSExtension of the top land

Claims

1. Piston (1) for an internal combustion engine, comprising a piston shaft (2) and a piston head (3) comprising a ring field (4) arranged thereon, wherein the piston shaft (2) comprises supporting shaft wall sections (5) and recessed box walls (14), which connect the shaft wall sections (5) to one another and comprise a curved shape and a bolt bore (7), an undercut clearance (21) being present below the ring field (4) in the region of the bolt bore (7) in the region of the piston head (3), wherein the piston (1) comprises a pressure side (12) and a counter pressure side (13), wherein the piston (1) comprises on its pressure side (12) a box wall distance (27) of the box walls (14) between 35% and 51% of the piston diameter (20) and / or that the piston (1) comprises on its counter pressure side (13) a box wall distance (28) of the box walls (14) between 26% and 39% of the piston diameter (20), wherein the box wall distance (27) of the pressure side (12) is measured between the center lines (15) of the opposing box walls (14) on the pressure side (12) as the respective center lines (15) pass through the shaft wall section (5) on the pressure side (12), wherein further the box wall distance (28) of the counter pressure side (13) is measured between the center lines (16) of the opposing box walls (14) on the counter pressure side (13) when the respective center lines (16) pass through the shaft wall section (5) on the counter pressure side (13), wherein the box wall distances (27, 28) are measured in a bottom view of the piston (1), and wherein a distance (X) between an upper edge of a fire land (29) and an apex (30) of the clearance (21) transverse to a bolt bore axis (8) of the piston (1) is smaller than an extension (FS) of the fire land (29).

2. Piston (1) according to claim 1, characterized in that the piston (1) comprises on its pressure side (12) a box wall distance (27) of the box walls (14) of between 40% and 51%, preferably between 46% and 49% of the piston diameter (20).

3. Piston (1) according to claim 1, characterized in that the piston (1) comprises a box wall distance (28) of the box walls (14) on its counter pressure side (13) of between 30% and 39%, preferably between 34% and 37% of the piston diameter (20).

4. Piston (1) according to one of the preceding claims, characterized in that a distance (Y) between the upper edge of the fire land (29) and the apex (30) of the clearance (21) parallel to the bolt bore axis (8) is smaller than the extension (FS) of the fire land (29).

5. Piston (1) according to claim 4, characterized in that the distance (X) between the upper edge of the fire land (29) and the apex (30) of the clearance (21) transverse to the bolt bore axis (8) of the piston (1) and / or the distance (Y) between the upper edge of the fire land (29) and the apex (30) of the clearance (21) parallel to the bolt bore axis (8) is between 50% and 95%, preferably between 65% and 90%, is smaller than the extension (FS) of the fire land (29).

6. Piston (1) according to one of the preceding claims, characterized in that a radial depth (Z) of a lifting groove (23) comprises a dimension of greater than or equal to 2 mm, preferably greater than or equal to 3 mm, in particular greater than or equal to 4 mm.

7. Piston (1) according to one of the preceding claims, characterized in that a distance (A) between the center line (15) of the box wall (14) on the pressure side (12) and a center line (25) of the piston (1) transverse to the bolt bore axis (8) is greater than a distance (B) between a center line (15) of the box wall (14) on the pressure side (12) and the center line (25) of the piston (1) transverse to the bolt bore axis (8) at the circumference of the piston (1).

8. Piston (1) according to claim 7, characterized in that a distance (C) between a center line (16) of the box wall (14) on the counter pressure side (13) and the center line (25) of the piston (1) transverse to the bolt bore axis (8) is less than the distance (A) between the center line (15) of the box wall (14) on the pressure side (12) and the center line (25) of the piston (1) transverse to the bolt bore axis (8).

9. Piston (1) according to claim 8, characterized in that a distance (D) between the center line (16) of the box wall (14) on the counter pressure side (13) and the center line (25) of the piston (1) transverse to the bolt bore axis (8) at the circumference of the piston (1) is less than the distance (C) between the center line (16) of the box wall (14) on the counter pressure side (13) and the center line (25) of the piston (1) transverse to the bolt bore axis (8).

10. Piston (1) according to claim 9, characterized in that a position of a point of intersection between the distance (A) between the center line (15) of the box wall (14) on the pressure side (12) and the center line (25) of the piston (1) transverse to the bolt bore axis (8) and the center line (15) of the box wall (14) is 10% to 35%, preferably 15% to 30%, in particular 20% to 25% of the piston diameter (20).