PISTON FOR AN INTERNAL COMBUSTION ENGINE

Description

Technical field

[0001] The invention relates to a piston for an internal combustion engine.

[0002] Pistons for internal combustion engines, particularly in the case of high specific power output gasoline engines (which can be on the order of 100 kW / l), are subjected to extremely high loads. This is due, on the one hand, to high ignition pressures, which can reach 120 bar, and, on the other hand, to the extremely high temperatures prevailing in the combustion chamber. Particularly high loads occur on the pressure side of the piston, and especially in the bottommost ring groove, due to the kinematics of the crankshaft assembly. Particularly in a load case that can be described as "maximum lateral force," high tensile stresses occur in the bottommost ring groove on the pressure side of the piston, because the piston skirt reacts more flexibly to lateral forces than the piston crown, which contains the ring field. Furthermore, it is necessary to save weight wherever possible in order to keep the load on the piston hub and other engine components due to inertial forces low.This is achieved, for example, by forming so-called pockets radially outside the piston pin in its axial direction. In other words, connecting walls that join the load-bearing shaft wall sections are set back radially inwards. State of the art

[0003] Numerous previously used pistons exhibit such a design. Often, a rounded section is formed between the shaft wall and the pocket. Pistons with a base support adjoining the shaft wall sections are known from CN 204 327 307 U or DE 10 2013 214738 A1. Description of the invention

[0004] Against this background, the invention is based on the objective of ensuring operational strength, particularly in the lowest groove of the piston, without a significant increase in piston weight, by reducing the maximum stresses occurring there in particular.

[0005] This is achieved by the piston according to claim 1. Accordingly, this piston has shaft wall sections that serve as supports in a cylinder or cylinder liner, to which so-called bottom supports are attached circumferentially towards the piston head. These bottom supports have at least one contour that forms a segment of a helical shape. In other words, the distance between the lower edge, i.e., the end of the bottom support furthest from the piston head, and the lowest annular groove follows a slope rolled along a cylinder. This lower edge can be the same over substantially the entire radial depth of the bottom support. In other words, viewed radially, the bottom support appears as a line. However, the described contour can only be present radially on the outside or inside of the bottom support, and the lower boundary surface of the bottom support can slope downwards or upwards from this edge.In Cartesian coordinates, the helix can be expressed as follows: . x → t = rcos t rsin t h 2 π t

[0006] Here, r is the radius of the cylinder, h is the pitch, and t is the curve parameter. The slope k is: k = h 2 πr

[0007] As initial simulations have shown, this significantly reduces the stresses in the lowest piston ring groove. Compared to the previous design, the maximum main stress can be reduced by approximately 30 MPa. This results in an improvement in operational strength of about 25%. Furthermore, it has been shown that the weight increase for a typical piston is only about 2 g. Thus, the invention advantageously combines the goals of a relatively lightweight yet strong piston. The piston crown support provides beneficial support for the piston crown.

[0008] Advantageous further developments of the piston according to the invention are described in the further claims.

[0009] Although the described design can be provided on both sides of a piston, due to the load situation described above, it is preferred that the contour according to the invention is provided at least on the pressure side of the piston.

[0010] Furthermore, it is preferred that the contour according to the invention is provided on both sides of the shaft wall section, so that the advantages of the invention can be extensively utilized.

[0011] This applies equally to the preferred measure whereby at least one ground support extends from a shaft wall section to the area of ​​a bolt hub boundary.

[0012] Initial simulations have shown that the slope of the helix according to the invention should be at least 1:10 and at most 1:1. Currently, a value of approximately 1:2 is preferred.

[0013] The bottom support designed according to the invention has a depth measured in the radial direction, preferably approximately equal to the depth of the lowest ring groove of the piston when measured in the same direction. This ensures particularly reliable, low-stress support of the area weakened by the piston ring groove. The described depth can be up to twice the depth of the piston ring groove, and in a typical gasoline piston, the described depth can be approximately 6 mm.

[0014] Radially within the described base supports are the connecting walls that join the shaft wall sections, and for weight reduction purposes, it is preferred that there be a distance between these walls; in other words, that at least one base support is spaced radially away from a connecting wall. This creates a "pocket" that is advantageous for weight reduction.

[0015] To avoid notch effects, a rounding is preferably provided at the transition between the shaft wall section and at least one bottom cover. Brief description of the drawings

[0016] A preferred embodiment of the invention is explained in more detail below with reference to the drawings. The drawings show: Fig. 1 shows a piston according to the invention in a side view; Fig. 2 shows a piston according to the invention in a bottom view; and Fig. 3 shows a piston according to the invention in a perspective bottom view with the helix shown. Detailed description of a preferred embodiment of the invention

[0017] As in Fig. 1 As can be seen, the piston according to the invention has a feature on its side as shown in the invention. Fig. 1 The upper surface comprises a piston base 12, a ring field 14 with a lowermost ring groove 16 and shaft wall sections 18, of which in Fig. 1 only one is fully recognizable. The shaft wall sections 18 have a circumferentially constant width. In the illustrated embodiment, the width varies along the (in Fig. 1 vertical) piston stroke axis approximately constant, with a slight widening towards the underside, i.e. away from the piston base 12.

[0018] According to the invention, so-called bottom supports 20 adjoin the circumferential direction on both sides of the pressure-side shaft wall section 18 shown, and in the case shown they are designed to be mirror-symmetrical. Fig. 1 The contour present on the underside of the floor support 20 can be recognized as a slope, from Fig. 3 However, it is evident that this contour follows a helix. A detailed description follows in connection with Fig. 3 With reference to Fig. 1 It should also be mentioned that the transition from the shaft wall section 18 to the respective ground support 20 is designed in the form of a rounding 22.

[0019] Out of Fig. 2The radial depth T of the bottom support 20 is also shown. It can also be seen that each bottom support 20 is spaced apart from the connecting wall 24 that joins the shaft wall sections, although the connecting walls 24 diverge slightly in the direction of the piston pin axis. This leaves pockets 26 between them, which are advantageous for weight reduction.

[0020] In Fig. 3 The contour of a ground support 20 is now shown in detail. It should be noted that this applies equally to the ground support on the other side, with the opposite helicity. The in Fig. 3 The depicted helicity can be described as positive. In other words, if the x-axis is mentally flipped onto the y-axis, the helix moves in the direction of the z-axis.

[0021] In Fig. 3It can also be seen that the ground support begins in the area of ​​the rounding 22 to the shaft wall section 18 (arrow B) and ends approximately in the area of ​​the bolt hub limit 28 (arrow A). In the case shown, the slope is approximately 1:2, and the depth T (cf. Fig. 2 ) is approximately 6 mm deep, about twice as deep as that of the lowest ring groove 16.

[0022] It should also be mentioned that the radial outer surface of at least one bottom support can lie on the same cylindrical surface as the shaft wall section. However, since the bottom support is not required for radial support against a cylinder (socket) wall, the bottom support can be set back radially relative to the shaft wall section.

Claims

1. A piston (10) for an internal combustion engine with shaft wall sections (18) for support in a cylinder or a cylinder liner, and at least one base support (20) adjoining it in the circumferential direction, which has at least one contour, characterized in that the contour forms a section of a helix.

2. The piston (10) according to claim 1, characterized in that a base support (20) is provided at least on the pressure side of the piston (10).

3. The piston (10) according to claim 1 or 2, characterized in that a base support (20) is provided on both sides of at least one shaft wall section (18).

4. The piston (10) according to any one of the preceding claims, characterized in that at least one base support extends into the region of a pin bolt limit (28).

5. The piston (10) according to any one of the preceding claims, characterized in that the helix has a slope of 1:10 to 1:1 and especially 1:2.

6. The piston (10) according to any one of the preceding claims, characterized in that the radially measured depth (T) of at least one base support (20) is at least equal to the radially measured depth of a lowermost ring groove (16) and / or at most twice as large.

7. The piston (10) according to any one of the preceding claims, characterized in that at least one base support (20) is spaced apart from a connecting wall (24) connecting the shaft wall sections (18).

8. The piston (10) according to any one of the preceding claims, characterized in that a transition between a shaft wall section (18) and at least one base support (20) is provided with a rounding (22).