Piston for an internal combustion engine

Abstract

A piston for an internal combustion engine may include a piston head, an encircling fire land, and at least one annular groove structured to receive a piston ring and disposed contiguous to the fire land. The piston may include a first fire land portion having a first axial height h1, a second fire land portion having a second axial height h2, and a third fire land portion having a third axial height h3. The first fire land portion may have an upper external diameter D1. The third fire land portion may have a lower external diameter D3. A transition from the first to the second fire land portion may have a first external diameter D12. A transition from the second to the third fire land portion may have a second external diameter D23. The relationship (D12D23)/h2>(D23D3)/h3 may apply.

Claims

1. A piston for an internal combustion engine, comprising: a piston head, an encircling fire land, and at least one annular groove structured to receive a piston ring, the at least one annular groove disposed contiguous to the fire land; a first fire land portion disposed contiguous to the piston head, a second fire land portion, and a third fire land portion disposed contiguous to the at least one annular groove, the second fire land portion disposed between and connecting the first fire land portion and the third fire land portions; the first fire land portion having a first axial height h1, the second fire land portion having a second axial height h2, and the third fire land portion having a third axial height h3; the first fire land portion having an upper external diameter D1, and the third fire land portion having a lower external diameter D3; wherein a transition from the first fire land portion to the second fire land portion has a first external diameter D12, and a transition from the second fire land portion to the third fire land portion has a second external diameter D23; and wherein (D12D23)/h2>(D23D3)/h3.

2. The piston according to claim 1, wherein the second fire land portion is conical and has an external diameter that decreases in a consistent manner in a direction of the third fire land portion.

3. The piston according to claim 2, wherein (D12D23)0.5 mm.

4. The piston according to one claim 1, further comprising a chamfer having an axial chamfer height hF of 0.5 mm or less, the chamfer disposed at one of (i) a transition from the piston head to the first fire land portion and (ii) a transition from the third fire land portion to the at least one annular groove.

5. The piston according to claim 4, wherein h1=h3.

6. The piston according to claim 1, wherein h1+h3=h2.

7. The piston according to claim 1, wherein: the second fire land portion includes a step; and the second external diameter D23 at the transition from the second fire land portion to the third fire land portion decreases in a stepped manner.

8. The piston according to claim 7, wherein h3=3h1.

9. The piston according to claim 7, wherein h3=h1.

10. The piston according to claim 1, wherein the second fire land portion is curved and has an external diameter that decreases in a consistent and monotonous manner from the first external diameter D12 to the second external diameter D23.

11. The piston according to claim 10, wherein h1+h3=h2 and h1=h3.

12. The piston according to claim 1, wherein h1+h2+h3=5.25 mm.

13. The piston according to claim 1, wherein the at least one annular groove includes a piston-head-proximal groove flank and a piston-head-distal groove flank, and wherein the piston-head-proximal groove flank and the piston-head-distal groove flank extend parallel to a radial direction.

14. The piston according to claim 1, wherein the first fire land portion is structured cylindrical such that D1=D12.

15. The piston according to claim 1, wherein the third fire land portion is structured cylindrical such that D23=D3.

16. The piston according to claim 1, wherein (i) a transition from the piston heat to the first fire land portion, and (ii) a transition from the third fire land portion to the at least one annular groove are each structured without a chamfer.

17. The piston according to claim 1, further comprising: a first chamfer having an axial chamfer height hF of 0.2 mm or less disposed at a transition from the piston head to the first fire land portion; and a second chamfer having an axial chamfer height hF of 0.2 mm or less disposed at a transition from the third fire land portion to the at least one annular groove.

18. The piston according to claim 1, wherein the upper external diameter D1 decreases in a consistent manner in a direction of the external diameter D12 at the transition from the first fire land portion to the second fire land portion.

19. The piston according to claim 1, wherein the external diameter D23 decreases in a consistent manner in a direction of the at least one annular groove.

20. An internal combustion engine, comprising a cylinder and a piston disposed in the cylinder, the piston including: a piston head, an encircling fire land, and at least one annular groove structured to receive a piston ring and disposed contiguous to the fire land; a first fire land portion disposed contiguous to the piston head, a second fire land portion, and a third fire land portion disposed contiguous to the at least one annular groove, the second fire land portion disposed between and connecting the first fire land portion and the third fire land portion; the first fire land portion having a first axial height h1, the second fire land portion having a second axial height h2, and the third fire land portion having a third axial height h3; the first fire land portion having an upper external diameter D1, and the third fire land portion having a lower external diameter D3; wherein a transition from the first fire land portion to the second fire land portion has a first external diameter D12, and a transition from the second fire land portion to the third fire land portion has a second external diameter D23, and wherein (D12D23)/h2>(D23D3)/h3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings, in each case in a schematic manner,

(2) FIG. 1 shows a sectional illustration through an internal combustion engine according to the invention, having a piston according to the invention, corresponding to a first embodiment;

(3) FIG. 2 shows a sectional illustration through an internal combustion engine according to the invention, having a piston according to the invention, corresponding to a second embodiment;

(4) FIG. 3 shows a sectional illustration through an internal combustion engine according to the invention, having a piston according to the invention, corresponding to a third embodiment;

(5) FIG. 4 shows a sectional illustration through an internal combustion engine according to the invention, having a piston according to the invention, corresponding to a fourth embodiment;

(6) FIG. 5 shows a sectional illustration through an internal combustion engine according to the invention, having a piston according to the invention, corresponding to a fifth embodiment; and

(7) FIG. 6 shows a sectional illustration through an internal combustion engine according to the invention, having a piston according to the invention, corresponding to a sixth embodiment.

DETAILED DESCRIPTION

(8) Corresponding to FIGS. 1 to 6, a piston 1 according to the invention for an internal combustion engine 2 has a piston head 3, an encircling fire land 4, as well as at least one annular groove 5 which for receiving a piston ring 6 is contiguous to the fire land 4. Provided according to the invention are now a first fire land portion 7 which is contiguous to the piston head 3, a third fire land portion 8 which is contiguous to the annular groove 5, as well as a second fire land portion 9 which connects the two fire land portions 7, 8 and is disposed therebetween. The annular groove 5 possesses groove flanks 12, 12 which preferably run in parallel and in the radial direction 10 in relation to the piston axis 11, specifically one piston-head-proximal groove flank 12 and one piston-head-distal groove flank 12. The first fire land portion 7 has an axial height h.sub.1, the second fire land portion 9 has an axial height h.sub.2, and the third fire land portion 8 has an axial height h.sub.3. The first fire land portion 7 possesses an upper external diameter D.sub.1, and the third fire land portion 8 possesses a lower external diameter D.sub.3, wherein the piston 1 at the transition from the first fire land portion 7 to the second fire land portion 9 has an external diameter D.sub.12, and at the transition from the second fire land portion 9 to the third fire land portion 8 has an external diameter D.sub.23. It now applies according to the invention that: (D.sub.12D.sub.23)/h.sub.2>(D.sub.23D.sub.3)/h.sub.3.

(9) In other words, this means that the first fire land portion 7 has a larger external diameter than the third fire land portion 8, and the second fire land portion 9 in terms of the external diameter thereof decreases from D.sub.12 to D.sub.23. The decrease is performed in a consistent manner (cf. FIGS. 1, 2, as well as 5 and 6) or in a stepped manner (cf. FIGS. 3 and 4), wherein the third fire land portion 8 can be configured so as to be cylindrical and thus to have an external diameter D.sub.23=D.sub.3. In the region of the third fire land portion 8, the external diameter D.sub.23 can alternatively also decrease in a consistent and/or monotonous manner in the direction of the annular groove 5.

(10) At the transition from the piston head 3 to the first fire land portion 7 and/or from the third fire land portion 8 to the annular groove 5, no chamfer 13 or a chamfer 13 having an axial chamfer height h.sub.F of at most 0.5 mm, preferably of at most 0.2 mm, can in each case be disposed. The chamfer height h.sub.F herein is a component part of the axial height h.sub.1 or h.sub.3. On account thereof, a comparatively sharp transition from the piston head 3 to the first fire land portion 7, or from the third fire land portion 8 into the annular groove 5, respectively, can be achieved.

(11) By way of the fire land 4 configured according to the invention it is possible for a spacing a.sub.1 between the piston 1 in the region of the piston head 3 thereof, or of the first fire land portion 7, respectively, and a cylinder wall 14 to be kept comparatively small, on account of which the invasion of a pressure surge from a combustion chamber 15 into a gap 16 between the cylinder wall 14 and the fire land 4 is at least impeded. A type of diffuser by way of which a pressure level of a pressure surge invading the gap 16 from the combustion chamber 15 can be reduced, can be achieved on account of the spacing a of the fire land 4 from the cylinder wall 14, said spacing a increasing in the direction of the third fire land portion 8, and thus on account of a reduction in the external diameter D. Moreover, an invasion of the pressure surge into the annular groove 5 can be impeded on account of the comparatively sharp transition from the third fire land portion 8 into the piston-head-proximal groove flank 12 of the annular groove 5, on account of which the risk of the fire land 4 breaking can be significantly reduced.

(12) According to FIGS. 1 and 2, the second fire land portion 9 herein is configured so as to be conical, wherein the external diameter in the second fire land portion 9, proceeding from D.sub.12 in the direction of the third fire land portion 8, decreases in a consistent or monotonous manner in the direction D.sub.23. The external diameter D herein is always determined in the manner proceeding from a piston axis 11 in the radial direction 10, and is provided with an index number in a manner analogous to the associated fire land portion 7, 8, 9.

(13) The first fire land portion 7 can be configured so as to be cylindrical, that is to say that D.sub.1=D.sub.12, or the upper external diameter D.sub.1 can decrease in a consistent and/or monotonous manner in the direction of the external diameter D.sub.12 at the transition to the second fire land portion 9. Overall, the external diameter in the second fire land portion herein can be decreased by approx. 0.5 mm, on account of which a gap widening a=a.sub.3a.sub.1=0.25 mm can be achieved. These dimensions apply in particular to pistons 1 having an axial overall height of the fire land 4 of approx. 5 mm.

(14) Furthermore observing FIGS. 1 to 6, it can be seen that the first fire land portion 7 has an axial height h.sub.1, the second fire land portion 9 has an axial height h.sub.2, and the third fire land portion 8 has an axial height h.sub.3, wherein it applies according to FIG. 1 that the sum of the axial heights h.sub.1 and h.sub.2 of the first and the second fire land portion 7, 9 corresponds approximately to the axial height h.sub.3 of the third fire land portion 8. By contrast, in the piston 1 illustrated according to FIG. 2 the axial height h.sub.1 of the first fire land portion 7 is significantly greater and corresponds substantially to the axial height h.sub.3 of the third fire land portion 8, wherein it applies that the sum of the two axial heights h.sub.1 and h.sub.3 of the first and the third fire land portion 7, 8 corresponds approximately to the axial height h.sub.2 of the second fire land portion 9. It thus applies that h.sub.1+h.sub.3=h.sub.2, wherein it applies that h.sub.1=h.sub.3.

(15) According to FIGS. 3 and 4, the second fire land portion 9 is configured as a step 18, or possesses a step 18 of this type, respectively, wherein the external diameter D.sub.12 to D.sub.23, at the transition of the second fire land portion 9 to the third fire land portion 8, decreases in the manner of a step, that is to say in an inconsistent or abrupt manner, respectively. It can apply herein, for example, that the axial height h.sub.3 of the third fire land portion 8 is approximately three times the axial height h.sub.1 of the first fire land portion 7 (cf. FIG. 3) so that h.sub.3=3h.sub.1 applies.

(16) Alternatively, it is also conceivable that the axial height h.sub.1 of the first fire land portion 7 corresponds to approximately the axial height h.sub.3 of the third fire land portion 8, such that the following formula applies in this case: h.sub.3=h.sub.1 or h.sub.3h.sub.1. In the case of a step-type transition in the second fire land portion 9, the latter possesses an axial height h.sub.2 which is close to zero. Therefore, the external diameter D.sub.12 and the external diameter D.sub.23 are drawn from above and below in FIGS. 3, 4.

(17) Observing the embodiments of the piston 1 according to the invention according to FIGS. 5 and 6, it can be seen therein that the second fire land portion 9 is configured in the manner of a curve, wherein the external diameter decreases in a consistent and monotonous but not conical manner from D.sub.12 to D.sub.23. Conical herein of course refers to the cross-sectional shape of the second fire land portion 9. In the case of the embodiment illustrated according to FIG. 5, it applies, for example, that h.sub.2=h.sub.3, while in the case of the embodiment illustrated according to FIG. 6, it applies that: h.sub.1+h.sub.3=h.sub.2 and h.sub.1=h.sub.3. The sum of the axial heights h.sub.1+h.sub.2+h.sub.3 in the case of a piston 1 according to the invention can be approx. 5.25 mm.

(18) At a transition from the piston head 3 to the first fire land portion 7 and/or from the third fire land portion 8 to the annular groove 5, no chamfer 13 or a chamfer 13 having an axial chamfer height h.sub.F of at most 0.5 mm, preferably of at most 0.2 mm, can in each case be disposed.

(19) By way of the piston 1 according to the invention, and thus also by way of the internal combustion engine 2 according to the invention, it is possible to keep a comparatively small spacing a.sub.1 between a cylinder wall 14 of the internal combustion engine 2 and the piston 1 in the region of the piston head 3, or in the region of the first fire land portion 7, respectively, on account of which the invasion of a pressure surge into the gap 16 is impeded, in particular in the case of pre-ignition.

(20) On account of the gap width (spacing a.sub.3) of the gap 16 which widens in the direction of the third fire land portion 8, a reduction in the pressure level can moreover be achieved, wherein an invasion of the pressure surge into the annular groove 5 can be impeded and the risk of the fire land 4 breaking can be thus reduced at the same time on account of the third fire land portion 8, which is designed in the manner of a cylinder, and the sharp-edged transition from the third fire land portion 8 into the annular groove 5. Overall, negative effects of low speed pre-ignition (LSPI) can be significantly reduced on account thereof.