Cylinder liner

Abstract

A cylinder liner for an internal combustion engine may have a running surface, in which by honing directed honing grooves may be introduced. The running surface may have a first region and a second region, wherein the first region may have a roughness that may be distinct from a roughness of the second region. A transition between the first region and the second region may proceed obliquely to a cylinder longitudinal axis at least in some portions. At least some of the honing grooves at the transition between the first region and the second region are uninterrupted.

Claims

1. A cylinder liner for an internal combustion engine, comprising: a running surface, in which by honing directed honing grooves are introduced and which has a first region and a second region, wherein the first region has a roughness that is distinct from a roughness of the second region; wherein a transition between the first region and the second region proceeds obliquely to a cylinder longitudinal axis at least in some portions; and wherein at least some of the honing grooves at the transition between the first region and the second region are uninterrupted.

2. The cylinder liner as claimed in claim 1, wherein the transition between the first region and the second region proceeds at least one of alternatingly and periodically at least in some portions.

3. The cylinder liner as claimed in claim 1, wherein one of: the transition between the first region and the second region proceeds wave-like at least in some portions; or the transition between the first region and the second region proceeds zigzag-shaped at least in some portions.

4. The cylinder liner as claimed in claim 1, wherein: an axial extent of a course of the transition between the first region and the second region defines a transition region between the first region and the second regions; and the transition region between the first region and the second region has an axial expanse that is less than 40 mm and greater than 0.5 mm.

5. The cylinder liner as claimed in claim 1, wherein the first region and the second region are axially adjacent to one another.

6. The cylinder liner as claimed in claim 1, wherein: the first region lies axially eccentrically and the second region lies axially centrically; and the roughness of the first region is greater than the roughness of the second region.

7. The cylinder liner as claimed in claim 5, wherein: the running surface includes a third region which has a roughness greater than the roughness of the second regions; and the third region is arranged eccentrically, adjoins the second region, and based on an axial center lies opposite the first region.

8. The cylinder liner as claimed in claim 7, wherein a transition between the second region and the third region proceeds obliquely to the cylinder longitudinal axis at least in some portions.

9. The cylinder liner as claimed in claim 8, wherein the transition between the second region and the third region proceeds at least one of alternatingly and periodically at least in some portions.

10. The cylinder liner as claimed in claim 7, wherein one of: the transition between the second region and the third region proceeds wave-like at least in some portions; or the transition between the second region and the third region proceeds zigzag-shaped at least in some portions.

11. The cylinder liner as claimed in claim 8, wherein: an axial extent of a course of the transition between the second region and the third region defines a transition region between the second region and the third region; and the transition region between the second region and the third region has an axial expanse that is less than 40 mm and greater than 0.5 mm.

12. The cylinder liner as claimed in claim 1, wherein the second region has a diameter which is greater by 1 to 10 m than a diameter of the first region.

13. A cylinder liner produced by a process comprising: honing an entire running surface of an unfinished cylinder liner, such that honing grooves are introduced into the running surface; after the honing, machining a second region of the running surface to reduce a roughness in the second region such that the roughness is less than a roughness of a first region of the running surface, wherein at least some of the honing grooves in the second region are retained; wherein a transition between the first region and the second region proceeds obliquely to a cylinder longitudinal axis at least in some portions; and wherein at least some of the honing grooves at the transition between the first region and the second region are uninterrupted.

14. A method for producing a cylinder liner, comprising: honing an entire running surface of an unfinished cylinder liner such that honing grooves are introduced into the running surface; after the honing, machining a second region of the running surface to reduce a roughness in the second region such that the roughness is less than a roughness of a first region of the running surface, wherein at least some of the honing grooves in the second region are retained, wherein a transition between the first region and the second region proceeds obliquely to a cylinder longitudinal axis at least in some portions; and wherein at least some of the honing grooves at the transition between the first region and the second region are uninterrupted.

15. The cylinder liner as claimed in claim 1, wherein most of the honing grooves at the transition between the first region and the second region are uninterrupted.

16. The cylinder liner as claimed in claim 4, wherein the axial expanse is less than 15 mm and greater than 0.5 mm.

17. The cylinder liner as claimed in claim 11, wherein the axial expanse is less than 15 mm and greater than 0.5 mm.

18. The cylinder liner as claimed in claim 12, wherein the diameter of the second region is greater by 1 to 5 m than the diameter of the first region.

19. The cylinder liner as claimed in claim 13, wherein most of the honing grooves at the transition between the first region and the second region are uninterrupted.

20. The method as claimed in claim 14, wherein most of the honing grooves at the transition between the first region and the second region are uninterrupted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings,

(2) FIG. 1 shows a sectional representation through a cylinder liner according to the invention as per a first embodiment,

(3) FIG. 2 shows a progression chart of the transition between two regions with different roughness on the running surface, wherein on the X-axis the circumferential direction is shown and on the Y-axis the axial position of the transition is shown,

(4) FIG. 3 shows a representation corresponding to FIG. 2, wherein a wave-like course of the transition is shown,

(5) FIG. 4 shows a representation corresponding to FIG. 3, wherein the shown course of the transition only comprises two wave troughs and two wave crests, and

(6) FIG. 5 shows a sectional representation through a cylinder liner according to a second embodiment, wherein three regions with different accuracy values are provided.

DETAILED DESCRIPTION

(7) A first embodiment of a cylinder liner 10 shown in FIGS. 1 and 2 is used in a reciprocating piston internal combustion engine. The cylinder liner 10 has a running surface 12 along which a piston of the reciprocating piston internal combustion engine slides. The piston preferentially comprises at least one piston ring which is in contact with the running surface 12 in order to achieve an optimal seal.

(8) The piston is coupled to a crankshaft resulting in a cyclical up and down movement of the piston. In the process, a top dead center, in which the piston lies in the cylinder liner 10 at a point most distant from the crankshaft axis, and a bottom dead center, in which the piston lies in the cylinder liner 10 at a point that is nearest the crankshaft axis, are obtained.

(9) In the vicinity of the two dead centers, the movement velocity of the piston is low. In the region in between, the movement velocity is greatest.

(10) In order to obtain an optimal lubrication, honing grooves are introduced by honing into the running surface 12, which form an oil retention volume. In order to achieve friction losses that are as low as possible, the running surface 12 of the cylinder liner 10 comprises a first region 14 and a second region 16, wherein the first region 14 has a greater roughness than the second region 16. When comparing the roughnesses, the mean peak-to-valley height R.sub.z is considered. This means that the first region 14 has a greater mean peak-to-valley height R.sub.z than the second region 16.

(11) The reduction of the roughness in the second region 16 is achieved by removing material on the running surface 12. Only so much material is removed that most of the introduced honing grooves are retained even in the second region 16.

(12) By removing the material, the second region 16 has a larger diameter than the first region 14. For example, the diameter of the second region 16 is greater by 1 to 10 m, preferentially by 1 to 5 m, than the diameter of the first region 14. It is to be understood that the enlargement of the diameter in the second region 16 has to be less than twice the depth of the honing grooves so that the honing grooves are retained even in the second region 16.

(13) The first region 14 is arranged at an axial end of the cylinder liner 10, which in the installation position later on faces away from the crankshaft. This means that when the piston is located in the region of the top dead center, the piston rings lie in the first region 14. When the piston is located in the bottom dead center or an intermediate region between the two dead centers, the piston rings lie in the second region 16.

(14) In the second region 16, the roughness is less than in the first region 14. Because of this, the friction losses can be reduced in the intermediate region, in which the piston velocity is high. Because of the increased roughness and thus deeper honing grooves, a greater oil retention volume is achieved in the first region 14, so that even with greater normal forces the wear between the cylinder liner 10 and the piston ring can be reduced.

(15) A transition 18 between the first region 14 and the second region 16 proceeds obliquely to a cylinder longitudinal axis 19 at least in some portions. Because of this, regions can be avoided in which the transition proceeds perpendicularly to the cylinder longitudinal axis 19. In the case of a perpendicular course, the piston ring or piston rings would reach the transition 18 simultaneously along the entire circumference of the piston ring. This could lead to an oil film interruption or to undesirably turbulent flows of the oil when the piston rings slide over the transition 18. In addition, a very abrupt force transmission to the piston rings could result.

(16) Through the course that is oblique at least in some portions between the first region 14 and the second region 16, the piston rings gradually slide over the transition 18. This means that in multiple circumferential positions, the piston rings already enter into contact with the transition 18 while other regions of the piston ring are not yet in contact with the transition 18. This results in a transition region 20 in which the piston rings slide over the transition 18. When the piston rings are in the transition region, the piston rings can thus push oil from the first region 14 laterally along the honing grooves or in the circumferential direction into the second region 16 so that an adequate oil lubrication is provided in the second region 16.

(17) The transition 18 itself has a finite width 21, within which the diameter and the roughness change. A course 17 of the transition 18 is defined by the course 17 of the respective center of the width 21 of the transition 18. The transition region 20 is defined by the course 17 of the transition 18. The transition region 20 proceeds in the axial direction over a region which is occupied by the transition 18 in the axial direction. Thus, the transition region 20 is limited in the axial direction by the axial extreme points of the course 17 of the transition 18.

(18) An axial extent 22 of the course 17 of the transition 18 and thus an axial expanse 23 of the transition region 20 is preferentially less than 40 mm, particularly preferably less than 15 mm, however greater than 0.5 mm.

(19) A favorable version provides that the course 17 of the transition 18 is zigzag-shaped, such as is shown for example in FIG. 2. It is to be understood that a wave-like course 17, such as shown for example in FIG. 3, is also possible. In FIG. 4, a version with two wave crests and two wave troughs is shown for example.

(20) A second embodiment of the cylinder liner 10 shown in FIG. 5 differs from the first embodiment of the cylinder liner 10 shown in FIGS. 1 and 2 in that the running surface 12 of the cylinder liner 10 has a third region 24 which has a roughness that is greater than the roughness of the second region 16. Preferentially, a transition 26 between the second region 16 and the third region 24 is also formed obliquely at least in some portions as was described for example regarding the transition 18 between the first region 14 and the second region 16. Thus, the risk of an oil shortage of the piston rings can also be reduced at the transition 26 between the second region 16 and the third region 24. Thus, reference is made in this regard to the above description regarding the transition 18 between the first region 14 and the second region 16.

(21) Otherwise, the second embodiment of the cylinder liner 10 shown in FIG. 5 corresponds to the first embodiment of the cylinder liner 10 shown in FIGS. 1 to 4 in terms of construction and function, to the above description of which reference is made in this regard.