Crankshaft

Abstract

The invention relates to a crankshaft (1) for a reciprocating piston internal combustion engine having at least two main bearings (2) a crank pin (3). Crankshaft flanges (4) are arranged between each of the main bearings and the crank pin and connect the main bearings to the crank pin. The crankshaft has at least one ring gear (5) spaced apart axially from a main bearing for a drive of a chain drive. A crankshaft surface between the main bearing and the first ring gear has an averaged roughness depth R z of less than 3 micrometres. Due to the configuration of the crankshaft according to the invention for a reciprocating piston internal combustion engine, higher torsional moments can be transmitted or the crankshaft can be designed to be lighter in the area having the higher surface quality.

Claims

1.-7. (canceled)

8. A crankshaft for a reciprocating-piston internal combustion engine, comprising: at least two main bearings; at least a first toothed ring for a drive of a chain drive; and a crankpin, wherein a respective crank web is arranged between the main bearings and the crankpin, the crank webs connect the main bearings to the crankpin, the first toothed ring is axially spaced apart from a main bearing, and a crankshaft surface between the main bearing and the first toothed ring has a mean roughness depth R.sub.z of less than 3 μm.

9. The crankshaft according to claim 8, further comprising: a second toothed ring that is provided so as to be axially spaced apart from the first toothed ring, wherein the crankshaft surface between the first toothed ring and the second toothed ring has a mean roughness depth R.sub.z of less than 3 μm.

10. The crankshaft according to claim 9, wherein the crankshaft surface adjacent to the second toothed ring, on the side opposite the first toothed ring, has a mean roughness depth R.sub.z of less than 3 μm.

11. The crankshaft according to claim 10, wherein the mean roughness depth R.sub.z is produced by grinding or finishing or rolling.

12. The crankshaft according to claim 11, wherein the crankshaft is produced from a steel material.

13. The crankshaft according to claim 12, wherein the steel material is C38+N or C38mod or 44MnSiVS6 or 37CrS4mod or 42CrMo4.

14. The crankshaft according to claim 13, wherein the crankshaft surface with the mean roughness depth R.sub.z of less than 3 μm extends up to toothed ring flanks.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows a view of a crankshaft according to the prior art; and

[0017] FIG. 2 shows a section through an end piece of a crankshaft with the inventive machining.

DETAILED DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 shows a view of a crankshaft 1 according to the prior art. By way of example, the crankshaft 1 illustrated in FIG. 1 is a stock crankshaft for the 6-cylinder BMW in-line engine with the internal designation B57.

[0019] The crankshaft 1 comprises seven main bearings 2 and six crankpins 3, wherein the main bearings 2 and the crankpins 3 are connected via crank webs 4. The crank webs 4 can be configured with or without counterweights. A flange 9 is located at an end of the crankshaft 1. Located between the flange 9 and the adjacently arranged main bearing 2 in the present exemplary embodiment are two toothed rings 5, 7, which are manufactured together with the crankshaft 1, for chain drives (not illustrated).

[0020] In the series version, a crankshaft surface between the flange 9 and the main bearing 2 has a mean roughness depth of about 7 um. Results on a torsional pulse test stand have shown that there is a limitation of the maximum possible torsional fatigue strength for this known crankshaft 1, since incipient cracks, which may lead to damage of the crankshaft 1, can occur in the region of the first toothed ring 5 and of the second toothed ring 7.

[0021] FIG. 2 shows a section through a flange-side end of a crankshaft 1 according to the invention in the region of the flange 9 and of the first toothed ring 5 and of the second toothed ring 7. According to the invention, the crankshaft surface 6 between the main bearing 2 and the first toothed ring 5 has a mean roughness depth R.sub.z of less than 3 μm. The crankshaft surface 6 between the first toothed ring 5 and the second toothed ring 7 also has a mean roughness depth R.sub.z of less than 3 μm. Furthermore, the crankshaft surface 6 which is located adjacent to the second toothed ring 7, on the side opposite the first toothed ring 5, also has a mean roughness depth R.sub.z of less than 3 μm.

[0022] In a particularly preferred embodiment, the crankshaft surface 6 with the mean roughness depth R.sub.z of less than 3 μm extends up to the toothed ring flanks 8.

[0023] The mean roughness depth R.sub.z of less than 3 μm is preferably produced by grinding or finishing or polishing. In addition, the crankshaft 1 is preferably formed of a steel material, such as, for example, C38+N or C38MOD or 44MNSIVS6 or 37CRS4MOD or 42CRMO4.

[0024] In principle, the crankshaft according to the invention can be forged or cast.

[0025] Investigations on a torsional pulse test stand have shown that the increase according to the invention in the surface quality in the abovementioned critical regions, in particular in the region of the transition radii to the sprocket, from approximately R.sub.z=7 μm to R.sub.z less than 3 μm makes it possible to achieve a demonstrable increase in the torsional fatigue strength of the entire crankshaft 1 in the range of 10 to 30%. By way of rolling in the form of deep rolling (increasing the internal compressive stress), a significantly higher increase in strength is again to be expected. Firstly, there is thus the possibility of transmitting higher torsional moments by way of the crankshaft 1. Secondly, in the context of a lightweight construction approach with an identical torque to be transmitted, the crankshaft 1 can be constructed in a more lightweight manner and thus with less starting material.

LIST OF REFERENCE DESIGNATIONS

[0026] 1. Crankshaft [0027] 2. Main bearing [0028] 3. Crankpin [0029] 4. Crank web [0030] 5. First toothed ring [0031] 6. Crankshaft surface [0032] 7. Second toothed ring [0033] 8. Toothed ring flank [0034] 9. Flange