Patent Application
20210404512
The disclosure relates to a crankshaft for a reciprocating-piston internal combustion engine.
With regard to the technical field, reference is made for example to an existing method for increasing the fatigue strength of crankshafts for piston machines, in particular internal combustion engines, in the case of which crankshafts the transition radii between a crankpin and adjoining crank webs are subjected to a particular treatment. Said treatment consists of a hardening in the region of the transition radii to a hardening depth of 2-3 mm, along with a machining of the surface, proceeding from an intersection edge between a bearing point and a transition radius as far as the end of the run-on collar, to a roughness depth Rz greater than 6.3 μm.
Furthermore, in an existing crankshaft that is provided in particular for air-compressing supercharged injection-type engines, the crankshaft comprises main bearing journals and connecting-rod bearing journals. The main bearing journals are loaded to a lesser extent than the connecting-rod bearing journals, wherein, prior to operation of the crankshaft, the main bearing journals have a greater roughness depth than the connecting-rod bearing journals.
Additionally, an existing bearing apparatus for internal combustion engines comprises a crankshaft of an internal combustion engine, wherein the crankshaft is held by bearings, and the crankshaft is produced from steel which has not undergone any surface hardening and which has a structure composed primarily of perlite and of a proportion of proeutectoid ferrite of at most 3%. The steel is also machined in order to have a roughness depth Rz of at most 0.8 μm, wherein the bearings comprise an aluminum bearing alloy which is connected to a base plate and, as an alloy constituent of said alloy, comprise less than 4 weight percent of silicon particles. In this way, prevention of premature wear and of scratching of the crankshaft occurs in such a way that it is equivalent or advantageous in comparison with the wear and the scratching in the case of conventional DCI shafts.
A crankshaft, which is used for the BMW in-line six-cylinder diesel engine with the internal designation B57, is also depicted by way of example in
The turning machining in said region generates a surface quality in the range of approximately Rz=7 μm. Results on a torsional pulse test stand show a limitation of the maximum possible torsional fatigue strength on account of possible incipient cracks in the critical region of the transition radii, inter alia as a result of comparatively high surface roughness.
It is an object of the present disclosure to increase the maximum transmittable torsional moment for a crankshaft of the generic type.
Said object and other object are achieved by the a crankshaft for a reciprocating-piston internal combustion engine of this application.
The use of different manufacturing processes makes it possible to increase the surface quality in the critical regions to a mean of the roughness depths Rz of less than 3 μm. Possible processes considered may in this case be, inter alia, grinding, finishing or else polishing (in the form of pure surface smoothing). All of the processes are associated with a significant smoothing of the surface in the critical region.
Investigations on a torsional pulse test stand have shown that the increase in the surface quality in critical regions, in particular in the region of the transition radii to the sprocket, from approximately Rz=7 μm to Rz less than 3 μm makes it possible to achieve a demonstrable increase in the torsional fatigue strength of the entire crankshaft 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. Secondly, in the context of a lightweight construction approach with an identical torque to be transmitted, the crankshaft can be constructed in a more lightweight manner and thus with less starting material.
With the configuration according to the crankshaft for a reciprocating-piston internal combustion engine of this application, the torsional fatigue strength can be further improved.
The manufacturing processes disclosed in this application are particularly preferred manufacturing processes.
The materials disclosed in this application are particularly preferred crankshaft materials.
With the configuration disclosed in this application, the formation of cracks is again significantly counteracted.
Other objects, advantages and novel features of the present disclosure will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings, in which:
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).
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.
In a particularly preferred embodiment, the crankshaft surface 6 with the mean roughness depth Rz of less than 3 μm extends up to the toothed ring flanks 8.
The mean roughness depth Rz 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.
In principle, the crankshaft according to the invention can be forged or cast.
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 Rz=7 μm to Rz 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 125 617.5 | Oct 2018 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/073659 | 9/5/2019 | WO | 00 |
