Load Carrying Capacity
The majority of research topics at FZG deal with the load-carrying capacity of the components spur, bevel / hypoid, and worm gears, as well as multi-disc clutches and synchronizers.
The results of many research projects are derived from theoretical and experimental investigations carried out in parallel. The methods validated in this way are often programmed as application software and thus made conveniently available for practical use. In order to develop a method, simulation models are usually created for the stress case under consideration, which are validated with extensive experiments on test parts. For this purpose, the test parts are extensively documented before and after the experiments, often during the tests. For the experimental investigations - i.e., for the construction, operation, and maintenance of the test rigs, the documentation of the test parts, and the execution of the tests - the necessary infrastructure is available at the FZG.
Pitting on gears often represents the service life limit. This is a near-surface fatigue phenomenon that, in addition, to contact pressure and sliding conditions, is primarily influenced by material, heat treatment, and lubricant.
In addition to S-N-curves (Wöhler lines), influences of the lubricant, in particular, are investigated in the FZG pitting test.
Under unfavorable lubrication conditions, micropitting can occur on the flanks of hardened gears, giving the flank a gray appearance (micropitting). Specially developed FZG micropitting test methods allow the influences of lubricating oils and additives to be detected.
Small lubricant film thicknesses are the main cause of high wear, particularly at circumferential speeds below 0.2 m/s. Particularly at risk are the gears of the slow-running stage in multi-stage gearboxes or gear stages, which, due to their function, have to be operated with low-viscosity lubricants. The FZG back-to-back test rig is used in standardized test procedures to investigate the wear behavior of different material pairings and lubricants in the range of low circumferential speeds.
In addition to load and sliding speed, the lubricant primarily influences scuffing. Hardened tooth flanks allow higher surface pressures and are mainly affected by this damage. Extensive investigations are being carried out at the FZG to identify the influences on scuffing. In the process, a method for testing and classifying industrial gear oils were also defined, which has been standardized as the "FZG fretting test" in DIN ISO 14635, CEC, and ASTM. Further test procedures were developed for testing the scuffing resistance of automotive gear oils of API classes GL4 and GL5.
Tooth root fracture describes progressive crack formation due to exceeding the strength value in the critical tooth root cross-section. The tooth root load carrying capacity is determined in pulsator tests and running tests in the FZG back-to-back test rig. The results are presented in the form of S-N-curves (Wöhler lines).
In order to demonstrate the transferability of the pulsator tests to the gears, running tests are carried out with identical gears.
Basic investigations on the influence of various parameters on the stresses occurring at the tooth root of external and internal gears and their effect on tooth root strength are carried out on static load test rigs with strain gauge measuring chains.
The stress state and the distribution of stress and contact stress are determined using closed analytical methods and finite element methods.
Tooth flank fracture is fatigue damage of the surface-hardened tooth flank under rolling stress. The crack occurs below the surface, approximately in the middle of the tooth height of the active flank, from where it runs to the tooth root rounding of the back flank.
With regard to tooth flank fracture, comprehensive theoretical and experimental investigations are carried out, the results of which form the basis of more advanced calculation models.