1st ICAI 2020

International Conference on Automotive Industry 2020

Mladá Boleslav, Czech Republic

The other important equation in the model describes the thickness of the lubrication film h(x) . First member of (4) describes a thickness of lubrication film in the central part of the contact, the second member defines undeformed geometry of two contact bodies by parameter of common curvature R’ and last member is a model of elastic deformation due to contact pressure. It is inseparable component of the EHL lubrication regime.

(4)

The EHL film model used within this study also contains equations describing relation of lubricant’s viscosity with pressure and density with pressure. Final equation (5), driving the solution of the model, is a balance between the integral value of pressure p(x) over the contact and external load of the contact P. The balance is achieved by iterative adjustment of the h c parameter in equation (4) during solution to satisfy condition defined by (5).

(5)

For the numerical solution, the 2nd order pressure-derivative in the Reynold’s equation (4) was replaced by finite differences and discretized on the 1D mesh. Equation (5) was further rewritten for each point of the mesh with integral term replaced by summation. All equations were subsequently solved iteratively using Newton-Raphson’s algorithm. To accelerate the convergence rate of the solution a multigrid method with Full Approximation Scheme (FAS) was employed. 2.2 Controlling parameters during experiments To ensure that data from experiments will be comparable with results of simulations, same inputs and assumptions had to be addressed during experiments. Inputs for models were therefore geometry parameters measured on a real bearing which included diameter of races, rollers and surface roughness. Assumption of constant temperature of lubricant in the model was addressed by implementation of system for accurate temperature sensing and control in the developed testing device. Bearing was lubricated by circulating oil with temperature in the reservoir kept at 40°C +/- 0.5°C. Also, temperature of bearing inner ring was continuously measured. When a big difference between the two temperatures (bearing inner ring and oil in the reservoir) was recorded, interpretation of results had to account for it. More details about the testing stand and its components is in the (Chmelar, 2019b). 2.3 Excitation and sensing of SAW The device for excitation, sensing and processing of surface acoustic waves, used for this research, developed company BestSens AG, and sell it under trade name BeMoS One. It consists of a pair of piezo elements (PZT) which are both attached to outer ring of bearing as viewed in Figure 2 a) and connected into the controller. The process of excitation and sensing of waves is precisely synchronized. Waves are excited in a short sine bursts as depicted in Figure 2 b), with amplitude modulated into a gaussian bell.

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