Transmission oiling 2.0

… how you know after just a few days whether your gearbox will be adequately lubricated before you have built it.

The calculation of the oil flow in a fast rotating gearbox is one of the most demanding tasks in numerical fluid mechanics (CFD).

In a gearbox partially filled with oil, complex geometry meets complex physics and complex dynamics.


An intensive man effort in the geometry preparation as well as uneconomical calculation times can make the use of a simulation seem unprofitable here. Modeling times and calculation times of several weeks are not economical and the results come too late in the development process.

Simulation method for calculating the oil distribution in real gears

Merkle & Partner already devoted itself intensively to this topic in 2010 and developed a simulation method that enables the calculation of the oil distribution in real gears in an economically profitable time.


Months became weeks, weeks became days.

During development we focused on the following points:

  • an effective geometry preparation with reduced manpower and time expenditure
  • no limitation of geometry, detailed flows in the bearings and bearing gaps should be mapped as well as the flow in the oil sump
  • The method should be equally applicable in simple two-stage gearboxes up to 7-speed double-clutch gearboxes or planetary gearboxes.
  • a robust meshing method whose number of elements guarantees economical calculation times
  • a robust but sufficiently accurate representation of physics, including multiphase flow (oil and air) and rotation


Development of a simulation kit

The simulation method was successively developed in cooperation with several OEMs and first-time suppliers and finally transferred to a special simulation kit.

The use in a multitude of transmission projects in the last 5 years confirmed the use and the simulation results of the “Merkle & Partner Öl-Sim” simulation kit.

Smoothed Particle Hydrodynamics Methode (SPH)

In 2018 the previous simulation process was extended byincorporating PreonLab, a CFD software based on the Smoothed Particle Hydrodynamics (SPH) method. This software is designed by FIFTY2 Technology GmbH from Freiburg, Germany.

PreonLab offers an enormous time advantage over conventional CFD methods. The decisive advantage of this method lies in a gridless process, whereby only a small amount of manpower and time has to be invested in geometry preparation and cross-linking. The geometry can be taken from the CAD data and used directly for the simulation.

This proverbial “Drag & Drop” simulation method is particularly suitable in a very early phase of development. The global flow effects, such as the functionality of oil reservoirs, oil wells or guide elements in the housing wall, can be calculated and visualized quickly and effectively.

Photorealistic representations as well as effective postprocessing possibilities are further advantages of PreonLab.

In addition to the rapid developments of PreonLab Software, the simulation kit is subject to continuous development and optimization at Merkle & Partner.

In 2018, for example, we developed and verified an improved model for mapping tooth mesh. In addition, simulation parameters were optimized in order to minimize numerical diffusion, especially at very high speeds, and to further improve the quality of the results.


The planetary gear shown in the attached videos is a heavily alienated project which we have carried out in-house using the “Merkle & Partner Öl-Sim” simulation kit. The example describes the new SPH method in more detail.


In the planetary gear, oil from an oil sump is to be pumped from the planetary gears upwards into an oil tank.

The function of the collecting ribs above the planets is to be evaluated and optimized.

From the customer’s point of view, the project was a complete success and confirms the correctness of our assumptions.

Do you also want to develop your gearboxes faster and more efficiently? Do you want to avoid unnecessary losses in the oil sump and still have all bearings adequately lubricated?

We are also happy to arrange a non-binding consultation appointment or a telephone consultation.

Phone: +49 (0)7321 9343-0

Of course you can also have a look at our website:

Stefan Merkle

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