Elmar Woschke

An effective vibration reduction concept for automotive applications based on granular-filled cavities

The acoustic behavior of a combustion engine is primarily dominated by the sound radiation of the oil pan. Therefore, the vibration behavior of the oil pan as the prominent noise emission source is investigated in this paper. The aim of this study is to present a new vibration reduction concept, which is based on the property of high damping possessed by granular materials. The efficiency of this concept is proven by measurements via a scanning laser vibrometer. Finally, it is shown that it is possible to create a lighter oil pan which shows much lower vibration amplitudes than the original one.

Influence of Bearing Geometry of Automotive Turbochargers on the Nonlinear Vibrations During Run-Up

This paper deals with the simulation of turbochargers run-up behaviour. To predict the main design criterions for turbocharger applications like vibrations, friction power loss, minimal gap etc. a detailed and efficient computation is needed. The rotor dynamic simulation of the turbocharger is, due to the nonlinearities resulting from the oil-film, interacting with rotor shaft bending, done within an appropriate multibody simulation. By reason of turbines high rotational speed full-floating-rings are used to reduce the oil velocity gradient in the fluid-films. The bearings are modeled based on a transient numerical solution of Reynolds’ equation at each step of time integration. The pressure distribution can be affected by geometrical modifications like annular grooves in the full-floating-rings. The effect of these changes on the run-up behaviour of an automotive turbocharger is being studied. In addition the cause of jumps between subsynchronous vibrations will be shown for an explicit turbocharger.

Design, optimisation and testing of a compact, inexpensive elastic element for series elastic actuators

This paper presents the development of a compact torsion spring for use as an elastic element in a lightweight series elastic actuator for an active orthosis. This orthosis is going to be utilised as an assistive device for motorically impaired stroke-patients. In the design a two-step optimisation strategy was implemented to meet all requirements for the torsion spring. The first step was to identify a promising topology for the element. In the second step, the shape was optimised based on a finite element model using two different optimisation methods in order to minimise the von Mises equivalent stresses. Four promising variants of the identified topology were extracted from these calculations, one of which was then chosen as the final design. A prototype was manufactured by a laser cutting process, which is a new procedure in the context of elastic elements for series elastic actuators. The calculation results were validated successfully by measurement of the spring properties of this prototype.

Vibration Analysis of an Electric Wheel Hub Motor at Stationary Operating Points

In the context of environmentally friendliness and challenging pollution limits the electrification of passenger cars becomes more and more important. In this contribution an innovative electrical drive for automobiles is presented and its vibration behavior is analyzed experimentally. In special, the vibrations of an electric wheel hub motor are studied in detail. For this purpose, a laser scanning vibrometer is used. To be able to measure the vibrations at the running engine a derotator is needed additionally to the laser scanning vibrometer. The electric wheel hub motor is investigated on a test bench at different stationary operating points which differ in the rotational speed as well as in the torque that is applied by an electric brake. Analyzing the vibroacoustic behavior of this special electric machine is of utmost importance as its sound radiation is directed straight to the passers-by of the car. The sound radiation of conventional cars drives is normally shielded and attenuated by the vehicle body and for this reason less critical. Moreover, the application of damping materials is more difficult if the engine is placed within a wheel. In the paper at hand different prototype stages of the electric wheel hub motor are presented. The working principle of this special engine is also explained. For the numerical simulations a holistic simulation workflow has been developed which takes into account the electromagnetic field as the most important vibration excitation as well as the structural vibrations coupled with an air volume around the engine to calculate the sound pressure. First, the electromagnetic forces are calculated which are then applied to excite the structural vibrations of the engine. Finally, the calculated surface velocity is used to excite the surrounding air volume under free field conditions to determine the radiated sound pressure level. In all three steps of the holistic methodology, the finite element method (FEM) is used for the numerical simulations. Beside identifying weak points of the engine prototype as well as obtaining a general understanding of such an electrical machine, the experimental data are used to validate a numerical model of the electric wheel hub motor. With the help of both the validated model and the gained experimental experiences the design of the wheel hub motor is improved. However, this contribution focusses on the experimental analysis of the structural vibrations of the running wheel hub motor.

Application of Regularised Cavitation Algorithm for Transient Analysis of Rotors Supported in Floating Ring Bearings

In order to analyse the dynamical behaviour of fast-rotating, lightly loaded rotors with floating ring bearings, which mainly occur in turbochargers, a suitable simulation method is required. For that purpose, an online solution of the Reynolds differential equation within a transient rotor dynamic simulation is applied. In addition to the hydraulic coupling of inner and outer lubrication film in the floating ring bearing, a mass-preserving cavitation model is introduced. Therefore, the algorithm of Elrod is adopted by use of a regularisation scheme in the differential equation in order to eliminate the originally occurring numerical problems under transient loads. The developed program is validated based on data available in the literature, as well as on the basis of test rig measurements for a passenger car turbocharger. Finally, the achievable result quality is examined in relation to the computational cost under successive reduction of the hydrodynamic modeling depth.

Simulation of the Ball Kinetic in Ball-Type Automatic Balancing Devices by Solving the Axisymmetric Navier-Stokes Equations in Annular Cavities

Automatic balancing devices are useful in order to balance rotating systems, which show variable unbalance configurations during operation, e.g. centrifuges, without the need for active components like controllers or actuators. The design of a ball-balancer consists of an annulus symmetric to the axis of rotation. It is filled with a viscous fluid and counterbalancing balls, which can move freely and oppose the rotor unbalance in the plane of the annulus when operated at supercritical speed. In order to determine the time for the balancing effect to be reached once the critical speed of the rotor is surpassed, sufficient modelling depth is needed to describe the movement of the balls during rotor run-up. Derived from transient simulations the influence of the balancer design parameters on the balancing process can be evaluated. A non-linear model of a ball-type automatic balancer is presented with which frictional forces based on Hertzian contact pressure and drag forces induced by the surrounding fluid are considered. Latter are obtained by solving the axisymmetric Navier-Stokes equations in the annular cavity by the method of finite differences. As a consequence, only one friction coefficient has to be quantified empirically. The model is included in multi-body simulations of tabletop centrifuges and the resulting angular movement of the balls is held against experimental data gained from video material of a balancer specimen with a transparent lid. Furthermore, the rotor deflection is compared with the simulation results.