Milan Klapka

Design of magnetorheological damper with short time response

For efficient fast control of suspension systems with magnetorheological dampers controlled by semi-active algorithms, the time response of the magnetorheological damper is one of the most important parameters which influences the performance of the suspension system. The time response of commercial magnetorheological dampers with common controllers is in the range of tens of milliseconds, which is too long for efficient real-time control of car suspension. This article describes the ways how to design magnetorheological damper with short response time. First part describes the elimination of long time response caused by high inductance of electrical circuit of magnetorheological damper using current controller. The second part describes elimination of long time response caused by eddy currents which are induced in the magnetic circuit of magnetorheological damper. The new piston of the magnetorheological damper is designed from material with high relative permeability but low electrical conductivity (ferrite). The time responses of magnetic induction and damper forces were measured and compared to original commercial Delphi damper. Results showed rapid improvement in time response when the current controller is used and when the piston is constructed from ferrite materials.

Limiting factors of the response time of the magnetorheological damper

Magnetorheological dampers seem to be suitable for the adaptive car suspension systems. For proper operation of the semi-active algorithms (skyhook, groundhook), the force response of the damper must be fast enough. In this paper, the response time of the Delphi vehicle MR damper is examined and the sources of the overall force time response on the control voltage are discussed. One of the main sources of the response time seems to be electro-magnetic circuit of the MR damper. A principle of an optimal controller for reducing response of the coils current on the control voltage is designed. However, the measured overall force time response with fast current controller was not reduced as expected. Therefore, a FEM simulation of the magnetic circuit was made. It shows that after an optimization of the current controller, eddy currents in the coils core cause long time response and therefore they are the limiting factor of the response time of the MR damper. These simulations were verified by the measurements and some recommendations about improving the pistons construction are given at the end.

The behavior of the MR fluid during durability test

The article describes results of durability test of a magnetorheological fluid (MRF), which was carried out in rheometer of own design. The rheometer design enables to measure the rheological properties of MR fluid and to expose it to a long-term loading simultaneously, without any manipulation of the measured sample. During the durability test a change of the two most important parameters of Bingham model describing the behavior of MR fluids can be followed – dynamic viscosity and yield stress. In this paper the yield stress and viscosity were evaluated depending on temperature in OFF-state. The results show a significant change of yield strength during durability test depending on temperature of loading. Dependence of yield stress on temperature was proved. The viscosity decreased by 36% from its initial value after the dissipation of 9÷20kJcm−3 from total 1.2 MJcm−3 and then has remained the same until the end of durability test. Viscosity was evaluated depending on temperature.

Reinvention of the EUSAMA diagnostic methodology

The authors use the mathematical model of the vehicle suspension to simulate the diagnostic procedure of the EUSAMA methodology. Simulations on large dataset of vehicle chassis are calculated to identify the causes of false-negative evaluation of car condition often found in the cars that are in good technical shape. It is proved that the most important cause of the methodology failure is the concurrence of current trend to use stiff car tyres and a high excitation stroke of currently used test rigs. Such high amplitudes of excitation do not correspond to the excitation from modern roads. Then, the authors verify the effects of non-linear characteristics of the damper and tyre stiffness on the results obtained by simulation diagnostic tests. This paper introduces the adjustments of the EUSAMA methodology, which should eliminate a growing set of tests with contradictory diagnosis results.

Reduction of Pneumatic Tyred Roller Fuel Consumption

This article deals with optimization of operational parameters of an energy regeneration module for a heavy vehicle. Recently, there was developed an energy regeneration module for a pneumatic tyred roller with hydrostatic drive. It was necessary to optimize its operational parameters to achieve good results in experimental tests on the actual vehicle. The optimization process was based on a numerical model of the vehicle using a parallelized modification of the differential evolution algorithm as an optimizer. Suggested parameter values were subsequently verified experimentally on the vehicle by analysis of the fuel consumption.

Assessment of the Stub-Shaft Sleeve Bearing Chaotic Behavior in Automotive Differential

This article is concerned with capabilities of analysis of a chaotic behavior of the stub-shaft sleeve bearing inside the automotive differential. Analytical methods based on phase-trajectory diagrams and fractal dimensions are used. Effect of the chaotic behavior on automotive differential noise is examined as well. The purpose of the article is to give an overview of practical use of the above mentioned methods. The potential advantages, disadvantages are discussed as well as expected contributions of application of the bifurcation analysis to solving the automotive differential journal bearing noise problem.

Identification of MR Fluids Properties in Mechatronic Damping Elements

Mechatronic systems often use a magnetorheological fluids for the damping of movement. A significant dependence of their rheological properties on a magnetic field is the main reason. Therefore these fluids are relatively well controllable in mechatronic systems. For correct control of these elements it is important to assign to MR fluids a suitable rheological model of behavior. This model describes flow and viscosity dependences by various magnetizing currents and various shear rates. This paper is concerned with measurement problems of flow and viscosity curves on standard and original rheometers. Based on measured data, a behavior of MR fluid can be mathematically described, a relevant model can be compiled, a behavior of different MR fluids can be compared or changes of mechanical properties during the measurement can be observed.

Over-crossing test to evaluation of shock absorber condition

On Faculty of Mechanical Engineering, Brno University of Technology it was state to life a new methodic for check quality of suspension wheel damping of means of transport so-called over-crossing test. The target group cars are categories, for those are unsuitable existing known routes. This paper is describing principle of methodology incumbent on evaluation behavior of suspension wheel after crossing of defined obstacle. This method was conquest experimental testing on real, experimental and virtual vehicle. This method is suitable for on-car test of shocks absorber on motorcycle, delivery and truck car.