Parametric Analysis of Magnetorheological Strut for Semiactive Suspension System Using Taguchi Method

Magnetorheological (MR) strut is among the leading advanced applications of semi-active suspension systems. The damping force of MR damper is controlled by varying the viscosity of MR fluid. In this work, the viscosity of MR damper varies by changing the current from 0.5A to 0.7A. The design of experiments is taken into account in concert with the product/process development as one completely advanced tool. The parameters used for ride comfort optimization are sprung mass, spring stiffness, tire pressure, current, and cylinder material with two levels of each. Taguchi orthogonal array method is used to select the best results by parameter optimization with a minimum number of test runs. In this paper, from Taguchi L16 array and S/N ratio analysis, it is observed that the cylinder material with Al and CS for damper cylinder is a key parameter for performance measure of semi-active suspension system. From regression analysis, a linear mathematical model is developed for Al and CS as cylinder materials. The interaction of cylinder materials with all four parameters is plotted. The methodology implemented for measurement of acceleration as a ride comfort is as per IS 26311997. The more economical model of magnetorheological damper will motivate Indian auto industry to broader applications. Keywords-magnetorheological damper; parametric analysis; semiactive


INTRODUCTION
An effective automotive mechanical system has to give comfort and good road holding ability, once the vehicle is moving on any road disturbance.The vehicle body is supposed to have considerable damping or resistance to avoid massive oscillations.Comfort optimization is predicated on spring stiffness, damping and sprung mass.Normally, such system types are developed by experimental approach.The procedure for designing and modeling of a novel large-stroke MR damper is tested in [1] under impact load and it is observed that the inertia damping force could not be ignored like in the common MR damper due to large acceleration.2D axisymmetric model was built up in [2] to investigate and analyze the MR damper qualities predicting the damping force characteristics.The Bingham model of MR damper was proposed and compared with experimental results for magnetic saturation.This work inferred that the obtained magnetic saturation model can show effect on current, amplitude and excitation frequency.The phenomenon of magnetic saturation is simulated in [3] and obtained results are compared with the experimental results.Optimization technique is used to maximize magnetic flux density which affects the force developed by damper [4].The MR fluid structure and properties, damper description and parametric damper models which are connected in various ways with the actual behavior of the MR fluid were presented in [5].Recommendations for the design of main-spring and shock absorber of motor vehicle suspensions were given in [6].Indications acquired for the shock absorber allow us to obtain the damping coefficients in the compression and rebound strokes and to calculate the power dissipated during the vehicle oscillatory movement.An extensive work has been done on the transmissibility of vibration isolator in [7], where authors proposed the concept of output frequency response function in order to examine the force transmissibility of MDOF structures with a cubic non-linear viscous damping device.Control strategies can be divided into two main categories: active and semiactive.In the case of active systems the performance is superior and optimum transmissibility has no resonance.Semiactive systems provide reliability comparable to passive suspension systems [8].In [9], it is observed that the vertical acceleration of body mass is substantially reduced by using a controlled MR damper.
Sensitivity analysis for leaf springs with different stiffness was done in [10] on roll bar of front suspension system by using Adams simulation software.Static test results were compared with the dynamic test ones.From the simulation results, it is observed that the parametric effect on suspension system is not satisfactory by using static analysis.The experimental results carried out in [11] regarded optimization of suspension system used for vehicle occupant seat for a quarter car model.The Taguchi method was implemented in order to reduce vibrations.From the simulation results it is observed that stiffness and damping preliminary values are the control variables of the suspension system.Authors in [12] studied the dynamic loads enforced on suspension components through bushings and joints.In order to predict the vehicle

Damping Fo
The damping and viscous co  aguchi method of the lower timization is ftware to mod ased on the T ution set and t obustness imp f car robustn n the current w as tire pressu st important, c ieve good ride the accelerati ed in Table I.

IV. EXPERIMENT DESIGN
The experiment design is taken into account in concert with the product/process development as one completely advanced tool.The experiment design takes into consideration wideranging applications in the development of product/process.There are the two approaches of DOE.

A. Full Factorial Design
In full factorial experimental approach, two (at least) or more factors are used in a feasible level and the required units take all probable combinations of all levels of these factors.For 9 factors with 2 levels for each, 512 runs are required for a full factorial design.In this method, each parametric effect on response variables and the interaction between factors is studied.

B. Taguchi Method
The major shortcoming of full factorial design is that the number of experiments to be carried out is large which means more laborious work on a large number of parameters.To avoid this troublesome work, Taguchi recommended a specially intended method called orthogonal array to learn the whole parameter effect with lesser quantity of experiments.

C. Selection of Control Factors
It is observed that spring stiffness and electric current need to be appropriately considered under positive range of sprung mass and road conditions.For exceedingly rigid suspension the vehicle system will be vastly stable but acceleration of occupant body will be high and comfort will be low.For a smaller amount of hard suspension, passenger comfort will increase but vehicle stability decreases.The selected parameters for suspension are described in Table III.

D. Orthogonal Arrays
Taguchi developed the orthogonal array method to study systems whose performance is affected by different factors, in a more convenient and rapid way.This method can be used to select the best results by optimization of parameters with a minimum number of test runs.Application of Taguchi method can achieve the best results out of various tests by selecting the optimum combination of different factors.Final product quality can be improved in terms of process optimization, product design and system analysis.To study a sufficient number of experiments with a large number of variables, Taguchi recommended the orthogonal array method for experimental design.The conclusions made after a sufficient number of experiments are usable over the whole experimental area covered by control factors and their ranges.Orthogonal array method was discovered before Taguchi implemented it for DOE.In this method, the columns of tabulated sets are orthogonal and consequently linear graphs are plotted to fit the specific project applications.In the current study, five parameters, tire pressure, spring stiffness, damper cylinder material, sprung mass and electric current, each one with two levels are used.Table IV defines the L16 array.The number following the "L" indicates the number of runs in the design, and 16 means the array requires 16 runs (2 5 ), which indicates that the design estimates up to 5 main parameters at 2 levels each.

E. Analysis of S/N Ratio
To measure the performance characteristics, Taguchi recommends the use of the loss function that is deviating from the desired target value.The value of this loss function is further transformed into signal-to-noise (S/N) ratio or SNR.The preferred parameter settings are determined through SNR analysis where the optimized parameters are considered those that maximize the appropriate SNR [15][16][17].To analyze SNR three types of performance characteristics are considered.
1) The Smaller the Better (for making the system response as small as possible) 2) The Nominal the Best (for reducing variability around a target) 3) The Larger the Better (for making the system response as large as possible): Lower values of passenger seat displacement and displacement settling time are the prime requirements to achieve passenger RC and safety, thus in present work, SNR with lower-is-better characteristic is selected.

F. Optimum Level Prediction
The results obtained are depicted in Table VI.It is observed that cylinder material ranks first and Figure 4 shows the optimum parameter level.From Table VI it is observed that cylinder material performs ranks first and from the main effect plot of SN Ratios (Figure 4), P34K8000CM-1M97I0.7 shows optimum level of parameter.Taguchi designs conventionally focus on the main effects, but it is important to test the supposed interactions.In order to determine the effect of one on another parameter with respect to its response, Taguchi uses a method known as interaction plot.To study the interaction plot, the interpretation of

VI. CONCLUSION
Taguchi L16 array and SNR analysis show the cylinder material with Al and CS for damper cylinder is a key parameter for performance measure of semi active suspension with MR damper.It is observed that damper cylinder material is a key parameter to design the MR damper.From the interaction plot, it is concluded that cylinder material interacts more with spring stiffness and tire pressure compared to sprung mass and current.The low price model developed will have wide range of applications to Indian auto industry.

TABLE II .
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Table V represents the L16 orthogonal array with acceleration as output. www.

TABLE V .
TAGUCHI L16 ARRAY WITH ACCELERATION AND SN RATIO

Table
VII is considered.According to SNR response table, ranks are established.From TableVI, cylinder material takes first rank.In order to check the cylinder material's effect on the other four parameters, its interaction plot with tire pressure, spring stiffness, sprung mass and current is plotted.TableVIIrepresents the interpretation of interaction lines.The regression equation (6) is generated from regression analysis.