app automotive shockabsorber

7/25/2019 App Automotive ShockAbsorber

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Application

ITISimulationX2008-03-07

Shock Absorbers

Evaluating of Shock Absorbers

Shock absorbers in motor vehicles greatly influence driving safety and comfort.Good shock absorbers exhibit the desired effects across a vast spectrum ofcontinuously varying operating conditions.Shock absorbers employ a large number of hydraulic resistors that have non-linearcharacteristic curves and are switched on and off as a function of the operationalmode. The working properties of shock absorbers are conventionally adapted at thecost of great experimental effort. SimulationXprovides an alternative for evaluatingtheir properties in advance of construction.

Figure 1: SimulationX quarter car model with double tube shock damper

The model of the shock absorber can be quickly generated using pre-definedSimulationX library elements. In the present example, it is important to integratemeasured characteristic curves for the pre-defined model objects. The modeltherefore contains many objects of the "Throttle Valve"type from the SimulationXHydraulicslibrary, in which measured characteristic curves are taken into account.As an alternative, hydraulic objects can also be parameterized via geometricinformation. Data on the dynamic properties of tires, roadway, axle and vehicle

mass, as well as shock absorbers is gathered with elements from the Mechanicslibrary in SimulationX, such as Springs/Dampers/Backlash, Mass and ExternalLoad.

Simulation ofdynamicproperties suchas stiffness,shock absorption,friction, massdistribution

Mechanics and

hydraulics in onemodel

Parameterspecificationusing geometricdata

Modeling of anynon-linearity

Model verificationand validation

Models indifferent levels forcomponentdesign and fastcalculation (HiL)


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ITI GmbH Webergasse 1 01067 Dresden Germany

Tel. +49 (351) 26050 0 Fax +49 (351) 26050 155

[email protected] www.simulationx.com www.iti.de

Using High-performance SimulationX Library Elements

The SimulationX models for mapping the shock absorber are designed with resistors and checkvalves. While the user demands extreme flexibility for the input of non-linear parameters andcharacteristic curves, SimulationXallows

Entering any number of variables and formulas in the input field of any

parameter, Using already in elements implemented data tables to import measured data

Reading in measured data using curve, curve set,2D-mapand 3D-mapelements andworking with references in elements.

The different curve and map elements provide several interpolations, approximation and extrapolationmethods.

Figure 2: SimulationX elements for implementing of measured data (left), shock absorber modelwith signal based force-velocity-characteristics

Figure 2 shows a selection of available curve and map elements. The model displayed in Figure 2uses a curve element to describe the force-velocity-dependency of the damper. The data in the curveelement could be measured or simulated data as well as fictive data to reach designated criteria duringthe design process of components and systems. These analogues models are well appropriated forimplementing in complete system models.


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Tel. +49 (351) 26050 0 Fax +49 (351) 26050 155


Analysis and Evaluation using SimulationX

Design and optimization of shock absorbers has been a demanding task. In particular, finding optimumvalues and characteristic curves for the hydraulic flow resistors requires great experimental effort and alot of experience. Computer handling at a reasonable cost and within a relevant time period in practicehas not been feasible up to now, due to the complexity of the problem, the interaction of mechanical

and hydraulic components, and the nonlinearities of the parameters and properties.SimulationX allows the simulation of combined hydraulic-mechanical models at the system level. It canbe used to optimize the hydraulic or mechanical structure as well as to find optimum settings for certainparameters in advance of the construction. This saves substantial costs and helps prevent failures indevelopment. The results obtained by simulation have been compared with experimental data andevaluated for their validity.

Figure 3: Damper test rig model

By varying the arrangement, the flowcharacteristics, geometric dimensions andopening pressures of the valves of thepiston valves and the base valves differentdamping characteristics are achievable.

Figure 3 shows the model which representsthe damper under test conditions in a testrig to determine the damper characteristics.

The one side fixed damper is excited withdifferent velocities and displacements. Thedamping force will be measured.

Results

Simulation results of these damper characteristics (progressive, linear and degressive) are shown in

Figure 4. Today in many cases for passenger car applications a degressive curve characteristic ispreferred.

Figure 4: Simulation results of damper F-x-characteristics (left) and F-v-characteristics (right):progressive (top), linear (middle) and degressive (bottom)


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The model shown in Figure 1 is used to simulate the dynamic behaviour of axle and chassis to aground excitation.

Figure 5: Response to a singular ground excitation of 50mm

Conclusion and future prospects

So far this application demonstrates the simulation of a passive twin tube shock damper. The dampingof these passive damping systems is only velocity dependant. Developments in recent years lead toactive shock damping system to improve the behaviour of damping systems to the desired application.Compared to passive shock dampers active systems can vary the damping depending on workingconditions, e.g. piston stroke, load dependent, excitation amplitude and acceleration.

One possibility to get an active damping system is to implement a proportional valve into the piston.The damping can be influenced by varying the proportional valve opening area. To analyze thebehaviour of an active damping system the model of the passive shock damper can be easilyextended with elements of the hydraulic library, e.g. proportional control valves. Furthermore inSimulationX the active damping control system can be designed, modelled and analyzed incombination with the physical damper model.

app automotive shockabsorber

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