Simulation and its results, the test of quasy-static pressure: measurements of the flow in an overused body.

Latifi, Ahmet ; Ibishi, Ismet Maliq ; Latifi, Bekim 等

1. INTRODUCTION

Here is elaborated the model structure of shock-absorber together with some measurements and evaluation techniques in order to improve the parameters of the model. For these models, the industry started to develop full approach of CAE which deals with the problem of adjustment, whereof this approach is classified in three stages:

1. Simulation of body system

2 Absorber model

3. Heruestic.

Through the parameters will be given data for static gas pressure, volume of gas and friction, and also through diagrams are given the results of flow through overused body measurement, results of dynamometer to the histories test. Through these estimated parameters of dynamometer test, wherein results that the base characteristics of the valve will be lower than the characteristics of valve flow of piston which will be higher than those of base.

2. SIMULATION

In the purpose of simulation of vehicle dynamics, it is developed the physical model of vehicle shock-absorber and it is implemented in software program for simulation of suspension system. In this chapter, the model structure of shock-absorber is briefly elaborated together with some measurements and evaluation techniques in order to improve the model parameters, surely only from dynamometer measurements. These techniques are applied in second-hand shock-absorbers in front suspension of the car BMW the 7th series. The construction of shock-absorber is done in several stages as in geometrical aspect, strength, stability and function. The aspect of function is on adjustment of the extinguishing valve which nowadays is still fundamentally used from the driver activity.. For this reason the industry started to develop full approach of CAE which deals with the problem of adjustment (Fig.1). This approach can be classified in three successive stages. Firstly, absorbers mode with the series of parameters that is adjusted can allow to obtain the force of speed function and displacement.

Secondly, by means of simulation of suspension system, the function of the vehicle is characterized by means of couple forces and of acceleration and then changed into measurement of driving by using heuristic.

Heuristics is described as the amount of quantified measurement weights of the signals as values of RMS, the factor of cam and the parameter of bending. Heuristics calculates the scalar value that shows the driving measurement and/or manipulation. Basing on heuristics, can be proposed the optimal construction. Such heuristics are chosen in ideal way by the representing group engineers of driving from the determined vehicle companies and can be changed for every special type. For example, the sports vehicle it isn't supposed to have the same driving as "stationary wagons".

Such modulation is initiated with the requirement of Consortium INVEC (program Brite-Euram), that is consisted by 7 producers of vehicles (Fiat, BMW, VW, Porsche, Daimler-Benz, Peugeot and Renault), in order to make a standard model of the absorber that joins the bearing of the absorber and offers the minimum of model structure and of parameters and simulation of body system. The purpose of this model is to include entirely nonlinearity and dynamic within frequencies with a strip to 30 Hz. Over 30 Hz, in the frequent strip of noise, it seems to be very difficult to simulate the function of the absorber in general way because of specific changes that can be various. View of methods to do problem researches with noise jointly with shock-absorbers of vehicles by means of measurements as well as of simulations is given by Lawyers and others.

[FIGURE 1 OMITTED]

3. TEST IN QUAYS-STATIC PRESSURE

By means of quays-static test, are determined three models of parameters: static pressure of gas [p.sub.rt,0], static volume of gas [V.sub.rt,gaz,0] in reserved pipe and friction value [F.sub.riction]. Surely that the roughness of striking button or returning striking and pressure striking can be determined during the same test. Quays-static test with slow pressure and then with shock-absorber extension with typical speed 2mm/s in purpose to minimize absorbing forces because of losses of viscosity so that the absorbing force mainly is caused by friction and only with gas pressure. For evaluation of parameters it is considered the inside pressures in three equal comers. Thus force of absorbing is modeled as follows:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)

By using small square test meter that minimizes the difference between modeled measured force with the middle square, there are identified three parameters.

In fig.2. the results of pressure test the sleeper of BMW are compared with better adaptation that gives value of RMS of he remain of 7N. Even though this value seems to influence in reasonable agreement, it is clear that the curve of force it isn't well planned. This is surely because of the selection of polytrophic strength Y = 1.4.

It is also interesting to point out static gas volume. With the diameter of the piston the volume will vary about 5cm3/cm of piston so that gas volume will compensate the maximal pressure from 20 cm.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

4. MEASUREMENT OF FLOW IN BODY

During the flow measurement in body a part of flow is due to cross through the equipment under test by means of the pump till they are together measured the fall of pressure and flow scale. The rank of the determined flow is cleaned by using slowly deviation in a typical period of 200s.

In fig. 4. is shown the flow measurement in body to the crack of the valve wherein the flow in general is shown in funk

[DELTA]p = [BQ.sup.r] (2)

That is accompanied with specific exponent r. The measurement includes the cracks with middle scale of the valve of piston of the type Monroe 1".

The figure shows two proofs different exponents, respectively 1.75 and 2. From the comparison between measurements and calculated values, it seems that the required exponent 7/4 (=1.75) belongs much more the pressure curve in increase comparing with classic exponent 2.00.

In the table. 2. is given the parameters register that identify the measured flow wherein inside the brackets are expressed in units of SI. The flow exponent is calculated by four measurements of four cracks of the same type in order to determine the variability of production by means of standard deviation of four values. The noted quality from the value of RMS of remain demonstrates clearly the required efficiency of the exponent.

By means of measurements of the flow in body, all parameters in relation of overall the valve can however determine that this type of procedure can be expandable time by time if there are used modules not standards.

Thus, in this chapter, is proposed a test by using dynamometer wherein the valve parameters are withdrawn directly from the relation between absorbing force and speed. However, by means of dynamometer it isn't usually possible to be distinguished the flow in pressuring entrance so the immediate identification of these entering parameters together with pressure parameters in valve isn't feasible. For this reason it is recommended to identify some values for non-competing that can be dealt in the entrance it doesn't influence in the pressure fall.

In fig. 4, constrained valve in entrance of standard valve of piston 1" of Monroe is measured to 20 l/min that is equal with the speed of shock-absorber of 0.85 m/s. Except the bend of nearly 0.5 bar, it is increased the pressure because of button tightness in entrance and reduction of cracks in entrance. In comparison of fall of pressure for the reason of fluid flow (usually between 20 and 100 bar), the entrance influences relatively little in fall of pressure.

[FIGURE 4 OMITTED]

5. CONCLUSION

At shock-absorbers the function aspect stands in adjustment of the absorbing valve which nowadays still in fundamental way is done by the driver activity, whereof are tested many prototypes by engineers that have driven the vehicles through paths, and then they have made the upraise nab adjustment and as also they have adjusted the absorber in order to have better driving and better features for vehicles. In this work is done even the comparison of the value of exponent GAMA, from which depends the form of diagram to the measurement of liquid flow through shock-absorber body, shown in fig,3

6. REFERENCES

Dupuis, H. and Zerlett, G. (1996). The Effects of Whole-Body Vibration, Springer Verlag, Berlin,

Fash, J.W. (1994). Modeling of Shock Absorber Behavior using Artificial Neural Networks, SAE paper 940248

Verschoore, R., Duquesne, F. and Kermis, L. (1996). Determination of the Vibration Comfort of Vehicles by Means of Simulation and Measurement, European Journal of Mechanical Engineering 41, 137-143

Tab. 1. Parameters from quays--statistic test of the sleeper of
series 7 of BMW

Static gas pressure [p.sub.rt,0] (Pa) 2.64E+05
Static gas volume Vn,gaz,0 ([m.sup.3]) 9.30E-05
Friction [F.sub.friction] (N) 23

Tab. 2. The appropriate parameters for measurements of the
flows in shaft

Flow exponent r 1.75 2

Valued [flow.sub.bar/(1/min)r 2.13 (4.9e13) 1.58 (5.7e14)
(Pa/(m3/s)r)]
of coefficient B

Standard deviation 0.2 (2e4) 0.7 (7e4)
of B of remain RMS bar(Pa)