Virtual mechatronic simulator for the dynamic analysis of the automotive guiding & suspension system.

Alexandru, Catalin ; Pozna, Claudiu ; Alexandru, Petre 等

1. INTRODUCTION

The revolutionary evolutions in the field of motor vehicles impose the development and utilization of high technologies both for manufacturing and design. Recent publications reveal a growing interest on analysis methods for multi-body systems (MBS), which facilitate building and simulating virtual prototypes for complex products (Alexandru & Pozna, 2007; Bernard, 2005; Fischer, 2007). Virtual prototyping consists mainly in conceiving a detailed model and using it in a virtual experiment, in a similar way with the real case (Haug et al., 1995). The virtual prototyping can be implemented in different applications specific to the automotive industry, such as suspension design or vehicle dynamics. Regarding the dynamic analysis of the guiding & suspension system, different models can be used, from simple 2D "bicycle" models to complex multi-body systems full-vehicle models (Alexandru, 2009; Hegazy et al., 1999; Silva & Costa, 2007. These models allow to individually evaluate the main motions of the vehicle, or to approach the global dynamics.

In this paper, we performed the dynamic analysis of the guiding & suspension system using a full-vehicle model, which includes the front & rear suspensions, the steering mechanism, and the car body. The prototype is analyzed by simulating the passing over bumps with a virtual stand, at which the controlled motions of the input elements (which move the wheels) simulate the road profile. The study is developed in mechatronic concept, by integrating the mechanical model and the control system of the input elements at the virtual prototype level. The virtual prototyping platform used in study includes specific software solutions for the mechatronic modelling, as follows: MBS (MultiBody Systems)--ADAMS (for developing the mechanical structure), C&C (Command & Control)--EASY5 (for developing the control system).

2. VIRTUAL PROTOTYPE OF THE VEHICLE

The dynamic model of the guiding & suspension system is characterized as a constrained, multibody, spatial mechanical system, in which rigid bodies are connected through compliant joints and force elements such as springs, dampers, bushings, bumpers limiting the suspension stroke, anti-roll bar, tires.

Double-wishbone mechanisms are used for the independent suspension of the front wheels. The linkage uses two lateral control arms to hold the wheel carrier. The lower and upper wishbones connect to the car body using bushings. Spherical joints constrain the upright parts to the control arms. Tie rods attach to the steering center link and to the wheel carriers through spherical joints. The springs and dampers are concentrically disposed between car body and upper control arms. For limiting the compression--extension stroke, non-stationary bumpers & rebound elements are used.

A quad-link mechanism is used for the guidance of the rear axle. Compliant joints (bushings) connect the upper and lower links to car body and axle, respectively. The translational springs and dampers are concentrically disposed between car body and axle, and the bumpers & rebound elements are disposed inside the dampers.

To reduce the roll of the vehicle body, the model contains front and rear anti-roll bars, which are transversely fitted to the front/rear suspension. The anti-roll bar consists of two bar halves connected by a torsional spring--damper element. Bushings attach the bar halves to the car body. Drop links transmit the suspension motion to the bar ends. The drop links attach to the lower control arms from the front/rear guiding mechanism and to the bar ends with spherical joints.

The parallel-link steering subsystem is essentially a four-bar mechanism consisting of a pitman arm, center link, and idler arm. A worm steering gear transmits motion from the steering wheel to the pitman arm. The pitman arm rotates to impart motion to the center link and idler arm. The translation of the center link pulls and pushes the tie rods to steer the wheels. The transmission shafts are connected using Hooke joints. The steering wheel shaft and the steering input shaft are connected to the car body through revolute joints.

In this way, the virtual prototype of the vehicle, shown in figure 1, has 98 degrees of freedom (i.e. independent generalized coordinates), of which 15 are active mobilities, as follows: vertical displacements of the wheels--4, steering rotation of the front wheels--1, car body's oscillations--6, rotations of the wheels around the wheel spindle--4.

The virtual prototype is analyzed in passing over bumps dynamic regime, by using a virtual simulator (see fig. 1). The simulator contains four linear actuators on which the wheels of the vehicle are anchored, the input elements executing vertical motion relative to the fixed structure, for simulating the road profile. The connection between the wheels and the sustaining plates are made using contact forces, which allow modelling the elastic and damping characteristics of the tires.

The next step consists in developing the control system of the actuating elements, using ADAMS/Controls and EASY5. For connecting the mechanical model and the control system, the input and output parameters have been defined. The motor forces developed by the driving actuators represent the input parameters in the mechanical model. The outputs, which are transmitted to the controller, are the vertical positions of the actuators (which define in fact the road profile).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The input and output data are saved in a specific file for EASY5 (*.inf); there are also generated a command file (*.cmd) and a dataset file (*.adm) that are used during simulation. With these files, the block diagram of the control system was created in EASY5 (fig. 2), in which the mechanical system block includes the MSC.ADAMS Plant. From the controller point of view, for obtaining reduced transitory period and small errors, we used PID controllers. In the mechatronic model, ADAMS accepts the control forces from EASY5 and integrates the mechanical model in response to them. At the same time, ADAMS provides the current vertical displacements (of the driving actuators) for EASY5 to integrate the control system model.

3. RESULTS AND CONCLUSIONS

The analysis purpose was to determinate the vehicle response, for evaluating the dynamic performances. The inputs applied to the actuating elements (which move the wheels) simulate the road profile, considering the passing of the vehicle over a bump with the amplitude h=50 mm, and the speed v=70 km/h defined by the difference (delay) between the displacement input signal of the front and rear actuators. The dynamic simulation was achieved for a time interval long enough to catch all relevant motions during the virtual test.

[FIGURE 3 OMITTED]

For example, in figure 3 there is presented the time history variation for the vertical acceleration of the car body, which is the main factor in the automotive comfort. Such results allow evaluating and optimizing the dynamic behaviour of the vehicle in a fraction of both the time and cost required with traditional build-and-test approaches. One of the most important advantages of this kind of simulation consists in the possibility of make easy virtual measurements in any point/area and for any parameter. This is not always possible in the real case due to the lack of space for transducers placement or lack of appropriate transducers. Virtual prototyping allows realizing the projected reductions in cycle times while increasing the vehicle performance, safety, and reliability.

In the present research stage, the mechatronic testing stand, which simulates the vertical displacement of the wheels, can be used for replicate the real road conditions only for different rectilinear profiles. Our future researches will be focused on the adaptation of the vehicle simulator for the general testing case, which involves the actuating in three directions, simulating in this way the vertical, lateral and longitudinal motions. At the same time, the actuating system will be configured using the magnetic records of the acceleration functions, which can be double-integrated for obtaining the displacement signals that reproduces the motion on the real road.

4. REFERENCES

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Haug, E.; Choi, K.; Kuhl, J. & Vargo, J. (1995). Virtual prototyping simulation for design of mechanical systems. Journal of Mechanical Design, Vol. 117, No. 63, 63-70, ISSN 0161-8458

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