A Consistent Preliminary Design Process for Mechatronic Systems - Simulation and Modeling Methodologies, Technologies and Application - page 96

This study covers the preliminary design phase of a mechatronic system, in order
to verify that the chosen design is in accordance with the system requirements and to
verify that this chosen design minimizes risks in further design phases. Following the
recent advances in Model Based System Engineering [3], the preliminary design can
be viewed as a model transformation process [4].
Based on the example of a power lift gate, our goal is to show how the engineering
knowledge can be formalized and used all along the three following phases of the
preliminary design process: requirements definition and functional analysis,
geometrical and physical modelling, optimization.
Once the early design phases have been performed with SysML models, the
physical modelling of the overall system has to be built, based on the topology of the
system, in order to generate the equations required for the optimization phase. This
being done, the Design Space Exploration can be executed in order to discover the
optimal design solution from all functional and architectural specifications and
constraints. Indeed, the most efficient way to explore this design space is to reason
about previous SysML models, thus proving in a mathematically rigorous way that all
required properties and constraints are met.

2 A Power Lift Gate Scenario

An automotive power lift gate (Fig. 1) includes a lift gate door hinged to a car body.
This system moves the lift gate between its open and closed positions, thanks to elec-
tric cylinders (Fig. 2) that replace the usual gas struts in a classic manual lift gate. It
includes a motor and a gearbox that are fixed to the base tube and a jackscrew that
drives the upper tube, helped by a spring, in order to sustain static forces. Both elec-
tric cylinders are identical and are fixed to the car body and the lift gate.
In order to ensure that the main requirements are fulfilled, such as the opening du-
ration and the power consumption, the electric cylinder has to be preliminarily
designed, whatever its internal structure is, meaning that the fixing points on the car-
body and the lift gate, the force needed to open and maintain the lift gate and its full
length and rest length have to be determined.

Fig. 1. The power lift gate location on a car body