# Kinematic and Dynamic Response of a Novel Engine Mechanism Design Driven by an Oscillation Arm
## 2 Simulation Method  
The principle of functionality of a classical mechanism is known and, for this reason, it will not be detailed. This kind of mechanism converts rotating motion of crank into a translation motion of a piston. The overall principle is shown in Figure 2a. In Figure 2b, we show the kinematic scheme for the case of a mechanism with an oscillating arm. The difference between these two types of mechanism concepts consists in how the con-rod is assembled in the mechanism: for a conventional engine, the con-rod is directly connected to the crankshaft, and for the engine with oscillating arm, the con-rod is connected to crankshaft through arm 2. This oscillating arm slides into an axial bearing (5) that is oscillated about D point, and it may also change the length of vector OB and the piston stroke. When the engine mechanism is running, the pivot point (D) can be moved in the vertical and horizontal direction and thus, the position of the oscillating arm is changed. In this way, we can obtain different values of the compression ratio and piston stroke. Finally, we can obtain an optimization of the engine working regimes depending also on the mechanical loading and crank speed. In case of the engine mechanism with oscillating arm, the trajectory of the con-rod big end obtained on a complete crankshaft rotation is an ellipse, unlike the circular trajectory obtained on a conventional engine mechanism (Figure 3). This elliptical trajectory will determine an increase of piston motion time between top dead center and bottom dead center comparison by a conventional engine. Figure 3: Trajectory of the con rod big end for a complete rotation of crank shaft: (**a**) classic; (**b**) VCR. Figure 2: Kinematic schema for two concept of engine mechanism: (**a**) classic; (**b**) with oscillating arm. Maintaining the piston closer to the TDC (top dead center) as long as possible will create better conditions for ignition process at constant volume and an improvement of efficiency. In order to demonstrate the advantages that the oscillating arm mechanism can bring, some scenario analysis has been made. As a particular case, we started the survey from a classical engine with the following characteristics: bore: 82 mm, stroke: 76 mm, crank speed range: 1000-6000 rpm. For a relevant comparative analysis, the same components were used for the two solutions analyzed. Basically, the element that makes the difference between the two solutions is the oscillating arm, together with the bearing in which it slides. The input data used for kinematic simulation is shown in the Table 1.  
As can be viewed in the Figure 4, the pivot point was modified on the vertical direction to indicate how the stroke parameter is influenced and also chamber volume and compression ratio. In Figures 4 and 5, the nominal position of the bearing joints that connected the bearing to the engine block was noted with the letter D as was used on the kinematic scheme. As can be viewed in Figure 2b, the mechanism is related to the global coordinate system placed in the axis of the crankshaft. With respect to this GCS (Global coordinate system), the notations that define a new position of the bearing joint D were used as follows:  
* Ff the bearing joint is moved in the opposite direction with respect to GCS axes, the number \"1\" is used as a secondary subscript of the letter D; the first subscript indicates the axis direction of the movement takes place;
* In a similar manner, a subscript number \"2\" will be used if the bearing joint is moved in the positive direction of the GCS axes. In the kinematic analysis, the movable range of pivot point has been considered as +/-40 mm on the horizontal direction and +/-25 mm on the vertical direction.