**2. Dynamics of a basic hybrid servomechanism**

The assessment of the static and dynamic behavior of a hybrid servomechanism was performed by numerical simulation using Simcenter Amesim language

*Hybrid Steering Systems for Automotive Applications DOI: http://dx.doi.org/10.5772/intechopen.94460*

produced by SIEMENS PLM Software [3, 4]. The simplified simulation network is shown in **Figure 2a**. The real hydro mechanical diagram of the system, proposed by Prof. J.-Ch. Mare in 2013 [5], shows a much more complex mechatronic system, with a mode selector (active or damping), a differential pressure transducer for the main loop, a rudder angle transducer, some hydraulic resistances modeling the system leakages etc. (**Figures 3** and **4**).

The core of the system is simple, but the whole assembly looks like a F1 hydraulic system with nine complex control loops: Power Steering, Gearshift Clutch, Differential, and Reverse gear, DRS, Brake by Wire, Throttle Inlet valves, and Turbo Wastegate. All of them are supplied in close loop by a single Parker swash plate axial pistons pump, pressure compensated! [6].

A simple design [5] based on a DC motor driving a gear pump, and a hydraulic cylinder can reveal both good enough dynamic performances, and some design

**Figure 3.** *Electric drive system and the position loop controller.*

**Figure 4.** *Hydraulic section of a complete hybrid servomechanism.*

problems involved in the lifetime of a hybrid servomechanism. The time constant can be easy found using a small voltage step input, for obtaining a piston displacement of 1.0 cm from a stroke of 2.5 cm. A reasonable force step input applied on the hydraulic cylinder piston rod can show the system capability to reject common disturbances. Both events were simulated with Simcenter Amesim language for a pump of 1 cc3/rev, reaching 9000 rev/min and 250 bar, driven by a small DC motor of 25 Nm at 270 V and 45 A, with shaft speed sensors used to allow the speed control. The results are presented on the same diagram from **Figure 5**. The time constant of the electro pump is less than 0.25 s, and the piston final position is reached in less than 0.7 s. A piston sudden load variation of 40,000 N generates a drift of about 20% from the nominal value 0f about 80,000N.

**Figures 6–8** show the evolution of the main parameters of the pump during the studied transient.

A sudden aerodynamic load on the aileron can generate a short cavitation period in the suction line of the pump. This dangerous event is avoided by loading the

#### **Figure 5.**

*Dynamic response for a common position request followed by the rejection of a sudden aerodynamic load: (a) Position request and the piston sliding position; (b) Aileron angular position as a function of time.*

*Hybrid Steering Systems for Automotive Applications DOI: http://dx.doi.org/10.5772/intechopen.94460*

**Figure 6.** *Pump flow rate evolution during the studied transient.*

**Figure 7.** *Pressure in the suction port at the beginning of the aerodynamic load.*

**Figure 8.** *Pump delivery pressure evolution during the studied load transient.*

hydraulic accumulator with nitrogen at 5-6 bar. The compensation of the aerodynamic load applied on the aileron needs a remnant voltage on the armature winding, and a corresponding current (**Figures 9** and **10**). However, the energy needed for the studied operation cycle is very low (less than 120 J).

It is useful to study the frequency response of a basic hybrid servomechanism. This task can easy be accomplished using the "transfer meter" block from the "control library" of Simcenter Amesim (**Figure 11**). A typical result (**Figure 12**) shows a normal behavior for small amplitude input signals: (a) low auto-oscillation risk; (b) lower, but dynamic good enough performance for practice.

The studied dynamic model, even simple, gives an overview of the wide facilities of the behavioral analysis by simulation. However, in reality, some parts of the system should be better considered to get a more predictive representation. Much more, the experimental validation of each new component needs a lot of experimental researches. The history of the high tech electro hydraulic manufacturers has shown a huge effort of fine-tuning and implementing new generations of components and systems [7–9]. Dominque van den Bossche [2] summarized some of developing stages of this process in close connection with the possible dangerous situations, which can occur in any flight control systems. Specific maintenance programs have to be implemented in all manufacturing process related to the automotive engineering.

**Figure 9.** *Variation of the input voltage applied to the armature winding.*

**Figure 10.** *Variation of the input current in the armature winding.*

*Hybrid Steering Systems for Automotive Applications DOI: http://dx.doi.org/10.5772/intechopen.94460*

**Figure 11.** *Simulation network for servomechanism frequency response.*

**Figure 12.** *Frequency response of a symmetric hybrid servomechanism.*

The new generation of mechatronic simulation languages reduced drastically this effort. The use of the Real Time Simulation with Hardware In-The-Loop accelerated this process [10–13]. For example, Amesim models can be imported in LabVIEW real time platforms in order to simulate the automotive systems using the general software platform from **Figure 13** [10].

A successful hardware implementation of this concept is presented in **Figure 14**, in order to speed up the design of the new automotive control programs.

The RT simulations with Amesim are frequently used for tailoring different applications of the electrohydraulic hybrid servomechanisms. For example, the complex steering systems of "Self-Propelled Modular Transporter" as that designed by Mammoet [14] need a RTS of all the path followed during the process. The independent propulsion and steering axles are regarded as "super component" in the simulation network of such a complex vehicle. The RTS platform from
