*Advanced Applications of Hydrogen and Engineering Systems in the Automotive Industry*

(**Figure 20**), and a single OBE analog input valve of the same size [20]. The software is individually tailored for the different configurations and combinations of the IAC-R valve by standard parameters set in the factory. Settings for the closed-loop and control parameters are done via the bus interface. Several characteristics define the last generation of electro hydraulic control: fully digitized valve and axis control electronics; position and force control of hydraulic axes directly in the valve; various controller functions available (pressure/flow rate, position and alternating control); input of set points, configuration and diagnosis via field bus (depending on the type via CANopen or Provirus DP). Additional analog set point interface can be used as an alternative to set point input via field bus, but the electromagnetic interferences can create serious troubles, which need safety requirements according ISO 26262.

The CANbus type of controller area network is best suited for multipoint, long range cabling in high electromagnetic interferences areas where analog feedback signals may fail. This new type of control is widely used in military, automotive and aerospace simulating platforms or other systems where accuracy is very important. The behavior of the servovalve in a digital position-closed loop was identified by the aid a special test platform, which includes a strong elastic component, and a variable mass load (**Figures 21** and **22**).

#### **Figure 20.**

*High-response valve with integrated digital axis controller (IAC-R) and field bus interface (REXROTH)*

#### **Figure 21.** *Hydraulic diagram of the platform for testing digital servovalves.*

**Figure 22.** *Test platform for identifying the digital servovalve performance [17].*

A magnetostrictive digital displacement transducer with SSI interface was used for the load. Position reference is set though CANopen bus, and the control algorithm is a PID made with the OBE of the digital servo valve. The reference value for the digital test was generated with the application provided by the manufacturer and sent with a USB<->CANopen adapter. The positioning accuracy depends on the friction force of the steering cylinder as a function of speed (**Figure 23**).

**Figure 24** shows a typical response of a servomechanism with P controller. The response time of the digital servovalve is very small: about 2 ms for a 10% input signal. Consequently, the frequency response is very fast (**Figure 25**).

The system performances were identified using a forestry articulated tractor (**Figure 26**) designed as prototype by the research department of the Romanian company "PROMEX" from Brăila [22]. The front chassis was locked, leaving free the back one to rotate on a circular raceway (**Figure 27**). The tractor steering system was studied by the aid of a rotary hydraulic motor controlled in closed loop by a servovalve (**Figure 28**). Then, the steering amplifier was replaced by the servovalve itself.

Usually, the control valve of the ORBITROL hydraulic steering unit is designed with open center for reducing both fuel consumption and steering mechanical

**Figure 23.** *Friction force of the steering cylinder as a function of speed [21].*

**Figure 24.**

*Typical response of the servomechanism for a P controller with KP = 4.*

**Figure 25.** *Frequency response of the servovalve spool position for a sine input of 1.0 V at 50 Hz (given by CANopen).*

**Figure 26.** *Overall view of the articulated full hydraulic tractor.*

shocks. The "price" of these gains is a big backlash (**Figures 29** and **30**) which increases with the input frequency [23].

The direct control of the steering angle by a servovalve needs a constant pressure supply but avoids the backlash (**Figures 31** and **32**). However, the hysteresis

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

**Figure 27.** *Plain view of the steering hydraulic cylinders with position transducer.*

**Figure 28.**

*Hybrid steering servo system driven by an ORBIT motor in close loop: (a) driving system view; (b) rotary feedback potentiometer driven by the motor.*

**Figure 29.** *Steering system response when ORBITROL unit is driven by a hydraulic motor (Ui = 1.0 V; f = 0,05 Hz).*

**Figure 30.**

*Steering system steady state characteristics when ORBITROL unit is driven by a hydraulic motor (Ui = 1.0 V; f = 0.05 Hz).*

#### **Figure 31.**

*Steering system frequency response when cylindres are driven by a servovalve (Ui = 1.0 V; f = 0,05 Hz; ps = 100 bar).*

increases with the input frequency. The normal friction forces inside the hydraulic cylinders increase the nonlinearity of the steady state characteristics.

The steering process quality can be improved by increasing the pressure supply, reducing the length of the hoses, and the servovalve gain around the null.

**Figure 32.** *Steady state characteristics for Ui = 1V, f = 0.05 Hz and ps = 100 bar.*

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

A common stepping motor with battery-less multi-turn absolute encoder can be regarded as a possible electromechanical interface in the ORBITROL steering system, but the size and the weight are too large for the normal input torque (about 10 Nm).
