Physical Drive Train Model

The physical drive train model used throughout this investigation corresponds to a scaled down reduced drive train of an Opel Corsa®. The scale down factor is defined so that an energy-equivalent model, where the vibrations lie in the desired judder

210 _{cf. 2.3.2}

frequency region, is achieved. Due to restrictions in the geometry and the mechanical properties of the materials, this can only be accomplished through modification of some parameters like the stiffness and strength of the side shaft and the values of the inertia of certain elements.

CAD-schematics of the mechanical configuration of the test bench can be observed in Figure 7.1.

Figure 7.1: Scaled down physical model of the reduced drive train

The components of the model are numbered from left to right. The first component is the linear actuator (1) responsible for the application of the clamping force in the clutch (5). The force is applied through the bar kinematics around the input dc motor (3). The value of the force is measured by the force sensor (2) located before the input DC motor (3) responsible for the reproduction of the combustion engine speed and torque. The latter is measured by a sensor that relies on the magnetorestriction effect of ferromagnetic materials of a permanently magnetized shaft (4). Afterwards, the clutch discs (5) are tested. The friction pads are mounted on the output disc of the clutch. Together with the side shaft (6) and the vehicle mass (7) (modeled as a disc with the equivalent inertia), they form the physical two-mass oscillation model of the drive train. Finally, the output DC motor (8) is found at the right end of Fig. 7.1.

The friction contact in the clutch consists of three pellets of the ceramic material Al2O3,

whereas the counter surface on the input side is made of the unalloyed steel C45. The speed of the input and output DC motors of the manufacturer SEW211F

212 _{is measured}

with their integrated resolvers. However, direct measurement of the absolute rotation

angle is not possible with the same device. The third speed of relevance for the purpose of this investigation is that of the clutch output disc, which is measured with an external laser surface vibrometer (LSV).

The clutch linear actuator is conceived as a stepping motor with a spindle that translates the rotational into a linear motion. The integrated rotary encoder enables a resolution of the axial travel path of 1𝜇𝑚. However, the actuator is only able to work in steps of 10𝜇𝑚. Target positions are defined in increments, where 1 𝑖𝑛𝑐𝑟. = 1𝜇𝑚. The control algorithms are programmed in a Matlab/Simulink212F

213 _{environment and the}

real time system ADwin Pro II213F

214_{. The output parameters of the DC motors and the}

clutch actuator are set via a CAN-bus connection. The input values, thus the speed of the DC motors, are processed through their resolvers but their value is converted into an incremental signal in their inverters, in order to reproduce the sensor signal usually available in commercial drive trains. The incremental signal is converted back to a speed value in the real time program. All relevant sensor input signals are read as analog signals.

The test bench represents the drive train following the XiL-framework introduced in 2.3. The “Vehicle” system is implemented in its Level 1 subsystem layer: the “powertrain- in-the-Loop” layer. The only virtual element of the system “vehicle” consists of the combustion engine, whose output and input signals are computed in real-time. All other elements are modeled as a physical two-mass oscillator, as described in earlier chapters. Thus, the entire output side of the power train is reduced to physical models of the clutch, the side shaft and the vehicle mass.

The system “Environment” is conceived in a manner that would allow an abstract virtual environment consisting of a set of resistances (e.g. air resistance) and a torque load resulting from the vehicle mass and the inclination of the road to be defined. For simplicity reasons no additional loads are defined and thus a virtual environment is not present. The environment of the physical elements of the test bench is ever present but generally neglected.

The system “Driver” consists of a real-time virtual driver that sets a constant speed controller for the engine and a force ramp for the clutch actuator whenever the RL- agent is not active. Furthermore, even though the reward is a key element of the RL framework, it is the driver’s expected behavior to judder vibrations, which was used to define this signal. Thus, the driver is responsible for the feedback that the agent receives regarding judder vibrations.

213 _{MathWorks 2015}

Finally, the system under development (SuD) consists of the RL framework introduced in earlier chapters. It controls the clutch actuator in real-time in order to optimize the perception of clutch judder through the driver.

The graphical overview of the application of the XiL-framework to the Mini-HiL test bench setup for the investigations in the context of this work can be taken from Figure 7.2.

Figure 7.2: Application of XiL-approach to the development of the RL framework for judder suppression on the Mini-HiL test bench setup214F

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