The ROboMObil is designed as X-By-Wire-System with a number of independently controllable vehicle dynamics actuators. An intelligent central control unit refines the driver input and computes the appropriate control signals for the current driving state. In contrast to conventional, automotive braking and steering systems there is no mechanical fallback level available in the ROboMObil. As a consequence the control system performance and robustness, as well as long-term behavior have to be examined and evaluated. Specialized test rigs enable a separated analysis of the vehicle’s subsystems to determine their physical behavior apart from the overall system. Component tests with repeatable conditions can be carried out. They also allow modification to components and control algorithms to be evaluated before they are fitted onto the ROboMObil. Measurements regarding powertrain stiffness and friction help to improve the corresponding models stored in the vehicle dynamics control. A Hardware-in-the-Loop setup allows component measurements during driving manoeveurs isolated from the physical vehicle.
The mechanical brake system in the ROboMObil is split in two independent brake circuits located in the vehicle’s front and rear axle module. Every circuit consists of an electrohydraulic brake actuator and two sets of disc brakes. To determine the fluid dynamic effects in the system the entire braking conduit along with the braking actuator and the brake calipers is replicated. The brake fluid pressure is monitored inside the brake actuator and at the brake calipers. Furthermore brake force and deflection of the brake caliper and the master brake cylinder are measured. The measured values improve the model-based simulation and lead to a deeper understanding in terms of dynamic behavior and friction in the brake system. Other fields of research are long-term studys regarding microbubble formation within the hydraulic system.
Brake-By-Wire Test Rig
In contrast to a convertional vehicle the ROboMObil is able to modulate four independent steering angles. The steering torque is provided by an electromechanic actuator attached to the wheelhub inside all four wheels. As a consequence the entire steering powertrain and the wheel properties are replicated in the testing environment. The examinee represents the wheel robot’s mass and interia and is mounted to a stationary steel frame. The electromechanic steering actuator along with the powertrain and the corresponding sensors are fitted onto the examinee. The substitute is able to rotate around its vertical axis within in the same angular range as the wheel robot representing the wheel’s movement during driving manoeuvers. The deflection of the powertrain components under specific forces is measured analogous to the brake-by-wire testrig. The resulting component stiffnesses together with flexible body simulation in Modelica lead to the overall stiffness of the steering system. This information can be used to improve and validate the steering models in the vehicle dynamics control. Other test scenarios help to determine positioning and repeating accuracy aswell as the the maximum deflection speeds and eigenfrequencies of the steering system in long term test cycles.
Steer-By-Wire Test Rig