HiL Axle Test Rig

Demonstrator: HiL Axle Test with Hydraulic Hexapod

An important demonstrator for our research work in Control Engineering and Mechatronics is the HIL test rig for vehicle axles which enables the reproduction of the wheel-sided excitation in all six degrees of freedom under real time conditions. Among other things, a highly-dynamically controlled hexapod is used as the excitation unit. Models of the remaining subsystems such as tires, the street and the vehicle are simulated simultaneously on a real-time computer to replicate the overall system in a HIL simulation. The control connection is provided by a real-time system calculating with a cycle of 8 kHz. For the hexapod alone, the test rig has six position sensors and six pressure sensors, one angle sensor, twelve valve slide position sensors and a wheel force sensor which measures the forces and torques at the contact point between hexapod and axis. The six control voltages for the servo valves are the output signals.

Hydraulic Hexapod

The excitation unit for the HIL axle test rig is a hydraulic hexapod which belongs to the category of parallel kinematics.

For serial kinematics, e.g. a conventional industrial robot, the movement of the end-effector (where the tool is fixed) results from a series of rotations and displacements of individual drives so that the human eye can easily follow it. In contrast, all drives of a parallel kinematic are mounted on the end-effector so that the movement of the end-effector does not result from a series of partial movements but is a result of a complex, simultaneous movement of multiple drives.

Hydraulic hexapod at the test rig

Our hexapod is actuated by six hydraulic cylinders while every hydraulic cylinder is connected to the lower end via a cardan joint with integrated oil feed at the base plate. At the higher end of every cylinder, there is a spherical joint to connect the cylinder to the work platform of the hexapod. By means of this design, the end-effector can be moved in all six degrees of freedom.

The video below shows the axle test rig following a measured signal from a rough road maneuver, as it is also used for the fatigue strength test of axles.