Electro-Hydraulic Axes Control Solution for a Car Wheel Bearing Test Stand

The development and production of wheel bearings requires comprehensive tests to achieve and maintain high quality standards. Bearings have to be tested for longevity of lifetime as well as suitability for different load conditions.

Testing of wheel bearings in a vehicle is time consuming and expensive. To automate testing of wheel bearings, a new test stand design was developed by Renk/FAG Kugelfischer AG. The challenge they faced was simulating the real load of a vehicle, which entailed designing the test stand with the capability to simulate all possible static and dynamic load conditions acting on a wheel bearing. For example this test stand must simulate the recorded load cycles measured in a specific vehicle driving on a racetrack.

Four electro-hydraulically controlled axes simulate the wheel bearing load conditions as follows:

  • Brake system to control position, force, or torque.
  • Horizontal load axis to control position or force.
  • Vertical load axis to control position or force.
  • Radial load axis to control position or force.

Technical Requirements

  • Requested dynamics - 20 Hz sinus @ 50 % of maximum demand
  • Requested accuracy - better than ± 2 % of full scale

The horizontal, vertical and radial axes simulate the 3D bearing loads caused by the surface of the road, steering angle, acceleration, and speed of vehicle while the 4th brake axis also simulates the brake loads caused by the vehicle's inertia. The heart of the electro-hydraulic axes are Moog's D765 Servovalves with customized flow characteristic.

In close cooperation with the test stand user FAG Kugelfischer AG and the test stand builder Renk, Moog developed the closed-loop electro-hydraulic axes control algorithms for all four axes as well as the CANopen bus communication with the host controller and data acquisition system.

MSC (Moog Servo Controller) With CAN-Bus, Profibus and Ethernet Interface

The control hardware is the Moog Servo Controller (MSC), the programming software is the Moog Axis Control Systems (MACS) which is based on CoDeSys the IEC 61131-3 programming system. CoDeSys is one of the most powerful IEC 61131-3 programming tools for controllers applicable under Windows. All five programming languages of the standard are supported. CoDeSys produces native machine code for all common processors. CoDeSys combines the power of advanced programming languages such as C or Pascal with the easy handling and operational functions of PLC programming systems.

About the Author

Bernhard Zervas is currently the Systems Engineering Manager for Moog's Industrial operations in Germany. He has over 30 years experience in the international hydraulic industry, with a focus on industrial electro-hydraulic closed-loop, electro mechanical and hybrid applications.