Volvo Construction Equipment Components AB (Volvo CE) develops electronic control systems for various vehicles in the field of construction equipment. Increasing demands on quality, safety and environmental care require more and more sophisticated and intelligent drive control systems.
These new systems are dependant on high quality input data from various sensors. One of these sensors is of inductive type and is used for measuring rotational speed of a gear wheel, and the method of doing this is the subject of this thesis.
The current method applied at Volvo CE for measuring this speed needs to be changed in order to cope with these new demands, especially at low velocities. The alternative method presented in this paper is based on Phase-locked loop (PLL) techniques, which is a closed loop frequency control system.
In this thesis two different ways of implementing a PLL are investigated; a Quadrature phaselocked loop (QPLL) in software and a second order PLL in hardware. The QPLL is derived through optimization theory and implemented in Simulink. The second order PLL is the integrated circuit LM565 from the manufacturer National Semiconductor.
The QPLL is tested in a wheel loader and compared with the current method used at Volvo CE today. The results show that in the general case the QPLL is not better than the current method but at fast retardations and when changes of the velocity directions occur the QPLL outperforms the current method. A drawback with the QPLL is its behaviour at constant low velocities where it tends to lose track of the signal.
The hardware-PLL is tested in a test bench with similar working conditions as in a machine. The results show that this method has a limited frequency interval but in this interval the performance is as good as the current method and very robust.
The conclusion of this thesis is that PLL methods are interesting and could improve the quality of the measurements when the velocity is changing very fast but in the general case the current method is just as good. Implementing a PLL would require some extra expenses in terms of additional hardware but with the results presented in this thesis it does not seem cost effective.
Source: KTH
Author: Willemsen, Niklas