Study, Design and Development of an Optical Torque Sensor for a New Generation of Steering System
N. Javahiraly and A. Chakari
We propose the study, design and achievement of an ultra sensitive polarimetric torque sensor for electrical power steering system. The principle is based on the measurement of the torsion angle induced on the shaft when a torque is applied on it. This optical torque sensor has been tested for aluminium, steel and Poly(methyl methacrylate) (PMMA) (Plexiglas) shafts with different designs and different geometries depending on the applications it is dedicated to. The torsion angle has been measured with 0.001º accuracy. We analysed the light propagation in an electromagnetic and opto-geometrical way applicable to the sensor and the analysis of the theoretical and the experimental responses of the sensor as a function of the material nature and its geometry is achieved. We obtained experimentally a high sensitivity and a very high stiffness adjustable depending on the application. The comparison between the theoretical and the experimental results gave a maximum difference between 1.68 and 3.40%. We tested the temperature fluctuations influence for ∆T = 130ºC and the results gave 7% difference with the theory. This sensor design offers, compared to some others, a simple, efficient and economic technique to measure the torque. This original technique permits the accurate measurement of torque applied on shaft with a very high stiffness. Torque sensor variable length (L = 5 to 32 cm) has demonstrated a maximum stiffness at 1190 Nm/rad which is very interesting because it is superior to existing stiffness for steering systems and desired data for automotive industry (new generation of steering systems). The main advantage of the studied sensor is that this actuator is adjustable as a function of the sensitivity and the stiffness wanted for different applications. These results give us good perspectives for our applications in automotive and aerospace industries.
Keywords: Steering system, torque, optical sensor, polarimetric sensor, torsion, shaft