Design of a non-contact torque sensor using photo-interrupters

Abstract

When steering the vehicle, the driver had to apply a lot of force when turning the steering wheel because of the friction forces, which are caused by the road. To solve this inconvenience, the automotive companies develop Power Steering System (PSS), which supplies the additional torque when steering the car. There are two types of PSS : Hydraulic Power Steering (HPS) system and Electric Power Steering (EPS) system. Although HPS system had used generally in early days, EPS system has used well now a days because the electric motor is improved enough to substitute the hydraulic power system, and the fuel efficiency and the eco-friendly system acquire a greater importance. EPS system can be divided into three parts: the sensor part, the control part, the actuator part. Among these parts, the sensor part is very important in the safety and performance view point. The non-contact torque sensor is used in EPS system to detect the torque that the additional power supplier such as the electric motor should apply. This paper suggests an optical type non-contact torque sensor, which uses photo-interrupters and has a new mechanism. The key component of the designed torque sensor is the coil. This is because the coil’s average deformation in radial direction is propor-tional to the input torque. This paper calculates the average deformations by using 4 information, which is detected by 4 photo-interrupters. After then, the torque can be detected by inputting the calculated deformation into the torque-average deformation map, which is made before the torque sensor is operated. To verify the performance of the suggested algorithm, designing the torque sensor components and simulations to check the accuracy and the resolution is conducted. Based on the simulation results, the feasibility check is conducted at the experiments. From the experiments, the average error, the maximum error, the nonlinearity, and the detection range is detected. As a result, this paper verifies the feasibility of the designed torque sensor although there is the necessity of the improvement. Moreover the designed torque sensor has advantages compared to the conventional torque sensor : a high Electro-Magnetic Compatibility (EMC) performance rather than the magnetic field detection type torque sensor, which is a general type in the market, a simple structure than the conventional optical type torque sensor, which causes easy installation and an affordable cost.