F2008-05-071
Development of a Displacement Sensor for Intelligent Suspension
This paper describes development of a new displacement sensor for intelligent suspension system in which the damping force has been controlled by MR(Magnetic Rheological) fluid. Most of the current vehicle height sensors have been installed at external place of the damper and connected to that by mechanical linkages so far. This mechanism has disadvantage of increasing complexity, instability, inaccuracy and so on. The proposed sensor could be installed into internal part of the MR CDC(Continuous Damping Control) dampers so that there is no misalignment between the damping force acting and the vehicle height measuring positions. The developed sensor has a new mechanism which detects movement of the sensor rod same as connecting rod in the suspension damper by using a GMR(Giant Magneto Resistance) sensor and convert it to the relative displacement from an initial position. Vehicle motion and the response characteristics of the suspension under various driving conditions were also analyzed with commercial software CarSim to specify displacement sensing requirements for the suspension control. Dimensional parameters of the sensor rod and configuration of the GMR sensor around the rod have been determined by analyzing the magnetic field around assembly of the GMR sensor and the rod. Sensor signal processing circuits have been also developed in order to satisfy the sensor requirement and communicate with an active damper ECU. The signal processing circuit was designed to have robustness from electric noise and physical environment variation and could be conducted by using OP amps of LMC7101 and TL082. A series of experiments have been conducted to evaluate the steady state as well as the transient state performances including with a resolution, a response time, an operating temperature, durability, repeatability and various EMI performances. The performance test experiments have been performed with MTS 849 S/A testing system. The hysteresis characteristics and electric noise robustness due to high level current applied in the damper coil have been also conducted. As the results, the developed sensors show that the sensor specifications can be satisfied with the accuracy under ±0.5%, the resolution of o.1 mm, the response time less than 0.2 msec and against requirements in environment.
Poster presentation: Electronics