This paper describes a Magneto-Rheological coupling based Hydraulic Power Steering (MRHPS) system developed for improving fuel economy in conventional vehicles. The MRHPS system reduces the parasitic losses associated with the power steering pump and improves fuel economy in full-size trucks (and SUVs) by up to 3%, while maintaining the production hydraulic power steering system performance. The MRHPS is a low cost alternative to electric power steering and electro-hydraulic power steering systems and requires significantly less electric power while resulting in similar fuel economy gains.
With the MR coupling the power steering pump is run at optimum speeds depending on the steering angle, angle rate and vehicle speed, and the pump is run in closed loop speed control mode so that factors like temperature, manufacturing tolerances, aging, etc. will not degrade the steering performance. A fail-safe, fault-management system was also developed that can take remedial action to keep the clutch functioning, when the nature of the fault permits continued operation thereby providing uninterrupted power assist without sacrificing the fuel economy gains. Several prototype clutches were built and installed in full-size trucks and the average improvement in fuel economy was found to be 3% which is quite significant. The prototype clutches also met the prescribed durability and high speed tests.
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