Characterization and Reduction of Power Steering Hiss noise for Passenger Car

Passenger comfort has become one of the key areas to achieve success in the passenger car market segment. New upcoming products are rejected by customers not because of durability, but more by irritants like noise and vibrations. Hiss noise is one of the major irritants in passenger cars employing hydraulic power steering.

This paper describes an attempt to evolve a structured methodology to identify and characterize power steering hiss noise from a rack and pinion type hydraulic power steering system.

Extensive testing and detailed analysis of noise data was performed for characterization of power steering hiss noise, from which frequencies responsible for hiss noise were identified at vehicle level and component level. Subsequently several solutions were tried to reduce the hiss noise to an acceptable level considering the limitations of manufacturing and cost.

Test results show the effectiveness of approach and methodology towards arriving at a solution for hiss noise. The most effective way to reduce hiss noise is by reducing noise at source i.e. at hydraulic rack and pinion valve. The design of Valve pinion assembly and the assembly of this in the rack housing were found to be the major contributors for hiss noise. Decoupling noise using compact noise isolator gives relatively less improvement over the reduction of noise at source.