Study the Effect of Fasteners Coating Materials to Resolve the Leakage Issue in Steering Gear Assembly

Abstract: In commercial vehicle industry, Hydraulic Power Assisted Steering (HPAS) gear plays a vital role to utilize the hydraulic force by amplifying the mechanical input. HPAS gear consists of housing, sector shaft, side cover, worm shaft, valve housing and rack piston. Side cover assembly is connected with housing assembly through bolts which is in exposure to high pressure hydraulic fluid. During high pressure running condition, torque relaxation in the bolt is observed which leads to the loosening of bolts and tends to hydraulic fluid leakage through bolts. Since, some of the bolts are exposed to the fluid environment in the inner surface of the housing, the existing phosphate coated bolts are relaxed and loosened due to the bolts that exposed to the oil environment which have insufficient coefficient of friction in bolt head and thread. To overcome the bolt failure during high pressure hydraulic application various bolt coating analysis is experimented to withstand the sufficient coefficient of friction in the bolt. The detailed comparison study is carried out for the bolts such as failure torque, load, frictional force, bearing stress and thread profile deviation. This paper deals with the failure analysis of bolts in a high pressure HPAS gear assembly and comparison study is carried out between analytical calculations and experimental validation. Key words: Bolt coating analysis, steering gear, coefficient of friction, bolt loosening and failure analysis.