Electric power steering assembly

#This invention relates in general to vehicle electric power steering assemblies and in particular to an improved rack drive assembly adapted for use in such a vehicle electric power steering assembly.

#One known electric power steering assembly for turning steerable wheels of a vehicle includes a ball nut for transmitting force between an axially movable rack member and an electric motor. Upon actuation of the electric motor of the power steering assembly, the ball nut is driven to rotate relative to the rack member. The rotational force of the ball nut is transmitted to the rack member by balls to drive the rack member axially. The axial movement of the rack member by the balls effects turning movement of the steerable wheels.

#The electric motor in the above-described electric power steering assembly can be coupled to drive the ball nut in various known methods. One such method includes a belt drive assembly wherein an output shaft of the electric motor is connected via a belt to a pulley assembly. The pulley assembly typically includes a pulley which is operatively fixed to the ball nut so that the ball nut rotates with the pulley when the electric motor is actuated. This type of electric power steering assembly has advantages over other known electric power steering assemblies. However, when this type of electric power steering assembly is actuated, undesirable noise can be produced from one or more of the associated components of the rack drive assembly. Thus, it would be desirable to provide an improved structure for a rack drive assembly of an electric power steering assembly which reduces noise in the assembly and yet is simple and inexpensive.

#FIG. 1 is a sectional view of a portion of a first embodiment of a vehicle electric power steering assembly in accordance with the present invention.

#FIG. 2 is a view of a portion of the vehicle electric power steering assembly illustrated in FIG. 1.

#FIG. 3 is an enlarged sectional view of a portion of the vehicle electric power steering assembly illustrated in FIGS. 1 and 2.

#Referring now to FIGS. 1-3, there is illustrated a first embodiment of a vehicle electric power steering assembly, indicated generally at 10, constructed in accordance with the present invention. The illustrated vehicle electric power steering assembly 10 is a vehicle electric belt driven rack drive steering assembly and is associated with the front driven wheels (not shown) of the vehicle. The general structure and operation of the electric power steering assembly 10 is conventional in the art. Thus, only those portions of the electric power steering assembly 10 which are necessary for a full understanding of this invention will be explained and illustrated in detail. Also, although this invention will be described and illustrated in connection with the particular electric power steering assembly 10 disclosed herein, it will be appreciated that this invention may be used in connection with other electric power steering assemblies.

#The illustrated electric power steering assembly 10 includes a vehicle steering wheel 12 and a rotatable input shaft 14 which is operatively coupled in a manner not shown, to the steering wheel 12 for rotation therewith about a steering axis X1. A torque sensor 16 is located inside a pinion housing 18 and encircles the input shaft 12. The torque sensor 16 includes coils (not shown) which respond to the rotation of the input shaft 12 and which generate over electrical lines 20 an electrical signal indicative of the direction and magnitude of the applied steering torque.

#A torsion bar 20 is provided to connect the input shaft 12 to a pinion 22 located inside the pinion housing 18. The torsion bar 20 twists in response to the steering torque applied to the steering wheel 12. When the torsion bar 20 twists, relative rotation occurs between the input shaft 12 and the pinion 22.