Flexibly coupled electric power assist steering system

#This invention relates generally to the field of vehicle steering systems, and more particularly relates to an electric power assist steering system having an electric motor flexibly coupled to a vehicle steering system.

#A Typical Steering System

#A typical steering system for a motor vehicle is illustrated in FIG. 1. The steering system 1 has rotating steering wheel 2 in the passenger compartment of the vehicle mounted to steering column 3 that is operatively connected to wheels 4 via steering assembly 5. In order to reduce the amount of driver effort (i.e., torque) that is required to rotate the steering wheel, many steering systems include a power-assisted actuator. The actuator assists the operator with rotation of the steering wheel to overcome opposing forces such as road load forces on the road wheels and friction forces in the steering assembly. The amount of power assistance generally varies depending on the speed of the vehicle and the amount of effort applied by the vehicle operator to the steering wheel. Conventional power assist steering systems typically employ either hydraulic power assist or electric power assist mechanisms. Electric power assist mechanisms are being used in an increasing number of vehicles due to their reduced size and higher energy efficiency than hydraulic mechanisms.

#FIG. 1 illustrates a typical vehicle steering system.

#FIG. 2 illustrates a rack and pinion steering mechanism of an electric power assist steering system, in which the electric motor is rigidly attached to the assist pinion gear reduction mechanism.

#FIG. 3 illustrates an embodiment of a rack and pinion steering mechanism of an electric power assist steering system of the present invention, in which the electric motor is flexibly coupled to the assist pinion gear reduction mechanism.

#An embodiment of the present invention may be better understood with reference to FIG. 3. Rack and pinion mechanism 20, such as that shown in FIG. 2, includes assist pinion gear reduction housing 22 that includes coupling fitting 24 for coupling 26. Coupling 26 couples electric motor 28 to the assist pinion gear reduction mechanism. In this embodiment, a conventional electric motor used in electric power assisted steering mechanisms and a conventional assist pinion gear reduction mechanism and housing are used. Therefore the bolt holes on and dimensions of flanged plate 30 of the motor housing correspond to those of flanged plate 32 on gear reduction mechanism housing 22.

#It has been surprisingly discovered that the assist motor can be remotely attached by a flexible coupling to the assist pinion without a substantial decrease in performance of the steering system.

#In a preferred embodiment, coupling 26 includes an outer flexible sleeve or conduit that contains a flexible shaft. The flexible shaft is connected to the motor output shaft at one end and to the gear reduction mechanism input shaft at its opposite end. The flexible shaft may be formed of steel or synthetic fiber that minimizes the loss of torque between the motor and pinion gear mechanism despite being flexible. Non-limiting examples of flexible couplings suitable for use with the present invention can be obtained from Motion Industries of Wichita Falls, Tex., and Dearborn, Mich., USA, and Stock Drive Products/Sterling Instrument of New Hyde Park, N.Y., USA. In addition to flexible shafts, it is contemplated that the electric motor may be coupled to the steering system via a single or double universal jointed shaft, in which the shaft has at least two rigid linear steel segments connected via at least one universal joint. A non-limiting example of a source for a suitable assist motor is Visteon Global Technologies, Inc. of Dearborn, Mich., USA or affiliate thereof, and a non-limiting example of a source for an assist pinion gear reduction mechanism is Nissei Corporation, Japan.