The invention relates to a power steering system, and more particularly to a power-assisted steering system for a vehicle, comprising a lead screw which is driven by a servo motor and which is composed of a nut that is mounted axially non-displaceably in a frame, and an axially displaceable component.
Power steering systems, and more particularly electrical power-assisted steering systems in passenger cars, in which the servo motor transmits the rotational speed and torque via a traction mechanism gear to a nut, and more particularly a recirculating ball nut, are known from the prior art. To this end, a servo motor and the toothed rack, or the spindle section of the rack, driven by the nut are frequently disposed axially parallel to each other.
For example, DE 103 10 492 A1 describes an electrical power steering system, wherein an electric motor drives a component which is mounted in a steering gear housing so as to be axially displaceable. The component is designed as a toothed rack, and a ball screw of the component is mounted in engagement with a nut thread of a frame designed as the steering gear housing in an axially non-displaceable manner. The nut is non-rotatably connected to a belt pulley of a traction mechanism gear between the servo motor and the lead screw thus formed. The nut is supported and mounted on the steering gear housing by way of a radial fixed bearing, which is a rolling bearing. The radial bearing is frequently designed as a four-point bearing, especially since axial forces must also be absorbed. An inner ring of the rolling bearing is axially supported on the components mounted on the nut, such as the belt pulley and a stop in form of a ring or snap ring. The radial bearing is frequently axially delimited in relation to the components of the power steering system by bearing disks, wherein some of the functions of the bearing disks can also be assumed by other components of the power steering system. This often requires applying a tilting moment to the outer ring of the radial bearing. In addition, the bearing disks are made of material which conducts sound well and they are frequently seated directly against a housing of the power steering system, so that sound can be directly radiated to the surroundings of the power steering system.
DE 103 10 492 A1 describes an electrical power-assisted steering system, comprising a lead screw which is driven by a servo motor and composed of a nut that is mounted axially non-displaceably in a frame, and an axially displaceable component, the thread of which is engaged with a thread of the nut, wherein the nut is mounted in the frame designed as a steering gear housing by means of a rolling bearing. An outer ring of the rolling bearing is directly supported on a gearbox cover of the power steering system.