System for providing steering assist torque based on a proportional gain value

#The present invention relates to a system for providing a steering assist torque, and in particular to a system for providing a steering assist torque based on a proportional gain value.

#A lane keeping system detects lane markers on the left and right side of the road, and provides an assist torque to a handwheel of a steering system to help keep a vehicle between the lane markers. The lane keeping system may also provide alerts to the driver using visual or audio aids such as, for example, a display, a voice indicator, or chimes. Some lane keeping systems use a lateral position of the vehicle for controlling functions such as the torque assist. The lateral acceleration may also be used during autonomous mode of the lane keeping system.

#When the lane keeping system is in autonomous mode, the amount of torque assist that is provided to the handwheel by the lane keeping system may sometimes create more handwheel movement than what a driver typically creates to drive the vehicle. This in turn may create variations in the lateral acceleration of the vehicle, which may be objectionable to the vehicle occupants. However, it should also be noted that sometimes the extra handwheel movement may keep a driver engaged in the driving process, without actually manipulating the handwheel.

#The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

#FIG. 1 is a diagram depicting a vehicle in a lane with lane markers in accordance with one aspect of the invention;

#FIG. 2 is a schematic diagram of the vehicle in FIG. 1 having an exemplary system for providing a steering assist torque to a handwheel according to another aspect of the invention;

#Referring now to FIG. 1, where the invention will be described with reference to specific embodiments without limiting same, an exemplary schematic diagram of a vehicle 10 driving within a lane 12 is illustrated. The lane 12 includes lane markers 14 on the left and right hand sides of the lane 12. The lane 12 includes a lane center 20 (the lane center is a calculated value, as there is no lane marker for the lane center 20) and the vehicle 10 includes a vehicle centerline 22. A heading angle θ (not shown in FIG. 1) is measured between the lane center 20 and the vehicle centerline 22, where a positive sign for the heading angle θ (e.g., θ+) is provided if the vehicle centerline 22 is to the right of the lane center 20, and a negative sign (e.g., θ−) for the heading angle θ is provided if the vehicle centerline 22 is to the left of the lane center 20. A lateral position Δ of the vehicle 10 is also illustrated in FIG. 1, where the lateral position Δ includes a positive sign if the vehicle centerline 22 is to the right of the lane center 20, and a negative sign if the vehicle centerline 22 is to the left of the lane center 20. In the embodiment as shown in FIG. 1, the lane 12 also includes a curvature ρ. In the embodiment as shown, the curvature ρ is positive, as the curvature ρ is oriented to the right side of the lane 12. If the curvature ρ is oriented to the left side of the lane 14, then the curvature ρ includes a negative sign.

#FIG. 1 also illustrates a near field heading angle θhnear and a far field heading angle θhfar. The near field heading angle θhnear is observed relatively close to the vehicle 10 (e.g., generally within about 40 meters of the vehicle 10). The lateral position Δ is also observed relatively close to the vehicle 10 as well (e.g., generally within about 40 meters of the vehicle 10). The near field heading angle θhnear, the far heading angle θhfar, and the lateral position A are then projected directly in front of the vehicle 10 (e.g., at zero meters). The curvature ρ of the lane 12 is generally calculated as an average value over a distance (where the distance is usually between about 5 to about 25 meters in front of the vehicle 10). The far field heading angle θhfar is located in an area labeled as a look ahead distance D. The look ahead distance D is generally in the range of between about 35 to about 70 meters. The far field heading angle θhfar is determined by calculating a tangent line T of the lane center 20 at the look ahead distance D. The far field heading angle θhfar is measured between the vehicle centerline 22 and the tangent line T at the look ahead distance D.

#Turning now to FIG. 2, the vehicle 10 includes a steering system 30. The steering system 30 includes a handwheel 34 coupled to a steering shaft 36. The steering system 30 is an electric power steering (EPS) system that further includes a steering assist unit 38 that couples to the steering shaft 36 of the steering system 30 and to tie rods 40, 42 of the vehicle 10. The steering assist unit 38 includes, for example, a rack and pinion steering mechanism (not shown) that may be coupled through the steering shaft 36 to a steering actuator motor and gearing. During operation, as the handwheel 34 is turned by a vehicle operator, the motor of the steering assist unit 38 provides the assistance to move the tie rods 40, 42 which in turn moves steering knuckles 44, 46, respectively, coupled to roadway wheels 48, 50, respectively of the vehicle 10.