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Previous work has shown power steering boost gains are uniquely determined given a vehicle and a single objective target. The objective target used was steering gain, Sg, vs. lateral acceleration, ay, where steering gain is defined as the slope of the torque vs. lateral acceleration relationship. The previous work is expanded and applied to real world steering systems. Specifically, methods are provided to determine boost gain shapes given a user-defined steering gain vs. lateral acceleration specification or steering gain vs. torque specification. Each specification method is described in detailed steps. Approximations of each method are discussed and analyzed for practical use. The influence of static friction on steering performance is derived. It is shown that the hysteresis of the steering system is due to a coupling between static friction and a vehicle parameter that is easily derived from the bicycle model. Test results are provided to validate predictions.

Optimal field weakening control of Permanent Magnet Synchronous Motors (PMSM) relies on accurate parameter knowledge. From a modeling perspective, a good parameter set allows better correlation between the model and physical system. Errors in inputs (parameters) such as back-emf (Ke), phase resistance (R), battery cable resistance (Rc), phase inductance (L) and voltage multiplier (Kv) have a coupled effect on the system outputs (measurements) such as torque, battery current and DC link voltage; the relationship between inputs and outputs is not one to one. A single parameter change affects more than one output or vice-versa. For example, in a torque-speed curve before the knee point (base speed), only the Ke parameter affects the output torque but after the knee, all parameters influence the torque. Also, any change in parameters can have unwanted affects like torque ripple, which can lead to NVH issues.

An approach to electric steering control and tuning is developed using vehicle dynamics and quantitative steering objectives. The steering objective chosen is the torque vs. lateral acceleration target for the driver termed the “steering gain”. Two parameters are derived using vehicle dynamics that substantially determine driver feel: the vehicle’s “manual gain” (total steering torque divided by lateral acceleration) and the vehicle’s lateral acceleration gain (lateral acceleration divided by steering angle). Lateral acceleration gain is a well-known quantity in the literature but “manual gain” is a nonstandard point of view for steering control systems. The total gain inside the controller is the loop gain; generally, the higher the loop gain, the better the controller rejects unwanted effects such as friction. For a typical torque-input electric steering topology, it is shown that the relationship between loop gain and steering gain is unique.

The transfer function required to control an electrically assisted steering gear is identified using a modified FIR filtering approach. The topology of the electrically assisted steering gear is described. The modified FIR filtering approach is explained with emphasis on the frequency domain implication of window choice when performing measurements. An example is provided using an analytic model of the steering gear so that the accuracy of the technique can be evaluated on a known system. The technique is applied to measure the transfer function of an actual electrically powered steering gear on a test bench and in a rolling vehicle.