Patent Application
20150375781
The present disclosure generally relates to steering systems of a vehicle, and more particularly relates to methods and systems for compensating a steering assist command to the steering system.
A steering system of a vehicle allows a driver to steer front wheels of the vehicle. The steering system may be an electric power steering system that uses an electric motor to provide a steering assist to a driver of the vehicle, thereby reducing effort by the driver in steering the vehicle.
In some cases, unwanted vibrations in the steering system may occur due to internal periodic excitation such as tire/wheel imbalance, tire irregularities, brake rotor imbalance and lack of precision piloting of the rotating members. These vibrations may cause discrepancies in the signals relied upon by the steering system. It is desirable to compensate for these discrepancies.
Accordingly, it is desirable to provide methods and systems for developing compensation values for steering assist. It is also desirable to provide methods and systems for controlling the steering system based on the compensation values. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
Methods and systems are provided for controlling an electric power steering system. In one embodiment, a method includes: storing a compensation table having compensation values that are associated with motor torque drive values; receiving a current motor torque drive signal; determining a compensation action the current motor torque drive signal; determining a compensation value based on the compensation action and the table; and generating a motor torque drive signal based on the compensation value.
In one embodiment, a system includes an electric power steering system, a torque sensor associated with the electric power steering system, and a first module. The first module stores a compensation table having compensation values that are associated with motor torque drive values, receives a current motor torque drive signal, determines a compensation action the current motor torque drive signal, determines a compensation value based on the compensation action and the table, and generates a motor torque drive signal based on the compensation value.
The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and:
The following detailed description is merely exemplary in nature and is not intended to limit the application and uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. As used herein, the term module refers to any hardware, software, firmware, electronic control component, processing logic, and/or processor device, individually or in any combination, including without limitation: application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.
With reference to
As depicted in
As can be appreciated, the vehicle 100 may be any one of a number of different types of automobiles, such as, for example, a sedan, a wagon, a truck, or a sport utility vehicle (SUV), and may be two-wheel drive (2WD) (i.e., rear-wheel drive or front-wheel drive), four-wheel drive (4WD) or all-wheel drive (AWD). The vehicle 100 may also incorporate any one of, or combination of, a number of different types of propulsion systems, such as, for example, a gasoline or diesel fueled combustion engine, a “flex fuel vehicle” (FFV) engine (i.e., using a mixture of gasoline and ethanol), a gaseous compound (e.g., hydrogen or natural gas) fueled engine, a combustion/electric motor hybrid engine, and an electric motor.
The steering system 112 includes a steering column 118 and a steering wheel 120. In various embodiments, the steering system 112 further includes various other features (not depicted in
In various embodiments, the steering system 112 is an Electric Power Steering system (EPS) that includes a motor 122 that is coupled to the steering system 112, and that provides torque or force to a rotatable or translational member of the steering system 112 (referred to as assist torque). The motor 122 can be coupled to the rotatable shaft of the steering column 118 or to the rack of the steering gear. In the case of a rotary motor, the motor 122 is typically connected through a geared or belt-driven configuration enabling a favorable ratio of motor shaft rotation to either column shaft rotation or rack linear movement. The steering system 112 in turn influences the steerable front road wheels 108 during steering based upon the assist torque received from the motor 122 along with any torque received from a driver of the vehicle 100 via the steering wheel 120.
The steering system 112 further includes one or more sensors that sense observable conditions of the steering system 112. In various embodiments, the steering system 112 includes a torque sensor 124 and a position sensor 126. The torque sensor 124 senses a rotational torque applied to the steering system by for example, a driver of the vehicle 100 via the steering wheel 120 and generates torque signals based thereon. The position sensor 126 senses a rotational position of the steering wheel 120 and generates position signals based thereon. The time derivatives of these signals, furthermore, provide additional information about the changing states of the vehicle. For instance, the derivative of the rotational position of the steering wheel 120, provides the rotational velocity. Various operational states of the vehicle are inferred by these signals and their derivatives to enable desired control compensation actions.
The control module 116 receives the sensor signals and controls operation of the steering system 112 based thereon. In general, the control module 116 generates control signals to the motor to control the amount of motor torque provided to the steering system 112. The control module 116 generates the control signals based on compensation actions that are determined according to compensation systems and methods of the present disclosure. Compensation actions can include, for example, but are not limited to, cessation of certain control actions (e.g., momentarily for fractions of a second, for multiple seconds, or sustained for many seconds depending on the state); modifying the parameters of the control functions; or combinations of the cessation and the modifying. The modifying of the control parameters, in turn, can include alteration of the gain and phase compensation parameters depending on the state of the controls. In general, the control module 116 applies the compensation values to a motor torque command value based on a frequency and the operational state of the vehicle 100 and steering system 112. The operational state of the vehicle 100 and the steering system 112 can be determined from signals received from the vehicle 100 and/or the steering system 112.
For example, as shown in
In various embodiments, the gain and phase compensation values are predetermined using compensation value determination methods and systems of the present disclosure. For example, as shown in
The signal modification module 130 receives an uncompensated control signal that requests a torque of the motor 122 from the control module 116 and generates a modified control signal based thereon. For example, the signal modification module 130 includes a dither generator that generates a dither signal and a combiner that combines (e.g., sums) the uncompensated control signal with the dither signal to generate a dithered control signal. The dithered control signal may be a superimposed sinewave signal that is generated at various frequencies. For example, the signal modification module 130 may vary the frequency based on dwell point testing, swept frequency testing, or other methods of varying the frequency. Dwell point testing, for example, holds the frequency constant for a brief period of time, increments the frequency, then holds again, and repeats until all desired frequencies are completed. Swept frequency testing, for example, continuously varies the frequency from a desired start to a desired end frequency at a slow rate of change of frequency. The rate of change of the frequency, furthermore, may be constant or, alternatively, may vary in order to achieve advantages in processing and interpretation. For example, the rate of change of frequency, may be proportional to the frequency in order to achieve even percentage changes in frequency over equal time periods.
The signal processing module 132 receives the uncompensated control signals from the control module 116 and torque signals that are generated by the torque sensor 124 during various steering maneuvers and processes the signals to determine the gain and phase compensation values. In general, the steering maneuvers produce data that represents continuous transient steering events that demand various amounts of motor torque. For example, the steering wheel 120 may be turned from left to right and right to left as the vehicle 100 is being driven at the speed X over a period of time Y.
Upon completion of the steering maneuvers, the signal processing module 132 processes the torque signals either offline or in realtime to determine the gain and phase compensation values. As shown in
With reference now to
As depicted in
Upon completion of the driving maneuvers for the time Y, the logged data is processed at 340 (e.g., either offline or in realtime). For example, based on the data, transfer functions are determined for various levels of torque drive (e.g., 0-8 A, 5-10 A, 8-12 A, 10-15 A, 15-20 A, etc.) as discussed above at 350. The data of the transfer functions are segmented based on the frequency ranges at 360. The segmented data is then evaluated at each frequency range to determine the relationship between the torque drive and the frequency as discussed above at 370. The compensation values are determined based on the relationships and a compensation table is populated at 380. Thereafter, the method may end at 390.
With reference now to
As depicted in
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.
