Patent Application
20130299270
The technical field generally relates to electronic power steering (EPS) systems for vehicles, and more particularly to an improved control system and method for an EPS system for a vehicle.
Conventional electronic power steering (EPS) systems often produce a driver perceptible “stickiness” or reluctance to respond, which typically requires additional driver steering torque to overcome. This “stickiness” (or “stiction” as commonly referred to) condition can be experienced when operating an EPS equipped vehicle at highway speeds while performing minor within-lane steering corrections, that is, at vehicle speeds of approximately 45-80 miles per hour (mph).
Typically, as a vehicle operator begins to correct the heading of an EPS equipped vehicle traveling at highway speeds, a resistance to steer can be felt in the wheel that must be overcome with increased effort. The level of increased effort can be as significant as 0.9 Newton meters (Nm), which many vehicle operators find objectionable or annoying while operating a vehicle.
Accordingly, it is desirable to provide improved control for an EPS system for a vehicle. Also, it is desirable to provide a control system that alleviates the perceivable “stickiness” condition without introducing a perceivable correction signal. Additionally, other desirable features and characteristics of the present disclosure will become apparent from the subsequent description taken in conjunction with the accompanying drawings and the foregoing technical field and background.
In accordance with exemplary embodiments, a dithered EPS system is provided for a vehicle. The system comprises a steering assembly having one or more sensors for sensing user steering input. A controller is responsive to the user steering input for providing a motor control signal. The EPS system also includes a dither signal generator providing a dither signal and a combiner for combining the motor control signal and the dither signal to provide a dithered motor control signal to control the motor of the EPS system.
In accordance with exemplary embodiments, a method for controlling a dithered EPS system is provided for a vehicle. The method comprises sensing user steering input via one or more sensors coupled to a steering assembly of a vehicle and generating a motor control signal responsive to the user steering input. A dither signal is generated and combined with the motor control signal to provide a dithered motor control signal which is used to control a motor of an EPS system.
The embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit 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.
In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Numerical ordinals such as “first,” “second,” “third,” etc. simply denote different singles of a plurality and do not imply any order or sequence unless specifically defined by the claim language.
Additionally, the following description refers to elements or features being “connected” or “coupled” together. As used herein, “connected” may refer to one element/feature being directly joined to (or directly communicating with) another element/feature, and not necessarily mechanically. Likewise, “coupled” may refer to one element/feature being directly or indirectly joined to (or directly or indirectly communicating with) another element/feature, and not necessarily mechanically. However, it should be understood that, although two elements may be described below, in one embodiment, as being “connected,” in alternative embodiments similar elements may be “coupled,” and vice versa. Thus, although the schematic diagrams shown herein depict example arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment.
Finally, for the sake of brevity, conventional techniques and components related to vehicle electrical and mechanical parts and other functional aspects of the system (and the individual operating components of the system) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in an embodiment of the invention. It should also be understood that
Referring to the drawings, wherein like reference numbers refer to like components,
The illustrated embodiment of the vehicle 100 includes an electronic power steering (EPS) system 102. The EPS system 102 includes a steering assembly 104, a steering gear assembly 106, a motor assembly 108, a controller 110 and two wheel steering assemblies 112 each coupled to a wheel (and tire) 114. These are, of course, only some of the components, devices, assemblies, systems, etc. that may be used with an EPS system 102, as others known in the art could be used in lieu of or in addition to those mentioned here. While a rack mounted EPS is illustrated in
Steering assembly 104 includes a steering wheel 116 rotatably coupled to a steering connection assembly 118, which transmits the steering intentions of a driver to the other portions of EPS system 102. Typically, a conventional steering connection assembly 118 includes one or more steering shafts and steering joints that are part of steering connection assembly 118. It should of course be appreciated that the foregoing description is only of a general and exemplary nature as myriad steering connection assembly embodiments, including those having more, less and/or different components could also be used.
The steering connection assembly 118 is coupled to a steering gear assembly 106, which converts rotational motion from the steering connection assembly 118 into lateral or cross-vehicle motion that can be used to turn the vehicle's wheels 114. In some embodiments, steering gear assembly 106 may be realized as a rack and pinion steering gear assembly, although other steering gear assemblies may be used.
The motor assembly 108 provides the EPS system 102 with power assist in order to supplement the manual steering force generated by the driver. This makes steering easier and more effortless. Typically, the motor assembly 108 includes an electric motor, a power input, and one or more gears, pulleys, belts, bearings, etc. for achieving preferred ratios of motor armature to rack velocities. Depending upon the particular embodiment implemented, the electric motor may be a brushless motor, brushed motor, or any other type of motor employed in the art as will be appreciated by those skilled in the art.
The motor assembly 108 operates to provide power assist to steering the vehicle 100 under direction of a controller 110. The controller 110 performs the computation and control functions of the EPS system 102, and may comprise any type of processor or multiple processors, single integrated circuits such as a microprocessor, or any suitable number of integrated circuit devices and/or circuit boards working in cooperation to accomplish the functions of a processing unit. During operation, the controller 110 receives data from sensors (or sensor arrays) 120 and 122, which is used by the controller to determine whether, and to what extent, to provide power assist to the steering effort of the driver of the vehicle 100.
Sensors 120 are coupled to (or integrated within) the steering gear assembly 106. Any sensor capable of taking measurements that provide steering information from the steering connection assembly 118 could be used within sensor 120. As an example, and not a limitation, sensors measuring steering input such as steering wheel angle; steering wheel torque; steering wheel velocity; steering wheel acceleration and steering wheel torque gradient could be useful in sensor array 120.
In addition to steering input derived from driver actions, other vehicle data or conditions may be useful in determining whether (and to what extent) to provide power assisted steering. Accordingly, sensors 122 may be distributed throughout the vehicle 100, but for convenience, are illustrated as a single sensor array coupled to the controller 110. Vehicle sensors that may be useful in determining how to control the motor assembly 108 include, but are not limited to, vehicle speed; vehicle fore-aft acceleration; vehicle lateral acceleration; driven wheel speed and non-driven wheel speed.
In operation of the EPS system 102, the motor assembly 108 provides power assist to move wheel steering assemblies 112, which are coupled to the motor assembly via tie rods 124. Typically, the wheel steering assemblies 112 carry the vehicle's tires and include a number of conventional revolving components. For example, it is common for the wheel steering assemblies 112 to include a rotating hub, a rotating disk or rotor, and a wheel with an installed tire. All of these devices co-rotate when the vehicle 100 is being driven. A disk brake system (not shown) can also be installed on the vehicle to interact with wheel steering assembly 112, although other braking systems like drum brakes could be used as well.
As noted earlier, one drawback of conventional EPS systems is perceived by the vehicle driver as a “stickiness” or reluctance to respond, which typically requires additional driver steering torque to overcome. Accordingly, exemplary embodiments of the present disclosure supplement the control signal supplied from the controller 110 to the motor assembly 108 with a “dither” signal. “Dithering” the motor control signal, that is, the intentional introduction of noise or other signal into the motor control signal, alleviates the stickiness sensation and allows for a smooth and easy steering experience for the vehicle driver as will be explained in more detail in connection with
Referring now to
In exemplary embodiments of the present disclosure, a dither signal generator 204 is included in the EPS system 102 and provides a dither signal 206 that is combined (e.g., summed, integrated, averaged) in combiner 208 to provide a dithered motor control signal 210. The combination of the dither signal 206 to the motor control signal 202 alleviates the perception of “stickiness” by having the motor assembly 108 in relative constant motion due to the ever changing dithered motor control signal 210. Thus, the dither signal may be any signal that would cause the motor assembly 108 to operate (even minutely) in the absence of a more direct instruction (or no instruction) to move as compared to the motor control signal 202. In one embodiment, the dither signal 206 is realized as a sine wave having a frequency of approximately 30 hertz. In other embodiments, other signal types may be employed such as, without limitation, random white or pink noise, filtered random white or pink noise, periodic waves comprising at least one sinusoidally varying component as, for example, square waves, triangular waves, and/or sawtooth waves.
In one embodiment, the dither signal generator 204 and combiner 208 may be separate units working in cooperation with the controller 110. In other embodiments, the dither signal generator 204′ and combiner 208′ may be integrated within the controller 110 to provide the dithered motor control signal 210′. Also, some embodiments utilizing the dither signal generator 204 provide a continuous dither signal 206. In other embodiments, the dither signal generator 204 is controlled (via programming line(s) 212) to conditionally provide the dither signal 206 depending upon the steering input, vehicle data or driving conditions. In still other embodiments, the controller 110 controls (via programming line(s) 212) the dither signal generator 204 to vary one or more parameters of the dither signal 206 responsive to driver steering input, vehicle data or driving conditions. Examples of such dither signal parameter modification include, but are not limited to, amplitude; frequency; waveform and duty cycle of the dither signal 206.
Referring back to decision 304, if the determination of decision 304 is that the dither signal generator is not currently active (e.g., vehicle stopped or operating at low speeds), step 310 activates the dither signal generator and the routine proceeds to decision 312. Also, the routine proceeds to decision 312 following a negative determination of decision 306 or after step 308 modifies the dither signal.
Decision 312 determines whether the condition or sensor data that required the dither signal has cleared or dissipated. If not, the routine continues to loop decision 306 and 308 (if required) until the condition clears, at which time step 314 deactivates the dither signal generator and the routine continues by looping back to the beginning and decision 302.
Accordingly, a dithered EPS system is provided for a vehicle. The dithered EPS system according to the various disclosed embodiments alleviates the driver perceived “stickiness” problem of conventional EPS system. While at least one exemplary embodiment has been presented in the foregoing summary and 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 disclosure in any way. Rather, the foregoing summary and 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 disclosure as set forth in the appended claims and the legal equivalents thereof.
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 disclosure 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 disclosure as set forth in the appended claims and the legal equivalents thereof.
