Patent Publication Number: US-9885638-B2

Title: Systems and methods for determining steering performance

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to steering systems and more particularly relates to systems and methods for determining performance of a steering gear associated with a steering system. 
     BACKGROUND 
     Many vehicles include a steering system to enable the operator to maneuver or steer the vehicle. In one example, the steering system includes a steering gear coupled to a hand wheel. The steering gear transmits the operator input from the hand wheel to the one or more road wheels. In some instances, steering gears may transmit vibrations from the one or more road wheels to the operator. Such vibrations may be undesirable to the operator. 
     Accordingly, it is desirable to provide systems and methods for determining steering performance to reduce undesired vibrations. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     SUMMARY 
     In one embodiment, a method is provided for determining a performance of a steering system. The method includes coupling at least one load source to the steering system and coupling a portion of the steering system to an angle input source. The method also includes outputting one or more control signals by a processor to the at least one load source to apply a load to the steering system and outputting one or more control signals by the processor to the angle input source to apply an input to the steering system. The method includes receiving torque data indicating a performance of the steering system based on the load applied to the steering system by the at least one load source and the input applied by the angle input source. 
     In one embodiment, a system for determining a performance of a steering system is provided. The system includes a testing structure coupled to the steering system. The system includes at least one load source coupled to the steering system to apply a load to the steering system. The system also includes an angle input source coupled to the steering system to apply an input to the steering system. The system also includes a diagnostic module that outputs one or more control signals to the at least one load source and the angle input source, and receives torque data indicating the performance of the steering system based on the output. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG. 1  is a schematic illustration of a system for determining steering performance of a steering gear in accordance with various embodiments; 
         FIG. 2  is a schematic illustration of a system for determining steering performance of a steering gear in accordance with various embodiments; 
         FIG. 3  is a schematic illustration of a system for determining steering performance of a steering gear in accordance with various embodiments; 
         FIG. 4  is a schematic illustration of a system for determining steering performance of a steering gear in accordance with various embodiments; 
         FIG. 5  is a dataflow diagram illustrating a control system of the system of  FIGS. 1-4  in accordance with various embodiments; 
         FIG. 6  is an exemplary chart generated by the control system of  FIG. 5  in accordance with various embodiments; 
         FIG. 7  is an exemplary chart generated by the control system of  FIG. 5  in accordance with various embodiments; and 
         FIG. 8  is a flowchart illustrating a control method of the system of  FIGS. 1-4  in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Embodiments of the present disclosure may be described herein in terms of functional and/or logical block components and various processing steps. It should be appreciated that such block components may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. For example, an embodiment of the present disclosure may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that embodiments of the present disclosure may be practiced in conjunction with any number of steering systems, and that the vehicle system described herein is merely one example embodiment of the present disclosure. 
     For the sake of brevity, conventional techniques related to signal processing, data transmission, signaling, control, and other functional aspects of the systems (and the individual operating components of the systems) 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 present disclosure. 
     With reference to  FIG. 1 , one example of a system  10  for determining steering system performance is shown. The system  10  includes a testing structure  12 , at least one load source  14 , an angle input source  16 , at least one sensor  18  and a diagnostic module  20  in accordance with various embodiments. As will be discussed further herein, the system  10  enables the determination of a performance of a steering system  22  coupled to the testing structure  12 . Although the figures shown herein depict an example with certain arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. It should also be understood that  FIG. 1  is merely illustrative and may not be drawn to scale. 
     The testing structure  12  supports the steering system  22  and can support one or more of the at least one load source  14 , the angle input source  16 , the at least one sensor  18  and the diagnostic module  20 . In one example, the steering system  22  is a steering system for use with a vehicle. The vehicle may be an automobile, an aircraft, a spacecraft, a watercraft, a sport utility vehicle, or any other type of vehicle. For exemplary purposes the disclosure will be discussed in the context of the steering system  22  being used with an automobile. As can be appreciated, the systems and methods of the present disclosure are not limited to an automobile, as the methods and systems for determining steering system performance can be implemented with a variety of steering systems or steering gears that accept input for maneuvering a vehicle. Thus, the steering system  22  illustrated and described herein is merely exemplary. In the example of  FIG. 1 , the steering system  22  is a rack and pinion based electric power steering system. It should be noted that the steering system  22  is merely exemplary, and the steering system  22  need not comprise an electric power steering system. Rather, the steering system  22  can comprise a hydraulic based steering system. 
     As a steering system  22  for an automobile can be generally known, the steering system  22  will not be discussed in great detail herein. Briefly, however, in this example, the steering system  22  includes a steering gear  28 , a steering assist unit  29 , a first tie-rod  30  and a second tie-rod  32 . The steering gear  28  is coupled to the first tie-rod  30  and the second tie-rod  32 . The steering gear  28  receives rotational input from the angle input source  16 , and through a suitable gearing, converts the rotational input into translational input to a belt-drive rack electric power system  31 , and the steering assist unit  29  assists the belt-drive rack electric power system  31  to move the first tie-rod  30  and the second tie-rod  32  based on the rotational input as is generally known. It should be noted that while the system  10  includes the first tie-rod  30  and the second tie-rod  32 , the performance of the steering system  22  can be determined without the use of the first tie-rod  30  and the second tie-rod  32 , and thus, the first tie-rod  30  and the second tie-rod  32  are optional. 
     In the example of the steering system  22 , the testing structure  12  includes a first fixture  34  coupled to a bedplate  36 . The bedplate  36  is generally coupled to the first fixture  34  and to a floor of a workspace to secure the first fixture  34  against movement. It should be noted that the number of fixtures illustrated herein is merely exemplary, as any number of fixtures can be employed with the testing structure  12  to determine the performance of the steering system  22 , including multiple fixtures. 
     The first fixture  34  supports at least the steering gear  28 , and includes one or more couplings  42 . The one or more couplings  42  are coupled to or about the steering gear  28  such that the steering gear  28  is fixed relative to the testing structure  12  in the same manner as the steering gear  28  would be coupled in a vehicle. Stated another way, the steering system  22  is coupled to the testing structure  12  in the same manner as the steering system  22  is coupled for use in a vehicle. Thus, the one or more couplings  42  are generally coupled to or about the steering gear  28  such that the first tie-rod  30  and second tie-rod  32  are movable relative to the steering gear  28 . In one example, the one or more couplings  42  are fixed or static couplings that rigidly couple the steering gear  28  of the steering system  22  to the first fixture  34 , however, the one or more couplings  42  can comprise slightly flexible or elastic couplings to couple the steering gear  28  to the first fixture  34 . 
     The at least one load source  14  is responsive to one or more control signals from the diagnostic module  20  to apply a load to at least one of the tie rods  30 ,  32 . In one example, the at least one load source  14  comprises a first load source  70  and a second load source  72 . The first load source  70  can be responsive to the one or more control signals from the diagnostic module  20  to apply a load to the first tie-rod  30 . The second load source  72  can be responsive to the one or more control signals to apply a load to the second tie-rod  32 . While the first load source  70  and the second load source  72  are not illustrated herein as being coupled to a fixture of the testing structure  12 , such as the first fixture  34 , it will be understood that one or more of the first load source  70  and the second load source  72  can be coupled to one or more fixtures of the testing structure  12 , if desired. Furthermore, while the first load source  70  and the second load source  72  are described and illustrated herein as applying a load to a respective one of the first tie-rod  30  and the second tie-rod  32 , the first load source  70  and the second load source  72  can apply a load directly to a movable link of the steering gear  28 , if desired. 
     In one example, the first load source  70  and the second load source  72  can comprise load cells, which can apply a load to the first tie-rod  30  and the second tie-rod  32  at a particular frequency. In one example, the first load source  70  and the second load source  72  each apply a first load at a first frequency to the respective one of the first tie-rod  30  and the second tie-rod  32 , and apply a second load at a second frequency to the respective one of the first tie-rod  30  and the second tie-rod  32 . Generally, the first load is different than the second load, and the first frequency is different than the second frequency. In one example, the first load is greater than the second load, and the first frequency is less than the second frequency. For example, the first load is about 1750 Newton (N), a maximum of the first load at the first frequency, and the second load is about 250 Newton (N), a maximum of the second load at the second frequency. The first frequency is about 0.1 Hertz (Hz) and the second frequency is about 15 Hertz (Hz). Thus, the first load source  70  and the second load source  72  are each capable of applying a low frequency load and a high frequency load to the respective ones of the first tie-rod  30  and the second tie-rod  32 . 
     The angle input source  16  is responsive to one or more control signals from the diagnostic module  20  to apply a torque to the steering system  22 . In one example, the angle input source  16  is coupled to the steering gear  28  to provide the torque or torsional input representative of a hand wheel angle input to the steering gear  28 . Alternatively, the angle input source  16  can be coupled to a hand wheel, steering shaft or intermediate shaft associated with the steering system  22 , and can apply the hand wheel angle input directly to one of the hand wheel, steering shaft or intermediate shaft. In one example, the angle input source  16  is a rotary actuator that rotates an input shaft  74  of the steering gear  28  between about −30 degrees and about 30 degrees relative to a longitudinal axis of the input shaft  74  at a frequency of about 0.1 Hertz (Hz). In one example, the angle input source  16  applies the torque to the steering system  22  that changes as a function of the first load applied by the first load source  70  such that a maximum value of the first load is applied to the steering system  22  at a maximum angle of the angle input source  16 . The first load is generally applied in a direction of opposing the motion generated by the angle input source  16 . Stated another way, the angle input source  16  rotates the input shaft  74  to a maximum angle (e.g. about −30 degrees, about 30 degrees) at the maximum load (e.g. +1750 N, −1750 N) for the first load applied by the first load source  70 . It should be noted that this input to the input shaft  74  is merely exemplary, as any input could be applied to the input shaft  74  to simulate the steering of the vehicle during operation of the vehicle. 
     The at least one sensor  18  is coupled to the steering system  22 . In one example, the at least one sensor  18  comprises a first force sensor  76 , a second force sensor  82 , a rotary sensor  84  and a torque sensor  86 . The first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  are each in communication with the diagnostic module  20  over a suitable communication architecture or arrangement that facilitates transfer of data, commands, power, etc. In one example, the first force sensor  76  comprises a first force transducer. The first force sensor  76  measures and observes a force acting on the first tie-rod  30  and generates sensor signals based thereon. The second force sensor  82  comprises a second force transducer. The second force sensor  82  measures and observes a force acting on the second tie-rod  32  and generates sensor signals based thereon. The rotary sensor  84  comprises a rotary encoder. The rotary sensor  84  measures and observes a rotation of the input shaft  74  and generates sensor signals based thereon. It should be noted that the use of a rotary encoder for the rotary sensor  84  is merely exemplary. In this regard, the rotary sensor  82  can comprise any suitable device for measuring and observing a rotation of the input shaft  74 , including, but not limited to, an analog potentiometer. 
     The torque sensor  86  is coupled to the input shaft  74 . The torque sensor  86  comprises a torque sensor or torque transducer. The torque sensor  86  measures and observes a torque acting on the input shaft  74  and generates sensor signals based thereon. It should be noted that while the torque sensor  86  is illustrated herein as being associated with measuring and observing a torque on the input shaft  74 , alternatively, the torque sensor  86  can measure and observe a torque on the steering shaft or intermediate shaft of the steering system  22  and generate sensor signals based thereon, for example. It should be noted that the use of a torque sensor or torque transducer coupled to the input shaft  74  as the torque sensor  86  is merely exemplary. In this regard, the torque sensor  86  can comprise any suitable device for measuring and observing a torque on the input shaft  74  of the steering system  22 , including, but not limited to, an internal torque sensor associated with the steering system  22 . Thus, the use of an externally mounted torque sensor is merely exemplary. 
     In various embodiments, with reference to  FIG. 1 , the diagnostic module  20  outputs one or more control signals to the first load source  70 , the second load source  72  and the angle input source  16  of the system  10  based on input data from an input device  78 . The diagnostic module  20  receives sensor signals from the first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  in response to the control signals. The diagnostic module  20  evaluates the sensor signals to determine a performance of the steering system  22 . The diagnostic module  20  generates data indicating the performance of the steering system  22 . The data includes display data for displaying the performance of the steering system  22  via a display  80 . The diagnostic module  20  also stores the data indicating the performance of the steering system  22  in a datastore. In one example, the diagnostic module  20  is coupled to or in communication with the display  80 . 
     The display  80  displays data for the operator of the test, and can display performance data associated with the steering system  22 . The display  80  can be implemented as a flat panel display coupled to the testing structure  12 , but can also comprise a hand held device or portable electronic device in communication with the diagnostic module  20 . The display  80  comprises any suitable technology for displaying information, including, but not limited to, a liquid crystal display (LCD), organic light emitting diode (OLED), plasma, or a cathode ray tube (CRT). The display  80  can also include the input device  78 , if desired. The display  80  and input device  78  are in communication with the diagnostic module  20  over a suitable communication architecture or arrangement that facilitates transfer of data, commands, power, etc. 
     In various embodiments, the diagnostic module  20  generates the control signals based on user input received from an operator. An input device  78  is manipulable by an operator of the system  10  to generate user input. In various embodiments, the user input can include a command to start or stop the testing of the steering system  22 , as will be discussed herein. The input device  78  can be implemented as a keyboard (not separately shown), a microphone (not separately shown), a touchscreen layer associated with or as part of the display  80 , or other suitable device to receive data and/or commands from the user. Of course, multiple input devices  78  can also be utilized. It should be noted that the input device  78 , the display  80  and the diagnostic module  20  can be implemented in various ways, and can comprise a handheld or stationary computing system, which can be in communication with the first load source  70 , the second load source  72 , the angle input source  16 , the first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  over a suitable architecture or arrangement that facilitates the transfer of data, commands, power, etc. 
     With reference now to  FIG. 2 , a system  400  for determining steering performance is shown. As the system  400  can be similar to the system  10  discussed with regard to  FIG. 1 , only the differences between the system  10  and the system  400  will be discussed in detail herein, with the same reference numerals used to denote the same or substantially similar components. With reference to  FIG. 2 , the system  400  includes the testing structure  12 , the at least one load source  14 , the angle input source  16 , the at least one sensor  18  and the diagnostic module  20  in accordance with various embodiments. As will be discussed further herein, the system  400  enables the determination of a performance of a steering system  402  coupled to the testing structure  12 . Although the figures shown herein depict an example with certain arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. It should also be understood that  FIG. 2  is merely illustrative and may not be drawn to scale. 
     The testing structure  12  supports the steering system  402  and can support one or more of the at least one load source  14 , the angle input source  16 , the at least one sensor  18  and the diagnostic module  20 . In one example, the steering system  402  is a steering system for use with a vehicle. The vehicle may be an automobile, an aircraft, a spacecraft, a watercraft, a sport utility vehicle, or any other type of vehicle. For exemplary purposes the disclosure will be discussed in the context of the steering system  402  being used with an automobile. In the example of  FIG. 2 , the steering system  402  is a column based electric power steering system. 
     As a steering system  402  for an automobile can be generally known, the steering system  402  will not be discussed in great detail herein. Briefly, however, in this example, the steering system  402  includes a steering column  401 , a steering assist unit  406 , an intermediate shaft  408 , a manual steering rack and pinion assembly  410 , the first tie-rod  30  and the second tie-rod  32 . The steering column  401  receives rotational input from the angle input source  16 , and transfers the rotational input into input for the intermediate shaft  408  with the steering assist unit  406  providing assist. The intermediate shaft  408  is coupled to the manual steering gear  410  and transfers the rotational input from the steering column  401  to the manual steering gear  410 . The manual steering gear  410 , through a suitable gearing, converts the rotational input into translational input to the first tie-rod  30  and the second tie-rod  32  as is generally known. It should be noted that while the system  400  includes the first tie-rod  30  and the second tie-rod  32 , the performance of the steering system  402  can be determined without the use of the first tie-rod  30  and the second tie-rod  32 , and thus, the first tie-rod  30  and the second tie-rod  32  are optional. 
     In the example of the steering system  402 , the testing structure  12  includes the first fixture  34  coupled to the bedplate  36 . The first fixture  34  supports at least the manual steering gear  410 , and includes the one or more couplings  42 . The one or more couplings  42  are coupled to or about the manual steering gear  410  such that the steering system  402  is fixed relative to the testing structure  12  in the same manner as the steering system  402  would be coupled to a vehicle. 
     The at least one load source  14  is responsive to one or more control signals from the diagnostic module  20  to apply a load to at least one of the tie rods  30 ,  32  via a respective one of the first load source  70  and the second load source  72 . The first load source  70  can be responsive to the one or more control signals from the diagnostic module  20  to apply a load to the first tie-rod  30 . The second load source  72  can be responsive to the one or more control signals to apply a load to the second tie-rod  32 . In one example, the first load source  70  and the second load source  72  each apply a first load at a first frequency to the respective one of the first tie-rod  30  and the second tie-rod  32 , and apply a second load at a second frequency to the respective one of the first tie-rod  30  and the second tie-rod  32 . Generally, the first load is different than the second load, and the first frequency is different than the second frequency. In one example, the first load is greater than the second load, and the first frequency is less than the second frequency. For example, the first load is about 1750 Newton (N), a maximum of the first load at the first frequency, and the second load is about 250 Newton (N), a maximum of the second load at the second frequency. The first frequency is about 0.1 Hertz (Hz) and the second frequency is about 15 Hertz (Hz). Thus, the first load source  70  and the second load source  72  are each capable of applying a low frequency load and a high frequency load to the respective ones of the first tie-rod  30  and the second tie-rod  32 . 
     The angle input source  16  is responsive to one or more control signals from the diagnostic module  20  to apply a torque to the steering column  401 . In one example, the angle input source  16  is coupled to the steering column  401  to provide the torque or torsional input representative of a hand wheel angle input to the steering column  401 . Alternatively, the angle input source  16  can be coupled to a hand wheel or steering shaft associated with the steering system  402 , and can apply the hand wheel angle input directly to one of the hand wheel or steering shaft. In one example, the angle input source  16  is a rotary actuator that rotates an input shaft  412  of the steering column  401  between about −30 degrees and about 30 degrees relative to a longitudinal axis of the input shaft  412  at a frequency of about 0.1 Hertz (Hz). In one example, the angle input source  16  applies the torque to the steering system  402  that changes as a function of the first load applied by the first load source  70  such that a maximum value of the first load is applied to the steering system  402  at a maximum angle of the angle input source  16 . The first load is generally applied in a direction of opposing the motion generated by the angle input source  16 . Stated another way, the angle input source  16  rotates the input shaft  412  to a maximum angle (e.g. about −30 degrees, about 30 degrees) at the maximum load (e.g. +1750 N, −1750 N) for the first load applied by the first load source  70 . It should be noted that this input to the input shaft  412  is merely exemplary, as any input could be applied to the input shaft  412  to simulate the steering of the vehicle during operation of the vehicle. 
     The at least one sensor  18  is coupled to the steering system  402 . In one example, the at least one sensor  18  comprises the first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86 . The first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  are each in communication with the diagnostic module  20  over a suitable communication architecture or arrangement that facilitates transfer of data, commands, power, etc. In one example, the first force sensor  76  comprises a first force transducer. The first force sensor  76  measures and observes a force acting on the first tie-rod  30  and generates sensor signals based thereon. The second force sensor  82  comprises a second force transducer. The second force sensor  82  measures and observes a force acting on the second tie-rod  32  and generates sensor signals based thereon. The rotary sensor  84  comprises a rotary encoder. The rotary sensor  84  measures and observes a rotation of the input shaft  412  and generates sensor signals based thereon. It should be noted that the use of a rotary encoder for the rotary sensor  84  is merely exemplary. In this regard, the rotary sensor  82  can comprise any suitable device for measuring and observing a rotation of the input shaft  412 , including, but not limited to, an analog potentiometer. 
     The torque sensor  86  is coupled to the input shaft  412 . The torque sensor  86  comprises a torque sensor or torque transducer. The torque sensor  86  measures and observes a torque acting on the input shaft  412  and generates sensor signals based thereon. It should be noted that while the torque sensor  86  is illustrated herein as being associated with measuring and observing a torque on the input shaft  412 , alternatively, the torque sensor  86  can measure and observe a torque on the steering shaft or intermediate shaft of the steering system  402  and generate sensor signals based thereon, for example. It should be noted that the use of a torque sensor or torque transducer coupled to the input shaft  412  as the torque sensor  86  is merely exemplary. In this regard, the torque sensor  86  can comprise any suitable device for measuring and observing a torque on the input shaft  412  of the steering system  604 , including, but not limited to, an internal torque sensor associated with the steering system  402 , such as an internal torque sensor associated with the steering assist unit  406 . Thus, the use of an externally mounted torque sensor is merely exemplary. 
     In various embodiments, with reference to  FIG. 2 , the diagnostic module  20  outputs one or more control signals to the first load source  70 , the second load source  72  and the angle input source  16  of the system  400  based on input data from an input device  78 . The diagnostic module  20  receives sensor signals from the first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  in response to the control signals. The diagnostic module  20  evaluates the sensor signals to determine a performance of the steering system  402 . The diagnostic module  20  generates data indicating the performance of the steering system  402 . The data includes display data for displaying the performance of the steering system  402  via a display  80 . The diagnostic module  20  also stores the data indicating the performance of the steering system  402  in a datastore. As discussed with regard to  FIG. 1 , the diagnostic module  20  is coupled to or in communication with the display  80  and the input device  78  over a suitable communication architecture or arrangement that facilitates transfer of data, commands, power, etc. 
     With reference now to  FIG. 3 , a system  500  for determining steering performance is shown. As the system  500  can be similar to the system  10  discussed with regard to  FIG. 1 , only the differences between the system  10  and the system  500  will be discussed in detail herein, with the same reference numerals used to denote the same or substantially similar components. With reference to  FIG. 3 , the system  500  includes the testing structure  12 , the at least one load source  14 , the angle input source  16 , the at least one sensor  18  and the diagnostic module  20  in accordance with various embodiments. As will be discussed further herein, the system  500  enables the determination of a performance of a steering system  502  coupled to the testing structure  12 . Although the figures shown herein depict an example with certain arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. It should also be understood that  FIG. 3  is merely illustrative and may not be drawn to scale. 
     The testing structure  12  supports the steering system  502  and can support one or more of the at least one load source  14 , the angle input source  16 , the at least one sensor  18  and the diagnostic module  20 . In one example, the steering system  502  is a steering system for use with a vehicle. The vehicle may be an automobile, an aircraft, a spacecraft, a watercraft, a sport utility vehicle, or any other type of vehicle. For exemplary purposes the disclosure will be discussed in the context of the steering system  502  being used with an automobile. In the example of  FIG. 3 , the steering system  502  is a center take-off based electric power steering system. 
     As a steering system  502  for an automobile can be generally known, the steering system  502  will not be discussed in great detail herein. Briefly, however, in this example, the steering system  502  includes a steering assist unit  506 , the first tie-rod  30  and the second tie-rod  32 . The steering assist unit  506  receives rotational input from the angle input source  16 , and through a suitable gearing, converts the rotational input into translational input for the first tie-rod  30  and the second tie-rod  32  as is generally known. It should be noted that while the system  500  includes the first tie-rod  30  and the second tie-rod  32 , the performance of the steering system  502  can be determined without the use of the first tie-rod  30  and the second tie-rod  32 , and thus, the first tie-rod  30  and the second tie-rod  32  are optional. 
     In the example of the steering system  502 , the testing structure  12  includes the first fixture  34  coupled to the bedplate  36 . The first fixture  34  supports at least the steering gear  506 , and includes the one or more couplings  42 . The one or more couplings  42  are coupled to or about the steering assist unit  506  such that the steering system  502  is fixed relative to the testing structure  12  in the same manner as the steering system  502  would be coupled to a vehicle. 
     The at least one load source  14  is responsive to one or more control signals from the diagnostic module  20  to apply a load to at least one of the tie rods  30 ,  32  via a respective one of the first load source  70  and the second load source  72 . The first load source  70  can be responsive to the one or more control signals from the diagnostic module  20  to apply a load to the first tie-rod  30 . The second load source  72  can be responsive to the one or more control signals to apply a load to the second tie-rod  32 . In one example, the first load source  70  and the second load source  72  each apply a first load at a first frequency to the respective one of the first tie-rod  30  and the second tie-rod  32 , and apply a second load at a second frequency to the respective one of the first tie-rod  30  and the second tie-rod  32 . Generally, the first load is different than the second load, and the first frequency is different than the second frequency. In one example, the first load is greater than the second load, and the first frequency is less than the second frequency. For example, the first load is about 1750 Newton (N), a maximum of the first load at the first frequency, and the second load is about 250 Newton (N), a maximum of the second load at the second frequency. The first frequency is about 0.1 Hertz (Hz) and the second frequency is about 15 Hertz (Hz). Thus, the first load source  70  and the second load source  72  are each capable of applying a low frequency load and a high frequency load to the respective ones of the first tie-rod  30  and the second tie-rod  32 . 
     The angle input source  16  is responsive to one or more control signals from the diagnostic module  20  to apply a torque to the steering assist unit  506 . In one example, the angle input source  16  is coupled to the steering assist unit  506  to provide the torque or torsional input representative of a hand wheel angle input to the steering assist unit  506 . Alternatively, the angle input source  16  can be coupled to a hand wheel or steering shaft associated with the steering system  502 , and can apply the hand wheel angle input directly to one of the hand wheel or steering shaft. In one example, the angle input source  16  is a rotary actuator that rotates an input shaft  508  of the steering assist unit  506  between about −30 degrees and about 30 degrees relative to a longitudinal axis of the input shaft  508  at a frequency of about 0.1 Hertz (Hz). In one example, the angle input source  16  applies the torque to the steering system  502  that changes as a function of the first load applied by the first load source  70  such that a maximum value of the first load is applied to the steering system  502  at a maximum angle of the angle input source  16 . The first load is generally applied in a direction of opposing the motion generated by the angle input source  16 . Stated another way, the angle input source  16  rotates the input shaft  508  to a maximum angle (e.g. about −30 degrees, about 30 degrees) at the maximum load (e.g. +1750 N, −1750 N) for the first load applied by the first load source  70 . It should be noted that this input to the input shaft  508  is merely exemplary, as any input could be applied to the input shaft  508  to simulate the steering of the vehicle during operation of the vehicle. 
     The at least one sensor  18  is coupled to the steering system  502 . In one example, the at least one sensor  18  comprises the first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86 . The first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  are each in communication with the diagnostic module  20  over a suitable communication architecture or arrangement that facilitates transfer of data, commands, power, etc. In one example, the first force sensor  76  comprises a first force transducer. The first force sensor  76  measures and observes a force acting on the first tie-rod  30  and generates sensor signals based thereon. The second force sensor  82  comprises a second force transducer. The second force sensor  82  measures and observes a force acting on the second tie-rod  32  and generates sensor signals based thereon. The rotary sensor  84  comprises a rotary encoder. The rotary sensor  84  measures and observes a rotation of the input shaft  508  and generates sensor signals based thereon. It should be noted that the use of a rotary encoder for the rotary sensor  84  is merely exemplary. In this regard, the rotary sensor  82  can comprise any suitable device for measuring and observing a rotation of the input shaft  508 , including, but not limited to, an analog potentiometer. 
     The torque sensor  86  is coupled to the input shaft  508 . The torque sensor  86  comprises a torque sensor or torque transducer. The torque sensor  86  measures and observes a torque acting on the input shaft  508  and generates sensor signals based thereon. It should be noted that while the torque sensor  86  is illustrated herein as being associated with measuring and observing a torque on the input shaft  508 , alternatively, the torque sensor  86  can measure and observe a torque on the steering shaft or intermediate shaft of the steering system  502  and generate sensor signals based thereon, for example. It should be noted that the use of a torque sensor or torque transducer coupled to the input shaft  508  as the torque sensor  86  is merely exemplary. In this regard, the torque sensor  86  can comprise any suitable device for measuring and observing a torque on the input shaft  508  of the steering system  502 , including, but not limited to, an internal torque sensor associated with the steering system  502 , such as an internal torque sensor associated with the steering assist unit  506 . Thus, the use of an externally mounted torque sensor is merely exemplary. 
     In various embodiments, with reference to  FIG. 3 , the diagnostic module  20  outputs one or more control signals to the first load source  70 , the second load source  72  and the angle input source  16  of the system  500  based on input data from an input device  78 . The diagnostic module  20  receives sensor signals from the first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  in response to the control signals. The diagnostic module  20  evaluates the sensor signals to determine a performance of the steering system  502 . The diagnostic module  20  generates data indicating the performance of the steering system  502 . The data includes display data for displaying the performance of the steering system  502  via a display  80 . The diagnostic module  20  also stores the data indicating the performance of the steering system  502  in a datastore. As discussed with regard to  FIG. 1 , the diagnostic module  20  is coupled to or in communication with the display  80  and the input device  78  over a suitable communication architecture or arrangement that facilitates transfer of data, commands, power, etc. 
     With reference now to  FIG. 4 , a system  600  for determining steering performance is shown is shown. As the system  600  can be similar to the system  10  discussed with regard to  FIG. 1 , only the differences between the system  10  and the system  600  will be discussed in detail herein, with the same reference numerals used to denote the same or substantially similar components. With reference to  FIG. 4 , the system  600  includes a testing structure  602 , the at least one load source  14 , the angle input source  16 , the at least one sensor  18  and the diagnostic module  20  in accordance with various embodiments. As will be discussed further herein, the system  600  enables the determination of a performance of a steering system  604  coupled to the testing structure  602 . Although the figures shown herein depict an example with certain arrangements of elements, additional intervening elements, devices, features, or components may be present in an actual embodiment. It should also be understood that  FIG. 4  is merely illustrative and may not be drawn to scale. 
     The testing structure  602  supports the steering system  604  and can support one or more of the at least one load source  14 , the angle input source  16 , the at least one sensor  18  and the diagnostic module  20 . In one example, the steering system  604  is a steering system for use with a vehicle. The vehicle may be an automobile, an aircraft, a spacecraft, a watercraft, a sport utility vehicle, or any other type of vehicle. For exemplary purposes the disclosure will be discussed in the context of the steering system  604  being used with an automobile. In the example of  FIG. 4 , the steering system  604  is a recirculating ball or integral steering system. The steering system  604  can be a hydraulic based system or an electric power system as known to those skilled in the art. 
     As a steering system  604  for an automobile can be generally known, the steering system  604  will not be discussed in great detail herein. Briefly, however, in this example, the steering system  604  includes a steering assist unit  606 , a pitman arm  608 , a relay rod  610 , an idler arm  612 , the first tie-rod  30  and the second tie-rod  32 . The steering assist unit  606  receives rotational input from the angle input source  16 , and through a suitable gearing, converts the rotational input into input for the pitman arm  608 . The pitman arm  608  transfers the input through the relay rod  610  to the first tie-rod  30  and the second tie-rod  32  as is generally known. It should be noted that while the system  600  includes the first tie-rod  30  and the second tie-rod  32 , the performance of the steering system  604  can be determined without the use of the first tie-rod  30  and the second tie-rod  32 , and thus, the first tie-rod  30  and the second tie-rod  32  are optional. 
     In the example of the steering system  604 , the testing structure  602  includes a first fixture  614  coupled to the bedplate  36  and a second fixture  615  coupled to the first fixture  614 . It should be noted that the second fixture  615  can be coupled to the bedplate  36 , if desired. The first fixture  614  supports at least the steering assist unit  606 , and the second fixture  615  includes one or more couplings  616 . The one or more couplings  616  are coupled to the idler arm  612  and the steering assist unit  606  such that the steering system  604  is fixed relative to the testing structure  602  in the same manner as the steering system  604  would be coupled to a vehicle. In one example, the steering assist unit  606  is substantially rigidly coupled to the second fixture  615 , and the idler arm  612  is coupled to the second fixture  615  so as to have one degree of rotational freedom relative to the second fixture  615 . 
     The at least one load source  14  is responsive to one or more control signals from the diagnostic module  20  to apply a load to at least one of the tie rods  30 ,  32  via a respective one of the first load source  70  and the second load source  72 . The first load source  70  can be responsive to the one or more control signals from the diagnostic module  20  to apply a load to the first tie-rod  30 . The second load source  72  can be responsive to the one or more control signals to apply a load to the second tie-rod  32 . In one example, the first load source  70  and the second load source  72  each apply a first load at a first frequency to the respective one of the first tie-rod  30  and the second tie-rod  32 , and apply a second load at a second frequency to the respective one of the first tie-rod  30  and the second tie-rod  32 . Generally, the first load is different than the second load, and the first frequency is different than the second frequency. In one example, the first load is greater than the second load, and the first frequency is less than the second frequency. For example, the first load is about 1750 Newton (N), a maximum of the first load at the first frequency, and the second load is about 250 Newton (N), a maximum of the second load at the second frequency. The first frequency is about 0.1 Hertz (Hz) and the second frequency is about 15 Hertz (Hz). Thus, the first load source  70  and the second load source  72  are each capable of applying a low frequency load and a high frequency load to the respective ones of the first tie-rod  30  and the second tie-rod  32 . 
     The angle input source  16  is responsive to one or more control signals from the diagnostic module  20  to apply a torque to the steering assist unit  606 . In one example, the angle input source  16  is coupled to the steering assist unit  606  to provide the torque or torsional input representative of a hand wheel angle input to the steering assist unit  606 . Alternatively, the angle input source  16  can be coupled to a hand wheel or steering shaft associated with the steering system  604 , and can apply the hand wheel angle input directly to one of the hand wheel or steering shaft. In one example, the angle input source  16  is a rotary actuator that rotates an input shaft  618  of the steering assist unit  606  between about −30 degrees and about 30 degrees relative to a longitudinal axis of the input shaft  618  at a frequency of about 0.1 Hertz (Hz). In one example, the angle input source  16  applies the torque to the steering system  604  that changes as a function of the first load applied by the first load source  70  such that a maximum value of the first load is applied to the steering system  604  at a maximum angle of the angle input source  16 . The first load is generally applied in a direction of opposing the motion generated by the angle input source  16 . Stated another way, the angle input source  16  rotates the input shaft  618  to a maximum angle (e.g. about −30 degrees, about 30 degrees) at the maximum load (e.g. +1750 N, −1750 N) for the first load applied by the first load source  70 . It should be noted that this input to the input shaft  618  is merely exemplary, as any input could be applied to the input shaft  618  to simulate the steering of the vehicle during operation of the vehicle. 
     The at least one sensor  18  is coupled to the steering system  604 . In one example, the at least one sensor  18  comprises the first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86 . The first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  are each in communication with the diagnostic module  20  over a suitable communication architecture or arrangement that facilitates transfer of data, commands, power, etc. In one example, the first force sensor  76  comprises a first force transducer. The first force sensor  76  measures and observes a force acting on the first tie-rod  30  and generates sensor signals based thereon. The second force sensor  82  comprises a second force transducer. The second force sensor  82  measures and observes a force acting on the second tie-rod  32  and generates sensor signals based thereon. The rotary sensor  84  comprises a rotary encoder. The rotary sensor  84  measures and observes a rotation of the input shaft  618  and generates sensor signals based thereon. It should be noted that the use of a rotary encoder for the rotary sensor  84  is merely exemplary. In this regard, the rotary sensor  82  can comprise any suitable device for measuring and observing a rotation of the input shaft  618 , including, but not limited to, an analog potentiometer. 
     The torque sensor  86  is coupled to the input shaft  618 . The torque sensor  86  comprises a torque sensor or torque transducer. The torque sensor  86  measures and observes a torque acting on the input shaft  618  and generates sensor signals based thereon. It should be noted that while the torque sensor  86  is illustrated herein as being associated with measuring and observing a torque on the input shaft  618 , alternatively, the torque sensor  86  can measure and observe a torque on the steering shaft or intermediate shaft of the steering system  604  and generate sensor signals based thereon, for example. It should be noted that the use of a torque sensor or torque transducer coupled to the input shaft  618  as the torque sensor  86  is merely exemplary. In this regard, the torque sensor  86  can comprise any suitable device for measuring and observing a torque on the input shaft  618  of the steering system  604 , including, but not limited to, an internal torque sensor associated with the steering system  604 , such as an internal torque sensor associated with the steering assist unit  606 . Thus, the use of an externally mounted torque sensor is merely exemplary. 
     In various embodiments, with reference to  FIG. 4 , the diagnostic module  20  outputs one or more control signals to the first load source  70 , the second load source  72  and the angle input source  16  of the system  600  based on input data from an input device  78 . The diagnostic module  20  receives sensor signals from the first force sensor  76 , the second force sensor  82 , the rotary sensor  84  and the torque sensor  86  in response to the control signals. The diagnostic module  20  evaluates the sensor signals to determine a performance of the steering system  604 . The diagnostic module  20  generates data indicating the performance of the steering system  604 . The data includes display data for displaying the performance of the steering system  604  via a display  80 . The diagnostic module  20  also stores the data indicating the performance of the steering system  604  in a datastore. As discussed with regard to  FIG. 1 , the diagnostic module  20  is coupled to or in communication with the display  80  and the input device  78  over a suitable communication architecture or arrangement that facilitates transfer of data, commands, power, etc. 
     It should be noted that the steering systems  22 ,  402 ,  502 ,  604  discussed with  FIGS. 1-4  are merely exemplary, and the systems and methods of determining steering system performance described herein can be applied to any applicable steering system, and thus, the testing structures  12 ,  602  illustrated herein are merely exemplary. For example, the various teachings of the present disclosure can be applied to determine the performance of a hydraulic power steering system (HPS), a dual pinion steering system, a rack concentric steering system, a pinion electric power steering system, etc. 
     Referring now to  FIG. 5 , and with continued reference to  FIGS. 1-4 , a dataflow diagram illustrates various embodiments of the diagnostic module  20 . Various embodiments of the diagnostic module  20  according to the present disclosure can include any number of sub-modules embedded within the diagnostic module  20 . As can be appreciated, the sub-modules shown in  FIG. 5  can be combined and/or further partitioned to similarly control the first load source  70 , the second load source  72  and the angle input source  16 , and to output the performance data. Inputs to the system can be received from the at least one sensor  18  ( FIGS. 1-4 ), received from one or more of the input devices  78  of the testing structure  12 ,  602 , received from other control modules (not shown), and/or determined/modeled by other sub-modules (not shown) within the diagnostic module  20 . In various embodiments, the diagnostic module  20  includes a test control module  102 , an evaluation module  104  and a user interface (UI) control module  106 . 
     The UI control module  106  generates user interface data  108  that may be used by the display  80  to display a chart  200  ( FIG. 6 ) on a suitable user interface that may include data regarding the performance of the steering system  22 ,  402 ,  502 ,  604 . In one example, the UI control module  106  generates the user interface data  108  based on performance data  110  and test performance data  112  received as input from the evaluation module  104 . As will be discussed in greater detail below, the performance data  110  comprises filtered data that indicates the performance of the steering system  22 ,  402 ,  502 ,  604  based on the sensor data  138 , as generated by the evaluation module  104 , for display on the chart  200 . As will be discussed further herein, the test performance data  112  comprises filtered data received from the evaluation module  104  that provides an indication that the test is operating normally. In one example, the test performance data  112  comprises load performance data  114  and angle performance data  116 . The load performance data  114  comprises filtered data regarding a load applied by the first load source  70  and the second load source  72 , and the angle performance data  116  comprises filtered data regarding an angle input applied to the input shaft  74 ,  412 ,  508 ,  618  by the angle input source  16 . 
     For example, with reference to  FIGS. 6 and 7 , an exemplary chart  200  output by the UI control module  106  for display on the display  80  is illustrated, in which the chart  200  comprises a graphical representation of the performance data  110  and the test performance data  112 . It should be noted that while the chart  200  is illustrated as being displayed on the display  80 , the chart  200  can be part of a graphical user interface displayed by the display  80 . In various embodiments, the graphical representation comprises a graph  202  of the performance data  110  and test performance data  112  over time. A y-axis  204  of the graph  202  represents the amplitudes and an x-axis  206  represents time in seconds (s). The performance data  110  is indicated by line  208 , the test performance data  112  is indicated by line  210  and line  212 . In this regard, the test performance data  112  comprises the load performance data  114 , which is indicated by line  210 , and the angle performance data  116 , which is indicated by line  212 . In one example, line  210  indicates measured load data  132  after a low pass filter with a corner frequency of 1.0 Hertz (Hz) is applied and line  212  indicates measured angle input data  136  after a gain of 100 is applied. Lines  210  and  212  provide visual indicators that the test of the steering system  22  is operating correctly. The performance data  110  indicated by line  208  provides a visual indicator as to the response of the steering system  22 ,  402 ,  502 ,  604  to the loads from the first load source  70 , the second load source  72  and the angle input source  16 . In one example, line  208  illustrates torque data  140  after a bandpass filter with corner frequencies of 13 Hertz (Hz) and 17 Hertz (Hz) and a gain of 1000 is applied. It should be noted that the chart  200  is merely exemplary, as any suitable graphical or textual representation can be employed to convey one or more of the performance data  110  and the test performance data  112 . Moreover, the filters and gains applied to the measured load data  132 , measured angle input data  136  and torque data  140  are merely exemplary. 
     The UI control module  106  can also generate user interface data  108  based on modulation data  118 . As will be discussed further below, the modulation data  118  comprises a modulation of a response of the steering system  22 ,  402 ,  502 ,  604  to the loads applied by the first load source  70 , the second load source  72  and the angle input source  16  and also indicates a performance of the steering system  22 ,  402 ,  502 ,  604 . The modulation data  118  can be output as a separate chart or user interface for display on the display  80 , or can be included on the chart  200  ( FIGS. 3 and 4 ). For example, the UI control module  106  can generate a “PASS” or “FAIL” user interface for display on the display  80  based on the modulation data  118 . 
     The UI control module  106  receives as input user input data  120  based on an operator&#39;s input to the input device  78  ( FIG. 1 ). In one example, the user input data  120  comprises a command  122  for the operation of a test of the steering system  22 ,  402 ,  502 ,  604 . For example, the user input data  120  can comprise a start command or a stop command for a test routine to determine the performance of the steering system  22 ,  402 ,  502 ,  604 . It should be noted, however, that the user input data  120  can also comprise one or more parameters for the operation of the first load source  70 , the second load source  72  and the angle input source  16 . The UI control module  106  interprets and provides the command  122  for the test control module  102 . 
     The test control module  102  receives as input the command  122 . Based on the command  122 , the test control module  102  queries a datastore  124 . The datastore  124  stores one or more tables (e.g., lookup tables) that indicate a load to be applied by the first load source  70  and the second load source  72 , and an angle input to be applied by the angle input source  16  based on the command  122 . The one or more tables comprise calibration tables, which are acquired based on experimental data, and in one example, can comprise at least one table for the at least one load source  14  and one table for the angle input source  16 . In various embodiments, the tables can be interpolation tables that are defined by one or more indexes. A target load test value  126  provided by at least one of the tables indicates a target load to be applied by the first load source  70  and the second load source  72  to the respective one of the first tie-rod  30  and the second tie-rod  32 . A target angle test value  128  provided by at least one of the tables indicates a target angle input to be applied by the angle input source  16  to the input shaft  74 ,  412 ,  508 ,  618 . 
     Based on the target load test value  126 , the test control module  102  outputs load control data  130 . In this regard, based on the target load test value  126 , the test control module  102  outputs the load control data  130  to the at least one load source  14 , and in this example, outputs the load control data  130  to each of the first load source  70  and the second load source  72 . The load control data  130  comprises the one or more control signals for the first load source  70  and the second load source  72 . Generally, the load control data  130  comprises one or more control signals to the first load source  70  and the second load source  72  to apply the first load at the first frequency and the second load at the second frequency. In one example, the first load is about 1750 Newton (N) representing a maximum of the first load at the first frequency and the second load is about 250 Newton (N) representing a maximum of the second load at the second frequency. The first frequency is about 0.1 Hertz (Hz) and the second frequency is about 15 Hertz (Hz). The waveshapes of the first frequency and the second frequency can be any shape with dominant frequency content at the respective frequencies. For example, triangular or sinewave shapes are convenient options amongst others known to those skilled in the art. In one example, a triangular waveshape is selected for the first load at the first frequency and a sinewave is selected for the second load at the second frequency. 
     Based on the target angle test value  128 , the test control module  102  outputs angle control data  134 . In this regard, based on the target angle test value  128 , the test control module  102  outputs the angle control data  134  to the angle input source  16 . The angle control data  134  comprises the one or more control signals for the angle input source  16 . Generally, the angle control data  134  comprises one or more control signals for the angle input source  16  to rotate the input shaft  74 ,  412 ,  508 ,  618  between about −30 degrees and about 30 degrees relative to the longitudinal axis of the input shaft  74 ,  412 ,  508 ,  618  at a frequency of about 0.1 Hertz (Hz). In one example, the angle control data  134  changes as a function of the first load such that the maximum value of the first load is at a maximum angle. The first load is generally applied in a direction of opposing the motion generated by the angle input source  16 . Stated another way, the angle control data  134  can output one or more control signals for the angle input source  16  such that the angle input source  16  rotates the input shaft  74 ,  412 ,  508 ,  618  to the maximum angle (e.g. about −30 degrees, about 30 degrees) at the maximum load (e.g. +1750 N, −1750 N) for the first load applied by the first load source  70 . 
     The evaluation module  104  receives as input measured load data  132 . The measured load data  132  comprises the sensor signals from the first force sensor  76  and the second force sensor  82 . Thus, the measured load data  132  comprises sensor data regarding the first load, the first frequency, the second load and the second frequency output by the first load source  70  and the second load source  72  to the respective ones of the first tie-rod  30  and the second tie-rod  32 . Stated another way, the measured load data  132  comprises sensor data regarding the loads (the first load and the second load) applied to the first tie-rod  30  and the second tie-rod  32  by the first load source  70  and the second load source  72  for the first frequency and the second frequency as measured and observed by the first force sensor  76  and the second force sensor  82 . 
     Based on the measured load data  132 , the evaluation module  104  determines the load performance data  114 . In various embodiments, the evaluation module  104  applies a low pass filter of about 1.0 Hertz (Hz) to the measured load data  132  to generate the load performance data  114 . The evaluation module  104  sets the load performance data  114  for the UI control module  106  and stores the load performance data  114  in a results datastore  142 . 
     The evaluation module  104  also receives as input measured angle input data  136 . The measured angle input data  136  comprises the sensor signals from the rotary sensor  84 . Thus, the measured angle input data  136  comprises sensor data regarding the angle input output by the angle input source  16  to the input shaft  74 ,  412 ,  508 ,  618 . Stated another way, the measured angle input data  136  comprises sensor data regarding the hand wheel angle input applied to the input shaft  74 ,  412 ,  508 ,  618  by the angle input source  16 . 
     Based on the measured angle input data  136 , the evaluation module  104  determines the angle performance data  116 . The evaluation module  104  sets the angle performance data  116  for the UI control module  106  and stores the angle performance data  116  in the results datastore  142 . 
     The evaluation module  104  receives torque data  140  as input. The torque data  140  comprises the sensor signals from the torque sensor  86 . Based on the torque data  140 , the evaluation module  104  determines the performance data  110  and the modulation data  118 . In various embodiments, the evaluation module  104  applies a bandpass filter to the torque data  140  to arrive at the performance data  110 . Generally, the bandpass filter is set to filter the torque data  140  between about 13 Hertz (Hz) and about 17 Hertz (Hz) to arrive at the performance data  110 . The evaluation module  104  sets the performance data  110  for the UI control module  106  and stores the performance data  110  in the results datastore  142 . 
     In various embodiments, the evaluation module  104  determines the modulation data  118  based on the performance data  110 . In this regard, given the performance data  110 , the evaluation module  104  calculates an envelope of the bandpassed carrier wave associated with the performance data  110 . Generally, the bandpassed carrier wave has a periodic waveform. In one example, the envelope of the carrier wave is calculated using the following equation:
 
 CWenv=|H ( BP ( CW ))|  (1)
 
     Wherein, CWenv is the envelope of the bandpassed carrier wave; BP(CW) is the bandpassed carrier wave from the performance data  110 ; H denotes a Hilbert transform applied to the bandpassed carrier wave BP(CW); and the vertical bars indicate an absolute value of the Hilbert transform H. The corner frequencies of the bandpass filter are proximate to the second frequency of the second load. The corner frequencies of the bandpass filter are user-selectable, and in one example, are set at a bandwidth of about 4 hz centered at the second frequency of the second load. The preferred order of the filter, furthermore, is set at 6, also resulting from a forward and reverse application of a 3rd order Butterworth filter. These operations, their consequences, alternative choices of filter implementations and orders are possible and well known to those skilled in the art. 
     Alternatively, the evaluation module  104  determines the modulation data  118  based on applying a low pass filter to the rectified bandpassed carrier wave of the performance data  110 . In various embodiments, the low pass filtered rectified bandpassed carrier wave is calculated using the following equation:
 
 CWlpf=F (| BP ( CW )|)  (2)
 
     Wherein CWlpf is the low pass filtered signal of the rectified, bandpass filtered carrier wave; F denotes a sixth order (forward-reverse application of a 3rd order Butterworth filter) low pass filter having a corner frequency of 5 Hertz (Hz); and BP(CW) is the bandpassed carrier wave from the performance data  110  as described previously using the Hilbert method for envelope detection in equation (1) of the preceding description. It should be noted that these operations, their consequences, alternative choices of filter implementations and orders are possible and well known to those skilled in the art. 
     Based on the envelope of the bandpassed carrier wave calculated from the performance data  110  in (1) or the low pass filtered rectified bandpassed carrier wave calculated from the performance data  110  in (2), the evaluation module  104  determines a percentage of modulation of the resultant periodic waveform. In one example, the percentage of modulation is calculated using the following equation: 
     
       
         
           
             
               
                 
                   
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                         max 
                       
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                         E 
                         min 
                       
                     
                     
                       
                         E 
                         max 
                       
                       + 
                       
                         E 
                         min 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     Wherein the Modulation Index is the modulation data  118 ; E max  is the maximum or peak value of the envelope of the carrier wave calculated in (1) or the maximum or peak value of the low pass filtered carrier wave calculated in (2); and E min  is the minimum value of the envelope of the carrier wave calculated in (1) or the minimum value of the low pass filtered carrier wave calculated in (2). 
     Based on the percentage of modulation, the evaluation module  104  sets modulation data  118  as pass or fail for the UI control module  106  and stores the modulation data  118  for the results datastore  142 . Generally, if the percentage of modulation is about 20 percent or less, the evaluation module  104  sets the modulation data  118  as pass. If the percentage of modulation is greater than about 20 percent, then the evaluation module  104  sets the modulation data  118  as fail. If the modulation data  118  indicates a pass, then the steering system  22 ,  402 ,  502 ,  604  has an acceptable performance. If the modulation data  118  indicates a fail, then the performance of the steering system  22 ,  402 ,  502 ,  604  is unacceptable. With reference to  FIG. 6 , the steering system  22 ,  402 ,  502 ,  604  has an acceptable performance, and with reference to  FIG. 7 , the steering system  22 ,  402 ,  502 ,  604  has an unacceptable performance. It should be noted that setting the modulation data  118  to pass or fail is merely exemplary, as the evaluation module  104  can set the percentage of modulation as the modulation data  118  for the UI control module  106  to generate the user interface data  108 , and can also store the percentage of modulation for the results datastore  142 . It should be noted that other classifications of performance of the steering system  22 ,  402 ,  502 ,  604  are possible, and may, for example, comprise metrics merely relying on the level of the amplitude modulation along a continuum scale. 
     The results datastore  142  stores the performance data  110 , the load performance data  114 , the angle performance data  116  and the modulation data  118  received from the evaluation module  104 . The results datastore  142  can be any non-volatile memory type that stores the information over the repeated use of the system  10 . Further, while the results datastore  142  is illustrated as being associated with the diagnostic module  20  of the system  10 , it should be noted that the results datastore  142  can be located remote from the system  10  and accessed through a suitable wired or wireless interface, as known to one skilled in the art. 
     Referring now to  FIG. 8 , and with continued reference to  FIGS. 1-5 , a flowchart illustrates a control method that can be performed by the diagnostic module  20  of  FIGS. 1-4  in accordance with the present disclosure. As can be appreciated in light of the disclosure, the order of operation within the method is not limited to the sequential execution as illustrated in  FIG. 8 , but may be performed in one or more varying orders as applicable and in accordance with the present disclosure. 
     In various embodiments, the method can be scheduled to run based on predetermined events, and/or can run based on the command  122  from the user input data  120 . 
     With reference to  FIG. 8 , a method  300  for determining the performance of the steering system  22 ,  402 ,  502 ,  604  is shown. The method begins at  302 . At  303 , the method determines if the command  122  to start the testing routine has been received. If the command  122  has been received, the method proceeds to  304 . Otherwise, the method continues with monitoring for the command  122  to start the testing routine. 
     At  304 , the method retrieves the target load test value  126  from the datastore  124  and outputs the control signals to the at least one load source  14 , and in this example, outputs the control signals to each of the first load source  70  and the second load source  72 , to apply the first load at the first frequency and the second load at the second frequency to the first tie-rod  30  and the second tie-rod  32 , respectively. At  306 , the method retrieves the target angle test value  128  from the datastore  124  and outputs the control signals to the angle input source  16  to move or rotate the input shaft  74 ,  412 ,  508 ,  618 . At  308 , the method receives the sensor data  138  from the first force sensor  76 , the second force sensor  82 , rotary sensor  84  and the torque sensor  86 . Stated another way, at  308 , the method receives the measured load data  132  from the first force sensor  76  and the second force sensor  82 , the measured angle input data  136  from the rotary sensor  84  and the torque data  140  from the torque sensor  86 . 
     At  310 , the method determines the performance data  110 , the load performance data  114 , the angle performance data  116  and the modulation data  118 . At  312 , the method outputs the performance data  110 , the load performance data  114 , the angle performance data  116  and the modulation data  118  as the chart  200  for display on the display  80  and stores the performance data  110 , the load performance data  114 , the angle performance data  116  and the modulation data  118  in the results datastore  142 . The method ends at  314 . 
     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.