Abstract:
A portable measurement apparatus is provided for measuring the load required to depress a foot pedal and the change in angular position of the foot pedal. A load plate is connected through at least one load cell to a pedal plate that engages a foot pedal. A linear motion driver is adjustably retained on the measurement apparatus to accommodate different types of foot pedals. A rotary encoder with an extendable cable is used to measure scrub throughout the range of movement of the foot pedal.

Description:
TECHNICAL FIELD 
     This disclosure relates to a tool and system for measuring foot pedal, and in particular accelerator pedal, performance characteristics. 
     BACKGROUND 
     Ergonomic aspects of vehicle controls are important to vehicle design. Foot pedals are actuators that are used to control brakes, acceleration and clutch engagement. Accelerator pedals are particularly important for driver comfort because they are substantially continuously contacted by the driver&#39;s foot whenever a vehicle is operated. 
     Factors that must be considered in the design of foot pedals include the angle of inclination, the force required to depress the pedal, and the sliding, or scrub, of a driver&#39;s shoe across the face of the pedal. These factors are important throughout the full range of movement of the pedal to assure driver comfort and vehicle response. Accelerator pedals are typically elongated members and a substantial portion of the pedal may be contacted by the driver&#39;s foot. 
     Testing devices for pedal operation generally consist of a single point contact that is operatively connected to a load cell. Such devices provide limited information regarding the force required to depress the pedal at the single point of engagement. 
     The above problems and other problems are addressed by this disclosure as summarized below. 
     SUMMARY 
     A pedal measurement apparatus is provided for a vehicle having a traction motor controlled by an accelerator pedal that controls a speed request output signal. The apparatus includes a base and a pedal plate that is connected to the base by a pivot connector. The pedal plate has a surface that is oriented to engage the accelerator pedal. A rotary potentiometer is operatively connected between the pedal plate and the base that provides an inclination signal representative of the angular position of the pedal plate surface. A load plate is attached to at least one load cell that is attached to the pedal plate. A linear motion driver is actuated by a motor and is attached to a pedal bracket to move the pedal plate between a retracted position and an extended position. The load plate provides a load signal that is representative of the load applied by the linear motion driver to the pedal plate. A controller receives the speed request output signal and correlates the speed request signal output to the force applied to the accelerator pedal and the inclination signal. 
     According to other aspects of the pedal measurement apparatus, an inclinometer may be attached to the pedal to measure the position of the pedal in the initial, non-depressed, or retracted position. The speed request signal provides a variable voltage signal to the traction motor that varies based upon the position of the pedal. The pedal measurement apparatus may further comprise an adjustment plate attached to the base that extends vertically above the base with the linear motion driver being attached to the adjustment plate in a range of vertically spaced positions above the base. The pedal measurement apparatus may also further comprise a bracket that secures the linear motion driver to the adjustment plate in a range of horizontally spaced positions relative to the pedal bracket. 
     Further aspects of the pedal measurement apparatus may comprise a revolution per minute (RPM) signal representative of the speed of rotation of the engine that is obtained from a sensor or CAN BUS source on the vehicle. The RPM signal is provided to the controller for correlation with the speed request signal output, the inclination signal, and the load signal to the RPM signal. 
     The pedal measurement apparatus may further comprise a rotary encoder having an elongated cable that is extended from the rotary encoder when the pedal plate is driven into engagement with the accelerator pedal and retracted from the rotary encoder when the pedal plate is withdrawn from the accelerator pedal. The distal end of the elongated cable is attached to a fixed point on the pedal plate and a cable guide is attached to the base plate proximate the pivot connector. The rotary encoder measures the distance that the cable is extended or retracted as the pedal plate is moved from an initial position to a wide open position and provides a scrub signal to the controller. A sleeve may be attached to the base for guiding the cable from the rotary encoder to the cable guide. 
     A method of measuring ergonomic parameters relating to a foot pedal in a vehicle with a portable measurement apparatus as described above, wherein method comprises placing the measurement apparatus on the floor of the vehicle, and placing the pedal plate at a specified fixed distance from engagement with the foot pedal and adjusting the angular orientation of the pedal plate to be parallel to the foot pedal. Connecting the speed request output signal to the controller and actuating the linear motion driver to move the foot pedal from a non-depressed position to a fully depressed position. The load signal and the inclination signal are provided to the controller from at least one load cell and the potentiometer as the foot pedal is moved from the non-depressed position to the fully depressed position. 
     According to other aspects of the method, the measurement apparatus may further comprise a rotary encoder having an elongated cable that is extended from the rotary encoder when the pedal plate is driven into engagement with the accelerator pedal and retracted from the rotary encoder when the pedal plate is withdrawn from the accelerator pedal. A distal end of the elongated cable is attached to a fixed point on the pedal plate, and a cable guide is attached to the base plate proximate the pivot connector. The method further comprises measuring the distance that the cable is extended or retracted as the pedal plate is moved from the non-depressed position to the fully depressed position to provide a scrub measurement value. 
     According to another aspect of the method, the measurement apparatus may further include providing an inclinometer that is attached to the pedal, and the method may further comprise measuring the angular orientation of the pedal in the non-depressed position with the inclinometer. 
     The above aspects of the method and apparatus and other aspects will be better understood in view of the attached drawings and the following detailed description of the illustrated embodiments of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary side elevation view of a vehicle with a portable measurement apparatus made according to one embodiment of the present invention; 
         FIG. 2  is a fragmentary side elevation view of the portable measurement apparatus shown in  FIG. 1 ; and 
         FIG. 3  is a side/front perspective view of the portable measurement apparatus shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of the illustrated embodiments of the present invention is provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention. 
     Referring to  FIG. 1 , a vehicle  10  is shown with a portable measurement apparatus  12  in position to measure changes in load, angular orientation and scrub as the foot pedal  16  is depressed to a fully depressed position or returned to a non-depressed position. The measurement apparatus  12  is placed on a floor  18  of the vehicle  10 . A speed request output signal  20  that is generated in normal vehicle operation as an accelerator foot pedal  16  is depressed and released. The speed request output signal  20  is provided to an engine controller  22 . The engine controller  22 , in turn, signals the traction motor  24  of the vehicle  10  to either increase or decrease speed depending upon the position of the foot pedal  16 . A testing controller  28 , for example a lap top computer with a data acquisition system, is provided to generate control signals and receive data and correlate the data for reports or displays, for example, on a handheld digital display device or on the lap top computer that serves as the testing controller  28 . 
     Referring to  FIGS. 2 and 3 , the measurement apparatus  12  is shown in greater detail. The measurement apparatus  12  includes a base  30  that is placed on the floor  18  of the vehicle  10  (as shown in  FIG. 1 ). The base  30  may have pins, feet or other adjustable elements that are used to level the base  30 . A pedal plate  32  is pivotally attached to the base  30 . A load plate  36  is attached to the pedal plate  32  with an upper load cell  38  and a lower load cell  40  being disposed between the load plate  36  and the pedal plate  32 . A pivot connector  42  connects the pedal plate  32  to the base  30  so that the pedal plate  32  pivots about the pivot connector  42 . 
     The pedal plate  32  has a convex engagement surface  46  that is provided to simulate the sole of a driver&#39;s foot engaging the foot pedal  16 . The convex shape of the engagement surface  46  provides a line of contact with the foot pedal  16  throughout the entire range of motion of the foot pedal  16  from the non-depressed to the fully depressed position. 
     A rotary potentiometer  48  is operatively connected between the pedal plate  32  and the base  30  to provide a signal that is representative of the angular inclination of the pedal plate  32  relative to the surface upon which the apparatus is placed. The rotary potentiometer  48  is preferably mounted coaxially with the pivot connector  42 . 
     A linear motion driver  50  is used to move the pedal plate  32  between the non-depressed position and the fully depressed position. The linear motion driver  50  includes a motor  52  that drives a gear reducer  54 . The gear reducer  54  connects the motor  52  to a gear drive  56  that extends and retracts the linear motion driver  50 . 
     A tower plate  60  is provided to facilitate adjustment of the measuring apparatus  12 . The tower plate  60  defines a vertical slot  62 . The tower plate  60  is secured to the base  30  and extends vertically upwardly from the base. An attachment plate  64  is secured to the tower plate  60  by fasteners that extend through the vertical slot  62 . The attachment plate  64  may be attached to the tower plate  60  in a range of vertical locations along the slot  62 . A hanger  66  is attached to the attachment plate  64  and extends from the attachment plate  64  to the linear motion driver  50 . A clamp  68  is provided as part of a hanger  66 . The clamp  68  may be loosened to permit the linear motion driver  50  to be moved horizontally towards and away from the foot pedal  16 . A bracket  70  is provided to connect the linear motion driver  50  to the load plate  36 . The bracket  70  is pivotally connected to the linear motion driver  50  to allow the pedal plate  32  to pivot as it follows movement of the foot pedal  16 . 
     An inclinometer  72 , such an inertial inclinometer, can be attached to load plate  36  and indirectly to the pedal plate  32 . The inclinometer  72  permits the pedal plate  32  to be set at an initial location corresponding to the design angular orientation of the foot pedal  16 . 
     Referring specifically to  FIG. 2 , a rotary encoder  76 , or string potentiometer, may be attached to the measurement apparatus  12  to measure the scrub or relative movement of the pedal plate  32  relative to the foot pedal  16 . The term “scrub” refers to the sliding movement of a driver&#39;s shoe as the foot pedal  16  is depressed and released. Ideally, scrub is minimized to prevent wear or driver discomfort. A cable  78  is provided by the rotary encoder  76  that may be extended and retracted as the foot pedal  16  is moved. The cable  78  extends through a cable guide  80 . The cable guide  80  is preferably located proximate the pivot connector  42  and is most preferably disposed at a coaxial location relative to the pivot axis of the pivot connector  42 . A sleeve  82  may be provided between the rotary encoder  76  and the cable guide  80 . The sleeve  82  permits the cable  78  to move freely and allows the rotary encoder  76  to be located at a location that is remote from the cable guide  80 . A fixed pin  84  is provided on the pedal plate  32 . A distal end  86  of the cable  78  is attached to the fixed pin  84 . As the foot pedal  16  is depressed and released, the extent to which the pedal is displaced relative to the cable guide  80  is measured by measuring the linear extent of extension and retraction of the cable  78  from the rotary encoder  76 . 
     A bubble level  88  may be provided on the base  30  to facilitate leveling the measuring apparatus  12 . The floor  18  of various vehicles may include grooves, raised areas and other irregular surface features that may make it difficult to set the measurement apparatus  12  in a level position on the floor  18 . Position screws, posts, or other adjustment devices may be provided on the base  30  for engaging the floor  18  to level the measurement apparatus  12 . 
     Referring to  FIG. 1 , a RPM input  90  may be provided from the engine controller  22 , CAN BUS, or from a sensor, that provides an input to the testing controller  28  that is indicative of the engine speed. The RPM signal provided by the RPM input  90  may be used to correlate the position signal, and load signal relative to the speed request output signal and RPM input. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.