Abstract:
A pedal assembly that provides a repeatable response force between different pedal assemblies by providing at least one of a wear surface or a pivotal shoe on a brake pad that will contact a portion of the pedal arm. The pedal assembly includes a housing, an elongated pedal arm having a rotatable drum defining a braking surface and rotatably mounted in the housing, the pedal arm being movable between an idle, first position and a second position, a brake pad assembly having a pivoting base and a contact portion pivotally mounted to the base, the contact portion having a contact surface adapted to frictionally engage the braking surface, and a biasing device operably coupled to the pedal arm and the brake pad assembly for urging the contact surface into frictional engagement with the braking surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is related to pending U.S. patent application Ser. No. 10/854,837, filed on May 27, 2004. The contents of which are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a pedal mechanism. In particular, the pedal may be an accelerator pedal in a vehicle.  
       BACKGROUND OF THE INVENTION  
       [0003]     Automobile accelerator pedals have conventionally been linked to engine fuel subsystems by a cable, generally referred to as a Bowden cable. While accelerator pedal designs vary, the typical return spring and cable friction together create a common and accepted tactile response for automobile drivers. For example, friction between the Bowden cable and its protective sheath otherwise reduce the foot pressure required from the driver to hold a given throttle position. Likewise, friction prevents road bumps felt by the driver from immediately affecting throttle position.  
         [0004]     Efforts are underway to replace the mechanical cable-driven throttle systems with a more fully electronic, sensor-driven approach. With the fully electronic approach, a position sensor reads the position of the accelerator pedal and outputs a corresponding position signal for throttle control. A sensor-based approach is especially compatible with electronic control systems in which accelerator pedal position is one of several variables used for engine control.  
         [0005]     Although such drive-by-wire configurations are technically practical, drivers generally prefer the feel, i.e., the tactile response, of conventional cable-driven throttle systems. Designers have therefore attempted to address this preference with mechanisms for emulating the tactile response of cable-driven accelerator pedals. For example, U.S. Pat. No. 6,360,631 Wortmann et al. is directed to an accelerator pedal with a plunger subassembly for providing a hysteresis effect.  
         [0006]     In this regard, prior art systems are either too costly or inadequately emulate the tactile response of conventional accelerator pedals. One such problem is small variations in manufacturing may result in widely varying friction resulting in widely varying feel and feedback to the driver.  FIGS. 15A and 15B  show how variations in manufacturing result in different feedback forces being felt by a driver. Both  FIGS. 15A and 15B  show a brake pad  244  which contacts a drum  229  of the pedal lever. More specifically, the drum  229  rotates as shown by arrow  230  when the pedal moves. A spring  49  is connected between the pedal arm and the brake pad  244  to provide a force F S . The brake pad  244  pivots at effective pivot point  246  in an attempt to bring contact surface  270  into contact with the outer surface  249  of drum  229 . Brake pad  244  slides at point  245 . However, due to manufacturing tolerances, the contact surface  270  does not mate flush against the drum surface  249 . As a result, only a point or line of contact  231  exists where the surfaces  270 ,  249  are in contact. As shown in  FIG. 15A  the point of contact  231  between the brake pad  244  and drum  229  is at the top of the brake pad contact surface  270 . As shown in  FIG. 15B  the point of contact  232  between the brake pad  244  and drum  229  is at the bottom of the brake pad contact surface  270 . The difference in frictional force between the devices of  FIGS. 15A and 15B  is symbolically shown. Specifically, the lever ratio equals the length L S  divided by the normal-friction length L N . The normal force F N  causes a friction force that provides feel to the driver. The normal force is calculated by multiplying the spring force F S  by the lever ratio (L S /L N ). The spring force F S  and spring length L S  are typically constant. However, the normal-friction length L N  changes based on the point of contact. The normal-friction length L N  is greater in  FIG. 15B  than in  FIG. 15A , which results in  FIG. 15B  having less normal force F N . The driver will feel less force from the brake pad  244  in  FIG. 15B  than from the  FIG. 15A  brake pad. It is desirable to provide a more predicable feedback force or feel to a driver. Thus, there continues to be a need for a cost-effective, electronic accelerator pedal assembly having the feel of cable-based systems and providing adequate, predictable feedback to the driver.  
       SUMMARY  
       [0007]     The accelerator pedal assembly includes a housing, an elongated pedal arm terminating at one end in a rotatable drum defining a curved braking surface, a brake pad assembly having a curved contact surface substantially complementary to the braking surface and a bias spring device operably situated between the pedal arm and the brake pad. The pedal arm is rotatably mounted to the housing such that the curved braking surface rotates as the pedal moves between an idle position to an open throttle position. The brake pad assembly defines a primary pivot axis and is pivotably mounted for frictional engagement with the braking surface. The brake pad assembly includes a portion adapted to provide a given force to the user regardless of manufacturing tolerances. The bias spring serves to urge the contact surface of the brake pad into frictional engagement with the braking surface of the drum. In an embodiment, the brake pad assembly has a contact portion pivotally mounted to a base. The contact portion is adapted to frictionally engage the drum braking surface. In an embodiment, the base has a projection and the contact portion includes a recess adapted to receive the projection. In an embodiment, the recess of the contact portion is larger than the projection such that the contact portion is free to pivot in any direction. In an embodiment, the recess and projection form a press fit such that the contact portion pivots in a direction substantially tangential to the braking surface of the drum. In an embodiment, the base includes a first web connected at an inward first end to the contact portion and a second web connected at an inward first end to the contact portion. In an embodiment, the contact portion includes a cavity inward of the first ends of the first and second web. In an embodiment, base includes a projection aligned with the cavity. The contact portion includes a first arm extending in a first direction from the first end of the first web and a second arm extending in a second direction from the first end of the second web, the first arm being spaced from the first web, and the second arm being spaced from the second web. In an embodiment, the contact surface of the contact portion pivots such that it substantially mates to the braking surface. In an embodiment, the contact surface has at least 75% of its surface in contact with the braking surface with the pedal arm moved from the first, idle position. In an embodiment, the contact surface has a first substantially constant radius of curvature. In an embodiment, the contact surface has a second substantially constant radius of curvature. In an embodiment, the braking surface has a substantially constant radius of curvature substantially equal to at least one of the first or second substantially constant radius of curvatures of the contact surface. In an embodiment, the contact portion includes a wear surface adapted to conform to the braking surface over time such that a normal friction force moves to a given center value over time. In an embodiment, the brake pad assembly includes opposed trunnions adapted to mount on the housing and define a primary pivot axis.  
         [0008]     In an embodiment, the pedal arm carries a magnet and a Hall effect position sensor is secured to the housing and responsive to the movement of the magnet for providing an electrical signal representative of pedal displacement. These and other objects, features and advantages will become more apparent in light of the text, drawings and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is an exploded isometric view of the accelerator pedal assembly of an embodiment of the present invention.  
         [0010]      FIG. 2  is an enlarged cross-sectional view of the pedal assembly shown in  FIG. 1 .  
         [0011]      FIG. 3  is a cross-sectional view of the pedal assembly showing the foot pedal and Hall effect position sensors.  
         [0012]      FIG. 4  is an enlarged side, cross-sectional view of the accelerator pedal assembly according to the present invention.  
         [0013]      FIG. 5  is an isometric view of the brake pad part of the accelerator pedal assembly.  
         [0014]      FIG. 6  is a side view of an embodiment of the brake pad of the accelerator pedal assembly.  
         [0015]      FIG. 7  is a top, plan view of the brake pad of the accelerator pedal assembly.  
         [0016]      FIGS. 8A through 8D  are force-displacement graphs mapped to simplified schematics illustrating the operation of accelerator pedal assemblies according to the present invention.  
         [0017]      FIGS. 9A through 9C  are force diagrams demonstrating the tunable tactile response of accelerator pedals according to the present invention.  
         [0018]      FIG. 10  is an enlarged side view of an embodiment of the brake pad of the accelerator pedal assembly.  
         [0019]      FIG. 11  is an enlarged side view of an embodiment of the brake pad of the accelerator pedal assembly.  
         [0020]      FIG. 12  is an enlarged side view of an embodiment of the brake pad of the accelerator pedal assembly.  
         [0021]      FIG. 13  is an enlarged side view of an embodiment of the brake pad of the accelerator pedal assembly.  
         [0022]      FIG. 14  is an enlarged side view of an embodiment of the brake pad of the accelerator pedal assembly.  
         [0023]      FIG. 15A  is a side view of a prior art brake pad of the accelerator pedal assembly. 
     
    
     DETAILED DESCRIPTION  
       [0024]     While this invention is susceptible to embodiment in many different forms, this specification and the accompanying drawings disclose only preferred forms as examples of the invention. The invention is not intended to be limited to the embodiments so described. The scope of the invention is identified in the appended claims.  
         [0025]     Referring to  FIG. 1 , a non-contacting accelerator pedal assembly  20  according to an embodiment of the present invention includes a housing  32 , a pedal arm  22  rotatably mounted to housing  32 , a brake pad assembly  44  and a bias spring device  46 . The labels “pedal beam” or “pedal lever” also apply to pedal arm  22 . Likewise, brake pad assembly  44  may be referred to as a “body” or “braking lever.” Pedal arm  22  has a footpad  27  at one end and terminates at its opposite proximal end  26  in a drum portion  29  that presents a curved, convex braking (or drag) surface  42 . Pedal arm  22  has a forward side  28  nearer and facing the front of the car and a rearward side  30  nearer the driver and facing the rear of the car. Footpad  27  may be integral with the pedal lever  22  or articulating and rotating at its connection at the lower end  24 . Braking surface  42  of pedal lever  22  preferably has the curvature of a circle of a radius R 1  which extends from the center of opening  40 , which is central to the drum portion  29  of assembly  20 . A non-circular curvature for braking surface is also contemplated. In an embodiment, as illustrated, surface  42  is curved and convex with a substantially constant radius of curvature. In alternate embodiments, surface  42  has a varying radius of curvature.  
         [0026]     Pedal arm  22  pivots from housing  32  via an axle connection through drum  29  such that drum  29  and its contact surface  42  rotate as pedal arm  22  is moved. Spring device  46  biases pedal arm  22  towards the idle position, e.g., upwardly as shown in  FIG. 1 . Brake pad assembly  44  has a base  44 A and a contact portion  44 B. The base  44 A is positioned to receive spring device  46 . Contact portion  44 B includes a contact surface  70  that is movably into contact with drum  29 . Contact surface  70  is adapted to provide a more complete contact to the drum regardless of fabrication tolerances to assembly tolerances. Brake pad assembly  44  is pivotally mounted to housing  32  such that the contact surface  70  is urged against braking surface  42  as pedal arm  22  is depressed, e.g., moved downwardly as shown in  FIG. 1 .  
         [0027]     Pedal arm  22  carries a magnet subassembly  80  for creating a magnetic field that is detected by redundant Hall effect sensors  92 A and  92 B which are secured in housing  32 . Acting together, magnet  80  and sensors  92  provide a signal representative of pedal displacement.  
         [0028]     It should be understood that a Hall effect sensor with magnet is representative of a number of sensor arrangements available to measure the displacement of pedal arm  22  with respect to housing  32  including other optical, mechanical, electrical, magnetic and chemical means. Specifically contemplated is a contacting variable resistance position sensor.  
         [0029]     In embodiments as illustrated, housing  32  also serves as a base for the mounted end  26  of pedal arm  22  and for sensors  92 . Proximal end  26  of pedal arm  22  is pivotally secured to housing  32  with axle  34 . More specifically, drum portion  29  of pedal arm  22  includes an opening  40  for receiving axle  34 , while housing  32  has a hollow portion  37  with corresponding openings  39 A and  39 B also for receiving axle  34 . Axle  34  is narrowed at its ends where it is collared by a bearing journal  19 .  
         [0030]     The base  44 A of brake pad  44  includes a top  52  which is relatively flat, a bottom  54  which consists of two flat planes  114  and  112  intersecting to a ridge  110 , a front face  56  which is substantially flat, and a circular back face  58  in an embodiment. Base  44 A also has opposed trunnions  60 A and  60 B (also called outriggers or flanges) to define a primary pivot axis positioned between spring device  46  and contact surface  70 . Contact surface  70  of contact portion  44 B is situated on one side of this pivot axis and a donut-shaped socket  104  for receiving one end of bias spring  46  is provided on the other side in the base  44 A.  
         [0031]     Contact surface  70  of contact portion  44 B is substantially complementary to braking surface  42 . In the preferred embodiment, as illustrated, contact surface  70  is curved and concave with a substantially constant radius of curvature. In alternate embodiments, braking surface has a varying radius of curvature. The frictional engagement between contact surface  70  and braking surface  42  may tend to wear either surface. The shape of contact surface  42  may be adapted to reduce or accommodate wear.  
         [0032]     Referring now also to  FIGS. 2 through 6 , housing  32  is provided with spaced cheeks  66  for slidably receiving the trunnions  60 A and  60 B. Trunnions  60 A and  60 B are substantially U-shaped and have an arc-shaped portion  62  and a rectilinear (straight) portion  64 . Brake pad assembly  44  pivots over cheeks  66  at trunnions  60 A and  60 B. As pedal arm  22  is moved in a first direction  72  (accelerate in the case of a accelerator pedal or brake in the case of a brake pedal) or the other direction  74  (decelerate or non-brake, respectively), the force Fs within compression spring  46  increases or decreases, respectively. Brake pad assembly  44  is moveable in response to the spring force Fs.  
         [0033]     As pedal arm  22  moves towards the non-active, e.g., idle/decelerate, position (direction  74 ), the resulting drag between braking surface  42  and contact surface  70  urges brake pad assembly  44  towards a position in which trunnions  60 A and  60 B are higher on cheeks  66 . This change in position is represented with phantom trunnions in  FIG. 4 . Although  FIG. 4  depicts a change in position with phantom trunnions to aid in understanding the invention, movement of brake pad assembly  44  may not be visibly detectable. As pedal arm  22  is depressed (direction  72 ), the drag between braking surface  42  and contact surface  70  draws brake pad assembly  44  further into hollow portion  37 . The sliding motion of brake pad assembly  44  is gradual and can be described as a “wedging” effect that either increases or decreases the force urging contact surface  70  into braking surface  22 .  
         [0034]     This directionally dependent hysteresis is desirable in that it approximates the feel of a conventional mechanically-linked accelerator pedal.  
         [0035]     When pedal force on arm  22  is increased, brake pad assembly  44  is urged forward on cheeks  66  by the frictional force created on contact surface  70  as braking surface  42  rotates forward (direction  120  in  FIG. 4 ). This urging forward of brake pad assembly  44  likewise urges trunnions  60 A and  60 B lower on cheeks  66  such that the normal, contact force of contact surface  70  into braking surface  42  is relatively reduced. When pedal force on arm  22  is reduced, the opposite effect is present: the frictional, drag force between brake pad assembly  44  and braking surface  42  urges brake pad assembly  44  backward on cheeks  66  (direction  121  in  FIG. 4 ). This urging backward of brake pad assembly  44  urges trunnions  60 A and  60 B higher on cheeks  66  such that the normal direction, contact force between braking surface  42  and contact surface  70  is relatively increased. The relatively higher contact force present as the pedal force on arm  22  decreases allows a driver to hold a given throttle position with less pedal force than is required to move the pedal arm for acceleration.  
         [0036]     Bias spring device  46  is situated within a recess  106  in pedal lever  22  ( FIG. 3 ) and between recess  106  and a receptacle  104  in base  44 A of brake pad assembly  44 . Spring device  46  includes two, redundant coil springs  46 A and  46 B in a concentric orientation, one spring nestled within the other. This redundancy is provided for improved reliability, allowing one spring to fail or flag without disrupting the biasing function. It is preferred to have redundant springs and for each spring to be capable—on its own—of returning the pedal lever  22  to its idle position.  
         [0037]     Also for improved reliability, brake pad assembly  44  is provided with redundant pivoting (or rocking) structures. In addition to the primary pivot axis defined by trunnions  60 A and  60 B, brake pad assembly  44  defines a ridge  110  which forms a secondary pivot axis, as best shown in  FIG. 6 . When assembled, ridge  110  is juxtaposed to a land  47  defined in housing  32 . Ridge  110  is formed at the intersection of two relatively flat plane portions at  112  and  114 . The pivot axis at ridge  110  is substantially parallel to, but spaced apart from, the primary pivot axis defined by trunnions  60 A and  60 B and cheeks  60 .  
         [0038]     The secondary pivot axis provided by ridge  110  and land  47  is a feature of vehicle pedals according to an embodiment the present invention to allow for failure of the structural elements that provide the primary pivot axis, namely, trunnions  60 A and  60 B and cheeks  66 . Over the useful life of an automobile, material relaxations, stress and or other aging type changes may occur to trunnions  60 A and  60 B and cheeks  66 . Should the structure of these features be compromised, the pivoting action of brake pad  44  can occur at ridge  110 .  
         [0039]     Pedal arm  22  has predetermined rotational limits in the form of an idle, return position stop  33  on side  30  and a depressed, open-throttle position stop  36  on side  28  in the case of an accelerator pedal. When pedal arm  22  is fully depressed, stop  36  comes to rest against portion  98  of housing  32  and thereby limits forward movement. Stop  36  may be elastomeric or rigid. Stop  33  on the opposite side  30  contacts a lip  35  of housing  32 . Housing  32  is securable to a wall via fasteners through mounting holes  38 . Pedal assemblies according to the present invention are suitable for both firewall mounting or pedal rack mounting by means of an adjustable or non-adjustable position pedal box rack.  
         [0040]     Magnet assembly  80  has opposing fan-shaped sections  81 A and  81 B, and a stem portion  87  that is held in a two-pronged plastic grip  86  extending from drum  29 . Magnet assembly  80  preferably has two major elements: a specially shaped, single-piece magnet  82  and a pair of (steel) magnetic flux conductors  84 A and  84 B. Single-piece magnet  82  has four alternating (or staggered) magnetic poles: north, south, north, south, collectively labeled with reference numbers  82 A,  82 B,  82 C,  82 D as best seen in  FIG. 2 . Each pole  82 A,  82 B,  82 C,  82 D is integrally formed with stem portion  87  and separated by air gaps  89  ( FIG. 1 ) and  88  ( FIG. 3 ). Magnetic flux flows from one pole to the other—like charge arcing the gap on a spark plug—but through the magnetic conductor  84 . A zero gauss point is located at about air gap  88 .  
         [0041]     Magnetic field conductors  84 A and  84 B are on the outsides of the magnet  82 , acting as both structural, mechanical support to magnet  82  and functionally tending to act as electromagnetic boundaries to the flux the magnet emits. Magnetic field conductors  84  provide a low impedance path for magnetic flux to pass from one pole (e.g.,  82 A) of the magnet assembly  80  to another (e.g.,  82 B).  
         [0042]     As best shown in  FIG. 2 , sensor assembly  90  is mounted to housing  32  to interact with magnet assembly  80 . Sensor assembly  90  includes a circuit board portion  94  received within the gap  89  between opposing magnet sections  81  A and  81  B, and a connector socket  91  for receiving a wiring harness connector plug. Circuit board  94  carries a pair of Hall Effect sensors  92 A and  92 B. Hall effect sensors  92  are responsive to flux changes induced by pedal arm lever displacement and corresponding rotation of drum  29  and magnet assembly  80 . More specifically, Hall effect sensors  92  measure magnet flux through the magnet poles  82 A and  82 B. Hall effect sensors  92  are operably connected via circuit board  94  to connector  91  for providing a signal to an electronic throttle control. Only one Hall effect sensor  92  is needed but two allow for comparison of the readings between the two Hall effect sensors  82  and consequent error correction. In addition, each sensor serves as a back up to the other should one sensor fail.  
         [0043]     Electrical signals from sensor assembly  90  have the effect of converting displacement of the foot pedal  27 , as indicated by displacement of the magnet  82 , into a dictated speed/acceleration command which is communicated to an electronic control module such as is shown and described in U.S. Pat. No. 5,524,589 to Kikkawa et al. and U.S. Pat. No. 6,073,610 to Matsumoto et al. hereby incorporated expressly by reference for any purpose.  
         [0044]     Referring to  FIGS. 2 and 3 , it is a feature of the present invention that the semi-circular contours of contact surface  70  and trunnion portion  62  can be aligned concentrically or eccentrically. A concentric alignment as illustrated in  FIG. 4 , with reference labels R  1  and R 2 , results in a more consistent force F N  applied between surface  42  and surface face  70  as pedal arm  22  is actuated up or down. An eccentric, alignment as illustrated in  FIG. 2 , tends to increase the hysteresis effect. In particular, the center of the circle that traces the contour of the surface  70  is further away from the firewall in the rearward direction  74 .  
         [0045]     The effect of this eccentric alignment is that depression of the footpad  27  leads to an increasing normal force F N  exerted by the contact surface  70  against braking surface  42 . A friction force F f  between the surface  70  and surface  42  is defined by the coefficient of dynamic friction multiplied by normal force F N . As the normal force F N  increases with increasing applied force F a  at footpad  27 , the friction force F f  accordingly increases. The driver feels this increase in his/her foot at footpad  27 . Friction force F f  runs in one of two directions along face  70  depending on whether the pedal lever is pushed forward  72  or rearward  74 . The friction force F f  opposes the applied force F a  as the pedal is being depressed and subtracts from the spring force F, as the pedal is being returned toward its idle position.  
         [0046]      FIGS. 8A, 8B ,  8 C,  8 D contain a force diagram demonstrating the directionally dependent actuation-force hysteresis provided by accelerator pedal assemblies according to the present invention. In  FIGS. 8A through 8D , the y-axis represents the foot pedal force F a  required to actuate the pedal arm, in Newtons (N). The x-axis is displacement of the footpad  27 . Path  150  represents the pedal force required to begin depressing pedal arm  22 . Path  152  represents the relatively smaller increase in pedal force necessary to continue moving pedal arm  22  after initial displacement toward mechanical travel stop, i.e., contact between stop  36  and surface  98 . Path  154  represents the decrease in foot pedal force allowed before pedal arm  22  begins movement toward idle position. This no-movement zone allows the driver to reduce foot pedal force while still holding the same accelerator pedal position. Over path  156 , accelerator pedal assembly  20  is in motion as the force level decreases.  FIGS. 8A, 8B ,  8 C,  8 D combine a force-displacement graph with simplified schematics showing selected features of accelerator pedals according to the invention. The schematic portion of  FIG. 8A  illustrates the status of accelerator pedal apparatus  20  for path  150  when initially depressed.  FIG. 8B  illustrates the status of apparatus  20  for path  152  when increasing pedal force causes relatively greater pedal displacement.  FIG. 8C  illustrates the status of apparatus  20  for path  154  when pedal force can decrease without pedal arm movement. Finally,  FIG. 8D  illustrates the status of apparatus  20  for path  156  as pedal arm  22  is allowed to return to idle position.  
         [0047]      FIGS. 8A through 8D  describe pedal operation according to an embodiment of the present invention over a complete cycle of actuation from a point of zero pedal pressure, i.e., idle position, to the fully depressed position and then back to idle position again with no pedal pressure. The shape of this operating curve also applies, however, to midcycle starts and stops of the accelerator pedal. For example, when the pedal is depressed to a mid-position, the driver still benefits from a no-movement zone when foot pedal force is reduced.  
         [0048]      FIGS. 8A through 9C  are additional force diagrams demonstrating the directionally dependent actuation-force hysteresis provided by accelerator pedal operation according to the present invention.  FIG. 9A  is a reproduction of the force diagram of  FIGS. 8A through 8D  for juxtaposition with  FIGS. 9B and 9C . As compared to the accelerator pedal assembly described in  FIG. 9A , the assembly described by  FIG. 9B  offers a larger no-movement zone  154 , i.e., increased hysteresis. In an embodiment, pedal force can be reduced 40 to 50 percent before pedal arm  22  begins to move towards idle.  FIG. 9C  is the operating response for an accelerator pedal requiring a greater increase in foot pedal force to actuate the pedal arm. In other words,  FIG. 9C  describes an accelerator pedal according to an embodiment of the present invention having a relatively “stiffer” tactile feel.  
         [0049]      FIG. 10  shows an embodiment of a brake pad assembly  144  that includes a pivoting base  144 A and a pivoting contact portion  144 B. Base  144 A includes a surface  146  facing and spaced from the rounded braking surface  42 . A rounded projection or connection point  147  extends outwardly from surface  146 . In the illustrated embodiment, the connection point  147  is an integrally formed projection. Contact portion  144 B includes a recess  149  adapted to receive the connection point  147 . The contact portion  144 B is pivotally fixed to the base  144 A. In an embodiment, the contact portion  144 B is fixed to base  144 A by a press fit. Contact  144 B is centrally connected to the base  144 A and has two segments or arms  152 ,  154  extending outwardly from the central connection. Each segment  152 ,  154  is spaced from the adjacent face of base  144 A such that one segment can move toward the base  144 A with the other segment moving away from the base  144 A to allow the contact portion  144 B to pivot relative to base  144 A, e.g., in the direction of arrow  158 . The contact portion  144 B also pivots with base  144 A about the primary pivot axis  150 . The primary pivot axis  150  is formed by trunnions and cheeks (not shown in  FIG. 10 ) as described herein. Contact portion  144 B has a rounded contact surface  170 . Rotation of the base  144 A in response to downward spring force  46  as shown in  FIG. 10  results in the contact surface  170  moving into contact with the surface  42  of pedal arm drum portion  29 . The contact portion  144 B acts as a shoe and pivots about connection point  147  so that its contact surface  170  maximizes its area in contact with the drum portion surface  42 . The pivotal contact portion  144 B more accurately maintains the force (normal friction force F N ) at the connection point between the contact portion  144 B and base  144 A, i.e., through the projection  147 , regardless of variations in manufacturing tolerances. As a first result, the normal force is substantially constant regardless of manufacturing tolerances. Moreover, a more full area of surface  170  is available for wear and contact. As a secondary result, the pivoting of the contact portion  144 B allows the contact friction area to be maximized as the contact surface  170  mates with the drum  29 . Brake pad assembly  144  can be formed from injection molded plastic.  
         [0050]      FIG. 11  shows an embodiment of a brake pad assembly  344  that includes a base  344 A and a contact portion  344 B pivotally connected to the base  344 A. In this embodiment, the contact portion  344 B is fabricated from a block of material that is integral with the base  344 A. In an embodiment, the material is an engineered polymer that has sufficient rigidity and durability to be used in vehicle applications. A through aperture  172  is cut into the integral base/contact portion to form a projection  147  centrally on the surface of base  344 A that will face the drum surface  42  and a substantially matching cavity  149  in contact portion  344 B. The aperture  172  further extends upwardly and downwardly from the projection  147 . Aperture  172  has a greater width adjacent the projection  147 . Aperture  172  decreases in width as it extends from the central projection. Aperture  172  extends from one side to the other side of base  344 A with the base surface facing the drum portion  29  and contact portion  344 B being a solid surface. An upper recess  174  is intermediate the base  344 A and the upper arm  154  of contact portion  344 B. The upper recess is closed adjacent the cavity  149  and open at the upper surface of the base  344 A. A web  175  of the base material remains intermediate the aperture  172  and upper recess  174 . In an embodiment, the web  175  is a solid. In an embodiment, the web  175  has apertures therein. A lower recess  176  is intermediate the base  344 A and a lower arm  156  of contact portion  344 B. The lower recess  176  is closed adjacent the cavity  149  and open at the lower surface of the base  344 A. A web  177  of the base material remains intermediate the aperture  172  and lower recess  176 . In an embodiment, the web  177  is a solid. In an embodiment, the web  177  has apertures therein. The contact portion, friction surface  170  is brought into contact with the drum surface  42  as described herein. Cavity  149  can contact projection  147  after assembly. The contact portion  344 B is a shoe that pivots about an axis generally positioned in the projection  147  and generally in the directions shown by arrow  158 . As a result, the contact friction area is maximized and remains relatively constant independent of manufacturing tolerances. Moreover, a more full area of surface  170  is available for wear and contact. Similar to the  FIG. 4  embodiment, the pivotal contact portion  344 B more accurately maintains the force (normal force F N ) central to the contact portion  344 B, i.e., at cavity  149  and projection  147 , regardless of variations in manufacturing tolerances. The force is also transmitted from the contact portion  344 B through webs  175 ,  177  to base  344 A if the contact portion does not contact projection  147 . If contact portion  344 B rests on projection  147  during activation, then the force principally transmits through the projection  147  to base  144 A. As a result, the lever force is substantially constant regardless of manufacturing tolerances.  
         [0051]      FIG. 12  shows an embodiment of a brake pad assembly  444  that includes a base  444 A and a contact portion  444 B pivotally connected to the base  444 A. In this embodiment, the contact portion  444 B is a separate component of the assembly  444 . Base  444 A includes a projection  147  adapted to be received in a cavity  149  of contact portion  444 B. In this embodiment, the projection  147  has a height greater than the depth of the cavity  149 , such that a gap separates the bottom surface of contact portion  444 B from the adjacent surface of base  444 A. This allows the contact portion  444 B to pivot on the projection  147  relative to base  444 A. The distance between the contact surface  170  and drum surface  42  is less than the depth of cavity  149  so that the contact portion  444 B can not fall off the projection  147  when the contact portion  444 B is in the idle position of the pedal assembly. This embodiment operates essentially the same as described herein to provide a tactile feedback to the user.  
         [0052]      FIG. 13  shows an embodiment of a brake pad assembly  544  that includes a base  544 A and a contact portion  544 B. In an embodiment, the contact portion  544 B is fixed to the base  544 A. The contact surface  170  includes a plurality of contact surfaces  170 A,  170 B, each with a separate radius. In the illustrated embodiment the number of contact surfaces is two. The radius  174  of the upper contact surface  170 A is spaced from the radius  176  of lower contact surface  170 B. Accordingly, the contact surface  170  is more likely to contact the drum surface  49  in a central area. It will be recognized that the plurality of contact surfaces  170 A,  170 B, etc., could be positioned on any of the other embodiments described herein. While contact surface  170  was shown with two contact surfaces, more or fewer contact surfaces could also be used.  
         [0053]      FIG. 14  shows an embodiment of a brake pad assembly  644  that includes a base  644 A and a contact portion  644 B. The contact portion  644 B includes a wear section  180  that forms the contact surface  170 . The contact surface  170  of the wear section  180  has a radius Rwear that is greater than the radius Rpedal of the drum surface  49 . In other words, the radius of the friction lever surface Rpedal is less than the radius of the pedal lever Rwear. This in turn narrows the possible contact area of the contact surface  170  to the drum surface  49 , which causes the contact area to start near the center of the contact surface  170  over time. As a result, the lever forces will tend toward the desired design quantity. This will result is a more consistent friction force that a user will feel. Base  644 A and contact portion  644  can be formed from injection molded plastic.  
         [0054]     Numerous variations and modifications of the embodiments described above may be effected without departing from the spirit and scope of the novel features of the invention. It is to be understood that no limitations with respect to the specific system illustrated herein are intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.