Patent Publication Number: US-2012031221-A1

Title: Accelerator Pedal for a Vehicle

Description:
CROSS-REFERENCE TO RELATED AND CO-PENDING APPLICATIONS 
     This application is a continuation application which claims the benefit of co-pending U.S. patent application Ser. No. 11/657,926 filed on Jan. 24, 2007 which is a continuation-in-part of U.S. patent application Ser. No. 10/854,837 filed on May 27, 2004 (now U.S. Pat. No. 7,404,342 which issued on Jul. 29, 2008), entitled Accelerator Pedal for Motorized Vehicle, the disclosures of which are explicitly incorporated herein by reference, as are all references cited therein. 
     This application also claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/764,594, filed on Feb. 2, 2006, the contents of which are explicitly incorporated by reference, as are all references cited therein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a pedal mechanism. In particular, the pedal may be an accelerator pedal in a vehicle. 
     BACKGROUND OF THE INVENTION 
     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. 
     Efforts are underway to replace the mechanical cable-driven throttle systems with a more fully electronic, sensor-driven approach. With the fully electronic approach, the position of the accelerator pedal is read with a position sensor and a corresponding position signal is made available 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. 
     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. 
     In this regard, prior art systems are either too costly or inadequately emulate the tactile response of conventional accelerator pedals. Thus, there continues to be a need for a cost-effective, electronic accelerator pedal assembly having the feel of cable-based systems. 
     SUMMARY 
     In one embodiment, the present invention provides a pedal assembly. The pedal assembly includes a housing and a pedal arm that has an end. The end has a rotatable drum that defines a braking surface. The pedal arm is rotatably mounted to the housing. A lever extends from the second end. A brake pad is retained by the housing and has a contact surface that is substantially complementary to the braking surface. The brake pad is adapted to be engaged with the braking surface. A bias spring device is situated between the lever and the brake pad for urging the contact surface of the brake pad into frictional engagement with the braking surface of the drum. A sensor is coupled to the pedal arm to sense the position of the pedal arm. 
     These and other objects, features and advantages will become more apparent in light of the text, drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an assembled isometric view of the accelerator pedal assembly of the present invention. 
         FIG. 2  is another assembled isometric view of the accelerator pedal assembly of the present invention. 
         FIG. 3  is an exploded isometric view of the accelerator pedal assembly of  FIG. 1 . 
         FIG. 4  is another exploded isometric view of the accelerator pedal assembly of  FIG. 1 . 
         FIG. 5  is an enlarged cross-sectional view of the accelerator pedal assembly of  FIG. 1  showing details of the braking surface. 
         FIG. 6  is an enlarged cross-sectional view of the accelerator pedal assembly of  FIG. 1  showing details of the braking surface and brake pad. 
         FIG. 7  is a cross-sectional view of the accelerator pedal assembly of  FIG. 1 . 
         FIG. 8  is an isometric view of the break pad of the accelerator pedal assembly. 
         FIG. 9  is another isometric view of the break pad of the accelerator pedal assembly. 
         FIG. 10  is a partial cut-away view of  FIG. 1  showing the brake pad mounted in the housing. 
         FIG. 11  is a partial cut-away view of  FIG. 1  showing the brake pad mounted in the housing. 
         FIG. 12  is an isometric view of the pedal arm, brake pad and spring. 
         FIG. 13  is a partial cut-away view of  FIG. 1  showing the kickdown lever. 
         FIG. 14  is a force diagram demonstrating the tactile response of the accelerator pedal according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible to embodiment in many different forms, this specification and the accompanying drawings disclose several forms as examples of the invention. The invention is not intended to be limited to the embodiments so described, however. The scope of the invention is identified in the appended claims. 
     Referring to  FIGS. 1-4 , a non-contacting accelerator pedal assembly  20  according to the present invention includes a housing  32 , a pedal arm  22  rotatably mounted to housing  32 , a brake pad  44  and a bias spring device  46 . The labels “pedal beam” or “pedal lever” also apply to pedal arm  22 . Likewise, brake pad  44  may be referred to as a “body” or “braking lever.” Pedal arm  22  has ends  22 A and  22 B. A footpad  27  is located toward end  22 A. Pedal arm end  22 B has a drum portion  29  that presents a curved, W-shaped braking (or drag) surface  42  (best seen in  FIGS. 5 and 6 ). Drum portion  29  also has a raised center ridge  43 . A lever  210  extends from pedal arm end  22 B adjacent to drum portion  29 . 
     Housing  32  has a sensor section  82  and a friction mechanism section  37 . A sensor  80  is mounted in sensor section  82  and a friction generating mechanism  270  is mounted in friction mechanism section  37 . 
     Pedal arm  22  has a forward side  28  nearer the front of the car and a rearward side  30  nearer the driver and rear of the car. Footpad  27  may be integral with the pedal lever  22  or articulating and rotating at its connection point to pedal lever  22 . Pedal arm  22  has an aperture  40 . Braking surface  42  of accelerator arm  22  includes braking surfaces  42 A,  42 B,  42 C and  42 D that define a W-shape. In alternate embodiments, surface  42  can have other shapes. 
     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. Brake pad  44  is positioned to receive spring device  46  at one end and contact drum  29  at the other end. Brake pad  44  is pivotally mounted to housing  32  such that a contact surface  70  is urged against braking surface  42  as pedal arm  22  is depressed. 
     Pedal arm  22  is coupled to a sensor assembly  80  in sensor section  82  for creating a signal representative of pedal displacement. Sensor assembly  80  can be a contacting variable resistance position sensor. Other sensors could also be used such as optical, mechanical, electrical, magnetic and chemical means. 
     In an embodiment as illustrated, housing  32  also serves as a base for the mounted end  22 B of pedal arm  22  and for sensor  80 . Proximal end  22 B of pedal arm  22  is pivotally secured to housing  32  with an axle  34 . More specifically, drum portion  29  of pedal arm  22  includes an opening  40  for receiving axle  34 , while housing  32  has a friction generating cavity or section  37  with corresponding openings  39 A and  39 B also for receiving axle  34 . Axle  34  may be press fit into opening  40 . Axle  34  is narrowed at its ends where it is collared and supported by bearing journals  19  that are mounted in openings  39 A and  39 B. A cover  220  is mounted to housing  32  and covers one end of axle  34  and bearing  19 . 
     Turning now to  FIGS. 8 and 9 , in addition to contact surface  70 , the other features of brake pad  44  include a top  230 , a bottom  231  a button  232 , a ridge  110  and ends  233  and  234 . 
     Contact surface  70  is W-shaped and is located at end  234 . Contact surface  70  includes contact surfaces  70 A,  70 B,  70 C and  70 D that define a W-shape. In alternate embodiments, contact surface  70  can have other shapes. Contact surfaces  70 A-D mate with braking surfaces  42 A-D to form a friction generating mechanism  270 . 
     Brake pad  44  also has opposed trunnions  60 A and  60 B (also called outriggers or flanges) to define a primary pivot axis  238  positioned between spring device  46  and contact surface  70 . Contact surface  70  of brake pad  44  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. 
     Brake pad  44  has stepped flanges  240 ,  241  and  242  located toward end  233 . An aperture  233  passes through flange  242 . Bias spring device  46  includes bias springs  46 A and  46 B. Spring  46 A is larger in diameter than spring  46 B. Springs  46 A and  46 B are co-axial with spring  46 B being located inside spring  46 A. Springs  46 A and  46 B provide redundancy in case one of the springs fail, another is able to operate. One end of spring  46 A goes over flange  241  and rests on flange  240 . One end of spring  46 B goes over flange  242  and rests on flange  241 . 
     Contact surface  70  is substantially complementary to braking surface  42 . In one embodiment, contact surface  70  is curved and W-shaped with a substantially constant radius of curvature. In alternate embodiments, braking surface has a varying radius of curvature and other shapes. 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. 
     Referring now to  FIGS. 1-7 , housing  32  is provided with spaced slots  66  for slidably receiving the trunnions  60 A and  60 B. Trunnions  60 A and  60 B are substantially cylindrical in shape. Brake pad  44  pivots on trunnions  60 A and  60 B in slots  66  and  67 . 
     With brake pad  44  mounted in trunnions  60 A and  60 B, ridge  110  may contact a portion  248  of housing  32  in cavity  37 . Ridge  110  and portion  248  may form a secondary pivot axis  250  on which brake pad  44  may pivot or rock. 
     Pedal arm  22  includes a lever  210  that extends from pedal arm end  22 B. Lever  210  includes a bottom  211 , a flat base portion  260 , a rounded flange  262  and another rounded flange  264 . One end of spring  46 A rests on base portion  260  and one end of spring  46 B rests on flange  262 . Therefore, bias spring device  46  is situated between lever  210  and brake pad  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 useful to have redundant springs and for each spring to be capable—on its own—of returning the pedal lever  22  to its idle position. 
     As pedal arm  22  is moved in a first direction  72  (accelerate) or the other direction  74  (decelerate), the force F s  within compression spring  46  increases or decreases, respectively. Brake pad  44  is moveable in response to the spring force F s . 
     As pedal arm  22  moves towards the idle/decelerate position (direction  74 ), the resulting drag between braking surface  42  and contact surface  70  urges brake pad  44  towards a position in which trunnions  60 A and  60 B move slightly outward in slots  66  and  67 . This change in position of brake pad  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  44  further into cavity portion  37  and causes trunnions  60 A and  60 B to move slightly inward in slots  66  and  67 . The sliding motion of brake pad  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  42 . This directionally dependent hysteresis is desirable in that it approximates the feel of a conventional mechanically-linked accelerator pedal. 
     When pedal force on arm  22  is increased, brake pad  44  is urged inwardly on slots  66  and  67  by the frictional force created on contact surface  70  as braking surface  42  rotates forward (direction  120  in  FIG. 7 ). This urging forward of brake pad  44  likewise urges trunnions  60 A and  60 B into slots  66  and  67 , such that the normal, contact force of contact surface  70  into braking surface  42  is relatively reduced. 
     It is noted that the W-shape of braking surface  42  and contact surface  70  provides a larger area to generate increased friction over than just a simple straight surface. 
     When pedal force on arm  22  is reduced, the opposite effect is present: the frictional, drag force between  44  and braking surface  42  urges brake pad  44  outward from slots  60 A and  60 B (direction  121  in  FIG. 7 ). This urging backward of brake pad  44  urges trunnions  60 A and  60 B outward from slots  60 A and  60 B 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. 
     Also for improved reliability, brake pad  44  is provided with redundant pivoting (or rocking) structures. In addition to the primary pivot axis  238  defined by trunnions  60 A and  60 B, brake pad  44  defines a ridge  110 , which forms a secondary pivot axis  250 . 
     When assembled, ridge  110  is juxtaposed to portion  248  and may form a secondary pivot axis  250  on which brake pad  44  may pivot or rock. The secondary pivot axis provided by ridge  110  and portion  248  is a feature of accelerator pedals according to 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 slots  66  and  67 . Should the structure of these features be compromised, the pivoting action of brake pad  44  can occur at ridge  110 . 
     With reference to  FIGS. 10-13 , pedal arm  22  has predetermined rotational limits in the form of an idle, return position stop  500  and a depressed, open-throttle position stop  520 . Open throttle position stop  520  comprises pedal arm posts  525  that extend out from each side of pedal arm  22  and stop walls  530  on housing  32 . When pedal arm  22  is fully depressed, pedal arm posts  525  come to rest against stop walls  530 , thereby limiting forward movement of pedal arm  22 . Stops  500  and  520  may be elastomeric or rigid. 
     Idle position stop  500  comprises pedal arm wall  505  and housing wall  510 . When pedal arm  22  is released, pedal arm wall  505  comes to rest against housing wall  510  and cannot move any further in direction  74  ( FIG. 7 ). 
     Turning back to  FIGS. 1-7 , housing  32  is securable to a vehicle 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. 
     Housing  32  also has a sensor section or cavity  82 . Sensor assembly  80  can be mounted in sensor section  82 . Sensor assembly  80  can include a Kapton flexible film  371  that has resistor tracks  372  and conductor tracks  374 . Film  371  is located in sensor cavity  82  and rests against wall  375 . One end of film  371  is located in slot  377 . Terminals  383  are insert molded into housing  32 . The terminals would extend into connector shroud  320  and can be connected with a wire harness. A metal pressure wedge  380  is pressure fit into slot  377  to make electrical connections between conductor tracks  374  and terminals  383 . A rotor  376  is pressure fit over shaft  34 . Rotor  376  has contactors or wipers  378  attached to one end of the rotor. A sensor cover  381  is ultrasonically welded to housing  32  to seal sensor cavity  82 . In operation rotor  376  moves as shaft  34  does. Shaft  34  is connected to pedal arm  22 . Movement of pedal arm  22  causes rotor  376  and contactors  378  to move along resistor tracks  372  and conductor tracks  374 . As the contactors  378  move, a voltage applied to the terminals will change magnitude. This is called an electrical output signal and is indicative of the position of pedal arm  22 . Additional details on the operation and construction of sensor assembly  80  are detailed in U.S. Pat. Nos. 5,416,295 and 6,474,191, the contents of which are specifically herein incorporated by reference in their entirety. 
     When a vehicle operator presses on pedal arm  22 , shaft  326  rotates. As shaft  326  rotates, rotor  376  turns which causes the wipers  378  to move along the resistor tracks  372  and conductor tracks  374  which causes the electrical output signal to change as a function of the pedal position. 
     A wire harness (not shown) would be mounted to connector shroud  320  and connect with terminals  383 . The wire harness typically connects with an engine control computer. The engine control computer controls an electric motor attached to a throttle plate mounted on the intake of the engine. In this manner, the pedal assembly is able to control the throttle setting on the engine electronically or through a wire. Systems of this type are called drive-by-wire systems. 
     Housing  32  can further have a kickdown clip opening or cavity  402  located on the side of housing  32 . A kickdown clip  400  can be mounted inside of and be retained by cavity  402 . Kickdown clip  400  can include a projecting button  404 . Pedal arm  22  may also include a kickdown lever  422  that has a flat wall portion  422 . Kickdown lever  422  extends from lever  210  along one side of spring  46 . 
     Additional details on the operation and construction of kickdown clip  400  are detailed in U.S. Pat. No. 6,418,813, entitled, “Kickdown Mechanism for a Pedal”, the contents of which are specifically herein incorporated by reference in their entirety. 
     When the pedal arm  22  is near a point of maximum depression, flat wall portion  422  presses on and engages button  404  of kickdown clip  400 . Extra force is then required to be applied to pedal arm  22  to cause button  404  to move inwardly into kickdown clip  400 . The kickdown clip provides a tactile feedback to the pedal operator that the pedal is at a maximum point of depression. The maximum point of pedal depression can correspond to a wide open engine throttle position or can be used to indicate a downshift point for an automatic transmission. 
     When a pedal operator lifts his foot from footpad  27 , the loaded bias spring device  46  causes pedal arm  22  to rotate about axle  34  back to the original starting position. This position corresponds to an idle engine throttle position. 
     When footpad  27  is depressed, an increasing normal force F N  is 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 1  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 s  as the pedal is being returned toward its idle position. 
     The pedal assembly  20  of the present invention can have a directionally dependent actuation-force hysteresis. Initially a larger amount of force may be required to start movement of pedal arm  22 . A smaller amount of force may then be needed to keep moving pedal arm  22 . 
     Pedal assembly  20  may further have a no-movement zone that allows the driver to reduce foot pedal force while still holding the same accelerator pedal position. 
       FIG. 14  shows a graph of force versus pedal arm travel demonstrating the directionally dependent actuation-force hysteresis provided by accelerator pedal assembly  20  of the present invention. In an embodiment, pedal force can be reduced 40 to 50 percent before pedal arm  22  begins to move towards an idle position. 
     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.