Abstract:
A pedal feel emulating system including a brake pedal fixedly mounted to a surface, the brake pedal including at least one piezoelectric material, and an electrical power source connected to the brake pedal to supply electrical energy to the piezoelectric material.

Description:
BACKGROUND 
       [0001]    The present application relates to brake-by-wire brake systems and, more particularly, to pedal feel emulators for brake-by-wire brake systems. 
         [0002]    Brake-by-wire brake systems have been developed to replace traditional hydraulic brake systems, which typically employ a hydraulic connection between a user&#39;s brake input (e.g., a brake pedal) and the brake unit (e.g., a brake caliper), with an electrical connection between the user&#39;s brake input and the brake unit. Therefore, in a typical brake-by-wire brake system, there may no longer be a need for a brake pedal adapted to pressurize hydraulic fluid in a master fluid cylinder. However, brake-by-wire brake systems typically require a user input device for communicating a user&#39;s braking commands to an electronic control unit. 
         [0003]    For convenience and simplicity, brake-by-wire brake systems typically employ a user input device that resembles a brake pedal similar to a brake pedal used on a conventional hydraulic brake-based vehicle. Furthermore, due to the prevalence of hydraulic brake-based vehicles, users often are more familiar with, and have grown accustomed to, the feel of a brake pedal having a non-linear pedal travel versus pedal force. 
         [0004]    Attempts have been made to replicate the non-linear pedal travel versus pedal force using, for example, mechanical springs, pistons and various linkages. However, such systems are often tedious and difficult to assemble. 
         [0005]    Accordingly, there is a need for an improved pedal feel emulating system for brake-by-wire brake systems capable of providing a non-linear pedal travel versus pedal force. 
       SUMMARY 
       [0006]    In one aspect, the disclosed pedal feel emulating system includes a brake pedal fixedly mounted to a surface, the brake pedal including at least one piezoelectric material, and an electrical power source connected to the brake pedal to supply electrical energy to the piezoelectric material. 
         [0007]    In another aspect, the disclosed pedal feel emulating system includes a brake pedal fixedly mounted to a surface, the brake pedal including at least one piezoelectric material, a force sensor connected to the brake pedal, the force sensor being adapted to generate a force signal indicative of a force applied to the brake pedal, a controllable electrical power source connected to the brake pedal, the controllable electrical power source being adapted to supply a variable electrical energy to the piezoelectric material, and an electronic control unit in communication with the force sensor and the controllable electrical power source, wherein the electronic control unit is adapted to control the variable electrical energy based upon the force signal. 
         [0008]    In another aspect, a method for obtaining a non-linear pedal travel versus pedal force of a brake pedal is provided and includes the steps of providing the brake pedal with at least one piezoelectric material, applying a force to the brake pedal, monitoring the force applied to the brake pedal and, based upon the monitored force, supplying a predetermined amount of electrical energy to the piezoelectric material. 
         [0009]    Other aspects of the disclosed pedal feel emulating system and associated method for obtaining a non-linear pedal travel versus pedal force will become apparent from the following description, the accompanying drawings and the appended claims. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a front elevational view of one aspect of the disclosed pedal feel emulating system; 
           [0011]      FIG. 2  is a front elevational view of a second aspect of the disclosed pedal feel emulating system; 
           [0012]      FIG. 3  is a sectional view, taken at line A-A of a pedal of the pedal feel emulating system of  FIG. 1 ; 
           [0013]      FIG. 4  is a top plan view of the section shown in  FIG. 3 ; and 
           [0014]      FIG. 5  is a graphical illustration of pedal travel versus pedal force of the pedal feel emulating system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    As shown in  FIG. 1 , one aspect of the disclosed pedal feel emulating system, generally designated  10 , may include a brake pedal  12 , a mounting surface  14 , an electronic control unit  16 , a controllable electrical power source  18  and a force sensor  20 . The mounting surface  14  may be positioned on the floor  15  of a vehicle (not shown) such that the pedal  12  extends upwardly from the floor  15 . The brake pedal  12  may be a cantilevered brake pedal and may include a mounting portion  11  and an engaging portion  13 . The mounting portion  11  of the pedal  12  may be securely connected to the mounting surface  14  by, for example, brackets, bolts, screws, adhesives, welding, rivets or any other available means. The engaging portion  13  of the pedal  12  may be adapted to be depressed by the foot  23  of a user  22 . 
         [0016]    Alternatively, in the system  10 ′ shown in  FIG. 2 , the mounting surface  14 ′ may be positioned above the floor  15 ′ of the vehicle such that the pedal  12 ′ is suspended from the mounting surface  14 ′ above the floor  15 ′. 
         [0017]    Referring again to  FIG. 1 , the force sensor  20 , which may be a strain gauge-type sensor, a piezoelectric-type sensor or the like, may be connected to the pedal  12  to sense a force supplied to the pedal  12  by the user  22 . In one aspect, the force sensor  20  may be adapted to communicate a sensed force to the electronic control unit  16  by, for example, a communication line  24 . Those skilled in the art will appreciate that communication line  24  may be a hard wired communication line or a wireless communication line. 
         [0018]    Referring to  FIGS. 3 and 4 , the pedal  12  may be formed from, may include or may be a composite of piezoelectric material. As used herein piezoelectric material is intended to include any material capable of applying a force to a member when electrical power is supplied thereto. In one aspect, the pedal  12  may be formed from a plurality of piezoelectric fibers  30  suspended or dispersed in a carrier  32 , such as a polymer matrix, wherein the piezoelectric fibers  30  are disposed between or connected to the two electrodes  34 ,  36 . 
         [0019]    Referring to  FIGS. 1 and 3 , the electrodes  34 ,  36  may be connected to the controllable electrical power source  18  by a supply line  38  and the controllable electrical power source  18  may in turn be connected to the electronic control unit  16  by a communication line  40  ( FIG. 1 ). Alternatively, referring to  FIG. 2 , the electronic control unit  16 ′ may include an integral controllable electrical power source  18 ′ and the electrodes  34 ,  36  may be directly connected to the electronic control unit  16 ′ by a supply line  38 ′. 
         [0020]    The piezoelectric fibers  30  may be woven or non-woven. In one aspect, the pedal  12  may be formed from a mesh of piezoelectric fibers  30  in a polymer matrix  32 , wherein the mesh of piezoelectric fibers  30  is positioned between or connected to the electrodes  34 ,  36 . Furthermore, the pedal  12  may include various reinforcing materials in or about the polymer matrix  32  to provide physical reinforcement to the pedal  12 . For example, in addition to piezoelectric fibers  30 , the pedal  12  may include fiberglass fibers, glass fibers, metal fibers and the like suspended in the polymer matrix  32 . 
         [0021]    Accordingly, when electrical power (e.g., a voltage) is supplied to the electrodes  34 ,  36 , the piezoelectric fibers  30  positioned therebetween may be activated according to the well-known piezoelectric effect, thereby supplying a force to the polymer matrix surrounding the fibers  30  and effectively increasing the rigidity or stiffness of the pedal  12  (i.e., the willingness of the pedal  12  to flex when depressed). Therefore, the rigidity/stiffness of the pedal  12  may be controlled by controlling the amount of power supplied to the electrodes  34 ,  36  by the controllable electrical power source  18 . 
         [0022]    Thus, by controlling the rigidity/stiffness of the pedal  12  based upon signals received from the force sensor  20 , the electronic control unit  16  may achieve a non-linear pedal travel versus pedal force, as shown in  FIG. 5 . For example, when the force sensor  20  detects a high force in the pedal  12 , the electronic control unit  16  may direct the controllable electrical power source  18  to apply a higher voltage to the piezoelectric materials in the pedal, thereby increasing the rigidity/stiffness of the pedal  12  such that the user  22  experiences a greater resistance when depressing the pedal  12 . 
         [0023]    Although various aspects of the disclosed pedal feel emulator have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.