Patent Publication Number: US-2018037207-A1

Title: Vehicle brake-by-wire system with a brake pedal emulator override device

Description:
FIELD OF THE INVENTION 
     The subject invention relates to a vehicle brake-by-wire (BBW) system, and more particularly, to a brake pedal emulator with an emulator override device. 
     BACKGROUND 
     Traditional service braking systems of a vehicle are typically hydraulic fluid based systems actuated by a driver depressing a brake pedal that generally actuates a master cylinder. In-turn, the master cylinder pressurizes hydraulic fluid in a series of hydraulic fluid lines routed to respective actuators at brakes located adjacent to each wheel of the vehicle. Such hydraulic braking may be supplemented by a hydraulic modulator assembly that facilitates anti-lock braking, traction control, and vehicle stability augmentation features. The wheel brakes may be primarily operated by the manually actuated master cylinder with supplemental actuation pressure gradients supplied by the hydraulic modulator assembly during anti-lock, traction control, and stability enhancement modes of operation. 
     When a plunger of the master cylinder is depressed by the brake pedal to actuate the wheel brakes, pedal resistance is encountered by the driver. This resistance may be due to a combination of actual braking forces at the wheels, hydraulic fluid pressure, mechanical resistance within the booster/master cylinder, the force of a return spring acting on the brake pedal, and other factors. Consequently, a driver is accustomed to and expects to feel this resistance as a normal occurrence during operation of the vehicle. Unfortunately, the ‘feel’ of conventional brake pedals are not adjustable to meet the desires of a driver. 
     More recent advancements in braking systems include BBW systems that actuate the vehicle brakes via an electric signal typically generated by an on-board controller. Brake torque may be applied to the wheel brakes without a direct hydraulic link to the brake pedal. The BBW system may be an add-on, (i.e., and/or replace a portion of the more conventional hydraulic brake systems), or may completely replace the hydraulic brake system (i.e., a pure BBW system). In either type of BBW system, the brake pedal ‘feel’, which a driver is accustomed to, must be emulated. 
     Accordingly, it is desirable to provide a brake pedal emulator that may simulate the brake pedal ‘feel’ of more conventional brake systems, and an emulator that is generally robust. 
     SUMMARY OF THE INVENTION 
     In one exemplary embodiment of the invention, a brake pedal apparatus for actuating a vehicle brake assembly includes a stationary structure, a brake pedal emulator assembly, and an emulator override device. The brake pedal emulator assembly includes a brake pedal operatively engaged to the stationary structure, and a brake pedal emulator operatively engaged between the stationary structure and the brake pedal along a centerline. The brake pedal emulator is configured to electrically operate the brake assembly. The emulator override device includes a mechanical linkage operatively engaged to the brake assembly, and a latch configured to selectively connect and disconnect the mechanical linkage from the brake pedal emulator assembly. The mechanical linkage is configured to mechanically operate the brake assembly via at least in-part movement of the brake pedal along the centerline. 
     In another exemplary embodiment of the invention, a vehicle includes a BBW system that has a brake assembly, a brake pedal emulator assembly and an emulator override device. The brake pedal emulator assembly is electrically connected to the brake assembly and the emulator override device is mechanically connected to the brake assembly. 
     The above features and advantages and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawings in which: 
         FIG. 1  is a schematic plan view of a vehicle having a BBW system as one non-limiting example in accordance with the present disclosure; 
         FIG. 2  is a schematic of the BBW system; 
         FIG. 3  is a schematic of a brake pedal apparatus of the BBW system; 
         FIG. 4  is a graph of a force profile of a force induction device of the BBW system as a function of brake pedal travel; 
         FIG. 5  is a graph depicting a damping coefficient profile as a function of brake pedal travel; 
         FIG. 6  is a schematic of the brake pedal apparatus in a BBW mode and without actuation of a brake pedal; 
         FIG. 7  is a schematic of the brake pedal apparatus in the BBW mode and with actuation of the brake pedal; 
         FIG. 8  is a schematic of the brake pedal apparatus in a mechanical backup mode and without actuation of the brake pedal; 
         FIG. 9  is a schematic of the brake pedal apparatus in the mechanical backup mode and with actuation of the brake pedal; 
         FIG. 10  is a schematic of a second embodiment of the brake pedal apparatus; and 
         FIG. 11  is a schematic of a third embodiment of the brake pedal apparatus. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the terms module and controller refer to processing circuitry that may include an 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. 
     In accordance with an exemplary embodiment of the invention,  FIG. 1  is a schematic of a vehicle  20  that may include a powertrain  22  (i.e., an engine, transmission, and differential), a plurality of rotating wheels  24  (i.e., four illustrated), and a braking system  26  that may be a BBW system as one, non-limiting, example. The BBW system  26  may include a brake assembly  28  for each respective wheel  24 , a brake pedal apparatus  30 , and a controller  32 . The powertrain  22  is adapted to drive at least one of the wheels  24  thereby propelling the vehicle  20  upon a surface (e.g., road). The BBW system  26  is configured to generally slow the speed and/or stop motion of the vehicle  20 . The vehicle  20  may be an automobile, truck, van, sport utility vehicle, or any other self-propelled or towed conveyance suitable for transporting a burden. 
     Each brake assembly  28  of the BBW system  26  may include a brake  34  and an actuator  36  configured to operate the brake. The brake  34  may include a caliper (not shown) and may be any type of brake including disc brakes, drum brakes, and others. As non-limiting examples, the actuator  36  may be an electro-hydraulic brake actuator (EHBA) or other actuators capable of actuating the brake  34  based on an electrical input signal that may be received from the controller  32 . More specifically, the actuator  36  may be, or may include, any type of motor capable of acting upon a received electric signal and as a consequence, converting energy into motion that controls movement of the brake  34 . Thus, the actuator  36  may be a direct current motor configured to generate electro-hydraulic pressure delivered to, for example, the calipers of the brake  34 . It is further contemplated and understood that the brake  34  and or the actuator  36  may further include a redundant actuating means that may include more traditional techniques such as a mechanical linkage between the brake  34  and the brake pedal (e.g., push/pull cable, hydraulics, and others). 
     The controller  32  may include a computer-based processor (e.g., microprocessor) and a computer readable and writeable storage medium. In operation, the controller  32  may receive one or more electrical signals from the brake pedal apparatus  30  over a pathway (see arrow  38 ) indicative of driver braking intent. In-turn, the controller  32  may process such signals, and based at least in-part on those signals, output an electrical command signal to the actuators  36  over a pathway (see arrow  40 ). Based on any variety of vehicle conditions, the command signals directed to each wheel  24  may be the same or may be distinct signals for each wheel  24 . The pathways  38 ,  40  may be wired pathways, wireless pathways, or a combination of both. 
     Non-limiting examples of the controller  32  may include an arithmetic logic unit that performs arithmetic and logical operations; an electronic control unit that extracts, decodes, and executes instructions from a memory; and, an array unit that utilizes multiple parallel computing elements. Other examples of the controller  32  may include an engine control module, and an application specific integrated circuit. It is further contemplated and understood that the controller  32  may include redundant controllers, and/or the system may include other redundancies, to improve reliability of the BBW system  26 . 
     Referring to  FIGS. 2 and 3 , the brake pedal apparatus  30  of the braking system  26  includes a brake pedal emulator assembly  41 , and an emulator override device  43 . The brake pedal emulator assembly  41  is configured to simulate the behavior and/or ‘feel’ of a more traditional hydraulic braking system, and includes a brake pedal  42  and a brake pedal emulator  44 . The brake pedal  42  is adapted to be actuated by a driver for operating the brake assemblies  28 . The brake pedal emulator  44  is adapted to adjust and simulate more traditional brake pedal ‘feel’ (e.g., that of a traditional hydraulic braking system) experienced by the driver. The emulator override device  43  is constructed and arranged, for example, to function as a back-up system if the BBW system  26  is in a faulted state such that the system is no longer able to supply sufficient braking capability. 
     The brake pedal  42  may be supported by, and in moving relationship too, a fixed structure  46  of the brake pedal apparatus  30 . Illustrated as one non-limiting example, the brake pedal  42  may be pivotally engaged to the fixed structure  46  about a first pivot axis  48 . The brake pedal emulator  44  may be supported by and extend between the brake pedal  42  and the fixed structure  46 . More specifically, the emulator  44  may be pivotally engaged to the brake pedal at a second pivot axis  50 , and may be in operable contact with the stationary structure  46  at a contact  52 . The second pivot axis  50  may be spaced from and substantially parallel to the first pivot axis  48 . It is contemplated and understood that the brake pedal  42  may not be pivotally connected to the stationary structure  46 , and instead, may be in sliding contact with the stationary structure with limited degrees of motion. It is further contemplated and understood that the contact  52  may include a third pivotal axis, or may be a sliding contact between the emulator  44  and the stationary structure  46  with limited degrees of motion. 
     The brake pedal emulator  44  may include a damping device  54  and a force induction device  56  to at least simulate the desired or expected ‘feel’ of the brake pedal  42  during operation by the driver. The damping device  54  is constructed and arranged to generally produce a damping force that is a function of the speed upon which a driver depresses the brake pedal  42 . The force induction device  56  produces an induced force (e.g., spring force) that is a function of brake pedal displacement. Both the damping device  54  and the force induction device  56  may be controlled, individually or in combination, by the controller  32  to at least simulate the desired pedal ‘feel.’ 
     One example of the force induction device  56  may be a resiliently compressible, coiled, spring. Other non-limiting examples of a force induction device  56  include elastomeric foam, a wave spring, and any other device capable of producing a variable force generally as a function of brake pedal displacement. One example of the damping device  54  may include a hydraulic cylinder having at least one internal orifice for the flow and exchange of hydraulic fluid between chambers. Such a damping device (and others) may be designed to exert a constant force when a constant speed is applied to the brake pedal throughout the brake pedal throw. One example of such a ‘constant force’ damping device  54  may be a hydraulic cylinder with a single orifice. Another non-limiting example of a damping device  54  may include a device designed to increase a force with increasing pedal displacement and when the brake pedal  42  is depressed at a constant speed. Such ‘variable force’ damping devices may be passive and dependent solely upon the brake pedal position and/or displacement, or may be active and controllable by the controller  32 . One example of a ‘passive variable force’ damping device may include a hydraulic cylinder with multiple orifices, sequentially exposed, based on brake pedal position. Other non-limiting examples of a damping device  54  may include a friction damper, and any other device capable of producing a variable force generally as a function of pedal actuation speed. Although illustrated in a parallel (i.e., side-by-side) relationship to one-another, it is further contemplated and understood that the orientation of the devices  54 ,  56  with respect to one-another may take any variety of forms. For example, the devices  54 ,  56  may be concentric to one-another along the centerline C (see  FIG. 6 ). 
     Referring to  FIG. 3 , the brake pedal emulator  44  may further include a linking member  58  that operatively connects the brake pedal  42  to the devices  54 ,  56  at the second pivot axis  50 . A displacement sensor  60  of the brake pedal emulator  44  may be configured to measure displacement (e.g., linear or angular displacement) of at least one of the brake pedal  42  and the linking member  58 . The emulator  44  may further include at least one pressure sensor  62  generally orientated at a reactive side of the devices  54 ,  56  (i.e., proximate to the contact  52 ) to measure applied pressure. It is contemplated and understood that the pressure sensor  62  may be a pressure transducer or other suitable pressure sensor configured or adapted to precisely detect, measure, or otherwise determine an applied pressure or force imparted to the brake pedal. 
     To optimize system reliability, the brake pedal emulator  44  may include more than one displacement sensor located at different locations of the brake pedal apparatus  30 . Similarly, the brake pedal emulator  44  may include more than one pressure sensor (i.e., force) configured to, for example, output redundant signals to more than one controller to facilitate fault tolerance for sensor faults. 
     In operation, the controller  32  is configured to receive a displacement signal (see arrow  64 ) and a pressure signal (see arrow  66 ) over pathway  38  and from the respective sensors  60 ,  62  as the brake pedal  42  is actuated by a driver. The controller  32  processes the displacement and pressure signals  64 ,  66  then sends appropriate command signal(s)  68  to the brake actuators  36  over the pathway  40 . It is contemplated and understood that the signal pathways  38 ,  40  may be wireless, hard wired, or a combination of both. 
     Referring to  FIG. 4 , one example of a force profile of the force induction device  56  is generally illustrated as a function of brake pedal travel T, illustrated in the graph as driver applied brake pedal force F verse the brake pedal travel T. The solid arcuate or curved line  71  represents the targeted profile, and the dashed lines  73  represent the outer bounds (i.e., tolerance) of the targeted profile. The force induction device  56  may be designed to meet this targeted profile  71 . 
     Referring to  FIG. 5 , one example of a damping coefficient profile is generally illustrated as a function of brake pedal travel T, illustrated in the graph as the brake pedal travel T verse a damping coefficient D. The solid arcuate or curved line  75  represents the targeted profile, and the dashed lines  77  represent the outer bounds (i.e., tolerance) of the targeted profile. Similar to the force induction device  56 , the damping device  54  may be designed to meet this targeted profile. It is further contemplated and understood that the data from the targeted force and damping force profiles along with pre-established target tolerances (i.e., bounds) may be programmed into the controller  32  for various processing functions. Although not specifically illustrated, it is further contemplated and understood that to various degrees, one or both of the devices  54 ,  56  may be adjustable with this adjustability being controlled by the controller  32  to, for example, meet the pre-programmed profiles of  FIGS. 4 and 5 . It is further noted that the damping coefficient D is a function of pedal position, and the damping force is a function of pedal apply rate and pedal position. 
     Referring to  FIGS. 6 and 7 , the brake pedal emulator  44  generally extends along a centerline C and between the brake pedal  42  and, generally, the stationary structure  46  at respective second pivot axis  50  and contact  52 . The emulator override device  43  is configured to selectively and mechanically operate the brake assembly  28  via, at least in-part, movement of the brake pedal  42  along the centerline C. 
     The brake pedal emulator  44  of the brake pedal emulator assembly  41  (also see  FIGS. 2 and 3 ) may further include a base member  72  detachably engaged to the stationary structure  46  when the brake pedal apparatus  30  is in a BBW mode of operation (see  FIGS. 6 and 7 ). The linking member  58  may include a first end portion  76  that may be pivotally engaged directly to the brake pedal  42  at the second pivot axis  50 , and an opposite second end portion  78  that may be enlarged. The damping and force induction devices  54 ,  56  bear upon and extend axially between the base member  72  and the end portion  78  of the linking member  58 . As best shown in  FIG. 6 , when the brake pedal  42  is not actuated and the brake pedal apparatus is in the BBW mode, the damping and force induction devices  54 ,  56  may be fully extended axially along centerline C. As best shown in  FIG. 7 , when the brake pedal  42  is substantially fully actuated, the devices  54 ,  56  may be fully compressed axially. It is further contemplated and understood that the force induction device  56  may also facilitate the return of the brake pedal  42  after the brake pedal is actuated and released by the driver. 
     The emulator override device  43  of the brake pedal apparatus  30  may include a mechanical linkage  80  (e.g., input rod) and a latch  82 . When the brake pedal apparatus  30  is in the BBW mode, the latch  82  generally engages, and holds rigid, the base member  72  to the stationary structure  46 . In one embodiment, the latch  82  may include an electric solenoid  84  and a bolt  85  configured to extend and retract from the solenoid based on whether the solenoid is electrically energized or not. The solenoid  84  may be controlled by the controller  32  and may be energized when the brake pedal apparatus  30  is in the BBW mode. In one embodiment, the solenoid  84  may be carried by the base member  72 . When the solenoid  84  is energized, the bolt  85  may project from the solenoid and into an opening  86  or other arrangement carried by the stationary structure  46 . With the bolt  85  in the opening  86 , the base member  72  is prevented from moving (i.e. at least axially along centerline C) with respect to the stationary structure  46 , and the devices  54 ,  56  may be compressed axially between the base member  72  and the linking member  58  which moves axially as the brake pedal  42  is actuated. 
     Referring to  FIGS. 8 and 9 , the brake pedal apparatus  30  is illustrated in a mechanical backup mode  88 . When the brake pedal apparatus  30  is in the mechanical backup mode  88  and the brake pedal  42  is not actuated, the damping and force induction devices  54 ,  56  may be fully extended axially along centerline C (see  FIG. 8 ). As best shown in  FIG. 9 , during brake pedal  42  actuation and when the brake pedal  42  is substantially fully actuated, the devices  54 ,  56  remain fully extended and generally do not exert the simulated axial forces upon the brake pedal  42  as previously described during normal operation. Instead, when the brake pedal apparatus  30  is in the mechanical backup mode  88 , the electric solenoid  84  of the latch  82  may be de-energized and the bolt  85  may be engaged to the end portion  78  of the linking member  58 . In one example and to facilitate this engagement, the bolt  85  may removeably project into a opening  90  in the end portion  78  of the linking member  58 . With the latch  82  forming a rigid connection between the base and linking members  72 ,  58 , the members substantially move axially along the centerline C as one piece when the brake pedal  42  is actuated. Furthermore, the base member  72  is no longer engaged (e.g., rigidly or pivotally) to the stationary structure  46 , and instead, is in sliding relationship (i.e., the contact  52 ) to the structure. That is, the structure  46  may facilitate guidance and limit motion of the base member  72  as the base member moves axially with the actuating brake pedal  42 . It is further contemplated and understood that the opening  90  may be a series of opening or holes enabling the emulator to lock at a current position if the solenoid is released while the pedal  42  is applied. 
     The base member  72  may include a first side  92  and an opposite second side  94 , both substantially disposed normal to the centerline C. The first side  92  may generally bear upon the damping and force induction devices  54 ,  56 . The second side  94  may bear upon the mechanical linkage  80  of the emulator override device  43 . When the brake pedal apparatus  30  is in the mechanical backup mode  88  and the brake pedal  42  is being actuated by the driver, the base and linking members  72 ,  58  move axially with the pedal  42  causing the second side  94  of the base member  72  to make contact with and move the mechanical linkage  80  in, for example, the axial direction. This motion (see arrow  96  in  FIG. 9 ) of the mechanical linkage  80  is utilized to actuate the brake assembly  28 . It is contemplated and understood that the mechanical linkage  80  as illustrated may be, or include, an input or push rod. It is further understood that the mechanical linkage  80  may include other components necessary to mechanically actuate the brake assembly  28  including a hydraulic line, a sheathed (push/pull) cable, a spring (i.e., to provide the necessary force to return the brake pedal  42  after actuation), and other components not illustrated but known to one skilled in the art for more traditional braking systems. 
     Referring to  FIG. 10 , a second embodiment of the present invention is illustrated wherein like elements to the first embodiment have like identifying numerals except with the addition of a prime symbol suffix. A brake pedal apparatus  30 ′ may include a stationary structure  46 ′, a brake pedal emulator assembly  41 ′, and an emulator override device  43 ′. The brake pedal emulator assembly  41 ′ includes a brake pedal  42 ′ and a brake pedal emulator  44 ′. The brake pedal  42 ′ may be supported by, and in moving relationship too, the stationary structure  46 ′. Illustrated as one non-limiting example, the brake pedal  42 ′ may be pivotally engaged to the stationary structure  46 ′ about a first pivot axis  48 ′. The brake pedal emulator  44 ′ may extend between, and is engaged to, the brake pedal  42 ′ and the stationary structure  46 ′ at respective second pivot axis  50 ′ and a contact  52 ′ that may be a third pivot axis. The brake pedal emulator  44 ′ may be generally orientated along a centerline C that may intersect the second and third pivot axes  50 ′,  52 ′. The pivot axes  48 ′,  50 ′,  52 ′ may be substantially parallel to, and spaced apart from one-another. 
     The brake pedal emulator  44 ′ may include a damping device  54 ′, a force induction device  56 ′, a linking member  58 ′, and a base member  72 ′. The devices  54 ′,  56 ′ may be orientated for compression along the centerline C and between the linking and base members  58 ′,  72 ′ during normal operation and as the brake pedal  42 ′ is actuated. The linking member  58 ′ may be pivotally engaged directly to the brake pedal  42 ′ at the second pivot axis  50 ′, and the base member may be pivotally engaged directly to the stationary structure  46 ′ at the third pivot axis  52 ′. 
     The emulator override device  43 ′ may include a mechanical linkage  80 ′ and an electric latch  82 ′ configured to engage and release at least a portion of the mechanical linkage  80 ′ from the brake pedal emulator  44 ′. The mechanical linkage  80 ′ may include a push/pull cable  100  that may be mounted to and/or guided through the base member  72 ′, and a pivot arm  102  pivotally engaged to the base member at a pivot axis  104 . A first end portion  106  of the pivot arm  102  may project radially outward from the pivot axis  104  and may pivotally connect to the linking member  58 ′ at a pivot axis  108 . A second end portion  110 , which may be opposite the first end portion  106  (i.e., end portions project in diametrically opposite directions), may carry an electric solenoid (not shown) of the latch  82 ′. A bolt (not shown) of the latch  82 ′ may be configured to retract and project, in and out of the solenoid  84 ′. 
     When the brake pedal apparatus  30 ′ is in a mechanical backup mode and the solenoid may be de-energized, the bolt of the latch  82 ′ may be located in an opening  112  (e.g., hole) defined by an enlarged end segment  114  of the cable  100  that projects out of the base member  72 ′. With the linking member  58 ′ thus engaged to the cable  100  of the mechanical linkage  80 ′, the cable  100  will move with the linking member  58 ′ and thereby mechanically actuate the brake assembly  28 . When the bolt of the latch  82 ′ is retracted and not in the opening  112 , the brake pedal apparatus  30 ′ is operating normally in BBW mode. 
     The opening  112  in the enlarged end segment  114  of the cable  100  may be a plurality of openings (e.g., holes) generally aligned side-by-side forming an arcuate pattern that extends substantially axially with respect to the centerline C. The distance between the outer openings along the path may correspond to the total throw (i.e., axial displacement) of the emulator  44 ′. The multiple openings  112  facilitate actuation of the emulator override device  43 ′ regardless of the brake pedal position. In this way, the linking member  58 ′ may continue to move toward the base member  72 ′, thus compressing the damping and force induction devices  54 ,  56  even though the BBW mode of operation may not be operative (i.e., the brake assemblies  28  are not receiving a wire brake command). 
     Referring to  FIG. 11 , a third embodiment of the invention is illustrated wherein like elements to the first and/or second embodiment have like identifying numerals except with the addition of a double prime symbol suffix. A brake pedal apparatus  30 ″ may include a stationary structure  46 ″, a brake pedal emulator assembly  41 ″, and an emulator override device  43 ″. The brake pedal emulator assembly  41 ″ includes a brake pedal  42 ″ and a brake pedal emulator  44 ″. The brake pedal  42 ″ may be supported by, and in moving relationship too, the stationary structure  46 ″. Illustrated as one non-limiting example, the brake pedal  42 ″ may be pivotally engaged to the stationary structure  46 ″ about a first pivot axis  48 ″. The brake pedal emulator  44 ″ may extend between, and is engaged to, the brake pedal  42 ″ and the stationary structure  46 ″ at respective second pivot axis  50 ″ and a contact  52 ″ that may be a third pivot axis. The brake pedal emulator  44 ″ may be generally orientated along a centerline C that may intersect the second and third pivot axes  50 ′,  52 ″. The pivot axes  48 ″,  50 ″,  52 ″ may be substantially parallel to, and spaced apart from one-another. 
     The emulator override device  43 ″ may include a mechanical linkage  80 ″ and an electric latch  82 ″ configured to engage and release at least a portion of the mechanical linkage  80 ″. The mechanical linkage  80 ″ may include a pivot arm  102 ″ pivotally engaged to the stationary structure  46 ″ at a pivot axis  104 ″. A first end portion  106 ″ of the pivot arm  102 ″ may project radially outward from the pivot axis  104 ″ for intermittent contact with the brake pedal  42 ″. A second end portion  110 ″ having a series of openings (e.g., holes) may be positioned opposite the first end portion  106 ″. The latch  82 ″ (e.g., electric solenoid with throw bolt) may be supported by the structure  46 ″, and may be configured to insert the throw bolt into one of the series of openings in the second end portion  110 ″. 
     Advantages and benefits of the present disclosure include a low cost back-up brake system that may automatically override a BBW system if an electric fault is present. Another advantage may include a means for providing a mechanical backup with minimal changes required to a pure BBW emulator. Yet another advantage may include an entire braking system without any need for hydraulic fluid. A further advantage includes an emulator capable of being packaged inline between a master cylinder and a pedal push rod. Yet further, the present disclosure may enable a compact mechanical part envelope that simplifies design and physical integration of a pedal module, along with simplifying diagnosis and servicing of the module. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the application.