Patent Publication Number: US-2018043866-A1

Title: Brake emulator of a brake-by-wire system

Description:
FIELD OF THE INVENTION 
     The subject invention relates to a brake-by-wire (BBW) system, and more particularly, to a brake emulator of the BBW system. 
     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 is 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 emulator that may simulate the brake pedal ‘feel’ of more conventional brake systems, and may be fault tolerant. 
     SUMMARY OF THE INVENTION 
     In one exemplary embodiment of the invention, a brake pedal assembly of a brake emulator includes a resiliently flexible arm constructed and arranged to include a flexibility that mimics at least in-part a pre-determined braking force profile. The flexible arm includes opposite first and second end portions and a pivot point disposed there-between. 
     In another exemplary embodiment of the invention, a vehicle brake emulator is actuated by a driver and includes a fixed structure and a resiliently flexible arm. The arm is connected to the fixed structure at a pivot axis, and includes a end portion constructed and arranged to receive an applied braking pressure by the driver. 
     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 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 including a brake emulator; 
         FIG. 3  is a perspective view of a brake pedal assembly of the brake emulator; 
         FIG. 4  is a side view of the brake emulator illustrated in flexed and un-flexed states; and 
         FIG. 5  is a graph of a braking force profile of the brake emulator. 
     
    
    
     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 BBW system  26  that may include a brake assembly  28  for each respective wheel  24 , a brake emulator  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 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 actuator 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 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 . 
     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 emulator  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 emulator  30  may include a brake pedal assembly  42 , a first contact stop  44 , a second contact stop  46 , a force sensor  48 , and a displacement sensor  50 . The brake pedal assembly  42  may include a multitude of arms  52  (i.e., two illustrated in  FIG. 3 ), a strain-based sensor  54  (e.g., strain gage) integrated into each arm  52 , and a brake pad  55 . Each arm  52  may be elongated, resiliently flexible, and aligned side-by-side to one another. The introduction of multiple arms  52 , as opposed to one, introduces a degree of fault tolerance. For example, if one arm is fatigued or should otherwise fail, the remaining arms  52  will suffice to achieve the braking action of the vehicle  20 . 
     Each arm  52  may include a front side  56 , an opposite back side  58 , a first end portion  60 , and an opposite second end portion  62 . Each arm  52  may be pivotally engaged to a support structure  64  that may be fixed (see  FIG. 2 ) at a pivot point  66  and aligned along a common pivot axis  68 . The pivot points  66  may be spaced between the end portions  60 ,  62  of the respective arms  52 . The arm  52  may be made of any material that can withstand cyclic stresses, and may include plastic, spring steel, and others. It is contemplated and understood that linear damping may be designed into the flexible arm  52  by fabricating the arm with multiple laminations such that relative motion between the laminations may create a damping force during deflection of the arm  52 . 
     The brake pad  55  of the brake pedal assembly  42  may be a brake foot pad and, in one example, may directly receive a pressure applied by the foot of a driver desiring to slow or stop the vehicle  20 . The first end portions  60  of each arm  52  may be engaged to the brake pad  55 . The brake pad  55  may further be engaged to or otherwise positioned against the front side  56  of each arm  52 . Other than the engagement of the brake pad  55  to the arms  52 , the arms may not otherwise be engaged and/or adhered to one-another, thereby providing a degree of independent operation should one arm fail. 
     The strain-based sensor or strain gage  54  of the brake pedal assembly  42  may be one type of sensor used to measure a strain or force associated with a pressure applied by the driver upon the brake pad  55 . Each strain gage  54  of each arm  52  may be located between the respective pivot points  66  and end portion  60  of each arm  52 , and may further be proximate to the front sides  56 . In operation, the strain gage  54  is configured to send a signal (see arrow  70  in  FIG. 2 ) over pathway  38  to the controller  32  for processing. 
     For explanation simplicity, one arm  52  will be further described, but it is understood that all of the arms may individually include respective interfacing components adding a degree of redundancy and fault tolerance into the BBW system  26 . The first contact stop  44  may generally be carried between the fixed structure  64  and the back side  58  of the arm  52 , and may be spaced between the pivot point  66  and the first end portion  60 . The second contact stop  46  may generally be carried between the fixed structure  64  and the front side  56  of the arm  52 , and may be proximate to the second end portion  62 . One or both stops  44 ,  46  may generally be, for example, a pad that may be resiliently pliable and adhered, or otherwise engaged, to either of the structure  64  or the arm  52 . The stops  44 ,  46  may be sufficiently soft to enable a degree of travel of the arm  52  (i.e., pivotal motion) generally before the arm begins flexing. One, non-limiting example of a stop material may be EPDM rubber. 
     Referring to  FIG. 4 , when the arm  52  is not flexed, the arm extends along a centerline C that may or may not be linear (i.e., shown to be substantially linear in the present example). When flexed, the two portions of the arm  52  may resiliently bend with each portion generally becoming offset from the centerline C. The first portion may generally be located between the contact stop  44  and the first end portion  60 , and the second portion  62  may be substantially located between the pivot point  66  and the contact stop  46 . It is further contemplated and understood that the structural rigidity of the arm  52  may be designed such that one of the two portions may not flex, or one of the two portions is designed to flex more than the other portion. 
     Referring to  FIGS. 2 and 4 , the force sensor  48  of the brake emulator  30  detects and measures a force associated with the pressure applied at the brake pad  55  by the driver. The force sensor  48  may be the strain gage  54 , may be in addition to the strain gage, or may generally be in place of the strain gage. If the force sensor  48  is not the strain gage previously described, the sensor  48  may generally be located at the second stop  46 . In operation, the force sensor  48  is configured to send a signal (see arrow  72  in  FIG. 2 ) over pathway  38  to the controller  32  for processing. It is contemplated and understood that the force sensor  48  may be located at the contact stop  44 , or other locations sufficient to measure a parameter associated with a pressure applied at the brake pad  55 . It is further understood that the emulator  30  may include more than one force sensor  48  (i.e., pressure) configured to, for example, output redundant signals to more than one controller to facilitate fault tolerance for sensor faults. 
     The travel sensor  50  of the brake emulator  30  detects and measures a displacement between the fixed structure  64  and the arm  52  of the brake pedal assembly  42 . The travel sensor  50  may be engaged to, and carried by, the arm  52  or the fixed structure  64 , and may be generally located between the strain gage  54  and the first end portion  60  of the arm  52 . The travel sensor  50  may be any number of types including ultrasonic, optical, and magnetic sensors. The actual location of the sensor  50  may be partially dependent upon packaging of the brake emulator  30  and/or partially dependent upon accuracy requirements (i.e., greater the displacement the greater the accuracy). In operation, the travel sensor  50  is configured to send a signal (see arrow  74  in  FIG. 2 ) over pathway  38  to the controller  32  for processing. To optimize system reliability and/or reduce systematic system failure, the brake emulator  30  may include more than one displacement sensor  50  placed at different locations. 
     The brake emulator  30  may be a ‘passive’ emulator in the sense that the emulator  30  may not be directly or actively controlled by the controller  32 , yet is configured to simulate the behavior and/or ‘feel’ of a more traditional hydraulic braking system (e.g., vacuum-boosted pedal characteristics). In operation, as a driver applies an initial pressure to the brake pad  55 , the arm  52  may begin to displace by pivoting about pivot point  66 . During this displacement, the contact stops  44 ,  46  may compress between the arm  52  and the fixed structure  64 . Also during this displacement, the travel sensor  50  sends the signal  74  indicative of the arm displacement to the controller  32 , and one or both of the force sensor  48  and the strain gage  54  sends respective signals  72 ,  70  indicative of the pressure or force applied to the brake pad  55  to the controller  32 . The controller  32  processes the signals  70 ,  72 ,  74  and sends an appropriate command signal (see arrow  76  in  FIG. 2 ) to the brake actuators  36  over pathway  40 . 
     Referring to  FIG. 4 , with an increase in pressure or force applied to the brake pad  55  by the driver, the contact stops  44 ,  46  may be substantially fully compressed and the arm  52  may begin to flex. During this additional displacement (i.e., measured from a reference point spaced from the pivot point  66  and at or toward the first end portion  60 ), the travel sensor  50  sends the signal  74  indicative of the additional arm displacement to the controller  32 , and one or both of the force sensor  48  and the strain gage  54  sends respective signals  72 ,  70  indicative of the additional pressure or force applied to the brake pad  55  to the controller  32 . The controller  32  processes the signals  70 ,  72 ,  74  and sends an appropriate command signal (see arrow  76  in  FIG. 2 ) to the brake actuators  36  over pathway  40  to increase brake actuation/pressure. 
     Referring to  FIG. 5 , a braking force profile graph of pedal travel T (i.e., arm  52  displacement) versus applied pedal force F (i.e., pressure) is illustrated. The profile or curve  90  reflects normal operation of the brake pedal assembly  42  where the resilient pliability of the contact stops  44 ,  46  and the resilient flexibility of the arm  52  is pre-determined by design to achieve profile  90 . As previously described, the brake pedal assembly  42  may include multiple arms  52 . In a scenario where, for example, one of the arms  52  becomes damaged, the braking force profile may resemble curve  92  where it requires less force to achieve greater pedal travel. The controller  32  may be programmed to detect such a change in the braking force profile, and thus take appropriate action. 
     Advantages and benefits of the present disclosure include a low-cost, passive, brake emulator  30  capable of mimicking the feel of a more traditional brake system such as a vacuum boosted system without the use of an external spring. Because braking stiffness or feel characteristics are integrated physically into the brake arm(s)  52  and brake stops  44 ,  46 , the brake emulator  30  does not require additional hardware. Yet further, the brake emulator  30  includes certain redundancies to limit or prevent failure. 
     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.