Patent Publication Number: US-2023150371-A1

Title: Automated friction brake assisted vehicle stop

Description:
INTRODUCTION 
     The disclosure relates to an automated friction brake assisted stop in a motor vehicle employing a drivetrain with an electric motor. 
     Motor vehicles generally employ a powerplant to generate propulsion and braking systems to inhibit the vehicle&#39;s motion. A traditional brake is typically a mechanical friction device designed to inhibit motion by converting kinetic energy into heat. Such mechanical braking systems apply a retarding force, typically via specifically adapted frictional elements at the vehicle&#39;s rotating axles or wheels, to slow the vehicle. 
     Friction brakes often include stationary shoes or pads that are lined with friction material and configured to be engaged with a rotating wear surface, such as a rotor or a drum. Common configurations include shoes that contact to rub on the outside of a rotating drum, commonly called a “band brake”, a rotating drum with shoes that expand to rub the inside of a drum, commonly called a “drum brake”, and pads that pinch a rotating disc, commonly called a “disc brake”. Generally, vehicle friction brakes absorb thermal energy and store the energy mainly in the brake disc or brake drum while the brakes are being applied, and then gradually transfer stored heat to the ambient. 
     Other methods of energy conversion may also be employed. For example, electric or hybrid-electric vehicles using traction motors for propulsion frequently employ regenerative braking, where the traction motor is operated in energy generation mode to retard vehicle motion. Generally, regenerative braking converts much of the vehicle&#39;s kinetic energy to electric energy, which may then be stored for later use in onboard batteries. Many modern electric and hybrid-electric vehicles employ braking systems that include a combination of mechanical friction and regenerative braking. 
     Occasionally, operation of braking systems may be accompanied by noise, vibration, and harshness (NVH) concerns in the host vehicle. In some instances, such NVH concerns may be due to performance characteristics of the mechanical braking system&#39;s friction elements. In other situations, NVH concerns may be experienced during transitions between vehicle drive, coast, and braking modes, for example uncovering or exacerbating effects of mechanical lash in the underlying propulsion and/or suspension systems. 
     SUMMARY 
     A method of assisting deceleration during a stop of a motor vehicle having a drivetrain including a traction motor, a road wheel operatively connected to the drivetrain, a friction brake configured to decelerate the road wheel, and an electronic controller includes detecting, via the electronic controller, a request to stop the vehicle. The method also includes commanding, via the electronic controller, the traction motor to provide regenerative braking in response to the request to stop the vehicle. The method additionally includes determining, via the electronic controller, a current vehicle operating state. The method also includes determining, via the electronic controller, an amount of brake drag torque to be generated by the friction brake based on the current vehicle operating state. The method further includes commanding, via the electronic controller, an application of the determined amount of the brake drag torque in parallel with the regenerative braking, thereby operating the friction brake as a mechanical drivetrain damper while assisting the regenerative braking to stop the motor vehicle. 
     According to the method, determining the current vehicle operating state may include determining a current grade of the vehicle. 
     Additionally, determining the amount of brake drag torque may be accomplished via a first look-up table. 
     According to the method, determining the current vehicle operating state may include determining a current road speed of the vehicle. 
     Additionally, commanding the application of the determined amount of the brake drag torque may be accomplished when the current road speed of the vehicle is below a vehicle road speed threshold, such as 3 kph. 
     The method may also include determining a rate of ramp-up of the brake drag torque based on the current vehicle operating state and the determined amount of the brake drag torque. 
     According to the method, determining the rate of ramp-up of the brake drag torque may be accomplished via a second look-up table based on the current road speed of the vehicle and the current grade of the vehicle. 
     Additionally, commanding the application of the determined amount of the brake drag torque may include commanding the rate of ramp-up of the brake drag torque. 
     The method may also include determining a desired incremental amount of the brake drag torque. Additionally, the method may include determining whether a difference between the desired incremental amount of the brake drag torque and the determined amount of the brake drag torque is greater than a predetermined incremental brake drag torque limit. Furthermore, the method may include commanding the application of the determined amount of the brake drag torque when the difference between the desired incremental amount of the brake drag torque and the determined amount of the brake drag torque is greater than the predetermined incremental brake drag torque limit. 
     The motor vehicle may include an accelerator switch in communication with the electronic controller. The method may further include monitoring, via the electronic controller, the accelerator switch for a vehicle acceleration request. According to the method, in such an embodiment, commanding the application of the determined amount of the brake drag torque may be accomplished when the vehicle acceleration request has not been detected. 
     A vehicle having an electronic controller configured or programmed to execute such a method is also disclosed. 
     The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of the embodiment(s) and best mode(s) for carrying out the described disclosure when taken in connection with the accompanying drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic plan view of a motor vehicle having a drivetrain, including a traction motor configured to provide regenerative braking, a friction brake subassembly at each road wheel, and employing a system for assisting vehicle deceleration to a stop using such friction brakes, according to the disclosure. 
         FIG.  2    is a schematic cross-sectional view of a disc brake embodiment of the brake subassembly shown in  FIG.  1   , wherein the brake subassembly is configured as a disc brake. 
         FIG.  3    is a schematic side view of a drum brake embodiment of the brake subassembly shown in  FIG.  1   . 
         FIG.  4    is a flow diagram of a method for assisting deceleration to a stop of a motor vehicle, such as depicted in  FIGS.  1 - 3   . 
     
    
    
     DETAILED DESCRIPTION 
     Those having ordinary skill in the art will recognize that terms such as “above,” “below,” “upward,” “downward,” “top,” “bottom,”, “left”, “right”, etc., are used descriptively for the figures, and do not represent limitations on the scope of the disclosure, as defined by the appended claims. Furthermore, the teachings may be described herein in terms of functional and/or logical block components and/or various processing steps. It should be realized that such block components may be comprised of a number of hardware, software, and/or firmware components configured to perform the specified functions. 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG.  1    shows a schematic view of a motor vehicle  10  positioned relative to a road surface  12 . The vehicle  10  may be a mobile platform, such as a passenger vehicle, an all-terrain vehicle (ATV), an airplane, etc., used for personal, commercial, or industrial purpose. As shown, the vehicle  10  includes a vehicle body  14  disposed along a longitudinal axis  16  and having respective left, right, front, and back sides. The vehicle body  14  also defines a vehicle interior  18  configured to accommodate a vehicle operator, passengers, and cargo. 
     With continued reference to  FIG.  1   , the vehicle  10  includes a plurality of road wheels, specifically shown as front wheels  22 A and rear wheels  22 B. The vehicle  10  also includes a drivetrain  24  configured to provide propulsion thereof. The drivetrain  24  includes one or more traction motors or electric motor-generators  26  operatively connected to at least some of the road wheels  22 A and  22 B and configured to generate motor drive torque T m . As shown, the drivetrain  24  may additionally include an internal combustion engine  28  configured to generate engine drive torque T e  and a transmission  30  operatively connecting the engine to at least some of the road wheels  22 A,  22 B for transmitting engine torque thereto. The drivetrain  24  may additionally include a fuel cell (not shown) operatively connected to at least some of the road wheels  22 A and  22 B. 
     As shown in  FIG.  1   , a vehicle suspension system  32  operatively connects the body  14  to the respective road wheels  22 A and  22 B for maintaining contact between the wheels and the road surface  12 , and for maintaining handling of the vehicle  10 . As also shown in  FIG.  1   , a vehicle steering system  34  is operatively connected to the front wheels  22 A for steering the vehicle  10 . The steering system  34  includes a steering wheel  36  that is operatively connected to the front wheels  22 A via a steering rack  38 . The steering wheel  36  is arranged inside the passenger compartment of the vehicle  10 , such that an operator of the vehicle may command the vehicle to assume a particular direction with respect to the road surface  12 . Additionally, an accelerator switch or pedal  40  is positioned inside the passenger compartment of the vehicle  10 , wherein the accelerator switch is operatively connected to the drivetrain  24  for commanding propulsion of the vehicle  10 . 
     A vehicle braking system  42  is operatively connected to the respective front and rear wheels  22 A,  22 B for retarding rotation of the wheels and decelerating the vehicle  10 . The braking system  42  includes a friction brake subassembly, or friction brake,  44  arranged at each of the respective front and rear wheels  22 A,  22 B and operatively connected to the vehicle suspension system  32 . In other words, the braking system  42  may include a plurality of friction brake subassemblies  44 . Each brake subassembly  44  may be configured as either a disc brake (shown in  FIG.  2   ) or a drum brake (shown in  FIG.  3   ). Each brake subassembly  44  includes a rotor  46  configured for synchronous rotation with the respective wheel  22 A or  22 B about a wheel axis  48 . Each brake subassembly  44  additionally includes an actuator  50  arranged in a brake caliper  50 - 1  of a disc brake (shown in  FIG.  2   ) or in a foundation  50 - 2  of a drum brake (shown in  FIG.  3   ), and configured to generate an actuator or brake force F. The actuator  50  may be configured as a hydraulically actuated piston, e.g., operated via hydraulic brake pressure P generated at a master brake cylinder  52 , or an electrically actuated servo-motor (not shown). 
     As shown in  FIGS.  2  and  3   , each brake subassembly  44  also includes one or more brake components or pads  54 , each having a wearable friction lining or element  56 . The friction lining  56  is configured to be pressed into contact with the rotor  46  by the actuator force F for retarding rotation of the respective wheel  22 A or  22 B to decelerate the vehicle  10 . The actuator force F may be controlled via a signal generated by a brake switch or pedal  58  and communicated electronically to the master brake cylinder  52  (shown in  FIG.  1   ). The brake switch  58  is generally positioned inside the passenger compartment of the interior  18 , and is adapted to be controlled by the operator of the vehicle  10 . 
     With reference to  FIG.  1   , the vehicle  10  also includes a first sensor  60  configured to detect a deceleration request to stop the vehicle  10 , such as via an application of the brake switch  58  or a vehicle-based request for a stop without a driver-initiated deceleration request. The vehicle  10  further includes one or more second sensors  62  configured to detect an operating state of the vehicle  10 , such as the vehicle road speed (V) and a grade or inclination (G) of the vehicle. Additionally, the vehicle  10  includes a third sensor  64  configured to detect a vehicle acceleration request, such as via an application of the accelerator switch  40 . The actuator force F may be controlled via the brake switch  58  to provide sufficient torque at the respective wheel  22 A or  22 B to bring the vehicle  10  to a stop, some drag torque T d  via light contact between the friction lining(s)  56  and the rotor  46  to generate nominal or trace retardation of wheel rotation, and various magnitudes of the actuator force in between to decelerate the vehicle at a desired rate. 
     Alternatively, the actuator force F may be similarly controlled via an on-board vehicle electronic controller  66  as part of a system for assisting vehicle deceleration to a stop using the friction brake(s)  44 . As shown in  FIG.  1   , the electronic controller  66  is in communication with the sensors  60  and  62 . The electronic controller  66  may alternatively be referred to as a control module, a control unit, a controller, a vehicle  10  controller, a computer, etc. The electronic controller  66  may include a computer and/or processor  68 , and include software, hardware, memory, algorithms, connections (such as to sensors  60  and  62 ), etc., for managing and controlling the operation of the vehicle  10 . As such, a method, described in detail below and generally represented in  FIG.  4   , may be embodied as a program or algorithm operable on the electronic controller  66 . It should be appreciated that the electronic controller  66  may include a device capable of analyzing data from the sensors  60  and  62 , comparing data, making the decisions required to control the operation of the vehicle  10 , and executing the required tasks to control the operation of the subject vehicle. 
     The electronic controller  66  may be embodied as one or multiple digital computers or host machines each having one or more processors  68 , read only memory (ROM), random access memory (RAM), electrically-programmable read only memory (EPROM), optical drives, magnetic drives, etc., a high-speed clock, analog-to-digital (A/D) circuitry, digital-to-analog (D/A) circuitry, and input/output (I/O) circuitry, I/O devices, and communication interfaces, as well as signal conditioning and buffer electronics. The computer-readable memory may include non-transitory/tangible medium which participates in providing data or computer-readable instructions. Memory may be non-volatile or volatile. Non-volatile media may include, for example, optical or magnetic disks and other persistent memory. Example volatile media may include dynamic random-access memory (DRAM), which may constitute a main memory. Other examples of embodiments for memory include a floppy, flexible disk, or hard disk, magnetic tape or other magnetic medium, a CD-ROM, DVD, and/or other optical medium, as well as other possible memory devices such as flash memory. 
     The electronic controller  66  also includes a tangible, non-transitory memory  70  on which are recorded computer-executable instructions, including one or more algorithms, for regulating operation of the motor vehicle  10 . Algorithms required by the controller  66  or accessible thereby may be stored in the memory and automatically executed to provide the required functionality. The subject algorithm(s) may specifically include an algorithm  72  for assisting a stop of the motor vehicle  10  to be described in detail below. The processor  68  of the electronic controller  66  is configured to execute the algorithm  72 . The electronic controller  66  is further configured to command an application of friction brake  44  drag torque (T d ) to thereby operate as a mechanical vehicle drivetrain damper to address noise, vibration, and harshness (NVH) concerns during a regenerative braking vehicle stop. 
     Typically, mechanical systems, such as the drivetrain  24  and suspension  32  of the vehicle  10 , have clearance or lost motion, a.k.a., backlash or lash, caused by clearance between system components. Such lash may be defined as the maximum distance or angle through which some part of a mechanical system may be moved in one direction without applying appreciable force or motion to the next part in mechanical sequence. An example of lash in the context of gears and geartrains is the amount of clearance between mated gear teeth. Gear lash may be seen when the direction of geartrain movement is reversed and the slack or lost motion is taken up before the reversal of motion is complete. Variations in lash in mechanical linkages may be due to allowances for lubrication, manufacturing tolerances, deflection under load, and thermal contraction/expansion. Additionally, in many mechanical systems some backlash is allowed specifically to prevent jamming. Backlash in drivetrain  24  and suspension  32  of the vehicle  10  may be exposed under operation of the braking system  42 , and generate NVH concerns, such as bumping and clunking. Such, NVH concerns may be experienced during transitions between vehicle drive, coast, and braking modes. Additional NVH concerns, such as creaking, may be experienced due to performance characteristics of the friction element(s)  56 . 
     Specifically, the electronic controller  66  is configured to detect, using the first sensor  60 , a request  74  to stop the vehicle  10 . The electronic controller  66  is also configured to command the traction motor  26  to provide regenerative braking in response to the request  74  to stop the vehicle  10 . The electronic controller  66  is additionally configured to determine, using the second vehicle sensor(s)  62 , a current vehicle operating state, such as current vehicle road speed (V) and current vehicle grade (G). The electronic controller  66  is also configured to determine an amount of brake drag torque (T d ) to be generated by the friction brake  44  based on the current vehicle operating state. The electronic controller  66  is further configured to command an application of the determined amount of the brake drag torque (T d ) in parallel with the regenerative braking, to thereby generate friction damping via the friction brake  44 , while assisting the regenerative braking to stop the vehicle  10 . Specifically, the algorithm  72  may compare the current road speed (V) to a vehicle road speed threshold  78 , such as 3 kph. 
     The electronic controller  66  may be configured to then command application of the determined amount of the brake drag torque (T d ) when the current road speed (V) of the vehicle  10  is below the road speed threshold  78 . The electronic controller  66  may be additionally configured to monitor the accelerator switch  40  for a vehicle acceleration request  80  and command application of the determined amount of the brake drag torque (T d ) when the vehicle acceleration request has not been detected. The electronic controller  66  may be also configured to determine the amount of brake drag torque (T d ) via a first look-up table  82  saved into the controller&#39;s memory. The first look-up table  82  may include data of brake drag torque (T d ) versus the vehicle grade (G) empirically developed on a representative vehicle under controlled test conditions. 
     The electronic controller  66  may be additionally configured to determine a rate of ramp-up of the brake drag torque (T d ′) based on the current vehicle operating state, such as the current road speed (V) and grade (G) of the vehicle  10 , and the determined amount of the brake drag torque (T d ). Accordingly, the electronic controller  66  may command the determined rate of ramp-up of the brake drag torque (T d ′) during application of the determined amount of the brake drag torque (T d ). The electronic controller  66  may be specifically configured to determine the rate of ramp-up of the brake drag torque (T d ′) via a second look-up table  84  saved into the controller&#39;s memory. The second look-up table  84  may include data of ramp-up of the brake drag torque (T d ′) versus the empirically developed vehicle road speed (V) and grade (G). Data from the first look-up table  82  may be specifically employed as an input to the second look-up table  84 . 
     In a particular embodiment, the electronic controller  66  may be configured to determine a desired incremental amount of the brake drag torque (ΔT d ) based on the determined amount of the brake drag torque (T d ) and the determined rate of ramp-up of the brake drag torque (T d ′). In such an embodiment, the electronic controller  66  may be additionally configured to determine whether a difference between the desired incremental amount of the brake drag torque (ΔT d ) and the determined amount of the brake drag torque (T d ) is greater than a predetermined incremental brake drag torque limit  86 . The electronic controller  66  may be configured to then command the application of the determined amount of the brake drag torque (T d ) when the difference between the desired incremental amount of the brake drag torque (ΔT d ) and the determined amount of the brake drag torque (T d ) is greater than the predetermined incremental brake drag torque limit  86 . 
     The electronic controller  66  may be further programmed to fully engage the friction brake(s)  44  once the vehicle  10  has come to a complete stop and the regenerative braking is no longer active. Accordingly, the electronic controller  66  is intended to regulate application of the friction brake(s)  44  to apply the drag torque (T d ) and thereby generate vehicle driveline hysteresis during vehicle deceleration while coming to a stop. The hysteresis provided by the drag torque (T d ) is thereby intended to operate as a mechanical or friction damper to minimize NVH issues due to driveline lash during a regenerative braking vehicle stop. Additionally, the vehicle driveline hysteresis provided by the drag torque (T d ) during the latter stages of vehicle deceleration permits a smooth and uninterrupted transition to a brake-held stationary vehicle  10 . 
       FIG.  4    depicts a method  100  of assisting deceleration of a motor vehicle, such as the vehicle  10  described above with respect to  FIGS.  1 - 3   , during the vehicle&#39;s stop. The method  100  commences in frame  102  with detecting movement of the vehicle  10  relative to the road surface  12 . In frame  102  the method may also include detecting via the controller  66 , such as using the first sensor  60 , the request  74  to stop the vehicle  10 . The method  100  then proceeds from frame  102  to frame  104 . In frame  104 , the method includes commanding, via the electronic controller  66 , the traction motor  26  to provide regenerative braking in response to the request  74  to stop the vehicle  10 . The method  100  then proceeds from frame  104  to frame  106 . In frame  106 , the method includes determining via the electronic controller  66  the current vehicle operating state, such as by using the second vehicle sensor(s)  62  to detect the current vehicle road speed (V) and current vehicle grade (G). Following frame  106 , the method  100  advances to frame  108 . 
     In frame  108  the method  100  includes determining, via the electronic controller  66 , the amount of brake drag torque (T d ) to be generated by the friction brake(s)  44  based on the current vehicle operating state. Determining the amount of brake drag torque (T d ) may be accomplished via the first look-up table  82  having data of brake drag torque (T d ) versus the vehicle grade (G). In frame  108  the method  100  may also include determining, via the electronic controller  66 , a particular rate of ramp-up of the brake drag torque (T d ′) based on the current vehicle operating state and the determined amount of the brake drag torque (T d ). Determining the rate of ramp-up of the brake drag torque (T d ) may be accomplished via the second look-up table  84  having data of ramp-up of the brake drag torque (T d ′) versus the vehicle road speed (V) and grade (G). 
     In frame  108  the method  100  may additionally include determining, via the electronic controller  66 , a particular desired incremental amount of the brake drag torque (ΔT d ) based on the determined amount of the brake drag torque (T d ) and the determined rate of ramp-up of the brake drag torque (T d ′). As described above with respect to  FIGS.  1 - 3   , in such an embodiment the method may further include determining, via the electronic controller  66 , whether the difference between the desired incremental amount of the brake drag torque (ΔT d ) and the determined amount of the brake drag torque (T d ) is greater than the predetermined incremental brake drag torque limit  86 . After frame  108 , the method  100  proceeds to frame  110 . 
     In frame  110 , the method  100  includes commanding via the electronic controller  66  the application of the determined amount of the brake drag torque (T d ) in parallel with the regenerative braking. Specifically, commanding the application of the determined amount of the brake drag torque (T d ) may be accomplished when the current road speed (V) of the vehicle  10  is below a particular vehicle road speed threshold  78 . Also, commanding the application of the determined amount of the brake drag torque (T d ) may include commanding the rate of ramp-up of the brake drag torque (T d ′). Additionally, commanding the application of the determined amount of the brake drag torque (T d ) may be accomplished when the difference between the desired incremental amount of the brake drag torque (ΔT d ) and the determined amount of the brake drag torque (T d ) is greater than the predetermined incremental brake drag torque limit  86 . Furthermore, commanding the application of the determined amount of the brake drag torque (T d ) in frame  110  may be accomplished when the vehicle acceleration request  80  has not been detected. Otherwise, the method may loop back to frame  102 . 
     As described above with respect to  FIGS.  1 - 3   , the commanded brake drag torque (T d ) operates the friction brake(s)  44  as a mechanical drivetrain damper to minimize NVH concerns, while assisting the regenerative braking to stop the motor vehicle  10 . The method may proceed from frame  110  to frame  112  where the electronic controller  66  includes commanding the friction brake(s)  44  to fully engage once the vehicle  10  has come to a complete stop and the regenerative braking is no longer active. Following a complete vehicle stop, the method may restart in frame  102  with detecting resumed movement of the vehicle  10  relative to the road surface  12 , thus enabling repetition of the method algorithm in frames  102  through  112  for assisting regenerative braking to stop the motor vehicle  10  while minimizing NVH concerns. The method  100  may also terminate at frame  114 . Accordingly, with respect to the method  100 , regenerative braking and brake drag torque (T d ) are employed to achieve different goals. Regenerative braking is primarily used to bring the vehicle  10  to a stop, while brake drag torque (T d ) is used to target NVH/driveline issues. 
     The detailed description and the drawings or figures are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed disclosure have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment may be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.