Patent Publication Number: US-2022212651-A1

Title: Hybrid vehicle operation

Description:
TECHNICAL FIELD 
     The present disclosure relates to vehicle powertrain operation. 
     BACKGROUND 
     In a hybrid electric vehicle, a controller may operate the vehicle between multiple propulsion modes including an electric only mode, an engine only mode, and a combination mode. 
     SUMMARY 
     A vehicle includes an engine and a controller. The controller selectively turns off the engine based on attribute data such that when the attribute data is indicative of an expected torque or power demand exceeding a corresponding threshold within a predefined duration of time after receipt of an engine off request, the engine is not turned off, and when the attribute data is indicative of an expected torque or power demand not exceeding the corresponding threshold within the predefined duration of time, the engine is turned off. 
     A method includes responsive to attribute data being indicative of an expected torque or power demand exceeding a corresponding threshold within a predefined duration of time after receipt of an engine off request, inhibiting shut down of an engine, and responsive to the attribute data being indicative of an expected torque or power demand exceeding the corresponding threshold after the predefined duration of time, permitting shut down of the engine. 
     A powertrain control system includes a controller that, when attribute data is indicative of an expected deceleration having a magnitude that exceeds a threshold within a predefined duration of time after receipt of an engine on request, inhibits start of an engine, and when the attribute data is indicative of an expected deceleration having a magnitude that does not exceed the threshold within the predefined duration, permits start of the engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an electrified vehicle illustrating drivetrain and energy storage components including an electric machine. 
         FIG. 2  is an example block topology of a vehicle system. 
         FIG. 3  is an example block diagram of the vehicle power control system. 
         FIG. 4  is an example flow diagram of a process for hybrid vehicle powertrain control. 
         FIGS. 5, 6, and 7  are example time graphs of hybrid vehicle powertrain control. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
       FIG. 1  depicts an electrified vehicle  112  that may be referred to as a plug-in hybrid-electric vehicle (PHEV), a battery electric vehicle (BEV), a mild hybrid-electric vehicle (MHEV), and/or full hybrid electric vehicle (FHEV). A plug-in hybrid-electric vehicle  112  may comprise one or more electric machines  114  mechanically coupled to a hybrid transmission  116 . The electric machines  114  may be capable of operating as a motor or a generator. In addition, the hybrid transmission  116  is mechanically coupled to an engine  118 . The hybrid transmission  116  is also mechanically coupled to a drive shaft  120  that is mechanically coupled to the wheels  122 . The electric machines  114  can provide propulsion and braking capability when the engine  118  is turned on or off. The electric machines  114  may also act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in a friction braking system. The electric machines  114  may also reduce vehicle emissions by allowing the engine  118  to operate at more efficient speeds and allowing the hybrid-electric vehicle  112  to be operated in electric mode with the engine  118  off under certain conditions. 
     A traction battery or battery pack  124  may store energy that can be used by the electric machines  114 . The vehicle battery pack  124  may provide a high voltage direct current (DC) output. The traction battery  124  may be electrically coupled to one or more power electronics modules  126  (such as a traction inverter). One or more contactors  125  may isolate the traction battery  124  from other components when opened and connect the traction battery  124  to other components when closed. The power electronics module  126  is also electrically coupled to the electric machines  114  and provides the ability to bi-directionally transfer energy between the traction battery  124  and the electric machines  114 . For example, a traction battery  124  may provide a DC voltage while the electric machines  114  may operate with a three-phase alternating current (AC) to function. The power electronics module  126  may convert the DC voltage to a three-phase AC current to operate the electric machines  114 . In a regenerative mode, the power electronics module  126  may convert the three-phase AC current from the electric machines  114  acting as generators to the DC voltage compatible with the traction battery  124 . 
     The vehicle  112  may include a variable-voltage converter (VVC) (not shown) electrically coupled between the traction battery  124  and the power electronics module  126 . The VVC may be a DC/DC boost converter configured to increase or boost the voltage provided by the traction battery  124 . By increasing the voltage, current requirements may be decreased leading to a reduction in wiring size for the power electronics module  126  and the electric machines  114 . Further, the electric machines  114  may be operated with better efficiency and lower losses. 
     In addition to providing energy for propulsion, the traction battery  124  may provide energy for other vehicle electrical systems. The vehicle  112  may include a DC/DC converter module  128  that converts the high voltage DC output of the traction battery  124  to a low voltage DC supply that is compatible with low-voltage vehicle loads. An output of the DC/DC converter module  128  may be electrically coupled to an auxiliary battery  130  (e.g., 12V battery) for charging the auxiliary battery  130 . The low-voltage systems having one or more low-voltage loads  131  may be electrically coupled to the auxiliary battery  130 . One or more electrical loads  132  may be coupled to the high-voltage bus/rail. The electrical loads  132  may have an associated controller that operates and controls the electrical loads  146  when appropriate. Examples of electrical loads  132  may be a fan, an electric heating element, and/or an air-conditioning compressor. 
     The electrified vehicle  112  may be configured to recharge the traction battery  124  from an external power source  134 . The external power source  134  may be a connection to an electrical outlet. The external power source  134  may be electrically coupled to a charger or electric vehicle supply equipment (EVSE)  136 . The external power source  134  may be an electrical power distribution network or grid as provided by an electric utility company. The EVSE  136  may provide circuitry and controls to regulate and manage the transfer of energy between the power source  134  and the vehicle  112 . The external power source  134  may provide DC or AC electric power to the EVSE  136 . The EVSE  136  may have a charge connector  138  for plugging into a charge port  140  of the vehicle  112 . The charge port  140  may be any type of port configured to transfer power from the EVSE  136  to the vehicle  112 . The charge port  140  may be electrically coupled to a charger or on-board power conversion module  142 . The power conversion module  142  may condition the power supplied from the EVSE  136  to provide the proper voltage and current levels to the traction battery  124 . The power conversion module  142  may interface with the EVSE  136  to coordinate the delivery of power to the vehicle  112 . The EVSE connector  138  may have pins that mate with corresponding recesses of the charge port  140 . Alternatively, various components described as being electrically coupled or connected may transfer power using a wireless inductive coupling. 
     One or more wheel brakes  144  may be provided for braking the vehicle  112  and preventing motion of the vehicle  112 . The wheel brakes  144  may be hydraulically actuated, electrically actuated, or some combination thereof. The wheel brakes  144  may be a part of a brake system  146 . The brake system  146  may include other components to operate the wheel brakes  144 . For simplicity, the figure depicts a single connection between the brake system  146  and one of the wheel brakes  144 . A connection between the brake system  146  and the other wheel brakes  144  is implied. The brake system  146  may include a controller to monitor and coordinate the brake system  146 . The brake system  146  may monitor the brake components and control the wheel brakes  144  for slowing the vehicle. The brake system  146  may respond to driver commands and may also operate autonomously to implement features such as stability control. The controller of the brake system  150  may implement a method of applying a requested brake force when requested by another controller or sub-function. 
     The powertrain of the vehicle  112  may be operated and controlled via a powertrain control module (PCM)  148  connected to various components of the vehicle  112  via an in-vehicle network (to be described in detail below). The PCM  148  may be configured to perform various features. For instance, the PCM  148  may be configured to control the operations of the engine  118  and the electric machine  114  based on user input via an accelerator pedal (not shown) and a brake pedal (not shown). Responsive to receiving a user power demand via one or more pedals, the PCM  148  may distribute the power between the engine  118  and the electric machine  114  to satisfy the user demand. Under certain predefined conditions when less power/torque is demanded, the PCM  148  may disable the engine  118  and only rely on the electric machine  114  to provide power output to the vehicle  112 . The PCM  148  may restart the engine  118  responsive to more power being needed. The PCM  148  may be further configured to perform power split between the electric machine  114  and the engine  118  using data received from other controllers of the vehicle  112  as coordinated by a computing platform  150 . 
     Referring to  FIG. 2 , an example block topology of a vehicle system  200  of one embodiment of the present disclosure is illustrated. As an example, the system  200  may include the SYNC system manufactured by The Ford Motor Company of Dearborn, Mich. It should be noted that the illustrated system  200  is merely an example, and more, fewer, and/or differently located elements may be used. 
     As illustrated in  FIG. 2 , the computing platform  150  may include one or more processors  206  configured to perform instructions, commands, and other routines in support of the processes described herein. For instance, the computing platform  150  may be configured to execute instructions of vehicle applications  208  to provide features such as navigation, remote controls, and wireless communications. Such instructions and other data may be maintained in a non-volatile manner using a variety of types of computer-readable storage medium  210 . The computer-readable medium  210  (also referred to as a processor-readable medium or storage) includes any non-transitory medium (e.g., tangible medium) that participates in providing instructions or other data that may be read by the processor  206  of the computing platform  150 . Computer-executable instructions may be compiled or interpreted from computer programs created using a variety of programming languages and/or technologies, including, without limitation, and either alone or in combination, Java, C, C++, C#, Objective C, Fortran, Pascal, Java Script, Python, Perl, and PL/SQL. 
     The computing platform  150  may be provided with various features allowing the vehicle occupants/users to interface with the computing platform  150 . For example, the computing platform  150  may receive input from HMI controls  212  configured to provide for occupant interaction with the vehicle  112 . As an example, the computing platform  150  may interface with one or more buttons, switches, knobs, or other HMI controls configured to invoke functions on the computing platform  150  (e.g., steering wheel audio buttons, a push-to-talk button, instrument panel controls, etc.). 
     The computing platform  150  may also drive or otherwise communicate with one or more displays  214  configured to provide visual output to vehicle occupants by way of a video controller  216 . In some cases, the display  214  may be a touch screen further configured to receive user touch input via the video controller  216 , while in other cases the display  214  may be a display only, without touch input capabilities. The computing platform  150  may also drive or otherwise communicate with one or more speakers  218  configured to provide audio output and input to vehicle occupants by way of an audio controller  220 . 
     The computing platform  150  may also be provided with navigation and route planning features through a navigation controller  222  configured to calculate navigation routes responsive to user input via, for example, the HMI controls  212 , and output planned routes and instructions via the speaker  218  and the display  214 . Location data that is needed for navigation may be collected from a global navigation satellite system (GNSS) controller  224  configured to communicate with multiple satellites and calculate the location of the vehicle  112 . The GNSS controller  224  may be configured to support various current and/or future global or regional location systems such as global positioning system (GPS), Galileo, Beidou, Global Navigation Satellite System (GLONASS) and the like. Map data used for route planning may be stored in the storage  210  as a part of the vehicle data  226 . Navigation software may be stored in the storage  210  as one the vehicle applications  208 . 
     The computing platform  150  may be configured to wirelessly communicate with a mobile device  228  of the vehicle users/occupants via a wireless connection  230 . The mobile device  228  may be any of various types of portable computing devices, such as cellular phones, tablet computers, wearable devices, smart watches, smart fobs, laptop computers, portable music players, or other devices capable of communication with the computing platform  150 . A wireless transceiver  232  may be in communication with a Wi-Fi controller  234 , a Bluetooth controller  236 , a radio-frequency identification (RFID) controller  238 , a near-field communication (NFC) controller  240 , and other controllers such as a Zigbee transceiver, an IrDA transceiver, a ultra-wide band (UWB) controller (not shown), and be configured to communicate with a compatible wireless transceiver  242  of the mobile device  228 . 
     The mobile device  228  may be provided with a processor  244  configured to perform instructions, commands, and other routines in support of the processes such as navigation, telephone, wireless communication, and multi-media processing. For instance, the mobile device  228  may be provided with location and navigation functions via a navigation controller  246  and a GNSS controller  248 . The mobile device  228  may be provided with the wireless transceiver  242  in communication with a Wi-Fi controller  250 , a Bluetooth controller  252 , a RFID controller  254 , an NFC controller  256 , and other controllers (not shown), configured to communicate with the wireless transceiver  232  of the computing platform  150 . The mobile device  228  may be further provided with a non-volatile storage  258  to store various mobile application  260  and mobile data  262 . 
     The computing platform  150  may be further configured to communicate with various components of the vehicle  112  via one or more in-vehicle networks  266 . The in-vehicle network  266  may include, but is not limited to, one or more of a controller area network (CAN), an Ethernet network, and a media-oriented system transport (MOST), as some examples. Furthermore, the in-vehicle network  266 , or portions of the in-vehicle network  266 , may be a wireless network accomplished via Bluetooth low-energy (BLE), Wi-Fi, UWB, or the like. 
     The computing platform  150  may be configured to communicate with various electronic control units (ECUs)  268  of the vehicle  112  configured to perform various operations. As discussed above, the computing platform  150  may be configured to communicate with the PCM  148  via the in-vehicle network  266 . The computing platform  150  may be further configured to communicate with a TCU  270  configured to control telecommunication between vehicle  112  and a wireless network  272  through a wireless connection  274  using a modem  276 . The wireless connection  274  may be in the form of various communication networks, for example, a cellular network. Through the wireless network  272 , the vehicle may access one or more servers  278  to access various content for various purposes. It is noted that the terms wireless network and server are used as general terms in the present disclosure and may include any computing network involving carriers, router, computers, controllers, circuitry or the like configured to store data and perform data processing functions and facilitate communication between various entities. The ECUs  268  may further include an autonomous driving controller (ADC)  280  configured to control an autonomous driving feature of the vehicle  112 . Driving instructions may be received remotely from the server  278 . The ADC  280  may be configured to perform the autonomous driving features using the driving instructions combined with navigation instructions from the navigation controller  222 . The ECUs  268  may be provided with or connected to one or more sensors  282  providing signals related to the operation of the specific ECU  268 . For instance, the sensors  282  may include an ambient temperature sensor configured to measure the ambient temperature of the vehicle  112 . The sensors  282  may further include one or more engine/coolant temperature sensors configured to measure the temperature of the engine/coolant and provide such data to the PCM  148 . The sensors  282  may further include a camera configured to capture an image near the vehicle to enable various features such as autonomous driving features via the ADC  280 . 
     The PCM  148  may be configured to operate the vehicle powertrain based on data received from various sources. Referring to  FIG. 3 , an example diagram  300  of the vehicle drivetrain control system is illustrated. In general, the data used by the PCM  148  may be classified into one of a static attribute  302  and a dynamic attribute  304  received from various sources. The static attribute  302  may reflect characteristics of a route on which the vehicle  112  traverses that does not vary over time. As a few non-limiting examples, the static attribute  302  may include various road attributes of the route such as number of lanes, speed limit, road pavement condition, road grade or the like. The static attribute  302  may further include road signs posted near or on the vehicle route. The static attribute  302  may further include one or more driver behavior attributes (driving pattern) of a vehicle user which records a pattern/habit of driving of the user operating the vehicle. The driver behavior may be previously recorded by the vehicle  112 . Alternatively, the driver behavior may be identified or received from a digital entity associated with the vehicle driver (such as the mobile device  228 ). The driver behavior attribute may reflect driving patterns of one or more drivers operating the vehicle. For instance, some drivers are more aggressive and drive faster by applying the accelerator pedal harder. The driver behavior attribute may affect the vehicle power and/or torque demand and driving speed. In some cases, the PCM  148  may use the driver behavior attribute to determine if the vehicle  112  can pass an intersection before the traffic light turns red as an example. 
     The dynamic attribute may reflect characteristics of the route that may vary over time. As a few non-limiting examples, the dynamic attribute  304  may include traffic and weather conditions on the route which may affect the operation of the vehicle  112 . The dynamic attribute  304  may further include road events such as accident and road work on the route. As an example, live traffic data and traffic signal timings may be sent to the vehicle  112 . Coupled with the static attributes  302 , the PCM  148  of the vehicle  112  may predict a motion pattern reflecting the time and location to accelerate, decelerate and stop on the vehicle route, so that the hybrid powertrain may be calibrated more accurately. 
     The vehicle  112  may be configured to obtain the static and dynamic attributes  302 ,  304  from a variety of sources. For instance, the vehicle  112  may obtain the attributes from one or more cloud servers  278  via the wireless network  272  through the TCU  270 . Additionally or alternatively, the vehicle  112  may be configured to access the servers  278  via the mobile device  228  associated with the vehicle user. The vehicle  112  may be further configured to communicate with an infrastructure device  306  via a vehicle-to-infrastructure (V2I) link to obtain the attributes. The infrastructure  306  may include sensor and communication devices along the vehicle route to provide driving information to the vehicle  112 . For instance, the infrastructure device  306  may include a smart traffic light transmitting signals indicating the status and timing of the traffic signal to vehicles nearby. The vehicle  112  may be further configured to communicate with one or more fleet vehicles  310  provided with compatible transceivers via a vehicle-to-vehicle (V2V) link  312 . For instance, the fleet vehicle  310  may detect an attribute via a fleet vehicle sensor and share the attribute to the vehicle  112 . The wireless network  272 , the V2I link  308  and the V2V link  312  may be collectively referred to as a vehicle-to-everything (V2X) connection. Additionally, the vehicle  112  may be configured to obtain the attributes via one or more sensors  282 . 
     Referring to  FIG. 4 , an example flow diagram of a process  400  for a hybrid vehicle powertrain control is illustrated. With continuing reference to  FIGS. 1-3 , the process  400  may be performed via one or more controllers/platforms of the vehicle  112 . For simplicity purposes, the following description will be primary made with regard to PCM  148  although the process  400  may be performed by other controllers in lieu of or in combination with the PCM  148 . The process  400  may be applied to any type of hybrid vehicle propelled by an electric machine  114  powered by electricity and another motor/engine  118  powered by a type of energy source other than electricity (e.g., gasoline, diesel, natural gas, hydrogen or the like). At operation  402 , the vehicle  112  identifies or plans a route responsive to a user starting to use the vehicle  112 . The route may be planned using the navigation software  208  via the navigation controller  222  responsive to a destination input by a user. Alternatively, the computing platform  150  and the navigation controller  222  may automatically identify a predicted route using the current location and/or historical route of the vehicle  112  in the absence of the navigation destination input by the user. Having the vehicle route available, at operation  404 , the vehicle  112  collects both the static and dynamic attributes  302 ,  304  along the route from various sources as described above with reference to  FIG. 3 . At operation  406 , the vehicle  112  predicts a vehicle motion pattern along the planned route using the attributes collected. The motion pattern may include a predicted vehicle speed at different sections of the route. For instance, the traffic attribute  304  may reflect a traffic flow and timing of a plurality of traffic lights on the vehicle route. The vehicle  112  may use the traffic flow data, combined with the driver behavior and other attributes, to predict the torque demand of the vehicle  112  at a given point on the route. The vehicle  112  may further predict the status of each traffic light when the vehicle  112  arrives, so as to determine if the vehicle  112  needs to stop or slow down at a red light, or to drive by without stopping when the light is green for example. At operation  408  the PCM  148  decides the operating status of the engine  118  using the predicted vehicle motion pattern. The details of operation  408  will be described with references to the examples illustrated in  FIGS. 5-7  below. 
     Referring to  FIG. 5 , example time graphs of the hybrid vehicle powertrain control of one embodiment are illustrated. With continuing reference to  FIGS. 1-4 , a first time graph  502  illustrates the speed of the vehicle  112  over time. A second time graph  504  illustrates the operation mode of the vehicle engine  118  (i.e., ON/OFF). A third time graph  506  illustrates an accelerator pedal position of the vehicle  112 . Referring to the time graphs, in the present example, the vehicle  112  starts to accelerate at time  510  as the accelerator pedal is gradually depressed. Based on the motion pattern as predicted at operation  406  illustrated in  FIG. 4 , the acceleration may be a long process beyond a predefined acceleration threshold until time  514  in the present example. Conventionally, the PCM  148  may not start the vehicle engine  118  until the acceleration has started for a period of time (e.g., at time  512  as illustrated by solid line  520  in the second time graph  504  in the present example) once the PCM  148  determines the acceleration continues and extra power and torque is needed from the engine  118 . Here, since the motion pattern that has been calculated in advance suggests the acceleration lasts longer than a predefined threshold, the PCM  148  may turn on the engine  118  earlier as illustrated in the dashed line  522  in the second paragraph to provide the extra power and torque to facilitate the long acceleration, which may in turn improve the performance of the vehicle as well as the user experience. The threshold to be used by the PCM  148  to decide whether an early engine start is needed may be any one of a time threshold (e.g., 5 seconds), a distance threshold (e.g., 200 meters), or a power and/or torque threshold. 
     Referring to  FIG. 6 , example time graphs of the hybrid vehicle powertrain control of another embodiment are illustrated. Similar to  FIG. 5 , three time graphs are illustrated in  FIG. 6 . A first time graph  602  illustrates the speed of the vehicle  112  over time. A second time graph  604  illustrates the operation mode of the vehicle engine  118 . A third time graph  606  illustrates an accelerator pedal position of the vehicle  112 . As an example,  FIG. 6  may be applied to a stop and go traffic situation. In the present example, the PCM  148  mostly operates the vehicle  112  in the electric only mode. Under the conventional approach, the engine  118  may be arbitrarily turned on at time  610  and  614  responsive to an acceleration, and turned off at time  614  and  616  shortly after responsive to a deceleration as illustrated in the solid line  620 . However, since the decelerations shortly after the acceleration within a predefined time threshold may be predicted in the motion pattern, the PCM  148  may reframe from turning on the engine  118  in response to the accelerations and operate in the electric only mode to increase the efficiency of the vehicle  112  and provide an improved user experience. 
     Referring to  FIG. 7 , example time graphs of the hybrid vehicle powertrain control of yet another embodiment are illustrated. A first time graph  702  illustrates the power and/or torque demand of the vehicle  112  over time. A second time graph  604  illustrates the operation mode of the vehicle engine  118 . As an example,  FIG. 6  may be applied to a large parking lot and parking garage situation where high power and/or torque demand is present (e.g., due to the ramps). As illustrated in the second time graph  504 , under the conventional approach without the attribute analysis, the PCM  148  may repeatedly turn the engine on and off within a short time frame. More specifically as illustrated in the solid line  720 , the PCM  148  may turn off the engine  118  at time  712  responsive to a reduced power/torque demand and turn the engine  118  back on responsive to an increased power torque demand at time  714 . The process repeats as the PCM  148  turns off the engine  118  responsive to another reduced power/torque demand at time  716  and turn on the engine  118  responsive to another increased power/torque demand at time  718 . With the motion pattern predicted, the PCM  148  inhibits turning off the engine  118  and keeps the engine  118  running responsive to the increased power/torque demand as predicted and illustrated in dashed line  722 . Here, one or more thresholds may be used by the PCM  148  to decide whether to inhibit the engine turn off. For instance, the PCM  148  may be configured to inhibit the engine turn off responsive to a torque demand above a torque threshold being anticipated to be within a time threshold from the turn off condition being met. The PCM  148  may be further configured to adjust one or more thresholds to accommodate the specific design needs. Continuing with the above example illustrated in  FIG. 7 , a greater torque threshold may be used responsive to a longer time between the conventional engine turn off command and the power/torque being anticipated (e.g. time between  712  and  714 , and time between  716  and  718  on time graph  704 ). 
     The processes, methods, or algorithms disclosed herein can be deliverable to/implemented by a processing device, controller, or computer, which can include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms can be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as Read Only Memory (ROM) devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, Compact Discs (CDs), Random Access Memory (RAM) devices, and other magnetic and optical media. The processes, methods, or algorithms can also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms can be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. 
     As previously described, the features of various embodiments can be combined to form further embodiments that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.