Patent Publication Number: US-9845781-B2

Title: Engine accessory drive system

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to the field of internal combustion engine systems. More particularly, the present disclosure relates to engine accessory drive systems for internal combustion engines. 
     BACKGROUND 
     Automotive manufacturers have developed various technologies to improve fuel economy and reduce emissions in response to consumer demand and government regulations. For example, start-stop systems operate to automatically shut down and restart a vehicle&#39;s internal combustion engine to reduce the amount of time that the engine spends idling, thereby reducing fuel consumption and emissions. This is most advantageous for vehicles that spend significant amounts of time waiting at traffic lights or that frequently come to a stop while driving. Fuel economy gains from this technology are typically in the range of five to fifteen percent or more. 
     Vehicle start-stop systems provide various design challenges. For example, conventional starter motors are not designed for the number of operational cycles required for start-stop systems compared to conventional systems. For example, starter motors in conventional non-start-stop systems are designed to perform at least 50,000 starting cycles over a vehicle&#39;s lifetime. In contrast, starter motors in start-stop systems are designed to perform as many as 500,000-800,000 cycles over a vehicle&#39;s lifetime. Accordingly, many conventional starter motors are inadequate for the demands of start-stop systems. 
     In addition, vehicle accessories, such as an alternator, power steering pump, coolant pump, vacuum pump, air conditioning compressor, fan, etc., are typically driven by the crankshaft of the engine via an accessory drive (e.g., serpentine) belt. However, in start-stop systems, the accessories are not driven by the engine when the engine is shut down. 
     SUMMARY 
     Various embodiments relate to engine accessory drive (EAD) systems for internal combustion engines. An example EAD system includes a motor-generator unit (MGU) operably coupled to an accessory. The EAD system also includes a gearbox assembly. The gearbox assembly includes a first gear train operably coupled to the MGU. The gearbox assembly also includes a second gear train operably coupled to an output of the engine, as well as a clutch selectively coupling the first gear train with a second gear train. A starter assembly includes a starter shaft operably coupled to the second gear train. The starter assembly also includes a starter pinion coupled to the starter shaft. The starter assembly further includes an actuator configured to selectively engage the starter pinion with a flywheel of the engine. An EAD controller is configured to selectively operate the EAD system in one of a generator mode, an accessory drive mode, and a starter mode. 
     Another example EAD system includes an MGU configured to selectively operate as an electric generator and an electric motor. The MGU is operably coupled to an energy storage system. A gearbox assembly is operably coupled to the MGU and to an output of the engine. An EAD controller is in operative communication with each of the MGU and the gearbox assembly. The EAD controller is structured to receive engine data indicative of an engine condition, and to receive state of charge data indicative of a state of charge of the energy storage system. The EAD system is also structured to interpret each of the engine data and the state of charge data, and to selectively operate the EAD system in one of a generator mode and an accessory drive mode. 
     Various other embodiments relate to a method, including providing an EAD controller that is operably coupled to each of an internal combustion engine and an EAD system. The EAD system includes an MGU configured to selectively operate as an electric generator and an electric motor. The EAD system also includes an energy storage system operably coupled to the MGU. The EAD system further includes a gearbox assembly operably coupled to the MGU and to an output of the engine. The method also includes receiving, by the EAD controller, engine data indicative of an engine condition, and state of charge data indicative of a state of charge of the energy storage system. The method further includes interpreting, by the EAD controller, each of the engine data and the state of charge data. The method further includes selectively operating, by the EAD controller, the EAD system in one of a generator mode and an accessory drive mode. 
     These and other features, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the several drawings described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  illustrate several example conventional vehicle powertrain systems. 
         FIG. 2  is a schematic diagram of an EAD system for use with an engine, according to an embodiment. 
         FIG. 3  is a block diagram of the EAD controller of  FIG. 2 , according to a particular embodiment. 
         FIGS. 4A-4D  are several perspective views of an EAD system operably coupled to an engine, according to an embodiment. 
         FIGS. 5A-5B  illustrate an EAD system operably coupled to an engine, according to another embodiment. 
         FIGS. 5C-5E  illustrate the starter assembly of the EAD system of  FIGS. 5A-5B . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a side view of a conventional vehicle powertrain system  100 . In general, the vehicle powertrain system  100  includes an engine  102  operably connected to a transmission  104  via a crankshaft  106 . A starter motor  108  is mounted to the engine  102 , and includes a drive pinion that, in operation (e.g., by activating a key-operated switch), meshes with a ring gear on a flywheel  110  of the engine  102 . The drive pinion on the starter motor  108  rotates the flywheel  110  so as to initiate the engine&#39;s  102  operation. During operation, the flywheel  110  operates to store angular momentum between combustion events within the engine  102 . A clutch  112  operates to selectively couple the engine  102  and the transmission  104 . 
     A crankshaft pulley  116  is coupled to the crankshaft  106  on a front side  118  of the engine  102 . A belt  120  is coupled to the crankshaft pulley  116  and to one or more accessories. For example, as illustrated in  FIG. 1A , the belt  120  is coupled to an accessory pulley  122  of an alternator  124  to drive the alternator  124 . The alternator  124  is configured to convert mechanical energy received via the belt  120  to electrical energy. The electrical energy may be transferred to a battery (not shown) to power the electrical system of the vehicle. According to various configurations, the powertrain system  100  may include several accessories in addition to the alternator  124 , such as a power steering pump, coolant pump, vacuum pump, air conditioning compressor, fan, etc. The crankshaft pulley  116 , the belt  120 , and the accessory pulley  122  may be collectively referred to as a “front engine accessory drive” (FEAD) because they are located on the front side  118  of the engine  102 , and they operate to drive the accessories, such as the alternator  124 . 
       FIG. 1B  is a side view of another example vehicle powertrain system  130 . The vehicle powertrain system  130  of  FIG. 1B  is similar to the system  100  of  FIG. 1A , except that the system  130  includes a belt-driven integrated starter-generator (ISG)  132  (also referred to as a “belted alternator starter”) instead of the discrete starter motor  108  and the alternator  124 . The ISG  132  performs the functions of both the starter motor  108  and the alternator  124 , namely, starting the engine  102  and generating power for the electrical system. In addition, the ISG  132  may be configured to convert the vehicle&#39;s kinetic energy into electrical energy through regenerative braking. 
     The system  130  of  FIG. 1B  may utilize the ISG  132  in conjunction with a start-stop system. For example, an electronic control system (not shown) can shut down the engine  102  when the engine  102  is at zero load (e.g., when standing at a traffic light), and automatically restart the engine  102  via the ISG  132  when the accelerator pedal is pressed. In some implementations, the system  130  may include a separate starter motor in addition to the ISG  132 . The starter motor may be used to start the engine  102  from a cold start, and the ISG  132  may be used to restart the engine  102  during start-stop operation. 
     Starting the engine by the ISG  132  requires a significant amount of torque output from the ISG  132 . Accordingly, the belt  120  of the system  130  of  FIG. 1B  must be tensioned to a higher belt tension than the belt  120  of the system  100  of  FIG. 1A . Therefore, the belt  120  of the system  130  of  FIG. 1B  must be stronger than the belt  120  of the system  100  of  FIG. 1A . Furthermore, due to the higher belt tension of the belt  120 , the bearings and mounting hardware of the ISG  132  and any additional accessories must be stronger than those of the alternator  124  and accessories of  FIG. 1A . 
       FIG. 1C  is a side view of still another vehicle powertrain system  140 . The system  140  of  FIG. 1C  includes a crankshaft-mounted ISG  142  coupled to the rear side  110  of the engine  102 , between the engine  102  and the transmission  104 . Similar to the ISG  132  of  FIG. 1B , the ISG  142  performs the functions of both the starter motor  108  and the alternator  124 , namely, starting the engine  102  and generating power for the electrical system. Because the ISG  142  is coupled directly to the crankshaft  106  without the use of the belt  120 , the system  140  avoids the design challenges of the system  130  of  FIG. 1B  related to torque and tension requirements. 
     The present disclosure is directed to an engine accessory drive (EAD) system for use with an internal combustion engine. The EAD system includes an electric motor-generator unit (MGU) configured to selectively operate as an electric motor and an electric generator. In an embodiment, the MGU includes a single input/output shaft operably coupled to each of an engine accessory and a gearbox assembly. The gearbox assembly may be operatively coupled to an engine output (e.g., crankshaft). The gearbox assembly includes multiple gear trains that may be selectively engaged depending on a selected operational mode. The gear trains may have different gear ratios. Unlike conventional gearboxes that typically have relatively close gear ratios (e.g., 1.5:1, 2:1, etc.), the gear trains of the gearbox assembly may have relatively wide gear ratios (e.g., 14.5:1 for a first gear trains and 3:1 for a second gear trains in one embodiment). 
     The EAD system is selectively operable in at least two operational modes, including a generator mode and an accessory drive mode. In some embodiments, the EAD system is also operable in a starter mode. In the generator mode, mechanical energy (e.g., torque) is transferred from the engine to the MGU through the gearbox assembly, and the MGU is configured to convert the mechanical energy to electrical energy, which may be stored in a battery system. In the accessory drive mode, the MGU is configured to convert electrical energy to mechanical energy to operate the engine accessories. In the starter mode, the MGU is configured to convert electrical energy to mechanical energy to operate a starter mechanism. 
     The EAD system of the present disclosure provides an integrated system that may replace several discrete components utilized in conventional engine systems. In particular, the MGU of the EAD system may function as each of an electrical generator, an electric accessory drive motor, and an electric starter motor. For example, the EAD system may be utilized in start-stop systems to automatically shut down and restart a vehicle&#39;s internal combustion engine to reduce the amount of time that the engine spends idling, thereby reducing fuel consumption and emissions. When the engine is shut down, the MGU may operate as an electric motor to operate engine accessories. In conventional start-stop systems, accessories are either non-operational when the engine is shut down, or the accessories are driven using one or more electric motors. The EAD system of the present disclosure provides an integrated system in which the MGU may operate accessories while the engine is shut down, may operate as a starter to start and restart the engine, and may also operate as a generator to charge the battery system. In addition, while the engine is in operation and the battery system has a sufficient state of charge, the MGU of the EAD system may power the accessories rather than the engine powering the accessories. Accordingly, the EAD system of the present disclosure results in reduced part count, weight, size, and cost, while also providing improved engine performance and reduced fuel consumption, compared to conventional systems. 
       FIG. 2  is a schematic diagram of an EAD system  200  for use with an engine  202 , according to an embodiment. The engine  202  may be an internal combustion engine, such as a compression-ignition (e.g., diesel-powered) engine or a spark-ignition (e.g., gasoline-powered) engine. The engine may be utilized to power a vehicle, a generator set, or may be used in other applications. As illustrated in  FIG. 2 , the EAD system  200  includes an MGU  204  having an input/output shaft  206 . The MGU  204  is operatively coupled, via the input/output shaft  206 , to an accessory  208 . For example, in an embodiment, a pulley  210  is coupled to a distal end of the input/output shaft  206 . The pulley  210  is configured to drive a belt  212 , which is operatively coupled to the accessory  208 . In some embodiments, the belt  212  may be coupled to multiple accessories  208 . In other embodiments, the input/output shaft  206  may operatively couple the MGU  204  and the accessory  208  using other coupling methods, such as gears, for example. 
     The MGU  204  is also operatively coupled, via the input/output shaft  206  to a gearbox assembly  214 . The gearbox assembly  214  may include one or more gear trains or gear sets. The gear trains may have one or more fixed or variable gear ratios. As illustrated in  FIG. 2 , the gearbox assembly  214  includes a first gear train  216  operably coupled to the MGU  204  via a pinion gear  218  coupled to the input/output shaft  206 . The gearbox assembly  214  also includes a second gear train  220  operably coupled to an output  222  (e.g., crankshaft) of the engine  202 . In some embodiments, the second gear train  220  is coupled directly to the output  222 . However, in other embodiments, the second gear train  220  is indirectly coupled to the output  222 . For example, the second gear train  220  may be operably coupled to a camshaft or power take-off shaft, which is driven by the crankshaft, thereby indirectly coupling the second gear train  220  to the output  222 . The first gear train  216  is selectively coupled to the second gear train  220  via a clutch  224 . The first gear train  216  is also operably coupled to each of a starter assembly  225  and a hydraulic pump  226 . 
     The EAD system  200  also includes an EAD controller  228 . The EAD controller  228  is structured to operatively communicate with the MGU  204  and as well as other various components. Communication between and among the components may be via any number of wired or wireless connections. For example, a wired connection may include a serial cable, a fiber optic cable, a CAT5 cable, or any other form of wired connection. In comparison, a wireless connection may include the Internet, Wi-Fi, cellular, radio, etc. In one embodiment, a controller area network (CAN) bus  229  provides the exchange of signals, information, and/or data. The CAN bus  229  includes any number of wired and wireless connections. For example, the EAD controller  228  may be structured to operatively communicate with at least one of an engine control unit (ECU)  230  and various sensors  232  (e.g., speed sensors, torque sensors, voltage and current sensors, etc.) via the CAN bus  229 . The ECU  230  and the sensors  232  are configured to provide any of several different measurement values (e.g., speed, torque, state of charge, etc.). The EAD controller  228  is structured to interpret the measurement values and to control the EAD system  200  based on such interpretations. 
     The EAD controller  228  may be configured to operate the EAD system  200  in various operational modes, including a generator mode, an accessory drive mode, and a starter mode. In the generator mode, the clutch  224  is engaged such that mechanical energy (e.g., torque) is transferred from the engine output  222  to the MGU  204  through the gearbox assembly  214 . In this operational mode, the MGU  204  is configured to convert the mechanical energy to electrical energy, which may be stored in an energy storage system  234  and used, for example, to operate an electrical system. In other words, the MGU  204  is configured to operate as an electrical generator (e.g., alternator) in the generator mode. The energy storage system  234  may include one or more batteries. In some embodiments, the energy storage system  234  may also include a battery control module. In the generator mode, the accessories  208  are driven using mechanical energy transferred from the engine output  222  to the accessories  208  through the gearbox assembly  214 . 
     In the accessory drive mode, the clutch  224  is disengaged to decouple the engine output  222  from the MGU  204 . The MGU  204  is configured to convert electrical energy (e.g., stored in the energy storage system  234 ) to mechanical energy to operate the engine accessories  208 . In other words, the MGU  204  is configured to operate as an electric motor in the accessory drive mode. Mechanical energy (e.g., torque) is transferred from the MGU to the accessories  208  via the input/output shaft  206 , as described above. 
     In the starter mode, the clutch  224  is disengaged to decouple the engine output  222  from the MGU  204 . The MGU  204  is configured to convert electrical energy (e.g., stored in the energy storage system  234 ) to mechanical energy to operate the starter assembly  225 . The starter assembly  225  includes a drive shaft operably coupled to the first gear train  216  at a first end and a sliding pinion gear at a second end. The sliding pinion gear may be engaged with the flywheel (not shown) of the engine  202  such that the mechanical energy from the MGU  204  is used to start the engine  202 . Accordingly, the EAD system  200  eliminates the need for a conventional starter motor. 
       FIG. 3  is a block diagram of the EAD controller  228  of  FIG. 2 , according to an embodiment. As illustrated in  FIG. 3 , the EAD controller  228  includes a processing circuit  302  including a processor  304  and a memory  306 . The processor  304  may be implemented as a general-purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a digital signal processor (DSP), a group of processing components, or other suitable electronic processing components. The one or more memory devices  306  (e.g., RAM, ROM, Flash Memory, hard disk storage, etc.) may store data and/or computer code for facilitating the various processes described herein. Thus, the one or more memory devices  306  may be communicably connected to the processor  304  and provide computer code or instructions to the processor  304  for executing the processes described in regard to the EAD controller  228  herein. Moreover, the one or more memory devices  306  may be or include tangible, non-transient volatile memory or non-volatile memory. Accordingly, the one or more memory devices  306  may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described herein. 
     The memory  306  is shown to include various modules for completing the activities described herein. More particularly, the memory  306  includes modules structured to optimize control of the EAD system  200  of  FIG. 2 . While various modules with particular functionality are shown in  FIG. 2 , it should be understood that the EAD controller  228  and memory  306  may include any number of modules for completing the functions described herein. For example, the activities of multiple modules may be combined as a single module, additional modules with additional functionality may be included, etc. Further, it should be understood that the EAD controller  228  may further control other vehicle activity beyond the scope of the present disclosure. 
     Certain operations of the EAD controller  228  described herein include operations to interpret and/or to determine one or more parameters. Interpreting or determining, as utilized herein, includes receiving values by any method known in the art, including at least receiving values from a datalink or network communication, receiving an electronic signal (e.g. a voltage, frequency, current, or PWM signal) indicative of the value, receiving a computer generated parameter indicative of the value, reading the value from a memory location on a non-transient computer readable storage medium, receiving the value as a run-time parameter by any means known in the art, and/or by receiving a value by which the interpreted parameter can be calculated, and/or by referencing a default value that is interpreted to be the parameter value. 
     As illustrated in  FIG. 3 , the EAD controller  228  includes a measurement module  308  and an operational mode module  310 . The measurement module  308  is in operative communication with the ECU  230  and various sensors  232  ( FIG. 2 ). The measurement module  308  is configured to receive measurement values  312  from the ECU  230  and/or the sensors  232 , and to interpret measurement values based on the received measurement values  312 . The sensors  232  may include any of various types of sensors configured to measure characteristics related to the engine and/or related systems. For example, the sensors  232  may include an engine speed sensor, an engine torque sensor, an oxygen sensor, a fuel sensor (e.g., a fuel injection monitor), an engine temperature sensor (e.g., on the block of the engine, near the exhaust valve of the engine to monitor an exhaust gas temperature, and any other location), a current and voltage sensor, etc. Accordingly, the measurement values  312  may include, but is not limited to, an engine speed (revolutions-per-minute (RPM)), an engine output power, an engine temperature, a state of the engine (e.g., ON or OFF), an engine load, a state of charge of the energy storage system and/or any other engine or vehicle characteristics. 
     The operational mode module  310  is configured to control operation of the EAD system  200  based on the interpreted measurement values  312 . For example, the operational mode module  310  may change operation of the EAD system  200  from one of the generator mode, the accessory drive mode, and the starter mode to another of the generator mode, the accessory drive mode, and the starter mode based on the interpreted measurement values  312 . In one embodiment, for example, the measurement values  312  may include a state of charge of the energy storage system  234 . The operational mode module  310  may be configured to change operation of the EAD system  200  from the accessory drive mode to the starter mode when the state of charge value falls below a predetermined value. The operational mode module may also change operation of the EAD system  200  from the starter mode to the generator mode upon detecting that the engine has started. 
     In another example, according to an embodiment, the measurement values  312  may include an accessory load demand value and a state of charge value. The measurement module  308  may determine an MGU output capacity based on the state of charge value. The operational mode module  310  may change operation of the EAD system  200  from the accessory drive mode to the starter mode when the accessory load demand value exceeds the MGU output capacity. The operational mode module may also change operation of the EAD system from the starter mode to the generator mode upon detecting that the engine has started. 
       FIG. 4A  is a perspective view of an EAD system  400  operably coupled to an engine  402 , according to an embodiment. In general, the EAD system  400  includes an MGU  404  mounted to a side of the engine  402 . According to various embodiments, the MGU  404  is an electric machine that is capable of selectively operating as an electric motor or electrical generator (e.g., alternator). The EAD system  400  also includes a gearbox assembly  406 . In general, the gearbox assembly  406  includes a first gear train  408  operably coupled to the MGU  404  and a second gear train  410  operably coupled to an output  412  (e.g., crankshaft) of the engine  402 . The first gear train  408  is selectively coupled to the second gear train  410  via a clutch  414 . 
     The EAD system  400  also includes a starter assembly  416  and a hydraulic pump  418 , each of which being operably coupled to the first gear train  408 . As discussed in further detail below, the starter assembly  416  is powered by the MGU  404  via the first gear train  408 . In contrast, conventional engine systems typically include electric starter motors. Because the EAD system  400  utilizes the MGU  404  to power the starter assembly  416 , the EAD system  400  eliminates the need for a separate starter motor. 
       FIG. 4B  is another perspective view of the EAD system  400  of  FIG. 4A , with a cover removed to illustrate an accessory drive shaft  420  of the MGU  404 . The accessory drive shaft  420  extends through the second gear train  410 . An accessory drive hub  422  is coupled to a distal end of the accessory drive shaft  420 . The accessory drive hub  422  may be a pulley configured to drive an accessory drive belt (not shown) so as to operate one or more engine accessories. 
       FIG. 4C  is another perspective view of the EAD system  400  of  FIGS. 4A and 4B , with a cover removed from the second gear train  410  to illustrate the configuration of the second gear train  410 , according to an embodiment. As illustrated in  FIG. 4C , the second gear train  410  includes several gears operably coupled to the engine output  412  so as to transfer torque from the engine output  412 , through the second gear train  410  and the clutch  414 , and to the first gear train  408 . The second gear train  410  may utilize various gear ratios, depending on application requirements. In some embodiments, the second gear train  410  is permanently meshed with the engine output  412 . In other embodiments, however, the second gear train  410  includes an engagement mechanism (e.g., a clutch) to selectively decouple the second gear train  410  and the engine output  412 . 
     As shown in  FIG. 4C , the accessory drive shaft  420  extends through the second gear train  410  and is supported by a bearing  424 . In some embodiments, the accessory drive shaft  420  is not engaged with the gears of the second gear train  410 . Instead, torque is transferred from the crankshaft to the MGU  404  through the second gear train  410 , the clutch  414 , and the first gear train  408 . In other embodiments, however, the accessory drive shaft  420  is engaged with the gears of the second gear train  410 . 
       FIG. 4D  is another perspective view of the of the EAD system  400  of  FIGS. 2A-2C , with a cover removed from the first gear train  408  to illustrate the configuration of the first gear train  408 , according to an embodiment. As illustrated in  FIG. 4C , the first gear train  408  includes several gears operably coupled to each of the MGU  404 , the clutch  414 , the hydraulic pump  418 , and the starter assembly  416 . The first gear train  408  may utilize various gear ratios, depending on application requirements. In one embodiment, the first gear train  408  utilizes a gear ratio of 0.5:1 (e.g., low speed) to drive the hydraulic pump  418 , and a gear ratio of 1:1 (e.g., high speed) to drive the starter drive shaft  426  of the starter assembly  416 . In some embodiments, the starter drive shaft  426  is permanently engaged with the first gear train  408 . In other embodiments, however, the first gear train  408  includes an engagement mechanism (e.g., a clutch) to selectively decouple the starter drive shaft  426  from the first gear train  408 . The starter assembly  416  may include a sliding pinion gear configured to engage a flywheel of the engine (not shown). When the pinion gear of the starter assembly  416  is engaged with the flywheel, the gear ratio between the MGU  404  and the flywheel is 14.5:1, according to one embodiment. In other embodiments, the gear ratio is at least 10:1. Accordingly, in some embodiments, the EAD system  400  is configured to employ relatively wide gear ratios, selectively and/or concurrently. 
       FIG. 5A  illustrates an EAD system  500  operably coupled to an engine  502 , according to another embodiment. Similar to the EAD system  400  of  FIGS. 4A-4D , the EAD system  500  of  FIG. 5A  includes an MGU  504  capable of selectively operating as an electric motor or an electric generator. The MGU  504  includes a first input/output shaft  506  operably coupled to a first gear train  508 , and a second output shaft  510  operably coupled to a second gear train  512 . The EAD system  500  also includes a hydraulic pump  514  operably coupled to the first gear train  508 , and an air compressor  516  selectively coupled to the first gear train  508  via a clutch  518 . 
     In some embodiments, engine accessories are powered by torque transferred thereto from the MGU  504  via the second gear train  512 . In some embodiments, the second gear train  512  is not coupled to an output of the engine  502  and the accessories are operable only via the MGU  504 . However, in other embodiments, the second gear train  512  is coupled to an output of the engine  502  and the accessories are selectively operable via the output of the engine  502 . The first gear train  508  is configured to receive torque transferred thereto from at least one of the MGU  504  and an output of the engine  502  either directly (e.g., via the crankshaft) or indirectly (e.g., via the camshaft). Such torque may be used to power the hydraulic pump  514  and/or the air compressor  516 . 
       FIG. 5B  illustrates the EAD system  500  of  FIG. 5A , further including a starter assembly  520 , according to an embodiment. The starter assembly  520  includes a starter shaft  522  and an engagement flange  524  by which the starter shaft  522  is operably coupled to a starter drive gear  526  of the first gear train  508 . The starter shaft  522  extends into a starter housing  528 . The starter housing  528  includes a mounting flange  530  by which the starter housing  528  is mounted to a flywheel housing  532  of the engine  502 . As explained in further detail below, the starter housing  528  supports a pinion shaft and a sliding pinion gear. The sliding pinion gear is configured to engage the flywheel (not shown) to start the engine  502 . 
       FIG. 5C  is a cross-sectional view of the starter assembly  520  of  FIG. 5B . As illustrated in  FIG. 5C , the starter shaft  522  has a first end  534  that extends into the engagement flange  524  and a second end  536  that extends into the starter housing  528 . The first end  534  of the starter shaft  522  is operably coupled to the starter drive gear  526  ( FIG. 5B ). For example, in an embodiment, the first end  534  is splined and matches female splines on the starter drive gear  526 . Because the starter shaft  522  engages the starter drive gear  526 , the starter shaft  522  is driven by the MGU  504  via the first gear train  508 . In some embodiments, the first end  534  is always engaged with the starter drive gear  526  during operation, such that the starter shaft  522  is free-spinning while the first gear train  508  is engaged. In other embodiments, however, the system  500  further includes an engagement mechanism (e.g., a clutch) to selectively engage the starter shaft  522  with the starter drive gear  526 . A first fluid seal  538  fluidly seals the engagement flange  524  against the starter shaft  522 . A retaining ring  540  operates to axially retain the starter shaft  522  relative to the engagement flange  524 . In an embodiment, the engagement flange  524  is secured to a housing of the first gear train  508  by fasteners (e.g., two bolts). 
       FIG. 5D  is a detail cross-sectional view of the engagement flange  524  of  FIG. 5C , further illustrating the first fluid seal  538  and the retaining ring  540 . In an embodiment, the fluid seal  538  may include an oil seal, and the retaining ring  540  may include a snap ring. However, other embodiments may utilize other types of fluid seals  538  and/or retaining rings  540 , or may not include the fluid seal  538  or the retaining ring  540 . 
     Referring back to  FIG. 5C , the starter housing  528  has a front housing portion  542  and a rear housing portion  544 . The second end  536  of the starter shaft  522  extends into the rear housing portion  544 . The rear housing portion  544  includes a fluid seal  546  to fluidly seal the starter housing  528  against the starter shaft  522 . The second end  536  of the starter shaft  522  engages a pinion shaft  548  positioned substantially within the front housing portion  542 . 
       FIG. 5E  is a perspective detail cross-sectional view of the interface between the starter shaft  522  and the starter housing  528  of  FIG. 5C . As illustrated in  FIGS. 3C and 3E , the second end  536  may include splines to engage a corresponding female splined portion  550  formed in the pinion shaft  548 . The pinion shaft  548  has an internal cavity  552  forward of the female splined portion  550 . During assembly with the engine  502 , the second end  536  of the starter shaft  522  may be slid into the internal cavity  552  to facilitate assembly. The pinion shaft  548  is supported by a bearing  554 . The bearing  554  may be press-fit onto a support  556  extending inward within the starter housing  528  proximate the interface between the front and rear housing portions  542 ,  544 . Although not shown in  FIG. 5C , the pinion shaft  548  may also be supported by a second bearing positioned at a second support  558  further within the front housing portion  542 . A pinion gear  560  is coupled to the pinion shaft  548 , and is configured to engage the ring gear of the flywheel (not shown) to start the engine  502 . For the purposes of the present disclosure, details of the pinion gear  560  and the engagement mechanism are not shown. In one embodiment, the engagement mechanism includes a forked lever that is engaged (e.g., electrically, hydraulically, etc.) to slide the pinion gear  560  forward on the pinion shaft  548  to engage the pinion gear  560  with the ring gear of the flywheel. 
     In certain implementations, the systems or processes described herein can include a controller structured to perform certain operations described herein. In certain implementations, the controller forms a portion of a processing subsystem including one or more computing devices having memory, processing, and communication hardware. The controller may be a single device or a distributed device, and the functions of the controller may be performed by hardware and/or as computer instructions on a non-transient computer readable storage medium. 
     In certain implementations, the controller includes one or more modules structured to functionally execute the operations of the controller. The description herein including modules emphasizes the structural independence of the aspects of the controller, and illustrates one grouping of operations and responsibilities of the controller. Other groupings that execute similar overall operations are understood within the scope of the present application. Modules may be implemented in hardware and/or as computer instructions on a non-transient computer readable storage medium, and modules may be distributed across various hardware or computer based components. More specific descriptions of certain embodiments of controller operations are included in the section referencing  FIGS. 2-5E . 
     Example and non-limiting module implementation elements include sensors providing any value determined herein, sensors providing any value that is a precursor to a value determined herein, datalink and/or network hardware including communication chips, oscillating crystals, communication links, cables, twisted pair wiring, coaxial wiring, shielded wiring, transmitters, receivers, and/or transceivers, logic circuits, hard-wired logic circuits, reconfigurable logic circuits in a particular non-transient state configured according to the module specification, any actuator including at least an electrical, hydraulic, or pneumatic actuator, a solenoid, an op-amp, analog control elements (springs, filters, integrators, adders, dividers, gain elements), and/or digital control elements. 
     The term “controller” encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or multiple ones, a portion of a programmed processor, or combinations of the foregoing. The apparatus can include special purpose logic circuitry, e.g., an FPGA or an ASIC. The apparatus can also include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment can realize various different computing model infrastructures, such as distributed computing and grid computing infrastructures. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     As utilized herein, the term “substantially” and any similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided unless otherwise noted. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims. Additionally, it is noted that limitations in the claims should not be interpreted as constituting “means plus function” limitations under the United States patent laws in the event that the term “means” is not used therein. 
     The terms “coupled,” “connected,” and the like as used herein mean the joining of two components directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two components or the two components and any additional intermediate components being integrally formed as a single unitary body with one another or with the two components or the two components and any additional intermediate components being attached to one another. 
     It is important to note that the construction and arrangement of the system shown in the various exemplary implementations is illustrative only and not restrictive in character. All changes and modifications that come within the spirit and/or scope of the described implementations are desired to be protected. It should be understood that some features may not be necessary and implementations lacking the various features may be contemplated as within the scope of the application, the scope being defined by the claims that follow. It should be understood that features described in one embodiment could also be incorporated and/or combined with features from another embodiment in manner understood by those of ordinary skill in the art. It should also be noted that the terms “example” and “exemplary” as used herein to describe various embodiments are intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such terms are not intended to connote that such embodiments are necessarily extraordinary or superlative examples).