Patent Publication Number: US-9429131-B2

Title: Starter system and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit under Title 35, U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 61/802,969, entitled STARTER SYSTEM AND METHOD, filed on Mar. 18, 2013, the entire disclosure of which is expressly incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to engine starter systems and, more particularly, to controlling the operation of starters in such systems. 
     Electric machines such as starters play important roles in the operation of vehicles. A typical vehicle includes a conventional starter system which, upon the vehicle driver closing an ignition switch, cranks the vehicle engine, which then, when started, runs continuously until the driver manually stops its operation by manipulating the ignition switch. Vehicles having starter systems capable of facilitating frequent engine start and stop operation while being driven to avoid or reduce engine idling periods are becoming more commonplace in modern vehicles, and such operation requires the starter to operate at high efficiency under both cold and warm engine cranking conditions. Moreover, such starter systems rely on control systems, rather than solely upon a driver-manipulated ignition switch, to activate and deactivate the starter, typically in response to vehicle conditions and/or driver inputs. The demands of frequent engine stop-start operations require starter systems and components that function evermore rapidly and efficiently to increase reliability, reduce energy consumption, and enhance the driving experience. 
     Implementing prior starter systems capable of frequent stop-start operations typically requires considerable additional control electronics and sensor beyond those normally present in vehicles having conventional starter systems. Such systems employ, for example, closed loop control systems that rely on feedback indicative of starter motor or pinion position or speed obtained through at least one additional, dedicated sensor incorporated into the starter system solely for that purpose. Moreover, such prior systems typically house the starter control electronics in a dedicated module adapted to receive the feedback signal(s) from the added starter speed/position sensor(s), significantly complicate packaging vehicle electronics, and increase system part complexity. 
     A starter system capable of facilitating frequent engine stop-start operations, so as to provide the above-mentioned benefits, and which also minimizes starter control electronics and modules therefor and does not require additional sensors beyond those normally present in vehicles employing even conventional starter systems, would provide a desirable advancement in the relevant art. 
     SUMMARY 
     A starter system according to the present disclosure is configured and arranged to properly engage the starter with the engine while at the same time reducing the energy consumption of the starter motor, and enhances the driving experience. A starter system according to the present disclosure performs well during cold cranking conditions at low starter speeds under relatively higher starter torque demands as well as during warm cranking conditions at high starter speeds under low starter torque demands. In conjunction with this operating parameter, some embodiments according to the present disclosure are configured and arranged to function so as to allow better engagement of the starter with the vehicle engine, which may not be at rest at the time of engagement. 
     Some embodiments according to the present disclosure provide a starter system including a starter having a solenoid assembly having a plunger, a motor that is coupled to a pinion that is coupled to the solenoid plunger, and an electronic control unit (ECU) that operatively controls the starter solenoid and motor. 
     An ECU for a starter system according to the present disclosure is capable of receiving data from one or more sensors, and calculating various starter system control parameters using one or more algorithms. The ECU for a starter system according to the present disclosure may be commonly housed in the electronics control unit containing circuitry for controlling typical engine operation functions in modern vehicles, even those vehicles employing only conventional starter systems. Advantageously, such a starter system requires no additional, dedicated sensors for obtaining feedback from the starter regarding the starter pinion or motor speed or position; the starter system facilitates determination of the starter pinion speed in an open loop manner, without the need for a control scheme reliant upon closed loop feedback by which the starter motor or pinion position or speed is sensed. 
     Additionally, vis-à-vis prior starter systems, a starter system according to the present disclosure simplifies facilitating engine stop-start operation capabilities, and does so without significantly complicating existing vehicle/engine electronic control architectures or increasing starter system part complexity. In some embodiments, the starter system can subsequently command the operational characteristics of one or more components of the system, including the starter itself. For example, the starter system can control the rotational speed of the starter motor and/or the solenoid plunger of the starter. The system can also, in some embodiments, control the meshing of the starter pinion with the engine ring gear to achieve a smooth, substantially synchronous engagement therebetween. 
     The present disclosure provides, as a first aspect, a method for controlling an engine starter system. The method includes: providing an electronic control unit having an engine speed input and at least one output; providing a starter capable of being controlled by the electronic control unit and having an electric motor and a pinion, the motor and pinion coupled together for transferring rotational torque from the motor to the pinion when the motor is activated; controlling activation of the motor with an electronic control unit output motor signal in response to an engine speed input signal; determining with the electronic control unit the pinion speed in an open loop manner based solely on the time since activation of the motor and the voltage applied to the motor; and selectively moving the pinion between a retracted state and an extended state in response to an electronic control unit output pinion signal, whereby the starter is capable of selectively engaging an engine for cranking the engine. 
     As a second aspect, in the above method the electronic control unit output motor signal and the electronic control unit output pinion signal are signals separately outputted from the electronic control unit. 
     As a third aspect, in this method the electronic control unit output motor signal and the electronic control unit output pinion signal are substantially simultaneously outputted from the electronic control unit. 
     As a fourth aspect, in the above method the electronic control unit output motor signal and the electronic control unit output pinion signal are a single signal outputted from the electronic control unit. 
     As a fifth aspect, in the above method the pinion speed determined by the electronic control unit is expressible as an explicit, closed form equation based on elapsed time since activation of the motor and the voltage applied to the motor. 
     As a sixth aspect, in this method the explicit, closed form equation is a quartic equation. 
     As a seventh aspect, in the above method, in determining the pinion speed with the electronic control unit the voltage applied to the motor is substantially battery voltage. 
     As an eighth aspect, in the above method, in determining the pinion speed with the electronic control unit the voltage applied to the motor is presumed to be a constant value. 
     As a ninth aspect, in the above method the pinion speed is a presumed predetermined speed after an identified period of time has elapsed since motor activation. 
     As a tenth aspect, in the above method the pinion speed is determined based at least in part as a function of an actual applied motor voltage. 
     As an eleventh aspect, the above method includes calculating the differential between the determined pinion speed and the engine speed input. 
     As a twelfth aspect, in this method the voltage applied to the motor is maintained if the determined pinion speed is less than the engine speed input. 
     As a thirteenth aspect, in this method the pinion is capable of being engaged with an engine ring gear if the determined pinion speed is at least the engine speed input. 
     The present disclosure also provides, as a fourteenth aspect, a starter system for cranking an engine. The starter system includes a starter having an electric motor and a pinion coupled together, and rotational torque from the motor is transferable to the pinion. The system also includes an electronic control unit having an engine speed input and at least one output. The motor is adapted for being activated under control of the electronic control unit in response to a motor signal outputted from the electronic control unit, and the pinion is adapted for being moved axially between a retracted state and an extended state in response to a pinion signal outputted from the electronic control unit. The starter is capable of engaging and cranking an engine in the pinion extended state, and the electronic control unit is capable of determining the pinion speed in an open loop manner based solely on the time since activation of the motor and the voltage applied to the motor. 
     As a fifteenth aspect, in the above starter system the electronic control unit is adapted to determine pinion speed based at least in part as a function of the voltage applied to the motor being substantially battery voltage. 
     As a sixteenth aspect, in the above starter system the electronic control unit is adapted to determine pinion speed based at least in part as a function of the voltage applied to the motor being presumed to be a constant value. 
     As a seventeenth aspect, in the above starter system the electronic control unit is adapted to adjust the pinion speed on the basis of a comparison by the electronic control unit between the determined pinion speed and the engine speed input. 
     As an eighteenth aspect, in the above starter system the electronic control unit has a motor output from which the motor signal is outputted from the electronic control unit and a separate pinion output from which the pinion signal is outputted from the electronic control unit. 
     As a nineteenth aspect, in this starter system the electronic control unit is capable of outputting the motor signal from the motor output and the pinion signal from the pinion output substantially simultaneously. 
     As a twentieth aspect, in the above starter system the electronic control unit output is a single output from which a single motor and pinion signal is outputted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned aspects and other characteristics and advantages of an apparatus and/or method according to the present disclosure will become more apparent and will be better understood by reference to the following description of exemplary embodiments taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a diagram of a first embodiment starter system according to the present disclosure; 
         FIG. 2A  is a cross-sectional view of a first embodiment starter used in the system of  FIG. 1 ; 
         FIG. 2B  is a partial view of a second embodiment starter used in the system of  FIG. 4 , showing a cross-section of its solenoid assembly; 
         FIG. 3  is a first graph indicating engine ring gear and starter pinion speeds over time during engine restart according to an embodiment of a starter system and method hereby disclosed; 
         FIG. 4  is a diagram of a second embodiment starter system according to the present disclosure; 
         FIGS. 5A and 5B , collectively referred to herein as  FIG. 5 , depict a flowchart of process steps of a starter system control process according to the present disclosure; 
         FIG. 6  is a second graph indicating engine ring gear and starter pinion speeds, and states of the starter motor and starter solenoid switches, over time during engine restart according to an embodiment of a starter system and method hereby disclosed; 
         FIG. 7  is a third graph indicating engine ring gear and starter pinion speeds, and states of the starter motor and starter solenoid switches, over time during engine restart according to an embodiment of a starter system and method hereby disclosed; 
         FIG. 8  is a fourth graph indicating engine ring gear and starter pinion speeds, and states of the starter motor and starter solenoid switches, over time during engine restart according to an embodiment of a starter system and method hereby disclosed; 
         FIG. 9  is a graph of starter pinion speeds over time during free speeding accelerations of starter motors; 
         FIG. 10  is a graph of starter pinion speeds over time during decelerations of starter motors; 
         FIG. 11  is a graph of starter pinion speeds computed according to the present disclosure superimposed upon a graph of measured starter pinion speeds over time during accelerations of starter motors; 
         FIG. 12  is a graph of starter pinion speeds over time during free speeding accelerations of a starter motor operated at 10V, 11V, and 12V; and 
         FIG. 13  is a graph of starter pinion speeds over time during free speeding accelerations of a starter motor over three consecutive cycles, showing temperature effects on starter motor acceleration. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the disclosed apparatus and method, the drawings are not necessarily to scale or to the same scale and certain features may be exaggerated or omitted in order to better illustrate and explain the present disclosure. Moreover, in accompanying drawings that show sectional views, cross-hatching of various sectional elements may have been omitted for clarity. It is to be understood that this omission of cross-hatching is for the purpose of clarity in illustration only. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S) 
     The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms or steps disclosed in the following detailed description, but have been chosen and are herein described so that others skilled in the art may appreciate and understand principles and practices according to the present disclosure. It is, therefore, to be understood that the invention herein described is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings, and is capable of having other embodiments and of being practiced or of being carried out in various ways. 
     Further, it is to be understood that the phraseology and terminology used herein has been adopted for the purpose of description and should not be regarded as limiting. For example, the use of “including,” “comprising,” or “having,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled,” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Moreover, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. The comparative rotational speeds of the engine ring gear and starter pinion are understood to be their tangential speeds at the radii at which they intermesh, or their rotational speeds normalized through their gear ratio and both represented by the rotational speed of one or the other. 
       FIG. 1  illustrates first embodiment starter system  20  for engine  22 . Engine  22  is an internal combustion engine for a vehicle. Although vehicles can include starter system  20 , it is to be understood that starter system  20  can be utilized in an apparatus having a stationary engine  22 . System  20  includes starter  24 , power source  26  such as a 12V battery, ECU  28 , which may also serve as an engine control unit for controlling engine operations and contain control circuitry for starter system  20 , and one or more sensors  30  used for determining engine speed. In the exemplary embodiments disclosed herein sensor  30  is used for detecting the position of engine ring gear  32 , by which the speed of engine  22  may be determined by ECU  28  in a manner well-known to those having ordinary skill in the art, and as is ordinarily done in modern vehicles regardless of starter system type, the output signal of sensor  30  being provided to the vehicle&#39;s engine control unit. ECU  28  thus receives a measured engine speed input from sensor  30 , which may already be included in the vehicle in a typical, known manner and need not be an additional sensor dedicated to starter system operation, thereby simplifying starter system packaging and minimizing part complexity. In the depicted embodiment, sensor  30  communicates with ECU  28  via wired and/or wireless communication protocols. 
     Referring to  FIG. 2A , first embodiment starter  24  is conventional, and includes starter motor  40  disposed within starter housing  42  for rotatably driving starter pinion  44  in a single rotational direction. Starter motor  40  and pinion  44  are operably coupled through first drive shaft  46 . In some embodiments, as shown, motor  40  has second drive shaft  48  which drives drive shaft  46  via gear train  50 , which may be of planetary type. As depicted, sun gear  52  of planetary gear train  50  is affixed to second drive shaft  48 , and ring gear  54  of planetary gear train  50  is affixed to first drive shaft  46 ; planetary gears  56  disposed between sun gear  52  and ring gear  54  transfer torque and rotary motion from second drive shaft  48  to first drive shaft  46 . Alternatively, in certain unshown embodiments of starter  24 , motor  40  drives first drive shaft  46  directly, rather than through gear train  50 . 
     Starter  24  includes overrunning clutch  58  disposed between pinion  44  and first drive shaft  46 . Clutch  58  allows pinion  44  to be rotated faster than first drive shaft  46  in their common direction of rotation, as may occur when pinion  44  and ring gear  32  are in meshed engagement and engine  22  causes pinion  44  to rotate at a speed faster than that of first drive shaft  46 . Thus, clutch  58  aids in reducing a risk of damage to starter  24  and its motor  40  by permitting pinion  44  to rotate relative to first drive shaft  46 , thereby allowing pinion  44  to be rotated, if still engaged with ring gear  32 , at speed faster than it would be driven by motor  40 , directly or through gear train  50 , and preventing motor  40  from being rotated under the influence of engine torque. 
     Starter  24  also includes solenoid assembly  60  which acts to drive pinion  44  axially from a retracted state or position (shown in  FIG. 2A ) in which pinion  44  and engine ring gear  32  are out of engagement, to an extended state or position (shown in  FIG. 1 ) in which pinion  44  and ring gear  32  are engaged. Pinion  44  is biased into its retracted state in a well-known manner. Referring to  FIGS. 2A and 2B , first and second embodiment starter  24  each includes solenoid assembly  60 . Solenoid assembly  60  includes solenoid plunger  62 , solenoid coil  64 , and a plurality of biasing members  66  such as springs or other structures capable of biasing portions of solenoid assembly  60  axially towards their respective, normal, de-energized position. 
     First embodiment starter  24  shown in  FIG. 2A  includes motor relay switch  68  activated through solenoid assembly  60 . In a well-known manner typical of conventional starter systems, motor relay switch  68  is coupled to solenoid plunger  62  and is closed in response to energization of solenoid coil  64 , resulting in battery voltage being provided to motor  40 . Motor relay switch  68  is biased by a biasing member  66  into an open condition wherein battery voltage is not provided to motor  40 . A single, common output signal from ECU  28  thus results both in activation of motor  40 , and engagement of pinion  44  and ring gear  32 . Second embodiment starter  24  partially shown in  FIG. 2B  includes solenoid assembly  60 , and separably actuated motor relay solenoid assembly  70  having motor relay solenoid plunger  72 , motor relay solenoid coil  74 , and biasing member(s)  66 . 
     In first or second embodiment starter  24 , its motor relay switch  68  includes contactor  76  that is moved axially upon energization of solenoid coil  64  or  74 , respectively, into electrical contact with terminals  78  of motor relay switch  68 ; terminals  78  include battery side terminal  78   b  and motor side terminal  78   m . Battery  26  is selectively connected to battery side terminal  78   b  of motor relay switch  68 , and motor  40  is connected to motor side terminal  78   m  of motor relay switch  68 . Movement of motor relay solenoid plunger  72  brings contactor  76  coupled thereto into contact with battery side terminal  78   b  and motor side terminal  78   m  of motor relay switch  68 . Terminals  78  are thus shorted through contactor  76 , by which battery voltage can be applied to starter motor  40  for energizing the motor and causing it and pinion  44  to spin. 
     Starter  24  includes shift lever  80 . First end  82  of shift lever  80  is coupled to solenoid plunger  62 , and second end  84  of shift lever  80  is coupled to pinion  44  and/or clutch  58  and/or first drive shaft  46 . The activation of solenoid coil  64  causes solenoid plunger  62  to move axially against the bias of a biasing member  66 , which movement is then transferred to pinion  44  via shift lever  80  to move pinion  44  out of its retracted state and towards its extended state, wherein pinion  44  is enmeshed with ring gear  32 . 
     Starter  24  can operate in a generally conventional manner. For example, in response to a signal (e.g., the vehicle driver closing a switch, such as an ignition switch), ECU  28  causes power from battery  26  to be supplied to solenoid assembly  60 , causing solenoid plunger  62  to move pinion  44  into engagement with engine ring gear  32  while engine  22  is at rest. This same signal may also cause electrical power from battery  26  to then be supplied to starter motor  40 , causing it to generate an electromotive force which is translated through gear train  50  and/or clutch  58  and/or first drive shaft  46  to pinion  44 , which is engaged with ring gear  32 , thereby cranking engine  22 . As a result, engine  22  is started and begins to run without the aid of starter  24 , at which time power to starter motor  40  and solenoid  60  is discontinued and pinion  44  is retracted from ring gear  32 . Such operation is known as a “cold start,” particularly if engine  22  had not been running immediately before coming to rest and being restarted. Typically, cold start operation demands high motor torque and is performed at relatively low motor speeds. 
     In addition to conventional starting or “cold start” episodes, starter system  20  can be used for other types of engine starting operations. In some embodiments, system  20  can be configured and arranged to enable a “stop-start” starting episode. For example, system  20  can start engine  22  when the engine has already been started and the vehicle continues to be in an active state (i.e., operational), but the engine is temporarily inactivated, as when fuel flow to it has been interrupted and the engine speed has fallen below idle speed to substantially or completely come to rest. 
     Moreover, in some embodiments, in addition to or in lieu of being configured and arranged to enable a stop-start starting episode, starter system  20  can be configured and arranged to enable a “change-of-mind” type stop-start starting episode. Starter system  20  can start engine  22  when the vehicle continues to be in an active state, the engine has been running, and the engine has been automatically deactivated (e.g., by fuel interruption), but continues to rotate as it decelerates towards rest. 
       FIG. 3  shows graph  300  representing speeds  302  of engine ring gear  32  along curves  306  and  314 , and the speed of starter pinion  44  along curves  310  and  314 , over time  318  during a change-of-mind engine restart. As illustrated, following deceleration of engine  22  after shut-down (i.e., after an auto-stop event), engine  22  may be restarted according to at least one embodiment of the invention.  FIG. 3  illustrates a change within the first 0.2 seconds from a normal engine idle speed of 700 RPM, to a subsequent, progressive deceleration of engine  22 . According to one embodiment of the invention, starter system  20  is configured and arranged to activate the motor coil to spin motor  40  when engine  22  reaches trigger speed  322  below which engine  22  cannot be restarted without help from starter  24 ; trigger speed  322  may, for example, be 500 RPM. Motor  40  is energized when engine  22  reaches trigger speed  322  and, over a short period of time  318 , the speed of motor  40  rises and, at a predetermined time after motor  40  is energized, system  20  activates solenoid coil  64 , moving pinion  44  from its retracted state towards its extended state. 
     Referring to  FIG. 3 , if, for example, after engine  22  receives a deactivation signal, but before the engine substantially or completely comes to rest, the vehicle driver decides to reactivate the engine (e.g., by removing his foot from the vehicle brake pedal), pinion  44  can engage ring gear  32  at point  330  as the engine coasting. After engaging pinion  44  and rotating ring gear  32 , starter  24  then restarts engine  22  by entering a cranking phase. During engine cranking the rotational speeds of the engaged pinion and ring gear increase together and the engine is restarted, at which time the starter and the engine are disengaged by discontinuing power to starter solenoid coil  64 . Restarting in such change-of-mind situations may be accomplished by resuming ignition and/or fuel flow at a sufficient engine speed. In some embodiments, system  20  can be configured for other starting episodes, such as a conventional “soft start” starting episodes, wherein motor  40  is at least partially activated during engagement of pinion  44  and ring gear  32 , for example. 
     In order to reduce the potential risk of damage to pinion  44 , and/or ring gear  32 , the speed of pinion  44  can be substantially synchronized with the speed of ring gear  32  (i.e., the speed of engine  22 ) when starter  24  attempts to engage pinion  44  with ring gear  32 . Thus, starter  24  may also be configured to provide synchronization between pinion  44  and engine ring gear  32 . Referring to  FIG. 2B , to better facilitate such synchronization during a change-of-mind engine restart, second embodiment starter  24  includes separate pinion solenoid assembly  60  and motor relay solenoid assembly  70 , as mentioned above. Motor relay solenoid coil  74  is selectively activated to cause axial movement of motor relay solenoid plunger  72  independently of the axial movement of pinion plunger  62  to effect energization of motor  40 . As described above with respect to first embodiment starter  24 , the activation of pinion solenoid assembly  60  effects movement of pinion  44  between its retracted and extended states. Thus, in second embodiment starter  12 , the rotation of pinion  44  and its engagement with ring gear  32  are individually activated. Generally, the synchronization process occurs as follows: the motor coil  74  is activated first, thereby starting motor  40  rotation, and when the speeds of pinion  44  and ring gear  32  are synchronized, pinion coil  64  is then activated to move pinion  44  out of its retracted state and into its extended state to engage still-rotating ring gear  32 . Notably, in some embodiments, there is no requirement to assure that the speeds of pinion  44  and ring gear  32  are synchronized, as pinion  44  may have previously become engaged with ring gear  32  prior to starter system  20  sending a restart signal. 
       FIG. 4  is a diagram representing a portion of second embodiment starter system  20  that includes second embodiment starter  24  and which is configured and arranged such that its ECU  28  selectively closes motor switch  90  to place motor  40  in communication with battery  26  through motor relay switch  68 . ECU  28  also selectively closes pinion switch  92  to place coil  64  of pinion solenoid assembly  60  in communication with battery  26 , which moves pinion solenoid plunger  62  against biasing members  66  to move pinion  44  out of its retracted state and towards its extended state. As discussed above, sensor  30  is provided for detecting the position of ring gear  32  and providing a signal to ECU  28  for determining engine speed. The variable speed of ring gear  32  is therefore continuously monitored and is determinable to system  20 . 
       FIG. 5  is a flow chart indicating steps in process  500  carried out by one or more embodiments of starter system  20 . In the following discussion, the respective “yes” or “no” outcome of each decision or determination in  FIG. 5  is also identified with an associated y or n reference numeral suffix, respectively. ECU  28  is configured and arranged to determine, at  502 , whether engine  22  is rotating. 
     If, at  502 , ECU  28  determines that engine  22  is not rotating  502   n  and therefore is at rest, ECU  28  then determines at  504  whether engine  22  is to be started. 
     If, at  504 , it is determined that nonrotating engine  22  is not to be started  504   n , process  500  returns, at  506 , to beginning  508 . If, at  504 , it is determined that nonrotating engine is to be started  504   y , system  20  then proceeds with a cold start operation  510  as described above, wherein engine  22  is cranked from a rest and subsequently started. Notably, system  20  may engage pinion  44  with ring gear  32  after engine  22  comes to rest to subsequently facilitate a quicker cold start if the vehicle is operational. 
     If, at  502 , it is determined that engine  22  is rotating  502   y  and therefore not at rest, ECU  28  determines, at  512 , whether an engine auto-stop shutdown event has occurred or stop-start mode has been entered. 
     If, at  512 , it is determined that an engine stop-start mode has not been entered  512   n , process  500  returns, at  506 , to beginning  508  and system  20  continues monitoring for a stop-start mode condition. If, at  512 , it is determined that an engine stop-start mode has been entered  512   y , ECU  28  determines, at  514 , whether an engine restart request has been issued. 
     If, at  514 , it is determined that an engine restart request has not been issued  514   n , process  500  returns, at  506 , to beginning  508 . If, at  514 , it is determined that an engine restart request has been issued  514   y , then, at  516 , ECU  28  determines whether the speed of engine  22  is high enough to allow starter motor pre-spin in preparation for pinion  44  to engage rotating ring gear  32  and starter  24  to crank engine  22 . 
     If, at  516 , it is determined that engine speed is of sufficient magnitude to allow starter motor pre-spin in preparation for pinion  44  to engage rotating ring gear  32 ,  516   y , then, at  518 , motor switch  90  is closed and contactor  76  of motor relay switch  68  shunts terminals  78 , whereby battery voltage is applied to starter motor  40 , energizing the motor and causing it to begin spinning. ECU  28  continuously monitors the rotational speed of engine  22  while also determining the speed of pinion  44 . In some embodiments of system  20 , the speed of pinion  44  is determined by monitoring the voltage of battery  26  as a function of time after battery voltage is applied to motor  40 , and applying a measured curve fit of the speed of motor  40  during its acceleration. Although the rotational speed of pinion  44  as a function of time can be theoretically modeled, experimental analysis of a motor  40  followed by curve fitting of the response has yielded a more accurate result. The speed of motor  40 , and thus the speed of pinion  44 , varies as a function of time and applied voltage. If the time t elapsed since motor activation is less than 0.3 seconds (t&lt;0.3 seconds), the expression set out in closed-form quartic equation (1) has been found useful for calculating the speed of pinion  44 :
 
pinion speed=−108752·( V− 0.9)/(12−0.9)· t   4 +283908·( V− 0.9)/(12−0.9)·t 3 −166874·( V− 0.9)/(12−0.9)· t   2 +38127·( V− 0.9)/(12−0.9)· t− 95  (1)
 
where V is the actual applied motor voltage and the resulting pinion speed is in RPM at a 1:1 motor-to-pinion speed ratio within starter  24 . If time t elapsed since motor activation is greater than or equal to 0.3 seconds (t≧0.3 seconds), then the pinion speed is a constant, predetermined level presumed to be about 3109 RPM.
 
     Alternatively, in some embodiments of system  20 , the control circuit of ECU  28  can perform a running evaluation of pinion speed by updating the result (i.e., the predicted speed of the starter pinion) over a continual series of small, discreet time steps each of duration t. In other words, a step-by-step evaluation of pinion speed would continue whereby the predicted pinion speed is determinable based on dynamic applied motor voltage (which changes with time) and time. For example, starting at the initial time step of duration t immediately following motor energization, ECU  28  can calculate the pinion speed over this time step based on either the average, the starting, or the final applied motor voltage during this time step. Each time step t, which is the ECU&#39;s pinion speed update interval, will be small; therefore, the stepped error will be also be small. Over each subsequent time step the ECU would compute the new pinion speed based on the initial pinion speed of that respective time step. This process continues for each of the series of discreet time steps, and a running evaluation of pinion speed based on equation (1) is obtained based on small, discreet time steps t, with the resulting speed of each step added to the speed calculated in the respective, immediately prior time step. Thus, the speed of pinion  44  at a particular time after motor energization is calculated in a manner to account for time-varying voltage. 
     Following step  518 , ECU  28  then, at  520 , compares the relative speeds of pinion  44  and ring gear  32  and determines whether the speed of pinion  44 , which may be calculated by an above-described method, is greater than or equal to the speed of ring gear  32 . If, at  520 , it is determined that the speed of pinion is not at least that of ring gear  32 ,  520   n , process  500  returns to above-described step  516 , wherein ECU  28  again determines whether the engine speed is high enough to pre-spin starter motor  40  in preparation for engaging pinion  44  with still-rotating ring gear  32 . If, at  520 , it is determined that the speed of pinion is at least that of ring gear  32 ,  520   y , pinion  44  is ready to engage ring gear  32  and begin cranking engine  22 , and pinion solenoid assembly  60  is activated at step  522 , thereby moving rotating pinion  44  from its retracted state towards its extended state. 
     In the embodiment of system  20  shown in  FIG. 4 , which employs second embodiment starter  24 , ECU  28  is configured and arranged to separately regulate the current flows through pinion solenoid coil  64  of pinion solenoid assembly  60 , and motor relay solenoid coil  74  of motor relay solenoid  70 . For example, ECU  28  can comprise, or be in communication with, pinion switch  92  through which pinion solenoid assembly  60  is operated in a substantially “on-off” fashion, with pinion switch  92  at least partially regulating current flow to pinion solenoid coil winding  64 . Upon receiving such an “on” signal from ECU  28 , pinion switch  92  is closed, at  522  of  FIG. 5 , to energize pinion solenoid coil winding  64 , which results in pinion solenoid plunger  62  moving against its biasing member  66 . Such movement of pinion solenoid plunger  62  effects movement of shift lever  80 , which in turn effects the movement of pinion  44  out of its retracted state, in which it is out of engagement with ring gear  32 , and towards its extended state, in which it is enmeshed with ring gear  32 . Pinion  44  thus becomes engaged with ring gear  32  at step  522 . Process  500  then continues to step  524 , at which ECU  28  determines whether the engine restart request is still active. 
     If, at  524 , it is determined that the engine restart request is still active  524   y , ECU  28  continues battery voltage application to both motor switch  90  and pinion switch  92  at step  526 , resulting in continued rotation and/or acceleration of motor  40  and cranking of engine  22 . At  528 , ECU  28  subsequently determines whether engine  22  has restarted. If, at  528 , it is determined that engine  22  has not restarted  528   n , process  500  returns to  526  and ECU  28  continues applying battery voltage to both motor switch  90  and pinion switch  92 . If, at  528 , it is determined that engine  22  has restarted  528   y , process  500  returns at  506  to beginning  508 . 
     If, at  524 , it is determined that the engine restart request is not still active  524   n , ECU  28  determines, at  530 , whether engine  22  has stopped, i.e., come to rest. If, at  530 , it is determined that engine  22  has not stopped and is still rotating  530   n , process  500  returns to above-discussed step  524  wherein it is determined whether the engine restart request is still active. If, at  530 , it is determined that engine has come to rest  530   y , ECU  28  opens pinion switch  92  at step  532 , deactivating pinion solenoid assembly  60 , and process  500  then returns, at  506 , to beginning  508 . 
     Some embodiments of system  20  alternatively operate to provide synchronous stop-start engagement of starter  24  and ring gear  32  if ECU  28  determines that a stop-start mode has been initiated  512   y  on the basis of data received from ring gear position sensor  30  and used, if an engine restart request has been issued  514   y , to determine at  516  whether the speed of engine  22  is high enough to allow starter pre-spin in preparation to crank the engine. If, at  516 , it is determined that the engine speed is high enough to allow starter pre-spin in preparation for cranking the still-rotating engine  516   y , the consequent steps of process  500  are those described above. If, however, at  516 , ECU  28  determines that the speed of engine  22  is not high enough to allow starter  24  pre-spin  516   n , ECU  28  then determines, at  534 , whether there is sufficient time to engage pinion  44  and ring gear  32  prior to rock-back of engine  22 . 
     If, at  534 , it is determined that that there is sufficient time to engage pinion  44  and ring gear  32  prior to rock-back of engine  22 ,  534   y , pinion solenoid assembly  60  is activated at  536 . If, at  534 , it is determined that that there is not sufficient time to engage pinion  44  and ring gear  32  prior to rock-back of engine  22 ,  534   n , pinion solenoid assembly  60  is activated immediately after engine rock-back, at  538 , when engine  22  is at rest. Following step  536  or  538 , process  500  then proceeds to above-described step  524  wherein it is determined whether the engine restart request is still active. The above-described steps consequent to  524   y  or  524   n  then follow. 
       FIG. 6 , which is similar to  FIG. 3 , shows graph  600  representing speeds  602  of engine ring gear  32  along curves  602  and  614 , and the speed of starter pinion  44  along curves  610  and  614 , over time  618 . Graph  600  also indicates the corresponding times at which motor switch  90  (and motor relay solenoid assembly  70 ) and pinion switch  92  (and pinion solenoid assembly  60 ) change between their respective off and on states, i.e., the times at which the respective switches are open or closed, respectively. Following engine deceleration from idle speed after occurrence of an engine auto-stop event, engine  22  may be restarted as illustrated.  FIG. 6  illustrates that during the first 0.2 seconds of a deceleration from a normal engine idle speed of about 700 RPM, motor switch  90  and pinion solenoid switch  92  are in their off states, (i.e., the switches are both open). If an engine restart request is present, motor switch  90  is turned on or closed by ECU  28  when ring gear  32  reaches threshold or trigger speed  622 , and battery voltage is applied to motor relay coil  74 , thereby energizing motor  40 . Trigger speed  622  is that at which engine  22  cannot restart itself without help from starter  24 ; trigger speed  622  may be, for example, 500 RPM. Motor  40  accelerates and engine  22  further decelerates over a short period of time and, at a predetermined elapsed time thereafter pinion switch  92  is turned on or closed by ECU  28 , and battery voltage is applied to pinion solenoid coil  64  of pinion solenoid assembly  60 , which immediately moves pinion  44  form its retracted position and towards its extended position, in which it engages engine ring gear  32 . 
     For various reasons, in some cases it may not be required that starter system  20  assure that the speeds of rotating starter pinion  44  and rotating ring gear  32  be synchronized at the time of their engagement. For example, pinion  44  may have become engaged with ring gear  32  prior to issuance of the engine restart request signal. However, once starter  24  and engine  22  are engaged, at point  630 , and engine  22  is being cranked, the rotational speed of the engine increases or is maintained under urging of starter  24  until restart occurs, with the ring gear and pinion both following curve  614  in  FIG. 6 . 
       FIG. 7 , which is similar to  FIG. 6 , shows graph  700  representing the speeds  702  of engine ring gear  32  along curves  706  and  714 , and the speed of starter pinion  44  along curves  710  and  714 , over time  718 . Graph  700  also indicates the corresponding times at which motor switch  90  (and motor relay solenoid assembly  70 ) and pinion switch  92  (and pinion solenoid assembly  60 ) change between their respective off and on states, i.e., the times at which the respective switches are open or closed, respectively. Following engine deceleration from a normal idle speed after occurrence of an engine auto-stop event, engine  22  may be restarted as illustrated.  FIG. 7  shows the change from a normal idle speed of about 700 RPM, and a subsequent deceleration. At this time, switches  90  and  92  are initially in their off states (i.e., the switches are both open). An embodiment of starter system  20  can be configured and arranged to activate motor solenoid coil  74  to spin starter motor  40  if an engine restart request is present, when the engine speed decelerates to threshold or trigger speed  722  at or below which engine  22  cannot restart itself without help from the starter  24 . When engine  22  reaches trigger speed  722 , which may, for example, be 500 RPM, motor switch  90  is closed and battery voltage applied across to motor relay switch  68 , resulting in motor  40  being energized as discussed above. Over a short period of time after motor  40  is energized, its speed rises and, when starter  24  reaches a maximum free rotational speed along curve  710 , system  20  closes pinion switch  92 , which applies battery voltage to pinion solenoid coil  64 . Consequently, pinion  44  is immediately brought into engagement with ring gear  32  at point  730 . Once starter  24  and engine  22  are engaged, the engine enters a cranking phase in which rotational speed of engine  22  increases under urging of starter  24  until engine restart occurs, with the engine and starter speeds indicated along curve  714  in  FIG. 7 . 
     In some embodiments, system  20  is configured and arranged such that if, upon issuance of an engine restart request after engine shut-down, the engine speed is determined to not be high enough to pre-spin motor  40  for restarting the decelerating engine, ECU  28  subsequently applies a control algorithm based on the status of engine rock-back, a state in which the engine is rotating at a slow rate of speed in an direction opposite to that of normal operation before coming to rest. Engine rock-back occurs because of the re-expansion of gases compressed in at least one engine cylinder. 
       FIG. 8  provides a graphical representation of engine and starter speeds during engine shutdown and restart under an engine rock-back scenario. Graph  800  shows the speeds  802  of engine ring gear  32  along curves  806  and  814 , and the speed of starter pinion  44  along curve  814 , over time  818 . Graph  800  also indicates the corresponding times at which motor switch  90  (and motor relay solenoid assembly  70 ) and pinion switch  92  (and pinion solenoid assembly  60 ) change between their respective off and on states, i.e., the times at which the respective switches are open or closed, respectively.  FIG. 8  shows the speed of ring gear  32  changing from a normal idle speed of, for example, about 700 RPM, through a subsequent deceleration after engine shutdown, to engine rock-back event  826 . As described earlier, if an engine restart request exists and ECU  28  determines there is not sufficient time to engage pinion  44  and ring gear  32  prior to engine rock-back (see  534   n  in  FIG. 5 ), ECU  28  activates pinion solenoid assembly  60  once engine  22  comes to rest immediately after engine rock-back, at point  830  of  FIG. 8 , at which point pinion  44  and ring gear  32  become enmeshed. Referring again to  FIG. 5 , ECU  28  then determines, at  524 , whether the engine restart request is still active. If, at  524 , it is determined that the engine restart request is still active,  524   y , ECU  28  closes motor switch  90  and pinion switch  92  substantially simultaneously, applying battery voltage to both motor relay solenoid coil  74  and pinion solenoid coil  64 , resulting, at point  830  of graph  800 , in the engagement of pinion  44  and ring gear  32  and the start of rotation, and the continued acceleration (to a speed no greater than a presumed predetermined, maximum speed), of enmeshed pinion  44  and ring gear  32  along curve  814  and the subsequent starting of engine  22 . Steps of process  500  consequent to ECU  28  determining, at  524 , that the engine restart request is not still active  524   n  are described above. Notably, restarting of engine  22  in this manner after encountering engine rock-back event  826  may be accomplished utilizing first or second embodiment starter  24 , and is similar to a cold start event. 
     As mentioned above, in some embodiments of system  20  a comparison of stator pinion and ring gear speeds is made by ECU  28  to synchronize the speed of starter  24  with the speed of the decelerating ring gear  32 , the latter of which is determinable from the signals received from sensor  30  by ECU  28 . In such embodiments, synchronous engagement of starter pinion  44  and ring gear  32  may be achieved by intermittently applying and discontinuing battery voltage to starter motor  40 , causing the speed of pinion  44  to increase and decrease in a predictable manner to substantially match the speed of ring gear  32 ; once their speeds are matched, pinion  44  is moved from its retracted state into its extended state and smoothly engages ring gear  32 , and starter  24  may then crank engine  22  to a speed at which the engine is restarted. The rotational speed of an energized starter motor  40  of the size of most interest for a starter  24  included in the various embodiments of system  20 , will accelerate and decelerate in a predictable manner as electrical power to it is intermittently applied and discontinued. 
       FIG. 9  shows the rotational speed of pinions  44  of such starters  24  during free speeding of their starter motors  40 , subsequent to motor energization at a given voltage level. As represented by the test data shown in  FIG. 9 , the acceleration rates of these motors  40  are substantially consistent. Pinions  44  of such starters  24  have also been shown to consistently decelerate at a substantially uniform and linear rate once power to their motors  40  is discontinued, as represented by the test data shown in  FIG. 10 . Thus, the speed of unloaded pinion  44  is demonstrably predictable as a function of time. If, for example, after energization of motor  40  the speed of starter pinion  44 , determinable by the elapsed time after motor energization, climbs to a level that is higher than the monitored speed of ring gear  32 , ECU  28  can open motor switch  90 , thereby de-energizing motor coil  74  and causing motor relay switch  68  to open, which interrupts the power application to motor  40  and causes rotation of pinion  44  to decelerate in a predictable manner to a speed determinable by the elapsed time after motor de-energization. Intermittent applications of power to motor  40 , repeatedly if necessary, can thus synchronize the speeds of pinion  44  and ring gear  32 . Once their speeds are suitably matched, these gears may be smoothly engaged and engine cranking thereafter performed. 
     As mentioned above, the rotational speed of pinion  44  can also be modeled. In some embodiments of starter system  20 , ECU  28  can perform an integration of the speed of pinion  44  to account for time-varying voltage, and this information can be used by starter system  20  to control various switches and solenoids to implement a synchronous engagement of starter pinion  44  and engine ring gear  32 . The speed of starter motor  40  can be determined by evaluating the voltage as a function of time applied to the motor, along with a measured curve fit of motor acceleration. For example,  FIG. 11  shows a computed rotational speed of pinion  44  according to one exemplary embodiment of system  20 , wherein, if the time t elapsed since motor activation is less than 0.3 seconds (t&lt;0.3 seconds), the speed y of pinion  44  in RPM is calculated by ECU  28  as a function of time by the formula set out in closed-form quartic equation (2):
 
 y=− 108752· t   4 +283908· t   3 −166874· t   2 +38127· t− 95  (2)
 
     As  FIG. 11  shows, the smooth curve fit line closely correlates to the pinion speed data obtained from testing, with a statistical coefficient of determination (known by those skilled in the art as R 2 ) of 0.9975. If time t elapsed since motor activation is greater than or equal to 0.3 seconds (t≧0.3 seconds), then the pinion speed is a constant, predetermined level presumed to be about 3109 RPM. Furthermore, the speed y of pinion  44  in RPM also varies as a function of voltage applied to starter motor  40 , which, for t&lt;0.3 seconds, leads to the formula set out in closed-form quartic equation (3):
 
 y=− 108752·( V− 0.9)/(12−0.9)· t   4 +283908·( V− 0.9)/(12−0.9)·t 3 −166874·( V− 0.9)/(12−0.9)·t 2 +38127·( V− 0.9)/(12−0.9)·t−95  (3)
 
in which V is the actual applied motor voltage and t, as above, is the time elapsed in seconds since motor activation. As indicated above, if time t elapsed since motor activation is greater than or equal to 0.3 seconds (t≧0.3 seconds), then the pinion speed is a constant, predetermined level presumed to be about 3109 RPM.
 
     In other embodiments of starter system  20 , ECU  28  can perform an incremental evaluation of the speed of pinion  44  in a manner similar to that described above to account for time-varying voltage. That is, the control circuit of ECU  28  can perform a running evaluation of pinion speed by updating the result (i.e., the predicted speed of the starter pinion) over a continual series of small, discreet time steps each of duration t. A step-by-step evaluation of pinion speed would continue whereby the predicted pinion speed is determinable based on dynamic applied motor voltage (which changes with time) and time. As described earlier, starting at the initial time step of duration t immediately following motor energization, ECU  28  can calculate the pinion speed over this time step, and, over each subsequent time step, the ECU would compute the new pinion speed based on the initial pinion speed of that respective time step, with the resultant speed added to that calculated for the immediately prior time step. This process continues for each of the series of discreet time steps, and a running evaluation of pinion speed is therefore obtained incrementally on the basis of small, discreet time steps. Thus, the speed of pinion  44  at a particular time after motor energization is calculated in a manner to account for time-varying voltage. 
     Furthermore, the time-varying voltage can be accurately modeled as demonstrated by the overlapping curves for 12V, 11V, and 10V voltage variations shown in  FIG. 12 . In some embodiments as shown, the individual curves for the rotational speed of pinion  44  substantially overlap, demonstrating the accuracy of the model at various voltages applied to motor  40 . In  FIG. 12 , the three curves (each representing a run at one of three different applied voltages) lay on top of each other when normalized to 12V operation, indicating that the effects of voltage variation on starter speed can be accurately modeled. 
     Moreover, as shown in  FIG. 13 , the accuracy of the model is not significantly affected by changes in starter motor temperature. As depicted, modeled data for pinion speed over three separate runs demonstrates that the models substantially overlap and are not significantly affected by temperature. The test was conducted by consecutively running a starter motor  40  for three (3) cycles, each of three (3) seconds on and two (2) seconds off, during which time the temperature of the copper windings in motor  40  would have been raised by 20-50° C. and the temperature of its motor brushes would have been raised by 50-100° C. In  FIG. 13 , the three curves (each representing one of the three consecutive runs) lay on top of each other, indicating that temperature variation is not a significant factor affecting pinion speed over the range of temperatures tested. 
     Accordingly, regardless of embodiment of starter system  20 , the rotational speed of motor  40 , and thus of pinion  44 , at a predetermined time, may be predicted on the basis of elapsed time after energization of motor  40 ; in some embodiments, the speed prediction may even account for variances in the applied motor voltage. In each embodiment or operational mode of system  20 , the time of starter motor activation and the applied starter motor voltage (which may be assumed to be battery voltage, and which may, in some embodiments, further be assumed to be, for example, a constant 12V,) are parameters that typically are already known or sensed and provided to the vehicle/engine electronics system, and thus to ECU  28 . As such, implementation of starter system  20  requires no dedicated, additional sensor(s) for obtaining the predicted speed of pinion  44  at a predetermined time after starter motor energization, facilitating its smooth engagement with engine ring gear  32 , regardless of whether engine  22  is to be cranked while already rotating (i.e., a warm start) or from rest (i.e., a cold start). From the preceding description, it can also be understood that each embodiment of starter system  20  facilitates determination of the starter pinion speed in an open loop manner, without the need for a control scheme reliant upon closed loop feedback by which the starter motor or pinion position or speed is sensed. Therefore, starter system  20  requires no dedicated, additional sensor(s) for obtaining the predicted speed at a predetermined time after starter motor energization, thereby simplifying starter system packaging and minimizing part complexity. Thus, incorporation of starter system  20  simplifies starter system packaging and minimizes system part complexity vis-à-vis prior starter systems having engine stop-start operation capabilities. 
     It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto.