Patent Publication Number: US-2012024252-A1

Title: System and method for starting an engine using low electric power

Description:
TECHNICAL FIELD 
     The invention relates to a system and method for starting an engine using low electric power. 
     BACKGROUND 
     In a motor vehicle, the vehicle&#39;s engine, such as an internal combustion engine, is typically rotated via a starter to cause the engine to begin powering itself. Such a starter is typically powered electrically, and draws its power from an energy storage device arranged on-board the vehicle. 
     In some vehicle applications, a stop-start system is employed, where the engine is automatically stopped or shut off to conserve fuel when vehicle propulsion is not required, and is then automatically restarted by a starter when vehicle drive is again requested. Such a stop-start system may be employed in a conventional vehicle having a single powerplant, or in a hybrid vehicle application that includes both an internal combustion engine and a motor/generator for powering the vehicle. 
     SUMMARY 
     A method is disclosed herein for starting an engine that is employed for propulsion of a vehicle. The method includes determining that an engine start via a starter is desired, wherein the starter is powered by an energy storage device that is arranged in the vehicle. The method also includes determining a state of charge of the energy storage device. The method additionally includes commanding the starter to crank the engine at a first predetermined speed, if the energy storage device is at or above a predetermined state of charge and supplying a fuel to the engine for a first predetermined number of fueling events. A state of charge of the energy storage device being at or above the predetermined state of charge signifies that the energy storage device is capable of providing a predetermined level of power. Furthermore, the method includes commanding the starter to crank the engine at a second predetermined speed that is lower than the first predetermined speed and supplying the fuel to the engine for a second predetermined number of fueling events, if the energy storage device is below the predetermined state of charge. A state of charge of the energy storage device being below the predetermined state of charge signifies that the energy storage device is incapable of providing the predetermined level of power. 
     According to the method, the acts of determining and commanding may each be accomplished via a controller in operative communication with each of the starter and the energy storage device. Additionally, according to the method the second predetermined number of fueling events may be greater than the first predetermined number of fueling events. 
     Additionally, the method may include determining a content of ethanol in the fuel. Furthermore, the method may include commanding the starter to crank the engine at the first predetermined speed, if the energy storage device is at or above the predetermined state of charge, whether the content of ethanol in the fuel is at, above, or below a predetermined level. Moreover, the method may include commanding the starter to crank the engine at the second predetermined speed, if the content of ethanol is at or above the predetermined level and the energy storage device is below the predetermined state of charge. 
     The engine may include a stop-start capability, and the vehicle may be a hybrid electric type that includes a motor/generator employed for propulsion of the vehicle. 
     A system for starting an engine employed for propulsion of a vehicle is also disclosed. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a motor vehicle powertrain, including a system for starting an engine; and 
         FIG. 2  is a flow chart illustrating a method for starting an engine employed for propulsion of a vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a schematic view of an exemplary embodiment of a starter system  5 , a.k.a. a system for starting an internal combustion engine  10 . Starter system  5  includes engine  10  that is employed for propulsion of a vehicle. Engine  10  receives a supply of fuel in discrete fueling events, wherein such fuel is combined with air into a fuel-air mixture for subsequent ignition via a spark plug (not sown) to thereby generate combustion and produce power. Although, as illustrated, starter system  5  is employed in a hybrid-electric vehicle powertrain, the system may be used in any vehicle powertrain having engine  10 . 
     Engine  10  includes a flywheel (or a flex-plate)  12  attached to a crankshaft (not shown) of the engine, and, as such, rotates at the same speed as the engine. Flywheel  12  is typically attached to the crankshaft via fasteners such as bolts or screws (not shown). A ring gear  14  having a specific gear tooth profile and spacing, is arranged on the outer perimeter of the flywheel  12 . Ring gear  14  typically has an outer diameter that is designed to facilitate effective starting of engine  10 , as understood by those skilled in the art. A starter  16  is arranged relative to the engine  10  in close proximity to the ring gear  14  for starting the engine. Starter  16  may be mounted directly on the engine to reduce the effect of manufacturing tolerances, as shown in  FIG. 1 . 
     Starter  16  includes an electric motor  18  that is employed to rotate a pinion gear  20 . Pinion gear  20  includes a gear tooth profile and spacing that corresponds to that of the ring gear  14  for accurate meshing and engagement therewith. Starter  16  also includes a pinion engagement solenoid assembly  22 , which incorporates a motor solenoid  24  and a pinion-shift solenoid  26 . Electric motor  18  is activated by motor solenoid  24  via an electrical connection  28  or via a suitable lever arrangement (not shown), in order to rotate pinion gear  20  up to a predetermined speed. Pinion-shift solenoid  26  is configured to energize a lever arrangement  30 . When energized by the pinion-shift solenoid  26 , lever arrangement  30  in turn displaces pinion gear  20  for meshed engagement with the ring gear  14 , in order to start engine  10 . 
     An energy storage device  32 , such as a battery, is arranged in the vehicle to selectively accept/store an electrical charge and, on demand, power various devices, including the starter  16 . While being used for its intended purpose, energy storage device  32  may become depleted of its electrical charge, such that the energy storage device becomes incapable of providing a predetermined requisite level of power. With respect to starter  16 , such a predetermined level of power is established based on the first predetermined cranking speed of engine  10  at which the engine may be started during a specific number of cranking revolutions. During the starting of engine  10 , each engine cranking revolution is accompanied by a fueling event adapted to deliver an appropriate amount of fuel to the engine in order to affect the firing, combustion, and sustained rotation of the engine. 
     The first predetermined cranking speed necessary to fire and start the engine is typically determined empirically during testing and calibration of engine  10 . In a situation when energy storage device  32  becomes depleted of its electrical charge, starter  16  may be incapable of cranking the engine  10  at the first predetermined cranking speed. In such a situation, the state of charge of the energy storage device  32  may only be sufficient to deliver sufficient power to the starter  16  to crank engine  10  at a second predetermined cranking speed that is lower than the first predetermined cranking speed. When engine  10  is cranked with the energy storage device  32  below its predetermined state of charge, the same number of engine revolutions as when the state of charge is higher may be insufficient to start the engine. Therefore, if the engine  10  needs to be started with energy storage device  32  below the predetermined state of charge, the speed of starter  16  will be lowered to the second predetermined cranking speed, while the number of fueling events may need to be increased. 
     Fuel is delivered to engine  10  from a fuel tank  34  via a fuel pump  36 . Fuel pump  36  may be powered by the energy storage device  32  to operate engine  10  on demand. The energy content of a fuel being used to operate engine  10  influences how much of the particular fuel must be provided during each engine revolution cranked by starter  16 . In particular, a content of ethanol in the fuel is a significant factor in starting engine  10 , because ethanol contains approximately 34% less energy per unit volume than gasoline. Hence, when a fuel being used contains a significant percentage of ethanol, especially during low electric power engine starting conditions, the amount of fuel per each fueling event must be increased along with the number of engine revolutions generated by starter  16 . 
     System  5  may be employed in any vehicle having an engine  10 , but is particularly beneficial in a vehicle where engine  10  has a stop-start feature. As is known by those skilled in the art, a stop-start feature in an engine is where the engine is capable of being shut off when engine power is not required, but which may also be immediately restarted when engine power is again called upon to power the vehicle. As shown in  FIG. 1 , system  5  may also include a transmission  38  that is connected to engine  10  for transmitting engine power to drive wheels (not shown) of the subject vehicle. Transmission  38  includes an appropriate gear-train arrangement, which is not shown, but the existence of which will be appreciated by those skilled in the art. Arranged inside transmission  38  is a motor-generator  44 . Motor-generator  44  is employed for propulsion of the subject vehicle either in concert with, or unaccompanied by engine  10 . Engine  10  is capable of being shut off when the motor-generator  44  is running, such that the system  5  may be employed even while the subject vehicle is on the move. 
     A controller  42  is arranged on the vehicle relative to the engine  10  and transmission  38 , and configured to control operation of both the engine and the transmission, including the shutting down and restarting of the engine during the stop-start procedure. Additionally, controller  42  is in operative communication with each of the starter  16  and the energy storage device  32 . Controller  42  is programmed to activate starter  16  on demand to extend the pinion gear  20  and restart engine  10 , based on predetermined vehicle operating parameters. The appropriate vehicle operating parameters may be predetermined empirically during calibration and testing phases of vehicle development, with the aim of optimizing performance, drivability and efficiency of the subject vehicle. 
     A method  50  for starting engine  10  employed for propulsion of a vehicle is shown in  FIG. 2 , and described below with reference to the structure shown in  FIG. 1 . Method  50  commences in frame  52  with determining that a start of engine  10  via starter  16  is desired. Such an engine start may be affected while the subject vehicle is either stationary or in motion, and is likewise applicable for either an ordinary engine start or for an engine restart during a stop-start maneuver. Following frame  52 , the method proceeds to frame  54 , where it includes determining a state of charge of the energy storage device  32 . 
     If the state of charge of the energy storage device  32  determined in frame  54  is at or above the predetermined state of charge, and is thus capable of providing the predetermined level of power to starter  16 , the method advances to frame  56 . In frame  56 , the method includes commanding starter  16  to automatically crank engine  10  by spinning flywheel  12  at the first predetermined speed. As described above, the first predetermined speed represents the engine speed required to crank, fire, and start engine  10  during the first predetermined number of fueling events. If the state of charge of the energy storage device  32  determined in frame  54  is below the predetermined state of charge, and is thus incapable of providing a predetermined level of power to starter  16 , after frame  54  the method advances to frame  58 . 
     In frame  58 , the method includes commanding starter  16  to automatically crank engine  10  at the second predetermined speed that is lower than the first predetermined speed. As described above, the second predetermined speed represents the speed that may be used to crank, fire, and start engine  10  when accompanied by the second predetermined number of fueling events while the state of charge of energy storage device  32  is below the predetermined state of charge. Hence, notwithstanding the depleted state of charge of starter  16 , by cranking engine  10  at the second predetermined speed, the method allows the engine to be started. The method will typically terminate in frame  60  upon the firing and starting of engine  10 . 
     The method  50  may additionally include determining a content of ethanol in the fuel and regulating starter  16  to crank engine  10  at the first predetermined engine speed when energy storage device  32  is at or above the predetermined state of charge. In such a situation, starter  16  is employed to crank engine  10  at the first predetermined engine speed whether the content of ethanol in the fuel is at, above, or below a predetermined level. Furthermore, the method may then proceed with commanding starter  16  to automatically crank engine  10  at the second predetermined speed, if the content of ethanol is at or above the predetermined level and energy storage device  32  is below the predetermined state of charge. 
     The predetermined, i.e., threshold, content of ethanol in the fuel at and above which the ease of starting and firing of engine  10  is sufficiently affected is typically established empirically during testing and calibration of the engine. The second predetermined speed of starter  16  may be accompanied by the second predetermined number of fueling events which may be greater than the first number of fueling events in order to facilitate the firing and starting of engine  10 . All of the above acts of determining and commanding may be accomplished by the controller  42  in order to provide the most effective starting of engine  10  despite a low power condition of energy storage device  32 , and/or a high content of ethanol in the fuel supplied by fuel pump  36 . 
     Overall, the number of revolutions and fueling events required to fuel, fire, and start engine  10  when the state of charge of energy storage device  32  is below the predetermined state of charge may need to increase when starter  16  operates at the second predetermined speed. Additionally, accompanying the reduced starter speed with an increased number of fueling events may become particularly advantageous when the content of ethanol in the fuel is sufficiently high so as to additionally negatively impact the starting of engine  10 . 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.