Patent Publication Number: US-7218010-B2

Title: Engine restart apparatus and method

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus and method to quickly and efficiently restart a start-stop “mild hybrid” internal combustion engine by separating the pinion gear shuttling circuit from the starter motor power relay circuit, pre-shuttling the pinion gear to the flywheel ring gear, and providing the power relay with a “prime current” to reduce the time lag before restart. 
     BACKGROUND OF THE INVENTION 
     With the current thrust for more fuel efficient and low emission vehicles, many novel solutions for internal combustion engine architectures and operating strategies have been developed. One such strategy is to simply shut off the engine when the engine is operating in an idle mode. Many configurations have been proposed to effect a quick restart of the engine. The simplest and most cost effective systems incorporate a traditional or “off the shelf” starter/pinion gear and flywheel/ring gear configuration. As such, this type of start-stop strategy has minimal impact on engine and transmission architectures compared to other hybrid strategies. The response time of this system may be lengthy, which is an important consideration as automakers try to deliver seamless vehicle restart and launch. The time required to energize the traditional power relay switching and the drive gear engagement mechanisms of the starter account for a significant fraction of the total delay time. 
     This delay time can be better understood by way of explanation of the operation of a traditional starting system. The typical starter controls found in a vehicle today have the starting contacts contained within a key operated ignition switch. However, a pedal operated ignition switch may be employed for a “mild hybrid” configuration. When the ignition key is turned against spring pressure from the “on” position to the “start” position, the starting contacts close. This in turn connects a starter motor solenoid to the vehicle battery. A solenoid is required since the starter motor needs a massive feed of electrical current from the battery to set its internal components working. 
     Upon connection, coils contained within the solenoid become energized producing a magnetic field that pulls an armature inward. This armature engages a pinion actuator at one end, which in turn shuttles a pinion gear mounted to the starter motor shaft to engage the ring gear of the engine&#39;s flywheel. Located behind the pinion gear is a coil spring that will ensure that the pinion gear meshes with the flywheel ring gear in the event the gear teeth do not mesh properly in a condition referred to as “butting”. Simultaneously, the armature movement forces a heavy switch to connect the starter motor to the battery and engine cranking will begin. The coils within the solenoid are of a sufficient magnetic strength to simultaneously shuttle the pinion gear and close the starter motor switch. A spring on the pinion actuator pulls the pinion out of mesh when the current to the solenoid is interrupted upon engine start. Although this method requires a lag time of only seconds, a more responsive method is desirable to ensure seamless operation of a start-stop “mild hybrid”. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention seeks to reduce the aforementioned lag time in the engine starting system for a start-stop “mild hybrid” engine utilizing a conventional engine starter and flywheel as well as providing a method to operate such a system. 
     The present invention separates the solenoid, which shuttles the pinion gear to the flywheel ring gear while providing the power connection to the starter motor, into two discrete circuits. The solenoid is retained to shuttle the pinion gear, however, a separate power relay provides the electrical connection between the battery and the starter motor. Controlled current sources, such as pulse width modulation devices, may be provided to allow both the pinion shuttle solenoid and the power relay to be energized with differing levels of current at different times during an engine stop condition. 
     By way of example, when the engine is stopped, the pinion shuttle solenoid is energized to the maximum pull-in current for a predetermined time to allow the pinion gear to shuttle to, and engage the flywheel ring gear. Should the teeth not mesh properly, in a condition referred to as a “butting”, a coil spring is provided behind the pinion gear to hold the pinion gear against the flywheel. The current to the solenoid is then reduced to a “holding level”. This holding level is also predetermined and dependent on the amount of current required to keep the pinion gear meshed with the flywheel ring gear teeth. An alternative method of accomplishing this reduced current “holding” state would be to provide two separate coils in the solenoid and allow one coil circuit to open when the solenoid armature is at full stroke. Concurrent with the pinion gear pre-shuttling operation, the power relay is provided a “prime current”. This “prime current” allows the coil current in the relay to build to a level just below the point at which switching will occur, thereby eliminating much of the time lag inherent when switching a power relay absent a “prime current”. Both the pinion gear and power relay are now in a favorable condition to allow a quick restart of the engine when a restart request is made. 
     Accordingly, the invention provides an internal combustion engine that is operable in start-stop mode which has: a starter motor having a pinion gear, a power relay for switching the starter motor, a battery for providing current to the starter, a pinion actuator solenoid for shuttling the pinion gear, a control unit with logic for operating said pinion actuator solenoid separately from the power relay, and a controlled current source for the power relay to provide a prime current level during engine off conditions and to increase the current to allow for switching of the power relay when a restart signal is sensed by the control unit. Another aspect of the foregoing internal combustion engine may also have a controlled current source for the pinion actuator solenoid that provides a maximum pull-in current for a predetermined amount of time during engine off conditions, and which decreases the current for the pinion actuator solenoid to a holding current at the end of the predetermined amount of time. The controlled current source for the power relay and the controlled current source for the pinion actuator solenoid may be pulse width modulation devices. In an alternative embodiment of the internal combustion engine of this invention, the pinion actuator solenoid may have two coils and an armature actuated set of electrical contacts openable to de-energize one coil, thereby energizing the pinion actuator solenoid at a relatively low current level in response to the control unit. 
     This invention also provides an improved method of current control for fast response to a restart signal for an engine having a flywheel ring gear and a traditional starter with a pinion gear and having a pinion actuator solenoid and a power relay and a control unit. The method includes: controlling current flow to the pinion actuator solenoid at maximum pull-in current for a predetermined amount of time sufficient to allow the pinion gear to shuttle to the flywheel ring gear, thereafter the pinion actuator solenoid current is decreased to a level to hold the pinion gear in mesh with the flywheel ring gear; and separately controlling current flow to the power relay at less than the minimum pull-in current to allow the relay coil current to ramp to a level that is insufficiently high enough to cause power switching of the power relay, but sufficiently high enough to eliminate a significant portion of the time required for the power relay to be switched in response to the restart signal. In an alternative embodiment of this method, the pinion actuator solenoid may have two coils and an armature actuated set of electrical contacts that are openable to energize the pinion actuator solenoid at a relatively low current level in response to the control unit to control the pinion actuator solenoid. 
     This invention further provides an improved system for restarting an engine having a pinion actuator solenoid and a power relay. The system includes: a first controlled current source for energizing the pinion actuator solenoid at a high and low current levels; a second controlled current source for energizing the power relay at a low and high current levels; and a control unit for the controlled current sources operative to control the first controlled current source at the high current level when the second controlled current source is controlled at the low current level; wherein the control unit being operative to control the first controlled current source at the low current level when the second controlled current source is being controlled at the high current level. 
     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 representation of the present invention showing a separate pinion actuator solenoid circuit and a separate starter motor power circuit with a power relay both circuits being energizable by controlled current sources; 
         FIG. 2  is a graphical illustration of the engine start stop control strategy for controlling current to the pinion actuator solenoid; 
         FIG. 3  is a graphical illustration of the engine start stop control strategy for controlling current to the pinion power relay; 
         FIG. 4  is a graphical illustration of the response of a traditional relay to applied current and demonstrates the lag time traditionally associated with energizing the coil within the relay; and 
         FIGS. 5   a  and  5   b  are schematic representations of a two coil pinion actuator solenoid in operation. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is shown schematically in  FIG. 1 . The engine control unit  30  for engine  11  receives various inputs from the on-vehicle sensors  12  such as engine RPM, start/stop requests, vehicle speed, etc. The cranking control unit  10  may be contained in the engine control unit  30  or may be entirely separate. The inputs  12  are processed by the control unit  10  to determine in what state the engine cranking system should be. The control unit  10  is electrically connected to a power relay controlled current source  13  as well as to a pinion actuator solenoid controlled current source  14 . The pinion actuator solenoid controlled current source  14  is connected to the pinion actuator solenoid  15 . The power relay controlled current source  13  is connected to a power relay  16 . The power relay  16  is connected in series linking the battery  17  and the starter motor  18 . The typical voltage for an automotive battery  17  is 12 volts; however, the voltage may be decreased or increased according to the application. The controlled current sources  13 ,  14  in the preferred embodiment will be pulse width modulation (PWM) devices. However, those skilled in the art will recognize that other devices, such as rheostats and analog amplifiers, may be used without changing the inventive concept. 
     The mode of operation for this arrangement will now be explained in further detail with reference to  FIGS. 1 ,  2 , and  3 . When the vehicle comes to rest, a request will be made by the engine control unit  30  to shut down the internal combustion engine  11 . Upon completion of this shut down event  20 , the control unit  10  of the engine cranking system will receive inputs  12 . The inputs  12 , such as engine RPM and vehicle speed, will confirm to the control unit  10  that the engine is in the proper condition to operate the present invention. The control unit  10  will then command the pinion actuator solenoid controlled current source  14  which, in turn, will command the maximum required pull-in current  22 (A) for a predetermined pinion shuttling time  23  allowing the pinion gear  58  (shown in  FIGS. 5   a  and  5   b ) to shuttle to the flywheel ring gear  60  (shown in  FIGS. 5   a  and  5   b ). Current level A is the maximum required solenoid pull-in current level specified by the manufacturer to guarantee pull-in of the pinion actuator solenoid  15 . The applied current is held at level A for the worst case pull-in time. At the completion of the shuttling maneuver  21 , the pinion actuator solenoid controlled current source  14  will then lower the current to the maximum holding current  24 (B) that is required to keep the pinion gear  58  in contact with the flywheel ring gear  60 . Current level B is the maximum holding current specified by the manufacturer that will guarantee that the pinion actuator solenoid  15  will remain in the pulled-in state. Concurrently, at the engine shut down event  20 , the control unit  10  will command the power relay controlled current source  13  to a “prime current” level  25 (C). The “prime current” level C is selected to be lower than the manufacturer specified minimum pull in current for the power relay  16 . This will ensure that the “prime current” level C is at a level of current just below that which the manufacturer specifies is required for switching of the power relay  16 . 
     After a period of time has elapsed, the operator or driver may command the engine  11  to crank, possibly by lifting his or her foot from the brake pedal. During the crank command, e.g. at  26 , the control unit  10  will command the power relay controlled current source  13  to command the maximum available relay current  27 (D). It is at this point that the power relay  16  is energized with sufficient current to allow the switching of the power relay  16  to occur. The time required to switch the power relay  16  has been reduced, since the power relay  16  has been provided a “prime current” level C. Upon switching, the connection between the starter motor  18  and the battery  17  will close causing the starter motor  18  to spin the pre shuttled pinion gear  58  against the flywheel ring gear  60  thereby cranking the engine  11 . Upon engine start  28 , the crank command is discontinued and the control unit  10  will cause both the power relay controlled current source  13  and the pinion actuator solenoid controlled current source  14  to disallow any current to both the power relay  16  and the pinion actuator solenoid  15 . 
       FIG. 4  is a graphical illustration of the response of a typical or traditional power relay  16  to an applied current. Even though the maximum available relay current level D is applied to the relay at T 0 , the armature of the relay does not begin to move until T 2 . This time lag can be attributed to the electro-magnetic “build up” required by the coil within the power relay  16 . At T 3  the armature is at full stroke. The total time from application of maximum available relay current D to the point in which the relay armature is at full stroke may be characterized by subtracting T 0  from T 3 . The present invention removes much of the lag time from the cranking system by providing a “prime current” level C to the power relay  16 . This “prime current” level C corresponds to the point T 1  on the time axis. The total time saved by providing the “prime current” level C can be characterized by T 0  subtracted from T 1 . For this particular example, the time saved by applying a “prime current” level C to the power relay  16  is approximately 50% of the power relay activation time. 
       FIGS. 5   a  and  5   b  are schematic illustrations of an alternate embodiment for controlling the current to the pinion actuator solenoid  15  during the “hold” period of the pinion gear  58  pre shuttling. The pinion actuator solenoid  15  consists of two coils, first coil  50  and second coil  52 . An armature  56  is operable within coils  50  and  52  when a current is applied to the terminal  51  of the pinion actuator solenoid  15 . When the maximum pull-in current A for the pinion gear actuator solenoid is commanded by the cranking control module  10  the armature  56  is forced to one side by the magnetic force generated by the first coil  50  and second coil  52 . This armature  56  in turn manipulates the pinion gear actuator  57  into engagement with the pinion gear  58 . The pinion gear  58  slides axially on the starter motor shaft  59  to mesh with the flywheel ring gear  60  teeth. Simultaneously, as shown in  FIG. 5   b , the armature  56  engages a set of electrical contacts  54  which then open causing an interruption in current to the second coil  52 . The force of the first coil  50  is sufficient to hold the pinion gear  58  in relation to the flywheel ring gear  60  during the “holding” portion of the pinion gear shuttling operation. This is an electro-mechanical method to reduce the pinion actuator solenoid  15  current during the “holding” portion of pinion gear  58  pre-shuttling. 
     Accordingly, the apparatus described previously provides an improved method for fast response to a restart signal for an engine  11  having a flywheel ring gear  60 , a traditional starter  18  with a pinion gear  58 , a pinion actuator solenoid  15 , and a power relay  16 , whereby the current flow to the pinion actuator solenoid  15  is controlled at a maximum pull-in current A for a predetermined amount of time  23 , sufficient to allow the pinion gear  58  to shuttle to the flywheel ring gear  60 . At which point, the pinion actuator solenoid  15  current is decreased to a level B to hold the pinion gear  58  in mesh with the flywheel ring gear  60 . During this operation, the current flow to the power relay  16  is separately controlled at less than the minimum pull-in current C to allow the relay coil to ramp to a level that is insufficiently high enough to cause power switching of the power relay  16 . This current should be sufficiently high enough to eliminate a significant portion of the time required for the power relay  16  to be switched in response to a restart signal. The method of controlling current flow to the pinion actuator solenoid  15  and separately controlling the current flow to the power relay  16  may include at least one pulse width modulation device. An alternative embodiment for the method of current control to the pinion actuator solenoid  15  is to provide two coils within the pinion actuator solenoid  15  along with a set of armature actuated electrical contacts  54  that are openable to energize the pinion actuator solenoid  15  at a relatively low current level in response to the control unit  10  to control the pinion actuator solenoid  15 . 
     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.