Abstract:
The present invention is directed to determining and controlling the appropriate moment at which a combined starter/alternator should transition from start-up mode to alternator/generator mode following an IC engine start-up sequence. The method relies on either belt/chain tensioner position or the position of the belt/chain itself to determine when the IC engine has achieved self-sustaining operation and signal the starter/alternator to transition from start-up to generator mode.

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of automotive electrical systems. Specifically, the invention is directed to a method of determining the moment following a start-up sequence for an IC engine as to when a starter/alternator should transition from start-up to generator function. 
     BACKGROUND OF THE INVENTION 
     The trend in automotive electrical systems has always been towards more power and higher voltages. At this time, an element of the trend involves the combination of the alternator and starter into a single IC engine driven unit. This combined starter/alternator can be driven either directly on the crankshaft of the IC engine as a part of the flywheel, on one end, or the balancer, on the other. Alternatively, the starter/alternator can be mounted for gear, belt, or chain drive from the crankshaft along with other IC engine driven components (i.e., waterpump/A/C compressor/power steering pump, etc.) 
     The starter/alternator has become more powerful not only for increasing power (current and voltage) but also for more rapid and more fequent starting cycles of the IC engine as enhanced operating efficiencies are sought. In pursuit of these goals, the starter/alternator has become more sophisticated in its control systems and its responsiveness to system requirements for both starter functions and generating functions. 
     In older systems where the alternator and starter function were performed by separate devices, the need to determine the optimal moment to transition from a starter function to an alternator function did not exist. Rather, the vehicle operator, relying on vehicle familiarity and overall driving experience, actuated the starter until engine startup was perceived. To limit the possibility of damaging the starter from overspeed, a special one-way disengaging drive was sometimes employed. 
     The alternator or generator was connected into older systems by virtue of a regulator that either accepted charge into the system to meet an electrical load, or for battery charging, or kept the alternator out of the system altogether as necessary. The alternator or generator in older systems did not change function from a starter to an alternator or generator. 
     In more modern vehicles with combined starter/alternator devices, a need exists to transition the device from starter to alternator/generator function at an appropriate moment following IC engine start-up. If the transition occurs too quickly, the IC engine may not, in-fact, have started. If it occurs too slowly, damage to the starter/alternator device may occur either directly or to the driving/driven mechanical connection between the IC engine and the device. In either case, premature wear and/or replacement is the likely outcome. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to determining and controlling the appropriate moment at which a belt or chain driven combined starter/alternator should transition from start-up mode to alternator/generator mode following an IC engine start-up sequence. The method relies on starter/alternator belt/chain tension or tensioner position to establish the timing of the transition. 
     In the tensioner position monitoring embodiment, the starter/alternator controller, or other monitoring controller, monitors the angular or linear position of the belt/chain tensioner for the drive belt/chain that includes the starter/alternator into the accessory drive system for the IC engine. The tensioner will rotate, or translate linearly, to a first position as the starter function is initiated and begins engine cranking. When the IC engine begins generating its own self-sustaining torque, the angular position, or linear position, of the tensioner will change accordingly in reaction to the change in drive being transferred to the IC engine. The starter/alternator controller will detect the change in position and then make the transition from starting mode to generation mode. 
     In the belt/chain tension monitoring embodiment, the belt/chain position is monitored for movement between a relatively slack and tensile condition. Following an initiation of IC engine cranking, the belt/chain position on the pull side of the starter/alternator pulley follows a straight line between the pulley tangent points of initial belt/chain contact. On the slack side of the starter/alternator pulley, the belt/chain is less straight and curves away from the line between the tangent points of contact at adjacent pulleys. When the IC engine begins to obtain self-sustaining operation, the slack side of the belt/chain is pulled straight as the IC engine accelerates. The monitoring controller will detect the change in belt/chain position and then signal the starter/alternator to make the transition from starting mode to generation mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an IC engine, starter/alternator system for accomplishing the methods of the present invention. 
     FIG. 2 is a schematic of a starter/alternator IC engine belt/chain pulley system incorporating a rotary type tensioner using the present method. 
     FIG. 3 is a schematic of a starter/alternator IC engine belt/chain pulley system incorporating a linear type tensioner using the present method. 
     FIG. 4 is a schematic of a starter/alternator IC engine belt/chain pulley system incorporating a tension monitor using the present method. 
     FIG. 5 a  shows an IC engine system using the present method, in combination with a fixed sensor apparatus, in an engine cranking mode. 
     FIG. 5 b  shows the IC engine system of FIG. 5 a  wherein the engine has obtained self-sustained operation. 
     FIG. 6 a  shows an IC engine system using the present method, in combination with a rotary sensor apparatus, in an engine cranking mode. 
     FIG. 6 b  shows the IC engine system of FIG. 6 a  wherein the engine has obtained self-sustained operation. 
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to a method of controlling a starter/alternator device and determining the appropriate moment to transition from starter function to alternator/generator function following a start-up sequence. The invention includes three embodiments. FIG. 1 is a block diagram of the component elements of an IC engine system that can accomplish the present method. FIG. 2 shows a schematic of a rotary tensioner embodiment of the present method, FIG. 3 shows a schematic for a linear tensioner embodiment system using the present method, and FIG. 4 shows a belt/chain tension monitor embodiment using the present method. 
     As shown in FIG. 1, the present method is intended to function in a system including an IC engine  2  and a belt or chain driven starter/alternator  1 . The system further includes a system controller  3  that supplies control signals to the IC engine as well as to and from the starter/alternator controller  4 . A battery  5  is also associated with the system and receives charging and loading as necessary by the controller  4 . 
     FIG. 2 is a schematic showing a starter/alternator pulley  10  and engine pulley  20  with a rotary type tensioner  30  positioned between the respective pulleys and in contact with a belt/chain  50 . A rotary type tensioner  30  herein is of the type where tension is maintained using a rotating translation of a lever or post mounted belt/chain contacting pulley or guide element. The tension can be maintained with a wound spring, hydraulic pressure, pneumatic pressure, etc., and the rotary position is monitored using a signal producing position sensor (either fixed as in FIG. 5 a , or rotary/angular as in  6   a ) that provides position information to controller  4 . 
     When a start cycle is initiated (see FIGS. 5 a ,  6   a ), the segment of belt/chain  50  between the starter/alternator pulley  10  and engine pulley  20  is pulled straight by virtue of the pull of the starter/alternator to rotate and crank the engine pulley  20 . This reaction of the belt/chain  50  urges it against the tensioner  30  and causes a change in position. For as long as the starter/alternator is cranking the engine pulley  20 , the tensioner  30  will maintain a steady position against the tension of the belt/chain  50  between the pulleys  20  and  10 . As the IC engine begins self sustaining operation, the tension in the belt/chain  50  segment between the pulleys  10  and  20  will decrease owing to the increasing speed of the self sustained engine and the decreasing cranking requirement of the starter/alternator to crank the IC engine. The lessening tension in the belt/chain will cause a change in tensioner  30  position as shown in FIGS. 5 b  and  6   b . The tensioner  30  position sensor will provide this information to the controller  4  and the controller will, in turn, transition the starter/alternator  1  from starter function to generator function. 
     FIG. 3 is a schematic showing a starter/alternator pulley  10  and engine pulley  20  with a linear type tensioner  32  positioned between the respective pulleys and in contact with a belt/chain  50 . A linear type tensioner  32  herein is of the type where tension is maintained using a linear translation of a belt/chain contacting pulley or guide element. The tension can be maintained with a wound spring, hydraulic pressure, pneumatic pressure, etc., and the linear position is monitored using one or more signal producing position sensor(s) that provide position information to controller  4 . 
     When a start cycle is initiated, the segment of belt/chain  50  between the starter/alternator pulley  10  and engine pulley  20  is pulled straight by virtue of the pull of the starter/alternator to rotate and crank the engine pulley  20 . This reaction of the belt/chain  50  urges it against the tensioner  32  and causes a change in position. For as long as the starter/alternator is cranking the engine pulley  20 , the tensioner  32  will maintain a steady position against the tension of the belt/chain  50  between the pulleys  20  and  10 . As the IC engine begins self sustaining operation, the tension in the belt/chain  50  segment between the pulleys  10  and  20  will decrease owing to the increasing speed of the self sustained engine and the decreasing cranking requirement of the starter/alternator to crank the IC engine. The lessening tension in the belt/chain will cause a change in tensioner  32  position. The tensioner  32  position sensor will provide this information to the controller  4  and the controller will, in turn, transition the starter/alternator  1  from starter function to generator function. 
     FIG. 4 is a schematic showing a starter/alternator pulley  10  and engine pulleys  15 ,  20  with a rotary or linear type tensioner  34  positioned between the respective pulleys and in contact with a belt/chain  52 . One or more belt/chain position sensor  36  (optical, electrical, etc.) are located along a pathway of the belt/chain  52  so that it can monitor the lateral position of belt/chain  52  as it passes between pulleys  10 &amp;  15 ,  15  &amp;  20 , or both. 
     When a start cycle is initiated, the segment of belt/chain  52  between the starter/alternator pulley  10  and engine pulley  20  is pulled straight by virtue of the pull of the starter/alternator to rotate and crank the engine pulley  20 . The belt/chain  52  segment between other pulleys, i.e., between 10 and 15, will slacken. This slack reaction of the belt/chain  52  urges it away from a straight tangential path between adjacent pulleys  10 ,  15 . For as long as the starter/alternator is cranking the engine pulley  20 , the belt/chain  52  will maintain a relatively steady position between the pulleys  10 ,  15 . As the IC engine begins self sustaining operation, the tension in the belt/chain  52  segment between the pulleys  10  and  15  will increase owing to the decreasing cranking requirement of the starter/alternator to crank the IC engine combined with the acceleration of the IC engine pulley  20 . The belt/chain  52  will follow a straighter more tangential path between pulleys  10 ,  15 . The position sensor  36  will provide this information to the controller  4  and the controller will, in turn, transition the starter/alternator  1  from starter function to generator function. 
     Sensors that are suitable for use with the tensioners  30 ,  32 ,  36  are any of available Hall effect, magnetic reed, optical, proximity radar, limit switch, potentiometer, etc., or their equivalent, that are robust and reliable enough for the harsh IC engine associated environment.