Abstract:
A starter system for a reciprocating internal combustion engine includes an input gear journaled for rotation upon a crankshaft in the engine, and a starter motor which applies a starting torque to an outer periphery of the input gear. A speed-sensitive clutch is interposed between the crankshaft and the input gear. The clutch selectively transmits torque between the input gear and the crankshaft by means of a series of pawls which are responsive to centrifugal force.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a starter motor and accompanying gear mechanism for cranking an internal combustion engine, such as a reciprocating internal combustion engine. 
   2. Disclosure Information 
   Internal combustion engines, particularly automotive internal combustion engines, have been equipped with electric self-starters since pioneering work by Charles Kettering led to the first automotive self-starter in 1912. As typically applied to automotive internal combustion engines, and, for that matter to most internal combustion engines, the self-starter uses a large diameter ring gear and a starter motor having an axis which is generally parallel to the engine&#39;s crankshaft. The starter motor is equipped with a spur gear that is driven into contact with the flywheel/ring gear by means of a solenoid. Unfortunately, conventional starters are noisy for a variety of reasons. First, the gears are unlubricated. As another source of noise, the gears are generally not enclosed within a case that is capable of muting sound generated by the gears. 
   A more troublesome drawback to present starting systems using large diameter ring gears is that the profile of the engine is adversely affected (e.g., made overly large). This presents a problem to vehicle designers because a large diameter ring gear prevents the engine from being moved farther down in a vehicle, thereby inhibiting efforts to produce more aerodynamic, fuel efficient vehicles. 
   A starter system according to the present invention uses a worm gear and worm drive system, including an input gear which is journaled for rotation, including relative rotation, to the engine&#39;s crankshaft. U.S. Pat. No. 6,758,181 discloses a worm gear starter system which, although being useful for a small one cylinder engine, as witnessed by the fact that the starter of the &#39;181 patent has a rope handle, as well as an electro-drive, is not useful for an automotive engine because it must be cantilevered from one end of the engine, and is therefore not amenable to packaging within an automotive engine requiring a front-end accessory drive, nor would it be expected to exhibit the durability characteristics needed for an automotive engine starter system. 
   SUMMARY OF THE INVENTION 
   A starter system for a reciprocating internal combustion engine includes an input gear journaled for rotation upon a crankshaft of the engine. The input gear is preferably a unitary gear including a hub journaled for rotation upon the engine&#39;s crankshaft, and a clutch driving member circumscribing an outer portion of the hub and defining an inner wall of an annular clutch cavity. An outer portion of the unitary input gear is configured as a worm gear. This outer portion defines an outer wall of the previously described annular clutch cavity. A starter motor applies a starting torque to the outer portion of the input gear, preferably by means of a worm which is coaxial with the starter motor, with the axes of both the starter motor shaft and the worm being in the plane of the worm gear and perpendicular in a plan view, to the center axis of the engine&#39;s crankshaft. 
   The present starter system also includes a speed-sensitive clutch which is interposed between the crankshaft and the input gear. This speed-sensitive clutch includes a generally annular pawl carrier rigidly mounted to a counterweight of the crankshaft and carrying a number of pawls for engaging a number of clutch abutments formed in the clutch driving member. The pawl carrier functions as the clutch driven member. Each of the pawls is responsive to centrifugal force such that torque will be transmitted between the input gear and the crankshaft only if the rotational speed of the crankshaft is below a threshold value. The clutch driven member is housed within an annular clutch cavity which is defined in the unitary input gear. In general, the unitary input gear, as noted above, includes a hub journaled for rotation upon the engine&#39;s crankshaft, and a clutch driving member which circumscribes an outer portion of the hub and defines an inner wall of the annular clutch cavity. An outer portion of the unitary input gear, configured as a worm gear, defines an outer wall of the annular clutch cavity. 
   The worm portion of the present starter system may be mounted within a main bearing cap of the engine, which may comprise either a rear main bearing cap or front main bearing cap of the engine or, for that matter, a middle main bearing cap, if the end counterweights are designed to be removable so that during assembly the end portion of the crankshaft can fit through the inner diameter of the starter mechanism. 
   It is an advantage of a starter system according to the present invention that the starter operates quietly because all parts of the starter may be lubricated, including the worm gear and worm. Quiet operation is also promoted by the fact that the worm gear and worm interface is inherently quiet, and the meshing parts are contained within a completely enclosed portion of the engine. 
   It is a further advantage of a starter system according to the present invention that the engine&#39;s vertical height, as well, in certain cases, as the engine&#39;s length, may be reduced by use of the present starting system. 
   It is a further advantage of a starter system according to the present invention that it is not possible to damage the present starting system by energizing the starter motor after the engine has accelerated above its cranking speed. 
   Other advantages, as well as features of the present invention, will become apparent to the reader of this specification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation of an engine having a starting system according to the present invention. 
       FIG. 2  is a sectional view of the engine of  FIG. 1 , taken along the line  2 - 2  of  FIG. 3 . 
       FIG. 3  is an end section of the engine of  FIGS. 1 and 2 , taken along the line  3 - 4  of  FIG. 2 .  FIG. 3  illustrates the present starter system in a cranking mode. 
       FIG. 4 , although similar to  FIG. 3 , illustrates the present starter system in an engine run mode in which the engine speed has increased above a predetermined threshold. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in  FIG. 1 , engine  10 , having crankshaft  18 , is started by means of starter  14 . It is easily seen from  FIG. 1 , as well as the other figures in the specification, that the shaft axis of starter motor  14  is in a plane which is perpendicular to the center axis of crankshaft  18 . 
   Turning now to  FIGS. 2 and 3 , starter motor  14  is shown in  FIG. 3  as being attached to cylinder block  22 . Starter motor  14  drives worm  38 , which is mounted within bore  34  formed in main bearing cap  30 . As shown in  FIG. 2 , main bearing cap  30  performs not only the traditional function of mounting crankshaft  18  within engine  10 , but also has, as noted above, integral bore  34  within which worm  38  is mounted. As shown in  FIG. 3 , worm  38  is mounted by means of bushings  45  and  47 . Thrust washer  43  accommodates the thrust load imposed upon worm  38  by the remainder of the gear train used in the present starting system. 
   Input gear  40  is at the heart of the present starter system. As shown in  FIGS. 2 and 3 , input gear  40  has an inner bore,  54 , which houses bushing  58 . Bushing  58  rides directly upon crankshaft  18  and allows input gear  40  to rotate freely with respect to crankshaft  18 , except when the clutch portion of the present device is engaged. This is important because input gear  40  must be free to allow crankshaft  18  to rotate freely when engine  10  has been started. 
   Moving outward from bore  54 , it is seen from  FIGS. 3 and 4  that input gear  40  has an inner portion serving as a clutch driving member,  46 . Clutch driving member  46  has a number of clutch abutments,  50 , formed thereupon. Clutch driving member  46  circumscribes an outer portion of hub  44 , and in so doing defines an inner wall of an annular clutch cavity,  48  ( FIG. 2 ). The outer wall of clutch cavity  48  is formed by the base of worm gear  42 , which is formed on the outer periphery of input gear  40 . Worm gear  42  meshes with worm  38 , and in so doing rotates clockwise when starter motor  14  is energized. Note that there is no clutch or other disengagement mechanism between starter motor  14  and worm  38 ; thus, whenever starter motor  14  has been energized, worm  38  and input gear  40  will turn, regardless of engine speed. This eliminates the need for a conventional engage and disengage gearset arrangement needed to couple most known starter motors to an engine&#39;s flywheel or flexplate. 
   The task of selectively transmitting torque between input gear  40  and crankshaft  18  falls in large part upon pawl carrier  70  and its associated hardware. Pawl carrier  70  includes a generally annular body which is bolted to crankshaft counterweight  26  by means of a number of bolts,  78 . Several pawls,  74 , are mounted within notches,  72 , formed in pawl carrier  70 . The purpose of pawls  74  is to transmit torque between input gear  40  and ultimately, crankshaft  18 , but only if the rotational speed of crankshaft  18  is below a threshold value, which may be set at a speed slightly in excess of the design cranking speed of engine  10 . 
   As noted above,  FIG. 3  illustrates the present device in a cranking mode characterized by rotation of the engine crankshaft in a clockwise direction. Accordingly, each of pawls  74  is engaged between one of clutch abutments  50  formed on clutch driving member  46 , and a corresponding portion of pawl carrier  70 . Once engine  10  starts, centrifugal force will drive pawls  74  radially outward against the force of springs  76 , allowing the present starter mechanism to become disengaged from crankshaft  18 . Crankshaft  18  will then be free to rotate within bushing  58 . When pawls  74  are disengaged, crankshaft  18  may move axially without restraint other than that imposed by the usual thrust bearing feature. In a preferred embodiment, springs  76  are selected to have a low “k” value so that when pawls  74  move radially outward, the outwardly directed centrifugal force acting upon the pawls increases more rapidly than the restoring force provided by springs  76 . In this manner, the hysteretic effect which is developed will help to avoid unwanted cyclical engagement/disengagement of pawls  74 . 
   The configuration of input gear  40  allows the incorporation of a relatively large thrust surface,  62 , which interfaces with a corresponding thrust surface,  66 , formed on main bearing cap  30 . This controls the axial position of input gear  40 . 
   Those skilled in the art will appreciate in view of this disclosure that an engine using the present starter may need to be rebalanced because a crankshaft counterweight must be modified to provide space for the cranking mechanism. Those skilled in the art will further appreciate that pawl carrier  70  may be either bolted with fastener  78  or welded to the crankshaft or attached by other means. 
   While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.