Abstract:
An electric starter assembly and, more specifically, an improved drive assembly that is responsive to inertia encountered during the fast acceleration of the starter armature and that also is responsive to the inertia encountered as a result of providing for a braking or rapid deceleration of the starter armature. The assembly also provides a positive engagement between the drive assembly of the starter motor and the engine member to be rotated during the cranking cycle. Engagement is maintained so long as the motor is energized, even if the engine is running.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an improved electric starter for an internal combustion engine. 
     In the past there have been numerous methods devised involving mechanisms to smoothly engage and reliably maintain engagement during the cranking cycle and, then, to smoothly disengage the starter from the engine once the engine has started. These methods have all either fallen short of one or more of the objectives or have resulted in bulky, heavy, and costly mechanisms making them impractical for many applications. For example, these earlier approaches include the use of a solenoid, the purpose of which is to move the drive axially on the starter shaft for engagement with the member on the engine to be rotated and to hold the drive in contact with the member during cranking. 
     Another approach, usually used on small engines and correspondingly smaller starters, is the use of drives that depend entirely on the acceleration of the armature shaft and the inertia of drive to provide axial movement of the drive along threaded areas between the drive and rotating shaft and, thereby, provide initial engagement of the drive with the engine member. This type drive has an undesirable characteristic, however, in that it is susceptible to premature disengagement from the engine rotating member resulting in false starts and, therefore, requiring repetitive attempts to start the engine. To overcome this problem, numerous approaches have been taken to lock this type drive into engagement with the engine. All of these approaches have been less than satisfactory, at least in part, because the various locking in mechanisms would stick and, thereby, not allow disengagement between the rotating engine member and the drive after cranking. 
     SUMMARY OF THE INVENTION 
     This invention provides an improved electric starter that provides the features of smooth engagement and disengagement and, also, provides a positive &#34;lock-in&#34; means while the engine is being cranked. The engagement of this drive utilizes the inertia between the accelerating shaft and the drive to provide axial movement of the drive along the shaft and, for disengagement, forces resulting from the flywheel of the cranked engine against the pinion and the inertial effect between the decelerating shaft and the drive are utilized in such a manner to assure the release of the &#34;lock-in&#34; means and, thereby, quickly allow the drive to return to a disengaged position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the starter of the present invention with the motor housing in section and with the motor armature and the drive in elevation; 
     FIG. 2 is a wiring diagram for the starting system; 
     FIG. 3 is a sectional view on an enlarged scale of the starter drive assembly mounted on the starter armature shaft; 
     FIG. 4 is an end view of the lock-in collar seen in section in FIG. 3; and 
     FIG. 5 is a side view of the collar of FIG. 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the starter motor consists of a tubular housing 10 with permanent magnets providing fields 14 and 16 secured therein. End caps 18 and 20 close each end of the housing. A conventional armature, generally designated 22 having windings 24 has its supporting shaft 26 journaled on each of the end caps 18 and 20 and is free to rotate within the housing 10 and within the magnetic field provided by the permanent magnets 14 and 16. Current is supplied to and from the winding of the armature by four brushes 28 supported in suitable brush holders 30 within end cap 20 and spring loaded so that they are urged in good electrical contact with the commutator 32. The armature shaft 26 extends out from the housing through end cap 18, and mounted on the shaft 26 is the starter drive assembly 34, the details of which can best be seen in the sectional view thereof in FIG. 3 and will be explained fully later in the specification. 
     FIG. 2 shows the preferred circuit plan for the starter wherein two brushes 28a and 28b are selectively connected through the control switch 38 to either a source of power such as a battery 36 or to ground. The operation of the circuit is such that when the control switch is in the position represented by the dashed line, current will flow from the battery through the switch to brushes 28a and 28b, then through the armature windings and to ground through brushes 28c and 28d. When the armature is energized by current flow, a magnetic field will surround the armature and interact with the ever present magnetic field provided by the permanent magnets. The interaction of the two fields, along with the switching of the current flow in the armature provided by the commutator, will cause the armature to rotate in a conventional manner. When the control switch is positioned as represented by the solid line, the starter is disconnected from the battery and brushes 28b and 28a are grounded through the switch. Therefore, all brushes are connected electrically together at ground providing closed circuits without an external potential source across the armature. As the armature coasts within the magnetic field provided by the permanent magnets, current is induced in its closed conductor loops and the starter then functions as a generator. Since each armature winding closed on itself provides a very low impedance, a high current is generated therein producing a magnetic force opposed to the field so that a sudden dynamic braking force is applied to the armature that slows the armature to a stop much sooner than would occur if the windings were left open. 
     FIG. 3 is a sectional view of the starter drive assembled on the shaft 26. A cup-like member 40 is coaxially arranged and connected to the armature shaft 26 so that its open end faces away from the armature and so that it moves rotationally with but cannot move axially along the shaft. The sidewalls of cup 40 have two portions. A larger diameter portion 40a at the lip of the cup is separated from a smaller diameter portion 40b by a shoulder 40c providing a sort of inclined plane between the constant diameter portions 40a and 40b. A spool 42 is provided with threads 42a along is inner diameter to engage helical threads 44 on shaft 26. The shoulder 46a between the shaft 26 and its reduced diameter portion 46 provides a stop limiting movement of spool 42 toward the armature 24. This threaded engagement between the spool 42 and the shaft portion 46 is designed so as to allow free movement within limits between them. The spool 42 has an outward extending circumferential flange 42b at the end remote from the armature against whose flat outer face rests a flat face 48a of a ring 48. Spaced axially from flat face 48a is a resilient generally parallel flat face 48b terminating necked down, reduced width section 48c of the ring. Flat face 48b rests against the flat inside bottom wall 50a of a cup shaped intermediate member 50. Intermediate cup shaped member 50 is of smaller diameter than cup 40 and is coaxially and rotatably supported by clutch plate 52a on smaller diameter shaft extension 54. Cup 50 brackets resilient ring 48 and its lip 48 and is formed to conform to the rounded shafts and embrace the outer edge of flange 42b and engage, thereby captivating, the resilient ring 48 between the flat planar face of the flange 42b of spool 42 and the inner bottom wall 50a of the cup 50. The outer face of bottom wall 50a is in this instance fixedly secured to plate 52a of a unidirectional clutch 52. The other plate 52b of the clutch is also rotatably supported on shaft portion 54. Plates 52a and 52b have interfitting radially extending teeth that have a steep slope on one side and a shallow slope on the other. It is anticipated, however, that other type clutches could be used such as a roller type clutch, for instance. As shown, a pinion gear 56 or other suitable engine engaging member, is secured to the second plate 52b of the clutch 52 and like that plate is rotatably supported on shaft portion 54. Thus, the pinion 56 and the clutch plates 52a and 52b are journaled on the shaft portion 54. A helical spring 58 surrounds the armature shaft portion 54. One end of spring 58 rests within a recess 56a of the pinion 56. The other end of the spring 58 is confined within a cup shaped stop member 60. The cup shaped stop 60 is held onto the shaft portion 54 against action of the spring 58 by a retaining ring 62 in a circumferential groove 54a in the armature shaft portion 54. 
     A lock-in 64 collar seen in FIGS. 4 and 5 engages the outer diameter of the spool 42 and is held in place axially between flange 42b and snap ring 66 and rotates with spool 42. The collar 64 and the spool 42 are preferably secured against rotation relative to one another so that relative rotation in not possible, for example, by interfitting cross sections, such as the hexagonal shape shown. Collar 64 is provided with spacing flange 64a which engages and spaces collar 64 from flange 42b. 
     The collar 64, preferably, is formed of a suitable plastic material such as Delrin (a trade name of E. I. du Pont deNemours &amp; Company, Incorporated, Wilmington, Delaware, for their Acetal resins). In FIGS. 4 and 5 it can be seen collar 64 has three equally spaced radially directed cylindrical bores 64b, 64c, and 64d that extend from the inside flats of the tubular member to the outer diameter thereof thereby forming three cylindrical openings as best seen in FIG. 3, the sectional view shows the position of one of the three pins 68. The pins 68 are free to move radially within the confines of the cylinders of the collar, and their outward movement is limited by the cup 40. 
     Having thus identified the functional components of the invention and their relationship to each other, the operation thereof is as follows: 
     The starter motor is mounted on an engine in a conventional manner such that the pinion 56 is out of engagement with and is axially spaced from mating teeth on the engine flywheel (not shown) most of the time during which the starter is inoperative. When the engine is to be started, the control switch 38 is closed to connect the starter to the battery 36, which causes the starter motor armature 22 and its supporting shaft 26 to rotate. The resulting rotational acceleration of the armature causes the starter drive assembly 34 to move axially to the right along the armature shaft portion 46 because engagement of the threads of worm 44 on the armature shaft 46 with the threads 42a of the drive assembly 13. The pinion 56 moves axially into engagement with the toothed surface of the engine flywheel and comes to rest against the stop member 60a on cup 60 in which position full operating mesh is obtained. Upon meshing, torque from the starter motor is applied to drive the flywheel and the engine begins to rotate. The movement of the starter drive assembly 34 causes pin guide collar 64 to move with respect to the axially fixed retained housing 40 past the step to the position opposite the larger diameter portion 40d. As the drive assembly 34 rotates, centrifugal force moves the pins 68 out into contact with the interior surface of the larger diameter portion 40a of the retainer housing 40. The pins remain in the extended position in contact with the wall 40a of retainer housing 40 so long as there is sufficient speed to provide the necessary centrifugal force. Any false starts or sudden momentary acceleration of the engine flywheel which might otherwise tend to kick the pinion out of mesh with the engine flywheel is prevented by engagement of the pins 68 against the stepped shoulder 40c of retainer housing 40. If sudden or momentary acceleration of the engine flywheel occurs, as is often caused by an unsustained start or even more frequently encountered when the engine piston is returning from a compression stroke without combustion, the slippage between the clutch plates 52a and 52b limits such acceleration from being transmitted back to the starter armature. In this situation, the clutch will allow the pinion 56, which is in mesh with the engine flywheel, to overrun the remainder of the drive and the armature. Preferably, the dimensions of the drive parts are such that when the pinion 56 is fully engaged with the engine flywheel, the pins 68 are far enough to the right of shoulder 40c to allow a slight amount of movement to the left when the teeth on clutch plates 52a and 52b slip past each other during an overrun condition. Were the momentary torque and resulting increased RPM allowed to be transmitted back through the drive assembly to the starter armature, it could damage both the drive assembly and the starter motor. Also, if sustained combustion is obtained by the engine (that is, the engine starts), and the operator is slow in releasing the control switch 38, the overrunning clutch will prevent damage to the starter and drive assembly. Under normal operating conditions, once the engine has started, the control switch will be released (opened) whereupon a circuit is completed across the armature through the control switch 38. Since inertia causes the armature 22 to continue to rotate in the magnetic field provided by the permanent magnets 14, 16, the armature immediately experiences a braking effect caused by generation of a current in the armature which creates an armature polarity opposing the field of the permanent magnets. This condition causes a dynamic braking, which rapidly slows down of the armature and drive assembly. When a point in reduced RPM is reached, the centrifugal force on the radially extended pins will not prevent them from being urged by the shoulder 40c back toward the armature shaft the relatively smooth curves of the stepped area 40c of cup shaped retainer housing 40 acting as a sort of cam. It has been found through extensive tests that induced deceleration of the armature shaft greatly improves the performance of the starter system of this invention. While it is anticipated that other means of deceleration, such as mechanical and electro-mechanical devices could be incorporated within the system to serve this function, dynamic braking, as disclosed herein, is preferred. 
     A resilient ring 48 absorbs both torsional and axial shock encountered during engagement of the drive assembly with the engine flywheel. When the initial torque of the starter is applied to the engine, the resilient ring 48 compresses as the flange 42b of the tubular axial drive member 40 moves toward the flat face 50a of cover member 50a. Also, the driving torque of the engine engaging pinion 26 is transmitted through the resilient ring. Some slippage between rotational parts is preferably allowed to absorb the high torsional forces encoutered when the gears engage and, if incorporated, will enhance the drive&#39;s durability. 
     The primary function of spring 58 shown in FIG. 3 is to prevent axial movement of the drive assembly when the starter is not in use. Vibrations produced by the engine might, otherwise, cause the drive to drift out and come in contact with the rotating engine flywheel. The spring also functions to hold the unidirectional clutch plates in engagement and to supply a force which must be overcome to disengage the clutch. 
     Having described this invention in terms of the preferred embodiments, it is to be understood that various changes can be made to the described structure within the scope of the appended claims, and that different structures may be made within the scope of the claims.