Starter device for internal combustion engines
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a starter device for internal combustion engines of automotive vehicles, and more particularly to an output structure thereof. 
     2. Description of the Related Art 
     FIG. 1 shows the output structure of a conventional starter device for the internal combustion engine of automobiles. The starter device, generally designated by reference numeral 1, comprises a front housing frame 2a and a rear housing frame 2b coupled to each other to form the housing of the device. The output structure of the starter comprises an output shaft 3 which is operatively connected with and driven by a motor, and an axially slidable hollow cylindrical assembly disposed coaxially around and driven by the shaft 3. The output shaft 3 may be a rotary shaft of a motor. The axially slidable assembly comprises a hollow shaft 4, an overrunning clutch 5, a pinion-carrying hollow cylinder 6, and a pinion 6a, and is slidable on the shaft 3 in the axial direction between a front position at which the pinion 6a engages a ring gear 7 of an engine (not shown) and a rear position at which the pinion 6a is out of engagement therewith. 
     The output shaft 3 rotatably supported by the housing has a stopper 3a fixed at the front end thereof to limit the axial translation of the axially slidable assembly. The enlarged diameter portion 3b, which is formed on the shaft 3 at an axial position thereof which is situated at the rear of the overrunning clutch 5 when the clutch 5 is in the rear position, has helical splines formed at the outer circumferential surface thereof. A portion 3c of the shaft 3 in front of a step at the front end of an enlarged diameter portion 3b is plated, for example, with chromium, to prevent the development of rust, etc. 
     The axially slidable assembly, on the other hand, is constructed as follows. The hollow shaft 4 engages the output shaft 3 by means of helical keyways which are formed in the interior surface thereof and mesh with the helical splines formed on the enlarged diameter portion 3b of the shaft 3. Thus, the hollow shaft 4 is slidable on the shaft 3 in the axial direction. The overrunning clutch 5 comprises an outer member 5a integral with the hollow shaft 4, an inner member 5c integral with the pinion carrying hollow cylinder 6, and a friction rollers 5b interposed therebetween to transmit a rotational driving force in one rotational direction. The pinion-carrying hollow cylindrical member 6 is rotatably supported by the shaft 3 by means of a sleeve bearing 6b which is fitted on the interior circumferential surface of the pinion-carrying cylinder 6 and is slidable on the shaft 3 in the axial direction. Further, the pinion-carrying cylinder 6 is rotatably supported by the front housing frame 2a through a ball bearing 2c to be slidable in the axial direction. The shift lever 8 slides the overrunning clutch 5 along the shaft 3 in the axial direction. 
     The operation of the starter device of FIG. 1 is as follows. When the internal combustion engine (not shown) is to be started, the shift lever 8 is activated to move the slidable output assembly (including the hollow shaft 4, the overrunning clutch 5 and the pinion-carrying cylinder 6) to the front limit position at which the front end of the pinion-carrying cylinder 6 abuts the stopper 3a and the pinion 6a engages the ring gear 7 of the engine. When the motor is energized, the rotational force of the output shaft 3, which is operatively connected with and driven by the motor or which may be the rotary shaft of the motor, is transmitted to the hollow shaft 4 splined thereto, and thence to the pinion-carrying cylinder 6 through the overrunning clutch 5. Thus, the pinion 6a engaging with the ring gear 7 drives and rotates it to start the engine. After the engine is thus started, the slidable output assembly including the pinion carrying cylinder 6 returns to its rear position. 
     The output structure of the starter of FIG. 1 has following disadvantage. The plating on the outer circumferential surface of the portion 3c of the output shaft 3 which slidably supports the hollow cylinder 6 may come off in a relatively short time to develop rust thereon at exposed portions, due to the extremely severe environmental condition under which the portion 3c is; when this happens, the sliding movement of the pinion-carrying cylinder 6 on the shaft 3 is obstructed. 
     FIG. 2 shows a modified output structure of a starter device. A cap-shaped cover 9 is detachably fitted on an annular projection 6c formed at the front end of the pinion-carrying hollow cylinder 6, the cover 9 being coupled to the cylinder 6 at the open end portion thereof to close an opening 6f of the hollow cylinder 6 to the exterior space, and the inwardly turned annular end portion of the cap 9 being fitted into an annular groove 6dformed at the base of the projection 6c. The cover 9, which is moved with the pinion-carrying hollow cylinder 6 and has an axial length enough to accommodate the front portion of the output shaft 3 even when the pinion-carrying hollow cylinder 6 is retracted to its rear limit position, closes the opening 6f of the hollow cylinder 6 and prevents dust, foreign matter, etc., from entering into the interior of the opening 6f, thereby enhancing the durability of the sleeve bearings 6b and the portion 3c of the shaft 3 which slidably supports the hollow cylinder 6. Apart from the cover 9, the projection 6c and the groove 6d formed at the front end of the hollow cylinder 6, the output structure of FIG. 2 is similar to that shown in FIG. 1 except that the structure of FIG. 2 comprises an annular oil seal 2d interposed between the front housing frame 2a and the pinion-carrying hollow cylinder 6, and, further, that two sleeve bearings 6b instead of one are interposed between the shaft 3 and the hollow cylinder 6. 
     The output structure of the starter device shown in FIG. 2 suffers from following disadvantages: 
     (a) When the pinion 6a is in engagement with the ring gear 7 of the engine and the pinion-carrying hollow cylinder 6 is driven by the engine at a high speed, the cover 9 may be disengaged from the pinion-carrying cylinder 6, or damaged, due to the centrifugal force resulting from the rotation. 
     (b) When the starter device is to be attached to the engine, the cover 9 may be damaged by being struck by surrounding devices, etc.; in such cases, its proper function as a dust preventing cover may be lost, or a concave deformation resulting from the damage may obstruct the sliding movement of the pinion-carrying cylinder 6 on the shaft 3. 
     (c) The cover 9 moves forward with the pinion-carrying hollow cylinder 6 to project further forward from the front end of the output shaft 3 when the hollow cylinder 6 is slid to the front limit position. Thus, an additional space is needed for the cover 9 in front of the front end of the output shaft 3. Consequently, the starter device requires wider space in the engine room of the vehicle for its installation. 
     SUMMARY OF THE INVENTION 
     Thus, a primary object of the present invention is to provide a starter device for an internal combustion engine which is free from the disadvantages of the abovementioned conventional devices. More particularly, the present invention aims at providing a starter device in which the durability of the output shaft and of the bearing for the pinion-carrying hollow cylinder are enhanced. 
     Another object of the present invention is to provide a starter device which requires smaller space for installation. 
     A further object of the present invention is to provide a starter device which has a simple structure and which can be produced at low cost. 
     According to one aspect of the present invention, a starter device for an internal combustion engine is provided which comprises: a housing; drive means in the form of a motor; an output shaft operatively connected with and driven by the motor; a hollow shaft splined to the output shaft so that the hollow shaft is slidable in the axial direction while being driven by the output shaft; a pinion-carrying hollow cylinder disposed coaxially around the output shaft at the front side of the hollow shaft; a pinion formed at the front end of the hollow cylinder which is placed into engagement with a ring gear of the associated internal combustion engine to drive it when the hollow cylinder is translated to the front position; a bearing in the form of a sleeve bearing rotatably supporting the hollow cylindrical member around the output shaft and being slidable on the output shaft in the axial direction to allow axial translation of the pinion-carrying hollow cylinder; a one-way clutch coupling the hollow shaft to the pinion-carrying hollow cylinder to transmit a rotational force in one rotational direction; means for sliding an axially slidable assembly (i.e., the hollow shaft and the pinion-carrying hollow cylinder coupled to each other by the one-way clutch) in the axial direction on the output shaft; and an annular sealing member in the form of an oil seal disposed between the inner circumferential surface of the pinion-carrying hollow cylinder and the outer circumferential surface of the output shaft. The sealing member is disposed coaxially around the output shaft at an axial position in front of the hollow-cylinder-supporting bearing. Thus, the sealing member substantially closes the front end opening of the pinion-carrying hollow cylinder and prevents water, dust and the like from entering therethrough the interior thereof. Consequently, the durability of the bearing and of the output shaft is enhanced. 
     According to another aspect of the present invention, a starter device for an internal combustion engine is provided which has a structure similar to that according to the first aspect. According to this aspect, however, instead of interposing the annular sealing member between the pinion-carrying hollow cylinder and the output shaft to protect the bearing and the outer circumferential surface of the output shaft, the outer circumferential surface of the output shaft is provided with a rust-preventive coating formed of an organic material such as a fluorocarbon resin or an epoxy resin, along an axial length which is situated axially in front of the bearing of the pinion-carrying hollow cylinder when the hollow cylinder is at the front limit position. The axial length provided with the rust-preventive coating includes at least the portion of the output shaft which projects from the front end of the hollow cylinder when the hollow cylinder is at the rear limit position. The resin-coated surface portion includes substantially all the area of the surface of the output shaft on which rust would develop. Thus, the development of rust on the outer surface of the output shaft can be effectively prevented by the organic coating; consequently, sliding difficulty of the pinion-carrying hollow cylinder resulting from rust can be prevented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details of the present invention will become more clear from the detailed description of a few preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a partially cutaway view of a conventional starter device for an internal combustion engine, showing the output structure thereof partially in cross section; 
     FIG. 2 is a partial cross-sectional view of another conventional starter device, showing the axial cross section of the output portion thereof; 
     FIG. 3 is a view similar to that of FIG. 1, but showing the output portion of a starter device according to the present invention; 
     FIG. 4 is a view similar to that of FIG. 2, but showing the output portion of another starter device according to the present invention; and 
     FIG. 5 is also a view similar to that of FIG. 2, but showing the output portion of a further starter device according to the present invention. 
    
    
     In the drawings, like reference numerals and characters represent like or corresponding parts or portions. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 3 of the drawings, a first embodiment according to the present invention is described. 
     The starter device 1 for the internal combustion engine of an automotive vehicle illustrated in FIG. 3 has a structure similar to that of the starter device of FIG. 1, except for the resin coating on an output shaft 3 thereof. 
     Thus, the output shaft 3, being driven by a motor and rotatably supported by a housing which is constituted by a front housing frame 2a and a rear housing frame 2b, comprises a ring-shaped stopper 3a fixed to the front end portion thereof for limiting the axial translation of a pinion-carrying cylinder 6, and an enlarged diameter portion 3b, which is situated axially at the rear of an overrunning clutch 5 when the clutch 5 is at its rear position and on the outer circumferential surface of which helical splines are formed. The outer circumferential surface of the portion 3c of the output shaft 3 situated in front of the enlarged diameter portion 3b is plated, for example, with chromium along the entire axial length thereof. Further, the outer circumferential surface of the portion 3c of the output shaft 3 is covered by a resin coating 3d along the axial length thereof that is situated in front of the sleeve bearing 6b when the sleeve bearing 6b is slid to the front limit position with the pinion-carrying cylinder 6. The resin coating may be formed of a fluorocarbon resin such as polytetrafluoroethylene, polychlorotrifluoroethylene and the like, or it may be formed of an epoxy resin. The resin coating covers at least the portion of the output shaft 3 which projects from the front end of the pinion-carrying hollow cylinder 6 when the hollow cylinder 6 is at its rear limit position. This portion of the output shaft 3 is under most severe environment because the water splashed up by the running vehicle may easily reach this portion and dust is rapidly deposited thereon; thus, rust develops fastest on this portion of the output shaft 3. As the resin coating 3d according to the present invention covers at least this portion of the output shaft 3 on which rust most easily develops, the sliding difficulty of the pinion carrying cylinder 6 due to the development of rust on the output shaft 3 can be effectively prevented. 
     An axially slidable assembly, which includes the hollow shaft 4, overrunning clutch 5, pinion-carrying hollow cylinder 6 and pinion 6a, has a structure identical to that of the device of FIG. 1. Thus, the hollow shaft 4 disposed coaxially around the output shaft 3 has helical keyways at the inner circumferential surface thereof which engages the helical splines on the outer circumferential surface of the enlarged diameter portion 3b of the output shaft 3. The integral front end portion of the hollow shaft 4 constitutes an outer member 5a of the overrunning clutch 5. The integral rear end portion of the hollow cylinder 6 constitutes an inner member 5c of the clutch 5 which transmits a rotational force in one rotational direction through friction rollers 5b interposed between the outer member 5a and the inner member 5c thereof. The hollow cylinder 6 disposed coaxially around the output shaft 3 has a pinion 6a formed integrally at the front end thereof. The inner diameter of the front portion of the hollow cylinder 6 including the portion at which the pinion 6a is formed is reduced, so that water and dust will not easily enter the interior 6h of the hollow cylinder 6. A sleeve bearing 6b fitted to the inner circumferential surface of the hollow cylinder 6 supports it rotatably and axially slidably on the output shaft 3. Further, the hollow cylinder 6 is rotatably and axially slidably supported by the front housing frame 2a through an annular ball bearing 2c fixed thereto. A shift lever 8, when activated, urges the overrunning clutch 5 in a direction X to slide the axially slidable assembly in such a direction on the output shaft 3 that the pinion 6a is placed into engagement with a ring gear 7 of the associated engine (not shown). 
     The operation of the starter device of FIG. 3 is similar to that of the device of FIG. 1. Thus, when the shift lever 8 is activated to urge the overrunning clutch 5, the clutch 5 is slid, together with the hollow shaft 4 and the pinion-carrying hollow cylinder 6, in the forward axial direction X on the output shaft 3 to the front limit position at which the front end of the hollow shaft 6 abuts the stopper 3a and the pinion 6a engages the ring gear 7 of the associated engine (not shown). At the same time, the D.C. motor operatively connected with the output shaft 3 is energized and drives the output shaft 3, which in turn drives the hollow shaft 4 splined thereto. The rotation of the hollow shaft 4 is transmitted to the pinion-carrying hollow cylinder 6 through the overrunning clutch 5. Thus, the pinion 6a drives the ring gear 7 to start the engine. After the engine is started, the pinion 6a is rotated at a high speed by the ring gear 7 during the time in which the pinion 6a is still engaged therewith. However, the resulting high speed rotation of the hollow cylinder 6 is not transmitted to the output shaft 3 due to the one-way rotational force transmitting function of the overrunning clutch 5. After the engine is started to run stably, the axially slidable assembly is returned to the rear limit position, and the pinion 6a is disengaged from the ring gear 7. 
     Referring now to FIG. 4 of the drawings, a second output structure of the starter device according to the present invention is described. 
     The structure of FIG. 4 is similar to that of FIG. 2 or FIG. 3. However, the inner diameter of the front end portion 6g of the pinion-carrying hollow cylinder 6 at which the pinion 6a is formed is reduced, compared with the inner diameter of the portion thereof at which the sleeve bearings 6b are fitted. Thus, the inner circumferential surface of the front end portion 6g under the teeth of the pinion 6a opposes the outer circumferential surface of the output shaft 3 with a small clearance 6f formed therebetween, and the portion 6g of the hollow cylinder 6 under the teeth of the pinion 6a has an enlarged thickness to enhance the mechanical strength of the pinion 6a. Further, an annular sealing member 10 in the form of, for example, an oil seal is attached to the inner circumferential surface of the hollow cylinder 6 so as to seal the opening formed between the outer circumferential surface of the output shaft 3 and the inner circumferential surface of the hollow cylinder 6. The sealing member 10 is positioned at the rear side of the front end portion 6g of a reduced inner diameter of the hollow cylinder 6, this axial position of the sealing member 10 being a position removed farthest from the bearings 6b in the forward direction. Due to the disposition of the sealing member 10 and the small clearance 6f between the output shaft 3 and the hollow cylinder 6, the entrance of water, dust and the like into the interior 6h of the hollow cylinder 6 through the front opening thereof can be prevented almost completely. By the way, in the case of the device of FIG. 4, two sleeve bearings 6b are disposed between the hollow cylinder 6 and the output shaft 3, and an annular oil seal 2d is mounted to the front housing frame 2a at the front side of the ball bearing 2c to seal the gap between the outer circumferential surface of the hollow cylinder 6 and the inner surface of the opening of the front housing frame 2a through which the hollow cylinder 6 extends. Otherwise, the structure and the operation of the device of FIG. 4 is similar to those of the devices described above. 
     FIG. 5 shows a third embodiment of the starter device according to the present invention which is substantially identical to the device of FIG. 4. In the case of the device of FIG. 5, however, the pinion-carrying hollow cylinder 6 comprises a portion 6i of an enlarged inner diameter in front of the reduced inner diameter portion 6g, and the annular sealing member 10 is mounted to the enlarged inner diameter portion of the hollow cylinder 6 in such a manner as to be interposed between the inner circumferential surface of the enlarged inner diameter portion of the hollow cylinder 6 and the outer circumferential surface of the output shaft 3 for sealing the opening between the output shaft 3 and the hollow cylinder 6. Otherwise, the structure and the operation of the device of FIG. 5 is identical to those of the device of FIG. 4.