1. Field Of The Invention
The present invention relates to an engine starter, and particularly to an engine starter of a coaxial type for a vehicle.
2. Prior Art
FIG. 1 shows a conventional starter 200 for the engine of a vehicle. The starter 200 comprises a DC motor 202, an overrunning clutch mechanism 106 slidably fitted on the extended portion 102a of the rotary shaft 102 of the armature of the DC motor, a front bracket 114 also serving as a bearing for the end of the extended portion of the rotary shaft, and a shift lever 117. One end of the shift lever 117 is engaged with a plunger rod 207 of an electromagnetic switch 118 provided alongside the DC motor for purposes of sliding the overrunning clutch mechanism 106 on the extended portion of the rotary shaft 102. The other end of the shift lever 117 is engaged with an annular member 208 attached to the overrunning clutch mechanism.
An armature 100 of the DC motor comprises a core 101, the rotary shaft 102 of the armature, a commutator 103 fitted to the rear portion of the rotary shaft, and an armature coil 104 wound on the core and connected to the commutator. A helical spline 105 is provided in the rotary shaft 102 in front of the armature core 101 and fitted with the overrunning clutch 106. Brushes 107 are supported in contact with the commutator 103 by brush holders 108 and secured to a rear bracket 109 by bolts 110. A bearing 111 is provided between the rear bracket 109 and the rear end portion of the rotary shaft 102. The overrunning clutch 106 includes an outer member 106a, rollers 106b, a pinion 106c for engaging a ring gear of an engine and supported on the rotary shaft 102 by a sleeve bearing 106d fitted on the inside surface of the pinion, and a cover 106e covering the body of the over-running clutch. The pinion 106c is slidable in the axial direction of the rotary shaft 102. A stopper 112 is provided on the rotary shaft 102 so that the pinion 106c comes into contact with the stopper when being moved forward. A sleeve bearing 113 is attached to the inside surface of the front end portion of the front bracket 114 and supports the rotary shaft 102 at the front end thereof. A plurality of permanent magnets 116, which function as a field for the armature 100, are secured to the inside surface of a yoke 115 provided to form a magnetic circuit and constitute a casing. The ends of a plastic level 117 are engaged with the plunger 119 of an electromagnetic switch 118 and the peripheral portion of the overrunning clutch 106. A movable contact 120 is attached to a rod 122 by an electric insulator 121. The rod 122 is inserted in a core 123 so that the rod is slidable back and forth along its axis. A fixed contact 124 is secured to a cap 125 made of an electric insulator. A driving coil 126 for moving the plunger 119 is wound on a plastic bobbin 127 and housed in a case 128. A lead wire 129 connects the fixed contact 124 and the corresponding brush 107 to each other. A return spring 130 is provided between the core 123 and the plunger 119.
The operation of the conventional engine starter will now be described. When an ignition switch is closed, the driving coil 126 of the electromagnetic switch 118 is supplied with electricity to move the plunger 119 backward (toward the rod 122) to push the rod 122 backward and bring the movable contact 120 in touch with the fixed contact 124. As a result, electricity is applied to the armature 100 through the fixed contact 124, the lead wire 129 and the brush 107 to rotate the armature. The turning force of the armature 100 is transmitted to the overrunning clutch 106 through the helical spline 105 of the peripheral portion of the rotary shaft 102 to rotate the pinion 106c. Since the plunger 119 is moved backward, the lever 117 is turned counterclockwise to slide the overrunning clutch 106 forward to engage the pinion 106c with the ring gear secured to a flywheel attached to the crankshaft of the engine.
Immediately after the engine is started, only the pinion 106c is moved together with the ring gear because of the one-way overrunning action of the overrunning clutch 106, so that the pinion races.
When the ignition switch is opened after starting the engine, the driving coil 126 is deenergized to return the plunger 119 to the original position thereof by the force of the return spring 130 in the electromagnetic switch 118 and also return the overrunning clutch 106 to its original position. Consequently, the engine starter stops.
However, the conventional starter 1 thus constituted has a disadvantage in that it needs the shift lever 117 for sliding the overrunning clutch mechanism 106 on the extended portion 102a of the rotary shaft 102. The conventional starter 1 has another disadvantage that the layout of the engine in the vehicle is severely restricted because the electromagnetic switch 118 for operating the shift lever 117 and applying electricity to the DC motor 202 is placed alongside the DC motor which results in a two-axial type starter. The conventional starter 1 has still another disadvantage that assembly is difficult, because the weight of the starter is heavy and the number of component parts thereof is large.
Since the electromagnetic switch 118 and the DC motor are disposed in parallel with each other in the conventional engine starter, it is necessary to allocate a space in the engine or in a vehicle or the like to house the electromagnetic switch so that the engine starter can be attached to the engine. For that reason, there is a problem that the layout of the engine in the vehicle or the like is restricted.
If the electromagnetic switch 118 and the DC motor are simply disposed in series with each other in order to solve the problem, the total length of the engine starter is increased to make it difficult to lay out the engine at the rear portion of the engine starter. This is another problem.
If the overrunning clutch, which is separately constructed, the driving coil of the electromagnetic switch and so forth are placed in the armature in order to solve the former problem, it is difficult to secure a good assembling property and a sufficient processing accuracy and properly form the magnetic circuit to attain satisfactory performance and quality. This is still another problem.