1. Field of the Invention
The present invention relates to a starter that starts an engine by pushing a pinion with a shift lever so that the pinion meshes with a ring gear of the engine.
2. Background Art
A structure often adopted by a starter of this type is as follows. That is, a lever device (shift lever) provided with a lever ring is swayed by exploiting a plunger attracting force of a magnet switch. A pinion provided integrally with a clutch shaft (output shaft) is then pushed in an axial direction by the lever ring and meshes with a ring gear to get the engine started. After the engine is started, the pinion is demeshed from the ring gear.
In order to start the engine, it is necessary to form the clutch shaft to be able to rotate at a high speed. Also, in order to allow the ring gear and the pinion to mesh with each other, it is necessary to form the clutch shaft to be movable in the axial direction and thereby become able to operate in association with an operation of the lever device including the lever ring. Further, in order to prevent displacement between the clutch shaft and the lever device, there is a case where the clutch shaft and the lever device are coupled to each other.
In this case, the starter adopts a fall-off preventing structure. More specifically, after components, such as the lever ring, a stop ring, and a washer, are attached to the clutch shaft, these components are fixed to the clutch shaft with a snap ring so as not to fall off (for example, Patent Document 1).
A C-type snap ring, which is a circular ring with a uniform peripheral rim width and having a notch, is used as the snap ring and serves as a retainer for the respective components when the engine is started normally. However, in a case where the pinion is not pushed back after the engine is started and the ring gear and the pinion remain in a meshed state, there occurs a phenomenon called an overrun that a motor rotates excessively due to rotations of the engine. In order to avoid this inconvenience, the starter of this type is provided with a one-way clutch. Nevertheless, it is still impossible to prevent an overrun at a predetermined region between the clutch and the pinion, that is, the clutch shaft to which the snap ring is attached, and the clutch shaft and the snap ring rotate at a high speed. Accordingly, an excessively large centrifugal force of the clutch shaft in a radially outward direction acts on the snap ring attached to the clutch shaft. As the clutch shaft rotates faster, the snap ring may possibly undergo deformation because of an increasing centrifugal force. When the centrifugal force exceeds fixing force of the snap ring, the snap ring may undergo expansion deformation to the extent that the snap ring falls off from the clutch shaft. As a result, the stop ring and the washer fall off from the clutch shaft. In a case where the lever device is unable to push the pinion provided integrally with the clutch shaft in the axial direction, the engine fail to start. In a case where the lever device is unable to demesh the pinion from the ring gear after the engine is started, the starter is damaged by the overrun. The starter in the related art therefore has a problem that the reliability is deteriorated considerably.
As a countermeasure to prevent a fall-off of the snap ring, the rim width of the snap ring may be increased to make the snap ring more rigid, so that the snap ring has not only the fixing force necessary to regulate the respective components attached to the clutch shaft in the axial direction but also the fixing force high enough to withstand the centrifugal force of the clutch shaft generated while the clutch shaft is rotating at a high speed. Another countermeasure may be to provide a holder that is fit onto the snap ring shown in FIG. 7 of Patent Document 1 from a radially outward direction to prevent the snap ring from undergoing deformation due to the centrifugal force, thereby making it possible to prevent a fall-off of the snap ring.
Patent Document 1: Japanese Patent No. 4375314
According to the former countermeasure to prevent a fall-off of the snap ring, however, because the snap ring is made more rigid by increasing the rim width thereof, a large force is necessary to attach or remove the snap ring when the starter is assembled or disassembled. The former countermeasure therefore has a problem that attaching and removing workability becomes poor. Meanwhile, the latter countermeasure requires an extra work to attach or remove the fall-off preventing holder when the starter is assembled or disassembled. The latter countermeasure therefore has a problem that attaching and removing workability of the snap ring becomes poor in comparison with a structure having no fall-off preventing holder.