1. Field of the Invention
The present invention generally relates to engine starter gearing for an engine. More specifically, this invention relates to engine starter gearing of a positive shift type, including a dentil clutch to provide driving and overrunning features and further including provisions for effecting the automatic separation of the clutch teeth after the engine becomes self-running.
2. Description of the Prior Art
The present invention is an improvement over U.S. Pat. No. 4,611,499 entitled "Engine Starter Gearing", issued September, 1986, to Giometti, and assigned to the assignee hereof, as well as a further improvement over the starter gearing system described in U.S. Pat. No. 3,263,509 entitled "Engine Starter Drive", issued Aug. 2, 1966, to Digby.
The Digby patent disclosed an engine starter gearing using centrifugal weights and a conical thrust washer for separating dentil clutch teeth after engine start-up to prevent long periods of clutch overrunning and accompanying deleterious wear on the clutch teeth. An annular recess is formed in a driving clutch member. A circular recess is provided in the face of a driven clutch member facing the driving clutch member. An annular thrust washer is fitted in the annular recess and abuts the driving clutch member. A conical surface is provided on the annular thrust washer facing the driven clutch member.
A plurality of centrifugal flyweight members are also provided in the circular recess. The centrifugal flyweight members are provided with an inclined surface cooperating with the conical surface in the annular thrust washer, such that, when an overrunning condition occurs, the centrifugal flyweight members move radially outwardly and the inclined surface engages the conical surface of the annular thrust washer so as to bias the driving clutch member away from the driven clutch member. The centrifugal flyweight members are prevented from axial or rotational movement with respect to the driven clutch member by pins extending through suitable bores in the driven clutch member and the centrifugal flyweight members.
While the engine starter gearing of Digby has been satisfactory in operation, it is difficult and expensive to assemble. This is true because a plurality of movable pins and centrifugal flyweight members must be somehow maintained in position relative to the driven clutch member during the assembly of the driven clutch member to the driving clutch member.
Furthermore, the weight and, therefore, the effectiveness of the centrifugal flyweight members is reduced by the existence of a substantial bore therethrough, in comparison to the size of the centrifugal flyweight members, for admission of the pin. The bore through the centrifugal flyweight members further reduces the strength of the centrifugal flyweight members and, accordingly, limits the materials and dimensions which may advantageously be used for the centrifugal flyweight members.
The embodiment of FIGS. 3 and 4 of U.S. Pat. No. 4,611,499 to Giometti solved many of the aforementioned engine starter gearing disadvantages, but such an embodiment requires the use of a driven clutch member whose circular recess is difficult to machine. As solutions thereto, U.S. Pat. No. 4,712,435 to Losey et al, U.S. Pat. No. 4,768,392 to Giometti, and U.S. Pat. No. 4,843,897 to Tallis Jr. disclosed various forms of annular inserts. Each of the disclosed annular inserts provided flyweight guides for guiding the flyweight members when they travel radially as a result of a centrifugal force produced during an overrunning condition. As such, the use of the annular inserts eliminated the requirement for precision machining of the circular recess of the driven clutch member.
However, in practice it has been determined that the flyweight guides of the latter patents cited are not adapted to limit the axial travel of the flyweight members as could the pin arrangement taught by Digby. As a consequence, during the overrunning condition the annular thrust washer can at times be forced back sufficiently by the interaction of the inclined surface of the flyweight members with the conical surface of the annular thrust washer to allow the flyweight members to travel axially toward the annular thrust washer until the flyweight members are beyond the flyweight guides. The flyweight members are then able to escape the flyweight guides and migrate circumferentially around the perimeter of the circular recess of the driven clutch member. Testing has indicated that this phenomenon results in momentary slipping between the driving and driven clutch members, causing high peak torques which are capable of twisting the mounting shaft splines.
Therefore, what is needed is an improved engine starter gearing using a centrifugal flyweight clutch separator which is capable of retaining the flyweight members as they travel in both the radial and axial directions such that the flyweight members are prevented from circumferentially migrating around the circular recess of the driven clutch member under all operating conditions. Furthermore, what is needed is such an engine starter gearing having a more solid, compact, and durable configuration for the centrifugal flyweight member which simplifies the manufacturing operations involved in manufacturing such engine starter gearing, particularly in regard to the driven clutch member component thereof.