Starter having intermediate gear for cranking internal combustion engine

A starter includes an electric motor, a pinion gear driven by the electric motor, and an intermediate gear driven by the pinion gear. The intermediate gear is coupled to the pinion gear by a coupler member in order to shift the intermediate gear toward a ring gear of an engine together with the pinion gear in a cranking operation. When the starter is not in operation, the intermediate gear is positioned at its rest position where a biasing force is applied to the intermediate gear to push it against the coupler member. Vibrant movement of the intermediate gear relative to the coupler member due to engine vibrations is prevented by the biasing force.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority of Japanese Patent Application No. 2002-37724 filed on Feb. 15, 2002, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a starter having an intermediate gear that is engaged with a ring gear of an internal combustion engine in a cranking operation.

2. Description of Related Art

An example of a starter having an intermediate gear is disclosed in JP-B2-2555492. In this starter, an intermediate shaft is disposed in parallel to an output shaft supporting a pinion gear thereon. An intermediate gear always engaging with the pinion gear is rotatably supported by the intermediate shaft. The pinion gear and the intermediate gear are coupled by a coupler member so that the intermediate gear shifts in its axial direction in accordance with an axial movement of the pinion gear. In a cranking operation, the intermediate gear is shifted toward a ring gear of an internal combustion engine, and a rotational torque of the pinion gear is transmitted to the ring gear via the intermediate gear.

The coupler member is coupled with the intermediate gear with a certain clearance in the axial direction in order to allow rotation of the intermediate gear relative to the coupler member while maintaining engagement with the pinion gear. Therefore, there is a problem that the intermediate gear vibrantly moves in its axial direction due to vibrations of the engine when the starter is not in operation. Such vibrant movement of the intermediate gear generates chattering noises and abrasion between the intermediate gear and the coupler member.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved starter having an intermediate gear, in which vibrant movement of the intermediate gear is suppressed.

The starter includes an electric motor powered by an on-board battery, a pinion gear driven by the electric motor, and an intermediate gear supported by an intermediate shaft disposed in parallel to an output shaft of the electric motor. The pinion gear is connected to the output shaft of the electric motor via a one-way clutch so that a rotational torque of the electric motor is transmitted to the pinion gear while preventing torque transmission from the pinion gear to the electric motor. The intermediate gear is coupled to the pinion gear by a coupling member so that the intermediate gear shifts in its axial direction together with an axial movement of the pinion gear. The intermediate gear always engages with the pinion gear and is driven by the pinion gear.

To crank up an internal combustion engine, the intermediate gear is shifted in its axial direction to be engaged with a ring gear of the engine. The engine is cranked up by the rotational torque of the electric motor transmitted via the pinion gear and the intermediate gear. After the engine is cranked up, the electric motor is stopped and the intermediate gear returns to its original rest position.

When the starter is not in operation and the intermediate gear is positioned at its rest position, a biasing force is applied to the intermediate gear to push it toward the coupler member. Preferably, a coil spring is disposed at a rear end of the intermediate gear for applying such a biasing force. The coil spring is able to generate a stable biasing force and is easily disposed at the rear end of the intermediated gear. A flange may be formed at the rear end of the intermediate gear, and the biasing force of the coil spring may be applied to a washer interposed between the flange and the coil spring.

Since the intermediate gear is pushed against the coupler member when the starter is not in operation, vibrant movement of the intermediated gear relative to the coupler member is suppressed. Accordingly, chattering noises and abrasion between the intermediate gear and the coupler member are effectively suppressed.

Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described with reference to accompanying drawings. First, referring toFIG. 1, a structure of a starter having an intermediate gear adapted to be engaged with a ring gear of an engine will be described. The starter1includes an electric motor7powered by an on-board battery, a speed reduction mechanism (not shown), a one-way clutch10, an output shaft3, a pinion gear2supported by the output shaft3, an intermediate shaft4, and an intermediate gear5supported by the intermediate shaft4. A front side and a rear side of the starter1are shown inFIG. 1in order to refer to them in the following description.

The output shaft3is disposed coaxially with an armature shaft (not shown) of the electric motor7and connected to the armature shaft through the speed reduction mechanism. Rotation of the armature shaft is transmitted to the output shaft3after a rotational speed of the armature shaft is reduced by the speed reduction mechanism. The electric motor7is a known type of a direct current electric motor. Electric power is supplied to the electric motor7from an on-board battery when an electromagnetic switch8is closed.

The electromagnetic switch8includes an electromagnetic coil8a,a plunger8bto be driven to the rear side of the starter1when the electromagnetic coil8ais energized, a return spring8cbiasing the plunger8btoward the front side, and motor contacts that are closed when the electromagnetic coil8ais energized. One end of a lever9pivotally supported in a housing11is connected to the plunger8b.When the electromagnetic coil8ais energized, the one-way clutch10is driven by the lever9toward the front side together with the pinion gear2.

The one-way clutch10is composed of an outer ring10b,an inner ring10cand rollers10ddisposed between both rings10b,10c.A barrel portion10aformed integrally with the outer ring10bis coupled to the output shaft3by means of helical spline connection. The pinion gear2is formed integrally with its cylindrical portion2aand the inner ring10cof the one-way clutch10. The one-way clutch10transmits a rotational torque of the output shaft3to the pinion gear2while interrupting torque transmission from the pinion gear2to the output shaft3.

The intermediate shaft4is inserted at its both ends into supporting holes11a,11bformed in the housing11and fixed to the housing by a pin12. The intermediate shaft4includes a rear end portion4b(shown inFIG. 3A) having a diameter smaller than a diameter of its main portion. A stepped surface4ais formed at a boundary of the rear end portion4band the main portion, as shown in FIG.3A. The pin12is inserted through the rear end portion4band fixed to the housing11. The intermediate shaft4is connected to the housing11so that it neither rotates nor moves in the axial direction.

The intermediate gear5has a cylindrical sleeve5aand a flange5b,all being integrally formed. The flange5bhaving a larger diameter is formed at the rear end of the cylindrical sleeve5a.The intermediate gear5is supported by the intermediate shaft4with bearings13interposed therebetween, so that the intermediate gear5is slidably movable in the axial direction and rotatable around the intermediate shaft4. The cylindrical portion2aof the pinion gear2and the cylindrical sleeve5aof the intermediate gear5are coupled by a coupler member14. The coupler member14is held in grooves formed on the cylindrical portion2aand the cylindrical sleeve5a.Thus, the intermediate gear5is slidable in its axial direction according to an axial movement of the pinion gear2, while maintaining engagement of the intermediate gear5with the pinion gear2. A washer16and a coil spring15are disposed at the rear end of the flange5b,so that the intermediate gear5is biased toward the front side when the starter1is not in operation.

The coupling member14is made of a resin material and has a uniform thickness in its axial direction. As shown inFIG. 2, the coupling member14has a first groove14athat slidably engages with the cylindrical portion2aof the pinion gear2and a second groove14bthat slidably engages with the cylindrical sleeve5aof the intermediate gear5. The first groove14ais connected to an opening14cthrough which the cylindrical portion2ais coupled to the first groove14a.The thickness of the coupler member14is made a little smaller than the width of the grooves formed on the cylindrical portion2aand the cylindrical sleeve5ain order to provide a small axial clearance between the coupler member14and the grooves. The coupler member14restricts relative movement between the pinion gear2and the intermediate gear5in the axial direction and allows rotation of both gears2,5relative to the coupler member14.

Referring toFIGS. 3A and 3B, the biasing function of the coil spring15will be described.FIG. 3Ashows a situation where the starter1is not in operation, i.e., the intermediate gear5is positioned at its rest position. (The rest position is also shown inFIG. 1.) At the front end of the supporting hole11b,a circular space for disposing the coil spring15therein is formed. The washer16is disposed to abut the rear end of the flange5b,and the coil spring15is disposed to bias the intermediate gear5toward the front side. Because an axial space is provided between the rear end of the flange5band the stepped surface4a,the washer16does not abut the stepped surface4a.The biasing force of the coil sprig15is set to a level lower than the biasing force of the return spring8cin the electromagnetic switch8in order not to push the intermediate gear5to the front side when the electromagnetic switch8is not energized.

FIG. 3Bshows a situation where the starter1is in operation, i.e., the intermediate gear5is pushed frontward by the lever9driven by the electromagnetic switch8. Under this situation, the washer16abuts the stepped surface4aof the intermediate shaft4, not abutting the flange5bof the intermediate gear5. Therefore, the biasing force is not given to the intermediate gear5.

Now, operation of the starter1will be described. Upon energization of the electromagnetic coil8a,the plunger8bis pulled toward the rear side, and the one-way clutch10is slidably pushed to the front side together with the pinion gear2by the lever9connected to the plunger8b.According to the frontward movement of the pinion gear2, the intermediate gear5coupled to the pinion gear2by the coupler member14is pushed frontward while keeping the engagement with the pinion gear2. The biasing force of the coil spring15is applied to the intermediate gear5until the washer16abuts the stepped surface4aof the intermediate shaft4.

After the intermediate gear5abuts the ring gear6of the engine, the plunger8bis further driven to the rear side, thereby closing the motor contacts. When the motor contacts are closed, the electric motor7is operated and the output shaft3is rotated. The rotational torque of the output shaft3is transmitted to the pinion gear2via the one-way clutch10. The intermediate gear5engaging with the pinion gear2rotates to an angular position where engagement of the intermediate gear5with the ring gear6is allowed. Upon establishment of the engagement between the intermediate gear5and the ring gear6, the rotational torque of the electric motor7is transmitted to the ring gear6to thereby crank up the engine. During a period in which the engine is being cranked, the biasing force of the coil spring15is not applied to the intermediate gear5. Therefore, the intermediate gear5is able to rotate without receiving the biasing force of the coil spring15, and abrasion between the intermediate gear5and the coupler member14does not occur.

After the engine is cranked up, the electromagnetic coil8ais de-energized. The plunger8bis returned to its original rest position by the return spring8c,and thereby the one-way clutch10is also returned to its rest position together with the pinion gear2. The intermediate gear5coupled to the pinion gear2returns to its rest position while maintaining its engagement with the pinion gear2. At this rest position, as shown inFIG. 3A, the biasing force of the coil spring15is applied to the intermediate gear5via the washer16. Accordingly, the flange5bof the intermediate gear5is pushed against the coupler member14, thereby establishing a close contact between the intermediate gear5and the coupler member14.

Following advantages are achieved in the embodiment described above. The biasing force of the coil spring15is applied to the intermediate gear5via the washer16when the intermediate gear5is at the rest position, i.e., when the starter1is not in operation. Therefore, the intermediate gear5is pushed against the coupler member14, and the axial movement of the intermediate gear5is restricted. As a result, chattering noises of the intermediate gear5due to vibrations of the engine are suppressed, and abrasion wear of the intermediate gear5and the coupler member14is suppressed.

During a course in which the intermediate gear5is returning to the rest position after the engine is cranked up, the intermediate gear5still continues rotation by its inertia. When the flange5bof the intermediate gear5abuts the washer16, the biasing force of the coil spring15is applied to the intermediate gear5. Therefore, the rotational speed of the intermediate gear5by its inertia is reduced by the biasing force of the coil spring15. If the starter1is operated again by a driver's error while the intermediate gear5is still rotating, and the intermediate gear5abuts the ring gear6, the ring gear6and the intermediate gear5are prevented from being damaged by such an erroneous operation because the rotational speed of the intermediate gear5is reduced by the biasing force of the coil spring15.

The biasing force of the coil spring15is applied to the intermediate gear5in a frontward direction when the starter1is not in operation, as shown in FIG.3A. Therefore, when the starter1is put into operation and the intermediate gear5initiates its frontward movement, the biasing force of the coil spring5helps such frontward movement at the initial stage. As a member to generate the biasing force, a resilient member other than the coil spring15may be used. However, it is preferable to use the coil spring15, because it can be easily disposed in the circular space formed in the housing11, and a stable biasing force can be obtained form the coil spring.