GB2270954A

GB2270954A - Starter motor

Info

Publication number: GB2270954A
Application number: GB9323025A
Authority: GB
Inventors: Shuzou Isozumi; Keiichi Konishi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1989-09-29
Filing date: 1993-11-09
Publication date: 1994-03-30
Anticipated expiration: 2010-09-19
Also published as: GB9323025D0; GB2270954B

Abstract

An engine starter comprises a DC motor having a hollow armature rotation shaft 3 connected by way of a planetary gear speed reducer 9 to an output rotation shaft 4 axially slidably received in the armature rotation shaft, the output rotation shaft 4 having a helical spline portion 4c engaged with a helical spline portion of an inner member 7b of an overrunning clutch device 7. A pin ion 5 is mounted on a front end of the output rotation shaft 4 to engage with a ring gear of an engine. The pinion 5 is formed integrally with a tubular portion 115 which is slidable relative to a portion 109 of the clutch inner member 7b and with the exterior of the output rotation shaft 4. <IMAGE>

Description

STARTER MOTOR This invention relates to a starter motor used mainly for starting an engine of a vehicle.

Figure 1 is a cross-sectional view of a portion of a conventional starter motor disclosed, for example, in Japanese Patent Application Unexamined Publication No. sho. 63-90665. This starter motor is of the coaxial type in which an armature rotation shaft 3 of a DC motor 2, an output rotation shaft 4 having a pinion 5 mounted on its front end (right end in the drawings), and an electromagnetic switch device (not shown) are disposed on a common axis. More specifically, the armature rotation shaft 3 is hollow, and a plunger rod 105 of the electromagnetic switch device disposed rearwardly of the DC motor 2 is extended into an internal passage 3a of the armature rotation shaft 3. The output rotation shaft 4 is received in a front end portion of the internal passage 3a, and the plunger rod 105 is abutted against the rear end face of the output rotation shaft 4 through a steel ball 106.Upon forward movement of the plunger rod 105, the output rotation shaft 4 is urged or pushed forwardly.

The output rotation shaft 4 has at its front end (right end) the pinion 5 meshingly engageable with a ring gear of the engine, and the rear portion of the output rotation shaft 4 is inserted in the internal passage 3a of the armature rotation shaft 3. This inserted portion å is borneiby a sleeve bearing 6 fixedly fitted in the internal passage 3a, so that output rotation shaft 4 is slidable axially. Means for transmitting.^à drive force from the armature rotation shaft 3 of the DC motor 2 to the axially slidable output rotation shaft 4 is constituted by a drive force transmitting device 8 including an overrunning clutch device (one-way clutch) 7.

Interposed between the inner peripheral portion (disposed inwardly of the pinion teeth) of the pinion 5 and the output rotation shaft 4 is a pinion spring 10 which normally urges the pinion in a forward direction.

More specifically, the drive force transmitting device 8 comprises a planetary gear speed reducer 9 including a sun gear 9a formed on the outer periphery of the armature rotation shaft 3 as well as planetary gears 9b, and the above-mentioned one-way clutch device 7 which includes a clutch outer member 7a to which central support shafts 9c for the planetary gears 9b are fixedly secured, and a clutch inner member 7b having at its inner peripheral surface helical spline grooves 109d meshed with a helical spline portion 4c formed on an outer periphery of an enlargedcliameter portion 4b of the output rotation shaft 4. Reference numeral 11 denotes a pinion stopper.

In the above conventional starter device of the coaxial type, when it is intended to reduce the size of the DC motor, it is considered that this can be achieved by reducing the number of the teeth of the pinion to increase the reduction ratio between the ring gear and the pinion. In this case, in the conventional device, the pinion spring is provided between the inner peripheral portion T of the pinion and the output rotation shaft in radially overlapping relation, and therefore with the construction of Figure 1, if the number of the teeth of the pinion is reduced, there is encountered a problem that the mechanical strength (i.e.s;:the strength of the inner peripheral portion T of the pinion and the strength of the shaft) is reduced.

On the other hand, the sun gear 9a of the planetary gear speed reducer 9 is formed on the front end of the armature rotation shaft 3. The planetary gear speed reducer 9 comprises the sun gear 9a, an inner gear 107b formed on an inner peripheral surface of a front bracket 108, and the planetary gears 9b rotatably supported by the respective central support shafts 9c and meshed with the sun gear 9a and the inner gear 107b.

The central support shafts 9c of the planetary gear speed reducer 9 are fixedly secured to the clutch outer member 7a of the overrunning clutch device 7, so that a reduction output of the armature rotation shaft 3 can be transmitted to the overrunning clutch device 7. The clutch inner member 7b is provided inwardly of the clutch outer member 7a, and rollers 109c are provided between the clutch outer 7a and inner members 7b, and these parts constitutes the overrunning clutch device 7.

Formed in the inner peripheral surface of the clutch inner member 7b are the helical spline grooves 109d meshed with the helical spline portion 4c formed on the enlarged-diameter portion 4b of the output rotation shaft 4. A return spring 110 is provided between a stepped portion 109e on the front end of the clutch inner member 7b and the helical spline portion 4c, and urges the output rotation shaft 4 rearwardly. The front end of the clutch inner member 7b is supported by a bearing 111 fitted in the front bracket 108.

The pinion 5 is spline-connected to a straight spline formed on the front end of the output rotation shaft 4, and a forward movement of the pinion 5 is limited by the stopper 11. The pinion spring 10 is provided inwardly of the inner periphery of the pinion 5, and acts between the pinion 5 and a stepped portion 104b on the output rotation shaft 4, the pinion spring 10 urging the pinion 5 forwardly. The pinion spring 10 is provided in order to normally urge the pinion 5 forwardly after the stopper 11 is fixed in position and also to dampen an impact produced when the pinion 5 is abutted against the ring gear. The bearing 6 is mounted within the internal passage 3a of the armature rotation shaft 3, and supports the rear portion of the output rotation shaft 4.

In the coaxial-type starter motor of the above construction, the rotational drive force of the DC motor 2 is transmitted to the overrunning clutch device 7 via the planetary gear speed reducer 9, and is further transmitted to the output rotation shaft 4 spline-fitted in the clutch inner member 7b. At this time, the plunger rod 105 is driven forwardly to move the output rotation shaft 4 forwardly, so that the pinion 5 is brought into meshing engagement with the ring gear (not shown) of the engine, thereby starting the engine. After the engine start, when the operator (driver) turns off the electromagnetic switch device, the plunger rod 105 is retracted, and the output rotation shaft 4 is returned to the original position (stationary position) under the influence of the return spring 110, so that the pinion 5 is disengaged from the ring gear. A reverse drive, applied from the engine immediately after the start of the engine, is prevented by the one-way clutch operation of the overrunning clutch device 7 from being transmitted to the DC motor 2.

The conventional starter motor is of the above construction, and the front portion of the output rotation shaft 4 is supported by the splinefitting between the helical spline grooves 1 09d of the clutch inner member 7b and the helical spline portion 4c. However, with respect to the helical spline fitting, it is difficult to extremely reduce a clearance in the fitting portion from the viewpoint of ensuring a sliding ability.

Therefore, a play of a certain amount is present between the output rotation shaft 4 and the clutch inner member 7b, and moreover since the fitting portion serving as the support portion is not provided at the front end portion of the clutch inner member 7b, the distance between this fitting portion and the pinion 5 is large, and hence a moment is large.

As a result, because of such a play and such a large moment, the conventional starter motor has problems that abnormal noises are produced and that in the worst case, the output rotation shaft 4 is broken. Further, the helical spline grooves 109d not only receive the load but also serve as the sliding surface for the output rotation shaft 4, and therefore depending on the determined value of the clearance, this has often been a factor in an improper sliding of the output rotation shaft 4 because of deterioration of grease on the spline fitting portion and of the deposition of dust on this portion.

With the above problems in view, it is an object of this invention to provide a coaxial-type starter device which can be of a smail-size without reducing the strength of the inner peripheral portion of the pinion and the strength of the shaft.

More specifically, according to the invention, there is provided a starter motor including an overrunning clutch device to which motor drive force is transmitted; an output rotation shaft fitted by helical splines in an interior surface of a clutch inner member serving as the output of said overrunning clutch device, in such a manner that said output shaft is movable axially; and a pinion mounted on the front end portion of said output rotation shaft so as to be brought into and out of engagement with a ring gear of an engine; characterised in that there is provided a tubular member integrally formed with said pinion, an outer surface of said tubular member being disposed in sliding contact with a portion of the interior surface of said clutch inner member disposed forwardly of the helical spline fitting portion of said clutch inner member, and an inner surface of said tubular member being disposed in sliding contact with said output rotation shaft.

Figure 1 is a cross-sectional view of a portion of the conventional starter motor; Figure 2 is a partly cross-sectional, front-elevational view of a first embodiment of a starter motor of the present invention; and Figure 3 is a partly cross-sectional, front-elevational view of a second embodiment of a starter motor of the present invention.

Figure 1 shows a first embodiment of a starter motor of the present invention. Reference numerals 1 to 14 in Figure 2 and Figure 1 denote corresponding portions, and therefore explanation of such corresponding portions is omitted here. A tubular portion 115 is extended integrally from a rear end of a pinion 5. The diameter of the inner peripheral surface of the tubular portion 115 is so determined as to provide such a clearance between this inner peripheral surface and an output rotation shaft 4 that the output rotation shaft 4 is slidable relative to the inner peripheral surface of the tubular portion 115. The outer peripheral surface of the tubular portion 115 is disposed in sliding contact with an inner peripheral surface of a support portion 1 09f formed on a front end of a clutch inner member 7b.A return spring 110 is provided between the rear end of the support portion 1 09f disposed outwardly of the tubular portion 115 and a front end of a helical spline portion 4c of the output rotation shaft 4. A pinion spring 10 is provided between the rear surface of the pinion 5 disposed inwardly of the tubular portion 115 and a stepped portion 1 04b on the output rotation shaft 4. An electromagnetic switch device 116 is provided adjacent to a rear end of a DC motor 2.

In the starter motor of the above construction, the output rotation shaft 4 is slidably supported by the support portion 109f of the clutch inner member 7b via the tubular portion 115, and therefore a clearance between the sliding portions of the clutch inner member 7b and the output rotation shaft 4 is small, and the output rotation shaft 4 is hardly shaken. Further, since the output rotation shaft 4 is supported at the front end of the clutch inner member 7b, and the distance between this support portion and the pinion 5 is small, and therefore a moment of the output rotation shaft 4 is small. In addition, since the supported tubular portion 115 is integral with the pinion 5, the pinion 5 itself is supported by the clutch inner member 7b, and therefore a play is not produced when the pinion 5 is meshed with the ring gear, and the eccentricity is prevented.

Further, in this embodiment, the pinion spring 10 is disposed rearwardly of the pinion 5, the inner peripheral portion of the pinion 5 can be reduced further as compared with the prior art in which the pinion spring 10 is disposed inwardly of the inner periphery of the pinion 5.

This enables the number of the teeth of the pinion 5 to be reduced.

Namely, conventionally, since the pinion spring 10 is disposed inwardly of the inner periphery of the pinion 5, it has been difficult to reduce the number of the teeth of the pinion 5 to less than a predetermined value, because the strength of the inner peripheral portion of the pinion must be ensured. In this embodiment, however, since the pinion spring 10 is not disposed inwardly of the inner periphery of the pinion 5, the diameter of the inner peripheral portion of the pinion can be reduced while keeping the strength of the inner peripheral portion of the pinion, and as a result the number of the teeth of the pinion can be reduced.

More specifically, if the tooth configuration has a level represented by M (module) = 2.54, the number of teeth which has conventionally been 8 at the best can be reduced to 7 in the present invention. Therefore, the reduction ratio between the ring gear and the pinion 5 can be increased, so that the relative torque is increased, which enables a small size of the starter motor.

In this embodiment, the engine start operation is the same as that of the prior art, its explanation is omitted here. In Figure 2, the upper side above the centre line represents the stationary condition, and the lower side represents the operative condition after the movement of the pinion 5 is completed.

Figure 3 shows a second embodiment of the invention. In this embodiment, the pinion spring 10 is provided between the rear surface of the tubular portion 115 and a front end surface of a helical spline portion 4c of an output rotation shaft 4. Except for this, the construction and operation of this embodiment are the same as those of the preceding embodiment, and this embodiment achieves the effects similar to those of the preceding embodiment.

In the above embodiments, although the support portion 1 09f of the clutch inner member 7b is in direct sliding contact with the tubular portion 115, a thin bearing may be interposed therebetween, in which case the sliding ability of the tubular portion 115 is enhanced.

Further, although the above embodiments are directed to the coaxial-type starter motor in which the electromagnetic switch device 116 is disposed rearwardly of the DC motor 2, the present invention is not restricted to such embodiments. For example, the present invention may be directed to a starter motor of the type in which the electromagnetic switch device and the motor portion are disposed parallel to each other, and a starter motor of the inertia sliding type having no electromagnetic switch device. Further, although the starter motors of the above embodiments include the planetary gear speed reducer 9, the starter motors achieve similar effects even if they are not provided with such speed reducer.

As described above, in the embodiments, the tubular member is formed integrally with the pinion, and the output rotation shaft is supported on the front portion of the clutch inner member via the tubular member.

Therefore, there is almost no play between the output rotation shaft and the clutch inner member, and a moment between the pinion and the support portion is small, and therefore advantageously the production of abnormal noises and the breakage of the output rotation shaft are prevented.

Further, since the output rotation shaft is supported by the clutch inner member not only through the helical spline fitting portion but also through the tubular member, there is almost no play between the clutch inner member and the output rotation shaft. Also, since its support portion is disposed forwardly of the helical spline fitting portion, the moment of the output rotation shaft is small.

Claims

1. A starter motor including an overrunning clutch device to which motor drive force is transmitted; an output rotation shaft fitted by helical splines in an interior surface of a clutch inner member serving as the output of said overrunning clutch device, in such a manner that said output shaft is movable axially; and a pinion mounted on the front end portion of said output rotation shaft so as to be brought into and out of engagement with a ring gear of an engine; characterised in that there is provided a tubular member integrally formed with said pinion, an outer surface of said tubular member being disposed in sliding contact with a portion of the interior surface of said clutch inner member disposed forwardly of the helical spline fitting portion of said clutch inner member, and an inner surface of said tubular member being disposed in sliding contact with said output rotation shaft.