EP2812563A1

EP2812563A1 - Vehicle starter and spline assembly thereof

Info

Publication number: EP2812563A1
Application number: EP13746729.6A
Authority: EP
Inventors: Fangmin Deng; Micheal STAHL; Andreas JURASCHKA
Original assignee: Bosch Automotive Products Changsha Co Ltd; Robert Bosch GmbH
Current assignee: SEG Automotive Germany GmbH
Priority date: 2012-02-06
Filing date: 2013-02-06
Publication date: 2014-12-17
Also published as: EP2812563A4; WO2013117158A1; CN103244570A; CN103244570B

Abstract

A spline assembly (5) for a vehicle starter, has two spline parts (20,30) each provided with spline teeth (32) with spline slots (22) formed therebetween. The spline teeth (32) of one spline part (30) are matched with the spline slots (22) of anther spline part (20) so that the two spline parts (2030) are axially slid opposite to each other. Top lands (36) of the spline teeth (32) of one spline part (30) are ground wholly in a single grinding process so that the radius of addendum circle of one spline part (30) is smaller than the radius of dedendum circle of anther spline part (20) by 0.02 to 0.15 mm. The spline assembly (5) has high torque transfer ability and simple structure.

Description

Vehicle Starter and Spline Assembly Thereof

Technical Field

The invention relates to a spline assembly used in a vehicle starter and a vehicle starter comprising such a spline assembly.

Background Art

Electric starters are generally used in current vehicles for starting the engines of the vehicles. A starter is such a component that converts the electricity stored in a battery of a vehicle into mechanical energy to drive the engine of the vehicle to operate, so that the engine is started.

A starter generally comprises a DC motor, a transmission mechanism, a control device, etc. When the engine of the vehicle is to be started, the motor is energized by a direct current from the battery to generate a rotational torque. The rotational torque is transmitted by the transmission mechanism to a ring gear on a flywheel of the engine to drive a crank shaft of the engine to rotate. The transmission mechanism comprises a speed reducing mechanism coupled with an output shaft of the motor, an overrunning clutch coupled with the speed reducing mechanism, a drive shaft having an inner end coupled with the overrunning clutch via a spline assembly, and a pinion mounted to an outer end of the drive shaft for driving the ring gear. The spline assembly comprises an internal spline part formed in the overrunning clutch and an external spline part formed on the inner end of the drive shaft, the external spline part being mating with the internal spline part and axially slidable with respect to it. The control device is able to control the operation of the motor, as well as to control the drive shaft to move axially so that the pinion is engaged with and disengaged from the ring gear.

When the drive shaft outputs the rotational torque to the ring gear at its outer end via the pinion, the outer end of the drive shaft receives a reaction force from the ring gear. The external spline part on the inner end of the drive shaft, under the reaction force, is displaced eccentrically with respect to the internal spline part in the overrunning clutch, so that a coaxiality error is generated. The coaxiality error negatively affects the transmission property of the starter significantly and should thus be depressed to a minimum extent.

In order to reduce the coaxiality error of the spline assembly, GB2165620A discloses a solution in which some splines of a sliding spline component of a spline assembly are each provided with axially spaced circumferentially extending resilient projections on its top surface. According to this solution, a supplementary structure is necessary if a high coaxiality of the spline assembly is required, thus the manufacturing cost of the spline assembly is increased.

Further, according to a solution disclosed in CN1530537A, as shown in Figure 1 in the drawings of the present application, a convexed spline part formed on an inner end of a drive shaft 10 of a starter is mating with a concaved spline part formed in an inner ring 11 of an overrunning clutch, and the inner ring 11 is formed with a stopper 12 having a through hole therethrough. The drive shaft 10 extends through the through hole of the stopper 12 to form a shaft-and-hole fitting structure which improves the coaxiality between the convexed and concaved spline parts in a supplementary manner. According to this solution, a supplementary structure thus formed is used for improving the coaxiality of the spline assembly, which results in increasing of the manufacturing cost of the spline assembly.

Thus, it is desired to solve the problem found in the prior art, i.e., increased cost arose from the supplementary structure which is adopted for improving the coaxiality of the spline assembly.

Summary of the Invention

An object of the invention is to improve the spline assembly of the vehicle starter, which contributes to a higher coaxiality of the spline assembly without using any supplementary structure.

According to one aspect of the invention, there provides a spline assembly of a vehicle starter which comprises a first spline part comprising a set of teeth with slots formed between neighboring teeth; and a second spline part mated with the first spline part and comprising a set of teeth with slots formed between neighboring teeth; wherein the teeth of the second spline part are engaged in corresponding slots of the first spline part, and the teeth of the first spline part are engaged in corresponding slots of the second spline part, so that the first spline part and the second spline part are slidable with respect to each other in an axial direction; and wherein top lands of the set of teeth of the first spline part are ground as a whole in a single grinding process in a manner that the radius of an addendum circle defined by the top lands of the first spline part is smaller than the radius of a dedendum circle defined by bottom lands of the slots of the second spline part by 0.02 to 0.15 mm.

Preferably, the radius of the addendum circle of the first spline part is smaller than the radius of the dedendum circle of the second spline part by 0.04 to 0.08 mm.

According to a preferred embodiment of the invention, the first spline part comprises an external spline part having radially outwardly protruded teeth, and the second spline part comprises an internal spline part having radially inwardly protruded teeth.

According to a preferred embodiment of the invention, the teeth of the first and second spline parts are helical teeth.

According to a preferred embodiment of the invention, in the operation state of the spline assembly, the central axis of the first spline part is displaced in an radial direction with respect to the central axis of the second spline part by such a distance that the top land and a pressure bearing flank of one of the teeth of the first spline part contact a corresponding bottom land and a corresponding pressure bearing flank of the second spline part respectively, while a pressure free flank of said one of the teeth of the first spline part is separated by a side clearance from a corresponding pressure free flank of the second spline part.

According to a preferred embodiment of the invention, each tooth of the first spline part comprises a pressure bearing flank edge on the top land in the form of a sharp edge generated in the grinding process, and the second spline part comprises an interference avoiding structure at an edge formed between the bottom land and a pressure bearing flank in each slot for avoiding any interference with the sharp edge.

According to a preferred embodiment of the invention, an edge formed between the top land and a pressure bearing flank of each tooth of the first spline part is chamfered.

According to a preferred embodiment of the invention, an edge formed between the top land and a pressure bearing flank of each tooth of the first spline part is rounded.

According to a preferred embodiment of the invention, the pressure bearing flank of each tooth of the second spline part has a pressure angle which is smaller than the pressure angle of the pressure bearing flank of each tooth of the first spline part.

According to another aspect of the invention, there provides a vehicle starter which comprises a motor; a speed reducing mechanism coupled with an output shaft of the motor; an overrunning clutch coupled with the speed reducing mechanism; a spline assembly as described above, with the second spline part of the spline assembly coupled with a driven part of the overrunning clutch; an drive shaft coupled with the first spline part of the spline assembly; and a pinion carried by the drive shaft for outputting a rotational movement.

According to the invention, the top land of one of the internal and external spline parts of the spline assembly of the starter is subjected to a grinding treatment in a manner that the clearance between the top and bottom lands of the internal and external spline parts is reduced. In this way, the coaxiality of the internal and external spline parts is increased significantly. In addition, according to the invention, the coaxiality of the internal and external spline parts can be improved by means of the spline assembly itself, without using any supplementary structure, so that the spline assembly may have a simple structure and relatively low cost. Further, the spline assembly may maintain high torque transmitting ability and structure reliability.

Brief Description of the Drawings

Figure 1 is a schematic view of a spline assembly used in a vehicle starter according to prior art.

Figure 2 is a schematic view of a portion of a vehicle starter according to a preferred embodiment of the invention.

Figure 3 is an enlarged schematic view of the spline assembly of the starter shown in Figure 2.

Figure 4 is an enlarged sectional view taken along line A-A in Figure 3.

Figure 5 is a schematic view for explaining the mating manner and the coaxiality error of the internal and external spline parts of the spline assembly according to prior art.

Figure 6 is a schematic view for explaining the relation between the top clearance and the side clearance of the internal and external spline parts of the spline assembly.

Figure 7 is a schematic view for explaining the mating manner and the coaxiality error of the internal and external spline parts of the spline assembly of the invention.

Figure 8 is a schematic view showing rounded edges on the top and bottom lands of the internal and external spline parts of the spline assembly according to prior art.

Figure 9 is a schematic view of the internal and external spline parts of the spline assembly according to a preferred embodiment of the invention, wherein the internal spline part comprises grounded top lands.

Figures 10-12 are schematic views showing some measures adopted in the invention for avoiding interference between the grounded top lands and the edges of the mating bottom lands.

Detailed Description of Preferred Embodiments

Now some preferred embodiments of the invention will be described with reference to the drawings. Figure 2 shows a portion of a vehicle starter according to a preferred embodiment of the invention. The starter mainly comprises a DC motor 1 , a transmission mechanism, a control device, etc.

The motor 1 is mounted in a housing (not shown) of the starter. When the engine of the vehicle is to be started, the control device functions to supply the motor 1 with a DC electric current from a battery of the vehicle, so that the motor 1 runs to generate a rotational torque. The rotational torque is transmitted to a ring gear 2 on a flywheel of the engine via the transmission mechanism to drive a crank shaft of the engine to rotate.

The transmission mechanism mainly comprises a speed reducing mechanism 3 coupled with an output shaft of the motor 1, an overrunning clutch 4 coupled with the speed reducing mechanism 3, a drive shaft 10 having an inner end (the end near the motor 1) coupled with the overrunning clutch 4 via the spline assembly 5, and a pinion mounted to an outer end (the end away from the motor 1) of the drive shaft 10 for driving the ring gear 2.

The speed reducing mechanism 3 may be any type of speed reducing mechanism, for example, a gear type speed reducing mechanism. Figure 2 shows a planetary gear type speed reducing mechanism, which comprises a central gear 3-1 mounted to the output shaft of the motor 1, a fixed outer ring gear 3-2 mounted concentrically around the central gear 3-1, at least one planetary gear 3-3 meshed between the central gear and the outer ring gear, and a planetary carriage 3-4 to which a central shaft of the planetary gear 3-3 is mounted. When the output shaft of the motor 1 drives the central gear 3-1 to rotate, the planetary carriage 3-4 outputs a rotational movement at a reduced speed.

As shown in Figures 2 and 3, the overrunning clutch 4 comprises an internal part 4-1, an external part 4-2, and movement transmitting means for transmitting unidirectional rotational movements from the internal part to the external part. In the embodiment shown in Figures 2 and 3, the movement transmitting means comprises rollers 4-3; it is appreciated that, however, the movement transmitting means may alternatively be in other forms known in the art, such as wedges, ratchets, or the like.

Further, in the embodiment shown in Figures 2 and 3, the internal part 4-1 forms a driving part of the overrunning clutch 4, and the external part 4-2 forms a driven part of the overrunning clutch 4. However, it is appreciated that the external part 4-2 may alternatively form a driving part, and the internal part 4-1 forms a driven part. The planetary carriage 3-4 of the speed reducing mechanism 3 is mounted to the driving part (the internal part 4-1 in Figures 2 and 3) or formed integrally with it. The driven part of the overrunning clutch 4 transmits a rotational movement from the speed reducing mechanism 3 to the drive shaft 10 via the spline assembly 5. As shown in Figures 2 and 3, the spline assembly 5 comprises an internal spline part 20 and an external spline part 30 mating with it. The internal spline part 20 forms or is mounted to the driven part (the external part 4-2 in Figures 2 and 3) of the overrunning clutch. The external spline part 30 forms or is mounted to the inner end of the drive shaft 10.

Each of the internal and external spline parts comprises teeth which are engaged in corresponding slots of the other of the internal and external spline parts, as shown in Figure 4.

Each tooth of the internal and external spline parts may have a profile that is in any form known in the art, such as a trapezoidal tooth profile, an involute tooth profile, or the like. In addition, the teeth may extend straightly or helically with respect to the central axis of the internal or external spline part. Helically extended teeth as shown in Figure 2 are preferred when operation property is taken into consideration.

The external spline part 30 is axially slidable with respect to the internal spline part 20 (in the condition that helical teeth are used, the external spline part 30 is additionally rotatable with respect to the internal spline part 20 at the same time) to apply an axial displacement to the drive shaft 10. Such an axial displacement is effected by a lever 14 of the control device. The lever 14 comprises a middle portion pivotably mounted to a fixed pivot shaft 14-1, a rear end 14-2 that can be pushed and pulled in substantially the axial direction of the drive shaft 10 by an actuating element (not shown) of the control device, and a front end 14-3 pivotably attached to the drive shaft 10. When the rear end of the lever 14 is pushed or pulled in the axial direction by means of the actuating element of the control device, the lever 14 pivots around the pivot shaft 14-1, so that the front end of the lever drives the drive shaft 10 to move in the axial direction (with the external spline part 30 sliding in the axial direction with respect to the internal spline part 20). Figure 2 shows that the drive shaft 10 (with the external spline part 30) is in the axially outmost position. For keeping the drive shaft 10 (with the external spline part 30) in this position, the inner end of the drive shaft 10 is provided with a stop 16 which can abut against the inner end of the internal spline part 20 (or abut against a portion of the external part 4-2), to prevent the external spline part 30 from further axially sliding in a distal direction (towards the left side in Figure 2) with respect to the internal spline part 20. In this position, the internal spline part 20 is able to drive the external spline part 30 to rotate together with it.

The drive shaft 10 is supported at its substantially middle portion in the housing of the starter via a bearing 18. Of course, the drive shaft may alternatively be supported at its other portions by a bearing. Further, a pinion 6 is mounted to the outer end of the drive shaft 10. By means of the axial displacement of the drive shaft 10, the pinion 6 is able to be engaged with the ring gear 2 on the flywheel of the engine and disengaged therefrom. In the state that the pinion 6 and the ring gear 2 are engaged or meshed with each other, as shown in Figure 2, the output rotational movement and the rotational torque of the motor 1 are transmitted to the ring gear 2 via the speed reducing mechanism 3, the overrunning clutch 4, the spline assembly 5, the drive shaft 10 and the pinion 6 in sequence, to drive the flywheel of the engine to rotate, so that the engine is started. Once the engine is started, the control device functions to drive the drive shaft 10 to move in a proximal direction (towards the right side in Figure 2) by means of the lever 14, so that the pinion 6 is disengaged from the ring gear 2.

In the state that the pinion 6 is meshed with the ring gear 2 and transmits the rotational torque thereto, the pinion 6 is subjected to a reaction force from the ring gear 2. The reaction force is transmitted to the outer end of the drive shaft 10, which results in an eccentrically displacement of the external spline part 30 on the inner end of the drive shaft 10 with respect to the internal spline part 20, and thus a coaxiality error is generated. As described above, the invention is aimed at reducing such coaxiality error.

The coaxiality error existed in the spline assemblies of the prior art and the invention will be explained now with reference to Figures 5 and 6.

It should be noted that, the drawings of the present application do not illustrate structural details in real scale; rather, for the sake of clarity, some structural details (especially tooth clearances) are enlarged. In addition, the distance between a pair of diametrically opposed teeth is reduced in Figures 5 and 6 so that the important aspects of the invention can be explained clearly.

The external spline part 30 comprises a plurality of radially outwardly protruded teeth on its outer periphery, with a slot formed between each pair of neighboring radially outwardly protruded teeth. The internal spline part 20 comprises a plurality of radially inwardly protruded teeth on its inner periphery, with a slot formed between each pair of neighboring radially inwardly protruded teeth. The teeth of the external spline part 30 are mated within corresponding slots of the internal spline part 20, while the teeth of the internal spline part 20 are mated within corresponding slots of the external spline part 30, as shown in Figure 4.

With reference to Figure 5, according to a general prior art, a pair of diametrically opposed teeth 32 of the external spline part 30 are mated in a pair of diametrically opposed slots 22 of the internal spline part 20. Each tooth 32 of the external spline part 30 comprises a top land 36, and a pressure bearing flank 34 and a pressure free flank 34' on opposite sides of the top land 36.

Each the slot 22 of the internal spline part 20 is defined by a bottom land 26 and opposing flanks (i.e., the pressure bearing flank 24 and the pressure free flank 24') of a pair of teeth on opposite sides of the bottom land 26. When the pressure bearing flank 24 of the internal spline part 20 pushes against the pressure bearing flank 34 of the external spline part 30, the internal spline part 20 drives the external spline part 30 to rotate.

As is known in the art, in order that the mated internal and external spline parts are axially slidable with respect to each other, top clearances and side clearances should be provided therebetween. According to a current standard, in the vehicle starter, the normal top clearances between the internal and external spline parts are generally larger than 0.4 mm, and the normal side clearances between them are generally larger than 0.2 mm.

Due to the forces applied to the drive shaft, the external spline part 30 generates an eccentricity or coaxiality error with respect to the internal spline part 20, so that the top clearances and the side clearances are varied accordingly.

As an example, it is assumed that the external spline part 30 is displaced with respect to the internal spline part 20, as shown in Figure 5, opposite flanks (the pressure bearing flank 34 and the pressure free flank 34') of one tooth 32 (the upper one in Figure 5) of the external spline part 30 are contacting respectively two opposing flanks (pressure bearing flank 24 and the pressure free flank 24') which define a corresponding slot 22 of the internal spline part 20. In this state, of course, the contacting pressure between pressure bearing flanks 34 and 24 is significantly higher than the contacting pressure between the pressure free flanks 34' and 24'. Now, the upper side clearance disappears, and the upper top clearance LI is reduced relative to the normal top clearance.

On the other hand, only the pressure bearing flank 34 of the opposite tooth 32 (the lower one in Figure 5) of the external spline part 30 is contacting a corresponding pressure bearing flank 24 of the internal spline part 20, while the side clearance L2' between the pressure free flank 34' of this tooth 32 and a corresponding pressure free flank 24' of the internal spline part 20 is increased relative to the normal side clearance. In this state, the lower top clearance LI ' is increased relative to the normal top clearance. Due to the increasing of the lower top clearance, the contacting area between the lower pressure bearing flanks is reduced, as a result of which, the torque transmitting ability of the spline assembly is decreased and the teeth are more liable to be damaged.

For other pairs of diametrically opposed teeth between the above described pair of diametrically opposed teeth, the same condition exists, that is, the top clearance and the side clearance on one side are reduced, while the top clearance and the side clearance on the other side are increased.

Due to the variations in the top clearances and the side clearances as described above, the central axis 30 A of the external spline part 30 is displaced with respect to the central axis 20A of the internal spline part 20, so that an eccentricity (coaxiality error) is generated, as shown in Figure 5.

Such eccentricity (coaxiality error) mainly depends on the amounts of the maximum variations of the top clearance and the side clearance. According to prior art, such eccentricity (coaxiality error) is generally 0.2 mm or more.

It should be noted that, the variation of the side clearance is related with the variation of the top clearance, which can be seen from the schematic view in Figure 6.

As shown in Figure 6, it is assumed that, in a cross section of a tooth, the flanks of this tooth are oblique by an angle Θ with respect to a direction parallel with the central axis of the tooth, then, the variation of the side clearance L2 is substantially equal to the variation of the top clearance LI times sin Θ.

According to the invention, the normal top clearance is reduced by grinding the addendum circle of one of the internal and external spline parts to suppress the variations of the top clearance and the side clearance.

It should be noted that, in the embodiment described below with reference to the drawings, the top land of the external spline part 30 is grounded as an example to reduce the top clearances between the teeth of the external spline part 30 and the slots of the internal spline part 20; however, it is appreciated that the invention is also applicable in the case that the top land of the internal spline part 20 is grounded to reduce the top clearances between the teeth of the internal spline part 20 and the slots of the external spline part 30. The description to the later case is omitted to avoid repeating.

As shown in Figure 7, after the external spline part 30 is produced as a single piece in a normal machining process (such as forging, numerically controlled machining, electrical spark machining, or the like), the top lands of the external spline part 30 is grounded as a whole in a single grinding process, so that the difference between the radius of the addendum circle defined by the top lands of the external spline part 30 and the radius of the dedendum circle defined by the bottom lands of the slots of the internal spline part 20, or the normal top clearance, is reduced with respect to that in the traditional art. By the grinding process in which high dimensional precision can be obtained, the radius of the addendum circle of the external spline part 30 may have increased dimensional precision, so that the normal top clearance can be controlled accurately. For example, according to a preferred embodiment of the invention, a dimensional precision in the range within ± 0.005 to 0.01 mm may be provided by the grinding process itself. On the other hand, the internal spline part 20 is generally formed in a broaching process by a broaching tool. For a broaching process, the dimensional precision of the radius thus obtained may be in the range within ± 0.010 to 0.015 mm. In the case that the internal spline part 20 is produced in a broaching process, and the external spline part 30 is treated by the above grinding process, it is possible to control the normal top clearance in a range of 0.02 to 0.15 mm, preferably in the range of 0.04 to 0.08 mm.

According to the invention, the normal top clearance can be reduced to about a few hundreds of that in the prior art, and thus, in the operation state of the starter, the variations of the top clearance and the side clearance will be reduced to similar levels. As a result, the eccentricity (the coaxiality error) between the internal and external spline parts may be controlled to a minimum level, for example, 0.04 mm or less, which is substantially lower than the eccentricity (the coaxiality error) in the traditional art, which is generally 0.2 mm or more, so that the property of the starter can be improved significantly.

In addition, as can be seen from Figure 7, in the condition that the normal top clearance is reduced, when the external spline part 30 is displaced with respect to the internal spline part 20, only an extremely small amount of displacement in an radial direction occurs, and then the top land 36 of one tooth 32 (the upper one in Figure 7) of the external spline part 30 comes into contact with the bottom land of a corresponding slot of the internal spline part 20. In this state, the pressure bearing flank 34 and the top land 36 of this tooth contact respectively the pressure bearing flank 24 and the bottom land 26 related with a corresponding slot 22 of the internal spline part 20, and a side clearance L2 exists between the pressure free flanks 34' and 24'. In other words, the top clearance of this tooth is reduced to zero, while the side clearance L2 of it is reduced by only a small amount with respect to the normal side clearance.

On the other hand, the pressure bearing flank 34 of the opposite tooth 32 (the lower one in Figure 7) of the external spline part 30 contacts a corresponding pressure bearing flank 24 of the internal spline part 20, and the pressure free flank 34' and the top land 36 of this tooth 32 are separated from a corresponding pressure free flank 24' and a corresponding bottom land 26 of the internal spline part 20 by a side clearance L2' and a top clearance LI ' respectively. Since the variation (reducing) of the upper top clearance is very small, the variations (increasing) of the lower top clearance LI ' and the side clearance L2' are also very small. According to this configuration, the eccentricity (coaxiality error) of the central axis 30A of the external spline part 30 with respect to the central axis 20A of the internal spline part 20 is extremely small.

Further, since the increased amount of the lower top clearance is very small, the decreased amount of the contacting area of the lower pressure bearing flank is also very small,. As a result, the spline assembly may maintain a very high level of torque transmitting ability, and the teeth are not liable to be damaged.

It should be noted that the edges of the top lands and the corresponding edges of the bottom lands of the internal and external spline parts of the spline assembly are generally rounded, as shown in Figure 8, and the radius Rl of the rounded edges of the top lands of the teeth is generally larger than the radius R2 of the rounded edges of the corresponding bottom lands. When the top lands of the external spline part 30 is grounded according to the invention, it is very likely that the edges of the top lands of the teeth of the external spline part 30 are formed as sharp edges, as shown in Figure 9. In this condition, the sharp edges of the top lands of the external spline part 30 may interfere with the rounded edges of the bottom lands of the internal spline part 20. In order to avoid this problem, the internal spline part 20 and/or the external spline part 30 should be additional treated. Some embodiments of possible treatments according to the invention will be described now with reference to Figures 10-12.

As shown in Figure 10, according to an embodiment of the invention, the pressure angle of the pressure bearing flanks of the teeth of the internal spline part 20 or the external spline part 30 may be varied in a manner that the pressure angle of the pressure bearing flanks of the teeth of the internal spline part 20 is smaller than the pressure angle of the pressure bearing flanks of the teeth of the external spline part 30, so that the pressure bearing flanks of the teeth of the internal spline part 20 and the external spline part 30 may be deviated relative to each other by a small angle a. For example, as seen in the cross section of the spline assembly, the pressure bearing flank of each tooth of the internal spline part 20 is oblique with respect to a direction parallel with the radial central axis of the tooth by an angle of 28 degrees, while the pressure bearing flank of each tooth of the external spline part 30 is oblique with respect to a direction parallel with the radial central axis of the tooth by an angle of 30 degrees. By means of the angle a of 2 degrees thus generated, the sharp edge between the pressure bearing flank and the top land of the tooth of the external spline part 30 is kept away from the rounded edge between the pressure bearing flank edge and the bottom land of the slot of the internal spline part 20 for avoiding interference therewith.

As shown in Figure 11 , according to another embodiment of the invention, a chamfer 40 may be produced along the edge between the pressure bearing flank and the top land of the tooth of the external spline part 30, so that the tooth of the external spline part is kept away from the rounded edge between the pressure bearing flank edge and the bottom land of the slot of the internal spline part 20 for avoiding interference therewith.

As shown in Figure 12, according to another embodiment of the invention, an undercut 42 may be produced along the rounded edge between the pressure bearing flank edge and the bottom land of the slot of the internal spline part 20, so that the tooth of the internal spline part is kept away from the sharp edge between the pressure bearing flank and the top land of the tooth of the external spline part 30 for avoiding interference therewith.

According to another embodiment of the invention (not shown), the rounded edge between the pressure bearing flank and the top land of the tooth of the external spline part has a relatively large radius before the grinding process, and a proportion of this rounded edge is left after the grinding process, which is enough for keeping the tooth of the external spline part away from the rounded edge between the pressure bearing flank edge and the bottom land of the slot of the internal spline part 20 for avoiding interference therewith.

It is appreciated by those skilled in the art that any other suitable interference avoiding structures may be used for avoiding the interference described above.

It can be seen that, according to the principle of the invention, the top land of one of the internal and external spline parts of the spline assembly of the vehicle starter is subjected to a single grinding treatment, so that the top clearance between the internal and external spline parts is reduced. In addition, during the operation of the starter, the grounded top lands of one of the spline parts abut against corresponding bottom lands of the other of the spline parts. In this way, the coaxiality of the internal and external spline parts can be increased significantly. Further, according to the invention, the coaxiality of the internal and external spline parts can be improved by means of the spline assembly itself, without adopting any supplementary structure used in the prior art, so that the spline assembly may have a simple structure and relatively low cost. Further, the spline assembly may maintain high torque transmitting ability and structure reliability.

The spline assembly of the invention is applicable in various vehicle starters, for example, starters for diesel vehicles.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. The attached claims and their equivalents are intended to cover all the modifications, substitutions and changes as would fall within the scope and spirit of the invention.

Claims

1. A spline assembly of a vehicle starter, comprising: a first spline part comprising a set of teeth with slots formed between neighboring teeth; and a second spline part mated with the first spline part and comprising a set of teeth with slots formed between neighboring teeth; wherein the teeth of the second spline part are engaged in corresponding slots of the first spline part, and the teeth of the first spline part are engaged in corresponding slots of the second spline part, so that the first spline part and the second spline part are slidable with respect to each other in an axial direction; and wherein top lands of the set of teeth of the first spline part are ground as a whole in a single grinding process in a manner that the radius of an addendum circle defined by the top lands of the first spline part is smaller than the radius of a dedendum circle defined by bottom lands of the slots of the second spline part by 0.02 to 0.15 mm.

2. The spline assembly of claim 1, wherein the radius of the addendum circle of the first spline part is smaller than the radius of the dedendum circle of the second spline part by 0.04 to 0.08 mm.

3. The spline assembly of claim 1 or 2, wherein the first spline part comprises an external spline part having radially outwardly protruded teeth, and the second spline part comprises an internal spline part having radially inwardly protruded teeth.

4. The spline assembly of any one of claims 1 to 3, wherein the teeth of the first and second spline parts are helical teeth.

5. The spline assembly of any one of claims 1 to 4, wherein in the operation state of the spline assembly, the central axis of the first spline part is displaced in an radial direction with respect to the central axis of the second spline part by such a distance that the top land and a pressure bearing flank of one of the teeth of the first spline part contact a corresponding bottom land and a corresponding pressure bearing flank of the second spline part respectively, while a pressure free flank of said one of the teeth of the first spline part is separated by a side clearance from a corresponding pressure free flank of the second spline part.

6. The spline assembly of any one of claims 1 to 5, wherein each tooth of the first spline part comprises a pressure bearing flank edge on the top land in the form of a sharp edge generated in the grinding process, and the second spline part comprises an interference avoiding structure at an edge formed between the bottom land and a pressure bearing flank in each slot for avoiding any interference with the sharp edge.

7. The spline assembly of any one of claims 1 to 5, wherein an edge formed between the top land and a pressure bearing flank of each tooth of the first spline part is chamfered.

8. The spline assembly of any one of claims 1 to 5, wherein an edge formed between the top land and a pressure bearing flank of each tooth of the first spline part is rounded.

9. The spline assembly of any one of claims 1 to 5, wherein the pressure bearing flank of each tooth of the second spline part has a pressure angle which is smaller than the pressure angle of the pressure bearing flank of each tooth of the first spline part.

10. A vehicle starter, comprising: a motor; a speed reducing mechanism coupled with an output shaft of the motor; an overrunning clutch coupled with the speed reducing mechanism; a spline assembly of any one of claims 1 to 9, with the second spline part of the spline assembly coupled with a driven part of the overrunning clutch; an drive shaft coupled with the first spline part of the spline assembly; and a pinion carried by the drive shaft for outputting a rotational movement.