FR2833043A1 - ELECTRIC STARTER OF A MOTOR VEHICLE EQUIPPED WITH A STARTER WITH IMPROVED SPLINES - Google Patents

Abstract

The invention concerns an electric starter comprising a starting motor (24) equipped with a drive pinion (14) for driving a flywheel ring gear, and a transmission device arranged between the drive pinion (14) and a drive hub (30), which consists of two series of helical splines (40, 42) matching in shape arranged respectively on the output shaft (12) and in an internal cylindrical bushing of the hub (30). In order to facilitate penetration of the drive pinion (14) of the starting motor into the ring gear (16), and to reduce mechanical stresses during operation, the helical splines (40, 42) of the drive hub (30) have a variable angle depending on the axial position of the starting motor (24) between the rest position and the working position, said contact angle being determined by the inclination of the tangent at the point of engagement of a tooth of the hub (42a) with one of the flanks (AB, CD) of two consecutive shaft teeth (40a, 40b). The contact angle is greater on the side of the rest position than on the side of the working position. The invention is applicable to a motor vehicle combustion engine.

Description

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 Electric starter for a motor vehicle fitted with a launcher with improved grooves.

Technical field of the invention
The invention relates to an electric starter for a combustion engine of a motor vehicle, and comprising: an electric motor powered by an electromagnet contactor, and having a rotor coupled to an output shaft, a launcher equipped with a pinion for driving a toothed ring of the flywheel of the combustion engine, said pinion being able to slide axially on the output shaft between a rest position in which it is disengaged from the crown, and an active working position in which it engages with said crown, a transmission device arranged between the pinion and a drive hub, which is composed of two series of helical grooves of complementary shapes arranged respectively on the output shaft, and in an internal cylindrical sleeve of the hub, said transmission device comprising means for driving the pinion in rotation during the normal start-up phase, and for disengaging the mechanical drive linkage when the pinion speed is higher than that of the hub, and a control lever associated with the movable core of the contactor for translational movement of the launcher between the two rest and working positions defined by stop means .

State of the art
According to Figures 1 and 2, a motor vehicle starter comprises in a conventional manner, a rotary electric motor 10 whose output shaft 12 is equipped with a

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 movable pinion 14 intended to cooperate with a toothed ring 16 of the flywheel to ensure the starting of the combustion engine (not shown) of the vehicle. The pinion 14 is slidably mounted on the output shaft 12 between a rest position in which it is disengaged from the toothed ring 16, and an active working position in which it meshes with said ring 16, which is linked in rotation to the vehicle combustion engine crankshaft.

 The electric motor 10 of the starter is associated with a contactor 18 with an electromagnet 17 disposed above the electric motor 10, and having a double function of supplying the electric motor 10 with current, and of moving the pinion 14 movable between the two rest and work positions.

The excitation of the electromagnet 17 of the contactor 18 is controlled by the actuation of the ignition key, which establishes the electrical circuit towards the battery, following the closing of the main power contact 19 of the contactor 18.

 The movable core 20 of the contactor 18 is mechanically connected by a control lever 22 to a launcher 24 comprising the pinion 14 and a freewheel transmission device 26. The control lever 22 in the form of a fork is pivotally mounted on an axis 28, and the freewheel 26 is axially interposed between the pinion 14 and a drive hub 30 actuated by the control lever 22. The output shaft 12 is rotatably mounted in a casing 32 by means of a bearing 34 and a bearing 36.

 Between the two rest and working positions, the pinion 14 of the starter 24 is guided in sliding on a smooth cylindrical section of the output shaft 12 by means of a bearing 38.

 The drive hub 30 is actuated in rotation by means of two series of helical splines 40, 42 of complementary shapes, arranged respectively on the output shaft 12, and in an internal cylindrical bush 31 of the drive hub 30 .

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 The pinion 14 is thus secured to the drive hub 30 by the freewheel transmission device 26, which makes it possible to drive the pinion 14 in a direction of rotation corresponding to that of the output shaft 12 during the normal phase of starting, and disengaging the mechanical rotation drive link when the speed of rotation of the pinion 14 is greater than that of the drive hub 30. At the end of starting the combustion engine, the presence of the freewheel transmission device 26 prevents the pinion 14 in engagement with the crown 16, driving the rotor 44 of the electric motor 10 at an excessive speed liable to damage the latter. Such a situation can occur when the driver does not cut the power to the contactor 18 immediately after starting.

 The freewheel 26 illustrated in FIGS. 1 and 2 is of the roller type, but it is clear that any other unidirectional transmission device can be used, in particular a conical friction clutch, as described in document FR-A 97 16111 of the plaintiff.

The operation of such a conventional launcher 24 is as follows:
The attraction of the mobile core 20 against the fixed core 46 of the contactor 18 causes the launcher 24 to move in translation towards the working position. When the pinion 14 comes in tooth against tooth on the crown 16, a spring 48 arranged inside the movable core 20, is compressed allowing the continuation of the movement of attraction of the movable core 20, which closes the main contact 19 in limit switch for excitation of the electric motor 10.

 At this time, the rotation of the electric motor 10 combined with the thrust of the spring 48, allows the pinion 14 to penetrate as soon as a tooth of the latter passes opposite a between tooth of the crown 16. The leading flank pinion 14 comes into contact with the driven flank of crown 16, but with incomplete penetration of pinion 14 which is of the order of 0.5 to

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 2 mm. The torque transmitted to the pinion 14 by the electric motor 10 creates the contact force on the tooth of the crown 16, which generates an antagonistic frictional force in the pursuit of the penetration of the pinion 14 in the crown 16, since the reaction of the spring 48 is insufficient to overcome the friction force. The transmission of the entire starting torque in this position of incomplete penetration of the pinion 14, would cause high contact pressures liable to rapidly deteriorate the teeth.

 The helical shape of the grooves 40, 42 of the drive hub 30 has improved the introduction phase of the pinion 14, since the propeller creates a force whose axial component, combined with the thrust of the spring 48, pushes the pinion 14 in the crown 16. This results in a screwing effect of the launcher 24 until the pinion 14 comes into axial abutment against a stop 50 carried by the shaft 12 near the bearing 36. During this stroke of penetration of pinion 14, the contact pressure on the teeth is relatively low.

 At the end of the penetration stroke of the launcher 24 corresponding to the working position, the pinion 14 drives the crown 16 in rotation. The torque then increases rapidly, since the resistive torque of the combustion engine must be overcome.

The contact pressure nevertheless remains acceptable since the length in engagement between pinion tooth 14 and crown tooth 16 is maximum.

 At the end of starting, the combustion engine takes its idling speed, and drives the pinion 14 of the starter 24 at a very high speed. The freewheel 26 is then biased in the opposite direction, and is released to protect the electric motor 10 from overspeed. The launcher 24 then tends to unscrew on the grooves 40 of the shaft 12, which generates an axial force tending to bring the launcher 24 towards a stop 52 located opposite the stop 50. This axial force of reaction is added to the restoring forces of the movable core 20 of the electromagnet 17 after the power supply to the

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 contactor 18. The pinion 14 quickly escapes from the crown 16 with a sufficient speed to avoid wear and deterioration of the ends of the teeth.

 The presence of the helical splines 40, 42 of the launcher 24 of FIGS. 1 and 2 thus has a double advantage: they facilitate the engagement of the pinion 14 in the crown 16 by preventing premature wear of the flanks of teeth; they increase the output speed of the pinion 14 while avoiding deterioration of the front faces of the teeth.

 The grooves 40, 42 of a conventional launcher have, in developed form, rectilinear sides having a constant angle of inclination relative to the axis of the shaft 12 (see FIG. 2).

 It has been found that these advantages are all the more pronounced the greater the inclination angle of the grooves 40, 42 relative to the longitudinal axis. However, the increase in the angle of inclination of the splines 40, 42 causes an increase in the axial force generated by the peaks of torque when the heat engine is driven. This force is exerted against the stop 50 which must be dimensioned accordingly to avoid premature wear. The stop 50 generally comprises an elastic ring 54 housed in an annular groove in the output shaft 12, and a circular ring 56 concentrically covering the ring 54. At the end of the working stroke, the pinion 14 abuts against the face front of ring 56.

The disadvantages of a too large spline angle are as follows: - risk of wear on the surface of the ring 54 in contact with the shaft 12; - risk of wear on the surface of the ring 54 in contact with the ring 56; - risk of shearing of the elastic ring 54; - risk of wear and even bursting of the ring
56;

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54 ; - risque de rupture de l'arbre 12 au niveau de la gorge. deterioration of the ring housing groove

54; - risk of rupture of the shaft 12 at the level of the groove.

 To reduce these risks, a strengthening of the mechanical strength of the stop 50 by increasing its dimensioning comes up against a problem of space. Indeed, the outer diameter of the ring 56 must not be greater than the diameter of the pinion 14 to avoid contact with the crown 16. An increase in the section of the ring 54 would require a larger groove, which weakens on the other hand the mechanical resistance of the shaft 12.

 Another drawback results from the noise generated by the mechanical shock of the pinion 14 abutting against the stop 50. The greater the angle of inclination of the grooves 40, 42, the greater the impact, as well as the noise. This noise also appears at each compression and decompression phase of the heat engine when the latter is driven by the starter. In fact, at each decompression, the heat engine drives the pinion 14 at a speed greater than that of the output shaft 12. This results in a momentary freewheeling shift with backlash of backlash, and recoil of the pinion 14. A the following compression, the starter again becomes leading with a take-up of the backlash and backlash against the stop 50 which results in a mechanical shock and a sound emission.

Subject of the invention
The invention aims to overcome these drawbacks, and to provide a starter facilitating the penetration of the starter pinion into the crown, and reducing the mechanical stresses during operation.

 According to the invention, this object is achieved by the fact that the helical splines of the drive hub have a variable contact angle as a function of the axial position of the

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 launcher between the rest position and the working position, said contact angle being determined by the inclination of the tangent at the point of engagement of a hub tooth with one of the flanks of two consecutive shaft teeth.

 The contact angle is advantageously greater on the side of the rest position than of the working position.

 Such a launcher thus makes it possible to achieve a double objective, consisting on the one hand of facilitating the penetration of the pinion into the crown, then its exhaust at the time of exit after start-up, and on the other hand reducing the mechanical reactions exerted by the pinion on the stopper at the end of engagement in the crown.

 According to a preferred embodiment, the contact angle is preferably between 15 and 30 when the pinion penetrates and when it exits the crown. The contact angle is between 0 and 20 when the pinion abuts against the stop in the working position, and during the drive of the combustion engine.

 To obtain a smooth engagement and escape of the pinion in and out of the crown, the device can advantageously be supplemented by one or more of the following characteristics: - the contact angle can be variable continuously or discontinuously; for a predetermined axial position of the launcher, the contact angle is different depending on whether the hub tooth cooperates with the flank of a shaft tooth, or with the opposite flank of the adjacent shaft tooth; - Each hub tooth is shaped to define an operating clearance between the corresponding sides of the shaft teeth, said clearance is minimum when the launcher is in the working position; the sides of the shaft teeth and the hub teeth have conjugate shapes, in particular segments

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 straight or curved, to increase the contact surface in engagement; - Each hub tooth has a rounded and elongated profile in the direction of movement in the shaft groove; - Each hub tooth has a prismatic shape cooperating with inclined straight line segments belonging to the sides of the shaft teeth.

Brief description of the drawings
Other advantages and characteristics will emerge more clearly from the description which follows of particular embodiments of the invention given by way of nonlimiting examples, and represented in the appended drawings, in which:
Figure 1 is a schematic sectional view of a starter known from the prior art.

FIG. 2 shows a view of the launcher equipping the starter of FIG. 1.

 Figures 3 to 7 are schematic views in developed of a first embodiment of a launcher according to the invention, the shaft splines and the launcher being in different positions during the engagement and exhaust phases of the pinion.

 Figures 8 to 12 show views similar to those of Figures 3-7 of an alternative embodiment of the grooves.

 Description of two preferred embodiments.

 The same reference numbers will be used to designate parts similar or identical to those of Figures 1 and 2.

 With reference to FIGS. 3 to 7, the present invention is based on helical splines 40, 42 having a variable helix angle as a function of the position of the launcher 24.

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 In Figure 3 corresponding to the rest position of the launcher 24, the geometric axis of the output shaft 12 of the starter is shown in XX '. Two of the shaft teeth 40a, 40b respectively have curved flanks AB, CD delimiting a shaft groove 40, which has a variable inclination relative to the axis XX ', unlike the rectilinear flanks with constant inclination angle used in starters of the prior art. The tooth 42a of a groove 42 of the driving hub 30 is shown diagrammatically by a rounded profile and generally elongated in a direction substantially similar to that of the shaft groove 40. A plurality of teeth 40a, 40b, 42a are distributed at regular intervals at the periphery of the shaft 12 to reduce the contact stresses during the operation of the starter.

 The axial position of the center of the tooth 42a of the hub 30 is represented by Xo on the axis x parallel to the axis XX'of the shaft 12. This position Xo corresponds to the rest position of the launcher, in which the tooth 42a is in contact in Kl with the flank leading AB. The tangent in Kl makes an angle al with the axis XX '.

 In Figure 4, the pinion 14 abuts against the crown 16, and the launcher 24 is at this instant in the axial position Xi. The distance XoXi represents the interval between the crown 16 and the launcher 24 at rest. The electric motor 10 begins to rotate (see arrow R illustrating the rotation of the shaft 12), which keeps the tooth 42a against the flank leading AB to point K2. The tangent to the point K2 makes an angle a2 with the axis XX ', favorable to the penetration of the pinion 14 in the crown 16. The value of the angle a2 is preferably chosen between 15 and 30.

 When a pinion tooth 4 arrives opposite a between tooth of the crown 16, the pinion 14 begins its penetration in the crown 16. The rotation of the electric motor 10 will then favor the pursuit of the penetration following the presence of a high angle a2.

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 In FIG. 5, the pinion 14 abuts against the stop 50, and the starter 24 is at this instant in the axial end position X2. The distance XOX2 represents the total axial travel of the pinion 14 between the rest position and the working position. Having to drive the combustion engine, the tooth 42a of the driving hub 30 is always in contact with the flank leading AB at point K3. The tangent to the point K3 makes an angle a3 with the axis of the shaft 12. The value of the angle a3 is less than the angle a2, so as to reduce the contact pressure against the stop 50. The value the angle a3 will preferably be chosen between 0 and 20.

 The speed of arrival of the pinion 14 against the stop 50 is thus reduced due to the decrease in the angle of inclination from a2 to a3. The shock and the noise which result therefrom are thus reduced, which reduces the stresses and the wear of the stop 50.

 In FIG. 6, the starter 24 is in freewheeling mode, since the pinion 14 rotates faster than the shaft 12. The frictional forces and the residual freewheeling torque bring the tooth 42a of the driving hub 30 in contact with the flank CD of the tooth 40b, which is separated from the flank 40a by the groove 40. The tangent to the contact point K4 forms an angle a4 with the axis of the shaft 12.

 The value of the angle a4 is preferably chosen between 0 and 20, that is to say of the same order of magnitude as that of the angle a3. This results in a reduction of the unscrewing forces on the grooves 40, 42, which are the source of back-and-forth movements against the stop 50 following the compression and decompression phases during the drive of the thermal motor. Such a4 value also reduces noise and wear.

 In FIG. 7, the pinion 14 of the launcher 24 emerges from the crown 16 following the interruption of the supply of the contactor 18. The intervention of the return forces of the spring 48 of the movable core 20, and of the unscrewing forces launcher 24

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 brings the latter back to the rest position. When the tooth 42a of the hub 30 arrives in the axial position Xi the pinion 14 has come out of the crown 16. The tooth 42a is in contact at point K5 with the flank CD of the tooth 40b, where the tangent with the axis XX 'makes an angle a5, which will preferably be chosen between 150 and 300. This high value of the angle a5 ensures rapid exit of the pinion 14 from the crown 16, which reduces wear by friction of the teeth faces.

 It can be seen that at the moment of the penetration of the pinion 14 and at the time of its escape from the crown 16, the groove angle is quite high (of the order of 15 to 30), while during the abutment against the 'Stop 50 at the end of engagement in the crown 16, and during the drive of the heat engine, the groove angle is significantly smaller (of the order of 00 to 200). The variation in inclination of the groove angle between the rest position and the working position is progressive and continuous.

 It is clear that the profile of the CD flank may be different from that of the AB flank. The clearance j between tooth 42a and flank AB can be variable as a function of the position of the launcher and of the launcher and shaft profiles chosen. This play is preferably greater than 0.05 mm to ensure good sliding without risk of jamming. Too much play will be avoided, especially in the working position to limit backlash shock during the drive phase of the engine.

 With reference to FIGS. 8 to 12 of an alternative embodiment, the tooth 142a of the driving hub 30 has a prismatic shape MNPQRS, obtained by molding, extrusion, or cold stamping. Each flank of the shaft teeth 140a, 140b is composed of two inclined straight line segments AA1, A1B; CC1, Clod.

 The segment AA1 makes an angle al with the axis of the shaft 12, preferably between 15 and 30. The segment A1B makes an angle a3 with the axis of the shaft 12, preferably between 00 and 200.

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 The segment DC1 makes an angle a4 with the axis of the shaft 12, preferably between 00 and 200. The segment CCI makes an angle a5 with the axis of the shaft 12, preferably between 150 and 300.

 The choice of the value of the angles corresponds to that described previously in Figures 3 to 7.

 FIG. 8 corresponds to the rest position, where the edge NM of the tooth 142a of the driving hub 30 is in contact with the segment AA1 of the shaft tooth 140a.

 FIG. 9 corresponds to the contact of the pinion 14 against the crown 16. The contact tilt angle between launcher 24 and shaft 12 remains equal to al until the point N arrives at the intermediate point Al.

 In FIG. 10, the contact tilt angle takes the value a3 until the arrival of the pinion 14 against the stop 50.

The edge PN of the tooth 142a of the driving hub 30 is in contact with the segment BAI of the shaft tooth 140a.

 FIG. 11 corresponds to the stop position against the stop 50. The edge RS of the tooth 142a of the driving hub 30 is in contact with the segment DC1 of the shaft tooth 140b.

 Figure 12 corresponds to the freewheeling phase for the return of the launcher to the rest position. The contact tilt angle changes from a4 to a5 when point R has passed point Cl.

 This results in a maximum contact surface, in particular in the working position and during backlash during drive of the heat engine.

Claims (11)

1. Electric starter for a combustion engine of a motor vehicle, and comprising: - an electric motor (10) powered by a contactor (18) with electromagnet (17), and having a rotor (44) coupled to a shaft of output (12), a launcher (24) equipped with a pinion (14) for driving a crown (16) toothed of the flywheel of the combustion engine, said pinion being able to slide axially on the output shaft (12 ) between a rest position in which it is disengaged from the crown (16), and an active working position in which it meshes with said crown (16), a transmission device arranged between the pinion (14) and a hub d 'drive (30), which is composed of two series of helical grooves (40,42) of complementary shapes respectively arranged on the output shaft (12), and in an internal cylindrical bush (31) of the hub (30), said transmission device comprising means for driving the pinion (14) in rotation during the normal start-up phase, and to disengage the mechanical drive link when the speed of the pinion (14) is greater than that of the hub (30), and a control lever (22) associated with the movable core (20 ) of the contactor (18) for translational movement of the launcher (24) between the two rest and working positions defined by stop means, characterized in that the helical grooves (40, 42) of the drive hub ( 30) have a contact angle (a1, a2, a3, a4, a5) which varies according to the axial position of the launcher (24) between the rest position and the working position, said contact angle being determined by the inclination of the tangent to the point of engagement of a tooth <Desc / Clms Page number 14>  hub (42a) with one of the flanks (AB, CD) of two consecutive shaft teeth (40a, 40b).  2. Starter according to claim 1, characterized in that the contact angle is greater on the side of the rest position than of the working position.  3. Starter according to claim 1 or 2, characterized in that the contact angle is variable continuously or discontinuously.  4. Starter according to one of claims 1 to 3, characterized in that the contact angle is between 15 and 30 at the time of the penetration of the pinion (14) and at the time of its exit from the crown (16) .  5. Starter according to claim 4, characterized in that the contact angle is between 00 and 200 when the pinion (14) abuts against the stop (50) in the working position, and during training of the combustion engine.  6. Starter according to claim 1 or 2, characterized in that for a predetermined axial position of the launcher (24), the contact angle is different depending on whether the hub tooth (42a) cooperates with the flank (AB) of the tree tooth (40a) or with the flank (CD) of the adjacent tree tooth (40b).  7. Starter according to one of claims 1 to 6, characterized in that each hub tooth (42a) is shaped to define an operating clearance between the flanks (AB, CD) of the corresponding shaft teeth (40a, 40b ).  8. Starter according to claim 7, characterized in that said clearance is minimum when the launcher (24) is in the working position.  9. Starter according to claim 7, characterized in that the sides of the shaft teeth (40a, 40b; 140a, 140b) and of the hub teeth (42a, 142b) have conjugate shapes, in particular rectilinear or curvilinear segments, to increase the contact surface in engagement.  10. Starter according to claim 9, characterized in that each hub tooth (42a) has a rounded profile and <Desc / CRUD Page number 15>  elongated in the direction of movement in the shaft groove (40).  11. Starter according to claim 9, characterized in that each hub tooth (142a) has a prismatic shape (MNPQRS) cooperating with inclined straight line segments (AA1, A1B; CC1, C1D) belonging to the sides of the shaft teeth (140a, 140b).