MOTOR VEHICLE STARTER EQUIPPED WITH A TORQUE SHOCK ABSORBING DEVICE

Abstract

The invention relates to an electric starter (1) for an internal combustion engine comprising a casing in which is arranged an electric motor comprising an internal shaft (20), rotatable relative to the casing and driving an output shaft (40) via a reduction assembly (10), said reduction assembly (10) comprising a toothed crown (100) mounted in the casing (500) and at least one damping device (200) housed in a cavity (540) of the casing, between the toothed crown (100) and complementary portions of said cavity (540), to immobilize the toothed crown in rotation relative to the casing and absorb a torque shock transmitted to the toothed crown, in which the damping device (200) has, during a first compression phase, a first stiffness (K1) of which a representative curve follows a first slope and, during a second compression phase,a second stiffness (K2) of which a representative curve follows a second slope. Figure for the abstract: Figure 2A,

Description

Title of the invention: MOTOR VEHICLE STARTER EQUIPPED WITH A TORQUE SHOCK ABSORBING DEVICE Technical field

[0001] The present invention relates to a starter, in particular for a motor vehicle, equipped with a device for damping torque shocks with progressive compression.

[0002] The invention finds applications in the field of motor vehicles with thermal engines and, in particular, in the field of starters for motor vehicles with thermal engines, in particular for vehicles equipped with the function of stopping and restarting the thermal engine called "stop and start", in Anglo-Saxon terms. STATE OF THE ART

[0003] In a manner known per se, a starter has the role of providing the impulse necessary to start the thermal engine of a vehicle. For this, the starter comprises an electromagnetically controlled electric motor mechanically connected to the thermal engine.

[0004] The starter comprises an electric motor, a contactor, a speed reducer, a casing, a launcher comprising a control lever, a shaft internal to the electric motor and an output shaft.

[0005] The electric motor is composed of an inductor stator and an induced rotor mounted coaxially, the stator surrounding the rotor, which is mounted rotating around an axis inside a cylinder head. The latter is integral with the starter housing intended to be fixed on a fixed part of the motor vehicle. The rotor is mounted rotating around the internal shaft of the electric motor. A sun gear is fixed to one end of the shaft.

[0006] The speed reducer comprises a planet carrier carrying planets meshing on the one hand with a toothed crown and the output shaft, and on the other hand with the sun gear fixed to the end of the internal shaft of the electric motor. At one end of the output shaft is fixed a drive pinion.

[0007] The gear ring of the speed reducer is hollow in shape and has a transverse wall with a central hole mounted on an attached hub ensuring its centering. The hub has a through opening in its center allowing the output shaft to pass through. Thus the transverse wall of the gear ring, centered in the housing, allows the output shaft carrying the satellites to be guided.

[0008] The crown gear, thus positioned inside the casing, undergoes the shocks caused by the torques generated when the thermal engine starts. Indeed, the engagement of the drive pinion in the crown gear generates a shock of the engine / starter inertias which itself causes stresses on all the components of the starter. In the case of vehicles equipped with the “stop and start” function, the number of shocks suffered by the components of the starter is increased, weakening these components and, in particular, the crown gear.

[0009] In order to protect the structure of the crown gear when the heat engine is started, it is known to equip the crown gear with a damping system. A known damping system consists of inserting one or more damping devices into suitable housings, between the outer wall of the crown gear and the casing. The damping device is generally a metal coil spring or a block made of a material with elastic properties. Whether it is to receive a coil spring or an elastic block, the housing is a cavity arranged between the casing and the outer wall of the crown gear so that the coil spring or the elastic block is compressed circumferentially between a stop formed by the casing and a stop formed by the crown gear.

[0010] Coil springs, like elastic blocks, are capable of absorbing part of the energy generated by torque shocks. However, coil springs and elastic blocks have the same drawback, namely that the coil spring or the elastic block invariably compresses by pressing against the same two elements, i.e. the stop formed by the housing and the stop formed by the toothed crown. Thus, the repeated compression of the damping device against the stop formed by the housing and the stop formed by the toothed crown has the effect of weakening these two stops and causing damage, most often in the toothed crown. Summary of the invention

[0011] To address the problem mentioned above of weakening of the stops of the damping device, the applicant proposes a reduction assembly for an electric starter in which the damping device is manufactured so as to have two different stiffnesses which ensure progressive compression of said damping device.

[0012] According to a first aspect, the invention relates to an electric starter for an internal combustion engine comprising a casing in which is arranged an electric motor comprising an internal shaft, rotatable relative to the casing and driving an output shaft via a reduction assembly, said reduction assembly comprising a toothed crown mounted in the casing and at least one damping device housed in a cavity of the casing, between the toothed crown and complementary portions of said cavity, to immobilize the crown gear in rotation relative to the casing and to absorb a torque shock transmitted to the crown gear. The starter is characterized by the fact that the damping device has, during a first compression phase, a first stiffness of which a representative curve follows a first slope and, during a second compression phase, a second stiffness of which a representative curve follows a second slope.

[0013] The damping device of this starter allows for progressive compression which protects the starter components from the effects of shocks and ensures a longer service life.

[0014] Advantageously, the slope of the first stiffness is less than the slope of the second stiffness. The stiffness of the damping device is thus lower during the first degrees of compression corresponding to the instant of the shock and increases until the shock is absorbed.

[0015] Advantageously, the slope of the first stiffness is dependent on a geometry of the damping device and the slope of the second stiffness is dependent on the material in which the damping device is formed.

[0016] According to certain embodiments, the electric starter comprises at least one pair of damping devices, the damping devices of the pair being positioned on either side of a radial stop projecting out of the toothed ring.

[0017] The electric starter may include one or more of the following features: - the damping device is an elastomer cushion with a rounded contour. - the damping device has a circular contour. - the damping device has a wavy contour. - the damping device has a substantially square-shaped contour with rounded corners. - the damping device is an elastomer cushion comprising at least one recess in a central area of the cushion. - the damping device is an elastomer cushion with a central swelling. - the damping device comprises a spring-forming part made of thermoplastic. - the spring-forming part has a honeycomb-type alveolar structure. BRIEF DESCRIPTION OF THE FIGURES

[0018] Other advantages and characteristics of the invention will appear on reading the description, illustrated by the figures in which: - [Fig.l] represents a partial semi-exploded schematic view of an electric starter equipped with a damping device according to the invention; - [Fig.2A] and [Fig.2B] represent, respectively, an assembled view and an exploded view of the reduction gear assembly of the starter of [Fig.l]; - [Fig.3A] and [Fig.3B] represent perspective and sectional views of a damping device according to a first embodiment, respectively, alone and mounted within the reduction assembly of [Fig.2A] and [Fig.2B]; - [Fig.3C] graphically represents the displacements and stiffness slopes of the damping device of [Fig.3A] and [Fig.3B]; - [Fig.4], [Fig.5], [Fig.6], [Fig.7], [Fig.8], [Fig.9] and [Fig.10] represent perspective and sectional views of various embodiments of a damping device adapted to be mounted in the reduction assembly of [Fig.2A] and [Fig.2B]; - [Fig. 11 A], [Fig. 11B] and [Fig. 11C] represent various perspective and sectional views of yet another embodiment of the damping device for the reduction gear assembly of [Fig. 2A] and [Fig. 2B].

[0019] DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

[0020] An exemplary embodiment of an electric starter, in which the reduction assembly is provided with a damping device having two different stiffnesses, is described in detail below, with reference to the accompanying drawings. This example illustrates the characteristics and advantages of the invention. It is however recalled that the invention is not limited to this example.

[0021] In the figures, identical elements are identified by identical references. For reasons of readability of the figures, the size scales between elements represented are not respected.

[0022] [Fig.l] represents a partial view of an electric starter according to the invention. This starter 1, the function of which is to ensure the starting of a thermal engine, for example of a vehicle, comprises an electric motor 30 adapted to drive in rotation an internal shaft 20 around which is mounted a reduction assembly 10. The starter 1 also comprises an electromagnetic contactor 60, carried by a casing, and ensuring the actuation of a launcher 50. The launcher 50, slidably mounted on the output shaft 40, comprises a drive pinion adapted to mesh with a drive ring (not shown) of the thermal engine.

[0023] The starter 1 further comprises a reduction assembly 10 mounted between the electric motor 30 and the launcher 50 to modify the torque ratio between the internal shaft 20 and the output shaft 40. The reduction assembly 10, more simply called a reduction gear, is shown in an assembled view in [Fig.2A] and an exploded view in [Fig.2B]. This reducer 10 comprises a planet carrier 400 integral in rotation with the output shaft 40. This planet carrier 400 carries satellites 410 each mounted in rotation around an axis 430 extending between two plates 420 of said planet carrier 400. These satellites 410 mesh on the one hand with a toothed crown 100 and on the other hand with a sun pinion (not shown) integral in rotation with the internal shaft 20.

[0024] The toothed crown 100, driven in rotation by the satellites 410, is a cylindrical part mounted in the casing 500 of the starter and comprising a toothed internal face 110 and a non-toothed external face 130. The casing 500 comprises a skirt 510 secured to a disc 520. The disc 520 is provided with a central opening 530 allowing the passage of the output shaft 40. The skirt 510 of the casing 500 comprises cavities 540 formed in the thickness of the casing and delimited circumferentially by walls 511 extending over the entire height of the skirt 510, these cavities being adapted to each receive at least one damping device 200 (called a “damper” in English terms). The damping device 200 is positioned against the external face 130 of the toothed crown, between the two walls 511 of a cavity 540.Each damping device 200 is thus housed between the toothed crown 100 and the walls 511 of the cavity 540, in order to absorb the torque shocks transmitted to the components of the starter, and in particular to the toothed crown, when the launcher 50 is docked.

[0025] The rotation of the toothed crown 100 changes the volume available for housing the dampers 200.

[0026] The reducer also comprises a sealing sheet 513, integral in rotation with the skirt 51, which axially blocks the other parts of the reducer. In particular, the sealing sheet axially blocks the damping devices.

[0027] In most embodiments, several pairs of damping devices 200 are distributed over the periphery of the toothed crown 100. In the examples of [Fig.2A] and [Fig.2B], a pair of damping devices is mounted in each cavity 540 of the casing 500, the skirt 510 comprising three cavities distributed over its circumference. In these embodiments, the two damping devices 200 forming a pair of damping devices, for example the damping devices 200a and 200b, are mounted close to each other, against the external wall 130, between two walls 511 of the same cavity 540. They are positioned symmetrically to each other, on either side of a stop 120 projecting from the external face 130 of the toothed crown. The 120 stop is a projected step radially from the external face 130 of the crown gear 100 towards the casing 500 and extending over the entire height of the crown gear and the depth of the cavity 540. Each pair of damping devices thus makes it possible to absorb torque shocks in both directions of rotation of the crown gear 100. Indeed, the damping device 200a of the pair 200a / 200b makes it possible, for example, to absorb torque shocks when the crown gear is rotating in the +R direction, while the damping device 200b absorbs torque shocks when the crown gear is rotating in the -R direction.

[0028] According to the invention, the damping device 200 is constituted so as to have: - during a first compression phase, a first stiffness of which a representative curve follows a first slope; this first stiffness is called the reception stiffness; and - during a second compression phase, a second stiffness of which a representative curve follows a second slope; this second stiffness is called posterior stiffness.

[0029] Thus, the compression of the damping device 200 is scalable. In other words, the damping device dampens the torque shock differently during the second compression phase than during the first compression phase, this first phase corresponding to the instant of the shock when the launcher approaches the reducer and the latter begins to load mechanically.

[0030] According to preferred embodiments, the slope of the first stiffness is less than the slope of the second stiffness. Thus, during the first compression phase, the absorption of the torque shock is less than during the second compression phase, which makes it possible to reduce the force on the other components of the starter, and in particular on the toothed ring, at the time of docking of the launcher.

[0031] Different embodiments of the damping device make it possible to obtain different stiffness slopes, the slope of the receiving stiffness depending mainly on the geometry of the damping device and the slope of the posterior stiffness depending mainly on the material from which the damping device is manufactured.

[0032] In some embodiments, several examples of which are shown in [Figure 3], [Fig.4], [Fig.5], [Fig.6], [Fig.7], [Fig.8], [Fig.9] and [Fig.10], the damping device 200, called cushion damper, is an elastomer cushion having a rounded contour. The elastomer is a material having a known slope stiffness for a square-shaped block. The rounded contour of the elastomer cushion makes it possible to reduce this stiffness during the first phase compression. The term "rounded contour" of the cushion means a contour free of edges and right angles.

[0033] [Fig.3A], [Fig.3B] and [Fig.3C] represent a first embodiment of a cushion shock absorber 200. In this embodiment, the cushion shock absorber 200 is an elastomer cushion whose contour is circular in shape. In this embodiment, the damping device 200 comprises a cylindrical central zone 202 surrounded by a curved outer zone forming a crown around the central zone.

[0034] [Fig.3A] shows, in particular, a perspective view of the cushion damper 200 as well as a front view and a sectional view of said cushion damper. [Fig.3B] shows a perspective view of a pair of cushion dampers 200a, 200b mounted in a reducer 10. Each of the cushion dampers 200a, 200b of the pair of damping devices is housed, as described previously in connection with [Fig.2A] and [Fig.2B], in a cavity 540 of the casing 500, on either side of the stop 120 of the toothed ring 100. More precisely, each cushion damper 200a, 200b is housed between a wall 511 of the cavity 540 and a wall 121 of the stop 120. The cushion dampers have identical dimensions, adapted to the dimensions of the cavities 540. Each cushion damper 200a, 200b is therefore mounted between a wall 511 and a wall 121 so as to be wedged circularly between these two walls.Each of these walls 511 and 121 may comprise a tangential offset, respectively, 512 and 122, ensuring radial wedging of the circular cushions 200a, 200b between the casing 500 and the toothed crown 100.

[0035] Thus, when the launcher 50 docks, the rotation of the toothed ring 100 inside the casing 500 is damped by the cushion dampers 200, with damping that evolves between the first and second compression phases, until the toothed ring is immobilized. The torque shock is thus absorbed thanks to an evolving compression. Those skilled in the art will understand that, in the example of [Fig.3B] where three pairs of cushion dampers 200a, 200b are distributed over the contour of the toothed ring 100, only three cushion dampers provide damping at each shock, the cushion damper 200a of each pair providing damping when the toothed ring is rotating in the +R direction, the cushion damper 200b of each pair providing damping when the toothed ring is rotating in the -R direction.

[0036] The evolving compression is an effect of the difference in slope between the receiving stiffness slope and the posterior stiffness slope. An example of the differences in slopes is shown in graphs C1 - C4 of [Fig.3C] where C1 shows a compression device of a cushion damper, C2 and C3 show the displacement of the cushion damper as a function of time along the X axis and the Y axis and C4 shows the stiffness of the cushion damper as a function of the displacement along the Z axis when said cushion damper is compressed (the solid curve corresponding to the measurements obtained during the compression test C1, the dotted curve corresponding to the theoretical values). [Fig.3C], and in particular graph C4, shows that the cushion damper has a low stiffness slope Kl during the first 0.5 cm of displacement - i.e. the initial stiffness slope - and a stiffness slope K2 greater than the stiffness slope Kl in the displacement interval between 0.5 and 3 cm - i.e. the posterior stiffness slope. This graph C4 therefore shows the break in slope, at point P, between the initial stiffness slope Kl during the first compression phase (displacement between 0 and 0.5 cm) and the posterior stiffness slope K2 during the second compression phase (displacement above 0.5 cm).

[0037] [Fig.4], [Fig.5], [Fig.6], [Fig.7], [Fig.8], [Fig.9] and [Fig.10] show other shapes of elastomer cushions with rounded contours. For example, [Fig.4] shows an elastomer cushion with a circular contour comprising a cylindrical central zone 202 surrounded by an ovoid outer zone 201. Seen in section, this cushion has a substantially elliptical shape which ensures a longer first compression phase than that of the circular cushion of [Fig.3A], [Fig.3B] and [Fig.3C].

[0038] [Fig. 10] shows another example of a rounded contour elastomer cushion shape in which the circular contour is partially flattened so that said contour has a substantially figure-8 shape. This cushion shock absorber has a constitution substantially identical to that of the circular cushion of [Fig. 3A] except that its contour includes convex arcuate portions and concave arcuate portions.

[0039] Circular cushion dampers have, in addition to scalable compression, the advantage of facilitating the mounting of the damping device in the starter because the positioning constraints generated by a particular orientation are eliminated. The operator simply has to place the circular cushion dampers each in a cavity of the casing without any other constraints. In addition, being circular allows the circular cushion damper to have an extended service life because the entire surface of the cushion contour works uniformly, which distributes the fatigue over the entire part.

[0040] [Fig.5] shows an example of a cushion damper whose contour comprises four rectilinear sides 203 connected to each other by rounded angles 204, the sides 203 and angles 204 being curved so that the contour forms a bead. This cushion damper, called a square cushion damper, comprises a central block 205 surrounded by the sides 203 and angles 204 forming a square outer ring. The term "ring" means a closed shape surrounding the central block 205 and comprising a rounded edge. [Fig. 6] shows another example of a square cushion damper comprising a central block 205 and a square outer ring 203 / 204, in which the area in the center of the block 205 is hollowed out. In the example of [Fig. 6], the recess 206 in the center of the block 205 is a hole passing through the block over its entire height. In another example of a square cushion damper, shown in [Fig. 7], the recess 206 in the center of the block 205 is formed within a cup 207. In a variant, not shown in the figures, the recess is a transverse slot passing through the central area of the block. In yet another variant, not shown in the figures, the central block has several recesses distributed at the limit of the outer ring 203 / 204. The recesses have the advantage of generating a receiving stiffness for the entire duration of compression of the area around the recess, the posterior stiffness being generated when the recess has been completely compressed.

[0041] [Fig. 8] shows yet another example of a square cushion damper comprising a central block 205 and a square outer ring 203 / 204, in which the area 208 in the center of the block 205 is curved and forms a central swelling. The square cushion damper of [Fig. 8] thus has a swollen shape, thicker in the center than at the periphery. In a variant, not shown in the figures, the square cushion damper has a peripheral groove around the central swelling.

[0042] [Fig. 9] shows yet another example of a cushion damper shape in which the contour 209 has a wavy shape forming rounded branches. This elastomeric cushion has a constitution substantially identical to that of the circular cushion damper of [Fig. 3A] or the square cushion damper of [Fig. 5], except that its contour is wavy.

[0043] [Fig.l 1A], [Fig.l 1B] and [Fig.l 1C] represent an embodiment of the damping device in which said damping device 200 is a spring-forming part. This spring-forming part, also called a spring damper, is manufactured, by molding, in a thermoplastic material such as for example polyamide. Due to the material, the spring damper 200 has elastic properties, which are amplified by the geometry of the part. Indeed, the spring damper 200 comprises a honeycomb-type alveolar structure comprising two rectilinear lateral strips 220 connected by a network 221 of strips intersecting with each other.This honeycomb structure allows the spring damper 200 to pass, under the effect of compression, from a free position in which the bands of the network 221 are spaced apart from each other to a compressed position in which the bands are joined to each other to form a block, as shown in [Fig. 11C].

[0044] As shown in [Fig. 11 A], spring dampers 200a, 200b may be housed, in pairs, in the cavities 540 of the casing 500 in a manner similar to the cushion dampers described in connection with [Fig. 3B]. Those skilled in the art may refer to the description of [figure 2] and [Fig. 3B] for the mounting of the spring damper in the reduction assembly. In this embodiment, the transition from the free position to the block position of the spring damper makes it possible to absorb torque shocks with two different levels of stiffness.

[0045] Whatever its embodiment, the damping device mounted in the reduction assembly of the invention is not only adapted to have different stiffnesses during the first and second compression phases, as explained previously, but also to return to its initial shape, i.e. uncompressed, when the torque shock has been absorbed. Indeed, in all the embodiments described, the geometry and the material of the damping device ensure that said damping device returns to an initial shape as soon as the compression has ended. The damping device is thus capable of absorbing repetitive shocks, such as those generated in vehicles equipped with the “stop and start” function.

[0046] Those skilled in the art will understand that, although each example of a reduction assembly has been described with identical damping devices, it is possible to combine different damping devices (corresponding to different embodiments) within the same reduction assembly. For example, each pair of damping devices may comprise a cushion damper and a spring damper, the cushion dampers providing, for example, damping in one direction of rotation and the spring dampers providing damping in the opposite direction of rotation. Any other combination of cushion dampers and / or springs may of course be envisaged.

[0047] Although described through a certain number of examples, variants and embodiments, the reduction assembly according to the invention includes various variants, modifications and improvements which will be obvious to those skilled in the art, it being understood that these variants, modifications and improvements are part of the scope of the invention.

Claims

Claims

1. Electric starter (1) for an internal combustion engine comprising a casing in which is arranged an electric motor comprising an internal shaft (20), rotatable relative to the casing and driving an output shaft (40) via a reduction assembly (10), said reduction assembly (10) comprising a toothed crown (100) mounted in the casing (500) and at least one damping device (200) housed in a cavity (540) of the casing, between the toothed crown (100) and complementary portions of said cavity (540), to immobilize the toothed crown in rotation relative to the casing and absorb a torque shock transmitted to the toothed crown, characterized in that the damping device (200) has, during a first compression phase, a first stiffness (Kl) of which a representative curve follows a first slope and, during a second compression phase,a second stiffness (K2) of which a representative curve follows a second slope, and in that the damping device (200) is an elastomer cushion having a rounded contour and has a circular contour.,

2. Electric starter according to claim 1, characterized in that the slope of the first stiffness (Kl) is less than the slope of the second stiffness (K2).

3. Electric starter according to claim 2, characterized in that the slope of the first stiffness is dependent on a geometry of the damping device (200) and the slope of the second stiffness is dependent on the material in which the damping device is formed.

4. Electric starter according to any one of claims 1 to 3, characterized in that it comprises at least one pair of damping devices (200a, 200b), the damping devices of the pair being positioned on either side of a radial stop (120) projecting out of the toothed crown (100).

5. Electric starter according to any one of the preceding claims, characterized in that the damping device is an elastomer cushion comprising at least one recess (206) in a central zone of the cushion. 12

6. Electric starter according to any one of claims 1 to 4, characterized in that the damping device (200) is an elastomer cushion comprising a central swelling (208).

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