FR3056647A1 - STARTER GEAR FOR MOTOR VEHICLE THERMAL MOTOR WITH IMPROVED MECHANICAL PERFORMANCE - Google Patents

Abstract

The invention relates mainly to a pinion (21) of a motor vehicle engine starter with teeth (212), characterized in that said pinion (21) is made of a sintered steel material having an apparent density between 7.4 and 7.65 g / cm3. Compared to sintered wheels having a lower apparent density, such a density range minimizes the porosity of the pinion and therefore improves its wear resistance.

Description

Holder (s): VALEO ELECTRIC EQUIPEMENTS MOTOR Simplified joint-stock company.

Extension request (s)

Agent (s): VALEO EQUIPEMENTS ELECTRIQUES MOTOR Simplified joint-stock company.

FR 3 056 647 - A1

154 / STARTER PINION FOR A HEAT ENGINE OF A MOTOR VEHICLE WITH IMPROVED MECHANICAL PERFORMANCE.

(© The invention relates mainly to a pinion (21) of a motor starter of a motor vehicle provided with teeth (212), characterized in that said pinion (21) is made of a material based on sintered steel having a bulk density between 7.4 and 7.65 g / cm3 Compared to sintered pinions having a lower bulk density, such a density range minimizes the porosity of the pinion and therefore improves its resistance to wear.

STARTER PINION FOR A VEHICLE ENGINE OF AN AUTOMOTIVE VEHICLE WITH IMPROVED MECHANICAL PERFORMANCE

The present invention relates to a starter pinion for a thermal engine of a motor vehicle with improved mechanical performance.

In order to start an internal combustion engine, in particular of a motor vehicle, it is known to use a rotating electric machine in the form of a starter provided with a launcher capable of transmitting rotation energy from the starter to a crankshaft of the heat engine via a drive ring.

This launcher is mounted on a drive shaft coupled to the shaft of the electric machine by means of a speed reducer. The launcher is mounted movable in translation on the drive shaft between a rest position in which the teeth of a drive pinion are disengaged from the teeth of a starter ring secured rigidly or resiliently to the crankshaft of the engine, and an activation position in which the teeth of the drive pinion mesh with teeth of the starter ring. In particular, the pinion is mounted on the shaft by means of a helical connection. This launcher can undergo significant mechanical shock during the operation of the starter. Thus, shocks can be observed in particular at the start of start-up, when the teeth of the drive pinion can strike and / or slide against the teeth of the start-up ring while engaging between them. After this engagement, by transmitting torque with the crown, the tooth flanks are stressed and wear out. .

This type of mechanical stress suffered by the pinion is particularly important for starters used with systems for stopping and automatically restarting the engine (so-called stop and start system) having to withstand a very large number of operating cycles (in particular of around 250,000 cycles).

In order to increase the life of the pinions, tests were carried out with sintered steel pinions having a density of 7.3 g / cm3. However, given the relatively large porosity of this material, such a configuration generates wear resistance problems during the transmission of torque. In addition, in the case where a heat treatment is carried out in the mass of the part, this increases the hardness in a homogeneous manner of the material of the pinion. When this hardness is too low there is a wear of the pinion during the transmission of torque too great to exceed 100,000 cycles and when the hardness is increased to withstand these 100,000 cycles there is a significant risk of breakage of the pinion during impact of the pinion on the crown.

The invention aims to remedy at least one of these drawbacks by proposing a motor vehicle thermal engine starter pinion provided with teeth, characterized in that said pinion is made of a material based on sintered steel having an apparent density. between 7.4 and 7.65 g / cm3. Compared to sintered pinions having a lower apparent density, such a density range minimizes the porosity of the pinion and therefore improves its wear resistance while having a porosity large enough to reduce the noise when the pinion enters. the crown. Indeed, especially since the appearance of the "stop-start", that is to say the restart after an engine stop wanted by the electronic control unit (ECU) of the vehicle for example at a red light or in the plugs to reduce CO2, it is important for the well-being of the driver to reduce the noise of the starter of the combustion engine as well as possible.

According to one embodiment, the apparent density of said pinion is between

7.4 and 7.5 g / cm3. Selecting values in the lower part of the basic preferential range allows an optimization between the noise reduction given the presence of porosities in the material which block the propagation of sound waves and sufficiently dense on the surface to resist wear.

According to one embodiment, the apparent density of said pinion is preferably worth

7.4 g / cm3. Such a density value makes it possible to obtain an optimum compromise in terms of mechanical and wear resistance and acoustic performance of the starter.

According to another invention, which aims to remedy at least one of the drawbacks described above by proposing a motor vehicle thermal engine starter pinion provided with teeth, characterized in that said pinion is made of a material based on sintered steel having an apparent density between 7.4 and 7.75 g / cm3.

Compared to the previous invention, the intensity of which was 7.4 to 7.65 g / cm3, this invention incorporates the range of 7.66 to 7.75 g / cm3 which includes a higher density than that of l 'previous invention but is significantly higher cost since this density leads to an over-densification operation by cold forging resulting in a cost significantly higher than the first invention.

In addition, for cost reasons, it is preferable to switch to a gear cut in the mass (that is to say not fried) to have a density greater than 7.75.

According to another invention which aims to remedy at least one of the drawbacks described above by proposing a motor vehicle thermal engine starter pinion provided with teeth, characterized in that said pinion is made of a material based on sintered steel having an apparent density between 7.66 and

7.75 g / cm3. Compared to sintered pinions having a lower apparent density, such a density range minimizes the porosity of the pinion and therefore improves its resistance to wear. Such a range is optimized for a starter capable of starting diesel engines with a displacement greater than

2.5 liters while the range of 7.4 to 7.65 is rather optimized for starter pinions capable of starting internal combustion engines of diesel vehicles with a displacement of less than 2.5 liters.

According to an embodiment of one of the three inventions previously described, said pinion has a decreasing hardness profile at least in the external peripheral zone of said teeth, so that between the two extreme hardness values, there is a ratio of at least 1/3. Such a hardness profile makes it possible to obtain a high hardness at the level of the teeth of the pinion in order to guarantee resistance in durability (resistance to mechanical wear, fatigue) and a lower hardness in depth, conferring good impact resistance (resilience ).

According to an embodiment of one of the three inventions previously described, said pinion has a microhardness range between 700 and 865 Vickers for a depth in said pinion between 0 and 0.4mm, and a microhardness range between 400 and 600 Vickers for a depth between 0.7 and 1.2mm. According to this preferred range, a sintered pinion according to the invention makes it possible to hold at least 150,000 operating cycles.

According to an embodiment of one of the three inventions previously described, said pinion has a microhardness range between 725 and 865 Vickers, nottamenet between 750 and 865 Vickers for a depth in said pinion between 0 and 0.4mm, and a microhardness range between 400 and 600 Vickers for a depth in said pinion between 0.9 and 1.2mm. According to this preferred range, a sintered pinion according to the invention makes it possible to hold at least 200,000 operating cycles.

According to an embodiment of one of the three inventions previously described, said pinion comprises a microhardness of between 740 and 850 Vickers between

0 and 0.2mm deep and includes microhardness between 430 and 575

Vickers at a depth between 0.9 and 1.2 mm from the contact surface. According to this preferred range, a sintered pinion according to the invention makes it possible to hold at least 250,000 operating cycles.

According to an embodiment of one of the three inventions previously described, said pinion has undergone tempered case hardening in order to obtain the aforementioned decreasing hardness profile.

According to an embodiment of one of the three inventions previously described, all of said pinion has undergone tempered case hardening.

According to an embodiment of one of the three inventions previously described, only the outer peripheral zone of said teeth of said pinion has undergone the tempering case hardening operation.

According to an embodiment of one of the three inventions previously described, said pinion is produced from a powder containing iron, carbon, and Molybdenum, the mass content of which is at least 0.85%. Such a powder composition makes it possible to obtain sufficient quenchability to obtain a martensitic structure in the cemented layer and a bainitic structure at its core.

According to an embodiment of one of the three inventions previously described, for a depth between 0 and 0.2mm, a carbon content is between 1.5 and 4 times higher than for a depth between 0.9mm and 1.2mm and preferably between 2 and 2.5 times higher. This allows good hardness on the surface to prevent premature wear.

According to an embodiment of one of the three inventions previously described, the pinion includes internal grooves to be mounted on the pinion body comprising complementary grooves for linking the pinion in rotation with the pinion body in order to transmit the pinion body torque to the pinion. The fact that the pinion has undergone inside and outside tempering case hardening implies that the pinion includes a microhardness range between 700 and 865 Vickers for a depth in said pinion between 0 and 0.4mm (flute side internal and external tooth side of the pinion) which is greater than a microhardness range of 400 to 600 vickers for a depth of between 0.9 and 1.2 mm allows the pinion to be ductile and therefore to better withstand shock while having superior hardness on the surface to resist wear. In fact, the entire torque of the pinion passes through the internal splines of the pinion which undergo significant impacts due to their small contact surface with the pinion shaft.

The invention also relates to a pinion assembly comprising:

- a pinion as defined above, and

- A pinion carrier shaft on which said pinion is mounted, said pinion being linked in rotation with said pinion carrier shaft.

According to an embodiment of one of the three inventions previously described, said pinion 5 is fixed in translation relative to said pinion shaft.

According to an embodiment of one of the three inventions previously described, said pinion is movable in translation relative to said pinion shaft and comprises a spring mounted between a shoulder of the pinion shaft and the pinion.

This reduces noise by reducing the impact between the pinion and the crown but also the wear of the pinion.

The inventions will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given only by way of illustration but in no way limit the invention.

Figure 1 is a schematic side view of a motor starter of a motor vehicle according to the present invention;

Figure 2 is a schematic perspective view of the pinion 20 of the starter according to the present invention;

FIG. 3 represents a preferred hardness profile as a function of the depth of the pinion according to the present invention;

Figure 4 is a perspective view of a pinion assembly according to the present invention.

Identical, similar or analogous elements keep the same references from one figure to another.

FIG. 1 schematically shows a starter 1 for an internal combustion engine of a motor vehicle. This direct current starter 1 comprises, on the one hand, a rotor 2, also called armature, which can rotate around an axis X, and on the other hand, a stator 3, also called inductor, positioned around the rotor 2. In the example illustrated, the rotary electrical machine formed by the stator 3 and the rotor 2 is of the six-pole type.

This stator 3 comprises a yoke 4 carrying a set of permanent magnets 5 intended to produce an inducing field. The permanent magnets 5 are shaped according to cylindrical segments, being angularly distributed at regular intervals inside the cylinder head 4, and uniformly separated from the rotor 2 by a radial air gap 30.

îo The rotor 2 comprises a rotor body 7 and a winding 8 wound in notches of the rotor body 7. The rotor body 7 consists of a package of sheets having longitudinal notches. To form the winding 8, pin-shaped conducting wires 11 are threaded inside the notches 16 generally on two separate layers. The winding 8 forms, on either side of the rotor body 7, buns 9.

The rotor 2 is provided, at the rear, with a manifold 12 comprising a plurality of contact parts electrically connected to the conductive elements, formed in the example considered by the pins 11 of the winding 8.

A group of brushes 13 and 14 is provided for the electrical supply of the winding 8, one of the brushes 13 being connected to the ground of the starter 1 and another of the brushes 14 being connected to an electrical terminal 15 of a contactor 17 The brushes are for example four in number.

The brushes 13 and 14 rub on the collector 12 when the rotor 2 is rotating, allowing the supply of the rotor 2 by switching the electric current in sections of the rotor 2.

The contactor 17 comprises, in addition to the terminal 15 connected to the brush 14, a terminal 29 connected, via an electrical connection element, to a power supply of the vehicle, in particular a battery.

The starter 1 also comprises a launcher assembly 19 slidably mounted on a drive shaft 18 and capable of being rotated around the axis X by the rotor 2.

A speed reducer assembly 20 is interposed between a rotor shaft 2 and the drive shaft 18. The launcher assembly 19 comprises a drive element formed by a pinion 21 and intended to engage on a member of combustion engine drive, such as a starter ring. Alternatively, it would be possible to use a pulley system.

The launcher assembly 19 further comprises a freewheel 22 and a pulley washer 23 defining between them a groove 24 for receiving the end 25 of a fork 27. The fork 27 is actuated by the contactor 17 to move the launcher assembly 19 with respect to the drive shaft 18, îo along the axis X, between a first position in which the launcher assembly drives the heat engine via the drive pinion

21, and a second position in which the launcher assembly 19 is disengaged from the drive crown of the heat engine. When the contactor 17 is activated, an internal contact plate (not shown) makes it possible to establish a connection between the terminals 15 and 29 in order to energize the electric motor. This connection will be cut when contactor 17 is deactivated.

Figure 2 shows the pinion 21 intended to mesh with the motor drive member. This pinion 21 comprises a body 211 of generally annular shape, provided with teeth 212 at its outer periphery, and with a face 213 grooved at the inner periphery.

The pinion 21 is made of a material based on sintered steel having an apparent density of between 7.4 and 7.65 g / cm3. Compared to sintered pinions having a lower apparent density, the porosity of pinion 21 is minimized and therefore its resistance to wear is improved. The apparent density of the pinion 21 is advantageously between 7.4 and 7.5 g / cm3. Selecting values in the lower part of the preferential range also makes it possible to reduce the noise taking into account the presence of porosities in the material which prevent the propagation of sound waves. In order to obtain an optimum compromise in terms of wear resistance and acoustic performance of the starter, the apparent density of the pinion 21 is preferably 7.4 g / cm3.

As is clearly visible in FIG. 3, the pinion 21 has a decreasing hardness profile when one moves from the external surface of the pinion 21 (in particular at the level of the teeth 212) towards the depth Pr of the material and this at less in the external peripheral zone of the teeth 212. The profile is such that between the two extreme hardness values, there is a ratio of at least 1/6 and on average 1/3. Such a hardness profile makes it possible to obtain a high hardness at the level of the teeth 212 in order to guarantee a resistance in durability (resistance to mechanical wear, fatigue) and a lower hardness in depth, conferring good impact resistance (resilience). .

îo Advantageously, the pinion 21 has a microhardness range of between 700 and 865 Vickers for a depth Pr in the pinion 21 of between 0 and 0.4 mm (0 corresponding to the external surface of the pinion 21 in contact with the atmosphere), and a microhardness range between 400 and 600 Vickers for a depth Pr between 0.7 and 1.2mm.

Ideally, as illustrated in FIG. 3, the pinion 21 has a microhardness range P1 between 725 and 865 Vickers for a depth Pr in the pinion 21 between 0 and 0.2mm, and a microhardness range P2 between 400 and 600 Vickers for a depth Pr in the pinion 21 between 0.9 and 1.2mm. Between these two hardness ranges P1, P2, the microhardness of the pinion 21 gradually decreases. According to this preferred microhardness profile, for a pinion comprising 13 teeth, the pinion 21 makes it possible to hold at least

250,000 operating cycles.

The pinion 21 has undergone a quenching quenching, rebound hardening operation in order to obtain the aforementioned decreasing hardness profile. This tempering case hardening operation consists of a thermochemical treatment, that is to say that it is a high temperature heat treatment which is accompanied by a modification of the chemical composition of the base alloy by carbon enrichment and diffusion provided by an atmosphere of the furnace rich in carbon element. The pinion 21 to be treated being in contact with this carbon-rich atmosphere in the treatment oven, the carbon will then enrich the surface and then diffuse over a certain depth Pr thus creating a decreasing carbon concentration gradient from the surface and over a certain depth Pr until the initial carbon content of the alloy is found.

Once this step has been carried out at high temperature, the quenching operation consisting of a brutal cooling phase of the part is then carried out. This will make it possible to obtain metallurgical structure transformations and hardness modifications in order to obtain the aforementioned decreasing hardness profile in the entire cemented surface layer (from the surface and over a certain depth Pr). Finally, the parts do not remain in the raw quenching state (otherwise they would be more fragile). The parts undergo an expansion income which has a slight impact on the hardness at the surface and nearby, that is to say at a depth Pr of the order of 0.2 mm for example but not on the rest of the profile. hardness.

The pinion 21 obtained at the end of the tempering case hardening operation present for a depth between 0 and 0.2 mm, a carbon content is between 1.5 and 4 times higher than for a depth between 0, 9mm and 1.2mm and preferably between 2 and 2.5 times higher. This allows good hardness on the surface to prevent premature wear. In the case where the rate between 0 and 0.2mm deep is less than twice the carbon rate between 0.9 and 1.2mm deep, it is preferable that the alloy contains materials which increase the hardenability, or any other chemical composition powder allowing sufficient hardenability to obtain the aforementioned decreasing hardness profile.

In order to evaluate the carbon profile at the surface (and therefore hardness) and at different depths Pr in the cemented layer, several techniques can be used depending on the geometry of the part, and the type of material. It will also be necessary to carry out hardness filiations under reduced load with a microdurometer.

It should be noted that the entire pinion 21 may undergo the tempering case hardening operation. Alternatively, only the external peripheral zone of the teeth 212 of the pinion 21 can undergo the tempering case hardening operation.

As part of the quenching and tempering case hardening operation, the pinion 21 is produced from a powder containing iron, carbon, and Molybdenum, the mass content of which is at least 0.85%. Such a powder composition makes it possible to obtain sufficient quenchability to obtain a martensitic structure in the cemented layer and a bainitic structure at its core.

The pinion 21 of Figure 2 described above can be mounted as is on the drive shaft 18. Alternatively, the pinion 21 belongs to a pinion assembly 31 shown in Figure 4. This assembly 31 thus comprises the pinion 21 mounted on a pinion shaft 32. The pinion shaft is provided at one of its ends with a track 33 of the freewheel 22 formed at the outer periphery of the shaft 32. In this case the internal face 213 of the internal periphery is smooth unlike the case of FIG. 2 for which the pinion has grooves on the internal surface 213. In fact, the pinion must be able to remain free to rotate relative to the drive shaft on which it is mounted when the freewheel (including track 33) is disengaged by the fact of the pinion which is driven faster in rotation than the drive shaft.

The pinion 21 is linked in rotation with the pinion shaft 32. The pinion 21 is fixed in translation relative to the pinion shaft 32, or movable in translation relative to the pinion shaft 32 in particular in the case where a shock absorption device is integrated in the pinion-carrying shaft 32. Such a device comprises a spring urging the pinion 21 against a stop in the rest state and in the event of axial impact with the teeth of the drive ring the spring is compressed by the translational movement of the pinion 21 which then tends to move back relative to the stop.

Claims (15)

1. Pinion (21) of a thermal engine starter of a motor vehicle for engaging in a crown of the thermal engine of the vehicle provided with teeth (212), characterized in that said pinion (21) is 5 made of a material based on sintered steel having an apparent density of between 7.4 and 7.65 g / cm3. 2. Pinion according to claim 1, characterized in that the apparent density of said pinion (21) is between 7.4 and 7.5 g / cm3. 3. Pinion according to claim 2, characterized in that the apparent density of said pinion (21) is preferably 7.4 g / cm3. 4. Pinion according to any one of claims 1 to 3, characterized in that said pinion (21) has a hardness profile 15 decreasing at least in the outer peripheral zone of said teeth (212), so that between the two extreme hardness values, there is a ratio of at least 1/6, preferably 1/3. 5. Pinion according to claim 4, characterized in that said pinion (21) has a microhardness range between 700 and 865 Vickers 20 for a depth (Pr) in said pinion (21) between 0 and 0.4mm, and a microhardness range between 400 and 600 Vickers for a depth (Pr) between 0.7 and 1.2mm. 6. Pinion according to claim 5, characterized in that said pinion (21) has a hardness range (P1) between 725 and 865 Vickers 25 for a depth (Pr) in said pinion (21) between 0 and 0.2mm, and a hardness range (P2) between 400 and 600 Vickers for a depth (Pr) in said pinion (21) between 0.9 and 1.2mm. 7. A pinion according to any one of claims 4 to 6, characterized in that said pinion (21) has undergone a tempered case hardening operation in order to obtain the aforementioned decreasing hardness profile. 8. Pinion according to claim 7, characterized in that the whole of said pinion (21) has undergone the tempering case hardening operation. 9. Pinion according to any one of the preceding claims, in which the pinion comprises internal grooves to be mounted on the pinion body comprising complementary grooves to link the pinion in rotation with the pinion body in order to transmit the torque of pinion body towards the pinion. 10. Pinion according to claim 7, characterized in that only the external peripheral zone of said teeth (212) of said pinion (21) has undergone the tempering case hardening operation. 11. Sprocket according to any one of claims 1 to 10, 15 characterized in that for a depth (Pr) between 0 and 0.2 mm, a carbon content is between 1.5 and 4 times higher than in a depth (Pr) between 0.9mm and 1.2mm and preferably between 2 and 2.5 times greater. 12. Pinion assembly (31) comprising: 20 - a pinion (21) as defined according to any one of the preceding claims, and - A pinion-holder shaft (32) on which said pinion (21) is mounted, said pinion (21) being linked in rotation with said pinion-holder shaft (32). 13. An assembly according to claim 12, characterized in that said pinion (21) is fixed in translation relative to said pinion shaft (32). 14. The assembly of claim 12, characterized in that said pinion (21) is movable in translation relative to said pinion shaft (32). 15. Motor vehicle thermal engine starter 30 comprising a pinion (21) as defined according to any one of claims 1 to 11 or a pinion assembly (31) as defined according to any one of claims 12 to 14 . 1/2 2/2 Hardness (in Vickers)