Title of the invention: Power transmission system for a powertrain of a motor vehicle

TECHNICAL FIELD

[001 ] The present invention relates to the field of vehicles, in particular motor vehicles, and is targeted more precisely to a power transmission system for a powertrain for driving the wheels of such motor vehicles.

PRIOR ART

[002] In a general manner, what is of interest here is a power transmission system which, in a motor vehicle, is targeted to driving at least one wheel of said vehicle to rotate by transmitting the torque provided by a drive shaft of an, in particular electric or hybrid, motorization system.

[003] In this regard, Document DE 2428356 is representative of the prior art. Said document describes a powertrain for driving the wheels of a rolling vehicle. Said powertrain comprises a power transmission system connected to the drive shaft. The power transmission system comprises a double-chain sprocket, the power being transmitted via a double chain and ring gears to the wheels of the vehicle.

[004] In this context, what is targeted here is a belt-type power transmission system, said belt being able to belong to a first reduction stage of a powertrain of a vehicle. It is important to note that the belt of the power transmission system, in the context of the present invention, is configured to drive at least one wheel. In other words, the belt is arranged in the torque transmission path between the motor and at least one wheel of the vehicle, in particular in the torque transmission path between the motor and two laterally opposite drive wheels of the vehicle. The belt is therefore configured to transmit the drive torque to at least one drive wheel of the vehicle, in particular to two laterally opposite drive wheels of the vehicle. According to one embodiment, the belt is configured to transmit the drive torque to all of the drive wheels of the vehicle.

[005] Thus, the first reduction stage of the powertrain here comprises two pulleys and a belt that are designed to transmit the torque coming from the motor with a speed reduction ratio.

[006] According to one embodiment, a ribbed belt is used. Preferably, the ribbed belt is a belt striated in the direction of the length. It provides transmission by adherence and/or by wedging. There are a numberof types of ribbed belt according to the profile of the ribs and the distance between the tops of the adjacent ribs. The belt may, for example, be a belt marketed under the trade name Flexonic®. The ribs may be similar to or resemble the ribs of the belt marketed under the trade name Poly V®.

[007] The number of ribs may also vary. It is known that ribbed belts have the advantage over flat belts or even V belts of having a greater efficiency, in particular by virtue of the longitudinal ribs that allow a larger contact area between the pulleys and the ribbed belts. This makes ribbed belts eligible for use in powertrains aimed at achieving a high torque transmission between the motor and the wheels in order to produce a torque at the wheel of, for example, more than 500 Nm. Ribbed belts also have the advantage that they can be used on smooth or ribbed pulleys. Furthermore, in relation tootherbelts, in particular V belts, ribbed belts can wrap around smaller-diameter pulleys, this being particularly advantageous when they are to be used for providing a speed reduction, in particular downstream of an electric machine.

[008] Also known are toothed belts, with single toothing or with double toothing, that also make it possible to transmit a high power. However, toothed belts have the disadvantage of being rigid. In addition, by definition, they are used only with toothed pulleys, and it is imperative, in a power transmission system using a toothed belt and toothed pulleys, that the length of the toothed belts strictly corresponds to the diameter of the pulleys, without any elasticity being tolerated, otherwise power losses would be suffered. Moreover, toothed belts, as is known, have an inferior acoustic performance to ribbed belts.

[009] Now, to avoid any slipping of the ribbed belt on the pulleys and the power loss that would be entailed thereby, it is known practice to use a compensation device to maintain the tension of the ribbed belt. Use is made in particular, in the prior art, of an assembly composed of a roller, of a tensioner and of a spring for maintaining the tension of the ribbed belt during its use throughout its service life.

[010] The presence of such a compensation device, described for example in FR 3011899, is constraining and involves the power transmission system being made more complex and having an increased cost. Furthermore, the use of tensioners is prejudicial in a powertrain, kinematically between the motor and drive wheels, since the torque may be negative or positive. The tensioner typically intervenes on the slack strand of the belt, that is to say on the opposite side from the traction. Since the torque of a powertrain can change direction, the use of a tensioner would cause tilting play, also termed “backlash”, which would be felt by the driver in the torque oscillation phases, in particularat lowtorque. [011] To overcome these disadvantages, the present invention proposes the use of an elastic belt prestressed in tension, in other words stretched, in such a way that this prestress absorbs the relaxation of the belt associated with its wear. Thus, the tension applied to said belt remains acceptable during the service life of the belt for transmitting the torque. The prestress of the elastic belt once mounted, in other words its initial elongation, is calibrated to compensate for the natural wear of the belt, in particular the wear of the ribs. The elasticity of the elastic belt makes it possible to maintain the tension of the belt in its normal operating range even in the absence of an external tensioner.

PRESENTATION OF THE INVENTION

[012] More precisely, the subject of the invention is a power transmission system for a powertrain of a motor vehicle, in particulara passenger transport motor vehicle, comprising an elastic belt, said elastic belt being configured to transmit a torque to at least one wheel of the motor vehicle.

[013] Advantageously, with the torque transmission system being able, on the one hand, to receive a torque coming from a motorization system and, on the other hand, to transmit a torque to said at least one wheel of the vehicle, the power transmission system comprises a torque transmission path between the motorization system and said at least one wheel, the elastic belt forming part of this torque transmission path.

[014] Advantageously, the elastic belt is tensioned solely by virtue of its intrinsic elasticity and of its mounting with elastic prestress. In other words, there is no tensioning device attached.

[015] The invention makes it possible in particular to maintain an appropriate tension of the elastic belt in the power transmission system and thus to improve the durability and the NVH (“Noise, Vibrations, Harshness”) performance of said system without the need for a compensation system based on a tensioner, including in spite of a significant elongation of said elastic belt on account of its wear. Specifically, the use of such an elastic belt, in particular mounted stretched with elastic prestress, makes it possible to attenuate certain vibratory interactions between the electric machine and the reduction gear unit.

[016] According to one embodiment, the elastic belt is a ribbed belt comprising ribs extending longitudinally.

[017] For example, the power transmission system comprises between 10 and 12 ribs. [018] According to one embodiment, the power transmission system comprises a reduction stage comprising two pulleys having a centre distance, and at least one auxiliary reduction gear unit, and in which the elastic belt is mounted on the two pulleys and is adapted to produce, in particular, with the auxiliary reduction gear unit, a conversion ratio of between 3/1 and 28/1.

[019] Advantageously, the power transmission system comprises a differential designed to drive two laterally opposite wheels of the vehicle, the elastic belt being designed to transmit the torque coming from the motor to the differential.

[020] Advantageously, the power transmission system comprises an auxiliary reduction gear unit arranged kinematically between, on the one hand, the reduction stage comprising the two pulleys and the elastic belt, and, on the otherhand, the differential, the two pulleys and the elastic belt thus forming a first speed reduction stage of the power transmission system.

[021 ] Advantageously, the stiffness of the elastic ribbed belt is in particular less than 12 000 N/rib/span/E% (in newtons/rib/span (spacing between the ribs)/percentage elongation of the belt (with respect to its original total length)). Its material can be chosen in this sense.

[022] Advantageously, the belt is able of transmit a torque greater than 40 Nm, in particular greaterthan 50 Nm. In practice, the torque transmitted by the belt may be between 0 and 80 Nm, in particular between 0 and 55 Nm. Advantageously, the torque at the output of the transmission system, i.e. downstream of the speed reduction stages, is between 0 and 1200 Nm, in particular between 0 and 900 Nm.

[023] Advantageously, the mounted belt has an elongation greateror equal to 1 ,5% of the original length of the elastic belt.

[024] Moreover, the invention is targeted to a range of power transmission systems for transmitting power between a motor and at least one wheel, said range comprising at least two power transmission systems as briefly described above, the two transmission systems having different reduction ratios between their motor and their said at least one wheel, the two power transmission systems having auxiliary reduction gear units having the same reduction ratio, the difference in reduction ratio between the two transmission systems being obtained by virtue of the two reduction stages each comprising the two pulleys and the elastic belt, these two reduction stages having different reduction ratios.

[025] The invention is also targeted to a powertrain for a motor vehicle comprising at least one wheel and a motorization and drive system for said at least one wheel, said motorization and drive system comprising a power transmission system as briefly described above, the power transmission system being designed to transmit a torque between the motorization system and said at least one wheel, the power transmission system being designed such that the elastic belt is situated in the torque transmission path between the motorization system and said at least one wheel.

[026] Advantageously, the motorization comprises an electric machine having a 48V voltage.

[027] Advantageously, the peak power is up to 11 kW. Advantageously, the continuous power output is up to 6kW.

[028] The invention is also targeted to a vehicle, in particular a three or four wheeler vehicle comprising this powertrain.

[029] The invention is additionally targeted to a method for mounting a power transmission system as briefly described above, in which the elastic belt is mounted around the two pulleys by elastic deformation of said elastic belt beyond a predetermined prestress threshold of the elastic belt in the mounted state.

PRESENTATION OF THE FIGURES

[030] The invention will be better understood from reading the following description, given by way of example, and by referring to the following figures that are given by way of non limiting examples and in which identical references are given to similar objects.

[031] [Fig. 1]: Figure 1 depicts an electric motor of a motor vehicle and an example of a power transmission system comprising a ribbed belt, according to one embodiment of the invention;

[032] [Fig.2]: Figure 2 depicts a partial view of the same example of a power transmission train, with a ribbed belt mounted on two pulleys;

[033] [Fig. 3]: Figure 3 shows a view of said elastic ribbed belt;

[034] [Fig. 4]: Figure 4 shows a close-up view of a slideway intended for mounting the elastic belt on two pulleys so as to ensure the prestress of said pulley;

[035] [Fig. 5]: Figure 5 illustrates a vehicle comprising a power transmission system according to the invention. [036] It should be noted that the figures explain one embodiment of the invention in a detailed manner for implementing the invention, said figures being able of course to serve to better define the invention, where appropriate.

DETAILED DESCRIPTION OF THE INVENTION

[037] The invention relates to a transmission system for a powertrain of a vehicle, comprising in particular an elastic belt. The present invention is targeted in particularto use in a motor vehicle but also to use in any rolling land vehicle intended fortransporting passengers or goods, namely a lightweight, intermediate or heavy duty vehicle, or else a construction vehicle or agricultural vehicle.

[038] The invention is aimed in particular at 3 or 4-wheel electric vehicles.

[039] With reference to Figure 1 , the present invention falls particularly within the context of a powertrain via which a motor 20 drives the rotation of two laterally opposite wheels of a vehicle via a differential.

[040] Figure 1 shows a powertrain comprising a motor 20, in particular an electric motor 20, of a motor vehicle, connected to a powertransmission system comprising a reduction stage comprising an, in particular ribbed, elastic belt 11 and two pulleys 12, 13, along with an auxiliary reduction gear unit 1 driving a differential. The use of a belt reduction stage supplementing the auxiliary reduction gear unit 1 makes it possible in particular to standardize the auxiliary reduction gear unit 1 , or even the electric motor 20 and the differential, in such a way as to intervene only on the belt reduction stage in order to modify the reduction ratio according to the characteristics of the vehicle. It is thus possible to standardize the auxiliary reduction gear unit 1 within a range of powertrains. Wth the belt reduction stage, it is possible to obtain a conversion ratio ranging from 3/1 to 28/1 .

[041] Furthermore, the use of a pulleys/belt subassembly downstream of the electric motor, in particular between the electric motor and an auxiliary reduction gear unit, makes it possible to transmit a torque without generating axial forces on the drive shaft and on the electric machine, as may be the case when gear pinions are mounted on the drive shaft.

[042] The elastic belt 11 is mounted prestressed on the two pulleys 12, 13, as can also be seen in Figure 2. In particular, the pulleys 12, 13 are fixed and there can optionally be provided a device for adjusting the centre distance E between said two pulleys 12, 13 so as to set the initial tension and elongation of the belt 11 . The elastic belt 11 is, for example, but not necessarily, made of polyamide. [043] The pulleys are ribbed here such that the ribs of the pulley are inserted between the ribs of the belt.

[044] The electric motor 20 can also be held between two fastening points, one of which forms a sliding connection making it possible to set the appropriate initial tension of the elastic belt 11 .

[045] Figure 4 represents a close-up view of a means, in the embodiment shown, for obtaining the desired prestress of the elastic belt 11 . According to this embodiment, there is provision for the respective frames of the electric motor 20 and of the auxiliary reduction gear unit 1 to be mounted on a pivot capable of translating in a slideway 30. When the elastic belt 11 is being mounted in the power transmission system 10, the pulleys 12, 13 can be drawi closer to one another, corresponding to moving the pivot in the slideway 30 into a first position A (or bottom position), the thus reduced centre distance E readily allowing the non-tensioned elastic belt 11 to be slipped over the two pulleys 12, 13. In a second step of the mounting operation, the corresponding pivot is translated in said slideway 30 to a second position B (or top position) in which the elastic belt 11 is tensioned with a predetermined elastic prestress threshold. The second position B is determined such that the initial elongation of the elastic belt 11 corresponds to the desired prestress of said elastic belt 11.

[046] This method is advantageous in that it facilitates repair and maintenance of the power transmission system 10. This method of prestressed mounting of the elastic belt 11 should not be interpreted as a limitation, since other mounting methods allowing the desired prestress of the elastic belt 11 to be obtained are envisaged.

[047] According to one variant, the elastic belt 11 is mounted around the two pulleys 12, 13 by deforming said elastic belt 11 beyond the predetermined prestress threshold of the elastic belt 11 in the mounted state, so as to position it around the two pulleys.

[048] Similarly, by means of a machine having mounting cones, the elastic belt 11 can be stretched so as to be able to be slipped over the pulleys 12, 13; then, the mounting-cone machine is disengaged, the elastic belt 11 being deposited on the pulleys 12, 13 while having the desired prestress, in other words the desired initial elongation.

[049] According to the invention, the belt 11 thus has an elastic nature. In particular, the elasticity of the belt 11 is adapted to compensate for the elongation of said belt 11 caused by its wear so as to maintain the tension exerted on said belt. This is made possible by the prestressed mounting of said elastic belt 11 . [050] In other words, the invention makes it possible to implement and maintain an adapted tension of the elastic belt 11 in the power transmission system 10 and therefore a satisfactory durability along with desired performance levels in terms of acoustics, vibrations and harshness (or “NVH” for “Noise, Vibrations, Harshness”) of the vehicle, with all this being achieved without the need for a tensioner-type compensation system.

[051 ] Specifically, the prestressed mounting of the elastic belt 11 , in otherwords its initial elongation, makes it possible to compensate for the elongation of the belt 11 that is caused by its wear and that would, in the absence of prestress, cause a relaxation of said elastic belt 11. By virtue of the prestress of the belt 11 , the elongation thereof is compensated for by maintaining an adapted value of its tension.

[052] It is therefore possible to dispense with the compensation assembly comprising a roller, a tensioner and a spring, which is imperative in the prior art to maintain the tension of the belt when an elastic tension is used.

[053] Thus, the power transmission system 10 is configured to transmit a torque to the wheels that can reach a maximum torque Cmax The elastic belt 11 is mounted prestressed and originally has a nominal tension Tnom. As has been described above, the wear of the elastic belt 11 , owing to its use in the power transmission system 10, causes its elongation and a reduction in its current tension T over time. It is known that the elastic belt 11 remains able to transmit the maximum torque Cmaxas long as it has a tension above a minimum threshold tension Tmin.

[054] According to the invention, the elastic belt 11 , owing to its elasticity and its being mounted elastically prestressed in tension, is configured such thatTnom > T > T min during the service life of said elastic belt 11 .

[055] In particular, by virtue of the invention, owing to its elasticity and its being mounted elastically prestressed in tension , the elastic belt 11 is able to withstand a significant elongation A while continuing to satisfy the condition relating to its current tension, T nom > T > T min.

[056] As can be seen from this embodiment, the belt is preferably ribbed, for example with

V-shaped grooves, such as those used in the belts sold under the trade name Poly V®.

[057] According to one embodiment depicted in Figure 1 , the power transmission system 10 is connected to an electric motor20 of the motor vehicle. The stiffness of the elastic ribbed belt 11 is in particular less than 12 000 N/rib/span/E% (in newtons/rib/span (spacing between the ribs)/percentage elongation of the belt (with respect to its original total length)). [058] By way of illustration, the elastic belt 11 is, for example, configured such that Tnom is greater than or equal to approximately 1 .2 T min. The nominal tension T nom of the elastic belt 11 is associated with an elongation E of the elastic belt 11 by elastic deformation. For example, the elongation E is greater than or equal to approximately 1 .5% of the original length of the elastic belt 11 , in particular greaterthan or equal to approximately 2% of said original length.

[059] The width of such an elastic ribbed belt 11 intended for implementation in an electric motor vehicle is particularly intended to allow the transmission of an adapted torque, including in extreme cold, that is to say in an environment in which the temperature is of the order of - 30°C, or including in the context of fording, even though very cold temperatures or humidity have a tendency to increase the risk of slipping of an elastic belt. T o overcome this risk, the width of the elastic ribbed belt 11 is increased by approximately three ribs, that is to say approximately 1 .05 cm with respect to the width that would in principle be sufficientto pass on the desired power in the context of said motor vehicle.

[060] By virtue of the invention, with an elasticity of the ribbed belt 11 configured as defined above, there results an improvement in the durability of said ribbed belt 11 which, in the context of a power transmission system 10, forms the first stage of a powertrain of an electric motor vehicle.

[061] In summary, the present invention therefore relates to a power transmission system 10 comprising an, in particular ribbed, elastic belt 11 forming a first stage of a powertrain connected to a motor 20, in particular an electric motor, of a motor vehicle.

[062] The elastic belt 11 can be mounted on two fixed pulleys 12, 13, and the elasticity of said belt 11 is taken advantage of for mounting said belt around the two pulleys 12, 13.

[063] Such a power transmission system 10 comprising an, in particular ribbed, elastic belt 11 can be used, according to the invention, while being connected to an electric motor 20 without axial load. One and the same elastic ribbed belt 11 can, according to the invention, be used to achieve a wide variety of conversion ratios according to the centre distance E and the diameter of the pulleys 12, 13 that are used.

[064] Figure 5 is a side view of a vehicle 100 comprising a power transmission system 10 according to the embodiment of figures 1 to 4. In the example shown the vehicle 100 is a three- wheeler electric vehicle.