FR3143702A1 - Motor vehicle powertrain - Google Patents

Abstract

The invention relates to a powertrain (10) for a motor vehicle comprising an electric machine (100) which comprises an output shaft, and a reduction gear (101) which comprises: - two shafts (110, 120) one of which is coupled to the output shaft of the electric machine, and the other of which is coupled to an input of an axle differential (130), - a fixed pinion (111) fixed to a first of the two shafts, and - a free gear (121) which meshes with said fixed gear and which is mounted on a second of the two shafts by means of a free wheel system (150). Figure for abstract: Fig.1

Description

Motor vehicle powertrain Technical field of the invention

The present invention generally relates to speed reducers with one, two or three speed ratios.

It relates more particularly to a powertrain for a motor vehicle comprising an electric machine which comprises an output shaft, and a speed reducer which comprises:
- two shafts, one of which is coupled to, or formed by, the output shaft of the electric machine, and the other of which is adapted to be coupled to the input of an axle differential,
- a fixed gear fixed to a first of the two shafts, and
- a free gear which meshes with said fixed gear and which is preferably mounted on a second of the two shafts.

The invention also relates to a motor vehicle equipped with such a powertrain.

It finds a particularly advantageous application in four-wheel drive vehicles and in sports vehicles equipped with multi-speed reduction gears.

State of the art

An internal combustion engine develops a torque which varies with the speed of rotation of the crankshaft. Such a motor has a restricted range of use. In a motor vehicle equipped with such an engine, it is then necessary to associate a gearbox with the engine.

In an electric (or hybrid) motor vehicle, there is provided an electric machine coupled to a speed reducer. As a general rule, this gearbox is single-ratio and constant mesh. A gearbox is therefore generally not provided. An electric machine is in fact adapted to deliver a substantially constant torque over a wide range of rotational speeds. It can therefore be used with such a reduction gear in a motor vehicle. The advantage of a single-speed gearbox is that it is simple, inexpensive, and does not pose a problem of torque loss (when changing gear).

However, we note that such a single-ratio, constant-mesh speed reducer suffers from several limitations, of which two examples can be given.

As we know, an electric machine, past a certain threshold of rotational speed, sees the torque it can deliver drop suddenly. Then the power it can generate saturates. In other words, the torque delivered by an electric motor is not constant indefinitely. Associating a multi-speed gearbox with such an electric machine can therefore remain of interest in the automotive field. Typically, a reduction gear with several ratios would make it possible either to reduce the size of the electric machine, or to use the electric machine in speed ranges where its consumption remains reduced, or to install the electric machine on particular vehicles such as utility vehicles capable of moving heavy loads, or in sports vehicles capable of reaching high speeds.

The disadvantage of a multi-speed gearbox is that currently it is complex, expensive, and heavy, or that it is slow when it comes to changing from one gear to another, which causes torque breaks which are not compatible with the automotive sector.

In a four-wheel drive motor vehicle, a single-speed constant mesh reduction gearbox does not allow certain wheels to be disengaged, for example when it is not necessary to rotate them all. To ensure this function, additional clutch systems are then provided, which are expensive and bulky.

Presentation of the invention

In order to remedy the aforementioned drawbacks of the state of the art, the present invention proposes a new speed reducer.

More particularly, according to the invention, we propose a powertrain as defined in the introduction, in which the free pinion of the speed reducer is adapted to be coupled to the second of the two shafts by means of a freewheel system.

Preferably, this free pinion is mounted on the free wheel system which is itself mounted on the second of the two shafts.

Thanks to the freewheel system, the freewheel couples to the second shaft only when their rotational speeds are equal. Otherwise stated, the passage of torque only takes place in one direction (from the electric machine to the wheels) and not in the other direction.

Thus, it is possible to automatically disengage (without an actuator and without manual intervention) the speed ratio offered by this pair of free gear and fixed gear. Therefore, when it stops, the electric machine automatically disengages from the vehicle wheels.

This technology will be useful for example in a four-wheel drive vehicle and two electric machines, during regenerative braking phases (during which braking energy is converted into electrical energy). In fact, it will be possible during these phases to automatically disengage one of the electrical machines in order to only recover energy with the other of the electrical machines. This aspect will be all the more advantageous when one of the electric machines drives two first wheels, and the other machine drives the other two wheels of the vehicle. In fact, this other machine will disengage automatically, which will limit the losses associated with its rotation or its drive in the regenerative braking phases (performed by the first machine).

This technology will also be useful in sports vehicles since it will make it possible to use a gearbox with several speed ratios at the output of an electric machine, while maintaining a fairly simple gearbox architecture. Indeed, thanks to the freewheel system, it will be possible to automatically disengage the gear ratio offered by this pair of free gear and fixed gear as soon as another gear is engaged, without resorting to expensive coupling systems.

Other advantageous and non-limiting characteristics of the powertrain according to the invention, taken individually or in all technically possible combinations, are as follows:
- the first shaft is constantly coupled to, or formed by, the output shaft of the electric machine and the second shaft is constantly coupled to the input of the axle differential;
- there is provided at least one secured pinion fixed to one of the two shafts, an idler gear which meshes with each secured pinion and which is mounted free to rotate on the other of the two shafts, and at least one controlled coupling system which is adapted to couple said idler gear to said other of the two shafts;
- two secured gears are provided which are fixed to one of the two shafts and two idle gears which are mounted free to rotate on the other shaft;
- each secured pinion being associated with a gear ratio, the controlled coupling system is adapted to pass the torque from one to the other of the idle gears during a change of gear ratio;
- the controlled coupling system includes two multi-disc clutches;
- the controlled coupling system comprises a system of clutches, comprising for example two wheels equipped with clutches and mounted movable relative to each other in order to be able to couple and decouple.

The invention also relates to a motor vehicle comprising at least one drive wheel and a powertrain as mentioned above.

Other advantageous and non-limiting characteristics of the vehicle conforming to the invention, taken individually or in all technically possible combinations, are as follows:
- the vehicle has two axles, each equipped with an axle differential;
- one of the axle differentials has an input coupled to a shaft of the aforementioned powertrain;
- the other of the axle differentials has an input coupled to an output shaft of a third-party motor;
- said third-party motor is electric;
- said third-party motor is adapted to develop a maximum power which is strictly greater than the maximum power which is adapted to develop the electric machine of the powertrain.

Of course, the different characteristics, variants and embodiments of the invention can be associated with each other in various combinations as long as they are not incompatible or exclusive of each other.

Detailed description of the invention

The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

On the attached drawings:

is a schematic view of a first embodiment of a powertrain according to the invention;

is a schematic view of a motor vehicle comprising the powertrain of the ;

is a schematic view of a second embodiment of a powertrain according to the invention;

is a schematic view of a motor vehicle comprising the powertrain of the .

In the remainder of the description, the term “coupled” will be used to designate a connection between two elements which makes it possible to transmit a torque from one of these elements to the other.

In Figures 1 and 3, two embodiments of a powertrain 10 of a motor vehicle are shown.

This motor vehicle conventionally comprises a chassis which delimits a passenger compartment and which forms a support for the powertrain 10. This chassis carries wheels, for example four in number, at least one of which is driving (i.e. i.e. driven in rotation by a motor).

In the embodiment of Figures 1 and 2, we will consider the case where the motor vehicle 1 has four driving wheels arranged in pairs on two axles. In this mode, the motor vehicle 1 comprises two separate powertrains 10, 20, which make it possible to respectively drive the drive wheels of the two axles via two differentials 130, 230.

The vehicle thus comprises a first power unit 20 to drive the drive wheels of the front (or respectively rear) axle and a second power unit 10 to drive the drive wheels of the rear (or respectively front) axle.

The first powertrain 20 will not be described in detail here. We can only specify that it includes a 200 engine which is either a combustion engine equipped with a gearbox, or an electric machine equipped with a speed reducer.

The second powertrain 10, which is more precisely the subject of the present invention, will be described in detail below, with reference to the .

In the embodiment of Figures 3 and 4, we will consider the case where the motor vehicle 1 is a sports car making it possible to ensure strong acceleration and reach high speeds (at least greater than 190 km/h ). This car then has a single powertrain 10, and exactly two driving wheels (front or rear).

In all cases, the powertrain 10 which is the subject of the present invention comprises at least one electric machine 100 and a reduction gear 101.

The electric machine 100 has at least one motor function. It can also have an alternator function. It can be of any type: axial or radial flow, permanent magnets or wound rotor, etc.

In any case, it comprises a carcass fixed to the chassis of the vehicle and an output shaft which is adapted to rotate relative to the carcass when supplied with electric current.

The reducer 101 for its part comprises at least two stages of shafts. Here it has exactly two, that is to say it has two shafts mounted to rotate in the carcass around parallel axes, by means of bearings.

It thus comprises a first shaft, called primary shaft 110, which is constantly coupled to the output shaft of the electrical machine 100. As shown in the figures, this primary shaft 110 is more exactly formed by the shaft output of the electric machine 110, but as a variant, these two shafts could be separate and joined by any coupling means.

The reducer 101 also includes a second shaft, called secondary shaft 120, which is coupled to the input of an axle differential 130.

As shown in Figures 1 and 3, this coupling is produced by means of an output pinion 124 which is fixed to the secondary shaft 120 (so as to be integral in rotation with it) and which meshes an input crown of the axle differential 130. It will be noted in these figures that this axle differential 130 also includes two transmission shafts 131 which are each coupled to one of the drive wheels of the vehicle.

One of the primary 110 and secondary 120 shafts carries a fixed gear while the other carries a free gear. We will consider here that the fixed gear 111 is carried by the primary shaft while the free gear 121 is carried by the secondary shaft 120.

These two fixed gears 111 and free gears 121 mesh constantly.

The first of these pinions is described as fixed since it is integral in rotation with the primary shaft 110.

The second of these pinions is described as free since, according to the invention, it is mounted on the secondary shaft 120 via a freewheel system 150.

Such a freewheel system is well known, typically on bicycles.

It allows torque to be transmitted in one direction only, from the electric machine 100 to the axle differential 130.

In other words, as long as the speed of the vehicle is such that the axle differential 130 rotates the secondary shaft 120 at a rotational speed greater than that of the freewheel, the freewheel system 150 is decoupled and does not transmits no torque. On the other hand, when the rotation speed of the output shaft of the electric machine 100 is such that the free pinion 121 reaches a rotation speed equal to that of the secondary shaft 120, the free wheel system 150 is coupled and transmits the torque of the electric machine 100 to the drive wheels.

Different technologies could be used to create this freewheel mechanism, based for example on a system of pawls, or a system of jamming rolling elements, or a system of cams, etc.

We can now describe more precisely the first embodiment of the reduction gear 101, in the case of Figures 1 and 2 where the powertrain 10 is on board a motor vehicle 1 with four-wheel drive.

In this embodiment, the primary shaft carries only one gear, namely the aforementioned fixed gear 111. For its part, the secondary shaft 120 has exactly two gears, namely the aforementioned free gear 121 and the output gear 124.

The reduction gear 101 can then be described as a disengageable single-ratio.

In practice, thanks to this reducer 101, it will be possible to stop the electric machine 100 to disengage the rear wheels of the vehicle, while the motor 200 of the first power unit 20 remains activated and continues to rotate the front drive wheels. of this vehicle or generates a regenerative braking torque (to convert the kinetic energy of the vehicle into electrical energy).

Thus, the electric machine 100 can be used only when it is useful for the vehicle to be propelled by its four drive wheels. It will be disabled otherwise, so that:
- during traction phases, the vehicle is propelled by two driving wheels only if it is not necessary to use all four wheels,
- during braking phases, the conversion of kinetic energy into electrical energy is done only by the motor 200 of the first power unit 20.

In this first mode, the electric machine 100 being intended to be used less than the motor 200 of the first power unit 20, it can be expected that it develops a maximum power lower than that of this motor 200.

In the embodiment of the , the speed reducer 101 has several reports. It could only have two. Here, as shown in and preferably, it has exactly three.

The first gear will be used when the vehicle is traveling at low speed, to allow it to accelerate strongly.

The third gear will be used when the vehicle is traveling at high speed, to allow it to reach a speed of over 250 km/h.

Otherwise, the second gear ratio will be used.

To reverse, any of the second or third gears will be used (preferably second).

The primary shaft 10 then carries, in addition to the fixed gear 111, two other fixed gears called “secured gears 112, 113”. These two secured gears 112, 113 are integral in rotation with this primary shaft 10. The three gears 111, 112, 113 carried by the primary shaft 110 have different diameters to offer distinct speed ratios, the fixed gear 111 being the one of smaller diameter in order to be used as a first gear ratio.

The secondary shaft 120 then carries two idler gears 122, 123 which respectively mesh with the two secured gears 112, 113. These gears are described as idler in the sense that they are mounted free to rotate on this shaft and that they are blocked in translation along this axis.

To transmit the torque from the primary shaft 110 to the secondary shaft 120, a system could be provided for interlocking the idler gears 122, 123 of the type used in gearboxes. However, in this eventuality, the transition from second gear to third gear would be with a loss of torque which is unpleasant for the passengers of the vehicle and deemed incompatible with the desired performance of the latter.

Therefore, it is preferred here to use a controlled coupling system 160 allowing you to move from one gear to another without breaking the torque. The technology used is that of multi-disc clutches. Such technology makes it possible, when a gear change is ordered (from second gear to third or vice versa), to ensure that the torque transmitted to the drive wheels does not drop suddenly. This system is thus controlled, not to open one clutch before closing the other, but to open one of the clutches while simultaneously closing the other.

Of course, alternatively, other technologists could be employed.

Note that in this mode, the use of the freewheel system 150 will make it possible to do without a controlled coupling system 160 for the first gear ratio.

We can then summarize the operation of this reducer 101 as follows.

When the vehicle is started, both clutches are controlled in the open state. Thus, the torque from the electric machine is fully transmitted to the drive wheels via the fixed gear 111 and the free gear 121.

To shift to the second gear, for example when the vehicle speed reaches a first threshold, the clutch associated with idler gear 122 closes gradually. During this closing, the idler gear 122 decelerates while the secondary shaft 120 continues to accelerate, which causes the freewheel system 150 to decouple. It is understood here that this gear ratio change occurs smoothly and without marital breakdown.

To shift to third gear, for example when the vehicle speed reaches a second threshold, the clutch associated with idler gear 123 gradually closes while that associated with idler gear 122 opens. During this operation, the idler gear 123 decelerates while the secondary shaft 120 accelerates, which keeps the freewheel system 150 decoupled. We understand here that this gear change still occurs smoothly and without loss of torque.

To return to the second gear, for example when the vehicle speed falls below a third threshold, the clutch associated with the idler gear 122 gradually closes while that associated with the idler gear 123 opens. During this operation, the idler gear 122 accelerates while the secondary shaft 120 decelerates. Here again, this gear change occurs smoothly and without loss of torque.

To return to first gear, for example when the vehicle speed drops below a fourth threshold, the clutch associated with idler gear 122 opens suddenly or gradually. During this operation, the secondary shaft 120 decelerates naturally, until it reaches the rotation speed of the free pinion 121 (it is also possible to increase the speed of the electric machine 100). Then, the freewheel system 150 will pass into the coupled state and will transmit the torque of the electric machine 100.

This transition from second gear to first gear can otherwise be done when the vehicle is stationary. Note in fact that if this is not the case and you want the vehicle to decelerate when changing from second gear to first gear, it will be useful to activate the brakes since the electric machine will not be able to to perform regenerative braking.

The present invention is in no way limited to the embodiments described and represented, but those skilled in the art will be able to make any variation conforming to the invention.

Typically, as a variant of the second embodiment, the freewheel system 150 could be installed not on the first gear ratio, but on the third, typically between the secondary shaft 120 and the pinion 123. In this variant, the controlled coupling system 160 will then be installed between pinions 121 and 122. In this way, it will be possible to carry out regenerative braking on the first and second gears (but not on the third which will in practice be the least used gear) .

According to another variant of the invention it would be possible to use the speed reducer illustrated on the in a four-wheel drive sports vehicle.

According to another variant of the invention, the freewheel system could have been installed between the primary shaft 110 and the fixed gear 111.

Claims (10)

Powertrain (10) for a motor vehicle, comprising an electric machine (100) which comprises an output shaft, and a reduction gear (101) which comprises:
- two shafts (110, 120) one of which is coupled to, or formed by, the output shaft of the electric machine (100), and the other of which is adapted to be coupled to the input of a axle differential (130),
- a fixed gear (111) fixed to a first of the two shafts (110), and
- a free gear (121) which meshes with said fixed gear (111),
characterized in that the free gear (121) is adapted to be coupled to the second of the two shafts (120) by means of a free wheel system (150). A power train (10) according to claim 1, wherein the first shaft (110) is constantly coupled to, or formed by, the output shaft of the electric machine (100) and the second shaft (120) is constantly coupled to the entrance to the axle differential (130). Powertrain (10) according to one of claims 1 and 2, in which there is provided at least one secured pinion (112, 113) fixed to one of the two shafts (110), an idler gear (122, 123) which meshes with each secured pinion (112, 113) and which is mounted free to rotate on the other of the two shafts (120), and at least one controlled coupling system (160) which is adapted to couple said idler gear (122, 123) to said other of the two trees (120). Powertrain (10) according to claim 3, in which two secured gears (112, 113) are provided fixed to one of the two shafts (110) and two idle gears (122, 123) mounted free to rotate on the other tree (120). Powertrain (10) according to claim 4, in which, each secured pinion (112, 113) being associated with a gear ratio, the controlled coupling system (160) is adapted to pass the torque from one to the other. another of the idle gears (122, 123) when changing gear ratios. Powertrain (10) according to claim 5, in which the controlled coupling system (160) comprises two multi-disc clutches or a clutch system. Motor vehicle comprising at least one drive wheel, characterized in that it comprises a powertrain (10) according to one of claims 1 to 6. Motor vehicle according to claim 7, comprising two axles each equipped with an axle differential (130, 230), one of the axle differentials (130) comprising an input coupled to a shaft of the powertrain (10), the other axle differentials (230) having an input coupled to an output shaft of a third party motor (200). Motor vehicle according to claim 8, wherein said third party motor (200) is electric. Motor vehicle according to claim 8 or 9, in which said third party engine (200) is adapted to develop a maximum power which is strictly greater than the maximum power which the electric machine (100) of the powertrain (10) is adapted to develop. .