The present invention relates to a transmission system for a hybrid propulsion vehicle, adapted to allow motion transmission from a vehicle's internal combustion engine and/or electrical machine to the vehicle's wheels.

Transmission systems for hybrid propulsion vehicles wherein the electrical machine is permanently connected or selectively connectable to a primary shaft or secondary shaft of a mechanical main gearbox in order to transmit torque to such shaft or receive torque from such shaft are well known. The electrical machine is thus able to perform not only the main functions of traction (i.e. generation of mechanical power for the vehicle's wheels by drawing energy from the vehicle's batteries) and regeneration (generation of electrical power for the vehicle's batteries by drawing energy from the recovery of kinetic energy from the vehicle or from the operation of the internal combustion engine when the vehicle is stationary), but also additional functions such as those of acting as an alternator and as a starter motor.

A transmission system for a hybrid propulsion vehicle according to the preamble of independent claim 1 is known from EP 1 232 891. According to this known solution, the transmission system comprises a primary line and a secondary line arranged parallel to one another. The primary line comprises two coaxial primary shafts, namely a first primary shaft adapted to be connected for rotation with a crankshaft of the internal combustion engine by means of a first engagement device and a second primary shaft adapted to be connected for rotation with a drive shaft of the electrical machine by means of a second engagement device, while the secondary line comprises a secondary shaft. The first primary shaft carries four first driving gearwheels, each permanently meshing with a respective first driven gearwheel carried by the secondary shaft. The first four driving gearwheels are made as fixed wheels, and are therefore permanently connected for rotation with the first primary shaft, while the associated first driven gearwheels are idly mounted on the secondary shaft and are selectively connectable for rotation with such shaft by means of two double-acting engagement sleeves. The second primary shaft carries two second driving gearwheels, each permanently meshing with a respective second driven gearwheel carried by the secondary shaft. The second primary shaft is connected to the electrical machine by means of a gearing mechanism, or similar connecting mechanism, arranged on the outside of a casing of the transmission system. The two second driving gearwheels are made as fixed wheels, while the associated second driven gearwheels are idly mounted on the secondary shaft and are selectively connectable for rotation with such shaft by means of another double-acting engagement sleeve. When the first and second primary shaft are decoupled from one another, the transmission system allows the operation of the vehicle in a purely internal combustion mode (i.e., with the drive torque generated solely by the internal combustion engine) with four forward gears available, or in a purely electrical mode (i.e., with the drive torque generated solely by the electrical machine acting as the motor) with two forward gears available. When the two primary shafts are coupled to one another, the transmission system provides six forward gears.

Such a transmission system has disadvantages in terms of size and number of components. The arrangement of the connecting mechanism that connects the electrical machine to the second primary shaft, and hence to the two second driving gearwheels, on the outside of the casing of the transmission system entails in fact an increase in size, as well as an increase in the number of components, of the transmission system and also involves the need to provide a special lubrication system in the case where the connecting mechanism must be lubricated.

It is an object of the present invention to provide a transmission system for a hybrid propulsion vehicle which is not affected by the aforementioned disadvantages of the prior art, but which at the same time maintains the advantage of providing two different gears for the operation of the vehicle in purely electrical mode.

This and other objects are fully achieved according to the present invention by virtue of a transmission system having the features defined in the appended independent claim 1. Preferred embodiments of the invention are set forth in the dependent claims, the subject- matter of which is to be understood as forming an integral and integrating part of the following description. In short, the invention is based on the idea of providing a transmission system of the type identified above, wherein the connecting means for connecting the drive shaft of the electrical machine to the first and second driving gearwheels of the gearbox are arranged inside the gear casing, and wherein the engagement device which is associated with the first and second driving gearwheels to selectively connect said gearwheels for rotation with the primary shaft is also associated with a third driving gearwheel which is idly mounted on the primary shaft, adjacent to the second driving gearwheel, for selectively connecting the third driving gearwheel for rotation with the primary shaft. Due to the fact that the same engagement device that is arranged to control the engagement of one of the gears of the gearbox is also used to control the connection between the electrical machine and the secondary line of the gearbox, a reduction in the number of components of the system is obtained.

Preferably, the connecting means comprise a pinion intended to be mounted on the drive shaft of the electrical machine, said pinion meshing directly or indirectly (i.e. by means of one or more intermediate gearwheels) with the first or the second driving gearwheel. For example, the pinion may mesh indirectly with the first or the second driving gearwheel by means of the first or the second driven gearwheel, respectively, and possibly by means of one or more additional intermediate gearwheels interposed between the pinion and the first or the second driven gearwheel.

By means of the first and second driving gearwheels on the primary line and the two associated driven gearwheels on the secondary line, it is possible to provide two different transmission ratios between the electrical machine and the secondary line, and thus transmit the motion to the vehicle's wheels in a purely electrical mode with two different gears, namely a first gear, or high gear, and a second gear, or low gear. To this end, the first and second driving gearwheels are kept uncoupled from the primary shaft, and either of the two associated driven gearwheels is connected to the secondary shaft to engage the high gear or the low gear.

By engaging one of these two gears and reversing the direction of rotation of the electrical machine, it is possible to drive the vehicle in reverse in a purely electrical mode, without having to provide a further specific gearing mechanism for the reverse gear.

As will be clearer from the following description, the present invention allows to obtain, with a limited number of additional components compared to a common mechanical gearbox (the additional components being substantially only the connecting means which connect the double gearwheel to the drive shaft of the electrical machine), a transmission system for hybrid propulsion vehicles wherein the electrical machine may be releasably connected to both the primary line and the secondary line independently of each other, the connection with the secondary line being obtainable with two different transmission ratios.

It is thus possible to transmit the motion to the vehicle's wheels by means of only the internal combustion engine, by means of only the electrical machine, or even simultaneously by means of the internal combustion engine and the electrical machine, summing therefore the torques generated by the internal combustion engine and by the electrical machine.

The transmission system of the present invention also allows to compensate, in whole or in part depending on the installed electrical power, for the interruption in the torque transmission during the gear shift process as the torque generated by the electrical machine can be transmitted directly to the secondary shaft, and hence to the vehicle's wheels.

It is furthermore possible to efficiently carry out the kinetic energy recovery function, disconnecting the primary line and then connecting the secondary line directly to the electrical machine.

A further advantage of the present invention is that in the purely electrical operating mode the primary line is stopped, which results in greater efficiency in the transmission of motion to the wheels and hence in a reduction in energy consumption. A further function made available by a transmission system according to the invention is the provision of mechanical power from the internal combustion engine to the electrical machine, which is obtained either by providing more power than that needed for the motion and consequently absorbing the excess power by means of the electrical machine acting as a generator or, with the vehicle stationary, by connecting the electrical machine to the primary line and at the same time disconnecting the secondary line in order to charge the vehicle's battery by means of the electrical machine acting as a generator.

Further characteristics and advantages of the invention will become more apparent from the following detailed description, given , purely by way of non-limiting example with reference to the accompanying drawings, wherein:

Figure 1 is an axial sectional view schematically showing a transmission system for a hybrid propulsion vehicle according to an embodiment of the present invention; and

Figure 2 is an axial sectional view schematically showing a transmission system for a hybrid propulsion vehicle according to a further embodiment of the present invention.

With reference to Figure 1, a transmission system for a hybrid propulsion vehicle according to an embodiment of the present invention basically comprises a mechanical gearbox 10, an electrical machine ME, and a connecting mechanism 12 for connecting the electrical machine ME to the gearbox 10.

The gearbox 10 comprises a primary line adapted to be releasably connected to an internal combustion engine MT of the vehicle, a secondary line adapted to be permanently connected, in a manner known per se, to the vehicle's driving wheels (not shown) by means of a differential 14, and a gear casing 16 inside which the primary line, the secondary line, the differential 14 and the electrical machine ME are mounted. The primary line comprises a primary shaft 18, preferably a single primary shaft, which extends along a first axis and is rotatably supported by the gear casing 16 by means of first bearings 20, and a friction clutch 22, of type known per se, adapted to releasably connect the primary shaft 18 ith a crankshaft 24 of the internal combustion engine MT. The secondary line comprises a secondary shaft 26, preferably a single secondary shaft, which extends along a second axis Y parallel to, but not coinciding with, the first axis X, and is rotatably supported by the gear casing 16 by means of second bearings 28. The secondary shaft 26 carries a final reduction pinion 30 permanently meshing with a ring gear 32 of the differential 14 to transmit the motion from the secondary shaft 26 to the vehicle's wheels. On the primary shaft 18 are mounted a plurality of driving gearwheels, each of which meshes permanently with a respective driven gearwheel mounted on the secondary shaft 26 to form a respective gear of the gearbox. More precisely, in the embodiment proposed the primary shaft 18 carries, in order from left to right with respect to the point of view of a person observing Figure 1, a first driving gearwheel 34, a second driving gearwheel 36, a third driving gearwheel 38, a fourth driving gearwheel 40 and a fifth driving gearwheel 42. The first driving gearwheel 34 and the second driving gearwheel 36 are rigidly connected to one another, preferably in such a way as to form a double gearwheel (generally indicated with 44). The double gearwheel 44 and the third driving gearwheel 38 adjacent to it are idly mounted on the primary shaft 18 and are selectively connectable for rotation with that shaft by means of a first engagement sleeve 46. The fourth driving gearwheel 40 and the fifth driving gearwheel 42, on the other hand, are made as fixed gearwheels and are therefore permanently connected for rotation with the primary shaft 18. According to an alternative embodiment, also the fourth driving gearwheel 40 and the fifth driving gearwheel 42 may be idly mounted on the primary shaft 18 and be selectively connectable for rotation with that shaft by means of a further engagement sleeve. The secondary shaft 26 carries, in order from left to right with respect to the point of view of a person observing Figure 1, a first driven gearwheel 48 permanently meshing with the first driving gearwheel 34, a second driven gearwheel 50 permanently meshing with the second driving gearwheel 36, a third driven gearwheel 52 permanently meshing with the third driving gearwheel 38, a fourth driven gearwheel 54 permanently meshing with the fourth driving gearwheel 40 and a fifth driven gearwheel 56 permanently meshing with the fifth driving gearwheel 42. The first driven gearwheel 48 and the second driven gearwheel 50 adjacent to it are idly mounted on the secondary shaft 26 and are selectively connectable for rotation with that shaft by means of a second engagement sleeve 58. The third driven gearwheel 52 is made as a fixed wheel and is therefore permanently connected for rotation with the secondary shaft 26. The fourth driven gearwheel 54 and the fifth driven gearwheel 56 adjacent to it are idly mounted on the secondary shaft 26 and are selectively connectable for rotation with that shaft by means of a third engagement sleeve 60. Alternatively, in the case where the fourth driving gearwheel 40 and the fifth driving gearwheel 42 are idly mounted on the primary shaft 18, the associated driven gearwheels 54 and 56 will be fixed on the secondary shaft 26. The connecting mechanism 12 connects a drive shaft 64 (which extends along an axis Z parallel to the axes X and Y and placed at a distance from these axes) of the electrical machine ME with the assembly formed by the first driving gearwheel 34 and the second driving gearwheel 36 in a manner such that the electrical machine ME is able to drive these driving gearwheels in rotation. According to an aspect of the invention, the connecting mechanism 12 is arranged inside the gear casing 16.

Preferably, the connecting mechanism 12 comprises a pinion 62 fitted on the drive shaft 64 of the electrical machine ME and an intermediate gearwheel 66 meshing on the one side with the pinion 62 and on the other with the first driving gearwheel 34 (or alternatively with the second driving gearwheel 36). The drive shaft 64 of the electrical machine ME is supported rotatably by the gear casing 16 of the gearbox 10 by means of a bearing 68. The intermediate wheel 66 is idly mounted on a lay shaft 70 fixed to the gear casing 16. The intermediate wheel 66 might be omitted, in which case the pinion 62 would mesh directly with the first driving gearwheel 34. The connecting mechanism 12 might, alternatively, be made as a belt or chain mechanism.

The operation of the transmission system described above is as follows.

With the first engagement sleeve 46 in the neutral position, i.e. in the position where this sleeve does not connect either the double gearwheel 44 or the third driving gearwheel 38 for rotation with the primary shaft 18, the electrical machine ME is connectable to the secondary shaft 26 by means of the connecting mechanism 12, the double gearwheel 44 and the first driven gearwheel 48 (if the second engagement sleeve 58 is shifted to the left to connect this wheel for rotation with the secondary shaft 26) or alternatively the second driven gearwheel 50 (if the second engagement sleeve 58 is shifted to the right to connect this wheel for rotation with the secondary shaft 26). In this way, the electrical machine ME is able to transmit the motion to the secondary shaft 26, and hence to the vehicle's wheels, with a first gear, or high gear (provided in this case by the gearing mechanism formed by the first driving gearwheel 34 and the first driven gearwheel 48), or with a second gear, or low gear (provided in this case by the gearing mechanism formed by the second driving gearwheel 36 and the second driven gearwheel 50). The vehicle can thus be moved in purely electrical mode, i.e. by means of the power generated solely by the electrical machine ME, with two different forward gears. By reversing the direction of rotation of the electrical machine ME it is possible to drive the vehicle in reverse gear, which will preferably be carried out using the lowest gear (and thus connecting the second driven gearwheel 50 for rotation with the secondary shaft 26 by means of the second engagement sleeve 58).

With the second engagement sleeve 58 in neutral position, i.e. in the position where this sleeve does not connect either the first driven gearwheel 48 or the second driven gearwheel 50 for rotation with the secondary shaft 26, and thus the electrical machine ME is decoupled from the secondary shaft 26, the electrical machine ME may be connected to the primary shaft 18, and thus to the internal combustion engine MT, by connecting the double gearwheel 40 to the primary shaft 18 by means of the first engagement sleeve 46. In this way, it is possible to operate the electrical machine ME as a generator, using the mechanical power supplied by the internal combustion engine MT, to recharge the battery.

Furthermore, with the first engagement sleeve 46 positioned so as to connect the double gearwheel 40 for rotation with the primary shaft 18, it is possible to drive the vehicle in hybrid mode by combining the power supplied by the internal combustion engine MT and that supplied by the electrical machine ME. In such operating mode, it is possible to select five different forward gears, namely:

the gear provided by the gearing mechanism formed by the first driving gearwheel

34 and the first driven gearwheel 48, such gear being obtained by shifting the second engagement sleeve 58 to the left so as to connect the first driven gearwheel 48 for rotation with the secondary shaft 26;

the gear provided by the gearing mechanism formed by the second driving gearwheel 36 and the second driven gearwheel 50, such gear being obtained by shifting the second engagement sleeve 58 to the right so as to connect the second driven gearwheel 50 for rotation with the secondary shaft 26;

the gear provided by the gearing mechanism formed by the third driving gearwheel

38 and the third driven gearwheel 52, such gear being obtained by shifting the first engagement sleeve 46 to the right so as to connect the first driving gearwheel 38 for rotation with the primary shaft 18;

the gear provided by the gearing mechanism formed by the fourth driving gearwheel 40 and the fourth driven gearwheel 54, such gear being obtained by shifting the third engagement sleeve 60 to the left so as to connect the fourth driven gearwheel 54 for rotation with the secondary shaft 26; and

the gear provided by the gearing mechanism formed by the fifth driving gearwheel 42 and the fifth driven gearwheel 56, such gear being obtained by shifting the third engagement sleeve 60 to the right so as to connect the fifth driven gearwheel 50 for rotation with the secondary shaft 26;

A further embodiment of the invention is shown in Figure 2, where parts and elements identical or corresponding to those of Figure 1 are identified with the same reference numbers as those used in Figure 1. Such further embodiment differs from that of Figure 1 substantially only in that the connecting mechanism 12 further comprises the first driven gearwheel 48 (or, alternatively, the second driven gearwheel 50). In this case, therefore, the transmission of motion from the electrical machine ME to the first driving gearwheel 34 takes place through the first driven gearwheel 48, which meshes directly or indirectly (e.g. by means of one or more intermediate gearwheels, such as the gearwheel 66 shown in Figure 2) with the pinion 62 fitted on the drive shaft 64 of the electrical machine ME. Also in this embodiment the electrical machine ME is able to transmit the motion to the secondary shaft 26 with two different gears. The first gear is defined by the gearing mechanism formed by the pinion 62, the intermediate gearwheel 66 (when present) and the first driven gearwheel 48, and is engaged by shifting the second engagement sleeve 58 to the left so as to connect the first driven gearwheel 48 for rotation with the ¹ secondary shaft 26. The second gear is defined by the gearing mechanism formed by the pinion 62, the intermediate gearwheel 66 (when present), the first driven gearwheel 48, the double gearwheel 44 and the second driven gearwheel 50, and is engaged by shifting the second engagement sleeve 58 to the right so as to connect the second driven gearwheel 50 for rotation with the secondary shaft 26. For the rest, the description given above with reference to the embodiment of Figure 1 still applies. Naturally, the principle of the invention remaining unchanged, the embodiments and constructional details may be greatly varied with respect to those described and illustrated here purely by way of a non-limiting example, without thereby departing from the scope of the invention as defined in the accompanying claims.