DESCRIPTION

[FIELD OF THE INVENTION]

The present invention relates to a connection device in a hybrid powertrain system, to a powertrain system, and to a related hybrid vehicle. The present invention is applicable to the field of vehicles with hybrid powertrains comprising a combustion engine and an electric motor, both of which can be used for propelling the vehicle. In particular, the present invention relates to a connection device for transforming a traditional vehicle with a combustion engine into a multi-modal electric hybrid vehicle.

[PRIOR ART]

The use of vehicles comprising a combustion engine fed with fuel such as petrol or diesel oil causes the emission of harmful gases into the atmosphere. Also, such vehicles burn a large quantity of fuel when in use, thus being very expensive for the user.

Therefore, in an attempt to improve the performance of these vehicles by reducing the harmful emissions and fuel consumption thereof, electric hybrid vehicles have been developed which additionally comprise an electric motor associated with the combustion engine for propelling the vehicle, thereby allowing a more efficient use thereof.

Said electric hybrid vehicles, also known simply as "hybrid vehicles", can be conceived as such from the very beginning of the design stage and then manufactured accordingly. At present, however, most vehicles in use are traditional ones, i.e. they are only equipped with a combustion engine. In order to improve the performance of these traditional vehicles as well, it is known to use retrofit system to transform them into hybrid vehicles. This transformation of a traditional vehicle into a hybrid vehicle is also commonly called "hybrid conversion" or "hybridization".

For example, patent US2009/0223725A1 describes a hybrid conversion kit for a vehicle. The conversion kit includes an electric motor, a battery with the associated electric and electronic controls, and a coupler. The coupler is used for modifying the vehicle downstream of the transmission. The coupler may be a gearbox that couples the electric motor to the driveshaft; as an alternative, the coupler may couple the electric motor directly to the differential of the drive wheels. Between the electric motor and the coupler there may be a clutch. The solution known from US2009/0223725A1 provides the hybrid conversion of a traditional vehicle in order to allow the latter to operate in different modes (e.g.: hybrid, generating, motoring, braking, electric only).

However, the solution known from US2009/0223725A1 has the drawback that it requires much room for housing the components of the conversion kit. In fact, this solution is mainly addressed to rear-wheel-drive or all-wheel-drive vehicles, such as trucks and all-terrain vehicles, the configurations of which are spacious enough to include the coupler.

Another hybrid retrofit solution is known from the scientific article by Gilberto Osorio Gomez and Roberto Vigano, "Proposal of bimodal solution for urban vehicular contamination problem", Revista de Ingenieria e Investigation, Vol. 27, No. 3, Dec. 2007 (143-148). This solution allows retrofitting a front-wheel-drive "city car" by means of an electromechanical kit. According to this solution, the combustion engine is flanked by a suitably controlled electric motor. The electric motor is connected to the mechanical transmission that transmits the motion from the engine to the front wheels, being connected to the secondary shaft of the gearbox through a belt transmission. Gomez and Vigano 's transformation method replaces the fifth-speed gear and allows to carry out a hybrid transformation even in the small spaces available in a front-wheel- drive city car.

However, also the solution known from Gomez and Vigano has a few drawbacks. For example, the vehicle no longer has a fifth speed. In addition, the vehicle thus retrofitted cannot be used in a fully flexible manner, because the kinematic and mechanic constraints imposed on the drivetrain transmission limit the modes of operation obtainable from a vehicle thus transformed. For example, the gearbox cannot be used in an electric-only operating mode, and in general the revolution speed of the electric motor is determined by the revolution speed of the drive wheels, without any possibility of controlling or decoupling it.

A further solution is described in patent US6332257B1, which relates to a hybrid vehicle comprising an internal combustion engine and a manual transmission, and being further equipped with an electric motor coupled to the main shaft of the manual transmission. According to patent US6332257B1, the coupling takes place through an extension of the main shaft, to which a gear is connected which meshes with a gear train transmission in order to transfer the motion from/to the electric motor. According to patent US6332257B1, a hybrid vehicle conceived as described above can also be created by converting an existing traditional vehicle. Such a conversion or transformation is however quite costly, because it requires an extension element which is difficult to insert into an existing transmission. Furthermore, the solution of patent US6332257B1 is not optimized for use in a gearbox that comprises gearpairs external to the gearbox housing.

[OBJECTS AND SUMMARY OF THE INVENTION]

The object of the present invention is to provide a connection device for a hybrid powertrain system which overcomes some drawbacks of the prior art.

In particular, it is one object of the present invention to provide a connection device for a hybrid powertrain system which allows transforming a hybrid vehicle and which can be easily implemented and applied to the most common traditional vehicles, in particular vehicles comprising gearboxes with one or more speeds provided by gearpairs that are external to the gearbox housing.

It is another object of the present invention to provide a connection device for a hybrid powertrain system which ensures flexibility of use and which effectively exploits the synergy between the electric motor and the combustion engine in every operating condition of the hybrid vehicle.

It is a further object of the present invention to provide a connection device for a hybrid powertrain system which cannot adversely affect the performance of the vehicle.

It is yet another object of the present invention to provide a connection device for a hybrid powertrain system which allows effecting a hybrid conversion of a vehicle without requiring much work, and which is easily reversible to restore the original conditions of the traditional vehicle.

These and other objects of the present invention are achieved through a connection device for a hybrid powertrain system, a hybrid powertrain system and a hybrid vehicle incorporating the features set out in the appended claims, which are an integral part of the present description.

The general idea at the basis of the present invention is to provide a connection device in a hybrid powertrain system. The hybrid powertrain system comprises a combustion engine and a drivetrain transmission adapted to transfer mechanical power from the combustion engine to a final drive unit through a gearbox, which comprises a main shaft connected through a first end to the combustion engine, and a secondary shaft connected to the final drive unit; the gearbox comprises a gearbox housing and a plurality of gearpairs respectively mounted on the main shaft and on the secondary shaft in order to change the transmission ratio between said shafts. The hybrid powertrain system further comprises an electric motor, and the connection device is adapted to transfer drive power from the electric motor to the final drive unit by connecting the electric motor to a second end of the main shaft of the gearbox, opposite to the first end of the main shaft to which the combustion engine is connected.

At least one gearpair of the gearbox gearpairs is mounted externally to the gearbox housing, and the connection device comprises a transmission wheel which rotates integrally with a transfer element mechanically connected to a selector adapted to clutch a gear of the external gearpair mounted on said main shaft.

Thanks to the connection device, it is possible to create a hybrid powertrain system also by retrofitting a traditional vehicle, wherein the electric motor contributes to the vehicle's propulsion. Advantageously, the connection device thus designed ensures higher flexibility of use of the hybrid powertrain system, because the gearbox can be actively and fully used while driving the vehicle, also in combination with the electric motor, without therefore adversely affecting the vehicle's performance.

The connection device advantageously simplifies the transformation of a traditional vehicle into a hybrid vehicle by simply employing an additional electric motor which can be connected to the powertrain system without requiring complex work or modifications. The most important advantage of the proposed solution is that it allows to minimize the invasivity of the connection to the electric motor with respect to the initial configuration of the manual gearbox, e.g. of a traditional vehicle.

Preferably, the transmission wheel is integrally connected to a transfer element, which is coupled to a gearbox selector that selects the speed corresponding to the external gearpair. Advantageously, therefore, the existing elements of the gearbox are used effectively to limit the invasivity of the interventions that must be carried out on the transmission and to ensure reversibility of the transformation of the hybrid powertrain system. Furthermore, the dimensions of the connection device are particularly small; also, the latter is easily accessible, thus making it possible to also retrofit vehicles where the room available for mounting additional components is limited. Preferably, the selector comprises a fixed selector rotating integrally with the main shaft, and the transmission wheel is integrally connected to the transfer element coupled to the fixed selector. This creates a more compact and less invasive connection solution.

Preferably, the fixed selector is further adapted to select a speed corresponding to the external gearpair. Also preferably, the selector further comprises a movable sleeve adapted to clutch the fixed selector under the action of a control element, thus engaging the gear.

The selector is preferably arranged on the main shaft, externally to said external gear. Preferably, the transfer element comprises a threaded surface to which a nut can be screwed in order to secure the transmission wheel axially. Also preferably, the gearpair external to the gearbox housing is positioned at the second end of the gearbox, i.e. the one opposite to the engine side.

In a preferred embodiment, the connection device comprises a mechanical transmission with a unitary transmission ratio, so that the electric motor is advantageously activated at the same revolution speed as that of the combustion engine. In this manner it is possible to improve the torque and power characteristics transmitted by the gearbox to the mechanical final drive unit, e.g. the drive wheels of a vehicle.

Preferably, the connection device comprises a pair of pinions and a transmission chain. According to a further aspect, the present invention relates to a hybrid powertrain system comprising a connection device according to the present invention.

Preferably, the hybrid powertrain system comprises a clutch adapted to mechanically decouple the combustion engine from the first end of the gearbox main shaft. In this manner, the configuration of the connection device is such that the electric motor can provide drive power also when the combustion engine is decoupled by disengaging the clutch. Advantageously, this improves the flexibility of use of the hybrid vehicle.

According to a further aspect, the present invention relates to a hybrid vehicle, the powertrain system of which may originally comprise or be transformed afterwards by means of a connection device according to the present invention.

Further objects and advantages of the present invention will become more apparent from the following detailed description.

[BRIEF DESCRIPTION OF THE DRAWINGS]

Some preferred and advantageous examples of embodiment of the present invention will now be described by way of non-limiting example with reference to the annexed drawings, wherein the same reference numerals are used to designate similar components, materials or functions, and wherein:

- Figure 1 schematically shows a hybrid powertrain system according to the present invention;

- Figure 2 schematically shows a drivetrain transmission of a traditional vehicle according to the prior art;

- Figure 3 schematically shows the drivetrain transmission of Fig. 2, which comprises one embodiment of a connection device according to the present invention;

- Figure 4 is a flow chart illustrating the hybrid transformation of a vehicle by using a connection device according to the present invention;

Figure 5 shows one embodiment of a part of a hybrid powertrain system according to the present invention;

- Figure 6 shows a further view of the embodiment of a part of the hybrid powertrain system of Fig. 5;

- Fig. 7 is a sectional view of one end of the gearbox main shaft of the embodiment of Fig. 6;

- Figure 8 shows an example of an operating mode of a hybrid powertrain system according to the present invention;

- Figure 9 shows an example of an operating mode of a hybrid powertrain system according to the present invention;

- Figure 10 shows an example of an operating mode of a hybrid powertrain system according to the present invention;

- Figure 11 shows an example of an operating mode of a hybrid powertrain system according to the present invention;

- Figure 12 shows an example of an operating mode of a hybrid powertrain system according to the present invention;

- Figure 13 shows an example of an operating mode of a hybrid powertrain system according to the present invention;

- Figure 14 shows an example of an operating mode of a hybrid powertrain system according to the present invention.

[DETAILED DESCRIPTION OF THE INVENTION] Fig. 1 schematically exemplifies one embodiment of a hybrid powertrain system 1 according to the present invention. The hybrid powertrain system 1 comprises a combustion engine 2 of a known type, e.g. an endothermal reciprocating engine, fed with fuel, e.g. petrol or diesel oil or bioethanol, contained in the tank 3.

The hybrid powertrain system 1 further comprises a drivetrain transmission 4, which transfers mechanical power to the final drive unit of the vehicle, e.g. to the drive wheels 5a and 5b, through the differential 6. In this manner, the hybrid powertrain system 1 allows the vehicle with which it is associated to operate in a "combustion" operating mode, i.e. wherein the propulsive thrust is provided by the combustion engine 2 alone. The drivetrain transmission 4 also comprises a gearbox 7 of a known type, which is adapted to change the transmission ratio between a main shaft 8a and a secondary shaft 8b. The drivetrain transmission 4 further comprises a clutch 9 of a known type, which is adapted to decouple the crankshaft of the combustion engine 2 from the other elements of the drivetrain transmission 4. In this manner, when the clutch 9 is engaged power can be transmitted from the combustion engine 2 to the drive wheels 5a and 5b; on the contrary, when the clutch 9 is disengaged the combustion engine is decoupled from the drivetrain transmission 4, thereby releasing the latter.

The hybrid powertrain system 1 further comprises an electric motor 10, connected to a plurality of electric accumulators, e.g. a pack of lithium batteries 1 la and 1 lb; the power flow between the batteries 11a and l ib and the electric motor 10 is regulated by a control unit 12. The control unit 12 is preferably associated with an inverter (not shown), which allows modulating the electric energy supplied by the batteries to operate the electric motor ad different revolution speeds.

The hybrid powertrain system 1 further comprises a connection device 13, which is adapted to couple the electric motor 10 to the drivetrain transmission 4. In this manner, the hybrid powertrain system 1 allows the vehicle with which it is associated to also operate in an "electric" operating mode, i.e. wherein the propulsive thrust received by the drive wheels 5a and 5b is provided by the electric motor 10 alone.

In particular, the connection device 13 is a mechanical transmission that connects the output shaft of the electric motor 10 to the main shaft 8a of the gearbox 7.

The above-described hybrid powertrain system 1 further comprises a plurality of accessory components adapted to ensure the proper operation of the system in accordance with good practice and with solutions known to those skilled in the art. For example, the hybrid powertrain system 1 may comprise further components not shown in the drawing, e.g. including, without limitation: "signal" type connections from the accelerator pedal and from the ignition switch, diagnostic electric connections, an auxiliary pump for the vacuum circuit of a brake booster, an inverter for powering the electric motor, a DC/DC converter for maintaining the charge of the vehicle's battery and for powering auxiliary services, an additional cooling system for the inverter and the electric motor, preferably comprising at least one radiator, connection hoses, circulation pumps and cooling fans, a plurality of fuses and an emergency contactor, a battery charger for recharging the drive accumulators from the power mains when the vehicle is parked in a garage.

Through the above-described hybrid powertrain system 1 , the drive power outputted by the electric motor 10 can be effectively and flexibly employed for propelling a vehicle; for example, it is possible to change the transmission ratio of the gearbox 7 in order to adapt it to the vehicle's operation, from time to time, even when the vehicle is operating in the electric-only propulsion mode 10.

Fig. 2 schematically shows a traditional drivetrain transmission 20 of a known type. The drivetrain transmission 20 is in particular adapted to be associated with a traditional powertrain system, i.e. comprising only one propulsor, e.g. a combustion engine. The drivetrain transmission 20 comprises a gearbox 21, in turn comprising a main shaft 22 and a secondary shaft 23. A plurality of gears 24 are mounted on the main shaft 22 and on the secondary shaft 23, which gears provide different transmission ratios that can be selected according to the operating conditions of the powertrain system with which the drivetrain transmission 20 is associated. In particular, the gearbox 21 comprises a gearbox housing 25, which acts as a support for the main shaft 22 and the secondary shaft 23 through suitable bearings and constraints, schematized in Fig. 2 as small triangles. These constraints locate two ends of each shaft 22 and 23 of the gear box; in particular, the constraints on the gearbox housing 25 locate a first end 26 of the main shaft 22. the first end 26 faces an engine, e.g. a combustion engine, which outputs mechanical power and which is schematized by torque 27 acting upon the end 26. Preferably, the end 26 comprises a thrust bearing 28 adapted to be coupled to a mechanical clutch, previously described with reference to Fig. 1. There is also a second end 29 of the main shaft 22, located by the bearings of the main shaft 22 obtained in the gearbox housing 25; the second end 29 lies opposite to the end 27 near the combustion engine.

In this example of embodiment, the second end 29 of the main shaft houses the gear system 30, which comprises a pair of gears 30a and 30b mounted externally to the gearbox housing 25, i.e. externally to the bearings of the main or secondary shaft with respect to an internal point of the shaft between the bearings. The gears 30a and 30b are protected by a cover 31 that is coupled to the gearbox housing 25, thereby preferably creating a closed chamber within which lubricating oil circulates.

The two gears 30a and 30b at the end 29 constitute, in this example, the gearpair that provides the longest transmission ratio for the fifth speed.

The gearbox 21 allows changing the transmission ratio between the main shaft 22 and the secondary shaft 23. At one end of the secondary shaft 23 a final mechanical transmission 32 is connected, which transfers motion and propulsive power to the final drive unit in accordance with the revolution speeds imposed by the gearbox 21 and by the engine 27.

In this example of embodiment, the final drive unit comprises a differential 33 adapted to distribute drive power to a pair of axles 34a and 34b. For example, a configuration of this kind is the one described with reference to the differential 6 and the drive wheels 5a and 5b of Fig. 1.

The gearbox 21 further comprises a plurality of known components, such as selectors, synchronizers, reverse gear and the like, which are not shown in Fig. 2 and will not be described herein for simplicity, but may possibly be included, without limitation whatsoever, for the purposes of the present invention.

In an alternative embodiment, the gearbox 21 may be an automatic, robotized or mechanically actuated unit.

Fig. 3 schematically shows a drivetrain transmission 40 according to the present invention. Numerous components of the drivetrain transmission 40 are the same as those of a traditional drivetrain transmission, such as the one described herein with reference to Fig. 2. Therefore, in Fig. 3 the same reference numerals are used to identify components which are similar to those already illustrated. As will be described more in detail below, a few additional components can be added, with limited effort, to transform a traditional powertrain system into a hybrid powertrain system in accordance with the present invention, thereby obtaining a hybrid transformation of a vehicle.

The drivetrain transmission 40 is coupled to the electric motor 10 through the connection device 13. In this embodiment, the electric motor 10 comprises an output shaft arranged parallel to the main shaft 22. The motor 10 is constrained in the position exemplified in the drawing by means of suitable supports and constraints (not shown). In the preferred embodiment, the connection device 13 comprises a chain transmission, wherein a chain 41 transmits rotary motion between a first pinion 42, rotating integrally with the output shaft of the electric motor 10, and a second pinion 43, rotating integrally with the main shaft 22. The pinion 43 is connected to the main shaft 22 in a manner that will be described more in detail below, in particular it being connected near the gear 30a at the end 29, i.e. the gear of the longest transmission ratio of the fifth speed, mounted externally to the gearbox housing 25. Therefore, the two pinions 42 and 43 are properly aligned to allow transmission of motion through the chain 41.

In general, both the main shaft 22 and the secondary shaft 23 are cantilevered shafts protruding outwards from the respective bearings, with at least one end (e.g. the end 29) external to the gearbox housing 25.

Alternatively, the connection device 13 may comprise a pair of pulleys and a transmission belt, e.g. a belt made of polymeric material with Kevlar inner reinforcement.

As a further alternative, the connection device 13 may comprise a plurality of gears creating a gear train transmission.

Preferably, the connection device 13 is protected by a cover 44, the shape of which is suitable for containing the whole connection device 13 and for ensuring adequate sealing to allow lubricant to circulate inside the chamber defined by the gearbox housing 25 and by the cover 44 itself.

The connection device 13 may further comprise known devices, which for simplicity will not be described herein, in order to improve the operation and performance thereof, e.g. a chain tensioner.

It is clear that the connection device according to the present invention can be applied easily and with little intervention to a traditional powertrain system, in particular to a known drivetrain transmission. With reference to Fig. 4, the following will exemplify the steps necessary for transforming a traditional powertrain system into a hybrid powertrain system by installing a connection device according to the present invention.

At step 401, the cover 31 is removed from the gearbox 21.

At step 402, an intervention is carried out on the end 29 of the main shaft 22, wherein the pinion 43 is fitted to said end 29 as will be described in detail below.

At step 403, the electric motor 10, including the pinion 42, is properly positioned and aligned.

At step 404, the transmission chain 41 is installed between the two pinions.

At step 405, the new cover 44 is installed in order to cover the connection device 13 thus implemented.

At step 406, the connection device 13 is installed and operational.

Fig. 5 shows a more detailed perspective view of one embodiment of the connection device 13, which comprises a pair of pinions 42 and 43 that transmit motion through the chain 41 from the electric motor 10 to the main shaft of the gearbox 22, which is constrained at the opposite end 29 to the combustion engine. As will be described below, the connection device according to the present invention clutches a component of the gearbox gear mounted outside the gearbox housing 25, which typically relates to the longest transmission ratio provided by the gearbox.

Fig. 6 is a side view of the connection device 13 of Fig. 5. This view clearly shows that the pinions 42 and 43 have the same number of teeth, i.e. the connection device 13 provides a 1 : 1 transmission ratio.

In general, it is advantageous to employ a transmission ratio close or, preferably, equal to 1 :1 (e.g. between 0.9: 1 and 1.1 :1) for the connection device 13. In this way, the revolution speed of the electric motor 10 will match the revolution speed of the gearbox main shaft 22, corresponding to the revolution speed of the combustion engine. When coupled together, the combustion engine and the electric motor will thus rotate at the same revolution speed, which is advantageous as regards the torque and power output curves available at the final drive unit.

Fig. 7 shows a view according to section X-X of Fig. 6. This sectional view illustrates in more detail the connection between the pinion 43 and the end 29 of the main shaft in accordance with the present invention, in the region adjacent to the fifth-speed gear 30a, in particular externally thereto.

The gearbox comprises a fork 50a adapted to act upon a sleeve 50b connected to a fixed element 51 of the selector, typically a synchronized one, for the fifth speed (i.e. the speed of the gear 30a) in order to control the engagement thereof. The fifth- speed gearpair is mounted externally to the gearbox housing 25.

In particular, the gear 30a is free to rotate on the main shaft 22 when the gear is not engaged, whereas it rotates integrally with the main shaft 22 when the gear is engaged through the selector, which also includes the elements 50a, 50b and 51.

In this embodiment, the pinion 43 is forced to rotate integrally with the end 29 of the main shaft; in particular, it is constrained to a transfer element 52 located near the gear synchronizer. The transfer element 52 is appropriately shaped, during the production stage or by subsequent mechanical machining, in a manner such as to house the pinion 43 as will be described below.

According to the present invention, the connection device is implemented by replacing or modifying the fixed part 51 of the fifth-speed selector, which part is directly connected to the main shaft 29, by applying a suitably shaped transfer element 52. The pinion 42 is thus connected to the main shaft 22 through the fixed selector 51 and the transfer element 52, which is suitably shaped and connected to the fixed selector 51. For this reason, the transfer element 52 is, on the one hand, geometrically adapted to be coupled to the fixed selector 51 that is acted upon by the sleeve 50b, which thus engages the fifth-speed gear 30a under the control of the fork 50a. On the other hand, the transfer element 52 is geometrically adapted to be coupled to and to rotate integrally with the pinion 43 of the connection device, which thus connects the end 29 of the main shaft to the electric motor.

The specific configuration of the connection device, in particular when retrofitting a traditional vehicle, can be established as a function of the available room and of the preferred solution on the basis of the original gearbox configuration.

In a preferred embodiment, the pinion 43 (i.e. a belt pulley or a gear) is constrained axially by means of a removable connection, which comprises a fastening nut 53 that is screwed onto a matching threaded surface of the transfer element 52, thereby ensuring that the pinion is axially secured to the end 29 of the main shaft; such a solution will replace the nut existing in the original gearbox. The solution described above can only be implemented on gearboxes having at least one gear external to the main structure of the gearbox housing, which encloses the gears for all the other speeds.

It is clear from Fig. 7 that the machining and modifications necessary for constraining the pinion 43 to the transfer element 52 and to the fixed part of the selector 51 are limited and can be carried out with relative ease even on a traditional vehicle after the production stage, i.e. as a retrofit transformation.

In an alternative embodiment, it is conceivable to connect the end 29 of the gearbox shaft to the pinion 43 through a solution comprising a larger number of elements, e.g. comprising an additional element for constraining the pinion 43 in abutment with the transfer element 52.

It is apparent from the above description that the interventions required for transforming and installing a connection device according to the present invention, even on a traditional powertrain system, are just a few and can be carried out easily and quickly. Likewise, said interventions are easily reversible, so that it is possible, at a later time, to restore the powertrain system to its original conditions by removing the connection device thus installed.

It is therefore clear that the present invention can advantageously be applied for transforming a traditional vehicle into a hybrid drive vehicle, which is converted by installing a connection device according to the present invention as well as any accessory components necessary to ensure the proper operation of the vehicle, which have been exemplified herein with reference to Fig. 1.

Fig. 8 schematically exemplifies an "electric" operating mode of a hybrid powertrain system 1 according to the present invention.

In this "electric-only" operating mode, the clutch 9a is disengaged, thus decoupling the combustion engine 2 from the drivetrain transmission 4.

In this figure and in the next ones, the thick black arrows represent some of the (electric or mechanic) power flows occurring between the different elements of the hybrid powertrain system 1 in the various conditions exemplified herein.

The accumulators 11a and l ib supply power to the electric motor 10, which in turn supplies mechanical power to the connection device 13. The connection device 13, transfers the mechanical power to the drivetrain transmission 4 through the gearbox 7, up to the final drive unit 6.

In this "electric" operating mode, traction is ensured by the power supplied by the pack of accumulators 1 1a and l ib. When the vehicle is braking, or in other comparable situations, such as the use of electric motor brake, the drive system is controlled in accordance with known energy recovery methods, wherein the mechanical final drive unit drags the drivetrain transmission 4 and the electric motor 10, thus generating a power flow which is inverse to the one previously described, which inverse power flow allows recharging the accumulators 1 1a and l ib by using the motor 10 as an electric generator.

Fig. 9 schematically exemplifies a "combustion" operating mode of a hybrid powertrain system 1 according to the present invention.

In this "combustion" operating mode, the clutch 9b is engaged and connects the combustion engine 2 to the drivetrain transmission 4, up to the final drive unit 6. In this operating mode, the combustion engine 2 is fed with fuel from the tank 3, and outputs drive power just like a traditional vehicle. The electric motor 10 is dragged idle, so as to offer the least possible resistance. In an alternative embodiment, in this "combustion" operating mode the electric motor 10 may be decoupled, e.g. by means of a clutch.

Fig. 10 schematically exemplifies a "hybrid" operating mode of a hybrid powertrain system 1 according to the present invention.

In this operating mode, the powertrain system 1 uses the power of both propulsion systems (i.e. the combustion and electric ones as described above) to minimize fuel consumption and exhaust emissions. In particular, the combustion engine 2 supplies drive power to the drivetrain transmission 4, while the electric motor 10, through the connection device 13, can provide propulsive power (e.g. when accelerating) and recover energy (e.g. when braking).

Fig. 11 schematically exemplifies a "recharge while driving" operating mode of a hybrid powertrain system 1 according to the present invention.

In this operating mode called "recharge while driving", the powertrain system 1 utilizes the power of the combustion engine 2 for both propelling the vehicle and recharging the accumulators 11a and l ib by using the electric motor 10 as a generator. Furthermore, e.g. when braking, additional energy may be recovered by exploiting the dragging of the electric motor 10 caused by the final drive unit 6. Fig. 12 schematically exemplifies a "plug-in recharge" operating mode of a hybrid powertrain system 1 according to the present invention.

This operating mode called "plug-in recharge" uses electric energy coming from a power mains 120 to directly recharge the accumulators 1 1a and l ib by means of a suitable battery charger of a known type (not shown). Typically, this "plug-in recharge" operation is carried out when the vehicle is parked in a garage, i.e. typically with the vehicle stationary, and provides higher recharge efficiency compared to other modes. Fig. 13 schematically exemplifies a "start & stop" operating mode of a hybrid powertrain system 1 according to the present invention.

In this operating mode called "start & stop", the combustion engine 2 is turned off when the vehicle stops; when the vehicle must set off again, the controlled engagement of the clutch 9 is used for providing the initial pick-up necessary to start the combustion engine 2. In this "start & stop" mode, the hybrid powertrain system 1 preferably outputs the drive power necessary for restarting the vehicle by exclusively using the electric propulsion system; in addition, the combustion engine 2 is only restarted in certain circumstances, e.g. when shifting from the first gear to the second gear of the gearbox 7, or when the charge of the accumulators 1 la and 1 lb is insufficient.

Fig. 14 schematically exemplifies a "bi-modal" operating mode of a hybrid powertrain system 1 according to the present invention.

In this "bi-modal" operating mode, the combustion engine 2 is fed and operating in order to supply power to auxiliary systems 140, such as, for example, air conditioner, lights, etc. Vehicle propulsion relies on the electric system, which independently acts upon the drivetrain transmission 4, which has been decoupled from the combustion engine 2 by permanently disengaging the clutch 9a. As far as electric drive is concerned, in this case the considerations made with reference to Fig. 8 will also apply.

It must be observed that the operating modes described herein with reference to Figs. 8 to 14 are not exclusive of each other when the vehicle is in operation: they may be combined together, even at close time intervals, preferably by providing suitable transitions between one mode and the next.

It is apparent from the above description that the connection device 13 allows to create a hybrid powertrain system 1 that keeps all the functionalities of the combustion powertrain system unchanged while implementing additional advantageous (electric or hybrid) modes of operation. This device is particularly suited for hybrid transformation or conversion of a traditional vehicle. Said transformation is easily reversible, if necessary.

The connection device allows retrofitting the powertrain systems of a large number of vehicles, for the purpose of reducing the environmental impact caused by their use. Likewise, the connection device also allows implementing hybrid powertrain systems on production vehicles.

It is apparent that many changes may be made to the present invention by those skilled in the art without departing from the protection scope thereof as stated in the appended claims.

For example, the number of available speeds in a manual gearbox concerned by the present invention is not limited to five as in the example described herein; solutions are also conceivable wherein there are more or less gearpairs, e.g. comprising a sixth speed, provided that at least one gear is mounted externally to the gearbox housing.