WO2011092643A1

WO2011092643A1 - A traction system for hybrid vehicles and a method of actuating a traction system for hybrid vehicles

Info

Publication number: WO2011092643A1
Application number: PCT/IB2011/050360
Authority: WO
Inventors: Antonio Francisco Cesaroni
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-01-27
Filing date: 2011-01-27
Publication date: 2011-08-04
Anticipated expiration: 2012-07-27
Also published as: IT1398083B1; ITPD20100016A1

Abstract

A traction system (10) f or vehicles com prises: a first power source (22) of the non- reversible type; a second power source (18) of the reversible type; - a transmission (100) connected to the first (22) and second (18) source and including a first differential device (34) with a first input or output branch (50) connected to the first source (22), a second input or output branch (118) connected to the second source, and a third input or output branch (130) which can be connected to an axle (30) of a vehicle, a device (62) f or controlling the transmission (100), wherein the transmission (100) com prises a variable speed drive (56) interposed between the first power source (22) and t he first branch (50) of said first differential device (34), and wherein the control device (62) acts on the variable speed drive (56) to set the transmission ratio between th e first power source (22) and the first branch ( 50) of the first differential device (34).

Description

TRACTION SYSTEM FOR HYBRID VEHICLES AND CONTROL METHOD

THEREOF

The present invention relates to a traction system for hybrid vehicles of the type described in the preamble of the principal claim and a method of actuating a traction system for hybrid vehicles.

In the fields of motor manufacture and industrial machinery, there is a plurality of known hybrid traction systems, each system comprising an internal combustion engine, an electric motor, a transmission for connecting the engine and motor to the wheels of a vehicle, and a control device for controlling the engine, motor and transmission.

Typically, in these systems, the electric motor is connected to the wheels with a fixed transmission ratio, and therefore the control system cannot control the speed of the electric motor independently of the speed of the vehicle. This is a disadvantage in terms of the overall efficiency of the vehicle, since the speed of the electric motor depends on the speed of the vehicle, and cannot, therefore, be kept at a level corresponding to the maximum efficiency of the electric motor.

In known hybrid traction systems, a second disadvantage is that the internal combustion engine is fitted with a gear change system having discrete transmission ratios, causing a significant dissipation of energy during gear changes. Furthermore, the internal combustion engine has to vary its speed continuously in order to adapt to the operating conditions of the vehicle, and therefore operates at the speed corresponding to the minimum fuel consumption for limited periods only. This reduces the overall efficiency of the vehicle still further. Moreover, in known hybrid traction systems, provision is made for operating conditions, typically at low speed, in which the internal combustion engine runs in neutral; in other words it is disconnected from the transmission. In these conditions, the wheels of the vehicle receive power solely from the electric motor, which must therefore be appropriately overdesigned, thus increasing the dimensions and cost.

In order to overcome the problem, some hybrid traction systems include a device for braking the internal combustion engine output in order to avoid neutral operating conditions. However, this device has the drawback of dissipating kinetic energy whenever it is actuated, thus reducing the overall efficiency of the vehicle.

In other hybrid traction systems in which the combustion engine is always connected to the transmission, in the aforesaid operating conditions at low speed and down to the complete stopping of the vehicle, the branch of the transmission connected to the combustion engine does not include the operating condition in which the transmission ratio of the aforesaid branch is such that the speed level in said branch is zero. In said systems, if a braking device connected to the wheels of the vehicle is applied when the vehicle is not operating, it is advantageously possible to start the combustion engine by the actuation and rotation of the electric motor. This is because, since the aforesaid transmission ratio of the branch connected to the combustion engine never has a zero value in any operating condition and since the speed of said branch is never zero, the motion of the electric motor is transmitted directly to the combustion engine until the latter is started. However, these hybrid traction systems have the drawback that, during the deceleration phases of the vehicle, some of the kinetic energy of the vehicle is inevitably transmitted from the wheels to the combustion engine through the branch connected to it, because the rotation speed of said branch is never zero. As is known, the combustion engine is not reversible, and consequently the energy transmitted to it during the deceleration phases of the vehicle is completely lost by dissipation and the overall efficiency of the vehicle is unsatisfactory.

Systems having one or more of the drawbacks described above include, in particular, those described in US 7241242, US 7223200 and US 6413185. US 7241242 describes a hybrid traction system for vehicles which uses frictional energy dissipation members such as a clutch and brakes, while US 7223200 proposes a transmission system with a gear change system having discrete ratios including the neutral position.

US 6413185 describes a hybrid traction system for industrial vehicles in which the combustion engine is always connected to the transmission, but which uses frictional energy dissipating members such as the brake connected to the wheels and the mechanical reverser. A vehicle with the transmission system described in US 6413185 does not include a dedicated device for starting the combustion engine, known as a starting motor. In order to allow the combustion engine to be started by the actuation of the electric motor, the structure of the transmission system must be such that, even during the deceleration phases, some of the kinetic energy of the vehicle is transmitted to the non-reversible combustion engine. As explained in the preceding paragraphs, the overall efficiency of a vehicle having this traction system is unsatisfactory because the part of the kinetic energy of the vehicle transmitted to the engine during deceleration is completely lost by dissipation. Additionally, in the description of the aforesaid system, there is only one continuous speed variation drive which is connected exclusively to the planet gear train of the first epicyclic differential, and the output sun gear of said first differential is subsequently connected to the planet gear train of the second epicyclic differential.

The technical problem which the present invention is intended to resolve is that of providing a traction system for hybrid vehicles without a discrete transmission ratio gear change system, clutch or brakes, which is structurally designed so as to overcome all the described drawbacks of the aforementioned prior art, while improving the overall efficiency of the vehicle in all operating conditions.

Another problem tackled by the present invention is that of providing a method of actuating a traction system for hybrid vehicles which is functionally designed so as to provide an optimal overall efficiency of the vehicle in all operating conditions.

These and other problems which will be made clearer in the following text are resolved by the invention with a traction system and a method for actuating a traction system, produced in accordance with the following claims.

The features and advantages of the invention will be made clearer by the detailed description of some examples of embodiment, illustrated, for the purposes of guidance and without restrictive intent, with reference to the attached drawings, in which: Figure 1 is a functional diagram of a traction system for hybrid vehicles according to the present invention;

Figure 2 is a schematic view of an example of a traction system for hybrid vehicles according to the present invention, in which some functions shown in Figure 1 are omitted;

Figures 3 and 4 are two examples of schematic views of two respective variant embodiments of the traction system of Figure

1, in which some functions are omitted;

Figure 5 is a complete schematic view of a traction system for hybrid vehicles according to the present invention, comprising all the functions of Figure 1.

In the drawings, the number 10 indicates the whole of a traction system for vehicles. The traction system 10 comprises a first power source 22, a second power source 18 and a transmission 100 connected to the first and second power sources 22 and 18.

The first power source 22 is of the non-reversible type, and is formed, for example, in the variant embodiments of Figures 2, 3, 4 and 5, by an internal combustion engine connected to a shaft 81 for transmitting the motion provided in the transmission 100.

In other possible variant embodiments of the invention, the first power source 22 is formed by a gas turbine, a steam turbine or other nonreversible power source.

The second power source 18 is of the reversible type, and is formed, for example, in the variant embodiments of Figures 2, 3, 4 and 5, by an alternating current electric motor connected to the transmission 100 by a motion output shaft 14. In other possible variant embodiments, the second power source 18 is formed by a direct current electric motor, an air compressor, or a hydraulic motor and pump assembly, or any other reversible power source. Optionally, a train of gears 26 (not present in Figures 2, 3, 4 and 5) is interposed between the second power source 18 and the shaft 14.

The second source 18 can be operated either to transmit power to the transmission 100 or to receive power therefrom, through the shaft 14. In this second operating mode, the power transmitted by the transmission 100 to the second source 18 is used to recharge an energy accumulator 54.

In the variants of Figures 2, 3, 4 and 5, the accumulator 54 is formed by a battery electrically connected to the electric motor 18 through a reverser 20 which is interposed between these two components. In practice, the electric motor 18 is supplied from the battery 54, through the reverser 20, when it transmits power to the transmission 100, and acts as an electrical generator when it receives power from the transmission 100, thus recharging the battery 54. The battery 54 can also be recharged by an alternator 58 to which it is electrically connected. The alternator 58 is mechanically connected to the internal combustion engine 22, from which it receives power.

In other possible variant embodiments, the accumulator 54 is chosen so as to be compatible with the second power source 18. For example, if the second power source 18 is an air compressor or a hydraulic motor and pump assembly, a hydraulic accumulator is used. The transmission 100 includes a first differential device 34 with a first branch 50, connected to the first power source 22 through a variable speed drive 56, a second branch 118, connected to the second power source 18, and a third branch 130, connected to an axle 30 of a road vehicle (not shown).

In other possible variant embodiments, the first branch 50 is connected to the second power source 18, while the second branch 118 is connected to the first power source 22.

The axle 30 is connected to a pair of driving wheels 38.

Each of the branches 50, 118 and 130 of the differential 34 can be used either for the input or the output of motion, in order to receive or transmit power, respectively, from or towards the shaft to which it is connected.

The transmission 100 comprises a variable speed drive 56 interposed between the first branch 50 of the differential 34 and the first power source 22. The variable speed drive 56 can be used for the continuous variation of the transmission ratio between the shaft 81 and the first branch 50 of the differential 34. The variable speed drive 56, in its most complete configuration, comprises at least two transmissions 46 and 48 connected in series with each other, a transmission 44 connected in parallel with the first two, and a differential 42.

The second branch 118 is directly connected to the shaft 14.

The third branch 130 comprises external teeth 32 which engage with a gear wheel 132 fixed to the axle 30.

In the exemplary embodiment of Figures 2, 3, 4 and 5, the differential 34 is of the epicyclic type in which the first branch 50 is formed by a ring gear having internal teeth 122, the second branch 118 is formed by a sun gear, and the third branch 130 is formed by a planet gear carrier on which a plurality of planet gears 126 are rotatably supported. The planet gears 126 engage with both the internal teeth 122 and the pinion gear 118.

Said differential 34 is also characterized by the first connecting branch 50 between the epicyclic ring gear 122 and the combustion engine 22, by the second connecting branch 118 between the sun gear and the electric motor 18, and by the third connecting branch 130 between the planet gear carrier of the differential and the axle 30, as shown in Figures 2, 3, 4 and 5.

In a possible variant embodiment of the differential 34 (not present in

Figures 2, 3, 4 and 5), the first branch 50 is connected to the sun gear, the second branch 118 is connected to the epicyclic ring gear 122 and the third branch 130 is connected to the planet gear carrier of the differential.

In both of the possible variant embodiments, the third branch 130 connects the planet gear carrier of the differential 34 to the axle 30.

In other possible variable embodiments, the differential 34 is constructed in another way, for example with bevel gears or epicyclic gears with more than one stage.

Because of known properties of epicyclic differentials, the characteristic magnitudes of the differential 34 are dependent on the relations A, B, C, D and E, as shown below:

A) Z₁₁₈N 118 + Z122 50 = ( 118 + Zi22)Ni30,

in which:

Z118 is the number of teeth on the pinion 118, Z122 is the number of teeth in the internal teeth 122,

N118 is the rotation speed of the sun gear 118 and the shaft 14,

N₅₀ is the rotation speed of the ring gear 50,

N 130 is the rotation speed of the planet gear carrier 130.

B) Tl30 = Tiis( ii8 + Zi22)/Zii8,

in which:

T₁₃₀ is the torque of the planet gear carrier130,

T₅₀ is the torque of the epicyclic ring gear 50,

I s is the torque of the sun gear 118,

P₅₀ is the power transmitted by the branch 50,

Pus is the power transmitted by the branch 118,

Pi3o is the power transmitted by the branch 130.

In the relations A, B, C and D, the direction of the rotation speed and that of the torque of each branch are conventionally considered to be positive in the clockwise direction, for an observer located along the axes of rotation of the branch 50 and of the branch 118 looking towards the differential 34. The rotation speed and the torque of the branch 130 are conventionally considered to be positive in the clockwise direction for an observer located along the axis of rotation 130 and looking from the differential 34 towards the branch 130. The power is considered to be positive when transmitted from the branch 50 and from the branch 118 to the differential 34 and from there to the branch 130. The value of the power transmitted by each branch is positive when the rotation speed and the torque have the same direction. For example, when Ni3o and Ti₃₀ both have a clockwise direction or both have an anticlockwise direction, the power transmitted by the differential 34 to the branch 130 is positive. However, when the direction of Ni₃₀ is opposite to that of Ti3o, the power transmitted from the branch 130 to the differential 34 is negative; in other words it is transmitted from the shaft 30 to the differential 34. It should be noted that the first operating mode is typically present when the power sources 18 and 22 are both transferring power to the vehicle for its acceleration, while the second operating mode is present when the vehicle gives up its kinetic energy, thus recharging the accumulator 54, during deceleration.

Similar considerations apply to the branches 50 and 118, in that, when the rotation speed and the torque have the same sign, the power transmitted from the single branch is delivered to the differential 34, but when the rotation speed and the torque have different directions, the power transmitted by each branch travels from the differential and towards the power sources 22 and 18.

The variable speed drive 56 comprises at least one continuous speed variation device 46 (or alternatively 146 or 246), connected to the shaft 81, which acts as a motion input or output shaft with respect to the variable speed drive 46.

The variable speed drive 56 comprises a transmission 48 connected in series with the device 46 (or alternatively 146 or 246). Said transmission 48 is of the continuous speed variation type. In some particular variant embodiments of the transmission 48, this can have only one discrete transmission ratio.

The variable speed drive 56 comprises a transmission 44 connected in parallel with the branch formed by the series connection between the transmission 48 and the device 46 (or alternatively 146 or 246). Said transmission 44 is of the continuous speed variation type. In some particular variant embodiments of the transmission 48, this can have only one discrete transmission ratio.

In the example of Figure 2, the device 46 comprises an axial piston hydraulic pump 66 with variable capacity, mechanically connected to the shaft 81, and a hydraulic motor 70, hydraulically connected to the hydraulic pump 66 and mechanically connected to a shaft 72 for the inward or outward transmission of motion, according to the operating mode of the variable speed drive 56.

In other variant embodiments, the device 46 (not shown in Figure 2) is of another type, for example of the variable pulley type or the friction wheel or cone type, provided that it can vary the transmission ratio between the shafts 81 and 72 continuously and provided that the device 46 is reversible, in other words capable of transmitting power either from the shaft 81 to the shaft 72 or, conversely, from the shaft 72 to the shaft 81. In the variant embodiment of Figure 3, the variable speed drive 56 comprises a continuous speed variation device 146 including a first variable diameter pulley 166 mechanically connected to the shaft 81 and a second variable diameter pulley 170 connected to the pulley 166 by means of the belt 168. The second pulley 170 is connected by direct coupling to a shaft 172 for inward or outward power transmission, according to the operating mode of the variable speed drive 56.

In other variant embodiments, the device 146 (not shown in Figure 3) is of another type, for example of the type having an axial piston hydraulic pump with variable capacity connected hydraulically to a hydraulic motor or of the friction wheel or cone type, provided that it can vary the transmission ratio between the shafts 81 and 172 continuously and provided that the device 146 is reversible, in other words capable of transmitting power either from the shaft 81 to the shaft 172 or, conversely, from the shaft 72 to the shaft 81.

In the variant embodiment of Figures 4 and 5, the variable speed drive 56 comprises a continuous speed variation device 246 including a first friction cone 266 mechanically connected to the shaft 81 and a second friction cone 270 connected to the first friction cone 266 by means of a pair of toroidal friction discs 268 of the variable position type. The second pulley 170 is connected by direct coupling to a shaft 272 for inward or outward power transmission, according to the operating mode of the variable speed drive 56.

In other variant embodiments, the device 246 (not shown in Figure 4) is of another type, for example of the type having an axial piston hydraulic pump with variable capacity connected hydraulically to a hydraulic motor or of the friction wheel or cone type, provided that it can vary the transmission ratio between the shafts 81 and 272 continuously and provided that the device 246 is reversible, in other words capable of transmitting power either from the shaft 81 to the shaft 272 or, conversely, from the shaft 72 to the shaft 81.

In the more complete variant embodiment of Figure 5, the variable speed drive 56 comprises a continuous speed variation device 48 (connected in series with the device 246) including a first friction cone 466 mechanically connected to the second friction cone 270 of the continuous speed variation device 246, and a second friction cone 470 connected to the first friction cone 466 by means of a pair of toroidal friction discs 468 of the variable position type. The second friction cone 170 is connected to a shaft 272 for inward or outward power transmission, according to the operating mode of the variable speed drive 56.

In the more complete variant embodiment of Figure 5, the variable speed drive 56 comprises a continuous speed variation device 44 (connected in parallel with the devices 246 and 48) including a first friction cone 366 mechanically connected to the shaft 81 and a second friction cone 370 connected to the first friction cone 366 by means of a pair of toroidal friction discs 368 of the variable position type. The second friction cone 370 is connected to the shaft 98 for inward or outward power transmission, according to the operating mode of the variable speed drive 56.

In other variant embodiments, the devices 48 and 44 (not shown in Figure 5) are of another type, for example the type with an axial piston hydraulic pump with variable capacity connected hydraulically to a hydraulic motor, or the type with a variable diameter pulley, provided that it is capable of varying the transmission ratio between the device 246 or the shaft 81 and the shaft 272 or the branch 98 respectively in a continuous way, in other words capable to transmitting power either from the device 246 or from the shaft 81 to the shaft 272 or to the branch 98 respectively, or, conversely, from the shaft 272 or from the branch 98 to the device 246 or to the shaft 81.

The variant embodiments of Figures 2, 3 and 4 are special cases of the variant embodiment of Figure 5 in which the devices 48 and 44 are of the continuous speed variation type with a single discrete transmission ratio. In other variant embodiments, the variable speed drive 56 comprises another type of continuous speed variation device, for example one with a different variable pulley geometry or a different friction wheel or cone geometry, or a motor and generator pair, or a hydraulic pump and motor pair, both having variable capacity.

In a similar way to the convention followed for the differential 34, the transmission of power from the variable speed drive 46 (or alternatively 146 or 246) takes place towards the differential 42 when the directions of the rotation speed and of the torque of the shaft 72 (or alternatively one of the shafts 172 and 272) are identical, and, conversely, from the differential 42 towards the variable speed drive 46 when the aforesaid directions are opposite.

With reference to the relations B, C and D shown above, the torque on the branch 112 of the differential 42 is positive when the vehicle is accelerating or running at constant speed, and is negative when it is decelerating. In the same way, the torque on the shaft 72 is positive in the first two operating conditions and negative in the third operating condition of the vehicle. In the example of Figure 2, when the capacity of the hydraulic pump 66 is positive, in other words when the direction of the flow of oil in the hydraulic connections with the hydraulic motor 70 is such that the rotor of the hydraulic motor is rotated in the same direction as the rotor of the hydraulic pump 66, the direction of rotation of the shaft 72 is the same as the directions of rotation of the shaft 81 and the branch 98.

Conversely, when the capacity of the hydraulic pump 66 is negative, in other words when the direction of the flow of oil in the hydraulic connections with the hydraulic motor 70 is reversed in such a way that the rotor of the latter is rotated in the opposite direction to that of the hydraulic pump 66, the direction of rotation of the shaft 72 is opposite to the directions of rotation of the shaft 81 and the branch 98.

In the variant embodiment of Figure 3, the direction of rotation of the shaft 172 is always the same as the direction of rotation of the shaft 81, but opposite to that of the branch 98. In the variant embodiment of Figure 4, the direction of rotation of the shaft 272 is always opposite to that of the shaft 81 and of the branch 98. In the variant embodiment of Figure 5, the direction of rotation of the shaft 272 is identical to that of the shaft 81, but is always opposite to that of the branch 98. Consequently, the direction of rotation of the branch 98 is always opposite to that of the branch 102.

In the examples of Figures 2 and 4, the variable speed drive 56 comprises a transmission with continuously variable speed with a single discrete transmission ratio, formed by a train of gears 44, connected in parallel with the device 46, 246, and a second epicyclic differential 42 provided with three branches 98, 102, 112, connected, respectively, to the train of gears 44, to the shaft 72, 272 and to the first branch 50 of the differential 34. The train of gears 44 comprises two gear wheels 90, 94, fixed to the opposite axial ends of a shaft 92, which engage, respectively, with a gear wheel 86, fixed to the shaft 81, and with external teeth 97 provided on the branch 98 of the epicyclic differential 42.

In the example of Figures 2, 4 and 5, the variable speed drive 46, 246 is connected to the sun gear of the differential 42, and the planet gear carrier is the connecting element between the differential 42 and the differential 34.

In other possible variant embodiments (not shown) of the examples of Figures 2, 4 and 5, the branch 98 of the differential 42 is connected to the shaft 72, while the branch 102 is connected to the transmission with continuous variable speed 44 (in Figures 2 and 4, with a single discrete transmission ratio formed by a train of gears 44).

In these other possible variant embodiments (not shown) of the examples of Figures 2, 4 and 5, the variable speed drive 46 (or alternatively 246) is connected to the epicyclic ring gear of the differential 42, while the planet gear carrier still forms the connecting element between the differential 42 and the differential 34.

In the example of Figure 3, the variable speed drive 56 comprises a transmission with continuously variable speed with a single discrete transmission ratio, formed by a train of gears 48, connected in series between the variable speed drive device 146 and the second epicyclic differential 42, wherein the three branches 98, 102, 112 are connected, respectively, to the train of gears 48, to the shaft 81, and to the first branch 50 of the differential 34. The train of gears 48 comprises a gear wheel 94, fixed to the shaft 172, which engages with external teeth 97 provided on the branch 98 of the epicyclic differential 42.

In the example of Figures 3, the variable speed drive 146 is connected to the epicyclic ring gear of the differential 42, and the planet gear carrier is the connecting element between the differential 42 and the differential 34. In other possible variant embodiments (not shown) of the example of Figure 3, the branch 98 of the differential 42 is connected to the shaft 81, while the branch 102 is connected to the train of gears 48.

In these other possible variant embodiments (not shown) of the example of Figure 3, the variable speed drive 146 is connected to the sun gear of the differential 42, while the planet gear carrier still forms the connecting element between the differential 42 and the differential 34.

In the examples of Figures 2, 3, 4 and 5, regardless of the variant embodiment, the variable speed drive 46 (or alternatively 146 or 246), the variable speed drive 48 and the variable speed drive 44 can be of any type, for example the type with an axial piston hydraulic pump with variable capacity connected hydraulically to a hydraulic motor, or the type with a variable diameter pulley or friction wheels or cones.

As a general rule (Figure 1), the variable speed drive 56 can comprise either the transmission with continuously variable speed which in some cases is formed by a single discrete transmission ratio with a single train of gears 44, or the transmission with continuously variable speed which in some cases is formed by a single discrete transmission ratio with a single train of gears 48. In the examples of Figures 2, 4 and 5, the branch 98 of the second epicyclic differential 42 is formed by a ring gear which is coaxial with the shaft 72, 272 and which has at one of its axial ends an external cylindrical surface, on which the external teeth 97 are formed, and an internal cylindrical surface having internal teeth 106, on the end axially opposed to the external teeth 97. The branch 102 is formed by a sun gear fixed to the shaft 72, 272, and the branch 112 is formed by a planet gear carrier to which a plurality of planet gears 110 is rotatably connected. The planet gears 110 engage with the gear 102 and with the internal teeth 106.

In the example of Figure 3, in the second epicyclic differential 42, the branch 98 is formed by a ring gear provided with external teeth 97 and with internal teeth 106, the branch 102 is formed by a sun gear fixed to the shaft 81, and the branch 112 is formed by a planet gear carrier to which a plurality of planet gears 110 are rotatably connected. The planet gears 110 engage with the gear 102 and with the internal teeth 106.

In other possible variant embodiments (not shown), the epicyclic differential 42 can be of a different type, for example a type using bevel gears or an epicyclic type with multiple stages.

Because of the known kinematic properties of epicyclic differentials, the characteristic magnitudes of the differential 42 are dependent on the relation F, shown below,

F) Z₁₀₂N 102 + Z-ioe gs = ( 102 + Z₁₀6)N₁₁₂,

in which:

Z102 is the number of teeth on the sun gear 118,

Z106 is the number of teeth in the internal teeth 106, N102 is the rotation speed of the sun gear 102,

N₉₈ is the rotation speed of the ring gear 98,

N112 is the rotation speed of the planet gear carrier 112.

The first branch 50 of the differential 34 comprises external teeth 124 which engage with external teeth 114 provided on the planet gear carrier 112 of the variable speed drive 56. The first branch 50 receives or transmits the motion, respectively, from or towards the variable speed drive 56 by means of the gearing comprising the teeth 114, 124.

The variant embodiment of Figure 5 is considerably more advantageous than those of Figures 2, 3 and 4, since the presence of more than one transmission with continuously variable speed 246, 48 and 44 provides a wider range of variation of the rotation speed of the branch 112. The vehicle can therefore reach greater maximum speeds with the configuration of Figure 5, or, alternatively, the single transmissions 246, 48 and 44 with continuously variable speed will transmit a lower power in the various operating conditions of the transmission 100. The overall efficiency of the vehicle is improved further with the configuration of Figure 5, since a reduction of the power transmitted by the single transmissions 246, 48 and 44 with continuously variable speed is accompanied by a reduction in the friction losses.

The traction system 10 comprises a device 62 for controlling the transmission 100 and the power sources 18, 22.

The control device 62 acts on the operating parameters of the second power source 18, by means of the reverser 20, and on those of the first power source 22, determining its rotation speed and torque. The control device 62 acts on the parameters of the second reversible power source 18, determining its rotation speed, its torque and the direction of the rotation speed.

The control device 62 also acts on the variable speed drive 56 to set the transmission ratio between the first power source 22 and the first branch 50 of the first epicyclic differential 34.

In the example of Figure 2, the control device 62 acts on the hydraulic pump 66 to vary its capacity, consequently varying the flow rate of the oil sent to the hydraulic motor 70 and consequently the speed of the shaft 72 connected thereto.

In the example of Figure 3, the control device 62 acts on the variable pulley 170 to vary its diameter, consequently varying its rotation speed by means of the belt 168, which is also connected to the variable pulley 166. The speed of the shaft 172 connected to the former pulley varies as a result.

In the example of Figure 4, the control device 62 acts on the pair of toroidal friction discs 268 to vary their position and point of contact with the friction cones 266 and 270. The speed of the shaft 272 connected to the disc varies as a result.

In the example of Figure 5, the control device 62 acts on the pair of toroidal friction discs 268, 468 and 368 to vary their position and point of contact with the friction cones 266 and 270, 466 and 470, and 366 and 370 respectively. Consequently the speed of the shaft 272 connected to the transmission 48 with continuously variable speed and the speed of the branch 98 vary. It is therefore possible to use the control device 62 to act on the variable speed drive 56 so as to set the speed of the shaft 72, 172 and 272 independently of the speed of the shaft 81 connected to the first power source 22.

The control device 62 receives the following input signals:

the position of an accelerator pedal 138 which can be operated by the user

the position or the transmission ratio of the variable speed drive

46, 146, 246, 48 and 44

the charge level of the accumulator 54,

the operating parameters of the reverser 20 and the operating parameters of the non-reversible power source 22.

The accelerator pedal 138, by means of which the driver communicates his intention to accelerate, decelerate or keep the vehicle at a constant speed, is connected to the control device 62 by an electrical, mechanical, hydraulic or other form of connection.

In other possible embodiments, the control device 62 also receives complementary input signals formed by the rotation speed of the shafts and branches, the pressure of the hydraulic circuit of the variable speed drive 46, and others.

In one method of controlling the traction system 10, the variable speed drive 56 can be actuated by means of the control device 62 so as to set a speed of the sun gear 102 equal to:

G) N-I02 = - (Zi06 -I02 )N₉₈

This value, which depends exclusively on the speed of the ring gear N₉₈, causes the speed N_l12 of the planet gear carrier 112 to be zero, as will be made clear by the substitution of relation G in relation F.

When the planet gear carrier 112 is stationary, the first branch 50 of the differential 34 which engages directly with it also has a speed of zero and therefore does not transmit any power.

Clearly, the substitution of the zero value of power transmitted by the branch 50 in the relation E gives the following relation H:

In the differential 34 in this situation, the power is transmitted from the second branch 118 to the third branch 130, or vice versa. In particular, in the case in which the vehicle is decelerating, the braking power transmitted from the wheels 38 to the axle 30 is transmitted entirely, except for mechanical losses, to the shaft 14, and from this to the second reversible source 18 and to the accumulator 54. During the deceleration of the vehicle, therefore, all the braking power can be used to recharge the accumulator 54.

To enable the planet gear carrier 112 to remain stationary independently of the rotation speed of the non-reversible source 22, it must be possible for the sun gear 102 on the same branch 102 to have a direction of rotation opposite to that of the epicyclic ring gear 106 positioned on the branch 98, as is clearly shown by the relation G. The opposite direction of rotation of the input branches 102 and 98 of the differential 42 which causes the speed of the planet gear carrier 112 to be zero is present at a specific discrete transmission ratio of the continuously variable speed drive 46 (or alternatively 146 or 246), 48 and 44. However, the branches 102 and 98 also have different directions of rotation at transmission ratios of the continuously variable speed drive 46 (or alternatively 146 or 246), 48 and 44 which are different from that at which the planet gear carrier 112 remains stationary. In the last-mentioned operating condition, an analysis of relations A to F applied to the differential 42 clearly shows that, since the torques in the branches 102 and 98 are synchronous, the values of the powers of said branches have different directions. By applying relation E to the differential 42, therefore, it can be seen that at least one of the two input branches 102 and 98 transmits power at a higher level than that transmitted by the output branch 112. However, the output power from the branch 112 continues to be of the same order of magnitude as the power supplied by the non-reversible source 22, and therefore at least one of the two branches 102 and 98 transmits a higher level of power than that supplied by the source 22. In the case of Figures 2, 3, 4 and 5, independently of their different variant embodiments, the continuously variable speed drive 46 (or alternatively 146 or 246) and 48, connected to the branch 102 or 98, transmits a higher level of power than that supplied by the source 22. Consequently, in order to enable the output branch 112 of the differential 42 to remain stationary in a specific operating condition corresponding to a transmission ratio of the continuously variable speed drive 46 (or alternatively 146 or 246), 48 and 44, the geometry of the variable speed drive 56 must allow the branches 102 and 98 to rotate in opposite directions and must allow the continuously variable speed drive 46 (or alternatively 146 or 246), 48 and 44 to transmit a higher level of power than that supplied by the source 22. In the condition in which the first branch 50 is stationary, the first power source 22, connected to it by means of the variable speed drive 56, can be switched off without any change in the conditions of motion of the vehicle. In another method of controlling the traction system 10, the speed of the shaft 14 and of the first branch 50 are set in such a way that the electric motor 18 operates at a speed as close as possible to the speed of maximum efficiency of the electric motor 18, of the reverser 20 and of the battery 54, with evident benefits in terms of the overall efficiency of the system 10.

In another method of controlling the traction system 10, when the accumulator 54 has a high charge level the control device 62 acts in such a way as to increase the power supplied by the second power source 18. Conversely, when the accumulator 54 has a low charge level, the control device 62 acts in such a way as to increase the power supplied by the first power source 22. In particular, the first power source 22 can be switched off when the accumulator 54 has a high charge level. This control method helps to minimize the charge fluctuations in the accumulator 54 and thus increases its service life.

The traction system 10 can enable the vehicle to decelerate without the need to use dissipation mechanisms such as brakes.

The traction system according to the present invention thus resolves the problems arising in the cited prior art, while offering numerous benefits. These include the possibility of controlling the speed of the first branch 50 of the differential 34 independently of the internal combustion engine which is normally used as the non-reversible first power source 22, in such a way that this source operates as closely as possible to its point of maximum efficiency and lowest fuel consumption.

Claims

1. A traction system (10) for vehicles, comprising:

a first power source (22) of the non-reversible type; a second power source (18) of the reversible type;

a transmission (100) connected to said first (22) and second (18) source and including a first differential device (34) with a first input or output branch (50) connected to said first source (22), a second input or output branch (118) connected to said second source, and a third input or output branch (130) which can be connected to an axle (30) of a vehicle;

a device (62) for controlling said transmission (100), wherein said transmission (100) comprises a variable speed drive (56) interposed between said first power source (22) and said first branch (50) of said first differential device (34), said control device (62) acting on said variable speed drive (56) to set the transmission ratio between said first power source (22) and said first branch (50) of said first differential device (34), characterized in that said variable speed drive (56) comprises:

a motion input or output shaft (81) connected to said first power source (22),

a continuous speed variation device (46, 146, 246) connected to said motion input or output shaft (81), at least one transmission (44, 48), connected in parallel or in series with said continuous speed variation device (46, 146, 246),

a second differential device (42) whose input or output branches (98, 102, 112) are connected, respectively, to said continuous speed variation device (46, 146, 246), to said transmission (44, 48), and to said first branch (50) of said first differential device (34);

said control device (62) being capable of setting said transmission ratio, during deceleration phases of the vehicle, in such a way that the transmission speeds of the branches of said second differential device (42) connected, respectively, to said continuous speed variation device (46, 146, 246) and to said transmission (44, 48) produce a rotation speed (N₅₀) of zero in said first branch (50).

A traction system (10) according to Claim 1, wherein said continuous speed variation device (46, 146, 246) is connected to said second differential device (42) so as to transmit a power greater than that supplied by the first source (22).

A traction system (10) according to Claim 1 or 2, wherein said transmission (44, 48) provides a further continuous speed variation.

A traction system (10) according to any one or more of the preceding claims, wherein said first source (22) is connected to a sun gear (118) or to an epicyclic ring gear (122) of said first differential device (34), and comprising a planet gear carrier (130) for connecting said first differential device (34) to said axle (30). A traction system (10) according to any one or more of the preceding claims, wherein

said continuous speed variation drive (46, 146, 246) is connected to a sun gear (102) or to an epicyclic ring gear (106) of said second differential device (42); and said second differential device (42) is connected to said first branch (50) of said first differential device (34) by means of a planet gear carrier (112) of said second differential device (42).

A traction system (10) according to any one or more of the preceding claims, wherein said continuous speed variation device (46) comprises a hydraulic pump (66) with a variable cylinder capacity and a hydraulic motor (70) connected in series with said hydraulic pump (66).

A traction system (10) according to any one or more of the preceding claims, wherein said continuous speed variation device (146) comprises at least two pulleys (166, 170) of variable diameter, interconnected by a belt (168).

A traction system (10) according to any one or more of the preceding claims, wherein said continuous speed variation device (246) comprises at least one pair of friction cones or wheels (266, 270) interconnected by at least one toroidal friction disc (268) of the variable position type.

A traction system (10) according to any one or more of the preceding claims, wherein said traction system (10) comprises an accumulator (54) for transferring energy from and towards said reversible second power source (18).

10. A traction system (10) according to Claim 9, wherein said first power source (22) is an internal combustion engine, connected to said accumulator (54) for supplying energy to said accumulator.

11. A traction system (10) according to Claim 9 or 10, wherein said second power source (18) is an electric motor and said accumulator (54) is a battery.

12. A traction system (10) according to any one or more of the preceding claims, wherein said first differential device (34) is of the epicyclic type and wherein said first branch (50) is formed by a ring gear, said second branch (118) is formed by a sun gear, and said third branch (130) is formed by a planet gear carrier.

13. A traction system (10) according to any one or more of the preceding claims, in which said system (10) comprises a command actuator (138) which can be actuated by the user, a control device (62) being connected to said actuator (138) in such a way that it receives the position of said command actuator (138) as an input parameter.

14. A traction system (10) according to any one or more of the preceding claims, wherein said transmission (44, 48) comprises at least one gear connected in parallel or in series with said continuous speed variation device (46, 146, 246).

15. A method of controlling a traction system (10) according to any one or more of the preceding claims, comprising the step of setting a value of the transmission of said variable speed drive (56) by means of said control device (62) such that the value of the speed of said first branch (50) of said first differential device (34) is zero. A control method according to Claim 15, comprising the additional step of turning off said first power source (22) when the speed of said first branch (50) of said first differential device (34) is zero.