Technical field

[0001 ] The present invention generally relates to a power distribution device for a hybrid drive train. Background Art

[0002] US 2005/01 15750 A1 discloses hybrid drive unit that includes an internal combustion engine (ICE), a first electric motor, a force distribution planetary gearing, a second electric motor for driving force assistance and a speed change unit. The hybrid drive unit further comprises a transfer that distributes driving force to front and rear wheels. The transfer is implemented as a planetary or epicyclic gearing with a differential-limiting clutch. When that clutch is engaged, the planetary carrier, which introduces the input torque from the motors and the ICE, is locked to the sun gear. As a consequence, the planetary carrier, the sun gear and the ring gear rotate as an integral unit. The front and rear wheel drive shafts thus rotate at the same speed. [0003] US 2001/00165532 A1 discloses a power distribution device using an epicyclic gearing. According to this document, a hybrid drive train of a hybrid electric vehicle includes a first motor connected to a battery through an inverter, the first motor functioning as a generator, a differential disposed between an ICE and the first motor to provide driving force from one of the first motor and the ICE, a final reduction gear engaged with the differential to transmit drive force to wheels, a second motor connected to the battery through the inverter to directly drive an axle shaft, a first one-way clutch disposed between the differential and the engine, and a second one-way clutch disposed within the differential. The second one-way clutches ascertain that, when the ICE is off or rotating at a lower angular speed than the first motor, the two input shafts of the differential rotate with the same angular speed. As a consequence, the carrier and the two input gears rotate as an integral unit. The driving force of the first motor is thus integrally transferred to the output of the differential (except for frictional losses).

[0004] A problem encountered with hybrid drives is the starting of the internal combustion engine, since it cannot be started under high load conditions. Existing solutions require that the ICE be decoupled from the drive train for starting. The ICE is thus started in decoupled state and only connected to the drive train once the vehicle has reached a certain minimum speed.

Technical problem

[0005] It is an object of the present invention to provide a power distribution system that with greater versatility. This object is achieved by a power distribution system as claimed in claim 1 .

General Description of the Invention

[0006] According to the invention, a power distribution device for a hybrid drive train comprises an epicyclic gearing including a first gear, a second gear and at least one planetary gear meshing with the first and second gears. The at least one planetary gear is mounted on a planetary carrier constrained to rotate at an angular velocity equal to half the algebraic sum of the angular velocities of the first gear and the second gear. A first input shaft (drivable e.g. by a first electric motor and/or an ICE) is connected in rotation-transmitting manner with the first gear, a second input shaft (drivable by a second electric motor and/or an ICE) is connected in rotation- transmitting manner with the second gear and an output shaft (e.g. connectable to the wheels of the hybrid vehicle) is connected in rotation-transmitting manner with the planetary carrier. The epicyclic gearing comprises a bypass gearing switchable between an engaged state and a disengaged state. When the bypass gearing is in the engaged state, it is connected in rotation-transmitting manner with both the first and second gears and constrains them to rotate with opposite angular velocities. When the bypass gearing is in the disengaged state, it is disengaged with at least one (possibly both) of the first and second gears.

[0007] As those skilled will appreciate, when the bypass gearing is in the engaged state, the first and second gears are constrained in opposite angular rotation. As a consequence, the angular speed of the planetary carrier is zero. Accordingly, no rotation is transmitted between the first or the second gear, on the one hand, and the planetary carrier, on the other hand. This is especially useful in a hybrid vehicle, in particular, if the first or the second gear may be driven by an internal combustion engine. Indeed, the ICE may be started under low load conditions when the bypass gearing is in the engaged state. Depending on the configuration of the hybrid drive train, a dedicated starter motor for the engine will not be necessary. Thanks to the invention, the hybrid drive train can be configured in such a way that the ICE may be selected (temporarily) as the only source of mechanical energy to put the vehicle in motion from a standstill. Conventional hybrid drives achieve the acceleration of the vehicle from 0 km/h to a certain minimum speed using the electric motor as a source of mechanical energy.

[0008] As used herein, the term "gear" (in singular) designates a toothed wheel (e.g. a gearwheel or a bevel wheel, etc.). "Gearing" designates a single gear (working upon another gear or a chain) or an assembly of gears. It will be understood that "epicyclic gearing" is intended to cover any gearing that is cinematically equivalent to a planetary gearing (with sun gear, planet gears on a planetary carrier and a ring gear). The term "algebraic sum" (instead of simply "sum") is used herein to clarify that the angular velocities have to be added as signed (+ or -) quantities.

[0009] As used herein, the expression "connected in rotation-transmitting manner" implies that the parts connected in that manner always rotate together (i.e. when one part rotates, the other must follow) with a fixed speed ratio (≠ 0 and≠ °°).

[0010] Preferably, the power distribution device comprises a brake for braking and/or stopping the first and/or the second gear.

[001 1 ] According to a preferred embodiment of the invention, the bypass gearing comprises a bypass gear movable into a first position, in which it is connected in rotation-transmitting manner with both the first and second gears (the first position thus corresponds to the above-mentioned engaged state), and into a second position in which the bypass gear is connected in rotation-transmitting manner with at most one of the first and second gears (the second position thus corresponds to the above-mentioned disengaged state). [0012] An aspect of the present invention concerns a hybrid drive train comprising a power distribution device configured as described hereinabove. The hybrid drive train preferably comprises a first electric motor (preferably an asynchronous motor that can be used as a generator) connected to the first gear via a first input shaft and a second electric motor (preferably an asynchronous motor that can be used as a generator) connected to the second gear via a second input shaft. An internal combustion engine is preferably mechanically couplable with the first input shaft (e.g. by means of a clutch arranged between the internal combustion engine and the first input shaft).

[0013] Most preferably, the hybrid drive train comprises a battery and a control unit for controlling flow of electric energy between the battery and each of the first and second electric motors.

[0014] An interesting advantage of the present invention is that an additional gearbox (transmission) enabling different gear ratios between the ICE and the wheels is not necessary. The full span of gear ratios can indeed by made available by the described power distribution device. The invention thus has the potential to significantly reduce the costs of hybrid drive trains.

Brief Description of the Drawings

[0015] Further details and advantages of the present invention will be apparent from the following detailed description of a not limiting embodiments with reference to the attached drawings, wherein: Fig. 1 is a schematic constructional diagram of a hybrid drive train according to a preferred embodiment of the invention, wherein the bypass gearing is in disengaged state;

Fig. 2 is another schematic constructional diagram of the hybrid drive train Fig. 1 with the bypass gearing in engaged state; Fig. 3 is a representation of an illustrative driving cycle of a hybrid vehicle equipped with a drive train as in Figs. 1 and 2.

Description of Preferred Embodiments

[0016] A schematic constructional diagram of a direct hybrid drive train (in short DHD) 10 according to a preferred embodiment of the invention is generally shown in Fig. 1 .

[0017] The DHD 10 comprises a power distribution device (PDD) 12, which is a differential unit with an additional bypass wheel (BW) 14 as the above-mentioned bypass gearing. One leg 16 of the PDD is connected to the drive shaft of an in-line motor/generator (MG1 ) 18, which, in turn is connected to the drive shaft 20 of an internal combustion engine (ICE) 22 via a clutch 24. The other leg 26 of the PDD is connected to the shaft of a second motor/generator (MG2) 28, which is equipped with a brake (BR) 30. The PDD output shaft 32 works as a drive train shaft (i.e. transfers the motion to one or more driven wheels directly or via a differential).

[0018] The PDD comprises an epicyclic gearing including a first gear 38, a second gear 40 and planetary gears 42, 44 meshing with the first and second gears. The planetary gears are on a planetary carrier 46 constrained to rotate at an angular velocity equal to half the algebraic sum of the angular velocities of the first gear and the second gear. The first gear 38 and the second gear 40 are connected in rotation- transmitting manner with the first leg 16 and the second leg 26, respectively. [0019] When the bypass wheel 14 is in the engaged state (Fig. 2), it is connected in rotation-transmitting manner with both the first 16 and second legs 26 of the PDD 12 and thereby constrains them to rotate with opposite angular velocities. The rotational speed of the output shaft 32 is thus forced to zero. The engaged state of the bypass wheel 14 thus allows starting the ICE without causing any disturbance on the PDD output.

[0020] In contrast, when the bypass wheel 14 is in the disengaged state, it is disengaged with at least one (in this example: both) of the first 16 and second 26 legs of the PDD 12. When the bypass wheel 14 is in disengaged state, the PDD 12 works like an ordinary differential, i.e. all the shafts 16, 26 32 can be at different speeds at a time.

[0021 ] The shaft of the first motor/generator 18 is directly connected (or connected in rotation-transmitting manner) to the first leg. The first motor/generator 18 is electrically connected to a control unit (CU) 34, e.g. a controller. The first motor/generator is configured and/or may be controlled to work: o as a motor, getting electric energy from a battery (BAT) 26 via the control unit 34 and driving the output shaft 32 via the PDD 12, or starting up the internal combustion engine 22; o as a generator, a) getting kinetic energy from the output shaft 32 via the PDD 12 and recharging the battery 36 via the control unit 34 (regenerative braking mode of operation), and/or b) getting kinetic energy from the ICE 22 and transforming it into electric energy for running the second motor/generator 28 or for loading the battery 36; or o as a torque direct transfer device between the ICE 22 and the output shaft 32 of the PDD12 (by activating the brake 30), which offers the following possibilities: a) to start the engine 22 when the battery 36 is low by pulling or pushing the vehicle; b) to perform engine braking; and c) to drive the hybrid vehicle using only the ICE 22.

[0022] The shaft of the second motor/generator 28 is directly connected (or connected in rotation-transmitting manner) to the second leg 26 of the PDD 12. The second motor/generator 28 is electrically connected to the control unit 34. The second motor/generator 28 is configured and/or may be controlled to work: o as a motor, getting electric energy from the battery 36 or the first motor/generator 18 via the control unit 34 and driving the output shaft 32 via the PDD 12; or o as a generator, a) getting kinetic energy from the output shaft 32 via the PDD 12 and recharging the battery 36 via the control unit 34 (regenerative braking mode of operation), and/or b) getting kinetic energy from the ICE 22 via the PDD 12 and transforming it into electric energy for charging the battery 36 via the control unit 34 (e.g. at a start up after a standstill when the battery 36 is discharged).

[0023] The shaft 20 of the ICE 22 can be connected to or disconnected from the shaft of the first motor/generator 18 via the clutch 24. When the clutch (coupling device) is in uncoupling position, the ICE 22 is separated from the remainder of the drive train 10 and may be switched off. Otherwise, the ICE 22 may serve as a primary or auxiliary source of mechanical power in the different driving situations. [0024] When the bypass wheel 14 is in engaged state (implying a standstill of the vehicle), the ICE 22 may charge the battery 36 via the first 18 and/or the second 28 motor/generator . When the bypass wheel 14 is in disengaged state, the engine 22 may be used as the sole source of mechanical power (e.g. when the battery 36 is low) or together with one or both of the electric motors/generators 18, 28 (hybrid drive).

[0025] When the brake 30 on the second leg 26 of the PDD 12 is active (rotational speed of the second leg equal to zero), it allows for direct power transmission between the first leg 16 and the output shaft 32 of the PDD 12. In this situation, the second motor/generator 28 is deactivated. The vehicle may be driven in electric mode or in hybrid mode using the first electric motor and/or the ICE.

[0026] The DHD of the present example allows combining the ICE 22, the first motor/generator 18 and the second motor/generator 28 in a number of different ways, depending on the specific requirements of the driving situation. Fig. 3 represents an illustrative sequence of driving situations (columns C2-C12) in form of a table. For each component of the DHD, Fig. 3 indicates the operational state (i.e. whether the component is on or off or in a particular state, if there are more possibilities than on and off). It should be noted that all the numerical values indicated in Fig. 3 are only for illustration. It is assumed that the vehicle is first at a standstill (C2 and C3: speed = 0 km/h) with the motors 18, 28 and the engine 22 initially shut off. The vehicle then accelerates to 60 km/h (C4-C5), where it remains for a while (C6-C7), comes to a short stop, accelerates again to 60 km/h (C8) and then to 180 km/h (C9-C12).

[0027] In order to start the ICE 22, the first motor/generator is used as a starter motor (C2). At this time, the bypass wheel 14 is engaged with the first 16 and second 26 legs of the PDD 12. The second motor/generator is freewheeling. Thanks to the bypass wheel, the first and second legs of the PDD rotate at opposite angular speeds, so that the output shaft of the PDD does not rotate. After the starting phase, the control unit switches the first motor/generator to freewheel operation (C3). The ICE is now the sole source of mechanical energy. When the bypass wheel is disengaged (C4), mechanical power from the ICE is distributed to the second leg of the PDD and the PDD output shaft. The control unit now operates the second motor/generator as a generator in order to control the split ratio of the power. The higher the load on the second leg, the higher is the angular acceleration of the PDD output shaft (assuming a constant load on the PDD output shaft). Electric energy generated by the second motor/generator is stored in the battery.

[0028] In the illustrative driving cycle of Fig. 3, the vehicle is then accelerated to 60 km/h using both the ICE and the first motor/generator (C5). The brake is applied on the second leg of the PDD. In this configuration, torque is transferred directly between the first leg and the output shaft.

[0029] When purely electric driving is desired, the ICE may be switched off. Firstly, the speed of the engine is reduced (C6). This may be achieved by operating the first motor/generator as a generator. The speed of the output shaft may be maintained by increasing the angular speed of the second motor/generator. Then, the clutch decouples the ICE from the drive train, and the engine is shut down (C7).

[0030] The ICE may be started while the vehicle is driving (C9-C10). To this end, the first motor/generator is stopped (C9). After the clutch is engaged, the ICE is started using the first motor/generator as a starter motor. During these steps, the control unit controls the second motor/generator to maintain the PDD output shaft at the desired speed.

[0031 ] For high-speed driving or high accelerations (C1 1 -C12), the ICE and both electric motors/generators may contribute mechanical power.

[0032] The example of Fig. 3 shows, in particular, that a PDD in accordance with the invention makes available all the necessary gear ratios for moving the vehicle in the speed range from 0 to 200 km/h. No additional gearbox between the ICE and the wheels is required, making the illustrated drive train very cost-efficient in comparison with conventional hybrid drive trains providing similar performance. Nevertheless, it should be noted that while an additional gearbox is not necessary in the illustrated example, specific embodiments of the invention might benefit from the presence of an additional gearbox. The invention thus shall not be construed to exclude an additional gearbox.

[0033] While specific embodiments have been described in detail, those skilled in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Legend:

10 Direct hybrid drive train

12 Power distribution device

14 Bypass wheel

16 First leg

18 First motor/generator

20 Drive shaft of internal combustion engine

22 Internal combustion engine

24 Clutch

26 Second leg

28 Second motor/generator

30 Brake

32 Output shaft

34 Control unit

36 Battery

38 First gear

40 Second gear

42 Planetary gear

44 Planetary gear

46 Planetary carrier

C2- Columns associated with different driving situations