Hybrid drive train for a vehicle

1 . In a vehicle having a first drive shaft driving first wheels and a second drive shaft driving second wheels, a hybrid drivetrain for selectively driving the first wheels of the first drive shaft and the second wheels of the second drive shaft, the hybrid drivetrain comprising:

first and second drive units, wherein the first drive unit is connectable to the first drive shaft, and wherein the second drive unit is connectable to the second drive shaft;

a connection clutch selectively connectable between the first and second drive units; and

a slip clutch assembly configured for allowing selective connection between the second drive unit and the second drive shaft, the slip clutch assembly comprising first and second slip clutches respectively located on opposite sides of a bevel gear, the first and second slip clutches being controllable so as to allow different rotational speeds of the second wheels driven by the second drive shaft.

2 . The hybrid drivetrain of claim 1 , further comprising a drive clutch configured for allowing selective connection between the first drive unit and the first drive shaft.

3 . The hybrid drivetrain of claim 1 , wherein the first drive unit is a combustion engine.

4 . The hybrid drivetrain of claim 1 , wherein the second drive unit is an electric motor.

5 . The hybrid drivetrain of claim 1 , wherein the first drive unit is connectable to the first drive shaft by a gearbox.

6 . The hybrid drivetrain of claim 1 , wherein the second drive unit is directly connectable to the second drive shaft without gear shift capabilities.

7 . The hybrid drivetrain of claim 6 , wherein the second wheels driven by the second drive shaft have a wheel size such that a total gearing of the wheels of the second drive shaft and the connection of the second drive shaft to the second drive unit provides a maximum rotational speed of the second drive unit that is reached at a vehicle speed lower than a top speed of the vehicle.

8 . The hybrid drivetrain of claim 7 , wherein the slip clutch assembly between the second drive unit and the second drive shaft is configured to be disconnected as the vehicle approaches a speed at which the second drive unit approaches its maximum rotational speed.

9 . A vehicle, comprising:

a first drive shaft driving first wheels and a second drive shaft driving second wheels; and

a hybrid drivetrain for selectively driving the first drive shaft and the second drive shaft, the hybrid drivetrain comprising:

first and second drive units, wherein the first drive unit is connectable to the first drive shaft, and wherein the second drive unit is connectable to the second drive shaft;

a connection clutch selectively connectable between the first and second drive units; and

a slip clutch assembly configured for allowing selective connection between the second drive unit and the second drive shaft, the slip clutch assembly comprising first and second slip clutches respectively located on opposite sides of a bevel gear, the first and second slip clutches being controllable so as to allow different rotational speeds of the second wheels driven by the second drive shaft.

10 . A method for controlling a hybrid drivetrain for selectively driving first wheels through a first drive shaft of a vehicle and second wheels through a second drive shaft of the vehicle, the hybrid drivetrain comprising: a first drive unit connectable to the first drive shaft; a second drive unit connectable to the second drive shaft; a connection clutch configured for selective connection between the first and second drive units; a drive clutch configured for selective connection between the first drive unit and the first drive shaft; and a slip clutch assembly configured for allowing selective connection between the second drive unit and the second drive shaft, the slip clutch assembly comprising first and second slip clutches respectively located on opposite sides of a bevel gear, the first and second slip clutches being controllable so as to allow different rotational speeds of the second wheels, the method comprising:

selecting a driving mode from the group consisting of: (a) a starter mode in which the second drive unit is energized, the connection clutch is engaged, and the slip clutch assembly and the drive clutch are disengaged; (b) a four-wheel drive mode in which the second drive unit is energized, the slip clutch assembly and the drive clutch are engaged, and the connection clutch is disengaged; (c) a two-wheel boosted drive mode, in which the second drive unit is energized, the slip clutch assembly is disengaged, and the connection clutch and the drive clutch are engaged; (d) a two-wheel electric mode, in which the second drive unit is energized, the slip clutch assembly is engaged, and the drive clutch and the connection clutch are disengaged; (e) a two-wheel combustion engine drive mode, in which the slip clutch assembly is disengaged, and the connection clutch and the drive clutch are engaged; (f) a battery charging mode, in which the connection clutch is engaged, and the second drive unit is controlled so as to function as a generator powered by the first drive unit; and (g) a regenerative braking mode, in which the slip clutch assembly is engaged, and the second drive unit is controlled so as to function as a generator and to store electrical power produced by the second drive unit in a battery; and

controlling energizing of the second drive unit and engagement and disengagement of the slip clutch assembly, the connection clutch, and the drive clutch according to the selected drive mode.

11 . The method of claim 10 , wherein the step of controlling is performed by a controller operatively connected to the second drive unit, the slip clutch assembly, the connection clutch and the drive clutch over a communication bus, the controller having non-volatile memory in which definitions of the driving modes are stored.