CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure claims the benefit of Japanese Patent Application No. 2017-050281 filed on Mar. 15, 2017 with the Japanese Patent Office.

BACKGROUND

Field of the Disclosure

Embodiments of the present disclosure relate to the art of a drive unit for a hybrid vehicle in which a prime mover includes an engine and two motors, and in which a drive torque generated by the prime mover is delivered to an output member connected to drive wheels.

Discussion of the Related Art

JP-A-2005-155891 describes a drive unit for hybrid vehicles that includes a Ravigneaux planetary gear unit having a first rotary element to which an engine is connected, a second rotary element to which a first motor/generator is connected, a third rotary element, and a fourth rotary element.

In the drive unit, it is possible to switch between a mode in which the third rotary element and drive wheels are connected to each other and a mode in which the fourth rotary element and the drive wheels are connected to each other by manipulating a clutch, such that an assist torque of a second motor can be synthesized with a drive torque delivered through the third rotary element or the fourth rotary element. In this drive unit, an operating mode can be selected from a hybrid vehicle (HV) mode in which a vehicle is operated by establishing a reaction torque from the first motor/generator to deliver a drive torque of the engine to the third rotary element or the fourth rotary element and an electronic vehicle (EV) mode in which the vehicle is operated by generating a drive torque by a second motor while stopping the engine.

However, in the drive unit taught by the above-mentioned prior art document, the first motor/generator may be rotated passively during propulsion in the EV mode, and there is a risk that power loss will be increased. In order to prevent such passive rotation of the first motor/generator, it is necessary for the first motor/generator to generate a torque counteracting against a torque acting on the first motor/generator by, for example, applying a predetermined current to the first motor/generator. However, this may result in an increase in electric power consumption. In order to avoid such disadvantage, in a conventional drive unit for hybrid vehicles, it is necessary to reduce electric power consumption during the propulsion in the EV mode.

SUMMARY

Aspects of embodiments of the present disclosure have been conceived noting the foregoing technical problems, and it is therefore an object of embodiments of the present disclosure to provide a drive unit for hybrid vehicles that reduces electric power consumption during propulsion in the EV mode.

In order to achieve the above object, the present disclosure provides a drive unit for a hybrid vehicle in which a prime mover includes an engine, a first motor, and a second motor, in which a drive torque generated by the prime mover is delivered to an output member connected to drive wheels, characterized by: a first differential mechanism including a first rotary element to which the engine is connected, a second rotary element to which the second motor and the output member are connected, and a third rotary element; and a second differential mechanism including a fourth rotary element to which the first motor is connected, a fifth rotary element connected to the third rotary element, and a sixth rotary element; a first engagement device adapted to selectively connect the first rotary element or the second rotary element and the sixth rotary element; and a second engagement device adapted to selectively connect any two of the fourth rotary element, the fifth rotary element, and the sixth rotary element.

In a non-limiting embodiment, the first engagement device may be adapted to selectively connect the first rotary element or the second rotary element to the sixth rotary element.

In a non-limiting embodiment, the second engagement device may be adapted to selectively connect two of the fourth to sixth rotary elements, and therefore the second engagement device may connect the fourth rotary element and the fifth rotary element, connect the fourth rotary element and the sixth rotary element, or connect the fifth rotary element and the sixth rotary element.

In a non-limiting embodiment, the first differential mechanism or the second differential mechanism may include a planetary gear unit, and the respective rotary elements may be any one of a sun gear, a ring gear, and a carrier.

According to the embodiment of the present disclosure, the first differential mechanism may be disconnected from the second differential mechanism to interrupt torque transmission therebetween by manipulating the first engagement device and the second engagement device. According to the embodiment of the present disclosure, therefore, the torque will not be applied to the first motor during propulsion in an electric vehicle mode and hence the first motor can be prevented from being rotated in the electric vehicle mode. For this reason, electric power consumption to keep stopping the first motor can be reduced. In addition, it is not necessary to increase an output power of the second motor to compensate a power loss resulting from rotating the first motor passively.

