Control system for hybrid vehicle

1. A control system for a hybrid vehicle in which a prime mover includes an engine and a plurality of motors, and in which an operating mode is selected depending on a required driving force from a first mode where the vehicle is powered by the engine, a second mode where the vehicle is powered by the plurality of motors, and a third mode where the vehicle is powered by any one of the motors, comprising:

a control unit that is configured to detect an output power of the prime mover and

to alter a selectability of the second mode in accordance with the output power of the prime mover,

wherein the control unit is further configured to reduce the selectability with an increase in the output of the prime mover.

2. The control system for a hybrid vehicle as claimed in claim 1 , wherein the required driving force is calculated based on an opening degree of an accelerator and a vehicle speed.

3. The control system for a hybrid vehicle as claimed in claim 1 ,

wherein the hybrid vehicle comprises:

a power distribution device as a differential gear unit having a first rotary element connected to the engine, a second rotary element connected to a first motor to serve as a reaction element against a rotation of the first motor, and a third rotary element that is connected to a second motor and a drive shaft and that is rotated at a speed governed by speeds of the first rotary element and the second rotary element; and

a brake that selectively halts a rotation of the first rotary element; and

wherein the power distribution device is adapted to transmit a torque between the prime mover and the drive shaft while splitting or synthesizing the torque.

4. The control system for a hybrid vehicle as claimed in claim 1 ,

wherein the controller is further configured to select the first mode if the required driving force is greater than a predetermined driving force,

to select the second mode if the required driving force is smaller than the predetermined driving force, and

to reduce the selectability of the second mode by reducing the predetermined driving force with an increase in the output of the prime mover.

5. A control system for a hybrid vehicle in which a prime mover includes an engine and a plurality of motors, and in which an operating mode is selected depending on a required driving force from a first mode where the vehicle is powered by the engine, a second mode where the vehicle is powered by the plurality of motors, and a third mode where the vehicle is powered by any one of the motors, comprising:

a control unit that is configured to detect an output power of the prime mover and to alter a selectability of the second mode in accordance with the output power of the prime mover,

wherein the control unit is further configured to inhibit the second mode if the output of the prime mover is greater than a predetermined value.

6. The control system for a hybrid vehicle as claimed in claim 5 ,

wherein the control unit is further configured to detect a speed of the engine, and to inhibit the second mode if the speed of the engine is greater than a predetermined value.

7. The control system for a hybrid vehicle as claimed in claim 5 ,

wherein the required driving force is calculated based on an opening degree of an accelerator and a vehicle speed.

8. The control system for a hybrid vehicle as claimed in claim 5 ,

wherein the hybrid vehicle comprises:

a power distribution device as a differential gear unit having a first rotary element connected to the engine, a second rotary element connected to a first motor to serve as a reaction element against a rotation of the first motor, and a third rotary element that is connected to a second motor and a drive shaft and that is rotated at a speed governed by speeds of the first rotary element and the second rotary element; and

a brake that selectively halts a rotation of the first rotary element; and

wherein the power distribution device is adapted to transmit a torque between the prime mover and the drive shaft while splitting or synthesizing the torque.

9. A control system for a hybrid vehicle in which a prime mover includes an engine and a plurality of motors, and in which an operating mode is selected depending on a required driving force from a first mode where the vehicle is powered by the engine, a second mode where the vehicle is powered by the plurality of motors, and a third mode where the vehicle is powered by any one of the motors, comprising:

a control unit that is configured to detect an output power of the prime mover and to alter a selectability of the second mode in accordance with the output power of the prime mover,

wherein the control unit is further configured to render the second mode unavailable to be selected if the output of the prime mover is greater than a predetermined value.

10. The control system for a hybrid vehicle as claimed in claim 9 ,

wherein the control unit is further configured to detect a speed of the engine, and

to render the second mode unavailable to be selected if the speed of the engine is greater than a predetermined value.

11. The control system for a hybrid vehicle as claimed in claim 9 ,

wherein the required driving force is calculated based on an opening degree of an accelerator and a vehicle speed.

12. The control system for a hybrid vehicle as claimed in claim 9 ,

wherein the hybrid vehicle comprises:

a power distribution device as a differential gear unit having a first rotary element connected to the engine, a second rotary element connected to a first motor to serve as a reaction element against a rotation of the first motor, and a third rotary element that is connected to a second motor and a drive shaft and that is rotated at a speed governed by speeds of the first rotary element and the second rotary element; and

a brake that selectively halts a rotation of the first rotary element; and

wherein the power distribution device is adapted to transmit a torque between the prime mover and the drive shaft while splitting or synthesizing the torque.