Hybrid vehicle

1. A hybrid vehicle comprising:

an engine;

a first motor;

a second motor;

a planetary gear set including at least one planetary gear, at least part of rotating elements of the at least one planetary gear being connected to the engine, the first motor, the second motor and a drive shaft coupled to an axle;

a rotation restriction mechanism configured to restrict rotation of the engine;

a battery configured to exchange electric power with the first motor and the second motor; and

an electronic control unit configured to:

(i) control, in one of a charge depleting mode and a charge sustaining mode, the engine, the first motor and the second motor such that the hybrid vehicle travels by using a required output for propelling the hybrid vehicle according to an accelerator operation, in any one of a hybrid drive mode, a single-drive mode and a double-drive mode, the hybrid drive mode being a mode in which the hybrid vehicle travels while the engine is operated by placing the engine in a rotating state, the single-drive mode being a mode in which the hybrid vehicle travels by using output from only the second motor in an electric drive mode in which the hybrid vehicle travels while the engine is placed in a rotation stopped state to cause the engine not to operate, and the double-drive mode being a mode in which the hybrid vehicle travels by using output from the first motor and the second motor in the electric drive mode,

(ii) cause a drive mode to shift into the hybrid drive mode by starting the engine when a predetermined high response request is not being issued, when the required output becomes larger than a first threshold in the charge sustaining mode in the single-drive mode, and

(iii) cause the drive mode to shift into the double-drive mode without starting the engine when the predetermined high response request is being issued, when the required output becomes larger than the first threshold in the charge sustaining mode in the single-drive mode.

2. The hybrid vehicle according to claim 1 , wherein the electronic control unit is configured to cause the drive mode to shift into the hybrid drive mode, when the predetermined high response request is being issued in the charge sustaining mode in the electric drive mode, and when the required output becomes larger than a second threshold larger than the first threshold.

3. The hybrid vehicle according to claim 2 , wherein

the second threshold is a value larger than a maximum double-drive output that is a maximum output outputtable to the drive shaft in the double-drive mode, and

the electronic control unit is configured to cause the drive mode to shift into the hybrid drive mode even when the required output is not larger than the second threshold, when the required output is larger than the first threshold and the predetermined high response request is being issued in the charge sustaining mode in the electric drive mode, and when the required output is larger than the maximum double-drive output.

4. The hybrid vehicle according to claim 2 , wherein the electronic control unit is configured to cause the drive mode to shift into the hybrid drive mode even when the required output is not larger than the second threshold, when the required output is larger than the first threshold and the predetermined high response request is being issued in the charge sustaining mode in the electric drive mode, and when at least one of a condition that the hybrid vehicle is traveling on a predetermined low μ road, a condition that a slip due to wheel spin of a drive wheel has been detected, and a condition that slip reduction control for reducing an extent of the slip is being executed is satisfied.