Control device of hybrid vehicle

1. A control device of a hybrid vehicle, the hybrid vehicle comprising an engine, a motor as a traveling power source, and a battery in which electric power to be supplied to the motor is stored, the control device comprising:

a transient operation controller configured to, based on absolute values of an outputtable electric power and a chargeable electric power of the battery being smaller than respective predetermined values at a time of a transient operation of the engine, perform a transient operation of:

controlling an operating point of the engine within a wide range from low output to high output, at a position where a thermal efficiency of the engine is lower than the thermal efficiency of the engine at a time of a steady operation, and

controlling the engine to operate in a combustion state where a margin to a combustion limit is greater than the margin in the steady operation,

wherein the outputtable electric power and the chargeable electric power are calculated based on a temperature of the battery or a state of charge of the battery.

2. The control device of the hybrid vehicle according to claim 1 , wherein

the hybrid vehicle is a series hybrid vehicle, and

the control device further comprises:

a fixed point operation controller configured to perform, in the steady operation, a fixed point operation in which the operating point of the engine is fixed at an operating point where high thermal efficiency is achieved, and

an output operation controller configured to perform, in a case where vehicle requested power is at or greater than a predetermined value, an output operation of:

controlling the operating point of the engine to be at a position which is closer to a high-output side than the operating point in the transient operation, and

controlling the engine to operate in a combustion state with a greater margin to the combustion limit than the margin in the transient operation.

3. The control device of the hybrid vehicle according to claim 2 , wherein

the fixed point operation controller comprises:

a first fixed point operation controller configured to perform a first fixed point operation of performing a fixed point operation at a first operating point that achieves a maximum thermal efficiency of the engine; and

a second fixed point operation controller configured to perform a second fixed point operation of performing a fixed point operation at a second operating point that is positioned on a low thermal-efficiency side and on the high-output side of the first operating point, and

wherein the first fixed point operation controller is configured to:

perform the first fixed point operation in a case where the vehicle requested power is smaller than a sum of engine output in a fixed point operation state and the outputtable electric power of the battery, and

performs the second fixed point operation in a case where the vehicle requested power is at or greater than the sum of the engine output in the fixed point operation state and the outputtable electric power of the battery.

4. The control device of the hybrid vehicle according to claim 1 , wherein

the engine is configured to perform a lean-burn operation, and

the transient operation controller is further configured to control an air-fuel ratio in the transient operation to be an air-fuel ratio that is on a rich side of a limit value on which a lean side is within a range of an air-fuel ratio that achieves a stable combustion in the steady operation.

5. The control device of the hybrid vehicle according to claim 1 , wherein

the engine comprises an exhaust gas recirculation device that is configured to recirculate a portion of exhaust gas, as EGR gas, from an exhaust passage to an intake passage through an EGR valve, and

the transient operation controller is configured to control an EGR ratio in the transient operation to be an EGR ratio that is on an EGR gas small-amount side of a limit value on which an EGR gas large-amount side is within a range of an EGR ratio where a stable combustion is achieved in the steady operation.

6. The control device of the hybrid vehicle according to claim 1 , wherein

the engine comprises a variable valve timing mechanism that is configured to change a valve overlap amount with respect to an intake valve and an exhaust valve, and

the transient operation controller is further configured to control a valve overlap amount in the transient operation to be a valve overlap amount on a smaller-amount side of a limit value on which a larger-amount side is where the overlap amount is within a range of the valve overlap amount where a stable combustion is achieved in the steady operation.