Hybrid electric vehicle and method of controlling engine speed for the same

1 . A method for controlling an engine speed of a hybrid electric vehicle, the method comprising:

determining, when a first end of an engine is directly connected to a first motor while driving in a state where an engine clutch is locked-up and when a second motor is connected to a second end of the engine, a compensation value based on a difference in rotational speed of the engine and the second motor when a cause of control entry is occurred, which induces the rotational speed mismatch of the engine and the second motor;

compensating an output torque of the first motor based on the compensation value,

wherein the cause of control entry comprises a request to start a fuel injection,

wherein determining the compensation value further comprises:

storing, when the difference in rotational speed exceeds a second reference value greater than a predetermined first reference value during an initial engine speed control for each of the causes of control entry, the torque of the first motor such that the difference in rotational speed is less than or equal to the first reference value; and

determining the stored torque as the compensation value; and

terminating an output torque compensation of the first motor when a locked-up state of the engine clutch is opened.

2 . The method according to claim 1 , wherein the cause of control entry comprises a request to stop a fuel injection.

3 . The method according to claim 1 , wherein the cause of control entry comprises a change in an accelerator pedal control state.

4 . The method according to claim 1 , wherein the compensation value is determined by further considering the cause of control entry.

5 . The method according to claim 4 , wherein the compensation value is determined by further considering a predetermined value to correspond to a plurality of sections, which is the difference between the rotational speed of the engine and the rotational speed of the second motor.

6 . The method according to claim 1 , further comprising compensating the output torque of the first motor additionally so that the difference in rotational speed is less than or equal to the predetermined first reference value when the difference in rotational speed exceeds the second reference value which is greater than the first reference value as a result of compensating the output torque of the first motor by applying the compensation value.

7 . A non-transitory computer-readable recording medium having a program recorded thereon, the program to direct a processor to perform acts of:

determining, when a first end of an engine is directly connected to a first motor while driving in a state where an engine clutch is locked-up and when a second motor is connected to a second end of the engine, a compensation value based on a difference in rotational speed of the engine and the second motor when a cause of control entry is occurred, which induces the rotational speed mismatch of the engine and the second motor;

compensating an output torque of the first motor based on the compensation value,

wherein the cause of control entry comprises a request to start a fuel injection,

wherein determining the compensation value further comprises:

storing, when the difference in rotational speed exceeds a second reference value greater than a predetermined first reference value during an initial engine speed control for each of the causes of control entry, the torque of the first motor such that the difference in rotational speed is less than or equal to the first reference value; and

determining the stored torque as the compensation value; and

terminating an output torque compensation of the first motor when a locked-up state of the engine clutch is opened.

8 . A hybrid electric vehicle comprising:

an engine clutch, of which a first motor directly connected to an engine at a first end and a second motor connected to a second end; and

a control unit configured to determine, in a state where the engine clutch is locked-up, a compensation value based on a difference in a rotational speed between the engine and the second motor when a cause of control entry is occurred, which induces a rotational speed mismatch of the engine and the second motor and compensating an output torque of the first motor based on the compensation value,

wherein the cause of control entry comprises a request to start a fuel injection, and

wherein the control unit is further configured to:

store, when the difference in rotational speed exceeds a second reference value greater than a predetermined first reference value during an initial engine speed control for each of the causes of control entry, the torque of the first motor such that the difference in rotational speed is less than or equal to the first reference value; and

determine the stored torque as the compensation value; and

terminate an output torque compensation of the first motor when a locked-up state of the engine clutch is opened.

9 . The vehicle according to claim 8 , wherein the cause of control entry comprises a request to stop a fuel injection.

10 . The vehicle according to claim 8 , wherein the cause of control entry comprises a change in an accelerator pedal control state.

11 . The vehicle according to claim 8 , wherein the compensation value is determined by further considering the cause of control entry.

12 . The vehicle according to claim 11 , wherein the compensation value is determined by further considering a predetermined value to correspond to a plurality of sections, which is the difference between the rotational speed of the engine and the rotational speed of the second motor.

13 . The vehicle according to claim 8 , wherein the control unit is configured to compensate the output torque of the first motor additionally so that the difference in rotational speed is less than or equal to the predetermined first reference value when the difference in rotational speed exceeds the second reference value greater than the predetermined first reference value as a result of compensating the output torque of the first motor by applying the compensation value.