Control apparatus and method of power transmission system for hybrid elecric vehicle

A control method of a power transmission system, comprising:

• an input shaft through which torque from an engine is input;
• first and second motor/generators configured to operate as both a motor and a generator;
• a planetary gear set disposed on a line from the input shaft and including a sun gear directly connected with the first motor/generator and selectively connected to a transmission housing, a planetary carrier directly connected with the input shaft and selectively connected to the transmission housing, and a ring gear operating as an output element and connected with the second motor/generator;
• an output shaft configured to transmit torque from the planetary gear set and the second motor/generator to driving wheels through a differential;
• a first brake disposed between the planetary carrier and the transmission housing;
• a second brake disposed between the sun gear and the transmission housing;
• a battery configured to supply electricity to the first motor/generator and the second motor/generator and charge electricity generated from the first motor/generator and the second motor/generator;
• and
• a controller configured to convert a hybrid electric vehicle (HEV) mode 1 in which an operation of the first brake and the second brake is released or an HEV mode 2 in which an operation of the second brake is operated,
• wherein the controller executes a series of commands including:
• determining a mechanical maximum efficiency range from a gear ratio of the planetary gear set;
• determining a required power of the engine from a vehicle speed and a required torque;
• determining a speed ratio from the required power and the vehicle speed;
• detecting a state of charge (SOC) of the battery;
• determining whether the speed ratio is within the mechanical maximum efficiency range;
• and
• converting an operation mode to the HEV mode 1 when the speed ratio is beyond the mechanical maximum efficiency range.

A non-transitory computer readable medium containing program instructions executed by a controller, the computer readable medium comprising:

• program instructions that determine a mechanical maximum efficiency range from a gear ratio of a planetary gear set disposed on a line from an input shaft through which torque from an engine is input and including a sun gear directly connected with a first motor/generator and selectively connected to a transmission housing, a planetary carrier directly connected with the input shaft and selectively connected to a transmission housing, and a ring gear operating as an output element and connected with a second motor/generator;
• program instructions that determine a required power of the engine from a vehicle speed and a required torque;
• program instructions that determine a speed ratio from the required power and the vehicle speed;
• program instructions that detect a state of charge (SOC) of a battery configured to supply electricity to the first motor/generator and the second motor/generator and charge electricity generated from the first motor/generator and the second motor/generator;
• program instructions that determine whether the speed ratio is within the mechanical maximum efficiency range;
• program instructions that convert a hybrid electric vehicle (HEV) mode 1 in which an operation of the first brake and the second brake is released or an HEV mode 2 in which an operation of the second brake is operated;
• and
• program instructions that convert an operation mode to the HEV mode 1 when the speed ratio is beyond the mechanical maximum efficiency range.