Power transmission system of hybrid electric vehicle

A power transmission system of a hybrid electric vehicle, comprising:

• an input shaft input with power of an engine;
• an output gear disposed on the input shaft without rotation interference;
• a first planetary gear set having a single pinion planetary gear set and disposed on the input shaft while including three rotation elements having a first sun gear, a first planetary carrier, and a first ring gear;
• a second planetary gear set having the single pinion planetary gear set and disposed on a same shaft line at a rear side of the first planetary gear set while including three rotation elements having a second sun gear, a second planetary carrier, and a second ring gear;
• a third planetary gear set having the single pinion planetary gear set and disposed on a same shaft line at a rear side of the second planetary gear set while including three rotation elements having a third sun gear, a third planetary carrier, and a third ring gear;
• a first rotation shaft configured to directly connect the first sun gear to a first motor and generator;
• a second rotation shaft connected to the output gear while directly connecting the first planetary carrier to the second planetary carrier;
• a third rotation shaft connected to the input shaft while directly connecting the first ring gear to the third planetary carrier;
• a fourth rotation shaft configured to directly connect the second sun gear to a second motor and generator;
• a fifth rotation shaft connected to the second ring gear to be selectively connected to a transmission housing;
• a sixth rotation shaft configured to connect the third sun gear to the transmission housing;
• and
• a seventh rotation shaft connected to the third ring gear to be selectively connected to the fourth rotation shaft;
• and
• three friction elements configured to selectively connect the respective rotation shafts to each other or selectively connect the respective rotation shafts to the transmission housing.

A power transmission system of a hybrid electric vehicle, comprising:

• an input shaft input with power of an engine;
• an output gear disposed on the input shaft without rotation interference;
• a first planetary gear set having a double pinion planetary gear set and disposed on the input shaft while including three rotation elements having a first sun gear, a first planetary carrier, and a first ring gear;
• a second planetary gear set having a single pinion planetary gear set and disposed on a same shaft line at a rear side of the first planetary gear set while including three rotation elements having a second sun gear, a second planetary carrier, and a second ring gear;
• a third planetary gear set having the single pinion planetary gear set and disposed on a same shaft line at a rear side of the second planetary gear set while including three rotation elements having a third sun gear, a third planetary carrier, and a third ring gear;
• a first rotation shaft configured to directly connect the first sun gear to a first motor and generator;
• a second rotation shaft connected to the output gear while directly connecting the first ring gear to the second planetary carrier;
• a third rotation shaft connected to the input shaft while directly connecting the first planetary carrier to the third planetary carrier;
• a fourth rotation shaft configured to directly connect the second sun gear to a second motor and generator;
• a fifth rotation shaft connected to the second ring gear to be selectively connected to a transmission housing;
• a sixth rotation shaft configured to connect the third sun gear to the transmission housing;
• and
• a seventh rotation shaft connected to the third ring gear to be selectively connected to the fourth rotation shaft;
• and
• three friction elements configured to selectively connect the respective rotation shafts to each other or selectively connect the respective rotation shafts to the transmission housing.