Heat pump system for a vehicle

A heat pump system for a vehicle, the heat pump system comprising:

• a compressor configured to compress a refrigerant;
• an HVAC module including an internal condenser and an evaporator connected to the compressor through a refrigerant line, and an opening/closing door configured to adjust air having passed through the evaporator to be selectively introduced into the internal condenser based on cooling or heating of a vehicle interior;
• a heat-exchanger connected to the internal condenser through the refrigerant line, the heat exchanger configured to condense or evaporate the refrigerant by exchanging heat between the refrigerant and air;
• a first expansion valve provided on the refrigerant line between the heat-exchanger and the evaporator;
• a first connection line disposed between the compressor and the evaporator, the first connection line having a first end connected to the refrigerant line and a second end connected to the refrigerant line between the heat-exchanger and the first expansion valve;
• a chiller provided on the first connection line, the chiller configured to exchange heat between the refrigerant introduced through the first connection line and a coolant to adjust a temperature of the coolant;
• a second expansion valve provided on the first connection line at an upstream end of the chiller;
• a gas injection device connected to the refrigerant line between the internal condenser and the heat-exchanger, the gas injection device configured to selectively expand the refrigerant supplied from the internal condenser or the heat-exchanger and flow the refrigerant expanded by the gas injection device and selectively supply a partial refrigerant among the refrigerant supplied to the gas injection device to the compressor to increase a flow rate of the refrigerant circulating through the refrigerant line;
• a second connection line having a first end connected to the refrigerant line between the heat-exchanger and the first expansion valve and a second end connected to the gas injection device;
• a third connection line having a first end connected to the second expansion valve and a second end connected to the refrigerant line between the evaporator and the compressor;
• and
• a fourth connection line having a first end connected to the refrigerant line between the heat-exchanger and the first end of the second connection line and a second end connected to the gas injection device.