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;
• a heating, ventilation, and air conditioning (HVAC) module internally provided with an internal condenser, an evaporator connected to the compressor via a refrigerant line, and an opening/closing door configured to adjust ambient air having passed through the evaporator to selectively flow into the internal condenser based on a cooling or heating mode of a vehicle interior;
• a heat-exchanger connected to the internal condenser via the refrigerant line, and configured to condense or evaporate the refrigerant by exchanging heat between the refrigerant supplied from the internal condenser and air;
• a first expansion valve connected to the heat-exchanger via the refrigerant line;
• a 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 refrigerant line between the heat-exchanger and the evaporator;
• a chiller provided on the connection line, and configured to adjust a temperature of a coolant by exchanging heat between the refrigerant introduced into the connection line and a coolant that is selectively introduced;
• a second expansion valve provided on the connection line at an upstream end of the chiller;
• and
• 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 and flow the refrigerant supplied from the internal condenser, to selectively supply a partial refrigerant among the supplied refrigerant to the compressor, and to increase a flow amount of the refrigerant circulating the refrigerant line,
• wherein a flow of the refrigerant is controlled based on at least one mode for a temperature adjustment of the vehicle interior.