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 condenser connected to the compressor through a refrigerant line, and configured to condense the refrigerant;
• a first expansion valve connected to the condenser through the refrigerant line;
• an evaporator connected to the first expansion valve through the refrigerant line, connected to the compressor through the refrigerant line, and configured to evaporate the refrigerant;
• a first connection line having a first end connected to the refrigerant line between the condenser and the first expansion valve, and a second end connected to the refrigerant line between the compressor and the evaporator;
• a chiller provided on the first connection line, and configured to adjust a temperature of a coolant by heat-exchanging the refrigerant introduced through the first connection line with the coolant;
• a second expansion valve provided on the first connection line at an upstream end of the chiller;
• a sub-heat-exchanger provided on the refrigerant line between the condenser and the first expansion valve, and configured to condense or evaporate selectively introduced refrigerant;
• and
• a gas injection device provided on the refrigerant line between the sub-heat-exchanger and the first expansion valve, the gas injection device being configured to selectively expand the refrigerant supplied from one of the condenser or the sub-heat-exchanger and allow the refrigerant expanded by the gas injection device to flow, 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,
• wherein, based on at least one mode of the heat pump system for adjusting a temperature of a vehicle interior, the flow rate of the refrigerant is controlled through an operation control of the gas injection device.