HEAT PUMP SYSTEM FOR A VEHICLE

A heat pump system for a vehicle capable of improving cooling and heating performance by applying a gas injection device selectively operating in an air conditioning mode of the vehicle interior to increase the flow rate of the refrigerant is disclosed. The heat pump system includes a compressor, a condenser, a first expansion valve, an evaporator, a first connection line, a chiller, a second expansion valve, a sub-heat-exchanger, and a gas injection device, wherein, depending on at least one mode 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.