Heat pump system for vehicle and method of controlling the same

Abstract

Disclosed therein are a heat pump system for a vehicle and a method of controlling the heat pump system, which determines that frosting begins on an exterior heat exchanger and carries out a defrosting control if a difference value between outdoor temperature and refrigerant temperature of an outlet side of the exterior heat exchanger is above a frosting decision temperature in a heat pump mode, thereby increasing frost-prevention and defrosting effects and enhancing heating performance and stability of the system because the system recognizes the beginning of frosting on the exterior heat exchanger at a proper time so as to carry out the defrosting control.

What is claimed is: 
     
         1 . A heat pump system for a vehicle comprising:
 a compressor mounted on a refrigerant circulation line for compressing and discharging refrigerant;   an interior heat exchanger mounted inside an air-conditioning case for exchanging heat between the air inside the air-conditioning case and the refrigerant discharged from the compressor;   an evaporator mounted inside the air-conditioning case for exchanging heat between the air inside the air-conditioning case and the refrigerant supplied to the compressor;   an exterior heat exchanger mounted outside the air-conditioning case for exchanging heat between the refrigerant circulating through the refrigerant circulation line and the outdoor air;   first expansion means mounted on the refrigerant circulation line of an inlet side of the evaporator for expanding refrigerant;   second expansion means mounted on the refrigerant circulation line located between the interior heat exchanger and the exterior heat exchanger for expanding refrigerant; and   a controlling part for controlling the heat pump system to defrost after determining that frosting is formed on the external heat exchanger if a difference value between outdoor temperature and refrigerant temperature of an outlet side of the exterior heat exchanger is above a frosting decision temperature in a heat pump mode.   
     
     
         2 . The heat pump system according to  claim 1 , wherein the controlling part variably sets the frosting decision temperature by outdoor temperature and determines whether or not frosting is formed on the external heat exchanger. 
     
     
         3 . The heat pump system according to  claim 2 , wherein based on that the frosting decision temperature is 10° C. when the outdoor temperature is 0° C., the controlling part sets the frosting decision temperature to increase as the outdoor temperature becomes lower when the outdoor temperature is below 0° C., and sets the frosting decision temperature to increase as the outdoor temperature becomes higher when the outdoor temperature is above 0° C. and below 10° C. 
     
     
         4 . The heat pump system according to  claim 1 , further comprising:
 a first bypass line adapted to connect the refrigerant circulation line of an inlet side of the first expansion means and the refrigerant circulation line of an outlet side of the evaporator so that the refrigerant circulating through the refrigerant circulation line selectively bypasses the first expansion means and the evaporator; and   heat supplying means mounted on the first bypass line to supply waste heat of electronic units of the vehicle to the refrigerant flowing along the first bypass line,   wherein the controlling part additionally determines the waste heat of the electronic units supplied through the heat supplying means if the difference value is above the frosting decision temperature, and determines that frosting is formed on the external heat exchanger if the waste heat of the electronic units is below a reference value.   
     
     
         5 . The heat pump system according to  claim 1 , wherein the controlling part additionally determines refrigerant pressure of the inlet side of the external heat exchanger if the difference value is above the frosting decision temperature, and determines that frosting is formed on the external heat exchanger if the refrigerant pressure is below the reference value. 
     
     
         6 . The heat pump system according to  claim 1 , wherein the controlling part additionally determines a decrease range of a discharge air temperature of the interior of the vehicle if the difference value is above the frosting decision temperature, and determines that frosting is formed on the external heat exchanger if the decrease range is above the reference value. 
     
     
         7 . The heat pump system according to  claim 1 , wherein the frosting decision temperature is 10° C. 
     
     
         8 . The heat pump system according to  claim 1 , wherein the controlling part controls the system to increase refrigerant pressure and temperature of the system during a defrosting control. 
     
     
         9 . The heat pump system according to  claim 6 , wherein the reference value is 3° C. 
     
     
         10 . The heat pump system according to  claim 1 , further comprising:
 a first bypass line adapted to connect the refrigerant circulation line of an inlet side of the first expansion means and the refrigerant circulation line of an outlet side of the evaporator so that the refrigerant circulating through the refrigerant circulation line selectively bypasses the first expansion means and the evaporator; and   heat supplying means mounted on the first bypass line to supply waste heat of electronic units of the vehicle to the refrigerant flowing along the first bypass line,   wherein the heat supplying means comprises a water cooling type heat exchanger, the water cooling type heat exchanger including: a refrigerant heat-exchanging part in which the refrigerant flowing along the first bypass line flows; and a cooling water heat-exchanging part which is disposed at one side of the refrigerant heat-exchanging part in such a way as to heat-exchange and in which cooling water circulating through the electronic units of the vehicle flows.   
     
     
         11 . The heat pump system according to  claim 1 , wherein the waste heat of the electronic units is temperature of cooling water circulating through the electronic units. 
     
     
         12 . A method of controlling a heat pump system for a vehicle, comprising the steps of:
 (S 1 ) determining whether or not the heat pump system is in a heat pump mode;   as the determination result of the step (S 1 ), when the system is in the heat pump mode, (S 2 ) determining whether or not a difference value between outdoor temperature and refrigerant temperature of an outlet side of the exterior heat exchanger is above a frosting decision temperature; and   as the determination result of the step (S 2 ), when the difference value is above the frosting decision temperature, (S 4 ) controlling the heat pump system to defrost after determining that frosting is formed on an external heat exchanger.   
     
     
         13 . The controlling method according to  claim 12 , wherein when the heat pump system is in the heat pump mode, the frosting decision temperature is variably set by outdoor temperature. 
     
     
         14 . The controlling method according to  claim 13 , wherein based on that the frosting decision temperature is 10° C. when the outdoor temperature is 0° C., the heat pump system is set to increase the frosting decision temperature as the outdoor temperature becomes lower when the outdoor temperature is below 0° C., and to increase the frosting decision temperature as the outdoor temperature becomes higher when the outdoor temperature is above 0° C. and below 10° C. 
     
     
         15 . The controlling method according to  claim 12 , further comprising the step of additionally determining waste heat of electronic units of the vehicle when the difference value is above the frosting decision temperature, and as the determination result, if the waste heat of the electronic units is below the reference value, determining that frosting is formed on the external heat exchanger. 
     
     
         16 . The controlling method according to  claim 12 , further comprising the step of additionally determining refrigerant pressure of an inlet side of the external heat exchanger when the difference value is above the frosting decision temperature, and as the determination result, if the refrigerant pressure is below the reference value, determining that frosting is formed on the external heat exchanger. 
     
     
         17 . The controlling method according to  claim 12 , further comprising the step of additionally determining a decrease range of a discharge air temperature of the interior of the vehicle when the difference value is above the frosting decision temperature, and as the determination result, if the decrease range is above the reference value, determining that frosting is formed on the external heat exchanger. 
     
     
         18 . The controlling method according to  claim 12 , wherein the frosting decision temperature is 10° C. 
     
     
         19 . The controlling method according to  claim 12 , wherein the step of controlling the heat pump system to defrost is to control the heat pump system to increase the refrigerant pressure and temperature of the heat pump system. 
     
     
         20 . The controlling method according to  claim 15 , wherein the waste heat of the electronic units is temperature of cooling water circulating through the electronic units. 
     
     
         21 . The controlling method according to  claim 17 , wherein the reference value is 3° C. 
     
     
         22 . The controlling method according to  claim 12 , further comprising the step of determining whether or not defrosting of the external heat exchanger is finished after the step of controlling the heat pump system to defrost, when defrosting is finished, returning to the step of determining whether or not the heat pump system is in the heat pump mode.