Method for controlling an air conditioning system of an electrified vehicle

Abstract

Method for controlling an air conditioning system (56) of an electrified vehicle (12), wherein the air conditioning system (56) includes a heat pump subsystem (66) designed to circulate a refrigerant, wherein the heat pump subsystem (66) includes a front evaporator (110), a rear evaporator (118), and an expansion valve (86), wherein the method comprises blocking the refrigerant flow to a rear part of the heat pump subsystem (66) in response to a defrosting request, wherein the rear part includes the rear evaporator (118) of the heat pump subsystem (66), wherein the expansion valve (86) is adapted to block the flow of refrigerant to the rear evaporator (118) in response to the defrosting request, wherein the defrosting request causes the heat pump subsystem (66) to operate in a dehumidification mode.to defrost a windshield or other window of the vehicle (12), characterized in that the control step of blocking the refrigerant flow is carried out if the electrified vehicle (12) is currently operating in an EV mode in which a motor (22), i.e. an electric machine, is used for vehicle propulsion.

Description

FIELD OF TECHNOLOGYThis disclosure relates to methods and systems for maximizing defrost functionality of an electrified vehicle equipped with an air conditioning system employing dual evaporators and dual heat exchanger blocks. During certain conditions, the climate control system may be controlled by disabling refrigerant flow to a portion of a heat pump subsystem in response to a defrost request.GENERAL STATE OF THE ARTElectrified vehicles, such as hybrid electric vehicles (HEVs), externally rechargeable hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), or fuel cell vehicles, are distinct from conventional motor vehicles because they are powered by electric machines (i.e., electric motors and / or electric generators) instead of or except by an internal combustion engine. High voltage power for driving these types of electric machines is typically supplied from one or more high voltage battery assemblies.Some electrified vehicles are equipped with an air conditioning system that employs a heat pump subsystem to warm, cool, and / or de-wet a passenger compartment. For example, the heat pump subsystem may be operated in a heating mode in which the passenger compartment is heated, a cooling mode in which the passenger compartment is cooled, and a dehumidifying mode in which a vehicle windshield defrosting function is supported. It is desirable that the operation of the air conditioning system be improved during certain conditions.DE 103 48 578 A1 relates to an air conditioning system for a vehicle, which comprises a front air conditioning unit for air conditioning a front region of a passenger compartment and a rear air conditioning unit for air conditioning a rear region of the passenger compartment. The front air conditioning unit allows outside air to be introduced to remove mist from a window.SUMMARY OF THE INVENTIONProceeding from this prior art, a method having the features of independent claim 1 is provided. Advantageous embodiments can be found in the dependent claims.A method according to an exemplary aspect of the present disclosure includes, among other things, controlling an air conditioning system of an electrified vehicle by blocking refrigerant flow to a rear of a heat pump subsystem in response to a defrost request.The controlling step of the above method is performed if the electrified vehicle is currently operating in the EV mode.Alternatively or additionally, the control step is performed if a fuel level of the electrified vehicle is below a predetermined threshold.The above method includes closing an expansion valve to block refrigerant flow to the rear.The rear portion includes a rear evaporator of the heat pump subsystem.In another non-exclusive embodiment of any of the above methods, the method includes disabling coolant flow to a portion of a coolant subsystem in response to the defrost request.In another non-exclusive embodiment of any of the above methods, the method includes closing a valve to block coolant flow to the part. The part includes a rear heat exchange block of the coolant subsystem.In another non-exclusive embodiment of any of the above methods, the method includes disabling a blower of a rear housing of a ventilation subsystem in response to the defrost request.In another non-exclusive embodiment of any of the above methods, the controlling step includes instructing operation of the heat pump subsystem in the dehumidifying mode in response to the defrosting request if the electrified vehicle is currently operating in the EV mode and a fuel level of the electrified vehicle is below a predetermined threshold.In another non-exclusive embodiment of any of the above methods, the heat pump subsystem is a dual evaporator / dual heat exchanger block vapor compression heat pump system.A method according to another exemplary aspect of the present disclosure not encompassed by the invention includes, among other things, operating a heat pump subsystem of an air conditioning system of an electrified vehicle in a dehumidifying mode and blocking refrigerant flow to an evaporator of the heat pump subsystem if a defrost request has been made.In another non-exclusive embodiment of the above methods, the operating step and the disabling step are performed if the electrified vehicle is currently operating in the EV mode and a fuel level of the electrified vehicle is below a predetermined threshold.In another non-exclusive embodiment of either of the above methods, the heat pump subsystem is a dual evaporator / dual heat exchanger block vapor compression heat pump system.In another non-exclusive embodiment of any of the above methods, the method includes actuating an expansion valve to block refrigerant flow.In another non-exclusive embodiment of any of the above methods, the method includes blocking coolant flow to a heat exchanger block of a coolant subsystem of the climate control system and / or disabling a blower of a ventilation subsystem of the climate control system.An air conditioning system not encompassed by the invention includes, among other things, a heat pump subsystem configured to circulate a refrigerant. The heat pump subsystem includes a front evaporator, a rear evaporator, and an expansion valve adapted to inhibit the flow of refrigerant to the rear evaporator in response to a defrost request.In another non-exclusive embodiment of the above system, a controller is configured to control operation of the expansion valve.In another non-exclusive embodiment of either of the above systems, a coolant subsystem is configured to circulate coolant for cooling an engine. The coolant subsystem includes a front heat exchanger block, a rear heat exchanger block, and a valve adapted to block the flow of coolant to the rear heat exchanger block in response to the defrost request.In another non-exclusive embodiment of any of the above systems, an intermediate heat exchanger is adapted to provide heat transfer between the refrigerant and the coolant.In another non-exclusive embodiment of any of the above systems, a ventilation subsystem includes a front housing that houses the front evaporator and a rear housing that houses the rear evaporator.The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be used independently or in any combination. Features described in connection with an embodiment are applicable to all embodiments unless such features are incompatible therewith.The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings attached to the detailed description are briefly described as follows.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 schematically illustrates the powertrain of an electrified vehicle. FIG. 2 schematically illustrates an air conditioning system of an electrified vehicle. FIG. 3 schematically illustrates a control strategy for controlling an air conditioning system of an electrified vehicle.DETAILED DESCRIPTIONThis disclosure relates to improving defrost functionality of an electrified vehicle equipped with an air conditioning system employing dual evaporators and dual heat exchanger blocks. The air conditioning system may be controlled by disabling refrigerant flow to a portion of a heat pump system and / or a portion of a coolant subsystem in response to a defrost request. In some embodiments, the defrost operation is maximized in situations where the electrified vehicle is currently operating in the EV mode, the fuel level is below a predetermined threshold, and a defrost request has been made. These and other features are discussed in more detail in the paragraphs that follow.FIG. 1 schematically illustrates a powertrain 10 of an electrified vehicle 12 Although depicted as PHEVs in this embodiment, it should be understood that the concepts described herein are not limited to PHEVs and could also extend to other electrified vehicles such as, but not limited to, HEVs and BEVs.In one embodiment, the powertrain 10 is a motive force distribution system employing a first traction drive system and a second traction drive system. The first traction drive system includes a combination of an engine 14 and a generator 18 (i.e., a first electric machine). The second drive system includes at least one motor 22 (i.e., a second electric machine), the generator 18, and a battery assembly 24. The first and second traction drive systems generate torque to drive one or more sets of vehicle traction drive wheels 28 of the electrified vehicle 12.The engine 14, which may be an internal combustion engine, and the generator 18 may be connected by a power transfer unit 30, such as a planetary gear set. Of course, power transfer units of other types, including other gear sets and transmissions, may also be used to connect the engine 14 to the generator 18. In a non-limiting embodiment, the power transfer unit 30 is a planetary gear set that includes a ring gear 32, a sun gear 34, and a carrier assembly 36.The generator 18 may be driven by the engine 14 through the power transfer unit 30 to convert kinetic energy into electrical energy. The generator 18 may alternatively function as a motor for converting electrical energy to kinetic energy, thereby outputting torque to a shaft 38 connected to the power transfer unit 30. Because the generator 18 is operatively connected to the engine 14, the speed of the engine 14 may be controlled by the generator 18.The ring gear 32 of the power transfer unit 30 may be connected to a shaft 40 that is connected to the vehicle drive wheels 28 through a second power transfer unit 44. The second power transmission unit 44 may include a wheel set having a plurality of wheels 46. Other power transmission units may also be suitable. The wheels 46 transmit torque from the engine 14 to a differential 48 to provide traction to the vehicle traction drive wheels 28. The differential 48 may include a plurality of wheels that enable torque to be transmitted to the vehicle traction drive wheels 28. In one embodiment, the second power transfer unit 44 is mechanically coupled to an axle 50 through the differential 48 to distribute torque to the vehicle drive wheels 28.The motor 22 may also be used to drive the vehicle drive wheels 28 by delivering torque to a shaft 52, which is also connected to the second power transfer unit 44. In one embodiment, the engine 22 and the generator 18 cooperate as components of a regenerative braking system in which both the engine 22 and the generator 18 may be employed as motors for delivering torque. For example, the motor 22 and the generator 18 may each output electrical power to the battery assembly 24.The battery assembly 24 is an example type of battery assembly of an electrified vehicle. The battery assembly 24 may include a high voltage battery pack capable of outputting electrical power to operate the motor 22 and the generator 18. Energy storage devices and / or output devices of other types may also be utilized to electrically propel the electrified vehicle 12.In a non-exclusive PHEV embodiment of the electrified vehicle 12, the battery assembly 24 may be recharged or partially recharged using a charging adapter 54 connected to a charging station powered by an external power source such as a power grid, solar panel, or the like.In a non-limiting embodiment, the electrified vehicle 12 has two basic operating modes. The electrified vehicle 12 may be operated in an electric vehicle (EV) mode in which the motor 22 (generally without the assistance of the engine 14) is utilized for vehicle propulsion, thereby reducing the state of charge of the battery assembly 24 to its maximum allowable discharge rate during certain drive pattern / cycles. The EV mode is an example of a charge-reduction mode of operation for the electrified vehicle 12. During the EV mode, the state of charge of the battery assembly 24 may increase in some circumstances, for example, due to a period of regenerative braking. The engine 14 generally may not be operated during a default EV mode, but could be operated based on a vehicle system state, if necessary, or permitted by the operator.The electrified vehicle 12 may additionally operate in a hybrid (HEV) mode in which both the engine 14 and the motor 22 are used for vehicle propulsion. The HEV mode is an example of a charge sustaining mode of operation for the electrified vehicle 12. During the HEV mode, the electrified vehicle 12 may make less use of propulsion by the motor 22 to maintain the state of charge of the battery assembly 24 at a constant or approximately constant level by making more use of propulsion by the engine 14. The electrified vehicle 12 may be operated in other modes of operation besides EV and HEV modes.FIG. 2 illustrates an air conditioning system 56 of an electrified vehicle, such as the electrified vehicle 12 of FIG. 1. In FIG. 2, devices and fluidic passages or conduits are shown by solid lines, and electrical connections are shown as dashed lines.In one embodiment, the electrified vehicle 12 includes a passenger compartment 58, an engine compartment 60, and the climate control system 56. A portion of the climate control system 56 may be housed within the passenger compartment 58.The engine compartment 60 is positioned proximate the passenger compartment 58. One or more power sources, such as an internal combustion engine 14, as well as a portion of the air conditioning system 56 may be housed within the engine compartment 60. The engine compartment 60 may be separated from the passenger compartment 58 via a bulkhead 62. The climate control system 56 may circulate air and / or regulate or alter the temperature of air circulated in the passenger compartment 58. The internal combustion engine 14 may also be thermally controlled by the air conditioning system 56 to reduce fuel consumption and emissions.The climate control system 56 may include a coolant subsystem 64, a heat pump subsystem 66, and a ventilation subsystem 68. Each of these systems will be described in detail below.The coolant subsystem 64, or coolant circuit, may circulate a coolant, such as glycol, to cool the engine 14. For example, waste heat generated by the engine 14 when the engine is operating may be transferred to the coolant and then circulated to a radiator 70 to cool the engine 14. In one embodiment, the coolant subsystem 64 includes a coolant pump 72, an intermediate heat exchanger 74, a front heat exchanger block 76, a rear heat exchanger block 78, and a bypass circuit 80 that may have fluidic interconnections through conduits or passageways such as pipes, hoses, conduit tubes, and / or the like. The radiator 70 transfers thermal energy from the coolant to the ambient air surrounding the electrified vehicle 12.The coolant subsystem 64 may additionally include valves 82, 84, and 86 for selectively adjusting the flow of coolant through the engine 14, the radiator 70, the intermediate heat exchanger 74, the front heat exchanger block 76, and / or the rear heat exchanger block 78. In one embodiment, valves 82, 84, and 86 are electrically operated valves that are selectively actuated via a controller 88. Alternatively, other types of valves may be used within the coolant subsystem 64.In operation, the coolant pump 72 circulates coolant through the coolant subsystem 64. The coolant pump 72 may be powered from electrical or non-electrical power sources. For example, the coolant pump 72 could be operatively coupled to the engine 14 or could be driven by an electric motor. The coolant pump 72 receives coolant from the engine 14 and circulates the coolant in a closed loop. For example, while the climate control system 56 is operating in a heating mode, coolant may be routed from the coolant pump 72 to the intermediate heat exchanger 74, thereby bypassing the radiator 70, and then routed to the front heat exchanger block 76 and / or the rear heat exchanger block 78 before returning to the engine 14. While the engine 14 is releasing thermal energy at relatively high levels, coolant may flow from the coolant pump 72 to the radiator 70 before returning to the engine 14 via the intermediate heat exchanger 74 and the front heat exchanger block 76 and / or the rear heat exchanger block 78. The valve 84 directs the coolant from the coolant pump 72 to the valve 82, either through the radiator 70 or around the radiator 70. the coolant may flow through or around the engine 14 based on the position of the valve 82.The intermediate heat exchanger 74 may mediate the transfer of thermal energy between the coolant subsystem 64 and the heat pump subsystem 66. Heat may be transferred from, for example, heat pump subsystem 66 to coolant subsystem 64, or vice versa. In one embodiment, the intermediate heat exchanger 74 is housed therein as part of both the coolant subsystem 64 and the heat pump subsystem 66. The intermediate heat exchanger 74 may include any suitable configuration. The intermediate heat exchanger 74 may have, for example, a fin plate, fin tube, or tube bundle configuration that mediates the transfer of thermal energy between the heat pump subsystem 66 and the coolant subsystem 64 without mixing or exchanging the heat transfer fluids of these systems.Under some conditions, the front heat exchanger block 76 and the rear heat exchanger block 78 may transfer thermal energy from the engine coolant to air in the passenger compartment 58. The front heat exchanger block 76 and the rear heat exchanger block 78 are located at different locations within the passenger compartment 58 in different sections of the ventilation subsystem 68, and could be any suitable configuration. In one embodiment, the front heat exchanger block 76 and the rear heat exchanger block 78 are configured as fin plate or finned tube heat exchangers. However, other heat exchanger block configurations are contemplated that are within the scope of this disclosure.The bypass circuit 80 guides the coolant so as not to be heated by the engine 14. The valve 82 may regulate the flow of the coolant through the bypass circuit 80. For example, when the valve 82 is in a first position, it may prevent the coolant from flowing through a bypass 90, and may inhibit the flow of coolant from the engine 14 to the intermediate heat exchanger 74. In such a position, a second coolant pump 92 may circulate the coolant through the bypass circuit 80 from the intermediate heat exchanger 74 to the front heat exchanger block 76 and the rear heat exchanger block 78, then to the bypass 90, and back to the second coolant pump 92. Accordingly, the coolant in the coolant subsystem 64 may be independently heated by the heat pump subsystem 66 via the intermediate heat exchanger 74. The valve 82 may also regulate the flow of coolant through the bypass 90 when positioned in a second position. The second coolant pump 92 may or may not circulate the coolant when the coolant is not flowing through the bypass 90.The heat pump subsystem 66, or refrigerant circuit, may circulate a refrigerant to transfer thermal energy into or out of the passenger compartment 58 and into or out of the coolant subsystem 64. In one embodiment, the heat pump subsystem 66 is configured as a dual evaporator / dual heat exchanger block vapor compression heat pump system in which a fluid, such as a refrigerant, is circulated through the heat pump subsystem 66 to transfer thermal energy into or out of the passenger compartment 58.The heat pump subsystem 66 is operable in various modes including a cooling mode, a heating mode, and a dehumidifying mode. In the cooling mode, the heat pump subsystem 66 may circulate a refrigerant to transfer thermal energy from the interior of the passenger compartment 58 to the exterior of the passenger compartment 58. In a heating mode, the heat pump subsystem 66 may transfer thermal energy from the refrigerant to the coolant of the coolant subsystem 64 via the intermediate heat exchanger 74 without circulating the refrigerant through any heat exchanger located in the passenger compartment 58. In a dehumidifying mode, the heat pump subsystem 66 may be operated to remove moisture from the passenger compartment 58 and provide heat to the coolant subsystem 64 via the intermediate heat exchanger 74, for example, to defrost a windshield of the electrified vehicle 12.In one embodiment, the heat pump subsystem 66 includes a compressor 94, the intermediate heat exchanger 74, a first expander 98, a solenoid 99, an outdoor heat exchanger 100, a 3-way valve 102, a receiver 106, a second expander 108, a front evaporator 110, a third expander 116, and a rear evaporator 118. The components of the heat pump subsystem 66 may be in fluidic communication via one or more conduits such as tubes, hoses, or the like.The compressor 94 pressurizes and circulates the refrigerant through the heat pump subsystem 66. The compressor 94 may be powered from an electrical or non-electrical power source. For example, the compressor 94 may be operatively coupled to the engine 14 or driven by an electric motor. In the heating mode of the climate control system 56, the compressor 94 directs the high pressure refrigerant to the intermediate heat exchanger 74, which in turn can transfer heat from the high pressure refrigerant to the coolant passing through the intermediate heat exchanger 74 to heat the coolant of the coolant subsystem 64.The first expansion member 98 is positioned between the intermediate heat exchanger 74 and the exterior heat exchanger 100 and is in fluid communication with these two heat exchangers. The first expansion member 98 is adapted to change the pressure of the refrigerant of the heat pump subsystem 66. The first expansion member 98 may be, for example, an electronic expansion valve, a thermostatic expansion valve (TXV), or a constant area valve, such as a capillary tube, which may or may not be externally controlled. The first expansion member 98 may reduce the pressure of the refrigerant passing from the intermediate heat exchanger 74 through the first expansion member 98 to the outdoor heat exchanger 100. Therefore, a high pressure refrigerant received from the intermediate heat exchanger 74 can exit the first expansion member 98 in the lower pressure heating mode and as a mixture of liquid and vapor.The solenoid 99 may be positioned in a bypass 122 that allows a portion of the refrigerant to bypass the first expansion member 98. The solenoid 99 may be opened during the cooling mode and closed during the heating mode. When open, refrigerant flow is directed largely through solenoid 99 because it provides the path with the least resistance. When the solenoid 99 is closed, all refrigerant flow is directed through the first expansion member 98 to measure refrigerant flow into the outdoor heat exchanger 100.The exterior heat exchanger 100 may be positioned within the engine compartment 60. In the cooling mode or in the context of air conditioning, the exterior heat exchanger 100 may function as a condenser to transfer heat to the surrounding environment by condensing the refrigerant from vapor to liquid. In the heating mode, the outdoor heat exchanger 100 may function as an evaporator to transfer heat from the surrounding environment to the refrigerant, thereby causing the refrigerant to evaporate.The 3-way valve 102 may be positioned between the exterior heat exchanger 100 and both the header 106 and the evaporator 110. The 3-way valve 102 may regulate the flow of the refrigerant exiting the exterior heat exchanger 100. In the heating mode, the 3-way valve 102 is actuated to allow the refrigerant to flow from the outdoor heat exchanger 100 along a bypass 104 to the accumulator 106, bypassing the flow through the evaporator 110. The 3-way valve 102 may alternatively be positioned such that the refrigerant may flow along a conduit 112 to the evaporator 110, such as during the cooling mode.The accumulator 106 serves as a reservoir for storing residual liquid refrigerant, so that a vapor refrigerant is provided to the compressor 94 instead of a liquid refrigerant. The accumulator 106 includes a desiccant that absorbs relatively small amounts of water moisture from the refrigerant.The second expansion member 108 may be positioned between and in fluid communication with the exterior heat exchanger 100 and the front evaporator 110. The third expansion member 116 may be positioned between and in fluid communication with the exterior heat exchanger 100 and the rear evaporator 118. The second expansion member 108 and the third expansion member 116 may have a structure as similar to the first expansion member 98, and are configured to change the pressure of the refrigerant as similar to the first expansion member 98. In one embodiment, the second expansion member 108 is closed to inhibit the flow of refrigerant from the exterior heat exchanger 100 to the front evaporator 110 in the heating mode. The third expansion member 116 may also be closed to inhibit the flow of refrigerant through the rear evaporator 118 during certain conditions.The front evaporator 110 is fluidically connected to the second expansion element 108. The front evaporator 110 may be positioned within the passenger compartment 58. In the cooling mode, the front evaporator 110 receives heat from the air in the passenger compartment 58 to evaporate the refrigerant. The refrigerant discharged from the front evaporator 110 is guided to the receiver 106. In the heating mode, the 3-way valve 102 supplies the refrigerant to the accumulator 106, bypassing the front evaporator 110.The rear evaporator 118 may be positioned within the passenger compartment 58, such as relative to a third row of seats of the electrified vehicle 12. In the cooling mode, the rear evaporator 118 receives heat from the air in the passenger compartment 58 to evaporate the refrigerant. The refrigerant discharged from the rear evaporator 118 is guided to the receiver 106. In the heating mode, the refrigerant is not routed to the rear evaporator 118 because the third expansion element 116 is closed.The ventilation subsystem 68 may circulate air within the passenger compartment 58. In one embodiment, the ventilation subsystem 68 includes a front housing 124 and a rear housing 126. For example, the front housing 124 may be positioned below a dashboard of the electrified vehicle 12 to circulate air in front portions of the passenger compartment 58, while the rear housing 126 may be positioned relative to a third row of seats of the electrified vehicle 12 to circulate air in rear portions of the passenger compartment 58.The front housing 124 of the ventilation subsystem 68 may house a blower 128 and a temperature door 130. An air inlet portion 132 may receive air 134 from the exterior of the electrified vehicle 12 and / or air from the interior of the passenger compartment 58. For example, the air inlet portion 132 may receive ambient air from the exterior of the electrified vehicle 12 via an inlet passage, an inlet passage, or an inlet opening located at any suitable location, such as near a cowl, wheel well, or other vehicle body portion. The air inlet portion 132 may also receive air from within the passenger compartment 58 and recirculate that air through the ventilation subsystem 68. One or more flaps or one or more air slots may also be provided to allow or inhibit air circulations.The blower 128, also called a pressure fan, is positioned proximate the air inlet portion 132 and may be configured as a centrifugal fan that circulates air through the front housing 124 of the ventilation subsystem 68.In one embodiment, the temperature door 130 is positioned between the front evaporator 110 and the front heat exchanger block 76, and may be positioned downstream of the front evaporator 110 and upstream of the front heat exchanger block 76. The temperature door 130 blocks or allows the flow of air 134 through the front heat exchanger block 76, which is conducive to controlling the temperature of air in the passenger compartment 58. For example, the temperature door 130 may allow air flows through the front heat exchanger block 76 in the heating mode such that heat from the coolant may be transferred to air passing through the front heat exchanger block 76. This heated air may then be provided to an air chamber for distribution to ducts and vents or outlets located in the passenger compartment 58. The temperature door 130 may be moved between a plurality of positions to provide air at a desired temperature. In the embodiment of FIG. 2, the temperature door 130 is shown in a maximum heating position in which the flow of air 134 is directed through the front heat exchanger block 76.The rear housing 126 may also house a blower 136 and a temperature door 138. An air inlet portion 140 may receive air 142 from within the passenger compartment 58. One or more flaps or one or more air slots may also be provided to allow or inhibit circulations of the air 142. The blower 136 circulates the air 142 through the rear housing 126 of the ventilation subsystem 68. The temperature door 138 blocks or allows the flow of air 142 through the rear heat exchanger block 78, which is conducive to controlling the temperature of air in the passenger compartment 58.The climate control system 56 may additionally be operated in a dehumidification mode to remove moisture from the passenger compartment 58. By operating the climate control system 56, and more specifically the heat pump subsystem 66, in the dehumidification mode, windshield defrosting functions of the electrified vehicle 12 are supported in the dehumidification mode. Under normal operating conditions, the heat pump subsystem 66 is operated in the dehumidification mode in which the exterior heat exchanger 100, the front evaporator 110, and the rear evaporator 118 receive the refrigerant. In the dehumidifying mode, the first expansion element 98 is opened, the solenoid valve 99 is closed, and the second expansion element 108 and the third expansion element 116 are opened.The controller 88 may be a component of a higher level vehicle control unit, such as a vehicle system controller (VSC), or alternatively could be a stand-alone control unit separate from the VSC. In one embodiment, the controller 88 includes executable instructions to interface with and operate the various components of the climate control system 56. The controller 88 may include inputs 144 and outputs 146 to interface with the various components of the climate control system 56. The controller 88 may also include a main processor 148 and a non-volatile memory device 150 for executing the various control strategies and modes of the climate control system 56.FIG. 3 schematically illustrates, with continued reference to FIGS. 1 and 2, a control strategy 200 for controlling the operation of the climate control system 56 of the electrified vehicle 12. Of course, the electrified vehicle 12 is capable of implementing and executing still other strategies within the scope of this disclosure. In one embodiment, the controller 88 of the climate control system 56 is programmed with one or more algorithms adapted to execute the control strategy 200 or any other control strategies. In other words, the control strategy 200 can be stored in the form of executable commands in the nonvolatile memory module 150 of the controller 88.As shown in FIG. 3, the control strategy 200 may begin at block 202 in response to a defrost request. An occupant may make a defrost request by pressing a button, button, or other input member for defrost on an air conditioning dashboard that is located within the passenger compartment 58 and in electrical communication with the controller 88. A defrost request indicates to the controller 88 that the heat pump subsystem 66 is to be operated in the dehumidification mode (either in series or in parallel) to defrost a windshield or other window of the electrified vehicle 12.The control strategy 200 activates a series of system checks before the dehumidification mode is activated. For example, at block 204, the control strategy 200 may determine whether the electrified vehicle 12 is operating in the EV mode. If the electrified vehicle 12 is not currently operating in the EV mode, the control strategy ends at block 206. However, if it is determined that the electrified vehicle 12 is operating in the EV mode, the control strategy 200 may proceed to block 208.At block 208, the control strategy 200 may determine whether the fuel level of the engine 14 is below a predetermined threshold. For example, a fuel tank that holds fuel for driving the engine 14 may include a sensor for determining the amount of fuel held by the tank. In one embodiment, the fuel level sensed by the sensor may be compared to a fuel level threshold stored in the controller 88. The control strategy 200 ends at block 206 if it is determined that the fuel level is not below the predetermined threshold.The control strategy 200 may proceed to block 210 if the fuel level is below a predetermined threshold. Refrigerant flow to the rear evaporator 118 of the heat pump subsystem 66 may be blocked at block 210. In one embodiment, the third expansion device 116 is actuated (i.e., closed) to block refrigerant flow through the rear evaporator 118.Optionally, coolant flow to the rear heat exchanger block 78 of the coolant subsystem 64 may be blocked at block 212 if the electrified vehicle 12 is operating in the EV mode and has a fuel level below a predetermined threshold. In one embodiment, coolant flow to the rear heat exchanger block 78 is blocked by closing the valve 86. The blower 136 of the rear housing 126 of the ventilation subsystem 68 may also optionally be shut down in response to a defrost request, an EV mode operation, and a fuel level below a predetermined threshold at block 214.Finally, at block 216, the control strategy 200 may instruct to operate the climate control system 56 in the dehumidification mode. By operating the climate control system 56 in the dehumidification mode after the third expansion element 116 and / or the valve 86 have been closed in response to a defrost request, the defrost function of the electrified vehicle 12 may be maximized even during conditions where its operation may not otherwise be optimal.While the various non-exclusive embodiments are illustrated with specific components or steps, the embodiments of this disclosure are not limited to these specific combinations. It is possible to use some of the components or features from any of the non-exclusive embodiments in combination with features or components from any of the other non-exclusive embodiments.It should be understood that like reference numerals identify corresponding or similar elements throughout the various drawings. It should be understood that while a particular component arrangement is disclosed and illustrated in these embodiments, the teachings of this disclosure could be advantageous for other arrangements as well.The above description is to be interpreted as exemplary and not in a limiting sense. Those of ordinary skill in the art would understand that some changes could fall within the scope of this disclosure. For these reasons, the following claims are intended to be used to determine the scope and content of this disclosure.

Claims

A method of controlling an air conditioning system (56) of an electrified vehicle (12), • the air conditioning system (56) including a heat pump subsystem (66) provided for circulating a refrigerant, • the heat pump subsystem (66) including a front evaporator (110), a rear evaporator (118), and an expansion valve (86), • the method comprising disabling refrigerant flow to a rear portion of the heat pump subsystem (66) in response to a defrost request, • the rear portion including the rear evaporator (118) of the heat pump subsystem (66), • the expansion valve (86) being adapted to disable the flow of the refrigerant to the rear evaporator (118) in response to the defrost request, • the defrost request causing, the heat pump subsystem (66) being operated in a dehumidifying mode to defrost a windshield or other window of the vehicle (12), characterized in that the controlling step of blocking refrigerant flow is performed if the electrified vehicle (12) is being operated in an EV mode in which an engine (22), i.e. an electric machine, is being used for vehicle propulsion.Method according to Claim 1, characterized in that the control step is carried out if a fuel level of the electrified vehicle (12) is below a predefined threshold.The method of claim 1, characterized in that it comprises disabling coolant flow to a portion of a coolant subsystem (64) in response to the defrost request.The method of claim 3, characterized in that it comprises closing a valve (86) to block coolant flow to the part, the part including a rear heat exchange block (78) of the coolant subsystem (64).The method of claim 1, characterized in that it comprises shutting down a blower (136) of a rear housing (126) of a ventilation subsystem (68) in response to the defrost request.The method of claim 1, wherein the heat pump subsystem (66) is a dual evaporator / dual heat exchanger block vapor compression heat pump system.

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