SYSTEM AND METHOD FOR COOLING AIR CONDITIONING SYSTEM ELECTRONICS

Abstract

A system, method and apparatus for cooling the electronic components that regulate power and commutation of a refrigerant compressor motor in an air conditioning system. The electronic components are juxtaposed upon a heat sink provided with a refrigerant passageway. The heat sink is fluidly disposed in the refrigeration line between the evaporator assembly and compressor such that refrigerant returning from the evaporator assembly to the compressor of the air conditioning system travels directly to the heat sink and through the refrigerant passageway before reaching the compressor.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/197,212, filed on Oct. 24, 2008, which is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM ON COMPACT DISC

Not applicable.

FIELD OF INVENTION

This invention relates to systems and methods for cooling the control electronics for a refrigerant compressor drive motor of an aircraft vapor cycle air conditioning system.

BACKGROUND OF THE INVENTION

A prior art vapor cycle air conditioning system (“a/c system”) for controlling the environment of an aircraft comprises a refrigeration circuit including a condenser, evaporator assembly, expansion device and a motor-driven compressor for moving refrigerant through the refrigeration circuit. In its simplest form the evaporation assembly consists of one evaporator. However, present day a/c systems typically use several evaporators either in series or parallel arrangement. Hence, as used herein the term “evaporator assembly” refers to a heat exchanging device, system or arrangement that comprises one or more evaporators. The typical compressor motor is a brushed electric motor. However, recent advances in brushless motors have led to their incorporation in air conditioning and refrigeration systems. In contrast to brushed motors using mechanical commutation methods, brushless motors rely on electronics to effect commutation. Hence, in addition to the control circuitry required for conventional compressor motors, brushless motors also require circuitry for commutation.

Controlling and reducing the heat generated by a/c system compressor motor control circuitry is a known problem in the prior art. Accordingly, the additional commutation electronics required of brushless motors can exacerbate heat generated by the compressor control circuitry. In passenger transport vehicles like planes, the motor control electronics are typically contained in their own housing to protect the electronics from the elements. This housing inhibits cooling of the electronic components by retaining the heat generated by them.

The conventional method of cooling the motor control electronics of an a/c system is to mount the transistorized components upon a heat sink. The heat sink of the prior art system consists of a formed mass of material (typically metal) having good thermal conductivity. The heat sink is formed with an exaggerated surface area of fins or baffles to allow a maximum of air or cooling fluid to circulate over its surface either through convection or forced air means. In the case of aircraft applications, the air conditioning systems are required to operate continuously at ambient temperature of 158 degrees Fahrenheit. The high ambient requirement plus the heat generated from the electronic components will generate temperatures inside the controller that exceed the maximum safe operating temperature of some components which in some cases may be as low as 185 degrees Fahrenheit. Keeping the electronics below this maximum limit is difficult using the conventional method of using a heat sink with passive or forced air cooling due to size and weight limitations imposed by aircraft installations.

Alternatively, it is known in the prior art to fluidly connect the heat sink to a coolant to absorb heat from the heat sink and carry it out of the system. It has also been proposed to use the refrigerant of the a/c loop to cool the compressor motor control electronics. In this regard, U.S. Pat. No. 5,220,809 proposes shunting a portion of the system refrigerant between a chill block juxtaposed with the motor control module. The chill block together with the control module forms a cooling groove that operates like an evaporator. In this regard, the portion of refrigerant received by the cooling groove expands to a saturated vapor and extracts heat from the controller.

U.S. Pat. No. 6,116,040 discloses an apparatus and method for cooling the electronics of a variable frequency drive used to control the motor of a compressor in a refrigeration system. According to this patent, refrigerant is shunted from the condenser and out of the refrigeration loop, passed through a heat sink in heat transfer relation to the motor control electronics and then returned to the compressor either directly or through the evaporator. While in the shunt circuit, the refrigerant is expanded so as to cool the heat sink. The apparatuses disclosed in U.S. Pat. Nos. 6,116,040 and 5,220,809 have two drawbacks. First, they require shunting of the refrigerant from the condenser and away from the evaporator assembly and thus use only a portion of the refrigerant for electronics cooling. Second, by shunting refrigerant before the expansion phase, these systems rely on two phase cooling of the refrigerant and therefore require additional components and more complicated systems to achieve their objective.

U.S. Pat. No. 7,009,318 discloses an electronics cooling system for an automobile a/c compressor system comprising a compressor unitarily housed with a motor and the motor electronics. This patent is directed to attaching the motor control electrical circuitry to or within the cylindrical outer surface of the compressor motor housing and including a refrigerant passage through the housing. The refrigerant is flushed through the housing and past the electrical motor and then compressed by the compressor. The heat generated by the electrical components of the electrical circuit is transferred to the refrigerant passing through the motor. The system is limitedly useful for those motor vehicle a/c systems having unitarily housed compressors, motors and electronics. This system does not address the electronic cooling needs of environmental control systems such as used in aircraft a/c systems that have motor control electronics remotely housed from the motor and compressor. In addition, the cooling capacity of the refrigerant vis a vis the electronic components is lost upon the compressor, the motor and those portions of the housing remotely situated from the heat producing electronic components.

SUMMARY OF THE INVENTION

This invention seeks to solve the foregoing problems associated with the electronic cooling methods for prior art a/c systems. It is therefore an object of the present invention to provide refrigerant cooling to the control electronics of a motor driven refrigeration system compressor in a more simplified and economical manner than currently suggested by the prior art. The present invention can be more specifically directed to an improved system and method for cooling the compressor motor control electronics for an aircraft air conditioning system using a DC motor drive. The present invention is also directed to an improved aircraft air conditioning compressor drive module. The invention is also directed to a system, method and compressor drive module that provides cooling to both the power and control electronics for a brushless motor driving an a/c system compressor. The invention is further directed to a system, method and compressor drive module that uses cool refrigerant vapor directly from the evaporator assembly returning in the compressor suction line to cool a heat sink attached to the motor control electronics. The invention is further directed to a cooling system, method and compressor drive module that isolates the electronic controller components from the compressor drive heat.

The present invention comprises a refrigeration loop including a compressor, a condenser, an expansion device and an evaporator assembly connected by refrigerant lines. A brushless motor preferably drives the compressor. In such embodiment, motor operation is governed by both power and commutation electronic circuitry. This electronic circuitry includes heat producing power electronic components in the form of mosfets and other transistorized components that require cooling.

The motor control electronics are separately housed from the motor and compressor. Inside the housing, the electronic components are mounted to a circuit board. The circuit board is juxtaposed in heat transfer relation to a heat sink. The heat sink is provided with a refrigerant passageway, preferably an interior tunnel that has a refrigerant receiving end and a refrigerant discharge end. These ends are respectively attached to inlet and outlet ports on the motor control housing. The interior tunnel could include exaggerated surface area to allow for maximum cooling. The heat sink is preferably a formed block of material with high thermal transfer properties. The block acts as a heat sink to draw heat away from the motor control electronics. The cooling capabilities of the heat sink are enhanced however by intercepting the flow of refrigerant directly from the evaporator assembly and delivering it to the inlet port of the motor control housing. The refrigerant travels through the tunneled heat sink cooling the electronics mounted thereon and exits the motor control housing via the outlet port. The outlet port is fluidly connected to the compressor intake, and hence the electronic-cooling refrigerant is returned to the a/c loop via the compressor outlet.

In contrast to prior art systems, the present invention system and module delivers refrigerant directly from the evaporator assembly to a dedicated heat sink that is attached to or is otherwise in heat transfer relation with the motor control electronics. As such, it dispenses with the need to provide a separate flow circuit to pass refrigerant from the system condenser to the compressor control electronics. It also, dispenses with the need to provide phase changing devices in the form of heat sinks and expansion valves in the separate flow circuit. By delivering the refrigerant directly to a dedicated heat sink juxtaposed with the motor control electronics, the electronic component cooling capacity of the refrigerant is maximized and not lost on ancillary structures like the compressor, the compressor motor or remote housing surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an a/c system incorporating the present invention motor control cooling system and apparatus.

FIG. 2 is a perspective view of the exterior of the present invention motor control unit adapted to receive expanded refrigerant gas directly from the evaporator assembly of an a/c loop, pass that refrigerant through a housed heat sink and discharge that refrigerant to the suction port of the refrigeration loop compressor.

FIG. 3 is a perspective view of the motor control circuitry of the present invention motor control unit of FIG. 1 mounted in heat transfer relation to a heat sink adapted to directly receive expanded refrigerant gas from the evaporator assembly of an a/c loop and transmit it to the compressor.

FIG. 4 is an exploded perspective view of the interior of the present invention motor control unit of FIG. 1 showing the motor control circuitry and heat sink adapted to directly receive and transmit expanded refrigerant gas from the evaporator assembly of an a/c loop to the compressor.

FIG. 5 is a perspective view of an aircraft a/c compressor drive module incorporating the present invention motor control cooling system and apparatus.

FIG. 6 is an alternate perspective view of the aircraft a/c compressor drive module of FIG. 5.

FIG. 7 is an overhead plan view of the aircraft a/c compressor drive module of FIG. 5.

FIG. 8 is a bottom plan view of the aircraft a/c compressor drive module of FIG. 5.

FIG. 9 is a left side elevation view of the aircraft a/c compressor drive module of FIG. 5.

FIG. 10 is a right side elevation view of the aircraft a/c compressor drive module of FIG. 5.

FIG. 11 is a rear elevation view of the aircraft a/c compressor drive module of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 depicts an aircraft a/c system 10 comprising the system and method for cooling the electronic components for the controller of a compressor motor, which in the preferred embodiment is a brushless motor. System 10 constitutes a loop or circuit that includes refrigerant lines 12a, 12b, 12c, 12d and 12e. These lines fluidly connect the various system components. The system further includes conventional a/c loop components, whose function is well known in the art, such as condenser 13, compressor 15 and evaporator assembly 17. Line 12a connects discharge outlet 14 of compressor 15 to condenser 13. Refrigerant flows from condenser 13 to expansion device 20 via line 12b. Expansion device 20 expands high pressure refrigerant leaving condenser 13 to a lower temperature and pressure. The expansion devices known in the prior art include throttling valves or capillary tubes. After leaving expansion device 20 the refrigerant travels via line 12c to evaporator assembly 17, where the refrigerant undergoes a low pressure phase change from liquid to vapor via absorption of heat from the walls of evaporator coils that are in heat transfer relation to ambient air pushed past the evaporator coils by a blower 18. In the conventional prior art a/c system loop, refrigerant (in vapor phase) would leave evaporator assembly 17 and proceed directly via refrigerant line 12d to suction port 16 of compressor 15, thereby completing the system loop. Compressor 15 intakes the vapor refrigerant and recirculates it through the system via outlet port 14.

As shown in FIG. 1, in the present invention system, line 12d leaving evaporator assembly 17 does not directly lead to compressor 15. Instead, evaporator assembly 17 is fluidly connected by line 12d to compressor motor control unit 29, interposed between evaporator assembly 17 and compressor 15. Line 12e, in turn, connects motor control unit 29 to the suction inlet port 16 of compressor 15.

FIG. 2 shows a preferred embodiment motor control unit 29. Motor control unit 29 contains power and commutation electronic components that control the operation of a brushless DC compressor motor. These electronic components, typically mosfets or other transistors, are represented by reference numeral 27 in the drawings. The prior art method of cooling control electronics 27 in an aircraft a/c system would involve mounting the electronics to a metal multi-baffled heat sink designed to radiate heat to ambient air. However, the additional electronics necessitated for commutation of a brushless motor increase the heat production of the control electronics. This increased heat production requires enhanced cooling measures, that due to avionics conditions, also do not require significant space.

FIG. 3 shows the motor control circuitry, including heat-producing components 27, of the present invention motor control unit 29 mounted in juxtaposition to a heat sink 30. Heat sink 30 is adapted to receive and transmit expanded refrigerant vapor from evaporator assembly 17 of a/c loop 10 to compressor 15. FIG. 4 shows the motor control circuitry and heat sink in exploded view. As illustrated in these figures, electronic components 27 of motor control unit 29 are mounted upon printed circuit board 28 which is directly attached to heat sink 30, which in the preferred embodiment forms the floor of motor control unit 29. Heat sink 30 is preferably fabricated from a block of metallic material that has a high coefficient of thermal conductivity such that the heat energy generated by the power electronic components is rapidly drawn away from and absorbed into the heat sink. Heat sink 30 includes refrigerant passageway 32, which in the preferred embodiment is a tunnel formed within the block of material. Refrigerant tunnel 32 includes refrigerant receiving end 33 and refrigerant discharge end 34. Preferably, tunnel 32 has an exaggerated (for example, grooved, pitted, dimpled or formed with pockets) interior surface and defines a serpentine route through heat sink 30 to maximize refrigerant-to-heat sink contact surface area. In the preferred embodiment, refrigerant tunnel 32 is integrally formed within heat sink 30. Alternatively, heat sink 30 and tunnel 32 could be composed of discrete components such as a metallic slab or strut and conjoined tubing respectively. By utilizing the refrigeration loop to remove heat from the motor control electronics, the heat transferred to the refrigerant is moved by a/c system compressor 15 to condenser 13 where it is discharged out of the a/c loop. The disclosed method thus employs a low pressure drop refrigerant path to minimize loss of system operating efficiency.

By providing heat sink 30 with refrigerant passageway 32 and using refrigerant for cooling, heat sink 30 can be made smaller than the heat sink found in prior art a/c systems. Alternatively, by adding rifling or fins to heat sink 30, its cooling properties can be enhanced. Heat sink 30 may also include sensors to provide temperature and pressure control feedback. The cooling effectiveness of heat sink 30 may be further enhanced by having returning refrigerant achieve multiple passes through the heat sink. Similarly, the cooling effectiveness of heat sink 30 may be enhanced by directly attaching the control electronics to it with electrical isolation.

Refrigerant receiving end 33 of tunnel 32 is connected to evaporator assembly 17 by supply line 12d. Tunnel 32 and line 12d interface at inlet port 35 situated on the housing 40 of motor control unit 29. Refrigerant discharge end 34 of tunnel 32 interfaces with line 12e at outlet port 36 situated on housing 40. Line 12e leads to inlet port 16 of compressor 15.

FIGS. 5-11 show a preferred embodiment aircraft a/c compressor drive module 50 incorporating the present invention motor control cooling system. Compressor drive module 50 includes isolated motor control unit 29, brushless DC motor 52 and compressor 15 mounted upon base 45. In the depicted embodiment compressor 15 is belt driven by motor 52, but the two components could be in direct drive arrangement. Motor control unit 29 includes motor input power connection 55 and motor ground connection 56. Though in the disclosed compressor drive module heat sink 30 is part of isolated motor control unit 29, heat sink 30 may be formed as an integral part of the compressor housing. In the depicted embodiment, compressor 15 may include high and low pressure sensors 98, 99 electrically connected to motor control unit 29.

The cooling system and method disclosed above provides improved cooling to the isolated motor control electronic components of an a/c refrigerant loop. While it is particularly adapted to a system employing a DC current brushless motor to drive the compressor, it can be used in systems utilizing brushed motors controlled by electronics. The present invention system delivers cooling refrigerant directly from an evaporator assembly to the control electronics. It thereby dispenses with the need to provide a separate flow circuit to pass refrigerant from the system condenser to the compressor control electronics. Likewise, the present invention system dispenses with the need to provide phase changing devices in the form of heat sinks or expansion valves in the separate flow circuit. It accomplishes the foregoing without adding any significant spacing requirement to the motor control unit.

While this invention has been explained with reference to the structure disclosed herein, it is not confined to the details set forth and this invention is intended to cover any modifications and changes as may come within the scope of the following claims.

Claims

1. A system for cooling the power and commutation electronics used to control the motor of a compressor in an air conditioning refrigeration system, the system comprising:

a refrigeration system including a compressor and an evaporator assembly connected by a refrigerant line;

a motor control unit electrically connected to the compressor motor, the motor control unit containing electronic components that control the compressor motor;

the electronic components being mounted in heat transfer relation to a heat sink;

the heat sink including a refrigerant passageway for the passage of refrigerant there through and being fluidly disposed in the refrigeration line between the evaporator assembly and compressor such that refrigerant returning from the evaporator assembly to the compressor of the air conditioning system travels directly to the heat sink and through the refrigerant passageway before reaching the compressor.

2. The system of claim 1 wherein the refrigerant returning from the refrigerant passageway travels directly to the compressor.

3. The system of claim 1 wherein the compressor motor is a brushless motor and the electronic components regulate the output and commutation of the compressor motor.

4. The system of claim 1 wherein the refrigerant passageway is a tunnel integrally formed in the heat sink.

5. The system of claim 1 wherein the refrigerant passageway is a discrete component attached to the heat sink.

6. A method of cooling the electronic components of a compressor motor in an air conditioning refrigeration system, the system having a compressor and an evaporator assembly, the method comprising:

mounting the electronic components in heat transfer relation with a heat sink having a refrigerant passageway; and

directing the vapor refrigerant leaving the evaporator assembly into the refrigerant passageway of the heat sink before returning the vapor refrigerant to the compressor.

7. The method of claim 6 wherein the refrigerant returning from the refrigerant passageway travels directly to the compressor.

8. The method of claim 6 wherein the refrigerant passageway is a tunnel integrally formed in the heat sink.

9. The method of claim 6 wherein the refrigerant passageway is a discrete component attached to the heat sink.

10. The method of claim 6 wherein the compressor motor is a brushless motor.

11. A compressor drive module for an air conditioning refrigeration system, the refrigeration system including a compressor and an evaporator assembly connected by a refrigerant line, the compressor drive module comprising:

a motor control unit and a motor, the motor adapted to drive the compressor;

the motor control unit being electrically connected to the motor, said motor control unit containing electronic components that control the motor;

the electronic components being mounted in heat transfer relation to a heat sink;

the heat sink including a refrigerant passageway for the passage of refrigerant there through and being fluidly disposed in the refrigeration line between the evaporator assembly and compressor such that refrigerant returning from the evaporator assembly to the compressor of the air conditioning system travels directly to the heat sink and through the refrigerant passageway before reaching the compressor.

12. The compressor drive module of claim 11 wherein the refrigerant returning from the refrigerant passageway travels directly to the compressor.

13. The method of claim 11 wherein the refrigerant passageway is a tunnel integrally formed in the heat sink.

14. The method of claim 11 wherein the refrigerant passageway is a discrete component attached to the heat sink.

15. The compressor drive module of claim 11 wherein the motor is a brushless motor and the electronic components regulate the output and commutation of the compressor motor.