MOTOR-DRIVEN CENTRIFUGAL AIR COMPRESSOR

Abstract: A motor-driven compressor assembly comprises a compressor air intake, a compressor rotor, a compressed air outlet and an electric motor for said compressor rotor, with the air intake of the compressor assembly being located so as to direct intake airflow to the compressor rotor into a heat transfer relationship with the electric motor. The motor-driven compressor includes an outer casing and a housing for the electric motor that together form the air intake so the intake airflow through the air intake so formed cools the motor housing. The motor housing is, in preferred embodiments, a central barrel carrying the electric motor within an outer casing so the intake airflow surrounds the central barrel. The outer casing may also form a mounting surface for motor control electronics, and provide inner finned surfaces in the path of the intake airflow to cool the control electronics. For some applications, the motor-driven compressor can include an operable air bypass between the compressor's air intake and compressed air outlet.

Description: MOTOR-DRIVEN CENTRIFUGAL AIR COMPRESSOR Field of the Invention This invention relates generally to systems for supplying compressed air and, more particularly, to motor-driven centrifugal air compressors and the use of compressed air for charging the cylinders of an internal combustion engine and for pneumatic conveying of dry bulk materials and for various other industrial processes. Background of the Invention Motor-driven compressors currently in use consist of a high-speed, brushless motor mounted in an aluminum housing attached to the back plate of centrifugal compressor. One current motor-driven compressor is shown in Fig. 1. As indicated in Fig. 1, the compressor wheel and casing are similar to those used in commercial internal combustion engine turbochargers. In the operation of such air compressors, the motor is energized from an external power source, such as a battery, through an electronic controller which changes the direct current from the battery to alternating current to produce a rotating magnetic field in the motor windings. The rotating field surrounding the motor magnets attached to the motor shaft generates torque that rotates the compressor wheel and shaft assembly. The compressor wheel induces air from the atmosphere or from an appropriate air cleaner and delivers it from the compressor casing at pressures above atmospheric pressure. In current motor-driven air compressors, the amount of power produced by the motor on a continuous basis is limited by the temperature generated in the windings and by the temperature level in the electronic controller from the electrical power losses therein. Conventional low-speed motors usually employ some sort of an internal fan attached to the shaft to produce a flow of cooling air through the motor and around its internal components to limit their temperatures, however, with high-speed, brushless motors the use of internal fans become rather difficult to implement. Summary of the Invention The invention provides a motor-driven compressor assembly, comprising a compressor air intake, a compressor rotor, a compressed air outlet and an electric motor for said compressor rotor, with the air intake of the compressor assembly being located so as to direct intake airflow to the compressor rotor into a heat transfer relationship with the electric motor. In the invention, the motor-driven compressor includes an outer casing and a housing for the electric motor that together form the air intake so the intake airflow through the air intake so formed cools the motor housing. The motor housing is, in preferred embodiments, a central barrel carrying the electric motor within an outer casing so the intake airflow surrounds the central barrel. The outer casing may also form a mounting surface for motor control electronics, and provide inner finned surfaces in the path of the intake airflow to cool the control electronics. Some embodiments of the invention include an operable air bypass between the compressor's air intake and compressed air outlet for use in some applications. In motor-driven centrifugal air compressors of the invention, the components of the assembly are so arranged to utilize the intake airflow of the centrifugal compressor as a cooling media for both the motor components and control electronics to overcome the temperature limitations to power output from uncooled motor components. Brief Description of the Drawings Fig. 1 is a cross-sectional view of a prior art motor-driven centrifugal air compressor taken at a plane through its center; Fig. 2 is a cross-sectional view of a preferred motor-driven centrifugal air compressor of the invention taken at a plane through its center; Fig. 3 is a cross-sectional view of another embodiment of the invention taken at a plane through its center; and Fig. 4 is a cross-sectional view of a third embodiment of the invention take at a plane through its center. Description of the Invention A preferred motor-driven centrifugal air compressor 10 of the invention is shown in cross-section in Fig. 2. In the motor-driven air compressor of Fig. 2, the compressor wheel 11 is mounted on a motor-driven shaft 12 with the air intake of the vanes 13 facing the motor 14. The motor magnet assembly 15 is constructed by encapsulating the magnets on the shaft 12 by an outer cylindrical sleeve 16. The motor windings 17 are mounted in a motor housing 18 within an outer casing 19. As shown in Fig. 2, the outer casing 19 and motor housing 18 form the air intake 20 to the compressor vanes 13 so that upon rotation of the compressor wheel 11 by the electric motor 14, the compressor vanes 13 draw an intake airflow through the air intake passage 20 formed between the outer casing 19, and motor housing 18. The intake air to compressor wheel 11 flows adjacent and in heat transfer relationship with the electric motor 14, that is, the intake airflow cools the motor housing 18 and thereby the motor windings 17, and the motor windings 17 are maintained at a lower temperature than if the motor housing were in contact with static ambient atmosphere as in the Fig. 1 apparatus. In addition, the ends of the motor housing 18 may be provided with openings 22 and 23 permitting the rotating compressor vanes 13 to induce a cooling airflow through the interior of motor housing 18 more directly adjacent the motor windings 17 and adjacent the motor magnets 15. Ball bearings 24, 25 rotatably support the shaft 12 at the ends of the motor housing 18 as shown. A housing end cover 26 is retained in the motor housing 18 by retaining ring 27, and spring 28 is provided to ensure the proper pre-loading on the ball bearings 24, 25. In the preferred embodiment shown in Fig. 2, the motor housing 18 is a central barrel located coaxially within and surrounded by the outer casing 19. The central barrel 18 is thus surrounded by the intake air passage 20 and is attached to the outer casing 19 by ribs 29. Air is induced through intake air passage 20 and through openings 22, 23 in the central barrel 18 by rotation of compressor wheel 11. The airflow over the central barrel 18 and adjacent the motor windings 17 cools the motor parts, keeping them at lower and acceptable operating temperatures. The intake air is compressed by the rotation of compressor wheel 11 , passes through diffuser passage 30, and flows into the compressor casing 31. A tangential outlet (not shown) from the compressor casing 31 can be, for example, connected to the air intake system of an internal combustion engine or the intake air system of some other industrial process that requires compressed air. The motor wires 32 exit the end plate 26 through one of the openings 23 and can be led to an appropriate electronic control unit (not shown in Fig. 2), which controls operation of the motor 14. An alternate preferred embodiment 33 of the invention is illustrated in Fig. 3. As illustrated in Fig. 3, one section 19a of the outer casing 19 protrudes to provide a mounting cavity 34 for the control electronics (not shown). The inner surface 35 of the outer casing adjacent the mounting cavity 34 includes a series of fins 36 in the intake airflow that can transfer heat generated in the control electronics to the intake airflow. Wire outlet 37 from the mounting cavity 34 is provided to permit electric current from a power source to enter the control electronics through electrical conduit 38. The motors of existing motor-driven compressors usually have the motor windings connected to a remotely located controller, necessitating an appreciable length of control wires that must be protected from damage. The present invention eliminates the need for protecting control wires by forming a cooled mounting for the electronics as an integral part of the outer casing 19 and allows the inner surface of the mounting to incorporate cooling fins in the intake air stream as a heat sink. The invention also provides motor-driven compressors for use in series with a turbocharger compressor on an internal combustion engine. An embodiment of motor-driven compressor 40 of the invention for such applications can include an internal air bypass valve 41 within the motor- driven compressor housing, as illustrated in Fig. 4. In such applications, a motor-driven compressor of Fig. 4 is provided upstream of the air intake of a conventional turbocharger for an internal combustion engine and is driven by the electrical system of the internal combustion engine to provide a flow of compressed air through the turbocharger air intake when the internal combustion engine is operating at idle or low speeds and the conventional turbocharger cannot supply a desirable flow of cylinder charge air. When the internal combustion engine is operating at rated load and speed in such systems, the motor-driven compressor may be de-energized to eliminate the use of electrical energy from the internal combustion engine electrical system, and the internal bypass valve 41 can be opened to allow the engine turbocharger to obtain its intake airflow with minimal resistance through the motor-driven compressor 40. As shown in Fig. 4, the air bypass valve 41 can be formed by a flapper 42 hinged to and supported by the outer casing 19 between the air intake passage 20 and the compressor casing 31. The flapper 42 may be operated by an electrical solenoid (not shown) mounted to the outer casing 19 and connected with an operating arm (not shown) attached to flapper 42. The sequence of operation of such internal combustion engine systems is as follows: When the internal combustion engine is started, the motor- driven compressor 40 is energized to a first speed level at which it provides a significant boost pressure to the internal combustion engine in preparation for engine acceleration under load. This level of boost is much higher than can be supplied by the engine turbocharger alone under these engine operating conditions. When the engine throttle is opened to accelerate the engine, the motor-driven compressor 40 is super-energized, for example, by increasing its speed of rotation with the control electronics, to assist the engine turbocharger in providing boost pressure during the acceleration period. When the engine turbocharger has reached a level where it is capable of supplying sufficient charge air for efficient combustion of the injected fuel, the motor-driven compressor is de-energized by the control electronics. The internal bypass valve 41 opens anytime the pressure in the compressor casing 31 falls below the pressure in the intake air passage 20. This allows the engine turbocharger to draw intake air through the motor-driven compressor with minimal resistance to the flow. If a motor-driven compressor of the invention 10, 33 is to be used for an application such as pneumatic conveying of dry bulk material, the air intake openings of the outer casings 19 may be fitted with an appropriate air filter. In other applications requiring compressed air, a simple screen to keep out foreign material may be used. Mounting feet may be located at convenient places on the outer casing 19, depending on the type of service in which the compressor is to be used. Integrating the compressor components, motor components, and electronic control in a single compact structure, where intake airflow is used to cool the motor parts, provides an economical, compact assembly that has a high power output rating by virtue of the large volume of the intake airflow that is used for cooling the electric motor, and the incorporation of an air bypass valve extends the applications in which such motor-driven compressors may be used. While we have shown and described what we believe to be the best mode of our invention, other embodiments may be derived by those skilled in the art without departing from the spirit and scope of the following claims, which are limited in scope by only the prior art.

Claims: We Claim; 1. A motor-driven compressor assembly, comprising a compressor air intake, a compressor rotor, a compressed air outlet and an electric motor for said compressor rotor, said air intake of the compressor assembly being located so as to direct intake airflow to the compressor rotor into a heat transfer relationship with the electric motor. 2. A motor-driven compressor as in claim 1 wherein an outer casing and a housing for said electric motor forming said air intake, said intake airflow flowing through said air intake in heat transfer relationship with the motor housing. 3. A motor-driven compressor as in claim 1, wherein the electric motor includes windings in a central barrel located in the air intake, said air intake being formed by an outer casing surrounding the central barrel. 4. A motor-driven compressor as in claim 3, where a protrusion of said outer casing forms a mounting surface for control electronics, and provides inner finned surfaces in the path of the intake airflow. 5. A motor-driven compressor as in claim 3, wherein the air intake includes an open end formed by the outer casing and covered by an air filter. 6. A motor-driven compressor as in claim 2, wherein the compressor assembly includes a bypass valve between the compressor air intake and compressed air outlet. 7. A compact motor-driven compressor, comprising a compressor housing including an outer casing and an internal motor support; an electric motor including motor windings and a plurality of magnets carried by and driving a rotating shaft carried by ball bearings supported by said internal motor support; a centrifugal compressor wheel carried and driven by said rotating shaft with an air intake facing said electric motor, said compressor housing forming a peripherally-located compressed air outlet from said compressor rotor, and said outer casing and internal motor support of said compressor housing forming a flow path for ambient air leading to the air intake of the compressor rotor. 8. A motor-driven compressor as in claim 7 wherein an electronic motor control is mounted on the housing in heat transfer relationship with the flow path for ambient air. 9. A motor-driven compressor as in claim 7 wherein a mounting for electronic controls is formed by the outer casing and a finned inner surface located in the ambient airflow path to provide a heat sink for the electronic controls. 10. A motor-driven air compressor, comprising means forming a coaxial compressor air inlet, a compressed air outlet and an electric motor housing, an electric motor carried by said electric motor housing within said compressed air inlet, said electric motor having a driven shaft extending outwardly of the electric motor housing within said compressed air outlet and carrying a compressor rotor wherein upon energization of said electric motor, said driven shaft rotates said compressor rotor, drawing ambient temperature air into said compressed air inlet adjacent said electric motor and thereafter compressing said air and directing compressed air to the compressed air outlet. 11. The motor-driven air compressor of claim 10 wherein said electric motor housing has open ends for transmission of ambient temperature air adjacent electric motor components. 12. The motor-driven air compressor of claim 10 wherein a control for the electric motor is mounted in heat transfer relationship with the air inlet portion of said forming means. 13. The motor-driven air compressor of claim 10 wherein the means forming a coaxial air inlet, compressed air outlet and an electric motor housing includes an operable air bypass between its air inlet portion and compressed air outlet portion. 14. The motor-driven air compressor of claim 12 wherein the interior of said air inlet portion includes a plurality of air-cooled heat transfer surfaces in heat transfer relationship with said control. 15. A compact motor-driven air compressor, comprising a motor housing for carrying an electric motor and a motor- driven shaft, with a portion of said shaft extending outwardly of the motor housing at one end, said outwardly extending portion of said motor-driven shaft carrying a compressor rotor, and an outer housing surrounding said motor housing and compressor rotor and carrying said motor housing, said outer housing forming an air inlet for said compressor and directing air adjacent said motor housing and to the compressor rotor, said outer housing also forming a casing for receiving compressed air from said compressor rotor. 16. The compact motor-driven air compressor of claim 15 wherein said motor housing is carried coaxially within said outer housing. 17. The compact motor-driven air compressor of claim 15 wherein said motor housing has open ends permitting airflow to reach its interior parts. 18. The compact motor-driven air compressor of claim 15 wherein control components for the electric motor are carried by the outer housing and cooled by air entering the air inlet. 19. The compact motor-driven air compressor of claim 18 wherein the control components are carried by the outer housing adjacent one or more cooling fins formed within the outer housing in the path of air entering the air inlet. 20. A method of operating an internal combustion engine, comprising providing an internal combustion engine with a turbocharger driven by exhaust gas energy of the internal combustion engine and having an air intake and a compressed air outlet connected to provide compressed cylinder charge air to the internal combustion engine, providing a motor-driven compressor, having a valve between an air intake and a compressed air outlet, upstream of the air intake of said turbocharger, energizing the motor-driven compressor with electrical energy to provide a flow of compressed air to the air intake of the turbocharger when the internal combustion engine is operated at speed sufficiently low that the turbocharger cannot supply an acceptable compressed charge air; and de-energizing the motor-driven compressor and opening the valve of the motor-driven compressor when the internal combustion engine is operated at speeds sufficiently high that the turbocharger can provide acceptable compressed charge air through the motor-driven compressor with the valve open. 21. The method of claim 20 further comprising super-energizing the motor-driven compressor upon a demand for acceleration of the internal combustion engine.

Inventors: HALIMI EDWARD M, WOOLLENWEBER WILLIAM E, HALIMI, EDWARD, M., WOOLLENWEBER, WILLIAM, E.
Applicants: TURBODYNE SYS INC, TURBODYNE SYSTEMS, INC.
Application year: 1997
Main classification: F02B
IPC codes: F02B37, F02B39, F04D25, F04D27