Sealed and Balanced Motor and Fluid Pump System

This invention relates to a pancake motor pump and especially to a hermetically sealed, magnetic-thrust-balanced, fluid pump system.

For spacecraft propulsion requiring pumps for propellant pressurization the preferred method is the electric motor pump drive operating at high speed requiring no purge gas and operating safely without seals. The commonly used method utilizes a hot gas tubine powering the propellant pump. High speed compact motors in the multiple horsepower range, however, are not readily available, even in the specialized electric motor industry. The replacement of the high temperature gas turbine to drive the propellant pump with a new type of high speed electric motor eliminates the following:

Problems related to high temperature and high structural stress.

Thermal heat soakback into the propellant pumps.

Separation of hot turbine gas and pump propellant fluid.

Helium purge gas.

Turbine gas generator and related hardware.

An object of the invention is to provide a lightweight and compact pancake-type, d.c., high-speed, electric motor, especially for use in conjunction with propellant pumps in rocket engines.

Another object is to provide such a motor in combination with a load which is integrally connected to the rotor component of the motor.

A further object is to provide such a motor in combination with a pump, wherein the pump impeller and shaft are integrally connected with the rotor component of the motor.

Yet another object is to provide such a motor in combination with a pump wherein the motor unit is hermetically sealed from the surrounding environment.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.

The invention comprises a pancake, d.c., electric motor in which the rotor element is integrally connected to the load which may, for example, be the impeller of a pump or turbine. The rotor is formed with a central, peripheral, annular recess into which the coils of the stator element extend. Faces of the rotor lie on opposite sides of the stator and permanent magnets are set into the rotor faces at the same radial extension as the stator-coil poles. The shaft of the motor is stationary and the rotor is coupled to a sleeve bearing which rotates around the shaft. The motor/pump assembly is hermetically sealed externally against leakage of the pumped fluid. Internally, a small amount of pressurized pumped fluid is allowed to leak past a labyrinthine seal and circulate through passages in the motor to cool the motor parts and to lubricate the sleeve bearing.

The single FIGURE is an axial cross-section of an embodiment of the invention.

The same elements or parts throughout the FIGURE of the drawing are designated by the same reference characters.

FIG. 1 is a cross-sectional view of an embodiment of the invention taken parallel to the motor's longitudinal axis. A brushless d.c. motor of the "pancake" type has an annular stator 12 including at least two stator coils 14. The stator 12 comprises a flange 15 lying inside a peripheral annular recess 16 in the center of the rotor 18 and is part of the motor housing, or casing, 28. On both sides of the stator 12 are faces 17 of the rotor 18 separated from the stator by an air gap 20. Inserted in each rotor face 17 adjacent to the stator 12 are permanent magnets 22 of samarium cobalt, or neodymium iron, (or other high-energy magnetic material) at the same radial extension as the stator coils 14.

A sleeve bearing 24, preferably made of carbon, surrounds the stationary shaft 26 of the pancake motor 10, the shaft 26 being bonded to the motor casing 28 by a suitable means such as welding. The bearing 24 is coupled to rotate with the rotor 18 by means of bolts 25.

One side (the right side in FIG. 1) of the rotor 18 is directly coupled to a load, in this case the rotating shaft 30 of a pump 32 used to move the liquid propellant of a rocket engine. The shaft 30 supports the blades of the pump inducer 34 and the pump impeller 36.

The propellant liquid flows in at the right side, as indicated by the arrows is pre-pressurized by the inducer 34 (if pressurization is needed, as in high-speed pumps, an inducer is used; otherwise not) and pushed to the left through the impeller 36 into the fluid collector volute recess 60 and out through the pump discharge in casing 28. A small amount of propellant liquid is used to cool the rotor and stator parts. In one method, the portion of the fluid used for motor coolant and bearing lubrication proceeds from the fluid collector volute recess 60 to leak past a labyrinthine seal 38 between the rotor 18 and the motor casing 28. Arrows 40 show the path of the coolant fluid. The fluid is forced through a coolant passage 42 into peripheral, annular coolant passages 44 annularly surrounding the stator coils 14 and located within the body of the stator 12. From annular coolant passages 44, the cooling and lubricating fluid flows down through passage 46 which divides into two sections 47 and 47'. The first section 47 directs a portion of the fluid between the sleeve bearing 24 and the shaft 26 to act as a lubricant and cooling medium for the sleeve bearing 24. The second section 47' communicates with radial hole or port 51 in the proximal end of shaft 26 which passes into a bore 48 extending through the center of the shaft 26. The bore 48 also communicates with the interface of the sleeve bearing 24 and the shaft 26, and fluid entering bore 48 flows through radial holes 49 and between sleeve bearing 24 and shaft 26. The fluid flowing between sleeve bearing 24 and the shaft 26 combines with the fluid passing out of the bore 48 through radial holes 49 and converge again in a recess 50, or low-pressure region, between the shaft 26 and the rotor 18 and then flow out to the main propellant flow between the inducer 34 and the impellers 36 through passages 52 in the rotating shaft 30.

A feature of the invention is that the shaft 26 of the motor 10 is sealed against the main propellant flow although a certain amount of leakage flow for cooling and lubrication is provided.

Another feature of the invention is that the rotor is axially thrust balanced with respect to magnetic forces because the rotor magnets are on opposite sides of the stator coil poles so that the thrust of one rotor is balanced out by the thrust of the other.

A further feature is that the casing is hermetically sealed to the internal components. The motor and pump components are sealed from each other except that some leakage flow is allowed for lubrication and cooling purposes.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.