Disk style centrifugal pump

An electric machine system includes an electric motor and an oil pump disposed within a housing. The oil pump is configured to disperse oil in a pattern about a rotational axis within the electric motor. A method for operating the electric machine system is also disclosed.

BACKGROUND OF THE INVENTION

Exemplary embodiments pertain to the art of electric machines and, more particularly, to an electric machine having oil cooling using a disk style centrifugal pump.

Electric vehicles (EVs) or hybrid electric vehicles (HEVs) are gaining in popularity as gas prices increase and consumers have greater awareness of environmental impacts caused by traditional vehicles. Both EVs and HEVs use a traction motor powered by electricity for propulsion to reduce emissions.

During operation, the traction motor generates heat that must be removed to avoid damage to the traction motor. Typically, power electronics used in EVs and HEVs and internal combustion engines used in HEVs are cooled by water. Hence, water may also be considered to directly cool the traction motor. However, oil cooling may be preferred for certain applications as oil provides a thermally efficient and cost effective solution for heat rejection from the internal components of the traction motor. Improving traction motor cooling technology is one path toward enhanced operational efficiency of electric motors.

BRIEF DESCRIPTION OF THE INVENTION

Disclosed is an electric machine system including an electric motor and an oil pump disposed within a housing enclosing the electrical motor. The oil pump is configured to disperse oil in a pattern about a rotational axis within the electric motor.

Also disclosed is a method of operating an electric machine. The method includes rotating a rotating disk spaced a distance D from a stationary disk to draw in oil into a space between the rotating disk and the stationary disk. The method also includes dispersing the oil in a pattern about a rotational axis within the electric motor using a plurality of vanes coupled to the rotating disk.

DETAILED DESCRIPTION OF THE INVENTION

An electric machine system in accordance with an exemplary embodiment is indicated generally at2inFIG. 1. Electric machine system2includes a housing3. Disposed within the housing3is an electric machine, shown in the form of an electric motor4. The electric motor4includes a stator5with a plurality of stator windings6. Internal to the stator5is a rotor7having a plurality of rotor windings8or permanent magnets (also represented by element8). A rotating magnetic field generated by the stator windings6interacts with the rotor windings8or the permanent magnets to urge the rotor7to rotate.

The electric machine system2uses oil as a medium to cool the electric motor4. In addition, the oil can be used to lubricate and cool rotating components such as the rotor7. Internal to the housing3is an oil pump10. The oil pump10receives oil from an oil sump11and disperses the oil in a dispersion pattern to evenly cool the stator5, the stator windings6, the rotor7, and/or the rotor windings8. In one embodiment, the dispersion pattern is 360 degrees about the longitudinal axis (i.e., rotor axis) of the electric motor4. The housing3defines an enclosed cooling system not requiring external connections for a cooling medium. The enclosed cooling system increases the reliability and lowers the cost of the electric machine system2.

The oil pump10with the oil sump11disposed in the bottom of the housing3has the benefit that suction at the bottom of housing3can help enhance drainage of the oil from the electric motor4in the main cavity.

Reference may now be had toFIG. 2depicting aspects of the oil pump10. As shown in a cross-sectional view inFIG. 2A, the oil pump10includes a stationary disk20and a rotating disk21spaced a distance D from the stationary disk20. The rotating disk21includes a center disk22and a plurality of blades or vanes23(such as fan-like blades or vanes) extending radially from the center disk22.FIG. 2Billustrates a side view of the oil pump10showing the center disk22and the plurality of vanes23with respect to the stationary disk21. Tips of the vanes23may extend beyond, be even with, or be shorter than the perimeter of the stationary disk20.

During operation, the rotation of the center disk22with respect to the stationary disk20creates a vacuum or low pressure between the disk20and the disk22to draw oil from the oil sump11. Oil tension between the disk20and the disk22also contributes to drawing oil. As the drawing of oil continues, the oil will flow towards the plurality of vanes23. As the oil reaches the plurality of vanes23, the oil will be dispersed in a 360-degree pattern by the plurality of vanes23about the rotational axis of the rotating disk22. The oil is dispersed by a throwing or slinging action from each of the vanes23. Once the initial vacuum establishes oil flow, the fluid tension action and the centrifugal forces on the oil slung out by the rotating disk21help to enhance the overall oil pumping action. In addition, the plurality of vanes23enables the oil pump10to be self-priming.

In addition to the 360-degree pattern, the oil can be dispersed axially along the longitudinal axis of the motor4. This axial dispersion can be achieved by forming an angle of an end portion of some or all of the vanes23in relation to the rotation axis. The angle can also be varied to achieve an even axial dispersion. In lieu of or in addition to the angled vanes23, one or more of the vanes23can have different lengths so that the perimeter defined by the tips of the vanes23is non-circular in order to alter the dispersion pattern.

The rotating disk21can be driven in various ways in different embodiments. In one embodiment, the rotating disk21is coupled coaxially to the rotor7and driven directly by the rotor7. In another embodiment, the rotating disk21is driven indirectly by the rotor7such as with a configuration using gears, a chain, or pulleys and belts. In another embodiment, the rotating disk21is driven by an auxiliary motor30as shown inFIG. 3. One advantage of the auxiliary motor30is that the oil pump10can provide cooling even if the rotor7is stalled or turning at a slow speed. The auxiliary motor30in one embodiment is electrically powered.

Flow control of the oil may be provided to enable the flow of oil to be within a selected range to avoid too little flow or too much flow. Flow control may be provided by varying the speed of the auxiliary motor30or by varying the distance D between the stationary disk20and the rotating disk21. Varying the gap between the stationary and rotating disks can be accomplished using a rotating disk actuator31coupled to the rotating disk21as shown inFIG. 3. In one embodiment, the rotating disk actuator31is an electric servo. An active rotating disk actuator31can be coupled to a flow sensor32and/or a speed sensor33to provide a feedback flow control loop. In one embodiment, the rotating disk actuator31is a passive device such as a spring-loaded device that pulls the disks apart at high speeds and/or at high oil pressures.

At this point it should be understood that the oil pump10can provide a symmetric 360-degree dispersion pattern to evenly cool the stator5and the plurality of stator windings6. In one embodiment, the rotational axis of the rotor7is substantially the same as the rotational axis of the rotating disk22so that the oil dispersion pattern is symmetric within the stator5. The symmetric cooling pattern avoids producing hot spots and, thus, reduces stresses experienced by components of the electric motor4.

It is also understood that the electric machine system2may include more than one main oil pump10. In one embodiment, the electric machine system2includes two main oil pumps10where one main oil pump10is disposed at one end of the rotor7and the other main oil pump10being disposed at the other end of the rotor7to provide even cooling.

In certain configurations, the electric machine system2may require a secondary oil pump to function while the rotor7is stalled or rotating at a very slow speed. The secondary oil pump has features similar to the main oil pump10depicted inFIGS. 1-3. The secondary oil pump can be electrically driven using a motor such as the auxiliary motor30and run whenever power is applied. Alternatively, the electrical motor driving the secondary oil pump can be switched on by the flow sensor32when oil flow is too low and/or by the speed sensor33when the rotational speed of the rotating disk22is too low.

Generally, when the electric machine system2is used in EV and HEV applications, the electric motor must rotate in both directions for forward and reverse movement. One of the advantages of the electric machine system2is that the oil pump10provides oil flow when the rotating disk22is rotating is either direction.

Another advantage of the electric machine system2is the energy required to run the oil pump10is minimal and mainly related to the lift and acceleration of the oil by the rotating disk22. The oil pump10operates at very low pressures and has minimal oil passages, all of which can be cast or machined into a single part.

The electric machine system2having the oil pump10internal to the housing3lends itself to a sealed oil-cooled motor design that can utilize a secondary external cooling system35as shown inFIG. 3. In one embodiment, the secondary external cooling system35removes heat from oil in the oil sump11and disposes the heat in a heat sink such as a radiator. One non-limiting example of a secondary cooling medium is water. Hence, the only external connections required for the electric machine system2having the secondary external cooling system35are connections for electrical power and for the secondary cooling medium.

FIG. 4presents one example of a method40for operating the electric machine system2. The method40calls for (step41) rotating the rotating disk21spaced a distance D from the stationary disk20to draw in oil into a space between the rotating disk21and the stationary disk20. Further, the method40calls for (step42) dispersing the oil in a 360-degree pattern about a rotational axis within the electric motor4using the plurality of vanes23.

Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The term “couple” relates to one component being coupled either directly to another component or indirectly to the another component via one or more intermediate components.