Electric propulsion system

Abstract

An electric propulsion system, comprising a propeller and a motor arranged to rotate the propeller, the motor comprising an axial flux motor comprising a rotor disc and a stator disc mounted in face-to-face relationship with an air gap defined therebetween, the rotor disc driven to rotate relative to the stator disc to cause magnetic flux in the air gap to cause rotation of the propeller, characterised in that the propeller is directly attached to the rotor disc to rotate with the rotor disc.

Claims

1. An electric propulsion system, comprising: a propeller; an axial flux motor arranged to rotate the propeller, the axial flux motor comprising an air gap between a rotor and a stator, the rotor driven to rotate relative to the stator to cause magnetic flux in the air gap to cause rotation of the propeller; wherein permanent magnets are provided on the face of the rotor facing the stator and windings are provided mounted to the stator; wherein the propeller is directly mounted to the rotor to rotate with the rotor; and wherein the propeller comprises propeller blades mounted radially inwards of an outer edge of the rotor; and a shaft on which the stator is fixedly mounted, the rotor being arranged to rotate about the shaft via bearings, wherein the bearings are provided between the shaft and the rotor.

2. The system of claim 1, wherein the propeller comprises the propeller blades mounted adjacent or on an outer edge of the rotor.

3. An aircraft including the electric propulsion system as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred examples will now be described by way of example only and with reference to the accompanying drawings.

(2) FIG. 1 is a schematic side view of an electric propulsion system according to the present disclosure.

(3) FIGS. 2A-2C shows moment forces for different locations of the propeller.

(4) FIGS. 3A and 3B are schematic side views of alternative embodiments of the system.

DETAILED DESCRIPTION

(5) Referring to FIG. 1, the electric propulsion system of the disclosure comprises a propeller 1 having two or more blades 2, 3. The propeller, in use, would be mounted to the exterior of a propulsion vehicle such as a propeller driven aircraft to rotate and drive the vehicle forward with a propulsion force.

(6) The propeller 1 is caused to rotate by means of an electric motor 4.

(7) The electric motor 4 is an axial flux motor comprising a rotor disc 5 and a stator disc 6. The rotor disc 5 and the stator disc 6 are mounted face to face in an axial direction A with an air gap 7 defined therebetween. Permanent magnets 8 are provided on the rotor disc, facing the stator disc 8 on which windings 9 are mounted.

(8) The rotor disc 5 is mounted on a shaft 10 via bearings 11 and is powered to rotate about the axis A relative to the stator disc 6. The relative motion between the permanent magnets and the windings creates a magnetic flux providing rotational power to the rotor disc 5 which, in turn, rotates the propeller 1 with the required speed to propel the vehicle.

(9) The axial flux motor is mounted such that the rotor disc 5 is more forward in the direction of propulsion that the stator disc 6.

(10) As indicated in FIG. 1 an axial propulsion force is created by the rotating propeller 1 against the direction of forward movement of the vehicle. A magnetic attractive force is also created between the stator disc and the rotor disc. In current engines, the thrust load acts through thrust bearings 11 that transmit the load to the engine and airframe. These bearings have minimal axial movement in them (bearing internal clearance only), and their use in an axial flux motor would adequately control the air gap, to retain the air gap against the attractive magnetic force. Magnetic force can be used to reduce the forces acting on the thrust bearings 11, therefore reducing the bearing and housing mass.

(11) The force on the rotor and bearings acting to counter the propulsion force will, when the rotor is mounted in the forward moving direction of the vehicle relative to the stator, be opposite the direction of the magnetic attractive force between the rotor disc and the stator disc. The resultant load on the rotor disc and bearings is the sum of the counter-force and the magnetic attractive force acting in opposite directions.

(12) Depending on the requirements of the vehicle being propelled, the moment forces can be adjusted by changing the relative positions between the magnetic and propulsion forces. One way to do this is by changing the position at which the propeller 1 is mounted on the rotor disc 5 relative to the magnets 8. Alternatively, the propeller blade length can be changed.

(13) FIG. 1 shows one example, having the propeller blades 2,3 mounted on the outer periphery of the rotor disc 5 close to the magnets 8. The resultant force diagram is shown in FIG. 2 (a).

(14) Alternatively, the propeller blades could be mounted on the outer face of the rotor disc just within the outer periphery as shown in FIG. 3A or, alternatively, mounted on the outer face, closer to the axis A as shown in FIG. 3B.

(15) If the propeller is mounted radially inwardly of the magnets 8, a force diagram may look like that shown in FIG. 2 (b). Alternatively, the magnets could by mounted radially inwardly relative to the propellers providing a force diagram as shown in FIG. 2 (c).

(16) In FIGS. 2 (a), (b) and (c), F.sub.p represents the force counteracting the propulsion, F.sub.m is the magnetic attractive force, L.sub.m is the radial distance from the hub centre to the point through which the magnet attraction forces act. and L.sub.p is the radial distance from the hub centre to the point through which the propeller thrust forces act. k is the ratio between L.sub.p and L.sub.m and is a factor representing the spacing between the propulsion force and the magnetic force.

(17) The attachment point of the propeller 1 relative to the position of the magnets 8 can be permanently set or can be dynamically adjusted by means of an actuator. Depending on the balance between the forces, an optimum attachment point can be determined.

(18) By mounting the propeller 1 directly onto the rotor disc 5, it is possible to control the moment force on the rotor disk to minimise stress on the bearings, the rotor and other motor components.

(19) As stress on the rotor is reduced, less strength in the components is required and so the weight of the system is reduced. Also, the load on the bearings is reduced, leading to a longer bearing life. The propulsion system has a simple constructions and the need for bearings on a propeller shaft is eliminated.