The present invention is related to a dual propeller counter-rotating (CR) aerial propulsion system according to the preamble of claim 1.

Background

Aerial propulsion systems with two CR propellers are known to have higher aerodynamic efficiency than the single-propeller systems. This results in lower power consumption in the CR aerial systems and consequently either longer flight times or greater payload capacity or both. Additionally, maximum available thrust, and dynamic response, is better in the CR systems.

CR arrangement of the propellers eliminates almost all reactive forces acting on the structure of a flying apparatus, such as a drone or a helicopter, - this allows for a lighter frame required for mounting the motors as there is no reactive torque to deal with.

In aerial propulsion applications, it is common to have the two propellers in the CR arrangement driven by two electric motors. In some cases, the dual-motor systems have concentric shafts so that the two propellers are mounted next to each other, above the two motors.

A single motor can be used for driving two propellers. One way to realize the single-motor system and make the propellers to rotate in opposite directions is by adding a gearbox to the system. Another way is to have slip rings as part of the system in order to transfer power to the rotating windings.

Usually the motors used in aerial applications have permanent magnets on the rotor and windings on the stator. Thus, in the concept with slip rings, the stator with its windings is made to rotate. Then the motor will have two electromagnetically interacting rotary parts (two rotors) and no stationary electromagnetic elements (no stator). The rotating parts will be rotating in opposite directions in relation to stationary structural parts of the aerial apparatus.

The latter solution is disclosed in US10116187B1. Reference is made to the attached Fig. 1, which describes the counter-rotating solution of US10116187B1. The two rotating parts of the motor will have relative rotational speed approximately doubled compared to the CR configuration with two motors, one motor for one propeller, wherein only one part of each motor, namely rotor, is rotating with the speed equal to the speed of the propeller driven by this motor. The higher relative speed improves self-cooling of the motor and results in lower temperature in the rotating active parts and extends its lifetime. Moreover, a motor with higher speed is smaller and cheaper for the same power than motor with lower speed.

Another advantage of the single-motor system is that it required only one electronic frequency converter (controller) instead of two in the dual-motor configuration.

The CR solution in US10116187B1 employs 3-phase AC power transfer to the rotating windings with the help of slip ring unit. Some possible embodiments of the slip rings unit are presented in US2019319415A1. Reference is made to the attached Fig. 2, which describes slip rings unit from US2019319415A1.

The electronic controller providing the 3-phase variable voltage and frequency is located outside of the CR arrangement (e.g. in the body of an aerial apparatus, such as a drone). In aerial applications, the electronic controller is often of DC/AC type, wherein the power is coming to the controller as DC current and DC voltage from a battery or a DC distribution grid of the aerial apparatus and the power is coming out of the controller as AC current and AC voltage of variable amplitude and frequency. The voltage is formed by PWM (Pulse-Width Modulation) or similar methods, so its pulses may have sharp fronts.

The prior art CR solution in US10116187B1 is however not free from drawbacks.

The slip ring unit in order to be able to continuously transferring AC power characterised by varying voltage, current and frequency must be relatively large and heavy. It requires regular maintenance. Since the voltage PWM-shaped waveform consists of multiple pulses with sharp fronts and the current waveform is usually distorted by ripple, this cause wear to the contacting surfaces of the slip rings. The slip rings for AC power transfer compromise the reliability of the aerial apparatus.

The motors usually have integrated thermal sensors and sometimes other sensors. Transfer of information from such sensors would require additional slip rings or alternative arrangement.

In addition, the system with single motor in US10116187B1 has lower redundancy compared to the dual motor system, where if one motor fails the other one will continue operation providing approximately 50% of thrust.

Low weight is crucial in aerial applications so there is a need for propulsion systems with lower weight. B

There is further a need for reliable and redundant solutions for aerial propulsion having long lifetime.

There is also a need for systems with lower losses and higher efficiency.

The power electronics used in aerial applications causes electromagnetic emissions and EMI (Electromagnetic interference) problems. There is a need to have the emissions below certain limits.

Object

The main object of the present invention is to provide a dual propeller counter-rotating aerial propulsion system partly or entirely solving the above-mentioned drawbacks of the prior art single- motor CR propulsion systems.

It is further an object of the present invention to provide a dual propeller counter-rotating aerial propulsion system with lower losses and higher efficiency.

An object of the present invention is to provide a dual propeller counter-rotating aerial propulsion system with lower amount of the power and control connections. It is an object of the present invention to provide a dual propeller counter-rotating aerial propulsion system that is space saving, compared to prior art solutions.

It is further an object of the present invention to provide a dual propeller counter-rotating aerial propulsion system with lower electromagnetic emissions.

It is an object of the present invention to provide a dual propeller counter-rotating aerial propulsion system with higher reliability, redundancy and lifetime.

It is further an object of the present invention to provide a dual propeller counter-rotating aerial propulsion system with lower weight, compared to prior art systems.

Further objects of the present invention will appear from the following description, claims and attached drawings. The invention

A dual propeller CR differential aerial propulsion system according to the present invention is defined by the technical features of claim 1. Preferable features of the system are described in the dependent claims.

The present invention discloses a counter-rotating (CR) aerial propulsion system that includes two oppositely rotating propellers that may be mounted to horizontal flight and vertical lift-off aircraft or a fan housing.

The present invention provides a dual propeller CR aerial propulsion system wherein an electronic controller controlling voltages and currents is arranged to a rotational member of an electric motor containing windings in order to supply the windings with AC power directly and not via slip rings.

The dual propeller CR aerial propulsion system according to the present invention will still require use of slip rings to deliver power to the electronic controller, but this power will be in the form of DC current and voltage without any spikes, ripple and zero crossings. Moreover, only two contact points are required for DC power transfer instead of three contact points for the 3-phase AC power transfer. DC slip rings will be smaller in size, have lower cost and lower weight, will be more reliable and will require less maintenance. They will also have longer lifetime. Losses in the DC slip rings will also be lower than in a solution with 3-phase AC rings.

Having the electronic controller rotating together with the rotational member provides good natural cooling by the air flow along the surface of the electronic controller. Thus, in the CR arrangement with two rotational members of the electric motor one achieve improved cooling for both the electric motor and the electronics, thus reducing thermal loads and increasing system lifetime.

Further, having the electronic controller integrated with the electric motor one saves space in the body of an aerial apparatus, where the electronics is usually located.

When the electronic controller and winding are located next to each other and stationary relative to each other, AC power cables become very short. Is some cases the length can be just a few centimetres. The connections to all kinds of sensors, such as for example thermal sensors, Hall sensors, resolvers etc., are also very short and do not have to be taken via auxiliary slip rings.

According to the present invention, power is transferred between the body of an aerial apparatus and the electronic controller integrated with the electric motor in a DC form. This have several positive consequences: - losses in the DC cable are lower than in AC cable for the same transferred power,

- two leads in the cable instead of three means lower cost of the cable, less wear and tear, lower weight, and

- since DC current and voltage do not contain much of higher harmonics caused by PWM (Pulse- With Modulation), there is no need for a shielded expensive cable.

When the electronic controller is integrated with the electric motor, it is possible to have the electronic controller consisting of several smaller controllers supplying parts of the winding. This provides the redundancy to the system as in case one part of the winding or one of the controllers fail, the other winding parts or the other small controllers will continue operation providing at least partial thrust.

The control signals from control units of the aerial apparatus to the electronic controller can be transmitted either wirelessly or via the main power connections together with the power transfer, by e.g. modulation of the control signal over the power signal, or via separate small slip rings e.g. integrated into the main DC slip rings. Further preferable features and advantageous details of the present invention will appear from the following example description, claims and attached drawings.

Example

The present invention will below be described in further detail with references to the attached drawings, where:

Fig. 1 is a principle drawing of a counter-rotating (CR) propulsion system according to prior art,

Fig. 2 is a principle drawing of a slip ring unit for three phase AC power transfer according to prior art,

Fig. 3, is a principle drawing of a first embodiment of a dual propeller CR aerial propulsion system according to the present invention,

Fig. 4 is a principle drawing of a second embodiment of the dual propeller CR aerial propulsion system according to the present invention, Fig. 5 is a principle drawing of a third embodiment of the dual propeller CR aerial propulsion system according to the present invention,

Fig. 6 is a principle drawing of a fourth embodiment of the dual propeller CR aerial propulsion system according to the present invention, with sensor arrangement, and

Fig. 7 is a principle drawing of a further embodiment of the dual propeller CR aerial propulsion system according to the present invention.

Reference is now made to Figure 1 showing a principle drawing of a counter-rotating (CR) propulsion system according to prior art US10116187B1. US10116187B1 is based on a controller located outside the propulsion unit and three leads going from the controller to a slip ring unit with three contact tracks.

Reference is now made to Figure 2 showing a principle drawing of a slip ring unit for three phase AC power transfer according to prior art US2019319415A1. The slip ring unit is a relatively massive and complex device.

Reference is now made to Figure 3 showing a principle cross-sectional drawing of a dual propeller counter-rotating (CR) aerial propulsion system 10 according to a first embodiment of the present invention. The dual propeller CR aerial propulsion system according to the present invention comprises a central shaft 70, which on one end (further referred to as second end) is fixed to a body of an aerial apparatus, such as for example a drone. According to the first embodiment of the present invention components of the CR aerial propulsion system 10 are located on the central shaft 70. A first rotational member 71, located proximate to the first end of the central shaft 70, is arranged on the central shaft 70 by means of bearings 61 and rotates about the central shaft 70. Blades of a first propeller 20 are fixed to the first rotational member 71 by means of blade mounting arrangements 80. A second rotational member 72, located between the first rotational member 71 and the second end of central shaft 70, is also arranged on the central shaft 70 by means of bearings 62 and rotates about the central shaft 70. Blades of a second propeller 21 are fixed to the second rotational member 72 by means of blade mounting arrangements 80. The first rotational member 71 rotates in an opposite direction to the second rotational member 72 and about the central shaft 70. The rotation is powered by electromagnetic interaction between the electromagnetic means 32, 31 associated with the first 71 and the second 72 rotational members, respectively. The electromagnetic means 32, 31 comprise the active parts of an electric motor. The electromagnetic means 32, 31 can contain windings and permanent magnets. The system 10 comprises an electronic controller 50 for controlling voltages and currents in the electromagnetic means 32, 31 associated with the first 71 and second 72 rotational member, wherein the electronic controller 50 is arranged to one of the rotational members 71, 72. In the shown embodiment, the electronic controller 50 is fixed to the second rotational member 72. Accordingly, in this embodiment the blades are mounted close to the central shaft 70. In this example, the windings of electromagnetic means 31 are supplied with AC power from the electronic controller 50 via a multiphase connection 41.

The electronic controller 50 in this example converts the power from DC to AC.

Electric power is delivered to the electronic controller 50 from an external DC power source, such as a battery, via DC connection 40 through DC power transfer means 90. The DC power transfer means 90 are located between the second rotational member 72 and the second end of the central shaft 70. The DC power transfer means 90 consist of stationary electric contacts 91 and rotary electric contacts 93 accommodated in stationary holder 92 and rotary holder 94, respectively. The stationary holder 92 is fixed to the central shaft 70 and the rotary holder (94) is fixed to the second rotational member 72.

There is arranged a passage 73 in carrying structure of the second rotational member 72 for electric connections 40.

Reference is now made to Figure 4 showing a cross-sectional drawing of a second embodiment of the dual propeller CR aerial propulsion system 10 according to the present invention. In the second embodiment, the blades of the first and second propeller 20, 21 are mounted closer to the periphery of the electric motor with the help of the blade mounting arrangements 80. Mechanical reinforcements 74 are added to carrying structures of the rotational members 71, 72. Accordingly, in this embodiment the blades are mounted closer to the periphery of the electric motor than in the first embodiment.

Reference is now made to Figure 5 showing a cross-sectional drawing of a third embodiment of the dual propeller CR aerial propulsion system 10 according to the present invention, wherein the electric motor has two air gaps. The electric motor according to the third embodiment has two electromagnetic means 32, 33 arranged to the first rotational member 71 and one electromagnetic means 31 arranged to the second rotational member 72, wherein the electromagnetic means 32, 33 of the first rotational member 71 are arranged at each side of the electromagnetic means 31 of the second rotational member 72. The electromagnetic means 31 has windings, while the electromagnetic means 32, 33, e.g., have permanent magnets. Reference is now made to Figure 6 showing a cross-sectional drawing of a fourth embodiment of the dual propeller CR aerial propulsion system 10 according to the present invention. In the fourth embodiment, the system 10 further comprises a sensor arrangement having at least two sensor elements 34, wherein at least one sensor element 34 is arranged to each of the rotational members 71, 72, in alignment with each other. In the embodiment of Figure 6, the at least one sensor element 34 is stationary in relation to the second rotational member 72, and is arranged to the mentioned electronic controller 50. The sensor arrangement allows estimation of relative position or speed of the two rotational members 71, 72, enabling improved control of the electric motor.

Reference is now made to Figure 7 showing a principle drawing of a further embodiment of the dual propeller CR aerial propulsion system 10 according to the present invention. The embodiment shows an alternative arrangement of the (upper) blades of the first propeller 20, wherein the blades are arranged substantially in line with the electric motor.

The above described embodiments can be combined and modified to form other embodiments within the scope of the attached claims.

Modifications

In a modification, the propellers 20, 21 can have any number of blades.

In a further modification, the electronic controller 50 can be arranged to any of the rotational members 71, 72.

In a further modification, each of the electromagnetic means 31-33 or parts of the electromagnetic means 31-33 can contain windings or permanent magnets or both.

In a further modification, number of electromagnetic means 31-33 is more than two, so they form multiple air gap structure.

In a further modification, the windings could be in the first rotational member 71. List of designations

10 - dual propeller counter-rotating aerial propulsion system

20 - first propeller

21 - second propeller 31, 32, 33 - electromagnetic means associated with first and second rotational members for powering the rotation of the first and second rotational members in opposite directions about a central shaft

34 - sensor element of a sensor system arrangement

40 - DC connection between electronic controller and DC source 41 - multiphase connection between electronic controller and the electromagnetic means

50 - electronic controller for controlling voltages and currents in the electromagnetic means

61, 62 - bearings

70 - a central shaft with a first and a second end

71 - a first rotational member, located proximate the first end of the central shaft, that rotates in a first direction about said central shaft

72 - a second rotational member, located between said first rotational member and said second end of said central shaft, that rotates in an opposite direction to the first rotational member's rotational direction and about the central shaft

73 - passage in carrying structure of second rotational member for electric connections 74 -mechanical reinforcements of carrying structures of first and second rotational members

80 -blade mounting arrangements

90 - means for transferring electric power from an exterior power source to the electronic controller, wherein said electric power transfer means are located between the second rotational member and the second end of the central shaft 91 - stationary contacts (part of the means for transmitting electricity from an external power source to the electronic controller)

92 - stationary holder for the electric contact

93 - rotary contacts 94 - rotary holder for the rotary contact