Field

The present invention relates to an electric powered marine inboard propulsion system.

More particularly, but not exclusively, the invention relates to a belt driven electric motor suitable for use with an inboard propulsion system

Background

Existing marine inboard propulsion systems are powered using internal combustion engines, which may be petrol or diesel.

Currently propellers powered directly from an electric motor drive system are relatively uncommon. However, due to the increasing need for carbon reduction in the marine environment, there is currently significant interest in providing an electric powered propulsion system for marine use.

A particular object is to provide an electric powered propulsion system which is capable of being fitted into existing vessel design when replacement of an internal combustion engine is planned.

Prior Art

Chinese patent application CN 111994250 (University of Jiangsu Science & Tech) discloses an electric propulsion device for a ship.

International patent application WO 2021/208661 (SHENZHEN XTOOLTECH INTELLIGENT CO LTD) discloses an automobile starting load measuring method and apparatus.

Summary of the Invention

According to a first aspect of the present invention there is provided a marine motor drive comprising: at least one pair of electric radial flux motors which are connected to an input shaft, each motor of a pair rotates in an opposite sense to the other, at least one of the motors is connected to the input shaft by a toothed drive belt; and the input shaft connects to an output propellor shaft. In some embodiments an output shaft of each motor, of a pair of motors, shares a common axis so that the two motors may be driven in opposite senses, one to another, thereby providing a combined input torque to a propulsion system of a vessel.

Ideally at least one of a pair of motors is connected to the input shaft by way of a toothed drive belt. An advantage of the toothed drive belt is to combine their respective output torques and so prevent motors from stalling or snatching and thereby smooth their outputs.

Ideally in some embodiments the input shaft transmits torque to the output propellor shaft via a gearbox.

As the marine motor drive is specifically intended to be suitable for retro-fitting into existing vessels, the motor drive is advantageously housed in a watertight container with a watertight connection to a propellor shaft for power delivery to a propellor thereby enabling operation in a harsh marine environment.

Preferably at least one pump is provided for delivering coolant to the motors. Thermostatic sensors in thermal contact with the motors, provide signals which cause the pump to pump coolant to one or more of the motors.

Ideally valve connections to permit flow of coolant to be directed to selected motors.

In some embodiments at least one additional pair of electric radial flux motors are connected to the input shaft. In this configuration additional pairs of motors may be connected in order to provide greater power output torque.

Preferably the drive system is provided in, and supported by, a rigid frame that is adapted to be fitted to and secured in a vessel, for example by a crane or hoist.

In some embodiments of the motor drive the mountings receive power and control lines via dedicated connections that may be supported by the rigid frame.

In some embodiments frame sections are separable one from another, and a flexible coupling enables removal of a drive belt. Ideally slots or mounting holes are provided for adjustment and alignment of an input shaft to the propellor shaft.

Optionally a removable flange and an adaptor are provided to facilitate connection to the propellor shaft. In some embodiments a power transfer mechanism with an interchangeable drive belt and pulley system are provided to modify a ratio of motor input rotational speed to drive shaft output rotational speed.

Preferably a drive belt tensioning means is provided to maintain correct drive belt tension. The belt tensioning means is unique in that it automatically maintains correct tension of a drive belt on a correct belt edge, regardless of motor direction. An advantage of this provides instant and uniform belt tensioning where the motor direction is reversed quickly and regularly.

In some embodiments a vibration sensor is provided which feeds back a vibration feedback signal to control a characteristic of at least one of the pair of electric radial flux motors. Ideally the vibration feedback signal is used to control a characteristic of at least one pair of smaller motors to cancel gyroscopic moments of inertia from the at least one of the pair of electric radial flux motors.

The propulsion system uses multiple radial flux electric direct current (DC) motors in preference to larger conventional axial flux alternating current (AC) motors. The multiple radial flux DC motors provide efficient, high power and also provide a resilience to failure which is desirable when at sea. The selection of the DC motor allows maximum efficiency of use of stored energy from DC battery systems.

The motors and associated parts are mounted to their chassis in a manner that allows ease of maintenance whilst built to appropriate standards and ratings to counter harsh conditions that are typically encountered in the hull of vessels. All electrical and hydraulic couplings are therefore industry standard mechanisms to allow ease of maintenance and rapid and straightforward replacement of components.

A chassis is effectively defined by the rigid frame and propellor shaft connection allow for installation adjustability and simple retrofit to existing vessel designs, as either a direct replacement or alternative to an internal combustion engine for new build vessels.

A toothed belt and pulley drive and assists in modularity, by enabling attaching of additional pairs of motor drives along a linear axis of a centre drive shaft. It is also understood that the chassis physical size of the rigid frame, chassis and other components are scalable for different power requirements of different sized vessels. During operation opposed direction gyroscopic inertia mass of the opposed motors are optimised so that they cancel any gyroscopic moment inertia effects on vessel stability and hull vibrations.

Furthermore the modular nature enables scaling to vary power output by way of multiple pairs of smaller motor configurations, thereby providing further resilience.

The system avoids distortional damage from natural hull flex of a power train comprising multiple pairs of smaller motors and so provides improved reliability on bearings and connections and reduces a requirement to build additional strengthening into a motor mounting area within a hull.

Furthermore employment of multiple, smaller, radial motor drives over conventional large, single axial drive motors reduces effort for installation and maintenance by eliminating a requirement for heavy duty lifting equipment and large access areas. The invention therefore offers operational resilience from motor redundancy and so provides increased safety against a stranded vessel.

The present invention will now be described, by way of example only, and with reference to the drawings, in which:

Brief Description of Drawings

Figure 1 is an overall view of one embodiment of a marine motor drive;

Figure 2 is an overall view of another embodiment of a marine motor drive an artist’s impression and shows two multiple motor drive assemblies connected in series and to a propeller drive shaft with propellor attached;

Figure 3 is a diagram which illustrates motion effects of a conventional axial motor drive system upon the hull of a vessel;

Figure 4 is a diagram which illustrates reduced motion effects of the invention upon the hull of a vessel;

Figure 5 is a diagrammatical view of an output drive shaft coupling and shows flex or play within the coupling, which allows for alignment error with a propellor drive shaft and flex, when the hull deflects under motion; Figure 6 is a diagram showing a vessel, at berth and when waterborne, which is fitted with a motor drive system, and shows effects of hull twist on a drive train;

Figure 7 is a diagram showing a vessel, at berth and when waterborne, which is fitted with an embodiment of a motor drive system and shows reduced effects of hull twist on the drive train;

Figure 8 is a diagrammatical view of another example of a motor drive assembly showing motor orientation and position within a rigid frame which supports a chassis, to allow access to motor couplings; and

Figure 9 is a diagrammatical view of another example of a motor drive assembly which includes a belt tensioning system that operates consistently regardless of rotational direction of motors.

Detailed Description of Preferred Embodiment of the Invention

Referring to the Figures, and in particular Figure 1 , the marine motor drive comprises: at least one pair of electric radial flux motors which are connected to an input shaft, each motor of a pair rotates in an opposite sense to the other, at least one of the motors is connected to the input shaft by a toothed drive belt; and the input shaft connects to an output propeller shaft.

More particularly the drive comprises N pairs of directly opposed electric radial DC motors 1 secured to a chassis 2. Output shafts of the motors are colinear with a centre drive shaft 3. Torque is transferred from the motors to a centre drive shaft 4 by means of toothed drive belts. The centre drive shaft is parallel to the drive motor’s rotational axis and N is a positive integer.

As shown in Figure 2, multiple sets of motor drive devices 1 and 2 can be coupled together along the linear axis of the propellor shaft 3 providing a modular capability to increase system power. The motor drive devices are coupled together with a drive shaft 4 between the motor drive devices centre drive shafts. The propulsion system is equipped with a propellor 5 profile modelled to suit the need of vessel operational requirements and the power characteristics of the selected motor drive system.

As shown in Figure 3, the layout configuration of a conventional axial motor creates undesirable motion effects on a vessel. The axial motor builds significant moments of inertia which are transferred to the vessel. Due to the vessel floating on water and not being a fixed point, inertia energy is transferred to vessel movement defined by the nautical definitions of yaw 2, roll 3 and sway 4.

A vessel is susceptible to movements in the port to starboard plane due to the relatively narrow dimensions in relation to fore and aft planes, whilst these effects are exacerbated by the keel protruding under the water to aid in the transfer of the energy. These movements cause steering difficulties for the vessel, create discomfort to occupants of the vessel, and lead to inefficiency in the motor drive system as power is used to drive against the inertia to steer in the correct direction.

Referring to Figure 4, the opposite rotational moments of inertia of pairs of opposed motors 1 , 2 can be seen to have a cancelling effect on inertia energy that is transferred to the vessel, as shown in Figure 3. When inertia energy is cancelled, undesired vessel movement for yaw, roll and sway is significantly reduced. Vessel behaviour for stability, steering and comfort is increased whilst providing better energy efficiency from driving a more stable vessel.

As shown in Figure 8 opposed motors 1 and 2, at either side of the drive shaft 3, are reversed on their respective axis of rotation, to allow mounting on opposite sides of the rigid chassis 4. This allows space on the main drive shaft for belt pulleys and eases access to supply connections 5 for controls, DC power, and coolant. Motor 2 is fitted with additional, ideally identically, sets of paired gears 6 between motor and drive shaft pulleys to allow opposite rotational of moments of inertia (shown by the arrows) to motor 1 . Another advantage of providing easier access is that repair and replacement of smaller motor sets is achieved, rather than the need to replace a single large engine installation.

As described in Figures 6 and 7, the invention therefore reduces wear and so reduces the risk of failure of system components potentially caused by natural hull flexing and twisting of a waterborne vessel.

Figure 6 shows two images of a conventional axial motor within the hull of a vessel. Figure 6A shows a vessel in a dry dock when its hull is in its natural straight form including the propellor shaft and the shaft of the motor. Figure 6B shows the flex in the hull of a waterborne vessel and the subsequent flex on the propellor shaft and the motor shaft. This flex causes premature wear and failure of motor components where typically heavy-duty motor casing, bearings and mountings are employed to minimise damage.

Figure 7 shows two images of a preferred embodiment of invention fitted in the hull of a vessel. Figure 7A shows the vessel in dry dock when the hull is in its natural straight form including the propellor shaft and the shaft of the motor. Figure 7B shows the flex in the hull of a waterborne vessel and the subsequent flex on the propellor shaft and the motor drive system.

Due to output shafts of each motor 1 being separate to the drive shaft 3 with power delivery made via a flexible drive belt, stresses exerted by the hull 2 upon the motors are eliminated. The length of centre drive shaft of the motor drive system shaft 1 , is sufficiently short that effects of hull flex are negligible. As mentioned above, the requirement for oversized motor casings, bearings and mountings are therefore eliminated.

As shown in Figure 5, the motor drive system employs flexible shaft couplings between drive shaft and propellor shaft and between motor drive systems coupled in series. This further reduces the hull flex effects as described for Figure 6 and Figure 7 whilst additionally enabling fine adjustments to avoid misalignment of motor drive system mounting in relation to the propellor shaft. Again these features reduce negative effects present in inherent propellor shafts, such as flex, vibration and tail whip. Coupling 1 is adaptable for various propellor shaft sizes and/or existing coupling methods.

Pulleys 3 that support the drive belts described in Figure 1 , and can be of differing sizes to allow a variety of gear ratio changes to suit specific operational requirements for motor power characteristics, vessel power delivery requirements and propellor design.

The chassis shown in Figure 1 employs slotted mounting location holes to allow for accurate alignment of the motor drive system chassis 2 to the propellor shaft.

Figure 8 is a diagrammatical view of another example of a motor drive assembly showing motor orientation and position within a rigid frame 4 which supports a motor drive system 1 , to allow access to motor couplings 3; for controls, power, and coolant supplies 5 and where the opposite rotation of opposed motors equalise their moments of inertia as indicated by the arrows.

The centre drive shaft described in 4 Figure 1 has a flexible coupling will the chassis 2 Figure 1 , splits in the axis perpendicular to the centre drive shaft to allow simple replacement of the drive belts.

Sufficient space is provided between the two walls of the chassis walls 2 for spare drive belts to be safely secured in position about the centre drive shaft on brackets (not shown). This enables fast installation and replacement of a worn or broken drive belt, without the need for disassembly of the centre drive shaft and chassis.

The invention has been described by way of examples only and it will be appreciated that variation may be made to the aforementioned embodiment, without departing form the scope of protection as defined in the claims.