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 and includes a mass or counterbalance.

Background

Existing marine inboard propulsion systems are predominantly powered using an internal combustion engine. There is an increasing need for carbon reduction in the marine environment. Consequently there is increasing interest to develop propeller powered craft driven directly from an electric motor drive system.

The electric motor drive system uses multiple radial flux electric direct current (DC) motors rather than larger axial flux alternating current (AC) motors. The multiple radial flux motors provide efficient, high power with resilience to motor failure which is desirable when at sea. Selection of the DC motor allows maximum efficiency of use of stored energy from in-board DC battery supplies.

A problem which can occur with any marine propulsion system is that motor drive system rotational inertia can exacerbate instabilities on the hull of a vessel from forces imposed by impacting waves while water pressure variations from the sea, applied to the propellor, can cause vibrations and shock to the motor drive system.

The present invention arose in order to mitigate the risk of the aforementioned problems and in order to improve output efficiency of a DC drive system.

Prior Art

Chinese utility model CN 2013671 11 (Wu Jinzeng) discloses an electricity-saving electrically powered boat with two accumulators and an electric motor which has a small generator connected to an electrical controller. An output shaft is provided with a counter weight flywheel and a rotating speed detector. Japanese patent application JP 2012006462 (Diesel United KK) discloses a counterrotating propeller propulsion device capable of driving both a rear propeller and a front propeller.

International patent application WO9414649 (ABB Stroemberg Drives OY) describes a propeller drive system for a vessel with two contra-rotating propellers disposed on two coaxial shafts. The power supplies comprise first and second frequency converters. A control unit comprises means for controlling the frequency converters so that the direction of rotation of the motors and their rotational speed can be varied.

Summary of the invention

According to a first aspect of the invention there is provided at least one pair of electric radial flux motors which are connected to an input shaft, each motor of a pair of motors rotates in the same sense as the other, at least one of the motors is connected to a rotating mass operating as a flywheel which rotates in an opposite sense to both the motors.

An advantage of the flywheel is that it is able to release stored kinetic energy when instantaneous power requirements increase; and it is able to absorb kinetic energy and vibrational shock loads, for example when there is a sudden loss of resistance to a propellor or continual, varying vibrational loads.

Another advantage of the rotating mass or flywheel is that it provides vibration damping from the propellor shaft. Where the mass of the propellor shaft exceeds that of the motor drive system the rotating mass or flywheel provides additional tortional vibration damping to all associated components in a drive train. This minimises shock vibration and so reduces related wear and risk of damage.

The rotating mass or flywheel also provides extra comfort and a ‘smoother’ ride as it acts as a counterbalance to rotational forces.

In extreme conditions as the belt drive and flexible couplings have a specific breaking strength, should either (or both) snap or fail this feature may be considered a sacrificial component of the system to minimise damage to the motor drive assembly and/or gearbox , for example in the event of a propellor snag.

As the motor drive requires no lubricants, coolants or large gearboxes, it is sustainable and smaller than similar power rated systems. In some embodiments the at least one motor is connected to a common input axis by way of at least one toothed drive belt. An advantage of this arrangement is that motor trains can be connected in order to provide variable power outputs.

The toothed belt allows precision synchronisation of each of the motors which helps to reduce EMC emissions caused by harmonic imbalance.

In some embodiments the at least one motor is connected to the mass, which is operable as a flywheel, by way of at least one toothed drive belt. Ideally an output shaft of each motor of a pair, shares a common axis.

Preferably the input shaft transmits torque to the output propellor shaft via a toothed belt.

In some embodiments at least one pump for delivering coolant to the motor.

In some embodiments at least one additional pair of electric radial flux motors are connected to the input shaft.

Ideally at least one of the additional motors is connected to a mass which is also operable as a flywheel.

Optionally the at least one motor is connected to the mass which is operable as a flywheel by way of at least one toothed drive belt.

Preferably the motor drive is supported within a rigid frame that is adapted to be secured to a vessel.

Where required valve connections permit flow of coolant to be directed to one or more selected motors. Mountings are optionally provided in the rigid frame to receive power and control lines.

In some embodiments separate frame sections are separable and a flexible coupling enables removal of a drive belt. Optionally slots or mounting holes are provided for adjustment and alignment of the input shaft to the propellor shaft.

Ideally the motor drive includes a removable flange and an adaptor for connection to the propellor shaft. A power transfer mechanism, with an interchangeable drive belt and pulley system, allows the gear ratio to be varied. A drive belt tensioning means helps to maintain correct drive belt tension. Thus another advantage of the invention is that it allows easier maintenance and access to restricted spaces and thereby enables quicker replacement and repair of chains and gearboxes.

In some embodiments the motor drive includes a sensor, such as an electro-magnetic interference (EMI) sensor which sends a feedback signal to control a characteristic of at least one of the pair of electric radial flux motors.

A feedback signal control is input into a processor in order to enable a characteristic of at least one pair of smaller motors to be monitored, and in response thereto, a drive current or the magnitude or phase of a drive current to be varied in order to cancel harmonics and/or reduce EMC emissions and/or reduce vibrations, and so improve efficiency from at least one of the pair of electric radial flux motors.

The motors and ancillary equipment are mounted to the rigid frame in a manner that allows ease of maintenance whilst built to appropriate ratings to counter harsh conditions found in the hull of marine vessel. Electrical and hydraulic couplings are industry standard mechanisms to allow ease of maintenance and replacement of components.

The chassis is mounted in the rigid frame and the propellor shaft connection allow for installation adjustability. These features simplify retrofitting to existing vessels as direct replacement of an internal combustion engine for new builds.

The toothed belt and pulley drive and chassis design allows for modularity by attaching additional pairs of motors drive devices along the linear axis of the centre drive shaft whilst chassis physical size and components are scalable for different power output motors.

During operation, opposed direction gyroscopic inertia mass, optionally driven by the main drive shaft, is designed to cancel gyroscopic moments of inertia effects on vessel stability and hull vibrations.

The fact that multiple smaller motor configurations may be deployed provides additional resilience to distortional damage from natural hull flex of the power train providing improved reliability on bearings and connections; and also reduce a requirement to build additional strengthening into a motor mounting part of the hull. Furthermore the 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 access space. The configuration builds in operational resilience from motor redundancy into the design providing increased safety against a stranded vessel.

The present invention will now be described 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 propellor 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 about the chassis allowing access to motor couplings for controls, power, and coolant supplies and opposed rotation of drive system to balance mass to neutralise moments of inertia; 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 propellor 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. 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 drives 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 at 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 the fore and aft plane 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 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 9, a belt drive system incorporating a tensioning device 3 comprises of a pair of tensioning wheels 1 attached to a free end of a pair of radial tensioning arms 2. At their opposite ends, the two tensioning arms share a pivot point 3 where they are connected to main chassis as shown in Figures 1 and 2.

Tension is applied by squeezing the tensioning wheels about loose sections of the belt by means of a threaded bar from the axle of the pair of tensioning wheels 1 . The floating pair of wheels allow correct tension of the belts regardless of direction of belt travel by naturally adjusting their position in tandem to the belt edge taughtened from motor torque thus always tensioning the loose belt edge.

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 4 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 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 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 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 the motor drive system within the hull of a vessel. The first image is in dry dock when the hull will be in its natural straight form including the propellor shaft and the shaft of the motor. The second image (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 the motors on a separate drive shaft that is perpendicular to the propellor shaft, the stresses are near eliminated. The length of the motor drive system is short enough that the effects of hull flex are negligible. The requirement for oversized motor casings, bearings and mountings are eliminated.

As shown in Figure 5, the motor drive system employs flexible shaft couplings between drive shaft and propellor shaft 1 and between motor drive systems coupled in series 2. This further reduces flexing effects of the hull as shown in Figures 6A and 6B and Figures 7A and 7B whilst managing fine misalignment of motor drive system mounting in relation to the propellor shaft 3 and propellor shaft flex, vibration and tail whip 4. The coupling is adaptable for various propellor shaft sizes and or existing couplings.

The pulleys that support the drive belts described in Figure 1 , 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 to the propellor shaft.

The centre drive shaft described in Figure 1 has a flexible coupling whilst the chassis 2 Figure 1 , splits in the axis perpendicular to the centre drive shaft to allow simple replacement of the drive belts. Mounting brackets located on the walls of the chassis allow spare drive belts to be safely secured in position about the centre drive shaft providing the fast installation of a new 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 embodiments described, without departing from the scope of protection, as defined by the claims.