Field of the Invention.

The present invention is concerned with an electric machine. More specifically, the present invention is concerned with an electric machine having rotor position detector means.

Background of the Invention.

Electric motors are one form of electric rotary actuator and use an electric input to produce a mechanical rotary output (a torque). Such motors are used in a wide variety of technical fields, and different types of motor are used for different applications, depending on the nature of the electrical input (e.g. AC/DC, phase etc) and the nature of the mechanical output required (high force low speed, low force high speed).

Known electric machines exhibit several problems.

Firstly, copper is often used for the rotor and/or stator windings. Copper is both expensive and heavy. Due to demand in recent years and increasing demand for the future as electrical actuation becomes more prevalent, it is likely to further increase in cost.

There is a drive to make electric machines more efficient both to manufacture and to operate (i.e. in terms of the percentage of energy successfully converted to the desired form of output). Improvements such as low friction materials for the rotor bearings, low friction brushes in brushed motors, high efficiency gear trains and such like have provided incremental increases.

Many motors, in particular, are used in applications where it is highly beneficial to be as light as possible. In particular, motors for actuation in vehicles benefit from being lighter, because the overall efficiency of the vehicle can be reduced. This benefits commercial aircraft, UAVs as well as electric and hybrid automobiles and other types of vehicles.

Higher efficiency is beneficial for battery powered motors because the batteries will last longer, thereby reducing the frequency of battery changes as well as the cost and environmental impact of battery production and disposal. Due to the level of precision required in motor design, as well as the high part count, electric machines can often make up the bulk unit cost of many products, particularly domestic products. As such, there is a need to reduce the cost of motors which will have a significant beneficial effect on the cost of the overall product. A further disadvantage of known electric machines is that high power motors require significant current at the motor terminals· This is a safety concern.

A yet still further disadvantage is that electric machines emit radio frequency signals which may interfere with other electronics. In some electric motors, it is necessary to know the rotational position of a pole of the rotor with respect to some datum such as a stator winding to enable the electric motor controller to energise stator windings in the correct sequence efficient operation of the motor. Typically, one or more Hall effect sensors are embedded in the stator or rotor to detect poles of the rotor during motor operation. The Hall effect sensors may also be used to obtain an estimated initial starting position of the rotor. A common problem, however, with this arrangement is that the initial starting position can often only be provided within an estimated but large window of rotation such as, for example, 60 degrees and this can hinder efficient and fast starting of the motor.

It is an aim of the present invention to provide an improved electric machine.

Objects of the Invention.

An object of the invention is to mitigate or obviate to some degree one or more problems associated with known electric machines.

The above object is met by the combination of features of the main claims; the sub- claims disclose further advantageous embodiments of the invention.

Another object of the invention is to provide an improved electric machine with rotor position detector means.

One skilled in the art will derive from the following description other objects of the invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention.

Summary of the Invention.

According to a first aspect of the invention, there is provided an electric machine comprising: a primary mechanical output; a plurality of electric sub-machines configured to drive the primary mechanical output, each of said plurality of electric sub-machines having a rotor with a known rotational relationship with the primary mechanical output; wherein two or more of said plurality of electric sub-machines includes a rotor position detector device; and wherein at least one of said two or more electric sub-machines has its rotor rotationally offset by a set amount relative to a rotor of at least one other of said two or more electric sub-machines.

Each rotor position detector device may comprise one or more Hall effect sensors which may be embedded into respective stators or rotors of said two or more electric sub machines.

The set amount for rotationally offsetting the rotor of one of said two or more electric sub-machines with respect to a rotor of another of said two or more electric sub-machines may comprise a selected, predetermined, or calculated amount which may be less than 180 N, where N is a number of stator winding pairs in each of said plurality of electric sub machines.

Preferably, at least half of said plurality of electric sub-machines includes a rotor position detector device wherein each of said electric sub-machines including a rotor position detector device has its rotor rotationally offset relative to rotors of remaining ones of said electric sub-machines including a rotor position detector device. The other half of the plurality of electric sub-machines may be paired with respective one of the electric sub machines provisioned with a rotor position detector device. This enables the motor drive controller to control pairs of the electric sub-machines based on at least data received from the rotor position detector device of one electric sub-machine in a pair of electric sub machines.

More preferably, a majority and more preferably all of said electric sub-machines includes a rotor position detector device wherein each of said plurality of electric sub machines has its rotor rotationally offset relative to rotors of remaining ones of said plurality of electric sub-machines.

Preferably also, initial rotor positions on start up for some or all of said electric sub machines are derived, extrapolated, or calculated from rotor position signals provided by some or of said rotor position detector devices.

A rotor of one of said plurality of electric sub-machines may be rotationally offset by a set amount relative to at least one other of said plurality of electric sub-machines by indexing a mechanical output of said one of said plurality of electric sub-machines with respect to the primary mechanical output of the electric machine.

Preferably, there is provided a controller configured to: monitor a parameter of the electric machine indicative of the power of the electric machine; and, electrically /electronically engage or electrically/electronically disengage one or more of the plurality of electric sub-machines dependent upon the monitored parameter, so as to increase the number of sub-machines simultaneously driving the primary mechanical output at higher electric machine powers. Each of the sub-machines may be configured to be selectively electrically disengaged. In other words, the power input/output to the sub-motor may be disconnected electronically.

The controller is preferably configured to store sub-machine usage information, electrically/electronically engage and electrically/electronically disengage each sub machine based on the sub-machine usage information. The controller may be configured to engage sub-machines with lowest usage first and configured to disengage sub-machines with highest usage first. The controller may be configured to engage a further sub-machine of the plurality of sub-machines at a power interval, in which each sub-machine has a maximum rated power of at least twice the power interval. This ensures that, for typical electric motors, they are operated at peak efficiency, rather than maximum power (which is less efficient). More preferably, each sub-machine has a maximum rated power of at least three times the power interval.

According to a second aspect of the invention there is provided a method of operating an electric machine, comprising the steps of: providing an electric machine having a primary mechanical output and a plurality of electric sub-machines configured to drive the primary mechanical output, each of said plurality of electric sub-machines having a rotor with a known rotational relationship with the primary mechanical output; providing two or more of said plurality of electric sub-machines with a rotor position detector device; and rotationally offsetting a rotor of at least one of said two or more electric sub-machines by a set amount relative to at least one other of said two or more electric sub-machines.

According to a third aspect of the invention there is provided an electric machine comprising: a primary mechanical output; a plurality of electric sub-machines configured to drive the primary mechanical output, each of said plurality of electric sub-machines having a rotor; wherein only one of said plurality of electric sub-machines includes an operational rotor position detector device; and wherein relative rotational positions of the rotors of all of the plurality of electric sub-machines with respect to the primary mechanical output are known. In the event that any of the other electric sub-machines has a rotor position detector device then such device can be made non-operational, but may be made operational again should the single operational rotor position detector device fail.

Preferably, the rotor position signals from said single operational rotor position detector device are used to control each of said plurality of electric sub-machines. According to a fourth aspect of the invention there is provided a method of operating an electric machine, comprising the steps of: providing an electric machine having a primary mechanical output and a plurality of electric sub-machines configured to drive the primary mechanical output, each of said plurality of electric sub-machines having a rotor with a known rotational relationship with respect to the primary mechanical output; providing only one of said plurality of electric sub-machines with an operational rotor position detector device; and controlling each of said plurality of electric sub-machines using rotor position signals from said rotor position detector device.

The electric machine is preferably an electric motor, in which case it preferably comprises a drive train connecting the outputs of the plurality of electric sub-machine rotors to simultaneously drive a primary output shaft.

The motor according to the present invention is intended to replace a conventional, single rotor electric motor.

Preferably, the electric machine comprises a plurality of separate electric sub-motors, each comprising individual rotors and stators. In this way, the invention can be manufactured using a plurality of “off the shelf’ motors as the electric sub-machines/sub-motors.

Preferably the motor comprises at least 3 separate electric sub-motors.

The provision of a plurality of electric sub-motor rotors in order to provide the required output has many advantages over the prior art, including a significant saving in the weight of the motor, as well as the weight of a gear box, which can be constructed from more lightweight material due to the division of the total output torque required across the number of sub-motors installed (e.g. six sub-motors would each provide one sixth of the torque etc). Therefore e.g. plastics materials may be used where metals were previously required.

Preferably the drive train comprises a substantially identical gear assembly for each of the plurality of sub-motors, each gear assembly configured to gear the output of the respective sub-motor, and each gear assembly engaged with a primary output gear connected to the primary output shaft.

The gear assemblies may be engaged with the primary output gear at equally spaced positions around the primary output gear. This results in a mechanically balanced output, reduced noise and wear on the rotor bearings or bushes.

The primary output gear is preferably fixed for rotation with the primary output shaft. Each gear assembly may comprise at least: an initial stage configured to gear the output from the respective sub-motor, a first intermediate stage configured to gear the output from the first stage, and, a final stage configured to engage the primary output gear. Each gear assembly may comprise a second intermediate stage between the first intermediate stage and the final stage.

This allows even higher gear ratios. It is advantageous because smaller electric motors tend to run optimally at higher speeds.

Preferably the initial stage and the second intermediate stage are coaxially aligned, and preferably the initial stage and the second intermediate stage are mounted on a first common shaft and are arranged to contra-rotate on the first common shaft.

The first intermediate stage and the final stage may be coaxially aligned. Preferably the first intermediate stage and the final stage are mounted on a second common shaft and are arranged to contra-rotate on the second common shaft.

By aligning gear stages on a common shaft and allowing them to contra-rotate, the shaft becomes less prone to noise, vibration and high forces in use as it is stabilised by the contra-rotating action.

Due to the reduced (split) torque on the gear arrangements, the drive train may comprise gears constructed from a plastics material in certain applications.

The following is an example of the benefits of a multi-core motor compared to a single-core motor and as such these benefits are apparent in electric machines constructed in accordance with the first to fourth aspects of the invention.

A traditional brushed or brushless electric motor of a known actuator may run at 12V DC at 3A, providing (for example) 60mNm of output torque at 6000 rpm (628 rad/s). This may be referred to as original motor A "OM-A". Such gear boxes are known in the art and reduce the speed by a factor of 2000 whilst increasing the torque by the same factor. Such a combined actuator and gear box will be referred to as original motor system "OMS-A". In OMS-A, losses through the gear box may be assumed to be 1 to 2% of the total output. The present invention breaks the single OM-A motor, referenced above, into a plurality, e.g. six individual, smaller sub-motors with the aim of producing the same mechanical output. The composite motor is known as CNM-A. If the rotor coil of the above referenced motor is split into sub-motors having six equal parts, each new individual sub-motor would provide lOmNm at 6000 rpm (one-sixth of the output torque at the same speed). By summing the output torques at the same speed, the same output as the original single motor system OM- A described above, would be provided.

It will be noted that each new smaller sub-motor (which we will referred to as NM- 1 to NM-6) will each only be required to carry one-sixth of the current, that is 0.5A at 12V DC. It will also be noted that the rotor wire needs only to be one-sixth of the thickness in order to carry this smaller current. As such, the amount of wire mass required for the six individual sub-motors compared with the original motor OM-A is approximately 80% less (i.e. only 20% or one fifth of the original wire mass).

Because the power requirement of each sub-motor is relatively low, the magnetic flux across the sub-motor coil is also lower than the equivalent single rotor motor. In other words, each of NM-1 to NM6 requires one sixth of the flux (and thus one sixth of the magnetised material).

In addition, the rotor of NM-1 to NM-6 is much smaller than OM-A. Therefore, the gap required between the stators in order to surround the rotor of each sub-motor is reduced. As such as well as requiring one sixth of the flux, each motor only requires it to be established across a smaller gap. This leads to a further benefit, by an inverse square law relative to the amount of magnetic material required. Therefore, each of NM-1 to NM-6 requires less than one-sixth of the magnetic material in OM-A. In reality, the approximate size and weight reduction of the total magnet mass is approximately 80%. In a similar system which utilises electro-magnets to establish the magnetic field of the stator, a similar power reduction into the stator coils would also be realised. This is because the strength of the magnetic field is dependent upon the power within the electromagnetic coil, and the air gap, both of which can be reduced for smaller motors.

Turning to Figure 1, various combinations of motors are shown in tabular form. The columns are as follows:

Column A Number of sub-motors Column B Potential difference across each sub-motor input Column C Current used per sub-motor Column D Output torque per sub-motor Column E Summed output torque Column F Percentage copper saving on rotor wire material Column G Percentage saving on magnetic material in stators.

Because the diameter of the rotor wire decreases the smaller the rotor is, the cross- sectional area also decreases and hence the amount of copper required.

The total torque output is always 60Nm (at the same speed for each arrangement). With the reduction in current comes the associated reduction in core wire diameter, and an associated reduction in cross sectional area in mm ² (which is proportional to the copper mass used). The final column represents the reduction in copper material required. The present example uses 6 motors and as such realises a reduction of about 80%.

An additional benefit of the composite motor is that the reduction of current in each sub-motor NM-1 to NM-6 means that, where NM-1 to NM-6 have brushes, the brushes can be made from steel, rather than carbon, which in part results in a much longer life of the motor. For example, a typical steel brush small motor of the above type will last approximately 875 hours compared to OM-A which may only last 500 hours. Small rotors have a high start-up torque and larger rotors have a lower star-up torque but a comparatively high running torque at low speed. A further benefit of the present invention is to provide both a high speed and a high torque from the same unit. Stall speed is also improved.

Preferably, the plurality of electric sub-motors comprises brushless DC (BLDC) motors. Preferably the plurality of electric sub-motors comprises at least 4 to 6 motors, more preferably 6 (although any number is envisaged including 8 motors or 10 motors). As can be seen from Figure 1 , the benefit in terms of copper saving becomes less as the number of motors increases. Six sub-motors and eight sub-motors each represent a good compromise between this saving and complexity/cost of manufacture.

In the case of six sub-motors, each gear assembly, or drive train is only required to handle one-sixth of the torque of the original prior art motor design and, as such, each of the gears can be constructed from light weight, low-strength materials such as plastics materials. It will be noted that only the final output gear and shaft needs to be able to carry the entire torque output of the system. Therefore, the primary output gear may also be constructed from a plastic material.

This results in a significant weight saving and manufacturing cost saving over the prior art systems, which typically require metal gears.

An experiment on a known industrial ball valve results in a known single-core motor (24V, 0.6A) turning the valve through 90 degrees (from an open to a shut position) in 16 seconds. Using six smaller sub-motors with the same total power requirement (24V, 0.6A) turns the same valve in 3 seconds. This is a clear energy saving of around 80%.

Turning to Figure 3a, the characteristics of a known electric motor OM-A are shown. The x-axis represents output torque (T), and the y-axis represents either current (A), speed (S), output power (P) or efficiency percentage (E). Known motors are usually run at maximum power (P) - i.e. around point PI in Figure 3a because it provides the best power- weight ratio. As will be noted, the efficiency E is far from the maximum possible. Operating at maximum efficiency (point P2) will not provide a beneficial power to weight ratio. Turning to Figure 3b, the characteristic of CNM-A is shown. The x-axis scale is the same. As a result of the above-mentioned weight saving by splitting the motor into several sub motors, each motor NM-1 to NM-6 can be over specified. The additional mass from overspecification of the motors would not be problematic as it is offset by the aforementioned savings. By over specifying the motors, each can be run nearer to its peak efficiency, whilst providing an improved power to weight ratio over OM-A (i.e. run at point P3).

It will be noted that the starting efficiency of the composite motor CNM-A in Figure 3b is not as high as the eventual running efficiency. To run CNM-A across a broad range of speeds, the invention according to the first to fourth aspects can be employed. This is shown in Figure 3c.

As the composite motor CNM-A starts, only one of the sub-motors NM-1 is engaged to drive the output (the remaining motors are preferably disengaged electromagnetically). As the power (P) of the composite motor CNM-A increases past a first threshold Tl, a second sub-motor NM-2 is engaged. The first threshold Tl is at the point where the efficiency (E) of a single motor is about to drop off, and as such the addition of a second motor NM-2 "stretches" the efficiency curve. Again, the efficiency of two motors will eventually drop off, and at threshold T3, a third sub-motor NM-3 is engaged, and so on. In this manner, the efficiency of the composite motor CNM-A is kept at a high level and also relatively constant across the operating range. As such, CNM-A can be run across a large range of powers with high efficiency, unlike known motor OM-A.

The invention according to the first to fourth aspects is suitable for use in a range of applications.

According to the invention there is provided a fluid pump comprising a motor according to one of the first to fourth aspects. The pump may be a liquid pump in the domestic, commercial or industrial field, for example: pumps in heating systems, fuel pumping systems, pumps for swimming pools, pressure pumps in fire engines, hoses and fountains, pumps in drinks coolers and ice making machines, pumps in oil refineries, chemical, pharmaceutical & power generating plants, pumps in drinks manufacturing, pumps in refrigeration and freezer systems, pumps in ships / boats / submarines, pumps in water cooling systems, cooling towers, server room temperature control, pumps in mines for de-watering or similar, pumps in de-salination plants, reverse osmosis plants, pumps in breweries, distilleries, bottling plants, pumps in the utility water industry, waste-water treatment and sewage treatment, filtration systems i7n the water industry, and pumps in pressure washers and showers.

The pump may be a gas pump in the domestic, commercial or industrial field, for example: pumps for air conditioning units, exhaust pumps/ fans in mines, air circulation fans, extraction fans, gas circulation units in the gas industry, gas circulation units in liquid bottling plants, motors in compressors, and domestic, commercial and industrial ventilation systems.

According to the invention there is provided a conveyor comprising a motor according to at least one of the first to fourth aspects. The conveyor may be employed in, for example: industrial conveyor belts, baggage handling systems, baggage carousel (airport), freight handling systems, moving walkways, pedestrian walkways, residential stair lifts, ski chair lifts, escalators, vehicle loading ramps, wheelchairs and mobile chairs, and mobile seating in lecture theatres and sports arenas.

According to the invention there is provided an aircraft system comprising a motor according to one of the first to fourth aspects. The system may be employed in, for example: helicopter rotor drive motors, propeller motors, flaps and control surfaces, landing gear deployment, remote control aeroplane or helicopter motors, aeroplane or helicopter doors, aeroplane extending entry ramps, cargo bay doors, loading ramps, and microlite aircraft.

According to the invention there is provided an aerospace system comprising a motor according to at least one of the first to fourth aspects. The system may be employed in, for example: large crawler systems for transporting heavy items, systems for unfurling solar panels, control systems for telescopes or other instrumentation, air recycling systems, environmental control systems, cargo doors, robotic arms and booms, and, assisted movement in spacesuits.

According to the invention there is provided a domestic, commercial or industrial appliance comprising a motor according to at least one of the first to fourth aspects. The appliance may be, for example: a blender, a fridge, a freezer, a dish / glass washer, a tumble dryer, a washing machine, a microwave, a toaster, a rotary oven, a spit roasting machine, a hand drier, a hair dryer, or, a power-tool.

According to the invention there is provided a fairground or theme park ride comprising a motor according to at least one of the first to fourth aspects. The ride may be, for example: a carousel, a ferris wheel, a roller coaster, or, dodgems.

According to the invention there is plant machinery comprising a motor according to at least one of the first to fourth aspects. The machinery may be, for example: grader systems for roads, digger scoops and arms, dumper tipping systems, cement mixer mobile, or, cement mixer vehicle based.

According to the invention there is provided a vehicle comprising a motor according to at least one of the first to fourth aspects used as a drive source. The vehicle may be, for example, wheel hub or engine replacement/hybrid system or used as a starter motor.

The vehicle may be a car or truck for example, or on a hybrid train.

Brief Description of the Drawings.

The foregoing and further features of the present invention will be apparent from the following description of preferred embodiments of various electric machines according to the present invention which are provided by way of example only in connection with the accompanying figures, of which:

FIGURE 1 is a table showing savings in the materials of the present invention;

FIGURE 2 is a graph of a statistic from Figure 1 ;

FIGURES 3a to 3c are motor performance graphs;

FIGURE 4a is a schematic underside view of a part of a first electric machine in accordance with the present invention;

FIGURE 4b is an underside schematic view of the electric machine of Figure 1 showing a casing;

FIGURE 4c is a side view of the electric machine of Figure 1 ;

FIGURE 5 is an end on cross-sectional view of an electric sub-machine for the electric machine of Figure 1 ;

FIGURE 6 is an electrical commutation diagram for a BLDC motor;

FIGURE 7 is a schematic of a control system for an electric machine in accordance with the present invention;

FIGURE 8 is a schematic view of a primary mechanical output for another embodiment of an electric machine in accordance with the invention;

FIGURE 9 is a schematic view of output gear indexing for the embodiment of the electric machine of Figure 8;

FIGURE 10 is a Hall effect transition diagram for the embodiment of the electric machine of Figure 8;

FIGURE 11 is a Hall effect transition diagram for another embodiment of an electric machine in accordance with the invention; FIGURE 12 is a schematic view of a pump assembly comprising a motor according to the present invention;

FIGURE 13 is a schematic view of a washing machine comprising a motor according to the present invention;

FIGURE 14 is a schematic view of a car comprising a motor according to the present invention; and

FIGURE 15 is a schematic view of a part of the car of Figure 14.

Description of Preferred Embodiments.

The following description is of preferred embodiments by way of example only and without limitation to the combination of features necessary for carrying the invention into effect.

Reference in this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments, but not other embodiments.

It should be understood that the elements shown in the FIGS, may be implemented in various forms of hardware, software or combinations thereof. These elements may be implemented in a combination of hardware and software on one or more appropriately programmed general-purpose devices, which may include a processor, memory and input/output interfaces.

The present description illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.

Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. Thus, for example, it will be appreciated by those skilled in the art that the block diagrams presented herein represent conceptual views of systems and devices embodying the principles of the invention.

The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term "processor" or "controller" should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor ("DSP") hardware, read-only memory ("ROM") for storing software, random access memory ("RAM"), and non-volatile storage.

Turning to Figure 4a, a motor 100 preferably comprises six electric sub-motors 102, although more or less electric sub-motors may be deployed depending on the use to which the motor 100 is put. There is, however at least two electric sub-motors as a minimum. Preferably, the electric sub-motors 102 are BLDC motors.

Each electric sub-motor 102 has an output shaft 104 on which a motor output gear 106 is mounted. The output shaft 104 and motor output gear 106 share a motor axis 108 (see Figure 4c). Parallel to and offset from the motor axis 108, a first gear assembly 110 is provided having an input gear 112 of diameter Dl, connected by a shaft 114 to an output gear 116 having a diameter D2. The gears 112, 116 and the shaft 114 are mounted to rotate about a first gear assembly axis 118. A second gear assembly 120 is provided, having an input gear 122 having a diameter D3 connected by a shaft 124 to an output gear 126 having a diameter D4. The gears 122, 126 and the shaft 124 are mounted to rotate about a second gear assembly axis 128.

The third gear assembly 130 is provided comprising an input gear 132 having a diameter D5, connected by a shaft 134 to an output gear 136 having a diameter D6. The gears 132, 136 and the shaft 134 are mounted to rotate about a third gear assembly axis 138. A fourth gear assembly 140 is provided having an input gear 142 having a diameter D7, connected by a shaft 144 to an output gear 146 having a diameter D8. The gears 142, 146 and shaft 144 are arranged to rotate about a fourth gear assembly axis 148.

The motor 100 comprises a primary output gear 150 connected to an output shaft 152 for rotation about an output axis 154. In use, the axis 108, 118, 128, 138, 148, 154 are all parallel. The gear assemblies 110, 120, 130, 140 successively form a drive train between the electric sub-motor 102 and the output shaft 152. As such, the motor output gear 106 is engaged for rotation with the input gear 112 of the first gear assembly 110. The output gear 116 of the first gear assembly 110 is engaged for rotation with the input gear 112 of the second gear assembly 120. The output gear 126 of the second gear assembly 120 is engaged for rotation with the input gear 132 of the third gear assembly 130. The output gear of the third gear assembly 130 is engaged for rotation with the input gear 142 of the fourth gear assembly 140. The output gear 146 of the fourth gear assembly 140 is engaged for rotation with the primary output gear 150 of the motor 100.

Due to the fact that each of the input gears 112, 122, 132, 142 each has a larger diameter (Dl, D3, D5, D7 respectively) than the output gears 116, 126, 136, 146 (D2, D4, D6, D8 respectively) the gear chain steps down the speed of the electric sub- motor 102 and consequently increases the torque thereof such that the input at the primary output gear 150 is of a relatively low speed and high torque compared to the output shaft 104 of the sub motor 102.

By making the input gears 112, 122, 132, 142 the same diameter (D1=D3=D5=D7), and the output gears 116, 126, 136, the same diameter (D2=D4=D6) the alternate gear assemblies 110, 130 can be stacked on top of each other and coaxial (i.e. axes 118 and 138 align). Alternate gear assemblies 120, 140 are also stacked and coaxial (i.e. axes 128 and 148 align). This makes the gear train more compact. Referring again to Figure 4a, six such assemblies are provided comprising six electric sub-motors 102, preferably equally spaced around the output axis 154 of the motor. As such, each of the output gears 146 of the gear chains engages in a different position around the circumference of the output gear 150 such that the forces applied to the output gear 150 are cumulative across each of the six sub motors 102.

Referring to Figure 4b, the entire assembly is placed within a compact housing 156 in which the series of individual sub-motors 103 may comprise “off the shelf’ BLDC motors.

Referring again to Figure 4c, the BLDC electric sub-motor 102 has a rotor 158 which may be a permanent magnet rotor. In this embodiment, the rotor 158 is surrounded by a stator 160 comprising a plurality of stator windings 161 (Figure 5). However, it will be understood that the principles described herein apply equally to BLDC electric sub-motors having an internal stator surrounded by an external rotor as is commonly found in BLDC motors for self-balancing scooters and the like.

In the motor 100 of Figure 4c, at least one and preferably at least two of the electric sub-motors includes a rotor position detector device 162. The rotor position detector device 162 preferably comprises at least one Hall effect sensor 164 and, in some embodiments comprises three such Hall effect sensors 164 as best seen in Figure 5 which shows an end view of an electric sub-motor 102. The three Hall effect sensors are preferably embedded in the stator rotationally separated by 120 degrees, although this is not essential. The Hall effect sensors 164 could, in some embodiments, be arranged in the rotor 158.

It will be understood that any suitable rotor position detector device or system may be employed in the invention.

Typically, in a BLDC motor such as any of the electric sub-motors 102, the stator windings 164 are energized in a certain sequence with typically one winding being positive, one winding being negative, and the third winding being powered off. Torque production is caused by the attraction and repulsion between the stator field and the permanent/electro magnets of the rotor 158. Maximum torque is achieved when these two fields are orientated at 90 degrees to each other, and torque diminishes as the fields align. Therefore, in order to keep the motor turning, the stator’s magnetic field changes position as the rotor field “catches up” with it.

In order to energize the correct stator winding at the correct or most efficient time, the rotor position must be known. Rotor position is detected by the one or more Hall effect sensors 164 which monitor or detect the rotor’s position, i.e. monitor or detect the rotor’s pole positions. BLDC motors typically have three Hall effect sensors mounted either to the stator as shown or to the rotor and use what is known as six-step electrical commutation as shown in Figure 6. When a rotor pole passes a sensor 164, it produces either a high or a low signal to indicate which rotor pole (N or S) has passed. This switching of the three hall effect sensors 164 from high to low or from low to high provides rotor position information every 60 degrees. As shown in Figure 6, in six-step electrical commutation, each of the three windings (U, V, W) is either energized positive, negative, or off, depending on whether each of the three Hall effect sensors 164 (HI, H2, H3) has a high or a low state. Consequently, in this arrangement, the electrical commutation occurs in 60-degree segments. Whilst this is normally sufficient for controlling continuous operation of the electric sub-motor 102, it creates a problem on initial start-up of the electric sub-motor.

At initial start-up, the initial rotor position based on a detected pole of the rotor 158 is only known within one of the sixty degree segments, i.e. there is an error margin of up to 60 degrees in the assumed initial position of the rotor 158, because, when the rotor 158 is stationary, the Hall effect sensors 164 in this embodiment are accurate to only 60 degrees. There is a need therefore to obtain a more accurate estimate of the position of the rotor 158 to enable a faster and more efficient start-up phase for the electric sub-motors 102. This is particularly desirable for stop-start motors, i.e. motors which are repeatedly being started and stopped in quick succession.

The invention also provides a controller and method of operating a composite electric machine which is configured to allow selective disengagement of its constituent sub- motors.

A composite electric machine 200 comprising a controller according to the present invention is shown in Figure 7. The machine 200 comprises three sub-machines 202, 204, 206 driving a primary shaft 208. Each sub-machine can be individually and selectively electrically or electronically disengaged from the shaft 208 by a controller 210.

Each sub-machine 202, 204, 206 is connected to an electrical power storage unit 212 by power lines 214, 216, 218. Electrical power sensors 220, 222, 224 are positioned in the power lines to measure the electrical power being converted by each sub-machine 202, 204, 206 respectively. Each sensor feeds back to the controller 210.

In use, the controller 210 can thereby monitor the electrical power being converted by the composite machine 200 and engage the required sub-machine in order to maintain high efficiency in accordance with Figure 3c.

The controller 210, which comprises control software running on a CPU with an associated memory, does not always engage the same sub-machines in the same order. In one embodiment, the controller 210 will engage alternate sub-machines as the first sub machine. For example, in the first use of the machine 200, sub-machine 202 may be engaged first, later supplemented by machines 204, 206. In another embodiment, the controller 210 retains a work history for each submachine on its memory. The controller will select the next sub-machine to be engaged depending on its work history, in order to encourage even use of all sub- machines. The sub-machine with the least use will be engaged next. The controller 210 does not always disengage the sub-machines in order. Instead, if the controller 210 needs to disengage a sub-machine based on a drop in machine power, it will disengage the sub machine with the highest use.

It will be understood that the controller 200 can control any number of sub-machines such as the electric sub-motorsl02 of Figures 4a to 4c. The controller 200 may also be configured to control said electric sub-motors 102 based on rotor position signals received from said one or more rotor position detector devices 162.

In an embodiment of the motor 100 of Figures 4a to 4c where there are six electric sub-motors 102, although the number of electric sub-motors 102 may be more than or less than six depending on the motor 100 application, the resulting electric motor assembly is such that each of the electric sub-motors 102 can be assembled with the primary output gear 150 such that a rotor 158 of at least one of said electric sub-motors 102 has a known rotational positional relationship with the primary output gear 150/primary output shaft 152. This can be implemented in embodiments of motor 100 without or without a drive train between the electric sub-motor 102 and the primary output gear 150 or primary output shaft 152, i.e. where an output gear 106 of the electric sub-motor 102 is meshed either directly or indirectly via a drive train with said primary output gear 150. It will be understood that, where the rotor 158 of an electric sub-motor 102 is assembled in the motor 100 such as to have a known rotational positional relationship with the primary output gear 150/primary output shaft 152 then, by extension, the same known rotational positional relationship exists between both the output shaft 104 and the output gear 106 of the electric sub-motor 102 with the primary output gear 150/primary output shaft 152.

In an embodiment of the motor 100 where each of the electric sub-motors 102 is assembled such that its rotor has a known rotational positional relationship with the primary output gear 150/primary output shaft 152, it is possible to provide only one of said electric sub-motors 102 with an operational rotor position detector device 162 and to use the signals from said operational rotor position detector device 162 in the controller to control motive operation of all of said electric sub-motors 102. This is because the rotor position signals from the only electric sub-motor 102 being provisioned with an operational rotor position detector device 162 can be applied to any and all other electric sub-motor 102 as the rotational positions of all of the rotors of the plurality of electric sub-motors 102 with respect to the primary output gear 150/primary output shaft 152 can be determined from their respective known rotor rotational positional relationships with the primary output gear 150/primary output shaft 152. This therefore simplifies control of the motor 100 and enables BLDC motors not having any operational rotor position detector device/system to be utilised as the electric sub-motors 102 save for one such motor. Control of the motor 100 is simplified further in this embodiment when all of the electric sub-motors 102 are assembled with their rotors in a same rotational position with respect to the primary output gear 150/primary output shaft 152 because then the signals from the one operational rotor position detector device 162 are identically applicable to controlling each of said electric sub-motors.

In a more preferred embodiment of the motor 100 in accordance with the invention, it is preferred that at least two, but preferably more of the electric sub-motors 102 are each provided with an operational rotor position detector device 162 and where said at least two electric sub-motors 102 each have a known rotational relationship with the primary output gear 150/primary output shaft 152.

In the following description, a reference to a rotor position detector device 162 should be taken as a reference to an operational rotor position detector device 162.

In this embodiment of the motor 100, at least one of said two or more electric sub machines 102 has its rotor 158 rotationally offset by a set amount relative to a rotor 158 of at least one other of said two or more electric sub-machines 102.

By offsetting one of the rotors 158 of one of the electric sub-machines 102 by a set amount, i.e. a selected, predetermined or calculated rotational amount, with respect to the position of one of the other rotors 158 and knowing the respective rotational relationships of said rotors 158 with the primary output gear 150/primary output shaft 152, it means that it is possible to determine from the signals from the two or more rotor position detector device 162 an initial stationary position of each of said rotors 158 within a reduced rotational error amount compared to a conventional motor arrangement. This can be better understood when considering the situation where each of the rotors 158 has a same rotational positional relationship with the primary output gear 150/primary output shaft 152. In such a case, because of the relative alignment of the rotors 158, when all of the rotors 158 rotate, their respective rotor position detector devices 162 (Hall effect sensors 164) will switch in unison thereby providing no new information about any of the rotor initial stationary positions as all of said rotor position detector devices 162 will exhibit the same rotor initial position error range of 60 degrees, for example. However, when the rotors 158 are rotationally offset relative to each other within their known rotational positional relationships with the primary output gear 150/primary output shaft 152, the outputs of the rotor position detector devices 162 provide new information which enables a determination of a decreased rotor initial position error range because said rotor position detector devices 162 will exhibit overlapping rotor initial position error ranges.

It follows from the foregoing that a greater reduction in rotor initial position error range can be achieved if most or all of the electric sub-machines 102 are provided with rotor position detector devices 162 and have their rotors 158 rotationally offset by known amounts with respect to each other and preferably such that none share the same offset rotational positional relationship with the primary output gear 150/primary output shaft 152.

In one embodiment, at least half of said plurality of electric sub-motors 102 include a rotor position detector device 162 with its rotor 158 rotationally offset relative to rotors 158 of remaining ones of said electric sub-motors 102. More preferably, all of said plurality of electric sub-motors 102 include a rotor position detector device 162 with its rotor 158 rotationally offset relative to rotors 158 of remaining ones of said plurality of electric sub motors 102.

In this embodiment, initial rotor positions on start up for some or all of said electric sub-motors 102 are derived, extrapolated, or calculated from rotor position signals provided by some or all of said rotor position detector devices 162.

A rotor 158 of at least one of said plurality of electric sub-motors 102 may be rotationally offset by a set amount relative a rotor 158 of at least one other of said plurality of electric sub-motors 102 by indexing a mechanical output of said one of said plurality of electric sub-motors 102 with respect to the primary output gear 150.

Referring to Figure 8, shown is another embodiment of the motor 100 in accordance with the invention in which the primary output gear 150 of the motor 100 is directly meshed with respective output gears 106 of eight electric sub-motors 102 although, in another embodiment, the primary output gear 150 of the motor 100 may be meshed with output gears 146 of drive trains connecting the output gears 106 of the eight electric sub-motors 102 with the primary output gear 150. In either case, as shown in Figure 9, it is possible to index different rotational offset positions for the rotors 158 of each of the eight electric sub-motors 102 by, for example, offsetting the pinion of the output gear 106/146 by one or more teeth.

In the embodiments illustrated by Figures 8 and 9, each output gear 106/146 has seventeen teeth and the primary output gear 150 has 102 teeth. Where each of the eight electric sub-motors 102 has a rotor position detector device 162 comprising three Hall effect sensors 164 then Figure 10 illustrates the Hall effect transitions versus rotational angle for the eight rotor position detector devices 162. This provides a non-uniformly spaced pattern of Hall effect transitions over one motor rotation of 360 degrees, but, despite this, it enables the rotor initial position error range for each of the eight electric sub-motors 102 to be substantially decreased as the pattern of Hall effect transitions repeats. In Figure 10, the transitions marked “T” comprise only the Hall effect transitions which would occur if all of the rotors 158 of the eight electric sub-motors 102 had the same rotational alignment with respect to the primary output gear 150.

If, in the embodiments illustrated by Figures 8 and 9, each output gear 106/146 is provisioned with an even number of teeth, for example, sixteen teeth, then Figure 11 illustrates the Hall effect transitions versus rotational angle for the eight rotor position detector devices 162. It can be seen that, in this embodiment, the Hall effect transitions are uniformly spaced by 7.5 degrees through one full rotation. The uniform set of Hall effect transitions, i.e. rotor pole transitions, enables the controller algorithm to be substantially simplified with very accurate estimates of initial rotor starting positions. Again, the transitions marked “T” comprise only the Hall effect transitions which would occur if all of the rotors 158 of the eight electric sub-motors 102 had the same rotational alignment with the primary output gear 150.

The above described electric machines can be used in a variety of applications.

The application of the invention to a motor is particularly well suited to drive pumps in various applications. For positive displacement pumps such as gear pumps, gerotor pumps and the like, prior art motors tend to project from the rear of the pump housing. As shown in Figure 12, a positive displacement pump 300 such as a gerotor has an inlet 302 and an outlet 304. A prior art motor 306 (shown in hidden line) drives the pump through an input shaft 308.

A motor 310 according to the present invention is provided in place of the prior art motor, comprising a plurality of sub-motors 312 connected to a gearbox 314 which in turn drives the shaft 308.

As can be seen, the provision of a motor according to the present invention provides a more compact arrangement. Because a number of smaller sub-motors is used, the system can be shorter and wider, which often better matches the footprint of the pump in use. Furthermore, the motor according to the present invention is more reliable because if one motor were to fail, the remaining motors would carry on. This is equally applicable to impeller-type pumps such as axial flow or centrifugal pumps.

In situations where it is beneficial to reduce the axial length of an assembly, the present invention is particularly well suited. For example, in a domestic washing machine or tumble dryer it is beneficial to use as much axial space as possible for the drum.

Referring to Figure 13 a washing machine 400 generally comprises a housing 402 containing a stationary drum 404 containing a rotating drum 1106 used to agitate and spin clothing during the washing cycle by rotating about an axis A.

In known machines, it is desirable to provide a drum 406 which is as deep as possible to increase the load capacity. As such, known motors such as a motor 408 as shown in Figure 13 are offset from the axis A and connected by a belt drive 400. This is because the motor 408 has to be large in order to provide the required torque and speed to spin the drum 406.

A further problem with this arrangement is that the motor 408 is off-centre and as such vibrations can occur which requires mass damping within the housing 402. This makes the unit heavy and cumbersome. A series of six sub-motors 412 is provided according to the present invention and shown schematically in Figure 13. It will be understood that a gearbox will be required between the sub-motors 412 and the drum 406, but it can be seen that the present invention can be positioned about the rotation axis A whilst leaving sufficient space for the drum 406.

This reduces the vibration caused by the offset mass of the motor 408, reducing the need for damping. It also provides a quieter and more efficient product as the belt drive can be eliminated. It also allows the unit to be made more compact (if required).

Turning to Figure 14, a hybrid car 500 is shown having an internal combustion engine 502 which drives wheels 504, 506, 508, 510. An example wheel 504 is shown in Figure 15 driven by a shaft 512 from the engine 502. As described, the car 500 is a hybrid, and can be driven using power from a battery 514. The battery 514 is connected to a wheel motor 516 comprising six individual motor cores 518 and a gearbox 520 which engages with the shaft 512. The motor 516 is configured in accordance with the present invention and the six motors provide a combined drive to the shaft 512 to rotate the wheel 504.

It will be noted that as a hybrid, when the shaft 512 is driven by the engine 502, the motor 516 can be back driven to power and charge the battery 514.

As can be seen in Figure 15, the individual sub-motors 518 can be positioned around the shaft 512 and even within the wheel 504 to provide a very compact arrangement which has minimum impact on vehicle packaging space.

Whilst car 500 has been described as a hybrid car, it will be understood that it could be a fully electrically driven car, i.e. not including an internal combustion engine unit in a hybrid configuration.

A significant technical advantage of the electric machine described herein is that, even if one or more of the electric sub-motors fail, the electric machine can continue to operate on remaining operational sub-machines albeit at a lower maximum output torque or power.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. It can be appreciated that any of the features described herein may be used with any embodiment. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims.

In the claims hereof, any element expressed as a means for performing a specified function is intended to encompass any way of performing that function including, for example, a) a combination of circuit elements that performs that function or b) software in any form, including, therefore, firmware, microcode or the like, combined with appropriate circuitry for executing that software to perform the function. The invention as defined by such claims resides in the fact that the functionalities provided by the various recited means are combined and brought together in the manner which the claims call for. It is thus regarded that any means that can provide those functionalities are equivalent to those shown herein.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art.