WO2017167617A1

WO2017167617A1 - In-wheel electric motor unit

Info

Publication number: WO2017167617A1
Application number: PCT/EP2017/056796
Authority: WO
Inventors: Martin Hugh BOUGHTWOOD
Original assignee: Deregallera Holdings Ltd
Priority date: 2016-03-30
Filing date: 2017-03-22
Publication date: 2017-10-05
Also published as: GB201605365D0

Abstract

An in- wheel electric motor unit (10) for installation in a vehicle wheel, the in-wheel electric motor unit (10) comprising: a body (20) defining a substantially cylindrical motor chamber (30) having a radius R and defining a central axis; an arrangement of n motor elements (60) circumferentially spaced around the central axis, wherein each of the n motor elements (60) comprises a rotor/stator pair formed by relatively rotatable inner and outer parts (64, 62), the inner and outer parts (64, 62) being separated by a substantially annular gap (66) having a mean radius r_n, wherein n ≥3 and Σ r_n > R; and a torque transfer mechanism (80) for transferring torque generated by the n motor elements (60) to a common output.

Description

TITLE: IN- WHEEL ELECTRIC MOTOR UNIT

DESCRIPTION

The present invention relates to an in- wheel electric motor unit and particularly but not exclusively to an in-wheel motor unit for high torque applications.

In- wheel electric motors (or "hub drive" motors) are constrained in many degrees: 1) by mass to keep suspension unsprung mass to a minimum; 2) by volume to enable the system to be incorporated inside the wheel hub space; 3) by torque/speed to generate the necessary torque to move heavy loads uphill whilst at the same time having a large enough speed range to travel at maximum desired speed; and 4) power handling capacity by having sufficiently high efficiency to ensure losses can be adequately dissipated or removed whilst delivered power is sufficient to meet the needs of the application. All of these factors conspire to make the design of a high performance hub drive a difficult and often highly compromised result.

To date solutions involve either direct drive systems where the integrated motor drives the hub wheel directly and geared systems where a motor drives the wheel via either fixed or changeable gears.

Current direct drive systems typically take the form of radial flux machines comprising an outer stator and an inner rotor spaced by a running air gap. The torque generated by these machines is limited by the active interface area between the rotor and stator which is limited by motor size.

Geared systems typically focus on use of a high speed motor feeding into a gear or series of gears to achieve enhanced torque using gear reduction ratios. Sometimes the systems use a selection of gear ratios to provide a match between load speed and torque demands as they dynamically change. The need to provide space for a motor and gear system in series limits the size of the high speed motor and consequentially the inherent torque delivery of the motor.

The present applicant has identified the need for an improved in- wheel motor design that is capable of providing increased torque delivery relative to prior art techniques.

In accordance with the present invention, there is provided an in- wheel electric motor unit for installation in a vehicle wheel, the in-wheel electric motor unit comprising: a body defining a substantially cylindrical motor chamber having a radius R and defining a central axis; an arrangement of n motor elements circumferentially spaced around the central axis, wherein each of the n motor elements comprises a rotor/stator pair formed by relatively rotatable inner and outer parts, the inner and outer parts being separated by a substantially annular gap (e.g. air gap) having a mean radius r«, wherein n >3 and∑ r« > R; and a torque transfer mechanism for transferring torque generated by the n motor elements to a common output.

In this way, an in-wheel electric motor unit is provided with a plurality of n motor elements having a combined active surface area between the rotor/stator pairs that is greater than the maximum active surface area achievable for a single rotor/stator pairing having a maximum radius R. Advantageously, the in-wheel electric motor unit of the present invention combines the output of all n motor elements to generate a high torque output suited to space critical/high torque applications (e.g. powering wheels of trucks, vans or military vehicles).

The present invention is applicable to all types of electric motor (e.g. including electromagnetic and electrostatic motors). However, typically the n motor elements will be electromagnetic motor elements.

In one embodiment, the n motor elements have rotational axes substantially equally spaced radially from the central axis (e.g. to form a ring of motor elements centred about the axis).

In a conventional electric motor the maximum torque generated by the motor is proportional to the active interface area between rotor and stator parts of the motor and in particular the level of force generated in the air gap between the rotor and stator. For a conventional single motor radial flux machine configured to fit inside a motor chamber of radius R the active area A of the motor will be:

A Ί ^'single where τ single is the mean radius r_Sm_gie of the air gap and L is the longitudinal length of the air gap, and:

^single R^— d where d is the sum of the clearance between the outer part of the motor/stator pair and the motor chamber wall, the radial thickness of the outer part, and 0.5 x the air gap with in the radial direction. Clearly the value of τ single will vary between different motor designs but will always be <R.

For the motor of the present invention, the effective active area A' is the sum of the active areas of the n motor elements of radius r« is

A'=2n ∑ r, Typically r« will be the same for each of the n motor elements (i.e. r« = r) in which case

For n motor elements of identical radius r arranged in a ring formation, the maximum outer motor radius r_min:that can be accommodated within a motor chamber of radius R is:

R

1 +

sin I

and the mean radius of the air gap for each motor element will be

Γ ^rnax d

where d is again the sum of the clearance between the outer part of the motor/stator pair and the motor chamber wall. Advantageously, providing the rotor as the outer part allows d to be minimised without any performance penalty.

Using the example of an in- wheel electric motor for a passenger vehicle with R = 210mm and d = 10mrn/20mrn, the increase in effective active area provided by the multi-motor arrangement of the present invention relative to active area A achievable in a conventional single motor unit is illustrated in the following tables: Table 1 : Relative increase in active area for different values of n (R=210mm, d=10mm)

Table 2: Relative increase in active area for different values of n (R=210mm, d=20mm)

As is apparent from the tables above, selection of n >3 provides the potential for a multi- motor arrangement with an active area A' significantly greater than the maximum active area A achievable with a single motor of the same length and therefore a higher force density per unit volume of motor chamber. Whilst in these examples the enhancement in active area A' is highest in the range 4< n <12, in other cases (e.g. where R is larger relative to d), the enhancement may also be obtained with greater values of n. However, taking into account the practical considerations in constructing the torque transfer mechanism it is expected that typically 3< n <12. Nevertheless, n >12 is conceivable for very high torque applications especially where R is large relative to d.

In one embodiment, n >4 (e.g. n >5). In one embodiment, n<\5 (e.g. n<\2).

In one embodiment, n = 5 or 6.

In one embodiment, 27 r„ > 1.1R (e.g. 27 r„ > 1.2R, 27 r„ > 1.3R, 27 r„ > 1.4R, 27 r„ > 1.5R, 27 r„ > 1.6R, 27 r„ > 1.7R, 27 r„ > 1.8R or even 27 r„ > 1.9R).

In one embodiment, the outer part of each rotor/stator pair is the rotor. In this way, radius r_n may be maximised since an outer rotor may be designed to have a significantly smaller radial depth than a corresponding outer stator without penalising performance.

In one embodiment, the common output is rotatable around the central axis.

In one embodiment, the torque transfer mechanism comprises n rotary members each operative to rotate with a respective rotor of one of the n motor elements about a rotational axis of the rotor.

In one embodiment, each of the n rotary members defines an outer torque transfer surface having a radius ri smaller than the mean radius r« of the substantially annular gap of its respective motor element (e.g. ri < r«/2). In this way, a further increase of torque may be delivered via the common output.

In one embodiment, the n rotary members are positioned around the central axis (e.g. each aligned with the rotational axis of their respective motor element).

In one embodiment, the n rotary members comprise driving pinions or pulleys.

In one embodiment, the common output comprises a centrally mounted gear assembly driven (e.g. directly) by the n rotary members.

In one embodiment, the centrally mounted gear assembly comprises one or more of a central sun gear and an annular outer driver gear (e.g. to form a planetary gear system).

In the case that the outer part of each rotor/stator pair of the n motor elements is the rotor, the in-wheel electric motor unit may further comprise a brake mechanism (e.g. parking brake mechanism) configured to apply a braking force to the rotor (e.g. outer part of the rotor) of one or more of the n motor elements. Advantageously, the brake mechanism may be configured to provide a breaking force that is magnified by the torque transfer mechanism.

In one embodiment the brake mechanism includes a rotor-engaging part located within a central cavity between the n motor elements, the rotor-engaging part being configurable between an inoperative configuration spaced from the n motor elements and an operative configuration in which the rotor-engaging part applies a braking force to one or more of the outer rotor parts of the n motor elements. Advantageously such an arrangement makes efficient use of space inside the ring of n motor elements.

In one embodiment, the in-wheel electric motor unit comprises a plurality of circumferentially spaced power units operative to power the n motor elements (e.g. n power units each operative to power a respective one of the n motor elements).

In one embodiment, the plurality of circumferentially spaced power units are mounted on a cooling plate defining a plurality of cooling channels connected to a coolant source (e.g. fluid coolant (e.g. water) source). In one embodiment, each cooling channel is associated with a different one of the plurality of circumferentially spaced power units.

In one embodiment, the plurality of circumferentially spaced power units are mounted on an opposed side of the cooling plate to the n motor elements.

In one embodiment, the plurality of cooling channels are connected in parallel to the coolant source.

In one embodiment, each power unit comprises a plurality of circumferentially spaced power devices (e.g. each aligned with a respective stator coil of a multi-coil stator).

In one embodiment, each cooling channel comprises a plurality of cooling sub-paths each associated with a different one of the plurality of circumferentially spaced power devices.

In one embodiment, each of the plurality of cooling sub-paths extend in parallel (e.g. radially) from a common inlet to a respective one of the circumferentially spaced power devices.

In one embodiment, the cooling plate defines a heat transfer surface for transmitting heat from the plurality of circumferentially spaced power units to the plurality of cooling channels.

In one embodiment, the heat transfer surface includes a phase change material for assisting transfer of heat away from the power units.

In one embodiment, each of the n motor elements defines a central motor core including a central motor core cooling path.

In one embodiment, each central motor core cooling path includes a first path configured to pass coolant through the motor element in a first direction (e.g. away from the cooling plate).

In one embodiment, each central motor core cooling path further includes a second path (e.g. in parallel to the first path) configured to direct coolant in a second direction opposed to the first direction (e.g. back toward the cooling plate). In this way coolant may be returned to the coolant source via the cooling plate.

In one embodiment, each of the plurality of cooling channels connect to a respective one of the central motor core cooling paths (e.g. each cooling sub-path includes a section for directing coolant towards the central motor core cooling path after absorbing heat from its respective power device).

In one embodiment, the in-wheel electric motor unit further comprises a sensor configured to monitor the angular position of at least one (e.g. each) rotor of the n motor elements relative to the body. The sensor may be used to provide feedback about the angular position and/or speed of the or each rotors that can be used by a control system for the apparatus.

In one embodiment, the sensor comprises a magnet (e.g. split axis magnet) and magnet sensor pairing. In one embodiment, the magnet is mounted to the rotor and the sensor is mounted to the stator.

In one embodiment, the in-wheel electric motor unit further comprises a cross roller bearing. In this way robust and precise load handling may be achieved using minimal space.

In one embodiment, the cross roller bearing and torque transfer mechanism are substantially axially aligned.

In one embodiment, the cross roller bearing and torque transfer mechanism are mounted substantially concentrically (e.g. with the torque transfer mechanism being contained substantially within an outer envelope of the cross roller bearing).

In one embodiment, the cross roller bearing is mounted on an opposed axial end of the body to the cooling plate.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1A shows a schematic perspective front view of an in-wheel electric motor unit in accordance with an embodiment of the present invention;

Figure IB is a schematic perspective rear view of the in-wheel electric motor unit of Figure 1A;

Figure 2A is schematic cross-sectional end view through the in-wheel electric motor unit of Figure 1A showing the multi-motor configuration;

Figure 2B is a schematic cross-sectional side view through the in-wheel electric motor unit of Figure 1A Figure 2C is schematic cross-sectional end view through the in- wheel electric motor unit of Figure 1A showing the torque transfer mechanism and output;

Figure 2D is detail view of an individual motor unit as shown in Figure 2B;

Figures 3A-C are schematic views of a layers forming a cooling plate of the in-wheel electric motor unit of Figure 1 A.

Figures 1A and IB show an in-wheel electric motor unit 10 for installation in a vehicle wheel (not shown).

In-wheel electric motor unit 10 comprises a substantially cylindrical body 20 defining a substantially cylindrical motor chamber 30 having a radius R and defining a central axis "A". Body 20 has a front end 22 and a rear end 24 defining a circumferentially extending flange 26. As illustrated in Figure 1 A the front end 22 of body 20 is capped by a wheel mounting plate 40 with a projecting spigot 42 for mounting a wheel rim. As illustrated in Figure IB the rear end 24 of body 20 is capped by an end cooling plate 50 supporting power/control circuitry 100.

As illustrated in Figure 2A-2D, motor chamber 30 houses an arrangement of n electromagnetic motor elements 60 (in this example 5 motor elements are shown) circumferentially spaced around the central axis "A" and a torque transfer mechanism 80 for transferring torque generated by the n motor elements 60 to a common output in the form of a centrally mounted gear assembly 90 rotatable around central axis "A".

As illustrated in Figure 2B the n motor elements 60 each have a rotational axis "B" positioned at equal radial distance from the axis to form a ring of motor elements centred about axis "A". Each of the n motor elements 60 comprises an outer rotor 62 and inner multi- coil stator 64 pairing separated by a substantially annular l-2mm air gap 66 having a mean radius r. As previously discussed above, the value of r may be calculated using the formula r = R - d, where d is the radial distance between the motor chamber wall and the centre of the air gap. Advantageously, the provision of an outer rotor allows d to be minimised since the outer rotor may be designed to have a significantly smaller radial depth than a corresponding outer stator without penalising performance resulting in a maximised value of r.

In the case of a typical passenger vehicle wheel hub, R = 210mm and outer rotor 62 may be designed such that d= 10mm. For a conventional single-motor geometry the effective active area of the motor A based on a maximum mean air gap radius singU = 200mm. As illustrated, the n motor elements are close packed such that r = 58 mm and nx = 289 mm to produce an effective active area A' = 1.69A and consequentially a significant increase in the inherent maximum torque output of the motor stage. A further increase in torque output is achieved by torque transfer mechanism 80 which comprises n driving pinions 82 each mounted on an output shaft 68 of a respective one of the n motor elements 60 and operative to rotate with the outer rotor 62 of its respective one of the n motor elements 60 about the rotational axis "B" of the outer rotor 62.

5 As illustrated in Figure 2C the n driving pinions 82 are positioned around the central axis "A" in alignment with the axes of their respective motor elements 60 and the centrally mounted gear assembly 90 comprises a central sun gear 92 and an annular outer ring driver gear 94 bolted to wheel mounting plate 40 and configured to be driven by the n driving pinions 82 acting as planet gears. Each of the n driving pinions 82 defines an outer torque transfer surface

10 84 having a radius ri smaller than the mean air gap radius r of its respective motor element 60 (e.g. and therefore much smaller than the radius of the annular outer ring driver gear 94 forming the output of the motor assembly). If ri = 19mm then the torque developed at the output of the outer ring driver gear 94 will be almost 3 times the torque produced by the external rotor 62 at the airgap interface. In this way, the in- wheel electric motor unit 10 of the present invention

15 combines the output of all n motor elements 60 to generate a high torque output suited to high torque applications such as powering wheels of trucks, vans or military vehicles. In this example the total output torque prior to gearing is approximately 5 times the torque available from a conventional single-motor unit. The final gearing ratio achieved by the machine can be any number from less than 1 to very high values of 1000s but in this example (for a practical vehicle 0 hub drive) the final ratio is in the order of 5 : 1.

As shown in Figure 2A, the space inside the ring of n motor elements 60 may be used to accommodate a brake mechanism 70 (e.g. parking brake mechanism) configured to apply a braking force to outer rotors 62 of the n motor elements 60. Advantageously, brake mechanism 70 may be configured to provide a breaking force that is magnified by the torque transfer 5 mechanism 80. Brake mechanism 70 will typically include a rotor-engaging part 72 located within a central cavity 3 OA between the n motor elements 60, the rotor-engaging part 72 being configurable between an inoperative configuration spaced from the n motor elements 60 and an operative configuration in which the rotor-engaging part applies a braking force to one or more of the outer rotor parts 62 of the n motor elements 60. Advantageously such an arrangement

30 makes efficient use of space inside the ring of n motor elements 60.

Power/control circuitry 100 comprises n circumferentially spaced power units 102 each mounted on a circuit board 103 and operative to power a respective one of the n motor elements 60. As illustrated in Figure 2B, power devices 102 are mounted on an opposed side of cooling plate 50 to the n motor elements 60and cooling plate 50 defines a plurality of cooling channels 50A each associated with a different one of power units 102 and connected in parallel to a coolant source (e.g. water source).

Each power unit 102 comprises a plurality of circumferentially spaced power devices 5 104 (typically pairs of phase leg power transistors) aligned with a respective coil 65 of multi- coil stator 64 and each cooling channel 50A comprises a plurality of cooling sub-paths 50B extending radially in parallel from a common inlet 50C, each cooling sub-path 50B being associated with a different one of the plurality of circumferentially spaced power devices 104. In the illustrated example each stator includes 12 separately connected copper coils 65 mounted 0 on stator teeth each driven by a respective pair of power transistors.

Cooling plate 50 defines a heat transfer surface 5 OF for transmitting heat from the plurality of circumferentially spaced power devices 104 to the plurality of cooling sub-paths 50B. By provision of efficient cooling maximum power/current may be supplied locally to each motor coil 65. Heat transfer surface 5 OF may include a phase change material for assisting5 transfer of heat away from the power devices 104.

As illustrated in Figure 2D, each of the n motor elements 60 defines a central aluminium stator core 66 with central motor core cooling path 68 extending therethrough, the central motor core cooling path 68 including a first path 68A configured to pass coolant through the motor element 60 in a first direction away from the cooling plate 50 and a second path 68B in parallel0 to the first path 68A configured to direct coolant in a second direction back toward the cooling plate 50. Each of the plurality of cooling channels 50A connect to a respective one of the central motor core cooling paths 68. In this way coolant may be returned to the coolant source via the cooling plate 50. As illustrated in Figure IB, cooling plate 50 is connected to the coolant source via an inlet 50E and an outlet 50D.

5 Each of the n motor elements 60 further comprises a split axis magnet 70 mounted to an internal end face of the outer rotor 62 centred about axis "B" and a magnet sensor 72 to an outer end of central stator core 66 configured to monitor the angular position of rotor 62 relative to its respective stator 64. The magnet sensor 72 may be used to provide feedback about the angular position and/or speed of the or each rotors that can be used by a control0 system for the apparatus.

Multi-redundancy may be achieved by having each of the n motor elements 60 driven independently via one of two or more independent communication lines (e.g. clockwise communication line and anticlockwise communication line) so that no single communication line breakage can stop the motor element from functioning.

A cross roller bearing 96 provided on front end 22 of body 20 and axially aligned with torque transfer mechanism 80/centrally mounted gear assembly 90, the cross roller bearing 96 being mounted concentrically around the annular outer ringer driver gear 94 of the centrally mounted gear assembly 90. In this way robust and precise load handling may be achieved using minimal space.

As illustrated in Figure 2B, cooling plate 50 is formed by multiple aluminium plates including a first (top) plate 51, a second plate 52, a third plate 53, a fourth plate 54 and a fifth plate 55. First plate 51, second plate 52 and fourth plate 54 are shown in more detail in Figures 3A-3C.

Top plate 51 defines a first array of fixing holes 51 A for attaching power/control circuitry 100 (multiple bolts are provided to ensure thermally good contact), a second array of fixing holes 5 IB for bolting cooling plate 50 to central stator core 66, and a third array of holes 51C for stator coil wires to pass. Top plate 51 further includes coolant return and inlet apertures 5 ID, 5 IE for connection to coolant source.

Second plate 52 defines first, second and third arrays of holes 52A, 52B, 52C positioned to registered with first, second and third arrays of holes 51 A, 5 IB and 51C respectively on first plate 51 and further defines (in combination with the top and third plates 51 , 53) a central coolant inlet chamber 52E and the plurality of cooling sub-paths (or "fingers") 50B extending radially in parallel from common inlet 50C and a coolant return aperture 52D. The cooling sub-paths 50B are positioned so that each transistor pair of the circumferentially spaced power devices 104 sits directly above one of the fingers 50B in order to achieve maximum cooling.

Fourth plate 54 defines first, second and third arrays of holes 54A, 54B, 54C positioned to registered with first, second and third arrays of holes 52A, 52B and 52C respectively on second plate 52 and further defines (in combination with the third and fifth plates 53, 55) a plurality of radially extending paths 54E for directing coolant to a respective one of the central motor core cooling paths 68A and a coolant return aperture 54D.

Claims

Claims:

1. An in- wheel electric motor unit for installation in a vehicle wheel, the in- wheel electric motor unit comprising:

a body defining a substantially cylindrical motor chamber having a radius R and defining a central axis;

an arrangement of n motor elements circumferentially spaced around the central axis, wherein each of the n motor elements comprises a rotor/stator pair formed by relatively rotatable inner and outer parts, the inner and outer parts being separated by a substantially annular gap having a mean radius r„, wherein n >3 and∑ r„ > R; and

a torque transfer mechanism for transferring torque generated by the n motor elements to a common output.

2. An in- wheel electric motor unit according to claim 1 , wherein n >4.

3. An in- wheel electric motor unit according to claim 2, wherein n >5.

4. An in- wheel electric motor unit according to any of the preceding claims, the outer part of each rotor/stator pair is the rotor.

5. An in- wheel electric motor unit according to any of the preceding claims, wherein the torque transfer mechanism comprises n rotary members each operative to rotate with a respective rotor of one of the n motor elements about a rotational axis of the rotor. 6. An in-wheel electric motor unit according to claim 5, wherein each of the n rotary members defines an outer torque transfer surface having a radius ri smaller than the mean radius r« of the substantially annular gap of its respective motor element.

7. An in-wheel electric motor unit according to claim 5 or claim 6, wherein the common output comprises a centrally mounted gear assembly driven by the n rotary members.

8. An in-wheel electric motor unit according to claim 7, wherein the centrally mounted gear assembly comprises one or more of a central sun gear and an annular outer driver gear.

9. An in-wheel electric motor unit according to claim 4 or any of claims 5-8 when dependent upon claim 4, wherein the in-wheel electric motor unit may further comprise a brake mechanism configured to apply a braking force to the rotor of one or more of the n motor elements.

10. An in-wheel electric motor unit according to claim 9, wherein the brake mechanism includes a rotor-engaging part located within a central cavity between the n motor elements, the rotor-engaging part being configurable between an inoperative configuration spaced from the n motor elements and an operative configuration in which the rotor-engaging part applies a braking force to one or more of the outer rotor parts of the n motor elements.

11. An in-wheel electric motor unit according to any of the preceding claims, wherein the in-wheel electric motor unit comprises a plurality of circumferentially spaced power units operative to power the n motor elements, the plurality of circumferentially spaced power units being mounted on a cooling plate defining a plurality of cooling channels connected to a coolant source.

12. An in-wheel electric motor unit according to claim 11, wherein each cooling channel is associated with a different one of the plurality of circumferentially spaced power units.

13. An in-wheel electric motor unit according to claim 11 or claim 12, wherein the plurality of circumferentially spaced power units are mounted on an opposed side of the cooling plate to the n motor elements.

14. An in-wheel electric motor unit according to any of claims 11-13, wherein the plurality of cooling channels are connected in parallel to the coolant source.

15. An in-wheel electric motor unit according to any of claims 11-14, wherein each power unit comprises a plurality of circumferentially spaced power devices.

17. An in-wheel electric motor unit according to claim 15, wherein each cooling channel comprises a plurality of cooling sub-paths each associated with a different one of the plurality of circumferentially spaced power devices.

18. An in- wheel electric motor unit according to any of claims 11-17, wherein the cooling plate defines a heat transfer surface for transmitting heat from the plurality of circumferentially spaced power units to the plurality of cooling channels, wherein the heat transfer surface includes a phase change material for assisting transfer of heat away from the power units.

19. An in- wheel electric motor unit according to any of claims 11-17, wherein each of the n motor elements defines a central motor core including a central motor core cooling path and each of the plurality of cooling channels connect to a respective one of the central motor core cooling paths.

20. An in-wheel electric motor unit according to any of the preceding claims, wherein the in-wheel electric motor unit further comprises a sensor configured to monitor the angular position of at least one rotor of the n motor elements relative to the body.

21. An in-wheel electric motor unit according to any of the preceding claims, wherein the in-wheel electric motor unit further comprises a cross roller bearing.