Description

Technical Field

The present invention relates to a railway vehicle wheel comprising an electric motor directly driving the railway vehicle wheel, the electric motor comprising a stator and a rotor, where the stator of the electric motor comprising a stator disk fastened onto a stationary tubular shaft of the railway vehicle, a plurality of soft magnetic cores axially arranged and incorporated in the stator disc, stator winding arranged on the respective iron cores; and the rotor of the electric motor comprising two rotor disks arranged on both sides of the stator and journalled to the tubular shaft via bearings, short circuiting windings or permanent magnets attached to the rotor disks, a ring surrounding the stator and clamping the rotor disks, where the ring clamping the rotor disks together and the wheel rim are fastened together or consist of one piece.

The invention is such a structure of a railway vehicle wheel driven directly by an elec- trie motor where the embedded electric motor is a symmetrical-, outer-rotor-, axial- flux- , multi-pole one with concentrated windings.

Background Art

Such kind of electric motors consists of a stator built onto the stationary vehicle wheel shaft with stator coils on soft magnetic cores while the rotor consisting of two disks on both sides of the stator is journalled to the shaft via bearings, permanent magnets or shorting winding on the rotor disks and a ring setting together the disks encapsulating the stator. The setting ring and the vehicle wheel rim are fixed together or consist of one joint piece.

Those kind of wheel-motor coupling which does not need gear that is the motor and the wheel speed is equal is called direct vehicle drive. Variations of this solution are those different kinds of electrical wheel-motor drives, which are originated in joining the wheel and the driving motor. A special kind of the latest is frequently called as hub motor or in-wheel motor. In-wheel motors can be applied to drive different kinds of railway-, road- and other vehicles. As it is known from the patent publications the hub- and in-wheel motor arrangement has a wind range of variations.

As it is known the traditional electric motors are radial- flux shaped and their stator is an outer one but the rotor is placed in the inner hole of the stator, so it was obvious that the in-wheel motor development followed this arrangement. Prototype of this solution is cognizable from DE 130694. In this carriage the rotor of the electric motor is fastened to the side-surface of the wheel, the wheel shaft bearings are placed in the stator hous- ing and the vehicle body is loaded on the stator via springs. It is apparent that the motor shaft and bearings are loaded with the vehicle mass and running dynamics. Problems coming out from this fact can be solved by significant strengthening or complicating the shaft, bearings and suspension only as it is shown e.g. in DE 2501134 or DE 3927311.

From the above it can be concluded, that an inner rotor motor is suitable to realize a ve- hicle direct drive, but the solution is not a real hub or in-wheel drive because the motor is built alongside the wheel. The inner rotor motor is not the proper one for a directly driven in-wheel motor which is mentioned for the sake of completeness only.

In case of a real in-wheel motor the rotor is placed outside by necessity. Common feature of outer rotor solutions is that against the traditional arrangement an inverted so called outer rotor motor (ORM) is applied which rotor is supported with bearings on a stationary shaft and the vehicle wheel rim is attached to him too. The rotating torque is transmitted from the motor stator built onto the stationary shaft to the rotor that is the vehicle wheel via the air gap.

Prior to deep investigation of outer rotor in-wheel motors an immanent deficiency of all in-wheel motor drives should be emphasized namely that due to joining the motor and the wheel the unsprung mass of the vehicle will be grown by necessity with the motor mass.

Hereinafter the real outer rotor in-wheel motors are discussed following the inventors' various proposals with their results: how to reduce wheel motor mass and volume, sim- plify structure, assembling and maintenance, increase efficiency and reliability.

It should be noted that the basic arrangement is known already more than a century. Patented in 1896, DE 94350 presents such a construction, where the stator of the electric motor is fixed onto the shaft on the outer side of the vehicle wheel while the rotor is fastened to the outer side surface of the wheel rotating on the shaft. Strictly saying this ver- sion is not a true in-wheel motor yet. But in the DE 120289 there is already a real in- wheel solution. In this case on both sides of the stator built onto the shaft there are two embedded disks fixed together with a ring. On the inner surface of the ring the rotor winding is placed and the vehicle wheel rim is fixed to the outer surface.

Both motors applied have wounded rotors with commutators.

The above patents due to lack of technical conditions could not be realized for almost a century. But at the end of the last century discovery of rare earth magnets with high coercive force made a progress toward competitive developments. Growing demand for low-floor vehicles affirmed these tendencies too.

There is a lot of patent claims submitted and accepted based on the outer rotor version which differ in details of structure to be realized such as - motor-wheel-rim layout, mo- tor types, stator and rotor arrangement, shaft shaping, bearing, cooling, suspension, auxiliaries, etc.

In case of the outer rotor basic arrangement one of the constructing principle, as it is described in e.g. JP 5-016800, JP 5-344680, JP 10-053031 or JP 2002-136082 is the same as of the hundred year old solutions. In this case on the vehicle wheel shaft there is (are) stator(s) built on the outer or both sides, but the journalled via bearings to the axle rotor is coupled to the wheel corresponding side surface.

Another constructing principle realization of the outer rotor basic layout can be recognized according to e.g. JP 5-328687, EP 0582563, EP 0865978 or EP 2003764 which are rather close to the idea of in-wheel motor. According to this arrangement at both sides on the stationary shaft mounted stator are the end bearings with the rotor housing. The vehicle wheel rim is locked to the cylindrical housing.

Structure according to US 7,256,526 is falling under the above in spite of the fact that the solution is proposed for not a railway but for a road vehicle. This is reminiscent best of the true in-wheel motor arrangement in spite of that in a proper sense there are two outer rotor motors built side-by-side under a common housing. Here should be emphasized the evidently more compact structure due to the application of permanent magnets and special winding. At the same time there are some disadvantages too because the major parts of the in-wheel motor structure should be "fabricated from a unitary non- ferromagnetic substance" according to the mentioned publication.

It is worth to mention arrangement shown in EP 0718139 which at first sight could come under the previous theme but in point of fact it includes an inner rotor electric motor. The vehicle wheel rim is journalled to such a high diameter tubular shaft via bearing which can include the electric motor too. The electric motor shaft by means of a cycloid gear system is connected to an inner cogged wheel secured to the vehicle wheel outer side. Similar solution can be recognized in DE 9302351 and JP 2001-10488 too.

A fully different solution is presented in EP 0866772 where the drive is provided by an outer rotor axial- flux electric motor. There is a secured to the stationary shaft stator disk with concentric ports in which separate magnetic cores are fit. Stator windings are pulled on both projecting ends of the magnetic cores. The rotor consists of two symme- trical cylindrical disks with flanges facing to each other, surrounding the stator and journalled to the axle. There are permanent magnets attached to the inner surface of disks. The vehicle wheel rim is fastened to one of the outer surfaces of disks. To increase the output power the solution has such a version too where two or more motors are cascade-like built-in one common house significantly increasing the axial size of the electric motor. (It should be noted, that this document does not concern the mechanical fastening of the stator-core windings - in any case metal can not be used - nor the machine cooling: neglecting this aspects the layout can not be realized.)

Vehicle wheel motor drive can be realized implementing inner rotor axial- flux motor too, e.g. according to WO 2008/015782.

Likewise a rather unusual solution is described in patent publication DE 10026959 too. The implemented unipolar traction motor in essence is placed beside the vehicle wheel so it can not be called not an inner- nor an outer rotor type one, but in spite of the originality this proposal does not promise any advance from the viewpoint of size- and weight reducing, moreover it leaves open a lot of technical problems to be solved.

As it is marked out from some patent publications in case of designing direct vehicle wheel drives the motor cooling is an essential aspect. To solve it there are available numerous solutions complying with different arrangements.

The wheel motor air cooling presented in patent publication DE 2501134 is the simplest solution. Between the right- and left sided motors placed under a common housing there is an air inlet and at the wheel side is placed an outer fan. Incoming from suction mouth air is streaming partly through motor air-gap partly between the rotor and the shaft and passing out via air gap and cutout ports of the rotor cope.

More efficient cooling can be reached in case of implementing a separate air forcing unit. According to patent publication JP 5-328687 beside the motor a ring-shaped duct with axial jets is placed and connected to the air supply apparatus. Both side of the mo- tor house have ports. The cooling air coming from the air supply unit via jets and one side ports of the motor house flows through the motor air-gap and goes out via outlet ports on the other side. Essentially a similar principle is applied for wheel drive air cooling in patent publications JP 2001-010488 and JP 2002-136082.

In case of wheel drive described in patent publication JP 5-344680 a separate air supply unit is providing the cooling air but the air is blown in through a tubular shaft. From the shaft air flows into the motor housing via radial ports on one of the sides of the stator then passing the air-gap and the axial slots of the stator is going out through the ports on the other side of the stator.

Wheel drive cooling presented in US 7,256,526 is like the previous solution. In this case the incoming and outgoing air of the supplier unit is flowing forwards and backwards via the channels in the shaft. Between the stator winding and the shaft there are axial holes in the magnetic core of the stator connected to the air inlet and outlet channels. Such a wheel-drive cooling system is described in patent publication EP 0868772 too.

Beside the relatively easy realizable air cooling, liquid cooling systems are turning up too. In case of wheel-drive known from patent publication JP 10-053131 there are two axial paths in the shaft connected to the cooling liquid circulating equipment.

In the stator between the stator windings and the shaft there are axial channels with ring-shaped distributing headers at both ends. Headers are connected to shaft axial paths via radial bores of the same shaft. Solution presented in patent publication EP 2003764 is the same.

Solution according to patent publication EP 0865978 is practically similar with some modification that between the magnetic core and the shaft a closed space shaped and connected to axial paths of the shaft. In patent publication EP 0582563 between the magnetic core and the shaft is a spiral cooling path connected to the shaft axial paths alike. To understand better incompleteness of existing solutions it is worth to summarize main technical requirements to be met by an up-to-date in- wheel motor as follows:

- proper traction power,

small power losses, high efficiency,

- negligible excess volume and weight compared to a traditional railway wheel

(that is less unsprung mass),

simple, reliable, robust construction, withstanding dynamic loads,

- totally enclosed performance excluding harmful influence (dust, humidity, contamination) of environment,

- minimal harmful environmental effect (noise, pollution), easy assembly/disassembly and less maintenance.

To realize the above conflicting requirements with an acceptable compromise, key factors are the proper selection of the motor structural arrangement and the cooling.

Survey of relevant patents well illustrate the efforts of inventors aimed to reach a com- pact integration of the railway wheel (rim) and a motor but which goal in spite of due diligence could not be entirely realized. The basic reason of fails is that in most cases there is an overwhelming axial dominancy of size and mass of the electric motor over the wheel moreover in case of implementing liquid cooling too. The opportunity of combining a properly sized to wheel geometry compact motor with an efficient cooling system has been still missed. A not proper space maximizing motor type could not be a winner in spite of the best possible cooling applied but a properly selected motor type can not be incorporated into the wheel successfully without efficient cooling.

It is a fact that most of recited patent publications are not discussing subjects of cooling and degree of protection of the motor at all or only very sloppily in spite of that this are decisive factors of size reducing and real practicability.

It would be promising and could result in a limited width according to publication a solution where on both sides of the motor ports are placed and the cooling air supplied is blown in the motor house on one side and flowing through the air-gap is coming out on the other side. But having a look at the layout it is obvious that the goal is not reached moreover air cooling implemented to cut the size does not solve rather increases the problems. Ventilation realized via holes of the rotor is necessarily very noisy (sirens are working on the principle of air flow modulation and this very idea is applied in this case as a cooling) moreover via the open ports the motor can be easy contaminated.

A solution is promising intensive cooling where an air supply unit blows the air into the electric motor. The air flow passes partly the air-gap partly the axial paths of the stator going out via ports opened on the opposite side of the stator. Inasmuch as the air inlet is possible via hollow shaft only, the shaft should be oversized or weakened to provide an intensive cooling furthermore the high speed cooling air flowing via the relatively nar- row holes and supplying the air compressor is pretty noisy which is a significant disadvantage.

Those liquid cooling solutions are much better where in the stator or between the stator and shaft there are one or more axial paths connected to a cooling liquid circulating unit via two axial holes machined in the shaft because the latest is not much weakened and by this way the stator cooling can be significantly improved in case of a totally enclosed motor performance too. In spite of the advantageous cooling system applied in this case the aimed volume and weight reduction could not be reached because the incorporated radial- flux type motor has weak specific features.

It is worth to note proposals which claim suitability in case of any vehicle that is in railway and road vehicles too so are essentially universal. In point of fact this inventions are suitable only for road or only for railway vehicles but in most cases for not any. Basic reason of this is that the dynamic loads of a road and a railroad vehicle wheels can differ by magnitudes. It is obvious if imagine and compare a car's running on the blacktop and a locomotive's on the steel rails. Between wheel motors driving a road and a railroad vehicle should be such a big difference than between a rubber tire and a steel rim respectively. The competitive solution is not universal but vehicle-specific and the universal solution maybe in principle operable but practically useless.

According to the above it is clear and not by chance that in spite of the numerous patents available real railway in-wheel motors till now are not in serial production yet. Object of the Invention

It is an object of the present invention to propose a railway vehicle wheel that overcomes the above-mentioned problems. A further object of present invention is to meet basic technical requirements listed in previously that is to create such an in- wheel motor which comes into existence so that a railway wheel and a motor is integrated in one closed unit with fundamental limitation that the active - current and flux conducting - parts of the electric motor are placed within the width (130...150 mm) of the railway wheel rim between the latter and the shaft. Consequently the main goal is to realize such a self driving railway wheel which looks like a traditional railway wheel with practical- ly the same dimensions and weight.

At the same time the invention should complete the task too that the incorporated into the wheel and strictly limited in volume and weight electric motor could develop enough power and torque to drive a railway vehicle.

General Description of the Invention

Recognition leading to the solution is that not the railway wheel and rim should be customized to some sort of an electric motor but just the opposite: strongly respecting the hundred year old perfectly shaped traditional railway wheel such a motor should be incorporated into the limited space between the wheel shaft and the rim which is capable to develop enough power and torque for railway traction. Otherwise speaking if instead of a generally accepted radial- flux motor a following optimally the wheel geometry, totally enclosed, multi-pole, axial-flux synchronous or induction motor is incorporated so that the wheel itself and it's main parts create the motor's housing, shaft and bearing furthermore the stator and the rotor of the motor is intensively cooled then this solution is capable to meet power and torque demand of majority of known railway vehicles. These objects are achieved by a railway vehicle wheel comprising an electric motor directly driving the railway vehicle wheel, the electric motor comprising a stator and a rotor, where the stator of the electric motor comprising a stator disk fastened onto a stationary tubular shaft of the railway vehicle, a plurality of soft magnetic cores axially arranged and incorporated in the stator disc, stator winding arranged on the respective iron cores; and the rotor of the electric motor comprising two rotor disks arranged on both sides of the stator and journalled to the tubular shaft via bearings, short circuiting windings or permanent magnets attached to the rotor disks, a ring surrounding the stator and clamping the rotor disks, where the ring clamping the rotor disks together and the wheel rim are fastened together or consist of one piece. According to the improvement the width of the stator is less than the width of the wheel rim, the stator is provided with a liquid cooling, where the stator coils forming the winding are surrounded by channels of the liquid cooling, and/or the stator coils are directly cooled; on the surfaces of rotor disks radial cooling ribs are shaped, the number of the radial cooling ribs on the surfaces of the rotor disks equals to the number of the rotor poles and the centre lines of the cooling ribs coincide with respective pole pitch lines.

According to a preferred embodiment of the railway vehicle wheel two stator plates are fastened to the shaft, the stator plates comprising openings in which soft magnetic core coils are fit and the interspace between the two stator plates is filled with synthetic resin.

According to a further preferred embodiment of the railway vehicle wheel the cooling channels forming a cooling system are placed in planes perpendicular to the shaft so that adjacent cooling channels are displaced relating to each other in a wavelike manner.

According to a yet further preferred embodiment of the railway vehicle wheel the stator winding is manufactured from tubular conductors also connected to a unit for circulating the cooling liquid.

According to a yet further preferred embodiment of the railway vehicle wheel an inner space of the in-wheel motor defined by the shaft, rotor disks and clamping ring is hermetically separated from the environment.

According to a yet further preferred embodiment of the railway vehicle wheel the outer surfaces of the rotor disks and the cooling ribs arranged on said outer surfaces are pro- vided with a self-cleaning layer.

According to a yet further preferred embodiment of the railway vehicle wheel the outer surface of the rotor disks between two ribs is deepened.

The in-wheel motor of the railway vehicle wheel according to the present invention is featured by large power (traction force) small sizes and unsprung mass which is reached by special shaping of the stator and the rotor and their intensive cooling. The invention solves the direct driving of the wheel excluding the necessity of a separate motor, gears or couplings so results in a significant reduction in vehicle mass and space and higher traction efficiency without the disadvantage of considerable growing of unsprung mass. The proposed wheel motor is exclusively simple, robust and excepting the rim and the bearings - which are all at once the vehicle bearings too - eliminates the necessity of any wearing part.

Brief Description of the Drawings

Further details of the present invention will now be discussed with reference to the following figures, wherein:

Fig. 1 illustrates a perspective view of a preferred embodiment of the railway vehicle wheel motor according to the invention;

Fig. 2 shows a view of a section I-II across the magnetic core and between them

marked in Fig. 1;

Fig. 3 illustrates a half section-half view III-IV marked on Fig. 2 perpendicular to the shaft plane;

Fig. 4 shows a central detail view of section V marked on Fig. 2 perpendicular to the shaft plane; and

Fig. 5 illustrates a peripheral detail view of section V marked on Fig. 2 perpendicular to the shaft plane.

Detailed Description

In a preferred and exemplary embodiment of a railway vehicle wheel 1 motor according to the invention the railway vehicle wheel is built together on a shaft 4 with a driving motor consisting of an inner stator 5 and an outer rotor 6.

Shaft 4 is of a hollow tubular type. Due to bearing sizes the shaft 4 diameter is relatively large hence there is no necessity to use solid shaft from mechanical considerations so this solution can reduce the vehicle mass and the unsprung mass of the in-wheel motor too. Tubular shaft makes easy to introduce different conductors to the elements of the wheel motor.

Shaft 4 can be locked to the corresponding vehicle parts by means of fastening slots 7 on both ends. The lock is not shown since a person skilled in the art know well many solutions to perform this job some of which were mentioned in the previous review.

As it can be seen from Fig. 2 in the middle there are two flanges 8 and 9 on the shaft 4. Between the two flanges in two planes are bored 3-3 radial holes 10 to introduce sepa- rate conductors. Radial holes 10 of the same plane include an angle 120° and the holes of the two separate planes are angled to each other by 60° weakening the shaft 4 minimally.

Stator plates 11 and 12 are fastened to the outer sides of flanges 8 and 9 with bolts 13 respectively. Stator plates 11 and 12 are made of glass-filament epoxide resin or other reinforced composite well known for a person skilled in the art. Between the perimeters of the stator plates 11 and 12 are linking spacers 14 which are made of similar type of electrically no conducting composite as the plates 11 and 12.

Circumferentially on the stator plates 11 and 12 segment-like openings 15 are cut out facing to each other. In the openings 15 magnetic cores 16 are fit. The magnetic cores are made of soft magnetic (dynamo or transformer) steel or specially pressed so called soft magnetic composite (SMC) material. In case of three-phase machines the number of magnetic cores 16 is divisible by 3, in present case this number is 33.

In compliance with Figs 2 and 3 between the two stator plates 11 and 12 are placed separate stator windings 17 on magnetic cores. In present case stator windings 17 are con- nected with each-other according to the known three-phase Y-scheme. Three ends of stator winding are connected to cables 19 which are led out via radial holes 10 and the inner passage of the tubular shaft 4.

Conductors 18 of stator windings 17 can be made of rectangular copper tubes which should be connected not only to the power supply but via proper distributing means to the cooling liquid circulating system too. It is not discussed further because such a system is known for a person skilled in the art.

Around the surface of the stator winding 17 a cooling channel system 20 is built. As it can be seen from Figures 2 and 3 around the stator windings 17 surface cooling channels 21 are embedded in four planes perpendicular to shaft 4. The four planes are taken symmetrically and equidistant between stator plates 11 and 12. Stator winding 17 is surrounded by separate wave-like cooling channels 21. Cooling channels 21 are placed side by side so that the adjacent cooling channels should be offset by a half- wave (to be in opposite phase) in order to take around both inner and outer sides of each stator coil evenly.

Cooling channels 21 can be made of simple tubes. Inasmuch - as it is discussed later - the cooling channels are incorporated in synthetic resin to reach a better embedding and heat flowing between the resin and the coolant, application of flexible conduit is preferable. Flexible conduit is mechanically stronger and permits practically arbitrary line routing without deformation of the cross section.

It should be noted that cooling channels 21 by their shape can be considered as consisting of radial parts and inner and outer cambered parts. Of course depending on the technology applied for the manufacturing of the cooling channel system 20 line routing can be various (e.g. ring shaped on the outer perimeter or spiral-shaped around the coils etc.) The key to efficient cooling is to surround the stator winding 17 with the cooling channel system 20 properly.

As it can be seen from Fig. 4 placed in separate planes cooling channels 21 are connected to the liquid cooling supplying-circulating system by means of tubes 23 passing through radial holes 10 between the two flanges 8 and 9 (see figure 2) of the tube shaft 4 via two collectors-distributors 22 placed around the shaft 4. In- and outlet ends of cooling channels 21 of separate planes to be connected to the two collectors-distributors 22 are turned by an angle compared to each-other.

Sixth of the radial holes 10 between the flanges 8 and 9 on the shaft 4 serves for the cabling of separate sensors embedded in the stator.

Inasmuch as the axial- flux outer rotor motors with concentrated windings have out- standing specific volume and material utilization but their weakness is that the stator 5 consists of a lot of separate coils forming the stator winding 17 hence the latter should be integrated in one mechanically solid unitary structure. It is solved so that the completely assembled stator 5 with the inserted cooling system 20 is bandaged by glass-tape 24 around the linking spacers 14 next all free space between stator plates 11 and 12 is cast with synthetic resin. Parts made of compounds or plastics (stator plates 11 and 12, linking spacers 14, cooling channels 21) and synthetic resin are selected to provide a maximum of cohesion (adhesive compatibility) and proper mechanical stator 5 strength with bubble-free cast.

The synthetic resin 25 having high heat storage and conducting properties improves the motor heat capacity which provides a better performance in case of city vehicles fea- tured by intermittent duty. As a result the stator 5 of the in- wheel motor has excellent mechanical strength, resistance to vibrations, efficient cooling and heat endurance which is a must in case of railway drives.

Stator plates 11 and 12, soft magnetic cores 16, stator windings 17 altogether with the cooling channel system 20 are composing the stator 5 which parts after assembly on the shaft 4 and casting with synthetic resin 25 constitutes one solid unbreakable unit.

Rotor disks 28 and 29 are journalled on both sides of the stator 5 to the shaft 4 via bearings 26 and 27. Bearings 26 and 27 are preferably tapered roller or other type which provide the axial support of the rotor disks 28 and 29 too.

To close magnetic flux of the motor, rotor disks 28 and 29 are manufactured from mag- netically permeable cast or structural steel.

Due to tight junction between rotor disks 28, 29 and the ring 30 and sealing between the shaft 4 and rotor disks 28 and 29 respectively the inner space of the in-wheel motor 1 is hermetically enclosed.

In present case ring 30 at the same time is the usual railway vehicle wheel 1 rim with conventional running surface 2 and flange 3.

On the inner surface of rotor disks 28 and 29 are attached with special adhesive permanent magnets 32. Permanent magnets 32 are arranged so that their magnetic axis is perpendicular to the disk plane but their polarity alternates (number of poles in our case 2p=32).

In case of induction motors instead of permanent magnets 32 short circuiting conductors (turns, rings) are embedded.

Rotor disks 28, 29 and permanent magnets 32 are composing the active part of the rotor 6.

On the outer side surfaces of the rotor disks 28, 29 cooling ribs 33 are shaped. Number of cooling ribs 33 is equal to the number of poles of the rotor 6 and the ribs are distributed so that the centre lines of the ribs coincide with respective pole pitch lines.

The outer side-surfaces of the rotor disks 28, 29 just between two cooling ribs are deepened which is allowable from the point of view of magnetic flux path but gains a lot increasing the cooling surfaces and cutting the weight of the rotor disks 28, 29.

In case of heavier loads (higher speed vehicle, smaller track radius etc.) the cooling ribs 33 can be elongated up to the disks' 28, 29 hubs and this spoke-like shaping can significantly improve the mechanical strength of the railway wheel 1.

The outer surface 34 of rotor disks 28, 29 are coated by a self-cleaning layer (e.g. PTFE or some nano-coating) to avoid contamination settlings reducing cooling effect.

Operation of the presented in-wheel motor does not need much explanation. In a known manner, supplying the stator windings 17 from a frequency converter the magnetic flux arising in the stator makes rotate the outer rotor 6 with the wheel rim. The machine can operate not only in motor but in generator regime too realizing energy saving recuperat- ing braking.

The supply system via the tube-conductors 18 of the stator winding 17 and/or the cooling channels 20 is circulating cooling liquid, which intensively cools the full stator. Around the cooling ribs 33 of the rotor disks 28, 29 coming into rotation the air- flow is rapidly growing providing intensive cooling of the rotor 6.

Examining the exemplary embodiment shown it can be easy conceded that the in-wheel motor traction based on present invention offers significant technical and economical advantages in case of any railway (city, underground, main line, etc.) vehicle.

Invention can meet any traction demand of - known at present - railway vehicles excepting high powered electric locomotives. In-wheel motor can be incorporated into the bogie or frame of a traditional vehicle preferably by tube or portal axle. The latter is advantageous in case of low- floor vehicles. At the same time the invention offers wide range of potentials to develop new types of steerable bogies, frames and suspensions. The in-wheel motor can be easy incorporated together with disc brake or brake-disc too.

The outline dimensions of the in-wheel motor practically are the same and the weight is max.15...20% more than of a traditional railway wheel. In this case the motor has no any "extra" so called inactive (electrically or magnetically not conductive) part such as housings, bearings, axle, etc. inasmuch as the wheel's necessary parts such as the axle, bearings (which are the vehicle axle and bearings in addition), rotor disks and the rim are playing the role of the motor inactive parts, so by this way a total integration of the wheel and the motor is realized without any compromise. High level of integration can be featured by that fact that if only one of the main parts from the in-wheel motor would be removed then there is no motor and no wheel existing any more.

The implemented cooling system makes possible to realize a totally enclosed (IP 44 or higher degree) performance of the in-wheel motor, excluding the harmful effect of con- tamination penetration into the closed space.

Lifetime of the electric motor depends first of all on the aging of the built in electrical insulation materials which aging process depends on the thermal load. Stator liquid cooling excludes the overheating of the insulation providing a long life-span.

The cooling efficacy of ribbed rotor disks can be improved blowing them by an aux- iliary air-compressor implemented. In case of occurring high load or ambient temperature the cooling effect can be further intensified adding a bit water to the air blown which at the same time can clean the disks from any contamination.

Proposed by the invention dual cooling system has one more advantage: in case of overheating the stator or the rotor, the surplus heat is immediately will flow by means of the intermediary air closed and intensively circulating inside the machine into the opposite direction while a new temperature balance is not reached of course already on a lower level.

Cooling of the stator can be improved even more implementing direct liquid cooling of the windings using hollow copper conductors. Increasing the cooling efficacy the in- wheel motor heat loadability can be multiplied altogether with the current, torque and power performance. The in-wheel motor and feeding the motor converter can be cooled by the same liquid cooling circulating system.

In-wheel motor according to present invention has the above and more direct and indirect advantages as follows:

- Significant reducing of investment, operation and maintenance costs with improv- ing reliability and safety,

- More compact structure compared to other traction drive systems and in- wheel motor solutions (surplus weight of the active parts of proposed motor is not more than 15... 20 % of the wheel weight),

- Increased life-span of the insulation and the whole motor due to synthetic resin casting and better cooling performance,

- Significant improvement of traction efficiency du to fully eliminating the mechanical power transmission,

- Easy assembly/disassembly, repair and maintenance,

- Elimination of problems connected to incorporation, gearing and coupling of traditional traction or other separate motors,

- Bogie structure can be simplified moreover can be fully taken out, because in this case a steerable vehicle frame with separate wheels (in- wheel motors) can be easy and economically realized,

- Driven and free-running bogies can be made of similar structure,

- Low- floor city vehicles can be built easier decreasing height and structure gauge,

- open new special vehicle design opportunity,

- applicability in vehicle modernization projects.

List of Reference Signs

1 - railway vehicle wheel

2 - running surface

3 - flange

4 - shaft

5 - stator

6 - rotor

7 - fastening slot

8 - flange 9 - flange

10 - radial hole

11 - stator plate

12 - stator plate

13 - bolt

14 - linking spacer

15 - opening

16 - magnetic core

17 - stator winding

18 - conductor

19 - cable

20 - cooling channel system

21 - cooling channel

22 - collector-distributor

23 - tube

24 - glass tape

25 - synthetic resin

26 - bearing

27 - bearing

28 - rotor disk

29 - rotor disk

30 - ring

31 - bolt

32 - permanent magnet

33 - cooling rib

34 - self- cleaning layer