TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to drive assemblies for propelling rail vehicles, and in particular to drive assemblies for rail vehicles having inboard bearings and comprising an electric motor mounted on or adjacent the axle.

BACKGROUND ART

[0002] The chassis of a rail vehicle may be integrated into the vehicle body or alternatively may comprise the frame of a bogie, the vehicle body being supported on the bogie, usually by pneumatic or other spring elements known as the secondary suspension. The chassis is supported on the rails by one or more wheelsets, each wheelset typically comprising a pair of wheels mounted on a common axle which rotates in bearings. The wheelset bearings are mounted in housings known as axleboxes, conventionally located outboard of the wheels, with the chassis being supported on the axleboxes by spring elements known as the primary suspension. The endfloat of the axle in the bearings may be constrained by shoulders which abut the axial end faces of conventional conical or cylindrical roller bearings.

[0003] In order to reduce cost and damage to the track, it is desirable to minimise the size and weight of the bogie. A significant reduction in the overall length and width and hence the cost and weight of the bogie can be achieved by arranging the axleboxes between the wheels of the wheelset, which is to say, by arranging the wheels outboard of the axleboxes, providing a so-called inboard bearing bogie as exemplified by the FLEXX (RTM) ECO family of bogies manufactured by the present applicant. Since the primary suspension elements of each wheelset are closer together, it is necessary to increase their vertical stiffness as compared with a conventional, outboard bearing bogie in order to control the roll angle of the vehicle body within acceptable limits as it negotiates a curved track.

[0004] Conveniently, each wheelset may be driven by an electric motor mounted on or adjacent the axle. [0005] Fig. 1 is a plan view of part of a known inboard bearing bogie comprising a known drive assembly of the last mentioned type. The wheels 1 are mounted on an axle 2 which rotates in bearings in the axleboxes 3, the bogie chassis 4 being supported by primary suspension (not visible) on the axleboxes. A double reduction gearbox 5 is supported on the axle 2 by bearings 6 and on the bogie chassis 4 by a bracket 7, which provides a torque reaction link. An electric traction motor 8 is mounted via resilient bushes 9 on the casing of the gearbox 5 alongside the axle 2 and supported on the chassis 4 by a bracket 10.

[0006] A particular problem with inboard bearing bogies is that the space available between the axleboxes to house the traction motor is much smaller than in the outboard bearing type, and so in order to obtain an adequate traction performance, the diameter of the motor must be increased. However, the space available alongside the axle is limited by the overall length of the bogie. Moreover, it is often desirable (particularly for passenger vehicles) to minimise the floor height of the rail vehicle, which restricts the space available above the axle.

[0007] In order to increase the output of the motor without increasing its diameter, it may be provided with forced ventilation, which however disadvantageously increases its complexity and noise emission.

[0008] US 6,868,793 B2 discloses a direct drive in which a permanent magnet motor is mounted as an unsprung mass coaxially on the axle. Since no gearbox is provided, the length of the motor is advantageously increased. However, the motor is required to run at the axle speed, which is considerably lower than the speed of a conventional traction motor, and so despite increased weight and greater length, its torque output is limited. This may necessitate the use of reduced diameter wheels, which may disadvantageously reduce wheel life and limit the available motor diameter. An increased wheel size allows a larger motor diameter but results in an increased unsprung mass, which may be disadvantageously increase track damage. SUMMARY OF THE INVENTION

[0009] It is the object of the present invention in view of the above mentioned problems to provide a less complex drive assembly for a rail vehicle which is better adapted in particular for use in a bogie with inboard bearings. [0010] In accordance with the various aspects of the present invention there are provided respectively a drive assembly and a bogie as defined in the claims.

[0011] According to one aspect of the invention, the drive assembly for a rail vehicle, comprises: a wheelset axle mounted in a pair of axle bearings to rotate about a rotation axis, a pair of wheels mounted on the axle, a traction motor having an output shaft rotating in motor bearings about a rotation axis parallel to the rotation axis of the axle, a gear train to transmit drive from the motor output shaft to the axle and - a casing housing the output shaft of the motor, gears, the motor bearings and the axle bearings.

[0012] Unlike a conventional axle hung drive assembly, the drive assembly has integrated axle bearings housed in the casing and the whole assembly is suspended from the axle bearings so that no additional bearings are required to support the motor or gear train on the axle eliminating the need for at least two bearings on the axle. Elimination of the extra bearings results in more space for the traction motor. This allows a longer motor and, according to a preferred embodiment, a single reduction gear train, which consists of two gears that are supported respectively by the motor bearings and the axle bearings. [0013] This drive assembly may become part of the primary suspension system, unlike a conventional axle hung drive. A link assembly can act as part of the primary suspension in the vertical and/or lateral and/or longitudinal direction. According to a preferred embodiment, the primary spring is offset from the axle centre line, which allows a lower height primary suspension and bogie frame. The offset load is then reacted by the link assembly.

DESCRIPTION OF THE FIGURES

[0014] An illustrative embodiment of the invention will now be described, purely by way of example and without limitation to the scope of the claims, and with reference to the accompanying drawings, in which:

Fig. 1 shows a prior art bogie as described above;

Fig. 2 is a plan view of part of a first bogie in accordance with a first embodiment of the present invention;

Fig. 3 is a side view of part of the first bogie of Fig. 2;

Fig. 4 is a plan view of a bogie in accordance with a second embodiment of the present invention;

Fig.5 is a side view of the bogie of Fig. 4. [0015] Corresponding reference numerals refer to the same parts in each of the figures.

DETAILED DESCRIPTION OF PREFERED EMBODIMENTS

[0016] Referring to Figs. 2 and 3, an inboard bearing bogie for a rail vehicle includes a steel chassis having a transverse axis of symmetry Yl through its transom 21 and a pair of side frame members 22 at either end, each side frame member terminating at its end 23 in a primary suspension mounting 24. A pair of brackets 25 are arranged, one on either side of the transom, on the central longitudinal axis X of the chassis, which extends in a reversible direction of travel of the rail vehicle.

[0017] The drive assembly 30 propels the rail vehicle in its direction of travel, and comprises a wheelset, a motor and gearbox assembly 50, and a reaction link 40. The wheelset comprises an axle 31 mounted in a pair of bearings 32, 33 and a pair of wheels 34 mounted on the axle outboard of the bearings. [0018] The motor and gearbox assembly 50 includes a steel casing 51, having a motor casing portion 52 formed integrally with a gearbox casing portion 53, a pair of axleboxes 54, 55, and a pair of primary suspension seats 56, 57. The electric traction motor 60 is mounted internally on the casing portion 52 on a motor axle 61, which is arranged in parallel with and alongside the axle 31 in bearings 62, 63. The single reduction geartrain 70 between the motor and the axle comprises a driving gear 71 mounted on the motor axle 61 and a driven gear 72 mounted on the axle 31, both rotating in an oil reservoir 73 within the casing 51 and separated from the motor by an oil seal (not shown) adjacent the bearing 62. The wheelset bearings 32, 33 are mounted in the axleboxes 54, 55 so that the whole assembly 50 is supported at one end by the wheelset bearings on the axle 31, whose rotation axis Y2 is transverse to the central longitudinal axis X of the chassis, and at its opposite end by the reaction link 40. The motor is preferably arranged to one side of the axle 31 (rather than vertically above it), which advantageously allows the floor of the rail vehicle to be lower. Advantageously, the motor may be arranged as shown so that when considered in plan view its rotation axis (axle 61) is located between the rotation axis Y2 of the wheelset and the reaction link 40, and also between the primary suspension and the reaction link, while in side view (Fig. 3) its axle 61 is located at rest in a horizontal plane lying slightly above the wheelset axis Y2 and above the seat 56 of the primary suspension and roughly intermediate the upper and lower brackets 25, 58 of the reaction link, and intermediate the wheelset axis Y2 and the upper surface of the chassis side members 22.

[0019] Since no separate bearings are required to support the casing 51 on the axle 31, the drive assembly can be arranged very close to the wheelset bearings 32, 33. Since the motor 60 is mounted directly on the casing 51, and preferably within the casing with the motor axle 61 being supported at each end via the bearings 62, 63 on the casing 51, no resilient bushes are required between the motor and the casing. Both of these measures allow the length of the motor to be increased, which in turn increases its traction performance without requiring forced ventilation or other special cooling arrangements. [0020] Since the motor is positioned close to the axle 31 and at a fixed radial distance from it, and since the power output of the motor is increased proportionately to its length, a single reduction geartrain can be used instead of a double reduction geartrain. The two gears are supported respectively by the motor bearings and the wheelset bearings, so that only the two motor bearings 62, 63 are required in addition to the wheelset bearings 32, 33. These measures provide a simple and efficient drive assembly with a reduced component count and reduced weight as compared with the prior art assembly of Fig. 1.

[0021] The reaction link 40 comprises a rod 41 which is coupled at its upper end to the chassis via bracket 25, and at its lower end to a bracket 58 which extends integrally from the motor casing portion 52. The rod 41 acts in tension to both support the weight of the casing and restrain rotation of the casing 51 about the axle 31.

[0022] The primary suspension means 80 comprises two conventional primary suspension elements 81, 82, such as rubber spring elements, coil springs or the like, which are arranged in compression between the mountings 24 of the chassis and the corresponding seats 56, 57 on the casing 51 to support the chassis on the casing.

[0023] Advantageously, each of the primary suspension elements 81, 82 is offset from the axle 31 and arranged between the axle and the reaction link when considered in a direction of the longitudinal axis X in plan view (Fig. 2). More specifically, each of the seats 56, 57, which define the point or points at which the primary suspension means is supported on the casing is offset in a direction of the longitudinal axis X of the chassis from a vertical plane containing the rotation axis Y2 of the axle 31. The seats 56, 57 may be arranged horizontally level with the rotation axis Y2 or alternatively at a level above or below the axle, i.e. they may be offset also from a horizontal plane containing the rotation axis Y2. The frame 20 is supported on the seats 56, 57 via the primary suspension elements 81, 82 and applies a torque to the casing 51, which in the side view of Fig. 2 is a clockwise torque about axis Y2. This torque is counteracted by the traction of the rod 41. [0024] Preferably, the primary suspension means is thus supported on the casing at a point or points between a vertical plane containing the rotation axis Y2 of the wheelset axle and a vertical plane containing the rotation axis (axle 61) of the motor. Since the axle 61 of the motor 60 is arranged between the rotation axis Y2 of the axle 31 and the reaction link40 when considered along a direction of the longitudinal axis X in plan view (Fig. 2), the rod 41 also reacts part of the mass of the motor as a downward force from the casing 51 against the chassis. Advantageously, the rod 41 is free to rotate slightly with respect to the respective brackets 25, 58, so that the assembly 50 can move slightly in rotation relative to the chassis to accommodate the deflection of the primary suspension means 80.

[0025] The casing 51 of the assembly 50 thus functions as part of the primary suspension, so that although the assembly 50 is hung from the axle 31, it nevertheless benefits from the action of the primary suspension elements 81, 82. This advantageously means that the mass of the assembly 50 and in particular the motor 60 is not applied as a pure unsprung mass to the axle 31, which in turn reduces damage to the track as well as reducing track usage charges, which are based inter alia on unsprung mass.

[0026] By offsetting the primary suspension elements from the axle 31, the seats 56, 57 may advantageously be arranged at a lower level than the top of the axlebox or even at a lower level than the top of the axle. As seen in Fig. 3, in the illustrated embodiment, the seats 56, 57 are arranged at approximately the same horizontal level as the central longitudinal axis Y2 of the axle 31. This enables the primary suspension elements 81, 82 and hence the mountings 24 and bogie chassis to be lower than in a conventional bogie, so that the bogie is suitable for use in a low floor rail vehicle. As seen in Fig. 3, the uppermost surface of the bogie chassis may even be lower than the uppermost point of the wheel rims. Since the motor may provide adequate traction performance without reducing the diameter of the wheels, the novel bogie thus advantageously allows a low floor train to be equipped with wheels of conventional diameter. [0027] A further advantage obtained by offsetting the primary suspension elements from the axle is that the overall length of the bogie sideframes and hence the weight of the chassis can be reduced. When considered in plan view, the central longitudinal axis Y2 of the axle may thus be offset along a direction of the longitudinal axis X by a distance dl beyond the end 23 of the side frame member 22 of the bogie chassis, as shown in Fig. 2.

[0028] Depending on the direction of rotation of the motor 60, the motor torque is reacted, either as an upward force, or as a downward force via the rod 41 against the chassis. The direction of rotation of the motor may be arranged so that in the normal forward direction of travel of the bogie, the motor torque is reacted as a downward force via the rod 41 against the chassis, in which case (where a single reduction geartrain is provided) the motor may be arranged in front of the wheelset axle in the direction of travel as shown, with the drive assembly on the trailing axle. Alternatively, the bogie may be bidirectional, in which case the drive assembly may be arranged on either the leading or the trailing axle. Alternatively, a drive assembly may be arranged on each of the bogie axles with the torque from the two motors being reacted in opposite (respectively upward and downward) directions.

[0029] The rod 41 is relatively short and is arranged vertically in tension along the line of force between the casing 51 and the chassis. As the primary suspension deflects with vertical movement of the chassis, the assembly 50 rotates about the axle 31 through a corresponding, small angular range of movement. By offsetting the primary suspension elements from the axle, this vertical movement of the chassis relative to the wheelset is applied to the primary suspension elements as a downward compressive force in which this small rotational component is substantially reduced. This allows conventional primary suspension elements to be used, further simplifying the assembly.

[0030] Advantageously, the wheelset bearing 32 within the axlebox 54 adjacent the geartrain can be lubricated by oil from the same oil reservoir 73 as the geartrain 70. This avoids the need for an oil seal between the gearbox casing portion 53 and the axlebox 54, which further simplifies the assembly and enables the geartrain to be placed yet closer to the bearing 32, further increasing the space available to house the motor 60, which allows it to be yet longer and hence more powerful.

[0031] In the embodiment illustrated, the axle 31 is partially exposed outside the casing 51, and the other wheelset bearing 33 in the axlebox 55 is lubricated conventionally by grease. In an alternative embodiment, the casing 51 may be extended to enclose the axle 31, or alternatively the two axleboxes may be connected by a passage arranged within the casing 51 or externally of it, in each case allowing both wheelset bearings to be oil lubricated together with the geartrain from a common oil reservoir. [0032] Advantageously, the novel drive assembly is suitable for use for example with a permanent magnet electric motor or a conventional wound electric motor, which may be interchangeably mounted on the casing.

[0033] Preferably the motor shaft 61 has a bearing at either end as shown, with the bearing 62 incorporating an oil seal and arranged between the motor 60 and the driving gear 71. Alternatively, the bearing 62 could be outboard of the driving gear 71. Alternatively, the motor shaft 61 could be releasably coupled to the driving gear 71, for example via a radial spline connection, with the driving gear 71 having two bearings, one on either side. Many other variations will be apparent to those skilled in the art. [0034] In less preferred embodiments, the primary suspension means could be arranged directly above the axle 31, or on the opposite side of the axle from the reaction link. Alternatively, primary suspension elements could be arranged on both sides of the axle 31 at each of its ends.

[0035] The novel drive assembly may be installed on a bogie or on the chassis of a rail vehicle without a bogie. In the bogie illustrated, a second, corresponding drive assembly might be arranged on an adjacent axle with its reaction link being coupled to the other bracket 25. More than one reaction link, e.g. a pair of reaction links, may be provided, and the or each reaction link need not necessarily be coupled to the chassis. In alternative embodiments, it or they could be coupled to the side frame members of a bogie, to an adjacent axlebox or even (via a separate bearing) to an adjacent axle. Where two drive assemblies are provided on a pair of axles (e.g. on a twin axle bogie), the reaction link could be arranged for example between the two casings to limit their rotation about their respective wheelset axles. [0036] In the embodiment illustrated, the drive assembly allows the link assembly 40 to act as part of the primary suspension assembly, instead of merely reacting the motor torque as known in the art. In alternative embodiments, the or each reaction link could be arranged to provide all or part of the required vertical and/or lateral and/or longitudinal stiffness of the primary suspension. The or each reaction link could also act in compression (comprising for example a rubber pad between two abutting brackets) rather than in tension, and could be arranged to constrain movement in more than one direction.

[0037] The primary suspension means need not comprise two primary suspension elements; for example, it may comprise more than two primary suspension spring elements. Instead of mounting the motor internally on the casing, it could be mounted externally on the casing, so that it has its own external casing and is removable and exchangeable as a module, which may be advantageous for example where the motor and gearbox are sourced from different manufacturers.

[0038] Advantageously, the longer motor 60 may provide adequate traction performance without the use of complex, forced ventilation or liquid cooling, and as a result, the casing 51 may be expected to expand slightly as the motor heats up. Since the drive assembly in the illustrated embodiment is asymmetrical, the casing 51 may also experience a slight elastic deformation under the forces applied by the motor as well as by relative movements between the axle 31, the mountings 24 and the bracket 25 resulting from deflection of the primary suspension and torsional flexure of the chassis. Deformation of the casing 51 will in turn cause the two integral axleboxes 54, 55 to move slightly, one relative to the other, which movement must be accommodated without causing the wheelset bearings to bind on the axle. [0039] This may be achieved by increasing the maximum endfloat of the axle in the wheelset bearings. However, it is desirable to limit the endfloat of the axle as much as possible.

[0040] Advantageously, this may be achieved by arranging a first one of the wheelset bearings 32, 33 to restrict axial movement of the axle 31, and the other one to permit axial movement of the axle within a limited range.

[0041] In one embodiment, the first one of the wheelset bearings may be a taper roller bearing, while the other one is a bearing that permits axial movement, such as, for example, a cylindrical roller bearing. [0042] In summary, a preferred inboard bearing drive assembly for a rail vehicle chassis comprises an electric traction motor and geartrain mounted in an axle hung casing with integral axleboxes. The primary suspension is mounted on the casing and preferably offset from the wheelset axle, with the casing being restrained in rotation by a reaction link, conveniently coupled to the chassis. One or both wheelset bearings may be lubricated from the gearbox oil reservoir, and deformation of the casing may be accommodated by dissimilar wheelset bearings, wherein only one provides an axial restraint.

[0043] A bogie according to another embodiment of the invention is illustrated in Figs. 4 and 5. The bogie of the second embodiment is provided with two identical drive assemblies, each arranged on one of the two axles of the bogie. Each of the two drive assemblies is similar to the drive assembly previously described with reference to Fig. 1-3. Hence, parts of the drive assembly 30A will be designated with the same reference numbers as the corresponding parts of the bogie of Figs. 1-3 with the addition of the suffix "A", while the corresponding parts of the drive assembly 30B will bear the suffix "B". In order to avoid repetition, the description of parts previously described with reference to the bogie of Figs. 1-3 will be dispensed with.

[0044] The two drive assemblies are coupled to a common reaction link 400. The reaction link 400 comprises a connecting rod 410 and an upper rubber bearing which is mounted fixed to the transom 21 of the bogie chassis. The downward end of the rod 410 extends through an eyelet formed at the end of the bracket 58A of the drive assembly 30A and an eyelet formed at the end of the bracket 58B of the drive assembly 30B. A rubber bearing 413 is interleaved between the two eyelets and provides a stiff pivot connection between drive assembly 30A and 30B. [0045] The chassis is suspended on the four suspension springs 81A, 81B and 82, which are preferably formed as flexicoil springs able to respond both to vertical and horizontal deflection. The weight of the chassis and of the vehicle body is transmitted to each of the seats 56A, 56B and 57 and generates a torque about each of the two axes Y2A and Y2B, such that the brackets 58A, 58B extending at the inward end of each of the two casings 51A, 5IB are forced downwards against the reaction of the traction rod 410.

[0046] On a straight track in ideal conditions, the axles are parallel with one another. However, whenever the wheels are subjected to longitudinal curving forces, e.g. when entering a curve, the upper bearing 411 allows the bottom of traction rod 410 and bearing 413 to swing laterally and the two axles are free to rotate in opposite directions about two vertical instantaneous axis and assume a new position at an angle respective to one another. If the primary suspension springs 81A, 81B have a flexicoil effect, they will counteract the rotation of the two axles and bias them towards the medium position of Fig. 4. [0047] Variants may be considered without departing from the scope of the claims. In particular, a double reduction geartrain could also be used, if required, which would then allow an even higher power output due to the increased length mentioned above and larger motor diameter.