BACKGROUND OF THE INVENTION
The present invention relates to a wheel arrangement for a rail vehicle, in particular, a light
rail vehicle, comprising a wheel unit and a support unit, wherein the wheel unit defines an
axis of rotation of the wheel unit. The support unit is configured to be connected to a rail
vehicle structure of the rail vehicle defining a vehicle longitudinal direction, a vehicle
transverse direction and a vehicle height direction. The support unit is further configured to
connect the wheel unit to the rail vehicle structure such that the wheel unit is rotatable about
the axis of rotation. The support unit comprises a primary suspension unit configured to
provide resilient support of the rail vehicle structure on the wheel unit at least in the vehicle
height direction. The primary suspension unit has a primary suspension transverse rigidity in
a direction parallel to the axis of rotation, wherein a distribution of the primary suspension
transverse rigidity across the primary suspension unit, in particular, in a static state of the rail
vehicle standing on a straight level track under a nominal load, defines a tilt axis of the wheel
unit parallel to the vehicle longitudinal direction. The invention further relates to a
corresponding rail vehicle unit comprising a rail vehicle structure and at least one such wheel
arrangement.
In a rail vehicle, the primary suspension represents the transition from the so-called unsprung
mass, i.e. the part of the vehicle which is directly subject to the loads introduced via the track
without the interposition of a spring element (and, typically, also a damping element), and the
remainder of the vehicle. With conventional running gears for rail vehicles the primary
suspension is typically arranged between the axle or wheel set shaft of the wheel unit (e.g. a
single wheel, a wheel pair or a wheel set) and a vehicle structure, typically a running gear
frame of the vehicle or eventually even the wagon body structure itself. Such a configuration
is known, for example, from EP 1 065 122 B1 (the entire disclosure of which is incorporated
herein by reference).
For passenger comfort and vehicle dynamics reasons, in particular, in so-called light rail
vehicles (LRV), it is typically desired to reduce the unsprung mass as far as possible. Hence,
typically, rail vehicle manufacturers strive to make the components forming the unsprung
mass as light as possible. However, this approach has its clear limitations in terms of
structural integrity and safety requirements.

A further problem with this kind of primary suspension can be the comparatively low lateral
stiffness or transverse rigidity of such primary spring configurations, especially if the wheel
unit is a single wheel subject to lateral loads introduced at the wheel to rail contact point (e.g.,
as constantly present for wheel to rail pairings with a certain conicity, but also as impact loads
when running over a switch or an irregularity in the track). While a low transverse rigidity may
be desired under the aspect of passenger comfort, especially with such single wheel running
gears a comparatively high transverse rigidity of the primary suspension may be required
under the aspect of derailment safety in order to guarantee proper wheel to rail contact under
any such lateral load conditions to be expected during operation of the rail vehicle.
In the field of industrial transport carts and lift trucks it is generally known, for example from
EP 0 104 714 B1 (the entire disclosure of which is incorporated herein by reference), to use a
single wheel suspension configuration with so called shear pads, typically layered metal
rubber springs, wherein the layers of the respective shear pad are arranged perpendicular to
the axis of rotation of the wheel. Such a configuration may be useful to considerably increase
the transverse rigidity without compromising the rigidity in the height direction in such non-
track bound industrial transport carts and lift trucks, where passenger comfort and derailment
safety however play no role. This concept is however not easily transferred to rail vehicle
applications where, to the contrary, passenger comfort and derailment safety play a
significant role but are competing goals.
SUMMARY OF THE INVENTION
Thus, it is the object of the present invention to provide a wheel arrangement for a rail vehicle
and a rail vehicle unit as described above, which do not show the disadvantages described
above, or at least show them to a lesser extent, and, in particular, allows in a simple, space
saving and efficient manner high derailment safety while at the same time keeping the
unsprung mass low and maintaining high passenger comfort during operation of the rail
vehicle.
The above objects are achieved starting from a wheel arrangement according to the
preamble of claim 1 by the features of the characterizing part of claim 1.
The present invention is based on the technical teaching that, it is possible to achieve in a
simple, space saving and efficient manner high derailment safety while at the same time
keeping the unsprung mass low and maintaining high passenger comfort during operation of

the rail vehicle if the primary suspension unit is configured such that the (virtual) tilt axis of the
wheel unit is located below the axis of rotation of the wheel unit (it should be noted that,
unless explicitly stated otherwise, geometric relations such as “above” and “below” given
herein in relation to the vehicle height direction). This tilt axis (in the static state of the rail
vehicle standing on a straight level track under the vehicle’s nominal load) runs parallel to the
vehicle longitudinal direction and is defined by the distribution of the transverse rigidity of the
primary suspension unit. More precisely, as the primary suspension unit is typically located
above the wheel to rail contact location, a transverse force or lateral load acting in the
transverse direction at the wheel to rail contact (e.g., as constantly present for wheel to rail
pairings with a certain conicity, but also as impact loads as a result of track irregularities or
the like) results not only in a transverse (or lateral) deflection of the wheel unit but also in a tilt
motion of the wheel unit (also referred to as a lateral track load induced tilt herein) about this
tilt axis which is defined by the primary suspension unit, more precisely, by the distribution of
the transverse rigidity of the primary suspension unit in the height direction.
The invention has realized that this tilt motion in response to such transverse forces has a
considerable impact on the deflection of the wheel unit at the wheel to rail contact location,
and, hence, on the derailment safety. Moreover, the invention has realized that, by selecting
a suitable distribution of the transverse rigidity of the primary suspension unit which locates
this (virtual) tilt axis below the axis of rotation of the wheel unit, such tilt related deflections of
the wheel unit can be reduced and, thus, derailment safety can be increased while at the
same time the keeping the overall transverse rigidity of the primary suspension unit
unchanged. In particular, it is also possible to keep the rigidity in the height direction
essentially unchanged. Hence, the unsprung mass may be kept low and passenger comfort
may be maintained while reducing the derailment risk or, put otherwise, passenger comfort
may be increased and the unsprung mass may be reduced while keeping a given low level of
the derailment risk.
It will be appreciated that this concept is particularly useful and effective in singe wheel
configurations where the primary suspension unit is the (eventually even only) component
defining this tilt axis. However, use of the above concept is not limited to single wheel
configurations and, for essentially the same reasons as given above, may also have
beneficial effects with other configurations (such as e.g. wheel pairs or wheel sets) where a
mechanical coupling exists between the two wheel units on both sides of the running gear.
Hence, according to one aspect, the present invention relates to a wheel arrangement for a
rail vehicle, in particular, a light rail vehicle, comprising a wheel unit and a support unit,

wherein the wheel unit defines an axis of rotation of the wheel unit. The support unit is
configured to be connected to a rail vehicle structure of the rail vehicle defining a vehicle
longitudinal direction, a vehicle transverse direction and a vehicle height direction. The
support unit is further configured to connect the wheel unit to the rail vehicle structure such
that the wheel unit is rotatable about the axis of rotation. The support unit comprises a
primary suspension unit configured to provide resilient support of the rail vehicle structure on
the wheel unit at least in the vehicle height direction. The primary suspension unit has a
primary suspension transverse rigidity in a direction parallel to the axis of rotation, wherein a
distribution of the primary suspension transverse rigidity across the primary suspension unit,
in particular, in a static state of the rail vehicle standing on a straight level track under a
nominal load, defines a tilt axis of the wheel unit parallel to the vehicle longitudinal direction.
The distribution of the primary suspension transverse rigidity is such that, in the vehicle
height direction, the tilt axis is located below the axis of rotation.
It will be appreciated that, basically, any desired height offset of the tilt axis from the axis of
rotation that has a noticeable positive effect on the lateral track load induced tilt can be
sufficient. Typically, the wheel unit has a rail contact surface defining a nominal diameter of
the wheel unit (typically in a new, unworn state of the wheel, but possibly also, in a re-profiled
state of the wheel), and the tilt axis, in the vehicle height direction, in particular, in the static
state of the rail vehicle, is located at a tilt axis distance from the axis of rotation. Preferably,
the tilt axis distance is at least 10%, preferably at least 20%, more preferably 15% to 50%, in
particular, 25% to 40%, of the nominal diameter. These configurations achieve a particularly
advantageous reduction of the lateral track load induced tilt of the wheel unit.
The distribution of the primary suspension transverse rigidity can have any desired
configuration as long as the desired height offset of the tilt axis with respect to the axis of
rotation is achieved. With particularly simple variants, the primary suspension unit is
separated in an upper, first primary suspension part and a lower, second primary suspension
part. The first primary suspension part has a first transverse rigidity in the direction parallel to
the axis of rotation, wherein the first primary suspension part, in the static state of the rail
vehicle, is located, in the vehicle height direction, above the axis of rotation. The second
primary suspension part has a second transverse rigidity in the direction parallel to the axis of
rotation, wherein the second primary suspension, in the static state of the rail vehicle, is
located, in the vehicle height direction, below the axis of rotation. The first transverse rigidity
is lower than the second transverse rigidity, thereby achieving the desired height offset of the
tilt axis with respect to the axis of rotation. Preferably, the first transverse rigidity is 5% to

99%, preferably 25% to 75%, more preferably 40% to 60%, of the second transverse rigidity,
thereby achieving particularly beneficial results.
It will be appreciated that the above distribution of the primary suspension transverse rigidity
may simply be achieved by two separate primary suspension elements (one forming the
upper primary suspension part, one forming the lower primary suspension part). It may of
course also be formed by any desired other number of primary suspension elements in either
of the upper and lower primary suspension part. Similarly, as will be explained further below,
one single primary suspension element may be sufficient to achieve this distribution.
Basically any desired type(s) of primary suspension element(s) may be used to form the
primary suspension unit achieving resilient primary suspension in the required degrees of
freedom. In particular, primary suspension elements of any desired configuration and shape
may be used. These may comprise conventional spring elements, such as, for example
helical metal spring elements or rubber spring elements alone or in combination with other
components, such as, for example, damping elements etc.
With simple and particularly space saving preferred configurations, the primary suspension
unit is a shear spring unit. Such shear spring units typically have the advantage that they
provide suitable spring motion in their shear direction, typically in a shear plane, while being
comparatively rigid in other directions (e.g. in a direction perpendicular to a shear plane of the
shear spring unit). Preferably, the shear spring unit comprises at least one primary
suspension element in the form of a shear spring element, configured to provide resilient
support of the rail vehicle structure on the wheel unit. Such shear spring elements are well-
known in the art and readily available in multiple configurations. Preferably, the at least one
primary suspension element is arranged and configured such that, in the static state of the
rail vehicle, the primary suspension element is at least primarily under a shear stress, in
particular, is at least substantially exclusively, under a shear stress. By this means
particularly compact yet effective configurations are achieved.
With certain simple and preferred variants, the primary suspension unit comprises at least
one primary suspension element configured to provide resilient support of the rail vehicle
structure on the wheel unit, wherein the primary suspension element comprises at least one
of a polymer element, a rubber element, and a laminated rubber metal spring element with a
plurality of layers. Preferably, the plurality of layers is configured to extend, in the static state
of the rail vehicle, in a plane perpendicular to the transverse direction. In any of these cases,

in a very compact configuration, particularly favorable suspension in the height direction may
be achieved with at the same time appropriate transverse rigidity.
It will be appreciated that, in general, the overall or total rigidity of the primary suspension unit
may be substantially the same in all three (translatory) directions, i.e., the longitudinal
direction, the transverse direction and the height direction. However, with certain
embodiments, the primary suspension unit may have different behavior in different directions
in order to account for the load cases to be expected during operation of the particular vehicle
the wheel arrangement is to be operated on. Hence, with certain preferred variants, the
primary suspension unit has a longitudinal rigidity in the longitudinal direction, the transverse
rigidity and a height rigidity in the height direction (i.e., in three mutually orthogonal
directions). With certain variants, the height rigidity is lower than at least one of the
longitudinal rigidity and the transverse rigidity (typically at least lower than the transverse
rigidity). By this means, a primary suspension may be achieved which is suitably compliant in
the height direction of the vehicle, while being comparatively rigid at least in the transverse
direction of the vehicle. In addition or as an alternative, the longitudinal rigidity is lower than
the transverse rigidity. In many embodiments according to the present design, the height
rigidity may be at least approximately the same as the longitudinal rigidity.
As noted above, one single primary suspension element may be sufficient to achieve the
desired distribution of the primary suspension transverse rigidity. Hence, with certain
variants, the primary suspension unit comprises at least one ring shaped primary suspension
element providing resilient support of the rail vehicle structure on the wheel unit. The at least
one primary suspension element may extend along an outer circumference of an axle unit of
the support unit, thereby achieving a particularly compact yet efficient configuration.
The desired distribution of the primary suspension transverse rigidity may be achieved in any
suitable way by properly choosing the materials used for the at least one primary suspension
element and/or by properly distributing the material(s) used for the at least one primary
suspension element and/or by properly choosing the dimensions of the at least one primary
suspension element.
With certain particularly simple, space saving and, hence, preferred variants, the at least one
ring shaped primary suspension element has a plane of main extension, wherein the at least
one ring shaped primary suspension element, in this plane of main extension, has an outer
circumferential contour with a maximum outer diameter and an inner circumferential contour
with a maximum inner diameter. The outer circumferential contour defines a first area center

of gravity, whereas the inner circumferential contour defines a second area center of gravity.
To achieve the desired distribution of the primary suspension transverse rigidity, the second
area center of gravity, in the vehicle height direction, is upwardly offset from the first area
center of gravity by an area center of gravity distance, the area center of gravity distance, in
particular, being 5% to 25%, preferably 7.5% to 15%, more preferably 9% to 12%, of the
maximum outer diameter. Moreover, in addition or as an alternative, the first area center of
gravity and the second area center of gravity may be at least substantially aligned in the
vehicle height direction, thereby also achieving a particularly simple and compact
configuration.
The respective outer and inner contour may have any desired and suitable shape. For
example, the respective outer and inner contour may be at least section-wise polygonal
and/or least section-wise curved. Particularly simple arrangement are achieved, if at least
one of the outer circumferential contour and the inner circumferential contour is an at least
essentially elliptic contour, in particular, an at least essentially circular contour.
The dimensions of the respective outer and inner contour may be chosen as desired and
suitable for the respective rail vehicle. With preferred variants, the maximum outer diameter
ranges from 100 mm to 1000 mm, preferably 150 mm to 750 mm, more preferably 200 mm to
500 mm. In addition or as an alternative the maximum inner diameter may range from
50 mm to 900 mm, preferably 75 mm to 700 mm, more preferably 100 mm to 400 mm. In
addition or as an alternative, the area center of gravity distance may range from 25 mm to
500 mm, preferably 50 mm to 250 mm, more preferably 75 mm to 100 mm.
As already noted above, with certain further variants the primary suspension unit may
comprise a plurality of primary suspension elements providing resilient support of the rail
vehicle structure on the wheel unit. In these cases, the plurality of primary suspension
elements may be distributed along an outer circumference of an axle unit of the support unit,
thereby achieving a compact configuration. Again, the primary suspension unit may be
separated in an upper primary suspension part and a lower primary suspension part, wherein
the upper primary suspension part, in the static state of the rail vehicle, is located, in the
vehicle height direction, above the axis of rotation, while the lower primary suspension part, in
the static state of the rail vehicle, is located, in the vehicle height direction, below the axis of
rotation.
Preferably, to achieve the desired distribution of the primary suspension transverse rigidity, a
number of the primary suspension elements in the upper primary suspension part is lower

than a number of the primary suspension elements in the lower primary suspension part. In
addition or as an alternative, to achieve the desired distribution of the primary suspension
transverse rigidity, a size of at least one of the primary suspension elements in the upper
primary suspension part may be smaller than a size of at least one of the primary suspension
elements in the lower primary suspension part.
It will be appreciated that the primary suspension unit can basically be located at any desired
and suitable point along the kinematic chain between the wheel unit and the vehicle structure.
In particular, the primary suspension unit may be located more or less remote from the wheel
unit. With preferred variants showing a very low unsprung mass (see above), the primary
suspension unit is located as close as possible the wheel unit along this kinematic chain.
Preferably, the support unit comprises an axle unit with a wheel bearing unit and a wheel
support unit, wherein the wheel bearing unit forms a bearing for the wheel unit. Here, to
achieve a low unsprung mass, the primary suspension unit is located kinematically in series
between the wheel support unit and the wheel bearing unit, such that the wheel support unit
is supported on the wheel bearing unit via the primary suspension unit.
Particularly compact yet lightweight configurations may be achieved if the wheel support unit
is essentially tube shaped. It will be appreciated that the primary suspension concept as
disclosed herein may in general be used in the context of driven or non-driven wheel units.
Hence, with certain variants, a drive shaft unit, at a first end, may be connected to the wheel
unit, wherein the drive shaft unit extends through an interior section of an essentially tube
shaped wheel support unit. The drive shaft unit, at a second end opposite to the first end,
may be configured to be connected to a drive unit of the rail vehicle. To this end, the drive
shaft unit may have a toothed section configured to connect to the drive unit.
With certain variants, a gap is formed between the wheel support unit and the wheel bearing
unit, and the primary suspension unit is connected to the wheel support unit and the wheel
bearing unit, wherein the primary suspension unit bridges at least a part of the gap between
the wheel support unit and the wheel bearing unit. By this means a very simple integration of
the primary suspension of unit may be achieved. In particular, the location and orientation of
the gap and the bridging primary suspension unit may be comparatively easily adapted to the
loads to be expected during operation.
Here, two primary types of relative motion between the parts of the wheel support unit and
the wheel bearing unit forming the bridged part of the gap may be taken into account. One is
essentially a shear motion which then typically leads to the use of one or more shear spring

elements for the primary suspension unit, whereas the other one is essentially a normal or
breathing motion (increasing or decreasing the width of the gap) which typically leads to the
use of one or more compression spring elements for the primary suspension unit. Of course,
eventually, any combination of these motions and spring elements, respectively, may also be
used, in particular, depending on the loads to be expected during operation of the vehicle.
It will be appreciated that, preferably, the primary suspension unit, in a neutral or unloaded
state, is under a compressive pre-stress in the transverse direction in order to properly adjust
the transverse stiffness (to a given desired level already in that neutral state with no
transverse load acting on the wheel unit). This compressive pre-stress may simply be
achieved by properly selecting the dimensions of the primary suspension unit and the gap in
the transverse direction.
With certain particularly compact and favorable variants, the wheel bearing unit has a recess,
and the wheel support unit at least partially extends into the recess. This reaching into the
recess of the wheel bearing unit has several advantages, one being the fact that this allows a
particularly compact design. Another advantage being the possibility to have the wheel
support unit reach through this recess and provide support on both lateral sides of the wheel
bearing unit. Such a configuration is also particularly beneficial in terms of failure safety and
failure running properties, since even upon failure of the primary suspension unit dislocation
of the wheel unit from the axle unit may prevented by simple safety means. Hence, with
preferred variants, the wheel support unit extends through the recess.
The above recess of the wheel bearing unit may generally be of any arbitrary design and
shape as long as it allows the wheel support units to reach into the recess. With particularly
simple variants allowing compact designs, the recess has a recess axis, the recess axis, in
an unloaded state of the wheel arrangement, extending at least substantially parallel to the
wheel axis of rotation.
It will be appreciated that, generally, one single primary suspension element may be sufficient
to achieve the desired primary suspension. Preferably, the wheel unit has an inner side and
an outer side, the wheel unit being configured such that, during use of the rail vehicle on a
track, the inner side faces towards a center of the track and the outer side faces away from
the center of the track. Here, at least one inner primary suspension element of the primary
suspension unit may be located on the inner side of the wheel bearing unit, whereas at least
one outer primary suspension element of the primary suspension unit is located on the outer

side of the wheel bearing unit. By this means, particularly compact yet robust configurations
may be achieved.
The present invention further relates to a rail vehicle unit comprising a rail vehicle structure,
and at least one wheel arrangement according to the invention connected to the rail vehicle
structure. It will be appreciated that the rail vehicle structure may comprise an entire rail
vehicle or a wagon body of the rail vehicle, respectively. With further variants, the rail vehicle
structure may comprise a running gear unit, in particular, a running gear frame, connected to
the at least one wheel arrangement. As noted above, the primary suspension concept as
disclosed herein is particularly useful if the at least one wheel arrangement is a single wheel
arrangement. With such a rail vehicle unit the above variants and advantages can be
achieved to the same extent, such that reference is made to the explanations given above.
The invention is explained in greater detail below with reference to embodiments as shown in
the appended Figures.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic side view of a part of a preferred embodiment of a rail vehicle
according to the present invention with a preferred embodiment of a wheel
arrangement according to the present invention;
Figure 2 is a schematic partially sectional view of the wheel arrangement of Figure 1 along
line II-II of Figure 1.
Figure 3 is a schematic sectional view of a primary suspension element of the wheel
arrangement of Figure 2 along line III-III of Figure 4 in an unloaded state.
Figure 4 is a schematic side view of the primary suspension element of Figure 3.
Figure 5 is a schematic sectional view of the primary suspension element of Figure 3 in a
loaded state (in a static state of the vehicle of Figure 1).
Figure 6 is a schematic side view of the primary suspension element of Figure 5.

Figure 7 is a schematic illustration comparing the tilt behavior of the wheel arrangement of
Figure 1 with a conventional wheel arrangement.
DETAILED DESCRIPTION OF THE INVENTION
With reference to Figures 1 to 7 preferred embodiments of a rail vehicle 101 according to the
present invention comprising a preferred embodiment preferred of a running gear 102
according to the invention further comprising a preferred embodiment of a wheel
arrangement 103 according to present the invention will now be described in greater detail.
In order to simplify the explanations given below, an xyz-coordinate system has been
introduced into the Figures, wherein (on a straight, level track T) the x-axis designates the
longitudinal axis (or direction, respectively) of the rail vehicle 101, the y-axis designates the
transverse axis (or direction, respectively) of the rail vehicle 101 and the z-axis designates
the height axis (or direction, respectively) of the rail vehicle 101 (the same, of course, applies
for the running gear 102). It will be appreciated that all statements made in the following with
respect to the position and orientation of components of the rail vehicle, unless otherwise
stated, refer to a static situation or state of the rail vehicle 101 with the rail vehicle 101
standing on a straight level track under nominal loading.
The vehicle 101 is a low floor light rail vehicle (LRV) such as a tramway or the like. The
vehicle 101 comprises a wagon body 101.1 supported by a suspension system on the
running gear 102. The running gear 102 comprises four wheel arrangements 103 according
to the invention supporting a vehicle structure in the form of the running gear frame 104.
Each wheel arrangement 103 integrates a primary suspension unit 105, while the running
gear frame 104 supports the wagon body via a secondary suspension unit 101.2.
In the present example, each of the wheel arrangements 103 is a motorized wheel
arrangement 103 driven by a drive unit 106 which typically includes a motor and an
associated gearbox. Of course, with certain variants, one motor may drive more than one
wheel arrangement 103 via a corresponding gears etc. Similarly, with other variants, some or
all of the wheel arrangements 103 may be non-motorized.
As can be seen from Figure 2, the wheel arrangement 103 comprises a wheel unit 107 and a
support unit in the form of an axle unit 108. In the mounted state as shown, the axle unit 108
is connected to the rail vehicle structure (running gear frame 104) of the rail vehicle 101. The

wheel unit 107 rotatably supports the axle unit 108 or vice versa. To this end, the axle unit
108 comprises a wheel bearing unit 108.1, wherein the wheel bearing unit comprises a
bearing 108.2 to form a bearing for the wheel unit 107 and to define a wheel axis of rotation
107.1 of the wheel unit 107 during operation of the rail vehicle 101. In the present example,
the bearing 108.2 is a conventional roller bearing. It will be appreciated, however, that with
other variants, any other type of bearing providing suitable role in support to the wheel unit
107 may be used.
The axle unit 108 further comprises a wheel support unit 108.3 and a primary suspension unit
105. The primary suspension unit 105 is located kinematically in series between the wheel
support unit 108.3 and the wheel bearing unit 108.1, such that the wheel support unit 108.3
supports the wheel bearing unit 108.1 via the primary suspension unit 105.
Hence, other than with conventional suspension systems for rail vehicles, where the primary
suspension is typically located kinematically in series between the axle unit and the running
gear frame (i.e., if theoretically mapped to Figure 2, would conventionally be located between
the support unit 108.3 and the running gear frame 104), the present variant integrates the
primary suspension within the axle unit 108.
By this integration of the primary suspension unit 105 into the axle unit 108, only the wheel
unit 107 and wheel bearing unit 108.1 still pertain to the primary unsprung mass of the rail
vehicle 101. Hence, the present solution greatly reduces the primary unsprung mass, while
still using comparatively simple and robust components. Thus, while of course still possible,
less focus has to be put on the weight reduction of the components of the wheel arrangement
103. This, in particular, allows use of different and/or less costly materials for the
components of the wheel unit 107 and the axle unit 108, such as lower grade steel or the like,
which are eventually less susceptible to damage, crack propagation etc.
It will be appreciated, however, that with other variants, the primary suspension unit 105 can
basically be located at any other desired and suitable point along the kinematic chain
between the wheel unit 107 and the rail vehicle structure, e.g. the running gear frame 104. In
particular, the primary suspension unit 105 may be located more or less remote from the
wheel unit 107.
It will be appreciated that, in principle, the primary suspension unit 105 may be integrated
within the axle unit 108 at any desired and suitable location in the kinematic chain between
the wheel support unit 108.3 and the wheel bearing unit 108.1. Moreover, the type and

working principle, respectively, of the primary suspension unit 105 may be adapted to the
location of the primary suspension unit 105. In any case, of course, the design and location
of the primary suspension unit 105 is adapted and, preferably, optimized, to the loads to be
expected during operation of the vehicle 101.
In the present example, a gap 109 is formed between the wheel support unit 108.3 and the
wheel bearing unit 108.1. The primary suspension unit 105 is connected to the wheel
support unit 108.3 and the wheel bearing unit 108.1 in such a manner that the primary
suspension unit 105 bridges a part of the gap 109. By this means a very simple integration of
the primary suspension of unit 105 into the axle unit 108 is achieved. In practice, the location
and orientation of the gap 109 and the bridging primary suspension unit 105 may be
comparatively easily adapted to the loads to be expected during operation of the vehicle 101.
The wheel bearing unit 108.1 has a central recess 110, wherein the wheel support unit 108.3
extends into and through the recess 110, such that a particularly compact design is achieved.
By means of the wheel support unit 108.3 reaching through this recess 110 support can be
provided to the wheel bearing unit 108.1 on both lateral sides of the wheel bearing unit 108.1.
Such a configuration is also particularly beneficial in terms of failure safety and failure running
properties, since even upon failure of the primary suspension unit 105 dislocation of the
wheel unit 107 from the axle unit 108 may be prevented by simple safety means as will be
explained further below.
It will be appreciated that the recess 110 of the wheel bearing unit 108.1 may generally be of
any arbitrary design and shape as long as it allows the wheel support unit 108.3 to reach into
the recess 110 under any conditions to be expected during normal operation the vehicle 101.
With particularly simple variants allowing compact designs, the recess 110 has a recess axis,
wherein the recess axis, in an unloaded state of the wheel arrangement 103, extends at least
substantially parallel to the wheel axis of rotation 107.1. Typically, as in the present example,
the recess axis substantially coincides with the wheel axis of rotation 107.1.
In the present example, the wheel support unit 108.3 defines a wheel support unit axial
direction AD, a wheel support unit circumferential direction CD and a wheel support unit
radial direction RD, wherein the wheel support unit axial direction AD, in an unloaded state of
the wheel arrangement (as shown in the solid lines in Figure 2), extends at least substantially
parallel to the wheel axis of rotation 107.1.

The wheel support unit 108.3 comprises two radial protrusions in the form of an inner radial
web element 108.4 and an outer radial web element 108.5 as well as a central support stub
108.6. The central support stub 108.6 is rigidly connected to the running gear frame 104.
Both, radial web elements 108.4, 108.5 protrude from the wheel support unit 108.3 in the
wheel support unit radial direction. It will be appreciated that, in the present embodiment, the
inner radial protrusion 108.4 is located on an inner side of the wheel bearing unit 108.1,
wherein this inner side, during use of the rail vehicle 101 on a track T, (in the vehicle
transverse direction, y-axis) faces towards a center of the track T. Consequently, the outer
radial protrusion 108.5 is located on an outer side of the wheel bearing unit 108.1, wherein
the outer side, during use of the rail vehicle 101, faces away from the center of the track T.
It will be appreciated that, in the present example, the outer radial web element 108.5 is
formed by a separate part not directly connected to the central support stub 108.6 of the
support unit 108.3 but rather connected to the running gear frame 104. It will be appreciated
that, with other variants, the outer radial web element 108.5 may also be in direct contact with
the central support stub 108.6 or be an integral part of the central support stub 108.6. Similar
applies to the inner radial web element 108.4, which in the present example is disengageably
connected to the central support stub 108.6, but may also be an integral part of the central
support stub 108.6 in other cases. Similarly, depending on the design of the running gear
frame 104, the inner radial web element might also be connected to the running gear frame
104. Furthermore, with certain variants, the respective interface for the primary suspension
unit 105 provided by the respective radial web element 108.4, 108.5 might also be directly
provided by a surface of the running gear frame 104.
In order to provide resilient support of the wheel unit 107 on the axle unit 103 via the primary
suspension unit 105, an inner primary suspension element 105.1 of the primary suspension
unit 105 is connected to a face of the inner radial web element 108.4 (facing the wheel
bearing unit 108.1) and to the wheel bearing unit 108.1, thereby bridging the gap 109. As
can be seen from Figure 2, the inner primary suspension element 105.1 is connected to an
associated inner radial segment 108.7 of the wheel bearing unit 108.1. Furthermore, an
outer primary suspension element 105.2 of the primary suspension unit 105 is connected to a
face of the outer radial web element 108.5 (facing the wheel bearing unit 108.1) and to the
wheel bearing unit 108.1, more precisely to an associated outer radial segment 108.8 of the
wheel bearing unit 108.1.
It will be appreciated that the design of the wheel bearing unit 108.1 with the radial segments
108.7 and 108.8 yields a comparatively lightweight design. Nevertheless, with other variants,

any other shape of the wheel bearing unit 108.1 may be selected as long as there is an
appropriate interface for the respective primary suspension element 105.1 and 105.2,
respectively.
It will be further appreciated that, generally, with other variants, one single protrusion or radial
web element 108.4, 108.5, respectively, located on one side of the wheel unit 107 may be
sufficient. However, as with the present example, beneficial support of the alternating lateral
loads acting along the axis of rotation 107.1 of the wheel unit 107 is achieved via the radial
protrusions or web element 108.4 and 108.5, located on both the inner and the outer side of
the wheel unit 107.
It will be further appreciated that one or more of these radial protrusions or web elements
108.4 and 108.5 may be provided at the same side of the wheel unit 107. Each protrusion
108.4, 108.5 may extend over a certain part of the circumference of the wheel support unit
108.3, the angle of extension along the circumferential direction of the wheel support unit
108.3 depending, in particular, on the number of protrusions 108.4, 108.5 provided on the
same side of the wheel unit 107. In particular, as is indicated in Figure 6 by the double-dot-
dashed contour 112.2, in the case of a plurality of primary suspension elements 112.2,
respectively, on either side, one protrusion or web element 108.4, 108.5, respectively, may
be provided per primary suspension element 105.1, 105.2. Preferably, the respective radial
protrusion 108.4, 108.5 extends along the wheel support unit circumferential direction over at
least 45%, preferably at least 60%, more preferably at least 80%, of the circumference of the
wheel support unit 108.3. In the present example, however, with one ring shaped primary
suspension element 105.1, 105.2, respectively, on either side, the respective protrusion or
web element 108.4 and 108.5 is a substantially ring-shaped component extending over 100%
of the circumference of the wheel support unit 108.3, thereby yielding a very robust and
simple design.
With the design as described above, in the present example, the wheel support unit 108.3
defines a radial cavity, the radial cavity 111 extending in the wheel support unit
circumferential direction CD and in the a wheel support unit radial direction RD. In the
present example, at least a part of the wheel bearing unit 108.1 is inserted, in the wheel
support unit radial direction RD, into the radial cavity 111. By this means, a particularly
compact configuration is achieved. Moreover, this configuration is particularly beneficial in
terms of its failure modes in case of potential failure of the primary suspension unit 105. This
is not least due to the fact that the insertion of the wheel bearing unit 108.1 in the radial cavity
111 ensures that the wheel bearing unit 108.1 and, consequently, the wheel unit 107 is

generally kept in place on the wheel support unit 108.3 even in case of a failure of the
primary suspension unit 105.
As had been explained above, generally, two primary types of relative motion between the
parts of the wheel support unit 108.3 and the wheel bearing unit 108.1 which form the bridged
part of the gap 109 may be taken into account or considered when integrating the primary
suspension unit 105. One is essentially a shear motion which then typically leads to the use
of one or more shear spring elements for the primary suspension unit 105. Such a design is
shown in the present example and will be described in further detail below.
Another type of motion which might be considered or used for the primary suspension motion
is essentially a normal or breathing motion (increasing or decreasing the width of the gap
109). Such a breathing motion could lead to the use of one or more compression spring
elements for the primary suspension unit 105. However, as is indicated in Figure 2 by the
dashed contour 112.1, here as well one or more shear spring elements 112.1 could be used
within the part of the gap 109 executing the breathing motion during operation. As shown,
the breathing motion part of the gap 109 could be located within the recess 110 such that a
particularly compact configuration may be achieved. In particular, a more or less
conventional primary spring arrangement could be used at the location of the elements 112.1.
Of course, eventually, any combination of these motions and spring elements 105.1, 105.2
and 112.1, respectively, may also be used, in particular, depending on the loads to be
expected during operation of the vehicle 101.
In the present embodiment, in a simple, space saving and efficient manner, the respective
wheel arrangement 103 further achieves high derailment safety while at the same time
keeping the unsprung mass low and maintaining high passenger comfort during operation of
the rail vehicle in that the primary suspension unit 105 is configured such that, at least in the
static sate of the rail vehicle 101 (i.e., with the rail vehicle 101 standing on a straight level
track under nominal loading – as indicated by the dashed contour 116 in Figure 2) the
(virtual) tilt axis 107.2 (see Figures 4 and 6) of the wheel unit 107 is located at a height level
107.3 (see Figures 2, 3 and 5) below the axis of rotation 107.1 of the wheel unit 107. In this
static sate of the rail vehicle 101 the axis of rotation 107.1 of the wheel unit substantially
coincides with the longitudinal axis 108.9 of the wheel support unit 108.3.
This tilt axis 107.2 (at least in the static state) runs parallel to the vehicle longitudinal direction
(x axis) and is defined by the distribution of the transverse rigidity of the primary suspension

unit 105. More precisely, as the primary suspension unit 105 is located above the wheel to
rail contact location, a transverse force F (also referred to as lateral load herein) acting in the
transverse direction (y axis) at the wheel to rail contact point CP (e.g., as constantly present
for wheel to rail pairings with a certain conicity, but also as impact loads as a result of track
irregularities or the like) results not only in a transverse (or lateral) deflection of the wheel unit
107 but also in a tilt motion of the wheel unit 107 (also referred to as a lateral track load
induced tilt herein) about this tilt axis 107.2 located at height level 107.3 (as is illustrated in
Figure 2, 6 and 7).
The tilt axis 107.2 (and its height level 107.3) is defined by the primary suspension elements
105.1 and 105.2 of the primary suspension unit 105. More precisely, the primary suspension
unit 105 has a primary suspension transverse rigidity PSTR (jointly defined by the primary
suspension elements 105.1, 105.2) in the transverse direction, i.e. a direction parallel to the
axis of rotation 107.1 (in the static state), and the tilt axis 107.2 is defined by the distribution
of the primary suspension transverse rigidity PSTR of the primary suspension unit 105 along
the height direction.
This tilt motion of the wheel unit 107 in response to such transverse forces F has a
considerable impact on the deflection of the wheel unit 107 at the wheel to rail contact
location CP, and, hence, on the derailment safety of the vehicle. As is illustrated in Figure 6
and 7, by selecting a suitable distribution of the transverse rigidity TR of the primary
suspension unit 105 which locates this (virtual) tilt axis 107.2 at a height level 107.3 below the
axis of rotation 107.1 of the wheel unit 107 (see Figure 7, left), tilt related transverse
deflection TD of the wheel unit 107 at the wheel to rail contact location CP can be reduced
compared to conventional wheel units 117 where the height level 117.3 of the tilt axis is
located at the same level as the axis of rotation 117.1 of the wheel unit 117 (see Figure 7,
right). Hence, in the present example, derailment safety can be increased (over such
conventional designs) while at the same time the keeping the overall transverse rigidity TR of
the primary suspension unit 105 unchanged. Hence, the unsprung mass can be kept low and
passenger comfort may be maintained while reducing the derailment risk or, put otherwise,
the unsprung mass may be reduced and passenger comfort may be increased while keeping
a given low level of the derailment risk.
It will be appreciated that, in the present example, the primary suspension unit 105, in a
neutral or unloaded state, is under a compressive pre-stress in the transverse direction in
order to properly adjust the transverse stiffness level or achieve an appropriate transverse
stiffness already in this neutral state (with no transverse loads acting on the wheel unit 117),

respectively. This compressive pre-stress may simply be achieved by properly selecting the
dimensions of the primary suspension unit 105 and the gap 109 in the transverse direction.
It will be appreciated that this concept is particularly useful and effective in singe wheel
configurations as in the present example where the primary suspension unit 105 is the major
component defining this tilt axis 107.2. However, use of this concept is not limited to single
wheel configurations and, for essentially the same reasons, may also have beneficial effects
with other configurations (such as e.g. wheel pairs or wheel sets) where a mechanical
coupling exists between the two wheel units on both sides of the running gear.
It will be appreciated that, basically, any desired height offset of the tilt axis 107.2 from the
axis of rotation 107.1 that has a noticeable positive effect on the lateral track load induced tilt
can be sufficient. Typically, the wheel unit 107 has a rail contact surface defining a nominal
diameter ND of the wheel unit 107, and the tilt axis 107.2, in the vehicle height direction, in
particular, in the static state of the rail vehicle, is located at a tilt axis distance TAD below the
axis of rotation 107.1. Preferably, the tilt axis distance TAD is at least 10%, preferably at
least 20%, more preferably 15% to 50%, in particular, 25% to 40%, of the nominal diameter
ND of the wheel unit 107. These configurations achieve a particularly advantageous
reduction of the lateral track load induced tilt of the wheel unit 107.
The distribution of the primary suspension transverse rigidity PSTR can have any desired
configuration as long as the desired height offset (or tilt axis distance TAD) of the tilt axis
107.2 with respect to the axis of rotation 107.1 is achieved. In the present example, the
primary suspension unit 105 is separated in an upper, first primary suspension part 105.3 and
a lower, second primary suspension part 105.4. In the static state of the rail vehicle 101, in
the vehicle height direction, the upper primary suspension part 105.3 is located above the
axis of rotation 107.1, while the second primary suspension part 107.2 is located below the
axis of rotation 107.1 (see Figure 5 and 6).
In the direction parallel to the axis of rotation 107.1, the upper primary suspension part 105.3
has a first transverse rigidity PSTR1, while the second primary suspension part 107.2 has a
second transverse rigidity PSTR2. To achieve the desired height offset of the tilt axis 107.2
from the axis of rotation 107.1, the first transverse rigidity PSTR1 is lower than the second
transverse rigidity PSTR2. Preferably, the first transverse rigidity PSTR1 is 5% to 99%,
preferably 25% to 75%, more preferably 40% to 60%, of the second transverse rigidity
PSTR2, thereby achieving particularly beneficial results.

It will be appreciated that the above distribution of the primary suspension transverse rigidity
PSTR may simply be achieved by two separate primary suspension elements 112.2 (one
forming the upper primary suspension part 105.3, one forming the lower primary suspension
part 105.4). It may of course also be formed by any desired other number of primary
suspension elements 112.2 in either of the upper and lower primary suspension part 105.3,
105.4. In these cases, the primary suspension elements 112.2 may be distributed along an
outer circumference of the axle unit 108, thereby achieving a compact configuration. In
certain embodiments, to achieve the desired distribution of the primary suspension
transverse rigidity PSTR, the number of the primary suspension elements 112.2 in the upper
primary suspension part 105.3 may be lower than the number of the primary suspension
elements 112.2 in the lower primary suspension part 105.4. In addition or as an alternative,
to achieve the desired distribution of the primary suspension transverse rigidity PSTR, the
size of at least one of the primary suspension elements 112.2 in the upper primary
suspension part 105.3 may be smaller than a size of at least one of the primary suspension
elements 112.2 in the lower primary suspension part 105.4.
Similarly, as in the present embodiment, one single primary suspension element on each side
of the wheel unit 107 may be sufficient to achieve the desired distribution of the primary
suspension transverse rigidity PSTR. Even one single primary suspension element 112.1 per
wheel unit 107 (see Figure 2) may be sufficient to achieve this distribution of the primary
suspension transverse rigidity PSTR.
It will be appreciated that, basically, any desired type(s) of primary suspension element(s)
may be used to form the primary suspension unit 105 achieving resilient primary suspension
in the required degrees of freedom. In particular, primary suspension elements 105 of any
desired configuration and shape may be used. These may comprise conventional spring
elements, such as, for example helical metal spring elements or rubber spring elements
alone or in combination with other components, such as, for example, damping elements etc.
Typically these primary suspension elements are of course adapted to the requirements, in
particular the loads to be taken, during operation of the rail vehicle 101. For example, one or
more block shaped primary suspension elements may be used, i.e. interposed between the
wheel bearing unit 108.1 and the wheel support unit 108.3.
In the present example, as noted, the primary suspension unit 105 comprises two ring
shaped primary suspension elements 105.1 and 105.2, respectively providing resilient
support of the wheel unit 107 on the axle unit 108 (see Figure 2). Thus, the respective ring
shaped primary suspension element 105.1, 105.2 fully surrounds the wheel support unit

108.3. This has the advantage that a particularly beneficial introduction of the loads from the
wheel bearing unit 108.1 into the wheel support unit 108.3 is achieved.
In the present example, as noted above, a simple and particularly space saving configuration
is achieved in that the primary suspension unit 105 is a shear spring unit. Such shear spring
units typically have the advantage that they provide suitable spring motion in their shear
direction, typically in a shear plane, while being comparatively rigid in other directions (e.g. in
a direction perpendicular to a shear plane of the shear spring unit). In the present case, the
two shear spring elements 105.1, 105.2 are arranged and configured such that, in the static
state of the rail vehicle (see Figure 5 and 6), the respective primary suspension element
105.1, 105.2 is at least primarily (here: substantially exclusively) under a shear stress and
under a compressive pre-stress in the transverse direction. By this means a particularly
compact yet effective primary suspension configuration is achieved.
In the present example, the primary suspension elements 105.1, 105.2 are laminated rubber
metal spring elements with a plurality of layers 105.5, 105.6. More precisely, the primary
suspension elements 105.1, 105.2 have alternating metal layers 105.5 and rubber (or
polymer) layers 105.6, the two outer ones of the metal layers 105.5 forming the mounting
interfaces of the primary suspension elements 105.1, 105.2. In the present example, the
primary suspension elements 105.1, 105.2 are substantially identical. It will however be
appreciated that, with other variants, the primary suspension elements 105.1, 105.2 may also
differ from each other.
The layers 105.5, 105.6, in the static state of the rail vehicle 101, extend in a plane (xz plane)
perpendicular to the transverse direction (y axis). Hence, in a very compact configuration,
particularly favorable suspension in the height direction is achieved with at the same time
appropriate transverse rigidity PSTR. It will be appreciated that, in principle, any desired and
suitable number of layers 105.5, 105.6 may be chosen. In principle (depending on the
mounting interface design) a single layer 105.6 may be sufficient. Typically the number of
layers 105.5, 105.6 ranges from 1 to 15, preferably 3 to 10, more preferably 3 to 5.
The desired distribution of the primary suspension transverse rigidity PSTR may be achieved
in any suitable way by properly choosing the materials used for the primary suspension
elements 105.1, 105.2 (or 112.2) and/or by properly distributing the material(s) used for the
respective primary suspension element 105.1, 105.2 (or 112.2) and/or by properly choosing
the dimensions of the respective primary suspension element 105.1, 105.2 (or 112.2).

In the present example, a particularly simple, space saving and, hence, preferred variant is
realized where, across the respective layer 105.5, 105.6, the material composition and the
material thickness are substantially uniform. The respective ring shaped primary suspension
element 105.1, 105.2 has a plane of main extension (see, e.g., xz plane in Figure 4 or 6) in
which the ring shaped primary suspension element 105.1, 105.2 has an outer circumferential
contour 105.7 with a maximum outer diameter MOD and an inner circumferential contour
105.8 with a maximum inner diameter MID. The outer circumferential contour 105.7 defines
a first area center of gravity 105.9, whereas the inner circumferential contour 105.8 defines a
second area center of gravity 105.10. To achieve the desired distribution of the primary
suspension transverse rigidity PSTR, the second area center of gravity 105.10, in the vehicle
height direction, is upwardly offset from the first area center of gravity 105.9 by an area
center of gravity distance ACGD. The area center of gravity distance ACGD preferably is 5%
to 25%, preferably 7.5% to 15%, more preferably 9% to 12%, of the maximum outer diameter
MOD. Moreover, in the present example, the first area center of gravity 105.9 and the
second area center of gravity 105.10 are at least substantially aligned in the vehicle height
direction, thereby also achieving a particularly simple and compact configuration.
It will be appreciated that, basically, the respective outer and inner contour 105.7, 105.8 may
have any desired and suitable shape. For example, the respective outer and inner contour
105.7, 105.8 may be at least section-wise polygonal and/or least section-wise curved. In the
present example, a particularly simple arrangement is achieved, in that the outer
circumferential contour 105.7 and the inner circumferential contour 105.8 is an at least
essentially elliptic contour, in the present particular case, an at least essentially circular
contour.
The dimensions of the respective outer and inner contour 105.7, 105.8 may be chosen as
desired and suitable for the respective rail vehicle 101. With preferred variants, the maximum
outer diameter MOD ranges from 100 mm to 1000 mm, preferably 150 mm to 750 mm, more
preferably 200 mm to 500 mm. Furthermore, the maximum inner diameter MID may range
from 50 mm to 900 mm, preferably 75 mm to 700 mm, more preferably 100 mm to 400 mm.
Finally, the area center of gravity distance ACGD may range from 25 mm to 500 mm,
preferably 50 mm to 250 mm, more preferably 75 mm to 100 mm. Each of these variants
(alone or in arbitrary combination) leads to a particularly advantageous primary spring
configuration.
As noted, in the present example, across the respective layer of the primary suspension
elements, the material composition and the material thickness are substantially uniform. It

will be appreciated that, with other variants, the desired distribution of the primary suspension
transverse rigidity PSTR may also be achieved by varying the material properties across one
or more of the layers 105.5, 105.6 of the primary suspension elements 105.1, 105.2, in
particular across the polymer layers 105.6. In addition or as alternative, the desired
distribution of the primary suspension transverse rigidity PSTR may also be achieved by
varying the thickness of the material across one or more of the layers 105.5, 105.6 of the
primary suspension elements 105.1, 105.2, in particular, across the polymer layers 105.6.
This may be achieved, for example, by providing corresponding (arbitrarily but of course
suitably shaped) recesses within the respective layer 105.5, 105.6, in particular, in the
polymer layers 105.6. It will be appreciated that, in any of these cases, the desired
distribution of the primary suspension transverse rigidity PSTR may then also be achieved
with substantially concentric outer and inner contours 105.7, 105.8.
It will be appreciated that, in general, the overall or total rigidity of the primary suspension unit
105 may be substantially the same in all three (translatory) directions, i.e., the longitudinal
direction, the transverse direction and the height direction. However, as in the present
example, the primary suspension unit 105 shows different behaviors in different directions in
order to account for the load cases to be expected during operation of the particular vehicle
101. Hence, the primary suspension unit 105 has a longitudinal rigidity PSLR in the
longitudinal direction, the transverse rigidity PSTR and a height rigidity PSHR in the height
direction (i.e., in three mutually orthogonal directions). With certain variants, the height rigidity
PSHR is lower than at least one of the longitudinal rigidity PSLR and the transverse rigidity
PSTR (typically lower than the transverse rigidity PSTR, sometimes lower than both the
longitudinal rigidity PSLR and transverse rigidity PSTR). By this means, a primary
suspension may be achieved which is suitably compliant in the height direction of the vehicle
101, while being comparatively rigid in the transverse direction of the vehicle 101. In the
present example, the longitudinal rigidity PSLR is lower than the transverse rigidity PSTR. It
may be the case that the height rigidity PSHR is lower than the longitudinal rigidity PSLR. In
the primary suspension unit 105 as well as in many other embodiments according to the
present design, however, the height rigidity PSHR is at least approximately the same as the
longitudinal rigidity PSLR.
It will be appreciated that the wheel support unit 108.3 may, in general, have any desired and
suitable shape. Preferably, as in the present example, it is an elongated element, which can
be substantially symmetric (typically rotationally symmetric) with respect to an axis 108.8
which (in an unloaded state) is substantially parallel to the axis of rotation 107.1 of the wheel
unit 107. With other variants, however, as in the present example, the wheel support unit

108.3 may be a (potentially only slightly) asymmetric component to account for differences in
the relative location of its components in their unloaded and loaded state. Moreover, the
wheel support unit may be a substantially solid or, as in the present example, a hollow
component.
In the present example, the wheel arrangement 103 is configured for use in a motorized
implementation. Hence, to achieve a very compact and beneficial configuration, the wheel
support unit 108.3 is essentially tube shaped, wherein a drive shaft unit 114, at a first end, is
connected to the wheel unit 107 (only shown in a highly schematic way) by a torsionally rigid
linkage 115. The drive shaft unit 114 extends through an interior section of the wheel support
unit 108.3. The drive shaft unit, at its other (second) end opposite to the first end, is
configured to be connected to the drive unit 106 of the rail vehicle 101. To this end, the drive
shaft unit 114 has a toothed section 114.1 configured to connect to the drive unit 106. By this
means a particularly beneficial and compact design may be achieved.
As can be seen from Figures 2 to 4 in an unloaded state of the wheel arrangement (shown in
solid lines), the primary suspension elements 105.1, 105.2 have a certain offset (along their
shear plane or along the z axis, respectively) between their mounting faces (for mounting to
the wheel bearing unit 108.1 and the wheel support unit 108.3, respectively) which holds the
wheel unit 107 and the wheel bearing unit 108.1 in such a manner that the axis of rotation
107.1 of the wheel unit is parallel but offset from the longitudinal axis 108.9 of the wheel
support unit 108.3. In the (statically) loaded state under nominal load, the wheel unit 107 is
pushed upwards with respect to the wheel support unit 108.3 (or vice versa), such that the
axis of rotation 107.1 of the wheel unit substantially coincides with the longitudinal axis 108.9
of the wheel support unit 108.3 (as it is indicated by the dashed contour 116). This situation
is accounted for in that the linkage 115 can follow this motion and in that the wheel support
unit 108 has a slightly asymmetric or eccentric design.
While the present invention, in the foregoing has been mainly described in the context of a
shear spring arrangement, it will be appreciated that the primary suspension unit, in principle,
may be designed in any other desired and suitable way to achieve resilient primary
suspension in the required degrees of freedom. In particular, primary suspension elements
of any desired configuration and shape may be used instead of suspension elements 105.1,
105.2. For example, conventional metal spring elements may be used alone or in
combination with other components, such as, for example, damping elements etc. Similarly,
polymer springs, rubber springs or laminated metal rubber springs may be used alone or in
arbitrary combination with other spring and/or damping elements.

Furthermore, while the present invention, in the foregoing, has been mainly described in the
context of a single or individual wheel unit, it will be appreciated that the invention may also
be used in any other wheel configuration, e.g. in the context of wheel pairs or wheel sets with
a torsionally rigid coupling between the wheel units.
While the present invention, in the foregoing has been exclusively described in the context of
light rail vehicles, it will be appreciated that the invention can also be applied for any other rail
vehicles, in particular, other rail vehicles operating at considerably higher nominal speeds.

WE CLAIM:
1. A wheel arrangement for a rail vehicle (101), in particular, a light rail vehicle,
comprising
- a wheel unit (107), and
- a support unit (108),
wherein
- said wheel unit (107) defines an axis of rotation (107.1) of said wheel unit (107),

- said support unit (108) is configured to be connected to a rail vehicle structure
(104) of said rail vehicle (101) defining a vehicle longitudinal direction, a vehicle
transverse direction and a vehicle height direction;
- said support unit (108) is configured to connect said wheel unit (107) to said rail
vehicle structure (104) such that said wheel unit (107) is rotatable about said axis
of rotation (107.1);
- said support unit (108) comprises a primary suspension unit (105) configured to
provide resilient support of said rail vehicle structure (104) on said wheel unit
(107) at least in said vehicle height direction;
- said primary suspension unit (105) has a primary suspension transverse rigidity
in a direction parallel to said axis of rotation (107.1), wherein a distribution of said
primary suspension transverse rigidity across said primary suspension unit (105),
in particular, in a static state of said rail vehicle (101) on a straight level track
under a nominal load, defines a tilt axis (107.2) of said wheel unit (107) parallel to
said vehicle longitudinal direction;
characterized in that
- said distribution of said primary suspension transverse rigidity is such that, in said
vehicle height direction, said tilt axis (107.2) is located below said axis of rotation
(107.1).
2. The wheel arrangement according to claim 1, wherein
- said wheel unit (107) has a rail contact surface defining a nominal diameter of
said wheel unit (107);

- said tilt axis (107.2), in said vehicle height direction, in particular, in said static
state of said rail vehicle (101), is located at a tilt axis distance from said axis of
rotation (107.1);
- said tilt axis distance is at least 10%, preferably at least 20%, more preferably
15% to 50%, in particular, 25% to 40%, of said nominal diameter.
3. The wheel arrangement according to claim 1 or 2, wherein
- said primary suspension unit (105) is separated in an upper, first primary
suspension part (105.3) and a lower, second primary suspension part (105.4);
- said first primary suspension part (105.3) has a first transverse rigidity in said
direction parallel to said axis of rotation (107.1),
- said first primary suspension part (105.3), in said static state of said rail vehicle
(101), is located, in said vehicle height direction, above said axis of rotation
(107.1);
- said second primary suspension part (105.4) has a second transverse rigidity in
said direction parallel to said axis of rotation (107.1),
- said second primary suspension, in said static state of said rail vehicle (101), is
located, in said vehicle height direction, below said axis of rotation (107.1);
- said first transverse rigidity is lower than said second transverse rigidity,
wherein, in particular,
- said first transverse rigidity is 5% to 99%, preferably 25% to 75%, more
preferably 40% to 60%, of said second transverse rigidity.
4. The wheel arrangement according to any one of the preceding claims, wherein
- said primary suspension unit (105) is a shear spring unit,
- said shear spring unit, in particular, comprising at least one primary suspension
element (105.1, 105.2; 112.1; 112.2) configured to provide resilient support of
said rail vehicle structure (104) on said wheel unit (107);
- said at least one primary suspension element (105.1, 105.2; 112.1; 112.2), in
particular, being arranged and configured such that, in said static state of said rail
vehicle (101), said primary suspension element (105.1, 105.2; 112.1; 112.2) is at
least primarily under a shear stress, in particular, is at least substantially
exclusively, under a shear stress.

5. The wheel arrangement according to any one of the preceding claims, wherein
- said primary suspension unit (105) comprises at least one primary suspension
element (105.1, 105.2; 112.1; 112.2) configured to provide resilient support of
said rail vehicle structure (104) on said wheel unit (107),
- said primary suspension element (105.1, 105.2; 112.1; 112.2) comprising at least
one of a polymer element, a rubber element, and a laminated rubber metal spring
element with a plurality of layers (105.5, 105.6), said plurality of layers (105.5,
105.6), in particular, being configured to extend, in said static state of said rail
vehicle (101), in a plane perpendicular to said transverse direction.
6. The wheel arrangement according to any one of the preceding claims, wherein
- said primary suspension unit (105) has a longitudinal rigidity in said longitudinal
direction and a height rigidity in said height direction,
wherein
- said height rigidity is lower than at least one of said longitudinal rigidity and said
transverse rigidity,
and/or
- said longitudinal rigidity is lower than said transverse rigidity.
7. The wheel arrangement according to any one of the preceding claims, wherein
- said primary suspension unit (105) comprises at least one ring shaped primary
suspension element (105.1, 105.2; 112.1) providing resilient support of said rail
vehicle structure (104) on said wheel unit (107),
- said at least one primary suspension element (105.1, 105.2; 112.1), in particular,
extending along an outer circumference of an axle unit of said support unit (108).
8. The wheel arrangement according to claim 7, wherein
- said at least one ring shaped primary suspension element (105.1, 105.2; 112.1)
has a plane of main extension;
- said at least one ring shaped primary suspension element (105.1, 105.2), in said
plane of main extension, has an outer circumferential contour (105.7) with a
maximum outer diameter and an inner circumferential contour (105.8) with a
maximum inner diameter;

- said outer circumferential contour (105.7) defines a first area center of gravity
(105.9);
- said inner circumferential contour (105.8) defines a second area center of gravity
(105.10);
wherein
- said second area center of gravity (105.10), in said vehicle height direction, is
upwardly offset from said first area center of gravity (105.9) by an area center of
gravity distance, said area center of gravity distance, in particular, being 5% to
25%, preferably 7.5% to 15%, more preferably 9% to 12%, of said maximum
outer diameter;
and/or
- said first area center of gravity (105.9) and said second area center of gravity
(105.10) are at least substantially aligned in said vehicle height direction.
9. The wheel arrangement according to claim 8, wherein
- at least one of said outer circumferential contour (105.7) and said inner
circumferential contour (105.8) is an at least essentially elliptic contour, in
particular, an at least essentially circular contour
wherein, in particular,
- said maximum outer diameter ranges from 100 mm to 1000 mm, preferably
150 mm to 750 mm, more preferably 200 mm to 500 mm,
and/or
- said maximum inner diameter ranges from 50 mm to 900 mm, preferably 75 mm
to 700 mm, more preferably 100 mm to 400 mm,
and/or
- said area center of gravity distance ranges from 25 mm to 500 mm, preferably
50 mm to 250 mm, more preferably 75 mm to 100 mm.
10. The wheel arrangement according to any one of the preceding claims, wherein
- said primary suspension unit (105) comprises a plurality of primary suspension
elements (105.1, 105.2; 112.2) providing resilient support of said rail vehicle
structure (104) on said wheel unit (107),

- said plurality of primary suspension elements (112.2), in particular, being
distributed along an outer circumference of an axle unit of said support unit (108),
wherein, in particular,
- said primary suspension unit (105) is separated in an upper primary suspension
part (105.3) and a second primary suspension part (105.4);
- said upper primary suspension part (105.3), in said static state of said rail vehicle
(101), is located, in said vehicle height direction, above said axis of rotation
(107.1);
- said second primary suspension part (105.4), in said static state of said rail
vehicle (101), is located, in said vehicle height direction, below said axis of
rotation (107.1); wherein
- a number of said primary suspension elements (112.2) in said upper primary
suspension part (105.3) is lower than a number of said primary suspension
elements (112.2) in said second primary suspension part (105.4);
and/or
- a size of at least one of said primary suspension elements (112.2) in said
upper primary suspension part (105.3) is smaller than a size of at least one of
said primary suspension elements (112.2) in said second primary suspension
part (105.4).
11. The wheel arrangement according to any one of the preceding claims, wherein
- said support unit (108) comprises an axle unit with a wheel bearing unit (108.1)
and a wheel support unit (108.3),
- said wheel bearing unit (108.1) forms a bearing for said wheel unit (107);
- said primary suspension unit (105) is located kinematically in series between said
wheel support unit (108.3) and said wheel bearing unit (108.1), such that said
wheel support unit (108.3) is supported on said wheel bearing unit (108.1) via
said primary suspension unit (105);
wherein, in particular,
- said wheel support unit (108.3) is essentially tube shaped,
and/or
- a drive shaft unit (114), at a first end, in particular, is connected to said wheel unit
(107), said drive shaft unit (114) extends through an interior section of an

essentially tube shaped wheel support unit (108.3), and said drive shaft unit
(114), at a second end opposite to said first end, is configured to be connected to
a drive unit (106) of said rail vehicle (101), in particular, has a toothed section
configured to connect to said drive unit (106).
12. The wheel arrangement according to claim 11, wherein
- a gap (109) is formed between said wheel support unit (108.3) and said wheel
bearing unit (108.1);
- said primary suspension unit (105) is connected to said wheel support unit
(108.3) and said wheel bearing unit (108.1); and
- said primary suspension unit (105) bridges at least a part of said gap (109)
between said wheel support unit (108.3) and said wheel bearing unit (108.1).
13. The wheel arrangement according to claim 11 or 12, wherein
- said wheel bearing unit (108.1) has a recess (110), and
- said wheel support unit (108.3) at least partially extends into said recess (110),
wherein, in particular,
- said wheel support unit (108.3) extends through said recess (110);
and/or
- said recess (110), in particular, defines a recess axis, said recess axis, in an
unloaded state of said wheel arrangement, extending at least substantially
parallel to said axis of rotation (107.1) of said wheel unit (107).
14. The wheel arrangement according to any one of the preceding claims, wherein
- said wheel unit (107) has an inner side and an outer side, said wheel unit (107)
being configured such that, during use of said rail vehicle (101) on a track, said
inner side faces towards a center of said track and said outer side faces away
from said center of said track,
- at least one inner primary suspension element (105.1) of said primary
suspension unit (105) is located on said inner side of said wheel bearing unit
(108.1),

- at least one outer primary suspension element (105.2) of said primary
suspension unit (105) is located on said outer side of said wheel bearing unit
(108.1).
15. A rail vehicle unit comprising
- a rail vehicle structure (104), and
- at least one wheel arrangement (103) according to any one of claims 1 to 14
connected to said rail vehicle structure (104),
wherein, in particular,
- said rail vehicle structure (104) comprises a running gear unit, in particular, a
running gear frame, connected to said at least one wheel arrangement (103);
and/or
- said at least one wheel arrangement (103) is a single wheel arrangement.