Damping arrangements, which are used for railway vehicles, comprise, usually, vertical dampers damping the vertical motions of the car body, lateral dampers damping the lateral motions of the car body and yaw dampers damping the rotary lateral motions of the car body. At least two vertical dampers are used in convention railway, which often are mounted as far as possible from each other on a respective side of a longitudinal centre line through the car body. The reason for mounting them as far as possible from each other is that the rolling damping increases with the distance to said centre line, whereas the vertical damping is not influenced by the distance and may thereby be kept on a relatively low level. In view of comfort, it is desired that the car body has a high rolling damping but a low vertical damping. By such location of the vertical dampers, an acceptable relation between the rolling and vertical damping is obtained, but it is far from optimal for obtaining a desired comfort. At the same time, said location of the dampers results in the fact that a space is used which in many cases may be suitable for location of other components. Furthermore, a more free location of the dampers is preferred.

In order to damp the lateral motion of the car body, conventional railway vehicles often comprise lateral dampers damping rectilinear lateral motion of the car body and yaw dampers damping lateral rotary motions of the car body. In view of comfort, it is preferred that the yaw dampers have a higher damping than the lateral dampers at the lateral motion of the car body.

SUMMARY OF THE INVENTION The object of the present invention is to provide a damping arrangement for a railway vehicle of the kind initially mentioned at which passengers in the car body obtain an optimal comfort with a minimum number of dampers.

The above mentioned object is achieved by the damping arrangement of the initially mentioned kind which is characterised in that the arrangement comprises means which results in rotary motions between the car body and the bogie obtaining a greater damping than rectilinear motions.

Thereby, passengers in the car body may obtain a high comfort since said means results in the rotary motions between the car body and the bogie, which decrease the comfort, being damped more heavily than the rectilinear motions.

According to a preferred embodiment of the invention, the dampers of the damping arrangement have a substantially common damping direction, and they are arranged to damp motions in a substantially common plane. Such dampers may be arranged to damp motions in a substantially vertical plane.

Thus, such dampers will damp the rolling motions of the car body more heavily than its vertical motions. Said damping arrangement may also comprise or alternatively comprise dampers, which are arranged to damp motions in a

substantially horizontal plane. The rotary motions of the car body in the horizontal plane may thereby be damped more heavily than its rectilinear lateral motions. Hereby, only two dampers account for the damping of the car body in the horizontal plane in contrast to the two lateral dampers and two yaw dampers, which are used at conventional damping.

Thereby, the number of dampers may be reduced with a maintained comfort for the passengers with regard to the lateral motions of the car body.

According to another preferred embodiment of the invention, the damping arrangement comprises dampers which comprise an inner space which is arranged to enclose a medium, which at motions between the car body and the bogie is allowed to flow with a resistance between a first and a second chamber of said space. By choosing dampers having a suitable flow resistance, a desired damping of motions between the car body and the bogie may be obtained. At this type of dampers, said means comprises first and second conduits connecting the respective chambers of the dampers to each other in such a manner that a medium flow between the dampers is allowed at rectilinear motions between the car body and bogie whereas no medium flow is allowed at rotary motions. At damping of the motions of the car body, an internal flow between the first and second chamber of the dampers arises such that an overpressure is established in one of these chambers and a subpressure in the other chamber. By knowledge of the location of the dampers, it is easy to understand in which chambers the overpressure respective the subpressure will arise during the rotary motions respectively the rectilinear motions of the car body. Said first and second conduits are at rolling motions arranged to connect the chambers of the respective dampers, which have an overpressure, and the chambers, which have a subpressure.

Since the same overpressure and subpressure prevails in these chambers connected to each other, no medium flow take

place between the dampers. However, said first and second conduits are arranged to connect a chamber having an overpressure to a chamber having a subpressure at rectilinear motions of the car body. Thereby, the medium may flow from the chamber of the dampers having an overpressure to the chamber of the other dampers having a subpressure. By that fact, the damping force of the dampers is reduced concerning rectilinear motions in relation to rolling motions. Advantageously, said conduits comprise restrictions. With a choice of a suitable restriction, the flow between the dampers may be controlled such that the damping properties of the dampers concerning rotary motions and rectilinear motions obtain a desired relation. Said restrictions may be adjustable, which is an advantage if one changes the relation between the damping of the rotary motions and the rectilinear motions of the dampers.

According to another preferred embodiment of the invention, said medium is an oil. Hereby, a hydraulic oil having suitable properties may be used. Advantageously, said dampers comprise a cylinder. Said cylinder may comprise a displaceable piston dividing the inner space of the cylinder in said first and second chambers. Thereby, the piston may comprise at least one passage allowing a flow of the medium between said first and second chambers. Said passage or passages may thereby have a cross-sectional area which is adapted to provide a suitable resistance when the medium is pressed through the passage between said first and second chamber. Consequently, since no medium flow is allowed between the dampers at rotary motions, the rotary motions are damped solely by the internal damping of the respective damper, via the medium flow through said passages. Said piston may, via a piston rod and a first connection, be connected to the car body of the vehicle and said cylinder may by a second connection be connected to the bogie. By the mounting of the dampers to the car body and the bogie by

said first and second connection, the dampers may effectively damp motions between these.

According to another preferred embodiment of the invention, the two dampers have a substantially identical construction and are provided at a substantially equal distance from the connection of the car body to the bogie, but on substantially opposite sides. Thereby, the damping arrangement obtains a substantially symmetrical construction with substantially identical dampers, which is favourable in view of expenses.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, preferred embodiments of the invention are described as examples with reference to the attached drawings, in which: Fig 1 shows schematically a damping arrangement, according to the present invention, for damping of the motion of the car body in a substantially vertical plane.

Fig 2 shows schematically, from below, a damping arrangement, according to the present invention, for damping of the motion of a car body in a substantially horizontal plane.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig 1 shows schematically a vertical section through a railway vehicle having a damping arrangement according to the present invention. The railway vehicle comprises a car body 1 and a bogie 2, which are connected to each other by a connection 3. Said connection 3 allows the car body 1 and the bogie 2 to have a certain range of movement in relation

to each other. In order to damp the vertical motion of the car body 1 in relation to the bogie 2, the vehicle comprises a first damper 4 and a second damper 5. The dampers 4,5 each comprise an upper articulated connection 6,7 to the car body 1 and a lower articulated connection 8,9 to the bogie 2. The dampers 4,5 have a substantially identical construction and each comprises a cylinder 10,11 enclosing a displaceable piston 12,13, which, via a piston rod 14, 15, is connected to the articulated connection 6,7 to the car body 1. The pistons 12,13 divide the inner space of the cylinders 10,11 in a first chamber 16,17 and a second chamber 18,19. The pistons 12,13 each comprises at least a passage 20,21 such that the medium in the cylinders 10,11 may flow between said first 16,17 and second 18,19 chambers at motions between the car body 1 and the bogie 2.

Since said passages 20,21 have a relatively small cross- section area, said medium flow goes on with a flow resistance through said passages 20,21, wherein the motion between the car body 1 and the bogie 2 is damped. This is conventional technique and has the drawback that the damping properties of the dampers 4,5 have to be adapted in order to suit rectilinear vertical movements between the car body 1 and the bogie 2 as well as rotary motions. Such an adaption often results in a compromise of the properties of the damper and an optimal comfort is therefor rarely obtained. To let the passengers in the car body 1 experience an optimal comfort during forward moving of the railway vehicle, said rotary motion between the car body 1 and the bogie 2 has to be damped considerably more heavily than pure rectilinear vertical motions. In conventional railway vehicles, such vertical dampers are therefore located laterally as far as possible from the centre line 22 of the train.

The damping arrangement comprises a first conduit 23 extending from the first chamber 16 of the damper 4 to the

second chamber 19 of the damper 5, and a second conduit 24 extending from the first chamber 17 of the damper 5 to the second chamber 18 of the damper 4. Said first 23 and second 24 conduits comprise a respective adjustable restriction 25, 26. In the cases when the car body 1 performs a pure rotary motion in relation to the bogie 2, for example, when the left side of the car body moves downwards whereas the right side moves upwards, the articulated connection 6 will be displaced downwards and displace the piston 12 downwards via the piston rod 14. Thereby, the medium in the second chamber 18 flows with a resistance through the passage 20 in the piston 12 to the first chamber 16. By the flow resistance of the passage 20, the medium in the second chamber 18 thereby has a higher pressure than the medium in the first chamber 16. At the same time, said rotary motion will displace the articulated connection 7 upwards wherein, the piston 13, via the piston rod 15, also is displaced upwards in the cylinder 11. During the displacement motion of the piston 13, the medium thus flows from the first chamber 11 of the damper 5 through the passage 21 of the piston 13 to the second chamber 19. Thereby, the medium in the first chamber 17 obtains a higher pressure than the medium in the second chamber 19. Since the first conduit 23 connects the first chamber 16 of the damper 4 and the second chamber 19 of the damper 5 to each other no flow does arise in the conduit 23 since said chamber 16,19 at a pure rotary motion have a substantially equal subpressure. Consequently, the second conduit 24 connects the first chamber 17 of the damper 5 to the second chamber 18 of the damper 4. Between these chambers arises neither a medium flow since these chambers have a substantially equal overpressure. Consequently, a pure rotary motion between the car body 1 and the bogie 2 is damped internally of the respective dampers 4,5 since no medium flow does arise in the first 23 and second 24 conduits between the dampers 4,5. If instead the car body 1 moves vertically rectilinearly, for example, upwards in

relation to the bogie 2, the both articulated connections 6, 7 move at the same time upwards, wherein the pistons 12,13 at the same time move upwards such that the medium in the dampers 4,5 flows from its first chamber 16,17 to its second chamber 18,19. Since the first chamber of the damper 4 thereby has an overpressure in relation to the second chamber 19 of the damper 5, which has a subpressure, the medium will flow through the first conduit 23 from the first chamber 16 of the damper 4 to the second chamber 19 of the damper 5. In a corresponding way, the medium will flow from the first chamber 17 of the damper 5, which has an overpressure, to the second chamber 18 of the damper 4 which has a subpressure. By said medium flow in the first 23 and second 24 conduit, the dampers 4,5 will have a considerably weaker damping at pure rectilinear vertical motions between the car body 1 and the bogie 2 than at rolling motions. In order to obtain an optimal comfort for the passengers in the car body 1, the first and second conduit 23,24 comprise restrictions 25,26, which are adjustable so that the medium flow in said first and second conduit 23,24 has an adjustable resistance. Thereby, the relation between damping of rectilinear vertical motions in relation to rotary motions by dampers 4,5 may be adjusted until it is optimal in view of comfort. Another advantage of the damping arrangement according to the present invention is that the dampers 4,5 may obtain a more free location. Consequently, they may be located closer to the centre line 22 and have an unchanged damping relation by adjustment of said restrictions 25,26.

Fig 2 shows an alternative embodiment of a damping arrangement, which is arranged to damp motions between the car body 1 and the bogie 2 in a substantially horizontal plane. Also in this case, it is suitable in view of comfort that the rectilinear lateral motions of the car body 1 are less damped than its rotary motions. Therefore, the damping

arrangement comprises a first damper 4'and a second damper 5', which have a corresponding construction as the dampers 4,5, shown in Fig 1. Thereby, the damper 4'has a first articulated connection 6'to the car body 1 and a second articulated connection 8'to the bogie 2. In a corresponding manner, the damper 5'has a first articulated connection 7' to the car body 1 and a second articulated connection 9'to the bogie 2. Also in this case, the damping arrangement comprises a first conduit 23'and a second conduit 24'. The first and second conduits 23', 24'also comprise restrictions 25', 26'. At a rotary motion between the car body 1 and the bogie 2, a medium flow neither arise here between the dampers 4', 5', since the first connection 21' connects a chamber of the first damper 4'to a chamber of the second damper 5', which has a corresponding subpressure or overpressure. The same counts for the second conduit 24'.

At pure rotary motions, the damping of the rotary motion will be provided entirely internally in the respective damper 4', 5'. However, if the car body 1 moves substantially rectilinearly laterally in relation to the bogie 2, the first conduit 23'and the second conduit 24' connect chambers having different pressure of the respective dampers 4', 5'to each other. Thereby, the medium will flow between the chambers of the dampers such that the damping force of the dampers 4', 5'decreases. Consequently, the dampers 4', 5'will damp rectilinear lateral motions less than rotary motions between the car body 1 and the bogie 2.

By adaptation of the adjustable restrictions 25', 26'a desired flow resistance may be obtained in the first 23'and the second 24'conduit, wherein an optimal relation between the damping of rectilinear lateral motions and rotary motions between the car body 1 and the bogie 2 may be obtained. Especially advantageous with the dampers 4', 5' shown in Fig 2 is that they by said adjustable damping of the rectilinear lateral motions and rotary motions may obtain an optimal damping with fewer dampers than in

conventional damping arrangements which usually comprise two yaw dampers and two lateral dampers.

Advantageously, a damping arrangement for a railway vehicle comprises both the damping shown in Fig 1 and 2, i. e. damping of the motions of the car body both in a vertical plane and in a horizontal plane. But it is possible to use the present invention for damping in only one plane and to combine it with a conventional damping arrangement in the other plane. Another advantage is here that the dampers 4', 5'are provided in front of respectively behind the bogie instead of externally along the sides of the bogie 2, which is the location of conventional yaw dampers. Thereby, the providing of screens along the sides of the bogie 2 is facilitated, which is favourable for the railway vehicle from both an acoustic and aerodynamic point of view.

The invention is not restricted to the embodiments described but may be varied freely within the scope of the claims.