Background Art Rail vehicles are usually made up having a carriage body which is supported by two bogies with one or more axles and associated wheels. When driving such a rail vehicle along a track, vibrations and oscillations from the track are propagated through one or more bogies to the carriage body. If the vibrations conform with the natural frequency of the carriage body, an oscillation is induced in the carriage body. Traditionally, carriage bodies with a high natural frequency have been built by making them rigid and of a limited length so that the frequency of the vibrations has essentially been lower than the natural frequency of the carriage body.

As the bogies roll along the track, they will in a well-known fashion move sinusoidally owing to the conicity of the wheels. The frequency of the sinusoidal motion increases as the wheels on the axles are being worn, and besides increases as the speed of the rail vehicle increases. The deviations from the ideal track position that appear in railway tracks have the highest amplitude at low frequencies, and therefore vibrations originating from irregularities in the track will be most powerful at low frequencies. However the frequency of the vibrations will increase as the speed of the rail vehicle increases.

There is an increasing demand for rail vehicles intended for high speeds. There is also a demand for longer carriages to obtain better space for passenger compartments. For improved performance characteristics there is also a demand for the carriages to have their own drive assembly and to be as light as possible to

achieve good efficiency of the rail vehicle. Owing to these factors, the natural frequency of the carriage bodies increases while at the same time a higher speed causes the frequency of the vibrations to increase. There is thus an increased risk of lateral oscillations being induced in the carriage body. The oscillations are not desirable since they result in a lower degree of comfort and especially since they cause an increased risk of derailment.

Swedish Patent 509,118 discloses a railway vehicle and a method for such a vehicle for reducing lateral oscillations in the carriage body of the railway vehicle by dynamically separating a partial mass from the total mass or bulk of the carriage body. As a result, the natural frequency of the bulk of the carriage body is increased, which causes elimination of the excitation of the carriage body oscillation. The partial mass is dynamically separated from the bulk of the carriage body with the aid of springs and damping means. However, it is necessary for the partial mass to be a relatively large part of the total mass of the carriage body for an opti- mal result. Moreover, the bulk of the carriage body must have a natural frequency which is higher than the fre- quencies that are excited by the sinusoidal motion of the bogies and irregularities in the track. This yields a restriction as to the reduction of the weight of the rail vehicle. Furthermore, the vibrations in the carriage body cannot be fully eliminated in a rail vehicle according to the above-mentioned Swedish patent.

Japanese Patent Publication 06249284 discloses a method, according to which lateral vibrations of a car- riage body are damped by moving a weight in relation to the carriage body in dependence on the measured lateral acceleration of the carriage body. A drawback of such a method is that oscillations with a measurable amplitude must have arisen before the signal from the measuring means becomes measurable.

There is consequently a need for a rail vehicle and method for such a vehicle in which the above-mentioned drawbacks have been minimised.

Summary of the Invention One object of the present invention is to provide a rail vehicle whose lateral oscillation is minimised.

A further object of the present invention is to pro- vide a rail vehicle whose lateral oscillation, owing to the sinusoidal motion of its bogie, is minimised.

One more object of the present invention is to pro- vide a method for minimising lateral oscillations in a rail vehicle.

An additional object of the present invention is to provide a method for minimising the effect of the bogies on the oscillations of the carriage body.

These objects are achieved by means of a rail vehicle and a method for a rail vehicle according to the appended claims.

The field of application of the invention is pre- ferably rail vehicles intended for high speeds, but the invention can be used for all types of rail vehicles.

A rail vehicle according to the invention comprises a carriage body supported by at least two bogies, the carriage body comprising a body part, which at least in the lateral direction is displaceable in relation to the remainder of the carriage body. A rail vehicle according to the invention is characterised in that it also com- prises a measuring means adapted to measure lateral motion of one of the bogies, a control means, which receives a signal, informing about the lateral motion of the bogie, from the measuring means, and a drive means for moving the body part in the lateral direction, the control means being adapted to control the drive means to move the body part in response to the signal from the measuring means, thereby counteracting lateral oscilla- tions in the carriage body.

By actively controlling, according to the invention, a laterally displaceable body part in response to a mea- sured lateral motion of a bogie, it is possible to obtain essentially complete elimination of the excitation of carriage body vibrations while at the same time the mass of the body part need only be a small part of the total mass of the carriage body. It is also possible to reduce the weight of the vehicle since the rigidity requirements are lower in a vehicle according to the invention compar- ed with previously known vehicles owing to the fact that the natural frequency of the carriage body is allowed to be lower.

The inventors have realised that the lateral oscil- lations in a carriage body are excited mainly by the sinusoidal motion of the bogies of the rail vehicle.

In most cases the carriage body cannot be considered a rigid body and it is therefore difficult to filter out the relevant frequencies from measured oscillations of the carriage body. Consequently it will be extremely dif- ficult to damp the oscillation of the carriage body in the lateral direction by merely measuring the oscillation of the carriage body. By instead measuring, according to the invention, the motion of the bogies, it will be con- siderably easier to compensate for the oscillation applied by the bogies.

The body part is advantageously displaced perpendi- cular to a longitudinal axis of the carriage body.

The control means is advantageously provided with information about the dynamic properties of the rail vehicle, which has been obtained through experiments or theoretical calculations and which is used by the control means to control the body part motion performed by the drive means in such manner that oscillations in the car- riage body are counteracted. For an optimal result, the control means must have detailed information about the dynamic properties of the rail vehicle.

According to a particularly preferred embodiment of the invention, the lateral motion of at least one of the bogies and the lateral oscillation of the carriage body are measured with the aid of a first measuring means and a second measuring means, respectively. The control means uses the signals from both the first and the second mea- suring means to control the drive means to move the body part for the purpose of counteracting lateral oscilla- tions of the carriage body. By the control means being fed forwards as well as backwards, lateral oscillations are efficiently counteracted while at the same time the demands for detailed information about the dynamic pro- perties of the rail vehicle can be somewhat lower compar- ed with the case if there is no feedback.

The lateral oscillation of the carriage body is advantageously measured by means of an accelerometer which measures acceleration in the lateral direction.

Alternatively, the longitudinal acceleration of the attachment of the transverse damping means to the car- riage body is measured. The bending of the carriage body can be determined by carrying out the measurement in at least two points which advantageously are located as far away as possible from the longitudinal symmetry axis of the carriage body.

When feedback control and feedforward control are combined, it is advantageous if the control system first of all takes the feedforward control into consideration.

It is particularly advantageous to measure the late- ral motion of both bogies in the rail vehicle. By con- trolling the body part in response to the lateral motion of both bogies, oscillations in the carriage body are efficiently counteracted.

Although the requirements as to the weight of the body part are lower in a vehicle according to the inven- tion, it is advantageous that the body part constitutes at least 1% of the mass of the rail vehicle in order to optimally counteract lateral oscillations of the carriage

body. However, advantages of the invention are achieved also in the case where the body part constitutes less than 1% of the mass of the rail vehicle.

The measurement of the lateral motion of the bogie can be carried out in a large number of ways. It is pre- ferred to measure the transverse motion of the bogie by means of a gyro.

The measurement of the lateral motion of the bogie can alternatively be carried out, for example, by measur- ing the force of the transverse damping means arranged between the bogie and the carriage body. The transverse damping means serve to damp the turning of the bogie in the lateral plane in relation to the carriage body.

Alternatively, the measurement can be carried out by measuring by means of an accelerator the lateral accele- ration of a point which is outside the centre of turning of the bogie.

It goes without saying that the above features can be combined in the same embodiment.

In order to further elucidate the invention, detail- ed embodiments will be described below, without, however, the invention being considered restricted thereto.

Brief Description of the Drawing Fig. 1 is a schematic view of a rail vehicle accord- ing to a preferred embodiment of the present invention.

Fig. 2 is a schematic block diagram of the function of a rail vehicle according to the present invention.

Detailed Description of the Invention Fig. 1 is a schematic view of a rail vehicle com- prising a carriage body 1, a body part 2, which is sus- pended by means of springs 3 from the body 1. The body part 2 is displaceable in the lateral direction essen- tially perpendicular to the longitudinal axis of the car- riage body with the aid of a drive means 4. The body part consists of e. g. a transformer. The carriage body is supported by bogies 5,6 which are suspended from the carriage body and turnable about a centre of turning 7,8

each. Each of the bogies has two axles 9,10,11,12 and associated wheels 13. A control means 14 is also arranged on the rail vehicle and is connected to the drive means 4 via a control line 15. An accelerometer 16 is arranged in the centre of the rail vehicle for measuring lateral oscillations of the carriage body perpendicular to the longitudinal axis of the carriage body. The accelerometer is connected to the control unit 14 via a line 17. On one bogie 5 a gyro 18 is arranged, which is connected to the control unit 14 via a line 19. A transverse damping means 20 is arranged between a fixing point 21 on the carriage body and a fixing point 22 on the bogie.

Fig. 2 is a schematic block diagram of the function of a rail vehicle according to the present invention.

With reference to both Fig. 1 and Fig. 2, the control means 14 corresponds to the contents within the dashed frame 23. When the rail vehicle is driven on rails, the bogie 5 will move along a sine curve. The transverse motion will be detected by the gyro 18 and will be pass- ed on to the guide means 14 via the line 19. In Fig. 2, the sinusoidal motion is represented as a disturbance 14 affecting the bogie 5. The lateral oscillation of the rail vehicle is affected by the transverse motions 24 of the bogie in a process 26. The transverse motion of the bogie in the form of sinusoidal motion is measured by the gyro 18 and passed on to the control means in block 27.

In block 27 there is information about the dynamic pro- perties of the rail vehicle, i. e. information about the process 26, which consists of the connection between the lateral motion of the bogie and the lateral oscillations of the carriage body. In block 27, a reproduction of the process is made and passed on to block 28, where the sig- nal from block 27 is added to the signal from block 31.

The sum from block 28 affects the drive means which is represented by block 29, in response to the signal from block 27 and block 31. The force of the drive means is added to the force of the sinusoidal motion of the

bogie, which is represented by block 25. Block 27 repre- sents feedforward control. The lateral oscillation of the carriage body is measured by means of the accelerometer 16, which is represented by block 30. Block 30 is con- nected to a regulator 31 in the control means. The drive means 29 is actuated in response also to the signal from block 31. Blocks 30 and 31 represent feedback control in the system. In block 28, the signal from block 27 is con- sidered most in order to obtain a quick reaction to the interference 24.

The accelerometer 16 can be replaced by a measur- ing means which consists of at least two accelerometers 32 for measuring longitudinal acceleration, which are arranged adjacent to the fixing point 21 of the trans- verse damping means in the carriage body. The accelero- meters 32 provide information about the bending of the carriage body.

A person skilled in the art understands that the invention is not restricted to the embodiment described above and that many modifications are feasible within the scope of the invention. For example, the gyro 18 can be replaced by an accelerometer 34 arranged on the bogie.

Alternatively, the gyro 18 can be replaced by a force- sensing device 33 in the transverse damping means 20, which measures the lateral motion of the bogie 5.

In an alternative embodiment, there is only one of the accelerometers 16 and 18. This means that there is only a feedforward control or a feedback control in the block diagram in Fig. 2.