Patent Description:
When operating a rail vehicle, it is important to have accurate knowledge about the current adhesion conditions at the wheel-rail interface, i.e. the applicable kinetic friction coefficient. Namely, this is key for speed control in terms of retardation as well as acceleration. To improve the overall throughput and enhance the flexibility of railway traffic, it is envisaged that control systems will be implemented that employ so-called dynamic moving blocks to operate the rail vehicles in a railway network. In simplified terms, this means that the free distances between different rail vehicles are reduced substantially and set dynamically depending various parameters, such as the speeds and overall weights of the respective rail vehicles. Of course, the kinetic friction coefficient on each rail segment is also an important parameter in this context. Provided that one has access to reliable values of the kinetic friction coefficient, the rail vehicles may be controlled to accelerate and decelerate in a highly efficient manner.

For even better speed control, it is also necessary to know exactly how the rail vehicle's weight is distributed over its wheel axles.

Namely, only a comparatively low traction/brake force can be applied to a relatively lightly loaded axle without risking that its wheels experience slippage against the rails, whereas a relatively heavily loaded axle may be subjected to a comparatively high traction/brake force before its wheels experience slippage against the rails. Both for efficiency reasons and to avoid material damage, wheel sliding shall be avoided whenever possible. Therefore, to be on the safe side, an estimated lowest axle weight typically determines the maximum allowed traction/brake force for a the rail vehicle. Of course, this results in an overall suboptimal ace-leration/braking performance.

Various attempts have been made to determine the total weight of a vehicle. For example, <CIT> describes a load estimation system and method for estimating vehicle load. The system includes a tire rotation counter for generating a rotation count from rotation of a tire; apparatus for measuring distance travelled by the vehicle; an effective radius calculator for calculating effective radius of the tire from the distance travelled and the rotation count; and a load estimation calculator for calculating the load carried by the vehicle tire from the effective radius of the tire. A center of gravity height estimation may be made from an estimated total load carried by the tires supporting the vehicle pursuant to an estimation of effective radius for each tire and a calculated load carried by each tire from respective effective radii.

<CIT> shows a method and a system for estimating a weight for a vehicle on the basis of at least two forces which act upon the vehicle. The forces are a motive force and at least one further force, and topographical information for a relevant section of road. The estimation is performed when the at least two forces are dominated by the motive force.

<CIT> discloses devices and methods, which relate to the arrangement of a sensor on the shaft of a rail vehicle to determine its mass. For example, an output signal of an acceleration sensor is evaluated, which is disposed on a shaft of the rail vehicle. The mass of a freight wagon can be determined in that it vibrates in a manner typical to the mass (frequency, amplitude) after impact (switching impact, running over a switch). The impact can be determined in direction and intensity by the acceleration sensor on the shaft (axle), the vibration can be determined by the same acceleration sensor or by a further sensor on the chassis. From this measurement data, the mass of the wagon and the mass of the load with known empty weight and thereby the loading state can be determined.

The above documents describe different strategies for determining the weight as well as other characteristic properties of vehicles. However, there is yet no satisfying solution for establishing how a vehicle's total weight is distributed over its axles, such that for example the acceleration of the vehicle may be improved.

The object of the present invention is to solve the above problems and offer a solution that enables determining the specific axle weights of a rail vehicle in an accurate and reliable manner.

According to one aspect of the invention, the object is achieved by a controller for estimating axle weights of a rail vehicle, which, in turn, contains a number of wheel axles and a set of drive units. Each drive unit is configured to apply a respective traction force to each wheel axle in a driving subset of the wheel axles so as to cause acceleration of the rail vehicle. The controller is configured to obtain a power signal and a speed signal. The power signal indicates an amount of power produced by the set of drive units to accelerate the rail vehicle from a first speed to a second speed, for example from zero to <NUM>/h. The speed signal indicates respective values of the first and second speeds. Based on the power and speed signals, the controller is configured to estimate an overall weight of the rail vehicle, and by executing the following steps, the controller is further configured to estimate how the overall weight is distributed over the vehicle's wheel axles: (a) obtaining wheel speed signals indicating respective rotational speeds of the wheel axles in the driving subset of the wheel axles; (b) producing an acceleration control signal to a specific drive unit in the set of drive units such that this drive unit applies a gradually increasing traction force to a specific wheel axle of the wheel axles in the driving subset of the wheel axles; (c) determining, repeatedly during production of the acceleration control signal, an absolute difference between the rotational speed of the specific wheel axle and an average rotational speed of the wheel axles In the driving subset of the wheel axles except the specific wheel axle; and in response to the absolute difference exceeding a threshold value (d) determining a parameter that reflects a friction coefficient between a pair of wheels on the specific wheel axle and a pair of rails upon which the rail vehicle travels; repeating steps (a) to (c) for each of the wheel axles in the driving subset of the wheel axles, and based thereon estimate a respective fraction of the overall weight carried by each of wheel axles in the driving subset of the wheel axles.

The above controller is advantageous because it provides accurate values of the overall weight of the rail vehicle as well as its axle weights. As a bonus effect, this also enables the rail vehicle to brake without risking slippage.

Furthermore, the proposed controller is beneficial, since it allows for dynamic adaptation of the acceleration and braking functionality during travel in response to any redistribution of the load, e.g. due to passengers moving around in a train. More important, it is possible to apply dynamic moving block control of a rail vehicle, wherein the control is appropriately adjusted in response to cargo being loaded/unloaded and/or passengers embarking/disembarking.

According to one embodiment of this aspect of the invention, for any non-driven wheel axle, the controller is further configured to: (e) obtain wheel speed signals indicating respective rotational speeds of each wheel axle of the rail vehicle, (f) produce a brake control signal to a brake unit configured to apply a brake force to the non-driven wheel axle such that this brake unit applies a gradually increasing brake force to the non-driven wheel axle, (g) determine, repeatedly during production of the brake control signal, an absolute difference between the rotational speed of the non-driven wheel axle and an average rotational speed of the wheel axles except the non-driven wheel axle; and in response to the absolute difference exceeding a threshold value (h) determine a parameter reflecting a friction coefficient between a pair of wheels on the specific wheel axle and the pair of rails upon which the rail vehicle travels. The controller is configured to repeat steps (e) to (g) for each of the non-driven wheel axles, and based thereon estimate a respective fraction of the overall weight carried by each of the non-driven wheel axles. Thereby, individual axle weights can be determined for the entire set of wheel axles of a rail vehicle.

According to another embodiment of this aspect of the invention, the controller contains a first interface configured to receive a first vector signal expressing an inclination angle of the rail vehicle relative to a horizontal plane. The controller is configured to adjust the power signal indicating the amount of power produced by the onboard motor and/or the speed signal indicating the second speed based on the inclination angle when estimating the overall weight of the rail vehicle. Such adjustment is necessary if the overall weight of the rail vehicle is estimated when the rail vehicle travels on non-horizontal ground because in an uphill slope a part of the motor power is converted into potential energy, and conversely, in a downhill slope a part of the kinetic energy originates from potential energy.

According to yet another embodiment of this aspect of the invention, the controller also has a second interface configured to receive a second vector signal expressing a respective rotational movement of the wheels on each wheel axle in the driving subset of the wheel axles, which rotational movement is performed in a plane orthogonal to a respective rotation axis of the wheel axle.

Here, the controller is further configured to obtain the wheel speed signals indicating the respective rotational speeds based on the first and second vector signals. Thereby, accurate values of the wheel speed can be derived without any tachometer. This, in turn, vouches for robust and reliable measurements.

According to another embodiment of this aspect of the invention, the controller is configured to provide the respective fractions of the overall weight to a traction controller to enable the traction controller to produce a respective acceleration control signal to each drive unit in the set of drive units. Hence, respective acceleration control signals may be based on the respective fractions of the overall weight, and the rail vehicle can be accelerated in an optimized manner, for example enabling efficient control of the rail vehicle according to the dynamic moving blocks principle.

Preferably, in the light of the above, the controller is co-located with the traction controller. For example the controller may be integrated into the traction controller, or vice versa.

According to yet another embodiment of this aspect of the invention, the controller is configured to transmit the acceleration control signal via a data bus in the rail vehicle. This renders the implementation cost-efficient and flexible.

According to another aspect of the invention, the object is achieved by a computer-implemented method for estimating specific axle weights of a rail vehicle that contains a number of wheel axles and a set of drive units. Each drive unit is configured to apply a respective traction force to each wheel axle in a driving subset of the wheel axles so as to cause acceleration of the rail vehicle. The method involves: obtaining a power signal indicating an amount of power produced by the set of drive units to accelerate the rail vehicle between first and second speeds; obtaining a speed signal indicating respective values of the first and second speeds, and based thereon estimating an overall weight of the rail vehicle. To estimate how the overall weight is distributed over the number of wheel axles, the method further involves: (a) obtaining wheel speed signals indicating respective rotational speeds of the wheel axles in the driving subset of the wheel axles; (b) producing an acceleration control signal to a specific drive unit in the set of drive units such that this drive unit applies a gradually increasing traction force to a specific wheel axle of the wheel axles in the driving subset of the wheel axles; (c) determining, repeatedly during production of the acceleration control signal, an absolute difference between the rotational speed of the specific wheel axle and an average rotational speed of the wheel axles in the driving subset of the wheel axles except the specific wheel axle; and in response to the absolute difference exceeding a threshold value (d) determining a parameter reflecting a friction coefficient between a pair of wheels on the specific wheel axle and a pair of rails upon which the rail vehicle travels. Steps (a) to (c) are repeated for each of the wheel axles in the driving subset of the wheel axles, and based thereon a respective fraction of the overall weight carried by each of wheel axles in the driving subset of the wheel axles is estimated. The advantages of this method, as well as the preferred embodiments thereof are apparent from the discussion above with reference to the proposed controller.

According to a further aspect of the invention, the object is achieved by a computer program loadable into a non-volatile data carrier communicatively connected to a processing unit. The computer program includes software for executing the above method when the program is run on the processing unit.

According to another aspect of the invention, the object is achieved by a non-volatile data carrier containing the above computer program.

In <FIG>, we see a schematic illustration of a rail vehicle <NUM> equipped with a controller <NUM> according to one embodiment of the invention.

The controller <NUM> is arranged to estimate the different axle weights of the rail vehicle <NUM>, which has a number of wheel axles. <FIG> exemplifies four such wheel axles in the form of <NUM>, <NUM>, <NUM> and <NUM> respectively. In response to acceleration control signals A1, A3 and A3 from acceleration controllers <NUM>, <NUM> and <NUM>, a set of drive units <NUM>, <NUM> and <NUM> is configured to apply a respective traction force to each wheel axle in a driving subset of the wheel axles <NUM>, <NUM> and <NUM>, such that the rail vehicle <NUM> accelerates. Analogously, in response to brake control signals B1, B2, B3 and B4 from brake controllers <NUM>, <NUM>, <NUM> and <NUM>, a set of brake units <NUM>, <NUM>, <NUM> and <NUM> is configured to apply a respective brake force to each of the wheel axles <NUM>, <NUM>, <NUM> and <NUM> respectively, such that the rail vehicle <NUM> decelerates.

Each of the brake units <NUM>, <NUM>, <NUM> and <NUM> is associated with a respective rotatable member <NUM>, <NUM>, <NUM> and <NUM>, such as a brake disc or a brake drum being mechanically linked to the respective wheel axle <NUM>, <NUM>, <NUM> and <NUM>. At least one respective pressing member of each brake unit is configured to apply a brake force to the rotatable member so as to cause retardation of the wheel axle and the wheels thereon.

In practice, a typical rail vehicle contains a substantially larger number of wheel axles than what is shown in <FIG>. Traditionally, each bogie has two wheel axles carrying altogether four wheels, and each car body of the rail vehicle <NUM> includes a respective bogie in the front and rear ends.

The rail vehicle <NUM> contains a set of drive units <NUM>, <NUM> and <NUM> respectively configured to apply a respective traction force to each of the wheel axles <NUM>, <NUM> and <NUM> in the driving subset of the wheel axles. The rail vehicle <NUM> also contains a set of brake units <NUM>, <NUM>, <NUM> and <NUM> respectively configured to apply a respective brake force to each of the wheel axles <NUM>, <NUM>, <NUM> and <NUM>. Consequently, by operating the brake units <NUM>, <NUM>, <NUM> and <NUM>, the rail vehicle <NUM> may be caused to retard/decelerate.

Referring now to <FIG>, the controller <NUM> is configured to obtain a power signal Pm indicating an amount of power being produced by the set of drive units <NUM>, <NUM> and <NUM> when accelerating the rail vehicle <NUM> from a first speed v<NUM> to a second speed v<NUM>, for example from a standstill to <NUM>/h. Of course, however, according to the invention, the power signal Pm may equally well be received during acceleration of the rail vehicle <NUM> between any other two speed levels. In any case, the controller <NUM> is configured to obtain a speed signal indicating respective values of the first and second speeds v<NUM> and v<NUM>.

Based on the power signal Pm and the values of the first and second speeds v<NUM> and v<NUM>, the controller <NUM> is configured to estimate an overall weight mtot of the rail vehicle <NUM>.

This may be done under the assumption that any losses in the motor and losses due to wind and rolling resistance are negligible, which is basically true for low speeds. Namely, under this assumption, all the supplied power is converted into kinetic energy of the rail vehicle, i.e. P·t =Wk, where P is the supplied power, t is the time during which the power has been supplied and Wk is the resulting kinetic energy.

The resulting kinetic energy Wk, in turn, may be expressed as: <MAT>.

In other words, the controller <NUM> may calculate the overall weight mtot of the rail vehicle <NUM> as: <MAT>.

Referring now also to <FIG>, the controller <NUM> is further configured to:.

<FIG> shows a graph illustrating an example of how the kinetic friction coefficient µk may be expressed as a function of the wheel slippage s, which here is understood to designate a spinning motion of the wheel relative to the rail. However, technically, the wheel slippage s may equally well express a sliding motion of the wheel relative to the rail. In other words, the wheel slippage s is applicable to an acceleration scenario as well as a retardation ditto.

Characteristically, for lower values, the kinetic friction coefficient µk increases relatively proportionally with increasing wheel slippage s. When approaching a peak value µe, however, the kinetic friction coefficient µk levels out somewhat. After having passed the peak value, the kinetic friction coefficient µk is essentially constant for all values of the wheel slippage s. Thus, the friction coefficient peak value µe is associated with an optimal wheel slippage se after which a further increase of wheel slippage s results in a gradually reduced, and then almost constant kinetic friction coefficient µk.

According to the invention, a parameter µm is determined that reflects the friction coefficient between the rail vehicle's <NUM> wheels and the rails <NUM> and <NUM> upon which the rail vehicle <NUM> travels. Ideally, the peak value µe should be derived. For example, the peak value µe may be derived as follows. When the absolute difference | ω<NUM> - ωa | between the rotational speed of the specific wheel axle <NUM> and an average rotational speed ωa of all the rail vehicle's <NUM> wheel axles in the driving subset except the specific wheel axle <NUM> exceeds the threshold value, this corresponds to a situation where the wheels 121a and 121b on the specific wheel axle <NUM> experiences a wheel slippage sm near the optimal wheel slippage se. The kinetic friction coefficient µk is given by the expression: <MAT>.

Under the assumption that the wheel slippage sm is near the optimal wheel slippage se, the peak value µe of the kinetic friction coefficient µk may be estimated relatively accurately; and the proximity of wheel slippage sm to the optimal wheel slippage se is ensured by said threshold value for the absolute difference | ω<NUM> - ωa | between the rotational speed of the specific wheel axle <NUM> and the average rotational speed ωa of all the rail vehicle's <NUM> wheel axles except the specific wheel axle <NUM>.

Finally, the controller <NUM> is configured to repeat the above steps (a) to (c) for each wheel axle <NUM>, <NUM> and <NUM> in the driving subset, and based thereon estimate a respective fraction m<NUM>, m<NUM> and m<NUM> of the overall weight mtot carried by each of these wheel axles.

It is worth mentioning that the above-mentioned specific wheel axle <NUM> does not need to be any particular wheel axle, e.g. a frontmost or a rearmost wheel axle of the rail vehicle <NUM>. On the contrary, the above procedure may start with an arbitrary selected wheel axle in the driving subset.

Moreover, it is generally advantageous to execute the above procedure in line with a schedule, fixed or dynamic, wherein each wheel axle in the driving subset alternately either represents the specific wheel axle or is included in the complement set, i.e. all the wheel axles except the specific wheel axle. Repeated execution of procedure is nevertheless beneficial to enable adjustment of the braking functionality in response to any changes in the overall weight mtot and/or a redistribution of the overall weight mtot over the wheel axles.

As exemplified by the wheel axle <NUM> in <FIG>, one or more of the rail vehicle's <NUM> wheel axles may be non-driven, i.e. not be comprised in the driving subset of the wheel axles <NUM>, <NUM> and <NUM>. To handle this case and thus enable estimation of the axle weights of the non-driven axles, according to one embodiment of the invention, the controller <NUM> is further configured execute the below procedure.

In the general case where the rail vehicle has more than one non-driven axle, the controller <NUM> is further configured to repeat steps (e) to (g) for each of the non-driven wheel axles, and based thereon estimate a respective fraction m<NUM> of the overall weight mtot carried by each of the non-driven wheel axles.

The controller <NUM> may be configured to generate a control message ctrlA to make the acceleration controllers <NUM>, <NUM> and <NUM> produce acceleration control signals A1, A2 and A3 to the drive units <NUM>, <NUM> and <NUM> respectively, such that an average drive force applied to the wheel axles <NUM>, and <NUM> except the specific wheel axles <NUM> is gradually decreased when the drive force applied to the specific wheel axle <NUM> is gradually increased. In other words, the driving on the other wheel axles <NUM> and <NUM> compensate for the somewhat excessive drive force applied to the specific wheel axle <NUM>.

Preferably, this compensation is temporally matched. This means that the controller <NUM> is configured to generate the control message ctrlA to cause the acceleration controllers <NUM>, <NUM> and <NUM> to produce acceleration control signals A1, A2 and A3 to the drive units <NUM>, <NUM> and <NUM> such that, at each point in time, the gradual decrease of the average drive force applied to the wheel axles <NUM> and <NUM> except the specific wheel axles <NUM> corresponds to the gradual increase of the drive force applied to the specific wheel axle <NUM>. Namely, thereby the deviating drive force applied to specific wheel axle <NUM> is masked by the opposite deviation represented by the drive force applied to the wheel axles <NUM> and <NUM> in the driving subset.

Referring again to <FIG>, we see a drive unit <NUM> according to one embodiment of the invention. The drive unit <NUM> is configured to receive the acceleration control signal A1 from the acceleration controller <NUM>, which, in turn, operates in response to the control message ctrlA from the controller <NUM>. The acceleration control signal A1 may for example be transmitted via a data bus <NUM>. In response to the acceleration control signal A1, the drive unit <NUM> is configured to drive the wheel axle <NUM>. The drive unit <NUM> may contain at least one electric motor whose generated traction force depends on a magnitude of an electric current fed to it.

Further, for the overall efficiency, the data bus <NUM> may, of course, be configured to transmit the all the acceleration and brake control signals A1, A2 and A3 and B1, B2, B3 and B4 respectively to each of the drive units <NUM>, <NUM> and <NUM> and each of the brake units <NUM>, <NUM>, <NUM> and <NUM>.

Referring now to <FIG>, according to one embodiment of the invention, the controller <NUM> contains at least one interface <NUM> and <NUM> configured to receive first and second vector signals VS1 and VS2 respectively. The first vector signal VS1 expresses an acceleration aX, aY, aZ, aR, aP, and/or aw of the rail vehicle <NUM> in at least one dimension, for instance linearly in one or more spatial directions and/or rotations around one or more of these directions. The second vector signal VS2 expresses a respective rotational movement of the wheels 121a, 121b; 122a, 122b; 123a, 123b and 124a, 124b on each of the wheel axles. Consequently, since each wheel is configured to rotate around a respective one of the wheel axles, the rotational movement is performed in a plane being orthogonal to a respective rotation axis of the wheel axle.

The controller <NUM> is configured to obtain the wheel speed signals indicating the respective rotational speeds ω<NUM>, ω<NUM>, ω<NUM> and ω<NUM> based on the first and second vector signals VS1 and VS2 by applying physical mechanics algorithms known in the art. Of course, determining the average rotational speed ωa is trivial once each of the individual rotational speeds ω<NUM>, ω<NUM>, ω<NUM> and ω<NUM> is known.

<FIG> schematically illustrates a first accelerometer <NUM> according to one embodiment of the invention. The first accelerometer <NUM> is arranged in a frame element <NUM> of the rail vehicle <NUM>. The first accelerometer <NUM> is configured to produce the first vector signal VS1 representing an acceleration of the a rail vehicle <NUM> in at least one dimension, typically in each of the three spatial directions aX, aY and aZ and respective rotations aR, aP and aW around axes along each of these directions.

Preferably, according to one embodiment of the invention, the first vector signal VS1 further expresses an inclination angle a of the rail vehicle <NUM> relative to a horizontal plane H. Here, the controller <NUM> is configured to adjust the power signal Pm indicating the amount of power produced by the onboard motor and/or the speed signal indicating the second speed v<NUM> based on the inclination angle α when estimating the overall weight mtot of the rail vehicle <NUM>. Consequently, the estimate of the overall weight mtot may be adequately adjusted if the rail vehicle <NUM> travels on non-horizontal ground when obtaining the power signal Pm and the speed signal, such that in an uphill slope the part of the motor power that is converted into potential energy is discarded; and conversely, in a downhill slope the part of the kinetic energy originating from potential energy is discarded.

Naturally, for the same reasons, it is also preferable to compensate for the inclination angle α when repeatedly executing the above steps (a) to (c) to estimate the respective fraction m<NUM>, m<NUM> and m<NUM> of the overall weight mtot carried by each of the wheel axles <NUM>, <NUM> and <NUM> in the driving subset of the rail vehicle's <NUM> wheel axles.

<FIG> illustrates a second accelerometer <NUM> that is eccentrically arranged relative to a rotation axis of at least one wheel, say <NUM>. The second accelerometer <NUM> is configured to produce the second vector signal VS2 expressing movements of the second accelerometer <NUM> in a plane orthogonal to the rotation axis of the at least one wheel <NUM>, and transmit a signal containing the second vector signal VS2 to the controller <NUM>.

<FIG> shows a block diagram of the controller <NUM> according to one embodiment of the invention. The controller <NUM> includes processing circuitry in the form of at least one processor <NUM> and a memory unit <NUM>, i.e. non-volatile data carrier, storing a computer program <NUM>, which, in turn, contains software for making the at least one processor <NUM> execute the actions mentioned in this description when the computer program <NUM> is run on the at least one processor <NUM>.

The controller <NUM> contains input interfaces configured to receive the first and second vector signals VS1 and VS2 respectively, the power signal Pm and the speed signal expressing the speeds v<NUM> and v<NUM> respectively. Further, the controller <NUM> contains outputs configured to provide the acceleration control signals A1, A2 and A3, the brake control signals B1, B2, B3 and B4, and information about the individual axle weights, such as the respective fractions m<NUM>, m<NUM>, m<NUM> and m<NUM> of the overall weight mtot. As mentioned above, one or more of the input and/or output signals may be communicated via the data bus <NUM>.

According to one embodiment of the invention, the controller <NUM> is configured to provide the respective fractions m<NUM>, m<NUM> and m<NUM> of the overall weight mtot to each of the acceleration controllers <NUM>, <NUM>, and <NUM> to enable the acceleration controllers to cause its associated drive unit <NUM>, <NUM> and <NUM> respectively to produce a respective appropriate traction force in response to the acceleration control signals A1, A2 and A3. Here, the appropriate traction force is based on the respective fraction m<NUM>, m<NUM> or m<NUM> of the overall weight mtot applicable to the wheel axle in question <NUM>, <NUM> or <NUM> respectively.

According to one embodiment of the invention, the controller <NUM> is co-located with the acceleration controller. Thus, for example, the controller <NUM> may be integrated into the acceleration controller <NUM>, or vice versa. Alternatively, the functionality of the controller <NUM> may be distributed over two or more of the acceleration controllers <NUM>, <NUM> and/or <NUM>.

In order to sum up, and with reference to the flow diagram in Figure <NUM>, we will now describe the computer-implemented method for a rail vehicle that is carried out by the controller <NUM>.

In a first step <NUM>, signals are obtained that express first and second speeds v<NUM> and v<NUM> and an amount of power produced by the drive units of the rail vehicle <NUM> to accelerate it from the first speed v<NUM> to the second speed v<NUM>.

In a step <NUM> thereafter, a speed signal is obtained, which indicates a rotational speed ω<NUM> of a specific one the rail vehicle's <NUM> wheel axles, say <NUM>.

In a step <NUM>, preferably essentially parallel to step <NUM>, an average value is obtained, which represents an average rotational speed ωa of the rotational speeds ω<NUM> and ω<NUM> of the wheel axles <NUM> and <NUM> respectively in the driving subset of the wheel axles except the specific wheel axle <NUM>.

In a step <NUM> subsequent to step <NUM> and preferably essentially parallel to step <NUM>, an acceleration control signal is produced that is configured to cause a drive unit to apply an increased traction force to the specific wheel axle <NUM>.

Thereafter, a step <NUM> checks if an absolute difference | ω<NUM> - ωa | between the rotational speed ω<NUM> of the specific wheel axle <NUM> and the average rotational speed ωa of the wheel axles in the driving subset except the specific wheel axle <NUM> exceeds a threshold value. If so, a step <NUM> follows. Otherwise, the procedure loops back to steps <NUM> and <NUM>.

In step <NUM>, a parameter µm is determined that reflects a friction coefficient µe between the wheels 121a and 121b on the specific wheel axle <NUM> and the rails <NUM> and <NUM> upon which the rail vehicle <NUM> travels.

Subsequently, a step <NUM> checks if all the wheel axles <NUM>, <NUM>, and <NUM> in the driving subset of the rail vehicle <NUM> have been tested. If so, the procedure ends. If not, the procedure continues to a step <NUM> in which a not yet tested driving wheel axle is selected.

Then, in a step <NUM>, a speed signal is obtained, which indicates a rotational speed of the selected wheel axle.

In a step <NUM>, preferably essentially parallel to step <NUM>, an average value is obtained, which represents an average of the rotational speeds of the rail vehicle's <NUM> wheel axles except the selected wheel axle.

In a step <NUM> subsequent to step <NUM> and preferably essentially parallel to step <NUM>, an acceleration control signal is produced that is configured to cause a drive unit to apply an increased traction force to the selected wheel axle.

Thereafter, a step <NUM> checks if an absolute difference between the rotational speed of the selected wheel axle and the average rotational speed of the wheel axles except the selected wheel axle exceeds a threshold value. If so, a step <NUM> follows. Otherwise, the procedure loops back to steps <NUM> and <NUM>.

In step <NUM>, a respective fraction of the overall weight mtot carried by the selected wheel axle is estimated. Thereafter, the procedure loops back to step <NUM>. It should be noted that the fraction of the overall weight mtot carried by the first wheel axle may be determined as a remaining faction of the overall weight mtot when the respective fractions on all the other wheel axles have been determined.

Referring now to <FIG>, we will describe one embodiment of the method according to the invention, which is applicable to determine the fractions of the overall weight mtot that are carried by any non-driven axles of a rail vehicle.

In a first step <NUM>, it is checked if the rail vehicle has at least one non-driving wheel axle. If not, the procedure ends; and otherwise, a step <NUM> follows.

In step <NUM>, one of the non-driven wheel axles is selected for testing. Thereafter, in a step <NUM>, a wheel speed signals is obtained, which indicates a rotational speed ω<NUM> of the selected wheel axle.

In a step <NUM>, preferably executed essentially in parallel with step <NUM>, an average speed signal is obtained, which represents an average rotational speed ωa of the rotational speeds ω<NUM>, ω<NUM> and ω<NUM> of each wheel axle of the rail vehicle except the selected non-driven wheel axle.

In a step <NUM> subsequent to step <NUM>, a brake control signal is produced, which is configured to cause a brake unit to apply brake force to the selected non-driven wheel axle such that this brake unit applies a gradually increasing brake force to the non-driven wheel axle.

A step <NUM> subsequent to steps <NUM> and <NUM>, determines during production of the brake control signal, an absolute difference between the rotational speed of the selected non-driven wheel axle and the average rotational speed of the rail vehicle's wheel axles except the selected non-driven wheel axle. If the absolute difference exceeds a threshold value, the procedure continues to a step <NUM>, and otherwise the procedure loops back to steps <NUM> and <NUM>.

In step <NUM>, a parameter is determined that reflects a friction coefficient between a pair of wheels on the selected wheel axle and the pair of rails upon which the rail vehicle travels. Based on the parameter, in turn, a fraction of the rail vehicle's overall weight carried by the selected non-driven wheel axles is determined.

Thereafter, a step <NUM> checks if all non-driven wheel axles have been tested; and if so, the procedure ends. Otherwise, a step <NUM> follows in which a not yet tested wheel axles is selected for testing, and the procedure loops back to steps <NUM> and <NUM>.

All of the process steps, as well as any sub-sequence of steps, described with reference to <FIG> and <FIG> may be controlled by means of a programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video/Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal, which may be conveyed, directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components. The term does not preclude the presence or addition of one or more additional elements, features, integers, steps or components or groups thereof. The indefinite article "a" or "an" does not exclude a plurality. In the claims, the word "or" is not to be interpreted as an exclusive or (sometimes referred to as "XOR"). On the contrary, expressions such as "A or B" covers all the cases "A and not B", "B and not A" and "A and B", unless otherwise indicated.

Claim 1:
A controller (<NUM>) for estimating axle weights of a rail vehicle (<NUM>) comprising a number of wheel axles (<NUM>, <NUM>, <NUM>, <NUM>) and a set of drive units (<NUM>, <NUM>, <NUM>) configured to apply a respective traction force to each wheel axle in a driving subset of the wheel axles (<NUM>, <NUM>, <NUM>) so as to cause acceleration of the rail vehicle (<NUM>), which controller (<NUM>) is configured to obtain:
a power signal (Pm) indicating an amount of power produced by the set of drive units (<NUM>, <NUM>, <NUM>) to accelerate the rail vehicle (<NUM>) from a first speed (v<NUM>) to a second speed (v<NUM>),
a speed signal indicating respective values of the first and second speeds (v<NUM>, v<NUM>), and
based thereon estimate an overall weight (mtot) of the rail vehicle (<NUM>), characterized in that the controller (<NUM>) is further configured to estimate how the overall weight (mtot) is distributed over the number of wheel axles (<NUM>, <NUM>, <NUM>, <NUM>) by:
(a) obtaining wheel speed signals indicating respective rotational speeds (ω<NUM>, ω<NUM>, ω<NUM>) of the wheel axles in the driving subset of the wheel axles (<NUM>, <NUM>, <NUM>),
(b) producing an acceleration control signal (A1) to a specific drive unit (<NUM>) in the set of drive units such that this drive unit applies a gradually increasing traction force to a specific wheel axle (<NUM>) of the wheel axles in the driving subset of the wheel axles (<NUM>, <NUM>, <NUM>),
(c) determining, repeatedly during production of the acceleration control signal (A1), an absolute difference (| ω<NUM> - ωa |) between the rotational speed of the specific wheel axle (<NUM>) and an average rotational speed (ωa) of the wheel axles (<NUM>, <NUM>) in the driving subset of the wheel axles except the specific wheel axle;
and in response to the absolute difference (| ω<NUM> - ωa |) exceeding a threshold value
(d) determining a parameter (µm) reflecting a friction coefficient (µe) between a pair of wheels (121a, 121b) on the specific wheel axle (<NUM>) and a pair of rails (<NUM>, <NUM>) upon which the rail vehicle (<NUM>) travels,
repeating steps (a) to (c) for each of the wheel axles in the driving subset of the wheel axles, and based thereon estimate a respective fraction (m<NUM>, m<NUM>, m<NUM>) of the overall weight (mtot) carried by each of wheel axles in the driving subset of the wheel axles (<NUM>, <NUM>, <NUM>).