CONTROLLER FOR ESTIMATING AXLE WEIGHTS OF A RAIL VEHICLE, COMPUTER IMPLEMENTED METHOD THEREFOR, COMPUTER PROGRAM AND NON-VOLATILE DATA CARRIER

Abstract

An overall weight (m.sub.tot) of a rail vehicle (100) is estimated by obtaining a power signal (P.sub.m) indicating an amount of power produced by a set of drive units (101, 102, 103) to accelerate the rail vehicle (100) between first and second speeds (v.sub.1; v.sub.2). Then, the following steps are executed: (a) obtaining wheel speed signals indicating respective rotational speeds (.sub.1, .sub.2, .sub.3) of the wheel axles in the driving subset of the wheel axles (131, 132, 133); (b) producing an acceleration control signal (A1) to a specific drive unit (101) in the set of drive units such that this drive unit applies a gradually increasing traction force to a specific wheel axle (131) of the wheel axles in the driving subset of the wheel axles (131, 132, 133); (c) repeatedly determining, during production of the acceleration control signal (A1), an absolute difference (|.sub.1.sub.a|) between the rotational speed of the specific wheel axle (131) and an average rotational speed (.sub.a) of the wheel axles (132, 133) in the driving subset of the wheel axles except the specific wheel axle; and in response to the absolute difference (|.sub.1.sub.a|) exceeding a threshold value; (d) determining a parameter (.sub.m) reflecting a friction coefficient (.sub.e) between a pair of wheels (121a, 121b) on the specific wheel axle (131) and a pair of rails (191, 192) upon which the rail vehicle (100) 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 (m.sub.1, m.sub.2, m.sub.3) of the overall weight (m.sub.tot) carried by each of wheel axles in the driving subset of the wheel axles (131, 132, 133) is estimated.

Claims

1. A controller (140) for estimating axle weights of a rail vehicle (100) comprising a number of wheel axles (131, 132, 133, 134) and a set of drive units (101, 102, 103) configured to apply a respective traction force to each wheel axle in a driving subset of the wheel axles (131, 132, 133) so as to cause acceleration of the rail vehicle (100), which controller (140) is configured to obtain: a power signal (P.sub.m) indicating an amount of power produced by the set of drive units (101, 102, 103) to accelerate the rail vehicle (100) from a first speed (v.sub.1) to a second speed (v.sub.2), a speed signal indicating respective values of the first and second speeds (v.sub.1, v.sub.2), and based thereon estimate an overall weight (m.sub.tot) of the rail vehicle (100), wherein the controller (140) is further configured to estimate how the overall weight (m.sub.tot) is distributed over the number of wheel axles (131, 132, 133, 134) by: (a) obtaining wheel speed signals indicating respective rotational speeds (.sub.1, .sub.2, .sub.3) of the wheel axles in the driving subset of the wheel axles (131, 132, 133), (b) producing an acceleration control signal (A1) to a specific drive unit (101) in the set of drive units such that this drive unit applies a gradually increasing traction force to a specific wheel axle (131) of the wheel axles in the driving subset of the wheel axles (131, 132, 133), (c) determining, repeatedly during production of the acceleration control signal (A1), an absolute difference (|.sub.1.sub.a|) between the rotational speed of the specific wheel axle (131) and an average rotational speed (.sub.a) of the wheel axles (132, 133) in the driving subset of the wheel axles except the specific wheel axle; and in response to the absolute difference (|.sub.1.sub.a|) exceeding a threshold value (d) determining a parameter (.sub.m) reflecting a friction coefficient (.sub.e) between a pair of wheels (121a, 121b) on the specific wheel axle (131) and a pair of rails (191, 192) upon which the rail vehicle (100) 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.sub.1, m.sub.2, m.sub.3) of the overall weight (m.sub.tot) carried by each of wheel axles in the driving subset of the wheel axles (131, 132, 133).

2. The controller (140) according to claim 1, wherein for any non-driven wheel axle (134) of said number of wheel axles, which non-driven wheel axle (134) is not comprised in the driving subset of the wheel axles (131, 132, 133), the controller (140) is further configured to: (e) obtain wheel speed signals indicating respective rotational speeds (.sub.1, .sub.2, .sub.3, .sub.4) of each wheel axle of said number of wheel axles (131, 132, 133, 134), (f) produce a brake control signal (B4) to a brake unit (184) configured to apply a brake force to the non-driven wheel axle (134) such that this brake unit applies a gradually increasing brake force to the non-driven wheel axle (134), (g) determine, repeatedly during production of the brake control signal (B4), an absolute difference (|.sub.4.sub.a|) between the rotational speed of the non-driven wheel axle (134) and an average rotational speed (.sub.a) of said number of wheel axles except the non-driven wheel axle (134); and in response to the absolute difference exceeding a threshold value (h) determine a parameter (.sub.m) reflecting a friction coefficient (.sub.e) between a pair of wheels (124a, 124b) on the specific wheel axle (134) and the pair of rails (191, 192) upon which the rail vehicle (100) travels, repeat steps (e) to (g) for each of the non-driven wheel axles, and based thereon estimate a respective fraction (m.sub.4) of the overall weight (m.sub.tot) carried by each of the non-driven wheel axles.

3. The controller (140) according to claim 1, comprising a first interface (511) configured to receive a first vector signal (VS1) expressing an inclination angle () of the rail vehicle (100) relative to a horizontal plane (H), and the controller (140) is configured to adjust at least one of the power signal (P.sub.m) indicating the amount of power produced by the onboard motor and the speed signal indicating the second speed (v.sub.2) based on the inclination angle () when estimating the overall weight (m.sub.tot) of the rail vehicle (100).

4. The controller (140) according to claim 3, comprising a second interface (512) configured to receive a second vector signal (VS2) expressing a respective rotational movement of the wheels (121a, 121b; 122a, 122b; 123a, 123b) on each wheel axle in the driving subset of the wheel axles (131, 132, 133), which rotational movement is performed in a plane orthogonal to a respective rotation axis of the wheel axle, and the controller (140) is further configured to obtain the wheel speed signals indicating the respective rotational speeds (.sub.1, .sub.2, .sub.3) based on the first and second vector signals (VS1, VS2).

5. The controller (140) according to claim 1, wherein the controller (140) is configured to provide the respective fractions (m.sub.1, m.sub.2, m.sub.3) of the overall weight (m.sub.tot) to a traction controller (161, 162, 163) to enable the traction controller to produce a respective acceleration control signal (A1, A2, A3) to each drive unit in the set of drive units (101, 102, 103), which respective traction force signal (A1, A2, A3) is based on the respective fractions (m.sub.1, m.sub.2, m.sub.3) of the overall weight (m.sub.tot).

6. The controller (140) according to claim 5, wherein the controller (140) is co-located with the traction controller (161, 162, 163).

7. The controller (140) according to claim 1, wherein the controller (140) is configured to transmit the acceleration control signal (A1, A2, A3) via a data bus (150) in the rail vehicle (100).

8. A computer-implemented method for estimating axle weights of a rail vehicle (100) comprising a number of wheel axles (131, 132, 133, 134) and a set of drive units (101, 102, 103) configured to apply a respective traction force to each wheel axle in a driving subset of the wheel axles (131, 132, 133) so as to cause acceleration of the rail vehicle (100), the method comprising: obtaining a power signal (P.sub.m) indicating an amount of power produced by the set of drive units (101, 102, 103) to accelerate the rail vehicle (100) from a first speed (v.sub.1) to a second speed (v.sub.2), obtaining a speed signal indicating respective values of the first and second speeds (v.sub.1, v.sub.2), and based thereon estimating an overall weight (m.sub.tot) of the rail vehicle (100) by estimating how the overall weight (m.sub.tot) is distributed over the number of wheel axles (131, 132, 133, 134) by: (a) obtaining wheel speed signals indicating respective rotational speeds (.sub.1, .sub.2, .sub.3) of the wheel axles in the driving subset of the wheel axles (131, 132, 133), (b) producing an acceleration control signal (A1) to a specific drive unit (101) in the set of drive units such that this drive unit applies a gradually increasing traction force to a specific wheel axle (131) of the wheel axles in the driving subset of the wheel axles (131, 132, 133), (c) determining, repeatedly during production of the acceleration control signal (A1), an absolute difference (|.sub.1.sub.a|) between the rotational speed of the specific wheel axle (131) and an average rotational speed (.sub.a) of the wheel axles (132, 133) in the driving subset of the wheel axles except the specific wheel axle; and in response to the absolute difference (|.sub.1.sub.a|) exceeding a threshold value (d) determining a parameter (.sub.m) reflecting a friction coefficient (.sub.e) between a pair of wheels (121a, 121b) on the specific wheel axle (131) and a pair of rails (191, 192) upon which the rail vehicle (100) 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.sub.1, m.sub.2, m.sub.3) of the overall weight (m.sub.tot) carried by each of wheel axles in the driving subset of the wheel axles (131, 132, 133).

9. The method according to claim 8, wherein for any non-driven wheel axle (134) of said number of wheel axles, which non-driven wheel axle (134) is not comprised in the driving subset of the wheel axles (131, 132, 133), the method further comprises: (e) obtaining wheel speed signals indicating respective rotational speeds (.sub.1, .sub.2, .sub.3, .sub.4) of each wheel axle of said number of wheel axles (131, 132, 133, 134), (f) producing a brake control signal (B4) to a brake unit (184) configured to apply a brake force to the non-driven wheel axle (134) such that this brake unit applies a gradually increasing brake force to the non-driven wheel axle (134), (g) determining, repeatedly during production of the brake control signal (B4), an absolute difference (|.sub.4.sub.a|) between the rotational speed of the non-driven wheel axle (134) and an average rotational speed (.sub.a) of said number of wheel axles except the non-driven wheel axle (134); and in response to the absolute difference exceeding a threshold value (h) determining a parameter (.sub.m) reflecting a friction coefficient (.sub.e) between a pair of wheels (124a, 124b) on the specific wheel axle (134) and the pair of rails (191, 192) upon which the rail vehicle (100) travels, repeating steps (e) to (g) for each of the non-driven wheel axles, and based thereon estimate a respective fraction (m.sub.4) of the overall weight (m.sub.tot) carried by each of the non-driven wheel axles.

10. The method according to claim 8, comprising: receiving a first vector signal (VS1) expressing an inclination angle () of the rail vehicle (100) relative to a horizontal plane (H), and adjusting at least one of the power signal (P.sub.m) indicating the amount of power produced by the onboard motor and the speed signal indicating the second speed (v.sub.2) based on the inclination angle () when estimating the overall weight (m.sub.tot) of the rail vehicle (100).

11. The method according to claim 10, comprising: receiving a second vector signal (VS2) expressing a respective rotational movement of the wheels (121a, 121b; 122a, 122b; 123a, 123b) on each wheel axle in the driving subset of the wheel axles (131, 132, 133), which rotational movement is performed in a plane orthogonal to a respective rotation axis of the wheel axle, and obtaining the wheel speed signals indicating the respective rotational speeds (.sub.1, .sub.2, .sub.3) based on the first and second vector signals (VS1, VS2).

12. The method according to claim 8, comprising: providing the respective fractions (m.sub.1, m.sub.2, m.sub.3) of the overall weight (m.sub.tot) to a traction controller (161, 162, 163) to enable the traction controller to produce a respective acceleration control signal (A1, A2, A3) to each drive unit in the set of drive units (101, 102, 103), which respective traction force signal (A1, A2, A3) is based on the respective fractions (m.sub.1, m.sub.2, m.sub.3) of the overall weight (m.sub.tot).

13. The method according to claim 8, comprising: transmitting the acceleration control signal (A1, A2, A3) via a data bus (150) in the rail vehicle (100).

14. A computer program (525) loadable into a non-volatile data carrier (520) communicatively connected to at least one processor (530), the computer program (525) comprising software for executing the method according to claim 8 when the computer program (525) is run on the at least one processor (530).

15. A non-volatile data carrier (520) containing the computer program (425) of the claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

[0023] FIG. 1 schematically illustrates a rail vehicle equipped with a controller according to one embodiment of the invention;

[0024] FIG. 2 shows a drive unit according to one embodiment of the invention;

[0025] FIG. 3 shows a graph illustrating an example of the friction coefficient as a function of wheel slippage;

[0026] FIG. 4 schematically illustrates an accelerometer according to one embodiment of the invention;

[0027] FIG. 5 shows a block diagram of a controller according to one embodiment of the invention;

[0028] FIG. 6 illustrates, by means of a flow diagram, the general method according to the invention; and

[0029] FIG. 7 illustrates, by means of a flow diagram, one embodiment of the method according to the invention

DETAILED DESCRIPTION

[0030] In FIG. 1, we see a schematic illustration of a rail vehicle 100 equipped with a controller 140 according to one embodiment of the invention.

[0031] The controller 140 is arranged to estimate the different axle weights of the rail vehicle 100, which has a number of wheel axles.

[0032] FIG. 1 exemplifies four such wheel axles in the form of 131, 132, 133 and 134 respectively. In response to acceleration control signals A1, A3 and A3 from acceleration controllers 161, 162 and 163, a set of drive units 101, 102 and 103 is configured to apply a respective traction force to each wheel axle in a driving subset of the wheel axles 131, 132 and 133, such that the rail vehicle 100 accelerates. Analogously, in response to brake control signals B1, B2, B3 and B4 from brake controllers 171, 172, 173 and 174, a set of brake units 181, 182, 183 and 184 is configured to apply a respective brake force to each of the wheel axles 131, 132, 133 and 134 respectively, such that the rail vehicle 100 decelerates.

[0033] Each of the brake units 181, 182, 183 and 184 is associated with a respective rotatable member 111, 112, 113 and 114, such as a brake disc or a brake drum being mechanically linked to the respective wheel axle 131, 132, 133 and 134. 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.

[0034] In practice, a typical rail vehicle contains a substantially larger number of wheel axles than what is shown in FIG. 1. Traditionally, each bogie has two wheel axles carrying altogether four wheels, and each car body of the rail vehicle 100 includes a respective bogie in the front and rear ends.

[0035] The rail vehicle 100 contains a set of drive units 101, 102 and 103 respectively configured to apply a respective traction force to each of the wheel axles 131, 132 and 133 in the driving subset of the wheel axles. The rail vehicle 100 also contains a set of brake units 181, 182, 183 and 184 respectively configured to apply a respective brake force to each of the wheel axles 131, 132, 133 and 134. Consequently, by operating the brake units 181, 182, 183 and 184, the rail vehicle 100 may be caused to retard/decelerate.

[0036] Referring now to FIG. 5, the controller 140 is configured to obtain a power signal P.sub.m indicating an amount of power being produced by the set of drive units 101, 102 and 103 when accelerating the rail vehicle 100 from a first speed v.sub.1 to a second speed v.sub.2, for example from a standstill to 10 km/h. Of course, however, according to the invention, the power signal P.sub.m may equally well be received during acceleration of the rail vehicle 100 between any other two speed levels. In any case, the controller 140 is configured to obtain a speed signal indicating respective values of the first and second speeds v.sub.1 and v.sub.2.

[0037] Based on the power signal P.sub.m and the values of the first and second speeds v.sub.1 and v.sub.2, the controller 140 is configured to estimate an overall weight m.sub.tot of the rail vehicle 100.

[0038] 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.Math.t=W.sub.k, where P is the supplied power, t is the time during which the power has been supplied and W.sub.k is the resulting kinetic energy.

[0039] The resulting kinetic energy W.sub.k, in turn, may be expressed as:

[00001]$W_k=m_{\mathrm{tot}}.Math.v^2/2,\mathrm{where}v=v_2-v_1.$

[0040] In other words, the controller 140 may calculate the overall weight m.sub.tot of the rail vehicle 100 as:

[00002]$m_{\mathrm{tot}}=\frac{{\left(v_2-v_1\right)}^2}{2\mathrm{Pt}}$

[0041] Referring now also to FIG. 2, the controller 140 is further configured to: [0042] (a) obtain wheel speed signals indicating respective rotational speeds .sub.1, .sub.2 and .sub.3 of the wheel axles 131, 132 and 133 respectively in the driving subset of wheel axles, [0043] (b) produce an acceleration control signal A1 to a specific drive unit 101 in the set of drive units such that this drive unit 101 applies a gradually increasing traction force to a specific wheel axle in the set of driving wheel axles, here exemplified by 131, [0044] (c) determine, repeatedly during production of the acceleration control signal A1, an absolute difference |.sub.1.sub.a| between the rotational speed .sub.1 of the specific wheel axle 131 and an average rotational speed .sub.a of all the wheel axles in the driving subset of the wheel axles except the specific wheel axle, i.e. here 132 and 133, and in response to the absolute difference |.sub.1.sub.a| exceeding a threshold value [0045] (d) determine a parameter .sub.m reflecting a friction coefficient .sub.e between a pair of wheels 121a and 121b respectively on the specific wheel axle 131 and a pair of rails 191 and 192 upon which the rail vehicle 100 travels.

[0046] FIG. 3 shows a graph illustrating an example of how the kinetic friction coefficient .sub.k 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.

[0047] Characteristically, for lower values, the kinetic friction coefficient pk increases relatively proportionally with increasing wheel slippage s. When approaching a peak value .sub.e, however, the kinetic friction coefficient .sub.k levels out somewhat. After having passed the peak value, the kinetic friction coefficient .sub.k is essentially constant for all values of the wheel slippage s. Thus, the friction coefficient peak value .sub.e is associated with an optimal wheel slippage s.sub.e after which a further increase of wheel slippage s results in a gradually reduced, and then almost constant kinetic friction coefficient .sub.k.

[0048] According to the invention, a parameter .sub.m is determined that reflects the friction coefficient between the rail vehicle's 100 wheels and the rails 191 and 192 upon which the rail vehicle 100 travels. Ideally, the peak value .sub.e should be derived. For example, the peak value .sub.e may be derived as follows. When the absolute difference |.sub.1.sub.a| between the rotational speed of the specific wheel axle 131 and an average rotational speed .sub.a of all the rail vehicle's 100 wheel axles in the driving subset except the specific wheel axle 131 exceeds the threshold value, this corresponds to a situation where the wheels 121a and 121b on the specific wheel axle 131 experiences a wheel slippage s.sub.m near the optimal wheel slippage s.sub.e. The kinetic friction coefficient .sub.k is given by the ex-pression:

[00003]${}_k=\frac{F}{m_{\mathrm{tot}}.Math.g}$

where F is the drive force applied by the drive unit, [0049] m.sub.tot is the overall weight of the rail vehicle 100, and [0050] g is the standard acceleration due to gravity.

[0051] Under the assumption that the wheel slippage s.sub.m is near the optimal wheel slippage s.sub.e, the peak value .sub.e of the kinetic friction coefficient .sub.k may be estimated relatively accurately; and the proximity of wheel slippage s.sub.m to the optimal wheel slippage s.sub.e is ensured by said threshold value for the absolute difference |.sub.1.sub.a| between the rotational speed of the specific wheel axle 131 and the average rotational speed .sub.a of all the rail vehicle's 100 wheel axles except the specific wheel axle 131.

[0052] Finally, the controller 140 is configured to repeat the above steps (a) to (c) for each wheel axle 131, 132 and 133 in the driving subset, and based thereon estimate a respective fraction m.sub.1, m.sub.2 and m.sub.3 of the overall weight m.sub.tot carried by each of these wheel axles.

[0053] It is worth mentioning that the above-mentioned specific wheel axle 131 does not need to be any particular wheel axle, e.g. a frontmost or a rearmost wheel axle of the rail vehicle 100. On the contrary, the above procedure may start with an arbitrary selected wheel axle in the driving subset.

[0054] 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 m.sub.tot and/or a redistribution of the overall weight m.sub.tot over the wheel axles.

[0055] As exemplified by the wheel axle 134 in FIG. 1, one or more of the rail vehicle's 100 wheel axles may be non-driven, i.e. not be comprised in the driving subset of the wheel axles 131, 132 and 133. 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 140 is further configured execute the below procedure.

[0056] (e) Obtain wheel speed signals indicating respective rotational speeds .sub.1, .sub.2, .sub.3 and .sub.4 of each rail vehicle's 100 wheel axles 131, 132, 133 and 134 respectively;

[0057] (f) produce a brake control signal B4 to a brake unit 184 configured to apply a brake force to the non-driven wheel axle 134 such that this brake unit applies a gradually increasing brake force to the non-driven wheel axle 134;

[0058] (g) determine, repeatedly during production of the brake control signal B4, an absolute difference |.sub.4.sub.a| between the rotational speed .sub.4 of the non-driven wheel axle 134 and an average rotational speed .sub.a of all the wheel axles 131, 132 and 133 except the non-driven wheel axle 134; and in response to the absolute difference exceeding a threshold value, preferably however not necessarily the same threshold value as referred to above in relation to FIG. 3

[0059] (h) determine a parameter .sub.m reflecting a friction coefficient pe between a pair of wheels 124a and 124b on the specific wheel axle 134 and a pair of rails 191 and 192 upon which the rail vehicle 100 travels,

[0060] In the general case where the rail vehicle has more than one non-driven axle, the controller 140 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.sub.4 of the overall weight m.sub.tot carried by each of the non-driven wheel axles.

[0061] The controller 140 may be configured to generate a control message ctrl.sub.A to make the acceleration controllers 161, 162 and 162 produce acceleration control signals A1, A2 and A3 to the drive units 101, 102 and 103 respectively, such that an average drive force applied to the wheel axles 132, and 133 except the specific wheel axles 131 is gradually decreased when the drive force applied to the specific wheel axle 131 is gradually increased. In other words, the driving on the other wheel axles 132 and 133 compensate for the somewhat excessive drive force applied to the specific wheel axle 131.

[0062] Preferably, this compensation is temporally matched. This means that the controller 140 is configured to generate the control message ctrl.sub.A to cause the acceleration controllers 161, 162 and 162 to produce acceleration control signals A1, A2 and A3 to the drive units 101, 102 and 103 such that, at each point in time, the gradual decrease of the average drive force applied to the wheel axles 132 and 133 except the specific wheel axles 131 corresponds to the gradual increase of the drive force applied to the specific wheel axle 131. Namely, thereby the deviating drive force applied to specific wheel axle 131 is masked by the opposite deviation represented by the drive force applied to the wheel axles 132 and 133 in the driving subset.

[0063] Referring again to FIG. 2, we see a drive unit 101 according to one embodiment of the invention. The drive unit 101 is configured to receive the acceleration control signal A1 from the acceleration controller 161, which, in turn, operates in response to the control message ctrl.sub.A from the controller 140. The acceleration control signal A1 may for example be transmitted via a data bus 150. In response to the acceleration control signal A1, the drive unit 101 is configured to drive the wheel axle 131. The drive unit 101 may contain at least one electric motor whose generated traction force depends on a magnitude of an electric current fed to it.

[0064] Further, for the overall efficiency, the data bus 150 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 101, 102 and 103 and each of the brake units 181, 182, 183 and 184.

[0065] Referring now to FIGS. 4 and 5, according to one embodiment of the invention, the controller 140 contains at least one interface 511 and 512 configured to receive first and second vector signals VS1 and VS2 respectively. The first vector signal VS1 expresses an acceleration a.sub.X, a.sub.Y, a.sub.Z, a.sub.R, a.sub.P, and/or a.sub.W of the rail vehicle 100 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.

[0066] The controller 140 is configured to obtain the wheel speed signals indicating the respective rotational speeds .sub.1, .sub.2, .sub.3 and .sub.4 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 .sub.a is trivial once each of the individual rotational speeds .sub.1, .sub.2, .sub.3 and .sub.4 is known.

[0067] FIG. 4 schematically illustrates a first accelerometer 425 according to one embodiment of the invention. The first accelerometer 425 is arranged in a frame element 110 of the rail vehicle 100. The first accelerometer 425 is configured to produce the first vector signal VS1 representing an acceleration of the a rail vehicle 100 in at least one dimension, typically in each of the three spatial directions a.sub.X, a.sub.Y and a.sub.Z and respective rotations a.sub.R, a.sub.P and a.sub.W around axes along each of these directions.

[0068] Preferably, according to one embodiment of the invention, the first vector signal VS1 further expresses an inclination angle of the rail vehicle 100 relative to a horizontal plane H. Here, the controller 140 is configured to adjust the power signal P.sub.m indicating the amount of power produced by the onboard motor and/or the speed signal indicating the second speed v.sub.2 based on the inclination angle when estimating the overall weight m.sub.tot of the rail vehicle 100. Consequently, the estimate of the overall weight m.sub.tot may be adequately adjusted if the rail vehicle 100 travels on non-horizontal ground when obtaining the power signal P.sub.m 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.

[0069] Naturally, for the same reasons, it is also preferable to compensate for the inclination angle when repeatedly executing the above steps (a) to (c) to estimate the respective fraction m.sub.1, m.sub.2 and m.sub.3 of the overall weight m.sub.tot carried by each of the wheel axles 131, 132 and 133 in the driving subset of the rail vehicle's 100 wheel axles.

[0070] FIG. 2 illustrates a second accelerometer 235 that is eccentrically arranged relative to a rotation axis of at least one wheel, say 121. The second accelerometer 235 is configured to produce the second vector signal VS2 expressing movements of the second accelerometer 235 in a plane orthogonal to the rotation axis of the at least one wheel 121, and transmit a signal containing the second vector signal VS2 to the controller 140.

[0071] FIG. 5 shows a block diagram of the controller 140 according to one embodiment of the invention. The controller 140 includes processing circuitry in the form of at least one processor 530 and a memory unit 520, i.e. non-volatile data carrier, storing a computer program 525, which, in turn, contains software for making the at least one processor 530 execute the actions mentioned in this disclosure when the computer program 525 is run on the at least one processor 530.

[0072] The controller 140 contains input interfaces configured to receive the first and second vector signals VS1 and VS2 respectively, the power signal P.sub.m and the speed signal expressing the speeds v.sub.1 and v.sub.2 respectively. Further, the controller 140 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.sub.1, m.sub.2, m.sub.3 and m.sub.4 of the overall weight m.sub.tot. As mentioned above, one or more of the input and/or output signals may be communicated via the data bus 150.

[0073] According to one embodiment of the invention, the controller 140 is configured to provide the respective fractions m.sub.1, m.sub.2 and m.sub.3 of the overall weight m.sub.tot to each of the acceleration controllers 161, 162, and 163 to enable the acceleration controllers to cause its associated drive unit 101, 102 and 103 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.sub.1, m.sub.2 or m.sub.3 of the overall weight m.sub.tot applicable to the wheel axle in question 131, 132 or 133 respectively.

[0074] According to one embodiment of the invention, the controller 140 is co-located with the acceleration controller. Thus, for example, the controller 140 may be integrated into the acceleration controller 161, or vice versa. Alternatively, the functionality of the controller 140 may be distributed over two or more of the acceleration controllers 161, 162 and/or 163.

[0075] In order to sum up, and with reference to the flow diagram in FIG. 6, we will now describe the computer-implemented method for a rail vehicle that is carried out by the controller 140.

[0076] In a first step 605, signals are obtained that express first and second speeds v.sub.1 and v.sub.2 and an amount of power produced by the drive units of the rail vehicle 100 to accelerate it from the first speed v.sub.1 to the second speed v.sub.2.

[0077] In a step 610 thereafter, a speed signal is obtained, which indicates a rotational speed .sub.1 of a specific one the rail vehicle's 100 wheel axles, say 131.

[0078] In a step 615, preferably essentially parallel to step 610, an average value is obtained, which represents an average rotational speed .sub.a of the rotational speeds .sub.2 and .sub.3 of the wheel axles 132 and 133 respectively in the driving subset of the wheel axles except the specific wheel axle 131

[0079] In a step 620 subsequent to step 610 and preferably essentially parallel to step 615, 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 131.

[0080] Thereafter, a step 625 checks if an absolute difference |.sub.1.sub.a| between the rotational speed .sub.1 of the specific wheel axle 131 and the average rotational speed .sub.a of the wheel axles in the driving subset except the specific wheel axle 131 exceeds a threshold value. If so, a step 630 follows. Otherwise, the procedure loops back to steps 610 and 615.

[0081] In step 630, a parameter .sub.m is determined that reflects a friction coefficient .sub.e between the wheels 121a and 121b on the specific wheel axle 131 and the rails 191 and 192 upon which the rail vehicle 100 travels.

[0082] Subsequently, a step 635 checks if all the wheel axles 131, 132, and 133 in the driving subset of the rail vehicle 100 have been tested. If so, the procedure ends. If not, the procedure continues to a step 640 in which a not yet tested driving wheel axle is selected.

[0083] Then, in a step 645, a speed signal is obtained, which indicates a rotational speed of the selected wheel axle.

[0084] In a step 650, preferably essentially parallel to step 645, an average value is obtained, which represents an average of the rotational speeds of the rail vehicle's 100 wheel axles except the selected wheel axle.

[0085] In a step 655 subsequent to step 645 and preferably essentially parallel to step 650, 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.

[0086] Thereafter, a step 660 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 665 follows. Otherwise, the procedure loops back to steps 645 and 650.

[0087] In step 665, a respective fraction of the overall weight m.sub.tot carried by the selected wheel axle is estimated. Thereafter, the procedure loops back to step 635. It should be noted that the fraction of the overall weight m.sub.tot carried by the first wheel axle may be determined as a remaining faction of the overall weight m.sub.tot when the respective fractions on all the other wheel axles have been determined.

[0088] Referring now to FIG. 7, we will describe one embodiment of the method according to the invention, which is applicable to determine the fractions of the overall weight m.sub.tot that are carried by any non-driven axles of a rail vehicle.

[0089] In a first step 705, it is checked if the rail vehicle has at least one non-driving wheel axle. If not, the procedure ends; and otherwise, a step 710 follows.

[0090] In step 710, one of the non-driven wheel axles is selected for testing. Thereafter, in a step 715, a wheel speed signals is obtained, which indicates a rotational speed .sub.4 of the selected wheel axle.

[0091] In a step 720, preferably executed essentially in parallel with step 715, an average speed signal is obtained, which represents an average rotational speed .sub.a of the rotational speeds .sub.1, .sub.2 and .sub.3 of each wheel axle of the rail vehicle except the selected non-driven wheel axle.

[0092] In a step 725 subsequent to step 715, 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.

[0093] A step 730 subsequent to steps 720 and 725, 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 735, and otherwise the procedure loops back to steps 715 and 720.

[0094] In step 735, 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.

[0095] Thereafter, a step 740 checks if all non-driven wheel axles have been tested; and if so, the procedure ends. Otherwise, a step 745 follows in which a not yet tested wheel axles is selected for testing, and the procedure loops back to steps 715 and 720.

[0096] All of the process steps, as well as any sub-sequence of steps, described with reference to FIGS. 6 and 7 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 semi-conductor 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.

[0097] 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. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0098] It is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

[0099] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0100] The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.