MACHINE AND METHOD FOR COMPACTING A BALLAST BED OF A TRACK

Abstract

The invention relates to a machine for compacting a ballast bed of a track with a machine frame supported on rail-based running gears and a height-adjustable stabilising unit connected thereto, comprising a vibration drive and an axle with wheel flange rollers movable on rails of the track, whose distance to each other extending perpendicularly to the longitudinal direction of the machine can be varied by means of a spreading drive, as well as a roller clamp that can be pressed against the rails by means of clamping drives. The spreading drive and/or the clamping drives are set up to apply a predefined variable horizontal load force to the rails, whereby a measuring device is arranged to detect a rail head deflection and/or track gauge change caused by the variable load force. In this way, it can be determined by means of the stabilising unit whether the track panel is intrinsically stable.

Description

FIELD OF TECHNOLOGY

The invention relates to a machine for compacting a ballast bed of a track with a machine frame supported on rail-based running gears and a height-adjustable stabilising unit connected thereto, comprising a vibration drive and an axle with wheel flange rollers movable on rails of the track, whose distance to each other extending perpendicularly to the longitudinal direction of the machine can be varied by means of a spreading drive, as well as a roller clamp that can be pressed against the rails by means of clamping drives. The invention further relates to a method for operating the machine.

PRIOR ART

In order to produce or restore a predefined track geometry, tracks with ballast beds are worked on by means of a tamping machine. Specifically, the position of the track panel bedded in the ballast bed, which consists of sleepers and rails fastened to them by means of rail fastenings, is corrected. During this correction process, the tamping machine travels along the track and lifts the track panel to an overcorrected target position by means of a lifting and lining unit. The new track position is fixed by means of a tamping unit tamping the track. Sufficient and, above all, uniform load-bearing capacity of the ballast bed is an essential prerequisite for the stability of the track position in railway operation.

Usually a machine is therefore used to stabilise the track after a tamping process. The track is loaded with a static load and set in vibration locally with a so-called Dynamic Track Stabiliser (DGS). The vibration causes the grains in the granular structure to become mobile, allowing them to be shifted and rearrange themselves with higher compactness. The resulting ballast compaction increases the load-bearing capacity of the track and replicates track settlements caused during operation. The increase in lateral track resistance also implies compaction.

EP 0 616 077 A1 discloses a corresponding machine with a stabilising unit arranged between two rail-based running gears. The stabilising unit comprises wheel flange rollers which are movable on a track and transmit vibrations generated by means of a vibration drive to the track. During a stabilising process, the wheel flange rollers arranged on a shared axle are pressed against the inner sides of the rail head by means of a spreading drive in order to avoid track gauge play.

Presentation of the Invention

The object of the invention is to improve a machine of the kind mentioned above in such a way that weak spots of the track are detected during a stabilising process. A further object of the invention is to indicate a corresponding method.

According to the invention, these objects are achieved by the features of claims 1 and 8. Dependent claims indicate advantageous embodiments of the invention.

The spreading drive and/or the clamping drives are set up to apply a predefined variable horizontal load force to the rails, whereby a measuring device is arranged to detect a rail head deflection and/or track gauge change caused by the variable load force. When activating this device, a mechanical spreading force with a predefined progression is applied to the rails crosswise to the longitudinal direction of the machine and the resulting change to the rail head deflection and/or track gauge is measured. In this way, it can be determined by means of the stabilising unit whether the track panel is intrinsically stable. No separate track possessions are necessary for this inspection because the measurements are carried out in the course of the maintenance measures by means of the stabilising unit.

With the arrangement according to the invention, the respective rail is clamped at the rail head between the wheel flange rollers and the roller clamp. The clamping force acting on the rails through the roller clamp is harmonised with the spreading force. Spreading force and clamping force add up to the varied load force that acts on the respective rail in addition to the dynamic impact force of the vibration drive. Specifically, changes to this load force are achieved by varying the spreading force and/or the clamping force. The track gauge change caused by a change to the load force subsequently provides information about the condition of the respective rail fastening.

Compared to an intact track panel, a damaged or insufficiently fixed rail fastening causes a greater track gauge change when the horizontal load force changes. The detected track gauge change can thus serve as a parameter for the condition of the rail fastenings. Loose rail fastenings occur, for example, due to overloading or destruction as a result of incorrect maintenance. Wooden sleepers age due to bacterial infestation and weather-related influences, which can cause rail fastenings to loosen. A visual inspection is usually insufficient here.

In addition, track sections with defective rail fastenings are often not detectable with conventional track inspection vehicles because safety-relevant limits have not yet been exceeded. The present invention provides that the dynamic impact forces of the stabilising unit cause previously damaged rail fastenings to be detected as such. In particular, existing material cracks in rail fastening components are made more extreme, enabling immediate detection. This synergy effect results directly from the use of the stabilising unit according to the invention for inspecting the stability of the track panel. Known systems (Gauge Restraint Measuring System, GRMS) only measure a changed track gauge as a result of a spreading axle guided along the track with static transverse forces. There is no dynamic component that causes previously damaged rail fastenings to be detected.

In an advantageous embodiment of the invention, control signals, which cause a periodically changed load force, are stored in a control equipment for actuating the spreading drive and the clamping drives. The periodic change to the load force takes place at a frequency that is significantly lower than a vibration frequency of the vibration drive. The stabilising unit is normally operated at a vibration frequency between 30 Hz and 35 Hz. By contrast, the period of the variable load force is approx. 1 second, so that the frequency of 1 Hz is clearly below the vibration frequency. In this way, a disturbing influence of the vibration on the rail head deflection caused by the load force is avoided. The measured deflection values or track gauge changes can be clearly assigned to the periodic, low-frequency progression of the load force.

Advantageously, the measuring device is coupled to the axle of the wheel flange rollers. The track gauge is thus measured directly in the force axis of the spreading force acting on the rails, whereby the direct correlation between spreading force and track gauge is identified.

In a further embodiment of the invention, the measuring device is coupled to an evaluation device, with the evaluation device being set up to assess a rail fastening on the basis of the detected rail head deflection and/or track gauge change. The evaluation device enables an automated evaluation of the condition of the respective rail fastening.

In this context, it is advantageous if the evaluation device is set up to evaluate rail head deflections and/or track gauge values detected at a measuring point as a function of a progression of changed load values in order to assess a condition of rail fastenings positioned in the area of the measuring point. In this way, pairs of values of a load-displacement curve are recorded and compared in order to derive a state variable of the respective rail fastening.

A further improvement provides that a position determination unit is arranged for a location-specific detection of the rail head deflections and/or the track gauge change. The location reference achieved in this way facilitates a comparison between the measuring results and the positions of the respective rail fastenings of the track in use. The location-specific detection is also advantageous for documentation purposes.

In a further development of the machine, two stabilising units are arranged one behind the other, each stabilising unit comprising a measuring device for detecting rail head deflections and/or the track gauge change caused by the respective horizontal load force. This arrangement enables measurements with different load forces on the same spot during the machine's continuous forward travel. First, the front stabilising unit measures with a first load force. As soon as the rear stabilising unit reaches the same measuring point, a second measurement with a second load force takes place.

In the method according to the invention, the stabilising unit with the wheel flange rollers is first lowered onto the rails of the track. In the next step, the rails are subjected to a predefined variable horizontal load force by means of the spreading drive and/or the clamping drives, with a rail head deflection and/or track gauge change caused by the load force being detected by means of the measuring device in order to indicate a condition of a rail fastening. This additional use of the stabilising unit requires little effort. A compaction process that is to be carried out in any case is linked to the condition inspection of the rail fastenings.

In an advantageous embodiment of the method, the horizontal load force is periodically changed by means of a control equipment with a frequency that is lower than a vibration frequency of the vibration drive. Herein, a periodic control signal of the spreading drive and/or the clamping drives is modulated with a low frequency (e.g. 1 Hz), as it were, onto the vibration progression of the vibration drive. The periodically changed load force results from the spreading force of the wheel flange rollers and the clamping force of the roller clamp placed against the rails from the outside. This varied load force superimposes the impact force acting on the rails, which is caused by the vibration drive. This is particularly useful when operating a single stabilising unit.

In a further method variant, the rails are subjected to a first horizontal load force by means of the stabilising unit, with the rails being additionally subjected to a second horizontal load force by means of a further stabilising unit. In this method, both stabilising units are used to measure the track gauge as a function of the respective load force. By specifying different horizontal load forces, it is possible to detect the track gauge change, which provides information on the condition of the rail fastenings.

In a further development of the method, the machine is moved continuously along the track. When passing, different spreading forces are applied to the rails in the area of the respective rail fastenings, and the effects on the track gauge are measured.

For an automated evaluation, it is useful if the track gauge change is detected and evaluated as a function of the varied load force by means of an evaluation device. For example, an algorithm is set up in the evaluation device which compares track gauge changes to predefined limiting values.

In a further development of this method, rail head deflection values and/or track gauge values detected at a measuring point by means of the evaluation device are jointly evaluated as a function of different load force values. Here, pairs of values of a load-displacement curve are set in relation to each other in order to indicate the condition of the respective rail fastening.

A further improvement provides that a position determination unit is used to determine the position of the measuring device for a location-specific detection of the rail head deflections and/or the track gauge changes. The resulting location specificity achieved in this way enables an easy assignment to the respective rail fastening afterwards.

It is useful if evaluation data of a respective rail fastening is stored with reference to its location in order to assess its condition. The saved data is subsequently used to document the track inspection that has been carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is explained by way of example with reference to the accompanying figures. The following figures show in schematic illustrations:

FIG. 1 Machine with two stabilising units on the track in side view

FIG. 2 Stabilising unit and track in cross section

FIG. 3 Progression of the impact force and the load force over time

FIG. 4 Rail profile

FIG. 5 Diagrams for FIG. 4

FIG. 6 Detailed view from FIG. 2

FIG. 7 Force progressions over time

FIG. 8 Load-displacement curve

FIG. 9 Stabilising units in top view

DESCRIPTION OF THE EMBODIMENTS

The machine 1 shown in FIG. 1 is a so-called Dynamic Track Stabiliser (DGS) having a machine frame 2 that is moveable on rail-based running gears 3 on a track 4. The track 4 comprises a track panel 5 consisting of rails 6, rail fastenings 7, and sleepers 8 that is bedded in a ballast bed 9. The machine 1 is usually used after a tamping process to replicate settlements of the track panel 5. The invention also relates to a combined tamping and stabilising machine not shown or to another track maintenance machine equipped with a stabilising unit 10.

Two stabilising units 10 are attached one behind the other in the longitudinal direction of the machine 11 to the machine frame 2 of the machine 1 shown. Furthermore, the machine 1 comprises a traction drive 12 and a measuring system 13 for detecting a track position as well as a cab 14 for operating staff. From a non-operating position, the respective stabilising unit 10 can be lowered onto the rails 6 by means of height-adjustment drives 15.

Each stabilising unit 10 has a vibration drive 16. Vibration is usually generated by means of rotating unbalanced masses. In addition, each stabilising unit 10 comprises an axle 17 aligned crosswise to the longitudinal direction of the machine 11 with wheel flange rollers 18. In the operating position, the stabilising unit 10 is movable on the rails 6 by means of these wheel flange rollers 18. A spreading drive 19 is arranged in the axle 17, by means of which the distance between the wheel flange rollers 18 can be changed. FIG. 2 shows the axle 17 with a left and a right wheel flange roller 18 and the spreading drive 19.

According to the invention, the spreading drive 19 is set up to apply a predefined spreading force F_S to the rails 6. Accordingly, the spreading drive 19 is not only intended to press the wheel flange rollers 18 against the inside of the respective rail head without play. In fact, the spreading force F_S is predefined with a specific value, which is subsequently set in relation to a measured track gauge s or track gauge difference Δs. The spreading force F_S is applied to the respective rail 6 from the inside.

The track gauge s or the track gauge difference Δs is measured by means of a measuring device 20. This comprises, for example, an electromechanical distance sensor coupled to the axle 17. In this case, a first component of the sensor is connected to a shaft portion, which is displaceably mounted in the direction of the axle and is connected to the left wheel flange roller 18. A second component of the sensor is connected to a displaceably mounted shaft portion of the right wheel flange roller 18. If the shaft portions are moved against each other by means of the spreading drive 19, the components of the sensor also shift towards each other, whereby a shifting path is measured. This shifting path corresponds to the track gauge difference Δs when the wheel flange rollers 18 are in contact with the rail heads.

The stabilising unit 10 shown in FIG. 2 comprises a roller clamp 21 with clamping rollers 22 that can be pressed against the respective rail head from the outside. The left clamping roller 22 is in clamping position. The right clamping roller 22 is shown in a free position. This position is also used during operation of the stabilising unit 10 to avoid obstacles (e.g. fish-plate rail joint).

In the clamping position, the clamping drives 23 exert a predefined clamping force F_K on the rails 6 via the clamping rollers 22, which counteracts the spreading force F_S. In this case, the clamping drives 23 and the spreading drive 19 are harmonised with each other by means of a control equipment 24 in such a way that a desired horizontal load force F_B acts on each rail 6.

In an advantageous embodiment of the invention, the load force F_B is periodically changed by means of the control equipment 24, as shown in FIG. 3. For example, the change to the load force F_B follows a circular function. The progression of the track gauge change following the load progression is evaluated. Herein, a periodic control signal of the spreading drive 19 and/or the clamping drives 23 is modulated with a low frequency (e.g. 1 Hz), as it were, onto the vibration progression of the vibration drive. At a forward speed of the stabilising unit 10 of approx. 2 to 2.5 km/h and usual sleeper spacing, a desired change to the load force F_B occurs at each rail fastening 7.

The frequency of the changed load force F_B is significantly lower than the vibration frequency, which is normally within the range of 30 Hz to 35 Hz. Mass inertias are negligible at this frequency value. A load force F_B acting alternately outwards and inwards also represents a useful variant. The rail fastenings 7 on the outside and inside of the rail are equally stressed.

FIG. 4 shows the forces and moments acting on the rail 6. A cross section of the rail 6 (rail profile) is shown, the rail foot of which is supported on an intermediate layer 25. A transverse force Y and a vertical force Q are exerted on the rail head by means of the stabilising unit 10. A load application height h is predefined due to the dimensions of the rail profile and is measured from the lower edge of the rail foot to the gauge face (14 mm below the top of rail). The transverse force Y leads to a bending moment in the rail (with respect to the rail foot plane), which forms a torsional moment in the longitudinal direction.

The torsional moment must be absorbed via several rail support points. In the rail support points, a reactive moment is developed on the rail foot due to the torsion of the rail 6. The rail head deflects to such an extent until an applied moment M_t and a reactive moment M_r are of equal size. The applied moment M_t depends on the transverse force Y:

$m_t=Y·h$

The reactive moment M_r (return moment) results from the vertical force Q and from hold-down forces F_Skl of the rail fastenings 7, with a distance b resulting in the rail foot plane between the rail foot centre and a centre of gravity of a pressure distribution:

$M_r=\left(Q+2·F_{\mathrm{Ski}}\right)·b$

The forces or moments cause a rail head deflection Δs_L/R and a rail foot edge depression a. At the rail foot edge, an edge compressive stress σ_R occurs in the intermediate layer 25. FIG. 5 shows the relationship between these variables for different hold-down forces F_Skl1, F_Skl2, F_Skl3. In the diagram at the bottom right it can be seen in particular that, in the case of a constant applied moment M_t¹, the rail head deflection Δs_L/R1, Δs_L/R2, Δs_L/R3 increases with decreasing hold-down force F_Skl3, F_Skl2, F_Skl1. With an unchanged rail profile, the constant applied moment M_t¹ is due to a constant transverse force Y. The diagram thus shows the relationship between the transverse force Y, the rail head deflection Δs_L/R and/or track gauge change and the hold-down force F_Skl, the latter representing the condition of the rail fastening 7.

The forces acting on the stabilising unit 10 and on the rails 6 are explained in detail with reference to FIG. 6 and FIG. 7. During track stabilisation, the load force F_B and the impact force F_V of the vibration drive 16 superimpose on each other. The resulting horizontal transverse force Y_L, Y_R acts on the respective rail 6. The predefined forces F_K, F_S and the detected rail head deflection Δs_L and/or track gauge difference are fed to an evaluation device 26. An algorithm for evaluating the condition of the respective rail fastening 7 is set up in the evaluation device 26. The evaluation device 26 comprises, for example, a radio module 27 for transmitting the results.

Favourably, the evaluation device 26 is also fed with the current load application height h of the horizontal transverse force Y_L, Y_R (FIG. 4). To determine the load application height h, it is useful if the machine 1 comprises sensors for automatically detecting the rail profile of the track 4 in use. Alternatively, the load application height h is inputted via an input device.

It is also useful to automatically detect the sleeper positions (support points of the rails 6) in order to determine the sleeper spacing. The frequency of the progression of the horizontal load force F_B (FIG. 3) is thereby adapted to the determined sleeper spacing and to a forward speed of the stabilising unit 10. The adjustment is achieved in such a way that the same load force F_B acts on each rail fastening 7.

The vertical force Q acting on the respective rail 6 is advantageously predefined with a periodic progression. In this case, the height-adjustment drives 15 are actuated with a periodic control signal in order to support the stabilising unit 10 with variable force against the machine frame 2. The frequency of the progression of the horizontal load force F_B is adapted to the progression of the vertical force Q. In this way, different pre-stress levels when pressing the intermediate layers 25 together are taken into account. The tilting spring effect of the respective rail fastening 7 (spring rate of the intermediate layer 25) can then be monitored.

In the measurement shown in FIG. 6, the spreading force F_S applied to the respective rail 6 is greater than the clamping force F_K acting from the outside. Accordingly, the resulting load force F_B is directed outwards. This causes an increase in the track gauge s. Here, the track gauge change exceeds a permissible level because the rail fastening 7 located at the measuring point is defective. In the specific example, the right threaded connection of the bracket resting against the rail foot is not tightened. This causes the rail 6 to twist to the outside in the loaded area.

FIG. 7 shows exemplary progressions of the individual forces F over time t. For illustration purposes, different and constant load forces F_B0, F_B1, F_B2 are assumed in three temporal phases I, II, III. While the impact force F_V acts synchronously on both rails 6, the load force F_B pushes the rails apart or towards each other. The impact force F_V results in a vibration of the loaded track panel section in the transverse direction of the track. The load force F_B acts within the track panel 5. This results in rail head deflections Δs_L/R and/or track gauge changes, the extent of which depends on the elasticity behaviour of the rails 6 and the condition of the rail fastenings 7.

In a first phase I, the load force F_B equals zero. Spreading force F_S and clamping force F_K are equal so that the respective rail 6 is only clamped without transverse force acting on it. The progression of the impact force F_V is shown with a thin solid line. In the first phase I, the effect of the impact force F_V is distributed uniformly on both rails 6. Thus, half the impact force F_V acts on each rail 6 as the resulting transverse force Y_L, Y_R.

In a second phase II, a modified spreading force F_S is predefined, which results in a first load force F_B1L, F_B1R acting on the respective rail 6. Equivalent to predefining a modified spreading force F_S, a modified clamping force F_K can also be predefined. Predefining the resulting first load force F_B1L, F_B1R can also be useful in an equivalent way. For example, the spreading force F_S and/or the clamping force F_K are modified in a control loop until the predefined first load force F_B1L, F_B1R is reached.

In FIG. 7, the respective first load force F_B1L, F_B1R acts outwards because the first spreading force F_S1 is greater than the clamping force F_K. Specifically, a left first load force F_B1L is directed against a right first load force F_B1R. In the diagram, forces directed to the left are shown as positive and forces directed to the right are shown as negative. Furthermore, the forces F_B1L, Y_1L, acting on the left rail 6 are shown with dash-dotted lines, and the forces F_B1R, Y_1R acting on the right rail 6 are shown with dashed lines.

In a third phase III, the control equipment 24 predefines a second spreading force F_S2 that is higher than the first spreading force F_S1. The respective clamping force F_K remains unchanged so that the second load force F_B2L. F_B2R acting on the respective rail 6 is also directed outwards. The changed load force F_B2L, F_B2R can also be predefined by changing the assigned clamping force F_K. With the load forces F_B1L, F_B1R, F_B2L, F_B2R of different sizes, the track gauge change s can be detected due to two different load conditions.

The transverse force Y_1L, Y_2L acting on the left rail 6 is the sum of forces of half the impact force F_V and the left load force F_B1L, F_B2L. The sum of forces of half the impact force F_V and the counteracting right load force F_B1R, F_B2R acts on the right rail 6 as transverse force Y_1R, Y_2R. To the outside, the two transverse forces Y_1L, Y_1R or Y_2L, Y_2R in turn add up to the total impact force F_V, with the load forces F_B1L, F_B1R or F_B2L, F_B2R cancelling each other out in the track panel and resulting in the track gauge change s.

FIG. 8 shows by way of example the dependence of the track gauge s on the spreading force F_S or on the resulting load force F_B. According to FIG. 7, the measured track gauge so remains unchanged in the first phase I because the spreading force F_S and the clamping force F_K cancel each other out. In the second phase II, a first increased spreading force F_S1 is predefined, resulting in the first load force F_B1L, F_B1R acting on the respective rail 6. The resulting new track gauge s₁ or a first track gauge difference Δs₁ is measured by means of the measuring device 20. In the third phase III, an increasingly increased second spreading force F_S2 is predefined. Due to the resulting increased load forces F_B2L, F_B2R, the track gauge s increases to a higher value s₂ and a second track gauge difference Δs₂ results.

It is possible to draw conclusions about the quality of the rail fastenings 7 located at the measuring point already from the first track gauge difference Δs₁. In particular, the difference Δs₂ of the two track gauge values s₁, s₂ under different load conditions forms a parameter for assessing the respective rail fastening 7. Derived parameters are also informative, such as the slope of the track gauge progression as a function of the load changes.

For the location-specific detection of the track gauge change, the machine 1 usefully comprises a position determination unit 28. For example, a GNSS module is arranged on the roof of the machine 1. To determine the position of a current measuring point, the relative position of the stabilising unit 10 or the measuring device 20 is also evaluated with respect to the GNSS module. The position determination unit 28 can also be arranged directly on the stabilising unit 10 or on a rail-based running gear 3.

In a simple embodiment of the invention, the measuring results of the measuring device 20 are displayed in real time to an operator in the cab 14. The operator can react immediately and document a defective rail fastening 7. With the position determination unit 28, measuring data or evaluation data can be stored in relation to a position. In this way, the conditions of the rail fastenings 7 on the entire section of the track 4 being travelled on by the machine 1 are automatically documented. If necessary, a radio module 27 transmits the results to a central control in order to organise the repair of defective rail fastenings 7.

For an efficient and precise condition inspection of the rail fastenings 7, the machine 1 comprises two stabilising units 10 arranged one behind the other, as shown in FIG. 1 and FIG. 9. The respective stabilising unit 10 is operated with a predefined spreading force F_S and has a separate measuring device 20. For this purpose, the spreading drives 19 of the respective front axle 17 are actuated by means of the assigned control equipment 24. For example, a first spreading force F_S1 is predefined for the front stabilising unit 10, which causes a constant first load force F_B1L, F_B1R. A predefined second spreading force F_S2 of the rear stabilising unit 10 causes a constant second load force F_B2L, F_B2R.

Position-related measurements of the respective track gauge s₁, s₂ are carried out by means of the two measuring devices 20. The detected track gauge values s₁, s₂ are fed to the evaluation device 26 in order to determine a position-related parameter. Due to the different load forces F_B1L, F_B1R, F_B2L, F_B2R, the difference of the track gauges s₁, s₂ are a meaningful indicator for the condition of the rail fastenings.

FIG. 8 shows the measuring result with intact rail fastenings 7 with a dashed line. The measured track gauges s₁, s₂ and track gauge differences Δs₁, Δs₂ result from the normal elasticity behaviour of the track panel 5. In the case of a defective condition of a rail fastening 7, starting from the existing track gauge so, changed measured values for the track gauge s₁′, s₂′ and the track gauge differences Δs₁′, Δs₂′ result (dash-dotted line in FIG. 8). The ratio of the measured values s₁′, s₂′, Δs₁′, Δs₂′ to each other also differs from the result with intact rail fastenings 7. For example, in the case of loose fastenings 7, the track gauge s increases even with a small increase of the spreading force F_S.

The measuring results thus provide a valid data basis for deriving parameters that serve to assess the condition of the respective rail fastening 7. In the simplest case, with the same increased spreading force F_S, the track gauge difference Δs₁ is evaluated compared to the normal track gauge s₀. If the rail fastening 7 is defective, a higher track gauge difference Δs₁ can be determined.

With the present dynamic measurement, any appropriately adapted Dynamic Track Stabiliser can be used to inspect the condition of the rail fastenings 7 directly on-site. The method is so accurate that individual loose fastenings 7 are detected. Due to the additional information about the condition of the rail fastenings of the rails 6, there is an increase in safety when opening the track 4 for traffic after a repair. During the stabilisation of newly laid tracks in particular, it frequently occurs that rail fastenings 7 have not yet been tightened firmly. The present invention is therefore particularly advantageous when maintaining newly laid tracks.

Claims

1: A machine for compacting a ballast bed of a track with a machine frame supported on rail-based running gears and a height-adjustable stabilising unit connected thereto, comprising a vibration drive,an axle with wheel flange rollers movable on rails of the track, whose distance to each other extending perpendicularly to the longitudinal direction of the machine can be varied by means of a spreading drive, anda roller clamp that can be pressed against the rails by means of clamping drives,

2: The machine according to claim 1, wherein control signals, which cause a periodically changed load force, are stored in a control equipment for actuating the spreading drive and the clamping drives.

3: The machine according to claim 1, wherein the measuring device is coupled to the axle of the wheel flange rollers.

4: A The machine according to claim 1, wherein the measuring device is coupled to an evaluation device, and that the evaluation device is set up to evaluate a rail fastening on the basis of the detected rail head deflection and/or track gauge change.

5: The machine according to claim 4, wherein the evaluation device is set up to evaluate rail head deflections and/or track gauge values detected at a measuring point as a function of a progression of changed load values in order to assess a condition of rail fastenings positioned in the area of the measuring point.

6: The machine according to claim 1, wherein a position determination unit is arranged for a location-specific detection of rail head deflections and/or the track gauge change.

7: The machine according to claim 1, wherein two stabilising units are arranged one behind the other, and that each stabilising unit for detecting rail head deflections and/or the track gauge change caused by the respective horizontal load force.

8: A method for operating a machine according to claim 1, with the stabilising unit with the wheel flange rollers being lowered onto the rails of the track, wherein the rails are subjected to a predefined variable horizontal load force by means of the spreading drive and/or the clamping drives, and that a rail head deflection and/or track gauge change caused by the horizontal load force is detected by means of the measuring device in order to indicate a condition of a rail fastening.

9: The method according to claim 8, the horizontal load force is periodically changed by means of a control equipment with a frequency that is lower than a vibration frequency of the vibration drive.

10: The method according to claim 8, wherein the rails are subjected to a first horizontal load force by means of the stabilising unit, and that the rails are subjected to a second horizontal load force by means of a further stabilising unit.

11: The method according to claim 8, wherein the machine is moved continuously along the track.

12: The method according to claim 8, the track gauge change is detected and evaluated as a function of the varied load force by means of an evaluation device.

13: The method according to claim 12, wherein rail head deflection values and/or track gauge values detected at a measuring point by means of the evaluation device are jointly evaluated as a function of different load force values.

14: The method according to claim 8, wherein a position determination unit is used to determine the position of the measuring device for a location-specific detection of the rail head deflections and/or the track gauge changes.

15: The method according to claim 14, wherein evaluation data of a respective rail fastening is stored with reference to its location in order to assess its condition.