In phase I, four DAC prototypes were subjected to intensive individual comparison trials. The aim was to gather sufficient knowledge and then submit the results to the European DAC Delivery Programme (EDDP) in order for this European committee which is made up of 84 partners, to be able to make a selection decision for a coupling system. The results were discussed and assessed in detail, with the EDDP being able to announce its decision to select the Scharfenberg latch-type design on 21 September 2021. It was then selected for introduction Europe-wide.

In this section, we take you through phase I and describe the testing concept and procedure, and summarise the results. You can download the detailed test reports from the BMDV website.

Freight wagon selection and wagon configuration

Four wagon groups, each with three freight wagons of the same type, were provided for testing the DAC prototypes. Each wagon group consists of a four-axle open bulk goods wagon (Eanos x-059), a two-axle sliding wall wagon (Hbbins 306) and a four-axle gas tank wagon (Zags 119). The aim of this wagon configuration is to test the couplings on freight wagons that are frequently used in European freight traffic and can therefore be considered representative.

A total of 687,495 freight wagons are registered in the European Vehicle Register ECVVR. The second largest wagon category with a total of 114,669 vehicles is the group of open freight wagons “E”, which also includes the selected four-axle Eanos.

The selected Zags tanker belongs to the third largest wagon category in Europe (“Z”) with a total of 109,728 vehicles. With a length over the buffer of 18.8 m, the Zags is the longest of the three selected freight wagon types. The use of freight wagons of different lengths for the tests is critical for testing automatic coupling in narrow track curves, among other things. The large overhang on this wagon is a particular challenge here.

In order to test the behaviour of light two-axle freight wagons when using a DAC in addition to four-axle freight wagons, a Hbbins type closed sliding wall wagon was selected as the third wagon category. A total of 45,345 “H” type freight wagons are in use throughout Europe. This means that in total, the three selected freight wagon types represent 269,742 freight wagons in Europe. As well as this, the selection laid out above means that the test results can be transferred to other two-axle and four-axle freight wagons with comparable dimensions.

All wagons are equipped with LL or K soles for the brakes, meaning they will comply with the legal requirements according to TSI Noise.

¹See Liebing, S. (2018), Quantification of the need to retrofit freight wagon fleets in Germany and member states of the European Union in light of the differing legal frameworks, TÜV Rheinland InterTraffic GmbH on behalf of the Eisenbahn-Bundesamt (Federal Railway Authority), Berlin, 2018.

Details of the wagons used in Phase I

Configuration of the demonstrator

In each of the four groups of wagons, the two inner coupling points were equipped with digital automatic couplings. Four manufacturers have participated in carrying out the tests by providing prototypes: CAF (SA3 type), Dellner (Latch type), Wabtec (Schwab type) and Voith (Scharfenberg type).

The outer wagons in each case, the Zags and Eanos wagons, were equipped with the standard equipment (screw coupling and buffers) on one side. This allowed the four groups of wagons to be connected to form a block train, regardless of the coupling capability of the DAC coupling systems with each other.

In order to be able to simulate different loading conditions in the test sequence, the Zags wagons are loaded with water, the Hbbins wagons with steel mesh boxes and sandbags and the Eanos wagons with concrete items.

Preparing the freight wagons
for electrical and technical measuring equipment

Additional extensions were necessary in order to be able to equip the wagons with measuring technology for test runs. Since all of the couplings were still in the prototype stage, a concept including three separate connection boxes was designed. This made it possible to create a uniform transfer point for the carriage cabling, independent of the coupling, and to work with uniform interfaces. The concept described below served as a test solution only for the duration of the test execution. The concept is not part of a solution that will later be used in this way for retrofitting freight wagons.

The “central connection box” for the power supply and data communication houses all the measuring equipment during the test and is connected to the “coupling connection boxes” via a central cable that is the same for all wagons.

A compact “coupling connection box” is fitted in the area of each coupling. This allows the manufacturers’ cable concepts, which are not yet standardised, to be wired consistently and communicate to the wagon via a main line.

As well as this, the coupling can be shunted at the coupling connection box with a plug connection in the event of a fault and the screw coupling the of the four groups of wagons are connected. In regular runs, the electric coupler takes over this function in the DAC area and connects the power and data lines of the coupled wagons.
Central connection box

Central connection box (With fitted weather covers)

Central connection box (Without fitted weather covers)

Coupling connection box

The pictures show the two boxes using an Eanos-x-509 wagon as an example.

Technical measuring equipment

For the tests in phase I, measuring technology was deployed on the freight wagons, which can be divided into three groups:

1   Measuring technology necessary for mechanical and pneumatic testing

2   Measuring technology that proves the functionality of the energy supply

3   Measuring technology for proving reliable data communication

These three groups are described in more detail below.

Mechanical and pneumatic measuring technology

The physical measured variables that were recorded during the tests and the sensor types used for each are listed below.

Two measuring coupling heads were provided for each of the four coupling types. This means a total of eight coupling heads were instrumented with strain gauges (SG) and calibrated for force. The strain gauges are full bridge circuits.

According to physical principles, the force (static) in both coupling heads is the same (F1 = F2), so it’s sufficient to determine the force in only one of the two heads. The figure on the right shows a schematic diagram of a DAC, with the measuring point where the strain gauges were applied, marked in pink.

Components for testing
the power supply and data communication

The components for testing the power supply and data communication are listed in the table below. These are integrated into the central connection box.

Test concept and tests

In phase I, the procured couplings were each tested using a detailed test concept agreed with the EDDP. The wagon configuration described at the beginning and the technical measuring equipment were applied.

Phase I was started in September 2020 after the demonstrator was installed (June to September 2020). However, due to unresolved technical questions regarding the coupling prototypes, the test programme could not be finalised by February 2021 as planned. Phase I was therefore extended until 30/06/2021 in close cooperation with all coupling manufacturers.

Loading conditions

Testing the couplings made it necessary to individually change the loading condition of the wagons. The number of variations should be kept as small as possible and yet all extreme conditions for the couplings should be represented. On the one hand, the loading condition influences the vertical height offset; on the other hand, the forces acting on the couplings change.

Two scenarios were identified for testing the couplings, the extreme cases of which were investigated. On the one hand, the mechanical load capacity of the couplings, i.e. testing the behaviour of the coupling when large forces are applied. On the other hand, the possible horizontal and a vertical grab range in which the couplings can be coupled and travel through different track geometries without restrictions.

The Zags wagon with a length over buffer of 18.8 m and a pivot spacing of 12.1 m generates the largest horizontal deflections of the coupling. The Hbbins wagon, on the other hand, shows the greatest change in buffer height when comparing the states “charged” to “empty”. This means the coupling process between the loaded Hbbins wagon and the empty Zags wagon was the biggest challenge for testing the grab range.

When examining for mechanical load capacity, the most relevant case is a full Hbbins wagon coupled to a heavy Eanos wagon. The maximum load of the Eanos wagon is 8 t greater than that of the Zags wagon, which has a higher empty weight with the same maximum weight. The greatest difference should therefore occur in the test between the loaded Hbbins and the loaded Eanos wagon in comparison to the empty Hbbins wagon and the loaded Eanos wagon.

The tests carried out at high speeds produced the greatest forces introduced into the carriage frame. In order to slowly approach the maximum values, the Hbbins wagon was initially only half ballasted. In all other tests, partial loading did not provide any additional findings.

Test descriptions

The mechanical tests were divided into coupling tests, operational tests (passing through geometries) and tests to investigate shear forces and derailment safety.

The tests of the test concept can be divided as follows:

Coupling and driving tests

The mechanical tests included coupling tests and operational tests (passing through different track geometries). Carrying out a large number of tests at different speeds in different geometries were necessary to prove a reliable coupling capability and unrestricted operation. To better assess the significance of a result and its repeatability, the tests were repeated five times.

Loading condition 1

The coupling point to be evaluated in coupling tests is located between the wagons marked in pink

Driving tests with a coupled three-wagon group are highlighted in blue

The overview in the table above shows the tests in loading condition 1. Here the fields with black text contain coupling tests and the fields with blue text contain the tests in which geometries were passed through in the coupled state (pulled and pushed).

Loading condition 1 tested the empty wagons. The focus here was on the coupling capability between the Zags and the Hbbins wagon.

As explained, loading condition 2 in the table below served as an intermediate step, so that only tests on the straight track were carried out here. Here, too, the speed was increased up to a maximum of 12 km/h, as in loading condition 1.

Loading condition 2

The coupling point to be evaluated in coupling tests is located between the wagons marked in pink

Driving tests with a coupled three-wagon group are highlighted in blue

Loading condition 3

The coupling point to be evaluated in coupling tests is located between the wagons marked in pink

Driving tests with a coupled three-wagon group are highlighted in blue

Loading condition 3 was used to test two aspects. On the one hand, the combination of the loaded Eanos and the loaded Hbbins wagon were transfered the greatest forces via the coupling. Secondly, the combination of the loaded Hbbins wagon and the empty Zags wagon had the largest vertical difference in height of the couplings, coupled with the largest horizontal difference due to the geometry of the Zags wagon.

The choice of these combinations covered all extreme cases. All other combinations fall between these extreme cases did not yield any further findings.

Results
The results of the coupling and driving trials with the tested prototypes are very different. One thing the couplings of all manufacturers have in common is that deficiencies and weaknesses were identified over the course of the tests, and repairs were required on all coupling designs. It was only possible to generate a comprehensive data base for all the prototypes included in the test by extending the test, as explained in the introduction, and with the repairs carried out by the manufacturers. The following examines the three DAC designs individually and lists the results in summary form for each design.

Scharfenberg design from manufacturer Voith
The driving trials ran overall without any noticeable problems. All infrastructures could be negotiated without restrictions. The coupling procedures with the first version of the Voith DAC failed in numerous cases. The electrical coupling procedures were also assessed as “not successful” in many cases (e.g. 24 of 72 trials at 6 km/h not successful). The contacts often externally showed clear wear marks after just a few trials which was determined as the cause for the negative assessment. In detail, it proved to be only a few contacts which had failed permanently. Voith has developed and made available a version 1.2 on which the coupling head has been adapted. During the coupling trials with this second version of the DAC design, the coupling procedures were successful at lower and medium speeds. The carriages only recoiled with not coupling procedure during coupling trials at 12 km/h. The problems with the contacts in the electrical coupling remained unchanged with version 1.2 of the prototypes.

Latch-type design from the manufacturer Dellner
The first generation of the Dellner latch-type design did not meet the requirements for mechanical strength, meaning that Dellner had to pronounce restrictions in relation to the coupling impacts. Specifically, coupling impacts at speeds higher than 10km/h were not permitted. However, the mechanical and pneumatic connections during the coupling procedures tested 100% successfully allowing for the restrictions. The second generation of the coupling included a mechanical upgrade of the DAC and the implementation of a stabilisation joint to improve the resistance to derailing.

The electrical coupling procedures were assessed as “not successful” in many cases (e.g. 27 of 27 trials at 2 km/h not successful). Also, the contacts often externally showed clear wear marks and the moving contact side jammed after just a few trials. In many cases, as is the case of the Voith coupling results, the failure of individual contacts was the cause for the negative result of the assessment. However, in at least one case, both E-couplings failed completely.

The driving trials with the generation 1 prototypes ran overall without any noticeable problems. All infrastructures could be negotiated without restrictions.

Schwab design from the manufacturer Wabtec
The Schwab prototype also required a second version in order to produce results which were suitable for assessment. With the DAC prototypes tested, the mechanical connection during the coupling procedures tested 100% successfully. The pneumatic coupling did not work in some cases (e.g. 12 of 104 trials at 2 km/h not successful). It was in part possible to couple Zags and Hbbins carriages in the 100 metre bend depending on the load of the Hbbins. It was not possible to couple Zags and Hbbins carriages in the 75 metre bend.
Constructional weaknesses on the moving parts of the electrical contact coupling arose during the tests. As a result, during most of the trials, the reports state that the electrical connection was not successfully closed (e.g. 48 of 104 trials at 2 km/h not successful).
Selected follow-up tests were carried our with the retrofitted E-couplings. In the process, it was only possible to reassess a limited speed range. In these follow-up tests, the measures taken were successful. There were not noticeable significant wear marks in the case of the E-contacts.

The driving trials were mechanically and electrically 100% successful. However, problems with the pneumatic connection were identified (pneumatically coupled in 30 of 142 trials not successful). In this case, there were no short-term air losses.

Over the course of the trials, the required force in order to separate two decoupled carriages proved to be greater and greater. This behaviour was eradicated towards the end of phase I by Wabtec by directing the coupling heads sideways in advance using an adapter on the coupling rod. As a result, the decoupling force seemed to have returned to within an acceptable scope. It was only possible to test this to a limited extent within the remaining time.

Shear force tests

In addition to the coupling and driving tests, the mechanical tests also included tests to test the shear forces and derailment safety. For testing the resulting shear forces and the bearable longitudinal compressive forces of the coupling designs, longitudinal compressive forces were specifically applied. The basis for the tests are the specifications according to UIC Code 530-2.

The tests were carried out on the 150 m S track curve with 6 m intermediate straight (similar to Spec. 4.10). The track geometry for the test is shown in the figure to the right.

Representation of test geometry
The test track consists of an s-shaped track curve with R = 150 m with an intermediate straight of 6 m length. The test track is not excessively elevated. The average track gauge is 1450 – 1465 mm.
Source: UIC Merkblatt 530-2, Güterwagen – Fahrsicherheit, 7. Ausgabe, December 2011

Representation of the structure of the test train
Source: UIC Merkblatt 530-2, Güterwagen – Fahrsicherheit, 7. Ausgabe, December 2011

The Hbbins wagon in the middle of the three-wagon configuration was tested specifically. We know that two-axle wagons are the most prone to derailment in such tests. The neighbouring Eanos and Zags wagons were fully charged. The test was running by pushing, with brake wagons coupled in front of the wagons to allow the test forces to be applied by the locomotives coupled at the rear. This structure is outlined in the figure to the left.

Taking measurements during tests
During the test, the following measured were recorded while going through the test track:

• Longitudinal compressive force F_Lxi
• Wheel lifts d_zij on all wheels
• Wheel contact forces and lateral wheel forces on all wheel sets
• Path (e.g. 1 m mark)

Measured variables during the shear force tests according to UIC 530-2
Note: The buffer lateral shifts have not been measured in the DAC4EU tests. The buffers are disassembled.
Source: UIC Merkblatt 530-2, Güterwagen – Fahrsicherheit, 7. Ausgabe, December 2011

In accordance with the specifications of the UIC Code and in order to identify the limits of the couplings, the longitudinal force, starting at 100 kN, was successively increased. The variables mentioned on the left were measured. The buffer lateral displacement that’s measured in tests with screw couplings is not applicable in tests with DAC. The distance is calculated indirectly by integrating the measured speed.

Results
In the banking trials, none of the couplings fell short of the required minimum value for the sustainable longitudinal compressive force of 200 kN for a screw-type coupling. Two of the three DAC prototypes tested were even able to clearly exceed the reference level of the screw-type coupling (in part by more than a factor of 2).

The Scharfenberg and latch-type designs derailed at 500 kN and 400 kN respectively. The trials with the Schwab design were stopped at 400 kN as there had already been a clear wheel reaction and, on request from the manufacturer, derailing was to be avoided. In addition, none of the couplings reached or exceeded the limit values for wheel lift and the highest permissible transverse wheelset bearing force. However, derailings occurred during the trials. It was not possible to conclusively clarify the reason for this circumstance, and it could be the focus of further research. The data base resulting from the trials could be essential for the path towards European approval.

Electrical tests

Each of the four DAC prototypes is equipped with an electrical coupling (E-coupling). In the case of the Schwab and the SA3 design, the E-couplings were each fitted underneath the mechanical coupling. On the Scharfenberg and latch-type designs, it was fitted above. Both the SA3 and the Scharfenberg and latch-type DACs have spring/fixed contacts. On the Schwab DAC, pin/socket contacts are installed.

Overall, four measurements were performed:

1. Measurement of the contact resistance
2. Measurement of insulation resistance
3. Power transmission via the train
4. Charging and discharging behaviour of the batteries

In the process, the measurements of the contact resistance and the insulation resistance measurements were carried out before starting the mechanical coupling trials as well as during and after the trial programme. In the case of (1), the DAC prototypes in coupled state whereas in the case of (2), they were in a decoupled state. The power transmission (3) was measured for each coupling design in the 3-carriage set and in a coupled state. The charging and discharging behaviour of the batteries (4) on the other hand was tested in the complete train set with nine carriages.

Results
The acceptance criteria during the measurements of the contact resistances were only met in part by the Scharfenberg, latch-type and Schwab DAC prototypes as the maximum resistances were partially only achieved for the supply and data lines (in the case of the latch-type design) or only for data lines (in the case of the Scharfenberg and the Schwab design).

The insulation resistances of the Scharfenberg design were too low. The acceptance criteria for (3) and (4) on the other hand were met by all E-coupling designs.

The following table summarises the results of the measurements:

Trials for power and data communication

An essential component of a DAC is the connection for power and data between the carriages. Therefore, three different communication systems were tested within the project:

• a system which uses the power lines: Powerline PLUS,
• a radio technology between the carriages: Wireless LAN and
• a 2-wire solution using separate lines: CAN-FD

The aim of the trials for power and data communication in phase I was to select a suitable communication topology for the field testing in phase II. The tests showed that all three communication systems are suitable for further evaluation in phase II. The trials in phase II have since provided further decisive results for the selection of a communication system for normal operation. The flow of data and power was tested in both the individual carriage groups and in the entire train set with 12 carriages. In the process, the connection to the carriage group was bridged with the SA3 design. When it came to the measurements in the individual carriage groups, no dependency on the coupling design was determined. In the train set, the communication systems were tested for resilience and resistance to interference, and stable communication was demonstrated.

An overview of data communication experiments:

Climatic chamber tests

Climate chamber tests were carried out to check that the couplings function properly in extreme climatic conditions. During the climate chamber tests, the wagons were in the following loading condition (loading condition 1):

• Eanos wagon: fully loaded
• Hbbins wagon: empty
• Zags wagon: empty

A critical situation was considered to be when two light (unloaded) wagons couple with ice without height offset (in this case the Zags wagon with the Hbbins wagon).

Successful establishment of the mechanical, pneumatic and electrical connections was tested.

During the tests, both the uncoupling behaviour of a connected air-conditioned coupling point and the coupling behaviour of two independently air-conditioned coupling heads were tested. The tests have been carried out only with the prototypes of the design of Latch Type-, Scharfenberg and Schwab.

Test conditions

The conditions and temperatures under which the coupling and uncoupling behaviour is tested:

Test sequence

Before the actual test is carried out, the wagons were exposed to the temperature set in the climatic chamber and the selected climatic ambient conditions for a sufficient length of time. The middle wagon (Hbbins) is coupled to the Eanos wagon on one side and uncoupled from the Zags wagon on the other side (see figure on the right).

At the beginning of the tests, the two coupled wagons (Eanos and Hbbins) were uncoupled to check the uncoupling behaviour.

On the still uncoupled side of the Hbbins wagon, the Zags wagon was pushed on at approx. 2 to 5 km/h and a coupling process is carried out between the Zags and Hbbins wagons. This coupling point was then separated again and the Hbbins wagon is pushed onto the Eanos wagon and coupled with it again.

Now the starting position was reached again and the next test could be prepared.

Results
The results of the climatic chamber trials showed that all three DAC prototypes had problems when coupling the E-coupling in the presence of slush (latch-type design) and/or ice (all three designs). The E-couplings could hardly couple or even not at all as the cover flaps and contacts were not suitable for these weather conditions. When it came to pneumatic coupling, the latch-type design performed the best: the pneumatic connection worked with each successful mechanical coupling procedure.

When testing the Schwab design, a different trial set-up to the regular one had to be used as it was not possible to disconnect the couplings between the E carriage and the H carriage manually. A stronger tensile force was required. Therefore, the H carriage was positioned to be free-standing for the initial position. The Schwab prototype was able to couple mechanically in the presence of snow but not in the presence of ice. Pneumatic and electrical connections were only established at +45°C.