Contributions to the hydrostatic buffers for railway vehicles.

Otlacan, Dimitrie ; Tusz, Francisc ; Duma, Virgil-Florin 等

1. INTRODUCTION

At the 150 reunion of the Expert Committee ORE (ERRI), the join symposium of the B12 and B36 commissions performed an evaluation of the state-of-the-art regarding the construction of the railway wagons, and of the necessities & possible evolutions in order to have a railway transport competitive with regard to its competitors, i.e., road transport.

Several problems to be solved were highlighted: 1) decrease of the costs related to railway items; 2) decrease of the costs related to the maintaining of railway material; 3) increase of the velocity of the trains; 4) insurance of the security of transports. The annual costs of the repairs of the wagons, consequence of minor accidents, was 16,678,000DM/year for DB (0.3% of them, in frontal parts), CFF and SNCF, while the costs of the payments due to bad condition of the items transported (consequence of the shocks produced by frontal contacts of the wagons) reached 22,421,000DM/year (ORE, 1995); 5) the decrease of the longitudinal forces for which the wagons are tested, by using frontal buffers with superior characteristics; 6) environment protection, especially for the transport of dangerous items (UIC, 2000a, b, c).

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In order to solve with low costs such problems, UIC recommended the pan-European cooperation of those interested (UIC 1998, 2001, ORE 1990a, b). For the European transport system, objectives to be reached until 2020 are: increasing by a factor of 2 the traffic of persons and by a factor of 3 of the traffic of different items & 50% reducing of pollution.

From a technical point of view, problems 3-6 may be solved, but the costs of the existing solutions do not allow their large scale application, because:

7) 140, even 160km/h velocities are possible with wagons for the transport of different items, but the cost of the bogie would be three times higher than the one of a bogie that reaches but 120km/h, while the wear of the railway and of the wheels may increase significantly, also due to the transversal forces that appear in the buffers when passing through curves (Otlacan et al, 2008);

8) Some buffers of the C category (with a minimum of 70 kJ and a displacement of 105 mm, according to UIC 526-1) and buffers of the L category (a 130 or 150mm displacement, according to UIC 526-3) may provide a sufficient protection of the structure of the wagons and of their load, but their price is 2-3 times higher (ORE, 1995) than the one of an A category (min. 30kJ and a displacement of 105mm), which has the minimum accepted and necessary characteristics for the new wagons.

As a consequence, in Europe, out of the two or three pair of wheels wagons, just 1% of them have the C category buffers and less than 0.1%, L category ones. Out of the 4 pair of wheels wagons, 4.5% have the C category buffers and less than 0.1% have L category ones. Because of the costs, superior characteristics buffers are used only where the UIC asks for that (for freight wagons of class 2 RID).

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9) A problem related to the buffers used, but also with implications on the safety of the transports and on the wear of the wheels, is given by the forces transversal with regard to the displacement direction, forces that appear in the buffers when passing through curves.

2. CHARACTERISTICS & ADVANTAGES OF THE DESIGNED SHOCK ABSORBER

In order to meet specific present and future requirements regarding the buffers, we have conceived a buffer (Otlacan, 1999) that is able to satisfy all the specified conditions. This element represents a development of the hydrostatic technology (Otlacan, 2000). The hydrostatic solution developed, used at the buffers of railway wagons (Dixon, 1998), is presented, with its constructive solution, in figure 1.

The diagram in a static regime of the spring & shock absorber developed assembly is presented in figure 2a, while in figure 2b, the functional diagram of the system in the dynamic regime (Otlacan, 2007) is drawn. One may notice that the spring-damper assembly has the functional characteristics (the level of the forces, the absorbed energy, the consumed energy and so on) at the level of the best existing solutions of the hydrodynamic spring-dampers.

We concluded that the forces that appear for the wagons provided with the proposed buffers are 2 ... 2.9 times smaller than in the case of the buffers built with the hydrostatic technology and 1.5 times smaller than those of the best nowadays buffers (Otlacan, 2009).

Other characteristics are: (i) constructive simplicity; easy to maintain; functional characteristics at the level of the best hydrodynamic buffers of the C and L category; (ii) the possibility of changing the static characteristic with regard to the condition of the wagon, both in repairs and functioning. In addition, these buffers can work differently in the situation when the wagon is single or in a convoy, without being necessary to link it at the air circuit of the wagon; (iii) the spring of the buffer may be designed with a displacement of up to 200 mm, in the overall size conditions imposed nowadays; the spring of the assembly and its characteristic may be adapted, with minimum costs, in order to be also used as the spring of the automatic couple, in the case when this type of couple will be applied in Europe as well; (iv) the spring designed especially for the automatic couple simplifies the way the head of the couple is linked to the shock absorber, reducing the costs; the spring may be designed for any type of railway wagon for passengers, freight or locomotives.

3. CONCLUSIONS

The use of the developed buffer, with a displacement of 105 mm, 150 mm or higher, with characteristics of the C or L category, brings advantages for all those involved in the railway transport: (i) for the owner of the wagon, by decreasing the costs of buying and maintenance; a better protection of the structure; smaller wears of the buffers, of the spring and of the wheels.

Although our research continues, a minimum of 50% increase of the transport distance between to repairs of the worn wheels is estimated and a reducing of the costs of the transfer to the automatic couple by using again the spring of the shock absorber; (ii) for the user (the transport company), by providing a better protection of the load of the wagon and by decreasing the curves in which the transport can be performed with no special measures like the ease of the screw of the elongation device and by reducing the necessary power of the driving engine at the train start, when the shock absorber and the elongation device or the automatic couple is used; (iii) for the owner of the railway, by reducing the wear in the curves; d) for the wagons manufacturer, by an increase of the guarantee period for some sub-assemblies. The cost for the manufacturing of this buffer is lower than of any of the nowadays C category.

4. REFERENCES

Dixon, J. (1998). The shock absorber handbook, Society of Automotive Engineers, Warendale, Pa

ORE B12 (1995). Report 64

ORE DT 230/B12/B36 (1990a). Advancements of the building technique of railway wagons. Perspectives for the near future. N.H.C.E. Zeevenhooven: Philosophy on the constructive parts and on the links in the circulation sense between the vehicles, Utrecht

ORE DT 230/B12/B36 (1990b). Advancements of the construction technique of wagons. Perspectives in a nearby future, Utrecht

Otlacan, D. (1999). Patent RO119142 (WO 03/067116; AU 2001/297520)

Otlacan, D. (2000). Shock absorber, Patent RO113229

Otlacan D. et al (2007). Contributions to the improvement of the dynamic characteristics of the hydrostatic springs, Proceedings of 18th DAAAM International Symposium, Katalinic, B. (Ed.), pp 533 - 534, ISBN 3-901509-58-5, Zadar, October 2007, DAAAM International Vienna

Otlacan D. et al (2009). Double buffers system for the improvement of railways vehicles behaviour in curves, Proceedings of 20th DAAAM International Symposium, Katalinic, B. (Ed.), ISBN 978-3-901509-70-4, Vienna, November 2009, DAAAM International Vienna UIC Press 152 (2000a). Encouraging the rail transport: an international objective for the reduction of the greenhouse effect, Word Conference of La Haye on the climate changes, Paris

UIC Press (2000b). The transport as the core of the planetary greenhouse effect. The railways, an efficient solution in order to achieve a reduction of the C[O.sub.2] emissions

UIC Press144 (2000c). Railways pan-european conference: A competitive railway system for the pan-european area, Budapest

UIC Press Release (2001). International Rail Exhibition Vienna

UIC 526-1 (1998) Wagons. Buffers with a 105 mm displacement, 2nd Edition