POTENCIÁL SKRÁTENIA JAZDNÝCH DÔB A ENERGETICKÁ NÁROČNOSŤ VOZIDIEL S NAKLÁPACÍMI SKRIŇAMI NA ŽSR POTENTIAL REDUCTION OF TRAVEL TIMES AND ENERGY CONSUMPTION OF TILTING BODY VEHICLES ON ŽSR POTENCIÁL SKRÁTENIA JAZDNÝCH DÔB A ENERGETICKÁ NÁROČNOSŤ VOZIDIEL S NAKLÁPACÍMI SKRIŇAMI NA ŽSR POTENTIAL REDUCTION OF TRAVEL TIMES AND ENERGY CONSUMPTION OF TILTING BODY VEHICLES ON ŽSR

Pendolino train set during run on the existing track under present-day speed limits and under the theoretical speed limits from curve negoti-ation by tilting body vehicles.


Vysokorýchlostná doprava v Európe a Japonsku
Podľa štatistík v ostatnom polstoročí od konca druhej svetovej vojny zažili železnice skutočný úpadok. V skutočnosti zisk Increasing the speed of passenger transport becomes an important task facing present-day railways. This task has risen both from the international agreements and from the necessity to keep competitiveness of the railway on the transport market. The paper presents a possibility to increase travel speed of passenger transport on ŽSR (Slovak Railways) by use of tilting body vehicles. For the selected ŽSR track sections accessible travel times were calculated for conventional design vehicles and for tilting body vehicles. From comparison of the results a remarkable reduction of accessible travel times can be found. Further, the energy-consumption demands have been evaluated for similar train sets of conventional design compared with the Pendolino train set during run on the existing track under present-day speed limits and under the theoretical speed limits from curve negotiation by tilting body vehicles.

Introduction
An important problem, which almost every European railway has to cope with at present, is increasing the speed of railway transport.
Train speed can be increased by building new railway lines, or by the radical reconstruction of old ones. However, building of new high-speed lines is a very demanding task, especially in countries that have very mountainous terrain or their finances are strictly limited. That is why the Italian Railways FS and Swedish Railways SJ had ordered vehicles that were capable to reach high speed even on existing lines with small curve radii -vehicles with tilting bodies. These vehicles, referring to the experience of several European countries, are able, even on existing tracks used for both passenger and freight traffic, to reach high speed and by that remarkably reduce travel times.

Aktivity na zvýšenie rýchlosti železníc OSŽD
OSŽD zahŕňa v súčasnosti 25 členských krajín -železníc z Európy a Ázie -od Českej republiky a Poľska na západe cez Čínu na východe a Irán na juhu. OSŽD podporuje kooperáciu v medzinárodnej železničnej preprave medzi krajinami Európy a Ázie. Pretože v jednotlivých krajinách oboch týchto kontinentov vládnu rozdielne podmienky, musel byť pre zvýšenie jazdnej rýchlosti a zavedenie vysokorýchlostnej dopravy najprv analyzovaný objem prepravy a musela byť vytvorená prognóza. Na základe uskutočnených prieskumov boli zachytené a opísané dôležité medzinárodné trate pre prepravu Európa -Ázia. Pri popísaní európskej časti sa plne zohľadnili príslušné podklady UIC ako aj rozhodnutia paneurópskych konferencií ministrov dopravy. Konferencia ministrov OSŽD schválila tento plán tratí na svojom zasadaní decline. In fact competitors to railway transport, road and air transport, gained profits from explosive growth of freight and passenger transport. But exclusive growth of these transport modes is hitting its constraints at present. In fact, if trends in road and air transport continue, they may result in increased environmental pollution and conflicts, which provoke defensive reactions observed in some places, especially on Alpine transit roads in Switzerland, Germany and Austria. The relative decline in railway traffic, observed in the last 50 years, was answered by the development of high-speed transport. In October 1964, on the occasion of Olympic games in Tokyo, Japan, the first high-speed line from Tokyo to Osaka (515 km) was opened. The running speed of 210 km/h in the beginning of operation by first train-sets was gradually increased to 270 km/h by introducing vehicles of newer generations. In spite of the immediate commercial success that was observed on this line, Europe had to wait until 1981 when operation on two high-speed lines -"Direttissima" from Rome to Florence and the TGV line from Paris to Lyon, were launched. Benefits from passenger transport by high-speed trains are very well known now and are generally recognised by passengers and railway companies. High speed has not purpose for itself as the goal is not to make a high technical performance; it allows to shorten travel time on the railway line almost to its half and by that door-to-door (including subsidiary lines) travel time can be remarkably shortened, which is a fundamental factor in customers' eyes when deciding on transport mode. To be competitive with a passenger car, which offers complete connection from door to door and can run on a highway at the speed of 130 km/h, the necessary average running train speed from station to station is 200 km/h -with high speeds from 250 to 300 km/h.
Upgrading of existing tracks for speed up to 200 -220 km/h is possible only if there are not curves of diameter smaller than 1500 m on the line. Track upgrading concerns stiffening of rails and catenary, elimination of railway level crossings and change in the signalling system. In some cases it is possible to modify small track curve radii in a limited extent, but especially in Western Europe this solution is often only illusion on the main roads built in the last century that followed the urbanisation. Moreover, the reconstruction costs must not be underestimated on these intensively operated lines

Activities for increasing speed on OSŽD railways
OSŽD is composed of 25 member countries -railways from Europe and Asia -from Czech Republic and Poland in the West to China in the East and Iran in the South. OSŽD promotes cooperation in international railway transport between countries of Europe and Asia. As there are different conditions in the individual countries of both continents, for increase of travel speed and introduction of high-speed transport, at first, the traffic volumes had to be analysed and prognosis had to be created. Based on the realised surveys the important international lines for Europe-Asia transport were recognised and described. In the description of the European part the corresponding UIC materials as well as decisions from pan-European conferences of ministers of transport were considered. The conference of OSŽD ministers had ap-
Further, it had been decided that conditions stated in AGC agreement for the most important project of railway infrastructure in Europe, would be respected to a great extent. Similarly, target highest speeds on the individual line sections as well as the time periods for reaching these speeds had been set up. From the materials adopted it results that the European members of OSŽD intend to increase running speed by modernisation and construction of new railway lines with total length of about 18,000 track kilometres. In the first step upgrading of lines to running speed of Second centre for building of future high-speed railway network Europe -Asia is the Chinese railway. Development of Chinese economy has positive influence on railway transport: there are plans for building new lines, construction of double-track lines, electrification and other methods of upgrading. Extent of this development can be seen from plans for the time period 1998 -2000 when construction of 5.340 km new lines is to be realised, 2.580 km of single track lines should be upgraded to double track and 4,400 km tracks should be electrified. At the same time the Chinese railways (KZD) are introducing rapid transport in passenger traffic. In the end of the year 1997 length of railway tracks with speed limit of 140 km/h was 5.500 km and 587 km track section has speed limit of 160 km/h. By the end of the year 2000 length of these lines should exceed 8,100 km.

Current state of tilting body technology in the world
At present a couple of countries are dealing with tilting body railway vehicles as they consider it a very effective system of modern transport. There are principally two kinds of body tilting: natural and forced. Trains with natural body tilting include Spanish train units RENFE called Talgo. The group with forced body tilting include, for example, Italian train sets FD Pendolino, German DB -VT 610 derived from Pendolino, another train set concept Swedish SJ -X 2000. Nowadays, a trend towards the use of trains with tilting technology is starting to grow rapidly, and there is vir-

Comparison of conventional trains with tilting body trains running in curve
Train sets with tilting bodies do not require reconstruction of curves as the train body tilts in small track radii to compensate effects of centrifugal force on passengers. The following pictures show effect from body tilt for system with natural tilting (figure 3) and with forced tilting ( figure 4). The pictures clearly show that forced tilting brings higher effect than the natural one, but it requires more complicated mechanism and control system for body tilting.
To compensate for centrifugal force acting on a vehicle during run in curve the outer rail is superelevated against the inner one (rail cant). This superelevation is called in case of fully compensated centrifugal force a theoretical superelevation. Acting forces or accelerations acting during a run of vehicle in curve are shown in the following diagram, where g stands for gravitation acceleration, a stands for acceleration by centrifugal force, p is a rail supe- Pre normálny rozchod koľaje 1435 mm, rýchlosť jazdy V a polomer oblúka R sa teda teoretické prevýšenie vypočíta podľa: Na železnici sa nepoužíva plne kompenzované teoretické prevýšenie, ale sa pripúšťa určitá veľkosť nevyrovnaného odstredivého zrýchlenia, čo je reprezentované tzv. nedostatkom prevýšenia (p np ). Základným typom prevýšenia u ŽSR je prevýšenie nižšiep n , znížené o 70 mm od teoretického. Ďalšími typmi prevýšenia sú prevýšenie znížené, (znížené o 85 mm) a najmenšie, znížené o 100 mm od teoretického.
Following equations are valid: From equal angles ␣ we have: ᎏ a g ᎏ ϭ ᎏ p e ᎏ And from that after substitution: For the standard rail gauge of 1435 mm, train velocity V and curve radius R the theoretical superelevation can be calculated from: Railway does not use fully compensated theoretical superelevation, but certain unbalanced lateral force is permitted, which is represented by so called lack of superelevation (p np ). The basic type of superelevation on ŽSR is lower superelevation -p n , lowered by 70 mm from the theoretical one. Other types of superelevation are lowered superelevation, (lowered by 85 mm) and the least, lowered by 100 mm from the theoretical one.
For calculation of tilting body vehicle running in curve, we need to determine the maximum permitted velocity (V dm ). Formula for its calculation can be derived as follows: 1. Formula for calculation of maximum permissible velocity at curve with radius R, maximum superelevation p m and cant deficiency pn p is: A further increase of speed without reducing passenger ride comfort (a n ϭ 0,457 m.s Ϫ2 ) can be gained by tilting the car body inwards toward the curve by certain angle , which represents additional superelevation p d . We get the permissible velocity with use of tilted body: This is not a complete solution because increasing of velocity, besides balancing the centrifugal force effecting passengers, brings increase of vehicle effects on the track.

Možnosti využitia vozidiel s naklápacími skriňami na ŽSR
Slovenská republika, ako štát stredoeurópskeho regiónu, bude musieť tiež uvažovať o zvyšovaní rýchlosti železničnej dopravy, aby udržala krok s ostatnými krajinami západnej Európy. and rail, which results in unbalanced centrifugal acceleration of vehicle a vn ϭ 1.65 Ϭ 1.8 m.s Ϫ2 and only exceptionally a vn ϭ ϭ 2.0 m.s Ϫ2 . The maximum permissible speed at total transversal acceleration a c will be then: The most important benefit of a tilting body vehicle compared with a conventional one is that it can negotiate curves at substantially higher speed and by that remarkably reduce travel time of a train. If we consider curves with same rail cant (superelevation) of p ϭ 150 mm and cant deficiency of 70 mm, respectively 100 mm, we can draw a diagram showing relation between maximum speed in curve and curve radius for a tilting body vehicle and for conventional one (see figure 5).
From the graph one can see that vehicle with tilting body can run at substantially higher velocity in even small curve radii than conventional vehicles. Speed limit in curve is given by already mentioned Proud'hom formulae, from which limit on maximum transversal force acts between wheel and rail.

Possibilities in using the tilting body vehicles with ŽSR
Slovak republic as a country of the Central European region will have to consider the increase of the rail traffic speed to keep pace with countries of Western Europe.
Run of the express trains used on ZSR is constrained by maximum track speed, which is very low comparing it with P R E H Ľ A D Y / R E V I E W S Obr. 5. Závislosť maximálnej rýchlosti prechodu oblúkom od polomeru oblúka Accessible speed has been determined according to theoretically possible maximum speed during curve negotiation, but lengths of track sections with speed limits were considered according to the currently existing sections, while in the individual sections the track-speed limit was set up by rounding the lowest theoretical track speed limit in the corresponding track section.
For the chosen lines based on a simplified calculation of accessible travel time (using a precise static method for calculation of travel time without considering train stops) we get the results given in the following table (table 1). Chosen lines can be travelled by vehicles with tilting bodies much faster and by that substantially speed up traffic between important towns in Slovakia and connections with foreign countries (connection with the Czech republic, Poland, Austria, Hungary). The calculated travel times are only theoretically accessible, they do not consider traffic technology times and other times existing in real operation. Actual effect from reduced travel time would be smaller than theoretical one.

Comparison of accessible travel times
Tab. 1 on the chosen ZSR lines

Reduction of travel times and energy demands
In the following we consider also trains' energy consumption on the selected lines as this plays an important role when running at high speed. Energy consumption will, especially in future, represent a major part of operational costs, and that's why it cannot be omitted in primary analysis of planned increasing speed.
facturer is reluctant to publish the technical data. In spite of that the calculation is sufficiently accurate and reflects reality.
Although the power of locomotive series 163 is remarkably lower, for maximum speed of 120 km/h currently used on given railway lines this locomotive is good enough. Calculated travel times for conventional locomotive-hauled train and Pendolino train set series ETR 470 on lines with existing speed limits do not differ by more than 1 % in favour of Pendolino, which is a negligible difference. However, benefits from increased speed in curves confirmed results of simplified calculations; although, the difference, according to more precise calculation, was a bit smaller. Moreover, in these calculations we considered speed limits in the same sections as they are at present, yet we also used theoretical speed limits for each curve while certainly the maximum speed of train ETR 470, which is 200 km/h, could not be exceeded. Selected calculation results are in table 2.
However, in the case of theoretical speed limits for each curve, increased energy consumption has remarkably gone up, as there were frequent changes in velocity (acceleration in sections with higher permissible speed). Comparison for Košice -Žilina line is in diagrams on figure 7 and 8, where in the case of theoretically permissible velocities in curves the travel time would be 101.8 min and energy consumption would be 3,172 kWh, but in the case of run with maximum speed limits in sections as they exist at present, the travel time would be 110.3 min. However, energy consumption is only 2188 kWh, which is approximately two-thirds while travel time would grow by about 8 %.
This result also shows the necessity to optimise length of the sections or the maximum speed on sections, from the minimum energy consumption point of view, certainly with respect to keep the shortest travel time. When looking at the speed limits for sections with lengths according to the existing state it is clear that some of them are too short for short-time speed increase with consequent deceleration. Such analysis requires more detailed study of track, i.e. real possibilities of curve modifications in sections with the most critical situation, etc.

Conclusion
Aim of the study was to present possibilities for increasing the travel speed in the current situation without construction, or without major reconstruction of existing lines. At the same time, to show the energy consumption of trains running at a higher speed, which compose a significant part of the operational costs. The results prove that there is a potential for remarkable shortening of travel times, while at the same time it is necessary to pay attention to selection of track sections with speed limits from the energy consumption versus a travel times point of view.