Tilting Trains - A SEMINAR

 

1. Introduction

                                                             

            Train is a mass transporter, which transports humans and goods from one place to another place. We have trains, which run by diesel and electricity. Among goods and passenger trains the most concerned one is passenger trains.

 

            The passenger train should move quickly with high speeds. The rail road will not be always straight it should pass through curves and turns. We all know that if you are driving in your car and you take a turning at speed you feel centrifugal forces. Well it is no different from trains, if a train takes a turning at speeds centrifugal forces will be experienced.

 

            The major problem for any trains is to pass over the curves and turns of the railroads. If the train moves with the same speed at the curves and turns the train may slip from the track, so the speed of the train will be slowdown drastically to avoid slip.

 

            This results in wastage of fuel and in turn reduces the speed of the train, which is main consideration for the passenger trains. One of the solution found to avoid this situation is the tilting trains. 

2. Problems with corners

            We all know that if your driving in your car and you take a corner at speed you feel centrifugal forces. Well it is no different from trains; if a train takes a corner at speed then centrifugal forces come in. Often train operating companies face a decision for building a high speed railway transport system... they can either invest money in the train to make it tilt but use existing railway lines, or they invest money in a new railway but don't need to spend money on expensive tilting mechanisms. This is why TGV, and ICE and bullet trains do not tilt, because they have their own dedicated high speed railway lines where curves are built with very high radii.

 

            It is worth pointing out that the centrifugal force is a function of v2/r where v is the velocity and r is the radius. This means if you double the velocity, you quadruple the centrifugal force. Similarly, if you want to triple the velocity but keep the centrifugal force the same, you must increase the radius by a factor of nine! Something not always possible. This is why even apparently gentle curves can be much more of a problem with high speeds than one might thing, because the force rises with the square of velocity.

 

3. What is tilting train?

 

            Tilting train consists of a tilting mechanism that enables increased speed on regular tracks.

 

            In the upper part of the tilting trains that is in which the passengers are seated can be tilted sideways. During the motion of the train if the train has to steer to left in a left turning the coaches of the train will be tilted to the left in order to compensate the centrifugal push to the right and conversely during the right turn.

 

            These trains are constructed such that inertial forces which cause the tilting can be controlled by a computer.

 

            If the trains travel at speeds more than the specified speeds at the turnings of the railway tracks their will be centrifugal forces acting on the train. Due to these centrifugal forces the train may slip and push out of the tracks. But in case of tilting trains which will not happen, because of the reason that centrifugal forces will be compensated by tilting mechanism.

4. Why tilting helps?

            When sitting on a corner going at speed there are two forces acting on you, gravitational force and the centrifugal force which is accelerating you into the corner. In physics when two forces act, then this causes a resultant force. The resultant force will push you into your seat and to the side. However if the train is tilting, then the normal contact force of you on your seat will be the same as the resultant force you are experiencing. This means as far as the passenger is concerned he or she is just being pulled into his or her seat, and he or she is used to that so no discomfort is felt.

 

            This is true also of aero planes, commercial planes tilt a large amount, up to 30 degrees when going around corners in some cases to cater for passenger comfort. As the tilting of the aero plane is to get rid of the problem of centrifugal forces, or more accurately to disguised the centrifugal forces as a part of gravity as far as the passengers are concerned. The only way you know if the aero plane is tilting is to look out of the window.

 

            Trains that tilt can go up to 25% to 40% faster around curves than conventional trains without upsetting the passengers, and as mentioned before this can significantly increase  average speeds and cut journey times.

5. How do trains tilt?

 

            Carriages have tilting mechanisms. Obviously the bogies cannot tilt because they ride on the track and must follow the path of the track. So the coaches have to tilt on the bogies. The way they do this is simple, the bogie acts a fulcrum in the center and it is free to tilt either side. Then pistons control how much the coach tilts. The pistons are controlled by a small computer, which uses a spirit level. The spirit level is used to check if things are horizontal remember, i.e. at right angles to the resultant force acting. Normally this force is gravity, but when going round a corner the resultant is a combination of gravity and centrifugal forces. This means the spirit level indicates it is no longer horizontal, so the computer adjusts the pistons until horizontal is read. Again this will not be horizontal to the ground, but as far as anyone on the train is concerned it will be horizontal, keeping the passengers happy.

 

            In the early days they tried to use inertial force to let the trains tilt… i.e. they would have no mechanism to make them tilt but the carriages would have a low center of gravity so centrifugal forces on the carriage would cause them to tilt. This proved unsuccessful.

 

6. Problems associated in tilting the track

            Well on high speed lines the track in the UK is heavily banked up on corners, although going in a high speed train you don't notice it at all. Occasionally when a high speed train in the UK comes to a stop because of a red signal or something on a curve you can really notice how much its slanted, on a stop on a curve put a bottle on the floor and will slide across to the other side.

 

            However there are limitations with tilting tracks, first of all the banking has to be designed with a specific speed in mind. A banked up track meant for 125mph trains is going to cause discomfort to passengers in a local 75mph train, as when a slower train goes round a banked corner it will make passengers feel like they are falling to a side. Of course you could build dedicated high speed lines, but then you would engineer them without tight curves. This limits the extent to which tracks can be banked up. If the track is banked too much for really fast trains, then if any train comes to a stop on the curve due to a red signal the slant will cause discomfort to passengers. Also arranging for the overhead pantrograph to make proper contact with a wire above a banked curve is a little tricky.

 

            Clearly trains themselves need to tilt, then you get the double benefit of tilted track and tilting train, and the train can tilt to exactly suit the speed it is going at.

 

7. Passenger comfortness

 

            One might think it is not safe to push a train round a corner at high speed. Indeed that is true. However the crucial thing is that the speed at which it becomes unsafe, i.e. the speed at which there is enough force to push the train off the track is incredibly high. In fact the force needed would be enough so that all passengers on the train couldn't move and would be stuck to the sides of the train. This implies that there is scope for increasing the speed of a train round corners a great deal without it becoming unsafe, however passengers will object.

 

            There are two reasons why it is bad for passengers. I have been on a late running Inter City 125 and it took a corner at some speed although only about 90mph and the corner wasn't tight enough to say see the train at the other end by looking out of the window. The corner wasn't tight enough to notice turning either. However you could feel the forces definitely, and empty cups rolled across tables, bags creaked and I felt pushed against the wall.

 

            Any faster and it would be extremely uncomfortable for passengers and they would rather the train slowed down and take a little longer. Also companies don't like to run trains at speed round corners because it upsets passengers, as when exposed to turning forces they may become worried the train is going to fly off the tracks (which incidentally has never happened). This might make people nervous about traveling on high speed trains. The reason no one is ever nervous about traveling at nearly 200mph on a train is because it is smooth and constant. If it was doing corners at these speeds people wouldn't like it. People get freaked out doing 50mph on a roller coaster which involves tight curves, imagine how they feel when serious speed is involved! Its all down to the forces a passenger feels, if a passenger feels a lot of strong forces then he or she is going to be nervous, and may avoid traveling on the train, or just choose a slow train.

 8. Countries who developed the tilting technology

 

8.1 Britain

            The UK was interested in developing the advanced passenger train for quite a while

 

8.2 France

            The development of the tilting train in France began in 1956 when eng. Mauzin built and experimented a single car unit that used inertial (non-assisted) tilting. This experiment were suspended because a natural tilting proved too difficult to accomplish. France preferred to built a vast network of high speed lines and the development of TGV started in the early seventies with a two-car modified turbo train. Today GEC-Alsthom has decided to start the development of a tilting TGV that has been delivered few weeks ago for testing and trials.

 

8.3 Spain

            With the ETR-401 Fiat delivered in 1976 a wide-gauge version to Spain that was designated Tren Basculante (RENFE Type 443). However like its Italian sibling it remained a single vehicle. Later Spain developed a tilting version of its own Talgo train (talgo pendular) that so far has proved itself the only successful example of natural tilting and has met with a huge success.

 

8.4 USA/Canada

            The first experiments were carried over in the thirties with non-powered cars (called pendulum), but the first successful tilting train in the USA was the Sikorsky Turbo Train which incorporated an inertial tilting mechanism. Later, in 1973 Amtrak tested an active tilting train called LRC (Light - Rapid - Comfortable) made of ten cars, that unfortunately had no success. Today Amtrak is trying again with the American Flyer built by Bombardier using some TGV-derived technologies.

 

8.5 Sweden

            ABB developed in the early seventies an active tilting mechanism that was alternative to the Italian and British ones. This was tested in the X15 vehicle and implemented in the X2000 series train that so far has had a good success. One curious feature of this trains is that the tilting mechanism is applied only to the passengers cars and not to the driving motor units.

 

8.6 Switzerland

            As a part of the IC-2000 project the Swiss railways are developing a tilting train that has the provisional designation ICN-2000 and will be built by SIG.

 

8.7 Germany

            Germany has adopted tilting technology on its 610 and 611 class series EMU and will built the ICT for long-range intercity services

 

9. Advantages

1. Fuel consumed by the trains can be minimized.
2. Speed of the trains can be maintained constant and hence time to reach the destination is minimized
3. Their will be Comfort ness for the passengers.

10. Disadvantages

1. Very costly to manufacture these kind of trains.
2. If the coaches do not tilt then it is dangerous.

 11. Summary

 

            While the Very high speed trains like the TGV could be regarded as the Rolls Royce of trains, tilting trains could be thought of as the cheep and cheerful mini metro. The price differential is fairly similar too, it costs about 20 times more per unit distance to build a dedicated high speed line than it does to upgrade existing lines for tilting trains. This is what makes tilting trains extremely attractive. However there are disadvantages. 140mph or 230km/h is about as fast as trains go when not on dedicated lines. And then they have to be fitted in with slower moving traffic.

 

            With rail travel growing all over Europe, the problems of railways reaching saturation point has forced new lines to be build. This is why despite the success of the Italian Pendolini a new high speed line with 300 km/h trains is being built, because existing lines are at saturation.

 

 Conclusion

 

Ø      The tilting trains can be considered as the cheerful mini metro trains.

Ø      To construct high speed lines it costs about 20 times more per unit distance than to upgrade existing lines for tilting trains.

Ø      Tilting trains can go up to 25% to 40% faster around corners than conventional trains without any discomfort ness to the passengers.

Bibliography

 

Books:

·         R.S.Khurmi, “Theory of Machines”, Inertia Forces and Resiprocating parts Pg.No.496-540, Gyroscopic Couple Pg.464-495.

·         V.A. Profilldis, “Railway Engineering”, Chapter.5 , Pg.No.105 to 115.”

 

Websites:

·         www.googlesearch/tiltingtrains.com