Tilting trains shorten transit time.
High-speed rail is fast becoming a popular mode of travel in Europe and more recently in North America, with countries planning new systems every year. Although national governments may be ready for trains speeding along at 250 kilometers per hour or more, the regional geography is not. Tracks often must snake through mountainous terrain and other obstacles, which can create problems at high speeds.
When trains head into these curve at high speed, passengers inside can feel gravity and centrifugal force pressing them into their seats. The lateral acceleration can become very uncomfortable for riders, making them feel like they're in an amusement-park ride; in the cafe cars, for example, diners will spill food and drink because of the forces occurring in the curves. To avoid this problem, trains must slow down, but this negates high-speed rail's greatest benefit and makes for longer journeys.
The seemingly simple solution would be to build straight railway tracks. France's Train a Grande Vitesse and Germany's InterCity Express high-speed systems have adopted this strategy of new lines dedicated to high-speed trains. This concept works best if the builder has a lot of open space, which has become a rare commodity not only in some parts of the United States but in a rapidly developing Europe as well. Such right-of-way construction also incurs high capital costs, takes a great deal of time, and has a variety of potentially harmful impacts on the environment.
Another option is to design trains that will tilt when negotiating curves on existing tracks so as to reduce centrifugal force on passengers yet maintain fast speeds on the ride. Two recent major rail projects have chosen this approach. London-based Virgin Rail has signed one of the largest international railroad contracts ever for a fleet of tilting trains from Fiat Ferroviaria S.p.A. in Savigliano, Italy, to run on Great Britain's high-speed West Coast Main Line. Half a world away, a line in the Pacific Northwest will use tilting trains from Patentes Talgo S.A. in Madrid, Spain, to move at up to 125 kilometers per hour - not exactly a high speed but still one that can reduce travel times significantly.
THE LITTLE PENDULUM
Engineers at Fiat designed their first tilting passenger trains nearly three decades ago. The trains are called Pendolino, or "little pendulum," because they automatically tilt the passenger cars by means of hydraulic or electromechanical tilt actuators - depending on operational requirements - connected to the wheel assemblies, or bogies, when negotiating curves at any speed. This system always positions the coaches in their optimal position.
"Only minimal modification of existing train tracks is required to accommodate the Pendolino," said Andrea Mazzotto, an economist and manager of export sales at Fiat. These changes mean ramping the outer rail progressively higher so the Pendolino's instruments can sense a curve better, and installing a signaling system that will alert drivers when they are moving faster than the top speed of 250 kilometers per hour. Even with these minor changes, the cost of using tilting trains for fast rail travel on existing tracks is significantly less - one estimate is 10 times less - than purchasing new high-speed trains and building dedicated tracks. In addition, the existing tracks can still be used for nontilting rolling stock.
The Pendolino actuators are controlled by a computer that receives signals from an accelerometer placed on the lead car to measures lateral acceleration going into the curve. A gyroscope, also on the lead car, confirms that acceleration is caused by a curve, according to Mazzotto, and not by the realignment of the train such as from an irregularity in the track.
Fiat engineers designed the Pendolino active tilting system to automatically lean the body shell of passenger cars by a maximum 8 degrees toward the inside of curves, so the Pendolino can compensate up to 1.35 meters per square second of the centrifugal acceleration felt by passengers. This permits a Pendolino to run with accelerations of 1.8 to 2 meters per square second and still remain well within the limits of comfort, determined by railway engineers to be 0.8 to 1 meters per square second. As a result, the train can negotiate curves at up to full speed, which is 35 to 45 percent faster than conventional trains without any effect on the quality of the ride.
A key feature of the Pendolino's system is its active lateral suspension. This particular device is fed by the signals coming from the accelerometers and compensates lateral accelerations due to track irregularities instantaneously, increasing running comfort.
The trains derive their performance from their modular bogie, control and auxiliary systems, suspensions, and lightweight double-skin cars made of extruded aluminum (requiring only longitudinal welds). The tilting system is mounted under the car's body to preserve the space in the vestibules and passenger compartments. Both the primary and secondary suspension of the bogie are helical to ensure protection against derailment.
The bogie frame, suspensions, and axles of the carrying and motor bogies are interchangeable; the sole exception is the motor or driving axle in the motor bogie, on which the final drive is mounted. The traction motors of the Pendolino are located under the body and connected to the reducer by a cardan shaft, which transmits power from the motor to the motor axle, to reduce the unsprung masses.
The Pendolino uses four-quadrant, converter/inverter traction equipment powered by a catenary 25-kilovolt, 50-hertz voltage that is supplied by eight three-phase, 500-kilowatt ac motors. Thyristors made by another Fiat subsidiary, Parizzi S.p.A. in Milan, Italy, supply the optimum energy needed by the train. The continuous power at the rim is 4,000 kilowatts to guarantee a maximum speed of 220 kilometers per hour.
The first Pendolino prototype, a single car, was produced in 1970. Tests were conducted from 1971 to 1973 on the serpentine route between the northwestern Italian towns of Trofarello and Asti as well as the high-speed line between Rome and Naples. The prototype exceeded speeds of 260 kilometers per hour and breezed through curves 15 to 30 percent faster than conventional operations.
These results were used for the first operational Pendolino, the ETR-401, a four-car train that served 120 first-class passengers. In this early design, a gyroscope and an accelerometer were located on each bogie, rather than on the lead car only, to measure the centrifugal forces in a curve. The Italian State Railways ran the train on the Rome-Ancona line from 1976 to 1985. based in part on test results from this period, in 1987 Fiat introduced the Pendolino ETR 450 high-speed tilting train, which used a gyroscope and accelerometer on the end cars to monitor curves. The tilting mechanism was electronically activated. Fiat engineers eliminated both rheostatic braking boxes on the roof of this model and anti-shimmy shock absorbers. The ETR 450, which can achieve 250 kilometers per hour, entered commercial service on the Milan-Rome line in 1988 and carried 220,000 passengers per year - a number that has increased tenfold today.
The latest generation of Pendolino train, the ETR 460, was introduced in 1993. This train carries up to 478 passengers at a top speed of 250 kilometers per hour. Each ETR 460 is made up of three traction units, each consisting of two motor cars and one trailer. These independent traction units provide equal power distribution to the motor cars, thereby ensuring electric-brake efficiency and reliability even at high speed. The mechanical braking system combines pneumatic cylinders on disk brakes and an antiskid system.
Fiat designed the ETR 460 bogies to distribute the low axle weight - an average 14 tons per axle - uniformly along the length of the train. The 2.7-meter wheel base of the bogies limits driving forces even on small bends of track. The bogies of the latest Pendolino house the hydraulic or electromechanical tilt actuators, leaving space inside the compartments to the passengers.
PARTNERS IN ADAPTATION
According to Mazzotto, the Pendolinos account for more than 70 percent of the tilting trains in service, in construction, or on order by rail authorities worldwide (except for Japan). Great Britain, the Czech Republic, Finland, Germany, Italy, Malaysia, Portugal, Slovenia, Spain, and Switzerland have chosen Pendolino tilting trains for their railways.
"Rather than buying into other rail companies," Mazzotto said, "we typically export the Pendolino technology by teaming up with local companies to design trains that fit that country's rail standards, level of crew training, and the local culture and taste." For example, Fiat has joined forces with Rautaruukki-Transtech in Oulu, Finland, to build a Finnish version of the ETR 460. The main design changes of the train: known as the S220, revolved around the Finnish climate. "This involved mechanically protecting the suspensions from ice and snow accumulation, and overpressurizing the traction compartments under the floor to keep dust, snow, and debris out," said Marzio Broda, an aeronautical engineer and manager for Fiat's sales to Britain. The S220 door profiles and steps are also heated to prevent ice from building up on them.
Designing the S220 project was a true technology transfer that benefited both Finland and Italy. "Before this project, Rautaruukki-Transtech only built railway wagons," Mazzotto said. "The company now manufactures large, extruded aluminum parts, and assembles electrical multiple units as well."
Fiat's 1 billion-pound contract with Virgin Rail, another example of such international partnerships, is the largest export deal for Pendolino. Together with local partner GEC Alsthom, Fiat will provide 54 Pendolino trains plus maintenance until May 2012. The British Pendolinos will traverse the West Coast Main Line, connecting London, Birmingham, Manchester, Liverpool, and Glasgow. "Twenty percent of the British live in those cities [plus] the towns directly on the route," Broda said.
With current train technology, the trip from London to Glasgow takes 5 hours 20 minutes. By 2002, a Pendolino will make the journey in 4 hours 20 minutes. Broda added that with a line upgrade program in 2005, it will complete the trip in 3 hours 50 minutes. The engineer remarked that Fiat is targeting its research on newer, lightweight materials and more-powerful motors to increase the speed and reduce the weight of the next-generation Pendolino even further.
THE TRAIN IN SPAIN
Like the Pendolinos, the trains designed by Patentes Talgo function like a pendulum when negotiating curves, able to reach speeds of up to 200 kilometers per hour. However, rather than actuators and the additional energy required by active tilting trains, the Talgo pendular train uses natural forces for its tilt.
Engineers raised the plane of support of their train's large diaphragm air springs well above the center of gravity of the coaches. They also positioned two cylindrical turrets over the head plates of the truck frames to raise the supporting level of the springs and act as the springs' auxiliary air reservoir. When a Talgo pendular train enters a curve, the higher placement of its springs creates a compressive force on the interior plane of the springs, tilting the train car to the inside of the curve by as much as 3.5 degrees. This reduces the affect of centrifugal force on the passengers.
In addition, the Talgo trains have one wheel set between each pair of cars to form a single articulated unit that provides each coach with a stable freedom of movement. Depending on the track layout, Talgo trains can cut travel times by up to 35 percent compared with conventional, nontilting trains, according to Gustavo Gonzalez, executive vice president and chief executive officer of U.S. subsidiary Talgo Inc. in Bellevue, Wash.
Patentes Talgo introduced its tilting trains into domestic service in Spain in 1980, with an international debut a year later. Currently, the trains are also used in Canada, France, Italy, Portugal, and Switzerland. In the United States, the Washington State Department of Transportation (WSDOT) in Olympia leased one Talgo in 1994 and another in 1996 to carry more than a half-million passengers between Seattle and Portland, Ore., as well as between Seattle and Vancouver, British Columbia. Amtrak and WSDOT have purchased four train sets to replace existing leased trains on daily Amtrak service on those routes as well as between Seattle and Eugene, Ore. Talgo will also assemble an additional train set in its Seattle facility. These trains - part of the first Amtrak/state agreement in the nation - will be partially constructed by Patentes Talgo and completed at a Pacifica Marine facility in Seattle.
Each new train will consist of two custom coaches with up to 26 seats, one care car, one dining car seating up to 30 passengers, six standard coaches with up to 36 seats each one service car, and one baggage car. Each car is approximately 44 feet long, about half as long as most Amtrak coaches, and will seat at least four people with wheelchairs. The trains are scheduled to enter service by the end of this year. The American subsidiary plans to market additional equipment in the United States.
The American Talgo trains will not exceed 126 kilometers per hour on the Pacific Northwest rail corridor for some time - the maximum according to federal regulations. Their ability to negotiate curves without slowing down is the key, according to Theresa Gren, a WSDOT rail communications specialist, reducing travel times between Seattle and Portland by 25 minutes without increasing maximum speeds limits or constructing track and grade crossing improvements.
The popularity of getting travelers to their destinations faster by rail is continuing unabated throughout the world, and will further the development of high-speed trains. The need to keep costs down and speeds up - using existing track in sometimes mountainous, often scenic regions - will prove to be the driving force behind tilting trains in the future.
RELATED ARTICLE: Leaning to Retrofit
Tilting trains are an alternative to pricey dedicated track for new high-speed trains, but their cost is still far from negligible. Retrofitting an active tilting system to existing rolling stock can provide an even less expensive option for fast train travel.
Waggonfabrik Talbot in Aachen, Germany, has developed the ContRoll active tilting system, which was installed in 1995 on a 25-year-old VT614 train operated by German Railways to test its retrofit applicability. Sintef Instrumentation in Oslo, Norway, supplied the electronic components for this first testing version of ContRoll. The system can be used for both high-speed trains and conventional railcars.
"The VT614 was originally designed to tilt approximately 4 degrees via air springs, but never operated as a tilting train," said Heiko Hofkamp, a mechanical engineer and project manager for Talbot's Bogie Department. "Talbot engineers retrofitted this train set with new bogies equipped with the hydraulic tilting cylinders that are connected by an antiroll bar."
The first passenger car of the VT614 is equipped with the gyroscopes and accelerometers needed to measure the lateral acceleration caused by entering a curve. These instruments send signals to a central computer that actuates the hydraulic cylinders with the aid of slave machines, tilting the cars to a maximum of 7 degrees. The retrofitted VT614 went through curves with a radius of 500 millimeters and maximum cant of 150 millimeters at 132 kilometers per hour, compared with 113 kilometers before ContRoll.
The retrofitted VT614, which was tested over a two-year period, now serves the Nuremberg area in southern Germany.
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|Title Annotation:||includes related article on Waggonfabrik Talbot's ContRoll active tilting system|
|Date:||Jun 1, 1998|
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