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The following is reproduced from a booklet titled "Advanced Passenger Train". |
The Advanced Passenger Train (APT) is designed to provide a cost effective solution to the problem of providing fast inter-urban transport on existing tracks, in both financial and energy consumption terms.
BR's APT originated in 1967 as a by-product of several years fundamental research into dynamic behaviour of railway vehicles. The new understanding of the interactions between vehicle and track enabled the technical potential of railways to be re-appraised and the economic feasibility of passenger travel of high speeds recognised.
The major attractions to inter-city passengers are shorter journey times and comfort. Average speeds are currently limited by restrictions on curves. The major objective of APT, therefore, is to raise operating speeds round curves by typically 20 to 40%, so enabling a high maximum speed of up to 250 km/h, to also result in a high average speed. Passenger comfort is maintained by tilting each vehicle body inwards by up to 9° on curves. Other objectives are low energy consumption, low noise generation, low track maintenance and a similar total cost per seat-kilometre as present day trains.
Initially, APT will be used on the electrified West Coast main line. Three prototype trains (APT-P) are now being built by British Rail Engineering Ltd. These each consist of two power cars and 12 coaches. Following extensive proving trials, the trains will enter commercial service in May 1979, to give a journey time of around 4 hours between London and Glasgow, initially at a maximum speed of 200 km/h.
The prototypes are the forerunners of a fleet of production APTs planned to start operation in 1982. These will each consist of one power car with up to 11 coaches.
At high speeds, the major source of train resistance is aerodynamic drag, which increases as speed-squared. Consequently, the energy and power used in traction tend to rise rapidly as operating speeds are increased.
Although train weight has only a small effect on energy consumption at constant speed on level track, its effects are important when climbing hills and during accelerating and braking. Train weight influences particularly the number of powered axles, and hence the amount of power equipment required for operation at acceptable adhesion levels.
For economic performance, therefore, a streamlined low-drag profile has been adopted for APTs together with lightweight construction. Since the effect of acceleration rate on Inter-City journey times is of secondary importance, only sufficient power is installed to give a train balancing speed on level track about 5% above the maximum operating speed.
The low aerodynamic drag of APT results from its nose and tail shape, its reduced cross-section, including lower roof height, and its general surface smoothness. Further drag, weight, and cost reductions are achieved by using an articulated formation with bogies shared between coaches.
The braking system for APT is designed to stop the train within existing signalling distances. Hydrokinetic (water turbine) brakes are used to meet the arduous braking duty, being capable of dealing with very high levels of energy and power dissipation.
APT vehicles tilt by up to 9° on curves. The requirement to stay within the BR loading gauge leads to their characteristic shape.
Each vehicle is tilted individually by hydraulic jacks mounted within the bogies. Power for the jacks is provided by a hydraulic power pack mounted below the vehicle floor. Tilting is controlled by an electronic box that measures the lateral acceleration of the bolster. This measurement is made by a "spirit level" accelerometer in which the position of the bubble is sensed by electrical connections. The tilt system design permits the vehicle body to adopt an upright position in the event of hydraulic system failure.
The 25 kV electric APT comprises two rakes of articulated trailer cars between which are positioned one or two power cars. Each trailer rake consists of a number of two-axle intermediate cars and two three-axle end cars. Each power car has four axles. Power cars and trailer rakes are easily uncoupled from each other in order to satisfy operating and maintenance requirements.
The train can be formed into alternative versions. The 200 km/h (1+11) low-powered version, with 11 trailer cars, represents the longest train that can be hauled by a single power car. The 250 km/h (2+12) high-powered version, with 14 vehicles total, is the longest train which can be accommodated within the existing platform lengths.
The train configuration, with power car positioned in the middle, has been adopted for two main reasons. Firstly, power cars cannot be positioned at the two ends of the train because current collection at 200 km/h with two pantographs is unlikely to be satisfactory with the existing overhead equipment. Secondly, two power cars cannot be positioned at one end of the train otherwise excessive buckling forces would be generated when pushing.
Communication between the two trailer rakes will normally be available to staff only, via a corridor through the power car. Passengers will be permitted access only in emergencies and when escorted by a member of staff. To minimise this disadvantage, each rake of trailer cars will be self-contained, incorporating both first-class and second-class accommodation and catering facilities. First-class accommodation will be in the middle of the train and second-class towards the ends, the division being marked by the intermediate catering car. The catering unit will provide full meals for first-class passengers in their seats and a buffet service for all passengers.
The APT-P power car is a steel semi-monocoque structure with deep side skirts, its construction meets UIC load requirements and dynamic stiffness demands.
It houses thyristor controlled ASEA power equipment with transmission via cardan shaft from body mounted motor and gearbox, then quill drive to wheelset. Power cars are equipped with anti-tilt mechanism to ensure that the pantograph is maintained central and level during body tilting.
Trailer cars are arranged in identical rakes each side of the power cars. Three basic types of vehicle are required to make up each rake, namely driving, intermediate and van trailer cars.
Lightweight vehicles are required not only for low total train mass, but also for acceptable axle loads, especially on articulated axles. To meet the mass targets, APT trailer car bodyshells are constructed in aluminium alloy, giving a 40% weight saving over a conventional steel coach.
The vehicle structures are designed to meet the International loading specifications for main-line coaches, including the 200 tonnes proof buffing load. The dominant design criterion tends to he stiffness rather than strength, as high flexural natural frequencies are essential for good ride quality at high speed.
APT vehicles are already emerging from BREL and the first power car has been handed over to CM & EE for commissioning and testing. A power car test train has been formed, hauled by an HST (Class 252) prototype power car. This train is presently undergoing initial brake and tilt systems testing in the Derby area, operating under diesel power only. Good progress is also being made on trailer vehicle production and a trailer rake test train will be formed in December with 3 or 6 APT trailer vehicles, also hauled by an HST prototype power car.
Early in 1978, the first APT will begin running on the Scottish Region, this will be regarded as the engineering test train and used initially for testing and commissioning purposes between Glasgow and Carlisle.
Two more trains will be produced each with two power cars and twelve trailer cars about August and November 1978. These, after brief commissioning periods, will be made available for driver training in the Scottish and London Midland Regions before entering conventional services between Glasgow and Euston in October 1978 and February 1979. Commercial service at APT timings, with two trains and one on standby, is planned to commence in May 1979.
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