Wheelset designs Railway gauge The gauge is the distance between the two wheel flanges, corresponding to the distance between the inner sides of the rails. Examples of widely used railway gauges: • standard gauge 1 435 mm (4 ft. 8 1/2 in.), comprises around 60% of total world track length • broad gauges, which are larger than standard gauge e.g. Russian broad gauge 1 520 mm (17%), Indian broad gauge 1 665 mm (5 ft. 6 in.) and Iberian broad gauge 1 668 mm (5 ft. 5 2⁄3 in.), together comprise 9% of total world track length • narrow gauges, which are smaller than standard gauge e.g. Meter gauge 1 000 mm (7%) and 1 067 mm (3 ft. 6 in.) Cape gauge, comprise 9% of total world track length Bogie designs for the standard gauge are in some cases adapted for broad gauge vehicles and vice versa. Standard gauge bogie designs can be used in some cases as a basis for redesigning it for narrow gauge vehicles, which then have to be mostly equipped with other bearing designs. Gauge Railway gauge measurement principle Axleload The permissible axleload is determined by bridges, roadbed and track design, such as load carrying capacity / weight of the rails, size and frequency of the sleepers, quantity and type of ballast, and depth of formation. On sharp curves, the frequency of sleepers often needs to be increased. Common axleloads are: • light metros: 14 t • high-speed vehicles: 17 t (for new generations) • heavy metros and multiple units: 18 t • locomotives and freight cars: up to 25 t • heavy haul freight cars: 32 t up to 40 t The axleload is calculated by: Vehicle weight + cargo or passenger load Axleload =————————————————— Number of axles The railway vehicle net weight includes the operating supplies like sand and for diesel powered vehicles a fully fuelled tank. The cargo refers to the payload of goods. The passenger load can be calculated by counting the number of seats plus, especially for mass transit vehicles, the number of standing persons. There are very different calculations applied, from 4 to 10 persons per m² and 70 or 80 kg average weight per person (with/without luggage) see prEN 15663:2007 Railway applications – Vehicle Mass definition. Further calculation methods are mentioned in specific standards and in customer specifications as well. Multiple units and articulated vehicles are designed mostly by applying powered and non-powered bogies. Different axleloads have to be considered
Wheel diameter Different wheel diameters are considered such as for new wheels, worn wheels or a medium dimension for half-worn wheels. This wheel diameter is mostly used for calculating the bearing rating life, which is a linear function of the wheel diameter. However, the wheel diameter influences the impact of dynamic forces acting on the axlebox bearings, especially by applying smaller wheels. Some examples of current wheel diameters: • high-speed vehicles, multiple units and passenger coaches: 750 to 950 mm • locomotives: 1 000 to 1 300 mm • freight cars: 900 to 1 000 mm • piggyback wagons: 350 to 450 mm (carrying trailers, semi-trailers or containers – intermodal freight transport) Wheelset arrangements In most cases, axle box housings are situated on the axle ends. Some vehicles, such as light rail vehicles, have inboard axleboxes that are situated between the wheels because of space limitations. Inboard bearing railway bogie designs have a potential for mass saving opportunities. However, there are a few applications where special axlebox bearing designs are needed. The dynamic forces acting on an inboard axlebox bearing can be heavier compared to outboard applications. The smaller support base of inboard bogie frames could cause more rolling of the vehicle body. Independent wheels Low-floor mass transit vehicles like tramways are equipped with special wheel arrangements to cope with limited available space. One design principle is the axlebridge design, which consists of a highly sophisticated cranked bridge covering the traditional axle function and two independent wheels fitted with the axlebox bearing units († page 58). The hub traction motor concept is based on a direct drive system with an integrated wheel function. Today, very different design principles are applied. One of these is a traction motor design that directly powers the wheel and wheelsets acts as wheel support and guidance without any gearbox or coupling components. The outside rotor directly powers the rubber spring-suspended wheel tyre. This space saving arrangement is especially suitable for 100% low-floor tramways, which have a plain floor without any steps or ramps.
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