New lightweight Bus range

A great deal of thought and innovative design went into the new city bus, the Scania OmniCity, also known as the ‘Smiling bus’.

The design team at Scania brought together designers, engineers, operators, marketing specialists, purchase staff and production experts.

The task was to produce a city bus which was lighter, easier to manufacture and which contained fewer components than its predecessors. It also had to accommodate more passengers, have a uniformly low floor throughout the interior and it had to be easy to build in a number of different variants.

The bus was designed using CAD, including 3DCAD, IDEAS, DADS and ABACUS, and the solution was a modular structure based on aluminium, fibreglass reinforced plastics and glass.

The materials had to be durable, and easy to handle both in repairs and, above all, when the time came for re-use, recycling or scrapping. To that end all the plastics are marked to aid sorting and re-use.

These materials brought down the total weight – by as much as 600kg compared to the current MaxCi city bus – and increased passenger capacity, at the same time making it possible to give the bus an attractive body with plenty of graceful curves.

As far as possible standard components from Scania’s truck range have been used. In fact no less than 85% of the components are the same in both product segments.

A significant departure from traditional chassis-building, where the front and rear suspensions are linked to each other by a network of steel beams, has been made. The current bus range uses 45 different complete chassis, but this will be replaced with just seven main modules covering the needs of all models, including articulated versions. Even the components, such as frames, axle mountings and radiators are the same, fit in the same place and conform to the modular principle.

The traditional chassis is a thing of the past with the modular structure.

There are just two main modules – the front axle section and the rear axle section with the components needed for attachment to the bus.

There are a number of ways these sections can be combined so that the exact task for the bus to perform can be specified. Various door configurations can be specified for the front and rear sections, and the rear portion can be built with either a short or a long overhang – and with a choice of seats or a platform. Irrespective of the interior layout there is always a rear bench seat above the engine compartment.

FULL-LENGTH LOW-LEVEL FLOOR

The front axle is positioned low down to permit a low entrance and a generously wide centre aisle between the wheel housings. The wheel deflection angle is 52 deg.

The rear axle is a drop-centre axle which allows the same low level along the full length of the vehicle. It was developed in conjunction with the supplier, who had responsibility for the designing, calculating, and testing for the whole unit. Drive to the rear wheels is via a four-speed or five-speed gearbox.

The bus is equipped with all-round air suspension. It features ELC.

(electronic level control) which automatically and exactly keeps the bus to the pre-selected ride height irrespective of the on board load. At the same time it nullifies any tendency to roll. The system can also be used to lower the bus in various ways, such as totally, only at the front, only at the rear, on one side or the other. It can lower the bus a total of 120mm. In order to avoid a jerky ride in temporarily rough conditions, such as a pot hole, ELC imposes a built in 15sec delay. Scania says the bus never surprises the driver, not even in an emergency manoeuvre.

The entry step is low – just 320mm at the front door – and can be lowered all the way down to 230mm. A number of kneeling functions can be programmed in during building, such as full-side or front door only. In addition, the air suspension system is used to raise and lower the bus in a variety of functions at the driver’s command.

The floor area between the axles is entirely free of pedestals, there is no step at the rear door, and the seats are wall-mounted to aid cleaning – a modification at the design stage, suggested by an operator, resulted in cleaning being made even easier.

Safety is a major consideration, and the braking system consists of an integrated retarder and ABS anti-lock disc brakes on all wheels, all designed to interact smoothly. The disc brake pneumatic system is activated by three separate circuits. In the event of an air leak in any one of the circuits, the line affected will shut down automatically. If the pressure drop is excessive, the driver will receive an audible buzzer warning.

Scanning sensors monitor brake wear so linings can be checked without removing the wheel. Once the lining are due for replacement the built-in indicators activate a lamp on the instrument panel.