Intercity bus transportation got redefined with the entry of premium rear engine coaches like Volvo in the early 2000. They offered extremely comfortable travel, primarily attributed to location of engine at rear and extremely well built body with very low NVH – Noise, Vibrarion and Harshness characteristics and a great suspension. Towards the end of decade, Volvo offered a multi axle variant and was a huge success and at one point of time, passenger demand was so high that having multi axle in fleet had become more or less mandatory for an operator. Subsequently Mercedes Benz and Scania did launch their range of products and rest was history. Many first time travellers in these coaches enjoy the comfortable jouBut there are many misconceptions about these coaches and here we throw some light on them
Comfortable travel in these premium coaches were falsely attributed to monocoque construction. These coaches are actually semi-integral, which means, the body is neither fully integrated nor is just a bolt on like front engine bus.
There is a frame at front and rear and are called as front and rear module and the body is integrated, along with them through body structure. Since the wheel base area doens’t have any frame and is integrated only with structures, its called as semi integral.
These coaches doesn’t have automatic transmission but rather an Automated Manual Transmission. Volvo uses a 12 speed gear box and Scania uses a 8 speed gear box. They are precisely controlled in such a way that gear changing is smooth and passengers enjoy a great ride. In contrary, Volvo 8400 uses a ZF 6 speed fully automatic transmission.
Its a global thumb rule that city buses has fully automatic transmission and Intercity buses has automated manual transmission. In India the exception being Jan Bus, which has Leymatic transmission which is an AMT.
Liftable tag axle
Volvo B9R had pusher axle, while Merc and Scania has tag axles. None of these axles can be lifted like the ones we see in trucks. Both 31T and 37T rigid haul trucks has the option to lift the tag/pusher axles, infact they are automated and if the load is less they are lifted automatically.
But coaches don’t have that feature and the least possible is to reduce the air pressure in bellows axle, which Volvo is offering.
6×2 or 6×4
All these coaches are 6×2 and only the twin tyre rear axle is driven and other axles are dead axles. Since they aren’t designed to carry load and mostly will be operated within the GVW, they have only 6×2
Independent front suspension
The single point of differentiation that these coaches offer is comfortable front suspension and this is again mislead as independent front suspension. But reality is they are rigid axle and have traditional axle beam. But air bellows along with torsional beam and links ensures the suspension is very cushy.
The article is based on the products on offer in India only.