Meeting demands

Mining and quarrying equipment, amphibious and multi-terrain vehicles and water taxis all have one thing in common when it comes to power transmissions — strength, durability and the capability to handle high power and torque in demanding environments.

The world’s highest capacity mobile sizing station, in Australia, features four power transmission gear units. Manufactured by world leader in mineral sizers, MMD of Derbyshire, the station can process over 10,000 tonnes/hr of overburden — the excess material removed when extracting minerals — and can rotate through 270º.

It has a slewing discharge conveyor and an apron plate feeder, which can be raised when the unit is moving. The whole unit weighs 1,760 tonnes, and its slewing conveyor is mounted on a turntable. The unit is also mounted on tracks, which allow it to move in conjunction with the large rope shovel feeding the unit. This, in turn, discharges on to a belt conveyor system.

Flender Power Transmission supplied four of its FZG bevel helical gear units — two for the apron plate feeder drive, one for the transfer conveyor drive, and one for the discharge conveyor drive. It was important to MMD that all components on the massive station could be bolted together, rather than attached to a central frame, so that everything could be separately transported by road.

The apron plate feeder drives — shaft-mounted with shrink discs and fitted with flexible input couplings —comprise the gear units. There are special sealing arrangements on the input and output shafts, and the units are mounted on bedframes with motors. Also mounted on each bedframe is an airblast oil cooler, and each of these two assemblies weighs more than 25 tonnes, excluding motors.

The one-off unit for the transfer conveyor drive consists of the bevel helical unit, shaft-mounted with shrink disc and fitted with a flexible input coupling. There is a special sealing arrangement on the input/output shafts, and the unit is mounted on a bedframe with motor.

On water the demands are no less challenging. Yorkshire-based power transmissions specialist Centa Transmissions has helped amphibious vehicle producer Covelink Marine to create the new Roylecraft Amphibious Jet Bus. Centa was called in to solve an intrusive noise and vibration problem in the 12m-long craft.

The Jet Bus is powered by a single diesel engine from which a number of drives are configured to power the main waterjet and the road wheels, as well as various smaller operations throughout the vehicle.

To achieve its on-road target speed of 62 mph and 30 knots on water, the vibration and noise emanating from the transmission was a major problem and had to be resolved.

Also, any solution had to address and overcome the complexities caused by the amphibious nature of the vehicle. And as a passenger-carrying vehicle, any transmission noise and vibration needed to be removed for passenger comfort and the elimination of wider environmental noise pollution.

The problem was overcome by using the Centax CX-16VFA coupling to isolate the torsional vibrations of the diesel engine from the driveline.

High torsional vibrations in the driveline ‘ring’ the thin wall-section of a cardan shaft and create ‘rumbling’ noise in the gearboxes, which generally reduce the life of the entire transmission.

The coupling also supports the cardan shaft it protects, providing a dynamically stable driveline at an economical cost. As in many marine drive situations, space was at a premium and to overcome this the design used a minimum length coupling.

Another amphibious multi-terrain tracked vehicle under development by Aris of Italy is the Aris Ark, designed to fulfil disaster relief and defence support roles. The vehicle — designed to handle a five-tonne payload on land and four tonnes in water — employs David Brown gear technology within its tracked drive system and to transfer power to hydraulic pumps in the marine propulsion system.

The Ark employs a fully-automated gearbox and power take-off linked to the vehicle’s 300bhp diesel engine. Based on the chassis of a logistic vehicle derived from the widely-used M113 armoured personnel carrier, the Ark is fully amphibious, providing great flexibility for flood relief roles, where it is capable of tackling the toughest terrain and the roughest seas.

The vehicle has a tilting bow to stabilise it in the water, an aluminium hull with waterproofed engine compartment and a sealed electric system.

Two stern ducts each incorporate a hydrostatically driven propeller operated through the specially-designed and developed power take-off (PTO), which is capable of transferring the full engine power by the engagement of a multiplate clutch fitted within the PTO.

On land the vehicle uses an innovative rubber track system. David Brown and Aris are also looking at incorporating the new transmission system into Aris amphibious vehicles for military and civil protection uses.

More sedate, but no less taxing, was the Venice Water Taxi that required an automatic marine gearbox to reduce boat creep speed and minimise damaging wash while manoeuvring in congested or restricted waterways.

The Newage Transmissions StepDrive two-speed unit is installed in a 9m craft powered by a Volvo Penta AD 41 engine and will undergo extensive trials in the city’s canal network over coming months. By providing an additional reduction ratio of around 25 per cent it claims to significantly increase propeller efficiencies at low speed.

As a result, fuel economy and boat handling characteristics are greatly improved, while emissions and noise are reduced.
In parallel, the capability to boost boat performance by around 20 per cent will minimise travelling times between stops, as well as significantly reduce journeys from the centre of Venice to the Lagoon or International Airport.

The gearbox has been designed both for use with turbocharged engines such as Volvo Penta AD31 and 41 series, as well as supercharged units up to the KAD 44.

During acceleration, it automatically changes from low to high gear at a pre-determined engine speed, which is optimised to the individual boat and engine combination. When the boat slows again, low gear is engaged as the engine speed falls below 1,500 rev/min.