Increased traction and startability and lower tyre wear are just a few benefits of a fully automatic transmission that have helped deliver improved vehicle productivity and reliability at a number of mines in Scotland.
Millbrook, UK – Fully automatic transmissions have much to offer to help the open cast mining operation achieve productivity and fuel-efficiency goals. Torque convertor transmissions provide additional advanced technical features to optimise fuel savings and prolong vehicle and component longevity in an arduous application that demands reliability. One company that has improved reliability and productivity from working closely, not only with the vehicle manufacturer, but also the transmission supplier, is Scottish Coal, which operates a fleet of Allison Transmission-equipped Terex dump trucks.
From nine sites across Scotland, Scottish Coal (part of the Scottish Resources Group (SRG)) provided over 3 million tonnes of coal to the UK’s major power generators in 2011. With a group-wide fleet of 35 excavators and more than 120 dump trucks, all of its mineral extraction uses surface mining techniques. Scottish Coal has been using Terex TR100 rigid dump trucks for several years and currently has 44 of the models working on three sites in what is known as the Central Valley, which runs from Dalmellington (East Ayrshire) in the south west to Glenrothes/Leven (Fife) in the north east.
“The TR100s are on the go for over 22 hours per day, five days per week, shifting 100 tonne payloads (40 to 50 m3 of overburden) in the harshest conditions,” says Andrew Foster, Managing Director of Scottish Coal. “The environment is ever-changing thanks to the unpredictable Scottish weather often bringing rain, snow and very slippery conditions. The site terrain is often rocky and abrasive due to the nature of coal and overburden and with long, steep gradients on haul roads, conditions are tough. Therefore we need a transmission that is reliable, durable and can stand up to what is thrown at it.
“Traction, to avoid slipping is one of the key benefits of the fully automatic transmission, especially as the TR100 drives the four rear wheels” Allison’s patented torque converter – the TC 890 in this case – multiples torque and delivers engine power directly to the wheels in a precise manner according to the load and ground conditions (whether that be dirt, mud, sand or gravel) while providing smooth, effortless shifting.
“We have always worked very closely with the equipment manufacturers to develop machinery to suit our exact needs and that will improve productivity,” continues Foster. “Liaising with Terex and Allison Transmission has delivered great results for us. For example, we have been working with Allison’s technical department in the UK on driveline improvements, creating a set-up specific to the duty cycle of specific trucks on site. The calibration on the transmissions has been tuned to optimise the shift patterns and tune the shift hysteresis.”
Lower tyre wear
Fully automatic transmissions are renowned for their ability to reduce wear and tear on brakes and driveline components, but increasingly they are cited as a tool to reduce the rising cost of tyres, as Foster explains: “At over £6,000 each, tyres are an incredible expense. By stopping the four rear wheels from sticking and spinning, the transmission helps slow the process of tyre wear.”
Better ‘startability’ even across gradients
In arduous, off-highway applications the consensus is that fully automatics provide more effective ‘rim pull’; where the wheel engages with the soil, wheel slip is reduced and the vehicle can pull away smoothly.
Often only the 1st gear ratio is used to judge a vehicle’s capability to launch and pull a load. The truth is that one has to consider the engine torque at the required launch rpm and torque multiplication of the torque converter. Manual and automated manual transmissions have to launch at very low engine rpm in order to prevent damage to the clutch. This means less torque available, which is why they have very ‘deep’ 1st gear ratios to help them overcome their clutch limitations. An Allison automatic uses the full torque from the engine and multiplies it with the torque converter. Thus, when the 1st gear ratio and rear axle ratio are factored in, the Allison often provides greater startability.
“To help get the best vehicle efficiency, we specify optimum gear ratios matched to the likely gradients on site. To assist with this, as a rule, we try and shape the sites so that the trucks do not have to encounter more than 10 percent gradients,” says Foster.
Rising productivity and fuel efficiency
Fuel is a major cost in mining operations of course, accounting for around 30 to 40 percent of operating cost at Scottish Coal. However, low fuel consumption should not be confused with fuel efficiency. It is important to evaluate efficiency as saving time on routes, leading to greater productivity and to getting more work done per litre of fuel. With full power shifts, fully automatic transmissions not only accelerate faster, they get up to and work within the duty cycle speeds faster and more efficiently.
Fuel efficiency can also be improved off-vehicle and is another area where Allison assists its customers to make the most of its products. This includes not only maintenance but also about the driver itself. “Driver training is a big element of reducing fuel consumption. We monitor drivers and invest a lot in software that increases the amount of information fed back from the machinery, so that we can make improvements,” says Foster of Scottish Coal.
A maintenance plan to minimise vehicle downtime and extend vehicle life
The Scottish Coal / Terex / Allison Transmission team is continuously collaborating to extend vehicle life and increase transmission service intervals.
“At about 9,000 hours, the transmission undergoes a precautionary rebuild by Allison’s approved UK and Ireland distributor, Mitchells Powersystems which has eight UK locations, including one relatively close by, in Glasgow. Here, the bearings, clutch packs and seals are replaced; the pinions and gears are inspected and replaced if necessary. Dye penetrant inspection techniques are applied to all the main drive shafts, gear carriers and pinions.
The team has been undertaking extensive trials with Allison’s Transynd, a purely synthetic, TES 295-certified oil developed by Allison and Castrol. When used in combination with Allison’s genuine high capacity oil filters, service intervals for dump trucks such as these can be extended.
While most vehicles are purchased for specific vocational use, they are not always specified to fit their particular operating conditions and this is where a three-party approach, involving the end user, the equipment manufacturer and the transmissions supplier, can create an optimal solution. As a supplier of a non-proprietary product, Allison transmissions are designed from the start to be easily integrated into a variety of customers’ trucks, making them simpler and more cost-effective to repair and maintain. Supplying OEMs and end-users around the world across vocations, the company has an immense library of mission profiles it can use as knowledge when fine-tuning driveline calibrations.
Another important benefit of modern advanced fully automatics is that their extended torque ranges and higher GVW capacities allow customers to specify a wider array of engine options. By making full use of the engine’s horsepower, an Allison automatic may allow surface mining operators to specify a smaller engine, saving money in capital expenditure, fuel and maintenance costs.