Software drives hardware improvements

The design of many mechanical systems is reaching a stage where significant improvements are getting harder to find. Further improvement of many systems is now more likely to come from intelligent software that will allow precise control and optimised operation of the mechanical components based on demand. For power transmission, this is exactly what Allison Transmission is looking to develop. For many years, epicyclic planetary automatic transmissions have used fairly generalised operating profiles, allowing a single platform to cope with a wide variety of vehicles, duty cycles and driving styles. While these have a certain amount of natural efficiency over varying conditions, it does leave scope for further improvement. Optimising a transmission for a specific 'mission profile' can yield significant savings in fuel economy, but the technology has the potential to bring numerous other benefits. "Think about a vehicle running in an operation. You generally simplify this to four phases of the duty cycle; accelerate, cruise, decelerate and stop," says Manlio Alvaro of Allison Transmission. "We use electronics that optimise the operation of the vehicle in each of these phases. We have the ability to adjust a range of parameters to optimise a transmission for an engine, vehicle, duty cycle, the terrain or even minimise the inefficiencies caused by poorly trained drivers." Allison has developed a system called load-based shift scheduling (LBSS) that automatically switches in real time from gearshifts that optimise fuel economy to shifts that deliver more power. By diagnosing the load of the vehicle as well as the topography of the route – i.e. on road, off-road, uphill, downhill – the system will automatically select the best operating profile. Another feature that is also becoming popular in numerous applications is vehicle acceleration control (VAC). This uses the engine control unit (ECU) to limit the torque of the engine to make sure that the vehicle always stays within a certain range or within a specific acceleration profile. The results are predetermined smooth acceleration curves for either duty cycle or fuel efficiency benefits. Testing on a known bus duty cycle suggests a 3% improvement in fuel economy is possible. "For obvious reasons this is subject to load and topography," says Alvaro. "This actually changes the acceleration profile of the vehicle, limiting torque and power of the engine. If the vehicle is fully loaded it will require more torque to move up an off-road hill than when it is completely unloaded on a flat road." The principle behind this technology is to bring the engine speed down to the lowest rpm without adversely affecting performance. Using a suite of sensors, control systems and proprietary algorithms the transmission is essentially in control of the engine's torque output. Much of the data needed to optimise a transmission for a given profile comes from the experience of the fleet operators, which often have a database of typical duty cycles. Allison also collaborates closely with engine manufacturers and OEMs to optimise transmissions for particular vehicles. Using software so heavily to control in real-time the engine output and gearshifts opens up the ability to record data and engine performance. Prognostic systems have now also been integrated in to the transmission systems to help with maintenance. At any point, the status of the oil, filters, operating time, output revolutions and shift density can be seen to help with planning maintenance schedules. The message to design engineers at large is that many mechanical systems are reaching a level whereby technical possibility and further gains in efficiency and operating proficiency are likely to be yielded from precise control and clever algorithms. That means designing mechanical components that naturally lend themselves to this level of control is likely to become a much more important aspect of mechanical product development in the future.