Challenging conventional views

There are many methods of transmitting and storing power, all of which have pros and cons, depending on the application. But many of the accepted norms are being challenged as new ways of doing things gradually evolve into better ways of doing things thanks to improving technology. It is often the case that design engineers will choose technology that they have experience with. But always worth keeping an open mind and finding the best method of power transmission and energy storage for a given application. SKF project manager, Mike Naismith, says: "Design engineers should recognise that each technology has its own strength and weakness and that will vary depending on what the application is and what the end customer actually wants." Pneumatic actuation has long been used by machine builders as a preferred solution to providing actuation and movement. Pneumatics give excellent power availability in a relatively small space envelope. It is also simple, reliable and low cost. But it does have compromises such as energy loss, reduced accuracy and noise. The firms that have a traditional backbone in pneumatic actuation are not turning their backs on the technology. However many do feel that a transition towards an electric or hybrid solution is inevitable as industry looks to reduce energy consumption and improve accuracy, while maintaining good power availability. There is a trend beginning to emerge and many machine designers are increasingly assessing electrical actuation as a real alternative. But many machines need the power delivered by pneumatics and as attractive as increased accuracy is, can not compromise. This has led a number of companies that traditionally specialise in pneumatic actuation to look at developing hybrid systems. The idea is to combine the power of pneumatics with the accuracy of electric systems. Several companies are either increasing their offering of electronic actuation or are introducing hybrid systems. Both SKF, Festo and SMC have experimented with hybrid systems providing bespoke systems for customers. And these have either already become, or are soon likely to be, catalogue parts. And both have increased electric actuation equipment products. "An electromechanical option will still not fit every application," says Naismith. "There are likely to be applications that are done far better pneumatically, hydraulically or electically. It is a matter of application engineering the solution to fit what customers actually want to achieve and selecting the proffered technology for the job. "In terms of power on demand, accuracy and repeatability then this is done better electrically. But really high levels of thrust you go for hydraulics." Although full electric actuation is a more expensive option, it has dropped in price significantly in recent years. And through life cost is actually less than pneumatics. And while power availability is not yet at the same level as pneumatics, it is perfectly sufficient for many tasks and will give machines better accuracy and controllability of movement. High accuracy is becoming increasingly important for many machines as companies seek to improve build quality to add value to processes. Another area where the norm is being challenged is the aerospace industry. Hydraulic systems are used on aircraft as they are exceptionally reliable. It is a known and proven technology that is relatively low cost and simple. The downside is weight. Hydraulic pipework, motors and pumps are interwoven throughout aircraft and add a tremendous amount of weight. And the oil that is used can be difficult to manage. It is a messy business changing and maintaining hydraulic systems. Boeing and Airbus are both trying to shed weight from aircraft to improve fuel efficiency. The idea of electric systems is something both of the majors are assessing and developing, so all powered surfaces and controls are essentially actuated by electrically powered devices and not hydraulics. Although this may seem some way, with improved reliability and significant improvements to motor efficiency, it is something that is now actively being pursued with Airbus reportedly trialling all electric landing gear that is possible for inclusion on its A350. It is a technology that would certainly have inclusion on the next generation of single isle aircraft. And another area of potential change is in energy storage for automotive kinetic energy recovery systems (KERS). At present most hybrid technology in production, or close to it, is based around the use of batteries. These can be spread around a vehicle to help with weight distribution and can extend fuel efficiency by as much as 30%. However, the drawback is that battery packs are heavy; take up a lot of room and many feel that there is still a lot of room for improvement for battery technology. This has spurred the development of alternatives. The first, and perhaps most likely to be integrated on to mainstream vehicles, is a mechanical flywheel. Several systems have so far come to market and won accolades from the automotive world. Flybrid systems uses a flywheel that rotates at more than 60,000rpm in a sealed vacuum. The unit is small and can easily be integrated in to vehicles. And Ricardo recently announced it has developed a mechanical KERS called Kinergy, which avoids using a vacuum pump and is designed to achieve a 30% fuel reduction with a fitted cost of less than £1000. These products are very close to production with both Flybrid and Ricardo working closely with OEMs to get the technology in to production models and on the road. "Mechanical hybridisation using Kinergy based systems offers the prospect of enabling a wide range of energy management solutions including low-carbon vehicle powertrain for applications where electric hybridisation is not considered to be cost-effective," says Ricardo group technology director Neville Jackson. But there is a growing school of thought that hydraulics should actually be used as a vehicle KERS device. Hydraulic systems traditionally suffer from parasitic losses which account for up to 50% of the energy transmitted to be lost. But two companies claim to have overcome the problem and are claiming fuel savings of up to 50%. The first is motion and control technology specialist, Parker Hannifin, which announced it had developed a hydraulic hybrid system earlier this year. Don Washkewicz, chairman and president of Parker, says: "The commercial application of our technology is recognition that our system has demonstrated several unique advantages over electric hybrids including significantly better fuel efficiency." Field testing of the system during the past year has indicated that the system is capable of generating as much as a 50 to 70% increase in miles per gallon in 'stop and go' applications when compared with traditional diesel powered vehicles that have automatic transmissions. The second is from Artemis Intelligent Power (AIP) which has developed a clever digital displacement technology that eliminates most of the normal associated losses. Tests on a BMW 530i showed that fuel efficiency over a typical town drive cycle was improved by some 50%. And the company is now exploring the possibility of using the same technology on wind turbines and other renewables. As AIP's digital displacement technology is easily scalable, it can be used to smooth out the intermittent power generated by renewable energy sources. This is particularly apt for wind turbines and the company is currently trialling the technology in conjunction with the Carbon Trust. The technology is also being trialled with wave power generating device Pelamis. Waverley Cameron, Chairman of Artemis Intelligent Power says: "The Artemis Digital Displacement technology will provide cost effective solutions to some of the most challenging engineering problems facing the large scale deployment of offshore wind, wave and tidal power generation." Despite all preconceptions, power transmission and energy storage systems are evolving and are increasingly overlapping and finding new applications as new materials, bearing technology and control systems are used to optimise efficiency and minimise losses. And it is up to design engineers to find these applications, push the technological boundaries and make sure the best and most applicable system is always used.