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HYDRAULICS & PNEUMATICS FEATURE Although the trend towards smaller machines is ushering in a host of new benefits, it is


also bringing a number of pertinent challenges. For instance, while design engineers must increasingly face up to the task of minimising machine size to improve weight and efficiency, there can be no compromise in the power needed to get the job done. With this


thought in mind, machine designers must find ways to fit components with the right power into tight spaces. The following sets out a few considerations concerning hydraulic pumps that will help engineers to strike the right balance. Brent Schenk, global product manager for medium-duty, closed-circuit piston pumps at Eaton Corp, comments


The benefits of back-to-back hydraulic pumps


Hysteresis is a


phenomenon in which the value


S


ectors such as agriculture and construction appear to be spearheading the drive towards


ever-smaller machines, as designers look to reduce running costs (smaller, lighter machines consume less fuel) or fall in line with regulatory requirements on emissions. Whatever the prompt, machine size is a factor that today’s design engineers cannot ignore. The task for designers is two-fold, because


a smaller, more efficient, machine is only advantageous if there is no compromise in productivity. In short, machinery must remain agile and versatile around the construction site or farm, despite its ever decreasing size. Further demands of the latest machines


include ease-of-use, which helps new operators get up to speed quicker, while smooth, precise movements are also desirable as they contribute to a straightforward driving experience. In addition, it is advisable for operators of industrial or mobile machines to give careful consideration to reliability. Of course, performance and reliability


are only as good as the selected build components. A case in point is the machine’s hydraulic servo pump.


THE RIGHT PUMP Servo pumps in back-to-back configuration allow operators to improve machine efficiency. These pump types are available in an extended range of useful sizes and offer both precision and repeatability. Back-to-back pumps can help overcome


hysteresis, for instance, which plagues many who rely on fluid power in mobile and industrial equipment.


of a physical property lags behind changes in the effect causing it. In hydraulic systems, hysteresis is an error that occurs due to a previous input, typically where effects such as drag and friction in the different interfaces of a control loop lead to unwanted variation. Such interfaces might include control pistons, servo valves, mechanical feedback links, rotating pumps, swash plates and swash feedback valves, for example. The effects of hysteresis may appear small,


but they are often sufficient to change the output flow of a hydraulic pump. In such instances, compensation by the operator would involve adjusting the input command to achieve the desired flow. Although historically seen as a


mere nuisance that machine operators must accept, hysteresis is often costly in terms of lost production time, efficiency and reliability. This undesirable effect can greatly degrade a machine’s precision, making it more difficult to operate, particularly for those with fewer skills. As these factors become more important for operators, many have reconsidered their machine requirements in order to improve their bottom line.


BACK-TO-BACK Today’s back-to-back pumps can assist designers in reducing hysteresis (and compatibility with programmable controllers)


/ DESIGNSOLUTIONS


through the provision of current to the solenoid valves. This current forces the controller (via a swash feedback sensor in the pump) to minimise the difference between the existing and desired positions. Notably, it is possible to let the controller dynamically adjust solenoid valve current based on working conditions as the swash feedback sensor is able to circumvent the origin of mechanical friction. This capability reduces the pump’s hysteresis and makes other control options possible. It is also worth highlighting that the pump


and controls can create a compact propel solution with better resulting precision when paired with a cartridge motor. Importantly, back-to-back pumps can be


equipped with roller bearings rather than conventional journal bearings, while swash roller bearings further reduce machine wear and hysteresis to reduce maintenance and increase productivity. The latest innovation


from Eaton in this technology area is the new X3 back-to-back pump (also available as a single pump solution). With


best-in-class hysteresis and the


market’s smallest package size, Eaton’s X3 helps machine designers to overcome the challenges discussed in this article. Of particular note, the compact dimensional envelope makes it easier for design engineers to fit the pump into smaller machines, a key attribute given the current direction of the construction and agricultural equipment markets.


Eaton Eaton.com/X3 DESIGN SOLUTIONS | JUNE 2021 35 Eaton.com


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