Hydraulic system developers are moving on many different fronts as they strive to improve performance and efficiency. A full-system approach that includes more sensors and advanced controls is helping design teams reduce component counts without sacrificing performance.
The multifaceted design challenges of today’s equipment are forcing engineers to take a broad view of the vehicle and its systems in order to get the most from valves, electronics, pumps and other equipment. Customer expectations and regulatory requirements are both rising, forcing engineers and planners to examine every element of a design.
“As the machine has more complexity in the system design, the requirements for the components to work together or be integrated to perform functions reliably and safely have increased,” said Terry Hershberger, director, sales product management, at Bosch Rexroth Corp. “ISO13849 standards and functional safety requirements push one to look at the machine holistically into what constitutes state-of-the-art design and ensure that the machine will perform the intended function in a safe and reliable way.”
Many elements of hydraulic systems are being refined to maximize efficiency. Danfoss Power Solutions recently rolled out segmented intelligent flow sharing, which combines proportional valves and electric controls on the pump. It offers three control modes. One is for very fine control when the pump is operating at a constant supply pressure. The second mode is designed for single operation, fast commands. The valve is commanded to fully open and the pump’s displacement control is used to manage the speed of the attachment. Finally, the third mode is for when multiple functions are commanded.
“In this mode, the benefits of pre-compensated load sense control are available while achieving the flow sharing characteristics of typical post-compensated hydraulic systems,” said Aaron Becker, market development manager at Danfoss Power Solutions. “In combination, this system provides extremely precise control during fine movements and minimized pressure drop and power loss during rapid movements, while also demonstrating the expected behavior of classic compensated load sense hydraulics.”
Sensors have become an important element in most system designs. Motion, pressure, temperature and other parameters can be precisely measured by solid-state sensors, improving precision and efficiency. Adding redundant sensors can also help the complete machine meet ISO13849 functional safety guidelines.
“More and more sensors are being placed on machines to not only provide information to the machine operator but as well to the owner or the fleet manager,” Hershberger said. “Much of this information is not only for showing the current status of the machine, but also for evaluating the loads and duty cycles of the machine in forecasting the health or life of machine components.”
Electronic control designs are also evolving. Often, control units are being integrated into hydraulic components. That trims size while also improving performance.
“Because controls are now integrated on the valve or the pump, there are fewer parts in the overall system,” Becker said. “Plus, the integration also allows for more control. For example, with integrated electrohydraulic controls our PVE actuators have an internally closed feedback loop, yielding higher levels of capability and precision. This can provide more predictable movement when initiating from a static condition and can reduce machine calibration complexity and time required.”
Implementing advanced electronics and taking a holistic view of the design can bring significant benefits. Danfoss eliminated a single pump in the all-wheel ground drive system of an agricultural sprayer. It uses one pump and four variable displacement motors, instead of the conventional tandem pump found on most four-wheel drive systems.
“By using electrohydraulic controls and sensing the input and individual wheel speeds, we are able to reduce the number of pumping units necessary for the system,” Becker said. “Now you can go from two pumps to one pump, and you can implement true active traction control at the wheels. This is especially beneficial when working in poor ground conditions.”Continue reading »