The Hybrid Integrated Tank offers a cost-effective upgrade for mobile hydraulic systems.

Hydraulic tank systems for mobile equipment must be crafted to handle diverse and multifaceted requirements. OEMs often take a do-it-yourself approach: purchase individual components such as tanks, filters, connectors, breathers and oil level indicators, and mount these parts to get a complete assembly.

When demand is sizeable, hydraulic systems suppliers will often manufacture customer-specific tank systems with filters, valves and sensors built-in. Now ARGO-HYTOS GmbH, headquartered in Kraichtal, Germany, has developed the Hybrid Integrated Tank (HIT) that offers similar benefits for short production runs. The hybrid tank combines two manufacturing technologies, rotational molding and injection molding, and integrates all required tank functions into a complete module that is cost-effective even in small quantities.

Tank basics
According to Thomas Weiser, Head of Global R&D Filter & Systems, Fluid Management at ARGO-HYTOS, hydraulic tanks for mobile machinery are primarily made of welded steel or aluminum; or rotational- or blow-molded plastic. In addition, ARGO-HYTOS offers two interesting alternatives: plastic injection-molding and hybrid construction.

With injection-molded products, tank halves are welded together abrasion-free to form one tank volume. Advantages include lighter weight than metal options and high resistance to mechanical and thermal stresses. The corrosion-resistant materials minimize contamination in the tank and render reworking and cleaning processes prior to installation unnecessary.

Engineers systematically implement customer-specified functions during development. And the tank’s shape, as well as accessibility for maintenance and service, can be adapted to fit complex installation spaces. It results in highly integrated tank modules that exactly meet application demands. The tank systems are leak-tested and delivered ready-to-install, therefore reducing assembly times. In addition, the company’s Quick-Connect-System allows for fast, correct and safe hose mounting without tools. It features low mounting forces and fault detection through a safety clip. The clip engages only when the connector is completely pushed onto the port. Otherwise, the clip protrudes visibly and can be detected by touch.

Hybrid Integrated Tank
The Hybrid Integrated Tank was developed to provide the same advantages of injection-molded tank systems for machines that see lower production volumes. Manufacturing the HIT involves welding injection-molded connection parts to a rotational-molded tank. For example, the welded ports of the Quick-Connect-System facilitate simple and safe hose assembly. Likewise, mating the upper part of the filter housing to the tank reduces the number of components as the filter head, usually made of cast aluminum, is no longer needed. And with the housing now part of the tank, there are no sealing points and therefore no risk of leakage. Flexibility of the process ensures that even subsequent modifications, such as installing additional connections, are easily made.

Tank geometry can be adapted as required to meet OEM preferences thanks to customized rotational-mold tooling. Likewise, many application-specific provisions can be addressed, such as the type of hydraulic and electrical connections, tank mounting attachments, internal flow controls and filter-connection dimensions. A common-part strategy takes advantage of an existing family of modular components such as filter covers and Quick Connect fittings and, thus, does not result in any tooling costs to the customer. This guarantees that the design economically meets users’ needs while reducing the complexity for in-house material planning and production, said Weiser.

Advanced functions
The basic functions of any hydraulic tank are to store and supply fluid. The HIT does much more. For example, contamination control can be enhanced with one or more return, return-suction, suction and filling filters. Large flow cross-sections for suction and return ports ensure a compact installation height. Filter elements are available with copy-protection to avoid counterfeits and knock-offs. That ensures proper filtration performance and can safeguard the OEM’s spare parts business. Copy protection involves soft sealing of a lip seal against an oval-shape face.

In addition to oil cleanliness, good air-separation capabilities are essential. Especially in applications with high circulation rates – meaning short dwell times of the oil in the tank – various measures can improve separation efficiency. Inlets and outlets can be arranged and aligned such that there is no direct fluid exchange. Special-shape extrusions can also be added to influence flow and significantly increase the coalescence of air bubbles. A larger buoyancy force to surface area ratio speeds up air separation.

Due to the variable working volume, breathers are needed for ventilating hydraulic tanks. Different sizes and designs are available for the HIT. Breathers with integrated pre-load valves can be used, depending on requirements and specifications. The temporary excess pressure in the tank improves suction performance in certain operating conditions. Simulation tools are used in the early development stages for dimensioning of pre-loaded tanks, especially plastic ones.

Finally, common auxiliary functions are easily integrated into the HIT system. Oil level indicators, sight glasses, oil drain plugs and valves, protective filling screens, as well as cable brackets, can be included as needed to address an application.

Technical features
The rotational-molded HIT wall is made from oil-resistant polyamide (PA 6). Compared with the widely used rotational-molding material cross-linked polyethylene (XPE), parts made from PA 6 are recommended for the use in hydraulic fluids with temperatures up to 100°C, and with temporary excursions permissible to 120°C. The unit is also suitable for environmentally friendly hydraulic fluids such as HEES and HETG.

Fusibility of the material lets injection-molded parts be readily welded to the tank. Laser-welding, similar to infrared welding, is an abrasion-free joining process that does not generate dirt or debris. The flexibility of the laser-welding system permits various welding geometries on one tank, without needing to change tools or fixtures.

Effective sealing between filter cover or breather and the rotational-molded tank is possible due to a high-quality surface with minimal deformation. Slow and uniform cooling of the molded parts, as well as the use of cooling fixtures, reduces part deformation. Subsequent conditioning reduces internal stress and increases elongation properties. Once solidified, the PA 6 virtually mirrors the mold surface, and thus meets requirements for roughness and contact area for sealing with standard seals, such as O-rings.

The modular filtration system encompasses various elements in different lengths that can handle flow rates from 150 to 350 lpm. In addition to commonly used grades of fineness – 10 µm(c) and 16 µm(c) – special configurations are possible.

Hydraulics 4.0
The available scope of the HIT system makes it possible to quickly design customized tank systems to suit a large variety of applications, and help address the growing need for tanks that must fit ever-tighter and more-complex installation spaces.

Another industry trend is the move toward detailed monitoring of oil conditions. Sensor technology connecting the digital and real worlds is one of the most important elements of Industry 4.0. But incorporating sensor technology into hydraulic tanks has lagged behind that of other fluid power components.

In the past, only the pressure upstream of the filter and the temperature of the oil were typically measured. In order to meet future requirements, the HIT makes it possible to integrate or adapt a moisture sensor Lubcos H20+; a wear sensor OPCom FerroS (ferromagnetic particles in the oil); and a continuous level and temperature sensor, which reads the oil volume even in tanks with complex geometries. All three sensors are proven ARGO-HYTOS products.

With the integration, ARGO-HYTOS meets customers’ desire for a product which enables condition monitoring or predictive maintenance. The capabilities are buiIt-in, with no need for a subsequent, usually complex assembly of external sensors.
Networking of sensor data is not just about forwarding data to higher-level systems, said company officials, but also about the clever interaction of several sensors. The focus is on merging data from different sensors to increase detection performance and to better classify data. Thanks to the use of three sensors in the tank that monitor diverse characteristics such as temperature, wear and water content, users can holistically track and evaluate the overall oil condition. By linking the individual sensor data, operational safety and reliability will be increased and errors detected at an early stage.

ARGO-HYTOS
argo-hytos.com