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Energy-efficient hydraulic fluids can assist OEMs and operators in meeting emissions targets. (Volvo CE)

Hydraulic fluids evolve to meet critical equipment-design trends

Standards fragmentation and new performance requirements for modern equipment pose challenges and opportunities for fluid developers.

Driven by a number of factors, hydraulic equipment such as excavators, lifts, presses, bulldozers, cranes, injection molding equipment and more are rapidly evolving to meet new needs. Lower emissions targets around the world necessitate that hydraulic equipment operates more efficiently, while end-users are demanding hydraulic machines that deliver higher levels of performance over extended periods of time.

As hydraulic-equipment manufacturers work to deliver on these needs, new design strategies have implications across the entire machine. Importantly, hydraulic fluids and lubricants must provide new kinds of performance to best protect and enable equipment to meet its full potential. Five critical trends are especially impacting hydraulic-equipment development:

  • Increasing power density and internal pressures: To compete with electric systems that are quickly capturing more of the market, hydraulic systems are increasingly lighter and more power-dense. Smaller pumps are expected to produce the same power, which in turn increases internal pressures with peak pressures of up to 450 bar (6,530 psi) becoming commonplace in current mobile equipment. Expert projections suggest that number will only continue to grow higher. Lubricant manufacturers increasingly are turning to high-performance additives to improve their protective qualities.
  • Minimized power loss: Equipment designers are more focused on efficiency than ever before and have reduced the number of bends, joints and filter differentials to boost overall machine efficiency. As the rising costs of energy encourage more end-users to seek out even the smallest energy savings, OEMs are examining the role energy-efficient hydraulic fluids can play in further improving performance.
  • Finer filtratio: It’s generally understood that hydraulic pumps are extremely sensitive to contamination, and the increased pressures as well as decreased clearances in valves and pumps have further accentuated the need for the fluid to be ultraclean. Finer filters are being employed to achieve the necessary cleanliness according to ISO 4406 standards. As a result, hydraulic fluids must be resistant to clogging these filters and retain their key performance parameters post filtration.
  • Smaller oil coolers and reservoirs: Smaller oil coolers and reservoirs employed in mobile equipment means that there is less opportunity for the fluid to cool between cycles. This will influence the effective life of the fluid — for example, a 10°C (18°F) rise in operating temperature could halve the oil drain interval (ODI). For this reason, hydraulic fluids must exhibit good thermal stability and antioxidant properties. With less lubricant available because of the smaller reservoirs, the remaining lubricant can come under enormous stress – which is why additive treat levels must increase to compensate for the additive being consumed more rapidly if today’s lubricant drain intervals are to be maintained.
  • Increasing electronic and digital control: Control systems employ an increasing array of electronics to match the hydraulic pressure and flow to precise torque requirements, which can maximize specific duty cycles. In fact, the majority of construction-equipment OEMs provide electric-drive capability while still using a hydraulic solution in combination.

In addition, precise control of equipment is being provided by using digital valves that are 25 to 100 times faster than analog valves. Modern hydraulic lubricants must have low air content and compressibility to prevent damage to these digital valves.

Implications for hydraulic fluids
As manufacturers develop the next generation of hydraulic lubricants, they must support new hydraulic equipment in several key areas. While it can be measured in different ways, improved efficiency is increasingly a goal of OEMs and operators of hydraulic equipment. Using energy-efficient hydraulic fluids can provide a solution without having to completely re-engineer the machines, which can be cost-prohibitive.

For most end-users, extending the ODI is critical to operating their hydraulic equipment. After all, draining and replacing hydraulic fluid means extended downtime and lost productivity. Premium hydraulic fluids need to be changed less often and can therefore provide the necessary durability and performance for longer periods of time.

Stick/slip performance is another goal of most OEMs. They want to reduce noise in their machines, and premium hydraulic fluids can help. Correctly formulated hydraulic packages provide the adequate balance between friction modification and traditional anti-wear components, leading to less noise without compromising system protection.

Considering the conductivity of a hydraulic fluid also is critical. OEMs express more concerns about finer fibers in the oil filter, together with higher flow rates and non-conductive circuits. High static discharge can rip a hole in a hydraulic filter leaving the whole hydraulic system vulnerable to harmful particles. Modern hydraulic fluids must exhibit conductivity particularly during cold-starts and manufacturers need to be attentive to this requirement moving forward.

Even though modern hydraulic fluids are subjected to more stresses than their predecessors, their essential function — to protect parts from wear — doesn’t change. As manufacturers modify their formulations to improve other areas of performance in their fluids, they cannot neglect this essential truth.

Pursuing the perfect hydraulic fluid
Despite the new performance challenges facing hydraulic fluids, industry standard specifications have largely not kept up with the needs of the market. New specification development has lagged the evolution of hardware, with many of them specifying performance that may have been top-of-the-line 20 years ago. Those performance criteria do not match the needs of today’s hydraulic systems in the field.

As a result, hydraulic-equipment OEMs and original vehicle manufacturers (OVM) have taken these matters into their own hands with the development of their own individualized specifications. In this way, OEMs and OVMs can ensure that hydraulic fluids meeting very specific performance characteristics are the only ones used in their equipment, helping to elongate service life and long-term performance.

The development of OEM- and OVM-specific specifications, however, has caused some fragmentation, making it virtually impossible for even the most advanced hydraulic fluid to meet every performance characteristic across a diversity of modern equipment. For fluid developers, this situation represents both a challenge and an opportunity.

Developing hydraulic fluids that deliver high levels of performance in certain areas that meet specific needs allows for differentiation beyond the industry-standard specifications. And with fluids that meet modern challenges, this dynamic should allow OEMs to continue to push the boundaries of hydraulic performance.

So, while there is no single fluid formulation that can meet every need of every challenging hydraulic application, there are still a few characteristics that all must keep in mind. The first is equipment protection – it is the fundamental job of every lubricant to offer robust protection and anti-wear performance. The second is extended oil drain intervals, something desired by every OEM and OVM. This creates the need for balance across the formulation. For example, some of the most reliable and widely used anti-wear additives in modern fluids are zinc-based, which have the tendency to reduce performance in key differentiation tests, such as the TOST lifetime at high volumes.

Fluids that can provide outstanding protection while remaining thermally and oxidatively stable for extended periods — while also delivering on specific OEM- and OVM-based needs — will be the gold standard into the future. It’ll take ongoing collaboration between all stakeholders, and the application of high-performance additive chemistry in modern fluid formulations, to get there.

Adrian Fitzpatrick, global industrial OEM manager, and Matt Thom, technology deployment manager at Lubrizol wrote this article for SAE Media.

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