Electro-hydraulics are enhancing off-highway automobile performance and effectivity, enabling machine management and offering the constructing blocks for energy-recovery techniques. Trade specialists give perception into the evolution of this expertise and predict future developments
Over the previous three many years off-highway automobile designers have moved away from constructing machines which have hydraulics managed by way of mechanical techniques and hydraulic pilot strains to utilising digital management – electro-hydraulics. However, whereas such techniques are nicely established, the complete potentialities of this structure are nonetheless being explored.
Although hydraulic actions are nonetheless very a lot analogue in nature, the controls that operators use are virtually wholly now within the digital age, although the change didn’t come about in a single day, quite by way of a gradual evolution.
That is borne out by part specs. Danfoss, for instance, after years of designing elements that might be used with both mechanical or digital interfaces, has now fully transitioned its new elements to electro-hydraulics.
“The interface of our hydraulic merchandise has gone by means of three levels of evolution,” says Jeff Herrin, senior vice chairman of R&D at Danfoss Energy Options. “The primary stage, courting again a few years, concerned hydraulic and mechanical interfaces. For instance, a hydraulic pump managed by a lever that an operator might use to create the specified move.
“The second stage launched designs with each lever entry and digital management. This transitional section was obligatory as a result of business shifts don’t occur in a single day. We wanted a 10-year plan the place clients who wished the legacy answer might nonetheless get it, whereas we additionally constructed within the trendy, future answer of a digital actuator that they might management.
“As soon as we reached a sure stage of adoption, we moved to the ultimate stage: merchandise particularly designed for digital management. These don’t carry the bags of mechanical gadgets, which add value and compromise designs.
“For many of our merchandise we’re already at this final stage so we not design future merchandise with legacy interfaces. If clients nonetheless want a mechanical interface, they will purchase the older era, which we nonetheless produce. They’ve totally different efficiency and security ranges, however they continue to be accessible.
“Our focus now could be on designing hydraulics with digital interfaces as a result of we all know the long run lies in electro-hydraulic techniques. The truth is, 100% of our new product improvement applications are focused in that course.”
New methods to maneuver
Just lately Volvo Building Gear has used electro-hydraulic structure in its new Impartial Metering Valve Know-how (IMVT), accessible on 50-tonne EC550 and EC530 excavators.
“IMVT marks a departure from the standard mechanically coupled hydraulic techniques and introduces clever digital management with quite a few variables,” says Sejong Ko, Volvo CE’s product supervisor for giant excavators. “The outcomes are as much as 25% improved gasoline effectivity and higher operator management.”
IMVT allows additional options utilizing a closed-centre valve-control system, which not like conventional open-centre techniques, can cease or decrease hydraulic move by means of the principle management valve when there’s no demand for a hydraulic actuator. This considerably reduces gasoline consumption and eliminates the necessity for an eco mode.
It additionally makes use of unbiased cylinder management, sensing and controlling both sides of a cylinder’s chamber independently, with out utilizing hydraulic spools and pilot strains. This ends in extra exact management of the excavator’s actions.
“IMVT replaces conventional spools with poppet and electro-hydraulic valves in the principle management valve (MCV), lowering strain losses and optimizing valve management primarily based on load circumstances,” says Sejong Ko. “This results in sooner cycle instances, improved regeneration and lowered move loss, with evaluation exhibiting a 20% increase in productiveness.”
Hydraulic hybridisation
Regardless of potential power restoration ranges in off-highway automobile hydraulics being comparatively small when in comparison with the well-established hybrid techniques utilized in hydraulic braking for automotive; in recent times, tighter emissions targets and rising power prices have supplied better demand, significantly in excavators, which generate probably the most carbon emissions of any automobile class within the off-highway world.
“However it’s not a trivial factor to do in hydraulics,” says Herrin. “It’s important to add extra complexity with extra elements and circuits, and to do it, you completely need to have an digital system.”
The worth proposition for that extra complexity has traditionally been pretty poor, with OEMs having to make the commerce off on complexity versus profit. However the rising push for sustainability is driving innovation. “We did a refresh on our industrial pump product line,” says Herrin. “It was designed 30 years in the past and is now being refreshed and up to date to trendy specs. The spec for this new pump was, in actual fact, to have the ability to recuperate power in addition to pump power.”
In 2020 Volvo CE first introduced that it had developed a Hybrid system for its excavators which recovers power straight from hydraulic techniques, not primarily by utilizing pumps, however as a substitute by way of a hydraulic accumulator. It captures and reuses hydraulic energy, leading to as much as 17% improve in gasoline effectivity and 15% discount in CO2 emissions. Just lately the OEM introduced this Hybrid expertise could be added to its massive EC400 and EC500 40 and 50 tonne machines, having already been accessible on 4 smaller autos within the vary – the EC380E Hybrid, EC350E Hybrid, EC300E Hybrid and EC250E Hybrid excavators.
“We do it by mounting a hydraulic accumulator simply behind the increase, and because the increase goes down, the high- strain oil that you just use to retard the increase dropping goes into the accumulator as a substitute of being routed to the tank,” says Dr Ray Gallant of Volvo CE. “This offers the accumulator a high-pressure cost that’s then routed by means of help motors and put again into the cylinders on the upswing. All the course of is managed mechanically – the operator isn’t required to do something. He merely sees a small image on the sprint that tells him when his accumulator is charging and discharging.”
Volvo CE’s hybrid hydraulic expertise doesn’t generate electrical energy or require batteries for storing it. “It requires minimal elements – there are not any electronics to program and no management techniques apart from system monitoring,” says Gallant. “Upkeep can be easy because the system is a basically a mix of hydraulic move and valves.
There are different options which are extra reliant on pumps being able to working in a bi-directional method. For instance, pump- managed actuators handle movement primarily by means of velocity and/or displacement management of particular person pumps, making the pump a central part within the system. It’s on this area that promising applied sciences embrace Danfoss’s Digital Displacement pumps, floating cup expertise, and high-speed pumps. “We anticipate these options to achieve the market over time,” says Hongsuk Kim, head of excavator medium and hydraulic platform at Volvo CE. “Notably for electrically powered machines, the place bi-directional speed- managed pumps can recuperate power again to {the electrical} energy system.”
Sooner or later extra steps might be taken with hydraulic power restoration applied sciences. For instance, dead-weight compensation techniques. “These use extra cylinders and hydraulic accumulators working in parallel with the principle hydraulic movement management system and will provide benefits in particular functions,” says Hongsuk Kim. “These techniques are comparatively easy and mustn’t face important hurdles to reaching market readiness.
“A extra superior answer is the widespread strain rail structure, which makes use of one or a number of semi- fixed strain ranges mixed with hydraulic accumulators. On this setup, power and velocity are managed by means of hydraulic transformers and multi-chamber cylinders, which symbolize state-of-the-art expertise. Even these superior techniques require a number of independently managed valves, very similar to IMVT, demonstrating that our improvement efforts in IMVT are paving the best way for future improvements in hydraulic power restoration.”
“Finally electrified linear actuation will get rid of hydraulic fluid on machines”
Electromechanical actuators
Quite a lot of prototype autos, in addition to Bobcat’s manufacturing all-electric T7X and S7X compact observe loaders and skid steers, have executed away with conventional hydraulics altogether and changed them with electromechanical linear actuators. Herrin sees continued evolution within the discipline. He notes that Danfoss Energy Options is investing in electromechanical actuators as
a complementary product line to their electrification portfolio. Whereas the use circumstances for this expertise are presently modest, Herrin anticipates that, “as electrification takes an even bigger maintain in off-highway tools, in the end electrified linear actuation will get rid of hydraulic fluid on machines. Rotary actuators (wheel drives, work features) shall be first, steering subsequent, and linear actuators final.
Volvo CE is already making use of electric-motor pushed actuators in a few of its excavators, and reviews constructive buyer suggestions. “You will need to notice that electrical motor-driven actuators can work along with hydraulics as an intermediate energy transmission medium or, in some circumstances, with out hydraulics altogether,” says Hongsuk Kim. “Nevertheless, each hydraulic and electrical techniques have their respective benefits and limitations. We don’t imagine that one expertise will absolutely dominate throughout all functions.
At Volvo, we’re not dedicated to phasing out hydraulics however as a substitute give attention to adopting the expertise that most accurately fits our clients’ wants. We acknowledge the challenges related to electro-mechanical drives, particularly for linear movement functions. These challenges are much less pronounced for rotary drives, making them extra possible to interchange hydraulics now.”
Enabling automation
One of many key benefits of electro- hydraulics is that’s has enabled machine management – whether or not that be semi-autonomous driver help techniques or full automation, having the ability to management actions by way of digital techniques is a important enabler.
“Considered one of our flagship innovation programmes is round autonomy,” says Herrin. “There are only a few use circumstances for absolutely autonomous machines proper now, however there’s an entire lot for semi-autonomous, which imply operators will be much less expert, as a result of the machine can function itself in cycles which are repeatable.”
This pattern in the direction of automation is driving the necessity for extra superior applied sciences. As Herrin factors out, “Whenever you get into that house, AI and machine studying are required. It’s the core digital algorithm expertise that permits automation.”
This text first appeared within the October problem of iVT
