The idea of battery-driven diggers may sound appealing, but in reality the energy requirements of off-road machinery make electric power very limited in practice.
As hopes rise that battery electric vehicles will clean up our cities, it might be tempting to assume that off-highway vehicles will go the same way.
But the hard duty cycles, high power requirements and tough environment of such vehicles make the economics of electrification extremely challenging. The energy consumption of a 20T excavator over a working day amounts to around 480kWh.
This would require around five Tesla-style batteries at a cost of around $100,000 (in other words more than the digger), and would need charging points in the middle of every muddy field.
So the diesel engine will be around for the foreseeable future – the question is, how can its energy be most efficiently controlled and distributed to the working functions?
Now one Scottish firm – Artemis Intelligent Power – is challenging the mainstream thinking that electrification is the only way to improve efficiency. Artemis are bringing to market a new digital hydraulic pump that is demonstrating the potential to reduce fuel consumption, and thereby emissions, at much lower cost than electric technology.
For more than a decade Artemis Intelligent Power has been developing Digital Displacement® hydraulics, a unique patented technology with applications as diverse as renewable energy, rail and off-road machinery.
Tier 1 engagement
With a 50-strong team based in a busy and expanding 3000m2 research and manufacturing facility near Edinburgh, the firm is working closely with a major Tier 1 manufacturer of hydraulic components, and multiple OEMs of construction and material handling equipment, on collaborative projects to bring their technology to market.
Managing Director Dr Niall Caldwell and his team has focussed on what they see as the biggest area for improvement – the hydraulic pump that lies at the heart of almost every off-highway machine.
“The traditional analogue swash plate pump mechanism was patented in 1893, around the same time as the diesel engine,” Caldwell says. “But whilst the modern common-rail diesel is a far cry from those first crude engines, the pump it powers has hardly changed.
“So, although we see state-of-the-art diesel vehicles equipped with sophisticated engine-management ECUs, vast amounts of the power they deliver goes to waste. We were shocked to discover in our testing that 70% of the engine shaft power of a modern excavator is lost as heat in the hydraulic system.”
“I can see how we got here,” Caldwell says. “The standard analogue pump and valve system is robust and well-understood – but it is tremendously inefficient.”
But now, Caldwell says, a new wave of digital hydraulic components and systems will change all that, dramatically cutting fuel use and emissions while preserving the high power density, low cost and ruggedness of conventional hydraulics.
The company’s Digital Displacement® pump technology replaces the variable stroke analogue pump mechanism with a fully digital principle, in which cylinders of a radial machine are individually controlled with digital solenoid valves. Just like common-rail diesel engines, every working cycle is initiated by an embedded digital controller.
Exceptional efficiency, especially at part load.
“The result is exceptional efficiency, especially at part load,” says Caldwell.
“Over a typical duty cycle, energy losses are between a third and a fifth of comparable analogue pumps, and in our laboratory tests we have shown that hydraulics can now equal electric machines for power transmission efficiency,” Caldwell asserts.
The company has great confidence in their technology, and has proven its scalability from tiny machines of a few kilowatts up to a 7 megawatt hydrostatic transmission – the world’s largest – which lies at the heart of the 7MW offshore wind demonstrator at Fukishima, Japan.
“This digital control brings other benefits,” Caldwell believes. “The control response of traditional analogue pumps is slow and inaccurate, and most give no feedback to the system controller about what is actually going on. Control functions are pre-configured in the factory, and if “parameters” are adjustable at all, it’s often with a screwdriver.
“By contrast, our machines are digital from the bottom up – so they are network ready, have much faster response to electronic demands and much higher control accuracy. The control modes and parameters can be adjusted in real time, much like calibrating an engine ECU – so they are an ideal match for common-rail diesel engines. We can even emulate analogue pump characteristics, making it possible to retrofit without needing to re-tune the whole system.”
“A single machine can have multiple independently-controllable fluid outlets – all at different pressures and flowrates, but with a common torque limit. “This enables radical new system architectures to eliminate throttling losses in analogue valves.” says Caldwell.
Fuel consumption down by 16-21 percent
This summer, Artemis completed field tests with a major manufacturer, replacing the analogue pump of a modern excavator with their E-dyn® 96 Digital Displacement® hydraulic pump.
The project, supported by government agency Scottish Enterprise, has shown exceptional results.
“Set against the benchmark of a conventional 16-tonne excavator, fuel consumption on a variety of standard work cycles was reduced between 16% and 21%, whilst at the same time, productivity (cycles per hour) was increased by 11-12%,” Caldwell says.
“Using the improved control inherent in a Digital Displacement pump, the load on the engine could be better controlled and more work extracted without fear of stalling the engine. Operating in enhanced productivity mode, the demonstration excavator produced a 28% increase in productivity while reducing fuel consumption by 10%, using the same engine and valve system as the standard machine.
“These results are ground-breaking given that no energy recovery methods were used and the system was not optimised in any way – this was a simple ‘pump swap’ trial. Operators loved the feeling of power and responsiveness even with reduced engine speed, and the complete lack of high frequency noise.”
But this is just the first step of an evolutionary roadmap which Artemis is now driving forward. In the next phase, by applying some incremental changes to the valve system, they expect to achieve 30% fuel reduction.
“Ultimately, we will make a ‘fully digital’ hydraulic hybrid system, replacing the analogue pump and valves with our Digital Displacement® technology, including hydraulic accumulator energy storage. In this configuration, we calculate fuel consumption will be reduced by more than 50 percent, with significant scope for reduced engine size– still with improved productivity.” Caldwell asserts.
“Think of the cost and risk of an equivalent electric hybrid system at full scale – running high voltage cables from a diesel-powered generator and a bank of ultracaps, to distributed power electronics and electric motors hanging off the boom, driving massive ballscrew actuators. Is it really feasible? We think the industry needs a new roadmap to the truly efficient hydraulic excavator.”
And according to Caldwell, Digital Displacement pumps are equally applicable to vehicles with dominant propel functions. Tests on IC forklift trucks showed 40% reduction of fuel compared to the common hydrodynamic transmissions.
In this setup a single Digital Displacement pump independently supplied both propel and working functions, offering superior control and drivability, with lower engine speed and hence noise.
Caldwell notes “at the flick of a switch, our transmission can emulate the traditional torque converter or hydrostat driving feel – so operators feel at home straight away.”
Route to market
Now that the components are proven, and applications have been demonstrated, the next step is scaling up manufacturing. Artemis is now producing pumps in pilot quantities for evaluation by key OEMs.
“After ramp-up, we don’t expect production cost to be much more than equivalent analogue pumps,” Caldwell says.
“The machines require no rare materials or exotic processes – just common low-cost manufacturing methods, and from the start we think OEMs can offer their customers a payback period measured in months rather than years. Once system cost reductions are realised, such as downsized engine and oil coolers, there may be no premium required for an excavator with substantially lower operational costs due to fuel and productivity advantages. This will be truly disruptive.”
For volume production, Artemis is in advanced discussions with a major Tier 1 manufacturer of hydraulic components, with the goal of offering products to the OEM market.
For those OEMs who make their own hydraulic components, Artemis offers a licensing model and the support of its specialist engineering consultancy services to make a bespoke design.
“15 years ago, common rail was exotic in this industry – now it’s the standard. Hydraulics is well overdue for its own digital revolution,” Caldwell concludes.
This article first appeared in iVT Off-Highway Annual