Type ‘electro hydraulics’ into a web browser and you’ll discover just how big an industry it has become. Most mobile machines remain diesel-powered, but supplementary equipment like backhoes, cranes and farming machinery use electro hydraulic actuators using electrical power.
Hybrid, a combination of diesel and electric, remains the go-between from fossil fuel to electric powertrains, but hybrid has already jettisoned the mechanical transmission with a power take off (PTO) to run the hydraulic oil pump. Critical to the hybrid evolution is how electro hydraulics has been used for power steering, removing hydraulic power steering components, such as the pump, hoses, fluid, drive belt, and pulley; making it much smaller and lighter.
The market is very competitive. Known for its transmission boxes, ZF manufacturer an electrically-powered hydraulic steering pump that can operate with traditional hydraulic pumps to provide power steering with hybrid and engine off-road operations, or full electric powertrains.
Component manufacturer Eaton, meanwhile, is pushing its next-generation of electro hydraulic steering and steer-by-wire systems. Its advanced steering valve can be programmed to allow the operator to adjust the steering knob position, number of wheel-turns lock-to-lock and handling. This year it introduced the ASV60 advanced steering valve, designed for mobile equipment using electro hydraulics or steer-by-wire for telehandlers, backhoe loaders, compact wheel loaders and tractors.
And Italian company Turolla manufactures ezeHelp, a direct-current (DC) electro-hydraulic pump that is part of a diesel-electric hybrid solution for lifting and in agriculture and construction for supplementary auxiliary steering and braking. Volvo Trucks also introduced its Volvo Dynamic Steering in 2013 to stop drivers wrestling with the steering wheel at low speeds and when off-road in construction vehicles. Using an electric motor connected to the steering gear, it receives information from several sensors. The motor is controlled 2,000 times every second using a torque overlay to correct unintentional steering movements and to provide extra torque when needed. The upshot is that you can turn the truck using a single finger at walking pace.
One of the critical trigger points in the wider commercial introduction of electro hydraulics is to be found on the New Routemaster, better known as the Boris Bus – a hybrid diesel-electric double-decker bus launched back in February 2012. Using a Cummins ISBe 4.5-litre engine, it worked with a Siemens hybrid transmission. The engine drives a generator that supplies energy to a lithium-phosphate battery pack, which in turn provides electrical current for the electric drive motors, replenished by regenerative braking technology.
For Gardner Denver, the Boris Bus proved to be a launchpad for its electrically driven air compressor to the wider market, explains market sector director for transit and transport Jonathan Marsh. “We now speak to 80% of the OEMs in Europe. Gardner Denver provides electrically-driven compressed air for the braking system and the suspension or the kneeling system of buses for people to disembark. We use a converter or inverter or drive system that takes power off the DC to power the electric motor for the compressor.
“The [electric vehicle] market is evolving in many different directions. I think there will need to be some technology consolidation at some point because economies of scale will be needed to help get the price of vehicles down. Even on compressed air there is the debate about high or low voltage, for example.”
Vehicle and mobile machine manufacturers have mainly focussed on propulsion and the associated systems for steering, braking and suspension. Market suppliers have been developing electric hydraulic solutions to power the add-ons like lifting equipment, and one such device is the electric PTO (ePTO) system developed by Hiab.
Hans Winscher, country manager at Hiab Sweden, says the ePTO minimises emissions and can replace conventional systems in vehicles. “The ePTO provides an equal lifting capacity to a conventional crane compared to a traditional PTO,” Winscher adds. The ePTO system comprises a battery with a 40kWh capacity, an electric motor, a hydraulic pump and a smart electronic control system. When the crane is not in use, the electric pump is automatically switched off to save energy and battery capacity. It is recharged at night.
ZF has also developed hybrid and electric turnkey solutions, and recently launched its electric drum mixer drive, called the CMe ECOMIX Electric Mixer Drive (pictured). Traditional mixer drums are driven by high-pressure oil-pump hydraulics that are powered through the truck’s combustion engine through a PTO.
Alexander Eisner, head of product communication from ZF’s off-highway systems, says this plug-in hybrid concept replaces the hydraulic motor in the mixer drive with a pre-connected electric motor and electro hydraulic pump with a generator. “The battery can be charged on the mixer system by cable and by a built-in generator when being driven. It is compact, has lower weight, and durability.
“During operation, the vehicle can access 60kW continuous power and a peak power of 125kW for a shorter period. The high voltage system was specially selected for reduced power loss. This is emerging as the standard in the electric commercial vehicles sector.”
ALREADY OUT THERE
While the industry inches slowly towards solely electric-power machines, there are already several out there. Last year, an electric dump truck weighing 58 tonnes, capable of carrying 65 tonnes, was unveiled. The eDumper is a joint development, with the 4.5 tonne lithium-ion battery supplied by Swiss company Lithium Storage.
It uses a synchronous electric motor generating 590kW continuous power and up to 9,500Nm torque. It loads at the surface and drops down into a mine, during which travel heat generated by the disc brakes charge the battery, which is then used to drive back to the surface. This shows what is possible without any real weight constriction and with a favourable working environment, in this case using gravity for regeneration to recharge the battery.
Lower down the weight scale, in the mobile machinery sector, the commercial move to all-electric powered engines has only just begun. Unlike the road-going sector, machines operating in agriculture and construction require continuous high horsepower working long duty cycles. This puts a lot of strain on the primary source of electric energy, so to compensate, most go for two electric motors, like the LX2 all-electric compact wheel loader introduced last year by Volvo CE. (See also www.is.gd/asidef).
Volvo CE is also experimenting with its excavator range and has demonstrated the EX2; a fully electric compact excavator. The EX2 stemmed from the company’s €7m research project.
Removing the hydraulic system and the combustion engine, as well as reducing the cooling needs, has led to significantly lower noise levels. However, at this stage, the EX2 is purely a research project and there are currently no plans for industrialisation, says Ahcène Nedjimi, electrics and electronics systems lead engineer and EX2 project leader.