Coordinating electrohydraulics

  • 16-Feb-2009 12:22 EST
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Electrohydraulic brake systems use electronics to provide control flexibility, while the hydraulics supply the power. Shown is a variety of electronic pedal configurations and sensing options from Mico.

Off-highway OEMs have found that electrohydraulics are particularly suited to platforms where there is a high degree of coordination required between the propulsion and work functions, as well as those where functional complexity or repetition of task is more suited to an automated approach. Now, they are turning to the technology to help them meet emerging emissions regulations in the U.S. and Europe.

“A major development has been the rapid and increasing demand for hydraulic-hybrid propulsion systems that are highly reliant on electronic controls and software functionality to allow them to deliver better fuel savings, reduce mechanical wear, and improve emissions in conjunction with the mechanical and fluid power subsystem,” said Clyde Thomas, Senior Manager of Technical Services at Eaton.

An example of electrohydraulic technology being employed to improve engine efficiency is with fan drives.

“It used to be oil was cheap and you just ran the fan all the time,” said David Ewel, Director of Engineering, Mico. “Well, you don’t need to run the fan all the time; you only need to run it under certain conditions. Electrohydraulics can reduce the requirement for the fan to be driven, and, hence, lower the requirements of the engine.

“I think what you saw before was an electrohydraulic brake system over here and a [non-integrated] electrohydraulic fan drive control over there. Now, we’re looking at integrating these two manifolds to make one manifold that’s lower in cost, and we can take advantage of the extra flow from the brake systems to run the fans. We’re starting to see how they can make use of the various systems for a better overall performing vehicle.”

Electrohydraulics can even help to compensate for the loss of engine power associated with emissions controls.

“Engineers modify engines to meet emissions standards, which can result in a drop in rpm and more heat in the system, taking away power,” said Branko Horvat, Product Portfolio Manager for Propel Products at Sauer-Danfoss. “With electrohydraulics, you can put the system into its best state and use energy only when it’s needed.”

Besides off-loading complex and repetitive functions, there are other reasons why the industry is transitioning away from electromechanical interfaces and discrete analog/digital connections such as hard-wired point-to-point cables to more digitized approaches that include programmable controls, CAN and other field busses, and software-configurable functions.

Providing more flexibility in platform design for space savings and weight reduction by using a networked architecture reduces the assembly and maintenance costs of systems relying on mechanical or fluid power pilot controls, or older-style electrical interfaces.

Integrating electronic operator interfaces such as joysticks and display panels can allow for a more manageable machine, as well as more capabilities in the areas of machine configuration, troubleshooting, and overall operation.

The use of an electrohydraulic system can more easily enable data logging, remote monitoring, and troubleshooting, in addition to upgrading a platform by using the system’s electronics, intelligence, and communication functions to support these capabilities.

There are also demographic and human-factors issues associated with the use of electrohydraulics. Lack of experienced operators is an issue, so automating some tasks provides less reliance on individual operator skills. Automating repetitive functions also reduces operator stress while potentially increasing consistent performance and efficiency. Keeping the operator in a safe environment while still being able to control and monitor the activity of the equipment is often more achievable with electrohydraulic approaches that remove hydraulic lines from the cab.

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