May 30, 2013

Getting Improved Fuel Efficiency Through Quality Hydraulic Fluid in Mobile Construction Equipment
by David Doyle, CLS, OMA I, OMA 2
Vice President & Operations Manager, North America

Hydraulic fluid performance can have a significant impact on the fuel efficiency of construction equipment, particularly earth moving equipment. Much of the fuel consumed in mobile equipment that relies on hydraulic power to perform the work is used for operating the hydraulic pump, which is the heart of the hydraulic system. Power generated by the engine is eventually transferred throughout the hydraulic system. The less efficiently this power is transmitted via the hydraulic fluid the more the engine is required to work, thus more fuel is consumed.

Good hydraulic oil improves pump efficiency. Improved pump efficiency improves fuel consumption. As hydraulic fluids lose the effectiveness to transmit power due to a lower VI or contamination the operator is forced to use more fuel to make the hydraulic pump work harder in order to compensate for the loss of workload that the system is handling. A correct operating viscosity provides the proper lubricating film thickness for hydraulic components, there’s a narrower viscosity range where power losses are minimized and power transfer is maximized. Contaminants such as particulate and water will contribute to inefficient power transmission in these systems as well.

Fuel efficiency depends on proper additive formulation, hydraulic fluid operating temperature, viscosity, viscosity index (VI), and shear stability. Shear-stable multigrade hydraulic fluids can improve fuel economy over monogrades. When polymers are used in energy-efficient fluids, they must be shear stable. Hydraulic oil containing friction modifiers in the additive formulation also contribute the overall fuel efficiency. Another formulation factor for the efficient power transmission is a high resistance to reduction in volume under pressure due to little or no compressibility (high bulk modulus).

Temperature control, contamination control, and aeration are system design factors that will influence how power is transferred throughout the hydraulic system. Systems are least efficient during startup. Determining the minimum starting temperature requirements aids in selecting an energy-efficient hydraulic fluid based on viscosity and the viscosity index. Aeration can also be a factor of system design which increases the fluids compressibility and waste power.

Laboratory analysis can help to optimize the power transmission efficiency of hydraulic fluids

  • Check for contaminants
  • Varnish potential
  • Aeration due to product performance instead of system design
  • Proper viscosity
  • Proper VI
  • VI shearing
  • Product compatibility

The laboratory analysis can be leveraged as another tool that compliments input from the lubricant provider and equipment manufacturer to optimize fuel efficiency in mobile construction equipment which depend on hydraulic systems to perform the work.


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