Influence of Bio-Hydraulic Oil on the Efficiency of a Mobile Machine

  Termperature-Viscosity Dependency of Various Oils with Experimental Excavator Copyright: © ifas

The efficiency of hydraulic systems can be influenced by selecting the oil viscosity or viscosity index. This shows that in particular a high viscosity index, i.e. a slight change in viscosity over temperature, is advantageous. By their very nature, bio-hydraulic oils have a much higher viscosity index than mineral oils. The aim of the project is therefore to quantify the influence of bio-hydraulic oil on the efficiency of an example mobile hydraulic system. Possible increases in efficiency and the associated savings potentials in fuel can contribute to increasing the market share of bio-lubricants.

Benefit Procedure
Measurement of the drive power when using mineral oil and bio-oil Equipping a test excavator with measuring electronics
Validation of the performance of biolubricants Acquisition of measured variables of the system
Determination of possible fuel savings Performance of a reference cycle with mineral oil



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Influence of Bio-Hydraulic Oil on the Efficiency of a Mobile Working Machine

Technical Requirements of Bio-Hydraulic Oils

At present, the market for bio-hydraulic fluids is stagnating. The market is inhibited by the significantly higher purchase price compared to mineral oil products. In terms of technical properties, bio-hydraulic oils are nowadays largely on a par with mineral-oil-based oils and fulfil the technical requirements according to DIN ISO 15380. The decisive property of hydraulic oils over a wide temperature range in mobile machinery is the temperature-viscosity behaviour. This is described by the viscosity index (VI) of a fluid. A value is given that is reciprocal to the slope of the viscosity curve over the temperature. This means that the higher the value given, the smaller the change in viscosity with temperature. A mineral oil-based HLP hydraulic oil has a VI of about 100, whereas a synthetic ester of the HEES class has a value of over 200.
The aim of the project was to identify the influence of the use of biohydraulic oil on the efficiency of a mobile crawler excavator. Possible increases in efficiency and the associated potential fuel savings were identified for this purpose. For this purpose, comparable working cycles of the construction machine with mineral oil and biohydraulic oil were compared with each other in terms of their fuel consumption. Based on the measurement results of the reference cycle with mineral oil, a biohydraulic oil was developed that was adapted to the thermal conditions of the temperature distribution during the cycle.

Equipping the Test Excavator with Measuring Electronics

Important hydraulic consumers of the test excavator (e.g. cylinders, valves, pipes), as well as pumps and motors were equipped with sensors for measuring volume flow, pressure and oil temperature. Based on the temperature measurement, the local viscosity of the oil could be determined. A fuel consumption measuring device recorded the fuel required for the cycles driven.

Reference Cycle and Oil Change

On the test site, the so-called "Dig and Dump" digging cycle is demonstrated with the test excavator. This cycle is common for performance measurements on excavators. The excavator was controlled automatically and followed a predefined path. The cycle was repeated until the measurement data showed sufficient statistical certainty. The environmental conditions were also recorded. Based on the measurement data, a bio-hydraulic oil was formulated that had the required minimum viscosity at the maximum fluid temperature occurring during the cycle. As a result of the higher VI of the bio-hydraulic oil, it has a lower viscosity below the maximum temperature and thus causes lower friction losses in throttle-shaped resistances. A fundamental lowering of the viscosity level compared to the mineral oil was dispensed with in order to ensure the operational safety of the machine. The test fluid produced meets the requirements of DIN 16807 according to the definition for biolubricants.

Comparison Cycle and Evaluation of the Measurement Results

Entsprechend dem beschriebenen Vorgehen wurde der „Dig and Dump“ Zyklus mit dem umgeölten Hydrauliksystem automatisiert wiederholt. Die Messergebnisse wurden sowohl im Hinblick auf den Energieverbrauch des Hydrauliksystems als auch auf den gesamten Energieverbrauch des Baggers ausgewertet.

Aus den Messergebnissen geht hervor, dass besonders bei niederen Tanktemperaturen Kraftstoff durch die Verwendung von Bio-Hydrauliköl eingespart werden kann. Bei höheren Fluidtemperaturen kehrt sich dieser Zusammenhang um. Der Grund für dieses Verhalten soll in weiteren Komponententests weiter erforscht werden.

Der in den Untersuchungen betrachtete Mini-Raupenbagger wird häufig für kurze Zeiträume auf Baustellen betrieben und damit liegt die mittlere Betriebstemperatur unter der Betriebstemperatur größerer Maschinen. Bei der Annahme einer durchschnittlichen Tanktemperatur im Bereich von 35–50 °C des Raupenbaggers ergeben sich Einsparungen von circa 4,65 % beim Betrieb mit Biohydrauliköl. Das Hydraulikölwechselintervall des Versuchsbaggers liegt bei 2.000 h. Pro Wechselintervall werden beim mineralölbasierten Hydrauliköl damit 7.590,2 € an Kraftstoffkosten fällig, beim Biohydrauliköl sind es 7.237,1 € bei einem Dieselpreis von 1,30 €/l. Es ergeben sich hiermit Einsparungen von 353,1 € bei der Durchführung des beschriebenen Grabzyklus.

  Excavator Copyright: © ifas  


The research project is funded by the Fachagentur Nachwachsender Rohstoffe e.V. (FNR). The project partners are Volvo Construction Equipment Germany GmbH and Panolin AG.



Title Author(s)
Bio-Based Hydraulic Fluids and the Influence of Hydraulic Oil Viscosity on the Efficiency of Mobile Machinery
Contribution to a book, Journal Article (2021)
Deuster, Sebastian (Corresponding author)
Schmitz, Katharina