The development of hydraulic components and systems concept has in recent decades been a clear focus on

energy efficiency and controllability. With today's components, such as electrically-driven pumps, motors and

valves, and electronic control systems have hydraulic technology flexibility significantly increased, which has

provided unique opportunities to build energy-efficient hydraulic system with good controllability. The

implementation of energy efficient systems is not simple, as it requires that the system concept closely matched

to the machine / vehicle primary power source, cycle and performance requirements, and that the hydraulic

system is integrated with the system's mechanical units so that frictional losses are minimized.

This article analyses some system solutions for mobile and industrial applications with regard to their energy

saving potential. Conventional systems are compared with energy-efficient systems and both valve and

pump-controlled mobile systems studied. Industrial system solutions discussed, especially the energy saving

potential of modern supply units offer. Use of accumulators for energy storage and energy recovery as well as

the hydraulic impact on system efficiency, are further examples of areas treated. Analysis shows that a plurality

of applications has a power budget potential of 20 - 50%, compared with the conventional system. In some

industrial systems can supply-units with speed-controlled fixed pumps and accumulator battery providing

energy savings up to 80%.

To meet the increased requirements on higher efficiency and better functionality of hydraulic systems, new components and system concepts have been developed over the years. However, the most important component in a hydraulic system, which has a major impact on system efficiency and wear are the fluid itself. The last decades, major attention on hydraulic fluid development, have been set upon environmental adaption. Today, energy efficiency has been a hot topic and a number of energy efficient fluids have been launched on the market. Besides energy efficiency, environmental adaption of fluids, are extremely important in mobile applications.

In this paper the focus is set on hydraulic fluid properties and its impact on system efficiency. Environmental adapted fluids will also be discussed. Synthetic saturated esters are analysed and compared with mineral oils. The main question that will be tried to answer is - “How to select the best fluid for a specific application?”.

Hydraulvätskan är ett av de viktigaste konstruktionselementen i ett hydraulsystem och har en avgörande inverkan på systemets energieffektivitet, driftsäkerhet och livslängd. Hydraulvätskans huvuduppgift är att svarar för en effektiv energiöverföring i systemet, från pump till cylinder/motor. Utöver själva energitransporten ska hydraulvätskan dessutom ge fullgod smörjning och kylning. Speciellt i mobila applikationer är det viktigt att minimera hydraulikens miljöpåverkan. Sammantaget ställer dessa kriterier synnerligen höga krav på hydraulvätskans fysikaliska egenskaper.

Utvecklingen av hydraulvätskor, har inte varit spikrak utan kantats av en rad problem vid praktisk användning som exempelvis introduktionen av rapsoljor. Dagens miljöanpassade hydraulvätskor har genomgående en hög kvalitet och tidigare problem är nästan helt eliminerade.

På ämnesområdet Fluida och mekatroniska system vid Linköpings universitet har drivits ett ”Miljöolje-projekt” som initierats och sponsrats av Intressentföreningen för Fluid Systemteknik (IFS). Arbetet har främst behandlat viskositetens inverkan på förlusterna i ett hydraulsystem. Denna artikel utgör ett sammandrag av de erfarenheter projektet givit. Såväl mätresultat som teoretiska beräkningar presenteras. Krav på hydraulvätskor och deras fysikaliska prestanda diskuteras.

The hydraulic fluids, is one of the key design elements of a hydraulic system and have a significant impact on system energy efficiency, reliability and durability. Hydraulic fluid main task is to ensure efficient energy transfer in the system, from the pump to the cylinder/motor. In addition to the energy transport the hydraulic fluid also has to provide adequate lubrication and cooling. Especially in mobile applications, it is important to minimize the hydraulic impact on the environment. Taken together, these criteria sets extremely high demands on the hydraulic fluid physical properties.

The development of hydraulic fluids, has not been plain sailing but punctuated by a number of problems in practical use, such as the introduction of rapeseed oils. Today's environmental friendly hydraulic fluids have consistently high quality and past problems are almost completely eliminated.

The division of Fluid and Mechatronic Systems at Linköping University has operated an "Environmental Oil Project", initiated and sponsored by the Association of Fluid System Technology (IFS). The work has focused primarily on the viscosity effect on the losses in hydraulic systems. This article is a summary of the experience the project given. Both measurements and theoretical calculations are presented. Demands on hydraulic fluids and their physical performances are discussed.

To increase energy efficiency and lower emissions in construction machines, the use ofhydromechanical power split drive trains shows high potential. The possibility of usingmultiple gear speeds without losing traction force makes the power split architecture especiallysuitable for heavier wheel loaders. This paper analyses two known concepts ofmulti-mode power split transmissions suitable for the wheel loader application and comparesthe solutions based on energy efficiency. The concepts are scalable in the sense thatadditional modes can be used without necessarily adding complexity to the transmission.Simulations are made with respect to steady-state transmission losses and the relationbetween number of modes and transmission efficiency is shown for each of the proposedconcepts. The operational characteristics of the hydraulic displacement machines stronglyaffects the transmission efficiency and the design choice of number of transmissionmodes.

Energy efficiency of propulsion systems for cars, trucks and construction machineries has become one of the most important topics in today’s mobile system design, mainly because of increased fuel costs and new regulations about engine emissions, which is needed to save the environment. To meet the increased requirements on higher efficiency and better functionality, components and systems have been developed over the years. For the last ten years the development of hybrid systems can be divided into two major technologies, electric hybrids and hydraulic hybrids. Today, there is a hard competition between these two branches. Therefore, it is interesting to compare these two technologies to figure out their individual capabilities.

This paper will discover the advantages of hydraulic hybrid systems over electric hybrids and how to succeed with the hybrid system design. One obvious advantage with hydraulic hybrid systems is that they create a unique opportunity to optimize the engine loading at all speeds. About the power density, hydraulic machines have around 5 times higher density than electric machines. This gives the opportunity to use direct hydraulic drive and remove mechanical gearings needed in an electric hybrid system. This fact has a large impact on the system overall efficiency.

By using hydraulic accumulators, a part of the potential load energy can be reused, which make it possible to design a system with improved endurance compared with a similar one without such devices. This kind of regenerative capabilities increase the power supply capability. The additional power can be used to improve the performance of the system, without increasing the primary engine power. Another advantage of using a hydraulic accumulator is that its round-trip efficiency is higher than for an electric battery, especially at frequent acceleration and braking.