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Optimised lifting hydraulics save up to 20% in fuel

Demand-based control of lifting hydraulics in forklift trucks brings about greater energy efficiency and higher levels of sustainability and environmental protection.

The challenge in terms of sustainability:

How can forklift trucks contribute towards achieving the goal of greater energy efficiency and therefore sustainability? Linde Material Handling considers this question afresh during each truck development process and with roadworthy prototypes and field tests has proven that alternative drive concepts promise increased efficiency in the future. However, due to high investment costs, hybrid and fuel-cell trucks are not yet profitable for the majority of customers. The conventional drivetrain with internal combustion engine and driving and lifting hydraulics does, however, offer further potential for improvement — with excellent profitability, which pays off financially for customers.

The initial situation:

The aim of Linde MH was, and indeed still is, to utilise this potential. The European market leader can build on the already very efficient and economical hydrostatic drive unit, which functions without a manual gearbox, differential or brake.
For the hydraulic work functions of a forklift truck, gear pumps with a constant displacement volume are normally used. The disadvantage of this is that the lifting hydraulics pump is linked directly to the engine speed and therefore always pumps hydraulic oil depending on the engine speed. During haulage when a high engine speed is required, for example, the maximum hydraulic oil quantity is circulated unnecessarily. This is known as a circulation loss. Finding a way of minimising this loss was the challenge presented to the Linde MH development team.

The solution:

When redesigning the Linde H40–H50 diesel truck series, Linde MH turned its attention to the lifting hydraulics and the optimum connection between the internal combustion engine and the lifting hydraulics.
The solution was an adjustable axial piston pump with variable displacement volume, developed in-house. With a variable displacement pump, the oil volume can be controlled and oil is only pumped as required. The electronic control system perfectly adapts the oil volume flow rate supplied by the pump to the usage requirements. Thanks to an "oversizing" of the pump with a greater oil displacement volume, the maximum lifting speed is reached at lower engine speed. Depending on the load, the drive motor now only requires 1600 to 2300 rpm, as opposed to the previous requirement of 2800 rpm, to reach the top lifting speed.

The sustainable strengths:

With the new variable displacement pump, the truck user can save energy — especially when lifting without a load or in the part-load operational range, i.e. loads below the rated capacity. More energy is saved the lower the weight of the load in comparison to the rated capacity of the truck and the more frequently empty lifts or lifts in the part-load operational range occur. Overall, fuel consumption and pollutant emissions are not only reduced, but the truck is also quieter when in operation.

Linde MH performed series of tests at the premises of various customers in the field and determined that the new drive concept reduces fuel consumption by up to 20%. The energy cost savings were equal to approx. EUR 1 per operating hour. A pleasing outcome is that the operating company does not suffer in terms of performance and productivity. Quite the opposite: The pump is controlled by the input signal and responds directly to the driver's commands and therefore to the electronic control system. This results in a lower energy consumption with the same performance.

The customer once again reaps the rewards, because all the expert knowledge in hydraulics is available in-house at Linde MH, as the integration of hydraulics and truck expertise plays an essential part in achieving such considerable reductions in consumption with the new drive concept.

Reductions in consumption of up to 20% with the same productivity, less noise, lower exhaust emissions and reduced wear are arguments to be considered when deciding what device to buy. At the same time, these factors make a positive contribution to a sustainable, environmentally friendly economy.  

The inventors:

The variable displacement pump with internal designation MPR50 was developed by Linde under the direction of Dr. Rolf Lasaar.

Brief profile of the company:

Name: Linde Material Handling GmbH
Headquarters: Aschaffenburg
Year established: 1904
Employees: 12,240 employees worldwide (2010)
Solutions: World's second-largest manufacturer of industrial trucks
Internationality: Worldwide