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To date, the simple and most-popular solution in

industry has been to optimize only the hydraulics. Such

an approach does offer some improvement but, unfor-

tunately, neglects the importance of the engine and its

effects on efficiency of the entire machine.

In contrast, the new STEAMmobile-hydraulic system

for excavators represents the first holistic approach to

optimize both energy efficiency and performance of

mobile machinery.

In contrast to today’s load-sensing and flow-con-

trolled systems, STEAM does not use the engine and

pump to directly supply flow to the actuators but, rather,

to maintain pressure levels in two separate hydraulic

accumulators (high and medium pressure).

This accumulator charging circuit makes it possible

to completely decouple the hydraulic actuators from the

engine and pump, letting these components operate far

more efficiently.

This not only enables operation at a considerably

lower and quieter engine speed of 1200 rpm but also

minimizes throttling losses and permits recovery of both

potential and kinetic energy from all the actuators.

Consequently, the machine is considered a hydraulic


In contrast to other hybrids, STEAM does not use

electrical storage devices or actuators. The already in-

stalled hydraulic system only needs to be modified, which

keeps costs low and avoids unnecessary energy conver-

sions. The robust and easy-to-maintain hydraulic hybrid

technology reportedly increases profitability for opera-

tors, as they can expect a more agile machine with sig-

nificantly lower fuel consumption.

Considering the constant concern over fuel costs and

more-stringent emission guidelines, STEAM is clearly a

very relevant and possibly game-changing innovation

for the construction equipment industry.

The prototype is currently being tested with prelim-

inary measurements showing that the hybrid is just as

fast and powerful as standard machines, but it operates

up to 40% more efficiently. More testing is underway to

accurately quantify the potential of the new technology

and make the results available to industry, thereby en-

couraging implementation in future applications.

Hybrid and Other Technologies

Whilst advances in hybrid technology will provide a vi-

able solution, there are alternatives such as electric,

battery or hydraulic driven. Electric driven excavators

have been a common feature in specific industries such

as waste and port handling where the machines are not

required to move very often.

However, the past few years has seen alternatives to

diesel power being introduced to mini and compact


Are Power Packs the

Future for Compact


Another alternative is to

use a hydraulic power

pack. Today, virtually all

movement of excavators is

hydraulically driven,

therefore, if a feeder

can prov i de the



fl o w

t h e n

t h e

engine become virtually obsolete. This is

a development of Wacker Neuson and now adopted by


A benefit of this option is the dual power versatility

it enables. Unplug the power pack and the excavator

immediately returns to a diesel power.

Caterpillar has added the model 300.9D VPS (Versatile

Power System) to the Cat range of mini-hydraulic exca-

vators under the partnering agreement with Wacker


It will be an attractive option to existing Caterpillar

plant hire and rental companies as well as those con-

tractors who often have to work in very restricted areas

where engine emissions may not be permuted (i.e.

internal refurbishment of shopping malls, etc.)

The versatile design benefits both the owner/oper-

ator and the rental company by allowing the machine—in

conjunction with its separate hydraulic power unit—to

work either with its diesel engine or from a remote

electrical power source, with no loss of performance.

Having an electrical drive system remote from the

machine enhances utilization and rental options. The

300.9D VPS can be rented alone for regular applica-

tions—or with the hydraulic power unit when the job

requires low noise and zero emission.

The Institute for Fluid Power Drives and Controls

(IFAS) of RWTH Aachen University

Steinbachstraße 53 - D-52074 Aachen

Tel: +49-241-80-27528

Dipl.-Ing. Milos Vukovic

Group Leader System and Control Technology

Roland Leifeld,



Net power

9.6 kW (13 hp)

Stick force

4.5 kN (1012 lbf)

Bucket force

8.9 kN (2000 lbf)

Digging depth

1,731 mm (68 in)

Dump height (max.)

2,035 mm (80 in)

Reach at ground level

3,027 mm (119 in)

Operating weight (min.)

1,088 kg (2399 lbs)

Shipping weight (min.)

988 kg (2178 lbs)

What's New in Plant & Equipment

Contractors World International Vol 7 No 4