DEVELOPMENT OF HYBRID HYDRAULIC...

DEVELOPMENT OF HYBRID HYDRAULIC EXCAVATORS

Hiroaki INOUE*

* System Test Group, Test Engineering Center, Development Division,

Komatsu Ltd.

3-25-1 Shinomiya, Hiratsuka-shi, Kanagawa 254-8555, Japan

(E-mail: hiroaki_ [email protected])

ABSTRUCT

More than 90% of the CO2 emissions in the lifecycle of machinery, from production to scrapping, are caused by its fuel

consumption at the time of operation, and any decrease in fuel consumption is directly linked to a decrease in

greenhouse gas emissions. For this reason, we have developed a hybrid system for a hydraulic excavator – construction

machinery with the highest number in use in Japan. This system uses an electric motor for the revolving upper structure

and regenerates, using a capacitor, energy hitherto released as heat when braking. Sales of the 20 ton class hydraulic

excavator PC200-8E0 started in 2008 [1]. We confirmed an average decrease of 25% in fuel consumption using data

from an on-board vehicle management system. This corresponds to a 20 ton decrease in CO2 emissions per vehicle per

year. For further popularization of hybrid excavators, we updated the hybrid components in late 2010[2], 2013 and

carried out a full model change. This is presented below in greater detail.

KEY WORDS

hydraulic excavator, hybrid, capacitor

INTRODUCTION

In recent years, hybrid passenger cars with greatly

reduced CO2 emissions have become widely popular and

sold as a step toward mitigating the global warming

problem. With the same goal as that for construction

machinery, the hybrid hydraulic excavator “PC200-8E0,”

which reuses the swing brake energy, was launched in

the domestic market as the world’s first hybrid excavator

in June 2008 [1], and sales were expanded to China and

the US in 2009. Capitalizing on the know-how and

technology accumulated through their sales performance,

we then carried out a full model change in December

2010[2]. Up until August 2013, 2250 Komatsu hybrid

hydraulic excavators were in operation worldwide, some

of which have exceeded 10000 operating hours. In light

of the increasing awareness about environmental

preservation, our proprietary hybrid system technology is

highly rated. The new model possesses a fuel efficiency

equivalent to that of the old model (PC200-8E0); in

addition, it also provides an arm crane (for the domestic

market), which is in high demand from customers, and

shared piping for attachments. The new model has a

broader spectrum of specifications so that it can deal

with a variety of work environments. Furthermore, by

improving the productivity of dedicated hybrid

components through in-house development and

production, we have provided a system that can meet the

supply needs of a global market. Here, we present the

outcome of our development of elemental technologies

and systems technology for the newly designed model

hybrid excavators HB205-2/HB215LC-2 (Figure 1).

Copyright © 2014 JFPS. ISBN 4-931070-10-8

Proceedings of the 9th JFPS International Symposiumon Fluid Power, Matsue, 2014

Oct. 28 - 31, 2014

93

1C1-1

Figure 1 HB205-2 overview.

KOMATSU HYBRID SYSTEM

The key components of the hybrid hydraulic excavator

are an electric swing motor, generator motor, inverter,

and capacitor. Figure 2 outlines the Komatsu hybrid

system. The electric swing motor converts the kinetic

energy of the revolving upper structure during swing

braking into electricity and supplies it (stores it) to the

capacitor. The generator motor then uses this electricity

to assist engine acceleration and generates electricity

when the capacitor’s electricity levels drop. The inverter

regulates the frequently changing flow of electricity to

and from the capacitor.

Figure 2 Outline of the Komatsu Hybrid System

For the current model change, we have updated the

hybrid components through in-house development and

production and are thus improving productivity. One of

the special features of the Komatsu hybrid system is its

use of a capacitor to enable efficient and instantaneous

charge and discharge of electric energy.

HYBRID COMPONENTS

Because these components increase the power density

and are compact in design, it is possible to install them

(these components) in a same size vehicle body as the 20

ton fully hydraulic standard excavator on which the

hybrid hydraulic excavator is based without requiring

any changes to the external body dimensions.

Figure 3 Outline of built-in hybrid components.

For this reason, the turning circle and operating range of

the hybrid hydraulic excavator have the same

specifications as those of a fully hydraulic standard

excavator. We present further details below.

GENERATOR MOTOR

As illustrated in Figure 4, the generator motor is

mounted between the engine and the hydraulic pump.

There is no loss in transmission efficiency to the

hydraulic pump, and electricity is supplied to the electric

swing-motor.

Figure 4 Generator motor

To ensure a reduction in the fuel consumption of the

Copyright © 2014 JFPS. ISBN 4-931070-10-8 94

hybrid machine, running of the engine at low speed,

which is the optimum condition for efficient fuel

consumption, is controlled by pumpmatching. The

required hydraulic discharge is assured, in addition to an

ultralow idling speed that turns the engine over at an

extremely low RPM while waiting. This pump matching

requires the acceleration of the engine to the required

RPM in immediate response to the lever operation. At

this point, indicated by the solid line in Figure 5, the

generator motor also functions to assist engine

acceleration. This driving energy is efficiently generated

when the engine is idling and charges the capacitor.

In other words, this generator motor is an important

component, functioning as both a generator and a motor.

Furthermore, a Switched Reluctance (SR) motor with a

magnet-less rotor is employed, thus doing away with the

need for rare earth metals.

Figure 5 Assisting engine acceleration

by generator motor

SWING MOTOR

Figure 6 An electric swing motor

Because conventional hydraulic motors employ

hydraulic release for upper structure braking, the energy

released as heat can be recovered by using an electric

motor. Fuel consumption can be greatly reduced by

re-using this energy during driving. Electric motors are

also more efficient than hydraulic motors during

acceleration. In addition, smooth swing performance is

an important feature.

INVERTER

An inverter is a device that converts DC electricity into

AC electricity and also has an inverse transformation

function. It converts electricity from the generator motor

and electric swing motor from AC to DC, transmits it to

the capacitor, and generates an AC electricity output

from DC electricity. Fuel efficiency can be greatly

improved by controlling the capacitor storage and output

effectively and instantaneously according to the

frequently changing drive conditions of the body.

Figure 7 Invertor and Capacitor

CAPACITOR

(Electric Double Layer Capacitor)

A capacitor is a component that stores and outputs

regenerated energy. Being integrated with the inverter, it

forms a compact component (Figure. 7). In contrast with

a conventional battery, it can charge and discharge by

electron and ion migration alone, and because it does not

utilize chemical reactions, it can charge and discharge

within brief periods of time. Hybrid passenger cars

require a large amount of energy during acceleration and

a comparatively fixed amount of energy during the

remainder of their operation. Therefore, they use a

battery that can discharge electricity over a long period

of time. On the other hand, hydraulic excavators

accelerate and slow down upper structures having large

inertia frequently in a brief period of time. Figure 8

shows difference of driving pattern between passenger

cars and hydraulic excavators.

Figure 8 Change of storing and outputting of

regenerated energy.

Because a large amount of processing power is also

required and chemical reactions are too slow, we arrived


at the use of a capacitor. Because capacitors theoretically

do not generate heat and show no degradation, they have

a long operating life and require no maintenance. They

are therefore very suitable for construction machinery,

which is in continuous operation over long periods of

time.

Figure 9 Characteristic diagram of capacitors and

batteries

In order to protect the capacitor from external impact,

revo frame is strengthened using a doublelayered

structure, as shown in Figure 10; an electrical leak

detection system that performs constant monitoring is in

place as a safety measure.

Figure 10 Protecting structures around a capacitor

EFFECT OF FUEL ECONOMY

In conventional hydraulic excavators, the entire engine

output is converted into hydraulic energy and distributed

to the individual actuators. Therefore, energy conversion

losses and losses resulting from hydraulic distribution

occur; these losses occur in addition to the so-called

meter-out loss, which is caused by the back pressure that

is usually applied in hydraulic system circuits to

facilitate speed control. In comparison, hydraulic loss

can be reduced by using a hybrid system that drives the

Figure 11 Average reduction effect on fuel consumption

Figure 12 Example case of reduction effect on fuel

consumption

Figure 13 KOMTRAX system image

upper structure with an electric motor and works in

coordination with other hydraulic equipment, and the

kinetic energy can be regenerated when the upper

structure slows down. Because the engine output can be

supplemented by the energy acquired through

regeneration, the engine’s operating range can be

matched to the most efficient range on the fuel

consumption map. This excavator achieves an average

reduction of 25% in fuel consumption as compared to

standard machinery in the same 20 ton class. Upon

measuring fuel consumption in the case of using the

excavator in comparison with other equipment used in an


average manner according to Komatsu’s internal

standards, we found good agreement of our data with

Japanese data (Figure 11) obtained using KOMTRAX,

the vehicle management system fitted to the entire

Komatsu fleet (a system that uses GPS and a

communication infrastructure to acquire a vehicle’s

operation status through the Internet see figure 13).

Through this vehicle management system, KOMTRAX,

a client’s workload status and operation patterns can also

be captured, and these are provided as an “Energy saving

operation support report.” Generally, the operational fuel

consumption of a excavator is governed by the way it is

used. Thus, the reduction of fuel consumption by hybrid

equipment needs to be evaluated separately. At high

swinging frequencies, reductions as large as

approximately 41% have been observed to be achieved

(Figure 12).

CONCLUSION

Conventional hydraulic excavators operate by converting

engine power into hydraulic power, whereas in hybrid

equipment, electrical power is added and the system

efficiency is improved. However, to prevent any

discomfort to the operator during its operation, all of the

engine, electrical, hydraulic, and control components

needed to be fully integrated. All these components were

developed and produced in-house, owing to which the

operational performance and productivity of the new

model improved further, and a production system could

be put in place that can meet the supply needs of a global

market. The increasing social need to reduce the burden

on the environment has given great impetus to the

preference for hybrid and electrical passenger cars in our

society.

Recently, many other construction machinery

manufactures produced hybrid excavators. They are used

both hydraulic motor and an electric motor for regenerate

of swig brake energy into capacitor. On the other hand,

without electric components, hydraulic swing motor

charges brake energy into accumulator directly and

release when it swing again. It’s called “hydraulic hybrid

system” So, there are 3 types of hybrid systems for

excavators. One is electric and one is hydraulic and last

one is both used. Will not be discussed superiority of

these systems in this paper, but the technology race that

share the same purpose of these is to drive the innovation

of the next generation. We want to strive for further rapid

advancements in this technology so that our excavator

can be deployed globally, allowing everybody to play a

part in reducing the environmental impact of

construction machinery.

REFERENCES

1. H. Inoue, Introduction of PC200-8 Hybrid Hydraulic

Excavator, Komatsu Technical Report, 2008, 54-161, pp.

26-31.

2. H. Yoshida, New Hybrid Hydraulic Excavator :

HB205-1/HB215LC-1, Construction Machinery and

Equipment, 2012, 48-1, pp. 37-42.


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