Electronic System

 

649

ELECTRONIC SYSTEMS FOR MODERN CONSTRUCTION MACHINES

Dr.-Ing. Winfried Walzer Liebherr-Werk Biberach GmbH

SUMMARY

Even under the very severe operating conditions typical for the construction machinery ar area ea electronic control systems are beeing used more and more. Examples of presently used electronic control systems in a big European construction machinery supplier's program of excavators, wheeled loaders and track type vehicles are presented.

1. INTRODUCTION The customers are always calling for us to come up with improved construction machinery with a wider range of functions, greater economy and simplified operating characteristics. characteristics. As a result, the conventional system modules of construction machines, (figure 1) namely the

 electrical

mechanical ,

hydraulic

and

modules, are beco becoming ming mo more re and more problematical.

lectric l

Electro - mech interface

  Electromagnets   Electric motors motors   Generators

nic l

  Lamps - Contactors

relays

Hydraulic

Mechanical  Diesel engines   Transmissions   Axles

- Sup porting porting structures  

- hydraulic Electro interface

Hydro - mechanical interface

Figure 1 : Conventional system modules of

 Valves   Hydraulic moto motors rs  Hydraulic pumps   Hydraulic cylinders

construction machines

On the one hand, these problems are partly due to the fact that the additional machine functions requested by customers increase the complexity of the mechanisms and the hydraulic and electrical systems.

 

650

On the other hand, in the field of construction machines there is an increasing number of cases to which conventional solutions are very difficult, if not impossible, to apply. This is true in the case of earthmoving machines, for example, where there is a requirement to incorporate the diesel engine and mechanical gearboxes together with the hydraulics into a unified control system.

Against the the background o of f the successf successful ul application of micro-electronics in the industrial field and above all in the

field of automobiles, this has resulted in the increasing use of electronics cs to solve problems associated with the contro rol of

construction machines. construction In consequence, there have been developed for the Liebherr construction struct ion machinery special electronic systems: the Litronic systems

system)) C ommunicati ommunication on interface   b us system

Electronic

- switching - displaying - monitoring - controlling - regulating

Sensors

 

Electrical- interface

Sensors

Electro - mechanical interf ce

Electro -hydraulic interf ce

ydro   m e c h n i c l interf ce

Figure 2 : System modules of the Litronic-generation of

construction constru ction machin machines es  

65 1

The range of applications to which Litronic systems are already applied covers nearly all vehicles and products included in the Liebherr construction machinery group's delivery programe.

Uti tili lizati zation on frequency Degree of complexit plexity y

II

SWITCHING --

U

 

DISPLAYI PLAYIN NG -^

 

 

MONITORING --^ CONTROLLING -^

 

REGULATING --v  

^ -w o h g h o w h g h Figure 3 : Electrical and electronic functions of construct construction ion machines

As figure 3 shows, the tasks performed by electronic systems in construction machinery relate to the following functions: - switching, - displaying, - monitoring, - controlling and - regulating. It is obvious that low-comp complexity electrical electrical functions functions still

account for the majority of applications, whereas the more complex electronic functions (like regulating ) are applied rather seldom, when one considers considers their potential benefits for the

system as a whole.

The reason for this is without doubt the fact that electron onic

systems for construction machines are usually more complex and expensive than conventional systems and are expected to cope with extreme requirements and tough operating conditions. Consequently, factors such as economy can scarcely be used as the main arguments for employing electronic systems on construction machinery. Instead, the main advantages are - the ability to achieve new and improved functions, and

- the ability ability to combine these individual functions to create system functions that were not previously practicable. In my further presentation examples of beneficial electronic systems syst ems and intelligent intelligent system applications with a high degre degree e of automatisation will be taken from the following areas: - excavators, - wheeled loaders - bulldozers.

 

6 52

2. LITRONIC IN HYDRAULIC EXCAVATORS

The primary power source of most hydraulic ex xc cavators is the

diesel engine, and the engine's power output must be put to the best possible use by the hydraulic system an and in particular by

the hydraulic pumps. Various operating criteria apply. To develop and apply such ex xc cavators on a la large sca al le, it is necessary necessar y to take into account the character characteristics istics of the hydraulic pumps on the one hand and the characte teristics of the

  ^

diesel engine, engine, working implements and hydraulic hydraulic system on the

other hand, at least to the extent, that these can be controlled by an overriding electronic electronic syst system. em.

r s e n s o r ever sensors for work ing hydrauli hydr aulics cs L ever

d e a y u n t D v e s Switching unit Display unit cockpit instruments

.

^ .

. . . . . .

Travellin O il level level

Consumers 1 H o i s t inin g g e a r / b u c k e t

-

.

.-. .-,.-.-.-..-,.-.-.-.-.-.-.J .-.-.J

Other sensor and excavator control system witchin g in p u t s H - switching - displaying O ther electrical - mon itoring itoring consumers - con trolling trolling - regulating

Consumers 2 S t e w i n g g e a r/ d i p p e r a r m

Diesel-engine speed reduction

D sel engine part-load potentiometer Coolant temperature

Actual diesel engine speed

ENJ- QII QII1Z 1Z

Liebherr D 904 T diesel engine

I LPVD 100 EP

Figure 4 : Litronic excavator control system (block circuit diagram)

As figure 4 shows, the driveline of such an excavator consists of the diesel engine, which drives a do double hydraulic pump with

electro-proportional control. The oil flow from the double pump is fed to the consumers via the control valve blocks. The control valve blocks are hydraulic pilot-controlled, with the pilot pressure shared by means of two pressure measuring elements that form part of the excavator's elec electronic tronic control system. A system laid out in this way allows the

excavator to perform

many useful functions, such as controlling the flow in relation to requirements by dividing

the available energy between the various consumers, - lever sensors for the working hydraulics with adjustable time  

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lags and automatic drops in the diesel engine speed during working pauses, an economy mode as well well as stepless adjustment of the die diesel sel engine's speed to the respective requirements of the operator, electronic underspeed control of the diesel engine, either in full load- or in part-load operation, to optimize optimize the exploitation of the diesel engine's engine's output power, - protection of the diesel engine and of the hydraulic syst system em against overload conditions monitoring of the entire system parameters by means of a functional operating and monitoring unit, with audible and visual warning systems and automatic prot protective ective mechanisms. As far as excavators and most other earthmoving machines machines are

concerned, the most important function is the electronic underspeed control for the diesel engine. The principle of this is shown in figure 5. Voltage at diesel

engine gas potentiometer (Volts) Voltage potentio   curve wat ithpotentiometer engine meter off-loa off-load) d)

Regulation starts before

diesel engine power is attained Regulating zone C urve for star startt of regulat ulation ion ]

Reduction in regulating regulating zone   app. 100/min) Reduction from idle to start of regulation   app. 150/min)   I( I I 1000

14

r r a 9

17

19

2

215

Full-pow er s^ Diesel eng engine ine speed 1 /min) Full-pow

      L r

Torque at idle spee

100 220 200 230

Fuel

3 0 0 2 4 0 c o n s u m p i in

I 9 Specific fuel

4 0 0khc o n s u m p t io nT o r q u e

70 500

 80

6

9 I

1 I

Diese engine

Torque I Power output N m k

I Pow er out output put

Figure 5 Litronic underspeed control funktio funktional nal diagram  

654

The three axes in this diagram show the voltage voltage at the diesel

engine's gas potentiometer'(and thus the desired value for diesel engine speed), the actual diesel engine speed and the associated diesel engine characteristics: torque, output power and specific fuel consumption.

Also included are two examples of excavator work ranges (namely the full-power range and the eco nomy range). It is obvious, that in the full power range the total engine

power can be transformed into usefull hydraulic power. It is also obvious, that in the economy-rang economy-range e at the diesel

engine speed of approx. 1550 1/min to 1700 1/min the fuel consumption is reduced by approximately 15 percent (caused by less speed an less specific fuel consumption) in relation to operating the excavator in the full power range.

2150

Diesel en gine J 1980 1980 speed [ 1 /m 1810

750

Hydraulic pump p ump 600 600 actuating current [mA]

450 300

200 Load pressu p ressure re [bar]

100

0 1 sec Figure 6 :

Dynamic response

system

of Litronic underspeed

control

 

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Figure 6 shows how the Litronic load regulator responds when the load suddenly suddenly jump umps from 50 50 bar to 320 bar in the full power

range.

The rating of the double hydraulic pump is more than double the power of the diesel eng gi ine, and must be regulated down to the

same value as the diesel engine's output power by the regulator within the shortest possible time. This high installed pump rating ensures that each of the two

hydraulic pumps can accept the full output power of the diesel engine as and when required, thus permitting each of the two

consumer

circuits

to

convert convert

the

full

diesel

power

into

excavating power.

3. LITRONIC

IN

WHEELED

LOADERS

To increase the effective ratio range of hydrostatically or hydrodynamically driven wheeled loaders, the larger types have a multi-ratio mechanical gearbox on the output side of the stepless hydraulic transmission (hydrodynamic converter or hydrostatic

transmission).

During the work phases, the wheeled loaders always move in the lowest gears and change their speed by varying their engine speed and using the stepless hydraulic transmission.

Shift direction Tr a v el

1 s t - 2nd gear

2n d

1st gear

 

situation On fl a t ro a d

 

insignificant

Uphill

 

Downhill

 

whether + or -

+ : Change of speed on shifting tends to accelerate vehicle - : C han hange ge of speed w hen shif shifting ting te tends nds to deceler decelerate ate vehicle

Figure 7 : Wheeled loader transmission shift mo modes des

 

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By using multi-ratio multi-ratio power shift mechanical gearboxes it is possible to vary the mechanical transmission r ra atio while the

wheeled loader is in motion and under load. However, if no steps are taken to adapt the output speed of the stepless

hydraulic

transmission transmission

to

the

input

speed

of

the

mechanical po power wer shift gearbox, the rigidity of the driveline can lead to a jerky shift. Whereas a transmission jerk jerk with an accelerative eff effect ect has

scarcely any disturbing results, a jerk with a rptardative effect can, depending on travel

speed, be severe enough in

extreme

situations (snow, wet road etc.) to lock the whee situations wheels. ls. Since such situations must be avoided for safety and refinement reasons, the task of the electronics is to delay the transmission jerk when shifting (fo (for r example downshifts at too high travel

speed or at driver errors) so that a smooth shift is obtained in all driving situations. Furthermore, it is the task of the power shift electronics, at the driver's option, either - to permit semi-automatic driving with manual gear selection, or

- to permit fully automatic driving with gears selected automatically automat ically according to speed and load.

Direction of travel l Gear ratio r

1p  

Diesel-engine start

Pow er-sh er-shift ift gea gearbox rbox control-system electronics

Idle switch

Bypass valve

Liebherr D904TID906T diesel engine

A4VG...DA

3 - speed power-shift gearbox

A 6 V M ... DA variable - displacement

variable - displacement pump

Inductive speed sensor

motor

Figure 8 : Control system electronics for L531

- L551

power-shift

gearboxes (block circuit diagr gram)  

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Figure 8

shows a simplified block schematic of the

the Liebherr L531, L541 and L551 wheeled

driveline for

loaders.

The Liebherr diesel engine drives a swashplate-type axial-p axial-piston iston pump with an automotive control system. The oil at high

pressure which is ge generated nerated by the pump is

supplied to an axial piston type motor, also with an automotive control system, which in turn drives the 3-sp 3-speed power shift

gearbox.

The hydraulic motor, and thus the hydrostatic transmission, can be short-circuited or decoupled by means of a bypass valve. This transmission system attenuates shift jerks by using the

bypass valve valve to reduce the high pressu pressure re in the hydraulic transmission during gear shifts, and restoring it by means of a ramp function when the shift has been completed.

A slightly simplified method has been adopted for the Liebherr L510 wheeled loader.

Gear selector switch switch m t Trav Travel el direction d irection switch switch I ., r, , , N

R

n m K

W P o w e rshift gearb gearb ox

control-system

10. electronics Inching switch

A 4 V G . ... . D A variab le-displaceme le-displacement nt pump

Inching pedal

A P o w e rA6V M .. . D variable - displacement shift m o t o rg e a r b o x _1

Diesel speedengine limit I

sensor

Diesel engine

IH

 

1

L

Figure 9 : Control-system electronics for L510 L510 p power ower shift gearbox (block circuit diagram)

 

65 8

Using an

ingenious principle, that is

to say permitting

downshifts to the next lower gear (for example from II to I) only when the accelera rator pedal is fully or almos ost fully depressed,

this

new

principle

enables

the

conventional

hyd hydrostat rostatic ic

transmission with its automotive hydraulic adjustment system to be left unchanged, and uses a special electronic control system - to determine the the correct shift point

to control the shift sequence and duration, and to

inhibit

shifts

when

operating

conditions

are

inappropriate. The automatic version of the shift system described here differs from the semi-automatic version in that the gear shift commands are generated automatically when certain road speeds are reached. The automatic versio ion achieves a standard of behaviour when in

motion comparable to an automobile with automatic transmission. The solution solution described here thus makes it poss possible ible to use digi digital tal switching logic as a means of greatly increasing the refinement of

the

wheeled

loader

when

in in

motion,

without

making

the

hydraulic equipment more complex.

Tractive force pot Handbrake Inch potentiometer

A utomati utomaticc 1-2-3-4 2-3-4 Travel direction 1^-

rt

z

 

4371

Diesel engin enginee start

LiG'or-lic

wheeled loader contra system

- swttcl ing -displaying

- monitoring -conUo ling

- regulating

Gas potentiometer

Liebherr D 9308 T diesel engine

4 -speed J

p o w e r s h ifi f t

  8 - c y l ... . 2 5 7 k W )

gearbox L . _ J L J L ._ . . _ J

Working hydraulics

Figure 10 : Litronic wheeled loader control system (block circuit diagram)

 

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After the description of this two electronic transmission control principles, a system will be presented d, , which far ex xc ceeds the

normal bounds of present stage of series applications. applications. That is to say the use of a microprocessor control system for the whole driveline management task of large wheeled loaders, such as the Liebherr L561 machine.

The objective when developing this wheeled loader control system was to use electronics to control and regulate all the functions relevant to travel movement, for management of the powershift

gearbox and for a tractive-force limiting system controllable by the driver. The driveline consists of a Liebherr V8 diesel engine, a hydrostatic transmission with electronic-proportional control of the variable hydraulic pump and motor and an output-side mechanical 4-speed power shift gearbox. In this form, the driveline fullfills the following functions:

1) Aut Automatic omatic electronic travel control (forward, reverse and inching) with proportional proportional electrical control of the hydraulic pump and of the hydraulic motor 2) Electronic underspeed control for the diesel engine engine 3) Electronic maximum pressure limiting (pressure cut-off)

4) A driver-operated driver-operated potentiometer potentiometer to regulate tractive force between 20% and 100% of the wheeled loader's maximum tractive force 5) Manual gear selection with electronic synchronizing of the hydraulic transmission and the mechanical power shift gearbox 6) Automatic gear selection with no action needed on the driver's part

These functions can be summed up as offering the following advantages: - Improved power utilization, using an automat automatic ic electronic travel controller and using an electronic underspeed controller for the diesel engin' engin's s output power - Variable pressure pressure setting in the travel hydraulics, to adapt tractive force to suit actual ground conditions - Avoidance of wheelspin and therefore of excessive or premature tyre wear - Full control of gear shifts by the microprocessor, so that the driver's workload is reduced (no need to shift the 4-speed gearbox)

No wear at the shift clutches in the gearbox, and reduced loads on the entire driveline as a result of the electronical synchronised gear shifts

 

660

4. LITRONIC IN CRAWLER TRACK VEHICLES

The new Litronic machines family for crawler-track crawler-track dozers is a further example of how effectively and beneficially mechanical, hydraulic, electrical and electronic elements can be integrated. When developing this new range of dozers, the objective was to position them right at the top of their class in terms of performance and weight, to give them a modern appearance suggestive of their advanced technical featu features res and to achieve a definite improvement in the efficiency and operating life of components and therefore of the system as a whole. In addition, the use of the electronic diesel engine underspeed control was intended to convert the installed engine power into higher dozing force and to effect a definite improvement improvement in the vehicle's straight-line running by means of electronic track

synchronizing. The dozer models developed with these objectives in mind are also equipped with full

hydrostatic transmissions

to the crawler

tracks, and therefore possess all the acknowledged advantages of their predecessors, such as: - straightforward, stepless control over the entire speed range

- high manoeuvrability and power-on turning - no-wear steering, with point-turn facility - no-wear braking and reversing. In addition to these features, it has so far

always been

difficult to ensure straight-line running of hydrostatic-transmission dozers regardless of load. The

reason

internal

for

oil

this

is

leakage

to

in

be

sought

the travel

in

different

hydraulic

at

rates

of

differen different t

operating conditions, and also in production tolerances in the characteristic chara cteristics s of the pumps and motors used. It is obvious that this problem does not admit of an easy solution if only conventional hydro-mechanical transmission

principles are at the designer's disposal. disposal.

 

66 1

Ignition Igniti on sw itch

Safety

Em er gency

Travel control Load fft fftching ching

ston

Tellt

Faultale L ad sw itchi itching ng

doz er control control system - switching

  displaying

- monitorin monitoring g - controlling - regulating

Liebherr D 904 T diesel engine

Figure 11 : Litronic dozer control sys system tem (block circuit circuit diagram) Figure 11 shows the schematic layout of the redesigned driveline as a block diagram. The diesel engine drives the two pumps, which have electronicproportional control, through a splitter gearbox. The hydraulic pumps run in closed circuits and supply oil at high pressure to two hydraulic motors, which also have electronic ic-proportional

control.

The principal functions the driveline - Continuously variableof speed regulationin this form are: - Electronic steering control right down to point turns

 

- No-wear electronically controlled hydrostatic braking - Diesel engine load limiting (with priority for the working hydraulics) - Synchronizing of the two hydraulic motors (and thus the crawler tracks) for accurate straight-line movement. The functions outlined above result in the following advantages for the electronically controlled dozer:

66 2

Central monitoring of all control and regulating functions in the electronic system Simple control of travel movements by a single joystick lever Precise electronic operation of all components regardless of temperature changes Higher utilization of engine power, thanks to electronic

On

underspeed control of the diesel engine Electronic synchronization for precise straight-line running A high level of safety, thanks to built-in overspeed protection and the automatic parking and safety brake n  th e welcom e the basis of the good results so far obtaine

given to these principles by our customers, it is intended to

convert the the entire Li Liebherr ebherr dozer range to electronic contro control l in successive stages.

5. CONCLUSION

This paper so far has been intended to illustrate the changes

that are sweeping through the construction machinery control and regulation areas.

Conventional systems and equipment are frequently no longer

capable of coping fully with growing demands in the construction industry for additional facilities and more accurate standards of control,

with

the

result

that

electronic electronic

systems

are

being

adopted gradually but to an increasing extent, and are g gi iven steadily improving results even in the very severe operating

conditions typical of the construct construction ion machinery area.

Electric motor m a n a g e m e n t Hydraulic

Mechanical

Hoisting gear m a n a g e m e n t Hydraulic

Mechanical

Stewing gear management Hydraulic

echanical

etc. Electrical

Electronic

Electrical

Electronic

Electrical

Electronic

Electronic information I and data exchange channel (e.g. CAN bus, A bus, etc....)

EIecltonle

Electrical

EltHronic

Axle management

etc.

MecM alca alcall

Mechanical

Mechanical

H y d r a u l ic

Diesel engine management Travel gear management

Hydraulic

T ra n smi ssio ssio n m a n a g e me n t

Figure 12 : Construction machinery with distributed intelligence (block circuit diagram)  

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Whereas many current developments are still largely concerned

with individual electronic systems at various points on the construction machine (isolated solutions), there are already clear signs that further stages in the process of integration involving the components and systems distributed through the vehicle or

plant will culminate in a single networked, overall system. The new degree of freedom afforded by the Litronic systems, with the

straightforward straightforward

exchange

of

electronic

data

between

individual functional systems at various points, makes joint use of operating syst system em parameters fro from m other installed sy systems stems

possible by way of the communication interface mentioned earlier and a data bus , s so o that the entire equipment's performance and efficiency benefits. The development and use of electronic electronic data exchange sys systems tems of this kind began in the automobile and commercial vehicle areas some years ago (the first examples being the CAN bus, the A bus etc.), and is certain to penetrate the construction industry as

microelectronics are used increasingly. In the years to come, we will therefore be called upon to undertake still further intensive ve development work in the field of

construction machinery electronics, so that we can firstly

develop complete, optimized systems for each type of machine and secondly offer our clients in the construction industry new

generations of products with added benefits as a result of the Litronic concept.