Frasch-e

79RE 00 207/10.00

Drive by wireElectronic Control System for Skid Steer Loaders


Michael Frasch / VMT3/EBrueninghaus Hydromatik GmbHElchingen PlantPhone +49 (0) 7308 / 82 25 20Fax +49 (0) 7308 / 53 38E-Mail [email protected]

Fig. 1

Control system Market share

Direct mechanical control MD approx. 50%

Pilot-operated mechanical control HW approx. 35%

Direct hydraulic control DG approx. 15%

Electronic control DE Prototypes

IntroductionThe popularity of skid steer loaders is still growingand the trend will continue as well in the future,due to the compact size and excellentmanoeuvrability of these machines. Starting fromthe classical US markets, these constructionmachines have now also become established inEurope and Asia. Around 90,000 such machineswill be built worldwide this year and the figure isrising at a rate of roughly 10% per year. Theinstalled power and service weight of this class ofloaders are constantly reaching new dimensions.Today, these machines are also used in theextraction industry and in multi-shift operation.This trend in particular, plus the fact that more andmore of these machines are being operated by hirecontractors, has prompted Rexroth to develop anew electronic control system for the travel drive.Before discussing this system in more detail. At firstlet us have a brief look at the control systemsavailable on the market (Fig. 1/2).

Control SystemsDirect mechanical controlMost of the skid steer loaders feature this type ofcontrol for the variable displacement pumps. Withthis system, the two axial piston pumps arecontrolled directly by means of two levers. Theactuating force on the lever increases as a functionof the swivel angle and pressure.

Pilot-operated mechanical controlWith this type of control, a pilot valve is adjustedin accordance with the stroke via levers and/or aBowden control. The pump is then adjusted via thecontrol pressure determined in the pilot valve.Every movement of the control lever correspondsto a certain pump displacement. The actuatingforce on the lever is importantly lower than in the

case of a pump with direct mechanical control, butcomplex mechanical installation is still required.

Direct hydraulic controlIn this case, the control pressure in the controlchambers of the travel pumps is specified via ajoystick with integrated pressure reducing valves.Since the joysticks are almost of ergonomic design

and the low actuating forces required are notdependent on load, this type of control is alsopermiting fatigue-free operation over extendedperiods of time. The disadvantage of the system islying in the complex hose connections required forthe hand-operated accelerator lever.

Operating weight 3200 kgEffective load 800 kg

Dimensions Length 3,4 mWidth 1,7 mHeight 2,0 m

Power 59 kW

Travel speed 1st gear 12 km/h2nd gear 18 km/h

Tractive effort 35 kN

Fig. 2: Performance data of prototypes

80 RE 00 207/10.00


A new development by Rexroth electronic drive by wire control

With this system, the control signals from the newelectronic signal generator M-Control areprocessed by a type MC6 microcontroller andforwarded to the proportional pressure reducingvalves integrated into the new compact pumpA20VG (Fig. 3/5). This concept offers a number ofadvantages: Ergonomically designed joysticks ensure

optimum handling Low actuating forces regardless of load Functional operation through switches in the

joystick Optimum utilization of the available power Speed-dependent steering Variable lever resolution depending on speed Compact components permit freedom of

design Control system can be individually adjusted

to the momentary driver Not dependent on temperature Load limitation control Easy maintenance with fault diagnosis and

fault memory With S-curve or C-curve, as requested

Fig. 3

Mikro-controller

MC

M-Control

A20VG

MCRMCV

Control blockRadialpiston motor

Variabledisplacementdouble pump

Micro-controller

Fig. 4

Advantages of electronic control

Ergonomically designed joysticks

Low actuating forces regardless of load

Functional operation

Individual adjustment of the control system

Optimum utilization of power

Speed-dependent steering

Individual adjustment of the control system

Improved precision controllability

S-curve or C-curve

Load limitation control

Not dependent on temperature

Freedom of design

Less fuel consumption

Less noise

Less tyre wear

Diagnostic function

Recall current operating data

More convenient

Optimized functionality

Reliable operation

Maintenance

Protection of the environment

81RE 00 207/10.00


Of all the advantages mentioned above, attentionhas to be drawn in particular to the freedom ofdesign, the load limitation control and the varia-ble lever range.Due to the new signal generator M-Control, thiselement can now be integrated directly into thesafety-bar armrest without requiring complex hoseconnections. The compact A20VG variabledisplacement pump is creating further space in themachine (Fig. 6). By using these components, thefloor of the loader can now be encapsulated, thusreducing the level of noise.

As these machines are more and more appliedowned by hire contractors, they are also operatedby drivers with very different skills. Electroniccontrol is a useful aid for inexperienced machineoperators in particular. The engine is frequentlyoverloaded by inexperienced drivers when digginginto the heap, as power is consumed by both thetravel drive and the implement hydraulics at thatmoment. Without the necessary fingertip control,the engine will normally stall or the machine willbecome embedded in soft ground. The integratedload limitation control is preventing the enginebeing strained or stalled; the extent to which thewheels dig into soft ground is similarly reduced.Load limitation control also makes it possible toset the engine speed selected via the hand-operated accelerator lever to less than themaximum speed of the engine. In this way, fuelconsumption and emissions can be reduced whilemaintaining almost the same amount of goods, asthe full power of the engine is usually needed fora brief moment only. Variable resolution of the leverstroke over the ground speed is another featureof the electronic control. The momentary groundspeed can be set as the new maximum speed viaa switch in the joystick and the lever resolution isnow spread to the new maximum speed. This isresulting in considerably better precisioncontrollability and is important when working withtrench milling units or when pushing off andlevelling.

Fig. 5: Circuit diagram of the A20VG45DE

Fig. 6

Forward Right

ReverseLeft

M-Control

Micro-controller

MCV

A10VO

1PF2G2

A1 A2MA1 MA2G X3 X4X1 X2

B1MB1 MB2B2

82 RE 00 207/10.00


Fig. 7

Variable displacement double pump A20VG

Radial piston motor MCR

M-Control

Microcontroller

Components (Fig. 7)Signal generatorThe M-Control has been specially developed by theRexroth Hydraulics division for use in mobilemachines and is characterized by a robustlymounted control lever, large range of ambienttemperatures and a high protection class for theelectronics. Movement of the lever is detected viacontactless sensors based on the magnetoresistiveprinciple and processed by an internalmicroprocessor. A potential of 0.5 to 4.5 Volt isused as the output signal. Up to four switches forspecial functions can be integrated into theergonomically shaped hand-operated lever.

MicrocontrollerA number of different microcontrollers areavailable, depending on requirements, i.e. thenumber of inputs and outputs required. TheMC6H/32 and MC6E/32 controllers developed bythe Brueninghaus Hydromatik division forapplications in mobile machines are designed forprogrammable control of electroproportionallyadjustable axial piston pumps. In addition to thepump control, other electrical actuators can alsobe controlled by the microcontroller, includingactuators for switching travel motors over fromworking to transport speed or for applying andlifting the parking brake.

Travel pumpA compact medium-pressure tandem pump hasbeen developed by Brueninghaus Hydromatik foruse as travel pump. Two A10 rotary groups arearranged back-to-back in the new A20VG 45. Theadvantage of such an arrangement lies in theextremely compact size. The A20VG is roughly 16%shorter than the standard tandem pumpA10VG 45 + A10VG 45. The internal feed pumphas been omitted, since the implement hydraulicspump normally acts as supply via a flow divider orvia a pressurized return line. The pump is controlledvia separate proportional pressure reducing valvesfor each control chamber. The A20VG is alsoavailable with direct hydraulic control with andwithout DA control cartridge (Fig. 6).

Travel motorsAs a rule, a radial piston motor of type MCR withconstant displacement will be used for each sideof the vehicle. These motors then drive the wheelsvia chains or gear wheels. Multi-speed radial pistonmotors are used here as higher ground speeds areincreasingly being demanded, particularly forlarger compact loaders. The new 4-port radialpiston motors no longer have a preferred directionof travel and are therefore ideal for mobile loaders.The division ratio of Vgmax to Vgmin is normally2:1, but other ratios can also be supplied.

ProspectsElectronic control systems for the travel drive willbe a genuine alternative to the former driveconcepts, particularly for machines in the upperperformance range. Sooner or later, electronicallycontrolled travel drives will prove their value,particularly as electronic systems have taken overmajor control and monitoring functions in moreand more construction machines. Electronic controlof an LUDV control block for the implementhydraulics has already been realized in a prototypein combination with a load-sensing variabledisplacement pump, but the system is not yet readyfor production in series.

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