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SPS IPC DRIVES I SPECIAL

One step ahead

Customer-specific encoders for continuously variable tractor transmissions

Hall 7A Stand 506

Markus Brunner

Even though agricultural machines look massive and

clumsy at first sight, they apply their power and

performances with highest precision and accurate

dosage. The suitable drive technology ensures here

the stepless "sensitivity". Kübler encoders support

this technology.

or over 20 years, CVT gearboxes are an integral part of mobile

machinery. Agricultural tractors have been the forerunners of this

trend. Two of the world's leading tractor manufacturers are mounting

Kübler encoders in their CVT systems: these encoders are used in a

special branch with highly specialized requirements. Tractors brave the

most adverse weather conditions and plough the most loamy and stony

grounds. They heave, tow or cut tons of crops.

Developed following customer request

In brief: encoders for such applications cannot be found in the catalog.

Both encoders that ensure today reliable positioning in modern tractors

are the result of extensive development projects – based on strict

customer specifications. The used encoders contribute

significantly to machine performance; they are

integrated in the servo actuator, which is made of

components perfectly matched to one another,

electrical motor with gearbox and encoder. This is where the accuracy

and the intelligence of the machine come together. Together, the three

components of the actuator form the communication interface.

For mobile machinery, the technical goal is to combine efficiency

improvement and energy consumption in relation with the maximizing

of the so-called area performance, that is to say the performance at the

work systems and longitudinal drive. In this project, the real challenge

on the way to the suitable encoder was to find the compromise between

high accuracy and repeatability, together with total insensitiveness to

magnetic fields and resistance against shocks and continuous vibration.

A wide temperature range and reliable protection against moisture and

humidity were also part of the basic project requirements.

Within the servo actuator, Kübler encoders help the used CVT

gearboxes to make the defined high-torque motion sequences even

smoother. This allows more accurate driving of the tractors. In addition,

since no gear change is required, there is no more power loss linked to

this gear change, which allows achieving constant engine speeds. But

what about the accuracy?

Reliable in harshest conditions

Accuracy is taken in charge a follows: A servo actuator converts the

signals of a controller in the required gearbox ratio in the vehicle.

Here, the precision gearbox and the servomotor merge with the encoder

to form one single unit. Used in tractors, it must master reliably the

whole temperature and supply voltage range thanks to its torque and

torsional rigidity. This task is made even more difficult by the

fact that the values must be provided and represented under

varying load situations.

Markus Brunner, Global Industry Manager

at Kübler in Villingen-Schwenningen

Team work leads to success As a component manufacturer for the latest

tractor generation of two renowned

manufacturers, Kübler went through the

whole PPAP production part approval

process

. This is a structured sampling process for

series parts in the automotive environment

that defines comprehensive requirements for

the advanced quality planning. At Kübler, the

Project manager is the main interface to the

customer in this context. The inter-divisional

team made of designers, electronic

developers, QM management - always

supported by their colleagues of the work

preparation and purchasing departments,

was also taking part at the milestone

reviews, even on site.

68 Mobile Maschinen 6/2015

MOM_AG_2015_06_068 68 22.10.2015 08:58:23

Motor

Planetary gear

Output

Hydraulic pump

Servo

Hydraulic motor

actuator

Joystick

02Operating principle

of a CVT gearbox

In addition, a servo actuator is part of a global solution. This complex

task required a group of highly specialized companies that worked

jointly to provide the impetus for this product innovation, up to series-

production readiness. Besides the sensor and electronic suppliers, the

project involved the developers of the electromechanical section, of the

software and of the motors. The result of this joint work: the CVT

gearbox ensures acceleration and deceleration processes almost without

adjustment times.

The highly accurate optical encoders specially developed by Kübler

for use in the servo actuators of agricultural machinery are based on the

combination of two interfaces: an incremental one with 2000 pulses and

the parallel 5-bit Grey code scanning. Thanks to their high optical

resolution they provide accurate measured values and, at the same time,

they are extremely robust. The customer-specific mounting options for

the flange and the shaft complete the very compact and slim encoder

construction designed especially for the integration in the actuator.

The special features continue with the cable, which is flatter than

usually. The actuator converts with high accuracy a CAN Bis

instruction into an angular position of the axial piston pump, the

encoder provides the feedback to the controller. The instruction is

triggered by a joystick in the driver's cabin. The angular position

determines the hydraulic oil throughput. This oil quantity finally

regulates steplessly the speed of the hydraulic motor, and thus the

gearbox ratio.

Surely an excellent service

Within the drive, the actuator, being a monitoring interface, has a great

relevance also from the safety point of view. Accidental adjusting

movements, which can lead to machine motion from standstill, as well

as missing adjusting movements, which in the worst case can result in

braking processes not performed, belong to the sources of hazards that

can lead to damages to men or to the machine. The communication

between the gearbox controller and the adjusting unit is based on a

safety-oriented Can-bus protocol. It integrates many diagnostic

functions and plausibility checks, such as the monitoring of the

temperature, the voltage and the current.

Within this process, safety comes from the correct understanding of

the requirements. Relying on its many years of experience, Kübler can

support its customers for all functional safety topics. In addition, this

sensor specialist offers a comprehensive portfolio of services for all

safety aspects.

www.kübler.com

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um die Uhr für Sie im Einsatz. Bei einem Maschinenausfall werden alle

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Anruf genügt: 0800 77 12345.

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