New breed of tractors gear up for take-off

New breed of tractors gear up for take-off
Stepless transmissions
New breed of tractors gear up for take-off
Stepless or continuously variable transmissions are the latest development in a push toward efficiency in tractor-based
farming operations. Instead of preset gear ratios, tractors with stepless transmissions have an infinite range of ratios to
suit any combination of travel speed and engine power. This report outlines the technology and the tractors available.
At a glance
• Stepless transmissions eliminate
fixed gear ratios, allowing the
operator to choose any desired
working ratio.
• Work rates can be increased as
gear ratio changes are made ‘on
the run’ automatically by the
tractor’s computer.
• Stepless transmissions are ideal for
power take-off work as the tractor’s
travel speed can be infinitely
adjusted while maintaining constant
engine and power take-off speed.
• Engine power is split into both
hydrostatic and mechanical power
trains to create a continuously
variable ratio, while maintaining
transmission efficiency.
• Different stepless transmissions
exist in other machinery as beltdrive or fully hydrostatic systems
but these are unsuitable for tractors
due to inefficient power transfer.
• Farmers participating in the
Kondinin Group review
overwhelmingly accepted the new
transmissions, with most rating the
machines as excellent to operate.
• When buying a tractor with a
stepless transmission, weigh up
the increased cost of the machine
versus potential savings from
increased efficiency and work rate.
• The power loss through a stepless
transmission is roughly the same
as for a four-speed powershift
transmission. Some control
systems will increase available
engine power at higher ratios
where torque is lower.
6
Ben White
• The new technology is claimed to
be more fuel-efficient than
conventional powershift
transmissions, as engine speed and
transmission ratio can be fine-tuned
to any particular operation.
Stepless transmissions are more than a passing fad now that five major tractor manufacturers have
machines on the Australian market. Kondinin Group engineer Josh Giumelli inspects the transmission
found in the Case IH CVX tractor.
F
armers can potentially save on fuel
costs and cut time off their working
day by using tractors fitted with stepless
transmissions.
The new stepless or continuously variable
transmissions (CVT) differ considerably from
conventional powershift units by using a
infinite range of gear ratios to suit any
combination of travel speed and engine
power rather than preset gear ratios.
Stepless transmissions offer increased power,
ease of operation and higher travel speeds
which can cut transport times — all of which
equals considerable fuel savings, even up to
23 per cent as tested by Profi International.
Fendt introduced the first tractor with a
stepless transmission internationally during
1995 with release of the Vario series.
Case IH, John Deere, Massey Ferguson and
Deutz have all since followed suit and have
entered the Australian market (see Table
1 opposite and Table 2, page 8).
Not all manufacturers use their own
individual transmission units.
For example, Massey Ferguson uses the
Vario transmission, Deutz and John Deere’s
6420 series tractors use a ZF Eccom unit,
while John Deere’s 7020 series is fitted with a
different transmission which the company
designed. Case IH uses a CVX transmission,
the same type as in the Steyr S-Matic series.
While some of these tractors share the
same transmission, each has its own complex
computer system, which controls the gear
ratio and engine speed.
Why go stepless?
Fuel efficiency, ease of operation and
time savings are the hallmarks of stepless
transmission tractor technology.
With a traditional gearbox, engine speed is
directly linked to travel speed.
For any given gear ratio, the faster the
engine speed, the faster the tractor travels.
But with a stepless gearbox, engine speed
and travel speed are independent.
The tractor’s computer can save fuel by
slowing the engine speed while maintaining
travel speed during light work.
Likewise, it can increase engine speed
and lower the transmission ratio to maintain
travel speed while boosting draught when
working under more difficult conditions.
For example, a conventional tractor
operating at eight kilometres per hour could
be overloaded if shifted into the next gear
Index
Case IH CVX transmission
10
Vario transmissions
12
John Deere IVT transmission
14
ZF Eccom transmissions
16
FA R M I N G A H E A D
No. 143
December 2003
Stepless transmissions
at 8.8km/h. But if the operator could select
the ideal working speed of 8.5km/h by
changing the transmission ratio and not
increasing the engine speed, the tractor would
use less fuel. The stepless transmission
allows this to occur.
The difference between travelling at 8km/h
and 8.5km/h also could reduce a 12-hour
work day by 40 minutes.
FIGURE 1 How a stepless transmission works
Hydraulic pump
with variable output
Engine
Extra options for PTO work
The stepless transmission allows travel
speed to be adjusted while power take-off
(PTO) revolutions per minute (rpm) are
held constant.
In effect, the operator can accelerate and
decelerate without changing engine speed.
The new technology allows for wider
working options as opposed to traditional
PTO-driven machinery that requires
maintaining a constant engine speed, so the
PTO operates at 1000rpm, 750rpm or 540rpm.
Traditional transmissions limit any ability
to fine-tune tractor travel speed, as the throttle
needs to stay set.
How the transmission works
At the heart of the stepless gearbox is two
power transmission systems — mechanical
and hydrostatic (see Figure 1).
In simple terms, power from the engine is
split into the hydrostatic and mechanical
drive trains and then recombined.
The hydrostatic system consists of a
hydraulic pump and a swash plate-style
hydraulic motor.
The mechanical system uses one or more
planetary gear trains. In some cases (such as
in the ZF Eccom and Case IH CVX) clutches
and brakes are used to engage and disengage
the various planetary elements.
A planetary gear train has three elements:
a central ‘sun’ gear; ‘planet’ gears orbiting
the sun gear; and a ring gear surrounding
the planets. The planets are attached to the
planet carrier, which can also rotate.
Research Report
Hydraulic
motor
0°
Ring Sun
gear gear
30°
Planet
gear
Planet
carrier
45°
Engine power is split into the hydrostatic and mechanical drive trains and then recombined.
The hydrostatic system has an hydraulic pump and motor and the mechanical system uses planetary
gear trains consisting of a central sun gear, planet gears orbiting the sun gear and a ring gear.
Inset: Hydraulic pump flow rate or hydraulic motor displacement is varied by changing the angle of the
swash plate or pump or motor (pictured) to alter the piston stroke. A longer piston stroke means a
higher pump flow rate or a lower shaft speed from the motor. Oil is not pumped at a zero angle but
angling the pump body or swash plate below zero reverses the flow direction.
Source: Profi International. Inset: Kondinin Group.
Drive can be taken from any element in the
planetary gear train but no gear ratio is fixed
if all elements are free to rotate. This is where
the hydrostatic system works by modifying
the rotational speed of the planetary system.
To understand the working of the system,
compare the action of the planetary gear train
to a vehicle’s differential system, which is also
a type of planetary gear train.
A vehicle’s differential allows the speed of
each rear wheel to change, so the outside
wheel can turn faster and the inside wheel
turns slower when cornering.
The slower one wheel turned, the faster the
other would turn, until the slow wheel ceased
to turn and the fast wheel would be turning
at twice its original speed. If the stationary
wheel was then turned in the opposite
direction, the speed of the fast wheel would
continue to increase.
Changing speeds
A hydraulic motor alters the speed output
of the planetary gear train just as slowing or
reversing the direction of one wheel changes
the speed of the opposite wheel.
To change the speed of the hydraulic
motor, the output flow rate of the hydraulic
pump is altered by either changing the swash
plate angle or the angle of the pump body,
which lengthens or shortens the stroke of the
pistons (see Figure 1 inset).
TABLE 1 Stepless transmissions as reviewed by Kondinin Group
se
Ca
Make
Transmission origin
IH
t
nd
Fe
z
ut
De
hn
Jo
e
er
De
hn
Jo
e
er
De
y on
se us
as erg
M F
CVX
TTV
Vario
Autopowr
(6020 series)
IVT
(7020 series)
Dyna-VT
Steyr S-Matic
ZF Eccom
Fendt
ZF Eccom
John Deere
Fendt
50
50
50
50
40
50
Maximum forward speed (km/h)
Number of working ranges
4
4
2
4
2
2
Variable
Variable
Variable
Variable
Variable
Variable
Hydrostatic motor displacement
Fixed
Fixed
Variable
Fixed
Fixed
Variable
Number of planetary gear trains
4
4
1
4
2
1
Number of transmission clutches
41
4
0
4
2
0
Number of transmission brakes
2
1
0
1
1
0
Hydraulic pump displacement
1. Positive engagement clutches (non-friction).
FA R M I N G A H E A D
No. 143
December 2003
Source: Kondinin Group.
7
Sharing the power load
Although fully hydrostatic transmissions
are common in harvesters and earthmoving
equipment, they are typically inefficient as
power is wasted due to friction in the
hydraulic oil flow.
A tractor fitted with a hydrostatic
transmission would be uneconomical to run
due to excessive fuel use.
TABLE 2 Price list
)
kW
(
r
we
Po
d
an l
e
e
ak d
M mo
Case IH
CVX 1135
CVX 1145
CVX 1155
CVX 1170
CVX 1190
89
96
103
114
129
$148,500
$156,200
$169,400
$188,650
$198,550
Deutz TTV
1130
1145
1160
99
108
115
$154,000
$158,400
$165,000
Fendt Vario
409
410
411
711
712
714
716
815
817
818
916
920
924
926
930
64
75
82
86
93
104
119
112
123
134
134
157
179
201
224
$104,499
$110,874
$117,300
$124,134
$133,824
$144,840
$153,000
$155,000
$162,531
$170,556
$175,681
$195,784
$207,123
$217,111
$232,716
John Deere
6420
6420S
6620
6820
6920
6920S
7320
7420
7520
7720
7820
7920
72
73
81
90
99
100
78
85
92
104
115
126
$117,811
$125,691
$133,695
$141,628
$149,895
$157,377
$135,478
$143,180
$151,286
$178,526
$188,393
$192,590
Massey Ferguson
7465
7475
7480
7485
7490
7495
82
93
101
108
119
130
$133,100
$142,890
$148,500
Not released 1
Not released 1
Not released 1
* All prices include goods and services tax.
1. The manufacturer has yet to release prices.
Source: Kondinin Group.
8
*
ice
Pr
Stepless transmissions
For this reason, the stepless transmission
retains the mechanical components.
The power splitting concept of the
stepless transmission aims to increase the
efficiency of hydrostatic transmission by
sharing the power flow with a more efficient
mechanical system.
Tests reveal a leading edge
Independent testing by Profi International
and Germany’s Nürtingen Technical College
has verified tractors fitted with stepless
transmissions are more fuel efficient,
powerful and save time compared with
powershift models.
For example, European tests carried out by
Profi International comparing the Case IH
CS150 and CVX150 tractors (which are
basically the same tractor, except the CVX
has a stepless transmission) showed a
3% increase in work rate and a 3% decrease in
fuel consumption in the stepless model when
both tractors were used in cultivation.
At higher speeds and towing a five-tonne
trailer the CVX150 used 23% less fuel than
the CS150 model. This was due to the
stepless tractor’s ability to reduce engine
speed but maintain travel speed under
lighter loads. When the trailer weight was
increased to about 30t, the CVX150 travelled
6km/h faster, using 11% less fuel.
Germany’s Nürtingen Technical College
tested two Fendt tractors that share the same
engine but one model, the Vario 916, had a
stepless transmission while the Favorit 816
was fitted with a four-speed powershift.
During mowing tests on undulating
ground the Vario 916 covered 8–16% more
area and used 10–16% less fuel than the
Favorit 816. In this test, the Favorit 816 had to
change working ranges continually.
PTO speed in the stepless tractor varied by
only 5%, while it changed by up to 20% in the
powershift tractor.
Farmers trials
Kondinin
Group
gauged
farmer
impressions of stepless transmission tractors
at a recent Leibe Group field day at
Dalwallinu, Western Australia. Farmers
operated a John Deere 7820 and the Fendt
Vario 714 and 930 model tractors.
Most farmers rated the tractors as excellent,
particularly for their ease of driving and
operating controls.
Farmers also praised the degree of control
when moving the tractor forward very slowly,
the ability to decelerate evenly and quickly
from a high speed and the ease of changing
between forward or reverse gears.
Most people could operate the machines
with as little as five minutes’ tuition, although
some found it difficult to adapt to the lack of
a clutch pedal.
Photos: Josh Giumelli
Research Report
James Erskine, Moora, Western Australia, reviewed
the John Deere 7820 after operating the machine at
the Leibe Group field day held at Dalwallinu, WA.
The tractors were considered suitable
for spraying and chaser-bin operations
and casual workers would be capable of
operating the machines with minimum
tuition. See Table 2 for tractor prices.
The pros and cons
efore buying a tractor with a stepless
transmission consider the benefits
and disadvantages of the technology.
B
Advantages
Better fuel economy as the engine can
‘power down’ under low load.
An increased work rate for faster
operations.
More suited to road work and are
usually capable of a top speed of 50
kilometres per hour.
Ease of driving as there is no gear
shifting or clutch use.
Suitable for operations where constant
power take-off (PTO) speed is critical.
Disadvantages
✗ Tractors with stepless transmissions
cost 10–20 per cent more than those
with a powershift transmission.
✗ Some newer models on the market
do not have a track record or proof
of reliability.
✗ There are low or nil fuel savings
when working under heavy cultivation
in even conditions compared with
a powershift tractor.
FA R M I N G A H E A D
No. 143
December 2003
Research Report
Stepless transmissions
Case develops the CVX transmission
C
ase IH’s CVX transmission was
developed by Steyr in conjunction with
transmission manufacturer ZF and is also
used in the Steyr CVT range of tractors (known
as the S-Matic).
The transmission shares some features
with the ZF Eccom unit such as four planetary
gear trains and four working ranges but
differs in its design and operation.
Four clutches are used to select the four
different working ranges, with an extra two
brake clutches for selecting forward or
reverse gears.
The clutches engage and disengage various
planet carriers, sun and ring gears to transfer
mechanical power flow through the planetary
gear trains. The clutches are toothed and
positively engage rather than the more
common friction clutch packs.
To understand this transmission it is
essential to know how the four clutches
operate (see Figure 2).
Clutch one engages the ring gear in the
second planetary to the intermediate shaft.
Clutch two engages the sun gear in the
second planetary to the intermediate shaft.
Clutch three connects the output shaft to
the first planet carrier through the shaft that
travels through the centre of the transmission.
Clutch four links the output shaft to the
intermediate shaft, which is connected to the
sun gears in the third and fourth planetary
gear trains.
Engine power is delivered directly to the
ring gear in the first planetary gear train.
The hydraulic pump is also directly enginedriven and has a variable swash plate angle
to alter the output flow rate. The hydraulic
motor has a fixed displacement and drives the
sun gear in the first planetary.
Standing still
If the engine turns the ring gear at a set
speed and the hydraulic motor turns the sun
gear at the same speed but in the opposite
direction, the planet carrier and planets will
not rotate around the shaft.
As a result, the transmission is locked
under power, as opposed to a neutral position
where the tractor can free-wheel.
The first clutch is in the engaged position,
which connects the locked output through
the ring gear to the intermediate shaft.
The forward brake is also engaged on
the fourth planetary, which locks the
intermediate shaft to the output shaft through
the planetary gears and carrier.
Moving off in first range
With the transmission in the locked
position, the hydraulic pump’s output is
reduced, slowing the speed of the hydraulic
motor and the sun gear.
The planet carrier will rotate, driving the
planets that turn the ring gear. This drives
the intermediate shaft and the output is
transferred through the fourth planetary to
the output shaft. All clutches and brakes
are in the same position as when the
transmission was in the locked position.
As the hydraulic motor continues to reduce
its speed, the difference in speed between the
sun gear and the ring gear in the first planetary
increases, adding speed to the first planet
carrier and the tractor as it travels forward.
Maximum speed in the first range is
reached when the hydraulic pump’s swash
plate is at a zero angle, which halts the
movement of the hydraulic motor and
Case IH CVX Evolution series
T
he Case IH CVX Evolution series was
released during September 2003 and is
an update of the previous CVX stepless
transmission range.
The tractors have a power range of
89–129 kilowatts (power take-off) and
use six-cylinder, turbocharged, intercooled
diesel engines.
The stepless CVX transmission shifts
between four working ranges automatically to
reach a top speed of 50 kilometres per hour.
The operator applies the accelerator
to move the tractor forward and when
released, the machine comes to a controlled
stop, including on sloping ground as
the transmission prevents the tractor
from rolling.
The manufacturer’s automatic productivity
management (APM) system integrates the
engine, transmission, power take-off (PTO),
hitch and cabin controls.
Engine speed and transmission ratio are
controlled to deliver power while maintaining
a practical level of fuel efficiency.
Engine speed is reduced for road transport
to improve fuel economy while the
transmission ratio is adjusted to maintain
travel speed.
For paddock operations, the APM will keep
the PTO at a constant speed and adjust travel
10
speed using the transmission ratio and not
engine speed.
Operators can select three speed ranges
of 0–14km/h, 0–25km/h and 0–50km/h for
better speed control via the accelerator pedal.
The main transmission controls are
mounted in the right armrest and on the
fixed joystick.
Three cruise control modes are available
and the computer will manage engine speed
and transmission ratio to maintain the set
travel speed.
A monitor on the A-pillar displays travel
speed, cruise speed, PTO revolutions per
minute, remote hydraulic flow rate and
other information.
Minimum engine speed can be set using a
small knob on the right armrest, which also
controls how the transmission responds to
load changes.
At the minimum setting, the transmission
will drop its ratio quickly as soon as the
engine speed starts to decrease under load
to maintain working speed and ensure
maximum power.
At the maximum setting, the engine
speed will fall to about 1600rpm before the
transmission ratio decreases for maximum
fuel economy.
2
4
1
3
Cabin controls in the tractor are: (1) the + and –
buttons control travel speed; (2) is the shuttle reverse;
(3) is the hand throttle; and (4) is the cruise control
interrupt–resume button.
Contact
Case IH
Phone: (02) 9673 7777
Fax:
(02) 9833 1031.
FA R M I N G A H E A D
No. 143
December 2003
Stepless transmissions
sun gear. At this point, the drive is
transmitted only by mechanical power.
Research Report
FIGURE 2 The Case CVX transmission
Hydraulic motor
Second range
To engage the second range, the first clutch
is released and the second clutch is activated.
Power now travels from the sun gear through
clutch two to the intermediate shaft, lifting
the drive ratio.
The hydraulic pump is reset to maximum
angle (maximum flow) and works its way
back to zero flow as speed in the second range
increases to maximum (100 per cent
mechanical). Power is transferred though the
fourth planetary to the output shaft.
Hydraulic pump
Intermediate shaft
Third range
Power from the planet carrier in the first
planetary gear train is now transferred directly
to the output shaft, effectively bypassing the
second, third and fourth planetary gear trains.
Clutch three is used to connect the output
shaft to the shaft running through the centre
of the intermediate shaft to the planet carrier
in the first planetary.
The forward brake on the fourth planetary is
disengaged to allow the planetary carrier to
rotate freely with the output shaft. Speed is
varied continuously with the hydrostatic drive.
Clutch three is disengaged and clutch four
engaged, which locks the fourth planetary
and allows it to rotate as a whole, effectively
locking together both the output and
intermediate shafts.
Fourth range
Engaging clutch two will transfer power from
the second sun gear to the intermediate shaft.
Reverse action
Engaging the reverse brake activates the
third planetary, which transfers power from
Source: Profi International.
ar y ar y tch tch ake ar y ar y ake tch tch
net lanet st clu d clu se br lanet lanet rd br th clu d clu
a
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t p d p Fir econ ever ird p r th p r w a our Thir
F
Firs econ
S R Th Fou Fo
S
the third sun gear via the planets to the ring
gear (now travelling in the opposite direction).
The third ring gear is attached to the
fourth planet carrier, which is attached to the
output shaft.
When the reverse brake is engaged,
the forward brake on the fourth planetary
will disengage.
This
space
is
deliberately
blank
FA R M I N G A H E A D
No. 143
December 2003
11
Research Report
Stepless transmissions
Vario takes complexity out of stepless style
T
he Vario transmission — the least
complicated system in use — is fitted on
both the Fendt Vario and Massey Ferguson
Dyna-VT range.
Only one planetary gear train is used in
conjunction with a variable output hydraulic
pump and two variable displacement
hydraulic motors.
The transmission has two ranges — a
working range of 0–28 kilometres per hour
and a travel range of 0–50km/h.
The engine is linked directly to the planet
carrier in the planetary gear train (see Figure 3).
The planet gears drive the sun gear, which
transmits power to the rear wheels and to the
ring gear to drive the hydraulic pump.
Both hydraulic motors are connected to
a ‘collecting shaft’ on the output side of
the transmission.
Neutral position
When the hydraulic pump is set at a zero
angle it will not pump oil but the shaft driving
the pump is free to rotate. As a result, the
engine-driven planet carrier and the ring
gear (which drives the pump) rotate around
the sun gear without actually turning it.
This means the planetary gear train ‘freewheels’ without turning the output shaft.
Moving forward
If the hydraulic pump is moved from its
zero angle, it will start to pump oil to the
hydraulic motors.
The motors are set on their maximum
angle and at this maximum displacement
they will turn the collecting shaft slowly when
supplied with oil.
As the tractor moves, the sun gear will
rotate, mechanically transferring some of the
engine’s power through the planetary gear
train. At slow operation speeds, most power
is transferred hydrostatically.
As the pump angle increases, more oil is
pumped, the collecting shaft turns more
quickly and the tractor travels faster.
As the speed of the collecting shaft increases,
so too does the sun gear, which means more
power is transferred mechanically.
Going faster
The pump is at maximum displacement
when its body is angled at 45 degrees.
To increase tractor speed further, the
hydraulic motors are angled back from 45
degrees, reducing their displacement but
increasing the speed at which they turn the
collecting shaft.
The tractor continues to accelerate and the
mechanical power share increases.
As the tractor travels even faster, the angle
of the hydraulic motors approaches zero.
At this point, the hydraulic pump ceases
to drive the motors as they have zero
displacement and the pump cannot supply oil
with the motors in this position.
But the collecting shaft is free to rotate,
so all power is transferred mechanically
Fendt Vario series
T
he 1995 release of the Fendt tractor
equipped with a Vario transmission was
the forerunner of all stepless tractors.
There are now 15 models in the 400, 700,
800 and 900 series.
The clutch pedal fitted to the Vario actually
operates a hydraulic proportional valve in the
transmission, which acts the same as a
conventional clutch would. This allows the
service brakes to be applied when the engine
speed is less than 1300 revolutions per
minute, without loading the transmission.
To move, the operator selects one of the two
working ranges (0–28 kilometres per hour or
0–50km/h), presses the switch on the back of
the joystick, then accelerates. The switch is a
safety feature to prevent accidental operation
of the tractor.
To increase the transmission ratio, the
operator holds the joystick forward while
applying the throttle and the tractor can now
accelerate to the maximum transmission ratio.
Alternatively, the joystick can be ‘bumped’
to shift the ratio up or down in steps.
To slow the tractor, pull back the joystick to
lower the transmission ratio. Holding the
joystick in position will make the tractor stop
quickly. With the tractor stationary, pull back
the joystick for reverse travel.
Changing from forward to reverse also can
be carried out automatically with the tractor
travelling at speed by tapping the joystick
to the left — the tractor will stop, then reverse
its direction.
12
The ratio of forward to reverse speed
can be adjusted. At default, the ratio is set
at 1:1, which means the tractor will travel
at the same speed in reverse as it will in
forward gear.
But the reverse mode can be set to operate
either slower or faster than the forward speed.
(The John Deere ‘Autopowr’ series also has
this option.)
Two cruise control speeds can be stored
and activated by tapping the joystick to the
right to either increase or decrease travel
speed to the preset level, irrespective of
engine speed or changing load.
The acceleration rate is set by a fourposition toggle on the side of the joystick.
This also controls how quickly the tractor
moves through its transmission ratios.
For slow operations (such as ‘inching up’ to
an implement), the setting is left on position
one for improved control.
The 800 and 900 series Vario tractors use
an advanced engine and transmission
management system called TMS, which
actively selects the most appropriate engine
speed for the transmission ratio in use.
The TMS also makes adjustments for the
acceleration rate selected on the joystick and
the tractor load.
The 700 series tractors will soon be fitted
with engines incorporating an electrical
rather than mechanical governor, which will
allow the TMS control system to be installed.
4
1
2
3
The joystick (1) moves forward or backward to
change the transmission ration, while (2) sets the
acceleration rate and a button (3) selects the
working range of I or II. The cruise control is set via
the monitor (4).
Contact
Agco Australia
Phone: 1800 802 914
Fax:
(03) 9311 8171.
FA R M I N G A H E A D
No. 143
December 2003
Stepless transmissions
and the tractor travels at top speed for
that range.
Research Report
FIGURE 3 The Vario stepless transmission
Changing ranges
Hydraulic motor
The Vario transmission has two ranges,
which can be changed ‘on-the-go’.
Planetary
gear train
But the control system can block the
change (for example, if there is engine
overload changing from low to high range).
The lower range of 0–28km/h is used for
paddock operations, while the higher
0–50km/h range is used for transport.
Reverse action
To change the direction of the collecting
shaft and the travel direction of the tractor,
the hydraulic pump body is moved back past
zero to a negative angle.
This reverses the flow of oil, with the
discharge side of the pump now becoming
the suction side.
Hydraulic pump
Collecting shaft
With a reversed oil flow, the hydraulic
motors will turn in the opposite direction,
rotating the collecting shaft in reverse.
To increase the reverse speed, the pump
can be angled to a maximum of –30 degrees.
Hydraulic pump
Two-speed range
Source: Profi International.
Massey Ferguson Dyna-VT
M
assey Ferguson has released the DynaVT tractor range — consisting of the
Perkins-engined 7465, 7475 and 7480 series
— based on the Fendt Vario transmission.
Larger tractors — the 7485, 7490 and 7495
series using Sisu engines — will be released
during 2004.
While the tractors use the Vario
transmission with two forward ranges of
0–28 kilometres per hour and 0–50km/h, the
operator interface and computer control
system are different.
Pushing the armrest lever forward will
move the tractor, pushing it forward further
will increase speed or pulling it back will
decelerate the tractor.
The left shuttle lever selects the tractor’s
travel direction and can be used to change the
transmission ratio.
The controls also can be changed to
allow all operations to be carried out via the
foot pedal.
When operating the tractor with the
armrest lever, a dial controls the way engine
speed and transmission ratio interact or how
forward speed is altered, depending on any
drop in engine speed.
If the dial is set to the power take-off (PTO)
position and the engine speed reduces, the
transmission ratio will lower to maintain
engine speed and a constant PTO speed.
FA R M I N G A H E A D
No. 143
December 2003
If set at the opposite extreme (a trailer
logo), the computer allows engine speed to
fall considerably before reducing the ratio.
Several settings are available for general
draughting and towing.
The tractor’s cruise control can memorise
two forward speeds in each range and
direction as well as a start-up speed in forward
and reverse.
The cruise control is adjustable using two
dials located on the console.
When operating the machine using the
foot pedal the tractor can use one of three
modes — power, eco or forager (PTO).
The power mode allows engine speed to
increase and be maintained at the rated
speed. The transmission ratio is changed
based on the engine load.
The eco mode maximises fuel economy by
increasing the transmission ratio rather than
engine speed under light loads.
The forager mode is used for PTO
operations and holds the engine speed
constant regardless of the tractor’s forward
speed. Acceleration in forager mode is via the
transmission instead of engine speed.
Contact
Agco Australia
Phone: 1800 802 914
Fax:
(03) 9311 8171.
1
2
3
The transmission speed lever (1) on this tractor
controls the ratio but is not used to select forward
or reverse, while two buttons (2) select the preset
cruise control speeds. Inset: This dial (3) controls
engine and transmission responses.
13
Research Report
Stepless transmissions
John Deere introduces IVT tractor range
T
he John Deere infinitely variable
transmission (IVT) incorporates two
planetary gear sets to enable seamless
shifting at up to 40 kilometres per hour and
contains only two clutches and one brake,
making it one of the more simple
transmissions in use.
The ITV uses a mechanical drive train (see
Figure 4).
Power from the engine drives the sun gears
in both planetary gear trains, as well as the
hydraulic pump.
Moving the swash plate through 45 degrees
in either direction varies the pump’s output
but the hydraulic motor has a fixed
displacement.
For the tractor to move, power needs to be
transferred through the planetary gear carrier
to the clutch pack.
FIGURE 4 John Deere’s infinitely variable transmission (IVT)
Hydraulic
pump
First
planetary
Re
se
ver
bra
Se
ke
con
la
dp
tch tch
clu e clu
e
g
g
ran h ran
w
g
i
Lo H
net
ar y
To
PTO
Hydraulic
motor
Front
axle
Source: Profi International.
Standing still
With the engine turning the first sun gear
and driving the hydraulic pump, the
hydraulic motor can rotate the ring gear at
the same speed in the opposite direction.
This means that while the planetary gear will
rotate, the planetary carrier stands still and
the tractor will not move.
The transmission can stay locked at any
engine speed as the hydraulic pump can
adjust its displacement to keep the ring gear
speed equal and opposite to the sun gear.
This
space
is
deliberately
blank
Moving off
To start moving, the hydraulic pump’s flow
rate is reduced, causing the hydraulic motor
and ring gear to operate slower.
The planet gears start to rotate the
planetary carrier, which drives the tractor
through the clutch pack (shown in green in
Figure 4).
The slower the hydraulic flow rate, the
faster the tractor travels.
When the pump’s flow rate slows to zero,
the swash plate angle also will be zero.
If the swash plate is rotated past this point,
the pump starts to drive (becomes a hydraulic
motor) and is driven by the hydraulic motor,
which is now operating as a pump.
In this situation, the ring gear is turning in
the same direction as the sun gear and the
tractor accelerates.
Switching ranges
The clutch pack can alternate drives (high
or low gear) between the two planetary
gear sets to increase the transmission’s
speed range.
The outer low-range clutch disengages and
the inner high-range clutch engages, which
switches off the first planetary gear train in
favour of the second gear train.
Reverse action
To select reverse, the inner and outer
clutches are both released.
A brake is engaged on the outer ring gear of
the second planetary gear train that will drive
the clutch pack through two sets of planet
gears (shown as grey and pink in Figure 4),
causing it to rotate in reverse.
14
The control system of the IVT 7020 series
tractor is similar to the John Deere 6020
Autopowr tractors (see page 17).
Contact
John Deere
Phone: 1800 800 981
Fax:
(07) 3803 6555.
1
2
The John Deere IVT tractor (pictured top) features
the cabin controls (below) of a (1) transmission
ratio control lever, which is also used to select
between ranges one and two, (2) speed control
knob, which is also used to set the cruise control.
FA R M I N G A H E A D
No. 143
December 2003
Research Report
Stepless transmissions
ZF Eccom transmission clocks up high speed
T
he ZF Eccom transmission has four
working ranges incorporating four
planetary gear trains, four clutches and one
brake to achieve working speeds of up to 50
kilometres per hour.
Figure 5 shows how the engine’s power is
delivered to the ring gear in the first planetary
gear train, which also doubles as the planetary
carrier for the second planetary gear train.
The hydraulic pump is driven from the far
right of the engine shaft.
The hydraulic pump has a variable
displacement and drives the fixed
displacement hydraulic motor, which, in turn,
rotates the sun gear (shown in dark blue in
Figure 5) in the first planetary gear train.
The ZF Eccom transmission is used in both
the John Deere 6020 Autopowr series and
Deutz TTV series of tractors.
Standing still
If the hydraulic motor (at engine speed)
rotates the sun gear in the first planetary train
in the opposite direction to the ring gear, the
planetary carrier (shown in red in Figure 5) in
the first planetary train will rotate at half the
engine speed.
The planetary carrier is attached to a large
drum-like element surrounding the first three
planetary gear trains and also serves as the
ring gear in the second planetary, as well as
the carrier in the third planetary gear train.
The second planetary carrier (attached to
the engine shaft) rotates at engine speed.
But because the ring gear in the second
planetary gear train is rotating at half the
engine speed, the result is that the sun gears
of planetaries two and three (which are
linked) rotate at twice the engine speed.
As the carrier in the third planetary train
is attached to the red drum, it rotates at
half the engine speed. When this is engaged
with the third sun gear in the centre rotating
at double the engine speed, the third ring
gear is stationary.
Even though the ring gear is not rotating, it
is engaged through the first clutch to the sun
gear of the fourth planetary set.
Because the brake on the fourth planetary’s
ring gear is engaged, the transmission output
is locked and the tractor stands still.
Moving off
Applying the transmission brake appears
complicated but it allows the tractor to move
by varying the speed of the hydraulic motor.
By reducing the pump output and
slowing the drive from the hydraulic motor,
the first planetary’s sun gear slows, causing
the first carrier and drum to accelerate,
which causes the sun gears of the second and
third planetaries (linked) to decelerate. As a
result, the third ring gear (which was
stationary) rotates.
The brake on the fourth ring gear is still
applied, so drive is transferred from the sun
gear to the carrier in the fourth planetary and
the tractor moves off.
First working range
As the speed of the hydraulically driven sun
gear in the first planetary is reduced, the
tractor accelerates.
When the output of the pump reaches
zero and the sun gear stops rotating, the
drive is fully mechanical. The pump then
reverses flow, which also reverses the
hydraulic motor and the sun gear direction to
increase tractor acceleration.
At maximum reverse pump flow, all
components in the first three planetary gear
trains rotate at engine speed. This is the
maximum speed in the first working range
or about 6km/h.
Second working range
When the tractor needs to accelerate faster
than 6kmh, the second clutch engages, the first
Deutz TTV Agrotron
T
he Deutz TTV tractor range uses the ZF
Eccom stepless transmission with a
maximum speed of 50 kilometres per hour.
All tractors are fitted with a liquid-cooled,
six-cylinder, turbocharged, intercooled Deutz
diesel engine.
The transmission operates in either a
manual, power take-off (PTO) or automatic
mode, which is selected by a button on the
armrest. The tractor reverts to automatic
mode as a default on start-up.
In automatic mode, the engine speed is
controlled by the computer, depending on
travel speed and power required.
The operator selects the travel direction
using a button on the joystick or a shuttle lever
mounted on the steering column.
To start travelling, the operator presses the
foot throttle and holds the joystick forward.
Pulling the joystick back will slow the tractor.
To set a constant travel speed for paddock
operations, push the joystick forward until the
desired speed is displayed on the monitor.
The tractor will accelerate to this speed
when the foot throttle is fully depressed.
In PTO mode, the hand throttle controls
PTO speed, while the foot throttle controls the
travel speed using the transmission only.
16
The maximum travel speed is determined
using the joystick.
The cruise control button can be used to
store the current travel speed. The tractor can
return to this speed after headland turning or
other operations.
The auto dial controls the engine speed
response. In the ‘Ecomax’ position, the
engine revolutions per minute are maintained
at 1000–1700rpm, depending on power
requirements.
In the ‘Powermin’ mode, the engine speed
will not fall below 1800rpm under load.
The operator also can set the mode dial to
any position between the two extremes.
In manual mode, the foot and hand
throttles work similarly to those of
conventional tractors.
The transmission ratio is changed as in
auto mode but the computer does not control
engine speed.
Manual operation is more suited to
transport and yard work. If more power is
required, the operator can reduce the
transmission ratio and increase engine speed.
The monitor on the A-pillar displays both the
current travel speed and the maximum speed
possible under full throttle in the current ratio.
1
3
2
4
The Deutz cabin features (1) a
joystick that moves forward
or backward to control the
transmission ratio; (2) hand
throttle; (3) shuttle reverse; (4)
mode select; (5) economy power
dial; and (6) acceleration rate.
5
6
An ‘active standstill’ mode will only operate
when the transmission is in auto mode and
will hold the tractor stationary on a slope as
soon as the foot throttle is released.
In manual mode, the tractor reverts
to neutral and the hand-brake needs to
be applied.
Contact
Landpower Australia
Phone: (03) 9369 1188
Fax:
(03) 9369 1944.
FA R M I N G A H E A D
No. 143
December 2003
Stepless transmissions
clutch disengages and the hydrostatic drive to
the first sun gear is reversed. This causes the
linked second and third sun gears to increase
in speed to twice the engine speed.
The second clutch connects the drive to the
fourth sun gear (shown in yellow in Figure 5)
and to the transmission output, doubling the
tractor’s speed range to 12km/h.
FIGURE 5 The ZF Eccom stepless transmission
Hydraulic
motor
Hydraulic
pump
Reverse Forward
clutch
clutch
First clutch
Second clutch
Third working range
With the second clutch engaged, the third
clutch will engage and the brake disengages.
All of the four planetary gear sets are
rotating together at the same speed, with the
hydrostatic speed variation operating only on
the first planetary gear train. In this range,
the tractor can accelerate to 24km/h.
Fourth working range
The fourth range will increase the tractor’s
maximum speed to about 50km/h by releasing
the third clutch and engaging the fourth
clutch. The second clutch remains engaged.
In this mode, the hydraulic motor can
accelerate both the first and second sun gears
to twice the speed of the engine.
Engaging the second and fourth clutches
transfers power to the output shaft, which will
rotate at the speed of the two sun gears.
Research Report
PTO
shaft
To
rear
axle
ry ry ry h h ry
eta eta eta lutc lutc eta
lan plan plan r th c ird c plan
p
t
d
d u Th r th
Firs econ Thir Fo
Fou
S
Front axle
drive clutch
Source: Profi International.
Selecting reverse
The selection of forward or reverse occurs
on the output shaft of the gearbox, using two
clutches (forward and reverse). When the
reverse clutch engages and the forward clutch
is disengaged, a gear is effectively eliminated
from the drive train, resulting in a reversal of
the shaft driving the rear axle.
John Deere 6020 Autopowr series
A
n earlier version of the John Deere
stepless transmission tractors is the 6020
Autopowr series tractors fitted with the ZF
Eccom transmission.
These tractors appeared on the market
before the John Deere 7020 series fitted with
the manufacturer’s own infinitely variable
transmission (IVT).
The transmission speed control lever on the
right armrest only has a single speed wheel on
top, which fine-tunes the travel speed.
To move the tractor, the operator uses the
left shuttle control, moving it from either
‘neutral’ or ‘park’ to forward or reverse before
applying the foot throttle.
The gear ratio is increased by pushing
forward the speed control lever. A gate in the
centre of the lever’s movement arc separates
the two working ranges (in reality, the
transmission shifts through four ranges to
reach a maximum speed of 50 kilometres
per hour).
The speed selector wheel on top of the
speed control lever can fine-tune the tractor’s
travel speed. The operator can program two
set speeds into the transmission simply by
shifting the control lever to the end of the slot
in either range and dialling in a speed with the
speed selector wheel.
A six-position dial on the right armrest
controls how the transmission responds to
varying loads. Position zero on the dial
indicates manual mode where operators can
FA R M I N G A H E A D
No. 143
December 2003
control the transmission using just the speed
control lever and either hand or foot throttle.
In position one, the engine speed has to drop
by 30 per cent before the transmission control
reduces the gearbox ratio. In position two, this
is reduced to an 18% engine speed drop.
Position three is ideal for power take-off
(PTO) operations, as the gearbox ratio will
lower as soon as the engine speed reduces
by 5%. This means PTO shaft speed can be
held at a constant speed as it is directly linked
to engine speed.
Positions four and five allow for more
efficient operation such as in the transport
mode when higher travel speeds are required
without the need for high engine speeds.
The computer will determine the power
required and reduce the engine speed
accordingly.
This needs to occur in
conjunction with an increase in transmission
ratio to maintain travel speed.
The transmission control also can adjust the
speed ratio between forward and reverse travel.
At default, the ratio is set at 1:1, which
means the tractor will travel at the same speed
in reverse as in forward travel. But reverse can
be set to operate at either 70% slower or 30%
faster than the forward travel speed.
Contact
John Deere
Phone: 1800 800 981
Fax:
(07) 3803 6555.
5
4
1
2
3
The Autopowr series features a (1) transmission
ratio control lever, which is also used to select
between ranges one and two; (2) speed control
knob, which is also used to set the cruise control;
(3) hand throttle; (4) Autopowr selector dial; and (5)
engine speed control for PTO work.
Acknowledgements
Profi International; Leibe Group, WA;
Jolly and Sons, WA; Donnie and Co, WA;
Agco and CNH Australia.
About the author
Josh Giumelli is an engineer with Kondinin Group’s
research team. Email: josh@kondinin.com.au
17
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