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When Volvo Construction Equipment began planning
the 2006 rollout of its next-generation motor graders several years ago,
they formed panels of grader operators to critique their machines and
those of the competition. As design work progressed on what would become
the G900 series graders, they continued bringing in panelists to
evaluate the designs.
The result is a new family of motor graders that
boast an intriguing combination of cutting edge engineering features and
a long list of subtler changes and innovations that experienced grader
operators love.
These new machines, seven models in all, were
officially introduced to the construction press in April. It was an
impressive debut. Even in the hands of editors, but especially in the
hands of experienced operators, the new machines got high marks for
smoothness, power, agility, and operator comfort.
Engineering features
Tier 3 engines were the stimulus for the new
series, and Volvo used V-Act equipped diesels for the grader line — the
7.2-liter D7E for the four popular-size models (34,000 to 37,000
pounds), and the 9.4-liter D9B for the three production size models
(39,000 to 46,000 pounds). The new engines meet Tier 3 standards with
in-cylinder solutions, eliminating the need for add-on treatments. The
new engines also bring more power and improved fuel efficiency to each
model in the family, mainly by providing enhanced torque
curves.
Performance and fuel efficiency are further
enhanced with Volvo’s variable horsepower settings — low range for high
fuel efficiency in low-load situations, mid range for average uses, and
high range for full-speed roading and other applications requiring
maximum horsepower.
Volvo also equips each grader with a “Power and
Speed” switch. Selecting Power mode allows the operator to set 1,900 rpm
as the maximum engine speed in the low and mid power ranges. Low end
torque is boosted to power through the tough spots, but it also helps to
save fuel as the engine isn’t running faster than necessary. In the
higher gears, or when the switch is set to the Speed mode, full rpm is
attainable for faster travel speeds.
Perhaps the most unique new engineering feature
on the new graders are two versions of a new powershift transmission,
developed in house specifically to achieve a level of smoothness not
possible with existing technology. What they created is a unique
direct-drive powershift transmission that can be operated manually or as
an automatic. The new design eliminates the master clutch and replaces
it with a low-effort inching pedal. It delivers ultra-smooth shifts at
working speeds, better fuel economy, and a new shuttle shift feature.
“Shuttle shift” allows the operator to directly
shift between forward and reverse in either direction without stopping,
clutching, or pausing. It increases operator productivity when working
on short runs and in tight spaces by making the shift in direction
faster and gentler, and letting the operator focus on positioning the
machine and the blade. In practice, when operators reach the end of a
run, they shift in one straight motion from forward to reverse then
immediately lift the blade. By the time the blade is up, the machine has
come to a soft stop and started backing up. The countershaft design
accepts the transition without damage or unusual wear.
The standard transmission is the HTE840, with
eight forward speeds and four reverse speeds. It tops out at 28 miles
per hour in forward, and 20 miles per hour in reverse. In standard trim,
it has a single, manual shifting mode; shifting is accomplished by
simply pushing the lever away from the operator for an upshift, and
toward the operator for a downshift. The
HTE840 can also be equipped with an optional “Autoshift” mode for
grading, and a “Travel” mode for roading. In Autoshift, the operator selects a target gear and the
transmission shifts automatically to adjust to turns and grades and
changing loads.
For sophisticated users,
Volvo also offers the
first 11-speed transmission in the motor grader industry, the HTE1160.
It features all three operation modes, including Autoshift, and it has
six reverse speeds. In addition to higher top-end speeds (30.8 miles per
hour forward and 23.4 miles per hour in reverse), the benefit of 11
forward speeds, say Volvo engineers, is the ability to more precisely
match the gear to the load at any given moment — more control at low
speeds, more precision at normal speeds, and more efficient travel at
high speeds.
For fine grading, for example, the HTE1160 has
three low gears for speeds up to 3.5 miles per hour, while the
eight-speed shifter has two. At the other end of the speed spectrum, the
11-speed gearbox has four travel-speed gears compared to three for the
eight-speed, giving the machine more efficiency in everything from
high-speed snow plowing to ascending grades at roading speeds.
Volvo’s powerful all-wheel-drive option, a carry
over feature from the previous series, was shown to good advantage at
the press introduction when snow and rain reduced the demonstration area
to a slippery mire. While only professional operators could grade with
conventional four-wheel-drive models, even the editors were able to take
aggressive cuts running six-wheel-drives in the slop. |
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Perhaps the most important feature of the
six-wheel-drive G946 and G976 is Volvo’s front-wheel-drive-only Creep
mode. Designed for ultra-fine grading, Creep mode gives the operator
infinitely adjustable speeds from 0 to 2.5 miles per hour via a
hydraulic drive system that lets the machine operate at speeds as low as
0.1 miles per hour without stalling or lugging. The benefits of Creep
mode include feather-soft starts and the total absence of shifts,
eliminating two main sources of ripples in a finished grade.
Power and agility
One of
Volvo’s priorities in this redesign was
to improve on the wide turning radius of the preceding series. They
accomplished this, even though they started by lengthening the wheel
base to give the G900 Series graders more stability and bladedown force.
They increased frame articulation to 23 degrees on the D7 platform and
21 degrees on the D9 platform, and they increased wheel lean on all
models to 18 degrees. The result: a turning radius of 290 inches on the
D7 family, and 312 inches for the D9 family.
The overarching goal of the frame and chassis
design was to focus the machine’s power and weight to maximize downward
forces on the blade and still provide high drawbar pull rates. To
further enhance blading efficiency, engineers gave the new series
wide-stance blade lift cylinders coupled with a low-angle side shift
cylinder to create what they claim is the most stable grading platform
in the industry.
Moldboard movements are controlled via
intelligent, load-sensing hydraulics, and a twin-gear, direct-drive
circle turn system.
The rear tandems get new planetary reduction
axles that reduce loading on the tandem chains and improve power and
traction. To cope with varying traction conditions, the operator can
lock or un-lock the rear axle differential with an on-off switch in the
cab.
Operator environment
Volvo designed the G900 series to appeal to
contractors and local agency buyers. Both groups favor high-content,
value-added graders, not only because of the work they do, but also
because they put a high value on motor grader operators and often make
purchase decisions based on the operators’ preferences.
So in addition to adding a bundle of new
engineering features to the new machines, Volvo took a serious run at
recreating the operator environment to reflect the input of the many
operators they consulted in the development process.
The result is a very comfortable workplace.
Sight lines forward, to both sides, and to the edges of the blade have
been cleared by going to six thin ROPs pillars rather than four thick
ones. Six interior and exterior mirrors and a sloping engine hood
provide good vision to the rear.
Soundproofing has reduced interior noise-levels
to a car-like 75 dBA under heavy load. The air-ride seat can be adjusted
on several planes. The interior air is double filtered. Low-effort,
short-throw levers provide precise, predictable blade control and get
high marks for feathering from veteran operators. Even the wiper blades
have been redesigned so they reach the lower corners of the windshield.
Many other cab enhancements involve small
touches, such as automatic lights that illuminate the steps when you
open the cab door to exit. And a great deal of effort went into placing
controls and readouts to meet the priorities of experienced blademen.
Designed for the times
Taken in total, what the G900 Series brings to
the motor grader field doesn’t suddenly antiquate a five- or 10-year-old
grader that’s doing the job for its current owner, but it definitely
redefines the state of the art in grader design and performance for the
most serious users.
What’s most impressive about the latest entry
from Volvo is how deftly they mixed new technology with comfort and
convenience issues to advance efficiency on both a mechanical and human
level.
As one Volvo manager put it, “The G900 Series is
the culmination of a long conversation with expert grader operators.
It’s about what they value and what they don’t in a grader.”
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