伊顿离合器

The Drivetrain Contribution
Axle and tire size dictate where the engine will operate during
cruise conditions, and should be selected to allow for good fuel
efficiency at the road speed and load where the vehicle will
spend most of its time. But trade-offs exist. Gearing the vehicle
too fast may result in having to shift too often on slight grades.
A good rule of thumb – gear the vehicle to allow it to pull a one
percent grade in top gear at nominal load conditions. With an
automated transmission and the burden of shifting removed,
gearing the vehicle faster allows the engine to operate closer to
its “Sweet Spot,” thereby improving fuel economy.
Transmission overall gear ratio range should be selected to
provide the required startability in the application, while still
providing top end gear ratio for the cruise speed operation.
The number of gears and step size should then be selected
to keep the engine operating in its best fuel efficiency area at
speeds below cruise speeds. Engines with narrow fuel islands
require smaller step size transmissions with more gears to get
best fuel economy, whereas engines with wider fuel islands
use larger step transmissions with fewer gears. The down side
of smaller steps and more gears – more shifting. Once again,
however, automated transmissions will eliminate this drawback.
An additional consideration is the use of 13-speed transmissions
with larger steps in lower gears and smaller steps in
higher gears. The larger steps in lower gears have minimal
impact on fuel economy since little time is spent in these
gears, and smaller steps in higher gears allow for increased
fuel economy in gears where the truck operates the most.
Axle design (apart from ratio selection)
may also impact fuel efficiency –
especially with the use of a differential
lube pump. Conventional differentials
and lube pumps operate continuously
and use energy. Various new axles
from Dana have on demand lube pumps
that only operate when needed
(i.e. compensating for different wheel speeds)
to help conserve fuel.
And speaking of lube, tests show “Next Generation”
Roadranger FE 75W-90 Fuel Efficient synthetic axle lubrication
can save up to 1% fuel costs annually.
The tests, which compared Roadranger FE 75W-90 synthetic
gear lubricant to traditional synthetic blends and semi-synthetic
blends, included those that were performed with two major
U.S. fleets, and a third that was conducted by an independent
fuel economy testing company. One-percent savings can mean
up to $500 per truck annually with today’s fuel prices.
The clutch has little
direct impact on fuel
economy as it is
mostly completely
engaged when the
vehicle is moving.
However, newer
engines operate at
best fuel economy
at lower engine
speeds, during
which potentially harmful torsional oscillations may damage
other drivetrain components. But the clutch contains an
internal element that dampens these oscillations to prevent
damage. So specifying the drivetrain to operate the
engine at lower speeds for fuel economy should include
a correct damper.
4
This guide is periodically updated throughout the year. The most current information can be found

on roadranger.com/spec
Direct Top-Gear Transmission versus
an Overdrive Top-Gear Alternative
For many applications, use of a direct top geared transmission
can be a simple, low cost alternative. That’s because gear and
bearing frictional losses during top gear operation (typically
85 to 95 percent of running time for most of today’s linehaul
trucks) is eliminated. That can result in fuel economy improvements
of up to one or two percent versus a comparable overdrive