XTRONIC CVT - Nissan Global

XTRONIC CVT
Technology Overview
C O N T I N U O U S LY V A R I A B L E T R A N S M I S S I O N
XTRONIC CVT
Technology Overview
Nissan’s 3rd generation
“XTRONIC CVT” further boosts
acceleration and fuel economy
CVT delivers enhanced fuel
economy and seamless
acceleration with a “direct”
drive feel for enhanced
AT driving pleasure.
CVT Advantages
Exceptional transmission efficiency for
enhanced fuel economy
The CVT’s outstanding environmental
performance and economy make this
innovative technology ideal for today’s and
tomorrow’s vehicles.
Smooth ratio transitions for enhanced
driving pleasure
Driving pleasure is enhanced by the linear
feeling of acceleration in response to
accelerator pedal inputs.
Nissan’s basic approach to powertrains is to achieve an equally high
measure of both environmental compatibility (fuel economy) and
driving pleasure (acceleration performance). For the XTRONIC CVT,
our efforts to improve fuel economy were not confined to catalog
specifications, but encompassed the practical fuel efficiency people
seek in everyday driving situations. For example, the majority of
Nissan customers drive mostly in urban and suburban areas and
about 60% run the air conditioner year-round. In developing the
XTRONIC CVT, we enhanced real-world fuel economy based upon
simulations of typical driving conditions.
Nissan offers CVTs
in an extensive range
of models
Quick to appreciate the CVT’s benefits of fuel
economy and seamless acceleration, Nissan offered CVTs as early as 1992 in the March and
Cube, followed by the 1.8-liter Primera and other
models. Through technological innovation in CVT
components, including the torque converter, oil
pump, belt and control system, Nissan, in 2002,
overcame the technological challenges to adapting the CVT to high-torque engines. The resulting XTRONIC CVT-M6 was the world’s first CVT
practicable for engine displacements as large as
3.5 liters. Today, Nissan’s CVT technology offers
smooth and fuel-efficient “fun-to-drive” performance in an extensive range of Nissan models, from
the compact class all the way up to high-powered
luxury vehicles.
Seeking to bring the CVT’s outstanding performance to even more customers, Nissan plans to expand sales of CVT-fitted models to around 1 million
units worldwide in fiscal year 2007, up from about
250,000 in fiscal year 2004.
Throttle opening
The CVT (Continuously Variable
Transmission) provides smooth and
“stepless” ratio changes, unlike
conventional transmission systems
that use sets of fixed gears. With
its seamless acceleration and fuel
economy benefits, the CVT has long
been an object of Nissan’s R&D
efforts, resulting in CVTs designed for
a wide range of engines, from the
1.5-liter class to the 3.5-liter class.
Better fuel economy for everyday driving
CVT for 3.5-liter class engine
Congested traffic
Suburban traffic
Vehicle speed
Response optimized for real-world conditions
Powerful and satisfying acceleration feel
CVT for 2.0-liter class engine
CVT performance is characterized by stepless shifting and seamless
acceleration. To refine these advantages, we significantly improved
gear shifting response in the XTRONIC CVT to provide tighter tracking of accelerator pedal inputs, as well as quick and powerful acceleration. In line with our emphasis on everyday driving conditions, we
concentrated less on full throttle performance, and more on quickly
responsive acceleration and smooth passing ability in urban traffic.
Acceleration
Conventional CVT
XTRONIC CVT
Elapsed time
contents
Seamless acceleration Improved response and efficiency
Improved dynamic performance and
powerful acceleration feel
2
Accelerator pedal depressed
4
5
CVT for 1.5-liter class engine
Enhanced acceleration feel
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3
XTRONIC CVT
Technology Overview
Seamless acceleration
Improved response and efficiency
Stepless shifting of gear ratios eliminates “shift shock” for a smooth driving experience.
Wider ratio spread and more precise control for outstanding acceleration and fuel economy.
CVT Structure
1. Wider gear ratio range
The CVT is an automatic transmission that uses
two pulleys with a steel belt running between them.
To continuously vary its gear ratios, the CVT simultaneously adjusts the diameter of the “drive pulley” that transmits torque from the engine and the
“driven pulley” that transfers torque to the wheels.
Because it is continuously variable, the CVT not
only avoids the shift-shock and peaks and dips
in torque transmission associated with a conventional AT, but also maintains optimum torque for
any given power demand. This makes the CVT
an exceptional transmission solution that delivers
smooth and powerful driving performance together
with excellent fuel economy.
Low gear
Narrowing (diameter increases)
Belt
From Engine
To Driveshaft
Widening
(diameter
decreases)
Driven Pulley
Drive Pulley
In the XTRONIC CVT, the gear ratio range* from
low to high gear is expanded, attaining a top-ofclass final gear reduction ratio of about 6, thanks
to pulley and steel belt improvements and the use
of high performance ATF (Automatic Transmission Fluid). This ratio spread is among the world’s
widest for a CVT designed for use with 1.5-liter
to 2.0-liter class engines. We extended the low
end of the range to improve acceleration, and the
high end to improve fuel economy. In addition, the
Nissan CVT is easily and flexibly tunable to match
engine characteristics, thereby enabling optimization of the balance between combustion efficiency
and acceleration.
Low gear
Smaller drive pulley radius
raises acceleration performance
Driven Pulley
Drive Pulley
*Gear ratio range: The ratio spread from low to high gear. The low gear
ratio divided by the high gear ratio.
High gear
High gear
Smaller driven pulley radius
enhances fuel economy
Widening (diameter decreases)
Belt
From Engine
Engine class
To Driveshaft
Narrowing
(diameter
increases)
Driven Pulley
Gear ratio
Low gear
High gear
3.5L
2.371
0.439
2.0L
2.349
0.394
1.5∼1.8L
2.561
0.427
Driven Pulley
Drive Pulley
Low gear
Improving
acceleration
Ratio range
Engine rev
Ring
Multi-layer high-tensile
strength steel
Drive Pulley
High gear
Improving
fuel economy
Element
400 highly rigid elements
Vehicle speed
CVT-belt construction
4
Expanded gear ratio range
5
XTRONIC CVT
Technology Overview
Improved dynamic performance and powerful
acceleration feel
Responsive to the driver’s intention with a natural feeling of acceleration.
2. Wide lockup range
Quicker CVT shift response
Lockup* of an automatic transmission’s torque
converter enables manual-transmission-like direct
transfer of engine power and improved fuel economy. Whereas a conventional AT locks up in the
mid-to-high speed range, the benefit of a torque
converter in a CVT is only during startup. Therefore,
the new XTRONIC CVT applies precise control of
ratio changes to extend the lockup operating area
even further into the low-speed range and thereby
boost fuel economy.
Torque converter
Driven pulley
*Lockup: The condition in which torque from the engine is transferred
directly to the pulley, without being affected by the torque converter.
Belt
Throttle opening
XTRONIC CVT
Conventional CVT
Engine speed
Elapsed time
Accelerator pedal depressed
The XTRONIC CVT shifts quickly to the optimum gear, and
the engine speed rises rapidly.
[%] 100
0
We improved the electronic control system and the
hydraulic system components under its control. In
addition, adoption of a new high-performance ATF
(Automatic Transmission Fluid) enhances response
and stability. As a result, the CVT shifts ratios about
30% faster than the previous version. Furthermore, the new XTRONIC CVT controls shifting so
that, up to a point, engine rpm will rise along with
vehicle speed. As a result, Nissan’s CVT technology provides a more pleasurable driving experience,
with nearly instantaneous response and a feeling of
naturally powerful acceleration, as well as dependable engine braking.
CVT shift control allows the engine speed to rise naturally with
vehicle acceleration.
Expanded lockup range with
new XTRONIC CVT
Drive pulley
AT lockup range
Acceleration
Vehicle speed
New XTRONIC CVT expands lockup range
Torque converter in a CVT
3. Comprehensive efficiency improvements
Elapsed time
Accelerator pedal depressed
Downsized, more efficient oil pump
The oil pump, which is the source of hydraulic
power for shifting and assuring torque transmission, has been substantially downsized and made
more efficient. This helps maintain control capability that closely follows accelerator pedal action,
while boosting fuel economy. For Nissan’s 2-liter
class CVT, we adopted a compact chain drive,
which contributes to downsizing of the transmission system as a whole.
The vehicle accelerates as soon as the driver presses the
accelerator.
Powerful acceleration is obtained immediately at any driving
speed.
Sustained power delivery allows the vehicle speed to rise
smoothly.
Drive chain
XTRONIC CVT offers rapid shifting
Reduced hydraulic pressure for
pulley control
We improved the precision of the control system
used to shift the diameters of the two pulleys, so
that sufficient lateral pressure on the belt can be
maintained with lower hydraulic pressure. This
achieves reliable torque transfer together with
high efficiency, thereby contributing to improved
fuel economy.
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Oil pump
Downsized high-efficiency oil pump with drive chain
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