|
A
flurry of innovations and developments is on the agenda in context of
transmission designs of the future. Major manufacturers are constantly
striving to improve existing technology as R&D divisions focus on
figuring out ways and means to conjure up better and simpler forms of
transmission units (even though the physics of it all is highly complex).
Here are some cutting edge transmission systems that are and will be production
realities in the cars of the future.
 |
The
Continuously Variable Transmission (CVT) system is slowly finding
acceptance with major automobile manufacturers though the technology
has been around for some time now employed in two wheelers expecially
scooters. A typical CVT gearbox (left) uses a toothed V-belt (below)
running between two pulleys. |
 |
CONTINUOUSLY
VARIABLE TRANSMISSION
A continuously variable transmission is an automatic that can select any
desired drive ratio within its operating range. Unlike a traditional three-,
four-, or five-speed automatic transmission, the CVT is an ‘infinite
speed’ transmission. It continually selects an optimum overall drive
ratio between engine and drive wheels for all operating conditions, whether
accelerating or cruising. Unlike conventional automatics, there are no
perceptible shifts. During maximum acceleration, the drive ratio is adjusted
to maintain peak engine horsepower. At a constant vehicle speed, the ratio
is set to maintain an optimum balance of fuel economy and driveability.
A CVT provides smooth, fast acceleration and high cruising efficiency
with the convenience of an automatic transmission.
The most common CVT design uses a segmented metal V-belt running between
two pulleys. Each pulley consists of a pair of cones that can be moved
close together or further apart to adjust the diameter at which the belt
operates. The pulley ratios are electronically controlled to select the
best overall drive ratio based on throttle position, vehicle speed and
engine speed. CVT systems are commonly in use in Audi’s multitronic,
Honda’s MMT and Mitsubishi’s INVECS-III CVT among others.
AUTO SHIFT MANUAL TRANSMISSION AND SELECT SHIFT MANUAL TRANSMISSION
Select Shift Manual (SSM) and Auto Shift Manual (ASM) employ a combination
of Auto-Clutch and Shift-By-Wire electronic control system technology
to offer the car driver a fun-to-shift experience along with significant
improvements in fuel economy over a base manual transmission. The Select
Shift Manual mode allows a driver to control gear changes according to
his/her personal preference as in a conventional manual transmission.
The Auto Shift Manual mode provides automatic gear shifting much like
automatic transmission.
Both the Auto-Clutch and Shift-By-Wire sub systems make use of an electro-hydraulic
or electro-mechanical actuation system controlled by a stand-alone transmission
control module. The driver requests a gear shift by using the appropriate
driver interface mechanism (shift lever, push buttons, etc). In place
of the usual cable/linkage (which is eliminated), a sensor informs the
controller of the requested gear shift. The controller processes the request
and commands the actuators to open/close the clutch and disengage/engage
the gear sequence with very fast response times. Engine torque is controlled
during the shift either by controlling the throttle directly (Drive-By-Wire)
or enabling ignition/fuel injection control to provide smooth shifts.
ADAPTIVE TRANSMISSION CONTROL (ATC)
The Adaptive Transmission Control system recognises individual styles
of driving (eg, aggressive vs relaxed) and adapts transmission shift parameters
accordingly. The two types of ATC are adaptive shift-scheduling and adaptive
shift-quality control. Adaptive shift scheduling uses information to assess
driving style and decides when to upshift or downshift. It can also identify
uphill or downhill gradients and recognise hard cornering. This helps
inhibit shifts that could be irritating to the driver or affect vehicle
stability. Adaptive shift-quality control uses information about the vehicle
or environment, such as changes in the transmission due to wear, to improve
the quality of shifts. This system can also adjust shift smoothness to
suit driving style (eg, crisper shifts for aggressive driving or smoother
shifts for normal driving).
Adaptive Shift Scheduling uses a microprocessor to read signals from various
sensors besides a complex algorithm and ongoing memory to decide when
to shift. For example, high lateral acceleration during cornering may
prevent shifting even if the accelerator is suddenly depressed or released.
This helps avert potential loss of tyre grip due to load reversal. Shift
points can be based on calibration curves in memory. Adaptive shift-quality
control adjusts parameters that affect the speed and smoothness of the
shift by interpreting data, including driveline feedback from various
sensors, as well as post shift parameters.
ELECTRONICALLY CONTROLLED AUTOMATIC TRANSMISSION
An Electronically Controlled Automatic Transmission utilises an electronic
control module to signal when to shift. The module also determines when
to lock and unlock the torque converter. By controlling these functions
electronically rather than mechanically, the transmission can be tuned
for better driveability.
Electronically Controlled Automatic Transmissions use computer-controlled
solenoids to control primary functions (internal pressure, converter lock-up,
shift and clutch scheduling) through the transmission hydraulic system.
Meanwhile, non-electronic transmissions rely on mechanical controls such
as centrifugal weights and mechanical valves.
Better control of transmission shifting improves driveability.
|
February 2003