Presented by-
VIDHYANAND.C.S

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ABSTRACT
ZEROSHIFT TECHNOLOGY
The topic i have selected for the seminar is zeroshift technology. The manual transmission we use takes its own time for shifting time. This reduces the performanceof the vehicle. This problem is solved by zeroshift technology.
Zeroshift technology is a seamless instantaneous means of changing gear ratios without interrupting the engine torque to the wheels. What this means a manual or automated manual transmission and the benafits of superior fuel economy and performance. Shifted by the conventional hydraulic / pneumatic methods or by noval shift by wire technique. The basic gearbox arcitecture and single dry clutch are retained.
It is sure that zeroshifttcchnology will revolutionize the way we drive an automobile by increasing performance, fuel economy and reducing emissions.
INTRODUCTION
The world is dominated by two forms of transmission, themanual transmission (MT) and the Automatic
Transmission (AT). The MT has a single dry clutch
operated by the driver whilst the AT uses wet clutches
that are automatically controlled. There are pros and
cons to both transmissions.
The MT is the most efficient transmission available. This
lends itself to providing good fuel economy for the
vehicles it is employed in. The efficiency of the MT is
dependent on the load applied. Over a representative
drive cycle its efficiency can approach 97% .
The MT is very easy to manufacture having very few
parts. It is reliable and easy to maintain.
Its main weakness is that it is less easy to drive than an
AT especially in congested traffic as it requires the driver
to operate the clutch for each gear shift. Gear shifts are
sometimes not smooth which causes discomfort for
passengers who will notice an interruption of engine
torque to the wheels when the transmission is between
gears. In severe situations the interruption of torque can
cause dynamic instability of the vehicle resulting in loss
of control.
The AT has many advantages which include ease of
driving and very smooth shift quality. The choice of gear
is determined by a transmission control unit (TCU) and
this will ensure that the best gear is chosen for the
vehicle road speed depending on whether the driver
requires fuel economy or performance. Drivers are
willing to pay a premium for this type of transmission
even though performance and fuel economy are inferior
to the MT.
A reduced performance and fuel economy is apparent
because of the lower efficiency of the transmission. Not
only are there parasitic losses to account for to operate
the hydraulic pump, but large amounts of slip in the
torque converter generates heat loss which warms the
transmission fluid rather than provide torque to the
wheels. In recent years a lock up clutch bypasses the
torque converter for a large proportion of the journey
which can improve the overall efficiency dramatically.
Over a representative drive cycle the efficiency of an AT
can be as high as 86% .
If a transmission could have the benefits of both the MT
and AT and the weaknesses of neither, this would
introduce a third option to segment the market.
Traditionally, the AMT has matched the MT for fuel
economy but has suffered from inferior performance
(compared to the MT) and bad shift quality. Zeroshift
corrects these latter two issues allowing simultaneously
good fuel economy, performance and shift quality. The
combination of these has not previously been seen in
any other transmission.
ZEROSHIFT CONCEPT
The zeroshift gearbox has a hub assembly consisting of a pair of drive rings, selector frocks, hub and acradle with springs.Shifting is done by a gear change barrel.Barrel is controlled by the signals from TCU.
TCU can be set in automatic mode and semi automatic mode.
In automatic mode gear change takes place based on engine speed, load.
In semi automatic mode traditional feel is retained by introduction of hand selector buttons.
The Zeroshift concept is to remove the synchromesh
components within a manual transmission and replace
them with Zeroshift rings, Figure 1. Synchronisation is
performed externally with the assistance of torque
intervention performed by the engine control unit and an
automated clutch (standard equipment in an AMT).
The Zeroshift rings act as a pair and represent a dog
engagement type transmission. The unacceptable
backlash found in dog engagement transmissions is
eliminated by splitting the dog into two halves. The first
Zeroshift ring is engaged to take up drive whilst the
SecondZeroshift ring is brought in afterwards to take up
the backlash.
Figure 1.Two Zeroshift rings between two gears.
When initiating a shift from the neutral position, one drivering is engaged with the dog faces on the gear and thesecond ring joins the first axially adjacent which providesdrive in the opposite direction to oppose engine overrunand, more importantly, eliminate perceivable backlash.
This ring is unloaded and is the ring to make the next
shift and as such requires less shift force i.e. much less
than synchroniser force (in the order of 1/25th).
Figure 2.Neutral position.
It is easier to see the actions of these rings if we look at
an exploded view, Figure 2. Each pair of rings has three
pairs of “bullets”. Here we see just one pair of bullets for
illustration purposes. On one side of the bullet is aretention angle to take up the drive whilst on the oppositeside is a ramp face to disengage drive.
The unique feature of Zeroshift is that it is able to changegear in zero time, just like a digital switch. We can see inFigure 3 how by shifting the blue ring and its bullets witha shift fork, drive is taken up on the 1st gear (top ofdiagram). Backlash is taken up by shifting the red ring,Figure 4(1st gear engaged).