SYNCHROMESH – DRIVE TRAIN
(TRANSMISSION)
GEAR SYNCHRO
 Vehicles fitted with manual transmissions (MT), automated manual
transmissions (AMT) and double clutch transmissions (DCT) need gear
synchronizers in order to perform a gearshift (upshift or downshift).
 The purpose of a gear synchronizer is to synchronize the speeds of the input
and output shafts of a gearbox. during a gearshift, before the engagement of
the upcoming gear.
CLASSIFICATION OF SYNCHROMESH TRANS.
There are several types of synchronizers used for manual transmissions. The most
commons way of classification is function of the number of friction elements
(friction cones). Therefore, we have:
 Single-cone Synchronizer
 Dual-cone Synchronizer
 Triple-cone Synchronizer
COMPONENTS OF GEAR SYNCHRONIZER
1.
2.
3.
4.
5.
6.
Gear Wheel
Synchronizer Ring
Ring Spring
Locking Element (strut)
Synchronizer Hub (body)
Sliding Sleeve
GEAR WHEEL
 The gear wheel is mounted on the output
shaft of the gearbox.
 It can rotate relative to the shaft (radial
motion) but it can not have an axial
movement along the shaft.
 Between the gear wheel and the shaft
there are usually needle roller bearings
which facilitate rotation.
SYNCHRONIZER RING
 The synchronizer ring also called blocking
ring, balk ring or friction ring, has a conical
surface which comes into contact with the
friction cone of the gear wheel.
 The purpose of the synchronizer ring is to
produce friction torque in order to
decelerate/accelerate the input shaft during
a gearshift.
 The synchronizer ring, together with the
friction cone of the gear wheel, form a
“conical clutch” which can be engaged and
disengaged through sliding.
LOCKING ELEMENT
 The locking elements, also called
synchronizer keys, central mechanism, strut
keys or winged struts are arranged on the
circumference of the synchronizer body, in
specific grooves, between the synchronizer
sleeve and synchronizer hub.
 The locking elements rotate together with
the synchronizer hub and can move axially,
relative to the sliding sleeve. The struts are
used for preliminary synchronization, which
means that they generate the load on
synchronizer
ring
to
perform
the
synchronization process.
 Usually, the synchronizer assembly has 3
locking elements, distributed at an angle of
120° .
SYNCHRONIZER HUB AND SLIDING SLEEVE
 The synchronizer hub is mounted on the
output shaft, rigidly connected by a spline. It
can move on the axial direction but it can
not rotate relative to the shaft. It contains
specific grooves which will contain the
locking elements.
 The sliding sleeve, also called gearshift
sleeve, synchronizer sleeve or coupling
sleeve, has a radial groove on the external
side for the gears shift fork. The interior has
splines that are in constant mesh with
the external splines of the synchronizer hub.
The sliding sleeve can only move on the axial
direction (left-right), from a neutral position
to an engaged position.
GEAR SYNCHRONIZATION PHASES
 The synchronization process, with the sliding sleeve starting from a neutral
position (central) and ending with a full gear engagement, can be described in
five steps.
 The synchronization process is going to be described using the parameters:
 F [N]–Gearshift force
 Δω [rad/s]–Speed difference between gear wheel and synchronizer hub
 Tf [Nm]–Friction torque between the synchronizer ring and friction cone
 Ti [Nm]–Inertia torque of the input shaft, gears and clutch secondary mass
PHASE 1: ASYNCHRONIZING
 Before the gearshift process starts, the sliding sleeve is held in the middle position by the
locking elements.
 The gearshift force generates the axial movement of the sliding sleeve, which pushes
forward the synchronizer ring against the friction cone gear wheel.
 The speed difference between the gear wheel and the synchronizer ring causes the
rotation of the synchronizer ring.
PHASE 2: SYNCHRONIZING (LOCKING)
 This is the main phase of the speed synchronization. The sliding sleeve is pushed further,
which brings the internal splines (teeth) of the sliding sleeve and the teeth of the
synchronizer ring into contact.
 In this phase, the friction torque starts to counteract the inertia torque and the speed
difference starts to decrease.
PHASE 3: UNLOCKING
 Phase 3: Unlocking (turn back synchronizer ring): The gearshift force is kept on the
synchronizer ring through the locking elements and the sliding sleeve. When speed
synchronization has been achieved, the friction force is reduced to zero and the
synchronizer ring is turn back slightly.
PHASE 4: MESHING
 Phase 4: Meshing (turn synchronizer hub): The sliding sleeve passes through the teeth of
the synchronizer ring and comes into contact with the locking toothing of the gear wheel.
PHASE 5: MESHING
 Phase 5: Engaging (gear lock): The sliding sleeve has completely moved into the locking
tooth of the gear wheel. Back tapers at the teeth of the sliding sleeve and the gear wheel
locking tooth avoid decoupling under load.