3. double cone synchronizer for vehicle transmission
DESCRIPTION
Double Cone Synchronizer for Vehicle TransmissionTRANSCRIPT
1.1 Abstract
The transmission system is one of the main parts that determines the
behavior, power and fuel economy of a vehicle. Transmission performance is
usually related to gear efficiency, gear noise and gear shift comfort during gear
change. Synchronizer mechanisms allow gear changing in a smooth way, noiseless
and without vibrations, both for the durability of the transmission and the comfort
for the users. As a consequence, it is aimed an improvement of the dynamic shift
quality, by reducing shifting time and effort, especially in heavy truck
applications. This paper deals with a study of the synchronization processes in
manual transmission gearboxes. A description of the different types of
synchronizers is given, followed by its components and how they interact with
each other in order to complete the gear changing process namely the
synchronization process. Then, quality factors are identified and their effect on the
performance and thus synchronizer efficiency. For comparison of Single Cone and
Double Cone Synchronizer, on Cone Torque Capacity a calculation has been
shown and the same has been implemented in Matlab to analyze the response.
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1.2 Introduction
Synchronizers are the key elements in manual transmissions (MT) as well
as in double-clutch transmissions (DCT) and automated manual transmissions
(AMT).
This paper gives an overview of their function, layout and design and
explains possible problems and solutions. Finally it is shown what tools and
processes are needed to develop, test and manufacture components and complete
synchronizer systems.
Synchronizers are the central component of the transmission featuring
interfaces to the output, the clutch and, by way of the gear shift, to the driver. The
layout and design of the synchronizers play an essential role in how the driver
experiences the gear shift.
The layout and the design of synchronizer systems have to take into account all
these aspects. The validation and the assessment of the synchronizer systems have
to be made at test rig as well as in the vehicle.
Synchronization systems align the differing shaft speeds between the constant
mesh gear and the shift element located on the shaft (synchronizer hub).
Current systems include,
Dog clutch (not shown) : designed as a direct shifting clutch without a
synchronizer
Multi-plate clutch synchronization : Synchronization made possible by
means of discs with friction surfaces, suitable for high-performance
transmissions
Friction clutch with synchronizer cone: The current standard unit for
mechanical manual transmissions in vehicles, designed as a blocking
synchronizer.
Blocking synchronization systems are used as
Single-cone synchronizers or
Multi-cone synchronizers.
In multi-cone synchronization systems, intermediate rings are used to increase the
number of mating friction surfaces.
Two operations are involved that ensure proper gear shifting:
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Synchronization (equalizing of shaft and gears speed)
Clutch engagement (positive locking between constant mesh gear and
shaft).
To ensure that synchronization occurs before clutching, a fine-tuned blocking
function is required.
1.3 The Synchronization
Synchronizers can be structured by the number of cones used. The next
pages show the exploded views of single-, dual- and triple-cone synchronizers and
the descriptions of the single components.
The synchronization process always follows the same sequences. The sleeve is
moved by the shift fork towards the gear to be engaged. As long as there is a speed
difference between the sleeve/hub-system and the gear wheel the sleeve is blocked
by the blocker ring and the synchronizer rings create a friction torque. When the
speeds are synchronized the sleeve can be moved further and engages into the
spline of the engagement ring at the gear wheel.
1.4 Design
The single-cone synchronizer is a conventional blocking synchromesh
based on the Borg Warner or ZF-B system. Synchronization is accomplished by
means of a friction clutch with a single cone at the constant mesh gear and the
blocker ring. This cone serves to support the total friction losses. Clutching is
accomplished by means of spline teeth located in the shift sleeve. These teeth join
the constant mesh gear clutching teeth. Blocking occurs when the “roof-shaped”
gear teeth on the synchronizer ring and the shift sleeve mesh.
1.4.1 Friction coefficient and shift behaviour
For the blocking mechanism to function properly, a sufficiently high coefficient of
sliding friction is required in the synchronizer cone friction clutch throughout the
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entire sliding phase. If the friction coefficient is too low, the blocking mechanism
will release prematurely, causing engagement to occur before synchronization.
Then undesirable noise may occur (e.g. so-called “upshift scratching”) if gear
clutching teeth, strike the shift sleeve teeth chamfers. For improved shifting
comfort, a low friction coefficient is required in the synchronizer-cone friction
clutch. In this way “smooth shifting behaviour” can be achieved. Thus, high-
performance synchronization with low friction coefficients is required.
Fig.1 Single Cone Synchronizer Assembly
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Fig.2 Multi-cone Synchronizer Assembly(Double-cone Synchronizer Assembly)
1.4.2 Components
Fig 3 · Components for single-cone synchronization [3]
a) Synchronizer hub
The synchronizer hub is positively locked with the transmission shaft. It
contains the components for pre-synchronization in a strut slot and guides the shift
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sleeve in a notch at the outside diameter. Three notches on the circumference
ensure that the blocker ring does not rotate.
b) Shift sleeve
On the inside diameter, the shift sleeve has spline teeth with roof-shaped
angles on the side faces. In a circumferential groove on the outside diameter, the
shift fork sliding surfaces mesh and move the shift sleeve in the axial direction.
Notches on the internal teeth centre the pre-synchronization assembly.
c) Struts
Struts – in this case detent assemblies – are used for pre-synchronization
(see page 7 for a description of struts).
d) Blocker ring
The blocker ring is made from a special brass alloy and is rough-forged. It
has a friction cone with turned grooves for oil dissipation on its inside diameter.
The blocker ring teeth with roof-shaped chamfers facing the shift sleeve are on the
outside diameter.
e) Gear cone body
The gear cone body is made from steel and is laser welded to the constant
mesh gear. It has an outer friction cone and clutching teeth with roof-shaped
chamfers facing the blocker ring.
f) Constant mesh gear
The constant mesh gear has needle roller bearing supports on the shaft and
is designed with involute gear teeth for the transmissions of torques.
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1.4.3 Operation
Fig.4 Shift phases exemplified by the locking and constant mesh
gearing. [3]
a) Synchronization
The shift sleeve is moved out of the neutral position and displaced axially toward
the constant mesh gear.
Because of chamfered teeth on the shift sleeve, the struts are also moved. They
press the blocker ring against the friction cone at the clutch body of the constant
mesh gear. This allows a frictional torque to build up and the gear is pre-
synchronized.
Due to the frictional torque, the blocker ring immediately rotates with the available
clearance of the notches in the sleeve support. The chamfered teeth on the shift
sleeve contact the blocker ring teeth, thereby preventing a premature, axial shifting
of the shift sleeve. The axial displacement force increases. The fully effective
frictional torque now aligns the differing speeds between the constant mesh gear
and the hub and the gear is synchronized.
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b) Disengaging
When equal speeds are reached, the frictional torque is removed. Since the shift
force continues to act on the blocker ring teeth the shift sleeve rotates the
frictionally engaged contacting bodies (blocker ring and the gear body). The teeth
on the shift sleeve slip into the gaps of blocker ring teeth.
c) Free flight
The moment of losses, due to splashing, inertia of masses, bearing and seal friction
accelerate or decelerate the constant mesh gear depending on the rotating
direction. In this way, a low speed-differential between shift sleeve/ blocker ring
and gear cone body occurs during the moment free travel.
d) Meshing
The teeth on the shift sleeve mesh with the chamfered teeth of the constant mesh
gear. The shift sleeve rotates the gear body, in such a way that the shift sleeve can
be shifted. The shift sleeve then reaches its final position. It is coupled and the gear
is shifted.
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1.5 Multi-Cone Synchronization
Fig. 5 Multi-cone synchronization (Double Cone Synchroniser) [3]
1.5.1 Design
The structure of the multi-cone synchronization system essentially
corresponds to that for single-cone synchronizers. A higher frictional force or a
higher frictional torque can be reached if more friction surfaces are present. In the
case of multi-cone synchronization systems, using intermediate rings, also known
as dual friction cones, increases the number of friction surfaces through the radial
arrangement of several friction surfaces to form mating friction surfaces. The shift
force thus acts on several surfaces. A larger friction surface in the single-cone
synchronization system will lower only the heat build-up during synchronization.
Frictional force and frictional torque remain unimpaired.
Multi-cone synchronization systems are preferably used for lower gears
(1st and 2nd gears). Because of the high speed-differentials, the greatest
synchronization performance is required here, and the shift forces are
correspondingly high. However, in the case of faulty gear changes (e.g. from 3rd
into 1st), a high synchronization performance can also have a detrimental effect –
for 80 km/hr (= 50 mph) the speed is synchronized in only approx. 0.2 sec. This
can damage the friction lining on the clutch between the engine and the
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transmission. On the other hand, this synchronization performance ensures that
little effort is required to shift from 2nd or 1st even at low temperatures (–25 ºC/–
13°F).
1.5.2 Shift Sleeve Shiftability
Fig. 6 Comparison of chamfer angles on shift sleeve teeth and
on blocker ring teeth of constant mesh gear [3]
1.5.3 Roof-shaped and interlock gear teeth
The shift sleeve must shift smoothly into the chamfered clutching teeth of the
constant mesh gear. However, to do this the friction connection must loosen
correctly after the speeds have been synchronized. If the cone pairs in a multi-cone
synchronization are optimally positioned with respect to each other (see section
entitled Cone Design and Figure 16), higher frictional torques are achieved for the
same shifting forces. Because the design can incorporate smaller angles for the
blocker ring teeth:
The circumferential force is increased.
The increased torque separates the friction connection securely.
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The effects of the angle size on shifting are shown in Fig. 5 a higher twisting
moment for the same shift forces
Thrust needle roller bearing for axial support. The sliding sleeve can be shifted
smoothly if,
the constant mesh gear is supported by a thrust needle roller bearing
This will allow the constant mesh gear to rotate easily, even for larger shift forces
– e.g. when shifting the vehicle at a standstill (taking off in first gear). However,
the friction phase during synchronization is longer since the sliding friction of the
constant mesh gear wheel has been reduced. This disadvantage is compensated by
the high-performance multi-cone synchronizer. False brinelling that may occur on
the thrust bearing raceways – for shifting from 1st or 2nd gear – is negligible
because of the short time it takes to shift these gears.
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1.6 Calculation
Fig. 7 Friction Torque and Blocking Release Torque [1]
Friction Torque
Blocking Release Torque
Where,
α : Cone Angle (Degrees)
β: : Chmafer Angle (Degrees)
μ: : Coefficient of friction of cone
μD : Coefficient of friction of chamfers
dm : Mean cone diameter (mm)
dD : Pitch diameter (mm)
Fa : Shift force at sleeve (N)
nc : Number of cones
,
Blocking Safety is given if TF > TZ
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1.6.1 Comparison of Single Cone and Multi-cone Synchronizers
on basis of Torque capacity:
If we are comparing two synchrocones (single cone and multi cone
synchronizer) on the basis of frictional torque, then it is difficult to analyse the
results, because there are two different variables, TF and Fa, i.e. Frictional Torque
and Shift force at sleeve. So for comparison purpose we will create a new term
Cone Torque Capacity = TF / Fa (Nm/N).
1.6.2 Example
Synchro-Cone data.
Coefficient of friction of cone μ 0.09
Cone Angle α 6°
Blocker ring PCD dD 57.6 mm
Blocker ring chamfer β 57.5°
Coefficient of friction of chamfers μD 0.09
Mean cone diameter dm 105 mm
Total Cone Area A 2007 mm2
Effectiveness E 100%
We will compare functionality for single and double cone synchronizer with above
mentioned data for Cone Torque Capacity.
A] Analytical Solution
I] For Single Cone Synchronizer:
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II] For Double Cone Synchronizer:
B] Matlab Solution
Comparing same results by using Matlab, we are getting following results.
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Fig. 8 Data for Synchro_1: (Single Cone Synchronizer)
Fig. 9 Data for Synchro_2: (Double Cone Synchronizer)
Fig. 10
Graph plotted for Cone Torque Capacity Vs Mean Cone Diameter.
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1.7 Summary
We can implement Double Cone Synchronizer in an existing single cone
synchronizer transmission with following benefits.
1. Shift effort (Fa) can be reduced by keeping same frictional torque capacity
(Tf) and same packaging dimensions. ( i.e. Mean Cone Diameter)
2. Frictional torque capacity (Tf) of synchronizer can be increased by
keeping same Shift effort (Fa) and same packaging dimensions. ( i.e. Mean
Cone Diameter)
Double cone synchronizers can be used while designing a new transmission
with less packaging dimensions in comparison with Single cone synchroniser of
same capacity.
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1.8 References
1. Basics of Synchronizers, by Otrmar Back, HOERBIGER Antriebstechnik
GmbH (Germany).
2. European Patent Application: EP 2 163 779 A2 by Oberlikon Graziano
S.p.A 10090 Rivoli Vica (TO) (IT)
3. Intermediate Rings for Multi-Cone Synchronizer Systems by M/s INA,
Schaeffler KG.
4. Research Paper on Manual transmission Synchronisers by Richard J. Socin
(Chrysler Corp.) and L. Kirk Walters (Chevolet Motor Div., General
Motors Corp)
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