3. Double Cone Synchronizer for Vehicle Transmission

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.

Siddhant College of Engineering. ME (Mechanical) (Design Engineering)

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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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Documents

3. Double Cone Synchronizer for Vehicle Transmission