Synchro Ring

November 5, 2017 | Author: Ashok | Category: Sintering, Wear, Manual Transmission, Forging, Friction
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Performance and cost optimization of friction systems for single and multiple surface synchronizers

HOERBIGER & CO, Schongau

Performance and cost optimization of friction systems for single and multiple surface synchronizers


Performance and cost optimization of friction systems for single and multiple surface synchronizers

Summary The synchronizer is one of the most important components of any manual gearbox. Increasing performance, reducing shift force and optimizing the „between the gears ” costs are the primary objectives for the new generation of synchronizer systems. Improvement in capacity of the brass system and the introduction of formed sinter cones are detailed in this article. With the help of these new developments, existing synchronizer designs can be economically re-engineered into more efficient designs.

1. Introduction The majority of European high volume production manual gearboxes presently use brass synchronizer rings (Borg Warner system) . In addition a single cone outer synchronizer is also used, offering a slightly higher load capacity for the same diameter. To fully optimize the available space, it is necessary to modify the complete system. The options available are to move to multiple cone synchronizers, increase the diameter, or to change to an alternative friction material (Molybdenum, Paper, Sinter). In recent years, the use of the HOERBIGER sinter friction lining, either as a welded foil, or as deep drawn single or dual cone rings, has resulted in many extremely successful solutions.

2. Current Situation In practice there are 2 basic systems, and developed derivatives of them, in use - Borg Warner and Outer Synchronizer systems. Figure 1 shows the schematic layout of these systems and the relative market share.


Borg Warner

Fig 1:


Outer Cone

Dual Cone

Triple Cone

Current Synchro Systems

Manufacturing of the most important components utilizes sintering, sinter forging and precision forging processes. The majority of mass production manual gearboxes, use a special brass alloy material (SoMs) on the basis of its advantageous cost / performance ratio. The brass alloy must function as a base material and a friction material, therefore a compromise between material strength and friction performance is needed. The oil grooves, necessary for function and cooling, require an expensive machining process. This results in a relatively low friction surface area, leading to high specific loads on the remaining surface. In the past, the only way to upgrade the load capacity of the brass was to coat the friction surface with molybdenum. This has only a small advantage, due to the tendency for the increased loads and pressure to exceed the mechanical capabilities of the brass material, resulting in deformation of the rings. Alternative higher strength materials can be used, but these require the expensive bonding/welding of additional friction material. The following table shows the available options and combinations.

Base Material

Friction Lining

Opposing Surface

Sinter Metal (PM) Formed Steel

Molybdenum - thin / thick layer Organic Friction lining Dispersion Sinter

Steel / PM - case hardened, ground and honed

Forged Part

2.1 Comparison of the most important friction linings for modern synchronizers In addition to brass and molybdenum, sinter and organic linings are also found in synchronizers. The sinter lining was to date exclusively found in high energy shift positions. Organic friction linings play only a minor role in European synchronizer applications. Organic Linings approx. 5% Brass approx. 55%


HOERBIGER & CO, Schongau

2.1.1 Wear behavior of the synchronizer friction surface External tests, carried out by various neutral research institutions [2], and field applications [1,3] have shown that under typical application conditions, sinter and moly linings show good to very good wear properties, while under the high surface pressure, resulting from the geometry of the synchronizer, brass and organic friction linings show a relatively high degree of wear.



Axial wear [mm]

Performance and cost optimization of friction systems for single and multiple surface synchronizers

Sinter approx. 15%

Paper 0,5 Molybdenum

Molybdenum approx. 25% 0,2

Fig 2:

Market Share of today’s friction materials in current synchronizers


- Dispersion Sinter Friction Linings During the sintering process, friction linings, consisting of brass powder, frictional stabilizers and non metallic elements (C, Si, etc.), are bonded to a steel carrier. This carrier is then either welded inside a blocker ring or formed into a single or dual cone (HOERBIGER Patent). - Molybdenum Applied using a flame spraying process, on a profiled blocker ring, ground (thick layer) and / or calibrated. - Organic Lining Fibrous material with an organic matrix, (Cotton, Phenolic Resin) with inclusions of frictional and structural stabilizers. Organic linings are normally bonded to the carrier ring using adhesive. The four friction materials, brass, sinter, molybdenum and organic, show considerable differences in their behavior.



Specific energy [J/mm2]

Fig 3: - Special Brass Alloy (SoMs) The friction surface is profiled during the forging process.


Wear behavior of synchronizer friction linings

2.1.2 Wear on the mating cones With mating cones hardened to 60 HRC, paper, brass and sinter friction linings show no wear on the mating cones, while molybdenum linings tend to show fretting on the mating cones.

2.1.3 Maximum permissible load A series of publications [1,2,5,6 ] documents that sinter friction linings show an extremely high load limit (Fig 4), not achievable with brass, organic or molybdenum linings. The high thermal conductivity and porosity of the sinter linings, in combination with the high thermal capacity of the oil stored within its pores, ensures a low temperature of the friction surface. This is of benefit not only to the friction material, but also the thermal stress of the oil Thin molybdenum coatings show almost equivalent performance to sintered friction linings, under low differential speeds. At higher surface speeds (10 m/s) traces of overheating (frictional martensite) are evident, developing into fretting on the cone surface.

HOERBIGER & CO, Schongau

Performance and cost optimization of friction systems for single and multiple surface synchronizers


Organic linings are basically a risk under high surface pressures in synchronizers. Even when operated below the thermal capacity limit, unacceptable reduction in the wear reserve can occur. Brass is unsuitable for permanent energy loads greater than 0.1 J / mm2, due to wear.

Step 1 2 3 4 5 6


V (m/s)

450 820 1230 1590 1800 1900

Energy (J)

2.3 4.2 6.4 8.2 9.3 9.8

Specific Energy

(J/mm2) 0.51 0.92 1.39 1.79 2.03 2.14

1237 2254 3381 4370 4950 5223

Table 1: „Abuse-Test” Maximum permissible friction loading (J/mm2)


to 4,0

3,0 2,5 2,0

2.1.5 Comparison An attribute performance comparison of the different linings is given in Table 2.

(Fretting) 1,5




Fig 4:

This „Abuse Test” led to the introduction of sinter linings in a mass production passenger car application.




Maximum permissible friction loading (J / mm2)

Attribute Wear (friction surface) Wear (mating cone) Load Capacity (J/mm2) Dynamic friction Frictional stability Abuse performance Oil compatibility

Sinter Paper

++ o +++ + + +++ ++

Mo-Thin Layer

-o ++ ++ ++ ++ ++

+ ++ + o o +

2.1.4 Overload capacity (Abuse conditions) Abuse tests are particularly common in the USA. Table 1 shows the test designed to simulate the behavior of the particularly sporty driver, who does not shift correctly. The assumption behind this test is that many of these drivers do not fully depress the clutch pedal while changing gear (grinding the gears) or force the synchro ring to the mating cone, without controlling the clutch (gear lever in neutral; a habit from using an automatic transmission).

Bewertungsbasis: Synchronring aus Sondermessing

In both cases this means that the synchronizer must absorb considerably more energy.

All variations of the brass single cone designs, have the disadvantage that the increase of the synchronizer capacity, by the addition of a friction lining, means a substantial increase in cost.

Table 2: Comparative assessment of alternative friction materials




50 lbs = 281 N 7.5:1 2109 N 2.5 s 100 mm

Fig 5:

Forged Ring+HOERBIGER Sintered Bronze

PM+HOERBIGER Sintered Bronze



Steel +Paper



Handball Load: Lever Ratio: Axial Force: Compression period: Synchro Ring Diameter:

Brass (SoMs) deterioration -- substantial - minor o none


This abuse test, with its high differential speeds, led to the functional problems with molybdenum and organic linings. The moly linings showed fretting while the matrix of the organic linings suffered a massive thermal overload (carbonization).

Basis improvement +++ substantial ++ clear + minor

Comparison of cost and permissible loading of currently available components on the market

Performance and cost optimization of friction systems for single and multiple surface synchronizers

3. HOERBIGER New Developments HOERBIGER has developed a cost effective manufacturing technology that makes it possible to use a sinter lining inside a brass or steel single cone synchronizer ring. In addition HOERBIGER has also introduced a modular system that allows upgrading from a single to a multi surface synchronizer, at minimum cost.

3.1 Components

3.1.1 Brass ring with formed HOERBIGER sinter (HS) foil


HOERBIGER & CO, Schongau Quality Assurance The mechanical connection between the sinter foil and the carrier blocker ring has been shown in several tests, to have a safety factor that is 10 times the real application load.

Max. Friction Torque

Achieved Torque

Max. Axial Force

Achieved Force

≈ 20 Nm

> 250 Nm

≈ 800 N

> 7000 N

Table 3: Mechanical test of the bonding (ring size 60 mm) Advantages compared to conventional systems


Fig 6:


Brass ring with formed HS Foil Background of the project The development goal of this project, was to combine the advantages of two well known and widely approved materials into a new product.

• 1 : 1 replacement of existing solution • Short development times for the customer • Use of a proven friction lining • Cost reduction when compared to conventional upgrades of a brass system • Improvement in shift comfort • Smoother shifts • Noise reduction • Improved durability • Cost savings in the mating cones (elimination of honing)

3.1.2 Deep drawn steel ring with sinter lining

- Low cost of brass as a base core material - High load capacity friction lining Manufacturing In a further development of the existing HOERBIGER manufacturing technology for double cone rings, a flat steel ring with friction lining is formed in a fully automatic process. This is then mechanically fixed, in a single step, inside a brass ring. The forming of the foil around a chamfer at the front and rear of the brass ring ensures the axial location, while the pressing of the foil into axial grooves prevents rotation.

Fig 7:

Deep drawn single cone ring

Performance and cost optimization of friction systems for single and multiple surface synchronizers

7 Background of the project Due to the material structure of the brass core, high loads can lead to typical failure modes of tooth wear or fracture of the ring. The higher heat expansion of brass also means that the axial gap needs to be higher. The alternative materials are all high cost options (Powder Metal parts, steel forged parts) .

The higher strength of the steel allows significant reduction of the thickness, offering a greater friction diameter. The necessary design changes are to modify the mating cone diameter, the center diameter of the hub and a minor change to the stone design. The structure of the friction material is such that the forming process does not influence it, meaning • Homogeneous porosity of the friction lining • Precise definition of oil grooves (for good cold performance)

The logical development goal was to improve the durability of the core material and to combine it with the advantages of a sinter lining.

Tensile Strength Elastictiy Limit E-Modul Heat Expension [N/mm2] [N/mm2] x 103 [N/mm2] x 10-6 1/K CuZn40Al2 SoMs Sint D 30 C 35





510 650

370 400

130 210

≈9 11

Extensive rig and transmission tests, have shown the function and load capacity performance of the formed single cone to at least match existing systems. Advantages compared to conventional systems • Weight reduction of approx. 45 % • Improved material • Increased friction radius • Cost effectiveness • Elimination of heat treatment

Table 4: Comparison of Materials for synchro rings Production A sintered sheet is formed using an automatic multi stage process, ideally suited for mass production, into a single cone ring with sintered friction lining, gear teeth and indexing lugs. The cold working of the teeth normally permits elimination of a heat treatment operation It is possible to form several types of indexing during this process.

3.1.3 Comparison of costs The new developments of brass ring and HS foil and deep drawn steel ring with HS foil, open new possibilities to use proven materials in a cost effective manner, ideally suited to mass production applications. Fig 9 shows the cost comparison of both conventional and HOERBIGER solutions in terms suitability for various application conditions. HOERBIGER product

Fig 9:

Drawn Steel Ring+HOERBIGER Sintered Bronze

Brass+HOERBIGER Sintered Bronze

Forged Ring+HOERBIGER Sintered Bronze

PM+HOERBIGER Sintered Bronze


Different indexing lugs


Fig 8:

Steel +Paper



passenger car





Comparison of standard solutions and HOERBIGER solution

The graph shows that both products offer very attractive production prices.


HOERBIGER & CO, Schongau

Performance and cost optimization of friction systems for single and multiple surface synchronizers


HOERBIGER & CO, Schongau

3.2 Synchronizer systems

3.2.1 Modular construction for synchronizer systems The ever increasing need in modern gearboxes for improved shift comfort and higher energy capacity, has led to the redesign of the single cone system. To date this was only achievable by using a larger diameter or multiple surfaces. Unlike other known single cone systems, HOERBIGER equips the inner cone with the friction lining. The cone is connected to the clutch ring by drive lugs.

Sliding sleeve Gear wheel Synchronizer ring Single cone friction ring Clutch body

Synchronizer body


System BW

Fig10: Comparison HOERBIGER / BW System

This system, in which only the outer surface of the inner ring is used, is similar in construction to the standard dual cone system. The design allows a capacity increase to the double or triple cone style, simply by adding more friction surfaces. (Fig 11). The modular system in Fig 11, shows a deep drawn steel ring replacing the conventional PM blocker ring.

Fig 11: Single / Double / Triple Cone System

HOERBIGER & CO, Schongau

3.2.2 Cost Optimized Friction Pairings The use of brass or moly gives rise to high requirements of geometry and surface finish on the mating cones. These costly operations can be eliminated by the use of HOERBIGER sinter linings. µ Axial Wear (% v baselinge) (% v baselinge)

Mating Surface Material

St. 1.2379 60 HRC PM 1 carbon nitrided PM 1 plasma nitrided PM 2 gas nitrided PM 3 final sintered PM 4 standard PM 5 standard PM 5 case hardened PM 5 HCO traitement

Performance and cost optimization of friction systems for single and multiple surface synchronizers


61.6 77.7 100.0 90.3 73.6 75.0 75.0 89.8 94.4

• uniform size of synchro ring on all gears • easily upgradeable to a multiple surface system • use of approved friction lining on all gears • no additional friction lining for highly loaded gears • manufacturing of components with no machining operations • wide range of applications • proven costs savings of up to 22 %

Ratio µStatic µDynamic

42.3 26.3 100.0 52.3 69.0 95.8 98.6 55.2 48.6

1.05 1.44 1.07 1.045 1.55 1.345 1.455 1.215 1.225

4. Conclusion As a result of continuous process development and the use of innovative production techniques, it is now possible to utilize the sinter friction linings in cost effective solutions for high volume applications of components and systems.

Table 5: HS 450 in conjunction with various surfaces The flexible structures of the new lining compositions allow the use of rougher or lower hardness surfaces on the mating cones. Table 5 shows the wear behavior characteristics of this new lining. The conclusion being that even unhardened surfaces can be used.

3.3 Cost Comparison The following comparison of a conventional design with an optimized dual cone system shows how the use of the above components leads to cost effectiveness

Synchro-system double cone brass

Advantages compared to a conventional system

Synchro-system double cone steel

The modular system is a further step towards the standardizing of all gears within a gearbox and its associated benefit of increased component volume, leading to more competitive prices.

Bibliography: [1]




Material powder metal

sintered part

Cost Index [%] 13


case hardened machined grooves

28 18

brass steel



Cost Index [%] 10




Sint D39

shifter sleeve blocker ring

20 14

calibrated deep drawn

Sint D39 steel




clutch body


stamped steel



hardened/ ground



deep drawn

steel / friction material


machined grooves


intermediate ring friction ring inner ring


deep drawn



springs balls






In addition to the available 22% cost reduction, the optimized system also offers performance advantages for the individual components.



Thelen E., P. Wunderlich, J. Foth und I. Schmidt: Reibungs- und Verschleißverhalten moderner Reibschichten für Synchronisierungen. Praxisforum, 1990 Pflaum H.: Das Reibungsverhalten ölgeschmierter Kegelreibkupplungen in Synchroneinrichtungen von Kfz-Schaltgetrieben. TU München, Dissertation, 1989 Brügel, E., K. Christian und P. Wunderlich: Entwicklung einer Mehrfach-Synchronisierung für Nfz-Getriebe. VDI Tagung Getriebe in Fahrzeugen heute und morgen. April 1991 Lanzerath, G. und H. Patzer: Neuartiger Synchronring mit organischem Belag. Antriebstechnik 25/1986 HOERBIGER Information: HS - Sinter-Reibbeläge in Synchronisierungen. August 1989 Vojacek, H. und H. Pflaum: Verwendung von Streusinter-Reibbelägen in Reibkupplungen. Deutsches Patent DE 317813 C1


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