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Engine drive systems Manual timing belt tensioner (MTBT) The original timing assembly process, when mounting onto the engine, was accomplished by manually setting the tensioner by rotating the tensioner unit and locking it permanently at the required tension. This meant that as the engine warmed up to ever higher temperatures, and new designs required different operating characteristics with higher performance, the fixed tension control from the manual BTU was not able to reach the desired performances for extended component life required by the designers. Automatic timing belt tensioner (ATBT) The ATBT promotes longer belt life, by better handling of the engine loads, and is less affected by running temperature variations after correct set up. This is why it has become the norm fitted to today’s belt-driven engines. These tensioner units are made up of many functional sub-components that ensure the correct operation of the automatic tensioner. Key ATBT components: 1. Mounting eccentric: Provides smooth adjustment by rotation to facilitate correct set-up of initial tension. 2. Bushing: Self-lubricating, highly wear-resistant polyamide component. Primary source of damping. Also provides axial alignment and sliding surface. 3. Bearing: Maintenance-free and sealed for life. The component is specifically adapted for the relevant application. 4 1. 2. 3. Belt load, N 4. 250 200 150 MTBT ATBT 4. Pulley: Metal or polyamide, depending on the application. 5. Hub: Transmits the torque of the spring to the pulley. 6. Spring: Designed to provide optimum belt tension control for engine running. 7. Pivot shaft/plate: Ensures proper placement and angular location on engine block. 5. Noise generation MTBT 100 ATBT 50 0 Belt losing grip 32 / 68 / 104 / 140 / 176 / 212 / 248 / 284 / 320 / 0 20 40 60 80 100 120 140 160 Engine temperature, °F / °C 6. MTBT vs ATBT chart 7.
Engine drive systems Variations of ATBT design Even an apparently basic pulley component may need to be used differently when the engineer sets his specification. There are pros and cons when it comes to the optimum choice of materials best suited to a particular engine’s requirements: The polyamide pulley: Positives: • Polyamide is light. • Polyamide retains heat longer than metal. • The clearance of the bearing is not affected by the moulding. Negatives: • Dirt and grit can be embedded in the plastic, risking belt damage. • Moulding process can affect the bearing and grease life. The metal pulley: Positives: • Thermal properties of steel dissipate heat efficiently. • Metal resists abrasion to maintain proper belt alignment. • Metal deflects dirt and grit particles. Negatives: • The assembly can affect the clearance of the bearing causing operation and life issues. • Metal is heavy compared to plastic. Hydraulic automatic timing belt tensioner The hydraulic system design is mainly used on applications with high loads and/or angular vibrations, where a mechanical automatic tensioner cannot provide sufficient damping or tensioner movement. Due to weight and space limitations, the design is limited to a few engine types and is not expected to become as common as the more compact ATBT. The unit can operate with a large range of dynamic belt lengths, unlike the mechanical tensioner, due to the length of stroke of the actuator and the lever design. The damping characteristics from the piston are particularly suitable for large V6/V8 engines (amongst others). These units are made up of many functional sub-components that provide the correct operation of the automatic tensioner. Hydraulic automatic timing belt tensioner 5
Page 1 and 2: Catalog 457702 2010 SKF Timing Belt
Page 3 and 4: Belt tensioner unit (TBT) The belt
Page 5 and 6: How to use this catalog This catalo
Page 7: Engine drive systems Technology and
Page 11 and 12: Engine drive systems Cooling system
Page 13 and 14: Engine drive systems Metal idler, w
Page 15 and 16: Failure analysis overview 90% of en
Page 17 and 18: Failure analysis overview Tensioner
Page 19 and 20: Failure analysis overview Water pum
Page 21 and 22: SKF Timing kits Application install
Page 23 and 24: SKF Timing kits Application install
Page 25 and 26: Abbreviation list ABS ............
Page 27 and 28: Manufacturer to model index Manufac
Page 29 and 30: Passenger cars, light & medium truc
Page 55 and 56: Timing belt kit contents TBK014P DE
Page 57 and 58: Timing belt kit contents •TBK101P
Page 59 and 60:
Timing belt kit contents •TBK145W
Page 61 and 62:
Timing belt kit contents •TBK165A
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Page 65 and 66:
Timing belt kit contents TBK214P DE
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Timing belt kit contents •TBK230P
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Page 77 and 78:
Timing belt kit contents •TBK324P
Page 79 and 80:
Belt performance and quality Timing
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Belt specifications SKF No. Width L
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Belt specifications SKF No. Width L
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Timing belt removal and installatio
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Troubleshooting and failure analysi
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Analyzing belt wear and damage A br
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Troubleshooting and failure analysi
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Good practices and helpful hints Ex
Page 95 and 96:
Setting up automatic tensioners: a
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Passenger cars, light & medium truc
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Passenger cars, light & medium truc
Page 101 and 102:
The Power of Knowledge Engineering
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