Schaeffler North America

Belt drive systems

Primary drive



Timing belt drives that drive camshafts or balancer shaft s have been volume produced for internal combustion engines for 40 years. In older designs, the timing belt was preloaded via either an accessory with eccentric bearings in the timing belt drive (e.g. water pumps) or through manually adjustable, fixed tension pulleys (e.g. eccentric tensioners).

This type of system does not allow for optimal adjustment of the belt force since neither belt force fluctuations resulting from temperature or wear nor dynamic effects (belt vibrations, impacts from the valve train) are compensated. Compensation of such fluctuations and effects by means of automated belt tensioning systems is essential in modern timing belt drives since this is the only way that a system life of up to 240 000 km and more (depending on the engine life) required in today’s automotive industry can be achieved.

Belt drive systems not optimally preloaded are susceptible to noise and susceptible to wear. Using an automated belt tensioning system considerably reduces preload force dispersion during initial installation and also keeps the preload force across the engine’s operating temperature range at nearly consistent levels. Automated belt tensioning systems have been used in timing belt drives in internal combustion engines since the early 90s and have largely replaced fixed systems for the reasons described above.

The above conditions result in the following primary requirements for automated tensioning systems:

  • Provide simple adjustment of the specified belt force during initial installation and maintenance (compensation of belt, diameter and position tolerances)
  • Maintain a defined belt force that is as consistent as possible under all operating conditions for the duration of the required system life (compensation of heat expansion, belt elongation and wear, consideration of crankshaft and camshaft dynamics)
  • Ensure an optimal noise level while also reducing belt vibrations
  • Prevent gear teeth jump

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