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Engine Drive Belts

Functionality of TVD’s

You may wonder why a torsional vibration damper (TVD), or crankshaft pulley, is required in modern ECU controlled engines. The simple fact is that on each ignition stroke, the force of combustion twists the crankshaft ahead of its natural rotation.

 

On the exhaust stroke, the crankshaft returns to its original position. The repeated twisting and untwisting of the crankshaft creates torsional vibration, causing metal fatigue and, if unchecked, this will lead to a loss of torque, power and fuel economy; it will also reduce the life of the associated bearings. A TVD on the crankshaft counteracts the destructive force of this torsional vibration.

Types of TVD

  • Coupled: mostly found on petrol engines – where moderate vibrations need to be dealt with
  • Decoupled: mostly found on diesel engines – where large amounts of vibration need to be dealt with

How Do They Work?

The working parts of the TVD can be divided into two main parts: the mass (or outer parts) and the energy absorber (the rubber or fluid filled centre). The mass serves to absorb irregular acceleration of the crankshaft, while the energy absorber dampens vibration.

Production Techniques

The most common way to produce a TVD assembly is to chemically treat the inner part (which is mounted onto the crankshaft) to provide a bonding surface. The outer mass is also treated in this way. The two parts are placed into a mould where liquid rubber is injected at high pressure (typically around 100-150 tons per square inch) into the cavity formed between the two. Once the rubber cures, the whole unit is balanced, torsionally checked and painted.

Failure and Replacement

A failed TVD can cause a harsh, noisy engine at best and at worse a failed crankshaft. Causes of failure vary between applications, but broadly speaking they can be divided into three categories:

  • Failure or degradation of the damping element over an extended period of time
  • Failure of the damping element due to external causes, such as excessive or unexpected load placed upon the TVD. This could be a failed air conditioning compressor, a failing auxiliary driven unit or an incorrectly tensioned auxiliary drive belt
  • Irregular firing of the engine over an extended period of time can also cause accelerated failure of the TVD

If it is suspected that an external factor has caused the failure, the cause must be investigated before a replacement unit is fitted. It is also worth noting that many engines use an element of the TVD assembly to reference engine position for the ECU. A failing TVD could therefore have implications not only for vibration and longevity of the engine, but also on power output, fuel consumption and tailpipe emissions. When dealing with TVDs it is essential to have knowledge of the external variables which can be affected. Understanding this enables factors and garages to provide their customers with solid product support and opens up the potential for sales of related auxiliary items.

Related Sales

The related sale is very application specific. For example, an application with power assisted steering or air conditioning may require additional auxiliary items. Certain Ford and Mazda applications require a new belt to be fitted alongside a new TVD. This is due to the design – there is no belt tensioner and the belt is a one piece self-tensioned unit. When replacing this item, the belt must be cut in order to remove it. A special tool is required to fit the replacement part. BGA’s comprehensive TVD range comprises both coupled and decoupled pulley types and provides extensive coverage of the UK car parc, including European, Japanese, Korean and imported applications. As with any technically critical part, the highest levels of quality are adhered to during the manufacturing process and the quality of materials is stringently checked so that the product can be sold through the supply chain with the utmost confidence.

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