Dual Mass Flywheels for Vehicles with a Start/Stop System – Teething Problems

Recently, an interesting question was raised at the end of a REPXPERT training course on dual mass flywheels. Can you replace a dual mass flywheel for vehicles equipped with a start/stop system with a conventional DMF? For some vehicles, there is an option to choose between the two variants in the catalog, which allows the customer to reduce the overall price of the vehicle slightly. What would happen, then, if you were to install a standard DMF in a start/stop system while keeping the same engine?

A Barely Visible Difference that Has a Big Impact!

Conventional engine starting systems are designed to easily withstand 50,000 starts. However, when a start-stop system is fitted, the number of start-stop cycles can be slightly over 500,000. This requires a more robust starting system. Specifically, this means that: The teeth of the starter pinion and of the starter ring on the DMF have to be more durable and stronger. When you look more closely at the teeth of a start-stop DMF, you can see that the geometry of the teething is different from that of a standard DMF. The teeth are wider at the base, which means that there are fewer teeth but the diameter of the teething gear is the same. There are between two and three teeth fewer on average.  

If a conventional DMF is used in a start-stop system, the geometry of the starter pinion will not match up with that of the starter ring gear. This may mean that the starter pinion is not able to engage or disengage. Furthermore, because the teeth do not connect perfectly, the constant sliding friction in the gear pair is impaired. This leads to an unusually high level of wear that can result in failure of the starting system after a short period of operation. 

In order to save the customer and the garage from unnecessary hassle, a dual mass flywheel that is suitable for use with the starting system should always be used. Items affected by this are highlighted with a clear notice in the catalog media.

Schaeffler will be exhibiting at this year’s Auto Trade EXPO, which takes place from Saturday and Sunday, October 15-16 at the RDS Simmonscourt in Dublin.

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Published on: August 22, 2022

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