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Engineering Materials

Plastic gears help to lightweight vehicles, increase fuel efficiency

For decades, scientists and engineers have focused on improving the materials used for gears while attempting to overcome several challenges, such as gear teeth breaking at the root due to fatigue, wear of the teeth at the flank, local overheating, too much noise, shock loading or hard stops, and noise vibration issues.

Today sintered metal gears are being replaced with high-performance plastic gears in automobiles because the demand to lightweight vehicles and increase fuel efficiency is far from just a trend—it is driven by meeting new and upcoming legislation to reduce emissions, and this must be met with cost-effective solutions—so the research and testing to improve gear design continues.

One of the cost-effective solutions to lightweight an automobile is the start-stop motor in which gears are made out of plastics that have excellent mechanical and tribological properties. These plastic gears reduce weight and cost. Plastic gears are also used in other automotive applications, including engine management actuators and power boosting systems, such as electric power steering and electric brake boosting—but for this blog we will focus on the start-stop motor application and DSM's gear testing capabilities.

Start-stop motor application

Conventional starter motors see as many as 40,000 engine starts over the lifetime of a vehicle, or up to 13 million load cycles for each plastic annulus gear tooth. Compare that to the start/stop starter motors that see the number of starts up to 350,000 or up to 45 million load cycles per annulus gear tooth.

Plus, start/stop starter motors can decrease fuel consumption up to 15 percent and carbon dioxide emissions up to 8%. As the automotive industry is striving to reduce CO2 emissions and vehicles weight, it’s easy to see why automotive manufacturers want a gear that is made from low weight materials, such as plastics that offer exceptional fatigue properties and wear rates to meet the durability requirements. DSM’s Stanyl meets  these tough material requirements across a range of power ratings.

Onsite tribology and application test methods

To best utilize Stanyl’s tribological properties and to understand the theoretical and practical relationship between the application and the material’s wear and friction properties, DSM runs various tests to understand the interface and environmental temperature conditions.

DSM’s approach goes beyond testing to industry standards, linking the testing parameters to the application to simulate the actual conditions. Combining this with the extensive knowledge base of our fundamental research team enables us to determine which material properties need to be improved. To carry out this advanced testing, DSM modifies its testing equipment to include precise temperature control in addition to pressure and sliding speed variables to best approximate practical applications.

At the Material Science Center in Geleen, The Netherlands, thrust-washer testing machines include thermal management to actively control temperature–by cooling and heating–up to 200°C at the frictional interface. We have also increased the mechanical stability to improve accuracy on measurements, including temperature sweeps, sliding speed sweeps or wear rate runs (see graph below). We can also measure wear and friction in lubricated conditions to gain knowledge about gear applications in lubricated systems.

DSM also has a disk-to-disk tester that runs two disks against each other to test polymer-to-polymer or metal-to-polymer behavior at controlled temperatures up to 150°C, speeds to 2,000 rpm (3.6m/s), and a maximum normal force of 2,000N. It also tests sliding and rolling combinations to better simulate the practical conditions seen in a gear mesh.

DSM has an onsite, state-of-the-art gear tester that is used to validate material performance on application level and correlate it with the basic material properties, such as tensile strength, fatigue resistance and tribological properties. 

With the gear tester we can vary the torque, speed, environmental temperature and lubrication effects.

This picture gives an impression of this gear tester. The machine has capability to vary the gear center distance and can be used to analyze backlash effects on the gear performance. 

Results (see graph below) from gear tests showed that at 2.5 Nm, Stanyl achieves 200k cycles before failure while other materials achieve 40k cycles or less. At high loads there is a longer lifetime compared to alternative materials. Also, for a lifetime of 200k cycles, Stanyl achieves 2.5 Nm torque; other materials can achieve only 2 Nm or less—a lower weight of the gear and saving of design space for a given lifetime is required.

DSM partners with OEMs and Tier 1-part manufacturers around the world to develop and test new gear designs to improve gears and actuators for motor management, engine control, and in-engine applications.

To learn more about the characteristics of Stanyl or to learn more about DSM’s Material Science Center and gear testing contact us for additional information. You can also visit plasticsfinder.com for additional information about Stanyl, including technical data sheets.

Adnan Hasanovic

Technical Manager

Published on

07 August 2019

Tags

High-performance plastics for gears improve efficiency, reduce fuel consumption

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ABOUT THE AUTHOR

Adnan Hasanovic

Technical Manager

Adnan Hasanovic is technical manager for gear actuators at DSM. In this global role, he focuses on tribological applications, such as gears and bushings, as well as structural applications for gear housings and covers. Adnan also supports global DEP activities in existing and new application areas. He joined DSM after he completed studies of mechanical engineering. Before joining DSM, Adnan worked as application development engineer and CAE engineer.

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