The role of precision metrology in the manufacture of gears for electric vehicles


The electric vehicle market continues to grow and as it does, there are major challenges for manufacturers as they push for various technical advancements that will allow for greater adoption.

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One of the biggest technical challenges is the need for sophisticated finishing and grinding methods that create very complex and exact surface characteristics in the teeth of electric vehicle gears. This improves efficiency and minimizes noise, thus increasing customer satisfaction.

Considering recent developments in processing and the more specific requirements of gear surfaces, precision metrology plays a critical role and is valuable for the discovery of key technological breakthroughs. As for the development of gears for electric vehicles, it can accurately, quickly and easily define the exact surface characteristics of different models and prototypes.

Optical metrology offers an exceptionally flexible inspection approach and currently occupies an important place in confirming the quality of gears and achieving design goals. Considered a first choice metrology solution, optical metrology has the advantage of being a non-contact, non-destructive, fast, very sensitive method with exceptional resolution and precision.

Make better gears

Two key aspects of electric vehicles are related to gear packs: the efficiency and noise of the gears. To attract more consumers, electric vehicles must achieve a “fuel range” similar to that of internal combustion vehicles. To achieve this, gears with extremely low surface texture are needed, the lower the surface friction, the longer the range of the vehicle.

The noise of the gears in a traditional vehicle is masked by the noise of the rest of the transmission. The frames and interiors of these vehicles have also been designed to minimize unwanted noise in the cabin. With the shift to quieter electric motors, gear noise can become a factor. New techniques and new processes could help in this area.

Depending on the method used, producing an accurate gear shape and texture is a bit of a balancing act. However, when the right systemic balance is achieved, it can create gears that meet surface shape and texture requirements at high production volumes. One of these techniques is continuous generation grinding. This technique uses threaded wheels that are in constant contact with the toothed gear part. This process and others have been shown to generate the texture and ripple requirements necessary to improve the connection of gear teeth while reducing noise.

Use contactless metrology

Non-contact metrology tools are extremely valuable when it comes to analyzing, learning and characterizing gear surfaces for vehicle optimization.

With the increasingly high standards of electric vehicle gears, typically at the micron scale, a high-precision measuring system is needed to meet accuracy requirements, along with metrology software specifically designed for measurement. gears. Accessibility is the main factor in such a measuring system because the gear teeth can block access, especially at the roots of the teeth. In addition, measurements to calculate noise at high rotational speeds are increasingly crucial. Noise-related measurements can involve roughness analysis on the tooth flanks or performance modeling based on a full surface analysis of the manufactured part.

To produce small gears, several essential measurements of the gear teeth are required. The profile and helix lines should be scanned and evaluated for deviations. For critical evaluations related to pitch and runout, individual points on each flank should be scanned. The tooth flank should also be captured at depth to assess changes to the flank.

Since these advanced gears are very valuable, non-contact solutions are needed to avoid compromising or damaging surfaces. A new contactless metrology solution from Connecticut-based Zygo uses coherence scanning interferometry (CSI). This technique uses optical microscope objectives to image and magnify a surface to generate a 3D topography. This method is completely non-contact and, compared to other similar microscope-based techniques, the CSI has a unique advantage: the height resolution is constant for all magnifications, from 1x to 100x.

This translates into a particular appeal for CSI-based methods, as the size and shape of the craft can restrict the types of targets that can reach an area of ​​interest. In other solutions, a long working distance lens may restrict the vertical resolution.

Another important aspect of Zygo’s metrology solution is assembly in the field. Similar to using a smartphone for panoramic photography, the metrology system can create a composite of overlaid measurements that capture more area than a single installed lens can capture on its own. When the system has acquired enough measurements to capture a target area, the data can be “stitched together” to create a large, complete image. This is particularly beneficial when measuring the fine texture of a gear flank, edge to edge, or sewing from root to tip. These stitched measurements can be made on uneven areas, including hypoid shaped areas. This system allows a user to re-analyze a hypoid gear with a high level of accuracy.

Resources and further reading

Schmidt, M. Growing role of precision metrology in the manufacture of gears for electric vehicles. Zygo Company. [Online] Available at:

Hexagon. High precision measurement of electric vehicle gears. Hexagon – Electric vehicle transmissions. [Online] Available at:

Delta research. Inspection System Upgrades Meet EV Equipment Challenges. [Online] Available at:

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