How optimising small parts gives big gains

Optimising small parts in exterior & interior applications can make a big difference to the consumer's perception of the car while allowing system suppliers and automakers to simplify the assembly process to keep production time and overall costs down.

Autocar Pro News Desk By Autocar Pro News Desk calendar 24 Nov 2015 Views icon4180 Views Share - Share to Facebook Share to Twitter Share to LinkedIn Share to Whatsapp
With 14 sites and six R&D centres globally, the Bearings & Tolerance Rings Group, a division of Saint-Gobain, provides engineered components to high volume auto manufacturers.

With 14 sites and six R&D centres globally, the Bearings & Tolerance Rings Group, a division of Saint-Gobain, provides engineered components to high volume auto manufacturers.

For most drivers, the routine is the same. You get in the car and adjust the mirrors and the seat for maximum comfort. These actions, even if automatic for some, greatly influence the perception of quality. Whether the mirror or seat, the trunk or the armrest; ensuring quality throughout every automotive mechanism is important for a positive driver experience and customer satisfaction. Yet automotive manufacturers must constantly balance new ways to meet consumer demands without increasing production costs or sacrificing safety standards.

Optimising small parts in exterior and interior applications can make a big difference to the consumer’s perception of the car while allowing system suppliers and automotive manufacturers to simplify the assembly process to keep production time and overall costs to a minimum. 


One example to illustrate the benefits that innovative solutions can bring to exterior automotive applications is the anti-pinch control in the automatic tailgate mechanism. To enhance safety for passengers, modern cars are equipped with a slip clutch device to prevent trunk closure when any object is in its path, whether a bag or a child’s hand.

Among the main requirements that system suppliers are looking for in the slip clutch mechanism are narrow torque tolerance, anti-pinch control safety features and small, lightweight solutions to minimise space and maximise automotive weight reduction efforts.

There are at least two options for this automotive mechanism. Some automated tailgates utilise an anti-pinch device consisting of a spindle drive, electronic sensors, electric motor and control units. As the trunk lowers, if sensors detect the slightest obstruction, they will send a signal to the motor to stop. 

Although this solution allows for accurate torque and protects passengers from being nipped by the trunk, there are a number of disadvantages. The system consists of a multitude of components and therefore adds weight and costs to the car, increasing assembly time and complexity. With the current demand for lightweight and fuel-efficient vehicles, any weight savings are critical.

Another option in development is the use of tolerance rings, radially sprung frictional fasteners, as simple mechanical slip-clutch controls. Flexible shims designed to fix two cylindrical parts together, the rings are used to mount gears in electric motors. The tolerance rings’ wavelike protrusions allow them to act as slip clutch mechanisms as they can be tuned to ensure the rings slip at a pre-determined torque level. In other words, in the event of excessive force or torque being applied to the motor shafts (as occurs when there is an object in the path of the trunk), the rings slip. This allows the shaft to rotate while the gears are stationary to ensure the trunk door does not close. In addition, this slip clutch option protects the motor from overheating and the gear teeth from being damaged by excessive force, thereby contributing to the vehicle’s long life and eliminating the need for expensive repairs. By replacing a heavier clutch device, tolerance rings contribute to further space and weight saving, enabling automotive manufacturers and system suppliers to enhance the smart design of their mechanisms.



For long drives or short-haul rides, we all can appreciate the comfort of an armrest in car seating. Torque control is crucial to hold the armrest in place, augmenting consumers’ overall evaluation of car quality.

Among the solutions to provide torque control in car seat armrests are plastic washers and spring-energised fixtures. As temperatures change, the properties of plastic washers also change, affecting their torque ratio. This leads to a looser feel in winter and a stiffer and more rigid feel in summer. In addition, plastic washers and spring-energised fixtures require a complex and precise assembly process.

As these components have to be press fitted between the pivot pin and housing, higher assembly forces are required. Consisting of several parts, plastic washers and spring-energised fixtures need lengthy production time and high assembly costs.

Tolerance rings, on the other hand, act as simple joining mechanisms at seat armrest pivots, holding armrests in place and preventing them from falling down even on the roughest terrain. Due to their waves and split-ring design, tolerance rings can compensate for thermal expansion, providing a perfect fit to ensure consistent performance in summer and winter. In contrast to plastic washers, they are unaffected by temperature fluctuations or wear. For enhanced comfort and driver satisfaction, tolerance rings’ wave-like protrusions absorb vibration and rattling in armrests, ensuring the noise-free passenger area.

Tolerance rings also simplify the assembly process for automotive manufacturers as they require a lower assembly force than traditional solutions thanks to the compressibility of their protrusions. By compensating for any misalignment, tolerance rings allow automotive manufacturers to save resources on precise machinery operations for maximum assembly efficiency.


Car seats can be equipped to be manually or automatically adjusted to 11 different positions for driver and passenger comfort. Automated seat adjusting drives consist of electric motors combined with gear systems. These automated mechanisms allow passengers and drivers to adjust their seats easily and quickly at any time.

If excessive force is applied to electric motors, the gears may break or the entire mechanism may burn out, such as when a passenger aggressively adjusts the seat unaware that an object may be obstructing the seat’s movement. Consequently, the entire adjustment system would need replacing, which becomes expensive and time-consuming for end-

Traditional gear mounts with electric motors include welding and adhesives. As neither provides a slip clutch function, there is a need for additional protection systems to avoid potential damage. Sensor-based mechanisms are typically used, but their design is bulky and heavy, making the production process more complicated, lengthier, and more expensive.

The need to protect motors and gears from potential damage or costly replacement can be met by use of tolerance rings fitted between the motor shafts and gears to act as simple slip clutch mechanisms. This mechanical solution can protect expensive motors from possible torque overload, ensuring the long life of the mechanism without adding weight or complicating the assembly process.


Tolerance rings offer simplified assembly and torque control for gear and motor protection, solving common engineering dilemmas for automotive mechanisms. They are an ideal solution for system suppliers to reduce manufacturing costs and automotive manufacturers seeking to provide consumers with worry-free, reliable and comfortable automobiles. With these small yet important components, drivers can get behind their steering wheels, adjust their car settings, turn on their engines and begin their journey with confidence, comfort and satisfaction. 

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