Tolerance ring solves ETC problems
A
Saint-Gobain Performance Plastics product story
Edited by the Engineeringtalk editorial team
Apr 24, 2009
Saint-Gobain Performance Plastics Rencol has designed a tolerance ring for reliable motor mount in throttle-body applications.
Electric motors are being used to drive a growing number of devices in cars.
One such application is within the throttle body to control the butterfly valve, commonly known as the electronic throttle control (ETC).
But the demanding environment where this assembly is mounted presents automotive engineers with many issues.
Operating temperatures of up to 150C are common place; if dissimilar materials are used, for example steel and aluminium alloy, the differential thermal expansion between the motor and housing can have a detrimental effect on the large tolerances.
The alignment of pinion gear can also be problematic.
The vibration of the car's engine vibrates the motor and can cause failure of the electrical connectors, via fretting corrosion of the terminals.
However, there is a solution that overcomes all of these problems: the tolerance ring.
These radially sprung steel-fasteners can handle direct torque-transfer, predictable and repeatable torque slip, axial retention, controlled collapse and radial loading between the mating components and can help reduce noise and vibration, avoid resonance frequencies and overcome differences in thermal expansion.
Saint-Gobain's engineers can customise the tolerance ring to exactly the right combination of properties needed.
In many applications, the motor is only fixed at the front.
As the rear of the motor is not supported, engine vibration can lead to fatigue failure or fretting corrosion of the electrical terminals.
To solve this problem, engineers have taken advantage of the unique properties of a Crown Ring used to mount the electric motor within the throttle housing.
The Crown Ring is a radial spring fastener with several sprung fingers that, while deflected, give a required load.
The height and number of sprung fingers can be altered to cope with specific system tolerances, thermal expansion and support of the motor weight.
This system combines the benefit of large diametrical tolerance compensation (in excess of 1mm is possible) with the additional benefit of low assembly forces.
Where engineers are restricted by physical component sizes, other solutions are available.
A tolerance ring comprising a series of waveforms can be used to create an interference fit, securely holding the motor in position.
The waveforms and other important criteria, such as ring thickness and hardness, are designed by engineers at Rencol working closely with the component manufacturer.
Where physical space is restricted further, a miniature ring can be used to secure the motor.
Here the tolerance ring is located on the bushing/bearing housing.
Upon assembly, the tolerance ring is aligned within the rear of the housing, generating an interference fit, locking the motor in position.
Tolerance rings solve the problems of devising an effective mounting method for the electric motor in almost every throttle-body application.
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Contact Saint-Gobain Performance Plastics
Tel +32 34 50 76 01
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