Moving Coil Actuators test Diesel Injectors | Automation.com

Moving Coil Actuators test Diesel Injectors

Moving Coil Actuators test Diesel Injectors
February 7, 2008 - SMAC Moving Coil Actuators (MCA) are helping SPE, a manufacturer of diesel injectors to reduce emissions by using an actuator to determine the spring characteristics in their injectors. The standard SMAC characteristics of programmable force control coupled to a sub-micron resolution encoder feedback ensures that the measurement of spring rates and deflection are carried out with great accuracy and repeatability.

An essential characteristic in any diesel injector is achieving a constant spring rate in the valve head of the injector. This accuracy of this spring rate has a direct effect upon emissions which is crucial in today’s climate. This is achieved by applying a constant load upon the spring and measuring deflection. Once the deflection is determined a compensating shim is added to achieve the correct performance. The tolerances on the setting of the spring rates are becoming tighter due to better vehicle performance and emissions regulations.

The traditional method of achieving this was to use a servo motor, ballscrew, load cell and LVDT. Predictably this led to a significant stack up of errors and a single device capable of force and position feedback was essential to meet the latest specifications. SMAC have supplied LAL300 and LAL500 systems to a specialist machine builder, SPE.

The operation cycle is as follows:
  • Measure the free position of the uncompressed spring
  • Apply constant (programmable load between 65N & 230N dependant upon product
  • Measure linear position differential between compressed and uncompressed heights
  • Output differential to PLC

    The data reported is used to specify the correct sized shim which is then fitted to the spring and valve assembly to guarantee correct spring rate. The implementation of the SMAC actuators has led to an immediate and significant increase in quality and reduction in rejects.

    Testimonial:
    Chris Baker, Technical Director of SPE, described the results.
    “By using the LAL units and mounting a high accuracy load cell directly in line we have been able to reduce measuring variation from approximately 6 to below 2 microns. This means that the customer is setting valves for the injectors within a much tighter tolerance. This has a subsequent affect that the first time pass rate on final function test for the new generation of injectors has improved massively from typically below 75% to over 95%.”
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