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Redundant Sensors for ETB Position

Reason for redundancy in ETB position sensing​

Redundancy provides safety in the critical sensors controlling the engine's power.

FOME tolerates up to 5% deviation in the redundant sensors, to account for slight non-linearity and inaccuracy in the sensors, and to allow for fluctuations due to environmental changes and extremes.

Throttle position and accelerator pedal position sensors support redundancy.

Fully Redundant sensors​

Sensors will typically be of this type, providing redundant sensing across the entire sensing range.

Things like 0.5-4.5 volt primary sensing with delta, inverted, or half-value characteristics for the secondary sensor.

Partial Redundancy sensors​

Some Ford and Toyota applications are of this type, either TPS, APPS, or both.

These sensors are linear like the fully redundant sensors, but the secondary sensor doesn't cover the full sensing range. Instead, it reaches full-scale well before the primary sensor, providing only "partial" redundancy and a overall non-linear output over the full range.

FOME supports these sensors with the tpsSecondaryMaximum and ppsSecondaryMaximum tune configurations. When necessary, these values should be tuned to indicate the percent of the primary sensor's full-scale reading at which the secondary sensor has just reached it's maximum. There are a number of techniques to determine this value, both directly/precisely and indirectly.

A direct method would be like:

  1. calibrate the sensor's minimum and maximum, e.g. tps1PrimaryMin/tps1PrimaryMax and tps1SecondaryMin/tps1SecondaryMax
  2. manipulate the sensor until the secondary value just reaches its maximum value, and record the primary's percentage at this point as the sensor's secondary maximum, e.g. tpsSecondaryMaximum

Another method is to iterate upon a close value, looking for TPS error while manipulating the sensor, and adjusting the value until the error goes away. This can lead to imprecision in the calibration however, and may lead to redundancy faults when environmental conditions change too much from that of its calibration.

Valid values are in the range of 20-100%, with 100 effectively disabling the feature. The value 0 also disables the feature, and values less than 20% are in error.