AQS汽车外空气质量传感器应用指南

Automotive Air Quality Sensors

Using MiCS Air Quality Sensors

This application note describes the appropriate integration of a MiCS Air Quality Sensor in a modern automobile. MiCS is the AQS brand of e2v technologies.

Important note : Reproduction and distribution of this document is restricted by e2v. The following specifications are subject to change to accommodate continuous improvement.

The AQS function

The Air Quality Sensor is based on two semiconductor gas sensors that detect pollution peaks in the traffic. It calculates an “Air Quality level” that is sent to the CPU of the HVAC. The HVAC can then open and close the recirculation flap so as to minimize the pollution in the cabin.

Location in vehicle

The AQS module must be exposed to a source of external air at all times. The location must be chosen so as to maximize air renewal; dead spaces must be avoided. The best location is in the air intake BEFORE (upstream) the filter. When the flap is closed, it can create a “pocket” of stagnant air; for that reason, the AQS module should not be too “deep in the duct”.

Preferably, the filtering membrane should be facing downward. If this is not possible, it should be vertical, but should never be facing upward, to prevent accumulation of dust

If the AQS module is attached with a bayonet to the air intake wall with its body “in the cabin”, the fixation should be sufficiently air tight so that no air from the cabin is pulled in front of the sensor head.

HVAC unit

Air inlet without AQS

Air

inlet with AQS Detailed

view

First possibility : bayonet attachment

Second possibility : attachment with plastic snap-in clip

Electrical integration

Connector reference : Tyco C-967642 coding “B”

Recommended control panel interface:

Note on warm-up time:

The Air Quality Sensor is turned on when the car is ignited. It takes approximately 20 seconds for the two sensitive elements to reach their chemical balance. During that time their resistances rise sharply. The output signal is exploitable only when the sensor resistances are sufficiently stable. The Air Quality Sensor output is therefore “valid” only after 20 seconds.

The Air Quality Sensor outputs 4 Air Quality levels indicating a “rate of change of the pollution”:

Î Fresh air : no pollution

Î Level 1 : small pollution

Î Level 2 : medium pollution

Î Level 3 : big pollution

A typical way to manage the air inlet door closing is:

If external temperature > 6°C:

¾Close door if Air Quality level is Î 1, 2 or 3

¾Open the door when the AQS level is Î “fresh air”

If external temperature <= 6°C:

¾Close door only if Air Quaity level is Î 3

¾Open the door when the AQS level is Î “fresh air” or after 2 minutes

(this will prevent too frequent closing and fogging of the windshield). Note that in cars equipped with an in-cabin Relative Humidity sensor, the Air Quality Sensor “recommendation” is typically overridden by the temperature and humidity conditions that can lead to flash windshield fogging. Similarly, when starting the car, under certain temperature conditions, the Air Quality Sensor signal will be ignored to favour a faster heating or cooling of the cabin.