Windshield Defogging Control Using Dew Point Comparison
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Solution Overview
Problem
Conventional defogging devices in vehicles consume excessive air conditioning energy by adjusting the windshield glass temperature to be higher than the dew point temperature, even when fogging or dew condensation is not imminent, due to measurement errors and spatial differences in temperature and humidity, leading to unnecessary energy use in hybrid and electric vehicles.
Innovation Solution
A defogging device that uses a single temperature sensor for both surface temperature and dew point temperature measurements, with an infrared sensor to detect the surface temperature and humidity sensors to measure ambient conditions, allowing for precise control by comparing the surface temperature with the dew point temperature, thereby minimizing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface temperature is adjusted to be higher than dew point temperature by a margin (e.g., 3°C or 5°C), then fogging prevention reliability is improved, but air conditioning energy consumption increases
Solution Approach 1:
The patent changes the control parameter from a fixed temperature margin (3°C or 5°C) to a dynamic margin based on measured measurement errors. The control unit calculates the actual measurement error by comparing the infrared sensor's surface temperature reading with the contact sensor's reading, then adjusts the defogging activation threshold dynamically. This allows the system to maintain reliable fogging prevention while minimizing unnecessary energy consumption by activating defogging only when truly needed.
Solution Approach 2:
The patent implements a feedback mechanism where the measurement error is continuously measured and used to adjust the defogging control strategy. The system feeds back the difference between infrared and contact temperature measurements to the control unit, which then adjusts the activation threshold accordingly. This closed-loop feedback enables the system to adapt to actual measurement conditions and avoid both over-defogging (wasting energy) and under-defogging (allowing fogging).
2Measurement precision
If separate temperature sensors are used for surface temperature and ambient temperature measurement, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges the function of measuring both surface temperature and ambient temperature into a single integrated system. The control unit receives temperature data from both infrared sensors (for surface temperature) and contact sensors (for ambient temperature) and processes them together to determine defogging needs. This integration reduces device complexity while maintaining measurement precision through the use of multiple sensor types working in coordination.
Solution Approach 2:
The control unit serves multiple functions: it processes temperature readings from different sensor types, calculates measurement errors, determines actual surface temperature, compares with dew point temperature, and controls defogging activation. This multi-functional approach consolidates what could be separate devices into a single intelligent control system, reducing overall system complexity while maintaining high measurement and control accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces air conditioning energy consumption by setting the conditions for defogging more precisely, avoiding unnecessary energy use and improving fuel efficiency and cruising distance in electric vehicles.
Implementation Method 1
an infrared sensor configured to measure an amount of infrared light emitted from an object
Data Source
AI summary
A defogging device includes a temperature sensor, an infrared sensor, a surface temperature measuring unit, a humidity sensor, a dew point temperature measuring unit, and a fogging/dew condensation determining unit. When the defogging device is instructed to perform measurement, the temperature sensor measures temperature. Additionally, measurement by the infrared sensor is performed, and based on an output of the infrared sensor and an output of the temperature sensor, the surface temperature measuring unit measures glass surface temperature. Measurement by the humidity sensor is performed, and based on an output of the humidity sensor and the output of the temperature sensor, the dew point temperature measuring unit measures dew point temperature. Lastly, the fogging/dew condensation determining unit compares the glass surface temperature with the dew point temperature to determine whether fogging or dew condensation occurs or not.