Windshield Fog Margin Control for Sensorless Vehicle Defogging
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Solution Overview
Problem
Conventional HVAC systems in vehicles lack automatic control mechanisms to prevent fogging during precipitation or cabin soaking conditions, as they do not account for the presence of precipitation and cabin temperature, leading to inefficient fog removal.
Innovation Solution
A method that calculates the windshield glass temperature using existing sensors, incorporating vehicle speed and ambient temperature, and adjusts the HVAC system based on a calculated fog margin, which considers precipitation and cabin soaking conditions by substituting ambient temperature for glass temperature in these scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional sensors (glass temperature sensor and humidity sensor) are installed to detect fogging conditions, then the accuracy of fog detection is improved, but the device complexity and installation cost increase
Solution Approach 1:
The system uses existing vehicle sensors (cabin temperature sensor, ambient temperature sensor, vehicle speed sensor) to self-determine fogging conditions without requiring additional dedicated fog detection sensors. The control unit processes data from these existing sensors to calculate fog margin and trigger appropriate HVAC responses.
Solution Approach 2:
Existing sensors designed for other purposes (cabin temperature control, ambient temperature monitoring, speed sensing) are repurposed to also detect fogging conditions. This multi-functional use of sensors eliminates the need for additional specialized sensors while maintaining detection accuracy.
2Reliability
If the HVAC system is activated manually after fogging occurs, then the system responds to actual fogging conditions, but the response time is delayed and visibility is reduced
Solution Approach 1:
The system calculates fog margin using data from existing sensors and predicts impending fogging conditions before they occur. When the fog margin indicates high risk, the HVAC system is proactively activated to prevent fogging, rather than waiting for fog to form and then responding manually.
Solution Approach 2:
The control unit continuously monitors cabin temperature, ambient temperature, vehicle speed, and other parameters to calculate fog margin in real-time. This feedback loop allows the system to dynamically adjust HVAC operation based on current conditions, maintaining optimal visibility prevention.
3Extent of automation
If the lookup table method is used to estimate glass temperature, then the system operates automatically without additional sensors, but the accuracy decreases during precipitation or cabin soaking conditions
Solution Approach 1:
The system dynamically adjusts the glass temperature estimation method based on detected conditions. During precipitation or cabin soaking conditions, the system switches from using the lookup table estimation to using ambient temperature as the glass temperature value, adapting to conditions where the lookup table method becomes inaccurate.
Solution Approach 2:
The system changes the parameter used for glass temperature based on environmental conditions. When precipitation or soaking is detected, the parameter source changes from calculated estimation (lookup table based on ambient temperature and vehicle speed) to direct ambient temperature measurement, improving accuracy under these specific conditions.
Data Source
AI summary
A method for controlling a vehicle HVAC system to automatically defog a windshield glass and to prevent fogging or condensation of the windshield glass. In-cabin air temperature and relative humidity are measured and used to determine a dewpoint. Further, ambient or outside temperature is measured. If windshield wipers are being used or if the cabin air temperature is less than a predetermined temperature, the ambient air temperature value is used as a glass temperature, otherwise the glass temperature is determined from the ambient air temperature and vehicle speed. A fog margin, which is a measure of the likelihood of fog formation, is based upon the difference between dewpoint and the windshield glass temperature. The fog margin is used to control the HVAC system to anticipate and respond to potential fogging conditions.