Vehicle AC Evaporator Control Using Dew-Point Temperature

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Solution Overview

Problem

Automatic temperature control (ATC) systems in vehicles maintain evaporator temperatures at low values to ensure cabin comfort, leading to continuous compressor operation, increased energy consumption, and decreased fuel efficiency.

Innovation Solution

A system that controls the compressor by operating the evaporator within a targeted temperature range based on dewpoint and psychrometric parameters, turning it off when the target temperature is reached, and includes a fog control module to manage windshield defogging.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the evaporator temperature is maintained at a low value to ensure cabin comfort, then the compressor operates continuously, but energy consumption increases and fuel efficiency decreases

Engineering Contradiction:

Improveevaporator temperatureVSAvoidenergy consumption

Core Design Contradiction:

TemperatureVSUse of energy by moving object

Solution Approach 1:

The evaporator temperature setpoint is made dynamic rather than fixed. The system continuously adjusts the target evaporator temperature based on real-time dewpoint measurements and psychrometric calculations, allowing the temperature to vary within an optimal range (e.g., 35-45°F) rather than maintaining a constant low value, thereby reducing unnecessary compressor operation

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the operating parameters by using dewpoint temperature and psychrometric charts to determine optimal evaporator temperature setpoints. Instead of maintaining a fixed low temperature, the system calculates and adjusts the temperature parameter based on ambient conditions, cabin humidity, and dewpoint differentials to achieve energy-efficient operation while maintaining comfort

Inventive Principle:

Principle #35Parameter changes

2Temperature

If the evaporator temperature is maintained at a low value to ensure cabin comfort, then the compressor operates continuously, but fuel efficiency decreases

Engineering Contradiction:

Improveevaporator temperatureVSAvoidfuel efficiency

Core Design Contradiction:

TemperatureVSLoss of energy

Solution Approach 1:

The system implements feedback control by continuously measuring the actual evaporator temperature, comparing it to the dynamically calculated target temperature based on dewpoint and psychrometric parameters, and adjusting the compressor operation accordingly. This feedback mechanism prevents unnecessary continuous operation by only running the compressor when needed to maintain the optimal temperature range

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Inventive Principle:

Principle #15Dynamics

3Use of energy by moving object

If the compressor is turned off when the sum of offsets is zero, then energy consumption is reduced, but cabin temperature control may be compromised

Engineering Contradiction:

Improveenergy consumptionVSAvoidcabin temperature control

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The system implements feedback control by continuously monitoring cabin temperature, evaporator temperature, dewpoint, and psychrometric parameters. The compressor is turned off only when the calculated offsets indicate that the target temperature has been achieved and conditions warrant shutdown, ensuring that temperature control reliability is maintained while reducing energy consumption

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary calculations of dewpoint temperature and psychrometric offsets before deciding to turn off the compressor. By anticipating when the target temperature will be reached based on current conditions and offset sums, the system can safely shut down the compressor while maintaining cabin comfort, rather than relying solely on reactive temperature control

Inventive Principle:

Principle #10Preliminary action

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 maintains cabin comfort while optimizing evaporator temperature to reduce energy consumption and enhance fuel efficiency without sacrificing occupant comfort.

Implementation Method 1

The evaporator temperature control module generates a target evaporator temperature based on a predetermined evaporator temperature and the offsets. The AC control module controls at least one of a compressor, a blower, and a mode of airflow inside the vehicle based on the target evaporator temperature.

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

The AC control module turns the compressor on until the evaporator reaches the target evaporator temperature.

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 3

The AC control module controls at least one of a compressor, a blower, and a mode of airflow inside the vehicle based on the target evaporator temperature.

Methodology Applied

Scientific EffectForced convection: Forced Convection

Data Source

PatentUS8463492B2Efficient AC operation using dew-point temperature

Publication Date: 2013.06.11 MERCEDES BENZ GROUP AG

AI summary

A system for controlling air-conditioning in a vehicle includes an input, a sensor, a first offset module, and an evaporator temperature control module. The input receives an input temperature. The first sensor measures a first dewpoint temperature of air adjacent to a windshield of the vehicle. The first offset module generates a second dewpoint temperature based on the input temperature and generates a first offset based on the first and second dewpoint temperatures. The evaporator temperature control module generates a target evaporator temperature based on the first offset.