Vehicle AC Evaporator Setpoint Control for Compressor Cycling

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Solution Overview

Problem

Automatic temperature control (ATC) systems in vehicles maintain evaporator temperatures at low values, leading to increased energy consumption and decreased fuel efficiency by continuously running the compressor, even when it is not necessary to maintain cabin comfort.

Innovation Solution

A system that controls the compressor by operating the evaporator within a targeted temperature range, using sensors to measure psychrometric parameters and generate offsets to determine a target evaporator temperature, turning the compressor off when the sum of offsets is zero, and incorporating a fog control module for defogging based on windshield dewpoint and glass temperature differences.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the evaporator temperature is maintained at a low value (e.g., 35 F to 38 F), then the desired cabin temperature is maintained, but the compressor is turned on at all times, increasing energy consumption and decreasing fuel efficiency

Engineering Contradiction:

Improvecabin temperatureVSAvoidenergy consumption

Core Design Contradiction:

TemperatureVSUse of energy by moving object

Solution Approach 1:

The system dynamically adjusts the evaporator temperature setpoint based on real-time psychrometric conditions (humidity, temperature, dew point) rather than maintaining a fixed low temperature. This allows the evaporator temperature to vary within an optimal range, enabling compressor cycling while maintaining cabin comfort and reducing energy consumption.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the operating parameters of the evaporator from a fixed low temperature to a variable temperature range determined by psychrometric calculations. By using dew point temperature and humidity ratios as control parameters, the system optimizes the evaporator temperature setpoint to allow compressor off-cycles while preventing condensation and maintaining comfort.

Inventive Principle:

Principle #35Parameter changes

2Temperature

If the evaporator temperature is maintained at a low value, then the desired cabin temperature is maintained, but the compressor is turned on at all times, decreasing fuel efficiency

Engineering Contradiction:

Improvecabin temperatureVSAvoidfuel efficiency

Core Design Contradiction:

TemperatureVSLoss of energy

Solution Approach 1:

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system uses psychrometric analysis to convert the potential harm of higher evaporator temperatures (risk of condensation) into a benefit by calculating the exact temperature threshold where condensation occurs. This allows operating at higher, more efficient temperatures while still preventing moisture problems.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Use of energy by moving object

If the evaporator temperature is increased to reduce energy consumption, then fuel efficiency improves, but the risk of condensation and fogging increases

Engineering Contradiction:

Improveenergy consumptionVSAvoidcondensation and fogging

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The system continuously monitors psychrometric parameters (temperature, humidity, dew point) and uses this feedback to dynamically adjust the evaporator temperature setpoint. The control algorithm calculates the maximum safe evaporator temperature based on real-time conditions, ensuring condensation prevention while maximizing energy efficiency. The fog control module provides additional feedback to prevent windshield fogging.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system takes preliminary anti-action by calculating the dew point temperature and using it to set the evaporator temperature threshold before condensation can occur. The fog control module similarly takes preliminary action by monitoring windshield temperature and psychrometric conditions to prevent fogging before it happens.

Inventive Principle:

Principle #9Preliminary anti-action

4Use of energy by moving object

If psychrometric sensors and offset modules are added to determine target evaporator temperature, then energy efficiency improves, but device complexity increases

Engineering Contradiction:

Improveenergy consumptionVSAvoidsystem complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The psychrometric sensors serve multiple functions: they measure cabin conditions for comfort control, calculate dew point for condensation prevention, determine the target evaporator temperature for efficiency optimization, and provide data for the fog control module. This multi-functionality justifies the added sensor complexity by eliminating the need for separate measurement systems.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The offset module uses the psychrometric data to automatically calculate the target evaporator temperature without requiring manual intervention or complex external control systems. The system serves itself by using its own sensor data to determine optimal operating parameters, reducing the need for additional complex control infrastructure.

Inventive Principle:

Principle #25Self-service

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 at the highest possible evaporator temperature, reducing energy consumption and increasing fuel efficiency by only running the compressor when necessary, while effectively managing defogging conditions.

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. The AC control module turns the compressor off when a sum of the offsets is zero.

Methodology Applied

Scientific EffectCompression: Compression

Implementation Method 3

The fog control module controls defogging of the windshield based on a difference between the psychrometric parameter and a glass temperature of the windshield measured by one of the sensors.

Methodology Applied

Scientific EffectCondensation: Condensation

Data Source

PatentUS8301335B2Efficient AC operation using dew-point temperature

Publication Date: 2012.10.30 CHRYSLER CORPORATION

AI summary

A system for controlling air-conditioning of a vehicle includes an input, an offset generator module, and an evaporator temperature control module. The input receives an input temperature. The offset generator module receives a psychrometric parameter of air inside the vehicle and generates offsets based on the input temperature and the psychrometric parameter. The evaporator temperature control module generates a target evaporator temperature based on the offsets.