Thermostat Failure Detection Using Dual Temperature Thresholds

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Solution Overview

Problem

Existing thermostat failure detection methods in internal combustion engine systems are prone to erroneous determination due to variations in vehicle conditions, particularly when a radiator shutter affects engine water temperature, leading to incorrect assessment of thermostat functionality.

Innovation Solution

A device and method that calculate normal-time minimum and failure-time maximum water temperatures based on engine operating conditions, using a control unit to determine thermostat failure by comparing actual water temperatures with these reference values, thereby preventing erroneous determinations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single reference determination temperature is used to detect thermostat failure, then the detection method is simple, but erroneous determination occurs depending on vehicle conditions

Engineering Contradiction:

Improvedetection method complexityVSAvoidthermostat failure detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The single reference temperature is segmented into two distinct reference temperatures: a first reference determination temperature for determining thermostat failure, and a second reference determination temperature for determining normal operation. This segmentation allows each reference to be optimized for its specific detection purpose, improving accuracy without significantly increasing system complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the temperature parameter from a single reference value to two different reference values. The first reference determination temperature is set lower than the second reference determination temperature, creating distinct thresholds for failure and normal operation detection. This parameter change enables accurate differentiation between actual thermostat failure and normal temperature variations under different vehicle conditions.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the reference determination temperature is lowered to detect thermostat failure, then sensitivity increases, but false positives increase due to radiator shutter effects

Engineering Contradiction:

Improvethermostat failure detection sensitivityVSAvoiddetection accuracy under varying conditions

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The invention introduces dynamic adjustment of reference temperatures based on vehicle operating conditions. The first and second reference determination temperatures are not fixed values but are adjusted according to factors such as radiator shutter position and engine load. This dynamic approach allows the system to maintain high sensitivity for failure detection while adapting to normal temperature variations caused by different operating conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system uses feedback from multiple temperature sensors and operating condition sensors to continuously adjust the reference determination temperatures. By monitoring actual engine water temperature, radiator shutter position, and other parameters, the system dynamically updates the reference values to distinguish between genuine thermostat failure and normal operational temperature fluctuations.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If two reference temperatures are used to improve detection accuracy, then detection precision improves, but device complexity increases

Engineering Contradiction:

Improvethermostat failure detection accuracyVSAvoiddetection system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The invention makes the existing temperature sensor and control unit multi-functional by enabling them to perform both single-reference and dual-reference determination modes. The same hardware infrastructure supports both the first and second reference determination temperatures, allowing improved detection accuracy without proportionally increasing device complexity. The control unit dynamically selects which reference temperature to use based on operating conditions.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS9534527B2Thermostat failure detection device and thermostat failure detection method

Publication Date: 2017.01.03 NISSAN MOTOR CO LTD

AI summary

A thermostat failure detection device sequentially calculates a normal-time minimum water temperature on an assumption that a thermostat is normal and an internal combustion engine is operated in a state where the engine water temperature is less likely to rise, sequentially calculates a failure-time maximum water temperature on an assumption that the thermostat is in a stuck-open failure state and the internal combustion engine is operated in a state where the engine water temperature is likely to rise, determines the failure of the thermostat if the engine water temperature is lower than the normal-time minimum water temperature, determines the normality of the thermostat if the engine water temperature is higher than the failure-time maximum water temperature, and determines neither the normality nor the failure if the engine water temperature is between the normal-time minimum water temperature and the failure-time maximum water temperature.