Vehicle Fan Control Circuit Diagnostic System
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Solution Overview
Problem
Diagnostic systems in vehicles are unable to reliably determine when a fan control circuit is electrically shorted to electrical ground or high voltage, or when a voltage sense line has impaired operation, such as being broken or non-conductive.
Innovation Solution
A diagnostic system that includes a microcontroller, a fan control circuit, and a sense line, which generates and receives PWM signals to detect duty cycles and frequencies indicative of the fan's operation, setting diagnostic flags based on predefined ranges to identify errors in the fan control circuit and sense line operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional diagnostic systems are used to monitor fan operation, then the system structure remains simple, but the system cannot reliably detect electrical shorts or sense line impairments
Solution Approach 1:
The patent implements feedback by having the fan control circuit send back fan command sense signals to the microcontroller, allowing the microcontroller to verify what commands are actually being received and executed, enabling reliable detection of electrical faults through comparison of commanded vs. actual signals
Solution Approach 2:
The patent introduces intermediary diagnostic components including sense lines that carry feedback signals, tachometer circuits that measure actual fan speed, and diagnostic flag mechanisms that mediate between raw sensor data and fault determination, enabling reliable fault detection without overwhelming system complexity
2Reliability
If no diagnostic feedback mechanism is implemented, then the system complexity remains low, but the system cannot detect when the fan control circuit is electrically shorted or when sense lines are impaired
Solution Approach 1:
The fan control circuit outputs fan command sense signals back to the microcontroller through sense lines, creating a feedback loop that allows continuous monitoring of the control signals and detection of electrical shorts or sense line impairments
Solution Approach 2:
The patent replaces complex mechanical diagnostic testing with electronic signal monitoring and comparison, using PWM duty cycle analysis and tachometer frequency detection to electronically identify faults without mechanical intervention
3Measurement precision
If the microcontroller monitors fan command signals and tachometer feedback, then accurate fault detection is achieved, but the processing complexity and computational load increase
Solution Approach 1:
The patent monitors changes in PWM duty cycle parameters and tachometer frequency parameters to detect faults, using parameter comparison against expected ranges to identify electrical shorts or sense line impairments with high measurement precision
Solution Approach 2:
The patent implements monitoring at multiple levels including fan command signals, buffer fan command signals, and tachometer feedback, using excessive monitoring points to ensure accurate fault detection while managing processing complexity through systematic analysis
Data Source
AI summary
A diagnostic system includes a fan control circuit coupled to an electric fan and a microcontroller, and a sense line coupled to the fan control circuit and the microcontroller. The fan control circuit outputs a fan command sense signal at a duty cycle through the sense line to the microcontroller. A tachometer generates a tachometer signal at a frequency indicative of the rotational speed of the electric fan. A fan tachometer circuit receives the tachometer signal and outputs the tachometer sense signal at a frequency to the microcontroller in response to the tachometer signal. The microcontroller sets a second diagnostic flag to an error value indicating that the sense line has impaired operation if the frequency of the tachometer sense signal is within a desired frequency range, and a first diagnostic flag is equal to a first error value.