Variable Valve Timing Control Device Sensor Failure Handling
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Solution Overview
Problem
In internal combustion engines with variable valve timing mechanisms, sensor failures can lead to excessive advancement or retardation of the rotational phase, causing collisions or engine stalls due to the inertia of the mechanism, which may result in interference between engine valves and pistons or inadequate intake air.
Innovation Solution
A control device and method that continue to detect the rotational phase of a cam shaft with respect to a crank shaft by calculating and selecting the larger rotation amount from multiple sensor inputs, ensuring continued control of the variable valve timing mechanism even with sensor failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensor detection is used to monitor rotational phase, then measurement precision is improved, but reliability deteriorates when sensor failure occurs
Solution Approach 1:
The rotational phase detection function is segmented into two independent calculation paths: one using crank angle sensor signals and another using cam angle sensor signals. This segmentation ensures that if one sensor fails, the other can still provide detection capability, thus improving reliability while maintaining measurement precision through redundant measurement channels.
Solution Approach 2:
The system prepares for sensor failure by establishing a backup detection mechanism in advance. When sensor failure is detected, the system automatically switches to using signals from the remaining functional sensors to calculate rotational phase, cushioning against the harmful effect of sensor failure and ensuring continuous reliable operation.
2Adaptability or versatility
If variable valve timing mechanism is used to adjust valve timing, then adaptability is improved, but harmful factors increase due to inertia causing excessive phase advancement or retardation
Solution Approach 1:
The system continuously monitors the rotational phase of the cam shaft relative to the crank shaft using dual sensor inputs and provides feedback to the control unit. This feedback mechanism enables real-time detection of phase deviations caused by inertia, allowing the controller to adjust motor commands and prevent excessive phase advancement or retardation, thus eliminating harmful factors while maintaining adaptability.
Solution Approach 2:
The patent replaces purely mechanical phase detection with an electronic control system that uses motor rotation angle sensors and control units to monitor and adjust the variable valve timing mechanism. This substitution enables precise electronic feedback control to counteract inertial effects, preventing excessive phase changes while maintaining the mechanical adaptability of the valve timing system.
3Reliability
If dual sensor inputs are processed to continue detection, then reliability is improved, but device complexity increases
Solution Approach 1:
The control unit is designed with multi-functionality to handle both normal dual-sensor operation and failure mode operation. It can universally process signals from either crank angle sensor or cam angle sensor depending on which are functional, eliminating the need for separate dedicated processing circuits for each sensor configuration and reducing overall system complexity while maintaining reliability.
Data Source
AI summary
The present invention relates to a control device and a control method for a variable valve timing mechanism that changes a valve timing by adjusting a rotational speed of a motor. The control device detects a phase angle RA1 based on an output of a crank angle sensor and an output of a cam angle sensor and calculates a change amount ΔRA of a rotational phase based on a difference between a rotation amount of a sprocket and a rotation amount of the motor. The control device stops calculating change amount ΔRA when a failure occurs in a motor rotation angle sensor. When a failure occurs in one of the crank angle sensor or the cam angle sensor, the control device stops calculating phase angle RA1 and calculates change amount ΔRA using a normal one of the sensors and the motor rotation angle sensor.