Variable Valve Timing Control for Low Engine Speed Accuracy
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Solution Overview
Problem
Existing variable valve timing systems face challenges in accurately controlling phase shifts, especially at low engine speeds, where the rotational speed of the camshaft is low, leading to inaccurate phase detection and potential erroneous control.
Innovation Solution
A variable valve timing apparatus that includes an actuator, a change mechanism, and an operation unit, which controls the opening/closing timing of intake and exhaust valves by adjusting the power supply to the actuator based on engine speed, stopping control when the rotational speed is equal to or lower than a predetermined threshold to prevent inaccurate phase control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the electric motor is used to rotate the camshaft, then the phase can be varied, but the torque for rotating the camshaft is difficult to obtain and the rotational speed of the output shaft is reduced by a speed reducer mechanism, thereby restricting the degree of phase shift
Solution Approach 1:
The patent employs a dynamic control mechanism where the control member can move radially within the rotor to directly engage and disengage from the camshaft. This dynamic engagement allows the electric motor to directly rotate the camshaft when torque is available, while allowing free rotation when torque is insufficient, thereby resolving the torque limitation without restricting phase shift capability
Solution Approach 2:
The control mechanism is segmented into distinct functional components: the electric motor, the control member with radial movement capability, and the camshaft. This segmentation allows independent optimization of each component - the electric motor provides phase variation control, while the mechanical engagement system provides torque assistance when needed
2Ease of operation
If the phase is controlled at low engine speeds, then the opening/closing timing can be adjusted, but the rotational speed of the camshaft is low leading to inaccurate phase detection and potential erroneous control
Solution Approach 1:
The patent implements preliminary anti-action by detecting engine speed before initiating phase control and preventing control operations when the speed is below the threshold. This preemptive measure avoids the inaccurate phase detection and erroneous control that would occur at low rotational speeds, rather than attempting to correct errors after they occur
3Manufacturing precision
If the control member's radial distance is varied to change phase, then the degree of phase shift can be controlled, but at low rotational speeds the phase detection becomes inaccurate leading to deterioration in phase accuracy
Solution Approach 1:
The control system performs preliminary detection of engine rotational speed and prevents radial movement of the control member when speed is below threshold. This preemptive action prevents the deterioration in phase accuracy that would result from attempting precise phase control under unreliable detection conditions
Data Source
AI summary
An ECU executes a program including the steps of: detecting engine speed NE (S100); and stopping power supply to an electric motor of an intake VVT mechanism (S104), if engine speed NE is equal to or lower than a threshold value NE (0) (YES at S102).