CVT Variator Gross Slip Detection via Dynamic Thresholds
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Solution Overview
Problem
Conventional methods for diagnosing variator slip in continuously variable transmissions (CVTs) often result in false diagnostic actions due to the use of constant calibration thresholds during transmission ratio changes, leading to unnecessary setting of gross slip flags during transient delays.
Innovation Solution
A method to determine variator gross slip by calculating the difference between actual input and output speeds of the CVT, using calibrated variator speed ratios, and setting a gross slip flag only when the calculated slip exceeds a calibrated value for a predetermined duration, thereby avoiding false diagnostic actions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a constant calibration threshold is used for variator slip detection during CVT operation, then the diagnostic system is simple to implement, but false diagnostic actions occur during ratio changes due to transient delays
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant threshold to a dynamic threshold that adapts based on CVT operating conditions. The threshold is adjusted according to the current speed ratio and its rate of change, allowing the system to accommodate transient delays during ratio changes while maintaining sensitivity to actual gross slip conditions. This dynamic adaptation resolves the contradiction by making the diagnostic system both reliable during transients and simple to implement.
Solution Approach 2:
The patent changes the threshold parameter from a fixed constant value to a variable parameter that depends on operating conditions such as speed ratio and ratio change rate. By modifying the threshold parameter dynamically based on these conditions, the system avoids false diagnostics during ratio changes while maintaining detection capability for actual gross slip. This parameter change approach maintains relative simplicity while improving reliability.
2Ease of operation
If a constant calibration threshold is used during CVT ratio changes, then the control logic is simple, but unnecessary gross slip flags are set during transient delays
Solution Approach 1:
The control logic transitions from using a static threshold to a dynamic threshold that automatically adjusts during ratio changes. This dynamic approach prevents false gross slip flagging during transients while maintaining straightforward control implementation. The system simply compares actual slip against the dynamically adjusted threshold, preserving ease of operation while eliminating false diagnostics.
Solution Approach 2:
The patent introduces an intermediary mechanism (the dynamic threshold calculation based on speed ratio and ratio change rate) that mediates between the simple control logic and the need to avoid false diagnostics. This intermediary threshold adapts to transient conditions, allowing the control logic to remain simple while preventing unnecessary gross slip flags during ratio changes.
3Measurement precision
If gross slip detection is highly sensitive during ratio changes, then actual gross slip can be detected accurately, but false positives occur during normal ratio transitions
Solution Approach 1:
The patent changes the detection threshold parameter dynamically based on operating conditions. During ratio changes, the threshold is adjusted to account for expected transient slip, while during steady-state operation, the threshold remains sensitive to actual gross slip. This parameter adaptation maintains measurement precision for detecting real problems while reducing false positives during normal transitions.
Solution Approach 2:
The patent applies local quality by making the detection threshold condition-dependent rather than uniform. Different threshold values are applied in different operating contexts (during ratio changes versus steady-state operation). This localized adaptation of the threshold quality allows accurate detection of actual gross slip while tolerating normal transient behavior during ratio transitions.
Data Source
AI summary
A vehicle includes an engine, drive wheels, a continuously variable transmission (CVT), and a controller. The CVT includes an input member connected to the engine, an output member delivering output torque to the wheels, and a variator assembly connecting the input and output members. The controller determines, via a method, an input and output speed of the variator assembly, converts the output speed to an equivalent input speed using a calibrated variator speed ratio, and calculates a gross slip of the variator assembly using the input and equivalent input speeds. A gross slip flag is set only when the gross slip exceeds a calibrated slip value for a predetermined duration. A CVT assembly includes the controller, input and output members, and variator assembly. The variator assembly may include drive and driven pulleys, a drive mechanism connecting the pulleys, and an actuator applying a clamping force to one of the pulleys.