CVT Control Using State Space Gain Scheduling
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Solution Overview
Problem
CVT transmissions in industrial machines face challenges in accurate control due to nonlinearity, leading to potential mechanical damage from over-speed and under-speed issues, which conventional error-based gain scheduling PID controllers struggle to address effectively.
Innovation Solution
Implementing a state space based gain scheduling system that uses 2 or 3 dimensional gain lookup tables to control the hydraulic variator actuator, scheduling individual P, I, or D controller gains based on the system's state space trajectory, thereby maintaining engine speed within permissible ranges and preventing overshoot and undershoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional error-based gain scheduling PID control is used, then the control system can handle some nonlinearity, but it cannot meet all performance requirements due to the complexity of non-linear system dynamics
Solution Approach 1:
The patent applies dynamic gain scheduling where controller gains are continuously adjusted based on real-time system state variables (engine speed, variator actuator position, and their derivatives). This dynamic adaptation allows the control system to handle varying non-linear dynamics throughout the operating range, improving control accuracy without requiring a fundamentally complex controller structure.
Solution Approach 2:
The patent changes the control parameters (PID gains) based on the system's operating state. By scheduling gains as functions of engine speed and actuator position, the controller adapts to different operating conditions, effectively managing the non-linear behavior of the CVT system while maintaining a relatively simple control architecture.
2Adaptability or versatility
If the CVT system allows engine speed to vary freely, then the system operates flexibly, but mechanical damage can occur from over-speed or under-speed conditions
Solution Approach 1:
The patent implements closed-loop feedback control where the controller continuously monitors engine speed and actuator position, compares them against desired values, and adjusts the actuator command accordingly. This feedback mechanism ensures engine speed remains within safe operating limits while allowing flexible operation across a wide speed range, preventing both over-speed and under-speed damage.
Solution Approach 2:
The control system takes preliminary action by predicting future engine speed trends based on current state and rate of change. The controller proactively adjusts the variator actuator position to prevent engine speed from reaching dangerous extremes, rather than merely reacting after the problem occurs. This predictive control prevents mechanical damage before it can occur.
3Speed
If the variator actuator responds rapidly to control commands, then the system response is fast, but overshoot and undershoot control becomes difficult due to nonlinearity
Solution Approach 1:
The patent employs dynamic gain scheduling that adjusts controller aggressiveness based on the current operating point. When the system is far from the target, higher gains enable rapid response. As the system approaches the target or operates in sensitive regions, gains are reduced to prevent overshoot and undershoot. This dynamic adjustment maintains both fast response and stability throughout the operating range.
Data Source
AI summary
An engine powered wheeled machine having improved engine over speed and under speed protection includes a parallel path transmission having a gear train with first and second transmission inputs and a transmission output, and including a hydraulic variator having a variator output driving the first transmission input, the hydraulic variator having a variator pump and a variator motor, the displacement of the variator pump being controlled by a variator actuator. The machine further includes an engine having an engine output driving the second transmission input and driving the variator pump and a controller for receiving one or more values indicative of one or more ranges of permissible engine speed, a value indicative of an actual engine speed, and a value indicative of the position of the variator actuator, with the controller being configured to control the position of the variator actuator based on state space gain mapping to maintain the engine speed within the one or more ranges of permissible engine speed.