Feedforward Compensation for Hydrostatic Power Unit Swash Plate Control
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Solution Overview
Problem
Closed loop control in hydrostatic power units of continuously variable transmissions suffers from oscillations and slow response due to disturbances caused by changes in hydrostatic power unit pressure and power flow direction during range shifts.
Innovation Solution
A feedforward compensation term is calculated based on hydrostatic power unit pressure, swash plate angle, and pump speed, which is added to the PID control terms to reduce reliance on closed loop control, improving system response and reducing oscillations by compensating for disturbances and avoiding integrator windup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If closed loop PID control is used for swash plate angle control, then the control system is simple to implement, but the system response is slow and oscillations occur during range shifts
Solution Approach 1:
The feedforward compensation term is calculated in advance based on the desired transmission reciprocal ratio and current operating conditions (pressure, pump speed). This preliminary calculation allows the control system to anticipate required swash plate angle adjustments before actual disturbances occur, enabling faster response without waiting for closed-loop error detection.
Solution Approach 2:
The control system uses pressure feedback from the hydrostatic power unit to dynamically adjust the feedforward compensation term. This feedback mechanism allows the system to adapt to changing operating conditions and maintain optimal compensation, reducing oscillations while preserving fast response.
2Device complexity
If closed loop PID control is used for swash plate angle control, then the control structure is simple, but oscillations occur due to pressure changes during range shifts
Solution Approach 1:
The feedforward compensation term anticipates pressure changes during range shifts by calculating the required swash plate angle adjustment in advance based on the desired transmission reciprocal ratio. This preliminary action prevents oscillations by proactively compensating for pressure disturbances before they affect system stability.
Solution Approach 2:
The feedforward compensation term acts as an intermediary between the desired transmission reciprocal ratio and the actual swash plate angle control. It mediates the effect of pressure changes during range shifts by providing a compensating signal that counteracts disturbances, thereby maintaining system stability without requiring complex control structures.
3Speed
If feedforward compensation based on pressure feedback is added to PID control, then system response improves and oscillations reduce, but control system complexity increases
Solution Approach 1:
The feedforward compensation term is calculated in advance using the desired transmission reciprocal ratio and current operating conditions, allowing the system to respond faster without waiting for closed-loop error detection. This preliminary calculation improves response speed while maintaining relatively simple control logic.
Solution Approach 2:
The system uses pressure feedback to dynamically adjust the feedforward compensation term, ensuring optimal compensation under varying operating conditions. This feedback mechanism improves response speed and reduces oscillations while adding only moderate complexity through a single pressure sensor input.
Data Source
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AI summary
A swash plate angle for a hydrostatic power unit of a continuously variable hydromechanical transmission is determined using a feedforward compensation term, to reduce reliance on closed loop control. The feedforward term is based on knowledge of the hydrostatic power unit determined as a function of knowledge of certain parameters, including, but not limited to, hydrostatic power unit pressure, swash plate angle, desired hydrostatic power unit ratio, and pump speed.