Hydrostatic Variator Torque Control via Pressure Sweep Calibration
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Solution Overview
Problem
Accurate torque control in continuously variable transmissions is challenging due to variability in hydrostatic variator components, such as valves and hydraulic pump and motor components, which traditional open-loop and closed-loop control methods cannot adequately address.
Innovation Solution
A method involving a controller that commands hydraulic pressure sweeps to a hydraulic actuator while recording corresponding motor speed ratios and output torques, constructing a map relating motor torque, motor speed ratio, and hydraulic pressure to achieve accurate torque control by scaling the recorded data, allowing for feed-forward control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional open-loop or closed-loop control methods are used, then the control system is simple to implement, but torque control accuracy is insufficient due to variability in hydrostatic variator components
Solution Approach 1:
The patent applies preliminary action by performing a calibration procedure before normal operation to characterize the hydrostatic variator. The calibration process involves sweeping the variator through its full operating range and recording actual motor speed ratios and output torques, which are then stored in lookup tables. This pre-characterization enables accurate torque control during subsequent operation without requiring complex real-time control algorithms.
Solution Approach 2:
The patent introduces intermediary elements (lookup tables containing pre-measured motor speed ratio and torque data) that mediate between the controller and the hydrostatic variator. Instead of directly controlling torque through complex calculations, the controller uses these intermediary data tables to translate desired torque commands into appropriate actuator pressure commands, simplifying the control system while improving accuracy.
2Adaptability or versatility
If hydrostatic variator components are used, then the transmission provides variable displacement capability, but component variability precludes accurate torque control
Solution Approach 1:
The patent applies parameter changes by systematically varying the actuator pressure across the full operating range during calibration and recording the corresponding motor speed ratios and torques. This creates a comprehensive data set that captures the actual behavior of the variable displacement components. During operation, the controller selects parameters from this calibrated data based on the desired torque and operating conditions, compensating for component variability.
3Measurement precision
If calibration data is collected across the full operating range, then comprehensive torque control is achieved, but calibration time and complexity increase
Solution Approach 1:
The patent applies segmentation by dividing the calibration process into distinct segments: collecting motor speed ratio data during a no-load sweep, collecting torque data during a locked-output sweep, and then combining these segmented data sets to populate the lookup tables. This segmentation allows efficient data collection without requiring complex simultaneous measurements, reducing calibration time while maintaining comprehensive coverage of the operating range.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables precise and efficient torque control in continuously variable transmissions by characterizing the relationship between hydraulic pressure, motor speed, and torque, improving the accuracy of torque calibration and control.
Implementation Method 1
a first hydraulic pressure sweep to the hydraulic actuator is commanded
Implementation Method 2
a transmission having a variable displacement variator with a hydraulic actuator for varying displacement, and having an output and an internal circuit pressure
Data Source
AI summary
In an embodiment, torque control operation is provided in a transmission having a variable displacement variator with a hydraulic actuator. The transmission is engaged in a neutral state such that the variator output experiences substantially zero torque, and a first hydraulic pressure sweep to the hydraulic actuator is commanded while a corresponding sweep of motor speed ratio of the variator is recorded. The transmission is engaged into a locked mode providing a fixed output speed and a second hydraulic pressure sweep to the hydraulic actuator is commanded, and a corresponding sweep of variator output torque is recorded during this sweep. A torque/pressure map is then constructed relating motor torque, motor speed ratio, and actuator pressure by scaling the sweep of motor speed ratios and the sweep of variator output torque. The resultant map is usable to provide feed forward torque control of the transmission.