Hydromechanical Transmission Feedforward Control for Stable Mode Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Prior hydromechanical variable transmission (HVT) control strategies struggle to efficiently switch between torque and speed control modes, leading to reduced transmission efficiency, instability, and control inaccuracies due to oversimplified kinematics and complex non-linear characteristics.
Innovation Solution
A feedforward control architecture using a non-linear, multi-coefficient model is implemented for the hydrostatic unit, allowing for efficient and accurate control by calibrating coefficients through an automatic procedure, and strategically varying inputs between torque and speed control modes based on vehicle conditions, with junction filters ensuring continuity during mode switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a mechanical feedback control loop is used to control pump displacement, then the control is simple and straightforward, but the differential pressure is not directly controllable
Solution Approach 1:
The patent introduces a hydraulic valve as an intermediary component between the controller and the pump control piston. The valve mediates the control by receiving controller signals and adjusting hydraulic pressure to the piston, enabling both simple control operation and precise differential pressure control through the valve's pressure regulation capability
2Adaptability or versatility
If direct pressure control of hydraulic fluid on control piston chambers is used, then flexibility is improved, but the system becomes complex with non-linear characteristics that are difficult to identify and use accurately
Solution Approach 1:
The patent implements a feedback mechanism where the controller receives information about the actual system state (pump displacement, differential pressure) and adjusts the valve control signals accordingly. This feedback loop simplifies the control by allowing the system to automatically compensate for non-linear characteristics without requiring complex identification models
Solution Approach 2:
The hydraulic valve serves as an intermediary that linearizes the control relationship. By controlling valve opening rather than directly controlling piston chamber pressure, the system transforms a non-linear pressure-displacement relationship into a more linear valve-opening-to-pressure relationship that is easier to control accurately
3Adaptability or versatility
If hydrostatic unit is controlled in torque control mode or speed control mode, then specific control objectives are met, but switching between modes causes control lag, instability, and oscillation
Solution Approach 1:
The patent implements dynamic mode switching with continuous control transition. The controller dynamically adjusts control parameters based on operating conditions and uses interpolation or blending between torque and speed control modes during transitions, preventing abrupt changes that cause oscillation and instability while maintaining adaptability to different operating requirements
4Ease of operation
If oversimplified transmission kinematics are used in control strategy, then control implementation is easier, but control accuracy is reduced
Solution Approach 1:
The patent changes the parameter representation from simplified kinematic relationships to actual measured operating parameters (actual pump displacement, actual differential pressure, motor speed, torque). By using real measured parameters instead of simplified calculated ones, the control maintains high accuracy while the controller implementation remains straightforward through direct sensor feedback
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
This approach enhances transmission performance by reducing control latency and conserving processing resources, enabling seamless switching between modes and improving accuracy and efficiency.
Implementation Method 1
a hydrostatic pump and motor. In some designs the hydrostatic pump is a variable displacement pump. In this design, a displacement of the pump depends on an angle of a swash plate
Implementation Method 2
the controller may adjust a position of a double-action pump control piston to control the angle of the swash plate, via a pressure of the hydraulic fluid
Implementation Method 3
a hydrostatic pump and motor
Data Source
AI summary
Methods and systems for controlling a hydromechanical transmission are proposed. In one example, a control method for a hydrostatic unit of a hydromechanical variable transmission (HVT) is presented, comprising controlling the hydrostatic unit via a feedforward control architecture including a non-linear, multi-coefficient model, wherein the hydrostatic unit comprises a hydrostatic pump and a hydrostatic motor and a desired differential pressure of the hydrostatic unit or a desired hydraulic pump displacement may be used as inputs for the model, where the model's output is a pressure difference for a pump control piston coupled to a swash plate of the hydrostatic unit. Use of the non-linear model permits the hydrostatic unit to be controlled based on load, speed, and/or torque, thereby increasing the adaptability of the control system.