Torque Control in Hydromechanical Transmissions
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Solution Overview
Problem
Hydromechanical transmissions in earth-moving machines face challenges in controlling torque due to the inability to accurately determine pump displacement under rapidly changing surface conditions, leading to undesirable accelerations and machine instability.
Innovation Solution
A control module is used to determine the desired torque and necessary pressure to adjust the displacement of a variable displacement pump, comprising a gear system, hydrostatic unit, actuator, and valve system, with sensors to monitor pressures and speeds, allowing for precise control of torque output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If speed control is implemented by controlling pump displacement using servo-feedback control, then speed control capability is improved, but system complexity increases and reliability decreases under rapidly changing surface conditions
Solution Approach 1:
The patent replaces the mechanical servo-feedback control system with an electronic control system that uses sensors to detect actual speed and a microprocessor to calculate required pump displacement. This substitution eliminates the hunting behavior and instability of mechanical feedback systems while maintaining speed control capability.
Solution Approach 2:
The patent implements electronic feedback by using speed sensors to continuously monitor actual machine speed and feed this information back to the control module. The control module then adjusts pump displacement based on the difference between desired and actual speed, providing stable and accurate speed control without the oscillations seen in mechanical feedback systems.
2Speed
If traditional speed control systems are used in earth-moving machines, then continuous speed control is provided, but torque control capability is lost leading to machine instability
Solution Approach 1:
The patent creates a control system that performs both speed control and torque control functions through the same electronic control module. By calculating pump displacement based on desired torque and measuring actual speed, the system achieves multi-functionality, providing both continuous speed control and torque control capability, thereby maintaining machine stability during earth-moving operations.
3Speed
If pump displacement is adjusted rapidly to respond to changing surface conditions, then speed responsiveness is improved, but machine stability deteriorates due to lugs and lurches
Solution Approach 1:
The patent implements dynamic control by continuously monitoring actual speed and torque conditions and adjusting pump displacement in real-time based on calculated requirements. The electronic control system dynamically adapts to changing surface conditions while maintaining smooth operation, avoiding the lugs and lurches that occur with rapid mechanical adjustments.
Solution Approach 2:
The control module calculates the required pump displacement in advance based on desired torque and current operating conditions, then applies this adjustment smoothly rather than reacting abruptly to speed deviations. This preliminary calculation approach prevents sudden mechanical shocks and maintains machine stability during transitions.
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 solution enables smooth speed transitions and stable torque control in earth-moving machines, even under varying conditions, by accurately adjusting the displacement of the variable displacement pump to maintain desired torque, improving machine performance and stability.
Implementation Method 1
determine an amount of pressure necessary to influence the displacement of a variable displacement pump to output the desired torque
Implementation Method 2
an actuator configured to influence displacement of the variable displacement pump
Data Source
AI summary
Apparatus, system, and method for controlling a desired torque output on a hydromechanical transmission. Controlling torque output of a hydromechanical transmission provides improved operator feel and control. A control module determines a desired torque output and determines a pressure necessary to influence the displacement of the variable displacement pump to output the desired torque output. A pressure-controlling valve applies that amount of pressure to an actuator, which moves in response thereto, to change the displacement of the variable displacement pump. When the motor speed changes, the control module adjusts the pressure applied to the actuator to provide the desired torque output.