Hydrostatic Transmission Displacement Control for Engine Overspeed
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Solution Overview
Problem
Existing hydrostatic transmissions in machines like mining vehicles and construction equipment face engine failure risks due to rapid changes in hydraulic unit displacements during acceleration and deceleration, exceeding engine limits and causing overspeed.
Innovation Solution
A control unit with adaptive displacement control, utilizing a PI-function, adjusts hydraulic unit displacements based on sensor inputs, machine parameters, and operator commands to maintain engine speed within limits, incorporating breaking and traction power sensors to prevent engine overload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rapid changes in hydraulic unit displacements are made during acceleration and deceleration, then productivity and response time are improved, but engine reliability deteriorates due to exceeding engine limits and causing overspeed
Solution Approach 1:
The control unit continuously monitors engine speed through a speed sensor and uses this feedback to dynamically adjust hydraulic unit displacements. The control unit compares actual engine speed against predetermined limits and modifies pump/motor displacement commands in real-time to prevent overspeed conditions, thereby maintaining both productivity and engine reliability
Solution Approach 2:
The system dynamically adjusts the displacement of hydraulic pump and motor based on operating conditions. During acceleration, displacement changes are optimized for rapid speed-up, while during deceleration and high-speed operations, displacement is reduced to limit engine speed and prevent overspeed, creating a dynamic adaptation that balances performance and reliability
2Speed
If rapid changes in hydraulic unit displacements are made during acceleration and deceleration, then deceleration performance is improved, but engine wear increases due to exceeding engine limits
Solution Approach 1:
The control unit uses continuous feedback from the engine speed sensor to monitor engine operating conditions. When deceleration commands would cause engine speed to exceed predetermined limits, the control unit automatically reduces the displacement change rate or reverses displacement adjustments, preventing harmful overspeed conditions that would increase engine wear while still achieving effective deceleration
Solution Approach 2:
The control unit applies beforehand cushioning by predicting potential overspeed conditions during deceleration and preemptively adjusting hydraulic unit displacements to limit engine speed before harmful conditions occur. This prevents engine overload and excessive wear by cushioning against extreme operating conditions
Data Source
Figure 1~2
Figure 3
AI summary
The present invention concerns a hydrostatic transmission (1) and a method to control the characteristics of a hydrostatic transmission (1) having an engine (2), a first and second hydraulic unit (4, 5) and a drive unit (3) which are connected to the control unit (10) having a memory unit, wherein each hydraulic unit comprises a sensor unit (8a, 8b), wherein the first and the second hydraulic units (4,5) are connected through a first fluid and second fluid connection (6,7) having a fluid connection sensor unit (9a, 9b) each. The objective of this invention is to regulate the engine negative torque and reduce the risk of engine overspeed. This objective is solved by a method of controlling a hydrostatic transmission (1) wherein the speed sensors and pressure sensor units (8a, 8b, 9a, 9b) are connected to the control unit (10), which controls a displacement of the hydraulic units (4,5) based on a set point, a modulation command, hydraulic unit commands, operator commands, information provided by the memory unit and/or sensor outputs.