Hydrostatic Transmission Traction Control via Leakage Flow
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Solution Overview
Problem
Conventional work vehicles with hydrostatic transmissions face challenges in controlling traction force efficiently and accurately, particularly at medium to large operation ranges, leading to low operability and decreased fuel efficiency due to unnecessary engine speed increases and reduced hydraulic motor efficiency from displacement limitations.
Innovation Solution
A work vehicle system that includes a hydrostatic transmission with a controller using leakage flow rate data to determine target differential pressure and flow rate of the traveling pump, allowing for precise control of traction force by correlating leakage flow rate with hydraulic circuit pressure, and adjusting engine speed and motor displacement to achieve desired traction levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the engine speed is increased to improve traction force, then the traction force increases, but the fuel efficiency decreases due to unnecessary engine speed increases at medium to large operation ranges
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the pump displacement control based on the relationship between engine speed and differential pressure. The controller modifies the pump displacement to maintain optimal differential pressure across different engine speeds, thereby achieving efficient traction force control without unnecessary engine speed increases, resolving the contradiction between traction force and fuel efficiency
Solution Approach 2:
The patent implements feedback control by using the differential pressure sensor to monitor the actual differential pressure in the hydraulic circuit and comparing it with the target differential pressure. The controller adjusts the pump displacement based on this feedback to maintain optimal operating conditions, ensuring fuel efficiency while providing adequate traction force
2Force
If the displacement of the traveling motor is limited to control maximum traction force, then the traction force is controlled, but the efficiency of the hydraulic motor decreases
Solution Approach 1:
The patent changes the control parameter from limiting motor displacement to controlling pump displacement. By adjusting the pump displacement to maintain optimal differential pressure, the system achieves traction force control while allowing the motor to operate at its most efficient displacement, thereby avoiding the efficiency loss associated with motor displacement limitation
3Speed
If the PQ characteristics are changed according to engine speed by adjusting pump pilot circuit pressure, then the transmission ratio is controlled, but the operability decreases due to inability to accurately control traction force at medium to large operation ranges
Solution Approach 1:
The patent implements feedback control by using the differential pressure sensor to monitor actual differential pressure and comparing it with the target value. The controller adjusts the pump displacement based on this feedback to precisely control traction force, significantly improving operability compared to the conventional open-loop PQ characteristic change method
Solution Approach 2:
The patent replaces the conventional mechanical/PQ-based transmission ratio control with an electronic control system that directly controls pump displacement based on differential pressure feedback. This substitution enables precise and flexible traction force control across all operation ranges, greatly enhancing operability
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 arbitrary, accurate, and efficient control of traction force in stalling conditions, improving operability and fuel efficiency by optimizing engine speed and hydraulic motor displacement.
Implementation Method 1
The traveling pump is driven by the engine and discharges hydraulic fluid
Implementation Method 2
The hydraulic fluid discharged from the traveling pump is supplied to the traveling motor via the hydraulic circuit
Implementation Method 3
The traveling motor is driven by hydraulic fluid from the traveling pump
Data Source
AI summary
A work vehicle includes an engine, a hydrostatic transmission, a storage device storing leakage flow rate data defining a relationship between a differential pressure of hydraulic fluid between the first drive circuit and the second drive circuit and a leakage flow rate of the hydraulic fluid in the hydraulic circuit in stalling, and a controller in communication with the storage device. The hydrostatic transmission includes a traveling pump, a hydraulic circuit with first and second drive circuits, and a traveling motor. The controller is configured to determine a target traction force of the work vehicle, determine a target differential pressure that is a target value of the differential pressure from the target traction force, determine the leakage flow rate from the target differential pressure with reference to the leakage flow rate data, and determine a target flow rate of the traveling pump from the leakage flow rate.