Hydrostatic Work Vehicle Clutch Switching With Flow Rate Compensation
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Solution Overview
Problem
Speed change shock occurs when switching from travel with two motors to travel with one motor in work vehicles equipped with hydrostatic transmission, due to rapid changes in hydraulic fluid flow rate.
Innovation Solution
A work vehicle with an engine, travel pump, hydraulic circuit, first and second travel motors, flow rate control device, drive shaft, clutch, and sensor, where the controller reduces the displacement of the first travel motor and controls the flow rate control device to offset excess flow rate, minimizing hydraulic fluid flow rate changes during clutch switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the displacement of the first travel motor is rapidly reduced to switch from two-motor travel to one-motor travel, then the clutch switching is achieved, but the flow rate of hydraulic fluid changes greatly causing speed change shock
Solution Approach 1:
The controller performs preliminary action by reducing the displacement of the first travel motor before actually switching the clutch to the disengaged state. This preliminary reduction of displacement prepares the hydraulic system for the upcoming clutch switching, minimizing the sudden flow rate changes that would otherwise cause speed change shock. The displacement reduction is performed in advance while the clutch is still engaged, allowing the hydraulic circuit to adapt gradually.
Solution Approach 2:
The invention applies beforehand cushioning by using the flow rate control device to compensate for the decrease in hydraulic fluid flow rate caused by reducing the first travel motor's displacement. The flow rate control device increases the flow rate through the second travel motor to cushion the overall flow rate change in the hydraulic circuit, preventing the sudden speed changes that would occur during clutch switching.
2Object-affected harmful factors
If the displacement of the first travel motor is reduced gradually to minimize flow rate changes, then speed change shock is reduced, but the clutch switching time is extended
Solution Approach 1:
The invention maintains continuity of useful action by keeping the clutch in the engaged state during the entire displacement reduction process of the first travel motor. This allows the hydraulic system to transition smoothly while the clutch remains connected, ensuring continuous power transmission. The clutch is only switched to the disengaged state after the displacement reduction is complete, maintaining the continuity of the control action throughout the process.
Solution Approach 2:
The invention utilizes parameter changes by adjusting the displacement parameter of the first travel motor in a controlled manner before clutch switching. The displacement is reduced from its initial value to a smaller value while the clutch remains engaged, changing the hydraulic system's operating parameters gradually. This parameter change approach allows the system to transition smoothly between operating modes without causing speed change shock.
3Object-affected harmful factors
If the flow rate control device is used to offset flow rate excess, then hydraulic fluid flow rate changes are minimized, but the control system complexity increases
Solution Approach 1:
The flow rate control device is designed with multi-functionality, serving both normal operation flow control and the specific function of compensating for flow rate changes during clutch switching. The same control device that manages hydraulic fluid distribution during regular operation is also used to offset flow rate excess when reducing the first travel motor's displacement, eliminating the need for a separate dedicated compensation device and reducing overall system complexity.
Solution Approach 2:
The flow rate control device performs self-service by automatically adjusting the flow rate distribution in response to the displacement reduction of the first travel motor. The controller monitors the displacement changes and automatically commands the flow rate control device to compensate for flow rate excess, making the system self-regulating during the clutch switching process without requiring additional external control mechanisms.
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
The solution effectively suppresses speed change shock by minimizing hydraulic fluid flow rate changes during the switching process, ensuring smoother transitions between two-motor and one-motor travel modes.
Implementation Method 1
A hydrostatic transmission includes a travel pump, a hydraulic circuit, a first travel motor, and a second travel motor. The travel pump is driven by an engine to discharge hydraulic fluid.
Implementation Method 2
The hydraulic fluid discharged by the travel pump is supplied to the first travel motor and the second travel motor via the hydraulic circuit. The first travel motor and the second travel motor are driven whereby the work vehicle travels.
Data Source
AI summary
When the vehicle speed increases and reaches a predetermined switching threshold, the controller reduces the displacement of the first travel motor and controls the flow rate control device to offset a flow rate excess in the hydraulic circuit in accordance with the reduction in the displacement of the first travel motor. After the vehicle speed has reached the switching threshold, the controller executes switching control to switch the clutch from an engaged state to a disengaged state.