Hand Fork-Lift Pump Assembly with Load-Pressure Reversing Valve
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Solution Overview
Problem
Existing pump assemblies for hand fork-lift trucks face challenges in quickly lifting smaller loads with minimal power loss, as current solutions either require excessive pumping actions or result in significant throttle losses due to the design of reversing valves.
Innovation Solution
The pump assembly employs a sliding valve element with constant pressure from a spring or atmospheric source, controlled by load pressure rather than pump pressure, and incorporates a throttle to prevent immediate flooding of the annulus collector, allowing smooth switching between lifting ratios with reduced power loss and ergonomic improvements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large pump volume is used to reduce the number of pumping actions, then productivity is improved, but the power required by the operator increases
Solution Approach 1:
The pump assembly dynamically switches between two pump ratios (first and second ratios) depending on the lifting condition. The reversing valve changes the effective piston surface area based on pressure conditions, allowing the system to adapt between quick-lift mode (larger effective area) and normal lifting mode (smaller effective area), resolving the contradiction between productivity and power requirement
Solution Approach 2:
The system changes the pump ratio parameter by switching the effective piston surface area of the pump piston between two states. The first pump ratio corresponds to the full piston surface area, while the second pump ratio corresponds to a reduced effective area, allowing optimization between pumping speed and power consumption based on operational needs
2Loss of energy
If a reversing valve with small radial gap is used to reduce throttle losses, then power loss is reduced, but the force required during normal lifting operation increases
Solution Approach 1:
The reversing valve dynamically adjusts the effective piston surface area based on pressure conditions. During normal lifting, the valve maintains a small radial gap to minimize throttle losses. When switching to quick-lift mode, the valve opens to connect the piston chamber with the annulus collector, changing the effective area without requiring force compensation, thus resolving the contradiction between energy loss and force requirement
3Speed
If pump pressure is used to control the reversing valve, then switching responsiveness is improved, but power loss increases due to frequent switching
Solution Approach 1:
The reversing valve uses load pressure feedback from the lifting cylinder to control switching between pump ratios. The valve monitors the pressure in the lifting cylinder and switches based on whether the load has been sufficiently raised, rather than switching with every pump stroke. This feedback mechanism reduces unnecessary switching and associated power losses while maintaining appropriate responsiveness to actual lifting needs
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 design enables trouble-free switching between lifting ratios with minimal power loss and improved ergonomics by using load pressure to control the reversing valve and preventing unwanted power loss, enhancing the efficiency and comfort of the lifting process.
Implementation Method 1
a valve element is pressed against the sealing surface by a spring which is held in a hole in the pump piston
Implementation Method 2
The piston chamber of the pump is filled through a check-valve during the suction stroke so that oil can be sucked out of the reservoir
Implementation Method 3
one embodiment of the invention plans a throttle for the reversing valve
Data Source
AI summary
Pump assembly for the lift cylinder of a hand fork-lift truck includes a piston pump activated by a bar of a hand fork-lift truck and has a piston chamber and an annulus collector. A three stage control valve connects the lift cylinder with a tank in the lowered setting and connects the piston chamber with the tank in a neutral setting and in a pump setting, connects the piston chamber with the lift cylinder through a first check-valve, with the tank through a second check-valve, a third check-valve between the piston chamber and the annulus collector open to the piston chamber, and a reversing valve between the piston chamber and the annulus collector.