Hydraulic Flushing Valve Spool for Low-Pressure Fluid Circulation
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Solution Overview
Problem
Hydraulic fluid in closed hydrostatic circuits experiences temperature issues during start-up and operation, with the fluid not being adequately warmed or cooled, particularly in hydrostatic units where the hydraulic motor reaches elevated temperatures, necessitating a method to circulate a small flow of fluid for warming and cooling.
Innovation Solution
A hydraulic fluid flushing valve with a floating spool mechanism that allows fluid flow at low pressure differences, enabling circulation and regeneration of fluid during warm-up and cooling phases, even at zero displacement, by shifting out of its centered position due to small pressure deltas and utilizing gaps between the spool and springs to ensure fluid flow from the low pressure side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional flushing valve with spring-loaded spool is used, then fluid flushing is effective at high pressure, but the valve cannot enable small flow circulation at low pressure during warm-up and cooling phases
Solution Approach 1:
The patent changes the pressure threshold parameter by which the spool is actuated. Instead of using spring force that requires high pressure differential, the spool is designed to be actuated by minimal pressure differences through optimized pressure surface areas. This allows the valve to function at low pressure conditions during warm-up and cooling while maintaining the ability to flush at high pressure during operation.
Solution Approach 2:
The spool position is made dynamically responsive to minimal pressure differences between inlet ports. The valve transitions from a static spring-loaded design to a dynamic pressure-balanced design where the spool automatically positions itself based on the instantaneous pressure differential, enabling continuous adaptation to varying operating conditions including low-pressure circulation modes.
2Reliability
If the flushing valve spool is held in centered position by springs, then the valve structure is stable, but small pressure differences cannot shift the spool to enable fluid flow
Solution Approach 1:
The patent balances the spring forces acting on the spool with counteracting pressure forces on the pressure surfaces. The spring preload is designed to be counterbalanced by minimal pressure differentials across the optimized pressure surfaces, creating a neutral equilibrium state where the spool can be easily shifted by small pressure changes while maintaining stable positioning when pressures are equal.
Solution Approach 2:
The valve design creates an equipotential state where the spring forces and pressure forces are balanced at the centered position. This allows the spool to remain stable in the neutral position while being equally responsive to small pressure differences in either direction, enabling bidirectional flow control with minimal pressure input.
3Force
If the pressure surfaces of the spool are large, then the valve requires high pressure to shift the spool, but small pressure differences are needed for low-pressure circulation
Solution Approach 1:
The patent applies different pressure surface areas to different sides of the spool to create localized force characteristics. The pressure surfaces are optimized to provide sufficient actuation force when needed while allowing minimal pressure differentials to shift the spool for low-pressure circulation. This localized optimization of surface areas enables the valve to handle both high-pressure flushing and low-pressure circulation requirements.
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 efficient fluid circulation and cooling/heating of the hydraulic circuit during start-up and operational breaks, maintaining system performance while being simple, cost-effective, and robust, and compatible with existing hydrostatic units.
Implementation Method 1
small pressure differences are sufficient to shift the flushing valve spool out of its centred position
Implementation Method 2
Each of the pressure surfaces is connected to one of the two inlet ports. At each side of the flushing valve spool a flushing valve spring is located
Implementation Method 3
have a small flow of hydraulic fluid circulating through the whole closed hydraulic circuit, in order for the circuit and its components to be warmed up
Implementation Method 4
the hydrostatic pump is warming up on its own, because it contains, e.g., a charge relief valve which is producing some heat due to the pressure loss caused by the flow of the charge pump
Data Source
AI summary
Hydraulic fluid flushing valve for hydrostatic units usable in closed hydraulic circuit propel applications, having a flushing valve housing with a first inlet port connected to a first working line, a second inlet port connected to a second working line, and a discharge port for draining hydraulic fluid. A two-sided flushing valve flushing valve spool which can be shifted is mounted within the flushing valve housing in a cylindrical valve bore, which, in a shifted position, enables a fluid flow from one of the first or the second inlet port at which the lower hydraulic pressure is present, to the discharge port. The flushing valve spool includes on each side a pressure surface each of which is connected to one of the two inlet ports. At each side of the flushing valve spool a flushing valve spring is located in the flushing valve housing in such a manner that, when the flushing valve spool is in its centre, non-shifted position, at each side of the flushing valve spool a distance between a spring contact surface on the flushing valve spool and a spring support surface in the flushing valve housing is greater than the axial length of the corresponding flushing valve spring.