Hydrostatic Fan Drive Fail-Safe Control via Mechanical Prestressing
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Solution Overview
Problem
Existing hydrostatic fan drives face issues with high adjustment complexity and limited directional control, leading to potential overheating and engine damage during power failures due to reliance on electroproportional control systems.
Innovation Solution
A hydrostatic drive with a variable displacement pump and an actuating cylinder prestressed to a basic position, adjustable via a pressure regulating valve, includes a directional valve for feed direction control and an external control oil supply for consistent pressure, ensuring continued operation even during signal failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If electroproportional pressure regulating valves are used to adjust the variable displacement pump, then the feed volume can be controlled, but the adjustment complexity increases and the system reliability decreases during power failures
Solution Approach 1:
The actuating cylinder is prestressed via a centering spring arrangement into a basic position corresponding to maximum feed volume flow before any control action is needed. This preliminary mechanical positioning ensures that in the event of control system failure, the pump automatically defaults to a safe maximum feed position without requiring active control signals.
Solution Approach 2:
The patent replaces the electroproportional control system with a mechanically prestressed actuating cylinder system. The centering spring arrangement provides a passive mechanical backup that ensures reliable operation during power failures, substituting electronic control with a fail-safe mechanical positioning system.
2Reliability
If the variable displacement pump is set to maximum feed volume in basic position, then operating reliability is improved during failures, but the device complexity increases due to additional prestressing mechanisms
Solution Approach 1:
The actuating cylinder with centering spring arrangement is a self-service mechanism that automatically positions the pump at maximum feed volume in the basic position without requiring external control signals or complex electronic systems. The mechanical prestressing system serves itself to ensure fail-safe operation.
3Device complexity
If internal control oil pick-off is used, then the system is compact, but the control oil pressure is subject to high fluctuations
Solution Approach 1:
The control oil supply is extracted from the internal hydraulic circuit and replaced with an external control oil supply system. This separation removes the control oil pressure fluctuations from the main hydraulic circuit, providing stable control pressure independent of the pump's operational variations.
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 enhances operating reliability by maintaining fan operation and preventing overheating, with a simple and compact setup that adapts control oil pressure to demand, ensuring continuous feed and reducing the risk of engine damage.
Implementation Method 1
The actuating cylinder (26) is adjustable by means of a control pressure set via a pressure regulating valve (54)
Implementation Method 2
the feed volume of which is adjustable by means of an adjusting device (10) having an actuating cylinder (26) which is prestressed into a basic position and is adjustable by means of a control pressure set via a pressure regulating valve (54)
Implementation Method 3
A directional valve (38) is arranged in the control oil flow path between the pressure regulating valve (54) and the actuating cylinder (26) for the purpose of setting the feed direction
Implementation Method 4
the variable displacement pump (20), in its mechanically predetermined basic position, continues to feed pressure medium
Data Source
AI summary
A hydrostatic drive, in particular a fan drive, with a variable displacement pump is configured to drive at least one hydraulic motor. The variable displacement pump is activated via a pressure regulating valve and a following directional valve predetermining the feed direction, via which valves the control spaces of an actuating cylinder can be acted upon with a control pressure difference. The variable displacement pump is prestressed into a basic position in which the feed volume flow is maximum.