Hydraulic Steering Flow Circuit With Pressure-Triggered Backup Pump
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Solution Overview
Problem
Existing power steering systems in work vehicles, such as agricultural tractors and construction machines, lack safety enhancements, user friendliness, and cost efficiency, particularly in hydraulic circuits.
Innovation Solution
A fluid control arrangement is introduced in the hydraulic circuit, incorporating a first and second pump, a steering cylinder, and a steering unit, with a flow direction control device and an emergency valve that switches to the second pump upon pressure drop, ensuring backup operation and failure detection, and includes a pressure sensor for monitoring and signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single pump is used in the hydraulic circuit, then the device complexity is reduced, but the reliability is insufficient for safety-critical power steering operation
Solution Approach 1:
The hydraulic system is segmented into two independent pump units (first pump and second pump), each capable of independently supplying pressurized fluid to the steering cylinder. This segmentation allows the system to maintain reliability through redundancy while keeping each pump module relatively simple in design.
Solution Approach 2:
The system incorporates a backup pump (second pump) that stands by in readiness to take over if the primary pump (first pump) fails. This prior cushioning approach ensures that safety is maintained by having a pre-positioned backup capability without requiring complex active monitoring or switching mechanisms.
2Reliability
If a backup pump is added to the hydraulic circuit, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The system uses the pressure differential that naturally exists during normal operation to automatically control the check valve and emergency valve. When the first pump operates normally, the pressure difference keeps the check valve closed and the emergency valve closed. When pressure drops, the valves automatically respond without requiring external control systems, thus improving reliability while minimizing added complexity.
Solution Approach 2:
A check valve is introduced as an intermediary element that automatically prevents backflow from the second pump to the first pump inlet when the first pump is operating normally. This intermediary component simplifies the control logic by using passive pressure-based valve actuation rather than requiring active control systems.
3Reliability
If flow direction control devices are added to prevent backflow, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The function of preventing backflow is extracted into a dedicated check valve component that operates autonomously based on pressure differential. This extraction isolates the backflow prevention function from the main pump control system, improving reliability through dedicated functionality while keeping the overall system complexity manageable by using a simple, well-understood valve mechanism.
4Reliability
If an emergency valve with control port is added for backup operation, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The emergency valve is designed to be self-actuating through a control port that responds automatically to pressure changes. When the first pump fails and pressure drops, the control port automatically opens the emergency valve to allow the second pump to supply fluid, without requiring external sensors, actuators, or control systems. This self-service approach improves reliability while minimizing the addition of complex control components.
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
Enhances safety and user friendliness while passing homologation tests, and reduces costs by providing a redundant safety function and efficient backup operation in hydraulic systems.
Implementation Method 1
a flow direction control device (e.g. a check valve) arranged and configured to prevent a flow of the fluid to the first inlet in response to a pressure difference across the flow direction control device
Implementation Method 2
a control connection to the control port for controlling the opening of the second flow path in response to a pressure drop in a section of the fluid circuit between the first pump and the flow direction control device
Data Source
Figure 1
Figure 2A~2E
Figure 3~4
AI summary
An arrangement for controlling a fluid circuit's flow from alternatively a first and a second pump (4a, 4b) to a tank via steering unit (1) and steering cylinder (5) of the circuit, comprising, a first flow path including a flow direction control device (C) for preventing a flow to a first inlet (P1) in response to a pressure difference across the device (C), a second flow path including an emergency valve (33) for opening of the second flow path comprising and controlled via a control port (33a), a connection between the first and the second flow path in accordance with a position of the flow direction control device (C) between the emergency valve (33) and the first inlet (P1), and a connection for responding to a pressure drop between the first pump (4a) and the flow direction control device (C) by opening of the second flow path.