Hydraulic Steering System with Input Horsepower Limiting Circuit
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Solution Overview
Problem
Hydraulic pumps in vehicle systems face damage risks due to excessive system loads, leading to temporary impairment of power steering and cooling fan operation, especially at lower engine speeds where insufficient hydraulic fluid flow occurs, necessitating priority-based fluid distribution to ensure critical system functionality.
Innovation Solution
A hydraulic system comprising first and second fixed displacement pumps with a common drive shaft, a priority valve with primary and secondary outputs, and pressure transducers, which divert excess hydraulic fluid to the cooling fan at low engine speeds, ensuring constant power steering fluid supply and optimizing fan speed and cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant flow rate pump is used to deliver hydraulic fluid to the power steering system, then the power steering system receives sufficient hydraulic fluid flow, but the pump is at risk of damage from excessive system loads and insufficient flow at lower engine speeds
Solution Approach 1:
A priority valve is introduced as an intermediary component between the pump and the power steering system. This valve mediates the hydraulic fluid flow by ensuring that the power steering system receives its required flow while allowing the pump to operate within safe pressure limits, thus protecting the pump from damage while maintaining power steering functionality.
Solution Approach 2:
The system changes the operating parameters of the pump by allowing variable flow rates depending on engine speed. At lower engine speeds, the pump operates at reduced flow rates without causing damage, while at higher engine speeds, it delivers the required constant flow. This is achieved through the priority valve and bypass mechanisms that adapt the system behavior to operating conditions.
2Reliability
If pressure relief mechanisms are provided to protect the pump from excessive loads, then pump damage is avoided, but temporary impairment of power steering and cooling fan operation occurs
Solution Approach 1:
The hydraulic system is segmented into separate bypass circuits for different components. Instead of a single relief valve that stops all flow, separate bypass mechanisms are provided for the power steering system and cooling fan. This allows localized relief of excess pressure to specific components without shutting down the entire system, maintaining service availability while protecting the pump.
Solution Approach 2:
The priority valve acts as an intermediary that manages pressure distribution between different system components. It ensures that when pressure relief is needed, it is directed appropriately to protect the pump while maintaining adequate flow to critical components like the power steering system.
3Reliability
If hydraulic fluid is prioritized for the power steering system, then power steering receives constant flow, but the cooling fan receives insufficient flow at lower engine speeds
Solution Approach 1:
The system dynamically adjusts the distribution of hydraulic fluid between the power steering system and cooling fan based on operating conditions. The priority valve and bypass mechanisms allow the system to adapt flow distribution in real-time, ensuring power steering receives priority flow while the cooling fan receives available excess flow, particularly at lower engine speeds where secondary flow can supplement fan operation.
Data Source
AI summary
A hydraulic system that provides hydraulic fluid to a power steering system of a vehicle at a substantially constant flow rate and can also divert excess hydraulic fluid to the air cooling fan of an associated vehicle at low engine speeds is disclosed. The resulting hydraulic system increases fan speed and increases cooling at low engine speeds while also limiting the input horsepower to one or more driving pumps based at least in part on the outlet pressure of the hydraulic pump unit.