CVT-Driven Hydraulic Power Steering Pump Speed Control
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Solution Overview
Problem
Existing power steering systems with fixed displacement pumps provide excess flow and pressure at highway speeds, leading to inefficiencies and increased energy consumption, as they are sized for maximum flow at engine idle, necessitating the use of flow control valves to divert excess fluid.
Innovation Solution
A hydraulic power steering system incorporating a continuously variable transmission (CVT) connected to the engine and pump, which adjusts the pump speed based on fluid flow levels and pressure differential across a fixed orifice, eliminating the need for a flow control valve by varying the transmission gear ratio to maintain optimal fluid flow during steering operations at any engine speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed displacement power steering pump is sized to provide maximum rated flow at engine idle, then the steering system can dry park the vehicle at idle speed, but the pump provides excess flow and excess pressure at highway speeds leading to increased energy consumption
Solution Approach 1:
The patent applies a continuously variable transmission (CVT) between the engine and the fixed displacement power steering pump, allowing the pump speed to vary dynamically with engine speed. At idle speeds, the CVT maintains a high gear ratio to drive the pump at maximum speed for dry parking capability. At highway speeds, the CVT reduces the gear ratio to limit pump speed, thereby reducing excess flow and pressure while maintaining adequate steering pressure through the orifice 38.
Solution Approach 2:
The system changes the operating parameters of the pump by using the CVT to vary pump speed based on engine speed. Additionally, the fixed orifice 38 creates a pressure drop that changes the effective pressure delivered to the steering gear depending on flow conditions. This parameter change approach allows the same fixed displacement pump to operate efficiently across a wide range of engine speeds.
2Quantity of substance
If a flow control valve is used to divert excess flow from the power steering pump at highway speeds, then the rated flow is received by the hydraulic steering gear, but energy is consumed to operate the flow control valve and excess flow is wasted
Solution Approach 1:
The patent extracts the flow control function from a separate valve component and integrates it into the hydraulic circuit through a fixed orifice 38 positioned in the supply line to the steering gear. This orifice passively diverts excess flow through its pressure drop characteristics without requiring an active control valve, thereby eliminating the energy consumption associated with valve operation while maintaining proper flow regulation to the steering gear.
3Productivity
If the pump is driven at high speed at highway engine speeds, then maximum flow is available, but excess pressure and flow are generated leading to inefficiency
Solution Approach 1:
The CVT dynamically adjusts the relationship between engine speed and pump speed, allowing the system to maintain high productivity at idle by driving the pump at maximum speed, while at highway speeds the CVT reduces pump speed to match actual steering demands, thereby eliminating excess flow and pressure generation while maintaining adequate flow availability when needed.
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 solution reduces energy and heat generation by ensuring the pump operates at the desired speed to provide the necessary hydraulic fluid flow without excess flow diversion, enhancing efficiency and reducing the power consumption of the steering system across varying engine speeds.
Implementation Method 1
The continuously variable transmission is operable under the influence of force transmitted from the engine of the vehicle to drive the pump at a first speed
Implementation Method 2
a second input controlled by a pressure differential across a fixed orifice in the supply conduit
Data Source
AI summary
An apparatus (10) for use in turning steerable vehicle wheels (14, 16) includes a hydraulic power steering motor (12). A pump (26) is connected in fluid communication with the hydraulic power steering motor (12) by a supply conduit (30). A continuously variable transmission (50) is connected with the engine (52) of the vehicle and with the pump (26). The continuously variable transmission (50) is operable under the influence of force transmitted from the engine (52) to drive the pump at a first speed when the flow of fluid from the pump (26) is at a first level. The continuously variable transmission (50) drives the pump (26) at a second speed different than the first speed when the flow of fluid from the pump is at a second level different than the first level.