Hydraulic Coupling Clutch Pressure Control Valves
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Solution Overview
Problem
Purely mechanical all-wheel drive systems face challenges during normal vehicle steering when driven road wheels across an axle rotate at different speeds, and changes in viscosity of the clutch operating fluid as the vehicle warms after a cold start affect the hydraulic clutch's performance.
Innovation Solution
A transmission coupling with a hydraulic actuator and valve system that adjusts fluid flow based on rotational speed differential and viscosity, featuring a first valve that dumps pressurized fluid above a predetermined pressure and a second valve that prevents fluid flow below a second pressure, ensuring reliable clutch engagement and disengagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a purely mechanical all-wheel drive system is used, then the system structure is simple, but the system cannot properly handle speed differential during steering and is affected by fluid viscosity changes
Solution Approach 1:
The patent introduces a hydraulic actuator system with pressure control valves to operate the clutch means. The hydraulic system includes a pump driven by speed differential and valve means that control fluid flow to the actuator based on pressure thresholds, enabling reliable clutch engagement and disengagement while compensating for viscosity changes in the fluid.
Solution Approach 2:
The patent uses pressure-sensitive valve means that respond to changes in hydraulic pressure parameters. The first valve opens at a higher pressure threshold to engage the clutch, while the second valve closes at a lower pressure threshold to disengage the clutch, creating a hysteresis effect that ensures reliable operation despite viscosity variations.
2Device complexity
If a hydraulic actuator with single valve is used, then the system is simple, but the clutch cannot engage and disengage reliably under varying pressure conditions
Solution Approach 1:
The patent divides the single valve function into two separate valves: a first pressure control valve with a first pressure threshold for engagement, and a second pressure control valve with a second pressure threshold for disengagement. This segmentation allows independent optimization of engagement and disengagement pressures, improving reliability.
Solution Approach 2:
The patent creates a dynamic pressure control system where the two valves operate at different pressure thresholds, establishing a hysteresis window. This dynamic approach ensures that once the clutch engages at the first threshold, it remains engaged until pressure drops below the second threshold, preventing premature disengagement and ensuring reliable operation under varying conditions.
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 the reliability and accuracy of clutch engagement, preventing unwanted activation during steering and compensating for viscosity changes, thereby improving the performance of four-wheel drive vehicles by ensuring proper torque distribution across wheels.
Implementation Method 1
a speed differential pump having a casing connected to the input and an output shaft, the pump being operated by a speed differential between the input and the output shaft
Implementation Method 2
a first valve controlling fluid flow into the actuator and which is biased to a closed condition, with a second valve controlling fluid flow from the actuator and which is biased to an open condition, each valve being responsive to hydraulic pressure for the opening and closing thereof
Implementation Method 3
the clutch plates are clamped together by a hydraulic piston which is actuated by hydraulic pressure generated by pumped transmission fluid
Data Source
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AI summary
A transmission coupling (56) having a casing (86) as a rotary input (86) and a rotary output (91) connected to the input through clutch means (93) being operated by a hydraulic actuator (104) having hydraulic fluid thereto delivered by a pump (95) operated by a speed difference between said input and outputs (86,91), and valve means (120,140) comprising a first valve (140) controlling fluid flow into the actuator (104) and second valve (120) controlling fluid flow from the actuator (104), and thereby controlling clutch engagement depending on the viscosity of the fluid.