Transmission Hydraulic Control System with Variable Displacement Pump
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Solution Overview
Problem
Hydraulic control systems in automatic transmissions face challenges in maintaining fluid flow and pressure during engine shutdowns, which affects clutch engagement and disengagement efficiency, particularly when transitioning between gear ratios and maintaining lubrication and torque converter functionality.
Innovation Solution
A hydraulic control system with a variable displacement pump and priority valve that adjusts fluid flow based on pressure thresholds, combined with an electrically driven pump for maintaining line pressure, and a thermal bypass valve for regulating lubrication, ensures continuous fluid supply and pressure management during engine shutdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the engine is shut off to reduce fuel consumption, then fuel economy is improved, but fluid pressure and flow are lost affecting clutch engagement and lubrication
Solution Approach 1:
The system pre-pressurizes the accumulator before engine shutdown, storing hydraulic energy in advance. This preliminary action ensures that when the engine stops, the clutch can still engage reliably using the pre-stored pressure rather than losing pressure immediately.
Solution Approach 2:
The accumulator acts as an intermediary energy storage device between the engine-driven pump and the clutch system. It decouples the clutch engagement function from continuous engine operation, allowing the clutch to operate reliably during engine shutdown periods.
2Use of energy by moving object
If the engine is shut off to reduce fuel consumption, then fuel economy is improved, but lubrication and torque converter functionality are compromised
Solution Approach 1:
The system pre-pressurizes the accumulator before engine shutdown, storing hydraulic energy in advance. This preliminary action ensures that when the engine stops, lubrication can continue using the pre-stored pressure rather than losing pressure immediately.
Solution Approach 2:
The accumulator serves as an intermediary that maintains system pressure during engine shutdown, enabling the lubrication system and torque converter to continue functioning without direct engine-driven pump operation.
3Reliability
If a fixed displacement pump is used to maintain fluid pressure, then pressure is maintained during engine shutdown, but energy is wasted when full pressure is not needed
Solution Approach 1:
The system uses a variable displacement pump that dynamically adjusts its output based on actual system needs. The pump controller modulates the pump displacement to match demand, preventing energy waste from maintaining full pressure when not required while ensuring adequate pressure for clutch engagement and lubrication.
Solution Approach 2:
The system changes the operational parameters of the pump by varying its displacement. This allows the pump to deliver appropriate pressure and flow only when needed, optimizing energy consumption while maintaining reliability for critical functions during engine shutdown.
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
Enables efficient clutch engagement and disengagement, maintains lubrication, and optimizes torque converter performance by ensuring consistent fluid pressure and flow, even during engine shutdowns, improving transmission efficiency and fuel economy.
Implementation Method 1
A variable displacement pump delivers fluid to a pump output circuit. The pump displacement varies in response to an increase in pressure in a displacement control circuit.
Implementation Method 2
A priority valve reduces flow in a lubrication circuit in response to pressure in the displacement control circuit being less than a threshold.
Implementation Method 3
A lube circuit regulator valve may control pressure in the lubrication circuit by venting fluid from the lubrication circuit through a variable size opening.
Implementation Method 4
A thermal bypass valve may route the fluid from the converter out circuit to the lubrication circuit either directly or via a cooler depending a temperature of the fluid.
Data Source
AI summary
An automatic transmission uses 6 shift elements applied in combinations of four to establish ten forward speed ratios and a reverse speed ratio. The automatic transmission uses a hydraulic control system to control engagement of the six elements, control engagement of a torque converter bypass clutch, control engagement of a parking pawl, and to provide fluid for a hydrodynamic torque converter and for lubrication. The parking pawl is disengaged in response to engagement of two of the six shift elements and remains disengaged in response to engagement of other shift elements. A single valve controls several different functions associated with the two-pass torque converter. Pressurized fluid is provided by a variable displacement engine driven pump and also by an electric pump. A priority valve reduces lubrication flow when other fluid demands are high as indicated by the pump displacement control circuit.