Accumulator Control for Automatic Engine Stop-Start
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Solution Overview
Problem
Conventional automatic transmission systems experience slippage and delays during engine restarts due to dropped hydraulic fluid pressure when the engine stops, and they lack control over engine stop-start operations based on vehicle conditions, particularly during brief stops or idling while moving.
Innovation Solution
A system and method that uses engine speed, vehicle speed, transmission temperature, and engine temperature to determine whether an automatic stop should be activated, and selectively controls an accumulator to prime the transmission for smooth restarts, inhibiting engine stop-starts when necessary, and utilizing the brake pedal position to manage accumulator discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the engine is stopped during idle or brief stops to improve fuel economy, then fuel consumption is reduced, but hydraulic fluid pressure drops causing clutch/brake disengagement and vehicle movement delay
Solution Approach 1:
The accumulator is pre-charged with hydraulic fluid pressure before engine stop-start events occur. When the engine stops and the pump ceases operation, the accumulator immediately supplies pressurized fluid to maintain clutch/brake engagement, eliminating movement delay. This preliminary preparation of stored energy resolves the contradiction by enabling fuel-saving engine stops without sacrificing vehicle responsiveness.
2Use of energy by moving object
If the engine is stopped during idle to improve fuel economy, then fuel consumption is reduced, but clutch and brake engagement reliability deteriorates due to pressure drop
Solution Approach 1:
The accumulator acts as an intermediary energy storage device between the engine-driven pump and the clutch/brake actuators. During engine stop-start operations, the accumulator mediates the pressure fluctuation by supplying supplemental hydraulic fluid pressure, ensuring continuous reliable engagement of torque transmitting devices while allowing the engine to stop for fuel economy.
3Ease of operation
If the accumulator is discharged to maintain hydraulic pressure during restart, then smooth restart is achieved, but the accumulator pressure depletes requiring recharge time
Solution Approach 1:
The system operates in periodic cycles where the accumulator is discharged during engine restart events to provide smooth operation, then recharged when the engine runs and the pump operates. This periodic charge-discharge pattern allows the accumulator to repeatedly support stop-start operations while maintaining adequate pressure duration between events.
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 seamless engine restarts by maintaining hydraulic fluid pressure through accumulator discharge, reducing slippage and delays, and providing controllability during engine stop-start operations based on vehicle conditions.
Implementation Method 1
a controller configured to control operation of the accumulator based on a desired state of the accumulator and at least one operating parameter of the transmission
Data Source
AI summary
A system and method for controlling automatic stop-start of a motor vehicle is provided. The system and method is configured to enable an automatic stop-start mode of operation based on vehicle conditions. In addition, the system and method is configured to selectively actuate an accumulator to prime the transmission for a smooth restart.