Electrohydraulic Parking Lock Valve Pressure Control
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Solution Overview
Problem
The existing electrohydraulic transmission control systems face challenges in maintaining efficient operation and spontaneous engagement of the parking lock during normal and emergency conditions, particularly due to low actuation pressures leading to inadequate hydraulic actuation and delayed engagement of the parking lock after shutdown.
Innovation Solution
An electrohydraulic transmission control system with a parking lock valve that utilizes adjustable pilot pressures and an electrohydraulic pressure adjuster to maintain the parking lock in a defined operating state, ensuring efficient operation and spontaneous engagement by applying actuation pressure above a defined level, and deactivating the self-holding action within desired times during shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If low actuation pressure is used to improve transmission efficiency during normal operation, then energy consumption is reduced, but the parking lock cannot be held in the disengaged operating state
Solution Approach 1:
The system dynamically adjusts the actuation pressure level based on the operating state. During normal operation, low actuation pressure is used for efficiency. During emergency operation, the system switches to high actuation pressure to ensure the parking lock can be reliably held in the disengaged state. This dynamic pressure adjustment resolves the contradiction between energy efficiency and reliability.
Solution Approach 2:
The patent changes the pressure parameter from a fixed low level to a variable level that can switch between low (for efficiency) and high (for reliability). The electrohydraulic pressure adjuster enables this parameter change by providing different pressure levels based on operational requirements, allowing the system to optimize both energy consumption and parking lock holding capability under different conditions.
2Reliability
If the parking lock is held in disengaged state during emergency operation with maximum actuation pressure, then the parking lock remains disengaged, but upon shutdown the actuation pressure collapses and causes delayed engagement
Solution Approach 1:
The system prepares for shutdown by pre-charging the hydraulic fluid volume accumulator with hydraulic fluid at maximum pressure during emergency operation. When shutdown occurs and actuation pressure collapses, the accumulator immediately discharges the stored hydraulic fluid to rapidly re-establish actuation pressure above the self-holding threshold, enabling spontaneous parking lock engagement without delay. This preliminary charging action resolves the time loss issue.
Solution Approach 2:
The hydraulic fluid volume accumulator acts as a cushioning element that stores hydraulic fluid under pressure in advance. During shutdown, this pre-stored pressurized hydraulic fluid compensates for the sudden pressure collapse, maintaining sufficient pressure to keep the parking lock in the disengaged state temporarily and enabling rapid engagement. This beforehand cushioning prevents the harmful effect of pressure collapse and delayed engagement.
3Reliability
If the self-holding pressure threshold is set above the minimum actuation pressure level, then the parking lock can be held in disengaged state, but the system cannot operate with optimized efficiency at low pressures
Solution Approach 1:
The system uses dynamic pressure adjustment where the actuation pressure level is changed based on operational mode. During normal operation, low actuation pressure is used to maximize transmission efficiency. During emergency operation, the pressure is increased to a level above the self-holding threshold to ensure reliable parking lock holding. This dynamic adaptation allows the system to optimize productivity during normal operation while maintaining reliability when needed.
Solution Approach 2:
The patent implements parameter changes by adjusting the actuation pressure level from low (for efficiency) to high (for reliability) based on operational conditions. The electrohydraulic pressure adjuster enables this parameter transition, allowing the system to operate at low pressures for optimized efficiency during normal operation, and switch to high pressures above the self-holding threshold during emergency operation to ensure the parking lock remains reliably held in the disengaged state.
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 system optimizes efficiency and spontaneity of the transmission by maintaining the parking lock in the disengaged state with low actuation pressure during normal operation and ensures timely engagement of the parking lock during emergency operations, preventing undesired disengagement and improving overall system performance.
Implementation Method 1
a hydraulic fluid volume accumulator known from DE 10 2013 209 932 A1... a hydraulic fluid volume is temporarily stored counter to a spring force of a spring device in the region of the hydraulic fluid volume accumulator, which hydraulic fluid volume can, in accordance with demand, be introduced into the line system of the hydraulic system
Implementation Method 2
a spring device in the region of the hydraulic fluid volume accumulator, which hydraulic fluid volume can, in accordance with demand, be introduced into the line system of the hydraulic system
Data Source
AI summary
An electrohydraulic transmission control system having a parking lock valve by which a parking lock cylinder of a parking lock device can be charged with an actuation pressure adjustable in an operating-state-dependent manner by at least one pilot pressure adjustable in the region of an electrohydraulic pressure adjuster and/or one pressure source. Above a defined actuation pressure level, the parking lock valve is held in a defined operating state in which the actuation pressure can be applied to the parking lock cylinder. The actuation and pilot pressures can be applied to a valve device such that when the actuation and pilot pressure levels approximately correspond to one another, the region of the control system which conducts the actuation pressure is operatively connected, upstream of the parking lock valve, to a pressure region in the region of the valve device with a pressure lower than the defined actuation pressure level.