Hydraulic Parking Lock Control Under Single-Valve Failure
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Solution Overview
Problem
The existing hydraulic systems for parking lock devices in automatic transmissions are prone to single-point failures in the parking lock valve and positioning valve, leading to unintentional actuations or failure to change operating conditions, which affects vehicle availability.
Innovation Solution
A method is introduced where the parking lock device is pilot-controllable, allowing the pressure chamber to be pressurized or vented to engage or disengage the device, with self-retain functions activated or deactivated based on pressure levels and actuating forces, ensuring engagement even in single-point failure scenarios and maintaining the disengaged condition during defined operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the parking lock valve and positioning valve are used in the hydraulic system, then the parking lock device can be controlled to engage and disengage, but single-point failures in these valves cause unintentional actuations or prevent demanded operating condition changes
Solution Approach 1:
The hydraulic control system is segmented into multiple independent control paths. The parking lock valve and positioning valve are controlled through separate pilot pressure circuits, allowing one valve to fail without completely disabling the other. This segmentation enables fallback control mechanisms where the positioning valve can influence parking lock valve operation through alternative pressure pathways.
Solution Approach 2:
The system performs preliminary actions by pre-positioning the parking lock device in a safe state (engaged condition) and using the positioning valve to maintain this state through pilot pressure control. The spring device is pre-loaded to provide automatic engagement force, and the hydraulic system is designed to maintain pressure that keeps the parking lock disengaged until a failure occurs, at which point the pre-loaded spring automatically engages the lock.
2Reliability
If the pressure chamber is pressurized with main pressure to disengage or hold the parking lock device, then the device can be reliably held in disengaged condition, but single-point failures cause unintentional actuations
Solution Approach 1:
The system incorporates a spring device that stores mechanical energy as a cushion against hydraulic failures. When hydraulic pressure is lost or malfunctioning valves cause unintended pressure changes, the spring device provides a cushioning force that ensures the parking lock engages reliably. This mechanical cushioning compensates for hydraulic system failures and prevents the parking lock from remaining unintentionally disengaged.
Solution Approach 2:
The system converts the potential harm of hydraulic pressure loss into a benefit by designing the parking lock to engage automatically when pressure is removed. The spring device is loaded to push the parking lock into the engaged position, and hydraulic pressure is used to overcome this spring force only when disengagement is intended. If hydraulic pressure fails, the spring force naturally engages the parking lock, converting a failure mode into a safe default 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
This method enables secure engagement and disengagement of the parking lock device, enhances vehicle availability by preventing unintentional actuations, and ensures the parking lock remains in the desired condition during hydraulic system operating progressions, even in the presence of single-point failures.
Implementation Method 1
A pressure chamber of a parking lock cylinder is pressurized with the main pressure, via the parking lock valve, in a defined operating condition range of the parking lock valve to disengage the parking lock device or hydraulically hold the parking lock device in the disengaged condition
Implementation Method 2
a parking lock valve which is pilot-controllable against an actuating force of a spring device
Data Source
AI summary
A method for operating a parking lock device (21) with a hydraulic system (1), the method including, when there is a demand to engage the parking lock device (21) originating from a disengaged operating condition of the parking lock device (21), applying a pilot pressure (p_EDS4) at the parking lock valve (PSV) and applying the main pressure (p_sys) at the parking lock valve (PSV), if necessary, via the positioning valve (POSV). The pilot pressure (p_EDS4) and the main pressure (p_sys) are each guided to defined pressure levels at which the parking lock valve (PSV) is transferrable into the further operating condition range of the parking lock valve (PSV) by the active actuating force against the pilot pressure (p_EDS4) and against the pressure between the parking lock valve (PSV) and the parking lock cylinder (23).