Shift-by-wire Park Brake Redundancy via Secondary Solenoid
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Solution Overview
Problem
Shift-by-wire (SBW) systems in automatic transmissions face issues with unintended loss of park function due to single point failures, particularly in electro-hydraulic systems, which lack redundancy and fail to maintain park engagement in error states.
Innovation Solution
A vehicle park-brake system incorporating a solenoid, servo, and secondary pressure source to ensure park engagement through hydraulic actuation, with a latch valve from the transmission clutch for redundancy and decoupling features to maintain park engagement even if primary control fails, using electro-mechanical and electro-hydraulic solenoids for reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electro-hydraulic SBW systems are used to reduce cost, then manufacturing cost is reduced, but reliability deteriorates due to single point failures causing unintended loss of park function
Solution Approach 1:
The patent implements a secondary control system that activates when the primary electro-hydraulic control fails. This includes a secondary solenoid valve and secondary pressure source that can independently engage the park brake, providing a safety net against single point failures before they result in loss of park function
Solution Approach 2:
The system changes the control mode from purely electro-hydraulic to a hybrid electro-mechanical/electro-hydraulic system. The secondary control path uses different physical principles (electromechanical actuation vs. electro-hydraulic actuation) to achieve the same park engagement function, ensuring reliability when one system fails
2Reliability
If redundant hardware is added to improve reliability, then park function reliability is improved, but device complexity increases
Solution Approach 1:
The secondary solenoid valve and pressure source share the same hydraulic circuit and park servo mechanism with the primary control system. Both control paths converge on the same actuation mechanism, allowing one system to back up the other without requiring completely separate redundant hardware chains
Solution Approach 2:
The control system uses an intermediary control architecture where the secondary solenoid valve can override or supplement the primary electro-hydraulic control. This intermediary path provides reliability without requiring full duplication of the entire control system, reducing complexity compared to complete redundancy
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 prevents loss of park engagement due to single point failures, ensuring reliable park engagement and disengagement through secondary control mechanisms, allowing for safe operation even if primary control or solenoid fails, thus enhancing safety and reliability.
Implementation Method 1
a force produced by a solenoid that actuates first and second pistons to disengage the park brake
Implementation Method 2
a first pressure source applied to a servo to disengage the park brake
Implementation Method 3
a second pressure source applied to the servo causing hydraulic pressure to vent from the servo
Data Source
AI summary
A vehicle park-brake system includes a park brake, a solenoid; a first pressure source; a servo for disengaging the park-brake using the first pressure source, and for disengaging the park-brake using a force produced by the solenoid that actuates first and second pistons; and a second pressure source applied to the servo causing hydraulic pressure to vent from the servo, the pistons to detach mutually, and the servo to engage the park brake.