Linear Actuator Safety Mechanism for Power-Loss Parking Shift
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Solution Overview
Problem
Existing linear actuators for automobile transmissions are either bulky, complex, or inefficient in automatically shifting into parking mode during power failures, particularly in shift-by-wire systems.
Innovation Solution
A compact linear actuator design featuring a worm drive mechanism with a worm screw and worm wheel, coupled with a spring-driven gear rack, and an electrically activated lock that releases the gear rack upon power loss, allowing the spring to displace the worm wheel and transmission control member to the end position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spring-driven forced parking mechanism is used to automatically shift into parking mode during power failure, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent combines the worm drive mechanism with a spring-driven forced parking mechanism into a single integrated system. The housing contains both the motor-driven worm drive and the spring mechanism, allowing automatic shifting into parking mode during power failure while maintaining a compact structure. This merging approach improves reliability without proportionally increasing overall device complexity.
Solution Approach 2:
The spring is pre-loaded during normal operation when the motor is functional, storing potential energy in advance. When power failure occurs, this pre-stored energy automatically activates the forced parking mechanism without requiring additional power or complex control systems. This preliminary action ensures reliable automatic parking engagement while simplifying the control architecture.
2Volume of moving object
If a compact linear actuator design is implemented, then device volume is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs a nested arrangement where the worm wheel is positioned within the housing and the gear rack is integrated into the same compact space. The worm drive mechanism and spring-driven parking mechanism are nested within each other, maximizing space utilization. This nested design reduces overall actuator volume while maintaining adequate clearance and meshing precision through careful spatial arrangement.
Solution Approach 2:
The patent optimizes geometric parameters of the worm drive and gear rack meshing to achieve compact dimensions. By adjusting parameters such as worm lead angle, gear rack tooth profile, and center distances, the design achieves both compact size and sufficient manufacturing tolerance margins, reducing the stringency of precision requirements while maintaining functional performance.
3Ease of operation
If an electrically activated lock is used to block the gear rack, then ease of operation is improved, but energy consumption increases
Solution Approach 1:
The electrically activated lock operates periodically rather than continuously - it is energized only when locking or unlocking is required during normal operation. During extended periods between operations, the lock remains disengaged without consuming power. This periodic activation maintains ease of operation while significantly reducing overall energy consumption compared to continuously engaged locking systems.
Solution Approach 2:
The patent extracts the locking function from a continuous power-consuming state and implements it as an on-demand electrical activation system. The electrically activated lock is engaged only when needed to prevent backward rotation during motor operation, and remains disengaged otherwise. This extraction of the locking function from continuous operation reduces energy consumption while maintaining operational control through electrical actuation.
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
Ensures reliable and automatic shifting into parking mode with a compact design, reducing the risk of mechanical failure and energy consumption, while maintaining efficient operation during power interruptions.
Implementation Method 1
a spring (15) arranged with the spring displaceable in the housing and configured to store mechanical energy and release the gear rack upon interruption of electric power supply to the lock
Implementation Method 2
a worm drive having a worm screw drivable by the electric motor and a worm wheel driven by the worm screw
Implementation Method 3
An electrically activated lock is arranged to block the gear rack against linear displacement with the spring in a compressed state
Data Source
AI summary
The invention relates to a linear actuator (1) for an automobile transmission comprising an electric motor (6) for moving a transmission control member (5) between a plurality of shift positions, a spring (15) for driving the transmission control member (5) to an end position of the shift range in case of electric power failure, and a worm screw (7) to drive a displaceable worm wheel (10) with a pinion (11) meshing with a displaceable gear rack (12). The transmission control member (5) is displaceably coupled to the worm wheel (10). The gear rack (2) is blocked by an electrically activated lock against linear displacement with the spring (15) in a compressed state such that upon interruption of power supply to the lock the gear rack (12) is released and linearly displaced by the spring (15) thereby shifting the transmission control element (5) to its end position.