Worm Gear Parking Lock Actuator Fail-Safe Design

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Solution Overview

Problem

Existing parking lock systems for automatic transmissions, especially in vehicles with electric parking brakes, require a redundant electrical supply to ensure secure parking across various gradients and in case of electrical failures, which complicates the design and increases equipment needs.

Innovation Solution

A parking lock actuator with a worm shaft fixed axially in the output gear, utilizing a spring and electromagnet mechanism to automatically engage the parking lock in case of electrical failure, eliminating the need for a redundant supply by pivoting the worm gear into the parking lock position without motor rotation, ensuring reliable engagement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a redundant electrical supply is installed to ensure secure parking during electrical failures, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improvesecure parking during electrical failureVSAvoidelectrical supply system

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of using an electromagnet to hold the parking lock engaged, the patent uses a spring to hold the parking lock engaged and an electromagnet to release it. This inversion means that during electrical failure, the spring automatically engages the parking lock without requiring electrical power, eliminating the need for redundant electrical supply while maintaining reliability.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The spring mechanism automatically engages the parking lock in the event of electrical failure without requiring any additional electrical supply or control systems. The system serves itself by using mechanical energy stored in the spring to ensure secure parking when the electrical system fails.

Inventive Principle:

Principle #25Self-service

2Reliability

If a spring and electromagnet mechanism is used to automatically engage the parking lock, then reliability during electrical failure is improved, but the worm shaft structure becomes more complex

Engineering Contradiction:

Improveautomatic engagement during electrical failureVSAvoidworm shaft structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the spring and electromagnet into a single integrated holding means that acts on the worm shaft. The spring and electromagnet work together in a unified mechanism where the electromagnet overcomes the spring force during normal operation to release the parking lock, and the spring automatically engages it during electrical failure.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The worm shaft serves multiple functions: it is driven by the electric motor during normal parking lock operation, and it is simultaneously actuated by the spring during electrical failure. This multi-functionality allows a single component to handle both electrically-controlled and fail-safe mechanical engagement scenarios.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Manufacturing precision

If the worm shaft is fixed axially in the output gear, then manufacturing precision is improved, but the ability to pivot the worm gear freely is reduced

Engineering Contradiction:

Improveaxial positioning of worm shaftVSAvoidpivoting movement of worm gear

Core Design Contradiction:

Manufacturing precisionVSAdaptability or versatility

Solution Approach 1:

The patent segments the worm shaft's degrees of freedom by fixing only the axial position while allowing rotational pivoting movement. This segmentation enables precise axial positioning for manufacturing purposes while maintaining the flexibility needed for the worm gear to pivot into the engaged position during electrical failure.

Inventive Principle:

Principle #1Segmentation

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 solution provides a compact, fail-safe mechanism that automatically engages the parking lock during electrical failures, ensuring vehicle security without requiring a redundant electrical supply, thus simplifying the design and enhancing reliability.

Implementation Method 1

A spring braces the worm shaft in an axial direction of the worm shaft against a holding means which is situated in a stop position

Methodology Applied

Scientific EffectSpring: Spring

Implementation Method 2

the holding means is fixed by means of an electrically energized electromagnet

Methodology Applied

Scientific EffectElectromagnet: Electromagnet

Data Source

PatentUS10995856B2Parking lock for an automatic transmission and method for operating the parking lock

Publication Date: 2021.05.04 DR ING H C F PORSCHE AG

AI summary

In a parking lock for an automatic transmission, an electrical parking lock actuator has an electric motor, a spur gear stage driveable by the electric motor, and a worm gear stage driveable by the spur gear stage. A worm shaft of the worm gear stage is connected rotationally conjointly to an output gear of the spur gear stage, and a worm gear of the worm gear stage is connected rotationally conjointly to a transmission-side parking lock shaft. The worm shaft is fixed in an axially displaceable manner in the output gear. A stop limits the pivoting movement of the worm gear when a parking lock position of the parking lock shaft is reached. A spring braces the worm shaft in an axial direction of the worm shaft against a holding mechanism which is situated in a stop position, in which the holding mechanism is fixed by an electrically energized electromagnet.