Park Lock Apparatus with Sequential Differential Engagement
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Solution Overview
Problem
Current park lock systems for vehicles do not effectively lock the transfer box differential when engaging the park lock, allowing one set of wheels to move relative to the other even when the park lock is applied, which can lead to unintended movement on sloped surfaces.
Innovation Solution
A park lock apparatus with a locking member that has three states: unlocked, locked differential, and engaged park lock, and an actuation member that moves between these states, ensuring the differential is locked before the park pawl is engaged, using a dog gear and Bowden cable or actuator to enforce sequential engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple park lock mechanism is used, then the device complexity is reduced, but the reliability of preventing unintended vehicle movement deteriorates
Solution Approach 1:
The park lock mechanism is segmented into two distinct functional states: a differential lock state (first position) and a park pawl engagement state (second position). The locking member is divided into separate functional zones that independently control the differential and the park pawl, allowing sequential engagement and ensuring reliable vehicle immobilization without requiring complex integrated mechanisms.
Solution Approach 2:
The mechanism requires the differential to be locked (first position) before the park pawl can be engaged (second position). This preliminary action ensures that the drive shafts are already mechanically connected and locked before the final parking lock is applied, preventing unintended vehicle movement while maintaining a relatively simple overall structure.
2Device complexity
If the park lock prevents movement of the input drive shaft only, then the device complexity is reduced, but the reliability of preventing wheel movement deteriorates
Solution Approach 1:
The locking member is segmented into distinct functional zones: one zone controls the differential lock to prevent independent rotation of front and rear drive shafts, while another zone controls the park pawl to prevent rotation of the input drive shaft. This segmentation ensures comprehensive wheel movement prevention without requiring overly complex mechanisms.
Solution Approach 2:
The differential lock acts as an intermediary mechanism between the park pawl and the drive shafts. By first locking the differential to connect the front and rear drive shafts mechanically, the system ensures that preventing input drive shaft rotation also prevents output shaft rotation, thereby reliably preventing wheel movement while maintaining structural simplicity.
3Reliability
If sequential engagement of differential lock and park pawl is enforced, then the reliability of park lock is improved, but the ease of operation deteriorates
Solution Approach 1:
The actuation mechanism is designed to dynamically guide the locking member through sequential positions. The mechanism automatically transitions through the differential lock state first, then enables park pawl engagement, creating a dynamic sequential engagement process that ensures reliability while requiring minimal operator intervention and maintaining ease of use.
Data Source
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AI summary
A park lock apparatus and control unit for a vehicle, the apparatus comprising: a locking member (28, 30; 50) having: a first state arranged to permit independent rotational movement of front and rear drive shafts (20, 22) of the vehicle relative to a fixed position on the vehicle; a second state arranged to prevent independent rotational movement of the front and rear drive shafts of the vehicle relative to the fixed position on the vehicle; and a third state arranged to prevent rotational movement of the front and rear drive shafts of the vehicle relative to the fixed position on the vehicle, and an actuation member (36; 64) for moving the locking member between the first, second and third states.