EV Dog Clutch Engagement Using Reversal to Clear Tooth Blocking
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Solution Overview
Problem
Existing methods for engaging dog clutches in electric vehicle powertrains are ineffective when one shaft is free to rotate, leading to blocking and unreliable coupling due to friction between teeth sets.
Innovation Solution
A method involving an actuator to apply an engaging force on a dog clutch, detect blocking, and adjust the rotation direction of the teeth to overcome friction, ensuring smooth engagement by alternating the rotation direction of the teeth sets to achieve reliable coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor shaft is rotated to unblock the dog clutch, then the relative movement between teeth sets occurs, but the shaft of the gearbox is driven in rotation by friction when free to rotate, preventing proper engagement
Solution Approach 1:
The method applies a braking force to the gearbox shaft before and during the engagement process to prevent it from rotating due to friction. This preliminary counter-action ensures that when the motor shaft rotates to create relative movement between teeth, the gearbox shaft remains stationary, allowing proper engagement to occur.
Solution Approach 2:
The system dynamically adjusts the engagement process by detecting the rotational state of the gearbox shaft and controlling the motor shaft rotation accordingly. The braking force is applied dynamically during the engagement sequence to maintain the shaft in a non-rotating state when needed, while allowing rotation when engagement is complete.
2Productivity
If the engaging force is applied continuously to move teeth towards each other, then the dog clutch engages, but blocking occurs when teeth are in contact but not properly engaged
Solution Approach 1:
The engagement process uses periodic action by rotating the motor shaft back and forth in small increments. Instead of continuous rotation, the system applies periodic rotational movements that create relative motion between teeth sets, allowing them to progressively engage while the braking force prevents gearbox shaft rotation. This periodic motion continues until full engagement is detected.
Solution Approach 2:
The system incorporates feedback by detecting whether the gearbox shaft is rotating during the engagement process. Based on this detection, the controller adjusts the motor shaft rotation and braking force application. When the shaft is detected to be rotating (indicating blocking), the system modifies its engagement strategy to resolve the blockage before continuing.
3Adaptability or versatility
If the shaft is free to rotate during engagement, then it can be decoupled from output components, but friction drives the shaft in rotation preventing unblocking of the dog clutch
Solution Approach 1:
The braking force applied to the gearbox shaft serves as a preliminary anti-action that counteracts the friction-driven rotation. By applying this counter-force before and during engagement, the system prevents the shaft from rotating even though it remains free to rotate and decoupled from output components, ensuring reliable dog clutch engagement.
Solution Approach 2:
The braking force acts as an intermediary element between the free-rotating shaft and the engagement process. It mediates the interaction by allowing the shaft to remain decoupled and free to rotate while simultaneously preventing the friction-driven rotation that would interfere with dog clutch engagement, thus resolving the contradiction between shaft flexibility and engagement reliability.
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 efficient coupling of shafts with the electric motor, minimizing tooth wear and vibration, and enhancing powertrain reliability by resolving blocking issues during engagement.
Implementation Method 1
driving in rotation the first set of teeth around the main axis in a first rotation direction, by the electric motor, while applying the engaging force so that the first set of teeth tends to drive the shaft in rotation around the main axis in the first direction of rotation by friction of the first set of teeth against the second set of teeth
Implementation Method 2
driving in rotation the first set of teeth around the main axis in a second direction of rotation opposite to the first direction of rotation, by the electric motor, while applying the engaging force, so that the first set of teeth tends to slip against the second set of teeth rotating in the first direction of rotation, enabling the dog clutch to reach the engaged configuration
Data Source
AI summary
This electric vehicle includes a dog clutch with a first set of teeth driven by an electric motor and a second set of teeth rotatably coupled to a shaft, and an actuator to engage the dog clutch. A method for engaging the dog clutch includes, in this order: detecting a blocking of the dog clutch in a teeth-to-teeth configuration while the actuator tries to engage the dog clutch and while the shaft is rotatably decoupled from output components of the vehicle; rotating the first set of teeth in a first direction, to drive the shaft in rotation by friction between the sets of teeth; and rotating the first set of teeth in a second direction opposite to the first, so that the first set of teeth slip against the second set of teeth, enabling the actuator to fully engage the dog clutch.