Dog-Clutch Gear Release Control to Prevent Engine Stall

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Solution Overview

Problem

Hybrid vehicles with dog-clutch gearboxes lacking a cut-off clutch face challenges in decoupling the engine from the wheels during braking, leading to engine stalling and resulting vibrations due to the engine operating in degraded conditions, which conventional actuators often fail to address effectively.

Innovation Solution

A method is introduced to control the disengagement of internal transmission couplers by detecting critical engine speed and deceleration zones, employing an 'anti-stall' strategy to force clutch release and a 'timing' strategy to prohibit fuel injection, ensuring smooth gear disengagement without a cut-off clutch.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a cut-off clutch is added to decouple the engine from the wheels during braking, then engine stalling is prevented, but device complexity increases

Engineering Contradiction:

Improveengine operation stabilityVSAvoidtransmission system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the cut-off clutch function from the transmission system by implementing engine braking through electric machine torque control. The electric machine acts as an independent decoupling mechanism, removing the need for a mechanical cut-off clutch while maintaining engine operation stability during braking events.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The electric machine serves multiple functions: it acts as both a propulsion device and a cut-off clutch equivalent. By controlling the electric machine's torque during braking, the system achieves engine decoupling without requiring a dedicated cut-off clutch component, thus reducing overall system complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Ease of operation

If conventional actuators are used to disengage dog clutches during braking, then gear changing is achieved, but engine stalling occurs due to insufficient torque reduction

Engineering Contradiction:

Improvegear disengagement capabilityVSAvoidengine operation stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent applies preliminary action by controlling the electric machine to reduce engine torque before the dog clutch disengagement occurs. This pre-action ensures that the torque on the clutch teeth is sufficiently reduced, allowing smooth gear changing without causing engine stalling or degraded operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control system continuously monitors engine speed and torque conditions, adjusting the electric machine's torque output in real-time based on feedback from sensors. This feedback mechanism ensures that torque is reduced to appropriate levels during braking and gear changes, preventing engine stalling while maintaining operational reliability.

Inventive Principle:

Principle #23Feedback

3Reliability

If the actuator forces clutch release in the first critical zone, then engine stalling is prevented, but transmission shocks and vibrations occur

Engineering Contradiction:

Improveengine operation stabilityVSAvoidtransmission shocks and vibrations

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by using the electric machine to counteract the torque that would cause shocks and vibrations during clutch release. The electric machine provides opposing torque to balance the forces on the clutch teeth, preventing harmful vibrations while still allowing the clutch to disengage and prevent engine stalling.

Inventive Principle:

Principle #9Preliminary anti-action

4Reliability

If the actuator cannot disengage the gear in the second critical zone, then torque reduction is insufficient, but engine stalling risk increases

Engineering Contradiction:

Improveengine operation stabilityVSAvoidgear disengagement capability

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent introduces the electric machine as an intermediary between the engine and the transmission system. In the second critical zone where the actuator cannot disengage the gear, the electric machine mediates by reducing engine torque through electric braking, allowing the system to safely manage the situation without causing engine stalling, even if gear disengagement is delayed.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP3740389B1Method for controlling the release of internal couplers of gear wheels on transmission shafts, transmission and power train

Publication Date: 2025.07.23 RENAULT SA

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AI summary

A method for controlling the release of the teeth of an internal transmission coupler (8, 12) controlled by a gearshift actuator (16) for applying or canceling a transmission ratio to or from the torque provided by a heat engine connected to the input of the transmission without a disconnect clutch, characterized in that when the heat engine enters a critical situation in which there is a risk of stalling during deceleration in an engaged gear, a first critical zone is determined in accordance with the speed of the heat engine (ω), in which first critical zone the actuator (16) is urged to release the engaged gear in order to prevent stalling, and a second critical zone is determined in accordance with the engine speed and the deceleration of the engine, in which second critical zone the engine stall is controlled by preventing the injection of fuel.