Transfer Case Torque Control for Driveline Disconnect

Solution Overview

Problem

In vehicles with switchable drive modes, the secondary driveline disconnect devices fail to disengage when the transfer case clutch is disengaged, leading to increased frictional losses and fuel consumption due to 'pinch torque', where components like the propeller shaft, differential, and half shafts continue to spin in two-wheel drive mode.

Innovation Solution

A method involving a gradual reduction and then increase in transfer case torque output to ensure the driveline disconnect clutch disengages properly, using a brief ramp-up to release residual torque and allow free sliding, thereby reducing frictional drag and fuel consumption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the transfer case clutch is disengaged to switch to two-wheel drive mode, then fuel consumption is reduced and power distribution is optimized, but the secondary driveline disconnect devices fail to disengage causing increased frictional losses

Engineering Contradiction:

Improvefuel consumptionVSAvoidfrictional losses

Core Design Contradiction:

Use of energy by moving objectVSLoss of energy

Solution Approach 1:

The system applies a preliminary torque ramp-up action before attempting to disengage the secondary driveline disconnect. By temporarily increasing torque to a higher level and then reducing it, the system creates the necessary force differential to overcome residual friction and successfully disengage the disconnect devices, ensuring complete separation of the secondary driveline and eliminating parasitic frictional losses.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system dynamically adjusts torque levels during the disengagement process rather than maintaining a static torque level. By implementing a torque profile that ramps up to a higher level and then ramps down to a lower level, the system creates time-varying force conditions that enable the disconnect devices to overcome static friction and transition from engaged to disengaged state, ensuring complete driveline separation.

Inventive Principle:

Principle #15Dynamics

2Reliability

If the driveline disconnect devices remain engaged during two-wheel drive mode, then torque transmission is maintained, but components continue to spin causing increased fuel consumption

Engineering Contradiction:

Improvetorque transmissionVSAvoidfuel consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The system applies a preliminary torque ramp-up action before attempting to disengage the secondary driveline disconnect. By temporarily increasing torque to a higher level and then reducing it, the system creates the necessary force differential to overcome residual friction and successfully disengage the disconnect devices, ensuring complete separation of the secondary driveline and eliminating parasitic frictional losses.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the torque parameter dynamically during the disengagement process. By ramping the torque up to a higher level and then down to a lower level, the system creates varying torque conditions that enable the disconnect devices to overcome static friction and transition from engaged to disengaged state, ensuring complete driveline separation and eliminating unnecessary energy consumption.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If a simple torque reduction is applied to disengage the disconnect clutch, then the shifting process is simplified, but residual torque prevents proper disengagement

Engineering Contradiction:

Improveshifting processVSAvoiddisengagement completeness

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The system applies a preliminary torque ramp-up action before attempting to disengage the secondary driveline disconnect. By temporarily increasing torque to a higher level and then reducing it, the system creates the necessary force differential to overcome residual friction and successfully disengage the disconnect devices, ensuring complete separation of the secondary driveline and eliminating parasitic frictional losses.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system dynamically adjusts torque levels during the disengagement process rather than maintaining a static torque level. By implementing a torque profile that ramps up to a higher level and then ramps down to a lower level, the system creates time-varying force conditions that enable the disconnect devices to overcome static friction and transition from engaged to disengaged state, ensuring complete driveline separation.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS10144284B2Four-wheel drive vehicle control system and methods

Publication Date: 2018.12.04 WARN AUTOMOTIVE LLC

AI summary

Methods and systems are provided for operating a four-wheel drive powertrain of a vehicle. In one example, a method may comprise: in response to a desired shift from a four-wheel drive mode to a two wheel-drive mode: decreasing a transfer case torque output to a secondary driveline to a lower first level and disengaging a disconnect device of the secondary driveline; increasing the transfer case torque output from the lower first level to a higher second level over a duration; and after the duration, reducing the transfer case torque.