Engine Torque Truncation for Transfer Case Clutch Slip
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Solution Overview
Problem
In four-wheel drive vehicles, the existing torque transfer cases can experience clutch slip and potential damage due to uneven traction wheel loads, particularly in off-road or winter conditions, leading to clutch failure and packaging constraints that make it difficult to accommodate peak torque requirements.
Innovation Solution
An engine torque truncation strategy that uses a friction clutch activated by an electromagnetic actuator, with a control algorithm to detect and mitigate clutch slip conditions by reducing engine torque and disabling the friction clutch if necessary, allowing the vehicle to operate in two-wheel drive mode to prevent damage, and strategically sizing the transfer case to use smaller, lighter components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the friction clutch is designed with sufficient capacity to effect a positive lock between the driveshafts under all four-wheel driving conditions, then the reliability of the clutch is improved, but the packaging constraints and device complexity are worsened
Solution Approach 1:
The patent changes the operational parameters of the clutch system by introducing controlled slip conditions through engine torque truncation. Instead of designing for 100% locking reliability under all conditions, the system accepts controlled slip (parameter change in clutch engagement state) and compensates through torque management, simplifying the clutch geometry while maintaining overall system reliability
Solution Approach 2:
The patent converts the potentially harmful clutch slip condition into a beneficial control mechanism. By intentionally allowing slip under specific conditions and using engine torque truncation to manage it, the system transforms what was previously a failure mode into a controllable operational state that simplifies clutch design
2Strength
If the transfer case is sized to accommodate the peak torque associated with a locked up friction clutch, then the strength of the torque transmitting components is improved, but the weight and cost of the components are worsened
Solution Approach 1:
The patent changes the torque parameter profile by implementing engine torque truncation that prevents the clutch from experiencing peak locked-up torque conditions. This reduces the maximum torque the transfer case components must withstand, allowing for lighter component design while maintaining safety through controlled torque management
Solution Approach 2:
The patent applies beforehand cushioning by using the engine control system to preemptively limit torque before it can reach damaging levels. The torque truncation acts as a protective buffer that prevents peak torque conditions from occurring, allowing the transfer case to be designed for lower, more manageable torque levels
3Power
If the friction clutch is designed for maximum torque transmitting capacity, then the power transmission capability is improved, but the ease of manufacture is worsened
Solution Approach 1:
The patent changes the operational torque parameter by implementing truncation control that keeps the clutch operating below its maximum capacity. This allows the clutch to be manufactured with simpler, more cost-effective components that don't need to handle extreme peak loads, while the control system ensures adequate power transmission within the reduced capacity range
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 effectively prevents clutch slip and damage by reducing engine torque during potentially damaging conditions and enables the vehicle to operate within safe torque limits, maintaining performance while reducing component stress and cost.
Implementation Method 1
The friction clutch is activated by an electromagnetic actuator
Implementation Method 2
a friction clutch with torque input friction elements connected driveably to one driving axle and companion torque output friction elements connected driveably to the other driving axle
Data Source
AI summary
A four wheel drive powertrain control for an automotive vehicle is disclosed. It includes a torque transfer case that distributes power from an engine-powered transfer case mainshaft to a secondary driving axle through a friction clutch as power is distributed directly from the engine-powered mainshaft to a primary driving axle. The friction clutch capacity is sufficient to mechanically lock the transfer case in a four wheel drive mode. If the clutch torque capacity is exceeded, a control algorithm will strategically ramp down engine torque requests by a powertrain controller to eliminate clutch slip.