Limited Slip Differential Preload Control for Torque Bias Adjustment
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Solution Overview
Problem
Existing driveline components with limited slip differentials struggle to achieve torque bias ratios (TBR) that approach those of an open differential in both drive and coast conditions, due to limitations in clutch pack compression control and friction materials.
Innovation Solution
The driveline power transmitting device incorporates a differential case, gearset, clutch packs, pressure rings, preload springs, cams, and preload control mechanisms, allowing for adjustable preload forces by varying the width of the preload control mechanisms, enabling torque bias ratio adjustments between drive and coast conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a limited slip differential uses a mechanism for controlling or limiting the compression of the clutch pack(s) and/or using complex friction materials within the clutch pack(s) to provide different TBR's in the drive and coast conditions, then the torque bias ratio can be adjusted between drive and coast conditions, but the TBR cannot approach that of an open differential in one of the drive and coast directions
Solution Approach 1:
The patent applies dynamics by making the clutch pack compression state variable rather than fixed. The clutch packs can be in different compression states (high compression for limited slip, low compression for open differential behavior) depending on the operational mode. This is achieved through the cam mechanisms that dynamically adjust the preload on the clutch packs based on whether the differential is in drive or coast mode, allowing the TBR to approach open differential values when needed.
Solution Approach 2:
The patent changes the compression parameter of the clutch packs to achieve different TBR values. By varying the compression force applied to the clutch packs through the cam and follower mechanisms, the system can transition between high TBR (limited slip) and low TBR (open differential-like) conditions. This parameter change is controlled differently for drive and coast conditions, enabling the TBR to approach open differential performance in both directions.
2Adaptability or versatility
If the clutch packs are configured to provide different torque bias ratios in drive and coast conditions, then the differential can adapt to different drive conditions, but the mechanism cannot permit the TBR to approach that of an open differential
Solution Approach 1:
The patent segments the preload control into separate mechanisms for drive and coast conditions. Instead of a single complex control system, there are distinct cam mechanisms (first cam for drive condition, second cam for coast condition) that independently control the clutch pack compression for each operational mode. This segmentation simplifies the overall control strategy while achieving the desired adaptability, allowing each cam to be optimized for its specific condition without compromising the ability to approach open differential TBR.
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
This configuration allows for precise control of torque bias ratios, enabling the driveline to approach open differential performance in both drive and coast conditions, enhancing power transmission efficiency and flexibility.
Implementation Method 1
Each of the preload control mechanisms has a second cam, a second follower and a defeat spring. The defeat springs bias the second followers about the axis relative to the second cams such that the pressure rings are disposed in neutral positions in which a predetermined preload force is generated by each of the preload springs and transmitted to each of the clutch packs.
Implementation Method 2
When the pressure rings are disposed in the neutral positions and rotary power is transmitted through the differential gearset that causes the second followers to rotate about the axis in a second, opposite rotational direction relative to the second cams, the second followers and the second cams cooperate to reduce compression of the preload springs such that forces that are generated by the preload springs and exerted on the clutch packs are relatively lower than the predetermined preload force.
Data Source
AI summary
A driveline power transmitting device that includes a limited slip differential having a differential case, a cross-pin, a pair of pressure rings, a pair of clutch packs, a pair of preload springs, and a pair of preload control mechanisms. The pressure rings are non-rotatably coupled to the differential case and are disposed on opposite sides of the cross-pin. The preload springs bias the pressure rings toward the clutch packs and thereby preload the clutch packs. The pressure rings are urged axially away from the cross-pin to further compress the clutch packs in response to rotation of the cross-pin relative to the differential case. The preload control mechanisms are employed to decrease the preload force on the clutch packs in certain situations.