Powertrain Gear Lash Management via Speed Profiling
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Solution Overview
Problem
In electrically-driven powertrain systems, torque reversals during gear lash events cause audible noises and physical jerks due to manufacturing clearances and thermal expansion, leading to undue stress on driveline components.
Innovation Solution
A powertrain system with a torque machine mechanically coupled to a drive wheel via a transfer gear set, where the gear set includes a first gear meshingly engaged to a second gear with a lash angle, and a control method to monitor output and wheel speeds, detect torque transitions, set an elapsed time for gear lash events, and adjust output speed to achieve a target profile that phase-shifts the lash angle from minimum to maximum, minimizing clunks and jerks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If gear lash clearance is maintained for assembly and thermal expansion, then ease of manufacture and component durability are improved, but audible noises and physical jerks occur during torque reversals
Solution Approach 1:
The control system detects impending torque reversals before they occur and pre-adjusts the output speed to minimize gear lash impacts. By anticipating the torque reversal event and preparing the system in advance, the control system eliminates the harmful clunks and jerks that would otherwise occur when gear lash is suddenly closed during the torque transition.
2Object-generated harmful factors
If gear lash clearance is reduced to minimize impacts, then audible noises and physical jerks are reduced, but assembly difficulty and thermal expansion accommodation worsen
Solution Approach 1:
Rather than physically reducing the gear lash clearance, the system dynamically changes the operational parameters by adjusting the output speed profile. The control system modifies the speed at which torque reversals occur, transforming the harmful mechanical impact into a controlled speed adjustment that eliminates noises and jerks while preserving the beneficial clearances for assembly and thermal expansion.
3Object-generated harmful factors
If output speed is adjusted to manage gear lash events, then audible noises and physical stress are reduced, but control complexity increases
Solution Approach 1:
The control system continuously monitors torque machine output speed, driveline state, and torque reversal conditions, using this feedback to dynamically adjust the output speed profile. This closed-loop feedback control enables the system to manage gear lash events effectively while maintaining relatively simple control logic that adapts to real-time operating conditions.
Data Source
AI summary
A powertrain system includes a torque machine mechanically rotatably coupled via a transfer gear set to a drive wheel. The transfer gear set includes a first gear meshingly engaged to a second gear with lash angle between the first and second gears. A method for operating the powertrain system includes monitoring an output speed associated with the torque machine and a wheel speed associated with the drive wheel. A transition between a first torque transfer state and a second torque transfer state is detected, the transition including a gear lash event across the transfer gear set. An elapsed time period for completing the gear lash event across the transfer gear set during the transition between the first torque transfer state and the second torque transfer state is set, and a target output speed derived from the wheel speed during and at the end of the elapsed time period is determined. A preferred output speed profile during the gear lash event is also determined, and includes prescribed changes in the output speed associated with phase-shifting the lash angle from a minimum lash angle to a maximum lash angle. The output speed is adjusted to be substantially equal to the target output speed at the end of the elapsed time period. The torque machine is controlled to achieve the preferred output speed profile.