Hybrid Vehicle Torque Transition Lash Crossing Mitigation
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Solution Overview
Problem
Hybrid vehicles experience a torque disturbance known as lash crossing when transitioning from positive to negative torque, which is exacerbated by the higher magnitude of regenerative braking, leading to audible noise and discomfort for occupants.
Innovation Solution
A controller-managed method that quickly reduces powertrain torque to a small positive threshold, applies negative braking torque, and then rapidly decreases torque to a negative target value, while managing Regenerative Torque Limit and Net Wheel Torque Demand to mitigate lash crossing disturbances without delaying negative torque delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the rate of change of torque is limited to mitigate lash crossing disturbance, then audible noise and torque disturbance are reduced, but the magnitude of negative torque delivery is delayed
Solution Approach 1:
The torque transition is divided into three distinct phases: (1) rapid reduction from initial positive torque to small positive threshold, (2) controlled reduction through zero torque with friction brakes engaged, and (3) rapid reduction to final negative torque. This segmentation allows each phase to be optimized independently, minimizing both disturbance and delay.
Solution Approach 2:
Friction brakes are applied in advance during the second phase to ensure they are ready to provide immediate negative torque once the powertrain torque reaches the small negative threshold. This preliminary engagement of friction brakes prevents any gap in torque delivery.
2Productivity
If friction brakes are applied during torque transition, then negative torque is delivered more quickly, but driveline disturbance may increase
Solution Approach 1:
Friction brakes are pre-engaged during the second phase before full negative torque is required. This ensures the brakes are already positioned and ready to deliver torque immediately when the powertrain transition completes, eliminating delivery delay without causing disturbance during the transition itself.
Solution Approach 2:
The friction brake system acts as an intermediary between the powertrain and wheels during the torque transition. By coordinating brake application with the powertrain torque reduction phases, the system smoothly transfers the torque delivery function from the powertrain alone to a combined powertrain-brake system.
Data Source
AI summary
A method of operating a hybrid electric vehicle coordinates operation of an internal combustion engine, a motor, and friction brakes to mitigate a driveline lash crossing without delaying generation of negative torque. In response to a request to transition from positive torque to negative torque, the engine and motor are controlled to rapidly reduce powertrain torque to a small positive value, slowly reduce powertrain torque through the driveline lash zone, and then rapidly reduce powertrain torque to the target. To avoid delay, the friction brakes are applied in a coordinated manner to supply the negative torque during the transition.