Two-Speed Transmission Shifting via Predictive Speed Synchronization
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Solution Overview
Problem
Off-highway battery electric vehicles face challenges in shifting two-speed transmissions due to large speed gaps between transmission shafts, leading to extended shift times and degraded drivability, as electric machines operate at high speeds, making synchronization difficult for synchronizers.
Innovation Solution
An electric propulsion system with a step gear ratio transmission, shifter actuator, and controllers that estimate the time for differential speed synchronization between transmission shafts, allowing smooth engagement of dog clutches by synchronizing rotational speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a two-speed transmission is installed to expand operating range, then the vehicle can operate at higher speeds and generate sufficient torque, but the large speed gap between transmission shafts makes synchronization difficult and extends shift time
Solution Approach 1:
The control system predicts the time required for speed synchronization before the shift is initiated. This allows the shifter actuator to be controlled in advance to complete the gear engagement exactly when the speed differential becomes acceptable, rather than reacting after the synchronization process has already begun. The predictive timing enables coordinated action between speed equalization and mechanical engagement.
Solution Approach 2:
The system continuously monitors the rotational speeds of the input and output shafts and uses this feedback to determine when the speed differential has reached an acceptable level. This real-time feedback allows the control system to know precisely when the synchronization condition is met and when to trigger the shifter actuator to complete the gear change.
2Adaptability or versatility
If a two-speed transmission is installed to expand operating range, then the vehicle can operate at higher speeds and generate sufficient torque, but the large speed gap between transmission shafts degrades drivability
Solution Approach 1:
The system performs speed synchronization as a preliminary action before the actual gear engagement occurs. By ensuring the shaft speeds are equalized beforehand, the mechanical engagement of the dog clutch happens under optimal conditions with minimal speed differential, resulting in smooth transitions and improved drivability.
Solution Approach 2:
The control system uses feedback from speed sensors to continuously monitor the synchronization process and determine when the speed differential has reached an acceptable threshold. This feedback mechanism ensures that gear changes are executed at the optimal moment, preventing harsh engagements and maintaining smooth drivability throughout the transition.
3Device complexity
If traditional shifter control is used without speed synchronization estimation, then the system is simpler, but the dog clutch may engage with speed differential causing shift shock and increased wear
Solution Approach 1:
The system performs speed synchronization as a preliminary action before the actual gear engagement occurs. By ensuring the shaft speeds are equalized beforehand, the mechanical engagement of the dog clutch happens under optimal conditions with minimal speed differential, resulting in smooth transitions and improved drivability.
Solution Approach 2:
The control system uses feedback from speed sensors to continuously monitor the synchronization process and determine when the speed differential has reached an acceptable threshold. This feedback mechanism ensures that gear changes are executed at the optimal moment, preventing harsh engagements and maintaining smooth drivability throughout the transition.
Data Source
AI summary
Methods and systems for shifting a transmission that includes a dog clutch are described. In one example, the transmission may be coupled to an electric machine and a rotational speed of the electric machine may be adjusted to reduce a speed differential between rotating transmission components. A position of a shifter actuator may be adjusted according to an estimate of when the speed differential is equal to a predetermined value.