Servo-Assisted Transmission Downshift Scheduling for Braking Stability
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Solution Overview
Problem
In vehicles with dual-clutch, servo-assisted transmissions, automatic gear shifting during slowing down can cause the internal combustion engine to run too slowly, leading to operation irregularities and discomfort due to insufficient time for downshifts, especially when the driver brakes suddenly.
Innovation Solution
A method where the control unit of the drivetrain calculates the necessary downshifts and schedules them to prevent the engine speed from falling below a threshold by transitioning to a lower gear, such as the second gear, within a calculated opening time interval, allowing for multiple downshifts if necessary, to maintain engine speed above the threshold and ensure comfortable braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the drivetrain operates in automatic mode with moderate speed and uses high gears to minimize fuel consumption, then fuel efficiency is improved, but when the driver brakes suddenly, the engine speed may fall below the lower threshold causing operation irregularities
Solution Approach 1:
The control unit calculates in advance the opening time interval required for the clutch to fully open and schedules multiple downshifts to occur before the engine speed falls below the lower threshold. This preliminary scheduling ensures that gear transitions are completed proactively, preventing engine operation irregularities during sudden braking while maintaining fuel efficiency during normal operation.
2Reliability
If the control unit speeds up downshifts to prevent engine from running too slowly, then engine speed stability is improved, but impulsive longitudinal accelerations occur reducing driving comfort
Solution Approach 1:
The control unit dynamically schedules multiple downshifts within the calculated opening time interval, allowing gear transitions to occur at optimized moments rather than forcing a single rapid downshift. This dynamic approach distributes the speed adjustments over time, maintaining engine speed stability while avoiding impulsive longitudinal accelerations that would reduce driving comfort.
3Loss of time
If multiple downshifts are scheduled within the opening time interval, then timely gear transitions are achieved, but the complexity of control logic increases
Solution Approach 1:
The control unit segments the gear transition process into multiple discrete downshifts scheduled within the opening time interval, rather than attempting to execute a single complex downshift. This segmentation of the control strategy simplifies the implementation by breaking down the timing problem into manageable individual gear transitions, reducing overall control complexity while achieving timely response.
Data Source
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AI summary
A method to control a road vehicle (1) provided with a servo-assisted transmission (7) during a slowing down phase; the control method comprises, when the servo-assisted transmission (7) is in an automatic operating mode, the steps of: calculating, assuming that a pressing of the brake pedal (23) remains constant, an opening time interval needed to allow the road vehicle (1) to reach an opening speed at which a clutch (16) of the servo-assisted transmission (7) is definitively opened; calculating a number of downshifts that can be carried out in the opening time interval based on a time needed to carry out a downshift; scheduling the downshifts to be carried out in order to get from the current gear engaged in the servo-assisted transmission (7) to an opening gear with which the clutch (16) of the servo-assisted transmission (7) is definitively opened, so as to carry out no more than the number of downshifts that can be carried out in the opening time interval; and carrying out the scheduled downshifts.