Lockup Clutch Engagement Timing in CVT Upshift Control
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Solution Overview
Problem
In vehicles with a torque converter and continuously variable transmission, simultaneous execution of lockup engagement and upshifting due to an accelerator depression operation leads to increased differential rotational speed of the lockup clutch, prolonging the time required for lockup engagement completion.
Innovation Solution
The control method delays the start of upshift control until lockup engagement is complete, temporarily disengaging the lockup clutch upon detecting an upshift request, and fixes the transmission ratio during re-engagement to prevent turbine rotational speed decrease, thereby reducing the time needed for lockup engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If upshift control is executed simultaneously with lockup engagement control, then the transmission mechanism responds quickly to accelerator depression, but the differential rotational speed of the lockup clutch increases and lockup engagement time is prolonged
Solution Approach 1:
The control device delays the start of upshift control until after lockup engagement control is completed. This preliminary sequencing ensures that the lockup clutch engages first under optimal conditions (lower differential rotational speed), and only after this critical engagement phase is complete does the upshift control begin, thus preventing the prolongation of lockup engagement time while still achieving timely overall response
Solution Approach 2:
The control device dynamically adjusts the timing of upshift control based on the progress of lockup engagement control. By making the upshift control start timing dependent on the completion of lockup engagement, the system adapts its control sequence to the actual operational state, optimizing both response speed and engagement completion time under varying conditions
2Loss of energy
If the coasting shift line is set on the lower side of the driving shift ratio, then fuel consumption is reduced during coasting, but it causes frequent upshift requests during accelerator depression from coasting state
Solution Approach 1:
The control device delays upshift control until after lockup engagement is complete, which prevents the harmful interaction between simultaneous upshift and lockup engagement. This preliminary sequencing action allows the system to maintain the fuel-efficient coasting shift line setting while avoiding the problem of prolonged lockup engagement that would otherwise be caused by simultaneous upshift requests
Solution Approach 2:
The control device converts the potentially harmful effect of frequent upshift requests during accelerator depression from coasting state into a beneficial outcome. By delaying upshift control until lockup engagement is complete, the system allows these frequent upshift requests to occur without causing the harmful prolongation of lockup engagement time, thus maintaining both fuel efficiency and operational reliability
Data Source
Figure 1
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Figure 4
AI summary
To reduce the time required for lockup engagement to be completed, in a travel scenario in which simultaneous execution of lockup engagement and upshift is required. A vehicle comprises an engine as a drive source and a continuously variable transmission (6) provided with a torque converter (4) having a lockup clutch (3). In this engine-equipped vehicle, when simultaneous execution of an upshift of the continuously variable transmission (6) and a lockup engagement of the lockup clutch (3) is required in accordance with an accelerator depression operation, the LU engagement control of the lockup clutch (3) is started in accordance with an LU engagement request. On the other hand, the upshift control using the continuously variable transmission (6) places the starting of the control with respect to the upshift request on standby and cancels the standby when the LU engagement control of the lockup clutch (3) enters a lockup engagement completion region and starts the upshift control (delayed control).