Automatic Transmission Shift Control Thermal Load Prediction
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Solution Overview
Problem
Conventional automatic transmission systems prohibit shifts based solely on time, regardless of shift type and input torque, leading to excessive limitations on upshifts and downshifts, which results in deteriorated drivability, increased fuel consumption, and reduced driving performance, especially on uphill roads.
Innovation Solution
A shift control device and method that predicts the thermal load state of friction elements, allowing shifts in a modified mode with reduced heat generation or prohibiting shifts based on the type of shift and road gradient, setting different thermal states for upshifts and downshifts to prevent clutch burnout and optimize driving conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shift prohibition is determined solely by time elapsed since last shift, then friction element burnout is prevented, but drivability deteriorates and fuel consumption increases due to excessive shift limitations
Solution Approach 1:
The patent changes the parameter basis for shift prohibition from time-only to a comprehensive evaluation including thermal load state, shift type (upshift/downshift), and input torque. This allows the system to adapt the prohibition criteria dynamically, preventing burnout when thermal load is high while allowing necessary shifts when thermal load is low, thus resolving the contradiction between reliability and drivability
Solution Approach 2:
The system dynamically adjusts shift prohibition decisions based on real-time conditions including current thermal load state, predicted thermal load after shift, shift type, and input torque. This dynamic evaluation replaces the static time-based prohibition, enabling the system to optimize both friction element protection and driving performance adaptively
2Device complexity
If identical shift prohibition threshold is used for both upshifts and downshifts, then friction element protection is simplified, but fuel consumption increases due to excessive limitation of upshifts
Solution Approach 1:
The patent applies different thermal load thresholds and evaluation criteria for upshifts versus downshifts. Specifically, upshifts use a first threshold value while downshifts use a second threshold value, recognizing that upshifts generate less heat and are more critical for fuel economy. This differentiated approach resolves the contradiction by optimizing each shift type independently
3Device complexity
If shift prohibition is applied uniformly regardless of road gradient, then control logic is simplified, but driving performance deteriorates on uphill roads due to unnecessary downshift prohibitions
Solution Approach 1:
The system incorporates road gradient as an additional parameter in the shift prohibition evaluation. When uphill driving is detected, the system adjusts the thermal load thresholds and evaluation criteria to allow downshifts that would otherwise be prohibited, ensuring adequate driving force is available while still protecting friction elements through modified evaluation rather than uniform prohibition
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves drivability by allowing necessary shifts while preventing clutch burnout, reducing fuel consumption, and enhancing driving performance on uphill roads by tailoring shift permissions to the specific conditions of upshifts and downshifts.
Implementation Method 1
the same friction element is engaged and disengaged repeatedly over a long time period, and therefore a thermal load applied to the friction element increases (the temperature rises)
Data Source
AI summary
A shift control device comprises: a thermal load prediction unit which predicts a thermal load state of a friction element upon completion of a shift from a current thermal load state of the friction element; and a shift control unit which, when the thermal load state upon shift completion predicted by the thermal load prediction unit corresponds to a predetermined state, either performs the shift in a modified shift mode in which a heat generation amount of the friction element is smaller than the heat generation amount of the friction element when the predetermined state is not established, or prohibits the shift. The predetermined state is set at a different state in a case where the shift is an upshift and in a case where the shift is a downshift, and is set on the basis of a gradient of a traveling road.