Kick-down Shift Control Device for Electric Vehicle Torque Management
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Solution Overview
Problem
During kick-down shifts in electric vehicles, the motor torque controlled based on accelerator pedal depression and motor rotation speed is reduced due to transmission friction element slippage, leading to inadequate vehicle acceleration and delayed response, exacerbated by the electric motor's torque characteristics which decrease with increased rotation speed.
Innovation Solution
A kick-down shift control device that restricts the upper limit of motor torque during the inertia phase of the shift, preventing torque drop as rotation speed increases, by setting a motor torque limit that ensures consistent torque transmission to the wheels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If general motor control is used to attain target motor torque based on motor rotation speed and accelerator pedal depression during kick-down shift, then the motor torque control follows standard characteristics, but the motor torque is reduced by transmission friction element slippage and cannot be fully transmitted to driving wheels during shift time
Solution Approach 1:
The control device performs preliminary action by detecting the start of kick-down shift in advance and proactively restricting motor torque before slippage occurs. The shift detection unit detects shift start based on transmission friction element status, and the restriction control unit immediately limits motor torque to prevent torque loss during the shift process, ensuring reliable torque transmission from the beginning of the shift operation.
Solution Approach 2:
The control system implements feedback by continuously monitoring transmission friction element engagement status through the shift detection unit. Based on this feedback information about whether a kick-down shift is occurring, the restriction control unit dynamically adjusts motor torque output - restricting torque when shift is detected and allowing normal torque when no shift is occurring, thereby optimizing both torque transmission reliability and acceleration response.
2Speed
If motor torque is increased in response to accelerator pedal depression to provide desired driving force, then acceleration response should improve, but motor rotation speed increases during inertia phase causing outputtable maximum motor torque to decrease
Solution Approach 1:
The control device applies preliminary anti-action by restricting motor torque in advance during the inertia phase of kick-down shift. Since increasing motor rotation speed during this phase would naturally reduce outputtable maximum motor torque due to motor characteristics, the restriction control proactively limits torque increase to counteract this effect, preventing torque drop and maintaining acceleration performance throughout the shift process.
3Adaptability or versatility
If transmission friction elements are changed between engagement and release during shift operation, then gear stage changeover is achieved, but a predetermined shift time is required causing delay in acceleration response
Solution Approach 1:
The control system performs preliminary action by detecting the start of kick-down shift based on transmission friction element status changes and immediately restricting motor torque before the shift completes. This proactive approach ensures that torque is stabilized during the entire shift duration, preventing torque loss and minimizing the impact of shift time on acceleration response.
4Force
If kick-down shift is executed to downshift to low-side gear ratio for large torque requirement, then driving force should increase, but input rotation speed of automatic transmission increases causing motor rotation speed to increase and maximum motor torque to decrease
Solution Approach 1:
The control device applies preliminary anti-action during kick-down shift by restricting motor torque to counteract the natural torque reduction caused by increasing motor rotation speed. The restriction control unit detects the inertia phase and proactively limits torque increase, preventing the torque drop that would otherwise occur due to motor characteristics during downshift, thereby maintaining driving force throughout the shift operation.
Data Source
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AI summary
By increasing accelerator opening APO from time t1 as shown in the drawing, kick-down shift is started at time t2. While the kick-down shift is carried out by changeover from a release element (direct clutch D/C) to an engagement element (high and low reverse clutch H&LR/C), a motor torque tTm that is increased as Tmo with an increase in accelerator opening APO is restricted as follows. In a shift initial stage from time t2 to inertia phase start time t3, motor torque tTm is restricted so as not to exceed upper limit value Tlimit (=Tmo2-Tip) obtained by subtracting an inertia phase progressing torque increment Tip from an inertia phase end outputtable maximum motor torque Tmo2 that is outputtable with motor rotation speed Nmo2 at inertia phase end time t4. During an inertia phase (t3-t4), the motor torque tTm is restricted to a value Tlimit+Tip (a value equal to Tmo2).