Shift Control Device for Work Vehicle
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Solution Overview
Problem
The rapid decrease in engine rotation rate during forward-to-reverse switchover in work vehicles with stepped automatic transmissions can cause sudden changes in the turbine runner rotation, leading to shift shocks.
Innovation Solution
A control device that gradually decreases the engine rotation rate to a target lower limit value, with an initial adjustment to a predetermined rotation rate if necessary, to prevent reverse rotation of the turbine runner and ensure smooth clutch switching without shift shock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the accelerator pedal is released during forward-to-reverse switchover, then the vehicle speed is quickly reduced, but the engine rotation rate decreases rapidly causing turbine runner reverse rotation and shift shock
Solution Approach 1:
The control device performs preliminary action by detecting the forward-to-reverse switchover operation in advance and proactively controlling the engine rotation rate to maintain it above the target lower limit value during the switchover period. This prevents the turbine runner from reversing rotation before the switchover is complete, thereby avoiding shift shock while still achieving quick vehicle speed reduction.
Solution Approach 2:
The control device uses feedback by continuously monitoring the accelerator pedal operation quantity and engine rotation rate, then adjusting the engine rotation rate control based on this feedback. During forward-to-reverse switchover, the system feedback-controls the engine rotation rate to ensure it remains above the target lower limit value, preventing turbine runner reverse rotation and shift shock.
2Loss of time
If the engine rotation rate is immediately decreased to a low value during switchover, then the vehicle speed reduces quickly, but the turbine runner reverses rotation causing shift shock
Solution Approach 1:
The control device applies preliminary action by detecting the forward-to-reverse switchover operation in advance and proactively maintaining the engine rotation rate above the target lower limit value during the switchover period. This prevents turbine runner reverse rotation before it occurs, thereby avoiding shift shock while achieving quick vehicle speed reduction.
Solution Approach 2:
The control device uses feedback control by continuously monitoring the accelerator pedal operation quantity and engine rotation rate, then adjusting the engine rotation rate based on this feedback. During switchover, the system maintains engine rotation rate above the target lower limit value through feedback control, preventing harmful reverse rotation while minimizing switchover time.
3Object-affected harmful factors
If the engine rotation rate is controlled to decrease gradually to the target lower limit value, then shift shock is prevented, but the vehicle speed reduction may be slower
Solution Approach 1:
The control device performs preliminary action by detecting the forward-to-reverse switchover operation in advance and proactively controlling the engine rotation rate to maintain it above the target lower limit value during the critical switchover period. This prevents turbine runner reverse rotation and shift shock while still allowing for relatively quick vehicle speed reduction through coordinated clutch control.
Solution Approach 2:
The control device uses feedback control to continuously monitor the accelerator pedal operation quantity and engine rotation rate, then adjusts the engine rotation rate accordingly. During switchover, feedback control maintains the engine rotation rate above the target lower limit value, preventing shift shock while coordinating with clutch control to achieve efficient vehicle speed reduction.
Data Source
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AI summary
A shift control device for a work vehicle that has a stepped automatic transmission includes: a control device that controls an engine rotation rate at the work vehicle and the stepped automatic transmission; a forward/reverseswitchover member that outputs a forward/reverse switchover command for the work vehicle; and an operation quantity detection device that detects an accelerator pedal operation quantity in the work vehicle is operated. As the forward/reverse switchover command is output via the forward/reverse switchover member, the control device executes forward/reverse switchover control for the stepped automatic transmission and also controls the engine rotation rate so as to decrease the engine rotation rate gradually to a target lower limit value selected to ensure that a reverse rotation of a turbine runner at a torque converter in the work vehicle does not occur.