Forklift Drive Control Managing Load-Dependent Speed Limits
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Solution Overview
Problem
Conventional forklift driving stability is compromised due to sudden changes in load state, particularly when the fork height or tilt angle changes, leading to unstable acceleration and deceleration, as existing control methods do not account for changes in the contents of limitation during driving.
Innovation Solution
A drive control apparatus for a forklift that includes a load state determining section, a limitation contents determining section, and a control section, which adjusts engine speed based on detected load states to limit maximum vehicle speed and acceleration/deceleration, and selects appropriate limitation values to manage changes in load state, ensuring stable driving by regulating acceleration and deceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the fork height is lowered and the limitation on vehicle speed is cancelled, then the forklift can accelerate according to accelerator pedal depression, but this causes abrupt acceleration and unstable driving
Solution Approach 1:
The control apparatus dynamically adjusts acceleration/deceleration limitations based on the current load state. When the load state changes (e.g., fork height lowered), the system transitions from a limited to unlimited state, but maintains acceleration limitation for a predetermined period to prevent abrupt changes. This dynamic adjustment resolves the contradiction by allowing productivity improvement while temporarily maintaining stability control.
Solution Approach 2:
The control apparatus executes preliminary control by maintaining the old acceleration limitation value for a predetermined period after the load state changes. This preliminary action prevents abrupt acceleration before the new unlimited state is fully implemented, thereby resolving the contradiction between improved vehicle speed and driving stability.
2Adaptability or versatility
If the limitation contents are changed when the load state changes during driving, then the control adapts to new conditions, but this causes sudden changes in vehicle speed and unstable driving
Solution Approach 1:
The system implements dynamic control by detecting load state changes and transitioning between limited and unlimited states. However, it applies a transition period during which the old acceleration limitation is maintained, preventing sudden changes. This resolves the contradiction by allowing adaptability while smoothing the transition to maintain stability.
Solution Approach 2:
The control apparatus provides beforehand cushioning by maintaining the previous acceleration limitation for a predetermined period after load state changes. This cushioning effect prevents sudden speed changes during state transitions, resolving the contradiction between control adaptation and driving stability.
3Reliability
If the acceleration limitation is strictly enforced to maintain stability, then driving stability is improved, but this reduces the forklift's responsiveness to accelerator pedal input
Solution Approach 1:
The control apparatus dynamically adjusts acceleration limitation based on load state. When the forklift is in an unlimited state (light load or low fork height), the acceleration limitation is relaxed or removed, improving accelerator responsiveness. When in a limited state (heavy load or high fork height), strict limitation maintains stability. This resolves the contradiction by making the system responsive when safe and stable when necessary.
Solution Approach 2:
The system changes the acceleration limitation parameter based on detected load state. When load state changes occur, the system transitions between limited and unlimited states, adjusting the acceleration parameter accordingly. This parameter change allows the system to be responsive when conditions permit while maintaining stability when conditions require it.
Data Source
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AI summary
A drive control apparatus for a forklift. Based on the load state, it is determined whether to limit a maximum vehicle speed and an acceleration/deceleration during traveling of the forklift. Limitation contents regarding the maximum vehicle speed and the acceleration/deceleration is determined based on a determination result of whether to put the limitations. A speed of the engine is adjusted based on the determined limitation contents, thereby controlling driving of the forklift. When the determined limitation contents are changed, an acceleration/deceleration limitation value is selected from a plurality of acceleration/deceleration limitation values according to the pattern of the change of the limitation contents, and drive control related to the acceleration/deceleration is executed to limit the acceleration/deceleration of the forklift by using the selected acceleration/deceleration limitation value.