Work Vehicle Clutch Torque Restriction for Lug Down Prevention
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Solution Overview
Problem
In work vehicles like wheel loaders, the transition from backward to forward travel results in a phenomenon called 'lug down' due to inertial energy and hydraulic load, leading to a temporary drop in engine rotational speed, which existing technologies fail to effectively prevent, especially when using HMT or EMT systems.
Innovation Solution
A work vehicle equipped with a variable-capacity hydraulic pump, a clutch device for forward and backward travel, and a controller that restricts the maximum absorbing torque of the hydraulic pump when the travel direction changes, ensuring the clutch engagement states match the instructed travel direction, thereby minimizing the load on the engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the work vehicle transitions from backward travel to forward travel while the hydraulic pump is driving the work device (arm), then the engine receives a large load from both the inertial energy of travel switching and the hydraulic pump load, but this causes lug down phenomenon where engine rotational speed temporarily drops
Solution Approach 1:
The control device detects the engagement state of the clutch device before the travel direction switching occurs. When the clutch is in engagement state (indicating upcoming travel switching), the control device proactively restricts the maximum absorbing torque of the hydraulic pump to a lower value. This preliminary action prevents the lug down phenomenon by reducing hydraulic load before the inertial load from travel switching combines with it, thereby maintaining engine rotational speed stability while still allowing work device operation.
2Reliability
If the maximum absorbing torque of the hydraulic pump is restricted to prevent lug down, then engine rotational speed stability improves, but the work device operation capability may be reduced
Solution Approach 1:
The control device dynamically adjusts the maximum absorbing torque of the hydraulic pump based on the engagement state of the clutch device. When the clutch is disengaged (normal operation), the hydraulic pump can absorb maximum torque for full work device capability. When the clutch is engaged (travel switching anticipated), the maximum absorbing torque is temporarily restricted to a lower value. This dynamic adjustment resolves the contradiction by adapting the torque restriction to the actual operational context, maintaining both engine stability and work device capability when appropriate.
Solution Approach 2:
The control device changes the parameter of maximum absorbing torque of the hydraulic pump based on the clutch engagement state. By switching between two different torque restriction levels (normal maximum torque vs. restricted lower torque) according to the clutch state, the system optimizes the balance between preventing lug down and maintaining work device operation capability.
Data Source
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AI summary
The work vehicle includes: a clutch device including a forward-travel clutch and a backward-travel clutch configured to cause, when being in an engagement state, the work vehicle to travel in a forward travel direction and a backward travel direction; a forward-backward travel instruction device configured to instruct the work vehicle to travel in the forward travel direction or the backward travel direction; a clutch state detection device configured to detect whether the forward-travel clutch and the backward-travel clutch are each in the engagement state; and a torque restriction section configured to restrict a maximum absorbing torque of the hydraulic pump to be low when a restriction condition holds, the restriction condition including a condition that a traveling direction of the work vehicle, which corresponds to an engagement state of the clutch device, and a traveling direction of the work vehicle, which is instructed by the forward-backward travel instruction device are opposite to each other.