Forklift Free Lift Mast Hydraulic Sequencing
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Solution Overview
Problem
Existing forklift systems lack the capability for both free lift and negative lift, which limits their operational flexibility, especially in areas with limited overhead clearance and during piggyback transportation, as they require raising extensible mast members to lift loads, increasing the forklift's height and restricting usage.
Innovation Solution
The implementation of a hydraulic system with double-acting actuators and sequencing valves that allow for free lift by lifting the carriage without raising the extensible mast members and enable negative lift by preventing mast elevation when lowering the carriage, using a three-stage mast assembly with properly sized actuators and hydraulic circuits to manage pressure and actuator operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If extensible mast members are raised to lift the fork carriage, then the fork carriage can be elevated to insert forks into receivers on a hauling vehicle, but the height of the forklift is increased, limiting usefulness in areas with limited overhead clearance
Solution Approach 1:
The mast is divided into multiple telescopic sections (first, second, and third extensible mast members) that can be independently controlled. During free lift operation, only the carriage is elevated while the mast sections remain retracted. During negative lift for piggybacking, the mast sections are extended to provide the necessary elevation, separating the elevation function from the mast extension function.
Solution Approach 2:
The system dynamically adjusts the state of mast extension based on operational requirements. The hydraulic system can selectively extend or retract mast sections depending on whether free lift or negative lift is being performed, allowing the forklift to adapt its height profile to match the operational context and avoid overhead clearance issues during normal lifting operations.
2Adaptability or versatility
If a conventional mast lift system is used, then the forklift can lift loads, but it lacks the capability for both free lift and negative lift, reducing operational flexibility
Solution Approach 1:
The hydraulic system is designed to perform multiple functions through a unified architecture. The same hydraulic actuators and control system that manage normal lifting operations also control the telescopic mast sections to enable negative lift for piggyback transportation. This multi-functional design achieves operational versatility without requiring entirely separate systems for different operations.
Solution Approach 2:
The hydraulic system acts as an intermediary that coordinates the interaction between the carriage actuator and the mast lift actuators. By controlling the sequencing and coordination of these actuators, the system enables both free lift and negative lift operations through a single integrated control mechanism, managing complexity through centralized hydraulic control rather than multiple independent systems.
3Ease of operation
If the carriage is lowered without preventing mast elevation, then the carriage can be positioned, but the extensible mast members are raised unnecessarily, increasing height and reducing operational efficiency
Solution Approach 1:
The hydraulic control system incorporates feedback mechanisms that monitor the state of the mast sections and carriage position. This feedback enables the control system to detect when the carriage is being lowered and automatically coordinate the retraction of mast sections, preventing unnecessary mast extension and ensuring the mast returns to its retracted state, thereby avoiding time loss and unnecessary height increase.
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 solution enables the forklift to operate with free lift and negative lift capabilities, reducing height requirements and facilitating piggyback transportation by ensuring the carriage is lifted without extending the mast, thus improving operational efficiency and versatility.
Implementation Method 1
a hydraulic actuator mounted to an extensible mast member for positively lifting and lowering a fork carriage slideably mounted on the extensible mast member
Implementation Method 2
supply of fluid pressure in the first pressure supply line to first operate the paired pressure relief valves to raise the fork carriage on the extensible mast member to full extension
Data Source
AI summary
A multi-lift mast for a forklift has hydraulic circuitry that provides free lift and negative lift capabilities for the forklift. The mast comprises a stationary member, at least one extensible member slideable on the stationary member and a carriage slideable on an extensible member. The extensible mast members are raised and lowered by double acting hydraulic actuators extending between the stationary member and an extensible member. The carriage is raised and lowered by a positively connected double acting carriage hydraulic actuator extending between an extensible mast and the carriage. The circuitry employs identical pairs of counterbalance valves controlling the supply and exit of hydraulic fluid for the bore and rod ends of the actuators, set to cause the carriage to fully extend before the extensible mast members extend, providing free lift, and set to cause the extensible mast members to fully lower before the carriage lowers. The hydraulic circuitry prevents the extensible masts from rising when forks of an elevated carriage are inserted in receivers on a hauling vehicle and the circuitry is operated as if to lower the carriage, causing the carriage to pull up the extensible mast and so lift the forklift off the ground (negative lift) for piggybacking on the hauling vehicle.