Scissor Lift Electrohydraulic Drive for High Initial Force
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Solution Overview
Problem
Existing electrohydraulic drives for scissor lifts, particularly those used for vehicles up to 4.2 tons, face challenges in generating high initial forces efficiently due to unfavorable lever ratios, often requiring bulky mechanical solutions or two electric motors, which are costly and space-intensive.
Innovation Solution
A combination of a gear pump and a smaller electric motor controlled by a frequency converter allows for high output pressures at the beginning of the extension, enabling a soft start and rapid extension, while reducing the need for two electric motors and saving space and costs, with the frequency converter operating within safe power limits to increase torque and pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single electric motor is used to drive the hydraulic pump, then costs and space requirements are reduced, but the ability to generate high initial forces is insufficient due to unfavorable lever ratios
Solution Approach 1:
The patent applies dynamics by making the motor speed variable through a frequency converter. The system transitions from a static single-motor configuration to a dynamic control system where motor speed and pump delivery pressure are continuously adjusted based on the scissor lift's extension stage, enabling a single motor to generate variable forces that compensate for unfavorable lever ratios during initial extension.
Solution Approach 2:
The patent changes the operational parameters of the electric motor and hydraulic pump by controlling motor speed through a frequency converter. This allows the system to operate in different speed and pressure ranges: high speed/low pressure during full extension, and low speed/high pressure during initial extension, enabling a single motor to deliver the high initial forces previously requiring two motors.
2Force
If the electric motor is controlled to provide high output pressure at the beginning of extension, then high initial forces are achieved, but the motor may exceed safe power limits
Solution Approach 1:
The patent implements periodic action by dividing the scissor lift extension into distinct stages (initial extension with unfavorable lever ratios, middle extension, and final extension). The frequency converter adjusts motor speed and pump pressure according to the current stage, applying high pressure only during the initial extension phase when needed, and reducing pressure during subsequent phases, thereby preventing continuous excessive power consumption.
Solution Approach 2:
The system dynamically adjusts motor operating parameters based on the scissor lift's real-time position and load conditions. The frequency converter continuously monitors and modifies motor speed to keep power consumption within safe limits while delivering the necessary force, transitioning from static full-power operation to dynamic adaptive power control.
3Volume of moving object
If the scissor arms are almost parallel at the initial state, then the compact stowed position is achieved, but unfavorable lever ratios result in insufficient mechanical advantage for extension
Solution Approach 1:
The patent replaces the mechanical lever mechanism with a hydraulic force amplification system. Instead of relying on mechanical advantage from arm geometry, the system uses hydraulic pressure generated by the frequency-controlled pump to directly apply force to the scissor arms, compensating for the unfavorable lever ratios that result from the compact parallel stowed configuration.
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 configuration enables a scissor lift to raise loads from the lowest to the highest position in approximately 20 seconds, reducing overall costs and space requirements, as demonstrated by using a single 4 kW electric motor for a 4.2-ton lift.
Implementation Method 1
An electrohydraulic drive is provided to act on the or each hydraulic cylinder. Such a drive comprises at least one electric motor, at least one hydraulic pump
Implementation Method 2
the pump is driven and pumps hydraulic oil into the hydraulic cylinder, whereupon the latter extends and as a result the two associated scissor arms are pivoted
Data Source
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AI summary
The invention relates to a drive unit for a lifting platform, in particular a scissor lift, comprising a hydraulic circuit with at least one hydraulic pump supplying at least one working cylinder with hydraulic fluid, an electric motor for driving the at least one hydraulic pump, a frequency converter for controlling the electric motor, and a control device for controlling the frequency converter and therefore the speed of the electric motor, so that in a first range with a lower speed the electric motor is controlled in such a way that the at least one hydraulic pump extends the at least one working cylinder at a lower speed, and in a second range with a higher speed the electric motor is controlled in such a way that the at least one hydraulic pump extends the at least one working cylinder faster.The invention also relates to a scissor lift platform comprising such a drive unit, and to a method for operating a drive for a scissor lift platform.