Forklift Lift Hydraulics With Switchable Lowering Speed Bypass
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Solution Overview
Problem
Industrial trucks face limitations in handling capacity due to the reliance on sensor devices for maintaining the maximum permissible lowering speed of 0.6 m/s, which requires high reliability and results in increased construction costs and potential operational disruptions if the sensor fails.
Innovation Solution
A three-port, two-position switching valve is introduced in the hydraulic system, allowing for electronic and spring-actuated control to activate or deactivate the discharge flow control valve, ensuring compliance with the 0.6 m/s speed limit even if the sensor device fails, and enabling higher lowering speeds when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flow control valve is provided in the reservoir line to limit the maximum lowering speed to 0.6 m/s, then the lowering speed compliance with legal limits is ensured, but the handling performance and productivity of the industrial truck deteriorates due to significantly reduced lowering speeds
Solution Approach 1:
The system dynamically switches between two operating modes: a first mode where the drain flow control valve limits lowering speed to comply with legal limits, and a second mode where the switching valve bypasses the drain flow control valve to enable faster lowering. This dynamic adaptation allows the system to optimize between safety compliance and productivity based on operational requirements.
Solution Approach 2:
The system changes the flow control parameter by switching the position of the switching valve. In the first position, the drain flow control valve is activated to maintain maximum lowering speed at 0.6 m/s. In the second position, the drain flow control valve is deactivated allowing higher lowering speeds, thus changing the system parameter to adapt to different operational needs.
2Measurement precision
If sensor devices are used to maintain the maximum permissible lowering speed, then the lowering speed control precision is improved, but the construction costs and device complexity increases
Solution Approach 1:
The invention extracts the speed control function from the sensor-based electronic control system and implements it through the mechanical/hydraulic drain flow control valve. By removing the dependency on sensor devices and electronic control, the system achieves speed limitation through passive hydraulic resistance, thereby reducing device complexity and construction costs while maintaining control precision.
Solution Approach 2:
The drain flow control valve provides self-regulating speed control through its inherent flow resistance characteristics. The valve automatically limits the lowering speed based on the hydraulic circuit configuration without requiring external sensing or active control, making the system self-regulating and reducing dependency on complex sensor devices.
3Adaptability or versatility
If a drain flow control valve is arranged in the container line with a switching valve, then the versatility of the hydraulic system is improved by enabling both speed-limited and high-speed lowering, but the device complexity increases
Solution Approach 1:
The switching valve serves multiple functions: it controls the activation/deactivation of the drain flow control valve, enables switching between compliance mode and high-performance mode, and provides a bypass path for the hydraulic fluid. This multi-functionality justifies the added complexity by providing versatile operational capabilities from a single component.
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 allows for continued operation of industrial trucks at the required speed limit without a functional sensor, enhancing handling capacity and reducing the reliability requirements and costs associated with sensor devices, while maintaining safety and efficiency.
Implementation Method 1
a hydraulic lifting cylinder assembly (11) is provided for raising and lowering the load-handling element (3)
Implementation Method 2
in the lowering operation of the lifting cylinder device, the pressure medium flow flows from the lifting cylinder device to the container via the drain flow control valve arranged in the container line
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a forklift truck with a lifting device (1) which has a load handling device (3) arranged on a lifting frame (2) that can be raised and lowered, wherein a hydraulic lifting cylinder device (11; 11a, 11b) is provided for raising and lowering the load handling device (3), which can be actuated by means of a control valve device (12), wherein the control valve device (12) is connected to a pressure medium line (19) leading to the lifting cylinder device (11; 11a, 11b) and to a container line (18) leading to a container (17), and wherein the control valve device (12) has a lowering position (13c) in which the pressure medium line (19) is connected to the container line (18), wherein a drain flow control valve (30) is arranged in the container line (18).In the container line (18) between the control valve assembly (12) and the outlet flow control valve (30) a switching valve (45) is arranged, which in a first switching position (45a) activates the outlet flow control valve (30) arranged in the container line (18) and which in a second switching position (45b) deactivates the outlet flow control valve (30) arranged in the container line (18), so that in lowering operation of the lifting cylinder assembly (11; 11a, 11b) the pressure medium flow bypasses the outlet flow control valve (30) arranged in the container line (18) and flows from the lifting cylinder assembly (11; 11a, 11b) to the container (17).