Emergency Lowering Circuit for Cranes and Excavators Under Overvoltage
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Solution Overview
Problem
Existing emergency lowering systems in cranes and excavators face damage to components due to overvoltage when the energy storage device in the DC intermediate circuit malfunctions, necessitating additional components like braking resistors or brake choppers, or incurring damage to holding brakes.
Innovation Solution
A device that utilizes a primary energy source to absorb energy generated during emergency lowering, convert kinetic energy into electrical energy, and supply necessary energy to holding brakes, eliminating the need for additional components and protecting the machine from overvoltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an energy storage device is provided in the DC intermediate circuit to enable emergency lowering, then the machine can safely lower loads during emergencies, but the system becomes vulnerable to overvoltage damage when the energy storage device fails
Solution Approach 1:
The patent introduces a voltage limiting device as an intermediary component between the electric drive and the DC intermediate circuit. This device mediates the energy flow during emergency lowering by limiting the voltage that can be fed back into the DC intermediate circuit, thereby protecting the system from overvoltage damage when the energy storage device fails. The voltage limiting device acts as a buffer that allows emergency lowering to proceed safely without requiring the energy storage device to be fully functional.
2Object-affected harmful factors
If braking resistors or brake choppers are added to prevent overvoltage damage during emergency lowering, then component damage is prevented, but the device complexity increases
Solution Approach 1:
The voltage limiting device is designed to perform multiple functions: it limits voltage during emergency lowering to prevent overvoltage damage, and it can also operate normally when the energy storage device is functional. This multi-functionality reduces the need for separate protective components like dedicated braking resistors or brake choppers, thereby limiting the increase in device complexity while still providing overvoltage protection.
3Reliability
If the holding brake is used for braking during emergency lowering, then the component can be secured, but severe damage occurs to the holding brake and interacting components
Solution Approach 1:
The patent extracts the braking function from the holding brake during emergency lowering operations. By using the electric drive in generator mode to provide controlled braking through regenerative braking, the holding brake is removed from the high-stress braking operation. This separation allows the holding brake to retain its original function of securing components without suffering severe damage from emergency braking operations.
4Object-affected harmful factors
If additional components like braking resistors are provided to handle energy during emergency lowering, then overvoltage is prevented, but the ease of operation and maintenance deteriorates
Solution Approach 1:
The voltage limiting device is designed to automatically regulate voltage during emergency lowering without requiring manual intervention or complex control systems. The device self-adjusts to limit voltage feedback into the DC intermediate circuit, eliminating the need for operators to manually activate braking resistors or manage complex energy dissipation systems. This automation maintains ease of operation while providing overvoltage protection.
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
Enables safe emergency lowering without additional components, allowing the machine to resume operation after rectifying the fault without further servicing.
Implementation Method 1
the at least one electric drive is designed to convert the kinetic energy generated thereby into electrical energy and feed it into the intermediate circuit
Implementation Method 2
the primary energy source is designed to absorb the energy fed into the intermediate circuit by the electric drive
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a working machine, in particular a crane or excavator, comprising a primary energy source for feeding electrical energy into an intermediate circuit, a unit for performing an operation of the working machine, at least one electric drive connected to the intermediate circuit to operate the unit of the working machine, a holding brake for locking or releasing the unit, and an energy storage device connected to the intermediate circuit to provide electrical energy requested from the intermediate circuit when a unit is actuated and/or to absorb electrical energy fed into the intermediate circuit, wherein in the event of an emergency lowering of the unit, the at least one electric drive is designed to convert the kinetic energy generated thereby into electrical energy and feed it into the intermediate circuit.where, in the event of a simultaneous unavailability or failure of the energy storage system during emergency lowering, the primary energy source is designed to absorb the energy fed into the intermediate circuit by the electric drive.