Closed-Circuit Swing Hydraulics for Reverse Lever Cavitation
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Solution Overview
Problem
In hydraulic closed-circuit systems of work machines like hydraulic excavators, reverse lever operation during swing deceleration can lead to negative pressures and cavitation due to the connection of the suction-side of the swing motor to the bidirectionally tiltable pump.
Innovation Solution
A work machine with a bidirectionally tiltable first hydraulic pump, a charge pump, and a supplementing valve device that controls the flow rate to prevent negative pressures by ensuring the delivery flow rate of the first hydraulic pump is lower than the pump flow rate during reverse lever operation, thereby preventing cavitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the suction-side of the swing motor is connected to the bidirectionally tiltable pump in a closed circuit, then energy regeneration is improved, but negative pressure and cavitation occur during reverse lever operation
Solution Approach 1:
A charge pump is introduced as an intermediary component between the swing motor and the bidirectionally tiltable pump. The charge pump supplies charge oil to the suction side of the swing motor, preventing negative pressure and cavitation while maintaining the closed circuit energy regeneration capability. This mediator resolves the contradiction by providing the necessary pressure support without disrupting the energy recovery function.
Solution Approach 2:
The charge pump proactively supplies charge oil to the swing motor suction side before negative pressure conditions develop during reverse lever operation. By performing this preliminary action, the system prevents cavitation from occurring in the first place, while still allowing the bidirectionally tiltable pump to regenerate energy during normal operation.
2Object-affected harmful factors
If the delivery flow rate of the first hydraulic pump is controlled to be lower than the pump flow rate, then negative pressure is prevented, but system productivity decreases
Solution Approach 1:
The charge pump acts as a mediator that compensates for the reduced delivery flow rate from the bidirectionally tiltable pump. By supplying additional charge oil, it ensures that the swing motor receives sufficient flow to maintain productivity while the bidirectionally tiltable pump operates at a lower flow rate to prevent negative pressure.
Solution Approach 2:
The hydraulic system is segmented into two independent flow paths: one through the bidirectionally tiltable pump for energy regeneration, and another through the charge pump for maintaining adequate flow rate. This segmentation allows each component to optimize its function without compromising the other, preventing negative pressure while maintaining productivity.
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
Prevents cavitation in the hydraulic closed-circuit system when reverse lever operation is performed during swing deceleration by maintaining a sufficient flow rate to avoid negative pressures.
Implementation Method 1
the first pump motor cannot singly regenerate the inertial energy that accompanies a swing
Implementation Method 2
there is a fear that the pressure of the suction-side of the bidirectionally tiltable pump becomes a negative pressure and that cavitation occurs
Implementation Method 3
a supplementing valve device that is provided between the two flow lines and the charge flow line and supplements a deficiency in a flow rate of the two flow lines with a flow from the charge flow line
Implementation Method 4
a swing-velocity sensor that senses a swing velocity of the upper swing structure
Data Source
AI summary
Provided is a work machine which makes it possible, in a hydraulic closed-circuit system, to prevent occurrence of cavitation when reverse lever operation which is an instruction for a swing in a direction opposite to a swing direction is performed during swing deceleration. A controller is configured to perform control such that a rate of a flow supplied from a bidirectionally tiltable hydraulic pump to a swing motor becomes lower than a pump flow rate according to an operation amount of the swing operation lever when a swing direction corresponding to a swing velocity sensed at a velocity sensor is different from a swing direction corresponding to operation of a swing operation lever.