Hydraulic Drive Arrangement for Presses with Variable Displacement Pump
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Solution Overview
Problem
Existing hydraulic drive arrangements for large cylinders, particularly in presses, are costly due to the need for separate pump drive stations and expensive directional control valves, with inefficient utilization of drive torque as most applications require long rapid traverse paths with low load for a small proportion of the cycle time.
Innovation Solution
A hydraulic drive arrangement that delays the reduction in pump delivery flow using an externally controllable hydraulic or mechanical drive device, allowing for time-adjusted flow to match motor or converter utilization, potentially reversing pump direction without motor direction change, and utilizing asynchronous motors with frequency converters for improved torque management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If separate pump drive arrangements are provided for working stroke and return stroke, then rapid traverse in both directions is achieved, but construction costs increase due to expensive motors, converters, and directional control valves
Solution Approach 1:
The patent combines two separate pump drive arrangements into a single pump drive unit that can supply both the rapid traverse piston and the working piston. This is achieved by providing a single pump with variable displacement that can be controlled to deliver appropriate flow rates to different cylinder chambers, thereby reducing the number of motors and converters while maintaining bidirectional rapid traverse capability
Solution Approach 2:
The single pump drive arrangement is designed to perform multiple functions: it can rapidly fill both piston chambers for bidirectional rapid traverse, and it can also supply pressure medium to the working piston for the working stroke. The pump's variable displacement mechanism allows it to adapt its output to different operational requirements, making one drive unit serve the functions previously requiring two separate systems
2Reliability
If variable displacement pumps with hydromechanical torque regulation are used, then drive torque is kept constant, but the utilization of motor and converter is inefficient as torque is reduced during low-load phases
Solution Approach 1:
The patent replaces the static hydromechanical torque regulation with a dynamic control system that continuously monitors motor utilization and adjusts pump displacement accordingly. The control device receives signals about motor operating state and dynamically modifies the pump's delivery flow to match actual system needs, allowing the motor to operate at optimal utilization levels throughout the entire cycle rather than being constrained by fixed torque characteristics
Solution Approach 2:
The control system implements feedback by monitoring the motor's utilization factor and using this information to adjust pump displacement in real-time. The control device receives actual operating data from the motor and converter, compares it with optimal operating parameters, and automatically adjusts the pump's delivery flow to maintain optimal motor utilization, thereby improving energy efficiency while maintaining reliable drive torque when needed
3Reliability
If pump delivery flow is reduced by hydromechanical control, then drive torque is limited, but cycle time increases because flow reduction cannot be delayed to match motor utilization
Solution Approach 1:
The control system performs preliminary action by pre-calculating the optimal pump displacement settings based on the known press cycle profile. Before the motor reaches its thermal limits, the control device has already prepared the appropriate pump adjustment strategy, allowing the system to maintain high flow rates during low-load phases and only reduce displacement when absolutely necessary, thereby minimizing cycle time while still protecting the motor
Solution Approach 2:
The system uses real-time feedback from motor utilization monitoring to dynamically adjust pump displacement. Rather than pre-limiting flow through mechanical means, the control device continuously receives feedback about motor operating conditions and adjusts pump delivery flow moment-by-moment, allowing the system to extract maximum performance from the motor throughout the cycle and only reduce flow when motor utilization approaches critical levels
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 enhances motor and converter utilization, reduces cycle times, and allows for energy-optimal operating points, increasing machine safety by minimizing unwanted movements and eliminating the need for separate pump control and sensors, thus lowering costs.
Implementation Method 1
A pump arrangement 30 with a pump 31, 32, in particular a variable-displacement pump, for delivering a pressure medium to the piston chambers 23A, 23C
Implementation Method 2
The drive 33 can be designed as an asynchronous motor with a frequency converter 200
Data Source
AI summary
In the case of an, in particular, pressure-accumulator-free hydraulic drive arrangement (10) for and comprising a consumer, in particular for presses, having a double action piston/cylinder arrangement (20) which comprises at least one reversibly movable operating piston (21) and at least one cylinder chamber, in which the at least one cylinder chamber or the cylinder chambers comprises/comprise at least one first piston chamber (23A) which loads the operating piston (21) with fluid pressure and possibly at least one second piston chamber (23C), having pressure lines (D1,…) which supply the piston chambers with a pressure medium, having at least one pump arrangement (30; 30A, 30B) which has at least one pump (31; 32) which is driven at least in a variable-speed manner and at least one variable-speed drive (33) which drives the at least one pump (31, 32), having at least one pressure medium supply which is connected or can be connected hydraulically to the piston/cylinder arrangement (20) and the pump arrangement (30; 30A, 30B), in which the at least one pump (31) is connected or can be connected to the first piston chamber (23A) via a first pressure line (D1), with the result that the hydraulic drive arrangement (10) can both be operated in at least one movement direction by means of a single one-motor drive train and achieves high operating pressures in the operation, an improved load of the drive motor and as far as possible also of its inverter is achieved by way of at least in each case one hydromechanic actuating cylinder (51; 51 A) which has at least one pump (32), a hydraulic connection/connecting line (D1') which is active between the actuating cylinder (51; 51 A) and the pressure line (D1) which is provided between the at least one pump (32) and the piston chamber (23A) which is assigned to it, and at least one hydraulic valve, in particular a proportional valve (50; 50A), wherein the at least one hydraulic valve is hydraulically active in the at least one connecting line (D1') between the actuating cylinder (51; 51 A) and the pressure line (D1) in such a way that the actuating cylinder (51; 51 A) can be loaded with a variable pressure by way of a variation of the position of said hydraulic valve by means of an external, in particular electric actuating signal which influences the position of the hydraulic valve.