Pumps – Motor driven – Relatively movable pumping members driven by relatively...
Reexamination Certificate
1998-09-25
2001-01-09
Yuen, Henry C. (Department: 3747)
Pumps
Motor driven
Relatively movable pumping members driven by relatively...
C417S344000, C417S345000
Reexamination Certificate
active
06171075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to a method and a device for controlling a thick matter pump having two conveying cylinders which are alternatingly operable by means of at least one hydraulic reversing pump and hydraulic drive cylinders driven thereby and which open into a material feed container with front face openings, and having a hydraulically actuatable pipe shunt which is disposed within the material feed container, the inlet side of which pipe shunt is adapted to be alternatingly coupled to the openings of the conveying cylinders, thereby vacating the respective other opening, and the outlet side of which pipe shunt is adapted to be connected to a conveying line, wherein a switching operation of the pipe shunt is effected upon ending a feed stroke in the conveying cylinders, wherein the drive cylinders are hydraulically connected at their one end to a respective port of the reversing pump under formation of a closed hydraulic circuit and at their other end to each other by way of an oscillating oil line, and wherein pressure oil is taken off directly from hydraulic lines which lead from the reversing pump to the drive cylinders in order to effect the switching of the pipe shunt.
2. Description of the Related Art
A method for controlling a two-cylinder thick matter pump of this kind is known (EP-B 0 446 206), wherein at the end of each pressure stroke in the conveying cylinders a switching process of the pipe shunt is effected, in which the pistons of the drive cylinders are held in their end position under the action of the pressure created by the reversing pump in the main circuit and the feed direction of the reversing pump is reversed only after finishing the switching process of the pipe shunt. When triggering the switching process of the pipe shunt, the feed quantity and/or the feed pressure of the reversing pump may be varied while keeping the feed direction constant. The switching of the pipe shunt is effected solely by means of a directional valve which is switched over while the reversing pump is still operated in the previous feed direction. This results in an undesireably hard start-up during the switching of the pipe shunt.
SUMMARY OF THE INVENTION
Based on this it is the object of the invention to develop a method and a device for controlling a thick matter pump of the type described above, in which a soft start-up during the switching of the pipe shunt is achieved using a circuit as simple as possible.
With the measures according to the invention it is achieved that the drive cylinders and the pipe shunt switching members operate in a single-circuit system, it still being possible to subject the drive cylinders to pressure oil in the free flow. This means that for the switching of the pipe shunt pressure oil is directly taken from a main circuit leading from the reversing pump to the drive cylinders. A particular aspect of the invention is that the pipe shunt is controlled with the aid of the switching reversing pump. This results in a soft start-up.
In order to prevent an unwanted reverse feed into the material feed container during the switching of the pipe shunt, the reversing pump is switched under reversal of through flow and reversing of the pipe shunt when the pistons of the drive cylinders reach their end positions, and the oscillating oil line is closed off at least momentarily during the switching of the reversing pump. Expediently, the oscillating oil line is closed off when the switching reversing pump is passing through a neutral position or with a time delay thereafter until the pipe shunt is fully switched. In principle it is also possible to open the closed oscillating oil line before the pipe shunt has been fully switched. In this latter case, the material to be conveyed is precompressed somewhat within the conveying cylinder, before the actual onset of the conveying process through the pipe shunt and the conveying line.
According to a second variant of the invention at least two reversing pumps connected in parallel are provided, which are switched under flow reversal when pistons of the drive cylinders reach their end positions, wherein during the switching at least one of the reversing pumps is closed off with respect to the drive cylinders under switching of the pipe shunt and at least one further reversing pump is closed off with respect to actuating members of the pipe shunt under switching of the drive cylinders. In order to synchronize the switching of the pipe shunt and the starting of the material conveying while precompressing the material in the conveying cylinder, the reversing pump which is closed off with respect to the pipe shunt can be switched time-delayed and/or choked relative to the reversing pump which is closed off with respect to the drive cylinders.
In both embodiments it can be of advantage when the feed quantity and/or the feed pressure of the reversing pump is varied during the switching of the pipe shunt as compared to the conveying operation. Furthermore, when feed quantity is modulated during the switching of the pipe shunt, for example starting with a small quantity (slow), then changing to a larger quatity (fast) and back again to a small quantity (slow), an especially soft yet quick switching can be achieved.
In a device for implementing the method according to the invention, the flow reversal of the reversing pump is effected in a first variant of the invention by means of the end position signals of the drive cylinders, and a stop valve which is adapted to be controlled by the end position signals of the drive cylinders and which can be controlled time-delayed, if needed, is disposed in the oscillating oil line.
In the case of the second variant of the invention at least two reversing pumps are disposed in the hydraulic lines of the hydraulic circuit, which are connected in parallel and which are adapted to be switched by means of the end position signals of the drive cylinders, of which at least one reversing pump is connected directly to the drive cylinders and at least one further reversing pump is connected indirectly to the drive cylinders by way of stop valves which each are adapted to be controlled by the end position signals, and the actuating members of the pipe shunt are connected to the hydraulic lines of the hydraulic circuit in a region between the first reversing pump and the corresponding stop valves.
REFERENCES:
patent: 5238371 (1993-08-01), Benckert
patent: 5316453 (1994-05-01), Schwing
patent: 5344290 (1994-09-01), Benckert
patent: 5458470 (1995-10-01), Mannhart et al.
patent: 32 43 576 A1 (1984-05-01), None
patent: 38 40 892 A1 (1990-06-01), None
JP 57-102579 A. In: Patents Abstracts of Japan, M-161, Oct. 5, 1982, vol. 6, No. 196.
M{umlaut over (u)}nzenmaier Werner
Schnitzler Christof
Castro Arnold
Pendorf & Cutliff
Putzmeister AG
Yuen Henry C.
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