Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Reissue Patent
2000-02-07
2003-12-23
Lopez, F. Daniel (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
C091S448000, C091S455000
Reissue Patent
active
RE038355
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to electrohydraulic control devices for double-acting consumers.
The invention is based on an electrohydraulic control device for a double-acting consumer. One such electrohydraulic control device is already known from European Patent Disclosure EP 0 110 126 A1, in which to control a double-acting consumer a longitudinally movable control slide can be actuated for a 4/3-way function of two magnets disposed oppositely on the housing. To keep the leakage slight, each consumer connection is secured in the manner of a seat valve by a hydraulically controlled blocking valve. The pilot control of these blocking valves is performed by those tappets that transmit the switching motion of the magnets to the control slide. Along with the functions of raising, holding and lowering, a fourth, free-float position can additionally be attained by briefly exciting both magnets at the same time. Moreover, the control device can also be used to control a single-acting consumer. A disadvantage of this control device, however, is that it works with magnets that merely switch, so that sensitive, proportional volumetric flow control is not possible. Moreover, the embodiment of the tappet as pilot control member makes for a relatively complicated structural design. The disposition of the switching magnets on opposite sides of the housing, in combination with the 4/3-way longitudinal slide and the tappets used for pilot control makes for a very long structure in the slide axis, which makes the control device unfavorable for mobile use.
An electrohydraulic control device is also known from German Patent Disclosure DE 41 40 604 A1; it works with a proportional magnet and is suitable for fine control of volumetric flows. The pilot control valve member disposed in a main valve member is actuated by the proportional magnet and cooperates like a followup controller with the main valve member, so that short response times and hence good regulating behavior are attained. The valve members for the main and pilot control stages are embodied as seat valves, which keeps the leakage slight. The control device is also embodied such that there is no need for a separate control oil supply. An unfavorable aspect of this control device is that it can execute only a 2/2-way function and is therefore unsuitable in this form for controlling a double-acting consumer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electrohydraulic control device for a double-acting consumer of the above-described type which avoids the above-described disadvantages.
According to the invention the electrohydraulic control device for a double-acting consumer includes
a first and second consumer connection, a first and second work conduit communicating with the first and second consumer connection respectively and including first and second blocking valves for blocking the consumer connections, a first lowering conduit communicating with the second consumer connection and a second lowering conduit communicating with the first consumer connection, each lowering conduit by-passing the blocking valves; and
electromagnetically actuable control means for blocking or connecting at least one consumer connection, which comprises a first four-way, two-position proportional magnet valve and a second four-way, two-position proportional magnet valve identical to the first four-way, two position proportional magnet valve. Each magnet valve includes a slidable valve member provided with control edges and having an initial position in which the connected work conduit is relieved, an inlet connection, a return connection, a first motor connection alternatively connected to the inlet connection or the return connection by operation of the slidable valve member with the control edges, a second motor connection and valve seat means for controlling, e.g. closing, the second motor connection. The first motor connection of the first magnet valve communicates with the first work conduit and the first motor connection of the second magnet valve communicates with the second work conduit. The second motor connection of the first magnet valve is connected with the first lowering conduit and thus the second consumer connection and the second motor connection of the second magnet valve is connected with the second lowering conduit and thus the first consumer connection.
The electrohydraulic control device according to the invention has the advantage over the prior art that while having a proportional mode of operation, it can control a double-acting consumer with little leakage. The magnet valves, because of the slide drives chosen, enable short response times, which leads to good regulating performance of the control device. The control device can attain a total of four work positions with only two magnets, so that in additional to the usual functions of raising, holding and lowering, a fourth, free-float position is possible by exciting both magnets; the switching sequence is arbitrary. The control device functions without a separate control oil supply and can moreover be used for a single-acting consumer. The control device is also compact in structure and is therefore suitable for mobile applications.
In preferred embodiments of the control device according to the invention used for regulating volumetric flow in each magnet valve the second motor connection is blocked by the seat valve means and the inlet connection is blocked by the slidable valve control member in its initial position and the slidable valve control member has a work position in which the inlet connection communicates with the first motor connection and the second motor connection communicates with the return connection.
Advantageously each slidable valve control member comprises a longitudinally movable main control member and each magnet valve comprises a pilot-controlled valve including the main control member, a proportional magnet and a pilot control member actuable by the proportional magnet to cooperate with the main control member so as to act as a followup controller. The seat valve means includes a main valve cone disposed on the main control member for blocking the second motor connection and is connected in series with a fine-control edge provided on the main control member for communication with the return connection and the control edges are disposed on the main control member spatially separated from each other.
In a particularly preferred embodiment the main control member has a thickened end portion having an end face defining an end-face pressure chamber adjoining the main control member so that a pressure in this pressure chamber urges the main control member in a closing direction. The pilot-controlled valve includes means for relieving the end-face pressure chamber including a slide edge, a pilot control cone connected in series with the slide edge, the slide edge and pilot control cone begin provided on the pilot control member, and a spring arranged to urge the pilot control member in a direction toward the initial position and opposite to another direction of motion of the pilot control member caused by operation of the proportional magnet. The main control member advantageously has at least one differential face and the main control member is urged in an opening direction by a pressure at the second motor connection acting on the at least one differential face. The main control member has a second differential face and is positionable so that a pressure at the inlet connection acts on the second differential face urging the main control member in an opening direction and the pilot-controlled valve includes means for connecting the end-face pressure chamber with the second motor connection or the inlet connection so that the end-face pressure chamber is selectively acted on by a higher pressure at the second motor connection or the inlet connection, and the means for connecting includes check valves and inlet throttles.
The pilot-controlled valve is provided with a slide bore for the mai
Lopez F. Daniel
Robert & Bosch GmbH
Striker Michael J.
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