The invention relates to a pressure retaining valve having at least one main control piston, which is guided longitudinally displaceably in a single-piece or multiple-piece valve housing and a non-return piston, wherein, in switching positions, in the form of
Pressure retaining valves of this type are prior art. In conjunction with hydraulic actuators in the form of load-lifting power cylinders, such valves also are referred to as counterbalance valves in technical terminology. Load-lifting power cylinders are frequently used in tools and equipment, also in the form of mobile devices such as excavators, forklifts and the like. Typically in such cases, an operator can control the pressure retaining valve by manual actuation of a control valve device. To prevent operating errors on the part of the staff in doing so, and preclude resulting hazards for both the equipment as well as for persons to the extent possible, due care shall be taken to ensure that the handling operations for the staff are simple and clear.
In view of these problems, the invention addresses the problem of providing a pressure retaining valve, for which the risk of incorrect operation and resulting malfunctions is minimized.
According to the invention, this problem is solved by a pressure retaining valve having the features of claim 1 in its entirety.
According to the characterizing portion of claim 1, one essential feature of the invention is that a monitoring device is provided, which detects the individual switching positions of the piston of the valve to ensure a reliable functioning of the pressure retaining valve. Due to the fact that the operator and/or an automatic machine control (PLC) has information about the respective switching state, the control operation proves to be simple and clear, substantially reducing the risk of incorrect operation.
With particular advantage, the monitoring device may be designed in such a way that the main control piston and/or the non-return piston interact with a signaling device, which inductively alters a field generated by a measuring device, as soon as the position of the signaling device changes in relation to the measuring device, due to the movement of the main piston and/or the non-return piston.
In a particularly advantageous manner, a kind of inductive travel measuring device is provided as a monitoring device, where the signaling device consists of a control unit connected to the main piston, the control unit having at least partially magnetic field altering constituents, in particular in the form of iron compounds, wherein the measuring device has at least one energizable winding coil, generating the magnetic field. Such an inductive measuring device can be integrated in the valve housing without difficulty or mounted as an additional housing to one end of the valve housing, from which the control unit extends into the additional housing.
In an advantageous manner, the control unit is part of a signal rod, the one free end of which engages with the main control piston and in the area of its other free end extends through a dual coil arrangement, whose individual coils are arranged in series at a predetermined spacing along the travel direction of the signal rod. In such an arrangement, the individual coils may be part of an inductive half-bridge, for a displacement measurement according to the so-called LVDT system (Linear Voltage Differential Transformer). Alternatively or additionally, the programming or design takes into account defined switching points, like a relaxation oscillator (Schmitt trigger). In that regard, only two switching points that can be easily monitored are then required. Another monitoring option is the use of commercially available Hall sensors.
The arrangement can advantageously be made in such a manner that a zero or starting position for the measuring device is calibrated relative to the valve housing which, when departed from in one direction or another due to the main control piston, starting from a predetermined output voltage, the respective switching position of the valve can be inferred in the manner of a switching point detection.
Preferably, the respective switching point determination for the unambiguous detection of the respective switching position is provided with a kind of hysteresis loop.
The measuring device can be particularly advantageously connected to evaluation electronics, preferably providing the operator with a visual indication of the preferred switching positions on an LED display. The electronic monitoring accomplishes an increase in the diagnostic coverage ratio (DC) in accordance with DIN EN ISO 13849. In doing so, a higher performance level (PL) can be achieved as well as a higher functional safety level.
In particularly advantageous exemplary embodiments, the valve housing has a stop shoulder for forming the zero or starting position, against which stop shoulder the non-return piston abuts in the hold-pressure position, wherein in the load lifting or load lowering position the main control piston moves forward or backward from a position close to the stop shoulder position towards a frontal housing port as the hydraulic actuator port.
In advantageous exemplary embodiments, in at least one position of the main control piston, a throttled fluid pressure, in addition to a main spring with a preferably adjustable spring force, acts on said main control piston, especially during lowering movements.
As a control valve means for controlling the pressure retaining valve for the media supply or return, said pressure retaining valve is advantageously connected to a control valve, in particular in the form of a 4/3-proportional directional valve. Pressure retaining valves should also include and comprise all types of counterbalance valves and all kinds of double check valves of the generic kind.
Below the invention is explained in detail using an exemplary embodiment shown in the drawing. In the drawings:
As shown in the circuit illustration of
The 4/3-directional valve 5 is spring biased to the position shown in
One actuator port 21 of the pressure retaining valve 1 is connected to the rod side 23 of the power cylinder 3, whose the piston side 25 is connected to a connection port 27, which is located, as can be seen, in particular in
For the transition from the holding position to the lifting position or the lowering position, the valve piston 17 of the 4/3-directional valve 5 is moved to the right, viewed in the transition to the lifting position in
If the directional control valve 5 is moved back from the lifting position to the holding position shown in
If the valve piston 17 of the directional control valve 5 moves to the left, viewed from the lifting position in
The pressure surfaces effective at the non-return piston 43 and at the main piston 39 are indicated in
Connected opposite the open end of the valve housing 29 forming the actuator port 21 is a spring housing 69 for the main spring 41. This is supported at one end via a spring plate 71 by the facing end of the main piston 39. The other end of the main spring 41 is supported on the end of a measurement housing 73 screwed into the spring housing 69, which, in turn, holds an end section of a monitoring device 75. This provides, for instance, a means for inductive position measurement by the known LVDT system (Linear Voltage Differential Transformer) and has two energizable, magnetic field-generating coil windings 77 and 79. As components of an inductive half-bridge, the winding coils 77, 79 act in conjunction with a signaling device in the form of a rod-like control unit 81, which is connected at one end to the main piston 39 and is axially movable with the latter, and at the other end has an end section 83 of a highly permeable ferrite that is movable as a coil core within the winding coils 77, 79.
Changes of the inductance of the coil windings 77, 79 caused by axial movements of the end section 83 corresponding to movements of the main piston 39 and the resulting changes in the bridge voltage Vout, the respective switching positions of the pressure retaining valve 1 are determined based on a zero or starting position, by means of evaluation electronics of the prior art. This starting position is, as schematically indicated in
For the unambiguous determination of a switching point, a hysteresis range 85 is taken into account, which extends over a small section of the distance. The same applies to the state shown in
Altogether, for two switching channels the following states result according to the following table:
As
Number | Date | Country | Kind |
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10 2013 014 673.9 | Sep 2013 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/002253 | 8/14/2014 | WO | 00 |