Pumps – With condition responsive pumped fluid control – Pressure responsive relief or bypass valve
Reexamination Certificate
2000-01-31
2001-08-14
Thorpe, Timothy S. (Department: 3746)
Pumps
With condition responsive pumped fluid control
Pressure responsive relief or bypass valve
C417S440000, C417S300000, C417S063000, C417S282000, C417S292000, C137S557000, C137S115180
Reexamination Certificate
active
06273686
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus and a method for controlling a rated system pressure in a pressure supply system such as a hydraulic system by simultaneously adjusting a pressure relief valve on a pressure generating or input side and operating a switch on the pressure consumption or output side of the pressure supply system.
BACKGROUND INFORMATION
Pressure supply systems such as hydraulic or pneumatic systems are operated by a pressure pump at a rated system pressure. When such systems are used in clamping operations, for example to hold a workpiece in a machine tool, it is often necessary to adjust the system pressure to a given situation requiring a different rated system pressure which may be higher or lower than the initially adjusted rated system pressure. Changing the rated system pressure, however, introduces a relatively large source of error or fault, since at least two elements that influence each other must be adjusted.
Such pressure supply systems, especially hydraulic systems, require a pressure relief valve, which limits the actual pressure to a maximal system pressure and simultaneously determines the safety of the system. Conventionally, a pressure switch governs the pressure generating pump, or rather, a motor driving the pump. The pressure relief valve controls the maximal pressure in the system by bleeding excess pressure fluid to an overflow line when the pressure exceeds a rated pressure. If it becomes necessary to change the system pressure, then the pressure relief valve and the pressure switch must be adjusted relative to each other in their response characteristic. Even minor errors in the adjustment can result in damage to system components or to pressure-driven devices connected to the system, such as workpiece holding clamps. In addition, the pressure switch functions imprecisely in the lower pressure range and with a large hysteresis. Adaptation of the system pressure of such a system to a new rated system pressure thus requires that the operating personnel have a great deal of expertise and experience in making such adjustments. Consequently, adjusting the system pressure can be problematic in many cases.
Prior art teaches mechanically coupling the pressure relief valve and the pressure switch to each other by arranging the valve and the switch on a common shaft. The disadvantage of such an arrangement is that a mechanical adjustment across greater pressure ranges is often inaccurate since the spring forces of the elements, i.e. in the pressure relief valve and in the pressure switch, differ. Different pressures are effective on these two elements because of their different tasks. As a result, differential forces flow into the mechanics, thus making it quite difficult and time-consuming to achieve an exact adjustment.
OBJECTS OF THE INVENTION
In view of the above, it is the aim of the invention to achieve the following objects singly or in combination:
to provide an apparatus and method for adjusting a rated system pressure in a pressure supply system by adjusting a single pressure adjustment element, whereby an increase or decrease of the rated system pressure shall be possible;
to provide such an apparatus and method for electronically generating adjustment parameters, derived from a newly adjusted rated system pressure, and for generating control signals derived from the adjustment;
to define the system response characteristics as a function of the value that is set at the pressure relief valve;
to provide a pressure responsive feedback control and error recognition capability, as well as to display pressure and/or error values to enable corrective measures; and
to avoid or overcome the disadvantages of the prior art and to achieve the advantages that a simultaneous adjustment of two elements becomes unnecessary.
The invention further aims to avoid or overcome the disadvantages of the prior art and to achieve additional advantages, as are apparent from the present description.
SUMMARY OF THE INVENTION
The above objects have been achieved in a pressure control system for adjusting a rated system pressure by first adjusting a single pressure adjustment member and enforcing any further required adjustments as follow-up adjustments. The pressure control system comprises a pressure relief valve, a check valve, a pressure sensor, a switch, a first and a second pressure adjustment member, a microcontroller and an actuator for the second adjustment member, wherein an operation of the actuator is linked to permitting an adjustment of the first pressure adjusting member of the pressure relief valve. The pressure relief valve connects a pressure supply line forming an input to a pressure return line. The check valve is connected in the pressure supply line between the input, to which a pump supplies fluid under pressure, and a pressure output, to which pressure users, not shown, are connected. The pressure sensor is arranged in the pressure supply line for sensing the actual pressure in the supply line and provides an actual pressure signal to the microcontroller, which under normal operating conditions sends a pump control signal to a pressure pump motor to initiate pumping, when or if the actual pressure falls below the rated system pressure. Thus, normally in the working mode, the pump does not need to work as long as a rated system pressure set in the microcontroller and the actual system pressure are equal to each other. However, if a new rated system pressure higher than the rated previous system pressure is required, the pump must be enabled or rather its motor must be energized even though pressure equality exists. For this purpose the switch of the invention is normally open but is momentarily closed when the system pressure is to be adjusted to a higher rated system pressure by adjusting the pressure relief valve.
The new rated system pressure is adjusted by adjusting the first pressure adjustment member of the pressure relief valve which changes the response pressure of the pressure relief valve.
However, the pressure relief valve according to the invention can only be adjusted if the check valve is momentarily disabled, that is, opened by its actuator and if the pressure relief valve adjustment member is accessible in response to the open status of the check valve, preferably the fully open check valve. Placing the actuator in a check valve open position simultaneously signifies that the rated system pressure is to be adjusted by closing the switch momentarily in addition to opening the check valve. The closed switch sends an enabling signal to the microcontroller to cause a pump control signal which switches the pump motor ON. With the check valve open equal pressures are present between the pressure generation input and the pressure output of the pressure supply line. Since the actuator is now in the check valve open position, the pressure relief valve can now be adjusted to a new higher or lower rated system pressure. A value representing a higher or lower system pressure is preferably stored in a memory and displayed on a display of the microcontroller for use by the operator when adjusting the pressure relief valve. After the adjustment of the pressure relief valve to the higher or lower rated system pressure, the actuator and thus the second pressure adjustment member and the check valve are returned to the normal position. If the new rated system pressure is higher than before, the check valve does not need an adjustment. Under normal operating conditions the check valve is open as long as a pressure supply pump is running.
The linking between the complete opening of the check valve and the enabling of the adjustment of the pressure relief valve can be accomplished electrically or mechanically. A mechanical link according to the invention is provided by the actuator having such a configuration that it prohibits access to the first pressure adjustment member during normal operation of the hydraulic system. When the actuator is brought into the adjustment position, an opening in the actuator is aligned with
Kroell Harald
Pitz Walter
A. Roemheld GmbH & Co KG
Fasse W. G.
Gasse W. F.
Gray Michael K.
Thorpe Timothy S.
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