Electrical Measured Value Processing for a Control Valve

The invention relates to an electrical measured value processing for a control valve.

Control valves are known as proportional valves or servo valves (MOOG P-Q proportional valve) in which a hydraulic pressure pickup is installed for detecting the pressure obtaining in a conduit leading to a consumer, in particular an injection cylinder, and/or a displacement pickup for determining the valve piston position. The two signals are supplied as actual values to a control circuit by which the proportional valve is driven in such a manner that specific pressure profiles can be followed in the injection cylinder.

It is also known in a control valve to transmit the pressure respectively upstream and downstream of the throttle cross-section via conduits to a flow control valve or the regulating means of a variable displacement pump and to subject said means to the pressure difference to adjust a specific volume flow.

The problem underlying the invention resides in providing a measured value detection or acquisition and measured value processing for a control valve which makes it possible to detect, monitor and/or influence the mode of operation of the hydraulic consumer connected to the control valve in that corresponding signals and/or signal combinations are supplied to the control circuit for driving the control valve.

With the aid of a plate associated with the control valve and a pressure measuring means provided on the plate as well as possibly logic units connected to the pressure measuring means and signal processing stages all electrical signals necessary for the desired signal processing can be acquired. Preferably, an intermediate plate is provided which is arranged between the control valve and a connection plate for the inlet (fluid source), the outlet (tank) and the working lines leading to the consumer. Pressure load cells are connected to the connecting bores. Preferably, the intermediate plate also carries the electrical signal processing stages, for example logic gate members and the control circuit, preferably in the form of a microcomputer, so that the necessary connecting lines and terminals can be largely dispensed with. The end stage for the control valve driven by the control circuit is preferably provided on the control valve itself.

The arrangement according to the invention for the measured value acquisition and processing is suitable in particular for a standardized design with uniform equipping. With a directional control valve for controlling the fluid paths between a fluid source, the tank and a consumer on the plate a pressure load cell will usually be provided at the inlet side for the admission pressure and a pressure load cell at the outlet side for each of the working conduits leading to the consumer. If desired a pressure measuring cell may also be provided for the tank pressure. This enables all the pressures occurring at the control valve to be detected.

With the aid of the evaluating electronics arranged on the plate the measuring signals are processed and the desired combined or derived signals formed. By integration of the pressure load cells and the evaluating electronics on the intermediate plate hydraulic and electrical connecting lines can be dispensed with. By using microcomputers as control circuit and serial data transmission the constructional expenditure is kept low.

In a particularly advantageous construction of the invention the evaluating electronics determine the differential pressures between the individual control edges of the control valve, i.e. the inlet-side and outlet-side difference. Together with the respective position of the valve piston of the control valve it is then possible to calculate therefrom the flow through the control valve, taking account of the geometry of the control edges of the respective control valve.

Furthermore, from the measurement of the pressure difference of the consumer and the pressure-subjected areas of the consumer the size and direction of the load of the consumer can be determined. If the working pressure of the consumer is differentiated the acceleration of the consumer can be determined and disturbing influences better detected to improve the control.

The pressure measured values supplied to the control circuit represent feedback values which also make it possible to drive the control valve in such a manner that it assumes a specific pressure (pressure control function), makes a specific acceleration possible (acceleration function) or keeps a specific flow constant (flow control function) so that an additional flow control valve for compensating different consumer loads can be dispensed with.

In advantageous further development of the invention there may be associated with each control circuit a table memory in which the flow characteristics of the respective control valve are stored and can be called up for correction. These flow characteristics can be individually determined for each individual control valve so that for each said valve a corresponding memory containing the individual characteristic of the control valve is available and thus the production expenditure for such valves can be reduced because from the memory values when called up correction values for the flow converted for the particular measured pressure conditions can be calculated. The table memory is preferably loaded with values of the flow determined in a measuring run of the control valve in dependence upon the valve piston position at a specific pressure The table memory may however also be loaded with mathematically determined values

A further possible use results when the control circuit is constructed as adaptive controller and thus includes a model of the controlled system for increasing the control quality. In this case the measured signals processed by the evaluating electronics can be used as input signals for the circuits simulating the controlled system.

As control valves proportional valves or servo valves may be used. Switching magnets may also be driven by pulse modulation in such a manner that proportional behaviour can be achieved.

An example of embodiment will be explained hereinafter with reference to the single FIGURE of the drawings in which a directional-control valve with intermediate plate is shown schematically.

Screwed to a 4/3-way proportional valve 10 is an intermediate plate 12 which comprises four bores 14, 15, 16 and 17. The bore 15 establishes the connection between a pump 20 and the P-connection of the valve, the bore 16 the connection between the tank connection T and the tank and the bores 14 and 17 respectively the connection between the A-connection and B-connection of the control valve to a consumer, that is a double-acting cylinder 21.

The bores 14 through 17, which contrary to the schematic illustration do not lie in a common plane, communicate each via a passage 23, indicated only schematically, with a respective pressure load cell 22. Since the intermediate plate 12 is shown schematically in the drawings the components which are mounted on this intermediate plate are contained within the dot dash lines in the FIGURE. The outputs of the pressure load cells 22 thus carry signals for the pressures A, B, P and T.

In a simplified embodiment the pressure measuring cell for the tank pressure T can be omitted and said pressure can be assumed to be zero. If however the consumer displaces relatively large amounts of fluid the tank pressure may rise to considerable values and consequently it is advisable to measure the pressure T.

Also arranged on the intermediate plate 12 is a logic circuit 25 consisting of individual summation stages which each have two inputs for pressure measured values and an output for the differential pressure determined. In this manner the differential pressures AT, AP, BT, BP and AB are determined.

The signals corresponding to the pressures or pressure difference are supplied to evaluating electronics or a control circuit 26 in which further units not shown in detail such as a table memory and differentiating stage are provided for the signal processing. It is possible to supply to the control circuit as feedback quantity the valve piston position which is measured by a displacement pickup 28. Furthermore, the control circuit receives desired value signals for a pressure to be adjusted and a flow to be adjusted as well as desired values for other quantities such as acceleration and pressure differences to be observed. In connection with the feedback quantities the control circuit generates control signals which are supplied via an end stage 29 preferably arranged at the control valve to the proportional magnet 30 of the control valve 10.