The present invention basically relates to the sector of electromechanical-actuation metering pumps for metering liquids.
Said metering pumps are used for metering additives of various sorts, by means of a regulation of a volumetric type of the fluid pumped at each cycle. They are devices that are widely used in numerous both industrial and domestic applications, such as for example:
treatment of drinking water;
public and private waterpools;
Entering into the detail of operation of a generic metering pump, it should be noted that metering occurs by means of a pulsating movement of a mechanical member present in the so-called pump body, referred to as “membrane”, which, pushed by a piston, injects the liquid to be metered into the purposely provided delivery passage of the pump body. The liquid to be metered is then introduced into the system to be treated, overcoming the counterpressure present in the piping in which it is injected.
The key element that must provide the force necessary in order for the liquid to be metered to be effectively mixed with the liquid to be treated is hence the piston, which constitutes the component designed to move the membrane that sucks in the liquid in the pump body from the intake pipe and injects it into the delivery pipe in a cyclic way.
Said piston is actuated by an electromagnet, which hence constitutes a fundamental part of the pump. The electromagnet is made up of a fixed part, housed in which is the armature, and a mobile part—referred to as “plate”—fixed with respect to the piston.
It should be noted that the plate constitutes, in effect, the closing element for the magnetic flux of the electromagnet, said flux having as effect that of recalling said plate to the remaining fixed part of the electromagnet, thus producing a displacement.
In other words, the electromagnet hence enables conversion of electrical energy into mechanical energy to obtain work and move the liquid.
The electrical and mechanical characteristics of the metering pump hence depend upon how said electromagnet is designed, driven, and controlled. The electronic card present in the pump will do nothing but supply the electromagnet and manage the electrical energy supplied thereto in the best way.
It is thus clear that the better said control is performed the higher the efficiency of the metering pump. This is a very important factor when, once the metering to be performed on the system to be treated has been established, it is necessary to perform said metering in a continuous way and with the minimum consumption of electrical energy.
Certain applications in effect require the metering pump to deliver small amounts of liquid at each injection, hence requiring a high number of injections so as to be able to meter the volume required for carrying out the treatment. Said target can be achieved by regulating the piston stroke causing that given the same injections, the volume of liquid can be properly metered via regulation of the aforesaid stroke. The present invention thus falls within the field of closed-loop regulation systems, where the input variable, which in the case of the present invention is the current supplied to the electromagnet, is regulated by the system through a feedback based upon control of appropriate physical quantities that can be brought down to the variable to be controlled: the injection volume.
The progress in time of the metering pump has followed the evolution of the electromagnet, as well as the study of the various driving and control systems. The target of said studies has been to prevent the following drawbacks:
waste of energy due to the fact that in the past applied to the electromagnet was a voltage pulse of a fixed duration, whatever the force necessary for overcoming the counterpressure of the system. In effect, the waste of energy is the greater the lower the pressure of the system present in which is the liquid to be treated and consequently the lower and the thrust necessary for overcoming said counterpressure;
excessive heating of the apparatus and in particular of the electromagnet due to the fact that in the past the energy to be supplied was not controlled on the basis of the force to be overcome according to what is described in the previous point, with consequent drop in performance due to an increase in the resistance of the armature over the medium-to-long term;
reduced service life caused by medium-to-high operating temperatures both of the electronic components and of the electromagnet;
the need to have mechanical means for calibration of the piston stroke to obtain the desired pump capacity, which results in the need to introduce shim washers inside the electromagnet;
the need to have mechanical systems for regulation of the stroke that limit only mechanically the piston stroke and hence reduce the injection without proportionally reducing the electrical energy supplied to the equipment: this fact entails a constancy in the levels of energy consumption even when the delivery of the product is minimal, given the same injections. Equipment of this sort is not characterized by high levels of efficiency.
Known from U.S. 2009 0206184 is a system for injection into the combustion chamber regarding control of a fuel injector by using a sensor that detects the displacement of a mobile piston that slides in an accessory channel and, which is distinct from the needle valve. The purpose of the system is to monitor and process the signal of displacement of the accessory piston in order to control operation of the injector in the case of any malfunctioning (blocking in ON or OFF position), in the cases of deterioration of the geometries of the nozzles, of the injector, or of the chamber, in the cases where it is necessary to modify the shape of the injection pulse. In U.S. 2009 0206184, the displacement of the piston is subordinate to the pressure difference existing between the two ends of the piston itself: the top one is subject to the supply pressure generated upstream of the injection system; the bottom one is subjected by the pressure in the “pre-injection” chamber, the volume of which depends upon the geometries involved. The aforesaid pressure difference obviously depends upon the supply pressure, the supply frequency, and the state of the injector. Three states of the injector may in fact be distinguished, namely, closed (“OFF”), intermediate (“blocking”), and open (“ON”), which determine, respectively, the following situations: OFF: the nozzles are closed by the needle, the pre-injection chamber is in communication with the supply, and the ends of the slidable piston are subject to one and the same pressure; blocking: the nozzles are still closed, and the supply ducts are geometrically closed, separating the pre-injection chamber from the supply; ON: the path to the nozzles is free, the pre-injection chamber does not communicate with the supply, and the mobile piston is displaced downwards following upon the negative pressure that is generated upon opening of the port of the nozzles.
The present invention presents a series of substantial differences as compared to what is described in the injection system of U.S. 2009 0206184 where, irrespective of the type of injector or of control exerted, the supply pump is completely separate from the injector. In fact, in the present invention the pumping action and the injection action are carried out by means of one and the same device comprising a controlled-energization magnet, a piston, and a diaphragm. The latter presses the liquid into a duct, opening/closing of which is ensured by specific valves that operate exclusively for the fluid-dynamic effect.
In addition, the document No. U.S. 2009 0206184 describes a control device obtained by means of an auxiliary piston, which displaces as the conditions of injection vary. Its displacement is detected by a specific sensor. The displacement datum is processed both to modify the conditions of supply upstream and to restore volumes and pressure in the pre-injection chamber.
According to the present invention, instead, by measuring the variation of impedance that is generated in the electrical circuit itself of the magnet as the position of the pumping piston varies, it is possible to determine the position of the piston itself and, from this, to control the energy involved in order to guarantee the pre-set flowrate of fluid. In other words, it is possible to carry out control of the displacement of the device by means of a measurement of its electrical characteristics, without the need to resort to indirect measurements of other mobile elements.
Finally, in the document No. U.S. 2009 0206184 the position of the auxiliary piston, in a certain configuration, can be corrected by means of an additional actuator. The displacement datum detected by the sensor is in this case processed also for restoring the volume and pressure in the pre-injection chamber. In the present invention, instead, by processing the measurement of the impedance of the electrical circuit of the magnet, it is possible to vary the position of the pumping piston and hence guarantee the pre-set flowrate of fluid. It is thus possible to carry out control of the displacement of the device by acting directly on the pumping piston without resorting to additional actuators in the pre-injection chamber.