ES2884113T3 - Solenoid Pump Actuator - Google Patents

Abstract

A method of driving a solenoid pump of the type comprising a metal shuttle driven by a solenoid against a spring with the spring providing the force for a pumping stroke of the shuttle, the method comprising applying a periodic drive voltage to the solenoid by emitting the periodic drive voltage from an actuator circuit, wherein each period of the drive voltage comprises a first portion during which the drive voltage is always increased from a minimum voltage to a maximum voltage to compress the spring, a second portion during which the drive voltage decreases from the maximum voltage to the minimum voltage to release the spring, and a third portion during which the drive voltage is maintained at the minimum voltage, wherein the duration of the second portion is substantially less than the duration of the first portion, the method further comprising providing u a required flow rate through the pump by controlling one or more of: the duration of the third portion; the maximum voltage; and the frequency of the driving voltage.

Description

DESCRIPTION

solenoid pump driver

This invention relates to a method and apparatus for driving an electromagnetic pump.

Background

Figure 1 is a sectional view of a known construction of an electromagnetic (or solenoid) pump, for example as shown in US 9,028,227. The pump is configured to pump fluid, such as water, from an inlet connection 1 to an outlet connection 2 in the direction of arrow A. The inlet connection 1 is formed as a plastic moulding, defining a chamber in which receives a power spring 3 and a shuttle 4. An electric solenoid 5 surrounds the chamber. An outer magnetic core 6 surrounds the solenoid 5. A non-magnetic spacer 7 breaks the magnetic circuit of the outer magnetic core 6. The shuttle 4 is made of stainless steel and is therefore magnetically movable by the solenoid 5. The shuttle 4 provides a core and a piston. The core is received within the chamber and engages power spring 3 at its proximal end. The piston extends from the core and is received within a cylinder 8. The shuttle 4 is hollow and provides a fluid passage through the core and piston. The fluid passage is closed at the distal end of the piston by a piston check valve 9, which is held in position by a spring within the fluid passage. A retaining washer 10 locates the piston within cylinder 8 and a sealing O-ring 11 seals the proximal end of cylinder 8. A non-return valve 12 is provided between cylinder 8 and outlet connection 2 to seal the distal end. of the cylinder 8. A secondary spring 13 is provided between the core and the distal wall of the chamber to dampen the movement of the shuttle 4.

In operation, solenoid 5 is electrically energized, which moves the core (and thus the entire shuttle 4) towards input port 1, compressing power spring 3. The shuttle 4 moves up and into the gap created in the outer magnetic core 6 by the non-magnetic spacer 7. The movement of the shuttle 4 reduces the pressure inside the cylinder 8, which is closed by the non-return valve 12. The reduced pressure in cylinder 8 opens piston check valve 9, which allows fluid to pass from inlet connection 1 through the chamber and passage of fluid within shuttle 4 to cylinder 8. In the return stroke of the pump, the power spring 3 pushes the core (and thus the entire shuttle 4) towards the outlet connection 1. Piston check valve 9 closes against the fluid pressure in cylinder 8 and this pressure causes check valve 12 to open in such a way that the piston expels fluid from cylinder 8 through connection 2 outlet under the action of power spring 3.

Although the currently described pump uses the electromagnet to fill the cylinder 8 and charge the power spring 3, and uses the charged power spring 3 to expel the fluid from the cylinder 8 through the outlet port 2, it is known to have a pump operating in the opposite direction. That is, it is known to use the spring to introduce fluid into the cylinder, and to use the electromagnet to expel the fluid from the cylinder through the outlet port.

Typically, the electric solenoid 5 is driven by a half-wave rectified voltage at mains frequency (50 Hz in Europe), which provides a single drive voltage signal to the solenoid 5.

The present invention, at least in its preferred embodiments, provides an alternative method of actuating a solenoid pump.

Brief Summary of Disclosure

According to the present invention there is provided a method of driving a solenoid pump of the type comprising a metal shuttle driven by a solenoid against a spring, the spring providing the force for a pumping stroke of the shuttle, for example the pump. described with reference to Figure 1. The method comprises applying a periodic driving voltage to the solenoid by outputting the periodic driving voltage from an actuator circuit. Each period of the drive voltage comprises a first portion during which the drive voltage increases from a minimum voltage to a maximum voltage to compress the spring, a second portion during which the drive voltage decreases from the maximum voltage to a minimum voltage to compress the spring. releasing the spring, and a third portion during which the drive voltage is maintained at the minimum voltage. The duration of the second portion is substantially less than the duration of the first portion. The method further comprises providing a required flow rate through the pump by controlling one or more of: the duration of the third portion; the maximum voltage; and the frequency of the driving voltage.

Thus, in accordance with the invention, the drive voltage is reduced relatively quickly from the maximum voltage to the minimum voltage during the second portion. In this way, the spring is quickly released to provide the force for the pumping stroke of the shuttle with minimal energy being wasted by the drive voltage causing the solenoid to act against the released spring.

The drive voltage may gradually decrease from the maximum voltage to the minimum voltage, for example linearly. The duration of the second portion may be less than half the duration of the first portion, particularly less than 10% of the duration of the second portion. In a particular embodiment, the drive voltage may decrease from the maximum voltage to the minimum voltage substantially instantaneously during the second portion. In this way, the duration of the second portion may be insignificant compared to the duration of the first portion.

In embodiments of the invention, the drive voltage increases from the minimum voltage to the maximum voltage in a substantially linear manner during the first portion. Although this configuration is currently preferred, it is possible for the drive voltage to increase other than linearly during the first portion. In embodiments of the invention, the drive voltage has a sawtooth waveform.

The frequency of the drive voltage may be different than the frequency of a supply voltage that provides electrical power for the drive voltage. Thus, the frequency of the supply voltage is not limited to 50 Hz/60 Hz. Therefore, where the frequency of the drive voltage is controlled to provide the required flow rate, the frequency of the drive voltage may comprise controlling the frequency of the drive voltage to be different from the frequency of the supply voltage that provides electrical power for the drive voltage.

Typically the minimum voltage is zero volts.

The invention extends to a solenoid pump driver circuit configured to generate a drive voltage in accordance with the method of the invention. The actuator circuit may be an analog circuit, a digital circuit, or a combination of analog and digital circuitry. The driver circuit may use pulse width modulation (PWM) to generate a sawtooth or other waveform. The invention further extends to a solenoid pump in combination with the driver circuit.

Brief description of the drawings

Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of an electromagnetic pump;

Fig. 2 is a graph showing a comparison between a known driving method for the electromagnetic pump of Fig. 1 and a driving method according to an embodiment of the present invention;

Fig. 3 is a graph illustrating a driving method according to a further embodiment of the present invention;

Fig. 4 is a graph illustrating a driving method according to a still further embodiment of the present invention; Y

Fig. 5 is a schematic of a drive circuit according to an embodiment of the present invention.

Detailed description

Figure 2 shows, in the upper graph, a comparison of a sawtooth drive voltage for a solenoid pump according to one embodiment of the invention (dashed line) with a half-wave rectified drive voltage of the art. above (continuous line). The solenoid pump may be of the type described in connection with Figure 1. The lower graph in Figure 2 shows the corresponding spring force of the power spring 3. As shown in Fig. 2, to achieve the same spring force of the power spring 3, the sawtooth drive voltage requires only 60% of the peak voltage of the rectified drive voltage. Additionally, the rapid sawtooth drive voltage drop from full voltage (60%) to zero volts also saves energy. The amount of energy saved by using the sawtooth drive voltage is shaded in Figure 2.

Figure 3 shows a sawtooth drive voltage variation of an embodiment of the invention in a representation corresponding to Figure 2. In this case, the first portion of the sawtooth waveform has a duration of 10ms, as in the waveform of Figure 2. The second portion of the sawtooth waveform, in which the drive voltage drops from a peak value to zero volts, is substantially instantaneous. In Figure 3, the duration of the third portion of the sawtooth waveform in which the drive voltage is held at zero volts is reduced relative to the waveform shown in Figure 2 from 10ms at 8ms. In this way, the frequency of the drive voltage is increased from 50 Hz to 56 Hz. The shorter duration of each period of the sawtooth waveform increases the rate of flow through the pump.

Figure 4 shows a sawtooth drive voltage variation of an embodiment of the invention in a representation corresponding to Figures 2 and 3. In this case, the first portion of the sawtooth waveform has a duration of 8ms, which is shorter than the waveform in Figures 2 and 3. The rate of change (gradient) of the drive voltage remains the same, however, such that the maximum voltage reached during the first portion of the waveform is reduced, compared to Figures 2 and 3. Again, the second portion of the waveform is sawtooth, in which the drive voltage drops from a maximum value at zero volts it is substantially instantaneous. In Figure 4, the duration of the third portion of the sawtooth waveform in which the drive voltage is held at zero volts is longer than in the waveforms of Figures 2 and 3 at 12ms. In this way, the drive voltage frequency is maintained at 50 Hz, as in Figure 3, but the rate of flow through the pump is reduced as the power spring 3 only reaches 80% of its maximum compression.

Sawtooth drive voltage has the advantage that it uses less energy to achieve the same spring force than a conventional drive voltage. This means a smaller power supply can be used and less heat is generated during pump operation, which increases the duty cycle of the pump. Additionally, the operating frequency of the pump can be "tuned" to achieve minimum mechanical noise from the pump components. For example, it has been found that known pumps can operate at their quietest level at a drive frequency of 47 Hz, instead of the conventional 50 Hz. Any suitable driver circuit can be used to generate the required sawtooth waveform.

Fig. 5 is a schematic of a drive circuit according to an embodiment of the present invention. Drive circuit 20 comprises a power supply 22 connected to a microcontroller 24. The microcontroller is connected to a pump solenoid 28 through a switching circuit 26. The pump solenoid is typically solenoid 5 as depicted in Figure 1. Microcontroller 24 comprises memory and at least one processor. The memory of microcontroller 24 includes instructions that, when executed, cause the at least one processor to control switching circuit 26 and pump solenoid 28 to operate in accordance with methods as previously described. The switching circuit 26 provides inputs for the microcontroller 24 to control the operation of the pump solenoid 28.

Briefly, there is disclosed a method of actuating a solenoid type pump comprising a metal shuttle driven by a solenoid against a spring with the spring providing the force for the pumping stroke of the shuttle. The method comprises applying a periodic drive voltage to the solenoid. Each period of the drive voltage comprises a first portion during which the drive voltage increases from a minimum voltage to a maximum voltage to compress the spring, a second portion during which the drive voltage decreases from the maximum voltage to a minimum voltage to compress the spring. releasing the spring, and a third portion during which the drive voltage is held at the minimum voltage. The duration of the second portion is substantially less than the duration of the first portion and may be substantially instantaneous. The drive voltage increases from the minimum voltage to the maximum voltage substantially linearly during the first portion, such that the drive voltage has a sawtooth waveform.

Throughout the description and claims of this specification, the words "comprise" and "contains" and variations thereof mean "including but not limited to", and are not intended to (and do not) exclude other components, integers or stages. Throughout the description and claims of this specification, the singular encompasses the plural unless the context requires otherwise. In particular, where the indefinite article is used, the specification is to be understood as covering both plurality and singularity, unless the context requires otherwise.

Features, integers, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example of the invention are to be understood as applicable to any other aspect, embodiment, or example described herein unless incompatible therewith. All features disclosed in this specification (including any accompanying claims, abstracts, and drawings), and/or all steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or stages are mutually exclusive. The invention is not restricted to the details of any previous embodiment. The invention extends to any novelty, or any novel combination, of the features disclosed in this specification (including any claims, abstracts, and accompanying drawings), or to any novelty, or any novel combination, of the steps of any method or process so disclosed. .

Claims (8)

1. A method of driving a solenoid pump of the type comprising a metal shuttle driven by a solenoid against a spring with the spring providing the force for a pumping stroke of the shuttle, the method comprising applying a periodic drive voltage to the solenoid outputting the periodic drive voltage from an actuator circuit, wherein each period of the drive voltage comprises a first portion during which the drive voltage is always increased from a minimum voltage to a maximum voltage to compress the spring, a second portion during which the drive voltage decreases from the maximum voltage to the minimum voltage to release the spring, and a third portion during which the drive voltage is held at the minimum voltage, wherein the duration of the second portion is substantially less that the duration of the first portion, comprising the method also provides r a required flow rate through the pump by controlling one or more of: the duration of the third portion; the maximum voltage; and the frequency of the driving voltage. 2. A method as claimed in claim 1, wherein the drive voltage decreases from the maximum voltage to the minimum voltage substantially instantaneously during the second portion. 3. A method as claimed in claim 1 or 2, wherein the driving voltage increases from the minimum voltage to the maximum voltage in a substantially linear manner during the first portion. 4. A method as claimed in claims 1, 2 and 3, wherein the drive voltage has a sawtooth waveform. 5. A method as claimed in any preceding claim, wherein when the frequency of the drive voltage is controlled to provide the required flow rate, the frequency of the drive voltage is controlled to be different than the frequency of a supply voltage. supply that provides electrical power for the drive voltage. 6. A method as claimed in any preceding claim, wherein the minimum voltage is zero volts. 7. A solenoid pump driver circuit configured to generate a drive voltage according to the method of any preceding claim. 8. A solenoid pump in combination with the actuator circuit of claim 7.