Title:
ELECTROMAGNETIC PUMP
United States Patent 3804558


Abstract:
An electromagnetic pump comprises a pump section including an inlet and outlet chambers adapted to receive fluid therein and separated from each other, and a pump means interconnecting said inlet and outlet chambers. Said pump means has a reciprocating piston so as to deliver the fluid from said inlet chamber to said outlet chamber by the reciprocating motion of said piston. A drive control circuit for actuating said piston to reciprocate is provided in said pump section, wherein said drive control circuit comprises a solenoid for actuating said piston, a feedback coil inductively coupled with said solenoid, a transistor having its collector-emitter circuit connected to a power supply in series with said solenoid and a series circuit of a diode and a voltage regulating unit. Said feedback coil is connected across the base and emitter of said transistor with the polarity such that said transistor is rendered more heavily conductive by a voltage induced across said feedback coil and applied across the base and emitter of said transistor when the current supply to said solenoid is increased. Said series circuit of a diode and a voltage regulating unit is connected in parallel with said solenoid to discharge a counter electromotive force induced in said solenoid.



Inventors:
NAITO M
Application Number:
05/245554
Publication Date:
04/16/1974
Filing Date:
04/19/1972
Assignee:
NIPPONDENSO CO LTD,JA
Primary Class:
International Classes:
F04B17/04; H02K33/02; (IPC1-7): F04B17/04
Field of Search:
307/265,271,275 417
View Patent Images:



Foreign References:
DE1196703B1965-07-15
Primary Examiner:
Husar C. J.
Attorney, Agent or Firm:
Cushman, Darby & Cushman
Claims:
1. An electromagnetic pump comprising:

2. An electromagnetic pump according to claim 1 wherein said pump section comprises:

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic pump operating on a DC power supply such as a battery and more particularly to a reciprocating piston type electromagnetic fuel feed pump.

2. Description of the Prior Art

This type of electromagnetic pump operating on a DC power supply, particularly a reciprocating piston type electromagnetic fuel feed pump that has been used employs a mechanical construction in which a housing of a magnetic material formed into a cylindrical shape is provided with a solenoid and a feedback coil concentrically stacked in the central portion of the housing which is hermetically sealed by means of a cap mounted at each end thereof. An inlet chamber and outlet chamber are formed on the opposite sides of said solenoid. A cylinder of a non-magnetic material extends through said solenoid and an inlet valve is disposed on the inlet chamber side of said cylinder. A hollow piston of a magnetic material is axially slidably mounted in said cylinder and the piston is opened toward the inlet chamber side. An outlet valve is mounted in the piston on the outlet chamber side thereof. The piston is normally biased by a spring into an output chamber side position in the cylinder so that the energization of said solenoid exerts a force on the piston urging it toward the inlet chamber side against the spring force. A self-excited blocking oscillator circuit is separately provided so that said oscillator circuit is self-excited into oscillation by the action of said feedback coil thereby energizing said solenoid periodically. Consequently, the piston reciprocates within the cylinder between the inlet chamber side and the outlet chamber side thereof. Thus, when the piston moves away from the inlet chamber side toward the outlet chamber side, the fuel in the inlet chamber is admitted into the cylinder and the hollowed portion of the piston by way of the inlet valve, and the fuel thus admitted into the cylinder and the hollowed portion of the piston is delivered into the outlet chamber through the outlet valve when the piston moves away from the outlet chamber side toward the inlet chamber side. In this manner, the electromagnetic pump operates as a fuel pump.

A disadvantage of the prior art devices of this type is that while the pump's output, i.e., the amount of fuel delivered is related to the bulk of the pump and the number of reciprocating motions of the piston, i.e., the oscillation frequency of the self-excited oscillator circuit, it is difficult to obtain a higher oscillation frequency and it is thus necessary to increase the bulk of the pump to increase the pump's output.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a piston type electromagnetic reciprocating pump whose output is markedly increased by increasing the number of reciprocating motion of its piston, but without any increase in the bulk of the pump.

It is another object of the present invention to provide a reciprocating piston type electromagnetic pump which is simple in construction and easy in assembling.

In accomplishing these and other equally desirable objects, the electromagnetic pump provided in accordance with the present invention comprises a pump section including fuel inlet and outlet chambers separated from each other and pump means interconnecting said fuel inlet and outlet chambers and having a reciprocating piston whereby the fuel in said inlet chamber is delivered into said outlet chamber by said pump means by virtue of the reciprocating motion of said piston, and a drive control circuit for controlling the reciprocating motion of said piston, and drive control circuit comprising a solenoid for actuating said piston, a feedback coil inductively coupled to said solenoid, a transistor having its collector-emitter circuit connected to a power supply in series with said solenoid, said feedback coil being connected across the base and emitter of said transistor with the polarity such that said transistor is rendered more conductive by a voltage induced across said feedback coil and applied across said base and emitter of said transistor when the current supply to said solenoid is increased, and a series circuit of a diode and a voltage regulating unit connected in parallel with said solenoid to discharge a counter electromotive force induced in said solenoid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the pump mechanism of an electromagnetic pump according to the present invention.

FIG. 2 is a side view of the pump mechanism of the electromagnetic pump shown in FIG. 1.

FIG. 3 is a sectional view of FIG. 2.

FIG. 4 is a schematic diagram of the control circuit used with the electromagnetic pump of FIG. 1.

FIG. 5 is a graph showing the characteristics of the control circuit shown in FIG. 4.

FIG. 6 is a schematic diagram of a conventional control circuit.

FIG. 7 is a graph showing the characteristics of the control circuit shown in FIG. 6.

FIG. 8 is a graph showing I-V characteristic curves of diode and resistor.

FIG. 9 is a graph showing the attenuation time of electric current relative to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 and 2, there is shown the pump section of an electromagnetic pump according to an embodiment of the present invention. In the figures, numeral 1 designates a housing of a magnetic material having a bottom wall and a cylindrical wall; 12 an inlet chamber casing of a non-magnetic material having an inlet port 1a and contiguously mounted on the bottom wall of the housing 1; 13 an output chamber casing of a non-magnetic material having an outlet port 1b and contiguously mounted on the housing 1 opposite to the housing bottom wall. Also mounted on the outside of the housing portion of the pump section is a circuit unit 11 incorporating the circuit elements of a drive control circuit which will be explained later in detail. A lead wire for supplying power to the drive control circuit extends from the circuit unit 11 to the outside thereof and is connected to a power supply 31 through a switch 30. In the sectional view of FIG. 3 illustrating the pump mechanism in detail, numeral 5 designates a hollow cylinder of a non-magnetic material which extends axially through the bottom wall of the housing 1 with its one end projecting to the inlet chamber 12 side and the other end to the outlet chamber 13 side. An inlet valve 20 is provided at the one end of the cylinder 5 and an opening is provided at the other end of the cylinder. An annular solenoid 2 and an annular feedback coil 35 surrounding the solenoid 2 are provided in the central portion of the housing 1 surrounding the cylinder 5. These coils will be explained later in detail. Numeral 3 designates a shielding plate of a magnetic material soldered to the cylinder 5 by a solder 6a. The shielding plate 3 is formed with a groove 3a for receiving an O-ring 15 in its surface contacting the housing 1. Numeral 4 designates a shielding plate of a magnetic material; 16 a brass plate disposed on the bottom of the housing 1 and soldered to the cylinder 5 by a solder 6b. A piston 21 of a magnetic material is axially slidably mounted within the cylinder 5 and a passage 21a extends axially therethrough with an outlet valve 23 provided at one end of the passage 21a. A groove 12a for receiving an O-ring 26 is formed in the surface of the inlet chamber casing 12 contacting the brass plate 16 and another groove 13a for receiving an O-ring 27 is formed in the surface of the outlet chamber casing 13 contacting the housing 1. The inlet chamber casing 12 and the outlet chamber casing 13 with the housing 1 disposed therebetween are joined together by three marginal through bolt connectors 17 at three points 120 degrees apart from one another. The solenoid 2, feedback coil 35 and circuit unit 11 are molded with a resin.

The pump section is assembled as follows: The magnetic shielding plate 4 and the solenoid 2 are first mounted in the cylindrical housing 1 with a closed bottom and then the O-ring 15 is fitted in the ring groove 3a in the shielding plate 3. After the cylinder 5 is inserted through and soldered by the solder 6b at an opening 16a of the brass plate 16 mounted on the bottom of the housing 1, the inlet valve 20, spring 22, outlet valve 23 and piston 21 are assembled in place to complete the pump section. Thereafter, the O-rings 26 and 27 are fitted in the ring grooves 12a and 13a of the inlet chamber casing 12 and outlet chamber casing 13, respectively, and the casings 12 and 13 are joined together with the marginal through bolt connectors 17 thus providing a complete assemblage.

It should be noted that the inlet port 1a and outlet port 1b may be pointed in any desired direction and all that is required to do so is simply to join the inlet chamber casing 12, housing 1 and outlet chamber casing 13 after the direction of the inlet and outlet port 1a and 1b have been selected and the relative positions of the casing 12, housing 1 and casing 13 have been determined. It will be seen from FIG. 2 that the position of the inlet port 1a may be changed as shown by phantom lines.

It should also be noted that the present invention is not intended to be limited to the described embodiment, since various modifications and changes may be obvious to those skilled in the art. For example, any desired number of the marginal through bolt connectors 17 may be used and they may also be placed at regular intervals.

The operation of the pump section will now be explained. As will be explained later in detail, when the solenoid 2 is energized, its magnetic force causes the piston 21 to move within the cylinder 5 toward the inlet chamber side against the force of the spring 22. When this occurs, the inlet valve 20 is closed and the outlet valve 23 is opened so that the fuel in the cylinder 5 is delivered into the outlet chamber through the outlet valve 23, passage 21a in the piston 21 and the open end of the cylinder 5. When the solenoid 2 is eventually deenergized, the piston 21 is moved toward the outlet chamber side under the pressure of the spring 22. At this time, the inlet valve 20 is opened and the outlet valve 21 is closed so that the fuel in the inlet chamber is admitted into the cylinder 5 by means of the vacuum that exists in the cylinder 5. The repetitions of this process deliver the fuel in the inlet chamber into the outlet chamber. The fuel to the inlet chamber is supplied from the sump (not shown) through the inlet port 1a and the fuel in the outlet chamber is discharged to any desired destination (not shown) through the outlet port 1b.

The drive control circuit which periodically energizes the solenoid 2 to operate the pump comprises a so-called self-excited blocking oscillator. FIG. 6 illustrates a known type of control circuit in which the solenoid 2 is connected in series with the collector-emitter circuit of a transistor 36 and to the power supply 31 through the switch 30. The feedback coil 35 is provided to surround the solenoid 2 as previously mentioned and thus the two coils are closely inductively coupled with each other. The feedback coil 35 is connected across the base and emitter of the transistor 36 with the polarity such that the transistor 36 is biased so that when the transistor 36 is conducted and thus the current supply to the solenoid 2 gradually increases, the current supply thereto is increased still further.

As described above, in an electromagnetic pump of this type the reciprocating motion of the piston 21 is effected by the alternating operations of the energizing force of the solenoid 2 and the force of the spring 22 to deliver fluid and thus the discharged volume Q (cc/min) per unit time is determined by the product of the sectional area S (cm) of the piston 21, the stroke l (cm) of the piston 21 and the number of reciprocating motion of the piston 21, i.e., the oscillation frequency f(HZ) × 60 of the self-excited blocking oscillator circuit. Therefore, in order to increase the amount of fuel delivered with a limited bulk, the number of reciprocating motion of the piston 21 and hence the oscillation frequency of the self-excited blocking oscillator circuit must be increased.

The oscillation frequency of the self-excited blocking oscillator circuit depends on the sum of the conduction time and cutoff time of the transistor 36, and in an attempt to increase the oscillation frequency of this self-excited blocking oscillator circuit a resistor 34 is connected in series with a counter electromotive force absorbing diode 38 connected in parallel with the solenoid 2, so that when the transistor 36 is cut off, the counter electromotive force induced in the solenoid 2 is quickly attenuated by means of the resistor 34 to decrease the cutoff time of the transistor 36 and thus to increase the oscillation frequency. In other words, the attenuation time of the counter electromotive force induced in the solenoid 2 depends on the value L/R, where R is the resistance value of a closed circuit comprising the solenoid 2, diode 38 and resistor 34 and L is the inductance of the solenoid 2. Consequently, this attenuation time will be decreased with the corresponding increase in the oscillation frequency as the resistance value of the resistor 34 is increased.

However, since the damped current I having a certain initial value flows in the closed circuit comprising the soldnoid 2, diode 38 and resistor 34, the value of voltage e applied across the solenoid 2 increases in proportion to an increase in the resistance value of the resistor 34 thus increasing the voltage applied across the emitter and collector of the transistor 36.

In the circuit shown in FIG. 6, the oscillation frequency f(HZ), the voltage VCE (V) across the emitter and collector of the transistor 36 and the delivered volume Q (cc/min) changed as shown in FIG. 7 with variations in the resistance value of the resistor 34.

The characteristic curves in FIG. 7 show the results obtained when the resistance Ra of the resistor 34 was varied from 0 to 30 ohms employing the solenoid 2 whose number of turns = 500 T, resistance value = 1.9 ohms and inductance = 25 mH, the feedback coil 35 having the number of turns = 450 T, resistance value = 19 ohms and inductance = 30 mH, the transistor 36 having the current amplification factor = 40 and the 1-ampere, 1-volt diode 38 for absorbing counter electromotive force. The attenuation time of counter electromotive force (equal to the cutoff time of the transistor 36) T2 varied over the range from 50 to 18 ms and the oscillation frequency f changed in the range between 14 and 24 HZ and the delivered volume Q could vary over the range from 1,600 to 2,500 cc/min, whereas the voltage VCE across the emitter and collector of the transistor 36 attained very high values ranging from 14 to 100 volts.

Consequently, if the voltage applied across the emitter and collector of the transistor 36 increases extra-ordinarily as described above, from the reliability point of view or the like, the transistor 36 must be such that it withstands a correspondingly higher voltage. There is thus a drawback in that the manufacturing cost of electromagnetic pumps employing high-voltage withstanding transistors tends to become very high, since such transistors are not readily available and at the same time they are very expensive.

According to the present invention, the control circuit is constructed as shown in FIG. 4. In the figure, the solenoid 2 of the pump section is connected in series with the emitter and collector of the transistor 36 and the feedback coil 35 is connected across the emitter and base of the transistor 36. The feedback coil 35 is closely coupled inductively with the solenoid 2 with the polarity such that the transistor 36 is rendered more conductive when the current supply to the solenoid 2 is increased.

The series circuit of the counter electromotive force absorbing diode 38 and a voltage regulating unit 37 consisting of at least one diode 37a is connected in parallel with the solenoid 2.

Numeral 31 designates a DC power supply such as a battery; 30 a power supply switch; 39 a starting resistor connected between the base of the transistor 36 and the positive terminal side of the solenoid 2; 40 a transistor protecting diode connected in parallel with the feedback coil 35; 41 a diode for protecting the transistor 36 from the external pulses.

With the construction described above, the operation of this control circuit will now be explained. When the power supply switch 30 is closed, the base current flows into the transistor 36 through the starting resistor 39. In consequence, the collector current starts flowing in the transistor 36 producing a voltage across the solenoid 2 and thus inducing a voltage across the feedback coil 35. This voltage is then applied to the transistor 36 in the form of positive feedback placing the transistor 36 into a higher conduction state. In this case, if the value of this positive feedback is designated by A and the amplification degree of the transistor 36 by B and if A and B are selected so that the condition A. B>1 holds, then the circuit comprising the solenoid 2, feedback coil 35 and transistor 36 satisfies the condition of oscillation so that it initiates and maintains self-excited blocking oscillations so long as the power supply switch 30 remains closed, thereby supplying the interrupted current to the solenoid 2.

In this case, if T1 and T2 are the conduction time and cutoff time of the transistor 36, respectively, then the oscillation frequency f of the self-excited blocking oscillator circuit is given by f = 1/(T1 + T2) and the oscillation frequency f can be increased by reducing the cutoff time T2. The cutoff time T2 of the transistor 36 depends on the time it takes the counter electromotive force induced in the solenoid 2 upon the cutting off of the transistor 36 to dissipate, that is, the time during which the damped current having a certain initial value remains flowing in the closed circuit comprising the solenoid 2, counter electromotive force absorbing diode 38 and diode 37a. Consequently, as previously explained, the more the resistance value of the closed circuit is increased, the more the cutoff time T2 is decreased with the corresponding increase in the oscillation frequency f.

Then, by connecting the counter electromotive force absorbing diode 38 and at least one additional diode 37a instead of the resistance (Ra) used in the prior art in series with the solenoid 2, the oscillation frequency f can be increased and further the voltage applied across the emitter and collector of the transistor 36 can be limited in low value compared with the circuit of FIG. 6 for reasons that will be explained hereunder. The maximum value IO of a current through a closing circuit of the power supply 31, switch 30, solenoid 2 and the transistor 36 at the conductive state of the transistor 36 is determined by the product of the base current IB of the transistor 36 and the amplification factor A, i.e., IB × A. Therefore, immediately after the transistor has been rendered non-conductive, the maximum current IO, which was carried through the transistor 36 till then, is led through the series circuit of the diodes 37a and 38.

The diode has an I-V characteristic as shown in FIG. 8. Assuming that the maximum current IO is 3 amperes, the voltage drop across the series circuit of the diodes is about 2 volts when the number of the diodes n is 1, and about 14 volts when n = 9. In contrast, the voltage drop across the series circuit of the diode 38 and the resistor 34 in the prior art circuit as shown in FIG. 6 is about 90 volts when the resistor Ra of 30 ohms is used, and about 3 volts when the resistor Ra of 1 ohm is used. As mentioned previously, however, if the resistor Ra of a low resistance such as 1 ohm is used, the current IO is hardly reduced and hence the transistor 36 remains in a non-conductive state for a considerably long time.

In the circuit as shown in FIG. 4, the effective resistance of the series circuit of the diodes is relatively low for the initial period when the current through the series circuit is relatively large, but increases rapidly due to the non-linear I-V characteristic of the diodes with attenuation of the current through the closing circuit of the transistor and the diodes. Thus the increase of the effective resistance of the diodes contributes accumulatively to attenuation of the current through the closing circuit. Attenuation curves, i.e., ampere I to time t curves, of the current IO through the closing circuit in FIG. 9 show this situation. The current IO decreases first along a curve for a low resistance of the fixed resistor Ra, but decreases last along a curve for a high resistance of the resistor. This attenuation time of the current IO, if the number of the diodes is 9, in effect, is equivalent to the attenuation time for 30 ohms of the resistor Ra.

Consequently, the counter electromotive force induced in the solenoid 2 is prevented from being increased excessively and the attenuation time of the current is small like as the fixed resistor of a high resistance inserted in the conventional circuit. Further, by the use of an integrating circuit of the diodes, the circuit can be manufactured economically.

With the embodiment described above, the oscillation frequency f(HZ), the attenuation time of counter electromotive force (equal to the cutoff time of the transistor 36) T2, the voltage VCE (V) across the emitter and collector of the transistor 36 and the delivered volume Q (cc/min) changed as shown in FIG. 5 when the number of the diodes 37a was increased progressively.

The characteristic curves shown in FIG. 5 indicate the results obtained when the 1-ampere, 1-volt diode 37a ranging in number from 0 to 9 were connected in series with the counter electromotive force absorbing diode 38 employing the solenoid 2 whose number of turns = 500 T, resistance = 1.9 ohms and inductance = 25 mH, feedback coil 35 whose number of turns = 450 T, resistance = 1.9 ohms and inductance = 30 mH, transistors 36 whose current amplification factor = 40, and the 1-ampere, 1-volt diode 38 for absorbing counter electromotive force. The attenuation time T2 varied in the range from 50 to 18 ms. The oscillation frequency f changed in the range between 14 and 24 HZ and the delivered volume Q was increased in the range between 1,600 and 2,300 cc/min, while the variation of the voltage VCE across the emitter and collector of the transistor 36 were very small ranging from 14 to 22 volts.

While in the embodiment described above the voltage regulating unit 37 connected in series with the counter electromotive force absorbing diode 38 has been explained as employing ordinary diodes, other voltage regulating elements, such as, Zener diodes or varistors may of course be employed. If a Zener diode is employed, its anode (cathode) should be connected to the anode (cathode) of the counter electromotive force absorbing diode 38.

As explained hereinbefore, a novel feature of the electromagnetic pump according to the present invention is that since the series circuit of the counter electromotive force absorbing diode 38 and the voltage regulating unit 37 is connected in parallel with the solenoid 2 of the self-excited blocking oscillator circuit, by suitably selecting the resistance value of the voltage regulating unit 37, the oscillation frequency of the self-excited blocking oscillator circuit can be increased with the resultant increase in the amount of fuel delivered without considerably increasing the voltage across the solenoid 2 and hence the voltage applied across the emitter and collector of the transistor 36. Thus, in contrast to the conventional devices in which the resistor 34 is connected in series with the counter electromotive force absorbing diode 38, a low-voltage proof and inexpensive transistor may be employed for the transistor 36 and moreover the construction of the electromagnetic pump is simplified. Thus, in accordance with the present invention, there is provided an electromagnetic pump which is small and compact, capable of providing a large output and inexpensive to manufacture.