Liquid aeration delivery apparatus

Abstract

The invention is to prevent a nozzle located at a position immediately preceding a mixing chamber from becoming closed off with crystallized solute contained in a liquid which has become deposited and to prevent air supplied into the mixing chamber from flowing backward to a metering pump in a liquid aeration delivery apparatus for mixing the liquid with the air and delivering it. Accordingly, a liquid pressurized at a metering pump is supplied via an outlet flow passage and is injected into a mixing chamber from an orifice, but a needle is inserted into the orifice and is made to move by an electromagnetic valve used to open/close the outlet flow passage, so that the orifice is cleaned. In addition, air for mixture is supplied to the mixing chamber, but a pulse synchronous with a pulse applied to the metering pump is supplied to an air control valve provided at an air flow passage, so that supply of the air can be synchronized with the liquid supply to prevent an air backward flow. This invention is also to prevent the liquid from freezing and to prevent the internal pressure from rising to an abnormally high level.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a liquid aeration delivery apparatus in which a liquid such as urea water used for purposes of exhaust gas purification is mixed with air and then delivered.

Urea water (a urea aqueous solution) is widely used as a reducing agent in the purification of exhaust gas from diesel engines and the like. As disclosed in JP H7-279650 A, JP 2000-8833 A, JP 2003-232215 A and U.S. Pat. No. 3874822, for instance, urea water is injected through an injection nozzle into a discharge pipe located further toward the exhaust gas upstream side relative to the reduction catalyst. The injected urea water becomes hydrolyzed with the heat from the exhaust gas, thereby generating ammonia, and NO_x in the exhaust gas is reduced by the ammonia thus generated on the catalyst. Namely, the NO_x is converted to harmless substances, i.e., nitrogen (N₂) and water (H₂O).

The urea water used as the reducing agent in the process described above is supplied by a pump, is mixed with air in a mixing chamber located halfway through the supply path and reaches the nozzle through which it is injected into the discharge pipe in an aerated and atomized state.

Urea water used in the application described above has a disadvantage in that an orifice located at a position immediately preceding the mixing chamber becomes closed off by urea which has become deposited from the solution and has become crystallized during an operation us well as when the pump is in a stopped state. In addition, if an electromagnetic pump which is caused to make reciprocal movement by a pulse current is utilized as the pump, the supply pressure with which the urea water is output pulsates synchronously with the number of pulses. This is the natural outcome of the pulse-driven electromagnetic pump making the reciprocal movement. The pulsating supply pressure may become lower than the pressure of the air supplied into the mixing chamber to be mixed with the urea water, and in such a case, the air is allowed to flow in the reverse direction toward the pump, if only temporarily, which affects the injection quantity at the nozzle to lead to destabilization of the injection quantity. This gives rise to a problem such that the stability and reproducibility of the injection quantity are compromised.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to prevent the nozzle from becoming clogged even when a solute of the solution becomes deposited and to prevent the air which is mixed with the liquid in the mixing chamber from flowing backward to the metering pump that supplies the liquid.

Other objects of the present invention are to prevent the liquid from freezing and to prevent the internal pressure from rising to an abnormally high level.

A liquid aeration delivery apparatus according to the present invention comprises at least a metering pump which can control an output volume; an outlet flow passage provided on an outlet side of said metering pump; a mixing chamber provided at an end of said outlet flow passage, in which a liquid supplied from the metering pump is mixed with air; an orifice through which the liquid is supplied into the mixing chamber; an electromagnetic valve for opening/closing the out flow passage; and a needle inserted at the office and moving in cooperation with opening/closing movement of the electromagnetic valve.

Since the orifice is constantly cleaned by moving the needle with the electromagnetic valve for opening/closing the outlet flow passage, the substance contained in the liquid (urea water) force-fed from the metering pump, which has become deposited and crystallized, is not allowed to clog the orifice.

The liquid aeration delivery apparatus further comprises a means for preventing backward flow which prevents backward flow of air from the mixing chamber to the metering pump.

In the structure described above, the orifice is constantly cleaned by moving the needle via the electromagnetic valve for opening/closing the outlet passage to prevent a substance contained the liquid, having become deposited and crystallized, from clogging the orifice. In addition, since it has the means for preventing backward flow, the backward flow from of air from the mixing chamber is prevented, so that injection quantity can be stabilized.

The means for preventing backward flow is an air control valve which is provided in an air flow passage for supplying air to said mixing chamber; said air control valve closing said air flow passage in non-operating state, a drive pulse of said metering pump applying to said air control valve in operating state to be driven synchronously with said metering pump.

Accordingly, the air control valve can be controlled synchronously with a drive pulse of the metering pump, so that air's discharge to the mixing chamber can be stopped synchronously to prevent the air backward flow.

It is preferred that the means for preventing backward flow is to make said electromagnetic valve opening/closing movement synchronously with a drive pulse of said metering pump. Accordingly, the outlet flow passage is closed synchronously by operating the electromagnetic valve synchronously with the drive pulse of the metering pump to prevent the air backward flow.

The metering pump includes an electromagnetic coil to which a pulse current is applied, a plunger which is caused to move reciprocally by the electromagnetic coil, and an intake valve and an outlet valve that in conjunction with the plunger, achieve a pump function. The metering pump also includes a stopper that comes into contact with the plunger pressed by a resilient spring provided at one side of the plunger and a magnetic pole which attracts the plunger toward the spring at the plunger. As a result, an advantage is achieved in that the plunger is allowed to start moving away from the stopper any time by applying a pulse, which in turn, allows the metering pump to vary its output volume over a wide application frequency range.

A pressure sensor that also functions as an accumulator may be provided at the outlet flow passage extending from the metering pump and the mixing chamber so as to use the output of the pressure sensor as an indicator to monitor the operation of the aeration atomizing apparatus. In this case, the operating state can be ascertained based upon the output of the pressure sensor. In addition, at the pressure sensor, the pressure inside the outlet flow passage is received via a diaphragm, a piston having a magnet is disposed on the side of the diaphragm opposite from the side where the pressure is received and any displacement of the piston is detected with a magnetic sensor.

A temperature sensor may be provided within the outlet flow passage extending from the metering pump to the mixing chamber or in the vicinity of the outlet flow passage. By adopting this structure, it becomes possible to detect freezing of the urea water inside the pump caused by a decrease in the outside air temperature or any abnormal heat generation.

A liquid aeration delivery apparatus according to the present invention further comprises a means such that heat is generated by applying a DC current to the electromagnetic coil if the temperature sensor detects a temperature level equal to or lower than a predetermined level in a non-operating state thereof and the current applied to the electromagnetic coil is turned on/off based upon the output from the temperature sensor. Accordingly, the temperature of the liquid inside the pump is monitored by the temperature sensor, and the DC current is supplied to the electromagnetic coil at the metering pump if the liquid temperature is lowered to the freezing level to generate heat and thus prevent freezing. It is to be noted that the power is turned on as the liquid temperature becomes lower than −7° C. and is turned off once the liquid temperature reaches 0C.

Furthermore, a liquid aeration delivery apparatus according to the present invention further comprises a means for preventing an inner pressure from rising to an excessively high level such that the electromagnetic valve controlling opening/closing of the outlet flow passage is opened if the pressure sensor detects that the pressure in the metering pump and in the outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof Since it is possible to release the pressure to the outside by opening the electromagnetic valve when, for instance, the volume of the liquid in the pump has increased due to freezing by adopting this structure, the pump does not become ruptured. It is to be noted that when the liquid temperature is lowered to the freezing level, the temperature sensor described earlier also functions in conjunction with the pressure sensor to keep the pressure from rising.

As described above, according to the present invention, the displacement of the electromagnetic valve for opening/closing the outlet flow passage causes the needle to move to constantly clean the orifice and, as a result, a substance contained in the liquid (e.g. urea water) being force-fed, having become deposited and crystallized, does not clog the orifice.

Furthermore, the means for preventing backward flow for preventing air backward flow from the mixing chamber stops supplying air or closes the outlet passage even if an output pressure of the liquid from the metering pump is in a low level, so that the backward flow can be prevented. Accordingly, stabilization of the injection quantity is achieved.

The air supplied for mixing is supplied into the mixing chamber synchronously with the drive pulse of the metering pump by the air control valve, so that the backward flow can be prevented.

Also, since the electromagnetic valve closes the outlet passage synchronously with an output pulsation of the liquid from the metering pump when an output pressure of the liquid from the metering pump is in a low level, the air backward flow is prevented to achieve stabilization of injection quantity. Accordingly, in this case, the air control valve can be omitted to distribute to minimization of a device.

The plunger is allowed to start moving away from the stopper any time by applying a pulse, which in turn, allows the metering pump to vary the output volume over a wide application frequency range.

The pressure sensor is utilized as an indicator for operational monitoring as well as a pressure gauge. Accordingly, it becomes possible to infer the proper function of the metering pump.

The pressure sensor disclosed in the invention is a simpler structure.

Temperature management in the apparatus may become possible by the temperature sensor according to the present invention.

Furthermore, according to the present invention, if the temperature sensor detects a freezing temperature level in a non-operating state, a DC current is supplied to the electromagnetic coil at the metering pump to generate heat and the current applied to the electromagnetic coil is controlled based upon the temperature detected at by the temperature sensor.

In addition, according to the present invention, a rupture is prevented by opening the electromagnetic valve for opening/closing the outlet flow passage and thus releasing the pressure to the outside if the pressure sensor detects that the pressure has risen to a dangerously high level in a non-operating state.

Other and further objects, features and advantages of the invention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a liquid aeration delivery apparatus according to a first embodiment of the present invention;

FIG. 2 is a sectional view of the metering pump which is a component of the liquid aeration delivery apparatus according to the first embodiment;

FIG. 3 is a sectional view of the mixing device which is a component of the liquid aeration delivery apparatus according to the first embodiment;

FIG. 4 is a sectional view of the air control valve which is a component of the liquid aeration delivery apparatus according to the first embodiment;

FIG. 5 is a sectional view of the pressure sensor which is a component of a liquid aeration delivery apparatus according to the first embodiment;

FIG. 6 is a control characteristic flowchart diagram of the first embodiment of the present invention;

FIG. 7 is a flowchart presenting an example of control implemented to prevent freezing based upon the output from the temperature sensor according to the first embodiment of the present invention;

FIG. 8 is a sectional view of a liquid aeration delivery apparatus according to a second embodiment of the present invention;

FIG. 9 is a sectional view of the metering pump which is a component of the liquid aeration delivery apparatus according to the second embodiment;

FIG. 10 is a sectional view of the mixing device which is a component of the liquid aeration delivery apparatus according to the second embodiment;

FIG. 11 is a sectional view of the pressure sensor which is a component of the liquid aeration delivery apparatus according to the second embodiment;

FIG. 12 is a flowchart presenting an example of control implemented to prevent freezing based upon the output from the temperature sensor according to the second embodiment of the present invention; and

FIG. 13 is a control characteristic flowchart diagram of the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a liquid aeration delivery apparatus 1 according to a first embodiment of the present invention. A metering pump 2 in the liquid aeration delivery apparatus 1 is now explained in reference to FIGS. 1 and 2. The metering pump 2 includes a case 4 constituted of a magnetic material such as iron and mounted at an apparatus main unit 5 at an open end thereof, and also an electromagnetic coil 6 disposed inside the case 4, to which a pulse current is applied from a control unit (not shown).

At the electromagnetic coil 6, which is formed by winding an electric wire around a resin bobbin 3, a non-magnetic guide pipe 9 is fitted at a through hole 8 passing through the center of the bobbin 3. A right plate 10 and a left plate 11 are provided at the right end and the left end of the bobbin 3 respectively, to constitute a magnetic circuit together with the case 4.

To the right of the guide pipe 9, a magnetic rod 13 to constitute a magnetic pole is disposed, whereas a stopper 14 is fitted at the left end of the guide pipe 9. The magnetic rod 13 is constituted of a magnetic material such as iron, with substantially half of the magnetic rod 13 on left side inserted at the guide pipe 9 via an O-ring 15 and the remaining half, i.e., the right half, inserted at a barrel portion 19 of an intake coupling 17 to be detailed later via an O-ring 16. In addition, a communicating hole 18 passing through along the lateral direction is formed inside the magnetic rod 13, and the communicating hole 18 is connected to a urea water tank (not shown). Reference numeral 24 indicates a filter provided at the communicating hole 18.

In a communicating hole 20 formed at the magnetic rod 13, a check valve (intake valve) 21 constituted of rubber, resin or the like is disposed, and the check valve 21 made to sit at a valve seat 23 provided at the communicating hole 20 with a pressing force imparted by a spring 22.

An electromagnetic plunger operation chamber in which an electromagnetic plunger 27 constituted of a magnetic material such as iron is disposed is formed inside the guide pipe 9. The electromagnetic plunger 27 includes a large diameter portion 27a and a small diameter portion 27b continuous to the large diameter portion 27a and projecting to the right. A through hole 29 is formed along the axial direction at the large diameter portion 27a and the small diameter portion 27b, and a check valve (outlet valve) 30 is disposed at the through hole 29 in the small diameter portion 27b and is made to sit at a valve seat 32 with a spring 31. In addition, the small diameter portion 27b is slidably inserted at a cylinder 34 mounted at the magnetic rod 13 via an O-ring 34a.

Pressure is applied to the electromagnetic plunger 27 from a return spring 35 which imparts a strong force and, as a result, although there is also a spring 37 imparting a force along the opposite direction, the left end of the electromagnetic plunger 27 is placed in contact with the stopper 14. Namely, if no power is supplied to the electromagnetic coil 6, the electromagnetic plunger 27 is set at the return position at which its left end is in contact with the stopper 14, but whenever a pulse is applied to the electromagnetic coil 6, the electromagnetic plunger 27 is allowed to start moving away from the stopper 14. It is to be noted that the spring 37, which imparts only a weak force, may be omitted depending upon the particulars of the design requirements.

The left end of the electromagnetic plunger operation chamber 28 is made to communicate with an outlet flow passage 39 formed at the apparatus main unit 5 via a hole 38 at the stopper 14, and the outlet flow passage 39 extends to a mixing chamber 64 detailed below.

As a pulse current that can be varied over wide range is supplied to the electromagnetic coil 6 in the metering pump 2 structured as described above, the electromagnetic plunger 27 makes reciprocal movement. Namely, as the pulse is supplied, the magnetic rod 13 becomes magnetized and the attraction of the magnetized magnetic rod 13 causes the electromagnetic plunger 27 to move against the force imparted by the return spring 35.

Then, as the pulse ceases, the energy stored in the return spring 35 resets the left end of the electromagnetic plunger 27 to the position at which it comes in contact with the stopper 14. When the pulse is applied to the electromagnetic coil 6 again, the electromagnetic plunger 27 is caused to move as described above and thus, a pump function is achieved with the check valves 21 and 30 through the repeated motion of the electromagnetic plunger 27. Namely, the liquid, i.e., the urea water, is force-fed into the mixing chamber 64 with its quantity increased substantially in proportion to the application frequency.

While the metering pump 2 is operated over a wide range with regard to the pulse applied to the electromagnetic coil 6, the characteristics of the electromagnetic pump poses a hindrance to increasing the output volume to a desired level simply by increasing the frequency. Accordingly, the metering pump is constituted as a pulse-width dependent constant-volume electromagnetic pump that varies the pulse width in proportion to the frequency so as to increase the proportion of the output volume relative to the proportion of the frequency. The specific ranges of frequency between 2 Hz to 40 Hz and pulse width between 5 ms and 12.5 ms are selected for illustration in FIG. 6. It is to be noted that the pulse width and the output volume in the low output volume range (Min shown in FIG. 6) are respectively 5 (ms) and 1.5(g/min), the pulse width and the output volume in the middle output volume range (Mid shown in FIG. 6) are respectively 7.5 (ms) and 30.0 (g/min) and the pulse width and the output volume in the high output volume range (Max shown in FIG. 6) are respectively 12.5 (ms) and 123.4(g/min). Since “1 g” and “1 cc” of pure water are equal in quantity, the unit “g” could be replaced with “cc” if the liquid was pure water.

Now, a mixing device 43 is explained in reference to FIGS. 1 and 3. The mixing device 43 located on the left side of the apparatus main unit 5 includes an electromagnetic valve 44 provided at the left end of the outlet flow passage 39 to control the open/closed state of the outlet flow passage 39. The electromagnetic valve 44 includes a case 45 which is located on the outside and having an open end thereof attached to the apparatus main unit 5, and also an electromagnetic coil 46 located inside the case 45.

At the electromagnetic coil 46, which is formed by winding an electric wire around a resin bobbin 47, a non-magnetic guide pipe 48 is fitted in a through hole passing through the center of the bobbin 47. A right plate 50 and a left plate 51 are provided at the right end and the left end respectively of the bobbin 47, to constitute a magnetic circuit together with the case 45.

A magnetic rod 52 to constitute a magnetic pole is provided to the right of the guide pipe 48, whereas a valve seat 53 is provided to the left of the guide pipe 48. At the magnetic rod 52, constituted of a magnetic material such as iron, a communicating hole 54 with an orifice 57 is formed so as to extend along the axis of the magnetic rod 52. In addition, an electromagnetic plunger operation chamber 56, in which an electromagnetic plunger 55 constituted of a magnetic material is housed, is formed inside the guide pipe 48. The electromagnetic plunger 55 includes a communicating hole 58 formed so as to extend along the central axis, and the electromagnetic plunger 55 is made to sit at the valve seat 53 by the force applied by a spring 59 to close the outlet flow passage 39. Then, as power is supplied to the electromagnetic coil 46, the electromagnetic plunger 55 becomes displaced against the force applied by the spring 59, thereby opening the outlet flow passage 39. An O-ring 60 is mounted at the front end of the electromagnetic plunger 55 located on the side opposite from the side where the magnetic rod is present with a needle 61 projecting out at the same end. The needle 61 is inserted at an orifice 62 at the valve seat 53.

The orifice 62 through which the flow rate of the liquid supplied (injected) into the mixing chamber 64 is raised is formed at the center of the valve seat 53 located at the left end of the guide pipe 48. As described above, the needle 61 is inserted at the orifice 62 so that as the electromagnetic valve 44 is turned on/off, the needle 61 becomes displaced to clean the inside of the orifice 62.

The mixing chamber 64 is formed inside a connection member 66 having an outlet port 65, with the orifice 62 described above and an air supply hole 68 formed at the right end thereof. Thus, air is supplied into the mixing chamber 64 in the required quantity from an air tank or the like (not shown) via an air control valve 72 to be detailed below, and the urea water having been injected into the mixing chamber 64 becomes aerated with the air and atomized. Since the air supply hole 68 is connected to the inner circumferential surface of the mixing chamber 64 along the tangential direction, the air is supplied into the mixing chamber 64 in a rotary motion to further promote the aerated atomization of the urea water. The urea water having been aerated and atomized is sent out from the outlet port 65 via a nozzle 69 into a discharge pipe which is an external device.

The air control valve 72 is now explained in reference to FIGS. 1 and 4. The air control valve 72 located above the apparatus main unit 5 includes a case 73 constituted of a magnetic material, provided on the outside and having an open end thereof mounted at the apparatus main unit 5, and also includes an electromagnetic coil 74 provided inside the case 73. At the electromagnetic coil 74, which is formed by winding an electric wire around a resin bobbin 75, a non-magnetic guide pipe 76 is fitted in a through hole passing through the center of the bobbin 75. An upper plate 77 and a lower plate 78 are provided at the upper end and the lower end of the bobbin 75 respectively, to constitute a magnetic circuit together with the case 73.

At the top of the guide pipe 76, a magnetic rod 80 to constitute a magnetic pole is provided, whereas toward the bottom of the guide pipe 76, a valve seat 81 is provided. The magnetic rod 80 constituted of a magnetic material such as iron includes a communicating hole 82 extending along its axis. Above the magnetic rod 80, an intake coupling 85 connecting with an air flow passage 83 through which the air is supplied from the air tank provided. The valve seat 81 includes a communicating hole 84 which communicates with the mixing chamber 64 on its downstream side via the airflow passage 83. Inside the guide pipe 76 partitioned into spaces housing the magnetic rod 80 and the valve seat 81 as described above, an electromagnetic plunger operation chamber 87 in which an electromagnetic plunger 86 is disposed, is formed.

The electromagnetic plunger 86 includes a communicating hole 89 extending along the central axis, and also has a spherical valve element 90 mounted at one end thereof. The valve element 90 at the electromagnetic plunger 86 supported by a pair of springs 91 and 92 and provided in the electromagnetic plunger operation chamber 87 is made to sit at the valve seat 81 and thus, the communicating hole 84 is closed when no power is supplied. Then, as power is supplied, the valve element 90 departs from the valve seat 81 to open the communicating hole 84.

The air control valve 72 structured as described above is controlled by applying a pulse current to the electromagnetic coil 74. The air control valve 72 is driven synchronously with the drive pulses of the metering pump 2 when a pulse width applied to the metering pump 2 is narrow (namely, a low output volume range Min), as shown in FIG. 6, in relation to the metering pump 2.

Namely, a drive pulse with a rising side synchronous with a falling side of the drive pulse of the metering pump is made at the low output volume range (Min) of the metering pump 2. It is preferred that a delay processing which delays the up of the drive pulse is operated. A width of the drive pulse of the air control valve 72 is limited by a rising side of a next drive pulse of the metering pump 2.

Since the air to be mixed with the urea water achieves a constant pressure of 15 psi and thus there is a risk of the air flowing backward unless the air is supplied synchronously when the injection quantity of the urea water injected from the metering pump 2 is small, i.e., in a so-called low pulse rate condition (Min shown in FIG. 6), and the pulsating pressure inherent to the electromagnetic pump dips lower than the air pressure. The drive pulse of the air control valve can resolve the risk.

A pressure sensor 93 is described in reference to FIGS. 1 and 5. A pressure sensor main unit 94 fitted in the apparatus main unit 5 assumes a tubular shape and includes a piston 96 disposed inside a central chamber 95 and having a magnet 98, with a spring 97 applying a force to the piston 96. At the center of the piston 96, a magnetic sensor 99, which may be a Hall IC or a magnetic resistor element that reacts to magnetism, is provided. The magnetic sensor 99 is located at a rod 100 screwed onto the pressure sensor main unit 94 and the sensor sensitivity is adjusted by varying the position of the rod 100.

The pressure sensor main unit 94 assuming the structure described above is fitted in the apparatus main unit 5 via a diaphragm 101 which is connected to the outlet flow passage 39 formed at the apparatus main unit 5 via a branch flow passage 39a. Thus, as the pressure in the outlet flow passage 39 increases, the diaphragm 101 becomes displaced and, at the same time, the piston 96, too, becomes displaced against the force applied by the spring 97. The displacement of the piston 96 is detected with the magnetic sensor 99, and it becomes possible to infer the proper function of the metering pump according to displaying the sensor output (an output characteristic of the pressure sensor shown in FIG. 6).

Based upon the output from the pressure sensor 93, any abnormal increase in the pressure in the outlet flow passage 39 can be detected, and if the pressure rises to an abnormally high level, power is supplied to the electromagnetic coil 46 at the electromagnetic valve 44 described earlier to open the electromagnetic valve 44, thereby releasing the pressure to the outside and, as a result, any rupture is prevented.

Besides, it is not necessary to define the pressure sensor 93 to only a structure for detecting displacement as above-mentioned. It may have a structure which is provided with a means for detecting distortion by the pressure, a means for detecting thermoelectromotive force by the pressure dependence of the thermal conductivity, a means for detecting a voltage by the pressure dependence of the break-down voltage, a means for detecting an ionic current due to gaseous ionization phenomenon, a means which detects a phase due to the interference phenomenon of the light, or a means for detecting the strength of the light due to micro vent loss.

Now, in reference to FIGS. 1 and 7, a temperature sensor 103 is described. The temperature sensor 103 constituted of a thermistor provided near the outlet flow passage 39 in the apparatus main unit 5 detects the temperature of the apparatus. It becomes engaged in operation as the external air temperature becomes low in a non-operating state to prevent the urea water from freezing. Besides, it is not necessary to define the temperature sensor 103 to the thermistor, but a thermo couple, a metal resistance temperature sensor (a resistance bulb), heat sensitive magnetic material such as a heat sensitive ferrite, a bimetal thermostat, an IC temperature sensor, an infrared ray detecting element, a crystal temperature sensor, or a fluorescence type fiber temperature sensor can be used.

Namely, as shown in FIG. 7 presenting its control flow, a temperature signal provided by the temperature sensor 103 is taken in during a temperature detection step 201. Then, the operation proceeds to step 202 to judge the temperature. In this step, a decision is made as to whether or not the temperature has become equal to or lower than −7° C., and if it is decided that the temperature is equal to or lower than −7° C. and thus, there is a risk of the urea water freezing, the operation proceeds to step 203 to apply a DC current (DC 24 V) to the electromagnetic coil 6 at the metering pump 2. Thus, the electromagnetic valve generates heat. Then, proceeding to steps 204 and 205, the electromagnetic valve 44 and the air control valve 72 are opened.

After that, the temperature sensor 103 monitors the temperature of the apparatus main unit 5, and once the heat rises above 0° C., the operation proceeds to steps 206, 207 and 208 to stop applying DC current to the metering pump 2, for the electromagnetic valve to be closed and for the air control valve to be closed. The urea water is prevented from freezing through this control. It is to be noted that since the internal pressure rises if the urea water starts to freeze, the rise in the pressure is detected with the pressure sensor 93 and once the pressure rises to a level exceeding a predetermined level, the electromagnetic valve 44 is opened to preempt any possible problem in conjunction with the temperature sensor 103.

In the structure described above, a pulse current (2 to 40 Hz) is applied to the electromagnetic coil 6 at the metering pump 2 and the electromagnetic plunger 27 is thus caused to vibrate 2 to 40 times per second to achieve a pump function. This metering pump 2 achieves a linear output which is in proportion to the pulse rate. The liquid supplied from the metering pump (i.e., the urea water) travels through the outlet flow passage 39 and is injected into the mixing chamber 64 via the orifice 62, and in the mixing chamber 64, it becomes mixed with the air supplied thereto.

The orifice 62, which is cleaned with the needle 61, never becomes clogged since urea having been deposited and crystallized which then adheres to the orifice 62 is removed through the movement of the needle 61 caused by the electromagnetic valve 44 at an operation start. In addition, in the low output volume range (Min), since control is implemented with the air control valve 72 to supply the air in synchronization with the supply of the liquid from the metering pump 2, the air is not allowed to flow back toward the metering pump 2, thereby achieving stable injection through the nozzle.

The first embodiment described above is to use an engine of a large vehicle such as a truck, and it is difficult to use in a small size vehicle with a small displacement because it is too large. Therefore, a second embodiment of this invention is to use the electromagnetic valve 44 installed in the device as the means for preventing backward flow. Thus, the air control valve 72 can be omitted.

FIGS. 8 though 13 show a liquid aeration delivery apparatus 301 according to a second embodiment of the present invention. A metering pump 302 includes a case 304 constituted of a magnetic material such as iron and mounted at an apparatus main unit 305 at an open end thereof as shown in FIG. 9 too, and also an electromagnetic coil 306 disposed inside the case 304, to which a pulse current is applied from a control unit (not shown).

At the electromagnetic coil 306, which is formed by winding an electric wire around a resin bobbin 303, a non-magnetic guide pipe 309 is fitted at a through hole 308 passing through the center of the bobbin 303. A right plate 310 and a left plate 311 are provided at the right end and the left end of the bobbin 303 respectively, to constitute a magnetic circuit together is with the case 304.

To the right of the guide pipe 309, a magnetic rod 313 to constitute a magnetic pole is disposed, whereas a stopper 314 is fitted at the left end of the guide pipe 309. The magnetic rod 313 is constituted of a magnetic material such as iron, with substantially half of the magnetic rod 313 on left side inserted at the guide pipe 309 via an O-ring 315 and the remaining half, i.e., the right half, inserted at a barrel portion 319 of an intake coupling 317 to be detailed later via an O-ring 316. In addition, a communicating hole 318 passing through along the lateral direction is formed inside the magnetic rod 313, and the communicating hole 318 is connected to a urea water tank (not shown). Reference numeral 324 indicates a filter provided at the communicating hole 318.

In a communicating hole 320 formed at the magnetic rod 313, a check valve (intake valve) 321 constituted of rubber, resin or the like is disposed, and the check valve 321 made to sit at a valve seat 323 provided at the communicating hole 320 with a pressing force imparted by a spring 322.

An electromagnetic plunger operation chamber in which an electromagnetic plunger 327 constituted of a magnetic material such as iron is disposed is formed inside the guide pipe 309. The electromagnetic plunger 327 includes a large diameter portion 327a and a small diameter portion 327b continuous to the large diameter portion 327a and projecting to the right. A through hole 329 is formed along the axial direction at the large diameter portion 327a and the small diameter portion 327b, and a check valve (outlet valve) 330 is disposed at the through hole 329 in the small diameter portion 327b and is made to sit at a valve seat 332 with a spring 331. In addition, the small diameter portion 327b is slidably inserted at a cylinder 334 mounted at the magnetic rod 313 via an O-ring 334a.

Pressure is applied to the electromagnetic plunger 327 from a return spring 335 which imparts a strong force and, as a result, although there is also a spring 337 imparting a force along the opposite direction, the left end of the electromagnetic plunger 327 is placed in contact with the stopper 314. Namely, if no power is supplied to the electromagnetic coil 306, the electromagnetic plunger 327 is set at the return position at which its left end is in contact with the stopper 314, but whenever a pulse is applied to the electromagnetic coil 306, the electromagnetic plunger 327 is allowed to start moving away from the stopper 314. It is to be noted that the spring 337, which imparts only a weak force, may be omitted depending upon the particulars of the design requirements.

The left end of the electromagnetic plunger operation chamber 328 is made to communicate with an outlet flow passage 339 formed at the apparatus main unit 305 via a hole 338 at the stopper 314, and the outlet flow passage 339 extends to a mixing chamber 364 detailed below.

As a pulse current that can be varied over a wide range is supplied to the electromagnetic coil 306 in the metering pump 302 structured as described above, the electromagnetic plunger 327 makes reciprocal movement. Namely, as the pulse is supplied, the magnetic rod 313 becomes magnetized and the attraction of the magnetized magnetic rod 313 causes the electromagnetic plunger 327 to move against the force imparted by the return spring 335.

Then, as the pulse ceases, the energy stored in the return spring 335 resets the left end of the electromagnetic plunger 327 to the position at which it comes in contact with the stopper 314. When the pulse is applied to the electromagnetic coil 306 again, the electromagnetic plunger 327 is caused to move as described above and thus, a pump function is achieved with the check valves 321 and 330 through the repeated motion of the electromagnetic plunger 327. Namely, the liquid, i.e., the urea water, is force-fed into the mixing chamber 364 with its quantity increased substantially in proportion to the application frequency.

While the metering pump 302 is operated over a wide range with regard to the pulse applied to the electromagnetic coil 306, the characteristics of the electromagnetic pump poses a hindrance to increasing the output volume to a desired level simply by increasing the frequency. Accordingly, the metering pump is constituted as a pulse-width dependent constant-volume electromagnetic pump that varies the pulse width in proportion to the frequency so as to increase the proportion of the output volume relative to the proportion of the frequency. The specific ranges of frequency between 2 Hz to 40 Hz and pulse width between 5 ms and 12.5 ms are selected for illustration in FIG. 13. It is to be noted that the pulse width and the output volume in the low output volume range (Min shown in FIG. 13) are respectively 5 (ms) and 1.5(g/min), the pulse width and the output volume in the middle output volume range (Mid shown in FIG. 13) are respectively 7.5 (ms) and 30.0 (g/min) and the pulse width and the output volume in the high output volume range (Max shown in FIG. 13) are respectively 12.5 (ms) and 123.4(g/min). Since “1 g” and “1 cc” of pure water are equal in quantity, the unit “g” could be replaced with “cc” if the liquid was pure water.

Now, a mixing device 343 is explained in reference to FIGS. 8 and 10. The mixing device 343 located on the left side of the apparatus main unit 305 includes an electromagnetic valve 344 provided at the left end of the outlet flow passage 339 to control the open/closed state of the outlet flow passage 339. The electromagnetic valve 344 includes a case 345 which is located on the outside and having an open end thereof attached to the apparatus main unit 5, and also an electromagnetic coil 346 located inside the case 345.

At the electromagnetic coil 346, which is formed by winding an electric wire around a resin bobbin 347, a non-magnetic guide pipe 348 is fitted in a through hole passing through the center of the bobbin 347. A right plate 350 and a left plate 351 are provided at the right end and the left end respectively of the bobbin 347, to constitute a magnetic circuit together with the case 345.

A magnetic rod 352 to constitute a magnetic pole is provided to the right of the guide pipe 348, whereas a valve seat 353 is provided to the left of the guide pipe 348. At the magnetic rod 352, constituted of a magnetic material such as iron, a communicating hole 354 with an orifice 357 is formed so as to extend along the axis of the magnetic rod 352. In addition, an electromagnetic plunger operation chamber 356, in which an electromagnetic plunger 355 constituted of a magnetic material is housed, is formed inside the guide pipe 348. The electromagnetic plunger 355 includes a communicating hole 358 formed so as to extend along the central axis, and the electromagnetic plunger 355 is made to sit at the valve seat 353 by the force applied by a spring 359 to close the outlet flow passage 339. Then, as power is supplied to the electromagnetic coil 346, the electromagnetic plunger 355 becomes displaced against the force applied by the spring 359, thereby opening the outlet flow passage 339. An O-ring 360 is mounted at the front end of the electromagnetic plunger 355 located on the side opposite from the side where the magnetic rod is present with a needle 361 projecting out at the same end. The needle 361 is inserted at an orifice 362 at the valve seat 353.

The orifice 362 through which the flow rate of the liquid supplied (injected) into the mixing chamber 364 is raised is formed at the center of the valve seat 353 located at the left end of the guide pipe 348. As described above, the needle 361 is inserted at the orifice 362 so that as the electromagnetic valve 344 is turned on/off, the needle 61 becomes displaced to clean the inside of the orifice 362.

The mixing chamber 364 is formed inside a connection member 366 having an outlet port 365, with the orifice 362 described above and an air supply hole 368 formed at the right end thereof. Thus, air is supplied into the mixing chamber 364 in the required quantity from an air tank or the like (not shown) via an air control valve 372 to be detailed below, and the urea water having been injected into the mixing chamber 364 becomes aerated with the air and atomized. Since the air supply hole 368 is connected to the inner circumferential surface of the mixing chamber 364 along the tangential direction, the air is supplied into the mixing chamber 364 in a rotary motion to further promote the aerated atomization of the urea water. The urea water having been aerated and atomized is sent out from the outlet port 365 via a nozzle 369 into a discharge pipe which is an external device.

A pressure sensor 393 is described in reference to FIGS. 8 and 11. A pressure sensor main unit 394 fitted in the apparatus main unit 305 assumes a tubular shape and includes a piston 396 disposed inside a central chamber 395 and having a magnet 398, with a spring 397 applying a force to the piston 396. At the center of the piston 396, a magnetic sensor 399, which may be a Hall IC or a magnetic resistor element that reacts to magnetism, is provided. The magnetic sensor 399 is located at a rod 400 screwed onto the pressure sensor main unit 394 and the sensor sensitivity is adjusted by varying the position of the rod 400.

The pressure sensor main unit 394 assuming the structure described above is fitted in the apparatus main unit 305 via a diaphragm 401 which is connected to the outlet flow passage 339 formed at the apparatus main unit 305 via a branch flow passage 339a. Thus, as the pressure in the outlet flow passage 339 increases, the diaphragm 401 becomes displaced and, at the same time, the piston 396, too, becomes displaced against the force applied by the spring 397. The displacement of the piston 396 is detected with the magnetic sensor 399, and it becomes possible to infer the proper function of the metering pump according to displaying the sensor output (an output characteristic of the pressure sensor shown in FIG. 13).

Based upon the output from the pressure sensor 393, any abnormal increase in the pressure in the outlet flow passage 339 can be detected, and if the pressure rises to an abnormally high level, power is supplied to the electromagnetic coil 346 at the electromagnetic valve 344 described earlier to open the electromagnetic valve 344, thereby releasing the pressure to the outside and, as a result, any rupture is prevented.

Besides, it is not necessary to define the pressure sensor 393 to only a structure for detecting displacement as above-mentioned. It may have a structure which is provided with a means for detecting distortion by the pressure, a means for detecting thermoelectromotive force by the pressure dependence of the thermal conductivity, a means for detecting a voltage by the pressure dependence of the break-down voltage, a means for detecting an ionic current due to gaseous ionization phenomenon, a means which detects a phase due to the interference phenomenon of the light, or a means for detecting the strength of the light due to micro vent loss.

Now, in reference to FIGS. 8 and 12, a temperature sensor 403 is described. The temperature sensor 403 constituted of a thermistor provided near the outlet flow passage 339 in the apparatus main unit 305 detects the temperature of the apparatus. It becomes engaged in operation as the external air temperature becomes low in a non-operating state to prevent the urea water from freezing. Besides, it is not necessary to define the temperature sensor 403 to the thermistor, but a thermo couple, a metal resistance temperature sensor (a resistance bulb), heat sensitive magnetic material such as a heat sensitive ferrite, a bimetal thermostat, an IC temperature sensor, an infrared ray detecting element, a crystal temperature sensor, or a fluorescence type fiber temperature sensor can be used.

Namely, as shown in FIG. 12 presenting its control flow, a temperature signal provided by the temperature sensor 403 is taken in during a temperature detection step 501. Then, the operation proceeds to step 502 to judge the temperature. In this step, a decision is made as to whether or not the temperature has become equal to or lower than −7° C., and if it is decided that the temperature is equal to or lower than −7° C. and thus, there is a risk of the urea water freezing, the operation proceeds to step 503 to apply a DC current (DC 24 V) to the electromagnetic coil 306 at the metering pump 302. Thus, the electromagnetic valve generates heat. Then, proceeding to step 504, the electromagnetic valve 344 is opened.

After that, the temperature sensor 403 monitors the temperature of the apparatus main unit 305, and once the heat rises above 0° C., the operation proceeds to steps 506 and 507 to stop applying DC current to the metering pump 2 and for the electromagnetic valve 344 to be closed. The urea water is prevented from freezing through this control. It is to be noted that since the internal pressure rises if the urea water starts to freeze, the rise in the pressure is detected with the pressure sensor 393 and once the pressure rises to a level exceeding a predetermined level, the electromagnetic valve 344 is opened to preempt any possible problem in conjunction with the temperature sensor 403.

In the structure described above, a pulse current (2 to 40 Hz) is applied to the electromagnetic coil 306 at the metering pump 302 and the electromagnetic plunger 327 is thus caused to vibrate 2 to 40 times per second to achieve a pump function. This metering pump 302 achieves a linear output which is in proportion to the pulse rate. The liquid supplied from the metering pump (i.e., the urea water) travels through the outlet flow passage 339 and is injected into the mixing chamber 364 via the orifice 362, and in the mixing chamber 364, it becomes mixed with the air supplied thereto.

The orifice 362, which is cleaned with the needle 361, never becomes clogged since urea having been deposited and crystallized which then adheres to the orifice 362 is removed through the movement of the needle 361 caused by the electromagnetic valve 344 at an operation start. In addition, the electromagnetic valve 344 is operated synchronously with the drive pulse of the metering pump 302 in order to prevent the air backward flow to the metering pump 302 in a range from the middle output volume range (Mid) to the low output volume range (Min), as shown in FIG. 13.

Namely, in the middle and the law outlet volume ranges, the electromagnetic valve 344 is opened by a rising side of the drive pulse synchronously with a falling side of the drive pulse of the metering pump 302, and is closed by falling down the drive pulse before the next drive pulse of the metering pump 302. As a result, since the liquid flows into the mixing chamber when the outlet pressure from the metering pump 302 is high and the outlet passage 339 is closed to prevent the air backward flow when the outlet pressure lowers, the injection quantity of the liquid is stabilized. Note that a rising of the drive pulse of the electromagnetic valve 344 is given about 2 ms delay.

Claims

1. A liquid aeration delivery apparatus comprising at least:

a metering pump which can control an output volume;

an outlet flow passage provided on an outlet side of said metering pump;

a mixing chamber provided at an end of said outlet flow passage, in which a liquid supplied from said metering pump is mixed with air;

an orifice through which said liquid is supplied into said mixing chamber;

an electromagnetic valve for opening/closing said out flow passage; and

a needle inserted at said office and moving in cooperation with opening/closing movement of said electromagnetic valve.

2. A liquid aeration delivery apparatus according to claim 1 further comprising a means for preventing backward flow which prevents backward flow of air from said mixing chamber to said metering pump.

3. A liquid aeration delivery apparatus according to claim 2, wherein:

said means for preventing backward flow is an air control valve which is provided in an air flow passage for supplying air to said mixing chamber; said air control valve closing said air flow passage in non-operating state, a drive pulse of said metering pump applying to said air control valve in operating state to be driven synchronously with said metering pump.

4. A liquid aeration delivery apparatus according to claim 2, wherein:

said means for preventing backward flow is to make said electromagnetic valve opening/closing movement synchronously with a drive pulse of said metering pump.

5. A liquid aeration delivery apparatus according to claim 1, wherein:

said metering pump is provided with an electromagnetic coil to which a pulse current is applied, a plunger which is caused to move reciprocally by said electromagnetic coil, and an intake valve and an output valve for achieving a pump function in cooperation with said plunger; and

said metering pump is further provided with a stopper which comes into contact with said plunger pressed by a spring provided on one side of said plunger and a magnetic pole attracts said plunger toward said spring.

6. A liquid aeration delivery apparatus according to claim 2, wherein:

said metering pump is provided with an electromagnetic coil to which a pulse current is applied, a plunger which is caused to move reciprocally by said electromagnetic coil, and an intake valve and an output valve for achieving a pump function in cooperation with said plunger; and

said metering pump is further provided with a stopper which comes into contact with said plunger pressed by a spring provided on one side of said plunger and a magnetic pole attracts said plunger toward said spring.

7. A liquid aeration delivery apparatus according to claim 3, wherein:

said metering pump is provided with an electromagnetic coil to which a pulse current is applied, a plunger which is caused to move reciprocally by said electromagnetic coil, and an intake valve and an output valve for achieving a pump function in cooperation with said plunger; and

said metering pump is further provided with a stopper which comes into contact with said plunger pressed by a spring provided on one side of said plunger and a magnetic pole attracts said plunger toward said spring.

8. A liquid aeration delivery apparatus according to claim 4, wherein:

said metering pump is provided with an electromagnetic coil to which a pulse current is applied, a plunger which is caused to move reciprocally by said electromagnetic coil, and an intake valve and an output valve for achieving a pump function in cooperation with said plunger; and

said metering pump is further provided with a stopper which comes into contact with said plunger pressed by a spring provided on one side of said plunger and a magnetic pole attracts said plunger toward said spring.

9. A liquid aeration delivery apparatus according to claim 1, wherein:

a pressure sensor that also functions as an accumulator is provided at said outlet flow passage extending from said metering pump and said mixing chamber so as to use the output of said pressure sensor as an indicator to monitor the operation of said aeration atomizing apparatus.

10. A liquid aeration delivery apparatus according to claim 2, wherein:

a pressure sensor that also functions as an accumulator is provided at said outlet flow passage extending from said metering pump and said mixing chamber so as to use the output of said pressure sensor as an indicator to monitor the operation of said aeration atomizing apparatus.

11. A liquid aeration delivery apparatus according to claim 3, wherein:

a pressure sensor that also functions as an accumulator is provided at said outlet flow passage extending from said metering pump and said mixing chamber so as to use the output of said pressure sensor as an indicator to monitor the operation of said aeration atomizing apparatus.

12. A liquid aeration delivery apparatus according to claim 4, wherein:

a pressure sensor that also functions as an accumulator is provided at said outlet flow passage extending from said metering pump and said mixing chamber so as to use the output of said pressure sensor as an indicator to monitor the operation of said aeration atomizing apparatus.

13. A liquid aeration delivery apparatus according to claim 9, wherein:

a pressure inside said outlet flow passage is received via a diaphragm at said pressure sensor, a piston having a magnet is disposed on the side of said diaphragm opposite from the side where the pressure is received and any displacement of said piston is detected with a magnetic sensor.

14. A liquid aeration delivery apparatus according to claim 10, wherein:

a pressure inside said outlet flow passage is received via a diaphragm at said pressure sensor, a piston having a magnet is disposed on the side of said diaphragm opposite from the side where the pressure is received and any displacement of said piston is detected with a magnetic sensor.

15. A liquid aeration delivery apparatus according to claim 11, wherein:

a pressure inside said outlet flow passage is received via a diaphragm at said pressure sensor, a piston having a magnet is disposed on the side of said diaphragm opposite from the side where the pressure is received and any displacement of said piston is detected with a magnetic sensor.

16. A liquid aeration delivery apparatus according to claim 12, wherein:

a pressure inside said outlet flow passage is received via a diaphragm at said pressure sensor, a piston having a magnet is disposed on the side of said diaphragm opposite from the side where the pressure is received and any displacement of said piston is detected with a magnetic sensor.

17. A liquid aeration delivery apparatus according to claim 5, wherein:

a temperature sensor is disposed within or near said outlet flow passage extending from said metering pump to said mixing chamber.

18. A liquid aeration delivery apparatus according to claim 6, wherein:

a temperature sensor is disposed within or near said outlet flow passage extending from said metering pump to said mixing chamber.

19. A liquid aeration delivery apparatus according to claim 7, wherein:

a temperature sensor is disposed within or near said outlet flow passage extending from said metering pump to said mixing chamber.

20. A liquid aeration delivery apparatus according to claim 8, wherein:

a temperature sensor is disposed within or near said outlet flow passage extending from said metering pump to said mixing chamber.

21. A liquid aeration delivery apparatus according to claim 17, further comprising a means for generating heat by applying a DC current to said electromagnetic coil if said temperature sensor detects a temperature level equal to or lower than a predetermined level in a non-operating state thereof and turning on/off the applied current based upon the output from said temperature sensor.

22. A liquid aeration delivery apparatus according to claim 18, further comprising a means for generating heat by applying a DC current to said electromagnetic coil if said temperature sensor detects a temperature level equal to or lower than a predetermined level in a non-operating state thereof and turning on/off the applied current based upon the output from said temperature sensor.

23. A liquid aeration delivery apparatus according to claim 19, further comprising a means for generating heat by applying a DC current to said electromagnetic coil if said temperature sensor detects a temperature level equal to or lower than a predetermined level in a non-operating state thereof and turning on/off the applied current based upon the output from said temperature sensor.

24. A liquid aeration delivery apparatus according to claim 20, further comprising a means for generating heat by applying a DC current to said electromagnetic coil if said temperature sensor detects a temperature level equal to or lower than a predetermined level in a non-operating state thereof and turning on/off the applied current based upon the output from said temperature sensor.

25. A liquid aeration delivery apparatus according to claim 17, further comprising a means for preventing an inner pressure from rising to an excessively high level which makes said electromagnetic valve open if said pressure sensor detects that the pressure in said metering pump and in said outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof.

26. A liquid aeration delivery apparatus according to claim 18, further comprising a means for preventing an inner pressure from rising to an excessively high level which makes said electromagnetic valve open if said pressure sensor detects that the pressure in said metering pump and in said outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof.

27. A liquid aeration delivery apparatus according to claim 19, further comprising a means for preventing an inner pressure from rising to an excessively high level which makes said electromagnetic valve open if said pressure sensor detects that the pressure in said metering pump and in said outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof.

28. A liquid aeration delivery apparatus according to claim 20, further comprising a means for preventing an inner pressure from rising to an excessively high level which makes said electromagnetic valve open if said pressure sensor detects that the pressure in said metering pump and in said outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof.

29. A liquid aeration delivery apparatus according to claim 21, further comprising a means for preventing an inner pressure from rising to an excessively high level which makes said electromagnetic valve open if said pressure sensor detects that the pressure in said metering pump and in said outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof.

30. A liquid aeration delivery apparatus according to claim 22, further comprising a means for preventing an inner pressure from rising to an excessively high level which makes said electromagnetic valve open if said pressure sensor detects that the pressure in said metering pump and in said outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof.

31. A liquid aeration delivery apparatus according to claim 23, further comprising a means for preventing an inner pressure from rising to an excessively high level which makes said electromagnetic valve open if said pressure sensor detects that the pressure in said metering pump and in said outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof.

32. A liquid aeration delivery apparatus according to claim 24, further comprising a means for preventing an inner pressure from rising to an excessively high level which makes said electromagnetic valve open if said pressure sensor detects that the pressure in said metering pump and in said outlet flow passage has risen to a level equal to or higher than a predetermined level in an non-operating state thereof.