U.S. patent application number 10/879226 was filed with the patent office on 2006-01-19 for liquid aeration delivery apparatus.
Invention is credited to Takashi Nakamura, Teruya Sawada, Yuin Wu.
Application Number | 20060013704 10/879226 |
Document ID | / |
Family ID | 35599623 |
Filed Date | 2006-01-19 |
United States Patent
Application |
20060013704 |
Kind Code |
A1 |
Sawada; Teruya ; et
al. |
January 19, 2006 |
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.
Inventors: |
Sawada; Teruya; (Sakado,
JP) ; Nakamura; Takashi; (Sakado, JP) ; Wu;
Yuin; (San Mateo, CA) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
35599623 |
Appl. No.: |
10/879226 |
Filed: |
June 30, 2004 |
Current U.S.
Class: |
417/311 |
Current CPC
Class: |
Y02T 10/24 20130101;
F01N 2610/08 20130101; F01N 2610/1453 20130101; F01N 3/2066
20130101; B01F 5/0057 20130101; F04B 17/046 20130101; B01F 3/0446
20130101; F01N 2610/1433 20130101; Y02T 10/12 20130101; F01N 3/208
20130101; B01F 15/00019 20130101; F04B 53/08 20130101; F04B 13/02
20130101 |
Class at
Publication: |
417/311 |
International
Class: |
F04B 49/00 20060101
F04B049/00 |
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.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.sub.x in the exhaust gas is reduced by the ammonia thus
generated on the catalyst. Namely, the NO.sub.x is converted to
harmless substances, i.e., nitrogen (N.sub.2) and water
(H.sub.2O).
[0003] 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.
[0004] 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
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.degree. C. and
is turned off once the liquid temperature reaches 0C.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] The pressure sensor disclosed in the invention is a simpler
structure.
[0026] Temperature management in the apparatus may become possible
by the temperature sensor according to the present invention.
[0027] 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.
[0028] 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.
[0029] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a sectional view of a liquid aeration delivery
apparatus according to a first embodiment of the present
invention;
[0031] 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;
[0032] 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;
[0033] 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;
[0034] 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;
[0035] FIG. 6 is a control characteristic flowchart diagram of the
first embodiment of the present invention;
[0036] 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;
[0037] FIG. 8 is a sectional view of a liquid aeration delivery
apparatus according to a second embodiment of the present
invention;
[0038] 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;
[0039] 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;
[0040] 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;
[0041] 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
[0042] FIG. 13 is a control characteristic flowchart diagram of the
second embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] 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).
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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).
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.degree. C., and if it is decided that the
temperature is equal to or lower than -7.degree. 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.
[0070] After that, the temperature sensor 103 monitors the
temperature of the apparatus main unit 5, and once the heat rises
above 0.degree. 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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).
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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).
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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.degree. C., and if it is decided that the
temperature is equal to or lower than -7.degree. 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.
[0095] After that, the temperature sensor 403 monitors the
temperature of the apparatus main unit 305, and once the heat rises
above 0.degree. 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.
[0096] 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.
[0097] 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.
[0098] 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.
* * * * *