U.S. patent application number 13/711767 was filed with the patent office on 2013-08-01 for urea-water pump device.
This patent application is currently assigned to DENSO CORPORATION. The applicant listed for this patent is Denso Corporation. Invention is credited to Takaaki IWADARE, Tomohisa NAGAYA.
Application Number | 20130192699 13/711767 |
Document ID | / |
Family ID | 48783909 |
Filed Date | 2013-08-01 |
United States Patent
Application |
20130192699 |
Kind Code |
A1 |
NAGAYA; Tomohisa ; et
al. |
August 1, 2013 |
UREA-WATER PUMP DEVICE
Abstract
A urea-water pump device for an exhaust gas cleaner includes a
pump, a motor, a temperature detection portion, a setting portion,
and a changing portion. The pump is accommodated in a tank and
supplies urea-water stored in the tank. The motor drives the pump.
The temperature detection portion directly or indirectly detects a
temperature of the urea-water stored in the tank. The setting
portion sets an upper-limit-value of a current supplied to the
motor. The changing portion changes the upper-limit-value of the
current supplied to the motor, based on the temperature of the
urea-water detected by the temperature detection portion.
Inventors: |
NAGAYA; Tomohisa; (Obu-city,
JP) ; IWADARE; Takaaki; (Tokai-city, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Denso Corporation; |
Kariya-city |
|
JP |
|
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
48783909 |
Appl. No.: |
13/711767 |
Filed: |
December 12, 2012 |
Current U.S.
Class: |
137/565.01 |
Current CPC
Class: |
Y10T 137/85978 20150401;
Y02T 10/12 20130101; F01N 2900/0422 20130101; Y02T 10/24 20130101;
F01N 3/208 20130101; F01N 2900/1811 20130101; F01N 2610/144
20130101; F01N 3/04 20130101 |
Class at
Publication: |
137/565.01 |
International
Class: |
F01N 3/04 20060101
F01N003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2012 |
JP |
2012-16578 |
Claims
1. A urea-water pump device for an exhaust gas cleaner cleaning
exhaust gas by adding a urea-water stored in a tank to the exhaust
gas flowing through an exhaust passage, the urea-water pump device
comprising: a pump accommodated in the tank, the pump supplying the
urea-water from the tank toward the exhaust passage; a motor
driving the pump; a temperature detection portion directly or
indirectly detecting a temperature of the urea-water stored in the
tank; a setting portion setting an upper-limit-value of a current
supplied to the motor; and a changing portion changing the
upper-limit-value of the current supplied to the motor based on the
temperature of the urea-water detected by the temperature detection
portion.
2. The urea-water pump device according to claim 1, wherein the
changing portion changes the upper-limit-value to a value larger
than a preset inherent initial value when the temperature of the
urea-water detected by the temperature detection portion is smaller
than or equal to a preset lower-limit-value.
3. The urea-water pump device according to claim 1, wherein the
changing portion changes the upper-limit-value to a preset inherent
initial value when the temperature of the urea-water detected by
the temperature detection portion is larger than a preset
lower-limit-value.
4. The urea-water pump device according to claim 1, wherein the
changing portion further has a time detection portion detecting an
elapsed time period from a point that the motor is activated, and
the changing portion changes the upper-limit-value to a preset
inherent initial value when the elapsed time period detected by the
time detection portion is larger than a preset setting time period.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The application is based on Japanese Patent Application No.
2012-16578 filed on Jan. 30, 2012, the disclosure of which is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a urea-water pump device
for an exhaust gas cleaner.
BACKGROUND
[0003] Conventionally, a urea selective catalyst reduction (SCR)
system is publicly known for reducing nitrogen oxide (NOx) included
in gas exhausted from an internal combustion engine by adding
urea-water. In a urea SCR system described in JP-2009-144644A,
urea-water stored in a tank is supplied to an injector provided in
an exhaust passage by a pump accommodated in the tank. When the
urea-water is frozen in a low temperature environment, the
urea-water is thawed by heat generated by a motor of the pump which
is activated. In a view of protecting the motor and a control
circuit for the motor, it is necessary to control a current
supplied to the motor at the startup time.
[0004] When the current supplied to the motor is constricted during
the startup time, a heat-generation amount of the motor may
decrease, because the heat-generation amount is proportional to the
supplied current. In this case, the heat-generation amount may be
not enough for thawing the urea-water in the tank.
SUMMARY
[0005] It is an object of the present disclosure to provide a
urea-water pump device so that thawing of urea-water can be
promoted and that protection of a motor and a control circuit can
be achieved.
[0006] According to an aspect of the present disclosure, an exhaust
gas cleaner cleans exhaust gas by adding a urea-water stored in a
tank to the exhaust gas flowing though an exhaust passage, and a
urea-water pump device for the exhaust gas cleaner includes a pump,
a motor, a temperature detection portion, a setting portion, and a
changing portion. The pump is accommodated in the tank, and
supplies the urea-water stored in the tank toward the exhaust
passage. The motor drives the pump. The temperature detection
portion directly or indirectly detects a temperature of the
urea-water stored in the tank. The setting portion sets an
upper-limit-value of current supplied to the motor. The changing
portion changes the upper-limit-value of the current supplied to
the motor, based on the temperature of the urea-water detected by
the temperature detection portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The above and other objects, features and advantages of the
present disclosure will become more apparent from the following
detailed description made with reference to the accompanying
drawings. In the drawings:
[0008] FIG. 1 is a block diagram illustrating an outline of a
urea-water pump device according to a first embodiment;
[0009] FIG. 2 is a schematic view illustrating an outline of an
exhaust gas cleaner having the urea-water pump device according to
the first embodiment;
[0010] FIG. 3 is a flowchart illustrating a procedure performed by
a controller of the urea-water pump device according to the first
embodiment;
[0011] FIG. 4 is a graph illustrating a relationship between time
and current supplied to a pump which discharges non-frozen
urea-water;
[0012] FIG. 5 is a graph illustrating a relationship between time
and current supplied, to a pump which discharges frozen urea-water,
according to the first embodiment;
[0013] FIG. 6 is a graph illustrating a relationship between time
and current supplied to a pump which discharges frozen urea-water,
according to a comparison example; and
[0014] FIG. 7 is a block diagram illustrating an outline of a
urea-water pump device according to a second embodiment,
DETAILED DESCRIPTION
[0015] Embodiments of the present disclosure will be described
hereafter referring to drawings. In the embodiments, a part that
corresponds to a matter described in a preceding embodiment may be
assigned with the same reference numeral, and redundant explanation
for the part may be omitted. When only a part of a configuration is
described in an embodiment, another preceding embodiment may be
applied to the other parts of the configuration. The parts may be
combined even if it is not explicitly described that the parts can
be combined. The embodiments may be partially combined even if it
is not explicitly described that the embodiments can be combined,
provided there is no harm in the combination.
First Embodiment
[0016] An exhaust gas cleaner 10 having a urea-water pump
controller 20 will be described referring to FIG. 2. The exhaust
gas cleaner 10 may correspond to a urea-water selective catalytic
reduction system (urea-water SCR system). In the urea-water SCR
system, urea-water is added into exhaust gas which is exhausted
from an internal combustion engine 11 mounted to a vehicle to
reduce nitrogen oxide (NOx) included in the exhaust gas. The
exhaust gas is exhausted to the atmosphere via an exhaust passage
13 defined by an exhaust pipe 12. The internal combustion engine 11
may be a diesel engine. The exhaust gas cleaner 10 is not limited
to be applied to the diesel engine. The exhaust gas cleaner 10 may
be applied to a gasoline engine or a gas turbine engine.
[0017] The exhaust gas cleaner 10 includes a tank 14, a pump 15, a
urea-water pipe 16, and an injector 17. The tank 14 stores the
urea-water (urea solution). The pump 15 is accommodated in the tank
14. At least a part of the pump 15 is immersed into the urea-water
in the tank 14. The urea-water pipe 16 couples the pump 15 and the
injector 17 with each other. The urea-water discharged from the
pump 15 is supplied to the injector 17 via a urea-water passage 18
defined by the urea-water pipe 16. The injector 17 is provided in
the exhaust pipe 12 which defines the exhaust passage 13. The
injector 17 is inserted into the exhaust pipe 12. The injector 17
includes an injection port (not shown) on the end portion. The end
portion of the injector 17 is exposed in the exhaust passage 13.
The urea-water is injected from the injection port of the injector
17 into the exhaust gas flowing through the exhaust passage 13. A
reduction catalyst 19 is provided in the exhaust passage 13. The
exhaust gas and the urea-water are mixed in the exhaust passage 13,
and then the mixture flows into the reduction catalyst 19. The NOx
included in the exhaust gas is reduced in the reduction catalyst 19
by reacting with the urea-water. The urea-water may be added into
the exhaust gas by other components instead of the injector 17.
[0018] The urea-water pump controller 20 includes a motor 21, a
control unit 22, and a temperature sensor 23 in addition of the
pump 15 of the exhaust gas cleaner 10. The motor 21 may be a DC
brushless motor activated by a current supplied from the control
unit 22. The motor 21 drives the pump 15. Thus, the pump 15
discharges the urea-water from the tank 14 to the urea-water
passage 18 by an operation of the motor 21. The motor 21 is unified
with the pump 15, and at least a part of the motor 21 is immersed
into the urea-water in the tank 14 as the same with the pump 15.
The temperature sensor 23 detects a temperature of the urea-water
in the tank 14. The temperature sensor 23 transmits an electrical
signal corresponding to the detected temperature of the urea-water
to the control unit 22.
[0019] The urea-water pump controller 20 further includes a
urea-water quantity sensor 24 and a heater 25. The urea-water
quantity sensor 24 detects a quantity of the urea-water stored in
the tank 14. The urea-water quantity sensor 24 transmits the
detected quantity of the urea-water to the control unit 22 as an
electrical signal. The heater 25 generates heat by an electrical
power supplied from the control unit 22. The temperature of the
urea-water is kept by the heat generated by the heater 25.
[0020] The control unit 22 will be described referring to FIG. 1.
The control unit 22 includes a controller 31 configured by a
microcomputer having a CPU, a ROM and a RAM (not shown). The
controller 31 may correspond to a temperature acquiring portion 32,
a changing portion 33, a setting portion 34, and a motor driver 35,
as a hard ware by a unified electronic circuit. In addition, based
on implementing a computer program stored in the ROM of the
controller 31, the temperature acquiring portion 32, the changing
portion 33, the setting portion 34, and the motor driver 35 may be
achieved by a combination of a soft ware and a hard ware.
[0021] The temperature acquiring portion 32 is coupled to the
temperature sensor 23, and acquires a detected temperature from the
temperature sensor 23. According to the present embodiment, the
temperature sensor 23 directly detects the temperature of the
urea-water in the tank 14. In this case, the temperature sensor 23
and the temperature acquiring portion 32 may configure a
temperature detection portion 36.
[0022] Further, the temperature detection portion 36 may also
indirectly detect the temperature of the urea-water. An outside
temperature, a coolant temperature of the internal combustion
engine 11, or a temperature of an environment surrounding the
control unit 22, relates to the temperature of the urea-water in
the tank 14. In this case, the temperature of the urea-water may be
indirectly measured based on at least one of the outside
temperature detected by an outside sensor, the coolant temperature
of the internal combustion engine 11 detected by a coolant sensor,
and a temperature of the control unit 22 detected by a temperature
sensor.
[0023] The changing portion 33 changes an upper-limit-value Ia for
a current supplied to the motor 21. The current supplied to the
motor 21 has a preset upper-limit-value for protecting elements of
electronic circuits configuring the motor 21 and the control unit
22. The upper-limit-value Ia is set to an initial value Id as an
inherent initial value of the motor 21 and the control unit 22. The
changing portion 33 changes the upper-limit-value Ia based on a
temperature of the urea-water detected by the temperature detection
portion 36.
[0024] Specifically, when the temperature of the urea-water is
smaller than or equal to a preset lower-limit-value 11, the
changing portion 33 changes the upper-limit-value Ia to a value
larger than the initial value Id. The lower-limit-value Ti
corresponds to a melting point of the urea-water.
[0025] The setting portion 34 sets the upper-limit-value of the
current supplied to the motor 21 to the upper-limit-value Ia
changed by the changing portion 33. The motor driver 35 is coupled
to the motor 21. The motor driver 35 controls the motor 21
according to a load of the pump 15 under a condition with the
upper-limit-value Ia set by the setting portion 34.
[0026] Since at least a part of the motor 21 is immersed in the
urea-water in the tank 14 as the same with the pump 15, the
temperature of the motor 21 relates to the temperature of the
urea-water in the tank 14. The motor 21 generates heat by a current
supplied from the control unit 22 for activating the motor 21. When
the temperature of the urea-water surrounding the motor 21 is low,
the raising in the temperature of the motor 21 is slight because
the heat generated by the motor 21 is absorbed by the urea-water
even though the current supplied to the motor 21 has a relatively
large value. When the temperature of the urea-water surrounding the
motor 21 is high, the temperature of the motor 21 may raise easily.
Therefore, the upper-limit-value Ia can be set larger when the
temperature of the urea-water is low.
[0027] The changing portion 33 changes the upper-limit-value la
based on the temperature of the urea-water detected in the
temperature detection portion 36. Specifically, when the
temperature of the urea-water is smaller than or equal to the
preset lower-limit-value Ti, the changing portion 33 changes the
upper-limit-value Ia to a value larger than the initial value Id.
The setting portion 34 sets the upper-limit-value of the current
supplied to the motor 21 to the upper-limit-value changed by the
changing portion 33. Therefore, a current value larger than the
initial value Id is supplied from the motor driver 35 to the motor
21.
[0028] Operation of the urea-water pump controller 20 will be
described with reference to FIG. 3.
[0029] At S101, the setting portion 34 sets the upper-limit-value
to the initial value Id when an engine control unit (ECU, not
shown) of the internal combustion engine 11 requires to activate
the pump 15. That is, the setting portion 34 sets the
upper-limit-value to the inherent initial value Id for safety.
Thus, the current supplied to the motor 21 is controlled up to the
initial value Id at first.
[0030] At S102, the temperature detection portion 36 detects the
temperature of the urea-water in the tank 14 from the temperature
sensor 23 and the temperature acquiring portion 32.
[0031] At S103, the changing portion 33 determines whether the
temperature of the urea-water detected at S102 is smaller than or
equal to the preset lower-limit-value Ti. Because the melting point
of the urea-water varies according to the concentration of the urea
in the urea solution, the lower-limit-value Ti is set according to
the concentration of the urea.
[0032] When the temperature of the urea-water is smaller than or
equal to the lower-limit-value Ti (S103: Yes), the initial value Id
set at S101 is changed at S104. That is, the changing portion 33
cancels the initial value Id, and changes the upper-limit-value to
infinity (unlimited) at S104. Alternatively, the changing portion
33 may change the upper-limit-value to an extended
upper-limit-value Ib which is preset according to the initial value
Id. The extended upper-limit-value Ib may be larger than the
initial value Id. The extended upper-limit-value Ib is set as an
optional value such that the motor 21 and the control unit 22 are
not damaged. Furthermore, the changing portion 33 may change the
upper-limit-value by using a function with respect to the
temperature of the urea-water. Thus, the changing portion 33
changes the upper-limit-value to a value larger than the initial
value Id according to the temperature detected at S102.
[0033] The setting portion 34 sets the upper-limit-value Ia, which
is changed at S104. When the temperature of the urea-water is
smaller than or equal to the lower-limit-value Ti which corresponds
to the melting point of the urea-water, the urea-water may freeze.
The generation of heat in the motor 21 is used for thawing the
urea-water even though the upper-limit-value Ia is changed to a
value larger than the initial value Id. An increase in the
temperature of the motor 21 is constricted by the thawing.
Therefore, since the setting portion 34 sets the upper-limit-value
Ia to a value larger than the initial value Id, a thawing of the
urea-water is promoted while the motor 21 is protected.
[0034] After the upper-limit-value Ia is changed at S104, the motor
21 is activated at S105. That is, the motor driver 35 supplies a
current to the motor 21 in a manner that the upper-limit-value of
the current corresponds to the upper-limit-value Ta changed at
S104.
[0035] When the temperature of the urea-water is larger than the
lower-limit-value Ti (S103: No), the changing portion 33 keeps the
upper-limit-value Ta to the initial value Id set at S101. In this
case, the motor driver 35 activates the motor 21 in a manner that
the upper-limit-value of the current supplied to the motor 21 is
set to the initial value Id which is set at S101.
[0036] When the motor 21 is activated, the controller 31 determines
whether a stop request for requesting a stop of the pump 15 is
transmitted from the ECU, at S106. When the controller 31 received
the stop request (S106: Yes), the controller 31 stops the motor 21
at S107. Then the procedure is completed.
[0037] When the controller 31 determines that no stop request is
received (S106: No), the temperature detection portion 36 detects
the temperature of the urea-water once again at S108. Then, at
S109, the changing portion 33 determines whether the temperature of
the urea-water detected at S108 is larger than the preset
lower-limit-value Ti.
[0038] When the changing portion 33 determines that the temperature
of the urea-water detected at S108 is larger than the
lower-limit-value Ti (S109: Yes), the changing portion 33 changes
the upper-limit-value Ia changed at S104 to the initial value Id
again at S110.
[0039] When the temperature of the urea-water is larger than the
lower-limit-value Ti, it is likely that the urea-water has thawed
completely. Thus, a urea-water quantity of absorbing the generation
of heat in the motor 21 decreases. If the upper-limit-value of the
current supplied to the motor 21 is kept to a value larger than the
initial value Id, the motor 21 may overheat, and then elements of
the motor 21 and the motor driver 35 may be damaged. In this case,
it is necessary that the changing portion 33 changes the
upper-limit-value Ta changed at S104 to the initial value Id
again.
[0040] When the upper-limit-value Ia is changed to the initial
value Id again at S110, the controller 31 returns to S106. When the
changing portion 33 determines that the temperature of the
urea-water is smaller than or equal to the lower-limit-value Ti
(S109: No), the changing portion 33 keeps the upper-limit-value Ta
changed at S104. That is, the changing portion 33 repeats the
routine without changing the upper-limit-value. When the
temperature of the urea-water is smaller than or equal to the
lower-limit-value Ti, it is likely that the urea-water has not
thawed yet. Therefore, the changing portion 33 keeps the
upper-limit-value to the upper-limit-value Ia changed at S104.
[0041] FIG. 4 illustrates a case where non-frozen urea-water is
discharged from the pump 15 to the injector 17. In this case, the
current supplied to the motor 21 increases in accordance with a
startup of the motor 21. The current flowing through the motor 21
becomes the maximum directly after the motor 21 is activated as a
startup current Is. Usually, the upper-limit-value is set to the
initial value Id for protecting the elements of the motor 21 and
the motor driver 35. Thus, the current reaches the initial value Id
before reaching the startup current Is, so the current is limited
to the initial value Id. When the motor 21 operates continuously, a
load of the pump 15 decreases, and thereby the value of the current
becomes smaller than the initial value Id. The motor 21 can operate
stably according to the current smaller than the initial value
Id.
[0042] FIG. 5 illustrates a case where frozen urea-water is
discharged from the pump 15 to the injector 17 according to the
first embodiment. In the first embodiment, the upper-limit-value Ia
is changed to a value larger than the initial value Id. Then, the
current supplied to the motor 21 reaches the startup current Is
larger than the initial value Id.
[0043] After the motor 21 is activated, the current supplied to the
motor 21 is lowered to become smaller than the startup current Is
in accordance with time. At this time, the current is kept to an
operation current Ir which is larger than the initial value Id by a
load applied to the pump 15 from the frozen urea-water.
[0044] According to the first embodiment, since the
upper-limit-value Ia is changed to a value larger than the initial
value Id, the operation current Ir supplied to the motor 21 is kept
as the value larger than the initial value Id. When the urea-water
is frozen, a current larger than the initial value Id is
continuously supplied to the motor 21. Thus, the generation of heat
in the motor 21 becomes larger, and the thawing of the urea-water
in the tank 14 is promoted. Since the urea-water is frozen, the
generation of heat in the motor 21 is used for thawing the
urea-water.
[0045] After the urea-water is thawed, the temperature of the
urea-water increases so that the temperature becomes larger than
the lower-limit-value Ti (melting point). When the temperature of
the urea-water is larger than the melting point, the
upper-limit-value Ia is changed to the initial value Id. Then, the
current supplied to the motor 21 is smaller than or equal to the
initial value Id. Thus, the generation of heat in the motor 21
decreases.
[0046] A comparison example will be described with reference to
FIG. 6 in which the current supplied to the motor 21 is limited to
the initial value Id. When the frozen urea-water is discharged from
the pump 15 to the injector 17, the upper-limit-value Ia is kept to
the initial value Id. The current supplied to the motor 21 is
limited to the initial value Id even during the startup of motor
21. Besides, the current supplied to the motor 21 is kept to the
initial value Id after the motor 21 is activated even when a load
is added to the pump 15 by the frozen urea-water.
[0047] In the comparison example, the current value corresponding
to the initial value Id is supplied to the motor 21, no matter
whether the urea-water is frozen. If a size of the motor 21 or the
control unit 22 is relatively smaller, the rated temperature is
low. In this case, if the upper-limit-value cannot be set to be a
value larger than the initial value Id, the generation of heat in
the motor 21 may not be enough so that it is difficult to thaw the
urea-water by the generation of heat.
[0048] In FIG. 5, the current supplied to the motor 21 is increased
by a hatched area with diagonal lines, according to the first
embodiment, with respect to the comparison example shown in FIG. 6.
A heat-generation amount of the motor 21 is proportional to the
supplied current. Thus, the heat-generation amount of the first
embodiment is larger than the heat-generation amount of the
comparison example. The thawing of the frozen urea-water is
promoted in the first embodiment.
[0049] Usually, a startup time limit-value of the current supplied
to the motor is set according to the motor and a controller for
controlling the motor. Specifically, the startup time limit-value
of the current flowing through the motor is set to a specified
value in a manner that the temperatures of the motor and the
controller are not exceeding the rated temperature when the motor
and the controller are used in the highest temperature environment
allowed for the motor and the controller.
[0050] Temperatures of the pump and the motor are substantially the
same as the temperature of the urea-water, so the motor is in a
sufficiently low temperature environment where the urea-water is
frozen. A controller for controlling the motor, such as a changing
portion or a setting portion, is most likely in the sufficiently
low temperature environment. In this case, an increase in the
temperature of the motor and the controller is constricted
according to the low temperature environment, even though the motor
is activated. Therefore, when a current larger than usual is
supplied to the motor, a heat-generation amount of the motor is
ensured, while the increase in the temperatures of the motor and
the control circuit are constricted.
[0051] The limit-value is set to a specified value within a range
in which the temperatures of the motor and the control circuit are
not exceeding the rated temperature, even in the highest
temperature environment. When the motor is activated in the low
temperature environment, the temperatures of the motor and the
controller are kept to a temperature sufficiently lower than the
rated temperature even though the current corresponding to the
limit-value is supplied. Thus, the limit-value can be set to a
value larger than usual, and the current having the value can be
supplied to the motor, when the motor and the control circuit are
in the low temperature environment.
[0052] According to the first embodiment, the changing portion 33
changes the upper-limit-value of the current supplied to the motor
21 based on the temperature of the urea-water of the tank 14
detected by the temperature detection portion 36. The temperatures
of the pump 15 and the motor 21 are substantially the same as the
temperature of the urea-water. When the urea-water is frozen, not
only the motor 21, but also the control unit 22 such as the
changing portion 33 or the setting portion 34 are in a sufficiently
low temperature environment. In this case, an increase in the
temperature of the motor 21 or the control unit 22 is constricted
according to the low temperature environment, even when a
relatively-large current flows through the motor 21. When a current
larger than usual is supplied to the motor 21, the heat-generation
amount of the motor 21 is ensured, while the increase in the
temperatures of the motor 21 and the control unit 22 are
constricted.
[0053] When the changing portion 33 changes the upper-limit-value
Ia based on the temperature of the urea-water, the setting portion
34 sets the current supplied to the motor 21 to the
upper-limit-value Ia changed by the changing portion 33. Since the
current larger than the initial value Id is supplied to the motor
21 in the low temperature environment, the heat-generation amount
of the motor 21 increases. Therefore, a large heat-generation
amount can be obtained even when the size of the motor 21 or the
control unit 22 is small, in which the rated temperature is
low.
[0054] Thus, a protection of the motor 21 or the control unit 22
can be achieved, and the thawing of the urea-water can be promoted.
The motor 21 can be used together with the heater 25 for thawing
the urea-water by using the generation of heat in the motor 21. In
this case, if a thawing time is fixed, an output of the heater 25
and the power consumption can be reduced. Further, if the output of
the heater 25 is maintained, the thawing can be rapidly
achieved.
[0055] According to the first embodiment, the changing portion 33
sets the upper-limit-value Ia to the inherent initial value Id when
the temperature of the urea-water is larger than the
lower-limit-value Ti. That is, the changing portion 33 sets the
upper-limit-value Ia to the initial value Id when the temperature
of the urea-water is larger than the melting point. When the
temperature of the urea-water surrounding the motor 21 increases,
the upper-limit-value of the current supplied to the motor 21 is
reset to the inherent initial value Id. Therefore, the protection
of the motor 21 or the control unit 22 can be achieved.
Second Embodiment
[0056] The urea-water pump controller 20 according to a second
embodiment is shown in FIG. 7.
[0057] The urea-water pump controller 20 according to the second
embodiment further includes a timer 41 as a time detection portion
compared with the first embodiment. The timer 41 detects an elapsed
time period from a point that the motor 21 is activated. The
changing portion 33 changes the upper-limit-value Ia to the
inherent initial value Id of the motor 21, when the elapsed time
period detected by the timer 41 is larger than a preset setting
time period.
[0058] The changing portion 33 changes the upper-limit-value Ia to
the initial value Id when the temperature of the urea-water is
larger than the lower-limit-value Ti (melting point) in the first
embodiment.
[0059] In contrast, in the second embodiment, the current supplied
to the motor 21 may be controlled by a supplying time instead of
the temperature of the urea-water, in a view of protecting the
motor 21. The supplying time is an elapsed time period where the
current supplied to the motor 21 is larger than the initial value
Id. Therefore, according to the second embodiment, the timer 41
detects the elapsed time period from a point that the motor 21 is
activated. When the elapsed time period is larger than the preset
setting time period, the changing portion 33 changes the
upper-limit-value Ia to the initial value Id. In the second
embodiment, the elapsed time period is controlled to be within the
setting time period.
[0060] According to the second embodiment, the changing portion 33
changes the upper-limit-value Ia to the inherent initial value Id
of the motor 21, when the elapsed time period is larger than the
setting time period. A time period, in which the current larger
than the initial value Id is supplied to the motor 21, is
controlled to be within the setting time period. Thus, an
electronic circuit of the motor 21 or the control unit 22 can be
protected.
[0061] Such changes and modifications are to be understood as being
within the scope of the present disclosure as defined by the
appended claims.
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