U.S. patent application number 13/907947 was filed with the patent office on 2014-12-04 for air driven reductant dosing system.
The applicant listed for this patent is Baohua Qi, Mi Yan. Invention is credited to Baohua Qi, Mi Yan.
Application Number | 20140352280 13/907947 |
Document ID | / |
Family ID | 51983566 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140352280 |
Kind Code |
A1 |
Qi; Baohua ; et al. |
December 4, 2014 |
AIR DRIVEN REDUCTANT DOSING SYSTEM
Abstract
A dosing system for delivering reductant into an exhaust gas
treatment system of an internal combustion engine using an air
driven hydraulic pump, which includes a pressure pump tank and a
liquid supply tank, for closed-loop controlling reductant pressure,
and a three-stage PWM control method for dosing rate control.
Reductant residue in the dosing system is purged by using
compressed air, and when the air driven hydraulic pumps is
positioned inside a reductant tank, heating means in the reductant
tank can also be used for heating the air driven hydraulic pump.
The closed-loop pressure control together with the three-stage PWM
control allow dosing accuracy insensitive to pressure variations in
compressed air, thereby a variety of compressed air sources can be
used.
Inventors: |
Qi; Baohua; (Columbus,
IN) ; Yan; Mi; (Columbus, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Qi; Baohua
Yan; Mi |
Columbus
Columbus |
IN
IN |
US
US |
|
|
Family ID: |
51983566 |
Appl. No.: |
13/907947 |
Filed: |
June 2, 2013 |
Current U.S.
Class: |
60/274 ;
60/286 |
Current CPC
Class: |
F01N 2610/1406 20130101;
F01N 2610/1493 20130101; Y02T 10/24 20130101; F01N 2900/0422
20130101; F01N 3/208 20130101; F01N 2610/1466 20130101; F01N
2610/02 20130101; F01N 2610/08 20130101; F01N 2900/1821 20130101;
F01N 2900/1808 20130101; Y02T 10/12 20130101; F01N 3/2066
20130101 |
Class at
Publication: |
60/274 ;
60/286 |
International
Class: |
F01N 3/10 20060101
F01N003/10 |
Claims
1. An apparatus for delivering reductants into an exhaust gas
system of an internal combustion engine comprising: a reductant
tank; a compressed air source; a liquid supply tank having a first
inlet port fluidly coupled to said reductant tank through a check
valve, a second inlet port fluidly coupled to said compressed air
source, a first outlet port for releasing compressed air from said
liquid supply tank, and a second outlet port for reductant inside
said liquid supply tank to flow out; a pressure pump tank
comprising a liquid inlet port fluidly coupled to said second
outlet port of said liquid supply tank through a check valve, and a
liquid outlet port; an injector with a reductant inlet fluidly
coupled to said liquid outlet port of said pressure pump tank for
controlling reductant flow rate to said exhaust gas system; a
pressure control means controlling air flow to said liquid supply
tank configured to control reductant pressure in said liquid supply
tank by refilling air to said liquid supply tank through said
second inlet port, and releasing air through said first outlet
port, and a dosing rate control means configured to energize open
said injector for a period of time in a periodically repeating
cycle in releasing reductant to said exhaust gas system.
2. The apparatus of claim 1, wherein said pressure control is
further configured to control reductant pressure in said liquid
supply tank higher than that in said pressure pump tank in
refilling said pressure pump tank, and configured to release air in
said liquid supply tank in refilling said liquid supply tank.
3. The apparatus of claim 1, further comprising: a pressure sensor
for providing sensing values indicative to a reductant pressure in
said pressure pump tank.
4. The apparatus of claim 3, wherein said pressure control is
further configured to control reductant pressure in said liquid
supply tank according to at least said sensing values obtained from
said pressure sensor.
5. The apparatus of claim 3, wherein said pressure pump tank
further comprises a gas inlet port fluidly coupled to said
compressed air source and said pressure control is further
configured to control reductant pressure in said pressure pump tank
according to at least said sensing values obtained from said
pressure sensor.
6. The apparatus of claim 5, wherein said pressure pump tank
further comprises a gas outlet for releasing air from said pressure
pump tank.
7. The apparatus of claim 3, wherein said dosing rate control means
is further configured to energize said injector open for a period
of time in a periodically repeating cycle according to at least
said sensing values obtained from said pressure sensor.
8. The apparatus of claim 1, further comprising: a fluid bypass
path including a reductant passage and a control valve, wherein
said fluid bypass path fluidly couples said reductant inlet of said
injector to said reductant tank.
9. The apparatus of claim 8, wherein said pressure control means is
further configured to control reductant pressure in said pressure
pump tank by opening said control valve in said fluid bypass path
to release reductant from said pressure pump.
10. A method for controlling reductant delivery rate of a reductant
dosing system including a pressure pump tank with a liquid outlet
port, an injector with a reductant inlet fluidly coupled to said
liquid outlet port of said pressure pump tank, a pressure sensor
for providing sensing values indicative to reductant pressure in
said pressure pump tank, a first signal generator generating a
first PWM signal, in a repeating cycle of which, a dosing target
value is generated, a second signal generator generating a second
PWM pulse signal, the duty cycle of which is determined by a second
duty cycle value, and a third signal generator generating a third
PWM signal for energizing and de-energizing said injector,
comprising: calculating a dosing amount value indicative to an
amount of reductant released in said repeating cycle of said first
PWM signal after said injector is energized open, according to at
least said sensing value obtained from said pressure sensor;
generating said second duty cycle value according to at least said
dosing amount value and said dosing target value, and setting duty
cycle for said third PWM signal generator according to as least
said second duty cycle value.
11. The method of claim 10, further comprising: setting said second
duty cycle value to a first value if a sum of said dosing amount
value and a threshold, which is indicative to an amount of
reductant released when said second duty cycle value is 100%, is
lower than said dosing target value; setting said second duty cycle
value to a second value if the sum of said dosing amount value and
said threshold is higher than said dosing target value, and said
dosing amount value is lower than said dosing target value, and
setting said second duty cycle value to a third value if said
dosing amount value is higher than said dosing target value.
12. The method of claim 10, further comprising: at a moment in a
repeating cycle of said first PWM signal, setting said third duty
cycle value to a first value if a time period starting from a
starting moment of said repeating cycle to said moment in said
repeating cycle is shorter than a pre-determined threshold, and
said second PWM signal is in its high state, otherwise, setting
said third duty cycle value to a second value if said time period
is longer than said pre-determined threshold, and said second PWM
signal is in its high state, and setting said third duty cycle
value to a third value if said second PWM signal is in its low
state.
13. A method for controlling a reductant dosing system including a
reductant tank, a compressed air source, a liquid supply tank
having a first inlet port fluidly coupled said reductant tank
through a check valve, a second inlet port fluidly coupled to said
compressed air source, a first outlet port for releasing compressed
air from said liquid supply tank, and a second outlet port for
reductant inside said liquid supply tank to flow out, a pressure
pump tank comprising a liquid inlet port fluidly coupled to said
second outlet port of said liquid supply tank through a check
valve, and a liquid outlet port, a pressure sensor for providing
sensing values indicative to reductant pressure in said pressure
pump tank, and an injector with a reductant inlet fluidly coupled
to said liquid outlet port of said pressure pump tank for
controlling reductant flow rate to said exhaust gas system,
comprising: releasing air in said liquid supply tank through said
first outlet port to refill said liquid supply tank; feeding
compressed air into said liquid supply tank through said second
inlet port to press reductant in said liquid supply tank into said
pressure pump tank, and energizing said injector open for a period
of time in a periodically repeating cycle when said sensing values
obtained from said pressure sensor are higher than a pre-determined
threshold.
14. The method of claim 13, wherein said pressure pump tank in said
reductant dosing system further includes a gas inlet port fluidly
coupled to said compressed air source.
15. The method of claim 14, further comprising: feeding compressed
air into said pressure pump tank through said gas inlet port to
compensate air loss.
16. The method of claim 14, wherein said pressure pump tank in said
reductant dosing system further includes a gas outlet port for
releasing air.
17. The method of claim 16, further comprising: maintaining
reductant pressure in said pressure pump tank within a
pre-determined range by releasing air from said pressure pump tank
through said gas outlet port and feeding compressed air into said
pressure pump tank through said gas inlet port according to said
sensing values obtained from said pressure sensor.
18. The method of claim 17, wherein an upper limit of said
pre-determined range is set lower than a pressure of said
compressed air.
19. The method of claim 13, wherein said reductant dosing system
further comprises a fluid bypass path including a reductant passage
and a control valve, wherein said fluid bypass path fluidly couples
said reductant inlet of said injector to said reductant tank.
20. The method of claim 19, further comprising: releasing reductant
back to said reductant tank through said fluid bypass path by
opening said control valve.
Description
[0001] This present application claims priority from U.S.
provisional application No. 61/689,517 having the same title as the
present invention and filed on Jun. 7, 2012.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to an apparatus and method for
delivering reductant into an exhaust gas treatment system of an
internal combustion engine for removing regulated species in
exhaust gas, and more specifically, to an apparatus and method
using an air driven hydraulic pump to deliver liquid reducing
agents into an exhaust gas treatment system of an internal
combustion engine.
BACKGROUND OF THE INVENTION
[0003] Environmentally harmful species in the exhaust gas emitted
from an internal combustion engine, such as hydrocarbons (HC),
carbon monoxide (CO), particulate matters (PM), and nitric oxides
(NOx) are regulated species that need to be removed from the
exhaust gas. In lean combustion engines, due to the existence of
large amount oxygen excess, passive means without extra dosing
agents, such as that using a three-way catalyst, normally are not
able to effectively remove the oxidative specie NOx, as that in
most of spark-ignition engines. To reduce NOx in lean combustion
engines, a variety of active means with reducing agents
(reductants) being dosed in exhaust gas are developed. In these
technologies, the reductant is metered and injected into the
exhaust gas, and the result mixture flows into a SCR (Selective
Catalytic Reduction) catalyst, where the reductant selectively
reacts with NOx generating non-poisonous species, such as nitrogen,
carbon dioxide, and water.
[0004] A variety of reductants, such as ammonia (NH3), HC, and
hydrogen (H2) can be used in SCR systems. Among them, ammonia SCR
is used most broadly due to high conversion efficiency and wide
temperature window. Ammonia can be dosed directly. However, due to
safety concerns and difficulties in handling pure ammonia, normally
urea solution is used in ammonia SCR systems. Urea can be
decomposed to ammonia through thermolysis and hydrolysis in exhaust
gas, and urea solution, therefore, is also called reductant in an
ammonia SCR system.
[0005] Typically, in a SCR control system, the required ammonia
dosing rate is calculated in an ECU (Engine Control Unit). If a
reductant other than ammonia, e.g., urea solution, is used, then
according to its ammonia conversion ratio, e.g. the ammonia
conversion ratio is 1:2 for urea (i.e. one urea molecule is able to
generate two ammonia molecules), the required reductant flow rate
is calculated and the dosing rate command is sent to a dosing
system, where reductant is metered and injected into exhaust gas.
Generally, similar to fueling control, there are two methods in
metering reductant. One method is using a metering pump, with which
the reductant flow rate is precisely controlled by controlling the
motor speed of the pump. The other method is more like that used in
a common rail fueling control system. In this method, a pressure is
built up and maintained constant in a reductant rail or a buffer,
and reductant flow rate is controlled by adjusting the open time of
an injector, which is fluidly connected to the buffer, in a
periodically repeating cycle.
[0006] Atomization of reductant is important to SCR conversion
efficiency, especially in a urea SCR system, where dosed urea needs
to be decomposed to ammonia through thermolysis and hydrolysis, and
the heat energy provided by exhaust gas is limited. In the first
reductant metering method, though the control is simple, the
reductant pressure is not controlled. Therefore, to have a good
atomization, in addition to having a well-designed nozzle
facilitating atomization, normally the reductant dosing needs to be
mixed with an extra air supply which provides a continuous air
flow. The requirements of a continuous air flow and a precisely
controlled metering pump limit the application of this method. The
second reductant metering method doesn't need an extra air supply
to facilitate atomization, since under high pressure, injected
reductant from a well-designed nozzle has good atomization.
However, in this method, due to the requirement of pressure
control, typically a liquid pump, such as a membrane pump driven by
a motor, is needed in establishing and maintaining the rail
pressure, and a motor control system is required.
[0007] Additionally, to avoid being frozen under low ambient
temperature, reductant residue inside the dosing system need to be
purged before the dosing system is shut off. In a system using the
first reductant metering method, compressed air can be used to
press reductant residue into exhaust air and back to reductant
tank, while in that using the second method, an extra reductant
flow control is needed to drive reductant residue back. In dosing
systems which have reductant residue in connection lines, line
heating means are also required. Different from reductant tank
heating control, line heating is a distributed heating and it is
difficult to use closed-loop controls. Except using costly PTC
(Positive Temperature Coefficient) materials, heating efficiency or
heating power and line durability need to be carefully balanced,
since locally high temperature could damage the heating line.
[0008] To decrease the complexity of a reductant dosing system and
at the same time achieve good performance, a primary object of the
present invention is to provide a reductant dosing apparatus using
air driven hydraulic pumps with simple pressure control to build up
and maintain a high pressure in a rail. The air driven hydraulic
pump doesn't have a motor inside and, therefore, doesn't need
electrical energy and a complex motor control to drive it. Neither
the air driven hydraulic pump needs a continuous air supply.
[0009] A further object of the present invention is to provide a
dosing rate control insensitive to variations in reductant
pressure, so that accurate pressure control is not required.
[0010] Another object of the present invention is to provide a
control means using compressed air to drain reductant residue back
to tank when dosing completes.
[0011] Yet another object of the present invention is to provide a
dosing apparatus with an air driven hydraulic pump positioned
inside a reductant tank, thereby no extra heating means other than
tank heating is required.
BRIEF SUMMARY OF THE INVENTION
[0012] The present invention provides an apparatus and method for
delivering reductant into an exhaust gas treatment system of an
internal combustion engine. More specifically, this apparatus
includes a reductant supply module with a pressure pump tank (PPT)
and a liquid supply tank (LST), a reductant tank, a dosing control
unit (DCU), and an injector. In an embodiment of the present
invention, a pressure sensor is positioned in the PPT to measure
the pressure of reductant supplied from the LST, which has a liquid
port fluidly coupled to the reductant tank and a gas port fluidly
connected to a three-way solenoid valve that further connects the
gas port either to compressed air or ambient depending on its
control status. When the three-way solenoid valve connects the gas
port to ambient, compressed air in the liquid supply tank is
released, and liquid reductant then flows from the reductant tank
to the LST. Reductant in the LST is pressed into the PPT when the
three-way solenoid valve connects the gas port of the LST to
compressed air. The PPT has a liquid port fluidly connected to the
injector, and a gas inlet port fluidly coupled to compressed air
through a two-way solenoid valve for compensating air loss in the
PPT. Reductant dosing rate is controlled by opening the injector
for a period of time in a periodically repeating cycle, and the LST
refills reductant to the PPT, i.e., the three-way solenoid valve of
the LST connects its gas port to compressed air, whenever the
reductant level in the PPT is detected low. The inlet of the
injector is also fluidly coupled to the reductant tank through a
flow control valve. After dosing finishes, the flow control valve
is energized open and reductant residue is then pressed back to the
reductant tank.
[0013] In another embodiment of the present invention, the PPT
further includes a gas outlet port, which is fluidly connected to
another two-way solenoid valve for releasing air. The gas outlet
port in the PPT allows pressure be controlled within a
pre-determined range. To refill PPT, the upper limit of the
pre-determined range should be lower than the compressed air
pressure.
[0014] In the dosing system of the present invention, control
signals are generated in the DCU. The control of the dosing system
includes five states: Off, Idle, Priming, Normal-dosing, and Purge.
The Off state is a state when the engine is keyed off. After engine
is keyed on, the control firstly goes into the Idle state, then
upon a command, the system enters the Priming state, in which the
PPT is filled with reductant to a pre-determined level. When a
dosing command is received, the Normal-dosing state starts, in
which both of the PPT pressure and the dosing rate are controlled,
and the PPT is refilled if the reductant level in the PPT is lower
than a threshold value. After dosing, when engine is keyed off or
an idle command is received, the system goes into the Purge state
and reductant residue in the PPT, the LST, and connecting passages
is emptied therefrom.
[0015] The structure of the dosing system allows the pressure
sensor together with the control solenoid valves be used in
detecting reductant level in the PPT, PPT pressure control, and
reductant dosing rate control. In detecting reductant level, both
of the change in PPT pressure and the ratio between dosing amount
and the change in PPT pressure are used in calculating PPT
reductant volume depending on control states. Also the changing
rate of the PPT pressure is used in detecting if the PPT is empty.
In PPT pressure control, in a system of the first embodiment,
sensing values obtained from the pressure sensor are used to
calculate the amount of trapped air in the PPT. When the calculated
amount is lower than a threshold value, the two-way solenoid valve
connected to the gas inlet port of the PPT is energized open to
refill air into the PPT. In a system of the second embodiment,
pressure sensing values are compared to the upper limit and the
lower limit of the predetermined range, and control modes, which
are the combination of the control status of the two-way solenoid
valves, are changed according to the comparison results.
[0016] In reductant dosing control, the pressure sensor is used in
a three-stage PWM controller, which generates a PWM signal for
driving the injector according to predetermined dosing commands. In
the three-stage PWM controller, the first stage control creates a
first-stage PWM signal by periodically setting control parameters
to the second stage controller, which generates a second-stage PWM
signal, while the control parameters of the second-stage control
are used in creating a third-stage PWM signal. The values of the
control parameters are calculated by the first stage controller
according to the sensing values obtained from the pressure sensor
positioned inside the PPT. In this way, variation in the pressure
is compensated by the PWM controller, and the dosing rate accuracy,
therefore, is insensitive to pressure variation in the PPT.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic representation of an internal
combustion engine with an exhaust gas treatment system;
[0018] FIG. 2a depicts an air driven hydraulic pump system with a
reductant tank, a pressure pump tank fluidly coupled to compressed
air, a liquid supply tank, a DCU, an injector, and control solenoid
valves;
[0019] FIG. 2b depicts an air driven hydraulic pump system with a
reductant tank, a pressure pump tank fluidly coupled to compressed
air and ambient, a liquid supply tank, a DCU, an injector, and
control solenoid valves;
[0020] FIG. 3 is a state flow diagram of a reductant delivery
control;
[0021] FIG. 4a is a flow chart of a routine for a sub-state PR1 in
a Priming state;
[0022] FIG. 4b is a flow chart of a routine for a sub-state PR2 in
a Priming state;
[0023] FIG. 4c is a flow chart of a service routine for a timer
based interrupt used in a Priming state for calculating reductant
volume in a PPT;
[0024] FIG. 4d is a flow chart of a routine for a sub-state PR3 in
a Priming state;
[0025] FIG. 5a a flow chart of a routine for a sub-state D1 in a
Normal-dosing state;
[0026] FIG. 5b is a flow chart of a service routine for a timer
based interrupt used in a sub-state D1 for calculating reductant
volume in a PPT;
[0027] FIG. 5c is a flow chart of a service routine for a timer
based interrupt used in a Normal-dosing state for controlling
reductant pressure in a PPT;
[0028] FIG. 5d is a flow chart of a service routine for a timer
based interrupt used in a sub-state D2 for calculating reductant
volume in a PPT;
[0029] FIG. 5e shows a timing chart of parameter values in a
service routine of FIG. 5d;
[0030] FIG. 6a is a block diagram of a three-stage PWM controller
for controlling reductant dosing rate;
[0031] FIG. 6b is a block diagram of a PWM signal controller in a
three-stage PWM controller of FIG. 6a;
[0032] FIG. 6c is a flow chart of a service routine for a timer
based interrupt used in a first-stage PWM signal generation for
calculating values for control parameters of a second-stage PWM
signal;
[0033] FIG. 6d shows a timing chart of parameter values in a
service routine of FIG. 6c;
[0034] FIG. 6e is a block diagram of a circuit for generating a
second-stage and a third-stage PWM signals;
[0035] FIG. 6f is a timing chart for signals generated in the
circuit of FIG. 6e;
[0036] FIG. 7a a flow chart of a routine for a sub-state PU1 in a
Purge state;
[0037] FIG. 7b a flow chart of a routine for a sub-state PU2 in a
Purge state;
DETAILED DESCRIPTION OF THE INVENTION
[0038] Referring to FIG. 1, in an engine aftertreatment system,
exhaust gas generated by an engine 100 enters a passage 166 through
a manifold 101. On the passage 166, a reductant injector 130 is
installed. The solenoid valve of the injector 130 is controlled by
a Dosing Control Unit (DCU) 140 through signal lines 145 connected
to a port 136. And reductant is provided by a redutant supply
module 110 through a pressure line 131 fluidly connected to a port
133. To avoid damages caused by high temperature exhaust gas,
engine coolant is cycled from an inlet port 134 to an outlet port
135. The reductant injected from the injector 130 mixes with
exhaust gas, and through a mixer and diffuser 161, the result gas
enters a catalyst 163, where SCR reactions reduce NOx in the
exhaust gas.
[0039] The reductant supply module 110 has a port 115 fluidly
connected to the port 133 of the injector 130 with the line 131 for
providing pressurized reductant supply to the injector. A pressure
sensor (not shown in FIG. 1) reports pressure value inside the
reductant supply module to the DCU through signal lines 143
connected to a port 114. The reductant supply module draws
reductant from a reductant tank 120 through a port 117, a supply
line 123, and a port 122 of the reductant tank. And compressed air
enters reductant supply module through an inlet port 111 to
pressurize the reductant inside, while the reductant pressure is
controlled by the DCU through signal lines 146 connected to a port
116. Compressed air is released from an outlet port 112.
[0040] A tank level sensor and a temperature sensor report,
respectively, reductant level and temperature inside the reductant
tank 120 to the DCU through signal lines 141 and 142, which are
connected to a port 126. And the reductant tank is heated by engine
coolant cycling through an inlet port 127 and an outlet port 128.
The engine coolant flow is controlled by a solenoid shutoff valve
127 commanded by the DCU through signal lines 147. To avoid
reductant residue inside the pressure line 131 being frozen under
low temperature when engine is off, a return line 125, and a port
121 are used as a passage for reductant to flow back to the tank in
a purge process. Reductant flow inside the return line 125 is
controlled by a shut-off valve 137 commanded by the DCU via signal
lines 148. Electrical heaters 132, 129, 124, and 113 controlled by
the DCU through signal lines 144 are used to thaw frozen reductant
in the pressure line 131, the return line 125, the supply line 123,
and the reductant supply module 110 respectively, and keep the
temperature above reductant freezing point.
[0041] Commands of reductant dosing rate to the DCU are generated
in the ECU according to catalyst inlet exhaust temperature reported
by a sensor 162 through signal lines 155, catalyst outlet
temperature reported by a sensor 164 through signal lines 154,
catalyst outlet NOx rate obtained from a sensor 165 through
communication lines 153, and engine information, such as engine
state, coolant and oil temperature, engine speed, fueling rate,
exhaust flow rate, NOx rate, and NO2/NOx ratio, obtained from
sensors in the engine 100 through signal lines 152, or calculated
from sensing values.
[0042] One embodiment of the reductant supply module 110 in FIG. 1
is an air driven pumping system depicted in FIG. 2a positioned in
the reductant tank 120. In the pumping system, a Liquid Supply Tank
(LST) 210 and a Pressure Pump Tank (PPT) 200 are positioned inside
the reductant tank 120, which has a cover 228 fastened on a
container 220 with bolts 229 mounted on a flanged portion. On the
cover 228, a cap 236 is used for refilling reductant. Since the PPT
and the LST are positioned inside the reductant tank, the reductant
passage line 131 is connected to the port 115 through a port 221 on
the cover 228, and the signal lines 143 are connected to the port
114 via a port 225. Inside the reductant tank 120, the LST 210 is
fixed by a restrainer 227 and has a liquid inlet port 211 fluidly
connected to the reductant liquid in the tank 120. A check valve
212 inside the port 211 prevents the liquid from flowing back into
the tank 120. The LST 210 also has a liquid outlet port 204 fluidly
coupled to an inlet port 201 of the PPT 200 through a passage 203.
Inside the port 201, a check valve 202 keeps liquid from flowing
back to the LST 210. On the top of the LST 210, through a passage
214 and a port 237 on the cover 228, a port 213 is connected to a
port 241 of a chamber 240, which is held by a restrainer 238, and
the port C of a three-way solenoid valve 232, which is hold by a
restrainer 234. The port B of the three-way solenoid valve 232 is
connected to an air muffler 233, which is fluidly connected to the
port 112, and the port A is connected to an outlet of a Tee
connector 235 through a passage 207. The three-way solenoid valve
232 is controlled by the DCU 140 via the signal lines 146.
Determined by control signals, the port C of the three-way solenoid
232 is either connected to the port A or the port B. Next to the
LST 210, the PPT 200 is fixed by a restrainer 226. On the top of
the PPT 200, through the liquid outlet port 115, a tubing 209 is
fluidly connected to the reductant passage line 131 extended
through the port 221 on the cover 228. A port 205 is connected to
the port A of the two-way solenoid valve 230, which is fixed on the
cover 228 by a restrainer 231, via a passage 206 passing through
the port 222. The port B of the two-way solenoid valve 230 is
connected to an outlet of the Tee connector 235, which has another
outlet connected to the three-way solenoid valve 232 and its inlet
connected to the port 111. Inside the PPT 200, a pressure sensor
250 is mounted, and the signals obtained from the pressure sensor
is sent to the DCU 140 via the signal lines 143 passing through the
port 114 of the PPT 200 and the port 225 on the cover 228. In
addition to the reductant supply pump tanks 200 and 210, inside the
reductant tank 120, there are a temperature sensor 224 linked to
the DCU through the signal lines 142 for detecting reductant
temperature and a level sensor 223 reporting reductant level to the
DCU through the signal lines 141. A coolant heating tube 225, which
is connected to the inlet 127 and the outlet 128, is used in
heating reductant.
[0043] The system of FIG. 2a works under the control of the DCU
140, and the basic control of the system includes a prime control,
a dosing control, and a purge control. In the prime control,
reductant fluid is loaded in the PPT 200 and trapped air is
released from the injector 130 and the liquid path from the PPT to
the reductant tank 120, including the reductant lines 131, 209, and
125 and the solenoid valve 137, while in a dosing control,
reductant deliver rate is accurately controlled according to a
dosing command generated in the ECU 150 (FIG. 1). After dosing
completes, the purge control empties the PPT 200, the liquid path
from the PPT to the injector, and the injector 130, to protect the
injector and save heating efforts when operating under low
temperature.
[0044] In the prime control, the first step is to refill reductant
fluid into the PPT 200 to a certain level. A variety of methods can
be used in this step. An example of such methods includes a volume
re-zero and a refilling control. In the volume re-zero control, the
compressed air is filled into the PPT 200, establishing a certain
pressure therein. And then the solenoid valve 137 is energized
open. Under the pressure, the reductant fluid remains inside the
PPT 200 is pressed back into the reductant tank 120 through the
tubing 209, the passage 131, the solenoid valve 137, and the
passage 125. When the PPT 200 is empty, compressed air is pressed
into the reductant tank 120, and a sudden change of pressure is
detected by the pressure sensor 250 due to the significant change
of fluid density. Upon the sudden pressure change, the liquid
volume in the PPT 200 is re-zeroed, and the solenoid valve 137 is
de-energized closed. After the liquid volume is re-zeroed, a
pressure is controlled to a level P1, which is lower than the
compressed air pressure Pc, by controlling the opening time of the
solenoid valve 230. And then the solenoid valve 230 is closed and
the solenoid 232 is energized, connecting its port A to port C, and
the pressure in the LST 210 is then increased to the compressed air
pressure Pc. Under the pressure drop between Pc and P1, reductant
liquid flows from the LST 210 into the PPT 200. By measuring the
pressure change in the PPT 200, the liquid level in the PPT can be
calculated if the re-fill time is short and thereby, liquid
temperature change is insignificant. When the liquid volume reaches
to a value Vh, the solenoid 232 is de-energized, connecting the
port B to port C, releasing pressure in the LST 210. At the same
time, the solenoid valve 137 is energized open for a period of time
to release trapped air in the passage 131 and the tubing 209, and
the solenoid valve 133 is also opened shortly to release trapped
air in it. Then the prime control completes. De-energizing the
solenoid 232 releases compressed air in the LST 210. When the
pressure in the LST 210 is lower than P1, the check valve 202
blocks liquid from flowing back to the LST, and if the LST pressure
decreases below the pressure drop across the check valve 211, the
LST is refilled with the reductant liquid in the tank 120.
[0045] In the prime control, when the solenoid valve 230 is closed
after the liquid level is re-zeroed and the pressure is controlled
at P1, compressed air is trapped in the PPT 200. If temperature in
the PPT 200 doesn't change, according to ideal gas law, the
pressure P and liquid volume V inside the PPT then have the
following relation:
P(Va-V)=P1*Va (1)
[0046] where Va is the volume of the trapped air after the liquid
level is re-zeroed. According to equation (1), the liquid volume V
then can be calculated with equation (2):
V=Va*(1-P1/P) (2)
[0047] After the prime control, the dosing control starts with
controlling the pressure inside the PPT to a value P2 through
controlling the opening time of the solenoid valve 230. The dosing
control includes a dosing rate control, a PPT refill control, and a
PPT pressure control. In the dosing rate control, the liquid
reductant in the PPT is released to exhaust air by opening the
injector 130, and the opening time of the injector 130 is
controlled according a dosing rate command Dc in a periodically
repeating cycle. The liquid volume in the PPT decreases with
dosing. When the liquid volume decreases below a value Vl, the PPT
needs to be refilled. In the PPT refill control, the solenoid valve
232 is energized, connecting the port A to the port C. The LST is
then pressurized. When the pressure in the LST is higher than the
pressure in the PPT, liquid reductant flows from the LST to the
PPT. When the liquid volume in the PPT is higher than a threshold
Vh, the solenoid valve 232 is de-energized, releasing the pressure
in the LST. With the compressed air in the LST being released, the
LST is refilled under the liquid pressure in the reductant tank 120
for the next PPT refill control. In the system of FIG. 2a, since
the solenoid 230 can only be used for pressurizing the PPT, the
trapped air in the PPT cannot be released through the solenoid 230.
As a result, in the PPT refill control, which requires a pressure
difference between LST and the PPT, at the volume Vh, the PPT
pressure should be lower than the LST pressure. According to
equation (1), the PPT pressure at volume Vl will be even lower, and
the pressure change is determined by the change in the volume V if
the temperature change is insignificant. When dosing time is long,
however, the amount of trapped air dissolved in the reductant
liquid and brought out by dosing will be significant, and a
pressure control is then required to compensate this loss. A
variety of methods can be used in the pressure control. One
exemplary method is calculating the mass of the trapped air in the
PPT using the ideal gas equation:
m=P*(Va-V)*Mw/RT (3)
[0048] where R is the gas constant and T is the temperature of the
liquid reductant measured with the temperature sensor 224, and Mw
is the molecular weight of the trapped air. When the calculated
mass m is lower than a threshold, then the solenoid valve 230 is
energized open to fill the compressed air into the PPT. The
solenoid valve 230 is de-energized when the mass m is higher than a
threshold.
[0049] The change of pressure in the PPT is not desirable in dosing
rate control. To decrease the pressure change, one method is
decreasing the ratio of Vh to Vl and refilling the PPT more
frequently. According to the ideal gas law, if temperature is
constant, the pressure change is determined by the volume change of
the trapped air. Therefore, decreasing the volume change lowers the
pressure change. Another method of decreasing the pressure change
is controlling the pressure in the PPT constant. To control the
pressure in the PPT, one method is using a solenoid valve to
release the trapped air in the PPT. An exemplary system based on
this method is shown in FIG. 2b. Compared to the system of FIG. 2a,
in the system of FIG. 2b, the port 205 of the PPT 200 is connected
to the central port of a Tee connector 253 instead of the port A of
the solenoid valve 230. The inlet port on the left side of the Tee
connector 253 is connected to the port B of a two-way solenoid
valve 250 that is normally closed, through a passage 252, while
through a passage 249, the outlet port on the right side is
connected to the port A of a two-way solenoid valve 244 that is
normally closed. The port A of the solenoid valve 250 is connected
to the outlet on the right side of a Tee connector 251, the central
port of which is connected to the port B of a three-way solenoid
valve 246, which has its port C connected to the port A when
de-energized and connected to the port B if energized. Compressed
air is provided through the port 111 to the inlet port on the left
side of the Tee connector 251. The port A of the solenoid valve 246
is connected to the central port of a tee connector 248, which has
the inlet port on its left side connected to the port B of the
solenoid valve 244. The outlet port on the right side of the Tee
connector 248 is coupled to the port 112 through a muffler 247.
Similar to that of the FIG. 2a, in FIG. 2b, the port 239 is
connected to the port C of the solenoid 246.
[0050] In the system of FIG. 2b, similar to that of FIG. 2a, when
the solenoid valve 246 is energized, its port B is connected to the
port C, passing compressed air into LST 210. If the solenoid valve
246 is de-energized, the port C is then connected to the port A,
releasing compressed air in the LST 210. The pressure in the PPT
200 can be controlled by energizing and de-energizing the solenoid
valves 250 and 244, and the controls to the two valves have four
modes shown in the following table.
TABLE-US-00001 TABLE 1 Mode Status of the Status of the number
valve 250 valve 244 Actions 0 Not energized Not energized Keeping
air in PPT 1 Not energized Energized Releasing air from PPT 2
Energized Not energized Filling air to PPT 3 Energized Energized
Releasing compressed air
[0051] In Mode 0, neither of the solenoid valves 250 and 244 is
energized, and compressed air is trapped in the PPT. In Mode 1,
since the solenoid valve 244 is energized and the solenoid valve
250 is de-energized, compressed air is released from the PPT. Mode
2 is an air refilling mode. In this mode, the solenoid valve 244 is
de-energized, disconnecting the PPT from ambient, while the
solenoid valve 250 is energized, connecting the PPT to the
compressed air supply. Mode 3 is a special mode and should be
avoided. In this mode, when both of the solenoid valves 250 and 244
are energized, the compressed air source is connected to
ambient.
[0052] A simple relay control can be used in controlling the PPT
pressure. In this control, when the PPT pressure increases higher
than an upper threshold, the mode 1 is triggered, releasing air
from the PPT and thereby decreasing the PPT pressure. If the PPT
pressure decreases lower than a bottom threshold, then the mode 2
is triggered, refilling air to the PPT. If the pressure is in
between these two thresholds, then the mode 0 is triggered,
trapping air in the PPT. A hysteresis can be used to avoid frequent
actions of the solenoid valves when the pressure is dithering
around thresholds.
[0053] In the systems of FIGS. 2a and 2b, since compressed air can
be filled in or released from the PPT 200, the reductant level in
the PPT 200 can be calculated using the pressure change in the
period of time when there is no action of the compressed air
control, assuming temperature change is negligible and the ratio of
the dissolved air in the reductant to the compressed air in the PPT
200 is low. According to the ideal gas equation, the relation
between the pressure change and the volume change in the PPT 200
follows the equation:
dP/dV=-P/(Va-V) (4)
[0054] assuming the mass of the trapped air and the temperature are
constant. With the measured pressure value of P, the reductant
volume V then can be calculated with the following equation:
V=Va+P*dV/dP (5)
[0055] where dV can be calculated using the amount of dosed
reductant, Dr, that causes the pressure change:
dV=Dr*.rho. (6)
[0056] where .rho. is the reductant density.
[0057] In reductant doing rate control, to increase control
accuracy, a three-stage PWM control can be used. In the three-stage
PWM control, the third stage is a PWM control for driving the
injector 130. When the injector is energized, this PWM control
generates a pull-in voltage to move the plunger in the injector to
a latched position, and a hold-in voltage for maintaining the
plunger at the latched position, by changing the duty cycle values
of a PWM signal. Upon this third stage PWM signal, a second-stage
PWM control and a first-stage PWM control work together to generate
an activation signal for the injector to open the injector
periodically according to a dosing rate command. The first-stage
PWM control periodically calculates an estimated dosing amount
based on pressure sensing values obtained from the pressure sensor
250. In a PWM cycle of the first-stage PWM control, the control
error, i.e., the difference between the estimated dosing amount and
a target value calculated based on the dosing rate command, is used
to determine the duty cycle of the second-stage PWM signal.
[0058] A variety of methods can be used in the determination of the
duty cycle of the second-stage PWM signal. In an exemplary method,
the duty cycle is set by using the ratio between the second-stage
PWM capacity to the control error. In this method, if in a PWM
cycle of the second-stage PWM control, the PWM capacity, i.e., the
maximum dosing amount at 100% duty cycle, is Dmax, and the
difference between the estimated dosing amount and the target value
is Er, then when Er is higher or equal to Dmax, a 100% duty-cycle
second-stage PWM signal is generated, otherwise, a duty-cycle of
Er/Dmax is set.
[0059] After dosing, the system needs to be purged to remove
reductant residue in the injector 130, the reductant passage 131,
the reductant passage lines, the PPT 200, the LST 210, and the
passage 203, to avoid damage caused by frozen reductant and to save
energy in thawing frozen reductant when operating under low
temperature. The purge can be done by using the compressed air to
press the reductant back to the tank 120. In doing so, referring to
FIG. 2a, firstly the solenoid valve 230 is de-energized and the
solenoid valve 232 is energized. Then the solenoid valve 137 is
energized. Under the pressure of the compressed air, reductant in
the LST 210 enters the PPT 200, and through the passages 209 and
131, the solenoid valve 137, and the passage 125, the reductant
flows back to the tank 120. When the path from the PPT 200 to the
passage 125 is empty, a sudden pressure drop will be detected by
the pressure sensor 114. Upon this signal, the solenoid 137 is
de-energized, and the compressed air is trapped in the path and the
LST 210. To clean the injector 130, after the solenoid 137 is
de-energized, the injector 130 can be opened for a short period of
time, releasing remains from the injector into the exhaust pipe.
When the purge process completes, the solenoid valve 232 is
de-energized. With air pressure being released, reductant is
refilled in the LST 210. However, due to the trapped compressed
air, the PPT 200 and the path from the PPT 200 to the passage 125
is still empty. To avoid damage to the LST 210 during frozen
expansion, the volume of the chamber 240 should be at least large
enough for the frozen expansion.
[0060] To avoid freezing damage to the LST 210, another method is
using a three-way solenoid valve with port A connected to port C
when de-energized, and connected to port B when energized, as the
solenoid valve 232. With this solenoid valve, when the purge
process completes, the solenoid valve 232 is de-energized,
connecting the path from the LST 210 to the solenoid 137 (including
the LST 210, the passage 203, the PPT 200, the tubing 209, the
passage 131, and the solenoid 137) to the compressed air source.
The air pressure in the path then keeps reductant from being
refilled into the path and thereby prevents freezing damage.
[0061] Referring back to FIG. 1, the reductant delivery control can
be realized with a routine run in the DCU 140, which receives
commands and system status from the ECU 150, and operates actuators
to release reductant in a rate as commanded by the ECU. In system
level, a state machine can be used in the reductant delivery
control. As shown in FIG. 3, in an exemplary reductant delivery
control routine, there are five main states: an Off state 301, an
Idle state 302, a Prime state 310, a Normal-dosing state 320, and a
Purge state 330.
[0062] Upon a Key-on flag, the routine goes from the Off state 301
into the Idle state 302. If a command CMD-Priming is received, then
the routine enters the Prime state 310, otherwise, if a Key-off
flag is received, then the routine goes back to the Off state 301.
The Prime state further includes three sub-states: a PR1 sub-state
311, in which the reductant volume in the PPT 200 is re-zeroed, a
PR2 sub-state 312 for filling the PPT 200 with reductant, and a PR3
sub-state for releasing trapped air in the injector 130. After the
Prime state is completed, if a command CMD-Normal dosing is
received, then the routine enters the Normal-dosing state 320,
otherwise, if a Key-off flag or a CMD-Idle command is obtained,
then the routine goes into the Purge state 330. The Normal-dosing
state also includes three sub-states: a D1 sub-state 321 in which
the LST is refilled, a D2 sub-state 322 for refilling reductant
from the LST 210 to the PPT 200, and a Dosing-rate control
sub-state 323, in which reductant delivery rate is controlled with
the three-stage PWM control. In the D1 sub-state and the D2
sub-state, reductant pressure in the PPT 200 is controlled at a
constant value (in a system of FIG. 2b) or within a range (in a
system of FIG. 2a). The Dosing-rate control sub-state is
independent to the D1sub-state and the D2 sub-state, i.e., in the
Normal-dosing state, the Dosing-rate control sub-state runs all the
time, while the D1 sub-state and D2 sub-state run alternately.
Running in the Normal-dosing state, if a command CMD-Idle or a
Key-off flag is received, the routine enters the Purge state. As
the Normal-dosing state, the Purge state also includes three
sub-states: a PU1 sub-state 331 for draining reductant in the path
from the LST 210 to the passage 125, a PU2 sub-state 332, in which
the remains in the injector is released into exhaust pipe, and a
PU3 sub-state 333, in which air is trapped in the PPT 200 or the
LST 210 is fluidly connected to a compressed air source for keeping
the PPT 200 or the LST 210 from being refilled.
[0063] Among all the states, the Off state 301 and the Idle state
302 are simple states. In the Off state 301, all actuators
including the solenoid valves and the injector, and reductant
temperature control are de-energized. In the Idle state 302,
reductant temperature control is enabled while actuators are still
de-energized.
[0064] In the Priming state 310, the sub-state PR1 can be realized
with a routine depicted in FIG. 4a. In this routine, the system is
initialized at the beginning. The initialization process, which
includes de-energizing the solenoid valves and the injector, is to
turn off the system before the priming process starts. After the
initialization, the state flag is set to PR1 and the PPT 200 is
connected to compressed air to build pressure in it. When the
pressure in the PPT is higher than a threshold Thd1, the PPT 200 is
disconnected from compressed air, and the solenoid valve 137 is
energized. Under the pressure in the PPT 200, remains in the PPT
flows back to the reductant tank 120. When a high pressure changing
rate is detected, indicating the PPT 200 and the path from the PPT
to the solenoid valve 137 are empty, the solenoid valve 137 is
de-energized, and the routine enters the sub-state PR2 after a
variable, Vr, which is an indication of the reductant volume in the
PPT 200, is set to 0, and the pressure variable P1 is initialized
with the currently measured pressure value, P.
[0065] A routine for the sub-state PR2 is shown in FIG. 4b. The
routine starts with setting the state flag to PR2. Then the LST 210
is connected to compressed air by connecting the port C of the
control solenoid valve (e.g. the solenoid valve 232 in FIG. 2a and
the solenoid valve 246 in FIG. 2b) to its port B, and the reductant
volume in the PPT 200, Vr, is compared to a threshold Thd2. If the
reductant level is higher than Thd2, then the LST 210 is
disconnected from compressed air by connecting the port C of the
control solenoid valve to its port A, and the routine goes into the
sub-state PR3. Otherwise, if a sudden pressure increase is
detected, i.e., the LST 210 is empty, then the LST 210 is
disconnected from compressed air for a period of time Tf for
refill. The PR2 restarts after the refill. If there is no sudden
pressure increase, the routine then waits until the reductant
volume Vr is higher than the threshold Thd2.
[0066] In the routine of FIG. 4b, the reductant volume Vr can be
calculated in a service routine running periodically for a
timer-based interrupt. As shown in FIG. 4c, the interrupt routine
starts with checking the State value. If it doesn't equal to PR2,
then the routine ends, otherwise, a timer TimerPR is incremented by
the execution period value dT. If the TimerPR value is higher or
equal to a time value TI, then the Vr value is calculated and the
TimerPR is reset to 0. The routine ends thereafter. Since in the
sub-state PR1, the reductant volume is re-zeroed, the Vr value can
be calculated with the measured pressure values according to
equation (2).
[0067] The routine enters sub-state PR3 after PR2 is completed. An
exemplary PR3 routine is depicted in FIG. 4d. At the beginning of
this routine, the State value is set to PR3. Then the injector 130
is energized open for a short period of time Tr to release trapped
air. The State value is set to Prime_completed thereafter and the
routine enters sub-state D1 upon receiving a command
CMD_Normal_Dosing from the ECU.
[0068] Referring to FIG. 5a, in an exemplary routine of the
sub-states D1 and D2, which belong to the Normal-dosing state 320,
a dosing initialization is executed at the beginning. During the
dosing initialization, pressure control for the PPT and dosing rate
control are enabled. After the dosing initialization, the State
value is set to D1 and the reductant volume Vr is compared to a
threshold Thd3. When the Vr value is higher than the threshold, a
variable D2N, which indicates a cycle number in the sub-state D2.
The State is then set to D2 and the reductant volume Vr is compared
to another threshold Thd4. The routine goes back to setting State
to D1 when the Vr value is higher than Thd4.
[0069] In the sub-state D1, the reductant volume Vr can be measured
based on the relation between the reductant volume change and PPT
pressure change, according to equation (5). An interrupt service
routine as shown in FIG. 5b can be used for the calculation of Vr.
The interrupt service routine runs periodically with a timer
interrupt. Referring to FIG. 5b, at the beginning, the State value
is checked. If it doesn't equal to D1, then the routine ends,
otherwise, the pressure control status is examined. If compressed
air is released from the PPT, e.g., the solenoid 244 (FIG. 2b) is
energized, or compressed air is filled into the PPT, e.g., the
solenoid 230 (FIG. 2a), or the solenoid 250 (FIG. 2b) is energized,
then a timer TimerD1 is reset to 0, and the routine ends,
otherwise, the value of TimerD1 is examined. If it is 0, then the
routine ends after a variable CmdSumD1, the value of which is the
dosing amount during pressure change, is set to 0, and the value of
a variable P0 is set to the current pressure sensing value P. If
the value of TimerD1 is not 0, then the variable CmdSumD1 is
incremented with the dosing amount calculated with the dosing rate
Dc and the interrupt execution period dT, and the variable TimerD1
is incremented with dT. The pressure change, deltaP, is calculated
thereafter and the value of the timer TimerD1 is compared to a
pressure sampling time Td1. Upon the TimerD1 value higher than Td1,
the reductant volume Vr is calculated using the following equation
according to equation (5) and (6), and the routine ends after the
variable TimerD1 is set to 0:
Vr=Va+P*CmdSumD1*p/deltaP (7)
[0070] where the volume of the PPT 200 can be used as the Va value.
If the TimerD1 value is not higher than the pressure sampling
timeTd1, the routine ends.
[0071] In the Normal-dosing state, in the system of FIG. 2a,
reductant pressure in the PPT is not controlled to a target value
or a range, and the pressure control is to compensate for the loss
of compressed air caused by leaking and dissolving in reductant.
The loss of compressed air is a slow process, therefore, in an
exemplary algorithm, the compressed air loss can be calculated and
compensated according to equation (2) in the sub-state D1 and the
pressure control is disabled in the sub-state D2. The algorithm can
be realized with a simple service routine running periodically with
a timer-based interrupt.
[0072] In the system of FIG. 2b, however, reductant pressure in the
PPT can be controlled within a pre-determined range. The pressure
control releases compressed air from the PPT when the reductant
pressure is high and refills when it is low. The pressure control
can also be realized with a service routine running periodically
for a timer-based interrupt. Referring to FIG. 5c, in an example of
the interrupt service routine, the value of a flag, State, is
examined first. If it doesn't equal to D1 or D2, then routine ends,
otherwise, the currently measured pressure value is compared to the
lower end of the pre-determined range, P1. If is not higher than
Pl, then the pressure control mode is set to 2 to refill compressed
air into the PPT, and the routine ends, otherwise, the pressure
value is compared to the upper end of the range, Ph. If it not
lower than Ph, then the pressure control mode is set to 1, and the
routine ends, otherwise, the pressure control keeps its previous
value when two conditions are satisfied before the routine ends.
One of the two conditions is that the pressure control mode is 1
and the pressure is higher than the middle value of the range, Pt,
and the other one is that the pressure control mode is 2 and the
pressure is lower than Pt. The pressure control mode is set to 0
before the routine ends if the two conditions are not
satisfied.
[0073] In the sub-state D2, the reductant volume Vr in the system
of FIG. 2a can be measured using a similar method used in the
Priming state with the pressure control disabled, while in the
system of FIG. 2b, since reductant pressure in the PPT is
controlled within a pre-determined range by filling in or releasing
compressed air from the PPT, a different algorithm needs to be
used. An example of such an algorithm is realized with a service
routine for a timer-based interrupt, as shown in FIG. 5d. The
routine starts with checking the State value. If it doesn't equal
to D2, then the routine ends, otherwise, the pressure control
status is checked. When the pressure control is in mode 2, i.e.,
compressed air is being filled into the PPT, the routine ends after
a flag RLFlag is reset to 0. The flag RLFlag is set to 1 if the
pressure control is in mode 1, i.e., compressed air is being
released from the PPT. When the pressure control is in mode 0,
i.e., compressed air is being trapped in the PPT, the RLFlag value
is examined. If RLFlag is not 1, the routine ends, otherwise,
RLFlag is reset to 0, and the variable D2N is incremented by 1, and
the reductant volume Vr is calculated before the routine ends.
[0074] With the pressure control algorithm of FIG. 5c, the
reductant volume Vr can be calculated with the D2N value and the
dosing amount CmdSumD2. As illustrated in FIG. 5e, in the pressure
control, each time when the control mode changes from 1 to 0,
(i.e., the RLFlag value changes from 1 to 0) compressed air is
released, and the pressure value changes from Ph to Pt. According
to the ideal gas equation, when there is no temperature change, the
reductant volume change in each cycle when the pressure increases
from Pt to Ph is determined by the values of Pt and Ph:
Vr(Ph)=Va-[Va-Vr(Pt)]*Ph/Pt (8)
[0075] where Vr(Ph) is the reductant volume at pressure Ph, and
Vr(Pt) is that at pressure Pt. Accordingly, when pressure releasing
time is short, in the routine of FIG. 5d, the reductant volume Vr
then can be calculated according to the equation:
Vr(D2N)=Va-[Va-Vr(D2N-1)]*Ph/Pt (9)
where Vr(D2N) and Vr(D2N-1) are the reductant volume values in
cycle D2N and D2N-1. In the equation (9), since Pt and Ph are
pre-determined values, and Va is a constant, the only factors that
determine the Vr value are the cycle number D2N and the initial Vr
value, which is the value of Vr when the sub-state D2 starts. If
the initial Vr value is set to a constant value, then the D2N
number can be used directly in FIG. 5a in deciding if the routine
needs to go back to sub-state D1 (replacing Vr in comparing with
Thd4).
[0076] Referring back to FIG. 3, in the sub-state 323 (Dosing-rate
control), a three-stage PWM control as shown in FIG. 6a can be used
in compensating the pressure variation in the PPT. In this control,
the signal obtained from the pressure sensor 250 is sent to a
sensor signal processing unit 602, where the analog pressure
sensing signal is filtered and converted to digital signal. The
result signal is fed into a PWM control module 610 in a PWM signal
controller 601 together with a dosing mass-flow rate command. The
PWM control module then calculates the values for control
parameters of a PWM signal generator 620 and set the values. A PWM
signal is generated by the PWM signal generator and provided to a
power switch circuit 603, where the PWM signal is converted to a
switching signal driving the solenoid valve of the injector 130
through signal lines 145.
[0077] The PWM signal generation in the PWM signal controller 601
includes three stages. In the first stage, the control parameters
for the PWM signal generator 620 are set. In the second stage, a
second stage PWM signal is created by the PWM signal generator 620.
A third-stage PWM signal, which provides the pull-in and hold-in
voltage, is also generated in the PWM signal generator 620 in the
third-stage signal generation.
[0078] An embodiment of the PWM control module 610 is shown in FIG.
6b. In this module, upon receiving the dosing mass-flow rate
command, in blocks 611 and 612, the duty cycle and period of the
first stage PWM signal are calculated and provided to a block 614,
where a target value is determined. The target value is then
compared with a current value calculated in a block 613 with the
pressure feedback value provided by the sensor signal processing
unit 602. And the result error value is used by a block 615 to
calculate the on-time setting value of the second stage PWM signal,
On-time2. The on-time value of the third stage PWM signal,
On-time3, is generated thereafter with the On-time2 value in a
block 618, which can also be implemented in the control module 620.
In the control module 610, the period setting value for the second
stage PWM signal, Period2, is determined with the dosing mass-flow
rate command in a block 616, and that for the third stage PWM
signal, Period3, is generated with the Period2 value in a block
617. Preferably, the control module 610 is realized with a routine
run in the DCU.
[0079] An exemplary routine for the control module 610 is a service
routine for a timer-based interrupt running periodically with a
time interval of P3. The flow chart of the exemplary routine is
shown in FIG. 6c. In this chart, t.sub.v and Fault_Thd are constant
values, and P1 is the period value of the first-stage PWM signal.
Status is the PWM pulse status flag. When the on-time variable of
the second-stage PWM signal, On_time2, is set to t.sub.v, the
Status value is ON, otherwise, it is OFF. The variable target_value
contains the target on-time value of the first-stage PWM signal,
while the variable current_value saves the calculated on-time value
of the first-stage PWM signal at the current moment. The value of
P2 is the cycle period value of the second-stage PWM signal, and
the variable Timer saves the current time in a first-stage PWM
cycle. Values of the variable C1 in this chart are indicative to
the PWM capacity of the second-stage PWM control.
[0080] When the interrupt routine is triggered, the C1 value is
calculated, and the value of Timer is compared to the period value
P1 of the first-stage PWM signal. If the current cycle is finished,
i.e., Timer >=P1, then the on_time value of the second stage PWM
signal is examined. When the on_time value is lower than t.sub.v,
the total error of this PWM cycle is calculated and assigned to a
variable previous_error. And after the Timer value is reset to P3,
in a step 636, the current_value is initialized, and the register
P2 and the variable target_value are updated for a new cycle, which
starts with calculating the error to be corrected in the current
cycle by adding the current_error value to the previous_error
value. If the error to be corrected is higher than t.sub.v, then
the on-time of the second PWM signal, On_time2, is set to t.sub.v
and the Status flag is set to ON, otherwise, the error value is
assigned to the variable On_time2, and the Status flag is reset to
OFF. The routine ends thereafter. Referring back to the comparison
between the Timer value and the P1 value, if current cycle ends
(Timer >=P1) with the On_time2 value not lower than t.sub.v,
then it means the error cannot be corrected in this PWM cycle. In
this case, the error in the previous cycle is calculated, and
assigned to the variable previous_error. And the Status flag is set
to ON after the Timer is set to P3 and the current_value is
initialized. Since the error is not corrected, it is accumulated.
When the accumulated error is higher than the threshold Fault_Thd,
a fault is reported before the routine ends. Again referring back
to the comparison between the Timer value and the P1 value, when
the Timer value is greater than P1 (the routine is called again in
the same first-stage PWM cycle), the Timer value is incremented by
P3, and then the Status flag is examined. If the Status flag is
OFF, then the variable On_time2 is cleared to 0, and the routine
ends, otherwise, current_value is calculated in a step 635 and the
error is updated thereafter. Before the routine ends, the error
value is compared to the product of t.sub.v and C1, t.sub.v*C1. If
the error value is equal or greater than the product, then the
On_time2 value is set to t.sub.v, otherwise, the value of error/C1
is set to On_time2 and the Status flag is reset to OFF.
[0081] In the interrupt routine, normally the t.sub.v value is
selected greater than the error to be corrected (e.g. t.sub.v
equals P2). And the interrupt period value (P3) can be the same as
that of the second-stage PWM signal (P2). With the interrupt
routine of FIG. 6c, a signal timing chart when t.sub.v equals P3
and P2 is shown in FIG. 6d. An interrupt is triggered at a moment
646. Since the error, which is calculated by comparing the value of
current_value and a target value 647, is higher than t.sub.v, the
On_time2 value is set to t.sub.v. The current_value accumulates
with time. At a moment 642, when the calculated error is lower than
the product of t.sub.v and C1, the value of error/C1 is assigned to
On_time2. In the next interrupt triggered at a moment 643, On_time2
is set to 0 and the current_value variable is locked at a value
648. At a moment 645, the current PWM cycle ends, and the
previous_error (FIG. 6c) is updated for the next cycle by including
the error between the current_value value 648 and the target value
647.
[0082] In the interrupt routine of FIG. 6c, the target_value can be
calculated with the reductant flow rate command using the following
formula:
target_value(i)=Massflow_rate_cmd*S.sub.0 (F1)
where Massflow_rate_cmd is the dosing mass-flow rate command to the
PWM control, and S.sub.o is the period value of the first stage PWM
signal. The formula for calculating current_value in the step 635
can be:
current_value(i)=K*sqrt(Pr(i)-Pc))*P3+current_value(i-1) (F2)
where i is the number of interrupts after Timer is reset to 0:
i=Timer/P3 (F3)
sqrt is the square root calculation, K a pre-determined constant,
Pr(i) the pressure sensing value for the calculation in the i-th
interrupt cycle, and Pc the pressure in the exhaust passage 166.
The constant K can be calculated using the discharge coefficient of
the injector, C.sub.D, the minimum area of the injector nozzle,
A.sub.n, and the density of the reductant, .rho.:
K=C'.sub.DA'.sub.n {square root over (2.rho.)} (10)
and the value of current_value(0) is set to 0 in the step 636. And
the C1 value can be calculated using the following equation:
C1=K*sqrt(Pr(i)-Pc))*P3/P2 (F4)
[0083] Referring back to FIG. 6a, the PWM signal generator 620 can
also be realized with a routine. However, to have a high PWM
frequency, especially for the third-stage PWM signal, it is
preferred to have it implemented with logic circuits. The block
diagram and signal flow chart of an exemplary circuit is shown in
FIG. 6e. In this circuit, the ratios of the period and on-time
values of the second signal to the period value of the third PWM
signal are set to a Period Register 621 and an On-time Register 622
respectively, and the period value of the third PWM signal is set
to the Period Register 621. Upon a rising edge of an LD signal 651
generated by a Load Control Logic 632, the values of the
second-stage PWM signal in the Period Register 621 and the On-time
Register 622 are further, respectively, loaded in a Period Counter
627 and an On-time Register 629. The Period Counter 627 is a
counting-down counter and its clock signal is a signal 650
generated in another Load Control Logic 625. When the Period
Counter 627 counts to 0, in the LD signal 651, a pulse is
generated. At a rising edge of the LD pulse, a signal 652, which is
ratio of the on-time value of the second-stage PWM signal to the
period of the third-stage PWM signal (On-time2/Period3) loaded in
the On-time Register 629, also appears at a port DB of a Signal
Control Logic 633, which has a port DA connected to an output of a
Timer 631. The Timer 631 can be a counting-up counter and has its
clock input connected to the signal 650 generated by the Load
Control Logic 625. The Timer 631 is reset by a signal generated in
a Latch 630, which can be latched by a signal 654 provided from an
output of the Signal Control Logic 633, Out1, and reset by the LD
signal produced by the Load Control Logic 632. In the Signal
Control Logic 633, if the value at the port DB is higher than that
at the port DA, then a high level latch signal is generated for the
Latch 630, otherwise, a zero signal is provided. The Signal Control
Logic 633 has another output Out2 connected to the Reset port of a
Timer 635, which can also be a counting-up counter, having its
clock input connected to the signal 650 and its data output
connected to a DB port of a Signal Control Logic 636. The Signal
Control Logic 636 has a DA port connected to the output of the
Timer 631, and an outlet port connected to a Flash Memory 634,
providing an address value. In the Signal Control Logic 633, when
its DB value is zero, then a reset signal of one is provided to the
Timer 635, otherwise a zero signal is provided, while in the Signal
Control Logic 636, a value of zero is generated to the Flash Memory
634 if its DA value is zero, and its DB value is provided
otherwise. The Flash Memory 634 is used to generate an on-time
value of the third-stage PWM signal for producing pull-in and
hold-in voltages. It functions as a one-dimensional look-up table
with a zero value saved in an address of zero, and pull-in and
hold-in on-time values saved thereafter. The output of the Flash
Memory 634 is connected to an On-time Counter 624, which is a
counting-down counter clamped at zero with its clock input
connected to a high frequency clock signal. Upon a rising edge of
the signal 650 produced by the Load Control Logic 625, the output
value of the Flash Memory 634, On-time3, is loaded into the On-time
Counter 624, and upon a falling edge of the signal 650, the period
value of the third-stage PWM signal saved in the Period Register
621, Period3, is loaded into a Period Counter 623, which is also a
counting down counter clocked by the high frequency clock signal.
The output of the Period Counter 623 communicates to a DA port of
the Load Control Logic 625, in which, a high level signal is
generated when its DA value is 0 and its clock is at high level,
while the output of the On-time Counter 624 is connected to a DA
port of a Signal Control Logic 626, which is clocked by the high
frequency clock signal, and a high level signal is generated when
the DA value is higher than 0 at a rising edge of its clock
signal.
[0084] A timing chart for the signals 650-655 is depicted in FIG.
6f. In the figure, the LD signal 650 is a pulse sequence 660.
Synchronized by the LD signal 650, the LD signal 651, which is
another pulse sequence 661, is generated. At the rising edge in the
pulse sequence 661, at a moment 667, the DB signal 652 is updated
to a new value as shown in a curve 662, and the latch signal 654,
which is a pulse sequence 664, is reset to 0. At a moment 668, a
falling edge in the pulse sequence 660 increments the value of the
DA signal 653, as shown in a curve 663, and at a moment 669, i.e.,
upon the following rising edge, the DA signal 665 is updated to a
new value, as shown in a curve 665. When the DA value of the Signal
Control Logic 633 equals to its DB value, at a moment 670, the
latch signal 654 is set to 1, resetting the DA signal 653 to 0. The
DA signal 655 is then updated to 0 thereafter upon the following
rising edge of the LD signal 650, and stays at the 0 value until
the next cycle starting at a moment 661.
[0085] Referring back to FIG. 3, in the Priming state 310 and the
Normal-dosing state 320, whenever a command CMD-Idle or a Key-Off
signal is received, the control enters the Purge state 330, which
includes three sub-states, PU1, PU2, and PU3. The sub-state PU1 can
be realized with a routine as shown in FIG. 7a. In this routine,
the system is initialized at the beginning. In the initialization
process, both of the solenoid valves and the injector are
de-energized. After the initialization, the state flag is set to
PU1 and the PPT 200 is connected to compressed air to build up
pressure. When the pressure in the PPT is higher than a threshold
Thd1, the PPT 200 is disconnected from compressed air, and the
solenoid valve 137 is energized. Under the pressure in the PPT 200,
reductant residue in the PPT flows back to the reductant tank 120.
When a high pressure changing rate is detected, indicating the PPT
200 and the fluid path from the PPT to the solenoid valve 137 is
empty, the solenoid valve 137 is de-energized, and the routine
enters the sub-state PU2.
[0086] A routine with a flow chart depicted in FIG. 7b can be used
for the sub-states PU2 and PU3. This routine starts with setting
the State to PU2. Then the injector solenoid valve is energized
open for a period of time is to purge the reductant residue in the
injector to exhaust pipe. The solenoid valve is de-energized
thereafter and the State is set to PU3. In the sub-state PU3, the
PPT 200 is connected to compressed air to refill air into the PPT.
When the PPT pressure is higher than a threshold Trap_Thd, the
refill stops, and the key flag is examined. If the key flag is
Key_off, then the control goes into the Off state, otherwise, the
control enters the Idle state.
[0087] While the present invention has been depicted and described
with reference to only a limited number of particular preferred
embodiments, as will be understood by those of skill in the art,
changes, modifications, and equivalents in form and function may be
made to the invention without departing from the essential
characteristics thereof. Accordingly, the invention is intended to
be only limited by the spirit and scope as defined in the appended
claims, giving full cognizance to equivalents in all respect.
* * * * *