U.S. patent application number 12/664440 was filed with the patent office on 2010-07-08 for process for starting a pump.
This patent application is currently assigned to INERGY AUTOMOTIVE SYSTEMS RESEARCH (Societe Anonyme). Invention is credited to Jean-Claude Habumuremyi.
Application Number | 20100172763 12/664440 |
Document ID | / |
Family ID | 38976108 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100172763 |
Kind Code |
A1 |
Habumuremyi; Jean-Claude |
July 8, 2010 |
Process for starting a pump
Abstract
Process for starting a pump intended to pump a liquid contained
in a tank and to produce a substantially constant outlet pressure
(setpoint pressure), according to which: 1/ the temperature (T1) of
the liquid held in the tank is determined and compared to a
setpoint temperature (T0); 2/ if the temperature (T1) is greater
than the setpoint temperature (T0), the pump is actuated; 3/ if the
temperature (T1) is less than or equal to the setpoint temperature
(T0), the tank is heated for a time t1; then 4/ the pump is
actuated for a time t2 during which the pump outlet pressure is
measured; 5/ if this pressure is stable and in an acceptable margin
of the setpoint pressure, the pump is kept going; and 6/ if this
pressure is not stable and/or is not in the acceptable margin of
the setpoint pressure, the pump is stopped and the tank is heated
for a time t3, at the end of which steps 4 to 6 are repeated.
Inventors: |
Habumuremyi; Jean-Claude;
(Haaltert, BE) |
Correspondence
Address: |
Solvay;c/o B. Ortego - IAM-NAFTA
3333 Richmond Avenue
Houston
TX
77098-3099
US
|
Assignee: |
INERGY AUTOMOTIVE SYSTEMS RESEARCH
(Societe Anonyme)
Brussels
BE
|
Family ID: |
38976108 |
Appl. No.: |
12/664440 |
Filed: |
June 16, 2008 |
PCT Filed: |
June 16, 2008 |
PCT NO: |
PCT/EP2008/057524 |
371 Date: |
December 14, 2009 |
Current U.S.
Class: |
417/32 |
Current CPC
Class: |
F01N 3/208 20130101;
F01N 2610/02 20130101; Y02T 10/12 20130101; F01N 2900/1808
20130101; F01N 2610/1493 20130101; F01N 2610/10 20130101; Y02T
10/24 20130101; F01N 2610/144 20130101; F01N 2900/1811 20130101;
F01N 2900/08 20130101 |
Class at
Publication: |
417/32 |
International
Class: |
F01N 3/20 20060101
F01N003/20; F04B 49/06 20060101 F04B049/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 20, 2007 |
FR |
0755875 |
Claims
1. A process for starting a pump intended to pump a liquid
contained in a tank and to produce a substantially constant outlet
pressure (setpoint pressure), wherein: 1. the temperature (T1) of
the liquid held in the tank is determined and compared to a
setpoint temperature (T0); 2. if the temperature (T1) is greater
than the setpoint temperature (T0), the pump is actuated; 3. if the
temperature (T1) is less than or equal to the setpoint temperature
(T0), the tank is heated for a time t1; then 4. the pump is
actuated for a time t2 during which the pump outlet pressure is
measured; 5. if this pressure is stable and in an acceptable margin
of the setpoint pressure, the pump is kept going; and 6. if this
pressure is not stable and/or is not in the acceptable margin of
the setpoint pressure, the pump is stopped and the tank is heated
for a time t3, at the end of which steps 4 to 6 are repeated.
2. The process according to claim 1, wherein the pump is driven by
a motor and is controlled by a controller, and wherein an ECM
(Electronic Control Module) sends, to the controller, a PWM (Pulse
Width Modulation) control signal having a duty cycle that varies as
a function of the desired operating conditions for the pump, the
controller acting on the motor to apply said operating conditions
to the pump.
3. The process according to claim 1, wherein the liquid is an
aqueous urea solution.
4. The process according to claim 1, wherein the pump is integrated
into a base plate submerged in the tank which also integrates other
active components of the tank.
5. The process according to claim 4, wherein the base plate
integrates a heating element.
6. The process according to claim 5, wherein a liquid feed line
comes out of the tank and a liquid return line arrives at the tank,
and wherein these lines are also equipped with a heating
element.
7. The process according to claim 6, wherein the pump is a rotary
pump, and wherein the lines are purged after each use of the pump
just before the is stopped by reversing its direction of rotation
for the time necessary to convey the liquid contained in the feed
and return lines back to the tank.
8. The process according to claim 6, wherein the time t1 is the
minimum time required to obtain a volume of liquid equal to the
volume of the injection line, the return line and the components in
these lines.
9. The process according to claim 2, wherein the controller is
connected to a pressure sensor, and wherein the controller
compares, in a loop, the pressure setpoint value with the value
measured by the sensor and consequently acts on the rotational
speed of the motor in order to attempt to stabilize the pressure at
the setpoint value.
10. The process according to claim 9, wherein during the period t2,
the pressure is measured periodically, and wherein a mathematical
criterion based on the variance is applied to the pressure
measurements and to the setpoint pressure.
11. The process according to claim 10, wherein, if the pressure is
not stable and/or is not in an acceptable margin with respect to
the setpoint pressure at the end of several iterations (of steps 4
to 6), the controller stops the pump and sends information to the
ECM, according to which information the pump has not been able to
be started.
12. The process according to claim 1, it which has been tested in a
MATLAB/SIMULINK.RTM. simulation environment and/or which has been
concretely applied to an SCR (Selective Catalytic Reduction)
system.
Description
[0001] The present application relates to a process for starting a
pump intended to pump a liquid that is capable of freezing or
solidifying. It relates, in particular, to starting pumps intended
for aqueous urea solutions.
[0002] Legislation on vehicle and heavy goods vehicle emissions
stipulates, amongst other things, a reduction in the release of
nitrogen oxides NO.sub.x into the atmosphere. One known way to
achieve this objective is to use the SCR (Selective Catalytic
Reduction) process which enables the reduction of nitrogen oxides
by injection of a reducing agent, generally ammonia, into the
exhaust line. This ammonia may derive from the pyrolytic
decomposition of an ammonia precursor solution, whose concentration
may be the eutectic concentration. Such an ammonia precursor is
generally a urea solution.
[0003] With the SCR process the high levels of NO produced in the
engine during combustion at optimized efficiency are treated in a
catalyst on exiting the engine. This treatment requires the use of
the reducing agent at a precise concentration and of extreme
quality. The solution is thus accurately metered and injected into
the exhaust gas stream where it is hydrolysed before converting the
nitrogen oxide (NO.sub.x) to nitrogen (N.sub.2) and water
(H.sub.2O).
[0004] In order to do this, it is necessary to equip the vehicles
with a tank containing an additive solution (generally an aqueous
urea solution) and also a device for metering the desired amount of
additive and injecting it into the exhaust line. Given that the
aqueous urea solution generally used for this purpose (eutectic
32.5 wt % urea solution) freezes at -11.degree. C., it is necessary
to provide a heating device to liquefy the solution in order to be
able to inject it into the exhaust line in the event of starting in
freezing conditions. This device should ideally cover at least one
part of the storage tank and also the line going from this tank to
the injector, and preferably also the devices encountered in this
line (filter, pump, etc.).
[0005] In motor vehicles, the temperature margin in which the
systems must operate generally lies between -40.degree. C. and
80.degree. C. (depending on the countries/regions). It is therefore
necessary to ensure that the pump can start in the low-temperature
ranges, knowing that the aforementioned solutions have a tendency
to crystallize starting from -8.degree. C.
[0006] Determination of the actuation time of the "cold" pump (i.e.
the time that it is necessary to wait in order to have melted a
minimum of liquid and to enable the pump to be started) may be
based on experimental data obtained at various temperatures over a
given system.
[0007] The tests that generate this data are generally carried out
in a cold room and the effects of wind, vehicle vibrations, changes
in the initial temperature conditions, etc. are not taken into
account. There are therefore situations where the pump will not be
actuated since the starting time has been underestimated (in the
case of changing situations, for example). These situations may
furthermore lead to irreversible pump damage. Conversely, the
actuation time may have been overestimated (which is furthermore
generally the case for safety reasons) and the pollution-control
system is then not optimal.
[0008] It should be noted that the starting time could also be
calculated based on thermodynamic and thermal data, but the results
obtained would again not take into account practical parameters of
variability.
[0009] Although some documents briefly describe the cold starting
of SCR systems (see, for example, documents U.S. Pat. No. 5,884,475
and US 2002/0088220), none of these documents addresses the problem
of the optimal determination of the pump actuation time.
[0010] The present invention aims to solve this problem by
providing a process which makes it possible to optimize the pump
starting time without damaging this pump.
[0011] For this purpose, the present application relates to a
process for starting a pump intended to pump a liquid contained in
a tank and to produce a substantially constant outlet pressure
(setpoint pressure), according to which: [0012] 1. the temperature
(T1) of the liquid held in the tank is determined and compared to a
setpoint temperature (T0); [0013] 2. if the temperature (T1) is
greater than the setpoint temperature (T0), the pump is actuated;
[0014] 3. if the temperature (T1) is less than or equal to the
setpoint temperature (T0), the tank is heated for a time t1; then
[0015] 4. the pump is actuated for a time t2 during which the pump
outlet pressure is measured; [0016] 5. if this pressure is stable
and in an acceptable margin of the setpoint pressure, the pump is
kept going; [0017] 6. if this pressure is not stable and/or is not
in the acceptable margin of the setpoint pressure, the pump is
stopped and the tank is heated for a time t3, at the end of which
steps 4 to 6 are repeated.
[0018] The pump to which the invention applies is a pump of any
known type, preferably driven by a motor and the operation of which
is controlled by a controller. Preferably, the pump is of the gear
pump type. It generally comprises a stator and a rotor and can
preferably operate in two opposite rotational directions, one
generally corresponding to supplying the feed line with liquid and
the other generally corresponding to a purge of the feed line.
[0019] Any type of rotary electric motor may be suitable.
Preferably, the motor is of the BLDC (brushless direct current)
motor type. In this case, the pump is driven by a magnetic coupling
between the rotor of the pump and a drive shaft of the motor.
[0020] The controller of this pump is a control module (generally
comprising a PID regulator and a motor rotational speed controller)
and an electric power supply unit which preferably supplies the
motor with the power required to rotate it at the desired speed and
which enables its direction of rotation to be reversed, where
necessary.
[0021] Most particularly preferably, an ECM (Electronic Control
Module) sends, to the pump controller, a PWM (Pulse Width
Modulation) control signal having a duty cycle that varies as a
function of the desired operating conditions for the pump and
according to which the controller acts on the motor to apply said
operating conditions to the pump. This preferred variant is the
subject of Application FR 0700358 in the name of the Applicant, the
subject of which is incorporated by reference in the present
application.
[0022] As explained previously, the liquid for which the invention
is intended is a liquid capable of freezing or solidifying (setting
solid) when the temperature reaches a low temperature threshold.
These may, for example, be aqueous solutions. One liquid to which
the present invention applies particularly well is urea.
[0023] The term "urea" is understood to mean any, generally
aqueous, solution containing urea. The invention gives good results
with eutectic water/urea solutions for which there is a standard
quality: for example, according to the standard DIN 70070, in the
case of the AdBlue.RTM. solution (commercial solution of urea), the
urea content is between 31.8% and 33.2% (by weight) (i.e.
32.5+/-0.7 wt %) hence an available amount of ammonia between 18.0%
and 18.8%. The invention may also be applied to the urea/ammonium
formate mixtures, also in aqueous solution, sold under the trade
name Denoxium.TM. and of which one of the compositions
(Denoxium-30) contains an equivalent amount of ammonia to that of
the Adblue.RTM. solution. The latter have the advantage of only
freezing from -30.degree. C. onwards (as opposed to -11.degree.
C.), but have the disadvantages of corrosion problems linked to the
possible release of formic acid and a less available market
(whereas urea is widely used and readily available even in fields
such as agriculture). The present invention is particularly
advantageous in the context of eutectic water/urea solutions.
[0024] According to the invention, the liquid is held in a tank
which may be made from any material, preferably one having good
chemical resistance to the liquid in question. In general, this is
metal or plastic. Polyolefins, in particular polyethylene (and more
particularly HDPE or high-density polyethylene), constitute
preferred materials, in particular in the case where the liquid is
urea.
[0025] This tank may be produced by any conversion processes known
in the case of hollow bodies. One preferred processing method, in
particular when the tank is made of plastic, and in particular
HDPE, is the extrusion-blow moulding process. In this case a
parison (in one or more parts) is obtained by extrusion, and is
then shaped by blow moulding in a mould. One-part moulding of the
tank from a single parison gives good results.
[0026] This tank is advantageously equipped with a base plate or
mounting plate (i.e. a support having substantially the shape of a
plate) onto which at least one active accessory of the urea storage
system and/or injection system is attached. This base plate
generally has a perimeter, closed up on itself, of any shape.
Usually, its perimeter has a circular shape.
[0027] In a particularly preferred manner, this base plate is a
submerged mounting plate, i.e. sealing an opening in the lower wall
of the tank. The expression "lower wall" is in fact understood to
mean the lower half of the tank (whether or not it is moulded in
one piece or from two parison sheets or cut-outs). Preferably, the
base plate is located in the lower third of the tank, and more
particularly preferably, in the lower quarter, or even squarely in
the bottom of this tank. It may be partly in the lower side wall,
in which case it is slightly slanted once mounted in the vehicle.
The location and/or direction of the base plate especially depends
on the location of the tank in the vehicle, and on the space
occupied around it (considering the components to be integrated
therein).
[0028] This base plate therefore incorporates at least one
component that is active during storage and/or injection. This is
understood to mean that the component is attached to or produced as
one part with the base plate. This component may be incorporated
inside the tank, or on the outside with, if necessary, a connection
(delivery tube) passing through it.
[0029] Preferably, the base plate according to this variant of the
invention integrates several active storage and/or metering
components and, most particularly preferably, it integrates all the
active components which are brought to be in contact with the
liquid additive found in, leaving from or arriving into the
additive tank.
[0030] Preferably, the component is chosen from the following
elements: a pump; a filter; a level gauge; a temperature sensor; a
quality sensor; a pressure sensor and a pressure regulator. It is
advantageous for the pump of the process according to the invention
to be integrated into such a base plate and for this base plate to
integrate other active components (preferably all the active
components) as defined above.
[0031] Preferably, the base plate also integrates at least one
heating element and most particularly preferably this heating
element comprises at least one flexible part (as described in
Application FR 0755118 in the name of the Applicant, the content of
which is incorporated by reference in the present application)
which is preferably a flexible heater, i.e. a heater comprising one
or more resistive track(s) affixed to a film or placed between two
films (i.e. two substantially flat supports, the material and
thickness of which are such that they are flexible). This film is
preferably made of a plastic (although any other insulating
material may be suitable) and, in particular, is based on an
elastomer. Most particularly preferably, this flexible heater
comprises one or more stainless steel resistive track(s) sandwiched
between two silicone resin films, one of which is covered with a
network of glass fibres.
[0032] Preferably, the heating element extends inside the tank, and
is therefore submerged (partially or completely) in the liquid when
the tank is full. Most particularly preferably, the heating element
predominantly consists of a flexible heater. Preferably, there is
also a heating element (wire or flexible heater) present around the
urea feed line up to the injector and the return line, where
appropriate. Specifically, in one preferred variant of the
invention, the pump intentionally meters too great an amount
(pressure) of liquid, the excess of which is returned to the tank,
for example using a line equipped with a calibrated valve. When the
urea is injected into the exhaust gases of an engine, this variant
makes it possible to cool the injector but it should however be
noted that the non-return lines are more advantageous, economically
speaking.
[0033] Preferably, the element heating these lines is also a
flexible heater.
[0034] In one advantageous variant of the invention, the feed line
is purged after each use of the pump (just before it is stopped) in
order to reduce the starting time of the system and avoid
prematurely damaging the lines (as the urea solutions expand when
it freezes). The purge may be carried out, for example, by
reversing the rotational direction of the pump just for the time
necessary to convey the liquid contained in the feed line back to
the tank.
[0035] As regards the return line, if present, it generally has a
relatively low volume and therefore, if it is heated, it should not
be purged while the pump is stopped. Therefore, to prevent the
liquid from going round in circles in the loop determined by the
feed line and the return line during the purge when this is carried
out by reversing the rotational direction of the pump, it is
advantageous to equip the return line with a non-return valve.
[0036] According to the invention, before starting the pump, the
temperature (T1) of the liquid held in the tank is determined and
compared to a setpoint temperature (T0) (step 1 of the process).
Generally, this measurement is carried out using a temperature
sensor which is advantageously integrated into a base plate as
described previously. The setpoint temperature (T0) is generally
that at which the liquid begins to solidify. When it is a question
of a liquid capable of freezing or crystallizing, this temperature
is generally that of the start of said crystallization (namely
around -8.degree. C. for eutectic water/urea solutions).
[0037] If the temperature measured is greater than T0, the pump is
actuated, for example by sending a PWM signal corresponding to the
setpoint pressure to the ECM.
[0038] If the temperature measured is less than or equal to T0, the
tank is heated for a time t1. This time is a function of the
temperature measured and is generally the minimum time required to
obtain a volume of liquid equal to the volume of the injection line
and the return line, where appropriate (including the internal
volume of the accessories placed in this line, such as filter,
pump, etc.). As explained previously, this time may be deduced from
experimental data and/or theoretical calculations.
[0039] In practice, the ECM may send a signal to a heating element
integrated into the tank (preferably into a submerged base plate as
explained previously), so that this tank is heated at a given power
for the time t1.
[0040] At the end of this time, the pump is actuated (with a
suitable command depending on the setpoint pressure) for a time t2
during which the pump outlet pressure is measured (step 4 of the
process, if necessary). Again, this may be carried out using the
ECM which sends a signal to the pump controller instructing it to
actuate the pump under the conditions required to reach the
setpoint pressure, for a time t2, and to effectively measure this
pressure. Measurement of the pressure over this period is carried
out at very precise times, which is generally possible via the use
of a real-time operating system (for example, every 50 ms).
[0041] In one advantageous variant, the controller is connected to
a pressure sensor and it compares, in a loop, the pressure setpoint
value with the value measured by the sensor and consequently acts
on the rotational speed of the motor in order to attempt to
stabilize the pressure at the setpoint value.
[0042] Generally, this is done using a pressure regulator which
carries out the comparison between the setpoint pressure and the
pressure measured and generates an error signal for the motor
rotational speed controller.
[0043] In this variant, the regulator may be of any known type, but
it is preferably of PID (Proportional-Integral-Derivative) type. As
regards the pressure sensor, it is preferably integrated with the
pump, that is to say that it may be attached to the pump by any
known attachment means.
[0044] The time t2, during which the stability of the pressure is
verified, is preferably short enough so that the pump does not risk
being damaged if it operates when empty and long enough so that the
stability of the outlet pressure can be verified. Generally, a time
of the order of seconds (even tens of seconds) is suitable.
[0045] If, during the period t2, the pressure was effectively
stable and in an acceptable margin of the setpoint value (see later
on) the controller keeps the pump going and signals to the ECM of
the system that the pump has started correctly.
[0046] If, on the other hand, this pressure was not stable and/or
was not in an acceptable margin with respect to the setpoint
pressure, the pump is stopped (generally via a specific PWM signal
sent by the ECM) and the tank is heated for a time t3 before
restarting the pump and again verifying the stability of the outlet
pressure over a period t2 in an iterative manner until a stable
setpoint pressure is reached and this information is sent to the
ECM, or information is sent to the ECM, according to which
information the pump has not been able to be started if, for
example, after a limited number (for example, 4) of attempts at
starting, a stable pressure has not been able to be obtained.
[0047] To verify the stability of the pressure and the accuracy of
its value (i.e. the fact that it is or is not in an acceptable
margin with respect to the setpoint pressure), the controller
applies a given mathematical criterion to the pressure measurements
and to the setpoint pressure. A criterion based on the variance
gives good results. According to this, over the interval t2, the
average distance of n successive pressure measurements carried out
over this interval is evaluated relative to the reference pressure
(i.e. for each of the n measurements, the square of the difference
between the pressure measured and the setpoint pressure is
calculated, the n values of the squares thus obtained are added
together and this sum is divided by n). Therefore, the average
variance of the pressure over the period t2 is in fact calculated
and it is compared with the maximum variance of the pump
specifications.
[0048] Generally, an acceptable margin is defined as being a few %
deviation with respect to the setpoint pressure. In practice, this
value should often not exceed 2% of the setpoint pressure after the
transient control phase. In this case, the pressure over the period
t2 will be stable if the average variance defined above and
calculated over the period t2 is less than (0.02).sup.2 multiplied
by the square of the pressure. If this is the case, the criterion
of variance is judged to be satisfied and the controller keeps the
pump going (for example by applying a voltage to it that
corresponds to the setpoint pressure).
[0049] If this is not the case, the controller stops the pump
(generally by means of a suitable command) or if the pump is
blocked, a pump diagnostics manager (if one exists) may
short-circuit the voltage (by earthing it).
[0050] The signal that the controller sends to the ECM in order to
signal to it if the pump has started correctly may consist of
precisely this voltage.
[0051] In practice, the time to measure a pressure and calculate
the average variance over the latter combined pressure measurements
is of the order of tens of ms (milliseconds) which makes it
possible, for a time t2 of the order of seconds, to carry out
several tens of separate determinations of the variance.
[0052] The process according to the invention has been successfully
tested in a MATLAB/SIMULINK.RTM. simulation environment and a
computer controlling an SCR system.
[0053] The present invention is illustrated, non-limitingly, by
appended FIGS. 1 and 2.
[0054] FIG. 1 consists of a block diagram of one preferred variant
of the process according to the invention applied to a system for
the injection of urea into the exhaust gases of an internal
combustion engine (or SCR system) and
[0055] FIG. 2 illustrates one preferred variant of such a
system.
[0056] From the start up of the urea system or SS (Start System),
the system controller verifies whether the temperature is above the
low temperature threshold (T1>T0) in the tank in order to be
able to start the pump without risk of damaging it.
[0057] If this is the case (Y or YES), it effectively starts the
pump (SP) and sends a corresponding signal (PS or Pump Started) to
an ECM.
[0058] If this is not the case (N or NO), it heats the tank and the
lines (urea feed and return lines, where appropriate) of the system
for a time t1 (H(t1)). Next, it starts the pump (SP) and over a
time t2, it regularly measures the pressure at the pump outlet and
calculates the change in its variance (RP(t2)). At the end of t2,
it compares the average variance of the pressure (or its
covariance) and compares it to a setpoint value (p OK?).
[0059] It this is below the setpoint value (Y), the controller
keeps the pump going and signals to the ECM that the pump has
indeed started (PS).
[0060] If the covariance is above the desired value (N), the
controller stops the pump (STP or Stop Pump). Next, it again heats
the tank and the lines for a time t3 (H(t3)) before restarting it
(SP) and reverifying the stability of the pressure over a period t2
(RP(t2)), etc. This continues until a stable setpoint pressure is
reached, the pump is kept going and the ECM is informed of that, or
is informed that the pump has a problem if, at the end of 4
iterations, a stable pressure has not been reached.
[0061] As mentioned above, FIG. 2 illustrates an SCR system to
which the block diagram from FIG. 1 applies and which comprises the
following components (previously described in the description):
[0062] 1: urea tank; [0063] 2: gauge (level sensor); [0064] 3:
flexible heater; [0065] 4: filter; [0066] 5: temperature sensor;
[0067] 6: current sensor for the flexible heater; [0068] 7: pump;
[0069] 8: speed sensor; [0070] 9: heating filament for the lines
and pump heating cartridge; [0071] 10: pressure sensor; [0072] 11:
current sensor for the line heater; [0073] 12: injector; [0074] 13:
non-return valve that prevents the liquid from going round in
circles (in the loop created by the feed line and that for return
to the tank) during the purge (when the pump rotates in reverse);
[0075] 14: calibrated orifice (restriction)- used to set the flow
rate and to add resistance in order to increase the pressure (by
increasing pressure drops in the return line); [0076] 15: (BLDC)
motor for driving the pump; [0077] 16: non-return valve that
enables the pressure at the pump outlet to be regulated.
* * * * *