U.S. patent application number 14/123170 was filed with the patent office on 2014-06-19 for method for heating an scr system using two resistive heating elements.
This patent application is currently assigned to INERGY AUTOMOTIVE SYS. RESEARCH (SOCIETE ANONYME). The applicant listed for this patent is Florent Barzic, Benone Dorneanu, Volodia Naydenov, Guillaume Zeller. Invention is credited to Florent Barzic, Benone Dorneanu, Volodia Naydenov, Guillaume Zeller.
Application Number | 20140166636 14/123170 |
Document ID | / |
Family ID | 44906499 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140166636 |
Kind Code |
A1 |
Naydenov; Volodia ; et
al. |
June 19, 2014 |
METHOD FOR HEATING AN SCR SYSTEM USING TWO RESISTIVE HEATING
ELEMENTS
Abstract
Method for heating an SCR system using at least two resistive
heating elements, according to which each of these resistive
elements is powered by a PWM signal, the two PWM signals being at
least partly in phase opposition.
Inventors: |
Naydenov; Volodia;
(Louvain-La-Neuve, BE) ; Zeller; Guillaume;
(Brussels, BE) ; Barzic; Florent; (Munich, DE)
; Dorneanu; Benone; (Brussels, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Naydenov; Volodia
Zeller; Guillaume
Barzic; Florent
Dorneanu; Benone |
Louvain-La-Neuve
Brussels
Munich
Brussels |
|
BE
BE
DE
BE |
|
|
Assignee: |
INERGY AUTOMOTIVE SYS. RESEARCH
(SOCIETE ANONYME)
Brussels
BE
|
Family ID: |
44906499 |
Appl. No.: |
14/123170 |
Filed: |
May 29, 2012 |
PCT Filed: |
May 29, 2012 |
PCT NO: |
PCT/EP2012/059994 |
371 Date: |
March 4, 2014 |
Current U.S.
Class: |
219/441 ;
219/438; 219/482; 219/494 |
Current CPC
Class: |
Y02T 10/40 20130101;
Y02A 50/20 20180101; F01N 2610/10 20130101; F01N 9/00 20130101;
Y02T 10/24 20130101; Y02T 10/47 20130101; Y02T 10/12 20130101; F01N
2610/02 20130101; F01N 2900/0602 20130101; F01N 3/208 20130101;
Y02A 50/2325 20180101; F01N 3/01 20130101 |
Class at
Publication: |
219/441 ;
219/482; 219/438; 219/494 |
International
Class: |
F01N 3/01 20060101
F01N003/01 |
Foreign Application Data
Date |
Code |
Application Number |
May 30, 2011 |
EP |
11168057.5 |
Claims
1. A method for heating an SCR system, the method comprising:
powering at least two resistive heating elements, wherein each of
these resistive elements is powered by a PWM signal comprising
power pulses and having a given duty cycle, the two PWM signals
being at least partly in phase opposition.
2. The method of claim 1, wherein the heating elements are metallic
heating wires attached inside an injection molded shell, which is
part of a urea tank.
3. The method of claim 2, wherein the shell comprises a pump and
wherein one of the heating wires is fixed in the neighborhood of
the pump.
4. The method of claim 1, wherein at least one temperature sensor
is employed and if this sensor detects a temperature less than or
equal to a threshold value, at least one of the heaters is powered
and thereafter or at the same time, the second one is powered too,
but with a PWM signal being at least partly in phase opposition
with the PWM signal of the first heater whenever possible depending
on the heating conditions.
5. The method of claim 1, wherein an overlap between the power
pulses of both PWM signals is optimized as a function of the
respective duty cycles (heating conditions).
6. The method of claim 1, wherein a time shift is introduced
between the switching on and off of both heaters during each period
of the PWM signal.
7. The method according to any of the of claim 1, being applied to
a urea tank of a vehicle comprising a battery, wherein the duty
cycle of each heater is a function of the power supply voltage
received from the battery, and is adapted for each heater according
to the temperature and a urea level in the tank.
8. The method of claim 7, wherein an electronic control unit (ECU)
is employed to specifically activate/deactivate each of the heaters
as a function of information received from sensor(s) and of the
power (voltage) available on the battery.
Description
[0001] The present application relates to a method for heating an
SCR system using two resistive heating elements and also to an SCR
system suitable for the application of this method.
[0002] Legislation on vehicle and truck 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.sub.x 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 (generally urea) solution and
also a device for metering the desired amount of additive and
injecting it into the exhaust line.
[0005] Since the aqueous urea solution generally used for this
purpose (eutectic solution of 32.5 wt % urea in water) 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.
[0006] Several systems have been provided in the prior art for this
purpose. Generally, these systems comprise heating devices that
involve either specific heating elements or a bypass of the engine
cooling circuit (for example, see Application WO 2006/064001 in the
name of the Applicant).
[0007] As regards the use of specific heating elements, it is known
to put resistive heating elements inside the tank containing the
urea solution, and optionally over the urea lines (feed lines and
return lines, where appropriate), over the pump, the filter, etc.
and other active components of the system.
[0008] Patent application EP 11150661.4 in the name of the
Applicant describes a tank for storing an SCR additive, said tank
being made as two halve shells (preferably injection moulded), the
lower one being equipped with means (upstanding pins with slots,
grooves, supporting baffles or the like) for fixing at least one
resistive heating wire to it. In one embodiment, the wire(s) can be
attached or put along a small tube whose fast thawing allows to
insure fast feeding of the pump/exhaust system.
[0009] It is indeed required to be able to start the SCR system as
soon as possible after starting the engine so that the area where
the pump sucks is preferably de-iced very quickly. However, it is
also required to heat the rest of the tank because otherwise, once
the additive in the vicinity of the pump will have been consumed,
the rest of the additive inside the tank will remain solid and
unavailable.
[0010] It would therefore be favorable to have at least two
resistive heaters: one covering the pumping area (for instance
fixed in or around the liquid trap where the pump is fixed) and one
covering the rest of the tank.
[0011] However, on a vehicle, the only power source available
generally is the battery which supplies around 13.5 volts nominal
(generally with a minimum of 9 volts and a maximum of 16 volts,
which are general OEM requirements). Hence, the fact of using two
heaters which must at least for some time, be functioning together,
might lead to such power consumption that other devices onboard the
vehicle (lights, heating inside the vehicle, defrosting of the
windows . . . ) can no longer function correctly. In this case, the
constraints for the SCR Electronic Controller itself are also
higher, especially considering the thermal dissipation.
[0012] It is known (for instance from US 2009/0061489) to power
resistive heaters by means of a PWM signal, which is a square
voltage wave, i.e. a train of rectangular power (voltage) pulses
having a given duration and amplitude and emitted with a given
period. Such a signal (of PWM type) is characterized by its duty
cycle, that is to say the ratio of the duration of the pulses to
their period, generally expressed in %.
[0013] The idea behind the present invention is to use this method
for powering two resistive heaters of an SCR system in a way such
that the power pulses of both heaters overlap as little as
possible, and ideally: do not overlap at all when possible,
considering the fact that in some conditions (for instance: when
starting the engine in frost conditions), the duty cycle of both
heaters will be too high for being able to avoid any overlapping
(typically: if the sum of both duty cycles exceeds 100%).
[0014] The object of the invention is therefore a method for
heating an SCR system using at least two resistive heating
elements, according to which each of these resistive elements is
powered by a PWM signal, the two PWM signals being at least partly
in phase opposition.
[0015] The expression "SCR system" is understood to mean a system
for the selective catalytic reduction of the NO.sub.x from the
exhaust gases of an internal combustion engine, preferably of a
vehicle, using preferably urea as a liquid ammonia precursor.
[0016] 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 quality
standard: 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. The present invention is
particularly advantageous in the context of eutectic water/urea
solutions.
[0017] As mentioned previously, SCR systems generally comprise at
least one tank for storing the urea solution and also a system for
feeding this to the exhaust gases, and which generally comprises
active components such as a pump, filter, valve(s), conduits (feed
and/or return conduits). The method according to the invention
applies to the heaters of any component of such a system, any part
of such a component and any combination of such components (or even
to a complete SCR system).
[0018] The method according to the invention uses at least two
separate resistive elements that can be activated (heated)
independently. They are preferably connected in parallel to one and
the same current source (which does not rule out the possibility of
the heating system also comprising one or more other resistive
elements connected in series). The fact of connecting the resistors
in parallel also makes it easier to diagnose their failure, where
necessary (see Application WO 2009/013329 in the name of the
Applicant, the content of which is incorporated for this purpose by
reference into the present application).
[0019] The resistive heating elements may be metallic heating
filaments (wires), flexible heaters, (that is to say heaters
comprising one or more resistive track(s) affixed to a film or
placed between two films (that is to say two substantially flat
supports, the material and thickness of which are such that they
are flexible)) or any other type of resistive elements that have a
shape, size and flexibility suitable for being inserted into and/or
wound around the components of the SCR system. For the tank and its
base plate (i.e. a mounting plate that integrates at least one and
preferably all the active components of the system, namely pump,
filter, gauge, etc.), where appropriate, metallic wires or flexible
heaters are particularly suitable. The present invention is
particularly well suited for metallic heating wires attached inside
an injection moulded shell aimed at being part of a urea tank as
described above.
[0020] Although the at least two heating elements may heat any
component(s) of the SCR system, one of them is preferably fixed in
the pumping area while the other one covers the rest of the tank.
Hence, in a preferred embodiment, the heating elements are heating
wires attached inside an injection moulded shell comprising a pump
and one of them is fixed in the neighbourhood of the pump.
[0021] According to the invention, the heating elements are
activated (heated) in freezing conditions and preferably, when the
component(s) to be heated are actually in contact with (a
substantial amount of) liquid or solid urea. Within the context of
the invention, the expression "freezing conditions" is generally
understood to mean an ambient temperature below -5.degree. C. This
is because, theoretically, eutectic urea solutions begin to freeze
around -8.degree. C. However, taking into account their ageing, it
is not uncommon for them to begin to freeze around -5.degree.
C.
[0022] Therefore, the method of the invention preferably uses at
least one temperature sensor and if this sensor detects a
temperature less than or equal to a threshold value (for instance
equal to -5.degree. C.: see above), at least one of the heaters is
powered and thereafter or at the same time, the second one is
powered too, but with a PWM signal being at least partly in phase
opposition with the PWM signal of the first heater whenever
possible depending on the heating conditions.
[0023] By "at least partly in phase opposition" is meant that the 2
PWM signals have the same frequency but that there is a
displacement between or among the waves of both signals. This is
generally possible when none of them has a duty cycle of 100%.
[0024] The method of the invention preferably comprises optimizing
the overlapping between the power pulses of both signals as a
function of the respective duty cycles (heating conditions). There
can be no overlapping at all if both duty cycles are significantly
below 50%, or there can be a total overlapping if at least one of
them is close to 100%.
[0025] Generally, to ensure the optimized heating performances
(minimize the urea defrosting time), the duty cycle of each heater
is a function of the power supply voltage received from the vehicle
battery to avoid damaging the heaters, and is adapted for each
heater according to the temperature in the tank and to the urea
level in the tank to allow a fast defrosting around the pump and
insure a priming in a shortened time.
[0026] In a preferred embodiment, the method also allows reducing
the peak current consumption by the SCR system, in order to
decrease the current peak to be delivered by the alternator. In
this embodiment, a time shift is introduced between the switching
on and off of both heaters during each period of the PWM signal.
This time shift is preferably optimized based on the duration of
the current peaks when switching on/off the heaters. A time shift
in the order of the tenths (typically 100) ms gives good results in
practice. Hence, the method according to that embodiment allows:
[0027] 1. To reduce the instantaneous system current consumption
[0028] 2. To reduce the peak current consumption by the SCR system
[0029] 3. To ensure the optimized heating performances (minimize
the urea defrosting time) [0030] 4. To minimize the voltage
perturbations [0031] 5. Reduce the EMC interferences
[0032] The method according to the invention generally uses an
electronic control unit (ECU) that makes it possible to
specifically activate/deactivate (i.e. supply with current or not)
each of the heaters as a function of the information received from
the sensor(s) (temperature, level . . . ) and also, as a function
of the power (voltage) available on the battery at that time.
[0033] It should be noted that there may be more than two separate
resistors in the method of the invention, in which case the phase
oppositions of the respective signals could be optimized as
well.
[0034] The present invention is illustrated in a non limitative way
by FIGS. 1 to 3 attached, wherein:
FIG. 1 shows the PWM signals and the current consumption of two
heaters which are not powered according to the method of the
invention
[0035] FIG. 2 shows the PWM signals and the current consumption of
two heaters which are powered according to one embodiment of the
invention
[0036] FIG. 3 shows the PWM signals of two heaters which are
powered according to another embodiment of the invention.
[0037] In these figures, the scales (namely the value of the
average current) are only illustrative.
[0038] When comparing the instantaneous current consumptions
between FIGS. 1 and 2, it is quite clear that the method of the
inventions allows reducing the time during which the instantaneous
consumption is maximal.
[0039] As to FIG. 3, it gives some indicative values for the duty
cycles of the heaters, for their pulsing period and the shift time
between both PWM signals.
* * * * *