Abstract
A Diesel Particulate Filter (DPF) system including a Venturi exhaust passage device, in which a temperature and a pressure in a high pressure passage are measured, together with a difference of pressures in the high pressure passage and a low pressure passage, while a pressure drop across a DPF is monitored. A PM amount and an exhaust flow rate, which are key parameters in DPF control, can be calculated with the measured values. With the Venturi exhaust passage device, a two-stage bootstrapping heating device with two DOCs and an electrical heater can be further used to heat exhaust gas at a temperature lower than a light-off temperature, while a flow-back passage fluidly connected to an outlet of the DPF can be used for increasing exhaust flow-rate and making PM distribution in the DPF more uniform.
Claims
1. An exhaust gas processing system of an internal combustion engine, comprising: a diesel particulate filter; an exhaust gas passage device positioned upstream from said diesel particulate filter including a first high pressure passage, a second high pressure passage fluidly connected to said diesel particulate filter, and a low pressure passage, wherein both of said first high pressure passage and said second high pressure passage have a larger cross-section area than said low pressure passage; a fuel injector in communication to said first high pressure passage for releasing a dosing fuel in regenerating said diesel particulate filter; a heating device fluidly connected to said first high pressure exhaust passage receiving a mixture of said dosing fuel and an exhaust gas flow; a first diesel oxidation catalyst positioned downstream from said heating device fluidly connected to said low pressure exhaust passage; a second diesel oxidation catalyst positioned in between said exhaust gas passage device and said diesel particulate filter; and a regeneration controller configured to control a power applied to said heating device and a flow rate of said dosing fuel in regenerating said diesel particulate filter.
2. The exhaust gas processing system of claim 1, wherein said heating device is an electrical heater.
3. The exhaust gas processing system of claim 1, wherein said regeneration controller is further configured to energize said heating device when a temperature in said second diesel oxidation catalyst is lower than a predetermined value.
4. The exhaust gas processing system of claim 3, wherein said regeneration controller is further configured to set said flow rate of said dosing fuel to a first level when said heating device is energized and to a second level when said temperature in said second diesel oxidation catalyst is above a light-off temperature thereof.
5. The exhaust gas processing system of claim 1, further comprising: a pressure sensor and a first temperature sensor for measuring a pressure and a temperature in said second high pressure passage respectively; and a first differential pressure sensor for measuring a pressure difference in between said second high pressure passage and said low pressure passage.
6. The exhaust gas processing system of claim 5, wherein said regeneration controller is further configured to control said power applied to said heating device and said flow rate of said dosing fuel in response to sensing values obtained from said first differential pressure sensor, said pressure sensor, and said first temperature sensor.
7. The exhaust gas processing system of claim 5, further comprising: a second temperature sensor positioned upstream from said exhaust gas passage device for measuring a temperature in said first high pressure passage; and a third temperature sensor positioned downstream from said second diesel oxidation catalyst for measure a temperature therein.
8. The exhaust gas processing system of claim 7, wherein said regeneration controller is further configured to control said power applied to said heating device and said flow rate of said dosing fuel in response to sensing values obtained from said first differential pressure sensor, said pressure sensor, said first temperature sensor, said second temperature sensor, and said third temperature sensor.
9. The exhaust gas processing system of claim 5, further comprising: a second differential pressure sensor for measuring a pressure drop across said diesel particulate filter.
10. The exhaust gas processing system of claim 9, wherein said regeneration controller is further configured to trigger a regeneration process for said diesel particulate filter in response to sensing values obtained from said first differential pressure sensor, said second differential pressure sensor, said pressure sensor, and said first temperature sensor.
11. The exhaust gas processing system of claim 10, wherein said regeneration controller is further configured to calculate a particulate amount value indicative of an amount of particulate matter deposited in said diesel particulate filter according to a ratio between sensing values obtained from said second differential pressure sensor and said first differential pressure sensor, and trigger said regeneration process in response to said particulate amount value.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a schematic representation of an exhaust gas processing system of an internal combustion engine including an exhaust gas passage device, a heating device and a diesel particulate filter;
(2) FIG. 2 is a flow chart of a service routine running periodically for a timer based interrupt for calculating an amount of PM deposited in a diesel particulate filter;
(3) FIG. 3 is a schematic representation of an exhaust gas processing system of an internal combustion engine including an exhaust gas passage device, a two-stage bootstrapping heating device and a diesel particulate filter;
(4) FIG. 4a is a flow chart of a service routine running periodically for a timer based interrupt for generating dosing fuel commands in regenerating a diesel particulate filter in a system of FIG. 3;
(5) FIG. 4b shows a block diagram of a feedback control in controlling dosing fuel flow-rate in regenerating a diesel particulate filter;
(6) FIG. 5a is a schematic representation of an exhaust gas processing system of an internal combustion engine including an exhaust gas passage device, a heating device positioned downstream from the exhaust gas passage device, a diesel particulate filter, and a flow-back passage.
(7) FIG. 5b is a schematic representation of an exhaust gas processing system of an internal combustion engine including an exhaust gas passage device, a heating device positioned upstream from the exhaust gas passage device, a diesel particulate filter, and a flow-back passage.
(8) FIG. 5c is a schematic representation of an exhaust gas processing system of an internal combustion engine including an exhaust gas passage device, a two-stage bootstrapping heating device, a diesel particulate filter, and a flow-back passage.
DETAILED DESCRIPTION OF THE INVENTION
(9) Referring to FIG. 1, an exhaust passage 102 is fluidly connected to an exhaust passage 104 with a smaller diameter through a cone transition 153. The exhaust passage 104 is fluidly connected to a DPF package 130 through a cone transition 152. Inside the DPF package 130, a heating device 110 is positioned upstream from a DPF 120. On the exhaust passage 102, through a probe 108, a pressure sensor 106, which communicates to a controller 140 through signal lines 142, is used to detect an exhaust gas pressure in the exhaust passage 102, and a differential pressure sensor 107, which is electrically connected to the controller 140 via signal lines 143, is used for measuring a difference between the pressure in the exhaust pipe 102 and that in the exhaust passage 104 through a probe 105 and the probe 108. The exhaust temperature in the exhaust passage 102, in between the heating device 110 and the DPF 120, and downstream from the DPF 120, are sensed, respectively, by temperature sensors 109, 111, and 116. The temperature sensor 109 communicates with the controller 140 through signal lines 144, while the temperature sensor 111 is electrically connected to the controller 140 through signal lines 146. The heating device 110 is controlled by the controller 140 via signal lines 145, and the temperature sensor 116 communicates with the controller 140 through signal lines 149. The pressure drop across the DPF 120 is detected by a differential pressure sensor 113 communicating with the controller 140 via signal lines 147, while the differential pressure sensor 113 is fluidly connected to the DPF package 130 in between the heating device 110 and the DPF 120 through a probe 112, and fluidly connected to the DPF package 130 downstream from the DPF 120 through a probe 115. The DPF package 130 is fluidly connected to a tailpipe 119 through a transition 151.
(10) In the system of FIG. 1, the exhaust passage 104 and the cone transitions 153 and 152 form a Venturi structure, thereby, the volume matric flow rate Q of an exhaust air flow passing through the heating device 110 and the DPF can be detected using a differential pressure value P.sub.2 obtained from the differential pressure sensor 107, a pressure value P.sub.106 obtained from the pressure sensor 106, and a temperature value T.sub.109 provided by the temperature sensor 109, according to the following equation:
(11)
where K.sub.Q is a constant and can be calculated using the following equation
(12)
where R is the specific gas constant; C.sub.d is the discharge coefficient; A.sub.1 is the cross section area of the exhaust passage 102, and A.sub.2 is the cross section area of the exhaust passage 104. And the mass flow rate m.sub. of the exhaust flow can be calculated using the following equation:
(13)
where K.sub.m is a constant and can be calculated using the equation:
(14)
(15) In addition to exhaust gas flow rate, sensing values obtained from the sensors 106, 107, 109, and 113 can be further used for detecting PM load in the DPF 120. With a differential pressure sensing value P.sub.1 obtained from the differential pressure sensor 113, at steady states, we have a relationship described with the following equations:
(16)
where (w.sub.p) is a function of a particulate layer thickness w.sub.p; C.sub.exh is the Sutherland's constant for exhaust gas, and C.sub.0 is a constant determined by the DPF volume V.sub.trap, the K.sub.Q value and a constant pressure drop coefficient :
(17)
K.sub.2 is a constant, and
K.sub.2=K.sub.Q{square root over (R)}(8),
wherein is a constant determined by the Sutherland's constant. The function (w.sub.p) can be a linear function:
(w.sub.p)=C.sub.1+C.sub.2w.sub.p(9),
where C.sub.1 and C.sub.2 are constants. In applications where a PM mass load m.sub.p is used for triggering regeneration processes, the PM mass load can be approximated linearly with the function (w.sub.p):
m.sub.p=C.sub.3+C.sub.4(w.sub.p)(10),
where C.sub.3 and C.sub.4 are constants.
(18) In the controller 140, the PM mass load m.sub.p can be calculated with a service routine running periodically for a timer based interrupt, as shown in FIG. 2. In the routine, a regeneration status is firstly checked. If the system is in a regeneration process, then the routine ends. Otherwise, a changing rate of the P.sub.1 value, d(P.sub.1)/dt, is compared with a threshold DP_THD. If it is higher than or equal to the threshold, i.e., the differential pressure sensor 113 is in transient, the routine ends, otherwise, the Y value and
(19)
value are calculated according to equations (6) and (5), and are assigned to the i-th element of vectors F and E, F(i) and E(i), respectively. The i value is then incremented and compared to a threshold NUM_THD. The routine ends if it is lower than the threshold, otherwise, the i value is reset to 0 and (w.sub.p) and m.sub.p values are calculated with the vectors E and F, and the routine ends thereafter. In the routine, the exclusion of transient values eliminates effects of mismatch of sensing values to the calculation of Y and
(20)
values caused by difference in sensor response time. And a variety of methods, including least squares methods, can be used in calculating the (w.sub.p) and m.sub.p values.
(21) In the system of FIG. 1, the heating device 110 is used for heating exhaust gas in regenerating the DPF 120. A variety of heating elements, including electrical heaters, fuel burners, and DOCs can be used in the heating device 110. With the help of the Venturi structure formed by the exhaust passage 104 and the cone transitions 153 and 152, a two-stage bootstrapping heating device can be used in regenerating the DPF 120 with low temperature exhaust gas. Referring to FIG. 3, in such as system, a heating device for regenerating the DPF 120 includes a temperature sensor 308, a fuel injector 300, an electrical heater 305, a front DOC 310 and a main DOC 315. The temperature sensor 308, the fuel injector 300 and the electrical heater 305 are in communication with the controller 140 through signal lines 345. And the fuel injector 300 is mounted on a connection pipe 306 fluidly connected to the exhaust passage 102 and the electrical heater 305. Upstream from the fuel injector 300, the temperature sensor 308 is positioned on the exhaust passage 102, while the front DOC 310 is positioned downstream from the electrical heater 305. A connection pipe 307 fluidly connects the front DOC 310 to the exhaust passage 104, and downstream from it, the main DOC 315 is positioned in between the temperature sensors 109 and 111.
(22) In the system of FIG. 3, after a DPF regeneration process starts, when exhaust gas temperature is low, the electrical heater 305 is energized on, and a bootstrapping dosing rate is generated through the injector 300. Through the electrical heater 305, the exhaust gas and dosing fuel are heated to a temperature higher than the light-temperature of the front DOC 310, where the dosing fuel is oxidized and the DOC and the exhaust gas are exothermically heated. The heated exhaust gas passes through the connection pipe 307 and mixes with the exhaust gas in the pipe 104. And the result exhaust gas then enters the main DOC 315 and heats it. When the bed temperature in the DOC 315 is higher than its light-off temperature, a normal dosing rate is generated through the injector 300, and the electrical heater 305 is de-energized off. The bootstrapping process then completes. In the bootstrapping process, the bootstrapping dosing rate is lower than the normal dosing rate, and dosing fuel can be fully oxidized in the front DOC 310, while after the bootstrapping process completes, not all dosing fuel can be burned in the front DOC 310, and the unburnt fuel is further oxidized in the main DOC 315 and the DPF 120. The exhaust flow rate through the electrical heater 305 is only a fraction of that in the exhaust passage 102. Therefore, electrical energy needed in heating the exhaust gas is significantly decreased.
(23) The control of the bootstrapping process can be realized with a service routine running periodically for a timer based interrupt. Referring to FIG. 4a, in such a routine, a regeneration status is examined first. The routine ends if the system is not in a regeneration process. Otherwise, a bed temperature of the main DOC 315, T.sub.DOC, is compared to a threshold LF_THD. If it is lower than the threshold, then a power value P_btstrap is set to a variable P_eh, which is used to control the power applied on the electrical heater 305, and a fuel dosing rate Dc_btstrap is set to a variable Dc controlling the fuel dosing rate through the injector 300. The routine ends thereafter. If the T.sub.DOC value is not lower than the threshold LF_THD, then the routine ends after the variable P_eh is set to zero, and the variable Dc is set to a normal dosing value of Dc_normal.
(24) In the routine of FIG. 4a, the T.sub.DOC can be calculated using a linear combination of temperature sensing values T.sub.109 and T.sub.111 obtained from the temperature sensors 109 and 111 respectively:
T.sub.DOC=W.sub.1*T.sub.109+W.sub.2*T.sub.111(11),
where W.sub.1 and W.sub.2 are constants. And the P_btstrap value can be calculated using a function of the calculated exhaust mass flow rate m.sub. and a sensing value T.sub.308 obtained from the temperature sensor 308:
P_btstrap=g(m.sub.,T.sub.308)(12),
where g( ) is a function that can be realized with a lookup table with inputs of the m.sub. and T.sub.308 values. The bootstrapping dosing rate can also be determined by the temperature T.sub.308 and the calculated exhaust mass flow rate m.sub.:
Dc_btstrap=h(m.sub.,T.sub.308),
where h( ) is also a function that can be realized with a lookup table. Both of the lookup tables for calculating the P_btstrap and Dc_btstrap values can be populated with experimental results obtained with different exhaust temperatures and flow rates.
(25) In calculating the normal dosing rate Dc_normal, a PID control can be used with a temperature sensing value T.sub.111 obtained from the temperature sensor 111 in its feedback loop. An exemplary control scheme is depicted in FIG. 4b. In this control, a target temperature value T.sub.trgt is calculated in a block 330 with a temperature sensing value T.sub.116 obtained from the temperature sensor 116 and the calculated particulate load value m.sub.p. Then a control error value is calculated by subtracting the T.sub.trgt value with the T.sub.111 value, and the T.sub.trgt value is further used in a block 335 for calculating a feed-forward control value together with the T.sub.308 value and the m.sub. value. The control error value together with the m.sub. value is used in a PID control block 340 for calculating a feedback control value, which is then added to the feed-forward control value, and the result value is passed through a limit block 345, where the normal dosing rate Dc_normal is generated after dosing rate limits being applied with the T.sub.109 value and an air-to-fuel ratio value in engine control.
(26) In the system of FIG. 1, the Venturi structure can also be used for increasing exhaust flow in regenerating the DPF 120. Referring to FIG. 5a, a connection pipe 118 is fluidly connected to the exhaust passage 104 and a control valve 117, which is also fluidly connected to the tailpipe 119 through another connection pipe 131. The control valve 117 is controlled by the controller 140 through signal lines 151, and the exhaust gas flow in the connection pipes 118 and 131 is controlled by energizing and de-energizing the control valve 117. In a DPF regeneration process, when the calculated exhaust flow rate m.sub. is low, the control valve 117 is energized open. Under a pressure in between the tailpipe 119 and the exhaust passage 104, exhaust gas flows back to the exhaust passage 104, resulting in a higher exhaust flow rate passing through the heating device 110 and the DPF 120. High exhaust flow rate brings more heat energy to the DPF, thereby PM mal-distribution is reduced, and the limit of exhaust flow rate can be lowered to allow more regeneration chances. Furthermore, higher exhaust flow rate also decreases system response time in temperature control, resulting in better control performance.
(27) High exhaust flow rate in the system of FIG. 5a also decreases resident time of exhaust flow in the heating device 110. If a DOC is used in the heating device 110, low resident time may lower HC conversion efficiency. In the system of FIG. 5a, low HC conversion efficiency can be avoided by de-energizing the control valve 117 when the exhaust flow rate m.sub. is too high. Another way to avoid low HC conversion efficiency is positioning the heating device 110 upstream from the Venturi structure. Referring to FIG. 5b, in such as system, a heating device 210 is fluidly connected to the cone transition 153 upstream from the exhaust passage 104. Upstream from the heating device 210 is a connection pipe 233, on which a temperature sensor 220 and a pressure sensing probe 204 are mounted. The connection pipe 233 is fluidly connected to an exhaust passage 232 with a smaller diameter through a cone transition 231, and another pressure sensing probe 201 is mounted on the exhaust passage 232. The pressure sensing probes 201 and 204 are fluidly connected to a differential pressure sensor 202, which is in communication with the controller 140 through signal lines 221, while a pressure sensor 203, which communicates to the controller 140 through signals lines 222, is fluidly connected to the pressure sensing probe 204. The temperature sensor 220 is electrically connected to the controller 140 through signal lines 223, and the heating device 210 is controlled by the controller 140 through signal lines 245. In this system, since high exhaust flow rate in the DPF 120 does not affect resident time in the heater 210, the control valve 117 is not required to shut off the exhaust flow-back path at high exhaust flow rates.
(28) Referring to FIG. 3 and FIG. 5b, the heating device in the system of FIG. 3 and the flow back device in the system of FIG. 5b can be used together for increasing regeneration performance with low temperature and low flow rate exhaust gas, which is normally generated by an engine operated at low torque modes, such as in idling. Referring to FIG. 5c, in such as system, a main DOC 515 is positioned in between the temperature sensors 220 and the cone transition 153, and a connection pipe 507 fluidly connects the exhaust passage 232 to a front DOC 510, which has an electrical heater 505 positioned upstream. The exhaust passage 232 is fluidly connected to an exhaust passage 502, which has a larger diameter, and the electrical heater 505 is fluidly connected to the exhaust passage 502 through a connection pipe 506, which has a fuel injector 500 mounted. Upstream from the connection pipe 506, a temperature sensor 508 is mounted on the exhaust passage 502, while the temperature sensor 508, the injector 500, and the electrical heater 505 are in communication with the controller 140 through signal lines 545. A control scheme of FIG. 4b and a control algorithm of FIG. 4a can be used for controlling the electrical heater 505 and the fuel injector 500.
(29) 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 respects.
