Regeneration device of exhaust gas purification filter and filter regeneration method

[0002] The present invention relates to a regeneration device, and more particularly, to a regeneration device of an exhaust gas purification filter and a filter regeneration method.

[0003] The number of automobiles has been increasing drastically. The amount of gas discharged from the internal combustion engines has also increased drastically in proportion to the increase in the number of automobiles. The various substances included in the exhaust gas of a diesel engine have caused pollution, which has a severe impact on the world environment. Further, there have been recent reports on research results stating that fine particulates included in the exhaust gas cause allergic disorders and a decrease in the number of sperms. Accordingly, the removal of the particulates from the exhaust gas is a problem that must be immediately coped with by mankind.

[0004] Under such circumstances, various types of exhaust gas purification apparatuses have been proposed. An exhaust gas purification apparatus includes a plurality of filters that eliminate particulates discharged from internal combustion engines, such as diesel engines. When a filter is used for a long time, particulates are deposited in the filter. The deposited filter increases the load on the engine. Thus, the particulates must be eliminated.

[0005] Presently, when the particulates on a filter approach a maximum collection amount, a switch valve switches the filter through which exhaust gas flows. The filter through which the exhaust gas no longer flows is heated by an electric heater until it reaches a temperature at which the particulates are ignited. The filer is regenerated by burning and removing the particulates.

[0006] However, in the conventional purification apparatus, the electric heater heats the filter even if the initial temperature of the filter that is to be regenerated is lower than the temperature of the engine exhaust gas. This prolongs the filter regeneration time. For example, when the diesel engine is running continuously, the filter temperature is about the same as the exhaust gas temperature. However, when the diesel engine is stopped over a long period, the filter temperature is low, and the increase rate of the filter temperature is low. Thus, much time is required for the particulates to reach the ignitable temperature. This increases the regenerating time. In addition, the prolonged regenerating time lengthens the activation time of the electric heater, increases power consumption, and lowers the durability of the electric heater.

[0007] It is an object of the present invention to provide a regeneration device of an exhaust gas purification filter and a filter regeneration method that reduces the regenerating time of a filter.

[0008] A first perspective of the present invention is a regeneration device of a filter in an exhaust gas purification apparatus of an internal combustion engine. The exhaust gas purification apparatus includes a plurality of casings arranged in a plurality of branch exhaust pipes of the internal combustion engine, a plurality of filters respectively accommodated in the casings, a plurality of heaters for heating the filters, and a plurality of switch valves arranged downstream to the casings to switch a flow route of exhaust gas. The regeneration device includes a plurality of first temperature detectors arranged in the casings to detect the temperature in each casing, and a second temperature detector for detecting the temperature of the exhaust gas. A processor is connected to the first temperature detectors and the second temperature detector. The processor compares the temperature of the exhaust gas and the temperature of at least one of the casings, opens the associated switch valve based on the comparison result, and preheats at least one of the filters with the exhaust gas. Accordingly, the heat of the exhaust gas increases the temperature of the filter from the initial temperature in a sudden manner and reduces the filter regeneration time.

[0009] A second perspective of the present invention is a method for regenerating a filter in an exhaust gas purification apparatus of an internal combustion engine. The regeneration method includes the steps of detecting the temperature of the exhaust gas, detecting the temperature of at least one of the casings, comparing the temperature of the exhaust gas and the temperature of the at least one of the casings, supplying exhaust gas to the at least one of the casings to preheat the associated filter with the heat of the exhaust gas by opening the associated switch valve when the comparison result is greater than a predetermined value, stopping the supply of exhaust gas to the at least one casing after the preheating is completed, and activating the associated heater to further heat the associated filter.

[0010] A third perspective of the present invention is a filter regeneration program executed by a computer in an exhaust gas purification apparatus. The program includes the steps of comparing the temperature of the exhaust gas and the temperature of at least one of the casings with the computer, supplying exhaust gas to the at least one of the casings to preheat the associated filter with the heat of the exhaust gas by opening the associated switch valve with the computer when the comparison result is greater than a predetermined value, stopping the supply of exhaust gas to the at least one casing with the computer after the preheating is completed, and activating the associated heater with the computer to further heat the associated filter.

[0011] A fourth perspective of the present invention is a computer-readable recording medium recording a program for regenerating a filter in an exhaust gas purification apparatus. The program includes the steps of comparing the temperature of the exhaust gas and the temperature of at least one of the casings, supplying exhaust gas to the at least one of the casings to preheat the associated filter with the heat of the exhaust gas by opening the associated switch valve when the comparison result is greater than a predetermined value, stopping the supply of exhaust gas to the at least one casing after the preheating is completed, and activating the associated heater with the computer to further heat the associated filter.

[0012] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings.

[0013] FIG. 1 is a schematic view showing a regeneration system of an exhaust gas purification apparatus according to an embodiment of the present invention;

[0014] FIG. 2 is a schematic block diagram of the exhaust gas purification apparatus;

[0015] FIG. 3 is a graph illustrating the relationship between the filter temperature and the filter heating time; and

[0016] FIG. 4 is a graph illustrating the relationship between the filter preheating time and the temperature difference.

[0017] An exhaust gas purification apparatus according to an embodiment of the present invention will now be discussed with reference to the drawings.

[0018] As shown in FIG. 1, an exhaust passage 11, which is connected to a diesel engine 10 serving as an internal combustion engine, includes two branch pipes 11a, 11b. A first exhaust gas purification device 20ais arranged in the branch pipe 11a, and a second exhaust gas purification device 20bis arranged in the branch pipe 20b. The exhaust gas purification device 20ahas a casing 21a, which accommodates a honeycomb-like first filter 23ato purify the exhaust gas. The exhaust gas purification device 20balso has a casing 21b, which accommodates a honeycomb-like second filter 23bto purify the exhaust gas.

[0019] Each filter 23a, 23bis made of a porous silicon carbide (SiC), and the sinter carries an exhaust gas purification catalyst. The filters 23a, 23bhave extremely high heat conductivity. Thus, the heat of exhaust gas is effectively conducted downstream and in the radial direction. When excessive burning occurs locally, the heat is efficiently dispersed.

[0020] A first electric heater 24afor heating the filter 23ais arranged in the casing 21anear the gas upstream side of the filter 23a. A second electric heater 24bfor heating the filter 23bis arranged in the casing 21bnear the gas upstream side of the filter 23b. The electric heaters 24a, 24bare helical resistor-heating heaters and are activated by power supplied from a battery (not shown). The shape of the electric heaters 24a, 24bis not limited to the helical form.

[0021] A first thermocouple 26ais arranged near the electric heater 24ain the casing 21a, and a second thermocouple 26bis arranged near the electric heater 24bin the casing 21b. A first electromagnetic valve 28ais arranged in the branch pipe 11adownstream to the filter 23a. A second electromagnetic valve 28bis arranged in the branch pipe 11bdownstream to the filter 23b. A pressure sensor 29ais arranged in the exhaust passage 11 upstream to the filters 23a, 23b, and a pressure sensor 29bis arranged in the exhaust passage 11 downstream to the filters 23a, 23b.

[0022] A regeneration device 100 of the exhaust gas purification filters 23a, 23bwill now be described with reference to FIG. 2.

[0023] Referring to FIG. 2, the first thermocouple 26adetects the temperature of the electric heater 24a, the exhaust gas temperature, and the temperature in the casing 21aand provides a first detection signal to a computer C. The second thermocouple 26bdetects the temperature of the electric heater 24b, the exhaust gas temperature, and the temperature in the casing 21band provides a second detection signal to the computer C.

[0024] The computer C includes a CPU 30, a ROM 31, and a RAM 32. The CPU 30 is provided with the first and second detection signals from the thermocouples 26a, 26b. The temperatures in the casings 21a, 21bcorrespond to the temperatures of the locations where the first and second thermocouples 26a, 26bare arranged. That is, the temperatures in the casings 21a, 21bcorrespond to the temperatures between the diesel engine 10 and the filters 23a, 23b. More specifically, the temperatures in the casings 21a, 21bcorrespond to the temperatures between the filters 23a, 23band the electric heaters 24a, 24b.

[0025] The ROM 31 stores a computer control program for controlling the regeneration device 100 of the exhaust gas purification filters 23a, 23b. The RAM 32 temporarily stores the data required to execute the control program, such as temperature data of the interior of the casing 21a, 21band temperature data of the exhaust gas. Further, the CPU 30 reads the control program from the ROM 31 and executes the control program.

[0026] The CPU 30 compares the temperature in the casing 21a(or 21b), which accommodates the filter that is to be regenerated, and the temperature of the exhaust gas, which is sent to the filter 23b(or 23a) used to purify the exhaust gas. The CPU 30 determines whether the comparison result is greater than or less than a predetermined value and controls the opening and closing of the electromagnetic valves 28a, 28bso that exhaust gas is sent to the first filter 23aor the second filter 23bin accordance with the comparison result. During filter regeneration, the CPU 30 provides the electric heaters 24a, 24bwith a drive signal to activate the electric heaters 24a, 24b.

[0027] The pressure sensor 29adetects a backpressure value of the exhaust gas upstream to the filter 23 and provides a detection signal to the CPU 30. The pressure sensor 29bdetects a backpressure value of the exhaust gas downstream to the filter 23 and provides a detection signal to the CPU 30. The CPU 30 calculates the pressure loss from the detection signal and detects the amount of particulates, such as soot, deposited in the filter 23. The pressure loss refers to the value obtained by subtracting the downstream side backpressure value of the filter 23 from the upstream side back pressure value. Thus, when the value of the pressure loss is high, the amount of the particulates deposited in the filter 23 is relatively large.

[0028] The RAM 32 stores a temperature increase map indicating the relationship between the temperatures of the filters 23a, 23band the filter heating time, as shown in FIG. 3. The vertical axis of the temperature increase map represents the filter temperature, and the horizontal axis represents the filter heating time of the electric heaters 24a, 24b. The temperature increase map of FIG. 3 shows a single filter temperature increase curve but actually includes a plurality of filter temperature increase curves respectively corresponding to a plurality of initial temperatures.

[0029] The RAM 32 stores a filter preheating map, which is referred to when performing preheating prior to regeneration, as shown in FIG. 4. The horizontal axis of the preheat processing map represents the temperature difference (t2−t1) between the temperatures t1 of the casings 21a, 21band the temperature t2 of the exhaust gas. The vertical axis represents the filter preheating time.

[0030] A process for activating the exhaust gas purification devices 20a, 20band regenerating the filters 23a, 23bwill now be discussed.

[0031] Among the two exhaust gas purification devices 20a, 20b, one of the devices removes the particulates included in the exhaust gas and the filter of the other device is regenerated. An example in which the first filter 23apurifies the exhaust gas while the second filter 23bis regenerated will now be discussed. In this case, the first electromagnetic valve 28ais opened, and exhaust gas is sent to the first filter 23a. That is, the exhaust gas of the diesel engine 10 first flows into cells of the first filter 23a. The exhaust gas then passes through inner walls defining the cells and is discharged from the downstream side of the first filter 23a. In this state, the particulates included in the exhaust gas do not pass through the inner walls of the first filter 23aand become trapped in the inner walls. As a result, purified exhaust gas is discharged from the downstream side of the first filter 23aand ultimately released into the atmosphere.

[0032] When the amount of the particulates deposited in the filter 23 approaches the maximum tolerable deposit amount, the regeneration of the first filter 23ais initiated, and the second filter 23bpurifies exhaust gas.

[0033] The first thermocouple 26adetects the temperature t1 in the first casing 21a, and the second thermocouple 26bdetects the temperature t2 of the exhaust gas flowing through the second casing 21b. When the temperature difference (t2−t1) is less than or equal to a predetermined value, the CPU 30 determines that the initial temperature of the first filter 23athat is to be regenerated is high enough. Based on the determination, the CPU 30 closes the first electromagnetic valve 28aand activates the first electric heater 24a. In this manner, the heat of the first electric heater 24aheats the first filter 23a. This completely burns and eliminates the particulates deposited in the filter 23.

[0034] While the first electric heater 24ais performing heating, the heating temperature of the first electric heater 24ais detected by the first thermocouple 26a. In accordance with the detection result, the heating time of the first electric heater 24ais adjusted at constant time intervals through feedback control. The heating time of the first electric heater 24a(i.e., the time during which the first electric heater 24ais supplied with power) is calculated from the temperature increase map of FIG. 3. The first electric heater 24ais supplied with power in accordance with the calculated heating time. After the heating time elapses, the supply of power to the electric heater 24 is stopped, and the regeneration of the first filter 23ais completed.

[0035] When the difference (t2−t1) between the temperature t1 in the first casing 21aand the temperature t2 of the exhaust gas flowing through the second casing 21bis greater than or equal to the predetermined value, it is determined that the initial temperature of the first filter 23a, which is to be regenerated, is low. Such a case occurs when, for example, the diesel engine 10 is stopped for a long period of time. When the engine 10 is not running and exhaust gas is not discharged from the diesel engine 10, the temperatures of the filters 23a, 23bdecrease.

[0036] When the initial temperature of the filter 23ais low, the CPU 30 performs preheating before regenerating the first filter 23a. More specifically, the CPU 30 opens the first and second electromagnetic valves 28a, 28band supplies exhaust gas to the first filter 23a, which is to be regenerated, in addition to the second filter 23b, which is to perform purification. As a result, the initial temperature of the first filter 23ais increased within a short period of time by the heat of the exhaust gas. The CPU 30 calculates the preheating time of the first filter 23a(i.e., exhaust gas supplying time) from the preheat processing map of FIG. 4 and supplies the first filter 23awith exhaust gas in accordance with the calculated time.

[0037] After the exhaust gas supplying time elapses, the CPU 30 closes the first electromagnetic valve 28aand stops the supply of exhaust gas to the first filter 23a. This completes the preheating of the first filter 23a. Then, the CPU 30 activates the first electric heater 24aand regenerates the first filter 23a. After the regeneration is completed, the CPU 30 controls the opening and closing of the electromagnetic valves 28a, 28bto switch the flow route of the exhaust gas and perform filter regeneration and exhaust gas purification.

[0038] The regeneration device 100 of the present invention has the advantages described below.

[0039] (1) When the difference between the exhaust gas temperature and the temperature of the filter 23a, 23bthat is to be regenerated is greater than the predetermined value, the electromagnetic valves 28a, 28bare opened and exhaust gas flows into the casings 21a, 21b. The heat of the exhaust gas heats the filters 23a, 23bto a predetermined temperature. Afterward, the filters 23a, 23bare further heated by the electric heaters 24a, 24b. As a result, the initial temperature of the filter that is to be regenerated increases within a short period of time. This reduces the filter regeneration time.

[0040] (2) When the initial temperature of the filters 23a, 23bare low, the exhaust gas heat is used to preheat the filters. This shortens the time during which the electric heaters 24a, 24bare supplied with power, prevents the power consumed by the electric heaters 24a, 24bfrom increasing, and prevents the durability of the electric heaters 24a, 24bfrom decreasing. In addition, the energy efficiency for regenerating the filters 23a, 23bis increased. This decreases the load on the automobile battery and suppresses battery drain.

[0041] (3) The thermocouples 26a, 26bare arranged in the flow route of the exhaust gas between the diesel engine 10 and the filters 23a, 23b. Thus, in comparison to when a thermocouple is arranged at a downstream side of the filters 23a, 23b, the time during which the filter 23a, 23bthat is to be regenerated reaches the predetermined temperature from the initial temperature is accurately predicted. Accordingly, the preheating of the filters 23a, 23bis guaranteed. In addition, the thermocouples 26a, 26bare arranged in the vicinity of the upstream side of the filters 23a, 23b. Thus, the exhaust gas temperature just before the exhaust gas is supplied to the filters 23a, 23bis detected. Accordingly, the time during which the filters 23a, 23breach the predetermined temperature from the initial temperature is further accurately predicted.

[0042] (4) The arrangement of the thermocouples 26a, 26bin the vicinity of the electric heaters enables temperature detection of the electric heaters 24a, 24b. This decreases the number of the thermocouples 26a, 26b, simplifies the structures of the exhaust gas purification devices 20a, 20b, and decreases manufacturing costs.

[0043] (5) When the exhaust gas heats the filters 23a, 23bfrom the initial temperature to the substantially maximum temperature (i.e., particulate ignition temperature), the preheating is completed, the electromagnetic valves 28a, 28bare closed, and the electric heaters are activated. Thus, the filters 23a, 23bare efficiently heated within a short period of time.

[0044] It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.

[0045] (a) When the initial temperature of the filter 23a, 23bthat is to be regenerated is low, the heat of the exhaust gas and the heat of the electric heaters 24a, 24bmay be used to increase the temperature from the initial temperature. This increases the temperature of the filters 23a, 23bfrom the initial temperature within a shorter time.

[0046] (b) When the initial temperature of the filter 23ais low, the CPU 30 may open the first electromagnetic valve 28a, supply the first filter 23athat is to be regenerated with exhaust gas, and preheat only the first filter 23a.

[0047] (c) Instead of comparing the temperatures in the casings 21a, 21bwith the exhaust gas temperature and determining whether or not to perform preheating based on the comparison result, thermocouples may be in direct contact with the filters 23a, 23bto detect the temperatures of the filters 23a, 23b.

[0048] (d) The present invention may be applied to an exhaust gas purification system having three or more casings, each accommodating a filter.

[0049] (e) Instead of detecting the exhaust gas temperature and the temperatures of the electric heaters 24a, 24bwith the thermocouples 26a, 26b, another thermocouple may be arranged in the exhaust passage 11 near a manifold of the diesel engine 10 to detect the temperature of the exhaust gas.

[0050] (f) The filter preheating map of FIG. 4 and the temperature increase map of FIG. 3 may be stored in the ROM 31 instead of the RAM 32.

[0051] (g) In addition to the ROM 31, which is a semiconductor memory, the control program of the exhaust gas purification filter regeneration device 100 may be stored in a recording medium, such as a floppy disk or a hard disk. The control program may also be stored in a portable type recording medium, such as a CD-ROM or a DVD.

[0052] (h) The computer C may be connected to a computer network, such a LAN, a WAN like the Internet, or a wireless communication network, and the control program may be stored in the RAM 32 of the computer C via the WAN or the computer network. Further, the control program stored in the ROM 31 may be transferred to the recording medium of another computer via the computer network.

[0053] The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.