JPH04284115A - Filter regeneration control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce driving loss of an air pump in a filter regeneration control device for supplying secondary air by the air pump at the time of regeneration of the filter. CONSTITUTION:In a filter regeneration control device, when a filter is regenerated, a map is searched from a detected differential pressure between the intake side pressure (Po) and the discharging side pressure (Ph) of an air pump 7 and a target secondary air amount so as to find out a target air pump driving voltage (Vp), and driving of the air pump 7 is controlled by a duty ratio (D) which is obtained from a battery voltage (BH) and a driving voltage (Vp).

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a filter for collecting particulates in exhaust gas in the exhaust system of an internal combustion engine, and when regenerating the filter, secondary air is supplied from an air pump to the filter to combust the particulates. The present invention relates to a filter regeneration control device.

0002

[Prior Art] For example, since the exhaust gas of a diesel engine contains exhaust particulates, that is, particulates, internal combustion engines are known in which a filter is installed in the exhaust system of the engine to collect the particulates. There is.

[0003]The filter installed in such an internal combustion engine periodically incinerates the collected particulates.
It is necessary to perform a so-called filter regeneration process, but in this regeneration method, an electric heater is installed at the end of the filter, and an electric air pump is installed outside the filter, and while the electric heater is energized during filter regeneration, the air pump is placed upstream of the filter. An exhaust gas purification device is known in which particulates are combusted by supplying air (hereinafter referred to as secondary air to distinguish it from air mixed with fuel) to the engine.

By the way, combustion of particulates during filter regeneration as described above requires an appropriate combustion temperature and an appropriate amount of secondary air, and if the amount of oxygen supplied is small and the combustion temperature is low, particulates will be If the incineration is not sufficient and the amount of oxygen is too large and the combustion temperature is too high, there is a problem that the filter itself will melt. In other words, in an exhaust gas purification device that performs filter regeneration by supplying secondary air from an air pump, control must be performed so that only a predetermined weight flow rate value of oxygen necessary for particulate combustion is supplied, but in reality, Due to changes in atmospheric pressure and temperature,
The filter regeneration conditions are unstable as it is susceptible to changes in weight flow rate.

[0005] To solve this problem, for example, Japanese Unexamined Patent Publication No. 1986-1
No. 9909 discloses a control device in which a secondary air amount control valve is provided downstream of the air pump, and the amount of air supplied from the air pump is controlled upstream of the secondary air amount control valve. A relief valve is provided to release a portion of the secondary air, and by adjusting this relief valve, the pressure upstream of the secondary air flow rate control valve is kept constant as an absolute pressure, and the secondary air flow rate is maintained regardless of changes in atmospheric pressure or atmospheric temperature. A filter regeneration control device is disclosed in which the opening degree of a secondary air amount control valve is controlled so that the (weight flow rate) is constant.

[0006]

The above-mentioned filter regeneration control device is a conventional device of the type that supplies secondary air using an air pump, and has relatively high precision in the amount of secondary air supplied. Basically, in order to always control the pressure on the upstream side of the secondary air flow control valve at a constant level without controlling the drive of the air pump, the air discharged from the air pump is released to the outside via a relief valve, and the air pump is not driven. There is a loss. Therefore, this device has problems such as poor fuel efficiency.

SUMMARY OF THE INVENTION In view of this problem, it is an object of the present invention to provide a filter regeneration control device that can supply a predetermined weight of secondary air to the air pump without causing drive loss during filter regeneration.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention collects particulates in exhaust gas by a filter provided in the exhaust system of an engine, and also collects particulates collected by the filter. An internal combustion engine that supplies secondary air for regeneration for particulate combustion upstream of the filter using an air pump during filter regeneration to incinerate curates, and as shown in FIG. 1, the suction side pressure and discharge side pressure of the air pump are a differential pressure detection means for detecting a differential pressure between the air pump, a map means for determining in advance a characteristic relationship between the differential pressure corresponding to each driving voltage of the air pump and the amount of secondary air discharged; target air pump drive voltage calculating means for calculating a target drive voltage of the air pump using the map means from the differential pressure obtained by the means and the target secondary air amount; and the obtained target air pump drive voltage and the current battery voltage. Provided is a filter regeneration control device having a duty ratio calculating means for calculating an air pump driving duty ratio from the above, and an air pump driving means for driving the air pump using the calculated duty ratio.

[0009]

[Operation] The target drive voltage of the air pump is determined so that the amount of secondary air discharged from the air pump becomes the target amount of secondary air, and the duty of the battery voltage is controlled to achieve this target drive voltage. Drive loss is also low.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described with reference to the drawings. FIG. 2 shows the configuration of a filter regeneration control device as an embodiment of the present invention, in which pressure sensors are provided upstream and downstream of the filter to detect exhaust pressure, and the difference in output characteristics between these two sensors is The present invention is applied to an exhaust gas purification system equipped with a mechanism for compensating for.

Referring to FIG. 2, 1 is a filter that collects particulates, 2 is an exhaust pipe that guides exhaust gas from the engine body (not shown) to filter 1 when collecting particulates, and 3 is an exhaust pipe that guides exhaust gas from the engine body (not shown) to filter 1 when filter 1 is regenerated. Filter gas 1
This is a bypass pipe that allows for a more detour.

Inside each of the exhaust pipe 2 and the bypass pipe 3, a first exhaust control valve 4 and a second exhaust control valve 5 are provided to achieve the exhaust gas flow during particulate collection and filter regeneration as described above. is provided, and its operation is controlled by a control circuit (ECU) 6 so that, for example, when collecting particulates, the valve occupies the position shown in the figure, and when regenerating the filter, it occupies the position shown by the dotted line around the valve. .

Between the first exhaust control valve 4 disposed inside the exhaust pipe 2 and the filter 1, a regeneration gas (for example, secondary air) for particulate combustion is supplied to the exhaust gas of the filter 1 during filter regeneration. An electric air pump 7 is provided for supplying air to the upstream side (hereinafter referred to as the upstream side), and is powered by a battery 9 together with a filter regeneration electric heater 8 disposed at the front end of the filter 1 . In addition, 10, 11
1 is a semiconductor relay that is turned on and off by the control circuit 6; 12 is an air pump filter; and 13 is a stop valve that prevents exhaust gas from flowing back into the air pump 7.

In order to detect the state of particulate collection in the filter 1, the exhaust pipes 1 upstream and downstream of the filter 1 are
are connected to pressure introduction pipes 14 and 15, respectively, and are provided with a pressure sensor 16 (filter upstream side) and a pressure sensor 17 (filter downstream side) that detect the exhaust pressure in the exhaust pipe area.

Further, in this embodiment, rotary pressure detection line switching valves 18 and 19 driven by the control circuit 6 are provided in the middle of the pressure introduction pipes 14 and 15, respectively, as the above-mentioned sensor output characteristic difference compensation mechanism. Intervened. These pressure detection line switching valves 18 and 19 guide atmospheric pressure to each pressure sensor 16 and 17 when detecting a difference in sensor output characteristics, and the correction method thereof will be omitted since it is not directly related to the present invention. In the following description, it is assumed that the difference in output characteristics between the two pressure sensors 16 and 17 has been compensated for in advance by the above mechanism, and there is virtually no difference in output characteristics between the sensors. Note that 20 and 21 are pressure sensor filters.

On the input side of the control circuit 6, in addition to the analog signals from the pressure sensors 16 and 17, there is also a filter on the input side.
An analog signal from exhaust temperature sensors 22 and 23 provided downstream, an analog signal indicating the atmospheric temperature To detected by the atmospheric temperature sensor 24, a signal indicating the intake air amount Ga detected by an air flow meter (not shown), Various signals indicating the current operating state of the engine, such as a signal indicating the engine rotational speed Ne, are input. The control circuit 6 controls the engine based on the operating information obtained from these various sensors, and outputs signals for driving the electric air pump 7 and electric heater 8 when the filter 1 is regenerated.

The operation of the filter regeneration control device according to the present invention will be specifically explained below with reference to FIGS. 3 and 4.

The flowcharts shown in FIGS. 3 and 4 show a control circuit for determining whether or not the filter 1 currently satisfies filter regeneration conditions, and when satisfying the regeneration conditions, for executing filter regeneration processing, which is a feature of the present invention. 6, which is a time interrupt routine that is processed every predetermined time, such as 50 msec, for example.

Regarding FIG. 3, first, from step 31 to step 34, various flags F1, F2, F3, F
4 is reset to 0. These flags are set to 1 in the later steps of this routine, and the specific processing contents will be described later, but they are initialized to 0 in advance when this routine is executed for the first time. It is assumed that there is

Yes in each of steps 31 to 34
If it is determined that this is the case, the routine proceeds to step 35, where it is determined for the first time whether or not it is time to regenerate the filter. Specifically, the pressure sensors 16 and 17 detect the exhaust pressure upstream and downstream of the filter, find the difference between them, that is, the filter pressure drop ΔP, and when the pressure drop ΔP is equal to or higher than a predetermined value that indicates the need for filter regeneration, the regeneration time ( Yes).

If it is determined that it is time to regenerate the filter, the routine then proceeds to step 36, in which a drive signal is output to each of the first exhaust control valve 4 and the second exhaust control valve 5, and the position indicated by the dotted line in FIG. , and the entire amount of exhaust gas is bypassed from the filter 1. Also, at this step 36, the control valve position switching flag F4 is set to 1 at the same time. Incidentally, if No in step 35, that is, if it is not time to regenerate the filter, the filter regeneration process to be described later is not executed, so the following steps are skipped and this routine ends.

Actually, it takes a certain amount of time (2 to 3 seconds) to change the positions of the first and second exhaust control valves 4 and 5.
It takes. Therefore, in step 37 following step 36, it is determined whether or not the position change of the control valve has been completed, for example, by checking the passage of the position change time. If it is determined that the switching has been completed (Yes), the routine proceeds to step 38 and resets the control valve position switching flag F4 to 0. Conversely, if switching is in progress (
No), skip the following steps and end this routine. Incidentally, in the case of No in step 37, in the next routine, it is determined as No in step 34 (because flag F4 is set to 1), and in step 35
, 36 are skipped and a determination is made again as to whether or not the control valve position switching is complete.

In addition to the process of resetting flag F4,
In step 38, the pressure sensor 16 detects the pressure on the upstream side of the filter. That is, since the pressure upstream of the filter after the position of the first exhaust control valve 4 is switched indicates the atmospheric pressure Po at that time until the air pump 7 is driven, by detecting the pressure upstream of the filter at this time, ,
The suction side pressure of the air pump 7 which is equal to this is determined. Additionally, in step 38, the atmospheric temperature sensor 24 detects the atmospheric temperature To at that time.

Next, in step 39, a process of outputting a drive signal to the semiconductor relay 11 is performed to start energizing the electric heater 8, and the heater energization flag F3 is set to 1. This process of energizing the electric heater 8 is performed for a predetermined period of time (for example, 3 minutes). Therefore, in step 40 following step 39, the elapsed time from the start of energization is checked, and the predetermined period of time is determined. It is determined whether or not time has elapsed, that is, whether it is time to end the energization. Then, if it is determined that it is time to end the energization at step 40 (Yes)
, the heater energization flag F3 is reset to 0 in step 41, and conversely, if the heater energization continues (N
o), step 41 will be skipped. In addition, if step 41 is skipped, after this routine ends, a negative determination will be made in step 33 of the next routine. In this case, steps 35 to 38 will be skipped and the heater energization process will continue in step 39. Then, in step 40, the energization end timing is determined again.

In step 42 following FIG. 3, it is again determined whether the flag F2 has been reset to 0, similarly to the previous step 32. This flag is set when the air pump is driven, which will be described later.Here, the next step 43 will be explained assuming that the determination is Yes.

In step 43, in order to determine the discharge side pressure Ph of the air pump 7, a process is executed in which the air pump 7 is temporarily driven as a model under predetermined standard operating conditions. That is, specifically, for example, filter pressure loss Δ
P is in a standard state (a state in which a predetermined amount of particulates is collected), and the atmospheric pressure and atmospheric temperature are each standard values Ps
td, Tstd (e.g. 760mmHg, 2
93°K) and the battery voltage BH is at the standard value, the standard drive duty ratio D is such that the air pump 7 achieves the air supply of the target secondary air amount Vstd.
The air pump 7 is driven with std. Note that this drive duty ratio Dstd is determined in advance through experiments or the like. Further, in this step 43, in addition to the air pump model drive process described above, a process of setting the air pump model drive flag F1 to 1 is performed.

By the way, even if the driving of the air pump 7 is started with the standard duty ratio Dstd as described above,
The discharge of secondary air from the air pump does not become stable immediately, and it usually takes 2 to 3 minutes after the power is turned on to stabilize the discharge.
It takes seconds. Therefore, in step 44 following step 43, it is determined whether or not the amount of secondary air discharged from the air pump 7 has stabilized, for example, by observing the elapsed time after energization, and if it is determined that it has stabilized (Yes), The routine proceeds to step 45, where the air pump model drive flag F1 is set to 0.
Execute the process to reset. Also, conversely, this step 4
If the determination in step 4 is No, it is determined that the air discharge from the air pump 7 is not yet stable, so the following steps are skipped and the routine proceeds to the next routine. In the next routine, since the flag F1 was set to 1 in the previous step 43, the flag F1 is set to 1 in step 31.
If the result is No, steps 39 to 41 or step 3
After executing the processes 9 and 40 (steps 32 to 38 are skipped), a Yes determination is made in step 42 (F2 = 0 still here), and the air pump 7 is continued in step 43.
The model continues to be driven, and the determination as to whether or not the secondary air discharge is stabilized is again repeated in step 44 (the same applies hereinafter).

When the air discharge from the air pump 7 is stabilized and the flag F1 is reset in step 45, the routine then proceeds to step 46, where the pressure sensor 16 is reset.
The air pump discharge side pressure Ph is detected by . Then, in the following step 47, the air pump suction side pressure (atmospheric pressure) Po obtained in the previous step 38,
Due to this air pump discharge side pressure Ph, the differential pressure P=Ph
−Po is determined, and the standard target secondary air amount Vstd mentioned above is determined by the actual atmospheric pressure P determined in the previous step 38.
o, actual target secondary air volume Vo corrected by atmospheric temperature To = Vstd×(Pstd/Po)・(To/Ts
td), the air pump 7 as shown in FIG.
Differential pressure P (= Ph − Po ) corresponding to each drive voltage V of
Using a map showing the relationship between and the discharge air flow rate, the differential pressure P
A target drive voltage Vp (for example, 20V in FIG. 5) that achieves the target secondary air amount Vo in the air pump 7 driven by the air pump 7 is calculated. Note that the map used for this calculation has been determined experimentally in advance for the air pump 7.

Once the target driving voltage Vp of the air pump 7 has been determined in the above manner, the voltage BH of the battery 9 is read in step 48, and both voltages Vp and BH are
From, air pump drive duty ratio D (= 100 x V
p/BH), that is, the ON time % of the semiconductor relay 10 is calculated. In the subsequent step 49, the air pump 7 is started to be driven by the calculated duty ratio D, and the air pump drive flag F2 is set to 1.

By the way, according to this embodiment, the calculation of the duty ratio D as described above is executed at predetermined time intervals such as 100 msec, and the discharge pressure P of the air pump 7 is
It is updated sequentially according to changes in h and battery voltage BH. Therefore, in step 50 following the air pump driving process in step 49, the air pump 7 with the duty ratio D is
It is determined whether or not the predetermined time has elapsed by looking at the elapsed time from the start of driving. And Yes in this step 50
That is, when it is determined that it is time to calculate the next duty ratio, the routine proceeds to step 51, resets the air pump drive flag F2 based on the duty ratio D to 0, returns to step 46 again, calculates the air pump discharge pressure Ph, and similarly calculates a new value. Execute processing to obtain the duty ratio D.

On the other hand, if the result in step 50 is No, that is, it is not determined that it is time for a new duty ratio calculation yet, the routine proceeds to step 52. In addition, when waiting for the upcoming duty ratio calculation time like this (flag F2 =
1), after executing the process of the subsequent step 52, the process proceeds to the next routine, where it is determined No in step 32, and after further executing the process of steps 39 to 41 or steps 39 and 40, the result is No in step 42. Therefore, steps 43 to 48 of the air pump model drive process and duty ratio calculation process are skipped, and the air pump drive process continues at step 49.

Next, in step 52, the elapsed time from the start of driving the air pump 7 is checked to determine whether a predetermined air pump driving time (for example, 20 minutes) required for filter regeneration has elapsed. If it is determined in step 52 that the filter regeneration is complete, the routine proceeds to step 5.
Step 3 stops the output of the drive signal from the air pump 7 to the semiconductor relay 10, resets the air pump drive flag F2 to 0, and ends this routine. If the result in step 52 is No, that is, the filter regeneration has not yet been completed, step 53 is skipped (the state of F2 = 1 is continued), this routine is ended, and the result is No in step 42 of the next routine. After the determination, the air pump driving process continues.

Although one embodiment of the present invention has been described above, taking as an example an exhaust purification system equipped with a pressure sensor output characteristic correction mechanism, the present invention is not limited to this example of application; It is also applicable to a normal exhaust purification mechanism that does not include a detection line switching valve. In addition, in the above flowchart, the suction side pressure of the air pump is substituted with the value detected by the pressure sensor on the upstream side of the filter at the start of filter regeneration, but in order to increase the reliability of the detected pressure value, an atmospheric pressure sensor is installed at the suction port of the air pump. It is also possible to provide direct detection.

[0034]

As explained above, according to this embodiment, the amount of secondary air discharged from the air pump 7 itself is controlled by controlling the air pump drive duty ratio D, so that the air pump does not need to be operated as in the conventional device. There is no need to release part of the air to the outside, and the drive loss of the air pump is reduced. Further, since the air pump drive duty ratio in the present invention changes depending on the battery voltage at that time, the amount of secondary air discharged by the air pump is maintained at the target value even if the battery voltage changes. In addition, in connection with this, even if there is a change in the differential pressure between the suction side pressure and the discharge side pressure of the air pump, the air pump drive voltage is changed in response to this change, so that the target amount of secondary air is always supplied. Therefore, stable filter regeneration processing can always be performed regardless of changes in filter pressure loss value as filter regeneration progresses (in the past, the secondary air volume would change as the pressure loss value changed, resulting in poor filter regeneration). .

[Brief explanation of the drawing]

FIG. 1 is a diagram corresponding to claims of the present invention.

FIG. 2 is a schematic configuration diagram of a filter regeneration control device as an embodiment of the present invention.

FIG. 3 is a diagram showing the first half of a flowchart explaining the operation of the control circuit in FIG. 2;

FIG. 4 is a diagram showing the latter half of the flowchart in FIG. 3;

FIG. 5 is a map diagram showing the relationship between the air pump differential pressure and the secondary air amount under each drive voltage, and is used when determining the target drive voltage of the air pump in the present invention.

[Explanation of symbols]

1...filter 6...Control circuit 7...Air pump 9...Battery 10...Semiconductor relay 16, 17...Pressure sensor

Claims (1)

[Claims] Claim 1: A filter installed in the exhaust system of an engine collects particulates in the exhaust gas, and during filter regeneration, in which the particulates collected by the filter are incinerated, an air pump is used to collect particulates upstream of the filter. In an internal combustion engine that supplies secondary air for regeneration for curated combustion, a differential pressure detection means for detecting a differential pressure between a suction side pressure and a discharge side pressure of the air pump; A map means is obtained in advance to show the characteristic relationship between the differential pressure and the amount of secondary air discharged, and the map means is used from the differential pressure found by the differential pressure detection means and the target amount of secondary air. a target air pump drive voltage calculation means for calculating a target drive voltage of the air pump; a duty ratio calculation means for calculating an air pump drive duty ratio from the obtained target air pump drive voltage and the current battery voltage; 1. A filter regeneration control device comprising: an air pump driving means.