JPH06173663A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent an EHC melting loss, and lengthen battery service life and the like by setting supply electric power to electric heating type catalyst (EHC) in the necessary minimum electric power. CONSTITUTION:When an engine is started, an EHC temperature is detected (S2), and when it is low, current supply is started (S4) in the maximum electric power. Afterwards, an exhaust gas flow rate Qg and an exhaust gas temperature Tg are found from the engine revolution number Ne and a load Tp, and an EHC reference temperature raising speed deltaTr is determined (S7, 8). Supply electric power W is controlled in W=W-(deltaT-deltaTr)XGAIN so that a difference between an actual temperature raising speed deltaT and the reference temperature raising speed deltaTr becomes a prescribed value (S12).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having an electrically heated catalyst (hereinafter referred to as EHC) in an exhaust passage.

[0002]

2. Description of the Related Art When an internal combustion engine is cold, a large amount of HC is produced by increasing the amount of fuel supplied in order to improve drivability because of poor atomization of fuel and by the extinction effect due to the low wall temperature.
Is discharged from the engine. On the other hand, since the temperature of the exhaust gas purification catalyst provided in the exhaust passage is low and the catalyst activity is insufficient, these HCs are released to the atmosphere without being substantially purified.

For this reason, it is required to raise the temperature of the catalyst more quickly to reduce the cold emission.
One solution is EHC in which the catalyst carrier is made of metal and is heated by supplying electricity to the catalyst carrier to rapidly raise the temperature (see Japanese Utility Model Laid-Open No. 63-67609).

[0004]

However, since a metal is used as a catalyst carrier, it is inferior in heat resistance as compared with a ceramic carrier, and when power is supplied more than necessary, it rapidly reaches a high temperature. There is a risk that it will be melted down. Moreover, when electricity is supplied to the EHC until the EHC temperature reaches the target temperature at the time of starting and after the starting, conventionally, the power supply is uniform and about 5 kW of electric power is supplied until the temperature reaches 400 ° C. at which the EHC is fully activated. Currently, it is supplied for about 30 seconds. Discharging such a large amount of power at one time is
The deterioration of the battery is promoted, and it takes a long time to recharge the battery.

The present invention has been made in view of the above circumstances, and the EHC
Power supply to the EHC is prevented, and the EHC is prevented from being melted and damaged, and the power supply to the EHC is set to the required minimum power, thereby minimizing the power consumption and extending the life of the battery. The purpose is to shorten the charging time.

[0006]

Therefore, according to the present invention, as shown in FIG. 1, the exhaust gas purification of an internal combustion engine in which the catalyst carrier is made of metal and EHC that can be heated by energizing it is installed in the exhaust passage. In the apparatus, an operating state detecting means for detecting an engine operating state, an exhaust temperature detecting means for detecting an exhaust gas temperature, a catalyst temperature detecting means for detecting a temperature of the electrically heated catalyst, and an electricity supply to the electrically heated catalyst. An electric power variable means for controlling the electric power supplied at the time based on the engine operating state, the exhaust temperature, the catalyst temperature and the rate of increase of the catalyst temperature per unit time,
The configuration is provided.

Further, the electric power varying means maximizes the electric power supplied when the catalyst temperature is judged to be equal to or lower than a predetermined value at the time of starting, and after starting the electric power is based on the rate of increase of the catalyst temperature per unit time. It may be configured to be controlled by. Also,
The rate of increase of the catalyst temperature in the electric power varying means may be controlled by comparison with a reference rate of increase determined based on the exhaust flow rate and the difference between the catalyst temperature and the exhaust temperature.

Further, as shown in FIG. 2, the catalyst carrier is made of metal, and an EHC which can be heated by energizing the catalyst carrier is installed in the exhaust passage and a secondary air supply means for supplying secondary air to the exhaust passage. In the exhaust gas purification apparatus for an internal combustion engine, the operating state detecting means for detecting the engine operating state, the exhaust temperature detecting means for detecting the exhaust temperature, the catalyst temperature detecting means for detecting the temperature of the electrically heated catalyst, The amount of secondary air supplied by the secondary air supply means is set to the engine operating state, exhaust temperature,
A secondary air supply amount control means for controlling based on the catalyst temperature and the rate of increase of the catalyst temperature per unit time may be provided.

[0009]

[Function] The catalytic activity is sufficiently high at and after starting.
EHC power required up to is for restarting after warm-up
(For example, in FIG. 3, the EHC temperature T₃When starting from), E
In case of cold start because HC temperature and exhaust temperature are high
(For example, in FIG. 3, the EHC temperature T ₁When starting from)
Small, yet the EHC heats up fast enough.

Therefore, assuming that the temperature of EHC is Tc, the EHC supply electric power at the time of starting is controlled so that the temperature rising rate dTc / dt at the time of starting (t = 0) becomes a target value.
It is possible to reduce the power consumption of the battery by minimizing the EHC supply power. The EHC is heated by energizing the heater, and the heat balance of the EHC is as shown in FIG. That is, when the amount of heat W is given to the EHC from the heater, Q1 is used to raise the temperature of the EHC,
The remaining Q2 is used for raising the temperature of the exhaust gas.

W = Q1 + Q2 ... Here, the temperature rising rate dTc / dt of EHC is proportional to Q1. Q1 = Wc · dTc / dt, where Wc is a proportional constant and Q2 is almost determined by the gas amount and the temperature difference between EHC and exhaust. Here, the exhaust volume, exhaust temperature, and EH
When the C temperature is decided, the EHC temperature rising temperature is decided. That is, the exhaust gas flow rate M, the specific heat of the exhaust gas Cg, the exhaust gas temperature before supplying electric power from the heater to the EHC is Tgi, and the exhaust temperature after supplying electric power from the heater to the EHC is Tgo, EHC
Let h be the heat transfer coefficient between the exhaust gas and the exhaust gas, and Sc be the total surface area of the catalyst for the EHC exhaust gas.

Q2 = (Tgo−Tgi) · Cg · M / 2 = [Tc− (Tgo + Tgi) / 2] · h · Sc Therefore, the electric power supplied to the EHC at the time of energization is controlled from the equation. It becomes possible. Also, when starting, EHC
When it is determined that the temperature Tc is equal to or lower than the predetermined value, first, the supply power is maximized, and after the start, the supply power is controlled based on the rate of increase in the catalyst temperature per unit time. It is possible to shorten the time required.

The operating condition, exhaust temperature Tg, and EH
According to the C temperature Tc, the EHC reference temperature rising rate δTr which is the reference at that time is set. Then, the actual heating rate d
Tc / dt is controlled by comparison with the EHC reference temperature rising rate δTr. In addition, operating conditions, exhaust temperature Tg, EHC
The secondary air supply amount is controlled based on the temperature Tc and the catalyst temperature increase rate.

From the above, when there is a rapid temperature rise due to unburned HC due to misfire, energization is stopped to prevent burnout. In addition, the amount of power consumption is minimized to extend the life of the battery and shorten the charging time.

[0015]

EXAMPLES Examples of the present invention will be described below. FIG. 5 shows the system configuration of the first embodiment of the present invention. An EHC 3 is installed in the exhaust passage 2 of the internal combustion engine 1. EHC
Reference numeral 3 denotes a catalyst which is carried on a metal carrier (metal carrier), and the metal carrier is housed in a converter container having an exhaust inlet and an outlet, and a pair of external electrodes for energizing the metal carrier. Electrodes 4a and 4b are provided so as to project.
In the metal carrier, for example, stainless corrugated plates and flat plates are alternately laminated to form a large number of passages in the exhaust flow direction.

One electrode 4a of the EHC 3 is connected to the positive terminal of the battery 6 by the harness 5, and the other electrode 4b is connected to the negative terminal of the battery 6 through the EHC power varying device 8 by the harness 7. The EHC power variable device 8 is
A switching element and a variable resistor are connected in series, and by turning on / off the switching element in response to a signal from the control unit 9, energization to the EHC 3 is controlled and the duty ratio of the pulse is changed (PMW).
Method) to control the electric power supplied to the EHC 3 during energization.

The control unit 9 has a built-in microcomputer, and according to a flow chart described later,
The EHC power variable device 8 is controlled. Because of this control, E
EHC temperature sensor 10 is installed in HC3, and EHC temperature T
c (specifically, EHC outlet exhaust temperature) is input to the control unit 9. Further, the control unit 9 is used for various controls (fuel injection control, ignition control, etc.) of the internal combustion engine 1, and from various sensors attached to the internal combustion engine 1, the engine cooling water temperature Tw, the engine speed Ne, the load. Tp
Information such as is entered.

FIG. 6 is a flowchart of the EHC energization control according to the first embodiment, which is executed, for example, every predetermined time τ. In step 1 (denoted as S1 in the drawing; the same applies hereinafter), it is determined whether the internal combustion engine 1 has been started. If it is determined that the internal combustion engine 1 has been started, the process proceeds to step 2 and subsequent steps. In step 2, the EHC temperature sensor 10 detects the EHC temperature Tc.

In step 3, the EHC temperature Tc is, for example, the activation temperature (400 ° C.) of the catalyst supported on the metal carrier.
It is determined whether it is higher or lower than a predetermined value T1 such as, and if it is determined to be lower, the process proceeds to step 4. In step 4,
Since it is necessary to quickly raise the temperature of the EHC 3 to activate it, energization is started with the maximum power W _MAX that can be supplied so that the EHC temperature Tc rises as quickly as possible. This is done via the EHC power variable device 8.

In step 5, the engine speed Ne and the load T
p, and the EHC temperature Tc is detected again. In step 6, the EHC temperature Tc is compared again with the predetermined value T1, and when it is determined that Tc> T1, it is determined that the EHC3 is activated, and the process proceeds to step 13 to energize the EHC3. Stop.

If it is determined that the EHC temperature Tc is less than or equal to the predetermined value T1, the process proceeds to step 7, and referring to a predetermined map (FIGS. 7 and 8), the engine speed Ne and the load Tp are compared. Exhaust flow rate Q of exhaust gas discharged from the engine 1 from
g and exhaust temperature Tg are obtained. Here, the exhaust gas flow rate Qg increases as the engine speed Ne and the load Tp increase, and the exhaust gas temperature Tg once increases from the low temperature to the high temperature as the engine speed Ne and the load Tp increase, and then slightly again. It decreases to medium temperature. The exhaust temperature Tg is basically high load
Although the higher the engine speed, the higher the engine speed, but the output air-fuel ratio range defined for each engine or vehicle type is set to a rich air-fuel ratio to suppress the rise in exhaust gas temperature.

Then, at step 8, the temperature difference ΔT (= Tc-T) between the exhaust gas flow rate Qg obtained at step 7 and the EHC temperature Tc and the exhaust gas temperature Tg obtained at step 7 above.
Then, the EHC reference temperature increase rate δTr is determined by referring to (g) and also a predetermined map (FIG. 9). Where E
The HC reference temperature increase rate δTr decreases as the exhaust gas flow rate Qg increases, and also decreases as the temperature difference Δ increases. Incidentally, E
As shown in the above expression, the HC reference temperature increase rate δTr is smaller because the amount of heat absorbed by the exhaust increases as the exhaust gas flow rate Qg increases and the temperature difference ΔT increases under high load and high rotation. That is, under the condition that heat can be expected to flow from the exhaust gas to the EHC 3 and the heat radiation to the exhaust gas is increased, even if the temperature rising speed is increased, it is useless, so that it is suppressed.

In step 9, the actual heating rate δT is calculated. Here, a value obtained by dividing the difference between the EHC temperature Tc and the EHC temperature Tc _OLD when the routine was last executed by the sampling time τ is set as an actual temperature rising rate δT (δT = (Tc-Tc _OLD ) / τ). In step 10,
The actual temperature rising rate δT obtained in step 9 and step 8
The difference from the EHC reference temperature rising rate δTr determined in
If the difference is larger than the predetermined value D1, that is, if the actual temperature rising rate δT is different from the EHC reference temperature rising rate δTr, the routine proceeds to step 13, where EHC
Stop energizing 3.

When it is determined that the difference is less than or equal to the predetermined value D1, the routine proceeds to step 11, where the actual temperature increase rate δT and the EHC reference temperature increase rate δTr are compared. When it is determined that the actual temperature increase rate δT is lower than the EHC reference temperature increase rate δTr, the process returns to step 5, and the EHC 3 is continuously energized with the maximum power W _MAX that can be supplied. On the other hand, the actual heating rate δT is equal to or higher than the EHC reference heating rate δTr (δ
If it is determined that T ≧ δTr), it is determined that the temperature has been sufficiently raised, and the process proceeds to step 12 to reduce the electric power W according to the following equation.

W = W- (δT-δTr) × GAIN where GAIN is a predetermined value. The steps 2 and 5 correspond to the operating state detecting means, the exhaust temperature detecting means and the catalyst temperature detecting means, and the steps 4 and 12
The portion of corresponds to the third power varying means.

Further, in the present embodiment, the exhaust temperature Tg
Is obtained from the engine speed Ne and the load Tp by using a map. As another embodiment, before the temperature is raised by the EHC 3 in the exhaust passage 2 on the upstream side and the exhaust passage 2 on the downstream side of the EHC 3, respectively. Of the exhaust gas temperature Tgi and the exhaust gas temperature Tgo after the temperature is raised by the EHC3. It goes without saying that the exhaust temperature Tg may be obtained by obtaining In this case, the actual exhaust temperatures Tgi and Tgo are detected, and the accuracy of the exhaust temperature Tg is improved as compared with the above embodiment.

That is, as described above, according to the first embodiment, the temperature of the EHC 3 is quickly raised after the start-up to activate the EHC 3, and thereafter the exhaust flow rate Qg,
Based on the exhaust gas temperature Tg and the EHC temperature Tc, the EHC supply power is controlled to the minimum so that the temperature rising rate dTc / dt becomes the target value, so that the EHC 3 can be prevented from burning.
It is possible to reduce the power consumption of the battery. Naturally, the HC emission amount is also optimally controlled without exceeding the allowable value.

Further, in this case, the activation of the catalyst is achieved at an early stage, and it is possible to prevent the emission deterioration due to the increase of the HC emission amount. Next, a second embodiment according to the present invention will be described. FIG. 10 shows the system configuration of the second embodiment of the present invention. The same components as those of the system configuration of the first embodiment shown in FIG.

In the second embodiment, the secondary air supply means 20 for introducing the secondary air into the exhaust passage 2 on the upstream side of the EHC 3 is provided. The secondary air supply means 20 includes an air supply source such as an electric air pump 21 and a secondary air supply pipe 22 connected to the electric air pump 21 and connected to the exhaust passage 2 on the upstream side of the EHC 3 for communication. The secondary air supply amount Qs is configured by controlling the discharge flow rate from the electric air pump 21.
Can be controlled.

The control unit 9 controls the EHC power variable device 8 and also controls the supply / interruption of the secondary air supply means 20 according to a flow chart described later. Next, referring to FIG. 11, the EHC according to the second embodiment
The energization control and the supply control of the secondary air supply means 20 will be described. However, steps having the same operations as those in the flowchart shown in FIG.

In step 3, the EHC temperature Tc is, for example, the activation temperature (400 ° C.) of the catalyst supported on the metal carrier.
It is determined whether it is higher or lower than a predetermined value T1 such as, and if it is determined to be lower, the process proceeds to step 21. In step 21,
For example, EHC determined by the starting coolant temperature TW ₀
Energization is started with electric power W ₀ .

Then, in step 22, EHC3 is swiftly released.
It is necessary to activate by raising the temperature of
The supply of the secondary air flow rate Qs is started at the maximum secondary air flow rate Q _MAX so as to increase the C temperature Tc as quickly as possible. This is performed via the discharge flow rate control of the electric air pump 21. In step 23, the EHC temperature Tc is compared again with the predetermined value T1, and when it is judged that Tc> T1, it is judged that the EHC3 is activated,
In step 26, the power supply to the EHC 3 is stopped and the operation of the secondary air supply means 20 is stopped.

In step 24, the difference between the actual temperature increase rate δT obtained in step 9 and the EHC reference temperature increase rate δTr determined in step 8 is compared with a predetermined value D1, and the difference is the predetermined value D1. If it is larger, that is, the actual heating rate δT
Is different from the EHC reference temperature rising rate δTr, the routine proceeds to step 26, where the energization to the EHC 3 is stopped and the operation of the secondary air supply means 20 is stopped.

When it is determined that the difference is less than or equal to the predetermined value D1, the routine proceeds to step 11, where the actual temperature increase rate δT and the EHC reference temperature increase rate δTr are compared. When it is determined that the actual temperature rising rate δT is lower than the EHC reference temperature rising rate δTr, the procedure returns to step 5 and the maximum supplyable amount is 2
Continue supplying secondary air at the secondary air flow rate Q _MAX .

On the other hand, in step 11, the actual heating rate δT is equal to or higher than the EHC reference heating rate δTr (δT ≧ δ
If it is determined to be Tr), it is determined that the temperature has been sufficiently raised, and the routine proceeds to step 25, where the secondary air flow rate Qs is reduced according to the following equation. Qs = Qs− (δT−δTr) × GAIN where GAIN is a predetermined value.

The steps 2 and 5 correspond to the operating state detecting means, the exhaust temperature detecting means and the catalyst temperature detecting means, and the steps 22 and 25 correspond to the secondary air supply amount controlling means. That is, as described above, according to the second embodiment, the EHC is the earliest after the start.
3 to activate the EHC3, and thereafter, based on the exhaust gas flow rate Qg, the exhaust gas temperature Tg, and the EHC temperature Tc, the secondary air supply amount is adjusted so that the temperature rising rate dTc / dt becomes a target value. Is controlled to the minimum, so EHC3
It is possible to prevent the burnout of the battery and reduce the power consumption of the battery.

[0037]

As described above, according to the present invention, the temperature of the EHC is raised in order to quickly activate the EHC after the engine is started, and thereafter the exhaust flow rate Qg and the exhaust temperature Tg are increased.
And the temperature rising rate dTc / dt based on the EHC temperature Tc
Since the EHC supply power is controlled to the minimum and the secondary air supply amount is controlled to the minimum so that
It is possible to prevent the EHC from being burnt out, and to reduce the power consumption of the battery.
It is also possible to extend the battery life by optimizing and saving C power supply.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention.

FIG. 2 is a functional block diagram showing the configuration of the present invention.

FIG. 3 is a diagram for explaining the operation

FIG. 4 is a diagram for explaining the operation.

FIG. 5 is a system configuration diagram showing a first embodiment of the present invention.

FIG. 6 is a flowchart for explaining the operation of the above embodiment.

FIG. 7 is a characteristic diagram relating to an exhaust flow rate Qg.

FIG. 8 is a characteristic diagram related to exhaust temperature Tg.

FIG. 9 is a characteristic diagram relating to EHC reference temperature rising rate δTr.

FIG. 10 is a system configuration diagram showing a second embodiment of the present invention.

FIG. 11 is a flowchart for explaining the operation of the above embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust passage 3 Electric heating type catalyst (EHC) 8 EHC electric power variable device 9 Control unit 10 EHC temperature sensor 20 Secondary air supply means

Claims (4)

[Claims] 1. An operating state detecting means for detecting an engine operating state in an exhaust gas purifying apparatus for an internal combustion engine, wherein a catalyst carrier is made of metal and an electrically heated catalyst which can be heated by energizing the catalyst carrier is installed in an exhaust passage, Exhaust temperature detecting means for detecting the exhaust temperature, catalyst temperature detecting means for detecting the temperature of the electrically heated catalyst, and power supplied to the electrically heated catalyst when the power is supplied to the engine operating state, exhaust temperature, catalyst temperature and An exhaust gas purifying apparatus for an internal combustion engine, comprising: an electric power varying means for controlling based on an increase rate of the catalyst temperature per unit time. 2. The power varying means maximizes the supplied power when it is determined that the catalyst temperature is equal to or lower than a predetermined value at the time of starting, and after the starting, the supplied power is based on the rate of increase of the catalyst temperature per unit time. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is configured to be controlled by the following. 3. The increase rate of the catalyst temperature is controlled by comparison with a reference increase rate that is determined based on the exhaust gas flow rate and the difference between the catalyst temperature and the exhaust temperature. Exhaust gas purification device for internal combustion engine. 4. An internal combustion engine in which a catalyst carrier is made of metal, an electrically heated catalyst which can be heated by energizing the catalyst carrier is installed in an exhaust passage, and secondary air supply means for supplying secondary air to the exhaust passage is provided. In an engine exhaust gas purification apparatus, an operating state detecting means for detecting an engine operating state, an exhaust temperature detecting means for detecting an exhaust temperature, a catalyst temperature detecting means for detecting a temperature of the electrically heated catalyst, and a secondary air supply. The secondary air supply amount by the means is controlled based on the engine operating state, the exhaust temperature, the catalyst temperature, and the rate of increase of the catalyst temperature per unit time.
An exhaust gas purification device for an internal combustion engine, comprising: a secondary air supply amount control means.