JP2557806B2 - Fuel vapor page control method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor purge control method for a vehicle including a fuel vapor adsorption device.

(Prior Art and Problems Thereof) In a vehicle, in general, in order to suppress the evaporative fuel from a fuel tank to be released into the atmosphere, the evaporative fuel is treated with charcoal (activated carbon) having a gas adsorbing property. A fuel vapor adsorption device for adsorbing and holding is provided.

In this type of fuel vapor adsorbing device, the stored fuel vapor is purged into the engine intake system through a suitable conduit and means for opening and closing the conduit (for example, Japanese Utility Model Publication 60-33).
No. 316). However, in general, when the engine is in a low temperature state, the amount of fuel is increased and the mixture becomes rich depending on the engine cooling water temperature, etc.When the above-mentioned fuel vapor purge is added to this, it becomes too rich and a large amount of CO It causes harmful effects such as being discharged to the. Especially, in the carburetor type internal combustion engine, the air-fuel ratio of the air-fuel mixture is rich during the first idle, and if the fuel vapor is further supplied from the fuel vapor adsorbing device side, the degree of the richness is further increased,
As a result, even if the air-fuel ratio is made lean by intake of the exhaust secondary air in front of the three-way catalyst to reduce CO, the effect is diminished and the emission is deteriorated.

Therefore, it is necessary to stop the fuel vapor purging when the engine is in a low temperature state.

On the other hand, on the fuel vapor adsorption device side, if the fuel vapor purge is started early, it can be used with a margin in the state of charcoal, so from this point, the engine will not warm up to a low temperature. It is desirable to carry out the purging even from the time, but if the purging of the fuel vapor is carried out in the low temperature state, the above-mentioned harmful effects will be brought about.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and a fuel vapor purge control method for preventing the adverse effect of purging of fuel vapor at a low temperature and also advancing the start timing of the purge. The purpose is to provide.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides an engine intake system from a fuel vapor adsorbing device to an engine intake system when the internal combustion engine of a vehicle equipped with the fuel vapor adsorbing device is in a low temperature state. In the fuel vapor purge control method for stopping the purging of fuel vapor, when the traveling speed of the vehicle is equal to or higher than a predetermined value higher than the traveling speed of the engine when the engine is idle, It is characterized in that purging is performed.

(Embodiment) An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram showing a carburetor type internal combustion engine incorporating an air-fuel ratio control device for implementing the method of the present invention.

In FIG. 1, reference numeral 1 is, for example, a four-cylinder internal combustion engine, and an intake pipe (intake manifold) 2 of the engine 1 is provided with an air cleaner 3 and a known carburetor (carburetor) 4. A choke valve 5 is provided upstream of the carburetor 4 of the intake pipe 2, and a throttle valve 6 is provided downstream thereof.
Each is provided.

The choke valve 5 is closed during the first idling, whereby the air intake port on the way from the air cleaner 3 to the carburetor 4 (the intake pipe portion between the secondary air supply passage inlet and the carburetor 4 described later). To restrict the supply of air to the carburetor 4.

The air-fuel ratio of the air-fuel mixture in the carburetor 4 is set to be slightly higher than the stoichiometric air-fuel ratio (14.7), and the air-fuel mixture supplied to the engine 1 described above is lighter than the secondary air supply described below. (That is, the stoichiometric air-fuel ratio) is supplied to the engine 1.

Reference numeral 7 denotes a secondary air supply passage (air conduit). One end (inlet) of the secondary air supply passage 7 is connected to the intake pipe 2 on the upstream side of the choke valve 5, and the other end (outlet) thereof is secondary (additional). The air supply port 8 is connected to the downstream side of the throttle valve 6 of the intake pipe 2, and a linear solenoid type solenoid valve 9 as a proportional control valve is provided in the middle of the air supply port 8.

The air taken in from one end of the secondary air supply passage 7 is supplied to the secondary air supply port 8 opened in the intake pipe 2 through the solenoid valve 9. The solenoid valve 9 is a solenoid 9a connected to an electronic control unit (hereinafter referred to as ECU) 10
And a valve element 9b for controlling the flow rate of the secondary air (additional air) supplied from the secondary air supply port 8 to the intake pipe 2, and the solenoid 9a is energized and controlled by the ECU 10. By driving the valve element 9b by the solenoid 9a, the solenoid valve 9 controls the secondary air supply amount in proportion to the amount of current supplied (linear solenoid drive current). The solenoid valve 9 is a normally closed type in which the valve element 9b opens when the solenoid 9a is energized, and the opening area is proportional to the current supplied to the solenoid 9a.

An absolute pressure (P _B ) sensor 11 is provided downstream of the throttle valve 6 in the intake pipe 2, and an absolute pressure signal detected by the absolute pressure sensor 11 is sent to the ECU 10. Also, supplied to the ECU10 outputs the electrical signal to a downstream indicative of the sensed intake air temperature is mounted an intake air temperature (T _A) sensor 12.

A cooling water temperature (Tw) sensor 13 is provided in the main body of the engine 1, and the sensor 13 is composed of a thermistor or the like, is mounted inside the engine cylinder peripheral wall filled with cooling water, and supplies the detected water temperature signal to the ECU 10.

An engine speed (Ne) sensor 14 is attached around a cam shaft or a crank shaft (not shown) of the engine. This is to output an engine speed signal, that is, a pulse signal (hereinafter referred to as "TDC" signal) generated at a predetermined crank angle position every 180 ° rotation of the engine crankshaft, and this TDC signal is sent to the ECU 10. .

A three-way catalyst 16 is arranged in an exhaust pipe (exhaust manifold) 15 of the engine 1 to purify HC, CO and NOx components in exhaust gas. The upstream side of the three-way catalyst 16 O ₂ sensor 17 as an exhaust gas sensor mounted in an exhaust pipe 15, the O ₂ sensor 17 detects the oxygen concentration in the exhaust gas, and supplies the detection signal to the ECU10 .

Further, a throttle opening sensor (not shown) and other sensors are connected to the ECU 10, and a vehicle speed sensor 18
Is connected, and the vehicle speed sensor 18 supplies the ECU 10 with pulse signals generated at intervals according to the vehicle speed V. The detection output of the vehicle speed sensor 18 is also used when it is determined whether the vehicle is in a predetermined traveling state and when it is determined whether the engine operating state is an idle operating state, as described later.

Liquid fuel stored in a fuel tank 19 is supplied to the carburetor 4 through a fuel passage (not shown), while the upper space of the fuel tank 19 is a pipeline.
The fuel vapor adsorbing device (hereinafter simply referred to as a canister) 21 such as a charcoal canister is connected via 20 and the evaporated fuel in the fuel tank 19 is guided to the latter. The canister 21 adsorbs and holds the evaporated fuel from the fuel tank 19 and stores it, and also supplies the fuel vapor to the intake pipe 2 through a conduit (fuel vapor purge conduit) 22.

The connection of the pipe line 22 to the intake pipe 2 is made by a purge port 23 provided between the secondary air supply port 8 and the engine 1, and from the canister 21 to the purge port 23.
An electromagnetic valve 24 for purge control is provided in the middle of the conduit 22 leading to.

The purge control solenoid valve 24 controls the purge, that is, the discharge of the fuel vapor from the canister 21 to the intake pipe 2 by selectively opening and closing the pipe line 22, and a solenoid connected to the ECU 10 ( Hereinafter, it has a purge (PU) solenoid, and the purge control is performed by energizing and deenergizing the PU solenoid. In the case of the present embodiment, the solenoid valve 24 shuts off the purge of fuel vapor into the intake pipe 2 (purge cut) when the PU solenoid is turned off by the ECU 10, and the PU solenoid is turned on. If so, the mode is switched so that the purge is turned on (that is, the purge is performed).

The ECU 10 shapes the input signal waveforms from the various sensors described above, corrects the voltage level to a predetermined level, and converts the analog signal values from the various sensors into digital signal values. Processing circuit (hereinafter "C
PU ") 10b, storage means 10c for storing various calculation programs executed by the CPU 10b, calculation results, etc., the linear solenoid type solenoid valve 9, and the purge control solenoid valve 24.
It is composed of an output circuit 10d for sending a drive signal to the ECU 10, the ECU 10 determines the operating state of the engine according to the output signals from the O ₂ sensor 17 and other various engine parameter sensors, and determines the determined operating state. Accordingly, the linear solenoid drive current I _OUT to the linear solenoid type solenoid valve 9 is calculated based on the following formula I _OUT = Q × K _O2 (1) in synchronization with the TDC signal, while the fuel vapor of the canister 21 is calculated. Regarding the purge control of, the operation timing for the purge control solenoid valve 24 is calculated.

In the above formula (1), Q is the reference value of the linear solenoid drive current of the solenoid valve 9 which is determined according to the engine speed Ne and the intake pipe absolute pressure P _B, and K _O2 is the air-fuel ratio correction coefficient. Where, when the determined operating state is in the feedback control operating region, it is obtained by a predetermined calculation method according to the output signal of the O ₂ sensor 17, and when it is in an operating region other than the feedback control operating region,
It is a coefficient set to a value according to each operating region.

The ECU 10 supplies a drive signal for opening the solenoid valve 9 to the solenoid 9a of the solenoid valve 9 based on the linear solenoid drive current I _OUT of the solenoid valve 9 obtained as described above, and the valve element 9b
Variably controls the opening area for secondary air supply.

As a result, when in the feedback control operation range, the value of the correction coefficient K _O2 is changed according to the output of the O ₂ sensor 17 arranged in the exhaust system of the engine 1 to change the stoichiometric air-fuel ratio or an air-fuel ratio close thereto. As can be obtained, feedback control of the air-fuel ratio is performed to increase / decrease the amount of secondary air with respect to the mixture of fuel and air from the carburetor 4.

The purge control of the fuel vapor to the intake pipe 2 is based on the input signals from the water temperature sensor 13 and the vehicle speed sensor 18, and further,
This is done by switching the purge control solenoid valve 24 according to the following control program based on the input signal of the intake air temperature sensor 12 and the linear solenoid drive current I _OUT calculated by the equation (1).

FIG. 2 is a flow chart showing the control procedure of the canister purge control by the solenoid valve 24.

This program basically stops the canister purging when the engine 1 is in a low temperature state, but if the vehicle is in a predetermined traveling state, even if the engine 1 remains in a low temperature state, the purging is performed. The control is performed so that

First, in steps 201 and 202, the temperature state of the engine 1 is determined. This determination is made using the output of the cooling water temperature sensor 13, and in step 201, the engine water temperature T
It is determined whether w is higher than a predetermined value T _W1 (for example, 63 ° C.). On the other hand, also in step 202, similarly, the engine water temperature Tw
Is determined to be higher than a predetermined value T _W2 , the temperature value to be compared in step 202 is set higher than the predetermined value T _W1 and, for example, when the engine 1 is warmed up. Set to 75 ℃ after the completion of machine operation.

After the engine 1 starts, when the engine 1 is still cold and the engine water temperature Tw has not risen to the predetermined value T _W1 ,
Since the determination result of step 201 is negative (No), the T _PU timer that measures T _PU for the predetermined time is set (step 20
6) Then, the PU solenoid of the purge control solenoid valve 24 remains off (step 207), and this program ends. It should be noted that, as will be described later, the above-mentioned predetermined time T _PU is the air-fuel ratio correction coefficient K _O2 when the PU solenoid is in the ON state (the state where the fuel vapor from the canister 21 is being purged into the intake pipe 2). When the (linear solenoid drive current I _OUT to be supplied to the solenoid 9a of the solenoid valve 9) exceeds a required limit value, a time used for turning off the PU solenoid after a certain time has elapsed from that point, For example, it is set to 30 seconds.

When the engine water temperature Tw does not reach the predetermined value T _W1 set lower than the predetermined value T _W2 , the purging of the fuel vapor is uniformly stopped as described above.

On the other hand, if the engine water temperature Tw gradually rises and exceeds the predetermined value T _W1 , the answer in step 201 becomes affirmative (Yes), and in such a state, the engine water temperature Tw becomes the next predetermined value T w.
_W2 is compared, and in accordance with the determination result in step 202, determination using the output of the vehicle speed sensor 18 is executed in steps 203 and 204. In these steps 203 and 204, by comparing with the preset vehicle speed values V ₁ and V ₂ , respectively, it is determined whether the engine water temperature Tw is lower or higher than a predetermined value T _W2 , and whether the vehicle is in an idle state, and the running state of the vehicle. To determine if. Regarding the predetermined value for comparison in each step, for example, V ₁ is set to about 3 km / H and V ₂ is set to about 20 km / H.

First, the engine water temperature Tw exceeds the predetermined value T _W1
When it is lower than _W2 , that is, when the engine 1 is still in the low temperature state, the answer to step 202 is negative (N
Therefore, in this case, it is determined whether the vehicle speed V is lower than the predetermined value V ₂ (step 203). If the answer is affirmative (Yes), the answer in step 201 above is negative (No).
As in the case of, the _TPU timer is set, the PU solenoid is kept off (steps 206 and 207), and when the answer is negative (No), the process proceeds to step 208 and subsequent steps described later to execute the process of inserting the purge (step). 211).

As described above, in the range where the engine water temperature Tw is lower than the predetermined value T _W1 , the PU solenoid is uniformly turned off, and the predetermined value T _W
Except when the vehicle is in the predetermined running state in the range of more than _W1 and less than the predetermined value T _W2 , the PU solenoid is turned off, so the fast idle state and the engine water temperature Tw are the predetermined values.
In the idle state where T _W2 is not reached, the fuel vapor supply can be cut off.
Excessive concentration of the air-fuel mixture due to canister purge at low water temperature is prevented. In particular, during fast idle, the air-fuel mixture is rich in order to promote warm-up, but it is possible to prevent the degree of richness from increasing further in this state, and therefore, the intake of the exhaust secondary air Therefore, the effect of reducing the CO by reducing the air-fuel ratio is not impaired. Moreover, depending on the determination result of step 203, the purge can be performed even when the PU solenoid is turned on and the temperature is low, so that the canister purge can be started early and the purge is performed at the low temperature. It is possible to achieve both the prevention of the enrichment of the air-fuel mixture and the advancement of the start time of the canister purge.

 This focuses on the following points.

That is, when the canister purge is performed in the low temperature state, the air-fuel mixture becomes thicker due to the canister purge. Moreover, in the idle state and the vehicle speed is not increased, the air-fuel mixture flowing in the intake passage 2 downstream of the throttle valve 6 is discharged. Since the flow rate is smaller than that in a traveling state in which the vehicle speed V is sufficiently high, the influence of the fuel vapor supplied from the canister 21 to the intake pipe 2 via the solenoid valve 24 is large. That is, the amount of the thickened gas due to the addition of the purge is not burned in the engine 1 and it becomes difficult to perform appropriate correction.

However, even in the low temperature state, if the vehicle is traveling at a sufficiently high vehicle speed V, the flow rate of the air-fuel mixture is large. Therefore, in this case, even if the canister purge is performed,
Since the ratio of the canister purge to the flow rate flowing through the intake passage 2 is sufficiently smaller than that in the above-mentioned idle state, the effect of adding purge is also small. That is, the purged portion is absorbed and burned by the engine 1 when the vehicle speed V is sufficiently increased.

Therefore, if the vehicle speed V is higher than the predetermined value V ₂ , step
It is supposed to proceed to 208 or later. Therefore, this step 2
Since the predetermined value V _{2 in} 03 is specifically set from the above points, the above-mentioned numerical value regarding V ₂ is not a limitation and is an example.

As described above, according to the result of the determination in step 203, the canister purge is started if the engine 1 is in a low temperature state but is not easily affected by the influence, that is, if the vehicle is in a predetermined traveling state. , The canister purge can be started earlier, and the canister 21
Can be accelerated.

When the engine water temperature Tw exceeds the predetermined value T _W2 , step 202
Since an affirmative answer is obtained at, the vehicle speed V is the predetermined value V ₁
If the answer is negative (No), the process proceeds to step 208 and thereafter. On the other hand, when the answer to step 204 is affirmative (Yes), that is, in the idle state,
It is determined whether or not the intake air temperature T _A is higher than a predetermined value T _A1 (for example, 65 ° C.) (step 205), and control is performed according to the intake air temperature according to the result of the determination.

Here, the determination step 205 is provided so that the air-fuel ratio of the air-fuel mixture changes depending on the intake air temperature and the air-fuel ratio of the air-fuel mixture changes. . When the intake air temperature T _A is high, the density of the weight of air is low, and therefore the air-fuel mixture is in a rich state. If the fuel vapor is further purged and the purge amount is added to it, the correction cannot be dealt with. Therefore, as a result of comparing the intake air temperature T _A with the predetermined value T _A1 in step 205, a positive answer is obtained. If so, the canister purge is not performed (steps 206 and 207).

However, if the answer to step 205 is negative (No), PU
Turn on the solenoid (step 211). That is, even if the engine water temperature Tw is higher than the predetermined value T _W2 (step 202) and the engine 1 is in the idle state (step 204),
When the intake air temperature T _A is lower than the predetermined value T _A1 , the canister 21
The canister purge will be performed from the standpoint that it can be sufficiently corrected even if the fuel vapor from is added.

As described above, when a negative answer (No) is obtained in step 203, that is, when the vehicle is in the predetermined traveling state even in the low temperature state, or in step 204 as described above, the negative (N
If the answer of o) is obtained, that is, the engine water temperature Tw is the predetermined value T
_{When the} vehicle speed is higher than _{W2 and the routine} proceeds to step 208, here, the linear solenoid drive current I _OUT represented by the formula (1) supplied to the linear solenoid type solenoid valve 9 is the predetermined value I. _{Determine if} it is less than _OUTFSH . This predetermined value I _OUTFSH is the air-fuel ratio correction coefficient K
_It indicates the fail safe limit amount of _O2 , and as a result of comparison with the predetermined value I _OUTFSH applied in step 208, if the linear solenoid drive current I _OUT is within the predetermined limit amount, a negative (No) answer is returned. _Therefore , the T _PU timer is set (step 209) and the PU solenoid is turned on (step 211).

When the PU solenoid is turned on, the purge control solenoid valve 24 is opened, and the canister 21 and the purge port 23 opened in the intake pipe 2 are in communication with each other. Therefore, the fuel vapor adsorbed and held in the canister 21 is absorbed in the intake pipe 2 Is sucked into the intake pipe 1 by the negative pressure and sent to the engine 1 for combustion. Canister
In the charcoal on the 21st side, the fuel vapor temporarily stored in this way is expelled in this way, so that the gas adsorbability is recovered by that amount and the evaporated fuel in the fuel tank 19 can be adsorbed again.

When the linear solenoid drive current I _OUT becomes larger than the predetermined value I _OUTFSH , that is, when the limit is exceeded, the answer in step 208 is affirmative (Yes), and in this case, the upper limit is exceeded. Predetermined time T _PU
It is determined whether or not the time has passed (step 210). Even if the upper limit is exceeded, the answer to step 210 is negative (No) until the predetermined time T _PU has elapsed, so the PU solenoid is kept on in this state (step 211). The state where the limit is exceeded is the predetermined time T _PU
When the above is continued, the answer in step 210 becomes affirmative (Yes), and the ON state of the PU solenoid is released at this point (step 207).

The reason why the purge cut is performed under the constant condition as described above is as follows. That is, while the secondary air supply amount control by the linear solenoid type solenoid valve 9 is being performed, the above (1)
The fact that the linear solenoid drive current I _OUT calculated by the formula is the upper limit means that the air-fuel ratio of the exhaust gas is rich, and it is too rich.
This is also to prevent the fuel vapor from the canister 21 from being added to the intake system in this state.

That is, if the canister purge is performed, the air-fuel ratio correction cannot be handled. Further, in this case, in step 208, when the determination result is affirmative (Yes), the PU solenoid is not turned off immediately and the purge cut is not performed. In other words, a certain margin time (T _PU The predetermined time T _PU by the timer is given to decide whether or not to perform the purge cut. It is determined that the air-fuel ratio of the exhaust gas is surely in the rich state, and the purge cut is performed only in such a state. This is because.

In this program example, the predetermined value T _W1 for the determination in step 201 for uniformly stopping the canister purge when the engine 1 is in the low temperature state is 63 ° C. as an example. However, this is set to different values depending on the vehicle equipped with the automatic transmission and the vehicle equipped with the manual transmission.

(Effects of the Invention) According to the present invention, when the internal combustion engine of the vehicle equipped with the fuel vapor adsorption device is in a low temperature state, the fuel vapor that stops purging of the fuel vapor from the fuel vapor adsorption device into the engine intake system is stopped. In the purge control method, when the traveling speed of the vehicle is equal to or higher than a predetermined value higher than the traveling speed of the engine when idle, the fuel vapor is purged even when the engine is in a low temperature state. It is possible to prevent the air-fuel ratio from becoming rich due to the purging of the fuel vapor in the low temperature state, and it is possible to start the purging of the fuel vapor early even when the engine is in the low temperature state. The purging of the fuel vapor can be promoted and the fuel vapor adsorption device can be effectively used.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an internal combustion engine of a vehicle equipped with a fuel vapor adsorption device to which the method of the present invention can be applied, and FIG. 2 is a flow chart showing a procedure of fuel vapor purge control according to an embodiment of the present invention. Is. 1 ... Internal combustion engine, 2 ... Intake pipe, 10 ... Electronic control unit, 21 ... Fuel vapor adsorption device, 23 ... Purge port, 24 ... Purge control solenoid valve.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Koseki, 1-4-1, Chuo, Wako-shi, Saitama, Ltd. Inside the Honda R & D Co., Ltd. (72) Inventor, Hiroshi Hasebe 4-1-1, Chuo, Wako, Saitama Incorporated in Honda R & D Co., Ltd. (56) References JP-A 61-149562 (JP, A) SAI 61-151064 (JP, U)

Claims (1)

(57) [Claims] 1. A fuel vapor purge control method for stopping the purging of fuel vapor from the fuel vapor adsorption device to the engine intake system when the internal combustion engine of a vehicle equipped with the fuel vapor adsorption device is in a low temperature state, A fuel vapor purge control method, wherein when the traveling speed of the vehicle is higher than a predetermined value higher than the traveling speed of the engine when the engine is idle, the fuel vapor is purged even when the engine is in a low temperature state.