JP7726037B2 - Purge valve control method and control device for evaporated fuel treatment device - Google Patents

Description

This invention relates to a fuel vapor treatment system using a canister, and in particular to the control of a purge valve installed in a purge passage between the canister and the intake passage of an internal combustion engine.

To prevent fuel vapor generated in a vehicle's fuel tank from escaping to the outside, a widely used fuel vapor treatment system temporarily adsorbs the vapor in a canister using an adsorbent such as activated carbon. Then, while the internal combustion engine is running, fresh air is introduced to purge the fuel components from the canister and introduce them into the engine's intake system. The purge valve installed in the purge passage is generally duty-controlled at an appropriate drive frequency to control the flow rate of purge gas introduced into the internal combustion engine's intake passage.

Patent Document 1 discloses a purge control method in which the drive frequency is set to 10 Hz when the target purge air flow rate is high, and to 40 Hz when the target purge air flow rate is low, and the duty ratio is determined by referencing a table that stores the correlation between the purge air flow rate and the duty ratio at each drive frequency.

Japanese Patent Application Laid-Open No. 2003-13811

In fuel vapor treatment systems that use a duty-controlled purge valve, the intermittent opening and closing of the purge valve causes pulsation in the purge passage (more specifically, the section between the purge valve and the canister). This creates a problem in that the actual purge gas flow rate varies depending on the relationship between the timing at which the pressure wave is reflected by the canister or the like and returns to the purge valve and the duration the purge valve is open.

The technology in Patent Document 1 does not take into consideration pressure pulsations within the purge passage caused by the opening and closing of the purge valve.

The present invention relates to an evaporated fuel treatment device in which a duty-controlled purge valve is provided in a purge passage between a canister and an intake passage of an internal combustion engine,
Calculate the basic duty ratio according to the target purge rate,
The value of the drive frequency in the above duty control is read,
correcting the basic duty ratio based on the drive frequency so as to suppress a change in flow rate due to pressure pulsation in a section of the purge passage between the purge valve and the canister, the change being caused by opening and closing the purge valve;
A method for controlling a purge valve of an evaporated fuel treatment device, comprising:
The correction amount required for each drive frequency value is calculated in advance,
A correction amount corresponding to the drive frequency is set,
The basic duty ratio is corrected by this correction amount to calculate the corrected duty ratio.

The pressure wave generated by opening and closing the purge valve travels through the purge passage toward the canister at the speed of sound, reflecting off the canister and returning to the purge valve, causing pressure pulsations just before the purge valve. If the pressure just before the purge valve is relatively high (the so-called peak of the waveform) due to the pressure wave or pressure pulsation when the purge valve opens in response to a subsequent pulse, the purge gas flow rate will increase from its intended value. Conversely, if the pressure just before the purge valve is relatively low (the so-called valley of the waveform), the purge gas flow rate will decrease from its intended value. The timing at which the peaks and valleys of the pressure wave reach the purge valve is basically determined by the drive frequency, so it is possible to correct the basic duty ratio based on the drive frequency to suppress changes in flow rate due to pressure pulsations.

According to this invention, by increasing or decreasing the basic duty ratio based on the drive frequency, the effects of pressure pulsation caused by the opening and closing operation of the purge valve itself can be at least partially suppressed, allowing for more accurate purge control.

1 is a diagram illustrating the configuration of an evaporated fuel treatment device according to the present invention; FIG. 3 is a functional block diagram of duty control. 4 is a time chart showing the relationship between the pressure waveform at a position immediately before the purge valve and the open period of the purge valve. 4 is a flowchart of duty control according to an embodiment.

An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram illustrating the configuration of an evaporative fuel treatment device for a vehicle equipped with an internal combustion engine 1. The evaporative fuel treatment device treats evaporative fuel generated in the vehicle's fuel tank 2 while the vehicle is parked, preventing it from escaping to the outside. It primarily comprises a canister 3 filled with an adsorbent material such as activated carbon to temporarily store evaporative fuel. The canister 3 has a charge port 3a and a purge port 3b at one end of its internal flow path, and a drain port 3c at the other end. The charge port 3a is connected to the upper space of the fuel tank 2 via a charge passage 4, while the purge port 3b is connected to the intake passage 7 of the internal combustion engine 1 via a purge passage 5. The drain port 3c is open to the atmosphere via a drain passage 6. A drain cut valve (not shown) may be provided in the drain passage 6 for leak testing, etc.

For example, evaporated fuel generated while the vehicle is stopped or during refueling is introduced into the canister 3 via the charge passage 4 and is adsorbed by the adsorbents in various parts as it flows through the adsorbent toward the drain port 3c. The adsorbed fuel components are purged from the adsorbent when atmospheric air is drawn in through the drain passage 6 due to the negative pressure generated in the intake system while the internal combustion engine 1 is operating, and are introduced into the intake system of the internal combustion engine 1 via the purge passage 5, and are ultimately combusted in the combustion chamber of the internal combustion engine 1 together with fuel from the fuel injection valve.

The internal combustion engine 1 shown in the figure is a four-stroke, spark-ignition engine, e.g., a supercharged engine equipped with a turbocharger. The intake passage 7 of this internal combustion engine 1 is equipped with a turbocharger compressor 11, and a throttle valve 12 is located downstream of this compressor 11. An admission valve 13, e.g., a butterfly valve, is located upstream of the compressor 11 in the intake passage 7 to generate negative pressure within the intake passage 7. The tip of the purge passage 5 is connected to the intake passage 7 between this admission valve 13 and the compressor 11. Therefore, even in the supercharged region, a certain degree of negative pressure is generated by the action of the admission valve 13, and the pressure difference with atmospheric pressure on the drain passage 6 side enables the canister 3 to be purged, i.e., purge gas can be introduced into the intake passage 7.

A purge valve 8 consisting of an electromagnetic valve is provided in the purge passage 5 to control the purge gas flow rate. The purge valve 8 is duty-controlled by a controller 9. The controller 9 is configured as part of an engine controller that performs various controls of the internal combustion engine 1 (including fuel injection control, ignition control, throttle valve 12 opening control, admission valve 13 opening control, etc.).

In this embodiment, the duty control corrects the duty ratio to offset the effects of pressure pulsations caused by the opening and closing of the purge valve 8 itself. When the purge valve 8 opens and closes in response to a pulse, pressure pulsations occur in the section of the purge passage 5 between the purge valve 8 and the canister 3. Specifically, a pressure wave generated at the purge valve 8 propagates through the purge passage 5 at the speed of sound, reflects off the canister 3, and returns to the purge valve 8. In this embodiment, the duty ratio is corrected to offset the effects of the pressure wave depending on when it reaches the purge valve 8. The relationship between the timing at which the pressure wave reaches the purge valve 8 and the open period in response to the subsequent pulse is basically determined by the pulse interval, i.e., the drive frequency. Note that the pressure wave does not necessarily reflect from the canister 3; it may also be reflected from the open end, etc., but in either case, the pressure wave is reflected and returns to the purge valve 8.

Figure 2 is a functional block diagram of the duty control executed by the controller 9, and includes a basic duty calculation unit 21 and a correction calculation unit 22. The basic duty calculation unit 21 calculates the basic duty ratio using the target purge rate (the ratio of purge gas to the intake air volume) as input. For example, the basic duty calculation unit 21 has a table or map with the target purge rate as one parameter, and determines the basic duty ratio by referencing this.

The correction calculation unit 22 receives the basic duty ratio and the value of the drive frequency for duty control at that time as input, corrects the basic duty ratio according to the drive frequency so as to suppress changes in flow rate due to pressure pulsation in the purge passage 5 corresponding to the drive frequency, and outputs the corrected duty ratio. For example, the correction amount required for each drive frequency value is stored in advance as a table, and the correction amount corresponding to the input drive frequency is used to correct the basic duty ratio. In one embodiment, the drive frequency is, for example, approximately 5 to 20 Hz, and is variably set by a drive frequency calculation unit (not shown) based on conditions such as engine rotation speed.

The correction calculation unit 22 may also input the gas density in the purge passage 5 between the canister 3 and the purge valve 8 and apply a correction based on this gas density. In one example, this correction based on gas density is achieved by further correcting the correction amount for each drive frequency described above based on the gas density. Alternatively, a map may be created in advance in which correction amounts are assigned using drive frequency and gas density as parameters, and values corresponding to drive frequency and gas density may be read out. When the gas density in the purge passage 5 changes, the speed of sound changes, changing the timing of the pressure wave returning to the purge valve 8. The correction based on gas density is intended to compensate for this change in speed of sound. Outside air temperature, which is relatively easy to detect, may also be used as an alternative to gas density.

Furthermore, if the effective passage length of the section of the purge passage 5 between the canister 3 (or the reflecting end) and the purge valve 8 changes due to switching of a valve (not shown), the correction calculation unit 22 may make a correction according to the passage length at that time. This correction according to the passage length is realized, for example, by further correcting the correction amount for each drive frequency described above based on the passage length. Alternatively, a map may be created in advance in which correction amounts are assigned using drive frequency and passage length as parameters, and the corresponding values may be read out.

When considering both gas density and passage length, for example, a map can be created in advance in which correction amounts are assigned using drive frequency, gas density, and passage length as parameters, and the corresponding values can be read out. Instead of a map, the necessary correction amount can be calculated.

Figure 3 is a time chart showing the relationship between the waveform of pressure pulsation in the purge passage 5 at the position immediately before the purge valve 8 (the position indicated by reference symbol 5a in Figure 1) and the open period of the purge valve 8, showing three examples (a), (b), and (c). For ease of understanding, this example uses a relatively small duty ratio, showing one open period in response to a pulse and a second open period in response to a subsequent pulse.

As shown in the figure, pressure pulsation is observed at position 5a immediately before purge valve 8 due to the opening and closing of purge valve 8 in response to a single pulse. The moment purge valve 8 opens, the pressure drops as purge gas begins to flow. The moment purge valve 8 closes, the gas flow is blocked, causing a sudden increase in pressure. This pressure wave propagates upstream and is reflected by the canister, causing pressure pulsation. In the example shown in Figure (a), based on the drive frequency at that time, the subsequent open period indicated by symbol V1 overlaps with the trough period (a period of low pressure) of the pressure waveform, as indicated by the dashed line in the figure. As a result, the pressure during this open period is lower than the average pressure when purge valve 8 is normally open. Therefore, the pressure difference across purge valve 8 is smaller than the average pressure difference, and the actual purge gas flow rate is lower than the intended purge gas flow rate corresponding to the length of the open period (i.e., the duty ratio). Therefore, in this case, the basic duty ratio is corrected upward.

In the example of Figure (b), the drive frequency is different from the example of Figure (a). Specifically, the drive frequency is relatively high, and therefore the open period cycle is shorter than in the example of Figure (a). As a result, the subsequent open period, designated by the symbol V2, overlaps with the peak period of the pressure waveform (the period of high pressure), as shown by the dashed line in the figure. In this case, the pressure during this open period is higher than the average pressure when the purge valve is always open. Therefore, the pressure difference before and after the purge valve 8 is larger than the average pressure difference, and the actual purge gas flow rate is higher than the original purge gas flow rate corresponding to the length of the open period (i.e., the duty ratio). Therefore, in this case, the basic duty ratio is corrected downward.

The above-mentioned increase and decrease corrections to the basic duty ratio are made at relatively small rates, so the basic timing relationship with the pressure waveforms shown in Figures (a) and (b) does not change significantly.

Figure (c) shows an example where the gas density in the purge passage 5 has changed, resulting in a slower sonic velocity. The timing of the open period indicated by the symbol V3 is the same as the timing of open period V1 in the example of Figure (a), meaning the drive frequency is unchanged from the example of Figure (a). In this case, the slower sonic velocity delays the timing at which the pressure wave returns to position 5a immediately before the purge valve 8. Therefore, in the example shown, open period V3 overlaps with the period when the pressure waveform peaks, increasing the actual purge gas flow rate. Therefore, in this case, the basic duty ratio is corrected downward.

Next, Figure 4 is a flowchart showing duty control in one embodiment. The routine shown in this flowchart is repeatedly executed by the controller 9 at predetermined calculation cycles. In step 1, a target purge rate is calculated based on the operating conditions (rotational speed and load) of the internal combustion engine 1 at that time. In step 2, the basic duty ratio required to achieve this target purge rate is calculated.

In step 3, the drive frequency determined by another routine (not shown) is read. As mentioned above, the drive frequency is determined taking into account factors such as engine rotation speed. Next, in step 4, the correction amount for the duty ratio corresponding to the drive frequency is calculated. For example, as mentioned above, the correction amount required for each drive frequency value is stored in advance as a table, and the correction amount corresponding to the drive frequency at that time is calculated. Note that, as mentioned above, correction based on gas density or outside temperature or correction based on passage length may also be added.

In step 5, the basic duty ratio is corrected using the above correction amount to obtain a corrected duty ratio. Then, in step 6, a drive command for the purge valve 8 is output based on this corrected duty ratio and drive frequency.

The above describes one embodiment of the present invention, but the present invention can also be applied to an evaporated fuel treatment system equipped with multiple purge valves 8 arranged in parallel. Furthermore, the basic duty ratio can be corrected in any suitable manner, such as by adding or subtracting a correction amount, or by multiplying a correction amount (correction coefficient).

REFERENCE SIGNS LIST 1 internal combustion engine 2 fuel tank 3 canister 5 purge passage 8 purge valve 9 controller

Claims (4)

In an evaporated fuel treatment device, a duty-controlled purge valve is provided in a purge passage between a canister and an intake passage of an internal combustion engine,
Calculate the basic duty ratio according to the target purge rate,
The value of the drive frequency in the above duty control is read,
correcting the basic duty ratio based on the drive frequency so as to suppress a change in flow rate due to pressure pulsation in a section of the purge passage between the purge valve and the canister, the change being caused by opening and closing the purge valve;
A method for controlling a purge valve of an evaporated fuel treatment device, comprising:
The correction amount required for each drive frequency value is calculated in advance,
A correction amount corresponding to the drive frequency is set,
The basic duty ratio is corrected by this correction amount to calculate a corrected duty ratio.
A method for controlling a purge valve of an evaporated fuel treatment device. Furthermore, the basic duty ratio is corrected based on the gas density in a purge passage between the canister and the purge valve or the outside air temperature.
2. The method for controlling a purge valve of an evaporated fuel treatment device according to claim 1 . Furthermore, the basic duty ratio is corrected based on the substantial length of the purge passage between the canister and the purge valve.
3. A method for controlling a purge valve of an evaporated fuel treatment device according to claim 1 . a canister for adsorbing evaporated fuel;
a purge valve provided in a purge passage between the canister and an intake passage of the internal combustion engine;
a controller that controls the duty of the purge valve;
In an evaporated fuel treatment device comprising:
The above controller is
Calculate the basic duty ratio according to the target purge rate,
The value of the drive frequency in the above duty control is read,
correcting the basic duty ratio based on the drive frequency so as to suppress a change in flow rate due to pressure pulsation in a section of the purge passage between the purge valve and the canister, the change being caused by opening and closing the purge valve;
A purge valve control device for an evaporated fuel treatment device,
The correction amount required for each drive frequency value is calculated in advance,
A correction amount corresponding to the drive frequency is set,
The basic duty ratio is corrected by this correction amount to calculate a corrected duty ratio.
Purge valve control device for evaporative fuel treatment system.