Purge valve control method and control device for evaporated fuel treatment device

Abstract

To suppress variation of a purge gas flow rate due to pressure pulsation generated in a purge passage between a purge valve and a canister when the purge valve is opened and closed.SOLUTION: A method for controlling a purge valve of an evaporation fuel treatment device includes: calculating a target purge rate (S1); calculating a corresponding basic duty ratio (S2); reading a variably set driving frequency (S3); calculating a correction amount of a duty ratio corresponding to the driving frequency (S4), where a correction amount required for each driving frequency value is stored in advance as a table; and after correcting the basic duty ratio using the correction amount (S5), giving a driving instruction to a purge valve 8 (S6).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an evaporated fuel treatment system using a canister, and more particularly to control of a purge valve provided in a purge passage between the canister and an intake passage of an internal combustion engine. [Background technology]

[0002] A widely used fuel vapor treatment system is a system in which fuel vapor generated in a vehicle fuel tank is temporarily adsorbed in a canister using an adsorbent such as activated carbon to prevent it from escaping to the outside, and 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 intake system of the internal combustion engine. A purge valve provided in a purge passage is generally duty-controlled at an appropriate drive frequency to control the flow rate of purge gas introduced into the intake passage of the internal combustion engine.

[0003] 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 large, and the drive frequency is set to 40 Hz when the target purge air flow rate is small, and the duty ratio is determined by referring to a table that stores the correlation between the purge air flow rate and the duty ratio under each drive frequency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-13811 Summary of the Invention [Problem to be solved by the invention]

[0005] In an evaporated fuel treatment device using 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), and 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 opening period of the purge valve.

[0006] The technology of Patent Document 1 does not take into consideration the pressure pulsation in the purge passage caused by the opening and closing operation of the purge valve. [Means for solving the problem]

[0007] This invention relates to a fuel vaporizer 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. Fee In the processing device, 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.

[0008] The pressure wave generated by opening and closing the purge valve travels through the purge passage toward the canister at the speed of sound, reflects off the canister, and returns to the purge valve, generating 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 influence of 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. [Effects of the Invention]

[0009] According to this invention, by increasing or decreasing the basic duty ratio based on the drive frequency, the influence of pressure pulsation caused by the opening and closing operation of the purge valve itself can be at least partially suppressed, thereby enabling more accurate purge control. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating the configuration of an evaporated fuel treatment device according to the present invention; [Figure 2] FIG. 2 is a functional block diagram of duty control. [Figure 3] 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. [Figure 4] 4 is a flowchart of duty control according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will now be described in detail with reference to the 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 a vehicle fuel tank 2 while the vehicle is stopped, 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 an 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.

[0012] For example, evaporated fuel generated while the vehicle is stopped or during refueling is introduced into the canister 3 through 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 air is taken in through the drain passage 6 due to 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 through 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.

[0013] The internal combustion engine 1 shown in the figure is a four-stroke, spark-ignition engine, such as a supercharged engine equipped with a turbocharger. The intake passage 7 of the internal combustion engine 1 is equipped with a turbocharger compressor 11, and a throttle valve 12 is located downstream of the compressor 11. An admission valve 13, such as 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 end of the purge passage 5 is connected to the intake passage 7 between the admission valve 13 and the compressor 11. Even in the supercharging range, the admission valve 13 generates a certain amount of negative pressure, allowing the canister 3 to be purged by the pressure difference between the drain passage 6 and atmospheric pressure, i.e., allowing purge gas to be introduced into the intake passage 7.

[0014] A purge valve 8 consisting of an electromagnetic valve is provided in the purge passage 5 to control the flow rate of purge gas. The purge valve 8 is duty controlled by a controller 9. The controller 9 is configured as a part of an engine controller that performs various controls of the internal combustion engine 1 (including fuel injection control, ignition control, opening control of the throttle valve 12, opening control of the admission valve 13, etc.).

[0015] In this embodiment, the duty control corrects the duty ratio to offset the effects of pressure pulsations caused by the opening and closing operation 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 position of the purge valve 8 propagates through the purge passage 5 at the speed of sound, is reflected by 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 the timing at which the pressure wave 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 end open to the atmosphere, but in either case, the pressure wave is reflected and returns to the purge valve 8.

[0016] 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 receives a target purge rate (the ratio of purge gas to the amount of intake air) as an input and calculates a basic duty ratio. 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 referring to this table or map.

[0017] The correction calculation unit 22 receives the basic duty ratio and the value of the drive frequency in 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, about 5 to 20 Hz, and is variably set in a drive frequency calculation unit (not shown) based on conditions such as engine rotation speed.

[0018] Furthermore, the correction calculation unit 22 may further input the gas density in the purge passage 5 between the canister 3 and the purge valve 8, and make a correction according to this gas density. In one example, this correction according to gas density is realized 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 to assign correction amounts using the drive frequency and gas density as parameters, and values corresponding to the drive frequency and gas density may be read out. When the gas density in the purge passage 5 changes, the speed of sound changes, and the timing of the pressure wave returning to the purge valve 8 changes. The correction according to gas density is intended to compensate for this change in speed of sound. As an alternative to gas density, the outside air temperature, which can be detected relatively easily, may be used.

[0019] Furthermore, if the effective passage length of the section of the purge passage 5 between the canister 3 (or the reflection end) and the purge valve 8 changes due to switching of some valve (not shown), the correction calculation unit 22 may make a correction according to the passage length at that time. In one example, this correction according to the passage length is realized 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 the drive frequency and the passage length as parameters, and the corresponding values may be read out.

[0020] When both the gas density and the passage length are taken into consideration, for example, a map in which correction amounts are assigned using the drive frequency, gas density, and passage length as parameters may be created in advance, and the corresponding values may be read out. Instead of using a map, the necessary correction amount may be calculated.

[0021] 3 is a time chart showing the relationship between the waveform of pressure pulsation in the purge passage 5 at a position immediately before the purge valve 8 (the position indicated by reference symbol 5a in FIG. 1) and the open period of the purge valve 8, and shows three examples (a), (b), and (c). For ease of understanding, an example is shown in which the duty ratio is relatively small, and one open period in response to a pulse and a second open period in response to a subsequent pulse are shown.

[0022] As shown in the figure, pressure pulsation is observed at a position 5a immediately before the purge valve 8 due to the opening and closing of the purge valve 8 in response to a single pulse. The moment the purge valve 8 opens, the pressure drops as the purge gas begins to flow. The moment the 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 (low pressure period) 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 the purge valve 8 is normally open. Therefore, the pressure difference before and after the 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 to increase.

[0023] In the example of Figure (b), the drive frequency is different from that of the example of Figure (a). Specifically, the drive frequency is relatively high, and therefore the open period cycle is shorter than that of the example of Figure (a). Therefore, the subsequent open period indicated by symbol V2 overlaps with the peak period of the pressure waveform (high pressure period), 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 normally 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.

[0024] The above-mentioned increase and decrease corrections of the basic duty ratio are made at a relatively small rate, so the basic timing relationship with the pressure waveforms shown in Figures (a) and (b) does not change significantly.

[0025] Figure (c) shows an example in which the gas density in the purge passage 5 changes and the sonic velocity decreases. The timing of the open period indicated by the symbol V3 is the same as the timing of the open period V1 in the example in Figure (a), meaning that the drive frequency is the same as in the example in Figure (a). In this case, the lower sonic velocity delays the timing at which the pressure wave returns to the position 5a immediately before the purge valve 8. Therefore, in the illustrated example, the open period V3 overlaps with the period when the pressure waveform peaks, and the actual purge gas flow rate increases. Therefore, in this case, the basic duty ratio is corrected to a lower value.

[0026] Next, Fig. 4 is a flowchart showing duty control according to 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 (rotation speed and load) of the internal combustion engine 1 at that time. In step 2, a basic duty ratio required to achieve this target purge rate is calculated.

[0027] In step 3, the drive frequency determined by another routine (not shown) is read. As described above, the drive frequency is determined taking into consideration, for example, the engine rotation speed. Next, in step 4, the correction amount of the duty ratio corresponding to the drive frequency is calculated. For example, as described 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 described above, correction based on the gas density or outside air temperature or correction based on the passage length may also be added.

[0028] 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 according to this corrected duty ratio and the drive frequency.

[0029] Although one embodiment of the present invention has been described above, the present invention can also be applied to an evaporated fuel treatment system having a plurality of purge valves 8 arranged in parallel. 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). [Explanation of symbols]

[0030] 1...Internal combustion engine 2. Fuel tank 3...Canister 5...Purge passage 8...Purge valve 9...Controller

Claims

1. 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.

2. 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.

3. 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.

4. 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.

Images