JP3750674B2 - Evaporative fuel purge control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an evaporated fuel purge control device for an internal combustion engine that purges evaporated fuel generated in a fuel tank and adsorbed to a canister together with air to an intake system of the internal combustion engine through a purge valve.
[0002]
[Prior art]
As this type of evaporated fuel purge control device, there is a technique disclosed in Patent Document 1. In this prior art, the target flow passage area is calculated from the target flow rate of the purge valve and the differential pressure before and after the purge valve so that the purge valve drive amount is determined only from the characteristics of the purge valve itself, and the purge valve is determined according to the flow passage area. The drive duty is calculated. Further, in this prior art, when a purge valve that adjusts the flow rate with a duty is used, the target flow path area is corrected in consideration of the purge valve flow rate characteristic gain calculated from the purge valve drive voltage. Yes. In other words, in the duty-controlled purge valve, when the purge valve drive voltage decreases, the slope of the flow rate characteristic may change even when driven with the same basic duty. The valve opening delay in the purge valve is eliminated by adding a rising duty to the basic duty, but this rising duty depends on the purge valve drive voltage (battery voltage) and temperature. Therefore, the rising duty increases as the drive voltage decreases, and the duty increases as the temperature rises.
[0003]
[Patent Document 1]
JP-A-6-93900
[Patent Document 2]
JP 2000-27718 A
[0004]
[Problems to be solved by the invention]
As shown in FIG. 8, the slope of the straight line “a” representing the flow rate characteristic representing the relationship between the duty and the flow rate ratio in the purge valve for duty control is basically “1”, and the flow rate ratio is 100% (duty 100%). The purge valve opens fully. In this purge valve, immediately after the start of energization, there is an electrical response delay, so the energization does not start immediately after energization, but there is an invalid energization time from the start of energization to the start of opening (there is a valve opening delay) . In FIG. 8, a straight line a is shown with the end point of the invalid energization time as the duty 0%. In the vicinity of 0% duty, the purge gas flowing through the purge valve does not flow as shown by the straight line a. Therefore, normally, a lower limit duty is set such that a duty lower than this is not used. That is, immediately after the engine is started, the purge valve is opened little by little, and when the flow rate is ensured to some extent and the degree of vapor concentration is known, the duty below the lower limit duty is not used. Here, the “vapor concentration” represents the ratio of evaporated fuel contained in the purge gas per 1% of the purge rate. “Purge rate” refers to the ratio of the purge gas flow rate to the intake air amount.
[0005]
By the way, in the evaporative fuel purge control apparatus as in the above prior art, when a duty-controlled purge valve is used, the flow rate linearity of the duty decreases due to a change in the operating state, for example, intake pipe negative pressure (intake pressure), and purge control is performed. And air-fuel ratio controllability may deteriorate.
[0006]
That is, as shown in FIG. 9, the target of the flow rate ratio (purge flow rate / full open purge flow rate) corresponding to the target value of drive duty (target drive duty) due to changes in the operating state such as negative pressure (intake pipe negative pressure). Deviation occurs between the value (target flow rate ratio) and the actual flow rate ratio (decrease in duty flow rate linearity). Due to the decrease in the flow rate linearity, the target purge flow rate corresponding to the target drive duty cannot be obtained when the target drive duty is determined with respect to the target flow rate (target purge flow rate) and the purge valve is driven. For this reason, there is a possibility that purge control corresponding to various purge requests such as how much purge gas should be put into the intake system cannot be performed as required (deterioration of purge controllability). Furthermore, when the flow rate linearity of the duty decreases, the actual purge flow rate (actual flow rate of purge gas) deviates from the target purge flow rate corresponding to the target drive duty. For this reason, the learning value of the vapor concentration itself is also shifted, and the actual purge flow rate cannot be accurately estimated, thereby deteriorating the air-fuel ratio controllability.
[0007]
Such a problem may occur when a duty control purge valve that is closed by intake pipe negative pressure is used. In this barge valve, the force pushing the valve body biased in the valve closing direction in the same direction increases as the intake pipe negative pressure increases (the intake pressure decreases, that is, the closer to the vacuum side value). It is comprised so that it may become.
[0008]
In the purge valve having such a structure, as the intake pipe negative pressure increases, that is, the difference between the intake pipe negative pressure and the atmospheric pressure (interval differential pressure) increases, the purge valve is less likely to open on the low duty side. (Purge valve characteristics). For this reason, there is a possibility that the flow rate of the purge gas corresponding to the drive duty cannot be obtained. Such a tendency becomes more prominent when the drive voltage is lowered.
[0009]
The above-described problem is not only when using a duty-controlled solenoid valve that controls the flow rate with a duty as a purge valve, but also by changing the opening by giving a drive signal with a current value corresponding to the target opening. This may also occur when using a solenoid valve that controls the flow rate (hereinafter referred to as a solenoid type purge valve). That is, this solenoid type purge valve may also occur when using the above-described characteristic that the purge valve is difficult to open on the low duty side (purge valve characteristic). The reason for this is that when a solenoid type purge valve is used, the purge valve is driven by determining the current value of the drive signal (target drive amount) according to the target opening. This is because the degree may deviate from the target opening, and the flow rate of the purge gas corresponding to the current value cannot be obtained. The current value of the drive signal in the solenoid type purge valve corresponds to the duty in the duty control purge valve.
[0010]
Further, the deviation between the target flow rate ratio corresponding to the target drive duty and the actual flow rate ratio (decrease in the flow linearity) due to the change in the operating state such as the intake pipe negative pressure as described above opens as the intake pipe negative pressure increases. This can occur with either a duty-controlled purge valve or a solenoid-type purge valve that has characteristics that facilitate it. This purge valve has a structure that is opened by the intake pipe negative pressure, that is, the force that pushes the valve body biased by a spring or the like in the valve closing direction in the same direction increases as the intake pipe negative pressure increases (intake pressure). It is configured to become smaller (as the value becomes smaller).
[0011]
The present invention has been made paying attention to such a conventional problem, and its purpose is to be able to correct fluctuations in flow characteristics due to changes in operating conditions such as intake pipe negative pressure, purge controllability, It is an object of the present invention to provide an evaporated fuel purge control device for an internal combustion engine that can improve air-fuel ratio controllability and drivability.
[0012]
[Means for Solving the Problems]
The means for achieving the above object and the effects thereof will be described below.
The invention according to claim 1 includes an evaporative fuel processing mechanism that purges the evaporated fuel adsorbed by the canister to the intake system of the internal combustion engine together with air via a purge valve, and evaporates the internal combustion engine that performs purge control and air-fuel ratio control. In the fuel purge control device, the fuel purge control device includes target drive amount calculation means for calculating a target drive amount that is a target value of the purge valve drive amount from a target purge flow rate, and the calculation means depends on characteristics of the purge valve, A deviation amount between the target flow rate ratio corresponding to the target drive amount and the actual flow rate ratio is estimated from a parameter such as an intake pressure representing an operating state and the target flow rate ratio, and the target drive according to the estimated deviation amount The gist is to calculate the amount.
[0013]
As described above, in the above-described prior art, the flow rate of the purge gas corresponding to the target drive duty cannot be obtained due to a change in the operation state such as the intake pressure (intake pipe negative pressure) or the like (the flow rate linearity of the duty is reduced).
[0014]
On the other hand, according to the first aspect of the present invention, the amount of deviation between the target flow rate ratio corresponding to the target drive amount and the actual flow rate ratio, which depends on the characteristics of the purge valve, can be expressed as an intake pressure or the like representing the operating state. The target drive amount is calculated from the parameter and the target flow rate ratio, and the target drive amount corresponding to the estimated deviation amount is calculated. Therefore, the flow rate of the purge gas corresponding to the target drive amount is obtained, and the flow rate linearity of the purge valve drive amount is obtained. Therefore, it is possible to correct the change in the flow characteristic due to the change in the differential pressure between the valves (the pressure difference between the inlet side and the outlet side of the purge valve), that is, the change in the intake pressure (negative pressure in the intake pipe). The fuel ratio controllability and drivability can be improved. The “purge valve characteristic” herein refers to, for example, a characteristic that the purge valve is more difficult to open as the intake pressure becomes smaller (the intake pipe negative pressure becomes larger), or conversely, the intake pipe negative pressure becomes larger. A characteristic that makes it easier to open. The “target flow ratio” refers to the ratio of the target flow rate (target purge flow rate) to the fully open flow rate (full open purge flow rate).
[0015]
According to a second aspect of the present invention, in the evaporative fuel purge control device for an internal combustion engine according to the first aspect of the present invention, the apparatus further comprises an actual flow rate calculating means for calculating an actual flow rate of the purge gas flowing while the purge valve is being driven. When calculating the actual flow rate of the purge gas from the operation state and the drive amount, the gist is to correct the deviation amount from a parameter such as an intake pressure representing the operation state and the drive amount.
[0016]
In the above prior art, the following problems may occur. That is, even if the influence of the invalid energizing time is ignored, the flow rate characteristic representing the relationship between the duty ratio and the flow rate ratio cannot be a straight line with a slope of “1” due to the characteristics of the purge valve, resulting in an error in the flow rate calculation. However, the air-fuel ratio controllability may be deteriorated. The reason is that, as shown in FIG. 10, the slope around the duty 0% becomes smaller and the duty around 100% is reduced due to the influence of the electrical response delay of the purge valve (electrical response delay at ON-OFF). This is because the inclination tends to increase. The actual purge gas flow rate (purge gas actual flow rate) cannot be accurately estimated due to such flow rate calculation errors. For this reason, it is not possible to accurately calculate the estimated purge rate necessary for calculating the correction amount of the injection amount performed when the purge control is executed, for example, the reduction amount of the injection amount, which may adversely affect the air-fuel ratio control. There is.
[0017]
On the other hand, according to the second aspect of the present invention, when the actual flow rate of the purge gas is calculated from the operation state of the engine speed, the load, etc. and the drive amount of the purge valve, the target flow rate ratio and the actual flow rate ratio The amount of deviation is corrected from a parameter such as intake pressure representing the operating state and a drive amount (for example, drive duty). For this reason, the slope of the flow rate characteristic decreases near the minimum value (duty 0%) of the drive amount and increases near the maximum value (duty 100%) of the drive amount due to the influence of the electrical response delay of the purge valve. Even so, the actual flow rate of the purge gas during the purge control can be accurately obtained. As a result, the estimated purge rate can be calculated with high accuracy, and air-fuel ratio controllability and drivability can be further improved.
[0018]
According to a third aspect of the present invention, in the evaporative fuel purge control device for an internal combustion engine according to the first or second aspect, the purge valve is a duty-controlled purge valve that adjusts a flow rate according to a drive duty, and the target drive The gist of the amount calculation means is to calculate a target drive duty as the target drive amount. According to this configuration, it is possible to obtain a purge gas flow rate according to the target drive duty.
[0019]
According to a fourth aspect of the present invention, in the evaporated fuel purge control apparatus for an internal combustion engine according to the third aspect, the target drive amount calculation means is configured such that the flow rate ratio with respect to the change amount of the drive duty on the lower duty side as the intake pressure increases. The gist is to calculate the target drive duty according to the deviation amount from a two-dimensional map that is set so that the amount of change in the difference is larger.
[0020]
As a prior art different from the prior art, in the prior art disclosed in Patent Document 2, the opening of the purge valve is referred to by interpolating the map based on the intake pipe pressure (corresponding to the intake pressure) and the target purge flow rate. Is set. The map stores a smaller opening of the purge valve as the intake pipe pressure detected by the absolute value is lower (negative pressure is larger) and the target purge flow rate is smaller. The map stores a larger value of the opening degree of the purge valve as the intake pipe pressure is higher (negative pressure is smaller) and the target purge flow rate is larger.
[0021]
However, in this prior art, the smaller the intake pressure (the greater the intake pipe negative pressure), the smaller the purge valve opening is set. For this reason, when a purge valve having a structure that is closed by negative pressure is used as the duty control purge valve, the purge valve is less likely to open on the low duty side as the intake pressure becomes smaller. I can't get it.
[0022]
On the other hand, according to the fourth aspect of the present invention, the target drive duty corresponding to the deviation amount is the amount of change in drive duty on the low duty side as the intake pressure increases (intake pipe negative pressure decreases). It is calculated from a two-dimensional map set so that the amount of change in the flow rate ratio with respect to For this reason, the target drive duty is set so that the purge gas flows more on the low duty side as the intake pressure becomes larger (load becomes smaller). As a result, when a duty control purge valve that is closed by negative pressure is used, the flow rate of the purge gas corresponding to the drive duty can be obtained on the low duty side even in an operation state where the intake pressure is high. Conversely, the smaller the intake pressure (the larger the load), the smaller the amount of change in the flow rate ratio relative to the amount of change in drive duty on the low duty side, and the flow rate characteristic approaches a straight line with a slope of “1”. Flow rate linearity is ensured. Therefore, even when a purge valve having a structure that is closed by a negative pressure is used as a duty control purge valve, it is possible to correct fluctuations in the flow rate characteristic due to changes in the operating state such as intake pressure, and so on. It is possible to improve drivability.
[0023]
According to a fifth aspect of the present invention, in the evaporative fuel purge control device for an internal combustion engine according to the third or fourth aspect, the actual flow rate calculation means is configured to reduce the flow rate ratio change amount on the low duty side as the intake pressure increases. Calculating the actual flow rate ratio according to the deviation amount from a two-dimensional map set so that the change amount of the drive duty is smaller, and calculating the actual flow rate of the purge gas from the calculated actual flow rate ratio; Is the gist.
[0024]
According to this configuration, the actual flow rate ratio according to the deviation amount is based on the two-dimensional map set so that the change amount of the drive duty with respect to the change amount of the flow rate ratio becomes smaller on the low duty side as the intake pressure becomes larger. Calculated. For this reason, the actual flow rate of the purge gas can be accurately obtained even when a duty control purge valve that is closed by negative pressure is used. This makes it possible to calculate the estimated purge rate with high accuracy even when using a duty control purge valve that closes by negative pressure, and further improves purge controllability, air-fuel ratio controllability, and drivability. Can be achieved.
[0025]
According to a sixth aspect of the present invention, in the evaporative fuel purge control device for an internal combustion engine according to any one of the first to fifth aspects, the lower limit value of the drive amount is set in order to ensure the flow rate linearity of the drive amount. The gist of the present invention is to include a lower limit value calculating means for calculating the lower limit value of the linearity based on the battery voltage and the intake pressure.
[0026]
Conventionally, the linearity lower limit value is determined by only one value, for example, battery voltage. That is, since the intake pressure is not considered when setting the linearity lower limit value, the flow rate of the purge gas changes due to the change of the intake pressure, and the flow rate of the purge gas corresponding to the drive amount such as the drive duty cannot be obtained.
[0027]
On the other hand, according to the invention described in claim 6, the linearity lower limit value set as the lower limit value of the drive amount in order to ensure the flow rate linearity of the purge valve drive amount is based on the battery voltage and the intake pressure. Fluctuate. Therefore, the actual flow rate of the purge gas during the purge control can be obtained more accurately, and the estimated purge rate can be calculated with higher accuracy. Thereby, the air fuel ratio controllability and drivability can be further improved.
[0028]
According to a seventh aspect of the invention, in the evaporative fuel purge control device for an internal combustion engine according to the sixth aspect, the lower limit value calculating means increases the linearity lower limit value as the battery voltage decreases, and increases the intake pressure. The gist is to calculate the linearity lower limit value from a two-dimensional map that is set so that the lower limit value becomes larger as the value becomes smaller.
[0029]
According to this configuration, the linearity lower limit value is set to a larger value as the battery voltage decreases, and is set to a larger value as the intake pressure decreases. For this reason, the optimal linearity lower limit value according to the battery voltage and the intake pressure can be set, and the region in which the flow rate linearity of the purge valve drive amount is ensured can be maximized.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
An evaporative fuel purge control apparatus for an internal combustion engine according to an embodiment of the present invention will be described with reference to FIGS.
[0031]
First, an outline of the evaporated fuel purge control device will be described with reference to FIG.
As shown in FIG. 1, the internal combustion engine 10 includes a fuel injection valve 12 that injects fuel from a fuel tank 21 to a combustion chamber 11 via a fuel supply path (not shown), and the injected fuel and intake. A spark plug 13 is provided for igniting the air-fuel mixture. The combustion chamber 11 is connected to an intake passage 14 constituting a part of the intake system and an exhaust passage 15 constituting a part of the exhaust system. A surge tank 16 is provided in the middle of the intake passage 14, and a throttle valve (for example, electronically controlled) 17 for adjusting the amount of intake air is further provided on the upstream side.
[0032]
On the other hand, the evaporated fuel purge control device is provided with an evaporated fuel processing mechanism 30. The evaporative fuel processing mechanism 30 includes a canister 31 connected to the fuel tank 21 via a vapor passage 32, and a purge passage 33 connecting the canister 31 and the surge tank 16 constituting the intake system. The evaporative fuel processing mechanism 30 further includes an air introduction passage 34 for introducing air into the canister 31 and a purge valve (VSV) 35 for opening and closing the purge passage 33.
[0033]
Here, the evaporated fuel generated in the fuel tank 21 is introduced into the canister 31 from the fuel tank 21 through the vapor passage 32 and is once adsorbed by the adsorbent provided therein. Then, the purge valve 35 is opened and the atmosphere is introduced into the canister 31 through the atmosphere introduction passage 34, so that the fuel adsorbed in the canister 31 is purged as purge gas into the surge tank 16 through the purge passage 33 ( Released). The fuel contained in the purge gas is combusted in the combustion chamber 11 together with the fuel injected from the fuel injection valve 12. Further, the flow rate of the purge gas purged to the intake system (surge tank 16) in this way is adjusted by the purge valve 35. The purge valve 35 is a duty-controlled purge valve that adjusts the flow rate by adjusting the opening according to the drive duty of the electrical signal that drives the valve. The purge valve 35 has a structure that is closed by the negative pressure described above, that is, the force that pushes the valve body biased by a spring or the like in the valve closing direction in the same direction increases as the intake pipe negative pressure increases (the vacuum side). A purge valve is used that is configured to be larger (closer to the value).
[0034]
Further, purge control for the internal combustion engine 10 and air-fuel ratio control that is control of the fuel injection amount by the fuel injection valve 12 are performed by the electronic control unit 40 in an integrated manner. In order to execute each of these controls, the electronic control device 40 is connected with various sensors for detecting the operating state of the internal combustion engine 10 and the detection signals from these sensors are appropriately captured.
[0035]
For example, the electronic control unit 40 is provided in the intake pressure sensor 51 for detecting the intake pressure (intake pipe negative pressure), which is the pressure in the surge tank 16, and the exhaust passage 15. The detection signal of the oxygen sensor 52 for detecting the (fuel ratio) is input. Further, detection signals from a rotational speed sensor 53 for detecting the engine rotational speed, an accelerator sensor 54 for detecting the depression amount (accelerator opening) of an accelerator pedal (not shown), and the like are input to the electronic control unit 40, respectively. ing.
[0036]
Each control such as purge control and air-fuel ratio control is executed by the electronic control unit 40 based on the operating state of the internal combustion engine 10 and the running state of the vehicle detected by these sensors 51 to 54 and the like. In addition, the electronic control device 40 includes a program 41 for executing each control, a calculation map, a memory 41 that stores various data calculated when the control is executed, and the like.
[0037]
Here, the air-fuel ratio control and the purge control will be briefly described. The air-fuel ratio control is based on the output of the oxygen sensor 52 so that the weight ratio of the intake air amount to the fuel injection amount, that is, the air-fuel ratio (A / F) is basically kept near the theoretical air-fuel ratio. This is performed by feedback control of the 12 fuel injection amounts.
[0038]
On the other hand, in the purge control, since the vapor concentration is not known immediately after the engine is started, the purge valve 35 is opened little by little. When the purge valve 35 is opened at once, the air-fuel ratio (A / F) or the air-fuel ratio feedback control center (F / B center) is shifted. Therefore, even if there is a shift, the purge valve 35 is slowly moved to the extent that the air-fuel ratio feedback is applied. Open it little by little. In this way, the initial vapor concentration is determined (learning of vapor concentration).
[0039]
When the purge rate is known, the deviation of the A / F or F / B center by the oxygen sensor 52 (deviation from the control center 1.0) is regarded as the deviation of the vapor concentration, and the vapor concentration learning value is updated. If the oxygen sensor 52 is a linear oxygen sensor, the A / F deviation is known from the deviation of the vapor concentration, and if the oxygen sensor is not linear, the deviation of the F / B center of the air-fuel ratio feedback control from the deviation of the vapor concentration. Recognize.
[0040]
Thus, although the purge gas having such a flow rate is now purged, the deviation of the A / F or F / B center is considered to be caused by the deviation of the vapor concentration, and the vapor concentration learning value is updated. Actually, the learning value of the vapor concentration is updated little by little while seeing a slight deviation of the center of A / F or F / B. After that, the control enters that the lower limit area of the drive duty is not used.
[0041]
While the purge is being performed by the purge control, a fuel injection amount reduction correction is performed to subtract the fuel amount contained in the purge gas from the fuel injection amount injected from the fuel injection valve 12. In general, the fuel injection amount reduction correction is performed by adjusting the valve opening time of the fuel injection valve 12. The amount of fuel in the purge gas is estimated and calculated every predetermined time by the electronic control unit 40 based on the learned vapor concentration and the like. Then, based on the calculated fuel amount, an injection time necessary for injecting the fuel amount from the fuel injection valve 12 is calculated, and the above reduction correction is performed.
[0042]
Next, purge control executed by the electronic control unit 40 will be described with reference to FIGS.
First, the “VSV drive duty calculation routine” will be described with reference to FIG. A series of processes shown in the flowchart of FIG. 2 is executed by the electronic control unit 40 as an interrupt process every predetermined time.
[0043]
First, in step S110, a fully open purge flow rate (fully open purge air flow rate) is calculated based on the current operating state. This “fully opened purge flow rate” is a flow rate of purge gas that flows when the purge valve 35 is fully opened, based on a parameter representing the operating state of the internal combustion engine 10, for example, the engine rotational speed (engine rotational speed), the load factor, etc. It is calculated with reference to (not shown).
[0044]
In step S120, the target flow rate ratio (target purge flow rate / full open purge flow rate) is set from the target purge flow rate (target purge air flow rate) and the full open purge flow rate calculated in step S110. The flow rate of the purge gas to be put into the surge tank 16 is determined by various purge requests. As these purge requests, for example, there is a request for suppressing evaporation (evaporated fuel discharge into the atmosphere). The purge rate is determined from such a purge request. The purge rate may be calculated in step S120, or may be calculated by another routine and used. When the purge rate is determined, the target purge flow rate is obtained from the current intake air amount. A value obtained by dividing the target purge flow rate by the fully opened purge flow rate is set as a “target flow rate ratio”. Thus, in step S120, the target purge flow rate is determined by the purge rate, and the target flow rate ratio is obtained based on the target purge flow rate and the fully opened purge flow rate.
[0045]
Next, the process proceeds to step S130, where the target flow rate and the intake pressure (load) set in step S120 are set as the target drive duty that is the target value (target drive amount) of the purge valve 35 drive amount. To do. That is, the target drive duty is obtained with reference to the two-dimensional map shown in FIG. 3 based on the target flow rate ratio and the intake pressure (load) set in step S120. As shown in FIG. 3, this two-dimensional map shows the flow rate ratio to the amount of change in drive duty on the low duty side as the intake pressure increases (intake pipe negative pressure decreases) (the load decreases). The amount of change is set to be larger. Thus, the target drive duty is set so that the purge gas flows more on the low duty side as the intake pressure becomes larger (load becomes smaller). Conversely, the smaller the intake pressure (the larger the load), the lower the duty side, the change in the flow rate ratio relative to the change in the drive duty is set closer to the straight line with the slope “1”.
[0046]
As described above, in step S130, when the target drive duty is obtained from the target purge flow rate, the deviation amount between the target flow rate ratio and the actual flow rate ratio corresponding to the target drive duty depending on the characteristics of the purge valve 35 is determined as the intake pressure and the target flow rate. Estimated from the flow rate ratio. The purge controllability is improved by calculating a target drive duty corresponding to the estimated deviation amount.
[0047]
The advantage that the purge controllability can be improved is particularly effective when a duty-controlled purge valve 35 that is closed by negative pressure as described above is used. The reason for this is that when a purge valve that is closed by negative pressure is used, the larger the intake pressure, the more difficult the purge valve 35 opens on the low duty side, and the purge gas flow rate corresponding to the drive duty cannot be obtained. It is.
[0048]
Thus, after calculating the target drive duty in step S130, the process proceeds to step S140. In step S140, after performing various guard processes (for example, a lower limit guard process for the target flow rate), the purge valve 35 is driven at the target drive duty calculated in step S130. Thereafter, this process is temporarily terminated.
[0049]
Note that step S130 corresponds to target drive amount calculation means.
Next, the “estimated purge rate calculation routine” will be described with reference to FIG. A series of processes shown in the flowchart of FIG. 4 is executed as an interruption process every predetermined time by the electronic control unit 40.
[0050]
First, in step S210, the actual flow rate ratio (actual flow rate ratio) during the driving of the purge valve 35 is the actual flow rate ratio, which is 2 of the target drive duty and the intake pressure (load) calculated in step S130. Set the dimension map value. That is, the actual flow rate ratio is obtained with reference to the two-dimensional map shown in FIG. 5 based on the target drive duty and the intake pressure (load).
[0051]
Since the intake pressure (load) naturally changes when the purge valve 35 is driven, the actual flow rate of the purge gas does not become a flow rate corresponding to the drive duty. That is, the actual flow rate of the purge gas does not correspond to the driving duty. Therefore, in step S210, the actual flow rate ratio is a two-dimensional map value of the drive duty and the intake pressure (load).
[0052]
Further, the two-dimensional map shown in FIG. 5 is set so that the amount of change in duty with respect to the amount of change in flow rate ratio becomes smaller on the low duty side as the intake pressure becomes larger (load becomes smaller). Conversely, the smaller the intake pressure (the larger the load), the lower the duty ratio, the relationship between the flow rate ratio and the duty, that is, the change amount of the duty with respect to the change amount of the flow rate becomes a straight line with a slope “1” indicated by the broken line It is set to approach.
[0053]
Note that the map shown in FIG. 5 is obtained by switching the horizontal axis and the vertical axis of the map shown in FIG. 3, and the data of both maps only need to be the same. As data, if there is data suitable for the three parameters of the flow rate ratio, the intake pressure (load), and the driving duty, one or two maps may be provided. Whether both maps are set to one or two is determined by calculation convenience.
[0054]
Thus, in step S210, the deviation amount between the target flow ratio and the actual flow ratio corresponding to the target drive duty depending on the characteristics of the purge valve 35 is corrected by the intake pressure (negative pressure) and the drive duty, and the actual flow ratio. Is calculated.
[0055]
Next, proceeding to step S220, the actual flow rate (the flow rate of the barge gas that is actually flowing) is calculated. This actual flow rate is calculated by multiplying the fully opened purge flow rate calculated based on the current operating state in step S110 and the actual flow rate ratio calculated in step S210.
[0056]
When the actual flow rate of the purge gas is calculated by the above-described steps S210 and S220 based on the operation state such as the engine speed and the load factor and the drive duty, the deviation amount between the target flow rate ratio and the actual flow rate ratio depending on the characteristics of the purge valve 35 is calculated. The correction is made based on the intake pressure and the drive duty.
[0057]
Steps S210 and S220 correspond to actual flow rate calculation means.
After execution of step S220, the process proceeds to step S230, and an estimated flow rate is calculated. There is a time lag (transportation delay) until the purge gas purged to the surge tank 16 reaches the combustion chamber 11, and therefore the estimated flow rate is a delay of the actual flow rate calculated in step S220 in consideration of the transport delay. I'll ask you for it. That is, at each injection timing, the estimated flow rate of the purge gas and the flow rate of the purge gas that reaches the combustion chamber 11 is determined by delaying the actual flow rate. The transport delay depends on the pumping effect caused by the rotation of the internal combustion engine 10, that is, the engine rotation speed.
[0058]
Next, proceeding to step S240, an estimated purge rate is calculated from the estimated flow rate and intake air amount calculated at step S230. This estimated purge rate is a value obtained by dividing the estimated flow rate by the intake air amount.
[0059]
Next, the process proceeds to step S250, where the estimated purge rate calculated in step S240 and the learned value of the vapor concentration are multiplied to calculate a reduction amount of the injection amount (purge reduction amount), and only the calculated reduction amount is described above. Reduce the injection amount. Thereafter, this process is temporarily terminated.
[0060]
Next, the “duty guard processing routine” will be described with reference to FIG. A series of processes shown in the flowchart of FIG. 6 is executed by the electronic control unit 40 as an interrupt process every predetermined time.
[0061]
First, in step S310, the upper limit duty A is calculated as a correction limit based on the vapor concentration learning value. For example, the upper limit duty A is calculated as a correction limit based on the vapor concentration learning value so that a purge gas having a vapor concentration that reduces the injection amount to 40% or more is not put into the surge tank 16.
[0062]
Next, the process proceeds to step S320, and it is determined whether or not the required duty (the target drive calculated in step S130) exceeds the upper limit duty A calculated in step S310. If the requested duty exceeds the upper limit duty A, the process proceeds to step S330; otherwise, the process proceeds to step S340.
[0063]
In step S330, the upper limit duty A is set as a required duty.
Next, the process proceeds to step S340, and a two-dimensional map value of the battery voltage and the intake pressure (load) that is the intake pipe negative pressure is set as the linearity lower limit value B in order to ensure the flow rate linearity of the duty. That is, the linearity lower limit value B is obtained with reference to the two-dimensional map shown in FIG. 7 based on the battery voltage and the intake pressure (load).
[0064]
When the battery voltage deteriorates, the purge valve 35 becomes difficult to open, and as the intake pressure becomes smaller (load becomes larger), the purge valve 35 becomes harder to open. Therefore, the two-dimensional map shown in FIG. 7 is created so that the lower limit of the linearity value B is set as the battery voltage decreases and the intake pressure decreases.
[0065]
Next, it progresses to step S350 and it is determined whether the request | requirement duty is less than the linearity lower limit B. If the determination result is affirmative, the process proceeds to step S360, and purging is prohibited. On the other hand, if the determination result is negative, the process is temporarily terminated.
[0066]
As described above, in the duty guard processing routine of FIG. 6, when setting the linearity lower limit value B in order to ensure the flow rate linearity of the drive duty, the linearity lower limit value is determined by the battery voltage (applied voltage) and the intake pressure (negative pressure). B is varied.
[0067]
Note that step S340 corresponds to the lower limit value calculating means.
According to the embodiment configured as described above, the following operational effects can be obtained.
2, the amount of deviation between the target flow rate ratio and the actual flow rate ratio corresponding to the target drive duty depending on the characteristics of the purge valve 35 is estimated from the intake pressure and the target flow rate ratio in step S130 of FIG. A target drive duty (target drive amount) corresponding to the amount is calculated. For this reason, the flow rate of the purge gas according to the target drive duty is obtained, and the flow rate linearity of the duty is obtained. Therefore, it is possible to correct a change in the inter-valve differential pressure (a pressure difference between the inlet side and the outlet side of the purge valve 35), that is, a change in the flow rate characteristic due to a change in the intake pressure. Can be improved.
[0068]
When calculating the actual flow rate ratio based on the engine speed, the operating condition such as the load, and the drive duty in steps S210 and S220 in FIG. 4, the deviation amount between the target flow rate ratio and the actual flow rate ratio is calculated from the intake pressure and the drive duty. to correct. For this reason, the actual flow rate of the purge gas during the purge control is accurate even if the slope of the flow rate characteristic decreases near 0% duty and increases near 100% duty due to the influence of the electrical response delay of the purge valve. Can be requested. As a result, the estimated purge rate can be calculated with high accuracy, and air-fuel ratio controllability and drivability can be further improved.
[0069]
2, the drive duty corresponding to the amount of deviation between the target flow rate ratio and the actual flow rate ratio is such that the flow rate ratio with respect to the change amount of the drive duty becomes lower on the lower duty side as the intake pressure that is the intake pipe negative pressure increases. It is calculated from a two-dimensional map set so that the amount of change becomes larger. For this reason, the target drive duty is set so that the flow rate of the purge gas increases on the low duty side as the intake pressure increases (load decreases).
[0070]
As a result, when a duty-controlled purge valve 35 that is closed by negative pressure is used, the flow rate of purge gas corresponding to the drive duty can be obtained on the low duty side even in an operating state where the intake pressure is high. Further, the smaller the intake pressure (the larger the load), the smaller the amount of change in the flow rate ratio with respect to the amount of change in the drive duty on the low duty side, and the flow rate characteristic approaches the straight line with the slope “1”. Linearity is ensured. Accordingly, even when a duty control purge valve that is closed by negative pressure is used, fluctuations in flow rate characteristics due to changes in operating conditions such as intake pressure can be suppressed, and purge controllability, air-fuel ratio controllability, and driver Can be improved.
[0071]
・ By step S210 in FIG. 4, the actual flow rate ratio according to the amount of deviation between the target flow rate ratio and the actual flow rate ratio is such that as the intake pressure increases, the change amount of the drive duty with respect to the change amount of the flow rate ratio becomes smaller on the low duty side. It is calculated from a two-dimensional map (see FIG. 5) set to be For this reason, even when the duty control purge valve 35 is configured to be closed by negative pressure, the actual flow rate of the barge gas can be accurately obtained. This makes it possible to calculate the estimated purge rate with high accuracy even when using a duty control purge valve that closes by negative pressure, and further improves purge controllability, air-fuel ratio controllability, and drivability. Can be achieved.
[0072]
6, the linearity lower limit value B set as the lower limit value of the drive duty in order to ensure the duty flow rate linearity (purge valve drive amount linearity) is changed based on the battery voltage and the intake pressure by step S340 in FIG. . Therefore, the actual flow rate of the purge gas during the purge control can be obtained more accurately, and the estimated purge rate can be calculated with higher accuracy. Thereby, the air fuel ratio controllability and drivability can be further improved.
[0073]
By step S340 in FIG. 6, the linearity lower limit B is set to a larger value as the battery voltage is lowered, and is set to be a larger value as the intake pressure is reduced. For this reason, the optimal linearity lower limit B corresponding to the battery voltage and the intake pressure can be set, and the region in which the flow rate linearity of the duty is ensured can be maximized. Further, the linearity lower limit B is set so as to increase as the intake pressure decreases, so that the linearity of the flow characteristics is ensured even when the duty control purge valve 35 is closed by negative pressure. can do.
[0074]
In addition, the said one Embodiment can also change the structure suitably as follows, for example.
In the above embodiment, a duty-controlled electromagnetic valve that controls the flow rate with a duty is used as the purge valve 35, but the present invention is also applicable to the case where the solenoid-type purge valve described above is used as the purge valve 35. Is applicable.
[0075]
In the above embodiment, the purge valve 35 has a characteristic (purge valve characteristic) that is difficult to open as the intake pipe negative pressure increases, but the present invention is not limited to this. For example, the deviation between the target flow rate ratio and the actual flow rate ratio (decrease in the flow rate linearity) corresponding to the target drive duty due to changes in the operating state such as intake pressure, etc. (duration control with a characteristic that becomes easier to open as the intake pipe negative pressure increases The present invention can also be applied to the case of using a purge valve of solenoid type or a solenoid type.
[0076]
In the above-described embodiment, in the maps shown in FIGS. 3, 5, and 7, the intake pressure is used as one of the parameters indicating the operating state, but other parameters corresponding to the intake pressure are used as the parameters indicating the operating state. A parameter may be used.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an evaporated fuel purge control device for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a purge valve drive duty calculation routine according to one embodiment.
FIG. 3 is an explanatory diagram showing a map used in the routine of FIG. 2;
FIG. 4 is a flowchart illustrating an estimated purge rate calculation routine according to an embodiment.
5 is an explanatory diagram showing a map used in the routine of FIG.
FIG. 6 is a flowchart illustrating a duty guard processing routine according to an embodiment.
7 is an explanatory diagram showing a map used in the routine of FIG.
FIG. 8 is a graph showing basic flow characteristics of the purge valve.
FIG. 9 is a graph showing a flow rate characteristic of a purge valve that changes depending on a negative pressure.
FIG. 10 is a graph showing a flow rate characteristic of a purge valve having a structure closed by a negative pressure.
[Explanation of symbols]
B ... Linearity lower limit value, 10 ... Internal combustion engine, 30 ... Evaporative fuel processing mechanism, 31 ... Canister, 35 ... Purge valve.

Claims (7)

In an evaporative fuel purge control apparatus for an internal combustion engine that includes an evaporative fuel processing mechanism that purges evaporative fuel adsorbed to a canister together with air to an intake system of the internal combustion engine via a purge valve, and performs purge control and air-fuel ratio control,
A target drive amount calculation unit that calculates a target drive amount that is a target value of the purge valve drive amount from a target purge flow rate, the calculation unit corresponds to the target drive amount that depends on the characteristics of the purge valve. The amount of deviation between the target flow rate ratio and the actual flow rate ratio is estimated from a parameter such as an intake pressure representing an operating state and the target flow rate ratio, and the target drive amount corresponding to the estimated deviation amount is calculated. An evaporative fuel purge control device for an internal combustion engine, characterized in that: An actual flow rate calculating means for calculating an actual flow rate of the purge gas flowing while the purge valve is driven, and the calculating means calculates the deviation amount when calculating the actual flow rate of the purge gas from the operating state and the drive amount; 2. The evaporative fuel purge control device for an internal combustion engine according to claim 1, wherein correction is performed from a parameter such as an intake pressure representing a state and the drive amount. The purge valve is a duty-controlled purge valve that adjusts a flow rate according to a drive duty, and the target drive amount calculation means calculates a target drive duty as the target drive amount. An evaporative fuel purge control device for an internal combustion engine according to claim 1. The target drive amount calculation means determines the amount corresponding to the amount of deviation from a two-dimensional map that is set such that the amount of change in the flow rate ratio with respect to the amount of change in the drive duty increases on the low duty side as the intake pressure increases. The evaporative fuel purge control device for an internal combustion engine according to claim 3, wherein a target drive duty is calculated. The actual flow rate calculation means determines the amount corresponding to the amount of deviation from a two-dimensional map set so that the amount of change in the drive duty with respect to the amount of change in the flow rate ratio becomes smaller on the low duty side as the intake pressure increases. 5. The evaporative fuel purge control apparatus for an internal combustion engine according to claim 3, wherein an actual flow rate ratio is calculated, and an actual flow rate of the purge gas is calculated from the calculated actual flow rate ratio. The apparatus further comprises lower limit value calculating means for calculating a linearity lower limit value set as a lower limit value of the drive amount in order to ensure the flow rate linearity of the drive amount based on the battery voltage and the intake pressure. The evaporated fuel purge control device for an internal combustion engine according to any one of claims 1 to 5. The lower limit value calculating means determines the linearity lower limit value from a two-dimensional map that is set such that the lower the battery voltage is, the larger the linearity lower limit value is, and the lower the intake pressure is, the larger the lower limit value is. The fuel vapor purge control apparatus for an internal combustion engine according to claim 6, wherein:

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