JP4058897B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification technology for an internal combustion engine, and more particularly to a technology for efficiently purifying hydrocarbons (HC) when cold.
[0002]
[Prior art]
As this type of prior art, there is, for example, JP-A-7-91237. This prior art has two exhaust valves for each cylinder, and after joining the exhaust gas flowing out from the first exhaust valve of each cylinder, it leads to the HC adsorption catalyst, while from the second exhaust valve of each cylinder After the exhaust gas flowing out is merged, the exhaust gas is guided downstream of the HC adsorption catalyst, merged with the exhaust gas flowing out from the first exhaust valve, and led to a catalytic converter (so-called three-way catalyst).
[0003]
Here, at the time of cold start, only the first exhaust valve is operated, and the discharged HC is adsorbed by the HC adsorption catalyst. After the temperature of the HC adsorption catalyst rises and the adsorbed HC begins to be desorbed, the first exhaust valve is stopped and only the second exhaust valve is operated to be discharged in the cold state. A large amount of HC is trapped in the HC adsorption catalyst. When the temperature of the catalytic converter reaches a predetermined value or more, the first exhaust valve is operated, and hydrocarbons discharged in the cold state are guided to the catalytic converter to purify the exhaust gas, thereby efficiently purifying exhaust gas. Yes.
[0004]
Another conventional technique is disclosed in Japanese Patent Laid-Open No. 9-256840. In this prior art, an exhaust heating means, an HC adsorption catalyst, and a three-way catalyst are arranged in order from the upstream, and a large amount of HC is adsorbed by the HC adsorption catalyst at the time of starting the engine. Thus, the most downstream three-way catalyst is activated at an early stage by operating the exhaust heating means. As a result, the HC desorbed from the HC adsorption catalyst is efficiently purified by the three-way catalyst.
[0005]
Further, as another conventional technique, there is a technique disclosed in Japanese Patent Laid-Open No. 5-44447. In this prior art, the first catalyst is arranged at the most upstream, the HC adsorption catalyst is arranged downstream thereof, and a bypass path for bypassing the HC adsorption catalyst is provided, and the exhaust is led to the bypass path or HC adsorption. Switching means capable of selecting whether to lead to the catalyst is provided, and further, a second catalyst is provided downstream of the exhaust pipe joined at the downstream of the bypass passage and the downstream of the HC adsorption catalyst. When the engine is cold, such as when the engine is started, the exhaust is guided to the HC adsorption catalyst, and HC that could not be purified is adsorbed. When the first catalyst is activated, the exhaust gas is led to the bypass and directly flows into the second catalyst. By controlling the exhaust to be led to the HC adsorption catalyst when the second catalyst is activated, hydrocarbons that could not be treated in the cold are purified by the second catalyst. In addition, air is introduced from upstream of the HC adsorption catalyst for the purpose of assisting HC adsorption to the HC adsorption catalyst. By introducing air, the temperature rise of the HC adsorption catalyst is suppressed, and HC flowing in for a longer time than usual can be adsorbed.
[0006]
Another conventional technique for introducing air from the upstream side of the HC adsorption catalyst is disclosed in Japanese Patent Laid-Open No. 9-228828. In this prior art, an air introduction means is arranged at the uppermost stream, an HC adsorption catalyst is arranged downstream thereof, and a three-way catalyst is arranged downstream. When cold, the air introduction means is not operated, and the discharged HC is adsorbed by the HC adsorption catalyst. Air is introduced from the upstream of the HC adsorption catalyst when the temperature of the HC adsorption catalyst reaches a predetermined temperature at which the adsorbed HC begins to desorb. As a result, the exhaust gas is in an oxygen excess state, and HC flowing out of the HC adsorption catalyst is efficiently purified by the downstream three-way catalyst. The prior art also describes that the engine is operated lean as a method other than the introduction of secondary air. If the engine is operated lean, the exhaust is in an oxygen-excess state, so the same effect as the introduction of secondary air can be obtained.
[0007]
As a conventional technique in which an HC adsorption catalyst is applied to a V-type internal combustion engine, there is a technique disclosed in Japanese Patent Laid-Open No. 8-99033. In this prior art, a pre three-way catalyst is arranged in each bank's exhaust pipe, the exhaust from each bank is joined downstream, an HC adsorption catalyst is installed downstream, and the main three-way catalyst is further downstream. Is arranged.
[0008]
[Problems to be solved by the invention]
However, for example, in the technique disclosed in Japanese Patent Laid-Open No. 7-91237, although a high purification rate can be obtained, a high cost due to the need for a one-side valve stop mechanism becomes a problem. In addition, a complicated mechanism such as one-side valve stop and a complicated shape of the exhaust manifold section increase the heat mass, so that it takes a longer time to activate the catalyst than usual, and there is a problem that the purification rate is deteriorated. The Further, at the moment when it is determined that the temperature of the catalytic converter has become sufficiently high and the valve mechanism is controlled so that the exhaust gas passes through the HC adsorption catalyst side, the exhaust gas flowing into the catalytic converter is also at a low temperature because the HC adsorption catalyst is at a low temperature. As a result, a problem that the purification rate of hydrocarbons desorbed from the HC adsorption catalyst is temporarily reduced is also assumed.
[0009]
Further, in the technique of JP-A-9-256840, although purification efficiency is higher than usual, an exhaust heating means is installed at the most upstream, and when the heating means is operated, the HC adsorption catalyst is heated. HC desorption from the HC adsorption catalyst is also promoted, and HC desorbed before the most downstream catalyst is fully activated is released to the atmosphere. In addition, there is a conventional technique in which the most downstream catalyst itself is heated by a heating means such as an electric heater. However, if the temperature of the inflowing exhaust gas is low, the heating effect by the heating means is small and the HC purification rate is not improved so much. . When trying to increase the amount of heat generated by the heating means, a large amount of energy is required, which is not effective in terms of practicality.
[0010]
In the technique disclosed in Japanese Patent Laid-Open No. 5-44447, the purification rate is considered to be very high. However, the increase in heat mass and the cost increase due to the addition of the bypass mechanism are problems. Further, when the most upstream catalyst reaches an activation temperature of about 300 ° C., it is considered that a cooling means is inevitably required to keep the temperature of the HC adsorption catalyst below the HC desorption temperature of about 100 ° C. It is assumed to be up. Further, there are problems such as leakage of exhaust gas due to the provision of the valve mechanism and sticking due to deterioration of the valve. Similarly to the technique of Japanese Patent Laid-Open No. 7-91237, in this conventional technique, when the bypass valve is closed because the second catalyst is sufficiently active, the low-temperature exhaust gas that has passed through the HC adsorption catalyst flows into the second catalyst. Therefore, it is conceivable that the purification rate of HC flowing out from the HC adsorption catalyst is lowered due to the temperature of the second catalyst being lowered for a certain period.
[0011]
In the case of the technique of Japanese Patent Laid-Open No. 9-228828, although the purification efficiency is improved more than usual, the HC adsorption catalyst is disposed upstream of the three-way catalyst. It is considered that most of the HC desorbed from the HC adsorption catalyst is released to the atmosphere without being purified by the downstream three-way catalyst. In the technique of JP-A-8-99033, although the purification rate is improved by improving the capacity of the HC adsorption catalyst, the activation temperature of the three-way catalyst arranged downstream of the HC adsorption catalyst is reduced from the HC adsorption catalyst. Since it is higher than the desorption temperature, most of the desorbed HC is released to the atmosphere.
[0012]
[Means for Solving the Problems]
  For this reason, the invention according to claim 1
  Of a V-type internal combustion engine mounted horizontally in a vehicleAn HC adsorption catalyst that adsorbs hydrocarbons that flow in in the cold and exhausts the adsorbed hydrocarbons when the temperature exceeds a predetermined value is provided in each exhaust pipe that guides the exhaust of each of the cylinder groups divided into a plurality of sections. ,
  These exhaust pipes are joined together downstream of each HC adsorption catalyst, and an exhaust purification catalyst for purifying at least hydrocarbons is disposed in the exhaust pipe downstream from the junction,
  When the V-type internal combustion engine is cold, the exhaust temperature is controlled by the cylinder group located on the rear bank side.The temperature raising operation for raising the temperature early is performed until the temperature of the exhaust purification catalyst reaches a predetermined temperature.
[0013]
According to the invention of claim 1,
When some of the cylinder groups are heated during cold, the HC adsorption catalyst of the cylinder group that does not perform the temperature raising operation reaches a temperature at which the adsorbed HC is desorbed before the exhaust gas purification on the downstream side. An activation temperature is reached at which the catalyst can sufficiently purify the exhaust. The temperature raising operation of some of the cylinder groups may be performed until the exhaust purification catalyst reaches the activation temperature, but may be performed until a predetermined temperature close to the activation temperature is reached.
[0014]
Thereafter, when the temperature of the HC adsorption catalyst in the cylinder group not performing the temperature increasing operation further rises and reaches the HC desorption temperature, the HC desorbed from the HC adsorption catalyst is activated by the exhaust purification. Purified efficiently by the catalyst. The purification performance of HC adsorbed on the HC adsorption catalyst of the cylinder group that performs the temperature raising operation is the same as that in the case where the normal HC adsorption catalyst and the exhaust purification catalyst are arranged in series. HC purification efficiency at the time can be greatly improved.
[0015]
  Further, the valve stop mechanism and the exhaust passage switching mechanism as in the technique of Japanese Patent Laid-Open No. 7-91237 are not required, and the exhaust manifold shape is not complicated, so that the exhaust purification catalyst can be realized at low cost. Since the upstream heat mass can also be reduced, activation of the exhaust purification catalyst can be accelerated.
  Further, since the exhaust gas is always supplied to the HC adsorption catalyst of the cylinder group not performing the temperature raising operation, the exhaust gas is discharged to the HC adsorption catalyst side which is a problem in the techniques of Japanese Patent Laid-Open Nos. 7-91237 and 5-44447. When the flow path is switched, a temporary temperature drop of the downstream exhaust purification catalyst can be avoided, and HC flowing out of the HC adsorption catalyst can be efficiently purified from the beginning.
  In a normal vehicle, exhaust gas is discharged rearward. In the case of a V-type internal combustion engine mounted horizontally on the vehicle, the exhaust piping on the front bank side is longer than that on the rear bank side. Further, the front bank side is easily cooled by the vehicle speed wind.
  Therefore, the temperature rise operation is performed in the cylinder group located on the rear bank side, and the temperature rise operation is performed on the exhaust purification catalyst and the temperature rise operation is performed on the cylinder group located on the front bank side so as not to perform the temperature rise operation. The temperature increase delay of the HC adsorption catalyst of the cylinder group that does not perform the operation can be effectively performed.
[0016]
  The invention according to claim 2
  HC adsorption that adsorbs hydrocarbons that flowed in the cold to each exhaust pipe that guides the exhaust of each cylinder group divided into a plurality of cylinders of a multi-cylinder internal combustion engine, and discharges the adsorbed hydrocarbons when the temperature exceeds a predetermined value Arrange the catalyst,
  These exhaust pipes are joined together downstream of each HC adsorption catalyst, and an exhaust purification catalyst for purifying at least hydrocarbons is disposed in the exhaust pipe downstream from the junction,
  A temperature increasing operation for quickly increasing the exhaust temperature in some cylinder groups when cold is performed until the temperature of the exhaust purification catalyst reaches a predetermined temperature,
  In addition, the internal combustion engine is divided into three or more cylinder groups, and the number of cylinder groups to be heated up can be switched.
  According to the invention of claim 2,
  For example, the temperature increase can be further promoted by increasing the number of cylinder groups that are heated at extremely low temperatures according to the temperature state.
[0017]
  Further, according to claim 3The invention
  Exhaust valveThe temperature rising operation is performed by operating the valve opening time earlier.
  Claim 3According to the invention according to
  By advancing the opening timing of the exhaust valve, the temperature of the exhaust when exhausted from the combustion chamber is raised, and the temperature raising operation is performed.
  In this way, it is possible to carry out an inexpensive and efficient temperature raising operation only by controlling a normally mounted variable valve timing device or the like.
  Also,Claim 4The invention according to
  The temperature raising operation is performed by operating at a rich air-fuel ratio.
  Claim 4According to the invention according to
  By operating at a rich air / fuel ratio, the temperature of the exhaust is increased and a temperature raising operation is performed.
[0018]
  In this way, it is not necessary to add a special device, and it is possible to carry out an efficient temperature raising operation that is inexpensive and does not increase in heat mass.
  Also,Claim 5The invention according to
  The spark ignition engine is characterized in that the temperature raising operation is performed by operating with a delayed ignition timing.
[0019]
  Claim 5According to the invention according to
  By delaying the ignition timing and delaying the end of the combustion stroke, the temperature of the exhaust when discharged from the combustion chamber is raised, and the temperature raising operation is performed.
  In this way, a special mechanism is not necessary for performing the temperature raising operation, and an efficient temperature raising operation can be performed at low cost without an increase in heat mass.
[0020]
  Also,Claim 6The invention according to
  In the compression ignition engine, the temperature raising operation is performed by at least one of delaying the fuel injection timing or reducing the intake air.
  Claim 6According to the invention according to
  By delaying the ignition timing and retarding ignition combustion, and by restricting the intake air, the residual gas ratio in the combustion chamber increases, and the temperature of the exhaust when exhausted from the combustion chamber is increased, and the temperature raising operation is performed. Is done.
[0021]
In the case of a recent diesel engine having an electronically controlled injection system in which the injection timing can be controlled, no additional device is required. If the intake throttle is provided for the purpose of detailed control of the EGR rate, it can be used for temperature rise control. As described above, it is possible to perform an inexpensive and efficient heating operation without adding a special device.
[0022]
  Also,Claim 5The invention according to
  During the period in which the temperature raising operation is performed in some cylinder groups, the low exhaust temperature operation in which the exhaust temperature is lowered from the normal operation is performed in the other cylinder groups in which the temperature raising operation is not performed.
  Claim 5According to the invention according to
  The HC adsorption catalyst of the cylinder group that performs the low exhaust temperature operation in order to perform the low exhaust temperature operation in the other cylinder groups that do not perform the temperature increase operation during the period during which some cylinder group soot operation is performed The desorption of HC adsorbed on can be delayed as much as possible.
[0023]
  For this reason, it is possible to increase the time required to reach the temperature at which the downstream exhaust purification catalyst is activated, and further improve the purification efficiency of HC desorbed from the HC adsorption catalyst of the cylinder group that performs the low exhaust temperature operation. Can be improved.
  Also,Claim 8The invention according to
  A low exhaust temperature operation is performed by operating at a lean air-fuel ratio.
[0024]
  Claim 8According to the invention according to
  In order to perform low exhaust temperature operation by operating at a lean air-fuel ratio, when applied to a spark ignition engine capable of lean burn or so-called stratified combustion, no additional special equipment is required, which is costly It becomes possible to purify the exhaust gas efficiently.
  Also,Claim 9The invention according to
  A low exhaust temperature operation is performed by introducing air from upstream of the HC adsorption catalyst disposed in the corresponding exhaust pipe.
[0025]
  Claim 9According to the invention according to
  In general, there is known a description of introducing air into an exhaust pipe upstream of an exhaust purification catalyst as means for accelerating the activation of the exhaust purification catalyst. If the engine system has such a device in advance, the effect of the low exhaust temperature operation can be obtained at low cost by diverting the device.
[0026]
  Also, aboveClaims 8 and 9In the invention according to the present invention, the HC desorbed from the HC adsorption catalyst of the cylinder group performing the temperature raising operation and the surplus oxygen flowing from the exhaust pipe of the cylinder group not performing the temperature raising operation react with each other in the exhaust purification catalyst. In addition, the HC can be treated, and at the same time, the reaction heat can accelerate the activity of the exhaust purification catalyst.
  Also,Claim 10The invention according to
  The cylinder group that performs the temperature raising operation and the cylinder group that does not perform the temperature raising operation are changed according to the number of times of the temperature raising operation.
[0027]
  Claim 10According to the invention according to
  Since the temperature raising operation is performed uniformly in all cylinders, it is possible to make the use state of the variable valve timing device, the fuel injection device, the ignition device, etc. constant in all cylinders, and the devices in a specific cylinder group become abnormal It becomes difficult to cause problems such as deterioration.
  Also,Claim 11The invention according to
  A cylinder group for performing the temperature raising operation is determined in advance, and only the exhaust pipe of the cylinder group is kept warm.
[0028]
  Claim 11According to the invention according to
  Since only the exhaust pipes of the cylinder groups that perform a predetermined temperature raising operation are kept warm, the effect of the temperature raising operation is further obtained, and the effect of the low exhaust temperature operation is obtained to the maximum because there is no heat retention.
[0031]
  Also,Claim 12The invention according to
  Each of the HC adsorption catalysts is disposed in an exhaust pipe portion where exhaust from each cylinder of each cylinder group merges.
  Claim 12According to the invention, the number of HC adsorption catalysts can be reduced, the exhaust pipe structure can be simplified, and the heat mass can be reduced.
[0032]
  Also,Claim 13The invention according to
  It is divided into two cylinder groups, and one cylinder group is temperature-raised.
  Claim 13According to the invention according to
  The present invention can be applied in the simplest form.
[0033]
  Also,Claim 14The invention according to
  Control is performed to suppress a torque difference between a cylinder group that performs a temperature raising operation and a cylinder group that does not.
[0034]
  Claim 14According to the invention according to
  Since a torque difference occurs between the cylinder group that performs the temperature raising operation and the cylinder group that does not perform the temperature raising operation as it is, for example, the cylinder group that does not perform the temperature raising operation with respect to the cylinder group that performs the temperature raising operation by retarding the ignition timing The torque difference can be suppressed by correcting the amount of fuel injection to be reduced, and the rotation fluctuation in the low rotation region can be suppressed.
[0035]
  Also,Claim 15The invention according to
  The cylinder group that performs temperature rising operation and the cylinder group that does not performThe number of cylinders is the same, andThe ignition sequence is set alternately.
  Claim 15According to the invention according to
  The high concentration HC desorbed from the HC adsorption catalyst of the cylinder group not performing the temperature raising operation is dispersed and guided to the exhaust purification catalyst, so that the HC can be efficiently and efficiently purified, and due to the difference in operation When fluctuations such as torque occur at high frequencies, it is possible to reduce how the human body feels.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a system configuration of a first embodiment in which the present invention is applied to a spark ignition engine capable of lean air-fuel ratio operation (lean burn). In the present embodiment, a four-cylinder engine is shown as an example, but a multi-cylinder engine can be configured similarly.
[0037]
The exhaust pipe connected to the combustion chamber 2 of the first cylinder group consisting of # 2 and 3 cylinders of the engine main body 1 is joined to form a first exhaust pipe 3, and the first exhaust pipe 3 has a first HC adsorption. A catalyst 4 is disposed. Further, the exhaust pipe connected to the combustion chamber 2 of the second cylinder group consisting of # 1 and 4 cylinders is joined to form a second exhaust pipe 5, and the second HC adsorption catalyst 6 is connected to the second exhaust pipe 5. Is disposed. The first HC adsorption catalyst 4 and the second HC adsorption catalyst 6 have a function of adsorbing HC in the exhaust when it is cold and discharging the adsorbed HC when the temperature reaches a predetermined value or more.
[0038]
The first exhaust pipe 3 and the second exhaust pipe 5 are joined downstream of the first HC adsorption catalyst 4 and the second HC adsorption catalyst 6, and the exhaust purification catalyst is placed downstream of the junction 7. 8 is provided. The exhaust purification catalyst 8 may be a normal three-way catalyst that reduces NOx while oxidizing HC and CO.
The first HC adsorption catalyst 5, the second HC adsorption catalyst 6, and the exhaust purification catalyst 8 are provided with temperature sensors 9, 10, and 11, respectively, and each part detected by these temperature sensors 9, 10, and 11 Is input to the engine control unit (ECU). In addition to these temperature signals, the ECU 12 receives at least signals from an engine speed sensor (crank angle sensor) and an intake air amount sensor (air flow meter) (not shown).
[0039]
The engine body 1 includes a fuel injection valve 13 and a spark plug 14, and controls to inject an optimal amount of fuel and ignite at an optimal timing according to the calculation result of the ECU 12. The first throttle valve 16 is connected to the first intake pipe 15 connected to the combustion chamber 2 of the first cylinder group, and the second intake pipe 17 is connected to the second intake pipe 17 connected to the combustion chamber 2 of the second cylinder group. A throttle valve 18 is provided, and the throttle valves 16 and 18 are controlled in opening degree according to the output of an accelerator opening sensor (not shown).
[0040]
Below, the control calculated by ECU12 is demonstrated. FIG. 2 is a block diagram illustrating a control flow in the first embodiment. It is determined whether or not the temperature raising operation is performed by the temperature raising operation permitting means in accordance with the temperature of the exhaust purification catalyst 8 measured by the temperature sensor 9 and other operating conditions.
When performing the temperature raising operation, the temperature rising operation is performed in the first cylinder group (# 2, 3 cylinder) by the temperature raising operation cylinder determining means, or the temperature raising operation is performed in the second cylinder group (# 1, 4 cylinder). The temperature raising operation is performed only for the cylinders selected to perform the temperature raising operation based on the calculated value of the temperature raising operation means.
[0041]
Thereafter, whether or not to perform low exhaust temperature operation in which the exhaust gas temperature is lower than that in the normal operation in the cylinder group that is not heated is determined whether the temperature of the HC adsorption catalyst 6 or 4 installed in the cylinder group that is not heated (temperature sensor 10). Alternatively, it is determined by the low exhaust temperature operation permission means according to (detected at 11).
When the low exhaust temperature operation is performed, the low exhaust temperature operation is performed based on the result calculated by the low exhaust temperature operation means.
[0042]
Next, a specific control flow of each control means will be described in detail. FIG. 3 corresponds to a flowchart of the temperature raising operation permission means.
In S 1, the temperature TCAT of the exhaust purification catalyst 8 is read as the output value of the temperature sensor 9. When the temperature is lower than the predetermined temperature TCATSL, the process proceeds to S3.
In S3, the operation condition flag FAREA is set according to the operation region defined by the basic fuel injection amount Tp and the engine speed Ne. Set to 1 for low-load and low-speed operation, and set to 0 for high-load and high-speed operation. Here, the basic fuel injection amount Tp is a value calculated by the following equation.
[0043]
Tp = k1 × Qa / Ne (1)
k1 is a constant
If it is determined in S4 that the operation is within the permitted temperature increase operation range (FAREA = 1), the temperature increase operation permission flag FHEAT is set to 1 in S5, and if it is determined that it is out of the permitted range, FAEAT is set to 0 in S6. .
[0044]
If TCAT> TCATSL in S2, it is determined that the exhaust purification catalyst 8 is at a temperature that can sufficiently purify the exhaust, and the temperature raising operation is not performed (FHEAT = 0).
FIG. 4 is a flowchart of the temperature raising operation cylinder determining means.
In S11, it is determined whether FCYL is 0 or 1. If it is 0, it indicates that the cylinder that performed the previous heating operation was the first cylinder group (# 2, 3 cylinders), and if it was 1, it indicated that it was the second cylinder group (# 1, 4 cylinders). Show.
[0045]
If FCYL = 0, FCYL = 1 is set in S12, and if FCYL: 1, FCYL = 0 is set in S13.
As a result, the temperature increase operation can be performed in a cylinder group different from the cylinder group that has performed the temperature increase operation last time, and the deterioration of the fuel injection valves 13 and the like can be maintained almost uniformly.
[0046]
FIG. 5 is a flowchart of the temperature raising operation means.
In S21, it is confirmed whether the temperature increase is permitted (FHEAT = 1). If not permitted, this flow is terminated as it is. If permitted, the map of the basic fuel injection amount Tp and the engine speed Ne is determined in S22. Further, the ignition timing ADVH during the temperature raising operation is read. The ignition timing is matched so as to be retarded from the ignition timing during normal operation.
[0047]
Further, in S23, the fuel injection amount correction coefficient THEAT during the temperature raising operation is read from the map of the basic fuel injection amount Tp and the engine speed Ne. The map values in S22 and S23 are matched beforehand by experiments so that the engine stability, the temperature rise effect, and the like are optimized.
In S24, the fuel injection amount Ti for the temperature raising operation is calculated from the basic fuel injection amount Tp and the temperature-increasing fuel injection amount correction coefficient THEAT by the following equation.
[0048]
Ti = Tp × THEAT (2)
Here, THEEAT> 1, and the fuel is increased.
In S25, the FCYL value is determined. If FCYL = 0, the temperature rises to the first cylinder group (# 2, 3 cylinders), and if FCYL = 1, the temperature rises to the second cylinder group (# 1, 4 cylinders). Signals of the ignition timing ADVH and the fuel injection amount Ti for operation are output.
[0049]
As described above, it is possible to perform exhaust temperature increase control by retarding the ignition timing and increasing the fuel injection amount.
FIG. 6 is a flowchart of the low exhaust temperature operation permission means.
In S31, it is determined whether the temperature raising operation is permitted. If not permitted, the low exhaust temperature operation is not permitted in S35 (FCOLD = 0), and this flow is terminated.
If the temperature raising operation is permitted, the second HC adsorption catalyst temperature THCT2 is read in S32. Here, the second HC adsorption catalyst is an HC adsorption catalyst into which the exhaust of the cylinder group that does not perform the temperature raising operation flows, and is determined by whether FCYL is 0 or 1.
[0050]
In S33, THCT2 and THCTSL are compared. If THCT2> THCTSL, the low exhaust temperature operation is permitted (FCOLD = 1) in S34, and if not, the low exhaust temperature operation is prohibited (FCOLD = O) in S35.
FIG. 7 is a flowchart of the low exhaust temperature operation means.
In S41, it is determined whether the low exhaust temperature operation is permitted (FCOLD = 1) or not (FCOLD = 0). If not allowed, this flow is terminated.
[0051]
If permitted, the low exhaust temperature operation timing ADVC is read from the map of Tp and Ne in S42, and the fuel injection amount correction coefficient TCOLD in the low exhaust temperature operation is read in S43. Here, ADVC is advanced from the ignition timing during normal operation, and TCOLD is 0 <TCOLD <1.
Next, in S44, the fuel injection amount Ti for low exhaust temperature operation is calculated by the following equation.
[0052]
Ti = Tp × TCOLD (3)
Thereby, TiC is corrected to be smaller than the normal fuel injection amount, and the lean air-fuel ratio operation becomes possible. When the engine is operated at a lean air-fuel ratio, the exhaust gas temperature is lower than that during normal operation, so that low exhaust temperature operation is possible.
In S45, the throttle opening degree correction coefficient TVOCOLD at the time of low exhaust temperature operation is read from the map of the basic fuel injection amount Tp and the engine speed Ne, and in S46, the throttle valve opening degree TVOC is calculated by the following equation.
[0053]
TVOC = TVO0 × TVOCOLD
Here, TVO0 is the throttle valve opening when the low exhaust temperature operation is not performed, and is determined according to the accelerator opening. Note that the throttle valve opening of the cylinder group performing the temperature raising operation is controlled to TVO0.
Next, if FCYL = 0 in S47, the ignition timing ADVC and the fuel injection amount TiC for the low exhaust temperature operation are output to the ignition plug 14 and the fuel injection valve 13 of the second cylinder group (# 1, 4 cylinder). In addition, the TVOC for low exhaust temperature operation is output to the second throttle valve 18 that regulates the intake air to the second cylinder group.
[0054]
On the other hand, if FCYL = 1, the ignition timing ADVC and the fuel injection amount TiC for the low exhaust temperature operation are output to the spark plug 14 and the fuel injection valve 13 of the first cylinder group (# 2, 3 cylinder), and The TVOC for low exhaust temperature operation is output to the first throttle valve 17. Here, ADVC, TCOLD, and TVOCOLD determined in S42, 43, and S45 are previously matched by experiment, and adjusted so that engine stability, exhaust performance, and the like are optimized.
[0055]
By executing the above hardware configuration and flow, good exhaust performance can be realized at low cost.
Further, in this embodiment, if a general ignition sequence # 1 → # 3 → # 4 → # 2 in a four-cylinder engine is performed, a cylinder group performing a temperature raising operation and not performing (a low exhaust temperature operation is performed). The cylinder groups are alternately ignited. For this reason, since the high concentration HC desorbed from the HC adsorption catalyst of the cylinder group not performing the temperature raising operation is dispersed and guided into the exhaust purification catalyst 8, it is possible to purify the HC efficiently and without difficulty. The fluctuation of torque and the like due to the difference in driving occurs at a high frequency, thereby reducing how the human body feels.
[0056]
Next, a second embodiment of the present invention will be described. FIG. 8 is an engine system diagram of this embodiment. The difference from the first embodiment is that a secondary air pump 21 and a secondary air inlet switching valve 22 are added. Further, since the control flow is different from the first embodiment only in the low exhaust temperature operation means, only the flow of the low exhaust temperature operation means will be described with reference to FIG.
[0057]
In S51, it is determined whether or not the low exhaust temperature operation is permitted. If not permitted, the secondary air pump 21 is turned off in S56 and this flow is terminated.
If the low exhaust temperature operation is permitted in S51, the secondary air pump 21 is turned on in S52, then the FCYL state is determined in S53, and if FCYL = 0, the second cylinder group (# 1, 4 ) The switching valve 22 is switched so that the secondary air is introduced to the side. If FCYL = 1, the secondary air is introduced to the first cylinder group (# 2, 3) side.
[0058]
As described above, low exhaust temperature operation is possible regardless of lean operation. Although it is disadvantageous in terms of cost, the degree of freedom is wider than that of the first embodiment in order to keep the temperature of the HC adsorption catalyst at a lower temperature.
Next, a third embodiment of the present invention will be described with reference to FIG. This embodiment is an example applied to a V-type horizontal engine. In addition, the same code | symbol is attached | subjected to the component which has the same function as the said 1st, 2nd embodiment. In the present embodiment, the cylinder in which the temperature raising operation is performed is not switched, the temperature raising operation is performed only in the rear side bank, and when the low exhaust temperature operation is performed, only the front side bank is performed. In a normal vehicle, exhaust is exhausted rearward, so the exhaust pipe on the front side is longer than the rear side. Further, the front side is easily cooled by the vehicle speed wind. Therefore, it is advantageous in a simple system in which the cylinder group that performs the temperature raising operation and the cylinder group that performs the low exhaust temperature operation are specified.
[0059]
That is, in the rear side bank that performs the temperature raising operation, the temperature decrease of the exhaust gas discharged from the combustion chamber is suppressed, the activity of the exhaust purification catalyst 8 is promoted, and the temperature raising operation is not performed (low exhaust temperature operation). In the front side bank, the HC desorption until the temperature rise of the HC adsorption catalyst 6 is delayed and the exhaust purification catalyst 8 reaches the activation temperature can be suppressed, so that the HC purification performance can be sufficiently improved.
[0060]
Further, if only the rear side exhaust pipe 3 that performs the temperature raising operation is kept warm by being wrapped with a heat insulating material, the temperature rise can be further promoted.
Next, a fourth embodiment of the present invention will be described with reference to FIG. In the present embodiment, the cylinder group is divided into three or more cylinder groups, and the cylinder group to be heated is switched according to the temperature state.
[0061]
Corresponding to the first cylinder group consisting of # 1,6 cylinders, the second cylinder group consisting of # 2,5 cylinders, and the third cylinder group consisting of # 3,4 cylinders of the engine body 21 of the in-line 6 cylinder engine The exhaust pipes 22, 23 and 24 are provided with HC adsorption catalysts 25, 26 and 27, respectively, joined at the downstream side, and the exhaust purification catalyst 28 is provided at the downstream side of the junction.
[0062]
Temperature sensors 29 to 32 are disposed on the HC adsorption catalysts 25, 26, 27 and the exhaust purification catalyst 28, respectively.
FIG. 12 shows a control flow of this embodiment.
In S61, it is determined whether the temperature Tc of the exhaust purification catalyst 28 is an extremely low temperature less than TLL.
[0063]
When it is determined that the temperature is extremely low, the process proceeds to S62, and two cylinder groups among the first to third cylinder groups are heated.
If it is determined that the temperature is not extremely low, the process proceeds to S63 to determine whether the temperature Tc is a low temperature below TL.
When it is determined that the temperature is low, the process proceeds to S64 and the temperature increasing operation is performed for one cylinder group.
[0064]
In addition, the cylinder group which does not perform the temperature increasing operation performs the normal operation or the low exhaust temperature operation.
In this way, at a very low temperature, the temperature increase operation of the exhaust purification catalyst 28 is accelerated by performing the temperature increase operation of the two cylinder groups, and the activity is further promoted. In addition, since the time for the exhaust purification catalyst 28 to reach the activation temperature is advanced, the temperature raising operation time can be shortened, and the temperature rise of the HC adsorption catalyst in the cylinder group performing the temperature raising operation can be suppressed, which also improves the HC purification rate. it can.
[0065]
Further, when only one cylinder group is heated (including the case where only one cylinder group is heated regardless of the temperature state), different cylinder groups are alternately heated at predetermined time intervals. It is also possible to keep the temperatures of the two HC adsorption catalysts below the HC desorption temperature at the end of the activation of the exhaust purification catalyst 28 without excessively raising the temperature of the individual HC adsorption catalysts. Become.
[0066]
Next, a fifth embodiment of the present invention will be described using the flowchart of FIG. In the present embodiment, a torque difference caused by a difference in operation between a cylinder group that performs a temperature raising operation and a cylinder group that does not perform a temperature increase operation is suppressed. Note that hardware can be applied to all the embodiments described above.
Increasing the exhaust temperature by the temperature raising operation increases the amount of exhaust heat, so that the thermal efficiency is lowered, and the torque is lower than that in the normal operation. Therefore, in S71, a torque difference from the case where the temperature raising operation is not performed is calculated by performing a predetermined temperature raising operation.
[0067]
In S72, correction control is performed to reduce the torque by the calculated torque difference for the cylinder group that is not operating at a temperature increase. Specifically, when the temperature raising operation is performed by retarding the ignition timing or the like, it can be executed by reducing the fuel injection amount of the cylinder group that is not temperature raising operation. In the first embodiment, the fuel injection amount is reduced by the lean air-fuel ratio control, and the throttle valve opening is adjusted to reduce the torque step between the cylinder groups. The fuel injection amount or the like is reduced to such an extent that the torque difference is suppressed, and it is not necessary to use a lean air-fuel ratio, so that a more precise torque step between the cylinder groups can be achieved. Further, the control for suppressing the torque difference may be executed only in a low rotation region where torque fluctuation is a problem.
[0068]
In the embodiment described above, the temperature increasing operation is set to the over-rich air-fuel ratio and retards the ignition timing. However, in addition to this, secondary air may be supplied, while variable valve timing is provided. In an engine equipped with the device, a configuration may be used in which the exhaust valve is opened earlier and the exhaust temperature at the time of opening is increased. Further, in a compression ignition engine, the temperature raising operation can be performed by delaying the injection timing to delay the ignition combustion, or reducing the intake air to increase the residual gas ratio in the combustion chamber.
[Brief description of the drawings]
FIG. 1 is a diagram showing a system configuration of a first embodiment.
FIG. 2 is a control block diagram according to the first embodiment.
FIG. 3 is a flowchart showing a routine of a temperature raising operation permission means in the first embodiment.
FIG. 4 is a flowchart showing a routine of a temperature raising operation cylinder determining unit in the first embodiment.
FIG. 5 is a flowchart showing a routine of a temperature raising operation unit in the first embodiment.
FIG. 6 is a flowchart showing a routine of a low exhaust temperature operation permission means in the first embodiment.
FIG. 7 is a flowchart showing a routine of low exhaust temperature operation means in the first embodiment.
FIG. 8 is a diagram showing a system configuration of a second embodiment.
FIG. 9 is a flowchart showing a routine of low exhaust temperature operation means in the second embodiment.
FIG. 10 is a diagram showing a system configuration of a third embodiment.
FIG. 11 is a diagram showing a system configuration of a fourth embodiment.
FIG. 12 is a flowchart showing a temperature raising operation routine in the fourth embodiment.
FIG. 13 is a flowchart showing a torque step avoidance routine in the fifth embodiment.
[Explanation of symbols]
1 Engine body
3 First exhaust pipe
4 First HC adsorption catalyst
5 Second exhaust pipe
6 Second HC adsorption catalyst
7 Junction
8 Exhaust gas purification catalyst
9-11 Temperature sensor
21 Engine body
22-24 Exhaust pipe
25-27 HC adsorption catalyst
28 Exhaust gas purification catalyst
29-32 temperature sensor

Claims (15)

Each exhaust pipe that guides the exhaust of each of the cylinder groups divided into a plurality of V-type internal combustion engines mounted horizontally on the vehicle adsorbs hydrocarbons that flow in in the cold, and adsorbs when the temperature exceeds a predetermined value. An HC adsorption catalyst that discharges hydrocarbons is installed,
These exhaust pipes are joined together downstream of each HC adsorption catalyst, and an exhaust purification catalyst for purifying at least hydrocarbons is disposed in the exhaust pipe downstream from the junction,
An internal combustion engine characterized in that, when the V-type internal combustion engine is cold, a temperature raising operation for quickly raising the exhaust temperature in the cylinder group located on the rear bank side is performed until the temperature of the exhaust purification catalyst reaches a predetermined temperature. Engine exhaust purification system. HC adsorption that adsorbs hydrocarbons that flowed in the cold to each exhaust pipe that guides the exhaust of each cylinder group divided into a plurality of cylinders of a multi-cylinder internal combustion engine, and discharges the adsorbed hydrocarbons when the temperature exceeds a predetermined value Arrange the catalyst,
These exhaust pipes are joined together downstream of each HC adsorption catalyst, and an exhaust purification catalyst for purifying at least hydrocarbons is disposed in the exhaust pipe downstream from the junction,
A temperature increasing operation for quickly increasing the exhaust temperature in some cylinder groups when cold is performed until the temperature of the exhaust purification catalyst reaches a predetermined temperature,
In addition, the internal combustion engine is divided into three or more cylinder groups, and the number of cylinder groups that are operated to be heated can be switched. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2 , wherein the temperature raising operation is performed by operating the exhaust valve at an earlier opening timing. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3 , wherein the temperature raising operation is performed by operating at a rich air-fuel ratio. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4 , wherein in the spark ignition engine, the temperature raising operation is performed by operating with a delayed ignition timing. 5. The internal combustion engine according to claim 1 , wherein in the compression ignition engine, the temperature raising operation is performed by at least one of delaying a fuel injection timing or restricting intake air. Exhaust purification equipment. Period that implement the heating operation in some of cylinder groups, claims 1, characterized in that to implement the low exhaust-temperature operation to lower the exhaust gas temperature from the normal operation in the cylinder groups without carrying out heating operation 6. The exhaust gas purification apparatus for an internal combustion engine according to any one of 6 above. The exhaust emission control device for an internal combustion engine according to claim 7 , wherein the low exhaust temperature operation is performed by operating at a lean air-fuel ratio. The exhaust gas purification apparatus for an internal combustion engine according to claim 7 or 8 , wherein the low exhaust temperature operation is performed by introducing air from upstream of the HC adsorption catalyst disposed in the corresponding exhaust pipe. A cylinder group to carry out the heating operation, according to any one of claims 1 to 9, characterized in that to change depending on the number of times of execution of non cylinder group and a raised operating Atsushi Nobori operation An exhaust purification device for an internal combustion engine. 10. The internal combustion engine according to claim 1, wherein a cylinder group for performing the temperature raising operation is determined in advance, and only the exhaust pipe of the cylinder group is kept warm. Exhaust purification equipment. The internal combustion engine according to any one of claims 1 to 11 , wherein each HC adsorption catalyst is disposed in an exhaust pipe portion where exhaust from each cylinder in each cylinder group merges. Exhaust purification device. 13. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus is divided into two cylinder groups, and one of the cylinder groups is operated to rise in temperature. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 13 , wherein control is performed to reduce a torque difference between a cylinder group that performs a temperature raising operation and a cylinder group that does not. A cylinder group that performs heating operation, the cylinder group is not performed, the same number of cylinders to one another, and, according to claim 1, firing order, characterized in that it is set alternately claim 3 wherein Item 15. The exhaust emission control device for an internal combustion engine according to any one of Items 14 to 14 .

Images