JP2017145777A - Control device of vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of a vehicle which can reduce a generation amount of N2O by reducing an operation switching frequency between a lean combustion operation and a stoichiometric combustion operation by using power generation by a generator which is mounted to a vehicle.SOLUTION: In the case where engine requirement torque Tqtgt reaches threshold torque Tqb or smaller from a state that the engine require torque Tqtgt is set larger than the threshold torque Tqb, and an air-fuel ratio of an air-fuel mixture is set at a lean air-fuel ratio, when a catalyst temperature Tcat is higher than an inactivation temperature of a three-way catalyst, the engine requirement torque Tqtgt is changed to the threshold torque Tqb or larger by increasing a power generation amount of a generator, and an operation of the engine is continued while maintaining the air-fuel ratio of the air-fuel mixture at the lean air-fuel ratio. In the case where the engine requirement torque Tqtgt reaches the threshold torque Tqb or smaller, when the catalyst temperature Tcat is not higher than the inactivation temperature, a control device sets the air-fuel ratio of the air-fuel mixture at a theoretical air-fuel ratio, and continues the operation of the engine.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a vehicle control device equipped with an internal combustion engine capable of lean combustion operation as a driving force source.

  2. Description of the Related Art Conventionally, there is known an internal combustion engine that can switch an air-fuel ratio of a gasoline mixture between a stoichiometric air-fuel ratio and an air-fuel ratio (lean air-fuel ratio) that is larger (lean) than the stoichiometric air-fuel ratio (for example, a patent See reference 1.) In this specification, the operation of the engine when the air-fuel ratio of the gasoline mixture is set to the stoichiometric air-fuel ratio is referred to as “stoichiometric combustion operation”, and the air-fuel ratio of the gasoline mixture is set to the lean air-fuel ratio. When the engine is running, it may be referred to as “lean combustion operation”.

JP 2003-65127 A

  By the way, for example, when the lean combustion operation is performed when the engine load is extremely small (that is, when the torque required for the engine is small) as in the idle operation state, the combustion temperature of the air-fuel mixture becomes low and misfiring occurs. There is a case. Further, when the lean combustion operation is performed during the idle operation immediately after starting, the time until the exhaust purification catalyst (hereinafter simply referred to as “catalyst”) reaches a temperature at which it normally functions (that is, until it is activated). There is a problem that the time is long. Therefore, the conventional control device switches the operation of the engine from the lean combustion operation to the stoichiometric combustion operation when the load on the engine becomes extremely small.

However, when the operation of the engine is switched between the stoichiometric combustion operation and the lean combustion operation, the air-fuel ratio of the gasoline mixture becomes an air-fuel ratio that “NOx is not completely reduced in the catalyst”. It has been clarified by the inventor's examination that there is a problem that dinitrogen oxide (nitrous oxide: N ₂ O) is generated. N ₂ O has a global warming potential of 298. That is, N ₂ O has 298 times the greenhouse effect compared to the same weight of CO ₂ . Therefore, even if a small amount of N ₂ O is present, it has a great influence on global warming, and it is desirable to suppress its generation as much as possible.

The present invention has been made to address the above problems. That is, one of the objects of the present invention is to reduce the frequency of operation switching between lean combustion operation and stoichiometric combustion operation by using power generation by a generator mounted on a vehicle, thereby generating N ₂ O production amount. It is an object of the present invention to provide a vehicle control device capable of reducing the above.

A vehicle control device of the present invention (hereinafter also referred to as “device of the present invention”) includes an internal combustion engine (20) as a drive source of the vehicle (10), and is mounted on the vehicle and driven by the engine. A generator (51) that generates electricity, a storage battery (53) that is mounted on the vehicle and is charged by the power generated by the generator, and a three-way catalyst (36) disposed in the exhaust passage of the engine ) And applied to vehicles equipped with,
Engine required torque determining means (step 510) for determining an engine required torque (Tqtgt) required for the engine based on a parameter correlated with a user required torque requested by a driver of the vehicle;
When the engine required torque is equal to or less than the threshold torque (Tqb), the air-fuel ratio of the air-fuel mixture formed in the combustion chamber (28) of the engine is set to the stoichiometric air-fuel ratio (Step 515: No and Step 535). ) When the engine required torque is larger than the threshold torque, the air-fuel ratio of the air-fuel mixture is set to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio (step 515: Yes and step 520), air-fuel ratio setting means ,When,
The control apparatus (70) containing is provided.

According to the device of the present invention, the stoichiometric combustion operation is performed when the engine required torque is equal to or less than the threshold torque (Tqb). Thereby, the occurrence of misfire is avoided. Further, according to the device of the present invention, when the engine required torque threshold torque (Tqb) is larger, the lean combustion operation is performed. Thereby, fuel consumption is improved. However, when the engine operation is switched between the lean combustion operation and the stoichiometric combustion depending on whether or not the engine required torque is equal to or greater than the threshold torque (Tqb), a large amount of N ₂ O may be generated.

Therefore, the control device acquires a temperature parameter having a correlation with the temperature (Tcat) of the three-way catalyst, and the engine required torque is obtained from a state where the air-fuel ratio of the air-fuel mixture is set to the lean air-fuel ratio. When it decreases and becomes below the threshold torque (step 525: Yes),
When the temperature (Tcat) of the three-way catalyst represented by the temperature parameter is higher than the deactivation temperature (Tnop = T1) at which the three-way catalyst is not activated at all, the power generation amount of the generator is increased. Thus, the engine required torque is changed to the threshold torque or more, and the engine is operated while maintaining the air-fuel ratio of the air-fuel mixture at the lean air-fuel ratio (Step 530: No, Step 545, Step 550, Step 510). , Step 515 and Step 520)
When the temperature (Tcat) of the three-way catalyst represented by the temperature parameter is equal to or lower than the deactivation temperature (Tnop = T1), the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio and the engine Run (Step 530: Yes and Step 535),
Configured as follows.

According to this, when the required engine torque decreases below the threshold torque from the state where the air-fuel ratio of the air-fuel mixture is set to the lean air-fuel ratio (that is, the engine operation is switched to the stoichiometric combustion operation in the conventional device). Even if the temperature of the three-way catalyst is higher than the deactivation temperature, the engine required torque is changed to be equal to or greater than the threshold torque by increasing the power generation amount of the generator, and the lean combustion operation is continued. The As a result, the air-fuel ratio of the gasoline mixture does not become an air-fuel ratio “NOx is not completely reduced in the catalyst”, so that the amount of N ₂ O generated can be reduced. In addition, the engine required torque is increased, so that misfire can be prevented from occurring in the lean combustion operation.

In addition, when the required engine torque decreases below the threshold torque from the state where the air-fuel ratio of the air-fuel mixture is set to the lean air-fuel ratio (that is, when the engine operation is switched to the stoichiometric combustion operation in the conventional device) Even when the temperature of the three-way catalyst is equal to or lower than the deactivation temperature, N ₂ O is not generated in the catalyst because NOx is not reduced in the catalyst. Therefore, the device of the present invention switches the engine operation from the lean combustion operation to the stoichiometric combustion operation. Thereby, the production amount of N ₂ O can be reduced while avoiding the occurrence of misfire. Furthermore, the activation of the catalyst can be promoted by raising the catalyst temperature as soon as possible.

  In the above description, in order to help understanding of the present invention, names and / or symbols used in the embodiment are attached to the configuration of the invention corresponding to the embodiment described later in parentheses. However, each component of the present invention is not limited to the embodiment defined by the reference numerals. Other objects, other features and attendant advantages of the present invention will be readily understood from the description of the embodiments of the present invention described with reference to the following drawings.

FIG. 1 is a schematic configuration diagram of a vehicle control apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an emission purification rate of the upstream catalyst of the vehicle control apparatus shown in FIG. FIG. 3 is a diagram illustrating a change in the N ₂ O concentration with respect to the air-fuel ratio mode at the outlet of the upstream side catalyst of the vehicle control apparatus shown in FIG. FIG. 4 is a graph showing a change in temperature and a change in N ₂ O concentration at the catalyst outlet when the internal combustion engine of the upstream catalyst of the vehicle control apparatus shown in FIG. 1 is started. FIG. 5 is a flowchart showing an “operation mode determination routine” executed by the CPU of the vehicle control device shown in FIG. FIG. 6 is a look-up table referred to by the CPU of the vehicle control device shown in FIG. FIG. 7 is a diagram showing the relationship between the engine speed and the required engine torque and the lean combustion operation region. FIG. 8 is a flowchart showing a “generated power up stop routine” executed by the CPU of the vehicle control device shown in FIG.

  Hereinafter, a vehicle control device according to an embodiment of the present invention (hereinafter referred to as “the present control device”) will be described with reference to the drawings.

(Constitution)
This control apparatus is applied to the vehicle 10 shown in FIG. The vehicle 10 includes an internal combustion engine 20, an alternator 51, a regulator 52, a storage battery 53, a power transmission mechanism 60, an electronic control device 70, and the like.

  The internal combustion engine (hereinafter also simply referred to as “engine”) 20 is a spark ignition type 4-cycle piston reciprocating type, in-line 4-cylinder, direct injection gasoline engine. The engine 20 includes a known engine actuator 21. The engine actuator 21 includes a fuel supply device including a fuel injection valve (injector) 22, an ignition device 23 including a spark plug, a throttle motor 24, and the like. The engine 20 can be operated in either a lean combustion operation or a stoichiometric combustion operation.

  When the engine 20 is operated in the stoichiometric combustion operation, the intake air amount is changed by changing the opening of the throttle valve 25 disposed in the intake passage by the throttle motor 24, and the intake air amount is changed to the intake air amount. The generated torque can be changed by changing the fuel injection amount accordingly. The engine 20 generates torque on a crankshaft 26 that is an output shaft of the engine 20.

  When the engine 20 is operated in the lean combustion operation, the throttle valve 25 is maintained almost fully open by the throttle motor 24, and the generated torque is changed by changing the fuel injection amount, the fuel injection timing, and the like. be able to.

  The engine 20 includes a main body 27 including a cylinder block, a cylinder head, a crankcase, and the like. Four cylinders (combustion chambers) 28 are formed in the main body 27. A fuel injection valve 22 and an ignition device 23 are disposed above each cylinder 28. The fuel injection valve 22 opens in response to an instruction from an electronic control unit 70 described later, and directly injects fuel into the cylinder.

  The engine 20 includes a fuel supply system 31 including a fuel pressurizing pump, a fuel delivery pipe, and a delivery pipe. The engine 20 further includes an intake manifold 32, an intake pipe 33, an exhaust manifold 34, an exhaust pipe 35, an upstream side catalyst 36, a NOx occlusion reduction type catalyst 37, and a downstream side catalyst 38. Hereinafter, the upstream catalyst 36 is referred to as “SC catalyst 36”, and the NOx storage reduction catalyst 37 is referred to as “NSR catalyst 37”. SC is an abbreviation for Start-up Converter, and NSR is an abbreviation for NOx Storage Reduction.

  The exhaust manifold 34 includes a branch portion connected to each cylinder 28 and a collective portion in which the branch portions are gathered. The exhaust pipe 35 is connected to a collecting portion of the exhaust manifold 34. The exhaust manifold 34 and the exhaust pipe 35 constitute an exhaust passage. An SC catalyst 36, an NSR catalyst 37, and a downstream catalyst 38 are disposed in the exhaust pipe 35 from the upstream side to the downstream side of the exhaust gas flow.

The SC catalyst 36 and the downstream catalyst 38 are so-called three-way catalyst devices (exhaust gas purification devices) that carry active components made of noble metals such as platinum and palladium. Each catalyst has a function of oxidizing unburned components such as HC and CO and reducing nitrogen oxides (NOx) when the air-fuel ratio of the gas flowing into each catalyst is the stoichiometric air-fuel ratio. This function is also called a catalyst function. Furthermore, each catalyst has an oxygen storage capacity for storing (storing) oxygen, and even if the air-fuel ratio shifts from the stoichiometric air-fuel ratio, unburned components and nitrogen oxides can be purified. This oxygen storage capacity is brought about by cerium oxide (CeO ₂ ) supported on the catalyst.

The NSR catalyst 37 stores NOx discharged without being purified by the SC catalyst 36 during the lean combustion operation of the internal combustion engine 20 in the storage material. With this function, it is possible to suppress the situation where NOx is released into the atmosphere during the lean combustion operation. Since the NOx occlusion capacity of the NSR catalyst 37 decreases as the NOx occlusion amount increases, NOx is not occluded and flows downstream of the NSR catalyst 37 when the lean combustion operation is continued for a long time. Therefore, the present control device executes rich spike control for periodically desorbing NOx stored in the NSR catalyst 37. More specifically, when the NOx occlusion amount of the NSR catalyst 37 reaches a predetermined occlusion limit amount (for example, an amount corresponding to 80% of the maximum NOx occlusion amount), the mixture is emptied for a very short time. A “rich spike” that introduces an air-fuel ratio smaller than the stoichiometric air-fuel ratio (rich) (for example, air-fuel ratio = 12) is introduced. At this time, NOx is reduced to N _{2 using} CO, H ₂ and HC in the exhaust gas as reducing agents.

One end of the crankshaft 26 is connected to an input shaft of a transmission 61 that is a part of the power transmission mechanism 60.
A crankshaft pulley 42 is fixed to the other end of the crankshaft 26.
The crankshaft pulley 42 is connected to an alternator pulley 43 through a belt 44 so that power can be transmitted.
The alternator pulley 43 rotates integrally with a rotor (not shown) of the alternator 51.

  The alternator 51 includes a three-phase AC power generation that includes a “stator coil having a three-phase winding, a field coil wound around the rotor, and a rectifier that rectifies an AC current generated in the stator coil into a DC current” (not shown). Machine. When a field current is passed through the field coil, the alternator 51 generates an induced current (three-phase alternating current) in the stator coil, rectifies the generated three-phase alternating current into a direct current, and outputs it.

  The regulator 52 converts the direct current generated by the alternator 51 into a constant voltage. The regulator 52 can control the current value of the field current based on an instruction from the electronic control unit (ECU) 70. Therefore, the regulator 52 can adjust the output voltage of the alternator 51, and as a result, the power generation amount of the alternator 51 can be adjusted.

  The storage battery 53 is a power storage unit that stores electrical energy for operating the engine actuator 21 and electrical components in the vehicle 10, and is configured by a secondary battery such as a lithium ion battery that can be repeatedly charged and discharged. . In addition, the storage battery 74 should just be an electrical storage apparatus which can be discharged and charged, Therefore, a nickel metal hydride battery, a lead storage battery, a nickel cadmium battery, and another secondary battery may be sufficient.

  In addition to the transmission 61, the power transmission mechanism 60 includes a propeller shaft 62, a differential gear 63, and a drive shaft (drive shaft) 64.

  The output shaft of the transmission 61 is connected to one end of the propeller shaft 62. The other end of the propeller shaft 62 is connected to a drive shaft 64 via a differential gear 63. Drive wheels W are attached to both ends of the drive shaft 64. Accordingly, the torque of the output shaft of the transmission 61 is transmitted to the drive wheels W via the differential gear 63 and the drive shaft 64. The vehicle 10 can travel by the torque transmitted to the drive wheels W.

  The electronic control unit (ECU) 70 is an electronic circuit including a known microcomputer, and includes a CPU, ROM, RAM, backup RAM (static RAM or nonvolatile memory), an interface, and the like. The electronic control device 70 is electrically connected to the fuel injection valve 22, the ignition device 23, the throttle motor 24, the regulator 52, the storage battery 53, and the like.

  The electronic control device 70 sends an instruction (drive) signal to actuators such as the fuel injection valve 22, the ignition device 23, and the throttle motor 24 in accordance with an instruction from the CPU. Further, the electronic control unit 70 includes a crank position sensor 91, an air flow meter 92, a throttle valve opening sensor 93, an accelerator operation amount sensor 94, a water temperature sensor 95, an upstream air-fuel ratio sensor 96, a downstream air-fuel ratio sensor 97, and an exhaust gas temperature. It is electrically connected to the sensor 98 and the like, and receives (inputs) signals from each sensor.

  The crank position sensor 91 outputs a signal having a narrow pulse every time the crankshaft 26 rotates 10 ° and a signal having a wide pulse every time the crankshaft 26 rotates 360 °. This signal is converted into an engine rotational speed NE (the rotational speed of the engine 20) by the electronic control unit 70.

  The air flow meter 92 outputs a signal corresponding to the mass flow rate of intake air flowing through the intake pipe 33 (hereinafter referred to as “intake air amount”) Ga.

  The throttle position sensor 93 detects the opening (throttle valve opening) of the throttle valve 25 and outputs a signal representing the throttle valve opening TA.

  The accelerator operation amount sensor 94 generates an output signal representing an operation amount of an accelerator pedal AP (hereinafter referred to as “accelerator operation amount Accp”) provided so as to be operable by a driver.

  The water temperature sensor 95 detects the temperature of the cooling water of the engine 20 and outputs a signal indicating the cooling water temperature THW.

  The upstream air-fuel ratio sensor 96 is an exhaust passage, and is disposed downstream of the collection portion of the exhaust manifold 34 or the collection portion thereof and upstream of the SC catalyst 36. The upstream air-fuel ratio sensor 96 is a limiting current type oxygen concentration sensor. The upstream air-fuel ratio sensor 96 outputs an output value Vabyfs that is a voltage corresponding to the air-fuel ratio of the exhaust gas flowing through the place where it is disposed. That is, the upstream air-fuel ratio sensor 96 is a wide-area air-fuel ratio sensor whose output continuously changes with respect to changes in the air-fuel ratio of the gas to be detected.

  The downstream air-fuel ratio sensor 97 is disposed in the exhaust passage, downstream of the NSR catalyst 37 and upstream of the downstream catalyst 38. The downstream air-fuel ratio sensor 97 is a known electromotive force type oxygen concentration sensor (a known concentration cell type oxygen concentration sensor using stabilized zirconia). The downstream air-fuel ratio sensor 97 generates an output value Voxs corresponding to the air-fuel ratio of the exhaust gas flowing through the installation location.

  The exhaust gas temperature sensor 98 is disposed in the exhaust passage and in the vicinity of the outlet of the SC catalyst 36. The exhaust gas temperature sensor 98 generates an output value corresponding to the temperature of the exhaust gas flowing out from the SC catalyst 36. The electronic control unit 70 treats this output value as the temperature Tcat of the SC catalyst 36 (hereinafter also referred to as “catalyst temperature Tcat”). That is, the output value of the exhaust gas temperature sensor 98 is a temperature parameter having a correlation with the temperature of the SC catalyst 36 (three-way catalyst).

(Generation of N ₂ O)
Next, the relationship between the air-fuel ratio of the air-fuel mixture formed in the cylinder (combustion chamber) 28 (hereinafter referred to as “engine air-fuel ratio”) and the generation of N ₂ O will be described.

When the catalyst temperature Tcat is a temperature at which the SC catalyst 36 is completely activated (for example, 450 ° C.), as shown in FIG. 2, the NOx purification rate of the SC catalyst 36 is an excess air ratio (= air-fuel ratio / 100 in a range where the stoichiometric air-fuel ratio is less than “1” (hereinafter referred to as “rich range”) and an excess air ratio is around “1” (hereinafter referred to as “theoretical air-fuel ratio range”). The value is close to%. That is, the NOx reduction reaction by the SC catalyst 36 is active in the rich range and the stoichiometric air-fuel ratio range. Therefore, when the air-fuel ratio of the engine is the air-fuel ratio corresponding to the first region RA1 (stoichiometric operation region RA1) in FIG. 2, in other words, when the operation of the engine 20 is the stoichiometric combustion operation, substantially all since NOx is reduced to _{N 2, N 2} O is not generated.

When the value of the excess air ratio is between “1.01” and “1.02”, the NOx purification rate of the SC catalyst 36 rapidly decreases. That is, when the air-fuel ratio of the engine is the air-fuel ratio corresponding to the second region RA2 in FIG. 2, the NOx reduction reaction by the SC catalyst 36 becomes inactive. Therefore, NOx changes to N ₂ and N ₂ O. As a result, N ₂ O is generated and released to the atmosphere.

The air-fuel ratio of the engine at the time of lean combustion operation is around 17, and the value of the excess air ratio is “around 1.16”. When the air-fuel ratio of the engine is an air-fuel ratio corresponding to the “third region RA3 in FIG. 2” corresponding to the air-fuel ratio of the engine during the lean combustion operation, the NOx purification rate is extremely low. In other words, when the lean combustion operation is performed, the NOx reduction reaction does not occur in the SC catalyst 36. As a result, when the air-fuel ratio of the engine is the air-fuel ratio corresponding to the third region RA3 (lean operation region RA3), in other words, when the operation of the engine 20 is the lean combustion operation, N ₂ O is generated from NOx. Never happen.

By the way, when the operation of the engine 20 is switched between the stoichiometric combustion operation and the lean combustion operation, the air-fuel ratio of the engine inevitably passes through the air-fuel ratio corresponding to the second region RA2. Therefore, even when the SC catalyst 36 is in a sufficiently activated state, when the operation of the engine 20 is switched between the stoichiometric combustion operation and the lean combustion operation, the air-fuel ratio of the engine corresponds to the “second region RA2”. N ₂ O is generated because the air-fuel ratio is reduced.

On the other hand, when the engine 20 is in a lean combustion operation when the engine load is extremely small (that is, when the engine required torque, which is a torque required for the engine is small), such as in an idle operation state, May cause misfire due to low combustion temperature. Therefore, the engine 20 is operated by stoichiometric combustion operation when the load on the engine is extremely small. Therefore, for example, when the vehicle 10 starts traveling from a stopped state, the load of the engine 20 changes from a very small state to a large state, and therefore the operation of the engine 20 is switched from the stoichiometric combustion operation to the lean combustion operation. . As a result, N ₂ O is generated. Alternatively, when the engine 20 is decelerated, the load (engine required torque) decreases, so the operation of the engine 20 is switched from the lean combustion operation to the stoichiometric combustion operation. As a result, N ₂ O is generated.

FIG. 3 shows the N ₂ O generation state when the operation of the engine 20 is switched between the lean combustion operation and the stoichiometric combustion operation. The “air-fuel ratio mode” in FIG. 3 is an air-fuel ratio (target air-fuel ratio) set as a target value for air-fuel ratio control of the engine 20. The air-fuel ratio mode during the lean combustion operation is a lean mode (air-fuel ratio = 17), and the air-fuel ratio mode during the stoichiometric combustion operation is a stoichiometric mode (air-fuel ratio = 14.6). Further, the period in which the air-fuel ratio mode is rich is a period in which rich spike control is executed. The air-fuel ratio during the rich spike control is 12.

As understood from FIG. 3, when the stoichiometric combustion operation is switched to the lean combustion operation (see time t12 and time t14), the concentration of N ₂ O at the outlet of the SC catalyst 36 increases rapidly. Further, the N ₂ O concentration at the outlet of the SC catalyst 36 also increases at the start of rich spike control (see time t15).

As described above, this is because the air-fuel ratio of the engine 20 passes through the air-fuel ratio corresponding to the second region RA2 in which the NOx reduction reaction is incomplete. Although the reason is not yet clear, when the lean combustion operation is switched to the stoichiometric combustion operation (see time t11 and time t13), the concentration of N ₂ O at the outlet of the SC catalyst 36 hardly increases. This is considered to be caused by the extremely short time for the air-fuel ratio of the engine 20 to converge to the target air-fuel ratio (that is, the theoretical air-fuel ratio = 14.6) when switching from the lean combustion operation to the stoichiometric combustion operation. However, if the time until the air-fuel ratio of the engine 20 converges to the stoichiometric air-fuel ratio when switching from lean combustion operation to stoichiometric combustion operation is long, the concentration of N ₂ O at the outlet of the SC catalyst 36 increases.

Thus, even when the SC catalyst 36 is fully activated, a large amount of N ₂ O is generated when the operation of the engine 20 is switched between the lean combustion operation and the stoichiometric combustion operation. . On the other hand, when the catalyst temperature Tcat is relatively low and the SC catalyst 36 is not sufficiently activated (not in a completely inactive state but not in a completely activated state), the NOx reduction reaction is inactive, so Even when the combustion operation is performed, N ₂ O may be generated. This point will be described with reference to FIG.

  In the graph of FIG. 4, the horizontal axis is the elapsed time from the start of the engine 20, and the vertical axis is the catalyst temperature Tcat (° C.). In this example, during the period from time t = 0 (when the engine 20 is started; the left end of the graph) to time t24, the target air-fuel ratio is set to the stoichiometric air-fuel ratio, and the stoichiometric combustion operation is performed. This is because a lean combustion operation with a low combustion temperature is not performed immediately after the start of the engine 20 because there is a risk of misfire. Thereafter, after time t24 when the SC catalyst 36 is sufficiently activated, the target air-fuel ratio is changed to a lean air-fuel ratio (for example, 17), and the lean combustion operation is performed.

In the region RT1 surrounded by a broken line in FIG. 4 (hereinafter also referred to as “first temperature region”), the SC catalyst 36 is not activated at all. Therefore, NOx reduction reaction does not occur in the first temperature region RT1, and therefore N ₂ O is not generated. Hereinafter, the temperature at which the SC catalyst 36 is not activated at all is referred to as “inactivation temperature”.

A temperature range of a region RT2 (hereinafter also referred to as “second temperature region”) surrounded by a broken line in FIG. 4 is higher than the deactivation temperature of the SC catalyst 36 and lower than the activation temperature Top. The temperature in this temperature range is sometimes referred to as a light-off temperature. In the second temperature region RT2, the SC catalyst 36 is in an insufficiently activated state. Therefore, NOx reduction reaction are not completely (i.e., NOx is not reduced to _{N 2), N 2} O is increases chance of being generated (see time t22.).

The temperature range of a region RT3 (hereinafter also referred to as “third temperature region”) surrounded by a broken line in FIG. 4 is higher than the activation temperature Top. Therefore, the SC catalyst 36 is completely activated in the third temperature region. Accordingly, the NOx reduction reaction is normally performed in this region, so that N ₂ O is not generated.

(Specific operation)
In order to prevent the situation where N ₂ O described above is generated as much as possible, the present control device operates as described below. That is, the CPU of the electronic control unit (ECU) 70 executes the routine shown by the flowchart in FIG. 5 every time a predetermined time elapses.

  Therefore, at the predetermined timing, the CPU starts the process from step 500 in FIG. 5 and proceeds to step 505, where the “engine speed NE, accelerator opening Accp and engine required basic torque Tqbse” shown in FIG. The engine required basic torque Tqbse is acquired by applying the acquired engine rotational speed NE and the acquired accelerator opening degree Accp to a lookup table that defines the relationship. This lookup table is determined in advance by experiments or the like and stored in the ROM of the electronic control unit 70. The accelerator opening degree Accp is a parameter having a correlation with the user request torque required by the driver of the vehicle 10.

  Next, the CPU proceeds to step 510, obtains a value obtained by adding a torque increase ΔTq determined in step 550 described later to the engine required basic torque Tqbse, and sets that value as the final engine required torque Tqtgt.

  Next, the CPU proceeds to step 515 to determine whether or not the operating point determined by the engine required torque Tqtgt and the engine speed NE is within the lean combustion operation region R1 shown in FIG. As shown in FIG. 7, in the lean combustion operation region R1, the engine required torque Tq is equal to or higher than a certain low side torque threshold Tqb and equal to or lower than a predetermined high side torque threshold Tqc, and the engine speed NE is low. This is an area that is not less than the threshold value NEL and not more than the high-side speed threshold value NEH. The stoichiometric combustion operation region R2 is a region other than the lean combustion operation region R1. Line L1 represents the maximum torque of engine 20. Further, the high-side torque threshold value Tqc decreases as the engine speed NE increases.

  When the operating point is within the lean combustion operation region R1, the CPU makes a “Yes” determination at step 515 to proceed to step 520 to perform the lean combustion operation. Thereafter, the CPU proceeds to step 522 to set the torque increase ΔTq to “0”, proceeds to step 595, and once ends this routine.

  On the other hand, when the operating point is in the stoichiometric combustion operation region R2, the CPU makes a “No” determination at step 515 to proceed to step 525, where the engine required basic torque Tqbse when this routine was executed last time is the threshold torque. It is determined whether it is greater than Tqb and less than or equal to the current engine basic demand torque Tqbse. That is, the CPU is in a state where the operating point is transitioning from the lean combustion operation region R1 to the stoichiometric combustion operation region R2 across the threshold torque Tqb line, as shown from the point P3 to the point S1 in FIG. Determine.

  If the determination condition of step 525 is not satisfied, the CPU makes a “No” determination at step 525 to directly proceed to step 535 to execute the stoichiometric combustion operation. Thereafter, the CPU proceeds to step 537 to set the torque increase ΔTq to “0”, proceeds to step 595, and once ends this routine.

  On the other hand, if the determination condition in step 525 is satisfied, the CPU determines “Yes” in step 525 and proceeds to step 530 where the catalyst temperature Tcat is equal to or lower than the deactivation temperature Tnop (= T1) of the SC catalyst 36. It is determined whether or not.

As described above, when the catalyst temperature Tcat is equal to or lower than the deactivation temperature Tnop (= T1), even if the operation of the engine 20 shifts from the lean combustion operation to the stoichiometric combustion operation, the NOx reduction reaction is performed in the SC catalyst 36. N ₂ O is not generated because it does not occur. Therefore, when the catalyst temperature Tcat is equal to or lower than the deactivation temperature Tnop (= T1), the CPU makes a “Yes” determination at step 530 to proceed to step 535 to execute the stoichiometric combustion operation. As a result, the operation of the engine 20 is changed from the lean combustion operation to the stoichiometric combustion operation, and the occurrence of misfire is avoided.

  On the other hand, if the catalyst temperature Tcat is higher than the deactivation temperature Tnop (= T1), the CPU makes a “No” determination at step 530 to proceed to step 540, where is the catalyst temperature Tcat lower than the predetermined temperature T2? Determine whether or not. The predetermined temperature T2 is higher than the activation temperature Top of the SC catalyst 36. For example, the predetermined temperature T2 is set to a temperature at which the catalyst temperature Tcat when the engine 20 is restarted after the idling stop is equal to or higher than the activation temperature Top. ing.

  If the catalyst temperature Tcat is lower than the predetermined temperature T2, the CPU makes a “Yes” determination at step 540 to proceed to step 545 to transmit an instruction to the regulator 52 to increase the power generation amount of the alternator 51. Next, the CPU proceeds to step 550, sets the torque increase ΔTq to “positive predetermined value A”, proceeds to step 595, and once ends this routine. This positive predetermined value A corresponds to an increase in torque that should be generated by the engine 20 in order to increase the power generation amount of the alternator 51.

In this state, when the CPU executes this routine again after a predetermined time has elapsed, the engine required torque Tqtgt determined in step 510 becomes a value larger than the engine required basic torque Tqbse by a predetermined value A. As a result, the operating point determined by the engine required torque Tqtgt and the engine speed NE remains in the lean combustion operation region R1, and therefore the lean combustion operation is continued. For example, when the operating point is originally shifted to the point S1 in FIG. 7, the engine required torque Tqtgt is increased by the predetermined value A by increasing the power generation amount, so that the operating point is shifted to S2. Therefore, combustion does not become unstable, and N ₂ O is not generated because there is no transition from lean combustion operation to stoichiometric combustion operation.

  If the catalyst temperature Tcat is equal to or higher than the predetermined temperature T2 at the time when the CPU executes the process of step 540, the CPU makes a “No” determination at step 540 to proceed to step 560 and perform S & S (start and stop, ie, , Idling stop) condition is determined.

  The S & S condition is that the speed (vehicle speed) of the vehicle 10 detected by a vehicle speed sensor (not shown) is “0”, the accelerator pedal operation amount Accp is “0”, and is detected by a brake sensor (not shown). This is established when the brake operation amount is greater than “0” (brake on) and the coolant temperature detected by a coolant temperature sensor (not shown) is equal to or higher than the warm-up completion temperature.

If the S & S condition is satisfied, the CPU makes a “Yes” determination at step 560 to proceed to step 565, stop the engine 20 and proceed to step 595 to end the present routine tentatively. In this case, when the accelerator pedal operation amount Accp becomes larger than “0” or the brake operation amount becomes “0”, the engine 20 is restarted. Even when this restart is performed, N ₂ O is not generated because the catalyst temperature Tcat is equal to or higher than the activation temperature Top. As a result, fuel consumption can be reduced while suppressing the generation of N ₂ O.

On the other hand, if the S & S condition is not satisfied, the CPU makes a “No” determination at step 560 to proceed to step 545 and subsequent steps. As a result, the operating point determined by the engine required torque Tqtgt and the engine speed NE remains in the lean combustion operation region R1, and therefore the lean combustion operation is continued. Therefore, combustion does not become unstable, and N ₂ O is not generated because there is no transition from lean combustion operation to stoichiometric combustion operation.

  Further, the CPU executes the routine shown by the flowchart in FIG. 8 every time a predetermined time elapses. Therefore, when the predetermined timing comes, the CPU starts the process from step 800 of FIG. 8 and proceeds to step 810 to determine whether or not the power generation amount is increased by the process of the previous step 545. If the power generation amount has not been increased, the CPU makes a “No” determination at step 810 to directly proceed to step 895 to end the present routine tentatively.

  On the other hand, if the power generation amount is increased, the CPU makes a “Yes” determination at step 810 to proceed to step 820, at which time the engine required basic torque Tqbse determined by the lookup table of FIG. And a combination of the engine speed NE (that is, an operating point) is determined whether or not it is within the lean combustion operation region R1.

  When the operating point is within the lean combustion operation region R1, the engine 20 can stably perform the lean combustion operation without increasing the power generation amount and increasing the engine required torque Tqtgt. Therefore, in this case, the CPU makes a “Yes” determination at step 820 to proceed to step 830 to stop the increase in the amount of power generation. Next, the CPU proceeds to step 840 to set the value of the torque increase ΔTq to “0”, proceeds to step 895, and once ends this routine. As a result, since the CPU proceeds to step 520 in FIG. 5, the lean combustion operation is continuously executed.

  On the other hand, if the operating point is not within the lean combustion operation region R1, the CPU makes a “No” determination at step 820 to directly proceed to step 895 to end the present routine tentatively. That is, in this case, the power generation amount continues to increase.

As a result, when the catalyst temperature Tcat is equal to or higher than the deactivation temperature Tnop, the mode switching frequency between the lean combustion operation and the stoichiometric combustion operation can be reduced. Furthermore, when the catalyst temperature Tcat is lower than the deactivation temperature Tnop, the catalyst temperature Tcat can be raised to the activation temperature Top early by performing the stoichiometric combustion operation instead of the lean combustion operation. As described above, the present control device can reduce the amount of N ₂ O produced.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention.

  For example, in the above embodiment, the catalyst temperature Tcat has been acquired as being equal to the exhaust gas temperature detected by the exhaust gas temperature sensor 98, but may be estimated based on the in-cylinder intake air amount, the engine rotational speed NE, and the like.

  Furthermore, in the above embodiment, Step 540, Step 560, Step 565, and Step 567 may be omitted. In this case, if the CPU determines “No” in step 530, the CPU may execute step 545 and step 550.

  Although the vehicle 10 of the above embodiment is a normal gasoline engine vehicle having only the internal combustion engine 20 as a driving force source of the vehicle 10, the present invention is applied to a hybrid vehicle having an internal combustion engine and a generator motor as a vehicle driving source. You can also. In this case, a generator motor (generator) included in the hybrid vehicle may be used in place of the alternator 51 as equipment used to increase the engine required torque.

DESCRIPTION OF SYMBOLS 10 ... Vehicle, 20 ... Internal combustion engine, 21 ... Engine actuator, 31 ... Fuel supply system, 36 ... Upstream catalyst (SC catalyst), 37 ... NSR catalyst, 41 ... Transmission, 42 ... Crankshaft pulley, 43 ... Alternator pulley , 44 ... belt, 51 ... alternator, 52 ... regulator, 53 ... storage battery, 60 ... driving force transmission mechanism, 70 ... electronic control unit (ECU), 96 ... upstream air-fuel ratio sensor, 98 ... exhaust gas temperature sensor.

Claims (1)

An internal combustion engine as a drive source for the vehicle;
A generator that generates electricity by being mounted on the vehicle and driven by the engine;
A storage battery mounted on the vehicle and charged by the power generated by the generator;
A three-way catalyst disposed in the exhaust passage of the engine;
Applied to vehicles equipped with
Engine request torque determining means for determining an engine request torque required for the engine based on a parameter having a correlation with a user request torque requested by a driver of the vehicle;
The air-fuel ratio of the air-fuel mixture formed in the combustion chamber of the engine is set to the stoichiometric air-fuel ratio when the engine required torque is equal to or lower than the threshold torque, and the air-fuel mixture is set when the engine required torque is larger than the threshold torque. An air-fuel ratio setting means for setting the air-fuel ratio of the engine to a lean air-fuel ratio greater than the stoichiometric air-fuel ratio;
In a vehicle control device comprising a control device including:
The controller is
The temperature parameter having a correlation with the temperature of the three-way catalyst is acquired, and the engine required torque is reduced to be equal to or less than the threshold torque from the state where the air-fuel ratio of the air-fuel mixture is set to the lean air-fuel ratio. If
When the temperature of the three-way catalyst represented by the temperature parameter is higher than the deactivation temperature at which the three-way catalyst is not activated at all, the engine required torque is set to the threshold value by increasing the power generation amount of the generator. The engine is operated while the air-fuel ratio of the air-fuel mixture is maintained at the lean air-fuel ratio by changing to more than the torque,
When the temperature of the three-way catalyst represented by the temperature parameter is equal to or lower than the deactivation temperature, the engine is operated by setting the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio. ,
Vehicle control device.

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