JP2023028186A - Internal combustion engine control method and control device - Google Patents

Abstract

To enable an intake amount to be instantly changed in stages during transition between a stoichiometric combustion mode and a lean combustion mode.SOLUTION: An internal combustion engine 2 for power generation in a series hybrid vehicle is operated at either a first operation point for achieving highest fuel economy and a second operation point for high output power generation with a rotation speed and a load higher than the same at the first operation point. The first operation point corresponds to a lean combustion mode for achieving a lean air-fuel ratio. The second operation point corresponds to a stoichiometric combustion mode for achieving a theoretical air-fuel ratio. A motor generator section 12c of an electrically assisted turbocharger 12 performs power running and regeneration during transition between the modes so as to cause an intake amount change to have a delay through opening control of a throttle valve 22 and a waste gate valve 34.SELECTED DRAWING: Figure 2

Description

The present invention provides a control method for an internal combustion engine capable of switching between a stoichiometric combustion mode with a stoichiometric air-fuel ratio as a target air-fuel ratio and a lean combustion mode in which combustion is performed with a lean air-fuel ratio as a target air-fuel ratio while supercharging, and Regarding the control device.

There is known an internal combustion engine capable of switching between a stoichiometric combustion mode with a stoichiometric air-fuel ratio as a target air-fuel ratio and a lean combustion mode with a lean air-fuel ratio as a target air-fuel ratio in order to reduce fuel consumption. Patent Document 1 discloses a supercharging lean combustion mode in which a target air-fuel ratio is set to a lean air-fuel ratio while performing supercharging using a turbocharger, and a non-supercharging mode in which a target air-fuel ratio is set to a stoichiometric air-fuel ratio without performing supercharging. An internal combustion engine with a stoichiometric combustion mode is disclosed. In such an internal combustion engine, since a large amount of intake air can be supplied into the cylinder by supercharging, lean combustion with a large air-fuel ratio, for example, lean combustion with an excess air ratio λ of about 2 is possible.

Patent Document 2 discloses, as a turbocharger for an internal combustion engine, an electrically assisted turbocharger provided with a motor serving as an auxiliary power source on a rotating shaft that directly connects a turbine and a compressor.

JP 2008-121511 A JP-A-2006-017053

In an internal combustion engine that is switched between a stoichiometric combustion mode and a lean combustion mode as in Patent Document 1, it is desirable to avoid operation at an intermediate air-fuel ratio as much as possible from the viewpoint of exhaust performance. It is desirable that the air-fuel ratio change stepwise between the target air-fuel ratio in the stoichiometric combustion mode and the target air-fuel ratio in the lean combustion mode. In order to realize such a stepwise change in the air-fuel ratio, the air amount must be changed stepwise. However, changes in the amount of air obtained by changes in the opening of the throttle valve and changes in the opening of the wastegate valve are relatively slow, and responsiveness is not sufficient.

The electrically assisted turbocharger disclosed in Patent Document 2 and the like is generally used to assist the motor when supercharging is insufficient with only the exhaust energy, and adjusts the air amount in the direction of decreasing the amount. The use of an electrically assisted turbocharger to do so is not disclosed.

The present invention is a control method for an internal combustion engine capable of switching between a stoichiometric combustion mode in which a stoichiometric air-fuel ratio is a target air-fuel ratio and a lean combustion mode in which combustion is performed with a lean air-fuel ratio as a target air-fuel ratio while supercharging. There is
Using an electric assist turbocharger having a motor generator unit coaxially with the turbine and compressor as a supercharging means,
Power running/regeneration of the motor generator section is controlled so as to compensate for transient changes in the amount of air caused by the throttle valve and/or the waste gate valve during transition between the stoichiometric combustion mode and the lean combustion mode.

According to the present invention, when shifting between the stoichiometric combustion mode and the lean combustion mode, the amount of air flowing into the combustion chamber can be changed with good responsiveness by power running and regeneration of the motor generator section of the electrically assisted turbocharger. .

FIG. 2 is a configuration explanatory diagram of a series hybrid vehicle; FIG. 1 is a configuration explanatory diagram of an internal combustion engine of one embodiment; FIG. 2 is a characteristic diagram showing operating points of an internal combustion engine;

An embodiment in which the present invention is applied to an internal combustion engine for power generation in a series hybrid vehicle will now be described. FIG. 1 schematically shows the configuration of a series hybrid vehicle. The series hybrid vehicle includes a motor generator 1 for power generation that mainly operates as a power generator, an internal combustion engine 2 that is used as an internal combustion engine for power generation that drives the motor generator 1 for power generation according to electric power demand, and an internal combustion engine 2 that mainly operates as a motor. It is composed of a traveling motor generator 4 that drives the drive wheels 3 as a driving force, and a battery 5 that temporarily stores the generated electric power. Electric power obtained by the internal combustion engine 2 driving the motor generator 1 is stored in the battery 5 via an inverter device (not shown). The driving motor generator 4 is driven and controlled using the electric power of the battery 5 . Electric power generated during regeneration by the motor generator 4 for traveling is stored in the battery 5 via an inverter device (not shown).

A controller 6 controls the operations of the motor generators 1 and 4 , the charging and discharging of the battery 5 , and the operation of the internal combustion engine 2 . The controller 6 includes a plurality of controllers connected so as to communicate with each other, such as a motor controller 7 that controls the motor generators 1 and 4, an engine controller 8 that controls the internal combustion engine 2, and a battery controller 9 that manages the battery 5. It is Information such as the degree of opening of an accelerator pedal (not shown) and vehicle speed is input to the controller 6 . The battery controller 9 also obtains the SOC of the battery 5 based on the voltage/current of the battery 5 . When the SOC drops to a predetermined lower limit level, the internal combustion engine 2 is started via the engine controller 8 to generate power. As operation modes of such a series hybrid vehicle, there are an EV mode in which the vehicle runs on the electric power of the battery 5 without combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating power by the combustion operation of the internal combustion engine 2. However, even if the SOC is equal to or higher than the lower limit level, when the required driving force of the vehicle is relatively large, the vehicle travels in the HEV mode.

FIG. 2 shows the system configuration of the internal combustion engine 2. As shown in FIG. The internal combustion engine 2 is a four-stroke cycle spark ignition internal combustion engine equipped with a turbocharger 12. A pair of intake valves 14 and a pair of exhaust valves 15 are arranged on the ceiling wall surface of each cylinder 13. , and an ignition plug 16 is arranged in a central portion surrounded by the intake valve 14 and the exhaust valve 15 . A fuel injection valve 17 that supplies fuel into the cylinder 13 is provided below the intake valve 14 . The engine controller 8 controls the ignition timing of the ignition plug 16 and the injection timing and injection amount of fuel by the fuel injection valve 17 . As will be described later, the internal combustion engine 2 has a stoichiometric combustion mode in which the target air-fuel ratio is the stoichiometric air-fuel ratio (λ=1), and a lean combustion mode in which combustion is performed with a lean air-fuel ratio as the target air-fuel ratio on the premise of supercharging. and can be switched between.

Here, the turbocharger 12 is an electrically assisted turbocharger having a motor generator section 12c coaxial with the turbine 12b and the compressor 12a. Conversely, it is possible to apply a braking force in the rotational direction to the rotor by the regenerative operation of the motor generator section 12c. The motor generator section 12 c is controlled by the engine controller 8 . Electric power necessary for the motor generator section 12c is supplied from the battery 5 for running the vehicle via an inverter circuit (not shown), and the electric power obtained by regeneration is similarly stored in the battery 5 for running the vehicle.

The intake passage 21 has an intake collector 21a, and an electronically controlled throttle valve 22 whose opening is controlled by a control signal from the engine controller 8 is provided upstream of the intake collector 21a. A compressor 12a of the turbocharger 12 is positioned upstream of the throttle valve 22, and an air flow meter 24 and an air cleaner 25 for detecting the amount of intake air are disposed upstream of the compressor 12a. A water-cooled intercooler 26, for example, is provided between the compressor 12a and the throttle valve 22 to cool the high temperature and high pressure intake air. A recirculation valve 27 is provided to communicate the discharge side and the suction side of the compressor 12a.

A turbine 12b of the turbocharger 12 is positioned in the exhaust passage 30, and a pre-catalyst device 31 and a main catalyst device 32 for purifying exhaust gas are disposed downstream thereof. The pre-catalyst device 31 is arranged at the outlet of the turbine 12b, and the main catalytic device 32 is arranged under the floor of the vehicle. An air-fuel ratio sensor 33 that detects the air-fuel ratio is arranged upstream of the turbine 12b in the exhaust passage 30 . Turbine 12b includes a wastegate valve 34 that bypasses a portion of the exhaust in response to boost pressure to control boost pressure. The wastegate valve 34 is, for example, of an electric type whose opening is controlled by the engine controller 8 .

As an exhaust gas recirculation passage for recirculating part of the exhaust gas from the exhaust passage 30 to the intake passage 21, a low-pressure exhaust gas recirculation passage 35 for recirculating the exhaust gas from the downstream side of the turbine 12b to a position upstream of the compressor 12a and the upstream side of the turbine 12b. A high-pressure exhaust gas recirculation passage 36 for recirculating the exhaust gas to a position downstream of the compressor 12a, for example, the intake collector 21a. The low-pressure exhaust gas recirculation passage 35 is provided with, for example, a water-cooled EGR gas cooler 37 and a low-pressure EGR valve 38 . A high pressure EGR valve 39 is provided in the high pressure exhaust gas recirculation passage 36 . Basically, the exhaust gas is recirculated through the low-pressure exhaust gas recirculation passage 35 in the supercharging region, and the exhaust gas is recirculated through the high-pressure exhaust gas recirculation passage 36 in the non-supercharging region.

In addition to the air flow meter 24 and the air-fuel ratio sensor 33, the engine controller 8 includes a crank angle sensor 41 for detecting the engine speed, a water temperature sensor 42 for detecting the cooling water temperature, and a supercharging sensor for detecting the supercharging pressure. Detection signals from sensors such as the pressure sensor 43 are input. Based on these detection signals and requests from other controllers 7 and 9, the engine controller 8 optimally controls the fuel injection amount, injection timing, ignition timing, opening of the throttle valve 22, supercharging pressure, etc. there is

The internal combustion engine 2 is basically started when the SOC of the battery 5 drops to a predetermined lower limit SOC value, and is stopped when the SOC recovers to a predetermined level. When the internal combustion engine 2 drives the electric power generating motor generator 1 to generate power in this way, the internal combustion engine 2 is basically operated at a predetermined first operating point near the best fuel consumption point. Further, when the demand for power generation is large, the engine is operated at a predetermined second operating point for high-output power generation which is set on the higher speed and higher load side than the first operating point.

FIG. 3 shows a first operating point OPA1 and a second operating point OPA2 preset with the rotational speed and load of the internal combustion engine 2 as parameters. WOT indicates the fully open characteristic of the internal combustion engine 2 . As shown in the figure, the first operating point OPA1 is set on the relatively low-load side and corresponds to the best fuel efficiency point of the internal combustion engine 2 . The second operating point OPA2 is set on the higher speed and higher load side than the first operating point OPA1, and in one embodiment, is set in the vicinity of the highest speed and high load point. It should be noted that these operating points are not strictly one point, but each include a relatively narrow range, but an appropriate range for the rotational speed and load.

The operating point of the internal combustion engine 2 is mainly determined by the power generation demand as described above. If the power generation demand is at a steady level, the first operating point OPA1 is selected. OPA2 is selected. The final operating point is determined including the cooling water temperature and other requests in addition to the power generation request, but in principle other operating points not included in the first operating point OPA1 and the second operating point OPA2 are Not used. Also, as is clear from FIG. 3, the first operating point OPA1 and the second operating point OPA2 are discontinuous, and therefore the operating point OPA1 and the second operating point OPA2 are discontinuous. When the point transitions, the rotational speed and load change stepwise.

Here, at the first operating point OPA1 where fuel efficiency is emphasized, the lean combustion mode is selected, and on the premise of supercharging, lean combustion is performed with the lean air-fuel ratio set to the target air-fuel ratio. For example, the internal combustion engine 2 is operated with a relatively high lean air-fuel ratio at which the excess air ratio λ is around "2". On the other hand, at the second operating point OPA2 where output is emphasized, the stoichiometric combustion mode is selected, and stoichiometric combustion is performed with the stoichiometric air-fuel ratio (λ=1) as the target air-fuel ratio.

For example, when the operating point is shifted from the second operating point OPA2 to the first operating point OPA1, the combustion mode is switched from the stoichiometric combustion mode (λ=1) to the lean combustion mode (λ=2), The target air-fuel ratio becomes equivalent to "λ=2". As the target air-fuel ratio changes, the required intake air amount (fresh air amount) increases even if the fuel amount (corresponding to the load) remains the same. The degree of opening increases rapidly. For example, the target opening degree of the throttle valve 22 is fully opened. Also, the target supercharging pressure becomes higher, and the opening of the waste gate valve 34 is reduced to achieve this supercharging pressure. That is, the intake air amount is increased stepwise by controlling the opening degrees of the throttle valve 22 and the waste gate valve 34 .

However, there is a delay in the change in the amount of intake air actually flowing into the cylinder due to changes in the opening degrees of the throttle valve 22 and the waste gate valve 34. amount will be reached. Therefore, the air-fuel ratio becomes an intermediate value transiently. In response to such a delay in intake air amount change, in this embodiment, when switching from the stoichiometric combustion mode to the lean combustion mode, power running control is performed on the motor generator section 12c of the turbocharger 12 to rotate the rotor of the turbocharger 12. to accelerate. That is, the rotational speed of the turbocharger 12 is increased so as to compensate for the transient change in the intake air amount caused by the throttle valve 22 and the waste gate valve 34, and the intake air amount flowing into the cylinder is rapidly increased.

As a result, it is possible to suppress the occurrence of a transient intake air shortage and an undesirable intermediate air-fuel ratio when shifting from the stoichiometric combustion mode to the lean combustion mode.

On the other hand, when the operating point is shifted from the first operating point OPA1 to the second operating point OPA2, the combustion mode is switched from the lean combustion mode to the stoichiometric combustion mode, and the target air-fuel ratio is equivalent to "λ=1". becomes. As the target air-fuel ratio changes, the required intake air amount (fresh air amount) decreases even if the fuel amount (corresponding to the load) remains the same. The degree of opening decreases rapidly. Also, the target supercharging pressure is lowered, and the opening of the waste gate valve 34 is increased due to the exhaust bypass. In other words, the intake air amount is reduced stepwise by controlling the opening degrees of the throttle valve 22 and the waste gate valve 34 .

However, since there is a delay in the change in intake air amount due to the control of the opening of the throttle valve 22 and the waste gate valve 34, in this embodiment, when switching from the lean combustion mode to the stoichiometric combustion mode, the turbocharger 12 regeneratively controls the motor generator portion 12c of the turbocharger 12 to decelerate the rotation of the rotor of the turbocharger 12. That is, the rotational speed of the turbocharger 12 is reduced so as to compensate for the transient change in the intake air amount caused by the throttle valve 22 and the waste gate valve 34, and the intake air amount flowing into the cylinder is quickly reduced.

As a result, when the lean combustion mode is shifted to the stoichiometric combustion mode, it is possible to suppress the occurrence of an excessive transient intake air amount and thus an undesirable intermediate lean air-fuel ratio.

The power running/regeneration of the motor generator unit 12c of the turbocharger 12 at the time of such combustion mode switching may be performed in the form of feedforward control, or may be performed in the form of feedback control based on appropriate parameters. good.

The electrically assisted turbocharger 12 having the motor-generator portion 12c is used for highly responsive intake air amount control when the internal combustion engine 2 is in steady operation with the target of the first operating point OPA1 or the second operating point OPA2. can also be used for For example, the power running/regenerative control of the motor generator section 12c can change the pressure in the intake collector 21a and thus the amount of intake air flowing into the cylinder with good responsiveness.

In a preferred embodiment, when the internal combustion engine 2 is operated under a high load (for example, when the engine is operated at the second operating point OPA2), the wastegate valve 34 is fully closed and the rotational speed of the turbine 12b or rotor is maintained at a predetermined level. The power generation torque of the motor generator section 12c is controlled so as to achieve the upper limit rotational speed. In other words, the motor generator section 12c is regeneratively controlled so that the rotor rotation speed does not exceed the upper limit rotation speed while maximizing the exhaust energy. As a result, wasteful disposal of exhaust energy is suppressed, and more electric power is recovered by regeneration of the motor generator section 12c. The recovered electric power can be used as a part of the electric power for running by the motor generator 4 for running, and by combining with the power generated by the motor generator 1 for power generation, the electric power larger than the maximum output power of the motor generator 1 for power generation can be supplied to the motor for running. A generator 4 can be driven.

In another preferred embodiment, when the internal combustion engine 2 is operating under high load (for example, operating at the second operating point OPA2), the waste gate valve 34 is fully closed while the supercharging pressure exceeds a predetermined upper limit. The power generation torque of the motor generator section 12c is controlled so as to supply the pressure. That is, the motor generator section 12c is regeneratively controlled so that the boost pressure does not exceed the upper limit boost pressure while maximizing the exhaust energy. As a result, wasteful disposal of exhaust energy is suppressed, and more electric power is recovered by regeneration of the motor generator section 12c. The recovered electric power can be used as a part of the electric power for running by the motor generator 4 for running, and by combining with the power generated by the motor generator 1 for power generation, the electric power larger than the maximum output power of the motor generator 1 for power generation can be supplied to the motor for running. A generator 4 can be driven.

In the above example, the internal combustion engine 2 is operated at one of the two operating points, the first operating point OPA1 and the second operating point OPA2, but may have three or more operating points. .

An embodiment in which the present invention is applied to an internal combustion engine for power generation in a series hybrid vehicle has been described above, but the present invention is not limited to the internal combustion engine for power generation in a series hybrid vehicle. It can be widely applied including internal combustion engines. The stoichiometric combustion mode may be non-supercharging or may be accompanied by supercharging.

DESCRIPTION OF SYMBOLS 1... Motor generator for electric power generation 2... Internal combustion engine 4... Motor generator for traveling 5... Battery 6... Controller 8... Engine controller 12... Turbocharger 12a... Compressor 12b... Turbine 12c... Motor generator part 22... Throttle valve 34... Waste gate valve

Claims (7)

A control method for an internal combustion engine capable of switching between a stoichiometric combustion mode in which a stoichiometric air-fuel ratio is a target air-fuel ratio and a lean combustion mode in which combustion is performed with a lean air-fuel ratio as a target air-fuel ratio while performing supercharging,
Using an electric assist turbocharger having a motor generator unit coaxially with the turbine and compressor as a supercharging means,
controlling the power running/regeneration of the motor generator so as to compensate for a transient change in the amount of air caused by a throttle valve and/or a waste gate valve when transitioning between the stoichiometric combustion mode and the lean combustion mode;
A control method for an internal combustion engine. When shifting from the stoichiometric combustion mode to the lean combustion mode, the amount of air is increased by the power running of the motor generator,
When the lean combustion mode is shifted to the stoichiometric combustion mode, the amount of air is reduced by regeneration of the motor generator unit.
A control method for an internal combustion engine according to claim 1. The internal combustion engine is a power generating internal combustion engine for a series hybrid vehicle that drives a power generating motor generator,
The internal combustion engine is operated with a plurality of specific operating points including a first operating point that is the best fuel efficiency point and a second operating point for high-output power generation as targets,
A lean combustion mode is set at the first operating point, and a stoichiometric combustion mode is set at the second operating point.
A control method for an internal combustion engine according to claim 1 or 2. Using the regenerated electric power of the motor generator unit as a part of electric power for running by the motor generator for running,
A control method for an internal combustion engine according to claim 3. controlling the power generation torque of the motor-generator unit so that the turbine rotation speed reaches a predetermined upper limit rotation speed while the waste gate valve is fully closed during high-load operation of the internal combustion engine;
A control method for an internal combustion engine according to any one of claims 1 to 4. controlling the power generation torque of the motor generator unit so that the boost pressure reaches a predetermined upper limit boost pressure while the waste gate valve is fully closed during high-load operation of the internal combustion engine;
A control method for an internal combustion engine according to any one of claims 1 to 4. an internal combustion engine;
an electrically assisted turbocharger having a motor generator section coaxially with the turbine and the compressor;
The internal combustion engine is operated by switching between a stoichiometric combustion mode in which the stoichiometric air-fuel ratio is the target air-fuel ratio and a lean combustion mode in which combustion is performed with the lean air-fuel ratio being the target air-fuel ratio while supercharging. a controller that controls power running/regeneration of the motor-generator section so as to compensate for transient changes in air amount caused by a throttle valve and/or a wastegate valve when transitioning between the combustion mode and the lean combustion mode;
A control device for an internal combustion engine, comprising:

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