JP3463616B2 - Control device for internal combustion engine for hybrid vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve temperature rise efficiency of a catalyst by two-step combustion and accelerate exhaust purification control immediately after cool- state startup in a control system for an internal combustion engine of a hybrid vehicle. SOLUTION: This control system has an internal combustion engine 1 for driving drive wheels 12a, 12b, and an electric motor 2. The internal combustion engine 1 is an in-cylinder injection internal combustion engine having a catalyst 8 for exhaust emission purification and a two-step combustion mode by which fuel is injected in a compression stroke and an expansion stroke at least during cold-state startup so as to accelerate temperature rise of the catalyst 8 for exhaust emission purification. The internal combustion engine 1 is further provided with an electric motor control means 21 that assists revolution of the in-cylinder injection internal combustion engine 1 by actuating the electric motor 2 while the engine is operated in the two-step combustion mode.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for a so-called hybrid vehicle having a direct injection internal combustion engine having an exhaust purification catalyst and an electric motor. 2. Description of the Related Art Conventionally, an exhaust purification catalyst (hereinafter simply referred to as a catalyst) is provided in an exhaust passage of an internal combustion engine (hereinafter referred to as an engine) such as a gasoline engine. In general, this catalyst cannot exhibit a sufficient exhaust gas purification function unless its temperature rises to a predetermined activation temperature range. The issue was how to raise the temperature to the temperature range. For example, Japanese Patent Application Laid-Open No. H10-15313
No. 8 discloses a fuel injection for main combustion that generates engine torque in a direct injection internal combustion engine (direct injection gasoline engine) in which fuel is directly injected into a cylinder of the engine and combustion is performed by spark ignition. During idling, normally, apart from performing the fuel injection during the compression stroke, additional fuel is injected during the expansion stroke that does not contribute to engine torque (hereinafter, also referred to as expansion stroke injection) to install a catalyst heater or the like. There is disclosed a technique for activating a catalyst at an early stage without using the catalyst. In this technology, the additional fuel is ignited by the flame propagation of the main combustion and burns using the excess air that has not contributed to the main combustion, and the high-temperature combustion gas generated thereby does not contribute to the output of the engine without catalyzing. , The temperature of the catalyst can be quickly raised to the activation temperature range. Injecting additional fuel and burning (additional combustion) during the expansion stroke together with main combustion in this way is called two-stage combustion. It is to be noted that the catalyst is most required to be heated when the engine is cold started. For a direct injection engine,
At the time of starting, a reliable start is performed by premixed combustion by the intake stroke injection, and at the time of idling after the completion of the start, stratified combustion by the compression stroke injection is switched to save fuel consumption. During a cold start, two-stage combustion is performed by performing additional combustion by expansion stroke injection in addition to main combustion by compression stroke injection. In addition, in the main combustion by the compression stroke injection, the air-fuel ratio is made extremely lean, so that there is an effect of saving fuel consumption. Therefore, the effect of raising the temperature of the catalyst is increased. When such a technique is applied to an automobile equipped with an automatic transmission (AT) (hereinafter, referred to as an AT car), an effect of increasing the temperature of the catalyst as shown in FIG. 4 is obtained, for example. As shown in FIG. 4, when the engine is started and the engine speed (rotation speed) Ne increases, the injection is switched to the compression stroke injection. At this time, a pulse signal is sent to the injector also during the expansion stroke separately from the compression stroke. Then, additional fuel is injected into the cylinder from the injector according to the pulse width of this signal. Thereby, for a predetermined time,
Two-stage combustion is performed, and the catalyst is activated early. As shown in FIG. 4, when the AT shift position is in the neutral position (N range) than in the drive position (D range), the catalyst temperature is more quickly increased by the two-stage combustion. Can be raised. That is, the additional combustion is performed by using the excess air of the main combustion, and the total air-fuel ratio (A
/ F) is limited to the vicinity of the stoichiometric air-fuel ratio as shown in FIG. 4. Therefore, if the intake air amount is constant, the leaner the A / F for the main combustion, the more additional fuel is increased, and the temperature of the catalyst can be raised efficiently.
When the main combustion is stratified combustion by the compression stroke injection, the fuel amount is adjusted according to the load condition of the engine. However, the amount of intake air is not changed so much to ensure the stratified combustion.
In the N range where the load is smaller than the range, the compression injection A / F for the main combustion can be made lean, and the expansion stroke injection amount (pulse width) for the additional combustion is increased by that amount to efficiently raise the catalyst. You can warm up. However, also in the case of the N range of an AT car, a torque converter and the like become loads in addition to the internal load of the engine, so that the engine (MT car) having a manual transmission (MT) is in a neutral state as in a neutral state. The engine load is larger than in the case of only the internal load, and the catalyst temperature raising effect is reduced by that much. In recent years, there has been developed a parallel hybrid electric vehicle (hereinafter simply referred to as a hybrid vehicle) that can drive a vehicle not only with an electric motor (hereinafter simply referred to as a motor) but also with an engine. Is being developed. For example, the drive system of this hybrid vehicle includes:
A motor rotation shaft is interposed between the output shaft of the engine and the input shaft on the drive wheel side, and a clutch is provided between the engine output shaft and the motor rotation shaft. Some have transmissions between them. It is conceivable to apply a direct injection internal combustion engine to such a parallel type hybrid vehicle engine. In this case, if the clutch between the engine output shaft and the motor rotation shaft is disengaged, the engine load becomes only the load inside the engine, so that additional combustion during two-stage combustion can be promoted and the catalyst temperature increasing effect can be enhanced. be able to. However, in recent years, as environmental issues have become increasingly important, it has been desired to activate the catalyst earlier at the time of cold start to further promote exhaust gas purification by the catalyst. The present invention has been devised in response to such a demand, and has been made to improve the catalyst temperature increasing effect by two-stage combustion and to promote the purification of exhaust gas immediately after a cold start.
An object of the present invention is to provide a control device for an internal combustion engine for a hybrid vehicle. For this reason, in the control apparatus for an internal combustion engine for a hybrid vehicle according to the present invention, a two-stage combustion operation mode in which fuel injection is performed in each of a compression stroke and an expansion stroke during a cold start is provided. At the same time, the electric motor is operated under the control of the electric motor control means to assist the rotation of the internal combustion engine. Therefore, the load on the internal combustion engine is reduced, and the excess air that does not contribute to the main combustion can be increased by making the air-fuel ratio in the compression stroke lean, and more fuel is used in the expansion stroke by using this excess air. Inject and burn
The temperature of the exhaust gas purifying catalyst can be quickly raised by a larger amount of thermal energy. Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are views showing a control device for an internal combustion engine for a hybrid vehicle as one embodiment of the present invention, and FIG. 1 shows a configuration of a hybrid vehicle to which the present invention is applied. As shown in FIG.
This hybrid vehicle has drive wheels (running wheels) 12a, 1
An engine (internal combustion engine) 1 as a drive source for driving
And an electric motor (hereinafter simply referred to as a motor) 2, and these drive sources are connected to a differential 4 connected to the drive shafts 11 a and 11 b via a transmission 3. An engine clutch (hereinafter, also simply referred to as a clutch) 5 is provided between the engine 1 and the motor 2.
A starting clutch (hereinafter, also simply referred to as a clutch) 6 is provided between the transmission 3 and the differential 4. The engine clutch 5 has an output shaft 10a of the engine 1 and an output shaft 10 of the motor 2 according to the traveling mode.
The engine clutch 5 is connected when the vehicle is driven only by the output of the engine 1 or when the vehicle is driven by the output of the engine 1 and the output of the motor 2. Thus, the output of the engine 1 is transmitted to the transmission 3. on the other hand,
When the vehicle runs only by the output of the motor 2, the engine clutch 5 is released to stop the engine 1, thereby improving fuel efficiency and reducing the running load by preventing the engine 1 from becoming a load on the motor 2. Has become. When the engine 1 is started, the engine clutch 5 is connected, and the motor 2 is used as a starter motor. The starting clutch 6 connects and disconnects the output shaft 10c of the transmission 3 and the input shaft 10d of the differential 4, and is used when starting the engine 1 or charging a running battery (not shown) while the vehicle is stopped. Can be At the time of starting by the engine 1, the starting clutch 6 is gradually connected from the disengaged state (this is referred to as starting clutch slip control) so that the starting can be started smoothly. When the running battery is charged while the vehicle is stopped, the starting clutch 6 is released, the drive system after the differential 4 is disconnected, and the engine 1 drives the motor 2 to generate power. In this hybrid vehicle, the operation control of the engine 1 and the motor 2 and the connection / disconnection control of the clutches 5 and 6 are controlled by the ECU.
(Control device) 20. EC
In U20, an appropriate traveling mode is selected according to the traveling state of the vehicle, and the engine 1, the motor 2, the clutches 5, 6 are controlled according to the traveling mode. For example, when a large output is required, such as during acceleration,
A mode in which the vehicle travels using only the engine 1 or a combination of the engine 1 and the motor 2 is selected. On the other hand, when the load is low, such as during steady running, a mode in which the vehicle travels mainly by the motor 2 is selected. In this case, the engine 1 is stopped, the engine clutch 5 is released so that the engine 1 does not become a load on the motor 2, and only the motor 2 is operated. The engine 1 is configured as an in-cylinder injection internal combustion engine (in-cylinder injection gasoline engine) that injects fuel directly into a cylinder and burns by spark ignition. An exhaust purification catalyst is provided in an exhaust passage 7 of the engine 1. (Hereinafter, simply referred to as a catalyst) 8, and when the engine 1 is cold started,
In order to activate the catalyst 8 at an early stage, a two-stage combustion operation mode (hereinafter referred to as
A two-stage combustion mode). In the two-stage combustion mode, as in the prior art,
Apart from fuel injection for main combustion for generating engine torque (compression stroke injection at the time of engine start as described above), additional fuel is injected into the cylinder during the expansion stroke. Then, the additional fuel is ignited by the flame propagation of the main combustion, whereby high-temperature combustion gas is supplied to the catalyst, so that the temperature of the catalyst can be quickly raised to the active temperature region. In this two-stage combustion, as the amount of additional fuel injected during the expansion stroke is larger, a larger amount of heat energy can be supplied to the catalyst 8 through the exhaust gas, and the early activation of the catalyst can be promoted. . The additional combustion is performed by using the excess air that has not contributed to the main combustion. Therefore, when the intake air amount cannot be significantly increased as in the case of the stratified combustion by the compression stroke injection, the A / A of the fuel injection for the main combustion is performed. As F is leaner, the amount of additional fuel injected can be increased to obtain a higher catalyst temperature increasing effect. However, A / F for main combustion
In order to make the engine lean, it is necessary to reduce the engine load. Therefore, in the present apparatus, at the time of cold start of the engine 1 (idle after completion of the start), the motor 2 is operated to assist the rotation of the engine 1 (this is referred to as assist drive). As a result, the A / F of the compression stroke injection relating to the main combustion is made leaner to increase the injection amount of additional fuel, thereby enabling early activation of the catalyst. For this reason, the electric motor control means 21 provided in the ECU 20 controls the operation of the motor 2 to perform the assist drive. The two-stage combustion is performed when the vehicle is stopped, and at this time, the starting clutch 6 is disconnected to reduce the load applied to the engine 1. In the present apparatus, two-stage combustion using motor assist is performed on condition that the engine is in the idling state after the completion of the cold start of the engine. Therefore, in this hybrid vehicle, the cooling water temperature of the engine (hereinafter, simply temperature hereinafter) coolant temperature sensor for detecting the T _W (hereinafter, simply water temperature as sensor) 31, an idle switch 32 which outputs an idle signal P, crankshaft (Not shown), which outputs a crank angle signal θcr.
3, various sensors such as an ignition switch 34 for outputting an ignition-on signal and a start command signal (starter-on signal) S are provided, and a detection signal from each sensor is sent to the ECU 20. In addition,
The ECU 20 determines the engine speed Ne based on the crank angle signal θcr detected by the crank angle sensor 33.
Is calculated. A water temperature sensor 31 determines whether the engine 1 is cold.
The completion of the starting operation (cranking) is determined by the fact that the engine speed Ne has reached a predetermined value when the start command signal S is output. At the time of cold start, combustion is started by premixed combustion by normal intake stroke injection, and when the start is completed, the operation of the motor 2 is stopped, and thereafter, the idle signal P is output from the idle switch 32 and the engine is turned off. EC under load
In response to a control command from U20, the mode is switched to stratified combustion by compression stroke injection. At the same time, additional fuel is injected during the expansion stroke to perform two-stage combustion for a predetermined period, and at the same time, the motor 2 is operated by a control command from the electric motor control means 21 to perform assist driving. Here, when the water temperature T _W detected by the water temperature sensor 31 is lower than the predetermined water temperature T _W0 , it is determined that the engine 1 is in a cold state. When a starter operation command is output and the engine speed Ne is higher than the start mode departure speed Ne ₀ , it is determined that cranking has been completed. Hereinafter, the engine mode during cranking is referred to as a start mode, and the engine mode after completion of cranking is referred to as a normal mode. A / F of compression stroke injection during two-stage combustion
The A / F of the expansion stroke injection is determined according to the water temperature T _W according to the first water temperature map and the second water temperature map stored in the ECU 20 in advance, and the lower the water temperature T _W , the higher the friction in the engine 1. load is increased, it is necessary to such a / F rich in main combustion, since more water temperature T _W is lower assist torque of the motor 2 is increased as described below, here, the water temperature T _W is lower However, the A / F for main combustion can be made relatively lean. Therefore,
The A / F of the expansion stroke injection is set to be relatively rich. Note that the A / F in the expansion stroke combustion indicates the ratio (War / Wf ₂ ) of the surplus air amount War that did not contribute to combustion in the compression stroke and the additional fuel amount Wf ₂ . Also,
The intake air amount Wa during the compression stroke, the fuel injection amount Wf ₁ during the compression stroke, and the fuel injection amount Wf ₂ during the expansion stroke are determined by the total A of the compression stroke injection and the expansion stroke injection so that the fuel does not become excessive. / F is set so as to be within a predetermined range (for example, 15 to 17). The two-stage combustion and the assist drive by the motor 2 are performed for a predetermined time (two-stage combustion continuation time) t ₀ , and the predetermined time t ₀ is determined according to a third water temperature map stored in the ECU 20 in advance. The predetermined time t ₀ is set longer as the water temperature T _W is lower.
The motor torque (assist torque) TQ at the time of assist driving of the motor 2 is a fourth torque stored in the ECU 20 in advance.
According to the water temperature map, the lower the water temperature T _W is, the larger the water temperature T _W is set to effectively perform the two-stage combustion. When the vehicle starts, the two-stage combustion ends because the idle switch 32 is turned off, and the idle start clutch 6 is gently connected by the start clutch slip control. Since the control apparatus for an internal combustion engine for a hybrid vehicle according to one embodiment of the present invention is configured as described above, for example, as shown in FIG.
First, when the ignition switch 34 is turned on, the control starts. In step S10, it is determined whether or not the engine 1 is started. If the engine speed Ne is 0, the engine 1 is not started (this state). Is referred to as an engine stall mode), and the process proceeds to step S20.
If the engine speed Ne is not 0, the engine 1 is determined to be in the start mode or the normal mode, and the process proceeds to step S70. In step S20, whether or not the engine 1 is in a cold state is detected by the water temperature sensor 31 as the water temperature T _W.
Is determined based on If the water temperature T _W is lower than the predetermined water temperature T _W0, it is determined that two-stage combustion is required to quickly activate the catalyst 8 because the engine 1 is in a cold state, and compression is performed in step S30 according to the first water temperature map. A in stroke injection
A / F in the expansion stroke injection according to the second water temperature map in step S40, the two-stage combustion continuation time (predetermined time) t _{0 in} accordance with the third water temperature map in step S50, and the fourth time in step S60. The assist torque TQ of the motor 2 is determined according to the water temperature T _W according to the water temperature map of
Proceed to step S70. On the other hand, if the water temperature T _W is equal to or higher than the predetermined water temperature T _W0 in step S20, the engine 1 is not in a cold state, and the routine returns assuming that two-stage combustion is unnecessary. In step S70, it is determined whether or not the normal mode flag is set. If the normal mode flag is set, the process proceeds to step S120 assuming that the normal mode is already set, and if the normal mode flag is not set, Proceed to step S80 to enter the start mode.
In step S80, if the starter operation command is output from the ECU 20 to the motor 2, the engine clutch 5 is connected in step S90, cranking is performed by the motor 2, and the process proceeds to step S100. If the starter operation command has not been output, the routine returns. In step S100, the engine speed N
e, the completion of cranking is determined, and if the engine speed Ne is higher than the start mode departure rotation Ne ₀ ,
As cranking is completed, the process proceeds is set normal mode flag to (step S110) step S120, if the engine speed Ne is starting mode disengaged rotation Ne ₀ or less, the cranking is returned as not completed. In step S120, it is determined whether or not the engine 1 is in a no-load state. When the detection signal P is output from the idle switch 32 and the engine is in a no-load state, the process proceeds to step S130. Does not output the detection signal P and the engine is in the load state, the routine returns without performing the two-stage combustion. In step S130, the elapsed time t after the start the two-stage combustion for a predetermined time (two-stage combustion duration after startup) set in step S50 is greater than t ₀ is determined, the elapsed time t reaches the predetermined time t ₀ Until the two-stage combustion is performed in step S140. The elapsed time t after the start of the two-stage combustion is t
Is calculated by a timer (not shown) provided in the ECU 20. Here, in the two-stage combustion in step S140, A in the compression stroke injection set in step S30.
/ F, A in the expansion stroke injection set in step S40
/ F, fuel injection is performed in the compression stroke and the expansion stroke, and the assist torque TQ set in step S60 is used.
, The assist drive is performed by the motor 2. The effect of the two-stage combustion with the assist drive performed at the time of the cold start will be described with reference to FIG. The solid line in FIG. 3 indicates the control of the present embodiment, and the dashed line indicates the shift position of the transmission 3 by simply disengaging the starting clutch 6 without using the motor 2 to assist the engine 1 as in the prior art. Shows a case where two-stage combustion is performed. As shown in FIG. 3, the engine starts and the engine speed N
When e exceeds the start mode departure rotation Ne ₀ and enters the normal mode, the motor 2 applies the motor assist torque TQ to the engine 1 by the motor 2 for a predetermined time t ₀ , and the engine 1 is assisted,
At the same time, during the expansion stroke, additional fuel is injected into the cylinder in accordance with the pulse width of the drive signal to the injector, and two-stage combustion is performed. As shown by the solid line in FIG. Can be done. That is, since the engine 1 is assisted, the engine load can be reduced as compared with the case where the starting clutch 6 is simply disconnected as in the N range mode.
The additional fuel is increased by making the main combustion leaner and the excess air is increased (that is, the pulse width of the output signal to the injector in the expansion injection stroke is increased), and the hotter exhaust gas is discharged to the catalyst 8. And the catalyst temperature can be raised more rapidly as shown by the solid line than in the conventional example indicated by the dashed line. Therefore, there is an advantage that the catalyst 8 can be activated earlier and the emission of harmful components in the exhaust gas can be suppressed as compared with the related art. The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the embodiment described above, two-stage combustion is depending on the water temperature T _W is adapted to be performed for a predetermined time t _0, or to carry out until the water temperature T _W is higher than a predetermined temperature, the catalyst temperature Two-stage combustion may be performed until the temperature reaches the activation temperature range. In this case, the catalyst 8
A thermometer may be provided on the downstream side to detect the catalyst temperature. In the above-described embodiment, the start clutch 6 is disconnected while the vehicle is stopped. For example, when the transmission 3 is configured by the AT, the start clutch 6 is connected even when the vehicle is stopped. Alternatively, the starting clutch 6 may transmit the torque corresponding to the vehicle creep. In this case, the motor 2 is controlled so as to assist the engine 1 with the torque obtained by adding the torque corresponding to the vehicle creep to the assist torque TQ, and the output torque of the motor 2 is more required. The transmission 3 may use not only the AT but also other types of transmission such as MT. In the above-described embodiment, the two-stage combustion is performed at the time of the cold start. However, the two-stage combustion may be performed not only at the time of the cold start but also when the temperature of the catalyst needs to be raised. As described in detail above, in the control apparatus for an internal combustion engine for a hybrid vehicle according to the present invention, when the two-stage combustion operation mode is executed, the electric motor rotates the in-cylinder injection internal combustion engine. The assist reduces the load on the in-cylinder injection internal combustion engine, increasing the excess air that does not contribute to main combustion,
This excess air can be used to burn more fuel in the expansion stroke. Thereby, there is an advantage that the catalyst temperature increasing effect by the two-stage combustion can be improved and the exhaust gas purification immediately after the cold start can be promoted.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a configuration of a hybrid vehicle according to an embodiment of the present invention. FIG. 2 is a flowchart showing a flow of a two-stage combustion control according to a control device for an internal combustion engine for a hybrid vehicle as one embodiment of the present invention. FIG. 3 is a diagram illustrating an example of a temperature increasing effect of an exhaust purification catalyst by a control device for an internal combustion engine for a hybrid vehicle as one embodiment of the present invention. FIG. 4 is a diagram showing an example of a temperature increasing effect of an exhaust purification catalyst obtained by two-stage combustion of a conventional direct injection internal combustion engine. [Description of Signs] 1 Engine (internal combustion engine) 2 Electric motor 8 Exhaust purification catalysts 12a, 12b Driving wheels (running wheels) 20 ECU (control device) 21 Electric motor control means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI B60K 6/04 730 B60K 6/04 730 ZHV F01N 3/20 D F01N 3/20 3/24 R 3/24 3/36 B 3 / 36 F02D 41/02 325A F02D 41/02 325 B60K 6/04 ZHV (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/20 F01N 3/36 B60K 6/02-6/04 B60L 11/00-11/18 F02D 29/00-29/06

Claims (1)

(57) [Claim 1] An internal combustion engine for driving a traveling wheel and an electric motor, wherein the internal combustion engine is a direct injection internal combustion engine having an exhaust purification catalyst. In order to promote the temperature rise of the exhaust gas purifying catalyst, there is provided a two-stage combustion operation mode in which fuel is injected at least during the compression stroke and the expansion stroke at the time of a cold start, and the electric motor is operated during the two-stage combustion operation mode A control device for an internal combustion engine for a hybrid vehicle, comprising an electric motor control means for assisting the rotation of the direct injection internal combustion engine.